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Sample records for optimal transport convection

  1. Optimal Transport, Convection, Magnetic Relaxation and Generalized Boussinesq Equations

    NASA Astrophysics Data System (ADS)

    Brenier, Yann

    2009-10-01

    We establish a connection between optimal transport theory (see Villani in Topics in optimal transportation. Graduate studies in mathematics, vol. 58, AMS, Providence, 2003, for instance) and classical convection theory for geophysical flows (Pedlosky, in Geophysical fluid dynamics, Springer, New York, 1979). Our starting point is the model designed few years ago by Angenent, Haker, and Tannenbaum (SIAM J. Math. Anal. 35:61-97, 2003) to solve some optimal transport problems. This model can be seen as a generalization of the Darcy-Boussinesq equations, which is a degenerate version of the Navier-Stokes-Boussinesq (NSB) equations. In a unified framework, we relate different variants of the NSB equations (in particular what we call the generalized hydrostatic-Boussinesq equations) to various models involving optimal transport (and the related Monge-Ampère equation, Brenier in Commun. Pure Appl. Math. 64:375-417, 1991; Caffarelli in Commun. Pure Appl. Math. 45:1141-1151, 1992). This includes the 2D semi-geostrophic equations (Hoskins in Annual review of fluid mechanics, vol. 14, pp. 131-151, Palo Alto, 1982; Cullen et al. in SIAM J. Appl. Math. 51:20-31, 1991, Arch. Ration. Mech. Anal. 185:341-363, 2007; Benamou and Brenier in SIAM J. Appl. Math. 58:1450-1461, 1998; Loeper in SIAM J. Math. Anal. 38:795-823, 2006) and some fully nonlinear versions of the so-called high-field limit of the Vlasov-Poisson system (Nieto et al. in Arch. Ration. Mech. Anal. 158:29-59, 2001) and of the Keller-Segel for Chemotaxis (Keller and Segel in J. Theor. Biol. 30:225-234, 1971; Jäger and Luckhaus in Trans. Am. Math. Soc. 329:819-824, 1992; Chalub et al. in Mon. Math. 142:123-141, 2004). Mathematically speaking, we establish some existence theorems for local smooth, global smooth or global weak solutions of the different models. We also justify that the inertia terms can be rigorously neglected under appropriate scaling assumptions in the generalized Navier-Stokes-Boussinesq equations

  2. Energy transport using natural convection boundary layers

    SciTech Connect

    Anderson, R

    1986-04-01

    Natural convection is one of the major modes of energy transport in passive solar buildings. There are two primary mechanisms for natural convection heat transport through an aperture between building zones: (1) bulk density differences created by temperature differences between zones; and (2) thermosyphon pumping created by natural convection boundary layers. The primary objective of the present study is to compare the characteristics of bulk density driven and boundary layer driven flow, and discuss some of the advantages associated with the use of natural convection boundary layers to transport energy in solar building applications.

  3. Stochastic models for convective momentum transport.

    PubMed

    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.

  4. Convective transport resistance in the vitreous humor

    NASA Astrophysics Data System (ADS)

    Penkova, Anita; Sadhal, Satwindar; Ratanakijsuntorn, Komsan; Moats, Rex; Tang, Yang; Hughes, Patrick; Robinson, Michael; Lee, Susan

    2012-11-01

    It has been established by MRI visualization experiments that the convection of nanoparticles and large molecules with high rate of water flow in the vitreous humor will experience resistance, depending on the respective permeabilities of the injected solute. A set of experiments conducted with Gd-DTPA (Magnevist, Bayer AG, Leverkusen, Germany) and 30 nm gadolinium-based particles (Gado CELLTrackTM, Biopal, Worcester, MA) as MRI contrast agents showed that the degree of convective transport in this Darcy-type porous medium varies between the two solutes. These experiments consisted of injecting a mixture of the two (a 30 μl solution of 2% Magnevist and 1% nanoparticles) at the middle of the vitreous of an ex vivo whole bovine eye and subjecting the vitreous to water flow rate of 100 μl/min. The water (0.9% saline solution) was injected at the top of the eye, and was allowed to drain through small slits cut at the bottom of the eyeball. After 50 minutes of pumping, MRI images showed that the water flow carried the Gd-DTPA farther than the nanoparticles, even though the two solutes, being mixed, were subjected to the same convective flow conditions. We find that the convected solute lags the water flow, depending on the solute permeability. The usual convection term needs to be adjusted to allow for the filtration effect on the larger particles in the form (1- σ) u . ∇ c with important implications for the modeling of such systems.

  5. Convective heat transport in geothermal systems

    SciTech Connect

    Lippmann, M.J.; Bodvarsson, G.S.

    1986-08-01

    Most geothermal systems under exploitation for direct use or electrical power production are of the hydrothermal type, where heat is transferred essentially by convection in the reservoir, conduction being secondary. In geothermal systems, buoyancy effects are generally important, but often the fluid and heat flow patterns are largely controlled by geologic features (e.g., faults, fractures, continuity of layers) and location of recharge and discharge zones. During exploitation, these flow patterns can drastically change in response to pressure and temperature declines, and changes in recharge/discharge patterns. Convective circulation models of several geothermal systems, before and after start of fluid production, are described, with emphasis on different characteristics of the systems and the effects of exploitation on their evolution. Convective heat transport in geothermal fields is discussed, taking into consideration (1) major geologic features; (2) temperature-dependent rock and fluid properties; (3) fracture- versus porous-medium characteristics; (4) single- versus two-phase reservoir systems; and (5) the presence of noncondensible gases.

  6. Wall to Wall Optimal Transport

    NASA Astrophysics Data System (ADS)

    Chini, Gregory P.; Hassanzadeh, Pedram; Doering, Charles R.

    2013-11-01

    How much heat can be transported between impermeable fixed-temperature walls by incompressible flows with a given amount of kinetic energy or enstrophy? What do the optimal velocity fields look like? We employ variational calculus to address these questions in the context of steady 2D flows. The resulting nonlinear Euler-Lagrange equations are solved numerically, and in some cases analytically, to find the maximum possible Nusselt number Nu as a function of the Péclect number Pe , a measure of the flow's energy or enstrophy. We find that in the fixed-energy problem Nu ~ Pe , while in the fixed-enstrophy problem Nu ~ Pe 10 / 17 . In both cases, the optimal flow consists of an array of convection cells with aspect ratio Γ (Pe) . Interpreting our results in terms of the Rayleigh number Ra for relevant buoyancy-driven problems, we find Nu <= 1 + 0 . 035 Ra and Γ ~ Ra - 1 / 2 for porous medium convection (which occurs with fixed energy), and Nu <= 1 + 0 . 115 Ra 5 / 12 and Γ ~ Ra - 1 / 4 for Rayleigh-Bénard convection (which occurs with fixed enstrophy and for free-slip walls). This work was supported by NSF awards PHY-0855335, DMS-0927587, and PHY-1205219 (CRD) and DMS-0928098 (GPC). Much of this work was completed at the 2012 Geophysical Fluid Dynamics (GFD) Program at Woods Hole Oceanographic Institution.

  7. Impact of convective transport on dialyzer clearance.

    PubMed

    Galach, Magda; Ciechanowska, Anna; Sabalińska, Stanislawa; Waniewski, Jacek; Wójcicki, Jan; Weryńskis, Andrzej

    2003-01-01

    The results of predictions of three mathematical models used to describe the impact of convective flow on dialyzer clearance are presented. These models are based on the ordinary differential equations, which describe changes of solute concentration and solute and fluid flows along the module length. One of the models takes into consideration the existence of the boundary layers on both sides of the membrane wall, by including in the equations two parameters kB and kD, which describe mass transport coefficients in blood and dialysate, respectively. In the second model, the boundary layers are included in one lumped membrane permeability parameter. The diffusive membrane permeability was calculated from pure diffusive clearance, which was taken from experimental results. In the third model, a linear dependence of transmittance coefficient and ultrafiltration flow was proposed. The theoretical results were compared with data obtained in experiments carried out in vitro with four types of high-flux hollow-fiber dialyzers. The comparisons demonstrate that the first two models are of similar accuracy and the third model is not suitable for small solutes.

  8. Role of convective scale momentum transport in climate simulation

    SciTech Connect

    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.

  9. New variational bounds on convective transport. II. Computations and implications

    NASA Astrophysics Data System (ADS)

    Souza, Andre; Tobasco, Ian; Doering, Charles R.

    2016-11-01

    We study the maximal rate of scalar transport between parallel walls separated by distance h, by an incompressible fluid with scalar diffusion coefficient κ. Given velocity vector field u with intensity measured by the Péclet number Pe =h2 < | ∇ u |2 >1/2 / κ (where < . > is space-time average) the challenge is to determine the largest enhancement of wall-to-wall scalar flux over purely diffusive transport, i.e., the Nusselt number Nu . Variational formulations of the problem are studied numerically and optimizing flow fields are computed over a range of Pe . Implications of this optimal wall-to-wall transport problem for the classical problem of Rayleigh-Bénard convection are discussed: the maximal scaling Nu Pe 2 / 3 corresponds, via the identity Pe2 = Ra (Nu - 1) where Ra is the usual Rayleigh number, to Nu Ra 1 / 2 as Ra -> ∞ . Supported in part by National Science Foundation Graduate Research Fellowship DGE-0813964, awards OISE-0967140, PHY-1205219, DMS-1311833, and DMS-1515161, and the John Simon Guggenheim Memorial Foundation.

  10. The efficiency of convective energy transport in the sun

    NASA Technical Reports Server (NTRS)

    Schatten, Kenneth H.

    1988-01-01

    Mixing length theory (MLT) utilizes adiabatic expansion (as well as radiative transport) to diminish the energy content of rising convective elements. Thus in MLT, the rising elements lose their energy to the environment most efficiently and consequently transport heat with the least efficiency. On the other hand Malkus proposed that convection would maximize the efficiency of energy transport. A new stellar envelope code is developed to first examine this other extreme, wherein rising turbulent elements transport heat with the greatest possible efficiency. This other extreme model differs from MLT by providing a small reduction in the upper convection zone temperatures but greatly diminished turbulent velocities below the top few hundred kilometers. Using the findings of deep atmospheric models with the Navier-Stokes equation allows the calculation of an intermediate solar envelope model. Consideration is given to solar observations, including recent helioseismology, to examine the position of the solar envelope compared with the envelope models.

  11. The efficiency of convective energy transport in the sun

    NASA Technical Reports Server (NTRS)

    Schatten, Kenneth H.

    1988-01-01

    Mixing length theory (MLT) utilizes adiabatic expansion (as well as radiative transport) to diminish the energy content of rising convective elements. Thus in MLT, the rising elements lose their energy to the environment most efficiently and consequently transport heat with the least efficiency. On the other hand Malkus proposed that convection would maximize the efficiency of energy transport. A new stellar envelope code is developed to first examine this other extreme, wherein rising turbulent elements transport heat with the greatest possible efficiency. This other extreme model differs from MLT by providing a small reduction in the upper convection zone temperatures but greatly diminished turbulent velocities below the top few hundred kilometers. Using the findings of deep atmospheric models with the Navier-Stokes equation allows the calculation of an intermediate solar envelope model. Consideration is given to solar observations, including recent helioseismology, to examine the position of the solar envelope compared with the envelope models.

  12. Convection in the Physical Vapor Transport Process. 1; Thermal

    NASA Technical Reports Server (NTRS)

    Duval, Walter M. B.

    1994-01-01

    The effects of convection on diffusive-convective physical vapor transport process are examined computationally. We analyze conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. This corresponds to thermal Rayleigh numbers Ra(sub tau) ranging from 1.80 x 10 to 1.92 x 10(exp 6). Our results indicate that the effect of the sublimation and condensation fluxes at the boundaries is to increase the threshold of instability. For typical ground based conditions, time dependent oscillatory convection can occur. This results in unsteady transport, and non-uniform temperature and concentration gradients at the crystal interface. Spectral analysis of the flow field shows parametric regions exhibiting both an oscillatory approach to steady state and a chaotic transient to a periodic state. Low gravity conditions stabilize the flow field. Convective effects are effectively reduced, thus resulting in uniform temperature and concentration gradients at the interface, a desirable condition for crystal growth.

  13. Convection in the Physical Vapor Transport Process-I: Thermal

    NASA Technical Reports Server (NTRS)

    Duval, Walter M. B.

    1994-01-01

    The effects of convection on diffusive-convective physical vapor transport process are examined computationally. We analyze conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. This corresponds to thermal Rayleigh numbers Ra, ranging from 1.80 x 10 to 1.92 x 10(exp 6). Our results indicate that the effect of the sublimation and condensation fluxes at the boundaries is to increase the threshold of instability. For typical ground based conditions, time dependent oscillatory convection can occur. This results in unsteady transport, and non- uniform temperature and concentration gradients at the crystal interface. Spectral analysis of the flow field shows parametric regions exhibiting both an oscillatory approach to steady state and a chaotic transient to a periodic state. Low gravity conditions stabilize the flow field. Convective effects are effectively reduced, thus resulting in uniform temperature and concentration gradients at the interface, a desirable condition for crystal growth.

  14. NUMERICALLY DETERMINED TRANSPORT LAWS FOR FINGERING ('THERMOHALINE') CONVECTION IN ASTROPHYSICS

    SciTech Connect

    Traxler, A.; Garaud, P.; Stellmach, S.

    2011-02-20

    We present the first three-dimensional simulations of fingering convection performed at parameter values approaching those relevant for astrophysics. Our simulations reveal the existence of simple asymptotic scaling laws for turbulent heat and compositional transport, which can be straightforwardly extrapolated from our numerically tractable values to the true astrophysical regime. Our investigation also indicates that thermo-compositional 'staircases', a key consequence of fingering convection in the ocean, cannot form spontaneously in the fingering regime in stellar interiors. Our proposed empirically determined transport laws thus provide simple prescriptions for mixing by fingering convection in a variety of astrophysical situations, and should, from here on, be used preferentially over older and less accurate parameterizations. They also establish that fingering convection does not provide sufficient extra-mixing to explain observed chemical abundances in red giant branch stars.

  15. Tracer Transport by Deep Convection: Implications of the Connection Between Convective Mass Fluxes and Large-Scale Circulations

    NASA Astrophysics Data System (ADS)

    Lawrence, M. G.; Salzmann, M.; Tost, H.; Joeckel, P.; Lelieveld, J.

    2007-12-01

    Global chemistry-transport models (CTMs) generally simulate vertical tracer transport by deep convection separately from the advective transport due to large-scale mean winds, even though a component of the large-scale transport, for instance in the Hadley and Walker cells, occurs in deep convective updrafts. This split treatment of vertical transport can have several significant implications for CTM simulations, such as numerical diffusion, misinterpretation of the transport characteristics in convectively active regions, and underestimation of the effects of convective tracer transport on ozone and other gases. Here we show that there is a significant overlap between the convective and large-scale advective vertical transport fluxes in the CTM MATCH, and discuss the main implications for tracer transport studies which can be expected due to this. We also give an outlook to the next step of this study, in which we are examining the connection between diagnosed convective mass fluxes and the vertical fluxes in the tropical Hadley and Walker Cells using the ECHAM5/MESSy GCM, which is set up with a flexible framework allowing the use of several different convection parameterizations. From the direct comparison of multiple deep convection parameterizations within the same model we expect to gain a better sense of the relationship between parameterized deep convection and large-scale circulations, as well as of the present uncertainty due to differences in convection parameterizations. This work is anticipated to contribute to the objectives of Activity 2 (vertical tracer distributions) of AC&C.

  16. Toward Optimal Transport Networks

    NASA Technical Reports Server (NTRS)

    Alexandrov, Natalia; Kincaid, Rex K.; Vargo, Erik P.

    2008-01-01

    Strictly evolutionary approaches to improving the air transport system a highly complex network of interacting systems no longer suffice in the face of demand that is projected to double or triple in the near future. Thus evolutionary approaches should be augmented with active design methods. The ability to actively design, optimize and control a system presupposes the existence of predictive modeling and reasonably well-defined functional dependences between the controllable variables of the system and objective and constraint functions for optimization. Following recent advances in the studies of the effects of network topology structure on dynamics, we investigate the performance of dynamic processes on transport networks as a function of the first nontrivial eigenvalue of the network's Laplacian, which, in turn, is a function of the network s connectivity and modularity. The last two characteristics can be controlled and tuned via optimization. We consider design optimization problem formulations. We have developed a flexible simulation of network topology coupled with flows on the network for use as a platform for computational experiments.

  17. 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

  18. Equilibrium Transport in Double-Diffusive Convection

    DTIC Science & Technology

    2011-06-01

    PAGE INTENTIONALLY LEFT BLANK 61 LIST OF REFERENCES Bagenal, F., Dowling, T. E., McKinnon, W. B., Jupiter : The Planet , Satellites, and...astrophysical fluid systems, from magmatic melts (Tait and Jaupart 1989) to the interiors of giant planets and stars (Guillot 1999; Vauclair 2004...convection changes in other environments. External planetary systems, such as the atmospheric makeup of planets within our solar system, are

  19. Heat transport in bubbling turbulent convection

    PubMed Central

    Lakkaraju, Rajaram; Stevens, Richard J. A. M.; Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Prosperetti, Andrea

    2013-01-01

    Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to numerous mechanisms, many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubble compounds with that of the liquid to give rise to a much-enhanced natural convection. In this article, we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh–Bénard convection process in a cylindrical cell with a diameter equal to its height. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping this difference constant, we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between 2 × 106 and 5 × 109. We find a considerable enhancement of the heat transfer and study its dependence on the number of bubbles, the degree of superheat of the hot cell bottom, and the Rayleigh number. The increased buoyancy provided by the bubbles leads to more energetic hot plumes detaching from the cell bottom, and the strength of the circulation in the cell is significantly increased. Our results are in general agreement with recent experiments on boiling Rayleigh–Bénard convection. PMID:23696657

  20. Heat transport in bubbling turbulent convection.

    PubMed

    Lakkaraju, Rajaram; Stevens, Richard J A M; Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Prosperetti, Andrea

    2013-06-04

    Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to numerous mechanisms, many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubble compounds with that of the liquid to give rise to a much-enhanced natural convection. In this article, we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh-Bénard convection process in a cylindrical cell with a diameter equal to its height. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping this difference constant, we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between 2 × 10(6) and 5 × 10(9). We find a considerable enhancement of the heat transfer and study its dependence on the number of bubbles, the degree of superheat of the hot cell bottom, and the Rayleigh number. The increased buoyancy provided by the bubbles leads to more energetic hot plumes detaching from the cell bottom, and the strength of the circulation in the cell is significantly increased. Our results are in general agreement with recent experiments on boiling Rayleigh-Bénard convection.

  1. Vertical transport by convective clouds: Comparisons of three modeling approaches

    NASA Technical Reports Server (NTRS)

    Pickering, Kenneth E.; Thompson, Anne M.; Tao, Wei-Kuo; Rood, Richard B.; Mcnamara, Donna P.; Molod, Andrea M.

    1995-01-01

    A preliminary comparison of the GEOS-1 (Goddard Earth Observing System) data assimilation system convective cloud mass fluxes with fluxes from a cloud-resolving model (the Goddard Cumulus Ensemble Model, GCE) is reported. A squall line case study (10-11 June 1985 Oklahoma PRESTORM episode) is the basis of the comparison. Regional (central U. S.) monthly total convective mass flux for June 1985 from GEOS-1 compares favorably with estimates from a statistical/dynamical approach using GCE simulations and satellite-derived cloud observations. The GEOS-1 convective mass fluxes produce reasonable estimates of monthly-averaged regional convective venting of CO from the boundary layer at least in an urban-influenced continental region, suggesting that they can be used in tracer transport simulations.

  2. Sensitivity of Cross-Tropopause Convective Transport to Tropopause Definition

    NASA Astrophysics Data System (ADS)

    Maddox, E.; Mullendore, G. L.

    2016-12-01

    An idealized three-dimensional cloud-resolving model is used to simulate cross-tropopause boundary layer mass transport in a midlatitude supercell. A ten-hour simulation is conducted to encompass the growth and decay cycle, with focus on irreversible transport above the tropopause. However, several tropopause definitions are present in the literature, and the impact of tropopause definition on irreversible cross-tropopause transport has not been quantified. Six previously published tropopause definitions are evaluated to determine the sensitivity of tropopause definition on midlatitude irreversible cross-tropopause transport. These definitions include specific values of altitude, temperature lapse rate (i.e., WMO definition), potential vorticity, stratospheric tracer concentration, static stability, and curvature of static stability. This investigation highlights the challenge of defining a tropopause during active deep convection and shows that some definitions (e.g., potential vorticity) may not be appropriate for cross-tropopause transport studies that resolve deep convection.

  3. Convective heat transport in compressible fluids.

    PubMed

    Furukawa, Akira; Onuki, Akira

    2002-07-01

    We present hydrodynamic equations of compressible fluids in gravity as a generalization of those in the Boussinesq approximation used for nearly incompressible fluids. They account for adiabatic processes taking place throughout the cell (the piston effect) and those taking place within plumes (the adiabatic temperature gradient effect). Performing two-dimensional numerical analysis, we reveal some unique features of plume generation and convection in transient and steady states of compressible fluids. As the critical point is approached, the overall temperature changes induced by plume arrivals at the boundary walls are amplified, giving rise to overshoot behavior in transient states and significant noise in the temperature in steady states. The velocity field is suggested to assume a logarithmic profile within boundary layers. Random reversal of macroscopic shear flow is examined in a cell with unit aspect ratio. We also present a simple scaling theory for moderate Rayleigh numbers.

  4. Convective Draft Structure and Transport Over the Amazonian Rain Forest

    NASA Astrophysics Data System (ADS)

    Scala, John Richard

    1990-01-01

    Field observations acquired during two expeditions to the Amazon rain forest of Brazil (ABLE-2A, ABLE-2B), and two-dimensional moist cloud model simulations are used to determine: (1) the vertical structure of convective up- and downdrafts, (2) the major levels of entrainment and detrainment, and (3) the role of temperature and moisture in convective scale transport over the continental tropics. The thermodynamic and kinematic structure of the convective troposphere is obtained from aircraft surveys flown during the dry season and a surface-based network triangle designed for wet season multi-instrumental sampling. Dry season deep convection develops in an environment marked by a mid-tropospheric minimum in equivalent potential temperature. The available supply of cool, dry air supports penetrating downdrafts which feed propagating gust fronts at the surface. Model results indicate the existence of organized cloud fields characterized by multiple updraft cores. The upward vertical transport of air from the subcloud layer to a broad anvil is accomplished without extensive mid-level detrainment. Undilute cores are required to perform the vertical exchange in the presence of mid-tropospheric heat and moisture sinks. Marked moisture gradients are absent in the well -mixed environment of the wet season. Model predicted column heating budgets suggest the evaporation of rainwater into a rear inflow is insufficient to sustain strong downdrafts or an extensive surface cool pool. Complex mid-tropospheric circulations, particularly the existence of a rotor, account for the observed redistribution of a conservative tracer. Undilute transport of boundary layer air to the upper troposphere is markedly reduced by multiple levels of detrainment. In one case, greater than 50% of the air transported to the anvil region originated at or above 6 km rather than directly from the boundary layer. The vertical distribution of boundary layer aerosols in the presence of convection is

  5. A sensitive in vivo model for quantifying interstitial convective transport of injected macromolecules and nanoparticles.

    PubMed

    Reddy, Sai T; Berk, David A; Jain, Rakesh K; Swartz, Melody A

    2006-10-01

    Effective interstitial transport of particles is necessary for injected drug/diagnostic agents to reach the intended target; however, quantitative methods to estimate such transport parameters are lacking. In this study, we develop an in vivo model for evaluating interstitial convection of injected macromolecules and nanoparticles. Fluorescently labeled macromolecules and particles are coinfused with a reference solute at constant infusion pressure intradermally into the mouse tail tip, and their relative convection coefficients are determined from spatial and temporal interstitial concentration profiles. Quantifying relative solute velocity with a coinfused reference solute eliminates the need to estimate interstitial fluid velocity profiles, greatly reducing experimental variability. To demonstrate sensitivity and usefulness of this model, we compare the effects of size (dextrans of 3, 40, 71, and 2,000 kDa and 40-nm diameter particles), shape (linear dextran 71 kDa vs. 69 kDa globular protein albumin), and charge (anionic vs. neutral dextran 3 kDa) on interstitial convection. We find significant differences in interstitial transport rates between each of these molecules and confirm expected transport phenomena, testifying to sensitivity of the model in comparing solutes of different size, shape, and charge. Our data show that size exclusion (within a specific size range) dominates molecular convection, while mechanical hindrance slows larger molecules and nanoparticles; proteins convect slower than linear molecules of equal molecular mass, and negative surface charges increase convection through matrix repulsion. Our in vivo model is presumably a sensitive and reliable tool for evaluating and optimizing potential drug/diagnostic vehicles that utilize interstitial and lymphatic delivery routes.

  6. Why convective heat transport in the solar nebula was inefficient

    NASA Technical Reports Server (NTRS)

    Cassen, P.

    1993-01-01

    The radial distributions of the effective temperatures of circumstellar disks associated with pre-main sequence (T Tauri) stars are relatively well-constrained by ground-based and spacecraft infrared photometry and radio continuum observations. If the mechanisms by which energy is transported vertically in the disks are understood, these data can be used to constrain models of the thermal structure and evolution of solar nebula. Several studies of the evolution of the solar nebula have included the calculation of the vertical transport of heat by convection. Such calculations rely on a mixing length theory of transport and some assumption regarding the vertical distribution of internal dissipation. In all cases, the results of these calculations indicate that transport by radiation dominates that by convection, even when the nebula is convectively unstable. A simple argument that demonstrates the generality (and limits) of this result, regardless of the details of mixing length theory or the precise distribution of internal heating is presented. It is based on the idea that the radiative gradient in an optically thick nebula generally does not greatly exceed the adiabatic gradient.

  7. Convective transport of very short lived bromocarbons to the stratosphere

    NASA Astrophysics Data System (ADS)

    Liang, Q.; Atlas, E.; Blake, D.; Dorf, M.; Pfeilsticker, K.; Schauffler, S.

    2014-06-01

    We use the NASA Goddard Earth Observing System (GEOS) Chemistry Climate Model (GEOSCCM) to quantify the contribution of the two most important brominated very short lived substances (VSLSs), bromoform (CHBr3) and dibromomethane (CH2Br2), to stratospheric bromine and its sensitivity to convection strength. Model simulations suggest that the most active transport of VSLSs from the marine boundary layer through the tropopause occurs over the tropical Indian Ocean, the tropical western Pacific, and off the Pacific coast of Mexico. Together, convective lofting of CHBr3 and CH2Br2 and their degradation products supplies ~8 ppt total bromine to the base of the tropical tropopause layer (TTL, ~150 hPa), similar to the amount of VSLS organic bromine available in the marine boundary layer (~7.8-8.4 ppt) in the active convective lofting regions mentioned above. Of the total ~8 ppt VSLS bromine that enters the base of the TTL at ~150 hPa, half is in the form of organic source gases and half in the form of inorganic product gases. Only a small portion (<10%) of the VSLS-originated bromine is removed via wet scavenging in the TTL before reaching the lower stratosphere. On average, globally, CHBr3 and CH2Br2 together contribute ~7.7 pptv to the present-day inorganic bromine in the stratosphere. However, varying model deep-convection strength between maximum (strongest) and minimum (weakest) convection conditions can introduce a ~2.6 pptv uncertainty in the contribution of VSLSs to inorganic bromine in the stratosphere (BryVSLS). Contrary to conventional wisdom, the minimum convection condition leads to a larger BryVSLS as the reduced scavenging in soluble product gases, and thus a significant increase in product gas injection (2-3 ppt), greatly exceeds the relatively minor decrease in source gas injection (a few 10ths ppt).

  8. A new method to optimize natural convection heat sinks

    NASA Astrophysics Data System (ADS)

    Lampio, K.; Karvinen, R.

    2017-08-01

    The performance of a heat sink cooled by natural convection is strongly affected by its geometry, because buoyancy creates flow. Our model utilizes analytical results of forced flow and convection, and only conduction in a solid, i.e., the base plate and fins, is solved numerically. Sufficient accuracy for calculating maximum temperatures in practical applications is proved by comparing the results of our model with some simple analytical and computational fluid dynamics (CFD) solutions. An essential advantage of our model is that it cuts down on calculation CPU time by many orders of magnitude compared with CFD. The shorter calculation time makes our model well suited for multi-objective optimization, which is the best choice for improving heat sink geometry, because many geometrical parameters with opposite effects influence the thermal behavior. In multi-objective optimization, optimal locations of components and optimal dimensions of the fin array can be found by simultaneously minimizing the heat sink maximum temperature, size, and mass. This paper presents the principles of the particle swarm optimization (PSO) algorithm and applies it as a basis for optimizing existing heat sinks.

  9. Turbulent-convective block for the ASTRA transport code

    NASA Astrophysics Data System (ADS)

    Dnestrovskij, A. Yu.; Pastukhov, V. P.; Chudin, N. V.

    2017-04-01

    A physical model for the enhanced transport code is presented, which explicitly takes into account the contribution of turbulent convection to the processes of particle and heat transport in the hot core of the tokamak plasma. The model is based on the specially developed CONTRA-A turbulent block, while an adapted version of the existing ASTRA transport code is used as a transport envelope. The CONTRA-A turbulent block, based on the adiabatically reduced quasi-2D magnetohydrodynamic equations, calculates the generation and self-consistent evolution of low-frequency turbulence, including the spatiotemporal structure of turbulent fluctuations of the plasma velocity, density, and temperatures of electrons and ions. Using the obtained data on fluctuations, the CONTRA-A block calculates the turbulent-convective particle and heat fluxes and transfers them to the modified ASTRA code, which computes the evolution of quasi-equilibrium plasma parameters. To illustrate the capabilities of the enhanced transport model, the results of simulations of turbulent plasma evolution in two discharge scenarios with nonstationary auxiliary plasma heating in the T-10 and T-15MD tokamaks are presented.

  10. Heat transport measurements in turbulent rotating Rayleigh-Benard convection

    SciTech Connect

    Ecke, Robert E; Liu, Yuanming

    2008-01-01

    We present experimental heat transport measurements of turbulent Rayleigh-Benard convection with rotation about a vertical axis. The fluid, water with Prandtl number ({sigma}) about 6, was confined in a cell which had a square cross section of 7.3 cm x 7.3 cm and a height of 9.4 cm. Heat transport was measured for Rayleigh numbers 2 x 10{sup 5} < Ra < 5 x 10{sup 8} and Taylor numbers 0 < Ta < 5 x 10{sup 9}. We show the variation of normalized heat transport, the Nusselt number, at fixed dimensional rotation rate {Omega}{sub D}, at fixed Ra varying Ta, at fixed Ta varying Ra, and at fixed Rossby number Ro. The scaling of heat transport in the range 10{sup 7} to about 10{sup 9} is roughly 0.29 with a Ro dependent coefficient or equivalently is also well fit by a combination of power laws of the form a Ra{sup 1/5} + b Ra{sup 1/3} . The range of Ra is not sufficient to differentiate single power law or combined power law scaling. The overall impact of rotation on heat transport in turbulent convection is assessed.

  11. Optimizing Stellarators for Turbulent Transport

    SciTech Connect

    H.E. Mynick, N.Pomphrey, and P. Xanthopoulos

    2010-05-27

    Up to now, the term "transport-optimized" stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.

  12. Classical convective energy transport in large gradient regions

    SciTech Connect

    Hinton, F.L.

    1996-12-31

    Large gradients in density and temperature occur near the edge in H-mode plasmas and in the core of tokamak plasmas with negative central shear. Transport in these regions may be comparable to neoclassical. Standard neoclassical theory does not apply when the gradient lengths are comparable to an ion orbit excursion, or banana width. A basic question for neoclassical transport in large gradient regions is: do ion-ion collisions drive particle transport? Near the plasma edge in H-mode, where ion orbit loss requires that the ion energy transport be convective, neoclassical particle transport due to ion-ion collisions may play an important role. In negative central shear plasmas, where transport is inferred to be near neoclassical, it is important to have accurate predictions for the neoclassical rate of energy and particle transport. A simple 2-D slab model has been used, with a momentum-conserving collision operator, to show that ion-ion collisions do drive particle transport. When the gradients are large, the {open_quotes}field particle{close_quotes} contribution to the particle flux is non-local, and does not cancel the {open_quotes}test particle{close_quotes} contribution, which is local. Solutions of the kinetic equation are found which show that the steepness of the density profile, for increasing particle flux, is limited by orbit averaging. The gradient length is limited by the thermal gyroradius, and the convective energy flux is independent of ion temperature. This will allow an ion thermal runaway to occur, if there are no other ion energy loss mechanisms.

  13. MECHANISMS OF CONVECTION-INDUCED MODULATION OF PASSIVE TRACER INTERHEMISPHERIC TRANSPORT INTERANNUAL VARIABILITY

    EPA Science Inventory

    Interannual variations of tropical convection impact atmospheric circulation and influence year-to-year variations of the transport of trace constituents in the troposphere. This study examines how two modes of convective variability-anomalous intensification and meridional disp...

  14. MECHANISMS OF CONVECTION-INDUCED MODULATION OF PASSIVE TRACER INTERHEMISPHERIC TRANSPORT INTERANNUAL VARIABILITY

    EPA Science Inventory

    Interannual variations of tropical convection impact atmospheric circulation and influence year-to-year variations of the transport of trace constituents in the troposphere. This study examines how two modes of convective variability-anomalous intensification and meridional disp...

  15. Convection and mass-transport in laser-induced chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Patnaik, S.; Brown, R. A.

    1988-01-01

    Gas flow and energy and species transport in laser-induced chemical vapor deposition (LICVD) of amorphous silicon films by silane pyrolysis are analyzed by finite element analysis of a two-dimensional model for the process. Spatial nonuniformity of the deposited film is shown to result from diffusion controlled transport of products between the beam and substrate. Deposition profiles are affected by buoyancy-driven convection only at increased gas pressures. Horizontal orientation of the reactor with respect to gravity is optimal because the stagnation-like flow, that results adjacent to the substrate, enhances mixing, and smoothes the film profile.

  16. Convective Effects During the Physical Vapor Transport Process. II - Thermosolutal Convection

    NASA Technical Reports Server (NTRS)

    Duval, Walter M. B.

    1993-01-01

    The effect of an inert gas on the diffusive-convective physical vapor transport process is investigated for the case when the temperature gradient is stabilizing, and the concentration gradient destabilizing, for a wide parametric range. When an inert gas is present, the thermal and solutal convection oppose each other. The solutal field is destabilizing while the thermal field and the advective-diffusive flux stabilize the flow field. When the pressure of the inert component is increased, the stabilizing effect of the advective-diffusive flux is decreased; thus, convection becomes more vigorous. The nonlinear dynamics of the flow field here show a transition from quasi-periodic to chaotic state. When both stabilizing mechanisms are present, the flow field shows a transition to a steady state. Toward steady state, growth and amalgamation of rolls occur, which result in an overturning motion. This leads to a superposed flow consisting of one roll and a unidirectional flow. However, when the pressure is increased, the advective-diffusive stability mechanism is decreased. and oscillations of the flow field occur. The low gravity environment is effective at eliminating oscillatory behavior of the flow field and results in uniform temperature and concentration gradients.

  17. Long- range transport of Xe-133 emissions under convective and non-convective conditions.

    NASA Astrophysics Data System (ADS)

    Kusmierczyk-Michulec, Jolanta; Gheddou, Abdelhakim

    2015-04-01

    The International Monitoring System (IMS) developed by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is a global system of monitoring stations, using four complementary technologies: seismic, hydroacoustic, infrasound and radionuclide. Data from all stations, belonging to IMS, are collected and transmitted to the International Data Centre (IDC) in Vienna, Austria. The radionuclide network comprises 80 stations, of which more than 60 are certified. The aim of radionuclide stations is a global monitoring of radioactive aerosols and radioactive noble gases, in particular xenon isotopes, supported by the atmospheric transport modeling (ATM). The aim of this study is to investigate the long-range transport of Xe-133 emissions under convective and non-convective conditions. For that purpose a series of 14 days forward simulations was conducted using the Lagrangian Particle Diffusion Model FLEXPART, designed for calculating the long-range and mesoscale dispersion of air pollution from point sources. The release point was at the ANSTO facility in Australia. The geographical localization to some extent justifies the assumption that the only source of Xe-133 observed at the neighbouring stations, comes from the ANSTO facility. In the simulations the analysed wind data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) were used with the spatial resolution of 0.5 degree. Studies have been performed to link Xe-133 emissions with detections at the IMS stations supported by the ATM, and to assess the impact of atmospheric convection on non-detections at the IMS stations. The results of quantitative and qualitative comparison will be presented.

  18. 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.

  19. Convection in the Physical Vapor Transport Process. Part 2; Thermosolutal

    NASA Technical Reports Server (NTRS)

    Duval, Walter M. B.

    1994-01-01

    We consider the effect of an inert gas on the diffusive-convective physical vapor transport process. We investigate the case when the temperature gradient is stabilizing and the concentration gradient is destabilizing for a wide parametric range. When an inert gas is present, the thermal and solutal convection oppose each other. The solutal field is destabilizing while the thermal field and the advective-diffusive flux stabilize the flow field. When the pressure of the inert component is increased, the stabilizing effect of the advective-diffusive flux is decreased. The intensity of convection as well as the oscillatory transient time increases. Below, the critical Rayleigh number, the nonlinear dynamics of the flow field show an oscillatory approach to steady state. For parametric values in the neighborhood of the critical Rayleigh number, the flow field undergoes a chaotic transient which settles to a periodic state. The asymptotic state of the flow field shows that growth and amalgamation of cells yields an overturning motion which results in an asymmetric cellular structure. The low gravity environment yields the stabilizing advective-diffusive flow which results in uniform temperature and concentration gradients near the crystal interface.

  20. Transport of Passive Scalars in Rayleigh-Benard Convection

    NASA Astrophysics Data System (ADS)

    Chiam, Keng-Hwee; Cross, Michael C.; Greenside, Henry S.

    2002-03-01

    Using direct numerical simulations of the full Boussinesq equations coupled to the transport equation for a passive scalar, we show how the diffusivity of a passive scalar is enhanced in the presence of bouyancy-driven convection. We consider time-independent and time-dependent flow structures in both two and three dimensions, and show how the enhanced diffusivity varies as a function of the Peclet number and the Rayleigh and Prandtl numbers. We compare our simulation results with previous experiments as well as theoretical predictions.

  1. A Problem on Optimal Transportation

    ERIC Educational Resources Information Center

    Cechlarova, Katarina

    2005-01-01

    Mathematical optimization problems are not typical in the classical curriculum of mathematics. In this paper we show how several generalizations of an easy problem on optimal transportation were solved by gifted secondary school pupils in a correspondence mathematical seminar, how they can be used in university courses of linear programming and…

  2. Albumin leakage in online hemodiafiltration, more convective transport, more losses?

    PubMed

    Vega, Almudena; Quiroga, Borja; Abad, Soraya; Aragoncillo, Inés; Arroyo, David; Panizo, Nayara; López-Gómez, Juan M

    2015-06-01

    Online hemodiafiltration (OL-HDF) has now demonstrated some benefits in reducing mortality. It seems that rising convective volumes improve the outcomes, but the risks of it, such as albumin leakage, are not well defined yet. The aim of the present study was to evaluate the albumin leakage using two different filters with 20 and 30 L of post-dilution OL-HDF. In this cross-sectional study, 20 prevalent patients receiving post-dilution OL-HDL were included. We analyzed two dialyzers: FX1000, FMC and Polyflux 210H, Gambro. During four consecutive dialysis sessions, monitors were programmed using control-volume to obtain 20 or 30 L with both dialyzers. We collected albumin samples of the effluent at 5, 15, 30, 45 and 60 min and performed area under the curve (AUC) determinations for evaluating the losses. Mean patient age was 60 ± 9 years, and 70% were men. Albumin leakage was significant higher with Polyflux 210H when compared to FX 1000 FMC. A convective volume of 30 L produced greater albumin leakage than 20 L with both filters, though only with the FX 1000 FMC was it significant (minimum albumin leakage during first hour with FX 1000 FMC 20 L: 79.2 [0.0-175.7] mg; 30 liters: 403.3 [63.5-960.7] mg; with PF 210 Gambro 20 L: 869.1 [420.0-3214.7] mg; 30 L: 1841.7 [443.8-3417.5] mg). During OL-HDF, convective transport causes albumin leakage at least during the first hour. The albumin concentration in the effluent differs according to the type of filter used and the convective volume.

  3. Adjoint optimization of natural convection problems: differentially heated cavity

    NASA Astrophysics Data System (ADS)

    Saglietti, Clio; Schlatter, Philipp; Monokrousos, Antonios; Henningson, Dan S.

    2016-06-01

    Optimization of natural convection-driven flows may provide significant improvements to the performance of cooling devices, but a theoretical investigation of such flows has been rarely done. The present paper illustrates an efficient gradient-based optimization method for analyzing such systems. We consider numerically the natural convection-driven flow in a differentially heated cavity with three Prandtl numbers (Pr=0.15{-}7 ) at super-critical conditions. All results and implementations were done with the spectral element code Nek5000. The flow is analyzed using linear direct and adjoint computations about a nonlinear base flow, extracting in particular optimal initial conditions using power iteration and the solution of the full adjoint direct eigenproblem. The cost function for both temperature and velocity is based on the kinetic energy and the concept of entransy, which yields a quadratic functional. Results are presented as a function of Prandtl number, time horizons and weights between kinetic energy and entransy. In particular, it is shown that the maximum transient growth is achieved at time horizons on the order of 5 time units for all cases, whereas for larger time horizons the adjoint mode is recovered as optimal initial condition. For smaller time horizons, the influence of the weights leads either to a concentric temperature distribution or to an initial condition pattern that opposes the mean shear and grows according to the Orr mechanism. For specific cases, it could also been shown that the computation of optimal initial conditions leads to a degenerate problem, with a potential loss of symmetry. In these situations, it turns out that any initial condition lying in a specific span of the eigenfunctions will yield exactly the same transient amplification. As a consequence, the power iteration converges very slowly and fails to extract all possible optimal initial conditions. According to the authors' knowledge, this behavior is illustrated here

  4. Optimization of convective trapezoidal profile circular pin fins

    SciTech Connect

    Das, S.; Razelos, P.

    1997-07-01

    Circular pin fins or spines are frequently used as heat exchange devices in air conditioners. Here, circular convective pin fins of trapezoidal profile are analyzed. The results are presented in a manner which is more useful than the conventional efficiency graphs given in the textbooks and handbooks. The solution of the optimal problem can be used to determine the optimum heat dissipation or volume and optimum dimensions of the pin fin. Performance of the pin fins for off-optimum conditions is also discussed.

  5. Optimal transport and the placenta

    SciTech Connect

    Morgan, Simon; Xia, Qinglan; Salafia, Carolym

    2010-01-01

    The goal of this paper is to investigate the expected effects of (i) placental size, (ii) placental shape and (iii) the position of insertion of the umbilical cord on the work done by the foetus heart in pumping blood across the placenta. We use optimal transport theory and modeling to quantify the expected effects of these factors . Total transport cost and the shape factor contribution to cost are given by the optimal transport model. Total placental transport cost is highly correlated with birth weight, placenta weight, FPR and the metabolic scaling factor beta. The shape factor is also highly correlated with birth weight, and after adjustment for placental weight, is highly correlated with the metabolic scaling factor beta.

  6. Hemoglobin-based oxygen carrier and convection enhanced oxygen transport in a hollow fiber bioreactor.

    PubMed

    Chen, Guo; Palmer, Andre F

    2009-04-15

    A mathematical model was developed to study O(2) transport in a convection enhanced hepatic hollow fiber (HF) bioreactor, with hemoglobin-based O(2) carriers (HBOCs) present in the flowing cell culture media stream of the HF lumen. In this study, four HBOCs were evaluated: PEG-conjugated human hemoglobin (MP4), human hemoglobin (hHb), bovine hemoglobin (BvHb) and polymerized bovine hemoglobin (PolyBvHb). In addition, two types of convective flow in the HF extra capillary space (ECS) were considered in this study. Starling flow naturally occurs when both of the ECS ports are closed. If one of the ECS ports is open, forced convective flow through the ECS will occur due to the imposed pressure difference between the lumen and ECS. This type of flow is referred to as cross-flow in this work, since some of the fluid entering the HF lumen will pass across the HF membrane and exit via the open ECS port. In this work, we can predict the dissolved O(2) concentration profile as well as the O(2) transport flux in an individual HF of the bioreactor by solving the coupled momentum and mass transport equations. Our results show that supplementation of the cell culture media with HBOCs can dramatically enhance O(2) transport to the ECS (containing hepatocytes) and lead to the formation of an in vivo-like O(2) spectrum for the optimal culture of hepatocytes. However, both Starling flow and cross-flow have a very limited effect on O(2) transport in the ECS. Taken together, this work represents a novel predictive tool that can be used to design or analyze HF bioreactors that expose cultured cells to defined overall concentrations and gradients of O(2).

  7. Energy transport by thermocapillary convection during Sessile-Water-droplet evaporation.

    PubMed

    Ghasemi, H; Ward, C A

    2010-09-24

    The energy transport mechanisms of a sessile-water droplet evaporating steadily while maintained on a Cu substrate are compared. Buoyancy-driven convection is eliminated, but thermal conduction and thermocapillary convection are active. The dominant mode varies along the interface. Although neglected in previous studies, near the three-phase line, thermocapillary convection is by far the larger mode of energy transport, and this is the region where most of the droplet evaporation occurs.

  8. Assessment of Plasma Transport and Convection at High Latitudes

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The high-latitude ionosphere is strongly coupled to the thermosphere and magnetosphere. The magnetospheric coupling occurs via electric fields, field-aligned currents, and particle precipitation. Owing to the interaction of the shocked solar wind with the geomagnetic field, an electric potential difference is generated across the tail of the magnetosphere, with the resulting electric field pointing from dawn to dusk. Energetic particle precipitation from the magnetosphere in the auroral region leads to the creation of ionization and to electron, ion, and neutral gas heating. In order to assess the current understanding of plasma transport and convection at high latitudes, it is necessary to take account of the strong coupling between the ionosphere, thermosphere, and magnetosphere.

  9. Iterative methods for stationary convection-dominated transport problems

    SciTech Connect

    Bova, S.W.; Carey, G.F.

    1994-12-31

    It is well known that many iterative methods fail when applied to nonlinear systems of convection-dominated transport equations. Most successful methods for obtaining steady-state solutions to such systems rely on time-stepping through an artificial transient, combined with careful construction of artificial dissipation operators. These operators provide control over spurious oscillations which pollute the steady state solutions, and, in the nonlinear case, may become amplified and lead to instability. In the present study, we investigate Taylor Galerkin and SUPG-type methods and compare results for steady-state solutions to the Euler equations of gas dynamics. In particular, we consider the efficiency of different iterative strategies and present results for representative two-dimensional calculations.

  10. Convective Transport of Trace Gases in the Maritime Continent

    NASA Astrophysics Data System (ADS)

    Harris, Neil

    2015-04-01

    Passage of air through the Tropical Tropopause Layer (TTL) is the major route for troposphere to stratosphere transport. The UK CAST (Co-ordinated Airborne Studies in the Tropics) campaign took place in the West Pacific in January/February 2014. The field campaign was based mainly in Guam (13.5oN, 144.8oE) and had three components: CAST with the NERC FAAM BAe-146 research aircraft; the NASA ATTREX project based around the Global Hawk; the NCAR-led CONTRAST campaign based around the Gulfstream V (HIAPER) aircraft. Together, these aircraft were able to make detailed measurements of atmospheric structure and composition from the ocean surface to 20 km. The CAST team also made ground-based and ozonesonde measurements at the ARM site on Manus Island in Papua New Guinea during February 2014, and halocarbon measurements were made at several West Pacific sites. I will present an overview of the CAST campaign along with the results of high resolution global Unified Model studies and NAME (Numerical Atmospheric-dispersion Modelling Environment) trajectory calculations to look at the transport of air into the TTL in convective systems over the Maritime continent and West Pacific. I will focus on the transport of air from in and around the boundary layer and will assess the possible importance of natural and anthropogenic emissions for TTL composition.

  11. Chemically generated convective transport of micron sized particles

    NASA Astrophysics Data System (ADS)

    Shklyaev, Oleg; Das, Sambeeta; Altemose, Alicia; Shum, Henry; Balazs, Anna; Sen, Ayusman

    2015-11-01

    A variety of chemical and biological applications require manipulation of micron sized objects like cells, viruses, and large molecules. Increasing the size of particles up to a micron reduces performance of techniques based on diffusive transport. Directional transport of cargo toward detecting elements reduces the delivery time and improves performance of sensing devices. We demonstrate how chemical reactions can be used to organize fluid flows carrying particles toward the assigned destinations. Convection is driven by density variations caused by a chemical reaction occurring at a catalyst or enzyme-covered target site. If the reaction causes a reduction in fluid density, as in the case of catalytic decomposition of hydrogen peroxide, then fluid and suspended cargo is drawn toward the target along the bottom surface. The intensity of the fluid flow and the time of cargo delivery are controlled by the amount of reagent in the system. After the reagent has been consumed, the fluid pump stops and particles are found aggregated on and around the enzyme-coated patch. The pumps are reusable, being reactivated upon injection of additional reagent. The developed technique can be implemented in lab-on-a-chip devices for transportation of micro-scale object immersed in solution.

  12. Promising approaches to crystallization of macromolecules suppressing the convective mass transport to the growing crystal

    NASA Astrophysics Data System (ADS)

    Boyko, K. M.; Popov, V. O.; Kovalchuk, M. V.

    2015-08-01

    Conditions of mass transport to growing crystals are important factors that have an impact on the size and quality of macromolecular crystals. The mass transport occurs via two mechanisms — by diffusion and convection. The crystal quality can be influenced by changing (either suppressing or enhancing) the convective mass transport. The review gives an overview and analysis of the published data on different methods of macromolecular crystallization providing the suppression of convective mass transport to growing crystals in order to improve the crystal quality. The bibliography includes 91 references.

  13. ANGULAR MOMENTUM TRANSPORT IN CONVECTIVELY UNSTABLE SHEAR FLOWS

    SciTech Connect

    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.

  14. 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.

  15. 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.

  16. Convective transport of electric charge within the planetary boundary layer

    NASA Astrophysics Data System (ADS)

    Nicoll, Keri; Harrison, Giles; Silva, Hugo; Silgado, Rui; Melgao, Marta

    2017-04-01

    Turbulent and convective processes within the planetary boundary layer are responsible for the transport of moisture, momentum and particulate matter, but are also of major importance in determining the electrical charge structure of the lower atmosphere. This paper presents rare experimental measurements of vertical profiles of charge measured during fair weather conditions by specially instrumented radiosonde balloons over Alqueva, Portugal during the summer of 2014. Space charge was measured directly using a sensitive electrometer, rather than the conventional method of deriving it from electric field measurements. The high frequency of balloon flights enabled the diurnal variation in the vertical profile of charge within the boundary layer to be examined in detail, with much smaller levels of charge (up to 20pC m-3) observed during stable night time periods than during the day. Following sunrise, the evolution of the charge profile was much more complex, showing a dependence on lofting of surface aerosol due to daytime convection. This produced charge up to 92pC m-3 up to 500m above the surface. The diurnal variation in the integrated column of charge above the measurement site was also found to track closely with the diurnal variation in near surface charge as measured by an electric field mill at the same site, confirming the importance of the link between surface charge generation processes and aloft. Co-located lidar backscatter measurements were also made during the measurement campaign and will be discussed here in the context of the effect of aerosol on the vertical charge profile.

  17. Chemical convection in the methylene-blue-glucose system: Optimal perturbations and three-dimensional simulations

    NASA Astrophysics Data System (ADS)

    Köllner, Thomas; Rossi, Maurice; Broer, Frauke; Boeck, Thomas

    2014-11-01

    A case of convection driven by chemical reactions is studied by linear stability theory and direct numerical simulations. In a plane aqueous layer of glucose, the methylene-blue-enabled catalytic oxidation of glucose produces heavier gluconic acid. As the oxygen is supplied through the top surface, the production of gluconic acid leads to an overturning instability. Our results complement earlier experimental and numerical work by Pons et al. First, we extend the model by including the top air layer with diffusive transport and Henry's law for the oxygen concentration at the interface to provide a more realistic oxygen boundary condition. Second, a linear stability analysis of the diffusive basic state in the layers is performed using an optimal perturbation approach. This method is appropriate for the unsteady basic state and determines the onset time of convection and the associated wavelength. Third, the nonlinear evolution is studied by the use of three-dimensional numerical simulations. Three typical parameters sets are explored in detail showing significant differences in pattern formation. One parameter set for which the flow is dominated by viscous forces, displays persistently growing convection cells. The other set with increased reaction rate displays a different flow regime marked by local chaotic plume emission. The simulated patterns are then compared to experimental observations.

  18. The Optimal Partial Transport Problem

    NASA Astrophysics Data System (ADS)

    Figalli, Alessio

    2010-02-01

    Given two densities f and g, we consider the problem of transporting a fraction {m in [0,min\\{\\|f\\|_{L^1},\\|g\\|_{L^1}\\}]} of the mass of f onto g minimizing a transportation cost. If the cost per unit of mass is given by | x - y|2, we will see that uniqueness of solutions holds for {m in [\\|fwedge g\\|_{L^1},min\\{\\|f\\|_{L^1},\\|g\\|_{L^1}\\}]} . This extends the result of C affarelli and M cCann in Ann Math (in print), where the authors consider two densities with disjoint supports. The free boundaries of the active regions are shown to be ( n - 1)-rectifiable (provided the supports of f and g have Lipschitz boundaries), and under some weak regularity assumptions on the geometry of the supports they are also locally semiconvex. Moreover, assuming f and g supported on two bounded strictly convex sets {{Ω,Λ subset mathbb {R}^n}} , and bounded away from zero and infinity on their respective supports, {C^{0,α}_loc} regularity of the optimal transport map and local C 1 regularity of the free boundaries away from {{Ω\\cap Λ}} are shown. Finally, the optimal transport map extends to a global homeomorphism between the active regions.

  19. Convective oxygen transport and tissue oxygen consumption in Weddell seals during aerobic dives.

    PubMed

    Davis, R W; Kanatous, S B

    1999-05-01

    Unlike their terrestrial counterparts, marine mammals stop breathing and reduce their convective oxygen transport while performing activities (e.g. foraging, courtship, aggressive interactions, predator avoidance and migration) that require sustained power output during submergence. Since most voluntary dives are believed to remain aerobic, the goal of this study was to examine the potential importance of the dive response in optimizing the use of blood and muscle oxygen stores during dives involving different levels of muscular exertion. To accomplish this, we designed a numerical model based on Fick's principle that integrated cardiac output (Vb), regional blood flow, convective oxygen transport (Q(O2)), muscle oxymyoglobin desaturation and regional rates of oxygen consumption (VO2). The model quantified how the optimal matching or mismatching of QO2 to VO2 affected the aerobic dive limit (ADL). We chose an adult Weddell seal Leptonycotes weddellii on which to base our model because of available data on the diving physiology and metabolism of this species. The results show that the use of blood and muscle oxygen stores must be completed at the same time to maximize the ADL for each level of VO2. This is achieved by adjusting Vb (range 19-94 % of resting levels) and muscle QO2 according to the rate of muscle oxygen consumption (VMO2). At higher values of VMO2, Vb and muscle perfusion must increase to maintain an appropriate QO2/VO2 ratio so that available blood and muscle oxygen stores are depleted at the same time. Although the dive response does not sequester blood oxygen exclusively for brain and heart metabolism during aerobic dives, as it does during forced submersion, a reduction in Vb and muscle perfusion below resting levels is necessary to maximize the ADL over the range of diving VO2 (approximately 2-9 ml O2 min-1 kg-1). Despite the reduction in Vb, convective oxygen transport is adequate to maintain aerobic metabolism and normal function in the

  20. New variational bounds on convective transport. I. Formulation and analysis

    NASA Astrophysics Data System (ADS)

    Tobasco, Ian; Souza, Andre N.; Doering, Charles R.

    2016-11-01

    We study the maximal rate of scalar transport between parallel walls separated by distance h, by an incompressible fluid with scalar diffusion coefficient κ. Given velocity vector field u with intensity measured by the Péclet number Pe =h2 < | ∇ u |2 >1/2 / κ (where < . > is space-time average) the challenge is to determine the largest enhancement of wall-to-wall scalar flux over purely diffusive transport, i.e., the Nusselt number Nu . Variational formulations of the problem are presented and it is determined that Nu <= cPe 2 / 3 , where c is an absolute constant, as Pe -> ∞ . Moreover, this scaling for optimal transport-possibly modulo logarithmic corrections-is asymptotically sharp: admissible steady flows with Nu >=c' Pe 2 / 3 /[ log Pe ] 2 are constructed. The structure of (nearly) maximally transporting flow fields is discussed. Supported in part by National Science Foundation Graduate Research Fellowship DGE-0813964, awards OISE-0967140, PHY-1205219, DMS-1311833, and DMS-1515161, and the John Simon Guggenheim Memorial Foundation.

  1. 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.

  2. Retrieval of dispersive and convective transport phenomena in fluids using stationary and nonstationary time domain analysis

    NASA Technical Reports Server (NTRS)

    Stephens, J. B.; St.john, R. M.

    1973-01-01

    Simultaneously occuring dispersive and convective components of fluid kinematics are obtained by a time domain analysis of optically retrieved temporal histories of the transport phenomena. Utilizing triangulation of collimated optical fields of view from two radiometers to obtain the temporal histories of the intensity fluctuations associated with the transport phenomena has enabled investigators to retrieve the local convective transport by employing correlation statistics. The location of the peak in the covariance curve determines the transit time from which the convection velocity is calculated; whereas, the change in shape of the peak in the covariance curve determines the change in average frequency of the wave packet from which the dispersion velocity is calculated. Thus, two-component analysis requires the maximum possible enhancement of the delineation for the transport. The convection velocity is the result of a fixed reference frame calculation whereas, the dispersion velocity is the result of a moving reference frame calcuation.

  3. Erosion/redeposition analysis of the ITER first wall with convective and non-convective plasma transport

    SciTech Connect

    Brooks, J. N.; Allain, J. P.; Rognlien, T. D.

    2006-12-15

    Sputtering erosion/redeposition is analyzed for IAEA [Report GA10FDR1-01-07-13 (2001)] plasma facing components, with scrape-off layer (SOL) plasma convective radial transport and nonconvective (diffusion-only) transport. The analysis uses the UEDGE code [T .D. Rognlien et al., J. Nucl. Mater. 196, 347 (1992)] and DEGAS code [D. P. Stotler et al., Contrib. Plasma Phys. 40, 221 (2000) ] to compute plasma SOL profiles and ion and neutral fluxes to the wall, TRIM-SP code [J. P. Biersack, W. Eckstein, J. Appl. Phys. A34, 73 (1984)] to compute sputter yields, and the REDEP/WBC code package [J. N. Brooks, Fusion Eng. Des. 60, 515 (2002)] for three-dimensional kinetic modeling of sputtered particle transport. Convective transport is modeled for the background plasma by a radially varying outward-flow component of the fluid velocity, and for the impurity ions by three models designed to bracket existing models/data. Results are reported here for the first wall with the reference beryllium coating and an alternative tungsten coating. The analysis shows: (1) sputtering erosion for convective flow is 20-40 times higher than for diffusion-only but acceptably low ({approx}0.3 nm/s) for beryllium, and very low ({approx}0.002 nm/s) for tungsten; (2) plasma contamination by wall sputtering, with convective flow, is of order 1% for beryllium and negligible for tungsten; (3) wall-to-divertor beryllium transport may be significant ({approx}10%-60% of the sputtered Be current); (4) tritium co-deposition in redeposited beryllium may be high ({approx}1-6 gT/400 s pulse)

  4. Optimal concentrations in transport systems.

    PubMed

    Jensen, Kaare H; Kim, Wonjung; Holbrook, N Michele; Bush, John W M

    2013-06-06

    Many biological and man-made systems rely on transport systems for the distribution of material, for example matter and energy. Material transfer in these systems is determined by the flow rate and the concentration of material. While the most concentrated solutions offer the greatest potential in terms of material transfer, impedance typically increases with concentration, thus making them the most difficult to transport. We develop a general framework for describing systems for which impedance increases with concentration, and consider material flow in four different natural systems: blood flow in vertebrates, sugar transport in vascular plants and two modes of nectar drinking in birds and insects. The model provides a simple method for determining the optimum concentration copt in these systems. The model further suggests that the impedance at the optimum concentration μopt may be expressed in terms of the impedance of the pure (c = 0) carrier medium μ0 as μopt 2(α)μ0, where the power α is prescribed by the specific flow constraints, for example constant pressure for blood flow (α = 1) or constant work rate for certain nectar-drinking insects (α = 6). Comparing the model predictions with experimental data from more than 100 animal and plant species, we find that the simple model rationalizes the observed concentrations and impedances. The model provides a universal framework for studying flows impeded by concentration, and yields insight into optimization in engineered systems, such as traffic flow.

  5. Optimal Transport for Domain Adaptation.

    PubMed

    Courty, Nicolas; Flamary, Remi; Tuia, Devis; Rakotomamonjy, Alain

    2017-09-01

    Domain adaptation is one of the most challenging tasks of modern data analytics. If the adaptation is done correctly, models built on a specific data representation become more robust when confronted to data depicting the same classes, but described by another observation system. Among the many strategies proposed, finding domain-invariant representations has shown excellent properties, in particular since it allows to train a unique classifier effective in all domains. In this paper, we propose a regularized unsupervised optimal transportation model to perform the alignment of the representations in the source and target domains. We learn a transportation plan matching both PDFs, which constrains labeled samples of the same class in the source domain to remain close during transport. This way, we exploit at the same time the labeled samples in the source and the distributions observed in both domains. Experiments on toy and challenging real visual adaptation examples show the interest of the method, that consistently outperforms state of the art approaches. In addition, numerical experiments show that our approach leads to better performances on domain invariant deep learning features and can be easily adapted to the semi-supervised case where few labeled samples are available in the target domain.

  6. Optimal concentrations in transport systems

    PubMed Central

    Jensen, Kaare H.; Kim, Wonjung; Holbrook, N. Michele; Bush, John W. M.

    2013-01-01

    Many biological and man-made systems rely on transport systems for the distribution of material, for example matter and energy. Material transfer in these systems is determined by the flow rate and the concentration of material. While the most concentrated solutions offer the greatest potential in terms of material transfer, impedance typically increases with concentration, thus making them the most difficult to transport. We develop a general framework for describing systems for which impedance increases with concentration, and consider material flow in four different natural systems: blood flow in vertebrates, sugar transport in vascular plants and two modes of nectar drinking in birds and insects. The model provides a simple method for determining the optimum concentration copt in these systems. The model further suggests that the impedance at the optimum concentration μopt may be expressed in terms of the impedance of the pure (c = 0) carrier medium μ0 as μopt∼2αμ0, where the power α is prescribed by the specific flow constraints, for example constant pressure for blood flow (α = 1) or constant work rate for certain nectar-drinking insects (α = 6). Comparing the model predictions with experimental data from more than 100 animal and plant species, we find that the simple model rationalizes the observed concentrations and impedances. The model provides a universal framework for studying flows impeded by concentration, and yields insight into optimization in engineered systems, such as traffic flow. PMID:23594815

  7. Magnetically Modulated Heat Transport in a Global Simulation of Solar Magneto-convection

    NASA Astrophysics Data System (ADS)

    Cossette, Jean-Francois; Charbonneau, Paul; Smolarkiewicz, Piotr K.; Rast, Mark P.

    2017-05-01

    We present results from a global MHD simulation of solar convection in which the heat transported by convective flows varies in-phase with the total magnetic energy. The purely random initial magnetic field specified in this experiment develops into a well-organized large-scale antisymmetric component undergoing hemispherically synchronized polarity reversals on a 40 year period. A key feature of the simulation is the use of a Newtonian cooling term in the entropy equation to maintain a convectively unstable stratification and drive convection, as opposed to the specification of heating and cooling terms at the bottom and top boundaries. When taken together, the solar-like magnetic cycle and the convective heat flux signature suggest that a cyclic modulation of the large-scale heat-carrying convective flows could be operating inside the real Sun. We carry out an analysis of the entropy and momentum equations to uncover the physical mechanism responsible for the enhanced heat transport. The analysis suggests that the modulation is caused by a magnetic tension imbalance inside upflows and downflows, which perturbs their respective contributions to heat transport in such a way as to enhance the total convective heat flux at cycle maximum. Potential consequences of the heat transport modulation for solar irradiance variability are briefly discussed.

  8. Transport of biomass burning smoke to the upper troposphere by deep convection in the equatorial region

    NASA Astrophysics Data System (ADS)

    Andreae, M. O.; Artaxo, P.; Fischer, H.; Freitas, S. R.; Grégoire, J.-M.; Hansel, A.; Hoor, P.; Kormann, R.; Krejci, R.; Lange, L.; Lelieveld, J.; Lindinger, W.; Longo, K.; Peters, W.; de Reus, M.; Scheeren, B.; Silva Dias, M. A. F.; Ström, J.; van Velthoven, P. F. J.; Williams, J.

    During LBA-CLAIRE-98, we found atmospheric layers with aged biomass smoke at altitudes >10 km over Suriname. CO, CO2, acetonitrile, methyl chloride, hydrocarbons, NO, O3, and aerosols were strongly enhanced in these layers. We estimate that 80-95% of accumulation mode aerosols had been removed during convective transport. Trajectories show that the plumes originated from large fires near the Brazil/Venezuela border during March 1998. This smoke was entrained into deep convection over the northern Amazon, transported out over the Pacific, and then returned to South America by the circulation around a large upper-level anticyclone. Our observations provide evidence for the importance of deep convection in the equatorial region as a mechanism to transport large amounts of pyrogenic pollutants into the upper troposphere. The entrainment of biomass smoke into tropical convective clouds may have significant effects on cloud microphysics and climate dynamics.

  9. Cross-Saharan transport of water vapor via recycled cold pool outflows from moist convection

    NASA Astrophysics Data System (ADS)

    Trzeciak, Tomasz M.; Garcia-Carreras, Luis; Marsham, John H.

    2017-02-01

    Very sparse data have previously limited observational studies of meteorological processes in the Sahara. We present an observed case of convectively driven water vapor transport crossing the Sahara over 2.5 days in June 2012, from the Sahel in the south to the Atlas in the north. A daily cycle is observed, with deep convection in the evening generating moist cold pools that fed the next day's convection; the convection then generated new cold pools, providing a vertical recycling of moisture. Trajectories driven by analyses were able to capture the direction of the transport but not its full extent, particularly at night when cold pools are most active, and analyses missed much of the water content of cold pools. The results highlight the importance of cold pools for moisture transport, dust and clouds, and demonstrate the need to include these processes in models in order to improve the representation of Saharan atmosphere.

