WorldWideScience

Sample records for buoyancy driven natural

  1. Buoyancy Driven Natural Ventilation through Horizontal Openings

    DEFF Research Database (Denmark)

    Heiselberg, Per

    2009-01-01

    An experimental study of the phenomenon of buoyancy driven natural ventilation through single-sided horizontal openings was performed in a full-scale laboratory test rig. The measurements were made for opening ratios L/D ranging from 0.027 to 4.455, where L and D are the length of the opening...... and the diameter of the opening, respectively. The basic nature of airflow through single-sided openings, including airflow rate, air velocity, temperature difference between the rooms and the dimensions of the horizontal openings, were measured. A bi-directional airflow rate was measured using the constant...... quite well with the Epstein's formula ratio are presented. In some cases the measured airflow rates fit quite well with the Epstein's formula but in other cases the measured data show clear deviations from the Epstein's formula. Thus, revised formulas for natural ventilation are proposed....

  2. Buoyancy Driven Natural Ventilation through Horizontal Openings

    DEFF Research Database (Denmark)

    Heiselberg, Per; Li, Zhigang

    2009-01-01

    An experimental study of the phenomenon of buoyancy driven natural ventilation through single-sided horizontal openings was performed in a full-scale laboratory test rig. The measurements were made for opening ratios L/D ranging from 0.027 to 4.455, where L and D are the length of the opening...... and the diameter of the opening, respectively. The basic nature of airflow through single-sided openings, including airflow rate, air velocity, temperature difference between the rooms and the dimensions of the horizontal openings, were measured. A bi-directional airflow rate was measured using the constant...... injection tracer gas technique. Smoke visualizations showed that the airflow patterns are highly transient and unstable, and that the airflow rate oscillates with time. Correlations between the Froude (Archimedes) number Fr (Ar) and the L/D ratio are presented. In some cases the measured airflow rates fit...

  3. Experimental study of buoyancy driven natural ventilation through horizontal openings

    DEFF Research Database (Denmark)

    Heiselberg, Per; Li, Zhigang

    2007-01-01

    An experimental study of buoyancy driven natural ventilation through single-sided horizontal openings was performed in a full-scale laboratory test rig. Measurements were made for opening ratios L/D range from 0.027 to 4.455, where L and D are the length and the diameter of the opening, respectiv......An experimental study of buoyancy driven natural ventilation through single-sided horizontal openings was performed in a full-scale laboratory test rig. Measurements were made for opening ratios L/D range from 0.027 to 4.455, where L and D are the length and the diameter of the opening......, respectively. The bidirectional air flow rate was measured using constant injection tracer gas technique. Smoke visualizations showed that the air flow patterns are highly transient, unstable and complex, and that air flow rates oscillate with time. Correlations between the Froude number Fr and the L/D ratio...... of a ventilation system, but also be implemented in more detailed models, especially multi-zone models, for simulation of the performance of natural ventilation systems...

  4. Characteristics of Buoyancy Driven Natural Ventilation through Horizontal Openings

    DEFF Research Database (Denmark)

    Li, Zhigang

    Air flow through horizontal openings is an important issue of mass and energy transfer between different zones in buildings. This kind of mass and energy transfer have important implications regarding energy saving, thermal comfort, control of contaminants, micro-organisms and spread of fire...... and smoke. Air flow through vertical openings has been widely investigated but little is known about the flow in the horizontal openings, especially when they are driven by buoyancy. A literature survey shows that the brine-water system and the scale model are normally used forthe research work of air flow....... Computational fluid dynamics (CFD) are used to study these two air flow cases. The air flow rate and air flow pattern are predicted and compared with the full-scale measurements. The measurement data are used to compare two CFD models: standard k- ε model and large eddy simulation (LES) model. The cases...

  5. Experimental Study of Wind-Opposed Buoyancy-Driven Natural Ventilation

    DEFF Research Database (Denmark)

    Andersen, A.; Bjerre, M.; Chen, Z. D.;

    Natural ventilation driven by natural forces, i.e. wind and thermal buoyancy, is an environmentally friendly system for buildings and has been increasingly used around the world in recent years to mitigate the impact on the global environment due to the significant energy consumption by heating......, ventilation and air-conditioning (HV AC). There is a need for the understanding and development of theories and tools related to the design, operation and control of natural ventilation systems....

  6. CFD modelling of buoyancy-driven natural ventilation opposed by wind

    Energy Technology Data Exchange (ETDEWEB)

    Cook, M.; Ji, Y. [De Montfort Univ., Leceister (United Kingdom). Inst. of Energy and Sustainable Development; Hunt, G. [Imperial College of London, London (United Kingdom). Dept. of Civil and Environmental Engineering

    2005-07-01

    This study formed the basis for generating guidelines on how to use computational fluid dynamics (CFD) to model natural ventilation in low-energy building designs. Previous studies have investigated steady natural displacement ventilation in a single space driven by buoyancy alone. The simulations used an external flow domain which allowed airflow through inlets and outlets to be modelled without the need for boundary conditions at these locations. CFD methods were used successfully to model buoyancy-driven displacement ventilation in which wind forces oppose the flow. Simulations were then conducted for a wind assisted buoyancy-driven displacement ventilation flow. The use of boundary conditions was the basic differences in the way these simulations were modelled. It was emphasized that the simulations are for natural displacement ventilation in which wind forces oppose buoyancy. Results of analytical predictions and experimental measurements were found to be in good agreement. The small discrepancies in the interface height separating the warm stratified air from the cooler ambient layer below can be attributed to differences in the plume behaviour and performance of the gauze used for inhibiting horizontal momentum. The under-prediction in the reduced gravity of the upper layer may also be due to the small differences in plume structure. 12 refs., 1 tab., 11 figs.

  7. Buoyancy-driven Magnetohydrodynamic Waves

    Science.gov (United States)

    Hague, A.; Erdélyi, R.

    2016-09-01

    Turbulent motions close to the visible solar surface may generate low-frequency internal gravity waves (IGWs) that propagate through the lower solar atmosphere. Magnetic activity is ubiquitous throughout the solar atmosphere, so it is expected that the behavior of IGWs is to be affected. In this article we investigate the role of an equilibrium magnetic field on propagating and standing buoyancy oscillations in a gravitationally stratified medium. We assume that this background magnetic field is parallel to the direction of gravitational stratification. It is known that when the equilibrium magnetic field is weak and the background is isothermal, the frequencies of standing IGWs are sensitive to the presence of magnetism. Here, we generalize this result to the case of a slowly varying temperature. To do this, we make use of the Boussinesq approximation. A comparison between the hydrodynamic and magnetohydrodynamic cases allows us to deduce the effects due to a magnetic field. It is shown that the frequency of IGWs may depart significantly from the Brunt-Väisälä frequency, even for a weak magnetic field. The mathematical techniques applied here give a clearer picture of the wave mode identification, which has previously been misinterpreted. An observational test is urged to validate the theoretical findings.

  8. Exploring Titan with Autonomous, Buoyancy Driven Gliders

    Science.gov (United States)

    Morrow, M. T.; Woolsey, C. A.; Hagerman, G. M.

    Buoyancy driven underwater gliders are highly efficient winged underwater vehicles which locomote by modifying their internal shape. The concept, which is already well-proven in Earth's oceans, is also an appealing technology for remote terrain exploration and environmental sampling on worlds with dense atmospheres. Because of their high efficiency and their gentle, vertical take-off and landing capability, buoyancy driven gliders might perform long duration, global mapping tasks as well as light-duty, local sampling tasks. Moreover, a sufficiently strong gradient in the planetary boundary layer may enable the vehicles to perform dynamic soaring, achieving even greater locomotive efficiency. Shape Change Actuated, Low Altitude Robotic Soarers (SCALARS) are an appealing alternative to more conventional vehicle technology for exploring planets with dense atmospheres. SCALARS are buoyancy driven atmospheric gliders with a twin-hulled, inboard wing configuration. The inboard wing generates lift, which propels the vehicle forward. Symmetric changes in mass distribution induce gravitational pitch moments that provide longitudinal control. Asymmetric changes in mass distribution induce twist in the inboard wing that provides directional control. The vehicle is actuated solely by internal shape change; there are no external seals and no exposed moving parts, save for the inflatable buoyancy ballonets. Preliminary sizing analysis and dynamic modeling indicate the viability of using SCALARS to map the surface of Titan and to investigate features of interest.

  9. Buoyancy driven turbulence and distributed chaos

    CERN Document Server

    Bershadskii, A

    2016-01-01

    It is shown, using results of recent direct numerical simulations, laboratory experiments and atmospheric measurements, that buoyancy driven turbulence exhibits a broad diversity of the types of distributed chaos with its stretched exponential spectrum $\\exp(-k/k_{\\beta})^{\\beta}$. The distributed chaos with $\\beta = 1/3$ (determined by the helicity correlation integral) is the most common feature of the stably stratified turbulence (due to the strong helical waves presence). These waves mostly dominate spectral properties of the vertical component of velocity field, while the horizontal component is dominated by the diffusive processes both for the weak and strong stable stratification ($\\beta =2/3$). For the last case influence of the low boundary can overcome the wave effects and result in $\\beta =1/2$ for the vertical component of the velocity field (the spontaneous breaking of the space translational symmetry - homogeneity). For the unstably stratified turbulence in the Rayleigh-Taylor mixing zone the di...

  10. Lagrangian chaos in three- dimensional steady buoyancy-driven flows

    Science.gov (United States)

    Contreras, Sebastian; Speetjens, Michel; Clercx, Herman

    2016-11-01

    Natural convection plays a key role in fluid dynamics owing to its ubiquitous presence in nature and industry. Buoyancy-driven flows are prototypical systems in the study of thermal instabilities and pattern formation. The differentially heated cavity problem has been widely studied for the investigation of buoyancy-induced oscillatory flow. However, far less attention has been devoted to the three-dimensional Lagrangian transport properties in such flows. This study seeks to address this by investigating Lagrangian transport in the steady flow inside a cubic cavity differentially-heated from the side. The theoretical and numerical analysis expands on previously reported similarities between the current flow and lid-driven flows. The Lagrangian dynamics are controlled by the Péclet number (Pe) and the Prandtl number (Pr). Pe controls the behaviour qualitatively in that growing Pe progressively perturbs the integable state (Pe =0), thus paving the way to chaotic dynamics. Pr plays an entirely quantitative role in that Pr1 amplifies and diminishes, respectively, the perturbative effect of non-zero Pe. S.C. acknowledges financial support from Consejo Nacional de Ciencia y Tecnología (CONACYT).

  11. Rigorous buoyancy driven bubble mixing for centrifugal microfluidics.

    Science.gov (United States)

    Burger, S; Schulz, M; von Stetten, F; Zengerle, R; Paust, N

    2016-01-21

    We present batch-mode mixing for centrifugal microfluidics operated at fixed rotational frequency. Gas is generated by the disk integrated decomposition of hydrogen peroxide (H2O2) to liquid water (H2O) and gaseous oxygen (O2) and inserted into a mixing chamber. There, bubbles are formed that ascent through the liquid in the artificial gravity field and lead to drag flow. Additionaly, strong buoyancy causes deformation and rupture of the gas bubbles and induces strong mixing flows in the liquids. Buoyancy driven bubble mixing is quantitatively compared to shake mode mixing, mixing by reciprocation and vortex mixing. To determine mixing efficiencies in a meaningful way, the different mixers are employed for mixing of a lysis reagent and human whole blood. Subsequently, DNA is extracted from the lysate and the amount of DNA recovered is taken as a measure for mixing efficiency. Relative to standard vortex mixing, DNA extraction based on buoyancy driven bubble mixing resulted in yields of 92 ± 8% (100 s mixing time) and 100 ± 8% (600 s) at 130g centrifugal acceleration. Shake mode mixing yields 96 ± 11% and is thus equal to buoyancy driven bubble mixing. An advantage of buoyancy driven bubble mixing is that it can be operated at fixed rotational frequency, however. The additional costs of implementing buoyancy driven bubble mixing are low since both the activation liquid and the catalyst are very low cost and no external means are required in the processing device. Furthermore, buoyancy driven bubble mixing can easily be integrated in a monolithic manner and is compatible to scalable manufacturing technologies such as injection moulding or thermoforming. We consider buoyancy driven bubble mixing an excellent alternative to shake mode mixing, in particular if the processing device is not capable of providing fast changes of rotational frequency or if the low average rotational frequency is challenging for the other integrated fluidic operations.

  12. Energy spectrum of buoyancy-driven turbulence

    KAUST Repository

    Kumar, Abhishek

    2014-08-25

    Using high-resolution direct numerical simulation and arguments based on the kinetic energy flux Πu, we demonstrate that, for stably stratified flows, the kinetic energy spectrum Eu(k)∼k-11/5, the potential energy spectrum Eθ(k)∼k-7/5, and Πu(k)∼k-4/5 are consistent with the Bolgiano-Obukhov scaling. This scaling arises due to the conversion of kinetic energy to the potential energy by buoyancy. For weaker buoyancy, this conversion is weak, hence Eu(k) follows Kolmogorov\\'s spectrum with a constant energy flux. For Rayleigh-Bénard convection, we show that the energy supply rate by buoyancy is positive, which leads to an increasing Πu(k) with k, thus ruling out Bolgiano-Obukhov scaling for the convective turbulence. Our numerical results show that convective turbulence for unit Prandt number exhibits a constant Πu(k) and Eu(k)∼k-5/3 for a narrow band of wave numbers. © 2014 American Physical Society.

  13. Buoyancy-Driven Polymerase Chain Reaction (PCR) Devices

    Energy Technology Data Exchange (ETDEWEB)

    Ness, K D; Wheeler, E K; Benett, W; Stratton, P; Christian, A; Chen, A; Ortega, J; Weisgraber, T H; Goodson, K E

    2004-09-28

    Polymerase chain reaction (PCR) facilitates DNA detection by significantly increasing the concentration of specific DNA segments. A new class of PCR instruments uses a buoyancy-driven re-circulating flow to thermally cycle the DNA sample and benefits from reduced cycle times, low sample volumes, a miniaturized format, and low power consumption. This paper analyzes a specific buoyancy PCR device in a micro-channel ''race-track'' geometry to determine key parameters about PCR cycle times and other figures of merit as functions of device dimensions. The 1-D model balances the buoyancy driving force with frictional losses. A hydrostatic pressure imbalance concept is used between the left and right sides of the fluid loop to calculate the buoyancy driving force. Velocity and temperature distributions within the channels are determined from two-dimensional analysis of the channel section, with developing region effects included empirically through scaled values of the local Nusselt number. Good agreement between four independent verification steps validate the 1-D simulation approach: (1) analytical expressions for the thermal entrance length are compared against, (2) comparison with a full 3-D finite element simulation, (3) comparison with an experimental flow field characterization, and (4) calculation of the minimum PCR runtime required to get a positive PCR signal from the buoyancy-driven PCR device. The 1-D approach closely models an actual buoyancy-driven PCR device and can further be used as a rapid design tool to simulate buoyancy PCR flows and perform detailed design optimizations studies.

  14. Mixing and dissipation in a geostrophic buoyancy-driven circulation

    Science.gov (United States)

    Vreugdenhil, Catherine A.; Gayen, Bishakhdatta; Griffiths, Ross W.

    2016-08-01

    Turbulent mixing and energy dissipation have important roles in the global circulation but are not resolved by ocean models. We use direct numerical simulations of a geostrophic circulation, resolving turbulence and convection, to examine the rates of dissipation and mixing. As a starting point, we focus on circulation in a rotating rectangular basin forced by a surface temperature difference but no wind stress. Emphasis is on the geostrophic regime for the horizontal circulation, but also on the case of strong buoyancy forcing (large Rayleigh number), which implies a turbulent convective boundary layer. The computed results are consistent with existing scaling theory that predicts dynamics and heat transport dependent on the relative thicknesses of thermal and Ekman boundary layers, hence on the relative roles of buoyancy and rotation. Scaling theory is extended to describe the volume-integrated rate of mixing, which is proportional to heat transport and decreases with increasing rotation rate or decreasing temperature difference. In contrast, viscous dissipation depends crucially on whether the thermal boundary layer is laminar or turbulent, with no direct Coriolis effect on the turbulence unless rotation is extremely strong. For strong forcing, in the geostrophic regime, the mechanical energy input from buoyancy goes primarily into mixing rather than dissipation. For a buoyancy-driven circulation in a basin comparable to the North Atlantic we estimate that the total rate of mixing accounts for over 95% of the mechanical energy supply, implying that buoyancy is an efficient driver of mixing in the oceans.

  15. Buoyancy Driven Mixing with Continuous Volumetric Energy Deposition

    Science.gov (United States)

    Wachtor, Adam J.; Jebrail, Farzaneh F.; Dennisen, Nicholas A.; Andrews, Malcolm J.; Gore, Robert A.

    2014-11-01

    An experiment involving a miscible fluid pair is presented which transitioned from a Rayleigh-Taylor (RT) stable to RT unstable configuration through continuous volumetric energy deposition (VED) by microwave radiation. Initially a light, low microwave absorbing fluid rested above a heavier, more absorbing fluid. The alignment of the density gradient with gravity made the system stable, and the Atwood number (At) for the initial setup was approximately -0.12. Exposing the fluid pair to microwave radiation preferentially heated the bottom fluid, and caused its density to drop due to thermal expansion. As heating of the bottom fluid continued, the At varied from negative to positive, and after the system passed through the neutral stability point, At = 0, buoyancy driven mixing ensued. Continuous VED caused the At to continue increasing and further drive the mixing process. Successful VED mixing required careful design of the fluid pair used in the experiment. Therefore, fluid selection is discussed, along with challenges and limitations of data collection using the experimental microwave facility. Experimental and model predictions of the neutral stability point, and onset of buoyancy driven mixing, are compared, and differences with classical, constant At RT driven turbulence are discussed.

  16. Phenomenology of buoyancy-driven turbulence: recent results

    CERN Document Server

    Verma, Mahendra K; Pandey, Ambrish

    2016-01-01

    In this paper, we review the recent developments in the field of buoyancy-driven turbulence. Scaling and numerical arguments show that the stably-stratified turbulence with moderate stratification has kinetic energy spectrum $E_u(k) \\sim k^{-11/5}$ and the kinetic energy flux $\\Pi_u(k) \\sim k^{-4/5}$, which is called Bolgiano-Obukhov scaling. The energy flux for the Rayleigh-B\\'{e}nard convection (RBC) however is approximately constant in the inertial range that results in Kolmorogorv's spectrum ($E_u(k) \\sim k^{-5/3}$) for the kinetic energy. The phenomenology of RBC should apply to other flows where the buoyancy feeds the kinetic energy, e.g. bubbly turbulence and fully-developed Rayleigh Taylor instability. This paper also covers several models that predict the Reynolds and Nusselt numbers of RBC. Recent works show that the viscous dissipation rate of RBC scales as $\\sim \\mathrm{Ra}^{1.3}$, where $\\mathrm{Ra}$ is the Rayleigh number.

  17. Nonlinear optimization of buoyancy-driven ventilation flow

    Science.gov (United States)

    Nabi, Saleh; Grover, Piyush; Caulfield, C. P.

    2016-11-01

    We consider the optimization of buoyancy-driven flows governed by Boussinesq equations using the Direct-Adjoint-Looping method. We use incompressible Reynolds-averaged Navier-Stokes (RANS) equations, derive the corresponding adjoint equations and solve the resulting sensitivity equations with respect to inlet conditions. For validation, we solve a series of inverse-design problems, for which we recover known globally optimal solutions. For a displacement ventilation scenario with a line source, the numerical results are compared with analytically obtained optimal inlet conditions available from classical plume theory. Our results show that depending on Archimedes number, defined as the ratio of the inlet Reynolds number to the Rayleigh number associated with the plume, qualitatively different optimal solutions are obtained. For steady and transient plumes, and subject to an enthalpy constraint on the incoming flow, we identify boundary conditions leading to 'optimal' temperature distributions in the occupied zone.

  18. Flow field topology of transient mixing driven by buoyancy

    Science.gov (United States)

    Duval, Walter M B.

    2004-01-01

    Transient mixing driven by buoyancy occurs through the birth of a symmetric Rayleigh-Taylor morphology (RTM) structure for large length scales. Beyond its critical bifurcation the RTM structure exhibits self-similarity and occurs on smaller and smaller length scales. The dynamics of the RTM structure, its nonlinear growth and internal collision, show that its genesis occurs from an explosive bifurcation which leads to the overlap of resonance regions in phase space. This event shows the coexistence of regular and chaotic regions in phase space which is corroborated with the existence of horseshoe maps. A measure of local chaos given by the topological entropy indicates that as the system evolves there is growth of uncertainty. Breakdown of the dissipative RTM structure occurs during the transition from explosive to catastrophic bifurcation; this event gives rise to annihilation of the separatrices which drives overlap of resonance regions. The global bifurcation of explosive and catastrophic events in phase space for the large length scale of the RTM structure serves as a template for which mixing occurs on smaller and smaller length scales. Copyright 2004 American Institute of Physics.

  19. A Review of Some Recent Studies on Buoyancy Driven Flows in an Urban Environment

    Directory of Open Access Journals (Sweden)

    Bodhisatta Hajra

    2014-01-01

    Full Text Available This paper reviews some recent studies (after 2000 pertaining to buoyancy driven flows in nature and thier use in reducing air pollution levels in a city (city ventilation. Natural convection flows occur due to the heating and cooling of various urban surfaces (e.g., mountain slopes, leading to upslope and downslope flows. Such flows can have a significant effect on city ventilation which has been the subject of study in the recent times due to increased pollution levels in a city. A major portion of the research reviewed here consists of natural convection flows occurring along mountain slopes, with a few studies devoted to flows along building walls. The studies discussed here primarily include field measurements and computational fluid dynamics (CFD models. This review shows that for densely populated cities with high pollution levels, natural convection flows (mountain slope or building walls can significantly aid the dispersion of pollutants. Additional studies in this area using CFD and water channel measurements can explain the physical processes involved in such flows and help improve CFD modelling. Future research should focus on a complete understanding of the mechanisms of buoyancy flows in nature and developing design guidelines for better planning of cities.

  20. Floating rings in vertical soap films : capillary driven bidimensional buoyancy

    CERN Document Server

    Adami, N

    2013-01-01

    The present study aims to investigate the motion of buoyant rings in vertical soap films. Thickness differences and related bi-dimensional densities are considered as the motor leading to bi-dimensional buoyancy. We show how this effect can be re-interpreted thanks to surface tension profiles in soap films. We propose a model involving surface tension profiles in order to describe the motion of buoyant particles in vertical soap films, and compare it to experimental data.

  1. Buoyancy driven flow in a hot water tank due to standby heat loss

    DEFF Research Database (Denmark)

    Fan, Jianhua; Furbo, Simon

    2012-01-01

    show that the CFD model predicts satisfactorily water temperatures at different levels of the tank during cooling by standby heat loss. It is elucidated how the downward buoyancy driven flow along the tank wall is established by the heat loss from the tank sides and how the natural convection flow......Results of experimental and numerical investigations of thermal behavior in a vertical cylindrical hot water tank due to standby heat loss of the tank are presented. The effect of standby heat loss on temperature distribution in the tank is investigated experimentally on a slim 150l tank...... parts of the tank is measured by experiments and used as input to the CFD model. Water temperatures at different levels of the tank are measured and compared to CFD calculated temperatures. The investigations focus on validation of the CFD model and on understanding of the CFD calculations.The results...

  2. Analysis of Buoyancy-Driven Ventilation of Hydrogen from Buildings: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Barley, C. D.; Gawlik, K.; Ohi, J.; Hewett, R.

    2007-08-01

    When hydrogen gas is used or stored within a building, as with a hydrogen-powered vehicle parked in a residential garage, any leakage of unignited H2 will mix with indoor air and may form a flammable mixture. One approach to safety engineering relies on buoyancy-driven, passive ventilation of H2 from the building through vents to the outside.

  3. CO$_2$ dissolution controlled by buoyancy driven shear dispersion in a background hydrological flow

    CERN Document Server

    Unwin, H Juliette T; Woods, Andrew W

    2015-01-01

    We present an analytical and numerical study of the long-time flow which controls the dissolution of a plume of CO$_2$ following injection into an anticline structure in a deep saline aquifer of finite vertical extent. Over times of tens to thousands of years, some of the CO$_2$ will dissolve into the underlying groundwater to produce a region of relatively dense, CO$_2$ saturated water directly below the plume of CO$_2$. Continued dissolution then requires the supply of CO$_2$ unsaturated aquifer water. This may be provided by a background hydrological flow or buoyancy driven flow caused by the density contrast between the CO$_2$ saturated and unsaturated water in the aquifer. At long times, the interaction of the cross-layer diffusive mixing with the buoyancy, leads to buoyancy driven shear dispersion of the CO$_2$. With a background hydrological flow, the upstream transport of dissolved CO$_2$ by this dispersion becomes balanced by the oncoming hydrological flow so that CO$_2$ rich water can only spread a ...

  4. Role of magnetic field strength and numerical resolution in simulations of the heat-flux driven buoyancy instability

    CERN Document Server

    Avara, Mark J; Bogdanović, Tamara

    2013-01-01

    The role played by magnetic fields in the intracluster medium (ICM) of galaxy clusters is complex. The weakly collisional nature of the ICM leads to thermal conduction that is channelled along field lines. This anisotropic heat conduction profoundly changes the stability of the ICM atmosphere, with convective stabilities being driven by temperature gradients of either sign. Here, we employ the Athena magnetohydrodynamic code to investigate the local non-linear behavior of the heat-flux driven buoyancy instability (HBI), relevant in the cores of cooling-core clusters where the temperature increases with radius. We study a grid of 2-d simulations that span a large range of initial magnetic field strengths and numerical resolutions. For very weak initial fields, we recover the previously known result that the HBI wraps the field in the horizontal direction thereby shutting off the heat flux. However, we find that simulations which begin with intermediate initial field strengths have a qualitatively different beh...

  5. Numerical Investigation of Heat Transfer with Thermal Radiation in an Enclosure in Case of Buoyancy Driven Flow

    Directory of Open Access Journals (Sweden)

    Christoph Hochenauer

    2014-08-01

    Full Text Available The purpose of this paper is to investigate state of the art approaches and their accuracy to compute heat transfer including radiation inside a closed cavity whereas buoyancy is the only driving force. This research is the first step of an all-embracing study dealing with underhood airflow and thermal management of vehicles. Computational fluid dynamic (CFD simulation results of buoyancy driven flow inside a simplified engine compartment are compared to experimentally gained values. The test rig imitates idle condition without any working fan. Thus, the airflow is only driven by natural convection. A conventional method used for these applications is to compute the convective heat transfer coefficient and air temperature using CFD and calculate the wall temperature separately by performing a thermal analysis. The final solution results from coupling two different software tools. In this paper thermal conditions inside the enclosure are computed by the use of CFD only. The impact of the turbulence model as well as the results of various radiation models are analyzed and compared to the experimental data.

  6. Experimental study of buoyancy-driven flow in a half-scale stairwell model

    Energy Technology Data Exchange (ETDEWEB)

    Zohrabian, A.S.; Mokhtarzadeh-Dehghan, M.R.; Reynolds, A.J. (Brunel Univ., Uxbridge (GB). Dept. of Mechanical Engineering); Marriott, B.S.T. (Logica EIS Ltd., London (GB))

    1989-01-01

    This paper describes an experimental study of buoyancy-driven flows of mass and energy in a half-scale model of a stairwell. Two different geometries are considered. The stairwell model forms a closed system, within which the circulation of air is maintained by the continuous operation of a heater placed in the lower floor. The rig, its instrumentation and the computerized data-logging system are described in detail. The overall features of the flow are also described. The results include the velocity and temperature distributions and the circulating volume flow. The effects of heat input rate on these parameters are also discussed. (author).

  7. Effects of buoyancy-driven convection on nucleation and growth of protein crystals.

    Science.gov (United States)

    Nanev, Christo N; Penkova, Anita; Chayen, Naomi

    2004-11-01

    Protein crystallization has been studied in presence or absence of buoyancy-driven convection. Gravity-driven flow was created, or suppressed, in protein solutions by means of vertically directed density gradients that were caused by generating suitable temperature gradients. The presence of enhanced mixing was demonstrated directly by experiments with crustacyanin, a blue-colored protein, and other materials. Combined with the vertical tube position the enhanced convection has two main effects. First, it reduces the number of nucleated hen-egg-white lysozyme (HEWL) crystals, as compared with those in a horizontal capillary. By enabling better nutrition from the protein in the solution, convection results in growth of fewer larger HEWL crystals. Second, we observe that due to convection, trypsin crystals grow faster. Suppression of convection, achieved by decreasing solution density upward in the capillary, can to some extent mimic conditions of growth in microgravity. Thus, impurity supply, which may have a detrimental effect on crystal quality, was avoided.

  8. Modeling Diffusion and Buoyancy-Driven Convection with Application to Geological CO2 Storage

    KAUST Repository

    Allen, Rebecca

    2015-04-01

    ABSTRACT Modeling Diffusion and Buoyancy-Driven Convection with Application to Geological CO2 Storage Rebecca Allen Geological CO2 storage is an engineering feat that has been undertaken around the world for more than two decades, thus accurate modeling of flow and transport behavior is of practical importance. Diffusive and convective transport are relevant processes for buoyancy-driven convection of CO2 into underlying fluid, a scenario that has received the attention of numerous modeling studies. While most studies focus on Darcy-scale modeling of this scenario, relatively little work exists at the pore-scale. In this work, properties evaluated at the pore-scale are used to investigate the transport behavior modeled at the Darcy-scale. We compute permeability and two different forms of tortuosity, namely hydraulic and diffusive. By generating various pore ge- ometries, we find hydraulic and diffusive tortuosity can be quantitatively different in the same pore geometry by up to a factor of ten. As such, we emphasize that these tortuosities should not be used interchangeably. We find pore geometries that are characterized by anisotropic permeability can also exhibit anisotropic diffusive tortuosity. This finding has important implications for buoyancy-driven convection modeling; when representing the geological formation with an anisotropic permeabil- ity, it is more realistic to also account for an anisotropic diffusivity. By implementing a non-dimensional model that includes both a vertically and horizontally orientated 5 Rayleigh number, we interpret our findings according to the combined effect of the anisotropy from permeability and diffusive tortuosity. In particular, we observe the Rayleigh ratio may either dampen or enhance the diffusing front, and our simulation data is used to express the time of convective onset as a function of the Rayleigh ratio. Also, we implement a lattice Boltzmann model for thermal convective flows, which we treat as an analog for

  9. Modeling and Assessment of Buoyancy-Driven Stratified Airflow in High-Space Industrial Hall

    Institute of Scientific and Technical Information of China (English)

    WANG Han-qing; CHEN Ke; HU Jian-jun; KOU Guang-xiao; WANG Zhi-yong

    2009-01-01

    In industrial environment,heat sources often are contaminant sources and health threatening con-taminants are mainly passive,so a detailed understanding of airflow mode can assist in work environment hy-giene measurement and prevention.This paper presented a numerical investigation of stratified airflow scenario in a high-space industrial hall with validated commercial code and experimentally acquired boundary conditions.Based upon an actually undergoing engineering project,this study investigated the performance of the buoyancy-driven displacement ventilation in a large welding hall with big components manufactured.The results have demonstrated that stratified airflow sustained by thermal buoyancy provides zoning effect in terms of clean and polluted regions except minor stagnant eddy areas.The competition between negative buoyant jets from displace-ment radial diffusers and positive buoyant plume from bulk object constitutes the complex transport characteris-tics under and above stratification interface.Entrainment,downdraft and turbulent eddy motion complicate the upper mixing zone,but the exhaust outlet plays a less important role in the whole field flow.And the corre-sponding suggestions concerning computational stability and convergence,further improvements in modeling and measurements were given.

  10. Buoyancy-driven instabilities of acid-base fronts: the case of a color indicator

    Science.gov (United States)

    Riolfo, L. A.; Kuster, S.; Trevelyan, P. M. J.; El Hasi, C.; Zalts, A.; Almarcha, C.; D'Onofrio, A.; de Wit, A.

    2011-11-01

    Buoyancy-driven hydrodynamic instabilities of acid-base fronts are studied both experimentally and theoretically in the case where an aqueous solution of a strong acid is put above a denser aqueous solution of a color indicator in the gravity field. The neutralization reaction between the acid and the color indicator as well as their differential diffusion modifies the initially stable density profile in the system and can trigger convective motion both above and below the initial contact line. The type of patterns observed as well as their wavelength and the speed of the reaction front are shown to depend on the value of the initial concentrations of the acid and of the color indicator and on their ratio. A reaction-diffusion model explains how the hydrodynamic instability scenarios change when the concentration of the reactants are varied.

  11. Dispersion enhancement and damping by buoyancy driven flows in 2D networks of capillaries

    CERN Document Server

    D'Angelo, Maria Veronica; Allain, Catherine; Rosen, Marta; Hulin, Jean-Pierre

    2008-01-01

    The influence of a small relative density difference on the displacement of two miscible liquids is studied experimentally in transparent 2D networks of micro channels. Both stable displacements in which the denser fluid enters at the bottom of the cell and displaces the lighter one and unstable displacements in which the lighter fluid is injected at the bottom and displaces the denser one are realized. Except at the lowest mean flow velocity U, the average $C(x,t)$ of the relative concentration satisfies a convection-dispersion equation. The dispersion coefficient is studied as function of the relative magnitude of fluid velocity and of the velocity of buoyancy driven fluid motion. A model is suggested and its applicability to previous results obtained in 3D media is discussed.

  12. DNS of buoyancy-driven flows and Lagrangian particle tracking in a square cavity at high Rayleigh numbers

    Energy Technology Data Exchange (ETDEWEB)

    Puragliesi, R., E-mail: riccardo.puragliesi@psi.ch [Nuclear Energy and Safety Research Department, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Laboratoire d' Ingenierie Numerique, Ecole Polytechnique Federale de Lausanne, Station 9, CH-1015 Lausanne (Switzerland); Dehbi, A., E-mail: abdel.dehbi@psi.ch [Nuclear Energy and Safety Research Department, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Leriche, E., E-mail: emmanuel.leriche@univ-st-etienne.fr [Universite de Lyon, F-42023 Saint-Etienne, LMFA-UJM St-Etienne, CNRS UMR 5509 Universite de St-Etienne, 23 rue Docteur Paul Michelon, F-42023 Saint-Etienne (France); Soldati, A., E-mail: soldati@uniud.it [Dipartimento di Energetica e Macchine, Universita di Udine, Via delle Scienze 208, IT-33100 Udine (Italy); Deville, M.O., E-mail: michel.deville@epfl.ch [Laboratoire d' Ingenierie Numerique, Ecole Polytechnique Federale de Lausanne, Station 9, CH-1015 Lausanne (Switzerland)

    2011-10-15

    Highlights: > 2D study of micro-size particle depletion driven by chaotic natural convective flows in square domains. > Description of velocity and temperature first and second moments with changing in the Rayleigh number. > Strong decoupling between the turbulent kinetic energy and the dissipation rate. > Particle recirculation sustained by the vertical hot boundary layer. > Deposition mostly induced by gravity, thermophoretic and lift forces are negligible. - Abstract: In this work we investigate numerically particle deposition in the buoyancy driven flow of the differentially heated cavity (DHC). We consider two values of the Rayleigh number (Ra = 10{sup 9}, 10{sup 10}) and three values of the particle diameter (d{sub p} = 15, 25, 35 [{mu}m]). We consider the cavity filled with air and particles with the same density of water {rho}{sub w} = 1000 [kg/m{sup 3}] (aerosol). We use direct numerical simulations (DNS) for the continuous phase, and we solve transient Navier-Stokes and energy transport equations written in an Eulerian framework, under the Boussinesq approximation, for the viscous incompressible Newtonian fluid with constant Prandtl number (Pr = 0.71). First- and second-order statistics are presented for the continuous phase as well as important quantities like turbulent kinetic energy (TKE) and temperature variance with the associated production and dissipation fields. The TKE production shows different behaviour at the two Rayleigh numbers. The Lagrangian approach has been chosen for the dispersed phase description. The forces taken into account are drag, gravity, buoyancy, lift and thermophoresis. A first incursion in the sedimentation mechanisms is presented. Current results indicate that the largest contribution to particle deposition is caused by gravitational settling, but a strong recirculating zone, which liftoffs and segregates particles, contributes to decrease settling. Deposition takes place mostly at the bottom wall. The influence of lift

  13. Buoyancy-driven convection around chemical fronts traveling in covered horizontal solution layers.

    Science.gov (United States)

    Rongy, L; Goyal, N; Meiburg, E; De Wit, A

    2007-09-21

    Density differences across an autocatalytic chemical front traveling horizontally in covered thin layers of solution trigger hydrodynamic flows which can alter the concentration profile. We theoretically investigate the spatiotemporal evolution and asymptotic dynamics resulting from such an interplay between isothermal chemical reactions, diffusion, and buoyancy-driven convection. The studied model couples the reaction-diffusion-convection evolution equation for the concentration of an autocatalytic species to the incompressible Stokes equations ruling the evolution of the flow velocity in a two-dimensional geometry. The dimensionless parameter of the problem is a solutal Rayleigh number constructed upon the characteristic reaction-diffusion length scale. We show numerically that the asymptotic dynamics is one steady vortex surrounding, deforming, and accelerating the chemical front. This chemohydrodynamic structure propagating at a constant speed is quite different from the one obtained in the case of a pure hydrodynamic flow resulting from the contact between two solutions of different density or from the pure reaction-diffusion planar traveling front. The dynamics is symmetric with regard to the middle of the layer thickness for positive and negative Rayleigh numbers corresponding to products, respectively, lighter or heavier than the reactants. A parametric study shows that the intensity of the flow, the propagation speed, and the deformation of the front are increasing functions of the Rayleigh number and of the layer thickness. In particular, the asymptotic mixing length and reaction-diffusion-convection speed both scale as square root Ra for Ra>5. The velocity and concentration fields in the asymptotic dynamics are also found to exhibit self-similar properties with Ra. A comparison of the dynamics in the case of a monostable versus bistable kinetics is provided. Good agreement is obtained with experimental data on the speed of iodate-arsenous acid fronts

  14. Buoyancy-driven instability of a miscible horizontal displacement in a Hele-Shaw cell

    Science.gov (United States)

    Haudin, F.; Riolfo, L. A.; Knaepen, B.; de Wit, A.

    2012-11-01

    In Hele-Shaw cells, viscous fingers are forming when a fluid is injected into a more viscous one. If the two fluids are reversed, with the less mobile fluid injected into the low viscosity one, the situation is expected to be stable from a viscous point of view. Nevertheless, a destabilization of the interface can be observed due to a buoyancy-driven effect if a density difference exists between the two miscible fluids. As a result, the Poiseuille profile established in the gap of the cell locally destabilizes and convection rolls are forming. In a view from above, a striped pattern is observed at the miscible interface between the two fluids. To characterize the development of this instability, we have performed an experimental study of viscously stable miscible displacements in a Hele-Shaw cell with radial injection. The displacing fluids are aqueous solutions of glycerol and the displaced ones are either dyed water or dyed glycerol solutions. The way the relative properties of the two fluids is influencing the onset time of the instability and the characteristic size of the pattern is studied. The influence of the gap width and of the flow rate on the buoyantly unstable dynamics is also characterized.

  15. BUOYANCY INSTABILITY IN THE NATURAL CONVECTION BOUNDARY LAYER AROUND A VERTICAL HEATED FLAT PLATE

    Institute of Scientific and Technical Information of China (English)

    颜大椿; 张汉勋

    2002-01-01

    A systematic research on the buoyancy instability in the natural convection boundary layer was conducted, including the basic characteristics such as its spectral components, wave length and velocity, the location of its critical layer,and amplitude distributions of the triple independent eigenmodes with the linear instability theory, the growth rates of its temperature and velocity fluctuations and the corresponding neutral curves for the buoyancy eigenmode were also obtained.Results indicated that the neutral curve of the velocity fluctuation had a nose shape consistent with that obtained in the numerical calculation, but for the temperature fluctuation, a ring-like region could be measured at a lower Grashof number before the nose-shaped main portion of the neutral curve.

  16. Microliter-bioreactor array with buoyancy-driven stirring for human hematopoietic stem cell culture.

    Science.gov (United States)

    Luni, Camilla; Feldman, Hope C; Pozzobon, Michela; De Coppi, Paolo; Meinhart, Carl D; Elvassore, Nicola

    2010-08-11

    This work presents the development of an array of bioreactors where finely controlled stirring is provided at the microliter scale (100-300 mul). The microliter-bioreactor array is useful for performing protocol optimization in up to 96 parallel experiments of hematopoietic stem cell (HSC) cultures. Exploring a wide range of experimental conditions at the microliter scale minimizes cost and labor. Once the cell culture protocol is optimized, it can be applied to large-scale bioreactors for stem cell production at the clinical level. The controlled stirring inside the wells of a standard 96-well plate is provided by buoyancy-driven thermoconvection. The temperature and velocity fields within the culture volume are determined with numerical simulations. The numerical results are verified with experimental velocity measurements using microparticle image velocimetry (muPIV) and are used to define feasible experimental conditions for stem cell cultures. To test the bioreactor array's functionality, human umbilical cord blood-derived CD34(+) cells were cultured for 7 days at five different stirring conditions (0.24-0.58 mums) in six repeated experiments. Cells were characterized in terms of proliferation, and flow cytometry measurements of viability and CD34 expression. The microliter-bioreactor array demonstrates its ability to support HSC cultures under stirred conditions without adversely affecting the cell behavior. Because of the highly controlled operative conditions, it can be used to explore culture conditions where the mass transport of endogenous and exogenous growth factors is selectively enhanced, and cell suspension provided. While the bioreactor array was developed for culturing HSCs, its application can be extended to other cell types.

  17. Buoyancy-driven detachment of a wall-bound pendant drop: interface shape at pinchoff and nonequilibrium surface tension.

    Science.gov (United States)

    Lamorgese, A; Mauri, R

    2015-09-01

    We present numerical results from phase-field simulations of the buoyancy-driven detachment of an isolated, wall-bound pendant emulsion droplet acted upon by surface tension and wall-normal buoyancy forces alone. Our theoretical approach follows a diffuse-interface model for partially miscible binary mixtures which has been extended to include the influence of static contact angles other than 90^{∘}, based on a Hermite interpolation formulation of the Cahn boundary condition as first proposed by Jacqmin [J. Fluid Mech. 402, 57 (2000)JFLSA70022-112010.1017/S0022112099006874]. In a previous work, this model has been successfully employed for simulating triphase contact line problems in stable emulsions with nearly immiscible components, and, in particular, applied to the determination of critical Bond numbers for buoyancy-driven detachment as a function of static contact angle. Herein, the shapes of interfaces at pinchoff are investigated as a function of static contact angle and distance to the critical condition. Furthermore, we show numerical results on the nonequilibrium surface tension that help to explain the discrepancy between our numerically determined static contact angle dependence of the critical Bond number and its sharp-interface counterpart based on a static stability analysis of equilibrium shapes after numerical integration of the Young-Laplace equation. Finally, we show the influence of static contact angle and distance to the critical condition on the temporal evolution of the minimum neck radius in the necking regime of drop detachment.

  18. Large eddy simulation of fire-induced buoyancy driven plume dispersion in an urban street canyon under perpendicular wind flow.

    Science.gov (United States)

    Hu, L H; Huo, R; Yang, D

    2009-07-15

    The dispersion of fire-induced buoyancy driven plume in and above an idealized street canyon of 18 m (width) x 18 m (height) x 40 m (length) with a wind flow perpendicular to its axis was investigated by Fire Dynamics Simulator (FDS), Large Eddy Simulation (LES). Former studies, such as that by Oka [T.R. Oke, Street design and urban canopy layer climate, Energy Build. 11 (1988) 103-113], Gayev and Savory [Y.A. Gayev, E. Savory, Influence of street obstructions on flow processes within street canyons. J. Wind Eng. Ind. Aerodyn. 82 (1999) 89-103], Xie et al. [S. Xie, Y. Zhang, L. Qi, X. Tang, Spatial distribution of traffic-related pollutant concentrations in street canyons. Atmos. Environ. 37 (2003) 3213-3224], Baker et al. [J. Baker, H. L. Walker, X. M. Cai, A study of the dispersion and transport of reactive pollutants in and above street canyons--a large eddy simulation, Atmos. Environ. 38 (2004) 6883-6892] and Baik et al. [J.-J. Baik, Y.-S. Kang, J.-J. Kim, Modeling reactive pollutant dispersion in an urban street canyon, Atmos. Environ. 41 (2007) 934-949], focus on the flow pattern and pollutant dispersion in the street canyon with no buoyancy effect. Results showed that with the increase of the wind flow velocity, the dispersion pattern of a buoyant plume fell into four regimes. When the wind flow velocity increased up to a certain critical level, the buoyancy driven upward rising plume was re-entrained back into the street canyon. This is a dangerous situation as the harmful fire smoke will accumulate to pollute the environment and thus threaten the safety of the people in the street canyon. This critical re-entrainment wind velocity, as an important parameter to be concerned, was further revealed to increase asymptotically with the heat/buoyancy release rate of the fire.

  19. Buoyancy-driven flow in a peat moss layer as a mechanism for solute transport

    NARCIS (Netherlands)

    Rappoldt, C.; Pieters, G.J.J.M.; Adema, E.B.; Baaijens, G.J.; Grootjans, A.P.; Duijn, van C.J.

    2003-01-01

    Transport of nutrients, CO2, methane, and oxygen plays an important ecological role at the surface of wetland ecosystems. A possibly important transport mechanism in a water-saturated peat moss layer (usually Sphagnum cuspidatum) is nocturnal buoyancy flow, the downward flow of relatively cold surfa

  20. Differential diffusion effects on buoyancy-driven instabilities of acid-base fronts: the case of a color indicator.

    Science.gov (United States)

    Kuster, S; Riolfo, L A; Zalts, A; El Hasi, C; Almarcha, C; Trevelyan, P M J; De Wit, A; D'Onofrio, A

    2011-10-14

    Buoyancy-driven hydrodynamic instabilities of acid-base fronts are studied both experimentally and theoretically in the case where an aqueous solution of a strong acid is put above a denser aqueous solution of a color indicator in the gravity field. The neutralization reaction between the acid and the color indicator as well as their differential diffusion modifies the initially stable density profile in the system and can trigger convective motions both above and below the initial contact line. The type of patterns observed as well as their wavelength and the speed of the reaction front are shown to depend on the value of the initial concentrations of the acid and of the color indicator and on their ratio. A reaction-diffusion model based on charge balances and ion pair mobility explains how the instability scenarios change when the concentration of the reactants are varied.

  1. It takes three to tango: 1. Simulating buoyancy-driven flow in the presence of large viscosity contrasts

    Science.gov (United States)

    Suckale, Jenny; Nave, Jean-Christophe; Hager, Bradford H.

    2010-07-01

    Buoyancy-driven flow is of fundamental importance for numerous geodynamic phenomena. Since the equations of motion governing multiphase flow are rarely amenable to analytical solutions, numerical simulations provide a compelling alternative. They offer the ability to carefully analyze flow phenomena under differing regimes, initial conditions, and flow dynamics. The three key challenges in these computations are (1) the accurate solution of the equations of motion in the presence of large viscosity contrasts, (2) the representation of strongly deforming interfaces between different fluids, and (3) the accurate coupling of fluid and interface solver. In three dimensions, these challenges become even more intricate, and the appropriate choice of numerical scheme has a profound influence on the tractability, accuracy, robustness, and efficiency of the computational simulation. This is the first paper of two that examine numerical simulations of buoyancy-driven flow in the presence of large viscosity contrasts. In this paper, we present our numerical approach which tackles the above three main challenges through a combination of three numerical methods, namely, (1) an extended ghost fluid type discretization which we developed specifically for the Stokes regime, (2) the level set method, and (3) the extension velocity technique. We find that all three components are crucial to obtain a versatile numerical tool for simulating complex structures in evolving flow. We validate our code by reproducing four benchmark problems in two and three dimensions. We devote special attention to comparing our method to other existing techniques, detailing the advantages of this approach. Finally, we highlight several types of geophysical flow problems for which we believe our method to be well suited.

  2. Passive urban ventilation by combined buoyancy-driven slope flow and wall flow: Parametric CFD studies on idealized city models

    Science.gov (United States)

    Luo, Zhiwen; Li, Yuguo

    2011-10-01

    This paper reports the results of a parametric CFD study on idealized city models to investigate the potential of slope flow in ventilating a city located in a mountainous region when the background synoptic wind is absent. Examples of such a city include Tokyo in Japan, Los Angeles and Phoenix in the US, and Hong Kong. Two types of buoyancy-driven flow are considered, i.e., slope flow from the mountain slope (katabatic wind at night and anabatic wind in the daytime), and wall flow due to heated/cooled urban surfaces. The combined buoyancy-driven flow system can serve the purpose of dispersing the accumulated urban air pollutants when the background wind is weak or absent. The microscopic picture of ventilation performance within the urban structures was evaluated in terms of air change rate (ACH) and age of air. The simulation results reveal that the slope flow plays an important role in ventilating the urban area, especially in calm conditions. Katabatic flow at night is conducive to mitigating the nocturnal urban heat island. In the present parametric study, the mountain slope angle and mountain height are assumed to be constant, and the changing variables are heating/cooling intensity and building height. For a typical mountain of 500 m inclined at an angle of 20° to the horizontal level, the interactive structure is very much dependent on the ratio of heating/cooling intensity as well as building height. When the building is lower than 60 m, the slope wind dominates. When the building is as high as 100 m, the contribution from the urban wall flow cannot be ignored. It is found that katabatic wind can be very beneficial to the thermal environment as well as air quality at the pedestrian level. The air change rate for the pedestrian volume can be as high as 300 ACH.

  3. Critical conditions for the buoyancy-driven detachment of a wall-bound pendant drop

    Science.gov (United States)

    Lamorgese, A.; Mauri, R.

    2016-03-01

    We investigate numerically the critical conditions for detachment of an isolated, wall-bound emulsion droplet acted upon by surface tension and wall-normal buoyancy forces alone. To that end, we present a simple extension of a diffuse-interface model for partially miscible binary mixtures that was previously employed for simulating several two-phase flow phenomena far and near the critical point [A. G. Lamorgese et al. "Phase-field approach to multiphase flow modeling," Milan J. Math. 79(2), 597-642 (2011)] to allow for static contact angles other than 90°. We use the same formulation of the Cahn boundary condition as first proposed by Jacqmin ["Contact-line dynamics of a diffuse fluid interface," J. Fluid Mech. 402, 57-88 (2000)], which accommodates a cubic (Hermite) interpolation of surface tensions between the wall and each phase at equilibrium. We show that this model can be successfully employed for simulating three-phase contact line problems in stable emulsions with nearly immiscible components. We also show a numerical determination of critical Bond numbers as a function of static contact angle by phase-field simulation.

  4. Influence of rheology on buoyancy driven instabilities of miscible displacements in 2D micromodels

    Science.gov (United States)

    D'Angelo, M. V.; Auradou, H.; Rosen, M.; Hulin, J. P.

    2009-05-01

    The stability of miscible displacements of Newtonian and shear-thinning fluids of slightly different densities (Δρ/ρ approx 3× 10-4) with a mean flow velocity U is investigated in a 2D transparent network of channels (average width = 0.33 mm). Concentration maps providing information at both the global and local scale are obtained through optical absorption measurements and compared in gravitationally stable and unstable vertical flow configurations; the influence of buoyant flows of typical velocity Ug is characterized by the gravity number Ng = Ug/|U|. For Ng glycerol solution, ld is only the same in the stable and unstable configurations for |Ng| 0.2, front spreading is not diffusive any more. In the stable configuration, in contrast, the front is flattened by buoyancy for Ng solution, both the concentration maps and the value of ld are the same in the stable and unstable configurations over the full range of U values investigated: this stabilization is explained by their high effective viscosity at low shear rates keeping Ng below the instability threshold even at the lowest velocities.

  5. Numerical experiments on the role of buoyancy and rheology during the formation of extension-driven gneiss domes

    Science.gov (United States)

    Korchinski, Megan; Rey, Patrice; Teyssier, Christian; Whitney, Donna; Mondy, Luke

    2016-04-01

    Domal structures that are cored with crystallized partially melted crustal rocks are ubiquitous features in active and exhumed orogens. The exposure of these gneiss/migmatite domes at the Earth's surface represents an opportunity to study the mechanisms of flow within the deep crust, and the mode of emplacement of high-pressure rocks into the shallow crust. End-member gneiss dome types include (1) extension-driven domes that core metamorphic core complexes, and (2) buoyancy-driven domes that are exhumed by diapiric flow. Numerical models are ideally suited to test the relative roles of buoyancy and extension-driven mechanisms in dome dynamics, and therefore to explore the interaction of physical parameters involved in doming. To that end, this research utilizes a 2D visco-plastic thermomechanical modeling framework to undertake a parametric numerical experiment where the density (range of 2700-3100 kg.m3) and viscosity (range of 1E19-1E21 Pa.s) of the lower crust are systematically varied. The style and timing of "intrusion" of partially molten lower crust into non-molten lower crust is similar for densities of 2700-3100 kg.m3 across two lower crustal viscosities tested here (1E19 Pa.s, 1E21 Pa.s). However, dome development and upwards flow of lower crust material for a relatively high-density, middle-viscosity lower crust (2900-3100 kg.m^3; 1E20 Pa.s) involves a significant upward translation of the Moho, relative to the low-density, middle-viscosity model results. In addition, the high-density, middle-viscosity model shows a decrease in the volume of partial melt in the lower crust, and distributed brittle faulting in the upper crust. Thus, this experiment suite illustrates that variations in density and viscosity of the lower crust influence (1) faults distribution in the upper crust, (2) flow patterns within the lower crust, (3) upward translation of the solidus into the lower crust, and (4) upward displacement of the Moho. The style of extension within the

  6. Numerical analysis of two and three dimensional buoyancy driven water-exit of a circular cylinder

    Directory of Open Access Journals (Sweden)

    Moshari Shahab

    2014-06-01

    Full Text Available With the development of the technology of underwater moving bodies, the need for developing the knowledge of surface effect interaction of free surface and underwater moving bodies is increased. Hence, the two-phase flow is a subject which is interesting for many researchers all around the world. In this paper, the non-linear free surface deformations which occur during the water-exit of a circular cylinder due to its buoyancy are solved using finite volume discretization based code, and using Volume of Fluid (VOF scheme for solving two phase flow. Dynamic mesh model is used to simulate dynamic motion of the cylinder. In addition, the effect of cylinder mass in presence of an external force is studied. Moreover, the oblique exit and entry of a circular cylinder with two exit angles is simulated. At last, water-exit of a circular cylinder in six degrees of freedom is simulated in 3D using parallel processing. The simulation errors of present work (using VOF method for maximum velocity and height of a circular cylinder are less than the corresponding errors of level set method reported by previous researchers. Oblique exit shows interesting results; formation of waves caused by exit of the cylinder, wave motion in horizontal direction and the air trapped between the waves are observable. In 3D simulation the visualization of water motion on the top surface of the cylinder and the free surface breaking on the front and back faces of the 3D cylinder at the exit phase are observed which cannot be seen in 2D simulation. Comparing the results, 3D simulation shows better agreement with experimental data, specially in the maximum height position of the cylinder.

  7. Modeling the buoyancy-driven Black Sea Water outflow into the North Aegean Sea

    Directory of Open Access Journals (Sweden)

    Nikolaos Kokkos

    2016-04-01

    Full Text Available A three-dimensional numerical model was applied to simulate the Black Sea Water (BSW outflux and spreading over the North Aegean Sea, and its impact on circulation and stratification–mixing dynamics. Model results were validated against satellite-derived sea surface temperature and in-situ temperature and salinity profiles. Further, the model results were post-processed in terms of the potential energy anomaly, ϕ, analyzing the factors contributing to its change. It occurs that BSW contributes significantly on the Thracian Sea water column stratification, but its signal reduces in the rest of the North Aegean Sea. The BSW buoyancy flux contributed to the change of ϕ in the Thracian Sea by 1.23 × 10−3 W m−3 in the winter and 7.9 × 10−4 W m−3 in the summer, significantly higher than the corresponding solar heat flux contribution (1.41 × 10−5 W m−3 and 7.4 × 10−5 W m−3, respectively. Quantification of the ϕ-advective term crossing the north-western BSW branch (to the north of Lemnos Island, depicted a strong non-linear relation to the relative vorticity of Samothraki Anticyclone. Similar analysis for the south-western branch illustrated a relationship between the ϕ-advective term sign and the relative vorticity in the Sporades system. The ϕ-mixing term increases its significance under strong winds (>15 m s−1, tending to destroy surface meso-scale eddies.

  8. Buoyancy-driven leakage of oil from a ruptured submarine pipeline

    NARCIS (Netherlands)

    Kranenburg, C.

    1983-01-01

    The rupture of a submarine oil pipeline starts various mechanisms leading to an oil spill. Among these mechanisms the leakage of oil driven by the difference in specific gravities of oil and sea-water is difficult to estimate. A simple mathematical model has been developed and laboratory experiments

  9. Buoyancy-Driven Radiative Unsteady Magnetohydrodynamic Heat Transfer over a Stretching Sheet with non-Uniform Heat Source/sink

    Directory of Open Access Journals (Sweden)

    Dulal Pal

    2016-01-01

    Full Text Available In the present study an unsteady mixed convection boundary layer flow of an electrically conduct- ing fluid over an stretching permeable sheet in the presence of transverse magnetic field, thermal radiation and non-uniform heat source/sink effects is investigated. The unsteadiness in the flow and temperature fields is due to the time-dependent nature of the stretching velocity and the surface temperature. Both opposing and assisting flows are considered. The dimensionless governing or- dinary non-linear differential equations are solved numerically by applying shooting method using Runge-Kutta-Fehlberg method. The effects of unsteadiness parameter, buoyancy parameter, thermal radiation, Eckert number, Prandtl number and non-uniform heat source/sink parameter on the flow and heat transfer characteristics are thoroughly examined. Comparisons of the present results with previously published results for the steady case are found to be excellent.

  10. Geometric aspect and buoyancy effects on nature convection flow in the complex annuli filled with micropolar fluids

    Science.gov (United States)

    Chen, Wen Ruey

    2016-10-01

    This paper studies the steady laminar natural convection of micropolar fluids in the complex annuli between the inner sphere and outer vertical cylinder to present a numerical analysis of the flow and heat transfer characteristics with buoyancy effects. Computations were carried out systematically by the several different parameters of geometric ratio, micropolar material parameter and Rayleigh number to determine the average Nusselt number and the skin friction coefficient on the flow and the thermal fields.

  11. Particle fluid interactivity deteriorates buoyancy driven thermal transport in nanosuspensions : A multi component lattice Boltzmann approach

    OpenAIRE

    S, Savithiri; Dhar,Purbarun; Pattamatta, Arvind; Das, Sarit K

    2015-01-01

    Severe contradictions exist between experimental observations and computational predictions regarding natural convective thermal transport in nanosuspensions. The approach treating nanosuspensions as homogeneous fluids in computations has been pin pointed as the major contributor to such contradictions. To fill the void, inter particle and particle fluid interactivities (slip mechanisms), in addition to effective thermophysical properties, have been incorporated within the present formulation...

  12. Particle fluid interactivity deteriorates buoyancy driven thermal transport in nanosuspensions : A multi component lattice Boltzmann approach

    CERN Document Server

    S, Savithiri; Pattamatta, Arvind; Das, Sarit K

    2015-01-01

    Severe contradictions exist between experimental observations and computational predictions regarding natural convective thermal transport in nanosuspensions. The approach treating nanosuspensions as homogeneous fluids in computations has been pin pointed as the major contributor to such contradictions. To fill the void, inter particle and particle fluid interactivities (slip mechanisms), in addition to effective thermophysical properties, have been incorporated within the present formulation. Through thorough scaling analysis, the dominant slip mechanisms have been identified. A Multi Component Lattice Boltzmann Model (MCLBM) approach has been proposed, wherein the suspension has been treated as a non homogeneous twin component mixture with the governing slip mechanisms incorporated. The computations based on the mathematical model can accurately predict and quantify natural convection thermal transport in nanosuspensions. The role of slip mechanisms such as Brownian diffusion, thermophoresis, drag, Saffman ...

  13. Analytical and experimental study of instabilities in buoyancy-driven convection in porous media

    Energy Technology Data Exchange (ETDEWEB)

    Georgiadis, J.G.; Behringer, R.; Johnson, G.A.

    1992-04-01

    During the second year of support under the DOE grant, significant progress was made in two directions: (1) Visualization of structure and tow field in randomly packed beds via Magnetic Resonance Imaging, and (2) Shadowgraphic visualization of natural convection in porous systems. This report describes the activities in detail, cite publications which resulted from this project, and conclude with plans for the last phase of the experimental investigation.

  14. Developing Buoyancy Driven Flow of a Nanofluid in a Vertical Channel Subject to Heat Flux

    Directory of Open Access Journals (Sweden)

    Nirmal C. Sacheti

    2014-01-01

    Full Text Available The developing natural convective flow of a nanofluid in an infinite vertical channel with impermeable bounding walls has been investigated. It is assumed that the nanofluid is dominated by two specific slip mechanisms and that the channel walls are subject to constant heat flux and isothermal temperature, respectively. The governing nonlinear partial differential equations coupling different transport processes have been solved numerically. The variations of velocity, temperature, and nanoparticles concentration have been discussed in relation to a number of physical parameters. It is seen that the approach to the steady-state profiles of velocity and temperature in the present work is different from the ones reported in a previous study corresponding to isothermal wall conditions.

  15. Experimental study on buoyancy-driven exchange flows through breaches of a tokamak vacuum vessel in a fusion reactor under the loss-of-vacuum-event conditions

    Energy Technology Data Exchange (ETDEWEB)

    Takase, Kazuyuki; Tomoaki, Kunugi; Ogawa, Masurou; Seki, Yasushi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)

    1997-02-01

    As one of thermofluid safety studies in the International Thermonuclear Experimental Reactor, buoyancy-driven exchange flow behavior through breaches of a vacuum vessel (VV) has been investigated quantitatively by using a preliminary loss-of-vacuum-event (LOVA) apparatus that simulated the tokamak VV of a fusion reactor with a small-scaled model. To carry out the present experiments under the atmospheric pressure condition, helium gas and air were provided as the working fluids. The inside of the VV was initially filled with helium gas and the outside was atmosphere. The breaches on the VV under the LOVA condition were simulated by opening six simulated breaches to which were set the different positions on the VV. When the buoyancy-driven exchange flow through the breach occurred, helium gas went out from the inside of the VV through the breach to the outside and air flowed into the inside of the VV through the breach from the outside. The exchange rate in the VV between helium gas and air was calculated from the measured weight change of the VV with time since the experiment has started. experimental parameters were breach position, breach number, breach length, breach size, and breach combination. The present study clarifies that the relation between the exchange rate and the breach position of the VV depended on the magnitude of the potential energy from the ground level to the breach position, and then, the exchange rate decreased as the breach length increased and as the breach size decreased.

  16. Buoyancy-driven mixing of fluids in a confined geometry; Melange gravitationnel de fluides en geometrie confinee

    Energy Technology Data Exchange (ETDEWEB)

    Hallez, Y

    2007-12-15

    The present work based on Direct Numerical Simulations is devoted to the study of mixing between two miscible fluids of different densities. The movement of these fluids is induced by buoyancy. Three geometries are considered: a cylindrical tube, a square channel and a plane two-dimensional flow. For cylindrical tubes, the results of numerical simulations fully confirm previous experimental findings by Seon et al., especially regarding the existence of three different flow regimes, depending on the tilt angle. The comparison of the various geometries shows that tridimensional flows in tubes or channels are similar, whereas the two-dimensional model fails to give reliable information about real 3D flows, either from a quantitative point of view or for a phenomenological understanding. A peculiar attention is put on a joint analysis of the concentration and vorticity fields and allows us to explain several subtle aspects of the mixing dynamics. (author)

  17. Algebraically explicit analytical solutions of two-buoyancy natural convection in porous media

    Institute of Scientific and Technical Information of China (English)

    CAI Ruixian; ZHANG Na; LIU Weiwei

    2003-01-01

    Analytical solutions of governing equations of various physical phenomena have their own irreplaceable theoretical meaning. In addition, they can also be the benchmark solutions to verify the outcomes and codes of numerical solution, and to develop various numerical methods such as their differencing schemes and grid generation skills as well. In order to promote the development of the discipline of natural convection, three simple algebraically explicit analytical solution sets are derived for a non-linear simultaneous partial differential equation set with five dependent unknown variables, which represents the natural convection in porous media with both temperature and concentration gradients. An extraordinary method separating variables with addition is applied in this paper to deduce solutions.

