WorldWideScience

Sample records for supercritical mixing layers

  1. Perturbation Effects on a Supercritical C7H16/N2 Mixing Layer

    Science.gov (United States)

    Okongo'o, Nora; Bellan, Josette

    2008-01-01

    A computational-simulation study has been presented of effects of perturbation wavelengths and initial Reynolds numbers on the transition to turbulence of a heptane/nitrogen mixing layer at supercritical pressure. The governing equations for the simulations were the same as those of related prior studies reported in NASA Tech Briefs. Two-dimensional (2D) simulations were performed with initially im posed span wise perturbations whereas three-dimensional (3D) simulations had both streamwise and spanwise initial perturbations. The 2D simulations were undertaken to ascertain whether perturbations having the shortest unstable wavelength obtained from a linear stability analysis for inviscid flow are unstable in viscous nonlinear flows. The goal of the 3D simulations was to ascertain whether perturbing the mixing layer at different wavelengths affects the transition to turbulence. It was found that transitions to turbulence can be obtained at different perturbation wavelengths, provided that they are longer than the shortest unstable wavelength as determined by 2D linear stability analysis for the inviscid case and that the initial Reynolds number is proportionally increased as the wavelength is decreased. The transitional states thus obtained display different dynamic and mixture characteristics, departing strongly from the behaviors of perfect gases and ideal mixtures.

  2. Large Eddy Simulations of Supercritical Mixing Layers for Air Force Applications

    Science.gov (United States)

    2010-05-01

    ier correlations, all benefit from inclusion of this new model 20100617305 15. SUBJECT TERMS Supercritical fluid mixing; compressible mixing...Taskinoglu and J. Bellan Species m( gmo \\-]) 7). (K) P,(MPa) N2 28.013 126.3 3.399 C7H16 100.205...gradients, a computation that the p correction is meant to improve. The SS model also benefits from the p correction which introduces features more

  3. A Priori Analysis of Subgrid-Scale Models for Large Eddy Simulations of Supercritical Binary-Species Mixing Layers

    Science.gov (United States)

    Okong'o, Nora; Bellan, Josette

    2005-01-01

    Models for large eddy simulation (LES) are assessed on a database obtained from direct numerical simulations (DNS) of supercritical binary-species temporal mixing layers. The analysis is performed at the DNS transitional states for heptane/nitrogen, oxygen/hydrogen and oxygen/helium mixing layers. The incorporation of simplifying assumptions that are validated on the DNS database leads to a set of LES equations that requires only models for the subgrid scale (SGS) fluxes, which arise from filtering the convective terms in the DNS equations. Constant-coefficient versions of three different models for the SGS fluxes are assessed and calibrated. The Smagorinsky SGS-flux model shows poor correlations with the SGS fluxes, while the Gradient and Similarity models have high correlations, as well as good quantitative agreement with the SGS fluxes when the calibrated coefficients are used.

  4. Supercritical fluid mixing in Diesel Engine Applications

    Science.gov (United States)

    Bravo, Luis; Ma, Peter; Kurman, Matthew; Tess, Michael; Ihme, Matthias; Kweon, Chol-Bum

    2014-11-01

    A numerical framework for simulating supercritical fluids mixing with large density ratios is presented in the context of diesel sprays. Accurate modeling of real fluid effects on the fuel air mixture formation process is critical in characterizing engine combustion. Recent work (Dahms, 2013) has suggested that liquid fuel enters the chamber in a transcritical state and rapidly evolves to supercritical regime where the interface transitions from a distinct liquid/gas interface into a continuous turbulent mixing layer. In this work, the Peng Robinson EoS is invoked as the real fluid model due to an acceptable compromise between accuracy and computational tractability. Measurements at supercritical conditions are reported from the Constant Pressure Flow (CPF) chamber facility at the Army Research Laboratory. Mie and Schlieren optical spray diagnostics are utilized to provide time resolved liquid and vapor penetration length measurement. The quantitative comparison presented is discussed. Oak Ridge Associated Universities (ORAU).

  5. Toward Better Modeling of Supercritical Turbulent Mixing

    Science.gov (United States)

    Selle, Laurent; Okongo'o, Nora; Bellan, Josette; Harstad, Kenneth

    2008-01-01

    study was done as part of an effort to develop computational models representing turbulent mixing under thermodynamic supercritical (here, high pressure) conditions. The question was whether the large-eddy simulation (LES) approach, developed previously for atmospheric-pressure compressible-perfect-gas and incompressible flows, can be extended to real-gas non-ideal (including supercritical) fluid mixtures. [In LES, the governing equations are approximated such that the flow field is spatially filtered and subgrid-scale (SGS) phenomena are represented by models.] The study included analyses of results from direct numerical simulation (DNS) of several such mixing layers based on the Navier-Stokes, total-energy, and conservation- of-chemical-species governing equations. Comparison of LES and DNS results revealed the need to augment the atmospheric- pressure LES equations with additional SGS momentum and energy terms. These new terms are the direct result of high-density-gradient-magnitude regions found in the DNS and observed experimentally under fully turbulent flow conditions. A model has been derived for the new term in the momentum equation and was found to perform well at small filter size but to deteriorate with increasing filter size. Several alternative models were derived for the new SGS term in the energy equation that would need further investigations to determine if they are too computationally intensive in LES.

  6. Subchannel analysis with turbulent mixing rate of supercritical pressure fluid

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Jianhui, E-mail: wjianhui1985@gmail.com [Department of Applied Physics, Waseda University, Tokyo 169-8555 (Japan); Oka, Yoshiaki [Emeritus Professor the University of Tokyo, Tokyo (Japan)

    2015-06-15

    Highlights: • Subchannel analysis with turbulent mixing rate law of supercritical pressure fluid (SPF) is carried out. • Turbulent mixing rate is enhanced, compared with that calculated by the law of pressurized water reactor (PWR). • Increase in maximum cladding surface temperature (MCST) is smaller comparing with PWR model. • The sensitivities of MCST on non-uniformity of subchannel area and power peaking are reduced by using SPF model. - Abstract: The subchannel analysis with turbulent mixing rate law of supercritical pressure fluid (SPF) is carried out for supercritical-pressurized light water cooled and moderated reactor (Super LWR). It is different from the turbulent mixing rate law of pressurized water reactor (PWR), which is widely adopted in Super LWR subchannel analysis study, the density difference between adjacent subchannels is taken into account for turbulent mixing rate law of SPF. MCSTs are evaluated on three kinds of fuel assemblies with different pin power distribution patterns, gap spacings and mass flow rates. Compared with that calculated by employing turbulent mixing rate law of PWR, the increase in MCST is smaller even when peaking factor is large and gap spacing is uneven. The sensitivities of MCST on non-uniformity of the subchannel area and power peaking are reduced.

  7. Supercritical and Transcritical Real-Fluid Mixing in Diesel Engine Applications

    Science.gov (United States)

    2015-09-01

    ARL-RP-0551 ● SEP 2015 US Army Research Laboratory Supercritical and Transcritical Real-Fluid Mixing in Diesel Engine ...ARL-RP-0551 ● SEP 2015 US Army Research Laboratory Supercritical and Transcritical Real-Fluid Mixing in Diesel Engine Applications by...COVERED (From - To) 1 January 2014–30 September 2014 4. TITLE AND SUBTITLE Supercritical and Transcritical Real-Fluid Mixing in Diesel Engine

  8. Experiments and numerical simulation of mixing under supercritical conditions

    Science.gov (United States)

    Schmitt, T.; Rodriguez, J.; Leyva, I. A.; Candel, S.

    2012-05-01

    Supercritical pressure conditions designate a situation where the working fluid pressure is above the critical point. Among these conditions, it is interesting to identify a transcritical range which corresponds to cases where the pressure is above the critical point, but the injection temperature is below the critical value. This situation is of special interest because it raises fundamental issues which have technological relevance in the analysis of flows in liquid rocket engines. This situation is here envisaged by analyzing the behavior of a nitrogen shear coaxial jet comprising an inner stream injected at temperatures close to the critical temperature and a coaxial flow at a higher temperature. Experiments are carried out both in the absence of external modulation and by imposing a large amplitude transverse acoustic field. Real gas large eddy simulations are performed for selected experiments. The combination of experiments and calculations is used to evaluate effects of injector geometry and operating parameters. Calculations retrieve what is observed experimentally when the momentum flux ratio of the outer to the inner stream J= (ρ _eu_e^2)/(ρ _iu_i^2) is varied. Results exhibit the change in flow structure and the development of a recirculation region when this parameter exceeds a critical value. The instantaneous flow patterns for different momentum flux ratios are used in a second stage to characterize the dynamical behavior of the flow in terms of power spectral density of velocity and density fluctuations. Results obtained under acoustic modulation provide insight into mixing enhancement of coaxial streams with a view of its possible consequences in high frequency combustion instabilities. It is shown in particular that the presence of strong acoustic modulations notably reduces the high density jet core length, indicating an increased mixing efficiency. This behavior is more pronounced when the jet is placed at the location of maximum transverse

  9. Turbulent mixing of a slightly supercritical Van der Waals fluid at Low-Mach number

    CERN Document Server

    Battista, Francesco; Casciola, Carlo Massimo

    2014-01-01

    Supercritical fluids near the critical point are characterized by liquid-like densities and gas-like transport properties. These features are purposely exploited in different contexts ranging from natural products extraction/fractionation to aerospace propulsion. Large part of studies concerns this last context, focusing on the dynamics of supercritical fluids at high Mach number where compressibility and thermodynamics strictly interact. Despite the widespread use also at low Mach number, the turbulent mixing properties of slightly supercritical fluids have still not investigated in detail in this regime. This topic is addressed here by dealing with Direct Numerical Simulations (DNS) of a coaxial jet of a slightly supercritical Van der Waals fluid. Since acoustic effects are irrelevant in the Low Mach number conditions found in many industrial applications, the numerical model is based on a suitable low-Mach number expansion of the governing equation. According to experimental observations, the weakly superc...

  10. Simulation of Oxygen Disintegration and Mixing With Hydrogen or Helium at Supercritical Pressure

    Science.gov (United States)

    Bellan, Josette; Taskinoglu, Ezgi

    2012-01-01

    The simulation of high-pressure turbulent flows, where the pressure, p, is larger than the critical value, p(sub c), for the species under consideration, is relevant to a wide array of propulsion systems, e.g. gas turbine, diesel, and liquid rocket engines. Most turbulence models, however, have been developed for atmospheric-p turbulent flows. The difference between atmospheric-p and supercritical-p turbulence is that, in the former situation, the coupling between dynamics and thermodynamics is moderate to negligible, but for the latter it is very significant, and can dominate the flow characteristics. The reason for this stems from the mathematical form of the equation of state (EOS), which is the perfect-gas EOS in the former case, and the real-gas EOS in the latter case. For flows at supercritical pressure, p, the large eddy simulation (LES) equations consist of the differential conservation equations coupled with a real-gas EOS. The equations use transport properties that depend on the thermodynamic variables. Compared to previous LES models, the differential equations contain not only the subgrid scale (SGS) fluxes, but also new SGS terms, each denoted as a correction. These additional terms, typically assumed null for atmospheric pressure flows, stem from filtering the differential governing equations, and represent differences between a filtered term and the same term computed as a function of the filtered flow field. In particular, the energy equation contains a heat-flux correction (q-correction) that is the difference between the filtered divergence of the heat flux and the divergence of the heat flux computed as a function of the filtered flow field. In a previous study, there was only partial success in modeling the q-correction term, but in this innovation, success has been achieved by using a different modeling approach. This analysis, based on a temporal mixing layer Direct Numerical Simulation database, shows that the focus in modeling the q

  11. Metal extraction from the artificially contaminated soil using supercritical CO2 with mixed ligands.

    Science.gov (United States)

    Park, Kwangheon; Lee, Jeongken; Sung, Jinhyun

    2013-04-01

    Supercritical fluids have good penetrating power with a high capacity to dissolve certain solutes in the fluid itself, making it applicable for soil cleaning. Supercritical CO2 along with mixed ligands has been used for cleaning artificially contaminated soil. The extraction of metal from the soil was successful, and the molar ratio of ligands to the extracted metal was as low as 3. Complicated structures with a large surface area of the real soil seemed to cause the lower efficiency. Reduced efficiency was also observed over time after the sample preparation, indicating the possibility of chemisorption of the metal ion onto the soil. The use of supercritical CO2 with dissolved mixed ligands was sufficient to extract metal from the soil. Copyright © 2013 Elsevier Ltd. All rights reserved.

  12. Martian Mixed Layer during Pathfinder Mission

    Science.gov (United States)

    Martinez, G. M.; Valero, F.; Vazquez, L.

    2008-09-01

    In situ measurements of the Martian Planetary Boundary Layer (MPBL) encompass only the sur- face layer. Therefore, in order to fully address the MPBL, it becomes necessary to simulate somehow the behaviour of the martian mixed layer. The small-scale processes that happen in the MPBL cause GCM's ([1], [2]) to describe only partially the turbulent statistics, height, convective scales, etc, of the surface layer and the mixed layer. For this reason, 2D and 3D martian mesoscale models ([4], [5]), and large eddy simulations ([4], [6], [7], [8]) have been designed in the last years. Although they are expected to simulate more accurately the MPBL, they take an extremely expensive compu- tational time. Alternatively, we have derived the main turbu- lent characteristics of the martian mixed layer by using surface layer and mixed layer similarity ([9], [10]). From in situ temperature and wind speed measurements, together with quality-tested simu- lated ground temperature [11], we have character- ized the martian mixed layer during the convective hours of Pathfinder mission Sol 25. Mean mixed layer turbulent statistics like tem- perature variance , horizontal wind speed variance , vertical wind speed variance , viscous dissipation rate , and turbu- lent kinetic energy have been calculated, as well as the mixed layer height zi, and the convective scales of wind w? and temperature θ?. Our values, obtained with negligible time cost, match quite well with some previously obtained results via LES's ([4] and [8]). A comparisson between the above obtained mar- tian values and the typical Earth values are shown in Table 1. Convective velocity scale w doubles its counterpart terrestrial typical value, as it does the mean wind speed variances and . On the other hand, the temperature scale θ? and the mean temperature variance are virtually around one order higher on Mars. The limitations of these results concern the va- lidity of the convective mixed layer similarity. This theory

  13. Stability of compressible reacting mixing layer

    Science.gov (United States)

    Shin, D. S.; Ferziger, J. H.

    1991-01-01

    Linear instability of compressible reacting mixing layers is analyzed with emphasis on the effects of heat release and compressibility. Laminar solutions of the compressible boundary-layer equations are used as the base flows. The parameters of this study are the adiabatic flame temperature, the Mach number of the upper stream, frequency, wavenumber, and the direction of propagation of the disturbance wave. Stability characteristics of the flow are presented. Three groups of unstable modes are found when the Mach number and/or heat release are large. Finally, it is shown that the unstable modes are two-dimensional for large heat release even in highly compressible flow.

  14. Cumulus cloud venting of mixed layer ozone

    Science.gov (United States)

    Ching, J. K. S.; Shipley, S. T.; Browell, E. V.; Brewer, D. A.

    1985-01-01

    Observations are presented which substantiate the hypothesis that significant vertical exchange of ozone and aerosols occurs between the mixed layer and the free troposphere during cumulus cloud convective activity. The experiments utilized the airborne Ultra-Violet Differential Absorption Lidar (UV-DIAL) system. This system provides simultaneous range resolved ozone concentration and aerosol backscatter profiles with high spatial resolution. Evening transects were obtained in the downwind area where the air mass had been advected. Space-height analyses for the evening flight show the cloud debris as patterns of ozone typically in excess of the ambient free tropospheric background. This ozone excess was approximately the value of the concentration difference between the mixed layer and free troposphere determined from independent vertical soundings made by another aircraft in the afternoon.

  15. Anelastic Rayleigh-Taylor mixing layers

    Science.gov (United States)

    Schneider, N.; Gauthier, S.

    2016-07-01

    Anelastic Rayleigh-Taylor mixing layers for miscible fluids are investigated with a recently built model (Schneider and Gauthier 2015 J. Eng. Math. 92 55-71). Four Chebyshev-Fourier-Fourier direct numerical simulations are analyzed. They use different values for the compressibility parameters: Atwood number (the dimensionless difference of the heavy and light fluid densities) and stratification (accounts for the vertical variation of density due to gravity). For intermediate Atwood numbers and finite stratification, compressibility effects quickly occurs. As a result only nonlinear behaviours are reached. The influence of the compressibility parameters on the growth speed of the RTI is discussed. The 0.1—Atwood number/0.4—stratification configuration reaches a turbulent regime. This turbulent mixing layer is analyzed with statistical tools such as moments, PDFs, anisotropy indicators and spectra.

  16. Deposition of Cu seed layer film by supercritical fluid deposition for advanced interconnects

    Institute of Scientific and Technical Information of China (English)

    Zhao Bin; Zhao Ming-Tao; Zhang Yan-Fei; Yang Jun-He

    2013-01-01

    The deposition of a Cu seed layer film is investigated by supercritical fluid deposition (SCFD) using H2 as a reducing agent for Bis(2,2,6,6-tetramethyl-3,5-heptanedionato) copper in supercritical CO2 (scCO2).The effects of deposition temperature,precursor,and H2 concentration are investigated to optimize Cu deposition.Continuous metallic Cu films are deposited on Ru substrates at 190 ℃ when a 0.002 mol/L Cu precursor is introduced with 0.75 mol/L H2.A Cu precursor concentration higher than 0.002 mol/L is found to have negative effects on the surface qualities of Cu films.For a H2concentration above 0.56 mol/L,the root-mean-square (RMS) roughness of a Cu film decreases as the H2 concentration increases.Finally,a 20-nm thick Cu film with a smooth surface,which is required as a seed layer in advanced interconnects,is successfully deposited at a high H2 concentration (0.75 mol/L).

  17. Mixed convection in fluid superposed porous layers

    CERN Document Server

    Dixon, John M

    2017-01-01

    This Brief describes and analyzes flow and heat transport over a liquid-saturated porous bed. The porous bed is saturated by a liquid layer and heating takes place from a section of the bottom. The effect on flow patterns of heating from the bottom is shown by calculation, and when the heating is sufficiently strong, the flow is affected through the porous and upper liquid layers. Measurements of the heat transfer rate from the heated section confirm calculations. General heat transfer laws are developed for varying porous bed depths for applications to process industry needs, environmental sciences, and materials processing. Addressing a topic of considerable interest to the research community, the brief features an up-to-date literature review of mixed convection energy transport in fluid superposed porous layers.

  18. VAN DER WAALS MIXING RULES FOR THE REDLICH-KWONG EQUATION OF STATE. APPLICATION FOR SUPERCRITICAL SOLUBILITY MODELING

    OpenAIRE

    Ratnawati Ratnawati

    2012-01-01

    A solid-supercritical fluid system is highly asymmetric in terms of the size and energy differences of the components. The key point in extending a cubic equation of state to such system is on the choice of proper mixing rules. New mixing rules for the Redlich-Kwong equation of state are developed. The developement is based on the statistical-mechanical theory of the van der Waals mixing rules. The Redlich Kwong equation of state with the proposed mixing rules along with the original o...

  19. On the meridional structure of the equatorial mixed layer

    OpenAIRE

    Mueller, P; Ross, M.

    1987-01-01

    The authors compare three two-dimensional models of the meridional structure of the mixed layer near the equator: a 1 1/2-layer linear reduced gravity model and two bulk mixed layer models, one with meridional advection and one with an atmospheric feedback. The reduced gravity model is a purely dynamic model; the two bulk mixed layer models include the thermodynamic processes of mixing and heating. The differences between the models become most pronounced when their response to changes in the...

  20. Atomic Layer Deposition of High-k Dielectrics Using Supercritical CO2

    Science.gov (United States)

    Shende, Rajesh

    2005-03-01

    Atomic layer deposition (ALD) of high-κdielectric was performed in supercritical CO2 (SCCO2), using a two-step reaction sequence. In step one, tetraethoxy silane (TEOS) precursor was injected in SCCO2 at 80-100 C and 50 MPa pressure to obtain a chemisorbed surface monolayer, which was then oxidized into SiO2 using peroxide entrained in SCCO2. ALD process was controlled by estimating precursor solubility and its mass transport with respect to the density of SCCO2, and correlating these parameters with precursor injection volume. In the ALD process, 7 pulses of precursor were used anticipating deposition of one atomic layer in each of the pulses. The thickness of the SiO2 atomic layers deposited using SCCO2 was measured by variable angle spectroscopic ellipsometry (VASE), and the C-V measurements were also performed. The result obtained using VASE indicates that there were 7 monolayers of SiO2 with total thickness of 35 å, and the dielectric constant of the deposited layers was 4.0±0.1. Our initial findings clearly demonstrate that SCCO2 is capable of atomic layer deposition of high quality dielectric films at very low process temperatures preventing interface reaction. More research is in progress to achieve ALD of HfO2 and TiO2 in SCCO2.

  1. Hanford/Rocky Flats collaboration on development of supercritical carbon dioxide extraction to treat mixed waste

    Energy Technology Data Exchange (ETDEWEB)

    Hendrickson, D.W.; Biyani, R.K. [Westinghouse Hanford Co., Richland, WA (United States); Brown, C.M.; Teter, W.L. [Kaiser-Hill Co., Golden, CO (United States)

    1995-11-01

    Proposals for demonstration work under the Department of Energy`s Mixed Waste Focus Area, during the 1996 through 1997 fiscal years included two applications of supercritical carbon dioxide to mixed waste pretreatment. These proposals included task RF15MW58 of Rocky Flats and task RL46MW59 of Hanford. Analysis of compatibilities in wastes and work scopes yielded an expectation of substantial collaboration between sites whereby Hanford waste streams may undergo demonstration testing at Rocky Flats, thereby eliminating the need for test facilities at Hanford. This form of collaboration is premised the continued deployment at Rocky Flats and the capability for Hanford samples to be treated at Rocky Flats. The recent creation of a thermal treatment contract for a facility near Hanford may alleviate the need to conduct organic extraction upon Rocky Flats wastes by providing a cost effective thermal treatment alternative, however, some waste streams at Hanford will continue to require organic extraction. Final site waste stream treatment locations are not within the scope of this document.

  2. Hanford/Rocky Flats collaboration on development of supercritical carbon dioxide extraction to treat mixed waste

    Energy Technology Data Exchange (ETDEWEB)

    Hendrickson, D.W.; Biyani, R.K. [Westinghouse Hanford Co., Richland, WA (United States); Brown, C.M.; Teter, W.L. [Kaiser-Hill Co., Golden, CO (United States)

    1995-11-01

    Proposals for demonstration work under the Department of Energy`s Mixed Waste Focus Area, during the 1996 through 1997 fiscal years included two applications of supercritical carbon dioxide to mixed waste pretreatment. These proposals included task RF15MW58 of Rocky Flats and task RL46MW59 of Hanford. Analysis of compatibilities in wastes and work scopes yielded an expectation of substantial collaboration between sites whereby Hanford waste streams may undergo demonstration testing at Rocky Flats, thereby eliminating the need for test facilities at Hanford. This form of collaboration is premised the continued deployment at Rocky Flats and the capability for Hanford samples to be treated at Rocky Flats. The recent creation of a thermal treatment contract for a facility near Hanford may alleviate the need to conduct organic extraction upon Rocky Flats wastes by providing a cost effective thermal treatment alternative, however, some waste streams at Hanford will continue to require organic extraction. Final site waste stream treatment locations are not within the scope of this document.

  3. On the compressibility effects in mixing layers

    Directory of Open Access Journals (Sweden)

    Khlifi Hechmi

    2016-01-01

    Full Text Available Previous studies of compressible flows carried out in the past few years have shown that the pressure-strain is the main indicator of the structural compressibility effects. Undoubtedly, this terms plays a key role toward strongly changing magnitude of the turbulent Reynolds stress anisotropy. On the other hand, the incompressible models of the pressure-strain correlation have not correctly predicted compressible turbulence at high speed shear flow. Consequently, a correction of these models is needed for precise prediction of compressibility effects. In the present work, a compressibility correction of the widely used incompressible Launder Reece and Rodi model making their standard coefficients dependent on the turbulent and convective Mach numbers is proposed. The ability of the model to predict the developed mixing layers in different cases from experiments of Goebel and Dutton is examined. The predicted results with the proposed model are compared with DNS and experimental data and those obtained by the compressible model of Adumitroiae et al. and the original LRR model. The results show that the essential compressibility effects on mixing layers are well captured by the proposed model.

  4. VAN DER WAALS MIXING RULES FOR THE REDLICH-KWONG EQUATION OF STATE. APPLICATION FOR SUPERCRITICAL SOLUBILITY MODELING

    Directory of Open Access Journals (Sweden)

    Ratnawati Ratnawati

    2012-02-01

    Full Text Available A solid-supercritical fluid system is highly asymmetric in terms of the size and energy differences of the components. The key point in extending a cubic equation of state to such system is on the choice of proper mixing rules. New mixing rules for the Redlich-Kwong equation of state are developed. The developement is based on the statistical-mechanical theory of the van der Waals mixing rules. The Redlich Kwong equation of state with the proposed mixing rules along with the original ones is used to predict solubilities of solids in supercritical fluid. The prediction is done with kij equal zero, as well as with optimized kij.  The results show superiority of the proposed mixing rules over the original ones. For most of the systems considered, the proposed mixing rules with the kij equal zero are closer to the experimental data than the original ones do. For 28 systems with 521 data points taken from various sources, the original and the proposed mixing rules give the overall AAD of 13.4%, while the original mixing rules give 45.9%.

  5. Investigation on flow and mixing characteristics of supersonic mixing layer induced by forced vibration of cantilever

    Science.gov (United States)

    Zhang, Dongdong; Tan, Jianguo; Lv, Liang

    2015-12-01

    The mixing process has been an important issue for the design of supersonic combustion ramjet engine, and the mixing efficiency plays a crucial role in the improvement of the combustion efficiency. In the present study, nanoparticle-based planar laser scattering (NPLS), particle image velocimetry (PIV) and large eddy simulation (LES) are employed to investigate the flow and mixing characteristics of supersonic mixing layer under different forced vibration conditions. The indexes of fractal dimension, mixing layer thickness, momentum thickness and scalar mixing level are applied to describe the mixing process. Results show that different from the development and evolution of supersonic mixing layer without vibration, the flow under forced vibration is more likely to present the characteristics of three-dimensionality. The laminar flow region of mixing layer under forced vibration is greatly shortened and the scales of rolled up Kelvin-Helmholtz vortices become larger, which promote the mixing process remarkably. The fractal dimension distribution reveals that comparing with the flow without vibration, the turbulent fluctuation of supersonic mixing layer under forced vibration is more intense. Besides, the distribution of mixing layer thickness, momentum thickness and scalar mixing level are strongly influenced by forced vibration. Especially, when the forcing frequency is 4000 Hz, the mixing layer thickness and momentum thickness are 0.0391 m and 0.0222 m at the far field of 0.16 m, 83% and 131% higher than that without vibration at the same position, respectively.

  6. Subharmonic resonance in a mixing layer

    Science.gov (United States)

    Mansour, N. N.; Hussain, Fazle; Buell, J. C.

    1988-01-01

    The subharmonic resonance phenomenon in a spatially evolving mixing layer is studied using direct simulations of the 2-D Navier-Stokes equations. The computational domain extends to + or - infinity in the cross-stream direction with U(1) = 1.25 and U(2) = 0.25 imposed at + infinity and - infinity respectively. The domain is finite in the streamwise direction with inflow and outflow boundary conditions imposed at x/delta sub omega = 0 and 100, respectively. A hyperbolic-tangent mean velocity profile is assumed at the inlet and the Reynolds number based on the inlet vorticity thickness and velocity difference is Re = 600. It is observed that the phase angle between the fundamental and its subharmonic plays a key role in the spatial development of these modes. Contour plots of vorticity show that varying the phase will have a dramatic effect on the dynamics of the vortices. Pairing or shredding is observed depending on the phase. Fourier decomposition of the time traces show that the fundamental grows, saturates and decays with the downstream distance. The subharmonic has a similar behavior. However, the level at which the modes will saturate is affected by the phase. At 0 deg phase, it was found that as the fundamental saturates, the growth rate of the subharmonic is enhanced. At 90 deg phase, it was found that as the fundamental saturates, the growth rate of the subharmonic is inhibited. In the later case, the growth rate of the subharmonic recovers after saturation of the fundamental. These results are in qualitative agreement with experimental data.

  7. Nomogram for the height of the daytime mixed layer

    DEFF Research Database (Denmark)

    Nyren, K.; Gryning, Sven-Erik

    1999-01-01

    A method to construct a nomogram of the daytime mixed-layer-height evolution is presented. The nomogram will be specific for a given location and land surface type and is intended to be an easy tool to achieve a general understanding of mixed-layer behaviour. Also it is a pedagogical graphical one......-pager that displays the bulk of data that controls the evolution of the mixed layer. Nomograms from northern, central and southern Europe are presented and discussed. Comparison with data from two sites shows good agreement although the nomograms overestimated the mixing height when it was low....

  8. Absolute instability in viscoelastic mixing layers

    Science.gov (United States)

    Ray, Prasun K.; Zaki, Tamer A.

    2014-01-01

    The spatiotemporal linear stability of viscoelastic planar mixing layers is investigated. A one-parameter family of velocity profiles is used as the base state with the parameter, S, controlling the amount of shear and backflow. The influence of viscoelasticity in dilute polymer solutions is modeled with the Oldroyd-B and FENE-P constitutive equations. Both models require the specification of the ratio of the polymer-relaxation and convective time scales (the Weissenberg number, We) and the ratio of solvent and solution viscosities (β). The maximum polymer extensibility, L, must also be specified for the FENE-P model. We examine how the variation of these parameters along with the Reynolds number, Re, affects the minimum value of S at which the flow becomes locally absolutely unstable. With the Oldroyd-B model, the influence of viscoelasticity is shown to be almost fully captured by the elasticity, E^* equiv (1-β ) We/Re, and Scrit decreases as elasticity is increased, i.e., elasticity is destabilizing. A simple approximate dispersion relation obtained via long-wave asymptotic analysis is shown to accurately capture this destabilizing influence. Results obtained with the FENE-P model exhibit a rich variety of behavior. At large values of the extensibility, L, results are similar to those for the Oldroyd-B fluid as expected. However, when the extensibility is reduced to more realistic values (L ≈ 100), one must consider the scaled shear rate, η _c equiv We S/2L, in addition to the elasticity. When ηc is large, the base-state polymer stress obtained by the FENE-P model is reduced, and there is a corresponding reduction in the overall influence of viscoelasticity on stability. Additionally, elasticity exhibits a stabilizing effect which is driven by the streamwise-normal perturbation polymer stress. As ηc is reduced, the base-state and perturbation normal polymer stresses predicted by the FENE-P model move towards the Oldroyd-B values, and the destabilizing

  9. Structure of binary mixed polymer Langmuir layers

    NARCIS (Netherlands)

    Bernardini, C.

    2012-01-01

    The possibility of preparing 2D stable emulsions through mixing of homopolymers in a Langmuir monolayer is the core topic of this thesis. While colloid science has achieved well established results in the study of bulk dispersed systems, accounts on properties of mixed monomolecular films are fewer,

  10. Structure of binary mixed polymer Langmuir layers

    NARCIS (Netherlands)

    Bernardini, C.

    2012-01-01

    The possibility of preparing 2D stable emulsions through mixing of homopolymers in a Langmuir monolayer is the core topic of this thesis. While colloid science has achieved well established results in the study of bulk dispersed systems, accounts on properties of mixed monomolecular films are fewer,

  11. Analytical solution for the convectively-mixed atmospheric boundary layer

    NARCIS (Netherlands)

    Ouwersloot, H.G.; Vilà-Guerau de Arellano, J.

    2013-01-01

    Based on the prognostic equations of mixed-layer theory assuming a zeroth order jump at the entrainment zone, analytical solutions for the boundary-layer height evolution are derived with different degrees of accuracy. First, an exact implicit expression for the boundary-layer height for a situation

  12. Observations of mixed layer deepening during an Antarctic gale

    Science.gov (United States)

    Lane-Serff, G. F.; Stansfield, K. L.

    2013-03-01

    of mixed layer deepening made during a gale in February 2005 near an ice shelf, Fimbulisen, Antarctica, are reported. The observations were made from the RRS James Clark Ross in the lee of the ice shelf, using repeated downcasts ("yo-yo") of a conductivity-temperature-depth package, together with shipboard meteorological and other measurements. The mixed layer deepened from less than 40 m to over 120 m over the course of 27 h, with a very rapid deepening from 80 m to 120 m over a period of under 11 h. The mixed layer became both colder and fresher, with the change in salinity and heat content likely to be caused by melting ice. Oxygen isotope results suggest the source of the fresh water was melting sea ice rather than precipitation or ice shelf melt. The input of melt water at the surface stabilizes the mixed layer, so extra energy is required to deepen the mixed layer. The observations suggest that approximately 1.8% of the available "wind-work" energy was used to mix the upper water column, while the stabilizing surface buoyancy flux inhibits the turbulence in the mixed layer, limiting the mixing length to 1.6 m. The eventual depth of the mixed layer is in line with estimates based on the planetary length scale u*/f. The rate of mixed layer deepening is given by Ue/u* = 0.035. The apparent peak ice melting rate was approximately 60 mm hr-1, although this is likely to be exaggerated by convergence and downwelling.

  13. Effect of property variations on the mixing of turbulent supercritical water streams in a T-junction

    Energy Technology Data Exchange (ETDEWEB)

    Bu, L.; Zhao, J. [Centre for E-City, School of Electrical and Electronics Engineering, Nanyang Technological Univ., Singapore, 639798 (Singapore)

    2012-07-01

    The supercritical water mixing phenomenon is investigated with a wide range of conditions, i.e. the inlet temperature of the streams ranges from 323.15 K to 723.15 K and the pressure ranges from 25 MPa to 45 MPa. A sensitivity study is carried out for the jet and main flow velocity ratio (VR) which is varying from 1 to 40. In addition, the effect of the inject angles of branch flow to main flow on the mixing is conducted by varying the inject angle from 80 deg. to 100 deg.. The results show that the maximum temperature gradient appears on the wall of the upstream side in all the cases, and the inclined angles can be optimized to mitigate the thermal stress. (authors)

  14. On the appearance of a system of ring vortices in the mixing layer of axially symmetric turbulent jets under acoustic action

    Science.gov (United States)

    Pimshtein, V. G.

    2016-07-01

    The shadow visualization method is applied to study the process of loss of stability of the mixing layer of a subsonic axially symmetric turbulent jet under longitudinal internal action of saw-tooth sound waves of finite amplitude. Such action leads to the formation of a system of ring vortices in the mixing layer at the frequency of its intrinsic instability. The interaction of the vortices can be accompanied by sound emission. A similar phenomenon is also observed in turbulent jets for small supercritical pressure fluctuations on a nozzle.

  15. Nomogram for the height of the daytime mixed layer

    Energy Technology Data Exchange (ETDEWEB)

    Nyren, K. [Ericsson EriSoft AB, Umeaa (Sweden); Gryning, S.E. [Risoe National Lab., Roskilde (Denmark)

    1997-10-01

    We present a nomogram that provide information about the general behaviour of the mixed layer at a given location. The nomogram is meant to be a practical and easy to use tool to determine the height of the mixed layer for i.e. weather forecaster, air pollution studies and planning of meteorological experiments. Use of the nomogram is restricted to flat, relatively homogeneous terrain. Inhomogeneous terrain with patch scales of 10 km or more might create organised circulation like i.e. lake breezes. The data represented in the nomogram is computed using a meteorological preprocessor and climatological temperature data for the location. The nomogram is simplified but retain main physical processes that control the evolution of the mixed layer and can be easily constructed for any chosen location on land. Nomogram of the mixed layer behavior at the location of Cabauw, the Netherlands is shown and discussed. (au)

  16. Investigation of turbulent plane mixing layer using generalized differential quadrature

    Energy Technology Data Exchange (ETDEWEB)

    Basirat Tabrizi, H.; Rezaei Niya, S.M.; Fariborz, S.J. [Amirkabir Univ. of Tech., Mechanical Engineering Dept., Tehran (Iran, Islamic Republic of)]. E-mail: hbasirat@aut.ac.ir; H.Basirat@dal.ca

    2004-07-01

    There is considerable interest in two-dimensional turbulent mixing layer, to name a few e.g. nature, combustion chamber, premixers of gas turbine combustor and many other technological applications. There features are the presence of large vortical structure, free turbulent characteristics, asymptotic behavior, faster growth rate. Some of the parameters that are known to affect the mixing layer behavior are investigated through the numerical models and experimental analysis during these past decades. A suitable solution for turbulent plane mixing layer requires the use of variable mesh size and an appropriate discretization scheme. The Generalized Differential Quadrature (GDQ) method is utilized to solve the problem. It can be a tool for evaluating the equations obtained for plane mixing layer. The present approach works well by refining mesh size, simplifying the calculation algorithms and less time for calculation anticipated. The numerical simulation is compared with the reported numerical and experimental results of others. (author)

  17. Interannual variability of the tropical Indian Ocean mixed layer depth

    Digital Repository Service at National Institute of Oceanography (India)

    Keerthi, M.G.; Lengaigne, M.; Vialard, J.; Montegut, C.deB.; Muraleedharan, P.M.

    Interannual fluctuations of the mixed layer depth (MLD) in the tropical Indian Ocean are investigated from a long-term (1960-2007) eddy permitting numerical simulation and a new observational dataset built from hydrographic in situ data including...

  18. Modeling a Rain-Induced Mixed Layer

    Science.gov (United States)

    1990-06-01

    te -)-A-- e e -2)- . (7) ’&Z AZ Az D Using the exponential relations with trigonometry , equation (7) becomes, Ok n) 3 (I- cos2ikAz)+ D (1- cos ikAz...completely unknown because there are no prior studies which predict what portion of total energy may go into subsurface mixing. The biggest obstacle

  19. MHD Turbulent Mixing Layers: Equilibrium Cooling Models

    CERN Document Server

    Esquivel, A; Cho, J; Lazarian, A; Leitner, S N

    2006-01-01

    We present models of turbulent mixing at the boundaries between hot (T~10^{6-7} K) and warm material (T~10^4 K) in the interstellar medium, using a three-dimensional magnetohydrodynamical code, with radiative cooling. The source of turbulence in our simulations is a Kelvin-Helmholtz instability, produced by shear between the two media. We found, that because the growth rate of the large scale modes in the instability is rather slow, it takes a significant amount of time (~1 Myr) for turbulence to produce effective mixing. We find that the total column densities of the highly ionized species (C IV, N V, and O VI) per interface (assuming ionization equilibrium) are similar to previous steady-state non-equilibrium ionization models, but grow slowly from log N ~10^{11} to a few 10^{12} cm^{-2} as the interface evolves. However, the column density ratios can differ significantly from previous estimates, with an order of magnitude variation in N(C IV)/N(O VI) as the mixing develops.

  20. Constitutive behaviour of mixed mode loaded adhesive layer

    DEFF Research Database (Denmark)

    Högberg, J.L.; Sørensen, Bent F.; Stigh, U.

    2007-01-01

    in the failure process zone. The constitutive behaviour of the adhesive layer is obtained by a so called inverse method and fitting an existing mixed mode cohesive model, which uses a coupled formulation to describe a mode dependent constitutive behaviour. The cohesive parameters are determined by optimizing......Mixed mode testing of adhesive layer is performed with the Mixed mode double Cantilever Bean? specimen. During the experiments, the specimens are loaded by transversal and/or shear forces; seven different mode mixities are tested. The J-integral is used to evaluate the energy dissipation...

  1. Direct simulations of chemically reacting turbulent mixing layers, part 2

    Science.gov (United States)

    Metcalfe, Ralph W.; Mcmurtry, Patrick A.; Jou, Wen-Huei; Riley, James J.; Givi, Peyman

    1988-01-01

    The results of direct numerical simulations of chemically reacting turbulent mixing layers are presented. This is an extension of earlier work to a more detailed study of previous three dimensional simulations of cold reacting flows plus the development, validation, and use of codes to simulate chemically reacting shear layers with heat release. Additional analysis of earlier simulations showed good agreement with self similarity theory and laboratory data. Simulations with a two dimensional code including the effects of heat release showed that the rate of chemical product formation, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release. Subsequent three dimensional simulations showed similar behavior, in agreement with laboratory observations. Baroclinic torques and thermal expansion in the mixing layer were found to produce changes in the flame vortex structure that act to diffuse the pairing vortices, resulting in a net reduction in vorticity. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers were shown to result from vorticity generation by baroclinic torques.

  2. Prediction of dynamic and mixing characteristics of drop-laden mixing layers using DNS and LES

    Science.gov (United States)

    Okong'o, N.; Leboissetier, A.; Bellan, J.

    2004-01-01

    Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) have been conducted of a temporal mixing layer laden with evaporating drops, in order to assess the ability of LES to reproduce dynamic and mixing aspects of the DNS which affect combustion, independently of combustion models.

  3. Thin TaC layer produced by ion mixing

    DEFF Research Database (Denmark)

    Barna, Árpád; Kotis, László; Pécz, Béla

    2012-01-01

    Ion-beam mixing in C/Ta layered systems was investigated. C 8nm/Ta 12nm and C 20nm/Ta 19nm/C 20nm layer systems were irradiated by Ga+ ions of energy in the range of 2–30keV. In case of the 8nm and 20nm thick C cover layers applying 5–8keV and 20–30keV Ga+ ion energy, respectively resulted...... in strongly asymmetric ion mixing; the carbon was readily transported to the Ta layer, while the reverse process was much weaker. Because of the asymmetrical transport the C/TaC interface remained sharp independently from the applied fluence. The carbon transported to the Ta layer formed Ta......Cx. The stoichiometry of the carbide produced varied along the depth. The TaCx layer contained implanted Ga, the concentration of which decreased with increasing depth. The thickness of the TaCx layer could be tailored by the ion fluence and energy making possible to produce coating layer of desired thickness....

  4. Speed of sound measurements and mixing characterization of underexpanded fuel jets with supercritical reservoir condition using laser-induced thermal acoustics

    Science.gov (United States)

    Baab, S.; Förster, F. J.; Lamanna, G.; Weigand, B.

    2016-11-01

    The four-wave mixing technique laser-induced thermal acoustics was used to measure the local speed of sound in the farfield zone of extremely underexpanded jets. N-hexane at supercritical injection temperature and pressure (supercritical reservoir condition) was injected into quiescent subcritical nitrogen (with respect to the injectant). The technique's capability to quantify the nonisothermal, turbulent mixing zone of small-scale jets is demonstrated for the first time. Consistent radially resolved speed of sound profiles are presented for different axial positions and varying injection temperatures. Furthermore, an adiabatic mixing model based on nonideal thermodynamic properties is presented to extract mixture composition and temperature from the experimental speed of sound data. High fuel mass fractions of up to 94 % are found for the centerline at an axial distance of 55 diameters from the nozzle followed by a rapid decay in axial direction. This is attributed to a supercritical fuel state at the nozzle exit resulting in the injection of a high-density fluid. The obtained concentration data are complemented by existing measurements and collapsed in a similarity law. It allows for mixture prediction of underexpanded jets with supercritical reservoir condition provided that nonideal thermodynamic behavior is considered for the nozzle flow. Specifically, it is shown that the fuel concentration in the farfield zone is very sensitive to the thermodynamic state at the nozzle exit. Here, a transition from supercritical fluid to subcritical vapor state results in strongly varying fuel concentrations, which implies high impact on the mixture formation and, consequently, on the combustion characteristics.

  5. The sensitivity of stratocumulus-capped mixed layers to cloud droplet concentration: do LES and mixed-layer models agree?

    Directory of Open Access Journals (Sweden)

    J. Uchida

    2010-05-01

    Full Text Available The sensitivity of a stratocumulus-capped mixed layer to a change in cloud droplet concentration is evaluated with a large-eddy simulation (LES and a mixed layer model (MLM. The strength of the second aerosol indirect effect simulated by the two model types agrees within 50% for cases in which the LES-simulated boundary layer remains well mixed, if the MLM entrainment closure includes the effects of cloud droplet sedimentation.

    To achieve this agreement, parameters in the MLM entrainment closure and the drizzle parameterization must be retuned to match the LES. This is because the LES advection scheme and microphysical parameterization significantly bias the entrainment rate and precipitation profile compared to observational best guesses. Before this modification, the MLM simulates more liquid water path and much more drizzle at a given droplet concentration than the LES and is more sensitive to droplet concentration, even undergoing a drizzle-induced boundary layer collapse at low droplet concentrations. After this modification, both models predict a comparable decrease of cloud liquid water path as droplet concentration increases, cancelling 30–50% of the Twomey effect for our case. The agreement breaks down at the lowest simulated droplet concentrations, for which the boundary layer in the LES is not well mixed.

    Our results highlight issues with both types of model. Potential LES biases due to inadequate resolution, subgrid mixing and parameterized microphysics must be carefully considered when trying to make a quantitative inference of the second indirect effect from an LES of a stratocumulus-topped boundary layer. On the other hand, even slight internal decoupling of the boundary layer invalidates the central assumption of an MLM, substantially limiting the range of conditions that MLM-predicted sensitivities to droplet concentration are meaningful.

  6. The sensitivity of stratocumulus-capped mixed layers to cloud droplet concentration: do LES and mixed-layer models agree?

    Directory of Open Access Journals (Sweden)

    P. N. Blossey

    2009-12-01

    Full Text Available The sensitivity of a stratocumulus-capped mixed layer to a change in cloud droplet concentration is evaluated with a large-eddy simulation (LES and a mixed layer model (MLM, to see if the two model types agree on the strength of the second aerosol indirect effect. Good agreement can be obtained if the MLM entrainment closure explicitly reduces entrainment efficiency proportional to the rate of cloud droplet sedimentation at cloud top for cases in which the LES-simulated boundary layer remains well mixed, with a single peak in the vertical profile of vertical velocity variance.

    To achieve this agreement, the MLM entrainment closure and the drizzle parameterization must be modified from their observationally-based defaults. This is because the LES advection scheme and microphysical parameterization significantly bias the entrainment rate and precipitation profile compared to observational best guesses. Before this modification, the MLM simulates more liquid water path and much more drizzle at a given droplet concentration than the LES and is more sensitive to droplet concentration, even undergoing a drizzle-induced boundary layer collapse at low droplet concentrations. After this modification, both models predict a similar decrease of cloud liquid water path as droplet concentration increases, cancelling 30–50% of the Twomey effect for our case. The agreement breaks down at the lowest simulated droplet concentrations, for which the boundary layer in the LES is not well mixed.

    Our results highlight issues with both types of model. Potential LES biases due to inadequate resolution, subgrid mixing and microphysics must be carefully considered when trying to make a quantitative inference of the second indirect effect from an LES of a stratocumulus-topped boundary layer. On the other hand, even slight internal decoupling of the boundary layer invalidates MLM-predicted sensitivity to droplet concentrations.

  7. Multiresolution analysis of density fluctuation in supersonic mixing layer

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Due to the difficulties in measuring supersonic density field, the multiresolution analysis of supersonic mixing layer based on experimental images is still a formidable challenge. By utilizing the recently developed nanoparticle based planar laser scattering method, the density field of a supersonic mixing layer was measured at high spatiotemporal resolution. According to the dynamic behavior of coherent structures, the multiresolution characteristics of density fluctuation signals and density field images were studied based on Taylor’s hypothesis of space-time conversion and wavelet analysis. The wavelet coefficients reflect the characteristics of density fluctuation signals at different scales, and the detailed coefficients reflect the differences of approximation at adjacent levels. The density fluctuation signals of supersonic mixing layer differ from the periodic sine signal and exhibit similarity to the fractal Koch signal. The similarity at different scales reveals the fractal characteristic of mixing layer flowfield. The two-dimensional wavelet decomposition and reconstruction of density field images extract the approximate and detailed signals at different scales, which effectively resolve the characteristic structures of the flowfield at different scales.

  8. The Total Energy Flux Leaving the Ocean's Mixed Layer

    NARCIS (Netherlands)

    Rimac, Antonija; von Storch, Jin-Song; Eden, Carsten

    2016-01-01

    The total energy flux leaving the ocean’s spatially and seasonally varying mixed layer is estimated using a global ⅝1/10° ocean general circulation model. From the total wind-power input of 3.33 TW into near-inertial waves (0.35 TW), subinertial fluctuations (0.87 TW), and the time-mean circulation

  9. Mixed mosaic membranes prepared by layer-by-layer assembly for ionic separations.

    Science.gov (United States)

    Rajesh, Sahadevan; Yan, Yu; Chang, Hsueh-Chia; Gao, Haifeng; Phillip, William A

    2014-12-23

    Charge mosaic membranes, which possess distinct cationic and anionic domains that traverse the membrane thickness, are capable of selectively separating dissolved salts from similarly sized neutral solutes. Here, the generation of charge mosaic membranes using facile layer-by-layer assembly methodologies is reported. Polymeric nanotubes with pore walls lined by positively charged polyethylenimine moieties or negatively charged poly(styrenesulfonate) moieties were prepared via layer-by-layer assembly using track-etched membranes as sacrificial templates. Subsequently, both types of nanotubes were deposited on a porous support in order to produce mixed mosaic membranes. Scanning electron microscopy demonstrates that the facile deposition techniques implemented result in nanotubes that are vertically aligned without overlap between adjacent elements. Furthermore, the nanotubes span the thickness of the mixed mosaic membranes. The effects of this unique nanostructure are reflected in the transport characteristics of the mixed mosaic membranes. The hydraulic permeability of the mixed mosaic membranes in piezodialysis operations was 8 L m(-2) h(-1) bar(-1). Importantly, solute rejection experiments demonstrate that the mixed mosaic membranes are more permeable to ionic solutes than similarly sized neutral molecules. In particular, negative rejection of sodium chloride is observed (i.e., the concentration of NaCl in the solution that permeates through a mixed mosaic membrane is higher than in the initial feed solution). These properties illustrate the ability of mixed mosaic membranes to permeate dissolved ions selectively without violating electroneutrality and suggest their utility in ionic separations.

  10. Measurements of Molecular Mixing in a High Schmidt Number Rayleigh-Taylor Mixing Layer

    Energy Technology Data Exchange (ETDEWEB)

    Mueschke, N J; Schilling, O; Youngs, D L; Andrews, M

    2007-12-03

    Molecular mixing measurements are performed for a high Schmidt number (Sc {approx} 10{sup 3}), small Atwood number (A {approx} 7.5 x 10{sup -4}) buoyancy-driven turbulent Rayleigh-Taylor mixing layer in a water channel facility. Salt was added to the top stream to create the desired density difference. The degree of molecular mixing was measured as a function of time by monitoring a diffusion-limited chemical reaction between the two fluid streams. The pH of each stream was modified by the addition of acid or alkali such that a local neutralization reaction occurred as the two fluids molecularly mixed. The progress of this neutralization reaction was tracked by the addition of phenolphthalein - a pH-sensitive chemical indicator - to the acidic stream. Accurately calibrated backlit optical techniques were used to measure the average concentration of the colored chemical indicator. Comparisons of chemical product formation for pre-transitional buoyancy- and shear-driven mixing layers are given. It is also shown that experiments performed at different equivalence ratios (acid/alkali concentration) can be combined to obtain a mathematical relationship between the colored product formed and the density variance. This relationship was used to obtain high-fidelity, quantitative measures of the degree of molecular mixing which are independent of probe resolution constraints. The dependence of such mixing parameters on the Schmidt and Reynolds numbers is examined by comparing the current Sc {approx} 10{sup 3} measurements with Sc = 0.7 gas-phase and Pr = 7 liquid-phase measurements. This comparison indicates that the Schmidt number has a large effect on the bulk quantity of mixed fluid at small Reynolds numbers Re{sub h} < 10{sup 3}. At late times, all mixing parameters indicated a greater degree of molecular mixing and a decreased Schmidt number dependence. Implications for the development and quantitative assessment of turbulent transport and mixing models appropriate for

  11. Turbulent correlation measurements in a two-stream mixing layer.

    Science.gov (United States)

    Jones, B. G.; Planchon, H. P.; Hammersley, R. J.

    1973-01-01

    Two point space-time measurements of the axial component of fluctuating velocity were made using linearized hot-wire anemometry. Space scales, convected frame correlations and time scales, and convection velocities in the shear layer were evaluated. Both filtered narrow and broad band convected frame autocorrelations were determined. Differences between axial broad band convection velocities and both mean turbulence and mean entrained fluid velocities were observed. Scaled broad band convection velocities for the mixing layer and simple round jets were found to collapse to a common curve. Axial narrow band convection velocities showed strong frequency and transverse position dependence.

  12. Dexamethasone-loaded poly(ε-caprolactone)/silica nanoparticles composites prepared by supercritical CO2 foaming/mixing and deposition.

    Science.gov (United States)

    de Matos, M B C; Piedade, A P; Alvarez-Lorenzo, C; Concheiro, A; Braga, M E M; de Sousa, H C

    2013-11-18

    A supercritical carbon dioxide (scCO2)-assisted foaming/mixing method (SFM) was implemented for preparing dexamethasone (DXMT)-loaded poly(ε-caprolactone)/silica nanoparticles (PCL/SNPs) composite materials suitable for bone regeneration. The composites were prepared from PCL and mesoporous SNPs (MCM-41/SBA-15) by means of scCO2-assisted SFM at several operational pressures, processing times and depressurization conditions. DXMT was loaded into SNPs (applying a scCO2 solvent impregnation/deposition method - SSID) and into PCL/SNPs composites (using the SFM method). The effects of the employed operational and compositional variables on the physicochemical and morphological features as well as in the in vitro release profiles of DXMT were analyzed in detail. This work demonstrates that the above-referred scCO2-based methods can be very useful for the preparation of DXMT-loaded PCL/SNPs composites with tunable physicochemical, thermomechanical, morphological and drug release properties and suitable for hard-tissue regeneration applications.

  13. A flow control study of a supersonic mixing layer via NPLS

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The flow control of a supersonic mixing layer was studied in a supersonic mixing layer wind tunnel with convective Mach number (Mc) at 0.5. The passive control of the mixing layer was achieved by perturbation tapes on the trailing edge of the splitter plate. The control effects of 2D and 3D perturbation tapes with different sizes were compared. The mixing layer was visualized via NPLS,and the transient fine structures were identifiable in NPLS images,which were used to analyze the effects of flow control. The results show that the 2D tapes can enhance the 2D characteristic of the mixing layer,delaying mixing layer transition; and the 3D tapes can enhance the 3D characteristic of the mixing layer,advancing mixing layer transition. 3D structures of the mixing layer were visualized,and the H-type Λ vortexes were found with 3D tapes control.

  14. Comparison of mixed layer models predictions with experimental data

    Energy Technology Data Exchange (ETDEWEB)

    Faggian, P.; Riva, G.M. [CISE Spa, Divisione Ambiente, Segrate (Italy); Brusasca, G. [ENEL Spa, CRAM, Milano (Italy)

    1997-10-01

    The temporal evolution of the PBL vertical structure for a North Italian rural site, situated within relatively large agricultural fields and almost flat terrain, has been investigated during the period 22-28 June 1993 by experimental and modellistic point of view. In particular, the results about a sunny day (June 22) and a cloudy day (June 25) are presented in this paper. Three schemes to estimate mixing layer depth have been compared, i.e. Holzworth (1967), Carson (1973) and Gryning-Batchvarova models (1990), which use standard meteorological observations. To estimate their degree of accuracy, model outputs were analyzed considering radio-sounding meteorological profiles and stability atmospheric classification criteria. Besides, the mixed layer depths prediction were compared with the estimated values obtained by a simple box model, whose input requires hourly measures of air concentrations and ground flux of {sup 222}Rn. (LN)

  15. Nonmixing layers

    Science.gov (United States)

    Gaillard, Pierre; Giovangigli, Vincent; Matuszewski, Lionel

    2016-12-01

    We investigate the impact of nonideal diffusion on the structure of supercritical cryogenic binary mixing layers. This situation is typical of liquid fuel injection in high-pressure rocket engines. Nonideal diffusion has a dramatic impact in the neighborhood of chemical thermodynamic stability limits where the components become quasi-immiscible and ultimately form a nonmixing layer. Numerical simulations are performed for mixing layers of H2 and N2 at a pressure of 100 atm and temperature around 120-150 K near chemical thermodynamic stability limits.

  16. Supercritical carbon dioxide-assisted rapid synthesis of few-layer black phosphorus for hydrogen peroxide sensing.

    Science.gov (United States)

    Yan, Shancheng; Wang, Bojun; Wang, Zhulan; Hu, Dong; Xu, Xin; Wang, Junzhuan; Shi, Yi

    2016-06-15

    Solutions with large-scale dispersions of 2D black phosphorus (BP), often referred to as phosphorene, are obtained through solvent exfoliation. But, rapid phosphorene synthesis remains a challenge. Furthermore, although the chemical sensing capability of BP-based sensors has been theoretically predicted, its experimental verification remains lacking. In this study, we demonstrate the use of supercritical carbon dioxide-assisted rapid synthesis (5h) of few-layer BP. In addition, we construct a non-enzymatic hydrogen peroxide (H2O2) sensor based on few-layer BP for the first time to utilize BP degradation under ambient conditions. The proposed H2O2 sensor exhibits a considerably lower detection limit of 1 × 10(-7) M compared with the general detection limit of 1 × 10(-7) M-5 × 10(-5)M via electrochemical methods. Overall, the results of this study will not only expand the coverage of BP research but will also identify the important sensing characteristics of BP.

  17. DNS and LES of a Shear-Free Mixing Layer

    Science.gov (United States)

    Knaepen, B.; Debliquy, O.; Carati, D.

    2003-01-01

    The purpose of this work is twofold. First, given the computational resources available today, it is possible to reach, using DNS, higher Reynolds numbers than in Briggs et al.. In the present study, the microscale Reynolds numbers reached in the low- and high-energy homogeneous regions are, respectively, 32 and 69. The results reported earlier can thus be complemented and their robustness in the presence of increased turbulence studied. The second aim of this work is to perform a detailed and documented LES of the shear-free mixing layer. In that respect, the creation of a DNS database at higher Reynolds number is necessary in order to make meaningful LES assessments. From the point of view of LES, the shear-free mixing-layer is interesting since it allows one to test how traditional LES models perform in the presence of an inhomogeneity without having to deal with difficult numerical issues. Indeed, as argued in Briggs et al., it is possible to use a spectral code to study the shear-free mixing layer and one can thus focus on the accuracy of the modelling while avoiding contamination of the results by commutation errors etc. This paper is organized as follows. First we detail the initialization procedure used in the simulation. Since the flow is not statistically stationary, this initialization procedure has a fairly strong influence on the evolution. Although we will focus here on the shear-free mixing layer, the method proposed in the present work can easily be used for other flows with one inhomogeneous direction. The next section of the article is devoted to the description of the DNS. All the relevant parameters are listed and comparison with the Veeravalli & Warhaft experiment is performed. The section on the LES of the shear-free mixing layer follows. A detailed comparison between the filtered DNS data and the LES predictions is presented. It is shown that simple eddy viscosity models perform very well for the present test case, most probably because the

  18. Electrochemistry in supercritical fluids

    Science.gov (United States)

    Branch, Jack A.; Bartlett, Philip N.