  10. Cross‐Saharan transport of water vapor via recycled cold pool outflows from moist convection

    PubMed Central

    Trzeciak, Tomasz M.; Garcia‐Carreras, Luis

    2017-01-01

    Abstract Very sparse data have previously limited observational studies of meteorological processes in the Sahara. We present an observed case of convectively driven water vapor transport crossing the Sahara over 2.5 days in June 2012, from the Sahel in the south to the Atlas in the north. A daily cycle is observed, with deep convection in the evening generating moist cold pools that fed the next day's convection; the convection then generated new cold pools, providing a vertical recycling of moisture. Trajectories driven by analyses were able to capture the direction of the transport but not its full extent, particularly at night when cold pools are most active, and analyses missed much of the water content of cold pools. The results highlight the importance of cold pools for moisture transport, dust and clouds, and demonstrate the need to include these processes in models in order to improve the representation of Saharan atmosphere. PMID:28344367

  11. Porous medium convection at large Rayleigh number: Studies of coherent structure, transport, and reduced dynamics

    NASA Astrophysics Data System (ADS)

    Wen, Baole

    statistically-steady porous medium convection results from an interplay between the competing effects of these two types of instability. Upper bound analysis is then employed to investigate the dependence of the heat transport enhancement factor, i.e. the Nusselt number Nu, on Ra and L. To solve the optimization problems arising from the "background field" upper-bound variational analysis, a novel two-step algorithm in which time is introduced into the formulation is developed. The new algorithm obviates the need for numerical continuation, thereby enabling the best available bounds to be computed up to Ra ≈ 2.65 x 104. A mathematical proof is given to demonstrate that the only steady state to which this numerical algorithm can converge is the required global optimal of the variational problem. Using this algorithm, the dependence of the bounds on L( Ra) is explored, and a "minimal flow unit" is identified. Finally, the upper bound variational methodology is also shown to yield quantitatively useful predictions of Nu and to furnish a functional basis that is naturally adapted to the boundary layer dynamics at large Ra..

  12. Evaluation of Convective Transport in the GEOS-5 Chemistry and Climate Model

    NASA Technical Reports Server (NTRS)

    Pickering, Kenneth E.; Ott, Lesley E.; Shi, Jainn J.; Tao. Wei-Kuo; Mari, Celine; Schlager, Hans

    2011-01-01

    The NASA Goddard Earth Observing System (GEOS-5) Chemistry and Climate Model (CCM) consists of a global atmospheric general circulation model and the combined stratospheric and tropospheric chemistry package from the NASA Global Modeling Initiative (GMI) chemical transport model. The subgrid process of convective tracer transport is represented through the Relaxed Arakawa-Schubert parameterization in the GEOS-5 CCM. However, substantial uncertainty for tracer transport is associated with this parameterization, as is the case with all global and regional models. We have designed a project to comprehensively evaluate this parameterization from the point of view of tracer transport, and determine the most appropriate improvements that can be made to the GEOS-5 convection algorithm, allowing improvement in our understanding of the role of convective processes in determining atmospheric composition. We first simulate tracer transport in individual observed convective events with a cloud-resolving model (WRF). Initial condition tracer profiles (CO, CO2, O3) are constructed from aircraft data collected in undisturbed air, and the simulations are evaluated using aircraft data taken in the convective anvils. A single-column (SCM) version of the GEOS-5 GCM with online tracers is then run for the same convective events. SCM output is evaluated based on averaged tracer fields from the cloud-resolving model. Sensitivity simulations with adjusted parameters will be run in the SCM to determine improvements in the representation of convective transport. The focus of the work to date is on tropical continental convective events from the African Monsoon Multidisciplinary Analyses (AMMA) field mission in August 2006 that were extensively sampled by multiple research aircraft.

  13. The Interplay between Proto--Neutron Star Convection and Neutrino Transport in Core-Collapse Supernovae

    NASA Astrophysics Data System (ADS)

    Mezzacappa, A.; Calder, A. C.; Bruenn, S. W.; Blondin, J. M.; Guidry, M. W.; Strayer, M. R.; Umar, A. S.

    1998-01-01

    We couple two-dimensional hydrodynamics to realistic one-dimensional multigroup flux-limited diffusion neutrino transport to investigate proto-neutron star convection in core-collapse supernovae, and more specifically, the interplay between its development and neutrino transport. Our initial conditions, time-dependent boundary conditions, and neutrino distributions for computing neutrino heating, cooling, and deleptonization rates are obtained from one-dimensional simulations that implement multigroup flux-limited diffusion and one-dimensional hydrodynamics. The development and evolution of proto-neutron star convection are investigated for both 15 and 25 M⊙ models, representative of the two classes of stars with compact and extended iron cores, respectively. For both models, in the absence of neutrino transport, the angle-averaged radial and angular convection velocities in the initial Ledoux unstable region below the shock after bounce achieve their peak values in ~20 ms, after which they decrease as the convection in this region dissipates. The dissipation occurs as the gradients are smoothed out by convection. This initial proto-neutron star convection episode seeds additional convectively unstable regions farther out beneath the shock. The additional proto-neutron star convection is driven by successive negative entropy gradients that develop as the shock, in propagating out after core bounce, is successively strengthened and weakened by the oscillating inner core. The convection beneath the shock distorts its sphericity, but on the average the shock radius is not boosted significantly relative to its radius in our corresponding one-dimensional models. In the presence of neutrino transport, proto-neutron star convection velocities are too small relative to bulk inflow velocities to result in any significant convective transport of entropy and leptons. This is evident in our two-dimensional entropy snapshots, which in this case appear spherically symmetric

  14. Improving representation of convective transport for scale-aware parameterization: 1. Convection and cloud properties simulated with spectral bin and bulk microphysics

    NASA Astrophysics Data System (ADS)

    Fan, Jiwen; Liu, Yi-Chin; Xu, Kuan-Man; North, Kirk; Collis, Scott; Dong, Xiquan; Zhang, Guang J.; Chen, Qian; Kollias, Pavlos; Ghan, Steven J.

    2015-04-01

    The ultimate goal of this study is to improve the representation of convective transport by cumulus parameterization for mesoscale and climate models. As Part 1 of the study, we perform extensive evaluations of cloud-resolving simulations of a squall line and mesoscale convective complexes in midlatitude continent and tropical regions using the Weather Research and Forecasting model with spectral bin microphysics (SBM) and with two double-moment bulk microphysics schemes: a modified Morrison (MOR) and Milbrandt and Yau (MY2). Compared to observations, in general, SBM gives better simulations of precipitation and vertical velocity of convective cores than MOR and MY2 and therefore will be used for analysis of scale dependence of eddy transport in Part 2. The common features of the simulations for all convective systems are (1) the model tends to overestimate convection intensity in the middle and upper troposphere, but SBM can alleviate much of the overestimation and reproduce the observed convection intensity well; (2) the model greatly overestimates Ze in convective cores, especially for the weak updraft velocity; and (3) the model performs better for midlatitude convective systems than the tropical system. The modeled mass fluxes of the midlatitude systems are not sensitive to microphysics schemes but are very sensitive for the tropical case indicating strong microphysics modification to convection. Cloud microphysical measurements of rain, snow, and graupel in convective cores will be critically important to further elucidate issues within cloud microphysics schemes.

  15. Improving representation of convective transport for scale-aware parameterization: 1. Convection and cloud properties simulated with spectral bin and bulk microphysics

    SciTech Connect

    Fan, Jiwen; Liu, Yi-Chin; Xu, Kuan-Man; North, Kirk; Collis, Scott; Dong, Xiquan; Zhang, Guang J; Qian, Chen; Kollias, Pavlos; Ghan, Steven

    2015-04-27

    The ultimate goal of this study is to improve the representation of convective transport by cumulus parameterization for mesoscale and climate models. As Part 1 of the study, we perform extensive evaluations of cloud-resolving simulations of a squall line and mesoscale convective complexes in midlatitude continent and tropical regions using the Weather Research and Forecasting model with spectral bin microphysics (SBM) and with two double-moment bulk microphysics schemes: a modified Morrison (MOR) and Milbrandt and Yau (MY2). Compared to observations, in general, SBM gives better simulations of precipitation and vertical velocity of convective cores than MOR and MY2 and therefore will be used for analysis of scale dependence of eddy transport in Part 2. The common features of the simulations for all convective systems are (1) themodel tends to overestimate convection intensity in the middle and upper troposphere, but SBM can alleviate much of the overestimation and reproduce the observed convection intensity well; (2) the model greatly overestimates Ze in convective cores, especially for the weak updraft velocity; and (3) the model performs better for midlatitude convective systems than the tropical system. The modeled mass fluxes of the midlatitude systems are not sensitive to microphysics schemes but are very sensitive for the tropical case indicating strong microphysics modification to convection. Cloud microphysical measurements of rain, snow, and graupel in convective cores will be critically important to further elucidate issues within cloud microphysics schemes

  16. Convective transport over the central United States and its role in regional CO and ozone budgets

    NASA Technical Reports Server (NTRS)

    Thompson, Anne M.; Pickering, Kenneth E.; Dickerson, Russell R.; Ellis, William G., Jr.; Jacob, Daniel J.; Scala, John R.; Tao, Wei-Kuo; Mcnamara, Donna P.; Simpson, Joanne

    1994-01-01

    We have constructed a regional budget for boundary layer carbon monoxide over the central United States (32.5 deg - 50 deg N, 90 deg - 105 deg W), emphasizing a detailed evaluation of deep convective vertical fluxes appropriate for the month of June. Deep convective venting of the boundary layer (upward) dominates other components of the CO budget, e.g., downward convective transport, loss of CO by oxidation, anthropogenic emissions, and CO produced from oxidation of methane, isoprene, and anthropogenic nonmethane hydrocarbons (NMHCs). Calculations of deep convective venting are based on the method pf Pickering et al.(1992a) which uses a satellite-derived deep convective cloud climatology along with transport statistics from convective cloud model simulations of observed prototype squall line events. This study uses analyses of convective episodes in 1985 and 1989 and CO measurements taken during several midwestern field campaigns. Deep convective venting of the boundary layer over this moderately polluted region provides a net (upward minus downward) flux of 18.1 x 10(exp 8) kg CO/month to the free troposphere during early summer. Shallow cumulus and synoptic-scale weather systems together make a comparable contribution (total net flux 16.2 x 10(exp 8) kg CO/month). Boundary layer venting of CO with other O3 precursors leads to efficient free troposheric O3 formation. We estimate that deep convective transport of CO and other precursors over the central United States in early summer leads to a gross production of 0.66 - 1.1 Gmol O3/d in good agreement with estimates of O3 production from boundary layer venting in a continental-scale model (Jacob et al., 1993a, b). On this respect the central U.S. region acts as s `chimney' for the country, and presumably this O3 contributes to high background levels of O3 in the eastern United States and O3 export to the North Atlantic.

  17. Convective transport over the central United States and its role in regional CO and ozone budgets

    NASA Technical Reports Server (NTRS)

    Thompson, Anne M.; Pickering, Kenneth E.; Dickerson, Russell R.; Ellis, William G., Jr.; Jacob, Daniel J.; Scala, John R.; Tao, Wei-Kuo; Mcnamara, Donna P.; Simpson, Joanne

    1994-01-01

    We have constructed a regional budget for boundary layer carbon monoxide over the central United States (32.5 deg - 50 deg N, 90 deg - 105 deg W), emphasizing a detailed evaluation of deep convective vertical fluxes appropriate for the month of June. Deep convective venting of the boundary layer (upward) dominates other components of the CO budget, e.g., downward convective transport, loss of CO by oxidation, anthropogenic emissions, and CO produced from oxidation of methane, isoprene, and anthropogenic nonmethane hydrocarbons (NMHCs). Calculations of deep convective venting are based on the method pf Pickering et al.(1992a) which uses a satellite-derived deep convective cloud climatology along with transport statistics from convective cloud model simulations of observed prototype squall line events. This study uses analyses of convective episodes in 1985 and 1989 and CO measurements taken during several midwestern field campaigns. Deep convective venting of the boundary layer over this moderately polluted region provides a net (upward minus downward) flux of 18.1 x 10(exp 8) kg CO/month to the free troposphere during early summer. Shallow cumulus and synoptic-scale weather systems together make a comparable contribution (total net flux 16.2 x 10(exp 8) kg CO/month). Boundary layer venting of CO with other O3 precursors leads to efficient free troposheric O3 formation. We estimate that deep convective transport of CO and other precursors over the central United States in early summer leads to a gross production of 0.66 - 1.1 Gmol O3/d in good agreement with estimates of O3 production from boundary layer venting in a continental-scale model (Jacob et al., 1993a, b). On this respect the central U.S. region acts as s `chimney' for the country, and presumably this O3 contributes to high background levels of O3 in the eastern United States and O3 export to the North Atlantic.

  18. Transport across the tropical tropopause layer and convection

    NASA Astrophysics Data System (ADS)

    Tissier, Ann-Sophie; Legras, Bernard; Tzella, Alexandra

    2015-04-01

    We investigate how air parcels detrained from convective sources enter the TTL. The approach is based on the comparison of unidimensional trajectories and Lagrangian backward and forward trajectories, using TRACZILLA and ERA-Interim. Backward trajectories are launched at 380K and run until they hit a deep convective cloud. Forward trajectories are launched at the top of high convective clouds identified by brightness temperature from CLAUS dataset. 1D trajectories are computed using Gardiner's method. Results show that the warm pool region during winter and the Bay of Bengal / Sea of China during summer are the prevalent sources as already identified in many previous studies and we quantify the respective role of the various regions. We show that the 1D model explains qualitatively and often quantitatively the 3d results. We also show that in spite of generating very high convection, Africa is quite ineffective as providing air that remains in the TTL while on the opposite the Tibetan Plateau is the most effective region in this respect although its total contribution is minor. Finally, we compare ERA-Interim, JRA-55 and MERRA reanalysis and find large similarities between the two formers.

  19. Numerical studies of convective transport associated with crystal growth in mirrogravity

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.

    1992-01-01

    Information on numerical studies of convective transport associated with crystal growth in microgravity is given in viewgraph form. Inferences drawn from the research are that protein crystals seem to grow at much larger relative supersaturations than small molecule crystals; growth rate is limited by attachment kinetics more than by transport; attachment kinetics are apparently influenced by convective flows, although the mechanism is uncertain; acceleration levels required to achieve D/L growth within Space Station Freedom specifications may not be achievable on manned vehicles; and D/L transport can help minimize incorporation of impurities, but growth cessation cannot be explained.

  20. Parallel measurement of conductive and convective thermal transport of micro/nanowires based on Raman mapping

    NASA Astrophysics Data System (ADS)

    Li, Man; Li, Changzheng; Wang, Jianmei; Xiao, Xiangheng; Yue, Yanan

    2015-06-01

    Heat conduction and convection are coupled effects in thermal transport of low-dimensional materials especially at micro/nanoscale. However, the parallel measurement is a challenge due to the limitation of characterization pathways. In this work, we report a method to study conductive and convective thermal transport of micro/nanowires simultaneously by using steady-state Joule-heating and Raman mapping. To examine this method, the carbon nanotubes (CNTs) fiber (36 μm in diameter) is characterized and its temperature dependence of thermal properties including thermal conductivity and convection coefficient in ambient air is studied. Preliminary results show that thermal conductivity of the CNTs fiber increases from 26 W/m K to 34 W/m K and convection coefficient decreases from 1143 W/m2 K to 1039 W/m2 K with temperature ranging from 312 to 444 K. The convective heat dissipation to the air could be as high as 60% of the total Joule heating power. Uncertainty analysis is performed to reveal that fitting errors can be further reduced by increasing sampling points along the fiber. This method features a fast/convenient way for parallel measurement of both heat conduction and convection of micro/nanowires which is beneficial to comprehensively understanding the coupled effect of micro/nanoscale heat conduction and convection.

  1. Optimization of the Conditions of Convective Drying of Thermosensitive Materials

    NASA Astrophysics Data System (ADS)

    Alyzhanov, M. K.; Sikhimbayev, M. R.; Kuzembayev, S. B.; Sherov, K. T.; Sikhimbayeva, D. R.; Khanov, T. A.; Kurmangaliyev, T. B.; Elemes, D. E.; Donenbayev, B. S.; Musaev, M. M.; Buzauova, T. M.

    2016-12-01

    The article proposes the solution of the problem with the application of thermal vibrations of heat-carrier flow in processes of convective drying, for the purpose of theoretical determination of optimum conditions of short-term excess of handling temperature, that do not influence the decrease of technological characteristics of the thermosensitive materials.

  2. Sensitivity of CO2 Simulation in a GCM to the Convective Transport Algorithms

    NASA Technical Reports Server (NTRS)

    Zhu, Z.; Pawson, S.; Collatz, G. J.; Gregg, W. W.; Kawa, S. R.; Baker, D.; Ott, L.

    2014-01-01

    Convection plays an important role in the transport of heat, moisture and trace gases. In this study, we simulated CO2 concentrations with an atmospheric general circulation model (GCM). Three different convective transport algorithms were used. One is a modified Arakawa-Shubert scheme that was native to the GCM; two others used in two off-line chemical transport models (CTMs) were added to the GCM here for comparison purposes. Advanced CO2 surfaced fluxes were used for the simulations. The results were compared to a large quantity of CO2 observation data. We find that the simulation results are sensitive to the convective transport algorithms. Overall, the three simulations are quite realistic and similar to each other in the remote marine regions, but are significantly different in some land regions with strong fluxes such as Amazon and Siberia during the convection seasons. Large biases against CO2 measurements are found in these regions in the control run, which uses the original GCM. The simulation with the simple diffusive algorithm is better. The difference of the two simulations is related to the very different convective transport speed.

  3. Optimization of precipitation and streamflow forecasts in the southwest Contiguous US for warm season convection

    NASA Astrophysics Data System (ADS)

    Lahmers, T.; Castro, C. L.; Gupta, H. V.; Gochis, D. J.; ElSaadani, M.

    2015-12-01

    Warm season convection associated with the North American Monsoon (NAM) provides an important source of precipitation for much of the Southwest Contiguous US (CONUS) and Northwest Mexico. Convection associated with the NAM can also result in flash flooding, a hazard to metropolitan areas such as Tucson and Phoenix, as well as rural areas where washouts of main roads can sever critical transportation infrastructure. In order to mitigate the effects of this problem, the National Oceanic and Atmospheric Administration (NOAA) National Water Center (NWC) is developing a national distributed hydrologic model using the WRF-Hydro framework with forcing from the High Resolution Rapid Refresh (HRRR) mesoscale atmospheric model. We aim to improve this National hydrologic and atmospheric modeling framework through the calibration of the WRF-Hydro model for the southwest CONUS and the optimization of planetary boundary layer and cloud microphysics schemes for the Weather Research and Forecasting (WRF) model in the same region. The WRF-Hydro model, with a similar structure as the national configuration used by the NWC, has been set up for the Gila River basin in southern Arizona. We demonstrate the utility of the model for forecasting high impact precipitation events in catchments with limited human modification. The WRF-Hydro model is spun up using past precipitation from the NCEP Stage-IV records and TRMM estimates. Atmospheric forcing for WRF-Hydro comes from the NASA Phase 2 North American Land Data Assimilation (NLDAS-2) dataset. WRF-Hydro is forced for selected high-impact events using a 3-km grid resolution Advanced Research WRF (WRF-ARW) atmospheric simulation. WRF-ARW is forced with the operational National Center for Environmental Prediction (NCEP) Global Forecasting System (GFS) operational model. This methodology demonstrates the modeling framework that will be used for future parameter calibration of WRF-Hydro and optimization of WRF-ARW.

  4. Increased Efficiency Thermoelectric Generator With Convective Heat Transport

    DTIC Science & Technology

    2011-02-25

    flow. The latter two are the dissipative losses that reduce efficiency below Carnot efficiency in an ideal TE heat engine. Convection can be...for the ideal case. It is readily apparent that the efficiency increases rapidly with δ, and Φ approaches the Carnot limit as δ approaches about 10. To...August 2002. 9. Echigo, R., et al., “An extended Analysis on Thermodynamic Cycle of Advanced Heating/Cooling Method by Porous Thermoelectric

  5. Convection in axially symmetric accretion discs with microscopic transport coefficients

    NASA Astrophysics Data System (ADS)

    Malanchev, K. L.; Postnov, K. A.; Shakura, N. I.

    2017-01-01

    The vertical structure of stationary thin accretion discs is calculated from the energy balance equation with heat generation due to microscopic ion viscosity η and electron heat conductivity κ, both depending on temperature. In the optically thin discs it is found that for the heat conductivity increasing with temperature, the vertical temperature gradient exceeds the adiabatic value at some height, suggesting convective instability in the upper disc layer. There is a critical Prandtl number, Pr = 4/9, above which a Keplerian disc become fully convective. The vertical density distribution of optically thin laminar accretion discs as found from the hydrostatic equilibrium equation cannot be generally described by a polytrope but in the case of constant viscosity and heat conductivity. In the optically thick discs with radiation heat transfer, the vertical disc structure is found to be convectively stable for both absorption-dominated and scattering-dominated opacities, unless a very steep dependence of the viscosity coefficient on temperature is assumed. A polytropic-like structure in this case is found for Thomson scattering-dominated opacity.

  6. A test of sensitivity to convective transport in a global atmospheric CO2 simulation

    NASA Astrophysics Data System (ADS)

    Bian, H.; Kawa, S. R.; Chin, M.; Pawson, S.; Zhu, Z.; Rasch, P.; Wu, S.

    2006-11-01

    Two approximations to convective transport have been implemented in an offline chemistry transport model (CTM) to explore the impact on calculated atmospheric CO2 distributions. Global CO2 in the year 2000 is simulated using the CTM driven by assimilated meteorological fields from the NASA's Goddard Earth Observation System Data Assimilation System, Version 4 (GEOS-4). The model simulates atmospheric CO2 by adopting the same CO2 emission inventory and dynamical modules as described in Kawa et al. (convective transport scheme denoted as Conv1). Conv1 approximates the convective transport by using the bulk convective mass fluxes to redistribute trace gases. The alternate approximation, Conv2, partitions fluxes into updraft and downdraft, as well as into entrainment and detrainment, and has potential to yield a more realistic simulation of vertical redistribution through deep convection. Replacing Conv1 by Conv2 results in an overestimate of CO2 over biospheric sink regions. The largest discrepancies result in a CO2 difference of about 7.8 ppm in the July NH boreal forest, which is about 30% of the CO2 seasonality for that area. These differences are compared to those produced by emission scenario variations constrained by the framework of Intergovernmental Panel on Climate Change (IPCC) to account for possible land use change and residual terrestrial CO2 sink. It is shown that the overestimated CO2 driven by Conv2 can be offset by introducing these supplemental emissions.

  7. A Test of Sensitivity to Convective Transport in a Global Atmospheric CO2 Simulation

    NASA Technical Reports Server (NTRS)

    Bian, H.; Kawa, S. R.; Chin, M.; Pawson, S.; Zhu, Z.; Rasch, P.; Wu, S.

    2006-01-01

    Two approximations to convective transport have been implemented in an offline chemistry transport model (CTM) to explore the impact on calculated atmospheric CO2 distributions. GlobalCO2 in the year 2000 is simulated using theCTM driven by assimilated meteorological fields from the NASA s Goddard Earth Observation System Data Assimilation System, Version 4 (GEOS-4). The model simulates atmospheric CO2 by adopting the same CO2 emission inventory and dynamical modules as described in Kawa et al. (convective transport scheme denoted as Conv1). Conv1 approximates the convective transport by using the bulk convective mass fluxes to redistribute trace gases. The alternate approximation, Conv2, partitions fluxes into updraft and downdraft, as well as into entrainment and detrainment, and has potential to yield a more realistic simulation of vertical redistribution through deep convection. Replacing Conv1 by Conv2 results in an overestimate of CO2 over biospheric sink regions. The largest discrepancies result in a CO2 difference of about 7.8 ppm in the July NH boreal forest, which is about 30% of the CO2 seasonality for that area. These differences are compared to those produced by emission scenario variations constrained by the framework of Intergovernmental Panel on Climate Change (IPCC) to account for possible land use change and residual terrestrial CO2 sink. It is shown that the overestimated CO2 driven by Conv2 can be offset by introducing these supplemental emissions.

  8. A Test of Sensitivity to Convective Transport in a Global Atmospheric CO2 Simulation

    NASA Technical Reports Server (NTRS)

    Bian, H.; Kawa, S. R.; Chin, M.; Pawson, S.; Zhu, Z.; Rasch, P.; Wu, S.

    2006-01-01

    Two approximations to convective transport have been implemented in an offline chemistry transport model (CTM) to explore the impact on calculated atmospheric CO2 distributions. GlobalCO2 in the year 2000 is simulated using theCTM driven by assimilated meteorological fields from the NASA s Goddard Earth Observation System Data Assimilation System, Version 4 (GEOS-4). The model simulates atmospheric CO2 by adopting the same CO2 emission inventory and dynamical modules as described in Kawa et al. (convective transport scheme denoted as Conv1). Conv1 approximates the convective transport by using the bulk convective mass fluxes to redistribute trace gases. The alternate approximation, Conv2, partitions fluxes into updraft and downdraft, as well as into entrainment and detrainment, and has potential to yield a more realistic simulation of vertical redistribution through deep convection. Replacing Conv1 by Conv2 results in an overestimate of CO2 over biospheric sink regions. The largest discrepancies result in a CO2 difference of about 7.8 ppm in the July NH boreal forest, which is about 30% of the CO2 seasonality for that area. These differences are compared to those produced by emission scenario variations constrained by the framework of Intergovernmental Panel on Climate Change (IPCC) to account for possible land use change and residual terrestrial CO2 sink. It is shown that the overestimated CO2 driven by Conv2 can be offset by introducing these supplemental emissions.

  9. Differential Rotation and Angular Momentum Transport Caused by Thermal Convection in a Rotating Spherical Shell

    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.

  10. The effect of perturbations of convective energy transport on the luminosity and radius of the Sun

    NASA Technical Reports Server (NTRS)

    Endal, A. S.; Twigg, L. W.

    1982-01-01

    The response of solar models to perturbations of the efficiency of convective energy transport is studied for a number of cases. Such perturbations primarily effect the shallow superadiabatic layer of the convective envelope (at depth of approx. 1000 km below the photosphere). Independent of the details of the perturbation scheme, the resulting change in the solar radius is always very small compared to the change in luminosity. This appears to be true for any physical mechanism of solar variability which operates in the outer layers of the convection zone. Changes of the solar radius have been inferred from historical observations of solar eclipses. Considering the constraints on concurrent luminosity changes, this type of solar variability must be indicative of changes in the solar structure at substantial depths below the superadiabatic layer of the convective envelope.

  11. The effect of perturbation of convective energy transport on the luminosity and radius of the sun

    NASA Technical Reports Server (NTRS)

    Endal, A. S.; Twigg, L. W.

    1982-01-01

    The response of solar models to perturbations of the efficiency of convective energy transport is studied. Such perturbations primarily affect the shallow superadiabatic layer of the convective envelope. Independent of the details of the perturbation scheme, the resulting change in the solar radius is always very small compared to the change in luminosity. This appears to be true for any physical mechanism of solar variability which operates in the outer layers of the convection zone. Changes of the solar radius have been inferred from historical observations of solar eclipses in 1715 and 1925. Considering the constraints on concurrent luminosity changes, this type of solar variability must be indicative of changes in the solar structure at substantial depths below the superadiabatic layer of the convective envelope.

  12. Bounds on heat transport in Bénard-Marangoni convection.

    PubMed

    Hagstrom, George; Doering, Charles R

    2010-04-01

    For Pearson's model of Bénard-Marangoni convection, the Nusselt number Nu is proven to be bounded as a function Marangoni number Ma according to Nu

  13. Implications of Convective Scrape-Off Layer Transport for Fusion Reactors with Solid and Liquid Walls

    SciTech Connect

    Kotschenreuther, M; Rognlien, T D; Valanju, P

    2003-11-13

    Recent experimental observations in tokamaks indicate enhanced convection of plasma blobs toward the main chamber wall. Potential implications of these observations for reactors are examined here. Two dimensional plasma edge calculations are performed with UEDGE, including convective transport consistent with present experiments. This is coupled to a kinetic neutral calculation using the code NUT, to compute the hot neutral flux to the wall. The inclusion of convection increases sputtering of the wall by roughly an order of magnitude. For tungsten walls, erosion (neglecting re-deposition) is estimated to be {approx}0.6 mm per year. Plasma contamination could be serious for high Z walls of W or Sn, and might preclude ignition (based on empirical screening estimates). Low Z liquid materials offer much better prospects for acceptable plasma contamination. Rough estimates of dust generation from such erosion rates imply significant safety issues. Plasma transport via blobs can also significantly modify models of impurity redeposition.

  14. Convective transport of reactive constituents to the tropical and mid-latitude tropopause region: I. Observations

    NASA Technical Reports Server (NTRS)

    Ridley, B.; Atlas, E.; Selkirk, H.; Pfister, L.; Montzka, D.; Walega, J.; Donnelly, S.; Stroud, V.; Richard, E.; Kelly, K.

    2004-01-01

    Measurements of ozone, reactive carbon and nitrogen, and other trace constituents from flights of the NASA WB-57F aircraft in the upper troposphere and lower stratosphere reveal that convection in the tropics can present a complex mix of surface-emitted constituents right up to the altitude of the lapse rate tropopause. At higher latitudes over the southern US, the strongest transport signal, in terms of constituent mixing ratios, occurred in the potential temperature range of 340-350K or approximately over the altitude range of 9-11km. Weaker convective signals were also seen up to near the tropopause. There was no evidence of convective transport directly into the lower stratosphere from these flights. $CPY 2003 Elsevier Ltd. All rights reserved.

  15. Convective transport of reactive constituents to the tropical and mid-latitude tropopause region: I. Observations

    NASA Technical Reports Server (NTRS)

    Ridley, B.; Atlas, E.; Selkirk, H.; Pfister, L.; Montzka, D.; Walega, J.; Donnelly, S.; Stroud, V.; Richard, E.; Kelly, K.

    2004-01-01

    Measurements of ozone, reactive carbon and nitrogen, and other trace constituents from flights of the NASA WB-57F aircraft in the upper troposphere and lower stratosphere reveal that convection in the tropics can present a complex mix of surface-emitted constituents right up to the altitude of the lapse rate tropopause. At higher latitudes over the southern US, the strongest transport signal, in terms of constituent mixing ratios, occurred in the potential temperature range of 340-350K or approximately over the altitude range of 9-11km. Weaker convective signals were also seen up to near the tropopause. There was no evidence of convective transport directly into the lower stratosphere from these flights. $CPY 2003 Elsevier Ltd. All rights reserved.

  16. A NEW MODEL FOR MIXING BY DOUBLE-DIFFUSIVE CONVECTION (SEMI-CONVECTION). II. THE TRANSPORT OF HEAT AND COMPOSITION THROUGH LAYERS

    SciTech Connect

    Wood, T. S.; Garaud, P.; Stellmach, S.

    2013-05-10

    Regions of stellar and planetary interiors that are unstable according to the Schwarzschild criterion, but stable according to the Ledoux criterion, are subject to a form of oscillatory double-diffusive (ODD) convection often called ''semi-convection''. In this series of papers, we use an extensive suite of three-dimensional (3D) numerical simulations to quantify the transport of heat and composition by ODD convection, and ultimately propose a new 1D prescription that can be used in stellar and planetary structure and evolution models. The first paper in this series demonstrated that under certain conditions ODD convection spontaneously transitions from an initial homogeneous state of weak wave-breaking turbulence into a staircase of fully convective layers, which results in a substantial increase in the transport of heat and composition. Here, we present simulations of ODD convection in this layered regime, we describe the dynamical behavior of the layers, and we derive empirical scaling laws for the transport through layered convection.

  17. Variational optimization of sub-grid scale convection parameters. Final report

    SciTech Connect

    Zivkovic-Rothman, M.

    1997-11-25

    Under the DOE CHAMMP/CLIMATE Program, a convective scheme was developed for use in climate models. The purpose of the present study was to develop an adjoint model of its tangent-linear model. the convective scheme was integrated within a single column model which provides radiative-convective equilibrium solutions applicable to climate models. The main goal of this part of the project was to develop an adjoint of the scheme to facilitate the optimization of its convective parameters. For that purpose, adjoint sensitivities were calculated with the adjoint code. Parameter optimization was based on TOGA COARE data which were also used in this study to obtain integrations of the nonlinear and tangent-linear models as well as the integrations of the adjoint model. Some inadequacies of the inner IFA data array were found, and did not permit a single numerical integration during the entire 4 months of data. However, reliable monthly radiative-convective equilibrium solutions and associated adjoint sensitivities were obtained and used to bring about the parameter optimization.

  18. Experimental validation of convection-diffusion discretisation scheme employed for computational modelling of biological mass transport

    PubMed Central

    2010-01-01

    Background The finite volume solver Fluent (Lebanon, NH, USA) is a computational fluid dynamics software employed to analyse biological mass-transport in the vasculature. A principal consideration for computational modelling of blood-side mass-transport is convection-diffusion discretisation scheme selection. Due to numerous discretisation schemes available when developing a mass-transport numerical model, the results obtained should either be validated against benchmark theoretical solutions or experimentally obtained results. Methods An idealised aneurysm model was selected for the experimental and computational mass-transport analysis of species concentration due to its well-defined recirculation region within the aneurysmal sac, allowing species concentration to vary slowly with time. The experimental results were obtained from fluid samples extracted from a glass aneurysm model, using the direct spectrophometric concentration measurement technique. The computational analysis was conducted using the four convection-diffusion discretisation schemes available to the Fluent user, including the First-Order Upwind, the Power Law, the Second-Order Upwind and the Quadratic Upstream Interpolation for Convective Kinetics (QUICK) schemes. The fluid has a diffusivity of 3.125 × 10-10 m2/s in water, resulting in a Peclet number of 2,560,000, indicating strongly convection-dominated flow. Results The discretisation scheme applied to the solution of the convection-diffusion equation, for blood-side mass-transport within the vasculature, has a significant influence on the resultant species concentration field. The First-Order Upwind and the Power Law schemes produce similar results. The Second-Order Upwind and QUICK schemes also correlate well but differ considerably from the concentration contour plots of the First-Order Upwind and Power Law schemes. The computational results were then compared to the experimental findings. An average error of 140% and 116% was demonstrated

  19. Anomalous heat transport and condensation in convection of cryogenic helium

    PubMed Central

    Urban, Pavel; Schmoranzer, David; Hanzelka, Pavel; Sreenivasan, Katepalli R.; Skrbek, Ladislav

    2013-01-01

    When a hot body A is thermally connected to a cold body B, the textbook knowledge is that heat flows from A to B. Here, we describe the opposite case in which heat flows from a colder but constantly heated body B to a hotter but constantly cooled body A through a two-phase liquid–vapor system. Specifically, we provide experimental evidence that heat flows through liquid and vapor phases of cryogenic helium from the constantly heated, but cooler, bottom plate of a Rayleigh–Bénard convection cell to its hotter, but constantly cooled, top plate. The bottom plate is heated uniformly, and the top plate is cooled by heat exchange with liquid helium maintained at 4.2 K. Additionally, for certain experimental conditions, a rain of helium droplets is detected by small sensors placed in the cell at about one-half of its height. PMID:23576759

  20. Momentum and heat transport scalings in laminar vertical convection.

    PubMed

    Shishkina, Olga

    2016-05-01

    We derive the dependence of the Reynolds number Re and the Nusselt number Nu on the Rayleigh number Ra and the Prandtl number Pr in laminar vertical convection (VC), where a fluid is confined between two differently heated isothermal vertical walls. The boundary layer equations in laminar VC yield two limiting scaling regimes: Nu∼Pr^{1/4}Ra^{1/4}, Re∼Pr^{-1/2}Ra^{1/2} for Pr≪1 and Nu∼Pr^{0}Ra^{1/4}, Re∼Pr^{-1}Ra^{1/2} for Pr≫1. These theoretical results are in excellent agreement with direct numerical simulations for Ra from 10^{5} to 10^{10} and Pr from 10^{-2} to 30. The transition between the regimes takes place for Pr around 10^{-1}.

  1. Anomalous heat transport and condensation in convection of cryogenic helium.

    PubMed

    Urban, Pavel; Schmoranzer, David; Hanzelka, Pavel; Sreenivasan, Katepalli R; Skrbek, Ladislav

    2013-05-14

    When a hot body A is thermally connected to a cold body B, the textbook knowledge is that heat flows from A to B. Here, we describe the opposite case in which heat flows from a colder but constantly heated body B to a hotter but constantly cooled body A through a two-phase liquid-vapor system. Specifically, we provide experimental evidence that heat flows through liquid and vapor phases of cryogenic helium from the constantly heated, but cooler, bottom plate of a Rayleigh-Bénard convection cell to its hotter, but constantly cooled, top plate. The bottom plate is heated uniformly, and the top plate is cooled by heat exchange with liquid helium maintained at 4.2 K. Additionally, for certain experimental conditions, a rain of helium droplets is detected by small sensors placed in the cell at about one-half of its height.

  2. Design of a convective cooling system for a Mach 6 hypersonic transport airframe

    NASA Technical Reports Server (NTRS)

    Helenbrook, R. G.; Anthony, F. M.

    1971-01-01

    Results of analytical and design studies are presented for a water-glycol convective cooling system for the airframe structure of a hypersonic transport. System configurations and weights are compared. The influences of system pressure drop and flow control schedules on system weight are defined.

  3. 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.

  4. Astrobiological and Geological Implications of Convective Transport in Icy Outer Planet Satellites

    NASA Technical Reports Server (NTRS)

    Pappalardo, Robert T.; Zhong, Shi-Jie; Barr, Amy

    2005-01-01

    The oceans of large icy outer planet satellites are prime targets in the search for extraterrestrial life in our solar system. The goal of our project has been to develop models of ice convection in order to understand convection as an astrobiologically relevant transport mechanism within icy satellites, especially Europa. These models provide valuable constraints on modes of surface deformation and thus the implications of satellite surface geology for astrobiology, and for planetary protection. Over the term of this project, significant progress has been made in three areas: (1) the initiation of convection in large icy satellites, which we find probably requires tidal heating; (2) the relationship of surface features on Europa to internal ice convection, including the likely role of low-melting-temperature impurities; and (3) the effectiveness of convection as an agent of icy satellite surface-ocean material exchange, which seems most plausible if tidal heating, compositional buoyancy, and solid-state convection work in combination. Descriptions of associated publications include: 3 published papers (including contributions to 1 review chapter), 1 manuscript in revision, 1 manuscript in preparation (currently being completed under separate funding), and 1 published popular article. A myriad of conference abstracts have also been published, and only those from the past year are listed.

  5. Salt tectonics and shallow subseafloor fluid convection: models of coupled fluid-heat-salt transport

    USGS Publications Warehouse

    Wilson, A.; Ruppel, C.

    2007-01-01

    Thermohaline convection associated with salt domes has the potential to drive significant fluid flow and mass and heat transport in continental margins, but previous studies of fluid flow associated with salt structures have focused on continental settings or deep flow systems of importance to petroleum exploration. Motivated by recent geophysical and geochemical observations that suggest a convective pattern to near-seafloor pore fluid flow in the northern Gulf of Mexico (GoMex), we devise numerical models that fully couple thermal and chemical processes to quantify the effects of salt geometry and seafloor relief on fluid flow beneath the seafloor. Steady-state models that ignore halite dissolution demonstrate that seafloor relief plays an important role in the evolution of shallow geothermal convection cells and that salt at depth can contribute a thermal component to this convection. The inclusion of faults causes significant, but highly localized, increases in flow rates at seafloor discharge zones. Transient models that include halite dissolution show the evolution of flow during brine formation from early salt-driven convection to later geothermal convection, characteristics of which are controlled by the interplay of seafloor relief and salt geometry. Predicted flow rates are on the order of a few millimeters per year or less for homogeneous sediments with a permeability of 10−15 m2, comparable to compaction-driven flow rates. Sediment permeabilities likely fall below 10−15 m2 at depth in the GoMex basin, but such thermohaline convection can drive pervasive mass transport across the seafloor, affecting sediment diagenesis in shallow sediments. In more permeable settings, such flow could affect methane hydrate stability, seafloor chemosynthetic communities, and the longevity of fluid seeps.

  6. Improving Representation of Convective Transport for Scale-Aware Parameterization – Part I: Convection and Cloud Properties Simulated with Spectral Bin and Bulk Microphysics

    SciTech Connect

    Fan, Jiwen; Liu, Yi-Chin; Xu, Kuan-Man; North, Kirk; Collis, Scott M.; Dong, Xiquan; Zhang, Guang J.; Chen, Qian; Ghan, Steven J.

    2015-04-27

    The ultimate goal of this study is to improve representation of convective transport by cumulus parameterization for meso-scale and climate models. As Part I of the study, we perform extensive evaluations of cloud-resolving simulations of a squall line and mesoscale convective complexes in mid-latitude continent and tropical regions using the Weather Research and Forecasting (WRF) model with spectral-bin microphysics (SBM) and with two double-moment bulk microphysics schemes: a modified Morrison (MOR) and Milbrandt and Yau (MY2). Compared to observations, in general, SBM gives better simulations of precipitation, vertical velocity of convective cores, and the vertically decreasing trend of radar reflectivity than MOR and MY2, and therefore will be used for analysis of scale-dependence of eddy transport in Part II. The common features of the simulations for all convective systems are (1) the model tends to overestimate convection intensity in the middle and upper troposphere, but SBM can alleviate much of the overestimation and reproduce the observed convection intensity well; (2) the model greatly overestimates radar reflectivity in convective cores (SBM predicts smaller radar reflectivity but does not remove the large overestimation); and (3) the model performs better for mid-latitude convective systems than tropical system. The modeled mass fluxes of the mid latitude systems are not sensitive to microphysics schemes, but are very sensitive for the tropical case indicating strong microphysics modification to convection. Cloud microphysical measurements of rain, snow and graupel in convective cores will be critically important to further elucidate issues within cloud microphysics schemes.

  7. Optimal convective brine drainage from sea ice and optimal brine channel spacing

    NASA Astrophysics Data System (ADS)

    Wells, A. J.; Wettlaufer, J. S.; Orszag, S.

    2010-12-01

    The state of the polar climate is intricately linked to the structure and evolution of sea ice. While it is well known that the drainage of brine from sea ice influences its structural properties, the exchange of heat and chemicals between ice and ocean, and forcing of the ocean thermohaline circulation, models often rely on ad hoc parameterizations in the absence of theoretical justification. We develop a theoretical model of the physical processes responsible for brine drainage driven by gravity. Sea ice consists of a porous array of ice crystals bathed in dense salty brine; a reactive porous medium. The buoyancy driven flow of brine leads to local dissolution of ice and the formation of brine channels: ice free conduits through which brine drains. It is observed that the spacing of brine channels and structure of the ice matrix evolve as sea ice grows. We consider nonlinear convection in a reactive porous medium undergoing steady state growth, applying a numerical model to investigate the mechanism controlling the spatial distribution of brine channels. The theory predicts a brine flux scaling law that is consistent with previous experiments, and the resulting dynamics yields insight into variations in sea ice microstructure and fluid transport through the ice.

  8. Location - Dependent Coronary Artery Diffusive and Convective Mass Transport Properties of a Lipophilic Drug Surrogate Measured Using Nonlinear Microscopy

    PubMed Central

    Keyes, Joseph T.; Simon, Bruce R.; Vande Geest, Jonathan P.

    2013-01-01

    Purpose Arterial wall mass transport properties dictate local distribution of biomolecules or locally delivered dugs. Knowing how these properties vary between coronary artery locations could provide insight into how therapy efficacy is altered between arterial locations. Methods We introduced an indocarbocyanine drug surrogate to the lumens of left anterior descending and right coronary (LADC; RC) arteries from pigs with or without a pressure gradient. Interstitial fluorescent intensity was measured on live samples with multiphoton microscopy. We also measured binding to porcine coronary SMCs in monoculture. Results Diffusive transport constants peaked in the middle sections of the LADC and RC arteries by 2.09 and 2.04 times, respectively, compared to the proximal and distal segments. There was no statistical difference between the average diffusivity value between LADC and RC arteries. The convection coefficients had an upward trend down each artery, with the RC being higher than the LADC by 3.89 times. Conclusions This study demonstrates that the convective and diffusive transport of lipophilic molecules changes between the LADC and the RC arteries as well as along their length. These results may have important implications in optimizing drug delivery for the treatment of coronary artery disease. PMID:23224981

  9. Real-Time Imaging of Perivascular Transport of Nanoparticles During Convection Enhanced Delivery in the Rat Cortex

    PubMed Central

    Foley, Conor P.; Nishimura, Nozomi; Neeves, Keith B.; Schaffer, Chris B.; Olbricht., William L.

    2012-01-01

    Convection enhanced delivery (CED) is a promising technique for administering large therapeutics that do not readily cross the blood brain barrier to neural tissue. It is of vital importance to understand how large drug constructs move through neural tissue during CED to optimize construct and delivery parameters so that drugs are concentrated in the targeted tissue, with minimal leakage outside the targeted zone. Experiments have shown that liposomes, viral vectors, high molecular weight tracers, and nanoparticles infused into neural tissue localize in the perivascular spaces of blood vessels within the brain parenchyma. In this work, we used two-photon excited fluorescence microscopy to monitor the real-time distribution of nanoparticles infused in the cortex of live, anesthetized rats via CED. Fluorescent nanoparticles of 24-nm and 100-nm nominal diameters were infused into rat cortex through microfluidic probes. We found that perivascular spaces provide a high permeability path for rapid convective transport of large nanoparticles through tissue, and that the effects of perivascular spaces on transport are more significant for larger particles that undergo hindered transport through the extra cellular matrix. This suggests that the vascular topology of the target tissue volume must be considered when delivering large therapeutic constructs via CED. PMID:22009318

  10. Optimizing Nutrient Uptake in Biological Transport Networks

    NASA Astrophysics Data System (ADS)

    Ronellenfitsch, Henrik; Katifori, Eleni

    2013-03-01

    Many biological systems employ complex networks of vascular tubes to facilitate transport of solute nutrients, examples include the vascular system of plants (phloem), some fungi, and the slime-mold Physarum. It is believed that such networks are optimized through evolution for carrying out their designated task. We propose a set of hydrodynamic governing equations for solute transport in a complex network, and obtain the optimal network architecture for various classes of optimizing functionals. We finally discuss the topological properties and statistical mechanics of the resulting complex networks, and examine correspondence of the obtained networks to those found in actual biological systems.

  11. Counter-gradient heat transport by large-scale circulation in two-dimensional turbulent convection

    NASA Astrophysics Data System (ADS)

    Qiang, Wei; Cao, Hui; Li, Weimin; Zhang, Fansiqi

    2017-06-01

    We investigate numerically the counter-gradient heat transport in two-dimensional turbulent Rayleigh-Bénard convection, which derives its existence from the descending hot plumes and ascending cold plumes with the large-scale circulation. Both qualitative and quantitative evidence is presented for the Rayleigh numbers from 104 to 1011 and the Prandtl number 1.0 in a domain of aspect ratio 2 with periodic boundary conditions in the horizontal direction. The counter-gradient heat transport increases with Rayleigh numbers, and becomes comparable to the gradient heat transport. The gradient heat transport has a power law dependence on the Rayleigh number with scaling exponent 1/3, while a phase transition of the counter-gradient heat transport can be identified around the critical Rayleigh number 2×107 . The Reynolds numbers of the gradient and counter-gradient heat transports exhibit identical power law dependence on the Rayleigh numbers with scaling exponent 1/2. The gradient heat transport is partially compensated by the counter-gradient heat transport with increasing Rayleigh numbers, which attenuates the effects of the large-scale circulation on the global heat transfer especially for high Rayleigh numbers. We emphasize that the counter-gradient heat transport also exists in the three-dimensional turbulent Rayleigh-Bénard convection, although the plume and flow structures therein are quite different.

  12. Optimization of microfluidic fuel cells using transport principles.

    PubMed

    Lee, Jinkee; Lim, Keng Guan; Palmore, G Tayhas R; Tripathi, Anubhav

    2007-10-01

    Microfluidic fuel cells exploit the lack of convective mixing at low Reynolds number to eliminate the need for a physical membrane to separate the fuel from the oxidant. Slow transport of reactants in combination with high catalytic surface-to-volume ratios often inhibit the efficiency of a microfluidic fuel cell. The performance of microfluidic devices that rely on surface electrochemical reactions is controlled by the interplay between reaction kinetics and the rate of mass transfer to the reactive surfaces. This paper presents theoretical and experimental work to describe the role of flow rate, microchannel geometry, and location of electrodes within a microfluidic fuel cell on its performance. A transport model, based on the convective-diffusive flux of reactants, is developed that describes the optimal conditions for maximizing both the average current density and the percentage of fuel utilized. The results show that the performance can be improved when the design of the device includes electrodes smaller than a critical length. The results of this study advance current approaches to the design of microfluidic fuel cells and other electrochemically-coupled microfluidic devices.

  13. Texture mapping via optimal mass transport.

    PubMed

    Dominitz, Ayelet; Tannenbaum, Allen

    2010-01-01

    In this paper, we present a novel method for texture mapping of closed surfaces. Our method is based on the technique of optimal mass transport (also known as the "earth-mover's metric"). This is a classical problem that concerns determining the optimal way, in the sense of minimal transportation cost, of moving a pile of soil from one site to another. In our context, the resulting mapping is area preserving and minimizes angle distortion in the optimal mass sense. Indeed, we first begin with an angle-preserving mapping (which may greatly distort area) and then correct it using the mass transport procedure derived via a certain gradient flow. In order to obtain fast convergence to the optimal mapping, we incorporate a multiresolution scheme into our flow. We also use ideas from discrete exterior calculus in our computations.

  14. Texture Mapping via Optimal Mass Transport

    PubMed Central

    Dominitz, Ayelet; Tannenbaum, Allen

    2010-01-01

    In this paper, we present a novel method for texture mapping of closed surfaces. Our method is based on the technique of optimal mass transport (also known as the “earth-mover’s metric”). This is a classical problem that concerns determining the optimal way, in the sense of minimal transportation cost, of moving a pile of soil from one site to another. In our context, the resulting mapping is area preserving and minimizes angle distortion in the optimal mass sense. Indeed, we first begin with an angle-preserving mapping (which may greatly distort area) and then correct it using the mass transport procedure derived via a certain gradient flow. In order to obtain fast convergence to the optimal mapping, we incorporate a multiresolution scheme into our flow. We also use ideas from discrete exterior calculus in our computations. PMID:20224137

  15. Modeling multi-phase transport in deformable, hygroscopic porous media: Applications to convective drying of lumber

    SciTech Connect

    Asensio, C.M.; Seyed-Yagoobi, J.

    1999-07-01

    A fundamental model of multi-phase flow in deformable, hygroscopic porous media has been developed through application of macroscopic energy and mass conservation equations. Microscopic effects are included via volume-averaging techniques for the three phases present in the porous media: liquid, gas, and solid. The model includes convective and capillary transport of free water, convective and diffusive transport of water vapor and air, and diffusive transport of bound water. Porosity variations in deformable media have been included during development of the governing equations. The model is applied to convective drying of lumber via appropriate boundary conditions and transport parameters which are available in the literature. The governing coupled, non-linear equations are rewritten and solved in terms of three governing variables: moisture content, temperature, and gas phase pressure. The conservation equations presented in vector notation have been simplified to one spatial dimension for solution here. Control-volume formulations are used to discretize the governing partial differential equations and boundary conditions with a power-law scheme used to proportion the diffusive and convective flux contributions across the control volume interfaces. An uncoupled solution strategy is employed although each conservation equation is solved implicitly. Presented model results include predictions of moisture, temperature, and gas phase pressure during drying both as averages over time for convective drying at two different ambient conditions and as distributions within the board at any time for high temperature air drying. Flows of individual moisture species (liquid/free water, water vapor, and bound water) within the board are also presented.

  16. Modeling the convective transport of pollutants from eastern Colorado, USA into Rocky Mountain National Park

    NASA Astrophysics Data System (ADS)

    Pina, A.; Schumacher, R. S.; Denning, S.

    2015-12-01

    Rocky Mountain National Park (RMNP) is a Class I Airshed designated under the Clean Air Act. Atmospheric nitrogen (N) deposition in the Park has been a known problem since weekly measurements of wet deposition of inorganic N began in the 1980s by the National Atmospheric Deposition Program (NADP). The addition of N from urban and agriculture emissions along the Colorado Front Range to montane ecosystems degrades air quality/visibility, water quality, and soil pH levels. Based on NADP data during summers 1994-2014, wet N deposition at Beaver Meadows in RMNP exhibited a bimodal gamma distribution. In this study, we identified meteorological transport mechanisms for 3 high wet-N deposition events (all events were within the secondary peak of the gamma distribution) using the North American Regional Reanalysis (NARR) and the Weather Research and Forecasting (WRF) model. The NARR was used to identify synoptic-scale influences on the transport; the WRF model was used to analyze the convective transport of pollutants from a concentrated animal feeding operation near Greeley, Colorado, USA. The WRF simulation included a passive tracer from the feeding operation and a convection-permitting horizontal spacing of 4/3 km. The three cases suggest (a) synoptic-scale moisture and flow patterns are important for priming summer transport events and (b) convection plays a vital role in the transport of Front Range pollutants into RMNP.

  17. Transport of forest fire smoke above the tropopause by supercell convection

    NASA Astrophysics Data System (ADS)

    Fromm, Michael D.; Servranckx, René

    2003-05-01

    A recent letter [Fromm et al., 2000] postulated a link between boreal forest fire smoke and observed stratospheric aerosol enhancements in 1998. Therein a case was made that severe convection played a role in the cross-tropopause transport. A similar occurrence of stratospheric aerosol enhancements in the boreal summer of 2001 was the stimulus to investigate the causal mechanism more deeply. Herein, we show a detailed case illustrating the unambiguous creation of a widespread, dense smoke cloud in the upper troposphere and lower stratosphere (UT/LS) by a Canadian forest fire and explosive convection in May 2001. This event is the apparent common point for several downstream stratospheric mystery cloud observations. Implications of this finding and those pertaining to the boreal summer of 1998 are that convection and boreal biomass burning have an under-resolved and under-appreciated impact on the upper troposphere, lower stratosphere, radiative transfer, and atmospheric chemistry.

  18. Prandtl-Number Dependence of Heat Transport in Laminar Horizontal Convection.

    PubMed

    Shishkina, Olga; Wagner, Sebastian

    2016-01-15

    We report the Prandtl-number (Pr) and Rayleigh-number (Ra) dependencies of the Reynolds number (Re) and mean convective heat transport, measured by the Nusselt number (Nu), in horizontal convection (HC) systems, where the heat supply and removal are provided exclusively through a lower horizontal surface of a fluid layer. For laminar HC, we find that Re∼Ra^{2/5}Pr^{-4/5}, Nu∼Ra^{1/5}Pr^{1/10} with a transition to Re∼Ra^{1/2}Pr^{-1}, Nu∼Ra^{1/4}Pr^{0} for large Pr. The results are based on direct numerical simulations for Ra from 3×10^{8} to 5×10^{10} and Pr from 0.05 to 50 and are explained by applying the Grossmann-Lohse approach [J. Fluid Mech. 407, 27 (2000)] transferred from the case of Rayleigh-Bénard convection to the case of laminar HC.

  19. Real-time visualization of convective transportation of solid materials at nanoscale.

    PubMed

    Wang, Zumin; Gu, Lin; Jeurgens, Lars P H; Phillipp, Fritz; Mittemeijer, Eric J

    2012-12-12

    Convective transportation of materials in the solid state occurring in a prototype solid bilayer system of Al and Si with negligible mutual solubility has been directly imaged in real time at nanoscale using a valence energy-filtered transmission electron microscope. Such solid-state convection is driven by the stress gradient developing in the bilayer system due to the amorphous to crystalline phase transformation of the Si sublayer. The process is characterized by compression experienced in the Si phase crystallizing within the Al sublayer, as well as by the development of mushroom-shaped "plumes" of Al nanocrystals in the Si sublayer as a result of compressive stress relaxation and discrete, new nucleation of crystalline Al. The real-time, atomistic observation and the thus-obtained fundamental understanding of solid-state convection enable highly sophisticated applications of such a complex process in advanced fabrication and processing of nanomaterials and solid-state devices.

  20. Deep Ice Formation in Convecting Ice-Ocean Systems: Implications for Trace Element Transport from Europa's Ocean to its Surface

    NASA Astrophysics Data System (ADS)

    Allu Peddinti, D.; McNamara, A. K.

    2013-12-01

    Outer planetary missions and telescopic discoveries, together with theoretical predictions, have identified a plethora of potential astrobiological candidates that possess diverse signatures such as liquid water, chemical circulation, mineral assemblages and optimal temperatures that may have or still favor biological life. Europa with its deformed surface, an ice shell with a putative subsurface liquid water ocean and an induced magnetic signal still presents one of the accessible targets of astrobiological exploration. Of critical interest is whether chemistry of the subsurface liquid water ocean can be transported to the surface to be detected by future missions. We hypothesize that for a convecting ice shell, the ice-ocean boundary involves melting in downwelling regions and freezing in upwelling regions. New ice formed by freezing at the phase change boundary could reflect the capture of trace elements from the fluid layer below and thus the study of its propagation can provide interesting speculations on transport of trace species from the ocean to the surface. We have initiated a study of the two phase convective system in order to understand the effects of the phase boundary between the solid and liquid components. First, we have established a solid ice-proxy fluid system that is a convenient approximation of the real system. This is achieved by employing a proxy fluid whose viscosity is higher than that of liquid water yet remains orders of magnitude smaller than that of ice viscosity. We have demonstrated that this approximation sufficiently decouples the convective dynamics of the solid and fluid layers with little variation on further decrease of the fluid viscosity. The numerical models employ tracers to track the new ice and the fractional density of the new ice is mapped throughout the shell. We then proceed to analyze the formation of new ice at the transition interface and its transport by solid state convection in the ice shell. The tracer density

  1. Architecture of optimal transport networks

    NASA Astrophysics Data System (ADS)

    Durand, Marc

    2006-01-01

    We analyze the structure of networks minimizing the global resistance to flow (or dissipative energy) with respect to two different constraints: fixed total channel volume and fixed total channel surface area. First, we show that channels must be straight and have uniform cross-sectional areas in such optimal networks. We then establish a relation between the cross-sectional areas of adjoining channels at each junction. Indeed, this relation is a generalization of Murray’s law, originally established in the context of local optimization. We establish a relation too between angles and cross-sectional areas of adjoining channels at each junction, which can be represented as a vectorial force balance equation, where the force weight depends on the channel cross-sectional area. A scaling law between the minimal resistance value and the total volume or surface area value is also derived from the analysis. Furthermore, we show that no more than three or four channels meet at each junction of optimal bidimensional networks, depending on the flow profile (e.g., Poiseuille-like or pluglike) and the considered constraint (fixed volume or surface area). In particular, we show that sources are directly connected to wells, without intermediate junctions, for minimal resistance networks preserving the total channel volume in case of plug flow regime. Finally, all these results are compared with the structure of natural networks.

  2. Numerical research and optimization of convective heat transfer for multi-segment amplifiers

    NASA Astrophysics Data System (ADS)

    Ren, Zhiyuan; Zhu, Jianqiang; Huang, Hongbiao; Liu, Zhigang

    2013-04-01

    Optimized convective heat transfer is applied to accelerate the thermal recovery of a large aperture multi-segment amplifier. The paper proposes a novel project of changing the structural parameters of the inlet jet to the Nd:glass slab in the multi-segment amplifier at the same flow rate. The convective heat transfer coefficient depends on the diameter of the inlet jet, as well as on the number of inlet jets. The simulation calculations indicate that at the same flow rate, different numbers of inlet jet lead to different temperature gradient contours and flow field distributions on the Nd:glass slab surface in the multi-segment amplifier. In addition, the convective heat transfer coefficient increases with the decrease of inlet diameter. This work analyzes the path of the coolant air over the slab surface to lessen the eddy and to achieve better convective heat transfer, as well as to determine the optimized number of inlet jets (5) and the optimized diameter (5 mm).

  3. Calibration of Richards' and convection dispersion equations to field-scale water flow and solute transport under rainfall conditions

    NASA Astrophysics Data System (ADS)

    Jacques, Diederik; Šimůnek, Jirka; Timmerman, Anthony; Feyen, Jan

    2002-03-01

    In this paper, the applicability of Richards' equation for water flow and the convection-dispersion equation for solute transport is evaluated to model field-scale flow and transport under natural boundary conditions by using detailed experimental data and inverse optimization. The data consisted of depth-averaged time series of water content, pressure head and resident solute concentration data measured several times a day during 384 d. In a first approach, effective parameters are estimated using the time series for one depth and assuming a homogeneous soil profile. In a second approach, all time series were used simultaneously to estimate the parameters of a multi-layered soil profile. Water flow was described by the Richards' equation and solute transport either by the equilibrium convection-dispersion (CDE) or the physical non-equilibrium convection-dispersion (MIM) equation. To represent the dynamics of the water content and pressure head data, the multi-layered soil profile approach gave better results. Fitted soil hydraulic parameters were comparable with parameters obtained with other methods on the same soil. At larger depths, both the CDE- and MIM-models gave acceptable descriptions of the observed breakthrough data, although the MIM performed somewhat better in the tailing part. Both models underestimated significantly the fast breakthrough. To describe the breakthrough curves at the first depth, only the MIM with a mixing layer close to the soil surface gave acceptable results. Starting from an initial value problem with solutes homogeneously distributed over the mobile and immobile water phase was preferable compared to the incorporation of a small layer with only mobile water near the soil surface.

  4. A case study of pyro-convection using transport model and remote sensing data

    NASA Astrophysics Data System (ADS)

    Damoah, R.; Spichtinger, N.; Servranckx, R.; Fromm, M.; Eloranta, E. W.; Razenkov, I. A.; James, P.; Shulski, M.; Forster, C.; Stohl, A.

    2006-01-01

    Summer 2004 saw severe forest fires in Alaska and the Yukon Territory that were mostly triggered by lightning strikes. The area burned (>2.7×106 ha) in the year 2004 was the highest on record to date in Alaska. Pollutant emissions from the fires lead to violation of federal standards for air quality in Fairbanks.

    This paper studies deep convection events that occurred in the burning regions at the end of June 2004. The convection was likely enhanced by the strong forest fire activity (so-called pyro-convection) and penetrated into the lower stratosphere, up to about 3 km above the tropopause. Emissions from the fires did not only perturb the UT/LS locally, but also regionally. POAM data at the approximate location of Edmonton (53.5° N, 113.5° W) show that the UT/LS aerosol extinction was enhanced by a factor of 4 relative to unperturbed conditions. Simulations with the particle dispersion model FLEXPART with the deep convective transport scheme turned on showed transport of forest fire emissions into the stratosphere, in qualitatively good agreement with the enhancements seen in the POAM data. A corresponding simulation with the deep convection scheme turned off did not result in such deep vertical transport. Lidar measurements at Wisconsin on 30 June also show the presence of substantial aerosol loading in the UT/LS, up to about 13 km. In fact, the FLEXPART results suggest that this aerosol plume originated from the Yukon Territory on 25 June.

  5. Representation of tropical deep convection in atmospheric models - Part 2: Tracer transport

    NASA Astrophysics Data System (ADS)

    Hoyle, C. R.; Marécal, V.; Russo, M. R.; Allen, G.; Arteta, J.; Chemel, C.; Chipperfield, M. P.; D'Amato, F.; Dessens, O.; Feng, W.; Hamilton, J. F.; Harris, N. R. P.; Hosking, J. S.; Lewis, A. C.; Morgenstern, O.; Peter, T.; Pyle, J. A.; Reddmann, T.; Richards, N. A. D.; Telford, P. J.; Tian, W.; Viciani, S.; Volz-Thomas, A.; Wild, O.; Yang, X.; Zeng, G.

    2011-08-01

    The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemical transport, and chemistry-climate models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short-lived tracers (with a lifetime of 6 h) within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to be different between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for modelling the halogen burden of the lowermost stratosphere through transport of species such as bromoform, or short-lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are strongly influenced by the convective transport parameterisations, and different boundary layer mixing parameterisations also have a large impact on the modelled tracer profiles. Preferential locations for rapid transport from the surface into the upper troposphere are similar in all models, and are mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, models do not indicate that upward transport is highest over western Africa.

  6. Computer simulation of radionuclide transport through thermal convection of groundwater from borehole repositories

    SciTech Connect

    Malkovsky, V.I.; Pek, A.A.

    1993-09-01

    Results are presented of numerical modeling of radionuclide transport by thermal convection of groundwater from a single well repository of high level waste. Because the problem possesses cylindrical symmetry, the process is described by a system of 2-D transient equations for momentum, convective heat transfer and convective mass transfer (taking into account hydrodynamic dispersion and radionuclide decay). Results of computer simulations for a selected range of system parameters were generalized by approximating analytical relationship, which can be used for safety assessment of a radioactive waste repository. The problem of the reciprocal relationship between thermoconvective transport processes and well spacing in an underground repository with a regularly spaced set of the waste-loaded wells is examined using a two-well model as an example. In this case, the transport problem becomes three-dimensional. A solution to this problem was obtained using a special system of orthogonal coordinates, which simplifies the computational algorithm and enhances accuracy. It is shown that thermoconvective transport of radionuclides in the vicinity of each well can be considered to be independent at well separations of the order of 100 m when reasonable values of other repository parameters are assumed.

  7. Optimal Protocols and Optimal Transport in Stochastic Thermodynamics

    NASA Astrophysics Data System (ADS)

    Aurell, Erik; Mejía-Monasterio, Carlos; Muratore-Ginanneschi, Paolo

    2011-06-01

    Thermodynamics of small systems has become an important field of statistical physics. Such systems are driven out of equilibrium by a control, and the question is naturally posed how such a control can be optimized. We show that optimization problems in small system thermodynamics are solved by (deterministic) optimal transport, for which very efficient numerical methods have been developed, and of which there are applications in cosmology, fluid mechanics, logistics, and many other fields. We show, in particular, that minimizing expected heat released or work done during a nonequilibrium transition in finite time is solved by the Burgers equation and mass transport by the Burgers velocity field. Our contribution hence considerably extends the range of solvable optimization problems in small system thermodynamics.

  8. Colloidal transport phenomena of milk components during convective droplet drying.

    PubMed

    Fu, Nan; Woo, Meng Wai; Chen, Xiao Dong

    2011-10-15

    Material segregation has been reported for industrial spray-dried milk powders, which indicates potential material migration during drying process. The relevant colloidal transport phenomenon and the underlying mechanism are still under debate. This study extended the glass-filament single droplet drying technique to observe not only the drying behaviour but also the dissolution behaviour of the correspondingly dried single particle. At progressively longer drying stage, a solvent droplet (water or ethanol) was attached to the semi-dried milk particle and the interaction between the solvent and the particle was video-recorded. Based on the different dissolution and wetting behaviours observed, material migration during milk drying was studied. Fresh skim milk and fresh whole milk were investigated using water and ethanol as solvents. Fat started to accumulate on the surface as soon as drying was started. At the initial stage of drying, the fat layer remained thin and the solubility of the semi-dried milk particle was much affected by lactose and protein present underneath the fat layer. Fat kept accumulating at the surface as drying progressed and the accumulation was completed by the middle stage of drying. The results from drying of model milk materials (pure sodium caseinate solution and lactose/sodium caseinate mixed solution) supported the colloidal transport phenomena observed for the milk drying. When mixed with lactose, sodium caseinate did not form an apparent solvent-resistant protein shell during drying. The extended technique of glass-filament single droplet approach provides a powerful tool in examining the solubility of individual particle after drying.

  9. Advanced modelling of the transport phenomena across horizontal clothing microclimates with natural convection

    NASA Astrophysics Data System (ADS)

    Mayor, T. S.; Couto, S.; Psikuta, A.; Rossi, R. M.