  18. Modeling and Analysis of a Buoyancy-Ballast Driven Airship%一类“浮力-压块”驱动飞艇建模与分析

    Institute of Scientific and Technical Information of China (English)

    邬依林; 刘屿

    2012-01-01

    In view of a new kind of buoyancy-ballast driven airship, the model and dynamics of a kind of buoyancy-ballast driven airship are studied. Based on Kirchhoff equations and Newton-Euler laws, we developed the six degree of freedom nonlinear dynamic model for an airship equipped with independent ballonets and moveable ballast by analysis its movement and stress. On the condition of little perturbation, the nonlinear dynamic model is divided into three group equations by restricting airship motion in longitudinal, lateral and e2-e3 planes respectively. Then the characteristics of mode and respond to input of airship are studied using linearization model and its related parameter. The results of simulation verify the correctness of established model and rationality of theoretical analysis on this kind of stratospheric airship, thus making itself a theoretical basis for the design of its control strategy.%针对一类新型“浮力-压块”驱动的自治飞艇,研究了该类飞艇的动力学建模和动力学特性.在Kirchhoff方程和Newton-Euler理论基础上,通过对飞艇运动及受力分析,建立了包括独立气囊和可运动压块的飞艇六自由度非线性动力学模型,并采用小扰动线性化方法,将飞艇运动分别限制在纵向、横侧向和e2-e3平面内,得到与之对应的三组飞艇线性化方程,其后基于飞艇相关参数和线性化模型,利用Matlab软件平台对飞艇运动模态和输入响应特性进行了分析研究.仿真结果验证了谊类飞艇模型的正确性和理论分析的合理性,为其后控制策略设计提供理论依据.

  19. Analytical and experimental study of instabilities in buoyancy-driven convection in porous media. Progress report, August 1991--April 1992

    Energy Technology Data Exchange (ETDEWEB)

    Georgiadis, J.G.; Behringer, R.; Johnson, G.A.

    1992-04-01

    During the second year of support under the DOE grant, significant progress was made in two directions: (1) Visualization of structure and tow field in randomly packed beds via Magnetic Resonance Imaging, and (2) Shadowgraphic visualization of natural convection in porous systems. This report describes the activities in detail, cite publications which resulted from this project, and conclude with plans for the last phase of the experimental investigation.

  20. Neutral Buoyancy Laboratory (NBL)

    Data.gov (United States)

    Federal Laboratory Consortium — The Neutral Buoyancy Laboratory (NBL) is an astronaut training facility and neutral buoyancy pool operated by NASA and located at the Sonny Carter Training Facility,...

  1. An Integrated Capillary, Buoyancy, and Viscous-Driven Model for Brine/CO2Relative Permeability in a Compositional and Parallel Reservoir Simulator

    KAUST Repository

    Kong, X.

    2012-11-03

    The effectiveness of CO2 storage in the saline aquifers is governed by the interplay of capillary, viscous, and buoyancy forces. Recent experimental study reveals the impact of pressure, temperature, and salinity on interfacial tension (IFT) between CO2 and brine. The dependence of CO2-brine relative permeability and capillary pressure on pressure (IFT) is also clearly evident in published experimental results. Improved understanding of the mechanisms that control the migration and trapping of CO2 in subsurface is crucial to design future storage projects that warrant long-term and safe containment. Simulation studies ignoring the buoyancy and also variation in interfacial tension and the effect on the petrophysical properties such as trapped CO2 saturations, relative permeability, and capillary pressure have a poor chance of making accurate predictions of CO2 injectivity and plume migration. We have developed and implemented a general relative permeability model that combines effects of pressure gradient, buoyancy, and IFT in an equation of state (EOS) compositional and parallel simulator. The significance of IFT variations on CO2 migration and trapping is assessed.

  2. Development and Assessment of CFD Models Including a Supplemental Program Code for Analyzing Buoyancy-Driven Flows Through BWR Fuel Assemblies in SFP Complete LOCA Scenarios

    Science.gov (United States)

    Artnak, Edward Joseph, III

    This work seeks to illustrate the potential benefits afforded by implementing aspects of fluid dynamics, especially the latest computational fluid dynamics (CFD) modeling approach, through numerical experimentation and the traditional discipline of physical experimentation to improve the calibration of the severe reactor accident analysis code, MELCOR, in one of several spent fuel pool (SFP) complete loss-ofcoolant accident (LOCA) scenarios. While the scope of experimental work performed by Sandia National Laboratories (SNL) extends well beyond that which is reasonably addressed by our allotted resources and computational time in accordance with initial project allocations to complete the report, these simulated case trials produced a significant array of supplementary high-fidelity solutions and hydraulic flow-field data in support of SNL research objectives. Results contained herein show FLUENT CFD model representations of a 9x9 BWR fuel assembly in conditions corresponding to a complete loss-of-coolant accident scenario. In addition to the CFD model developments, a MATLAB based controlvolume model was constructed to independently assess the 9x9 BWR fuel assembly under similar accident scenarios. The data produced from this work show that FLUENT CFD models are capable of resolving complex flow fields within a BWR fuel assembly in the realm of buoyancy-induced mass flow rates and that characteristic hydraulic parameters from such CFD simulations (or physical experiments) are reasonably employed in corresponding constitutive correlations for developing simplified numerical models of comparable solution accuracy.

  3. Fatal nosocomial Legionnaires' disease: relevance of contamination of hospital water supply by temperature-dependent buoyancy-driven flow from spur pipes.

    Science.gov (United States)

    Patterson, W J; Seal, D V; Curran, E; Sinclair, T M; McLuckie, J C

    1994-06-01

    The investigation, epidemiology, and effectiveness of control procedures during an outbreak of Legionnaires' disease involving three immunosuppressed patients are described. The source of infection appeared to be a network of fire hydrant spurs connected directly to the incoming hospital mains water supply. Removal of these hydrants considerably reduced, but failed to eliminate, contamination of water storage facilities. As an emergency control procedure the incoming mains water was chlorinated continuously. Additional modifications to improve temperature regulation and reduce stagnation also failed to eliminate the legionellae. A perspex test-rig was constructed to model the pre-existing hospital water supply and storage system. This showed that through the hydraulic mechanism known as 'temperature buoyancy', contaminated water could be efficiently and quickly exchanged between a stagnant spur pipe and its mains supply. Contamination of hospital storage tanks from such sources has not previously been considered a risk factor for Legionnaires' disease. We recommend that hospital water storage tanks are supplied by a dedicated mains pipe without spurs.

  4. Fun with Buoyancy.

    Science.gov (United States)

    Cuicchi, Paul M.; Winter, Joshua B.; Hamil, Burnette

    2003-01-01

    Presents an activity to teach buoyancy. The lab determines what mass of sand can be added to the open end of hollow plastic containers of various shapes so that objects just float at the surface, without sinking, with their entire volume submerged. Discusses Archimedes' principle and aligns with current national science education standards.…

  5. Dynamics of the Leeuwin Current: Part 2. Impacts of mixing, friction, and advection on a buoyancy-driven eastern boundary current over a shelf

    Science.gov (United States)

    Benthuysen, Jessica; Furue, Ryo; McCreary, Julian P.; Bindoff, Nathaniel L.; Phillips, Helen E.

    2014-03-01

    depth. When the timescale δt is sufficiently short, the poleward current is nearly barotropic. The current's spatial structure over the shelf is controlled by horizontal mixing, having the structure of a Munk layer. Increasing vertical diffusion deepens the upper layer thickness and strengthens the alongshore current speed. Bottom drag leads to an offshore flow along the bottom, reducing the net onshore transport and weakening the current's poleward acceleration. When δt is long, poleward advection of buoyancy forms a density front near the shelf break, intensifying poleward speeds near the surface. With bottom drag, a bottom Ekman flow advects density offshore, shifting the jet core offshore of the shelf break. The resulting cross-shelf density gradient reverses the meridional current's direction at depth, leading to an equatorward undercurrent.

  6. Improved head-driven statistical models for natural language parsing

    Institute of Scientific and Technical Information of China (English)

    袁里驰

    2013-01-01

    Head-driven statistical models for natural language parsing are the most representative lexicalized syntactic parsing models, but they only utilize semantic dependency between words, and do not incorporate other semantic information such as semantic collocation and semantic category. Some improvements on this distinctive parser are presented. Firstly, "valency" is an essential semantic feature of words. Once the valency of word is determined, the collocation of the word is clear, and the sentence structure can be directly derived. Thus, a syntactic parsing model combining valence structure with semantic dependency is purposed on the base of head-driven statistical syntactic parsing models. Secondly, semantic role labeling(SRL) is very necessary for deep natural language processing. An integrated parsing approach is proposed to integrate semantic parsing into the syntactic parsing process. Experiments are conducted for the refined statistical parser. The results show that 87.12% precision and 85.04% recall are obtained, and F measure is improved by 5.68% compared with the head-driven parsing model introduced by Collins.

  7. The Island Wind-Buoyancy Paradox

    Science.gov (United States)

    de Boer, A. M.; Nof, D.

    2003-04-01

    In recent years, a variety of studies have suggested that the meridional overturning circulation is at least partially controlled by the Southern Ocean winds. However, the overturning requires transformation of water masses, a process driven by buoyancy fluxes. This seems paradoxical as the wind and buoyancy fluxes are generally thought to be independent. The paradox is resolved qualitatively, using salinity and temperature mixed dynamical-box models, and quantitatively, employing a numerical model. The salinity and temperature box models suggest that stronger southern winds will tend to weaken the vertical and horizontal salinity stratification so that it is easier for the conversion of deep to surface water (and vice versa) to take place. The (process-orientated) reduced-gravity numerical model is adapted to include a thermodynamic parameterization for the surface heat and freshwater fluxes. In response to stronger southern winds, the thermocline thickens in the north, releasing more heat to the atmosphere and, thereby, converting more surface to deep water.

  8. Radiatively-driven natural supersymmetry at the LHC

    CERN Document Server

    Baer, Howard; Huang, Peisi; Mickelson, Dan; Mustafayev, Azar; Sreethawong, Warintorn; Tata, Xerxes

    2013-01-01

    Radiatively-driven natural supersymmetry (RNS) potentially reconciles the Z and Higgs boson masses close to 100 GeV with gluinos and squarks lying beyond the TeV scale. Requiring no large cancellations at the electroweak scale in constructing M_Z=91.2 GeV while maintaining a light Higgs scalar with m_h 125 GeV implies a sparticle mass spectrum including light higgsinos with mass 100-300 GeV, electroweak gauginos in the 300-1200 GeV range, gluinos at 1-4 TeV and top/bottom squarks in the 1-4 TeV range (probably beyond LHC reach), while first/second generation matter scalars can exist in the 5-30 TeV range (far beyond LHC reach). We investigate several characteristic signals for RNS at LHC14. Gluino pair production yields a reach up to m_{\\tg} 1.7 TeV for 300 fb^{-1}. Wino pair production -- pp\\to\\tw_2\\tz_4 and \\tw_2\\tw_2 -- leads to a unique same-sign diboson (SSdB) signature accompanied by modest jet activity from daughter higgsino decays; this signature provides the best reach up to m_{\\tg} 2.1 TeV within th...

  9. The Solar Vortex: Electric Power Generation using Anchored, Buoyancy-Induced Columnar Vortices

    Science.gov (United States)

    Glezer, Ari

    2015-04-01

    Naturally-occurring, buoyancy-driven columnar vortices (``dust devils'') that are driven by the instability of thermally stratified air layers and sustained by the entrainment of ground- heated air, occur spontaneously in the natural environment with core diameters of 1-50 m and heights up to 1 km. These vortices convert low-grade waste heat in the air layer overlying the warm surface into a solar-induced wind with significant kinetic energy. Unlike dust devil vortices that are typically free to wander laterally, the Solar Vortex (SoV) is deliberately triggered and anchored within a cylindrical domain bounded by an azimuthal array of stationary ground-mounted vertical vanes and sustained by continuous entrainment of the ground-heated air through these vanes. The mechanical energy of the anchored vortex is exploited for power generation by coupling the vortex to a vertical-axis turbine. This simple, low-cost electric power generating unit is competitive in cost, intermittency, and capacity factor with traditional solar power technologies. The considerable kinetic energy of the vortex column cannot be explained by buoyancy alone, and the fundamental mechanisms associated with the formation, evolution, and dynamics of an anchored, buoyancy-driven columnar vortex were investigated experimentally and numerically with specific emphasis on flow manipulation for increasing the available kinetic energy and therefore the generated power. These investigations have also considered the dependence of the vortex scaling and strength on the thermal resources and on the flow enclosure in the laboratory and in the natural environment. Preliminary outdoor tests of a two-meter scale prototype successfully demonstrated the ability to engender and anchor a columnar vortex using only solar radiation and couple the flow to a vertical axis wind turbine. A kilowatt-scale outer door prototype will be tested during the summer of 2015.

  10. A new method for deriving analytical solutions of partial differential equations-Algebraically explicit analytical solutions of two-buoyancy natural convection in porous media

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Analytical solutions of governing equations of various phenomena have their irre-placeable theoretical meanings. In addition, they can also be the benchmark solu-tions to verify the outcomes and codes of numerical solutions, and even to develop various numerical methods such as their differencing schemes and grid generation skills as well. A hybrid method of separating variables for simultaneous partial differential equation sets is presented. It is proposed that different methods of separating variables for different independent variables in the simultaneous equa-tion set may be used to improve the solution derivation procedure, for example, using the ordinary separating method for some variables and using extraordinary methods of separating variables, such as the separating variables with addition promoted by the first author, for some other variables. In order to prove the ability of the above-mentioned hybrid method, a lot of analytical exact solutions of two-buoyancy convection in porous media are successfully derived with such a method. The physical features of these solutions are given.

  11. Wave Dragon Buoyancy Regulation Study

    DEFF Research Database (Denmark)

    Jakobsen, Jens; Kofoed, Jens Peter

    Wave Dragon is a wave energy converter, which was deployed offshore at Nissum Bredning in Denmark in 2003. The experience gained from operating Wave Dragon during 2003 and 2004 has shown that the buoyancy regulation system can be improved in a number of ways. This study describes the current situ...... situation, and proposes a number of activities in order to improve the buoyancy regulation system. This work was performed under EU ENERGIE contract no. ENK5-CT-2002-00603, and is a contribution to WP 2.3/2.4 and D40/D41....

  12. EFFECTS OF BUOYANCY RATIO ON CONVECTIVE HEAT AND SOLUTE TRANSFER IN NEWTONIAN FLUID SATURATED INCLINED POROUS CAVITY

    Directory of Open Access Journals (Sweden)

    A LATRECHE

    2014-12-01

    Full Text Available This paper summarizes a numerical study of the effects of buoyancy ratio on double-diffusive natural convection in square inclined cavity filled with fluid saturated porous media. Transverse gradients of heat and solute are applied on the two horizontal walls of the cavity, while the other two walls are impermeable and adiabatic. The Darcy model with the Boussinesq approximation is used to solve the governing equations. The flow is driven by a combined buoyancy effect due to both temperature and concentration variations. A finite volume approach has been used to solve the non-dimensional governing equations. The results are presented in streamline, isothermal, iso-concentration, Nusselt and Sherwood contours for different values of the non-dimensional governing parameters.

  13. Pharmacophore-driven identification of PPARγ agonists from natural sources

    DEFF Research Database (Denmark)

    Petersen, R. K.; Christensen, Kathrine Bisgaard; Assimopoulou, A. N.;

    2011-01-01

    In a search for more effective and safe anti-diabetic compounds, we developed a pharmacophore model based on partial agonists of PPARγ. The model was used for the virtual screening of the Chinese Natural Product Database (CNPD), a library of plant-derived natural products primarily used in folk...

  14. UK Natural Gas: Gas-Specific or Oil Driven Pricing?

    OpenAIRE

    2013-01-01

    In this paper we investigate the time-varying relationship between oil and natural gas in the UK. We develop a model where relative prices can move between pricing-regimes; markets switch between being decoupled and integrated. Our model endogenously accounts for periods where oil and natural gas temporarily decouple due to gas specific pricing. We show that gas-specific pricing is primarily related to fall/winter peak-load gas pricing and that mean reversion in relative prices is dependent o...

  15. Pharmacophore-driven identification of PPARγ agonists from natural sources

    Science.gov (United States)

    Petersen, Rasmus K.; Christensen, Kathrine B.; Assimopoulou, Andreana N.; Fretté, Xavier; Papageorgiou, Vassilios P.; Kristiansen, Karsten; Kouskoumvekaki, Irene

    2011-02-01

    In a search for more effective and safe anti-diabetic compounds, we developed a pharmacophore model based on partial agonists of PPARγ. The model was used for the virtual screening of the Chinese Natural Product Database (CNPD), a library of plant-derived natural products primarily used in folk medicine. From the resulting hits, we selected methyl oleanonate, a compound found, among others, in Pistacia lentiscus var. Chia oleoresin (Chios mastic gum). The acid of methyl oleanonate, oleanonic acid, was identified as a PPARγ agonist through bioassay-guided chromatographic fractionations of Chios mastic gum fractions, whereas some other sub-fractions exhibited also biological activity towards PPARγ. The results from the present work are two-fold: on the one hand we demonstrate that the pharmacophore model we developed is able to select novel ligand scaffolds that act as PPARγ agonists; while at the same time it manifests that natural products are highly relevant for use in virtual screening-based drug discovery.

  16. Buoyancy instability of homologous implosions

    CERN Document Server

    Johnson, Bryan M

    2015-01-01

    I consider the hydrodynamic stability of imploding gases as a model for inertial confinement fusion capsules, sonoluminescent bubbles and the gravitational collapse of astrophysical gases. For oblate modes under a homologous flow, a monatomic gas is governed by the Schwarzschild criterion for buoyant stability. Under buoyantly unstable conditions, fluctuations experience power-law growth in time, with a growth rate that depends upon mean flow gradients and is independent of mode number. If the flow accelerates throughout the implosion, oblate modes amplify by a factor (2C)^(|N0| ti)$, where C is the convergence ratio of the implosion, N0 is the initial buoyancy frequency and ti is the implosion time scale. If, instead, the implosion consists of a coasting phase followed by stagnation, oblate modes amplify by a factor exp(pi |N0| ts), where N0 is the buoyancy frequency at stagnation and ts is the stagnation time scale. Even under stable conditions, vorticity fluctuations grow due to the conservation of angular...

  17. Exact equations of motion for natural orbitals of strongly driven two-electron systems

    CERN Document Server

    Rapp, J; Bauer, D

    2014-01-01

    Natural orbital theory is a computationally useful approach to the few and many-body quantum problem. While natural orbitals are known and applied since many years in electronic structure applications, their potential for time-dependent problems is being investigated only since recently. Correlated two-particle systems are of particular importance because the structure of the two-body reduced density matrix expanded in natural orbitals is known exactly in this case. However, in the time-dependent case the natural orbitals carry time-dependent phases that allow for certain time-dependent gauge transformations of the first kind. Different phase conventions will, in general, lead to different equations of motion for the natural orbitals. A particular phase choice allows us to derive the exact equations of motion for the natural orbitals of any (laser-) driven two-electron system explicitly, i.e., without any dependence on quantities that, in practice, require further approximations. For illustration, we solve th...

  18. Short-term airing by natural ventilation

    DEFF Research Database (Denmark)

    Perino, Marco; Heiselberg, Per

    2009-01-01

    traditional mechanical ventilation components with natural ventilation devices, such as motorized windows and louvers. Among the various ventilation strategies that are currently available, buoyancy driven single-sided natural ventilation has proved to be very effective and can provide high air change rates......The need to improve the energy efficiency of buildings requires new and more efficient ventilation systems. It has been demonstrated that innovative operating concepts that make use of natural ventilation seem to be more appreciated by occupants. This kind of system frequently integrates...... that was aimed at developing and validating numerical models for the analysis of buoyancy driven single-sided natural ventilation systems. Once validated, these models can be used to optimize control strategies in order to achieve satisfactory indoor comfort conditions and IAQ....

  19. Numerically quantifying the relative importance of topography and buoyancy in driving groundwater flow

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Both topography and buoyancy can drive groundwater flow;however,the interactions between them are still poorly understood.In this paper,the authors conduct numerical simulations of variable-density fluid flow and heat transport to quantify their relative importance.The finite element modeling experiments on a 2-D conceptual model reveal that the pattern of groundwater flow depends largely upon the relative magnitude of the flow rate due to topography alone and the flow rate due to buoyancy alone.When fluid velocity due to topography is greater than that due to buoyancy at large water table gradients,topography-driven ’forced convection’ overwhelms buoyancy-driven ’free convection’.When flow velocity due to buoyancy is greater than that due to topography at small water table gradients,mixed free and forced convection takes place.In this case,free convection becomes dominant,but topography-driven flow still plays an important role since it pushes the free convection cells to migrate laterally in the downhill direction.Consequently,hydrothermal fluid flow remains changing periodically with time and no steady state can be reached.The presence of a low-permeability layer near the surface helps eliminate the topography effect on the underlying free convection.

  20. MyProLang - My Programming Language: A Template-Driven Automatic Natural Programming Language

    CERN Document Server

    Bassil, Youssef

    2012-01-01

    Modern computer programming languages are governed by complex syntactic rules. They are unlike natural languages; they require extensive manual work and a significant amount of learning and practicing for an individual to become skilled at and to write correct programs. Computer programming is a difficult, complicated, unfamiliar, non-automated, and a challenging discipline for everyone; especially, for students, new programmers and end-users. This paper proposes a new programming language and an environment for writing computer applications based on source-code generation. It is mainly a template-driven automatic natural imperative programming language called MyProLang. It harnesses GUI templates to generate proprietary natural language source-code, instead of having computer programmers write the code manually. MyProLang is a blend of five elements. A proprietary natural programming language with unsophisticated grammatical rules and expressive syntax; automation templates that automate the generation of in...

  1. Buoyancy Instabilities in a Weakly Collisional Intracluster Medium

    CERN Document Server

    Kunz, Matthew W; Reynolds, Christopher S; Stone, James M

    2012-01-01

    The intracluster medium of galaxy clusters is a weakly collisional, high-beta plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign, the magnetothermal instability (MTI) in the outskirts of non-isothermal clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena MHD code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e. Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We highlight the importance of the microscale instabilities that inevitably accompany and regulate the pressure anisotropies generated by the HBI and MTI. We find that, in all but the innermost regions of cool-core clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal...

  2. Supersymmetry with Radiatively-Driven Naturalness: Implications for WIMP and Axion Searches

    Directory of Open Access Journals (Sweden)

    Kyu Jung Bae

    2015-05-01

    Full Text Available By insisting on naturalness in both the electroweak and quantum chromodynamics (QCD sectors of the minimal supersymmetric standard model (MSSM, the portrait for dark matter production is seriously modified from the usual weakly interacting massive particle (WIMP miracle picture. In supersymmetry (SUSY models with radiatively-driven naturalness (radiative natural SUSY or radiative natural SUSY (RNS which include a Dine–Fischler–Srednicki–Zhitnitsky (DFSZ-like solution to the strong charge-conjugation-parity (CP and SUSY \\(\\mu\\ problems, dark matter is expected to be an admixture of both axions and higgsino-like WIMPs. The WIMP/axion abundance calculation requires simultaneous solution of a set of coupled Boltzmann equations which describe quasi-stable axinos and saxions. In most of parameter space, axions make up the dominant contribution of dark matter although regions of WIMP dominance also occur. We show the allowed range of Peccei-Quinn (PQ scale \\(f_a\\ and compare to the values expected to be probed by the axion dark matter search experiment (ADMX axion detector in the near future. We also show WIMP detection rates, which are suppressed from usual expectations, because now WIMPs comprise only a fraction of the total dark matter. Nonetheless, ton-scale noble liquid detectors should be able to probe the entirety of RNS parameter space. Indirect WIMP detection rates are less propitious since they are reduced by the square of the depleted WIMP abundance.

  3. Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction

    CERN Document Server

    Sharma, P; Quataert, E; Parrish, I J

    2009-01-01

    Using a linear stability analysis and two and three-dimensional nonlinear simulations, we study the physics of buoyancy instabilities in a combined thermal and relativistic (cosmic ray) plasma, motivated by the application to clusters of galaxies. We argue that cosmic ray diffusion is likely to be slow compared to the buoyancy time on large length scales, so that cosmic rays are effectively adiabatic. If the cosmic ray pressure $p_{cr}$ is $\\gtrsim 25 %$ of the thermal pressure, and the cosmic ray entropy ($p_{\\rm cr}/\\rho^{4/3}$; $\\rho$ is the thermal plasma density) decreases outwards, cosmic rays drive an adiabatic convective instability analogous to Schwarzschild convection in stars. Global simulations of galaxy cluster cores show that this instability saturates by reducing the cosmic ray entropy gradient and driving efficient convection and turbulent mixing. At larger radii in cluster cores, the thermal plasma is unstable to the heat flux-driven buoyancy instability (HBI), a convective instability genera...

  4. Supersymmetry with radiatively-driven naturalness: implications for WIMP and axion searches

    CERN Document Server

    Bae, Kyu Jung; Barger, Vernon; Savoy, Michael R; Serce, Hasan

    2015-01-01

    By insisting on naturalness in both the electroweak and QCD sectors of the MSSM, the portrait for dark matter production is seriously modified from the usual WIMP miracle picture. In SUSY models with radiatively-driven naturalness (radiative natural SUSY or RNS) which include a DFSZ-like solution to the strong CP and SUSY mu problems, dark matter is expected to be an admixture of both axions and higgsino-like WIMPs. The WIMP/axion abundance calculation requires simultaneous solution of a set of coupled Boltzmann equations which describe quasi-stable axinos and saxions. In most of parameter space, axions make up the dominant contribution of dark matter although regions of WIMP dominance also occur. We show the allowed range of PQ scale f_a and compare to the values expected to be probed by the ADMX axion detector in the near future. We also show WIMP detection rates which are suppressed from usual expectations because now WIMPs comprise only a fraction of the total dark matter. Nonetheless, ton-scale noble liq...

  5. Prospects for Higgs coupling measurements in SUSY with radiatively-driven naturalness

    CERN Document Server

    Bae, Kyu Jung; Nagata, Natsumi; Serce, Hasan

    2015-01-01

    In the post-LHC8 world-- where a Standard Model-like Higgs boson has been established but there is no sign of supersymmetry (SUSY)-- the detailed profiling of the Higgs boson properties has emerged as an important road towards discovery of new physics. We present calculations of the expected deviations in Higgs boson couplings $\\kappa_{\\tau ,b}$, $\\kappa_t$, $\\kappa_{W,Z}$, $\\kappa_g$ and $\\kappa_\\gamma$ versus the naturalness measure $\\Delta_{\\rm EW}$. Low values of $\\Delta_{\\rm EW}\\sim 10-30$ give rise to a natural Little Hierarchy characterized by light higgsinos with a mass of $\\mu\\sim m_Z$ while top squarks are highly mixed but lie in the several TeV range. For such models with radiatively-driven naturalness, one expects the Higgs boson $h$ to look very SM-like although deviations can occur. The more promising road to SUSY discovery requires direct higgsino pair production at a high energy $e^+e^-$ collider operating with the center-of-mass energy $\\sqrt{s}>2\\mu\\sim \\sqrt{2\\Delta_{\\rm EW}}m_Z$.

  6. Sub-natural linewidth resonances in coherently-driven double system

    Indian Academy of Sciences (India)

    Niharika Singh; Q V Lawande; R D’souza; A Ray; B N Jagatap

    2010-12-01

    We investigate theoretically the pump-probe spectroscopy of coherently-driven four-level system with two closely spaced excited common levels, thereby forming a double system. Using the master equation approach, analytical results are obtained for the absorption spectrum of a weak probe in the presence of a strong pump. The model is applied to the double system 52 1/2 = 1, 2 → 523/2 ' = 1, 2 of 87Rb atom. It is shown that the absorption spectrum consists of a triplet, of which one resonance is of sub-natural linewidth depending on the atom–field interaction parameters. The effect of Doppler broadening on the absorption spectrum is also investigated.

  7. Buoyancy-driven flow excursions in fuel assemblies

    Energy Technology Data Exchange (ETDEWEB)

    Laurinat, J.E.; Paul, P.K.; Menna, J.D. [Westinghouse Savannah River Company, Aiken, SC (United States)

    1995-09-01

    A power limit criterion was developed for a postulated Loss of Pumping Accident (LOPA) in one of the recently shut down heavy water production reactors at the Savannah River Site. These reactors were cooled by recirculating heavy water moderator downward through channels in cylindrical fuel tubes. Powers were limited to safeguard against a flow excursion in one of more of these parallel channels. During-full-power operation, limits safeguarded against a boiling flow excursion. At low flow rates, during the addition of emergency cooling water, buoyant forces reverse the flow in one of the coolant channels before boiling occurs. As power increased beyond the point of flow reversal, the maximum wall temperature approaches the fluid saturation temperature, and a thermal excursion occurs. The power limit criterion for low flow rates was the onset of flow reversal. To determine conditions for flow reversal, tests were performed in a mock-up of a fuel assembly that contained two electrically heated concentric tubes surrounded by three flow channels. These tests were modeled using a finite difference thermal-hydraulic code. According to code calculations, flow reversed in the outer flow channel before the maximum wall temperature reached the local fluid saturation temperature. Thermal excursions occurred when the maximum wall temperature approximately equaled the saturation temperature. For a postulated LOPA, the flow reversal criterion for emergency cooling water addition was more limiting than the boiling excursion criterion for full power operation. This criterion limited powers to 37% of the limiting power for previous long-term reactor operations.

  8. Buoyancy-driven flow excursions in fuel assemblies

    Energy Technology Data Exchange (ETDEWEB)

    Laurinat, J.E.; Paul, P.K.; Menna, J.D.

    1995-12-31

    A power limit criterion was developed for a postulated Loss of Pumping Accident (LOPA) in one of the recently shut down heavy water production reactors at the Savannah River Site. These reactors were cooled by recirculating moderator downward through channels in cylindrical fuel tubes. Powers were limited to prevent a flow excursion from occurring in one or more of these parallel channels. During full-power operation, limits prevented a boiling flow excursion from taking place. At low flow rates, during the addition of emergency cooling water, buoyant forces reverse the flow in one of the coolant channels before boiling occurs. As power increases beyond the point of flow reversal, the maximum wall temperature approaches the fluid saturation temperature, and a thermal excursion occurs. The power limit criterion for low flow rates was the onset of flow reversal. To determine conditions for flow reversal, tests were performed in a mock-up of a fuel assembly that contained two electrically heated concentric tubes surrounded by three flow channels. These tests were modeled using a finite difference thermal-hydraulic code. According to code calculations, flow reversed in the outer flow channel before the maximum wall temperature reached the local fluid saturation temperature. Thermal excursions occurred when the maximum wall temperature approximately equaled the saturation temperature. For a postulated LOPA, the flow reversal criterion for emergency cooling water addition was more limiting than the boiling excursion criterion for full power operation. This criterion limited powers to 37% of historical levels.

  9. 14 CFR 29.755 - Hull buoyancy.

    Science.gov (United States)

    2010-01-01

    ... STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Design and Construction Floats and Hulls § 29.755 Hull buoyancy. Water-based and amphibian rotorcraft. The hull and auxiliary floats, if used, must have enough... stability great enough to minimize the probability of capsizing the rotorcraft for the worst combination...

  10. 14 CFR 27.751 - Main float buoyancy.

    Science.gov (United States)

    2010-01-01

    ... STANDARDS: NORMAL CATEGORY ROTORCRAFT Design and Construction Floats and Hulls § 27.751 Main float buoyancy. (a) For main floats, the buoyancy necessary to support the maximum weight of the rotorcraft in...

  11. 14 CFR 29.751 - Main float buoyancy.

    Science.gov (United States)

    2010-01-01

    ... STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Design and Construction Floats and Hulls § 29.751 Main float buoyancy. (a) For main floats, the buoyancy necessary to support the maximum weight of the rotorcraft...

  12. Predator-driven brain size evolution in natural populations of Trinidadian killifish (Rivulus hartii).

    Science.gov (United States)

    Walsh, Matthew R; Broyles, Whitnee; Beston, Shannon M; Munch, Stephan B

    2016-07-13

    Vertebrates exhibit extensive variation in relative brain size. It has long been assumed that this variation is the product of ecologically driven natural selection. Yet, despite more than 100 years of research, the ecological conditions that select for changes in brain size are unclear. Recent laboratory selection experiments showed that selection for larger brains is associated with increased survival in risky environments. Such results lead to the prediction that increased predation should favour increased brain size. Work on natural populations, however, foreshadows the opposite trajectory of evolution; increased predation favours increased boldness, slower learning, and may thereby select for a smaller brain. We tested the influence of predator-induced mortality on brain size evolution by quantifying brain size variation in a Trinidadian killifish, Rivulus hartii, from communities that differ in predation intensity. We observed strong genetic differences in male (but not female) brain size between fish communities; second generation laboratory-reared males from sites with predators exhibited smaller brains than Rivulus from sites in which they are the only fish present. Such trends oppose the results of recent laboratory selection experiments and are not explained by trade-offs with other components of fitness. Our results suggest that increased male brain size is favoured in less risky environments because of the fitness benefits associated with faster rates of learning and problem-solving behaviour.

  13. Modelling of Natural and Hybrid Ventilation

    DEFF Research Database (Denmark)

    Heiselberg, Per

    be installed in existing buildings after a few modifications. In contrast, ventilation systems using only natural forces such as wind and thermal buoyancy need to be designed together with the building, since the building itself and its components are the elements that can reduce or increase air movement...... as well as influence the air content (dust, pollution etc.). Architects and engineers need to acquire qualitative and quantitative information about the interactions between building characteristics and natural ventilation in order to design buildings and systems consistent with a passive low......-energy approach. These lecture notes focus on modelling of natural and hybrid ventilation driven by thermal buoyancy, wind and/or mechanical driving forces for a single zone with one, two or several openings....

  14. 46 CFR 197.342 - Buoyancy-changing devices.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Buoyancy-changing devices. 197.342 Section 197.342... STANDARDS GENERAL PROVISIONS Commercial Diving Operations Equipment § 197.342 Buoyancy-changing devices. (a) A dry suit or other buoyancy-changing device not directly connected to the exhaust valve of...

  15. A Model of Secondary Hydrocarbon Migration As a Buoyancy-Driven Separate Phase Flow Un modèle de migration secondaire des hydrocarbures considéré comme un écoulement en phases séparées régi par la poussée d'Archimède

    Directory of Open Access Journals (Sweden)

    Lehner F. K.

    2006-11-01

    Full Text Available A mathematical model of secondary migration is described which permits the prediction of hydrocarbon migration and accumulation patterns in a sedimentary basin, if source rock expulsion rates and geometrical and hydraulic properties of major carrier systems are known through geological time. In this model, secondary migration is treated as buoyancy-driven, segregated flow of hydrocarbons in hydrostatic aquifers. Lateral, updip migration is conceived as a Boussinesq-type, free-surface flow, with source and sink terms representing supply from source rocks and leakage through cap rocks and faults. This permits a two-dimensional, map-view mathematical description of a three-dimensional, time-dependent secondary migration system. A nine-point finite difference approximation has been developed to minimize numerical dispersion, and upstream-weighting is used to obtain stable solutions. Example computations for simple, single carrier bed structures are presented. L'article décrit un modèle mathématique de migration secondaire prédisant la migration des hydrocarbures et leur accumulation dans un bassin sédimentaire, lorsque les taux d'expulsion des roches mères et les propriétés géométriques et hydrauliques des principaux systèmes de drainage sont connus à l'échelle du temps géologique. Dans ce modèle, la migration secondaire est traitée comme un écoulement des hydrocarbures en phase séparée, contrôlé par la poussée d'Archimède, dans des aquifères hydrostatiques. La migration latérale est considérée comme un écoulement de type Boussinesq, à surface libre, avec des termes sources et puits représentant les apports venant des roches mères et les fuites à travers les couvertures et les failles. Ceci permet une description mathématique bidimensionnelle cartographiable d'un système de migration secondaire tridimensionnel et dépendant du temps. On utilise une approximation type différences finies à neuf points pour minimiser

  16. Drag, but not buoyancy, affects swim speed in captive Steller sea lions

    Directory of Open Access Journals (Sweden)

    Ippei Suzuki

    2014-04-01

    Full Text Available Swimming at an optimal speed is critical for breath-hold divers seeking to maximize the time they can spend foraging underwater. Theoretical studies have predicted that the optimal swim speed for an animal while transiting to and from depth is independent of buoyancy, but is dependent on drag and metabolic rate. However, this prediction has never been experimentally tested. Our study assessed the effects of buoyancy and drag on the swim speed of three captive Steller sea lions (Eumetopias jubatus that made 186 dives. Our study animals were trained to dive to feed at fixed depths (10–50 m under artificially controlled buoyancy and drag conditions. Buoyancy and drag were manipulated using a pair of polyvinyl chloride (PVC tubes attached to harnesses worn by the sea lions, and buoyancy conditions were designed to fall within the natural range of wild animals (∼12–26% subcutaneous fat. Drag conditions were changed with and without the PVC tubes, and swim speeds were recorded and compared during descent and ascent phases using an accelerometer attached to the harnesses. Generalized linear mixed-effect models with the animal as the random variable and five explanatory variables (body mass, buoyancy, dive depth, dive phase, and drag showed that swim speed was best predicted by two variables, drag and dive phase (AIC = −139. Consistent with a previous theoretical prediction, the results of our study suggest that the optimal swim speed of Steller sea lions is a function of drag, and is independent of dive depth and buoyancy.

  17. Using the computer-driven VR environment to promote experiences of natural world immersion

    Science.gov (United States)

    Frank, Lisa A.

    2013-03-01

    In December, 2011, over 800 people experienced the exhibit, :"der"//pattern for a virtual environment, created for the fully immersive CAVETM at the University of Wisconsin-Madison. This exhibition took my nature-based photographic work and reinterpreted it for virtual reality (VR).Varied responses such as: "It's like a moment of joy," or "I had to see it twice," or "I'm still thinking about it weeks later" were common. Although an implied goal of my 2D artwork is to create a connection that makes viewers more aware of what it means to be a part of the natural world, these six VR environments opened up an unexpected area of inquiry that my 2D work has not. Even as the experience was mediated by machines, there was a softening at the interface between technology and human sensibility. Somehow, for some people, through the unlikely auspices of a computer-driven environment, the project spoke to a human essence that they connected with in a way that went beyond all expectations and felt completely out of my hands. Other interesting behaviors were noted: in some scenarios some spoke of intense anxiety, acrophobia, claustrophobia-even fear of death when the scene took them underground. These environments were believable enough to cause extreme responses and disorientation for some people; were fun, pleasant and wonder-filled for most; and were liberating, poetic and meditative for many others. The exhibition seemed to promote imaginative skills, creativity, emotional insight, and environmental sensitivity. It also revealed the CAVETM to be a powerful tool that can encourage uniquely productive experiences. Quite by accident, I watched as these nature-based environments revealed and articulated an essential relationship between the human spirit and the physical world. The CAVETM is certainly not a natural space, but there is clear potential to explore virtual environments as a path to better and deeper connections between people and nature. We've long associated contact

  18. The nature of blast-wave-driven interfacial instabilities - important implications for modeling supernovae explosions

    Science.gov (United States)

    Miles, Aaron

    2004-11-01

    In this talk we discuss the nature of late-time, broad-banded instability development at an interface when a strong blast wave travels from a heavier to lighter fluid, as is the case in a supernova explosion. After a short period of Richtmyer-Meshkov growth, the interface is unstable via the Rayleigh-Taylor mechanism, which rapidly becomes the dominant energy source for growth. This situation is distinct from the classical case in two important ways, both of which can be understood in terms of a bubble merger model we have developed for blast-wave-driven systems. Rather than the constant acceleration feeding the instability to spawn ever larger scales and accelerate the growth, the decaying acceleration in the blast-wave case leads to a decay in the RT growth rate, and a freezing in of a preferred largest scale, which is dependent on the precise details of the system. In the language of bubble-merger models, this can be understood in terms of the time for the generation of the next largest scale being longer than the lifetime of the blast wave. Secondly, the continual expansion behind the blast front precludes the emergence of a self-similar regime, independent of the initial conditions, in the planar case. Self-similarity may be recovered in diverging systems but may be difficult to observe in reality because of rather restrictive conditions that must be met. These observations are borne out by hi-resolution numerical simulations using the higher order Godunov AMR hydrocode Raptor in 2 and 3D, and explain other simulations of instability growth in supernovae explosions; the initial "interfacial" structure is likely very important in determining the late-time growth. The model predictions are also consistent with numerous images of natural and manmade explosions.

  19. Biologically inspired highly efficient buoyancy engine

    Science.gov (United States)

    Akle, Barbar; Habchi, Wassim; Abdelnour, Rita; Blottman, John, III; Leo, Donald

    2012-04-01

    Undersea distributed networked sensor systems require a miniaturization of platforms and a means of both spatial and temporal persistence. One aspect of this system is the necessity to modulate sensor depth for optimal positioning and station-keeping. Current approaches involve pneumatic bladders or electrolysis; both require mechanical subsystems and consume significant power. These are not suitable for the miniaturization of sensor platforms. Presented in this study is a novel biologically inspired method that relies on ionic motion and osmotic pressures to displace a volume of water from the ocean into and out of the proposed buoyancy engine. At a constant device volume, the displaced water will alter buoyancy leading to either sinking or floating. The engine is composed of an enclosure sided on the ocean's end by a Nafion ionomer and by a flexible membrane separating the water from a gas enclosure. Two electrodes are placed one inside the enclosure and the other attached to the engine on the outside. The semi-permeable membrane Nafion allows water motion in and out of the enclosure while blocking anions from being transferred. The two electrodes generate local concentration changes of ions upon the application of an electrical field; these changes lead to osmotic pressures and hence the transfer of water through the semi-permeable membrane. Some aquatic organisms such as pelagic crustacean perform this buoyancy control using an exchange of ions through their tissue to modulate its density relative to the ambient sea water. In this paper, the authors provide an experimental proof of concept of this buoyancy engine. The efficiency of changing the engine's buoyancy is calculated and optimized as a function of electrode surface area. For example electrodes made of a 3mm diameter Ag/AgCl proved to transfer approximately 4mm3 of water consuming 4 Joules of electrical energy. The speed of displacement is optimized as a function of the surface area of the Nafion

  20. On the general concept of buoyancy in sedimentation and ultracentrifugation

    Science.gov (United States)

    Piazza, Roberto; Buzzaccaro, Stefano; Secchi, Eleonora; Parola, Alberto

    2013-08-01

    Gravity or ultracentrifuge settling of colloidal particles and macromolecules usually involves several disperse species, either because natural and industrial colloids display a large size polydispersity, or because additives are put in on purpose to allow for density-based fractionation of the suspension. Such ‘macromolecular crowding’, however, may have surprising effects on sedimentation, for it strongly affects the buoyant force felt by a settling particle. Here we show that, as a matter of fact, the standard Archimedes' principle is just a limiting law, valid only for mesoscopic particles settling in a molecular fluid, and we obtain a fully general expression for the actual buoyancy force providing a microscopic basis to the general thermodynamic analysis of sedimentation in multi-component mixtures. The effective buoyancy also depends on the particle shape, being much more pronounced for thin rods and discs. Our model is successfully tested on simple colloidal mixtures, and used to predict rather unexpected effects, such as denser particles floating on top of a lighter fluid, which we actually observe in targeted experiments. This ‘generalized Archimedes principle’ may provide a tool to devise novel separation methods sensitive to particle size and shape.

  1. Naturally driven variability in the global secondary organic aerosol over a decade

    Directory of Open Access Journals (Sweden)

    K. Tsigaridis

    2005-01-01

    Full Text Available In order to investigate the variability of the secondary organic aerosol (SOA distributions and budget and provide a measure for the robustness of the conclusions on human induced changes of SOA, a global 3-dimensional chemistry transport model describing both the gas and the particulate phase chemistry of the troposphere has been applied. The response of the global budget of SOA to temperature and moisture changes as well as to biogenic emission changes over a decade (1984-1993 has been evaluated. The considered emissions of biogenic non-methane volatile organic compounds (VOC are driven by temperature, light and vegetation. They vary between 756 and 810 Tg Cy-1 and are therefore about 5.5 times higher than the anthropogenic VOC emissions. All secondary aerosols (sulphuric, nitrates and organics are computed on-line together with the aerosol associated water. Over the studied decade, the computed natural variations (8% in the chemical SOA production from biogenic VOC oxidation equal the chemical SOA production from anthropogenic VOC oxidation. Maximum values are calculated for 1990 (warmer and drier and minimum values for 1986 (colder and wetter. The SOA computed variability results from a 7% increase in biogenic VOC emissions from 1986 to 1990 combined with 8.5% and 6% increases in the wet and dry deposition of SOA and leads to about 11.5% increase in the SOA burden of biogenic origin. The present study also demonstrates the importance of the hydrological cycle in determining the built up and fate of SOA in the atmosphere. It also reveals the existence of significant positive and negative feedback mechanisms in the atmosphere responsible for the non linear relationship between emissions of biogenic VOC and SOA burden.

  2. Naturally driven variability in the global secondary organic aerosol over a decade

    Directory of Open Access Journals (Sweden)

    K. Tsigaridis

    2005-03-01

    Full Text Available In order to investigate the variability of the secondary organic aerosol (SOA distributions and budget and provide a measure for the robustness of the conclusions on human induced changes of SOA, a global 3-dimensional chemistry transport model describing both the gas and the particulate phase chemistry of the troposphere has been applied. The response of the global budget of SOA to temperature and moisture changes as well as to biogenic emission changes over a decade (1984–1993 has been evaluated. The considered emissions of biogenic non-methane volatile organic compounds (VOC are driven by temperature, light and vegetation. They vary between 756 and 810 TgC y-1 and are therefore about 5.5 times higher than the anthropogenic VOC emissions. All secondary aerosols (sulphuric, nitrates and organics are computed on-line together with the aerosol associated water. Over the studied decade, the computed natural variations (8% in the chemical SOA production from biogenic VOC oxidation equal the chemical SOA production from anthropogenic VOC oxidation. This computed variability results from a 7% increase in biogenic VOC emissions combined with 8.5% and 6% increases in the wet and dry deposition of SOA and leads to about 11.5% increase in the SOA burden of biogenic origin. The present study also demonstrates the importance of the hydrological cycle in determining the built up and fate of SOA in the atmosphere. It also reveals the existence of significant positive and negative feedback mechanisms in the atmosphere responsible for the non linear relationship between emissions of biogenic VOC and SOA burden.

  3. Potential fate of SOC eroded from natural crusted soil surface under simulated wind driven storm

    Science.gov (United States)

    Xiao, Liangang; Fister, Wolfgang; Greenwood, Philip; Hu, Yaxian; Kuhn, Nikolaus J.

    2016-04-01

    Improving the assessment of the impact of soil erosion on carbon (C) cycling requires a better understanding of the redistribution of eroded sediment and associated soil organic carbon (SOC) across agricultural landscapes. Recent studies conducted on dry-sieved aggregates in the laboratory demonstrated that aggregation can profoundly skew SOC redistribution and its subsequent fate by accelerating settling velocities of aggregated sediment compared to mineral grains, which in turn can increase SOC mineralization into greenhouse gases. However, the erodibility of the soil in the field is more variable than in the laboratory due to tillage, crus formation, drying-wetting and freeze-thaw cycles, and biological effects. This study aimed to investigate the potential fate of the SOC eroded from naturally developed soil surface and to compare the observations with those made in the laboratory. Simulated, short, high intensity wind driven storms were conducted on a crusted loam in the field. The sediments were fractionated with a settling tube according to their potential transport distances. The soil mass, SOC concentration and cumulative 80-day CO2 emission of each fraction were identified. The results show: 1) 53% of eroded sediment and 62% of eroded SOC from the natural surface in the field would be deposited across landscapes, which is six times and three times higher compared to that implied by mineral grains, respectively; 2) the preferential deposition of SOC-rich fast-settling sediment potentially releases approximately 50% more CO2 than the same layer of the non-eroded soil; 3) the respiration of the slow-settling fraction that is potentially transported to the aquatic systems was much more active compared to the other fractions and the bulk soil. Our results confirm in general the conclusions drawn from laboratory and thus demonstrate that aggregation can affect the redistribution of sediment associated SOC under field conditions, including an increase in

  4. Effects of Buoyancy on Langmuir Circulation

    Institute of Scientific and Technical Information of China (English)

    SONG Jun; SONG Jin-Bao

    2008-01-01

    Based on the Navier-Stokes equation,an equation describing the Langmuir circulation is derived by a perturbation method when the influences of Coriolis force and buoyancy force are both considered.The approach used in the analysis is similar to the works carried out by Craik and Leibovich[J.Fluid Mech.73 (1976)401],Leibovich [J.Fluid Mech.79 (1977) 715]and Huang[J.Fluid Mech.91 (1979) 191].Potential applications of the equation proposed are discussed in the area of Antarctic circumpolar current.

  5. Unexpected Positive Buoyancy in Deep Sea Sharks, Hexanchus griseus, and a Echinorhinus cookei.

    Directory of Open Access Journals (Sweden)

    Itsumi Nakamura

    Full Text Available We do not expect non air-breathing aquatic animals to exhibit positive buoyancy. Sharks, for example, rely on oil-filled livers instead of gas-filled swim bladders to increase their buoyancy, but are nonetheless ubiquitously regarded as either negatively or neutrally buoyant. Deep-sea sharks have particularly large, oil-filled livers, and are believed to be neutrally buoyant in their natural habitat, but this has never been confirmed. To empirically determine the buoyancy status of two species of deep-sea sharks (bluntnose sixgill sharks, Hexanchus griseus, and a prickly shark, Echinorhinus cookei in their natural habitat, we used accelerometer-magnetometer data loggers to measure their swimming performance. Both species of deep-sea sharks showed similar diel vertical migrations: they swam at depths of 200-300 m at night and deeper than 500 m during the day. Ambient water temperature was around 15°C at 200-300 m but below 7°C at depths greater than 500 m. During vertical movements, all deep-sea sharks showed higher swimming efforts during descent than ascent to maintain a given swimming speed, and were able to glide uphill for extended periods (several minutes, indicating that these deep-sea sharks are in fact positively buoyant in their natural habitats. This positive buoyancy may adaptive for stealthy hunting (i.e. upward gliding to surprise prey from underneath or may facilitate evening upward migrations when muscle temperatures are coolest, and swimming most sluggish, after spending the day in deep, cold water. Positive buoyancy could potentially be widespread in fish conducting daily vertical migration in deep-sea habitats.

  6. Unexpected Positive Buoyancy in Deep Sea Sharks, Hexanchus griseus, and a Echinorhinus cookei.

    Science.gov (United States)

    Nakamura, Itsumi; Meyer, Carl G; Sato, Katsufumi

    2015-01-01

    We do not expect non air-breathing aquatic animals to exhibit positive buoyancy. Sharks, for example, rely on oil-filled livers instead of gas-filled swim bladders to increase their buoyancy, but are nonetheless ubiquitously regarded as either negatively or neutrally buoyant. Deep-sea sharks have particularly large, oil-filled livers, and are believed to be neutrally buoyant in their natural habitat, but this has never been confirmed. To empirically determine the buoyancy status of two species of deep-sea sharks (bluntnose sixgill sharks, Hexanchus griseus, and a prickly shark, Echinorhinus cookei) in their natural habitat, we used accelerometer-magnetometer data loggers to measure their swimming performance. Both species of deep-sea sharks showed similar diel vertical migrations: they swam at depths of 200-300 m at night and deeper than 500 m during the day. Ambient water temperature was around 15°C at 200-300 m but below 7°C at depths greater than 500 m. During vertical movements, all deep-sea sharks showed higher swimming efforts during descent than ascent to maintain a given swimming speed, and were able to glide uphill for extended periods (several minutes), indicating that these deep-sea sharks are in fact positively buoyant in their natural habitats. This positive buoyancy may adaptive for stealthy hunting (i.e. upward gliding to surprise prey from underneath) or may facilitate evening upward migrations when muscle temperatures are coolest, and swimming most sluggish, after spending the day in deep, cold water. Positive buoyancy could potentially be widespread in fish conducting daily vertical migration in deep-sea habitats.

  7. Buoyancy under control: underwater locomotor performance in a deep diving seabird suggests respiratory strategies for reducing foraging effort.

    Directory of Open Access Journals (Sweden)

    Timothée R Cook

    Full Text Available BACKGROUND: Because they have air stored in many body compartments, diving seabirds are expected to exhibit efficient behavioural strategies for reducing costs related to buoyancy control. We study the underwater locomotor activity of a deep-diving species from the Cormorant family (Kerguelen shag and report locomotor adjustments to the change of buoyancy with depth. METHODOLOGY/PRINCIPAL FINDINGS: Using accelerometers, we show that during both the descent and ascent phases of dives, shags modelled their acceleration and stroking activity on the natural variation of buoyancy with depth. For example, during the descent phase, birds increased swim speed with depth. But in parallel, and with a decay constant similar to the one in the equation explaining the decrease of buoyancy with depth, they decreased foot-stroke frequency exponentially, a behaviour that enables birds to reduce oxygen consumption. During ascent, birds also reduced locomotor cost by ascending passively. We considered the depth at which they started gliding as a proxy to their depth of neutral buoyancy. This depth increased with maximum dive depth. As an explanation for this, we propose that shags adjust their buoyancy to depth by varying the amount of respiratory air they dive with. CONCLUSIONS/SIGNIFICANCE: Calculations based on known values of stored body oxygen volumes and on deep-diving metabolic rates in avian divers suggest that the variations of volume of respiratory oxygen associated with a respiration mediated buoyancy control only influence aerobic dive duration moderately. Therefore, we propose that an advantage in cormorants--as in other families of diving seabirds--of respiratory air volume adjustment upon diving could be related less to increasing time of submergence, through an increased volume of body oxygen stores, than to reducing the locomotor costs of buoyancy control.

  8. Large eddy simulation of pollutant gas dispersion with buoyancy ejected from building into an urban street canyon.

    Science.gov (United States)

    Hu, L H; Xu, Y; Zhu, W; Wu, L; Tang, F; Lu, K H

    2011-09-15

    The dispersion of buoyancy driven smoke soot and carbon monoxide (CO) gas, which was ejected out from side building into an urban street canyon with aspect ratio of 1 was investigated by large eddy simulation (LES) under a perpendicular wind flow. Strong buoyancy effect, which has not been revealed before, on such pollution dispersion in the street canyon was studied. The buoyancy release rate was 5 MW. The wind speed concerned ranged from 1 to 7.5m/s. The characteristics of flow pattern, distribution of smoke soot and temperature, CO concentration were revealed by the LES simulation. Dimensionless Froude number (Fr) was firstly introduced here to characterize the pollutant dispersion with buoyancy effect counteracting the wind. It was found that the flow pattern can be well categorized into three regimes. A regular characteristic large vortex was shown for the CO concentration contour when the wind velocity was higher than the critical re-entrainment value. A new formula was theoretically developed to show quantitatively that the critical re-entrainment wind velocities, u(c), for buoyancy source at different floors, were proportional to -1/3 power of the characteristic height. LES simulation results agreed well with theoretical analysis. The critical Froude number was found to be constant of 0.7.

  9. On the Anisotropic Nature of MRI-driven Turbulence in Astrophysical Disks

    DEFF Research Database (Denmark)

    Murphy, Gareth; Pessah, Martin E.

    2015-01-01

    The magnetorotational instability (MRI) is thought to play an important role in enabling accretion in sufficiently ionized astrophysical disks. The rate at which MRI-driven turbulence transports angular momentum is intimately related to both the strength of the amplitudes of the fluctuations...

  10. On the Anisotropic Nature of MRI-driven Turbulence in Astrophysical Disks

    DEFF Research Database (Denmark)

    Murphy, Gareth; Pessah, Martin E.

    2015-01-01

    The magnetorotational instability (MRI) is thought to play an important role in enabling accretion in sufficiently ionized astrophysical disks. The rate at which MRI-driven turbulence transports angular momentum is intimately related to both the strength of the amplitudes of the fluctuations on v...

  11. What buoyancy really is. A Generalized Archimedes Principle for sedimentation and ultracentrifugation

    OpenAIRE

    Piazza, Roberto; Buzzaccaro, Stefano; Secchi, Eleonora; Parola, Alberto

    2012-01-01

    Particle settling is a pervasive process in nature, and centrifugation is a much versatile separation technique. Yet, the results of settling and ultracentrifugation experiments often appear to contradict the very law on which they are based: Archimedes Principle - arguably, the oldest Physical Law. The purpose of this paper is delving at the very roots of the concept of buoyancy by means of a combined experimental-theoretical study on sedimentation profiles in colloidal mixtures. Our analysi...

  12. Microgravity Flow Regime Data: Buoyancy and Mixing Apparatus Effects

    Science.gov (United States)

    Shephard, Adam; Best, Frederick

    2010-01-01

    Zero-g two-phase flow data set qualification and flight experiment design have not been standardized and as a result, agreement among researchers has not been reached regarding what experimental conditions adequately approximate those of microgravity. The effects of buoyancy forces and mixing apparatus on the flow regime transitions are presented in this study. The gravity conditions onboard zero-g aircraft are at best 10-3 g which is used to approximate the 10-5 g conditions of microgravity, thus the buoyancy forces present on zero-g aircraft can become significantly large and unrepresentative of microgravity. When buoyancy forces approach those of surface tension forces, buoyancy induced coalescence occurs. When discussing flow regime transitions, these large buoyancy forces lead to flow regime transitions which otherwise would not occur. The buoyancy attributes of the two-phase flow data sets available in the literature are evaluated to determine which data sets exhibit buoyancy induced transitions. Upon comparison of the representative data sets, the affects of different mixing apparatus can be seen in the superficial velocity flow regime maps.

  13. Influence of input data on airflow network accuracy in residential buildings with natural wind- and stack-driven ventilation

    DEFF Research Database (Denmark)

    Arendt, Krzysztof; Krzaczek, Marek; Tejchman, Jacek

    2017-01-01

    The airflow network (AFN) modeling approach provides an attractive balance between the accuracy and computational demand for naturally ventilated buildings. Its accuracy depends on input parameters such as wind pressure and opening discharge coefficients. In most cases, these parameters...... are obtained from secondary sources which are solely representative for very simplified buildings, i.e. for buildings without facade details. Although studies comparing wind pressure coefficients or discharge coefficients from different sources exist, the knowledge regarding the effect of input data on AFN...... is still poor. In this paper, the influence of wind pressure data on the accuracy of a coupled AFN-BES model for a real building with natural wind- and stack-driven ventilation was analyzed. The results of 8 computation cases with different wind pressure data from secondary sources were compared...

  14. Neutral Buoyancy Simulator - SADE NBS Test

    Science.gov (United States)

    1983-01-01

    One of the main components of the Hubble Space Telescope (HST) is the Solar Array Drive Electronics (SADE) system. This system interfaces with the Support System Module (SSM) for exchange of operational commands and telemetry data. SADE operates and controls the Solar Array Drive Mechanisms (SADM) for the orientation of the Solar Array Drive (SAD). It also monitors the position of the arrays and the temperature of the SADM. During the first HST servicing mission, the astronauts replaced the SADE component because of some malfunctions. This turned out to be a very challenging extravehicular activity (EVA). Two transistors and two diodes had been thermally stressed with the conformal coating discolored and charred. Soldered cornections became molten and reflowed between the two diodes. The failed transistors gave no indication of defective construction. All repairs were made and the HST was redeposited into orbit. Prior to undertaking this challenging mission, the orbiter's crew trained at Marshall Space Flight Center's (MSFC) Neutral Buoyancy Simulator (NBS) to prepare themselves for working in a low gravity environment. They also practiced replacing HST parts and exercised maneuverability and equipment handling. Pictured is an astronaut practicing climbing a space platform that was necessary in making repairs on the HST.

  15. Neutral Buoyancy Simulator- NB38 -Space Telescope

    Science.gov (United States)

    1980-01-01

    The Hubble Space Telescope (HST) is a cooperative program of the European Space Agency (ESA) and the National Aeronautical and Space Administration (NASA) to operate a long-lived space-based observatory. It was the flagship mission of NASA's Great Observatories program. The HST program began as an astronomical dream in the 1940s. During the 1970s and 1980s, the HST was finally designed and built becoming operational in the 1990s. The HST was deployed into a low-Earth orbit on April 25, 1990 from the cargo bay of the Space Shuttle Discovery (STS-31). The design of the HST took into consideration its length of service and the necessity of repairs and equipment replacement by making the body modular. In doing so, subsequent shuttle missions could recover the HST, replace faulty or obsolete parts and be re-released. Pictured is MSFC's Neutral Buoyancy Simulator (NBS) that served as the test center for shuttle astronauts training for Hubble related missions. Shown are astronauts Bruce McCandless and Sharnon Lucid being fitted for their space suits prior to entering the NBS to begin training on the space telescope axial scientific instrument changeout.

  16. Velocity measurements and concentration field visualizations in copper electrolysis under the influence of Lorentz forces and buoyancy

    Science.gov (United States)

    Weier, T.; Cierpka, C.; Huller, J.; Gerbeth, G.

    2006-12-01

    Velocity measurements and shadowgraph visualizations for copper electrolysis under the influence of a magnetic field are reported. Experiments in a rectangular cell show the expected strong correlation between flow features and limiting current density. The flow can be understood as driven by the interplay of Lorentz force and buoyancy. For a cylindrical cell with only slightly non-parallel electric and magnetic field lines, the presence and importance of the Lorentz force is demonstrated by velocity measurements. Figs 6, Refs 13.

  17. Towards theory driven structure elucidation of complex natural products: mandelalides and coibamide A.

    Science.gov (United States)

    Snyder, Kevin M; Sikorska, Justyna; Ye, Tao; Fang, Lijing; Su, Wu; Carter, Rich G; McPhail, Kerry L; Cheong, Paul H-Y

    2016-06-28

    The effectiveness of computational tools in determining relative configurations of complex molecules is investigated, using natural products mandelalides A-D and coibamide A, towards a generalized recipe for the scientific community at large. Ultimately, continuing efforts in this vein will accelerate and strengthen relative structure elucidation of complex molecules, such as natural products. Molecular mechanics conformational search, quantum mechanical NMR chemical shift predictions, and DP4 analyses led to confirmation of the revised structures of mandelalides A-D and coibamide A. All chiral centers in the northern hemisphere of mandelalides A-D are inverted with respect to the originally proposed structures, in agreement with recent total syntheses of mandelalide A by Ye, Fürstner & Carter. In the case of coibamide A, it was found that Fang & Su's revision, in which both the macrocycle [MeAla(11)] and the side chain [HIV(2)] residues are inverted from l to d, was consistent with the authentic natural product and computations.