    2015-01-01

    A wide range of supercritical fluids (SCFs) have been studied as solvents for electrochemistry with carbon dioxide and hydrofluorocarbons (HFCs) being the most extensively studied. Recent advances have shown that it is possible to get well-resolved voltammetry in SCFs by suitable choice of the conditions and the electrolyte. In this review, we discuss the voltammetry obtained in these systems, studies of the double-layer capacitance, work on the electrodeposition of metals into high aspect ratio nanopores and the use of metallocenes as redox probes and standards in both supercritical carbon dioxide–acetonitrile and supercritical HFCs. PMID:26574527

  19. Electrochemistry in supercritical fluids.

    Science.gov (United States)

    Branch, Jack A; Bartlett, Philip N

    2015-12-28

    A wide range of supercritical fluids (SCFs) have been studied as solvents for electrochemistry with carbon dioxide and hydrofluorocarbons (HFCs) being the most extensively studied. Recent advances have shown that it is possible to get well-resolved voltammetry in SCFs by suitable choice of the conditions and the electrolyte. In this review, we discuss the voltammetry obtained in these systems, studies of the double-layer capacitance, work on the electrodeposition of metals into high aspect ratio nanopores and the use of metallocenes as redox probes and standards in both supercritical carbon dioxide-acetonitrile and supercritical HFCs.

  20. Design and calibration of the mixing layer and wind tunnel

    Science.gov (United States)

    Bell, James H.; Mehta, Rabindra D.

    1989-01-01

    A detailed account of the design, assembly and calibration of a wind tunnel specifically designed for free-shear layer research is contained. The construction of this new facility was motivated by a strong interest in the study of plane mixing layers with varying initial and operating conditions. The Mixing Layer Wind tunnel is located in the Fluid Mechanics Laboratory at NASA Ames Research Center. The tunnel consists of two separate legs which are driven independently by centrifugal blowers connected to variable speed motors. The blower/motor combinations are sized such that one is smaller than the other, giving maximum flow speeds of about 20 and 40 m/s, respectively. The blower speeds can either be set manually or via the Microvax II computer. The two streams are allowed to merge in the test section at the sharp trailing edge of a slowly tapering splitter plate. The test section is 36 cm in the cross-stream direction, 91 cm in the spanwise direction and 366 cm in length. One test section side-wall is slotted for probe access and adjustable so that the streamwise pressure gradient may be controlled. The wind tunnel is also equipped with a computer controlled, three-dimensional traversing system which is used to investigate the flow fields with pressure and hot-wire instrumentation. The wind tunnel calibration results show that the mean flow in the test section is uniform to within plus or minus 0.25 pct and the flow angularity is less than 0.25 deg. The total streamwise free-stream turbulence intensity level is approximately 0.15 pct. Currently the wind tunnel is being used in experiments designed to study the three-dimensional structure of plane mixing layers and wakes.

  1. Transient evolution and high stratification scaling in horizontal mixing layers

    Science.gov (United States)

    Arratia, C.; Ortiz, S.; Chomaz, J. M.

    Mixing layers (sheared flows in homogeneous or stratified fluid) are present in many geophysical contexts and may lead to turbulence and mixing. In several cases, mixing layers are known to exhibit the Kelvin-Helmholtz instability leading to the roll-up of spanwise vortices, the Kelvin-Helmholtz (KH) billows. This is an essentially two-dimensional (2D) process. In fact, in the homogeneous cases the Squire's theorem implies that the most unstable mode is 2D. However, Squire's theorem applies only for the exponentially growing perturbations that control the large time dynamics and is not valid for the transient dynamics at short time. Indeed, Iams et al.[1] have shown that, in the non-stratified case, the most amplified optimal perturbations for short times are three-dimensional (3D) and result from a cooperation between the lift-up and Orr mechanisms[2]. This provides a finite time mechanism for spanwise scale selection, scale that may persist at later times if nonlinearities are strong enough.

  2. Fluctuations of a passive scalar in a turbulent mixing layer

    KAUST Repository

    Attili, Antonio

    2013-09-19

    The turbulent flow originating downstream of the Kelvin-Helmholtz instability in a mixing layer has great relevance in many applications, ranging from atmospheric physics to combustion in technical devices. The mixing of a substance by the turbulent velocity field is usually involved. In this paper, a detailed statistical analysis of fluctuations of a passive scalar in the fully developed region of a turbulent mixing layer from a direct numerical simulation is presented. Passive scalar spectra show inertial ranges characterized by scaling exponents −4/3 and −3/2 in the streamwise and spanwise directions, in agreement with a recent theoretical analysis of passive scalar scaling in shear flows [Celani et al., J. Fluid Mech. 523, 99 (2005)]. Scaling exponents of high-order structure functions in the streamwise direction show saturation of intermittency with an asymptotic exponent ζ∞=0.4 at large orders. Saturation of intermittency is confirmed by the self-similarity of the tails of the probability density functions of the scalar increments at different scales r with the scaling factor r−ζ∞ and by the analysis of the cumulative probability of large fluctuations. Conversely, intermittency saturation is not observed for the spanwise increments and the relative scaling exponents agree with recent results for homogeneous isotropic turbulence with mean scalar gradient. Probability density functions of the scalar increments in the three directions are compared to assess anisotropy.

  3. Simulated seasonal and interannual variability of mixed layer heat budget in the northern Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    DeBoyer Montegut, C.; Vialard, J.; Shenoi, S.S.C.; Shankar, D.; Durand, F.; Ethe, C.; Madec, G.

    A global Ocean General Circulation Model (OGCM) is used to investigate the mixed layer heat budget of the Northern Indian Ocean (NIO). The model is validated against observations and shows a fairly good agreement with mixed layer depth data...

  4. Supercritical water

    CERN Document Server

    Marcus, Yizhak

    2012-01-01

    Discover the many new and emerging applications of supercritical water as a green solvent Drawing from thousands of original research articles, this book reviews and summarizes what is currently known about the properties and uses of supercritical water. In particular, it focuses on new and emerging applications of supercritical water as a green solvent, including the catalytic conversion of biomass into fuels and the oxidation of hazardous materials. Supercritical Water begins with an introduction that defines supercritical fluids in general. It then defines supercritical wa

  5. Linear models for sound from supersonic reacting mixing layers

    Science.gov (United States)

    Chary, P. Shivakanth; Samanta, Arnab

    2016-12-01

    We perform a linearized reduced-order modeling of the aeroacoustic sound sources in supersonic reacting mixing layers to explore their sensitivities to some of the flow parameters in radiating sound. Specifically, we investigate the role of outer modes as the effective flow compressibility is raised, when some of these are expected to dominate over the traditional Kelvin-Helmholtz (K-H) -type central mode. Although the outer modes are known to be of lesser importance in the near-field mixing, how these radiate to the far-field is uncertain, on which we focus. On keeping the flow compressibility fixed, the outer modes are realized via biasing the respective mean densities of the fast (oxidizer) or slow (fuel) side. Here the mean flows are laminar solutions of two-dimensional compressible boundary layers with an imposed composite (turbulent) spreading rate, which we show to significantly alter the growth of instability waves by saturating them earlier, similar to in nonlinear calculations, achieved here via solving the linear parabolized stability equations. As the flow parameters are varied, instability of the slow modes is shown to be more sensitive to heat release, potentially exceeding equivalent central modes, as these modes yield relatively compact sound sources with lesser spreading of the mixing layer, when compared to the corresponding fast modes. In contrast, the radiated sound seems to be relatively unaffected when the mixture equivalence ratio is varied, except for a lean mixture which is shown to yield a pronounced effect on the slow mode radiation by reducing its modal growth.

  6. Simulation of the convective mixed layer in Athens

    Energy Technology Data Exchange (ETDEWEB)

    Frank, H.P. [Risoe National Lab., Roskilde (Denmark)

    1997-10-01

    The region of Athens, Greece, has a highly complicated terrain with irregular coastline and mountains next to the sea. This results in complex flow fields. A case study of a simulation of a sea breeze with the Karlsruhe Atmospheric Mesoscale model KAMM is presented together with remarks on the advection of mixed layer air. The valley of Athens is open to the sea towards the south-west and surrounded by mountains on the other sides. Gaps between the mountains channel the flow into the valley. Simulations were done for 14 September 1994 to compare them with measurements at 6 masts by Risoe during the MEDCAPHOT-TRACE experiment. (au)

  7. Effect of mixed layer crystallinity on the performance of mixed heterojunction organic photovoltaic cells.

    Science.gov (United States)

    Song, Byeongseop; Rolin, Cedric; Zimmerman, Jeramy D; Forrest, Stephen R

    2014-05-01

    Organic vapor-phase deposition (OVPD) is used to grow tetraphenyldibenzoperiflanthen (DBP):C70 mixed heterojunction photovoltaic devices. Compared with vacuum thermal evaporation (VTE), the OVPD-grown film develops nanocrystalline domains of C70. Optimized OVPD-grown OPVs have a 61% fill factor for a 100 nm active layer thickness, whereas VTE-grown devices have a 47% fill factor at the same thickness.

  8. Statistics of High Atwood Number Turbulent Mixing Layers

    Science.gov (United States)

    Baltzer, Jon; Livescu, Daniel

    2015-11-01

    The statistical properties of incompressible shear-driven planar mixing layers between two miscible streams of fluids with different densities are investigated by means of Direct Numerical Simulations. The simulations begin from a thin interface perturbed by a thin broadband random disturbance, and the mixing layers are allowed to develop to self-similar states. The temporal simulations are performed in unprecedented domain sizes, with grid sizes up to 6144 x 2048 x 1536, which allows turbulent structures to grow and merge naturally. This allows the flow to reach states far-removed from the initial disturbances, thereby enabling high-quality statistics to be obtained for higher moments, pdfs, and other quantities critical to developing closure models. A wide range of Atwood numbers are explored, ranging from nearly constant density to At=0.87. The consequences of increasing the density contrast are investigated for global quantities, such as growth rates, and asymmetries that form in statistical profiles. Additional simulations in smaller domains are performed to study the effects of domain size.

  9. Bending elasticity of charged surfactant layers: the effect of mixing.

    Science.gov (United States)

    Bergström, L Magnus

    2006-08-01

    Expressions have been derived from which the spontaneous curvature (H(0)), bending rigidity (k(c)), and saddle-splay constant (k(c)) of mixed monolayers and bilayers may be calculated from molecular and solution properties as well as experimentally available quantities such as the macroscopic hydrophobic-hydrophilic interfacial tension. Three different cases of binary surfactant mixtures have been treated in detail: (i) mixtures of an ionic and a nonionic surfactant, (ii) mixtures of two oppositely charged surfactants, and (iii) mixtures of two ionic surfactants with identical headgroups but different tail volumes. It is demonstrated that k(c)H(0), k(c), and k(c) for mixtures of surfactants with flexible tails may be subdivided into one contribution that is due to bending properties of an infinitely thin surface as calculated from the Poisson-Boltzmann mean field theory and one contribution appearing as a result of the surfactant film having a finite thickness with the surface of charge located somewhat outside the hydrophobic-hydrophilic interface. As a matter of fact, the picture becomes completely different as finite layer thickness effects are taken into account, and as a result, the spontaneous curvature is extensively lowered whereas the bending rigidity is raised. Furthermore, an additional contribution to k(c) is present for surfactant mixtures but is absent for k(c)H(0) and k(c). This contribution appears as a consequence of the minimization of the free energy with respect to the composition of a surfactant layer that is open in the thermodynamic sense and must always be negative (i.e., k(c) is generally found to be brought down by the process of mixing two or more surfactants). The magnitude of the reduction of k(c) increases with increasing asymmetry between two surfactants with respect to headgroup charge number and tail volume. As a consequence, the bending rigidity assumes the lowest values for layers formed in mixtures of two oppositely charged

  10. Inertial particles in a shearless mixing layer: direct numerical simulations

    Science.gov (United States)

    Ireland, Peter; Collins, Lance

    2010-11-01

    Entrainment, the drawing in of external fluid by a turbulent flow, is present in nearly all turbulent processes, from exhaust plumes to oceanic thermoclines to cumulus clouds. While the entrainment of fluid and of passive scalars in turbulent flows has been studied extensively, comparatively little research has been undertaken on inertial particle entrainment. We explore entrainment of inertial particles in a shearless mixing layer across a turbulent-non-turbulent interface (TNI) and a turbulent-turbulent interface (TTI) through direct numerical simulation (DNS). Particles are initially placed on one side of the interface and are advanced in time in decaying turbulence. Our results show that the TTI is more efficient in mixing droplets than the TNI. We also find that without the influence of gravity, over the range of Stokes numbers present in cumulus clouds, particle concentration statistics are essentially independent of the dissipation scale Stokes number. The DNS data agrees with results from experiments performed in a wind tunnel with close parametric overlap. We anticipate that a better understanding of the role of gravity and turbulence in inertial particle entrainment will lead to improved cloud evolution predictions and more accurate climate models. Sponsored by the U.S. NSF.

  11. Three dimensional chaotic advection by mixed layer baroclinic instabilities

    CERN Document Server

    Mukiibi, Daniel; Serra, Nuno

    2015-01-01

    Three dimensional (3D) Finite Time Lyapunov Exponents (FTLEs) are computed from numerical simulations of a freely evolving mixed layer (ML) front in a zonal channel undergoing baroclinic instability. The 3D FTLEs show a complex structure, with features that are less defined than the two-dimensional (2D) FTLEs, suggesting that stirring is not confined to the edges of vortices and along filaments and posing significant consequences on mixing. The magnitude of the FTLEs is observed to be strongly determined by the vertical shear. A scaling law relating the local FTLEs and the nonlocal density contrast used to initialize the ML front is derived assuming thermal wind balance. The scaling law only converges to the values found from the simulations within the pycnocline, while it displays differences within the ML, where the instabilities show a large ageostrophic component. The probability distribution functions of 2D and 3D FTLEs are found to be non Gaussian at all depths. In the ML, the FTLEs wavenumber spectra d...

  12. Turbulent Mixing Layer Control using Ns-DBD Plasma Actuators

    Science.gov (United States)

    Singh, Ashish; Little, Jesse

    2016-11-01

    A low speed turbulent mixing layer (Reθo =1282, U1 /U2 = 0 . 28 and U2 = 11 . 8 m / s) is subject to nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation. The forcing frequency corresponds to a Strouhal number (St) of 0.032 which is the most amplified frequency based on stability theory. Flow response is studied as a function of the pulse energy, the energy input time scale (carrier frequency) and the duration of actuation (duty cycle). It is found that successful actuation requires a combination of forcing parameters. An evaluation of the forcing efficacy is achieved by examining different flow quantities such as momentum thickness, vorticity and velocity fluctuations. In accordance with past work, a dependence is found between the initial shear layer thickness and the energy coupled to the flow. More complex relationships are also revealed such as a limitation on the maximum pulse energy which yields control. Also, the pulse energy and the carrier frequency (inverse of period between successive pulses) are interdependent whereby an optimum exists between them and extreme values of either parameter is inconsonant with the control desired. These observations establish a rich and complex process behind ns-DBD plasma actuation. Air Force Office of Scientific Research (FA9550-12-1-0044).

  13. Laboratory simulations of the atmospheric mixed-layer in flow over complex topography

    Science.gov (United States)

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundar...

  14. Relative contributions of temperature and salinity to seasonal mixed layer density changes and horizontal density gradients

    OpenAIRE

    Johnson, Gregory C.; Schmidtko, Sunke; Lyman, John M.

    2012-01-01

    Temperature and salinity both contribute to ocean density, including its seasonal cycle and spatial patterns in the mixed layer. Temperature and salinity profiles from the Argo Program allow construction and analysis of a global, monthly, mixed layer climatology. Temperature changes dominate the seasonal cycle of mixed layer density in most regions, but salinity changes are dominant in the tropical warm pools, Arctic, and Antarctic. Under the Intertropical Convergence Zone, temperature and sa...

  15. Laboratory simulations of the atmospheric mixed layer in flow over complex terrain

    Data.gov (United States)

    U.S. Environmental Protection Agency — A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the...

  16. Chlorophyll modulation of mixed layer thermodynamics in a mixed-layer isopycnal general circulation model - An example from Arabian Sea and Equatorial Pacific

    Digital Repository Service at National Institute of Oceanography (India)

    Nakamoto, S.; PrasannaKumar, S.; Oberhuber, J.M.; Saito, H.; Muneyama, K.

    in the ocean isopycnal general circulation model (OPYC). A higher abundance of chlorophyll increases absorption of solar irradiance and heating rate in the upper ocean, resulting in decreasing the mixed layer thickness than they would be under clear waer...

  17. In situ laser sensing of mixed layer turbulence

    Science.gov (United States)

    Dalgleish, Fraser; Hou, Weilin; Vuorenkoski, Anni; Nootz, Gero; Ouyang, Bing

    2013-06-01

    This paper will discuss and compare some recent oceanic test results from the Bahamas Optical Turbulence Exercise (BOTEX) cruise, where vertical profiling was conducted with both time-resolved laser backscatter measurements being acquired via a subsurface light detection and ranging (lidar) profiling instrument, and laser beam forward deflection measurements were acquired from a matrix of continuous wave (cw) laser beams (i.e. structured lighting) being imaged in the forward direction with a high speed camera over a one-way path, with both transmitter and camera firmly fixed on a rigid frame. From the latter, it was observed that when within a natural turbulent layer, the laser beams were being deflected from their still water location at the image plane, which was 8.8 meters distance from the laser dot matrix transmitter. As well as suggesting that the turbulent structures being encountered were predominately larger than the beam diameter, the magnitude of the deflection has been confirmed to correlate with the temperature dissipation rate. The profiling lidar measurements which were conducted in similar conditions, also used a narrow collimated laser beam in order to resolve small-scale spatial structure, but with the added attribute that sub-nanosecond short pulse temporal profile could potentially resolve small-scale vertical structure. In the clear waters of the Tongue of the Ocean in the Bahamas, it was hypothesized that the backscatter anomalies due to the effect of refractive index discontinuities (i.e. mixed layer turbulence) would be observable. The processed lidar data presented herein indicates that higher backscatter levels were observed in the regions of the water column which corresponded to higher turbulent mixing which occurs at the first and second themoclines. At the same test stations that the laser beam matrix and lidar measurements were conducted, turbulence measurements were made with two non-optical instruments, the Vertical Microstructure

  18. ON THE EVOLUTION OF LARGE SCALE STRUCTURES IN THREE-DIMENSIONAL MIXING LAYERS

    Institute of Scientific and Technical Information of China (English)

    罗纪生; H.E, Fiedler

    2001-01-01

    In this paper, several mathematical models for the large scale structures in some special kinds of mixing layers, which might be practically useful for enhancing the mixing, are proposed. First, the linear growth rate of the large scale structures in the mixing layers was calculated. Then, using the much improved weakly non-linear theory, combined with the energy method, the non-linear evolution of large scale structures in two special mixing layer configurations is calculated. One of the mixing layers has equal magnitudes of the upstream velocity vectors, while the angles between the velocity vectors and the trailing edge were π/2 - and π/2 + ,respectively. The other mixing layer was generated by a splitter-plate with a 45-degree-sweep trailing edge.

  19. Online Detection of Mixed Layer Depth for Autonomous Underwater Vehicles

    Science.gov (United States)

    Chu, S.; Estlin, T.; Castano, R.; Woodward, G.; Gierach, M. M.; Thompson, A. F.; Schaffer, S.

    2015-12-01

    The accurate determination of the mixed layer depth (MLD) plays a crucial role in studying ocean dynamics and climate change. Various methods to estimate MLD have been proposed [1, 2]. However there is no current consensus on the best model, which leads to large uncertainty in the estimation. The variability, coupled with the complexity of physical, chemical and biological processes involved and the uncertainty and instabilities of the upper ocean surface, makes estimating MLD a challenging task. MLD varies significantly, even across a small spatial area (autonomous underwater vehicle (AUV). Using an online method permits a more adaptive approach to estimating MLD. Our proposed algorithm is based on an ensemble approach, which includes data mining techniques for real-time peak and change detection, learned seasonal variability profile, combined with MLD estimation criteria in [1]. In this study, we analyze measurements using glider data collected from the OSMOSIS (Ocean Surface Mixing, Ocean Submesoscale Interaction Study) project, concatenated into a year-long time series [3]. The glider data consists of nine full-depth moorings, which were deployed in a 15 km by 15 km box at the Porcupine Abyssal Plain in the northeast Atlantic, centered at 16.2°W, 48.7°N. Our algorithm utilizes direct measurements of salinity, temperature, depth and time and the design is based on the spatial and temporal variability of MLD learned. We will present our initial work on tracking the MLD based on real-time simulations using the OSMOSIS glider data and discussed for the case of deploying on a single AUV. Using an online algorithm for estimating MLD in-situ enables the system to rapidly adapt to the variability in a real-world environment and also allows for the intelligent operation of the limited sampling resources available on an AUV. We will discuss the autonomy architecture and algorithm design for implementing this methodology and present results from our initial

  20. Direct and Large-Eddy Simulation of the Compressible Turbulent Mixing Layer

    NARCIS (Netherlands)

    Vreman, A.W.

    1995-01-01

    The Large-Eddy Simulation technique of compressible flows and the effect of compressibility on mixing layers are the main subjects of this thesis. Direct Numerical Simulations (DNS) and Large-Eddy Simulations (LES) of the temporal compressible mixing layer at various Mach and Reynolds numbers have

  1. Direct numerical simulation of three-dimensional coherent structure in plane mixing layer

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The three-dimensional temporally evolving plane mixing layer is sinulated by directly solying the Navier-Stokes equations using pseudo-spectral method. The process of loss of stability, and the formation paring, and development of vortex are presented. The simulated result shows that the evolving characteristics of coherent structure are important mechanism of growing and entrainment of mixing layer.

  2. Efficient charge balance in blue phosphorescent organic light emitting diodes by two types of mixed layer

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Hyung Jin; Lee, Ho Won; Lee, Song Eun; Sun, Yong; Hwang, Kyo Min; Yoo, Han Kyu; Lee, Sung Kyu [Department of Information Display, Hongik University, Seoul 121-791 (Korea, Republic of); Kim, Woo Young, E-mail: wykim@hoseo.edu [Department of Green Energy & Semiconductor Engineering, Hoseo University, Asan 336-795 (Korea, Republic of); Kim, Young Kwan, E-mail: kimyk@hongik.ac.kr [Department of Information Display, Hongik University, Seoul 121-791 (Korea, Republic of)

    2015-07-31

    The authors have demonstrated a highly efficient and long-lifetime blue phosphorescent organic light emitting diode (PHOLED) that uses two types of mixed layers. The mixed layers play the role of carrier injection control and exciton generation zone extension. One of the layers is applied for mixing the hole transport layer (HTL) and host material at the HTL side for carrier injection control. The other works as a mixed electron transporting layer (ETL) and host material at the ETL side. The optimized blue PHOLED has been shown to achieve high performance owing to the mixed layer effects. It gave a maximum luminous efficiency of 25.55 cd/A, maximum external quantum efficiency of 13.05%, and lifetime of 7.24 h under 500 cd/m{sup 2}. These results indicate that applying mixed layers is a simple and efficient method that does not require significant structural change. - Highlights: • Highly efficient blue phosphorescent organic light-emitting diode (PHOLEDs) • Hole transporting layer consists with mixed layer for delayed hole injection • The blue PHOLEDs with long lifetime due to suppression of quenching process.

  3. Interannual variability of mixed layer depth and heat storage of upper layer in the tropical Pacific Ocean

    Institute of Scientific and Technical Information of China (English)

    LIN Yihua; YOU Xiaobao; GUAN Yuping

    2004-01-01

    By using the upper layer data (downloaded trom the web of the Scripps Institution of Oceanography ),the interannual variability of the heat storage of upper layer(from surface to 400 m depth) and the mixed layer depth in the tropical Pacific Ocean are investigated. The abnormal signal of the warm event comes from the central and west Pacific Ocean, whereas it is regarded that the abnormal signal of the warm event comes from the east Pacific Ocean in the popular viewpoint. From the viewpoint on the evolution of the interannual variability of the mixed layer depth and the heat storage of the whole upper layer, the difference between the two types of El Nino is so smallthat it can be neglected. During these two El Nino/La Nina events(1972/1973 and 1997/1998), other than the case of the heat storage or for the mixed layer depth, the abnormal signal propagates from the central and west Pacific Ocean to the east usually by the path along the equator whereas the abnormal signal propagates from the east to the west by the path northern to the equator. For the interannual variability, the evolution of the mixed layer depth corresponds to that of the heat storage in the upper layer very well. This is quite different from the evolution of seasonality.

  4. Ordered mixed-layer structures in the Mighei carbonaceous chondrite matrix

    Science.gov (United States)

    Mackinnon, I. D. R.

    1982-01-01

    High resolution transmission electron microscopy of the Mighei carbonaceous chondrite matrix has revealed the presence of a new mixed layer structure material. This mixed-layer material consists of an ordered arrangement of serpentine-type (S) and brucite-type (B) layers in the sequence SBBSBB. Electron diffraction and imaging techniques show that the basal periodicity is approximately 17 A. Discrete crystals of SBB-type material are typically curved, of small size (less than 1 micron) and show structural variations similar to the serpentine group minerals. Mixed-layer material also occurs in association with planar serpentine. Characteristics of SBB-type material are not consistent with known terrestrial mixed-layer clay minerals. Evidence for formation by a condensation event or by subsequent alteration of pre-existing material is not yet apparent.

  5. Enhancement of Exciton Emission in Lead Halide-Based Layered Perovskites by Cation Mixing.

    Science.gov (United States)

    Era, Masanao; Komatsu, Yumeko; Sakamoto, Naotaka

    2016-04-01

    Spin-coated films of a lead halide, PbX: X = I and Br, layered perovskites having cyclohexenylethyl ammonium molecule as an organic layer, which were mixed with other metal halide-based layered perovskites consisting of various divalent metal halides (for example, Ca2, Cdl2, FeI2, SnBr2 and so on), were prepared. The results of X-ray diffraction measurements exhibited that solid solution formation between PbX-based layered perovskite and other divalent metal halide-based layered perovskites was observed up to very high molar concentration of 50 molar% in the mixed film samples when divalent cations having ionic radius close to that of Pb2+ were employed. In the solid solution films, the exciton emission was much enhanced at room temperature. Exciton emission intensity of Pbl-based layered perovskite mixed with Cal-based layered perovskite (20 molar%) is about 5 times large that of the pristine Pbl-based layered perovskite, and that of PbBr-based layered perovskite mixed with SnBr-based layered perovskite (20 molar%) was also about 5 times large that of the pristine PbBr-based layered perovskite at room temperature.

  6. The ocean mixed layer under Southern Ocean sea-ice: seasonal cycle and forcing.

    Science.gov (United States)

    Violaine, P.; Sallee, J. B.; Schmidtko, S.; Roquet, F.; Charrassin, J. B.

    2016-02-01

    The mixed-layer at the surface of the ocean is the gateway for all exchanges between air and sea. A vast area of the Southern Ocean is however seasonally capped by sea-ice, which alters this gateway and the characteristic the ocean mixed-layer. The interaction between the ocean mixed-layer and sea-ice plays a key role for water-mass formation and circulation, carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the mixed layer, as well as the processes responsible for its evolution, are poorly understood due to the lack of in-situ observations and measurements. We urgently need to better understand the forcing and the characteristics of the ocean mixed-layer under sea-ice if we are to understand and predict the world's climate. In this study, we combine a range of distinct sources of observation to overcome this lack in our understanding of the Polar Regions. Working on Elephant Seal-derived data as well as ship-based observations and Argo float data, we describe the seasonal cycle of the characteristics and stability of the ocean mixed layer over the entire Southern Ocean (South of 40°S), and specifically under sea-ice. Mixed-layer budgets of heat and freshwater are used to investigate the main forcings of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget, and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity and vertical entrainment play only secondary role.Our results suggest that changes in regional sea-ice distribution or sea-ice seasonal cycle duration, as currently observed, would widely affect the buoyancy budget of the underlying mixed-layer, and impacts large-scale water-mass formation and transformation.

  7. Determination of the Mixing Layer Height Over two Sites, Using Pilot Balloons During the MILAGRO Campaign

    Science.gov (United States)

    Wohrnschimmel, H.; Alonso, A. L.; Ángeles, F.; Sosa, G.; Varela, J.; Cárdenas, B.

    2007-12-01

    Among the mechanisms that affect air quality there is a variety of meteorological processes. An important process in this context are the changes in the mixing layer height during a day and over the year. The mixing layer height is the portion of the atmosphere close to the surface layer where air pollutants get diluted, without leaving this layer. Therefore, it is important to describe the variations in the height of the mixing layer, i.e. the vertical dilution of air pollution, since this is a process mitigating naturally the impact of emissions. There exist different methods to obtain information on the mixing layer height, among them radio soundings, the application of vertical wind profilers, and launching pilot balloons. In this study, pilot balloons have been used simultaneously over two sites of the Mexico City Metropolitan Area during the MILAGRO campaign in March 2006. The objective was to determine the vertical wind profiles and derive information on the mixing layer height. Daily, four pilot balloons were launched, at 9:00, 12:00, 15:00, and 18:00 hours, over Tenango del Aire (a rural area in the Southeast of Mexico City), and over Ciudad Universitaria, in the Southern metropolitan area. At some occasions, night time measurements have been carried out at 21:00 and 24:00. A variability of the diurnal evolution of the mixing layer was observed along March, which could be related to surface temperature. The diurnal evolution showed a sudden growth of the mixing layer between 9:00 and 12:00 hours. Data intercomparisons were carried out for pilot balloons versus radio soundings during a few days at a third site, Tula, in the North of Mexico City. Both intercomparisons showed that pilot balloons are an effective method to obtain information about the development of the mixing layer.

  8. Properties of mixed Be+C layers on beryllium and hydrogen accumulation therein

    Science.gov (United States)

    Guseva, Mariya I.; Danelyan, Leon S.; Gureev, Viktor M.; Kolbasov, Boris N.; Korshunov, Sergej N.; Kulikauskas, Vatslavas S.; Skorlupkin, Igor D.; Stolyarova, Valentina G.; Zatyokin, Vladimir V.

    2006-05-01

    The presence of two different plasma contacting materials (Be and C) in the vacuum chamber of the International Thermonuclear Experimental Reactor (ITER) will result in the formation of mixed Be + C layers. Such layers were obtained experimentally by irradiating Be specimens with an acetylene plasma flux (with ˜300 eV molecular ion C2H2+ energy and 1021 m-2s-1 intensity) from a plasma accelerator. Irradiation doses were 1023, 2ṡ1023 and 1024 m-2. During the experiments, the temperature of a Be target surface was maintained at 670 K. The chemical composition of the mixed Be + C layers (except for the H content) was determined using Rutherford backscattering technique. Hydrogen distribution across the mixed layers was measured using the elastic recoil detection analysis. The surface microstructure and component composition of the mixed layers appeared to depend on the irradiation dose. The carbon content in the mixed layers grows with increasing dose. The Be/C atomic concentration ratio varies from 0.34 to 0.70 in mixed layers formed during irradiation by a 1023 m-2 dose. A mixed layer forming on Be surface exposed to a 1024 m-2 dose contains more carbon and has a spongy surface structure with Be/C atomic ratio as low as ˜0.04. Integral hydrogen concentration in the mixed Be + C layers decreases with growing irradiation dose. As the dose increases from 1023 to 1024 m-2, the H/(Be + C) atomic concentration ratio in the 1 μm thick layer decreases from 0.3 to 0.07.

  9. Comparison of T-piece and concentric mixing systems for continuous flow synthesis of anatase nanoparticles in supercritical isopropanol/water

    Science.gov (United States)

    Toft, Lars L.; Aarup, David F.; Bremholm, Martin; Hald, Peter; Iversen, Bo B.

    2009-03-01

    T-piece and concentric counter-flow mixing systems are compared in continuous flow supercritical solvothermal synthesis of TiO 2 at identical system parameters. The phase pure anatase nanoparticle products were characterized with powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS), and the particle size, size distribution and absolute crystallinity mapped as a function of temperature, precursor concentration, flow rate and pressure for the two different continuous flow reactors. The particles synthesized with the T-piece geometry are smaller with a narrower size distribution, possibly indicating a more effective mixing, than particles synthesized at the same conditions with concentric counter-flow geometry. In general, an increased synthesis temperature leads to an increase in absolute crystallinity. For the particles synthesized with the concentric reactor geometry crossing of the critical point of the solvent causes a decrease in the particle size and size distribution, and conditions just above the critical temperature are demonstrated to be optimal for continuous solvothermal synthesis of anatase.

  10. Ocean Mixed Layer Response to Gap Wind Scenarios

    Science.gov (United States)

    2006-12-01

    LAYER ........5 B. GAP WINDS AND GAP FLOW .............................7 III MODELS AND DATA SOURCES ................................13 A. COUPLED...atmospheric and the oceanic boundary layer during gap flow conditions were made by a research aircraft with dropsonde and AXBTs. This dataset gave us the...Polar Regions (http://oceanworld.tamu.edu/resources/ocng textbook , last visited 26 October 2006). B. GAP WINDS AND GAP FLOW Gap winds are low

  11. Estimation of urban mixed layer height in Zanjan using LIDAR observations and numerical modeling

    Indian Academy of Sciences (India)

    A A Bidokhti; M Khoshsima; S Sabetghadam; H M Khalesifard

    2008-12-01

    Air pollution predictions often require the height of atmospheric mixed layer in time especially in big cities. Here, the variation of the height of this layer is estimated from direct measurements and also from a numerical forecast model with a high resolution boundary layer scheme. The height of the daytime mixed layer for the city of Zanjan (48.5°N, 36.7°E, 1700 m above sea level)is measured using a LIDAR (532 nm)system, which works based on aerosols scattering of laser light. The mixed layer height () for Zanjan city, well above mean sea level compared to other major cities in the world,is found to be between 1.4 km typically in spring and 2.2 km in summer, for synoptic calm conditions. Also, the MM5 forecast model with a proper boundary layer scheme (MRF)is used to estimate which shows rather good agreement with direct observations using the LIDAR system. The entrainment zone of the mixed layer was also found to undergo some occasional temporal growth that may be attributed to shear instability that led to more mixed layer growth.

  12. Mixed layer variability and chlorophyll a biomass in the Bay of Bengal.

    Digital Repository Service at National Institute of Oceanography (India)

    Narvekar, J.; PrasannaKumar, S.

    The mixed layer is the most variable and dynamically active part of the marine environment that couples the underlying ocean to the atmosphere and plays an important role in determining the oceanic primary productivity. We examined the basin...

  13. An experimental study of aero-optical aberration and dithering of supersonic mixing layer via BOS

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The optical performance of supersonic mixing layer is heavily deteriorated by the aero-optical aberration and dithering of coherent structures, but current measuring methods limit the spatiotemporal resolution in relevant studies. A high resolution whole-field aero-optical aberration and dithering measuring method based on the Background Orient Schlieren (BOS) technique was studied. The systematic structure, sensitivity and resolution of BOS are analyzed in this paper. The aero-optical aberration and dithering of streamwise structures in supersonic mixing layers were quantificationally studied with BOS. The aberration field of spanwise structures revealed the ribbon-like aberration structures, which heavily restrict the optical performance of a mixing layer. The quantifications of aero-optical aberration and dithering are very important in studying aero-optical performance of supersonic mixing layer.

  14. Detailed characteristics of drop-laden mixing layers: LES predictions compared to DNS

    Science.gov (United States)

    Okong'o, N.; Leboissetier, A.; Bellan, J.

    2004-01-01

    Results have been compared from Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) of a temporal mixing layer laden with evaporating drops, to assess the ability of LES to reproduce detailed characteristics of DNS.

  15. Plasma interfacial mixing layers: Comparisons of fluid and kinetic models

    Science.gov (United States)

    Vold, Erik; Yin, Lin; Taitano, William; Albright, B. J.; Chacon, Luis; Simakov, Andrei; Molvig, Kim

    2016-10-01

    We examine plasma transport across an initial discontinuity between two species by comparing fluid and kinetic models. The fluid model employs a kinetic theory approximation for plasma transport in the limit of small Knudsen number. The kinetic simulations include explicit particle-in-cell simulations (VPIC) and a new implicit Vlasov-Fokker-Planck code, iFP. The two kinetic methods are shown to be in close agreement for many aspects of the mixing dynamics at early times (to several hundred collision times). The fluid model captures some of the earliest time dynamic behavior seen in the kinetic results, and also generally agrees with iFP at late times when the total pressure gradient relaxes and the species transport is dominated by slow diffusive processes. The results show three distinct phases of the mixing: a pressure discontinuity forms across the initial interface (on times of a few collisions), the pressure perturbations propagate away from the interfacial mixing region (on time scales of an acoustic transit) and at late times the pressure relaxes in the mix region leaving a non-zero center of mass flow velocity. The center of mass velocity associated with the outward propagating pressure waves is required to conserve momentum in the rest frame. Work performed under the auspices of the U.S. DOE by the LANS, LLC, Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396. Funding provided by the Advanced Simulation and Computing (ASC) Program.

  16. Performance properties of asphalt mixes for rich bottom layers (RBL)

    Science.gov (United States)

    Bureš, Petr; Fiedler, Jiří; Kašpar, Jiří; Sýkora, Michal; Hýzl, Petr

    2017-09-01

    The binder content of asphalt mixes has an important influence on the performance properties. Higher binder content improves fatigue resistance. That is why the concept of RBL was developed in USA and applied for “perpetual pavements”. However excessive binder content could lead to the decrease of the mix stiffness and to permanent deformations of asphalt pavement during hot summer. The advantages and limitations of RBL concept have been studied in research project CESTI. Fatigue tests of mixes with road bitumen and polymer modified bitumen and RBL were realised. Deformation behaviour of these mixes was also evaluated. The experience from the test section with RBL laid in 2015 will be presented. The results corresponded to expectations. However, low void content was obtained on one subsection. In spite of it, there were no permanent deformations during summer 2016. The analysis of methods for the prediction of the permanent deformation was also undertaken in research project CESTI. Some information about the results of these analysis related to the use of RBL will be also briefly mentioned.

  17. The Upper Mixed Layer during Coastal Upwelling Events on the Northern Portugal Shelf

    Institute of Scientific and Technical Information of China (English)

    ZUO Juncheng; SHENG Hong; Alvaro Peliz; Santos A. Miguel

    2003-01-01

    The upper mixed layer (UML) depth obtained from temperature is very close to that from density:thc maximum is about 15 m. This indicates that temperature is a good indicator of mixed layer during measurements. When the surface heat flux is balanced by a cross-shore heat flux, the surface mixed layer depth obtained from the WM model (Weatherly and Martin, 1978), hpRT, is roughly the same as observed. The mixed layer depth calculated from the PWP model (Price, Wellcr and Pinkel, 1986) is close to the depth obtained from thermistor chain temperature data. The results show that both thc WM model and PWP model can provide a good estimate of stratification in the study area during the cruise. The value of log (h/u3)is about 9.5 in the study area, which shows that the study area is strongly stratified in summer. Observations on the northern Portugal shelf reveal high variability in stability, giving rise to semi-diurnal, semi-monthly and diurnal oscillations, and long term variations. The fortnightly oscillations are highlighted by post-springs and post-neaps. The stirring of spring tide is reinforced by strong wind mixing which brings about complete vertical homogeneity everywhere. The semi-diurnal periodic stratification is very pronounced because the major axis of the tidal ellipse is orientated acrossshorc, even though thc tidal current is weak in this area, the maximum stratification is observed around the middle of ebb, and, the water at this time is much warmer. The diurnal oscillation results from the upper ocean response to heating and wind mixing when solar heating warms and stabilizes the upper ocean. There is a clear relationship between upper mixed layer depth and wind-stress magnitude at subtidal frequencies. Stronger winds result in a dccper surface mixed layer. Typically, the surface mixed layer depth lags the wind stress by 6-12h.

  18. Lidar Characterization of Boundary Layer Transport and Mixing for Estimating Urban-Scale Greenhouse Gas Emissions

    Science.gov (United States)

    Hardesty, R. Michael; Brewer, W. Alan; Sandberg, Scott P.; Weickmann, Ann M.; Shepson, Paul B.; Cambaliza, Maria; Heimburger, Alexie; Davis, Kenneth J.; Lauvaux, Thomas; Miles, Natasha L.; Sarmiento, Daniel P.; Deng, A. J.; Gaudet, Brian; Karion, Anna; Sweeney, Colm; Whetstone, James

    2016-06-01

    A compact commercial Doppler lidar has been deployed in Indianapolis for two years to measure wind profiles and mixing layer properties as part of project to improve greenhouse measurements from large area sources. The lidar uses vertical velocity variance and aerosol structure to measure mixing layer depth. Comparisons with aircraft and the NOAA HRDL lidar generally indicate good performance, although sensitivity might be an issue under low aerosol conditions.

  19. Lidar Characterization of Boundary Layer Transport and Mixing for Estimating Urban-Scale Greenhouse Gas Emissions

    Directory of Open Access Journals (Sweden)

    Hardesty R. Michael

    2016-01-01

    Full Text Available A compact commercial Doppler lidar has been deployed in Indianapolis for two years to measure wind profiles and mixing layer properties as part of project to improve greenhouse measurements from large area sources. The lidar uses vertical velocity variance and aerosol structure to measure mixing layer depth. Comparisons with aircraft and the NOAA HRDL lidar generally indicate good performance, although sensitivity might be an issue under low aerosol conditions.

  20. Using dissolved oxygen concentrations to determine mixed layer depths in the Bellingshausen Sea

    Directory of Open Access Journals (Sweden)

    K. Castro-Morales

    2012-01-01

    Full Text Available Concentrations of oxygen (O2 and other dissolved gases in the oceanic mixed layer are often used to calculate air-sea gas exchange fluxes. The mixed layer depth (zmix may be defined using criteria based on temperature or density differences to a reference depth near the ocean surface. However, temperature criteria fail in regions with strong haloclines such as the Southern Ocean where heat, freshwater and momentum fluxes interact to establish mixed layers. Moreover, the time scales of air-sea exchange differ for gases and heat, so that zmix defined using oxygen may be different than zmix defined using temperature or density. Here, we propose to define an O2-based mixed layer depth, zmix(O2, as the depth where the relative difference between the O2 concentration and a reference value at a depth equivalent to 10 dbar equals 0.5 %. This definition was established by analysis of O2 profiles from the Bellingshausen Sea (west of the Antarctic Peninsula and corroborated by visual inspection. Comparisons of zmix(O2 with zmix based on potential temperature differences, i.e., zmix(0.2 °C and zmix(0.5 °C, and potential density differences, i.e., zmix(0.03 kg m−3 and zmix(0.125 kg m−3, showed that zmix(O2 closely follows zmix(0.03 kg m−3. Further comparisons with published zmix climatologies and zmix derived from World Ocean Atlas 2005 data were also performed. To establish zmix for use with biological production estimates in the absence of O2 profiles, we suggest using zmix(0.03 kg m−3, which is also the basis for the climatology by

  1. Comparison of numerical schemes in large-eddy simulation of the temporal mixing layer

    NARCIS (Netherlands)

    Vreman, A.W.; Geurts, Bernardus J.; Kuerten, Johannes G.M.

    1996-01-01

    A posteriori tests of large-eddy simulations for the temporal mixing layer are performed using a variety of numerical methods in conjunction with the dynamic mixed subgrid model for the turbulent stress tensor. The results of the large-eddy simulations are compared with filtered direct numerical

  2. Laboratory simulations of the atmospheric mixed-layer in flow over complex topography

    Science.gov (United States)

    Perry, Steven G.; Snyder, William H.

    2017-02-01

    A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundary layer can have a strong influence on the concentration of pollutants within this layer. Deflections of streamlines at the height of the interface are primarily a function of hill Froude number (Fr), the ratio of mixed-layer height (zi) to terrain height (h), and the crosswind dimension of the terrain. The magnitude of the deflections increases as Fr increases and zi/h decreases. For mixing-height streamlines that are initially below the terrain top, the response is linear with Fr; for those initially above the terrain feature the response to Fr is more complex. Once Fr exceeds about 2, the terrain-related response of the mixed layer interface decreases somewhat with increasing Fr (toward more neutral flow). Deflections are also shown to increase as the crosswind dimensions of the terrain increase. Comparisons with numerical modeling, limited field data, and other laboratory measurements reported in the literature are favorable. Additionally, visual observations of dye streamers suggest that the flow structure exhibited for our elevated inversions passing over three dimensional hills is similar to that reported in the literature for continuously stratified flow over two-dimensional hills.

  3. A Fundamental Study of Convective Mixing of CO2 in Layered Heterogeneous Saline Aquifers with Low Permeability Zones using Surrogate Fluids and Numerical Modeling

    Science.gov (United States)

    Agartan, E.; Illangasekare, T. H.; Cihan, A.; Birkholzer, J. T.; Zhou, Q.; Trevisan, L.

    2013-12-01

    Dissolution trapping is one of the primary mechanisms contributing to long-term and stable storage of supercritical CO2 (scCO2) in deep saline geologic formations. When entrapped scCO2 dissolves in formation brine, density-driven convective fingers are expected to be generated due to the higher density of the solution compared to brine. These fingers enhance mixing of dissolved scCO2 in brine (Ennis-King & Paterson, 2003). The goal of this study is to evaluate the contribution of convective mixing to dissolution trapping of CO2 in naturally layered heterogeneous formations with low permeability zones via experimental and numerical analyses. To understand the fundamental process of dissolution trapping in the laboratory under ambient pressure and temperature conditions, a group of surrogate fluids were selected according to their density and viscosity values before and after dissolution. Fluids were tested in a variety of porous media systems. After selection of the appropriate fluid mixture based on the closest behavior to scCO2 brine systems, a set of experiments in a small homogeneously packed test tank was performed to analyze the fingering behaviors. A second set of experiments was conducted in the same test tank with layered soil systems to study the effects of formation heterogeneity on convective mixing. A finite volume method based numerical code was developed to capture the dominant processes observed in the experiments. This model was then used to simulate more complex heterogeneous systems that were not represented in the limited set of experiments. Results of these analyses suggest that convective fingers developed in homogeneous formations may not be significantly contributing to mixing and hence dissolution trapping in heterogeneous formations depending on the permeability contrasts and thickness of the low permeability layers.

  4. Chlorophyll modulation of mixed layer thermodynamics in a mixed-layer isopycnal General Circulation Model - An example from Arabian Sea and equatorial Pacific

    Indian Academy of Sciences (India)

    S Nakamoto; S Prasanna Kumar; J M Oberhuber; H Saito; K Muneyama; R Frouin

    2002-09-01

    Western tropical Indian Ocean, Arabian Sea, and the equatorial Pacific are known as regions of intense bio-chemical-physical interactions: the Arabian Sea has the largest phytoplankton bloom with seasonal signal, while the equatorial Pacific bloom is perennial with quasi-permanent upwelling. Here, we studied three dimensional ocean thermodynamics comparing recent ocean observation with ocean general circulation model (OPYC) experiment combined with remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS). Using solar radiation parameterization representing observations that a higher abundance of chlorophyll increases absorption of solar irradiance and heating rate in the upper ocean, we showed that the mixed layer thickness decreases more than they would be under clear water conditions. These changes in the model mixed layer were consistent with Joint Global Ocean Flux Study (JGOFS) observations during the 1994-1995 Arabian Sea experiment and epi-fluorescence microscopy (EFM) on samples collected during Equatorial Pacific Ocean Climate Study (EPOCS) in November, 1988. In the Arabian Sea, as the chlorophyll concentrations peak in October (3mg/m3) after the summer plankton bloom induced by coastal upwelling, the chlorophyll induced biological heating enhanced the sea surface temperature (SST) by as much as 0.6°C and sub-layer temperature decreases and sub-layer thickness increases. In the equatorial Pacific, modest concentrations of chlorophyll less than 0.3mg/m3 is enough to introduce a meridional differential heating, which results in reducing the equatorial mixed layer thickness to more than 20 m. The anomalous meridional tilting of the mixed layer bottom enhances off equatorial westward geostrophic currents. Consequently, the equatorial undercurrent transports more water from west to east. We proposed that these numerical model experiments with use of satellite and in situ ocean observations are consistent under three

  5. Mixing-Height Time Series from Operational Ceilometer Aerosol-Layer Heights

    Science.gov (United States)

    Lotteraner, Christoph; Piringer, Martin

    2016-07-01

    A new method is described to derive mixing-height time series directly from aerosol-layer height data available from a Vaisala CL51 ceilometer. As complete as possible mixing-height time series are calculated by avoiding outliers, filling data gaps by linear interpolation, and smoothing. In addition, large aerosol-layer heights at night that can be interpreted as residual layers are not assigned as mixing heights. The resulting mixing-height time series, converted to an appropriate data format, can be used as input for dispersion calculations. Two case examples demonstrate in detail how the method works. The mixing heights calculated using ceilometer data are compared with values determined from radiosounding data at Vienna by applying the parcel, Heffter, and Richardson methods. The results of the parcel method, obtained from radiosonde profiles at noon, show the best fit to the ceilometer-derived mixing heights. For midnight radiosoundings, larger deviations between mixing heights from the ceilometer and those deduced from the potential temperature profiles of the soundings are found. We use data from two Vaisala CL51 ceilometers, operating in the Vienna area at an urban and rural site, respectively, during an overlapping period of about 1 year. In addition to the case studies, the calculated mixing-height time series are also statistically evaluated and compared, demonstrating that the ceilometer-based mixing height follows an expected daily and seasonal course.

  6. Mixing-Height Time Series from Operational Ceilometer Aerosol-Layer Heights

    Science.gov (United States)

    Lotteraner, Christoph; Piringer, Martin

    2016-11-01

    A new method is described to derive mixing-height time series directly from aerosol-layer height data available from a Vaisala CL51 ceilometer. As complete as possible mixing-height time series are calculated by avoiding outliers, filling data gaps by linear interpolation, and smoothing. In addition, large aerosol-layer heights at night that can be interpreted as residual layers are not assigned as mixing heights. The resulting mixing-height time series, converted to an appropriate data format, can be used as input for dispersion calculations. Two case examples demonstrate in detail how the method works. The mixing heights calculated using ceilometer data are compared with values determined from radiosounding data at Vienna by applying the parcel, Heffter, and Richardson methods. The results of the parcel method, obtained from radiosonde profiles at noon, show the best fit to the ceilometer-derived mixing heights. For midnight radiosoundings, larger deviations between mixing heights from the ceilometer and those deduced from the potential temperature profiles of the soundings are found. We use data from two Vaisala CL51 ceilometers, operating in the Vienna area at an urban and rural site, respectively, during an overlapping period of about 1 year. In addition to the case studies, the calculated mixing-height time series are also statistically evaluated and compared, demonstrating that the ceilometer-based mixing height follows an expected daily and seasonal course.

  7. Discrete element simulation of charging and mixed layer formation in the ironmaking blast furnace

    Science.gov (United States)

    Mitra, Tamoghna; Saxén, Henrik

    2016-11-01

    The burden distribution in the ironmaking blast furnace plays an important role for the operation as it affects the gas flow distribution, heat and mass transfer, and chemical reactions in the shaft. This work studies certain aspects of burden distribution by small-scale experiments and numerical simulation by the discrete element method (DEM). Particular attention is focused on the complex layer-formation process and the problems associated with estimating the burden layer distribution by burden profile measurements. The formation of mixed layers is studied, and a computational method for estimating the extent of the mixed layer, as well as its voidage, is proposed and applied on the results of the DEM simulations. In studying a charging program and its resulting burden distribution, the mixed layers of coke and pellets were found to show lower voidage than the individual burden layers. The dynamic evolution of the mixed layer during the charging process is also analyzed. The results of the study can be used to gain deeper insight into the complex charging process of the blast furnace, which is useful in the design of new charging programs and for mathematical models that do not consider the full behavior of the particles in the burden layers.

  8. The Effects of Curvature on Turbulent Mixing Layers,

    Science.gov (United States)

    1984-01-01

    bances when the Taylor number is smaller than a critical value of 1708 (the numerical value cited was obtained by Peliew and Southwell [ 1940 ] by a...streamwise vortices are caused by Taylor- Gortler instability and are similar to Taylor vortices. Aryshev. Golovin , and Ershin (1981) indicated that an...layer. According to Aryshev, Golovin and Ershin (1981), the local streamline cur- vature associated with such colliding streams can lead to Taylor

  9. Supercritical flows past a square cylinder with rounded corners

    Science.gov (United States)

    Cao, Yong; Tamura, Tetsuro

    2017-08-01

    Large-eddy simulations were used to investigate the supercritical aerodynamics of a square cylinder with rounded corners in comparison with those in the subcritical regime. First, the numerical methods, especially the dynamic mixed model, were validated on the basis of their prediction of supercritical flows past a circular cylinder. Then, the supercritical flows past a rounded-corner square cylinder were simulated and systematically clarified. Strong Reynolds number (Re) effects existed in the forces and local pressures as Re increased from o(104) to o(106). Changeover of flow patterns occurred as Re increased. At the supercritical Re, the free stream overall flowed along the cross sections of the cylinder, separated from the leeward corners and generated Karman vortices behind the cylinder. This pattern resulted in a much smaller recirculation region behind the cylinder compared with the subcritical flow. At the micro level, the flow experienced laminar separation and flow reattachment near the frontal corners, followed by the spatial development of turbulent boundary layers (TBLs) on the side faces and turbulent separation near the leeward corners. The feedback by large-scale primary vortex shedding and the small-scale turbulent motions in the high-frequency region with a slope of -5/3 were detected in the TBL. Their interaction affected the spanwise correlations of wall pressure fluctuations. The TBL on the side face differed from the zero-pressure-gradient flat-plate one; it was subjected to pressure gradients varying in space and time.

  10. Mixing and non-equilibrium chemical reaction in a compressible mixing layer. M.S. Thesis Final Report

    Science.gov (United States)

    Steinberger, Craig J.

    1991-01-01

    The effects of compressibility, chemical reaction exothermicity, and non-equilibrium chemical modeling in a reacting plane mixing layer were investigated by means of two dimensional direct numerical simulations. The chemical reaction was irreversible and second order of the type A + B yields Products + Heat. The general governing fluid equations of a compressible reacting flow field were solved by means of high order finite difference methods. Physical effects were then determined by examining the response of the mixing layer to variation of the relevant non-dimensionalized parameters. The simulations show that increased compressibility generally results in a suppressed mixing, and consequently a reduced chemical reaction conversion rate. Reaction heat release was found to enhance mixing at the initial stages of the layer growth, but had a stabilizing effect at later times. The increased stability manifested itself in the suppression or delay of the formation of large coherent structures within the flow. Calculations were performed for a constant rate chemical kinetics model and an Arrhenius type kinetic prototype. The choice of the model was shown to have an effect on the development of the flow. The Arrhenius model caused a greater temperature increase due to reaction than the constant kinetic model. This had the same effect as increasing the exothermicity of the reaction. Localized flame quenching was also observed when the Zeldovich number was relatively large.

  11. An applied model for the height of the daytime mixed layer and the entrainment zone

    DEFF Research Database (Denmark)

    Batchvarova, E.; Gryning, Sven-Erik

    1994-01-01

    -layer height: friction velocity, kinematic heat flux near the ground and potential temperature gradient in the free atmosphere above the entrainment zone. When information is available on the horizontal divergence of the large-scale flow field, the model also takes into account the effect of subsidence......A model is presented for the height of the mixed layer and the depth of the entrainment zone under near-neutral and unstable atmospheric conditions. It is based on the zero-order mixed layer height model of Batchvarova and Gryning (1991) and the parameterization of the entrainment zone depth...

  12. Protected Sulfur Cathode with Mixed Conductive Coating Layer for Lithium Sulfur Battery

    Science.gov (United States)

    Jin, Jun; Wen, Zhaoyin; Wang, Qingsong; Gu, Sui; Huang, Xiao; Chen, Chunhua

    2016-10-01

    A mixed conductive coating layer composed of lithium ion conductive ceramic powder, carbon and binder was introduced on the surface of a sulfur electrode. This coating layer is designed to suppress the migration of lithium polysulfides from the sulfur electrode, and improve the cycling capacity of a lithium sulfur battery. The protected sulfur cathode with a mixed conductive coating layer delivered an initial specific capacity of 1236 mAh g-1 at 0.5C and maintained a capacity of 842 mAh g-1 after 100 cycles. In particular, a soft package battery with protected cathode exhibits improved cycling capacity and excellent rate performance.

  13. Nanostructure of Poly(Acrylic Acid) Adsorption Layer on the Surface of Activated Carbon Obtained from Residue After Supercritical Extraction of Hops

    Science.gov (United States)

    Wiśniewska, M.; Nosal-Wiercińska, A.; Ostolska, I.; Sternik, D.; Nowicki, P.; Pietrzak, R.; Bazan-Wozniak, A.; Goncharuk, O.

    2017-01-01

    The nanostructure of poly(acrylic acid) (PAA) adsorption layer on the surface of mesoporous-activated carbon HPA obtained by physical activation of residue after supercritical extraction of hops was characterized. This characterization has been done based on the analysis of determination of adsorbed polymer amount, surface charge density, and zeta potential of solid particles (without and in the PAA presence). The SEM, thermogravimetric, FTIR, and MS techniques have allowed one to examine the solid surface morphology and specify different kinds of HPA surface groups. The effects of solution pH, as well as polymer molecular weight and concentration, were studied. The obtained results indicated that the highest adsorption on the activated carbon surface was exhibited by PAA with lower molecular weight (i.e., 2000 Da) at pH 3. Under such conditions, polymeric adsorption layer is composed of nanosized PAA coils (slightly negatively charged) which are densely packed on the positive surface of HPA. Additionally, the adsorption of polymeric macromolecules into solid pores is possible.