    2015-12-01

    The ability of clothing to provide protection against external environments is critical for wearer's safety and thermal comfort. It is a function of several factors, such as external environmental conditions, clothing properties and activity level. These factors determine the characteristics of the different microclimates existing inside the clothing which, ultimately, have a key role in the transport processes occurring across clothing. As an effort to understand the effect of transport phenomena in clothing microclimates on the overall heat transport across clothing structures, a numerical approach was used to study the buoyancy-driven heat transfer across horizontal air layers trapped inside air impermeable clothing. The study included both the internal flow occurring inside the microclimate and the external flow occurring outside the clothing layer, in order to analyze the interdependency of these flows in the way heat is transported to/from the body. Two-dimensional simulations were conducted considering different values of microclimate thickness (8, 25 and 52 mm), external air temperature (10, 20 and 30 °C), external air velocity (0.5, 1 and 3 m s-1) and emissivity of the clothing inner surface (0.05 and 0.95), which implied Rayleigh numbers in the microclimate spanning 4 orders of magnitude (9 × 102-3 × 105). The convective heat transfer coefficients obtained along the clothing were found to strongly depend on the transport phenomena in the microclimate, in particular when natural convection is the most important transport mechanism. In such scenario, convective coefficients were found to vary in wavy-like manner, depending on the position of the flow vortices in the microclimate. These observations clearly differ from data in the literature for the case of air flow over flat-heated surfaces with constant temperature (which shows monotonic variations of the convective heat transfer coefficients, along the length of the surface). The flow patterns and

  10. Advanced modelling of the transport phenomena across horizontal clothing microclimates with natural convection.

    PubMed

    Mayor, T S; Couto, S; Psikuta, A; Rossi, R M

    2015-12-01

    The ability of clothing to provide protection against external environments is critical for wearer's safety and thermal comfort. It is a function of several factors, such as external environmental conditions, clothing properties and activity level. These factors determine the characteristics of the different microclimates existing inside the clothing which, ultimately, have a key role in the transport processes occurring across clothing. As an effort to understand the effect of transport phenomena in clothing microclimates on the overall heat transport across clothing structures, a numerical approach was used to study the buoyancy-driven heat transfer across horizontal air layers trapped inside air impermeable clothing. The study included both the internal flow occurring inside the microclimate and the external flow occurring outside the clothing layer, in order to analyze the interdependency of these flows in the way heat is transported to/from the body. Two-dimensional simulations were conducted considering different values of microclimate thickness (8, 25 and 52 mm), external air temperature (10, 20 and 30 °C), external air velocity (0.5, 1 and 3 m s(-1)) and emissivity of the clothing inner surface (0.05 and 0.95), which implied Rayleigh numbers in the microclimate spanning 4 orders of magnitude (9 × 10(2)-3 × 10(5)). The convective heat transfer coefficients obtained along the clothing were found to strongly depend on the transport phenomena in the microclimate, in particular when natural convection is the most important transport mechanism. In such scenario, convective coefficients were found to vary in wavy-like manner, depending on the position of the flow vortices in the microclimate. These observations clearly differ from data in the literature for the case of air flow over flat-heated surfaces with constant temperature (which shows monotonic variations of the convective heat transfer coefficients, along the length of the surface). The flow

  11. Supersonic transport grid generation, validation, and optimization

    NASA Technical Reports Server (NTRS)

    Aaronson, Philip G.

    1995-01-01

    The ever present demand for reduced flight times has renewed interest in High Speed Civil Transports (HSCT). The need for an HSCT becomes especially apparent when the long distance, over-sea, high growth Pacific rim routes are considered. Crucial to any successful HSCT design are minimal environmental impact and economic viability. Vital is the transport's aerodynamic efficiency, ultimately effecting both the environmental impact and the operating cost. Optimization, including numerical optimization, coupled with the use of computational fluid dynamics (CFD) technology, has and will offer a significant improvement beyond traditional methods.

  12. A regional estimate of convective transport of CO from biomass burning

    NASA Technical Reports Server (NTRS)

    Pickering, Kenneth E.; Scala, John R.; Thompson, Anne M.; Tao, Wei-Kuo; Simpson, Joanne

    1992-01-01

    A regional-scale estimate of the fraction of biomass burning emissions that are transported to the free troposphere by deep convection is presented. The focus is on CO and the study region is a part of Brazil that underwent intensive deforestation in the 1980s. The method of calculation is stepwise, scaling up from a prototype convective event, the dynamics of which are well-characterized, to the vertical mass flux of carbon monoxide over the region. Given uncertainties in CO emissions from biomass burning and the representativeness of the prototype event, it is estimated that 10-40 percent of CO emissions from the burning region may be rapidly transported to the free troposphere over the burning region. These relatively fresh emissions will produce O3 efficiently in the free troposphere where O3 has a longer lifetime than in the boundary layer.

  13. Heat transport in Rayleigh-Bénard convection and angular momentum transport in Taylor-Couette flow: a comparative study.

    PubMed

    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'.

  14. Heat transport in Rayleigh-Bénard convection and angular momentum transport in Taylor-Couette flow: a comparative study

    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.

  15. Understanding and Prediction of Convective Transport, Scavenging, and Lightning-Produced Nitrogen Oxides Based on DC3 Thunderstorm Cases

    NASA Astrophysics Data System (ADS)

    Barth, M. C.; Bela, M. M.; Pickering, K. E.; Huntrieser, H.; Brune, W. H.; Cantrell, C. A.; Rutledge, S. A.

    2014-12-01

    The Deep Convective Clouds and Chemistry (DC3) field campaign, which took place in the central U.S. in May and June 2012, provides in situ aircraft measurements of trace gases and aerosols in the inflow and upper troposphere convective outflow regions of different types of deep convection. In this study, we survey the DC3 storms showing evidence of trace gas convective transport, scavenging, and production of nitrogen oxides from lightning by examining vertical profiles of carbon monoxide (a marker of convective transport), volatile organic compounds with a range of solubilities, nitrogen oxides, and soluble trace gases such as nitric acid, hydrogen peroxide, and sulfur dioxide. These results are placed in context of other field campaigns (e.g. STERAO) to determine how typical the DC3 observations are to other time periods and locations. The measurements also allow us to evaluate the capabilities of chemistry transport models in representing deep convection and chemistry. While convection-resolving simulations give more explicit information on the storm processes affecting the composition of the troposphere, air quality and chemistry climate models rely on convective parameterizations to represent these convective processes. Thus, we analyze results from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), which are conducted at 15 km grid spacing requiring a convective parameterization. The capability of WRF-Chem to represent the DC3 storms is evaluated by examining the timing, location, and convective strength using radar and lightning data. By producing profiles similar to those constructed from the measurements, the comparison between model and observations should identify gaps in our understanding of convective processing of different trace gases.

  16. Convective Transport of Very-short-lived Bromocarbons to the Stratosphere

    NASA Technical Reports Server (NTRS)

    Liang, Qing; Atlas, Elliot Leonard; Blake, Donald Ray; Dorf, Marcel; Pfeilsticker, Klaus August; Schauffler, Sue Myhre

    2014-01-01

    We use the NASA GEOS Chemistry Climate Model (GEOSCCM) to quantify the contribution of two most important brominated very short-lived substances (VSLS), bromoform (CHBr3) and dibromomethane (CH2Br2), to stratospheric bromine and its sensitivity to convection strength. Model simulations suggest that the most active transport of VSLS from the marine boundary layer through the tropopause occurs over the tropical Indian Ocean, the Western Pacific warm pool, and off the Pacific coast of Mexico. Together, convective lofting of CHBr3 and CH2Br2 and their degradation products supplies 8 ppt total bromine to the base of the Tropical Tropopause Layer (TTL, 150 hPa), similar to the amount of VSLS organic bromine available in the marine boundary layer (7.8-8.4 ppt) in the above active convective lofting regions. Of the total 8 ppt VSLS-originated bromine that enters the base of TTL at 150 hPa, half is in the form of source gas injection (SGI) and half as product gas injection (PGI). Only a small portion (< 10%) the VSLS-originated bromine is removed via wet scavenging in the TTL before reaching the lower stratosphere. On global and annual average, CHBr3 and CH2Br2, together, contribute 7.7 pptv to the present-day inorganic bromine in the stratosphere. However, varying model deep convection strength between maximum and minimum convection conditions can introduce a 2.6 pptv uncertainty in the contribution of VSLS to inorganic bromine in the stratosphere (BryVSLS). Contrary to the conventional wisdom, minimum convection condition leads to a larger BryVSLS as the reduced scavenging in soluble product gases, thus a significant increase in PGI (2-3 ppt), greatly exceeds the relative minor decrease in SGI (a few 10ths ppt.

  17. Convective transport of very-short-lived bromocarbons to the stratosphere

    NASA Astrophysics Data System (ADS)

    Liang, Q.; Atlas, E.; Blake, D.; Dorf, M.; Pfeilsticker, K.; Schauffler, S.

    2014-01-01

    We use the NASA GEOS Chemistry Climate Model (GEOSCCM) to quantify the contribution of two most important brominated very short-lived substances (VSLS), bromoform (CHBr3) and dibromomethane (CH2Br2), to stratospheric bromine and its sensitivity to convection strength. Model simulations suggest that the most active transport of VSLS from the marine boundary layer through the tropopause occurs over the tropical Indian Ocean, the Western Pacific warm pool, and off the Pacific coast of Mexico. Together, convective lofting of CHBr3 and CH2Br2 and their degradation products supplies ∼8 ppt total bromine to the base of the Tropical Tropopause Layer (TTL, ∼150 hPa), similar to the amount of VSLS organic bromine available in the marine boundary layer (∼7.8-8.4 ppt) in the above active convective lofting regions. Of the total ∼8 ppt VSLS-originated bromine that enters the base of TTL at ∼150 hPa, half is in the form of source gas injection (SGI) and half as product gas injection (PGI). Only a small portion (< 10%) the VSLS-originated bromine is removed via wet scavenging in the TTL before reaching the lower stratosphere. On global and annual average, CHBr3 and CH2Br2, together, contribute ∼7.7 pptv to the present-day inorganic bromine in the stratosphere. However, varying model deep convection strength between maximum and minimum convection conditions can introduce a ∼2.6 pptv uncertainty in the contribution of VSLS to inorganic bromine in the stratosphere (BryVSLS). Contrary to the conventional wisdom, minimum convection condition leads to a larger BryVSLS as the reduced scavenging in soluble product gases, thus a significant increase in PGI (2-3 ppt), greatly exceeds the relative minor decrease in SGI (a few 10ths ppt).

  18. Temperature, humidity and air flow in the emplacement drifts using convection and dispersion transport models

    SciTech Connect

    Danko, G.; Birkholzer, J.T.; Bahrami, D.; Halecky, N.

    2009-10-01

    A coupled thermal-hydrologic-airflow model is developed, solving for the transport processes within a waste emplacement drift and the surrounding rockmass together at the proposed nuclear waste repository at Yucca Mountain. Natural, convective air flow as well as heat and mass transport in a representative emplacement drift during post-closure are explicitly simulated, using the MULTIFLUX model. The conjugate, thermal-hydrologic transport processes in the rockmass are solved with the TOUGH2 porous-media simulator in a coupled way to the in-drift processes. The new simulation results show that large-eddy turbulent flow, as opposed to small-eddy flow, dominate the drift air space for at least 5000 years following waste emplacement. The size of the largest, longitudinal eddy is equal to half of the drift length, providing a strong axial heat and moisture transport mechanism from the hot to the cold drift sections. The in-drift results are compared to those from simplified models using a surrogate, dispersive model with an equivalent dispersion coefficient for heat and moisture transport. Results from the explicit, convective velocity simulation model provide higher axial heat and moisture fluxes than those estimated from the previously published, simpler, equivalent-dispersion models, in addition to showing differences in temperature, humidity and condensation rate distributions along the drift length. A new dispersive model is also formulated, giving a time- and location-variable function that runs generally about ten times higher in value than the highest dispersion coefficient currently used in the Yucca Mountain Project as an estimate for the equivalent dispersion coefficient in the emplacement drift. The new dispersion coefficient variation, back-calculated from the convective model, can adequately describe the heat and mass transport processes in the emplacement drift example.

  19. Convective transport in ATM simulations and its relation to the atmospheric stability conditions

    NASA Astrophysics Data System (ADS)

    Kusmierczyk-Michulec, Jolanta

    2017-04-01

    The International Monitoring System (IMS) developed by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is a global system of monitoring stations, using four complementary technologies: seismic, hydroacoustic, infrasound and radionuclide. Data from all stations, belonging to IMS, are collected and transmitted to the International Data Centre (IDC) in Vienna, Austria. The radionuclide network comprises 80 stations, of which more than 60 are certified. The aim of radionuclide stations is a global monitoring of radioactive aerosols and radioactive noble gases, in particular xenon isotopes, supported by the atmospheric transport modeling (ATM). One of the important noble gases, monitored on a daily basis, is radioxenon. It can be produced either during a nuclear explosion with a high fission yield, and thus be considered as an important tracer to prove the nuclear character of an explosion, or be emitted from nuclear power plants (NPPs) or from isotope production facilities (IPFs). To investigate the transport of xenon emissions, the Provisional Technical Secretariat (PTS) operates an Atmospheric Transport Modelling (ATM) system based on the Lagrangian Particle Dispersion Model FLEXPART. To address the question whether including the convective transport in ATM simulations will change the results significantly, the differences between the outputs with the convective transport turned off and turned on, were computed and further investigated taking into account the atmospheric stability conditions. For that purpose series of 14 days forward simulations, with convective transport and without it, released daily in the period January 2011 to February 2012, were analysed. The release point was at the ANSTO facility in Australia. The unique opportunity of having access to both daily emission values for ANSTO as well as measured Xe-133 activity concentration (AC) values at the IMS stations, gave a chance to validate the simulations.

  20. Optimal concentration for sugar transport in plants

    PubMed Central

    Jensen, Kaare H.; Savage, Jessica A.; Holbrook, N. Michele

    2013-01-01

    Vascular plants transport energy in the form of sugars from the leaves where they are produced to sites of active growth. The mass flow of sugars through the phloem vascular system is determined by the sap flow rate and the sugar concentration. If the concentration is low, little energy is transferred from source to sink. If it is too high, sap viscosity impedes flow. An interesting question is therefore at which concentration is the sugar flow optimal. Optimization of sugar flow and transport efficiency predicts optimal concentrations of 23.5 per cent (if the pressure differential driving the flow is independent of concentration) and 34.5 per cent (if the pressure is proportional to concentration). Data from more than 50 experiments (41 species) collected from the literature show an average concentration in the range from 18.2 per cent (all species) to 21.1 per cent (active loaders), suggesting that the phloem vasculature is optimized for efficient transport at constant pressure and that active phloem loading may have developed to increase transport efficiency. PMID:23516065

  1. Optimal concentration for sugar transport in plants.

    PubMed

    Jensen, Kaare H; Savage, Jessica A; Holbrook, N Michele

    2013-06-06

    Vascular plants transport energy in the form of sugars from the leaves where they are produced to sites of active growth. The mass flow of sugars through the phloem vascular system is determined by the sap flow rate and the sugar concentration. If the concentration is low, little energy is transferred from source to sink. If it is too high, sap viscosity impedes flow. An interesting question is therefore at which concentration is the sugar flow optimal. Optimization of sugar flow and transport efficiency predicts optimal concentrations of 23.5 per cent (if the pressure differential driving the flow is independent of concentration) and 34.5 per cent (if the pressure is proportional to concentration). Data from more than 50 experiments (41 species) collected from the literature show an average concentration in the range from 18.2 per cent (all species) to 21.1 per cent (active loaders), suggesting that the phloem vasculature is optimized for efficient transport at constant pressure and that active phloem loading may have developed to increase transport efficiency.

  2. Convective Heat Transfer in the Reusable Solid Rocket Motor of the Space Transportation System

    NASA Technical Reports Server (NTRS)

    Ahmad, Rashid A.; Cash, Stephen F. (Technical Monitor)

    2002-01-01

    This simulation involved a two-dimensional axisymmetric model of a full motor initial grain of the Reusable Solid Rocket Motor (RSRM) of the Space Transportation System (STS). It was conducted with CFD (computational fluid dynamics) commercial code FLUENT. This analysis was performed to: a) maintain continuity with most related previous analyses, b) serve as a non-vectored baseline for any three-dimensional vectored nozzles, c) provide a relatively simple application and checkout for various CFD solution schemes, grid sensitivity studies, turbulence modeling and heat transfer, and d) calculate nozzle convective heat transfer coefficients. The accuracy of the present results and the selection of the numerical schemes and turbulence models were based on matching the rocket ballistic predictions of mass flow rate, head end pressure, vacuum thrust and specific impulse, and measured chamber pressure drop. Matching these ballistic predictions was found to be good. This study was limited to convective heat transfer and the results compared favorably with existing theory. On the other hand, qualitative comparison with backed-out data of the ratio of the convective heat transfer coefficient to the specific heat at constant pressure was made in a relative manner. This backed-out data was devised to match nozzle erosion that was a result of heat transfer (convective, radiative and conductive), chemical (transpirating), and mechanical (shear and particle impingement forces) effects combined.

  3. Effect of secondary convective cells on turbulence intensity profiles, flow generation, and transport

    SciTech Connect

    Yi, S.; Kwon, J. M.; Rhee, T.; Diamond, P. H.

    2012-11-15

    This paper reports the results of gyrokinetic simulation studies of ion temperature gradient driven turbulence which investigate the role of non-resonant modes in turbulence spreading, turbulence regulation, and self-generated plasma rotation. Non-resonant modes, which are those without a rational surface within the simulation domain, are identified as nonlinearly driven, radially extended convective cells. Even though the amplitudes of such convective cells are much smaller than that of the resonant, localized turbulence eddies, we find from bicoherence analysis that the mode-mode interactions in the presence of such convective cells increase the efficiency of turbulence spreading associated with nonlocality phenomena. Artificial suppression of the convective cells shows that turbulence spreading is reduced, and that the turbulence intensity profile is more localized. The more localized turbulence intensity profile produces stronger Reynolds stress and E Multiplication-Sign B shear flows, which in turn results in more effective turbulence self-regulation. This suggests that models without non-resonant modes may significantly underestimate turbulent fluctuation levels and transport.

  4. The effect of convection upon charged particle transport in random magnetic fields

    NASA Technical Reports Server (NTRS)

    Earl, J. A.

    1984-01-01

    In a coordinate system moving with the plasma and random magnetic fields of a wind that blows with constant velocity in the direction of the guiding field, transport of energetic particles is described by a Boltzmann equation which is similar to the one that describes unconvected transport. Although this formulation is mathematically identical to that developed by Luhmann, which refers to the system where the guiding field is static, there are both practical and fundamental reasons to adopt the new approach. It leads to first-order approximate transport equations which are similar to those that apply in the absence of convection. However, these equations are more general than Parker's description of diffusion and convection, for they describe the coherent modes of transport that appear when the mean free path is large compared to the scale length for spatial variations of the guiding field, and they are valid for arbitrary wind velocity. The latter characteristic opens up new possibilities for analyzing particle transport in relativistic flows seen in some astronomical objects.

  5. Beryllium/Tungsten Mixed Material Analysis of FIRE Plasma Facing Components Including Convective Transport

    NASA Astrophysics Data System (ADS)

    Alman, D. A.; Ruzic, D. N.

    2003-10-01

    Extensive computer modeling for the Fusion Ignition Research Experiment (FIRE) design study focused on Be/W mixed-material erosion issues, combining several computer codes. Since the FIRE design calls for a beryllium first wall and tungsten divertor, Be can be sputtered and transported to the divertor, forming a Be/W mixture. The goal is to determine the amount of Be deposited on divertor surfaces and to model the mixture's erosion/redeposition properties. Sputtering is calculated from deuterium neutral fluxes (obtained from DEGAS2) and D^+ flux from the plasma. The ion flux includes both the diffusive flux from the UEDGE fluid code and approximations of convective (non-diffusive) transport. The sputtering of Be is determined by VFTRIM-3D. WBC+, part of Argonne's REDEP impurity transport package, calculates the transport of Be to the divertor. Results show that convective transport dominates, increasing Be sputtering to 8x10^21 s-1, with 4x10^21 s-1 reaching the divertor plates. The next step is analysis of the erosion properties of the Be/W mixed material with the ITMC code at ANL.

  6. Optimal transport on supply-demand networks.

    PubMed

    Chen, Yu-Han; Wang, Bing-Hong; Zhao, Li-Chao; Zhou, Changsong; Zhou, Tao

    2010-06-01

    In the literature, transport networks are usually treated as homogeneous networks, that is, every node has the same function, simultaneously providing and requiring resources. However, some real networks, such as power grids and supply chain networks, show a far different scenario in which nodes are classified into two categories: supply nodes provide some kinds of services, while demand nodes require them. In this paper, we propose a general transport model for these supply-demand networks, associated with a criterion to quantify their transport capacities. In a supply-demand network with heterogeneous degree distribution, its transport capacity strongly depends on the locations of supply nodes. We therefore design a simulated annealing algorithm to find the near optimal configuration of supply nodes, which remarkably enhances the transport capacity compared with a random configuration and outperforms the degree target algorithm, the betweenness target algorithm, and the greedy method. This work provides a start point for systematically analyzing and optimizing transport dynamics on supply-demand networks.

  7. Connection between Mature Stages of Deep Convection and the Vertical Transport of Aerosols in the Upper Troposphere

    NASA Astrophysics Data System (ADS)

    Chakraborty, S.; Fu, R.; Massie, S. T.; Pan, L.

    2011-12-01

    Convective transport of aerosol has implications to aerosol-cloud interactions and is an important problem for climate studies. We use along-track Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (Calipso) vertical feature mask data, CloudSat data, and International Satellite Cloud Climatology Project (ISCCP) deep convection tracking data to study the impact of deep convection on the transport of aerosols to the upper troposphere (UT) over the South Asian region (0-40N, 70-100E). To minimize misclassification among aerosols and the clouds at UT, we have only used data having large magnitude of cloud aerosol discrimination (CAD) scores for the period of June 2006 to June 2008 when CloudSat and Calipso overlap with the ISCCP deep convection tracking data. Preliminary results suggest that active clouds most likely transport aerosols to high altitudes, whereas decaying clouds are least likely to transport aerosols to the UT. Mature clouds act in-between the active and decaying clouds. Active clouds that transport aerosols are different than decaying clouds in terms of higher cloud water path, cloud water content at 10 km altitude, number of convective clusters, and convective fraction. The NASA Goddard Global Modeling and Assimilation Office wind data, projected onto the CloudSat tracks, suggests a strong updraft associated with active clouds in favor of aerosol transportation, and a low level or mid-level subsidence associated with decaying clouds.

  8. CO signatures in subtropical convective clouds and anvils during CRYSTAL-FACE: An analysis of convective transport and entrainment using observations and a cloud-resolving model

    NASA Astrophysics Data System (ADS)

    Lopez, Jimena P.; Fridlind, Ann M.; Jost, Hans-Jürg; Loewenstein, Max; Ackerman, Andrew S.; Campos, Teresa L.; Weinstock, Elliot M.; Sayres, David S.; Smith, Jessica B.; Pittman, Jasna V.; Hallar, A. Gannet; Avallone, Linnea M.; Davis, Sean M.; Herman, Robert L.

    2006-05-01

    Convective systems are an important mechanism in the transport of boundary layer air into the upper troposphere. The Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign, in July 2002, was developed as a comprehensive atmospheric mission to improve knowledge of subtropical cirrus systems and their roles in regional and global climate. In situ measurements of carbon monoxide (CO), water vapor (H2Ov), and total water (H2Ot) aboard NASA's WB-57F aircraft and CO aboard the U.S. Navy's Twin Otter aircraft were obtained to study the role of convective transport. Three flights sampled convective outflow on 11, 16 and 29 July found varying degrees of CO enhancement relative to the free troposphere. A cloud-resolving model used the in situ observations and meteorological fields to study these three systems. Several methods of filtering the observations were devised here using ice water content, relative humidity with respect to ice, and particle number concentration as a means to statistically sample the model results to represent the flight tracks. A weighted histogram based on ice water content observations was then used to sample the simulations for the three flights. In addition, because the observations occurred in the convective outflow cirrus and not in the storm cores, the model was used to estimate the maximum CO within the convective systems. In general, anvil-level air parcels contained an estimated 20-40% boundary layer air in the analyzed storms.

  9. CO Signatures in Subtropical Convective Clouds and Anvils during CRYSTAL-FACE: An Analysis of Convective Transport and Entrainment using Observations and a Cloud-Resolving Model

    NASA Technical Reports Server (NTRS)

    Lopez, Jimena P.; Fridlind, Ann M.; Jost, Hans-Juerg; Loewenstein, Max; Ackerman, Andrew S.; Campos, Teresa L.; Weinstock, Elliot M.; Sayres, David S.; Smith, Jessica B.; Pittman, Jasna V.

    2006-01-01

    Convective systems are an important mechanism in the transport of boundary layer air into the upper troposphere. The Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign, in July 2002, was developed as a comprehensive atmospheric mission to improve knowledge of subtropical cirrus systems and their roles in regional and global climate. In situ measurements of carbon monoxide (CO), water vapor (H2Ov), and total water (H2Ot) aboard NASA's WB-57F aircraft and CO aboard the U.S. Navy's Twin Otter aircraft were obtained to study the role of convective transport. Three flights sampled convective outflow on 11, 16 and 29 July found varying degrees of CO enhancement relative to the free troposphere. A cloud-resolving model used the in situ observations and meteorological fields to study these three systems. Several methods of filtering the observations were devised here using ice water content, relative humidity with respect to ice, and particle number concentration as a means to statistically sample the model results to represent the flight tracks. A weighted histogram based on ice water content observations was then used to sample the simulations for the three flights. In addition, because the observations occurred in the convective outflow cirrus and not in the storm cores, the model was used to estimate the maximum CO within the convective systems. In general, anvil-level air parcels contained an estimated 20-40% boundary layer air in the analyzed storms.

  10. CO Signatures in Subtropical Convective Clouds and Anvils During CRYSTAL-FACE: An Analysis of Convective Transport and Entertainment Using Observations and a Cloud-Resolving Model

    NASA Technical Reports Server (NTRS)

    Lopez, Jimena P.; Fridlind, Ann M.; Jost, Hans-Jurg; Loewenstein, Max; Ackerman, Andrew S.; Campos, Teresa L.; Weinstock, Elliot M.; Sayres, David S.; Smith, Jessica B.; Pittman, Jasna V.; hide

    2006-01-01

    Convective systems are an important mechanism in the transport of boundary layer air into the upper troposphere. The Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign, in July 2002, was developed as a comprehensive atmospheric mission to improve knowledge of subtropical cirrus systems and their roles in regional and global climate. In situ measurements of carbon monoxide (CO), water vapor (H20v), and total water (H20t) aboard NASA's . WB-57F aircraft and CO aboard the U.S. Navy's Twin Otter aircraft were obtained to study the role of convective transport. Three flights sampled convective outflow on 11, 16 and 29 July found varying degrees of CO enhancement relative to the fiee troposphere. A cloud-resolving model used the in situ observations and meteorological fields to study these three systems. Several methods of filtering the observations were devised here using ice water content, relative humidity with respect to ice, and particle number concentration as a means to statistically sample the model results to represent the flight tracks. A weighted histogram based on ice water content observations was then used to sample the simulations for the three flights. In addition, because the observations occurred in the convective outflow cirrus and not in the storm cores, the model was used to estimate the maximum CO within the convective systems. In general, anvil-level air parcels contained an estimated 20-40% boundary layer air in the analyzed storms.

  11. Deep convective cross-tropopause transport in the tropics and evidence by A-Train satellites

    NASA Astrophysics Data System (ADS)

    Wang, P.; Su, S.,; Charvat, Z.; Setvak, M.; Cheng, K.

    2012-04-01

    Cross-tropopause transport by deep convective clouds can be an (and perhaps the most) important source of water vapor in the stratosphere. Our previous studies have verified that deep convective cross-tropopause transport does occur rather regularly in midlatitudes. This transport is demonstrated by the presence of cloud top features of above anvil cirrus plumes and jumping cirrus phenomenon that have been observed by aircraft, satellite and ground-based observations. The present paper will demonstrate that the same mechanism occurs in the tropics. Because the tropics typically have weaker wind shear at the tropopause level, previous observation did not show clear evidence of the presence of such cross-tropopause features. But the recent NSAS A-Train satellites, especially CloudSat, CALIPSO and MODIS, provide both horizontal cloud top and vertical cross-sectional views of the cloud structure and making the identification of such features much less unambiguous. In this study, we will first use cloud resolving model simulations of tropical deep connective storms to show that the gravity wave breaking mechanism and instability will cause moisture (condensed water and vapor) to be transported through the tropopause even in this weaker wind shear environment. Model animations will be shown in the conference. We will then show that the modeled storm top features match well with many recent observations by A-Train satellites. The model results and satellite observations agree not only in morphological similarity but also in the spatial extent and structure in both horizontal and vertical structure. Thus, both the model results and satellite observations demonstrate unambiguously that cross-tropopause transport of water vapor by deep convective clouds in the tropics does occur, and it should be assessed carefully for its global climatic impact.

  12. Convective Influence and Transport Pathways Controlling the Tropical Distribution of Carbon Monoxide at 100 Hpa

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Bergman, John; Pfister, Leonard; Ueyama, Rei; Kinnison, Doug

    2014-01-01

    Trajectory calculations with convective influence diagnosed from geostationary-satellite cloud measurements are used to evaluate the relative importance of different Tropical Tropopause Layer (TTL) transport pathways for establishing the distribution of carbon monoxide (CO) at 100 hPa as observed by the Microwave Limb Sounder (MLS) on board the Aura satellite. Carbon monoxide is a useful tracer for investigating TTL transport and convective influence because the CO lifetime is comparable to the time require for slow ascent through the TTL (a couple of months). Offline calculations of TTL radiative heating are used to determine the vertical motion field. The simple trajectory model does a reasonable job of reproducing the MLS CO distributions during Boreal wintertime and summertime. The broad maximum in CO concentration over the Pacific is primarily a result of the strong radiative heating (indicating upward vertical motion) associated with the abundant TTL cirrus in this region. Sensitivity tests indicate that the distinct CO maximum in the Asian monsoon anticyclone is strongly impacted by extreme convective systems with detrainment of polluted air above 360 K potential temperature. The relative importance of different CO source regions will also be discussed.

  13. Adaptation and optimization of biological transport networks.

    PubMed

    Hu, Dan; Cai, David

    2013-09-27

    It has been hypothesized that topological structures of biological transport networks are consequences of energy optimization. Motivated by experimental observation, we propose that adaptation dynamics may underlie this optimization. In contrast to the global nature of optimization, our adaptation dynamics responds only to local information and can naturally incorporate fluctuations in flow distributions. The adaptation dynamics minimizes the global energy consumption to produce optimal networks, which may possess hierarchical loop structures in the presence of strong fluctuations in flow distribution. We further show that there may exist a new phase transition as there is a critical open probability of sinks, above which there are only trees for network structures whereas below which loops begin to emerge.

  14. Gravity-driven convection studies in compound semiconductor crystal growth by physical vapor transport

    NASA Technical Reports Server (NTRS)

    Zoutendyk, J. A.; Akutagawa, W. M.

    1982-01-01

    Experimental results are summarized, and it is pointed out that gravity-driven convection can alter the diffusive-advective mass transport behavior in the growth of crystals by physical vapor transport. Specially designed and constructed transparent furnaces are described which are being used to study the effects of gravity in the crystal growth of the compound semiconductors PbTe and CdTe. The theory underlying vapor transport behavior is reviewed, with attention given to the vapor-solid behavior of compound materials, to one-dimensional mass transport, and to gravity-induced (natural) convection. In the transparent furnaces, the quartz capillary tube mounted along the axis of the main quartz ampoule is used to measure the temperature at the growth surface (vapor-solid crystal interface) and the source, as well as the complete temperature profile along the axis of the tube. The light-pipe works to remove heat from the growth end of the ampoule by radiative heat transfer. The ampoules are sealed after being evacuated to the low 10 to the -8th torr range with a cryogenic vacuum pump.

  15. Convective Momentum Transport Associated with the Madden-Julian Oscillation Based on Reanalysis Dataset

    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.

  16. Insights into capacity-constrained optimal transport.

    PubMed

    Korman, Jonathan; McCann, Robert J

    2013-06-18

    A variant of the classical optimal transportation problem is the following: among all joint measures with fixed marginals and that are dominated by a given density, find the optimal one. Existence and uniqueness of solutions to this variant were established by Korman and McCann. In the present article, we expose an unexpected symmetry leading to explicit examples in two and more dimensions. These are inspired in part by simulations in one dimension that display singularities and topology and in part by two further developments: the identification of all extreme points in the feasible set and an approach to uniqueness based on constructing feasible perturbations.

  17. Analysis of nuclide transport under natural convection and time dependent boundary condition using TOUGH2

    SciTech Connect

    Javeri, V.

    1995-03-01

    After implementation of TOUGH2 at GRS in summer 91, it was first used to analyse the gas transport in a repository for the nuclear waste with negligible heat generation and to verify the results obtained with ECLIPSE/JAV 92/. Since the original version of TOUGH2 does not directly simulate the decay of radionuclide and the time dependent boundary conditions, it is not a appropriate tool to study the nuclide transport in a porous medium/PRU 87, PRU 91/. Hence, in this paper some modifications are proposed to study the nuclide transport under combined influence of natural convection diffusion, dispersion and time dependent boundary condition. Here, a single phase fluid with two liquid components is considered as in equation of state model for water and brine/PRU 91A/.

  18. Convection-Enhanced Transport into Open Cavities : Effect of Cavity Aspect Ratio.

    PubMed

    Horner, Marc; Metcalfe, Guy; Ottino, J M

    2015-09-01

    Recirculating fluid regions occur in the human body both naturally and pathologically. Diffusion is commonly considered the predominant mechanism for mass transport into a recirculating flow region. While this may be true for steady flows, one must also consider the possibility of convective fluid exchange when the outer (free stream) flow is transient. In the case of an open cavity, convective exchange occurs via the formation of lobes at the downstream attachment point of the separating streamline. Previous studies revealed the effect of forcing amplitude and frequency on material transport rates into a square cavity (Horner in J Fluid Mech 452:199-229, 2002). This paper summarizes the effect of cavity aspect ratio on exchange rates. The transport process is characterized using both computational fluid dynamics modeling and dye-advection experiments. Lagrangian analysis of the computed flow field reveals the existence of turnstile lobe transport for this class of flows. Experiments show that material exchange rates do not vary linearly as a function of the cavity aspect ratio (A = W/H). Rather, optima are predicted for A ≈ 2 and A ≈ 2.73, with a minimum occurring at A ≈ 2.5. The minimum occurs at the point where the cavity flow structure bifurcates from a single recirculating flow cell into two corner eddies. These results have significant implications for mass transport environments where the geometry of the flow domain evolves with time, such as coronary stents and growing aneurysms. Indeed, device designers may be able to take advantage of the turnstile-lobe transport mechanism to tailor deposition rates near newly implanted medical devices.

  19. Influence of atmospheric convection on the long and short-range transport of Xe133 emissions.

    NASA Astrophysics Data System (ADS)

    Kusmierczyk-Michulec, Jolanta; Krysta, Monika; Gheddou, Abdelhakim; Nikkinen, Mika

    2014-05-01

    The International Monitoring System (IMS) developed by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is a global system of monitoring stations, using four complementary technologies: seismic, hydroacoustic, infrasound and radionuclide. Data from all stations, belonging to IMS, are collected and transmitted to the International Data Centre (IDC) in Vienna, Austria. The radionuclide network comprises 79 stations, of which more than 60 are certified. The aim of radionuclide stations is a global monitoring of radioactive aerosols and radioactive noble gases supported by the atmospheric transport modelling (ATM). The ATM system is based on the Lagrangian Particle Dispersion Model, FLEXPART, designed for calculating the long-range and mesoscale dispersion of air pollution from point sources. In the operational configuration only the transport of the passive tracer is simulated. The question arises whether including other atmospheric processes, like convection, will improve results. To answer this question a series of forward simulations was conducted, assuming the maximum transport of 14 days. Each time 2 runs were performed: one with convection and one without convection. The release point was at the ANSTO facility in Australia. Due to the fact that CTBTO has recently received a noble gas emission inventory from the ANSTO facility we had a chance to do more accurate simulations. Studies have been performed to link Xe133 emissions with detections at the IMS stations supported by the ATM. The geographical localization to some extend justifies the assumption that the only source of Xe133 observed at the neighbouring stations, e.g. AUX04, AUX09 and NZX46, comes from the ANSTO facility. In simulations the analysed wind data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) were used with the spatial resolution of 0.5 degree. The results of quantitative and qualitative comparison will be presented.

  20. Stochastic-Convective Transport with Nonlinear Reaction: Biodegradation With Microbial Growth

    NASA Astrophysics Data System (ADS)

    Ginn, T. R.; Simmons, C. S.; Wood, B. D.

    1995-01-01

    The representation of subsurface flow and reactive transport as an ensemble of one-dimensional stream tubes is extended to account for nonlinear biodegradation with coupled microbial growth. The Stochastic-convective reaction (SCR) model is derived for bioreaction of a single solute by a single class of microorganisms coupled with dynamic microbial growth. A new global variable, the integral of the solute degraded per unit length of system traversed, accounts for degradation. Dimensionless scaling and the method of characteristics are used to reduce the model, written for a single convecting reactor (stream tube), to a pair of coupled nonlinear functional equations for solute concentration and microbial biomass. Existence of a solution to the stream tube system is shown, both numerical and approximate analytical approaches to the solution are given, and example computations using both methods are presented. Conditions under which the stream tube solution is "canonical," or scalable to fit any permissible stream tube travel time function, arise from requirements for invariance (over the stream tube ensemble) of effective one-dimensional stream tubes used to represent transport along real stream tubes in three-dimensional space. Averaging of the stream tube solution over travel time and reaction properties representative of physical and chemical heterogeneities is described as a way to separate and upscale the processes of macrodispersion and microbiological reaction. The approach is exercised to simulate Monte Carlo average behavior of bioreactive transport in physically heterogeneous two-dimensional media. Results show that the method captures the ensemble average large-scale effects of the nonlinear reactions more accurately than done in the classical reactive convection-dispersion equation (CDR), even when the appropriate scale dependent dispersion coefficient is afforded to the CDR.

  1. High speed civil transport aerodynamic optimization

    NASA Technical Reports Server (NTRS)

    Ryan, James S.

    1994-01-01

    This is a report of work in support of the Computational Aerosciences (CAS) element of the Federal HPCC program. Specifically, CFD and aerodynamic optimization are being performed on parallel computers. The long-range goal of this work is to facilitate teraflops-rate multidisciplinary optimization of aerospace vehicles. This year's work is targeted for application to the High Speed Civil Transport (HSCT), one of four CAS grand challenges identified in the HPCC FY 1995 Blue Book. This vehicle is to be a passenger aircraft, with the promise of cutting overseas flight time by more than half. To meet fuel economy, operational costs, environmental impact, noise production, and range requirements, improved design tools are required, and these tools must eventually integrate optimization, external aerodynamics, propulsion, structures, heat transfer, controls, and perhaps other disciplines. The fundamental goal of this project is to contribute to improved design tools for U.S. industry, and thus to the nation's economic competitiveness.

  2. Fluctuations and Redundancy in Optimal Transport Networks

    NASA Astrophysics Data System (ADS)

    Corson, Francis

    2010-01-01

    The structure of networks that provide optimal transport properties has been investigated in a variety of contexts. While many different formulations of this problem have been considered, it is recurrently found that optimal networks are trees. It is shown here that this result is contingent on the assumption of a stationary flow through the network. When time variations or fluctuations are allowed for, a different class of optimal structures is found, which share the hierarchical organization of trees yet contain loops. The transitions between different network topologies as the parameters of the problem vary are examined. These results may have strong implications for the structure and formation of natural networks, as is illustrated by the example of leaf venation networks.

  3. Convective Troposphere-Stratosphere Transport in the Tropics and Hydration by ice Crystals Geysers

    NASA Astrophysics Data System (ADS)

    Pommereau, J.

    2008-12-01

    Twenty-five years ago the suggestion was made by Danielsen of direct fast convective penetration of tropospheric air in the stratosphere over land convective systems. Although the existence of the mechanism is accepted, it was thought to be rare and thus its contribution to Troposphere-Stratosphere Transport (TST) of chemical species and water vapour at global scale unimportant at global scale. In contrast to this assumption, observations of temperature, water vapour, ice particles, long-lived tropospheric species during HIBISCUS, TROCCINOX and SCOUT-O3 over Brazil, Australia and Africa and more recently CALIPSO aerosols observations suggest that it is a general feature of tropical land convective regions in the summer. Particularly relevant to stratospheric water vapour is the observation of geyser like ice crystals in the TTL over overshooting events which may result in the moistening of the stratosphere. Although such events successfully captured by small scale Cloud-Resolving Models may have a significant impact on stratospheric ozone chemistry and climate, they are currently totally ignored by NWPs, CTMs and CCMs. Several recent balloon and aircraft observations of overshoots and CRM simulations will be shown illustrating the mechanism, as well as observations from a variety of satellites suggesting a significant impact at global scale.

  4. Convective heat transport in stratified atmospheres at low and high Mach number

    NASA Astrophysics Data System (ADS)

    Anders, Evan H.; Brown, Benjamin P.

    2017-08-01

    We study fully compressible convection in the context of plane-parallel, polytropically stratified atmospheres. We perform a suite of two- (2D) and three-dimensional (3D) simulations in which we vary the initial superadiabaticity (ɛ ) and the Rayleigh number (Ra) while fixing the initial density stratification, aspect ratio, and Prandtl number. The evolved heat transport, quantified by the Nusselt number (Nu), follows scaling relationships similar to those found in the well-studied, incompressible Rayleigh-Bénard problem. This scaling holds up in both 2D and 3D and is not appreciably affected by the magnitude of ɛ .

  5. Numerical optimization of unsteady natural convection heat transfer from a pair of horizontal cylinders

    NASA Astrophysics Data System (ADS)

    Pelletier, Quentin; Persoons, Tim; Murray, Darina B.

    2016-09-01

    This paper presents the results of a numerical study of unsteady natural convection heat transfer from a pair of isothermally heated horizontal cylinders in water. In conjunction with the developed numerical model, a genetic algorithm is designed to search for the optimal spacing between the two cylinders that maximizes their overall heat transfer. When the cylinders are vertically aligned, the heat transfer effectiveness of the upper cylinder is affected by buoyancy-induced fluid flow induced by the lower cylinder. The established and validated CFD model is used to analyse spectral data of local Nusselt number and velocity. The optimization procedure identifies the optimal spacing for Rayleigh numbers ranging from 1e+6 to 1e+7.

  6. Convective transport of biomass burning emissions over Brazil during TRACE A

    NASA Astrophysics Data System (ADS)

    Pickering, Kenneth E.; Thompson, Anne M.; Wang, Yansen; Tao, Wei-Kuo; McNamara, Donna P.; Kirchhoff, Volker W. J. H.; Heikes, Brian G.; Sachse, Glen W.; Bradshaw, John D.; Gregory, Gerald L.; Blake, Donald R.

    1996-10-01

    A series of large mesoscale convective systems that occurred during the Brazilian phase of GTE/TRACE A (Transport and Atmospheric Chemistry near the Equator-Atlantic) provided an opportunity to observe deep convective transport of trace gases from biomass burning. This paper reports a detailed analysis of flight 6, on September 27, 1992, which sampled cloud- and biomass-burning-perturbed regions north of Brasilia. High-frequency sampling of cloud outflow at 9-12 km from the NASA DC-8 showed enhancement of CO mixing ratios typically a factor of 3 above background (200-300 parts per billion by volume (ppbv) versus 90 ppbv) and significant increases in NOx and hydrocarbons. Clear signals of lightning-generated NO were detected; we estimate that at least 40% of NOx at the 9.5-km level and 32% at 11.3 km originated from lightning. Four types of model studies have been performed to analyze the dynamical and photochemical characteristics of the series of convective events. (1) Regional simulations for the period have been performed with the NCAR/Penn State mesoscale model (MM5), including tracer transport of carbon monoxide, initialized with observations. Middle-upper tropospheric enhancements of a factor of 3 above background are reproduced. (2) A cloud-resolving model (the Goddard cumulus ensemble (GCE) model) has been run for one representative convective cell during the September 26-27 episode. (3) Photochemical calculations (the Goddard tropospheric chemical model), initialized with trace gas observations (e.g., CO, NOx, hydrocarbons, O3) observed in cloud outflow, show appreciable O3 formation postconvection, initially up to 7-8 ppbv O3/d. (4) Forward trajectories from cloud outflow levels (postconvective conditions) put the ozone-producing air masses in eastern Brazil and the tropical Atlantic within 2-4 days and over the Atlantic, Africa, and the Indian Ocean in 6-8 days. Indeed, 3-4 days after the convective episode (September 30, 1992), upper tropospheric levels

  7. Optimized setup for two-dimensional convection experiments in thin liquid films

    SciTech Connect

    Winkler, Michael; Abel, Markus

    2016-06-15

    We present a novel experimental setup to investigate two-dimensional thermal convection in a freestanding thin liquid film. Such films can be produced in a controlled way on the scale of 5–1000 nm. Our primary goal is to investigate convection patterns and the statistics of reversals in Rayleigh-Bénard convection with varying aspect ratio. Additionally, questions regarding the physics of liquid films under controlled conditions can be investigated, like surface forces, or stability under varying thermodynamical parameters. The film is suspended in a frame which can be adjusted in height and width to span an aspect ratio range of Γ = 0.16–10. The top and bottom frame elements can be set to specific temperature within T = 15 °C to 55 °C. A thickness to area ratio of approximately 10{sup 8} enables only two-dimensional fluid motion in the time scales relevant for turbulent motion. The chemical composition of the film is well-defined and optimized for film stability and reproducibility and in combination with carefully controlled ambient parameters allows the comparison to existing experimental and numerical data.

  8. Heat transport measurements in turbulent rotating Rayleigh-Bénard convection.

    PubMed

    Liu, Yuanming; Ecke, Robert E

    2009-09-01

    We present experimental heat transport measurements of turbulent Rayleigh-Bénard convection with rotation about a vertical axis. The fluid, water with a Prandtl number (sigma) of about 6, was confined in a cell with a square cross section of 7.3 x 7.3 cm2 and a height of 9.4 cm. Heat transport was measured for Rayleigh numbers 2 x 10(5)transport, the Nusselt number, at fixed dimensional rotation rate OmegaD, at fixed Ra varying Ta, at fixed Ta varying Ra, and at fixed Rossby number Ro. The scaling of heat transport in the range of 10(7) to about 10(9) is roughly 0.29 with a Ro-dependent coefficient or equivalently is also well fit by a combination of power laws of the form a Ra1/5+b Ra1/3. The range of Ra is not sufficient to differentiate single power law or combined power-law scaling. The data are roughly consistent with an assumption that the enhancement of heat transport owing to rotation is proportional to the number of vortical structures penetrating the boundary layer. We also compare indirect measures of thermal and Ekman boundary layer thicknesses to assess their potential role in controlling heat transport in different regimes of Ra and Ta.

  9. Carbon dioxide and climate: The effects of water transport in radiative-convective models

    NASA Astrophysics Data System (ADS)

    Hummel, John R.; Reck, Ruth A.

    1981-12-01

    Considerable attention is being focused on the possible climatic effects resulting from increases in the concentration of atmospheric carbon dioxide. In calculating CO2 influence on the thermal structure of the atmosphere, the role of clouds is critically important. Not only are the cloud properties, such as amount, numbers of clouds, altitudes, and optical properties important but also whether or not these properties are fixed or coupled to model temperatures. The transport of water vapor determines whether or not a region has clouds, the cloud properites, and the water vapor profiles appropriate for clear and cloudy skies. Results are presented of the change in surface temperature with changes in carbon dioxide content for two radiative-convective models with three different cloud coverages. We used (1) the Manabe-Wetherald radiative-convective model in which three clouds with fixed pressures, thicknesses, and optical properties and a single water vapor profile are inputed and (2) the Hummel-Kuhn model, which couples radiative heating, convection, and water vapor transport in order to calculate locations and thicknesses. The Hummel-Kuhn model yields temperature increases for doubled CO2 larger than the Manabe-Wetherald model for various assumed total cloud cover amounts. For assumed standard cloud cover amounts the Hummel-Kuhn estimate is 20% larger than the Manabe-Wetherald estimate. For reduced and enhanced cloud cover amounts the Hummel-Kuhn estimates are 37% and 17% larger, respectively. The calculated cloud locations and thicknesses did not change in the calculations; therefore the increased sensitivity in the Hummel-Kuhn model is due to the larger water vapor amounts in the Hummel-Kuhn model and the added infrared absorption by the water vapor dimer.

  10. Effects of Convective Solute and Impurity Transport in Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.; Thomas, Bill R.; Rosenberger, Franz

    1998-01-01

    High-resolution optical interferometry was used to investigate the effects of forced solution convection on the crystal growth kinetics of the model protein lysozyme. Most experiments were conducted with 99.99% pure protein solutions. To study impurity effects, approx. 1% of lysozyme dimer (covalently bound) was added in some cases. We show that the unsteady kinetics, corresponding to bunching of growth steps, can be characterized by the Fourier components of time traces of the growth rate. Specific Fourier spectra are uniquely determined by the solution conditions (composition, temperature, and flow rate) and the growth layer source activity. We found that the average step velocity and growth rate increase by approx. I0% with increasing flow rate, as a result of the enhanced solute supply to the interface. More importantly, faster convective transport results in lower fluctuation amplitudes. This observation supports our rationale for system-dependent effects of transport on the structural perfection of protein crystals. We also found that solution flow rates greater than 500 microns/s result in stronger fluctuations while the average growth rate is decreased. This can lead to growth cessation at low supersaturations. With the intentionally contaminated solutions, these undesirable phenomena occurred at about half the flow rates required in pure solutions. Thus, we conclude that they are due to enhanced convective supply of impurities that are incorporated into the crystal during growth. Furthermore, we found that the impurity effects are reduced at higher crystal growth rates. Since the exposure time of terraces is inversely proportional to the growth rate, this observation suggests that the increased kinetics instability results from impurity adsorption on the interface. Finally, we provide evidence relating earlier observations of "slow protein crystal growth kinetics" to step bunch formation in response to nonsteady step generation.

  11. Effects of Convective Solute and Impurity Transport in Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.; Thomas, Bill R.; Rosenberger, Franz

    1998-01-01

    High-resolution optical interferometry was used to investigate the effects of forced solution convection on the crystal growth kinetics of the model protein lysozyme. Most experiments were conducted with 99.99% pure protein solutions. To study impurity effects, approx. 1% of lysozyme dimer (covalently bound) was added in some cases. We show that the unsteady kinetics, corresponding to bunching of growth steps, can be characterized by the Fourier components of time traces of the growth rate. Specific Fourier spectra are uniquely determined by the solution conditions (composition, temperature, and flow rate) and the growth layer source activity. We found that the average step velocity and growth rate increase by approx. I0% with increasing flow rate, as a result of the enhanced solute supply to the interface. More importantly, faster convective transport results in lower fluctuation amplitudes. This observation supports our rationale for system-dependent effects of transport on the structural perfection of protein crystals. We also found that solution flow rates greater than 500 microns/s result in stronger fluctuations while the average growth rate is decreased. This can lead to growth cessation at low supersaturations. With the intentionally contaminated solutions, these undesirable phenomena occurred at about half the flow rates required in pure solutions. Thus, we conclude that they are due to enhanced convective supply of impurities that are incorporated into the crystal during growth. Furthermore, we found that the impurity effects are reduced at higher crystal growth rates. Since the exposure time of terraces is inversely proportional to the growth rate, this observation suggests that the increased kinetics instability results from impurity adsorption on the interface. Finally, we provide evidence relating earlier observations of "slow protein crystal growth kinetics" to step bunch formation in response to nonsteady step generation.

  12. Silicon nanopore membrane (SNM) for islet encapsulation and immunoisolation under convective transport

    PubMed Central

    Song, Shang; Faleo, Gaetano; Yeung, Raymond; Kant, Rishi; Posselt, Andrew M; Desai, Tejal A; Tang, Qizhi; Roy, Shuvo

    2016-01-01

    Problems associated with islet transplantation for Type 1 Diabetes (T1D) such as shortage of donor cells, use of immunosuppressive drugs remain as major challenges. Immune isolation using encapsulation may circumvent the use of immunosuppressants and prolong the longevity of transplanted islets. The encapsulating membrane must block the passage of host’s immune components while providing sufficient exchange of glucose, insulin and other small molecules. We report the development and characterization of a new generation of semipermeable ultrafiltration membrane, the silicon nanopore membrane (SNM), designed with approximately 7 nm-wide slit-pores to provide middle molecule selectivity by limiting passage of pro-inflammatory cytokines. Moreover, the use of convective transport with a pressure differential across the SNM overcomes the mass transfer limitations associated with diffusion through nanometer-scale pores. The SNM exhibited a hydraulic permeability of 130 ml/hr/m2/mmHg, which is more than 3 fold greater than existing polymer membranes. Analysis of sieving coefficients revealed 80% reduction in cytokines passage through SNM under convective transport. SNM protected encapsulated islets from infiltrating cytokines and retained islet viability over 6 hours and remained responsive to changes in glucose levels unlike non-encapsulated controls. Together, these data demonstrate the novel membrane exhibiting unprecedented hydraulic permeability and immune-protection for islet transplantation therapy. PMID:27009429

  13. Silicon nanopore membrane (SNM) for islet encapsulation and immunoisolation under convective transport

    NASA Astrophysics Data System (ADS)

    Song, Shang; Faleo, Gaetano; Yeung, Raymond; Kant, Rishi; Posselt, Andrew M.; Desai, Tejal A.; Tang, Qizhi; Roy, Shuvo

    2016-03-01

    Problems associated with islet transplantation for Type 1 Diabetes (T1D) such as shortage of donor cells, use of immunosuppressive drugs remain as major challenges. Immune isolation using encapsulation may circumvent the use of immunosuppressants and prolong the longevity of transplanted islets. The encapsulating membrane must block the passage of host’s immune components while providing sufficient exchange of glucose, insulin and other small molecules. We report the development and characterization of a new generation of semipermeable ultrafiltration membrane, the silicon nanopore membrane (SNM), designed with approximately 7 nm-wide slit-pores to provide middle molecule selectivity by limiting passage of pro-inflammatory cytokines. Moreover, the use of convective transport with a pressure differential across the SNM overcomes the mass transfer limitations associated with diffusion through nanometer-scale pores. The SNM exhibited a hydraulic permeability of 130 ml/hr/m2/mmHg, which is more than 3 fold greater than existing polymer membranes. Analysis of sieving coefficients revealed 80% reduction in cytokines passage through SNM under convective transport. SNM protected encapsulated islets from infiltrating cytokines and retained islet viability over 6 hours and remained responsive to changes in glucose levels unlike non-encapsulated controls. Together, these data demonstrate the novel membrane exhibiting unprecedented hydraulic permeability and immune-protection for islet transplantation therapy.

  14. An extended convection diffusion model for red blood cell-enhanced transport of thrombocytes and leukocytes

    NASA Astrophysics Data System (ADS)

    Hund, S. J.; Antaki, J. F.

    2009-10-01

    Transport phenomena of platelets and white blood cells (WBCs) are fundamental to the processes of vascular disease and thrombosis. Unfortunately, the dilute volume occupied by these cells is not amenable to fluid-continuum modeling, and yet the cell count is large enough that modeling each individual cell is impractical for most applications. The most feasible option is to treat them as dilute species governed by convection and diffusion; however, this is further complicated by the role of the red blood cell (RBC) phase on the transport of these cells. We therefore propose an extended convection-diffusion (ECD) model based on the diffusive balance of a fictitious field potential, Ψ, that accounts for the gradients of both the dilute phase and the local hematocrit. The ECD model was applied to the flow of blood in a tube and between parallel plates in which a profile for the RBC concentration field was imposed and the resulting platelet concentration field predicted. Compared to prevailing enhanced-diffusion models that dispersed the platelet concentration field, the ECD model was able to simulate a near-wall platelet excess, as observed experimentally. The extension of the ECD model depends only on the ability to prescribe the hematocrit distribution, and therefore may be applied to a wide variety of geometries to investigate platelet-mediated vascular disease and device-related thrombosis.

  15. Comparison of Deep Convective Transport in Cumulus-Parameterized and Cloud-Resolved WRF-Chem Simulations of Different Scale Storms during the DC3 Field Campaign

    NASA Astrophysics Data System (ADS)

    Li, Y.; Pickering, K. E.; Barth, M. C.; Bela, M.; Cummings, K.; Allen, D. J.; Carey, L. D.; Mecikalski, R.; Fierro, A. O.

    2016-12-01

    Deep convective transport of surface moisture and pollution from the planetary boundary layer (PBL) to the upper troposphere and lower stratosphere (UTLS) can affects the atmospheric radiation budget and climate. This study uses WRF-Chem to analyze deep convective transport in thunderstorms at three different spatial scales from the 2012 Deep Convective Clouds and Chemistry (DC3) field campaign: the May 21 Alabama airmass thunderstorm, May 29 Oklahoma multicell severe convection, and the June 11 mesoscale convective system (MCS). Lightning data assimilation (LDA) is used to improve the WRF-Chem simulations. WRF-Chem with LDA successfully reproduced storm locations, vertical structures and chemical fields. The analysis shows that deep convective transport of pollutants is strongest in the May 29 multi-cell severe convection and weakest in the June 11 MCS case. Tracer experiments demonstrate that the strong rear inflow jet in the June 11 MCS case brought cleaner mid-level air down to the low-level, which then entered the updraft. The injection of this cleaner air weakened the deep convective transport of boundary layer trace gases in the June 11 case by diluting boundary layer air. The cloud-resolved vertical transport results are used to evaluate cloud-parameterized deep convective vertical transport in WRF-Chem run at 15 km horizontal resolution. We examine convective transport from three parameterizations, the modified Kain-Fritsch, Grell 3D, and Grell-Freitas schemes.

  16. Convective transport of pollutants from eastern Colorado concentrated animal feeding operations into the Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Pina, A.; Denning, A.; Schumacher, R. S.

    2013-12-01

    As the population of the urban corridor along the eastern Front Range grows at an unprecedented rate, concern about pollutant transport into the Rocky Mountains is on the rise. The confluence of mountain meteorology and major pollution sources conspire to transport pollutants across the Front Range, especially nitrogen species (NH3, NH4+, orgN, and NO3-) from concentrated animal feeding operations and urban regions, into the Rocky Mountains. The Rocky Mountains have coarse-textured soils which disallow the uptake nitrogen-rich precipitation, allowing most ions in precipitation to reach, be stored in, and eutrophicate alpine terrestrial and aquatic ecosystems. The focus of this study was to examine the meteorological conditions in which atmospheric deposition of pollutants at two mountain sites was anomalously high due to convective transport. We looked at 19 years (1994-2013) of precipitation and wet deposition data from two National Atmospheric Deposition Program (NAPD) sites in the Rocky Mountains: Beaver Meadows (CO19) and Loch Vale (CO98). Loch Vale (3159 m) and Beaver Meadows (2477 m) are located approximately 11 km apart but differ in height by 682 m resulting in different seasonal precipitation composition and totals. The Advanced Research WRF model was used to simulate the meteorology at a high resolution for the progression of the upslope event that led to high nitrogen deposition in the Rocky Mountains. Data from the North American Regional Reanalysis (NARR) was used to observe and verify synoptic conditions produced by the WRF model that influenced the high-deposition events. Dispersion plumes showed a mesoscale mountain circulation caused by differential heating between mountains-tops and the plains was the main driver of the westward convective transport towards the mountains. Additionally and unexpectedly, a lee trough and high precipitable water values associated with a cold front played significant roles in the nitrogen deposition into the Rocky

  17. Multidisciplinary optimization applied to a transport aircraft

    NASA Technical Reports Server (NTRS)

    Giles, G. L.; Wrenn, G. A.

    1984-01-01

    Decomposition of a large optimization problem into several smaller subproblems has been proposed as an approach to making large-scale optimization problems tractable. To date, the characteristics of this approach have been tested on problems of limited complexity. The objective of the effort is to demonstrate the application of this multilevel optimization method on a large-scale design study using analytical models comparable to those currently being used in the aircraft industry. The purpose of the design study which is underway to provide this demonstration is to generate a wing design for a transport aircraft which will perform a specified mission with minimum block fuel. A definition of the problem; a discussion of the multilevel composition which is used for an aircraft wing; descriptions of analysis and optimization procedures used at each level; and numerical results obtained to date are included. Computational times required to perform various steps in the process are also given. Finally, a summary of the current status and plans for continuation of this development effort are given.

  18. Effect of repulsive interactions on the rate of doublet formation of colloidal nanoparticles in the presence of convective transport.

    PubMed

    Lattuada, Marco; Morbidelli, Massimo

    2011-03-01

    In this work, we have performed a systematic investigation of the effect of electrostatic repulsive interactions on the aggregation rate of colloidal nanoparticles to from doublets in the presence of a convective transport mechanism. The aggregation rate has been computed by solving numerically the Fuchs-Smoluchowski diffusion-convection equation. Two convective transport mechanisms have been considered: extensional flow field and gravity-induced relative sedimentation. A broad range of conditions commonly encountered in the applications of colloidal dispersions has been analyzed. The relative importance of convective to diffusive contributions has been quantified by using the Peclet number Pe. The simulation results indicate that, in the presence of repulsive interactions, the evolution of the aggregation rate as a function of Pe can always be divided into three distinct regimes, no matter which convective mechanism is considered. At low Pe values the rate of aggregation is independent of convection and is dominated by repulsive interactions. At high Pe values, the rate of aggregation is dominated by convection, and independent of repulsive interactions. At intermediate Pe values, a sharp transition between these two regimes occurs. During this transition, which occurs usually over a 10-100-fold increase in Pe values, the aggregation rate can change by several orders of magnitude. The interval of Pe values where this transition occurs depends upon the nature of the convective transport mechanism, as well as on the height and characteristic lengthscale of the repulsive barrier. A simplified model has been proposed that is capable of quantitatively accounting for the simulations results. The obtained results reveal unexpected features of the effect of ionic strength and particle size on the stability of colloidal suspensions under shear or sedimentation, which have relevant consequences in industrial applications.

  19. Tropical deep convection and its impact on composition in global and mesoscale models - Part 2: Tracer transport

    NASA Astrophysics Data System (ADS)

    Hoyle, C. R.; Marécal, V.; Russo, M. R.; Arteta, J.; Chemel, C.; Chipperfield, M. P.; D'Amato, F.; Dessens, O.; Feng, W.; Harris, N. R. P.; Hosking, J. S.; Morgenstern, O.; Peter, T.; Pyle, J. A.; Reddmann, T.; Richards, N. A. D.; Telford, P. J.; Tian, W.; Viciani, S.; Wild, O.; Yang, X.; Zeng, G.

    2010-08-01

    The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemistry transport, and climate chemistry models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short lived tracers (with a lifetime of 6 hours) within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to differ between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for the modelling of the halogen burden of the lowermost stratosphere through species such as bromoform, or for the transport of short lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are found to be strongly influenced by the convective transport parameterisations, and boundary layer mixing parameterisations of the models. The location of rapid transport into the upper troposphere is similar among the models, and is mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, none of the models indicates significant enhancement in upward transport over western Africa. The mean mixing ratios of an idealised CO like tracer in the upper tropical troposphere are found to be sensitive to the surface CO mixing ratios in the regions with the most active

  20. Multi-objective optimization of electronics heat sinks cooled by natural convection

    NASA Astrophysics Data System (ADS)

    Lampio, K.; Karvinen, R.

    2016-09-01

    Fins and fin arrays with constant temperature at the fin base have known solutions for natural convection. However, in practical applications, no simple solution exists for maximum temperature of heat sink with many heat dissipating components located at the base plate. A calculation model is introduced here to solve this practical problem without time consuming CFD modelling of fluid flow and heat transfer. Solutions with the new model are compared with some simple analytical and CFD solutions to prove that the results are accurate enough for practical applications. Seminal here is that results are obtained many orders of magnitude faster than with CFD. This much shorter calculation time scale makes the model well suited for multi-objective optimization in, e.g., simultaneous minimization of heat sink maximum temperature, size, and mass. An optimization case is presented in which heat sink mass and size are significantly reduced over those of the original reference heat sink.

  1. The Arctic Mediterranean Sea - Deep convection, oceanic heat transport and freshwater

    NASA Astrophysics Data System (ADS)

    Rudels, Bert

    2014-05-01

    The speculations about the driving forces behind the oceanic meridional circulation and the importance of the northward transports of oceanic heat for the ice conditions in the Arctic Ocean have a long history, but only after the Fram expedition 1893-1896 and from the studies by Nansen, Helland-Hansen and Sandström in the early 1900s did these speculations attain observational substance. In the late 1970s and onward these questions have again risen to prominence. A study of deep convection in the Greenland Sea, then assumed to drive the global thermohaline circulation, started with the Greenland Sea Project (GSP), while the investigation of the exchanges of volume and heat through Fram Strait had a more hesitant start in the Fram Strait Project (FSP). Not until 1997 with the EC project VEINS (Variation of Exchanges in the Northern Seas) was a mooring array deployed across Fram Strait. This array has been maintained and has measured the exchanges ever since. Eberhard Fahrbach was closely involved in these studies, as a secretary for the GSP and as the major driving force behind the Fram Strait array. Here we shall examine the legacy of these projects; How our understanding of these themes has evolved in recent years. After the 1980s no convective bottom water renewal has been observed in the Greenland Sea, and the Greenland Sea deep waters have gradually been replaced by warmer, more saline deep water from the Arctic Ocean passing through Fram Strait. Small-scale convective events penetrating deeper than 2500m but there less dense than their surroundings were, however, observed in the early 2000s. The Fram Strait exchanges have proven difficult to estimate due to strong variability, high barotropic and baroclinic eddy activity and short lateral coherence scales. The fact that the mass transports through Fram Strait do not balance complicates the assessment of the heat transport through Fram Strait into the Arctic Ocean and mass (volume) and salt (freshwater

  2. Evidence of Deep Convective Transport of Reactive Constituents to the Tropical Tropopause Layer Using Convective Influence Calculations

    NASA Astrophysics Data System (ADS)

    Selkirk, H. B.; Pfister, L.; Ridley, B. A.; Atlas, E.

    2003-12-01

    Isentropic convective influence calculations are performed to identify upstream convective systems impacting air sampled just below the subtropical and tropical tropopause on a flight of the NASA WB-57F from Houston, Texas south to 5° N during the September 1999 airborne mission Atmospheric Chemistry of Combustion Effects Near the Tropopause (ACCENT). Interpretation of ensembles of in situ tracer measurements, in particular NOy, O3, and CH3I, have indicated that much of the air sampled on this flight had been recently injected by deep convection, although from non-pristine marine boundary layers. In addition there were more limited stretches of the flight track with evidence of biomass burning and industrial sources. Consistent with this finding, convective influence calculations indicate that the great majority of the parcels along the flight track had been affected by deep convective events at some time in the seven days preceding the flight; the majority of these were oceanic systems. Under the anticyclonic upper tropospheric flow pattern prevailing north of ˜11° N, the marine convective influence came from systems in the Gulf of Mexico, around Cuba and over the waters east of the Bahamas. Influence from continental systems was sporadic except for one extended portion of the track with air that the calculations indicated had been injected by land-based systems over Guatemala within the previous 12-24 hours. South of ˜11° N, a group of systems east of the Lesser Antilles were major contributors of marine influence. However, as the aircraft approached its turnaround at 5° N, the calculations also show influence from land-based systems over Colombia, consistent with the tracer measurements. One important feature of the results is that the convective influence over the course of the 2600-km flight track is derived from a relatively small number of systems. This is a direct result of the minimal dispersion of the trajectories, particularly those emanating from

  3. Optimal transport exponent in spatially embedded networks

    NASA Astrophysics Data System (ADS)

    Li, G.; Reis, S. D. S.; Moreira, A. A.; Havlin, S.; Stanley, H. E.; Andrade, J. S., Jr.