  18. Time-dependent renormalized-natural-orbital theory applied to laser-driven H$_2^+$

    CERN Document Server

    Hanusch, A; Brics, M; Bauer, D

    2016-01-01

    Recently introduced time-dependent renormalized-natural orbital theory (TDRNOT) is extended towards a multi-component approach in order to describe H$_2^+$ beyond the Born-Oppenheimer approximation. Two kinds of natural orbitals, describing the electronic and the nuclear degrees of freedom are introduced, and the exact equations of motion for them are derived. The theory is benchmarked by comparing numerically exact results of the time-dependent Schr\\"odinger equation for a H$_2^+$ model system with the corresponding TDRNOT predictions. Ground state properties, linear response spectra, fragmentation, and high-order harmonic generation are investigated.

  19. Predicting natural streamflows in regulated snowmelt-driven watersheds using regionalization methods

    Directory of Open Access Journals (Sweden)

    D. Kim

    2013-07-01

    Full Text Available Predicting streamflows in snow-fed watersheds in the Western United States is important for water allocation. Since many of these watersheds are heavily regulated through canal networks and reservoirs, predicting expected natural flows and therefore water availability under limited data is always a challenge. This study investigates the applicability of the flow duration curve (FDC method for predicting natural flows in gauged and ungauged snow-fed watersheds. Point snow observations, air temperature, precipitation, and snow water equivalent, are used to simulate snowmelt process with SNOW-17 model and extended to streamflow generation by a FDC method with modified current precipitation index. For regulated (ungauged watersheds, a parametric regional FDC method is applied to reconstruct natural flow. For comparison, a simplified Tank Model is used as well. The proximity regionalization method is used to generate streamflow using the Tank Model in ungauged watersheds. The results show that the FDC method can produce acceptable natural flow estimates in both gauged and ungauged watersheds under data limited conditions. The performance of the FDC method is better in watersheds with relatively low evapotranspiration (ET. Multiple donor data sets including current precipitation index are recommended to reduce uncertainty of the regional FDC method for ungauged watersheds. In spite of its simplicity, the FDC method can perform better than the Tank Model under minimal data availability.

  20. TAO/TRITON, RAMA, and PIRATA Buoys, Daily, Buoyancy Flux

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This dataset has daily Buoyancy Flux data from the TAO/TRITON (Pacific Ocean, http://www.pmel.noaa.gov/tao/), RAMA (Indian Ocean,...

  1. TAO/TRITON, RAMA, and PIRATA Buoys, Quarterly, Buoyancy Flux

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This dataset has quarterly Buoyancy Flux data from the TAO/TRITON (Pacific Ocean, http://www.pmel.noaa.gov/tao/), RAMA (Indian Ocean,...

  2. Buoyancy in tropical cyclones and other rapidly rotating atmospheric vortices

    Science.gov (United States)

    Smith, Roger K.; Montgomery, Michael T.; Zhu, Hongyan

    2005-07-01

    Motivated primarily by its application to understanding tropical-cyclone intensification and maintenance, we re-examine the concept of buoyancy in rapidly rotating vortices, distinguishing between the buoyancy of the symmetric balanced vortex or system buoyancy, and the local buoyancy associated with cloud dynamics. The conventional definition of buoyancy is contrasted with a generalized form applicable to a vortex, which has a radial as well as a vertical component. If, for the special case of axisymmetric motions, the balanced density and pressure distribution of a rapidly rotating vortex are used as the reference state, the buoyancy field then characterizes the unbalanced density perturbations, i.e. the local buoyancy. We show how to determine such a reference state without approximation. The generation of the toroidal circulation of a vortex, which is necessary for vortex amplification, is characterized in the vorticity equation by the baroclinicity vector. This vector depends, inter-alia, on the horizontal (or radial) gradient of buoyancy evaluated along isobaric surfaces. We show that for a tropical-cyclone-scale vortex, the buoyancy so calculated is significantly different from that calculated at constant height or on surfaces of constant σ ( σ = ( p - p*)/( ps - p*), where p is the actual pressure, p* some reference pressure and ps is the surface pressure). Since many tropical-cyclone models are formulated using σ-coordinates, we examine the calculation of buoyancy on σ-surfaces and derive an expression for the baroclinicity vector in σ-coordinates. The baroclinic forcing term in the azimuthal vorticity equation for an axisymmetric vortex is shown to be approximately equal to the azimuthal component of the curl of the generalized buoyancy. A scale analysis indicates that the vertical gradient of the radial component of generalized buoyancy makes a comparatively small contribution to the generation of toroidal vorticity in a tropical cyclone, but may be

  3. What buoyancy really is. A generalized Archimedes' principle for sedimentation and ultracentrifugation

    Science.gov (United States)

    Piazza, Roberto; Buzzaccaro, Stefano; Secchi, Eleonora; Parola, Alberto

    Particle settling is a pervasive process in nature, and centrifugation is a much versatile separation technique. Yet, the results of settling and ultracentrifugation experiments often appear to contradict the very law on which they are based: Archimedes Principle - arguably, the oldest Physical Law. The purpose of this paper is delving at the very roots of the concept of buoyancy by means of a combined experimental-theoretical study on sedimentation profiles in colloidal mixtures. Our analysis shows that the standard Archimedes' principle is only a limiting approximation, valid for mesoscopic particles settling in a molecular fluid, and we provide a general expression for the actual buoyancy force. This "Generalized Archimedes Principle" accounts for unexpected effects, such as denser particles floating on top of a lighter fluid, which in fact we observe in our experiments.

  4. The nature of the jet-driven outflow in the radio galaxy 3C305

    CERN Document Server

    Hardcastle, M J; Harris, D E; Baum, S A; Bianchi, S; Chiaberge, M; Morganti, R; O'Dea, C P; Siemiginowska, A

    2012-01-01

    We present Chandra X-ray and VLA radio observations of the radio galaxy 3C305. The X-ray observations reveal the details of the previously known extended X-ray halo around the radio galaxy. We show using X-ray spectroscopy that the X-ray emission is consistent with being shock-heated material and can be modelled with standard collisional-ionization models, rather than being photoionized by the active nucleus. On this basis, we can make a self-consistent model in which the X-ray-emitting plasma is responsible for the depolarization of some regions of the radio emission from the jets and hotspots, and to place lower and upper limits on the magnetic field strength in the depolarizing medium. On the assumption that the X-ray-emitting material, together with the previously-known extended emission-line region and the outflow in neutral hydrogen, are all being driven out of the centre of the galaxy by an interaction with the jets, we derive a detailed energy budget for the radio galaxy, showing that the X-ray-emitti...

  5. March of buoyancy elements during extreme rainfall over India

    Science.gov (United States)

    Krishnamurti, T. N.; Kumar, Vinay; Simon, Anu; Thomas, Aype; Bhardwaj, Amit; Das, Sweta; Senroy, Soma; Roy Bhowmik, S. K.

    2017-03-01

    A major rain storm in Uttarakhand (India) caused heavy rains and major loss of life from floods and land slide during 16-18 June, 2013. The observed daily maximum rainfall rates (3-hourly) during the 16th and 17th June were 220 and 340 mm respectively. This event is addressed via sensitivity studies using a cloud resolving non-hydrostatic model with detailed microphysics. The streaming of moist air from the east-south-east and warmer air from the south-west contributed to the sustained large population and amplitude of buoyancy and the associated CAPE contributed to the longer period of heavy rains. This study addresses the concept of Buoyancy as a means for large vertical accelerations, stronger vertical motions, extreme rain rates and the mechanisms that relate to the time rates of change. A post-processing algorithm provides an analysis of time rate of change for the buoyancy. Moist air streams and warm/moist air intrusions into heavily raining clouds are part of this buoyancy enhancement framework. Improvements in modeling of the extreme rain event came from adaptive observational strategy that showed lack of moisture data sets in these vital regions. We show that a moist boundary layer near the Bay of Bengal leads to moist rivers of moisture where the horizontal convergence confines a large population of buoyancy elements with large magnitudes of buoyancy that streams towards the region of extreme orographic rains. The areas covered in this study include: (i) Use of high resolution cloud modeling (1-km), (ii) Now casting of rains using physical initialization with a Newtonian relaxation, (iii) Use of an adaptive observational strategy, (iii) Sensitivity of the evolution of fields and population of buoyancy elements to boundary layer moisture, (iv) Role of orography and details of buoyancy budget.

  6. Neutral Buoyancy underwater electrical cornector test

    Science.gov (United States)

    1978-01-01

    Once the United States' space program had progressed from Earth's orbit into outerspace, the prospect of building and maintaining a permanent presence in space was realized. To accomplish this feat, NASA launched a temporary workstation, Skylab, to discover the effects of low gravity and weightlessness on the human body, and also to develop tools and equipment that would be needed in the future to build and maintain a more permanent space station. The structures, techniques, and work schedules had to be carefully designed to fit this unique construction site. The components had to be lightweight for transport into orbit, yet durable. The station also had to be made with removable parts for easy servicing and repairs by astronauts. All of the tools necessary for service and repairs had to be designed for easy manipulation by a suited astronaut. And construction methods had to be efficient due to limited time the astronauts could remain outside their controlled environment. In lieu of all the specific needs for this project, an environment on Earth had to be developed that could simulate a low gravity atmosphere. A Neutral Buoyancy Simulator (NBS) was constructed by NASA Marshall Space Flight Center (MSFC) in 1968. Since then, NASA scientists have used this facility to understand how humans work best in low gravity and also provide information about the different kinds of structures that can be built. Included in the plans for the space station was a space telescope. This telescope would be attached to the space station and directed towards outerspace. Astronomers hoped that the space telescope would provide a look at space that is impossible to see from Earth because of Earth's atmosphere and other man made influences. Pictured is a large structure that is being used as the antenna base for the space telescope.

  7. MyProLang - My Programming Language: A Template-Driven Automatic Natural Programming Language

    OpenAIRE

    Youssef A. Bassil; Aziz M. Barbar

    2012-01-01

    Modern computer programming languages are governed by complex syntactic rules. They are unlike natural languages; they require extensive manual work and a significant amount of learning and practicing for an individual to become skilled at and to write correct programs. Computer programming is a difficult, complicated, unfamiliar, non-automated, and a challenging discipline for everyone; especially, for students, new programmers and end-users. This paper proposes a new programming language an...

  8. A natural driven membrane process for brackish and wastewater treatment: photovoltaic powered ED and FO hybrid system.

    Science.gov (United States)

    Zhang, Yang; Pinoy, Luc; Meesschaert, Boudewijn; Van der Bruggen, Bart

    2013-09-17

    In isolated locations, remote areas, or islands, potable water is precious because of the lack of drinking water treatment facilities and energy supply. Thus, a robust and reliable water treatment system based on natural energy is needed to reuse wastewater or to desalinate groundwater/seawater for provision of drinking water. In this work, a hybrid membrane system combining electrodialysis (ED) and forward osmosis (FO), driven by renewable energy (solar energy), denoted as EDFORD (ED-FO Renewable energy Desalination), is proposed to produce high-quality water (potable) from secondary wastewater effluent or brackish water. In this hybrid membrane system, feedwater (secondary wastewater effluent or synthetic brackish water) was drawn to the FO draw solution while the organic and inorganic substances (ions, compounds, colloids and particles) were rejected. The diluted draw solution was then pumped to the solar energy driven ED. In the ED unit, the diluted draw solution was desalted and high-quality water was produced; the concentrate was recycled to the FO unit and reused as the draw solution. Results show that the water produced from this system contains a low concentration of total organic carbon (TOC), carbonate, and cations derived from the feedwater; had a low conductivity; and meets potable water standards. The water production cost considering the investment for membranes and solar panel is 3.32 to 4.92 EUR m(-3) (for 300 days of production per year) for a small size potable water production system.

  9. Single-sided natural ventilation driven by wind pressure and temperature difference

    DEFF Research Database (Denmark)

    Larsen, Tine Steen; Heiselberg, Per

    2008-01-01

    direction, the turbulence characteristics in the wind and the pressure variations caused by e.g. wind gusts. Finally, it also depends on the size, type and location of the opening. Many of these parameters are unsteady which makes the calculation of air-change rates even more complicated. In this work, full......-scale wind tunnel experiments have been made with the aim of making a new expression for calculation of the airflow rate in single-sided natural ventilation. During the wind tunnel experiments it was found that the dominating driving force differs between wind speed and temperature difference depending...

  10. Heat transfer on a naturally cross-driven ventilated triangular cavity with openings

    Energy Technology Data Exchange (ETDEWEB)

    Berli, M E; Saita, F A [INTEC, Universidad Nacional del Litoral, Gueemes 3450, 3000, Santa Fe (Argentina); Paolo, J Di, E-mail: mberli@santafe-conicet.gov.a [GIMEF, Departamento IngenierIa Industrial, FRSF - UTN, Lavaise 610, 3000, Santa Fe (Argentina)

    2009-05-01

    This work addresses the problem of heat transfer through the roof of a family home with the purpose of improving air-conditioning energy savings during hot summer days. To this end, the air natural convection in a right-angle triangular cavity, resembling an attic, is numerically analyzed. The air cavity is assumed as naturally ventilated through two openings that induce an external air-stream flowing into and out of the cavity. The governing equations for both flow and heat transfer are simultaneously solved with appropriate boundary conditions. Finite element technique is employed to transform the original set of differential equations into a non-linear discrete one, which is finally solved by Newton iteration. Two major assumptions are made, namely: radiation heat transfer is negligible and the air flow is in laminar regime; in addition, the usual Boussinesq approximation is employed. Under these assumptions the numerical predictions show that the amount of heat transferred through the ceiling rapidly diminishes as the flow through the cavity increases. Therefore; whether or not the ceiling is insulated, the energy transfer is reduced by more than 50% and energy savings are considerably improved.

  11. Researcher-driven Campaigns Engage Nature's Notebook Participants in Scientific Data Collection

    Science.gov (United States)

    Crimmins, Theresa M.; Elmore, Andrew J.; Huete, Alfredo; Keller, Stephen; Levetin, Estelle; Luvall, Jeffrey; Meyers, Orrin; Stylinski, Cathlyn D.; Van De Water, Peter K.; Vukovic, Ana

    2013-01-01

    One of the many benefits of citizen science projects is the capacity they hold for facilitating data collection on a grand scale and thereby enabling scientists to answer questions they would otherwise not been able to address. Nature's Notebook, the plant and animal phenology observing program of the USA National Phenology Network (USA-NPN) suitable for scientists and non-scientists alike, offers scientifically-vetted data collection protocols and infrastructure and mechanisms to quickly reach out to hundreds to thousands of potential contributors. The USA-NPN has recently partnered with several research teams to engage participants in contributing to specific studies. In one example, a team of scientists from NASA, the New Mexico Department of Health, and universities in Arizona, New Mexico, Oklahoma, and California are using juniper phenology observations submitted by Nature's Notebookparticipants to improve predictions of pollen release and inform asthma and allergy alerts. In a second effort, researchers from the University of Maryland Center for Environmental Science are engaging Nature's Notebookparticipants in tracking leafing phenophases of poplars across the U.S. These observations will be compared to information acquired via satellite imagery and used to determine geographic areas where the tree species are most and least adapted to predicted climate change. Researchers in these partnerships receive benefits primarily in the form of ground observations. Launched in 2010, the juniper pollen effort has engaged participants in several western states and has yielded thousands of observations that can play a role in model ground validation. Periodic evaluation of these observations has prompted the team to improve and enhance the materials that participants receive, in an effort to boost data quality. The poplar project is formally launching in spring of 2013 and will run for three years; preliminary findings from 2013 will be presented. Participants in these

  12. Single-sided Natural Ventilation Driven by a Combination of Wind Pressure and Temperature Difference

    DEFF Research Database (Denmark)

    Larsen, Tine Steen; Heiselberg, Per

    2007-01-01

    Natural ventilation is a commonly used principle when ventilation systems for buildings are designed. The ventilation can either be obtained by automatically controlled openings in the building envelope, or it can just be the simple action of opening a door or a window to let the fresh air in....... In both situations the aim is to obtain a good indoor environment but to control the amount of air, some basic knowledge of the flow through an opening is necessary. The amount of air going through the window opening in single-sided ventilation will depend on the wind speed near the building......, which make the prediction difficult. From earlier work, a few design expressions for single-sided ventilation already exist, but none of these include the wind direction, which here is an important parameter. Therefore several wind tunnel experiments are made in this work to find a new design expression...

  13. Cytokine balance and cytokine-driven natural killer cell dysfunction in systemic juvenile idiopathic arthritis.

    Science.gov (United States)

    Avau, Anneleen; Put, Karen; Wouters, Carine H; Matthys, Patrick

    2015-02-01

    Systemic juvenile idiopathic arthritis (sJIA) is a severe inflammatory childhood disorder, characterized by a specific pattern of systemic features and a typical cytokine profile. Patients are at risk to develop macrophage activation syndrome (MAS), an acute life-threatening condition defined by excessive proliferation and activation of macrophages and T cells. Defects of unknown cause in the natural killer (NK) cell cytotoxic capacity are presumed to underlie the pathogenesis of MAS and have been detected in sJIA patients. Here, we provide an overview of the cytokine profiles in sJIA and related mouse models. We discuss the influence of cytokines on NK cell function, and hypothesize that NK cell dysfunction in sJIA is caused by altered cytokine profiles.

  14. Computational analysis and visualisation of wind driven naturally ventilated flows around a school building

    Directory of Open Access Journals (Sweden)

    Chanawat Nitatwichit

    2008-03-01

    Full Text Available Most Thai state schools are designed to use cross flow natural ventilation as a passive cooling system. The aim of this study was to investigate the effects of geometry and orientation of school building to the airflow distribution around it. Computational fluid dynamics (CFD commercial software was used as a tool in this simulation. The 3-D flow simulation of building domain was performed with prevailing wind to identify a proper strategy of managing flows around the building. It was found that cross orientation of the building to wind direction might not necessarily result in good ventilation in classrooms. Flow visualization with hydrogen bubble technique was setup to qualitatively validate the numerical results. A water flow was maintained at 3.7 cm/s, corresponding to flow Reynolds number of 3,556. The numerical results were found to agree well with experimental results.

  15. Numerical Simulation on Floating Behavior of Buoyancy Tank Foundation of Anemometer Tower

    Institute of Scientific and Technical Information of China (English)

    丁红岩; 韩艳丽; 张浦阳

    2014-01-01

    The intact stability and damage stability of a model of an anemometer tower with buoyancy tank founda-tion are computed by the finite element software MOSES in this paper. The natural period of the anemometer tower is discussed through frequency domain analysis. The influence of a single factor, such as towing point position, wave height, wave direction and wave period, on towing stability is discussed through time domain analysis. At the same time, the towing stability under the condition of various combinations of many factors is analyzed based on the meas-ured data of the target area. Computer simulation results show that the intact stability is preferable and the damage stability is sufficient under the condition of plenty of subdivisions. Within the scope of the buoyancy tank foundation, the higher the towing point position is, the better the stability is. Wave height has a great impact on the motion ampli-tude of buoyancy tank foundation, but the effect on the acceleration is not obvious;wave period has a great impact on the acceleration, while the effect on the motion amplitude is not obvious;following-waves towing is more conducive to safety than atry.

  16. Buoyancy effect on the flow pattern and the thermal performance of an array of circular cylinders

    CERN Document Server

    Fornarelli, Francesco; Oresta, Paolo

    2016-01-01

    In this paper we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are iso-thermal and they are aligned with the Earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between -1 and 1. Two values of center to center spacing (s=3.6d - 4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=-1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard d...

  17. Computational and Experimental Investigation for an Optimal Design of Industrial Windows to Allow Natural Ventilation during Wind-Driven Rain

    Directory of Open Access Journals (Sweden)

    Kritana Prueksakorn

    2015-08-01

    Full Text Available With an increased awareness of sustainability issues, natural ventilation has become an elegant method for reducing the costs and environmental effects of the energy that is used to maintain comfortable indoor air quality rather than using mechanical ventilation. The windows in many industrial buildings are continuously open to exhaust pollutants and intake fresh air. Though windows are functional and efficient for natural ventilation, rainwater is able to penetrate through the windows during wind-driven rain. For industries in which the moisture content affects the quality of the product, the intrusion of a large amount of rainwater through windows must be prevented without compromising the effective ventilation. The aim of this research is to determine an innovative design for windows to accomplish the optimum of high ventilation and low rain penetration. For this purpose, windows are variously innovated and tested in full-scale measurements, reduced-scale wind-tunnel measurements and computational fluid dynamics (CFD. An artificial rain and wind velocity to mimic the average of the maximum values in Korea are created. The maximum reduction in rain penetration of over 98% compared to basic 90° open windows is attained with only a 4%–9% decrement of ventilation efficiency in the two recommended designs.

  18. Future ocean hypercapnia driven by anthropogenic amplification of the natural CO2 cycle

    Science.gov (United States)

    McNeil, Ben I.; Sasse, Tristan P.

    2016-01-01

    High carbon dioxide (CO2) concentrations in sea-water (ocean hypercapnia) can induce neurological, physiological and behavioural deficiencies in marine animals. Prediction of the onset and evolution of hypercapnia in the ocean requires a good understanding of annual variations in oceanic CO2 concentration, but there is a lack of relevant global observational data. Here we identify global ocean patterns of monthly variability in carbon concentration using observations that allow us to examine the evolution of surface-ocean CO2 levels over the entire annual cycle under increasing atmospheric CO2 concentrations. We predict that the present-day amplitude of the natural oscillations in oceanic CO2 concentration will be amplified by up to tenfold in some regions by 2100, if atmospheric CO2 concentrations continue to rise throughout this century (according to the RCP8.5 scenario of the Intergovernmental Panel on Climate Change). The findings from our data are broadly consistent with projections from Earth system climate models. Our predicted amplification of the annual CO2 cycle displays distinct global patterns that may expose major fisheries in the Southern, Pacific and North Atlantic oceans to hypercapnia many decades earlier than is expected from average atmospheric CO2 concentrations. We suggest that these ocean ‘CO2 hotspots’ evolve as a combination of the strong seasonal dynamics of CO2 concentration and the long-term effective storage of anthropogenic CO2 in the oceans that lowers the buffer capacity in these regions, causing a nonlinear amplification of CO2 concentration over the annual cycle. The onset of ocean hypercapnia (when the partial pressure of CO2 in sea-water exceeds 1,000 micro-atmospheres) is forecast for atmospheric CO2 concentrations that exceed 650 parts per million, with hypercapnia expected in up to half the surface ocean by 2100, assuming a high-emissions scenario (RCP8.5). Such extensive ocean hypercapnia has detrimental implications for

  19. Future ocean hypercapnia driven by anthropogenic amplification of the natural CO2 cycle.

    Science.gov (United States)

    McNeil, Ben I; Sasse, Tristan P

    2016-01-21

    High carbon dioxide (CO2) concentrations in sea-water (ocean hypercapnia) can induce neurological, physiological and behavioural deficiencies in marine animals. Prediction of the onset and evolution of hypercapnia in the ocean requires a good understanding of annual variations in oceanic CO2 concentration, but there is a lack of relevant global observational data. Here we identify global ocean patterns of monthly variability in carbon concentration using observations that allow us to examine the evolution of surface-ocean CO2 levels over the entire annual cycle under increasing atmospheric CO2 concentrations. We predict that the present-day amplitude of the natural oscillations in oceanic CO2 concentration will be amplified by up to tenfold in some regions by 2100, if atmospheric CO2 concentrations continue to rise throughout this century (according to the RCP8.5 scenario of the Intergovernmental Panel on Climate Change). The findings from our data are broadly consistent with projections from Earth system climate models. Our predicted amplification of the annual CO2 cycle displays distinct global patterns that may expose major fisheries in the Southern, Pacific and North Atlantic oceans to hypercapnia many decades earlier than is expected from average atmospheric CO2 concentrations. We suggest that these ocean 'CO2 hotspots' evolve as a combination of the strong seasonal dynamics of CO2 concentration and the long-term effective storage of anthropogenic CO2 in the oceans that lowers the buffer capacity in these regions, causing a nonlinear amplification of CO2 concentration over the annual cycle. The onset of ocean hypercapnia (when the partial pressure of CO2 in sea-water exceeds 1,000 micro-atmospheres) is forecast for atmospheric CO2 concentrations that exceed 650 parts per million, with hypercapnia expected in up to half the surface ocean by 2100, assuming a high-emissions scenario (RCP8.5). Such extensive ocean hypercapnia has detrimental implications for

  20. The Effect of Buoyancy Force in Computational Fluid Dynamics Simulation of a Two-Dimensional Continuous Ohmic Heating Process

    Directory of Open Access Journals (Sweden)

    Elzubier A. Salih

    2009-01-01

    Full Text Available Problem statement: Earlier research on ohmic heating technique focused on viscous food and foods containing solid particles. In this study, use of ohmic heating on sterilization of guava juice is carried out. Computational fluid dynamics was used to model and simulate the system. Investigate the buoyancy effect on the CFD simulation of continuous ohmic heating systems of fluid foods. Approach: A two-dimensional model describing the flow, temperature and electric field distribution of non-Newtonian power law guava juice fluid in a cylindrical continuous ohmic heating cell was developed. The electrical conductivity, thermo physical and rheological properties of the fluid was temperature dependent. Numerical simulation was carried out using FLUENT 6.1 software package. A user defined functions available in FLUENT 6.1 was employed for the electric field equation. The heating cell used consisted of a cylindrical tube of diameter 0.05 m, height 0.50 m and having three collinear electrodes of 0.02 m width separated by a distance of 0.22 m. The sample was subjected to zero voltage at the top and bottom of electrodes while electrical potential of 90 volts (AC 50-60 Hz was set at the middle electrode. The inlet velocity is 0.003 m sec-1 and the temperature is in the range of 30-90°C. Results: Simulation was carried with and without buoyancy driven force effect. The ohmic heating was successfully simulated using CFD and the results showed that the buoyancy had a strong effect in temperature profiles and flow pattern of the collinear electrodes configuration ohmic heating. A more uniform velocity and temperature profiles were obtained with the buoyancy effect included. Conclusion: For accurate results, the inclusion of buoyancy effect into the CFD simulation is important.

  1. The effects of buoyancy on turbulent nonpremixed jet flames in crossflow

    Science.gov (United States)

    Boxx, Isaac G.

    became apparent in the JFICF at around xiy = 3.1 and grew in influence to become a dominant flow-field characteristic approximately xi y = 4.3. The PLMS images also yielded physical-insight into the nature of the fore-aft asymmetry of JFICF characteristics noted by previous researchers. Ensemble-averages of PLMS images were used to investigate centerline mixture fraction decay. Consistent with previous studies of non-reacting JICF studies, the mixture-fraction of the JFICF showed a power-law decay profile which scaled with (rd)-0.66. Over the region these measurements were made (xiy = 0--1.9), the mixture fraction decay scaling showed little sensitivity to buoyancy. Taken as a whole, these measurements show that buoyancy has the potential to significantly modify both the mean and instantaneous flow-field of a turbulent JFICF, even at relatively modest length-scales.

  2. How did Archimedes discover the law of buoyancy by experiment?

    Science.gov (United States)

    Kuroki, Hidetaka

    2016-03-01

    After Archimedes and Vitruvius era, for more than 2000 years, it has been believed that the displaced water measurement of golden crown is impossible, and at his Eureka moment, Archimedes discovered the law of buoyancy (Proposition 7 of his principles) and proved the theft of a goldsmith by weighing the golden crown in water. A previous study showed that a small amount of displaced water was able to be measured with enough accuracy by the introduced method. Archimedes measured the weight of displaced water. He did not find the law of buoyancy but rather specific gravity of things at the moment. After which, Archimedes continued to measure the specific gravity of various solids and fluids. Through these measurements, he reached the discovery of the law of buoyancy directly by experiment. In this paper, the process to the discovery of Archimedes' principle (Proposition 5) is presented.

  3. The naturally processed CD95L elicits a c-yes/calcium/PI3K-driven cell migration pathway.

    Directory of Open Access Journals (Sweden)

    Sébastien Tauzin

    2011-06-01

    Full Text Available Patients affected by chronic inflammatory disorders display high amounts of soluble CD95L. This homotrimeric ligand arises from the cleavage by metalloproteases of its membrane-bound counterpart, a strong apoptotic inducer. In contrast, the naturally processed CD95L is viewed as an apoptotic antagonist competing with its membrane counterpart for binding to CD95. Recent reports pinpointed that activation of CD95 may attract myeloid and tumoral cells, which display resistance to the CD95-mediated apoptotic signal. However, all these studies were performed using chimeric CD95Ls (oligomerized forms, which behave as the membrane-bound ligand and not as the naturally processed CD95L. Herein, we examine the biological effects of the metalloprotease-cleaved CD95L on CD95-sensitive activated T-lymphocytes. We demonstrate that cleaved CD95L (cl-CD95L, found increased in sera of systemic lupus erythematosus (SLE patients as compared to that of healthy individuals, promotes the formation of migrating pseudopods at the leading edge of which the death receptor CD95 is capped (confocal microscopy. Using different migration assays (wound healing/Boyden Chamber/endothelial transmigration, we uncover that cl-CD95L promotes cell migration through a c-yes/Ca²⁺/PI3K-driven signaling pathway, which relies on the formation of a CD95-containing complex designated the MISC for Motility-Inducing Signaling Complex. These findings revisit the role of the metalloprotease-cleaved CD95L and emphasize that the increase in cl-CD95L observed in patients affected by chronic inflammatory disorders may fuel the local or systemic tissue damage by promoting tissue-filtration of immune cells.

  4. An Analytic Model for Buoyancy Resonances in Protoplanetary Disks

    CERN Document Server

    Lubow, Stephen H

    2014-01-01

    Zhu, Stone, and Rafikov (2012) found in 3D shearing box simulations a new form of planet-disk interaction that they attributed to a vertical buoyancy resonance in the disk. We describe an analytic linear model for this interaction. We adopt a simplified model involving azimuthal forcing that produces the resonance and permits an analytic description of its structure. We derive an analytic expression for the buoyancy torque and show that the vertical torque distribution agrees well with results of Athena simulations and a Fourier method for linear numerical calculations carried out with the same forcing. The buoyancy resonance differs from the classic Lindblad and corotation resonances in that the resonance lies along tilted planes. Its width depends on damping effects and is independent of the gas sound speed. The resonance does not excite propagating waves. At a given large azimuthal wavenumber k_y > 1/h (for disk thickness h), the buoyancy resonance exerts a torque over a region that lies radially closer to...

  5. Using Surface Integrals for Checking Archimedes' Law of Buoyancy

    Science.gov (United States)

    Lima, F. M. S.

    2012-01-01

    A mathematical derivation of the force exerted by an "inhomogeneous" (i.e. compressible) fluid on the surface of an "arbitrarily shaped" body immersed in it is not found in the literature, which may be attributed to our trust in Archimedes' law of buoyancy. However, this law, also known as Archimedes' principle (AP), does not yield the force…

  6. EVA Development and Verification Testing at NASA's Neutral Buoyancy Laboratory

    Science.gov (United States)

    Jairala, Juniper C.; Durkin, Robert; Marak, Ralph J.; Sipila, Stepahnie A.; Ney, Zane A.; Parazynski, Scott E.; Thomason, Arthur H.

    2012-01-01

    As an early step in the preparation for future Extravehicular Activities (EVAs), astronauts perform neutral buoyancy testing to develop and verify EVA hardware and operations. Neutral buoyancy demonstrations at NASA Johnson Space Center's Sonny Carter Training Facility to date have primarily evaluated assembly and maintenance tasks associated with several elements of the International Space Station (ISS). With the retirement of the Shuttle, completion of ISS assembly, and introduction of commercial players for human transportation to space, evaluations at the Neutral Buoyancy Laboratory (NBL) will take on a new focus. Test objectives are selected for their criticality, lack of previous testing, or design changes that justify retesting. Assembly tasks investigated are performed using procedures developed by the flight hardware providers and the Mission Operations Directorate (MOD). Orbital Replacement Unit (ORU) maintenance tasks are performed using a more systematic set of procedures, EVA Concept of Operations for the International Space Station (JSC-33408), also developed by the MOD. This paper describes the requirements and process for performing a neutral buoyancy test, including typical hardware and support equipment requirements, personnel and administrative resource requirements, examples of ISS systems and operations that are evaluated, and typical operational objectives that are evaluated.

  7. Modeling the Buoyancy System of a Wave Energy Power Plant

    DEFF Research Database (Denmark)

    Pedersen, Tom S.; Nielsen, Kirsten M.

    2009-01-01

    A nonlinear dynamic model of the buoyancy system in a wave energy power plant is presented. The plant ("Wave Dragon") is a floating device using the potential energy in overtopping waves to produce power. A water reservoir is placed on top of the WD, and hydro turbines lead the water to the sea...

  8. Redirecting photosynthetic electron flow into light-driven synthesis of alternative products including high-value bioactive natural compounds.

    Science.gov (United States)

    Lassen, Lærke Münter; Nielsen, Agnieszka Zygadlo; Ziersen, Bibi; Gnanasekaran, Thiyagarajan; Møller, Birger Lindberg; Jensen, Poul Erik

    2014-01-17

    Photosynthesis in plants, green algae, and cyanobacteria converts solar energy into chemical energy in the form of ATP and NADPH, both of which are used in primary metabolism. However, often more reducing power is generated by the photosystems than what is needed for primary metabolism. In this review, we discuss the development in the research field, focusing on how the photosystems can be used as synthetic biology building blocks to channel excess reducing power into light-driven production of alternative products. Plants synthesize a large number of high-value bioactive natural compounds. Some of the key enzymes catalyzing their biosynthesis are the cytochrome P450s situated in the endoplasmic reticulum. However, bioactive compounds are often synthesized in low quantities in the plants and are difficult to produce by chemical synthesis due to their often complex structures. Through a synthetic biology approach, enzymes with a requirement for reducing equivalents as cofactors, such as the cytochrome P450s, can be coupled directly to the photosynthetic energy output to obtain environmentally friendly production of complex chemical compounds. By relocating cytochrome P450s to the chloroplasts, reducing power can be diverted toward the reactions catalyzed by the cytochrome P450s. This provides a sustainable production method for high-value compounds that potentially can solve the problem of NADPH regeneration, which currently limits the biotechnological uses of cytochrome P450s. We describe the approaches that have been taken to couple enzymes to photosynthesis in vivo and to photosystem I in vitro and the challenges associated with this approach to develop new green production platforms.

  9. On the role of buoyancy force in the ore genesis of SEDEX deposits: Example from Northern Australia

    Institute of Scientific and Technical Information of China (English)

    YANG JianWen; FENG ZuoHai; LUO XianRong; CHEN YuanRong

    2009-01-01

    Finite element modeling on a highly conceptualized 2-D model of fluid flow and heat transport is un-dertaken to simulate the paleo-hydrological system as if the Mount Ise deposits were being formed in the Mount Isa basin, Northern Australia, and to evaluate the potential of buoyancy force in driving ba-sin-scale fluid flow for the formation of sedimentary-exhalative (SEDEX) deposits. Our numerical case studies indicate that buoyancy-driven fluid flow is controlled mainly by the fault penetration depth and its spatial relation with the aquifer. Marine water recharges the basin via one fault and flows through the aquifer where it is heated from below. The heated metalliferous fluid discharges to the basin floor via the other fault. The venting fluid temperatures are computed to be in the range of 115 to 160℃, with fluid velocities of 2.6 to 4.1 m/year over a period of 1 Ma. These conditions are suitable for the formation of a Mount Isa-sized zinc deposit, provided a suitable chemical trap environment is present. Buoyancy force is therefore a viable driving mechanism for basin-scale ore-forming hydrothermal fluid migration, and it is strong enough to lead to the genesis of supergiant SEDEX deposits like the Mount Isa deposit, Northern Australia.

  10. Numerical Simulation of Inter-Flat Air Cross-Contamination under the Condition of Single-Sided Natural Ventilation

    DEFF Research Database (Denmark)

    Liu, Xiaoping; Niu, Jianlei; Perino, Marco;

    2008-01-01

    the two sides, each of which has a flat fa ade with openable windows. When the wind speed is extremely low, with doors closed and windows opened, the flats become single-sided naturally ventilated driven by buoyancy effects. The air pollutants can travel from a lower flat to a vertically adjacent upper...... flat through open windows, caused by indoor/outdoor temperature-difference induced buoyancy. Computational fluid dynamics is employed to explore the characteristics of this process. Based on the comparison with experimental data about the air flow distribution in and around a single-sided naturally...... be a major route of the air cross-contamination in high-rise residential buildings. Finally, an assessment index is proposed to evaluate the potential infection risks associated with this inter-flat air flow occurring in high-rise residential buildings....

  11. 46 CFR 160.010-5 - Buoyant apparatus with plastic foam buoyancy.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 6 2010-10-01 2010-10-01 false Buoyant apparatus with plastic foam buoyancy. 160.010-5... Vessels § 160.010-5 Buoyant apparatus with plastic foam buoyancy. (a) Buoyant apparatus with plastic foam buoyancy must have a plastic foam body with an external protective covering. The body may be reinforced...

  12. Buoyancy Effect on MHD Flow Past a Permeable Bed

    Directory of Open Access Journals (Sweden)

    S. Venkataramana

    1986-10-01

    Full Text Available In this paper, the effect of buoyancy force on the parallel flows bounded above by a rigid permeable plate which may be moving or stationary and below, by a permeable bed has been investigated. To discuss the solution, the flow region is divided into two zones. In Zone 1, the flow is laminar and is governed by the Navier-Stokes equations from the impermeable upper rigid plate to the permeable bed. In Zone 2, the flow is governed by the Darcy law in the permeable bed below the nominal surface. The expressions for velocity and temparature distributions, Slip velocity, slip temperature, mass flow rate and the rates of heat transfer coefficients are obtained. The effects of magnetic, porous, slip and buoyancy parameters and Biot number on the above physical quantities are investigated. The thickness of the boundary layer in Zone 2 has been evaluated.

  13. Buoyancy-corrected gravimetric analysis of lightly loaded filters.

    Science.gov (United States)

    Rasmussen, Pat E; Gardner, H David; Niu, Jianjun

    2010-09-01

    Numerous sources of uncertainty are associated with the gravimetric analysis of lightly loaded air filter samples (cut sizes (0.056-9.9 microm). By maintaining tight controls on humidity (within 0.5% RH of control setting) throughout pre- and postweighing at each stepwise increase in RH, it was possible to quantify error due to water absorption: 45% of the total mass change due to water absorption occurred between 16 and 50% RH, and 55% occurred between 50 and 60% RH. The buoyancy corrections ranged from -3.5 to +5.8 microg in magnitude and improved relative standard deviation (RSD) from 21.3% (uncorrected) to 5.6% (corrected) for a 7.2 microg sample. It is recommended that protocols for weighing low-mass particle samples (e.g., nanoparticle samples) should include buoyancy corrections and tight temperature/humidity controls. In some cases, conditioning times longer than 24 hr may be warranted.

  14. Design and Analysis of Typical Buoyancy Tank Riser Tensioner Systems

    Institute of Scientific and Technical Information of China (English)

    Zhuang Kang; Lusheng Jia; Liping Sun; Wenzhou Liang

    2012-01-01

    The method for design and analysis of a buoyancy tank riser tensioner system (BTRTS) was put forward in this paper,taking the free standing hybrid riser's top buoyancy tank as an example.The design procedure was discussed and was also illustrated in a flowchart,after a short description of the global arrangement,structure configuration,and the function of different types of buoyancy tanks (BT).The objective of this paper is to describe a way of developing a BT with minimal hydro force,maximal net lift,and no redundancy of comparunents.The method of determining the main dimensions of the BT,namely the length and the outer diameter,was outlined.A series of investigations was conducted for a West Africa FSHR BT design,and the effect of the ratio of the length to the outer diameter (L/D) on the hydrodynamics and the weight of the BT was discussed.The methodology of designing the internal structure of the BT was presented.The effects of the number of compartments and the dimension of the inner stem on the BT weight and strength were compared.The relationship between inner structure and the number one index of the BT as well as the riser's top tension factor (TTF) were illustrated for normal operating conditions and conditions with one or more compartments (or inner stem) damaged.A design instance was given in this paper,when L/D is 4-6,the BT weight and the drag force are compromised.When the BT is divided into 10 compartments,the riser TTF will reach the maximum value,and the ratio of the stem OD to shell OD is about 0.3.A global strength analysis method of the BT and the main load case matrix was also included in the paper,together with the local strength analysis of the buoyancy tank's pad-eye assembly.

  15. Buoyed by geophysics : geophysics, just-in-time procurement help save millions on Ekwan pipeline buoyancy control

    Energy Technology Data Exchange (ETDEWEB)

    Roche, P.

    2005-09-01

    Large-diameter natural gas pipelines buried in wet muskeg have the potential to rise to the surface due to buoyancy. Until recently, the most reliable method to prevent this was to attach specially manufactured bolt-on concrete weights at closely spaced intervals. However, these weights significantly increase capital budgets by millions of dollars because each weight weighs 2,540 kg and costs $1,000. A less costly alternative for buoyancy control in shallow muskeg is for the contractor to simply dig a deeper ditch. Another option is to hold down the pipeline by polyester straps attached to screw anchors. The challenge of applying these less costly options is that heavy equipment cannot be brought to the site to determine ground conditions until after all procurement, assessment and design is completed. Engineers must therefore select a buoyancy control measure based only on air photos and possibly a few drill holes. However, air photos do not indicate the depth of muskeg. Although some muskeg areas may turn out to be thick enough to avoid buoyancy control altogether, once construction is underway, it is too late to opt for cheaper alternatives. EnCana Corporation's 24-inch Ekwan pipeline was recently constructed through a remote area of British Columbia to connect the Greater Sierra natural gas discovery to a tie-in point on Nova Gas Transmission's northwest mainline. Air photos indicated that half of the route was through muskeg. AMEC E and C Services Inc. was responsible for the engineering and management of the project. The company used a combination of geophysical techniques to learn about the ground conditions. Toboggan mounted portable equipment was hauled by snowmobiles along trails made earlier by the survey crews. Ground penetrating radar assessed the muskeg thickness. Fixed frequency electromagnetic surveys also enhanced the results of the ground penetrating radar. The number of bolt-on weights was reduced from 9,000 to 3,700, a savings of $3

  16. Exploring a Detonation Nature of Mesoscopic Perturbations and Ejecta Formation from the Mesoscale Probing of the PBX-driven Liners

    Science.gov (United States)

    Plaksin, Igor; Guiruis, Raafat; Rodrigues, Luis; Mendes, Ricardo; Plaksin, Svyatoslav; Fernandes, Eduardo; Ferreira, Claudia

    2015-06-01

    Ejecting debris from free surface of liner is of considerable interest at optimization of explosive devices, in which the PBX-driven liner effects shock compression of gaseous matter. Following factors were historically considered as main drivers of material ejection: granular microstructure of liner material, roughness and surface defects of liner, and shock pressure time history in PBX-driven liner. In contrast to existing models, we are considering the small scale fluctuations of detonation flow as probable dominating factor of surface jetting in the PBX-driven collapsing liners. Obtained experimental evidence is indicative that jetting from the liners is caused by meso-scale perturbations of PBX detonations, which are identified as (1) ejecta of overdriven detonation products through detonation front, (2) ejecta-driven detonation cells, and (3) galloping detonation front motion. Spatially resolved scenarios of each of phenomena (1-3) were obtained in experiments with copper-liners and HMX-based PBXs fabricated on maximum packing density of crystalline constituents. Both the DRZ-induced perturbations translated to a PBX-driven liner and the ejected debris were recorded and quantitatively measured in the mesoscale range with application of the 96-channel optical analyzer MCOA-UC. Work was supported by the ONR and ONR Global Grants N00014-12-1-0477 and N62909-12-1-7131 with Drs. Clifford Bedford and John Zimmerman Program Managers.

  17. Buoyancy Effects on Flow Structure and Instability of Low-Density Gas Jets

    Science.gov (United States)

    Pasumarthi, Kasyap Sriramachandra

    2004-01-01

    A low-density gas jet injected into a high-density ambient gas is known to exhibit self-excited global oscillations accompanied by large vortical structures interacting with the flow field. The primary objective of the proposed research is to study buoyancy effects on the origin and nature of the flow instability and structure in the near-field of low-density gas jets. Quantitative rainbow schlieren deflectometry, Computational fluid dynamics (CFD) and Linear stability analysis were the techniques employed to scale the buoyancy effects. The formation and evolution of vortices and scalar structure of the flow field are investigated in buoyant helium jets discharged from a vertical tube into quiescent air. Oscillations at identical frequency were observed throughout the flow field. The evolving flow structure is described by helium mole percentage contours during an oscillation cycle. Instantaneous, mean, and RMS concentration profiles are presented to describe interactions of the vortex with the jet flow. Oscillations in a narrow wake region near the jet exit are shown to spread through the jet core near the downstream location of the vortex formation. The effects of jet Richardson number on characteristics of vortex and flow field are investigated and discussed. The laminar, axisymmetric, unsteady jet flow of helium injected into air was simulated using CFD. Global oscillations were observed in the flow field. The computed oscillation frequency agreed qualitatively with the experimentally measured frequency. Contours of helium concentration, vorticity and velocity provided information about the evolution and propagation of vortices in the oscillating flow field. Buoyancy effects on the instability mode were evaluated by rainbow schlieren flow visualization and concentration measurements in the near-field of self-excited helium jets undergoing gravitational change in the microgravity environment of 2.2s drop tower at NASA John H. Glenn Research Center. The jet

  18. Laboratory experiments with a buoyancy forced circulation in a rotating basin

    Science.gov (United States)

    Vreugdenhil, Catherine; Griffiths, Ross; Gayen, Bishakhdatta

    2016-11-01

    We consider the relative influence of buoyancy forcing and Coriolis effects on convection forced by a differential in heating at a horizontal surface in a rectangular basin. Laboratory experiments with water are reported for a rotating f-plane basin and a range of Ekman number E = 2 ×10-7 - 1 ×10-5 . Heating is applied over half of the base as a uniform flux and cooling applied over the other half as a uniform temperature, resulting in a flux Rayleigh number RaF = O (1014) large enough to ensure turbulent convection, where RaF defined in terms of domain length L. Compared to the non-rotating circulation where Nusselt number (a measure of the convective to conductive heat transfer) scales as Nu RaF1 / 6 , the strongly rotating regime is determined by a geostrophic balance of the larger scales of horizontal flow in the inviscid thermal boundary with Nu Ro 1 / 6 , where Ro =B 1 / 2 / (f 3 / 2 L) is the natural Rossby number (B is buoyancy flux per unit area and f is Coriolis parameter). We also find evidence for a further transition into a regime where the circulation is dominated by deep 'chimney' convection in a field of small vortical plumes and Nu is more weakly dependent on rotation.

  19. A 1 kW-class multi-stage heat-driven thermoacoustic cryocooler system operating at liquefied natural gas temperature range

    Science.gov (United States)

    Zhang, L. M.; Hu, J. Y.; Wu, Z. H.; Luo, E. C.; Xu, J. Y.; Bi, T. J.

    2015-07-01

    This article introduces a multi-stage heat-driven thermoacoustic cryocooler capable of reaching cooling capacity about 1 kW at liquefied natural gas temperature range without any moving mechanical parts. The cooling system consists of an acoustically resonant double-acing traveling wave thermoacoustic heat engine and three identical pulse tube coolers. Unlike other traditional traveling wave thermoacoustic heat engines, the acoustically resonant double-acting thermoacoustic heat engine is a closed-loop configuration consists of three identical thermoacoustic conversion units. Each pulse tube cooler is bypass driven by one thermoacoustic heat engine unit. The device is acoustically completely symmetric and therefore "self-matching" for efficient traveling-wave thermoacoustic conversion. In the experiments, with 7 MPa helium gas as working gas, when the heating temperature reaches 918 K, total cooling capacity of 0.88 kW at 110 K is obtained with a resonant frequency of about 55 Hz. When the heating temperature is 903 K, a maximum total cooling capacity at 130 K of 1.20 kW is achieved, with a thermal-to-cold exergy efficiency of 8%. Compared to previously developed heat-driven thermoacoustic cryocoolers, this device has higher thermal efficiency and higher power density. It shows a good prospect of application in the field of natural gas liquefaction and recondensation.

  20. A continuous and prognostic convection scheme based on buoyancy, PCMT

    Science.gov (United States)

    Guérémy, Jean-François; Piriou, Jean-Marcel

    2016-04-01

    A new and consistent convection scheme (PCMT: Prognostic Condensates Microphysics and Transport), providing a continuous and prognostic treatment of this atmospheric process, is described. The main concept ensuring the consistency of the whole system is the buoyancy, key element of any vertical motion. The buoyancy constitutes the forcing term of the convective vertical velocity, which is then used to define the triggering condition, the mass flux, and the rates of entrainment-detrainment. The buoyancy is also used in its vertically integrated form (CAPE) to determine the closure condition. The continuous treatment of convection, from dry thermals to deep precipitating convection, is achieved with the help of a continuous formulation of the entrainment-detrainment rates (depending on the convective vertical velocity) and of the CAPE relaxation time (depending on the convective over-turning time). The convective tendencies are directly expressed in terms of condensation and transport. Finally, the convective vertical velocity and condensates are fully prognostic, the latter being treated using the same microphysics scheme as for the resolved condensates but considering the convective environment. A Single Column Model (SCM) validation of this scheme is shown, allowing detailed comparisons with observed and explicitly simulated data. Four cases covering the convective spectrum are considered: over ocean, sensitivity to environmental moisture (S. Derbyshire) non precipitating shallow convection to deep precipitating convection, trade wind shallow convection (BOMEX) and strato-cumulus (FIRE), together with an entire continental diurnal cycle of convection (ARM). The emphasis is put on the characteristics of the scheme which enable a continuous treatment of convection. Then, a 3D LAM validation is presented considering an AMMA case with both observations and a CRM simulation using the same initial and lateral conditions as for the parameterized one. Finally, global

  1. Using surface integrals for checking the Archimedes' law of buoyancy

    OpenAIRE

    Lima, F. M. S.

    2011-01-01

    A mathematical derivation of the force exerted by an \\emph{inhomogeneous} (i.e., compressible) fluid on the surface of an \\emph{arbitrarily-shaped} body immersed in it is not found in literature, which may be attributed to our trust on Archimedes' law of buoyancy. However, this law, also known as Archimedes' principle (AP), does not yield the force observed when the body is in contact to the container walls, as is more evident in the case of a block immersed in a liquid and in contact to the ...

  2. Rethinking the process of detrainment: jets in obstructed natural flows

    Science.gov (United States)

    Mossa, Michele; de Serio, Francesca

    2016-12-01

    A thorough understanding of the mixing and diffusion of turbulent jets released in porous obstructions is still lacking in literature. This issue is undoubtedly of interest because it is not strictly limited to vegetated flows, but also includes outflows which come from different sources and which spread among oyster or wind farms, as well as aerial pesticide treatments sprayed onto orchards. The aim of the present research is to analyze this process from a theoretical point of view. Specifically, by examining the entrainment coefficient, it is deduced that the presence of a canopy prevents a momentum jet from having an entrainment process, but rather promotes its detrainment. In nature, detrainment is usually associated with buoyancy-driven flows, such as plumes or density currents flowing in a stratified environment. The present study proves that detrainment occurs also when a momentum-driven jet is issued in a not-stratified obstructed current, such as a vegetated flow.

  3. Equilibrium models of coronal loops that involve curvature and buoyancy

    CERN Document Server

    Hindman, Bradley W

    2013-01-01

    We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.

  4. Equilibrium Models of Coronal Loops That Involve Curvature and Buoyancy

    Science.gov (United States)

    Hindman, Bradley W.; Jain, Rekha

    2013-12-01

    We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.

  5. Relations between morphology, buoyancy and energetics of requiem sharks

    Science.gov (United States)

    Papastamatiou, Yannis P.

    2016-01-01

    Sharks have a distinctive shape that remained practically unchanged through hundreds of millions of years of evolution. Nonetheless, there are variations of this shape that vary between and within species. We attempt to explain these variations by examining the partial derivatives of the cost of transport of a generic shark with respect to buoyancy, span and chord of its pectoral fins, length, girth and body temperature. Our analysis predicts an intricate relation between these parameters, suggesting that ectothermic species residing in cooler temperatures must either have longer pectoral fins and/or be more buoyant in order to maintain swimming performance. It also suggests that, in general, the buoyancy must increase with size, and therefore, there must be ontogenetic changes within a species, with individuals getting more buoyant as they grow. Pelagic species seem to have near optimally sized fins (which minimize the cost of transport), but the majority of reef sharks could have reduced the cost of transport by increasing the size of their fins. The fact that they do not implies negative selection, probably owing to decreased manoeuvrability in confined spaces (e.g. foraging on a reef). PMID:27853556

  6. Multidisciplinary design approach and safety analysis of ADSR cooled by buoyancy driven flows

    NARCIS (Netherlands)

    Ceballos Castillo, C.A.

    2007-01-01

    Transmutation is useful to reduce the storing time and the amount of nuclear waste to be stored in the geological repository. Transmutation can be achieved in all types of reactors: thermal systems, fast systems, critical and subcritical systems. Fast spectrum systems have significant advantages bec

  7. Microliter-bioreactor array with buoyancy-driven stirring for human hematopoietic stem cell culture

    OpenAIRE

    Luni, Camilla; Feldman, Hope C.; Pozzobon, Michela; De Coppi, Paolo; Meinhart, Carl D.; Elvassore, Nicola

    2010-01-01

    This work presents the development of an array of bioreactors where finely controlled stirring is provided at the microliter scale (100–300 μl). The microliter-bioreactor array is useful for performing protocol optimization in up to 96 parallel experiments of hematopoietic stem cell (HSC) cultures. Exploring a wide range of experimental conditions at the microliter scale minimizes cost and labor. Once the cell culture protocol is optimized, it can be applied to large-scale bioreactors for ste...

  8. Study on buoyancy convection phenomenon in the crystal growth process

    Institute of Scientific and Technical Information of China (English)

    DUAN Li; KANG Qi

    2009-01-01

    Real-time phase shift Mach-Zehnder interference technique,imaging technique,and computer image processing technique were combined to perform a real-time diagnosis of NaCIO3 crystal,which described both the dissolution process end the crystallization process of the NaCIO3 crystal in real-time condition.The dissolution fringes and the growth fringes in the process were obtained.Moreover,a distribution of concentration field in this process was obtained by inversion calculation.Finally,the buoyancy convection phenomenon caused by gravity in the crystal growth process was analyzed.The results showed that this convection phenomenon directly influences the growth rate of each crystal face in the crystal.

  9. Study on buoyancy convection phenomenon in the crystal growth process

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Real-time phase shift Mach-Zehnder interference technique, imaging technique, and computer image processing technique were combined to perform a real-time diagnosis of NaClO3 crystal, which de- scribed both the dissolution process and the crystallization process of the NaClO3 crystal in real-time condition. The dissolution fringes and the growth fringes in the process were obtained. Moreover, a distribution of concentration field in this process was obtained by inversion calculation. Finally, the buoyancy convection phenomenon caused by gravity in the crystal growth process was analyzed. The results showed that this convection phenomenon directly influences the growth rate of each crystal face in the crystal.

  10. Seasonal dynamics of fish assemblages on breakwaters and natural rocky reefs in a temperate estuary: consistent assemblage differences driven by sub-adults.

    Science.gov (United States)

    Fowler, Ashley M; Booth, David J

    2013-01-01

    Development of infrastructure around cities is rapidly increasing the amount of artificial substrate (termed artificial reef, 'AR') in coastal marine habitats. However, effects of ARs on marine communities remain unknown, because it is unclear whether ARs can maintain similar communities to natural reefs. We investigated whether well-established (> 30 years old) breakwaters could consistently approximate fish assemblages on interspersed rocky reefs in a temperate estuary over 6 consecutive seasons using regular visual surveys between June 2009 (winter) and November 2010 (spring). We examined whether assemblage differences between reef types were driven by differences in juvenile recruitment, or were related to differences in older life-stages. Assemblages on both reef types were dominated by juveniles (61% of individuals) and sub-adults (34% of individuals). Seasonal fluctuations in assemblage parameters (species richness, diversity, sub-adult abundance) were similar between reef types, and levels of species diversity and assemblage composition were generally comparable. However, abundance and species richness were consistently higher (1.9-7.6 and 1.3-2.6 times, respectively) on breakwaters. These assemblage differences could not be explained by differences in juvenile recruitment, with seasonal patterns of recruitment and juvenile species found to be similar between reef types. In contrast, abundances of sub-adults were consistently higher (1.1-12 times) at breakwaters, and assemblage differences appeared to be driven by this life-stage. Our results indicate that breakwaters in temperate estuaries are capable of supporting abundant and diverse fish assemblages with similar recruitment process to natural reefs. However, breakwaters may not approximate all aspects of natural assemblage structure, with differences maintained by a single-life stage in some cases.

  11. Statistical Change Detection for Diagnosis of Buoyancy Element Defects on Moored Floating Vessels

    DEFF Research Database (Denmark)

    Blanke, Mogens; Fang, Shaoji; Galeazzi, Roberto;

    2012-01-01

    Floating platforms with mooring systems are used extensively in off-shore operations. Part of the mooring systems are underwater buoyancy elements that are attached to the mooring lines. Loss or damage of a buoyancy element is invisible but changes the characteristics of the mooring system...

  12. Niche-driven evolution of metabolic and life-history strategies in natural and domesticated populations of Saccharomyces cerevisiae

    Directory of Open Access Journals (Sweden)

    Sicard Delphine

    2009-12-01

    Full Text Available Abstract Background Variation of resource supply is one of the key factors that drive the evolution of life-history strategies, and hence the interactions between individuals. In the yeast Saccharomyces cerevisiae, two life-history strategies related to different resource utilization have been previously described in strains from different industrial origins. In this work, we analyzed metabolic traits and life-history strategies in a broader collection of yeast strains sampled in various ecological niches (forest, human body, fruits, laboratory and industrial environments. Results By analysing the genetic and plastic variation of six life-history and three metabolic traits, we showed that S. cerevisiae populations harbour different strategies depending on their ecological niches. On one hand, the forest and laboratory strains, referred to as extreme "ants", reproduce quickly, reach a large carrying capacity and a small cell size in fermentation, but have a low reproduction rate in respiration. On the other hand, the industrial strains, referred to as extreme "grasshoppers", reproduce slowly, reach a small carrying capacity but have a big cell size in fermentation and a high reproduction rate in respiration. "Grasshoppers" have usually higher glucose consumption rate than "ants", while they produce lower quantities of ethanol, suggesting that they store cell resources rather than secreting secondary products to cross-feed or poison competitors. The clinical and fruit strains are intermediate between these two groups. Conclusions Altogether, these results are consistent with a niche-driven evolution of S. cerevisiae, with phenotypic convergence of populations living in similar habitat. They also revealed that competition between strains having contrasted life-history strategies ("ants" and "grasshoppers" seems to occur at low frequency or be unstable since opposite life-history strategies appeared to be maintained in distinct ecological niches.

  13. Importance of initial buoyancy field on evolution of mantle thermal structure: Implications of surface boundary conditions

    Directory of Open Access Journals (Sweden)

    Petar Glišović

    2015-01-01

    Full Text Available Although there has been significant progress in the seismic imaging of mantle heterogeneity, the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models. To address this question, we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns. A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow, without imposing prescribed surface velocities (i.e., plate-like boundary condition. As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip (rigid boundary condition. A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved, and its geographical location is fixed during the evolution of mantle flow. Considering the impact of different assumed surface boundary conditions (rigid and plate-like on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure. Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term, stable pattern of thermal heterogeneity in the lowermost mantle that resembles the present-day Large Low Shear Velocity Provinces (LLSVPs, especially below the Pacific. The evolution of subduction zones may be, however, influenced by the mantle-wide flow driven by deeply-rooted and long-lived superplumes since Archean times. These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique

  14. NUMERICAL MODELLING OF VELOCITY AND TEMPERATURE DISTRIBUTIONS OF THE BUOYANCY CONVECTION EFFECT IN KNbO3 MELT

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    @@ Numerical modelling of velocity and temperature fields in high-temperature KNbO3 melt of a loop-shaped Pt wire heater is carried out by using the commercial com putational code ANSYS for the mathematical solution of the governing equations.Based on the experimental boundary conditions and the Boussinesq approximation,the numerical modelling of a steady and two-dimensional model is applied to study the process under consideration of the buoyancy-driven convection condition. The result is compared with the previous experimental and theoretical data obtained in our laboratory, and the former is in agreement with the latter. Thus a theoretical guide for reasonable growth conditions is provided by studying in depth the real fluid flow effects in the crystal growth from the melt.

  15. Long-term natural remediation process in textile dye-polluted river sediment driven by bacterial community changes.

    Science.gov (United States)

    Ito, Tsukasa; Adachi, Yusuke; Yamanashi, Yu; Shimada, Yosuke

    2016-09-01

    The textile and dyeing industries are major sources of environmental water pollution all over the world. The textile wastewater effluents discharged into rivers often appear dark red-purple in color due to azo dyes, which can be transformed into carcinogenic aromatic amines. The chemicals used in dyeing are not readily degraded in nature and thus precipitate in river sediment. However, little is known about how dyeing chemicals affect river sediment and river water or how long they persist because they are difficult to monitor. To assess undetectable dyes and byproducts in river sediments, we evaluated the potential of river sediment bacteria to degrade dyes and aromatic amines. We describe the natural remediation of river sediment long-contaminated by textile dyeing effluent. After cessation of wastewater discharge, the dye-degradation potential decreased, and the aromatic amine-degradation potential increased initially and then declined over time. The changes in degradation potential were consistent with changes in the sediment bacterial community. The transition occurred on the order of years. Our data strongly suggest that dyes remained in the river sediment and that aromatic amines were produced even in transparent- and no longer colored-river water, but these chemicals were degraded by the changing sediment bacteria. Time-course monitoring of the degradation activities of key bacteria thus enables assessment of the fate of dye pollutants in river sediments.

  16. The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster

    CERN Document Server

    Zhuravleva, I; Arevalo, P; Schekochihin, A A; Forman, W R; Allen, S W; Simionescu, A; Sunyaev, R; Vikhlinin, A; Werner, N

    2016-01-01

    Cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft- and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ~ 8-70 kpc scales in the inner region have an isobaric nature, i.e., are consistent with slow displacements of the gas in pressure equilibrium with ambient medium. Observed variance translates to the ratio of non-thermal to thermal energy of ~13 per cent. In the region dominated by weak "ripples", about half of the total variance is also associated with isobaric perturbations on scales ~ a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should fi...

  17. The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster

    Science.gov (United States)

    Zhuravleva, I.; Churazov, E.; Arévalo, P.; Schekochihin, A. A.; Forman, W. R.; Allen, S. W.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.

    2016-05-01

    Cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft- and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ˜8-70 kpc scales in the core have an isobaric nature, i.e. are consistent with subsonic displacements of the gas in pressure equilibrium with the ambient medium. The observed variance translates to the ratio of energy in perturbations to thermal energy of ˜13 per cent. In the region dominated by weak `ripples', about half of the total variance is associated with isobaric perturbations on scales of a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should first go into bubbles rather than into shocks. Using simulations of a shock propagating through the Perseus atmosphere, we found that models reproducing the observed features of a central shock have more than 50 per cent of the AGN-injected energy associated with the bubble enthalpy and only about 20 per cent is carried away with the shock. Such energy partition is consistent with the AGN-feedback model, mediated by bubbles of relativistic plasma, and supports the importance of turbulence in the cooling-heating balance.

  18. Long-Wavelength Rupturing Instability in Surface-Tension-Driven Benard Convection

    Science.gov (United States)

    Swift, J. B.; Hook, Stephen J. Van; Becerril, Ricardo; McCormick, W. D.; Swinney, H. L.; Schatz, Michael F.

    1999-01-01

    A liquid layer with a free upper surface and heated from below is subject to thermocapillary-induced convective instabilities. We use very thin liquid layers (0.01 cm) to significantly reduce buoyancy effects and simulate Marangoni convection in microgravity. We observe thermocapillary-driven convection in two qualitatively different modes, short-wavelength Benard hexagonal convection cells and a long-wavelength interfacial rupturing mode. We focus on the long-wavelength mode and present experimental observations and theoretical analyses of the long-wavelength instability. Depending on the depths and thermal conductivities of the liquid and the gas above it, the interface can rupture downwards and form a dry spot or rupture upwards and form a high spot. Linear stability theory gives good agreement to the experimental measurements of onset as long as sidewall effects are taken into account. Nonlinear theory correctly predicts the subcritical nature of the bifurcation and the selection between the dry spot and high spots.