  14. Mixed-layer deepening during Heinrich events: a multi-planktonic foraminiferal delta18O approach.

    Science.gov (United States)

    Rashid, Harunur; Boyle, Edward A

    2007-10-19

    Proxies from Greenland ice cores and North Atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle, including periods of intense ice rafting called Heinrich events (HEs). We have found similar oxygen isotope variations recorded in mixed-layer-and thermocline-dwelling planktonic foraminifera during HEs 0, 1, and 4, suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column. This implies that the surface mixed layer was deeper during HEs. Similar deepening occurred on the northern margin of the ice-rafted-debris belt, implying that these deep mixed layers during HEs were widespread in the region. We suggest that an increase in storminess during HEs intensified the vertical mixing of meltwater from ice rafting in the upper ocean.

  15. Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump

    Science.gov (United States)

    Dall'Olmo, Giorgio; Dingle, James; Polimene, Luca; Brewin, Robert J. W.; Claustre, Hervé

    2016-11-01

    The ocean region known as the mesopelagic zone, which is at depths of about 100-1,000 m, harbours one of the largest ecosystems and fish stocks on the planet. Life in this region is believed to rely on particulate organic carbon supplied by the biological carbon pump. Yet this supply appears insufficient to meet mesopelagic metabolic demands. An additional organic carbon source to the mesopelagic zone could be provided by the seasonal entrainment of surface waters in deeper layers, a process known as the mixed-layer pump. Little is known about the magnitude and spatial distribution of this process globally or its potential to transport carbon to the mesopelagic zone. Here we combine mixed-layer depth data from Argo floats with satellite estimates of particulate organic carbon concentrations to show that the mixed-layer pump supplies an important seasonal flux of organic carbon to the mesopelagic zone. We estimate that this process is responsible for a global flux of 0.1-0.5 Pg C yr-1. In high-latitude regions where the mixed layer is usually deep, this flux amounts on average to 23% of the carbon supplied by fast sinking particles, but it can be greater than 100%. We conclude that the seasonal mixed-layer pump is an important source of organic carbon for the mesopelagic zone.

  16. The roll-up and merging of coherent structures in shallow mixing layers

    Science.gov (United States)

    Lam, M. Y.; Ghidaoui, M. S.; Kolyshkin, A. A.

    2016-09-01

    The current study seeks a fundamental explanation to the development of two-dimensional coherent structures (2DCSs) in shallow mixing layers. A nonlinear numerical model based on the depth-averaged shallow water equations is used to investigate the temporal evolution of shallow mixing layers, where the mapping from temporal to spatial results is made using the velocity at the center of the mixing layers. The flow is periodic in the streamwise direction. Transmissive boundary conditions are used in the cross-stream boundaries to prevent reflections. Numerical results are compared to linear stability analysis, mean-field theory, and secondary stability analysis. Results suggest that the onset and development of 2DCS in shallow mixing layers are the result of a sequence of instabilities governed by linear theory, mean-field theory, and secondary stability theory. The linear instability of the shearing velocity gradient gives the onset of 2DCS. When the perturbations reach a certain amplitude, the flow field of the perturbations changes from a wavy shape to a vortical (2DCS) structure because of nonlinearity. The development of the vertical 2DCS does not appear to follow weakly nonlinear theory; instead, it follows mean-field theory. After the formation of 2DCS, separate 2DCSs merge to form larger 2DCS. In this way, 2DCSs grow and shallow mixing layers develop and grow in scale. The merging of 2DCS in shallow mixing layers is shown to be caused by the secondary instability of the 2DCS. Eventually 2DCSs are dissipated by bed friction. The sequence of instabilities can cause the upscaling of the turbulent kinetic energy in shallow mixing layers.

  17. Mixed layer variability and chlorophyll a biomass in the Bay of Bengal

    Directory of Open Access Journals (Sweden)

    J. Narvekar

    2013-10-01

    Full Text Available Mixed layer is the most variable and dynamically active part of the marine environment that couples the underlying ocean to the atmosphere and plays an important role in determining the chlorophyll concentration. In this paper we examined the seasonal variability of the mixed layer depth in the Bay of Bengal, the factors responsible for it and the coupling of mixed layer processes to the chlorophyll biomass using a suite of in situ as well as remote sensing data. The basin-wide mixed layer depth was the shallowest during spring intermonsoon, which was associated with strong themohaline stratification of the upper water column. The prevailing winds which were the weakest of all the seasons were unable to break the stratification leading to the observed shallow mixed layer. Consistent with the warm oligotrophic upper ocean, the surface chlorophyll concentrations were the least and the vertical profile of chlorophyll was characterized by a subsurface chlorophyll maximum. Similarly, during summer though the monsoon winds were the strongest they were unable to break the upper ocean haline-stratification in the northern Bay brought about by a combination of excess precipitation over evaporation and fresh water influx from rivers adjoining the Bay of Bengal. Consistent with this though the nitrate concentrations were high in the northern part of the Bay, the chlorophyll concentrations were low indicating the light limitation. In contrast, in the south, advection of high salinity waters from the Arabian Sea coupled with the westward propagating Rossby waves of annual periodicity were able to decrease stability of the upper water column and the prevailing monsoon winds were able to initiate deep mixing leading to the observed deep mixed layer. The high chlorophyll concentration observed in the south resulted from the positive wind stress curl which pumped nutrient rich subsurface waters to the euphotic zone. The southward extension of the shallow mixed

  18. Monolayers and mixed-layers on copper towards corrosion protection

    Energy Technology Data Exchange (ETDEWEB)

    Sinapi, F. [Fonds pour la Formation a la Recherche dans l' Industrie et dans l' Agriculture, Rue d' Egmont 5, B-1000 Brussels (Belgium); Julien, S.; Auguste, D.; Hevesi, L.; Delhalle, J. [Laboratory of Chemistry and Electrochemistry of Surfaces, University of Namur, FUNDP, Rue de Bruxelles, 61, B-5000 Namur (Belgium); Mekhalif, Z. [Laboratory of Chemistry and Electrochemistry of Surfaces, University of Namur, FUNDP, Rue de Bruxelles, 61, B-5000 Namur (Belgium)], E-mail: zineb.mekhalif@fundp.ac.be

    2008-05-01

    In order to improve the protection abilities of (3-mercaptopropy)trimethoxysilane (MPTS) self-assembled monolayers on copper surfaces, mixed monolayers have been formed successfully by successive immersions in MPTS and in n-dodecanethiol (DT). A newly synthesised molecule, (11-mercaptoundecyl)trimethoxysilane (MUTS), has also been employed to form a thicker organic film on copper surfaces and, thereby, enhance the inhibitory action of the coating. The grafting has been confirmed by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS) and water contact angle. The protective efficiency of each protective organic film has been evidenced by cyclic voltammetry (CV) and polarization curve measurements (CP). It was shown that the MUTS and unhydrolyzed MPTS/DT films exhibited significant corrosion protection properties.

  19. Determination of regional heat fluxes from the growth of the mixed layer

    Energy Technology Data Exchange (ETDEWEB)

    Gryning, S.E. [Risoe National Lab., Roskilde (Denmark); Batchvarova, E. [National Inst. of Meteorology and Hydrology, Sofia (Bulgaria)

    1997-10-01

    The distribution of surface sensible heat flux is a critical factor in producing and modifying the mesoscale atmospheric flows, turbulence and evaporation. Parameterizations that assume homogeneous land characteristics are inappropriate to represent the spatial variability often found in nature. One possibility to overcome this problem is to increase the resolution of the model grid which demands unrealistic computing resources and data for model initialization. Area averaged fluxes can be obtained from aircraft measurements. It is essential that the flights are performed at a height where the individual surface features are not felt. A large number of flights and appropriate pattern to meet the task are needed in order to achieve a fair statistics. The mixed layer grows in response to the regional turbulent fluxes including the aggregation and small scale processes. The region of influence in upwind direction is typically 20 times the height of the mixed layer for convective and 100 times the height of the mixed layer for atmospheric near neutral conditions. In this study we determine the regional integrated sensible heat flux from information on the evolution of the mixed layer over the area. The required information to use the method can be derived from wind speed and temperature profiles obtained by radio-soundings when performed frequently enough to provide a reasonably detailed structure of the development of the mixed-layer. The method is applied to estimate the regional heat flux over the NOPEX experimental area for three days during the campaign in 1994. (au)

  20. Radiation of mixed layer near-inertial oscillations into the ocean interior

    CERN Document Server

    Moehlis, J; Moehlis, Jeff; Smith, Stefan G. Llewellyn

    1999-01-01

    The radiation from the mixed layer into the interior of the ocean of near-inertial oscillations excited by a passing storm in the presence of the beta effect is reconsidered as an initial-value problem. Making use of the fact that the mixed layer depth is much smaller than the total depth of the ocean, the solution is obtained in the limit of an ocean that is effectively infinitely deep. For a uniform initial condition, analytical results for the velocity, horizontal kinetic energy density and fluxes are obtained. The resulting decay of near-inertial mixed layer energy in the presence of the beta effect occurs on a timescale similar to that observed.

  1. INFLUENCE OF LARGE-SCALE VORTICAL STRUCTURES ON THE PARTICLE DISPERSION IN A PLANE MIXING LAYER

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The present study considers the developing mixing layer that is formed by merging of two free streams initially separated by a splitter plate. To investigate the influence of the vortical structures on the particle dispersion, numerical simulation was conducted when the velocity ratio, defined as R=(U∞-U-∞)/(U∞+U-∞), is 0.5. Large-Eddy Simulation (LES) was employed to understand the effect of large-scale vortical structures originated by the Kelvin-Helmholtz instability on the partical dispersion. The flyash with the particle sizes 10, 50, 100, 150, and 200μm respectively were loaded at the origin of the two-dimensional mixing layer. It is confirmed that the particle dispersion depends strongly on the motion of large-scale vortical structures. The particle dispersion is visualized numerically by following the particle trajectories in the mixing layer undergoing pairing interaction.

  2. Observations of boundary layer, mixed-phase and multi-layer Arctic clouds with different lidar systems during ASTAR 2007

    Directory of Open Access Journals (Sweden)

    A. Lampert

    2009-07-01

    Full Text Available During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR, which was conducted in Svalbard in March and April 2007, tropospheric Arctic clouds were observed with two ground-based backscatter lidar systems (micro pulse lidar and Raman lidar and with an airborne elastic lidar. An increase in low-level (cloud tops below 2.5 km cloud cover from 51% to 65% was observed above Ny-Ålesund during the time of the ASTAR campaign. Four different case studies of lidar cloud observations are analyzed: With the ground-based Raman lidar, a pre-condensation layer was observed at an altitude of 2 km. The layer consisted of small droplets with a high number concentration (around 300 cm−3 at low temperatures (−30°C. Observations of a boundary layer mixed-phase cloud by airborne lidar were evaluated with the measurements of concurrent airborne in situ and spectral solar radiation sensors. Two detailed observations of multiply layered clouds in the free troposphere are presented. The first case was composed of various ice layers with different optical properties detected with the Raman lidar, the other case showed a mixed-phase double layer and was observed by airborne lidar.

    The analysis of these four cases confirmed that lidar data provide information of the whole range from subvisible to optically thick clouds. Despite the attenuation of the laser signal in optically thick clouds and multiple scattering effects, information on the geometrical boundaries of liquid water clouds were obtained. Furthermore, the dominating phase of the clouds' particles in the layer closest to the lidar system could be retrieved.

  3. Construction of a supercritical fluid extraction (SFE equipment: validation using annatto and fennel and extract analysis by thin layer chromatography coupled to image

    Directory of Open Access Journals (Sweden)

    Júlio Cezar Flores JOHNER

    2016-01-01

    Full Text Available Abstract The present work describes setting up a laboratory unit for supercritical fluid extraction. In addition to its construction, a survey of cost was done to compare the cost of the homemade unit with that of commercial units. The equipment was validated using an extraction of annatto seeds’ oil, and the extraction and fractionation of fennel oil were used to validate the two separators; for both systems, the solvent was carbon dioxide. The chemical profiles of annatto and fennel extracts were assessed using thin layer chromatography; the images of the chromatographic plates were processed using the free ImageJ software. The cost survey showed that the homemade equipment has a very low cost (~US$ 16,000 compared to commercial equipment. The extraction curves of annatto were similar to those obtained in the literature (yield of 3.8% oil. The separators were validated, producing both a 2.5% fraction of fennel seed extract rich in essential oils and another extract fraction composed mainly of oleoresins. The ImageJ software proved to be a low-cost tool for obtaining an initial evaluation of the chemical profile of the extracts.

  4. Feasibility of correlating separation of ternary mixtures of neutral analytes via thin layer chromatography with supercritical fluid chromatography in support of green flash separations.

    Science.gov (United States)

    Ashraf-Khorassani, M; Yan, Q; Akin, A; Riley, F; Aurigemma, C; Taylor, L T

    2015-10-30

    Method development for normal phase flash liquid chromatography traditionally employs preliminary screening using thin layer chromatography (TLC) with conventional solvents on bare silica. Extension to green flash chromatography via correlation of TLC migration results, with conventional polar/nonpolar liquid mixtures, and packed column supercritical fluid chromatography (SFC) retention times, via gradient elution on bare silica with a suite of carbon dioxide mobile phase modifiers, is reported. Feasibility of TLC/SFC correlation is individually described for eight ternary mixtures for a total of 24 neutral analytes. The experimental criteria for TLC/SFC correlation was assumed to be as follows: SFC/UV/MS retention (tR) increases among each of the three resolved mixture components; while, TLC migration (Rf) decreases among the same resolved mixture components. Successful correlation of TLC to SFC was observed for most of the polar organic solvents tested, with the best results observed via SFC on bare silica with methanol as the CO2 modifier and TLC on bare silica with a methanol/dichloromethane mixture. Copyright © 2015 Elsevier B.V. All rights reserved.

  5. Simulation of the ocean surface mixed layer under the wave breaking

    Institute of Scientific and Technical Information of China (English)

    SUN Qun; SONG Jinbao; GUAN Changlong

    2005-01-01

    A one-dimensional mixed-layer model, including a Mellor-Yamada level 2.5 turbulence closure scheme, was implemented to investigate the dynamical and thermal structures of the ocean surface mixed layer in the northern South China Sea. The turbulent kinetic energy released through wave breaking was incorporated into the model as a source of energy at the ocean surface, and the influence of the breaking waves on the mixed layer was studied. The numerical simulations show that the simulated SST is overestimated in summer without the breaking waves. However, the cooler SST is simulated when the effect of the breaking waves is considered, the corresponding discrepancy with the observed data decreases up to 20% and the MLD calculated averagely deepens 3.8 m. Owing to the wave-enhanced turbulence mixing in the summertime, the stratification at the bottom of the mixed layer was modified and the temperature gradient spread throughout the whole thermocline compared with the concentrated distribution without wave breaking.

  6. SCALE INTERACTION IN A MIXING LAYER. THE ROLE OF THE LARGE-SCALE GRADIENTS

    KAUST Repository

    Fiscaletti, Daniele

    2015-08-23

    The interaction between scales is investigated in a turbulent mixing layer. The large-scale amplitude modulation of the small scales already observed in other works depends on the crosswise location. Large-scale positive fluctuations correlate with a stronger activity of the small scales on the low speed-side of the mixing layer, and a reduced activity on the high speed-side. However, from physical considerations we would expect the scales to interact in a qualitatively similar way within the flow and across different turbulent flows. Therefore, instead of the large-scale fluctuations, the large-scale gradients modulation of the small scales has been additionally investigated.

  7. Photo-polarimetric sensitivities to layering and mixing of absorbing aerosols

    Directory of Open Access Journals (Sweden)

    O. V. Kalashnikova

    2011-09-01

    Full Text Available We investigate to what extent multi-angle polarimetric measurements are sensitive to vertical mixing/layering of absorbing aerosols, adopting calibration uncertainty of 1.5% in intensity and 0.5% in the degree of linear polarization of Multiangle Spectro-Polarimetric Imager (MSPI. Employing both deterministic and Monte Carlo radiative transfer codes with polarization, we conduct modeling experiments to determine how the measured Stokes vector elements are affected at UV and short visible wavelengths by the vertical distribution, mixing and layering of smoke and dust aerosols for variety of microphysical parameters. We find that multi-angular polarimetry holds the potential to infer dust-layer heights and thicknesses at blue visible channel due to its lesser sensitivity to changes in dust coarse mode optical properties, but higher sensitivity to the dust vertical profiles. Our studies quantify requirements for obtaining simultaneous information on aerosol layer height and absorption under MSPI measurement uncertainties.

  8. Mixing Acid Salts and Layered Double Hydroxides in Nanoscale under Solid Condition

    OpenAIRE

    2014-01-01

    The immobilization of potassium sorbate, potassium aspartate and sorbic acid in layered double hydroxide under solid condition was examined. By simply mixing two solids, immobilization of sorbate and aspartate in the interlayer space of nitrate-type layered double hydroxide, so called intercalation reaction, was achieved, and the uptakes, that is, the amount of immobilized salts and the interlayer distances of intercalation compounds were almost the same as those obtained in aqueous solution...

  9. HST STIS Observations of the Mixing Layer in the Cat’s Eye Nebula

    Science.gov (United States)

    Fang, Xuan; Guerrero, Martín A.; Toalá, Jesús A.; Chu, You-Hua; Gruendl, Robert A.

    2016-05-01

    Planetary nebulae (PNe) are expected to have a ˜105 K interface layer between the ≥slant 106 K inner hot bubble and the ˜104 K optical nebular shell. The PN structure and evolution, and the X-ray emission, depend critically on the efficiency of the mixing of material at this interface layer. However, neither its location nor its spatial extent have ever been determined. Using high-spatial resolution HST STIS spectroscopic observations of the N v λ λ 1239,1243 lines in the Cat’s Eye Nebula (NGC 6543), we have detected this interface layer and determined its location, extent, and physical properties for the first time in a PN. We confirm that this interface layer, as revealed by the spatial distribution of the N v λ1239 line emission, is located between the hot bubble and the optical nebular shell. We estimate a thickness of 1.5× {10}16 cm and an electron density of ˜200 cm-3 for the mixing layer. With a thermal pressure of ˜2 × 10-8 dyn cm-2, the mixing layer is in pressure equilibrium with the hot bubble and ionized nebular rim of NGC 6543. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The observations are associated with program #12509.

  10. HST STIS observations of the mixing layer in the Cat's Eye Nebula

    CERN Document Server

    Fang, Xuan; Toala, Jesus A; Chu, You-Hua; Gruendl, Robert A

    2016-01-01

    Planetary nebulae (PNe) are expected to have a ~10$^{5}$ K interface layer between the $\\geq$10$^{6}$ K inner hot bubble and the ~10$^{4}$ K optical nebular shell. The PN structure and evolution, and the X-ray emission depend critically on the efficiency of mixing of material at this interface layer. However, neither its location nor its spatial extent has ever been determined so far. Using high-spatial resolution HST STIS spectroscopic observations of the N V 1239,1243 lines in the Cat's Eye Nebula (NGC 6543), we have detected this interface layer and determined its location, extent, and physical properties for the first time in a PN. We confirm that this interface layer, as revealed by the spatial distribution of the N V 1239 line emission, is located between the hot bubble and the optical nebular shell. We estimate a thickness of 1.5$\\times$10$^{16}$ cm and an electron density of ~200 cm$^{-3}$ for the mixing layer. With a thermal pressure of ~2$\\times$10$^{-8}$ dyn cm$^{-2}$, the mixing layer is in pressu...

  11. Comparison of different remote sensing methods for mixing layer height monitoring

    Science.gov (United States)

    Emeis, Stefan; Schäfer, Klaus; Münkel, Christoph; Friedl, Roman; Suppan, Peter

    2010-10-01

    Since 2006 different remote monitoring methods for mixing layer height have been operated in Augsburg. One method is based on eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter intensities recorded with these ceilometers provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the tops of mixed layers. A special software for these ceilometers provides routine retrievals of lower atmosphere layering. A second method, based on SODAR (Sound Detection and Ranging) observations, detects the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component. This information is extended by measurements with a RASS (Radio-Acoustic Sounding System) which provide the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions which mark atmospheric layers. These SODAR and RASS data are the input to a software-based determination of mixing layer heights developed with MATLAB. A comparison of results of the three remote sensing methods during simultaneous measurements was performed. The information content of the ceilometer data is assessed by comparing it to the results from the other two instruments and near-by radiosonde data.

  12. Mixed layer warming-deepening in the Mediterranean Sea and its effect on the marine environment

    Science.gov (United States)

    Rivetti, Irene; Boero, Ferdinando; Fraschetti, Simonetta; Zambianchi, Enrico; Lionello, Piero

    2015-04-01

    This work aims at investigating the evolution of the ocean mixed layer in the Mediterranean Sea and linking it to the occurrence of mass mortalities of benthic invertebrates. The temporal evolution of selected parameters describing the mixed layer and the seasonal thermocline is provided for the whole Mediterranean Sea for spring, summer and autumn and for the period 1945-2011. For this analysis all temperature profiles collected in the basin with bottles, Mechanical Bathy-Thermographs (MBT), eXpendable Bathy-Thermographs (XBT), and Conductivity-Temperature-Depth (CTD) have been used (166,990). These data have been extracted from three public sources: the MEDAR-MEDATLAS, the World Ocean Database 2013 and the MFS-VOS program. Five different methods for estimating the mixed layer depth are compared using temperature profiles collected at the DYFAMED station in the Ligurian Sea and one method, the so-called three-segment method, has been selected for a systematic analysis of the evolution of the uppermost part of the whole Mediterranean Sea. This method approximates the upper water column with three segments representing mixed layer, thermocline and deep layer and has shown to be the most suitable method for capturing the mixed layer depth for most shapes of temperature profiles. Mass mortalities events of benthic invertebrates have been identified by an extensive search of all data bases in ISI Web of Knowledge considering studies published from 1945 to 2011. Studies reporting the geographical coordinates, the timing of the events, the species involved and the depth at which signs of stress occurred have been considered. Results show a general increase of thickness and temperature of the mixed layer, deepening and cooling of the thermocline base in summer and autumn. Possible impacts of these changes are mass mortalities events of benthic invertebrates that have been documented since 1983 mainly in summer and autumn. It is also shown that most mass mortalities

  13. A Hybrid Numerical Method for Turbulent Mixing Layers. Degree awarded by Case Western Reserve Univ.

    Science.gov (United States)

    Georgiadis, Nicholas J.

    2001-01-01

    A hybrid method has been developed for simulations of compressible turbulent mixing layers. Such mixing layers dominate the flows in exhaust systems of modern day aircraft and also those of hypersonic vehicles currently under development. The method configurations in which a dominant structural feature provides an unsteady mechanism to drive the turbulent development in the mixing layer. The hybrid method uses a Reynolds-averaged Navier-Stokes (RANS) procedure to calculate wall bounded regions entering a mixing section, and a Large Eddy Simulation (LES) procedure to calculate the mixing dominated regions. A numerical technique was developed to enable the use of the hybrid RANS-LES method on stretched, non-Cartesian grids. Closure for the RANS equations was obtained using the Cebeci-Smith algebraic turbulence model in conjunction with the wall-function approach of Ota and Goldberg. The wall-function approach enabled a continuous computational grid from the RANS regions to the LES region. The LES equations were closed using the Smagorinsky subgrid scale model. The hybrid RANS-LES method is applied to a benchmark compressible mixing layer experiment. Preliminary two dimensional calculations are used to investigate the effects of axial grid density and boundary conditions. Vortex shedding from the base region of a splitter plate separating the upstream flows was observed to eventually transition to turbulence. The location of the transition, however, was much further downstream than indicated by experiments. Actual LES calculations, performed in three spatial directions, also indicated vortex shedding, but the transition to turbulence was found to occur much closer to the beginning of the mixing section. which is in agreement with experimental observations. These calculations demonstrated that LES simulations must be performed in three dimensions. Comparisons of time-averaged axial velocities and turbulence intensities indicated reasonable agreement with experimental

  14. Estimation of the mixing layer height over a high altitude site in Central Himalayan region by using Doppler lidar

    Energy Technology Data Exchange (ETDEWEB)

    Shukla, K. K.; Phanikumar, D. V.; Newsom, Rob K.; Kumar, Niranjan; Ratnam, Venkat; Naja, M.; Singh, Narendra

    2014-03-01

    A Doppler lidar was installed at Manora Peak, Nainital (29.4 N; 79.2 E, 1958 amsl) to estimate mixing layer height for the first time by using vertical velocity variance as basic measurement parameter for the period September-November 2011. Mixing layer height is found to be located ~0.57 +/- 0.1and 0.45 +/- 0.05km AGL during day and nighttime, respectively. The estimation of mixing layer height shows good correlation (R>0.8) between different instruments and with different methods. Our results show that wavelet co-variance transform is a robust method for mixing layer height estimation.

  15. [Mineralogy and genesis of mixed-layer clay minerals in the Jiujiang net-like red soil].

    Science.gov (United States)

    Yin, Ke; Hong, Han-Lie; Li, Rong-Biao; Han, Wen; Wu, Yu; Gao, Wen-Peng; Jia, Jin-Sheng

    2012-10-01

    Mineralogy and genesis were investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) to understand the mineralogy and its genesis significance of mixed-layer clay minerals in Jiujiang red soil section. XRD and FTIR results show that the net-like red soil sediments are composed of illite, kaolinite, minor smectite and mixed-layer illite-smectite and minor mixed-layer kaolinite-smectite. HRTEM observation indicates that some smectite layers have transformed into kaolinite layers in net-like red soil. Mixed-layer illite-smectite is a transition phase of illite transforming into smectite, and mixed-layer kaolinite-smectite is a transitional product relative to kaolinite and smectite. The occurrence of two mixed-layer clay species suggests that the weathering sequence of clay minerals in net-like red soil traversed from illite to mixed-layer illite-smectite to smectite to mixed-layer kaolinite-smectite to kaolinite, which indicates that net-like red soil formed under a warm and humid climate with strengthening of weathering.

  16. Deepening of the ocean mixed layer at the northern Patagonian continental shelf: a numerical study

    CERN Document Server

    Zanella, Juan; Pescio, Andres; Dragani, Walter

    2014-01-01

    A possible deepening of the ocean mixed layer was investigated at a selected point of the Patagonian continental shelf where a significant positive wind speed trend was estimated. Using a 1-dimensional vertical numerical model (S2P3) forced by atmospheric data from NCEP/NCAR I reanalysis and tidal constituents from TPXO 7.2 global model on a long term simulation (1979-2011), it was found that the mixed layer thickness presents a significant and positive trend of 10.1 +/- 1.4 cm/yr. Several numerical experiments were carried out in order to evaluate the impact of the different atmospheric variables (surface zonal and latitudinal wind components, air temperature, atmospheric pressure, specific humidity and cloud coverage) considered in this study. As a result it was found that an increase in the wind speed can be considered as the main responsible of the ocean mixed layer deepening at the selected location of the Patagonian continental shelf. A possible increasing in the mixed layer thickness could be directly ...

  17. Numerical simulation of a plane turbulent mixing layer, with applications to isothermal, rapid reactions

    Science.gov (United States)

    Lin, P.; Pratt, D. T.

    1987-01-01

    A hybrid method has been developed for the numerical prediction of turbulent mixing in a spatially-developing, free shear layer. Most significantly, the computation incorporates the effects of large-scale structures, Schmidt number and Reynolds number on mixing, which have been overlooked in the past. In flow field prediction, large-eddy simulation was conducted by a modified 2-D vortex method with subgrid-scale modeling. The predicted mean velocities, shear layer growth rates, Reynolds stresses, and the RMS of longitudinal velocity fluctuations were found to be in good agreement with experiments, although the lateral velocity fluctuations were overpredicted. In scalar transport, the Monte Carlo method was extended to the simulation of the time-dependent pdf transport equation. For the first time, the mixing frequency in Curl's coalescence/dispersion model was estimated by using Broadwell and Breidenthal's theory of micromixing, which involves Schmidt number, Reynolds number and the local vorticity. Numerical tests were performed for a gaseous case and an aqueous case. Evidence that pure freestream fluids are entrained into the layer by large-scale motions was found in the predicted pdf. Mean concentration profiles were found to be insensitive to Schmidt number, while the unmixedness was higher for higher Schmidt number. Applications were made to mixing layers with isothermal, fast reactions. The predicted difference in product thickness of the two cases was in reasonable quantitative agreement with experimental measurements.

  18. Regional heat flux over the NOPEX area estimated from the evolution of the mixed-layer

    DEFF Research Database (Denmark)

    Gryning, Sven-Erik; Batchvarova, E.

    1999-01-01

    of forest, agricultural fields, mires and lakes within the boreal zone, was determined for 3 days of the campaign in 1994. It was found to be lower than the heat flux over forest and higher than the heat Aux over agricultural fields. The regional heat flux estimated by the mixed-layer evolution method...

  19. Transient effects in unstable ablation fronts and mixing layers in HEDP

    Science.gov (United States)

    Clarisse, J.-M.; Gauthier, S.; Dastugue, L.; Vallet, A.; Schneider, N.

    2016-07-01

    We report results obtained for two elementary unstable flow configurations relevant to high energy density physics: the ablation front instability and the Rayleigh-Taylor -instability induced mixing layer. These two flows are characterized by a transience of their perturbation dynamics. In the ablative flow case, this perturbation dynamics transience takes the form of finite-durations of successive linear-perturbation evolution phases until reaching regimes of decaying oscillations. This behaviour is observed in various regimes: weakly or strongly accelerated ablation fronts, irradiation asymmetries or initial external-surface defects, and is a result of the mean-flow unsteadiness and stretching. In the case of the Rayleigh-Taylor-instability induced mixing layer, perturbation dynamics transience manifests itself through the extinction of turbulence and mixing as the flow reaches a stable state made of two stably stratified layers of pure fluids separated by an unstratified mixing layer. A second feature, also due to compressibility, takes the form of an intense acoustic wave production, mainly localized in the heavy fluid. Finally, we point out that a systematic short-term linear-perturbation dynamics analysis should be undertaken within the framework of non-normal stability theory.

  20. Mixed layer heat budget of Kuroshio-Tango Triangle using satellite and ship observations

    Digital Repository Service at National Institute of Oceanography (India)

    Pankajakshan, T.; Akiyama, M.; Sugimori, Y; Wuwa, J.; Okada, Y; Siripong, A

    Using a three dimensional heat flux model, variation of heat storage in the mixed layer of a triangular oceanic area, embedded in the Kuroshio has been studied for a period of a few days in the month of November, 1983. For the estimation of vertical...

  1. Significant mixed layer nitrification in a natural iron-fertilized bloom of the Southern Ocean

    Science.gov (United States)

    Fripiat, F.; Elskens, M.; Trull, T. W.; Blain, S.; Cavagna, A.-J.; Fernandez, C.; Fonseca-Batista, D.; Planchon, F.; Raimbault, P.; Roukaerts, A.; Dehairs, F.

    2015-11-01

    Nitrification, the microbially mediated oxidation of ammonium into nitrate, is generally expected to be low in the Southern Ocean mixed layer. This paradigm assumes that nitrate is mainly provided through vertical mixing and assimilated during the vegetative season, supporting the concept that nitrate uptake is equivalent to the new primary production (i.e., primary production which is potentially available for export). Here we show that nitrification is significant (~40-80% of the seasonal nitrate uptake) in the naturally iron-fertilized bloom over the southeast Kerguelen Plateau. Hence, a large fraction of the nitrate-based primary production is regenerated, instead of being exported. It appears that nitrate assimilation (light dependent) and nitrification (partly light inhibited) are spatially separated between the upper and lower parts, respectively, of the deep surface mixed layers. These deep mixed layers, extending well below the euphotic layer, allow nitrifiers to compete with phytoplankton for the assimilation of ammonium. The high contributions of nitrification to nitrate uptake are in agreement with both low export efficiency (i.e., the percentage of primary production that is exported) and low seasonal nitrate drawdown despite high nitrate assimilation.

  2. Shear rheology of mixed protein adsorption layers vs their structure studied by surface force measurements

    NARCIS (Netherlands)

    Danov, K.D.; Kralchevsky, P.A.; Radulova, G.M.; Basheva, E.S.; Stoyanov, S.D.; Pelan, E.G.

    2015-01-01

    The hydrophobins are proteins that form the most rigid adsorption layers at liquid interfaces in comparison with all other investigated proteins. The mixing of hydrophobin HFBII with other conventional proteins is expected to reduce the surface shear elasticity and viscosity, Esh and ¿sh,

  3. Structure of the oceanic mixed layer in western Bay of Bengal during MONEX

    Digital Repository Service at National Institute of Oceanography (India)

    Anto, A.F.; Somayajulu, Y.K.

    Based on the hourly BT and six hourly CSTD data, collected from two stations in the western Bay of Bengal during July 1979, the diurnal variations of temperature in the oceanic mixed layer (OML) were analysed as a function of the prevailing surface...

  4. Mixed layer depth variations in the Kuroshio Extension in relation to Japanese sardine

    Science.gov (United States)

    Yasuda, I.; Nishikawa, H.; Itoh, S.

    2008-12-01

    Mixed layer depths in and south of the Kuroshio Extension changed from deep to shallow states in the late- 1980s and early-1990s. This change corresponded to the collapse of Japanese sardine (Sardinops melanostictus). This mixed layer shoaling was accompanied by lower temperature in 200-400m depths and higher temperature near the surface. Wintertime field survey in 2006 (Hakuho-maru KH06-1 cruise) demonstrated that late winter maximum mixed layer depth reach deeper with the greater isothermal depth of 14-15degC and higher temperature in 300-400m depth. High-resolution ocean model hindcast data suggests that the accelerated near-surface Kuroshio/Kuroshio Extension associated with the elevated sea-surface height anomaly enhanced the heat transport near the surface. This greater heat advection near the surface overrides the cooler subtropical mode water that was created in the previous years possibly causes the shallower winter mixed layer and collapse of the Japanese sardine.

  5. The three-dimensional evolution of a plane mixing layer - The Kelvin-Helmholtz rollup

    Science.gov (United States)

    Rogers, Michael M.; Moser, Robert D.

    1992-01-01

    The hydrodynamic evolution of an incompressible plane mixing layer is addressed to elucidate scalar mixing in free shear flows. A detailed description of the onset of three-dimensionality in a mixing layer before or in the absence of pairing is presented. Various simulations were performed to investigate the sensitivity of these results to variations in initial conditions. These variations included changes in amplitude, wavelength, functional form, and relative phasing of the initial low-wavenumber disturbances. Pierrehumber and Widnall's (1982) translative instability eigenfunctions are found to include rib vortices in the braid region and oppositely signed streamwise vorticity in the roller core. The translative instability is an instability of the late-time oversaturated flow. Three-dimensional perturbation growth similar to that of the translative instability can occur whenever spanwise vorticity is present in the braid region. The nonlinear effects that occur when the initial rib circulation is sufficiently high are discussed.

  6. An updated length-scale formulation for turbulent mixing in clear and cloudy boundary layers

    Science.gov (United States)

    Lenderink, G.; Holtslag, A. A. M.

    2004-10-01

    A new mixing-length scale is presented for turbulence-closure schemes, with special emphasis on neutral-to-convective conditions in clear and cloudy boundary layers. The length scale is intended for a prognostic turbulent-kinetic-energy closure. It is argued that present-day length-scale formulations may easily fail in one of two limiting situations. Schemes based on a local stability measure (e.g.the Richardson number) display unrealistic behaviour and instabilities in the convective limit. This strongly limits the representation of mixing in cloudy boundary layers. On the other hand, it is shown that non-local parcel methods may misrepresent mixing near the surface. The new length-scale formulation combines local and non-local stability in a new way; it uses vertical integrals over the stability (the Richardson number) in a simple 'parcel' framework. The length scale matches with surface-layer similarity for near-neutral conditions and displays a realistic convective limit. The use of the length-scale formulation can be extended easily to cloudy boundary layers. The scheme is numerically stable and computationally cheap. The behaviour of the length scale is evaluated in a single-column model (SCM) and in a high-resolution limited-area model (LAM). The SCM shows good behaviour in three cases with and without boundary-layer clouds. The prediction of the near-surface wind and temperature in the LAM compares favourably with tower measurements at Cabauw (the Netherlands).

  7. Buoyant production and consumption of turbulence kinetic energy in cloud-topped mixed layers

    Science.gov (United States)

    Randall, D. A.

    1984-01-01

    It is pointed out that studies of the entraining planetary boundary layer (PBL) have generally emphasized the role of buoyancy fluxes in driving entrainment. The buoyancy flux is proportional to the rate of conversion of the potential energy of the mean flow into the kinetic energy of the turbulence. It is not unusual for conversion to proceed in both directions simultaneously. This occurs, for instance, in both clear and cloudy convective mixed layers which are capped by inversions. A partitioning of the net conversion into positive parts, generating turbulence kinetic energy (TKE), and negative parts (TKE-consuming), would make it possible to include the positive part in the gross production rate, and closure would be achieved. Three different approaches to partitioning have been proposed. The present investigation is concerned with a comparison of the three partitioning theories. Particular attention is given to the cloud-topped mixed layer because in this case the differences between two partitioning approaches are most apparent.

  8. Comparison of organic light emitting diodes with different mixed layer structures

    Energy Technology Data Exchange (ETDEWEB)

    Kee, Y.Y.; Siew, W.O. [Faculty of Engineering, Multimedia University, 63100 Cyberjaya (Malaysia); Yap, S.S. [Faculty of Engineering, Multimedia University, 63100 Cyberjaya (Malaysia); Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia); Tou, T.Y., E-mail: tytou@mmu.edu.my [Faculty of Engineering, Multimedia University, 63100 Cyberjaya (Malaysia)

    2014-11-03

    A mixed-source thermal evaporation method was used to fabricate organic light emitting diodes (OLEDs) with uniformly mixed (UM), continuously graded mixed (CGM) and step-wise graded, mixed (SGM) light-emitting layers. N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine and Tris-(8-hydroxyquinoline)aluminum were used, respectively, as the hole- and electron-transport materials. As compared to the conventional, heterojunction OLED, the maximum brightness of UM-, CGM- and SGM-OLEDs without charge injection layers were improved by 2.2, 3.8 and 2.1 times, respectively, while the maximum power efficiencies improved by 1.5, 3.2 and 1.9 times. These improvements were discussed in terms of more distributed recombination zone and removal of interfacial barrier. - Highlights: • Fabrication of OLEDs using a mixed-source evaporation technique • Three different types of mixed-host OLEDs with better brightness • Improved electroluminescence and power efficiencies as compared to conventional OLED.

  9. Nutrient interleaving below the mixed layer of the Kuroshio Extension Front

    Science.gov (United States)

    Nagai, Takeyoshi; Clayton, Sophie

    2017-08-01

    Nitrate interleaving structures were observed below the mixed layer during a cruise to the Kuroshio Extension in October 2009. In this paper, we investigate the formation mechanisms for these vertical nitrate anomalies, which may be an important source of nitrate to the oligotrphoc surface waters south of the Kuroshio Extension Front. We found that nitrate concentrations below the main stream of the Kuroshio Extension were elevated compared to the ambient water of the same density ( σ 𝜃 = 23.5-25). This appears to be analogous to the "nutrient stream" below the mixed layer, associated with the Gulf Stream. Strong turbulence was observed above the vertical nitrate anomaly, and we found that this can drive a large vertical turbulent nitrate flux >O (1 mmol N m-2 day-1). A realistic, high-resolution (2 km) numerical simulation reproduces the observed Kuroshio nutrient stream and nitrate interleaving structures, with similar lateral and vertical scales. The model results suggest that the nitrate interleaving structures are first generated at the western side of the meander crest on the south side of the Kuroshio Extension, where the southern tip of the mixed layer front is under frontogenesis. Lagrangian analyses reveal that the vertical shear of geostrophic and subinertial ageostrophic flow below the mixed layer tilts the existing along-isopycnal nitrate gradient of the Kuroshio nutrient stream to form nitrate interleaving structures. This study suggests that the multi-scale combination of (i) the lateral stirring of the Kuroshio nutrient stream by developed mixed layer fronts during fall to winter, (ii) the associated tilting of along-isopycnal nitrate gradient of the nutrient stream by subinertial shear, which forms vertical interleaving structures, and (iii) the strong turbulent diffusion above them, may provide a route to supply nutrients to oligotrophic surface waters on the south side of the Kuroshio Extension.

  10. Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

    Energy Technology Data Exchange (ETDEWEB)

    Flippo, K. A.; Doss, F. W.; Kline, J. L.; Merritt, E. C.; Capelli, D.; Cardenas, T.; DeVolder, B.; Fierro, F.; Huntington, C. M.; Kot, L.; Loomis, E. N.; MacLaren, S. A.; Murphy, T. J.; Nagel, S. R.; Perry, T. S.; Randolph, R. B.; Rivera, G.; Schmidt, D. W.

    2016-11-23

    Using a large volume high-energy-density fluid shear experiment (8.5 cm3) at the National Ignition Facility, we have demonstrated for the first time the ability to significantly alter the evolution of a supersonic sheared mixing layer by controlling the initial conditions of that layer. By altering the initial surface roughness of the tracer foil, we demonstrate the ability to transition the shear mixing layer from a highly ordered system of coherent structures to a randomly ordered system with a faster growing mix layer, indicative of strong mixing in the layer at a temperature of several tens of electron volts and at near solid density. Simulations using a turbulent-mix model show good agreement with the experimental results and poor agreement without turbulent mix.

  11. Using supercritical fluids to refine hydrocarbons

    Science.gov (United States)

    Yarbro, Stephen Lee

    2015-06-09

    A system and method for reactively refining hydrocarbons, such as heavy oils with API gravities of less than 20 degrees and bitumen-like hydrocarbons with viscosities greater than 1000 cp at standard temperature and pressure, using a selected fluid at supercritical conditions. A reaction portion of the system and method delivers lightweight, volatile hydrocarbons to an associated contacting unit which operates in mixed subcritical/supercritical or supercritical modes. Using thermal diffusion, multiphase contact, or a momentum generating pressure gradient, the contacting unit separates the reaction products into portions that are viable for use or sale without further conventional refining and hydro-processing techniques.

  12. Statistics and scaling of turbulence in a spatially developing mixing layer at Reλ = 250

    KAUST Repository

    Attili, Antonio

    2012-03-21

    The turbulent flow originating from the interaction between two parallel streams with different velocities is studied by means of direct numerical simulation. Rather than the more common temporal evolving layer, a spatially evolving configuration, with perturbed laminar inlet conditions is considered. The streamwise evolution and the self-similar state of turbulence statistics are reported and compared to results available in the literature. The characteristics of the transitional region agree with those observed in other simulations and experiments of mixing layers originating from laminar inlets. The present results indicate that the transitional region depends strongly on the inlet flow. Conversely, the self-similar state of turbulent kinetic energy and dissipation agrees quantitatively with those in a temporal mixing layer developing from turbulent initial conditions [M. M. Rogers and R. D. Moser, “Direct simulation of a self-similar turbulent mixing layer,” Phys. Fluids6, 903 (1994)]. The statistical features of turbulence in the self-similar region have been analysed in terms of longitudinal velocity structure functions, and scaling exponents are estimated by applying the extended self-similarity concept. In the small scale range (60 < r/η < 250), the scaling exponents display the universal anomalous scaling observed in homogeneous isotropic turbulence. The hypothesis of isotropy recovery holds in the turbulent mixing layer despite the presence of strong shear and large-scale structures, independently of the means of turbulence generation. At larger scales (r/η > 400), the mean shear and large coherent structures result in a significant deviation from predictions based on homogeneous isotropic turbulence theory. In this second scaling range, the numerical values of the exponents agree quantitatively with those reported for a variety of other flows characterized by strong shear, such as boundary layers, as well as channel and wake flows.

  13. Growth rate of a shocked mixing layer with known initial perturbations [Mixing at shocked interfaces with known perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Christopher R. [Univ. of Wisconsin, Madison, WI (United States); Cook, Andrew W. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Bonazza, Riccardo [Univ. of Wisconsin, Madison, WI (United States)

    2013-05-14

    Here we derive a growth-rate model for the Richtmyer–Meshkov mixing layer, given arbitrary but known initial conditions. The initial growth rate is determined by the net mass flux through the centre plane of the perturbed interface immediately after shock passage. The net mass flux is determined by the correlation between the post-shock density and streamwise velocity. The post-shock density field is computed from the known initial perturbations and the shock jump conditions. The streamwise velocity is computed via Biot–Savart integration of the vorticity field. The vorticity deposited by the shock is obtained from the baroclinic torque with an impulsive acceleration. Using the initial growth rate and characteristic perturbation wavelength as scaling factors, the model collapses the growth-rate curves and, in most cases, predicts the peak growth rate over a range of Mach numbers (1.1 ≤Mi≤1.9), Atwood numbers (₋0.73 ≤ A ≤ ₋0.35 and 0.22 ≤ A ≤ 0.73), adiabatic indices (1.40/1.67≤γ12≤1.67/1.09) and narrow-band perturbation spectra. Lastly, the mixing layer at late times exhibits a power-law growth with an average exponent of θ=0.24.

  14. Mixing and trapping of dissolved CO2 in deep geologic formations with shale layers

    Science.gov (United States)

    Agartan, Elif; Cihan, Abdullah; Illangasekare, Tissa H.; Zhou, Quanlin; Birkholzer, Jens T.

    2017-07-01

    For dissolution trapping, the spatial variability of the geologic properties of naturally complex storage formations can significantly impact flow patterns and storage mechanisms of dissolved CO2. The significance of diffusive mixing that occurs in low permeability layers embedded between relatively higher permeability materials was highlighted by Agartan et al. (2015) using a highly controlled laboratory experimental study on trapping of dissolved CO2 in multilayered systems. In this paper, we present a numerical modeling study on the impacts of low permeability layers on flow and storage of dissolved CO2 in realistic field-scale settings. The simulator of variable-density flow used in this study was first verified using the experimental data in Agartan et al. (2015) to capture the observed processes. The simulator was then applied to a synthetic, field-scale multilayered system, with 19 sensitivity cases having variable permeability and thickness of the shale layers as well as the source strength and geometry of the source zone of dissolved CO2. Simulation results showed that the presence of continuous shale layers in the storage system disrupts the convective mixing by enhancing lateral spreading of dissolved CO2 in sandstone layers and retarding the vertical mixing of dissolved CO2. The effectiveness of trapping of dissolved CO2 depends on the physical properties of the shale layers and configurations of the source zone. The comparison to homogeneous cases with effective vertical permeability shows that it is important to capture these continuous thin shale layers in a storage formation and include them in the models to enhance dissolution trapping.

  15. Shear, Stability and Mixing within the Ice-Shelf-Ocean Boundary Layer

    Science.gov (United States)

    Jenkins, Adrian

    2016-04-01

    Ocean-forced basal melting has been implicated in the widespread thinning of Antarctic ice shelves that has been causally linked with acceleration in the outflow of grounded ice. What determines the distribution and rates of basal melting and freezing beneath an ice shelf and how these respond to changes in the ocean temperature or circulation are therefore key questions. Recent years have seen major progress in our ability to observe basal melting and the ocean conditions that drive it, but data on the latter remain sparse, limiting our understanding of the key processes of ice-ocean heat transfer. In particular, we have no observations of current profiles through the buoyancy- and frictionally-controlled flows along the ice shelf base that drive mixing through the ice-ocean boundary layer. This presentation represents an attempt to address this gap in our knowledge through application of a very simple model of such boundary flows that considers only the spatial dimension perpendicular to the boundary. Initial results obtained with an unrealistic assumuption of constant eddy viscosity/diffusivity are nevertheless informative. For the buoyancy-driven flow two possible regimes exist: a weakly-stratified, geostrophic cross-slope current with an embedded Ekman layer, somewhat analogous to a conventional density current on a slope; or a strongly-stratified upslope jet with weak cross-slope flow, more analogous to an inverted katabatic wind. The latter is most appropriate when the ice-ocean interface is very steep, while for the gentle slopes typical of ice shelves the buoyant Ekman regime prevails. Introduction of a variable eddy viscosity/diffusivity derived from a local turbulence closure scheme modifies the current structure and stratification. There is a sharp step in properties across the surface layer, where the viscosity/diffusivity is low, weak gradients across the outer part of the boundary layer, where shear-driven mixing is strong, and a relatively strong

  16. Eulerian-Lagranigan simulation of aerosol evolution in turbulent mixing layer

    KAUST Repository

    Zhou, Kun

    2016-09-23

    The formation and evolution of aerosol in turbulent flows are ubiquitous in both industrial processes and nature. The intricate interaction of turbulent mixing and aerosol evolution in a canonical turbulent mixing layer was investigated by a direct numerical simulation (DNS) in a recent study (Zhou, K., Attili, A., Alshaarawi, A., and Bisetti, F. Simulation of aerosol nucleation and growth in a turbulent mixing layer. Physics of Fluids, 26, 065106 (2014)). In this work, Monte Carlo (MC) simulation of aerosol evolution is carried out along Lagrangian trajectories obtained in the previous simulation, in order to quantify the error of the moment method used in the previous simulation. Moreover, the particle size distribution (PSD), not available in the previous works, is also investigated. Along a fluid parcel moving through the turbulent flow, temperature and vapor concentration exhibit complex fluctuations, triggering complicate aerosol processes and rendering complex PSD. However, the mean PSD is found to be bi-modal in most of the mixing layer except that a tri-modal distribution is found in the turbulent transition region. The simulated PSDs agree with the experiment observations available in the literature. A different explanation on the formation of such PSDs is provided.

  17. On hot-wire diagnostics in Rayleigh-Taylor mixing layers

    Energy Technology Data Exchange (ETDEWEB)

    Kraft, Wayne N. [Texas A and M University, Department of Mechanical Engineering, College Station, TX (United States); Banerjee, Arindam [Missouri University of Science and Technology, Department of Mechanical and Aerospace Engineering, Rolla, MO (United States); Andrews, Malcolm J. [Texas A and M University, Department of Mechanical Engineering, College Station, TX (United States); Los Alamos National Laboratory, NM (United States)

    2009-07-15

    Two hot-wire flow diagnostics have been developed to measure a variety of turbulence statistics in the buoyancy driven, air-helium Rayleigh-Taylor mixing layer. The first diagnostic uses a multi-position, multi-overheat (MPMO) single wire technique that is based on evaluating the wire response function to variations in density, velocity and orientation, and gives time-averaged statistics inside the mixing layer. The second diagnostic utilizes the concept of temperature as a fluid marker, and employs a simultaneous three-wire/cold-wire anemometry technique (S3WCA) to measure instantaneous statistics. Both of these diagnostics have been validated in a low Atwood number (A{sub t}{<=} 0.04), small density difference regime, that allowed validation of the diagnostics with similar experiments done in a hot-water/cold-water water channel facility. Good agreement is found for the measured growth parameters for the mixing layer, velocity fluctuation anisotropy, velocity fluctuation p.d.f behavior, and measurements of molecular mixing. We describe in detail the MPMO and S3WCA diagnostics, and the validation measurements in the low Atwood number regime (A{sub t}{<=} 0.04). We also outline the advantages of each technique for measurement of turbulence statistics in fluid mixtures with large density differences. (orig.)

  18. Mixing process of a binary gas in a density stratified layer

    Energy Technology Data Exchange (ETDEWEB)

    Takeda, Tetsuaki [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment

    1997-09-01

    This study is to investigate the effect of natural convection on the mixing process by molecular diffusion in a vertical stratified layer of a binary fluid. There are many experimental and analytical studies on natural convection in the vertical fluid layer. However, there are few studies on natural convection with molecular diffusion in the vertical stratified layer of a binary gas. Experimental study has been performed on the combined phenomena of molecular diffusion and natural convection in a binary gas system to investigate the mixing process of the binary gas in a vertical slot consisting of one side heated and the other side cooled. The range of Rayleigh number based on the slot width was about 0 < Ra{sub d} < 7.5 x 10{sup 4}. The density change of the gas mixture and the temperature distribution in the slot was obtained and the mixing process when the heavier gas ingress into the vertical slot filled with the lighter gas from the bottom side of the slot was discussed. The experimental results showed that the mixing process due to molecular diffusion was affected significantly by the natural convection induced by the slightly temperature difference between both vertical walls even if a density difference by the binary gas is larger than that by the temperature difference. (author). 81 refs.

  19. Turbulent mixing layers in supersonic protostellar outflows, with application to DG Tauri

    CERN Document Server

    White, Marc C; Sutherland, Ralph S; Salmeron, Raquel; McGregor, Peter J

    2015-01-01

    Turbulent entrainment processes may play an important role in the outflows from young stellar objects at all stages of their evolution. In particular, lateral entrainment of ambient material by high-velocity, well-collimated protostellar jets may be the cause of the multiple emission-line velocity components observed in the microjet-scale outflows driven by classical T Tauri stars. Intermediate-velocity outflow components may be emitted by a turbulent, shock- excited mixing layer along the boundaries of the jet. We present a formalism for describing such a mixing layer based on Reynolds decomposition of quantities measuring fundamental properties of the gas. In this model, the molecular wind from large disc radii provides a continual supply of material for entrainment. We calculate the total stress profile in the mixing layer, which allows us to estimate the dissipation of turbulent energy, and hence the luminosity of the layer. We utilize MAPPINGS IV shock models to determine the fraction of total emission t...

  20. Vorticity-production mechanisms in shock/mixing-layer interaction problems

    Science.gov (United States)

    Tritarelli, R. C.; Kleiser, L.

    2017-03-01

    In this study, we investigate analytically the importance of different vorticity-production mechanisms contributing to the shock-induced vorticity caused by the interaction of a steady oblique shock wave with a steady, planar, supersonic, laminar mixing layer. The inviscid analysis is performed under the condition of a supersonic post-shock flow, which guarantees that the shock refraction remains regular. Special attention is paid to the vorticity production induced by a change in shock strength along the shock. Our analysis subdivides the total vorticity production into its contributions due to bulk or volumetric compression, pre-shock density gradients and variable shock strength. The latter is the only contribution dependent on the shock-wave curvature. The magnitudes of these contributions are analysed for two limiting cases, i.e., the interaction of an oblique shock wave with a constant-density shear layer and the interaction with a constant-velocity mixing layer with density gradients only. Possible implications for shock/mixing-layer interactions occurring in scramjet combustors are briefly discussed.

  1. Simulation of aerosol nucleation and growth in a turbulent mixing layer

    KAUST Repository

    Zhou, Kun

    2014-06-25

    A large-scale simulation of aerosol nucleation and growth in a turbulent mixing layer is performed and analyzed with the aim of elucidating the key processes involved. A cold gaseous stream is mixed with a hot stream of vapor, nanometer sized droplets nucleate as the vapor becomes supersaturated, and subsequently grow as more vapor condenses on their surface. All length and time scales of fluid motion and mixing are resolved and the quadrature method of moments is used to describe the dynamics of the condensing, non-inertial droplets. The results show that a region of high nucleation rate is located near the cold, dry stream, while particles undergo intense growth via condensation on the hot, humid vapor side. Supersaturation and residence times are such that number densities are low and neither coagulation nor vapor scavenging due to condensation are significant. The difference in Schmidt numbers of aerosol particles (approximated as infinity) and temperature and vapor (near unity) causes a drift of the aerosol particles in scalar space and contributes to a large scatter in the conditional statistics of aerosol quantities. The spatial distribution of the aerosol reveals high volume fraction on the hot side of the mixing layer. This distribution is due to drift against the mean and is related to turbulent mixing, which displaces particles from the nucleation region (cold side) into the growth region (hot side). Such a mechanism is absent in laminar flows and is a distinct feature of turbulent condensing aerosols.

  2. A new mixed-mode failure criterion for weak snowpack layers

    Science.gov (United States)

    Reiweger, I.; Gaume, J.; Schweizer, J.

    2015-03-01

    The failure of a weak snow layer is the first in a series of processes involved in dry-snow slab avalanche release. The nature of the initial failure within the weak layer is not yet fully understood but widely debated. The knowledge of the failure criterion is essential for developing avalanche release models and hence for avalanche hazard assessment. Yet different release models assume contradictory criteria as input parameters. We analyzed loading experiments on snow failure performed in a cold laboratory with samples containing a persistent weak snow layer of either faceted crystal, depth hoar, or buried surface hoar. The failure behavior of these layers can be described well with a modified Mohr-Coulomb model accounting for the possible compressive failure of snow. We consequently propose a new mixed-mode shear-compression failure criterion that can be used in avalanche release models.

  3. Erosion study of Fe–W binary mixed layer prepared as model system for RAFM steel

    Energy Technology Data Exchange (ETDEWEB)

    Sugiyama, K., E-mail: kazuyoshi.sugiyama@ipp.mpg.de [Max-Planck-Institut für Plasmaphysik, Garching (Germany); Roth, J. [Max-Planck-Institut für Plasmaphysik, Garching (Germany); Alimov, V.Kh. [Max-Planck-Institut für Plasmaphysik, Garching (Germany); Hydrogen Isotope Research Center, University of Toyama, Toyama (Japan); Schmid, K.; Balden, M.; Elgeti, S.; Koch, F.; Höschen, T. [Max-Planck-Institut für Plasmaphysik, Garching (Germany); Baldwin, M.J.; Doerner, R.P. [Center for Energy Research, University of California at San Diego, La Jolla, CA (United States); Maier, H.; Jacob, W. [Max-Planck-Institut für Plasmaphysik, Garching (Germany)

    2015-08-15

    Fe–W binary mixed layers were prepared as a model system for reduced-activation ferritic–martensitic (RAFM) steel for studying their dynamic erosion behavior resulting from energetic deuterium (D) irradiation. This investigation aims toward an assessment of RAFM steels as plasma-facing material. The surface composition of the model layers is modified by D irradiation. W is enriched at the surface with D irradiation fluence due to the preferential sputtering of Fe. It depends on the D impinging energy as well as the initial W fraction of the Fe–W layer. No significant development of surface topography was observed within the examined conditions. The erosion yield of a Fe–W layer is comparable to that of pure Fe in the low-fluence range and decreases with increasing D fluence. These results indicate that the dynamic change of erosion yield is significantly correlated with the surface W enrichment.

  4. Mixed convection boundary layer flow over a horizontal circular cylinder in a Jeffrey fluid

    Science.gov (United States)

    Zokri, S. M.; Arifin, N. S.; Mohamed, M. K. A.; Salleh, M. Z.; Kasim, A. R. M.; Mohammad, N. F.

    2017-05-01

    In this paper, the mixed convection boundary layer flow and heat transfer of Jeffrey fluid past a horizontal circular cylinder with viscous dissipation effect and constant heat flux is discussed. The governing nonlinear partial differential equations are transformed into dimensionless forms using the appropriate non-similar transformation. Numerical solutions are obtained by using the Keller-box method, which is proven well-tested, flexible, implicit and unconditionally stable. The numerical results for the velocity, temperature, skin friction coefficient and local Nusselt number are attained for various values of mixed convection parameter.