    2013-04-01

    The imposition of a cost constraint for constructing the optimal navigation structure surely represents a crucial ingredient in the design and development of any realistic navigation network. Previous works have focused on optimal transport in small-world networks built from two-dimensional lattices by adding long-range connections with Manhattan length rij taken from the distribution Pij˜rij-α, where α is a variable exponent. It has been shown that, by introducing a cost constraint on the total length of the additional links, regardless of the strategy used by the traveler (independent of whether it is based on local or global knowledge of the network structure), the best transportation condition is obtained with an exponent α=d+1, where d is the dimension of the underlying lattice. Here we present further support, through a high-performance real-time algorithm, on the validity of this conjecture in three-dimensional regular as well as in two-dimensional critical percolation clusters. Our results clearly indicate that cost constraint in the navigation problem provides a proper theoretical framework to justify the evolving topologies of real complex network structures, as recently demonstrated for the networks of the US airports and the human brain activity.

  4. BV Estimates in Optimal Transportation and Applications

    NASA Astrophysics Data System (ADS)

    De Philippis, Guido; Mészáros, Alpár Richárd; Santambrogio, Filippo; Velichkov, Bozhidar

    2016-02-01

    In this paper we study the BV regularity for solutions of certain variational problems in Optimal Transportation. We prove that the Wasserstein projection of a measure with BV density on the set of measures with density bounded by a given BV function f is of bounded variation as well and we also provide a precise estimate of its BV norm. Of particular interest is the case f = 1, corresponding to a projection onto a set of densities with an L ∞ bound, where we prove that the total variation decreases by projection. This estimate and, in particular, its iterations have a natural application to some evolutionary PDEs as, for example, the ones describing a crowd motion. In fact, as an application of our results, we obtain BV estimates for solutions of some non-linear parabolic PDE by means of optimal transportation techniques. We also establish some properties of the Wasserstein projection which are interesting in their own right, and allow, for instance, for the proof of the uniqueness of such a projection in a very general framework.

  5. Improving representation of convective transport for scale-aware parameterization: 2. Analysis of cloud-resolving model simulations

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Chin; Fan, Jiwen; Zhang, Guang J.; Xu, Kuan-Man; Ghan, Steven J.

    2015-04-01

    Following Part I, in which 3-D cloud-resolving model (CRM) simulations of a squall line and mesoscale convective complex in the midlatitude continental and the tropical regions are conducted and evaluated, we examine the scale dependence of eddy transport of water vapor, evaluate different eddy transport formulations, and improve the representation of convective transport across all scales by proposing a new formulation that more accurately represents the CRM-calculated eddy flux. CRM results show that there are strong grid-spacing dependencies of updraft and downdraft fractions regardless of altitudes, cloud life stage, and geographical location. As for the eddy transport of water vapor, updraft eddy flux is a major contributor to total eddy flux in the lower and middle troposphere. However, downdraft eddy transport can be as large as updraft eddy transport in the lower atmosphere especially at the mature stage of midlatitude continental convection. We show that the single-updraft approach significantly underestimates updraft eddy transport of water vapor because it fails to account for the large internal variability of updrafts, while a single downdraft represents the downdraft eddy transport of water vapor well. We find that using as few as three updrafts can account for the internal variability of updrafts well. Based on the evaluation with the CRM simulated data, we recommend a simplified eddy transport formulation that considers three updrafts and one downdraft. Such formulation is similar to the conventional one but much more accurately represents CRM-simulated eddy flux across all grid scales.

  6. Effects of Convective Transport of Solute and Impurities on Defect-Causing Kinetics Instabilities in Protein Crystallization

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.

    2002-01-01

    The objective of the proposed research is to obtain further insight into the onset and development of the defect-causing instabilities that anise due to the coupling of the bulk transport and nonlinear-interfacial kinetics during growth in the mixed regime, utilizing the reduction of the convective contribution to the bulk transport under microgravity. These studies will build upon the data on the effects of quantitative variations of the forced convection velocity on the averaged and time-dependent kinetic behavior of protein crystal growth systems that have recently been obtained in our laboratory.

  7. Diffusive and convective transport through hollow fiber membranes for liver cell culture.

    PubMed

    Curcio, E; De Bartolo, L; Barbieri, G; Rende, M; Giorno, L; Morelli, S; Drioli, E

    2005-05-25

    For an efficient membrane bioreactor design, transport phenomena determining the overall mass flux of metabolites, catabolites, cell regulatory factors, and immune-related soluble factors, need to be clarified both experimentally and theoretically. In this work, experiments and calculations aimed at discerning the simultaneous influence of both diffusive and convective mechanisms to the transport of metabolites. In particular, the transmembrane mass flux of glucose, bovine serum albumin (BSA), APO-transferrin, immunoglobulin G, and ammonia was experimentally measured, under pressure and concentration gradients, through high-flux microporous hydrophilic poly-ether-sulphone (PES-HFMs) and poly-sulphone hollow fiber membranes (PS-HFMs). These data were analyzed by means of a model based on the mechanism of capillary pore diffusion, assuming that solute spherical molecules pass through an array of solvent-filled cylindrical pores with a diffusive permeation corrected for friction and steric hindrances. Additionally, resistances to the mass transfer were taken into account. Convective permeation data were discussed in terms of morphological properties of the polymeric membranes, molecular Stokes radius, and solute-membrane interactions according to information given by contact angle measurements. The observed steady-state hydraulic permeance of PS-HFMs was 0.972 L/m2hmbar, about 15.6-fold lower than that measured for PES-HFMs (15.2 L/m2h); in general, PS-HFMs provided a significant hindrance to the transport of target species. Diffusion coefficients of metabolites were found to be similar to the corresponding values in water through PES-HFMs, but significantly reduced through PS-HFMs (D(Glucose)(Membrane)=2.8x10(-6)+/-0.6x10(-6)cm2/s, D(BSA)(Membrane)=6.4 x 10(-7)+/-1 x 10(-7)cm(/s, D(Apotransferrin)(Membrane)=2.3 x 10(-7)+/-0.25 x 10(-7)cm2/s).

  8. VO(2max) and Microgravity Exposure: Convective versus Diffusive O(2) Transport.

    PubMed

    Ade, Carl J; Broxterman, Ryan M; Barstow, Thomas J

    2015-07-01

    Exposure to a microgravity environment decreases the maximal rate of O2 uptake (VO(2max)) in healthy individuals returning to a gravitational environment. The magnitude of this decrease in VO(2max) is, in part, dependent on the duration of microgravity exposure, such that long exposure may result in up to a 38% decrease in VO(2max). This review identifies the components within the O(2) transport pathway that determine the decrease in postmicrogravity VO(2max) and highlights the potential contributing physiological mechanisms. A retrospective analysis revealed that the decline in VO(2max) is initially mediated by a decrease in convective and diffusive O(2) transport that occurs as the duration of microgravity exposure is extended. Mechanistically, the attenuation of O(2) transport is the combined result of a deconditioning across multiple organ systems including decreases in total blood volume, red blood cell mass, cardiac function and mass, vascular function, skeletal muscle mass, and, potentially, capillary hemodynamics, which become evident during exercise upon re-exposure to the head-to-foot gravitational forces of upright posture on Earth. In summary, VO(2max) is determined by the integration of central and peripheral O(2) transport mechanisms, which, if not maintained during microgravity, will have a substantial long-term detrimental impact on space mission performance and astronaut health.

  9. Volumetric vs Mass Velocity in Analyzing Convective-Diffusive Transport Processes in Liquids

    NASA Astrophysics Data System (ADS)

    Brenner, Howard

    2000-11-01

    Because mass rather than volume is preserved in fluid-mechanical problems involving density changes, a natural predilection exists for quantifying convective-diffusive transport phenomena in terms of a velocity field based upon mass, rather than volume. Indeed, in the classic BSL "Transport Phenomena" textbook, but a single reference exists even to the very concept of a volume velocity, and even then it is relegated to a homework assignment. However, especially when dealing with transport in fluids in which the mass density of the conserved property being transported (e.g., chemical species, internal energy, etc.) is independent of the prevailing pressure, as is largely true in the case of liquids, overwhelming advantages exist is preferring the volume velocity over the more ubiquitous and classical mass velocity. In a generalization of ideas pioneered by D. D. Joseph and co-workers, we outline the reasons for this volumetric velocity preference in a broad general context by identifying a large class of physical problems whose solutions are rendered more accessible by exploiting this unconventional velocity choice.

  10. Transport from convective overshooting of the extratropical tropopause and the role of large-scale lower stratosphere stability

    NASA Astrophysics Data System (ADS)

    Homeyer, Cameron R.; Pan, Laura L.; Barth, Mary C.

    2014-03-01

    Simulations of observed convective systems with the Advanced Research Weather Research and Forecasting (ARW-WRF) model are used to test the influence of the large-scale lower stratosphere stability environment on the vertical extent of convective overshooting and transport above the extratropical tropopause. Three unique environments are identified (double tropopause, stratospheric intrusion, and single tropopause), and representative cases with comparable magnitudes of convective available potential energy are selected for simulation. Convective injection into the extratropical lower stratosphere is found to be deepest for the double-tropopause case (up to 4 km above the lapse-rate tropopause) and at comparable altitudes for the remaining cases (up to 2 km above the lapse-rate tropopause). All simulations show evidence of gravity wave breaking near the overshooting convective top, consistent with the identification of its role as a transport mechanism in previous studies. Simulations for the double-tropopause case, however, also show evidence of direct mixing of the overshooting top into the lower stratosphere, which is responsible for the highest levels of injection in that case. In addition, the choice of bulk microphysical parameterization for ARW-WRF simulations is found to have little impact on the transport characteristics for each case.

  11. Effects of Convective Transport on the Budget of Amazonian Aerosol under Background Conditions

    NASA Astrophysics Data System (ADS)

    Wang, J.; Krejci, R.; Giangrande, S. E.; Kuang, C.; Barbosa, H. M.; Brito, J.; Carbone, S.; Chi, X.; Comstock, J. M.; Ditas, F.; Lavric, J. V.; Manninen, H. E.; Mei, F.; Moran, D.; Pöhlker, C.; Pöhlker, M. L.; Saturno, J.; Schmid, B.; Souza, R. A. F. D.; Springston, S. R.; Tomlinson, J. M.; Toto, T.; Walter, D.; Wimmer, D.; Smith, J. N.; Machado, L.; Artaxo, P.; Andreae, M. O.; Martin, S. T.

    2016-12-01

    Aerosol particles can strongly influence the radiative properties of clouds, and they represent one of the largest uncertainties in computer simulations of climate change. The large uncertainty is in large part due to a poor understanding of processes under natural conditions, which serves as the baseline to measure change against. Understanding the processes under natural conditions is critical for a reliable assessment and quantification of ongoing and future climate change. The Amazon rainforest is one of the few continental regions where aerosol particles and their precursors can be studied under near-natural conditions. Here we examine the aerosol number and CCN budget under background conditions in the Amazon basin using data collected during the Observations and Modeling of the Green Ocean Amazon (GoAmazon 2014/5) campaign, which took place from January 2014 to December 2015 near Manaus, Brazil. The aerosol size spectrum was observed at the Amazon Tall Tower Observatory (ATTO), 150 km upwind of Manaus, and its variation with convection and precipitation during the wet season is presented. Air masses arriving at the ATTO during the wet season are typically brought by the northeasterly trade winds and travel across at least 1000 km of undeveloped tropical rainforest, therefore are generally clean. Also shown are vertical profiles of aerosol observed onboard the DOE Gulfstream-1 research aircraft. The impact of convective transport on the budget of boundary layer aerosol and CCN under the background conditions is discussed.

  12. Heat transport in low-Rossby-number Rayleigh-Bénard convection.

    PubMed

    Julien, Keith; Knobloch, Edgar; Rubio, Antonio M; Vasil, Geoffrey M

    2012-12-21

    We demonstrate, via simulations of asymptotically reduced equations describing rotationally constrained Rayleigh-Bénard convection, that the efficiency of turbulent motion in the fluid bulk limits overall heat transport and determines the scaling of the nondimensional Nusselt number Nu with the Rayleigh number Ra, the Ekman number E, and the Prandtl number σ. For E < 1 inviscid scaling theory predicts and simulations confirm the large Ra scaling law Nu-1 ≈ C(1)σ(-1/2)Ra(3/2)E(2), where C(1) is a constant, estimated as C(1) ≈ 0.04 ± 0.0025. In contrast, the corresponding result for nonrotating convection, Nu-1 ≈ C(2)Ra(α), is determined by the efficiency of the thermal boundary layers (laminar: 0.28 ≤ α ≤ 0.31, turbulent: α ~ 0.38). The 3/2 scaling law breaks down at Rayleigh numbers at which the thermal boundary layer loses rotational constraint, i.e., when the local Rossby number ≈ 1. The breakdown takes place while the bulk Rossby number is still small and results in a gradual transition to the nonrotating scaling law. For low Ekman numbers the location of this transition is independent of the mechanical boundary conditions.

  13. Dynamics and mass transport of solutal convection in a closed porous media system

    NASA Astrophysics Data System (ADS)

    Wen, Baole; Akhbari, Daria; Hesse, Marc

    2016-11-01

    Most of the recent studies of CO2 sequestration are performed in open systems where the constant partial pressure of CO2 in the vapor phase results in a time-invariant saturated concentration of CO2 in the brine (Cs). However, in some closed natural CO2 reservoirs, e.g., Bravo Dome in New Mexico, the continuous dissolution of CO2 leads to a pressure drop in the gas that is accompanied by a reduction of Cs and thereby affects the dynamics and mass transport of convection in the brine. In this talk, I discuss the characteristics of convective CO2 dissolution in a closed system. The gas is assumed to be ideal and its solubility given by Henry's law. An analytical solution shows that the diffusive base state is no longer self-similar and that diffusive mass transfer declines rapidly. Scaling analysis reveals that the volume ratio of brine and gas η determines the behavior of the system. DNS show that no constant flux regime exists for η > 0 nevertheless, the quantity F /Cs2 remains constant, where F is the dissolution flux. The onset time is only affected by η when the Rayleigh number Ra is small. In this case, the drop in Cs during the initial diffusive regime significantly reduces the effective Ra and therefore delays the onset.

  14. Universality of intermittent convective transport in the scrape-off layer of magnetically confined devices

    NASA Astrophysics Data System (ADS)

    Antar, Ghassan Y.; Counsell, Glenn; Yu, Yang; Labombard, Brian; Devynck, Pascal

    2003-02-01

    The nature of intermittency, long observed in magnetic fusion devices, was revisited lately [G. Antar et al., Phys. Rev. Lett. 87, 065001 (2001)]. It was shown that intermittency is caused by large-scale events with high radial velocity reaching about 1/10th of the sound speed. These type of structures were named "avaloids." In the present article, the universality of convective turbulence in magnetically confined plasmas is investigated. Turbulence properties in the scrape-off layer of four different magnetic fusion devices are compared. Namely, the Tore Supra tokamak [Tore Supra Team, Nuclear Fusion, 40, 1047 (2000)] with circular cross-section limiter-bounded plasma, the Alcator C-Mod tokamak [B. LaBombard et al., Phys. Plasmas 8, 2107 (2001)] which is a divertor device, the Mega-Ampere Spherical Tokamak (MAST) [A. Sykes et al., Phys. Plasmas 8, 2101 (2001)] with vacuum chamber walls far from the plasma last closed flux surface and the PISCES linear plasma device [D. Geobel et al., Rev. Sci. Istrum. 56, 1717 (1985)]. The statistical properties of the turbulent signals in the four devices are found to be identical allowing us to conclude that intermittent convective transport by avaloids is universal in the sense that it occurs and has the same properties in many confinement devices with different configurations.

  15. Theoretical analysis of the effect of convective flow on solute transport and insulin release in a hollow fiber bioartificial pancreas.

    PubMed

    Pillarella, M R; Zydney, A L

    1990-05-01

    The bioartificial pancreas, in which transplanted pancreatic tissue or isolated cells are cultured on a hollow fiber membrane, is an attractive approach to restore physiologic insulin delivery in the treatment of diabetes. Insulin response in prototype devices has been unacceptable due to the large mass transport limitations associated with the membrane and the surrounding shell region. Although available theoretical analyses provide some insight into the combined effects of transport and reaction in the bioartificial pancreas, they cannot quantitatively account for the effects of convective recirculation flow, complex intrinsic insulin secretory kinetics, and non-uniform distribution of pancreatic cells. We have developed a detailed model for glucose and insulin transport and insulin secretion in the hollow fiber bioartificial pancreas based on the solution of the mass and momentum conservation equations describing flow and transport in the lumen, matrix, and shell. Model predictions are in good agreement with literature data obtained in a hollow fiber device with minimal radial convective flow. Although no quantitative data are available for a device with significant radial convection, model simulations demonstrate that convective recirculation flow can dramatically improve insulin response, allowing the device to accurately capture the bi-phasic insulin secretion characteristic of the normal physiologic response. Results provide fundamental insights into the coupling between kinetics and transport in the hollow fiber system and a rational basis for the design of clinical devices.

  16. Impacts of the Convective Transport Algorithm on Atmospheric Composition and Ozone-Climate Feedbacks in GEOS-CCM

    NASA Technical Reports Server (NTRS)

    Pawson, S.; Nielsen, Jon E.; Oman, L.; Douglass, A. R.; Duncan, B. N.; Zhu, Z.

    2012-01-01

    Convective transport is one of the dominant factors in determining the composition of the troposphere. It is the main mechanism for lofting constituents from near-surface source regions to the middle and upper troposphere, where they can subsequently be advected over large distances. Gases reaching the upper troposphere can also be injected through the tropopause and play a subsequent role in the lower stratospheric ozone balance. Convection codes in climate models remain a great source of uncertainty for both the energy balance of the general circulation and the transport of constituents. This study uses the Goddard Earth Observing System Chemistry-Climate Model (GEOS CCM) to perform a controlled experiment that isolates the impact of convective transport of constituents from the direct changes on the atmospheric energy balance. Two multi-year simulations are conducted. In the first, the thermodynamic variable, moisture, and all trace gases are transported using the multi-plume Relaxed-Arakawa-Schubert (RAS) convective parameterization. In the second simulation, RAS impacts the thermodynamic energy and moisture in this standard manner, but all other constituents are transported differently. The accumulated convective mass fluxes (including entrainment and detrainment) computed at each time step of the GCM are used with a diffusive (bulk) algorithm for the vertical transport, which above all is less efficient at transporting constituents from the lower to the upper troposphere. Initial results show the expected differences in vertical structure of trace gases such as carbon monoxide, but also show differences in lower stratospheric ozone, in a region where it can potentially impact the climate state of the model. This work will investigate in more detail the impact of convective transport changes by comparing the two simulations over many years (1996-2010), focusing on comparisons with observed constituent distributions and similarities and differences of patterns

  17. 77 FR 33793 - Optimized Transportation Management, Inc.; Order of Suspension of Trading

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-07

    ... COMMISSION Optimized Transportation Management, Inc.; Order of Suspension of Trading June 5, 2012. It appears... concerning the securities of Optimized Transportation Management, Inc. (``Optimized Transportation Management... protection of investors require a suspension of trading in the securities of Optimized Transportation...

  18. Slip effects on mixed convective peristaltic transport of copper-water nanofluid in an inclined channel.

    PubMed

    Abbasi, Fahad Munir; Hayat, Tasawar; Ahmad, Bashir; Chen, Guo-Qian

    2014-01-01

    Peristaltic transport of copper-water nanofluid in an inclined channel is reported in the presence of mixed convection. Both velocity and thermal slip conditions are considered. Mathematical modelling has been carried out using the long wavelength and low Reynolds number approximations. Resulting coupled system of equations is solved numerically. Quantities of interest are analyzed through graphs. Numerical values of heat transfer rate at the wall for different parameters are obtained and examined. Results showed that addition of copper nanoparticles reduces the pressure gradient, axial velocity at the center of channel, trapping and temperature. Velocity slip parameter has a decreasing effect on the velocity near the center of channel. Temperature of nanofluid increases with increase in the Grashoff number and channel inclination angle. It is further concluded that the heat transfer rate at the wall increases considerably in the presence of copper nanoparticles.

  19. Slip Effects on Mixed Convective Peristaltic Transport of Copper-Water Nanofluid in an Inclined Channel

    PubMed Central

    Abbasi, Fahad Munir; Hayat, Tasawar; Ahmad, Bashir; Chen, Guo-Qian

    2014-01-01

    Peristaltic transport of copper-water nanofluid in an inclined channel is reported in the presence of mixed convection. Both velocity and thermal slip conditions are considered. Mathematical modelling has been carried out using the long wavelength and low Reynolds number approximations. Resulting coupled system of equations is solved numerically. Quantities of interest are analyzed through graphs. Numerical values of heat transfer rate at the wall for different parameters are obtained and examined. Results showed that addition of copper nanoparticles reduces the pressure gradient, axial velocity at the center of channel, trapping and temperature. Velocity slip parameter has a decreasing effect on the velocity near the center of channel. Temperature of nanofluid increases with increase in the Grashoff number and channel inclination angle. It is further concluded that the heat transfer rate at the wall increases considerably in the presence of copper nanoparticles. PMID:25170908

  20. Influence of diffusion and convective transport on dendritic growth in dilute alloys

    NASA Technical Reports Server (NTRS)

    Glicksman, M. E.; Singh, N. B.; Chopra, M.

    1982-01-01

    Experimentation has been carried out in which the kinetics and morphology of dendritic growth were measured as a function of thermal supercooling, solute concentration, and spatial orientation of the dendritic growth axis. The crystal growth system studied is succinonitrile, NC(CH2)2CN, with additions of argon (up to 0.1 mole percent). This system is especially useful as a model for alloy studies because kinetic data are available for high purity (7-9's) succinonitrile. The influence of the solute, at fixed thermal supercooling, is to increase the growth velocity and correspondingly decrease intrinsic crystal dimensions. Morphological measurements are described in detail relating tip size, perturbation wavelength, supercooling, and solute concentration. The analysis of these effects based on morphological stability theory is also discussed, and experiments permitting the separation of convective and diffusive heat transport during crystal growth of succinonitrile are described. The studies underscore the importance of gravitationally-induced buoyancy effects on crystal growth.

  1. Radon-222 as a test of convective transport in a general circulation model

    NASA Technical Reports Server (NTRS)

    Jacob, Daniel J.; Prather, Michael J.

    1990-01-01

    A three-dimensional tracer model based on the Goddard Institude of Space Studies GCM is used to simulate the distribution of Rn-222 over North America to test the ability of the model to describe the transport of pollutants in the boundary layer and the exchange of mass between the boundary layer and the free troposphere. The model results are compared with surface observations from five sites in the U.S., showing that Rn-222 concentrations are primarily regulated by dry convection. The simulations show satisfactory agreement with observations although the model underpredicts observations at night and the simulated Rn-222 concentrations over the northeastern U.S. are too high in the spring and too low in the fall.

  2. Radon-222 as a test of convective transport in a general circulation model

    NASA Technical Reports Server (NTRS)

    Jacob, Daniel J.; Prather, Michael J.

    1990-01-01

    A three-dimensional tracer model based on the Goddard Institude of Space Studies GCM is used to simulate the distribution of Rn-222 over North America to test the ability of the model to describe the transport of pollutants in the boundary layer and the exchange of mass between the boundary layer and the free troposphere. The model results are compared with surface observations from five sites in the U.S., showing that Rn-222 concentrations are primarily regulated by dry convection. The simulations show satisfactory agreement with observations although the model underpredicts observations at night and the simulated Rn-222 concentrations over the northeastern U.S. are too high in the spring and too low in the fall.

  3. Scatter-free collimated convection and cosmic-ray transport at 1 AU

    NASA Technical Reports Server (NTRS)

    Roelof, E. C.

    1975-01-01

    Observations of solar cosmic rays between 0.1 MeV and 1 GeV are more consistent with scatter-free than diffusive propagation near 1 AU. Since these particles also are constrained to interplanetary magnetic field lines, the parallel and transverse flow are decoupled by collimated convection. Local propagation is therefore more appropriately described by Liouville's equation, and transport properties can be examined from the exact zeroeth and first moments of the equation averaged over all directions in momentum space. Observational results which may be explained directly without invoking local scattering include the decay of solar flare events as well as the radial gradient, diurnal and semidiurnal variation of galactic cosmic rays.

  4. Advanced transport design using multidisciplinary design optimization

    NASA Technical Reports Server (NTRS)

    Barnum, Jennifer; Bathras, Curt; Beene, Kirk; Bush, Michael; Kaupin, Glenn; Lowe, Steve; Sobieski, Ian; Tingen, Kelly; Wells, Douglas

    1991-01-01

    This paper describes the results of the first implementation of multidisciplinary design optimisation (MDO) techniques by undergraduates ina design course. The objective of the work was to design a civilian transport aircraft of the Boeing 777 class. The first half of the two semester design course consisted of application of traditional sizing methods and techniques to form a baseline aircraft. MDO techniques were then applied to this baseline design. This paper describes the evolution of the design with special emphasis on the application of MDO techniques, and presents the results of four iterations through the design space. Minimization of take-off gross weight was the goal of the optimization process. The resultant aircraft derived from the MDO procedure weighed approximately 13,382 lbs (2.57 percent) less than the baseline aircraft.

  5. Analysis of subgrid-scale vertical transport in convective boundary layers at gray-zone resolutions

    NASA Astrophysics Data System (ADS)

    Shin, Hyeyum Hailey; Hong, Song-You

    2013-04-01

    The gray zone of a physics process in numerical models is defined as the range of model resolution in which the process is partly resolved by model dynamics and partly parameterized. In this study, we examine the effects of grid size on resolved and parameterized vertical transport for horizontal grid scales including the gray zone. To assess how stability alters the dependency on grid size, four convective boundary layer (CBL)s with different surface heating and geostrophic winds are considered. For this purpose, reference data for grid-scale (GS) and subgrid-scale (SGS) fields are constructed for 50-4000 mesh sizes by filtering 25-m large-eddy simulations (LES) data. As wind shear becomes stronger, turbulent kinetic energy and the vertical transport of potential temperature and momentum are more resolved for a given grid spacing. A passive scalar with bottom-up diffusion behaves in a similar fashion. For a top-down diffusion scalar, the cospectral peak scale of the scalar flux is larger than the horizontal size of the thermals and increases in time. For the scalar, the entrainment ratio, in conjunction with the shear, influences the mesh-size dependency of GS and SGS transport. The total vertical transport of heat and the bottom-up scalar is decomposed into a non-local mixing owing to the coherent structures and remaining local mixing. The contribution of the resolved parts is larger when roll-like structures are present than when only thermals exist, for both non-local and local fluxes. The grid-size dependency of the non-local flux and its sensitivity to stability predominantly determines the dependency of total (non-local plus local) transport.

  6. Transport Phenomena Projects: Natural Convection between Porous, Concentric Cylinders--A Method to Learn and to Innovate

    ERIC Educational Resources Information Center

    Saatadjian, Esteban; Lesage, Francois; Mota, Jose Paulo B.

    2013-01-01

    A project that involves the numerical simulation of transport phenomena is an excellent method to teach this subject to senior/graduate chemical engineering students. The subject presented here has been used in our senior/graduate course, it concerns the study of natural convection heat transfer between two concentric, horizontal, saturated porous…

  7. Short circuit of water vapor and polluted air to the global stratosphere by convective transport over the Tibetan Plateau.

    PubMed

    Fu, Rong; Hu, Yuanlong; Wright, Jonathon S; Jiang, Jonathan H; Dickinson, Robert E; Chen, Mingxuan; Filipiak, Mark; Read, William G; Waters, Joe W; Wu, Dong L

    2006-04-11

    During boreal summer, much of the water vapor and CO entering the global tropical stratosphere is transported over the Asian monsoon/Tibetan Plateau (TP) region. Studies have suggested that most of this transport is carried out either by tropical convection over the South Asian monsoon region or by extratropical convection over southern China. By using measurements from the newly available National Aeronautics and Space Administration Aura Microwave Limb Sounder, along with observations from the Aqua and Tropical Rainfall-Measuring Mission satellites, we establish that the TP provides the main pathway for cross-tropopause transport in this region. Tropospheric moist convection driven by elevated surface heating over the TP is deeper and detrains more water vapor, CO, and ice at the tropopause than over the monsoon area. Warmer tropopause temperatures and slower-falling, smaller cirrus cloud particles in less saturated ambient air at the tropopause also allow more water vapor to travel into the lower stratosphere over the TP, effectively short-circuiting the slower ascent of water vapor across the cold tropical tropopause over the monsoon area. Air that is high in water vapor and CO over the Asian monsoon/TP region enters the lower stratosphere primarily over the TP, and it is then transported toward the Asian monsoon area and disperses into the large-scale upward motion of the global stratospheric circulation. Thus, hydration of the global stratosphere could be especially sensitive to changes of convection over the TP.

  8. Short circuit of water vapor and polluted air to the global stratosphere by convective transport over the Tibetan Plateau

    PubMed Central

    Fu, Rong; Hu, Yuanlong; Wright, Jonathon S.; Jiang, Jonathan H.; Dickinson, Robert E.; Chen, Mingxuan; Filipiak, Mark; Read, William G.; Waters, Joe W.; Wu, Dong L.

    2006-01-01

    During boreal summer, much of the water vapor and CO entering the global tropical stratosphere is transported over the Asian monsoon/Tibetan Plateau (TP) region. Studies have suggested that most of this transport is carried out either by tropical convection over the South Asian monsoon region or by extratropical convection over southern China. By using measurements from the newly available National Aeronautics and Space Administration Aura Microwave Limb Sounder, along with observations from the Aqua and Tropical Rainfall-Measuring Mission satellites, we establish that the TP provides the main pathway for cross-tropopause transport in this region. Tropospheric moist convection driven by elevated surface heating over the TP is deeper and detrains more water vapor, CO, and ice at the tropopause than over the monsoon area. Warmer tropopause temperatures and slower-falling, smaller cirrus cloud particles in less saturated ambient air at the tropopause also allow more water vapor to travel into the lower stratosphere over the TP, effectively short-circuiting the slower ascent of water vapor across the cold tropical tropopause over the monsoon area. Air that is high in water vapor and CO over the Asian monsoon/TP region enters the lower stratosphere primarily over the TP, and it is then transported toward the Asian monsoon area and disperses into the large-scale upward motion of the global stratospheric circulation. Thus, hydration of the global stratosphere could be especially sensitive to changes of convection over the TP. PMID:16585523

  9. Entropy Budget of an Atmosphere in Radiative-Convective Equilibrium. Part II: Latent Heat Transport and Moist Processes.

    NASA Astrophysics Data System (ADS)

    Pauluis, Olivier; Held, Isaac M.

    2002-01-01

    In moist convection, atmospheric motions transport water vapor from the earth's surface to the regions where condensation occurs. This transport is associated with three other aspects of convection: the latent heat transport, the expansion work performed by water vapor, and the irreversible entropy production due to diffusion of water vapor and phase changes. An analysis of the thermodynamic transformations of atmospheric water yields what is referred to as the entropy budget of the water substance, providing a quantitative relationship between these three aspects of moist convection. The water vapor transport can be viewed as an imperfect heat engine that produces less mechanical work than the corresponding Carnot cycle because of diffusion of water vapor and irreversible phase changes.The entropy budget of the water substance provides an alternative method of determining the irreversible entropy production due to phase changes and diffusion of water vapor. This method has the advantage that it does not require explicit knowledge of the relative humidity or of the molecular flux of water vapor for the estimation of the entropy production. Scaling arguments show that the expansion work of water vapor accounts for a small fraction of the work that would be produced in the absence of irreversible moist processes. It is also shown that diffusion of water vapor and irreversible phase changes can be interpreted as the irreversible counterpart to the continuous dehumidification resulting from condensation and precipitation. This leads to a description of moist convection where it acts more as an atmospheric dehumidifier than as a heat engine.

  10. Transport Phenomena Projects: Natural Convection between Porous, Concentric Cylinders--A Method to Learn and to Innovate

    ERIC Educational Resources Information Center

    Saatadjian, Esteban; Lesage, Francois; Mota, Jose Paulo B.

    2013-01-01

    A project that involves the numerical simulation of transport phenomena is an excellent method to teach this subject to senior/graduate chemical engineering students. The subject presented here has been used in our senior/graduate course, it concerns the study of natural convection heat transfer between two concentric, horizontal, saturated porous…

  11. Influence of hydrodynamic slip on convective transport in flow past a circular cylinder

    NASA Astrophysics Data System (ADS)

    Rehman, Nidhil M. A.; Kumar, Anuj; Shukla, Ratnesh K.

    2017-02-01

    The presence of a finite tangential velocity on a hydrodynamically slipping surface is known to reduce vorticity production in bluff body flows substantially while at the same time enhancing its convection downstream and into the wake. Here, we investigate the effect of hydrodynamic slippage on the convective heat transfer (scalar transport) from a heated isothermal circular cylinder placed in a uniform cross-flow of an incompressible fluid through analytical and simulation techniques. At low Reynolds (Re≪ 1 ) and high Péclet (Pe≫ 1 ) numbers, our theoretical analysis based on Oseen and thermal boundary layer equations allows for an explicit determination of the dependence of the thermal transport on the non-dimensional slip length l_s . In this case, the surface-averaged Nusselt number, Nu transitions gradually between the asymptotic limits of Nu ˜ Pe^{1/3} and Nu ˜ Pe^{1/2} for no-slip (l_s → 0 ) and shear-free (l_s → ∞) boundaries, respectively. Boundary layer analysis also shows that the scaling Nu ˜ Pe^{1/2} holds for a shear-free cylinder surface in the asymptotic limit of Re≫ 1 so that the corresponding heat transfer rate becomes independent of the fluid viscosity. At finite Re, results from our two-dimensional simulations confirm the scaling Nu ˜ Pe^{1/2} for a shear-free boundary over the range 0.1 ≤ Re≤ 10^3 and 0.1≤ Pr≤ 10 . A gradual transition from the lower asymptotic limit corresponding to a no-slip surface, to the upper limit for a shear-free boundary, with l_s , is observed in both the maximum slip velocity and the Nu. The local time-averaged Nusselt number Nu_{θ } for a shear-free surface exceeds the one for a no-slip surface all along the cylinder boundary except over the downstream portion where unsteady separation and flow reversal lead to an appreciable rise in the local heat transfer rates, especially at high Re and Pr. At a Reynolds number of 10^3 , the formation of secondary recirculating eddy pairs results in

  12. Influence of hydrodynamic slip on convective transport in flow past a circular cylinder

    NASA Astrophysics Data System (ADS)

    Rehman, Nidhil M. A.; Kumar, Anuj; Shukla, Ratnesh K.

    2017-06-01

    The presence of a finite tangential velocity on a hydrodynamically slipping surface is known to reduce vorticity production in bluff body flows substantially while at the same time enhancing its convection downstream and into the wake. Here, we investigate the effect of hydrodynamic slippage on the convective heat transfer (scalar transport) from a heated isothermal circular cylinder placed in a uniform cross-flow of an incompressible fluid through analytical and simulation techniques. At low Reynolds (Re≪ 1) and high Péclet (Pe≫ 1) numbers, our theoretical analysis based on Oseen and thermal boundary layer equations allows for an explicit determination of the dependence of the thermal transport on the non-dimensional slip length l_s. In this case, the surface-averaged Nusselt number, Nu transitions gradually between the asymptotic limits of Nu ˜ Pe^{1/3} and Nu ˜ Pe^{1/2} for no-slip (l_s → 0) and shear-free (l_s → ∞) boundaries, respectively. Boundary layer analysis also shows that the scaling Nu ˜ Pe^{1/2} holds for a shear-free cylinder surface in the asymptotic limit of Re≫ 1 so that the corresponding heat transfer rate becomes independent of the fluid viscosity. At finite Re, results from our two-dimensional simulations confirm the scaling Nu ˜ Pe^{1/2} for a shear-free boundary over the range 0.1 ≤ Re ≤ 10^3 and 0.1≤ Pr ≤ 10. A gradual transition from the lower asymptotic limit corresponding to a no-slip surface, to the upper limit for a shear-free boundary, with l_s, is observed in both the maximum slip velocity and the Nu. The local time-averaged Nusselt number Nu_{θ } for a shear-free surface exceeds the one for a no-slip surface all along the cylinder boundary except over the downstream portion where unsteady separation and flow reversal lead to an appreciable rise in the local heat transfer rates, especially at high Re and Pr. At a Reynolds number of 10^3, the formation of secondary recirculating eddy pairs results in

  13. Optimization of intermittent microwave–convective drying using response surface methodology

    PubMed Central

    Aghilinategh, Nahid; Rafiee, Shahin; Hosseinpur, Soleiman; Omid, Mahmoud; Mohtasebi, Seyed Saeid

    2015-01-01

    In this study, response surface methodology was used for optimization of intermittent microwave–convective air drying (IMWC) parameters with employing desirability function. Optimization factors were air temperature (40–80°C), air velocity (1–2 m/sec), pulse ratio) PR ((2–6), and microwave power (200–600 W) while responses were rehydration ratio, bulk density, total phenol content (TPC), color change, and energy consumption. Minimum color change, bulk density, energy consumption, maximum rehydration ratio, and TPC were assumed as criteria for optimizing drying conditions of apple slices in IMWC. The optimum values of process variables were 1.78 m/sec air velocity, 40°C air temperature, PR 4.48, and 600 W microwave power that characterized by maximum desirability function (0.792) using Design expert 8.0. The air temperature and microwave power had significant effect on total responses, but the role of air velocity can be ignored. Generally, the results indicated that it was possible to obtain a higher desirability value if the microwave power and temperature, respectively, increase and decrease. PMID:26286706

  14. Convective Transport Theory for Surface Fluxes Tested over the Western Pacific Warm Pool.

    NASA Astrophysics Data System (ADS)

    Greischar, Lawrence; Stull, Roland

    1999-07-01

    Turbulent flux measurements from five flights of the National Center for Atmospheric Research Electra aircraft during the Tropical Oceans and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) are used to test convective transport theory (CTT) for a marine boundary layer. Flights during light to moderate winds and under the clearest sky conditions available were chosen. Fluxes of heat, moisture, and momentum were observed by the eddy-correlation method. Mean kinematic values for the observed sensible and latent heat fluxes and momentum flux were 0.0061 K m s1, 0.0313 g kg1 m s1, and 0.0195 m2 s2, respectively.For the range of mixed-layer wind speeds (0.8-8.4 m s1) studied here, the version of CTT that includes the mixed effects of buoyant and shear-driven transport give a better fit to the observations than either the COARE bulk algorithm or the pure free-convection version of CTT. This is to be expected because both of those latter parameterizations were designed for light winds (<5 m s1 approximately).The CTT empirical coefficients listed in Table 3 exhibited slight sensitivity to the COARE light flux conditions, compared to their previous estimates during larger fluxes over land. For example, COARE heat fluxes were roughly 10 times smaller than previous land-based flux measurements used to calculate CTT coefficients, but the corresponding empirical mixed-layer transport coefficients were only 3% smaller. COARE momentum fluxes were also roughly 10 times smaller, but the CTT coefficients were about four times smaller. The greater variation in momentum coefficient may be due, in part, to insufficient flight-leg length used to compute momentum fluxes, to uncertainties in the effects of the ocean surface current and waves, or perhaps to roughness differences.

  15. Mass transport studies in conventional and microfabricated free convection proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Modroukas, Dean

    This thesis presents the design, modeling and testing of both conventional and non-conventional free convection proton exchange membrane fuel cells (PEMFC) which are particularly attractive for low power (<100W), man portable applications. As part of this investigation, experimental data coupled with computational simulations has provided a deeper understanding into the mechanisms that limit operability. In particular, the low temperatures of operation (<50°C) and lack of forced air convection generate high levels of saturation within the cell thereby reducing the available catalytic sites. A 2-D, single- and two-phase computational model for an open-cathode, free convection PEMFC was developed. The two-phase modeling has provided significant insight into the mass transport limitations caused primarily by liquid water flooding while the single phase simulations present an upper limit in performance assuming product water exists only in vapor form. A set of parametric experiments were performed using conventional gas diffusion media (GDM) along with numerous 1cm2 stainless steel grid-based current collectors having open area ratios of 10%, 25% and 50%. These experiments provided a data set that was used to "tune" and validate the model. Single cell polarization data experienced limiting currents ranging from 190mA/cm2 to 600mA/cm 2 at operating cell temperatures of 38°C-45°C, depending on the open area ratio. The two-phase model captured the effect of current collector porosity as well as the increase in limiting current associated with rising cell temperature. Once validated, the model was used with confidence as a design tool for MEMS-based tailored mass transfer media (TMTM) that provide more advanced functionality than customary GDM. They were based on a microfabricated hydrophobic silicon mesh comprised of square pores with discrete zones made to be hydrophilic using a carbon-polyethylene oxide treatment. The TMTM were engineered to localize the removal of

  16. Observations of cross-Saharan transport of water vapour via cycle of cold pools and moist convection

    NASA Astrophysics Data System (ADS)

    Trzeciak, Tomasz; Garcia-Carreras, Luis; Marsham, John H.

    2017-04-01

    Very limited observational data has previously limited our ability to study meteorological processes in the Sahara. The Sahara is a key component of the West African monsoon and the world's largest dust source, but its representation is a major uncertainty in global models. Past studies have shown that there is a persistent warm and dry model bias throughout the Sahara, and this has been attributed to the lack of convectively-generated cold pools in the model, which can ventilate the central Sahara from its margins. Here we present an observed case from June 2012 which explains how cold pools are able to transport water vapour across a large area of the Sahara over a period of several days. A daily cycle is found to occur, where deep convection in the evening generates moist cold pools that then feed the next day's convection; the new convection in turn generates new cold pools, providing a vertical recycling of moisture. Trajectories driven by analyses can capture the general direction of transport, but not its full extent, especially at night when cold pools are most active, highlighting the difficulties for models to capture these processes. These results show the importance of cold pools for moisture transport, dust and clouds in the region, and demonstrate the need to include these processes in models to improve the representation of the Saharan atmosphere.

  17. Optimal and robust control and estimation of transition, convection, and turbulence

    NASA Astrophysics Data System (ADS)

    Bewley, Thomas Robinson

    The large increases in drag, cyclic structural loading, internal stresses, mixing, and heat transfer caused by turbulence in flows of engineering interest have motivated engineers to study turbulence and attempt to alter its effects. Recent advances in MEMS capabilities may soon make it possible to measure small-scale turbulent fluctuations of a flow and, subsequently, to apply coordinated small-scale forcing to the flow in order to achieve a desired large-scale effect. The present work attempts to develop techniques to derive the necessary control strategies for such control problems from first principles, leveraging our knowledge of the Navier-Stokes equation which governs these flows and our ability to simulate this equation accurately in simple configurations. By so doing, we bypass the ad hoc assumptions about the turbulence dynamics often used to determine such control strategies and develop several new tools for analysis of flow systems in the control setting. Approaching this difficult problem in steps of gradually increasing complexity, optimal and robust control theories are used in the present work to derive and demonstrate effective control and estimation strategies for three important model problems in fluid mechanics. The model problems considered are: (1)the application of linear optimal/robust control theory to the linear paths to transition in a plane channel, (2)the application of linear optimal/robust control theory to a low-order nonlinear chaotic convection problem, and (3)the application of optimal control theory in a DNS-based predictive control setting to the fully nonlinear problem of turbulence. In order to develop feedback algorithms for practical (disturbed) environments, it is recognized that a degree of robustness will be necessary in the control rules. In the final section of this work, a general framework for robust control for problems governed by the Navier-Stokes equation is established by mathematical analysis, laying the

  18. Particle swarm optimization - Genetic algorithm (PSOGA) on linear transportation problem

    NASA Astrophysics Data System (ADS)

    Rahmalia, Dinita

    2017-08-01

    Linear Transportation Problem (LTP) is the case of constrained optimization where we want to minimize cost subject to the balance of the number of supply and the number of demand. The exact method such as northwest corner, vogel, russel, minimal cost have been applied at approaching optimal solution. In this paper, we use heurisitic like Particle Swarm Optimization (PSO) for solving linear transportation problem at any size of decision variable. In addition, we combine mutation operator of Genetic Algorithm (GA) at PSO to improve optimal solution. This method is called Particle Swarm Optimization - Genetic Algorithm (PSOGA). The simulations show that PSOGA can improve optimal solution resulted by PSO.

  19. Heuristic Optimization Approach to Selecting a Transport Connection in City Public Transport

    NASA Astrophysics Data System (ADS)

    Kul'ka, Jozef; Mantič, Martin; Kopas, Melichar; Faltinová, Eva; Kachman, Daniel

    2017-02-01

    The article presents a heuristic optimization approach to select a suitable transport connection in the framework of a city public transport. This methodology was applied on a part of the public transport in Košice, because it is the second largest city in the Slovak Republic and its network of the public transport creates a complex transport system, which consists of three different transport modes, namely from the bus transport, tram transport and trolley-bus transport. This solution focused on examining the individual transport services and their interconnection in relevant interchange points.

  20. Improving Representation of Convective Transport for Scale-Aware Parameterization, Part II: Analysis of Cloud-Resolving Model Simulations

    SciTech Connect

    Liu, Yi-Chin; Fan, Jiwen; Zhang, Guang J.; Xu, Kuan-Man; Ghan, Steven J.

    2015-04-27

    Following Part I, in which 3-D cloud-resolving model (CRM) simulations of a squall line and mesoscale convective complex in the mid-latitude continental and the tropical regions are conducted and evaluated, we examine the scale-dependence of eddy transport of water vapor, evaluate different eddy transport formulations, and improve the representation of convective transport across all scales by proposing a new formulation that more accurately represents the CRM-calculated eddy flux. CRM results show that there are strong grid-spacing dependencies of updraft and downdraft fractions regardless of altitudes, cloud life stage, and geographical location. As for the eddy transport of water vapor, updraft eddy flux is a major contributor to total eddy flux in the lower and middle troposphere. However, downdraft eddy transport can be as large as updraft eddy transport in the lower atmosphere especially at the mature stage of 38 mid-latitude continental convection. We show that the single updraft approach significantly underestimates updraft eddy transport of water vapor because it fails to account for the large internal variability of updrafts, while a single downdraft represents the downdraft eddy transport of water vapor well. We find that using as few as 3 updrafts can account for the internal variability of updrafts well. Based on evaluation with the CRM simulated data, we recommend a simplified eddy transport formulation that considers three updrafts and one downdraft. Such formulation is similar to the conventional one but much more accurately represents CRM-simulated eddy flux across all grid scales.

  1. Resolution-dependent behavior of subgrid-scale vertical transport in the Zhang-McFarlane convection parameterization

    NASA Astrophysics Data System (ADS)

    Xiao, Heng; Gustafson, William I.; Hagos, Samson M.; Wu, Chien-Ming; Wan, Hui

    2015-06-01

    To better understand the behavior of quasi-equilibrium-based convection parameterizations at higher resolution, we use a diagnostic framework to examine the resolution-dependence of subgrid-scale vertical transport of moist static energy as parameterized by the Zhang-McFarlane convection parameterization (ZM). Grid-scale input to ZM is supplied by coarsening output from cloud-resolving model (CRM) simulations onto subdomains ranging in size from 8 × 8 to 256 × 256 km2. Then the ZM-based parameterization of vertical transport of moist static energy for scales smaller than the subdomain size (w'h'>¯ZM) are compared to those directly calculated from the CRM simulations (w'h'>¯CRM) for different subdomain sizes. The ensemble mean w'h'>¯CRM decreases by more than half as the subdomain size decreases from 128 to 8 km across while w'h'>¯ZM decreases with subdomain size only for strong convection cases and increases for weaker cases. The resolution dependence of w'h'>¯ZM is determined by the positive-definite grid-scale tendency of convective available potential energy (CAPE) in the convective quasi-equilibrium (QE) closure. Further analysis shows the actual grid-scale tendency of CAPE (before taking the positive definite value) and w'h'>¯CRM behave very similarly as the subdomain size changes because they are both tied to grid-scale advective tendencies. We can improve the resolution dependence of w'h'>¯ZM significantly by averaging the grid-scale tendency of CAPE over an appropriately large area surrounding each subdomain before taking its positive definite value. Even though the ensemble mean w'h'>¯CRM decreases with increasing resolution, its variability increases dramatically. w'h'>¯ZM cannot capture such increase in the variability, suggesting the need for stochastic treatment of convection at relatively high spatial resolution (8 or 16 km).

  2. Optimization of municipal solid waste collection and transportation routes

    SciTech Connect

    Das, Swapan Bhattacharyya, Bidyut Kr.

    2015-09-15

    Graphical abstract: Display Omitted - Highlights: • Profitable integrated solid waste management system. • Optimal municipal waste collection scheme between the sources and waste collection centres. • Optimal path calculation between waste collection centres and transfer stations. • Optimal waste routing between the transfer stations and processing plants. - Abstract: Optimization of municipal solid waste (MSW) collection and transportation through source separation becomes one of the major concerns in the MSW management system design, due to the fact that the existing MSW management systems suffer by the high collection and transportation cost. Generally, in a city different waste sources scatter throughout the city in heterogeneous way that increase waste collection and transportation cost in the waste management system. Therefore, a shortest waste collection and transportation strategy can effectively reduce waste collection and transportation cost. In this paper, we propose an optimal MSW collection and transportation scheme that focus on the problem of minimizing the length of each waste collection and transportation route. We first formulize the MSW collection and transportation problem into a mixed integer program. Moreover, we propose a heuristic solution for the waste collection and transportation problem that can provide an optimal way for waste collection and transportation. Extensive simulations and real testbed results show that the proposed solution can significantly improve the MSW performance. Results show that the proposed scheme is able to reduce more than 30% of the total waste collection path length.

  3. Rapid Transport of Carbon Monoxide and Water Vapor from Troposphere to Stratosphere via Tropical Convection During Stratospheric Sudden Warming

    NASA Astrophysics Data System (ADS)

    Eguchi, N.; Kodera, K.; Ueyama, R.; Takashima, H.; Deushi, M.

    2015-12-01

    A potential transport mechanism of various tracers from the tropical troposphere to the lower stratosphere (LS) across the tropical tropopause layer (TTL) is the overshooting convective clouds which inject air with tropospheric characteristics (high carbon monoxide (CO), high water vapor (H2O), low ozone (O3) into the LS over a period of a few days. Evidence of such convective intrusions is observed at the end of January and beginning of February in 2010 associated with increased convective activity over the southern African continent following the onset of stratospheric sudden warming (SSW) event. The modulation of tropical upwelling by SSW appears to force stronger and deeper tropical convection, particularly in the Southern Hemisphere (SH) tropics. The simulation analysis with fine vertical resolution also showed that deep convection especially in the SH became stronger during the SSW event because the upwelling associated with SSW destabilized the TTL [Eguchi et al., ACP, 2015]. The January 2010 SSW event induced the lowest recorded LS temperature in MLS history (2004-13), which destabilized the TTL allowing an unprecedented clear detection of stratosphere-troposphere exchange process by way of CO, H2O and O3 intrusions. The present study suggests that short duration, overshooting clouds can have a large impact on the zonally averaged fields of LS composition.

  4. A multi-resolution approach for optimal mass transport

    NASA Astrophysics Data System (ADS)

    Dominitz, Ayelet; Angenent, Sigurd; Tannenbaum, Allen

    2007-09-01

    Optimal mass transport is an important technique with numerous applications in econometrics, fluid dynamics, automatic control, statistical physics, shape optimization, expert systems, and meteorology. Motivated by certain problems in image registration and medical image visualization, in this note, we describe a simple gradient descent methodology for computing the optimal L2 transport mapping which may be easily implemented using a multiresolution scheme. We also indicate how the optimal transport map may be computed on the sphere. A numerical example is presented illustrating our ideas.

  5. A Planning Problem Combining Calculus of Variations and Optimal Transport

    SciTech Connect

    Carlier, G. Lachapelle, A.

    2011-02-15

    We consider some variants of the classical optimal transport where not only one optimizes over couplings between some variables x and y but also over some control variables governing the evolutions of these variables with time. Such a situation is motivated by an assignment problem of tasks with workers whose characteristics can evolve with time (and be controlled). We distinguish between the coupled and decoupled case. The coupled case is a standard optimal transport with the value of some optimal control problem as cost. The decoupled case is more involved since it is nonlinear in the transport plan.

  6. Aqueous gradient by balancing diffusive and convective mass transport (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Habhab, Mohammed-Baker I.; Ismail, Tania; Lo, Joe F.; Haque, Arefa

    2016-03-01

    In wounds, cells secret biomolecules such as vascular endothelial growth factor (VEGF), a protein that controls many processes in healing. VEGF protein is expressed in a gradient in tissue, and its shape will be affected by the tissue injury sustained during wounding. In order to study the responses of keratinocyte cell migration to VEGF gradients and the geometric factors on wound healing, we designed a microfluidic gradient device that can generate large area gradients (1.5 cm in diameter) capable of mimicking arbitrary wound shapes. Microfluidic devices offer novel techniques to address biological and biomedical issues. Different from other gradient microfluidics, our device balances diffusion of biomolecules versus the convective clearance by a buffer flow on the opposite ends of the gradient. This allows us to create a large area gradient within shorter time scales by actively driving mass transport. In addition, the microfluidic device makes use of a porous filter membrane to create this balance as well as to deliver the resulting gradient to a culture of cells. The culture of cells are seeded above the gradient in a gasket chamber. However, Keratinocytes do not migrate effectively on filter paper. Therefore, in order to improve the motility of cells on the surface, we coated the filter paper with a 30m thick layer of gelatin type B. after observation under the microscope we found that the gelatin coated sample showed cells with more spread out morphology, with 97% viability, suggesting better adhesion than the non-coated sample.

  7. Global heat transport scaling in plume-controlled regime in turbulent Rayleigh-Bénard convection

    NASA Astrophysics Data System (ADS)

    Chong, Kai Leong; Huang, Shi-Di; Xia, Ke-Qing

    2016-11-01

    Previous study by Chong et al. has introduced a normalized aspect-ratio Γ /Γopt (Γopt = 29 . 37 Ra - 0 . 31) where the plume coverage at fixed Γ /Γopt is invariant with respect to Ra in the so-called plume-controlled regime in Rayleigh-Bénard convection. We have studied the global heat transport scaling (expressed as Nusselt number Nu) at fixed Γ /Γopt with the Rayleigh number Ra between 107 and 1010 at fixed Prandtl number Pr = 4 . 38 by direct numerical simulations. It is found that at Γ /Γopt = 1 where the thermal plume becomes highly coherent and system-sized, Nu exhibits the scaling Nu - 1 Ra 0 . 327 +/- 0 . 001 over three decades of Ra . This scaling is different from that found at Γ = 1 for which Nu - 1 Ra 0 . 308 +/- 0 . 001 , and this difference in scaling can be shown evidently in the compensated plots. This work was supported by RGC of HKSAR (No. CUHK404513), CUHK Direct Grant (No. 3132740) and through a HKPhD Fellowship.

  8. Non-dispersive carrier transport in molecularly doped polymers and the convection-diffusion equation

    NASA Astrophysics Data System (ADS)

    Tyutnev, A. P.; Parris, P. E.; Saenko, V. S.

    2015-08-01

    We reinvestigate the applicability of the concept of trap-free carrier transport in molecularly doped polymers and the possibility of realistically describing time-of-flight (TOF) current transients in these materials using the classical convection-diffusion equation (CDE). The problem is treated as rigorously as possible using boundary conditions appropriate to conventional time of flight experiments. Two types of pulsed carrier generation are considered. In addition to the traditional case of surface excitation, we also consider the case where carrier generation is spatially uniform. In our analysis, the front electrode is treated as a reflecting boundary, while the counter electrode is assumed to act either as a neutral contact (not disturbing the current flow) or as an absorbing boundary at which the carrier concentration vanishes. As expected, at low fields transient currents exhibit unusual behavior, as diffusion currents overwhelm drift currents to such an extent that it becomes impossible to determine transit times (and hence, carrier mobilities). At high fields, computed transients are more like those typically observed, with well-defined plateaus and sharp transit times. Careful analysis, however, reveals that the non-dispersive picture, and predictions of the CDE contradict both experiment and existing disorder-based theories in important ways, and that the CDE should be applied rather cautiously, and even then only for engineering purposes.

  9. Pattern formation by boundary forcing in convectively unstable, oscillatory media with and without differential transport.

    PubMed

    McGraw, Patrick N; Menzinger, Michael

    2005-08-01

    Convectively unstable, open reactive flows of oscillatory media, whose phase is fixed or periodically modulated at the inflow boundary, are known to result in stationary and traveling waves, respectively. The latter are implicated in biological segmentation. The boundary-controlled pattern selection by this flow-distributed oscillator (FDO) mechanism has been generalized to include differential flow (DIFI) and differential diffusion (Turing) modes. Our present goal is to clarify the relationships among these mechanisms in the general case where there is differential flow as well as differential diffusion. To do so we analyze the dispersion relation for linear perturbations in the presence of periodic boundary forcing, and show how the solutions are affected by differential transport. We find that the DIFI and FDO modes are closely related and lie in the same frequency range, while the Turing mechanism gives rise to a distinct set of unstable modes in a separate frequency range. Finally, we substantiate the linear analysis by nonlinear simulations and touch upon the issue of competition of spatial modes.

  10. Heat-transport enhancement in rotating turbulent Rayleigh-Bénard convection.

    PubMed

    Weiss, Stephan; Wei, Ping; Ahlers, Guenter

    2016-04-01

    We present new Nusselt-number (Nu) measurements for slowly rotating turbulent thermal convection in cylindrical samples with aspect ratio Γ=1.00 and provide a comprehensive correlation of all available data for that Γ. In the experiment compressed gasses (nitrogen and sulfur hexafluride) as well as the fluorocarbon C_{6}F_{14} (3M Fluorinert FC72) and isopropanol were used as the convecting fluids. The data span the Prandtl-number (Pr) range 0.74transport Nu_{r}(1/Ro)≡Nu(1/Ro)/Nu(0) as a function of the dimensionless inverse Rossby number 1/Ro at constant Ra is reported. For Pr≈0.74 and the smallest Ra=3.6×10^{8} the maximum enhancement Nu_{r,max}-1 due to rotation is about 0.02. With increasing Ra, Nu_{r,max}-1 decreased further, and for Ra≳2×10^{9} heat-transport enhancement was no longer observed. For larger Pr the dependence of Nu_{r} on 1/Ro is qualitatively similar for all Pr. As noted before, there is a very small increase of Nu_{r} for small 1/Ro, followed by a decrease by a percent or so, before, at a critical value 1/Ro_{c}, a sharp transition to enhancement by Ekman pumping takes place. While the data revealed no dependence of 1/Ro_{c} on Ra, 1/Ro_{c} decreased with increasing Pr. This dependence could be described by a power law with an exponent α≃-0.41. Power-law dependencies on Pr and Ra could be used to describe the slope S_{Ro}^{+}=∂Nu_{r}/∂(1/Ro) just above 1/Ro_{c}. The Pr and Ra exponents were β_{1}=-0.16±0.08 and β_{2}=-0.04±0.06, respectively. Further increase of 1/Ro led to further increase of Nu_{r} until it reached a maximum value Nu_{r,max}. Beyond the maximum, the Taylor-Proudman (TP) effect, which is expected to lead to reduced vertical fluid transport in the bulk region, lowered Nu_{r}. Nu_{r,max} was largest for the largest Pr. For Pr=28.9, for example, we measured an increase of the heat transport by up to 40% (Nu_{r}-1

  11. Heat-transport enhancement in rotating turbulent Rayleigh-Bénard convection

    NASA Astrophysics Data System (ADS)

    Weiss, Stephan; Wei, Ping; Ahlers, Guenter

    2016-04-01

    We present new Nusselt-number (Nu) measurements for slowly rotating turbulent thermal convection in cylindrical samples with aspect ratio Γ =1.00 and provide a comprehensive correlation of all available data for that Γ . In the experiment compressed gasses (nitrogen and sulfur hexafluride) as well as the fluorocarbon C6F14 (3M Fluorinert FC72) and isopropanol were used as the convecting fluids. The data span the Prandtl-number (Pr) range 0.74 transport Nur(1 /Ro ) ≡Nu (1 /Ro ) /Nu (0 ) as a function of the dimensionless inverse Rossby number 1 /Ro at constant Ra is reported. For Pr ≈0.74 and the smallest Ra =3.6 ×108 the maximum enhancement Nur ,max-1 due to rotation is about 0.02. With increasing Ra, Nur ,max-1 decreased further, and for Ra ≳2 ×109 heat-transport enhancement was no longer observed. For larger Pr the dependence of Nur on 1/Ro is qualitatively similar for all Pr. As noted before, there is a very small increase of Nur for small 1/Ro, followed by a decrease by a percent or so, before, at a critical value 1 /Roc , a sharp transition to enhancement by Ekman pumping takes place. While the data revealed no dependence of 1 /Roc on Ra, 1 /Roc decreased with increasing Pr. This dependence could be described by a power law with an exponent α ≃-0.41 . Power-law dependencies on Pr and Ra could be used to describe the slope SRo+=∂ Nur/∂ (1 /Ro ) just above 1 /Roc . The Pr and Ra exponents were β1=-0.16 ±0.08 and β2=-0.04 ±0.06 , respectively. Further increase of 1/Ro led to further increase of Nur until it reached a maximum value Nur ,max. Beyond the maximum, the Taylor-Proudman (TP) effect, which is expected to lead to reduced vertical fluid transport in the bulk region, lowered Nur. Nur ,max was largest for the largest Pr. For Pr =28.9 , for example, we measured an increase of the heat transport by up to 40% (Nur-1 =0.40 ) for the smallest Ra =2.2

  12. Convective and Diffusive O2 Transport Components of Peak Oxygen Uptake Following Long-duration Spaceflight

    NASA Technical Reports Server (NTRS)

    Ade, Carl J.; Moore, A. D.

    2014-01-01

    Spaceflight reduces aerobic capacity and may be linked with maladaptations in the O2 transport pathway. The aim was to 1) evaluate the cardiorespiratory adaptations following 6 months aboard the International Space Station and 2) model the contributions of convective (Q (raised dot) O2) and peripheral diffusive (DO2) components of O2 transport to changes in peak O2 uptake (V (raised dot) O2PEAK). To date, 1 male astronaut (XX yrs) completed an incremental exercise test to measure V (raised dot) O2PEAK prior to and 2 days post-flight. Cardiac output (Q (raised dot) ) was measured at three submaximal work rates via carbon dioxide rebreathing. The Q (raised dot) :V (raised dot) O2 relationship was extrapolated to V (raised dot) O2PEAK to determine Q (raised dot) PEAK. Hemoglobin concentration was measured at rest via a venous blood sample. These measurements were used to model the changes in Q (raised dot) O2 and DO2 using Fick's principle of mass conservation and Law of Diffusion as established by Wagner and colleagues (Annu. Rev. Physiol 58: 21-50, 1996 and J. Appl. Physiol. 73: 1067-1076, 1992). V (raised dot) O2PEAK decreased postflight from 3.72 to 3.45 l min-1, but Q (raised dot) PEAK increased from 24.5 to 27.7 l min-1. The decrease in V (raised dot) O2PEAK post-flight was associated with a 21.2% decrease in DO2, an 18.6% decrease in O2 extraction, but a 3.4% increase in Q (raised dot) O2. These preliminary data suggest that long-duration spaceflight reduces peripheral diffusing capacity and that it largely contributes to the post-flight decrease in aerobic capacity.

  13. Microphysics of mass-transport in coupled droplet-pairs at low Reynolds number and the role of convective dynamics

    NASA Astrophysics Data System (ADS)

    Dong, Qingming; Sau, Amalendu

    2016-06-01

    Interfacial mass-transport and redistribution in the micro-scale liquid droplets are important in diverse fields of research interest. The role of the "inflow" and the "outflow" type convective eddy-pairs in the entrainment of outer solute and internal relocation are examined for different homogeneous and heterogeneous water droplet pairs appearing in a tandem arrangement. Two micro-droplets of pure (rain) water interact with an oncoming outer air stream (Re ≤ 100) contaminated by uniformly distributed SO2. By virtue of separation/attachment induced non-uniform interfacial shear-stress gradient, the well-defined inflow/outflow type pairs of recirculating eddy-based convective motion quickly develops, and the eddies effectively attract/repel the accumulated outer solute and control the physical process of mass-transport in the droplet-pair. The non-uniformly shear-driven flow interaction and bifurcation of the circulatory internal flow lead to growth of important micro-scale "secondary" eddies which suitably regroup with the adjacent "primary" one to create the sustained inflow/outflow type convective dynamics. The presently derived flow characteristics and in-depth analysis help to significantly improve our understanding of the micro-droplet based transport phenomena in a wider context. By tuning "Re" (defined in terms of the droplet diameter and the average oncoming velocity of the outer air) and gap-ratio "α," the internal convective forcing and the solute entrainment efficiency could be considerably enhanced. The quantitative estimates for mass entrainment, convective strength, and saturation characteristics for different coupled micro-droplet pairs are extensively examined here for 0.2 ≤ α ≤ 2.0 and 30 ≤ Re ≤ 100. Interestingly, for the compound droplets, with suitably tuned radius-ratio "B" (of upstream droplet with respect to downstream one) the generated "inflow" type coherent convective dynamics helped to significantly augment the centre

  14. Heat transport and dynamics of the large-scale circulation of turbulent Rayleigh-Benard convection

    NASA Astrophysics Data System (ADS)

    Brown, Eric

    Experimental studies of turbulent Rayleigh-Benard convection in cylindrical water-filled containers of equal height and diameter, with an applied vertical temperature difference DeltaT are presented. High-precision measurements of the heat flux Q were shown to agree with the Grossman-Lohse (GL) scaling model of thermal convection for small DeltaT, but for large DeltaT a regime was reached where Q ∝ DeltaT 1/3 in disagreement with the GL model. A prediction that the heat transport in the fluid would be reduced for endplates with finite conductivity was confirmed by switching out plates with different thermal conductivities. The effect of the spatial variation of fluid properties with temperature was measured by comparing experiments in samples of different sizes with the same dimensionless control parameters but different DeltaT. Thermistors on the sidewall were used to measure various aspects of the large-scale circulation (LSC). The turnover and an azimuthally twisting oscillatory mode were found to have the same frequency for small DeltaT which agrees with the GL model, but the frequencies were found to differ from each other and from the GL model for large DeltaT. The azimuthal orientation theta0(t) of the LSC was found to meander in time as a diffusive process over long time scales. In addition it contained spontaneous events in which the orientation changed by a large angle Deltatheta, either by a rotation of the circulation plane, or by a cessation of the circulation followed by a restart in a randomly chosen direction as seen by the uniform probability distribution p(Deltatheta). Rotations occurred with a monotonically decreasing p(Deltatheta). The distribution of rotations and cessations in time followed Poissonian statistics. Also presented is a model of the dynamics of the LSC consisting of a pair of stochastic differential equations motivated by the Navier-Stokes equations. The equations have terms representing buoyancy, drag, and angular momentum of

  15. Anomalous convection diffusion and wave coupling transport of cells on comb frame with fractional Cattaneo-Christov flux

    NASA Astrophysics Data System (ADS)

    Liu, Lin; Zheng, Liancun; Liu, Fawang; Zhang, Xinxin

    2016-09-01

    An improved Cattaneo-Christov flux model is proposed which can be used to capture the effects of the time and spatial relaxations, the time and spatial inhomogeneous diffusion and the spatial transition probability of cell transport in a highly non-homogeneous medium. Solutions are obtained by numerical discretization method where the time and spatial fractional derivative are discretized by the L1-approximation and shifted Grünwald definition, respectively. The solvability, stability and convergence of the numerical method for the special case of the Cattaneo-Christov equation are proved. Results indicate that the fractional convection diffusion-wave equation is an evolution equation which displays the coexisting characteristics of parabolicity and hyperbolicity. In other words, for α in (0, 1), the cells transport occupies the characteristics of coupling convection diffusion and wave spreading. Moreover, the effects of pertinent time parameter, time and spatial fractional derivative parameters, relaxation parameter, weight coefficient and the convection velocity on the anomalous transport of cells are shown graphically and analyzed in detail.