  19. Effects of Lateral Window Position and Wind Direction on Wind-Driven Natural Cross Ventilation of a Building: A Computational Approach

    Directory of Open Access Journals (Sweden)

    M. Z. I. Bangalee

    2014-01-01

    Full Text Available Energy is saved when an effective natural ventilation system can provide comfort air to the occupants in a building by replacing a mechanical ventilation system. It also minimizes the risk of the environmental pollution and the global warming. A one story, full scale building was considered to carry out a comparative study of three different cases of wind-driven natural (WDN cross ventilation with the help of computational fluid dynamics (CFD. In each case, the location of window was changed in lateral direction to predict the probable position for optimum ventilation performance and the angle of wind was varied to check the sensitivity of the wind direction on the flow field. After validating the current methodology through two satisfactory comparisons with the experimental investigations, the governing equations subjected to the corresponding boundary conditions were solved using commercial software and then the results were analyzed. A better location for the windows in each case was proposed. The ventilation purpose was served quite well even if the wind angle was changed in a moderate range from the original design. Furthermore, the velocity components, ventilation rate, surface pressure, ventilation time, and so forth in each case were investigated and compared extensively with those in other cases.

  20. Climate-driven increase of natural wetland methane emissions offset by human-induced wetland reduction in China over the past three decades

    Science.gov (United States)

    Zhu, Qiuan; Peng, Changhui; Liu, Jinxun; Jiang, Hong; Fang, Xiuqin; Chen, Huai; Niu, Zhenguo; Gong, Peng; Lin, Guanghui; Wang, Meng; Wang, Han; Yang, Yanzheng; Chang, Jie; Ge, Ying; Xiang, Wenhua; Deng, Xiangwen; He, Jin-Sheng

    2016-11-01

    Both anthropogenic activities and climate change can affect the biogeochemical processes of natural wetland methanogenesis. Quantifying possible impacts of changing climate and wetland area on wetland methane (CH4) emissions in China is important for improving our knowledge on CH4 budgets locally and globally. However, their respective and combined effects are uncertain. We incorporated changes in wetland area derived from remote sensing into a dynamic CH4 model to quantify the human and climate change induced contributions to natural wetland CH4 emissions in China over the past three decades. Here we found that human-induced wetland loss contributed 34.3% to the CH4 emissions reduction (0.92 TgCH4), and climate change contributed 20.4% to the CH4 emissions increase (0.31 TgCH4), suggesting that decreasing CH4 emissions due to human-induced wetland reductions has offset the increasing climate-driven CH4 emissions. With climate change only, temperature was a dominant controlling factor for wetland CH4 emissions in the northeast (high latitude) and Qinghai-Tibet Plateau (high altitude) regions, whereas precipitation had a considerable influence in relative arid north China. The inevitable uncertainties caused by the asynchronous for different regions or periods due to inter-annual or seasonal variations among remote sensing images should be considered in the wetland CH4 emissions estimation.

  1. Consistent Two-Equation Closure Modelling for Atmospheric Research: Buoyancy and Vegetation Implementations

    DEFF Research Database (Denmark)

    Sogachev, Andrey; Kelly, Mark C.; Leclerc, Monique Y.

    2012-01-01

    A self-consistent two-equation closure treating buoyancy and plant drag effects has been developed, through consideration of the behaviour of the supplementary equation for the length-scale-determining variable in homogeneous turbulent flow. Being consistent with the canonical flow regimes of grid......}$$ is the dissipation rate of turbulent kinetic energy, E, and $${\\omega = \\varepsilon/E}$$ is the specific dissipation), comparing the suggested buoyancy-modified closure against Monin–Obukhov similarity theory. Assessment of the closure implementing both buoyancy and plant drag together has been done, comparing...

  2. Basal buoyancy and fast-moving glaciers: in defense of analytic force balance

    Science.gov (United States)

    van der Veen, C. J.

    2016-06-01

    The geometric approach to force balance advocated by T. Hughes in a series of publications has challenged the analytic approach by implying that the latter does not adequately account for basal buoyancy on ice streams, thereby neglecting the contribution to the gravitational driving force associated with this basal buoyancy. Application of the geometric approach to Byrd Glacier, Antarctica, yields physically unrealistic results, and it is argued that this is because of a key limiting assumption in the geometric approach. A more traditional analytic treatment of force balance shows that basal buoyancy does not affect the balance of forces on ice streams, except locally perhaps, through bridging effects.

  3. Control of a Buoyancy-Based Pilot Underwater Lifting Body

    Directory of Open Access Journals (Sweden)

    Finn Haugen

    2010-04-01

    Full Text Available This paper is about position control of a specific small-scale pilot underwater lifting body where the lifting force stems from buoyancy adjusted with an air pocket in the lifting body. A mathematical model is developed to get a basis for a simulator which is used for testing and for designing the control system, including tuning controller parameters. A number of different position controller solutions were tried both on a simulator and on the physical system. Successful control on both the simulator and the physical system was obtained with cascade control based on feedback from measured position and height of the air pocket in the lifting body. The primary and the secondary controllers of the cascade control system were tuned using Skogestad's model-based PID tuning rules. Feedforward from estimated load force was implemented in combination with the cascade control system, giving a substantial improvement of the position control system, both with varying position reference and varying disturbance (load mass.

  4. Using surface integrals for checking the Archimedes' law of buoyancy

    CERN Document Server

    Lima, F M S

    2011-01-01

    A mathematical derivation of the force exerted by an \\emph{inhomogeneous} (i.e., compressible) fluid on the surface of an \\emph{arbitrarily-shaped} body immersed in it is not found in literature, which may be attributed to our trust on Archimedes' law of buoyancy. However, this law, also known as Archimedes' principle (AP), does not yield the force observed when the body is in contact to the container walls, as is more evident in the case of a block immersed in a liquid and in contact to the bottom, in which a \\emph{downward} force that \\emph{increases with depth} is observed. In this work, by taking into account the surface integral of the pressure force exerted by a fluid over the surface of a body, the general validity of AP is checked. For a body fully surrounded by a fluid, homogeneous or not, a gradient version of the divergence theorem applies, yielding a volume integral that simplifies to an upward force which agrees to the force predicted by AP, as long as the fluid density is a \\emph{continuous func...

  5. Buoyancy and Penrose Process Produce Jets from Rotating Black Holes

    CERN Document Server

    Semenov, V S; Heyn, M F

    2014-01-01

    The exact mechanism by which astrophysical jets are formed is still unknown. It is believed that necessary elements are a rotating (Kerr) black hole and a magnetised accreting plasma. We model the accreting plasma as a collection of magnetic flux tubes/strings. If such a tube falls into a Kerr black hole, then the leading portion loses angular momentum and energy as the string brakes, and to compensate for this loss, momentum and energy is redistributed to the trailing portion of the tube.} {We found that buoyancy creates a pronounced helical magnetic field structure aligned with the spin axis. Along the field lines, the plasma is centrifugally accelerated close to the speed of light. This process leads to unlimited stretching of the flux tube since one part of the tube continues to fall into the black hole and simultaneously the other part of the string is pushed outward. Eventually, reconnection cuts the tube, the inner part is filled with new material and the outer part forms a collimated bubble-structured...

  6. Neutral Buoyancy Simulator - NB32 - Large Space Structure

    Science.gov (United States)

    1980-01-01

    The Hubble Space Telescope (HST) is a cooperative program of the European Space Agency (ESA) and the National Aeronautical and Space Administration (NASA) to operate a long-lived space-based observatory; it was the flagship mission of NASA's Great Observatories program. The HST program began as an astronomical dream in the 1940s. During the 1970s and 1980s, HST was finally designed and built; and it finally became operational in the 1990s. HST was deployed into a low-Earth orbit on April 25, 1990 from the cargo bay of the Space Shuttle Discovery (STS-31). The design of the HST took into consideration its length of service and the necessity of repairs and equipment replacement by making the body modular. In doing so, subsequent shuttle missions could recover the HST, replace faulty or obsolete parts and be re-released. MSFC's Neutral Buoyancy Simulator served as the training facility for shuttle astronauts for Hubble related missions. Shown is astronaut Sharnon Lucid having her life support system being checked prior to entering the NBS to begin training on the space telescope axial scientific instrument changeout.

  7. Temporal Genetic Variance and Propagule-Driven Genetic Structure Characterize Naturalized Rainbow Trout (Oncorhynchus mykiss) from a Patagonian Lake Impacted by Trout Farming

    Science.gov (United States)

    Seeb, Lisa W.; Seeb, James E.; Arismendi, Ivan; Hernández, Cristián E.; Gajardo, Gonzalo; Galleguillos, Ricardo; Cádiz, Maria I.; Musleh, Selim S.

    2015-01-01

    Knowledge about the genetic underpinnings of invasions—a theme addressed by invasion genetics as a discipline—is still scarce amid well documented ecological impacts of non-native species on ecosystems of Patagonia in South America. One of the most invasive species in Patagonia’s freshwater systems and elsewhere is rainbow trout (Oncorhynchus mykiss). This species was introduced to Chile during the early twentieth century for stocking and promoting recreational fishing; during the late twentieth century was reintroduced for farming purposes and is now naturalized. We used population- and individual-based inference from single nucleotide polymorphisms (SNPs) to illuminate three objectives related to the establishment and naturalization of Rainbow Trout in Lake Llanquihue. This lake has been intensively used for trout farming during the last three decades. Our results emanate from samples collected from five inlet streams over two seasons, winter and spring. First, we found that significant intra- population (temporal) genetic variance was greater than inter-population (spatial) genetic variance, downplaying the importance of spatial divergence during the process of naturalization. Allele frequency differences between cohorts, consistent with variation in fish length between spring and winter collections, might explain temporal genetic differences. Second, individual-based Bayesian clustering suggested that genetic structure within Lake Llanquihue was largely driven by putative farm propagules found at one single stream during spring, but not in winter. This suggests that farm broodstock might migrate upstream to breed during spring at that particular stream. It is unclear whether interbreeding has occurred between “pure” naturalized and farm trout in this and other streams. Third, estimates of the annual number of breeders (Nb) were below 73 in half of the collections, suggestive of genetically small and recently founded populations that might experience

  8. TAO/TRITON, RAMA, and PIRATA Buoys, 5-Day, Buoyancy Flux

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This dataset has 5-day Buoyancy Flux data from the TAO/TRITON (Pacific Ocean, http://www.pmel.noaa.gov/tao/), RAMA (Indian Ocean,...

  9. Annual and seasonal mean buoyancy fluxes for the tropical Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Prasad, T.G.

    INSAT-derived monthly mean precipitation, combined with estimates of evaporation from COADS, are used to prepare the annual mean and seasonal distributions of evaporation-precipitation (E-P)) and buoyancy fluxes for the tropical Indian Ocean...

  10. The Role of Magnetic Buoyancy in a Babcock-Leighton Type Solar Dynamo

    Indian Academy of Sciences (India)

    Dibyendu Nandy; Arnab Rai Choudhuri

    2000-09-01

    We study the effects of incorporating magnetic buoyancy in a model of the solar dynamo—which draws inspiration from the Babcock-Leighton idea of surface processes generating the poloidal field. We present our main results here.

  11. Maximum acceptable inherent buoyancy limit for aircrew/passenger helicopter immersion suit systems.

    Science.gov (United States)

    Brooks, C J

    1988-12-01

    Helicopter crew and passengers flying over cold water wear immersion suits to provide hypothermic protection in case of ditching in cold water. The suits and linings have trapped air in the material to provide the necessary insulation and are thus very buoyant. By paradox, this buoyancy may be too much for a survivor to overcome in escaping from the cabin of a rapidly sinking inverted helicopter. The Canadian General Standard Board requested that research be conducted to investigate what should be the maximum inherent buoyancy in an immersion suit that would not inhibit escape, yet would provide adequate thermal insulation. This experiment reports on 12 subjects who safely escaped with 146N (33 lbf) of added buoyancy from a helicopter underwater escape trainer. It discusses the logic for and recommendation that the inherent buoyancy in a helicopter crew/passenger immersion suit system should not exceed this figure.

  12. Buoyancy package for self-contained acoustic doppler current profiler mooring

    Digital Repository Service at National Institute of Oceanography (India)

    Venkatesan, R.; Krishnakumar, V.

    A buoyancy package for self-contained Acoustic Doppler Current Profiler(SC-ADCP 1200 RD instruments USA) was designed and fabricated indigenously, for subsurface mooring in coastal waters. The system design is discussed. The design to keep SC...

  13. Effect of Thermal Buoyancy on Fluid Flow and Inclusion Motion in Tundish without Flow Control Devices--Part Ⅰ: Fluid Flow

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li-feng; ZHI Jian-jun; MOU Ji-ning; CUI Jian

    2005-01-01

    The κ-ε two-equation model is used to simulate the fluid flow in the continuous casting tundish coupling with the effect of thermal buoyancy. The natural convection induced by the thermal buoyancy generates an upward flow pattern especially at the outlet zone, and has little effect on the fluid flow in the inlet zone. The maximum viscosity is 700 times larger than the laminar viscosity, which indicates the strong turbulent flow in the tundish. The maximum temperature difference in the whole tundish is 8.2 K. The temperature near the stopper rod and the short wall is obviously lower than that in the inlet zone. The existence of the stopper rod has a big effect on the fluid flow entering the SEN and the mold. All the characteristics of the tundish geometry should be considered to accurately simulate the fluid flow in the tundish.

  14. Neutral Buoyancy Simultor (NBS) NB-1 Large Mass Transfer simulation

    Science.gov (United States)

    1980-01-01

    Once the United States' space program had progressed from Earth's orbit into outerspace, the prospect of building and maintaining a permanent presence in space was realized. To accomplish this feat, NASA launched a temporary workstation, Skylab, to discover the effects of low gravity and weightlessness on the human body, and also to develop tools and equipment that would be needed in the future to build and maintain a more permanent space station. The structures, techniques, and work schedules had to be carefully designed to fit this unique construction site. The components had to be lightweight for transport into orbit, yet durable. The station also had to be made with removable parts for easy servicing and repairs by astronauts. All of the tools necessary for service and repairs had to be designed for easy manipulation by a suited astronaut. And construction methods had to be efficient due to limited time the astronauts could remain outside their controlled environment. In lieu of all the specific needs for this project, an environment on Earth had to be developed that could simulate a low gravity atmosphere. A Neutral Buoyancy Simulator (NBS) was constructed by NASA Marshall Space Flight Center (MSFC) in 1968. Since then, NASA scientists have used this facility to understand how humans work best in low gravity and also provide information about the different kinds of structures that can be built. Pictured is a Massachusetts Institute of Technology (MIT) student working in a spacesuit on the Experimental Assembly of Structures in Extravehicular Activity (EASE) project which was developed as a joint effort between MFSC and MIT. The EASE experiment required that crew members assemble small components to form larger components, working from the payload bay of the space shuttle.

  15. Gravitaxis of Euglena gracilis depends only partially on passive buoyancy

    Science.gov (United States)

    Richter, Peter R.; Schuster, Martin; Lebert, Michael; Streb, Christine; Häder, Donat-Peter

    In darkness, the unicellular freshwater flagellate Euglena gracilis shows a pronounced negative gravitactic behavior, and the cells swim actively upward in the water column. Up to now it was unclear whether this behavior is based on a passive (physical) alignment mechanism (e.g., buoyancy due to a fore-aft asymmetry of the cell body) or on an active physiological mechanism. A sounding rocket experiment was performed in which the effect of sub-1g-accelerations (0.05, 0.08, 0.12, and 0.2g) on untreated living cells and immobilized (fixation with liquid nitrogen) cells was observed. By means of computerized image analysis the angles of the cells long axis with respect to the acceleration vector were analyzed in order to calculate and compare the reorientation kinetics of the immobilized cells versus that of the controls. In both groups, the reorientation kinetics depended on the dose, but the reorientation of the living cells was about five times faster than that of the immobilized cells. This indicates that in young cells gravitaxis can be explained by a physical mechanism only to a small extend. In older cultures, in which the cells often have a drop shaped cell body, the physical reorientation is considerably faster, and a more pronounced influence of passive alignment caused by fore/aft asymmetry (drag-gravity model) can not be excluded. In addition to these results, Euglena gracilis cells seem to respond very sensitively to small accelerations when they are applied after a longer microgravity period. The data indicate that gravitactic orientation occurred at an acceleration as low as 0.05g.

  16. Effects of body condition on buoyancy in endangered North Atlantic right whales.

    Science.gov (United States)

    Nousek-McGregor, Anna E; Miller, Carolyn A; Moore, Michael J; Nowacek, Douglas P

    2014-01-01

    Buoyancy is an important consideration for diving marine animals, resulting in specific ecologically relevant adaptations. Marine mammals use blubber as an energy reserve, but because this tissue is also positively buoyant, nutritional demands have the potential to cause considerable variation in buoyancy. North Atlantic right whales Eubalaena glacialis are known to be positively buoyant as a result of their blubber, and the thickness of this layer varies considerably, but the effect of this variation on buoyancy has not been explored. This study compared the duration and rate of ascending and descending glides, recorded with an archival tag, with blubber thickness, measured with an ultrasound device, in free-swimming right whales. Ascending whales with thicker blubber had shorter portions of active propulsion and longer passive glides than whales with thinner blubber, suggesting that blubber thickness influences buoyancy because the buoyant force is acting in the same direction as the animal's movement during this phase. Whales with thinner layers also used similar body angles and velocities when traveling to and from depth, while those with thicker layers used shallower ascent angles but achieved higher ascent velocities. Such alterations in body angle may help to reduce the cost of transport when swimming against the force of buoyancy in a state of augmented positive buoyancy, which represents a dynamic response to reduce the energetic consequences of physiological changes. These results have considerable implications for any diving marine animal during periods of nutritional stress, such as during seasonal migrations and annual variations in prey availability.

  17. Parametric Studies on Buoyancy Induced Flow through Circular Pipes in Solar water heating system

    Directory of Open Access Journals (Sweden)

    Dr. S. V. Prayagi

    2011-01-01

    Full Text Available Solar energy is the primary source of energy for our planet. The average solar energy reaching the earth in the tropical zone is about 1kWh/m2 giving approximately 5 to 10 kWh/m2 per day. Increased utilization of solar energy in India would result in all around benefits, both in term of cleaner environment and monetary gain.The energy from the sun can be used for various purposes such as water heating, water distillation, refrigeration, drying, power generation etc. The present work deals with solar water heating system in particular. Performance of the solar collectors can be determined using the famous Hottel-Whillier-Bliss equation [1]. The analysis is simple for the forced convection situation, where the flow rate is artificially maintained constant to a desired value and the heat transfer coefficient can easily be predicted using the information available in the literature. However the natural convection situation it is very difficult to analyze as appropriate correlations for predicting the values of induced mass flow rate due to thermosiphon effect and the associated heat transfer coefficient are not available. The aim of the present investigation, therefore, is to establish correlations for heat transfer and flow characteristics for the buoyancy induced flow through inclined tubes in case of solar water heating system in particular. Considering the complexity of the problem, experimental approach is preferred. In order to produce required data, experiments were performed using inclined tubes of various lengths, diameters, inclinations, and different heat inputs.

  18. Multi-phase Nature of a Radiation-Driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus

    CERN Document Server

    Wada, Keiichi; Meijerink, Rowin

    2016-01-01

    The structures and dynamics of molecular, atomic, and ionized gases are studied around a low-luminosity active galactic nucleus (AGN) with a small ($2\\times 10^6 M_\\odot$) black hole using 3D radiation hydrodynamic simulations. We studied, for the first time, the non-equilibrium chemistry for the X-ray dominated region in the "radiation-driven fountain" (Wada 2012) with supernova feedback. A double hollow cone structure is naturally formed without postulating a thick "torus" around a central source. The cone is occupied with an inhomogeneous, diffuse ionized gas and surrounded by a geometrically thick ($h/r \\gtrsim 1$) atomic gas. Dense molecular gases are distributed near the equatorial plane, and energy feedback from supernovae enhances their scale height. Molecular hydrogen exists in a hot phase ( > 1000 K) as well as in a cold ( $10^3$ cm$^{-3}$) phase. The velocity dispersion of H$_2$ in the vertical direction is comparable to the rotational velocity, which is consistent with near infrared observations o...

  19. An Instability-driven Dynamo for $\\gamma$ Ray Bursts

    CERN Document Server

    Araya-Gochez, R A

    2000-01-01

    We show that an MHD-instability driven dynamo (IDD) operating in a hot accretion disk is capable of generating energetically adequate magnetic flux deposition rates above and below a mildly advective accretion disk structure. The dynamo is driven by the magnetorotational instability (MRI) of a toroidal field in a shear flow and is limited by the buoyancy of `horizontal' flux and by reconnection in the turbulent medium. The efficiency of magnetic energy deposition is estimated to be comparable to the neutrino losses although an MHD collimation mechanism may deem this process a more viable alternative to neutrino-burst-driven models of gamma ray bursts.

  20. Academic Buoyancy and Academic Outcomes: Towards a Further Understanding of Students with Attention-Deficit/Hyperactivity Disorder (ADHD), Students without ADHD, and Academic Buoyancy Itself

    Science.gov (United States)

    Martin, Andrew J.

    2014-01-01

    Background: Academic buoyancy is students' capacity to successfully overcome setback and challenge that is typical of the ordinary course of everyday academic life. It may represent an important factor on the psycho-educational landscape assisting students who experience difficulties in school and schoolwork. Aims: This study investigated the…

  1. Buoyancy-activated cell sorting using targeted biotinylated albumin microbubbles.

    Directory of Open Access Journals (Sweden)

    Yu-Ren Liou

    Full Text Available Cell analysis often requires the isolation of certain cell types. Various isolation methods have been applied to cell sorting, including fluorescence-activated cell sorting and magnetic-activated cell sorting. However, these conventional approaches involve exerting mechanical forces on the cells, thus risking cell damage. In this study we applied a novel isolation method called buoyancy-activated cell sorting, which involves using biotinylated albumin microbubbles (biotin-MBs conjugated with antibodies (i.e., targeted biotin-MBs. Albumin MBs are widely used as contrast agents in ultrasound imaging due to their good biocompatibility and stability. For conjugating antibodies, biotin is conjugated onto the albumin MB shell via covalent bonds and the biotinylated antibodies are conjugated using an avidin-biotin system. The albumin microbubbles had a mean diameter of 2 μm with a polydispersity index of 0.16. For cell separation, the MDA-MB-231 cells are incubated with the targeted biotin-MBs conjugated with anti-CD44 for 10 min, centrifuged at 10 g for 1 min, and then allowed 1 hour at 4 °C for separation. The results indicate that targeted biotin-MBs conjugated with anti-CD44 antibodies can be used to separate MDA-MB-231 breast cancer cells; more than 90% of the cells were collected in the MB layer when the ratio of the MBs to cells was higher than 70:1. Furthermore, we found that the separating efficiency was higher for targeted biotin-MBs than for targeted avidin-incorporated albumin MBs (avidin-MBs, which is the most common way to make targeted albumin MBs. We also demonstrated that the recovery rate of targeted biotin-MBs was up to 88% and the sorting purity was higher than 84% for a a heterogenous cell population containing MDA-MB-231 cells (CD44(+ and MDA-MB-453 cells (CD44-, which are classified as basal-like breast cancer cells and luminal breast cancer cells, respectively. Knowing that the CD44(+ is a commonly used cancer

  2. A novel pyroelectric generator utilising naturally driven temperature fluctuations from oscillating heat pipes for waste heat recovery and thermal energy harvesting

    Science.gov (United States)

    Zabek, D.; Taylor, J.; Ayel, V.; Bertin, Y.; Romestant, C.; Bowen, C. R.

    2016-07-01

    Low temperature thermal to electrical energy converters have the potential to provide a route for recovering waste energy. In this paper, we propose a new configuration of a thermal harvester that uses a naturally driven thermal oscillator free of mechanical motion and operates between a hot heat source and a cold heat sink. The system exploits a heat induced liquid-vapour transition of a working fluid as a primary driver for a pyroelectric generator. The two-phase instability of a fluid in a closed looped capillary channel of an oscillating heat pipe (OHP) creates pressure differences which lead to local high frequency temperature oscillations in the range of 0.1-5 K. Such temperature changes are suitable for pyroelectric thermal to electrical energy conversion, where the pyroelectric generator is attached to the adiabatic wall of the OHP, thereby absorbing thermal energy from the passing fluid. This new pyroelectric-oscillating heat pipe (POHP) assembly of a low temperature generator continuously operates across a spatial heat source temperature of 55 °C and a heat sink temperature of 25 °C, and enables waste heat recovery and thermal energy harvesting from small temperature gradients at low temperatures. Our electrical measurements with lead zirconate titanate (PZT) show an open circuit voltage of 0.4 V (AC) and with lead magnesium niobate-lead titanate (PMN-PT) an open circuit voltage of 0.8 V (AC) at a frequency of 0.45 Hz, with an energy density of 95 pJ cm-3 for PMN-PT. Our novel POHP device therefore has the capability to convert small quantities of thermal energy into more desirable electricity in the nW to mW range and provides an alternative to currently used batteries or centralised energy generation.

  3. Ceramic Spheres—A Novel Solution to Deep Sea Buoyancy Modules

    Directory of Open Access Journals (Sweden)

    Bo Jiang

    2016-06-01

    Full Text Available Ceramic-based hollow spheres are considered a great driving force for many applications such as offshore buoyancy modules due to their large diameter to wall thickness ratio and uniform wall thickness geometric features. We have developed such thin-walled hollow spheres made of alumina using slip casting and sintering processes. A diameter as large as 50 mm with a wall thickness of 0.5–1.0 mm has been successfully achieved in these spheres. Their material and structural properties were examined by a series of characterization tools. Particularly, the feasibility of these spheres was investigated with respect to its application for deep sea (>3000 m buoyancy modules. These spheres, sintered at 1600 °C and with 1.0 mm of wall thickness, have achieved buoyancy of more than 54%. As the sphere’s wall thickness was reduced (e.g., 0.5 mm, their buoyancy reached 72%. The mechanical performance of such spheres has shown a hydrostatic failure pressure above 150 MPa, corresponding to a rating depth below sea level of 5000 m considering a safety factor of 3. The developed alumina-based ceramic spheres are feasible for low cost and scaled-up production and show great potential at depths greater than those achievable by the current deep-sea buoyancy module technologies.

  4. On the coupling between buoyancy forces and electroconvective instability near ion-selective surfaces

    CERN Document Server

    Karatay, Elif; Mani, Ali

    2016-01-01

    Recent investigations have revealed that ion transport from aqueous electrolytes to ion-selective surfaces is subject to electroconvective instability that stems from coupling of hydrodynamics with electrostatic forces. Electroconvection is shown to enhance ion mixing and the net rate of transport. However, systems subject to electroconvection inherently involve fluid density variation set by salinity gradient in the bulk fluid. In this study we thoroughly examine the interplay of gravitational convection and chaotic electroconvection. Our results reveal that buoyant forces can significantly influence the transport rates, otherwise set by electroconvection, when the Rayleigh number $Ra$ of the system exceeds a value $Ra \\sim 1000$. We show that buoyancy forces can significantly alter the flow patterns in these systems. When the buoyancy acts in the stabilizing direction, it limits the extent of penetration of electroconvection, but without eliminating it. When the buoyancy destabilizes the flow, it alters the...

  5. Origin of Domes on Europa: The Role of Thermally Induced Compositional Buoyancy,

    Science.gov (United States)

    Pappalardo, R. T.; Barr, A. C.

    2004-01-01

    The surface of Jupiter's moon Europa is peppered by topographic domes, interpreted as sites of intrusion and extrusion. Diapirism is consistent with dome morphology, but thermal buoyancy alone cannot produce sufficient driving pressures to create the observed dome elevations. Instead, diapirs may initiate by thermal convection that induces compositional segregation. Exclusion of impurities from warm upwellings allows sufficient buoyancy for icy plumes to create the observed surface topography, provided the ice shell has a small effective elastic thickness (0.2 to 0.5 km) and contains low-eutectic point impurities at the few percent level. This model suggests that the ice shell may be depleted in impurities over time.

  6. Natural versus forced convection in laminar starting plumes

    CERN Document Server

    Rogers, Michael C

    2009-01-01

    A starting plume or jet has a well-defined, evolving head that is driven through the surrounding quiescent fluid by a localized flux of either buoyancy or momentum, or both. We studied the scaling and morphology of starting plumes produced by a constant flux of buoyant fluid from a small, submerged outlet. The plumes were laminar and spanned a wide range of plume Richardson numbers Ri. Ri is the dimensionless ratio of the buoyancy forces to inertial effects, and is thus our measurements crossed over the transition between buoyancy-driven plumes and momentum-driven jets. We found that the ascent velocity of the plume, nondimensionalized by Ri, exhibits a power law relationship with Re, the Reynolds number of the injected fluid in the outlet pipe. We also found that as the threshold between buoyancy-driven and momentum-driven flow was crossed, two distinct types of plume head mophologies existed: confined heads, produced in the Ri > 1 regime, and dispersed heads, which are found in the Ri < 1 regime. Head di...

  7. Thermal-solutal capillary-buoyancy flow of a low Prandtl number binary mixture with a -1 capillary ratio in an annular pool

    Science.gov (United States)

    Yu, Jia-Jia; Wu, Chun-Mei; Li, You-Rong; Chen, Jie-Chao

    2016-08-01

    A series of three-dimensional numerical simulations on thermal-solutal capillary-buoyancy flow in an annular pool were carried out. The pool was filled with silicon-germanium melt with an initial silicon mass fraction of 1.99%. The Prandtl number and the Lewis number of the working fluid are 6.37 × 10-3 and 2197.8, respectively. Both the radial temperature gradient and the solute concentration gradient were applied to the annular pool. The capillary ratio was assumed to be -1, which means that the solutal and thermal capillary effects were equal and opposite. Results show that the thermal-solutal capillary-buoyancy flow always occurs at this special case with the capillary ratio of -1, and even in a shallow annular pool with an aspect ratio of 0.05. With the increase of the thermal Marangoni number, four kinds of flow patterns appear orderly, including concentric rolls, petal-like, spoke, and rosebud-like patterns. These flow patterns are strongly influenced by the local interaction between the solutal and thermal capillary effects and the vertical solute concentration gradient near the outer cylinder. A small vortex driven by the dominant solutal capillary effect emerges near the inner cylinder, which is different from the flow pattern in a pure fluid. In addition, the critical thermal Marangoni number of the initial three-dimensional flow decreases with the increase of the aspect ratio of the annular pool.

  8. Investigating Students' Ideas about Buoyancy and the Influence of Haptic Feedback

    Science.gov (United States)

    Minogue, James; Borland, David

    2016-01-01

    While haptics (simulated touch) represents a potential breakthrough technology for science teaching and learning, there is relatively little research into its differential impact in the context of teaching and learning. This paper describes the testing of a haptically enhanced simulation (HES) for learning about buoyancy. Despite a lifetime of…

  9. Numerical investigation of the onset of centrifugal buoyancy in a rotating cavity

    Science.gov (United States)

    Pitz, Diogo B.; Marxen, Olaf; Chew, John

    2016-11-01

    Buoyancy-induced flows in a differentially heated rotating annulus present a multitude of dynamics when control parameters such as rotation rate, temperature difference and Prandtl number are varied. Whilst most of the work in this area has been motivated by applications involving geophysics, the problem of buoyancy-induced convection in rotating systems is also relevant in industrial applications such as the flow between rotating disks of turbomachinery internal air systems, in which buoyancy plays a major role and poses a challenge to accurately predict temperature distributions and heat transfer rates. In such applications the rotational speeds involved are very large, so that the centrifugal accelerations induced are much higher than gravity. In this work we perform direct numerical simulations and linear stability analysis of flow induced by centrifugal buoyancy in a sealed rotating annulus of finite gap with flat end-walls, using a canonical setup representative of an internal air system rotating cavity. The analysis focuses on the behaviour of small-amplitude disturbances added to the base flow, and how those affect the onset of Rossby waves and, ultimately, the transition to a fully turbulent state where convection columns no longer have a well-defined structure. Diogo B. Pitz acknowledges the financial support from the Capes foundation through the Science without Borders program.

  10. Investigating Students' Ideas About Buoyancy and the Influence of Haptic Feedback

    Science.gov (United States)

    Minogue, James; Borland, David

    2016-04-01

    While haptics (simulated touch) represents a potential breakthrough technology for science teaching and learning, there is relatively little research into its differential impact in the context of teaching and learning. This paper describes the testing of a haptically enhanced simulation (HES) for learning about buoyancy. Despite a lifetime of everyday experiences, a scientifically sound explanation of buoyancy remains difficult to construct for many. It requires the integration of domain-specific knowledge regarding density, fluid, force, gravity, mass, weight, and buoyancy. Prior studies suggest that novices often focus on only one dimension of the sinking and floating phenomenon. Our HES was designed to promote the integration of the subconcepts of density and buoyant forces and stresses the relationship between the object itself and the surrounding fluid. The study employed a randomized pretest-posttest control group research design and a suite of measures including an open-ended prompt and objective content questions to provide insights into the influence of haptic feedback on undergraduate students' thinking about buoyancy. A convenience sample (n = 40) was drawn from a university's population of undergraduate elementary education majors. Two groups were formed from haptic feedback (n = 22) and no haptic feedback (n = 18). Through content analysis, discernible differences were seen in the posttest explanations sinking and floating across treatment groups. Learners that experienced the haptic feedback made more frequent use of "haptically grounded" terms (e.g., mass, gravity, buoyant force, pushing), leading us to begin to build a local theory of language-mediated haptic cognition.

  11. "'Sink or Swim': Buoyancy and Coping in the Cognitive Test Anxiety--Academic Performance Relationship"

    Science.gov (United States)

    Putwain, David W.; Daly, Anthony L.; Chamberlain, Suzanne; Sadreddini, Shireen

    2016-01-01

    This study explores the relationship between students' self-report levels of cognitive test anxiety (worry), academic buoyancy (withstanding and successfully responding to routine school challenges and setbacks), coping processes and their achieved grades in high-stakes national examinations at the end of compulsory schooling. The sample comprised…

  12. Influence of Buoyancy Control Performance on Power Production by the Wave Dragon Nissum Bredning Prototype

    DEFF Research Database (Denmark)

    Kofoed, Jens Peter; Tedd, James; Friis-Madsen, E.

    2007-01-01

    This paper reports on the real sea performance of the buoyancy control system of Wave Dragon, a floating wave energy converter using the overtopping principle. The device operates with the full independent control system which has been tested during three years of operation. The impact...

  13. Buoyancy frequency profiles and internal semidiurnal tide turning depths in the oceans

    NARCIS (Netherlands)

    King, B.; Stone, M.; Zhang, H.P.; Gerkema, T.; Marder, M.; Scott, R.B.; Swinney, H.L.

    2012-01-01

    We examine the possible existence of internal gravity wave "turning depths," depths below which the local buoyancy frequency N(z) becomes smaller than the wave frequency. At a turning depth, incident gravity waves reflect rather than reaching the ocean bottom as is generally assumed. Here we conside

  14. An analytical theory of the buoyancy-Kolmogorov subrange transition in turbulent flows with stable stratification.

    Science.gov (United States)

    Sukoriansky, Semion; Galperin, Boris

    2013-01-13

    The buoyancy subrange of stably stratified turbulence is defined as an intermediate range of scales larger than those in the inertial subrange. This subrange encompasses the crossover from internal gravity waves (IGWs) to small-scale turbulence. The energy exchange between the waves and small-scale turbulence is communicated across this subrange. At the same time, it features progressive anisotropization of flow characteristics on increasing spatial scales. Despite many observational and computational studies of the buoyancy subrange, its theoretical understanding has been lagging. This article presents an investigation of the buoyancy subrange using the quasi-normal scale elimination (QNSE) theory of turbulence. This spectral theory uses a recursive procedure of small-scale modes elimination based upon a quasi-normal mapping of the velocity and temperature fields using the Langevin equations. In the limit of weak stable stratification, the theory becomes completely analytical and yields simple expressions for horizontal and vertical eddy viscosities and eddy diffusivities. In addition, the theory provides expressions for various one-dimensional spectra that quantify turbulence anisotropization. The theory reveals how the dispersion relation for IGWs is modified by turbulence, thus alleviating many unique waves' features. Predictions of the QNSE theory for the buoyancy subrange are shown to agree well with various data.

  15. 40 CFR 1065.690 - Buoyancy correction for PM sample media.

    Science.gov (United States)

    2010-07-01

    ...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Calculations and Data Requirements § 1065.690... mass uncorrected for buoyancy. ρ air = density of air in balance environment. ρ weight = density of... Where: p abs = absolute pressure in balance environment. M mix = molar mass of air in...

  16. Core-annular flow through a horizontal pipe: Hydrodynamic counterbalancing of buoyancy force on core

    NARCIS (Netherlands)

    Ooms, G.; Vuik, C.; Poesio, P.

    2007-01-01

    A theoretical investigation has been made of core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity liquid annular layer through a horizontal pipe. Special attention is paid to the question of how the buoyancy force on the core, caused by a density difference betwe

  17. Importance of initial buoyancy field on evolution of mantle thermal structure:Implications of surface boundary conditions

    Institute of Scientific and Technical Information of China (English)

    Petar Glisovic; Alessandro M. Forte

    2015-01-01

    Although there has been significant progress in the seismic imaging of mantle heterogeneity, the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models. To address this question, we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns. A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow, without imposing prescribed surface velocities (i.e., plate-like boundary condition). As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip (rigid) boundary condition. A rigid boundary condition dem-onstrates that the initial thermally-dominated structure is preserved, and its geographical location is fixed during the evolution of mantle flow. Considering the impact of different assumed surface boundary conditions (rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure. Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term, stable pattern of thermal heterogeneity in the lowermost mantle that resembles the present-day Large Low Shear Velocity Provinces (LLSVPs), especially below the Pacific. The evolution of sub-duction zones may be, however, influenced by the mantle-wide flow driven by deeply-rooted and long-lived superplumes since Archean times. These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature

  18. On the nature of local instabilities in rotating galactic coronae and cool cores of galaxy clusters

    CERN Document Server

    Nipoti, Carlo

    2014-01-01

    A long-standing question is whether radiative cooling can lead to local condensations of cold gas in the hot atmospheres of galaxies and galaxy clusters. We address this problem by studying the nature of local instabilities in rotating, stratified, weakly magnetized, optically thin plasmas in the presence of radiative cooling and anisotropic thermal conduction. For both axisymmetric and non-axisymmetric linear perturbations we provide the general equations that can be applied locally to specific systems to establish whether they are unstable and, in case of instability, to determine the kind of evolution (monotonically growing or over-stable) and the growth rates of unstable modes. We present results for models of rotating plasmas representative of Milky Way-like galaxy coronae and cool-cores of galaxy clusters. It is shown that the unstable modes arise from a combination of thermal, magnetothermal, magnetorotational and heat-flux-driven buoyancy instabilities. Local condensation of cold clouds tends to be ha...

  19. Examination of Buoyancy-Reduction Effect in Induction-Heating Cookers by Using 3D Finite Element Method

    Science.gov (United States)

    Yonetsu, Daigo; Tanaka, Kazufumi; Hara, Takehisa

    In recent years, induction-heating (IH) cookers that can be used to heat nonmagnetic metals such as aluminum have been produced. Occasionally, a light pan moves on a glass plate due to buoyancy when heated by an IH cooker. In some IH cookers, an aluminum plate is mounted between the glass plate and the coil in order to reduce the buoyancy effect. The objective of this research is to evaluate the buoyancy-reduction effect and the heating effect of buoyancy-reduction plates. Eddy current analysis is carried out by 3D finite element method, and the electromagnetic force and the heat distribution on the heating plate are calculated. After this calculation is performed, the temperature distribution of the heating plate is calculated by heat transfer analysis. It is found that the shape, area, and the position of the buoyancy reduction plate strongly affect the buoyancy and the heat distribution. The impact of the shape, area, and position of the buoyancy reduction plate was quantified. The phenomena in the heating were elucidated qualitatively.

  20. Numerical and Experimental Study on Negative Buoyance Induced Vortices in N-Butane Jet Flames

    KAUST Repository

    Xiong, Yuan

    2015-07-26

    Near nozzle flow field in flickering n-butane diffusion jet flames was investigated with a special focus on transient flow patterns of negative buoyance induced vortices. The flow structures were obtained through Mie scattering imaging with seed particles in a fuel stream using continuous-wave (CW) Argon-ion laser. Velocity fields were also quantified with particle mage velocimetry (PIV) system having kHz repetition rate. The results showed that the dynamic motion of negative buoyance induced vortices near the nozzle exit was coupled strongly with a flame flickering instability. Typically during the flame flickering, the negative buoyant vortices oscillated at the flickering frequency. The vortices were distorted by the flickering motion and exhibited complicated transient vortical patterns, such as tilting and stretching. Numerical simulations were also implemented based on an open source C++ package, LaminarSMOKE, for further validations.

  1. Optical Tracking Measurement on Vortex Induced Vibration of Flexible Riser with Short-Length Buoyance Module

    Science.gov (United States)

    Fan, Dixia; Du, Honglin; Triantafyllou, Michael

    2016-11-01

    We address experimentally the vortex induced vibrations (VIV) of long flexible cylinders. We employ optical tracking, using an array of high speed cameras. Compared to strain gauges and accelerometers, this non-intrusive approach, allows direct measurement of the flexible cylinder displacement with far denser spatial distribution. The measurements reveal essential features of flexible cylinder VIV, including complex geometries such as cylinders containing short-length buoyancy modules, with module to cylinder diameter ratio of 1:3.2 and module to bare cylinder length ratio of 1:1. The experiments are conducted with aspect ratio of 170 and 3 different coverage ratios, of 100%, 50% and 20%. The measurements demonstrate bi-frequency response due to excitation from both buoyancy module and bare cylinder, at low Strouhal number, down to values of 0.08, and the generation of traveling wave patterns.

  2. Natural convection gas pendulum and its application in accelerometer and tilt sensor

    Institute of Scientific and Technical Information of China (English)

    ZHANG Fuxue

    2005-01-01

    It is discovered that the natural convection gas has the pendulum characteristic, which leads to the introduction of the new concept of gas pendulum. In this paper, the buoyancy lift of natural convection gas is analyzed in a hermetic chamber, and the relationship between the buoyancy lift and the change of temperature is formulated. The experimental results show that the gas pendulum,similar to the solid pendulum and liquid pendulum, can be utilized to sense the acceleration and the tilt angle.

  3. Buoyancy-Driven Fluid Flow Generated by Bacterial Metabolism and its Proposed Relationship to Increased Bacterial Growth in Space

    Science.gov (United States)

    2007-11-02

    Escherichia coli. Carnegie Institute, Washington, DC, p. 184, 1955. Robinson, T. P., Ocio , M. J., Kaloti, A., et al. The effect of the growth...environment on the lag phase of Listeria monocytogenes. Int. J. Food Microbiol. 44, 83-92, 1998. Robinson, T. P., Ocio , M. J. Kaloti, A., et al. The

  4. Neutral buoyancy testing of architectural and environmental concepts of space vehicle design

    Science.gov (United States)

    Lenda, J. A.; Rosener, A. A.; Stephenson, M. L.

    1972-01-01

    Design guidelines are presented that are applicable to providing habitability areas and furniture elements for extended periods in a zero gravity environment. This was accomplished by: (1) analyzing the existing habitability crew area requirements, mobility and restraint aids, cross-cultural design, and establishing a man model for zero gravity; (2) designing specific furniture elements, chair and table, and volumes for a stateroom, office, bathroom, galley, and wardroom; and (3) neutral buoyancy testing and evaluation of these areas.

  5. Buoyancy Effects on the Scaling Characteristics of Atmospheric Boundary Layer Wind Fields in the Mesoscale Range

    CERN Document Server

    Kiliyanpilakkil, V P; Ruiz-Columbié, A; Araya, G; Castillo, L; Hirth, B; Burgett, W

    2015-01-01

    We have analyzed long-term wind speed time-series from five field sites up to a height of 300 m from the ground. Structure function-based scaling analysis has revealed that the scaling exponents in the mesoscale regime systematically depend on height. This anomalous behavior is shown to be caused by the buoyancy effects. In the framework of the extended self-similarity, the relative scaling exponents portray quasi-universal behavior.

  6. Zero Power Buoyancy Control for Distributed Autonomous Sensor Networks Conducted During Crimson Viper 2010 Field Experiment

    Science.gov (United States)

    2011-03-04

    STATEMENT 13. SUPPLEMENTARY NOTES 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: a. REPORT 19a. NAME OF RESPONSIBLE PERSON 19b. TELEPHONE...producing simple, small, power-efficient data harvesting nodes with variable buoyancy, enabling unsupervised underwater sensing with subsequent surfacing...aerosol samples for subsequent analysis at NRL. At regular intervals, a hand-held hyperspectral sensor as to be used to collect near-water optical

  7. Fluid mechanics of ventilation system generated by buoyancy and momentum sources and experiments research

    Institute of Scientific and Technical Information of China (English)

    WANG Xin; HUANG Chen; FU Yu-ying; CAO Wei-wu

    2010-01-01

    This paper presents fluid mechanics of ventilation system formed by the momentum source and the buoyancy source,which investigates inter-action between the plume and the non-isothermal air jet since buoyancy source is produced by the plume and momentum source is generated by the air jet,respectively.The interaction is discussed by a mathematical model,an idealized situation of the plume rising from a point heat source of buoyancy alone-in particular the initial momentum flux at the source is zero.Furthermore,the paper discusses the effects of the parameters such as strength of source,air-flow volume and air-flow velocity used in the mathematical-physical model.Considering the effect of the plume generated by the indoor heat source,one expression of trajectory of the non-isothermal air jet produced by jet diffuser is deduced.And field-experiment has also been carried out to illustrate the effect on flowing-action of the air jet and validate the theoretical work.It can be concluded that the heat sources do have effect on the flowing-action of the air jet,and the effect mainly depends on the interaction produced by the plume and the air jet.The results show that the thermal buoyant effect of plumes on the air jet should be taken into account if the indoor heat sources are large enough.Numerical simulation is conducted and coincides with the experimental results as well.

  8. Buoyancy effects on rotation and translation of large particles in turbulent flow

    Science.gov (United States)

    Byron, Margaret; Tao, Yiheng; Variano, Evan

    2013-11-01

    We use laboratory experiments to investigate the effects of homogeneous, isotropic turbulence on particles of varying buoyancy, size, and shape. The buoyancy is varied between a specific gravity of 1.001 and 1.05. All particles are roughly 1 cm, which in this flow is close to Taylor's turbulent microscale. We vary the shape to compare spherical particles to non-spherical particles while matching the settling velocity, volume, and/or surface area. Particles are fabricated in custom shapes using transparent hydrogels whose refractive index is close to water. We embed tracers within the particles and use PIV to image the interior of the particle simultaneously with the exterior flowfield of homogeneous isotropic turbulence, generated by two active-grid synthetic jet arrays. We find that the settling velocity of these particles, regardless of shape, is reduced relative to the quiescent settling velocity as predicted by the Clift-Gauvin model. We explore the distribution of rotation rates, as characterized by the variance of angular velocity. We find significant anisotropy in the angular velocities of negatively buoyant particles, which vanishes as particles approach neutral buoyancy. We also see differences in angular velocity distribution between particles of varying eccentricity.

  9. Numerical Study of Buoyancy Convection of Air under Permanent Magnetic Field and Comparison with That under Gravity Field

    Directory of Open Access Journals (Sweden)

    Kewei Song

    2014-01-01

    Full Text Available Magnetothermal free convection of air in a square enclosure under a nonuniform magnetic field provided by a permanent neodymium-iron-boron magnet is numerically studied. The natural convection under the gravity field alone is also studied for comparison. The physical fields of magnetizing force, velocity, and temperature as well as the local distribution characteristic of Nusselt number are all presented in this paper. The results show that the buoyancy convection of air in the square enclosure under magnetic field is quite different from that under the gravity field. The local value of Nusselt number under the magnetic field supplied by a permanent magnet with a residual magnetic flux density of about 4.5 Tesla can reach a high value of about three times larger than the maximum local value of Nusselt number under the gravity field. Relatively uniform distributions of temperature gradient and Nusselt number can be obtained along the cold wall of the enclosure under the magnetic field. A permanent magnet with high magnetic energy product with Br reaching to 3.5 Tesla can play a comparative role on the averaged Nusselt number compared with that under the gravity environment.

  10. Battleship Buoyancy

    Science.gov (United States)

    Dishaw, J. Patrick

    2010-04-01

    One of the most dramatic demonstrations of the Archimedes principle is the simple fact that battleships float. I estimate the depth of a battleship in seawater as an example in my physics classes. I use the battleship Arizona as an exemplar of a class of U.S. battleships used during World War II. The Arizona was 608 ft (185.3 m) long and 97 ft 1 in (29.6 m) wide at its widest dimension. The unloaded weight of the ship was 31,400 U.S. tons (2.79× 108 N). How deep would the Arizona sink into seawater of density 1028 kg/m3?

  11. Sink or swim? Bone density as a mechanism for buoyancy control in early cetaceans.

    Science.gov (United States)

    Gray, Noel-Marie; Kainec, Kimberly; Madar, Sandra; Tomko, Lucas; Wolfe, Scott

    2007-06-01

    Previous analyses have shown that secondarily aquatic tetrapods, including whales, exhibit osteological adaptations to life in water as part of their complex buoyancy control systems. These structural specializations of bone span hyperostosis through osteoporosis. The past 15 years of paleontological effort has provided an unprecedented opportunity to examine the osteological transformation of whales as they make their transition to an obligate aquatic lifestyle over a 10-million-year period. It is hypothesized that whales manifest their osteological specialization in the same manner as extant semiaquatic and fully aquatic mammals. This study presents and analysis of the microstructural features of bone in early and late archaic cetaceans, and in a comparative sample of modern terrestrial, semiaquatic, and aquatic mammals. Bone histology was examined from the ribs of 10 fossilized individuals representing five early cetacean families, including Pakicetidae, Ambulocetidae, Protocetidae, Remintonocetidae, and Basilosauridae. Comparisons were then made with rib histology from nine genera of extant mammals including: Odocoileus (deer), Bos (cow), Equus (horse), Canis (dog), Lutra (river otter), Enhydra (sea otter), Choeropsis (pygmy hippo), Trichechus (sea cow), and Delphinus (dolphin). Results show that the transition from terrestrial, to semiaquatic, to obligate aquatic locomotion in archaeocetes involved a radical shift in bone function achieved by means of profound changes at the microstructural level. A surprising finding was that microstructural change predates gross anatomical shift in archaeocetes associated with swimming. Histological analysis shows that high bone density is an aquatic specialization that provides static buoyancy control (ballast) for animals living in shallow water, while low bone density is associated with dynamic buoyancy control for animals living in deep water. Thus, there was a shift from the typical terrestrial form, to osteopetrosis

  12. Consistency of neutron cross-section data, S /SUB N/ calculations, and measured tritium production for a 14-MeV neutron-driven sphere of natural lithium deuteride

    Energy Technology Data Exchange (ETDEWEB)

    Reupke, W.A.; Davidson, J.N.; Muir, D.W.

    1982-12-01

    The authors present algorithms, describe a computer program, and gives a computational procedure for the statistical consistency analysis of neutron cross-section data, S /SUB N/ calculations, and measured tritium production in 14-MeV neutron-driven integral assemblies. Algorithms presented include a reduced matrix manipulation technique suitable for manygroup, 14-MeV neutron transport calculations. The computer program incorporates these algorithms and is expanded and improved to facilitate analysis of such integral experiments. Details of the computational procedure are given for a natural lithium deuteride experiment performed at the Los Alamos National Laboratory. Results are explained in terms of calculated cross-section sensitivities and uncertainty estimates. They include a downward adjustment of the /sup 7/Li(n,xt) 14-MeV cross section from 328 + or - 22 to 284 + or - 24 mb, which is supported by the trend of recent differential and integral measurements. It is concluded that with appropriate refinements, the techniques of consistency analysis can be usefully applied to the analysis of 14-MeV neutron-driven tritium production integral experiments.

  13. A transient thermal model of a neutral buoyancy cryogenic fluid delivery system

    Science.gov (United States)

    Bue, Grant C.; Conger, Bruce S.

    A thermal-performance model is presently used to evaluate a preliminary Neutral Buoyancy Cryogenic fluid-delivery system for underwater EVA training. Attention is given to the modeling of positional transients generated from the moving of internal components, including the control of cycling artifacts, as well as to the convection and boiling characteristics of the cryofluid, 250-psi N2/O2 gas, and water contained in the tank. Two piston designs are considered according to performance criteria; temperature and heat-transfer rate profiles are presented.

  14. Effect of tracer buoyancy on tracer experiments conducted in fractured crystalline bedrock

    Science.gov (United States)

    Becker, Matthew W.

    2003-02-01

    Tracer buoyancy has been shown to influence breakthrough from two-well tracer experiments conducted in porous media. Two-well tracer experiments are presented from fractured crystalline bedrock, in which the specific gravity of the tracer injectate varied from 1.0002 to 1.0133. Under the forced hydraulic conditions imposed, no difference in breakthrough was noted for the three experiments. These results show that even relatively dense tracer injectate solutions may have an insignificant effect on breakthrough when imposed gradients are sufficiently large.

  15. Dynamic effects of plate-buoyancy subduction at Manila Trench, South China Sea

    Science.gov (United States)

    Jiang, L.; Zhan, W.; Sun, J.; Li, J.

    2015-12-01

    Bathymetric map of SCS plate shows two subducting buoyancies, the fossil ridge and the oceanic plateau, which are supposed to impact slab segmentation into the north from Taiwan to 18°N, and the south from 17°N to Mindoro. Hypocenter distribution show that slab dip angle turns lower southwards from 45° to 30° in the north segment, and relatively equals ~45° in the south segment at the depth of 100km. Moreover, volcano distribution can be segmented into Miocene WVC, Quaternary EVC in the north and combined SVC in the south (Fig. A). We found that WVC and SVC mostly locate in a parallel belt ~50km apart to Manila trench, however EVC turn father southwards from 50km to 100km (Fig. B). Above characters congruously indicate that SCS plate kept equal dip angle in Miocene; then the north segment shallowed at 18°N and developed northwards in Quaternary, resulting in lower dip angle than the invariant south segment. To check the transformation of slab dip angle from 45° to 30° between 17~18°N, focal mechanism solution nearby 17°N are found 90° in rake and dip angle, strike parallel to the fossil ridge, indicating a slab tear located coincident with the ridge, where is a weak zone of higher heat flow and lower plate coupling ratio than the adjacent zones and slab can be easily tore as an interface for SCS plate segmentation. Subduction of the two buoyancies within SCS plate is supposed as influential dynamic factor: It caused the trench retreat rate reduced, forming a cusp and a flat convex of Manila trench shape; Moreover, the buoyancies resisted subduction, resulting in shear stress heterogeneity of SCS plate, in consequence the fossil ridge as a fragile belt potentially became stress concentration zone that easily tore; Then the buoyant oceanic plateau might lead to shallowing of the northern SCS plate. To examine the hypothesis, dynamic effects of the two subducting buoyancies are being respectively investigated based on numerical models. (Grt. 41376063, 2013

  16. A coastal cline in sodium accumulation in Arabidopsis thaliana is driven by natural variation of the sodium transporter AtHKT1;1.

    Directory of Open Access Journals (Sweden)

    Ivan Baxter

    2010-11-01

    Full Text Available The genetic model plant Arabidopsis thaliana, like many plant species, experiences a range of edaphic conditions across its natural habitat. Such heterogeneity may drive local adaptation, though the molecular genetic basis remains elusive. Here, we describe a study in which we used genome-wide association mapping, genetic complementation, and gene expression studies to identify cis-regulatory expression level polymorphisms at the AtHKT1;1 locus, encoding a known sodium (Na(+ transporter, as being a major factor controlling natural variation in leaf Na(+ accumulation capacity across the global A. thaliana population. A weak allele of AtHKT1;1 that drives elevated leaf Na(+ in this population has been previously linked to elevated salinity tolerance. Inspection of the geographical distribution of this allele revealed its significant enrichment in populations associated with the coast and saline soils in Europe. The fixation of this weak AtHKT1;1 allele in these populations is genetic evidence supporting local adaptation to these potentially saline impacted environments.

  17. Electrically Driven Liquid Film Boiling Experiment

    Science.gov (United States)

    Didion, Jeffrey R.

    2016-01-01

    This presentation presents the science background and ground based results that form the basis of the Electrically Driven Liquid Film Boiling Experiment. This is an ISS experiment that is manifested for 2021. Objective: Characterize the effects of gravity on the interaction of electric and flow fields in the presence of phase change specifically pertaining to: a) The effects of microgravity on the electrically generated two-phase flow. b) The effects of microgravity on electrically driven liquid film boiling (includes extreme heat fluxes). Electro-wetting of the boiling section will repel the bubbles away from the heated surface in microgravity environment. Relevance/Impact: Provides phenomenological foundation for the development of electric field based two-phase thermal management systems leveraging EHD, permitting optimization of heat transfer surface area to volume ratios as well as achievement of high heat transfer coefficients thus resulting in system mass and volume savings. EHD replaces buoyancy or flow driven bubble removal from heated surface. Development Approach: Conduct preliminary experiments in low gravity and ground-based facilities to refine technique and obtain preliminary data for model development. ISS environment required to characterize electro-wetting effect on nucleate boiling and CHF in the absence of gravity. Will operate in the FIR - designed for autonomous operation.

  18. The impact of the weather conditions on the cooling performance of the heat pump driven by an internal natural gas combustion engine

    Directory of Open Access Journals (Sweden)

    Janovcová Martina

    2015-01-01

    Full Text Available Market with sources of heat and cold offers unlimited choice of different power these devices, design technology, efficiency and price categories. New progressive technologies are constantly discovering, about which is still little information, which include heat pumps powered by a combustion engine running on natural gas. A few pieces of these installations are in Slovakia, but no studies about their work and effectiveness under real conditions. This article deals with experimental measurements of gas heat pump efficiency in cooling mode. Since the gas heat pump works only in system air – water, air is the primary low – energy source, it is necessary to monitor the impact of the climate conditions for the gas heat pump performance.

  19. Simulation of buoyancy-induced turbulent flow from a hot horizontal jet

    Institute of Scientific and Technical Information of China (English)

    El-AMIN M. F.; SUN Shuyu; SALAM Amgad

    2014-01-01

    Experimental visualizations and numerical simulations of a horizontal hot water jet entering cold water into a rectangular storage tank are described. Three different temperature differences and their corresponding Reynolds numbers are considered. Both experimental visualization and numerical computations are carried out for the same flow and thermal conditions. The realizable k-e model is used for modeling the turbulent flow while the buoyancy is modeled using the Boussinesq approximation. Polynomial approximations of the water properties are used to compare with the Boussinesq approximation. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank as well as the Froude number are analyzed. The experimental visualizations are performed at intervals of five seconds for all different cases. The simulated results are compared with the visualized results, and both of them show the stratification phenomena and buoyancy force effects due to temperature difference and density variation. After certain times, depending on the case condition, the flow tends to reach a steady state.

  20. Simulation of buoyancy-induced turbulent flow from a hot horizontal jet

    KAUST Repository

    El-Amin, Mohamed

    2014-02-01

    Experimental visualizations and numerical simulations of a horizontal hot water jet entering cold water into a rectangular storage tank are described. Three different temperature differences and their corresponding Reynolds numbers are considered. Both experimental visualization and numerical computations are carried out for the same flow and thermal conditions. The realizable k - ε model is used for modeling the turbulent flow while the buoyancy is modeled using the Boussinesq approximation. Polynomial approximations of the water properties are used to compare with the Boussinesq approximation. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank as well as the Froude number are analyzed. The experimental visualizations are performed at intervals of five seconds for all different cases. The simulated results are compared with the visualized results, and both of them show the stratification phenomena and buoyancy force effects due to temperature difference and density variation. After certain times, depending on the case condition, the flow tends to reach a steady state. © 2014 Publishing House for Journal of Hydrodynamics.

  1. Plate tectonics on the early Earth: Limitations imposed by strength and buoyancy of subducted lithosphere

    Science.gov (United States)

    van Hunen, Jeroen; van den Berg, Arie P.

    2008-06-01

    The tectonic style and viability of modern plate tectonics in the early Earth is still debated. Field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the Archean continue to accumulate. Here, we present the first numerical modeling results that address for a hotter Earth the viability of subduction, one of the main requirements for plate tectonics. A hotter mantle has mainly two effects: 1) viscosity is lower, and 2) more melt is produced, which in a plate tectonic setting will lead to a thicker oceanic crust and harzburgite layer. Although compositional buoyancy resulting from these thick crust and harzburgite might be a serious limitation for subduction initiation, our modeling results show that eclogitization significantly relaxes this limitation for a developed, ongoing subduction process. Furthermore, the lower viscosity leads to more frequent slab breakoff, and sometimes to crustal separation from the mantle lithosphere. Unlike earlier propositions, not compositional buoyancy considerations, but this lithospheric weakness could be the principle limitation to the viability of plate tectonics in a hotter Earth. These results suggest a new explanation for the absence of ultrahigh-pressure metamorphism (UHPM) and blueschists in most of the Precambrian: early slabs were not too buoyant, but too weak to provide a mechanism for UHPM and exhumation.

  2. Vortex ring formation in starting forced plumes with negative and positive buoyancy

    Science.gov (United States)

    Gao, L.; Yu, S. C. M.

    2016-11-01

    The limiting process of vortex ring formation in starting forced plumes, with Richardson number in the range of -0.06 ≤ Ri ≤ 0.06, was studied numerically under the Boussinesq approximation. The examination of the dynamics of the starting flow evolution reveals that the plume-ambient density difference affects the vortex ring pinch-off mainly through three mechanisms, i.e., the baroclinic production of vorticity, the buoyancy acceleration (or deceleration) on the vortical structures, and its effect on the trailing shear layer instability. As Ri increases from negative to positive values, three regimes can be identified in terms of the vortex interaction patterns during the pinch-off process, i.e., the weak-interaction regime (-0.06 results show that the variation trends of formation number and separation number against Ri change near the critical value of Ric ≈ - 0.02. In the weak-interaction regime, both formation number and separation number increase rapidly against Ri. While in the transition and strong-interaction regimes alike, the formation number increases at a much slower rate than in the weak-interaction regime, and the separation number declines dramatically as Ri increases. Finally, a qualitative explanation on the variation patterns of formation number and separation number is proposed based on the buoyancy effects on the dynamic properties of the leading vortex ring and the vortex interaction patterns.

  3. EXPERIMENTAL INVESTIGATION INTO HOT WATER SLOT JETS WITH NEGATIVELY BUOYANCY IN CROSS FLOW

    Institute of Scientific and Technical Information of China (English)

    YANG Zhong-hua; HUAI Wen-xin; DAI Hui-chao

    2005-01-01

    An experiment was conducted to examine the near-field behavior of negatively buoyant planar jets in flowing environment. Hot water jet was projected downwards at different angles from a slot into a uniform cross flow. Micro Acoustic Doppler Velocimeter (Micro ADV) system is used to measure the velocity and turbulent fluxes of Reynolds stresses. The whole field temperatures were measured with fast response thermocouples. Pure jets experiments were made also to study the effect of buoyancy in negatively buoyant jets. It is found that the influenced area of hot jets is larger than which of pure jets when the jet angle is 90° and the influenced area of hot jets is smaller than which of pure jets when the jet angle is 45°. The difference is not obvious at 60° angle jets. This means that the rising of temperature has effect not only on negatively buoyancy, but also on the intensity of turbulence. The contrast of these two influences dominates the trend of jet flow.