  5. a Novel pt and Npt Mixed Igbt Having a New n-BUFFER Layer

    Science.gov (United States)

    Zhang, Fei; Luo, Shuhua; Zhang, Liang; Wang, Wei; Yu, Wen; Li, Chengfang; Sun, Xiaowei

    For the first time, a novel mixed insulated gate bipolar transistor (MIGBT) is proposed and verified by two-dimensional (2D) mixed device-circuit simulations. The structure of the proposed device is almost identical with that of the conventional IGBT, except for the buffer layer which is formed by employing the n+/n- structure, so that the trade-off relation between the conduction and switching losses is greatly improved and efficiently decoupled. Furthermore, the proposed device exhibits larger forward blocking voltage and positive temperature coefficient of the forward voltage drop, facilitating parallel integration.

  6. Mixing Acid Salts and Layered Double Hydroxides in Nanoscale under Solid Condition

    Directory of Open Access Journals (Sweden)

    Hirokazu Nakayama

    2014-07-01

    Full Text Available The immobilization of potassium sorbate, potassium aspartate and sorbic acid in layered double hydroxide under solid condition was examined. By simply mixing two solids, immobilization of sorbate and aspartate in the interlayer space of nitrate-type layered double hydroxide, so called intercalation reaction, was achieved, and the uptakes, that is, the amount of immobilized salts and the interlayer distances of intercalation compounds were almost the same as those obtained in aqueous solution. However, no intercalation was achieved for sorbic acid. Although intercalation of sorbate and aspartate into chloride-type layered double hydroxide was possible, the uptakes for these intercalation compounds were lower than those obtained using nitrate-type layered double hydroxide. The intercalation under solid condition could be achieved to the same extent as for ion-exchange reaction in aqueous solution, and the reactivity was similar to that observed in aqueous solution. This method will enable the encapsulation of acidic drug in layered double hydroxide as nano level simply by mixing both solids.

  7. The influence of velocity and density ratio on the dynamics of spatially developing mixing layers

    Science.gov (United States)

    Strykowski, P. J.; Niccum, D. L.

    1992-04-01

    The dynamics of countercurrent mixing is examined in the shear layer of an axisymmetric jet. Experiments were designed to establish conditions of absolute instability in a spatially developing shear layer and to document how the instability influences the jet development. By applying suction around the jet periphery, shear-layer velocity ratios R greater than 1 could be studied. Here, R=(U1-U2)/(U1+U2), where U1 is the velocity of the forward jet stream and U2 is the velocity of the counterflowing stream created by suction. The density ratio S=ρ1/ρ2 of the mixing layer was also varied to determine the stability boundary in the S-R plane. The density of the forward stream ρ1 was increased by adding sulfur hexafluoride to the air jet, which provided density ratios between 1 and 5.1. Hot-wire anemometry and flow visualization revealed that a global transition occurs when conditions of absolute instability are established in the jet shear layers. One consequence of this transition is an abrupt decrease in the jet spread rate. The experimentally determined transition between globally stable and globally unstable flow regimes in the S-R plane agrees quite well with predictions of the convective/absolute instability boundary based on the linear stability theory [Pavithran and Redekopp, Phys. Fluids A 1, 1736 (1989)].

  8. A model study of mixing and entrainment in the horizontally evolving atmospheric convective boundary layer

    Energy Technology Data Exchange (ETDEWEB)

    Fedorovich, E.; Kaiser, R. [Univ. Karlsruhe, Inst. fuer Hydrologie und Wasserwirtschaft (Germany)

    1997-10-01

    We present results from a parallel wind-tunnel/large-eddy simulation (LES) model study of mixing and entrainment in the atmospheric convective boundary layer (CBL) longitudinally developing over a heated surface. The advection-type entrainment of warmer air from upper turbulence-free layers into the growing CBL has been investigated. Most of numerical and laboratory model studies of the CBL carried out so far dealt with another type of entrainment, namely the non-steady one, regarding the CBL growth as a non-stationary process. In the atmosphere, both types of the CBL development can take place, often being superimposed. (au)

  9. Mixing height over water and its role on the correlation between temperature and humidity fluctuations in the unstable surface layer

    DEFF Research Database (Denmark)

    Sempreviva, A.M.; Gryning, Sven-Erik

    2000-01-01

    Results from an experimental investigation of the mixing height over inner Danish waters carried out from September 1990 to October 1992, are discussed. The statistical analysis of the mixed-layer height (z(i)) over the sea does not exhibit the daily variation that is characteristic of the mixed ...

  10. Mixed-mode shear-compression failure criterion for weak snowpack layers

    Science.gov (United States)

    Reiweger, Ingrid; Gaume, Johan; Schweizer, Jürg

    2015-04-01

    The failure of a weak snow layer below a cohesive slab is a prerequisite for the release of a dry-snow snow slab avalanche. Once an initial failure in the weak layer reaches its critical size to become self-propagating, the slab will release as an avalanche - provided the slope is steep enough. However, the nature of the initial failure within the weak layer is still unknown - but strongly debated among avalanche researchers. Moreover, different avalanche release models assume contradictory failure criteria as input parameters. We analysed a unique data set stemming from laboratory experiments on snow failure with samples containing a weak snow layer of either depth hoar or buried surface hoar. Depth and surface hoar layers are the most relevant weak layers for avalanche release. The failure behaviour of these types of weak layers can well be described with a modified Mohr-Coulomb model. We therefore propose a mixed-mode failure criterion to be used in avalanche release models.

  11. The fractal measurement of experimental images of supersonic turbulent mixing layer

    Institute of Scientific and Technical Information of China (English)

    ZHAO YuXin; YI ShiHe; TIAN LiFeng; HE Lin; CHENG ZhongYu

    2008-01-01

    Flow Visualization of supersonic mixing layer has been studied based on the high spatiotemporal resolution Nano-based Planar Laser Scattering (NPLS) method in SML-1 wind tunnel. The corresponding images distinctly reproduced the flow structure of laminar, transitional and turbulent region, with which the fractal meas-urement can be implemented. Two methods of measuring fractal dimension wereintroduced and compared. The fractal dimension of the transitional region and the fully developing turbulence region of supersonic mixing layer were measured based on the box-counting method. In the transitional region, the fractal dimension will increase with turbulent intensity. In the fully developing turbulent region, the fractal dimension will not vary apparently for different flow structures, which em-bodies the self-similarity of supersonic turbulence.

  12. Crossover between two- and three-dimensional turbulence in spatial mixing layers

    Science.gov (United States)

    Biancofiore, Luca

    2016-11-01

    We investigate how the domain depth affects the turbulent behaviour in spatially developing mixing layers by means of large-eddy simulations (LES) based on a spectral vanishing viscosity technique. Analyses of spectra of the vertical velocity, of Lumley's diagrams, of the turbulent kinetic energy and of the vortex stretching show that a two-dimensional behaviour of the turbulence is promoted in spatial mixing layers by constricting the fluid motion in one direction. This finding is in agreement with previous works on turbulent systems constrained by a geometric anisotropy, pioneered by Smith, Chasnov & Waleffe. We observe that the growth of the momentum thickness along the streamwise direction is damped in a confined domain. A full two-dimensional turbulent behaviour is observed when the momentum thickness is of the same order of magnitude as the confining scale.

  13. Efficiency of eddy mixing in a stable stratified atmospheric boundary layer

    Science.gov (United States)

    Kurbatskiy, A. F.; Kurbatskaya, L. I.

    2011-12-01

    Based on a mesoscale RANS model of turbulence, the behavior of turbulent eddy mixing parameters is found to agree with the latest data of laboratory and atmospheric measurements. Some problems of the description of turbulent eddy mixing in the atmospheric boundary layer are studied. When the flow transforms to an extremely stable state, in particular, it is found the flux Richardson number Ri f can change nonmonotonically: it increases with increasing gradient Richardson number Rig until the state of saturation is reached at Ri g ≃ 1 and then decreases. The behavior of the coefficients of eddy diffusion of momentum and heat agrees with the concept of momentum (but not heat) transfer by internal waves propagating in an extremely stable atmospheric boundary layer.

  14. The fractal measurement of experimental images of supersonic turbulent mixing layer

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Flow visualization of supersonic mixing layer has been studied based on the high spatiotemporal resolution Nano-based Planar Laser Scattering(NPLS) method in SML-1 wind tunnel. The corresponding images distinctly reproduced the flow structure of laminar,transitional and turbulent region,with which the fractal measurement can be implemented. Two methods of measuring fractal dimension were introduced and compared. The fractal dimension of the transitional region and the fully developing turbulence region of supersonic mixing layer were measured based on the box-counting method. In the transitional region,the fractal dimension will increase with turbulent intensity. In the fully developing turbulent region,the fractal dimension will not vary apparently for different flow structures,which em-bodies the self-similarity of supersonic turbulence.

  15. Sodar measurements of the mixed-layer depth over a large city

    Energy Technology Data Exchange (ETDEWEB)

    Shurygin, E.A. [Russia Academy of Sciences, Inst. of Atmospheric Physics, Moscow (Russian Federation)

    1997-10-01

    The results of synchronous sodar`s measurements on a territory of city and suburban area have shown: (a) The types of stratification over centre of the city and periphery considerably differ, and these distinctions are more often displayed in morning and evening transition period. The agreement between types of stratification in the centre and on the periphery was observed in 40% of cases; (b) At equal temperature stratification the mixed-layer depth in centre of the city is about 50-150 m higher at inversions in comparison with a periphery, at advanced convection - these depths are identical; (c) At different stratification between the city and periphery the distinction in the mixed-layer depth can reach 200. (au)

  16. Influence of convective conditions on three dimensional mixed convective hydromagnetic boundary layer flow of Casson nanofluid

    Energy Technology Data Exchange (ETDEWEB)

    Rauf, A., E-mail: raufamar@ciitsahiwal.edu.pk [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Siddiq, M.K. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Abbasi, F.M. [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Meraj, M.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Ashraf, M. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Shehzad, S.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan)

    2016-10-15

    The present work deals with the steady laminar three-dimensional mixed convective magnetohydrodynamic (MHD) boundary layer flow of Casson nanofluid over a bidirectional stretching surface. A uniform magnetic field is applied normal to the flow direction. Similarity variables are implemented to convert the non-linear partial differential equations into ordinary ones. Convective boundary conditions are utilized at surface of the sheet. A numerical technique of Runge–Kutta–Fehlberg (RFK45) is used to obtain the results of velocity, temperature and concentration fields. The physical dimensionless parameters are discussed through tables and graphs. - Highlights: • Mixed convective boundary layer flow of Casson nanofluid is taken into account. • Impact of magnetic field is examined. • Convective heat and mass conditions are imposed. • Numerical solutions are presented and discussed.

  17. Closed-loop control of an experimental mixing layer using machine learning control

    CERN Document Server

    Parezanović, Vladimir; Cordier, Laurent; Noack, Bernd R; Delville, Joël; Bonnet, Jean-Paul; Segond, Marc; Abel, Markus; Brunton, Steven L

    2014-01-01

    A novel framework for closed-loop control of turbulent flows is tested in an experimental mixing layer flow. This framework, called Machine Learning Control (MLC), provides a model-free method of searching for the best function, to be used as a control law in closed-loop flow control. MLC is based on genetic programming, a function optimization method of machine learning. In this article, MLC is benchmarked against classical open-loop actuation of the mixing layer. Results show that this method is capable of producing sensor-based control laws which can rival or surpass the best open-loop forcing, and be robust to changing flow conditions. Additionally, MLC can detect non-linear mechanisms present in the controlled plant, and exploit them to find a better type of actuation than the best periodic forcing.

  18. RESEARCH ON COHERENT STRUCTURES IN A MIXING LAYER OF THE FENE-P POLYMER SOLUTION

    Institute of Scientific and Technical Information of China (English)

    邵雪明; 林建忠; 余钊圣

    2001-01-01

    The evolution of the coherent structures in a two-dimensional time-developing mixing layer of the FENE-P fluids is examined numerically. By the means of an appropriate filtering for the polymer stress, some characteristics of the coherent structures at high b were obtained, which Azaiez and Homsy did not address. The results indicate that adding polymer to the Newtonian fluids will cause stronger vorticity diffusion, accompanied with weaker fundamental and subharmonical perturbations and slower rotational motion of neighboring vortices during pairing. This effect decreases with the Weissenberg number, but increases with b. In addition, the time when the consecutive rollers are completely coalesced into one delays in the viscoelastic mixing layer compared with the Newtonian one of the same total viscosity.

  19. Asymptotic solution of the turbulent mixing layer for velocity ratio close to unity

    Science.gov (United States)

    Higuera, F. J.; Jimenez, J.; Linan, A.

    1996-01-01

    The equations describing the first two terms of an asymptotic expansion of the solution of the planar turbulent mixing layer for values of the velocity ratio close to one are obtained. The first term of this expansion is the solution of the well-known time-evolving problem and the second, which includes the effects of the increase of the turbulence scales in the stream-wise direction, obeys a linear system of equations. Numerical solutions of these equations for a two-dimensional reacting mixing layer show that the correction to the time-evolving solution may explain the asymmetry of the entrainment and the differences in product generation observed in flip experiments.

  20. Experimental study of thermal mixing layer using variable temperature hot-wire anemometry

    Science.gov (United States)

    Sodjavi, Kodjovi; Carlier, Johan

    2013-10-01

    The buoyancy effects on the development of the thermal mixing layer downstream from a horizontal separating plate were studied by comparing stable and unstable counter-gradient configurations. In this study, the novel experimental technique called parameterizable constant temperature anemometer, proposed by Ndoye et al. (Meas Sci Technol 21(7):075401, 2010), was improved to make possible the simultaneous measurement of temperature and two velocity components with an x-wire probe. The buoyancy effects on the flow are discussed through the transport equations of turbulent kinetic energy and temperature variance. In view of the low Richardson numbers at stake ( Ri f < 0.03), the buoyancy forces appeared logically to be quantitatively negligible compared to the main driving forces, but such a low-energy forcing mechanism was in fact sufficient in unstable configurations to increase the shear stress and the expansion rate of the mixing layer significantly, both phenomena being associated with enhanced production of turbulence.

  1. Direct Numerical Simulation of Gas-Solid Two-Phase Mixing Layer

    Institute of Scientific and Technical Information of China (English)

    Wenchun LI; Guilin HU; Zhe ZHOU; Jianren FAN; Kefa CEN

    2005-01-01

    In this paper, the spatially evolving of the higher Reynolds numbers gas-solid mixing layer under compressible conditions was investigated by a new direct numerical simulation technology. A high-resolution solver was performed for the gas-phase flow-field, particles with different Stokes numbers were traced by the Lagrangian approach based on one-way coupling. The processes of the vortex rolling up and pairing in the two-dimensional mixing layer were captured precisely. The large-scale structures developed from the initial inflow are characterized by the counter-rotating vortices. The mean velocity and the fluctuation intensities profiles agree well with the experimental data. Particles with smaller Stokes numbers accumulate at the vortex centers due to the smaller aerodynamic response time; particles with moderate Stokes numbers tend to orbit around individual streamwise vortices and in the periphery of paring vortices; particles with larger Stokes numbers disperse less evenly, showing a concentration distribution in the flow field.

  2. Direct numerical simulation of particle-fluid flows in turbulent mixing layer

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The coherent structures of a three-dimensional temporally mixing layer and the associated dispersion patterns of particles are numerically studied using a pseudospectral method for fluid and the Lagrangian approach for tracing particles at different Stokes numbers without consideration of particle-particle interactions. The results show that the particles with Stokes number of the order of unity have the largest concentration near the outer edges of the large-scale spanwise vortex structures. The study validates the effect of the streamwise large-scale structures on the particle distribution along the spanwise and transverse directions and it enhances with the development of the three-dimensionality of the mixing layer, which results in a ‘mushroom’ shape of the particle distribution in the spanwise direction.

  3. Mixed-layered bismuth--oxygen--iodine materials for capture and waste disposal of radioactive iodine

    Energy Technology Data Exchange (ETDEWEB)

    Krumhansl, James L; Nenoff, Tina M

    2015-01-06

    Materials and methods of synthesizing mixed-layered bismuth oxy-iodine materials, which can be synthesized in the presence of aqueous radioactive iodine species found in caustic solutions (e.g. NaOH or KOH). This technology provides a one-step process for both iodine sequestration and storage from nuclear fuel cycles. It results in materials that will be durable for repository conditions much like those found in Waste Isolation Pilot Plant (WIPP) and estimated for Yucca Mountain (YMP). By controlled reactant concentrations, optimized compositions of these mixed-layered bismuth oxy-iodine inorganic materials are produced that have both a high iodine weight percentage and a low solubility in groundwater environments.

  4. Simulation of mixed-host emitting layer based organic light emitting diodes

    Science.gov (United States)

    Riku, C.; Kee, Y. Y.; Ong, T. S.; Yap, S. S.; Tou, T. Y.

    2015-04-01

    `SimOLED' simulator is used in this work to investigate the efficiency of the mixed-host organic light emitting devices (MH-OLEDs). Tris-(8-hydroxyquinoline) aluminum(3) (Alq3) and N,N-diphenyl-N,N-Bis(3-methylphenyl)-1,1-diphenyl-4,4-diamine (TPD) are used as the electron transport layer (ETL) material and hole transport layer (HTL) material respectively, and the indium-doped tin oxide (ITO) and aluminum (Al) as anode and cathode. Three MH-OLEDs, A, B and C with the same structure of ITO / HTM (15 nm) / Mixed host (70 nm) / ETM (10 nm) /Al, are stimulated with ratios TPD:Alq3 of 3:5, 5:5, and 5:3 respectively. The Poole-Frenkel model for electron and hole mobilities is employed to compute the current density-applied voltage-luminance characteristics, distribution of the electric field, carrier concentrations and recombination rate.

  5. Modeling turbulent mixing and sand distribution in the bottom boundary layer

    CERN Document Server

    Absi, Rafik

    2011-01-01

    For the calculation of turbulent mixing in the bottom boundary layer, we present simple analytical tools for the mixing velocity wm and the mixing length lm. Based on observations of turbulence intensity measurements, the mixing velocity wm is represented by an exponential function decaying with z. We suggest two theoretical functions for the mixing length, a first lm1 obtained from the k-equation written as a constant modeled fluctuating kinetic energy flux and a second lm2 based on von K\\'arm\\'an's similarity hypothesis. These analytical tools were used in the finite-mixing-length model of Nielsen and Teakle (2004). The modeling of time-mean sediment concentration profiles C(z) over wave ripples shows that at the opposite of the second equation lm2 which increases the upward convexity of C(z), the first equation lm1 increases the upward concavity of C(z) and is able to reproduce the shape of the measured concentrations for coarse sand.

  6. Numerical Study of Turbulent Mixing Layers with Non-Equilibrium Ionization Calculations

    CERN Document Server

    Kwak, Kyujin

    2010-01-01

    Highly ionized species such as C IV, N V, and O VI, are commonly observed in diffuse gas in various places in the universe, such as in our Galaxy's disk and halo, high velocity clouds (HVCs), external galaxies, and the intergalactic medium. One possible mechanism for producing high ions is turbulent mixing of cool gas with hotter gas in locations where these gases slide past each other. By using hydrodynamic simulations with radiative cooling and non-equilibrium ionization (NEI) calculations, we investigate the physical properties of turbulent mixing layers and the production of high ions. We find that most of the mixing occurs on the hot side of the hot/cool interface and that the mixed region separates into a tepid zone containing radiatively cooled, C IV-rich gas and a hotter zone which is rich in C IV, N V, and O VI. Mixing occurs faster than ionization or recombination, making the mixed gas a better source of C IV, N V, and O VI in our NEI simulations than in our collisional ionization equilibrium (CIE) ...

  7. Corrosion behavior of Hastelloy C-276 in supercritical water

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Qiang [National Key Laboratory for Nuclear Fuel and Materials, Nuclear Power Institute of China, P.O. Box 436, Chendu 610041 (China); Tang Rui [National Key Laboratory for Nuclear Fuel and Materials, Nuclear Power Institute of China, P.O. Box 436, Chendu 610041 (China)], E-mail: xajttr@163.com; Yin Kaiju; Luo Xin [National Key Laboratory for Nuclear Fuel and Materials, Nuclear Power Institute of China, P.O. Box 436, Chendu 610041 (China); Zhang Lefu [College of Nuclear Science and Technology, Shanghai Jiaotong University, Shanghai 200240 (China)

    2009-09-15

    The corrosion behavior of a nickel-based alloy Hastelloy C-276 exposed in supercritical water at 500-600 deg. C/25 MPa was investigated by means of gravimetry, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. An oxide scale with dual-layer structure, mainly consisting of an outer NiO layer and an inner Cr{sub 2}O{sub 3}/NiCr{sub 2}O{sub 4}-mixed layer, developed on C-276 after 1000 h exposure. Higher temperature promoted oxidation, resulting in thicker oxide scale, larger weight gain and stronger tendency of oxide spallation. The oxide growth mechanism in SCW seems to be similar to that in high temperature water vapor, namely solid-state growth mechanism.

  8. Shear rheology of mixed protein adsorption layers vs their structure studied by surface force measurements.

    Science.gov (United States)

    Danov, Krassimir D; Kralchevsky, Peter A; Radulova, Gergana M; Basheva, Elka S; Stoyanov, Simeon D; Pelan, Eddie G

    2015-08-01

    The hydrophobins are proteins that form the most rigid adsorption layers at liquid interfaces in comparison with all other investigated proteins. The mixing of hydrophobin HFBII with other conventional proteins is expected to reduce the surface shear elasticity and viscosity, E(sh) and η(sh), proportional to the fraction of the conventional protein. However, the experiments show that the effect of mixing can be rather different depending on the nature of the additive. If the additive is a globular protein, like β-lactoglobulin and ovalbumin, the surface rigidity is preserved, and even enhanced. The experiments with separate foam films indicate that this is due to the formation of a bilayer structure at the air/water interface. The more hydrophobic HFBII forms the upper layer adjacent to the air phase, whereas the conventional globular protein forms the lower layer that faces the water phase. Thus, the elastic network formed by the adsorbed hydrophobin remains intact, and even reinforced by the adjacent layer of globular protein. In contrast, the addition of the disordered protein β-casein leads to softening of the HFBII adsorption layer. Similar (an even stronger) effect is produced by the nonionic surfactant Tween 20. This can be explained with the penetration of the hydrophobic tails of β-casein and Tween 20 between the HFBII molecules at the interface, which breaks the integrity of the hydrophobin interfacial elastic network. The analyzed experimental data for the surface shear rheology of various protein adsorption layers comply with a viscoelastic thixotropic model, which allows one to determine E(sh) and η(sh) from the measured storage and loss moduli, G' and G″. The results could contribute for quantitative characterization and deeper understanding of the factors that control the surface rigidity of protein adsorption layers with potential application for the creation of stable foams and emulsions with fine bubbles or droplets. Copyright © 2014

  9. The sensitivity of subannual and intraseasonal tropical variability to model ocean mixed layer depth

    Science.gov (United States)

    Watterson, I. G.

    2002-01-01

    The influence of air-sea interaction on subannual and intraseasonal tropical variability is explored through analysis of three long simulations of the Commonwealth Scientific and Industrial Research Organisation atmospheric general circulation model (GCM) with differing ocean specifications: a coupled ocean GCM, a simple 50-m mixed layer model, or climatological sea surface temperatures (SST); together with 50-year simulations with mixed layer depths of 10 m and 20 m. The analysis focuses initially on a signal similar to a Madden-Julian Oscillation (MJO) contained in the first two empirical orthogonal functions (EOF) of monthly anomalies of tropical 807-hPa winds in January in the coupled model. Time-lag regression is used to demonstrate that these patterns propagate eastward, although at only half the speed of the MJO, and induce perturbations to the Australian monsoon. The specified SST model shows no such propagation. Similar results are then obtained using daily data filtered to retain subannual periods. The eastward propagation speed is faster in the shallower mixed layer cases, with the 10-m case producing speeds close to observations. In the interactive models, surface energy fluxes force SST anomalies propagating ahead of the EOF convergence. These fluxes are largely consistent with evaporation perturbed by wind anomalies to the monsoon westerlies, augmented by solar radiation. The SST anomalies then further perturb the winds, as is confirmed by a separate SST perturbation experiment. From the examination of other seasons, it is seen that air-sea interaction generally enhances the amplitude of the MJO-like patterns. It also enhances their eastward propagation along westerly wind bands. Analysis of zonal wave number one winds confirms the strong sensitivity to mixed layer depth in the amplitude and period of the eastward propagating component, particularly during September through February. The results suggest that air-sea interaction may be important to the

  10. Magnetic behavior of Mg-Al-Zn-Fe mixed oxides from precursors layered double hydroxide

    Energy Technology Data Exchange (ETDEWEB)

    Oliva, M.I., E-mail: marcosivanoliva@gmail.com [Facultad de Matematica, Astronomia y Fisica, Universidad Nacional de Cordoba, M. Allende y H. de la Torre Ciudad Universitaria, 5000 Cordoba (Argentina); IFFAM AF (CONICET - FaMAF UNC), M. Allende y H. de la Torre Ciudad Universitaria, 5000 Cordoba (Argentina); Heredia, A. [CITeQ - Facultad R. Cordoba, Universidad Tecnologica Nacional Maestro Lopez esq. Cruz Roja Argentina, CP 5016 Cordoba (Argentina); Zandalazini, C.I. [Centro Laser de Ciencias Moleculares. INFIQC-FCQ-Grupo de Ciencia de Materiales-FaMAF-Universidad Nacional de Cordoba, Ciudad Universitaria, CP5000 Cordoba, Argentina CONICET (Argentina); Crivello, M. [CITeQ - Facultad R. Cordoba, Universidad Tecnologica Nacional Maestro Lopez esq. Cruz Roja Argentina, CP 5016 Cordoba (Argentina); Corchero, E. [Facultad de Matematica, Astronomia y Fisica, Universidad Nacional de Cordoba, M. Allende y H. de la Torre Ciudad Universitaria, 5000 Cordoba (Argentina)

    2012-08-15

    Mixed oxides of Mg-Al-Zn-Fe were obtained by calcination of layered double hydroxides (LDH) prepared by coprecipitation reaction with hydrothermal treatment. The structural characterization of precursors and oxides was carried out by X rays diffraction, showing increases of ZnO phase with the increase of the zinc content. Magnetic behavior was studied by vibrating sample magnetometer (VSM) and by a superconducting quantum interference device (SQUID) showing both paramagnetic and super paramagnetic behavior depending on both particles size and composition.

  11. Tropical Cyclone Footprint in the Ocean Mixed Layer Observed by Argo in the Northwest Pacific

    Science.gov (United States)

    2014-10-25

    suggests a dominant role played by the Ekman pumping under the slow TCs. However, the correlation between the ILT and ILD change induced by the fast TCs...convergence in the outside edge of the TC-active region. Our results also support that the TC-winds can strengthen climatological background Ekman pumping...distribution of wind stress and faster translation under the fast TCs. The mixed layer response is dominated by the Ekman pumping for the slow TCs

  12. Surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea

    Science.gov (United States)

    Lincoln, B. J.; Rippeth, T. P.; Simpson, J. H.

    2016-08-01

    Inertial oscillations are a ubiquitous feature of the surface ocean. Here we combine new observations with a numerical model to investigate the role of inertial oscillations in driving deepening of the surface mixed layer in a seasonally stratified sea. Observations of temperature and current structure, from a mooring in the Western Irish Sea, reveal episodes of strong currents (>0.3 m s-1) lasting several days, resulting in enhanced shear across the thermocline. While the episodes of strong currents are coincident with windy periods, the variance in the shear is not directly related to the wind stress. The shear varies on a subinertial time scale with the formation of shear maxima lasting several hours occurring at the local inertial period of 14.85 h. These shear maxima coincide with the orientation of the surface current being at an angle of approximately 90° to the right of the wind direction. Observations of the water column structure during windy periods reveal deepening of the surface mixed layer in a series of steps which coincide with a period of enhanced shear. During the periods of enhanced shear gradient, Richardson number estimates indicate Ri-1 ≥ 4 at the base of the surface mixed layer, implying the deepening as a result of shear instability. A one-dimensional vertical exchange model successfully reproduces the magnitude and phase of the shear spikes as well as the step-like deepening. The observations and model results therefore identify the role of wind shear alignment as a key entrainment mechanism driving surface mixed layer deepening in a shallow, seasonally stratified sea.

  13. Boundary Layer CO2 mixing ratio measurements by an airborne pulsed IPDA lidar

    Science.gov (United States)

    Ramanathan, A. K.; Mao, J.; Abshire, J. B.; Allan, G. R.

    2014-12-01

    Since the primary signature of CO2 fluxes at the surface occurs in the planetary boundary layer (PBL), remote sensing measurements of CO2 that can resolve the CO2 absorption in the PBL separate from the total column are more sensitive to fluxes than those that can only measure a total column. The NASA Goddard CO2 sounder is a pulsed, range-resolved lidar that samples multiple (presently 30) wavelengths across the 1572.335 nm CO2 absorption line. The range resolution and line shape measurement enable CO2 mixing ratio measurements to be made in two or more altitude layers including the PBL via lidar cloud-slicing and multi-layer retrievals techniques. The pulsed lidar approach allows range-resolved backscatter of scattering from ground and cloud tops. Post flight data analysis can be used split the vertical CO2 column into layers (lidar cloud-slicing) and solve for the CO2 mixing ratio in each layer. We have demonstrated lidar cloud slicing with lidar measurements from a flight over Iowa, USA in August 2011 during the corn-growing season, remotely measuring a ≈15 ppm drawdown in the PBL CO2. We will present results using an improved lidar cloud slicing retrieval algorithm as well as preliminary measurements from the upcoming ASCENDS 2014 flight campaign. The CO2 absorption line is also more pressure broadened at lower altitudes. Analyzing the line shape also allows solving for some vertical resolution in the CO2 distribution. By allowing the retrieval process to independently vary the column concentrations in two or more altitude layers, one can perform a best-fit retrieval to obtain the CO2 mixing ratios in each of the layers. Analysis of airborne lidar measurements (in 2011) over Iowa, USA and Four Corners, New Mexico, USA show that for altitudes above 8 km, the CO2 sounder can detect and measure enhanced or diminished CO2 mixing ratios in the PBL even in the absence of clouds. We will present these results as well as preliminary measurements from the upcoming

  14. Mixed convection boundary layer flow over a horizontal elliptic cylinder with constant heat flux

    Science.gov (United States)

    Javed, Tariq; Ahmad, Hussain; Ghaffari, Abuzar

    2015-12-01

    Mixed convection boundary layer flow of a viscous fluid over a horizontal elliptic cylinder with a constant heat flux is investigated numerically. The governing partial differential equations are transformed to non-dimensional form and then are solved by an efficient implicit finite different scheme known as Keller-box method. The solutions are expressed in the form of skin friction and Nusselt number, which are plotted against the eccentric angle. The effect of pertinent parameters such as mixed convection parameter, aspect ratio (ratio of lengths of minor axis to major axis), and Prandtl number on skin friction and Nusselt number are illustrated through graphs for both blunt and slender orientations. The increase in the value of mixed convection parameter results in increase in skin friction coefficient and Nusselt number for blunt as well as slender orientations.

  15. An assumed pdf approach for the calculation of supersonic mixing layers

    Science.gov (United States)

    Baurle, R. A.; Drummond, J. P.; Hassan, H. A.

    1992-01-01

    In an effort to predict the effect that turbulent mixing has on the extent of combustion, a one-equation turbulence model is added to an existing Navier-Stokes solver with finite-rate chemistry. To average the chemical-source terms appearing in the species-continuity equations, an assumed pdf approach is also used. This code was used to analyze the mixing and combustion caused by the mixing layer formed by supersonic coaxial H2-air streams. The chemistry model employed allows for the formation of H2O2 and HO2. Comparisons are made with recent measurements using laser Raman diagnostics. Comparisons include temperature and its rms, and concentrations of H2, O2, N2, H2O, and OH. In general, good agreement with experiment was noted.

  16. Vertical distribution and composition of phytoplankton under the influence of an upper mixed layer.

    Science.gov (United States)

    Ryabov, Alexei B; Rudolf, Lars; Blasius, Bernd

    2010-03-01

    The vertical distribution of phytoplankton is of fundamental importance for the dynamics and structure of aquatic communities. Here, using an advection-reaction-diffusion model, we investigate the distribution and competition of phytoplankton species in a water column, in which inverse resource gradients of light and a nutrient can limit growth of the biomass. This problem poses a challenge for ecologists, as the location of a production layer is not fixed, but rather depends on many internal parameters and environmental factors. In particular, we study the influence of an upper mixed layer (UML) in this system and show that it leads to a variety of dynamic effects: (i) Our model predicts alternative density profiles with a maximum of biomass either within or below the UML, thereby the system may be bistable or the relaxation from an unstable state may require a long-lasting transition. (ii) Reduced mixing in the deep layer can induce oscillations of the biomass; we show that a UML can sustain these oscillations even if the diffusivity is less than the critical mixing for a sinking phytoplankton population. (iii) A UML can strongly modify the outcome of competition between different phytoplankton species, yielding bistability both in the spatial distribution and in the species composition. (iv) A light limited species can obtain a competitive advantage if the diffusivity in the deep layers is reduced below a critical value. This yields a subtle competitive exclusion effect, where the oscillatory states in the deep layers are displaced by steady solutions in the UML. Finally, we present a novel graphical approach for deducing the competition outcome and for the analysis of the role of a UML in aquatic systems.

  17. Spin-mixing conductances of metallic and half-metallic magnetic layers.

    Science.gov (United States)

    Turek, I; Carva, K

    2007-09-12

    The spin-mixing conductance of a thin ferromagnetic layer attached epitaxially to two semi-infinite non-magnetic metallic leads is formulated in terms of non-equilibrium Green's functions. The spin-mixing conductance is obtained as a response of the spin torque acting on the ferromagnet with respect to the spin accumulation in one of the leads, while the spin torque is defined as a time derivative of the spin magnetic moment. The equivalence of the derived formula with a previous expression of the Landauer-Büttiker scattering theory is sketched and an implementation within the ab initio tight-binding linear muffin-tin orbital method is briefly described. Applications are made for metallic Co- and Ni-based slabs embedded between Cu(111) leads and for half-metallic Co(2)MnSi films sandwiched by Cr(001) leads. The calculated results throw serious doubts on the general validity of two features: fast convergence of the spin-mixing conductance with increasing thickness of the magnetic layer and negligible values of the imaginary part of the spin-mixing conductance as compared to the real part.

  18. Effects of Transition-Metal Mixing on Na Ordering and Kinetics in Layered P 2 Oxides

    Science.gov (United States)

    Zheng, Chen; Radhakrishnan, Balachandran; Chu, Iek-Heng; Wang, Zhenbin; Ong, Shyue Ping

    2017-06-01

    Layered P 2 oxides are promising cathode materials for rechargeable sodium-ion batteries. In this work, we systematically investigate the effects of transition-metal (TM) mixing on Na ordering and kinetics in the NaxCo1 -yMnyO2 model system using density-functional-theory (DFT) calculations. The DFT-predicted 0-K stability diagrams indicate that Co-Mn mixing reduces the energetic differences between Na orderings, which may account for the reduction of the number of phase transformations observed during the cycling of mixed-TM P 2 layered oxides compared to a single TM. Using ab initio molecular-dynamics simulations and nudged elastic-band calculations, we show that the TM composition at the Na(1) (face-sharing) site has a strong influence on the Na site energies, which in turn impacts the kinetics of Na diffusion towards the end of the charge. By employing a site-percolation model, we establish theoretical upper and lower bounds for TM concentrations based on their effect on Na(1) site energies, providing a framework to rationally tune mixed-TM compositions for optimal Na diffusion.

  19. Simultaneous Concentration and Velocity Field Measurements in a Shock-accelerated Mixing Layer

    Science.gov (United States)

    Reese, Daniel; Oakley, Jason; Weber, Chris; Rothamer, David; Navarro, Jose; Bonazza, Riccardo

    2013-11-01

    The Richtmyer-Meshkov instability (RMI) is experimentally investigated at the Wisconsin Shock Tube Laboratory. Simultaneous concentration and velocity field measurements from the mixing layer of experimental RMI images are obtained through the application of the Advection-Corrected Correlation Image Velocimetry (ACCIV) technique. A statistically repeatable broadband initial condition is created by first setting up a gravitationally stable stagnation plane of helium +acetone over argon and then injecting the gases horizontally at the interface to create a shear layer. The shear layer is then accelerated by a Mach 2.2 planar shock wave that causes the growth of any perturbations present at the interface, and time-separated image pair data of the mixing layer are obtained using planar laser induced fluorescence (PLIF). The image pair is corrected to show relative acetone concentration, and is then used as input to the ACCIV algorithm to obtain velocity field results. These velocity field measurements are compared with those obtained from numerical simulations. Turbulent kinetic energy spectra are compared with particle imaging velocimetry (PIV) and simulation results to validate regions of applicability. We wish to thank the Department of Energy National Nuclear Security Administration for supporting this work.

  20. Influence of Subgrade and Unbound Granular Layers Stiffness on Fatigue Life of Hot Mix Asphalts - HMA

    Directory of Open Access Journals (Sweden)

    Hugo A. Rondón-Quintana

    2013-11-01

    Full Text Available The mainly factors studied to predict fatigue life of hot mix asphalt-HMA in flexible pavements are the loading effect, type of test, compaction methods, design parameters of HMA (e.g., particle size and size distribution curve, fine content, type of bitumen and the variables associated with the environment (mainly moisture, temperature, aging. This study evaluated through a computer simulation, the influence of the granular layers and subgrade on the fatigue life of asphalt layers in flexible pavement structures. Mechanics parameters of granular layers of subgrade, base and subbase were obtained using the mathematical equations currently used for this purpose in the world. The emphasis of the study was the city of Bogotá, where the average annual temperature is 14°C and soils predominantly clay, generally experience CBR magnitudes between 1% and 4%. General conclusion: stiffness of the granular layers and subgrade significantly affect the fatigue resistance of HMA mixtures. Likewise, the use of different equations reported in reference literature in order to characterize granular layers may vary the fatigue life between 4.6 and 48.5 times, varying the thickness of the pavement layers in the design.

  1. Observing entrainment mixing, photochemical ozone production, and regional methane emissions by aircraft using a simple mixed-layer framework

    Science.gov (United States)

    Trousdell, Justin F.; Conley, Stephen A.; Post, Andy; Faloona, Ian C.

    2016-12-01

    In situ flight data from two distinct campaigns during winter and summer seasons in the San Joaquin Valley (SJV) of California are used to calculate boundary-layer entrainment rates, ozone photochemical production rates, and regional methane emissions. Flights near Fresno, California, in January and February 2013 were conducted in concert with the NASA DISCOVER-AQ project. The second campaign (ArvinO3), consisting of 11 days of flights spanning June through September 2013 and 2014, focused on the southern end of the SJV between Bakersfield and the small town of Arvin, California - a region notorious for frequent violations of ozone air quality standards. Entrainment velocities, the parameterized rates at which free tropospheric air is incorporated into the atmospheric boundary layer (ABL), are estimated from a detailed budget of the inversion base height. During the winter campaign near Fresno, we find an average midday entrainment velocity of 1.5 cm s-1, and a maximum of 2.4 cm s-1. The entrainment velocities derived during the summer months near Bakersfield averaged 3 cm s-1 (ranging from 0.9 to 6.5 cm s-1), consistent with stronger surface heating in the summer months. Using published data on boundary-layer heights we find that entrainment rates across the Central Valley of California have a bimodal annual distribution peaking in spring and fall when the lower tropospheric stability (LTS) is changing most rapidly.Applying the entrainment velocities to a simple mixed-layer model of three other scalars (O3, CH4, and H2O), we solve for ozone photochemical production rates and find wintertime ozone production (2.8 ± 0.7 ppb h-1) to be about one-third as large as in the summer months (8.2 ± 3.1 ppb h-1). Moreover, the summertime ozone production rates observed above Bakersfield-Arvin exhibit an inverse relationship to a proxy for the volatile organic compound (VOC) : NOx ratio (aircraft [CH4] divided by surface [NO2]), consistent with a NOx-limited photochemical

  2. Comparison of Four Mixed Layer Mesoscale Parameterizations and the Equation for an Arbitrary Tracer

    Science.gov (United States)

    Canuto, V. M.; Dubovikov, M. S.

    2011-01-01

    In this paper we discuss two issues, the inter-comparison of four mixed layer mesoscale parameterizations and the search for the eddy induced velocity for an arbitrary tracer. It must be stressed that our analysis is limited to mixed layer mesoscales since we do not treat sub-mesoscales and small turbulent mixing. As for the first item, since three of the four parameterizations are expressed in terms of a stream function and a residual flux of the RMT formalism (residual mean theory), while the fourth is expressed in terms of vertical and horizontal fluxes, we needed a formalism to connect the two formulations. The standard RMT representation developed for the deep ocean cannot be extended to the mixed layer since its stream function does not vanish at the ocean's surface. We develop a new RMT representation that satisfies the surface boundary condition. As for the general form of the eddy induced velocity for an arbitrary tracer, thus far, it has been assumed that there is only the one that originates from the curl of the stream function. This is because it was assumed that the tracer residual flux is purely diffusive. On the other hand, we show that in the case of an arbitrary tracer, the residual flux has also a skew component that gives rise to an additional bolus velocity. Therefore, instead of only one bolus velocity, there are now two, one coming from the curl of the stream function and other from the skew part of the residual flux. In the buoyancy case, only one bolus velocity contributes to the mean buoyancy equation since the residual flux is indeed only diffusive.

  3. A conceptual framework to quantify the influence of convective boundary layer development on carbon dioxide mixing ratios

    Directory of Open Access Journals (Sweden)

    D. Pino

    2011-12-01

    Full Text Available Interpretation of observed diurnal carbon dioxide (CO2 mixing ratios near the surface requires knowledge of the local dynamics of the planetary boundary layer. In this paper, we quantify the relationship between the boundary layer dynamics and the CO2 budget in convective conditions through a newly derived set of analytical equations. From these equations, we are able to quantify how uncertainties in boundary layer dynamical variables or in the morning CO2 distribution in the mixed-layer or in the free atmosphere influence the bulk CO2 mixing ratio.

    We find that the largest uncertainty incurred on the mid-day CO2 mixing ratio comes from the prescribed early morning CO2 mixing ratios in the stable boundary layer, and in the free atmosphere. Errors in these values influence CO2 mixing ratios inversely proportional to the boundary layer depth (h, just like uncertainties in the assumed initial boundary layer depth and surface CO2 flux. The influence of uncertainties in the boundary layer depth itself are one order of magnitude smaller. If we "invert" the problem and calculate CO2 surface exchange from observed or simulated CO2 mixing ratios, the sensitivities to errors in boundary layer dynamics also invert: they become linearly proportional to the boundary layer depth.

    We demonstrate these relations for a typical well characterized situation at the Cabauw tower in the Netherlands, and conclude that knowledge of the temperature and carbon dioxide vertical profiles in the early morning are of vital importance to correctly interpret observed CO2 mixing ratios during midday.

  4. A conceptual framework to quantify the influence of convective boundary layer development on carbon dioxide mixing ratios

    Science.gov (United States)

    Pino, D.; Vilà-Guerau de Arellano, J.; Peters, W.; Schröter, J.; van Heerwaarden, C. C.; Krol, M. C.

    2012-03-01

    Interpretation of observed diurnal carbon dioxide (CO2) mixing ratios near the surface requires knowledge of the local dynamics of the planetary boundary layer. In this paper, we study the relationship between the boundary layer dynamics and the CO2 budget in convective conditions through a newly derived set of analytical equations. From these equations, we are able to quantify how uncertainties in boundary layer dynamical variables or in the morning CO2 distribution in the mixed-layer or in the free atmosphere (FA) influence the bulk CO2 mixing ratio. We find that the largest uncertainty incurred on the mid-day CO2 mixing ratio comes from the prescribed early morning CO2 mixing ratios in the stable boundary layer, and in the free atmosphere. Errors in these values influence CO2 mixing ratios inversely proportional to the boundary layer depth (h), just like uncertainties in the assumed initial boundary layer depth and surface CO2 flux. The influence of uncertainties in the boundary layer depth itself is one order of magnitude smaller. If we "invert" the problem and calculate CO2 surface exchange from observed or simulated CO2 mixing ratios, the sensitivities to errors in boundary layer dynamics also invert: they become linearly proportional to the boundary layer depth. We demonstrate these relations for a typical well characterized situation at the Cabauw site in The Netherlands, and conclude that knowledge of the temperature and carbon dioxide profiles of the atmosphere in the early morning are of vital importance to correctly interpret observed CO2 mixing ratios during midday.

  5. A relativistic mixing-layer model for jets in low-luminosity radio galaxies

    CERN Document Server

    Wang, Y; Laing, R; Alexander, P; Pavlovski, G; Knigge, C

    2009-01-01

    We present an analytical model for jets in Fanaroff & Riley Class I (FRI) radio galaxies, in which an initially laminar, relativistic flow is surrounded by a shear layer. We apply the appropriate conservation laws to constrain the jet parameters, starting the model where the radio emission is observed to brighten abruptly. We assume that the laminar flow fills the jet there and that pressure balance with the surroundings is maintained from that point outwards. Entrainment continuously injects new material into the jet and forms a shear layer, which contains material from both the environment and the laminar core. The shear layer expands rapidly with distance until finally the core disappears, and all of the material is mixed into the shear layer. Beyond this point, the shear layer expands in a cone and decelerates smoothly. We apply our model to the well-observed FRI source 3C31 and show that there is a self-consistent solution. We derive the jet power, together with the variations of mass flux and and en...

  6. Oceanic Mixing Processes in Disko Bay-Ilulissat Icefjord System: Can We Quantify the Heat Loss from the Atlantic Water Layer?

    Science.gov (United States)

    Djoumna, G.; Holland, D. M.

    2014-12-01

    Ilulissat Icefjord (IIF) has been the site of few hydrographic observations. Recent hydrographic data from Disko Bay (DB) showed a significant warming from the below of the cold Polar Water entering DB from the mid-to-late 19901990s onward, and the sill at the fjord mouth prevented the modified West Greenland Irminger Waters (WGIW) to fill the IIF basin. Here we identify and attempt to quantify the fluxes associated with the small-scale processes that contribute to the upward diapycnal fluxes of heat, salt and from the modified WGIW to the surface-mixed layer using five years of summer data (2009 - 2013). The interaction between the WGIW and Egedesminde Dyb trough cutting across the continental shelf from the shelf break into DB creates the cold/warm layering of water masses which contribute to the formation of double diffusive thermohaline staircases. We found evidence of thermohaline staircase consists of series of sharp interfaces across which both TT and SS increase with depth separated by thick well-defined convective layers. We hypothesize that the warming of the PW layer in DB may have been caused by the upward heat fluxes from the AW driven double diffusive convection. Vertical heat fluxes estimated from laboratory-based flux laws for the diffusive regime of double diffusive convection were up to 0.20.2Wm-2^{-2}. The other major player responsible for the Atlantic water heat loss is shear instabilities in the internal wave and tides generated by barotropic tidal flow over the Egedesminde Dyb trough, the continental shelf and across the sill at the entrance of IIF. Using moored pressure data, we found that the fjord could be described as a wave-fjord during neap tide and turns into a tidal jet-fjord during spring tide, therefore a weak nonlinear response due to supercritical conditions with flow separation over the sill and a linear baroclinic tidal response due to the deeper right side of the sill could be expected. We found enhanced eddy diffusivity K

  7. Mixed layer modeling in the East Pacific warm pool during 2002

    Energy Technology Data Exchange (ETDEWEB)

    Van Roekel, Luke P. [Colorado State University, Department of Atmospheric Science, Fort Collins, CO (United States); University of Colorado at Boulder, Boulder, CO (United States); Maloney, Eric D. [Colorado State University, Department of Atmospheric Science, Fort Collins, CO (United States)

    2012-06-15

    Two vertical mixing models (the modified dynamic instability model of Price et al.; PWP, and K-Profile Parameterizaton; KPP) are used to analyze intraseasonal sea surface temperature (SST) variability in the northeast tropical Pacific near the Costa Rica Dome during boreal summer of 2002. Anomalies in surface latent heat flux and shortwave radiation are the root cause of the three intraseasonal SST oscillations of order 1 C amplitude that occur during this time, although surface stress variations have a significant impact on the third event. A slab ocean model that uses observed monthly varying mixed layer depths and accounts for penetrating shortwave radiation appears to well-simulate the first two SST oscillations, but not the third. The third oscillation is associated with small mixed layer depths (<5 m) forced by, and acting with, weak surface stresses and a stabilizing heat flux that cause a transient spike in SST of 2 C. Intraseasonal variations in freshwater flux due to precipitation and diurnal flux variability do not significantly impact these intraseasonal oscillations. These results suggest that a slab ocean coupled to an atmospheric general circulation model, as used in previous studies of east Pacific intraseasonal variability, may not be entirely adequate to realistically simulate SST variations. Further, while most of the results from the PWP and KPP models are similar, some important differences that emerge are discussed. (orig.)

  8. Wave breaking on turbulent energy budget in the ocean surface mixed layer

    Institute of Scientific and Technical Information of China (English)

    SUN Qun; GUAN Changlong; SONG Jinbao

    2008-01-01

    As an important physical process at the air-sea interface.wave movement and breaking have a significant effect on the ocean surface mixed layer (OSML).When breaking waves occur at the ocean surface,turbulent kinetic energy (TKE) is input downwards,and a sublayer is formed near the surface and turbulence vertical mixing is intensively enhanced.A one-dimensional ocean model including the Mellor-Yamada level 2.5 turbulence closure equations was employed in our research on variations in turbulent energy budget wimin OSML.The influence of wave breaking could be introduced into the model by modifying an existing surface boundary condition of the TKE equation and specifying its input.The vertical diffusion and dissipation of TKE were effectively enhanced in the sublayer when wave breaking was considered.Turbulent energy dissipated in the sublayer was about 92.0% of the total depth-integrated dissipated TKE,which is twice higher than that of non-wave breaking.The shear production of TKE decreased bv 3.5% because the mean flow fields tended to be uniform due to wave-enhanced turbulent mixing.As a result.a new local equilibrium between diffusion and dissipation of TKE was reached in the wave-enhanced layer.Below the sublayer,the local equilibrium between shear production and dissipation of TKE agreed with the conclusion drawn from the classical law-of-the-wall (Craig and Banner,1994).

  9. Direct numerical simulation of a small Atwood number Rayleigh-Taylor instability-driven mixing layer

    Science.gov (United States)

    Mueschke, Nicholas; Schilling, Oleg; Andrews, Malcolm

    2005-11-01

    A direct numerical simulation (DNS) of a small Atwood number Rayleigh-Taylor mixing layer was performed using a spectral/compact-difference scheme. The initial conditions were parameterized from interfacial and velocity perturbations measured from water channel experiments at Texas A&M University. Turbulence and mixing statistics, as well as energy spectra, obtained from experimental measurements are compared with those from the DNS to validate the use of experimental measurements as computational initial conditions. The experimental and numerical data are used to examine the transitional dynamics of the mixing layer. The DNS results indicate that initial conditions including both interfacial and velocity perturbations are required to accurately simulate the flow. This research was sponsored by the U.S. DOE National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant #DE-FG03- 02NA00060. This work was also performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W- 7405-Eng-48. UCRL-ABS-214352.

  10. Evaluation of the heat balance constituents of the upper mixed layer in the North Atlantic

    Science.gov (United States)

    Polonsky, A. B.; Sukhonos, P. A.

    2016-11-01

    Different physical mechanisms which cause interannual and interdecadal temperature anomalies in the upper mixed layer (UML) of the North Atlantic are investigated using the data of ORA-S3 reanalysis for the period of 1959-2011. It is shown that the annual mean heat budget in UML is mainly caused by the balance between advective heat transfer and horizontal turbulent mixing (estimated as a residual term in the equation of thermal balance). The local UML temperature change and contribution from the heat fluxes on the lower boundary of the UML to the heat budget of the upper layer are insignificant for the time scale under consideration. The contribution of the heat fluxes on the upper UML boundary to the low-frequency variability of the upper layer temperature in the whole North Atlantic area is substantially less than 30%. Areas like the northwestern part of the Northern Subtropical Anticyclonic Gyre (NSAG), where their contribution exceeds 30-60%, are exceptions. The typical time scales of advective heat transfer variability are revealed. In the NSAG area, an interannual variability associated with the North Atlantic Oscillation dominates, while in the North Atlantic subpolar gyre, an interdecadal variability of advective transfers with periods of more than 30 years prevails.

  11. Mixed-layer water oscillations in tropical Pacific for ENSO cycle

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The main modes of interannal variabilities of thermocline and sea surface wind stress in the tropical Pacific and their interactions are investigated, which show the following results. (1) The thermocline anomalies in the tropical Pacific have a zonal dipole pattern with 160°W as its axis and a meridional seesaw pattern with 6-8°N as its transverse axis. The meridional oscillation has a phase lag of about 90° to the zonal oscillation, both oscillations get together to form the El Ni(n)o/La Ni(n)a cycle, which behaves as a mixed layer water oscillates anticlockwise within the tropical Pacific basin between equator and 12°N. (2) There are two main patterns of wind stress anomalies in the tropical Pacific, of which the first component caused by trade wind anomaly is characterized by the zonal wind stress anomalies and its corresponding divergences field in the equatorial Pacific, and the abnormal cross-equatorial flow wind stress and its corresponding divergence field, which has a sign opposite to that of the equatorial region, in the off-equator of the tropical North Pacific, and the second component represents the wind stress anomalies and corresponding divergences caused by the ITCZ anomaly. (3) The trade winds anomaly plays a decisive role in the strength and phase transition of the ENSO cycle, which results in the sea level tilting, provides an initial potential energy to the mixed layer water oscillation, and causes the opposite thermocline displacement between the west side and east side of the equator and also between the equator and 12°N of the North Pacific basin, therefore determines the amplitude and route for ENSO cycle. The ITCZ anomaly has some effects on the phase transition. (4) The thermal anomaly of the tropical western Pacific causes the wind stress anomaly and extends eastward along the equator accompanied with the mixed layer water oscillation in the equatorial Pacific, which causes the trade winds anomaly and produces the anomalous wind

  12. Observations of upper layer turbulent mixing in the southern South China Sea

    Institute of Scientific and Technical Information of China (English)

    SHANG Xiaodong; QI Yongfeng; CHEN Guiying; LIANG Changrong

    2015-01-01

    A turbulent microstructure experiment was undertaken at a low latitude of 10°N in the South China Sea in late August 2012. The characteristics of the eddy diffusivity above 650 m were analyzed, which is one order of magnitude larger than that in the open ocean at that low latitude. Enhanced eddy diffusivities by strong shears and sharp changes in topography were observed. The strongest eddy diffusivity occurred in the mixed layer, and it reachedO(10–2 m2/s). Strong stratification in the thermocline inhibited the penetration of surface eddy diffusivities through the thermocline, where the mixing was weakest. Below the thermocline, where the background eddy diffusivity was approximatelyO(10–6 m2/s), the eddy diffusivity increased with depth, and its largest value wasO(10–3 m2/s).

  13. Homotopy simulation of axisymmetric laminar mixed convection nanofluid boundary layer flow over a vertical cylinder

    Directory of Open Access Journals (Sweden)

    Freidooni Mehr N.

    2012-01-01

    Full Text Available In this paper, the semi-analytical/numerical technique known as the homotopy analysis method (HAM is employed to derive solutions for the laminar axisymmetric mixed convection boundary-layer nanofluid flow past a vertical cylinder. The similarity solutions are employed to transform the parabolic partial differential conservation equations into system of nonlinear, coupled ordinary differential equations, subject to appropriate boundary conditions. A comparison has been done to verify the obtained results with the purely numerical results of Grosan and Pop (2011 with excellent correlation achieved. The effects of nanoparticle volume fraction, curvature parameter and mixed convection or buoyancy parameter on the dimensionless velocity and temperature distributions, skin friction and wall temperature gradients are illustrated graphically. HAM is found to demonstrate excellent potential for simulating nanofluid dynamics problems. Applications of the study include materials processing and also thermal enhancement of energy systems.

  14. An investigation of two dimensional parallel and non-parallel steady mixing layers

    Energy Technology Data Exchange (ETDEWEB)

    Shabani, A. [Azad Islamic Univ., Faculty of Mechanical Engineering, School of Engineering, Research and Science Inst., Tehran (Iran, Islamic Republic of)]. E-mail: ario.shabani@cic.aut.ac.ir; Basirat Tabrizi, H. [Amirkabir Univ. of Technology, Dept. of Mechanical Engineering, Tehran (Iran, Islamic Republic of)

    2004-07-01

    A CFD code was generated to simulate the steady state behavior of two dimensional, parallel and nonparallel merging mixing layers. For the free stream velocity ratios of 0.7 and 0.9, the effect of the merging angle of free stream velocities of between 0.0 to 18.0 degrees on the mixing zone's velocity distribution, and on the physical spreading of the turbulent domain was numerically simulated and studied. The results were in good agreement with the available theoretical and experimental results, and indicated that increasing the angle of merging of the two free streams, or increasing their associated free stream velocity ratios increases the spatial growth rate and decreases the turbulent development distance. (author)

  15. THREE-DIMENSIONAL PAIRING OF COHERENT STRUCTURES IN A PLANE MIXING LAYER

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The three-dimensional (3D) pairing process of coherent structures in a plane mixing layer was simulated numerically with the pseudo-spectral method. The behaviors of spanwise cup-shaped vortices, streamwise rib-shaped vortices and quadrupoles were obtained in terms of their iso-surfaces. The results show that three-dimensional structures are strongly influenced by the initial ampiitude of the 3D disturbance, and that in most cases the local pairing finishes in a roughly two-dimensional manner. In pairing region, the streamwise vortices are chaotic after pairing due to the breakdown of the engulfed ribs and especially the subsequent breakdown of the quadrupoles. The surviving ribs extend to the top (or bottom) of the paired vortices under the stretch of them. In addition, it is revealed that three dimensional vortices pairing can enhance the mixing of fluid. Finally, some patterns of numerical flow visualization are presented by computing the passive scalar.

  16. Chlorophyll modulation of sea surface temperature in the Arabian Sea in a mixed-layer isopycnal general circulation model

    Digital Repository Service at National Institute of Oceanography (India)

    Nakamoto, S.; PrasannaKumar, S.; Muneyama, K.; Frouin, R.

    Remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS) are used to estimate biological heating rate and investigate the biological modulation of the sea surface temperature (SST) in a bulk mixed layer model...