  16. Investigating convective transport processes and large scale stratospheric dynamics with ICON-ART

    NASA Astrophysics Data System (ADS)

    Stassen, Christian; Ruhnke, Roland; Schröter, Jennifer; Daniel, Rieger; Bischoff-Gauss, Ingeborg; Vogel, Heike; Vogel, Bernhard

    2015-04-01

    We have extended the global ICON (ICOsahedral Nonhydrostatic) modelling framework. ICON is a joint development by the German Weather Service (DWD) and the Max-Planck-Institute for Meteorology (MPI-M). We added modules for gas-phase chemistry and aerosol dynamics (ART, Aerosols and Reactive Trace gases) [1]. ICON allows a regional grid refinement with two-way interactions between the different horizontal grids. It is used by DWD for numerical weather predictions and will be used by MPI-M for climate projections [2]. The extended modelling framework ICON-ART is developed in an analogous way to its predecessors COSMO-ART [3], so that aerosol and chemical composition feedbacks can be considered in a comprehensive way. Up to now, ICON-ART accounts for volcanic ash tracers, radioactive tracers, sea salt and mineral dust aerosols. Additionally, several gaseous tracers have been introduced. For the dynamics (transport and diffusion) of aerosol and gaseous tracers, the original ICON tracer framework is used. For the model physics, numerical time integration follows a process splitting approach separating physical processes. Each process is called independently via an interface module. Currently, the processes of emission, dry and wet deposition, sedimentation, and first order chemical reactions are included. We will present a simulation of the transport of ozone depleting short-lived trace gases from the surface into the stratosphere as well as of long-lived tracers. The simulated tracer distributions are used to investigate the ability of ICON-ART to simulate convective vertical transport in the troposphere as well as of large-scale stratospheric dynamics. [1] Rieger, D., et al. (2014), ICON-ART - A new online-coupled model system from the global to regional scale, submitted to Geosci. Model Dev. [2] Zängl, G., et al. (2014), The ICON (ICOsahedral Non-hydrostatic) modelling framework of DWD MPI-M: Description of the non-hydrostatic dynamical core. Q.J.R. Meteorol. Soc

  17. Optimal trajectories for efficient atomic transport without final excitation

    SciTech Connect

    Chen Xi; Torrontegui, E.; Muga, J. G.; Stefanatos, Dionisis; Li, Jr-Shin

    2011-10-15

    We design optimal harmonic-trap trajectories to transport cold atoms without final excitation, combining an inverse engineering technique based on Lewis-Riesenfeld invariants with optimal control theory. Since actual traps are not really harmonic, we keep the relative displacement between the center of mass of the transport modes and the trap center bounded. Under this constraint, optimal protocols are found according to different physical criteria. The minimum time solution has a ''bang-bang'' form, and the minimum displacement solution is of ''bang-off-bang'' form. The optimal trajectories for minimizing the transient energy are also discussed.

  18. Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores

    NASA Astrophysics Data System (ADS)

    Guervilly, C.; Cardin, P.

    2017-10-01

    We study rapidly rotating Boussinesq convection driven by internal heating in a full sphere. We use a numerical model based on the quasi-geostrophic approximation for the velocity field, whereas the temperature field is 3-D. This approximation allows us to perform simulations for Ekman numbers down to 10-8, Prandtl numbers relevant for liquid metals (˜10-1) and Reynolds numbers up to 3 × 104. Persistent zonal flows composed of multiple jets form as a result of the mixing of potential vorticity. For the largest Rayleigh numbers computed, the zonal velocity is larger than the convective velocity despite the presence of boundary friction. The convective structures and the zonal jets widen when the thermal forcing increases. Prograde and retrograde zonal jets are dynamically different: in the prograde jets (which correspond to weak potential vorticity gradients) the convection transports heat efficiently and the mean temperature tends to be homogenized; by contrast, in the cores of the retrograde jets (which correspond to steep gradients of potential vorticity) the dynamics is dominated by the propagation of Rossby waves, resulting in the formation of steep mean temperature gradients and the dominance of conduction in the heat transfer process. Consequently, in quasi-geostrophic systems, the width of the retrograde zonal jets controls the efficiency of the heat transfer.

  19. Confined Rayleigh-Bénard, Rotating Rayleigh-Bénard, and Double Diffusive Convection: A Unifying View on Turbulent Transport Enhancement through Coherent Structure Manipulation

    NASA Astrophysics Data System (ADS)

    Chong, Kai Leong; Yang, Yantao; Huang, Shi-Di; Zhong, Jin-Qiang; Stevens, Richard J. A. M.; Verzicco, Roberto; Lohse, Detlef; Xia, Ke-Qing

    2017-08-01

    Many natural and engineering systems are simultaneously subjected to a driving force and a stabilizing force. The interplay between the two forces, especially for highly nonlinear systems such as fluid flow, often results in surprising features. Here we reveal such features in three different types of Rayleigh-Bénard (RB) convection, i.e., buoyancy-driven flow with the fluid density being affected by a scalar field. In the three cases different stabilizing forces are considered, namely (i) horizontal confinement, (ii) rotation around a vertical axis, and (iii) a second stabilizing scalar field. Despite the very different nature of the stabilizing forces and the corresponding equations of motion, at moderate strength we counterintuitively but consistently observe an enhancement in the flux, even though the flow motion is weaker than the original RB flow. The flux enhancement occurs in an intermediate regime in which the stabilizing force is strong enough to alter the flow structures in the bulk to a more organized morphology, yet not too strong to severely suppress the flow motions. Near the optimal transport enhancements all three systems exhibit a transition from a state in which the thermal boundary layer (BL) is nested inside the momentum BL to the one with the thermal BL being thicker than the momentum BL. The observed optimal transport enhancement is explained through an optimal coupling between the suction of hot or fresh fluid and the corresponding scalar fluctuations.

  20. The Effect of Online Hemodiafiltration on Infections: Results from the CONvective TRAnsport STudy

    PubMed Central

    den Hoedt, Claire H.; Grooteman, Muriel P. C.; Bots, Michiel L.; Blankestijn, Peter J.; van der Tweel, Ingeborg; van der Weerd, Neelke C.; Penne, E. Lars; Mazairac, Albert H. A.; Levesque, Renée; ter Wee, Piet M.; Nubé, Menso J.; van den Dorpel, Marinus A.

    2015-01-01

    Background Hemodialysis (HD) patients have a high risk of infections. The uremic milieu has a negative impact on several immune responses. Online hemodiafiltration (HDF) may reduce the risk of infections by ameliorating the uremic milieu through enhanced clearance of middle molecules. Since there are few data on infectious outcomes in HDF, we compared the effects of HDF with low-flux HD on the incidence and type of infections. Patients and Methods We used data of the 714 HD patients (age 64 ±14, 62% men, 25% Diabetes Mellitus, 7% catheters) participating in the CONvective TRAnsport STudy (CONTRAST), a randomized controlled trial evaluating the effect of HDF as compared to low-flux HD. The events were adjudicated by an independent event committee. The risk of infectious events was compared with Cox regression for repeated events and Cox proportional hazard models. The distributions of types of infection were compared between the groups. Results Thirty one percent of the patients suffered from one or more infections leading to hospitalization during the study (median follow-up 1.96 years). The risk for infections during the entire follow-up did not differ significantly between treatment arms (HDF 198 and HD 169 infections in 800 and 798 person-years respectively, hazard ratio HDF vs. HD 1.09 (0.88–1.34), P = 0.42. No difference was found in the occurrence of the first infectious event (either fatal, non-fatal or type specific). Of all infections, respiratory infections (25% in HDF, 28% in HD) were most common, followed by skin/musculoskeletal infections (21% in HDF, 13% in HD). Conclusions HDF as compared to HD did not result in a reduced risk of infections, larger studies are needed to confirm our findings. Trial Registration ClinicalTrials.gov NCT00205556 PMID:26288091

  1. Optimal shortcuts for atomic transport in anharmonic traps

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Muga, J. G.; Guéry-Odelin, D.; Chen, Xi

    2016-06-01

    We design fast trap trajectories to transport cold atoms in anharmonic traps, combining invariant-based inverse engineering, perturbation theory, and optimal control theory. Among the ideal trajectories for harmonic traps, we choose the ones that minimize the anharmonic energy.

  2. Complex quantum networks: From universal breakdown to optimal transport.

    PubMed

    Mülken, Oliver; Dolgushev, Maxim; Galiceanu, Mircea

    2016-02-01

    We study the transport efficiency of excitations on complex quantum networks with loops. For this we consider sequentially growing networks with different topologies of the sequential subgraphs. This can lead either to a universal complete breakdown of transport for complete-graph-like sequential subgraphs or to optimal transport for ringlike sequential subgraphs. The transition to optimal transport can be triggered by systematically reducing the number of loops of complete-graph-like sequential subgraphs in a small-world procedure. These effects are explained on the basis of the spectral properties of the network's Hamiltonian. Our theoretical considerations are supported by numerical Monte Carlo simulations for complex quantum networks with a scale-free size distribution of sequential subgraphs and a small-world-type transition to optimal transport.

  3. Complex quantum networks: From universal breakdown to optimal transport

    NASA Astrophysics Data System (ADS)

    Mülken, Oliver; Dolgushev, Maxim; Galiceanu, Mircea

    2016-02-01

    We study the transport efficiency of excitations on complex quantum networks with loops. For this we consider sequentially growing networks with different topologies of the sequential subgraphs. This can lead either to a universal complete breakdown of transport for complete-graph-like sequential subgraphs or to optimal transport for ringlike sequential subgraphs. The transition to optimal transport can be triggered by systematically reducing the number of loops of complete-graph-like sequential subgraphs in a small-world procedure. These effects are explained on the basis of the spectral properties of the network's Hamiltonian. Our theoretical considerations are supported by numerical Monte Carlo simulations for complex quantum networks with a scale-free size distribution of sequential subgraphs and a small-world-type transition to optimal transport.

  4. Optimization of municipal solid waste collection and transportation routes.

    PubMed

    Das, Swapan; Bhattacharyya, Bidyut Kr

    2015-09-01

    Optimization of municipal solid waste (MSW) collection and transportation through source separation becomes one of the major concerns in the MSW management system design, due to the fact that the existing MSW management systems suffer by the high collection and transportation cost. Generally, in a city different waste sources scatter throughout the city in heterogeneous way that increase waste collection and transportation cost in the waste management system. Therefore, a shortest waste collection and transportation strategy can effectively reduce waste collection and transportation cost. In this paper, we propose an optimal MSW collection and transportation scheme that focus on the problem of minimizing the length of each waste collection and transportation route. We first formulize the MSW collection and transportation problem into a mixed integer program. Moreover, we propose a heuristic solution for the waste collection and transportation problem that can provide an optimal way for waste collection and transportation. Extensive simulations and real testbed results show that the proposed solution can significantly improve the MSW performance. Results show that the proposed scheme is able to reduce more than 30% of the total waste collection path length. Copyright © 2015 Elsevier Ltd. All rights reserved.

  5. Optimal error analysis of the intraseasonal convection due to uncertainties of the sea surface temperature in a coupled model

    NASA Astrophysics Data System (ADS)

    Li, Xiaojing; Tang, Youmin; Yao, Zhixiong

    2017-04-01

    The predictability of the convection related to the Madden-Julian Oscillation (MJO) is studied using a coupled model CESM (Community Earth System Model) and the climatically relevant singular vector (CSV) approach. The CSV approach is an ensemble-based strategy to calculate the optimal initial error on climate scale. In this study, we focus on the optimal initial error of the sea surface temperature in Indian Ocean, where is the location of the MJO onset. Six MJO events are chosen from the 10 years model simulation output. The results show that the large values of the SVs are mainly located in the bay of Bengal and the south central IO (around (25°S, 90°E)), which is a meridional dipole-like pattern. The fast error growth of the CSVs have important impacts on the prediction of the convection related to the MJO. The initial perturbations with the SV pattern result in the deep convection damping more quickly in the east Pacific Ocean. Moreover, the sensitivity studies of the CSVs show that different initial fields do not affect the CSVs obviously, while the perturbation domain is a more responsive factor to the CSVs. The rapid growth of the CSVs is found to be related to the west bay of Bengal, where the wind stress starts to be perturbed due to the CSV initial error. These results contribute to the establishment of an ensemble prediction system, as well as the optimal observation network. In addition, the analysis of the error growth can provide us some enlightment about the relationship between SST and the intraseasonal convection related to the MJO.

  6. MHD thermosolutal marangoni convection heat and mass transport of power law fluid driven by temperature and concentration gradient

    NASA Astrophysics Data System (ADS)

    Jiao, Chengru; Zheng, Liancun; Ma, Lianxi

    2015-08-01

    This paper studies the magnetohydrodynamic (MHD) thermosolutal Marangoni convection heat and mass transfer of power-law fluids driven by a power law temperature and a power law concentration which is assumed that the surface tension varies linearly with both the temperature and concentration. Heat and mass transfer constitutive equation is proposed based on N-diffusion proposed by Philip and the abnormal convection-diffusion model proposed by Pascal in which we assume that the heat diffusion depends non-linearly on both the temperature and the temperature gradient and the mass diffusion depends non-linearly on both the concentration and the concentration gradient with modified Fourier heat conduction for power law fluid. The governing equations are reduced to nonlinear ordinary differential equations by using suitable similarity transformations. Approximate analytical solution is obtained using homotopy analytical method (HAM). The transport characteristics of velocity, temperature and concentration fields are analyzed in detail.

  7. Decreases in Maximal Oxygen Uptake Following Long-duration Spaceflight: Role of Convective and Diffusive O2 Transport Mechanisms.

    PubMed

    Ade, Carl J; Broxterman, Ryan M; Moore, Alan; Barstow, Thomas J

    2017-02-02

    We have previously predicted that the decrease in maximal oxygen uptake (VO2max) that accompanies time in microgravity reflects decrements in both convective and diffusive O2 transport to the mitochondria of the contracting myocytes. The aim of this investigation was therefore to quantify the relative changes in convective O2 transport (QO2) and O2 diffusing capacity (DO2) following long duration spaceflight. In 9 astronauts, resting hemoglobin concentration ([Hb]), VO2max, maximal cardiac output (QTmax), and differences in arterial and venous O2 contents (CaO2-CvO2) were obtained retrospectively for International Space Station Increments 19 through 33 (April 2009-November 2012). QO2 and DO2 were calculated from these variables via integration of Fick's Principle of Mass Conservation and Fick's Law of Diffusion. VO2max significantly decreased from pre- to post-flight (-53.9 ± 45.5%, P =0.008). The significant decrease in Q ̇_Tmax (-7.8±9.1%, P =0.05), despite an unchanged [Hb] resulted in a significantly decreased QO2 (-11.4±10.5%, P = 0.02). DO2 significantly decreased from pre- to post-flight by -27.5±24.5% (P =0.04), as did the peak CaO2-CvO2 (-9.2±7.5%, P =0.007). Using linear regression analysis, changes in VO2max were significantly correlated with changes in DO2 (R2=0.47; P = 0.04). These data suggest that space flight decreases both convective and diffusive O2 transport. These results have practical implications for future long-duration space missions and highlight the need to resolve the specific mechanisms underlying these spaceflight-induced changes along the O2 transport pathway.

  8. Optimal directional volatile transport in retronasal olfaction

    PubMed Central

    Ni, Rui; Michalski, Mark H.; Brown, Elliott; Doan, Ngoc; Zinter, Joseph; Ouellette, Nicholas T.; Shepherd, Gordon M.

    2015-01-01

    The ability of humans to distinguish the delicate differences in food flavors depends mostly on retronasal smell, in which food volatiles entrained into the airway at the back of the oral cavity are transported by exhaled air through the nasal cavity to stimulate the olfactory receptor neurons. Little is known whether food volatiles are preferentially carried by retronasal flow toward the nasal cavity rather than by orthonasal flow into the lung. To study the differences between retronasal and orthonasal flow, we obtained computed tomography (CT) images of the orthonasal airway from a healthy human subject, printed an experimental model using a 3D printer, and analyzed the flow field inside the airway. The results show that, during inhalation, the anatomical structure of the oropharynx creates an air curtain outside a virtual cavity connecting the oropharynx and the back of the mouth, which prevents food volatiles from being transported into the main stream toward the lung. In contrast, during exhalation, the flow preferentially sweeps through this virtual cavity and effectively enhances the entrainment of food volatiles into the main retronasal flow. This asymmetrical transport efficiency is also found to have a nonmonotonic Reynolds number dependence: The asymmetry peaks at a range of an intermediate Reynolds number close to 800, because the air curtain effect during inhalation becomes strongest in this range. This study provides the first experimental evidence, to our knowledge, for adaptations of the geometry of the human oropharynx for efficient transport of food volatiles toward the olfactory receptors in the nasal cavity. PMID:26553982

  9. Optimally designed quantum transport across disordered networks.

    PubMed

    Walschaers, Mattia; Diaz, Jorge Fernandez-de-Cossio; Mulet, Roberto; Buchleitner, Andreas

    2013-11-01

    We establish a general mechanism for highly efficient quantum transport through finite, disordered 3D networks. It relies on the interplay of disorder with centrosymmetry and a dominant doublet spectral structure and can be controlled by the proper tuning of only coarse-grained quantities. Photosynthetic light harvesting complexes are discussed as potential biological incarnations of this design principle.

  10. Optimal directional volatile transport in retronasal olfaction.

    PubMed

    Ni, Rui; Michalski, Mark H; Brown, Elliott; Doan, Ngoc; Zinter, Joseph; Ouellette, Nicholas T; Shepherd, Gordon M

    2015-11-24

    The ability of humans to distinguish the delicate differences in food flavors depends mostly on retronasal smell, in which food volatiles entrained into the airway at the back of the oral cavity are transported by exhaled air through the nasal cavity to stimulate the olfactory receptor neurons. Little is known whether food volatiles are preferentially carried by retronasal flow toward the nasal cavity rather than by orthonasal flow into the lung. To study the differences between retronasal and orthonasal flow, we obtained computed tomography (CT) images of the orthonasal airway from a healthy human subject, printed an experimental model using a 3D printer, and analyzed the flow field inside the airway. The results show that, during inhalation, the anatomical structure of the oropharynx creates an air curtain outside a virtual cavity connecting the oropharynx and the back of the mouth, which prevents food volatiles from being transported into the main stream toward the lung. In contrast, during exhalation, the flow preferentially sweeps through this virtual cavity and effectively enhances the entrainment of food volatiles into the main retronasal flow. This asymmetrical transport efficiency is also found to have a nonmonotonic Reynolds number dependence: The asymmetry peaks at a range of an intermediate Reynolds number close to 800, because the air curtain effect during inhalation becomes strongest in this range. This study provides the first experimental evidence, to our knowledge, for adaptations of the geometry of the human oropharynx for efficient transport of food volatiles toward the olfactory receptors in the nasal cavity.

  11. Supergranular Convection

    NASA Astrophysics Data System (ADS)

    Udayashankar, Paniveni

    2015-12-01

    Observation of the Solar photosphere through high resolution instruments have long indicated that the surface of the Sun is not a tranquil, featureless surface but is beset with a granular appearance. These cellular velocity patterns are a visible manifestation of sub- photospheric convection currents which contribute substantially to the outward transport of energy from the deeper layers, thus maintaining the energy balance of the Sun as a whole.Convection is the chief mode of transport in the outer layers of all cool stars such as the Sun (Noyes,1982). Convection zone of thickness 30% of the Solar radius lies in the sub-photospheric layers of the Sun. Here the opacity is so large that heat flux transport is mainly by convection rather than by photon diffusion. Convection is revealed on four scales. On the scale of 1000 km, it is granulation and on the scale of 8-10 arcsec, it is Mesogranulation. The next hierarchial scale of convection , Supergranules are in the range of 30-40 arcsec. The largest reported manifestation of convection in the Sun are ‘Giant Cells’or ‘Giant Granules’, on a typical length scale of about 108 m.'Supergranules' is caused by the turbulence that extends deep into the convection zone. They have a typical lifetime of about 20hr with spicules marking their boundaries. Gas rises in the centre of the supergranules and then spreads out towards the boundary and descends.Broadly speaking supergranules are characterized by the three parameters namely the length L, the lifetime T and the horizontal flow velocity vh . The interrelationships amongst these parameters can shed light on the underlying convective processes and are in agreement with the Kolmogorov theory of turbulence as applied to large scale solar convection (Krishan et al .2002 ; Paniveni et. al. 2004, 2005, 2010).References:1) Noyes, R.W., The Sun, Our Star (Harvard University Press, 1982)2) Krishan, V., Paniveni U., Singh , J., Srikanth R., 2002, MNRAS, 334/1,2303) Paniveni

  12. CHEMICAL TRANSPORT AND SPONTANEOUS LAYER FORMATION IN FINGERING CONVECTION IN ASTROPHYSICS

    SciTech Connect

    Brown, Justin M.; Garaud, Pascale; Stellmach, Stephan

    2013-05-01

    A region of a star that is stable to convection according to the Ledoux criterion may nevertheless undergo additional mixing if the mean molecular weight increases with radius. This process is called fingering (thermohaline) convection and may account for some of the unexplained mixing in stars such as those that have been polluted by planetary infall and those burning {sup 3}He. We propose a new model for mixing by fingering convection in the parameter regime relevant for stellar (and planetary) interiors. Our theory is based on physical principles and supported by three-dimensional direct numerical simulations. We also discuss the possibility of formation of thermocompositional staircases in fingering regions, and their role in enhancing mixing. Finally, we provide a simple algorithm to implement this theory in one-dimensional stellar codes, such as KEPLER and MESA.

  13. Southern Ocean deep convection in global climate models: A driver for variability of subpolar gyres and Drake Passage transport on decadal timescales

    NASA Astrophysics Data System (ADS)

    Behrens, Erik; Rickard, Graham; Morgenstern, Olaf; Martin, Torge; Osprey, Annette; Joshi, Manoj

    2016-06-01

    We investigate the individual and joint decadal variability of Southern Ocean state quantities, such as the strength of the Ross and Weddell Gyres, Drake Passage transport, and sea ice area, using the National Institute of Water and Atmospheric Research UK Chemistry and Aerosols (NIWA-UKCA) model and CMIP5 models. Variability in these quantities is stimulated by strong deep reaching convective events in the Southern Ocean, which produce an Antarctic Bottom Water-like water mass and affect the large-scale meridional density structure in the Southern Ocean. An increase in the (near) surface stratification, due to freshwater forcing, can be a precondition for subsequent strong convection activity. The combination of enhanced-gyre driven sea ice and freshwater export, as well as ongoing subsurface heat accumulation, lead to a time lag between changes in oceanic freshwater and heat content. This causes an ongoing weakening of the stratification until sudden strong mixing events emerge and the heat is released to the atmosphere. We find that strong convection reduces sea ice cover, weakens the subpolar gyres, increases the meridional density gradient and subsequently results in a positive Drake Passage transport anomaly. Results of available CMIP5 models confirm that variability in sea ice, Drake Passage transport, and the Weddell Gyre strength is enhanced if models show strong open ocean convective events. Consistent relationships between convection, sea ice, Drake Passage transport, and Ross Gyre strength variability are evident in most models, whether or not they host open ocean convection.

  14. Probabilistic Swarm Guidance using Optimal Transport

    DTIC Science & Technology

    2014-10-10

    y ) 0 0.005 0.01 0.015 0.02 ( a ) ( b ) Figure 1. ( a ) The initial probability mass function (pmf) µ(x) (in blue) is transported to the desired pmf ν...first making a localized guess and then reaching an agreement across the network using the consensus algorithm [24]. Step 2 is elucidated in Section II- B ...Section VI. B . Notation The time index is denoted by a right subscript and the agent index is denoted by a lower-case right superscript. Let N, R, R

  15. Grid optimization and multigrid techniques for fluid flow and transport problems

    NASA Astrophysics Data System (ADS)

    Pardhanani, Anand L.

    1992-01-01

    Special numerical techniques for the efficient and accurate solution of fluid flow and certain other transport processes are investigated. These include adaptive redistribution and optimization of computational grids, multigrid techniques for convection-diffusion problems, and multigrid time-marching methods for non-stationary and nonlinear problems. The grid optimization strategy is based on constructing and minimizing a mathematical objective function which defines the desired grid properties. For convection-diffusion problems, it is demonstrated that standard multigrid techniques fail when the coarse grids violate mesh-size restrictions. A variety of alternate multigrid strategies are explored, including artificial dissipation, fine grid pre-elimination, self-adjoint formulation, defect correction, and combination with grid redistribution. Multilevel techniques are also developed for time-dependent problems, including evolution problems with non-steady or transient solutions, and steady-state problems solved with artificial time-marching. Both explicit and implicit integration schemes are investigated, and it is shown that significant performance improvements can be gained with the use of multigrid. These techniques are implemented and tested on representative model problems as well as practical applications of current research interest. The grid investigations involve optimization in model problems, and in large-scale 3-D aircraft wing-body configurations. The multigrid applications range from model convection-diffusion problems, to time-dependent problems, to coupled nonlinear problems in two major application areas. The first application involves simulating spatio-temporal patterns in a coupled, nonlinear, reaction-diffusion problem that models the behavior of the Belousov-Zhabotinskii reaction. This multi-species reaction, which exhibits intricate patterns in laboratory experiments, has attracted considerable interest in the field of nonlinear dynamics. The

  16. The Role of Thermal Convection in Heat and Mass Transport in the Subarctic Snow Cover

    DTIC Science & Technology

    1991-10-01

    ice-poor. Ice-rich Temperature (aC) fuoi hasf tie.rm as ondumdtivty oth ti (0ue ydywiht n r10 osue soil as ther al conductivit four times Figure 36...and F. Touvier (1987) btude experimentale de la convection thermique dans la neige. Journal de Physique Terre, 48(C 1): 257-261. Bryson, R. A. and F

  17. Numerical modelling of convective heat transport by air flow in permafrost talus slopes

    NASA Astrophysics Data System (ADS)

    Wicky, Jonas; Hauck, Christian

    2017-06-01

    Talus slopes are a widespread geomorphic feature in the Alps. Due to their high porosity a gravity-driven internal air circulation can be established which is forced by the gradient between external (air) and internal (talus) temperature. The thermal regime is different from the surrounding environment, leading to the occurrence of permafrost below the typical permafrost zone. This phenomenon has mainly been analysed by field studies and only few explicit numerical modelling studies exist. Numerical simulations of permafrost sometimes use parameterisations for the effects of convection but mostly neglect the influence of convective heat transfer in air on the thermal regime. In contrast, in civil engineering many studies have been carried out to investigate the thermal behaviour of blocky layers and to improve their passive cooling effect. The present study further develops and applies these concepts to model heat transfer in air flows in a natural-scale talus slope. Modelling results show that convective heat transfer has the potential to develop a significant temperature difference between the lower and the upper parts of the talus slope. A seasonally alternating chimney-effect type of circulation develops. Modelling results also show that this convective heat transfer leads to the formation of a cold reservoir in the lower part of the talus slope, which can be crucial for maintaining the frozen ground conditions despite increasing air temperatures caused by climate change.

  18. Optimal convection volume for improving patient outcomes in an international incident dialysis cohort treated with online hemodiafiltration

    PubMed Central

    Canaud, Bernard; Barbieri, Carlo; Marcelli, Daniele; Bellocchio, Francesco; Bowry, Sudhir; Mari, Flavio; Amato, Claudia; Gatti, Emanuele

    2015-01-01

    Online hemodiafiltration (OL-HDF), the most efficient renal replacement therapy, enables enhanced removal of small and large uremic toxins by combining diffusive and convective solute transport. Randomized controlled trials on prevalent chronic kidney disease (CKD) patients showed improved patient survival with high-volume OL-HDF, underlining the effect of convection volume (CV). This retrospective international study was conducted in a large cohort of incident CKD patients to determine the CV threshold and range associated with survival advantage. Data were extracted from a cohort of adult CKD patients treated by post-dilution OL-HDF over a 101-month period. In total, 2293 patients with a minimum of 2 years of follow-up were analyzed using advanced statistical tools, including cubic spline analyses for determination of the CV range over which a survival increase was observed. The relative survival rate of OL-HDF patients, adjusted for age, gender, comorbidities, vascular access, albumin, C-reactive protein, and dialysis dose, was found to increase at about 55 l/week of CV and to stay increased up to about 75 l/week. Similar analysis of pre-dialysis β2-microglobin (marker of middle-molecule uremic toxins) concentrations found a nearly linear decrease in marker concentration as CV increased from 40 to 75 l/week. Analysis of log C-reactive protein levels showed a decrease over the same CV range. Thus, a convection dose target based on convection volume should be considered and needs to be confirmed by prospective trials as a new determinant of dialysis adequacy. PMID:25945407

  19. Stochastic-convective transport with nonlinear reactions and mixing: finite streamtube ensemble formulation for multicomponent reaction systems with intra-streamtube dispersion.

    PubMed

    Ginn, T R

    2001-01-01

    An effective streamtube ensemble method is developed to upscale convective-dispersive transport with multicomponent nonlinear reactions in steady nonuniform flow. The transport is cast in terms of a finite ensemble of independent discrete streamtubes that approximate convective transport along macroscopically averaged pathlines and dispersive transport longitudinally as microscopic mixing within streamtubes. The representation of fate and transport via a finite ensemble of effective linear streamtubes, allows the treatment of arbitrarily complex reaction systems involving both homogeneous and heterogeneous reactions, and longitudinal dispersive/diffusive mixing within streamtubes. This allows the use of reactive-transport codes designed to solve such problems in an Eulerian framework, as opposed to reliance on closed-form (convolutional or canonical) expressions for reactive transport in exclusively convective streamtubes. The approach requires both reactive-transport solutions for a representative ensemble of one-dimensional convective-dispersive-reactive streamtubes and the distribution of flux over the streamtube ensemble variants, and it does not allow for lateral mixing between streamtubes. Here, the only ensemble variant is travel time. The discussion details the way that the conventional Eulerian fate and transport model is converted first into an ensemble of transports along three-dimensional streamtubes of unknown geometry, and then to approximate one-dimensional streamtubes that are designed to honor the important global properties of the transport. Conditions under which such an 'equivalent' ensemble of one-dimensional streamtubes are described. The breakthrough curve of a nonreactive tracer in the ensemble is expressed as a combined Volterra-Fredholm integral equation, which serves as the basis for estimation of the distribution of flux over the variant of the ensemble, travel time. Transient convective speed and the effects of errors in flux

  20. Statistical optimization for passive scalar transport: maximum entropy production versus maximum Kolmogorov-Sinai entropy

    NASA Astrophysics Data System (ADS)

    Mihelich, M.; Faranda, D.; Dubrulle, B.; Paillard, D.

    2015-03-01

    We derive rigorous results on the link between the principle of maximum entropy production and the principle of maximum Kolmogorov-Sinai entropy for a Markov model of the passive scalar diffusion called the Zero Range Process. We show analytically that both the entropy production and the Kolmogorov-Sinai entropy, seen as functions of a parameter f connected to the jump probability, admit a unique maximum denoted fmaxEP and fmaxKS. The behaviour of these two maxima is explored as a function of the system disequilibrium and the system resolution N. The main result of this paper is that fmaxEP and fmaxKS have the same Taylor expansion at first order in the deviation from equilibrium. We find that fmaxEP hardly depends on N whereas fmaxKS depends strongly on N. In particular, for a fixed difference of potential between the reservoirs, fmaxEP(N) tends towards a non-zero value, while fmaxKS(N) tends to 0 when N goes to infinity. For values of N typical of those adopted by Paltridge and climatologists working on maximum entropy production (N ≍ 10-100), we show that fmaxEP and fmaxKS coincide even far from equilibrium. Finally, we show that one can find an optimal resolution N* such that fmaxEP and fmaxKS coincide, at least up to a second-order parameter proportional to the non-equilibrium fluxes imposed to the boundaries. We find that the optimal resolution N* depends on the non-equilibrium fluxes, so that deeper convection should be represented on finer grids. This result points to the inadequacy of using a single grid for representing convection in climate and weather models. Moreover, the application of this principle to passive scalar transport parametrization is therefore expected to provide both the value of the optimal flux, and of the optimal number of degrees of freedom (resolution) to describe the system.

  1. A simple parameterization for the turbulent kinetic energy transport terms in the convective boundary layer derived from large eddy simulation

    NASA Astrophysics Data System (ADS)

    Puhales, Franciano Scremin; Rizza, Umberto; Degrazia, Gervásio Annes; Acevedo, Otávio Costa

    2013-02-01

    In this work a parametrization for the transport terms of the turbulent kinetic energy (TKE) budget equation, valid for a convective boundary layer (CBL) is presented. This is a hard task to accomplish from experimental data, especially because of the difficulty associated to the measurements of pressure turbulent fluctuations, which are necessary to determine the pressure correlation TKE transport term. Thus, employing a large eddy simulation (LES) a full diurnal planetary boundary layer (PBL) cycle was simulated. In this simulation a forcing obtained from experimental data is used, so that the numerical experiment represents a more realistic case than a stationary PBL. For this study all terms of the TKE budget equation were determined for a CBL. From these data, polynomials that describe the TKE transport terms’ vertical profiles were adjusted. The polynomials found are a good description of the LES data, and from them it is shown that a simple formulation that directly relates the transport terms to the TKE magnitude has advantages on other parameterizations commonly used in CBL numerical models. Furthermore, the present study shows that the TKE turbulent transport term dominates over the TKE transport by pressure perturbations and that for most of the CBL these two terms have opposite signs.

  2. Experimental Investigation of Transport Enhancement in Convective Air Flow by the Use of a Vortex Promoter

    NASA Astrophysics Data System (ADS)

    Jaluria, Yogesh; Gomes, Kevin

    2015-11-01

    This paper focuses on the effect of placing a passive vortex generator in a flow and the resulting increase in transport rates. The flow circumstance considered is that of a flat plate with protruding heat sources, placed in a uniform flow, with a vortex generator located upstream of the leading edge. The study consists of three parts. In the first part, the flow due to the vortex promoter by itself is considered. The periodic or chaotic behavior in the wake behind the promoter is investigated. By studying different sizes and shapes of vortex promoters, it is determined which configuration offers the largest disturbance in the flow and the frequency at which it occurs. In the second part of the study, the flow over a plate with isolated, finite-sized, protruding heat sources, without a vortex promoter, is considered. Again, the frequency of the disturbance downstream is investigated to determine the nature of the resulting flow and the disturbance frequency. The effect of varying the dimensions and locations of the heat sources on the flow downstream is investigated. It is found that a larger separation distance between two sources leads to higher transport rates. In the last part of the study, tests are done for the combination of vortex promoter and the plate, placing a vortex promoter in front of the plate. An effort is made to match the frequencies of the disturbances due to the vortex generator with those due to the plate in an attempt to achieve resonance. From these results, an optimal promoter is chosen that would lead to maximum heat transfer rate.

  3. Transport optimization of coupled flashing ratchets in viscoelastic media

    NASA Astrophysics Data System (ADS)

    Wang, Hai-Yan; Bao, Jing-Dong

    2017-08-01

    In the paper, we investigate the transport properties of coupled flashing ratchets in viscoelastic media. Using generalized Langevin equation, subvelocity Vα, subdiffusive coefficient Dα and generalized Peclet number Peα are calculated as functions of the temperature T and the flashing period τ with different subdiffusive exponents α. The results show that the transport of coupled flashing ratchets can be optimized in viscoelastic media.

  4. Optimization of Nonlinear Transport-Production Task of Medical Waste

    NASA Astrophysics Data System (ADS)

    Michlowicz, Edward

    2012-09-01

    The paper reflects on optimization of transportation - production tasks for the processing of medical waste. For the existing network of collection points and processing plants, according to its algorithm, the optimal allocation of tasks to the cost of transport to the respective plants has to be determined. It was assumed that the functions determining the processing costs are polynomials of the second degree. To solve the problem, a program written in MatLab environment equalization algorithm based on a marginal cost JCC was used.

  5. Transport optimization considering the node aggregation ability

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Li, Lian; Guo, Jiawei; Li, Zheng

    2015-10-01

    Using the theories of complex networks and gravitational field, we study the dynamic routing process under the framework of node gravitational field, define the equation of gravitation of travel path to data package and introduce two parameters α and γ for adjusting the dependences of transmission data on the unblocked degree of node, the transmission capacity of node and the path length. Based on the path's attraction, a gravitational field routing strategy under node connection ability constraint is proposed with considering the affect of node aggregation ability to transport process, and a parameter is used to adjust the control strength of routing process to node aggregation ability. In order to clarify the efficiency of suggested method, we introduce an order parameter η to measure the throughput of the network by the critical value of phase transition from free state to congestion state, and analyze the distribution of betweenness centrality and traffic jam. Simulation results show that, compared with the traditional shortest path routing strategy, our method greatly improve the throughput of a network, balance the network traffic load and most of the network nodes are used efficiently. Moreover, the network throughput is maximized under μ = -1, and the transmission performance of the algorithm is independent of the values of α and γ, which indicate the routing strategy is stable and reliable.

  6. Area-preservation mapping using optimal mass transport.

    PubMed

    Zhao, Xin; Su, Zhengyu; Gu, Xianfeng David; Kaufman, Arie; Sun, Jian; Gao, Jie; Luo, Feng

    2013-12-01

    We present a novel area-preservation mapping/flattening method using the optimal mass transport technique, based on the Monge-Brenier theory. Our optimal transport map approach is rigorous and solid in theory, efficient and parallel in computation, yet general for various applications. By comparison with the conventional Monge-Kantorovich approach, our method reduces the number of variables from O(n2) to O(n), and converts the optimal mass transport problem to a convex optimization problem, which can now be efficiently carried out by Newton's method. Furthermore, our framework includes the area weighting strategy that enables users to completely control and adjust the size of areas everywhere in an accurate and quantitative way. Our method significantly reduces the complexity of the problem, and improves the efficiency, flexibility and scalability during visualization. Our framework, by combining conformal mapping and optimal mass transport mapping, serves as a powerful tool for a broad range of applications in visualization and graphics, especially for medical imaging. We provide a variety of experimental results to demonstrate the efficiency, robustness and efficacy of our novel framework.

  7. A MILP-Model for the Optimization of Transports

    NASA Astrophysics Data System (ADS)

    Björk, Kaj-Mikael

    2010-09-01

    This paper presents a work in developing a mathematical model for the optimization of transports. The decisions to be made are routing decisions, truck assignment and the determination of the pickup order for a set of loads and available trucks. The model presented takes these aspects into account simultaneously. The MILP model is implemented in the Microsoft Excel environment, utilizing the LP-solve freeware as the optimization engine and Visual Basic for Applications as the modeling interface.

  8. Effect of Melt Convection and Solid Transport on Macrosegregation and Grain Structure in Equiaxed Al-Cu Alloys

    NASA Technical Reports Server (NTRS)

    Rerko, Rodney S.; deGroh, Henry C., III; Beckermann, Christoph; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    Macrosegregation in metal casting can be caused by thermal and solutal melt convection, and the transport of unattached solid crystals. These free grains can be a result of, for example, nucleation in the bulk liquid or dendrite fragmentation. In an effort to develop a comprehensive numerical model for the casting of alloys, an experimental study has been conducted to generate benchmark data with which such a solidification model could be tested. The specific goal of the experiments was to examine equiaxed solidification in situations where sinking of grains is (and is not) expected. The objectives were: 1) experimentally study the effects of solid transport and thermosolutal convection on macrosegregation and grain size distribution patterns; and 2) provide a complete set of controlled thermal boundary conditions, temperature data, segregation data, and grain size data, to validate numerical codes. The alloys used were Al-1 wt. pct. Cu, and Al-10 wt. pct. Cu with various amounts of the grain refiner TiB2 added. Cylindrical samples were either cooled from the top, or the bottom. Several trends in the data stand out. In attempting to model these experiments, concentrating on experiments that show clear trends or differences is recommended.

  9. Effects of Melt Convection and Solid Transport on Macrosegregation and Grain Structure in Equiaxed Al-Cu Alloys

    NASA Technical Reports Server (NTRS)

    Rerko, Rodney S.; deGroh, Henry C., III; Beckermann, Christoph

    2000-01-01

    Macrosegregation in metal casting can be caused by thermal and solutal melt convection, and the transport of unattached solid crystals resulting from nucleation in the bulk liquid or dendrite fragmentation. To develop a comprehensive numerical model for the casting of alloys, an experimental study has been conducted to generate benchmark data with which such a solidification model could be tested. The objectives were: (1) experimentally study the effects of solid transport and thermosolutal convection on macrosegregation and grain size; and (2) provide a complete set of boundary conditions temperature data, segregation data, and grain size data - to validate numerical models. Through the control of end cooling and side wall heating, radial temperature gradients in the sample and furnace were minimized. Thus the vertical crucible wall was adiabatic. Samples at room temperature were 24 cc and 95 mm long. The alloys used were Al-1 wt. pct. Cu, and Al- 10 wt. pct. Cu; the starting point for solidification was isothermal at 710 and 685 C respectively. To induce an equiaxed structure various amounts of the grain refiner TiB2 were added. Samples were either cooled from the top, or the bottom. Several trends in the data stand out. In attempting to model these experiments, concentrating on these trends or differences may be beneficial.

  10. Side-wall gas 'creep' and 'thermal stress convection' in microgravity experiments on film growth by vapor transport

    NASA Technical Reports Server (NTRS)

    Rosner, Daniel E.

    1989-01-01

    While 'no-slip' boundary conditions and the Navier-Stokes equations of continuum fluid mechanics have served the vapor transport community well until now, it is pointed out that transport conditions within highly nonisothermal ampoules are such that the nonisothermal side walls 'drive' the dominant convective flow, and the familiar Stokes-Fourier-Fick laws governing the molecular fluxes of momentum, energy, and (species) mass in the 'continuum' field equations will often prove to be inadequate, even at Knudsen numbers as small as 0.001. The implications of these interesting gas kinetic phenomena under microgravity conditions, and even under 'earth-bound' experimental conditions, are outlined here, along with a tractable approach to their systematic treatment.

  11. Coupled groundwater flow and transport: 2. Thermohaline and 3D convection systems

    NASA Astrophysics Data System (ADS)

    Diersch, H.-J. G.; Kolditz, O.

    This work continues the analysis of variable density flow in groundwater systems. It focuses on both thermohaline (double-diffusive) and three-dimensional (3D) buoyancy-driven convection processes. The finite-element method is utilized to tackle these complex non-linear problems in two and three dimensions. The preferred numerical approaches are discussed regarding appropriate basic formulations, balance-consistent discretization techniques for derivative quantitites, extension of the Boussinesq approximation, proper constraint conditions, time marching schemes, and computational strategies for solving large systems. Applications are presented for the thermohaline Elder and salt dome problem as well as for the 3D extension of the Elder problem with and without thermohaline effects and a 3D Bénard convection process. The simulations are performed by using the package FEFLOW. Conclusions are drawn with respect to numerical efforts and the appropriateness for practical needs.

  12. Numerical Study of the Role of Shallow Convection in Moisture Transport and Climate

    NASA Technical Reports Server (NTRS)

    Seaman, Nelson L.; Stauffer, David R.; Munoz, Ricardo C.

    2001-01-01

    The objective of this investigation was to study the role of shallow convection on the regional water cycle of the Mississippi and Little Washita Basins of the Southern Great Plains (SGP) using a 3-D mesoscale model, the PSU/NCAR MM5. The underlying premise of the project was that current modeling of regional-scale climate and moisture cycles over the continents is deficient without adequate treatment of shallow convection. At the beginning of the study, it was hypothesized that an improved treatment of the regional water cycle can be achieved by using a 3-D mesoscale numerical model having high-quality parameterizations for the key physical processes controlling the water cycle. These included a detailed land-surface parameterization (the Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) sub-model of Wetzel and Boone), an advanced boundary-layer parameterization (the 1.5-order turbulent kinetic energy (TKE) predictive scheme of Shafran et al.), and a more complete shallow convection parameterization (the hybrid-closure scheme of Deng et al.) than are available in most current models. PLACE is a product of researchers working at NASA's Goddard Space Flight Center in Greenbelt, MD. The TKE and shallow-convection schemes are the result of model development at Penn State. The long-range goal is to develop an integrated suite of physical sub-models that can be used for regional and perhaps global climate studies of the water budget. Therefore, the work plan focused on integrating, improving, and testing these parameterizations in the MM5 and applying them to study water-cycle processes over the SGP. These schemes have been tested extensively through the course of this study and the latter two have been improved significantly as a consequence.

  13. Investigation of convective transport in the tropical stratosphere using a lightweight uv-visible spectrometer sonde

    NASA Astrophysics Data System (ADS)

    Vicomte, M.; Pommereau, J.-P.

    2012-04-01

    The occurrence of deep convective overshooting reaching altitudes up to 20 km is known for long above the tropical continents. They were shown recently shown to carry tropospheric chemical species, ice crystals, and possibly lightning NOx, in the lower stratosphere. For better investigating such process, a light UV-Visible spectrometer SAOZ balloon sonde, called mini-SAOZ, was developed on more advanced technology than the older instrument. The payload, weighting 9 kg, includes two spectrometers: a visible-near IR system for the measurement of O3, NO2, H2O, O4 and O2 and aerosol attenuation, and a UV system for BrO, OClO and CH2O). The mini-SAOZ sonde has been tested and qualified in flight with the help of CNES In Kiruna in Northern Sweden in 2010 and 2011. The plan is to fly several times this sonde on small balloons of 1500 m3 in South East Brazil in February-March 2012, next or immediately above convective systems during a TRO-pico campaign dedicated to the study of stratospheric hydration by geyser like injection of ice crystals and more generally fast convective lofting of tropospheric air in the stratosphere across the tropopause. After a short description of the instrument, the presentation will show the first results of those flights.

  14. Convective Instability and Mass Transport of the Diffusion Layer in CO2 Sequestration

    NASA Astrophysics Data System (ADS)

    Backhaus, S.

    2011-12-01

    The long-term fate of supercritical (sc) CO2 in saline aquifers is critical to the security of carbon sequestration, an important option for eliminating or reducing the emissions of this most prevalent greenhouse gas. scCO2 is less dense than brine and floats to the top of the aquifer where it is trapped in a metastable state by a geologic feature such as a low permeability cap rock. Dissolution into the underlying brine creates a CO2-brine mixture that is denser than brine, eliminating buoyancy and removing the threat of CO2 escaping back to the atmosphere. If molecular diffusion were the only dissolution mechanism, the CO2 waste stream from a typical large coal-fired electrical power plant may take upward of 10,000 years to no longer pose a threat, however, a convective instability of the dense diffusion boundary layer between the scCO2 and the brine can dramatically increase the dissolution rates, shortening the lifetime of the scCO2 waste pool. We present results of 2D and 3D similitude-correct, laboratory-scale experiments using an analog fluid system. The experiments and flow visualization reveal the onset of the convective instability, the dynamics of the fluid flows during the convective processes, and the long-term mass transfer rates.

  15. The effects of convection and oxygen presence on thermal testing of thin-shelled transportation packages

    SciTech Connect

    Feldman, M.R.

    1995-11-01

    Several experiments were performed in an attempt to determine the effects of both convection and oxygen levels during hypothetical thermal accident testing of thin-shelled Celotex{trademark}-based packages in furnaces. Obsolete DT-22 packages were used and experiments were performed in two separate furnaces, one gas-fired and one electric, each of which has previously been used for this type of testing. Oxygen levels were varied and measured in the gas-fired furnace, while the electric furnace was operated in a standard manner. The gas-fired furnace is constructed so as to induce a very strong convective field within. After testing, the packages were evaluated by several methods to determine the effects of the thermal testing on the package. In general, there were no differences found for the packages tested in the two different furnaces or for packages tested in the same furnace under different conditions. Therefore, after careful consideration, it is concluded that thermal testing can still be performed in electric furnaces in which the oxygen supply is not refurbished and there is no forced convection heat transfer.

  16. RESEARCH PAPERS : Eigendecomposition of the two-point correlation tensor for optimal characterization of mantle convection

    NASA Astrophysics Data System (ADS)

    Balachandar, S.

    1998-01-01

    The two-point correlation tensor provides complete information on mantle convection accurate up to second-order statistics. Unfortunately, the two-point spatial correlation tensor is in general a data-intensive quantity. In the case of mantle convection, a simplified representation of the two-point spatial correlation tensor can be obtained by using spherical symmetry. The two-point correlation can be expressed in terms of a planar correlation tensor, which reduces the correlation's dependence to only three independent variables: the radial locations of the two points and their angular separation. The eigendecomposition of the planar correlation tensor provides a rational methodology for further representing the second-order statistics contained within the two-point correlation in a compact manner. As an illustration, results on the planar correlation are presented for the thermal anomaly obtained from the tomographic model of Su, Woodward & Dziewonski (1994) and the corresponding velocity field obtained from a simple constant-viscosity convection model Zhang & Christensen 1993). The first 10 most energetic eigensolutions of the planar correlation, which constitute an almost three orders of magnitude reduction in the data, capture the two-point correlation to 97 per cent accuracy. Furthermore, the energetic eigenfunctions efficiently characterize the thermal and flow structures of the mantle. The signature of the transition zone is clearly evident in the most energetic temperature eigenfunction, which clearly shows a reversal of thermal fluctuations at a depth of around 830 km. In addition, a local peak in the thermal fluctuations can be observed around a depth of 600 km. In contrast, due to the simplicity of the convection model employed, the velocity eigenfunctions exhibit a simple cellular structure that extends over the entire depth of the mantle and do not exhibit transition-zone signatures.

  17. Indirect estimation of the Convective Lognormal Transfer function model parameters for describing solute transport in unsaturated and undisturbed soil.

    PubMed

    Mohammadi, Mohammad Hossein; Vanclooster, Marnik

    2012-05-01

    Solute transport in partially saturated soils is largely affected by fluid velocity distribution and pore size distribution within the solute transport domain. Hence, it is possible to describe the solute transport process in terms of the pore size distribution of the soil, and indirectly in terms of the soil hydraulic properties. In this paper, we present a conceptual approach that allows predicting the parameters of the Convective Lognormal Transfer model from knowledge of soil moisture and the Soil Moisture Characteristic (SMC), parameterized by means of the closed-form model of Kosugi (1996). It is assumed that in partially saturated conditions, the air filled pore volume act as an inert solid phase, allowing the use of the Arya et al. (1999) pragmatic approach to estimate solute travel time statistics from the saturation degree and SMC parameters. The approach is evaluated using a set of partially saturated transport experiments as presented by Mohammadi and Vanclooster (2011). Experimental results showed that the mean solute travel time, μ(t), increases proportionally with the depth (travel distance) and decreases with flow rate. The variance of solute travel time σ²(t) first decreases with flow rate up to 0.4-0.6 Ks and subsequently increases. For all tested BTCs predicted solute transport with μ(t) estimated from the conceptual model performed much better as compared to predictions with μ(t) and σ²(t) estimated from calibration of solute transport at shallow soil depths. The use of μ(t) estimated from the conceptual model therefore increases the robustness of the CLT model in predicting solute transport in heterogeneous soils at larger depths. In view of the fact that reasonable indirect estimates of the SMC can be made from basic soil properties using pedotransfer functions, the presented approach may be useful for predicting solute transport at field or watershed scales. Copyright © 2012 Elsevier B.V. All rights reserved.

  18. A new optimization method for a class of time fractional convection-diffusion-wave equations with variable coefficients

    NASA Astrophysics Data System (ADS)

    Dahaghin, M. Sh.; Hassani, H.

    2017-03-01

    In this paper, we consider a class of time fractional convection-diffusion-wave equations (TFCDWE) with variable coefficients involving fractional derivatives in the Caputo sense. We also propose an optimization method based on the generalized polynomials (GPs) for solving TFCDWE. Our objective in the proposed method is to expand the solution of the problem under consideration in terms of GPs with unknown free coefficients and control parameters. Furthermore, we derive some operational matrices of the ordinary and fractional derivatives for these basis functions. Finally, we obtain the free coefficients and control parameters optimally by minimizing the error of the approximate solution. Some numerical examples are provided to demonstrate the validity and accuracy of the proposed method. The obtained results show that the proposed method is very efficient and accurate.

  19. Heat transport and coupling modes in Rayleigh-Bénard convection occurring between two layers with largely different viscosities

    NASA Astrophysics Data System (ADS)

    Yoshida, Masaki; Iwamori, Hikaru; Hamano, Yozo; Suetsugu, Daisuke

    2017-09-01

    A high-resolution numerical simulation model in two-dimensional cylindrical geometry was used to discuss the heat transport and coupling modes in two-layer Rayleigh-Bénard convection with a high Rayleigh number (up to the order of 109), an infinite Prandtl number, and large viscosity contrasts (up to 10-3) between an outer, highly viscous layer (HVL) and an inner, low-viscosity layer (LVL). In addition to mechanical and thermal interaction across the HVL-LVL interface, which has been investigated by Yoshida and Hamano ["Numerical studies on the dynamics of two-layer Rayleigh-Bénard convection with an infinite Prandtl number and large viscosity contrasts," Phys. Fluids 28(11), 116601 (2016)], the spatiotemporal analysis in this study provides new insights into (1) heat transport over the entire system between the bottom of the LVL and the top of the HVL, in particular that associated with thermal plumes, and (2) the convection regime and coupling mode of the two layers, including the transition mechanism between the mechanical coupling mode at relatively low viscosity contrasts and the thermal coupling mode at higher viscosity contrasts. Although flow in the LVL is highly time-dependent, it shares the spatially opposite/same flow pattern synchronized to the nearly stationary upwelling and downwelling plumes in the HVL, corresponding to the mechanical/thermal coupling mode. In the transitional regime between the mechanical and thermal coupling modes, the LVL exhibits periodical switching between the two phases (i.e., the mechanical and thermal coupling phases) with a stagnant period. A detailed inspection revealed that the switching was initiated by the instability in the uppermost boundary layer of the LVL. These results suggest that convection in the highly viscous mantle of the Earth controls that of the extremely low-viscosity outer core in a top-down manner under the thermal coupling mode, which may support a scenario of top-down hemispherical dynamics

  20. Optimizing velocities and transports for complex coastal regions and archipelagos

    NASA Astrophysics Data System (ADS)

    Haley, Patrick J.; Agarwal, Arpit; Lermusiaux, Pierre F. J.

    2015-05-01

    We derive and apply a methodology for the initialization of velocity and transport fields in complex multiply-connected regions with multiscale dynamics. The result is initial fields that are consistent with observations, complex geometry and dynamics, and that can simulate the evolution of ocean processes without large spurious initial transients. A class of constrained weighted least squares optimizations is defined to best fit first-guess velocities while satisfying the complex bathymetry, coastline and divergence strong constraints. A weak constraint towards the minimum inter-island transports that are in accord with the first-guess velocities provides important velocity corrections in complex archipelagos. In the optimization weights, the minimum distance and vertical area between pairs of coasts are computed using a Fast Marching Method. Additional information on velocity and transports are included as strong or weak constraints. We apply our methodology around the Hawaiian islands of Kauai/Niihau, in the Taiwan/Kuroshio region and in the Philippines Archipelago. Comparisons with other common initialization strategies, among hindcasts from these initial conditions (ICs), and with independent in situ observations show that our optimization corrects transports, satisfies boundary conditions and redirects currents. Differences between the hindcasts from these different ICs are found to grow for at least 2-3 weeks. When compared to independent in situ observations, simulations from our optimized ICs are shown to have the smallest errors.

  1. Convective transport of highly plasma protein bound drugs facilitates direct penetration into deep tissues after topical application.

    PubMed

    Dancik, Yuri; Anissimov, Yuri G; Jepps, Owen G; Roberts, Michael S

    2012-04-01

    Many products are applied to human skin for local effects in deeper tissues. Animal studies suggest that deep dermal and/or subcutaneous delivery may be facilitated by both dermal diffusion and transport via the cutaneous vasculature. However, the relationship between the extent and pathways of penetration, drug physicochemical properties and deeper tissue physiology is not well understood. We have used a physiologically based pharmacokinetic model to analyze published human cutaneous microdialysis data, complemented by our own in vitro skin penetration studies. We found that convective blood, lymphatic and interstitial flow led to significant deep tissue concentrations for drugs that are highly plasma protein bound. In such cases, deeper tissue concentrations will occur earlier and may be several orders of magnitude greater than predicted by passive dermal diffusion alone. To relate the varying dermal, subcutaneous and muscle microdialysate concentrations found in man after topical application to the nature of the drug applied and to the underlying physiology. We developed a physiologically based pharmacokinetic model in which transport to deeper tissues was determined by tissue diffusion, blood, lymphatic and intersitial flow transport and drug properties. The model was applied to interpret published human microdialysis data, estimated in vitro dermal diffusion and protein binding affinity of drugs that have been previously applied topically in vivo and measured in deep cutaneous tissues over time. Deeper tissue microdialysis concentrations for various drugs in vivo vary widely. Here, we show that carriage by the blood to the deeper tissues below topical application sites facilitates the transport of highly plasma protein bound drugs that penetrate the skin, leading to rapid and significant concentrations in those tissues. Hence, the fractional concentration for the highly plasma protein bound diclofenac in deeper tissues is 0.79 times that in a probe 4.5

  2. On Matrix-Valued Monge–Kantorovich Optimal Mass Transport

    PubMed Central

    Ning, Lipeng; Georgiou, Tryphon T.; Tannenbaum, Allen

    2016-01-01

    We present a particular formulation of optimal transport for matrix-valued density functions. Our aim is to devise a geometry which is suitable for comparing power spectral densities of multivariable time series. More specifically, the value of a power spectral density at a given frequency, which in the matricial case encodes power as well as directionality, is thought of as a proxy for a “matrix-valued mass density.” Optimal transport aims at establishing a natural metric in the space of such matrix-valued densities which takes into account differences between power across frequencies as well as misalignment of the corresponding principle axes. Thus, our transportation cost includes a cost of transference of power between frequencies together with a cost of rotating the principle directions of matrix densities. The two endpoint matrix-valued densities can be thought of as marginals of a joint matrix-valued density on a tensor product space. This joint density, very much as in the classical Monge–Kantorovich setting, can be thought to specify the transportation plan. Contrary to the classical setting, the optimal transport plan for matrices is no longer supported on a thin zero-measure set. PMID:26997667

  3. Reducing long-term remedial costs by transport modeling optimization.

    PubMed

    Becker, David; Minsker, Barbara; Greenwald, Robert; Zhang, Yan; Harre, Karla; Yager, Kathleen; Zheng, Chunmiao; Peralta, Richard

    2006-01-01

    The Department of Defense (DoD) Environmental Security Technology Certification Program and the Environmental Protection Agency sponsored a project to evaluate the benefits and utility of contaminant transport simulation-optimization algorithms against traditional (trial and error) modeling approaches. Three pump-and-treat facilities operated by the DoD were selected for inclusion in the project. Three optimization formulations were developed for each facility and solved independently by three modeling teams (two using simulation-optimization algorithms and one applying trial-and-error methods). The results clearly indicate that simulation-optimization methods are able to search a wider range of well locations and flow rates and identify better solutions than current trial-and-error approaches. The solutions found were 5% to 50% better than those obtained using trial-and-error (measured using optimal objective function values), with an average improvement of approximately 20%. This translated into potential savings ranging from 600,000 dollars to 10,000,000 dollars for the three sites. In nearly all cases, the cost savings easily outweighed the costs of the optimization. To reduce computational requirements, in some cases the simulation-optimization groups applied multiple mathematical algorithms, solved a series of modified subproblems, and/or fit "meta-models" such as neural networks or regression models to replace time-consuming simulation models in the optimization algorithm. The optimal solutions did not account for the uncertainties inherent in the modeling process. This project illustrates that transport simulation-optimization techniques are practical for real problems. However, applying the techniques in an efficient manner requires expertise and should involve iterative modification to the formulations based on interim results.

  4. Transport path optimization algorithm based on fuzzy integrated weights

    NASA Astrophysics Data System (ADS)

    Hou, Yuan-Da; Xu, Xiao-Hao

    2014-11-01

    Natural disasters cause significant damage to roads, making route selection a complicated logistical problem. To overcome this complexity, we present a method of using a trapezoidal fuzzy number to select the optimal transport path. Using the given trapezoidal fuzzy edge coefficients, we calculate a fuzzy integrated matrix, and incorporate the fuzzy multi-weights into fuzzy integrated weights. The optimal path is determined by taking two sets of vertices and transforming undiscovered vertices into discoverable ones. Our experimental results show that the model is highly accurate, and requires only a few measurement data to confirm the optimal path. The model provides an effective, feasible, and convenient method to obtain weights for different road sections, and can be applied to road planning in intelligent transportation systems.

  5. Optimization of magnetic switches for single particle and cell transport

    SciTech Connect

    Abedini-Nassab, Roozbeh; Yellen, Benjamin B.; Murdoch, David M.; Kim, CheolGi

    2014-06-28

    The ability to manipulate an ensemble of single particles and cells is a key aim of lab-on-a-chip research; however, the control mechanisms must be optimized for minimal power consumption to enable future large-scale implementation. Recently, we demonstrated a matter transport platform, which uses overlaid patterns of magnetic films and metallic current lines to control magnetic particles and magnetic-nanoparticle-labeled cells; however, we have made no prior attempts to optimize the device geometry and power consumption. Here, we provide an optimization analysis of particle-switching devices based on stochastic variation in the particle's size and magnetic content. These results are immediately applicable to the design of robust, multiplexed platforms capable of transporting, sorting, and storing single cells in large arrays with low power and high efficiency.

  6. Optimal mass transport for shape matching and comparison.

    PubMed

    Su, Zhengyu; Wang, Yalin; Shi, Rui; Zeng, Wei; Sun, Jian; Luo, Feng; Gu, Xianfeng

    2015-11-01

    Surface based 3D shape analysis plays a fundamental role in computer vision and medical imaging. This work proposes to use optimal mass transport map for shape matching and comparison, focusing on two important applications including surface registration and shape space. The computation of the optimal mass transport map is based on Monge-Brenier theory, in comparison to the conventional method based on Monge-Kantorovich theory, this method significantly improves the efficiency by reducing computational complexity from O(n(2)) to O(n) . For surface registration problem, one commonly used approach is to use conformal map to convert the shapes into some canonical space. Although conformal mappings have small angle distortions, they may introduce large area distortions which are likely to cause numerical instability thus resulting failures of shape analysis. This work proposes to compose the conformal map with the optimal mass transport map to get the unique area-preserving map, which is intrinsic to the Riemannian metric, unique, and diffeomorphic. For shape space study, this work introduces a novel Riemannian framework, Conformal Wasserstein Shape Space, by combing conformal geometry and optimal mass transport theory. In our work, all metric surfaces with the disk topology are mapped to the unit planar disk by a conformal mapping, which pushes the area element on the surface to a probability measure on the disk. The optimal mass transport provides a map from the shape space of all topological disks with metrics to the Wasserstein space of the disk and the pullback Wasserstein metric equips the shape space with a Riemannian metric. We validate our work by numerous experiments and comparisons with prior approaches and the experimental results demonstrate the efficiency and efficacy of our proposed approach.

  7. Optimal Mass Transport for Shape Matching and Comparison

    PubMed Central

    Su, Zhengyu; Wang, Yalin; Shi, Rui; Zeng, Wei; Sun, Jian; Luo, Feng; Gu, Xianfeng

    2015-01-01

    Surface based 3D shape analysis plays a fundamental role in computer vision and medical imaging. This work proposes to use optimal mass transport map for shape matching and comparison, focusing on two important applications including surface registration and shape space. The computation of the optimal mass transport map is based on Monge-Brenier theory, in comparison to the conventional method based on Monge-Kantorovich theory, this method significantly improves the efficiency by reducing computational complexity from O(n2) to O(n). For surface registration problem, one commonly used approach is to use conformal map to convert the shapes into some canonical space. Although conformal mappings have small angle distortions, they may introduce large area distortions which are likely to cause numerical instability thus resulting failures of shape analysis. This work proposes to compose the conformal map with the optimal mass transport map to get the unique area-preserving map, which is intrinsic to the Riemannian metric, unique, and diffeomorphic. For shape space study, this work introduces a novel Riemannian framework, Conformal Wasserstein Shape Space, by combing conformal geometry and optimal mass transport theory. In our work, all metric surfaces with the disk topology are mapped to the unit planar disk by a conformal mapping, which pushes the area element on the surface to a probability measure on the disk. The optimal mass transport provides a map from the shape space of all topological disks with metrics to the Wasserstein space of the disk and the pullback Wasserstein metric equips the shape space with a Riemannian metric. We validate our work by numerous experiments and comparisons with prior approaches and the experimental results demonstrate the efficiency and efficacy of our proposed approach. PMID:26440265

  8. Flow and particle dispersion in a pulmonary alveolus--part I: velocity measurements and convective particle transport.

    PubMed

    Chhabra, Sudhaker; Prasad, Ajay K

    2010-05-01

    The alveoli are the smallest units of the lung that participate in gas exchange. Although gas transport is governed primarily by diffusion due to the small length scales associated with the acinar region (approximately 500 microm), the transport and deposition of inhaled aerosol particles are influenced by convective airflow patterns. Therefore, understanding alveolar fluid flow and mixing is a necessary first step toward predicting aerosol transport and deposition in the human acinar region. In this study, flow patterns and particle transport have been measured using a simplified in-vitro alveolar model consisting of a single alveolus located on a bronchiole. The model comprises a transparent elastic 5/6 spherical cap (representing the alveolus) mounted over a circular hole on the side of a rigid circular tube (representing the bronchiole). The alveolus is capable of expanding and contracting in phase with the oscillatory flow through the tube. Realistic breathing conditions were achieved by exercising the model at physiologically relevant Reynolds and Womersley numbers. Particle image velocimetry was used to measure the resulting flow patterns in the alveolus. Data were acquired for five cases obtained as combinations of the alveolar-wall motion (nondeforming/oscillating) and the bronchiole flow (none/steady/oscillating). Detailed vector maps at discrete points within a given cycle revealed flow patterns, and transport and mixing of bronchiole fluid into the alveolar cavity. The time-dependent velocity vector fields were integrated over multiple cycles to estimate particle transport into the alveolar cavity and deposition on the alveolar wall. The key outcome of the study is that alveolar-wall motion enhances mixing between the bronchiole and the alveolar fluid. Particle transport and deposition into the alveolar cavity are maximized when the alveolar wall oscillates in tandem with the bronchiole fluid, which is the operating case in the human lung.