  4. Nonlinear waves in stratified Taylor--Couette flow. Part 2. Buoyancy flux

    CERN Document Server

    Leclercq, Colin; Caulfield, Colm-Cille P; Dalziel, Stuart B; Linden, Paul F

    2016-01-01

    This paper is the second part of a two-fold study of mixing, i.e. the formation of layers and upwelling of buoyancy, in axially stratified Taylor--Couette flow, with fixed outer cylinder. In a first paper, we showed that the dynamics of the flow was dominated by coherent structures made of a superposition of nonlinear waves. (Mixed)-ribbons and (mixed)-cross-spirals are generated by interactions between a pair of linearly unstable helical modes of opposite `handedness', and appear to be responsible for the formation of well-mixed layers and sharp density interfaces. In this paper, we show that these structures are also fully accountable for the upwards buoyancy flux in the simulations. The mechanism by which this occurs is a positive coupling between the density and vertical velocity components of the most energetic waves. This coupling is primarily caused by diffusion of density at low Schmidt number Sc, but can also be a nonlinear effect at larger Sc. Turbulence was found to contribute negatively to the buo...

  5. Results of Buoyancy-gravity Effects in ITER Cable-in- Conduit Conductor with Dual Channel

    Science.gov (United States)

    Bruzzone, P.; Stepanov, B.; Zanino, R.; Richard, L. Savoldi

    2006-04-01

    The coolant in the ITER cable-in-conduit conductors (CICC) flows at significant higher speed in the central channel than in the strand bundle region due to the large difference of hydraulic impedance. When energy is deposited in the bundle region, e.g. by ac loss or radiation, the heat removal in vertically oriented dual channel CICC with the coolant flowing downward is affected by the reduced density of helium (buoyancy) in the bundle region, which is arising from the temperature gradient due to poor heat exchange between the two channels. At large deposited power, flow stagnation and back-flow can cause in the strand bundle area a slow temperature runaway eventually leading to quench. A new test campaign of the thermal-hydraulic behavior was carried out in the SULTAN facility on an instrumented section of the ITER Poloidal Field Conductor Insert (PFIS). The buoyancy-gravity effect was investigated using ac loss heating, with ac loss in the cable calibrated in separate runs. The extent of upstream temperature increase was explored over a broad range of mass flow rate and deposited power. The experimental behavior is partly reproduced by numerical simulations. The results from the tests are extrapolated to the likely operating conditions of the ITER Toroidal Field conductor with the inboard leg cooled from top to bottom and heat deposited by nuclear radiation from the burning plasma.

  6. Preferential flow paths and heat pipes: Results from laboratory experiments on heat-driven flow in natural and artificial rock fractures

    Energy Technology Data Exchange (ETDEWEB)

    Kneafsey, T.J.; Pruess, K. [Lawrence Berkeley National Lab., CA (United States). Earth Sciences Div.

    1997-06-01

    Water flow in fractures under the conditions of partial saturation and thermal drive may lead to fast flow along preferential localized pathways and heat pipe conditions. Water flowing in fast pathways may ultimately contact waste packages at Yucca Mountain and transport radionuclides to the accessible environment. Sixteen experiments were conducted to visualize liquid flow in glass fracture models, a transparent epoxy fracture replica, and a rock/replica fracture assembly. Spatially resolved thermal monitoring was performed in seven of these experiments to evaluate heat-pipe formation. Depending on the fracture apertures and flow conditions, various flow regimes were observed including continuous rivulet flow for high flow rates, intermittent rivulet flow and drop flow for intermediate flow rates, and film flow for low flow rates and wide apertures. These flow regimes were present in both fracture models and in the replica of a natural fracture. Heat-pipe conditions indicated by low thermal gradients were observed in five experiments. Conditions conducive to heat-pipe formation include an evaporation zone, condensation zone, adequate space for vapor and liquid to travel, and appropriate fluid driving forces. In one of the two experiments where heat pipe conditions were not observed, adequate space for liquid-vapor counterflow was not provided. Heat pipe conditions were not established in the other, because liquid flow was inadequate to compensate for imbibition and the quantity of heat contained within the rock.

  7. The use of spirometry to evaluate pulmonary function in olive ridley sea turtles (Lepidochelys olivacea) with positive buoyancy disorders.

    Science.gov (United States)

    Schmitt, Todd L; Munns, Suzanne; Adams, Lance; Hicks, James

    2013-09-01

    This study utilized computed spirometry to compare the pulmonary function of two stranded olive ridley sea turtles (Lepidochelys olivacea) presenting with a positive buoyancy disorder with two healthy captive olive ridley sea turtles held in a large public aquarium. Pulmonary function test (PFT) measurements demonstrated that the metabolic cost of breathing was much greater for animals admitted with positive buoyancy than for the normal sea turtles. Positively buoyant turtles had higher tidal volumes and significantly lower breathing-frequency patterns with significantly higher expiration rates, typical of gasp-type breathing. The resulting higher energetic cost of breathing in the diseased turtles may have a significant impact on their long-term survival. The findings represent a method for clinical respiratory function analysis for an individual animal to assist with diagnosis, therapy, and prognosis. This is the first study, to our knowledge, to evaluate objectively sea turtles presenting with positive buoyancy and respiratory disease using pulmonary function tests.

  8. Numerical Study of Double Diffusive Convection in a Lid Driven Cavity with Linearly Salted Side Walls

    Directory of Open Access Journals (Sweden)

    Nithish Reddy

    2017-01-01

    Full Text Available Double diffusive convection phenomenon is widely seen in process industries, where the interplay between thermal and solutal (mass buoyancy forces play a crucial role in governing the outcome. In the current work, double diffusive convection phenomenon in a lid driven cavity model with linearly salted side walls has been studied numerically using Finite element simulations. Top and bottom walls of the cavity are assumed cold and hot respectively while other boundaries are set adiabatic to heat and mass flow. The calculations of energy and momentum transport in the cavity is done using velocity-vorticity form of Navier-Stokes equations consisting of velocity Poisson equations, vorticity transport, energy and concentration equations. Galerkin’s weighted residual method has been implemented to approximate the governing equations. Simulation results are obtained for convective heat transfer for 100buoyancy ratio is positive and vice versa. Maximum Nusselt number is recorded at buoyancy ratio 50 and Richardson number 3.0, on the other hand low Nusselt number is witnessed for buoyancy ratio 50.

  9. Century-long increasing trend and variability of dissolved organic carbon export from the Mississippi River basin driven by natural and anthropogenic forcing

    Science.gov (United States)

    Ren, Wei; Tian, Hanqin; Cai, Wei-Jun; Lohrenz, Steven E.; Hopkinson, Charles S.; Huang, Wei-Jen; Yang, Jia; Tao, Bo; Pan, Shufen; He, Ruoying

    2016-09-01

    There has been considerable debate as to how natural forcing and anthropogenic activities alter the timing and magnitude of the delivery of dissolved organic carbon (DOC) to the coastal ocean, which has ramifications for the ocean carbon budget, land-ocean interactions, and coastal life. Here we present an analysis of DOC export from the Mississippi River to the Gulf of Mexico during 1901-2010 as influenced by changes in climate, land use and management practices, atmospheric CO2, and nitrogen deposition, through the integration of observational data with a coupled hydrologic/biogeochemical land model. Model simulations show that DOC export in the 2000s increased more than 40% since the 1900s. For the recent three decades (1981-2010), however, our simulated DOC export did not show a significant increasing trend, which is consistent with observations by U.S. Geological Survey. Our factorial analyses suggest that land use and land cover change, including land management practices (LMPs: i.e., fertilization, irrigation, tillage, etc.), were the dominant contributors to the century-scale trend of rising total riverine DOC export, followed by changes in atmospheric CO2, nitrogen deposition, and climate. Decadal and interannual variations of DOC export were largely attributed to year-to-year climatic variability and extreme flooding events, which have been exacerbated by human activity. LMPs show incremental contributions to DOC increase since the 1960s, indicating the importance of sustainable agricultural practices in coping with future environmental changes such as extreme flooding events. Compared to the observational-based estimate, the modeled DOC export was 20% higher, while DOC concentrations were slightly lower. Further refinements in model structure and input data sets should enable reductions in uncertainties in our prediction of century-long trends in DOC.

  10. Swim bladder function and buoyancy control in pink snapper (Pagrus auratus) and mulloway (Argyrosomus japonicus).

    Science.gov (United States)

    Stewart, John; Hughes, Julian M

    2014-04-01

    Physoclist fish are able to regulate their buoyancy by secreting gas into their hydrostatic organ, the swim bladder, as they descend through the water column and by resorbing gas from their swim bladder as they ascend. Physoclists are restricted in their vertical movements due to increases in swim bladder gas volume that occur as a result of a reduction in hydrostatic pressure, causing fish to become positively buoyant and risking swim bladder rupture. Buoyancy control, rates of swim bladder gas exchange and restrictions to vertical movements are little understood in marine teleosts. We used custom-built hyperbaric chambers and laboratory experiments to examine these aspects of physiology for two important fishing target species in southern Australia, pink snapper (Pagrus auratus) and mulloway (Argyrosomus japonicus). The swim bladders of pink snapper and mulloway averaged 4.2 and 4.9 % of their total body volumes, respectively. The density of pink snapper was not significantly different to the density of seawater (1.026 g/ml), whereas mulloway were significantly denser than seawater. Pink snapper secreted gas into their swim bladders at a rate of 0.027 ± 0.005 ml/kg/min (mean ± SE), almost 4 times faster than mulloway (0.007 ± 0.001 ml/kg/min). Rates of swim bladder gas resorption were 11 and 6 times faster than the rates of gas secretion for pink snapper and mulloway, respectively. Pink snapper resorbed swim bladder gas at a rate of 0.309 ± 0.069 ml/kg/min, 7 times faster than mulloway (0.044 ± 0.009 ml/kg/min). Rates of gas exchange were not affected by water pressure or water temperature over the ranges examined in either species. Pink snapper were able to acclimate to changes in hydrostatic pressure reasonably quickly when compared to other marine teleosts, taking approximately 27 h to refill their swim bladders from empty. Mulloway were able to acclimate at a much slower rate, taking approximately 99 h to refill their swim bladders. We estimated that the

  11. Consistent model driven architecture

    Science.gov (United States)

    Niepostyn, Stanisław J.

    2015-09-01

    The goal of the MDA is to produce software systems from abstract models in a way where human interaction is restricted to a minimum. These abstract models are based on the UML language. However, the semantics of UML models is defined in a natural language. Subsequently the verification of consistency of these diagrams is needed in order to identify errors in requirements at the early stage of the development process. The verification of consistency is difficult due to a semi-formal nature of UML diagrams. We propose automatic verification of consistency of the series of UML diagrams originating from abstract models implemented with our consistency rules. This Consistent Model Driven Architecture approach enables us to generate automatically complete workflow applications from consistent and complete models developed from abstract models (e.g. Business Context Diagram). Therefore, our method can be used to check practicability (feasibility) of software architecture models.

  12. Safety divers prepare HST mockup in the Neutral Buoyancy Simulator at MSFC

    Science.gov (United States)

    1993-01-01

    Safety divers in the Neutral Buoyancy Simulator (NBS) at the Marshall Space Flight Center (MSFC) prepare a mockup of the Hubble Space Telescope (HST) for one of 32 separate training sessions conducted by four of the STS-61 crew members in June. The three-week process allowed mission trainers to refine the timelines for the five separate spacewalks scheduled to be conducted on the actual mission scheduled for December 1993. The HST is separated into two pieces since the water tank depth cannot support the entire structure in one piece. The full length payload bay mockup shows the Solar Array Carrier in the foreground and the various containers that will house replacement hardware that will be carried on the mission.

  13. Does size and buoyancy affect the long-distance transport of floating debris?

    Science.gov (United States)

    Ryan, Peter G.

    2015-08-01

    Floating persistent debris, primarily made from plastic, disperses long distances from source areas and accumulates in oceanic gyres. However, biofouling can increase the density of debris items to the point where they sink. Buoyancy is related to item volume, whereas fouling is related to surface area, so small items (which have high surface area to volume ratios) should start to sink sooner than large items. Empirical observations off South Africa support this prediction: moving offshore from coastal source areas there is an increase in the size of floating debris, an increase in the proportion of highly buoyant items (e.g. sealed bottles, floats and foamed plastics), and a decrease in the proportion of thin items such as plastic bags and flexible packaging which have high surface area to volume ratios. Size-specific sedimentation rates may be one reason for the apparent paucity of small plastic items floating in the world’s oceans.

  14. Buoyancy leads to high productivity of the Changjiang diluted water: a note

    Institute of Scientific and Technical Information of China (English)

    CHEN Chen-Tung Arthur

    2008-01-01

    Being the mightiest river emptying into the East China Sea (ECS) and the Pacific Ocean,compounded with the large increase of nitrogen and phosphorus input due to anthropogenic activities,the Changjiang River (Yangtze River) has become a dominating source of these nutrients to the estuary.The high nutrient concentrations notwithstanding,however,outside of the estuary the high biological productivity of the Changjiang diluted water (CDW) are most probably fueled mainly by nutrient-rich subsurface waters originating from the upwelled Kuroshio waters.This is because while the buoyancy of the CDW spreads it out on the ECS continen-tal shelf,the CDW entrains subsurface waters along with the nutrients.Nutrients thus supplied are several times more than those supplied by the Changjiang River.

  15. Heart Rate Responses to Unaided Orion Side Hatch Egress in the Neutral Buoyancy Laboratory

    Science.gov (United States)

    English, Kirk L.; Hwang, Emma Y.; Ryder, Jeffrey W.; Kelly, Cody; Walker, Thomas; Ploutz-Snyder, Lori

    2016-01-01

    The Orion capsule will be the next NASA-built vehicle used for near and deep space exploration. The nominal landing scenario for Orion involves splashdown in the Pacific Ocean and subsequent aided crew egress conducted by military personnel. Contingency operations, however, require the crew to egress the capsule unaided, deploy an inflatable life raft, and to ingress the raft. Unaided egress is expected to be physiologically demanding, but no data exist to corroborate this. Thus, we evaluated the heart rate response to unaided Orion side hatch egress and raft ingress as par of the NASA crew Survival Engineering Team's evaluation of egress procedures using the Post-landing Orion Recovery Trainer (PORT) article in the Neutral Buoyancy Laboratory (NBL).

  16. Solving problems to learn concepts, how does it happen? A case for buoyancy

    Science.gov (United States)

    Buteler, Laura; Coleoni, Enrique

    2016-12-01

    Problem solving is a preferred activity teachers choose to help students learn concepts. At the same time, successful problem solving is widely regarded as a very good indicator of conceptual learning. Many studies have provided evidence that problem solving often improves students' chances of learning concepts. Still, the question remains relatively unexplored as to how this activity is useful to promote concept learning. In this study we explore this question in the setting of three university students solving a problem on hydrostatics, in which the concept of buoyancy is involved. We use coordination class theory to study how these students progress on their conceptual understanding. We were able to describe how this progress is related to contextual traits, as well as to students' particular epistemic stances. Finally, we discuss some implications for research and for teaching.

  17. Buoyancy effects on the 3D MHD stagnation-point flow of a Newtonian fluid

    Science.gov (United States)

    Borrelli, A.; Giantesio, G.; Patria, M. C.; Roşca, N. C.; Roşca, A. V.; Pop, I.

    2017-02-01

    This work examines the steady three-dimensional stagnation-point flow of an electrically conducting Newtonian fluid in the presence of a uniform external magnetic field H0 under the Oberbeck-Boussinesq approximation. We neglect the induced magnetic field and examine the three possible directions of H0 which coincide with the directions of the axes. In all cases it is shown that the governing nonlinear partial differential equations admit similarity solutions. We find that the flow has to satisfy an ordinary differential problem whose solution depends on the Hartmann number M, the buoyancy parameter λ and the Prandtl number Pr. The skin-friction components along the axes are computed and the stagnation-point is classified. The numerical integration shows the existence of dual solutions and the occurrence of the reverse flow for some values of the parameters.

  18. Simulation of DPM distribution in a long single entry with buoyancy effect

    Institute of Scientific and Technical Information of China (English)

    Zheng Yi; Thiruvengadam Magesh; Lan Hai; Tien C. Jerry

    2015-01-01

    Diesel particulate matter (DPM) is considered carcinogenic after prolonged exposure. With more diesel-powered equipment used in underground mines, miners’ exposure to DPM has become an increasing concern. This paper used computational fluid dynamics (CFD) method to study DPM distribution based on an experiment conducted by the Diesel Emissions Evaluation Program (DEEP) in Canada. Twenty-four cases were simulated where the emissions from both truck and load-haul-dumps (LHDs) were examined. Each vehicle was placed in two stream wise locations, and the vehicles were oriented either facing or with the rear end toward the main fresh airflow. A species transport model with buoyancy effect was then used to examine the DPM dispersion pattern. High DPM regions were identified downstream, around, and even upstream of diesel engines. This can provide guidelines for good working practices and selection of diesel emission reduction technologies underground.

  19. Numerical experiments modeling the buoyancy of bubbles in a vertical plane layer of a magnetic fluid

    Energy Technology Data Exchange (ETDEWEB)

    Tsebers, A.O.

    1985-12-01

    The buoyancy of elliptical bubbles in the absence of surface tension are determined through a numerical experiment as a function of the semiaxis ratio, and the results are found to be in good agreement with the well-known Taylor-Saffman solution. Particular attention is given to the effect of the motion of bubbles on the development of a MHD instability in a transverse magnetic field, and it is shown that this motion stabilizes the development of perturbations in the motion direction and intensifies perturbations in the direction transverse to the motion. It is further shown that in the presence of a magnetic field, the configurations of the buoyant bubbles are not determined uniquely by physical parameters but also depend on their initial profiles. 6 references.

  20. The Enabling and Protective Role of Academic Buoyancy in the Appraisal of Fear Appeals Used Prior to High Stakes Examinations

    Science.gov (United States)

    Symes, Wendy; Putwain, David W.; Remedios, Richard

    2015-01-01

    Prior to high stakes examinations, teachers may engage in instructional practices to encourage their students to prepare well for their exams, including the use of "fear appeals". The current study examined whether academic buoyancy played a role in student appraisals of fear appeals as threatening or challenging. High school students…

  1. Hydrogen Production by Steam Reforming of Liquefied Natural Gas (LNG) Over Nickel-Phosphorus-Alumina Xerogel Catalyst Prepared by a Carbon-Templating Epoxide-Driven Sol-Gel Method.

    Science.gov (United States)

    Bang, Yongju; Park, Seungwon; Han, Seung Ju; Yoo, Jaekyeong; Choi, Jung Ho; Kang, Tae Hun; Lee, Jinwon; Song, In Kyu

    2016-05-01

    A nickel-phosphorus-alumina xerogel catalyst was prepared by a carbon-templating epoxide-driven sol-gel method (denoted as CNPA catalyst), and it was applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, a nickel-phosphorus-alumina xerogel catalyst was also prepared by a similar method in the absence of carbon template (denoted as NPA catalyst). The effect of carbon template addition on the physicochemical properties and catalytic activities of the catalysts in the steam reforming of LNG was investigated. Both CNPA and NPA catalysts showed excellent textural properties with well-developed mesoporous structure. However, CNPA catalyst retained a more reducible nickel aluminate phase than NPA catalyst. XRD analysis of the reduced CNPA and NPA catalysts revealed that nickel sintering on the CNPA catalyst was suppressed compared to that on the NPA catalyst. From H2-TPD and CH4-TPD measurements of the reduced CNPA and NPA catalysts, it was also revealed that CNPA catalyst with large amount of hydrogen uptake and strong hydrogen-binding sites showed larger amount of methane adsorption than NPA catalyst. In the hydrogen production by steam reforming of LNG, CNPA catalyst with large methane adsorption capacity showed a better catalytic activity than NPA catalyst.

  2. Buoyancy effects on upward brine displacement caused by CO2 injection

    Energy Technology Data Exchange (ETDEWEB)

    Oldenburg, C.M.; Rinaldi, A.

    2010-01-15

    Upward displacement of brine from deep reservoirs driven by pressure increases resulting from CO{sub 2} injection for geologic carbon sequestration may occur through improperly sealed abandoned wells, through permeable faults, or through permeable channels between pinch-outs of shale formations. The concern about upward brine flow is that, upon intrusion into aquifers containing groundwater resources, the brine may degrade groundwater. Because both salinity and temperature increase with depth in sedimentary basins, upward displacement of brine involves lifting fluid that is saline but also warm into shallower regions that contain fresher, cooler water. We have carried out dynamic simulations using TOUGH2/EOS7 of upward displacement of warm, salty water into cooler, fresher aquifers in a highly idealized two-dimensional model consisting of a vertical conduit (representing a well or permeable fault) connecting a deep and a shallow reservoir. Our simulations show that for small pressure increases and/or high-salinity-gradient cases, brine is pushed up the conduit to a new static steady-state equilibrium. On the other hand, if the pressure rise is large enough that brine is pushed up the conduit and into the overlying upper aquifer, flow may be sustained if the dense brine is allowed to spread laterally. In this scenario, dense brine only contacts the lower-most region of the upper aquifer. In a hypothetical case in which strong cooling of the dense brine occurs in the upper reservoir, the brine becomes sufficiently dense that it flows back down into the deeper reservoir from where it came. The brine then heats again in the lower aquifer and moves back up the conduit to repeat the cycle. Parameter studies delineate steady-state (static) and oscillatory solutions and reveal the character and period of oscillatory solutions. Such oscillatory solutions are mostly a curiosity rather than an expected natural phenomenon because in nature the geothermal gradient prevents the

  3. Numerical simulation of heat transfer and natural convection of the indirect-driven cryogenic target%黑腔冷冻靶传热与自然对流的数值模拟研究∗

    Institute of Scientific and Technical Information of China (English)

    黄鑫; 彭述明; 周晓松; 余铭铭; 尹剑; 温成伟

    2015-01-01

    ICF design requires smooth and uniform deuterium-tritium (D-T) ice layers in a spherical shell. Thermal environ-ment around the capsule is the key to reach the low-mode ice layer roughness requirement and obtain a high quality ice layer. In this paper, we present the results of three-dimensional simulation for an indirect-driven cryogenic target, focusing on the issues of heat transfer and natural convection flow inside the hohlraum. A thermal and hydrodynamic calculation is first proposed to investigate the convection heat transfer effect on the D-T ice layer. Comparing the two cases with gravity considered or neglected, we find that the temperature variation at the ice layer inner surface caused by the natural convection flow and the hohlraum’s structure are of the same order of magnitude. Then the parameters study on Rayleigh number, which is a dimensionless number associated with free convection, is carried out. Thermal simulations on different Rayleigh number are provided. Temperature variation at the D-T ice layer inner surface is to increase as soon as the Rayleigh number reaches 60. Comparisons among different gases under different operating pressure conditions are made. In order to avoid the convection heat transfer effect in a wide range of pressure, it is necessary to take pure helium or mixture gas with a small amount of hydrogen as the tamping gas. The influence of hohlraum’s orientation on the natural convection is also studied. It is found that the convective heat transfer effect in a horizontally orientated hohlraum is stronger than that in a vertical one. Based on these, we discuss the possibility to eliminate the convection flow by partitioning the hohlraum into several regions. The calculated results for several cases of different gas-region models indicate that the convection flow can be eliminated with an appropriate division in a vertically orientated hohlaum but cannot in a horizontally orientated one. The conclusions in this paper have

  4. Penguin lungs and air sacs: implications for baroprotection, oxygen stores and buoyancy.

    Science.gov (United States)

    Ponganis, P J; St Leger, J; Scadeng, M

    2015-03-01

    The anatomy and volume of the penguin respiratory system contribute significantly to pulmonary baroprotection, the body O2 store, buoyancy and hence the overall diving physiology of penguins. Therefore, three-dimensional reconstructions from computerized tomographic (CT) scans of live penguins were utilized to measure lung volumes, air sac volumes, tracheobronchial volumes and total body volumes at different inflation pressures in three species with different dive capacities [Adélie (Pygoscelis adeliae), king (Aptenodytes patagonicus) and emperor (A. forsteri) penguins]. Lung volumes scaled to body mass according to published avian allometrics. Air sac volumes at 30 cm H2O (2.94 kPa) inflation pressure, the assumed maximum volume possible prior to deep dives, were two to three times allometric air sac predictions and also two to three times previously determined end-of-dive total air volumes. Although it is unknown whether penguins inhale to such high volumes prior to dives, these values were supported by (a) body density/buoyancy calculations, (b) prior air volume measurements in free-diving ducks and (c) previous suggestions that penguins may exhale air prior to the final portions of deep dives. Based upon air capillary volumes, parabronchial volumes and tracheobronchial volumes estimated from the measured lung/airway volumes and the only available morphometry study of a penguin lung, the presumed maximum air sac volumes resulted in air sac volume to air capillary/parabronchial/tracheobronchial volume ratios that were not large enough to prevent barotrauma to the non-collapsing, rigid air capillaries during the deepest dives of all three species, and during many routine dives of king and emperor penguins. We conclude that volume reduction of airways and lung air spaces, via compression, constriction or blood engorgement, must occur to provide pulmonary baroprotection at depth. It is also possible that relative air capillary and parabronchial volumes are

  5. The buoyancy of large siliceous magma chambers is sufficient to initiate supereruptions

    Science.gov (United States)

    Malfait, W.; Sanchez-Valle, C.; Seifert, R.; Petitgirard, S.; Perrillat, J.; Ota, T.; Nakamura, E.; Lerch, P.; Mezouar, M.

    2012-12-01

    The geological record shows abundant evidence for rare, but extremely large caldera-forming eruptions of siliceous magmas that dwarf all historical volcanic episodes in erupted volume [1] and environmental impact [2, 3]. Because of the large size of the magma chambers that feed these eruptions, the overpressure generated by magma recharge is insufficient to fracture the cap rock and trigger an eruption [4]. For these thick magma chambers, the buoyancy of the magma potentially creates a sufficient overpressure capable of fracturing the cap rock, but the lack of data on the density of rhyolite melts precludes the appropriate estimation of the overpressure and the role of buoyancy in initiating supervolcano eruptions. The density of rhyolite melts has not been determined at super-liquidus temperatures or elevated pressures because traditional techniques, including Archimedean methods, sink/float experiments and acoustic measurements, are limited by the high melt viscosity. Here, we measured the density of rhyolitic/granitic melts with 0, 4.5 and 7.7 wt% of dissolved water at geologically relevant conditions: 0.9 to 3.6 GPa, 1270 to 1950 K. High pressure and temperature conditions were generated in a Paris-Edinburgh large volume press. Before and after each density measurement, the molten state of the sample was verified by X-ray diffraction. The density of the melt (ρPT) was determined from the X-ray attenuation coefficient of the sample, determined in situ (μPT) and at room conditions (μ0), and the density at room conditions (ρ0): ρPT=ρ0.(μPT/μ0). The acquired data were combined with available ambient pressure data on super-cooled liquids [5, 6] to derive a third order Birch-Murnaghan equation of state that accurately predicts the density of rhyolite melts as a function of pressure, temperature and water content, and the partial molar volume of dissolved water. Application of the melt equation of state to calculate the overpressure at the roof of supervolcano

  6. China’s industrial growth:capital-driven or resource-driven?

    Institute of Scientific and Technical Information of China (English)

    张其仔; 郭朝先

    2009-01-01

    Economic growth can take different forms;growth can be resource-driven,labor-driven,capital-driven,or technology-driven.Numerous studies conclude that China’s economic growth is capital-driven.Such a conclusion is derived after excluding any effects of resource and environmental factors.In this article,resource and environmental factors are incorporated in order to stndy the influence of factors on industrial growth.This study found that resource and environmental factors contribute much more than capital to industrial growth,and China’s industrial growth is still resource-driven.The nature of China’s industrial growth also suggests that the country’s economic growth has not completely extricated itself from a resource-driven model,which in turn exerts considerable influence on the country’s macroeconomic policies.

  7. Superhydrophobic treatment using atmospheric-pressure He/C4F8 plasma for buoyancy improvement

    Science.gov (United States)

    Noh, Sooryun; Moon, A.-Young; Moon, Se Youn

    2015-04-01

    A superhydrophobic miniature boat was fabricated with aluminum alloy plates treated with atmospheric-pressure helium (He)/octafluorocyclobutane (C4F8) plasma using 13.56 MHz rf power. When only 0.13% C4F8 was added to He gas, the contact angle of the surface increased to 140° and the surface showed superhydrophobic properties. On the basis of chemical and morphological analyses, fluorinated functional groups (CF, CF2, and CF3) and nano-/micro-sized particles were detected on the Al surface. These features brought about superhydrophobicity similar to the lotus effect. While the miniature boat, assembled with plasma-treated plates, was immersed in water, a layer of air (i.e., a plastron) surrounded the superhydrophobic surfaces. This effect contributed to the development of a 4.7% increase in buoyancy. In addition, the superhydrophobic properties lasted for two months under the submerged condition. These results demonstrate that treatment with atmospheric-pressure He/C4F8 plasma is a promising method of improving the load capacity and antifouling properties, and reducing the friction of marine ships through a fast and low-cost superhydrophobic treatment process.

  8. Neutral Buoyancy Simulator-NB50B-SADE Training Exercises

    Science.gov (United States)

    1983-01-01

    One of the main components of the Hubble Space Telescope (HST) is the Solar Array Drive Electronics (SADE) system. This system interfaces with the Support System Module (SSM) for exchange of operational commands and telemetry data. SADE operates and controls the Solar Array Drive Mechanisms (SADM) for the orientation of the Solar Array Drive (SAD). It also monitors the position of the arrays and the temperature of the SADM. During the first HST servicing mission, the astronauts replaced the SADE component because of some malfunctions. This turned out to be a very challenging extravehicular activity (EVA). Two transistors and two diodes had been thermally stressed with the conformal coating discolored and charred. Soldered cornections became molten and reflowed between the two diodes. The failed transistors gave no indication of defective construction. All repairs were made and the HST was redeposited into orbit. Prior to undertaking this challenging mission, the orbiter's crew trained at Marshall Space Flight Center's (MSFC) Neutral Buoyancy Simulator (NBS) to prepare themselves for working in a low gravity environment. They also practiced replacing HST parts and exercised maneuverability and equipment handling. Pictured are crew members practicing on a space platform.

  9. Buoyancy effects in vertical rectangular duct with coplanar magnetic field and single sided heat load

    Energy Technology Data Exchange (ETDEWEB)

    Kirillov, I.R. [NIIEFA – JSC “D.V. Efremov Institute of Electrophysical Apparatus”, St. Petersburg, 196641 (Russian Federation); Obukhov, D.M., E-mail: obukhov@sintez.niiefa.spb.su [NIIEFA – JSC “D.V. Efremov Institute of Electrophysical Apparatus”, St. Petersburg, 196641 (Russian Federation); Genin, L.G. [MPEI – National Research University “Moscow Power Engineering Institute”, 14 Krasnokazarmennaya str., Moscow (Russian Federation); Sviridov, V.G.; Razuvanov, N.G.; Batenin, V.M.; Belyaev, I.A. [JIHT – Joint Institute of High Temperatures of the Russian Academy of Science, 13/19, Igorskaya str., Moscow (Russian Federation); Poddubnyi, I.I. [MPEI – National Research University “Moscow Power Engineering Institute”, 14 Krasnokazarmennaya str., Moscow (Russian Federation); Pyatnitskaya, N.Yu. [JIHT – Joint Institute of High Temperatures of the Russian Academy of Science, 13/19, Igorskaya str., Moscow (Russian Federation)

    2016-03-15

    Highlights: • Heat transfer in vertical duct mercury flow in coplanar magnetic field is studied. • Mean velocity, temperature and temperature pulsations are measured. • Buoyancy influence on heat transfer is found. - Abstract: This article investigates an effect which was found out in downward flow of liquid metal (LM) in vertical rectangular duct in coplanar magnetic field (MF). The experiments have been performed on facility which located in JIHT. This facility is magneto hydrodynamic (MHD) mercury close-loop. The temperature field measurements have been performed at one side heating conditions in coplanar magnetic field. The averaged temperature fields, wall temperature distributions and statistical characteristics of temperature fluctuation have been obtained. The strong influence of counter thermo-gravitational convection (TGC) on average and fluctuation parameters has been observed. The influence of TGC in magnetic field leads to developing of temperature low-frequency fluctuations with high magnitude. The temperature fluctuation amplitude in a wide range of operating conditions is higher than turbulence level.

  10. Hypergravity to Explore the Role of Buoyancy in Boiling in Porous Media

    Science.gov (United States)

    Lioumbas, John S.; Krause, Jutta; Karapantsios, Thodoris D.

    2013-02-01

    Boiling in porous media is an active topic of research since it is associated with various applications, e.g. microelectronics cooling, wetted porous media as thermal barriers, food frying. Theoretical expressions customary scale boiling heat and mass transfer rates with the value of gravitational acceleration. Information obtained at low gravity conditions show a deviation from the above scaling law but refers exclusively to non-porous substrates. In addition, the role of buoyancy in boiling at varying gravitational levels (i.e. from microgravity—important to satellites and future Lunar and Martial missions, to high-g body forces—associated with fast aerial maneuvers) is still unknown since most experiments were conducted over a limited range of g-value. The present work aims at providing evidence regarding boiling in porous media over a broad range of hypergravity values. For this, a special device has been constructed for studying boiling inside porous media in the Large Diameter Centrifuge (LDC at ESA/ESTEC). LDC offers the unique opportunity to cancel the shear stresses and study only the effect of increased normal forces on boiling in porous media. The device permits measurement of the temperature field beneath the surface of the porous material and video recordings of bubble activity over the free surface of the porous material. The preliminary results presented from experiments conducted at terrestrial and hypergravity conditions, reveal for the first time the influence of increased levels of gravity on boiling in porous media.

  11. Innovation Ecosystem:Exploring the Nature of Innovation-Driven and Innovation Paradigm Change%创新生态系统:创新驱动的本质探源与范式转换

    Institute of Scientific and Technical Information of China (English)

    刘雪芹; 张贵

    2016-01-01

    经济新常态下,创新生态系统已成为一种新的市场竞争模式和创新范式,创新驱动的本质直接体现为创新生态系统的构建和优化。通过探讨创新生态系统的源起及必要性,构建了创新生态系统要素模型,包括有形资产“硬件”与无形机制“软件”,其中体制机制作为活跃的创新要素,激发了热带雨林式创新,是创新生态系统的异质性所在。目前我国正处于向创新生态系统范式过渡阶段,应紧扣创新生态系统的内在特质,以我国创新活动中存在的问题为导向,从构建创新生态系统形成的基础体系、运行支撑体系、演化引导体系三个方面推进创新生态系统建设。%Under the new economic pattern ,innovation ecosystem has become a new mode of market competition and inno‐vation paradigm .And the nature of innovation‐driven embodies directly building and optimizing innovation ecosystems .In this paper the origin and necessity of the innovation ecosystem are discussed ,then the innovation ecosystem formula inclu‐ding tangible ingredients "hardware"and invisible mechanism "software"is constructed .The mechanism "software"acti‐vates the innovation factors and stimulates the innovation of tropical rainforest .Now our country is in a transition phase towards innovation ecosystem paradigm .Based on the nature and characteristics of innovation ecosystem ,we should pro‐mote the development of innovation ecosystem from three aspects :constructing the basic system of the formation ,the sup‐porting system of operation and the guiding system of evolution .

  12. Effects of buoyancy on lean premixed v-flames, Part II. VelocityStatistics in Normal and Microgravity

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, R.K.; Bedat, B.; Yegian, D.T.

    1999-07-01

    The field effects of buoyancy on laminar and turbulent premixed v-flames have been studied by the use of laser Doppler velocimetry to measure the velocity statistics in +1g, -1g and {micro}g flames. The experimental conditions covered mean velocity, Uo, of 0.4 to 2 m/s, methane/air equivalence ratio, f, of 0.62 to 0.75. The Reynolds numbers, from 625 to 3130 and the Richardson number from 0.05 to 1.34. The results show that a change from favorable (+1g) to unfavorable (-1g) mean pressure gradient in the plume create stagnating flows in the far field whose influences on the mean and fluctuating velocities persist in the near field even at the highest Re we have investigated. The use of Richardson number < 0.1 as a criterion for momentum dominance is not sufficient to prescribe an upper limit for these buoyancy effects. In {micro}g, the flows within the plumes are non-accelerating and parallel. Therefore, velocity gradients and hence mean strain rates in the plumes of laboratory flames are direct consequences of buoyancy. Furthermore, the rms fluctuations in the plumes of {micro}g flames are lower and more isotropic than in the laboratory flames to show that the unstable plumes in laboratory flames also induce velocity fluctuations. The phenomena influenced by buoyancy i.e. degree of flame wrinkling, flow acceleration, flow distribution, and turbulence production, can be subtle due to their close coupling with other flame flow interaction processes. But they cannot be ignored in fundamental studies or else the conclusions and insights would be ambiguous and not very meaningful.

  13. Effects of salinity and sea salt type on egg activation, fertilization, buoyancy and early embryology of European eel, Anguilla anguilla

    DEFF Research Database (Denmark)

    Sørensen, Sune Riis; Butts, Ian; Munk, Peter;

    2016-01-01

    sizes, while the remaining four salt types resulted in smaller eggs. All salt types except NaCl treatments led to high fertilization rates and had no effect on fertilization success as well as egg neutral buoyancies at 7 h post-fertilization. The study points to the importance of considering ionic...... composition of the media when rearing fish eggs and further studies are encouraged...

  14. Effects of buoyancy and thermal radiation on MHD flow over a stretching porous sheet using homotopy analysis method

    Directory of Open Access Journals (Sweden)

    Yahaya Shagaiya Daniel

    2015-09-01

    Full Text Available This paper investigates the theoretical influence of buoyancy and thermal radiation on MHD flow over a stretching porous sheet. The model which constituted highly nonlinear governing equations is transformed using similarity solution and then solved using homotopy analysis method (HAM. The analysis is carried out up to the 5th order of approximation and the influences of different physical parameters such as Prandtl number, Grashof number, suction/injection parameter, thermal radiation parameter and heat generation/absorption coefficient and also Hartman number on dimensionless velocity, temperature and the rate of heat transfer are investigated and discussed quantitatively with the aid of graphs. Numerical results obtained are compared with the previous results published in the literature and are found to be in good agreement. It was found that when the buoyancy parameter and the fluid velocity increase, the thermal boundary layer decreases. In case of the thermal radiation, increasing the thermal radiation parameter produces significant increases in the thermal conditions of the fluid temperature which cause more fluid in the boundary layer due to buoyancy effect, causing the velocity in the fluid to increase. The hydrodynamic boundary layer and thermal boundary layer thickness increase as a result of increase in radiation.

  15. Analytical Investigation of Laminar Viscoelastic Fluid Flow over a Wedge in the Presence of Buoyancy Force Effects

    Directory of Open Access Journals (Sweden)

    B. Rostami

    2014-01-01

    Full Text Available An analytical strong method, the homotopy analysis method (HAM, is employed to study the mixed convective heat transfer in an incompressible steady two-dimensional viscoelastic fluid flow over a wedge in the presence of buoyancy effects. The two-dimensional boundary-layer governing partial differential equations (PDEs are derived by the consideration of Boussinesq approximation. By the use of similarity transformation, we have obtained the ordinary differential nonlinear (ODE forms of momentum and energy equations. The highly nonlinear forms of momentum and energy equations are solved analytically. The effects of different involved parameters such as viscoelastic parameter, Prandtl number, buoyancy parameter, and the wedge angle parameter, which is related to the exponent m of the external velocity, on velocity and temperature distributions are plotted and discussed. An excellent agreement can be seen between the results and the previously published papers for f′′(0 and θ′(0 in some of the tables and figures of the paper for velocity and temperature profiles for various values of viscoelastic parameter and Prandtl number. The effects of buoyancy parameter on the velocity and temperature distributions are completely illustrated in detail.

  16. Light-driven cytochrome P450 hydroxylations

    DEFF Research Database (Denmark)

    Jensen, Kenneth; Jensen, Poul Erik; Møller, Birger Lindberg

    2011-01-01

    Plants are light-driven "green" factories able to synthesize more than 200,000 different bioactive natural products, many of which are high-value products used as drugs (e.g., artemisinin, taxol, and thapsigargin). In the formation of natural products, cytochrome P450 (P450) monooxygenases play...

  17. Large Eddy simulation of turbulence: A subgrid scale model including shear, vorticity, rotation, and buoyancy

    Science.gov (United States)

    Canuto, V. M.

    1994-01-01

    The Reynolds numbers that characterize geophysical and astrophysical turbulence (Re approximately equals 10(exp 8) for the planetary boundary layer and Re approximately equals 10(exp 14) for the Sun's interior) are too large to allow a direct numerical simulation (DNS) of the fundamental Navier-Stokes and temperature equations. In fact, the spatial number of grid points N approximately Re(exp 9/4) exceeds the computational capability of today's supercomputers. Alternative treatments are the ensemble-time average approach, and/or the volume average approach. Since the first method (Reynolds stress approach) is largely analytical, the resulting turbulence equations entail manageable computational requirements and can thus be linked to a stellar evolutionary code or, in the geophysical case, to general circulation models. In the volume average approach, one carries out a large eddy simulation (LES) which resolves numerically the largest scales, while the unresolved scales must be treated theoretically with a subgrid scale model (SGS). Contrary to the ensemble average approach, the LES+SGS approach has considerable computational requirements. Even if this prevents (for the time being) a LES+SGS model to be linked to stellar or geophysical codes, it is still of the greatest relevance as an 'experimental tool' to be used, inter alia, to improve the parameterizations needed in the ensemble average approach. Such a methodology has been successfully adopted in studies of the convective planetary boundary layer. Experienc e with the LES+SGS approach from different fields has shown that its reliability depends on the healthiness of the SGS model for numerical stability as well as for physical completeness. At present, the most widely used SGS model, the Smagorinsky model, accounts for the effect of the shear induced by the large resolved scales on the unresolved scales but does not account for the effects of buoyancy, anisotropy, rotation, and stable stratification. The

  18. Investing the role of buoyancy in iceberg calving dynamics from tidewater glaciers

    Science.gov (United States)

    Trevers, Matt; Payne, Tony; Cornford, Stephen

    2016-04-01

    The Greenland Ice Sheet (GIS) currently makes a major and accelerating contribution to sea level rise (SLR), with its contribution split roughly evenly between surface mass balance changes due to increased melting and dynamic ice loss through calving. In recent decades, many of Greenland's major outlet glaciers have retreated dramatically due to increased iceberg calving, associated with an increase in velocity and inland thinning. The potential contribution to SLR of a complete collapse of the GIS is ~7m. Iceberg calving is an important process not only as a major source of mass loss from the GIS, but also for the controlling influence it has on the dynamics of the grounding line and over the ice sheet as a whole. Despite plenty of scientific attention and a diverse body of literature, the processes involved in calving, their controlling factors and how it feeds back into glacier and ice sheet dynamics are still not fully understood. This presents a major uncertainty into projections of SLR over the coming decades and centuries. Using Elmer/Ice, a state-of-the-art full-Stokes finite-element model, we are able to resolve the stress distributions in high resolution at the calving front. Buoyancy forces have been proposed as a major influencing factor in inducing calving. By investigating the stress distributions induced in a buoyant calving front, we hope to gain an understanding of how environmental influences such as surface thinning and waterline notch-cutting influence the calving rate, and compare this to observations from calving glaciers in Greenland.

  19. Performance enhancement of a Lorentz force velocimeter using a buoyancy-compensated magnet system

    Science.gov (United States)

    Ebert, R.; Leineweber, J.; Resagk, C.

    2015-07-01

    Lorentz force velocimetry (LFV) is a highly feasible method for measuring flow rate in a pipe or a duct. This method has been established for liquid metal flows but also for electrolytes such as saltwater. A decrease in electrical conductivity of the medium causes a decrease of the Lorentz force which needs to be resolved, affecting the accuracy of the measurement. We use an electrical force compensation (EFC) balance for the determination of the tiny force signals in a test channel filled with electrolyte solution. It is used in a 90°-rotated orientation with a magnet system hanging vertically on its load bar. The thin coupling elements of its parallel guiding system limit the mass of the magnets to 1 kg. To overcome this restriction, which limits the magnetic flux density and hence the Lorentz forces, a weight force compensation mechanism is developed. Therefore, different methods such as air bearing are conceivable, but for the elimination of additional horizontal force components which would disturb the force signal, only compensation by lift force provided by buoyancy is reasonable. We present a swimming body setup that will allow larger magnet systems than before, because a large amount of the weight force will be compensated by this lift force. Thus the implementation of this concept has to be made with respect to hydrodynamical and mechanical stability. This is necessary to avoid overturning of the swimming body setup and to prevent inelastic deformation. Additionally, the issue will be presented and discussed whether thermal convection around the lifting body diminishes the signal-to-noise ratio (SNR) significantly or not.

  20. Thermo capillary and buoyancy flows instabilities; Instabilites d`ecoulements thermocapillaires et de thermogravite

    Energy Technology Data Exchange (ETDEWEB)

    Mercier, J.F.

    1997-10-22

    Fluid flows in which liquid layers are submitted to temperature gradient applied horizontally are studied. The thermo capillary and buoyancy effects are thus described. In the experiments, the form of the cell which contains the fluid is different and the fluid heating position too. Each of these experiments reveals a different aspect of the mechanism which is responsible of the flow instability. In the first experiment, the fluid is contained in a rectangular cell longer than larger and whose two longer vertical walls are differentially heated. The waves lengths, frequencies, propagation directions and instability thresholds of stationary, unsteady or oscillating modes obtained theoretically are compared to the structures observed experimentally. The instability mechanisms are essentially bound to the temperature vertical profile in the fluid and the heat exchanges between the fluid and the ambient air are particularly described. In the second experiment, the fluid is contained in an annular cell whose vertical cylindrical walls are differentially heated. The results obtained in the rectangular cell can be transposed to the annular cell substituting the constant thermal gradient of the rectangular geometry by those of the annular geometry, inversely proportional to the radial distance. The introduction of local parameters allows to show that the instability is developed at first near the inside cylinder. In the last experiment, the fluid layer is heated by an electric wire immersed in a parallel direction to the free surface. The development of an ascending vertical flow above the wire induces a deformation of the free surface which can be added to the instability mechanisms of the previous cells. (O.M.) 58 refs.

  1. Neutral Buoyancy Simulator: MSFC-Langley joint test of large space structures component assembly:

    Science.gov (United States)

    1978-01-01

    Once the United States' space program had progressed from Earth's orbit into outerspace, the prospect of building and maintaining a permanent presence in space was realized. To accomplish this feat, NASA launched a temporary workstation, Skylab, to discover the effects of low gravity and weightlessness on the human body, and also to develop tools and equipment that would be needed in the future to build and maintain a more permanent space station. The structures, techniques, and work schedules had to be carefully designed to fit this unique construction site. The components had to be lightweight for transport into orbit, yet durable. The station also had to be made with removable parts for easy servicing and repairs by astronauts. All of the tools necessary for service and repairs had to be designed for easy manipulation by a suited astronaut. And construction methods had to be efficient due to limited time the astronauts could remain outside their controlled environment. In lieu of all the specific needs for this project, an environment on Earth had to be developed that could simulate a low gravity atmosphere. A Neutral Buoyancy Simulator (NBS) was constructed by NASA Marshall Space Flight Center (MSFC) in 1968. Since then, NASA scientists have used this facility to understand how humans work best in low gravity and also provide information about the different kinds of structures that can be built. Another facet of the space station would be electrical cornectors which would be used for powering tools the astronauts would need for construction, maintenance and repairs. Shown is an astronaut training during an underwater electrical connector test in the NBS.

  2. Tectonic controls on earthquake size distribution and seismicity rate: slab buoyancy and slab bending

    Science.gov (United States)

    Nishikawa, T.; Ide, S.

    2014-12-01

    There are clear variations in maximum earthquake magnitude among Earth's subduction zones. These variations have been studied extensively and attributed to differences in tectonic properties in subduction zones, such as relative plate velocity and subducting plate age [Ruff and Kanamori, 1980]. In addition to maximum earthquake magnitude, the seismicity of medium to large earthquakes also differs among subduction zones, such as the b-value (i.e., the slope of the earthquake size distribution) and the frequency of seismic events. However, the casual relationship between the seismicity of medium to large earthquakes and subduction zone tectonics has been unclear. Here we divide Earth's subduction zones into over 100 study regions following Ide [2013] and estimate b-values and the background seismicity rate—the frequency of seismic events excluding aftershocks—for subduction zones worldwide using the maximum likelihood method [Utsu, 1965; Aki, 1965] and the epidemic type aftershock sequence (ETAS) model [Ogata, 1988]. We demonstrate that the b-value varies as a function of subducting plate age and trench depth, and that the background seismicity rate is related to the degree of slab bending at the trench. Large earthquakes tend to occur relatively frequently (lower b-values) in shallower subduction zones with younger slabs, and more earthquakes occur in subduction zones with deeper trench and steeper dip angle. These results suggest that slab buoyancy, which depends on subducting plate age, controls the earthquake size distribution, and that intra-slab faults due to slab bending, which increase with the steepness of the slab dip angle, have influence on the frequency of seismic events, because they produce heterogeneity in plate coupling and efficiently inject fluid to elevate pore fluid pressure on the plate interface. This study reveals tectonic factors that control earthquake size distribution and seismicity rate, and these relationships between seismicity and

  3. Composition, buoyancy regulation and fate of ice algal aggregates in the Central Arctic Ocean.

    Directory of Open Access Journals (Sweden)

    Mar Fernández-Méndez

    Full Text Available Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8-35 and 9-40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m(-2, maintaining an estimated net primary production of 0.4-40 mg C m(-2 d(-1, and accounted for 3-80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities.

  4. Composition, buoyancy regulation and fate of ice algal aggregates in the Central Arctic Ocean.

    Science.gov (United States)

    Fernández-Méndez, Mar; Wenzhöfer, Frank; Peeken, Ilka; Sørensen, Heidi L; Glud, Ronnie N; Boetius, Antje

    2014-01-01

    Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8-35 and 9-40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m(-2), maintaining an estimated net primary production of 0.4-40 mg C m(-2) d(-1), and accounted for 3-80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities.

  5. Developer Driven and User Driven Usability Evaluations

    DEFF Research Database (Denmark)

    Bruun, Anders

    2013-01-01

    Usability evaluation provide software development teams with insights on the degree to which a software application enables a user to achieve his/her goals, how fast these goals can be achieved, how easy it is to learn and how satisfactory it is in use Although usability evaluations are crucial....... The four primary findings from my studies are: 1) The developer driven approach reveals a high level of thoroughness and downstream utility. 2) The user driven approach has higher performance regarding validity 3) The level of reliability is comparable between the two approaches. 4) The user driven...

  6. Analysis of natural convection in a low gravity environment

    Science.gov (United States)

    Mattor, Ethan E.; Durgin, William W.; Bloznalis, Peter; Schoenberg, Richard

    1992-01-01

    Natural convection inside a spherical container was studied experimentally with two apparatuses at low buoyancy levels. The data generated by these experiments, plotted nondimensionally as the Nusselt versus Rayleigh numbers, give correlations for Rayleigh numbers between 1000 and 10 exp 8, a range previously untested. These results show that natural convection has significant effects at a Rayleigh number of 1000 and higher, although the behavior of the Nusselt number as the conduction limit is approached is still unknown for a spherical geometry.

  7. Thermally driven upslope flow in mountainous terrain

    Science.gov (United States)

    Liberzon, Dan; Hocut, Christopher; Fernando, Harindra; Environmental Fluid Dynamics Team

    2011-11-01

    Buoyancy driven up-slope flow and its separation from mountain apex are two important processes that determine meso and regional flows in mountainous areas. Such flow configurations have applications from mountain meteorology to large scale monsoonal circulation. A combined experimental and theoretical study toward improving our understanding of the mechanisms governing upslope flow processes, in particular, generation of upstream circulating cells and plume rise at the apex is presented. The experiments were performed in a 1.25x.35x.3 m water tank, using an inclined (10 to 30 degrees from the horizontal) electrical foil as the heated slope. Under certain condition the flow configuration produced stable circulation cells and rising limited plumes of finite height. Particle Tracking Velocimetry and flow visualization techniques were used for the diagnostics of velocity field and plume rise height, and relevant salient dimensionless quantities were evaluated in terms of governing parameters. Theoretical arguments are presented to explain the results. Parameter ranges for the appearance of characteristic flow patterns are also delineated.

  8. Laboratory experiments on rain-driven convection: Implications for planetary dynamos

    Science.gov (United States)

    Olson, Peter; Landeau, Maylis; Hirsh, Benjamin H.

    2017-01-01

    Compositional convection driven by precipitating solids or immiscible liquids has been invoked as a dynamo mechanism in planets and satellites throughout the solar system, including Mercury, Ganymede, and the Earth. Here we report laboratory experiments on turbulent rain-driven convection, analogs for the flows generated by precipitation within planetary fluid interiors. We subject a two-layer fluid to a uniform intensity rainfall, in which the rain is immiscible in the upper layer and miscible in the lower layer. Rain falls through the upper layer and accumulates as a two-fluid emulsion in the interfacial region between the layers. In experiments where the rain is denser than the lower fluid, rain-injected vortices evolve into small-scale plumes that rapidly coalesce into larger structures, resulting in turbulent convection throughout the lower layer. The turbulent convective velocity in our experiments increases approximately as the cube root of the rain buoyancy flux, implying little or no dependence on viscous and chemical diffusivities. Applying diffusion-free scaling laws for magnetic field generation, we find that precipitation-driven convection can be an effective dynamo mechanism in planetary cores provided the precipitation buoyancy flux is large and the convecting region is deep and nearly adiabatic.

  9. Lessons from Natural CO2 Leakage Analogue Site Studies and their Application to Secure CO2 Storage and Monitoring

    Science.gov (United States)

    Han, W.; McPherson, B. J.; Kim, K.; Chae, G.; Yum, B.

    2011-12-01

    At CO2 injection sites, CO2 leakage from the storage formation could be catastrophic. CO2 is a highly compressible fluid, typically injected at high pressure and temperature conditions. If this compressed CO2 reaches highly permeable conduits such as faults and fractures, CO2 could leak unabated to other formations (e.g. fresh water aquifers) and/or to the surface. Assuming a fast-flow path to the surface, CO2 escaping from the storage formation instantaneously reaches the surface while experiencing adiabatic expansion, which results in Joule-Thomson cooling. The addressed eruptive mechanisms are analogues to natural CO2 eruption mechanisms, which are found in CO2-driven cold-water geysers around the world. A notable example of a CO2-driven cold-water geyser is the Crystal Geyser in central Utah. The fluid mechanics of this regularly erupting geyser was investigated by instrumenting its conduit with pressure, temperature, pH, EC, and dissolved oxygen sensors, measuring every 1 minute during and between eruptions. Results of these measurements suggest that the time-scale of a single-eruption cycle is composed of four successive eruption types with two recharge periods ranging from 30 to 40 hours. Current eruption patterns exhibit a bimodal distribution although previous measurements and anecdotal evidence suggests that this pattern was different prior to recent seismic activity. This cold geyser's eruptions are regular and predictable, and reflect pressure, temperature, EC, pH, and dissolved oxygen changes resulting from Joule-Thomson cooling, endothermic CO2 exsolution, and exothermic CO2 dissolution. Specifically, the perturbation of pressure and temperature data observed at the Crystal Geyser suggested the possibility of using temperature sensing technology within the observation well at the engineered CO2 sequestration site. With the lessons learned from the Crystal Geyser studies, we established the theoretical framework of temperature changes caused by CO2

  10. Silicate melts density, buoyancy relations and the dynamics of magmatic processes in the upper mantle

    Science.gov (United States)

    Sanchez-Valle, Carmen; Malfait, Wim J.

    2016-04-01

    with results from ab initio calculations. The density model has been applied to examine the mineral-melt buoyancy relations at depth and the implications of these results for the dynamics of magma chambers, crystal settling and the stability and mobility of magmas in the upper mantle will be discussed.

  11. Buoyancy-induced squeezing of a deformable drop through an axisymmetric ring constriction

    Science.gov (United States)

    Ratcliffe, Thomas; Zinchenko, Alexander Z.; Davis, Robert H.

    2010-08-01

    Axisymmetric boundary-integral (BI) simulations were made for buoyancy-induced squeezing of a deformable drop through a ring constriction. The algorithm uses the Hebeker representation for the solid-particle contribution. A high-order, near-singularity subtraction technique is essential for near-critical squeezing. The drop velocity and minimum drop-solid spacing were determined for different ring and hole sizes, viscosity ratios, and Bond numbers, where the latter is a dimensionless ratio of gravitational to interfacial forces. The drop velocity decelerates typically 100-fold or more, and the drop-solid spacing reduces to typically 0.1%-1% of the nondeformed drop radius as the drop passes through the constriction. The critical Bond number (below which trapping occurs) was determined for different conditions. For supercritical conditions, the nondimensional time required for the drop to pass through the ring increases for a fixed drop-to-hole size with increasing viscosity ratio and decreasing Bond number, but it has a nonmonotonic dependence on the ratio of the radii of the drop and ring cross section. Numerical results indicate that the square of the drop squeezing time is inversely proportional to the Bond number minus the critical Bond number for near-critical squeezing. The critical Bond number, determined from dynamic BI calculations, compares favorably to that obtained precisely from a static algorithm. The static algorithm uses the Young-Laplace equation to calculate the pendant and sessile portions of the drop interface coupled through the conditions of global pressure continuity and total drop volume conservation. Over a limited parameter space, the critical Bond number increases almost linearly with the drop-to-hole ratio and is a weak function of the ratio of the ring cross-sectional radius to the hole radius. Another dynamic phenomenon, in addition to drop squeezing, is a drop "dripping" around the outer edge of the ring constriction, and a critical

  12. Buoyancy induced limits for nanoparticle synthesis experiments in horizontal premixed low-pressure flat-flame reactors

    Science.gov (United States)

    Weise, C.; Faccinetto, A.; Kluge, S.; Kasper, T.; Wiggers, H.; Schulz, C.; Wlokas, I.; Kempf, A.

    2013-06-01

    Premixed low-pressure flat-flame reactors can be used to investigate the synthesis of nanoparticles. The present work examines the flow field inside such a reactor during the formation of carbon (soot) and iron oxide (from Fe(CO)5) nanoparticles, and how it affects the measurements of nanoparticle size distribution. The symmetry of the flow and the impact of buoyancy were analysed by three-dimensional simulations and the nanoparticle size distribution was obtained by particle mass spectrometry (PMS) via molecular beam sampling at different distances from the burner. The PMS measurements showed a striking, sudden increase in particle size at a critical distance from the burner, which could be explained by the flow field predicted in the simulations. The simulation results illustrate different fluid mechanical phenomena which have caused this sudden rise in the measured particle growth. Up to the critical distance, buoyancy does not affect the flow, and an (almost) linear growth is observed in the PMS experiments. Downstream of this critical distance, buoyancy deflects the hot gas stream and leads to an asymmetric flow field with strong recirculation. These recirculation zones increase the particle residence time, inducing very large particle sizes as measured by PMS. This deviation from the assumed symmetric, one-dimensional flow field prevents the correct interpretation of the PMS results. To overcome this problem, modifications to the reactor were investigated; their suitability to reduce the flow asymmetry was analysed. Furthermore, 'safe' operating conditions were identified for which accurate measurements are feasible in premixed low-pressure flat-flame reactors that are transferrable to other experiments in this type of reactor. The present work supports experimentalists to find the best setup and operating conditions for their purpose.

  13. Experimental study of gliding arc plasma channel motion: buoyancy and gas flow phenomena under normal and hypergravity conditions

    Science.gov (United States)

    Potočňáková, Lucia; Šperka, Jiří; Zikán, Petr; van Loon, Jack J. W. A.; Beckers, Job; Kudrle, Vít

    2017-04-01

    The details of plasma channel motion are investigated by frame-by-frame image analysis of high speed recording of a gliding arc. The gliding arc is operated in several noble gases at various flow rates, voltages and artificial gravity levels. Several peculiarities in evolution of individual glides are observed, described and discussed, such as accelerating motion of plasma channel or shortcutting events of various kinds. Statistics of averaged parameters are significantly different for buoyancy and gas drag dominated regimes, which is put into relation with differing flow patterns for hypergravity and high gas flow.

  14. Buoyancy Effects on Unsteady MHD Flow of a Reactive Third-Grade Fluid with Asymmetric Convective Cooling

    Directory of Open Access Journals (Sweden)

    Tirivanhu Chinyoka

    2015-01-01

    Full Text Available This article examines the combined effects of buoyancy force and asymmetrical convective cooling on unsteady MHD channel flow and heat transfer characteristics of an incompressible, reactive, variable viscosity and electrically conducting third grade fluid. The chemical kinetics in the flow system is exothermic and the asymmetric convective heat transfers at the channel walls follow the Newton’s law of cooling. The coupled nonlinear partial differential equations governing the problem are derived and solved numerically using a semi-implicit finite difference scheme. Graphical results are presented and physical aspects of the problem are discussed with respect to various parameters embedded in the system.

  15. Solutions to Buoyancy-Drag Equation for Dynamical Evolution of Rayleigh-Taylor and Richtmyer-Meshkov Mixing Zone

    Institute of Scientific and Technical Information of China (English)

    Y.G. Cao; W.K. Chow; N.K. Fong

    2011-01-01

    With a self-similar parameter b(At) = Hi/λi, where At is the Atwood number, Hi and λi are the a.mplluae and wavelength of bubble (i = 1) and spike (i = 2) respectively, we derive analytically the solutions to the buoyancy-drag equation recently proposed for dynamical evolution of Rayleigh-Taylor and Richtmyer-Meshkov mixing zone. Numerical solutions are obtained with a simple form ofb(At)--- 1/(1 + At) and comparisons with recent LEM (linear electric motor) experiments are made, and an agreement is found with properly chosen initial conditions.

  16. Effect of Thermal Buoyancy on Fluid Flow and Inclusion Motion in Tundish without Flow Control Devices--Part Ⅱ: Inclusion Motion

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li-feng

    2005-01-01

    Following up the fluid flow simulation in a 60 t tundish, the trajectories of inclusions in the 60 t tundish without flow control are simulated by considering the force balance between the drag force and the inertial buoyancy force. The Stochastic model yields more accurate inclusion motion than the non-Stochastic model due to including the effect of the turbulent fluctuation. The average residence time of inclusions decreases with increasing size. The thermal buoyancy favors inclusions removal especially the small inclusions. Using solute transport like the dye injection in water model and copper addition in the real steel tundish cannot accurately study the motion of the inclusions. In the simulation, more than 68% inclusions bigger than 10μm are removed to the top, and less than 32% enters the mold. The thermal buoyancy has little effect on the fraction of inclusions moved to the top of the inlet zone, and it mainly favors the removal of inclusions smaller than 100μm to the top surface of the outlet zone. For inclusions bigger than 100μm , the effect of thermal buoyancy on their motion can be ignored compared to the inertial buoyancy effect.

  17. Heart Rate Responses to Unaided Orion Side Hatch Egress in the Neutral Buoyancy Laboratory

    Science.gov (United States)

    English, Kirk L.; Hwang Emma Y.; Ryder, Jeffrey W.; Kelly, Cody; Walker, Thomas; Ploutz-Snyder, Lori L.