  17. Response of the equatorial Pacific to chlorophyll pigment in a mixed layer isopycnal ocean general circulation model

    Digital Repository Service at National Institute of Oceanography (India)

    Nakamoto, S.; PrasannaKumar, S.; Oberhuber, J.M.; Ishizaka, J.; Muneyama, K.; Frouin, R.

    The influence of phytoplankton on the upper ocean dynamics and thermodynamics in the equatorial Pacific is investigated using an isopycnal ocean general circulation model (OPYC) coupled with a mixed layer model and remotely sensed chlorophyll...

  18. A theoretical model for the evolution of two-dimensional large-scale coherent structures in a mixing layer

    Institute of Scientific and Technical Information of China (English)

    周恒; 马良

    1995-01-01

    By a proper combination of the modified weakly nonlinear theory of hydrodynamic stability and the energy method, the spatial evolution of the large-scale coherent structures in a mixing layer has been calculated. The results are satisfactory.

  19. Ocean bio-geophysical modeling using mixed layer-isopycnal general circulation model coupled with photosynthesis process

    Digital Repository Service at National Institute of Oceanography (India)

    Nakamoto, S.; Saito, H.; Muneyama, K.; Sato, T.; PrasannaKumar, S.; Kumar, A.; Frouin, R.

    or exchange of energy, material, and entropy between ocean biological system and the surrounding oceanic turbulent mixed layer is examined. It is proposed that a possibility of the biophysical feedback for the maintenance of steady and spontaneous ocean geo...

  20. Variability of mixed layer depth in the northern Indian Ocean during 1977 and 1979 summer monsoon seasons

    Digital Repository Service at National Institute of Oceanography (India)

    Gopalakrishna, V.V.; Sadhuram, Y.; RameshBabu, V.

    Influences of wind stress (tau) and wind stress curl (Grad Gamma) on the short term variability of the mixed layer depth at different locations in the northern Indian Ocean during different phases of summer monsoon activity were examined...

  1. Mixing layer height and its implications for air pollution over Beijing, China

    Science.gov (United States)

    Tang, Guiqian; Zhang, Jinqiang; Zhu, Xiaowan; Song, Tao; Münkel, Christoph; Hu, Bo; Schäfer, Klaus; Liu, Zirui; Zhang, Junke; Wang, Lili; Xin, Jinyuan; Suppan, Peter; Wang, Yuesi

    2016-03-01

    The mixing layer is an important meteorological factor that affects air pollution. In this study, the atmospheric mixing layer height (MLH) was observed in Beijing from July 2009 to December 2012 using a ceilometer. By comparison with radiosonde data, we found that the ceilometer underestimates the MLH under conditions of neutral stratification caused by strong winds, whereas it overestimates the MLH when sand-dust is crossing. Using meteorological, PM2.5, and PM10 observational data, we screened the observed MLH automatically; the ceilometer observations were fairly consistent with the radiosondes, with a correlation coefficient greater than 0.9. Further analysis indicated that the MLH is low in autumn and winter and high in spring and summer in Beijing. There is a significant correlation between the sensible heat flux and MLH, and the diurnal cycle of the MLH in summer is also affected by the circulation of mountainous plain winds. Using visibility as an index to classify the degree of air pollution, we found that the variation in the sensible heat and buoyancy term in turbulent kinetic energy (TKE) is insignificant when visibility decreases from 10 to 5 km, but the reduction of shear term in TKE is near 70 %. When visibility decreases from 5 to 1 km, the variation of the shear term in TKE is insignificant, but the decrease in the sensible heat and buoyancy term in TKE is approximately 60 %. Although the correlation between the daily variation of the MLH and visibility is very poor, the correlation between them is significantly enhanced when the relative humidity increases beyond 80 %. This indicates that humidity-related physicochemical processes is the primary source of atmospheric particles under heavy pollution and that the dissipation of atmospheric particles mainly depends on the MLH. The presented results of the atmospheric mixing layer provide useful empirical information for improving meteorological and atmospheric chemistry models and the forecasting

  2. Scale interactions in a mixing layer – the role of the large-scale gradients

    KAUST Repository

    Fiscaletti, D.

    2016-02-15

    © 2016 Cambridge University Press. The interaction between the large and the small scales of turbulence is investigated in a mixing layer, at a Reynolds number based on the Taylor microscale of , via direct numerical simulations. The analysis is performed in physical space, and the local vorticity root-mean-square (r.m.s.) is taken as a measure of the small-scale activity. It is found that positive large-scale velocity fluctuations correspond to large vorticity r.m.s. on the low-speed side of the mixing layer, whereas, they correspond to low vorticity r.m.s. on the high-speed side. The relationship between large and small scales thus depends on position if the vorticity r.m.s. is correlated with the large-scale velocity fluctuations. On the contrary, the correlation coefficient is nearly constant throughout the mixing layer and close to unity if the vorticity r.m.s. is correlated with the large-scale velocity gradients. Therefore, the small-scale activity appears closely related to large-scale gradients, while the correlation between the small-scale activity and the large-scale velocity fluctuations is shown to reflect a property of the large scales. Furthermore, the vorticity from unfiltered (small scales) and from low pass filtered (large scales) velocity fields tend to be aligned when examined within vortical tubes. These results provide evidence for the so-called \\'scale invariance\\' (Meneveau & Katz, Annu. Rev. Fluid Mech., vol. 32, 2000, pp. 1-32), and suggest that some of the large-scale characteristics are not lost at the small scales, at least at the Reynolds number achieved in the present simulation.

  3. Implementation of a 3D mixing layer code on parallel computers

    Energy Technology Data Exchange (ETDEWEB)

    Roe, K.; Thakur, R.; Dang, T.; Bogucz, E. [Syracuse Univ., NY (United States)

    1995-09-01

    This paper summarizes our progress and experience in the development of a Computational-Fluid-Dynamics code on parallel computers to simulate three-dimensional spatially-developing mixing layers. In this initial study, the three-dimensional time-dependent Euler equations are solved using a finite-volume explicit time-marching algorithm. The code was first programmed in Fortran 77 for sequential computers. The code was then converted for use on parallel computers using the conventional message-passing technique, while we have not been able to compile the code with the present version of HPF compilers.

  4. Seasonal cycle of the mixed-layer heat and freshwater budget in the eastern tropical Atlantic

    Science.gov (United States)

    Rath, Willi; Dengler, Marcus; Lüdke, Jan; Schmidtko, Sunke; Schlundt, Michael; Brandt, Peter; Partners, Preface

    2016-04-01

    A new seasonal mixed-layer heat flux climatology is used to explore the mechanisms driving seasonal variability of sea surface temperature and salinity in the eastern tropical Atlantic (ETA) with a focus on the eastern boundary upwelling regions. Until recently, large areas at the continental margins of the ETA were not well covered by publically available hydrographic data hampering a detailed understanding of the involved processes. In a collaborative effort between African and European partners within the EU-funded PREFACE program, a new seasonal climatology for different components of the heat and freshwater budget was compiled for the ETA using all publically available hydrographic data sets and a large trove of previously not-publically available hydrographic measurements from the territorial waters of western African countries, either from national programs or from the FAO supported EAF-Nansen program. The publically available data includes hydrographic data from global data repositories including most recent ARGO floats and glider measurements. This data set was complemented by velocity data from surface drifter and ARGO floats to allow determining horizontal heat and freshwater advection. Monthly means of air-sea heat fluxes were derived from the TropFlux climatology while precipitation rates were derived from monthly mean fields of the Global Precipitation Climatology Project. Finally, microstructure data from individual measurement campaigns allow estimating diapycnal heat and salt fluxes for certain regions during specific months. A detailed analysis of the seasonal cycle of mixed-layer heat and freshwater balance in previously poorly covered regions in the eastern tropical Atlantic upwelling is presented. In both eastern boundary upwelling region, off Senegal/Mauritania and off Angola/Namibia, average net surface heat fluxes warm the mixed layer at a rate between 50 and 80 W/m2 with maxima in the respective summer seasons. Horizontal advection

  5. The effect of ocean mixed layer depth on climate in slab ocean aquaplanet experiments.

    Science.gov (United States)

    Donohoe, A.

    2014-12-01

    The effect of ocean mixed layer depth on climate is explored in a suite of slab ocean aquaplanet simulations with different mixed layer depths ranging from a globally uniform value of 50-2.4 m. In addition to the expected increase in the amplitude of the seasonal cycle in temperature with decreasing ocean mixed layer depth, the simulated climates differ in several less intuitive ways including fundamental changes in the annual mean climate. The phase of seasonal cycle in temperature differs non-monotonically with increasing ocean mixed layer depth, reaching a maximum in the 12 m slab depth simulation. This result is a consequence of the change in the source of the seasonal heating of the atmosphere across the suite of simulations. For ocean depth less than 12 m, the seasonal heating of the atmosphere is dominated by the surface energy fluxes which are lagged with respect to the insolation due to storage in the oceanic column. In contrast, in the deep ocean runs, the seasonal heating is dominated by direct shortwave absorption within the atmospheric column which is in phase with insolation. Thus the total heating comes back in phase with the insolation as the ocean deepens. The intertropical convergence zone follows the seasonally varying insolation and maximum sea surface temperatures into the summer hemisphere in the shallow ocean runs whereas it stays fairly close to the equator in the deep ocean runs. As a consequence, the tropical precipitation and region of high planetary albedo is spread more broadly across the low latitudes in the shallow runs, resulting in an apparent expansion of the tropics relative to the deep ocean runs. As a result, the global and annual mean planetary albedo is substantially (20 %) higher in the shallow ocean simulations which results in a colder (7C) global and annual mean surface temperature. The increased tropical planetary albedo in the shallow ocean simulations also results in a decreased equator-to-pole gradient in absorbed

  6. The effect of ocean mixed layer depth on climate in slab ocean aquaplanet experiments

    Science.gov (United States)

    Donohoe, Aaron; Frierson, Dargan M. W.; Battisti, David S.

    2014-08-01

    The effect of ocean mixed layer depth on climate is explored in a suite of slab ocean aquaplanet simulations with different mixed layer depths ranging from a globally uniform value of 50-2.4 m. In addition to the expected increase in the amplitude of the seasonal cycle in temperature with decreasing ocean mixed layer depth, the simulated climates differ in several less intuitive ways including fundamental changes in the annual mean climate. The phase of seasonal cycle in temperature differs non-monotonically with increasing ocean mixed layer depth, reaching a maximum in the 12 m slab depth simulation. This result is a consequence of the change in the source of the seasonal heating of the atmosphere across the suite of simulations. In the shallow ocean runs, the seasonal heating of the atmosphere is dominated by the surface energy fluxes whereas the seasonal heating is dominated by direct shortwave absorption within the atmospheric column in the deep ocean runs. The surface fluxes are increasingly lagged with respect to the insolation as the ocean deepens which accounts for the increase in phase lag from the shallow to mid-depth runs. The direct shortwave absorption is in phase with insolation, and thus the total heating comes back in phase with the insolation as the ocean deepens more and the direct shortwave absorption dominates the seasonal heating of the atmosphere. The intertropical convergence zone follows the seasonally varying insolation and maximum sea surface temperatures into the summer hemisphere in the shallow ocean runs whereas it stays fairly close to the equator in the deep ocean runs. As a consequence, the tropical precipitation and region of high planetary albedo is spread more broadly across the low latitudes in the shallow runs, resulting in an apparent expansion of the tropics relative to the deep ocean runs. As a result, the global and annual mean planetary albedo is substantially (20 %) higher in the shallow ocean simulations which results in

  7. Nonstationary Axisymmetric Temperature Field in a Two-Layer Slab Under Mixed Heating Conditions

    Science.gov (United States)

    Turchin, I. N.; Timar, I.; Kolodii, Yu. A.

    2015-09-01

    With the use of the Laguerre and Hankel integral transforms, the solution of a two-dimensional initial-boundary-value heat conduction problem for a two-layer slab under mixed boundary conditions is constructed: one of the surfaces is heated by a heat flux distributed axisymmetrically in a circle of radius R and is cooled by the Newton law outside this circle. The solution of the problem is reduced to a sequence of infinite quasi-regular systems of algebraic equations. The results of numerical analysis of the temperature field in the two-layer slab made from an aluminum alloy and ceramicsare presented depending on the relative geometric properties of the components and cooling intensity.

  8. Studies on Recast-layer in EDM using Aluminium Powder Mixed Distilled Water Dielectric Fluid

    Directory of Open Access Journals (Sweden)

    Khalid Hussain Syed

    2013-04-01

    Full Text Available In this paper, an attempt has been made to study the effect of aluminium powder when mixed in the distilled water dielectric fluid. The work and tool electrode materials used are W300 diesteel and electrolytic copper respectively. Pulse peak current, pulse on-time and concentration of aluminium powder are taken as the process parameters. The output response considered is white layer thickness (WLT. The experiments are planned using face centered central composite design procedure. Empirical model is developed for WLT using response surface methodology (RSM to study the effect ofprocess parameters. Optical microscopy results show that low thickness of white-layer 17.14 μm is obtained at high concentration of powder of 4 g/l and low peak current of 6 A.

  9. Preliminary mixed-layer model results for FIRE marine stratocumulus IFO conditions

    Science.gov (United States)

    Barlow, R.; Nicholls, S.

    1990-01-01

    Some preliminary results from the Turton and Nicholls mixed layer model using typical FIRE boundary conditions are presented. The model includes entrainment and drizzle parametrizations as well as interactive long and shortwave radiation schemes. A constraint on the integrated turbulent kinetic energy balance ensures that the model remains energetically consistent at all times. The preliminary runs were used to identify the potentially important terms in the heat and moisture budgets of the cloud layer, and to assess the anticipated diurnal variability. These are compared with typical observations from the C130. Sensitivity studies also revealed the remarkable stability of these cloud sheets: a number of negative feedback mechanisms appear to operate to maintain the cloud over an extended time period. These are also discussed. The degree to which such a modelling approach can be used to explain observed features, the specification of boundary conditions and problems of interpretation in non-horizontally uniform conditions is also raised.

  10. Soft chemical control of the crystal and magnetic structure of a layered mixed valent manganite oxide sulfide

    Directory of Open Access Journals (Sweden)

    Jack N. Blandy

    2015-04-01

    Full Text Available Oxidative deintercalation of copper ions from the sulfide layers of the layered mixed-valent manganite oxide sulfide Sr2MnO2Cu1.5S2 results in control of the copper-vacancy modulated superstructure and the ordered arrangement of magnetic moments carried by the manganese ions. This soft chemistry enables control of the structures and properties of these complex materials which complement mixed-valent perovskite and perovskite-related transition metal oxides.

  11. Stability and phase separation in mixed monopolar lipid/bolalipid layers.

    Science.gov (United States)

    Longo, Gabriel S; Thompson, David H; Szleifer, I

    2007-10-15

    The phase stability of a fluid lipid layer that is a mixture of conventional monopolar lipids and C20 bipolar bolalipids was studied using a mean field theory that explicitly includes molecular details and configurational properties of the lipid molecules. The effect of changing the fraction of bolalipids, as well as the length of the hydrocarbon chain of the monopolar lipids, was probed. A phase separation between two liquid lipid phases was found when a mismatch exists in the optimal hydrophobic thicknesses of the pure bolalipid and monopolar lipid layers. The lipid mixture phase separates into a thin bolalipid-rich layer and a thicker monopolar-rich layer. The thin membrane phase is mainly composed of transmembrane bolalipid molecules whose polar heads are positioned at opposite membrane-water interfaces. In the monopolar lipid-rich phase, bolalipids are the minor component and most of them assume a looping configuration where both headgroups are present at the same membrane-water interface. For mixed layers that form a single lipid phase across all bolalipid concentrations, the hairpin-transmembrane ratio strongly depends on the hydrocarbon chain length of the monopolar lipid and the bolalipid concentration. The C-D bond order parameters of the different species have been calculated. Our findings suggest that the concentration-dependent phase transition should be experimentally observable by measuring of the order parameters through quadrupolar splitting experiments. The driving force for the phase separation in the monopolar lipid/bolalipid mixture is the packing mismatch between hydrophobic regions of the monopolar lipid hydrocarbon chains and the membrane-spanning bolalipid chains. The results from the molecular theory may be useful in the design of stable lipid layers for integral membrane protein sensing.

  12. Observed and modeled mixed-layer variability on the continental shelf of Sardinia (Western Mediterranean)

    Science.gov (United States)

    Onken, Reiner

    2016-04-01

    An important task of Military Oceanography is the prediction of mixed-layer properties and their spatial and temporal variability. In the mainframe of the REP14-MED sea trial which was conducted under the lead of CMRE in June 2014 in the waters west of Sardinia, an oceanographic mooring was deployed on the continental shelf which recorded the seawater temperature between the surface and 40-m depth with high resolution for about twelve days; meteorological parameters were collected at the same time on top of the mooring by a meteorological buoy. A series of ROMS model runs was conducted and validated against the observations. Those runs applied different setups for the forcing at the lateral open boundaries and at the surface, different arrangements of the vertical coordinates, and different strategies for the assimilation of data from CTD casts and gliders. The goal was to test the sensitivity of the forecast skill to the different setups and to find a "cheap" setup which predicts the observed temperature and the mixed-layer depth and their temporal variabilities to a satisfactory degree. That setup is supposed to provide also reliable forecasts for the other areas of the model domain.

  13. Global and Koopman modes analysis of sound generation in mixing layers

    Energy Technology Data Exchange (ETDEWEB)

    Song, G.; Robinet, J.-C.; Gloerfelt, X. [Laboratoire DynFluid, Arts et Métiers ParisTech, 151 Boulevard de l’Hopital, 75013 Paris (France); Alizard, F. [Laboratoire DynFluid, CNAM, 151 Boulevard de l’Hopital, 75013 Paris (France)

    2013-12-15

    It is now well established that linear and nonlinear instability waves play a significant role in the noise generation process for a wide variety of shear flows such as jets or mixing layers. In that context, the problem of acoustic radiation generated by spatially growing instability waves of two-dimensional subsonic and supersonic mixing layers are revisited in a global point of view, i.e., without any assumption about the base flow, in both a linear and a nonlinear framework by using global and Koopman mode decompositions. In that respect, a timestepping technique based on disturbance equations is employed to extract the most dynamically relevant coherent structures for both linear and nonlinear regimes. The present analysis proposes thus a general strategy for analysing the near-field coherent structures which are responsible for the acoustic noise in these configurations. In particular, we illustrate the failure of linear global modes to describe the noise generation mechanism associated with the vortex pairing for the subsonic regime whereas they appropriately explain the Mach wave radiation of instability waves in the supersonic regime. By contrast, the Dynamic Mode Decomposition (DMD) analysis captures both the near-field dynamics and the far-field acoustics with a few number of modes for both configurations. In addition, the combination of DMD and linear global modes analyses provides new insight about the influence on the radiated noise of nonlinear interactions and saturation of instability waves as well as their interaction with the mean flow.

  14. A study on mixed coal simulation soft layer of gas adsorption

    Institute of Scientific and Technical Information of China (English)

    LI Shu-gang; ZHAO Peng-xiang; PAN Hong-yu; HUANG Jin-xing

    2011-01-01

    Based on the single coal adsorption gas,hard coal and soft coal of intake airway in Shanxi Heshun Tianchi Coal Mine were chosen to simulate the soft coal seams in coalbed as those in different qualities are mixed with delamination.Experiments on characteristics of adsorption gas of hard coal and soft coal in different quality ratios were done according to the Langmuir single molecule layer absorption theory.Gas constant mensuration instrument WY-98B was used during the experiments.Isothermal adsorption curves,adsorption constants a and b of the mixed coal samples in different quality ratios were established for qualitative and quantitative analysis.The relationship curves of adsorption quantity with changing pressure and variation equation of adsorption constants a,b with changing thickness ratio shows that the thickness of soft layer and hard coal approximately equal,thus resulting in outburst at greatest risk,then a theoretical base for the mechanism of coal and gas outburst has been put forward and a technical support scheme for engineering control of gas outburst is laid out.

  15. WAVELET ANALYSIS OF COHERENT STRUCTURES IN A THREE-DIMENSIONAL MIXING LAYER

    Institute of Scientific and Technical Information of China (English)

    林建忠; 邵雪明; 倪利民

    2002-01-01

    Wavelet analysis is applied to the results obtained by the direct nu-merical simulation of a three-dimensional (3D) mixing layer in order to investigatecoherent structures in dimension of scale. First, 3D orthonormal wavelet bases areconstructed, and the corresponding decomposition algorithm is developed. Then theNavier-Stokes equations are transformed into the wavelet space and the architecturefor multi-scale analysis is established. From this architecture, the coarse field imagesin different scales are obtained and some local statistical quantities are calculated.The results show that, with the development of a mixing layer, the energy spectrumdensities for different wavenumbers increase and the energy is transferred from theaverage flow to vortex structures in different scales. Due to the non-linear interactionsbetween different scales, cascade processes of energy are very complex. Because vor-tices always roll and pair at special areas, for a definite scale, the energy is obtainedfrom other scales at some areas while it is transferred to other scales at other areas.In addition, energy dissipation and transfer always occur where an intense interactionbetween vortices exists.

  16. Profiling float-based observations of net respiration beneath the mixed layer

    Science.gov (United States)

    Hennon, Tyler D.; Riser, Stephen C.; Mecking, Sabine

    2016-06-01

    We employ profiling floats with dissolved oxygen sensors to observe in situ temporal oxygen evolution below the mixed layer, allowing us to characterize net respiration of organic carbon in eight distinct regions over the globe. Export and export efficiency are generally high in locations with strong seasonal variability and low in locations of weak seasonality. Vertically integrated respiration is weakly, yet significantly, correlated with remote observations of chlorophyll, net primary production, and planktonic community size structure. These correlations suggest that regimes of high net primary production and large phytoplankton fuel elevated respiration at depth. Several regions of float-based observations intersect with sites of other detailed observations (e.g., Hawaii and Sargasso Sea), which allows us to compare our results to independent studies. We find that there is good agreement among export production estimates at highly seasonal locations, and that float-based observations may be biased low at weakly seasonal locations. We posit that the reason for the low-latitude discrepancy is the relative steady state of oxygen concentration caused by weak seasonality and shallow wintertime mixed layer depths.

  17. Transport of desert dust mixed with North African industrial pollutants in the subtropical Saharan Air Layer

    Science.gov (United States)

    Rodríguez, S.; Alastuey, A.; Alonso-Pérez, S.; Querol, X.; Cuevas, E.; Abreu-Afonso, J.; Viana, M.; Pérez, N.; Pandolfi, M.; de La Rosa, J.

    2011-07-01

    An analysis of chemical composition data of particulate matter samples (TSP, PM10 and PM2.5) collected from 2002 to 2008 in the North Atlantic free troposphere at the Izaña Global Atmospheric Watch (GAW) observatory (Tenerife, Canary Islands) shows that desert dust is very frequently mixed with particulate pollutants in the Saharan Air Layer (SAL). The study of this data set with Median Concentrations At Receptor (MCAR) plots allowed the identification of the potential source regions of the dust and particulate pollutants. Areas located at the south of the southern slope of the Atlas mountains emerge as the most frequent source of the soil desert dust advected to the northern edge of the SAL in summer. Industrial emissions occurring in Northern Algeria, Eastern Algeria, Tunisia and the Atlantic coast of Morocco appear as the most important source of the nitrate, ammonium and a fraction of sulphate (at least 60 % of the sulphate pollutants may be mixed with desert dust and exported to the North Atlantic in the Saharan Air Layer.

  18. Simulation of mixed-host emitting layer based organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Riku, C.; Kee, Y. Y.; Ong, T. S.; Tou, T. Y. [Faculty of Engineering, Multimedia University, 631000 Cyberjaya (Malaysia); Yap, S. S. [Faculty of Engineering, University of Malaya, 50603 Kuala Lampur (Malaysia)

    2015-04-24

    ‘SimOLED’ simulator is used in this work to investigate the efficiency of the mixed-host organic light emitting devices (MH-OLEDs). Tris-(8-hydroxyquinoline) aluminum(3) (Alq{sub 3}) and N,N-diphenyl-N,N-Bis(3-methylphenyl)-1,1-diphenyl-4,4-diamine (TPD) are used as the electron transport layer (ETL) material and hole transport layer (HTL) material respectively, and the indium-doped tin oxide (ITO) and aluminum (Al) as anode and cathode. Three MH-OLEDs, A, B and C with the same structure of ITO / HTM (15 nm) / Mixed host (70 nm) / ETM (10 nm) /Al, are stimulated with ratios TPD:Alq{sub 3} of 3:5, 5:5, and 5:3 respectively. The Poole-Frenkel model for electron and hole mobilities is employed to compute the current density-applied voltage-luminance characteristics, distribution of the electric field, carrier concentrations and recombination rate.

  19. Mixed convection boundary-layer flow about an isothermal solid sphere in a nanofluid

    Energy Technology Data Exchange (ETDEWEB)

    Tham, L [Faculty of Agro Industry and Natural Resources, Universiti Malaysia Kelantan, Kelantan (Malaysia); Nazar, R [School of Mathematical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Selangor (Malaysia); Pop, I, E-mail: rmn72my@yahoo.com [Faculty of Mathematics, University of Cluj, Cluj (Romania)

    2011-08-01

    The steady mixed convection boundary-layer flow of a nanofluid about a solid sphere with constant surface temperature has been studied for cases of both assisting and opposing flows. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme known as the Keller-box method. The solutions for the flow and heat-transfer characteristics are evaluated numerically for various values of the parameters, namely the nanoparticle volume fraction {psi} and the mixed convection parameter {lambda} at Prandtl numbers Pr=0.7 and 6.2. The three different types of nanoparticles considered are Al{sub 2}O{sub 3}, Cu and TiO{sub 2}, using water-based fluid with Pr=6.2. It is found that for each particular nanoparticle, as the nanoparticle volume fraction {psi} increases, the skin friction coefficient and the heat-transfer rate at the surface also increase. This leads to an increase in the value of the mixed convection parameter {lambda}, which at first gives no separation.

  20. Efficient green phosphorescent tandem organic light emitting diodes with solution processable mixed hosts charge generating layer

    Energy Technology Data Exchange (ETDEWEB)

    Talik, N.A.; Yeoh, K.H.; Ng, C.Y.B [Low Dimensional Research Center, Department of Physics, University Malaya, 50603 Kuala Lumpur (Malaysia); ItraMAS Corporation. Sdn. Bhd., 542A-B Mukim 1, Lorong Perusahaan Baru 2, Kawasan Perindustrian, Perai 13600, Penang (Malaysia); Yap, B.K. [Center of Microelectronic and Nanotechnology Engineering (CeMNE), College of Engineering, Universiti Tenaga Nasional, Jln. Uniten-Ikram, 4300 Kajang, Selangor (Malaysia); Woon, K.L., E-mail: ph7klw76@um.edu.my [Low Dimensional Research Center, Department of Physics, University Malaya, 50603 Kuala Lumpur (Malaysia)

    2014-10-15

    A novel solution processable charge generating layer (CGL) that consists of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN{sub 6})/Poly(N-vinylcarbazole) (PVK): 1,1-bis-(4-bis(4-tolyl)-aminophenyl) cyclohexene (TAPC) for a tandem green phosphorescent organic light emitting diode (PHOLED) is demonstrated. The use of orthogonal solvent to dissolve HATCN{sub 6} and PVK:TAPC is the key to overcome the interface erosion problem for the solution processed CGL. The current efficiency of the 2 wt% TAPC mixed with PVK is the highest at 24.2 cd/A, which is more than three-folds higher than that of the single device at 1000 cd/m{sup 2}. - Highlights: • A solution processable tandem OLED is built using a novel charge generating layer. • HATCN{sub 6} and PVK:TAPC are shown to be effective charge generating layers. • The turn on voltages for tandem devices are almost similar to single unit. • 2 wt% TAPC blended with PVK exhibits three-folds increase in efficiency.

  1. Recent changes of Mixed Layer Depth in the East/Japan Sea: 1994-2007

    Science.gov (United States)

    Chang, Pil-Hun; Cho, Chun-Ho; Ryoo, Sang-Boom

    2011-11-01

    Recent changes of Mixed Layer Depth (MLD) in the East/Japan Sea (EJS) is investigated by using ocean reanalysis data. There is a significant shoaling of MLD in the southern EJS for 1994-2007, showing the change rate of - 1.24 m yr-1. The present study demonstrates that the wind stress curl mostly attributes to the MLD changes. The long-term variation of wind stress curl with a positive trend in the southern EJS is generally well consistent with the MLD variation. In addition, upward displacement estimated from the wind stress curl reaches 14.6 m during 14 years, which is comparable to the shoaling of MLD (i.e., 17.4 m). Thus, the wind stress curl with positive trend would induce the increase of upward Ekman pumping which in turn lead to the shoaling of MLD. The change of temperature structure in the subsurface layer, that is shrinking and upward displacement of thermal layer from the reanalysis and observational data, also supports this conclusion.

  2. Mixed layer depth trends in the Bay of Biscay over the period 1975-2010.

    Directory of Open Access Journals (Sweden)

    Xurxo Costoya

    Full Text Available Wintertime trends in mixed layer depth (MLD were calculated in the Bay of Biscay over the period 1975-2010 using the Simple Ocean Data Assimilation (SODA package. The reliability of the SODA database was confirmed correlating its results with those obtained from the experimental Argo database over the period 2003-2010. An iso-thermal layer depth (TLD and an iso-pycnal layer depth (PLD were defined using the threshold difference method with ΔT = 0.5°C and Δσθ = 0.125 kg/m3. Wintertime trends of the MLD were calculated using winter extended (December-March anomalies and annual maxima. Trends calculated for the whole Bay of Biscay using both parameters (TLD and PLD showed to be dependent on the area. Thus, MLD became deeper in the southeastern corner and shallower in the rest of the area. Air temperature was shown to play a key role in regulating the different spatial behavior of the MLD. Negative air temperature trends localized in the southeastern corner coincide with MLD deepening in this area, while, positive air temperature trends are associated to MLD shoaling in the rest of the bay. Additionally, the temperature trend calculated along the first 700 m of the water column is in good agreement with the different spatial behavior revealed for the MLD trend.

  3. [Characteristics of Winter Atmospheric Mixing Layer Height in Beijing-Tianjin-Hebei Region and Their Relationship with the Atmospheric Pollution].

    Science.gov (United States)

    Li, Meng; Tang, Gui-qian; Huang, Jun; Liu, Zi-rui; An, Jun-lin; Wang, Yue-si

    2015-06-01

    Atmospheric mixing layer height (MLH) is one of the main factors affecting the atmospheric diffusion and plays an important role in air quality assessment and distribution of the pollutants. Based on the ceilometers data, this paper has made synchronous observation on MLH in Beijing-Tianjin-Hebei region (Beijing, Tianjin, Shijiazhuang and Qinhuangdao) in heavy polluted February 2014 and analyzed the respective overall change and its regional features. Results show that in February 2014,the average of mixing layer height in Qinhuangdao is the highest, up to 865 +/- 268 m, and in Shijiazhuang is the lowest (568 +/- 207 m), Beijing's and Tianjin's are in between, 818 +/- 319 m and 834 +/- 334 m respectively; Combined with the meteorological data, we find that radiation and wind speed are main factors of the mixing layer height; The relationship between the particle concentration and mixing layer height in four sites suggests that mixing layer is less than 800 m, concentration of fine particulate matter in four sites will exceed the national standard (GB 3095-2012, 75 microg x m(-3)). During the period of observation, the proportion of days that mixing layer is less than 800 m in Beijing, Tianjin, Shijiazhuang and Qinhuangdao are 50%, 43%, 80% and 50% respectively. Shijiazhuang though nearly formation contaminant concentration is high, within the atmospheric mixed layer pollutant load is not high. Unfavorable atmospheric diffusion conditions are the main causes of heavy pollution in Shijiazhuang for a long time. The results of the study are of great significance for cognitive Beijing-Tianjin-Hebei area pollution distribution, and can provide a scientific reference for reasonable distribution of regional pollution sources.

  4. Mechanisms Controlling the Interannual Variation of Mixed Layer Temperature Averaged over the Nino-3 Region

    Science.gov (United States)

    Kim, Seung-Bum; Lee, Tong; Fukumori, Ichiro

    2007-01-01

    The present study examines processes governing the interannual variation of MLT in the eastern equatorial Pacific.Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the Nino-3 domain (5 deg N-5 deg S, 150 deg-90 deg W) are studied using an ocean data assimilation product that covers the period of 1993-2003. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. This allows the authors to characterize external advective processes that warm or cool the water within the domain as a whole. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed to mostly by Ekman current advecting large-scale temperature anomalies through the southern boundary of the domain. Unlike many previous studies, the subsurface processes that consist of vertical mixing and entrainment are explicitly evaluated. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to the temporal change in ML depth is negligible compared to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in upwelling and the temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Nina cooling events. However, such a warming tendency is overwhelmed by the cooling tendency associated with the large-scale upwelling by a factor of

  5. Supercritical fluid extraction

    Science.gov (United States)

    Wai, Chien M.; Laintz, Kenneth

    1994-01-01

    A method of extracting metalloid and metal species from a solid or liquid material by exposing the material to a supercritical fluid solvent containing a chelating agent. The chelating agent forms chelates that are soluble in the supercritical fluid to allow removal of the species from the material. In preferred embodiments, the extraction solvent is supercritical carbon dioxide and the chelating agent is a fluorinated or lipophilic crown ether or fluorinated dithiocarbamate. The method provides an environmentally benign process for removing contaminants from industrial waste without using acids or biologically harmful solvents. The chelate and supercritical fluid can be regenerated, and the contaminant species recovered, to provide an economic, efficient process.

  6. Implementation of Turbulent Mixing over a Stratocumulus-Topped Boundary Layer and Its Impact in a GCM

    Institute of Scientific and Technical Information of China (English)

    Sun-Hee SHIN; Kyung-Ja HA

    2009-01-01

    The effect of a vertical diffusion scheme over a stratocumulus topped boundary layer (STBL) was investigated using the YONU AGCM (Yonsei University Atmospheric General Circulation Model).To consider the impact of clouds on the turbulence production,the turbulence mixing term,driven by radiative cooling at the cloud top,is implemented as an extended non-local diffusion scheme.In the model with this new scheme,the STBL parameterization significantly influences the lower atmosphere over the tropical and subtropical regions.Consideration of the turbulent mixing within the cloud layer leads to continuous stratocumulus formation.The cloud-top radiative cooling tends to favor more rapid entrainment and produces top-down turbulent mixing.This cooling develops a mixed layer without initiation of deep convection by surface fluxes.Variations in thermodynamical and dynamical features are produced by planetary boundary layer (PBL)cloud development.The simulated stratocumulus induces more mixing of heat and moisture due to the cloud forcing.Over STBL regions,the lower boundary layer bccomes warmer and drier.It also weakens vertical motion and zonal trade winds in the eastern Pacific,which indicates that stratocumulus cloud cover plays a role in weakening the Walker circulation;that is,cloud cover damps the tropical circulation.

  7. Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. II: Multi layered cloud

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, H.; McCoy, Renata; Klein, Stephen A.; Xie, Shaocheng; Luo, Yali; Avramov, Alexander; Chen, Mingxuan; Cole, Jason N.; Falk, Michael; Foster, Mike; Del Genio, Anthony D.; Harrington, Jerry Y.; Hoose, Corinna; Khrairoutdinov, Marat; Larson, Vince; Liu, Xiaohong; McFarquhar, Greg; Poellot, M. R.; Von Salzen, Knut; Shipway, Ben; Shupe, Matthew D.; Sud, Yogesh C.; Turner, David D.; Veron, Dana; Walker, Gregory K.; Wang, Zhien; Wolf, Audrey; Xu, Kuan-Man; Yang, Fanglin; Zhang, G.

    2009-05-21

    Results are presented from an intercomparison of single-column and cloud resolving model simulations of a deep, multi-layered, mixed-phase cloud system observed during the ARM Mixed-Phase Arctic Cloud Experiment. This cloud system was associated with strong surface turbulent sensible and latent heat fluxes as cold air flowed over the open Arctic Ocean, combined with a low pressure system that supplied moisture at mid-level. The simulations, performed by 13 single-column and 4 cloud-resolving models, generally overestimate the liquid water path and strongly underestimate the ice water path, although there is a large spread among the models. This finding is in contrast with results for the single-layer, low-level mixed-phase stratocumulus case in Part I of this study, as well as previous studies of shallow mixed-phase Arctic clouds, that showed an underprediction of liquid water path. The overestimate of liquid water path and underestimate of ice water path occur primarily when deeper mixed-phase clouds extending into the mid-troposphere were observed. These results suggest important differences in the ability of models to simulate Arctic mixed-phase clouds that are deep and multi-layered versus shallow and single-layered. In general, the cloud-resolving models and models with a more sophisticated, two-moment treatment of the cloud microphysics produce a somewhat smaller liquid water path that is closer to observations. The cloud-resolving models also tend to produce a larger cloud fraction than the single column models. The liquid water path and especially the cloud fraction have a large impact on the cloud radiative forcing at the surface, which is dominated by the longwave flux for this case.

  8. Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. Part II: Multi-layered cloud

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, H; McCoy, R B; Klein, S A; Xie, S; Luo, Y; Avramov, A; Chen, M; Cole, J; Falk, M; Foster, M; Genio, A D; Harrington, J; Hoose, C; Khairoutdinov, M; Larson, V; Liu, X; McFarquhar, G; Poellot, M; Shipway, B; Shupe, M; Sud, Y; Turner, D; Veron, D; Walker, G; Wang, Z; Wolf, A; Xu, K; Yang, F; Zhang, G

    2008-02-27

    Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a deep, multi-layered, mixed-phase cloud system observed during the ARM Mixed-Phase Arctic Cloud Experiment. This cloud system was associated with strong surface turbulent sensible and latent heat fluxes as cold air flowed over the open Arctic Ocean, combined with a low pressure system that supplied moisture at mid-level. The simulations, performed by 13 single-column and 4 cloud-resolving models, generally overestimate the liquid water path and strongly underestimate the ice water path, although there is a large spread among the models. This finding is in contrast with results for the single-layer, low-level mixed-phase stratocumulus case in Part I of this study, as well as previous studies of shallow mixed-phase Arctic clouds, that showed an underprediction of liquid water path. The overestimate of liquid water path and underestimate of ice water path occur primarily when deeper mixed-phase clouds extending into the mid-troposphere were observed. These results suggest important differences in the ability of models to simulate Arctic mixed-phase clouds that are deep and multi-layered versus shallow and single-layered. In general, models with a more sophisticated, two-moment treatment of the cloud microphysics produce a somewhat smaller liquid water path that is closer to observations. The cloud-resolving models tend to produce a larger cloud fraction than the single-column models. The liquid water path and especially the cloud fraction have a large impact on the cloud radiative forcing at the surface, which is dominated by the longwave flux for this case.

  9. Unsteady Mixed Convection Boundary Layer from a Circular Cylinder in a Micropolar Fluid

    Directory of Open Access Journals (Sweden)

    Anati Ali

    2010-01-01

    Full Text Available Most industrial fluids such as polymers, liquid crystals, and colloids contain suspensions of rigid particles that undergo rotation. However, the classical Navier-Stokes theory normally associated with Newtonian fluids is inadequate to describe such fluids as it does not take into account the effects of these microstructures. In this paper, the unsteady mixed convection boundary layer flow of a micropolar fluid past an isothermal horizontal circular cylinder is numerically studied, where the unsteadiness is due to an impulsive motion of the free stream. Both the assisting (heated cylinder and opposing cases (cooled cylinder are considered. Thus, both small and large time solutions as well as the occurrence of flow separation, followed by the flow reversal are studied. The flow along the entire surface of a cylinder is solved numerically using the Keller-box scheme. The obtained results are compared with the ones from the open literature, and it is shown that the agreement is very good.

  10. White organic light-emitting devices with mixed interfaces between light emitting layers

    Science.gov (United States)

    Lee, Young Gu; Kee, In Seo; Shim, Hong Shik; Ko, Ick Hwan; Lee, Soonil; Koh, Ken Ha

    2007-06-01

    White organic light-emitting devices with mixed interfaces between emitting layers (MI-EML WOLEDs) showed luminance and efficiency as large as 26213cd/m2 and 9.85cd/A. Efficiencies of MI-EML WOLEDs were about 1.5 times better than those of conventional three-EML WOLEDs for luminance of 1000-5000cd/m2, and their half-decay lifetime showed 3.1 times improvement. Note that if the authors operate typical active-matrix mobile-phone displays based on combination of WOLED and color filters to produce standard white emission for high definition televisions and illumination sources, MI-EML WOLEDs will have advantages of 25% less power consumption and 2.8 times longer lifetime over conventional three-EML WOLEDs.

  11. Mixed Convection Boundary Layer Flow Embedded in a Thermally Stratified Porous Medium Saturated by a Nanofluid

    Directory of Open Access Journals (Sweden)

    Mohd Hafizi Mat Yasin

    2013-01-01

    Full Text Available We present the numerical investigation of the steady mixed convection boundary layer flow over a vertical surface embedded in a thermally stratified porous medium saturated by a nanofluid. The governing partial differential equations are reduced to the ordinary differential equations, using the similarity transformations. The similarity equations are solved numerically for three types of metallic or nonmetallic nanoparticles, namely, copper (Cu, alumina (Al2O3, and titania (TiO2, in a water-based fluid to investigate the effect of the solid volume fraction or nanoparticle volume fraction parameter φ of the nanofluid on the flow and heat transfer characteristics. The skin friction coefficient and the velocity and temperature profiles are presented and discussed.

  12. Analysis of flow structures in supersonic plane mixing layers using the POD method

    Institute of Scientific and Technical Information of China (English)

    YANG Qin; FU Song

    2008-01-01

    The proper orthogonal decomposition (POD) method was applied to analyzing the database obtained from the direct numerical simulation (DNS) of supersonic plane mixing layers. The effect of different forms of the inner products in the POD method was investigated. It was observed that the mean flow contributes to a predominant part of the total flow energy, and the energy spectrum of the turbulence fluctuations covers a wide range of POD modes. The patterns of leading (high energy) POD modes reveal that the flow structures exhibit spanwise counter rotating rolls, as well as oblique vortices. These flow patterns are insensitive to the velocity of the observer. As the convective Mach number increases, the energy spectrum be-comes wider, the leading POD modes contain more complicated structures, and the flow becomes more chaotic.

  13. Analysis of flow structures in supersonic plane mixing layers using the POD method

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The proper orthogonal decomposition(POD) method was applied to analyzing the database obtained from the direct numerical simulation(DNS) of supersonic plane mixing layers.The effect of different forms of the inner products in the POD method was investigated.It was observed that the mean flow contributes to a predominant part of the total flow energy,and the energy spectrum of the turbulence fluctuations covers a wide range of POD modes.The patterns of leading(high energy) POD modes reveal that the flow structures exhibit spanwise counter rotating rolls,as well as oblique vortices.These flow patterns are insensitive to the velocity of the observer.As the convective Mach number increases,the energy spectrum be-comes wider,the leading POD modes contain more complicated structures,and the flow becomes more chaotic.

  14. Structure function scaling in a Reλ = 250 turbulent mixing layer

    KAUST Repository

    Attili, Antonio

    2011-12-22

    A highly resolved Direct Numerical Simulation of a spatially developing turbulent mixing layer is presented. In the fully developed region, the flow achieves a turbulent Reynolds number Reλ = 250, high enough for a clear separation between large and dissipative scales, so for the presence of an inertial range. Structure functions have been calculated in the self-similar region using velocity time series and Taylor\\'s frozen turbulence hypothesis. The Extended Self-Similarity (ESS) concept has been employed to evaluate relative scaling exponents. A wide range of scales with scaling exponents and intermittency levels equal to homogeneous isotropic turbulence has been identified. Moreover an additional scaling range exists for larger scales; it is characterized by smaller exponents, similar to the values reported in the literature for flows with strong shear.

  15. Mixed oxides derived from layered double hydroxides as novel catalysts for phenol photodegradation

    Science.gov (United States)

    Puscasu, C. M.; Carja, G.; Mureseanu, M.; Zaharia, C.

    2017-08-01

    The removal of organic pollutants is nowadays a very challenging aspect of the environmental research. There are strong interests to develop novel semiconducting photocatalysts able to efficiently promote advanced oxidation reactions. The development of photocatalysts based on the mixtures of mixed oxides derived from layered double hydroxides (LDHs) - a family of naturally occurring anionic clays - might offer novel environmental-friendly solutions for the cost effective removal of organic pollutants. This work presents ZnO/ZnAl2O4, ZnO/Zn2TiO4 and ZnO/ZnCr2O4 as novel photocatalytic formulations for phenol degradation under UV irradiation. They were obtained by the controlled thermal treatment of the layered double hydroxides matrices (LDHs), as precursors materials, type ZnM-LDH (M = Al3+, Cr3+ or Ti4+). The LDHs were synthesized by the co-precipitation method at a constant pH. Controlled calcination at 650°C gives rise to solutions of mixed metal oxides. The structural and nanoarchitectonics characteristics of the studied catalysts were described by: XRD, SEM/TEM and TG/DTG techniques. Results show that in the photocatalytic process of the phenol degradation from aqueous solutions, ZnO/ZnCr2O4 and ZnO/ZnAl2O4 showed the best performance degrading ∼98% of phenol after 3.5 hs and 5 hs, respectively; while ZnO/Zn2TiO4 has degraded almost 80 % after 7.5 hs of UV irradiation. These results open new opportunities in the development of new cost effective photoresponsive formulations able to facilitate the photo-degradation of the organic pollution as “green” solution for removal of dangerous pollutants.

  16. Transport of desert dust mixed with North African industrial pollutants in the subtropical Saharan Air Layer

    Directory of Open Access Journals (Sweden)

    S. Rodríguez

    2011-07-01

    Full Text Available An analysis of chemical composition data of particulate matter samples (TSP, PM10 and PM2.5 collected from 2002 to 2008 in the North Atlantic free troposphere at the Izaña Global Atmospheric Watch (GAW observatory (Tenerife, Canary Islands shows that desert dust is very frequently mixed with particulate pollutants in the Saharan Air Layer (SAL. The study of this data set with Median Concentrations At Receptor (MCAR plots allowed the identification of the potential source regions of the dust and particulate pollutants. Areas located at the south of the southern slope of the Atlas mountains emerge as the most frequent source of the soil desert dust advected to the northern edge of the SAL in summer. Industrial emissions occurring in Northern Algeria, Eastern Algeria, Tunisia and the Atlantic coast of Morocco appear as the most important source of the nitrate, ammonium and a fraction of sulphate (at least 60 % of the sulphate <10 μm transported from some regions observed in the SAL. These emissions are mostly linked to crude oil refineries, phosphate-based fertilizer industry and power plants. Although desert dust emissions appear as the most frequent source of the phosphorous observed in the SAL, high P concentrations are observed when the SAL is affected by emissions from open mines of phosphate and phosphate based fertilizer industry. The results also show that a significant fraction of the sulphate (up to 90 % of sulphate <10 μm transported from some regions observed in the SAL may be influenced by soil emissions of evaporite minerals in well defined regions where dry saline lakes (chotts are present. These interpretations of the MCAR plots are consistent with the results obtained with the Positive Matrix Factorization (PMF2 receptor modelling. The results of this study show that North African industrial pollutants may be mixed with desert dust and exported to the North Atlantic in the Saharan Air Layer.

  17. Transport of desert dust mixed with North African industrial pollutants in the subtropical Saharan Air Layer

    Directory of Open Access Journals (Sweden)

    S. Rodríguez

    2011-03-01

    Full Text Available The chemical composition of particulate matter samples (TSP, PM10 and PM2.5 collected from 2002 to 2008 in the North Atlantic free troposphere at Izaña Global Atmospheric Watch (GAW observatory (Tenerife, The Canary Islands was studied. The analysis of the samples collected in the Saharan Air Layer (SAL shows that soil desert dust is very frequently mixed with particulate pollutants. An analysis of this data set with Median Concentrations At Receptor (MCAR plots allowed to identify the potential source regions of the dust and particulate pollutants. Areas located at the south of the Southern slope of Atlas emerge as the most frequent source of the soil desert dust advected to the northern edge of the SAL in summer. Industrial emissions occurring along the Atlantic coast of Morocco, Northern Algeria, Eastern Algeria and Tunisia appear as the most important source of the nitrate, ammonium and a fraction of sulphate (at least a 60% of the sulphate <10 μm transported from some regions observed in the SAL. These emissions are mostly linked to crude oil refineries, phosphate-based fertilizer industry and power plants. Although desert dust emissions appear as the most frequent source of the phosphorous observed in the SAL, high P concentrations are observed when the SAL is affected by emissions from open mines of phosphate and phosphate based fertilizer industry. The results also show that a significant fraction of the sulphate (up to 90% of sulphate <10 μm transported from some regions observed in the SAL is linked to soil emissions of evaporite minerals in well defined regions where dry saline lakes (chotts are present. These interpretations of the MCAR plots are consistent with the results obtained with the Positive Matrix Factorization receptor modelling. The results of this study show that North African industrial pollutants may be mixed with desert dust and exported to the North Atlantic in the Saharan Air Layer.

  18. Introduction to supercritical fluids a spreadsheet-based approach

    CERN Document Server

    Smith, Richard; Peters, Cor

    2013-01-01

    This text provides an introduction to supercritical fluids with easy-to-use Excel spreadsheets suitable for both specialized-discipline (chemistry or chemical engineering student) and mixed-discipline (engineering/economic student) classes. Each chapter contains worked examples, tip boxes and end-of-the-chapter problems and projects. Part I covers web-based chemical information resources, applications and simplified theory presented in a way that allows students of all disciplines to delve into the properties of supercritical fluids and to design energy, extraction and materials formation systems for real-world processes that use supercritical water or supercritical carbon dioxide. Part II takes a practical approach and addresses the thermodynamic framework, equations of state, fluid phase equilibria, heat and mass transfer, chemical equilibria and reaction kinetics of supercritical fluids. Spreadsheets are arranged as Visual Basic for Applications (VBA) functions and macros that are completely (source code) ...

  19. SPREADING LAYERS IN ACCRETING OBJECTS: ROLE OF ACOUSTIC WAVES FOR ANGULAR MOMENTUM TRANSPORT, MIXING, AND THERMODYNAMICS

    Energy Technology Data Exchange (ETDEWEB)

    Philippov, Alexander A.; Rafikov, Roman R.; Stone, James M., E-mail: sashaph@princeton.edu [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)

    2016-01-20

    Disk accretion at a high rate onto a white dwarf (WD) or a neutron star has been suggested to result in the formation of a spreading layer (SL)—a belt-like structure on the object's surface, in which the accreted matter steadily spreads in the poleward (meridional) direction while spinning down. To assess its basic characteristics, we perform two-dimensional hydrodynamic simulations of supersonic SLs in the relevant morphology with a simple prescription for cooling. We demonstrate that supersonic shear naturally present at the base of the SL inevitably drives sonic instability that gives rise to large-scale acoustic modes governing the evolution of the SL. These modes dominate the transport of momentum and energy, which is intrinsically global and cannot be characterized via some form of local effective viscosity (e.g., α-viscosity). The global nature of the wave-driven transport should have important implications for triggering Type I X-ray bursts in low-mass X-ray binaries. The nonlinear evolution of waves into a system of shocks drives effective rearrangement (sensitively depending on thermodynamical properties of the flow) and deceleration of the SL, which ultimately becomes transonic and susceptible to regular Kelvin–Helmholtz instability. We interpret this evolution in terms of the global structure of the SL and suggest that mixing of the SL material with the underlying stellar fluid should become effective only at intermediate latitudes on the accreting object's surface, where the flow has decelerated appreciably. In the near-equatorial regions the transport is dominated by acoustic waves and mixing is less efficient. We speculate that this latitudinal nonuniformity of mixing in accreting WDs may be linked to the observed bipolar morphology of classical nova ejecta.

  20. Mapping the Interactions between Shocks and Mixing Layers in a 3-Stream Supersonic Jet

    Science.gov (United States)

    Lewalle, Jacques; Ruscher, Christopher; Kan, Pinqing; Tenney, Andrew; Gogineni, Sivaram; Kiel, Barry

    2015-11-01

    Pressure is obtained from an LES calculation of the supersonic jet (Ma1 = 1 . 6) issuing from a rectangular nozzle in a low-subsonic co-flow; a tertiary flow, also rectangular with Ma3 = 1 insulates the primary jet from an aft-deck plate. The developing jet exhibits complex three-dimensional interactions between oblique shocks, multiple mixing layers and corner vortices, which collectively act as a skeleton for the flow. Our study is based on several plane sections through the pressure field, with short signals (0.1 s duration at 80 kHz sampling rate). Using wavelet-based band-pass filtering and cross-correlations, we map the directions of propagation of information among the various ``bones'' in the skeleton. In particular, we identify upstream propagation in some frequency bands, 3-dimensional interactions between the various shear layers, and several key bones from which the pressure signals, when taken as reference, provide dramatic phase-locking for parts of the skeleton. We acknowledge the support of AFRL through an SBIR grant.

  1. Mg-Fe-mixed oxides derived from layered double hydroxides: A study of the surface properties

    Directory of Open Access Journals (Sweden)

    Marinković-Nedučin Radmila P.

    2011-01-01

    Full Text Available The influence of surface properties on the selectivity of the synthesized catalysts was studied, considering that their selectivity towards particular hydrocarbons is crucial for their overall activity in the chosen Fischer- -Tropsch reaction. Magnesium- and iron-containing layered double hydroxides (LDH, with the general formula: [Mg1-xFex(OH2](CO3x/2?mH2O, x = = n(Fe/(n(Mg+n(Fe, synthesized with different Mg/Fe ratio and their thermally derived mixed oxides were investigated. Magnesium was chosen because of its basic properties, whereas iron was selected due to its well-known high Fischer-Tropsch activity, redox properties and the ability to form specific active sites in the layered LDH structure required for catalytic application. The thermally less stable multiphase system (synthesized outside the optimal single LDH phase range with additional Fe-phase, having a lower content of surface acid and base active sites, a lower surface area and smaller fraction of smaller mesopores, showed higher selectivity in the Fischer-Tropsch reaction. The results of this study imply that the metastability of derived multiphase oxides structure has a greater influence on the formation of specific catalyst surface sites than other investigated surface properties.

  2. Observed Variability of Global Atmospheric Mixing Layer Height from 1971 to 2014

    Science.gov (United States)

    Wang, Xiaoyan; Wang, Kaicun

    2015-04-01

    It is important to determine the mixing layer height (MLH) for understanding the transport process in the troposphere, weather prediction, and climate monitoring. MLH is a key parameter in air pollution models which determines the volume available for pollutants to dispersion. The long-term variation of MLH can drive the change of surface air quality. Many methods have been proposed to estimate MLH from the temperature or atmospheric composition profiles provided by radiosonde and remote sounding systems. Radiosonde data are usually considered as a reference by other methods owing to its long-term history and direct observation. However, disagreements exist between MLHs derived from different variable profiles of radiosonde data. In this study, a method integrating the information of potential temperature, relative humidity, specific humidity, atmospheric refractivity and the effect of cloud on the boundary layer turbulence was applied to the global radiosonde data to generate long-term variation of the global MLH from 1971 to 2014. The radiosonde observations were released by the Integrated Global Radiosonde Archive (IGRA) of National Climatic Data Center (NCDC). The MLHs in the North America are fairly deep, with an average value between 1800 and 2200 m, however, the Europe and the Eastern Asia have shallow MLHs between 1200 and 1500 m. The majority of the North America and Australia stations showed a negative trend during the period of 1971 to 2014, while, for the Europe and Japan, the MLHs increased over time. The MLH had a negative correlation with surface relative humidity and a positive association with surface air temperature. Besides the effect of thermodynamic factors, the dynamical factors including the surface wind speed and its shear in the boundary layer influence the development of the boundary layer. However, there is no significant correlation between the surface wind speeds and MLH in this study. Weak negative association was found between

  3. Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

    Science.gov (United States)

    Jähn, Michael; Muñoz-Esparza, Domingo; Chouza, Fernando; Reitebuch, Oliver; Knoth, Oswald; Haarig, Moritz; Ansmann, Albert; Tegen, Ina

    2016-04-01

    Large eddy simulations (LESs) with ASAM (All Scale Atmospheric Model) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. This method is now also validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE (Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment) field campaign is used for both model initialization and comparisons. Several sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" or when the turbulent marine boundary layer flow is replaced by laminar winds. Additional simulation cases deal with modified surface characteristics and their impacts on the simulation results. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with lidar data show similarities in the downwind vertical wind structure and accurately reproduces the development of the daytime convective boundary layer measured by the Raman lidar.

  4. The Impact of Ocean Mixed Layer on Regional NWP Model around the Korea Peninsula

    Science.gov (United States)

    Min, Jae-Sik; Jee, Joon-Bum; Park, Jeong-Gyun; Lee, Hankyung; Lee, Jung-Hoon

    2017-04-01

    Ocean mixed layer (OML) affects diurnal cycle of sea surface temperature (SST) induced by change of solar radiation absorption and heat budget in ocean surface. The diurnal SST variation can lead to convection in ocean, which can impact on localized precipitation both over coastal and inland. In this study, we investigate The OML characteristics affecting the diurnal cycle of SST for the Korea Peninsula and surrounding areas. To analyze OML characteristics, HYCOM oceanic mixed layer depth (MLD) and 10 m wind fields of ERA-interim during the period of 2008-2016 are used. In the winter season, oceanic MLD is deeply formed when the strong wind field is formed perpendicular to continental slope over deep seafloor areas. Besides, cooling SST-induced vertical mixing in OML is reinforced by cold and dry air originated from Siberia. The OML in summer is shallowly distributed about 20 m over the analyzed areas. To estimate the impact of adapting OML model in high horizontal resolution (1 km) NWP model, four sensitivity tests are performed. At this time, the prognostic scheme of skin SST is applied in NWP to simulate diurnal SST variation. The simulation results of summer case show that CNTL (off-OML) overestimates diurnal SST variation, while EXPs (on-OML) indicate similar results to observations. And, the prediction of precipitation for the performance of EXPs shows improvement compared with CNTL over coastal as well as inland. In winter, on the other hand, there is no significant difference in CNTL and EXPs. The average heat budget at sea surface in February, which is the case period, is close to zero. As a results, it is considered that radiation balance at the sea surface occurs and diurnal SST variation due to net radiation in the prognostic scheme is small. This results suggest that the application of the OML model in the summer season properly that simulates diurnal SST variation, can contribute to improving the prediction for performance of SST and precipitation

  5. Heterogeneous distribution of plankton within the mixed layer and its implications for bloom formation in tropical seas

    KAUST Repository

    Calbet, Albert

    2015-06-11

    Intensive sampling at the coastal waters of the central Red Sea during a period of thermal stratification, prior to the main seasonal bloom during winter, showed that vertical patches of prokaryotes and microplankton developed and persisted for several days within the apparently density uniform upper layer. These vertical structures were most likely the result of in situ growth and mortality (e.g., grazing) rather than physical or behavioural aggregation. Simulating a mixing event by adding nutrient-rich deep water abruptly triggered dense phytoplankton blooms in the nutrient-poor environment of the upper layer. These findings suggest that vertical structures within the mixed layer provide critical seeding stocks that can rapidly exploit nutrient influx during mixing, leading to winter bloom formation.