  9. Simulation Tool for Optimizing Non-Combatant Evacuation (STONE): Optimization of Evacuation Time and Transportation Resource Utilization

    DTIC Science & Technology

    2015-05-01

    STONE ) Optimization of evacuation time and transportation resource utilization Jean-Denis Caron Bohdan L. Kaluzny Canadian Joint Operations Command OR...Simulation Tool for Optimizing Non-Combatant Evacuation ( STONE ) Optimization of evacuation time and transportation resource utilization Jean-Denis Caron...Combatant Evacuation ( STONE ) analysis toolset to support NEO planning. This Scientific Report documents the STONE optimization component, STONE (Opt

  10. Model calculation of the characteristic mass for convective and diffusive vapor transport in graphite furnace atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Bencs, László; Laczai, Nikoletta; Ajtony, Zsolt

    2015-07-01

    A combination of former convective-diffusive vapor-transport models is described to extend the calculation scheme for sensitivity (characteristic mass - m0) in graphite furnace atomic absorption spectrometry (GFAAS). This approach encompasses the influence of forced convection of the internal furnace gas (mini-flow) combined with concentration diffusion of the analyte atoms on the residence time in a spatially isothermal furnace, i.e., the standard design of the transversely heated graphite atomizer (THGA). A couple of relationships for the diffusional and convectional residence times were studied and compared, including in factors accounting for the effects of the sample/platform dimension and the dosing hole. These model approaches were subsequently applied for the particular cases of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn analytes. For the verification of the accuracy of the calculations, the experimental m0 values were determined with the application of a standard THGA furnace, operating either under stopped, or mini-flow (50 cm3 min- 1) of the internal sheath gas during atomization. The theoretical and experimental ratios of m0(mini-flow)-to-m0(stop-flow) were closely similar for each study analyte. Likewise, the calculated m0 data gave a fairly good agreement with the corresponding experimental m0 values for stopped and mini-flow conditions, i.e., it ranged between 0.62 and 1.8 with an average of 1.05 ± 0.27. This indicates the usability of the current model calculations for checking the operation of a given GFAAS instrument and the applied methodology.

  11. The CONvective TRansport of Active Species in the Tropics (CONTRAST) Experiment

    NASA Astrophysics Data System (ADS)

    Pan, L.; Atlas, E. L.; Salawitch, R. J.

    2014-12-01

    The CONTRAST experiment was conducted from Guam (13.5° N, 144.8° E) using the NSF/NCAR Gulfstream V (GV) research aircraft during January and February 2014. The main objective of the experiment was to investigate the impact of deep convection on chemical composition and ozone photochemical budget. The experiment was part of three coordinated experiments to target the tropical Western Pacific during Northern Hemisphere winter, when and where the most extensive deep convection in Earth's climate system develops. The partner missions were ATTREX (Airborne Tropical Tropopause Experiment), which deployed the high-altitude NASA Global Hawk, and CAST (Coordinated Airborne Studies in the Tropics), which used the UK FAAM BAe 146 research aircraft to investigate the lower to mid-troposphere of the Western Pacific. A total of 16 research flights were conducted using the GV, with measurement of ozone, CO, CH4, and CO2, as well as a large suite of chemical tracer measurements including organic and inorganic halogen species, NMHCs, and OVOCs. The research flights from Guam covered 20°S to 40°N latitude, 130°E to 165°E longitude, and 0.1 to 15.2 km ASL in altitude, successfully sampled the recent and aged outflows from active deep convective storms and defined the background chemical conditions of the tropical western Pacific during boreal winter. The results are expected to bring new insights into the ozone and halogen budgets of the tropical troposphere. These airborne observations, especially in combination with the CAST and ATTREX data, provide key measurements and diagnostics for evaluating and constraining chemistry-climate models. Highlights of the experiment and initial findings will be presented.

  12. Transportation of MHD nanofluid free convection in a porous semi annulus using numerical approach

    NASA Astrophysics Data System (ADS)

    Sheikholeslami, M.; Ganji, D. D.

    2017-02-01

    Nanofluid free convection in presence of Lorentz forces in a permeable semi annulus is simulated using Control Volume based Finite Element Method. Impact of porous media on governing equations is considered by means of Darcy law. Brownian motion impact on properties of nanofluid is taken into account using Koo-Kleinstreuer-Li (KKL) model. Important parameters are inclination angle (ξ) , CuO-water volume fraction (ϕ) , Hartmann (Ha) and Rayleigh (Ra) numbers for porous medium. A formula for Nuave is provided. Results indicated that temperature gradient detracts with enhance of Ha but it enhances with rise of ξ, Ra . Heat transfer augmentation enhances with rise of Lorentz forces.

  13. Influence of Natural Convection and Thermal Radiation Multi-Component Transport in MOCVD Reactors

    NASA Technical Reports Server (NTRS)

    Lowry, S.; Krishnan, A.; Clark, I.

    1999-01-01

    The influence of Grashof and Reynolds number in Metal Organic Chemical Vapor (MOCVD) reactors is being investigated under a combined empirical/numerical study. As part of that research, the deposition of Indium Phosphide in an MOCVD reactor is modeled using the computational code CFD-ACE. The model includes the effects of convection, conduction, and radiation as well as multi-component diffusion and multi-step surface/gas phase chemistry. The results of the prediction are compared with experimental data for a commercial reactor and analyzed with respect to the model accuracy.

  14. Diffusion and convection in collagen gels: implications for transport in the tumor interstitium.

    PubMed Central

    Ramanujan, Saroja; Pluen, Alain; McKee, Trevor D; Brown, Edward B; Boucher, Yves; Jain, Rakesh K

    2002-01-01

    Diffusion coefficients of tracer molecules in collagen type I gels prepared from 0-4.5% w/v solutions were measured by fluorescence recovery after photobleaching. When adjusted to account for in vivo tortuosity, diffusion coefficients in gels matched previous measurements in four human tumor xenografts with equivalent collagen concentrations. In contrast, hyaluronan solutions hindered diffusion to a lesser extent when prepared at concentrations equivalent to those reported in these tumors. Collagen permeability, determined from flow through gels under hydrostatic pressure, was compared with predictions obtained from application of the Brinkman effective medium model to diffusion data. Permeability predictions matched experimental results at low concentrations, but underestimated measured values at high concentrations. Permeability measurements in gels did not match previous measurements in tumors. Visualization of gels by transmission electron microscopy and light microscopy revealed networks of long collagen fibers at lower concentrations along with shorter fibers at high concentrations. Negligible assembly was detected in collagen solutions pregelation. However, diffusion was similarly hindered in pre and postgelation samples. Comparison of diffusion and convection data in these gels and tumors suggests that collagen may obstruct diffusion more than convection in tumors. These findings have significant implications for drug delivery in tumors and for tissue engineering applications. PMID:12202388

  15. Transport coefficient free scaling laws for convection and magnetism in fast rotating planets

    NASA Astrophysics Data System (ADS)

    Starchenko, S. V.

    2013-09-01

    In the limit of negligible molecular diffusivity, viscosity and magnetic diffusivity effects, Scaling laws for convection and magnetism are derived for fast rotating planets. In the Earth, Jupiter, Saturn and ancient dynamo active Mars it is reasonable to suppose domination of magnetic energy over kinetic one that results in the typical magnetic field B proportional to the third root of the buoyancy flux F [3] driving the convection, while B is independent on conductivity σ and angular rotation rate Ω. The same scaling law was previously obtained via compilation of many numerical planetary dynamo simulations [1-3]. Besides, new scaling laws are obtained for typical hydrodynamic scale h, velocity V, Archimedean acceleration A, electromagnetic scale d and sinus of the angle between magnetic and velocity vector s. In Uranus, Neptune and Ganymede a local magnetic Reynolds number rm=μσVd~1 with magnetic permeability in vacuum μ. Correspondent magnetic energy could be of order kinetic energy resulting in relatively lower magnetic field strength B=(μρ)1/2V with density ρ. That may explain magnetic field values and non-dipolar structures in Uranus, Neptune and Ganymede.

  16. Optimal transport in time-varying small-world networks

    NASA Astrophysics Data System (ADS)

    Chen, Qu; Qian, Jiang-Hai; Zhu, Liang; Han, Ding-Ding

    2016-03-01

    The time-order of interactions, which is regulated by some intrinsic activity, surely plays a crucial role regarding the transport efficiency of transportation systems. Here we study the optimal transport structure by measure of the length of time-respecting paths. Our network is built from a two-dimensional regular lattice, and long-range connections are allocated with probability Pi j˜rij -α , where ri j is the Manhattan distance. By assigning each shortcut an activity rate subjected to its geometric distance τi j˜rij -C , long-range links become active intermittently, leading to the time-varying dynamics. We show that for 0 optimal structural exponent αopt that slightly grows with C as αopt˜log(C ) , while for C ≫2 the αopt→∞ . The unique restriction between C and α unveils an optimization principle in time-varying transportation networks. Empirical studies on British Airways and Austrian Airlines provide consistent evidence with our conclusion.

  17. Transport of Formaldehyde to the Upper Troposphere In Deep Convective Storms During the 2012 DC3 Study

    NASA Astrophysics Data System (ADS)

    Fried, A.; Weibring, P.; Richter, D.; Walega, J.; Olson, J. R.; Crawford, J. H.; Barth, M. C.; Apel, E. C.; Hornbrook, R. S.; Bela, M. M.; Toon, O. B.; Blake, D. R.; Blake, N. J.; Luo, Z. J.

    2014-12-01

    scavenging efficiencies in the 49-55% range. Although somewhat higher than previous determinations, there is still sufficient transport of CH2O to the UTLS, thus providing an important source to the HOx budget in convective outflow regions.

  18. Transport Across Chloroplast Membranes: Optimizing Photosynthesis for Adverse Environmental Conditions.

    PubMed

    Pottosin, Igor; Shabala, Sergey

    2016-03-07

    Chloroplasts are central to solar light harvesting and photosynthesis. Optimal chloroplast functioning is vitally dependent on a very intensive traffic of metabolites and ions between the cytosol and stroma, and should be attuned for adverse environmental conditions. This is achieved by an orchestrated regulation of a variety of transport systems located at chloroplast membranes such as porines, solute channels, ion-specific cation and anion channels, and various primary and secondary active transport systems. In this review we describe the molecular nature and functional properties of the inner and outer envelope and thylakoid membrane channels and transporters. We then discuss how their orchestrated regulation affects thylakoid structure, electron transport and excitation energy transfer, proton-motive force partition, ion homeostasis, stromal pH regulation, and volume regulation. We link the activity of key cation and anion transport systems with stress-specific signaling processes in chloroplasts, and discuss how these signals interact with the signals generated in other organelles to optimize the cell performance, with a special emphasis on Ca(2+) and reactive oxygen species signaling. Copyright © 2016 The Author. Published by Elsevier Inc. All rights reserved.

  19. Influences of rotation and thermophoresis on MHD peristaltic transport of Jeffrey fluid with convective conditions and wall properties

    NASA Astrophysics Data System (ADS)

    Hayat, T.; Rafiq, M.; Ahmad, B.

    2016-07-01

    This article aims to predict the effects of convective condition and particle deposition on peristaltic transport of Jeffrey fluid in a channel. The whole system is in a rotating frame of reference. The walls of channel are taken flexible. The fluid is electrically conducting in the presence of uniform magnetic field. Non-uniform heat source/sink parameter is also considered. Mass transfer with chemical reaction is considered. Relevant equations for the problems under consideration are first modeled and then simplified using lubrication approach. Resulting equations for stream function and temperature are solved exactly whereas mass transfer equation is solved numerically. Impacts of various involved parameters appearing in the solutions are carefully analyzed.

  20. Optimizing the patient transport function at Mayo Clinic.

    PubMed

    Kuchera, Dustin; Rohleder, Thomas R

    2011-01-01

    In this article, we report on the implementation of a computerized scheduling tool to optimize staffing for patient transport at the Mayo Clinic. The tool was developed and implemented in Microsoft Excel and Visual Basic for Applications and includes an easy-to-use interface. The tool allows transport management to consider the trade-offs between patient waiting time and staffing levels. While improved staffing efficiency was a desire of the project, it was important that patient service quality was also maintained. The results show that staffing could be reduced while maintaining historical patient service levels.

  1. Optimizing the National TRU waste system transportation program.

    SciTech Connect

    Lott, S. A.; Countiss, S.

    2002-01-01

    The goal of the National TRU Waste Program (NTP) is to operate the system safely and cost-effectively, in compliance with applicable regulations and agreements, and at full capacity in a fully integrated mode. One of the objectives of the Department of Energy's Carlsbad Field Office (DOE/CBFO) is to complete the current Waste Isolation Pilot Plant (WIPP) mission for the disposal of the nation's legacy transuranic (TRU) waste at least IO years earlier thus saving approximately %7B. The National TRU Waste Optimization Plan (1) recommends changes to accomplish this. This paper discusses the optimization of the National TRU Waste System Transportation Program.

  2. Wall shear stress and near-wall convective transport: Comparisons with vascular remodelling in a peripheral graft anastomosis

    NASA Astrophysics Data System (ADS)

    Gambaruto, A. M.; Doorly, D. J.; Yamaguchi, T.

    2010-08-01

    Fluid dynamic properties of blood flow are implicated in cardiovascular diseases. The interaction between the blood flow and the wall occurs through the direct transmission of forces, and through the dominating influence of the flow on convective transport processes. Controlled, in vitro testing in simple geometric configurations has provided much data on the cellular-level responses of the vascular walls to flow, but a complete, mechanistic explanation of the pathogenic process is lacking. In the interim, mapping the association between local haemodynamics and the vascular response is important to improve understanding of the disease process and may be of use for prognosis. Moreover, establishing the haemodynamic environment in the regions of disease provides data on flow conditions to guide investigations of cellular-level responses. This work describes techniques to facilitate comparison between the temporal alteration in the geometry of the vascular conduit, as determined by in vivo imaging, with local flow parameters. Procedures to reconstruct virtual models from images by means of a partition-of-unity implicit function formulation, and to align virtual models of follow-up scans to a common coordinate system, are outlined. A simple Taylor series expansion of the Lagrangian dynamics of the near-wall flow is shown to provide both a physical meaning to the directional components of the flow, as well as demonstrating the relation between near-wall convection in the wall normal direction and spatial gradients of the wall shear stress. A series of post-operative follow-up MRI scans of two patient cases with bypass grafts in the peripheral vasculature are presented. These are used to assess how local haemodynamic parameters relate to vascular remodelling at the location of the distal end-to-side anastomosis, i.e. where the graft rejoins the host artery. Results indicate that regions of both low wall shear stress and convective transport towards the wall tend to be

  3. Nanofluidic Transport over a Curved Surface with Viscous Dissipation and Convective Mass Flux

    NASA Astrophysics Data System (ADS)

    Mehmood, Zaffar; Iqbal, Z.; Azhar, Ehtsham; Maraj, E. N.

    2017-03-01

    This article is a numerical investigation of boundary layer flow of nanofluid over a bended stretching surface. The study is carried out by considering convective mass flux condition. Contribution of viscous dissipation is taken into the account along with thermal radiation. Suitable similarity transformations are employed to simplify the system of nonlinear partial differential equations into a system of nonlinear ordinary differential equations. Computational results are extracted by means of a shooting method embedded with a Runge-Kutta Fehlberg technique. Key findings include that velocity is a decreasing function of curvature parameter K. Moreover, Nusselt number decreases with increase in curvature of the stretching surface while skin friction and Sherwood number enhance with increase in K.

  4. CFD Analysis of nanofluid forced convection heat transport in laminar flow through a compact pipe

    NASA Astrophysics Data System (ADS)

    Yu, Kitae; Park, Cheol; Kim, Sedon; Song, Heegun; Jeong, Hyomin

    2017-08-01

    In the present paper, developing laminar forced convection flows were numerically investigated by using water-Al2O3 nano-fluid through a circular compact pipe which has 4.5mm diameter. Each model has a steady state and uniform heat flux (UHF) at the wall. The whole numerical experiments were processed under the Re = 1050 and the nano-fluid models were made by the Alumina volume fraction. A single-phase fluid models were defined through nano-fluid physical and thermal properties calculations, Two-phase model(mixture granular model) were processed in 100nm diameter. The results show that Nusselt number and heat transfer rate are improved as the Al2O3 volume fraction increased. All of the numerical flow simulations are processed by the FLUENT. The results show the increment of thermal transfer from the volume fraction concentration.

  5. Peristaltic Transport of Prandtl-Eyring Liquid in a Convectively Heated Curved Channel

    PubMed Central

    Hayat, Tasawar; Bibi, Shahida; Alsaadi, Fuad; Rafiq, Maimona

    2016-01-01

    Here peristaltic activity for flow of a Prandtl-Eyring material is modeled and analyzed for curved geometry. Heat transfer analysis is studied using more generalized convective conditions. The channel walls satisfy complaint walls properties. Viscous dissipation in the thermal equation accounted. Unlike the previous studies is for uniform magnetic field on this topic, the radial applied magnetic field has been utilized in the problems development. Solutions for stream function (ψ), velocity (u), and temperature (θ) for small parameter β have been derived. The salient features of heat transfer coefficient Z and trapping are also discussed for various parameters of interest including magnetic field, curvature, material parameters of fluid, Brinkman, Biot and compliant wall properties. Main observations of present communication have been included in the conclusion section. PMID:27304458

  6. Representations of transport, convection, and the hydrologic cycle in chemical transport models: Implications for the modeling of short-lived and soluble species

    NASA Astrophysics Data System (ADS)

    Rasch, P. J.; Mahowald, N. M.; Eaton, B. E.

    1997-12-01

    We compare chemical transport simulations performed in a model using archived meteorological data (an off-line transport model) to those performed in a model in which the meteorological data are predicted every time step (an on-line model). We identify the errors associated with using data sampled at timescales much longer than those operating in the atmosphere or in the on-line model, and strategies for ameleorating those errors. The evaluation is performed in the context of a global off-line chemical transport model called the Model of Atmospheric Transport and Chemistry (MATCH) for three test problems: (1) the passive advection of blobs initially concentrated in the lower and upper troposphere; (2) the surface emission of radon and its decay to lead; and (3) the removal of lead from the atmosphere by wet and dry deposition processes. These problems exercise the important processes of transport by resolved scale winds, rapid transport by smaller scale convection processes, and wet removal (which depends on the representation of the hydrologic cycle). We show that the errors in off-line model simulations (compared to the on-line simulations) can be made small when the sampling interval is order 6 hours or less. We also show that one can accurately reproduce the subgrid-scale processes within the off-line model, rather than needing to archive the results of those processes as input to the off-line model. This suggests that for the spatial and temporal scales treated in global models it is possible to treat many problems nearly as accurately in an off-line mode as one can with an on-line treatment.

  7. The role of optimal vortex formation in biological fluid transport.

    PubMed

    Dabiri, John O; Gharib, Morteza

    2005-08-07

    Animal phyla that require macro-scale fluid transport for functioning have repeatedly and often independently converged on the use of jet flows. During flow initiation these jets form fluid vortex rings, which facilitate mass transfer by stationary pumps (e.g. cardiac chambers) and momentum transfer by mobile systems (e.g. jet-propelled swimmers). Previous research has shown that vortex rings generated in the laboratory can be optimized for efficiency or thrust, based on the jet length-to-diameter ratio (L/D), with peak performance occurring at 3.5optimization have been inconclusive, due to the inability to properly account for the diversity of jet kinematics found across animal phyla. We combine laboratory experiments, in situ observations and a framework that reduces the kinematics to a single parameter in order to quantitatively show that individual animal kinematics can be tuned in correlation with optimal vortex ring formation. This new approach identifies simple rules for effective fluid transport, facilitates comparative biological studies of jet flows across animal phyla irrespective of their specific functions and can be extended to unify theories of optimal jet-based and flapping-based vortex ring formation.

  8. The role of optimal vortex formation in biological fluid transport

    PubMed Central

    Dabiri, John O; Gharib, Morteza

    2005-01-01

    Animal phyla that require macro-scale fluid transport for functioning have repeatedly and often independently converged on the use of jet flows. During flow initiation these jets form fluid vortex rings, which facilitate mass transfer by stationary pumps (e.g. cardiac chambers) and momentum transfer by mobile systems (e.g. jet-propelled swimmers). Previous research has shown that vortex rings generated in the laboratory can be optimized for efficiency or thrust, based on the jet length-to-diameter ratio (L/D), with peak performance occurring at 3.5optimization have been inconclusive, due to the inability to properly account for the diversity of jet kinematics found across animal phyla. We combine laboratory experiments, in situ observations and a framework that reduces the kinematics to a single parameter in order to quantitatively show that individual animal kinematics can be tuned in correlation with optimal vortex ring formation. This new approach identifies simple rules for effective fluid transport, facilitates comparative biological studies of jet flows across animal phyla irrespective of their specific functions and can be extended to unify theories of optimal jet-based and flapping-based vortex ring formation. PMID:16048770

  9. Role of Joule heating in dispersive mixing effects in electrophoretic cells: convective-diffusive transport aspects.

    PubMed

    Bosse, M A; Arce, P

    2000-03-01

    This contribution addresses the problem of solute dispersion in a free convection electrophoretic cell for the batch mode of operation, caused by the Joule heating generation. The problem is analyzed by using the two-problem approach originally proposed by Bosse and Arce (Electrophoresis 2000, 21, 1018-1025). The approach identifies the carrier fluid problem and the solute problem. This contribution is focused on the latter. The strategy uses a sequential coupling between the energy, momentum and mass conservation equations and, based on geometrical and physical assumptions for the system, leads to the derivation of analytical temperature and velocity profiles inside the cell. These results are subsequently used in the derivation of the effective dispersion coefficient for the cell by using the method of area averaging. The result shows the first design equation that relates the Joule heating effect directly to the solute dispersion in the cell. Some illustrative results are presented and discussed and their implication to the operation and design of the device is addressed. Due to the assumptions made, the equation may be viewed as an upper boundary for applications such as free flow electrophoresis.

  10. Convective heat transport in a rotating fluid layer of infinite Prandtl number: optimum fields and upper bounds on Nusselt number.

    PubMed

    Vitanov, Nikolay K

    2003-02-01

    By means of the Howard-Busse method of the optimum theory of turbulence we investigate numerically upper bounds on convective heat transport for the case of infinite fluid layer with stress-free vertical boundaries rotating about a vertical axis. We discuss the case of infinite Prandtl number, 1-alpha solution of the obtained variational problem and optimum fields possessing internal, intermediate, and boundary layers. We investigate regions of Rayleigh and Taylor numbers R and Ta, where no analytical bounds can be derived, and compare the analytical and numerical bounds for these regions of R and Ta where such comparison is possible. The increasing rotation has a different influence on the rescaled optimum fields of velocity w(1), temperature theta(1) and the vertical component of the vorticity f(1). The increasing Ta for fixed R leads to vanishing of the boundary layers of w(1) and theta(1). Opposite to this, the increasing Ta leads first to a formation of boundary layers of the field f(1) but further increasing the rotation causes vanishing of these boundary layers. We obtain optimum profiles of the horizontal averaged total temperature field which could be used as hints for construction of the background fields when applying Doering-Constantin method to the problems of rotating convection. The wave number alpha(1) corresponding to the optimum fields follows the asymptotic relationship alpha(1)=(R/5)(1/4) for intermediate Rayleigh numbers. However, when R becomes large with respect to Ta, after a transition region, the power law for alpha(1) becomes close to the power law for the case without rotation. The Nusselt number Nu is close to the nonrotational bound 0.32R(1/3) for the case of large R and small Ta. Nu decreases with increasing Taylor number. Thus, the upper bounds reflect the tendency of inhibiting thermal convection by increasing rotation for a fixed Rayleigh number. For the regions of Rayleigh and Taylor numbers where the numerical and asymptotic

  11. An experimental study of the flow pattern and heat transport behavior in horizontal convection with large Rayleigh number and small aspect ratio

    NASA Astrophysics Data System (ADS)

    Xia, Ke-Qing; Huang, Shi-Di

    2014-11-01

    Horizontal convection is a simple conceptual model to understand the role of buoyancy in the Meridional Overturning Circulation (MOC). Here we report an experimental study of the flow pattern and heat transport behavior in horizontal convection with Rayleigh number Ra up to 2 ×1012 and aspect ratio of 0.1 using a long apparatus. Flow visualization studies reveal that it is not necessary for the returning flow to penetrate the strong stratification in the thermal BLs, suggesting that much less energy may be required to maintain a global circulation than is generally believed. Moreover, both the heat transport efficiency and thermal BL thicknesses are found to follow a 0.3 power law, which indicates a stronger heat transport in horizontal convection with large Ra number than is suggested in the literature. These findings on horizontal convection may be relevant to the driving mechanism of the MOC. This work is supported by the Hong Kong Research Grants Council under Grant No. CUHK403811.

  12. Designing Nanostructures for Phonon Transport via Bayesian Optimization

    NASA Astrophysics Data System (ADS)

    Ju, Shenghong; Shiga, Takuma; Feng, Lei; Hou, Zhufeng; Tsuda, Koji; Shiomi, Junichiro

    2017-04-01

    We demonstrate optimization of thermal conductance across nanostructures by developing a method combining atomistic Green's function and Bayesian optimization. With an aim to minimize and maximize the interfacial thermal conductance (ITC) across Si-Si and Si-Ge interfaces by means of the Si /Ge composite interfacial structure, the method identifies the optimal structures from calculations of only a few percent of the entire candidates (over 60 000 structures). The obtained optimal interfacial structures are nonintuitive and impacting: the minimum ITC structure is an aperiodic superlattice that realizes 50% reduction from the best periodic superlattice. The physical mechanism of the minimum ITC can be understood in terms of the crossover of the two effects on phonon transport: as the layer thickness in the superlattice increases, the impact of Fabry-Pérot interference increases, and the rate of reflection at the layer interfaces decreases. An aperiodic superlattice with spatial variation in the layer thickness has a degree of freedom to realize optimal balance between the above two competing mechanisms. Furthermore, the spatial variation enables weakening the impact of constructive phonon interference relative to that of destructive interference. The present work shows the effectiveness and advantage of material informatics in designing nanostructures to control heat conduction, which can be extended to other nanostructures and properties.

  13. Hydrodynamics and convection enhanced macromolecular fluid transport in soft biological tissues: Application to solid tumor.

    PubMed

    Dey, Bibaswan; Sekhar, G P Raja

    2016-04-21

    This work addresses a theoretical framework for transvascular exchange and extravascular transport of solute macromolecules through soft interstitial space inside a solid tumor. Most of the soft biological tissues show materialistic properties similar to deformable porous material. They exhibit mechanical behavior towards the fluid motion since the solid phase of the tumor tissue gets compressed by the drag force that is associated with the extracellular fluid flow. This paper presents a general view about the transvascular and interstitial transport of solute nutrients inside a tumor in the macroscopic level. Modified Starling׳s equation is used to describe transvascular nutrient transport. On the macroscopic level, motion of extracellular fluid within the tumor interstitium is modeled with the help of biphasic mixture theory and a spherical symmetry solution is given as a simpler case. This present model describes the average interstitial fluid pressure (IFP), extracellular fluid velocity (EFV) and flow rate of extracellular fluid, as well as the deformation of the solid phase of the tumor tissue as an immediate cause of extracellular fluid flow. When the interstitial transport is diffusion dominated, an analytical treatment of advection-diffusion-reaction equation finds the overall nutrient distribution. We propose suitable criteria for the formation of necrosis within the tumor interstitium. This study introduces some parameters that represent the nutrient supply from tumor blood vessels into the tumor extracellular space. These transport parameters compete with the reversible nutrient metabolism of the tumor cells present in the interstitium. The present study also shows that the effectiveness factor corresponding to a first order nutrient metabolism may reach beyond unity if the strength of the distributive solute source assumes positive non-zero values. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. Aerosol transport and wet scavenging in deep convective clouds: a case study and model evaluation using a multiple passive tracer analysis approach

    SciTech Connect

    Yang, Qing; Easter, Richard C.; Campuzano-Jost, Pedro; Jimenez, Jose L.; Fast, Jerome D.; Ghan, Steven J.; Wang, Hailong; Berg, Larry K.; Barth, Mary; Liu, Ying; Shrivastava, ManishKumar B.; Singh, Balwinder; Morrison, H.; Fan, Jiwen; Ziegler, Conrad L.; Bela, Megan; Apel, Eric; Diskin, G. S.; Mikoviny, Tomas; Wisthaler, Armin

    2015-08-20

    The effect of wet scavenging on ambient aerosols in deep, continental convective clouds in the mid-latitudes is studied for a severe storm case in Oklahoma during the Deep Convective Clouds and Chemistry (DC3) field campaign. A new passive-tracer based transport analysis framework is developed to characterize the convective transport based on the vertical distribution of several slowly reacting and nearly insoluble trace gases. The passive gas concentration in the upper troposphere convective outflow results from a mixture of 47% from the lower level (0-3 km), 21% entrained from the upper troposphere, and 32% from mid-atmosphere based on observations. The transport analysis framework is applied to aerosols to estimate aerosol transport and wet-scavenging efficiency. Observations yield high overall scavenging efficiencies of 81% and 68% for aerosol mass (Dp < 1μm) and aerosol number (0.03< Dp < 2.5μm), respectively. Little chemical selectivity to wet scavenging is seen among observed submicron sulfate (84%), organic (82%), and ammonium (80%) aerosols, while nitrate has a much lower scavenging efficiency of 57% likely due to the uptake of nitric acid. Observed larger size particles (0.15 - 2.5μm) are scavenged more efficiently (84%) than smaller particles (64%; 0.03 - 0.15μm). The storm is simulated using the chemistry version of the WRF model. Compared to the observation based analysis, the standard model underestimates the wet scavenging efficiency for both mass and number concentrations with low biases of 31% and 40%, respectively. Adding a new treatment of secondary activation significantly improves simulation results, so that the bias in scavenging efficiency in mass and number concentrations is reduced to <10%. This supports the hypothesis that secondary activation is an important process for wet removal of aerosols in deep convective storms.

  15. Optimal control of wind farms for power tracking using simplified one-dimensional convection-diffusion equation

    NASA Astrophysics Data System (ADS)

    Shapiro, Carl; Bauweraerts, Pieter; Meyers, Johan; Meneveau, Charles; Gayme, Dennice

    2015-11-01

    Coordinated control of wind turbines within a wind farm, accounting for wake interactions and associated flow phenomena, has the potential to provide a number of important services to the power grid. In this work we develop a simple time-dependent extension of a standard steady-state wake model that is used to obtain an optimal control strategy for tracking a time-varying power signal. First, we introduce a one-dimensional convection-diffusion equation for wind turbine wakes that is based on the Jensen wake model and the actuator disk model. This equation is tested during wind farm start up by comparing to large-eddy simulations of wind farms with both aligned and staggered turbine arrangements. Second, we investigate optimal control for power tracking applications, where turbines are controlled via the local thrust coefficient. The control strategy is designed to minimize the squared difference between the modeled farm power and a given power reference signal. Finally, the control strategies obtained are tested using large-eddy simulations. CS, CM, and DG are supported by NSF (SEP-1230788 and IIA-1243482, the WINDINSPIRE project). PB and JM are supported by ERC (ActiveWindFarms, grant no: 306471).

  16. Effects of Convective Transport of Solute and Impurities on Defect-Causing Kinetics Instabilities

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.; Higginbotham, Henry Keith (Technical Monitor)

    2001-01-01

    For in-situ studies of the formation and evolution of step patterns during the growth of protein crystals, we have designed and assembled an experimental setup based on Michelson interferometry with the surface of the growing protein crystal as one of the reflective surfaces. The crystallization part of the device allows optical monitoring of a face of a crystal growing at temperature stable within 0.05 C in a developed solution flow of controlled direction and speed. The reference arm of the interferometer contains a liquid-crystal element that allows controlled shifts of the phase of the interferograms. We employ an image processing algorithm which combines five images with a pi/2 phase difference between each pair of images. The images are transferred to a computer by a camera capable of capturing 6-8 frames per second. The device allows data collection data regarding growth over a relatively large area (approximately .3 sq. mm) in-situ and in real time during growth. The estimated dept resolution of the phase shifting interferometry is about 100 A. The lateral resolution, depending on the zoom ratio, varies between 0.3 and 0.6 micrometers. We have now collected quantitative results on the onset, initial stages and development of instabilities in moving step trains on vicinal crystal surfaces at varying supersaturation, position on the facet, crystal size and temperature with the proteins ferritin, apoferritin and thaumatin. Comparisons with theory, especially with the AFM results on the molecular level processes, see below, allow tests of the rational for the effects of convective flows and, as a particular case, the lack thereof, on step bunching.

  17. Reactive Transport Modeling of the Enhancement of Density-Driven CO2 Convective Mixing in Carbonate Aquifers and its Potential Implication on Geological Carbon Sequestration

    PubMed Central

    Islam, Akand; Sun, Alexander Y.; Yang, Changbing

    2016-01-01

    We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO2 sequestration. PMID:27094448

  18. Reactive transport modeling of the enhancement of density-driven CO2 convective mixing in carbonate aquifers and its potential implication on geological carbon sequestration

    DOE PAGES

    Islam, Akand; Sun, Alexander Y.; Yang, Changbing

    2016-04-20

    We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the densitymore » increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Furthermore, early saturation of the reservoir can have negative impact on CO2 sequestration.« less

  19. Reactive transport modeling of the enhancement of density-driven CO2 convective mixing in carbonate aquifers and its potential implication on geological carbon sequestration

    SciTech Connect

    Islam, Akand; Sun, Alexander Y.; Yang, Changbing

    2016-04-20

    We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Furthermore, early saturation of the reservoir can have negative impact on CO2 sequestration.

  20. Three-dimensional benchmark for variable-density flow and transport simulation: matching semi-analytic stability modes for steady unstable convection in an inclined porous box

    USGS Publications Warehouse

    Voss, Clifford I.; Simmons, Craig T.; Robinson, Neville I.

    2010-01-01

    This benchmark for three-dimensional (3D) numerical simulators of variable-density groundwater flow and solute or energy transport consists of matching simulation results with the semi-analytical solution for the transition from one steady-state convective mode to another in a porous box. Previous experimental and analytical studies of natural convective flow in an inclined porous layer have shown that there are a variety of convective modes possible depending on system parameters, geometry and inclination. In particular, there is a well-defined transition from the helicoidal mode consisting of downslope longitudinal rolls superimposed upon an upslope unicellular roll to a mode consisting of purely an upslope unicellular roll. Three-dimensional benchmarks for variable-density simulators are currently (2009) lacking and comparison of simulation results with this transition locus provides an unambiguous means to test the ability of such simulators to represent steady-state unstable 3D variable-density physics.

  1. Reactive Transport Modeling of the Enhancement of Density-Driven CO2 Convective Mixing in Carbonate Aquifers and its Potential Implication on Geological Carbon Sequestration

    NASA Astrophysics Data System (ADS)

    Islam, Akand; Sun, Alexander Y.; Yang, Changbing

    2016-04-01

    We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO2 sequestration.

  2. Reactive Transport Modeling of the Enhancement of Density-Driven CO2 Convective Mixing in Carbonate Aquifers and its Potential Implication on Geological Carbon Sequestration.

    PubMed

    Islam, Akand; Sun, Alexander Y; Yang, Changbing

    2016-04-20

    We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO2 sequestration.

  3. New evidence and modeling studies of cross-tropopause transport of water substance by deep convective storms

    NASA Astrophysics Data System (ADS)

    Wang, P. K.

    2016-12-01

    Water vapor in the stratosphere can intercept substantial amount of terrestrial infrared radiation, thus causing exasperation of global warming at the surface due to increasing CO2. It also serves as the source material for making stratospheric odd hydrogen species that may cause ozone depletion through certain catalytic cycles. It is therefore very important to identify the process via which water vapor is transported across the tropopause into the stratosphere. Transport of water substance into the stratosphere by deep convective storms have been investigated by the author since around 2000, and in 2003 he proposed that it is the internal gravity wave breaking at the storm top that causes the water substance to penetrate through the tropopause and enter the stratosphere. Since then increasing evidence, including the observation of above-anvil cirrus plumes, jumping cirrus at the storm top, and the so-called pancake clouds, have been suggested as the manifestation of this wave breaking phenomenon. Cloud-resolving model studies did show the clear connection between these phenomena and wave breaking. Still there are several unresolved questions such as whether or not the jumping cirrus eventually evolves into plumes and whether the pancake clouds really exist. In this paper, I will show new aircraft and satellite observational evidence that confirm the above questions. These evidence demonstrate that the jumping cirrus can indeed evolve into plumes as observed by satellite storm images and that new rapid scan satellite storm images reveal the existence of the pancake clouds. New high resolution model simulations show cloud top features that match the observation very well and thus vindicating the role of gravity wave breaking in this process. Model results also give an estimate of the cross-tropopause transport of water substance that is much larger than previously thought.

  4. Relationships of dispersive mass transport and stochastic convective flow through hydrologic systems

    SciTech Connect

    Simmons, C.S.

    1981-01-01

    Uncertainty in water flow velocity appears to be a major factor in determining the magnitude of contaminant dispersion expected in a ground water system. This report discusses some concepts and mathematical methods relating dispersive contaminant transport to stochastic aspects of ground water flow. The theory developed should not be construed as absolutely rigorous mathematics, but is presented with the intention of clarifying the physical concepts.

  5. Convection and bulk transport. [review of theoretical developments in low gravity processing

    NASA Technical Reports Server (NTRS)

    Brown, R. A.

    1986-01-01

    Progress in the theoretical understanding of transport phenomena for materials processing systems in a microgravity environment is assessed. Fluid experiments and processing in space may be performed without containers. Processes that are secondary on the earth may become significant in space, e.g., the natural oscillation of a fluid. Results are summarized from experiments on oscillatory behavior, the effects of electrical charge, and nonaxisymmetric disturbances in suspended drops in a microgravity environment.

  6. Response of convective-diffusive transport to spatial and temporal variations in effective gravity

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.; Ouazzani, Jalil; Rosenberger, Franz

    1988-01-01

    The response of heat, mass, and momentum transport to conditions characteristic of the microgravity environment is studied. It is found that the orientation of the experiment with respect to the steady component of the residual gravity is a crucial factor in determining the suitability of the spacecraft as a means of suppressing or eliminating unwanted effects caused by buoyant fluid motion. The process is highly sensitive to transient disturbances.

  7. Polymer heat transport enhancement in thermal convection: the case of Rayleigh-Taylor turbulence.

    PubMed

    Boffetta, G; Mazzino, A; Musacchio, S; Vozella, L

    2010-05-07

    We study the effects of polymer additives on turbulence generated by the ubiquitous Rayleigh-Taylor instability. Numerical simulations of complete viscoelastic models provide clear evidence that the heat transport is enhanced up to 50% with respect to the Newtonian case. This phenomenon is accompanied by a speed-up of the mixing layer growth. We give a phenomenological interpretation of these results based on small-scale turbulent reduction induced by polymers.

  8. Effects of Surface Heat Flux Anomalies on Stratification, Convective Growth and Vertical Transport within the Saharan Boundary Layer

    NASA Astrophysics Data System (ADS)

    Huang, Qian; Marsham, John; Parker, Doug; Tian, Wenshou; Grams, Christian; Cuesta, Juan; Flamant, Cyrille

    2010-05-01

    The very large surface sensible and very low latent heat fluxes in the Sahara desert lead to its unusually deep, almost dry-adiabatic boundary layer, that often reaches 6 km. This is often observed to consist of a shallow convective boundary layer (CBL) with a near neutral residual layer above (the Saharan Residual Layer, or SRL). It has been shown that the SRL can be both spatially extensive and persist throughout the day. Multiple near-neutral layers are frequently observed within the SRL, or within the SAL, each with a different water vapour and/or dust content, and each separated by a weak lid (e.g., Figure 1). A local maximum in not only relative humidity, but also water vapour mixing ratio (WVMR) is often seen at the top of the SRL or SAL. This structure suggests that in some locations, at some times, convection from the surface is mixing the full depth of the Saharan boundary layer, but in most locations and times this is not the case, and varying horizontal advection leads to the multiple layering observed. During the GERBILS (GERB Intercomparison of Longwave and Shortwave radiation) field campaign in the Sahara, coherent couplings were observed between surface albedo, CBL air temeperatures and CBL winds. Using two cases based on observations from GERBILS, large eddy model (LEM) simulations have been used to investigate the effects of surface flux anomalies on the growth of the summertime Saharan CBL into the Saharan Residual layer (SRL) above, and transport from the CBL into the SRL. Hot surface anomalies generated updraughts and convergence in the CBL that increased transport from the CBL into the SRL. The induced subsidence in regions away from the anomalies inhibited growth of the CBL there. If the domain-averaged surface fluxes were kept constant this led to a shallower, cooler CBL. If fluxes outside the anomalies were kept constant, so that stronger anomalies led to increased domain-averaged fluxes, this gave a warmer, shallower CBL. These effects

  9. Shield weight optimization using Monte Carlo transport calculations

    NASA Technical Reports Server (NTRS)

    Jordan, T. M.; Wohl, M. L.

    1972-01-01

    Outlines are given of the theory used in FASTER-3 Monte Carlo computer program for the transport of neutrons and gamma rays in complex geometries. The code has the additional capability of calculating the minimum weight layered unit shield configuration which will meet a specified dose rate constraint. It includes the treatment of geometric regions bounded by quadratic and quardric surfaces with multiple radiation sources which have a specified space, angle, and energy dependence. The program calculates, using importance sampling, the resulting number and energy fluxes at specified point, surface, and volume detectors. Results are presented for sample problems involving primary neutron and both primary and secondary photon transport in a spherical reactor shield configuration. These results include the optimization of the shield configuration.

  10. Optimal Filtering in Mass Transport Modeling From Satellite Gravimetry Data

    NASA Astrophysics Data System (ADS)

    Ditmar, P.; Hashemi Farahani, H.; Klees, R.

    2011-12-01

    Monitoring natural mass transport in the Earth's system, which has marked a new era in Earth observation, is largely based on the data collected by the GRACE satellite mission. Unfortunately, this mission is not free from certain limitations, two of which are especially critical. Firstly, its sensitivity is strongly anisotropic: it senses the north-south component of the mass re-distribution gradient much better than the east-west component. Secondly, it suffers from a trade-off between temporal and spatial resolution: a high (e.g., daily) temporal resolution is only possible if the spatial resolution is sacrificed. To make things even worse, the GRACE satellites enter occasionally a phase when their orbit is characterized by a short repeat period, which makes it impossible to reach a high spatial resolution at all. A way to mitigate limitations of GRACE measurements is to design optimal data processing procedures, so that all available information is fully exploited when modeling mass transport. This implies, in particular, that an unconstrained model directly derived from satellite gravimetry data needs to be optimally filtered. In principle, this can be realized with a Wiener filter, which is built on the basis of covariance matrices of noise and signal. In practice, however, a compilation of both matrices (and, therefore, of the filter itself) is not a trivial task. To build the covariance matrix of noise in a mass transport model, it is necessary to start from a realistic model of noise in the level-1B data. Furthermore, a routine satellite gravimetry data processing includes, in particular, the subtraction of nuisance signals (for instance, associated with atmosphere and ocean), for which appropriate background models are used. Such models are not error-free, which has to be taken into account when the noise covariance matrix is constructed. In addition, both signal and noise covariance matrices depend on the type of mass transport processes under

  11. A revised model of fluid transport optimization in Physarum polycephalum.

    PubMed

    Bonifaci, Vincenzo

    2017-02-01

    Optimization of fluid transport in the slime mold Physarum polycephalum has been the subject of several modeling efforts in recent literature. Existing models assume that the tube adaptation mechanism in P. polycephalum's tubular network is controlled by the sheer amount of fluid flow through the tubes. We put forward the hypothesis that the controlling variable may instead be the flow's pressure gradient along the tube. We carry out the stability analysis of such a revised mathematical model for a parallel-edge network, proving that the revised model supports the global flow-optimizing behavior of the slime mold for a substantially wider class of response functions compared to previous models. Simulations also suggest that the same conclusion may be valid for arbitrary network topologies.

  12. Optimal device and method for transportation of isolated porcine islet.

    PubMed

    Kim, T-S; Lee, H-S; Oh, S-H; Moon, H; Lee, S; Song, S; Shin, M; Park, J B; Kim, S-J; Joh, J-W; Lee, S-K

    2013-10-01

    We investigated the optimal method for transportation of isolated porcine islets from an isolation facility to a transplant hospital or research center in terms of temperature, oxygen supply, and shaking effect. Commercially available insulator boxes with thermoregulators exposed for 5 hours under two external temperatures (4°C and 37°C) were monitored using HOBO temperature loggers. To find the optimal transport device, we compared islet counts, viability, quality, and function in conical tubes, gas-permeable bags (GPB) and gas-permeable flasks (GPF) after 1, 3 and 5 hours. To evaluate the effects of shaking on islets, we also analyzed the difference between a control and a shaking group in each device with time. Commercially available Styrofoam insulators with thermoregulators maintained the internal temperature near the target. Islet recovery rate for GPF, which was higher than other devices, was maintained, while those decreased with time for conical tube and GPB containers adenosine diphosphate/adenosine triphosphate (ADP/ATP) ratio for GPF was lower than other devices, albeit not significantly fluoroscein acrimide/propidium iodide (AO/PI) ratio for GPF was higher than other devices after 5 hours. Glucose stimulated index was not different among the devices. In comparison with the control group, shaking yielded comparable islet survival, viability and function. Our study demonstrated that the use of commercially available insulator boxes with thermoregulators maintained internal temperature close to the target value and that GPF was more favorable for islet oxygenation during transportation. This study also suggested negligible impact of shaking on isolated porcine islets during transportation. Copyright © 2013 Elsevier Inc. All rights reserved.

  13. Local design optimization for composite transport fuselage crown panels

    NASA Technical Reports Server (NTRS)

    Swanson, G. D.; Ilcewicz, L. B.; Walker, T. H.; Graesser, D.; Tuttle, M.; Zabinsky, Z.

    1992-01-01

    Composite transport fuselage crown panel design and manufacturing plans were optimized to have projected cost and weight savings of 18 percent and 45 percent, respectively. These savings are close to those quoted as overall NASA ACT program goals. Three local optimization tasks were found to influence the cost and weight of fuselage crown panels. This paper summarizes the effect of each task and describes in detail the task associated with a design cost model. Studies were performed to evaluate the relationship between manufacturing cost and design details. A design tool was developed to aid in these investigations. The development of the design tool included combining cost and performance constraints with a random search optimization algorithm. The resulting software was used in a series of optimization studies that evaluated the sensitivity of design variables, guidelines, criteria, and material selection on cost. The effect of blending adjacent design points in a full scale panel subjected to changing load distributions and local variations was shown to be important. Technical issues and directions for future work were identified.

  14. Surrogate-Based Optimization of Biogeochemical Transport Models

    NASA Astrophysics Data System (ADS)

    Prieß, Malte; Slawig, Thomas

    2010-09-01

    First approaches towards a surrogate-based optimization method for a one-dimensional marine biogeochemical model of NPZD type are presented. The model, developed by Oschlies and Garcon [1], simulates the distribution of nitrogen, phytoplankton, zooplankton and detritus in a water column and is driven by ocean circulation data. A key issue is to minimize the misfit between the model output and given observational data. Our aim is to reduce the overall optimization cost avoiding expensive function and derivative evaluations by using a surrogate model replacing the high-fidelity model in focus. This in particular becomes important for more complex three-dimensional models. We analyse a coarsening in the discretization of the model equations as one way to create such a surrogate. Here the numerical stability crucially depends upon the discrete stepsize in time and space and the biochemical terms. We show that for given model parameters the level of grid coarsening can be choosen accordingly yielding a stable and satisfactory surrogate. As one example of a surrogate-based optimization method we present results of the Aggressive Space Mapping technique (developed by John W. Bandler [2, 3]) applied to the optimization of this one-dimensional biogeochemical transport model.

  15. Concurrent Monte Carlo transport and fluence optimization with fluence adjusting scalable transport Monte Carlo

    PubMed Central

    Svatos, M.; Zankowski, C.; Bednarz, B.

    2016-01-01

    Purpose: The future of radiation therapy will require advanced inverse planning solutions to support single-arc, multiple-arc, and “4π” delivery modes, which present unique challenges in finding an optimal treatment plan over a vast search space, while still preserving dosimetric accuracy. The successful clinical implementation of such methods would benefit from Monte Carlo (MC) based dose calculation methods, which can offer improvements in dosimetric accuracy when compared to deterministic methods. The standard method for MC based treatment planning optimization leverages the accuracy of the MC dose calculation and efficiency of well-developed optimization methods, by precalculating the fluence to dose relationship within a patient with MC methods and subsequently optimizing the fluence weights. However, the sequential nature of this implementation is computationally time consuming and memory intensive. Methods to reduce the overhead of the MC precalculation have been explored in the past, demonstrating promising reductions of computational time overhead, but with limited impact on the memory overhead due to the sequential nature of the dose calculation and fluence optimization. The authors propose an entirely new form of “concurrent” Monte Carlo treat plan optimization: a platform which optimizes the fluence during the dose calculation, reduces wasted computation time being spent on beamlets that weakly contribute to the final dose distribution, and requires only a low memory footprint to function. In this initial investigation, the authors explore the key theoretical and practical considerations of optimizing fluence in such a manner. Methods: The authors present a novel derivation and implementation of a gradient descent algorithm that allows for optimization during MC particle transport, based on highly stochastic information generated through particle transport of very few histories. A gradient rescaling and renormalization algorithm, and the

  16. Study of global heat transport and plume morphology in severely-confined Rayleigh-Bénard convection

    NASA Astrophysics Data System (ADS)

    Xia, Ke-Qing; Chong, Kai Leong

    2016-11-01

    We study systematically how severe geometrical confinement influences the global heat transport (expressed as Nusselt number Nu) and the plume morphology in Rayleigh-Bénard convection (RBC) by means of direct numerical simulations. Broad ranges of width-to-height aspect-ratio (1 / 128 <= Γ <= 1) and Rayleigh number (3 ×104 <= Ra <=1011) at fixed Prandtl number Pr = 4 . 38 are considered in present study. It is found that Nu exhibits the scaling Nu - 1 Ra 0 . 61 over three decades of Ra at Γ = 1 / 128 and the flow is dominated by finger-like, long-lived plume columns for such severely-confined situation. The Nu scaling and the flow structures contrast sharply to that found at Γ = 1 for which Nu exhibits the scaling Nu - 1 Ra 0 . 31 and the flow is dominated by mushroom-like, fragmented thermal plumes. Analogy is made between the severely-confined RBC and strongly rotating RBC. This work was supported by RGC of HKSAR (No. CUHK404513), CUHK Direct Grant (No. 3132740) and through a HKPhD Fellowship.

  17. Effect of polymer additives on heat transport and large-scale circulation in turbulent Rayleigh-Bénard convection

    NASA Astrophysics Data System (ADS)

    Cheng, Jian-Ping; Zhang, Hong-Na; Cai, Wei-Hua; Li, Si-Ning; Li, Feng-Chen

    2017-07-01

    The present paper presents direct numerical simulations of Rayleigh-Bénard convection (RBC) in an enclosed cell filled with the polymer solution in order to investigate the viscoelastic effect on the characteristics of heat transport and large-scale circulation (LSC) of RBC. To overcome the difficulties in numerically solving a high Weissenberg number (Wi) problem of viscoelastic fluid flow with strong elastic effect, the log-conformation reformulation method was implemented. Numerical results showed that the addition of polymers reduced the heat flux and the amount of heat transfer reduction (HTR) behaves nonmonotonically, which firstly increases but then decreases with Wi. The maximum HTR reaches around 8.7 % at the critical Wi. The nonmonotonic behavior of HTR as a function of Wi was then corroborated with the modifications of the period of LSC and turbulent energy as well as viscous boundary layer thickness. Finally, a standard turbulent kinetic energy (TKE) budget analysis was done for the whole domain, the boundary layer region, and the bulk region. It showed that the role change of elastic stress contributions to TKE is mainly responsible for this nonmonotonic behavior of HTR.

  18. Experiences performing conceptual design optimization of transport aircraft

    NASA Technical Reports Server (NTRS)

    Arbuckle, P. D.; Sliwa, S. M.

    1984-01-01

    Optimum Preliminary Design of Transports (OPDOT) is a computer program developed at NASA Langley Research Center for evaluating the impact of new technologies upon transport aircraft. For example, it provides the capability to look at configurations which have been resized to take advantage of active controls and provide and indication of economic sensitivity to its use. Although this tool returns a conceptual design configuration as its output, it does not have the accuracy, in absolute terms, to yield satisfactory point designs for immediate use by aircraft manufacturers. However, the relative accuracy of comparing OPDOT-generated configurations while varying technological assumptions has been demonstrated to be highly reliable. Hence, OPDOT is a useful tool for ascertaining the synergistic benefits of active controls, composite structures, improved engine efficiencies and other advanced technological developments. The approach used by OPDOT is a direct numerical optimization of an economic performance index. A set of independent design variables is iterated, given a set of design constants and data. The design variables include wing geometry, tail geometry, fuselage size, and engine size. This iteration continues until the optimum performance index is found which satisfies all the constraint functions. The analyst interacts with OPDOT by varying the input parameters to either the constraint functions or the design constants. Note that the optimization of aircraft geometry parameters is equivalent to finding the ideal aircraft size, but with more degrees of freedom than classical design procedures will allow.

  19. An optimal transportation approach for nuclear structure-based pathology

    PubMed Central

    Wang, Wei; Ozolek, John A.; Slepčev, Dejan; Lee, Ann B.; Chen, Cheng; Rohde, Gustavo K.

    2012-01-01

    Nuclear morphology and structure as visualized from histopathology microscopy images can yield important diagnostic clues in some benign and malignant tissue lesions. Precise quantitative information about nuclear structure and morphology, however, is currently not available for many diagnostic challenges. This is due, in part, to the lack of methods to quantify these differences from image data. We describe a method to characterize and contrast the distribution of nuclear structure in different tissue classes (normal, benign, cancer, etc.). The approach is based on quantifying chromatin morphology in different groups of cells using the optimal transportation (Kantorovich-Wasserstein) metric in combination with the Fisher discriminant analysis and multidimensional scaling techniques. We show that the optimal transportation metric is able to measure relevant biological information as it enables automatic determination of the class (e.g. normal vs. cancer) of a set of nuclei. We show that the classification accuracies obtained using this metric are, on average, as good or better than those obtained utilizing a set of previously described numerical features. We apply our methods to two diagnostic challenges for surgical pathology: one in the liver and one in the thyroid. Results automatically computed using this technique show potentially biologically relevant differences in nuclear structure in liver and thyroid cancers. PMID:20977984

  20. Optimization of atmospheric transport models on HPC platforms

    NASA Astrophysics Data System (ADS)

    de la Cruz, Raúl; Folch, Arnau; Farré, Pau; Cabezas, Javier; Navarro, Nacho; Cela, José María

    2016-12-01

    The performance and scalability of atmospheric transport models on high performance computing environments is often far from optimal for multiple reasons including, for example, sequential input and output, synchronous communications, work unbalance, memory access latency or lack of task overlapping. We investigate how different software optimizations and porting to non general-purpose hardware architectures improve code scalability and execution times considering, as an example, the FALL3D volcanic ash transport model. To this purpose, we implement the FALL3D model equations in the WARIS framework, a software designed from scratch to solve in a parallel and efficient way different geoscience problems on a wide variety of architectures. In addition, we consider further improvements in WARIS such as hybrid MPI-OMP parallelization, spatial blocking, auto-tuning and thread affinity. Considering all these aspects together, the FALL3D execution times for a realistic test case running on general-purpose cluster architectures (Intel Sandy Bridge) decrease by a factor between 7 and 40 depending on the grid resolution. Finally, we port the application to Intel Xeon Phi (MIC) and NVIDIA GPUs (CUDA) accelerator-based architectures and compare performance, cost and power consumption on all the architectures. Implications on time-constrained operational model configurations are discussed.

  1. Analysis regarding the transport network models. Case study on finding the optimal transport route

    NASA Astrophysics Data System (ADS)

    Stîngă, V.-G.

    2017-08-01

    Transport networks are studied most of the time from a graph theory perspective, mostly studied in a static way, in order to emphasize their characteristics like: topology, morphology, costs, traffic flows etc. There are many methods used to describe these characteristics at local and global level. Usually when analysing the transport network models, the aim is to achieve minimum capacity transit or minimum cost of operating or investment. Throughout this paper we will get an insight into the many models of the transport network that were presented over the years and we will try to make a short analysis regarding the most important ones. We will make a case study on finding the optimal route by using one of the models presented within this paper.

  2. Forced convection and transport effects during hyperbaric laser chemical vapor deposition

    SciTech Connect

    Maxwell, James L; Chavez, Craig A; Espinoza, Miguel; Black, Marcie; Maskaly, Karlene; Boman, Mats

    2009-01-01

    This work explores mass transport processes during HP-LCYD, including the transverse forced-flow of precursor gases through a nozzle to enhance fiber growth rates. The use of laser trapping and suspension of nano-scale particles in the precursor flow is also described, providing insights into the nature of the gas flow, including jetting from the fiber tip and thermodiffusion processes near the reaction zone. The effects of differing molecular-weight buffer gases is also explored in conjunction with the Soret effect, and it is found that nucleation at the deposit surface (and homogeneous nucleation in the gas phase) can be enhanced/ retarded, depending on the buffer gas molecular weight. To demonstrate that extensive microstructures can be grown simultaneously, three-dimensional fiber arrays are also grown in-parallel using diffractive optics--without delatory effects from neighboring reaction sites.

  3. Impact of internal transport on the convective mass transfer from a droplet into a submerging falling film

    NASA Astrophysics Data System (ADS)

    Landel, Julien R.; Thomas, Amalia; McEvoy, Harry; Dalziel, Stuart B.

    2015-11-01

    We investigate the convective mass transfer of dilute passive tracers contained in small viscous drops into a submerging falling film. This problem has applications in industrial cleaning, domestic dishwashers, and decontamination of hazardous material. The film Peclet number is very high, whereas the drop Peclet number varies from 0.1 to 1. The characteristic transport time in the drop is much larger than in the film. We model the mass transfer using an analogy with Newton's law of cooling. This empirical model is supported by an analytical model solving the quasi-steady two-dimensional advection-diffusion equation in the film that is coupled with a time-dependent one-dimensional diffusion equation in the drop. We find excellent agreement between our experimental data and the two models, which predict an exponential decrease in time of the drop concentration. The transport characteristic time is related to the drop diffusion time scale, as diffusion within the drop is the limiting process. Our theoretical model not only predicts the well-known relationship between the Sherwood number and the external Reynolds number in the case of a well-mixed drop Sh ~ Re1/3, it also predicts a correction in the case of a non-uniform drop concentration. The correction depends on Re, the film Schmidt number, the drop aspect ratio and the diffusivity ratio between the two phases. This prediction is in good agreement with experimental data. This material is based upon work supported by the Defense Threat Reduction Agency under Contract No. HDTRA1-12-D-0003-0001.

  4. Flight Experiments of Physical Vapor Transport of ZnSe: Growth of Crystals in Various Convective Conditions

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    2015-01-01

    A low gravity material experiment will be performed in the Material Science Research Rack (MSRR) on International Space Station (ISS). The flight experiment will conduct crystal growths of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, by physical vapor transport (PVT). The main objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the grown crystals as results of buoyancy-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions. This talk will focus on the ground-based studies on the PVT crystal growth of ZnSe and related ternary compounds, especially the effects of different growth orientations related to gravity direction on the grown crystals.

  5. Seasonal differences of vertical-transport efficiency in the tropical tropopause layer: On the interplay between tropical deep convection, large-scale vertical ascent, and horizontal circulations

    NASA Astrophysics Data System (ADS)

    Bergman, John W.; Jensen, Eric J.; Pfister, Leonhard; Yang, Qiong

    2012-03-01

    Winter-summer differences in the transport of air from the boundary layer to the lower stratosphere at low latitudes are investigated with ensembles of back trajectory calculations that track parcels from the 380 K isentropic surface to their convective detrainment in the tropical tropopause layer (TTL) during the winter of 2006-2007 and summer of 2007. Horizontal displacements for the trajectories are calculated from reanalysis data; potential temperature displacements are calculated from radiative heating rates derived from observed cloud, water vapor, ozone, and temperature variations; and the locations' convective detrainments are determined by satellite observations of convective clouds. Weaker upwelling in the TTL during boreal summer compared with that of winter both slows the ascent through the TTL and raises the height threshold that convective detrainment must surpass in order for ascent to occur, restricting the injection of new air into the stratosphere during summer. In addition, anticyclonic circulations associated with convective activity contribute to vertical transport in the TTL by guiding detrained air parcels through regions with the strongest upwelling. These features combine to make monsoon-related convection over the Indian subcontinent the dominant source of new air during summer. In contrast, winter sources are spread over the southern continents and the western Pacific Ocean. These seasonal differences imply that air entering the tropical stratosphere during summer is older but might nevertheless be more polluted than air entering during winter. While poor data sampling in the TTL makes it difficult to validate our results, they are bolstered by favorable comparisons with previous studies of the TTL, by sensitivity tests that reveal important dynamical influences on surface-to-stratospheric transport, and by the robustness of dynamical interactions that systematically associate deep convection with anticyclonic circulations and strong

  6. Connecting Surface Emissions, Convective Uplifting, and Long-Range Transport of Carbon Monoxide in the Upper Troposphere: New Observations from the Aura Microwave Limb Sounder

    NASA Technical Reports Server (NTRS)

    Jiang, Jonathan H.; Livesey, Nathaniel J.; Su, Hui; Neary, Lori; McConnell, John C.; Richards, Nigel A. D.

    2007-01-01

    Two years of observations of upper tropospheric (UT) carbon monoxide (CO) from the Aura Microwave Limb Sounder are analyzed; in combination with the CO surface emission climatology and data from the NCEP analyses. It is shown that spatial distribution, temporal variation and long-range transport of UT CO are closely related to the surface emissions, deep-convection and horizontal winds. Over the Asian monsoon region, surface emission of CO peaks in boreal spring due to high biomass burning in addition to anthropogenic emission. However, the UT CO peaks in summer when convection is strongest and surface emission of CO is dominated by anthropogenic source. The long-range transport of CO from Southeast Asia across the Pacific to North America, which occurs most frequently during boreal summer, is thus a clear imprint of Asian anthropogenic pollution influencing global air quality.

  7. Connecting Surface Emissions, Convective Uplifting, and Long-Range Transport of Carbon Monoxide in the Upper Troposphere: New Observations from the Aura Microwave Limb Sounder

    NASA Technical Reports Server (NTRS)

    Jiang, Jonathan H.; Livesey, Nathaniel J.; Su, Hui; Neary, Lori; McConnell, John C.; Richards, Nigel A. D.

    2007-01-01

    Two years of observations of upper tropospheric (UT) carbon monoxide (CO) from the Aura Microwave Limb Sounder are analyzed; in combination with the CO surface emission climatology and data from the NCEP analyses. It is shown that spatial distribution, temporal variation and long-range transport of UT CO are closely related to the surface emissions, deep-convection and horizontal winds. Over the Asian monsoon region, surface emission of CO peaks in boreal spring due to high biomass burning in addition to anthropogenic emission. However, the UT CO peaks in summer when convection is strongest and surface emission of CO is dominated by anthropogenic source. The long-range transport of CO from Southeast Asia across the Pacific to North America, which occurs most frequently during boreal summer, is thus a clear imprint of Asian anthropogenic pollution influencing global air quality.

  8. Implicit solution of the material transport in Stokes flow simulation: Toward thermal convection simulation surrounded by free surface

    NASA Astrophysics Data System (ADS)

    Furuichi, Mikito; May, Dave A.

    2015-07-01

    We present implicit time integration schemes suitable for modeling free surface Stokes flow dynamics with marker in cell (MIC) based spatial discretization. Our target is for example thermal convection surrounded by deformable surface boundaries to simulate the long term planetary formation process. The numerical system becomes stiff when the dynamical balancing time scale for the increasing/decreasing load by surface deformation is very short compared with the time scale associated with thermal convection. Any explicit time integration scheme will require very small time steps; otherwise, serious numerical oscillation (spurious solutions) will occur. The implicit time integration scheme possesses a wider stability region than the explicit method; therefore, it is suitable for stiff problems. To investigate an efficient solution method for the stiff Stokes flow system, we apply first (backward Euler (BE)) and second order (trapezoidal method (TR) and trapezoidal rule-backward difference formula (TR-BDF2)) accurate implicit methods for the MIC solution scheme. The introduction of implicit time integration schemes results in nonlinear systems of equations. We utilize a Jacobian free Newton Krylov (JFNK) based Newton framework to solve the resulting nonlinear equations. In this work we also investigate two efficient implicit solution strategies to reduce the computational cost when solving stiff nonlinear systems. The two methods differ in how the advective term in the material transport evolution equation is treated. We refer to the method that employs Lagrangian update as "fully implicit" (Imp), whilst the method that employs Eulerian update is referred to as "semi-implicit" (SImp). Using a finite difference (FD) method, we have performed a series of numerical experiments which clarify the accuracy of solutions and trade-off between the computational cost associated with the nonlinear solver and time step size. In comparison with the general explicit Euler method

  9. Convection and hemoglobin-based oxygen carrier enhanced oxygen transport in a hepatic hollow fiber bioreactor.

    PubMed

    Sullivan, Jesse P; Harris, David R; Palmer, Andre F

    2008-01-01

    Hepatic hollow fiber bioreactors are a promising class of bioartificial liver assist device (BLAD). The development of this type of device is currently hindered by limited oxygen transport to cultured hepatocytes, due to low solubility of oxygen in aqueous media. In order to increase the oxygen spectrum to cultured hepatocytes housed within a hollow fiber bioreactor, several different engineering strategies were explored in this study. These included: supplementing the circulating media stream of the hollow fiber bioreactor with a hemoglobin-based oxygen carrier (bovine red blood cells) with defined oxygen binding and release kinetics and operating the bioreactor with media flow through the hollow fiber membrane into the extracapillary space (ECS). We hypothesize that these two strategies can be used to improve hepatocyte oxygenation and possibly attain an in vivo-like pO(2) spectrum, similar to that observed in vivo in the liver sinusoid. This work is significant, since provision of an in vivo-like pO(2) spectrum should create a fully functional BLAD that could potentially bridge thousands of liver failure patients towards native liver regeneration of damaged tissue or, if necessary, orthotopic liver transplantation.

  10. Aerosol transport and wet scavenging in deep convective clouds: A case study and model evaluation using a multiple passive tracer analysis approach

    NASA Astrophysics Data System (ADS)

    Yang, Qing; Easter, Richard C.; Campuzano-Jost, Pedro; Jimenez, Jose L.; Fast, Jerome D.; Ghan, Steven J.; Wang, Hailong; Berg, Larry K.; Barth, Mary C.; Liu, Ying; Shrivastava, Manishkumar B.; Singh, Balwinder; Morrison, Hugh; Fan, Jiwen; Ziegler, Conrad L.; Bela, Megan; Apel, Eric; Diskin, Glenn S.; Mikoviny, Tomas; Wisthaler, Armin

    2015-08-01

    Wet scavenging of aerosols by continental deep convective clouds is studied for a supercell storm complex observed over Oklahoma during the Deep Convective Clouds and Chemistry campaign. A new passive-tracer-based transport analysis framework is developed to characterize convective transport using vertical profiles of several passive trace gases. For this case, the analysis estimates that observed passive gas mixing ratios in the upper troposphere convective outflow consist of 47% low level (<3 km) inflow air, 32% entrained midtroposphere air, and 21% upper troposphere air. The new analysis framework is used to estimate aerosol wet scavenging efficiencies. Observations yield high overall scavenging efficiencies of 81% for submicron aerosol mass. Organic, sulfate, and ammonium aerosols have similar wet scavenging efficiencies (80%-84%). The apparent scavenging efficiency for nitrate aerosol is much lower (57%), but the scavenging efficiency for nitrate aerosol plus nitric acid combined (84%) is close to the other species. Scavenging efficiencies for aerosol number are high for larger particles (84% for 0.15-2.5 µm diameter) but are lower for smaller particles (64% for 0.03-0.15 µm). The storm is simulated using the chemistry version of the Weather Research and Forecasting model. Compared to the observation-based analysis, the standard model strongly underestimates aerosol scavenging efficiencies by 32% and 41% in absolute differences for submicron mass and number. Adding a new treatment of secondary activation significantly improves simulated aerosol scavenging, producing wet scavenging efficiencies that are only 7% and 8% lower than observed efficiencies. This finding emphasizes the importance of secondary activation for aerosol wet removal in deep convective storms.