    2016-01-01

    NASA is developing the Orion capsule as a vehicle for transporting crewmembers to and from the International Space Station (ISS) and for future human space exploration missions. Orion and other commercial vehicles are designed to splash down in the ocean where nominally support personnel will assist crewmembers in egressing the vehicle. However, off-nominal scenarios will require crewmembers to egress the vehicle unaided, deploy survival equipment, and ingress a life raft. PURPOSE: To determine the heart rate (HR) responses to unaided Orion side hatch egress and raft ingress as a part of the NASA Crew Survival Engineering Team's evaluation of the PORT Orion mockup in the Neutral Buoyancy Laboratory (NBL). METHODS: Nineteen test subjects, including four astronauts (N=19, 14 males/5 females, 38.6+/-8.4 y, 174.4+/-9.6 cm, 75.7+/-13.1 kg), completed a graded maximal test on a cycle ergometer to determine VO2peak and HRpeak and were divided into five crews of four members each; one subject served on two crews. Each crew was required to deploy a life raft, egress the Orion vehicle from the side hatch, and ingress the life raft with two 8 kg emergency packs per crew. Each crew performed this activity one to three times; a total of ten full egresses were completed. Subjects wore a suit that was similar in form, mass, and function to the Modified Advanced Crew Escape Suit (MACES) including helmet, gloves, boots, supplemental O2 bottles, and a CO2-inflated life preserver (approx.18 kg); subjects began each trial seated supine in the PORT Orion mockup with seat belts and mockup O2 and communication connections and ended each trial with all four crewmembers inside the life raft. RESULTS: VO2peak was 40.8+/-6.8 mL/kg/min (3.1+/-0.7 L/min); HRpeak was 181+/-10 bpm. Total egress time across trials was 5.0+/-1.6 min (range: 2.8-8.0 min); all subjects were able to successfully complete all trials. Average maximum HR at activity start, at the hatch opening, in the water, and in the

  18. Query Driven Visualization

    CERN Document Server

    Buddelmeijer, Hugo

    2011-01-01

    The request driven way of deriving data in Astro-WISE is extended to a query driven way of visualization. This allows scientists to focus on the science they want to perform, because all administration of their data is automated. This can be done over an abstraction layer that enhances control and flexibility for the scientist.

  19. Implementing Nonlinear Buoyancy and Excitation Forces in the WEC-Sim Wave Energy Converter Modeling Tool: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Lawson, M.; Yu, Y. H.; Nelessen, A.; Ruehl, K.; Michelen, C.

    2014-05-01

    Wave energy converters (WECs) are commonly designed and analyzed using numerical models that combine multi-body dynamics with hydrodynamic models based on the Cummins Equation and linearized hydrodynamic coefficients. These modeling methods are attractive design tools because they are computationally inexpensive and do not require the use of high performance computing resources necessitated by high-fidelity methods, such as Navier Stokes computational fluid dynamics. Modeling hydrodynamics using linear coefficients assumes that the device undergoes small motions and that the wetted surface area of the devices is approximately constant. WEC devices, however, are typically designed to undergo large motions in order to maximize power extraction, calling into question the validity of assuming that linear hydrodynamic models accurately capture the relevant fluid-structure interactions. In this paper, we study how calculating buoyancy and Froude-Krylov forces from the instantaneous position of a WEC device (referred to as instantaneous buoyancy and Froude-Krylov forces from herein) changes WEC simulation results compared to simulations that use linear hydrodynamic coefficients. First, we describe the WEC-Sim tool used to perform simulations and how the ability to model instantaneous forces was incorporated into WEC-Sim. We then use a simplified one-body WEC device to validate the model and to demonstrate how accounting for these instantaneously calculated forces affects the accuracy of simulation results, such as device motions, hydrodynamic forces, and power generation.

  20. Buoyancy and Dissolution of the Floating Crust Layer in Tank 241-SY-101 During Transfer and Back-Dilution

    Energy Technology Data Exchange (ETDEWEB)

    CW Stewart; JH Sukamto; JM Cuta; SD Rassat

    1999-11-22

    To remediate gas retention in the floating crust layer and the potential for buoyant displacement gas releases from below the crust, waste will be transferred out of Hanford Tank 241-SY-101 (SY-101) in the fall of 1999 and back-diluted with water in several steps of about 100,000 gallons each. To evaluate the effects of back-dilution on the crust a static buoyancy model is derived that predicts crust and liquid surface elevations as a function of mixing efficiency and volume of water added during transfer and back-dilution. Experimental results are presented that demonstrate the basic physics involved and verify the operation of the models. A dissolution model is also developed to evaluate the effects of dissolution of solids on crust flotation. The model includes dissolution of solids suspended in the slurry as well as in the crust layers. The inventory and location of insoluble solids after dissolution of the soluble fraction are also tracked. The buoyancy model is applied to predict the crust behavior for the first back-dilution step in SY-101. Specific concerns addressed include conditions that could cause the crust to sink and back-dilution requirements that keep the base of the crust well above the mixer pump inlet.

  1. Buoyancy-Driven Heat Transfer During Application of a Thermal Gradient for the Study of Vapor Deposition at Low Pressure Using and Ideal Gas

    Science.gov (United States)

    Frazier, D. O.; Hung, R. J.; Paley, M. S.; Penn, B. G.; Long, Y. T.

    1996-01-01

    A mathematical model has been developed to determine heat transfer during vapor deposition of source materials under a variety of orientations relative to gravitational accelerations. The model demonstrates that convection can occur at total pressures as low as 10-2 mm Hg. Through numerical computation, using physical material parameters of air, a series of time steps demonstrates the development of flow and temperature profiles during the course of vapor deposition. These computations show that in unit gravity vapor deposition occurs by transport through a fairly complicated circulating flow pattern when applying heat to the bottom of the vessel with parallel orientation with respect to the gravity vector. The model material parameters for air predict the effect of kinematic viscosity to be of the same order as thermal diffusivity, which is the case for Prandtl number approx. 1 fluids. Qualitative agreement between experiment and the model indicates that 6-(2-methyl-4-nitroanilino)-2,4-hexadiyn-l-ol (DAMNA) at these pressures indeed approximates an ideal gas at the experiment temperatures, and may validate the use of air physical constants. It is apparent that complicated nonuniform temperature distribution in the vapor could dramatically affect the homogeneity, orientation, and quality of deposited films. The experimental test i's a qualitative comparison of film thickness using ultraviolet-visible spectroscopy on films generated in appropriately oriented vapor deposition cells. In the case where heating of the reaction vessel occurs from the top, deposition of vapor does not normally occur by convection due to a stable stratified medium. When vapor deposition occurs in vessels heated at the bottom, but oriented relative to the gravity vector between these two extremes, horizontal thermal gradients induce a complex flow pattern. In the plane parallel to the tilt axis, the flow pattern is symmetrical and opposite in direction from that where the vessel is positioned vertically. The ground-based experiments are sufficient preliminary tests of theory and should be of significant interest regarding vapor deposited films in microgravity.

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

    CERN Document Server

    Khaibrakhmanov, Sergey A; Parfenov, Sergey Yu; Sobolev, Andrey M

    2016-01-01

    We investigate the fossil magnetic field in the accretion and protoplanetary discs using the Shakura and Sunyaev approach. The distinguishing feature of this study is the accurate solution of the ionization balance equations and the induction equation with Ohmic diffusion, magnetic ambipolar diffusion, buoyancy and the Hall effect. We consider the ionization by cosmic rays, X-rays and radionuclides, radiative recombinations, recombinations onto dust grains, and also thermal ionization. The buoyancy appears as the additional mechanism of magnetic flux escape in the steady-state solution of the induction equation. Calculations show that Ohmic diffusion and magnetic ambipolar diffusion constraint the generation of the magnetic field inside the `dead' zones. The magnetic field in these regions is quasi-vertical. The buoyancy constraints the toroidal magnetic field strength close to the disc inner edge. As a result, the toroidal and vertical magnetic fields become comparable. The Hall effect is important in the re...

  3. Laser-Driven Fusion.

    Science.gov (United States)

    Gibson, A. F.

    1980-01-01

    Discusses the present status and future prospects of laser-driven fusion. Current research (which is classified under three main headings: laser-matter interaction processes, compression, and laser development) is also presented. (HM)

  4. Discovery Driven Growth

    DEFF Research Database (Denmark)

    Bukh, Per Nikolaj

    2009-01-01

    Anmeldelse af Discovery Driven Growh : A breakthrough process to reduce risk and seize opportunity, af Rita G. McGrath & Ian C. MacMillan, Boston: Harvard Business Press. Udgivelsesdato: 14 august......Anmeldelse af Discovery Driven Growh : A breakthrough process to reduce risk and seize opportunity, af Rita G. McGrath & Ian C. MacMillan, Boston: Harvard Business Press. Udgivelsesdato: 14 august...

  5. Effects of Viscosity on the Gravi-kinesis Responses of Swimming Paramecia Studied Using Manetic Force Buoyancy Variation

    Science.gov (United States)

    Jung, Ilyong; Valles, James M.

    2013-03-01

    Previous studies have shown that paramecia exhibit negative gravi-kinesis. They exert a stronger propulsive force when swimming up than when swimming down. This behavior is very surprising since it suggests they sense their tiny apparent weight of only ~ 80pN. In an effort to understand the mechanism of this sensing, we are testing how the viscosity of the swimming medium influences their gravi-kinetic response. We employ the technique of magnetic force buoyancy variation to simulate different effective gravity levels on swimming Paramecia. We are analyzing their swimming response employing a phenomenological model that relates the parameters describing their helical trajectories to the beating of their cilia. This work was supported by NSF PHY0750360 and at the NHMFL by NSF DMR-0084173

  6. Effects of vehicle station-keeping and end-effector disturbance compensation on neutral-buoyancy teleoperation

    Science.gov (United States)

    Valdez, Michael S.

    1993-12-01

    Experiments were conducted with a neutral-buoyancy robot to test whether vehicle station keeping and end effector disturbance compensation significantly affect human teleoperation performance. The vehicle used for experiments, called the Submersible for Telerobotic Astronautical Research (STAR) is a free-flying underwater telerobot equipped with a three degree of freedom arm, a stereo pan/tilt camera platform, and a vision-based navigation system. Using visual feedback from a fixed onboard camera, test subject performed a Fitts- type tapping task with the arm while the vision navigator and control system held the vehicle steady relative to a visual reference target. This paper describes the testbed vehicle, experiments, data analysis, and conclusions.

  7. Regulation of biofilm formation and cellular buoyancy through modulating intracellular cyclic di-GMP levels in engineered cyanobacteria.

    Science.gov (United States)

    Agostoni, Marco; Waters, Christopher M; Montgomery, Beronda L

    2016-02-01

    The second messenger cyclic dimeric (3'→5') GMP (cyclic di-GMP or c-di-GMP) has been implicated in the transition between motile and sessile lifestyles in bacteria. In this study, we demonstrate that biofilm formation, cellular aggregation or flocculation, and cellular buoyancy are under the control of c-di-GMP in Synechocystis sp. PCC 6803 (Synechocystis) and Fremyella diplosiphon. Synechocystis is a unicellular cyanobacterium and displays lower levels of c-di-GMP; F. diplosiphon is filamentous and displays higher intracellular c-di-GMP levels. We transformed Synechocystis and F. diplosiphon with a plasmid for constitutive expression of genes encoding diguanylate cylase (DGC) and phosphodiesterase (PDE) proteins from Vibrio cholerae or Escherichia coli, respectively. These engineered strains allowed us to modulate intracellular c-di-GMP levels. Biofilm formation and cellular deposition were induced in the DGC-expressing Synechocystis strain which exhibited high intracellular levels of c-di-GMP; whereas strains expressing PDE in Synechocystis and F. diplosiphon to drive low intracellular levels of c-di-GMP exhibited enhanced cellular buoyancy. In addition, the PDE-expressing F. diplosiphon strain showed elevated chlorophyll levels. These results imply roles for coordinating c-di-GMP homeostasis in regulating native cyanobacterial phenotypes. Engineering exogenous DGC or PDE proteins to regulate intracellular c-di-GMP levels represents an effective tool for uncovering cryptic phenotypes or modulating phenotypes in cyanobacteria for practical applications in biotechnology applicable in photobioreactors and in green biotechnologies, such as energy-efficient harvesting of cellular biomass or the treatment of metal-containing wastewaters.

  8. Buoyancy of Rigid Body in the Invariant Density and Static Fluid%匀质、静止流体中刚性物体所受的浮力

    Institute of Scientific and Technical Information of China (English)

    张丽辉; 谢颖; 吴永超

    2012-01-01

    根据流体静力学的结论,计算了重力场内匀质、静止流体中刚性物体在三种不同情形下所受的浮力,与阿基米德原理给出的结论一致.计算和讨论过程加深了对浮力本质的认识.%Principle of Archimedes is important way to compute buoyancy of object in the fluid. In gravitational field, we use basics principle of fluid statics, analyze buoyancy of object in the invariant density and static fluid , and obtain buoyancy of object in three different condition. It is indication that, we obtain buoyancy of object in three different condition agree with principle of Archimedes. In the process of calculation and discussion, we can understand the essence of buoyancy.

  9. Natural gas; Gas Natural

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, Carlos A.; Moraes, Claudia C.D. [Eletricidade de Sao Paulo S.A. (ELETROPAULO), Sao Paulo, SP (Brazil); Fonseca, Carlos H.F. [Centrais Eletricas de Santa Catarina S.A., Florianopolis, SC (Brazil); Silva, Clecio Fabricio da; Alves, Ricardo P. [Companhia Paranaense de Energia (COPEL), Curitiba, PR (Brazil); Sposito, Edivaldo Soares; Hulle, Lutero [Espirito Santo Centrais Eletricas S.A. (ESCELSA), Vitoria, ES (Brazil); S. Martins, Icaro da [Centrais Eletricas do Norte do Brasil S.A. (ELETRONORTE), Belem, PA (Brazil); Vilhena, Joao Luiz S. de [Companhia Energetica de Minas Gerais (CEMIG), Belo Horizonte, MG (Brazil); Fagundes, Zaluar Aquino [Companhia Estadual de Energia Eletrica do Estado do Rio Grande do Sul, Porto Alegre, RS (Brazil)

    1996-12-31

    An increase in the consumption of natural gas in Brazil is an expected fact in what concerns energetic planning. This work presents the existing situation in what concerns natural gas utilization in the main world economies, as well as an analysis of the participation of this fuel among the energy final consumption per sources. The Brazilian consumption of natural gas is also analysed as well as the international agreement between Brazil and Bolivia for natural gas commercialization. Some legal, institutional and political aspects related to natural gas commercialization are also discussed. Finally, several benefits to be brought by the utilization of natural gas are presented 10 refs., 3 tabs.

  10. Experimental study of the structure of flow regions with negative turbulent kinetic energy production in confined three-dimensional shear flows with and without buoyancy

    Science.gov (United States)

    Liberzon, A.; Lüthi, B.; Guala, M.; Kinzelbach, W.; Tsinober, A.

    2005-09-01

    Regions of negative turbulent kinetic energy (TKE) production are observed and studied in two different flows, namely in turbulent thermal Rayleigh-Bénard convection in a cubic cell, and in a mechanically agitated shear flow in absence of buoyancy, with a main focus on the small scale structure of the flow. The experimental investigation is performed using three-dimensional (3D) particle tracking velocimetry, which allows for measuring the three velocity components and the full tensor of velocity derivatives in a finite 3D volume. The capability to compute the TKE production term in its complete form P =-⟨uiuj⟩Sij is crucial due to the three dimensionality of the flows. A comparative analysis of four different flow situations is performed in regions with positive and negative TKE production with and without buoyancy effects. In both, convective shear flow and shear flow without buoyancy, negative TKE production is associated with the unusual, more pronounced alignment of the velocity vector u with the first eigenvector λ1S of the mean rate-of-strain tensor, related to the stretching eigenvalue, Λ1S, in contrast to the positive TKE production associated with the alignment with the third eigenvector (i.e., related to the negative, compressing eigenvalue). In the negative TKE production region of convective flow we find (i) increased values for mean strain, (ii) increased values of the first contribution PΛ1 in the eigenframe of the mean rate-of-strain tensor, and decreased values of the vertical contribution to the production term in a fixed frame of reference, (iii) stronger anisotropy of u, (iv) higher levels of fluctuating strain s2 and enstrophy ω2, as well as (v) higher rates of their production, -sijsjkski and ωiωjsij, compared to the respective values in positive TKE production region. In the shear flow without buoyancy, all the mentioned quantities are lower in the negative TKE production region than in the positive TKE production region. From this

  11. Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

    Directory of Open Access Journals (Sweden)

    Zhigang Shen

    2012-08-01

    Full Text Available The impacts of ventilation ratio and vent balance on cooling load and air flow of naturally ventilated attics are studied in this paper using an unsteady computational fluid dynamics (CFD model. Buoyancy-driven turbulent ventilations in attics of gable-roof residential buildings are simulated for typical summer conditions. Ventilation ratios from 1/400 to 1/25 combined with both balanced and unbalanced vent configurations are investigated. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the variations in ventilation ratio and vent configuration. The predicted temperature fields are characterized by thermal stratification, except for the soffit regions. It is demonstrated that an increase in ventilation ratio will reduce attic cooling load. Compared with unbalanced vent configurations, balanced attic ventilation is shown to be the optimal solution in both maximizing ventilating flow rate and minimizing cooling load for attics with ventilation ratio lower than 1/100. For attics with ventilation ratios greater than 1/67, a configuration of large ridge vent with small soffit vent favors ventilating air flow enhancement, while a configuration of small ridge vent with large soffit vent results in the lowest cooling energy consumption.

  12. Laminar Natural Convective Heat Transfer in the Enclosed Evacuated Collector Tube with East—West Symmetric Heat Input

    Institute of Scientific and Technical Information of China (English)

    ZhangHeng-Yun; GeXin-Shi

    1997-01-01

    Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection problem driven by buoyancy.Because of its complexity,no effective theoretical model is available despite of limited experimental work which is confined to one aspect.The present work aims to depict the convective heat transfer inside a two-ended inclined tube with East-West symmetric heat input using numerical methods,Based on reasonable assumptions,governing equations of the inside fluid are established.The corresponding discretizated equations are solved by emplogying numerical metholds.The calculated results are displayed for velocity and temperature profiles on different cross-sectional plasnes.which present the flow pattern characterized by upflow and downflow along the axial direction and adherent flow along the peripheral direction,and the heat transfer rpocess from the wall to the center,Furthermore,the transient Nusselt number and average temperature level are shown and discussed.Finally,the parametric effects of the tube radius and the heat input on the flow and heat transfer are also given.

  13. Non-hotspot volcano chains produced by migration of shear-driven upwelling toward the East Pacific Rise (Invited)

    Science.gov (United States)

    Ballmer, M. D.; Conrad, C. P.; Smith, E. I.; Harmon, N.

    2013-12-01

    intraplate volcanism that progresses towards the MOR, spreads laterally close to the axis, and weakly continues on the opposite plate. These predictions can explain the anomalously-fast eastward progression of volcanism, and its spatial distribution near the EPR. Moreover, for a heterogeneous mantle source involving a fertile mantle component embedded in a matrix of peridotite, the systematics of volcanism predicted by the models can account for the geochemical trend observed along the Pukapuka ridge (from C/FOZO [5] in the west toward MOR-basalt in the east), as well as the anomaly of MOR volcanism at the EPR-Pukapuka intersection (documenting C/FOZO influence). Our study highlights the role of horizontal asthenospheric flow and mantle heterogeneity in producing linear chains of intraplate volcanism independent of a (deep-rooted) buoyancy source. [1] Conder, J. A., D. W. Forsyth, E. M. Parmentier (2002): J. Geophys. Res., 107(B12), 2344. [2] Conrad, C. P., T. A. Bianco, E. I. Smith, P. Wessel (2011): Nature Geosci., 4, 317-321. [3] Harmon, N., D. W. Forsyth, D. S. Weeraratne, Y. Yang, S. C. Webb (2011): Earth Planet. Sci. Lett., 311, 306-315. [4] Ballmer, M. D., C. P. Conrad, E. I. Smith, N. Harmon (2013): Geology, 41, 479-482. [5] Zindler, A., Hart, S., 1986. Earth Planet. Sci. Lett., 14, 493-571.

  14. Non-hotspot volcano chains produced by migration of shear-driven upwelling toward the East Pacific Rise

    Science.gov (United States)

    Ballmer, Maxim D.; Conrad, Clinton P.; Harmon, Nicholas; Smith, Eugene I.

    2013-04-01

    , spreads laterally close to the axis, and weakly continues on the opposite plate. These predictions can explain the anomalously-fast eastward progression of volcanism, and its spatial distribution near the EPR. Moreover, for a heterogeneous mantle source involving a fertile component in addition to peridotite, the predicted systematics of volcanism can account for the geochemical trend observed along the Pukapuka ridge, and the enriched anomaly of EPR MOR-basalt at 16°S-20.5°S. Our study highlights the role of horizontal asthenospheric flow and mantle heterogeneity in producing linear chains of intraplate volcanism independent of a (deep-rooted) buoyancy source. [1] Conder, J. A., D. W. Forsyth, E. M. Parmentier (2002): J. Geophys. Res., 107(B12), 2344. [2] Conrad, C. P., T. A. Bianco, E. I. Smith, P. Wessel (2011): Nature Geoscience, 4, 317-321. [3] Harmon, N., D. W. Forsyth, D. S. Weeraratne, Y. Yang, S. C. Webb (2011): Earth Planet. Sci. Lett., 311, 306-315. [4] Ballmer, M. D., C. P. Conrad, E. I. Smith, N. Harmon (2013): Geology, in press.

  15. Investigating Reaction-Driven Cracking

    Science.gov (United States)

    Kelemen, P. B.; Hirth, G.; Savage, H. M.

    2013-12-01

    Many metamorphic reactions lead to large volume changes, and potentially to reaction-driven cracking [1,2]. Large-scale hydration of mantle peridotite to produce serpentine or talc is invoked to explain the rheology of plate boundaries, the nature of earthquakes, and the seismic properties of slow-spread ocean crust and the 'mantle wedge' above subduction zones. Carbonation of peridotite may be an important sink in the global carbon cycle. Zones of 100% magnesite + quartz replacing peridotite, up to 200 m thick, formed where oceanic mantle was thrust over carbonate-bearing metasediments in Oman. Talc + carbonate is an important component of the matrix in subduction mélanges at Santa Catalina Island , California, and the Sanbagawa metamorphic belt, Japan. Engineered systems to emulate natural mineral carbonation could provide relatively inexpensive CO2 capture and storage [3]. More generally, engineered reaction-driven cracking could supplement or replace hydraulic fracture in geothermal systems, solution mining, and extraction of tight oil and gas. The controls on reaction-driven cracking are poorly understood. Hydration and carbonation reactions can be self-limiting, since they potentially reduce permeability and armor reactive surfaces [4]. Also, in some cases, hydration or carbonation may take place at constant volume. Small changes in volume due to precipitation of solid products increases stress, destabilizing solid reactants, until precipitation and dissolution rates become equal at a steady state stress [5]. In a third case, volume change due to precipitation of solid products causes brittle failure. This has been invoked on qualitative grounds to explain, e.g., complete serpentinization of mantle peridotite [6]. Below ~ 300°C, the available potential energy for hydration and carbonation of olivine could produce stresses of 100's of MPa [2], sufficient to fracture rocks to 10 km depth or more, causing brittle failure below the steady state stress required

  16. Experimental and Theoretical Studies on Velocity Field of Buoyancy Convection in KNbO3 Melt

    Institute of Scientific and Technical Information of China (English)

    JIN Wei-Qing; Shinichi YODA; JIANG Yuan-Fang; PAN Zhi-Lei; LIANG Xin-An

    2001-01-01

    The Schlieren technique coupling with a differential interference microscope was applied to visualize the KNbOa melt motion in a loop-shaped Pt wire heater. The natural convection in KNbOa melt was traced by observing themovement of the tiny KNbO3 crystals (~ 10 μm) and the stream velocities of these tracer crystals were measured. In theoretical analysis, the Navier-Stokes equation was solved as a stable field. The general solution for this system of the differential equation was expressed by an approximate power series of azimuth and radius vector. The expression was substituted in the differential equation; a non-trivial solution was obtained exactly. The velocity distribution in the vertical section was obtained which is in qualitative agreement with the experimental result.

  17. EXPERIMENTAL AND THEORETICAL STUDIES ON VELOCITY FIELD OF BUOYANCY CONVECTION IN KNbO3 MELT

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    @@ The Schlieren technique coupling with a differential interference microscope was applied to visualize the KNbO3 melt motion in a loop-shaped Pt wire heater. The natural convection in KNbO3 melt was traced by observing the movement of the tiny KNbO3 crystals (~10μm) and the stream velocities of these tracer crystals were measured. In theoretical analysis, the Navier-Stokes equation was solved as a stable field. The general solution for this system of the differential equation was expressed by an approximate power series of azimuth and radius vector. The expression was substituted in the differential equation; a non-trivial solution was obtained exactly.The velocity distribution in the vertical section was obtained which is in qualitative agreement with the experimental result.

  18. The Driven Spinning Top

    Science.gov (United States)

    Grosu, Ioan; Featonby, David

    2016-01-01

    This driven top is quite a novelty and can, with some trials, be made using the principles outlined here. This new top has many applications in developing both understanding and skills and these are detailed in the article. Depending on reader's available time and motivation they may feel an urge to make one themselves, or simply invest a few…

  19. Design of Natural and Hybrid Ventilation

    DEFF Research Database (Denmark)

    Heiselberg, Per

    as well as influence the air content (dust, pollution etc.). Architects and engineers need to acquire qualitative and quantitative information about the interactions between building characteristics and natural ventilation in order to design buildings and systems consistent with a passive low......The effectiveness of natural ventilation, i.e. its ability to ensure indoor air quality and passive cooling in a building, depends greatly on the design process. Mechanical ventilation systems can be designed separately from the design of the building in which they are installed. They can also...... be installed in existing buildings after a few modifications. In contrast, ventilation systems using only natural forces such as wind and thermal buoyancy need to be designed together with the building, since the building itself and its components are the elements that can reduce or increase air movement...

  20. Dynamic signatures of driven vortex motion.

    Energy Technology Data Exchange (ETDEWEB)

    Crabtree, G. W.; Kwok, W. K.; Lopez, D.; Olsson, R. J.; Paulius, L. M.; Petrean, A. M.; Safar, H.

    1999-09-16

    We probe the dynamic nature of driven vortex motion in superconductors with a new type of transport experiment. An inhomogeneous Lorentz driving force is applied to the sample, inducing vortex velocity gradients that distinguish the hydrodynamic motion of the vortex liquid from the elastic and-plastic motion of the vortex solid. We observe elastic depinning of the vortex lattice at the critical current, and shear induced plastic slip of the lattice at high Lorentz force gradients.

  1. Coexisting contraction-extension consistent with buoyancy of the crust and upper mantle in North-Central Italy

    CERN Document Server

    Aoudia, A; Ismail-Zadeh, A T; Panza, G F; Pontevivo, A

    2002-01-01

    The juxtaposed contraction and extension observed in the crust of the Italian Apennines and elsewhere has, for a long time, attracted the attention of geoscientists and is a long-standing enigmatic feature. Several models, invoking mainly external forces, have been put forward to explain the close association of these two end-member deformation mechanisms clearly observed by geophysical and geological investigations. These models appeal to interactions along plate margins or at the base of the lithosphere such as back-arc extension or shear tractions from mantle flow or to subduction processes such as slab roll back, retreat or pull and detachment. We present here a revisited crust and upper mantle model that supports delamination processes beneath North-Central Italy and provides a new background for the genesis and age of the recent magmatism in Tuscany. Although external forces must have been important in the building up of the Apennines, we show that internal buoyancy forces solely can explain the coexist...

  2. Test-driven programming

    Science.gov (United States)

    Georgiev, Bozhidar; Georgieva, Adriana

    2013-12-01

    In this paper, are presented some possibilities concerning the implementation of a test-driven development as a programming method. Here is offered a different point of view for creation of advanced programming techniques (build tests before programming source with all necessary software tools and modules respectively). Therefore, this nontraditional approach for easier programmer's work through building tests at first is preferable way of software development. This approach allows comparatively simple programming (applied with different object-oriented programming languages as for example JAVA, XML, PYTHON etc.). It is predictable way to develop software tools and to provide help about creating better software that is also easier to maintain. Test-driven programming is able to replace more complicated casual paradigms, used by many programmers.

  3. Electrically driven optical antennas

    Science.gov (United States)

    Kern, Johannes; Kullock, René; Prangsma, Jord; Emmerling, Monika; Kamp, Martin; Hecht, Bert

    2015-09-01

    Unlike radiowave antennas, so far optical nanoantennas cannot be fed by electrical generators. Instead, they are driven by light or indirectly via excited discrete states in active materials in their vicinity. Here we demonstrate the direct electrical driving of an in-plane optical antenna by the broadband quantum-shot noise of electrons tunnelling across its feed gap. The spectrum of the emitted photons is determined by the antenna geometry and can be tuned via the applied voltage. Moreover, the direction and polarization of the light emission are controlled by the antenna resonance, which also improves the external quantum efficiency by up to two orders of magnitude. The one-material planar design offers facile integration of electrical and optical circuits and thus represents a new paradigm for interfacing electrons and photons at the nanometre scale, for example for on-chip wireless communication and highly configurable electrically driven subwavelength photon sources.

  4. CFD Study on Inter-Action and Heat Transfer between Non-Isothermal Airflow of Momentum Source and Plume of Buoyancy Force in an Air-Conditioned Space

    Directory of Open Access Journals (Sweden)

    Wuwei Cao

    2010-10-01

    Full Text Available This paper presents indoor airflow and thermal environment which is formed by a cooling jet and a local heat source in a ventilated room. To illustrate the effects of the combined the plume and the jet-flow, a series of simulated values with different calculated conditions such as different buoyancy flux are analysed by Fluent simulation software. This paper presents an index θ to describe the physical phenomenon by the thermal interaction between the cold jetflow and the plume. It is concluded that if the heat source is increasing considerably, the buoyancy source will be a leading factor of the indoor thermal field, though its initial momentum is considered to be zero.

  5. Affinity driven social networks

    Science.gov (United States)

    Ruyú, B.; Kuperman, M. N.

    2007-04-01

    In this work we present a model for evolving networks, where the driven force is related to the social affinity between individuals of a population. In the model, a set of individuals initially arranged on a regular ordered network and thus linked with their closest neighbors are allowed to rearrange their connections according to a dynamics closely related to that of the stable marriage problem. We show that the behavior of some topological properties of the resulting networks follows a non trivial pattern.

  6. Thermo capillary and buoyancy convection in a fluid locally heated on its free surface; Convection thermocapillaire et thermogravitaire dans un fluide chauffe localement sur sa surface libre

    Energy Technology Data Exchange (ETDEWEB)

    Favre, E.

    1997-09-26

    coupled buoyancy and thermo-capillary convection lead to a convective motion of the interface liquid/gas which drastically changes the heat and mass transfer across the liquid layer. Two experiments were considered, depending on the fluid: oil or mercury. The liquid is set in a cooled cylindrical vessel, and heated by a heat flux across the center of the free surface. The basic flow, in the case of oil, is a torus. When the heat parameter increases, a stationary flow appears as petals or rays when the aspect ratio. The lateral confinement selects the azimuthal wavelength. In the case of petals-like flow, a sub-critical Hopf bifurcation is underlined. The turbulence is found to be `weak`, even for the largest values of the Marangoni number (Ma = 1.3 10{sup 5}). In the case of mercury, the thermo-capillary effect is reduced to zero to impurities at the surface which have special trajectories we describe and compare to a simpler experiment. Only the buoyancy forces induce a unstationary, weakly turbulent flow as soon as the heating power exceeds 4W (Ra = 4.5 10{sup 3}, calculated with h = 1 mm). The past part concerns the analysis of the effect on the flow of the boundary conditions, the geometry, the Prandtl number and the buoyancy force with the help of the literature. Results concerning heat transfer, in particular the exponent of the law Nusselt number vs. heating power, were compared with available data. (author) 115 refs.

  7. Passive and Driven Trends in the Evolution of Complexity

    CERN Document Server

    Yaeger, Larry; Sporns, Olaf

    2011-01-01

    The nature and source of evolutionary trends in complexity is difficult to assess from the fossil record, and the driven vs. passive nature of such trends has been debated for decades. There are also questions about how effectively artificial life software can evolve increasing levels of complexity. We extend our previous work demonstrating an evolutionary increase in an information theoretic measure of neural complexity in an artificial life system (Polyworld), and introduce a new technique for distinguishing driven from passive trends in complexity. Our experiments show that evolution can and does select for complexity increases in a driven fashion, in some circumstances, but under other conditions it can also select for complexity stability. It is suggested that the evolution of complexity is entirely driven---just not in a single direction---at the scale of species. This leaves open the question of evolutionary trends at larger scales.

  8. The initial transient of natural convection during copper electrolysis in the presence of an opposing Lorentz force: Current dependence

    Science.gov (United States)

    Yang, Xuegeng; Mühlenhoff, Sascha; Nikrityuk, Petr A.; Eckert, Kerstin

    2013-03-01

    Magnetic fields are well-established in electrochemistry as an attractive tool to improve both the quality of the deposit as well as the deposition rate. The key mechanism is a mass transfer enhancement by Lorentz-force-driven convection. However, during electrolysis this convection interacts with buoyancy-driven convection, which arises from concentration differences, in a sometimes intriguing way. In the case of a Lorentz force opposing buoyancy, this is due to the growth of a bubble-like zone of less-concentrated cupric ion solution at the lower part of the vertical cathode when copper electrolysis is performed. If buoyancy is strong enough to compete with the Lorentz force, this zone rises along the cathode and causes surprisingly unsteady initial transient behaviour. We explore this initial transient under galvanostatic conditions by analyzing the development of the concentration and velocity boundary layers obtained by Mach-Zehnder interferometry and particle image velocimetry. Particular attention is also paid to higher current densities above the limiting current, obtained from potentiodynamic measurements, at which a chaotic advection takes place. The results are compared by scaling analysis.

  9. Rotating convection-driven dynamos at low Ekman number.

    Science.gov (United States)

    Rotvig, Jon; Jones, Chris A

    2002-11-01

    We present a fully 3D self-consistent convection-driven dynamo model with reference to the geodynamo. A relatively low Ekman number regime is reached, with the aim of investigating the dynamical behavior at low viscosity. This regime is computationally very demanding, which has prompted us to adopt a plane layer model with an inclined rotation vector, and to make use of efficiently parallelized code. No hyperdiffusion is used, all diffusive operators are in the classical form. Our model has infinite Prandtl number, a Rayleigh number that scales as E(-1/3) (E being the Ekman number), and a constant Roberts number. The optimized model allows us to study dynamos with Ekman numbers in the range [10(-5),10(-4)]. In this regime we find strong-field dynamos where the induced magnetic fields satisfy Taylor's constraint to good accuracy. The solutions are characterized by (i) a MAC balance within the bulk, i.e., Coriolis, pressure, Lorentz, and buoyancy forces are of comparable magnitude, while viscous forces are only significant in thin boundary layers, (ii) the Elsasser number is O(10), (iii) the strong magnetic fields cannot prevent small-scale structures from becoming dominant over the large-scale components, (iv) the Taylor-Proudman effect is detectable, (v) the Taylorization decreases as the Ekman number is lowered, and (vi) the ageostrophic velocity component makes up 80% of the flow.

  10. Isotropically Driven versus Outflow Driven Turbulence: Observational Consequences for Molecular Clouds

    CERN Document Server

    Carroll, Jonathan J; Blackman, Eric G

    2010-01-01

    Feedback from protostellar outflows can influence the nature of turbulence in star forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star forming regions, we previously (Carroll et al. 2009) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner 2007 although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scal...

  11. Relationship between level of neutral buoyancy and dual-Doppler observed mass detrainment levels in deep convection

    Directory of Open Access Journals (Sweden)

    G. L. Mullendore

    2013-01-01

    Full Text Available Although it is generally accepted that the level of neutral buoyancy (LNB is only a coarse estimate of updraft depth, the LNB is still used to understand and predict storm structure in both observations and modeling. This study uses case studies to quantify the variability associated with using environmental soundings to predict detrainment levels. Nine dual-Doppler convective cases were used to determine the observed level of maximum detrainment (LMD to compare with the LNB. The LNB for each case was calculated with a variety of methods and with a variety of sources (including both observed and simulated soundings. The most representative LNB was chosen as the proximity sounding from NARR using the most unstable parcel and including ice processes.

    The observed cases were a mix of storm morphologies, including both supercell and multicell storms. As expected, the LMD was generally below the LNB, the mean offset for all cases being 2.2 km. However, there was a marked difference between the supercell and non-supercell cases. The two supercell cases had LMDs of 0.3 km and 0.0 km below the LNB. The remaining cases had LMDs that ranged from 4.0 km below to 1.6 km below the LNB, with a mean offset of 2.8 km below. Observations also showed that evolution of the LMD over the lifetime of the storm can be significant (e.g., >2 km altitude change in 30 min, and this time evolution is lacking from models with coarse time steps, missing significant changes in detrainment levels that may strongly impact the amount of boundary layer mass transported to the upper troposphere and lower stratosphere.

  12. 80-Myr history of buoyancy and volcanic fluxes along the trails of the Walvis and St. Helena hotspots (South Atlantic)

    Science.gov (United States)

    Vidal, V.; Adam, C.; Escartin, J.

    2007-12-01

    Walvis and St.~Helena are the only long-lived hotspot chains in the South Atlantic. Therefore, their characterization is important to constrain the processes associated with mantle plume formation, their temporal evolution, and the interaction with plate and mantle dynamics in the region. We study the temporal evolution of plume buoyancy and magma production rate along both hotspot chains, which are constrained from the swell and volume of volcanic materials emplaced along the chain. The regional depth anomaly is calculated by correcting the 2' bathymetry grid of Smith & Sandwell (1997) for thermal subsidence and sediment loading. We separate the topography associated with volcanism and the swell surrounding the hotspot chains using the MiFil filtering method (Adam et al., 2005). We then estimate the temporal variations associated with both parameters by computing volumes along the hotspot tracks. Neither Walvis nor St.~Helena show a 'classical' hotspot behavior. We find that two plumes are at the origin of the St.~Helena chain. This study also shows a swell associated with the Circe seamount, supporting the existence of a hotspot NW of the St.~Helena trail. The variation in swell and volcanic fluxes suggests temporal variability in the plume behavior at time scales of 10-20~m.y. and 5~m.y., which may be related to oscillations and instabilities of the plume conduit, respectively. Cumulative fluxes in the area are largest for Walvis and weakest for Circe, and all are significantly lower than that reported for the Hawai'i hotspot.

  13. Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers

    CERN Document Server

    Calkins, Michael A; Nieves, David; Julien, Keith; Tobias, Steven M

    2016-01-01

    Most large-scale planetary magnetic fields are thought to be driven by low Rossby number convection of a low magnetic Prandtl number fluid. Here kinematic dynamo action is investigated with an asymptotic, rapidly rotating dynamo model for the plane layer geometry that is intrinsically low magnetic Prandtl number. The thermal Prandtl number and Rayleigh number are varied to illustrate fundamental changes in flow regime, ranging from laminar cellular convection to geostrophic turbulence in which an inverse energy cascade is present. A decrease in the efficiency of the convection to generate a dynamo, as determined by an increase in the critical magnetic Reynolds number, is observed as the buoyancy forcing is increased. This decreased efficiency may result from both the loss of correlations associated with the increasingly disordered states of flow that are generated, and boundary layer behavior that enhances magnetic diffusion locally. We find that the spatial characteristics of $\\alpha$, and thus the large-sca...

  14. Far Field Evolution of Momentum Driven and Scalar Dominated Flow Field

    Directory of Open Access Journals (Sweden)

    V. Ilangovan

    2016-01-01

    Full Text Available To capture the effect of initial conditions in far field evolution of momentum driven and scalar dominated flow field, Witze scaling has been used for collapsing vector and scalar data to attain asymptotic state at self-preserving region of the jet. It incorporates the initial mass, momentum, energy to capture the effect of heating level on both near and far field development of strongly heated coaxial turbulent round air jets entering into quiescent ambient. This paper compares the effectiveness of potential core length and jet effective diameter as the length scales to collapse both mean and fluctuating components of velocity vector and temperature scalar. Similarity considerations with Witze length scale using the initial momentum flux and buoyancy flux gives a good collapse at all levels of heating.

  15. Constellations-driven innovation

    DEFF Research Database (Denmark)

    Hansbøl, Mikala

    2013-01-01

    The paper presents a science and technology studies and actor-network-theory inspired approach to understanding the development and ongoing re-didactication and re-design of a Danish developed presentation tool called the Theme Board (Tematavlen.dk). It is argued that this approach provides a par...... a particularly useful point of departure for engaging in researching innovation and didactic design of digital teaching and learning instruments such as the Theme Board that are programmed and serviced 'in the sky'. I call this approach: constellation-driven innovations....

  16. Improved optically driven microrotors

    Science.gov (United States)

    Asavei, Theodor; Loke, Vincent L. Y.; Nieminen, Timo A.; Heckenberg, Norman R.; Rubinsztein-Dunlop, Halina

    2008-08-01

    Two-photon polymerization of optically curing resins is a powerful method to fabricate micron sized objects which can be used as tools to measure properties at small scales. These microdevices can be driven by means of externally applied focused laser beams (optical tweezers) through angular momentum exchange, giving rise to a net torque. The advantage of the optical drive is that no contact is required, therefore making the microdevices suited to non-invasive biological applications. The fabrication method is versatile and allows building objects of any 3D shape. We discuss the design and modelling of various optically driven rotors. In particular, we consider fabrication of microspheres with an internal shape birefringence in order to obtain rotation in an optical trap. The reason for fabricating this type of object is that they are well-suited for studies of mechanical properties of single biomolecules such as the torsional stiffness of DNA or torque generated by molecular motors. The microspheres fabricated are able to transduce torques of 2000 pNnm with optical powers of 500 mW and could be rotated with frequencies up to 40 Hz in circularly polarized light.

  17. Libration driven multipolar instabilities

    CERN Document Server

    Cébron, David; Herreman, Wietze

    2014-01-01

    We consider rotating flows in non-axisymmetric enclosures that are driven by libration, i.e. by a small periodic modulation of the rotation rate. Thanks to its simplicity, this model is relevant to various contexts, from industrial containers (with small oscillations of the rotation rate) to fluid layers of terrestial planets (with length-of-day variations). Assuming a multipolar $n$-fold boundary deformation, we first obtain the two-dimensional basic flow. We then perform a short-wavelength local stability analysis of the basic flow, showing that an instability may occur in three dimensions. We christen it the Libration Driven Multipolar Instability (LDMI). The growth rates of the LDMI are computed by a Floquet analysis in a systematic way, and compared to analytical expressions obtained by perturbation methods. We then focus on the simplest geometry allowing the LDMI, a librating deformed cylinder. To take into account viscous and confinement effects, we perform a global stability analysis, which shows that...

  18. Heat driven pulse pump

    Science.gov (United States)

    Benner, Steve M (Inventor); Martins, Mario S. (Inventor)

    2000-01-01

    A heat driven pulse pump includes a chamber having an inlet port, an outlet port, two check valves, a wick, and a heater. The chamber may include a plurality of grooves inside wall of the chamber. When heated within the chamber, a liquid to be pumped vaporizes and creates pressure head that expels the liquid through the outlet port. As liquid separating means, the wick, disposed within the chamber, is to allow, when saturated with the liquid, the passage of only liquid being forced by the pressure head in the chamber, preventing the vapor from exiting from the chamber through the outlet port. A plurality of grooves along the inside surface wall of the chamber can sustain the liquid, which is amount enough to produce vapor for the pressure head in the chamber. With only two simple moving parts, two check valves, the heat driven pulse pump can effectively function over the long lifetimes without maintenance or replacement. For continuous flow of the liquid to be pumped a plurality of pumps may be connected in parallel.

  19. An evaluation of gas transfer velocity parameterizations during natural convection using DNS

    Science.gov (United States)

    Fredriksson, Sam T.; Arneborg, Lars; Nilsson, Hâkan; Zhang, Qi; Handler, Robert A.

    2016-02-01

    Direct numerical simulations (DNS) of free surface flows driven by natural convection are used to evaluate different methods of estimating air-water gas exchange at no-wind conditions. These methods estimate the transfer velocity as a function of either the horizontal flow divergence at the surface, the turbulent kinetic energy dissipation beneath the surface, the heat flux through the surface, or the wind speed above the surface. The gas transfer is modeled via a passive scalar. The Schmidt number dependence is studied for Schmidt numbers of 7, 150 and 600. The methods using divergence, dissipation and heat flux estimate the transfer velocity well for a range of varying surface heat flux values, and domain depths. The two evaluated empirical methods using wind (in the limit of no wind) give reasonable estimates of the transfer velocity, depending however on the surface heat flux and surfactant saturation. The transfer velocity is shown to be well represented by the expression, ks=A |Bν|1/4 Sc-n, where A is a constant, B is the buoyancy flux, ν is the kinematic viscosity, Sc is the Schmidt number, and the exponent n depends on the water surface characteristics. The results suggest that A=0.39 and n≈1/2 and n≈2/3 for slip and no-slip boundary conditions at the surface, respectively. It is further shown that slip and no-slip boundary conditions predict the heat transfer velocity corresponding to the limits of clean and highly surfactant contaminated surfaces, respectively. This article was corrected on 22 MAR 2016. See the end of the full text for details.

  20. A Model-Driven Probabilistic Parser Generator

    CERN Document Server

    Quesada, Luis; Cortijo, Francisco J

    2012-01-01

    Existing probabilistic scanners and parsers impose hard constraints on the way lexical and syntactic ambiguities can be resolved. Furthermore, traditional grammar-based parsing tools are limited in the mechanisms they allow for taking context into account. In this paper, we propose a model-driven tool that allows for statistical language models with arbitrary probability estimators. Our work on model-driven probabilistic parsing is built on top of ModelCC, a model-based parser generator, and enables the probabilistic interpretation and resolution of anaphoric, cataphoric, and recursive references in the disambiguation of abstract syntax graphs. In order to prove the expression power of ModelCC, we describe the design of a general-purpose natural language parser.

  1. Post shut-down decay heat removal from nuclear reactor core by natural convection loops in sodium pool

    Energy Technology Data Exchange (ETDEWEB)

    Rajamani, A. [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Sundararajan, T., E-mail: tsundar@iitm.ac.in [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Prasad, B.V.S.S.S. [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Parthasarathy, U.; Velusamy, K. [Nuclear Engineering Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)

    2016-05-15

    Highlights: • Transient simulations are performed for a worst case scenario of station black-out. • Inter-wrapper flow between various sub-assemblies reduces peak core temperature. • Various natural convection paths limits fuel clad temperatures below critical level. - Abstract: The 500 MWe Indian pool type Prototype Fast Breeder Reactor (PFBR) has a passive core cooling system, known as the Safety Grade Decay Heat Removal System (SGDHRS) which aids to remove decay heat after shut down phase. Immediately after reactor shut down the fission products in the core continue to generate heat due to beta decay which exponentially decreases with time. In the event of a complete station blackout, the coolant pump system may not be available and the safety grade decay heat removal system transports the decay heat from the core and dissipates it safely to the atmosphere. Apart from SGDHRS, various natural convection loops in the sodium pool carry the heat away from the core and deposit it temporarily in the sodium pool. The buoyancy driven flow through the small inter-wrapper gaps (known as inter-wrapper flow) between fuel subassemblies plays an important role in carrying the decay heat from the sub-assemblies to the hot sodium pool, immediately after reactor shut down. This paper presents the transient prediction of flow and temperature evolution in the reactor subassemblies and the sodium pool, coupled with the safety grade decay heat removal system. It is shown that with a properly sized decay heat exchanger based on liquid sodium and air chimney stacks, the post shutdown decay heat can be safely dissipated to atmospheric air passively.

  2. Important Parameters Design of Inverter-driven Cryogenic Induction Motor for Submerged Liquid Natural Gas Pump%潜液式液化天然气泵用变频低温异步电机的关键参数设计

    Institute of Scientific and Technical Information of China (English)

    艾程柳; 黄元峰; 王海峰; 顾国彪

    2015-01-01

    Cryogenic electrical motors are the key component of submerged liquid natural gas (LNG) pumps. In this paper, some design aspects of an inverter-driven cryogenic electrical motor for a submerged LNG pump were presented. First of all, the characteristics of conductive material and magnetic material in the motor were discussed to determine the electric and magnetic loadings of the cryogenic induction motor by combining with the thermal analysis. Secondly, this paper proposed to design the motor starting with its rotor. And its slots, especially the rotor slots should be designed as short and fat shape to decrease leakage inductances and friction losses. Finally, the designed 11kW prototype was simulated to analyze its performance in?161℃ LNG and?196℃ liquid nitrogen. And we tested the prototype in liquid nitrogen. The experimental results matched the simulation data so that the theoretical analysis was validated. Therefore, the proposed design aspects can serve as a designing reference for ainverter-driven cryogenic induction motor.%低温电机是潜液式液化天然气(liquefied natural gas, LNG)泵的核心部件.该文主要讨论了潜液式LNG泵用变频低温异步电机的设计方案.首先研究了电机电磁材料的低温特性,结合低温异步电机温升情况确定了电机的电磁负荷.建议从转子开始设计变频低温异步电机,并认为变频低温异步电机的槽形特别是转子槽,应设计为"矮胖"形以减少该类电机的漏抗和转子摩擦损耗.仿真分析了 11 kW 设计样机在LNG(?161℃)及液氮(?196℃)的运行性能,并进行了液氮低温试验,试验数据与仿真分析相吻合,验证了理论分析的正确性,该文的研究成果可为变频低温异步电机的设计提供参考.

  3. Data-driven computational mechanics

    CERN Document Server

    Kirchdoerfer, Trenton

    2015-01-01

    We develop a new computing paradigm, which we refer to as data-driven computing, according to which calculations are carried out directly from experimental material data and pertinent constraints and conservation laws, such as compatibility and equilibrium, thus bypassing the empirical material modeling step of conventional computing altogether. Data-driven solvers seek to assign to each material point the state from a prespecified data set that is closest to satisfying the conservation laws. Equivalently, data-driven solvers aim to find the state satisfying the conservation laws that is closest to the data set. The resulting data-driven problem thus consists of the minimization of a distance function to the data set in phase space subject to constraints introduced by the conservation laws. We motivate the data-driven paradigm and investigate the performance of data-driven solvers by means of two examples of application, namely, the static equilibrium of nonlinear three-dimensional trusses and linear elastici...

  4. Scaling up nanoscale water-driven energy conversion into evaporation-driven engines and generators

    Science.gov (United States)

    Chen, Xi; Goodnight, Davis; Gao, Zhenghan; Cavusoglu, Ahmet H.; Sabharwal, Nina; Delay, Michael; Driks, Adam; Sahin, Ozgur

    2015-06-01

    Evaporation is a ubiquitous phenomenon in the natural environment and a dominant form of energy transfer in the Earth's climate. Engineered systems rarely, if ever, use evaporation as a source of energy, despite myriad examples of such adaptations in the biological world. Here, we report evaporation-driven engines that can power common tasks like locomotion and electricity generation. These engines start and run autonomously when placed at air-water interfaces. They generate rotary and piston-like linear motion using specially designed, biologically based artificial muscles responsive to moisture fluctuations. Using these engines, we demonstrate an electricity generator that rests on water while harvesting its evaporation to power a light source, and a miniature car (weighing 0.1 kg) that moves forward as the water in the car evaporates. Evaporation-driven engines may find applications in powering robotic systems, sensors, devices and machinery that function in the natural environment.

  5. 92 K thermoacoustically driven pulse tube refrigerator

    Institute of Scientific and Technical Information of China (English)

    TANG Ke; CHEN Guobang; JIN Tao; KONG Bo; BAO Rui; QIU Limin; GAN Zhihua

    2004-01-01

    @@ A thermoacoustic prime mover, instead of a mechanical compressor, was firstly proposed in 1990 by Radebaugh and Swift et al. to drive a pulse tube refrigerator [1]. The so-called thermoacoustically driven pulse tube refrigerator (TADPTR) has a number of advantages. First,it is characterized by its long-term stable operation for it has no moving components. Besides, solar energy and waste fuel gas can be adopted as its driving source. Utilization of low-grade energy not only improves its overall thermal efficiency, but also is most attractively applicable to the case which is short of electricity but abundant in heat energy. The potential applications, such as thermoacoustic natural gas liquefier, are under development[2].It burns part of natural gas to drive a pulse tube refrigerator whose cooling capacity is then used to liquefy the rest natural gas.

  6. Muscle-driven nanogenerators

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhong L. (Marietta, GA); Yang, Rusen (Atlanta, GA)

    2011-03-01

    In a method of generating electricity, a plurality of living cells are grown on an array of piezoelectric nanowires so that the cells engage the piezoelectric nanowires. Induced static potentials are extracted from at least one of the piezoelectric nanowires when at least one of the cells deforms the at least one of the piezoelectric nanowires. A cell-driven electrical generator that includes a substrate and a plurality of spaced-apart piezoelectric nanowires disposed on the substrate. A plurality of spaced-apart conductive electrodes interact with the plurality of piezoelectric nanowires. A biological buffer layer that is configured to promote growth of cells is disposed on the substrate so that cells placed on the substrate will grow and engage the piezoelectric nanowires.

  7. Soliton driven angiogenesis

    Science.gov (United States)

    Bonilla, L. L.; Carretero, M.; Terragni, F.; Birnir, B.

    2016-08-01

    Angiogenesis is a multiscale process by which blood vessels grow from existing ones and carry oxygen to distant organs. Angiogenesis is essential for normal organ growth and wounded tissue repair but it may also be induced by tumours to amplify their own growth. Mathematical and computational models contribute to understanding angiogenesis and developing anti-angiogenic drugs, but most work only involves numerical simulations and analysis has lagged. A recent stochastic model of tumour-induced angiogenesis including blood vessel branching, elongation, and anastomosis captures some of its intrinsic multiscale structures, yet allows one to extract a deterministic integropartial differential description of the vessel tip density. Here we find that the latter advances chemotactically towards the tumour driven by a soliton (similar to the famous Korteweg-de Vries soliton) whose shape and velocity change slowly. Analysing these collective coordinates paves the way for controlling angiogenesis through the soliton, the engine that drives this process.

  8. Employee-driven innovation

    DEFF Research Database (Denmark)

    Kesting, Peter; Ulhøi, John Parm

    2015-01-01

    Purpose – The purpose of this paper is to outline the “grand structure” of the phenomenon in order to identify both the underlying processes and core drivers of employee-driven innovation (EDI). Design/methodology/approach – This is a conceptual paper. It particularly applies the insights...... of contemporary research on routine and organizational decision making to the specific case of EDI. Findings – The main result of the paper is that, from a theoretical point of view, it makes perfect sense to involve ordinary employees in innovation decisions. However, it is also outlined that naıve or ungoverned...... participation is counterproductive, and that it is quite difficult to realize the hidden potential in a supportive way. Research limitations/implications – The main implication is that basic mechanisms for employee participation also apply to innovation decisions, although often in a different way. However...

  9. Ischemia-driven angiogenesis.

    Science.gov (United States)

    Dor, Y; Keshet, E

    1997-11-01

    New blood vessels usually develop in places where they are most needed. A prime example of neovascularization representing a positive feedback response to insufficient perfusion is the development of collateral blood vessels in the ischemic myocardium and leg. The recent discoveries of hypoxia-inducible transcription and angiogenic factors have provided important mechanistic links between the metabolic consequences of ischemia and compensatory angiogenesis. Vascular endothelial growth factor (VEGF) has emerged as the key mediator of ischemia-driven angiogenesis. Environmental stresses, including hypoxia, hypoglycemia, and hypoferremia, upregulate VEGF expression at both the transcriptional and posttranscriptional levels. VEGF acts in turn on adjacent vascular beds expressing cognate receptors and induces sprouting and capillary growth toward the ischemic tissue. In addition to expanding the vasculature at sites where existing vessels have been occluded or obliterated, VEGF also functions to match the vascular density according to development and physiologic increases in oxygen consumption. Fine adjustment of the vasculature includes a step of oxygen-regulated vascular pruning mediated by VEGF in its capacity as a survival factor for newly formed vessels. Pathologic settings of ischemia-driven angiogenesis include a major component of stress-induced angiogenesis during tumor neovascularization and abnormal vessel growth associated with retinopathies. The latter represents an excessive angiogenic response to conditions of severe retinal ischemia. Further insights into the mechanism of stress-induced angiogenesis are likely to suggest new ways to augment growth of collateral vessels and to restrain unwarranted neovascularization in tumors and retinopathies. (Trends Cardiovasc Med 1997;7:289-294). © 1997, Elsevier Science Inc.

  10. Numerical investigation of mixed convection heat transfer from two isothermal circular cylinders in tandem arrangement: buoyancy, spacing ratio, and confinement effects

    Science.gov (United States)

    Salcedo, Erick; Cajas, Juan C.; Treviño, César; Martínez-Suástegui, Lorenzo

    2016-11-01

    This paper presents a two-dimensional numerical study for mixed convection in a laminar cross-flow with a pair of stationary equal-sized isothermal cylinders in tandem arrangement confined in a channel. The governing equations are solved using the control volume method on a nonuniform orthogonal Cartesian grid, and the immersed boundary method is employed to identify the cylinders placed in the flow field. The numerical scheme is first validated against standard cases of symmetrically confined isothermal circular cylinders in plane channels, and grid convergence tests were also examined. The objective of the present study was to investigate the influence of buoyancy and the blockage ratio constraint on the flow and heat transfer characteristics of the immersed cylinder array. Using a fixed Reynolds number based on cylinder diameter of ReD = 200 , a fixed value of the Prandtl number of Pr = 7 , and a blockage ratio of D/H = 0.2 , all possible flow regimes are considered by setting the longitudinal spacing ratio (σ = L/D ) between the cylinder axes to 2, 3, and 5 for values of the buoyancy parameter (Richardson number) in the range -1≤ Ri≤ 4 . The interference effects and complex flow features are presented in the form of mean and instantaneous velocity, vorticity, and temperature distributions. The results demonstrate how the buoyancy, spacing ratio, and wall confinement affect the wake structure and vortex dynamics. In addition, local and average heat transfer characteristics of both cylinders are comprehensively presented for a wide range in the parametric space.

  11. Numerical investigation of mixed convection heat transfer from two isothermal circular cylinders in tandem arrangement: buoyancy, spacing ratio, and confinement effects

    Science.gov (United States)

    Salcedo, Erick; Cajas, Juan C.; Treviño, César; Martínez-Suástegui, Lorenzo

    2017-04-01

    This paper presents a two-dimensional numerical study for mixed convection in a laminar cross-flow with a pair of stationary equal-sized isothermal cylinders in tandem arrangement confined in a channel. The governing equations are solved using the control volume method on a nonuniform orthogonal Cartesian grid, and the immersed boundary method is employed to identify the cylinders placed in the flow field. The numerical scheme is first validated against standard cases of symmetrically confined isothermal circular cylinders in plane channels, and grid convergence tests were also examined. The objective of the present study was to investigate the influence of buoyancy and the blockage ratio constraint on the flow and heat transfer characteristics of the immersed cylinder array. Using a fixed Reynolds number based on cylinder diameter of ReD = 200, a fixed value of the Prandtl number of Pr = 7, and a blockage ratio of D/H = 0.2, all possible flow regimes are considered by setting the longitudinal spacing ratio (σ = L/D) between the cylinder axes to 2, 3, and 5 for values of the buoyancy parameter (Richardson number) in the range -1≤ Ri≤ 4. The interference effects and complex flow features are presented in the form of mean and instantaneous velocity, vorticity, and temperature distributions. The results demonstrate how the buoyancy, spacing ratio, and wall confinement affect the wake structure and vortex dynamics. In addition, local and average heat transfer characteristics of both cylinders are comprehensively presented for a wide range in the parametric space.

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

    Science.gov (United States)

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

    2017-01-01

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

  13. Numerical Study of Natural Convection in Vertical Enclosures Utilizing Nanofluid

    Directory of Open Access Journals (Sweden)

    M. Alipanah

    2014-01-01

    Full Text Available Enhancement of buoyancy-driven convection heat transfer within vertical cavities containing nanofluids subjected to different side wall temperatures and various aspect ratios is investigated. The computations are based on an iterative, finitevolume numerical procedure (SIMPLE that incorporates the Boussinesq approximation to simulate the buoyancy term. With the base fluid being water, three different nanoparticles (Cu, TiO2, and Al2O3 are considered as the nanofluids. This study has been carried out for the pertinent parameters in the following ranges: the Rayleigh number, Raf = 105–107 and the volumetric fraction of nanoparticle between 0 and 5 percent. The results are presented for different length-to-height ratios varying from 0.1 to 1.0. The comparisons show that the mean Nusselt numbers and velocity magnitudes increase with volume fraction for the whole range of the Rayleigh numbers. The predictions show a noticeable heat transfer enhancement compared to pure fluid. It is also found that the heat transfer enhancement utilizing nanofluid is more pronounced at low aspect ratios than high aspect ratios. Moreover, the results depict that the addition of nanoparticles to the pure fluid has more effects at lower Rayleigh numbers.

  14. A decoupled monolithic projection method for natural convection problems

    Science.gov (United States)

    Pan, Xiaomin; Kim, Kyoungyoun; Lee, Changhoon; Choi, Jung-Il

    2016-06-01

    We propose an efficient monolithic numerical procedure based on a projection method for solving natural convection problems. In the present monolithic method, the buoyancy, linear diffusion, and nonlinear convection terms are implicitly advanced by applying the Crank-Nicolson scheme in time. To avoid an otherwise inevitable iterative procedure in solving the monolithic discretized system, we use a linearization of the nonlinear convection terms and approximate block lower-upper (LU) decompositions along with approximate factorization. Numerical simulations demonstrate that the proposed method is more stable and computationally efficient than other semi-implicit methods, preserving temporal second-order accuracy.

  15. Cross-diffusion-driven hydrodynamic instabilities in a double-layer system: General classification and nonlinear simulations

    Science.gov (United States)

    Budroni, M. A.

    2015-12-01

    Cross diffusion, whereby a flux of a given species entrains the diffusive transport of another species, can trigger buoyancy-driven hydrodynamic instabilities at the interface of initially stable stratifications. Starting from a simple three-component case, we introduce a theoretical framework to classify cross-diffusion-induced hydrodynamic phenomena in two-layer stratifications under the action of the gravitational field. A cross-diffusion-convection (CDC) model is derived by coupling the fickian diffusion formalism to Stokes equations. In order to isolate the effect of cross-diffusion in the convective destabilization of a double-layer system, we impose a starting concentration jump of one species in the bottom layer while the other one is homogeneously distributed over the spatial domain. This initial configuration avoids the concurrence of classic Rayleigh-Taylor or differential-diffusion convective instabilities, and it also allows us to activate selectively the cross-diffusion feedback by which the heterogeneously distributed species influences the diffusive transport of the other species. We identify two types of hydrodynamic modes [the negative cross-diffusion-driven convection (NCC) and the positive cross-diffusion-driven convection (PCC)], corresponding to the sign of this operational cross-diffusion term. By studying the space-time density profiles along the gravitational axis we obtain analytical conditions for the onset of convection in terms of two important parameters only: the operational cross-diffusivity and the buoyancy ratio, giving the relative contribution of the two species to the global density. The general classification of the NCC and PCC scenarios in such parameter space is supported by numerical simulations of the fully nonlinear CDC problem. The resulting convective patterns compare favorably with recent experimental results found in microemulsion systems.

  16. Comparing alternative data-driven ontological vistas of natural history

    NARCIS (Netherlands)

    van Erp, M.G.J.; Lendvai, P.K.; van den Bosch, A.; Bunt, H.; Petukhova, V.; Wubben, S.

    2009-01-01

    Traditionally, ontologies are created manually, based on human experts' view of the concepts and relations of the domain at hand. We present ongoing work on two approaches to the automatic construction of ontologies from a flat database of records, and compare them to a manually constructed ontology

  17. Natural Ventilation Driven by Wind and Temperature Difference

    DEFF Research Database (Denmark)

    Larsen, Tine Steen

    the incidence angle of the wind, which is an important parameter in this type of ventilation. Several wind tunnel experiments are made and from the results of these, a new design expression is made which includes the wind pressure, temperature difference, incidence angle of the wind and the fluctuations...... in pressure at the opening. A discussion is made regarding the correctness of using wind tunnel measurements for a design expression to be used outdoors, but here it is concluded from analysis of the different types of wind that this can be done with some knowledge of the differences. Finally, the new...... driving forces are still wind pressure and temperature differences as with cross-ventilation, but here the turbulence in the wind and the pulsating flow near the opening also affect the flow through the opening. From earlier work, some design expressions already exist, but none of these include...