  6. The influence of temperature and salinity variability on the upper ocean density and mixed layer

    Directory of Open Access Journals (Sweden)

    R. W. Helber

    2010-08-01

    Full Text Available The relative influence of both temperature and salinity on the mixed layer depth (MLD is evaluated using a relationship of binned regressions of MLD on vertical density compensation and isothermal layer depth (ILD from a global set of in situ profile observations. Our approach is inspired by the observations of the difference between the MLD and the sonic layer depth (SLD that evolve seasonally around the global ocean. In this article, we hypothesize that vertical density compensation governs SLD-MLD differences and can be used for mapping the relative influence of temperature and salinity on upper ocean structure. The Turner angle, computed between the surface and 200 m (bulk Turner angle, BTA, serves as a measure of vertical density compensation that quantifies times and areas where either temperature or salinity is destabilizing. For temperature destabilization the ocean exhibits cool/fresh overlying hot/salty water. For salinity destabilization the ocean exhibits hot/salty overlying cool/fresh water. These two classes of density compensation have seasonal variability with different geographical characteristics. Profiles with salinity controlled stable density and destabilizing temperature gradient are found most often at high latitudes. Profiles with temperature controlled stable density and destabilizing salinity gradient are found in the tropics and subtropics of all oceans. Results indicate that about half of the ocean has vertical density compensation that is a necessary condition for SLD-MLD differences. While density compensation is necessary, it is not a sufficient condition for predicting the dependence of MLD on BTA. Density compensation is the dominant factor in MLD variability in heavy river input and subduction regions that cover only ~14% of the ocean.

  7. Mixing layer height measurements determines influence of meteorology on air pollutant concentrations in urban area

    Science.gov (United States)

    Schäfer, Klaus; Blumenstock, Thomas; Bonn, Boris; Gerwig, Holger; Hase, Frank; Münkel, Christoph; Nothard, Rainer; von Schneidemesser, Erika

    2015-10-01

    Mixing layer height (MLH) is a key parameter to determine the influence of meteorological parameters upon air pollutants such as trace gas species and particulate concentrations near the surface. Meteorology, and MLH as a key parameter, affect the budget of emission source strengths, deposition, and accumulation. However, greater possibilities for the application of MLH data have been identified in recent years. Here, the results of measurements in Berlin in 2014 are shown and discussed. The concentrations of NO, NO2, O3, CO, PM1, PM2.5, PM10 and about 70 volatile organic compounds (anthropogenic and biogenic of origin) as well as particle size distributions and contributions of SOA and soot species to PM were measured at the urban background station of the Berlin air quality network (BLUME) in Nansenstr./Framstr., Berlin-Neukölln. A Vaisala ceilometer CL51, which is a commercial mini-lidar system, was applied at that site to detect the layers of the lower atmosphere in real time. Special software for these ceilometers with MATLAB provided routine retrievals of MLH from vertical profiles of laser backscatter data. Five portable Bruker EM27/SUN FTIR spectrometers were set up around Berlin to detect column averaged abundances of CO2 and CH4 by solar absorption spectrometry. Correlation analyses were used to show the coupling of temporal variations of trace gas compounds and PM with MLH. Significant influences of MLH upon NO, NO2, PM10, PM2.5, PM1 and toluene (marker for traffic emissions) concentrations as well as particle number concentrations in the size modes 70 - 100 nm, 100 - 200 nm and 200 - 500 nm on the basis of averaged diurnal courses were found. Further, MLH was taken as important auxiliary information about the development of the boundary layer during each day of observations, which was required for the proper estimation of CO2 and CH4 source strengths from Berlin on the basis of atmospheric column density measurements.

  8. Long-term study of air urban quality together with mixing layer height

    Science.gov (United States)

    Schäfer, Klaus; Ling, Hong; Münkel, Christoph; Emeis, Stefan

    2013-10-01

    Air pollution episodes in urban areas often occur during low wind speeds and low mixing layer height (MLH) and can not only be ascribed to increased local anthropogenic emissions. The continuous knowledge of MLH is supporting the understanding of processes directing air quality. If the MLH is located near to the ground, which occurs mainly during winter and night-time, air pollution can be high due to a strongly limited air mass dilution. The Vaisala ceilometer CL31, which is an eye-safe commercial mini-lidar system, is used for long-term continuous remote sensing of MLH. The ceilometer measurements provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the borders of mixed layers. Special software for this ceilometer developed with MATLAB provides routine retrievals of lower atmosphere layering from vertical profiles of laser backscatter data. To study the gaseous pollutants and those compounds important for secondary aerosol formation like NO and NO2 as well as O3 The data retrieval software is extended to improve remote sensing of MLH. The original 10-minute-interval values are used to calculate continuous 1-hour-mean values. Gaps and strong variations of the original data are considered. The results of investigations of the meteorological influences and the role of emissions within the context of the air quality in Augsburg are discussed. a DOAS is operated since March 2012 in Augsburg. Information about different road traffic emissions is provided by this one instrument i.e. by path-integrated air pollution information in different directions. The DOAS contains an analyser and an emitter/receiver unit pointing to three retroreflectors. The retroreflectors were installed at lamp masts so that the paths were about 10 m above street level and perpendicular across the streets. The emitter/receiver unit was in a distance of about 20 m to an in situ air pollution measurement station at the ground. Ground

  9. Use of a mixed layer model to investigate problems in operational prediction of return flow

    Science.gov (United States)

    Lewis, J. M.

    2006-12-01

    Inaccuracy in the numerical prediction of the moisture content of return-flow air over the Gulf of Mexico continues to plague operational forecasters. At the Environmental Modeling Center/National Centers for Environmental Prediction (EMC/NCEP) in the United States, the prediction errors have exhibited bias — typically too dry in the early-1990s and too moist from the mid-1990s to present. This research explores the possible sources of bias by using a Lagrangian formulation of the classic mixed-layer model. Justification for use of this low-order model rests on careful examination of the upper-air thermodynamic structure in a well- observed event during the Gulf of Mexico Experiment (GUFMEX). The mixed-layer constraints are shown to be appropriate for the first phase of return flow, viz., the outflow phase. The research begins by evaluating the model's estimates of sensitivity — the change in the model output (at the termination point of outflow) in response to inaccuracies in the elements of the control vector (the initial conditions, the boundary conditions, and the physical and empirical parameters). This evaluation is accomplished by recourse to a known analytic solution to the mixed-layer equations (a special case). Results indicate that the fourth-order Runge-Kutta integration scheme produces extremely accurate evolutions of the fields, and equally important, delivers accurate measures of the sensitivity. Further, the dynamical system is shown to be `weakly nonlinear', i. e., solutions that result from perturbations to the control vector are well approximated by the first-order terms in the Taylor series expansion about the base state. The second stage of research examines the relative importance of elements of the control vector on the moisture forecast for the general case. Results indicate that inaccuracies in the initial conditions are significant, yet they are secondary to inaccuracies in the boundary conditions and physical/empirical parameters. The

  10. Radon-222, a proxy for vertical mixing of emissions in the urban nocturnal boundary layer

    Science.gov (United States)

    Chambers, S.; Williams, A. G.; Griffiths, A.; Crawford, J.; Zahorowski, W.

    2012-04-01

    There has been growing concern in recent decades regarding the health implications of fine particles (≤ 2.5μm), which are readily deposited deep within the lungs. In the interests of public health, and improving the predictive ability of Chemical Transport Models, it is imperative to improve our understanding of the diurnal variability of primary pollutant and precursor concentrations by, among others, improving our understanding of the underlying physics of transport and mixing processes. From the time of their release until they are removed from the atmosphere, the level of public exposure to emissions is closely related to rates of near-surface horizontal and vertical dispersion, the depth of the atmospheric boundary layer, and the venting from the boundary layer. These parameters, in turn, are dependent upon the amount and nature of mixing, which is closely related to atmospheric stability. With the exception of bushfires and dust storms, the greatest risk of public exposure to emissions occurs under "inversion" conditions, when the atmosphere is stably stratified. These very conditions are notoriously the most problematic for contemporary weather and chemical transport models. At such times the structure of the lowest 10-100m of the atmosphere can be quite complex, potentially containing multiple disconnected layers, and even stability measures based on surface similarity theory can fail (or yield inconclusive results) without sufficient vertical and temporal measurement resolution. Near-surface radon measurements provide a direct measure of the degree of dilution of surface-emitted scalar quantities by vertical mixing at night that is completely independent of local meteorological measurements and does not fail under conditions of near calm, which occur on the most stable nights. As such, they are a valuable proxy for potential pollution accumulation. In this study we analyse and discuss 22 months of continuous hourly observations within an urban airshed

  11. Observations of wind and waves in the central Bay of Bengal during BOBMEX-99 and their effect on mixed layer depth variability due to forced mixing

    Indian Academy of Sciences (India)

    J Swain; R K Shukla; A Raghunadha Rao; J K Panigrahi; N R Venkitachalam

    2003-06-01

    Time-series wind and wave measurements were carried out onboard INS Sagardhwani in the central Bay of Bengal during BOBMEX-99. Various other marine meteorological and oceanographic measurements relevant to monsoon studies were also collected simultaneously. The observed variations of wind and waves and the associated mixed layer depth (MLD) variability based on both temperature and density criteria at 3 hourly intervals are presented in this paper as a case study. At the time-series location (13°N, 87°E) wind varied between 6 and 16 m/s and the predominant direction was southwesterly. The significant wave height and period varied from 1.9 to 3.7m and 8 to 13 s respectively. Some of the available statistical predictive methods for the determination of MLD by forced mixing are utilized to test the extent of mechanical mixing within the top layer of water by the local wind and wave activity. The same is extended to formulate a new empirical relation for gross estimation of effective depth within which the sound energy is generally trapped during its transmission in the surface duct. The present analysis aiming for estimation of observed MLD variability (35 to 75 m) using the suggested simple empirical relation reveals that, the mixed layer variability observed during the experiment depends on both local ocean variability as well as remote forcing as reported earlier.

  12. Variable temperature hot wire anemometry applied to the joint analysis of the velocity and temperature fluctuations in a mixing layer

    OpenAIRE

    Ndoye, M.; Delville, J.; Dorignac, E.; Arroyo, G.

    2011-01-01

    International audience; Our study provides a detailed description of the thermal mixing process in an anisothermal mixing layer. Velocity and temperature are simultaneously measured at the same point by using a new hot wire anemometer. This anemometer implements the multiple overheat principle, associated with a non linear Levenberg-Marquardt signal processing. These simultaneous measurements allowed an analysis based on conditional Probability Density Functions (PDFs), joint PDFs and a quadr...

  13. Existence of shocklets in a two-dimensional supersonic mixing layer and its influence on the flow structure

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The spatial evolution of a T-S wave and its subharmonic wave, introduced at the inlet in a 2-D supersonic mixing layer, was investigated by using DNS. The relationship between the amplitude of the disturbance wave and the strength of the shocklet caused by the disturbance was investigated. We analyzed the shape of the disturbance velocity profile on both sides of the shocklet, and found that the existence of shocklet affected appreciably the disturbance velocity. The effects on the high speed side and low speed side of the mixing layer were found to be different.

  14. The seasonal cycle of the mixing layer height and its impact on black carbon concentrations in the Kathmandu Valley (Nepal)

    Science.gov (United States)

    Mues, Andrea; Rupakheti, Maheswar; Hoor, Peter; Bozem, Heiko; Münkel, Christoph; Lauer, Axel; Butler, Tim

    2016-04-01

    The properties and the vertical structure of the mixing layer as part of the planetary boundary layer are of key importance for local air quality. They have a substantial impact on the vertical dispersion of pollutants in the lower atmosphere and thus on their concentrations near the surface. In this study, ceilometer measurements taken within the framework of the SusKat project (Sustainable Atmosphere for the Kathmandu Valley) are used to investigate the mixing layer height in the Kathmandu Valley, Nepal. The applied method is based on the assumption that the aerosol concentration is nearly constant in the vertical and distinctly higher within the mixing layer than in the air above. Thus, the height with the steepest gradient within the ceilometer backscatter profile marks the top of the mixing layer. Ceilometer and black carbon (BC) measurements conducted from March 2013 through February 2014 provide a unique and important dataset for the analysis of the meteorological and air quality conditions in the Kathmandu Valley. In this study the mean diurnal cycle of the mixing layer height in the Kathmandu Valley for each season (pre-monsoon, monsoon, post-monsoon and winter season) and its dependency on the meteorological situation is investigated. In addition, the impact of the mixing layer height on the BC concentration is analyzed and compared to the relevance of other important processes such as emissions, horizontal advection and deposition. In all seasons the diurnal cycle is typically characterized by low mixing heights during the night, gradually increasing after sun rise reaching to maximum values in the afternoon before decreasing again. Seasonal differences can be seen particularly in the height of the mixing layer, e.g. from on average 153/1200 m (pre-monsoon) to 241/755 m (monsoon season) during the night/day, and the duration of enhanced mixing layer heights during daytime (around 12 hours (pre-monsoon season) to 8 hours (winter)). During the monsoon

  15. Heat Transfer Phenomena of Supercritical Fluids

    Energy Technology Data Exchange (ETDEWEB)

    Krau, Carmen Isabella; Kuhn, Dietmar; Schulenberg, Thomas [Forschungszentrum Karlsruhe, Institute for Nuclear and Energy Technologies, 76021 Karlsruhe (Germany)

    2008-07-01

    In concepts for supercritical water cooled reactors, the reactor core is cooled and moderated by water at supercritical pressures. The significant temperature dependence of the fluid properties of water requires an exact knowledge of the heat transfer mechanism to avoid fuel pin damages. Near the pseudo-critical point a deterioration of heat transfer might happen. Processes, that take place in this case, are not fully understood and are due to be examined systematically. In this paper a general overview on the properties of supercritical water is given, experimental observations of different authors will be reviewed in order to identify heat transfer phenomena and onset of occurrence. The conceptional design of a test rig to investigate heat transfer in the boundary layer will be discussed. Both, water and carbon dioxide, may serve as operating fluids. The loop, including instrumentation and safety devices, is shown and suitable measuring methods are described. (authors)

  16. Seasonal variability of the mixed layer in the central Bay of Bengal and associated changes in nutrients and chlorophyll

    Digital Repository Service at National Institute of Oceanography (India)

    Narvekar, J.; PrasannaKumar, S.

    Bay. We also show that the nitrate and chlorophyll distribution in the upper ocean during spring intermonsoon is strongly coupled to the mixed-layer depth, whereas during summer river runoff and cold-core eddies appear to play a major role...

  17. Lack of seasonal and geographic variation in mesozooplankton biomass in the Arabian Sea and its structure in the mixed layer

    Digital Repository Service at National Institute of Oceanography (India)

    Madhupratap, M.; Gopalakrishnan, T.C.; Haridas, P.; Nair, K.K.C.; Aravindakshan, P.N.; Padmavati, G.; Paul, S.

    in the mixed layer compared to deeper strata. A noteworthy feature was that the standing stocks and abundances did not vary significantly between seasons and areas. Vertical migrations appeared to be in a low key. In all seasons herbivores dominated, followed...

  18. Coupled atmosphere-mixed layer ocean response to ocean heat flux convergence along the Kuroshio current extension

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Young-Oh [Woods Hole Oceanographic Institution, Physical Oceanography Department, Woods Hole, MA (United States); Deser, Clara [National Center for Atmospheric Research, Boulder, CO (United States); Cassou, Christophe [CNRS-CERFACS, Toulouse (France)

    2011-06-15

    The winter response of the coupled atmosphere-ocean mixed layer system to anomalous geostrophic ocean heat flux convergence in the Kuroshio Extension is investigated by means of experiments with an atmospheric general circulation model coupled to an entraining ocean mixed layer model in the extra-tropics. The direct response consists of positive SST anomalies along the Kuroshio Extension and a baroclinic (low-level trough and upper-level ridge) circulation anomaly over the North Pacific. The low-level component of this atmospheric circulation response is weaker in the case without coupling to an extratropical ocean mixed layer, especially in late winter. The inclusion of an interactive mixed layer in the tropics modifies the direct coupled atmospheric response due to a northward displacement of the Pacific Inter-Tropical Convergence Zone which drives an equivalent barotropic anomalous ridge over the North Pacific. Although the tropically driven component of the North Pacific atmospheric circulation response is comparable to the direct response in terms of sea level pressure amplitude, it is less important in terms of wind stress curl amplitude due to the mitigating effect of the relatively broad spatial scale of the tropically forced atmospheric teleconnection. (orig.)

  19. RESEARCH ON PARTICLE DISPERSION IN A PLANE MIXING LAYER WITH COHERENT STRUCTURES

    Institute of Scientific and Technical Information of China (English)

    林建忠; 林江; 邵雪明; 石兴

    2003-01-01

    The numerical simulation with two-way coupling was performed in a liquid -particle mixing layer and the corresponding experiment study was made. In the process of vortex rolling up and vortices pairing, the particles with different St number have a very different pattern of dispersion. The mean velocity of particle with St = 1 is higher than that of the fluid phase on the low-speed side, and lower than that of the fluid phase on the high-speed side. The RMS of particle approaches that of the fluid phase with decreasing particle St number. The RMS in the transverse direction is smaller than that in the streamwise direction. The velocity fluctuation correlation of particle is smaller than the Reynolds shear stress, the "overshoot" phenomenon that the velocity fluctuation correlation of particle is larger than the Reynolds shear stress does not appear. The larger the St number of particle is, the wider the range of the particle dispersion will be. The computed results are in agreement with the experimental ones.

  20. Baroclinic mixing of potential vorticity as the principal sharpening mechanism for the extratropical Tropopause Inversion Layer

    Science.gov (United States)

    Wang, Shu Meir; Geller, Marvin A.

    2016-09-01

    Previous works have shown that a dry, idealized general circulation model could produce many features of the extratropical Tropopause Inversion Layer (TIL). In particular, the following have been shown, but no explanations were given for these results. (1) A sharper extratropical TIL resulted more from increased horizontal resolution than from increased vertical resolution. (2) If the Equator-to-Pole temperature gradient was varied, the annual variation of the extratropical TIL found in observations could be reproduced. (3) The extratropical TIL altitude showed excellent correlation with the upper tropospheric relative vorticity, as had been previously proposed. (4) Increased horizontal model resolutions led to extratropical TILs that were at lower altitudes. We show that these conclusions follow from baroclinic mixing of high stratospheric potential vorticity into the troposphere being the principal sharpening mechanism for the extratropical TIL and the increased baroclinic activity occurring in higher horizontal resolution models. We furthermore suggest that the distance from the jet exerts a greater influence on the height and sharpness of the extratropical TIL than does the upper tropospheric relative vorticity, and this accounts for the annual behavior of the extratropical TIL found in observations and reproduced with a dry, mechanistic, global model.

  1. Statistics of the turbulent/non-turbulent interface in a spatially developing mixing layer

    KAUST Repository

    Attili, Antonio

    2014-06-02

    The thin interface separating the inner turbulent region from the outer irrotational fluid is analysed in a direct numerical simulation of a spatially developing turbulent mixing layer. A vorticity threshold is defined to detect the interface separating the turbulent from the non-turbulent regions of the flow, and to calculate statistics conditioned on the distance from this interface. The conditional statistics for velocity are in remarkable agreement with the results for other free shear flows available in the literature, such as turbulent jets and wakes. In addition, an analysis of the passive scalar field in the vicinity of the interface is presented. It is shown that the scalar has a jump at the interface, even stronger than that observed for velocity. The strong jump for the scalar has been observed before in the case of high Schmidt number (Sc). In the present study, such a strong jump is observed for a scalar with Sc ≈ 1. Conditional statistics of kinetic energy and scalar dissipation are presented. While the kinetic energy dissipation has its maximum far from the interface, the scalar dissipation is characterised by a strong peak very close to the interface. Finally, it is shown that the geometric features of the interfaces correlate with relatively large scale structures as visualised by low-pressure isosurfaces. © 2014 Taylor & Francis.

  2. Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

    Energy Technology Data Exchange (ETDEWEB)

    Sulmonetti, Taylor P.; Pang, Simon H.; Claure, Micaela Taborga; Lee, Sungsik; Cullen, David A.; Agrawal, Pradeep K.; Jones, Christopher W.

    2016-05-01

    The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the other catalysts, with promising activity compared to related catalysts in the literature. The use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.

  3. FerryBox-assisted monitoring of mixed layer pH in the Norwegian Coastal Current

    Science.gov (United States)

    Reggiani, Emanuele R.; King, Andrew L.; Norli, Marit; Jaccard, Pierre; Sørensen, Kai; Bellerby, Richard G. J.

    2016-10-01

    The evaluation of marine carbonate system variability and the impacts of ocean acidification (OA) on coastal marine ecosystems increasingly rely on monitoring platforms capable of delivering near real-time in situ carbonate system observations. These observations are also used for developing models and scenarios of OA, including potential impacts on marine ecosystem structure and function. An embedded flow-through spectrophotometric pH detection system has been developed alongside an underway seawater sampling system - termed a FerryBox - operating on ships of opportunity (SOOP), and can deliver a continuous data stream of mixed layer seawater pH with an in situ uncertainty of summer periods of 2015. Spring and summertime pH was generally 0.1 higher, and up to 0.255 higher, in comparison to winter pH observations. Here we show the necessity for a regular, high density monitoring approach, and the suitability of this pH detection technique for unmanned observational platforms.

  4. A Model Chain Application to Estimate Mixing Layer Height Related to PM10 Dispersion Processes

    Directory of Open Access Journals (Sweden)

    F. Guarnieri

    2015-01-01

    Full Text Available The mixing layer height (MLH is a crucial parameter in order to investigate the near surface concentrations of air pollutants. The MLH can be estimated by measurements of some atmospheric variables, by indirect estimates based on trace gases concentration or aerosol, or by numerical models. Here, a modelling approach is proposed. The developed modelling system is based on the models WRF-ARW and CALMET. This system is applied on Firenze-Prato-Pistoia area (Central Italy, during 2010, and it is compared with in situ measurements. The aim of this work is to evaluate the use of MLH model estimates to characterize the critical episodes for PM10 in a limited area. In order to find out the meteorological conditions predisposing accumulation of PM10 in the atmosphere’s lower level, some indicators are used: daily mean wind speed, cumulated rainfall, and mean MLH estimates from CALMET model. This indicator is linked to orography, which has important consequences on local weather dynamics. However, during critical events the local emission sources are crucial to the determination of threshold exceeding of PM10. Results show that the modelled MLH, together with cumulative rainfall and wind speed, can identify the meteorological conditions predisposing accumulation of air pollutant at ground level.

  5. MetUM-GOML: a near-globally coupled atmosphere–ocean-mixed-layer model

    Directory of Open Access Journals (Sweden)

    L. C. Hirons

    2014-09-01

    Full Text Available Well-resolved air–sea interactions are simulated in a new Ocean Mixed Layer coupled configuration of the Met Office Unified Model (MetUM-GOML, comprising the MetUM coupled to the Multi-Column K Profile Parametrization ocean (MC-KPP. This is the first globally coupled system which provides a vertically resolved, high near-surface resolution ocean at comparable computational cost to running in atmosphere-only mode. As well as being computationally inexpensive, this modelling framework is adaptable – the independent MC-KPP columns can be applied selectively in space and time – and controllable – by using temperature and salinity corrections the model can be constrained to any ocean state. The framework provides a powerful research tool for process-based studies of the impact of air–sea interactions in the global climate system. MetUM simulations have been performed which separate the impact of introducing interannual variability in sea surface temperatures (SSTs from the impact of having atmosphere–ocean feedbacks. The representation of key aspects of tropical and extra-tropical variability are used to assess the performance of these simulations. Coupling the MetUM to MC-KPP is shown, for example, to reduce tropical precipitation biases, improve the propagation of, and spectral power associated with, the Madden–Julian Oscillation and produce closer-to-observed patterns of springtime blocking activity over the Euro-Atlantic region.

  6. Statistics of Vortical Structures in Variable-Density Turbulent Mixing Layers

    Science.gov (United States)

    Baltzer, Jon; Livescu, Daniel

    2016-11-01

    Direct Numerical Simulations are performed of temporal incompressible shear-driven planar mixing layers between two miscible streams of fluids with different densities. The simulations begin from thin disturbed interfaces and develop into self-similar states. We use very large domain sizes, corresponding to grids of up to 6144 x 2048 x 1536 points, to produce high-quality statistics and allow natural growth of turbulent structures. A wide range of Atwood numbers are explored, ranging from nearly constant density to A=0.87 (or a density ratio of 14). At high Atwood numbers, a variety of statistics show that variable-density effects produce significant asymmetries. Here we focus on the differences in vortical structure of the light and heavy fluid streams and the importance of non-Boussinesq effects as Atwood number increases. Detailed budgets of vorticity moments are examined in conjunction with the alignments of vorticity relative to other flow quantities. The results display the variable density effects due to compositional variations, a distinctly different mechanism from the density variations associated with compressibility in high-speed flows.

  7. Direct Numerical Simulation of Concentration and Orientation Distribution of Fibers in a Mixing Layer

    Directory of Open Access Journals (Sweden)

    Kun Zhou

    2013-01-01

    Full Text Available The concentration and orientation of suspended fibers in a mixing layer are investigated numerically. Two cases (diffusive and nondiffusive are investigated for the fiber concentration distribution. The fine structures of the instantaneous distributions under these two cases are very different due to molecular diffusion. Sharp front of concentration is observed in the nondiffusive case. However, there is no obvious difference in the mean concentration between the two cases. With regard to the orientation, a fiber may rotate periodically or approach an asymptotic orientation, which is determined by a determinant defined with the stain rate. The symmetric part of the strain rate tends to make a fiber align to an asymptotic orientation, while the antisymmetric part drives a fiber to rotate. When a fluid parcel passes through a region with relatively high shear rate, fibers carried by the fluid parcel are most likely to rotate incessantly. On the other hand, in the region of relatively high extension rate, fibers tend to align to some asymptotic orientation. Generally, fibers tend to align with the shear plane. This fact has significant implications in predicting the rheological properties of fiber suspension flows.

  8. Statistics of the turbulent/non-turbulent interface in a spatially evolving mixing layer

    KAUST Repository

    Cristancho, Juan

    2012-12-01

    The thin interface separating the inner turbulent region from the outer irrotational fluid is analyzed in a direct numerical simulation of a spatially developing turbulent mixing layer. A vorticity threshold is defined to detect the interface separating the turbulent from the non-turbulent regions of the flow, and to calculate statistics conditioned on the distance from this interface. Velocity and passive scalar statistics are computed and compared to the results of studies addressing other shear flows, such as turbulent jets and wakes. The conditional statistics for velocity are in remarkable agreement with the results for other types of free shear flow available in the literature. In addition, a detailed analysis of the passive scalar field (with Sc 1) in the vicinity of the interface is presented. The scalar has a jump at the interface, even stronger than that observed for velocity. The strong jump for the scalar has been observed before in the case of high Schmidt number, but it is a new result for Schmidt number of order one. Finally, the dissipation for the kinetic energy and the scalar are presented. While the kinetic energy dissipation has its maximum far from the interface, the scalar dissipation is characterized by a strong peak very close to the interface.

  9. A Lie-group derivation of a multi-layer mixing length formula for turbulent channel and pipe flow

    CERN Document Server

    She, Zhen-Su; Hussain, Fazle

    2011-01-01

    A novel Lie-group analysis of the (unclosed) mean momentum equation (MME) for turbulent channel and pipe flows yields an analytic multi-layer formula for the mixing length (hence the mean velocity profile) as a candidate invariant solution. Two kinds of local invariant solutions are proposed: one describing viscous sublayer, buffer layer, log-layer, and a newly discovered central core, and the other describing the bulk zone where a quasi-balance is established between turbulent production and dissipation. In particular, a simple form, 1-r^m, is derived for describing the mixing length in the bulk zone of channel (m=4) and pipe (m=5) flows. Furthermore, an ansatz based on a relation between prolonged Lie-group invariants is proposed to derive composite invariant solutions to the MME, yielding the entire mixing length profile. The theory proposes a thorough quantification of commonly recognized multi-layer structure using three kinds of parameters: scaling, layer thickness and transition sharpness. All the abov...

  10. Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

    Science.gov (United States)

    Jähn, M.; Muñoz-Esparza, D.; Chouza, F.; Reitebuch, O.; Knoth, O.; Haarig, M.; Ansmann, A.

    2016-01-01

    Large eddy simulations (LESs) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind and Raman lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the downwind vertical wind structure. Additionally, the model results accurately reproduce the

  11. Spring-summer imbalance of dissolved inorganic carbon in the mixed layer of the northwestern Sargasso Sea

    Energy Technology Data Exchange (ETDEWEB)

    Marchal, O.; Monfray, P. [Centre National de la Recherche Scientifique (CNRS), 91 - Gif-sur-Yvette (France). Centre des Faibles Radioactivites; Bates, N.R. [Bermuda Biological Station for Research, Ferry Reach (Bermuda)

    1995-02-01

    The surface concentration of dissolved inorganic carbon (DIC) at the Bermuda Atlantic Time-series Study site (BATS) decreased gradually by ca. 30 {mu}mol kg{sup -1} from April to October in 1989. This decrease occurred almost in the absence of measurable nitrate in the mixed layer. Although ancillary data about the C system point to the possible importance of lateral transport, horizontal gradients in surface DIC and the mean flow in the area indicate that local effects should prevail in the seasonal drawdown of DIC. On the basis of an one-dimensional model, we hence estimate the mixed layer budget of DIC for this period, from surface data, temperature profiles, and concomitant meteorological records. According to model uncertainties, the drawdown should be mostly explained (71-93%) by a net community production (NCP) averaging 1.4-2.3 mgC m{sup -3} d{sup -1}, and to a lesser extent, by outgassing of CO{sub 2} to the atmosphere. These losses are partially compensated by mixing with DIC-rich waters of the thermocline. This NCP must be regarded as a lower estimate, since the mean flow from the northeast should bring waters with slightly higher DIC to the mixed layer at the BATS site. The model, which is sensitive to short-term variations in atmospheric forcing (<1 day), indicates that this layer has never reached the nitrocline for spring-summer 1989, even as a hurricane passed through the region. Hence, the surface NCP should not have been supported by unsampled, pulse-like supplies of deep nutrients. Wet atmospheric deposition of nitrogen measured concurrently on Bermuda could contribute to the biological N requirement. According to historical estimates, N{sub 2} fixation seems however insufficient to meet the remaining demand. Comparison between NCP and primary production measured in situ suggests that most of photosynthetically fixed C is not respired in the mixed layer. 77 refs, 10 figs, 2 tabs

  12. Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. I: Single layer cloud

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Stephen A.; McCoy, Renata; Morrison, H.; Ackerman, Andrew; Avramov, Alexander; DeBoer, GIJS; Chen, Mingxuan; Cole, Jason N.; DelGenio, Anthony D.; Falk, Michael; Foster, Mike; Fridlind, Ann; Golaz, Jean-Christophe; Hashino, Tempei; Harrington, Jerry Y.; Hoose, Corinna; Khairoutdinov, Marat; Larson, Vince; Liu, Xiaohong; Luo, Yali; McFarquhar, Greg; Menon, Surabi; Neggers, Roel; Park, Sungsu; Poellot, M. R.; Schmidt, Jerome M.; Sednev, Igor; Shipway, Ben; Shupe, Matthew D.; Spangenberg, D.; Sud, Yogesh; Turner, David D.; Veron, Dana; Von Salzen, Knut; Walker, Gregory K.; Wang, Zhien; Wolf, Audrey; Xie, Shaocheng; Xu, Kuan-Man; Yang, Fanglin; Zhang, G.

    2009-05-21

    Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a cold-air outbreak mixed-phase stratocumulus cloud observed during the ARM Mixed-Phase Arctic Cloud Experiment. The observed cloud occurred in a well-mixed boundary layer with a cloud top temperature of –15°C. While the cloud was water dominated, ice precipitation appears to have lowered the liquid water path to about 2/3 of the adiabatic value. The simulations, which were performed by seventeen single column and nine cloud-resolving models, generally underestimate the liquid water path with the median single-column and cloud-resolving model liquid water path a factor of 3 smaller than observed. While the simulated ice water path is in general agreement with the observed values, results from a sensitivity study in which models removed ice microphysics indicate that in many models the interaction between liquid and ice phase microphysics is responsible for the strong model underestimate of liquid water path. Although no single factor is found to lead to a good simulation, these results emphasize the need for care in the model treatment of mixed-phase microphysics. This case study, which has been well observed from both aircraft and ground-based remote sensors, could be benchmark for model simulations of mixed-phase clouds.

  13. Supercritical Airfoil Coordinates

    Data.gov (United States)

    National Aeronautics and Space Administration — Rectangular Supercritical Wing (Ricketts) - design and measured locations are provided in an Excel file RSW_airfoil_coordinates_ricketts.xls . One sheet is with Non...

  14. Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

    Directory of Open Access Journals (Sweden)

    M. Jähn

    2015-08-01

    Full Text Available Large eddy simulations (LES are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ~ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength and wind shear. Comparisons of LES model output with wind lidar data show similarities in the formation of the daytime convective plume and the mean vertical wind structure.

  15. Simulation and Exploration of the Mechanisms Underlying the Spatiotemporal Distribution of Surface Mixed Layer Depth in a Large Shallow Lake

    Institute of Scientific and Technical Information of China (English)

    ZHAO Qiaohua; SUN Jihua; ZHU Guangwei

    2012-01-01

    The aquatic eco-environment is significantly affected by temporal and spatial variation of the mixed layer depth (MLD) in large shallow lakes.In the present study,we simulated the three-dimensional water temperature of Taihu Lake with an unstructured grid with a finite-volume coastal ocean model (FVCOM)using wind speed,wind direction,short-wave radiation and other meteorological data measured during 13-18 August 2008. The simulated results were consistent with the measurements. The temporal and spatial distribution of the MLD and the possible relevant mechanisms were analyzed on the basis of the water temperature profile data of Taihu Lake. The results indicated that diurnal stratification might be established through the combined effect of the hydrodynamic conditions induced by wind and the heat exchange between air and water.Compared with the net heat flux,the changes of the MLD were delayed approximately two hours.Furthermore,there were significant spatial differences of the MLD in Taihu Lake due to the combined impact of thermal and hydrodynamic forces. Briefly,diurnal stratification formed relatively easily in Gonghu Bay,Zhushan Bay,Xukou Bay and East Taihu Bay,and the surface mixed layer was thin.The center of the lake region had the deepest surface mixed layer due to the strong mixing process.In addition,Meiliang Bay showed a medium depth of the surface mixed layer.Our analysis indicated that the spatial difference in the hydrodynamic action was probably the major cause for the spatial variation of the MLD in Taihu Lake.

  16. Mixed-layer ocean responses to anthropogenic aerosol dimming from 1870 to 2000

    Science.gov (United States)

    Dallafior, Tanja; Folini, Doris; Knutti, Reto; Wild, Martin

    2016-04-01

    It is still debated, to what extent anthropogenic aerosol-induced changes in surface solar radiation (SSR) since industrialization affected surface temperatures (tsurf). We use mixed-layer ocean (MLO) experiments with the general circulation model ECHAM6.1 and explicit aerosols (HAM2.2) to identify regions where this effect is discernible. For each decade from 1870 to 2000 we derive three equilibria: anthropogenic aerosol emissions and greenhouse gas concentrations at the respective decade's levels (ALL), either aerosols or greenhouse gases fixed at year 1850 levels (GHG and AERO). We duplicated parts of the experiments with different prescribed divergence of ocean heat transport (Q_ALL, Q_AERO, Q_GHG). Comparing year 2000 with year 1870 equilibria, we find global average cooling of -1.4K for AERO, and warming of 1.4K for GHG. ALL and Q_ALL warm by 0.6K and 0.4K, respectively. The way divergence of ocean heat transport is prescribed thus matters. Pattern correlations of year 2000 tsurf responses in ALL with the sum of AERO and GHG are higher (0.88) than with Q_ALL (0.71) confirming additivity of global patterns, but not of global means. The imprint of anthropogenic aerosols on tsurf response patterns in ALL is distinct, thus potentially detectable. Over the decades, ocean fractions affected by either changing aerosol optical depth or all-sky SSR vary in concert, supporting linkage between anthropogenic aerosols and all-sky SSR. SSR changes and tsurf responses are marginally collocated. Oceanic regions with strongest tsurf response to aerosol-induced SSR changes are the northern mid-latitudes and North Pacific with tsurf sensitivities up to -0.7K per Wm-2 SSR change. Results presented have been published under the same title in the Journal of Geophysical Research, Volume 121, DOI 10.1002/2015JD024070.

  17. Mixed Layer Sub-Mesoscale Parameterization - Part 1: Derivation and Assessment

    Science.gov (United States)

    Canuto, V. M.; Dubovikov, M. S.

    2010-01-01

    Several studies have shown that sub-mesoscales (SM 1km horizontal scale) play an important role in mixed layer dynamics. In particular, high resolution simulations have shown that in the case of strong down-front wind, the re-stratification induced by the SM is of the same order of the de-stratification induced by small scale turbulence, as well as of that induced by the Ekman velocity. These studies have further concluded that it has become necessary to include SM in ocean global circulation models (OGCMs), especially those used in climate studies. The goal of our work is to derive and assess an analytic parameterization of the vertical tracer flux under baroclinic instabilities and wind of arbitrary directions and strength. To achieve this goal, we have divided the problem into two parts: first, in this work we derive and assess a parameterization of the SM vertical flux of an arbitrary tracer for ocean codes that resolve mesoscales, M, but not sub-mesoscales, SM. In Part 2, presented elsewhere, we have used the results of this work to derive a parameterization of SM fluxes for ocean codes that do not resolve either M or SM. To carry out the first part of our work, we solve the SM dynamic equations including the non-linear terms for which we employ a closure developed and assessed in previous work. We present a detailed analysis for down-front and up-front winds with the following results: (a) down-front wind (blowing in the direction of the surface geostrophic velocity) is the most favorable condition for generating vigorous SM eddies; the de-stratifying effect of the mean flow and re-stratifying effect of SM almost cancel each other out,

  18. Seasonal and interannual variations of mixed layer salinity in the southeast tropical Indian Ocean

    Science.gov (United States)

    Zhang, Ningning; Feng, Ming; Du, Yan; Lan, Jian; Wijffels, Susan E.

    2016-07-01

    In this study, seasonal and interannual variations of the mixed layer salinity (MLS) in the southeast tropical Indian Ocean (SETIO) are analyzed using satellite observations, historical data sets, and data-assimilating ocean model outputs. On the seasonal cycle, the MLS in the SETIO becomes fresher in austral winter and saltier in austral summer: between the Java-Lesser Sunda coast and the South Equatorial Current (SEC, 12°S), where positive entrainment and fresh advections counterbalance each other, the annual cycle of the MLS closely follows the variation of the air-sea freshwater forcing; off the northwest and west Australian coasts, the MLS variations are influenced by the annual cycles of the Indonesian Throughflow (ITF) and Leeuwin Current (LC) transports as well as the air-sea freshwater forcing, with eddy fluxes acting to freshen the MLS along the SEC, the Eastern Gyral Current, and the LC. On the interannual-scale, El Niño (La Niña) events are typically associated with saltier (fresher) MLS in the SETIO. Composite and budget analyses reveal that interannual variations in precipitations drive the MLS anomalies off the Java-Lesser Sunda coast; between 12°S and the northwest Australian coast, the MLS variations are influenced by both advection anomalies and local precipitation anomalies; whereas anomalous meridional currents contribute to the MLS variations off the west Australian coast. Both enhanced local precipitations and the ITF transport anomalies have substantial contributions to the drastic freshening of the Indonesian-Australian Basin between the Java-Lesser Sunda coast and the northwest Australian coast during the extended La Niña events in 1999-2001 and 2010-2012.

  19. Investigating CloudSat Retrievals Sensitivity to Forward Iterative Algorithm Parameters in the Mixed Cloud Layers

    Science.gov (United States)

    Qiu, Yujun; Lu, Chunsong

    2016-09-01

    When millimeter-wave cloud radar data are used for the forward iterative retrieval of the liquid water content (LWC) and effective radius of cloud droplets ( R e) in a cloud layer, the prior values and tolerance ranges of the cloud droplet number density ( N t), scale parameter ( R g) and spectral width parameter ( W g) in the iterative algorithm are the main factors that affect the retrieval accuracy. In this study, we used data from stratus and convective clouds that were simultaneously observed by CloudSat and aircraft to conduct a sensitivity analysis of N t, R g, and W g for the retrieval accuracies of LWC and R e in both stratus and convective clouds. N t is the least sensitive parameter for accurately retrieving stratus LWC and R e in both stratus and convective clouds, except for retrieving the convective cloud LWC. Opposite to N t, R g is the most sensitive parameter for both LWC and R e retrievals. As to the effects of parameter tolerance ranges on the retrievals of LWC and R e, the least important parameter is the N t tolerance range; the most important one is the W g tolerance range for retrieving convective cloud LWC and R e, the R g is the important parameter for retrieving stratus LWC and R e. To obtain accurate retrieved values for clouds in a specific region, it is important to use typical values of the sensitive parameters, which could be calculated from in situ observations of cloud droplet size distributions. In addition, the sensitivities of the LWC and R e to the three parameters are stronger in convective clouds than in stratus clouds. This may be related to the melting and merging of solid cloud droplets during the convective mixing process in the convective clouds.

  20. Derivation and assessment of a mixed layer sub-mesoscale model

    Directory of Open Access Journals (Sweden)

    V. M. Canuto

    2009-09-01

    Full Text Available Present studies of mixed layer sub-mesoscales rely primarily on high resolution numerical simulations. Only few of these studies have attempted to parameterize the ensuing buoyancy submesoscale fluxes in terms of the resolved fields so that they can be used in OGCMs (ocean circulation models that do not resolve sub-mesoscales. In reality, OGCMs used in climate studies include a carbon-cycle which also requires the flux of a passive tracer.

    The goal of this work is to derive and assess a parameterization of the submesoscale vertical flux of an arbitrary tracer in terms of the resolved fields. The parameterization is obtained by first solving the dynamic equations governing the velocity and tracer fields that describe sub-mesoscales and then constructing second-order moments such as the tracer fluxes. A key ingredient of the present approach is the modeling of the non-linear terms that enter the dynamic equations of the velocity and tracer fields, a problem that we discuss in two Appendices.

    The derivation of the sub-mesoscale tracer vertical flux is analytical and can be followed in detail since no additional information is required. The external forcing includes both baroclinic instabilities and wind stresses.

    We compare the model results with data from sub-mesoscale resolving simulations available in the literature which are of two kinds, one with no wind (baroclinic instabilities only and the other with both baroclinic instabilities and wind. In both cases, the model results reproduce the simulation data satisfactorily.

  1. Dimming over the oceans: mixed layer ocean experiments from 1870 to 2000

    Science.gov (United States)

    Dallafior, Tanja; Folini, Doris; Knutti, Reto; Wild, Martin

    2015-04-01

    Sea surface temperature (SSTs) changes are known to affect precipitation patterns. However, it is still subject to debate, whether anthropogenic aerosols are capable of affecting SSTs, which could feed back on precipitation patterns. To influence SSTs, anthropogenic aerosols need to reduce incoming surface solar radiation (SSR) through direct or indirect effects for a sufficiently long time span over a sufficiently large area. To quantify the maximum potential SST response to anthropogenic aerosol dimming over the past decades, we performed equilibrium experiments with the general circulation model, ECHAM and explicit aerosol representation (ECHAM6-HAM2.2) and a mixed-layer ocean (MLO). Every ten years, we let the system equilibrate to the conditions (aerosol and greenhouse gas burdens, GHG) of that specific year. Each experiment is conducted over 50 years, of which the first 10 years are discarded. We generated three sets of decadal equilibria covering the entire 20th century and part of the 19th century (from 1870) : One, where both GHG and anthropogenic aerosols are set to the respective decade, one where GHG levels are held constant at 1850s levels, and one where anthropogenic aerosols are held constant at 1850s levels. Deep ocean heat fluxes are prescribed based on the surface energy flux climatology derived from an atmosphere-only integration with pre-industrial (year 1850) conditions for aerosols and GHG and climatological SSTs (average of Hadley Center SSTs, observation based, over the years 1871-1900). Results of these findings will be discussed, especially the SST and precipitation responses seen in the different equilibria. Moreover, results will be put in context with transient experiments with prescribed SSTs. The presented results are part of a project aiming at quantifying the effect of anthropogenic aerosols on SSTs. The results will serve as a basis for future experiments using a dynamic ocean model to quantify the transient response of the ocean

  2. Mixed-layer ocean responses to anthropogenic aerosol dimming from 1870 to 2000

    Science.gov (United States)

    Dallafior, T. N.; Folini, D.; Knutti, R.; Wild, M.

    2016-01-01

    It is debated to what extent surface solar radiation (SSR) changes through varying anthropogenic aerosol emissions since industrialization affected surface temperatures (tsurf). We use mixed-layer ocean experiments with the general circulation model ECHAM6.1 and explicit aerosols (HAM2.2) to identify regions where this effect is discernible. For each decade from 1870 to 2000 we derive three equilibria: anthropogenic aerosol emissions and greenhouse gas concentrations at the respective decade's levels (ALL), either aerosols or greenhouse gases fixed at year 1850 levels (GHG and AERO). We duplicated parts of the experiments with different prescribed divergence of ocean heat transport (Q_ALL, Q_AERO, and Q_GHG). Comparing year 2000 with year 1870 equilibria, we find global average cooling of -1.4 K for AERO and warming of 1.4 K for GHG. ALL and Q_ALL warm by 0.6 K and 0.4 K, respectively. The way divergence of ocean heat transport is prescribed thus matters. Pattern correlations of year 2000 tsurf responses in ALL with the sum of AERO and GHG are higher (0.88) than with Q_ALL (0.71) confirming additivity of global patterns, but not of global means. The imprint of anthropogenic aerosols on tsurf response patterns in ALL is distinct, thus potentially detectable. Over the decades, ocean fractions affected by either changing aerosol optical depth or all-sky SSR vary in concert, supporting linkage between anthropogenic aerosols and all-sky SSR. SSR changes and tsurf responses are marginally collocated. Oceanic regions with strongest tsurf response to aerosol-induced SSR changes are the northern midlatitudes and North Pacific with tsurf sensitivities up to -0.7 K W m-2 SSR change.

  3. A Physically Based Horizontal Subgrid-scale Turbulent Mixing Parameterization for the Convective Boundary Layer in Mesoscale Models

    Science.gov (United States)

    Zhou, Bowen; Xue, Ming; Zhu, Kefeng

    2017-04-01

    Compared to the representation of vertical turbulent mixing through various PBL schemes, the treatment of horizontal turbulence mixing in the boundary layer within mesoscale models, with O(10) km horizontal grid spacing, has received much less attention. In mesoscale models, subgrid-scale horizontal fluxes most often adopt the gradient-diffusion assumption. The horizontal mixing coefficients are usually set to a constant, or through the 2D Smagorinsky formulation, or in some cases based on the 1.5-order turbulence kinetic energy (TKE) closure. In this work, horizontal turbulent mixing parameterizations using physically based characteristic velocity and length scales are proposed for the convective boundary layer based on analysis of a well-resolved, wide-domain large-eddy simulation (LES). The proposed schemes involve different levels of sophistication. The first two schemes can be used together with first-order PBL schemes, while the third uses TKE to define its characteristic velocity scale and can be used together with TKE-based higher-order PBL schemes. The current horizontal mixing formulations are also assessed a priori through the filtered LES results to illustrate their limitations. The proposed parameterizations are tested a posteriori in idealized simulations of turbulent dispersion of a passive scalar. Comparisons show improved horizontal dispersion by the proposed schemes, and further demonstrate the weakness of the current schemes.

  4. Evolution of a Western Arctic Ice Ocean Boundary Layer and Mixed Layer Across a Developing Thermodynamically Forced Marginal Ice Zone

    Science.gov (United States)

    2016-09-01

    sufficient buoyancy to the summer halocline to prevent subsequent wind events from mixing out the NSTM. Ice Camp observations captured the development of a... ice zone (MIZ), thermal heterogeneities in the upper ocean led to large ocean-to- ice heat fluxes (100–200 Wm-2) and enhanced basal ice melt (3–6 cm... Ice Zone, turbulent heat flux, heat partitioning; melt pond drainage, through- ice radiative transmission, near- surface temperature maximum, summer

  5. Low-temperature Raman scattering spectra of GaSe{sub x}S{sub 1-x} layered mixed crystals

    Energy Technology Data Exchange (ETDEWEB)

    Gasanly, N.M. [Department of Physics, Middle East Technical University, 06531 Ankara (Turkey); Aydinli, A. [Department of Physics, Bilkent University, 06533 Ankara (Turkey)

    2002-07-01

    Raman scattering has been used to study the vibrational spectra of GaSe{sub x}S{sub 1-x} layered mixed crystals at 10 K. We report the frequency dependencies of different modes on composition x, with particular emphasis on A'{sub 1}{sup (2)} (A{sub 1g}{sup 1}) and A'{sub 1}{sup (4)} (A{sub 1g}{sup 2}) intralayer compressional modes having low dispersion in the Brillouin zone. The appearance of additional bands is attributed to multimode behavior typically exhibited by mixed crystals of anisotropic compounds. (Abstract Copyright[2002], Wiley Periodicals, Inc.)

  6. Upper mixed layer temperature anomalies at the North Atlantic storm-track zone

    Science.gov (United States)

    Moshonkin, S. N.; Diansky, N. A.

    1995-10-01

    Synoptic sea surface temperature anomalies (SSTAs) were determined as a result of separation of time scales smaller than 183 days. The SSTAs were investigated using daily data of ocean weather station C (52.75°N; 35.5°W) from 1 January 1976 to 31 December 1980 (1827 days). There were 47 positive and 50 negative significant SSTAs (lifetime longer than 3 days, absolute value greater than 0.10 °C) with four main intervals of the lifetime repetitions: 1. 4-7 days (45% of all cases), 2. 9-13 days (20-25%), 3. 14-18 days (10-15%), and 4. 21-30 days (10-15%) and with a magnitude 1.5-2.0 °C. An upper layer balance model based on equations for temperature, salinity, mechanical energy (with advanced parametrization), state (density), and drift currents was used to simulate SSTA. The original method of modelling taking into account the mean observed temperature profiles proved to be very stable. The model SSTAs are in a good agreement with the observed amplitudes and phases of synoptic SSTAs during all 5 years. Surface heat flux anomalies are the main source of SSTAs. The influence of anomalous drift heat advection is about 30-50% of the SSTA, and the influence of salinity anomalies is about 10-25% and less. The influence of a large-scale ocean front was isolated only once in February-April 1978 during all 5 years. Synoptic SSTAs develop just in the upper half of the homogeneous layer at each winter. We suggest that there are two main causes of such active sublayer formation: 1. surface heat flux in the warm sectors of cyclones and 2. predominant heat transport by ocean currents from the south. All frequency functions of the ocean temperature synoptic response to heat and momentum surface fluxes are of integral character (red noise), though there is strong resonance with 20-days period of wind-driven horizontal heat advection with mixed layer temperature; there are some other peculiarities on the time scales from 5.5 to 13 days. Observed and modelled frequency functions

  7. Mixed

    Directory of Open Access Journals (Sweden)

    Pau Baya

    2011-05-01

    Full Text Available Remenat (Catalan (Mixed, "revoltillo" (Scrambled in Spanish, is a dish which, in Catalunya, consists of a beaten egg cooked with vegetables or other ingredients, normally prawns or asparagus. It is delicious. Scrambled refers to the action of mixing the beaten egg with other ingredients in a pan, normally using a wooden spoon Thought is frequently an amalgam of past ideas put through a spinner and rhythmically shaken around like a cocktail until a uniform and dense paste is made. This malleable product, rather like a cake mixture can be deformed pulling it out, rolling it around, adapting its shape to the commands of one’s hands or the tool which is being used on it. In the piece Mixed, the contortion of the wood seeks to reproduce the plasticity of this slow heavy movement. Each piece lays itself on the next piece consecutively like a tongue of incandescent lava slowly advancing but with unstoppable inertia.

  8. The role of PEG conformation in mixed layers: from protein corona substrate to steric stabilization avoiding protein adsorption

    Directory of Open Access Journals (Sweden)

    Joan Comenge

    2015-03-01

    Full Text Available Although nanoparticles (NPs have been traditionally modified with a single ligand layer, mixture of ligands might help to combine different functionalities and to further engineer the NP surface. A detailed study of the competition between an alkanethiol (11-mercaptoundecanoic acid and SH-PEG for the surface of AuNPs and the resultant behaviors of this model nanoconjugate is presented here. As a result, the physicochemical properties of these conjugates can be progressively tuned by controlling the composition and especially the conformation of the mixed monolayer. This has implications in the physiological stability. The controlled changes on the SH-PEG conformation rather than its concentration induce a change in the stabilization mechanism from electrostatic repulsion to steric hindrance, which changes the biological fate of NPs. Importantly, the adsorption of proteins on the conjugates can be tailored by tuning the composition and conformation of the mixed layer.

  9. Measuring ice- and liquid-water properties in mixed-phase cloud layers at the Leipzig Cloudnet station

    Science.gov (United States)

    Bühl, Johannes; Seifert, Patric; Myagkov, Alexander; Ansmann, Albert

    2016-08-01

    An analysis of the Cloudnet data set collected at Leipzig, Germany, with special focus on mixed-phase layered clouds is presented. We derive liquid- and ice-water content together with vertical motions of ice particles falling through cloud base. The ice mass flux is calculated by combining measurements of ice-water content and particle Doppler velocity. The efficiency of heterogeneous ice formation and its impact on cloud lifetime is estimated for different cloud-top temperatures by relating the ice mass flux and the liquid-water content at cloud top. Cloud radar measurements of polarization and Doppler velocity indicate that ice crystals formed in mixed-phase cloud layers with a geometrical thickness of less than 350 m are mostly pristine when they fall out of the cloud.

  10. Lidar measurements of the atmospheric entrainment zone and the potential temperature jump across the top of the mixed layer

    Science.gov (United States)

    Boers, R.; Eloranta, E. W.

    1986-01-01

    Lidar data of the atmospheric entrainment zone from six days of clear air convection obtained in central Illinois during July 1979 are presented. A new method to measure the potential temperature jump across the entrainment zone based on only one temperature sounding and continuous lidar measurements of the mixed layer height is developed. An almost linear dependence is found between the normalized entrainment rate and the normalized thickness of the entrainment zone.

  11. Optimization for Fast Zone Multilayer Fuel Assembly of Mixed Supercritical Water-Cooled Reactor%混合能谱超临界水堆快谱组件优化设计

    Institute of Scientific and Technical Information of China (English)

    杨婷; 刘晓晶; 程旭

    2011-01-01

    In order to improve the safety and sustainability of a supercritical water-cooled reactor (SCWR) core, both sub-channel and MCNP analysis were carried out to assess thermal-hydraulic and neutronic performances of the fuel assembly, which was proposed for the fast zone of a mixed-spectrum SCWR (SCWR-M). This fast zone assembly had a multilayer structure and was axially divided into several seed and blanket regions. The effects of some design parameters, I. E. Axial configuration, fuel rod diameter, pitch to diameter ratio and duct wall clearance on the thermal-hydraulic and neutronic performance of assemblies were investigated and an optimized parameter ranges were obtained.%本工作从热工水力和中子物理两方面对混合能谱超临界水堆混合谱堆芯的快谱区多层组件进行优化设计.对于轴向以再生区和裂变区交替布置的快谱组件,分别改变其轴向布置方式、燃料芯块直径、栅径比及外围燃料棒距组件盒最小距离,并分析它们对组件热工和物理性能的影响,从而得到较优的参数范围,尽可能提高混合谱超临界水堆的固有安全性和经济性.

  12. Imaging of oil layers, curvature and contact angle in a mixed-wet and a water-wet carbonate rock

    Science.gov (United States)

    Singh, Kamaljit; Bijeljic, Branko; Blunt, Martin J.

    2016-03-01

    We have investigated the effect of wettability of carbonate rocks on the morphologies of remaining oil after sequential oil and brine injection in a capillary-dominated flow regime at elevated pressure. The wettability of Ketton limestone was altered in situ using an oil phase doped with fatty acid which produced mixed-wet conditions (the contact angle where oil contacted the solid surface, measured directly from the images, θ=180°, while brine-filled regions remained water-wet), whereas the untreated rock (without doped oil) was weakly water-wet (θ=47 ± 9°). Using X-ray micro-tomography, we show that the brine displaces oil in larger pores during brine injection in the mixed-wet system, leaving oil layers in the pore corners or sandwiched between two brine interfaces. These oil layers, with an average thickness of 47 ± 17 µm, may provide a conductive flow path for slow oil drainage. In contrast, the oil fragments into isolated oil clusters/ganglia during brine injection under water-wet conditions. Although the remaining oil saturation in a water-wet system is about a factor of two larger than that obtained in the mixed-wet rock, the measured brine-oil interfacial area of the disconnected ganglia is a factor of three smaller than that of oil layers.

  13. Observation and analysis of emergent coherent structures in a high-energy-density shock-driven planar mixing layer experiment

    Science.gov (United States)

    Doss, F. W.; Flippo, K. A.; Merritt, E. C.

    2016-08-01

    Coherent emergent structures have been observed in a high-energy-density supersonic mixing layer experiment. A millimeter-scale shock tube uses lasers to drive Mbar shocks into the tube volume. The shocks are driven into initially solid foam (60 mg /cm3 ) hemicylinders separated by an Al or Ti metal tracer strip; the components are vaporized by the drive. Before the experiment disassembles, the shocks cross at the tube center, creating a very fast (Δ U > 200 km/s) shear-unstable zone. After several nanoseconds, an expanding mixing layer is measured, and after 10+ ns we observe the appearance of streamwise-periodic, spanwise-aligned rollers associated with the primary Kelvin-Helmholtz instability of mixing layers. We additionally image roller pairing and spanwise-periodic streamwise-aligned filaments associated with secondary instabilities. New closures are derived to connect length scales of these structures to estimates of fluctuating velocity data otherwise unobtainable in the high-energy-density environment. This analysis indicates shear-induced specific turbulent energies 103-104 times higher than the nearest conventional experiments. Because of difficulties in continuously driving systems under these conditions and the harshness of the experimental environment limiting the usable diagnostics, clear evidence of these developing structures has never before been observed in this regime.