  11. Universal scaling of optimal current distribution in transportation networks.

    PubMed

    Simini, Filippo; Rinaldo, Andrea; Maritan, Amos

    2009-04-01

    Transportation networks are inevitably selected with reference to their global cost which depends on the strengths and the distribution of the embedded currents. We prove that optimal current distributions for a uniformly injected d -dimensional network exhibit robust scale-invariance properties, independently of the particular cost function considered, as long as it is convex. We find that, in the limit of large currents, the distribution decays as a power law with an exponent equal to (2d-1)/(d-1). The current distribution can be exactly calculated in d=2 for all values of the current. Numerical simulations further suggest that the scaling properties remain unchanged for both random injections and by randomizing the convex cost functions.

  12. Hydromagnetic transport phenomena from a stretching or shrinking nonlinear nanomaterial sheet with Navier slip and convective heating: A model for bio-nano-materials processing

    NASA Astrophysics Data System (ADS)

    Uddin, M. J.; Bég, O. Anwar; Amin, N.

    2014-11-01

    Steady two-dimensional magnetohydrodynamic laminar free convective boundary layer slip flow of an electrically conducting Newtonian nanofluid from a translating stretching/shrinking sheet in a quiescent fluid is studied. A convective heating boundary condition is incorporated. The transport equations along with the boundary conditions are first converted into dimensionless form and following the implementation of a linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth fifth order method from Maple. Validation of the Maple solutions is achieved with previous non-magnetic published results. The effects of the emerging thermophysical parameters; namely, stretching/shrinking, velocity slip, magnetic field, convective heat transfer and buoyancy ratio parameters, on the dimensionless velocity, temperature and concentration (nanoparticle fraction) are depicted graphically and interpreted at length. It is found that velocity increases whilst temperature and concentration reduce with the velocity slip. Magnetic field causes to reduce velocity and enhances temperature and concentration. Velocity, temperature as well as concentration rises with convective heating parameter. The study is relevant to the synthesis of bio-magnetic nanofluids of potential interest in wound treatments, skin repair and smart coatings for biological devices.

  13. Experimental container shape dependence and heat transport scaling of Rayleigh-Bénard convection of high-Prandtl-number fluids

    NASA Astrophysics Data System (ADS)

    Johnston, Stephen; Fonda, Enrico; Sreenivasan, Katepalli R.; Ranjan, Devesh

    2016-11-01

    Both experiments and simulations on Rayleigh-Bénard convection with fluids of Prandtl numbers 5 and below have shown that the container shape influences the flow structure. Here, we investigate similar dependences of convection of fluids with Prandtl numbers of up to 104. The convection cells have aspect ratio of order unity, and we use cubic and cylindrical shapes. Visual analysis using a noninvasive photochromic dye technique indicates the distinct large-scale flow patterns in both square and cylindrical test cells. The stability of these flow patterns is explored. Also presented are results on the Nusselt-Rayleigh scaling for moderate Rayleigh numbers.

  14. Stochastic-convective transport with nonlinear reaction and mixing: application to intermediate-scale experiments in aerobic biodegradation in saturated porous media.

    PubMed

    Ginn, T R; Murphy, E M; Chilakapati, A; Seeboonruang, U

    2001-03-01

    Aerobic biodegradation of benzoate by Pseudomonas cepacia sp. in a saturated heterogeneous porous medium was simulated using the stochastic-convective reaction (SCR) approach. A laboratory flow cell was randomly packed with low permeability silt-size inclusions in a high permeability sand matrix. In the SCR upscaling approach, the characteristics of the flow field are determined by the breakthrough of a conservative tracer. Spatial information on the actual location of the heterogeneities is not used. The mass balance equations governing the nonlinear and multicomponent reactive transport are recast in terms of reactive transports in each of a finite number of discrete streamtubes. The streamtube ensemble members represent transport via a steady constant average velocity per streamtube and a conventional Fickian dispersion term, and their contributions to the observed breakthroughs are determined by flux-averaging the streamtube solute concentrations. The resulting simulations were compared to those from a high-resolution deterministic simulation of the reactive transport, and to alternative ensemble representations involving (i) effective Fickian travel time distribution function, (ii) purely convective streamtube transport, and (iii) streamtube ensemble subset simulations. The results of the SCR simulation compare favorably to that of a sophisticated high-resolution deterministic approach.

  15. Stochastic-convective transport with nonlinear reaction and mixing: application to intermediate-scale experiments in aerobic biodegradation in saturated porous media

    NASA Astrophysics Data System (ADS)

    Ginn, T. R.; Murphy, E. M.; Chilakapati, A.; Seeboonruang, U.

    2001-03-01

    Aerobic biodegradation of benzoate by Pseudomonas cepacia sp. in a saturated heterogeneous porous medium was simulated using the stochastic-convective reaction (SCR) approach. A laboratory flow cell was randomly packed with low permeability silt-size inclusions in a high permeability sand matrix. In the SCR upscaling approach, the characteristics of the flow field are determined by the breakthrough of a conservative tracer. Spatial information on the actual location of the heterogeneities is not used. The mass balance equations governing the nonlinear and multicomponent reactive transport are recast in terms of reactive transports in each of a finite number of discrete streamtubes. The streamtube ensemble members represent transport via a steady constant average velocity per streamtube and a conventional Fickian dispersion term, and their contributions to the observed breakthroughs are determined by flux-averaging the streamtube solute concentrations. The resulting simulations were compared to those from a high-resolution deterministic simulation of the reactive transport, and to alternative ensemble representations involving (i) effective Fickian travel time distribution function, (ii) purely convective streamtube transport, and (iii) streamtube ensemble subset simulations. The results of the SCR simulation compare favorably to that of a sophisticated high-resolution deterministic approach.

  16. Development of a real-time transport performance optimization methodology

    NASA Technical Reports Server (NTRS)

    Gilyard, Glenn

    1996-01-01

    The practical application of real-time performance optimization is addressed (using a wide-body transport simulation) based on real-time measurements and calculation of incremental drag from forced response maneuvers. Various controller combinations can be envisioned although this study used symmetric outboard aileron and stabilizer. The approach is based on navigation instrumentation and other measurements found on state-of-the-art transports. This information is used to calculate winds and angle of attack. Thrust is estimated from a representative engine model as a function of measured variables. The lift and drag equations are then used to calculate lift and drag coefficients. An expression for drag coefficient, which is a function of parasite drag, induced drag, and aileron drag, is solved from forced excitation response data. Estimates of the parasite drag, curvature of the aileron drag variation, and minimum drag aileron position are produced. Minimum drag is then obtained by repositioning the symmetric aileron. Simulation results are also presented which evaluate the affects of measurement bias and resolution.

  17. Cerebrospinal and Interstitial Fluid Transport via the Glymphatic Pathway Modeled by Optimal Mass Transport

    PubMed Central

    Ratner, Vadim; Gao, Yi; Lee, Hedok; Elkin, Rena; Nedergaard, Maiken; Benveniste, Helene; Tannenbaum, Allen

    2017-01-01

    The glymphatic pathway is a system which facilitates continuous cerebrospinal fluid (CSF) and interstitial fluid (ISF) exchange and plays a key role in removing waste products from the rodent brain. Dysfunction of the glymphatic pathway may be implicated in the pathophysiology of Alzheimer's disease. Intriguingly, the glymphatic system is most active during deep wave sleep general anesthesia. By using paramagnetic tracers administered into CSF of rodents, we previously showed the utility of MRI in characterizing a macroscopic whole brain view of glymphatic transport but we have yet to define and visualize the specific flow patterns. Here we have applied an alternative mathematical analysis approach to a dynamic time series of MRI images acquired every 4 min over ∼3 hrs in anesthetized rats, following administration of a small molecular weight paramagnetic tracer into the CSF reservoir of the cisterna magna. We use Optimal Mass Transport (OMT) to model the glymphatic flow vector field, and then analyze the flow to find the network of CSF-ISF flow channels. We use 3D visualization computational tools to visualize the OMT defined network of CSF-ISF flow channels in relation to anatomical and vascular key landmarks from the live rodent brain. The resulting OMT model of the glymphatic transport network agrees largely with the current understanding of the glymphatic transport patterns defined by dynamic contrast-enhanced MRI revealing key CSF transport pathways along the ventral surface of the brain with a trajectory towards the pineal gland, cerebellum, hypothalamus and olfactory bulb. In addition, the OMT analysis also revealed some interesting previously unnoticed behaviors regarding CSF transport involving parenchymal streamlines moving from ventral reservoirs towards the surface of the brain, olfactory bulb and large central veins. PMID:28323163

  18. Cerebrospinal and interstitial fluid transport via the glymphatic pathway modeled by optimal mass transport.

    PubMed

    Ratner, Vadim; Gao, Yi; Lee, Hedok; Elkin, Rena; Nedergaard, Maiken; Benveniste, Helene; Tannenbaum, Allen

    2017-03-18

    The glymphatic pathway is a system which facilitates continuous cerebrospinal fluid (CSF) and interstitial fluid (ISF) exchange and plays a key role in removing waste products from the rodent brain. Dysfunction of the glymphatic pathway may be implicated in the pathophysiology of Alzheimer's disease. Intriguingly, the glymphatic system is most active during deep wave sleep general anesthesia. By using paramagnetic tracers administered into CSF of rodents, we previously showed the utility of MRI in characterizing a macroscopic whole brain view of glymphatic transport but we have yet to define and visualize the specific flow patterns. Here we have applied an alternative mathematical analysis approach to a dynamic time series of MRI images acquired every 4min over ∼3h in anesthetized rats, following administration of a small molecular weight paramagnetic tracer into the CSF reservoir of the cisterna magna. We use Optimal Mass Transport (OMT) to model the glymphatic flow vector field, and then analyze the flow to find the network of CSF-ISF flow channels. We use 3D visualization computational tools to visualize the OMT defined network of CSF-ISF flow channels in relation to anatomical and vascular key landmarks from the live rodent brain. The resulting OMT model of the glymphatic transport network agrees largely with the current understanding of the glymphatic transport patterns defined by dynamic contrast-enhanced MRI revealing key CSF transport pathways along the ventral surface of the brain with a trajectory towards the pineal gland, cerebellum, hypothalamus and olfactory bulb. In addition, the OMT analysis also revealed some interesting previously unnoticed behaviors regarding CSF transport involving parenchymal streamlines moving from ventral reservoirs towards the surface of the brain, olfactory bulb and large central veins.

  19. A concept for adaptive performance optimization on commercial transport aircraft

    NASA Technical Reports Server (NTRS)

    Jackson, Michael R.; Enns, Dale F.

    1995-01-01

    An adaptive control method is presented for the minimization of drag during flight for transport aircraft. The minimization of drag is achieved by taking advantage of the redundant control capability available in the pitch axis, with the horizontal tail used as the primary surface and symmetric deflection of the ailerons and cruise flaps used as additional controls. The additional control surfaces are excited with sinusoidal signals, while the altitude and velocity loops are closed with guidance and control laws. A model of the throttle response as a function of the additional control surfaces is formulated and the parameters in the model are estimated from the sensor measurements using a least squares estimation method. The estimated model is used to determine the minimum drag positions of the control surfaces. The method is presented for the optimization of one and two additional control surfaces. The adaptive control method is extended to optimize rate of climb with the throttle fixed. Simulations that include realistic disturbances are presented, as well as the results of a Monte Carlo simulation analysis that shows the effects of changing the disturbance environment and the excitation signal parameters.

  20. Modeling marine surface microplastic transport to assess optimal removal locations

    NASA Astrophysics Data System (ADS)

    Sherman, Peter; van Sebille, Erik

    2016-01-01

    Marine plastic pollution is an ever-increasing problem that demands immediate mitigation and reduction plans. Here, a model based on satellite-tracked buoy observations and scaled to a large data set of observations on microplastic from surface trawls was used to simulate the transport of plastics floating on the ocean surface from 2015 to 2025, with the goal to assess the optimal marine microplastic removal locations for two scenarios: removing the most surface microplastic and reducing the impact on ecosystems, using plankton growth as a proxy. The simulations show that the optimal removal locations are primarily located off the coast of China and in the Indonesian Archipelago for both scenarios. Our estimates show that 31% of the modeled microplastic mass can be removed by 2025 using 29 plastic collectors operating at a 45% capture efficiency from these locations, compared to only 17% when the 29 plastic collectors are moored in the North Pacific garbage patch, between Hawaii and California. The overlap of ocean surface microplastics and phytoplankton growth can be reduced by 46% at our proposed locations, while sinks in the North Pacific can only reduce the overlap by 14%. These results are an indication that oceanic plastic removal might be more effective in removing a greater microplastic mass and in reducing potential harm to marine life when closer to shore than inside the plastic accumulation zones in the centers of the gyres.

  1. Advanced subgrid-scale modeling for convection-dominated species transport at fluid interfaces with application to mass transfer from rising bubbles

    NASA Astrophysics Data System (ADS)

    Weiner, Andre; Bothe, Dieter

    2017-10-01

    This paper presents a novel subgrid scale (SGS) model for simulating convection-dominated species transport at deformable fluid interfaces. One possible application is the Direct Numerical Simulation (DNS) of mass transfer from rising bubbles. The transport of a dissolving gas along the bubble-liquid interface is determined by two transport phenomena: convection in streamwise direction and diffusion in interface normal direction. The convective transport for technical bubble sizes is several orders of magnitude higher, leading to a thin concentration boundary layer around the bubble. A true DNS, fully resolving hydrodynamic and mass transfer length scales results in infeasible computational costs. Our approach is therefore a DNS of the flow field combined with a SGS model to compute the mass transfer between bubble and liquid. An appropriate model-function is used to compute the numerical fluxes on all cell faces of an interface cell. This allows to predict the mass transfer correctly even if the concentration boundary layer is fully contained in a single cell layer around the interface. We show that the SGS-model reduces the resolution requirements at the interface by a factor of ten and more. The integral flux correction is also applicable to other thin boundary layer problems. Two flow regimes are investigated to validate the model. A semi-analytical solution for creeping flow is used to assess local and global mass transfer quantities. For higher Reynolds numbers ranging from Re = 100 to Re = 460 and Péclet numbers between Pe =104 and Pe = 4 ṡ106 we compare the global Sherwood number against correlations from literature. In terms of accuracy, the predicted mass transfer never deviates more than 4% from the reference values.

  2. Uncertainties in atmospheric chemistry modelling due to convection parameterisations and subsequent scavenging

    NASA Astrophysics Data System (ADS)

    Tost, H.; Lawrence, M. G.; Brühl, C.; Jöckel, P.; Gabriel Team; Scout-O3-Darwin/Active Team

    2010-02-01

    Moist convection in global modelling contributes significantly to the transport of energy, momentum, water and trace gases and aerosols within the troposphere. Since convective clouds are on a scale too small to be resolved in a global model their effects have to be parameterised. However, the whole process of moist convection and especially its parameterisations are associated with uncertainties. In contrast to previous studies on the impact of convection on trace gases, which had commonly neglected the convective transport for some or all compounds, we investigate this issue by examining simulations with five different convection schemes. This permits an uncertainty analysis due to the process formulation, without the inconsistencies inherent in entirely neglecting deep convection or convective tracer transport for one or more tracers. Both the simulated mass fluxes and tracer distributions are analysed. Investigating the distributions of compounds with different characteristics, e.g., lifetime, chemical reactivity, solubility and source distributions, some differences can be attributed directly to the transport of these compounds, whereas others are more related to indirect effects, such as the transport of precursors, chemical reactivity in certain regions, and sink processes. The model simulation data are compared with the average regional profiles of several measurement campaigns, and in detail with two campaigns in fall and winter 2005 in Suriname and Australia, respectively. The shorter-lived a compound is, the larger the differences and consequently the uncertainty due to the convection parameterisation are, as long as it is not completely controlled by local production that is independent of convection and its impacts (e.g. water vapour changes). Whereas for long-lived compounds like CO or O3 the mean differences between the simulations are less than 25%), differences for short-lived compounds reach up to ±100% with different convection schemes. A rating

  3. Thermocapillary Convection in Liquid Droplets

    NASA Technical Reports Server (NTRS)

    1986-01-01

    The purpose of this video is to understand the effects of surface tension on fluid convection. The fluid system chosen is the liquid sessile droplet to show the importance in single crystal growth, the spray drying and cooling of metal, and the advance droplet radiators of the space stations radiators. A cross sectional representation of a hemispherical liquid droplet under ideal conditions is used to show internal fluid motion. A direct simulation of buoyancy-dominant convection and surface tension-dominant convection is graphically displayed. The clear differences between two mechanisms of fluid transport, thermocapillary convection, and bouncy dominant convection is illustrated.

  4. Multigrid optimal mass transport for image registration and morphing

    NASA Astrophysics Data System (ADS)

    Rehman, Tauseef ur; Tannenbaum, Allen

    2007-02-01

    In this paper we present a computationally efficient Optimal Mass Transport algorithm. This method is based on the Monge-Kantorovich theory and is used for computing elastic registration and warping maps in image registration and morphing applications. This is a parameter free method which utilizes all of the grayscale data in an image pair in a symmetric fashion. No landmarks need to be specified for correspondence. In our work, we demonstrate significant improvement in computation time when our algorithm is applied as compared to the originally proposed method by Haker et al [1]. The original algorithm was based on a gradient descent method for removing the curl from an initial mass preserving map regarded as 2D vector field. This involves inverting the Laplacian in each iteration which is now computed using full multigrid technique resulting in an improvement in computational time by a factor of two. Greater improvement is achieved by decimating the curl in a multi-resolutional framework. The algorithm was applied to 2D short axis cardiac MRI images and brain MRI images for testing and comparison.

  5. Transportation optimization with fuzzy trapezoidal numbers based on possibility theory.

    PubMed

    He, Dayi; Li, Ran; Huang, Qi; Lei, Ping

    2014-01-01

    In this paper, a parametric method is introduced to solve fuzzy transportation problem. Considering that parameters of transportation problem have uncertainties, this paper develops a generalized fuzzy transportation problem with fuzzy supply, demand and cost. For simplicity, these parameters are assumed to be fuzzy trapezoidal numbers. Based on possibility theory and consistent with decision-makers' subjectiveness and practical requirements, the fuzzy transportation problem is transformed to a crisp linear transportation problem by defuzzifying fuzzy constraints and objectives with application of fractile and modality approach. Finally, a numerical example is provided to exemplify the application of fuzzy transportation programming and to verify the validity of the proposed methods.

  6. The impact of ENSO on water vapor isotopologues in the tropical pacific: Evidence for changes in long-range transport and convective activity

    NASA Astrophysics Data System (ADS)

    Jonson Sutanto, Samuel; Hoffmann, Georg; Scheepmaker, Remco A.; Röckmann, Thomas

    2014-05-01

    ENSO (El Niño-Southern Oscillation) is characterized by quasi-periodic changes of tropical sea surface temperature (SST), near-global atmospheric circulation and associated changes in precipitation patterns. Due to the profound effects of ENSO on the global water cycle and on the associated fractionation processes of the water isotopologues, many isotope-based studies have been carried out to study the ENSO variability in the tropics. These studies conclude that "the isotope amount effect'' is a key factor controlling the isotopic signature of water vapor and precipitation close to the surface. The goal of this study is to investigate the hydrologic processes governing the changes in isotopic composition of water vapor at the surface and at higher altitudes during ENSO events. We used the isotopic composition of water vapor modeled by an isotope-enabled GCM (ECHAM4), and measured by the TES (Tropospheric Emission Spectrometer) instrument onboard the Aura satellite. The isotopic composition of precipitation was modeled by ECHAM4 and observed by the GNIP network (Global Network of Isotopes in Precipitation). The amount of precipitation was modeled by ECHAM4 and ERA-Interim (ECMWF Re-Analysis), and measured by the TRMM (Tropical Rainfall Measuring Mission) satellite. Our results agree with previous studies focusing on the lower atmosphere: rainout processes, less rain re-evaporation of falling droplets, and increase of convective updrafts and diffusive exchange within the convective systems (all these processes contribute to "the isotope amount effect'') isotopically deplete the water vapor during wet conditions (e.g. El Niño in Central Pacific and La Niña in West Pacific). However, we find that the isotope signal of water vapor at higher altitudes (e.g. 500 hPa) associated with ENSO events diverges from the near surface signature. Analysis suggests that at higher altitudes, transport of enriched water vapor from lower atmospheric layers through convective updrafts

  7. Magneto-convection.

    PubMed

    Stein, Robert F

    2012-07-13

    Convection is the transport of energy by bulk mass motions. Magnetic fields alter convection via the Lorentz force, while convection moves the fields via the curl(v×B) term in the induction equation. Recent ground-based and satellite telescopes have increased our knowledge of the solar magnetic fields on a wide range of spatial and temporal scales. Magneto-convection modelling has also greatly improved recently as computers become more powerful. Three-dimensional simulations with radiative transfer and non-ideal equations of state are being performed. Flux emergence from the convection zone through the visible surface (and into the chromosphere and corona) has been modelled. Local, convectively driven dynamo action has been studied. The alteration in the appearance of granules and the formation of pores and sunspots has been investigated. Magneto-convection calculations have improved our ability to interpret solar observations, especially the inversion of Stokes spectra to obtain the magnetic field and the use of helioseismology to determine the subsurface structure of the Sun.

  8. Tropical Convection's Roles in Tropical Tropopause Cirrus

    NASA Technical Reports Server (NTRS)

    Boehm, Matthew T.; Starr, David OC.; Verlinde, Johannes; Lee, Sukyoung

    2002-01-01

    The results presented here show that tropical convection plays a role in each of the three primary processes involved in the in situ formation of tropopause cirrus. First, tropical convection transports moisture from the surface into the upper troposphere. Second, tropical convection excites Rossby waves that transport zonal momentum toward the ITCZ, thereby generating rising motion near the equator. This rising motion helps transport moisture from where it is detrained from convection to the cold-point tropopause. Finally, tropical convection excites vertically propagating tropical waves (e.g. Kelvin waves) that provide one source of large-scale cooling near the cold-point tropopause, leading to tropopause cirrus formation.

  9. Numerical study of the influence of forced melt convection on the impurities transport in a silicon directional solidification process

    NASA Astrophysics Data System (ADS)

    Popescu, Alexandra; Vizman, Daniel

    2017-09-01

    Time dependent three-dimensional numerical simulations were carried out in order to understand the effects of forced convection induced by electromagnetic stirring of the melt, on the crucible dissolution rate and on the impurity distribution in multicrystalline silicon (mc-Si) melt for different values of the diffusion coefficient and electric and magnetic field parameters. Once the electromagnetic stirring is switched on, in a relative short period of time approx. 400 s the impurities are almost homogenized in the whole melt. The dissolution rate was estimated from the total mass of impurities that was found in the silicon melt after a certain period of time. The obtained results show that enhanced convection produced by the electromagnetic stirring leads to a moderate increase of the dissolution rate and also to a uniform distribution of impurities in the melt.

  10. Effects of the aspect ratio on the optimal tilting angle for maximum convection heat transfer across air-filled rectangular enclosures differentially heated at sides

    NASA Astrophysics Data System (ADS)

    Cianfrini, C.; Corcione, M.; Habib, E.; Quintino, A.

    2017-06-01

    Natural convection in air-filled rectangular cavities inclined with respect to gravity, so that the heated wall is facing upwards, is studied numerically under the assumption of two-dimensional laminar flow. A computational code based on the SIMPLE-C algorithm is used for the solution of the system of the mass, momentum and energy transfer governing equations. Simulations are performed for height-to-width aspect ratios of the enclosure from 0.25 to 8, Rayleigh numbers based on the length of the heated and cooled walls from 102 to 107, and tilting angles of the enclosure from 0° to 75°. The existence of an optimal tilting angle is confirmed for any investigated configuration, at a location that increases as the Rayleigh number is decreased, and the height-to-width aspect ratio of the cavity are increased, unless the value of the Rayleigh number is that corresponding to the onset of convection or just higher. Dimensionless correlating equations are developed to predict the optimal tilting angle and the heat transfer performance of the enclosure.

  11. Advanced Understanding of Convection Initiation and Optimizing Cloud Seeding by Advanced Remote Sensing and Land Cover Modification over the United Arab Emirates

    NASA Astrophysics Data System (ADS)

    Wulfmeyer, V.; Behrendt, A.; Branch, O.; Schwitalla, T.

    2016-12-01

    A prerequisite for significant precipitation amounts is the presence of convergence zones. These are due to land surface heterogeneity, orography as well as mesoscale and synoptic scale circulations. Only, if these convergence zones are strong enough and interact with an upper level instability, deep convection can be initiated. For the understanding of convection initiation (CI) and optimal cloud seeding deployment, it is essential that these convergence zones are detected before clouds are developing in order to preempt the decisive microphysical processes for liquid water and ice formation. In this presentation, a new project on Optimizing Cloud Seeding by Advanced Remote Sensing and Land Cover Modification (OCAL) is introduced, which is funded by the United Arab Emirates Rain Enhancement Program (UAEREP). This project has two research components. The first component focuses on an improved detection and forecasting of convergence zones and CI by a) operation of scanning Doppler lidar and cloud radar systems during two seasonal field campaigns in orographic terrain and over the desert in the UAE, and b) advanced forecasting of convergence zones and CI with the WRF-NOAHMP model system. Nowcasting to short-range forecasting of convection will be improved by the assimilation of Doppler lidar and the UAE radar network data. For the latter, we will apply a new model forward operator developed at our institute. Forecast uncertainties will be assessed by ensemble simulations driven by ECMWF boundaries. The second research component of OCAL will study whether artificial modifications of land surface heterogeneity are possible through plantations or changes of terrain, leading to an amplification of convergence zones. This is based on our pioneering work on high-resolution modeling of the impact of plantations on weather and climate in arid regions. A specific design of the shape and location of plantations can lead to the formation of convergence zones, which can

  12. A continuous linear optimal transport approach for pattern analysis in image datasets

    PubMed Central

    Kolouri, Soheil; Tosun, Akif B.; Ozolek, John A.; Rohde, Gustavo K.

    2015-01-01

    We present a new approach to facilitate the application of the optimal transport metric to pattern recognition on image databases. The method is based on a linearized version of the optimal transport metric, which provides a linear embedding for the images. Hence, it enables shape and appearance modeling using linear geometric analysis techniques in the embedded space. In contrast to previous work, we use Monge's formulation of the optimal transport problem, which allows for reasonably fast computation of the linearized optimal transport embedding for large images. We demonstrate the application of the method to recover and visualize meaningful variations in a supervised-learning setting on several image datasets, including chromatin distribution in the nuclei of cells, galaxy morphologies, facial expressions, and bird species identification. We show that the new approach allows for high-resolution construction of modes of variations and discrimination and can enhance classification accuracy in a variety of image discrimination problems. PMID:26858466

  13. Plasma confinement modification and convective transport suppression in the scrape-off layer using additional gas puffing in the STOR-M tokamak

    NASA Astrophysics Data System (ADS)

    Dreval, M.; Hubeny, M.; Ding, Y.; Onchi, T.; Liu, Y.; Hthu, K.; Elgriw, S.; Xiao, C.; Hirose, A.

    2013-03-01

    The influence of short gas puffing (GP) pulses on the scrape-off layer (SOL) transport is studied. Similar responses of ion saturation current and floating potential measured near the GP injection valve and in the 90° toroidally separated cross-section suggest that the GP influence on the SOL region should be global. A drop in plasma temperature and a decrease in the rotational velocity of the plasma are observed in the SOL region immediately after the GP pulse; however, an unexpected increase in electron and ion temperatures is observed in the second stage of the plasma response. The decrease in floating potential fluctuations indicates that the turbulent transport is dumped immediately after the GP pulse. The GP-induced modification of turbulence properties in the SOL points to a convective transport suppression in the STOR-M tokamak. A substantial decrease in the skewness and kurtosis of ion saturation current fluctuations is observed in the SOL region resulting in the probability distribution function (PDF) getting closer to the Gaussian distribution. The plasma potential reduction, the change in plasma rotation and the suppression of turbulent transport in the SOL region indicate that the plasma confinement is modified after the GP injection. Some features of the H-mode-like confinement in the plasma bulk also accompany the SOL observations after application of the additional sharp GP pulse.

  14. Parametric study of a canard-configured transport using conceptual design optimization

    NASA Technical Reports Server (NTRS)

    Arbuckle, P. D.; Sliwa, S. M.

    1985-01-01

    Constrained-parameter optimization is used to perform optimal conceptual design of both canard and conventional configurations of a medium-range transport. A number of design constants and design constraints are systematically varied to compare the sensitivities of canard and conventional configurations to a variety of technology assumptions. Main-landing-gear location and canard surface high-lift performance are identified as critical design parameters for a statically stable, subsonic, canard-configured transport.

  15. On a global aerodynamic optimization of a civil transport aircraft

    NASA Technical Reports Server (NTRS)

    Savu, G.; Trifu, O.

    1991-01-01

    An aerodynamic optimization procedure developed to minimize the drag to lift ratio of an aircraft configuration: wing - body - tail, in accordance with engineering restrictions, is described. An algorithm developed to search a hypersurface with 18 dimensions, which define an aircraft configuration, is discussed. The results, when considered from the aerodynamic point of view, indicate the optimal configuration is one that combines a lifting fuselage with a canard.

  16. OPTIMIZING COLLAGEN TRANSPORT THROUGH TRACK-ETCHED NANOPORES

    PubMed Central

    Bueno, Ericka M.; Ruberti, Jeffrey W.

    2008-01-01

    Polymer transport through nanopores is a potentially powerful tool for separation and organization of molecules in biotechnology applications. Our goal is to produce aligned collagen fibrils by mimicking cell-mediated collagen assembly: driving collagen monomers in solution through the aligned nanopores in track-etched membranes followed by fibrillogenesis at the pore exit. We examined type I atelo-collagen monomer transport in neutral, cold solution through polycarbonate track-etched membranes comprising 80-nm-diameter, 6-μm-long pores at 2% areal fraction. Source concentrations of 1.0, 2.8 and 7.0 mg/ml and pressure differentials of 0, 10 and 20 inH2O were used. Membrane surfaces were hydrophilized via covalent poly(ethylene-glycol) binding to limit solute-membrane interaction. Collagen transport through the nanopores was a non-intuitive process due to the complex behavior of this associating molecule in semi-dilute solution. Nonetheless, a modified open pore model provided reasonable predictions of transport parameters. Transport rates were concentration- and pressure-dependent, with diffusivities across the membrane in semi-dilute solution two-fold those in dilute solution, possibly via cooperative diffusion or polymer entrainment. The most significant enhancement of collagen transport was accomplished by membrane hydrophilization. The highest concentration transported (5.99±2.58 mg/ml) with the highest monomer flux (2.60±0.49 ×103 molecules s-1 pore-1) was observed using 2.8 mg collagen/ml, 10 inH2O and hydrophilic membranes. PMID:21394216

  17. Pareto optimal calibration of highly nonlinear reactive transport groundwater models using particle swarm optimization

    NASA Astrophysics Data System (ADS)

    Siade, A. J.; Prommer, H.; Welter, D.

    2014-12-01

    Groundwater management and remediation requires the implementation of numerical models in order to evaluate the potential anthropogenic impacts on aquifer systems. In many situations, the numerical model must, not only be able to simulate groundwater flow and transport, but also geochemical and biological processes. Each process being simulated carries with it a set of parameters that must be identified, along with differing potential sources of model-structure error. Various data types are often collected in the field and then used to calibrate the numerical model; however, these data types can represent very different processes and can subsequently be sensitive to the model parameters in extremely complex ways. Therefore, developing an appropriate weighting strategy to address the contributions of each data type to the overall least-squares objective function is not straightforward. This is further compounded by the presence of potential sources of model-structure errors that manifest themselves differently for each observation data type. Finally, reactive transport models are highly nonlinear, which can lead to convergence failure for algorithms operating on the assumption of local linearity. In this study, we propose a variation of the popular, particle swarm optimization algorithm to address trade-offs associated with the calibration of one data type over another. This method removes the need to specify weights between observation groups and instead, produces a multi-dimensional Pareto front that illustrates the trade-offs between data types. We use the PEST++ run manager, along with the standard PEST input/output structure, to implement parallel programming across multiple desktop computers using TCP/IP communications. This allows for very large swarms of particles without the need of a supercomputing facility. The method was applied to a case study in which modeling was used to gain insight into the mobilization of arsenic at a deepwell injection site

  18. An intravascular bioartificial pancreas device (iBAP) with silicon nanopore membranes (SNM) for islet encapsulation under convective mass transport.

    PubMed

    Song, Shang; Blaha, Charles; Moses, Willieford; Park, Jaehyun; Wright, Nathan; Groszek, Joey; Fissell, William; Vartanian, Shant; Posselt, Andrew M; Roy, Shuvo

    2017-05-16

    Diffusion-based bioartificial pancreas (BAP) devices are limited by poor islet viability and functionality due to inadequate mass transfer resulting in islet hypoxia and delayed glucose-insulin kinetics. While intravascular ultrafiltration-based BAP devices possess enhanced glucose-insulin kinetics, the polymer membranes used in these devices provide inadequate ultrafiltrate flow rates and result in excessive thrombosis. Here, we report the silicon nanopore membrane (SNM), which exhibits a greater hydraulic permeability and a superior pore size selectivity compared to polymer membranes for use in BAP applications. Specifically, we demonstrate that the SNM-based intravascular BAP with ∼10 and ∼40 nm pore sized membranes support high islet viability (>60%) and functionality (<15 minute insulin response to glucose stimulation) at clinically relevant islet densities (5700 and 11 400 IE per cm(2)) under convection in vitro. In vivo studies with ∼10 nm pore sized SNM in a porcine model showed high islet viability (>85%) at clinically relevant islet density (5700 IE per cm(2)), c-peptide concentration of 144 pM in the outflow ultrafiltrate, and hemocompatibility under convection. These promising findings offer insights on the development of next generation of full-scale intravascular devices to treat T1D patients in the future.

  19. Gas transport processes in sea ice: How convection and diffusion processes might affect biological imprints, a challenge for modellers

    NASA Astrophysics Data System (ADS)

    Tison, J.-L.; Zhou, J.; Thomas, D. N.; Rysgaard, S.; Eicken, H.; Crabeck, O.; Deleu, F.; Delille, B.

    2012-04-01

    Recent data from a year-round survey of landfast sea ice growth in Barrow (Alaska) have shown how O2/N2 and O2/Ar ratios could be used to pinpoint primary production in sea ice and derive net productivity rates from the temporal evolution of the oxygen concentration at a given depth within the sea ice cover. These rates were however obtained surmising that neither convection, nor diffusion had affected the gas concentration profiles in the ice between discrete ice core collections. This paper discusses examples from three different field surveys (the above-mentioned Barrow experiment, the INTERICE IV tank experiment in Hamburg and a short field survey close to the Kapisilit locality in the South-East Greenland fjords) where convection or diffusion processes have clearly affected the temporal evolution of the gas profiles in the ice, therefore potentially affecting biological signatures. The INTERICE IV and Barrow experiment show that the initial equilibrium dissolved gas entrapment within the skeletal layer basically governs most of the profiles higher up in the sea ice cover during the active sea ice growth. However, as the ice layers age and cool down under the temperature gradient, bubble nucleation occurs while the concentration in the ice goes well above the theoretical one, calculated from brine equilibrium under temperature and salinity changes and observed brine volumes. This phase change locks the gases within the sea ice structure, preventing "degassing" of the ice, as is observed for salts under the mushy layer brine convection process. In some cases, mainly in the early stages of the freezing process (first 10-20 cm) where temperature gradients are strong and the ice still permeable on its whole thickness, repeated convection and bubble nucleation can actually increase the gas concentration in the ice above the one initially acquired within the skeletal layer. Convective processes will also occur on ice decay, when ice permeability is restored and the

  20. Optimal Region of the Putamen for Image-Guided Convection-Enhanced Delivery of Therapeutics in Human and Non-human Primates

    PubMed Central

    Yin, Dali; Valles, Francisco E.; Fiandaca, Massimo S.; Bringas, John; Gimenez, Francisco; Berger, Mitchel S.; Forsayeth, John; Bankiewicz, Krystof S.

    2009-01-01

    Optimal results in the direct brain delivery of brain therapeutics such as growth factors or viral vector into primate brain depends on reproducible distribution throughout the target region. In the present study, we retrospectively analyzed MRI of 25 convection-enhanced delivery (CED) infusions with MRI contrast into the putamen of non-human primates (NHP). Infused volume (Vi) was compared to total volume of distribution (Vd), vs. Vd within the target putamen. Excellent distribution of contrast agent within the putamen was obtained in 8 cases that were used to define an optimal target volume, or “green” zone. Partial or poor distribution with leakage into adjacent anatomical structures was noted in 17 cases, defining “blue” and “red” zones respectively. Quantitative containment (99 ± 1%) of infused Gadoteridol within the putamen was obtained when the cannula was placed in the green zone, 87 ± 3% in the blue zone and 49 ± 0.05% in the red zone. These results were used to determine a set of 3D stereotactic coordinates that define an optimal site for putaminal infusions in NHP and human putamen. We conclude that cannula placement and definition of optimal (green zone) stereotactic coordinates have important implications in ensuring effective delivery of therapeutics into the putamen utilizing routine stereotactic MRI localization procedures, and should be considered when local therapies such as gene transfer or protein administration are being translated into clinical therapy. PMID:19761848

  1. Effect of increased convective clearance by on-line hemodiafiltration on all cause and cardiovascular mortality in chronic hemodialysis patients – the Dutch CONvective TRAnsport STudy (CONTRAST): rationale and design of a randomised controlled trial [ISRCTN38365125

    PubMed Central

    Penne, E Lars; Blankestijn, Peter J; Bots, Michiel L; van den Dorpel, Marinus A; Grooteman, Muriel P; Nubé, Menso J; van der Tweel, Ingeborg; ter Wee, Piet M

    2005-01-01

    Background The high incidence of cardiovascular disease in patients with end stage renal disease (ESRD) is related to the accumulation of uremic toxins in the middle and large-middle molecular weight range. As online hemodiafiltration (HDF) removes these molecules more effectively than standard hemodialysis (HD), it has been suggested that online HDF improves survival and cardiovascular outcome. Thus far, no conclusive data of HDF on target organ damage and cardiovascular morbidity and mortality are available. Therefore, the CONvective TRAnsport STudy (CONTRAST) has been initiated. Methods CONTRAST is a Dutch multi-center randomised controlled trial. In this trial, approximately 800 chronic hemodialysis patients will be randomised between online HDF and low-flux HD, and followed for three years. The primary endpoint is all cause mortality. The main secondary outcome variables are fatal and non-fatal cardiovascular events. Conclusion The study is designed to provide conclusive evidence whether online HDF leads to a lower mortality and less cardiovascular events as compared to standard HD. PMID:15907201

  2. Effect of increased convective clearance by on-line hemodiafiltration on all cause and cardiovascular mortality in chronic hemodialysis patients - the Dutch CONvective TRAnsport STudy (CONTRAST): rationale and design of a randomised controlled trial [ISRCTN38365125].

    PubMed

    Penne, E Lars; Blankestijn, Peter J; Bots, Michiel L; van den Dorpel, Marinus A; Grooteman, Muriel P; Nubé, Menso J; van der Tweel, Ingeborg; Ter Wee, Piet M

    2005-05-20

    BACKGROUND: The high incidence of cardiovascular disease in patients with end stage renal disease (ESRD) is related to the accumulation of uremic toxins in the middle and large-middle molecular weight range. As online hemodiafiltration (HDF) removes these molecules more effectively than standard hemodialysis (HD), it has been suggested that online HDF improves survival and cardiovascular outcome. Thus far, no conclusive data of HDF on target organ damage and cardiovascular morbidity and mortality are available. Therefore, the CONvective TRAnsport STudy (CONTRAST) has been initiated. METHODS: CONTRAST is a Dutch multi-center randomised controlled trial. In this trial, approximately 800 chronic hemodialysis patients will be randomised between online HDF and low-flux HD, and followed for three years. The primary endpoint is all cause mortality. The main secondary outcome variables are fatal and non-fatal cardiovascular events. CONCLUSION: The study is designed to provide conclusive evidence whether online HDF leads to a lower mortality and less cardiovascular events as compared to standard HD.

  3. Cost and fuel consumption per nautical mile for two engine jet transports using OPTIM and TRAGEN

    NASA Technical Reports Server (NTRS)

    Wiggs, J. F.

    1982-01-01

    The cost and fuel consumption per nautical mile for two engine jet transports are computed using OPTIM and TRAGEN. The savings in fuel and direct operating costs per nautical mile for each of the different types of optimal trajectories over a standard profile are shown.

  4. Optimal efficiency of quantum transport in a disordered trimer.

    PubMed

    Giusteri, Giulio G; Celardo, G Luca; Borgonovi, Fausto

    2016-03-01

    Disordered quantum networks, such as those describing light-harvesting complexes, are often characterized by the presence of peripheral ringlike structures, where the excitation is initialized, and inner structures and reaction centers (RCs), where the excitation is trapped and transferred. The peripheral rings often display distinguished coherent features: Their eigenstates can be separated, with respect to the transfer of excitation, into two classes of superradiant and subradiant states. Both are important to optimize transfer efficiency. In the absence of disorder, superradiant states have an enhanced coupling strength to the RC, while the subradiant ones are basically decoupled from it. Static on-site disorder induces a coupling between subradiant and superradiant states, thus creating an indirect coupling to the RC. The problem of finding the optimal transfer conditions, as a function of both the RC energy and the disorder strength, is very complex even in the simplest network, namely, a three-level system. In this paper we analyze such trimeric structure, choosing as the initial condition an excitation on a subradiant state, rather than the more common choice of an excitation localized on a single site. We show that, while the optimal disorder is of the order of the superradiant coupling, the optimal detuning between the initial state and the RC energy strongly depends on system parameters: When the superradiant coupling is much larger than the energy gap between the superradiant and the subradiant levels, optimal transfer occurs if the RC energy is at resonance with the subradiant initial state, whereas we find an optimal RC energy at resonance with a virtual dressed state when the superradiant coupling is smaller than or comparable to the gap. The presence of dynamical noise, which induces dephasing and decoherence, affects the resonance structure of energy transfer producing an additional incoherent resonance peak, which corresponds to the RC energy being

  5. Optimal efficiency of quantum transport in a disordered trimer

    NASA Astrophysics Data System (ADS)

    Giusteri, Giulio G.; Celardo, G. Luca; Borgonovi, Fausto

    2016-03-01

    Disordered quantum networks, such as those describing light-harvesting complexes, are often characterized by the presence of peripheral ringlike structures, where the excitation is initialized, and inner structures and reaction centers (RCs), where the excitation is trapped and transferred. The peripheral rings often display distinguished coherent features: Their eigenstates can be separated, with respect to the transfer of excitation, into two classes of superradiant and subradiant states. Both are important to optimize transfer efficiency. In the absence of disorder, superradiant states have an enhanced coupling strength to the RC, while the subradiant ones are basically decoupled from it. Static on-site disorder induces a coupling between subradiant and superradiant states, thus creating an indirect coupling to the RC. The problem of finding the optimal transfer conditions, as a function of both the RC energy and the disorder strength, is very complex even in the simplest network, namely, a three-level system. In this paper we analyze such trimeric structure, choosing as the initial condition an excitation on a subradiant state, rather than the more common choice of an excitation localized on a single site. We show that, while the optimal disorder is of the order of the superradiant coupling, the optimal detuning between the initial state and the RC energy strongly depends on system parameters: When the superradiant coupling is much larger than the energy gap between the superradiant and the subradiant levels, optimal transfer occurs if the RC energy is at resonance with the subradiant initial state, whereas we find an optimal RC energy at resonance with a virtual dressed state when the superradiant coupling is smaller than or comparable to the gap. The presence of dynamical noise, which induces dephasing and decoherence, affects the resonance structure of energy transfer producing an additional incoherent resonance peak, which corresponds to the RC energy being

  6. Optimal policy for mitigating emissions in the European transport sector

    NASA Astrophysics Data System (ADS)

    Leduc, Sylvain; Piera, Patrizio; Sennai, Mesfun; Igor, Staritsky; Berien, Elbersen; Tijs, Lammens; Florian, Kraxner

    2017-04-01

    A geographic explicit techno-economic model, BeWhere (www.iiasa.ac.at/bewhere), has been developed at the European scale (Europe 28, the Balkans countries, Turkey, Moldavia and Ukraine) at a 40km grid size, to assess the potential of bioenergy from non-food feedstock. Based on the minimization of the supply chain from feedstock collection to the final energy product distribution, the model identifies the optimal bioenergy production plants in terms of spatial location, technology and capacity. The feedstock of interests are woody biomass (divided into eight types from conifers and non-conifers) and five different crop residuals. For each type of feedstock, one or multiple technologies can be applied for either heat, electricity or biofuel production. The model is run for different policy tools such as carbon cost, biofuel support, or subsidies, and the optimal mix of technologies and biomass needed is optimized to reach a production cost competitive against the actual reference system which is fossil fuel based. From this approach, the optimal mix of policy tools that can be applied country wide in Europe will be identified. The preliminary results show that high carbon tax and biofuel support contribute to the development of large scale biofuel production based on woody biomass plants mainly located in the northern part of Europe. Finally the highest emission reduction is reached with low biofuel support and high carbon tax evenly distributed in Europe.

  7. Soret and Dufour effects on MHD peristaltic transport of Jeffrey fluid in a curved channel with convective boundary conditions

    PubMed Central

    Alsaedi, Ahmad

    2017-01-01

    The purpose of present article is to examine the peristaltic flow of Jeffrey fluid in a curved channel. An electrically conducting fluid in the presence of radial applied magnetic field is considered. Analysis of heat and mass transfer is carried out. More generalized realistic constraints namely the convective conditions are utilized. Soret and Dufour effects are retained. Problems formulation is given for long wavelength and low Reynolds number assumptions. The expressions of velocity, temperature, heat transfer coefficient, concentration and stream function are computed. Effects of emerging parameters arising in solutions are analyzed in detail. It is found that velocity is not symmetric about centreline for curvature parameter. Also maximum velocity decreases with an increase in the strength of magnetic field. Further it is noticed that Soret and Dufour numbers have opposite behavior for temperature and concentration. PMID:28222160

  8. Momentum, heat, and neutral mass transport in convective atmospheric pressure plasma-liquid systems and implications for aqueous targets

    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.

  9. Inverse transport calculations in optical imaging with subspace optimization algorithms

    SciTech Connect

    Ding, Tian Ren, Kui

    2014-09-15

    Inverse boundary value problems for the radiative transport equation play an important role in optics-based medical imaging techniques such as diffuse optical tomography (DOT) and fluorescence optical tomography (FOT). Despite the rapid progress in the mathematical theory and numerical computation of these inverse problems in recent years, developing robust and efficient reconstruction algorithms remains a challenging task and an active research topic. We propose here a robust reconstruction method that is based on subspace minimization techniques. The method splits the unknown transport solution (or a functional of it) into low-frequency and high-frequency components, and uses singular value decomposition to analytically recover part of low-frequency information. Minimization is then applied to recover part of the high-frequency components of the unknowns. We present some numerical simulations with synthetic data to demonstrate the performance of the proposed algorithm.

  10. Inverse transport calculations in optical imaging with subspace optimization algorithms

    NASA Astrophysics Data System (ADS)

    Ding, Tian; Ren, Kui

    2014-09-01

    Inverse boundary value problems for the radiative transport equation play an important role in optics-based medical imaging techniques such as diffuse optical tomography (DOT) and fluorescence optical tomography (FOT). Despite the rapid progress in the mathematical theory and numerical computation of these inverse problems in recent years, developing robust and efficient reconstruction algorithms remains a challenging task and an active research topic. We propose here a robust reconstruction method that is based on subspace minimization techniques. The method splits the unknown transport solution (or a functional of it) into low-frequency and high-frequency components, and uses singular value decomposition to analytically recover part of low-frequency information. Minimization is then applied to recover part of the high-frequency components of the unknowns. We present some numerical simulations with synthetic data to demonstrate the performance of the proposed algorithm.

  11. Mixed magnetohydrodynamic convection in a Cu-water-nanofluid-filled ventilated square cavity using the Taguchi method: A numerical investigation and optimization

    NASA Astrophysics Data System (ADS)

    Milani Shirvan, Kamel; Öztop, Hakan F.; Al-Salem, Khaled

    2017-05-01

    In this paper, the optimal condition of mixed magnetohydrodynamic convection in a ventilated square cavity filled with a Cu-water nanofluid with different positions of inlet and outlet port is analyzed. To serve the purpose, the L16 (43) orthogonal Taguchi array is used by means of the Taguchi method. Discretization of the governing equations is obtained through the finite volume method and then solved with the SIMPLE algorithm. A very effective mode, namely the Taguchi method, is used for the L16 (43) orthogonal Taguchi array. The effects of Richardson number (0.01-10), Hartmann number (0-50), and inlet and outlet positions (0-0.9 H) at Φ = 1% are investigated. The entire analysis is performed for fixed Grashof number 104. It is found that the mean Nusselt number decreases by increasing the Richardson number, Hartmann number and the position of the inlet port, whereas the position of the outlet port has an increment effect on the mean Nusselt number. The optimal distance of outlet port position from the upper wall of the cavity is 0.9H at Richardson number 0.01, while the Hartmann number of optimal design for heat transfer is noted as 30. Comparison with existing studies is made as a limiting case of the considered problem.

  12. Additional double-wall roof in single-wall, closed, convective incubators: Impact on body heat loss from premature infants and optimal adjustment of the incubator air temperature.

    PubMed

    Delanaud, Stéphane; Decima, Pauline; Pelletier, Amandine; Libert, Jean-Pierre; Stephan-Blanchard, Erwan; Bach, Véronique; Tourneux, Pierre

    2016-09-01

    Radiant heat loss is high in low-birth-weight (LBW) neonates. Double-wall or single-wall incubators with an additional double-wall roof panel that can be removed during phototherapy are used to reduce Radiant heat loss. There are no data on how the incubators should be used when this second roof panel is removed. The aim of the study was to assess the heat exchanges in LBW neonates in a single-wall incubator with and without an additional roof panel. To determine the optimal thermoneutral incubator air temperature. Influence of the additional double-wall roof was assessed by using a thermal mannequin simulating a LBW neonate. Then, we calculated the optimal incubator air temperature from a cohort of human LBW neonate in the absence of the additional roof panel. Twenty-three LBW neonates (birth weight: 750-1800g; gestational age: 28-32 weeks) were included. With the additional roof panel, R was lower but convective and evaporative skin heat losses were greater. This difference can be overcome by increasing the incubator air temperature by 0.15-0.20°C. The benefit of an additional roof panel was cancelled out by greater body heat losses through other routes. Understanding the heat transfers between the neonate and the environment is essential for optimizing incubators.

  13. High speed civil transport: Sonic boom softening and aerodynamic optimization

    NASA Technical Reports Server (NTRS)

    Cheung, Samson

    1994-01-01

    An improvement in sonic boom extrapolation techniques has been the desire of aerospace designers for years. This is because the linear acoustic theory developed in the 60's is incapable of predicting the nonlinear phenomenon of shock wave propagation. On the other hand, CFD techniques are too computationally expensive to employ on sonic boom problems. Therefore, this research focused on the development of a fast and accurate sonic boom extrapolation method that solves the Euler equations for axisymmetric flow. This new technique has brought the sonic boom extrapolation techniques up to the standards of the 90's. Parallel computing is a fast growing subject in the field of computer science because of its promising speed. A new optimizer (IIOWA) for the parallel computing environment has been developed and tested for aerodynamic drag minimization. This is a promising method for CFD optimization making use of the computational resources of workstations, which unlike supercomputers can spend most of their time idle. Finally, the OAW concept is attractive because of its overall theoretical performance. In order to fully understand the concept, a wind-tunnel model was built and is currently being tested at NASA Ames Research Center. The CFD calculations performed under this cooperative agreement helped to identify the problem of the flow separation, and also aided the design by optimizing the wing deflection for roll trim.

  14. Supergranulation, a convective phenomenon

    NASA Astrophysics Data System (ADS)

    Udayashankar, Paniveni

    2015-08-01

    Observation of the Solar photosphere through high resolution instruments have long indicated that the surface of the Sun is not a tranquil, featureless surface but is beset with a granular appearance. These cellular velocity patterns are a visible manifestation of sub- photospheric convection currents which contribute substantially to the outward transport of energy from the deeper layers, thus maintaining the energy balance of the Sun as a whole.Convection is the chief mode of transport in the outer layers of all cool stars such as the Sun (Noyes,1982). Convection zone of thickness 30% of the Solar radius lies in the sub-photospheric layers of the Sun. Convection is revealed on four scales. On the scale of 1000 km, it is granulation and on the scale of 8-10 arcsec, it is Mesogranulation. The next hierarchial scale of convection ,Supergranules are in the range of 30-40 arcsec. The largest reported manifestation of convection in the Sun are ‘Giant Cells’or ‘Giant Granules’, on a typical length scale of about 108 m.'Supergranules' is caused by the turbulence that extends deep into the convection zone. They have a typical lifetime of about 20hr with spicules marking their boundaries. Gas rises in the centre of the supergranules and then spreads out towards the boundary and descends.Broadly speaking supergranules are characterized by the three parameters namely the length L, the lifetime T and the horizontal flow velocity vh . The interrelationships amongst these parameters can shed light on the underlying convective processes and are in agreement with the Kolmogorov theory of turbulence as applied to large scale solar convection (Krishan et al .2002 ; Paniveni et. al. 2004, 2005, 2010).References:1) Noyes, R.W., The Sun, Our Star (Harvard University Press, 1982)2) Krishan, V., Paniveni U., Singh , J., Srikanth R., 2002, MNRAS, 334/1,2303) Paniveni , U., Krishan, V., Singh, J., Srikanth, R., 2004, MNRAS, 347, 1279-12814) Paniveni , U., Krishan, V., Singh, J

  15. Optimal resource allocation in random networks with transportation bandwidths

    NASA Astrophysics Data System (ADS)

    Yeung, C. H.; Wong, K. Y. Michael

    2009-03-01

    We apply statistical physics to study the task of resource allocation in random sparse networks with limited bandwidths for the transportation of resources along the links. Recursive relations from the Bethe approximation are converted into useful algorithms. Bottlenecks emerge when the bandwidths are small, causing an increase in the fraction of idle links. For a given total bandwidth per node, the efficiency of allocation increases with the network connectivity. In the high connectivity limit, we find a phase transition at a critical bandwidth, above which clusters of balanced nodes appear, characterized by a profile of homogenized resource allocation similar to the Maxwell construction.

  16. Anomalously weak solar convection.

    PubMed

    Hanasoge, Shravan M; Duvall, Thomas L; Sreenivasan, Katepalli R

    2012-07-24

    Convection in the solar interior is thought to comprise structures on a spectrum of scales. This conclusion emerges from phenomenological studies and numerical simulations, though neither covers the proper range of dynamical parameters of solar convection. Here, we analyze observations of the wavefield in the solar photosphere using techniques of time-distance helioseismology to image flows in the solar interior. We downsample and synthesize 900 billion wavefield observations to produce 3 billion cross-correlations, which we average and fit, measuring 5 million wave travel times. Using these travel times, we deduce the underlying flow systems and study their statistics to bound convective velocity magnitudes in the solar interior, as a function of depth and spherical-harmonic degree ℓ. Within the wavenumber band ℓ < 60, convective velocities are 20-100 times weaker than current theoretical estimates. This constraint suggests the prevalence of a different paradigm of turbulence from that predicted by existing models, prompting the question: what mechanism transports the heat flux of a solar luminosity outwards? Advection is dominated by Coriolis forces for wavenumbers ℓ < 60, with Rossby numbers smaller than approximately 10(-2) at r/R([symbol: see text]) = 0.96, suggesting that the Sun may be a much faster rotator than previously thought, and that large-scale convection may be quasi-geostrophic. The fact that isorotation contours in the Sun are not coaligned with the axis of rotation suggests the presence of a latitudinal entropy gradient.

  17. Anomalously Weak Solar Convection

    NASA Technical Reports Server (NTRS)

    Hanasoge, Shravan M.; Duvall, Thomas L.; Sreenivasan, Katepalli R.

    2012-01-01

    Convection in the solar interior is thought to comprise structures on a spectrum of scales. This conclusion emerges from phenomenological studies and numerical simulations, though neither covers the proper range of dynamical parameters of solar convection. Here, we analyze observations of the wavefield in the solar photosphere using techniques of time-distance helioseismology to image flows in the solar interior. We downsample and synthesize 900 billion wavefield observations to produce 3 billion cross-correlations, which we average and fit, measuring 5 million wave travel times. Using these travel times, we deduce the underlying flow systems and study their statistics to bound convective velocity magnitudes in the solar interior, as a function of depth and spherical- harmonic degree l..Within the wavenumber band l < 60, convective velocities are 20-100 times weaker than current theoretical estimates. This constraint suggests the prevalence of a different paradigm of turbulence from that predicted by existing models, prompting the question: what mechanism transports the heat flux of a solar luminosity outwards? Advection is dominated by Coriolis forces for wavenumbers l < 60, with Rossby numbers smaller than approximately 10(exp -2) at r/R-solar = 0.96, suggesting that the Sun may be a much faster rotator than previously thought, and that large-scale convection may be quasi-geostrophic. The fact that isorotation contours in the Sun are not coaligned with the axis of rotation suggests the presence of a latitudinal entropy gradient.

  18. Convection in White Dwarfs

    NASA Astrophysics Data System (ADS)

    Provencal, Judith L.; Shipman, H.; Dalessio, J.; M, M.

    2012-01-01

    Convection is one of the largest sources of theoretical uncertainty in our understanding of stellar physics. Current studies of convective energy transport are based on the mixing length theory. Originally intended to depict turbulent flows in engineering situations, MLT enjoys moderate success in describing stellar convection. However, problems arising from MLT's incompleteness are apparent in studies ranging from determinations of the ages of massive stars, to understanding the structure F and early A stars, to predicting the pulsation periods of solar stars, to understanding the atmosphere of Titan. As an example for white dwarfs, Bergeron et al. (1995) show that model parameters such as flux, line profiles, energy distribution, color indices, and equivalent widths are extremely sensitive to the assumed MLT parameterization. The authors find systematic uncertainties ranging from 25% for effective temperatures to 11% for mass and radius. The WET is engaged in a long term project to empirically determine the physical properties of convection in the atmospheres of pulsating white dwarfs. The technique, outlined by Montgomery et al. (2010), uses information from nonlinear (non-sinusoidal) pulse shapes of the target star to empirically probe the physical properties of its convection zone. Approximately two thirds of all white dwarfs show nonlinear characteristics in their light curves. We present current results from WET targets in 2008-2011.

  19. Sensitivity of the optimal preliminary design of a transport to operational constraints and performance index

    NASA Technical Reports Server (NTRS)

    Sliwa, S. M.

    1980-01-01

    Constrained parameter optimization was used to perform the optimal preliminary design of a medium range transport configuration. The impact of choosing a performance index was studied and the required fare for a 15 percent return-on-investment was proposed as a figure-of-merit. A number of design constants and constraint functions were systematically varied to document the sensitivities of the optimal design to a variety of economic and technological assumptions. Additionally, a comparison is made for each of the parameter variations between the baseline configuration and the optimally redesigned configuration.

  20. Use of constrained optimization in the conceptual design of a medium-range subsonic transport

    NASA Technical Reports Server (NTRS)

    Sliwa, S. M.

    1980-01-01

    Constrained parameter optimization was used to perform the optimal conceptual design of a medium range transport configuration. The impact of choosing a given performance index was studied, and the required income for a 15 percent return on investment was proposed as a figure of merit. A number of design constants and constraint functions were systematically varied to document the sensitivities of the optimal design to a variety of economic and technological assumptions. A comparison was made for each of the parameter variations between the baseline configuration and the optimally redesigned configuration.

  1. Price of anarchy in transportation networks: efficiency and optimality control.

    PubMed

    Youn, Hyejin; Gastner, Michael T; Jeong, Hawoong

    2008-09-19

    Uncoordinated individuals in human society pursuing their personally optimal strategies do not always achieve the social optimum, the most beneficial state to the society as a whole. Instead, strategies form Nash equilibria which are often socially suboptimal. Society, therefore, has to pay a price of anarchy for the lack of coordination among its members. Here we assess this price of anarchy by analyzing the travel times in road networks of several major cities. Our simulation shows that uncoordinated drivers possibly waste a considerable amount of their travel time. Counterintuitively, simply blocking certain streets can partially improve the traffic conditions. We analyze various complex networks and discuss the possibility of similar paradoxes in physics.

  2. Optimized Superconducting Quadrupole Arrays for Multiple Beam Transport

    SciTech Connect

    Meinke, Rainer, B.; Goodzeit, Carl, L.; Ball, Millicent, J.

    2005-09-20

    This research project advanced the development of reliable, cost-effective arrays of superconducting quadrupole magnets for use in multi-beam inertial fusion accelerators. The field in each array cell must be identical and meet stringent requirements for field quality and strength. An optimized compact array design using flat double-layer pancake coils was developed. Analytical studies of edge termination methods showed that it is feasible to meet the requirements for field uniformity in all cells and elimination of stray external field in several ways: active methods that involve placement of field compensating coils on the periphery of the array or a passive method that involves use of iron shielding.

  3. A method to simulate viscous diffusion of vorticity by convective transport of vortices at a non-solenoidal velocity

    SciTech Connect

    Kempka, S.N.; Strickland, J.H.

    1993-08-01

    A numerical method to simulate viscous diffusion of vorticity using vortex blobs (i.e., without a grid) is presented. The method consists of casting the effects of viscous diffusion into an effective ``diffusion velocity`` at which vortex blobs convect. The diffusion velocity was proposed previously by Ogami and Akamatsu, but they did not consider the effects of the divergence of the diffusion velocity. In fact, the diffusion velocity is highly non-solenoidal, which significantly affects the area over which a vortex blob diffuses. A formulation is presented that relates the area expansion to the diffusion velocity divergence. By taking into account the area expansion, more accurate simulations of diffusion are obtained, as demonstrated by a comparison of numerical and analytical diffusion solutions. Results from simulations show that vortex areas expand significantly in regions of large vorticity gradients. As a result of the area expansion, adjacent vortices remain overlapped, thereby maintaining smooth solution fields. The non-solenoidal diffusion velocity method is easily implemented in vortex blob algorithms, thus facilitating the development of vortex methods to simulate flows with finite Reynolds numbers.

  4. Role of stochasticity in turbulence and convective intermittent transport at the scrape off layer of Ohmic plasma in QUEST

    SciTech Connect

    Banerjee, Santanu Ishiguro, M.; Tashima, S.; Mishra, K.; Zushi, H.; Hanada, K.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A.; Nagashima, Y.; Matsuoka, K.; Nishino, N.; Liu, H. Q.

    2014-07-15

    Statistical features of fluctuations are investigated using the fast camera imaging technique in the scrape of layer (SOL) of electron cyclotron resonance heated Ohmic plasma. Fluctuations in the SOL towards low field side are dominated by coherent convective structures (blobs). Two dimensional structures of the higher order moments (skewness s and kurtosis k) representing the shape of probability density function (PDF) are studied. s and k are seen to be functions of the magnetic field lines. s and k are consistently higher towards the bottom half of the vessel in the SOL showing the blob trajectory along the field lines from the top towards bottom of the vessel. Parabolic relation (k=As{sup 2}+C) is observed between s and k near the plasma boundary, featuring steep density gradient region and at the far SOL. The coefficient A, obtained experimentally, indicates a shift of prominence from pure drift-wave instabilities towards fully developed turbulence. Numerical coefficients characterizing the Pearson system are derived which demonstrates the progressive deviation of the PDF from Gaussian towards gamma from the density gradient region, towards the far SOL. Based on a simple stochastic differential equation, a direct correspondence between the multiplicative noise amplitude, increased intermittency, and hence change in PDF is discussed.

  5. Analytical Solution for Peristaltic Transport of Viscous Nanofluid in an Asymmetric Channel with Full Slip and Convective Conditions

    NASA Astrophysics Data System (ADS)

    Ebaid, Abdelhalim; Aly, Emad H.; Vajravelu, K.

    2017-07-01

    The peristaltic flow of nanofluids is a relatively new area of research. Scientists are of the opinion that the no-slip conditions at the boundaries are no longer valid and consequently, the first and the second order slip conditions should be addressed. In this paper, the effects of slip conditions and the convective boundary conditions at the boundary walls on the peristaltic flow of a viscous nanofluid are investigated for. Also, the exact analytical solutions are obtained for the model. The obtained results are presented through graphs and discussed. The results reveal that the two slip parameters have strong effects on the temperature and the nanoparticles volume fraction profiles. Moreover, it has been seen that the temperature and nanoparticles volume fraction profiles attain certain values when the first slip condition exceeds a specified value. However, no limit value for the second slip parameter has been detected. Further, the effects of the various emerging parameters on the flow and heat transfer characteristics have been presented.

  6. Role of stochasticity in turbulence and convective intermittent transport at the scrape off layer of Ohmic plasma in QUEST

    NASA Astrophysics Data System (ADS)

    Banerjee, Santanu; Zushi, H.; Nishino, N.; Hanada, K.; Ishiguro, M.; Tashima, S.; Liu, H. Q.; Mishra, K.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A.; Nagashima, Y.; Matsuoka, K.

    2014-07-01

    Statistical features of fluctuations are investigated using the fast camera imaging technique in the scrape of layer (SOL) of electron cyclotron resonance heated Ohmic plasma. Fluctuations in the SOL towards low field side are dominated by coherent convective structures (blobs). Two dimensional structures of the higher order moments (skewness s and kurtosis k) representing the shape of probability density function (PDF) are studied. s and k are seen to be functions of the magnetic field lines. s and k are consistently higher towards the bottom half of the vessel in the SOL showing the blob trajectory along the field lines from the top towards bottom of the vessel. Parabolic relation ( k = A s 2 + C) is observed between s and k near the plasma boundary, featuring steep density gradient region and at the far SOL. The coefficient A, obtained experimentally, indicates a shift of prominence from pure drift-wave instabilities towards fully developed turbulence. Numerical coefficients characterizing the Pearson system are derived which demonstrates the progressive deviation of the PDF from Gaussian towards gamma from the density gradient region, towards the far SOL. Based on a simple stochastic differential equation, a direct correspondence between the multiplicative noise amplitude, increased intermittency, and hence change in PDF is discussed.

  7. Convective solution transport -- An improved technique for the growth of big crystals of the superconducting {alpha}-FeSe using KCl as solvent

    SciTech Connect

    Rao, S. M.; Ling, M. C.; Ke, C. T.; Chen, T. C.; Chen, C. L.; Huang, T. W.; Wu, M. K.; Mok, B. H.; Wu, T. B.; Tsai, I.-M.; Lin, Y.-L.; Liu, H. L.; Hsu, F. C.