  18. Driven by Nature: The Future of the Arctic

    DEFF Research Database (Denmark)

    Wang, Nils

    2014-01-01

    that lead to genuine breakthroughs.We look at the worlds of business, philanthropy, diplomacy, economics, investing, geopolitics, media, agriculture, logistics, technology and healthcare.These fascinating studies and interviews reveal how innovations and breakthroughs succeed or fail....

  19. Optimality of Contraction-Driven Crawling

    Science.gov (United States)

    Recho, P.; Joanny, J.-F.; Truskinovsky, L.

    2014-05-01

    We study a particular mechanism of cell motility allowing a precise formulation of the condition of optimal trade-off between performance and metabolic cost. In the model, a steadily crawling fragment is represented by a layer of active gel placed on a frictional surface and driven by contraction only. We find analytically the distribution of contractile elements (pullers) ensuring that the efficiency of self-propulsion is maximal. We then show that natural assumptions about advection and diffusion of pullers produce a distribution that is remarkably close to the optimal one and is qualitatively similar to the one observed in experiments on fish keratocytes.

  20. Optimality of contraction-driven crawling

    CERN Document Server

    Recho, P; Truskinovsky, L

    2014-01-01

    We study a model of cell motility where the condition of optimal trade-off between performance and metabolic cost can be made precise. In this model a steadily crawling fragment is represented by a layer of active gel placed on a frictional surface and driven by contraction only. We find analytically the distribution of contractile elements (pullers) ensuring that the efficiency of self-propulsion is maximal. We then show that natural assumptions about advection and diffusion of pullers produce a distribution that is remarkably close to the optimal one and is qualitatively similar to the one observed in experiments on fish keratocytes.

  1. Cosmic ray driven outflows

    CERN Document Server

    Hanasz, Michal; Naab, Thorsten; Gawryszczak, Artur; Kowalik, Kacper; Wóltański, Dominik

    2013-01-01

    We present simulations of the magnetized interstellar medium (ISM) in models of massive star forming (40 Msun / yr) disk galaxies with high gas surface densities (~100 Msun / pc^2) similar to observed star forming high-redshift disks. We assume that type II supernovae deposit 10 per cent of their energy into the ISM as cosmic rays and neglect the additional deposition of thermal energy or momentum. With a typical Galactic diffusion coefficient for CRs (3e28 cm^2 / s) we demonstrate that this process alone can trigger the local formation of a strong low density galactic wind maintaining vertically open field lines. Driven by the additional pressure gradient of the relativistic fluid the wind speed can exceed 1000 km/s, much higher than the escape velocity of the galaxy. The global mass loading, i.e. the ratio of the gas mass leaving the galactic disk in a wind to the star formation rate becomes of order unity once the system has settled into an equilibrium. We conclude that relativistic particles accelerated i...

  2. Digitally-Driven Architecture

    Directory of Open Access Journals (Sweden)

    Henriette Bier

    2014-07-01

    Full Text Available The shift from mechanical to digital forces architects to reposition themselves: Architects generate digital information, which can be used not only in designing and fabricating building components but also in embedding behaviours into buildings. This implies that, similar to the way that industrial design and fabrication with its concepts of standardisation and serial production influenced modernist architecture, digital design and fabrication influences contemporary architecture. While standardisation focused on processes of rationalisation of form, mass-customisation as a new paradigm that replaces mass-production, addresses non-standard, complex, and flexible designs. Furthermore, knowledge about the designed object can be encoded in digital data pertaining not just to the geometry of a design but also to its physical or other behaviours within an environment. Digitally-driven architecture implies, therefore, not only digitally-designed and fabricated architecture, it also implies architecture – built form – that can be controlled, actuated, and animated by digital means.In this context, this sixth Footprint issue examines the influence of digital means as pragmatic and conceptual instruments for actuating architecture. The focus is not so much on computer-based systems for the development of architectural designs, but on architecture incorporating digital control, sens­ing, actuating, or other mechanisms that enable buildings to inter­act with their users and surroundings in real time in the real world through physical or sensory change and variation.

  3. Invention-driven marketing

    Science.gov (United States)

    Carlson, William E.

    1994-01-01

    Suppose you have just created a revolutionary bicycle suspension which allows a bike to be ridden over rough terrain at 60 miles per hour. In addition, suppose that you are deeply concerned about the plight of hungry children. Which should you do: be sure all hungry children have bicycles; transfer the technology for your new suspension to bicycle manufacturers worldwide; or start a company to supply premium sports bicycle based on your patented technology, and donate the profits to a charity which feeds hungry children? Woven through this somewhat trivial example is the paradox of technology transfer - the supplier (owner) may want to transfer technology; but to succeed, he or she must reformulate the problem as a user need for which there is a new and better solution. Successful technology transfer is little more than good marketing applied to an existing invention, process, or capability. You must identify who needs the technology, why they need it, why the new technology is better than alternatives, how much the customers are willing and able to pay for these benefits, and how to distribute products based on the technology tc the target customers. In market-driven development, the term 'technology transfer' is rarely used. The developers focus on studying user needs and designing solution They may have technology needs, but they don't have technology in search of a use.

  4. Isotropically Driven Versus Outflow Driven Turbulence: Observational Consequences for Molecular Clouds

    Science.gov (United States)

    Carroll, Jonathan J.; Frank, Adam; Blackman, Eric G.

    2010-10-01

    Feedback from protostellar outflows can influence the nature of turbulence in star-forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star-forming regions, we previously (Carroll et al.) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here, we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scales effectively reducing the formation of large-scale turbulent density structures. These effects are qualitatively independent of resolution. We have also carried out Principal Component Analysis (PCA) for synthetic data from our simulations. We find that PCA as a tool for identifying the driving scale of turbulence has a misleading bias toward low amplitude large-scale velocity structures even when they are not necessarily the dominant energy containing scales. This bias is absent for isotropically forced turbulence but manifests strongly for collimated outflow driven turbulence.

  5. Transient laminar opposing mixed convection in a symmetrically heated duct with a plane symmetric sudden contraction-expansion: Buoyancy an inclination effects

    Science.gov (United States)

    Martínez-Suástegui, Lorenzo; Barreto, Enrique; Treviño, César

    2015-11-01

    Transient laminar opposing mixed convection is studied experimentally in an open vertical rectangular channel with two discrete protruded heat sources subjected to uniform heat flux simulating electronic components. Experiments are performed for a Reynolds number of Re = 700, Prandtl number of Pr = 7, inclination angles with respect to the horizontal of γ =0o , 45o and 90o, and different values of buoyancy strength or modified Richardson number, Ri* =Gr* /Re2 . From the experimental measurements, the space averaged surface temperatures, overall Nusselt number of each simulated electronic chip, phase-space plots of the self-oscillatory system, characteristic times of temperature oscillations and spectral distribution of the fluctuating energy have been obtained. Results show that when a threshold in the buoyancy parameter is reached, strong three-dimensional secondary flow oscillations develop in the axial and spanwise directions. This research was supported by the Consejo Nacional de Ciencia y Tecnología (CONACYT), Grant number 167474 and by the Secretaría de Investigación y Posgrado del IPN, Grant number SIP 20141309.

  6. Impacts of a wind stress and a buoyancy flux on the seasonal variation of mixing layer depth in the South China Sea

    Institute of Scientific and Technical Information of China (English)

    XIAO Xianjun; WANG Dongxiao; ZHOU Wen; ZHANG Zuqiang; QIN Yinghao; HE Na; ZENG Lili

    2013-01-01

    The seasonal variation of mixing layer depth (MLD) in the ocean is determined by a wind stress and a buoy-ance flux. A South China Sea (SCS) ocean data assimilation system is used to analyze the seasonal cycle of its MLD. It is found that the variability of MLD in the SCS is shallow in summer and deep in winter, as is the case in general. Owing to local atmosphere forcing and ocean dynamics, the seasonal variability shows a regional characteristic in the SCS. In the northern SCS, the MLD is shallow in summer and deep in winter, affected coherently by the wind stress and the buoyance flux. The variation of MLD in the west is close to that in the central SCS, influenced by the advection of strong western boundary currents. The eastern SCS presents an annual cycle, which is deep in summer and shallow in winter, primarily impacted by a heat flux on the air-sea interface. So regional characteristic needs to be cared in the analysis about the MLD of SCS.

  7. Salinity driven oceanographic upwelling

    Science.gov (United States)

    Johnson, D.H.

    1984-08-30

    The salinity driven oceanographic upwelling is maintained in a mariculture device that includes a long main duct in the general shape of a cylinder having perforated cover plates at each end. The mariculture device is suspended vertically in the ocean such that one end of the main duct is in surface water and the other end in relatively deep water that is cold, nutrient rich and relatively fresh in comparison to the surface water which is relatively warm, relatively nutrient deficient and relatively saline. A plurality of elongated flow segregating tubes are disposed in the main duct and extend from the upper cover plate beyond the lower cover plate into a lower manifold plate. The lower manifold plate is spaced from the lower cover plate to define a deep water fluid flow path to the interior space of the main duct. Spacer tubes extend from the upper cover plate and communicate with the interior space of the main duct. The spacer tubes are received in an upper manifold plate spaced from the upper cover plate to define a surface water fluid flow path into the flow segregating tubes. A surface water-deep water counterflow is thus established with deep water flowing upwardly through the main duct interior for discharge beyond the upper manifold plate while surface water flows downwardly through the flow segregating tubes for discharge below the lower manifold plate. During such counterflow heat is transferred from the downflowing warm water to the upflowing cold water. The flow is maintained by the difference in density between the deep water and the surface water due to their differences in salinity. The upwelling of nutrient rich deep water is used for marifarming by fertilizing the nutrient deficient surface water. 1 fig.

  8. Performance of Gas-Engine Driven Heat Pump Unit

    Energy Technology Data Exchange (ETDEWEB)

    Abdi Zaltash; Randy Linkous; Randall Wetherington; Patrick Geoghegan; Ed Vineyard; Isaac Mahderekal; Robert Gaylord

    2008-09-30

    Air-conditioning (cooling) for buildings is the single largest use of electricity in the United States (U.S.). This drives summer peak electric demand in much of the U.S. Improved air-conditioning technology thus has the greatest potential impact on the electric grid compared to other technologies that use electricity. Thermally-activated technologies (TAT), such as natural gas engine-driven heat pumps (GHP), can provide overall peak load reduction and electric grid relief for summer peak demand. GHP offers an attractive opportunity for commercial building owners to reduce electric demand charges and operating expenses. Engine-driven systems have several potential advantages over conventional single-speed or single-capacity electric motor-driven units. Among them are variable speed operation, high part load efficiency, high temperature waste heat recovery from the engine, and reduced annual operating costs (SCGC 1998). Although gas engine-driven systems have been in use since the 1960s, current research is resulting in better performance, lower maintenance requirements, and longer operating lifetimes. Gas engine-driven systems are typically more expensive to purchase than comparable electric motor-driven systems, but they typically cost less to operate, especially for commercial building applications. Operating cost savings for commercial applications are primarily driven by electric demand charges. GHP operating costs are dominated by fuel costs, but also include maintenance costs. The reliability of gas cooling equipment has improved in the last few years and maintenance requirements have decreased (SCGC 1998, Yahagi et al. 2006). Another advantage of the GHP over electric motor-driven is the ability to use the heat rejected from the engine during heating operation. The recovered heat can be used to supplement the vapor compression cycle during heating or to supply other process loads, such as water heating. The use of the engine waste heat results in greater

  9. Light-driven rotary molecular motors : an ultrafast optical study

    NARCIS (Netherlands)

    Augulis, Ramunas; Klok, Martin; Loosdrecht, Paul H.M. van; Feringa, Bernard

    2009-01-01

    Molecular rotary motors, though common in nature, were first synthesized rather recently. One of the most promising categories of light-driven rotary molecular motors which allow for optical control is based on helical overcrowded alkenes. In this category of motors, the rotation of the motor’s roto

  10. Conceptual models of the wind-driven and thermohaline circulation

    NARCIS (Netherlands)

    Drijfhout, S.S.; Marshall, D.P.; Dijkstra, H.A.

    2013-01-01

    Conceptual models are a vital tool for understanding the processes that maintain the global ocean circulation, both in nature and in complex numerical ocean models. In this chapter we provide a broad overview of our conceptual understanding of the wind-driven circulation, the thermohaline circulatio

  11. Turbulent natural convection in vertical parallel-plate channels

    Energy Technology Data Exchange (ETDEWEB)

    Badr, H.M.; Habib, M.A.; Anwar, S.; Ben-Mansour, R.; Said, S.A.M. [King Fahd University of Petroleum and Minerals, Mechanical Engineering Department, Dhahran (Saudi Arabia)

    2006-11-15

    The problem of buoyancy driven turbulent flow in parallel-plate channels is investigated. The investigation is limited to vertical channels of uniform cross-section with different modes of heating. The details of the flow and thermal fields are obtained from the solution of the conservation equations of mass, momentum, and energy in addition to equations of the low Reynolds number turbulence model. The study covers Rayleigh number ranging from 10{sup 5} to 10{sup 7} and focuses on the effect of channel geometry on the characteristic of the flow and thermal fields as well as the local and average Nusselt number variation. A Nusselt number correlation has been developed in terms of a modified Rayleigh number and channel aspect ratio for the cases of symmetrically heated isothermal and isoflux conditions. (orig.)

  12. User-Driven CHAOS

    DEFF Research Database (Denmark)

    Lykke, Marianne; Lund, Haakon; Skov, Mette

    2016-01-01

    is to provide access to broadcasts and provide tools to segment and manage concrete segments of radio broadcasts. Although the assigned metadata are project-specific, they serve as invaluable access points for fellow researchers due to their factual and neutral nature. The researchers particularly stress LARM.fm...... researchers apply the metadata scheme in their research work. The study consists of two studies, a) a qualitative study of subjects and vo-cabulary of the applied metadata and annotations, and 5 semi-structured interviews about goals for tagging. The findings clearly show that the primary role of LARM.fm...

  13. User-Driven Chaos

    DEFF Research Database (Denmark)

    Lykke, Marianne; Lund, Haakon; Skov, Mette

    2016-01-01

    and vocabulary of the applied metadata and annotations, and b) five semistructured interviews about goals for tagging. The findings clearly show that the primary role of LARM.fm is to provide access to broadcasts and provide tools to segment and manage concrete segments of radio broadcasts. Although the assigned...... metadata are project-specific, they have been applied to serve as invaluable access points for fellow researchers due to their factual and neutral nature. The researchers particularly stress LARM.fm’s strength in providing streaming access to a large, shared corpus of broadcasts....

  14. Syntactic-Head-Driven Generation

    CERN Document Server

    Koenig, E

    1994-01-01

    The previously proposed semantic-head-driven generation methods run into problems if none of the daughter constituents in the syntacto-semantic rule schemata of a grammar fits the definition of a semantic head given in Shieber et al. 1990. This is the case for the semantic analysis rules of certain constraint-based semantic representations, e.g. Underspecified Discourse Representation Structures (UDRSs) (Frank/Reyle 1992). Since head-driven generation in general has its merits, we simply return to a syntactic definition of `head' and demonstrate the feasibility of syntactic-head-driven generation. In addition to its generality, a syntactic-head-driven algorithm provides a basis for a logically well-defined treatment of the movement of (syntactic) heads, for which only ad-hoc solutions existed, so far.

  15. Economics-driven software architecture

    CERN Document Server

    Mistrik, Ivan; Kazman, Rick; Zhang, Yuanyuan

    2014-01-01

    Economics-driven Software Architecture presents a guide for engineers and architects who need to understand the economic impact of architecture design decisions: the long term and strategic viability, cost-effectiveness, and sustainability of applications and systems. Economics-driven software development can increase quality, productivity, and profitability, but comprehensive knowledge is needed to understand the architectural challenges involved in dealing with the development of large, architecturally challenging systems in an economic way. This book covers how to apply economic consider

  16. User Driven Innovation Construct Development

    Directory of Open Access Journals (Sweden)

    Tine Nagy

    2011-12-01

    Full Text Available In this paper by the literature review we interpreted changes in societyand other changing conditions that have contributed to the emergenceof user-driven innovation and a ‘design thinking’ approach. Thetwo areas are very similar in practice, so we suggest combining theminto a construct. The construct is a pioneer contribution to the developmentof science in the field of user-driven innovation and the designthinking approach.

  17. Self-driven jamming in growing microbial populations

    Science.gov (United States)

    Delarue, Morgan; Hartung, Jörn; Schreck, Carl; Gniewek, Pawel; Hu, Lucy; Herminghaus, Stephan; Hallatschek, Oskar

    2016-08-01

    In natural settings, microbes tend to grow in dense populations where they need to push against their surroundings to accommodate space for new cells. The associated contact forces play a critical role in a variety of population-level processes, including biofilm formation, the colonization of porous media, and the invasion of biological tissues. Although mechanical forces have been characterized at the single-cell level, it remains elusive how collective pushing forces result from the combination of single-cell forces. Here, we reveal a collective mechanism of confinement, which we call self-driven jamming, that promotes the build-up of large mechanical pressures in microbial populations. Microfluidic experiments on budding yeast populations in space-limited environments show that self-driven jamming arises from the gradual formation and sudden collapse of force chains driven by microbial proliferation, extending the framework of driven granular matter. The resulting contact pressures can become large enough to slow down cell growth, to delay the cell cycle in the G1 phase, and to strain or even destroy the micro-environment through crack propagation. Our results suggest that self-driven jamming and build-up of large mechanical pressures is a natural tendency of microbes growing in confined spaces, contributing to microbial pathogenesis and biofouling.

  18. The Blast-Wave-Driven Instability as a Vehicle for Understanding Supernova Explosion Structure

    Energy Technology Data Exchange (ETDEWEB)

    Miles, A R

    2008-05-27

    Blast-wave-driven instabilities play a rich and varied role throughout the evolution of supernovae from explosion to remnant, but interpreting their role is difficult due to the enormous complexity of the stellar systems. We consider the simpler and fundamental hydrodynamic instability problem of a material interface between two constant-density fluids perturbed from spherical and driven by a divergent central Taylor-Sedov blast wave. The existence of unified solutions at high Mach number and small density ratio suggests that general conclusions can be drawn about the likely asymptotic structure of the mixing zone. To this end we apply buoyancy-drag and bubble merger models modified to include the effects of divergence and radial velocity gradients. In general, these effects preclude the true self-similar evolution of classical Raleigh-Taylor, but can be incorporated into a quasi-self-similar growth picture. Loss of memory of initial conditions can occur in the quasi-self-similar model, but requires initial mode numbers higher than those predicted for pre-explosion interfaces in Type II SNe, suggesting that their late-time structure is likely strongly influenced by details of the initial perturbations. Where low-modes are dominant, as in the Type Ia Tycho remnant, they result from initial perturbations rather than generation from smaller scales. Therefore, structure observed now contains direct information about the explosion process. When large-amplitude modes are present in the initial conditions, the contribution to the perturbation growth from the Richtmyer-Meshkov instability is significant or dominant compared to Rayleigh-Taylor. Such Richtmyer-Meshkov growth can yield proximity of the forward shock to the growing spikes and structure that strongly resembles that observed in the Tycho. Laser-driven high-energy-density laboratory experiments offer a promising avenue for testing model and simulation descriptions of blast-wave-driven instabilities and making

  19. Designing Data-Driven Battery Prognostic Approaches for Variable Loading Profiles: Some Lessons Learned

    Data.gov (United States)

    National Aeronautics and Space Administration — Among various approaches for implementing prognostic algorithms data-driven algorithms are popular in the industry due to their intuitive nature and relatively fast...

  20. The response of subsurface oceans in icy satellites to tidally driven forcing

    Science.gov (United States)

    Chen, E. M.; Glatzmaier, G. A.; Nimmo, F.

    2009-12-01

    Observations from the Galileo and Cassini spacecraft suggest that subsurface global water oceans are likely present on multiple icy satellites of Jupiter and Saturn. However, the dynamics of these oceans, under the influence of a time-varying tidal potential and buoyancy and coriolis forces, have not been investigated in detail. We have investigated the large scale ocean flow in two ways. First, we simulate the 3-D global circulation of the subsurface oceans on Europa and Titan driven primarily by a time-varying tidal potential and secondarily by heating at the base of the ocean. Second, we analyze the behavior of tidally-forced subsurface oceans in two-dimensions using quasi-nonlinear shallow water theory. These approaches allow us to predict potentially observable effects, in particular non-synchronous rotation of the ice shell driven by ocean torques and spatial variations in the heat flow supplied to the base of the ice shell, and magnetic induction effects due to the ocean circulation. Time-series analyses suggest that the ocean responds primarily at the tidal frequency; however, there are responses at lower frequencies as well. Preliminary results of full 3-D simulations will be presented, and comparisons will be made to the forced shallow water model.

  1. Numerical simulation of losses along a natural circulation helium loop

    Science.gov (United States)

    Knížat, Branislav; Urban, František; Mlkvik, Marek; RidzoÅ, František; Olšiak, Róbert

    2016-06-01

    A natural circulation helium loop appears to be a perspective passive method of a nuclear reactor cooling. When designing this device, it is important to analyze the mechanism of an internal flow. The flow of helium in the loop is set in motion due to a difference of hydrostatic pressures between cold and hot branch. Steady flow at a requested flow rate occurs when the buoyancy force is adjusted to resistances against the flow. Considering the fact that the buoyancy force is proportional to a difference of temperatures in both branches, it is important to estimate the losses correctly in the process of design. The paper deals with the calculation of losses in branches of the natural circulation helium loop by methods of CFD. The results of calculations are an important basis for the hydraulic design of both exchangers (heater and cooler). The analysis was carried out for the existing model of a helium loop of the height 10 m and nominal heat power 250 kW.

  2. Superfluid stiffness of a driven dissipative condensate with disorder.

    Science.gov (United States)

    Janot, Alexander; Hyart, Timo; Eastham, Paul R; Rosenow, Bernd

    2013-12-01

    Observations of macroscopic quantum coherence in driven systems, e.g. polariton condensates, have strongly stimulated experimental as well as theoretical efforts during the last decade. We address the question of whether a driven quantum condensate is a superfluid, allowing for the effects of disorder and its nonequilibrium nature. We predict that for spatial dimensions d<4 the superfluid stiffness vanishes once the condensate exceeds a critical size, and treat in detail the case d=2. Thus a nonequilibrium condensate is not a superfluid in the thermodynamic limit, even for weak disorder, although superfluid behavior would persist in small systems.

  3. Performance-Driven Interface Contract Enforcement for Scientific Components

    Energy Technology Data Exchange (ETDEWEB)

    Dahlgren, T

    2007-02-22

    Several performance-driven approaches to selectively enforce interface contracts for scientific components are investigated. The goal is to facilitate debugging deployed applications built from plug-and-play components while keeping the cost of enforcement within acceptable overhead limits. This paper describes a study of global enforcement using a priori execution cost estimates obtained from traces. Thirteen trials are formed from five, single-component programs. Enforcement experiments conducted using twenty-three enforcement policies are used to determine the nature of exercised contracts and the impact of a variety of sampling strategies. Performance-driven enforcement appears to be best suited to programs that exercise moderately expensive contracts.

  4. Research on the Self-balancing Sinking Pipe Technology by Temporary Buoyancy Plug%加临时浮力塞自平衡浮力法下管技术研究

    Institute of Scientific and Technical Information of China (English)

    余大有; 陈月化; 唐志宏

    2014-01-01

    Single-plug-buoyancy-method-was-used-to-sink-gas-pipe,-but-space-under-the-plug-was-small.-With-creasing-depth-of-the-gas-hole,-air-under-the-plug-had-been-compressed,-then-the-buoyancy-provided-by-air-decreased-too-much-to-meet-demand-of-sinking-pipe.-To-increase-the-length-of-air-column,-temporary-buoyancy-plug-was-been-made.-This-plug-has-been-placed-same-depth-of-the-single-plug-self-balancing-method-to-sink-pipe.-A-sealing-plate-was-welded-as-temporary-buoyancy-plug,-and-this-method-also-used-upon-empty-pipe-section-to-pro-duce-buoyancy.-When-the-upon-empty-pipe`s-length-reached-de-signed-length,-concrete-buoyancy-plug-was-going-to-be-installed.-And-air-will-be-aerated-into-the-empty-pipe-under-the-concrete-plug,-with-the-pressure-increasing,-the-steel-ball-which-was-placed-in-the-temporary-buoyancy-plug,-exfoliated-into-mud.-Air-was-aerated-into-space-under-the-temporary-buoyancy-plug.-Compared-to-single-plug-self-balancing-buoyancy-method,-tem-porary-buoyancy-plug-has-increased-length-of-air-column,-then-the-buoyancy-produced-by-air-was-also-increased.-Implementa-tion-is-that-all-steel-pipe-can-be-sinked-only-with-one-time-aera-tion.%现有单塞自平衡浮力法下管,塞下充气量较小,并且随着下管深度的增加,塞下空气进一步压缩,提供的浮力逐渐减小,无法满足下管要求。为增加管内储气段长度,设置临时浮力塞。所加临时浮力塞与单塞自平衡下管时的浮力塞处于同一深度,在此处焊接带加强筋的封板作为临时浮力塞,利用常规空管提供浮力。当临时浮力塞上部空管高度达到设计值时,加设混凝土材质浮力塞并充气,随着充气压力的增大,设置在临时浮力塞下部的钢球脱落,空气进入临时浮力塞下部空间。与单塞自平衡浮力法相比,增加了临时浮力塞下这段充气量,因此提供的浮力也增大,从而实现一次性充气下完全布钢管。

  5. Displaying Nature

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Beijing Museum of Natural History is located in Chongwen District, close to the Temple of Heaven and Tianqiao Theater. It was founded in 1951 and formally named Beijing Museum of Natural History in 1962.

  6. The tide driven geodynamo

    Science.gov (United States)

    Gregori, G. P.

    2003-04-01

    The geodynamo theory was formerly exploited as a generalisation of stellar homogenous MHD dynamos, based on the available observational evidence, and relying on sound arguments for that time. They chose to exploit a speculated theoretical model, to be later checked by observations. However, some newly available observational inferences, which progressively accumulated during over half a century, raised increasing difficulties and unavoidably implied ad hoc complications of the original simple conceptual scheme. In contrast, a mere inductive approach, based on a minimum speculative content, and allowing for maximum possible freedom to Mother Nature while choosing replies to specific enquiries for explaining observations, led to a different proposal, reviving a former mechanism speculated by Elsasser. Such hypothesis was, however, unduly abandoned shortly after its proposal, due to criticisms that now appear unsustainable. Upon rescanning the original literature of the ‘40’s, the former reasons can be inferred that led to such misunderstanding. Scientists exploited their great mathematical skill, while they apparently never reconsidered an a priori revision of their axioms.

  7. Data Driven Dark Ages

    Science.gov (United States)

    Thurner, Stefan

    If physics is the experimental science of matter that interacts through the four basic interactions, the science of complex systems is its natural extension, where the concepts of matter and interactions are generalized. Matter can be anything that is capable of interacting, interactions can be anything that is able to change states of the constituents of a system. Complex systems are made from many constituents (parts) that interact through interaction networks. These parts are characterized by states that change over time. At the same time the interaction networks may change over time. What makes a system complex is that the states of the parts change as a function F of the interaction network (and the states), and, simultaneously, the interaction networks change as another function G of the states of the nodes (and the networks). Physics is about the predictive understanding of the dynamics and changes of states once the interactions and initial and boundary conditions are specified. In complex systems interactions also change over time, and to make things really complicated, these changes are coupled to the dynamics of the state-changes. States co-evolve with the interaction networks. In this sense complex systems often are chicken-egg problems. They are evolutionary, show emergent behavior, can be self-organized critical, show power laws, etc...

  8. Some Exact Solutions of Boundary Layer Flows along a Vertical Plate with Buoyancy Forces Combined with Lorentz Forces under Uniform Suction

    Directory of Open Access Journals (Sweden)

    Asterios Pantokratoras

    2008-01-01

    Full Text Available Exact analytical solutions of boundary layer flows along a vertical porous plate with uniform suction are derived and presented in this paper. The solutions concern the Blasius, Sakiadis, and Blasius-Sakiadis flows with buoyancy forces combined with either MHD Lorentz or EMHD Lorentz forces. In addition, some exact solutions are presented specifically for water in the temperature range of 0∘C≤≤8∘C, where water density is nearly parabolic. Except for their use as benchmarking means for testing the numerical solution of the Navier-Stokes equations, the presented exact solutions with EMHD forces have use in flow separation control in aeronautics and hydronautics, whereas the MHD results have applications in process metallurgy and fusion technology. These analytical solutions are valid for flows with strong suction.

  9. Combined Effect of Buoyancy Force and Navier Slip on MHD Flow of a Nanofluid over a Convectively Heated Vertical Porous Plate

    Directory of Open Access Journals (Sweden)

    Winifred Nduku Mutuku-Njane

    2013-01-01

    Full Text Available We examine the effect of magnetic field on boundary layer flow of an incompressible electrically conducting water-based nanofluids past a convectively heated vertical porous plate with Navier slip boundary condition. A suitable similarity transformation is employed to reduce the governing partial differential equations into nonlinear ordinary differential equations, which are solved numerically by employing fourth-order Runge-Kutta with a shooting technique. Three different water-based nanofluids containing copper (Cu, aluminium oxide (Al2O3, and titanium dioxide (TiO2 are taken into consideration. Graphical results are presented and discussed quantitatively with respect to the influence of pertinent parameters, such as solid volume fraction of nanoparticles (φ, magnetic field parameter (Ha, buoyancy effect (Gr, Eckert number (Ec, suction/injection parameter (fw, Biot number (Bi, and slip parameter (β, on the dimensionless velocity, temperature, skin friction coefficient, and heat transfer rate.

  10. Improving the buoyancy force and Archimedes principle experiment%对浮力实验和阿基米德实验的改进

    Institute of Scientific and Technical Information of China (English)

    陈风青

    2013-01-01

    An experiment of exploring the direction of buoyancy force was put forward ,which could be conducted by students independently . The Archimedes principle experiment was also im-proved .The experiment errors were reduced ,the experimental results were intuitive and clear .At the same time ,some suggestions and comments regarding the arrangement of teaching were proposed .%  通过学生自主实验,提出了相对简易的探究浮力方向的实验方法,同时对阿基米德实验进行了改进。改进后的阿基米德实验降低了实验偏差,实验效果直观、明显。本文还对教材的编排提出了建议和意见。

  11. Hysteresis in pressure-driven DNA denaturation.

    Directory of Open Access Journals (Sweden)

    Enrique Hernández-Lemus

    Full Text Available In the past, a great deal of attention has been drawn to thermal driven denaturation processes. In recent years, however, the discovery of stress-induced denaturation, observed at the one-molecule level, has revealed new insights into the complex phenomena involved in the thermo-mechanics of DNA function. Understanding the effect of local pressure variations in DNA stability is thus an appealing topic. Such processes as cellular stress, dehydration, and changes in the ionic strength of the medium could explain local pressure changes that will affect the molecular mechanics of DNA and hence its stability. In this work, a theory that accounts for hysteresis in pressure-driven DNA denaturation is proposed. We here combine an irreversible thermodynamic approach with an equation of state based on the Poisson-Boltzmann cell model. The latter one provides a good description of the osmotic pressure over a wide range of DNA concentrations. The resulting theoretical framework predicts, in general, the process of denaturation and, in particular, hysteresis curves for a DNA sequence in terms of system parameters such as salt concentration, density of DNA molecules and temperature in addition to structural and configurational states of DNA. Furthermore, this formalism can be naturally extended to more complex situations, for example, in cases where the host medium is made up of asymmetric salts or in the description of the (helical-like charge distribution along the DNA molecule. Moreover, since this study incorporates the effect of pressure through a thermodynamic analysis, much of what is known from temperature-driven experiments will shed light on the pressure-induced melting issue.

  12. Neutrino oscillations in magnetically driven supernova explosions

    Energy Technology Data Exchange (ETDEWEB)

    Kawagoe, Shio; Kotake, Kei [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo, 181-8588 (Japan); Takiwaki, Tomoya, E-mail: shio.k@nao.ac.jp, E-mail: takiwaki.tomoya@nao.ac.jp, E-mail: kkotake@th.nao.ac.jp [Center for Computational Astrophysics, National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo, 181-8588 (Japan)

    2009-09-01

    We investigate neutrino oscillations from core-collapse supernovae that produce magnetohydrodynamic (MHD) explosions. By calculating numerically the flavor conversion of neutrinos in the highly non-spherical envelope, we study how the explosion anisotropy has impacts on the emergent neutrino spectra through the Mikheyev-Smirnov-Wolfenstein effect. In the case of the inverted mass hierarchy with a relatively large θ{sub 13} (sin{sup 2} 2θ{sub 13} ∼> 10{sup −3}), we show that survival probabilities of ν-bar {sub e} and ν{sub e} seen from the rotational axis of the MHD supernovae (i.e., polar direction), can be significantly different from those along the equatorial direction. The event numbers of ν-bar {sub e} observed from the polar direction are predicted to show steepest decrease, reflecting the passage of the magneto-driven shock to the so-called high-resonance regions. Furthermore we point out that such a shock effect, depending on the original neutrino spectra, appears also for the low-resonance regions, which could lead to a noticeable decrease in the ν{sub e} signals. This reflects a unique nature of the magnetic explosion featuring a very early shock-arrival to the resonance regions, which is in sharp contrast to the neutrino-driven delayed supernova models. Our results suggest that the two features in the ν-bar {sub e} and ν{sub e} signals, if visible to the Super-Kamiokande for a Galactic supernova, could mark an observational signature of the magnetically driven explosions, presumably linked to the formation of magnetars and/or long-duration gamma-ray bursts.

  13. Data-driven batch schuduling

    Energy Technology Data Exchange (ETDEWEB)

    Bent, John [Los Alamos National Laboratory; Denehy, Tim [GOOGLE; Arpaci - Dusseau, Remzi [UNIV OF WISCONSIN; Livny, Miron [UNIV OF WISCONSIN; Arpaci - Dusseau, Andrea C [NON LANL

    2009-01-01

    In this paper, we develop data-driven strategies for batch computing schedulers. Current CPU-centric batch schedulers ignore the data needs within workloads and execute them by linking them transparently and directly to their needed data. When scheduled on remote computational resources, this elegant solution of direct data access can incur an order of magnitude performance penalty for data-intensive workloads. Adding data-awareness to batch schedulers allows a careful coordination of data and CPU allocation thereby reducing the cost of remote execution. We offer here new techniques by which batch schedulers can become data-driven. Such systems can use our analytical predictive models to select one of the four data-driven scheduling policies that we have created. Through simulation, we demonstrate the accuracy of our predictive models and show how they can reduce time to completion for some workloads by as much as 80%.

  14. Magnetically driven quantum heat engine

    Science.gov (United States)

    Muñoz, Enrique; Peña, Francisco J.

    2014-05-01

    We studied the efficiency of two different schemes for a magnetically driven quantum heat engine, by considering as the "working substance" a single nonrelativistic particle trapped in a cylindrical potential well, in the presence of an external magnetic field. The first scheme is a cycle, composed of two adiabatic and two isoenergetic reversible trajectories in configuration space. The trajectories are driven by a quasistatic modulation of the external magnetic-field intensity. The second scheme is a variant of the former, where the isoenergetic trajectories are replaced by isothermal ones, along which the system is in contact with macroscopic thermostats. This second scheme constitutes a quantum analog of the classical Carnot cycle.

  15. Statistical mechanics of driven diffusive systems

    CERN Document Server

    Schmittmann, B

    1995-01-01

    Far-from-equilibrium phenomena, while abundant in nature, are not nearly as well understood as their equilibrium counterparts. On the theoretical side, progress is slowed by the lack of a simple framework, such as the Boltzmann-Gbbs paradigm in the case of equilibrium thermodynamics. On the experimental side, the enormous structural complexity of real systems poses serious obstacles to comprehension. Similar difficulties have been overcome in equilibrium statistical mechanics by focusing on model systems. Even if they seem too simplistic for known physical systems, models give us considerable insight, provided they capture the essential physics. They serve as important theoretical testing grounds where the relationship between the generic physical behavior and the key ingredients of a successful theory can be identified and understood in detail. Within the vast realm of non-equilibrium physics, driven diffusive systems form a subset with particularly interesting properties. As a prototype model for these syst...

  16. User-Driven Innovation: An Exploratory Study

    Directory of Open Access Journals (Sweden)

    Blanka Tacer

    2015-03-01

    Full Text Available Despite the relatively robust promotion of user-driven innovation (UDI in practice, research on UDI remains in its early stages. Following a grounded theory analysis approach, this paper makes a contribution by conducting exploratory research of the field. Nine interviews yield an empirical basis for extracting categories connected with existing conceptual issues. The results reveal three key elements of the UDI (user involvement, searching for feedback, and design orientation. The results also indicate the interdisciplinary nature of UDI with branding, design, and company-user interaction as complementary fields in creating user experience. The analysis leads to four theoretical propositions for future studies. The article concludes with limitations and implications for future research.

  17. Runtime Adaptability driven by Negotiable Quality Requirements

    CERN Document Server

    Mosincat, Adina

    2011-01-01

    Two of the common features of business and the web are diversity and dynamism. Diversity results in users having different preferences for the quality requirements of a system. Diversity also makes possible alternative implementations for functional requirements, called variants, each of them providing different quality. The quality provided by the system may vary due to different variant components and changes in the environment. The challenge is to dynamically adapt to quality variations and to find the variant that best fulfills the multi-criteria quality requirements driven by user preferences and current runtime conditions. For service-oriented systems this challenge is augmented by their distributed nature and lack of control over the constituent services and their provided quality of service (QoS). We propose a novel approach to runtime adaptability that detects QoS changes, updates the system model with runtime information, and uses the model to select the variant to execute at runtime. We introduce n...

  18. Fluid-driven fractures in brittle hydrogels

    Science.gov (United States)

    O'Keeffe, Niall; Linden, Paul

    2016-11-01

    Hydraulic fracturing is a process in which fluid is injected deep underground at high pressures that can overcome the strength of the surrounding matrix. This results in an increase of surface area connected to the well bore and thus allows extraction of natural gas previously trapped in a rock formation. We experimentally study the physical mechanisms of these fluid-driven fractures in low permeability reservoirs where the leak-off of fracturing fluid is considered negligible. This is done through the use of small scale experiments on transparent and brittle, heavily cross-linked hydrogels. The propagation of these fractures can be split into two distinct regimes depending on whether the dominant energy dissipation mechanism is viscous flow or material toughness. We will analyse crack growth rates, crack thickness and tip shape in both regimes. Moreover, PIV techniques allow us to explore the flow dynamics within the fracture, which is crucial in predicting transport of proppants designed to prevent localisation of cracks.

  19. PLURALIZING NATURE

    DEFF Research Database (Denmark)

    Clemmensen, Thomas Juel

    2014-01-01

    Denmark is widely recognised for its democratic approach to planning and the idea of planning for the common good. This interest in the common good and common values seems also to be reflected in the way which nature restoration is planned and managed – one common nature directed by the public...... authorities. But nature restoration is far from being a neural undertaking. Just like any other type of heritage production it can be the source of dissonance – ‘our’ nature is not necessary ‘their’ nature. Often this dissonance is managed in ways, which are not particular sensitive to site......-specificity. As exemplified by the Skjern River Restoration Project (1999-2003), one interpretation of the landscape sometimes suppresses other valid interpretations neglecting its diverse history. However, evidence from Switzerland suggests that planning for the common good, in the case of nature restoration, does...

  20. Data-Driven Proficiency Profiling

    Science.gov (United States)

    Mostafavi, Behrooz; Liu, Zhongxiu; Barnes, Tiffany

    2015-01-01

    Deep Thought is a logic tutor where students practice constructing deductive logic proofs. Within Deep Thought is a data-driven mastery learning system (DDML), which calculates student proficiency based on rule scores weighted by expert-decided weights in order to assign problem sets of appropriate difficulty. In this study, we designed and tested…

  1. Light-driven molecular motors

    OpenAIRE

    van Delden, RA; FERINGA, BL; Kuzmany, H.; Fink, J.; Mehring, M.; Roth, S.

    2004-01-01

    Molecular motors can be defined as molecules that are able to convert any type of energy input (a fuel) into controlled motion. These systems can be categorized into linear and rotary motors, depending on the motion induced. This brief account will discuss the state of affairs of the research on light-driven rotary molecular motors.

  2. Synchrotron-driven spallation sources

    CERN Document Server

    Bryant, P J

    1996-01-01

    The use of synchrotrons for pulsed neutron spallation sources is an example of scientific and technological spin-off from the accelerator development for particle physics. Accelerator-driven sources provide an alternative to the continuous-flux, nuclear reactors that currently furnish the majority of neutrons for research and development. Although the present demand for neutrons can be adequately met by the existing reactors, this situation is unlikely to continue due to the increasing severity of safety regulations and the declared policies of many countries to close down their reactors within the next decade or so. Since the demand for neutrons as a research tool is, in any case,expected to grow, there has been a corresponding interest in sources that are synchrotron-driven or linac-driven with a pulse compression ring and currently several design studies are being made. These accelerator-driven sources also have the advantage of a time structure with a high peak neutron flux. The basic requirement is for a...

  3. Pattern Formation in Driven Systems

    Science.gov (United States)

    Klymko, Katherine

    Model colloidal particles of two types, driven in opposite directions, will in two dimensions segregate into lanes, a phenomenon studied extensively by Lowen and co-workers [Dzubiella et al. Phys. Rev. E 65, 021402 (2002)]. We have simulated mixtures of oppositely-driven particles using three numerical protocols. We find that laning results from enhanced diffusion, in the direction perpendicular to the drive, of particles surrounded by particles of the opposite type, consistent with the observation of Vissers et al. [Soft Matter 7, 6, 2352 (2011)]. By comparing protocols we find that enhanced diffusion follows from a simple geometrical constraint: oppositely-driven particles must, in the time taken to encounter each other in the direction of the drive, diffuse in the perpendicular direction by about one particle diameter. This constraint implies that the effective lateral diffusion constant grows linearly with drive speed and as the square root of the packing fraction, a prediction supported by our numerics. By invoking an analogy between hard particles with environment-dependent mobilities and mutually attractive particles we argue that there exists an equilibrium system whose pattern-forming properties are similar to those of the driven system. Katherine Klymko acknowledges support from the NSF Graduate Research Fellowship.

  4. Matematica Natural.

    Science.gov (United States)

    Lozano, Patricia; Medearis, Linda

    Matematica Natural (Natural Mathematics) is a mathematics curriculum for young children based on the assumption that they learn mathematics through concrete, real life, relevant experiences and that educational differences rather than cultural differences influence math achievement. The curriculum uses hands-on materials and activities to teach…

  5. Nature Detectives

    Science.gov (United States)

    Harr, Natalie; Lee, Richard E.; Jr.

    2010-01-01

    Richard Louv's "Last Child in the Woods" (2008) added to a growing consensus to get children outside and experiencing nature. Using ideas from place-based education, the authors present a simple year-long project that brings science, nature, and other curriculum standards to life right in your school yard. With a focus on journaling, this project…

  6. Dissonant Nature

    DEFF Research Database (Denmark)

    Clemmensen, Thomas Juel

    2013-01-01

    Nature restoration is far from being a neural undertaking. Just like any other type of heritage production it can be the source of dissonance – ‘our’ nature is not necessary ‘their’ nature. Often this dissonance is managed in ways, which are not particular sensitive to site......-specificity. As exemplified by the Skjern River Restoration Project (1999-2003), one interpretation of the landscape sometimes suppresses other valid interpretations neglecting its diverse history. Landscape architecture might, however, provide an alternative approach to nature restoration that is more site specific...... and allows for multiple interpretations to coexist. Evidence can be found in the Re-naturalization of River Aire (2002-2015), a restoration project, which reveals approaches that could be labelled landscape architecture specific....

  7. The Lure of Extractive Natural Resource Development

    DEFF Research Database (Denmark)

    Buur, Lars; Kjær, Anne Mette; Therkildsen, Ole

    Natural resource-driven development in Africa has emerged as a hot topic. The hope is that extractive industries will generate foreign revenues, create jobs and boost economic growth – but how can the possibilities best be exploited for industrial development purposes?......Natural resource-driven development in Africa has emerged as a hot topic. The hope is that extractive industries will generate foreign revenues, create jobs and boost economic growth – but how can the possibilities best be exploited for industrial development purposes?...

  8. Wave-driven Rotation in Supersonically Rotating Mirrors

    Energy Technology Data Exchange (ETDEWEB)

    A. Fetterman and N.J. Fisch

    2010-02-15

    Supersonic rotation in mirrors may be produced by radio frequency waves. The waves produce coupled diffusion in ion kinetic and potential energy. A population inversion along the diffusion path then produces rotation. Waves may be designed to exploit a natural kinetic energy source or may provide the rotation energy on their own. Centrifugal traps for fusion and isotope separation may benefit from this wave-driven rotation.

  9. Track guided self-driven container wagon

    NARCIS (Netherlands)

    Hansen, I.A.

    1999-01-01

    The linear motor consists of a series of stator coils (2) located along the Track guided self-driven container wagon Track guided self-driven container wagon track and a reaction rail (3) fitted under the wagon chassis (4).

  10. Effects-Driven IT Development

    DEFF Research Database (Denmark)

    Hertzum, Morten; Simonsen, Jesper

    2011-01-01

    For customers information technology (IT) is a means to an end. This tight association between IT systems and their use is, however, often absent during their development and implementation, resulting in systems that may fail to produce desired ends. Effects-driven IT development aims to avoid...... the chasm between development and implementation through a sustained focus on the effects to be achieved by users through their adoption and use of a system. This involves iteratively (a) specifying the purpose of the system in terms of effects, (b) developing an IT system and associated organizational...... change that realize the specified effects, and (c) measuring the absence or presence of the specified effects during pilot use of the system while also remaining alert to the emergence of beneficial but hitherto unspecified effects. In this paper we explore effects-driven IT development and discuss...

  11. Effects-Driven IT Development

    DEFF Research Database (Denmark)

    Hertzum, Morten; Simonsen, Jesper

    2010-01-01

    We present effects-driven IT development as an instrument for pursuing and reinforcing Participatory Design (PD) when it is applied in commercial information technology (IT) projects. Effects-driven IT development supports the management of a sustained PD process throughout design...... and organizational implementation. The focus is on the effects to be achieved by users through their adoption and use of a system. The overall idea is to (a) specify the purpose of a system as effects that are both measurable and meaningful to the users, and (b) evaluate the absence or presence of these effects...... during real use of the system. Effects are formulated in a user-oriented terminology, and they can be evaluated and revised with users in an iterative and incremental systems-development process that involves pilot implementations. In this paper we investigate the design, pilot implementation...

  12. Pulsed Power Driven Fusion Energy

    Energy Technology Data Exchange (ETDEWEB)

    SLUTZ,STEPHEN A.

    1999-11-22

    Pulsed power is a robust and inexpensive technology for obtaining high powers. Considerable progress has been made on developing light ion beams as a means of transporting this power to inertial fusion capsules. However, further progress is hampered by the lack of an adequate ion source. Alternatively, z-pinches can efficiently convert pulsed power into thermal radiation, which can be used to drive an inertial fusion capsule. However, a z-pinch driven fusion explosion will destroy a portion of the transmission line that delivers the electrical power to the z-pinch. They investigate several options for providing standoff for z-pinch driven fusion. Recyclable Transmission Lines (RTLs) appear to be the most promising approach.

  13. Model-Driven Constraint Programming

    CERN Document Server

    Chenouard, Raphael; Soto, Ricardo; 10.1145/1389449.1389479

    2010-01-01

    Constraint programming can definitely be seen as a model-driven paradigm. The users write programs for modeling problems. These programs are mapped to executable models to calculate the solutions. This paper focuses on efficient model management (definition and transformation). From this point of view, we propose to revisit the design of constraint-programming systems. A model-driven architecture is introduced to map solving-independent constraint models to solving-dependent decision models. Several important questions are examined, such as the need for a visual highlevel modeling language, and the quality of metamodeling techniques to implement the transformations. A main result is the s-COMMA platform that efficiently implements the chain from modeling to solving constraint problems

  14. Optimizing Event-Driven Simulations

    CERN Document Server

    De Michele, Cristiano

    2010-01-01

    Event-driven molecular dynamics is a valuable tool in condensed and soft matter physics when particles can be modeled as hard objects or more generally if their interaction potential can be modeled in a stepwise fashion. Hard spheres model has been indeed widely used both for computational and theoretical description of physical systems. Recently further developments of computational techniques allow simulations of hard rigid objects of generic shape. In present paper we will present some optimizations for event-driven simulations that offered significant speedup over previous methods. In particular we will describe a generalization of well known linked list method and an improvement on nearest neighbor lists method recently proposed by us.

  15. Electrically-driven optical antennas

    CERN Document Server

    Kern, Johannes; Prangsma, Jord C; Emmerling, Monika; Kamp, Martin; Hecht, Bert

    2015-01-01

    Unlike radiowave antennas, optical nanoantennas so far cannot be fed by electrical generators. Instead, they are driven by light or via optically active materials in their proximity. Here, we demonstrate direct electrical driving of an optical nanoantenna featuring an atomic-scale feed gap. Upon applying a voltage, quantum tunneling of electrons across the feed gap creates broadband quantum shot noise. Its optical frequency components are efficiently converted into photons by the antenna. We demonstrate that the properties of the emitted photons are fully controlled by the antenna architecture, and that the antenna improves the quantum efficiency by up to two orders of magnitude with respect to a non-resonant reference system. Our work represents a new paradigm for interfacing electrons and photons at the nanometer scale, e.g. for on-chip wireless data communication, electrically driven single- and multiphoton sources, as well as for background-free linear and nonlinear spectroscopy and sensing with nanometer...

  16. Writing Nature

    Directory of Open Access Journals (Sweden)

    Kristin Asdal

    2014-06-01

    Full Text Available This special issue of the Nordic Journal of Science and Technology Studies is interested in how nature, in different versions and forms, is invited into our studies, analyses, and stories. How is it that we “write nature”? How is it that we provide space for, and actually describe the actors, agents, or surroundings, in our stories and analyses? The articles in the issue each deal with different understandings of both the practices of writing and the introduction of various natures into these. In this introduction to the issue the editors engage with actor-network theory as a material semiotic resource for writing nature. We propose to foreground actor-network theory as a writing tool, at the expense of actor-network theory as a distinct vocabulary. In doing this and pointing out the semiotic origins to material-semiotics we also want to problematize a clear-cut material approach to writing nature.

  17. Natural Communities

    Data.gov (United States)

    Kansas Data Access and Support Center — This dataset shows the locations of known tracts of high quality natural communities in Kansas, generalized to the PLSS section. It is not a compehensive dataset of...

  18. Natural Propositions

    DEFF Research Database (Denmark)

    Stjernfelt, Frederik

    Preface -- Introduction -- The generality of signs -- Dicisigns -- Some consequences of the dicisign doctrine -- Dicisigns and cognition -- Natural propositions--the evolution of semiotic self-control -- Dicisigns beyond language -- Operational and optimal iconicity in Peirce's diagrammatology...

  19. Driven optical matter (Conference Presentation)

    Science.gov (United States)

    Figliozzi, Patrick; Sule, Nishant; Yan, Zijie; Vaikuntanathan, Suriyanarayanan; Rice, Stuart A.; Scherer, Norbert F.

    2016-09-01

    Optical trapping has enabled studying a wide variety of questions and systems in chemistry, biology, physics, and materials science. For example, optical trapping has been used to understand hydrodynamic interactions in dilute and dense colloidal fluids and discover connections to granular materials. In this presentation we show that shaped optical fields and gradients can be used to study the electrodynamic interactions amongst nanoparticles (NPs) and drive them into new ordered states. We demonstrate the formation and use of NP-based optical matter to study a range of nonequilibrium phenomena in solution; field-driven barrier crossing phenomena and noise-driven ordering. Optical matter, a material that forms only in the presence of an optical field, involves NP interactions by optical scattering and interference. Metal NPs can be formed into regular arrangements in minimally shaped fields; e.g., in focused Gaussian beams, line traps, and optical ring traps. Inter-particle interactions and motions are also affected when the optical matter is driven. Particles recirculate in an optical ring vortex trap allowing long term measurements to examine rare events. In particular, particles can hop between optical binding sites, move past electrodynamic obstacles or pass each other while moving around the ring. The polarization state of the optical beam can be used to produce periodic variations of the NP electrodynamic interactions. As particles circulate this "noise" causes NP clusters to be less stable as if the temperature of the system is increased. Conversely, we observe noise-driven ordering in dense systems. We will explain these phenomena using simulations and theory.

  20. Security and policy driven computing

    CERN Document Server

    Liu, Lei

    2010-01-01

    Security and Policy Driven Computing covers recent advances in security, storage, parallelization, and computing as well as applications. The author incorporates a wealth of analysis, including studies on intrusion detection and key management, computer storage policy, and transactional management.The book first describes multiple variables and index structure derivation for high dimensional data distribution and applies numeric methods to proposed search methods. It also focuses on discovering relations, logic, and knowledge for policy management. To manage performance, the text discusses con

  1. Edge-driven microplate kinematics

    Science.gov (United States)

    Schouten, Hans; Klitgord, Kim D.; Gallo, David G.

    1993-01-01

    It is known from plate tectonic reconstructions that oceanic microplates undergo rapid rotation about a vertical axis and that the instantaneous rotation axes describing the microplate's motion relative to the bounding major plates are frequently located close to its margins with those plates, close to the tips of propagating rifts. We propose a class of edge-driven block models to illustrate how slip across the microplate margins, block rotation, and propagation of rifting may be related to the relative motion of the plates on either side. An important feature of these edge-driven models is that the instantaneous rotation axes are always located on the margins between block and two bounding plates. According to those models the pseudofaults or traces of disrupted seafloor resulting from the propagation of rifting between microplate and major plates may be used independently to approximately trace the continuous kinematic evolution of the microplate back in time. Pseudofault geometries and matching rotations of the Easter microplate show that for most of its 5 m.y. history, block rotation could be driven by the drag of the Nazca and Pacific plates on the microplate's edges rather than by a shear flow of mantle underneath.

  2. 不同高宽比的矩形空腔内流体浮升流动特性分析%Flow characteristics of free fluid driven by buoyancy in rectangular cavities with different aspect ratios

    Institute of Scientific and Technical Information of China (English)

    赵忠超; 张娇娇; 成华; 丰威仙

    2014-01-01

    In this paper, the mathematic model of buoyant lift flow in a rectangular cavity was developed by the dimensionless analysis.The effects of aspect ratio of the rectangular cavity on the heat convection were simulated and analyzed through this mathematic model under same working conditions.The results show that the aspect ra-tio of rectangular cavity has great effects on the character of buoyant lift flow and heat convection efficiency.With the aspect ratio increased, the transition layer of laminar flow has the tendency to decrease the Rayleigh number. When the Rayleigh number is kept constant, the average Nusselt number dramatically approaches the maximum and then decreases gradually.The eddy amount, intensity of buoyant flow and the average Nusselt number in-crease with the Rayleigh number.The maximum of average Nusselt number also has the tendency to move in the direction of smaller aspect ratio.%应用无量纲分析方法,建立了矩形空腔内流体浮升流动的数学模型,研究了相同工况下不同高宽比对其流动换热的影响。研究结果表明:不同高宽比对流体的浮升流动具有较大影响,随着高宽比的增大,空腔内流体流动的层流过渡层向Ra值减小的方向偏移,且当Ra数一定时,Numean随高宽比迅速地达到最大值后缓慢减小;随着Ra值的增加,空腔中涡的数量逐渐增加,浮升流动强度增大,Numean增大,且Numean的最大值向高宽比减小的方向偏移。

  3. Analysis of Thermal-Hydraulic Gravity/ Buoyancy Effects in the Testing of the ITER Poloidal Field Full Size Joint Sample (PF-FSJS)

    Science.gov (United States)

    Zanino, R.; Bruzzone, P.; Ciazynski, D.; Ciotti, M.; Gislon, P.; Nicollet, S.; Savoldi Richard, L.

    2004-06-01

    The PF-FSJS is a full-size joint sample, based on the NbTi dual-channel cable-in-conduit conductor (CICC) design currently foreseen for the International Thermonuclear Experimental Reactor (ITER) Poloidal Field coil system. It was tested during the summer of 2002 in the Sultan facility of CRPP at a background peak magnetic field of typically 6 T. It includes about 3 m of two jointed conductor sections, using different strands but with identical layout. The sample was cooled by supercritical helium at nominal 4.5-5.0 K and 0.9-1.0 MPa, in forced convection from the top to the bottom of the vertical configuration. A pulsed coil was used to test AC losses in the two legs resulting, above a certain input power threshold, in bundle helium backflow from the heated region. Here we study the thermal-hydraulics of the phenomenon with the M&M code, with particular emphasis on the effects of buoyancy on the helium dynamics, as well as on the thermal-hydraulic coupling between the wrapped bundles of strands in the annular cable region and the central cooling channel. Both issues are ITER relevant, as they affect the more general question of the heat removal capability of the helium in this type of conductors.

  4. Naturalness redux

    CERN Document Server

    Fabbrichesi, Marco

    2015-01-01

    The idea of naturalness, as originally conceived, refers only to the finite renormalization of the Higgs boson mass induced by the introduction of heavier states. In this respect, naturalness is still a powerful heuristic principle in model building beyond the standard model whenever new massive states are coupled to the Higgs field. The most compelling case is provided by the generation of neutrino masses. In this paper we confront this problem from a new perspective. The right-handed sector responsible for the seesaw mechanism---which introduces a large energy threshold above the electroweak scale---is made supersymmetric to comply with naturalness while the standard model is left unchanged and non-supersymmetric. Cancellations necessary to the naturalness requirement break down only at two loops, thus offering the possibility to increase the right-handed neutrino mass scale up to one order of magnitude above the usual values allowed by naturalness. If also the weak boson sector of the standard model is mad...

  5. Ultrasonic Concentration in a Line-Driven Cylindrical Tube

    Energy Technology Data Exchange (ETDEWEB)

    G.R. Goddard

    2004-12-15

    The fractionation of particles from their suspending fluid or noninvasive micromanipulation of particles in suspension has many applications ranging from the recovery of valuable reagents from process flows to the fabrication of microelectromechanical devices. Techniques based on size, density, solubility, or electromagnetic properties exist for fulfilling these needs, but many particles have traits that preclude their use such as small size, neutral buoyancy, or uniform electromagnetic characteristics. While separation by those techniques may not be possible, often compressibility differences exist between the particle and fluid that would allow fractionation by acoustic forces. The potential of acoustic separation is known, but due to inherent difficulties in achieving and maintaining accurate alignment of the transduction system, it is rarely utilized. The objective of this project is to investigate the use of structural excitation as a potentially efficient concentration/fractionation method for particles in suspension. It is demonstrated that structural excitation of a cylindrically symmetric cavity, such as a tube, allows non-invasive, fast, and low power concentration of particles suspended in a fluid. The inherent symmetry of the system eliminates the need for careful alignment inherent in current acoustic concentration devices. Structural excitation distributes the acoustic field throughout the volume of the cavity, which also significantly reduces temperature gradients and acoustic streaming in the fluid; cavitation is no longer an issue. The lowest-order coupled modes of a long cylindrical glass tube and fluid-filled cavity, driven by a line contact, are tuned, via material properties and aspect ratio, to achieve a coupled dipolar vibration of the system, shown to generate efficient concentration of particles to the central axis of the tube. A two dimensional elastodynamic model of the system was developed and subsequently utilized to optimize particle

  6. Ultrasonic Concentration in a Line-Driven Cylindrical Tube

    Energy Technology Data Exchange (ETDEWEB)

    Goddard, Gregory Russ [Portland State Univ., Portland, OR (United States)

    2004-01-01

    The fractionation of particles from their suspending fluid or noninvasive micromanipulation of particles in suspension has many applications ranging from the recovery of valuable reagents from process flows to the fabrication of microelectromechanical devices. Techniques based on size, density, solubility, or electromagnetic properties exist for fulfilling these needs, but many particles have traits that preclude their use such as small size, neutral buoyancy, or uniform electromagnetic characteristics. While separation by those techniques may not be possible, often compressibility differences exist between the particle and fluid that would allow fractionation by acoustic forces. The potential of acoustic separation is known, but due to inherent difficulties in achieving and maintaining accurate alignment of the transduction system, it is rarely utilized. The objective of this project is to investigate the use of structural excitation as a potentially efficient concentration/fractionation method for particles in suspension. It is demonstrated that structural excitation of a cylindrically symmetric cavity, such as a tube, allows non-invasive, fast, and low power concentration of particles suspended in a fluid. The inherent symmetry of the system eliminates the need for careful alignment inherent in current acoustic concentration devices. Structural excitation distributes the acoustic field throughout the volume of the cavity, which also significantly reduces temperature gradients and acoustic streaming in the fluid; cavitation is no longer an issue. The lowest-order coupled modes of a long cylindrical glass tube and fluid-filled cavity, driven by a line contact, are tuned, via material properties and aspect ratio, to achieve a coupled dipolar vibration of the system, shown to generate efficient concentration of particles to the central axis of the tube. A two dimensional elastodynamic model of the system was developed and subsequently utilized to optimize particle

  7. Ley Natural

    OpenAIRE

    2010-01-01

    1. La expresión «ley natural» en la historia de las ideas. Uso ético y uso científico. 2. La cuestión de las leyes naturales en el ámbito de la naturaleza y en el ámbito de la conducta humana. 3. La ley natural como teoría moral se desarrolla en dos planos: a) plano práctico: el obrar humano responde a razones, depende de principios que constituyen una única ley; b) plano de fundamentación metafísica: la ley natural como participación de la ley eterna en la criatura racional. 4. La ley nat...

  8. Natural games

    CERN Document Server

    Anttila, Jani

    2011-01-01

    Behavior in the context of game theory is described as a natural process that follows the 2nd law of thermodynamics. The rate of entropy increase as the payoff function is derived from statistical physics of open systems. The thermodynamic formalism relates everything in terms of energy and describes various ways to consume free energy. This allows us to associate game theoretical models of behavior to physical reality. Ultimately behavior is viewed as a physical process where flows of energy naturally select ways to consume free energy as soon as possible. This natural process is, according to the profound thermodynamic principle, equivalent to entropy increase in the least time. However, the physical portrayal of behavior does not imply determinism. On the contrary, evolutionary equation for open systems reveals that when there are three or more degrees of freedom for behavior, the course of a game is inherently unpredictable in detail because each move affects motives of moves in the future. Eventually, wh...

  9. Emancipating Nature

    DEFF Research Database (Denmark)

    Munk, Anders Kristian

    2012-01-01

    The issue of riverine flooding in the UK is closely tied up with computer simulations. Arguably, these modelling practices are ripe with the anticipation of nature. They aspire to pre-empt it, hence expect it to be ‘out there’, and ultimately work through formalized distillations of it – hydrodyn......The issue of riverine flooding in the UK is closely tied up with computer simulations. Arguably, these modelling practices are ripe with the anticipation of nature. They aspire to pre-empt it, hence expect it to be ‘out there’, and ultimately work through formalized distillations...... of it – hydrodynamic equations – which have their own anticipations and place their own demands on their modellers. Through the experience of a flood modelling apprenticeship I argue that the taking-place of such anticipations paradoxically relies on the birth of a hybrid, the model-modeller, and thus on a nature...

  10. Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers

    Science.gov (United States)

    Calkins, Michael A.; Long, Louie; Nieves, David; Julien, Keith; Tobias, Steven M.