  14. Self-similarity of a Rayleigh-Taylor mixing layer at low Atwood number with a multimode initial perturbation

    Science.gov (United States)

    Morgan, Brandon; Olson, Britton; White, Justin; McFarland, Jacob

    2016-11-01

    High-fidelity large eddy simulation (LES) of a low-Atwood number (A = 0.05) Rayleigh-Taylor mixing layer is performed using the tenth-order compact difference code Miranda. An initial multimode perturbation spectrum is specified in Fourier space as a function of mesh resolution such that a database of results is obtained in which each successive level of increased grid resolution corresponds approximately to one additional doubling of the mixing layer width, or generation. The database is then analyzed to determine approximate requirements for self-similarity, and a new metric is proposed to quantify how far a given simulation is from the limit of self-similarity. It is determined that the present database reaches a high degree of self-similarity after approximately 4.5 generations. Finally, self-similar turbulence profiles from the LES database are compared with one-dimensional simulations using the k- L- a and BHR-2 Reynolds-averaged Navier-Stokes (RANS) models. The k- L- a model, which is calibrated to reproduce a quadratic turbulence kinetic energy profile for a self-similar mixing layer, is found to be in better agreement with the LES than BHR-2 results. This work was preformed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

  15. Selective chelation and extraction of lanthanides and actinides with supercritical fluids

    Energy Technology Data Exchange (ETDEWEB)

    Brauer, R.D.; Carleson, T.E.; Harrington, J.D.; Jean, F.; Jiang, H.; Lin, Y.; Wai, C.M.

    1994-01-01

    This report is made up of three independent papers: (1) Supercritical Fluid Extraction of Thorium and Uranium with Fluorinated Beta-Diketones and Tributyl Phosphate, (2) Supercritical Fluid Extraction of Lanthanides with Beta-Diketones and Mixed Ligands, and (3) A Group Contribution Method for Predicting the Solubility of Solid Organic Compounds in Supercritical Carbon Dioxide. Experimental data are presented demonstrating the successful extraction of thorium and uranium using fluorinated beta-diketones to form stable complexes that are extracted with supercritical carbon dioxide. The conditions for extracting the lanthanide ions from liquid and solid materials using supercritical carbon dioxide are presented. In addition, the Peng-Robison equation of state and thermodynamic equilibrium are used to predict the solubilities of organic solids in supercritical carbon dioxide from the sublimation pressure, critical properties, and a centric factor of the solid of interest.

  16. Reactive diffusion bonding of SiCp/Al composites by insert layers of mixed Al-Si and Al-Si-SiC powders

    Institute of Scientific and Technical Information of China (English)

    Jihua Huang; Yueling Dong; Yun Wan; Jiangang Zhang; Hua Zhang

    2005-01-01

    Mixed Al-Si and Al-Si-SiC powders were employed as insert layers to reactive diffusion bond SiCp/6063 MMC (metal matrix composites). The results show that SiCp/6063 MMC joints bonded by the insert layer of the mixed Al-Si powder have a dense joining layer with a typical hypoeutectic microstructure. Using the mixed Al-Si-SiC powder as the insert layer, SiCp/6063 MMC can be reactive diffusion bonded by a composite joint. Because of the SiC segregation, however, there are a number of porous zones in the joining layer, which results in the bad shear strength of the joints reactive diffusion bonded by the insert layer of the mixed Al-SiSiC powder, even lower than that of the joints reactive diffusion bonded by the insert layer of the mixed Al-Si powder. Ti and Mg added in the insert layers obviously improve the strength of the joints reactive diffusion bonded by the insert layer of the mixed AlSi-SiC powder, especially, Mg has a more obvious effect.

  17. Sensitivity of the Arctic Climate to Leads in a Coupled Atmosphere-Mixed Layer Ocean Model.

    Science.gov (United States)

    Vavrus, Stephen J.

    1995-02-01

    The thermodynamic sea ice code in a coupled atmosphere-mixed layer ocean GCM has been altered to allow the presence of open water within an ice pack (leads) and a prescribed turbulent oceanic heat flux at the ice bottom. Two experiments with the GCM are then performed: one with leads included and one without. A comparison between the two model runs is presented, in addition to a comparison between observations and the simulation with leads. Selected sea ice and atmospheric variables in the high-latitude Northern Hemisphere are analyzed to assess the sensitivity of these climatic components to the presence of leads and to identify feedback mechanisms that are introduced by leads.The inclusion of leads causes Northern Hemispheric sea ice concentration to decrease in every season, with year-round statistically significant reductions at the highest latitude band (81°N). Using the improved sea ice code, the model's simulation of sea ice concentration in the central Arctic is consistent with observations in every season. Simulated summertime sea ice concentration at 81°N averages 93.8%, which agrees well with observations. There is a pronounced longitudinal variation to the lead fraction in summer, with the smallest values (0.01) neat the Canadian Archipelago and the largest (0.25) north of the East Siberian Sea. Consistent with observations, the model produces wintertime turbulent sensible heat fluxes over leads that are one to two orders of magnitude larger than over adjacent sea ice and of the opposite sign. Annual solar radiation absorption by leads in the central Arctic is 1.8 times as large as over adjacent sea ice, resulting in a summertime shortwave energy gain of over 2.5 W m2 at 8 1°N compared to the model run without leads.The inclusion of leads causes thicker sea ice in every season, because the very rapid ice growth rate in the leads is translated into enhanced accretion at the bottom of adjacent sea ice once a prescribed minimum lead fraction is reached

  18. Influence of Computational Drop Representation in LES of a Droplet-Laden Mixing Layer

    Science.gov (United States)

    Bellan, Josette; Radhakrishnan, Senthilkumaran

    2013-01-01

    Multiphase turbulent flows are encountered in many practical applications including turbine engines or natural phenomena involving particle dispersion. Numerical computations of multiphase turbulent flows are important because they provide a cheaper alternative to performing experiments during an engine design process or because they can provide predictions of pollutant dispersion, etc. Two-phase flows contain millions and sometimes billions of particles. For flows with volumetrically dilute particle loading, the most accurate method of numerically simulating the flow is based on direct numerical simulation (DNS) of the governing equations in which all scales of the flow including the small scales that are responsible for the overwhelming amount of dissipation are resolved. DNS, however, requires high computational cost and cannot be used in engineering design applications where iterations among several design conditions are necessary. Because of high computational cost, numerical simulations of such flows cannot track all these drops. The objective of this work is to quantify the influence of the number of computational drops and grid spacing on the accuracy of predicted flow statistics, and to possibly identify the minimum number, or, if not possible, the optimal number of computational drops that provide minimal error in flow prediction. For this purpose, several Large Eddy Simulation (LES) of a mixing layer with evaporating drops have been performed by using coarse, medium, and fine grid spacings and computational drops, rather than physical drops. To define computational drops, an integer NR is introduced that represents the ratio of the number of existing physical drops to the desired number of computational drops; for example, if NR=8, this means that a computational drop represents 8 physical drops in the flow field. The desired number of computational drops is determined by the available computational resources; the larger NR is, the less computationally

  19. Physical and chemical properties of the regional mixed layer of Mexico's Megapolis

    Science.gov (United States)

    Baumgardner, D.; Grutter, M.; Allan, J.; Ochoa, C.; Rappenglueck, B.; Russell, L. M.; Arnott, P.

    2009-08-01

    The concentration of gases and aerosol particles have been measured at the mountain site of Altzomoni, 4010 m in altitude, located 60 km southeast of Mexico City, 50 km east of Puebla and 70 km northeast of Cuernavaca. The objective of this study was to evaluate the properties of gases and particles in the Regional Mixed Layer (RML) of Mexico's Megapolis. Altzomoni is generally above the RML from late evening until late morning at which time the arrival of the RML is marked by increasing concentrations of CO and aerosol particles that reach their maxima in mid-afternoon. The average diurnal cycles for fourteen days in March, 2006 were evaluated during which time the synoptic scale circulation had three principal patterns: from the east (E), southwest (SW) and west northwest (WNW). The original hypothesis was that air arriving from the direction of Mexico City would have much higher concentrations of anthropogenic gases and particles than air from Puebla or Cuernavaca, due to the relatively large differences in populations. In fact, not only were the average, maximum concentrations of CO and O3 (0.3 and 0.1 ppmv) approximately the same for air originating from the WNW and E, but the average maximum concentrations of Peroxyacyl nitrates (PAN,PPN) and particle organic matter (POM) in air from the E exceeded those in air from the WNW. Comparisons of measurements from the mountain site with those made by aircraft during the same period, using the same type of aerosol mass spectrometer, show that the total masses of POM, NO3-, SO42- and NH4+ were approximately the same from aircraft measurements made over Mexico City and when winds were from the east at the mountain site. In contrast 75% of the total aerosol mass at the mountain site was POM whereas over Mexico City the fraction of POM was less than 60%. The measurements suggest the occasional influence of emissions from the nearby volcano, Popocatepetl, as well as possible incursions of biomass combustion; however, the

  20. Inferring strength and deformation properties of hot mix asphalt layers from the GPR signal: recent advances

    Science.gov (United States)

    Tosti, Fabio; Benedetto, Andrea; Bianchini Ciampoli, Luca; Adabi, Saba; Pajewski, Lara

    2015-04-01

    , of both the different strength provision of each layer composing the hot mix asphalt pavement structure, and of the attenuation occurring to electromagnetic waves during their in-depth propagation. Promising results are achieved by matching modelled and measured elastic modulus data. This continuous statistically-based model enables to consider the whole set of information related to each single depth, in order to provide a more comprehensive prediction of the strength and deformation behavior of such a complex multi-layered medium. Amongst some further developments to be tackled in the near future, a model improvement could be reached through laboratory activities under controlled conditions and by adopting several frequency bandwidths suited for purposes. In addition, the perspective to compare electromagnetic data with mechanical measurements retrieved continuously, i.e., by means of specifically equipped lorries, could pave the way to considerable enhancements in this field of research. Acknowledgements - This work has benefited from networking activities carried out within the EU funded COST Action TU1208 "Civil Engineering Applications of Ground Penetrating Radar".

  1. Influence of the liquid layer within mixed-phase clouds on radar observations

    NARCIS (Netherlands)

    Pfitzenmaier, L.; Dufournet, Y.; Unal, C.M.H.; Russchenberg, H.W.J.

    2014-01-01

    Mixed-phase clouds play an important role in the earth system. They affect earth radiative balance and the climate (Comstock et al., 2007; Solomon et al., 2007) as well as the formation of precipitation (de Boer et al., 2009; Fan et al., 2011; Lamb and Verlinde, 2011). Within such mixed-phase clouds

  2. Simultaneous Graphite Exfoliation and N Doping in Supercritical Ammonia.

    Science.gov (United States)

    Sasikala, Suchithra Padmajan; Huang, Kai; Giroire, Baptiste; Prabhakaran, Prem; Henry, Lucile; Penicaud, Alain; Poulin, Philippe; Aymonier, Cyril

    2016-11-16

    We report the exfoliation of graphite and simultaneous N doping of graphene by two methods: supercritical ammonia treatment and liquid-phase exfoliation with NH4OH. While the supercritical ammonia allowed N doping at a level of 6.4 atom % in 2 h, the liquid-phase exfoliation with NH4OH allowed N doping at a level of 2.7 atom % in 6 h. The N doped graphene obtained via the supercritical ammonia route had few layers (supercritical ammonia as an exfoliation agent and N doping precursor for graphene. Notably, the N doped graphene showed electrocatalytic activity toward oxygen reduction reaction with high durability and good methanol tolerance compared to those of commercial Pt/C catalyst.

  3. Density functional theory investigation of the electronic structure and thermoelectric properties of layered MoS{sub 2}, MoSe{sub 2} and their mixed-layer compound

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Changhoon; Hong, Jisook [Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Lee, Wang Ro [Faculty of Liberal Education, Chonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of); Kim, Dae Yeon [Agency for Defense Development (ADD), Chinhae, Kyungnam 645-600 (Korea, Republic of); Shim, Ji Hoon, E-mail: jhshim@postech.ac.kr [Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Divisions of Advanced Nuclear Engineering, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)

    2014-03-15

    First principles density functional theory calculations were carried out for the 2H-MoQ{sub 2} (Q=S and Se) and their hypothetical mixed-layer compound. Due to the different electronegativities of S and Se atoms on MoQ{sub 2}, the band gap size could be adjusted in mixed-layer compound MoS{sub 2}/MoSe{sub 2}. Also, the indirect band gap in pure MoQ{sub 2} compounds is changed to the pseudo direct band gap in mixed-layer MoS{sub 2}/MoSe{sub 2} which is similar to the monolayer compound. The layer mixing enhances the thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Therefore, we suggest that this layer mixing approach should be regarded as a useful way to modulate their electronic structures and to improve their thermoelectric properties. -- Graphical abstract: On the basis of density functional calculations we predict that the mixed-layer compounds 2H-MoS{sub 2}/2H-MoSe{sub 2}, in which two different layers 2H-MoS{sub 2} and 2H-MoSe{sub 2}, have enhanced thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Highlights: • We explored a way of improving TE properties of 2H-MoQ{sub 2} on DFT methods. • The mixed-layer compounds MoS{sub 2}/MoSe{sub 2} have enhanced thermoelectric properties. • This is caused by modulated electronic structure of mixed layer compound. • Layer mixing approach should be regarded as a useful way to improve TE properties.

  4. Research and application of multiple model predictive control in Ultra-supercritical boiler-turbine system

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Hengfeng; Yan, Weiwu; Wang, Guoliang; Hu, Yong; Li, Nan [Shanghai Jiao Tong Univ., Shanghai (China). Dept. of Automation; Ministry of Education of China, Shanghai (China). Key Lab. of System Control and Information Processing; Chen, Shihe; Zhang, Xi [Guangdong Electric Power Research Institute, Guangzhou (China)

    2013-07-01

    Based on analyzing the characteristics of Ultra-supercritical unit, this paper introduced a multiple model MCPC (Multivariable Constrained Predictive Control) structure with three inputs and three outputs for coordination control of Ultra-supercritical unit. In the structure, double-layer structure of optimization was used to obtain good steady and dynamic performance, and piecewise linear models at the different operating points of Ultra-supercritical unit were used to deal with nonlinearity. In the real-time simulation, nonlinear model of 1000MW Ultra-supercritical unit in was considered. Finally, the result of real-time simulation was given in the paper.

  5. Drug delivery goes supercritical

    Directory of Open Access Journals (Sweden)

    Patrick J. Ginty

    2005-08-01

    Full Text Available In the field of drug delivery, the ability to control the size, morphology, and release of drug particles is fundamental to good targeting, but is often hampered by harsh processing conditions or inadequate methods; likewise for the processing of polymeric controlled-release systems. However, the use of supercritical fluids such as supercritical CO2 (scCO2 has provided a ‘clean’ and effective alternative to traditional methods of drug and polymer processing. In particular, scCO2 has a number of unique properties that make it possible to process both bioactive molecules and amorphous polymers without using toxic organic solvents or elevated temperatures. Here, we review the positive impact that supercritical fluids have had on the micronization, encapsulation, and impregnation of molecules of interest to both the pharmaceutical and biotechnology industries.

  6. Experimental study of elliptical jet from sub to supercritical conditions

    Science.gov (United States)

    Muthukumaran, C. K.; Vaidyanathan, Aravind

    2014-04-01

    The jet mixing at supercritical conditions involves fluid dynamics as well as thermodynamic phenomena. All the jet mixing studies at critical conditions to the present date have focused only on axisymmetric jets. When the liquid jet is injected into supercritical environment, the thermodynamic transition could be well understood by considering one of the important fluid properties such as surface tension since it decides the existence of distinct boundary between the liquid and gaseous phase. It is well known that an elliptical liquid jet undergoes axis-switching phenomena under atmospheric conditions due to the presence of surface tension. The experimental investigations were carried out with low speed elliptical jet under supercritical condition. Investigation of the binary component system with fluoroketone jet and N2 gas as environment shows that the surface tension force dominates for a large downstream distance, indicating delayed thermodynamic transition. The increase in pressure to critical state at supercritical temperature is found to expedite the thermodynamic transition. The ligament like structures has been observed rather than droplets for supercritical pressures. However, for the single component system with fluoroketone jet and fluoroketone environment shows that the jet disintegrates into droplets as it is subjected to the chamber conditions even for the subcritical pressures and no axis switching phenomenon is observed. For a single component system, as the pressure is increased to critical state, the liquid jet exhibits gas-gas like mixing behavior and that too without exhibiting axis-switching behavior.

  7. Experimental study of elliptical jet from sub to supercritical conditions

    Energy Technology Data Exchange (ETDEWEB)

    Muthukumaran, C. K.; Vaidyanathan, Aravind, E-mail: aravind7@iist.ac.in [Department of Aerospace Engineering, Indian Institute of Space Science and Technology, Trivandrum, Kerala 695547 (India)

    2014-04-15

    The jet mixing at supercritical conditions involves fluid dynamics as well as thermodynamic phenomena. All the jet mixing studies at critical conditions to the present date have focused only on axisymmetric jets. When the liquid jet is injected into supercritical environment, the thermodynamic transition could be well understood by considering one of the important fluid properties such as surface tension since it decides the existence of distinct boundary between the liquid and gaseous phase. It is well known that an elliptical liquid jet undergoes axis-switching phenomena under atmospheric conditions due to the presence of surface tension. The experimental investigations were carried out with low speed elliptical jet under supercritical condition. Investigation of the binary component system with fluoroketone jet and N{sub 2} gas as environment shows that the surface tension force dominates for a large downstream distance, indicating delayed thermodynamic transition. The increase in pressure to critical state at supercritical temperature is found to expedite the thermodynamic transition. The ligament like structures has been observed rather than droplets for supercritical pressures. However, for the single component system with fluoroketone jet and fluoroketone environment shows that the jet disintegrates into droplets as it is subjected to the chamber conditions even for the subcritical pressures and no axis switching phenomenon is observed. For a single component system, as the pressure is increased to critical state, the liquid jet exhibits gas-gas like mixing behavior and that too without exhibiting axis-switching behavior.

  8. Materials processing using supercritical fluids

    Directory of Open Access Journals (Sweden)

    Orlović Aleksandar M.

    2005-01-01

    Full Text Available One of the most interesting areas of supercritical fluids applications is the processing of novel materials. These new materials are designed to meet specific requirements and to make possible new applications in Pharmaceuticals design, heterogeneous catalysis, micro- and nano-particles with unique structures, special insulating materials, super capacitors and other special technical materials. Two distinct possibilities to apply supercritical fluids in processing of materials: synthesis of materials in supercritical fluid environment and/or further processing of already obtained materials with the help of supercritical fluids. By adjusting synthesis parameters the properties of supercritical fluids can be significantly altered which further results in the materials with different structures. Unique materials can be also obtained by conducting synthesis in quite specific environments like reversed micelles. This paper is mainly devoted to processing of previously synthesized materials which are further processed using supercritical fluids. Several new methods have been developed to produce micro- and nano-particles with the use of supercritical fluids. The following methods: rapid expansion of supercritical solutions (RESS supercritical anti-solvent (SAS, materials synthesis under supercritical conditions and encapsulation and coating using supercritical fluids were recently developed.

  9. Anatomy of a metabentonite: nucleation and growth of illite crystals and their colescence into mixed-layer illite/smectite

    Science.gov (United States)

    Eberl, D.D.; Blum, A.E.; Serravezza, M.

    2011-01-01

    The illite layer content of mixed-layer illite/smectite (I/S) in a 2.5 m thick, zoned, metabentonite bed from Montana decreases regularly from the edges to the center of the bed. Traditional X-ray diffraction (XRD) pattern modeling using Markovian statistics indicated that this zonation results from a mixing in different proportions of smectite-rich R0 I/S and illite-rich R1 I/S, with each phase having a relatively constant illite layer content. However, a new method for modeling XRD patterns of I/S indicates that R0 and R1 I/S in these samples are not separate phases (in the mineralogical sense of the word), but that the samples are composed of illite crystals that have continuous distributions of crystal thicknesses, and of 1 nm thick smectite crystals. The shapes of these distributions indicate that the crystals were formed by simultaneous nucleation and growth. XRD patterns for R0 and R1 I/S arise by interparticle diffraction from a random stacking of the crystals, with swelling interlayers formed at interfaces between crystals from water or glycol that is sorbed on crystal surfaces. It is the thickness distributions of smectite and illite crystals (also termed fundamental particles, or Nadeau particles), rather than XRD patterns for mixed-layer I/S, that are the more reliable indicators of geologic history, because such distributions are composed of well-defined crystals that are not affected by differences in surface sorption and particle arrangements, and because their thickness distribution shapes conform to the predictions of crystal growth theory, which describes their genesis.

  10. Supercritical Synthesis of Biodiesel

    Directory of Open Access Journals (Sweden)

    Michel Vaultier

    2012-07-01

    Full Text Available The synthesis of biodiesel fuel from lipids (vegetable oils and animal fats has gained in importance as a possible source of renewable non-fossil energy in an attempt to reduce our dependence on petroleum-based fuels. The catalytic processes commonly used for the production of biodiesel fuel present a series of limitations and drawbacks, among them the high energy consumption required for complex purification operations and undesirable side reactions. Supercritical fluid (SCF technologies offer an interesting alternative to conventional processes for preparing biodiesel. This review highlights the advances, advantages, drawbacks and new tendencies involved in the use of supercritical fluids (SCFs for biodiesel synthesis.

  11. Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. Part I: Single layer cloud

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Stephen A.; McCoy, Renata B.; Morrison, Hugh; Ackerman, Andrew S.; Avramov, Alexander; de Boer, Gijs; Chen, Mingxuan; Cole, Jason N.S.; Del Genio, Anthony D.; Falk, Michael; Foster, Michael J.; Fridlind, Ann; Golaz, Jean-Christophe; Hashino, Tempei; Harrington, Jerry Y.; Hoose, Corinna; Khairoutdinov, Marat F.; Larson, Vincent E.; Liu, Xiaohong; Luo, Yali; McFarquhar, Greg M.; Menon, Surabi; Neggers, Roel A. J.; Park, Sungsu; Poellot, Michael R.; Schmidt, Jerome M.; Sednev, Igor; Shipway, Ben J.; Shupe, Matthew D.; Spangenberg, Douglas A.; Sud, Yogesh C.; Turner, David D.; Veron, Dana E.; von Salzen, Knut; Walker, Gregory K.; Wang, Zhien; Wolf, Audrey B.; Xie, Shaocheng; Xu, Kuan-Man; Yang, Fanglin; Zhang, Gong

    2009-02-02

    Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a cold-air outbreak mixed-phase stratocumulus cloud observed during the Atmospheric Radiation Measurement (ARM) program's Mixed-Phase Arctic Cloud Experiment. The observed cloud occurred in a well-mixed boundary layer with a cloud top temperature of -15 C. The observed average liquid water path of around 160 g m{sup -2} was about two-thirds of the adiabatic value and much greater than the average mass of ice crystal precipitation which when integrated from the surface to cloud top was around 15 g m{sup -2}. The simulations were performed by seventeen single-column models (SCMs) and nine cloud-resolving models (CRMs). While the simulated ice water path is generally consistent with the observed values, the median SCM and CRM liquid water path is a factor of three smaller than observed. Results from a sensitivity study in which models removed ice microphysics suggest that in many models the interaction between liquid and ice-phase microphysics is responsible for the large model underestimate of liquid water path. Despite this general underestimate, the simulated liquid and ice water paths of several models are consistent with the observed values. Furthermore, there is evidence that models with more sophisticated microphysics simulate liquid and ice water paths that are in better agreement with the observed values, although considerable scatter is also present. Although no single factor guarantees a good simulation, these results emphasize the need for improvement in the model representation of mixed-phase microphysics.

  12. Study of the equatorial Atlantic Ocean mixing layer using a one-dimensional turbulence model

    Directory of Open Access Journals (Sweden)

    Udo Tersiano Skielka

    2010-06-01

    Full Text Available The General Ocean Turbulence Model (GOTM is applied to the diagnostic turbulence field of the mixing layer (ML over the equatorial region of the Atlantic Ocean. Two situations were investigated: rainy and dry seasons, defined, respectively, by the presence of the intertropical convergence zone and by its northward displacement. Simulations were carried out using data from a PIRATA buoy located on the equator at 23º W to compute surface turbulent fluxes and from the NASA/GEWEX Surface Radiation Budget Project to close the surface radiation balance. A data assimilation scheme was used as a surrogate for the physical effects not present in the one-dimensional model. In the rainy season, results show that the ML is shallower due to the weaker surface stress and stronger stable stratification; the maximum ML depth reached during this season is around 15 m, with an averaged diurnal variation of 7 m depth. In the dry season, the stronger surface stress and the enhanced surface heat balance components enable higher mechanical production of turbulent kinetic energy and, at night, the buoyancy acts also enhancing turbulence in the first meters of depth, characterizing a deeper ML, reaching around 60 m and presenting an average diurnal variation of 30 m.O modelo General Ocean Turbulence Model (GOTM é aplicado para diagnosticar o campo de turbulência da camada de mistura oceânica (CM na região equatorial do Oceano Atlântico. Foram investigadas as estações chuvosa e seca, definidas, respectivamente, pela presença da zona de convergência intertropical e pelo seu deslocamento para norte. Simulações foram realizadas usando dados da bóia PIRATA (0º, 23ºW para o cálculo dos fluxos turbulentos de superfície e dados do Projeto NASA/GEWEX Surface Radiation Budget para "fechar" o balanço de radiação na superfície. Um esquema para assimilação de dados foi usado para considerar os mecanismos físicos não representados pelo modelo unidimensional

  13. Interfacial mixing in as-deposited Si/Ni/Si layers analyzed by x-ray and polarized neutron reflectometry

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharya, Debarati, E-mail: debarati@barc.gov.in [Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Basu, Saibal; Singh, Surendra [Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Roy, Sumalay; Dev, Bhupendra Nath [Department of Materials Science, Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, Jadavpur, Kolkata 700032 (India)

    2012-12-15

    Highlights: Black-Right-Pointing-Pointer Room temperature diffusion in Si/Ni/Si trilayer detected through complementary x-ray and polarized neutron reflectometry. Black-Right-Pointing-Pointer Analyses of XPNR data generated the construction of the layered structure in terms of physical parameters along with alloy layers created by diffusion. Black-Right-Pointing-Pointer Scattering length density information from XPNR provided quantitative assessment of the stoichiometry of alloys formed at the Si/Ni and Ni/Si interfaces. - Abstract: Interdiffusion occurring across the interfaces in a Si/Ni/Si layered system during deposition at room temperature was probed using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR). Exploiting the complementarity of these techniques, both structural and magnetic characterization with nanometer depth resolution could be achieved. Suitable model fitting of the reflectivity profiles identified the formation of Ni-Si mixed alloy layers at the Si/Ni and Ni/Si interfaces. The physical parameters of the layered structure, including quantitative assessment of the stoichiometry of interfacial alloys, were obtained from the analyses of XRR and PNR patterns. In addition, PNR provided magnetic moment density profile as a function of depth in the stratified medium.

  14. Experimental characterization of initial conditions and spatio-temporal evolution of a small Atwood number Rayleigh-Taylor mixing layer

    Energy Technology Data Exchange (ETDEWEB)

    Mueschke, N J; Andrews, M J; Schilling, O

    2006-03-24

    The initial multi-mode interfacial velocity and density perturbations present at the onset of a small Atwood number, incompressible, miscible, Rayleigh-Taylor instability-driven mixing layer have been quantified using a combination of experimental techniques. The streamwise interfacial and spanwise interfacial perturbations were measured using high-resolution thermocouples and planar laser-induced fluorescence (PLIF), respectively. The initial multi-mode streamwise velocity perturbations at the two-fluid density interface were measured using particle-image velocimetry (PIV). It was found that the measured initial conditions describe an initially anisotropic state, in which the perturbations in the streamwise and spanwise directions are independent of one another. The evolution of various fluctuating velocity and density statistics, together with velocity and density variance spectra, were measured using PIV and high-resolution thermocouple data. The evolution of the velocity and density statistics is used to investigate the early-time evolution and the onset of strongly-nonlinear, transitional dynamics within the mixing layer. The early-time evolution of the density and vertical velocity variance spectra indicate that velocity fluctuations are the dominant mechanism driving the instability development. The implications of the present experimental measurements on the initialization of Reynolds-averaged turbulent transport and mixing models and of direct and large-eddy simulations of Rayleigh-Taylor instability-induced turbulence are discussed.

  15. Experimental characterization of initial conditions and spatio-temporal evolution of a small Atwood number Rayleigh-Taylor mixing layer

    Energy Technology Data Exchange (ETDEWEB)

    Mueschke, N J; Andrews, M J; Schilling, O

    2005-09-26

    The initial multi-mode interfacial velocity and density perturbations present at the onset of a small Atwood number, incompressible, miscible, Rayleigh-Taylor instability-driven mixing layer have been quantified using a combination of experimental techniques. The streamwise interfacial and spanwise interfacial perturbations were measured using high-resolution thermocouples and planar laser-induced fluorescence (PLIF), respectively. The initial multi-mode streamwise velocity perturbations at the two-fluid density interface were measured using particle-image velocimetry (PIV). It was found that the measured initial conditions describe an initially anisotropic state, in which the perturbations in the streamwise and spanwise directions are independent of one another. The evolution of various fluctuating velocity and density statistics, together with velocity and density variance spectra, were measured using PIV and high-resolution thermocouple data. The evolution of the velocity and density statistics is used to investigate the early-time evolution and the onset of strongly-nonlinear, transitional dynamics within the mixing layer. The early-time evolution of the density and vertical velocity variance spectra indicate that velocity fluctuations are the dominant mechanism driving the instability development. The implications of the present experimental measurements on the initialization of Reynolds-averaged turbulent transport and mixing models and of direct and large-eddy simulations of Rayleigh-Taylor instability-induced turbulence are discussed.

  16. Using supercritical fluids to refine hydrocarbons

    Science.gov (United States)

    Yarbro, Stephen Lee

    2014-11-25

    This is a method to reactively refine hydrocarbons, such as heavy oils with API gravities of less than 20.degree. and bitumen-like hydrocarbons with viscosities greater than 1000 cp at standard temperature and pressure using a selected fluid at supercritical conditions. The reaction portion of the method delivers lighter weight, more volatile hydrocarbons to an attached contacting device that operates in mixed subcritical or supercritical modes. This separates the reaction products into portions that are viable for use or sale without further conventional refining and hydro-processing techniques. This method produces valuable products with fewer processing steps, lower costs, increased worker safety due to less processing and handling, allow greater opportunity for new oil field development and subsequent positive economic impact, reduce related carbon dioxide, and wastes typical with conventional refineries.

  17. CO ppb sensors based on monodispersed SnOx:Pd mixed nanoparticle layers: Insight into dual conductance response

    Science.gov (United States)

    Aruna, I.; Kruis, F. E.; Kundu, S.; Muhler, M.; Theissmann, R.; Spasova, M.

    2009-03-01

    This study reports the modifications in CO sensing of SnOx nanoparticle layers by utilizing monodispersed Pd nanoparticles. The distinct advantage of monosized particles and contaminant-free samples with open porosity in addition to size effects resulted in improved CO sensing with decrease in Pd nanoparticle size to 5 nm, decreasing the lowest detection levels of CO using SnOx-based sensor technology down to 10 ppb (parts per billion) in dry synthetic air. The homogeneously mixed nanoparticle layers also exhibit discrimination capability between CO and ethanol in dry air as a manifestation of the dual conductance response. Detailed x-ray photoelectron spectroscopy studies clearly reveal "Mars-van Krevelen" as the key mechanism responsible for the observed sensing in mixed nanoparticle layers. The interfacial/surface PdO formed upon pretreatment in air is continuously "consumed" and "reformed" upon exposure, respectively, to CO and synthetic air. In contrast to the case of ethanol exposure with n-type response, the Pd aided reduction of tin oxide surface in CO ambient leads to p-type response. The sensors of the present study have a wide range of promising applications from air quality control to food and fuel industries.

  18. Temperature stability of ultra-thin mixed BaSr-oxide layers and their transformation.

    Science.gov (United States)

    Müller-Sajak, D; Islam, S; Pfnür, H; Hofmann, K R

    2012-08-01

    In the context of investigations of physical, chemical and electrical properties of ultra-thin layers of epitaxial and monocrystalline Sr(0.3)Ba(0.7)O on Si(100), we also investigated their thermal stability with x-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and low energy electron diffraction (LEED). At temperatures above 400 °C, transformation into silicate layers sets in. The stoichiometry after complete transformation was determined to be close to (Ba(0.8)Sr(0.2))(2)SiO(4) except for layers of only a few monolayers, where the silicate is not stoichiometric. There are strong indications that this silicate is stable until it desorbs at temperatures above 750 °C. Crystallinity, as seen with LEED, is lost during this transformation. Although transformation into silicate is coupled with metal desorption and compactification of the layers, they seem to remain closed. In addition, traces of Ba silicide at the Si interface were detected after layer desorption. This silicide cannot be desorbed thermally. The silicate layer has a bandgap of 5.9 ± 0.2 eV already for 3 ML thickness. Upon exposure to air, carbon and oxygen containing species, but no hydroxide, are formed irreversibly.

  19. Oxidation behavior of Incoloy 800 under simulated supercritical water conditions

    Energy Technology Data Exchange (ETDEWEB)

    Fulger, M. [Institute for Nuclear Research Pitesti, POB 78, Campului Street, No. 1, 115400 Mioveni (Romania)], E-mail: manuela.fulger@nuclear.ro; Ohai, D.; Mihalache, M.; Pantiru, M. [Institute for Nuclear Research Pitesti, POB 78, Campului Street, No. 1, 115400 Mioveni (Romania); Malinovschi, V. [University of Pitesti, Research Center for Advanced Materials, Targul din Vale Street, No. 1, 110040 Pitesti (Romania)

    2009-03-31

    For a correct design of supercritical water-cooled reactor (SCWR) components, data regarding the behavior of candidate materials in supercritical water are necessary. Corrosion has been identified as a critical problem because the high temperature and the oxidative nature of supercritical water may accelerate the corrosion kinetics. The goal of this paper is to investigate the oxidation behavior of Incoloy 800 exposed in autoclaves under supercritical water conditions for up to 1440 h. The exposure conditions (thermal deaerated water, temperatures of 723, 773, 823 and 873 K and a pressure of 25 MPa) have been selected as relevant for a supercritical power plant concept. To investigate the structural changes of the oxide films, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and electrochemical impedance spectroscopy (EIS) analyses were used. Results show changes in the oxides chemical composition, microstructure and thickness versus testing conditions (pressure, temperature and time). The oxide films are composed of two layers: an outer layer enriched in Fe oxide and an inner layer enriched in Cr and Ni oxides corresponding to small cavities supposedly due to internal oxidation.

  20. Application of Neutron Radiography to Flow Visualization in Supercritical Water

    Science.gov (United States)

    Takenaka, N.; Sugimoto, K.; Takami, S.; Sugioka, K.; Tsukada, T.; Adschiri, T.; Saito, Y.

    Supercritical water is used in various chemical reaction processes including hydrothermal synthesis of metal oxide nano-particles, oxidation, chemical conversion of biomass and plastics. Density of the super critical water is much less than that of the sub-critical water. By using neutron radiography, Peterson et al. have studied salt precipitation processes in supercritical water and the flow pattern in a reverse-flow vessel for salt precipitation, and Balasko et al. have revealed the behaviour of supercritical water in a container. The nano-particles were made by mixing the super critical flow and the sub critical water solution. In the present study, neutron radiography was applied to the flow visualization of the super and sub critical water mixture in a T-junction made of stainless steel pipes for high pressure and temperature conditions to investigate their mixing process. Still images by a CCD camera were obtained by using the neutron radiography system at B4 port in KUR.

  1. Ellipsometric study of optical properties of GaSxSe1-x layered mixed crystals

    Science.gov (United States)

    Isik, Mehmet; Gasanly, Nizami

    2016-04-01

    Spectroscopic ellipsometry measurements were performed on GaSxSe1-x mixed crystals (0 ⩽ x ⩽ 1) in the 1.2-6.2 eV range. Spectral dependence of optical parameters; real and imaginary components of pseudodielectric function, pseudorefractive index and pseudoextinction coefficient were reported in the present work. Critical point (CP) analyses on second-energy derivative spectra of the pseudodielectric function were accomplished to find the interband transition energies. The revealed energy values were associated with each other taking into account the fact that band gap energy of mixed crystals rises with increase in sulfur content. The variation of CP energies with composition (x) was also plotted. Peaks in the spectra of studied optical parameters and CP energy values were observed to be shifted to higher energy values as sulfur concentration is increased in the mixed crystals.

  2. Vertically-resolved particle size distribution within and above the mixing layer over the Milan metropolitan area

    Directory of Open Access Journals (Sweden)

    L. Ferrero

    2010-04-01

    Full Text Available Vertical aerosol profiles were directly measured over the city of Milan during three years (2005–2008 of field campaigns. An optical particle counter, a portable meteorological station and a miniaturized cascade impactor were deployed on a tethered balloon. More than 300 vertical profiles were measured, both in winter and summer, mainly in conditions of clear, dry skies.

    The mixing height was determined from the observed vertical aerosol concentration gradient, and from potential temperature and relative humidity profiles. Results show that inter-consistent mixing heights can be retrieved highlighting good correlations between particle dispersion in the atmosphere and meteorological parameters. Mixing height growth speed was calculated for both winter and summer showing the low potential atmospheric dispersion in winter.

    Aerosol number size distribution and chemical composition profiles allowed us to investigate particle behaviour along height. Aerosol measurements showed changes in size distribution according to mixing height. Coarse particle profiles (dp>1.6 μm were distributed differently than the fine ones (dp<1.6 μm were, at different heights of the mixing layer. The sedimentation process influenced the coarse particle profiles, and led to a reduction in mean particle diameter for those particles observed by comparing data above the mixing height with ground data (−14.9±0.6% in winter and −10.7±1.0% in summer. Conversely, the mean particle diameter of fine particles increased above the mixing height under stable atmospheric conditions; the average increase, observed by comparing data above the mixing height with ground data, was +2.1±0.1% in winter and +3.9±0.3% in summer. A hierarchical statistical model was created to describe the changes in the size distribution of fine particles along height. The proposed model can be used to estimate the typical vertical

  3. Mixed convection boundary layer flow past vertical flat plate in nanofluid:case of prescribed wall heat flux

    Institute of Scientific and Technical Information of China (English)

    R. TRˆIMBIT¸AS¸; T.GROSAN; I.POP

    2015-01-01

    An analysis is carried out to investigate the steady mixed convection bound-ary layer flow of a water based nanofluid past a vertical semi-infinite flat plate. Using an appropriate similarity transformation, the governing partial differential equations are transformed into the coupled, nonlinear ordinary (similar) differential equations, which are then solved numerically for the Prandtl number Pr = 6.2. The skin friction coeffi-cient, the local Nusselt number, and the velocity and temperature profiles are presented graphically and discussed. Effects of the solid volume fractionφand the mixed convection parameterλon the fluid flow and heat transfer characteristics are thoroughly examined. Different from an assisting flow, it is found that the solutions for an opposing flow are non-unique. In order to establish which solution branch is stable and physically realizable in practice, a stability analysis is performed.

  4. Employing X-ray Photoelectron Spectroscopy for Determining Layer Homogeneity in Mixed Polar Self-Assembled Monolayers.

    Science.gov (United States)

    Hehn, Iris; Schuster, Swen; Wächter, Tobias; Abu-Husein, Tarek; Terfort, Andreas; Zharnikov, Michael; Zojer, Egbert

    2016-08-04

    Self-assembled monolayers (SAMs) containing embedded dipolar groups offer the particular advantage of changing the electronic properties of a surface without affecting the SAM-ambient interface. Here we show that such systems can also be used for continuously tuning metal work functions by growing mixed monolayers consisting of molecules with different orientations of the embedded dipolar groups. To avoid injection hot-spots when using the SAM-modified electrodes in devices, a homogeneous mixing of the two components is crucial. We show that a combination of high-resolution X-ray photoelectron spectroscopy with state-of-the-art simulations is an ideal tool for probing the electrostatic homogeneity of the layers and thus for determining phase separation processes in polar adsorbate assemblies down to inhomogeneities at the molecular level.

  5. Consequences of inhibition of mixed-layer deepening by the West India coastal current for winter phytoplankton bloom in the northeastern Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Vijith, V.; Vinayachandran, P.N.; Thushara, V.; Amol, P.; Shankar, D; Anil, A.C.

    than in the northern NEAS. The inhibition of mixed-layer deepening in the south affects the size-based distribution of small and large phytoplankton, nutrient limitation terms and growth rate, and their elemental composition. The WICC, which inhibits...

  6. Examination of evaporative fraction diurnal behaviour using a soil-vegetation model coupled with a mixed-layer model

    Directory of Open Access Journals (Sweden)

    J.-P. Lhomme

    1999-01-01

    Full Text Available In many experimental conditions, the evaporative fraction, defined as the ratio between evaporation and available energy, has been found stable during daylight hours. This constancy is investigated over fully covering vegetation by means of a land surface scheme coupled with a mixed-layer model, which accounts for entrainment of overlying air. The evaporation rate follows the Penman-Monteith equation and the surface resistance is given by a Jarvis type parameterization involving solar radiation, saturation deficit and leaf water potential. The diurnal course of the evaporative fraction is examined, together with the influence of environmental factors (soil water availability, solar radiation input, wind velocity, saturation deficit above the well-mixed layer. In conditions of fair weather, the curves representing the diurnal course of the evaporative fraction have a typical concave-up shape. Around midday (solar time these curves appear as relatively constant, but always lower that the daytime mean value. Evaporative fraction decreases when soil water decreases or when solar energy increases. An increment of saturation deficit above the mixed-layer provokes only a slight increase of evaporative fraction, and wind velocity has almost no effect. The possibility of estimation daytime evaporation from daytime available energy multiplied by the evaporative fraction at a single time of the day is also investigated. It appears that it is possible to obtain fairly good estimates of daytime evaporation by choosing adequately the time of the measurement of the evaporative fraction. The central hours of the day, and preferably about 3 hr before or after noon, are the most appropriate to provide good estimates. The estimation appears also to be much better when soil water availability (or evaporation is high than when it is low.

  7. Synthesis, characterization and magnetic behavior of Mg–Fe–Al mixed oxides based on layered double hydroxide

    Energy Technology Data Exchange (ETDEWEB)

    Heredia, Angélica C., E-mail: angelicacheredia@gmail.com [Universidad Tecnológica Nacional, Facultad Regional Córdoba-CITeQ, Maestro López esq. Cruz Roja Argentina, Ciudad Universitaria, 5016 Córdoba (Argentina); Oliva, Marcos I. [IFEG, Universidad Nacional de Córdoba, Córdoba (Argentina); CONICET (Argentina); Agú, Ulises [Universidad Tecnológica Nacional, Facultad Regional Córdoba-CITeQ, Maestro López esq. Cruz Roja Argentina, Ciudad Universitaria, 5016 Córdoba (Argentina); CONICET (Argentina); Zandalazini, Carlos I. [CONICET (Argentina); INFIQC, FCQ Universidad Nacional de Córdoba, Córdoba (Argentina); Marchetti, Sergio G. [CINDECA, UNLP, Buenos Aires (Argentina); Herrero, Eduardo R.; Crivello, Mónica E. [Universidad Tecnológica Nacional, Facultad Regional Córdoba-CITeQ, Maestro López esq. Cruz Roja Argentina, Ciudad Universitaria, 5016 Córdoba (Argentina)

    2013-09-15

    In the present work, Mg–Al–Fe layered double hydroxides were prepared by coprecipitation reaction with hydrothermal treatment. The characterization of precursors and their corresponding calcinated products (mixed oxides) were carried out by X ray diffraction, X-ray photoelectron spectroscopy (XPS), termogravimetric analysis and differential scanning calorimetry, diffuse reflectance UV–vis spectroscopy, specific surface area, Mössbauaer and magnetic properties. The Fe{sup 3+} species were observed in tetrahedrally and octahedrally coordination in brucite layered. The XPS analysis shows that the Fe{sup 3+} ions can be found in two coordination environments (tetrahedral and octahedral) as mixed oxides, and as spinel-structure. Oxides show a decrease in the specific surface areas when the iron loading is increased. The magnetic and Mössbauaer response show that MgAlFe mixed oxides are different behaviours such as different population ratios of ferromagnetic, weak-ferromagnetic, paramagnetic and superparamagnetic phases. The better crystallization of spinel structure with increased temperature, is correlated with the improved magnetic properties. - Highlights: • Mg–Al–Fe were successfully prepared by coprecipitation with hydrothermal treatment. • MgO, α-Fe{sub 2}O{sub 3,} MgFe{sub 2}O{sub 4} were detected by XRD in the calcined samples. • The Fe{sup 3+} is in tetrahedral and octahedral coordination in the brucite layered. • The specific surface area is directly related with the iron content. • The magnetic properties and MgFe{sub 2}O{sub 4} improve with increasing calcination temperature.

  8. Towards Automated Characterization of Canopy Layering in Mixed Temperate Forests Using Airborne Laser Scanning

    Directory of Open Access Journals (Sweden)

    Reik Leiterer

    2015-11-01

    Full Text Available Canopy layers form essential structural components, affecting stand productivity and wildlife habitats. Airborne laser scanning (ALS provides horizontal and vertical information on canopy structure simultaneously. Existing approaches to assess canopy layering often require prior information about stand characteristics or rely on pre-defined height thresholds. We developed a multi-scale method using ALS data with point densities >10 pts/m2 to determine the number and vertical extent of canopy layers (canopylayer, canopylength, seasonal variations in the topmost canopy layer (canopytype, as well as small-scale heterogeneities in the canopy (canopyheterogeneity. We first tested and developed the method on a small forest patch (800 ha and afterwards tested transferability and robustness of the method on a larger patch (180,000 ha. We validated the approach using an extensive set of ground data, achieving overall accuracies >77% for canopytype and canopyheterogeneity, and >62% for canopylayer and canopylength. We conclude that our method provides a robust characterization of canopy layering supporting automated canopy structure monitoring.

  9. RESEARCH ON THE MIXING LAYER OF FIBER SUSPENSIONS AND DIRECT SIMULATION ON THE MOTION OF CYLINDRICAL PARTICLES

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The mixing layer of fiber suspensions was simulated numerically with the spectral method and the fibers in the flow were traced individually with calculation. The corresponding experiments were made. The results show that the Stokes number of particles is the key parameter to determine the spatial distribution of fibers and the coherent structures control the orientation of fibers. Direct simulations of the motion of cylindrical particles were carried out via lattice Boltzmann method. It is found that the aspect ratio of particles has significant effects on the translation and rotation of the cylindrical particles. A new lattice Boltzmann method which is convenient to deal with the curved boundary is proposed.

  10. Impact of numerical method on auto-ignition in a temporally evolving mixing layer at various initial conditions

    Science.gov (United States)

    Rosiak, A.; Tyliszczak, A.

    2016-10-01

    Numerical analysis of the auto-ignition of turbulent mixing layer between the cold fuel (hydrogen) and hot oxidizer (air) is presented. The research were performed using an Implicit-Large Eddy Simulation (ILES) method with attention on auto-ignition time, flame kernel localisation and propagation. We focused on an impact of discretization method on auto-ignition scenario and flame development. The results obtained showed that numerical approach plays an important role and to some extent may falsify the results, especially for low oxidiser temperatures.

  11. Turbulent mixing and layer formation in double-diffusive convection: 3D numerical simulations and theory

    CERN Document Server

    Rosenblum, Erica; Traxler, Adrienne; Stellmach, Stephan

    2010-01-01

    Double-diffusive convection, often referred to as semi-convection in astrophysics, occurs in thermally and compositionally stratified systems which are stable according to the Ledoux-criterion but unstable according to the Schwarzchild criterion. This process has been given relatively little attention so far, and its properties remain poorly constrained. In this paper, we present and analyze a set of three-dimensional simulations of this phenomenon in a Cartesian domain under the Boussinesq approximation. We find that in some cases the double-diffusive convection saturates into a state of homogeneous turbulence, but with turbulent fluxes several orders of magnitude smaller than those expected from direct overturning convection. In other cases the system rapidly and spontaneously develops closely-packed thermo-compositional layers, which later successively merge until a single layer is left. We compare the output of our simulations with an existing theory of layer formation in the oceanographic context, and fi...

  12. Comparative Study of MIL-96(Al) as Continuous Metal-Organic Frameworks Layer and Mixed-Matrix Membrane.

    Science.gov (United States)

    Knebel, Alexander; Friebe, Sebastian; Bigall, Nadja Carola; Benzaqui, Marvin; Serre, Christian; Caro, Jürgen

    2016-03-23

    MIL-96(Al) layers were prepared as supported metal-organic frameworks membrane via reactive seeding using the α-alumina support as the Al source for the formation of the MIL-96(Al) seeds. Depending on the solvent mixture employed during seed formation, two different crystal morphologies, with different orientation of the transport-active channels, have been formed. This crystal orientation and habit is predefined by the seed crystals and is kept in the subsequent growth of the seeds to continuous layers. In the gas separation of an equimolar H2/CO2 mixture, the hydrogen permeability of the two supported MIL-96(Al) layers was found to be highly dependent on the crystal morphology and the accompanied channel orientation in the layer. In addition to the neat supported MIL-96(Al) membrane layers, mixed-matrix membranes (MMMs, 10 wt % filler loading) as a composite of MIL-96(Al) particles as filler in a continuous Matrimid polymer phase have been prepared. Five particle sizes of MIL-96(Al) between 3.2 μm and 55 nm were synthesized. In the preparation of the MIL-96(Al)/Matrimid MMM (10 wt % filler loading), the following preparation problems have been identified: The bigger micrometer-sized MIL-96(Al) crystals show a trend toward sedimentation during casting of the MMM, whereas for nanoparticles aggregation and recrystallization to micrometer-sized MIL-96(Al) crystals has been observed. Because of these preparation problems for MMM, the neat supported MIL-96(Al) layers show a relatively high H2/CO2 selectivity (≈9) and a hydrogen permeance approximately 2 magnitudes higher than that of the best MMM.

  13. Pristine fullerenes mixed by vacuum-free solution process: Efficient electron transport layer for planar perovskite solar cells

    Science.gov (United States)

    Dai, Si-Min; Tian, Han-Rui; Zhang, Mei-Lin; Xing, Zhou; Wang, Lu-Yao; Wang, Xin; Wang, Tan; Deng, Lin-Long; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun

    2017-01-01

    Discovery of organic-inorganic hybrid perovskites ignites the dream of next-generation solar cells fabricated by low-cost solution processing. To date, fullerene derivative [6,6]-phenyl-C61- butyric acid methyl ester (PC61BM), is the most prevalently used electron transport layer for high efficiency p-i-n planar heterojunction perovskite solar cells. Compared with PC61BM, pristine fullerenes, such as C60 and C70, have shown superiority of higher electron mobility and much lower costs. Due to the poor solubility and strong tendency to crystallize for pristine fullerenes in solution process, it is still a challenge to deposit compact and continuous film of pristine fullerenes for p-i-n type perovskite solar cells by solution processing. Herein, solution processed pristine fullerenes (C60 and C70) were used as electron transport layers to replace PC61BM in perovskite solar cells with high performance and enhanced stability. Power conversion efficiency of 14.04% was obtained by using mixture of C60 and C70 as electron transport layer, which is comparable to that of PC61BM based device (13.74%). We demonstrated that the strong tendency of pristine fullerenes to crystallize during solvent removal can be largely mitigated by mixing different kinds of pristine fullerenes. These findings implicate pristine fullerenes as promising electron transport layers for high performance perovskite solar cells.

  14. Copper(II) Schiff base complexes and their mixed thin layers with ZnO nanoparticles

    Indian Academy of Sciences (India)

    MAGDALENA BARWIOLEK; ROBERT SZCZĘSNY; EDWARD SZŁYK

    2016-07-01

    Cu(II) complexes with Schiff bases derived from ethylenediamine (en) and 2-pyridinecarboxaldehyde (pyca), 2,5-dimethoxybenzaldehyde (dmbaH) or 4-imidazolecarboxaldehyde (4Him) were obtained and studied by elemental analysis, UV-VIS and IR spectra. Zinc oxide was synthesized using a simple homogeneous precipitation method with zinc acetate as a starting material. Thin layers of the studied Cu(II) complexes were deposited on Si(111) or ZnO/Si(111) substrates by a spin coating method and characterized with a scanningelectron microscopy (SEM/EDS), atomic force microscopy (AFM) and fluorescence spectroscopy. For Cu(II) layers the most intensive fluorescence bands due to intra-ligand transitions were observed between 462 and 503 nm. The fluorescence intensity of thin layers was corelated to the rotation speed. In the case of the [Cu(II)(en(4Him)₂)Cl₂](2a)/ZnO/Si and [Cu(en(dmbaH)₂)Cl₂](3a)/ZnO/Si layers the quenching of the emission band from ZnO at 440 nm (λex = 330 nm) associated with various intrinsic or extrinsic lattice defects was noted.

  15. Behavior and mixing of a cold intermediate layer near a sloping boundary

    NARCIS (Netherlands)

    Cyr, F.; Bourgault, D.; Galbraith, P.S.

    2015-01-01

    As in many other subarctic basins, a cold intermediate layer (CIL) is found during ice-free months in the Lower St. Lawrence Estuary (LSLE), Canada. This study examines the behavior of the CIL above the sloping bottom using a high-resolution mooring deployed on the northern side of the estuary. Obse

  16. A MIXED BOOLEAN AND DEPOSIT MODEL FOR THE MODELING OF METAL PIGMENTS IN PAINT LAYERS

    Directory of Open Access Journals (Sweden)

    Enguerrand Couka

    2015-06-01

    Full Text Available Pigments made of metal particles of around 10 µm or 20 µm produce sparkling effects in paints, due to the specular reflection that occurs at this scale. Overall, the optical aspect of paints depend on the density and distribution in space of the particles. In this work, we model the dispersion of metal particles of size up to 50 µm, visible to the eyes, in a paint layer. Making use of optical and scanning electron microscopy (SEM images, we estimate the dispersion of particles in terms of correlation functions. Particles tend to aggregate into clusters, as shown by the presence of oscillations in the correlation functions. Furthermore, the volume fraction of particles is non-uniform in space. It is highest in the middle of the layer and lowest near the surfaces of the layer. To model this microstructure, we explore two models. The first one is a deposit model where particles fall onto a surface. It is unable to reproduce the observed measurements. We then introduce a "stack" model where clusters are first modeled by a 2D Poisson point process, and a bi-directional deposit model is used to implant particles in each cluster. Good agreement is found with respect to SEM images in terms of correlation functions and density of particles along the layer height.

  17. Numerical investigation of 3D effects on a 2D-dominated shocked mixing layer

    Science.gov (United States)

    Reese, Daniel; Weber, Christopher

    2016-11-01

    A nominally two-dimensional interface, unstable to the Rayleigh-Taylor or Richtmyer-Meshkov instability, will become three-dimensional at high Reynolds numbers due to the growth of background noise and 3D effects like vortex stretching. This three-dimensionality changes macroscopic features, such as the perturbation growth rate and mixing, as it enhances turbulent dissipation. In this study, a 2D perturbation with small-scale, 3D fluctuations is modeled using the hydrodynamics code Miranda. A Mach 1.95 shockwave accelerates a helium-over-SF6 interface, similar to the experiments of Motl et al. ["Experimental validation of a Richtmyer-Meshkov scaling law over large density ratio and shock strength ranges," Phys. Fluids 21(12), 126102 (2009)], to explore the regime where a 2D dominated flow will experience 3D effects. We report on the structure, growth, and mixing of the post-shocked interface in 2D and 3D.

  18. Cobalt carbonyl catalyzed olefin hydroformylation in supercritical carbon dioxide

    Science.gov (United States)

    Rathke, Jerome W.; Klingler, Robert J.

    1993-01-01

    A method of olefin hydroformylation is provided wherein an olefin reacts with a carbonyl catalyst and with reaction gases such as hydrogen and carbon monoxide in the presence of a supercritical reaction solvent, such as carbon dioxide. The invention provides higher yields of n-isomer product without the gas-liquid mixing rate limitation seen in conventional Oxo processes using liquid media.

  19. Supercritical water oxidation data acquisition testing. Final report, Volume I

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1996-11-01

    This report discusses the phase one testing of a data acquisition system for a supercritical water waste oxidation system. The system is designed to destroy a wide range of organic materials in mixed wastes. The design and testing of the MODAR Oxidizer is discussed. An analysis of the optimized runs is included.

  20. Contribution of mixing to upward transport across the tropical tropopause layer (TTL

    Directory of Open Access Journals (Sweden)

    P. Konopka

    2007-06-01

    Full Text Available During the second part of the TROCCINOX campaign that took place in Brazil in early 2005, chemical species were measured on-board the high-altitude research aircraft Geophysica (ozone, water vapor, NO, NOy, CH4 and CO in the altitude range up to 20 km (or up to 450 K potential temperature, i.e. spanning the entire TTL region roughly extending between 350 and 420 K.

    Here, analysis of transport across the TTL is performed using a new version of the Chemical Lagrangian Model of the Stratosphere (CLaMS. In this new version, the stratospheric model has been extended to the earth surface. Above the tropopause, the isentropic and cross-isentropic advection in CLaMS is driven by meteorological analysis winds and heating/cooling rates derived from a radiation calculation. Below the tropopause, the model smoothly transforms from the isentropic to the hybrid-pressure coordinate and, in this way, takes into account the effect of large-scale convective transport as implemented in the vertical wind of the meteorological analysis. As in previous CLaMS simulations, the irreversible transport, i.e. mixing, is controlled by the local horizontal strain and vertical shear rates.

    Stratospheric and tropospheric signatures in the TTL can be seen both in the observations and in the model. The composition of air above ≈350 K is mainly controlled by mixing on a time scale of weeks or even months. Based on CLaMS transport studies where mixing can be completely switched off, we deduce that vertical mixing, mainly driven by the vertical shear in the tropical flanks of the subtropical jets and, to some extent, in the the outflow regions of the large-scale convection, offers an explanation for the upward transport of trace species from the main convective outflow at around 350 K up to the tropical tropopause around 380 K.