    2011-12-01

    An improved technique of convective solution transport using KCl as solvent at 840-790 deg. C (where mass transport takes place across a vertical temperature gradient) is described for the growth of crystals of the recently discovered superconductor {alpha}-FeSe{sub x} (x = 1-0.8). The crystals were annealed in situ at 400-350 deg. C for 20-30 h to improve the superconducting properties. Hexagonal plate like crystals measuring 5-6 mm across and 0.25-0.5 mm thick were obtained. High resolution transmission electron microscopy (HRTEM) measurements show good crystallinity and the energy dispersive x-ray analysis (EDX) gives a composition very close to the starting powders. The zero resistance temperature of the crystals was found to increase from 6.5 to 9 K as the composition is decreased from x = 0.95 to 0.9 and decrease thereafter. Similar behavior was also observed in the powder x-ray diffraction (XRD) patterns and Raman spectra with the main peak shifting to higher value until 0.9 and decrease thereafter. In addition the XRD patterns show reducing hexagonal phase reflections as x decreases to 0.9. Anisotropic magnetic behavior was observed when the magnetic field is applied parallel and perpendicular to the (101) face.

  8. Nanoparticle transport effect on magnetohydrodynamic mixed convection of electrically conductive nanofluids in micro-annuli with temperature-dependent thermophysical properties

    NASA Astrophysics Data System (ADS)

    Malvandi, A.; Moshizi, S. A.; Ganji, D. D.

    2017-04-01

    This is a numerical investigation of nanoparticle transport effect on magnetohydrodynamic mixed convective heat transfer of electrically conductive nanofluids in micro-annuli with temperature-dependent thermophysical properties. The modified Buongiorno's non-homogeneous model is applied for the nanoparticle-fluid suspension to simulate the migration of nanoparticles into the base fluid, originating from the thermophoresis (nanoparticle migration because of temperature gradient) and Brownian motion (nanoparticle slip velocity because of concentration gradient). Due to surface roughness at the solid-fluid interface in micro-annuli, the wall surfaces are subjected to a linear slip condition to assess the non-equilibrium region near the interface. The fluid flow has been assumed to be fully developed, and the governing equations including continuity, momentum, energy, and nanoparticle transport equation are reduced to a system of ordinary differential equations, before they have been solved numerically. The results are presented with and without considering the dependency of thermophysical properties upon the temperature. It is indicated that ignoring the temperature dependency of thermophysical properties does not significantly affect the flow fields and heat transfer behavior of nanofluids, but it changes the relative magnitudes. Furthermore, in the presence of magnetic field, smaller nanoparticles are more appropriate than larger ones.

  9. Convective solution transport — An improved technique for the growth of big crystals of the superconducting α-FeSe using KCl as solvent

    NASA Astrophysics Data System (ADS)

    Rao, S. M.; Mok, B. H.; Ling, M. C.; Ke, C. T.; Chen, T. K.; Tsai, I.-M.; Lin, Y.-L.; Liu, H. L.; Chen, C. L.; Hsu, F. C.; Huang, T. W.; Wu, T. B.; Wu, M. K.

    2011-12-01

    An improved technique of convective solution transport using KCl as solvent at 840-790 °C (where mass transport takes place across a vertical temperature gradient) is described for the growth of crystals of the recently discovered superconductor α-FeSex (x = 1-0.8). The crystals were annealed in situ at 400-350 °C for 20-30 h to improve the superconducting properties. Hexagonal plate like crystals measuring 5-6 mm across and 0.25-0.5 mm thick were obtained. High resolution transmission electron microscopy (HRTEM) measurements show good crystallinity and the energy dispersive x-ray analysis (EDX) gives a composition very close to the starting powders. The zero resistance temperature of the crystals was found to increase from 6.5 to 9 K as the composition is decreased from x = 0.95 to 0.9 and decrease thereafter. Similar behavior was also observed in the powder x-ray diffraction (XRD) patterns and Raman spectra with the main peak shifting to higher value until 0.9 and decrease thereafter. In addition the XRD patterns show reducing hexagonal phase reflections as x decreases to 0.9. Anisotropic magnetic behavior was observed when the magnetic field is applied parallel and perpendicular to the (101) face.

  10. Isentropic Analysis of Convective Motions

    NASA Technical Reports Server (NTRS)

    Pauluis, Olivier M.; Mrowiec, Agnieszka A.

    2013-01-01

    This paper analyzes the convective mass transport by sorting air parcels in terms of their equivalent potential temperature to determine an isentropic streamfunction. By averaging the vertical mass flux at a constant value of the equivalent potential temperature, one can compute an isentropic mass transport that filters out reversible oscillatory motions such as gravity waves. This novel approach emphasizes the fact that the vertical energy and entropy transports by convection are due to the combination of ascending air parcels with high energy and entropy and subsiding air parcels with lower energy and entropy. Such conditional averaging can be extended to other dynamic and thermodynamic variables such as vertical velocity, temperature, or relative humidity to obtain a comprehensive description of convective motions. It is also shown how this approach can be used to determine the mean diabatic tendencies from the three-dimensional dynamic and thermodynamic fields. A two-stream approximation that partitions the isentropic circulation into a mean updraft and a mean downdraft is also introduced. This offers a straightforward way to identify the mean properties of rising and subsiding air parcels. The results from the two-stream approximation are compared with two other definitions of the cloud mass flux. It is argued that the isentropic analysis offers a robust definition of the convective mass transport that is not tainted by the need to arbitrarily distinguish between convection and its environment, and that separates the irreversible convective overturning fromoscillations associated with gravity waves.

  11. CFD assessment of the effect of convective mass transport on the intracellular clearance of intracellular triglycerides in macrosteatotic hepatocytes.

    PubMed

    Yarmush, Gabriel; Santos, Lucas; Yarmush, Joshua; Koundinyan, Srivathsan; Saleem, Mubasher; Nativ, Nir I; Yarmush, Martin L; Berthiaume, Francois; Maguire, Timothy J; Guaghan, Chris

    2017-08-01

    Donor livers available to transplant for patients with end-stage liver disease are in severe shortage. One possible avenue to expand the donor pool is to recondition livers that would be otherwise discarded due to excessive fat content. Severely steatotic livers (also known as fatty livers) are highly susceptible to ischemia-reperfusion injury and as a result, primary liver non-function post-transplantation. Prior studies in isolated perfused rat livers suggest that "defatting" may be possible in a timeframe of a few hours; thus, it is conceivable that fatty liver grafts could be recovered by machine perfusion to clear stored fat from the organ prior to transplantation. However, studies using hepatoma cells and adult hepatocytes made fatty in culture report that defatting may take several days. Because cell culture studies were done in static conditions, we hypothesized that the defatting kinetics are highly sensitive to flow-mediated transport of metabolites. To investigate this question, we experimentally evaluated the effect of increasing flow rate on the defatting kinetics of cultured HepG2 cells and developed an in silico combined reaction-transport model to identify possible rate-limiting steps in the defatting process. We found that in cultured fatty HepG2 cells, the time required to clear stored fat down to lean control cells can be reduced from 48 to 4-6 h by switching from static to flow conditions. The flow required resulted in a fluid shear of .008 Pa, which did not adversely affect hepatic function. The reaction-transport model suggests that the transport of L-carnitine, which is the carrier responsible for taking free fatty acids into the mitochondria, is the key rate-limiting process in defatting that was modulated by flow. Therefore, we can ensure higher levels of L-carnitine uptake by the cells by choosing flow rates that minimize the limiting mass transport while minimizing shear stress.

  12. An optimal transport approach for seismic tomography: application to 3D full waveform inversion

    NASA Astrophysics Data System (ADS)

    Métivier, L.; Brossier, R.; Mérigot, Q.; Oudet, E.; Virieux, J.

    2016-11-01

    The use of optimal transport distance has recently yielded significant progress in image processing for pattern recognition, shape identification, and histograms matching. In this study, the use of this distance is investigated for a seismic tomography problem exploiting the complete waveform; the full waveform inversion. In its conventional formulation, this high resolution seismic imaging method is based on the minimization of the L 2 distance between predicted and observed data. Application of this method is generally hampered by the local minima of the associated L 2 misfit function, which correspond to velocity models matching the data up to one or several phase shifts. Conversely, the optimal transport distance appears as a more suitable tool to compare the misfit between oscillatory signals, for its ability to detect shifted patterns. However, its application to the full waveform inversion is not straightforward, as the mass conservation between the compared data cannot be guaranteed, a crucial assumption for optimal transport. In this study, the use of a distance based on the Kantorovich-Rubinstein norm is introduced to overcome this difficulty. Its mathematical link with the optimal transport distance is made clear. An efficient numerical strategy for its computation, based on a proximal splitting technique, is introduced. We demonstrate that each iteration of the corresponding algorithm requires solving the Poisson equation, for which fast solvers can be used, relying either on the fast Fourier transform or on multigrid techniques. The development of this numerical method make possible applications to industrial scale data, involving tenths of millions of discrete unknowns. The results we obtain on such large scale synthetic data illustrate the potentialities of the optimal transport for seismic imaging. Starting from crude initial velocity models, optimal transport based inversion yields significantly better velocity reconstructions than those based on

  13. Convective transport and scavenging of peroxides by thunderstorms observed over the central U.S. during DC3

    NASA Astrophysics Data System (ADS)

    Barth, M. C.; Bela, M. M.; Fried, A.; Wennberg, P. O.; Crounse, J. D.; St. Clair, J. M.; Blake, N. J.; Blake, D. R.; Homeyer, C. R.; Brune, W. H.; Zhang, L.; Mao, J.; Ren, X.; Ryerson, T. B.; Pollack, I. B.; Peischl, J.; Cohen, R. C.; Nault, B. A.; Huey, L. G.; Liu, X.; Cantrell, C. A.

    2016-04-01

    One of the objectives of the Deep Convective Clouds and Chemistry (DC3) field experiment was to determine the scavenging of soluble trace gases by thunderstorms. We present an analysis of scavenging of hydrogen peroxide (H2O2) and methyl hydrogen peroxide (CH3OOH) from six DC3 cases that occurred in Oklahoma and northeast Colorado. Estimates of H2O2 scavenging efficiencies are comparable to previous studies ranging from 79 to 97% with relative uncertainties of 5-25%. CH3OOH scavenging efficiencies ranged from 12 to 84% with relative uncertainties of 18-558%. The wide range of CH3OOH scavenging efficiencies is surprising, as previous studies suggested that CH3OOH scavenging efficiencies would be <10%. Cloud chemistry model simulations of one DC3 storm produced CH3OOH scavenging efficiencies of 26-61% depending on the ice retention factor of CH3OOH during cloud drop freezing, suggesting ice physics impacts CH3OOH scavenging. The highest CH3OOH scavenging efficiencies occurred in two severe thunderstorms, but there is no obvious correlation between the CH3OOH scavenging efficiency and the storm thermodynamic environment. We found a moderate correlation between the estimated entrainment rates and CH3OOH scavenging efficiencies. Changes in gas-phase chemistry due to lightning production of nitric oxide and aqueous-phase chemistry have little effect on CH3OOH scavenging efficiencies. To determine why CH3OOH can be substantially removed from storms, future studies should examine effects of entrainment rate, retention of CH3OOH in frozen cloud particles during drop freezing, and lightning-NOx production.

  14. Optimal transportation network with concave cost functions: loop analysis and algorithms.

    PubMed

    Shao, Zhen; Zhou, Haijun

    2007-06-01

    Transportation networks play a vital role in modern societies. Structural optimization of a transportation system under a given set of constraints is an issue of great practical importance. For a general transportation system whose total cost C is determined by C = Sigma(ioptimal network topology is a tree if C(ij) proportional |I(ij)|(gamma) with 0 < gamma < 1. The same conclusion also holds in the more general case where all the flow costs are strictly concave functions of the flow I(ij). To further understand the qualitative difference between systems with concave and convex cost functions, a loop analysis of transportation cost is performed in the present paper, and an alternative mathematical proof of the optimality of tree-formed networks is given. The simple intuitive picture of this proof then leads to an efficient global algorithm for the searching of optimal structures for a given transportation system with concave cost functions.

  15. Optimization of a neutron detector design using adjoint transport simulation

    SciTech Connect

    Yi, C.; Manalo, K.; Huang, M.; Chin, M.; Edgar, C.; Applegate, S.; Sjoden, G.

    2012-07-01

    A synthetic aperture approach has been developed and investigated for Special Nuclear Materials (SNM) detection in vehicles passing a checkpoint at highway speeds. SNM is postulated to be stored in a moving vehicle and detector assemblies are placed on the road-side or in chambers embedded below the road surface. Neutron and gamma spectral awareness is important for the detector assembly design besides high efficiencies, so that different SNMs can be detected and identified with various possible shielding settings. The detector assembly design is composed of a CsI gamma-ray detector block and five neutron detector blocks, with peak efficiencies targeting different energy ranges determined by adjoint simulations. In this study, formulations are derived using adjoint transport simulations to estimate detector efficiencies. The formulations is applied to investigate several neutron detector designs for Block IV, which has its peak efficiency in the thermal range, and Block V, designed to maximize the total neutron counts over the entire energy spectrum. Other Blocks detect different neutron energies. All five neutron detector blocks and the gamma-ray block are assembled in both MCNP and deterministic simulation models, with detector responses calculated to validate the fully assembled design using a 30-group library. The simulation results show that the 30-group library, collapsed from an 80-group library using an adjoint-weighting approach with the YGROUP code, significantly reduced the computational cost while maintaining accuracy. (authors)

  16. Phase transitions and optimal transport in stochastic roundabout traffic

    NASA Astrophysics Data System (ADS)

    Foulaadvand, M. Ebrahim; Maass, Philipp

    2016-07-01

    We study traffic in a roundabout model, where the dynamics along the interior lane of the roundabout are described by the totally asymmetric simple exclusion process (TASEP). Vehicles can enter the interior lane or exit from it via S intersecting streets with given rates, and locally modified dynamics at the junctions take into account that collisions of entering vehicles with vehicles approaching the entrance point from the interior lane should be avoided. A route matrix specifies the probabilities for vehicles to arrive from and to exit to certain intersecting streets. By subdividing the interior lane into segments between consecutive intersecting streets with effective entrance and exit rates, a classification of the stationary roundabout traffic in terms of TASEP multiphases is given, where each segment can be in either the low-density, high-density, or maximum current TASEP phase. A general methodology is developed, which allows one to calculate the multiphases and optimal throughput conditions based on a mean-field treatment. Explicit analytical results from this treatment are derived for equivalent interesting streets. The results are shown to be in good agreement with kinetic Monte Carlo simulations.

  17. Phase transitions and optimal transport in stochastic roundabout traffic.

    PubMed

    Foulaadvand, M Ebrahim; Maass, Philipp

    2016-07-01

    We study traffic in a roundabout model, where the dynamics along the interior lane of the roundabout are described by the totally asymmetric simple exclusion process (TASEP). Vehicles can enter the interior lane or exit from it via S intersecting streets with given rates, and locally modified dynamics at the junctions take into account that collisions of entering vehicles with vehicles approaching the entrance point from the interior lane should be avoided. A route matrix specifies the probabilities for vehicles to arrive from and to exit to certain intersecting streets. By subdividing the interior lane into segments between consecutive intersecting streets with effective entrance and exit rates, a classification of the stationary roundabout traffic in terms of TASEP multiphases is given, where each segment can be in either the low-density, high-density, or maximum current TASEP phase. A general methodology is developed, which allows one to calculate the multiphases and optimal throughput conditions based on a mean-field treatment. Explicit analytical results from this treatment are derived for equivalent interesting streets. The results are shown to be in good agreement with kinetic Monte Carlo simulations.

  18. A multiobjective optimization approach to the operation and investment of the national energy and transportation systems

    NASA Astrophysics Data System (ADS)

    Ibanez, Eduardo

    Most U.S. energy usage is for electricity production and vehicle transportation, two interdependent infrastructures. The strength and number of the interdependencies will increase rapidly as hybrid electric transportation systems, including plug-in hybrid electric vehicles and hybrid electric trains, become more prominent. There are several new energy supply technologies reaching maturity, accelerated by public concern over global warming. The National Energy and Transportation Planning Tool (NETPLAN) is the implementation of the long-term investment and operation model for the transportation and energy networks. An evolutionary approach with underlying fast linear optimization are in place to determine the solutions with the best investment portfolios in terms of cost, resiliency and sustainability, i.e., the solutions that form the Pareto front. The popular NSGA-II algorithm is used as the base for the multiobjective optimization and metrics are developed for to evaluate the energy and transportation portfolios. An integrating approach to resiliency is presented, allowing the evaluation of high-consequence events, like hurricanes or widespread blackouts. A scheme to parallelize the multiobjective solver is presented, along with a decomposition method for the cost minimization program. The modular and data-driven design of the software is presented. The modeling tool is applied in a numerical example to optimize the national investment in energy and transportation in the next 40 years.

  19. A transilient matrix for moist convection

    SciTech Connect

    Romps, D.; Kuang, Z.

    2011-08-15

    A method is introduced for diagnosing a transilient matrix for moist convection. This transilient matrix quantifies the nonlocal transport of air by convective eddies: for every height z, it gives the distribution of starting heights z{prime} for the eddies that arrive at z. In a cloud-resolving simulation of deep convection, the transilient matrix shows that two-thirds of the subcloud air convecting into the free troposphere originates from within 100 m of the surface. This finding clarifies which initial height to use when calculating convective available potential energy from soundings of the tropical troposphere.

  20. Optimal Mass Transport for Statistical Estimation, Image Analysis, Information Geometry, and Control

    DTIC Science & Technology

    2017-01-10

    years has increasingly impacted a large number of other fields (probability theory, partial differential equations, physics, meteorology ). We have...in recent years has increasingly impacted a large number of other fields (probability theory, partial differential equations, physics, meteorology ...econometrics, fluid dynamics, automatic control, transportation, statistical physics, shape optimization, expert systems, and meteorology [52, 68]. The problem

  1. High Speed Civil Transport Design Using Collaborative Optimization and Approximate Models

    NASA Technical Reports Server (NTRS)

    Manning, Valerie Michelle

    1999-01-01

    The design of supersonic aircraft requires complex analysis in multiple disciplines, posing, a challenge for optimization methods. In this thesis, collaborative optimization, a design architecture developed to solve large-scale multidisciplinary design problems, is applied to the design of supersonic transport concepts. Collaborative optimization takes advantage of natural disciplinary segmentation to facilitate parallel execution of design tasks. Discipline-specific design optimization proceeds while a coordinating mechanism ensures progress toward an optimum and compatibility between disciplinary designs. Two concepts for supersonic aircraft are investigated: a conventional delta-wing design and a natural laminar flow concept that achieves improved performance by exploiting properties of supersonic flow to delay boundary layer transition. The work involves the development of aerodynamics and structural analyses, and integration within a collaborative optimization framework. It represents the most extensive application of the method to date.

  2. Convection towers

    DOEpatents

    Prueitt, Melvin L.

    1994-01-01

    Convection towers which are capable of cleaning the pollution from large quantities of air and of generating electricity utilize the evaporation of water sprayed into the towers to create strong airflows and to remove pollution from the air. Turbines in tunnels at the skirt section of the towers generate electricity. Other embodiments may also provide fresh water, and operate in an updraft mode.

  3. Convection towers

    DOEpatents

    Prueitt, M.L.

    1996-01-16

    Convection towers which are capable of cleaning the pollution from large quantities of air, of generating electricity, and of producing fresh water utilize the evaporation of water sprayed into the towers to create strong airflows and to remove pollution from the air. Turbines in tunnels at the skirt section of the towers generate electricity, and condensers produce fresh water. 6 figs.

  4. Convection towers

    DOEpatents

    Prueitt, Melvin L.

    1995-01-01

    Convection towers which are capable of cleaning the pollution from large quantities of air, of generating electricity, and of producing fresh water utilize the evaporation of water sprayed into the towers to create strong airflows and to remove pollution from the air. Turbines in tunnels at the skirt section of the towers generate electricity, and condensers produce fresh water.

  5. Convection towers

    DOEpatents

    Prueitt, Melvin L.

    1996-01-01

    Convection towers which are capable of cleaning the pollution from large quantities of air, of generating electricity, and of producing fresh water utilize the evaporation of water sprayed into the towers to create strong airflows and to remove pollution from the air. Turbines in tunnels at the skirt section of the towers generate electricity, and condensers produce fresh water.

  6. Modeling Convection

    ERIC Educational Resources Information Center

    Ebert, James R.; Elliott, Nancy A.; Hurteau, Laura; Schulz, Amanda

    2004-01-01

    Students must understand the fundamental process of convection before they can grasp a wide variety of Earth processes, many of which may seem abstract because of the scales on which they operate. Presentation of a very visual, concrete model prior to instruction on these topics may facilitate students' understanding of processes that are largely…

  7. Modeling Convection

    ERIC Educational Resources Information Center

    Ebert, James R.; Elliott, Nancy A.; Hurteau, Laura; Schulz, Amanda

    2004-01-01

    Students must understand the fundamental process of convection before they can grasp a wide variety of Earth processes, many of which may seem abstract because of the scales on which they operate. Presentation of a very visual, concrete model prior to instruction on these topics may facilitate students' understanding of processes that are largely…

  8. Using a derivative-free optimization method for multiple solutions of inverse transport problems

    DOE PAGES

    Armstrong, Jerawan C.; Favorite, Jeffrey A.

    2016-01-14

    Identifying unknown components of an object that emits radiation is an important problem for national and global security. Radiation signatures measured from an object of interest can be used to infer object parameter values that are not known. This problem is called an inverse transport problem. An inverse transport problem may have multiple solutions and the most widely used approach for its solution is an iterative optimization method. This paper proposes a stochastic derivative-free global optimization algorithm to find multiple solutions of inverse transport problems. The algorithm is an extension of a multilevel single linkage (MLSL) method where a meshmore » adaptive direct search (MADS) algorithm is incorporated into the local phase. Furthermore, numerical test cases using uncollided fluxes of discrete gamma-ray lines are presented to show the performance of this new algorithm.« less

  9. Using a derivative-free optimization method for multiple solutions of inverse transport problems

    SciTech Connect

    Armstrong, Jerawan C.; Favorite, Jeffrey A.

    2016-01-14

    Identifying unknown components of an object that emits radiation is an important problem for national and global security. Radiation signatures measured from an object of interest can be used to infer object parameter values that are not known. This problem is called an inverse transport problem. An inverse transport problem may have multiple solutions and the most widely used approach for its solution is an iterative optimization method. This paper proposes a stochastic derivative-free global optimization algorithm to find multiple solutions of inverse transport problems. The algorithm is an extension of a multilevel single linkage (MLSL) method where a mesh adaptive direct search (MADS) algorithm is incorporated into the local phase. Furthermore, numerical test cases using uncollided fluxes of discrete gamma-ray lines are presented to show the performance of this new algorithm.

  10. Scale-free convection theory

    NASA Astrophysics Data System (ADS)

    Pasetto, Stefano; Chiosi, Cesare; Cropper, Mark; Grebel, Eva K.

    2015-08-01

    Convection is one of the fundamental mechanism to transport energy, e.g., in planetology, oceanography as well as in astrophysics where stellar structure customarily described by the mixing-length theory, which makes use of the mixing-length scale parameter to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pressure scale height of the star, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun.No strong arguments exist to claim that the mixing-length parameter is the same in all stars and all evolutionary phases. Because of this, all stellar models in literature are hampered by this basic uncertainty.In a recent paper (Pasetto et al 2014) we presented the first fully analytical scale-free theory of convection that does not require the mixing-length parameter. Our self-consistent analytical formulation of convection determines all the properties of convection as a function of the physical behaviour of the convective elements themselves and the surrounding medium (being it a either a star, an ocean, a primordial planet). The new theory of convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations, i.e. the Bernoulli equation for a perfect fluid, but expressed in a non-inertial reference frame co-moving with the convective elements. In our formalism, the motion of convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time dependent formalism.We obtained an analytical, non-local, time-dependent solution for the convective energy transport that does not depend on any free parameter. The predictions of the new theory in astrophysical environment are compared with those from the standard mixing-length paradigm in stars with

  11. Scale-free convection theory

    NASA Astrophysics Data System (ADS)

    Pasetto, Stefano; Chiosi, Cesare; Cropper, Mark; Grebel, Eva K.

    Convection is one of the fundamental mechanisms to transport energy, e.g., in planetology, oceanography, as well as in astrophysics where stellar structure is customarily described by the mixing-length theory, which makes use of the mixing-length scale parameter to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pressure scale height of the star, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun. No strong arguments exist to claim that the mixing-length parameter is the same in all stars and all evolutionary phases. Because of this, all stellar models in the literature are hampered by this basic uncertainty. In a recent paper (Pasetto et al. 2014) we presented the first fully analytical scale-free theory of convection that does not require the mixing-length parameter. Our self-consistent analytical formulation of convection determines all the properties of convection as a function of the physical behaviour of the convective elements themselves and the surrounding medium (be it a star, an ocean, or a primordial planet). The new theory of convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations, i.e. the Bernoulli equation for a perfect fluid, but expressed in a non-inertial reference frame co-moving with the convective elements. In our formalism, the motion of convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time dependent formalism. We obtained an analytical, non-local, time-dependent solution for the convective energy transport that does not depend on any free parameter. The predictions of the new theory in astrophysical environment are compared with those from the standard mixing-length paradigm in stars with

  12. Measuring the misfit between seismograms using an optimal transport distance: application to full waveform inversion

    NASA Astrophysics Data System (ADS)

    Métivier, L.; Brossier, R.; Mérigot, Q.; Oudet, E.; Virieux, J.

    2016-04-01

    Full waveform inversion using the conventional L2 distance to measure the misfit between seismograms is known to suffer from cycle skipping. An alternative strategy is proposed in this study, based on a measure of the misfit computed with an optimal transport distance. This measure allows to account for the lateral coherency of events within the seismograms, instead of considering each seismic trace independently, as is done generally in full waveform inversion. The computation of this optimal transport distance relies on a particular mathematical formulation allowing for the non-conservation of the total energy between seismograms. The numerical solution of the optimal transport problem is performed using proximal splitting techniques. Three synthetic case studies are investigated using this strategy: the Marmousi 2 model, the BP 2004 salt model, and the Chevron 2014 benchmark data. The results emphasize interesting properties of the optimal transport distance. The associated misfit function is less prone to cycle skipping. A workflow is designed to reconstruct accurately the salt structures in the BP 2004 model, starting from an initial model containing no information about these structures. A high-resolution P-wave velocity estimation is built from the Chevron 2014 benchmark data, following a frequency continuation strategy. This estimation explains accurately the data. Using the same workflow, full waveform inversion based on the L2 distance converges towards a local minimum. These results yield encouraging perspectives regarding the use of the optimal transport distance for full waveform inversion: the sensitivity to the accuracy of the initial model is reduced, the reconstruction of complex salt structure is made possible, the method is robust to noise, and the interpretation of seismic data dominated by reflections is enhanced.

  13. Optimal Transport Destination for Ischemic Stroke Patients With Unknown Vessel Status: Use of Prehospital Triage Scores.

    PubMed

    Schlemm, Eckhard; Ebinger, Martin; Nolte, Christian H; Endres, Matthias; Schlemm, Ludwig

    2017-08-01

    Patients with acute ischemic stroke (AIS) and large vessel occlusion may benefit from direct transportation to an endovascular capable comprehensive stroke center (mothership approach) as opposed to direct transportation to the nearest stroke unit without endovascular therapy (drip and ship approach). The optimal transport strategy for patients with AIS and unknown vessel status is uncertain. The rapid arterial occlusion evaluation scale (RACE, scores ranging from 0 to 9, with higher scores indicating higher stroke severity) correlates with the National Institutes of Health Stroke Scale and was developed to identify patients with large vessel occlusion in a prehospital setting. We evaluate how the RACE scale can help to inform prehospital triage decisions for AIS patients. In a model-based approach, we estimate probabilities of good outcome (modified Rankin Scale score of ≤2 at 3 months) as a function of severity of stroke symptoms and transport times for the mothership approach and the drip and ship approach. We use these probabilities to obtain optimal RACE cutoff scores for different transfer time settings and combinations of treatment options (time-based eligibility for secondary transfer under the drip and ship approach, time-based eligibility for thrombolysis at the comprehensive stroke center under the mothership approach). In our model, patients with AIS are more likely to benefit from direct transportation to the comprehensive stroke center if they have more severe strokes. Values of the optimal RACE cutoff scores range from 0 (mothership for all patients) to >9 (drip and ship for all patients). Shorter transfer times and longer door-to-needle and needle-to-transfer (door out) times are associated with lower optimal RACE cutoff scores. Use of RACE cutoff scores that take into account transport times to triage AIS patients to the nearest appropriate hospital may lead to improved outcomes. Further studies should examine the feasibility of translation into

  14. Effects of optimal initial errors on predicting the seasonal reduction of the upstream Kuroshio transport

    NASA Astrophysics Data System (ADS)

    Zhang, Kun; Wang, Qiang; Mu, Mu; Liang, Peng

    2016-10-01

    With the Regional Ocean Modeling System (ROMS), we realistically simulated the transport variations of the upstream Kuroshio (referring to the Kuroshio from its origin to the south of Taiwan), particularly for the seasonal transport reduction. Then, we investigated the effects of the optimal initial errors estimated by the conditional nonlinear optimal perturbation (CNOP) approach on predicting the seasonal transport reduction. Two transport reduction events (denoted as Event 1 and Event 2) were chosen, and CNOP1 and CNOP2 were obtained for each event. By examining the spatial structures of the two types of CNOPs, we found that the dominant amplitudes are located around (128°E, 17°N) horizontally and in the upper 1000 m vertically. For each event, the two CNOPs caused large prediction errors. Specifically, at the prediction time, CNOP1 (CNOP2) develops into an anticyclonic (cyclonic) eddy-like structure centered around 124°E, leading to the increase (decrease) of the upstream Kuroshio transport. By investigating the time evolution of the CNOPs in Event 1, we found that the eddy-like structures originating from east of Luzon gradually grow and simultaneously propagate westward. The eddy-energetic analysis indicated that the errors obtain energy from the background state through barotropic and baroclinic instabilities and that the latter plays a more important role. These results suggest that improving the initial conditions in east of Luzon could lead to better prediction of the upstream Kuroshio transport variation.

  15. A linear optimal transportation framework for quantifying and visualizing variations in sets of images

    PubMed Central

    Wang, Wei; Slepčev, Dejan; Basu, Saurav; Ozolek, John A.

    2012-01-01

    Transportation-based metrics for comparing images have long been applied to analyze images, especially where one can interpret the pixel intensities (or derived quantities) as a distribution of ‘mass’ that can be transported without strict geometric constraints. Here we describe a new transportation-based framework for analyzing sets of images. More specifically, we describe a new transportation-related distance between pairs of images, which we denote as linear optimal transportation (LOT). The LOT can be used directly on pixel intensities, and is based on a linearized version of the Kantorovich-Wasserstein metric (an optimal transportation distance, as is the earth mover’s distance). The new framework is especially well suited for computing all pairwise distances for a large database of images efficiently, and thus it can be used for pattern recognition in sets of images. In addition, the new LOT framework also allows for an isometric linear embedding, greatly facilitating the ability to visualize discriminant information in different classes of images. We demonstrate the application of the framework to several tasks such as discriminating nuclear chromatin patterns in cancer cells, decoding differences in facial expressions, galaxy morphologies, as well as sub cellular protein distributions. PMID:23729991

  16. Particle Swarm Optimization for inverse modeling of solute transport in fractured gneiss aquifer

    NASA Astrophysics Data System (ADS)

    Abdelaziz, Ramadan; Zambrano-Bigiarini, Mauricio

    2014-08-01

    Particle Swarm Optimization (PSO) has received considerable attention as a global optimization technique from scientists of different disciplines around the world. In this article, we illustrate how to use PSO for inverse modeling of a coupled flow and transport groundwater model (MODFLOW2005-MT3DMS) in a fractured gneiss aquifer. In particular, the hydroPSO R package is used as optimization engine, because it has been specifically designed to calibrate environmental, hydrological and hydrogeological models. In addition, hydroPSO implements the latest Standard Particle Swarm Optimization algorithm (SPSO-2011), with an adaptive random topology and rotational invariance constituting the main advancements over previous PSO versions. A tracer test conducted in the experimental field at TU Bergakademie Freiberg (Germany) is used as case study. A double-porosity approach is used to simulate the solute transport in the fractured Gneiss aquifer. Tracer concentrations obtained with hydroPSO were in good agreement with its corresponding observations, as measured by a high value of the coefficient of determination and a low sum of squared residuals. Several graphical outputs automatically generated by hydroPSO provided useful insights to assess the quality of the calibration results. It was found that hydroPSO required a small number of model runs to reach the region of the global optimum, and it proved to be both an effective and efficient optimization technique to calibrate the movement of solute transport over time in a fractured aquifer. In addition, the parallel feature of hydroPSO allowed to reduce the total computation time used in the inverse modeling process up to an eighth of the total time required without using that feature. This work provides a first attempt to demonstrate the capability and versatility of hydroPSO to work as an optimizer of a coupled flow and transport model for contaminant migration.

  17. Particle Swarm Optimization for inverse modeling of solute transport in fractured gneiss aquifer.

    PubMed

    Abdelaziz, Ramadan; Zambrano-Bigiarini, Mauricio

    2014-08-01

    Particle Swarm Optimization (PSO) has received considerable attention as a global optimization technique from scientists of different disciplines around the world. In this article, we illustrate how to use PSO for inverse modeling of a coupled flow and transport groundwater model (MODFLOW2005-MT3DMS) in a fractured gneiss aquifer. In particular, the hydroPSO R package is used as optimization engine, because it has been specifically designed to calibrate environmental, hydrological and hydrogeological models. In addition, hydroPSO implements the latest Standard Particle Swarm Optimization algorithm (SPSO-2011), with an adaptive random topology and rotational invariance constituting the main advancements over previous PSO versions. A tracer test conducted in the experimental field at TU Bergakademie Freiberg (Germany) is used as case study. A double-porosity approach is used to simulate the solute transport in the fractured Gneiss aquifer. Tracer concentrations obtained with hydroPSO were in good agreement with its corresponding observations, as measured by a high value of the coefficient of determination and a low sum of squared residuals. Several graphical outputs automatically generated by hydroPSO provided useful insights to assess the quality of the calibration results. It was found that hydroPSO required a small number of model runs to reach the region of the global optimum, and it proved to be both an effective and efficient optimization technique to calibrate the movement of solute transport over time in a fractured aquifer. In addition, the parallel feature of hydroPSO allowed to reduce the total computation time used in the inverse modeling process up to an eighth of the total time required without using that feature. This work provides a first attempt to demonstrate the capability and versatility of hydroPSO to work as an optimizer of a coupled flow and transport model for contaminant migration. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. Optimizing Air Transportation Service to Metroplex Airports. Par 2; Analysis Using the Airline Schedule Optimization Model (ASOM)

    NASA Technical Reports Server (NTRS)

    Donoue, George; Hoffman, Karla; Sherry, Lance; Ferguson, John; Kara, Abdul Qadar

    2010-01-01

    The air transportation system is a significant driver of the U.S. economy, providing safe, affordable, and rapid transportation. During the past three decades airspace and airport capacity has not grown in step with demand for air transportation; the failure to increase capacity at the same rate as the growth in demand results in unreliable service and systemic delay. This report describes the results of an analysis of airline strategic decision-making that affects geographic access, economic access, and airline finances, extending the analysis of these factors using historic data (from Part 1 of the report). The Airline Schedule Optimization Model (ASOM) was used to evaluate how exogenous factors (passenger demand, airline operating costs, and airport capacity limits) affect geographic access (markets-served, scheduled flights, aircraft size), economic access (airfares), airline finances (profit), and air transportation efficiency (aircraft size). This analysis captures the impact of the implementation of airport capacity limits, as well as the effect of increased hedged fuel prices, which serve as a proxy for increased costs per flight that might occur if auctions or congestion pricing are imposed; also incorporated are demand elasticity curves based on historical data that provide information about how passenger demand is affected by airfare changes.

  19. Seismology of Convection in the Sun

    NASA Astrophysics Data System (ADS)

    Hanasoge, Shravan

    2015-08-01

    Solar convection lies in extraordinary regime of dynamical parameters. Convective processes in the Sun drive global fluid circulations and magnetic fields, which in turn affect its visible outer layers (solar activity) and, more broadly, the heliosphere (space weather). The precise determination of the depth of solar convection zone, departures from adiabaticity of the temperature gradient, and the internal rotation rate as a function of latitude and depth are among the seminal contributions of helioseismology towards understanding convection in the Sun. Contemporary helioseismology, which is focused on inferring the properties of three-dimensional convective features, suggests that transport velocities are substantially smaller than theoretical predictions. Furthermore, helioseismology provides important constraints on the anisotropic Reynolds stresses that control the global dynamics of the solar convection zone. In this review, I will discuss the state of our understanding of convection in the Sun, with a focus on helioseismic diagnostics.

  20. A strategy for representing the effects of convective momentum transport in multiscale models: Evaluation using a new superparameterized version of the Weather Research and Forecast model (SP-WRF)

    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.

  1. ETRANS: an energy transport system optimization code for distributed networks of solar collectors

    SciTech Connect

    Barnhart, J.S.

    1980-09-01

    The optimization code ETRANS was developed at the Pacific Northwest Laboratory to design and estimate the costs associated with energy transport systems for distributed fields of solar collectors. The code uses frequently cited layouts for dish and trough collectors and optimizes them on a section-by-section basis. The optimal section design is that combination of pipe diameter and insulation thickness that yields the minimum annualized system-resultant cost. Among the quantities included in the costing algorithm are (1) labor and materials costs associated with initial plant construction, (2) operating expenses due to daytime and nighttime heat losses, and (3) operating expenses due to pumping power requirements. Two preliminary series of simulations were conducted to exercise the code. The results indicate that transport system costs for both dish and trough collector fields increase with field size and receiver exit temperature. Furthermore, dish collector transport systems were found to be much more expensive to build and operate than trough transport systems. ETRANS itself is stable and fast-running and shows promise of being a highly effective tool for the analysis of distributed solar thermal systems.

  2. Hierarchical transport networks optimizing dynamic response of permeable energy-storage materials.

    PubMed

    Nilson, Robert H; Griffiths, Stewart K

    2009-07-01

    Channel widths and spacing in latticelike hierarchical transport networks are optimized to achieve maximum extraction of gas or electrical charge from nanoporous energy-storage materials during charge and discharge cycles of specified duration. To address a range of physics, the effective transport diffusivity is taken to vary as a power, m , of channel width. Optimal channel widths and spacing in all levels of the hierarchy are found to increase in a power-law manner with normalized system size, facilitating the derivation of closed-form approximations for the optimal dimensions. Characteristic response times and ratios of channel width to spacing are both shown to vary by the factor 2/m between successive levels of any optimal hierarchy. This leads to fractal-like self-similar geometry, but only for m=2 . For this case of quadratic dependence of diffusivity on channel width, the introduction of transport channels permits increases in system size on the order of 10;{4} , 10;{8} , and 10;{10} , without any reduction in extraction efficiency, for hierarchies having 1, 2 and, 8 levels, respectively. However, we also find that for a given system size there is an optimum number of hierarchical levels that maximizes extraction efficiency.

  3. Integration of numerical analysis tools for automated numerical optimization of a transportation package design

    SciTech Connect

    Witkowski, W.R.; Eldred, M.S.; Harding, D.C.

    1994-09-01

    The use of state-of-the-art numerical analysis tools to determine the optimal design of a radioactive material (RAM) transportation container is investigated. The design of a RAM package`s components involves a complex coupling of structural, thermal, and radioactive shielding analyses. The final design must adhere to very strict design constraints. The current technique used by cask designers is uncoupled and involves designing each component separately with respect to its driving constraint. With the use of numerical optimization schemes, the complex couplings can be considered directly, and the performance of the integrated package can be maximized with respect to the analysis conditions. This can lead to more efficient package designs. Thermal and structural accident conditions are analyzed in the shape optimization of a simplified cask design. In this paper, details of the integration of numerical analysis tools, development of a process model, nonsmoothness difficulties with the optimization of the cask, and preliminary results are discussed.

  4. Anomalously weak solar convection

    PubMed Central

    Hanasoge, Shravan M.; Duvall, Thomas L.

    2012-01-01

    Convection in the solar interior is thought to comprise structures on a spectrum of scales. This conclusion emerges from phenomenological studies and numerical simulations, though neither covers the proper range of dynamical parameters of solar convection. Here, we analyze observations of the wavefield in the solar photosphere using techniques of time-distance helioseismology to image flows in the solar interior. We downsample and synthesize 900 billion wavefield observations to produce 3 billion cross-correlations, which we average and fit, measuring 5 million wave travel times. Using these travel times, we deduce the underlying flow systems and study their statistics to bound convective velocity magnitudes in the solar interior, as a function of depth and spherical-harmonic degree ℓ. Within the wavenumber band ℓ < 60, convective velocities are 20–100 times weaker than current theoretical estimates. This constraint suggests the prevalence of a different paradigm of turbulence from that predicted by existing models, prompting the question: what mechanism transports the heat flux of a solar luminosity outwards? Advection is dominated by Coriolis forces for wavenumbers ℓ < 60, with Rossby numbers smaller than approximately 10-2 at r/R⊙ = 0.96, suggesting that the Sun may be a much faster rotator than previously thought, and that large-scale convection may be quasi-geostrophic. The fact that isorotation contours in the Sun are not coaligned with the axis of rotation suggests the presence of a latitudinal entropy gradient. PMID:22665774

  5. Convection towers

    DOEpatents

    Prueitt, M.L.

    1994-02-08

    Convection towers which are capable of cleaning the pollution from large quantities of air and of generating electricity utilize the evaporation of water sprayed into the towers to create strong airflows and to remove pollution from the air. Turbines in tunnels at the skirt section of the towers generate electricity. Other embodiments may also provide fresh water, and operate in an updraft mode. 5 figures.

  6. Responses to hyperthermia. Optimizing heat dissipation by convection and evaporation: Neural control of skin blood flow and sweating in humans.

    PubMed

    Smith, Caroline J; Johnson, John M

    2016-04-01

    Under normothermic, resting conditions, humans dissipate heat from the body at a rate approximately equal to heat production. Small discrepancies between heat production and heat elimination would, over time, lead to significant changes in heat storage and body temperature. When heat production or environmental temperature is high the challenge of maintaining heat balance is much greater. This matching of heat elimination with heat production is a function of the skin circulation facilitating heat transport to the body surface and sweating, enabling evaporative heat loss. These processes are manifestations of the autonomic control of cutaneous vasomotor and sudomotor functions and form the basis of this review. We focus on these systems in the responses to hyperthermia. In particular, the cutaneous vascular responses to heat stress and the current understanding of the neurovascular mechanisms involved. The available research regarding cutaneous active vasodilation and vasoconstriction is highlighted, with emphasis on active vasodilation as a major responder to heat stress. Involvement of the vasoconstrictor and active vasodilator controls of the skin circulation in the context of heat stress and nonthermoregulatory reflexes (blood pressure, exercise) are also considered. Autonomic involvement in the cutaneous vascular responses to direct heating and cooling of the skin are also discussed. We examine the autonomic control of sweating, including cholinergic and noncholinergic mechanisms, the local control of sweating, thermoregulatory and nonthermoregulatory reflex control and the possible relationship between sudomotor and cutaneous vasodilator function. Finally, we comment on the clinical relevance of these control schemes in conditions of autonomic dysfunction. Copyright © 2016 Elsevier B.V. All rights reserved.

  7. Effect of convective transport in porous media on the conditions of organic matter maturation and generation of hydrocarbons in trap rocks complexes

    NASA Astrophysics Data System (ADS)

    Yurie Khachay, Professor; Mindubaev, Mansur

    2016-04-01

    One of the main problems of the study of the intrusion thermal effects on the maturation of the organic matter is to estimate the volume, intensity, thermal effects of the intrusion and its redistribution in porous media by convection. A numerical algorithm for solving the problem of the developed convection in two-dimensional and three-dimensional models of the porous medium depending on the incline angle is developed. It is defined that the convective stability in the medium decreases with increasing incline angle. It was found that depending on the incline angle the structure of convection from many cells for a flat horizontal layer changes and it transfers to more elongated structures along the layer. It is shown that depending on the incline angles, invading sill and imbedding volume of the porous medium it can be realized either stationary or non-stationary convection that provides a principal different thermal conditions of hydrocarbons maturation in the motherboard porous medium. We give numerical examples of the influence of the incline angle on the flow structure inside the porous inclusion. By the stationary convection the volume of the boundary layers between the convective sells increases. That can lead to increasing of the part of motherboard rocks that are outer the temperature conditions of oil catalysis and as a consequence to the overestimation of the deposits.

  8. REGRESSION APPROXIMATIONS FOR TRANSPORT MODEL CONSTRAINT SETS IN COMBINED AQUIFER SIMULATION-OPTIMIZATION STUDIES.

    USGS Publications Warehouse

    Alley, William M.

    1986-01-01

    Problems involving the combined use of contaminant transport models and nonlinear optimization schemes can be very expensive to solve. This paper explores the use of transport models with ordinary regression and regression on ranks to develop approximate response functions of concentrations at critical locations as a function of pumping and recharge at decision wells. These response functions combined with other constraints can often be solved very easily and may suggest reasonable starting points for combined simulation-management modeling or even relatively efficient operating schemes in themselves.

  9. Optimizations of the energy grid search algorithm in continuous-energy Monte Carlo particle transport codes

    NASA Astrophysics Data System (ADS)

    Walsh, Jonathan A.; Romano, Paul K.; Forget, Benoit; Smith, Kord S.

    2015-11-01

    In this work we propose, implement, and test various optimizations of the typical energy grid-cross section pair lookup algorithm in Monte Carlo particle transport codes. The key feature common to all of the optimizations is a reduction in the length of the vector of energies that must be searched when locating the index of a particle's current energy. Other factors held constant, a reduction in energy vector length yields a reduction in CPU time. The computational methods we present here are physics-informed. That is, they are designed to utilize the physical information embedded in a simulation in order to reduce the length of the vector to be searched. More specifically, the optimizations take advantage of information about scattering kinematics, neutron cross section structure and data representation, and also the expected characteristics of a system's spatial flux distribution and energy spectrum. The methods that we present are implemented in the OpenMC Monte Carlo neutron transport code as part of this work. The gains in computational efficiency, as measured by overall code speedup, associated with each of the optimizations are demonstrated in both serial and multithreaded simulations of realistic systems. Depending on the system, simulation parameters, and optimization method employed, overall code speedup factors of 1.2-1.5, relative to the typical single-nuclide binary search algorithm, are routinely observed.

  10. 3D nonrigid registration via optimal mass transport on the GPU.

    PubMed

    Ur Rehman, Tauseef; Haber, Eldad; Pryor, Gallagher; Melonakos, John; Tannenbaum, Allen

    2009-12-01

    In this paper, we present a new computationally efficient numerical scheme for the minimizing flow approach for optimal mass transport (OMT) with applications to non-rigid 3D image registration. The approach utilizes all of the gray-scale data in both images, and the optimal mapping from image A to image B is the inverse of the optimal mapping from B to A. Further, no landmarks need to be specified, and the minimizer of the distance functional involved is unique. Our implementation also employs multigrid, and parallel methodologies on a consumer graphics processing unit (GPU) for fast computation. Although computing the optimal map has been shown to be computationally expensive in the past, we show that our approach is orders of magnitude faster then previous work and is capable of finding transport maps with optimality measures (mean curl) previously unattainable by other works (which directly influences the accuracy of registration). We give results where the algorithm was used to compute non-rigid registrations of 3D synthetic data as well as intra-patient pre-operative and post-operative 3D brain MRI datasets.

  11. Rate-distortion optimal video transport over IP allowing packets with bit errors.

    PubMed

    Harmanci, Oztan; Tekalp, A Murat

    2007-05-01

    We propose new models and methods for rate-distortion (RD) optimal video delivery over IP, when packets with bit errors are also delivered. In particular, we propose RD optimal methods for slicing and unequal error protection (UEP) of packets over IP allowing transmission of packets with bit errors. The proposed framework can be employed in a classical independent-layer transport model for optimal slicing, as well as in a cross-layer transport model for optimal slicing and UEP, where the forward error correction (FEC) coding is performed at the link layer, but the application controls the FEC code rate with the constraint that a given IP packet is subject to constant channel protection. The proposed method uses a novel dynamic programming approach to determine the optimal slicing and UEP configuration for each video frame in a practical manner, that is compliant with the AVC/H.264 standard. We also propose new rate and distortion estimation techniques at the encoder side in order to efficiently evaluate the objective function for a slice configuration. The cross-layer formulation option effectively determines which regions of a frame should be protected better; hence, it can be considered as a spatial UEP scheme. We successfully demonstrate, by means of experimental results, that each component of the proposed system provides significant gains, up to 2.0 dB, compared to competitive methods.

  12. Application of the Modified Method of Transporting Trajectory to Optimize Interplanetary Transfers Combining Low and High Thrust

    NASA Astrophysics Data System (ADS)

    Kharitonov, A. M.

    2013-09-01

    An approach to optimize trajectories of interplanetary transfers combining low and high trust is proposed. The approach employs the modified method of transporting trajectory to optimize the heliocentric section of the trajectory. An Earth-Mars transfer in 180 astronomical days is used as an example to compare the optimal trajectories and parameters of spacecraft predicted by the classical and modified methods of transporting trajectory

  13. Convection in Type 2 supernovae

    SciTech Connect

    Miller, Douglas Scott

    1993-10-15

    Results are presented here from several two dimensional numerical calculations of events in Type II supernovae. A new 2-D hydrodynamics and neutrino transport code has been used to compute the effect on the supernova explosion mechanism of convection between the neutrinosphere and the shock. This convection is referred to as exterior convection to distinguish it from convection beneath the neutrinosphere. The model equations and initial and boundary conditions are presented along with the simulation results. The 2-D code was used to compute an exterior convective velocity to compare with the convective model of the Mayle and Wilson 1-D code. Results are presented from several runs with varying sizes of initial perturbation, as well as a case with no initial perturbation but including the effects of rotation. The M&W code does not produce an explosion using the 2-D convective velocity. Exterior convection enhances the outward propagation of the shock, but not enough to ensure a successful explosion. Analytic estimates of the growth rate of the neutron finger instability axe presented. It is shown that this instability can occur beneath the neutrinosphere of the proto-neutron star in a supernova explosion with a growth time of ~ 3 microseconds. The behavior of the high entropy bubble that forms between the shock and the neutrinosphere in one dimensional calculations of supernova is investigated. It has been speculated that this bubble is a site for γ-process generation of heavy elements. Two dimensional calculations are presented of the time evolution of the hot bubble and the surrounding stellar material. Unlike one dimensional calculations, the 2D code fails to achieve high entropies in the bubble. When run in a spherically symmetric mode the 2-D code reaches entropies of ~ 200. When convection is allowed, the bubble reaches ~60 then the bubble begins to move upward into the cooler, denser material above it.

  14. Evaluation and optimization of mass transport of redox species in silicon microwire-array photoelectrodes.

    PubMed

    Xiang, Chengxiang; Meng, Andrew C; Lewis, Nathan S

    2012-09-25

    Physical integration of a Ag electrical contact internally into a metal/substrate/microstructured Si wire array/oxide/Ag/electrolyte photoelectrochemical solar cell has produced structures that display relatively low ohmic resistance losses, as well as highly efficient mass transport of redox species in the absence of forced convection. Even with front-side illumination, such wire-array based photoelectrochemical solar cells do not require a transparent conducting oxide top contact. In contact with a test electrolyte that contained 50 mM/5.0 mM of the cobaltocenium(+/0) redox species in CH(3)CN-1.0 M LiClO(4), when the counterelectrode was placed in the solution and separated from the photoelectrode, mass transport restrictions of redox species in the internal volume of the Si wire array photoelectrode produced low fill factors and limited the obtainable current densities to 17.6 mA cm(-2) even under high illumination. In contrast, when the physically integrated internal Ag film served as the counter electrode, the redox couple species were regenerated inside the internal volume of the photoelectrode, especially in regions where depletion of the redox species due to mass transport limitations would have otherwise occurred. This behavior allowed the integrated assembly to operate as a two-terminal, stand-alone, photoelectrochemical solar cell. The current density vs. voltage behavior of the integrated photoelectrochemical solar cell produced short-circuit current densities in excess of 80 mA cm(-2) at high light intensities, and resulted in relatively low losses due to concentration overpotentials at 1 Sun illumination. The integrated wire array-based device architecture also provides design guidance for tandem photoelectrochemical cells for solar-driven water splitting.

  15. Evaluation and optimization of mass transport of redox species in silicon microwire-array photoelectrodes

    PubMed Central

    Xiang, Chengxiang; Meng, Andrew C.; Lewis, Nathan S.

    2012-01-01

    Physical integration of a Ag electrical contact internally into a metal/substrate/microstructured Si wire array/oxide/Ag/electrolyte photoelectrochemical solar cell has produced structures that display relatively low ohmic resistance losses, as well as highly efficient mass transport of redox species in the absence of forced convection. Even with front-side illumination, such wire-array based photoelectrochemical solar cells do not require a transparent conducting oxide top contact. In contact with a test electrolyte that contained 50 mM/5.0 mM of the cobaltocenium+/0 redox species in CH3CN–1.0 M LiClO4, when the counterelectrode was placed in the solution and separated from the photoelectrode, mass transport restrictions of redox species in the internal volume of the Si wire array photoelectrode produced low fill factors and limited the obtainable current densities to 17.6 mA cm-2 even under high illumination. In contrast, when the physically integrated internal Ag film served as the counter electrode, the redox couple species were regenerated inside the internal volume of the photoelectrode, especially in regions where depletion of the redox species due to mass transport limitations would have otherwise occurred. This behavior allowed the integrated assembly to operate as a two-terminal, stand-alone, photoelectrochemical solar cell. The current density vs. voltage behavior of the integrated photoelectrochemical solar cell produced short-circuit current densities in excess of 80 mA cm-2 at high light intensities, and resulted in relatively low losses due to concentration overpotentials at 1 Sun illumination. The integrated wire array-based device architecture also provides design guidance for tandem photoelectrochemical cells for solar-driven water splitting. PMID:22904185

  16. Fast Algorithms for Earth Mover Distance Based on Optimal Transport and L1 Regularization II

    DTIC Science & Technology

    2016-09-01

    FAST ALGORITHMS FOR EARTH MOVER DISTANCE BASED ON OPTIMAL TRANSPORT AND L1 REGULARIZATION II WUCHEN LI, STANLEY OSHER, AND WILFRID GANGBO Abstract...We modify a fast algorithm which we designed in [15] for computing the Earth mover’s distance (EMD), whose cost is a Manhattan metric. From the theory...and converges very rapidly. Several numerical examples are presented. 1. Introduction The Earth Mover’s distance (EMD), also named the Monge problem

  17. Problems of optimal transportation on the circle and their mechanical applications

    NASA Astrophysics Data System (ADS)

    Plakhov, Alexander; Tchemisova, Tatiana

    2017-02-01

    We consider a mechanical problem concerning a 2D axisymmetric body moving forward on the plane and making slow turns of fixed magnitude about its axis of symmetry. The body moves through a medium of non-interacting particles at rest, and collisions of particles with the body's boundary are perfectly elastic (billiard-like). The body has a blunt nose: a line segment orthogonal to the symmetry axis. It is required to make small cavities with special shape on the nose so as to minimize its aerodynamic resistance. This problem of optimizing the shape of the cavities amounts to a special case of the optimal mass transportation problem on the circle with the transportation cost being the squared Euclidean distance. We find the explicit solution for this problem when the amplitude of rotation is smaller than a fixed critical value, and give a numerical solution otherwise. As a by-product, we get explicit description of the solution for a class of optimal transportation problems on the circle.

  18. Cascade Optimization Strategy Maximizes Thrust for High-Speed Civil Transport Propulsion System Concept

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The design of a High-Speed Civil Transport (HSCT) air-breathing propulsion system for multimission, variable-cycle operations was successfully optimized through a soft coupling of the engine performance analyzer NASA Engine Performance Program (NEPP) to a multidisciplinary optimization tool COMETBOARDS that was developed at the NASA Lewis Research Center. The design optimization of this engine was cast as a nonlinear optimization problem, with engine thrust as the merit function and the bypass ratios, r-values of fans, fuel flow, and other factors as important active design variables. Constraints were specified on factors including the maximum speed of the compressors, the positive surge margins for the compressors with specified safety factors, the discharge temperature, the pressure ratios, and the mixer extreme Mach number. Solving the problem by using the most reliable optimization algorithm available in COMETBOARDS would provide feasible optimum results only for a portion of the aircraft flight regime because of the large number of mission points (defined by altitudes, Mach numbers, flow rates, and other factors), diverse constraint types, and overall poor conditioning of the design space. Only the cascade optimization strategy of COMETBOARDS, which was devised especially for difficult multidisciplinary applications, could successfully solve a number of engine design problems for their flight regimes. Furthermore, the cascade strategy converged to the same global optimum solution even when it was initiated from different design points. Multiple optimizers in a specified sequence, pseudorandom damping, and reduction of the design space distortion via a global scaling scheme are some of the key features of the cascade strategy. HSCT engine concept, optimized solution for HSCT engine concept. A COMETBOARDS solution for an HSCT engine (Mach-2.4 mixed-flow turbofan) along with its configuration is shown. The optimum thrust is normalized with respect to NEPP results

  19. CONVECTION REACTOR

    DOEpatents

    Hammond, R.P.; King, L.D.P.

    1960-03-22

    An homogeneous nuclear power reactor utilizing convection circulation of the liquid fuel is proposed. The reactor has an internal heat exchanger looated in the same pressure vessel as the critical assembly, thereby eliminating necessity for handling the hot liquid fuel outside the reactor pressure vessel during normal operation. The liquid fuel used in this reactor eliminates the necessity for extensive radiolytic gas rocombination apparatus, and the reactor is resiliently pressurized and, without any movable mechanical apparatus, automatically regulates itself to the condition of criticality during moderate variations in temperature snd pressure and shuts itself down as the pressure exceeds a predetermined safe operating value.

  20. Multimodal Registration of White Matter Brain Data via Optimal Mass Transport.

    PubMed

    Rehman, Tauseefur; Haber, Eldad; Pohl, Kilian M; Haker, Steven; Halle, Mike; Talos, Florin; Wald, Lawrence L; Kikinis, Ron; Tannenbaum, Allen

    2008-09-01

    The elastic registration of medical scans from different acquisition sequences is becoming an important topic for many research labs that would like to continue the post-processing of medical scans acquired via the new generation of high-field-strength scanners. In this note, we present a parameter-free registration algorithm that is well suited for this scenario as it requires no tuning to specific acquisition sequences. The algorithm encompasses a new numerical scheme for computing elastic registration maps based on the minimizing flow approach to optimal mass transport. The approach utilizes all of the gray-scale data in both images, and the optimal mapping from image A to image B is the inverse of the optimal mapping from B to A. Further, no landmarks need to be specified, and the minimizer of the distance functional involved is unique. We apply the algorithm to register the white matter folds of two different scans and use the results to parcellate the cortex of the target image. To the best of our knowledge, this is the first time that the optimal mass transport function has been applied to register large 3D multimodal data sets.

  1. Multimodal Registration of White Matter Brain Data via Optimal Mass Transport

    PubMed Central

    Rehman, Tauseefur; Haber, Eldad; Pohl, Kilian M.; Haker, Steven; Halle, Mike; Talos, Florin; Wald, Lawrence L.; Kikinis, Ron; Tannenbaum, Allen

    2017-01-01

    The elastic registration of medical scans from different acquisition sequences is becoming an important topic for many research labs that would like to continue the post-processing of medical scans acquired via the new generation of high-field-strength scanners. In this note, we present a parameter-free registration algorithm that is well suited for this scenario as it requires no tuning to specific acquisition sequences. The algorithm encompasses a new numerical scheme for computing elastic registration maps based on the minimizing flow approach to optimal mass transport. The approach utilizes all of the gray-scale data in both images, and the optimal mapping from image A to image B is the inverse of the optimal mapping from B to A. Further, no landmarks need to be specified, and the minimizer of the distance functional involved is unique. We apply the algorithm to register the white matter folds of two different scans and use the results to parcellate the cortex of the target image. To the best of our knowledge, this is the first time that the optimal mass transport function has been applied to register large 3D multimodal data sets. PMID:28626844

  2. Optimization of monitoring networks based on uncertainty quantification of model predictions of contaminant transport

    NASA Astrophysics Data System (ADS)

    Vesselinov, V. V.; Harp, D.

    2010-12-01

    The process of decision making to protect groundwater resources requires a detailed estimation of uncertainties in model predictions. Various uncertainties associated with modeling a natural system, such as: (1) measurement and computational errors; (2) uncertainties in the conceptual model and model-parameter estimates; (3) simplifications in model setup and numerical representation of governing processes, contribute to the uncertainties in the model predictions. Due to this combination of factors, the sources of predictive uncertainties are generally difficult to quantify individually. Decision support related to optimal design of monitoring networks requires (1) detailed analyses of existing uncertainties related to model predictions of groundwater flow and contaminant transport, (2) optimization of the proposed monitoring network locations in terms of their efficiency to detect contaminants and provide early warning. We apply existing and newly-proposed methods to quantify predictive uncertainties and to optimize well locations. An important aspect of the analysis is the application of newly-developed optimization technique based on coupling of Particle Swarm and Levenberg-Marquardt optimization methods which proved to be robust and computationally efficient. These techniques and algorithms are bundled in a software package called MADS. MADS (Model Analyses for Decision Support) is an object-oriented code that is capable of performing various types of model analyses and supporting model-based decision making. The code can be executed under different computational modes, which include (1) sensitivity analyses (global and local), (2) Monte Carlo analysis, (3) model calibration, (4) parameter estimation, (5) uncertainty quantification, and (6) model selection. The code can be externally coupled with any existing model simulator through integrated modules that read/write input and output files using a set of template and instruction files (consistent with the PEST

  3. In situ evidence of rapid, vertical, irreversible transport of lower tropospheric air into the lower tropical stratosphere by convective cloud turrets and by larger-scale upwelling in tropical cyclones

    SciTech Connect

    Danielsen, E.F. )

    1993-05-20

    The author describes evidence from three different cloud types observed in the Australian monsoon, continental-maritime convective, maritime convective, and tropical cyclones, which contribute to transport of tropospheric air masses into the lower stratosphere. Measurements were made from ER-2 aircraft flying out of Darwin, Australia, equipped to measure an array of different parameters, including water vapor, temperatures, pressures, radon, etc. Maritime environmental conditions do not produce as much bouyancy for ascending air masses near Darwin, as do continental-maritime conditions when intense solar heating over the arid continental center of Australia heat and drys air masses which flow over the moist surface marine layers and have bouyancy to allow deep penetration into the lower stratosphere. For the tropical cyclones, their large scale, slower ascending air seems to mix into the stratosphere by gravity wave generation, which produces turbulence enough to drive air mass mixing across the inversions which cap these features.

  4. The Spectral Signature of Rotating, Stratified Convection

    NASA Astrophysics Data System (ADS)

    Featherstone, N. A.; Hindman, B.

    2016-12-01

    Recent helioseimic measurements of convective amplitudes in the Sun indicate that deep solar convection may be operating in a surprisingly low-Rossby number regime. Solar convection, it seems, might share more in common with convection in Earth's core than is generally assumed. Convection, an indispensable component of the dynamo, occurs in the midst of rotation, and yet we know troublingly little about how the influence of that rotation manifests across the broad range of convective scales present in the Sun. We are nevertheless well aware that the interaction of rotation and convection profoundly impacts many aspects of the solar dynamo. The structure of deep meridional circulation, which may bear on the timing of the solar cycle, is sensitive to the degree of rotational constraint felt by its underlying convective motions. The differential rotation, a vital source of large-scale shear in some dynamo models, results from convective motions that transport not just heat, but angular momentum. Rotation imbues convection with a sense of helicity, supplying a source of turbulent EMF to the dynamo, and it is only in regimes of strong rotational constraint that fully nonlinear models of stellar convection have evinced cyclic dynamo behavior. As we leverage helioseismic analyses in seeking further insight into the operation of the solar dynamo, it is prudent to ask ourselves how rotation shapes the spectral distribution of convective power. A solid understanding of such spectral signatures will only serve to complement helioseismic analyses directed toward understanding the operation of the dynamo. I will present numerical results from a series of nonrotating and rotating convection simulations conducted in full spherical geometry. This presentation will focus on how convective velocity spectra differ between the rotating and non-rotating models and how that behavior changes as simulations are pushed toward rotationally-constrained regimes that are, in many ways, more

  5. Reactive Transport Modeling of Effects of Different (Physical, Chemical and Computational) Factors on the Convection Process during CO2 Geological Sequestration in Deep Saline Aquifers

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Wang, S.

    2014-12-01

    Density-driven convective activity can significantly accelerate the transformation of the injected CO2 from supercritical or gas phase into liquid phase, thus improving the long-term storage security. It is well known that the convective instability is only caused by the heterogeneity of porous medium. However, we found that numerical perturbation resulted from the spatial and temporal discretization and the convergence criteria will affect the modeling results. Partial simulation results as follows: (1) the increase in vertical permeability (kv) has a strong effect on the convection process compared to the increasing horizontal permeability. The higher kv also can accelerate the downward migration of fingers and the CO2 dissolution; (2) increase in magnitude of medium (porosity and permeability) perturbation promotes the onset of convective activity, but does not affect the evolution of convection. However, for same magnitudes of the medium perturbation, the modification in permeability can lead to a more rapid onset of convective activity than that in porosity; and (3) the geochemical reactions and mineral compositions are important not only to the CO2 dissolution, but also to the dissolution of other species from mineral dissolution, which both can increase the water density. In additional, 3D and 2D modeling results indicated that their effect on the convection onset is similar. The CO2 dissolution rate for the higher-resolution 3D model is greatly slower than that for the higher-resolution 2D model, due to the increase in dimension for 3D model enhances the interaction of fingers. However, we found that once the bottom boundary becomes important, the decrease in CO2 dissolution rate for the 2D model is more significant than that for the 3D model. This is because the more significant interaction of fingers in the 3D model than that in the 2D model delays the downward propagation of fingers and then the impact of the bottom boundary.

  6. The potential for free and mixed convection in sedimentary basins

    USGS Publications Warehouse

    Raffensperger, J.P.; Vlassopoulos, D.

    1999-01-01

    Free thermal convection and mixed convection are considered as potential mechanisms for mass and heat transport in sedimentary basins. Mixed convection occurs when horizontal flows (forced convection) are superimposed on thermally driven flows. In cross section, mixed convection is characterized by convection cells that migrate laterally in the direction of forced convective flow. Two-dimensional finite-element simulations of variable-density groundwater flow and heat transport in a horizontal porous layer were performed to determine critical mean Rayleigh numbers for the onset of free convection, using both isothermal and semi-conductive boundaries. Additional simulations imposed a varying lateral fluid flux on the free-convection pattern. Results from these experiments indicate that forced convection becomes dominant, completely eliminating buoyancy-driven circulation, when the total forced-convection fluid flux exceeds the total flux possible due to free convection. Calculations of the thermal rock alteration index (RAI=q????T) delineate the patterns of potential diagenesis produced by fluid movement through temperature gradients. Free convection produces a distinct pattern of alternating positive and negative RAIs, whereas mixed convection produces a simpler layering of positive and negative values and in general less diagenetic alteration. ?? Springer-Verlag.

  7. Convective overshoot at the solar tachocline

    NASA Astrophysics Data System (ADS)

    Brown, Benjamin; Oishi, Jeffrey S.; Anders, Evan H.; Lecoanet, Daniel; Burns, Keaton; Vasil, Geoffrey M.

    2017-08-01

    At the base of the solar convection zone lies the solar tachocline. This internal interface is where motions from the unstable convection zone above overshoot and penetrate downward into the stiffly stable radiative zone below, driving gravity waves, mixing, and poss