    2016-12-01

    Most large-scale planetary magnetic fields are thought to be driven by low Rossby number convection of a low magnetic Prandtl number fluid. Here kinematic dynamo action is investigated with an asymptotic, rapidly rotating dynamo model for the plane layer geometry that is intrinsically low magnetic Prandtl number. The thermal Prandtl number and Rayleigh number are varied to illustrate fundamental changes in flow regime, ranging from laminar cellular convection to geostrophic turbulence in which an inverse energy cascade is present. A decrease in the efficiency of the convection to generate a dynamo, as determined by an increase in the critical magnetic Reynolds number, is observed as the buoyancy forcing is increased. This decreased efficiency may result from both the loss of correlations associated with the increasingly disordered states of flow that are generated, and boundary layer behavior that enhances magnetic diffusion locally. We find that the spatial characteristics of the large-scale magnetic field is dependent only weakly on changes in flow behavior. In contrast, the behavior of the small-scale magnetic field is directly dependent on, and therefore shows significant variations with, the small-scale convective flow field. However, our results are limited to the linear, kinematic dynamo regime; future simulations that include the Lorentz force are therefore necessary to assess the robustness of these results.

  11. Turbulent convection driven by internal radiative heating of melt ponds on sea ice

    Science.gov (United States)

    Wells, Andrew; Langton, Tom; Rees Jones, David; Moon, Woosok

    2016-11-01

    The melting of Arctic sea ice is strongly influenced by heat transfer through melt ponds which form on the ice surface. Melt ponds are internally heated by the absorption of incoming radiation and cooled by surface heat fluxes, resulting in vigorous buoyancy-driven convection in the pond interior. Motivated by this setting, we conduct two-dimensional direct-numerical simulations of the turbulent convective flow of a Boussinesq fluid between two horizontal boundaries, with internal heating predicted from a two-stream radiation model. A linearised thermal boundary condition describes heat exchange with the overlying atmosphere, whilst the lower boundary is isothermal. Vertically asymmetric convective flow modifies the upper surface temperature, and hence controls the partitioning of the incoming heat flux between emission at the upper and lower boundaries. We determine how the downward heat flux into the ice varies with a Rayleigh number based on the internal heating rate, the flux ratio of background surface cooling compared to internal heating, and a Biot number characterising the sensitivity of surface fluxes to surface temperature. Thus we elucidate the physical controls on heat transfer through Arctic melt ponds which determine the fate of sea ice in the summer.

  12. Natural aerodynamics

    CERN Document Server

    Scorer, R S

    1958-01-01

    Natural Aerodynamics focuses on the mathematics of any problem in air motion.This book discusses the general form of the law of fluid motion, relationship between pressure and wind, production of vortex filaments, and conduction of vorticity by viscosity. The flow at moderate Reynolds numbers, turbulence in a stably stratified fluid, natural exploitation of atmospheric thermals, and plumes in turbulent crosswinds are also elaborated. This text likewise considers the waves produced by thermals, transformation of thin layer clouds, method of small perturbations, and dangers of extra-polation.Thi

  13. [Natural selection].

    Science.gov (United States)

    Mayr, E

    1985-05-01

    Much of the resistance against Darwin's theory of natural selection has been due to misunderstandings. It is shown that natural selection is not a tautology and that it is a two-step process. The first step, the production of variation, is under the control of chance; the second step, selection proper, is an anti-chance process, but subject to many constraints. The target of selection is the individual as a whole, and many neutral mutations can be retained as hitchhikers of successful genotypes. Sexual selection results from selection for pure reproductive success.

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

    Science.gov (United States)

    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.

  15. Data driven marketing for dummies

    CERN Document Server

    Semmelroth, David

    2013-01-01

    Embrace data and use it to sell and market your products Data is everywhere and it keeps growing and accumulating. Companies need to embrace big data and make it work harder to help them sell and market their products. Successful data analysis can help marketing professionals spot sales trends, develop smarter marketing campaigns, and accurately predict customer loyalty. Data Driven Marketing For Dummies helps companies use all the data at their disposal to make current customers more satisfied, reach new customers, and sell to their most important customer segments more efficiently. Identifyi

  16. Thermoacoustic natural gas liquefier

    Energy Technology Data Exchange (ETDEWEB)

    Swift, G.W. [Los Alamos National Lab., NM (United States). Condensed Matter and Thermal Physics Group

    1997-05-01

    Cryenco and Los Alamos are collaborating to develop a natural-gas-powered natural-gas liquefier that will have no moving parts and require no electrical power. It will have useful efficiency, remarkable reliability, and low cost. The liquefaction of natural gas, which occurs at only 115 Kelvin at atmospheric pressure, has previously required rather sophisticated refrigeration machinery. The 1990 invention of the thermoacoustically driven orifice pulse-tube refrigerator (TA-DOPTR) provides cryogenic refrigeration with no moving parts for the first time. In short, this invention uses acoustic phenomena to produce refrigeration from heat. The required apparatus consists of nothing more than helium-filled heat exchangers and pipes, made of common materials, without exacting tolerances. In the Cryenco-Los Alamos collaboration, the authors are developing a version of this invention suitable for use in the natural-gas industry. The project is known as acoustic liquefier for short. The present program plans call for a two-phase development. Phase 1, with capacity of 500 gallon per day (i.e., approximately 40,000 scfd, requiring a refrigeration power of about 7 kW), is large enough to illuminate all the issues of large-scale acoustic liquefaction without undue cost, and to demonstrate the liquefaction of 60--70% of input gas, while burning 30--40%. Phase 2 will target versions of approximately 10{sup 6} scfd = 10,000 gallon per day capacity. In parallel with both, they continue fundamental research on the technology, directed toward increased efficiency, to build scientific foundations and a patent portfolio for future acoustic liquefiers.

  17. Kritikkens natur

    DEFF Research Database (Denmark)

    Schatz-Jakobsen, Claus

    1999-01-01

    Artiklen introducerer det nye forskningsfelt inden for samtænkning af litteratur, kultur og natur, den såkaldt økologiske kritik, og kaster et kritisk blik på  dens brug af romantisk litteratur som proto-økologisk kanon....

  18. Nature Watch

    Science.gov (United States)

    Sterling, Donna R.

    2010-01-01

    Children are naturally curious about the world in which they live. To focus this sense of wonder, have your students investigate their local habitat as it changes over the year. This multiseason study will build connections and add relevance to the habitats that children learn about. This series of activities for grades 4-6 explores the changing…

  19. Nature's Palette

    Science.gov (United States)

    McBride, Brooke B.; Brewer, Carol A.

    2010-01-01

    Flower petals, acorn hats, exoskeletons of beetles, and lichens are just a few of the objects students may find in a surprising array of vivid colors. These tiny examples from nature's palette can be discovered in a school yard, a park, or even along the edges of a paved sidewalk...it simply takes careful observation! This article describes a…

  20. Natural ecosystems

    Science.gov (United States)

    Fleishman, Erica; Belnap, Jayne; Cobb, Neil; Enquist, Carolyn A.F.; Ford, Karl; MacDonald, Glen; Pellant, Mike; Schoennagel, Tania; Schmit, Lara M.; Schwartz, Mark; van Drunick, Suzanne; Westerling, Anthony LeRoy; Keyser, Alisa; Lucas, Ryan

    2013-01-01

    Natural Ecosystems analyzes the association of observed changes in climate with changes in the geographic distributions and phenology (the timing of blossoms or migrations of birds) for Southwestern ecosystems and their species, portraying ecosystem disturbances—such as wildfires and outbreaks of forest pathogens—and carbon storage and release, in relation to climate change.

  1. Bibliography of Research in Natural Language Generation

    Science.gov (United States)

    1993-11-01

    17-19, 1979. [575] Ronald Kaplan, Klaus Netter, Jorgen Wedekind , [589] Martin Kiy. Unification grammar. Technical re- and Annie Zaenen. Translation by...ble, parallel model ofNatural [11801 Jllrgen Wedekind . Generation as structure driven Language Generation. PhD thegi, University of derivation. In

  2. Generating natural language under pragmatic constraints

    CERN Document Server

    Hovy, Eduard H

    2013-01-01

    Recognizing that the generation of natural language is a goal- driven process, where many of the goals are pragmatic (i.e., interpersonal and situational) in nature, this book provides an overview of the role of pragmatics in language generation. Each chapter states a problem that arises in generation, develops a pragmatics-based solution, and then describes how the solution is implemented in PAULINE, a language generator that can produce numerous versions of a single underlying message, depending on its setting.

  3. Driven fragmentation of granular gases.

    Science.gov (United States)

    Cruz Hidalgo, Raúl; Pagonabarraga, Ignacio

    2008-06-01

    The dynamics of homogeneously heated granular gases which fragment due to particle collisions is analyzed. We introduce a kinetic model which accounts for correlations induced at the grain collisions and analyze both the kinetics and relevant distribution functions these systems develop. The work combines analytical and numerical studies based on direct simulation Monte Carlo calculations. A broad family of fragmentation probabilities is considered, and its implications for the system kinetics are discussed. We show that generically these driven materials evolve asymptotically into a dynamical scaling regime. If the fragmentation probability tends to a constant, the grain number diverges at a finite time, leading to a shattering singularity. If the fragmentation probability vanishes, then the number of grains grows monotonously as a power law. We consider different homogeneous thermostats and show that the kinetics of these systems depends weakly on both the grain inelasticity and driving. We observe that fragmentation plays a relevant role in the shape of the velocity distribution of the particles. When the fragmentation is driven by local stochastic events, the long velocity tail is essentially exponential independently of the heating frequency and the breaking rule. However, for a Lowe-Andersen thermostat, numerical evidence strongly supports the conjecture that the scaled velocity distribution follows a generalized exponential behavior f(c) approximately exp(-cn) , with n approximately 1.2 , regarding less the fragmentation mechanisms.

  4. Design of Complex Systems to Achieve Passive Safety: Natural Circulation Cooling of Liquid Salt Pebble Bed Reactors

    Science.gov (United States)

    Scarlat, Raluca Olga

    This dissertation treats system design, modeling of transient system response, and characterization of individual phenomena and demonstrates a framework for integration of these three activities early in the design process of a complex engineered system. A system analysis framework for prioritization of experiments, modeling, and development of detailed design is proposed. Two fundamental topics in thermal-hydraulics are discussed, which illustrate the integration of modeling and experimentation with nuclear reactor design and safety analysis: thermal-hydraulic modeling of heat generating pebble bed cores, and scaled experiments for natural circulation heat removal with Boussinesq liquids. The case studies used in this dissertation are derived from the design and safety analysis of a pebble bed fluoride salt cooled high temperature nuclear reactor (PB-FHR), currently under development in the United States at the university and national laboratories level. In the context of the phenomena identification and ranking table (PIRT) methodology, new tools and approaches are proposed and demonstrated here, which are specifically relevant to technology in the early stages of development, and to analysis of passive safety features. A system decomposition approach is proposed. Definition of system functional requirements complements identification and compilation of the current knowledge base for the behavior of the system. Two new graphical tools are developed for ranking of phenomena importance: a phenomena ranking map, and a phenomena identification and ranking matrix (PIRM). The functional requirements established through this methodology were used for the design and optimization of the reactor core, and for the transient analysis and design of the passive natural circulation driven decay heat removal system for the PB-FHR. A numerical modeling approach for heat-generating porous media, with multi-dimensional fluid flow is presented. The application of this modeling

  5. Computational Analysis of Natural Ventilation Flows in Geodesic Dome Building in Hot Climates

    Directory of Open Access Journals (Sweden)

    Zohreh Soleimani

    2016-08-01

    Full Text Available For centuries, dome roofs were used in traditional houses in hot regions such as the Middle East and Mediterranean basin due to its thermal advantages, structural benefits and availability of construction materials. This article presents the computational modelling of the wind- and buoyancy-induced ventilation in a geodesic dome building in a hot climate. The airflow and temperature distributions and ventilation flow rates were predicted using Computational Fluid Dynamics (CFD. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS equations were solved using the CFD tool ANSYS FLUENT15. The standard k-epsilon was used as turbulence model. The modelling was verified using grid sensitivity and flux balance analysis. In order to validate the modelling method used in the current study, additional simulation of a similar domed-roof building was conducted for comparison. For wind-induced ventilation, the dome building was modelled with upper roof vents. For buoyancy-induced ventilation, the geometry was modelled with roof vents and also with two windows open in the lower level. The results showed that using the upper roof openings as a natural ventilation strategy during winter periods is advantageous and could reduce the indoor temperature and also introduce fresh air. The results also revealed that natural ventilation using roof vents cannot satisfy thermal requirements during hot summer periods and complementary cooling solutions should be considered. The analysis showed that buoyancy-induced ventilation model can still generate air movement inside the building during periods with no or very low wind.

  6. Elasticity-Driven Backflow of Fluid-Driven Cracks

    Science.gov (United States)

    Lai, Ching-Yao; Zheng, Zhong; Dressaire, Emilie; Ramon, Guy; Huppert, Herbert E.; Stone, Howard A.

    2016-11-01

    Fluid-driven cracks are generated by the injection of pressurized fluid into an elastic medium. Once the injection pressure is released, the crack closes up due to elasticity and the fluid in the crack drains out of the crack through an outlet, which we refer to as backflow. We experimentally study the effects of crack size, elasticity of the matrix, and fluid viscosity on the backflow dynamics. During backflow, the volume of liquid remaining in the crack as a function of time exhibits a transition from a fast decay at early times to a power law behavior at late times. Our results at late times can be explained by scaling arguments balancing elastic and viscous stresses in the crack. This work may relate to the environmental issue of flowback in hydraulic fracturing. This work is supported by National Science Foundation via Grant CBET-1509347 and partially supported by Andlinger Center for Energy and the Environment at Princeton University.

  7. A buoyancy-based screen of Drosophila larvae for fat-storage mutants reveals a role for Sir2 in coupling fat storage to nutrient availability.

    Directory of Open Access Journals (Sweden)

    Tânia Reis

    2010-11-01

    Full Text Available Obesity has a strong genetic component, but few of the genes that predispose to obesity are known. Genetic screens in invertebrates have the potential to identify genes and pathways that regulate the levels of stored fat, many of which are likely to be conserved in humans. To facilitate such screens, we have developed a simple buoyancy-based screening method for identifying mutant Drosophila larvae with increased levels of stored fat. Using this approach, we have identified 66 genes that when mutated increase organismal fat levels. Among these was a sirtuin family member, Sir2. Sirtuins regulate the storage and metabolism of carbohydrates and lipids by deacetylating key regulatory proteins. However, since mammalian sirtuins function in many tissues in different ways, it has been difficult to define their role in energy homeostasis accurately under normal feeding conditions. We show that knockdown of Sir2 in the larval fat body results in increased fat levels. Moreover, using genetic mosaics, we demonstrate that Sir2 restricts fat accumulation in individual cells of the fat body in a cell-autonomous manner. Consistent with this function, changes in the expression of metabolic enzymes in Sir2 mutants point to a shift away from catabolism. Surprisingly, although Sir2 is typically upregulated under conditions of starvation, Sir2 mutant larvae survive better than wild type under conditions of amino-acid starvation as long as sugars are provided. Our findings point to a Sir2-mediated pathway that activates a catabolic response to amino-acid starvation irrespective of the sugar content of the diet.

  8. Satellite (Natural)

    Science.gov (United States)

    Murdin, P.

    2000-11-01

    In its most general sense, any celestial object in orbit around a similar larger object. Thus, for example, the Magellanic Clouds are satellite galaxies of our own Milky Way galaxy. Without qualification, the term is used to mean a body in orbit around a planet; an alternative term is moon. The term natural satellite distinguishes these bodies from artificial satellites—spacecraft placed in orbi...

  9. Knockout driven reactions in complex molecules and their clusters

    Science.gov (United States)

    Gatchell, Michael; Zettergren, Henning

    2016-08-01

    Energetic ions lose some of their kinetic energy when interacting with electrons or nuclei in matter. Here, we discuss combined experimental and theoretical studies on such impulse driven reactions in polycyclic aromatic hydrocarbons (PAHs), fullerenes, and pure or mixed clusters of these molecules. These studies show that the nature of excitation is important for how complex molecular systems respond to ion/atom impact. Rutherford-like nuclear scattering processes may lead to prompt atom knockout and formation of highly reactive fragments, while heating of the molecular electron clouds in general lead to formation of more stable and less reactive fragments. In this topical review, we focus on recent studies of knockout driven reactions, and present new calculations of the angular dependent threshold (displacement) energies for such processes in PAHs. The so-formed fragments may efficiently form covalent bonds with neighboring molecules in clusters. These unique molecular growth processes may be important in astrophysical environments such as low velocity shock waves.

  10. Disorder-Driven Metal-Insulator Transitions in Deformable Lattices

    Science.gov (United States)

    Di Sante, Domenico; Fratini, Simone; Dobrosavljević, Vladimir; Ciuchi, Sergio

    2017-01-01

    We show that, in the presence of a deformable lattice potential, the nature of the disorder-driven metal-insulator transition is fundamentally changed with respect to the noninteracting (Anderson) scenario. For strong disorder, even a modest electron-phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder-enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate "bad insulator" transport regime which displays resistivity values exceeding the Mott-Ioffe-Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature-induced rearrangements of electronic states due to enhanced interaction effects close to the disorder-driven metal-insulator transition.

  11. 空心微珠/环氧树脂高强浮力材料的性能及断裂分析%Performance and fracture of hollow glass microsphere/epoxy resin high-strength buoyancy material

    Institute of Scientific and Technical Information of China (English)

    林碧兰; 路新瀛; 陈勤

    2011-01-01

    The high-strength buoyancy material was synthesized with adhesive matrix of epoxy resin and filler of hollow glass microsphere (HGM) activated by silane coupling agent. The characteristics of HGM treated with silane were analyzed by XRD and FRIR. The effect of type and content of HGM on performance of buoyancy material was investigated through density test and uniaxial static compression test. The fracture characteristics and water absorption of buoyancy material were studied by SEM and water absorption test. The results show that the structure of HGM is amorphous. Silane is grafted on the surface of HGM after activation. HGM is perfectly combined with epoxy resin and there is no gap between their interface. The high specific compression strength of HGM is beneficial to the performance of buoyancy material. The density, compression strength and specific compression strength of buoyancy material are 0. 645 ~ 0. 850 g/cm3 , 60 ~ 93 MPa and 92 ~ 112 MPa · cm3 · g-1, respectively. On the fracture surface of buoyancy material with less HGM, HGM is destroyed and there is tailing in the matrix, while the damage degree of HGM increases with the increase of HGM content and finally HGM is destroyed thoroughly. The water absorption of buoyancy material is low.%以环氧树脂为基体,经硅烷活化处理的空心玻璃微珠(HGM)为填充剂,制备了高强浮力材料.采用XRD、FRIR分析了HGM的结构和硅烷处理效果,通过密度测试和单轴静态压缩试验研究了HGM的类型和含量对浮力材料性能的影响,利用SEM和吸水率试验研究了浮力材料的断裂特性和吸水性.结果表明:HGM为无定形结构;硅烷分子接枝在HGM表面,使得HGM与环氧树脂完好结合且两者界面没有间隙沟槽;HGM的较大比压缩强度有利于提高浮力材料的性能;高强浮力材料密度为0.645~0.850 g/cm3,抗压强度为60~93 MPa,比压缩强度为92~112 MPa·cm3·g-1;HGM 含量较少时,浮力材料断裂表面HGM破

  12. Confirmation of EMIC wave-driven relativistic electron precipitation

    Science.gov (United States)

    Hendry, Aaron T.; Rodger, Craig J.; Clilverd, Mark A.; Engebretson, Mark J.; Mann, Ian R.; Lessard, Marc R.; Raita, Tero; Milling, David K.

    2016-06-01

    Electromagnetic ion cyclotron (EMIC) waves are believed to be an important source of pitch angle scattering driven relativistic electron loss from the radiation belts. To date, investigations of this precipitation have been largely theoretical in nature, limited to calculations of precipitation characteristics based on wave observations and small-scale studies. Large-scale investigation of EMIC wave-driven electron precipitation has been hindered by a lack of combined wave and precipitation measurements. Analysis of electron flux data from the POES (Polar Orbiting Environmental Satellites) spacecraft has been suggested as a means of investigating EMIC wave-driven electron precipitation characteristics, using a precipitation signature particular to EMIC waves. Until now the lack of supporting wave measurements for these POES-detected precipitation events has resulted in uncertainty regarding the driver of the precipitation. In this paper we complete a statistical study comparing POES precipitation measurements with wave data from several ground-based search coil magnetometers; we further present a case study examining the global nature of this precipitation. We show that a significant proportion of the precipitation events correspond with EMIC wave detections on the ground; for precipitation events that occur directly over the magnetometers, this detection rate can be as high as 90%. Our results demonstrate that the precipitation region is often stationary in magnetic local time, narrow in L, and close to the expected plasmapause position. Predominantly, the precipitation is associated with helium band rising tone Pc1 waves on the ground. The success of this study proves the viability of POES precipitation data for investigating EMIC wave-driven electron precipitation.

  13. Evaluation of Respondent-Driven Sampling

    OpenAIRE

    McCreesh, N; Frost, SD; Seeley, J.; Katongole, J; Tarsh, MN; Ndunguse, R; Jichi, F; Lunel, NL; Maher, D.; Johnston, LG; Sonnenberg, P; Copas, AJ; Hayes, RJ; White, RG

    2012-01-01

    : BACKGROUND:: Respondent-driven sampling is a novel variant of link-tracing sampling for estimating the characteristics of hard-to-reach groups, such as HIV prevalence in sex workers. Despite its use by leading health organizations, the performance of this method in realistic situations is still largely unknown. We evaluated respondent-driven sampling by comparing estimates from a respondent-driven sampling survey with total population data. METHODS:: Total population data on age, tribe, rel...

  14. Design Driven Testing Test Smarter, Not Harder

    CERN Document Server

    Stephens, M

    2010-01-01

    The groundbreaking book Design Driven Testing brings sanity back to the software development process by flipping around the concept of Test Driven Development (TDD) - restoring the concept of using testing to verify a design instead of pretending that unit tests are a replacement for design. Anyone who feels that TDD is "Too Damn Difficult" will appreciate this book. Design Driven Testing shows that, by combining a forward-thinking development process with cutting-edge automation, testing can be a finely targeted, business-driven, rewarding effort. In other words, you'll learn how to test

  15. Disentangling Competition Among Platform Driven Strategic Groups

    DEFF Research Database (Denmark)

    Kazan, Erol; Tan, Chee-Wee; Lim, Eric

    2015-01-01

    competition within platform-driven markets, we opted for the UK mobile payment market as our empirical setting. By embracing the theoretical lens of strategic groups and digital platforms, this study supplements prior research by deriving a taxonomy of platform-driven strategic groups that is grounded......In platform-driven markets, competitive advantage is derived from superior platform design and configurations. For this reason, platform owners strive to create unique and inimitable platform configurals to maintain and extend their competitiveness within network economies. To disentangle firm...... on competitive attributes of platform- driven markets; namely interfirm modularity and strategic linkages....

  16. Asynchronous Event-Driven Particle Algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Donev, A

    2007-08-30

    We present, in a unifying way, the main components of three asynchronous event-driven algorithms for simulating physical systems of interacting particles. The first example, hard-particle molecular dynamics (MD), is well-known. We also present a recently-developed diffusion kinetic Monte Carlo (DKMC) algorithm, as well as a novel stochastic molecular-dynamics algorithm that builds on the Direct Simulation Monte Carlo (DSMC). We explain how to effectively combine event-driven and classical time-driven handling, and discuss some promises and challenges for event-driven simulation of realistic physical systems.

  17. Asynchronous Event-Driven Particle Algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Donev, A

    2007-02-28

    We present in a unifying way the main components of three examples of asynchronous event-driven algorithms for simulating physical systems of interacting particles. The first example, hard-particle molecular dynamics (MD), is well-known. We also present a recently-developed diffusion kinetic Monte Carlo (DKMC) algorithm, as well as a novel event-driven algorithm for Direct Simulation Monte Carlo (DSMC). Finally, we describe how to combine MD with DSMC in an event-driven framework, and discuss some promises and challenges for event-driven simulation of realistic physical systems.

  18. Investigation of Current Driven Loudspeakers

    DEFF Research Database (Denmark)

    Schneider, Henrik; Agerkvist, Finn T.; Knott, Arnold

    2015-01-01

    Current driven loudspeakers have previously been investigated but the literature is limited and the advantages and disadvantages are yet to be fully identified. This paper makes use of a non-linear loudspeaker model to analyse loudspeakers with distinct non-linear characteristics under voltage...... and current drive. A multi tone test signal is used in the evaluation of the driving schemes since it resembles audio signals to a higher degree than the signals used in total harmonic distortion and intermodulation distortion test methods. It is found that current drive is superior over voltage drive in a 5......” woofer where a copper ring in the pole piece has not been implemented to compensate for eddy currents. However the drive method seems to be irrelevant for a 5” woofer where the compliance, force factor as well as the voice coil inductance has been optimized for linearity....

  19. Customer-driven Product Development

    DEFF Research Database (Denmark)

    Sommer, Anita Friis

    2011-01-01

    Demand chain management is a research area of increasing attention. It is the undertaking of reacting to customer requirements through a responsive chain going from customers through a focal company towards raw material distributors. With faster growing markets and increasing competition, companies...... look for new ways to gain competitive advantage. In competitive markets there is a tendency of shorter product life cycles, and thus a competitive factor is to keep at pace with the market or even driving the market by developing new products. This research study seeks to investigate Customer......-driven Product Development (CDPD) from a demand chain management perspective. CDPD is the counterpart to typical research and development processes, which has no direct customer involvement. The proposition is that letting customers initiate and participate in the product development process...

  20. Employee-Driven Innovation (EDI)

    DEFF Research Database (Denmark)

    Kesting, Peter; Ulhøi, John Parm

      The responsibility to be innovative and think of useful ideas and the privilege of making decisions in processes of innovation are typically restricted to specifically assigned R&D functions and/or upper echelon managers. Given the importance of innovation to most organizations, it may seem...... illogical to reserve such a 'license' to so few individuals. This paper argues that some parts of that license should indeed be extended to include 'ordinary' employees, as they are potential drivers of innovation. Research on Employee Driven Innovation (EDI) is still at its beginnings. In the paper we...... outline the 'grand structure' of the phenomenon in order to identify underlying processes as well as the most relevant drivers of EDI. Based on these insights we identify open research questions and make suggestions for the next steps. Our main argument is that 'ordinary' employees can specially...

  1. Wonder-driven Entrepreneurship Teaching

    DEFF Research Database (Denmark)

    Hansen, Finn Thorbjørn; Herholdt-Lomholdt, Sine Maria

    2015-01-01

    Contemporary research on creativity, innovation and entrepreneurship have now for a decade or more been focusing on social constructive, pragmatic, socio-cultural and socio-material dimensions of creative and innovative processes and entrepreneurship (Bager et al. 2010, Brinkmann & Tangaard 2010......- and entrepreneurship processes. In this paper we want to continue in line with this new framework of meaning- and wonder-driven innovation by focusing on the possible educational consequences of such an approach. Our empirical departure is our three-year phenomenological action research project called ‘Wonder......-based Entrepreneurship Teaching in Professional bachelor Education’. Ten senior lecturers in nursing and pedagogy participated. The purpose was to investigate whether and how Socratic and philosophical dialogues and different forms of phenomenological and existential reflections upon one´s own professional assumptions...

  2. Photogated humidity-driven motility

    Science.gov (United States)

    Zhang, Lidong; Liang, Haoran; Jacob, Jolly; Naumov, Panče

    2015-06-01

    Hygroinduced motion is a fundamental process of energy conversion that is essential for applications that require contactless actuation in response to the day-night rhythm of atmospheric humidity. Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light. A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min-1. The element can lift objects ~85 times heavier and can transport cargos ~20 times heavier than itself. Having an azobenzene-containing conjugate as a photoactive dopant, this entirely humidity-driven self-actuation can be controlled remotely with ultraviolet light, thus setting a platform for next-generation smart biomimetic hybrids.

  3. Coevolutionary success-driven multigames

    CERN Document Server

    Szolnoki, Attila

    2014-01-01

    Wealthy individuals may be less tempted to defect than those with comparatively low payoffs. To take this into consideration, we introduce coevolutionary success-driven multigames in structured populations. While the core game is always the weak prisoner's dilemma, players whose payoffs from the previous round exceed a threshold adopt only a minimally low temptation to defect in the next round. Along with the strategies, the perceived strength of the social dilemma thus coevolves with the success of each individual player. We show that the lower the threshold for using the small temptation to defect, the more the evolution of cooperation is promoted. Importantly, the promotion of cooperation is not simply due to a lower average temptation to defect, but rather due to a dynamically reversed direction of invasion along the interfaces that separate cooperators and defectors on regular networks. Conversely, on irregular networks, in the absence of clear invasion fronts, the promotion of cooperation is due to inte...

  4. Modelling of thermally driven groundwater flow in a facility for disposal of spent nuclear fuel in deep boreholes

    Energy Technology Data Exchange (ETDEWEB)

    Marsic, Nico; Grundfelt, Bertil [Kemakta Konsult AB, Stockholm (Sweden)

    2013-09-15

    In this report calculations are presented of buoyancy driven groundwater flow caused by the emission of residual heat from spent nuclear fuel deposited in deep boreholes from the ground surface in combination with the natural geothermal gradient. This work has been conducted within SKB's programme for evaluation of alternative methods for final disposal of spent nuclear fuel. The basic safety feature of disposal of spent nuclear fuel in deep boreholes is that the groundwater at great depth has a higher salinity, and hence a higher density, than more superficial groundwater. The result of this is that the deep groundwater becomes virtually stagnant. The study comprises analyses of the effects of different inter-borehole distances as well as the effect of different permeabilities in the backfill and sealing materials in the borehole and of different shapes of the interface between fresh and saline groundwater. The study is an update of a previous study published in 2006. In the present study, the facility design proposed by Sandia National Laboratories has been studied. In this design, steel canisters containing two BWR elements or one PWR element are stacked on top of each other between 3 and 5 kilometres depth. In order to host all spent fuel from the current Swedish nuclear programme, about 80 such holes are needed. The model used in this study comprises nine boreholes spaced 100 metres alternatively 50 metres apart in a 3{Chi}3 matrix. In one set of calculations the salinity in the groundwater was assumed to increase from zero above 700 metres depth to 10% by weight at 1500 metres depth and below. In another set, a sharper salinity gradient was applied in which the salinity increased from 0 to 10% between 1400 and 1500 metres depth. A geothermal gradient of 16 deg C/km was applied. The heat output from the spent fuel was assumed to decrease by time in manner consistent with the radioactive decay in the fuel. When the inter-borehole distance decreased from

  5. Biocommunication and natural genome editing

    Institute of Scientific and Technical Information of China (English)

    Guenther; Witzany

    2010-01-01

    The biocommunicative approach investigates communication processes within and among cells,tissues,organs and organisms as sign-mediated interactions,and nucleotide sequences as code,i.e.language-like text,which follows in parallel three kinds of rules:combinatorial (syntactic),context-sensitive(pragmatic),and contentspecific(semantic).Natural genome editing from a bio-communicative perspective is competent agent-driven generation and integration of meaningful nucleotide sequences into pre-existing genomic content arrangements and the ability to(re-)combine and(re-)regulate them according to context-dependent(i.e.adaptational) purposes of the host organism.

  6. Advances in Optimizing Weather Driven Electric Power Systems.

    Science.gov (United States)

    Clack, C.; MacDonald, A. E.; Alexander, A.; Dunbar, A. D.; Xie, Y.; Wilczak, J. M.

    2014-12-01

    The importance of weather-driven renewable energies for the United States (and global) energy portfolio is growing. The main perceived problems with weather-driven renewable energies are their intermittent nature, low power density, and high costs. The National Energy with Weather System Simulator (NEWS) is a mathematical optimization tool that allows the construction of weather-driven energy sources that will work in harmony with the needs of the system. For example, it will match the electric load, reduce variability, decrease costs, and abate carbon emissions. One important test run included existing US carbon-free power sources, natural gas power when needed, and a High Voltage Direct Current power transmission network. This study shows that the costs and carbon emissions from an optimally designed national system decrease with geographic size. It shows that with achievable estimates of wind and solar generation costs, that the US could decrease its carbon emissions by up to 80% by the early 2030s, without an increase in electric costs. The key requirement would be a 48 state network of HVDC transmission, creating a national market for electricity not possible in the current AC grid. These results were found without the need for storage. Further, we tested the effect of changing natural gas fuel prices on the optimal configuration of the national electric power system. Another test that was carried out was an extension to global regions. The extension study shows that the same properties found in the US study extend to the most populous regions of the planet. The extra test is a simplified version of the US study, and is where much more research can be carried out. We compare our results to other model results.

  7. Natural Family Planning

    Science.gov (United States)

    ... Sex and Birth Control Birth Control Natural Family Planning Natural Family Planning Birth ControlPrevention and WellnessSex and Birth Control Share Natural Family Planning Natural Family PlanningWhat is natural family planning?Natural ...

  8. Natural relaxation

    Science.gov (United States)

    Marzola, Luca; Raidal, Martti

    2016-11-01

    Motivated by natural inflation, we propose a relaxation mechanism consistent with inflationary cosmology that explains the hierarchy between the electroweak scale and Planck scale. This scenario is based on a selection mechanism that identifies the low-scale dynamics as the one that is screened from UV physics. The scenario also predicts the near-criticality and metastability of the Standard Model (SM) vacuum state, explaining the Higgs boson mass observed at the Large Hadron Collider (LHC). Once Majorana right-handed neutrinos are introduced to provide a viable reheating channel, our framework yields a corresponding mass scale that allows for the seesaw mechanism as well as for standard thermal leptogenesis. We argue that considering singlet scalar dark matter extensions of the proposed scenario could solve the vacuum stability problem and discuss how the cosmological constant problem is possibly addressed.

  9. Energy partitioning in an inductively driven rail gun

    Science.gov (United States)

    Sen, K. K.; Ray, P. K.

    1984-01-01

    The equations describing the performance of an inductively driven rail are analyzed numerically. Friction between the projectile and rails is included through an empirical formulation. The equations are applied to the experiment of Rashleigh and Marshall to obtain an estimate of energy distribution in rail guns as a function of time. It is found that only 15 percent of energy delivered by the inductor to the gun is transformed into the kinetic energy of the projectile. This study provides an insight into the nature of nonlinear coupling involved in the electromechanical interactions in a rail gun.

  10. Perceived importance and responsibility for market-driven pig welfare

    DEFF Research Database (Denmark)

    Thorslund, Cecilie A H; Aaslyng, Margit Dall; Lassen, Jesper

    2017-01-01

    This review explores barriers and opportunities for market-driven pig welfare in Europe. It finds, first, that consumers generally rank animal welfare as important, but they also rank it low relative to other societal problems. Second, consumers have a wide range of concerns about pig welfare......, but they focus especially on naturalness. Third, pig welfare is seen as an important indicator of meat quality. Fourth, consumers tend to think that responsibility for pig welfare lies with several actors: farmers, governments and themselves. The paper concludes that there is an opportunity for the market...

  11. Fractal Modeling and Scaling in Natural Systems - Editorial

    Science.gov (United States)

    The special issue of Ecological complexity journal on Fractal Modeling and Scaling in Natural Systems contains representative examples of the status and evolution of data-driven research into fractals and scaling in complex natural systems. The editorial discusses contributions to understanding rela...

  12. Test-driven modeling of embedded systems

    DEFF Research Database (Denmark)

    Munck, Allan; Madsen, Jan

    2015-01-01

    To benefit maximally from model-based systems engineering (MBSE) trustworthy high quality models are required. From the software disciplines it is known that test-driven development (TDD) can significantly increase the quality of the products. Using a test-driven approach with MBSE may have a sim...

  13. Motor-Driven Giant Magnetostrictive Actuator

    DEFF Research Database (Denmark)

    Zhang, Lihui; Xia, Yongming; Lu, Kaiyuan

    2015-01-01

    to produce the desired magnetic field when an output strain should be maintained. The GMA does not produce any mechanical power in this condition, but constant power is being consumed by the excitation coil. This paper presents a new type of motor-driven GMA (MDGMA), which works in a coil-free driven manner...

  14. Gravity-Driven Hydraulic Fractures

    Science.gov (United States)

    Germanovich, L. N.; Garagash, D.; Murdoch, L. C.; Robinowitz, M.

    2014-12-01

    This study is motived by a new method for disposing of nuclear waste by injecting it as a dense slurry into a hydraulic fracture that grows downward to great enough depth to permanently isolate the waste. Disposing of nuclear waste using gravity-driven hydraulic fractures is mechanically similar to the upward growth of dikes filled with low density magma. A fundamental question in both applications is how the injected fluid controls the propagation dynamics and fracture geometry (depth and breadth) in three dimensions. Analog experiments in gelatin [e.g., Heimpel and Olson, 1994; Taisne and Tait, 2009] show that fracture breadth (the short horizontal dimension) remains nearly stationary when the process in the fracture "head" (where breadth is controlled) is dominated by solid toughness, whereas viscous fluid dissipation is dominant in the fracture tail. We model propagation of the resulting gravity-driven (buoyant or sinking), finger-like fracture of stationary breadth with slowly varying opening along the crack length. The elastic response to fluid loading in a horizontal cross-section is local and can be treated similar to the classical Perkins-Kern-Nordgren (PKN) model of hydraulic fracturing. The propagation condition for a finger-like crack is based on balancing the global energy release rate due to a unit crack extension with the rock fracture toughness. It allows us to relate the net fluid pressure at the tip to the fracture breadth and rock toughness. Unlike the PKN fracture, where breadth is known a priori, the final breadth of a finger-like fracture is a result of processes in the fracture head. Because the head is much more open than the tail, viscous pressure drop in the head can be neglected leading to a 3D analog of Weertman's hydrostatic pulse. This requires relaxing the local elasticity assumption of the PKN model in the fracture head. As a result, we resolve the breadth, and then match the viscosity-dominated tail with the 3-D, toughness

  15. Estrogen Receptor Driven Inhibitor Synthesis

    Science.gov (United States)

    2006-09-01

    Engstrom O, Ohman L, Greene GL, Gustaffson JA, Carlquist M. Molecular basis of agonism and antagonism in the oestrogen receptor. Nature 389, 753-758...oxidatively modified proteins in Bacillus subtilis, Mol. Microbiol. 58 (2005) 409–425. [7] K. Tyagarajan, E. Pretzer, J.E. Wiktorowicz, Thiol-reactive dyes

  16. Flutter-driven triboelectrification for harvesting wind energy.

    Science.gov (United States)

    Bae, Jihyun; Lee, Jeongsu; Kim, SeongMin; Ha, Jaewook; Lee, Byoung-Sun; Park, YoungJun; Choong, Chweelin; Kim, Jin-Baek; Wang, Zhong Lin; Kim, Ho-Young; Park, Jong-Jin; Chung, U-In

    2014-09-23

    Technologies to harvest electrical energy from wind have vast potentials because wind is one of the cleanest and most sustainable energy sources that nature provides. Here we propose a flutter-driven triboelectric generator that uses contact electrification caused by the self-sustained oscillation of flags. We study the coupled interaction between a fluttering flexible flag and a rigid plate. In doing so, we find three distinct contact modes: single, double and chaotic. The flutter-driven triboelectric generator having small dimensions of 7.5 × 5 cm at wind speed of 15 ms(-1) exhibits high-electrical performances: an instantaneous output voltage of 200 V and a current of 60 μA with a high frequency of 158 Hz, giving an average power density of approximately 0.86 mW. The flutter-driven triboelectric generation is a promising technology to drive electric devices in the outdoor environments in a sustainable manner.

  17. Explosively driven air blast in a conical shock tube.

    Science.gov (United States)

    Stewart, Joel B; Pecora, Collin

    2015-03-01

    Explosively driven shock tubes present challenges in terms of safety concerns and expensive upkeep of test facilities but provide more realistic approximations to the air blast resulting from free-field detonations than those provided by gas-driven shock tubes. Likewise, the geometry of conical shock tubes can naturally approximate a sector cut from a spherically symmetric blast, leading to a better agreement with the blast profiles of free-field detonations when compared to those provided by shock tubes employing constant cross sections. The work presented in this article documents the design, fabrication, and testing of an explosively driven conical shock tube whose goal was to closely replicate the blast profile seen from a larger, free-field detonation. By constraining the blast through a finite area, large blasts (which can add significant damage and safety constraints) can be simulated using smaller explosive charges. The experimental data presented herein show that a close approximation to the free-field air blast profile due to a 1.5 lb charge of C4 at 76 in. can be achieved by using a 0.032 lb charge in a 76-in.-long conical shock tube (which translates to an amplification factor of nearly 50). Modeling and simulation tools were used extensively in designing this shock tube to minimize expensive fabrication costs.

  18. Explosively driven air blast in a conical shock tube

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, Joel B., E-mail: joel.b.stewart2.civ@mail.mil; Pecora, Collin, E-mail: collin.r.pecora.civ@mail.mil [U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States)

    2015-03-15

    Explosively driven shock tubes present challenges in terms of safety concerns and expensive upkeep of test facilities but provide more realistic approximations to the air blast resulting from free-field detonations than those provided by gas-driven shock tubes. Likewise, the geometry of conical shock tubes can naturally approximate a sector cut from a spherically symmetric blast, leading to a better agreement with the blast profiles of free-field detonations when compared to those provided by shock tubes employing constant cross sections. The work presented in this article documents the design, fabrication, and testing of an explosively driven conical shock tube whose goal was to closely replicate the blast profile seen from a larger, free-field detonation. By constraining the blast through a finite area, large blasts (which can add significant damage and safety constraints) can be simulated using smaller explosive charges. The experimental data presented herein show that a close approximation to the free-field air blast profile due to a 1.5 lb charge of C4 at 76 in. can be achieved by using a 0.032 lb charge in a 76-in.-long conical shock tube (which translates to an amplification factor of nearly 50). Modeling and simulation tools were used extensively in designing this shock tube to minimize expensive fabrication costs.

  19. Research into the transmission of natural gas by gas pipeline

    Energy Technology Data Exchange (ETDEWEB)

    Gadonneix, P.

    1998-12-31

    This paper is the press release of the talk given at the `Gaz de France scientific meeting with the press` by P. Gadonneix, chairman of Gaz de France company, on October 7, 1998. The aim of this talk concerns the new French and European supply link for bringing natural gas from the Norwegian North Sea fields. This new supply link is the first direct link between Norway and France and the NorFra gas pipeline which brings natural gas from the North Sea to France is the longest offshore pipeline in the world. The `Artere des Hauts de France` pipeline (the largest diameter gas pipeline ever laid in France) is devoted to the transfer of natural gas from Dunkerque to the Gournay-sur-Aronde underground storage site. This paper describes successively: the French European gas supply hub, the NorFra project, the Artere des Hauts de France pipeline, the network performance research, the safety and quality guaranties, the reduction of overland natural gas transmission costs (improvement of pipe-laying techniques and optimization of line route and welding operations), the specific techniques used for road and river crossing (micro-tunnel digging, river-crossing ditches) and for anchoring (buoyancy compensation). Finally, the environmental impact of the laying operations is briefly described. (J.S.)

  20. Teaching About Nature's Nuclear Reactors

    CERN Document Server

    Herndon, J M

    2005-01-01

    Naturally occurring nuclear reactors existed in uranium deposits on Earth long before Enrico Fermi built the first man-made nuclear reactor beneath Staggs Field in 1942. In the story of their discovery, there are important lessons to be learned about scientific inquiry and scientific discovery. Now, there is evidence to suggest that the Earth's magnetic field and Jupiter's atmospheric turbulence are driven by planetary-scale nuclear reactors. The subject of planetocentric nuclear fission reactors can be a jumping off point for stimulating classroom discussions about the nature and implications of planetary energy sources and about the geomagnetic field. But more importantly, the subject can help to bring into focus the importance of discussing, debating, and challenging current thinking in a variety of areas.

  1. QED-driven laser absorption

    CERN Document Server

    Levy, M C; Ratan, N; Sadler, J; Ridgers, C P; Kasim, M; Ceurvorst, L; Holloway, J; Baring, M G; Bell, A R; Glenzer, S H; Gregori, G; Ilderton, A; Marklund, M; Tabak, M; Wilks, S C; Norreys, P A

    2016-01-01

    Absorption covers the physical processes which convert intense photon flux into energetic particles when a high-power laser illuminates optically-thick matter. It underpins important petawatt-scale applications today, e.g., medical-quality proton beam production. However, development of ultra-high-field applications has been hindered since no study so far has described absorption throughout the entire transition from the classical to the quantum electrodynamical (QED) regime of plasma physics. Here we present a model of absorption that holds over an unprecedented six orders-of-magnitude in optical intensity and lays the groundwork for QED applications of laser-driven particle beams. We demonstrate 58% efficient \\gamma-ray production at $1.8\\times 10^{25}~\\mathrm{W~ cm^{-2}}$ and the creation of an anti-matter source achieving $4\\times 10^{24}\\ \\mathrm{positrons}\\ \\mathrm{cm^{-3}}$, $10^{6}~\\times$ denser than of any known photonic scheme. These results will find applications in scaled laboratory probes of bla...

  2. Driven tracers in narrow channels

    Science.gov (United States)

    Cividini, J.; Mukamel, D.; Posch, H. A.

    2017-01-01

    Steady-state properties of a driven tracer moving in a narrow two-dimensional (2D) channel of quiescent medium are studied. The tracer drives the system out of equilibrium, perturbs the density and pressure fields, and gives the bath particles a nonzero average velocity, creating a current in the channel. Three models in which the confining effect of the channel is probed are analyzed and compared in this study: the first is the simple symmetric exclusion process (SSEP), for which the stationary density profile and the pressure on the walls in the frame of the tracer are computed. We show that the tracer acts like a dipolar source in an average velocity field. The spatial structure of this 2D strip is then simplified to a one-dimensional (1D) SSEP, in which exchanges of position between the tracer and the bath particles are allowed. Using a combination of mean-field theory and exact solution in the limit where no exchange is allowed gives good predictions of the velocity of the tracer and the density field. Finally, we show that results obtained for the 1D SSEP with exchanges also apply to a gas of overdamped hard disks in a narrow channel. The correspondence between the parameters of the SSEP and of the gas of hard disks is systematic and follows from simple intuitive arguments. Our analytical results are checked numerically.

  3. Cosmic ray driven Galactic winds

    CERN Document Server

    Recchia, S; Morlino, G

    2016-01-01

    The escape of cosmic rays from the Galaxy leads to a gradient in the cosmic ray pressure that acts as a force on the background plasma, in the direction opposite to the gravitational pull. If this force is large enough to win against gravity, a wind can be launched that removes gas from the Galaxy, thereby regulating several physical processes, including star formation. The dynamics of these cosmic ray driven winds is intrinsically non-linear in that the spectrum of cosmic rays determines the characteristics of the wind (velocity, pressure, magnetic field) and in turn the wind dynamics affects the cosmic ray spectrum. Moreover, the gradient of the cosmic ray distribution function causes excitation of Alfven waves, that in turn determine the scattering properties of cosmic rays, namely their diffusive transport. These effects all feed into each other so that what we see at the Earth is the result of these non-linear effects. Here we investigate the launch and evolution of such winds, and we determine the impli...

  4. Metrics for Event Driven Software

    Directory of Open Access Journals (Sweden)

    Neha Chaudhary

    2016-01-01

    Full Text Available The evaluation of Graphical User Interface has significant role to improve its quality. Very few metrics exists for the evaluation of Graphical User Interface. The purpose of metrics is to obtain better measurements in terms of risk management, reliability forecast, project scheduling, and cost repression. In this paper structural complexity metrics is proposed for the evaluation of Graphical User Interface. Structural complexity of Graphical User Interface is considered as an indicator of complexity. The goal of identifying structural complexity is to measure the GUI testability. In this testability evaluation the process of measuring the complexity of the user interface from testing perspective is proposed. For the GUI evaluation and calculating structural complexity an assessment process is designed which is based on types of events. A fuzzy model is developed to evaluate the structural complexity of GUI. This model takes five types of events as input and return structural complexity of GUI as output. Further a relationship is established between structural complexity and testability of event driven software. Proposed model is evaluated with four different applications. It is evident from the results that higher the complexities lower the testability of application.

  5. Cosmic ray driven Galactic winds

    Science.gov (United States)

    Recchia, S.; Blasi, P.; Morlino, G.

    2016-11-01

    The escape of cosmic rays from the Galaxy leads to a gradient in the cosmic ray pressure that acts as a force on the background plasma, in the direction opposite to the gravitational pull. If this force is large enough to win against gravity, a wind can be launched that removes gas from the Galaxy, thereby regulating several physical processes, including star formation. The dynamics of these cosmic ray driven winds is intrinsically non-linear in that the spectrum of cosmic rays determines the characteristics of the wind (velocity, pressure, magnetic field) and in turn the wind dynamics affects the cosmic ray spectrum. Moreover, the gradient of the cosmic ray distribution function causes excitation of Alfvén waves, that in turn determines the scattering properties of cosmic rays, namely their diffusive transport. These effects all feed into each other so that what we see at the Earth is the result of these non-linear effects. Here, we investigate the launch and evolution of such winds, and we determine the implications for the spectrum of cosmic rays by solving together the hydrodynamical equations for the wind and the transport equation for cosmic rays under the action of self-generated diffusion and advection with the wind and the self-excited Alfvén waves.

  6. Bubble-Driven Inertial Micropump

    CERN Document Server

    Torniainen, Erik D; Markel, David P; Kornilovitch, Pavel E

    2012-01-01

    The fundamental action of the bubble-driven inertial micropump is investigated. The pump has no moving parts and consists of a thermal resistor placed asymmetrically within a straight channel connecting two reservoirs. Using numerical simulations, the net flow is studied as a function of channel geometry, resistor location, vapor bubble strength, fluid viscosity, and surface tension. Two major regimes of behavior are identified: axial and non-axial. In the axial regime, the drive bubble either remains inside the channel or continues to grow axially when it reaches the reservoir. In the non-axial regime the bubble grows out of the channel and in all three dimensions while inside the reservoir. The net flow in the axial regime is parabolic with respect to the hydraulic diameter of the channel cross-section but in the non-axial regime it is not. From numerical modeling, it is determined that the net flow is maximal when the axial regime crosses over to the non-axial regime. To elucidate the basic physical princi...

  7. Optically switchable natural silk

    Energy Technology Data Exchange (ETDEWEB)

    Krasnov, Igor, E-mail: Igor.Krasnov@hzg.de; Müller, Martin, E-mail: Martin.Mueller@hzg.de [Institut für Experimentelle und Angewandte Physik, Universität Kiel, D-24098 Kiel (Germany); Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), D-21502 Geesthacht (Germany); Krekiehn, Nicolai R.; Jung, Ulrich; Magnussen, Olaf M. [Institut für Experimentelle und Angewandte Physik, Universität Kiel, D-24098 Kiel (Germany); Krywka, Christina [Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), D-21502 Geesthacht (Germany); Zillohu, Ahnaf U.; Strunskus, Thomas [Institut für Materialwissenschaft, Universität Kiel, D-24098 Kiel (Germany); Elbahri, Mady [Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), D-21502 Geesthacht (Germany); Institut für Materialwissenschaft, Universität Kiel, D-24098 Kiel (Germany)

    2015-03-02

    An optically active bio-material is created by blending natural silk fibers with photoisomerizable chromophore molecules—azobenzenebromide (AzBr). The material converts the energy of unpolarized light directly into mechanical work with a well-defined direction of action. The feasibility of the idea to produce optically driven microsized actuators on the basis of bio-material (silk) is proven. The switching behavior of the embedded AzBr molecules was studied in terms of UV/Vis spectroscopy. To test the opto-mechanical properties of the modified fibers and the structural changes they undergo upon optically induced switching, single fiber X-ray diffraction with a micron-sized synchrotron radiation beam was combined in situ with optical switching as well as with mechanical testing and monitoring. The crystalline regions of silk are not modified by the presence of the guest molecules, hence occupy only the amorphous part of the fibers. It is shown that chromophore molecules embedded into fibers can be reversibly switched between the trans and cis conformation by illumination with light of defined wavelengths. The host fibers respond to this switching with a variation of the internal stress. The amplitude of the mechanical response is independent of the applied external stress and its characteristic time is shorter than the relaxation time of the usual mechanical response of silk.

  8. NGTC`s natural gas heat pumps

    Energy Technology Data Exchange (ETDEWEB)

    Binet, M. [Natural Gas Technologies Centre, Boucherville, PQ (Canada)

    1996-12-01

    An overview of natural gas heat pumps and cooling systems evaluation projects carried out by the Natural Gas Technologies Centre (NGTC) in Boucherville, Quebec, was presented. Technological description of three natural gas engine-driven technologies were provided, as well as the results of laboratory and field tests. The residential sector was covered by the 3-ton York Triathlon heat pump, the commercial sector by the 10-ton Trico natural gas engine-driven condensing unit, and the institutional sector by 25-ton Carrier engine-driven rooftops. The York Triathlon heat pump showed a good performance at the given conditions, with an average COP of 1.29 in cooling mode and of 1.03 in heating mode. The Trico unit was fully instrumented at NGTC; performance testing will be carried out later in 1996. The Carrier rooftops showed performance levels below those of the manufacturer`s suggested characteristics, although user satisfaction with the comfort provided by the units was high. 7 refs., 9 figs., 3 tabs.

  9. Shadow-driven 4D haptic visualization.

    Science.gov (United States)

    Zhang, Hui; Hanson, Andrew

    2007-01-01

    Just as we can work with two-dimensional floor plans to communicate 3D architectural design, we can exploit reduced-dimension shadows to manipulate the higher-dimensional objects generating the shadows. In particular, by taking advantage of physically reactive 3D shadow-space controllers, we can transform the task of interacting with 4D objects to a new level of physical reality. We begin with a teaching tool that uses 2D knot diagrams to manipulate the geometry of 3D mathematical knots via their projections; our unique 2D haptic interface allows the user to become familiar with sketching, editing, exploration, and manipulation of 3D knots rendered as projected imageson a 2D shadow space. By combining graphics and collision-sensing haptics, we can enhance the 2D shadow-driven editing protocol to successfully leverage 2D pen-and-paper or blackboard skills. Building on the reduced-dimension 2D editing tool for manipulating 3D shapes, we develop the natural analogy to produce a reduced-dimension 3D tool for manipulating 4D shapes. By physically modeling the correct properties of 4D surfaces, their bending forces, and their collisions in the 3D haptic controller interface, we can support full-featured physical exploration of 4D mathematical objects in a manner that is otherwise far beyond the experience accessible to human beings. As far as we are aware, this paper reports the first interactive system with force-feedback that provides "4D haptic visualization" permitting the user to model and interact with 4D cloth-like objects.

  10. Principles-Driven Forensic Analysis

    OpenAIRE

    Peisert, Sean; Bishop, Matt; Karin, Sidney; Marzullo, Keith

    2005-01-01

    It is possible to enhance our understanding of what has happened on a computer system by using forensic techniques that do not require prediction of the nature of the attack, the skill of the attacker, or the details of the system resources or objects affected. These techniques address five fundamental principles of computer forensics. These principles include recording data about the entire operating system, particularly user space events and environments, and interpreting events at differen...

  11. Laboratory blast wave driven instabilities

    Science.gov (United States)

    Kuranz, Carolyn

    2008-11-01

    This presentation discusses experiments involving the evolution of hydrodynamic instabilities in the laboratory under high-energy-density (HED) conditions. These instabilities are driven by blast waves, which occur following a sudden, finite release of energy, and consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. Instabilities evolving under HED conditions are relevant to astrophysics. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 μm plastic layer that is followed by a low-density foam layer. A blast wave structure similar to those in supernovae is created in the plastic layer. The blast wave crosses an interface having a 2D or 3D sinusoidal structure that serves as a seed perturbation for hydrodynamic instabilities. This produces unstable growth dominated by the Rayleigh-Taylor (RT) instability in the nonlinear regime. We have detected the interface structure under these conditions using x-ray backlighting. Recent advances in our diagnostic techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the RT spike and penetrating further than previously observed or predicted by current simulations. The observed effect is potentially of great importance as a source of mass transport to places not anticipated by current theory and simulation. I will discuss the amount of mass in these spike extensions, the associated uncertainties, and hypotheses regarding their origin We also plan to show comparisons of experiments using single mode and multimode as well as 2D and 3D initial conditions. This work is sponsored by DOE/NNSA Research Grants DE-FG52-07NA28058 (Stewardship Sciences Academic Alliances) and DE-FG52-04NA00064 (National Laser User

  12. PC analysis of stochastic differential equations driven by Wiener noise

    KAUST Repository

    Le Maitre, Olivier

    2015-03-01

    A polynomial chaos (PC) analysis with stochastic expansion coefficients is proposed for stochastic differential equations driven by additive or multiplicative Wiener noise. It is shown that for this setting, a Galerkin formalism naturally leads to the definition of a hierarchy of stochastic differential equations governing the evolution of the PC modes. Under the mild assumption that the Wiener and uncertain parameters can be treated as independent random variables, it is also shown that the Galerkin formalism naturally separates parametric uncertainty and stochastic forcing dependences. This enables us to perform an orthogonal decomposition of the process variance, and consequently identify contributions arising from the uncertainty in parameters, the stochastic forcing, and a coupled term. Insight gained from this decomposition is illustrated in light of implementation to simplified linear and non-linear problems; the case of a stochastic bifurcation is also considered.

  13. Disentangling Competition Among Platform Driven Strategic Groups

    DEFF Research Database (Denmark)

    Kazan, Erol; Tan, Chee-Wee; Lim, Eric

    2015-01-01

    In platform-driven markets, competitive advantage is derived from superior platform design and configurations. For this reason, platform owners strive to create unique and inimitable platform configurals to maintain and extend their competitiveness within network economies. To disentangle firm...... competition within platform-driven markets, we opted for the UK mobile payment market as our empirical setting. By embracing the theoretical lens of strategic groups and digital platforms, this study supplements prior research by deriving a taxonomy of platform-driven strategic groups that is grounded...

  14. Quasi-Periodically Driven Quantum Systems

    Science.gov (United States)

    Verdeny, Albert; Puig, Joaquim; Mintert, Florian

    2016-10-01

    Floquet theory provides rigorous foundations for the theory of periodically driven quantum systems. In the case of non-periodic driving, however, the situation is not so well understood. Here, we provide a critical review of the theoretical framework developed for quasi-periodically driven quantum systems. Although the theoretical footing is still under development, we argue that quasi-periodically driven quantum systems can be treated with generalisations of Floquet theory in suitable parameter regimes. Moreover, we provide a generalisation of the Floquet-Magnus expansion and argue that quasi-periodic driving offers a promising route for quantum simulations.

  15. On fusion driven systems (FDS) for transmutation

    Energy Technology Data Exchange (ETDEWEB)

    Aagren, O (Uppsala Univ., Aangstroem laboratory, div. of electricity, Uppsala (Sweden)); Moiseenko, V.E. (Inst. of Plasma Physics, National Science Center, Kharkov Inst. of Physics and Technology, Kharkov (Ukraine)); Noack, K. (Forschungszentrum Dresden-Rossendorf (Germany))

    2008-10-15

    This report gives a brief description of ongoing activities on fusion driven systems (FDS) for transmutation of the long-lived radioactive isotopes in the spent nuclear waste from fission reactors. Driven subcritical systems appears to be the only option for efficient minor actinide burning. Driven systems offer a possibility to increase reactor safety margins. A comparatively simple fusion device could be sufficient for a fusion-fission machine, and transmutation may become the first industrial application of fusion. Some alternative schemes to create strong fusion neutron fluxes are presented

  16. Spurious haloes and discreteness-driven relaxation in cosmological simulations

    Science.gov (United States)

    Power, C.; Robotham, A. S. G.; Obreschkow, D.; Hobbs, A.; Lewis, G. F.

    2016-10-01

    There is strong evidence that cosmological N-body simulations dominated by warm dark matter (WDM) contain spurious or unphysical haloes, most readily apparent as regularly spaced low-mass haloes strung along filaments. We show that spurious haloes are a feature of traditional N-body simulations of cosmological structure formation models, including WDM and cold dark matter models, in which gravitational collapse proceeds in an initially anisotropic fashion, and arises naturally as a consequence of discreteness-driven relaxation. We demonstrate this using controlled N-body simulations of plane-symmetric collapse and show that spurious haloes are seeded at shell crossing by localized velocity perturbations induced by the discrete nature of the density field, and that their characteristic separation should be approximately the mean inter-particle separation of the N-body simulation, which is fixed by the mass resolution within the volume. Using cosmological N-body simulations in which particles are split into two collisionless components of fixed mass ratio, we find that the spatial distribution of the two components show signatures of discreteness-driven relaxation on both large and small scales. Adopting a spline kernel gravitational softening that is of order the comoving mean inter-particle separation helps to suppress the effect of discreteness-driven relaxation, but cannot eliminate it completely. These results provide further motivation for recent developments of new algorithms, which include, for example, revisions of the traditional N-body approach by means of spatially adaptive anistropric gravitational softenings or explicit solution of the evolution of dark matter in phase space.

  17. Fano Resonance in an Electrically Driven Plasmonic Device

    Science.gov (United States)

    Vardi, Yuval; Cohen-Hoshen, Eyal; Shalem, Guy; Bar-Joseph, Israel

    Electrically driven plasmonic devices offer unique opportunities as a research tool and for practical applications. In such devices, current that flows across a metallic tunnel junction excites a plasmon, which gives rise to light emission. This local nature of the excitation allows access into ''dark'' modes, which are not easily excited by far field illumination. We present an electrically driven plasmonic device, based on a gold nanoparticle single-electron-transistor, and investigate the light emission due to the tunneling current. The applied voltage determines the emitted spectral lineshape, enables an excellent control of the plasmonic spectrum. We show that the use of this structure allows us to characterize the electrical properties of the two tunnel barriers, and determine their role in the light emission process. Furthermore, we find a Fano resonance, resulting from interference between the nanoparticle and electrodes dipoles. This resonance is seen due to the local nature of the excitation, and is manifested as a sharp asymmetrical spectral dip. We show that the spectral position of this resonance can be conveniently controlled by the design of the structural parameters. Such devices may be a step toward the realization of an on-chip nano-optical emitters and sensors.

  18. Test-driven development with Django

    CERN Document Server

    Harvey, Kevin

    2015-01-01

    This book is for Django developers with little or no knowledge of test-driven development or testing in general. Familiarity with the command line, setting up a Python virtual environment, and starting a Django project are assumed.

  19. Distributed simulation a model driven engineering approach

    CERN Document Server

    Topçu, Okan; Oğuztüzün, Halit; Yilmaz, Levent

    2016-01-01

    Backed by substantive case studies, the novel approach to software engineering for distributed simulation outlined in this text demonstrates the potent synergies between model-driven techniques, simulation, intelligent agents, and computer systems development.

  20. Molecular dynamics for irradiation driven chemistry

    DEFF Research Database (Denmark)

    Sushko, Gennady B.; Solov'yov, Ilia A.; Solov'yov, Andrey V.

    2016-01-01

    that describe the classical MD of complex molecular systems under irradiation. The proposed irradiation driven molecular dynamics (IDMD) methodology is designed for the molecular level description of the irradiation driven chemistry. The IDMD approach is implemented into the MBN Explorer software package...... capable to operate with a large library of classical potentials, many-body force fields and their combinations. IDMD opens a broad range of possibilities for modelling of irradiation driven modifications and chemistry of complex molecular systems ranging from radiotherapy cancer treatments to the modern...... technologies such as focused electron beam deposition (FEBID). As an example, the new methodology is applied for studying the irradiation driven chemistry caused by FEBID of tungsten hexacarbonyl W(CO)6 precursor molecules on a hydroxylated SiO2 surface. It is demonstrated that knowing the interaction...