  1. Contribution of mixing to upward transport across the tropical tropopause layer (TTL)

    Science.gov (United States)

    Konopka, P.; Günther, G.; Müller, R.; Dos Santos, F. H. S.; Schiller, C.; Ravegnani, F.; Ulanovsky, A.; Schlager, H.; Volk, C. M.; Viciani, S.; Pan, L. L.; McKenna, D.-S.; Riese, M.

    2007-06-01

    During the second part of the TROCCINOX campaign that took place in Brazil in early 2005, chemical species were measured on-board the high-altitude research aircraft Geophysica (ozone, water vapor, NO, NOy, CH4 and CO) in the altitude range up to 20 km (or up to 450 K potential temperature), i.e. spanning the entire TTL region roughly extending between 350 and 420 K. Here, analysis of transport across the TTL is performed using a new version of the Chemical Lagrangian Model of the Stratosphere (CLaMS). In this new version, the stratospheric model has been extended to the earth surface. Above the tropopause, the isentropic and cross-isentropic advection in CLaMS is driven by meteorological analysis winds and heating/cooling rates derived from a radiation calculation. Below the tropopause, the model smoothly transforms from the isentropic to the hybrid-pressure coordinate and, in this way, takes into account the effect of large-scale convective transport as implemented in the vertical wind of the meteorological analysis. As in previous CLaMS simulations, the irreversible transport, i.e. mixing, is controlled by the local horizontal strain and vertical shear rates. Stratospheric and tropospheric signatures in the TTL can be seen both in the observations and in the model. The composition of air above ≍350 K is mainly controlled by mixing on a time scale of weeks or even months. Based on CLaMS transport studies where mixing can be completely switched off, we deduce that vertical mixing, mainly driven by the vertical shear in the tropical flanks of the subtropical jets and, to some extent, in the the outflow regions of the large-scale convection, offers an explanation for the upward transport of trace species from the main convective outflow at around 350 K up to the tropical tropopause around 380 K.

  2. Mixed Layer Mesoscales for OGCMs: Model development and assessment with T/P, WOCE and Drifter data

    CERN Document Server

    Canuto, V M; Leboissetier, A

    2011-01-01

    We present a model for mixed layer (ML) mesoscale (M) fluxes of an arbitrary tracer in terms of the resolved fields (mean tracer and mean velocity). The treatment of an arbitrary tracer, rather than only buoyancy, is necessary since OGCMs time step T, S, CO2, etc and not buoyancy. The particular case of buoyancy is used to assess the model results. The paper contains three parts: derivation of the results, discussion of the results and assessment of the latter using, among others, WOCE, T/P and Drifter data. Derivation. To construct the M fluxes, we first solve the ML M dynamic equations for the velocity and tracer M fields. The goal of the derivation is to emphasize the different treatments of the non-linear terms in the adiabatic vs. diabatic ocean (deep ocean vs. mixed layer). Results. We derive analytic expressions for the following variables: a) vertical and horizontal M fluxes of an arbitrary tracer, b) M diffusivity in terms of the EKE, c) surface value of the EKE in terms of the vertical M buoyancy fl...

  3. Temporal and spatial changes in mixed layer properties and atmospheric net heat flux in the Nordic Seas

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, A; Alekseev, G [SI ' Arctic and Antarctic Research Institute' , St. Petersburg (Russian Federation); Korablev, A; Esau, I, E-mail: avsmir@aari.nw.r [Nansen Environmental and Remote Sensing Centre, Bergen (Norway)

    2010-08-15

    The Nordic Seas are an important area of the World Ocean where warm Atlantic waters penetrate far north forming the mild climate of Northern Europe. These waters represent the northern rim of the global thermohaline circulation. Estimates of the relationships between the net heat flux and mixed layer properties in the Nordic Seas are examined. Oceanographic data are derived from the Oceanographic Data Base (ODB) compiled in the Arctic and Antarctic Research Institute. Ocean weather ship 'Mike' (OWS) data are used to calculate radiative and turbulent components of the net heat flux. The net shortwave flux was calculated using a satellite albedo dataset and the EPA model. The net longwave flux was estimated by Southampton Oceanography Centre (SOC) method. Turbulent fluxes at the air-sea interface were calculated using the COARE 3.0 algorithm. The net heat flux was calculated by using oceanographic and meteorological data of the OWS 'Mike'. The mixed layer depth was estimated for the period since 2002 until 2009 by the 'Mike' data as well. A good correlation between these two parameters has been found. Sensible and latent heat fluxes controlled by surface air temperature/sea surface temperature gradient are the main contributors into net heat flux. Significant correlation was found between heat fluxes variations at the OWS 'Mike' location and sea ice export from the Arctic Ocean.

  4. Warmer, deeper, and greener mixed layers in the North Atlantic subpolar gyre over the last 50 years.

    Science.gov (United States)

    Martinez, Elodie; Raitsos, Dionysios E; Antoine, David

    2016-02-01

    Shifts in global climate resonate in plankton dynamics, biogeochemical cycles, and marine food webs. We studied these linkages in the North Atlantic subpolar gyre (NASG), which hosts extensive phytoplankton blooms. We show that phytoplankton abundance increased since the 1960s in parallel to a deepening of the mixed layer and a strengthening of winds and heat losses from the ocean, as driven by the low frequency of the North Atlantic Oscillation (NAO). In parallel to these bottom-up processes, the top-down control of phytoplankton by copepods decreased over the same time period in the western NASG, following sea surface temperature changes typical of the Atlantic Multi-decadal Oscillation (AMO). While previous studies have hypothesized that climate-driven warming would facilitate seasonal stratification of surface waters and long-term phytoplankton increase in subpolar regions, here we show that deeper mixed layers in the NASG can be warmer and host a higher phytoplankton biomass. These results emphasize that different modes of climate variability regulate bottom-up (NAO control) and top-down (AMO control) forcing on phytoplankton at decadal timescales. As a consequence, different relationships between phytoplankton, zooplankton, and their physical environment appear subject to the disparate temporal scale of the observations (seasonal, interannual, or decadal). The prediction of phytoplankton response to climate change should be built upon what is learnt from observations at the longest timescales.

  5. Diversity of planktonic Ostracods (Crustacea: Ostracoda in the mixed layer of northeastern Arabian Sea during the summer monsoon

    Directory of Open Access Journals (Sweden)

    Jasmine Purushothaman

    2015-03-01

    Full Text Available Planktonic ostracods contribute significantly to the biomass of zooplankton in the Arabian Sea with an unusually high density due to swarming.  However, due to the small size, their abundance is often underestimated.  In this paper, the diversity of planktonic ostracods in the mixed layer depth of the northeastern Arabian Sea in relation to environmental parameters during the summer monsoon is presented.  The mean abundance in the mixed layer depth was very high.  About 26 species belonging to 17 genera representing two families were recognized.  Out of this, 25 species belonged to (3 sub families, 16 genera the order Myodocopa and one to the order Myodocopida.  The dominant species were Cypridina dentata, Euconchoecia aculeata, Conchoecia subarcuata and Orthoconchoecia atlantica.  Cypridina dentata and Euconchoecia aculeata contributed to about 89% of the total abundance.  The results suggest that the distribution and diversity of ostracods were very much influenced by the hydrographic conditions of the Arabian Sea during the summer monsoon. 

  6. The role of snow-surface coupling, radiation, and turbulent mixing in modeling a stable boundary layer over Arctic sea ice

    NARCIS (Netherlands)

    Sterk, H.A.M.; Steeneveld, G.J.; Holtslag, A.A.M.

    2013-01-01

    To enhance the understanding of the impact of small-scale processes in the polar climate, this study focuses on the relative role of snow-surface coupling, radiation and turbulent mixing in an Arctic stable boundary layer. We extend the GABLS1 (GEWEX Atmospheric Boundary-Layer Study 1) model interco

  7. Structural Transition in Supercritical Fluids

    Directory of Open Access Journals (Sweden)

    Boris I. Sedunov

    2011-01-01

    Full Text Available The extension of the saturation curve ( on the PT diagram in the supercritical region for a number of monocomponent supercritical fluids by peak values for different thermophysical properties, such as heat capacities and and compressibility has been studied. These peaks signal about some sort of fluid structural transition in the supercritical region. Different methods give similar but progressively diverging curves st( for this transition. The zone of temperatures and pressures near these curves can be named as the zone of the fluid structural transition. The outstanding properties of supercritical fluids in this zone help to understand the physical sense of the fluid structural transition.

  8. Evaluation of simulated climatological diurnal temperature range in CMIP5 models from the perspective of planetary boundary layer turbulent mixing

    Science.gov (United States)

    Wei, Nan; Zhou, Liming; Dai, Yongjiu

    2017-07-01

    This study examines the effects of modeled planetary boundary layer (PBL) mixing on the simulated temperature diurnal cycle climatology over land in 20 CMIP5 models with AMIP simulations. When compared with observations, the magnitude of diurnal temperature range (DTR) is systematically underestimated over almost all land areas due to a widespread warm bias of daily minimum temperature (Tmin) and mostly a cold bias of daily maximum temperature (Tmax). Analyses of the CMIP5 multi-model ensemble means suggest that the biases of the simulated PBL mixing could very likely contribute to the temperature biases. For the regions with the cold bias in Tmax, the daytime PBL mixing is generally underestimated. The consequent more dry air entrainment from the free atmosphere could help maintain the surface humidity gradient, and thus produce more surface evaporation and potentially lower the Tmax. The opposite situation holds true for the regions with the warm bias of Tmax. This mechanism could be particularly applicable to the regions with moderate and wet climate conditions where surface evaporation depends more on the surface humidity gradient, but less on the available soil moisture. For the widespread warm bias of Tmin, the widely-recognized overestimated PBL mixing at nighttime should play a dominant role by transferring more heat from the atmosphere to the near-surface to warm the Tmin. Further analyses using the high resolution CFMIP2 output also support the CMIP5 results about the connections of the biases between the simulated turbulent mixing and the temperature diurnal cycle. The large inter-model variations of the simulated temperature diurnal cycle primarily appear over the arid and semi-arid regions and boreal arctic regions where the model differences in the PBL turbulence mixing could make equally significant contributions to the inter-model variations of DTR, Tmax and Tmin compared to the model differences in surface radiative processes. These results

  9. Evaluation of simulated climatological diurnal temperature range in CMIP5 models from the perspective of planetary boundary layer turbulent mixing

    Science.gov (United States)

    Wei, Nan; Zhou, Liming; Dai, Yongjiu

    2016-08-01

    This study examines the effects of modeled planetary boundary layer (PBL) mixing on the simulated temperature diurnal cycle climatology over land in 20 CMIP5 models with AMIP simulations. When compared with observations, the magnitude of diurnal temperature range (DTR) is systematically underestimated over almost all land areas due to a widespread warm bias of daily minimum temperature (Tmin) and mostly a cold bias of daily maximum temperature (Tmax). Analyses of the CMIP5 multi-model ensemble means suggest that the biases of the simulated PBL mixing could very likely contribute to the temperature biases. For the regions with the cold bias in Tmax, the daytime PBL mixing is generally underestimated. The consequent more dry air entrainment from the free atmosphere could help maintain the surface humidity gradient, and thus produce more surface evaporation and potentially lower the Tmax. The opposite situation holds true for the regions with the warm bias of Tmax. This mechanism could be particularly applicable to the regions with moderate and wet climate conditions where surface evaporation depends more on the surface humidity gradient, but less on the available soil moisture. For the widespread warm bias of Tmin, the widely-recognized overestimated PBL mixing at nighttime should play a dominant role by transferring more heat from the atmosphere to the near-surface to warm the Tmin. Further analyses using the high resolution CFMIP2 output also support the CMIP5 results about the connections of the biases between the simulated turbulent mixing and the temperature diurnal cycle. The large inter-model variations of the simulated temperature diurnal cycle primarily appear over the arid and semi-arid regions and boreal arctic regions where the model differences in the PBL turbulence mixing could make equally significant contributions to the inter-model variations of DTR, Tmax and Tmin compared to the model differences in surface radiative processes. These results

  10. Convective mixing in vertically-layered porous media: The linear regime and the onset of convection

    Science.gov (United States)

    Ghorbani, Zohreh; Riaz, Amir; Daniel, Don

    2017-08-01

    We study the effect of permeability heterogeneity on the stability of gravitationally unstable, transient, diffusive boundary layers in porous media. Permeability is taken to vary periodically in the horizontal plane normal to the direction of gravity. In contrast to the situation for vertical permeability variation, the horizontal perturbation structures are multimodal. We therefore use a two-dimensional quasi-steady eigenvalue analysis as well as a complementary initial value problem to investigate the stability behavior in the linear regime, until the onset of convection. We find that thick permeability layers enhance instability compared with thin layers when heterogeneity is increased. On the contrary, for thin layers the instability is weakened progressively with increasing heterogeneity to the extent that the corresponding homogeneous case is more unstable. For high levels of heterogeneity, we find that a small change in the permeability field results in large variations in the onset time of convection, similar to the instability event in the linear regime. However, this trend does not persist unconditionally because of the reorientation of vorticity pairs due to the interaction of evolving perturbation structures with heterogeneity. Consequently, an earlier onset of instability does not necessarily imply an earlier onset of convection. A resonant amplification of instability is observed within the linear regime when the dominant perturbation mode is equal to half the wavenumber of permeability variation. On the other hand, a substantial damping occurs when the perturbation mode is equal to the harmonic and sub-harmonic components of the permeability wavenumber. The phenomenon of such harmonic interactions influences both the onset of instability as well as the onset of convection.

  11. Measurement of turbulence in the oceanic mixed layer using Synthetic Aperture Radar (SAR

    Directory of Open Access Journals (Sweden)

    S. G. George

    2012-09-01

    Full Text Available Turbulence in the surface layer of the ocean contributes to the transfer of heat, gas and momentum across the air-sea boundary. As such, study of turbulence in the ocean surface layer is becoming increasingly important for understanding its effects on climate change. Direct Numerical Simulation (DNS techniques were implemented to examine the interaction of small-scale wake turbulence in the upper ocean layer with incident electromagnetic radar waves. Hydrodynamic-electromagnetic wave interaction models were invoked to demonstrate the ability of Synthetic Aperture Radar (SAR to observe and characterise surface turbulent wake flows. A range of simulated radar images are presented for a turbulent surface current field behind a moving surface vessel, and compared with the surface flow fields to investigate the impact of turbulent currents on simulated radar backscatter. This has yielded insights into the feasibility of resolving small-scale turbulence with remote-sensing radar and highlights the potential for extracting details of the flow structure and characteristics of turbulence using SAR.

  12. A mixing-length model for the prediction of convex curvature effects on turbulent boundary layers. [for turbine blade convective heat transfer prediction

    Science.gov (United States)

    Adams, E. W.; Johnston, J. P.

    1983-01-01

    A mixing-length model is developed for the prediction of turbulent boundary layers with convex streamwise curvature. For large layer thickness ratio, delta/R greater than 0.05, the model scales mixing length on the wall radius of curvature, R. For small delta/R, ordinary flat wall modeling is used for the mixing-length profile with curvature corrections, following the recommendations of Eide and Johnston (1976). Effects of streamwise change of curvature are considered; a strong lag from equilibrium is required when R increases downstream. Fifteen separate data sets were compared, including both hydrodynamic and heat transfer results. Six of these computations are presented and compared to experiment.

  13. Intercomparison of cloud model simulations of Arctic mixed-phase boundary layer clouds observed during SHEBA/FIRE-ACE

    Directory of Open Access Journals (Sweden)

    Mikhail Ovchinnikov

    2011-06-01

    Full Text Available An intercomparison of six cloud-resolving and large-eddy simulation models is presented. This case study is based on observations of a persistent mixed-phase boundary layer cloud gathered on 7 May, 1998 from the Surface Heat Budget of Arctic Ocean (SHEBA and First ISCCP Regional Experiment - Arctic Cloud Experiment (FIRE-ACE. Ice nucleation is constrained in the simulations in a way that holds the ice crystal concentration approximately fixed, with two sets of sensitivity runs in addition to the baseline simulations utilizing different specified ice nucleus (IN concentrations. All of the baseline and sensitivity simulations group into two distinct quasi-steady states associated with either persistent mixed-phase clouds or all-ice clouds after the first few hours of integration, implying the existence of multiple equilibria. These two states are associated with distinctly different microphysical, thermodynamic, and radiative characteristics. Most but not all of the models produce a persistent mixed-phase cloud qualitatively similar to observations using the baseline IN/crystal concentration, while small increases in the IN/crystal concentration generally lead to rapid glaciation and conversion to the all-ice state. Budget analysis indicates that larger ice deposition rates associated with increased IN/crystal concentrations have a limited direct impact on dissipation of liquid in these simulations. However, the impact of increased ice deposition is greatly enhanced by several interaction pathways that lead to an increased surface precipitation flux, weaker cloud top radiative cooling and cloud dynamics, and reduced vertical mixing, promoting rapid glaciation of the mixed-phase cloud for deposition rates in the cloud layer greater than about 1-2x10-5 g kg-1 s-1. These results indicate the critical importance of precipitation-radiative-dynamical interactions in simulating cloud phase, which have been neglected in previous fixed-dynamical parcel

  14. Intercomparison of cloud model simulations of Arctic mixed-phase boundary layer clouds observed during SHEBA/FIRE-ACE

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, H.; Zuidema, Paquita; Ackerman, Andrew; Avramov, Alexander; de Boer, Gijs; Fan, Jiwen; Fridlind, Ann; Hashino, Tempei; Harrington, Jerry Y.; Luo, Yali; Ovchinnikov, Mikhail; Shipway, Ben

    2011-06-16

    An intercomparison of six cloud-resolving and large-eddy simulation models is presented. This case study is based on observations of a persistent mixed-phase boundary layer cloud gathered on 7 May, 1998 from the Surface Heat Budget of Arctic Ocean (SHEBA) and First ISCCP Regional Experiment - Arctic Cloud Experiment (FIRE-ACE). Ice nucleation is constrained in the simulations in a way that holds the ice crystal concentration approximately fixed, with two sets of sensitivity runs in addition to the baseline simulations utilizing different specified ice nucleus (IN) concentrations. All of the baseline and sensitivity simulations group into two distinct quasi-steady states associated with either persistent mixed-phase clouds or all-ice clouds after the first few hours of integration, implying the existence of multiple equilibria. These two states are associated with distinctly different microphysical, thermodynamic, and radiative characteristics. Most but not all of the models produce a persistent mixed-phase cloud qualitatively similar to observations using the baseline IN/crystal concentration, while small increases in the IN/crystal concentration generally lead to rapid glaciation and conversion to the all-ice state. Budget analysis indicates that larger ice deposition rates associated with increased IN/crystal concentrations have a limited direct impact on dissipation of liquid in these simulations. However, the impact of increased ice deposition is greatly enhanced by several interaction pathways that lead to an increased surface precipitation flux, weaker cloud top radiative cooling and cloud dynamics, and reduced vertical mixing, promoting rapid glaciation of the mixed-phase cloud for deposition rates in the cloud layer greater than about 1-2x10-5 g kg-1 s-1. These results indicate the critical importance of precipitation-radiative-dynamical interactions in simulating cloud phase, which have been neglected in previous fixed-dynamical parcel studies of the cloud

  15. Inhibition of mixed-layer deepening during winter in the northeastern Arabian Sea by the West India Coastal Current

    Science.gov (United States)

    Shankar, D.; Remya, R.; Vinayachandran, P. N.; Chatterjee, Abhisek; Behera, Ambica

    2016-08-01

    Though the deep mixed layers (MLs) that form in the northeastern Arabian Sea (NEAS) during the winter monsoon (November-February) have been attributed to convective mixing driven by dry, cool northeasterly winds from the Indian subcontinent, data show that the deepest MLs occur in the northern NEAS and the maxima of latent-heat and net heat fluxes in the southern NEAS. We use an oceanic general circulation model to show that the deep MLs in the NEAS extend up to ~20°N till the end of December, but are restricted poleward of ~22°N (~23°N) in January (February). This progressive restriction of the deep mixed layers within the NEAS is due to poleward advection of water of lower salinity by the West India Coastal Current (WICC). The deep MLs are sustained till February in the northern NEAS because convective mixing deepens the ML before the waters of lower salinity reach this region and the wind stirring and convective overturning generate sufficient turbulent energy for the ML to maintain the depth attained in January. Though the atmospheric fluxes tend to cool the ML in the southern NEAS, this cooling is countered by the warming due to horizontal advection. Likewise, the cooling due to entrainment, which continues in the southern NEAS even as the ML shallows during January-February, is almost cancelled by the warming caused by a downwelling vertical velocity field. Therefore, the SST changes very little during December-February even as the ML shallows dramatically in the southern NEAS. These deep MLs of the NEAS also preclude a strong intraseasonal response to the intraseasonal variability in the fluxes. This role of horizontal advection implies that the ML depth in the NEAS is determined by an interplay of physical processes that are forced differently. The convective mixing depends on processes that are local to the region, but the advection is due to the WICC, whose seasonal cycle is primarily forced by remote winds. By inhibiting the formation of deep MLs in

  16. Si iv Column Densities Predicted from Non-Equilibrium Ionization Simulations of Turbulent Mixing Layers and High-Velocity Clouds

    CERN Document Server

    Kwak, Kyujin; Henley, David B

    2015-01-01

    We present predictions of the Si iv ions in turbulent mixing layers (TMLs) between hot and cool gas and in cool high-velocity clouds (HVCs) that travel through a hot halo, complementing the C iv, N v, and O vi predictions in Kwak & Shelton, Kwak et al., and Henley et al. We find that the Si iv ions are most abundant in regions where the hot and cool gases first begin to mix or where the mixed gas has cooled significantly. The predicted column densities of high velocity Si iv and the predicted ratios of Si iv to C iv and O vi found on individual sightlines in our HVC simulations are in good agreement with observations of high velocity gas. Low velocity Si iv is also seen in the simulations, as a result of decelerated gas in the case of the HVC simulations and when looking along directions that pass perpendicular to the direction of motion in the TML simulations. The ratios of low velocity Si iv to C iv and O vi in the TML simulations are in good agreement with those recorded for Milky Way halo gas, while t...

  17. Research on Pump Primers for Friction Reduction of Wet-Mix Shotcrete Based on Precreating Lubricating Layer

    Directory of Open Access Journals (Sweden)

    Guoming Liu

    2017-01-01

    Full Text Available Wet-mix shotcrete has lower water content even though looking wet which is generally less than 8% of total content. The inner surface of pipes will absorb water from fresh concrete to wet itself if concrete pump primers is not pumped early; meanwhile, the saturated concrete is transformed into the unsaturated concrete, and pipe blockage often occurs. In order to minimize the loss of water and wet pipes, a new type of pump primers was developed to precreate the lubricating layer that is one of the most dominant factors in determining the pumping capability, which would provide a cost-effective replacement for premium priced cement-based primers. Experiments were conducted to measure the viscosity, stability, and strength of mix solution during development stage. The optimal formula was obtained by orthogonal matching tests with 0.5% sodium stearate, 0.75% xanthan gum, 0.3% polyacrylamide, and 0.4% blender (mass ratio related to mix water. The pressure drop reduction of new primers was larger than that of common primers.

  18. Supercritical Mixing in a Shear Coaxial Injector

    Science.gov (United States)

    2016-07-27

    remaining terms such as enthalpy, entropy and respective derivatives are computed as departure functions from the ideal gas law . A plot of density...0.3) Here, P and T are pressure and temperature respectively, R is the universal gas constant and ma and mb are the mixture properties...other provision of law , no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a

  19. Performance test of the synergetic use of simulated lidar and microwave radiometer observations for mixing-layer height detection

    Science.gov (United States)

    Saeed, Umar; Rocadenbosch, Francesc; Crewell, Susanne

    2015-10-01

    There are several instruments and methods to retrieve the atmospheric Mixing Layer Height (MLH). However, none of these instruments or methods can measure the development of the MLH under all atmospheric conditions. For example, aerosol signatures measured by backscatter lidars can be used to determine the MLH but this approach is reasonable only when the atmosphere is well-mixed. Microwave Radiometer (MWR) derived profiles have low vertical resolution and cannot resolve fine structures in the boundary layer, especially, at higher altitudes. Here we propose a method which combines data from a ground-based lidar and a MWR, in simulated as well as real measurements scenarios, to overcome these limitations. The method works by fitting an erf-like transition model function to the section of range-corrected lidar backscatter signal. The section of the lidar backscatter signal for fitting the model function is obtained by incorporating the MWR estimates of MLH along with their uncertainties. The fitting is achieved by using an extended Kalman filter (EKF). The proposed approach, by exploiting the synergy between the two instruments, enables to detect MLH with original vertical and temporal resolutions. Test cases combining simulated data for a co-located lidar-ceilometer and a MWR are presented. The simulated data is obtained from the Dutch Atmospheric Large Eddy Simulation (DALES) model for boundary layer studies. Doppler wind lidar along with radiosondes (whenever available) data is used to assess the quality of the synergetic MLH estimates. Data from the HD(CP)2 Observational Prototype Experiment (HOPE) campaign at Jülich, Germany is used to test the proposed method.

  20. I/S and C/S mixed layers, some indicators of recent physical-chemical changes in active geothermal systems: The case study of Chipilapa (El Salvador)

    Energy Technology Data Exchange (ETDEWEB)

    Beaufort, D.; Papapanagiotou, P.; patrier, P.; Fouillac, A.M.; Traineau, H.

    1996-01-24

    I/S and C/S mixed layers from the geothermal field of Chipilapa (El Salvador) have been studied in details in order to reevaluate their potential use as indicator of the thermodynamic conditions in which they were formed. It is funded that overprinting of clay bearing alteration stages is common. For a given alteration stage, the spatial variation of I/S and C/S mixed layer ininerals is controlled by kinetics of mixed layer transformation and not only by temperature. Clay geo-thermometers cannot give reliable results because the present crystal-chemical states of the I/S and C/S mixed layers is not their initial state, it was aquired during the overall hydrothermal history which post dated the nucleation of smectitic clay material at high temperature. Occurrences of smectites or smectite-rich mixed layers at high temperature in reservoirs is a promising guide for reconstruct the zones in which boiling or mixing of non isotherinal fluids occurred very recently or still presently.

  1. Supercritical solvent coal extraction

    Science.gov (United States)

    Compton, L. E. (Inventor)

    1984-01-01

    Yields of soluble organic extract are increased up to about 50% by the supercritical extraction of particulate coal at a temperature below the polymerization temperature for coal extract fragments (450 C.) and a pressure from 500 psig to 5,000 psig by the conjoint use of a solvent mixture containing a low volatility, high critical temperature coal dissolution catalyst such as phenanthrene and a high volatility, low critical temperature solvent such as toluene.

  2. Mixing ALD/MLD-grown ZnO and Zn-4-aminophenol layers into various thin-film structures.

    Science.gov (United States)

    Sundberg, Pia; Sood, Anjali; Liu, Xuwen; Karppinen, Maarit

    2013-11-14

    Building 2D inorganic-organic hybrids by combining inorganic and organic constituents with molecular-layer precision is an attractive approach to fabricate novel materials with a tailored combination of properties from both entities. Here we demonstrate the potential of the combined atomic and molecular layer deposition (ALD/MLD) technique for the state-of-the-art synthesis of such materials and to fabricate both homogeneous thin-film mixtures and nanolaminates of ZnO and the Zn-4-aminophenol inorganic-organic hybrid. The thin films are deposited by varying the number of precursor cycles during the depositions. Diethyl zinc and 4-aminophenol (AP) are used as precursors for the Zn-AP hybrid depositions, and diethyl zinc and water for the ZnO depositions. The characterization of the mixed Zn-AP and ZnO films reveals that crystallinity, density, surface roughness, chemical stability, hardness and contact modulus are sensitively altered by even a minor insertion of Zn-AP hybrid into the ZnO structure. Fabrication of Zn-AP + ZnO nanolaminates with different thicknesses of the Zn-AP and ZnO layers provides us with an even better way to control the hardness and contact modulus, and also to enhance the chemical stability of the films.

  3. Supercritical Water Oxidation Data Acquisition Testing

    Energy Technology Data Exchange (ETDEWEB)

    K. M. Garcia

    1996-08-01

    Supercritical Water Oxidation (SCWO) is a high pressure oxidation process that blends air, water, and organic waste material in an oxidizer in which where the temperature and pressure in the oxidizer are maintained above the critical point of water. Supercritical water mixed with hydrocarbons, which would be insoluble at subcritical conditions, forms a homogeneous phase which possesses properties associated with both a gas and a liquid. Hydrocarbons in contact with oxygen and SCW are readily oxidized. These properties of SCW make it an attractive means for the destruction of waste streams containing organic materials. SCWO technology holds great promise for treating mixed wastes in an environmentally safe and efficient manner. In the spring of 1994 the U.S. Department of Energy (DOE) initiated a Supercritical Water Oxidation Data Acquisition Testing (SCWODAT) program. The SCWODAT program provided further information and operational data on the effectiveness of treating both simulated mixed waste and typical Navy hazardous waste using the SCWO technology. The program concentrated on the acquisition of data through pilot plant testing. The Phase I DOE testing used a simulated waste stream that contained a complex machine cutting oil and metals, that acted as surrogates for radionuclides. The Phase II Navy testing included pilot testing using hazardous waste materials to demonstrate the effectiveness of the SCWO technology. The SCWODAT program demonstrated that the SCWO process oxidized the simulated waste stream containing complex machine cutting oil, selected by DOE as representative of one of the most difficult of the organic waste streams for which SCWO had been applied. The simulated waste stream with surrogate metals in solution was oxidized, with a high destruction efficiency, on the order of 99.97%, in both the neutralized and unneutralized modes of operation.

  4. Lipid absorption triggers drug supersaturation at the intestinal unstirred water layer and promotes drug absorption from mixed micelles.

    Science.gov (United States)

    Yeap, Yan Yan; Trevaskis, Natalie L; Porter, Christopher J H

    2013-12-01

    To evaluate the potential for the acidic intestinal unstirred water layer (UWL) to induce drug supersaturation and enhance drug absorption from intestinal mixed micelles, via the promotion of fatty acid absorption. Using a single-pass rat jejunal perfusion model, the absorptive-flux of cinnarizine and (3)H-oleic acid from oleic acid-containing intestinal mixed micelles was assessed under normal acidic microclimate conditions and conditions where the acidic microclimate was attenuated via the co-administration of amiloride. As a control, the absorptive-flux of cinnarizine from micelles of Brij® 97 (a non-ionizable, non-absorbable surfactant) was assessed in the absence and presence of amiloride. Cinnarizine solubility was evaluated under conditions of decreasing pH and decreasing micellar lipid content to assess likely changes in solubilization and thermodynamic activity during micellar passage across the UWL. In the presence of amiloride, the absorptive-flux of cinnarizine and (3)H-oleic acid from mixed micelles decreased 6.5-fold and 3.0-fold, respectively. In contrast, the absorptive-flux of cinnarizine from Brij® 97 micelles remained unchanged by amiloride, and was significantly lower than from the long-chain micelles. Cinnarizine solubility in long-chain micelles decreased under conditions where pH and micellar lipid content decreased simultaneously. The acidic microclimate of the intestinal UWL promotes drug absorption from intestinal mixed micelles via the promotion of fatty acid absorption which subsequently stimulates drug supersaturation. The observations suggest that formulations (or food) containing absorbable lipids (or their digestive precursors) may outperform formulations that lack absorbable components since the latter do not benefit from lipid absorption-induced drug supersaturation.

  5. The roles of convection, extratropical mixing, and in-situ freeze-drying in the Tropical Tropopause Layer

    Directory of Open Access Journals (Sweden)

    W. G. Read

    2008-10-01

    Full Text Available Mechanisms for transporting and dehydrating air across the tropical tropopause layer (TTL are investigated with a conceptual two dimensional (2-D model. The 2-D TTL model combines the Holton and Gettelman cold trap dehydration mechanism (Holton and Gettelman, 2001 with the two column convection model of Folkins and Martin (2005. We investigate 3 possible transport scenarios through the TTL: 1 slow uniform ascent across the level of zero radiative heating without direct convective mixing, 2 convective mixing of H2O vapor at 100% relative humidity with respect to ice (RHi with no ice retention, and 3 convective mixing of extremely subsaturated air (100% RHi following the moist adiabatic temperature above the level of neutral buoyancy with sufficient ice retention such that total H2O is 100%RHi. The three mechanisms produce similar seasonal cycles for H2O that are in good quantitative agreement with the Aura Microwave Limb Sounder (MLS measurements. We use Aura MLS measurement of CO and Atmospheric Chemistry Experiment-Fourier Transform Spectrometer measurement of HDO to distinguish among the transport mechanisms. Model comparisons with the observations support the view that H2O is predominantly controlled by regions having the lowest cold point tropopause temperature but the trace species CO and HDO support the convective mixing of dry air and lofted ice. The model provides some insight into the processes affecting the long term trends observed in stratospheric H2O.

  6. Porous layered and open-framework mixed-valence copper tellurites

    Science.gov (United States)

    Markovski, Mishel R.; Siidra, Oleg I.; Kayukov, Roman A.; Nazarchuk, Evgeni W.

    2016-11-01

    |Cu+Cl3|[Cu2+2(TeO3)] (1), |Cu+1.7Cl3.8|[Cu2+4O(TeO3)2] (2) and Tl+2[Cu2+2Te6+Te4+6O18] (3) were obtained by CVT and hydrothermal methods in CuCl-CuCl2-TeO2 and Tl2CO3-CuO-TeO2 systems. 1 demonstrates layered topology with pores (1×0.65 nm), whereas 2 has open-framework structural architecture with two-dimensional system of channels (1.16×0.74 nm). Channels in open-framework of 3 are occupied by Tl+ cations. 'Host-guest' structural organization of 1 and 2 with host Cu2+-tellurite units of different dimensionality formed by oxocentered OCu4 tetrahedra and OCu2Te triangles and guest Cu+-chloride species is the result of formation from gases in CVT reactions. Oxocentered units determine basic topologies of the structures of 1 and 2 and influence their stability and properties. [Te6+Te4+6O18]6- polytellurite-tellurate framework in 3 can be represented as consisting of Kagome-like layers.

  7. Parameterization for the Depth of the Entrainment Zone above the Convectively Mixed Layer

    Institute of Scientific and Technical Information of China (English)

    SUN Jianning; JIANG Weimei; CHEN Ziyun; YUAN Renmin

    2005-01-01

    It has been noted that when the convective Richardson number Ri* is used to characterize the depth of the entrainment zone, various parameterization schemes can be obtained. This situation is often attributed to the invalidity of parcel theory. However, evidence shows that the convective Richardson number Ri*might be an improper characteristic scaling parameter for the entrainment process. An attempt to use an innovative parameter to parameterize the entrainment-zone thickness has been made in this paper.Based on the examination of the data of water-tank experiments and atmospheric measurements, it is found that the total lapse rate of potential temperature across the entrainment zone is proportional to that of the capping inversion layer. Inserting this relationship into the so-called parcel theory, it thus gives a new parameterization scheme for the depth of the entrainment zone. This scheme includes the lapse rate of the capping inversion layer that plays an important role in the entrainment process. Its physical representation is reasonable. The new scheme gives a better ordering of the data measured in both watertank and atmosphere as compared with the traditional method using Ri*. These indicate that the parcel theory can describe the entrainment process suitably and that the new parameter is better than Ri*.

  8. Experimental study of elliptical jet from supercritical to subcritical conditions using planar laser induced fluorescence

    Science.gov (United States)

    Muthukumaran, C. K.; Vaidyanathan, Aravind

    2015-03-01

    The study of fluid jet dynamics at supercritical conditions involves strong coupling between fluid dynamic and thermodynamic phenomena. Beyond the critical point, the liquid-vapor coexistence ceases to exist, and the fluid exists as a single phase known as supercritical fluid with its properties that are entirely different from liquids and gases. At the critical point, the liquids do not possess surface tension and latent heat of evaporation. Around the critical point, the fluid undergoes large changes in density and possesses thermodynamic anomaly like enhancement in thermal conductivity and specific heat. In the present work, the transition of the supercritical and near-critical elliptical jet into subcritical as well as supercritical environment is investigated experimentally with nitrogen and helium as the surrounding environment. Under atmospheric condition, a liquid jet injected from the elliptical orifice exhibits axis switching phenomena. As the injection temperature increases, the axis switching length also increases. Beyond the critical temperature, the axis switching is not observed. The investigation also revealed that pressure plays a major role in determining the thermodynamic transition of the elliptical jet only for the case of supercritical jet injected into subcritical chamber conditions. At larger pressures, the supercritical jet undergoes disintegration and formation of droplets in the subcritical environment is observed. However, for supercritical jet injection into supercritical environment, the gas-gas like mixing behavior is observed.

  9. Experimental study of elliptical jet from supercritical to subcritical conditions using planar laser induced fluorescence

    Energy Technology Data Exchange (ETDEWEB)

    Muthukumaran, C. K.; Vaidyanathan, Aravind, E-mail: aravind7@iist.ac.in [Department of Aerospace Engineering, Indian Institute of Space Science and Technology, Trivandrum, Kerala 695547 (India)

    2015-03-15

    The study of fluid jet dynamics at supercritical conditions involves strong coupling between fluid dynamic and thermodynamic phenomena. Beyond the critical point, the liquid-vapor coexistence ceases to exist, and the fluid exists as a single phase known as supercritical fluid with its properties that are entirely different from liquids and gases. At the critical point, the liquids do not possess surface tension and latent heat of evaporation. Around the critical point, the fluid undergoes large changes in density and possesses thermodynamic anomaly like enhancement in thermal conductivity and specific heat. In the present work, the transition of the supercritical and near-critical elliptical jet into subcritical as well as supercritical environment is investigated experimentally with nitrogen and helium as the surrounding environment. Under atmospheric condition, a liquid jet injected from the elliptical orifice exhibits axis switching phenomena. As the injection temperature increases, the axis switching length also increases. Beyond the critical temperature, the axis switching is not observed. The investigation also revealed that pressure plays a major role in determining the thermodynamic transition of the elliptical jet only for the case of supercritical jet injected into subcritical chamber conditions. At larger pressures, the supercritical jet undergoes disintegration and formation of droplets in the subcritical environment is observed. However, for supercritical jet injection into supercritical environment, the gas-gas like mixing behavior is observed.

  10. On the annual cycle of the sea surface temperature and the mixed layer depth in the Gulf of Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Mendoza, V.M.; Villanueva, E.E.; Adem, J. [Centro de Ciencias de la Atmosfera, Universidad Nacional Autonoma de Mexico, UNAM, Mexico, D.F. (Mexico)

    2005-04-01

    Using an integrated mixed layer model, we carry out a simulation of the annual cycle of the sea surface temperature (SST) and of the mixed layer depth (MLD) in the Gulf of Mexico. We also compute the annual cycle of the entrainment velocity in the deepest region of the Gulf of Mexico. The model is based on the thermal energy equation and on an equation of mechanical and thermal energy balance based on the Kraus-Turner theory; both equation are coupled and are vertically integrated in the mixed layer. The model equations are solved in a uniform grid of 25 km in the Gulf of Mexico, the northwestern region of the Caribbean Sea and the eastern coast of Florida. The surface ocean current velocity and the atmospheric variables are prescribed in the model using observed values. We show the importance of the Ekman pumping in the entrainment velocity. We found that the upwelling plays an important role in increasing the entrainment velocity, producing an important reduction in the SST and diminishing the depth of the mixed layer in the Campeche Bay. In the rest of the Gulf of Mexico the downwelling tends to reduce the entrainment velocity, increasing the SST and the MLD. Comparison of the computed annual cycle of the SST and the MLD with the corresponding observations reported by Robinson (1973) shows a good agreement. In the deepest region of the Gulf of Mexico, the photosynthetic pigment concentration data obtained from the Mexican Pacific Cd-Rom of environmental analysis shows significant correlation with the computed annual cycle of the computed entrainment velocity only in January, April, May, June and September. [Spanish] Usando un modelo integrado en la capa de mezcla hemos obtenido una simulacion del ciclo anual de la temperatura de la superficie del mar (SST), de la profundidad de la capa de mezcla (MLD) en el Golfo de Mexico, asi como el ciclo anual de la velocidad de penetracion vertical turbulenta a traves de la termoclina en la region mas profunda del golfo de

  11. Mixed convection boundary layer flow over a moving vertical flat plate in an external fluid flow with viscous dissipation effect.

    Directory of Open Access Journals (Sweden)

    Norfifah Bachok

    Full Text Available The steady boundary layer flow of a viscous and incompressible fluid over a moving vertical flat plate in an external moving fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface.

  12. Sound generated by instability waves of supersonic flows. I Two-dimensional mixing layers. II - Axisymmetric jets

    Science.gov (United States)

    Tam, C. K. W.; Burton, D. E.

    1984-01-01

    An investigation is conducted of the phenomenon of sound generation by spatially growing instability waves in high-speed flows. It is pointed out that this process of noise generation is most effective when the flow is supersonic relative to the ambient speed of sound. The inner and outer asymptotic expansions corresponding to an excited instability wave in a two-dimensional mixing layer and its associated acoustic fields are constructed in terms of the inner and outer spatial variables. In matching the solutions, the intermediate matching principle of Van Dyke and Cole is followed. The validity of the theory is tested by applying it to an axisymmetric supersonic jet and comparing the calculated results with experimental measurements. Very favorable agreements are found both in the calculated instability-wave amplitude distribution (the inner solution) and the near pressure field level contours (the outer solution) in each case.

  13. Thermodynamic behaviour of supercritical matter.

    Science.gov (United States)

    Bolmatov, Dima; Brazhkin, V V; Trachenko, K

    2013-01-01

    Since their discovery in 1822, supercritical fluids have been of enduring interest and have started to be deployed in many important applications. Theoretical understanding of the supercritical state is lacking and is seen to limit further industrial deployment. Here we study thermodynamic properties of the supercritical state and discover that specific heat shows a crossover between two different regimes, an unexpected result in view of currently perceived homogeneity of supercritical state in terms of physical properties. We subsequently formulate a theory of system thermodynamics above the crossover, and find good agreement between calculated and experimental specific heat with no free-fitting parameters. In this theory, energy and heat capacity are governed by the minimal length of the longitudinal mode in the system only, and do not explicitly depend on system-specific structure and interactions. We derive a power law and analyse supercritical scaling exponents in the system above the Frenkel line.

  14. Calibration of the K-Profile Parameterization of ocean boundary layer mixing. Part I: Development

    CERN Document Server

    Zedler, S E; Yao, F; Heimbach, P; Kohl, A; Scott, R B; Hoteit, I

    2016-01-01

    In model comparisons with observational data, not all data contain information that is useful for answering a specific science question. If non-relevant or highly uncertain data are included in a comparison metric, they can reduce the significance of other observations that matter for the scientific process of interest. Sources of noise and correlations among summed quantities within a comparison metric affect the significance of a signal that is useful for testing model skill. In the setting of the tropical Pacific, we introduce an "inquiry dependent" (ID) metric of model-data comparison that determines the relative importance of the TOGA-TAO buoy observations of the ocean temperature, salinity, and horizontal currents for influencing upper-ocean vertical turbulent mixing as represented by the K-Profile Parameterization (KPP) embedded in the MIT general circulation model (MITgcm) for the 2004-2007 time period. The ID metric addresses a challenge that the wind forcing is likely a more significant source of un...

  15. Determination of particulate organic carbon sources to the surface mixed layer of the Canada Basin, Arctic Ocean

    Science.gov (United States)

    Brown, Kristina A.; McLaughlin, Fiona; Tortell, Philippe D.; Varela, Diana E.; Yamamoto-Kawai, Michiyo; Hunt, Brian; Francois, Roger

    2014-02-01

    Stable isotope ratios of particulate organic carbon (POC), together with other tracers, were analyzed in samples from the Canada Basin surface mixed layer in 2008 and 2009. Sampling was conducted during the end of the 2008 melt season and at the beginning of the 2009 freezeup under a variety of surface conditions, including open water, newly formed seasonal ice, and multiyear ice. In both years, POC exhibited a wide isotopic range (δ13C-POC -24.5 to -31.1‰), with the most isotopically depleted material generally found in the central basin. Isotopically enriched material was found on the shelves, consistent with higher biological production and strongly correlated with in situ carbon-uptake rates. In contrast, offshore in the central basin, there was no significant relationship between δ13C-POC distributions and either chlorophyll a or aqueous CO2 concentrations, suggesting that in situ biological production was not the dominant control. Analysis of freshwater sources suggested that the sea ice melt contribution of POC to surface waters in the central Canada Basin exerted a negligible influence on δ13C-POC distributions, and instead isotopically depleted POC in the surface waters of the central Canada Basin were sourced externally through advective transport of riverine organic matter. We show that alkalinity and meteoric water content can be used to distinguish POC inputs from North American and Russian rivers and our analysis suggests that Russian river inputs are the predominant source of 13C-depleted organic matter to the mixed layer of the central Canada Basin.

  16. Enzyme-level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean

    Science.gov (United States)

    Kemeny, P. C.; Weigand, M. A.; Zhang, R.; Carter, B. R.; Karsh, K. L.; Fawcett, S. E.; Sigman, D. M.

    2016-07-01

    In the Southern Ocean, the nitrogen (N) isotopes of organic matter and the N and oxygen (O) isotopes of nitrate (NO3-) have been used to investigate NO3- assimilation and N cycling in the summertime period of phytoplankton growth, both today and in the past. However, recent studies indicate the significance of processes in other seasons for producing the annual cycle of N isotope changes. This study explores the impact of fall conditions on the 15N/14N (δ15N) and 18O/16O (δ18O) of NO3- and nitrite (NO2-) in the Pacific Antarctic Zone using depth profiles from late summer/fall of 2014. In the mixed layer, the δ15N and δ18O of NO3- + NO2- increase roughly equally, as expected for NO3- assimilation; however, the δ15N of NO3--only (measured after NO2- removal) increases more than does NO3--only δ18O. Differencing indicates that NO2- has an extremely low δ15N, often < -70‰ versus air. These observations are consistent with the expression of an equilibrium N isotope effect between NO3- and NO2-, likely due to enzymatic NO3--NO2- interconversion. Specifically, we propose reversibility of the nitrite oxidoreductase (NXR) enzyme of nitrite oxidizers that, having been entrained from the subsurface during late summer mixed layer deepening, are inhibited by light. Our interpretation suggests a role for NO3--NO2- interconversion where nitrifiers are transported into environments that discourage NO2- oxidation. This may apply to surface regions with upwelling, such as the summertime Antarctic. It may also apply to oxygen-deficient zones, where NXR-catalyzed interconversion may explain previously reported evidence of NO2- oxidation.

  17. Spreading layers in accreting objects: role of acoustic waves for angular momentum transport, mixing and thermodynamics

    CERN Document Server

    Philippov, Alexander A; Stone, James M

    2015-01-01

    Disk accretion at high rate onto a white dwarf or a neutron star has been suggested to result in the formation of a spreading layer (SL) - a belt-like structure on the object's surface, in which the accreted matter steadily spreads in the poleward (meridional) direction while spinning down. To assess its basic characteristics we perform two-dimensional hydrodynamic simulations of supersonic SLs in the relevant morphology with a simple prescription for cooling. We demonstrate that supersonic shear naturally present at the base of the SL inevitably drives sonic instability that gives rise to large scale acoustic modes governing the evolution of the SL. These modes dominate the transport of momentum and energy, which is intrinsically global and cannot be characterized via some form of local effective viscosity (e.g. $\\alpha$-viscosity). The global nature of the wave-driven transport should have important implications for triggering Type I X-ray bursts in low mass X-ray binaries. The nonlinear evolution of waves ...

  18. Homotopy analysis method for mixed convective boundary layer flow of a nanofluid over a vertical circular cylinder

    Directory of Open Access Journals (Sweden)

    Dinarvand Saeed

    2015-01-01

    Full Text Available This article deals with the study of the steady axisymmetric mixed convective boundary layer flow of a nanofluid over a vertical circular cylinder with prescribed external flow and surface temperature. By means of similarity transformation, the governing partial differential equations are reduced into highly non-linear ordinary differential equations. The resulting non-linear system has been solved analytically using an efficient technique namely homotopy analysis method (HAM. Expressions for velocity and temperature fields are developed in series form. In this study, three different types of nanoparticles are considered, namely alumina (, titania (, and copper ( with water as the base fluid. For copper-water nanofluid, graphical results are presented to describe the influence of the nanoparticle volume fraction on the velocity and temperature fields for the forced and mixed convection flows. Moreover, the features of the flow and heat transfer characteristics are analyzed and discussed for foregoing nanofluids. It is found that the skin friction coefficient and the heat transfer rate at the surface are highest for copper-water nanofluid compared to the alumina-water and titania-water nanofluids.

  19. Numerical analysis for supersonic turbulent mixing layers of different species gases. lst report. ; Mixing characteristics of uniform flows. Choonsoku ishu gas ranryu kongoso no suchi kaiseki. 1. ; Ichiyoryu no kongo tokusei

    Energy Technology Data Exchange (ETDEWEB)

    Nakano, S.; Ikegawa, M. (Hitachi Ltd., Tokyo (Japan))

    1990-07-25

    Flow field in which two supersonic turbulent flows with different species gases mix, was analyzed with a two-equation turbulence model and the mixing characteristics of 2 supersonic parallel flows were investigated by making the inlet flow condition of high speed gas constant and by ststematically changing the inlet flow condition of low speed gas. When mixing is carried out so that high speed gas is taken in the low speed gas, high spreading rate of the mixing layer is obtained and this tendency is emphasized markedly as the ratio such as velocity, density and pressure between low and high speed gases become small. The spreading of low mass ratio layer of low speed gas and that of low mass ratio layer of high speed gas are assymmetric and the spreading of the former is suppressed at the coindition where the latter expands. The tendency of developing rate of mixing layer to the correlating parameter in this calculation agreed well with results of visualized experiment. 14 refs., 10 figs., 3 tabs.

  20. Slow relaxation of the magnetization in non-linear optical active layered mixed metal oxalate chains.

    Science.gov (United States)

    Cariati, Elena; Ugo, Renato; Santoro, Giuseppe; Tordin, Elisa; Sorace, Lorenzo; Caneschi, Andrea; Sironi, Angelo; Macchi, Piero; Casati, Nicola

    2010-12-06

    New Co(II) members of the family of multifunctional materials of general formula [DAMS](4)[M(2)Co(C(2)O(4))(6)]·2DAMBA·2H(2)O (M(III) = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+)] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn(II), Mn(II), and Ni(II). This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS(+)] and the efficiency of the crystalline network which organizes [DAMS(+)] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties. In particular, the magnetic data of the Rh(III) derivative demonstrate that high spin octacoordinated Co(II) centers behave very similarly to the hexacoordinated Co(II) ones, being dominated by a large orbital contribution. The Cr(III) derivative is characterized by ferromagnetic Cr(III)-Co(II) interactions. Most relevantly, the Fe(III) compound is characterized by a moderate antiferromagnetic interaction between Fe(III) and Co(II), resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (τ(0) = 8.6 × 10(-11) s and ΔE = 21.4 K) and make this a candidate for the second oxalate-based single chain magnet (SCM) reported up to date, a property which in this case is coupled to the second order non linear optical (NLO) ones.

  1. Mixed sand and gravel beaches: accurate measurement of active layer depth and sediment transport volumes using PIT tagged tracer pebbles

    Science.gov (United States)

    Holland, A.; Moses, C.; Sear, D. A.; Cope, S.

    2016-12-01

    As sediments containing significant gravel portions are increasingly used for beach replenishment projects globally, the total number of beaches classified as `mixed sand and gravel' (MSG) increases. Calculations for required replenishment sediment volumes usually assume a uniform layer of sediment transport across and along the beach, but research into active layer (AL) depth has shown variations both across shore and according to sediment size distribution. This study addresses the need for more accurate calculations of sediment transport volumes on MSG beaches by using more precise measurements of AL depth and width, and virtual velocity of tracer pebbles. Variations in AL depth were measured along three main profile lines (from MHWS to MLWN) at Eastoke, Hayling Island (Hampshire, UK). Passive Integrated Transponder (PIT) tagged pebbles were deployed in columns, and their new locations repeatedly surveyed with RFID technology. These data were combined with daily dGPS beach profiles and sediment sampling for detailed analysis of the influence of beach morphodynamics on sediment transport volumes. Data were collected over two consecutive winter seasons: 2014-15 (relatively calm, average wave height sandy lower foreshore reduced the AL to 10% of wave height in this area. The disparity in AL depth across the beach profile indicates that traditional models are not accurately representing bulk sediment transport on MSG beaches. It is anticipated that by improving model inputs, beach managers will be better able to predict necessary volumes and sediment grain size proportions of replenishment material for effective management of MSG beaches.

  2. Observations of Mixing Layer Heights from the Micropulse Lidar Network and Potential Implications for Regional and Global Models

    Science.gov (United States)

    Lewis, J. R.; Welton, E. J.; Hegarty, J. D.; Henderson, J.; McGrath-Spangler, E. L.; Scarino, A. J.; Berkoff, T.; Ferrare, R. A.; Stewart, S. A.; DeCola, P.

    2016-12-01

    Long-term, continuous measurements of the planetary boundary layer (PBL) height are rare, but necessary to ascertain its seasonal and diurnal changes. Autonomous ground-based lidar measurements from the NASA Micropulse Lidar Network (MPLNET) have the potential to contribute to our current knowledge of the PBL. MPLNET is a global network of micropulse lidars which has operated for over 16 years using a standard instrument and suite of processing algorithms. In this work, we investigate the daytime mixing layer height (MLH) determined from aerosol backscatter profiles using the wavelet covariance transform and a fuzzy-logic scheme. First, we evaluate simulations from the Weather Research and Forecasting (WRF) Model in the Washington D.C. - Baltimore, MD urban corridor during the July 2011 DISCOVER-AQ field campaign. In addition to MPLNET data, this field campaign utilizes data from field-deployed mini-Micropulse lidars, the CALIPSO satellite, and the NASA Langley Airborne High-Spectral Resolution Lidar. Next, we show a multi-year, multi-site comparison of MPLNET retrievals to PBL heights retrieved from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). We discuss differences between the modeled and observed quantities and the potential for future research.

  3. Direct numerical simulation of gaseous mixing layers laden with multicomponent-liquid drops: liquid-specific effects

    Science.gov (United States)

    Le Clercq, Patrick C.; Bellan, Josette

    2005-06-01

    A representation of multicomponent-liquid (MC-liquid) composition as a linear combination of two single-Gamma probability distribution functions (PDFs) is used to describe a large number of MC-liquid drops evaporating in a gas flow. The PDF, called the double-Gamma PDF, depends on the molar mass. The gas-phase conservation equations are written in an Eulerian frame and the drops are described in a Lagrangian frame. Gas conservation equations for mass, momentum, species and energy are combined with differential conservation equations for the first four moments of the gas-composition PDF and coupled to the perfect gas equation of state. Source terms in all conservation equations account for the gas/drop interaction. The drop governing equations encompass differential conservation statements for position, mass, momentum, energy and four moments of the liquid-composition PDF. Simulations are performed for a three-dimensional mixing layer whose lower stream is initially laden with drops colder than the surrounding gas. Initial perturbations excite the layer to promote the double pairing of its four initial spanwise vortices to an ultimate vortex. During the layer evolution, the drops heat and evaporate. The results address the layer evolution, and the state of the gas and drops when layers reach a momentum-thickness maximum past the double vortex pairing. Of interest is the influence of the liquid composition on the development of the vortical features of the flow, on the vortical state reached after the second pairing, and on the gas temperature and composition. The MC-liquid simulations are initiated with a single-Gamma PDF composition so as to explore the development of the double-Gamma PDF. Examination of equivalent simulations with n-decane, diesel and three kerosenes as the liquid, permits assessment of the single-species versus the MC-liquid aspect, and of mixture composition specific effects. Global layer growth and global rotational characteristics are

  4. Driving Interconnected Networks to Supercriticality

    Directory of Open Access Journals (Sweden)

    Filippo Radicchi

    2014-04-01

    Full Text Available Networks in the real world do not exist as isolated entities, but they are often part of more complicated structures composed of many interconnected network layers. Recent studies have shown that such mutual dependence makes real networked systems potentially exposed to atypical structural and dynamical behaviors, and thus there is an urgent necessity to better understand the mechanisms at the basis of these anomalies. Previous research has mainly focused on the emergence of atypical properties in relation to the moments of the intra- and interlayer degree distributions. In this paper, we show that an additional ingredient plays a fundamental role for the possible scenario that an interconnected network can face: the correlation between intra- and interlayer degrees. For sufficiently high amounts of correlation, an interconnected network can be tuned, by varying the moments of the intra- and interlayer degree distributions, in distinct topological and dynamical regimes. When instead the correlation between intra- and interlayer degrees is lower than a critical value, the system enters in a supercritical regime where dynamical and topological phases are no longer distinguishable.

  5. Statistical mechanical description of supercritical fluid extraction and retrograde condensation

    Science.gov (United States)

    Park, S. J.; Kwak, T. Y.; Mansoori, G. A.

    1987-07-01

    The phenomena of supercritical fluid extraction (SFE) and its reverse effect, which is known as retrograde condensation (RC), have found new and important applications in industrial separation of chemical compounds and recovery and processing of natural products and fossil fuels. Full-scale industrial utilization of SFE/RC processes requires knowledge about thermodynamic and transport characteristics of the asymmetric mixtures involved and the development of predictive modeling and correlation techniques for performance of the SFE/RC system under consideration. In this report, through the application of statistical mechanical techniques, the reasons for the lack of accuracy of existing predictive approaches are described and they are improved. It is demonstrated that these techniques also allow us to study the effect of mixed supercritical solvents on the solubility of heavy solutes (solids) at different compositions of the solvents, pressures, and temperatures. Fluid phase equilibrium algorithms based on the conformal solution van der Waals mixing rules and different equations of state are presented for the prediction of solubilities of heavy liquid in supercritical gases. It is shown that the Peng-Robinson equation of state based on conformal solution theory can predict solubilites of heavy liquid in supercritical gases more accurately than the van der Waals and Redlich-Kwong equations of state.

  6. Seasonal development of mixed layer depths, nutrients, chlorophyll and Calanus finmarchicus in the Norwegian Sea - A basin-scale habitat comparison

    KAUST Repository

    Bagøien, Espen

    2012-09-01

    Seasonal patterns for mixed layer depths, nutrients, chlorophyll, and Calanus finmarchicus in different water masses between 62 and 70°N of the Norwegian Sea were compared using spatiotemporally aggregated basin-scale data. Norwegian Coastal Water was stratified throughout the year due to a low-salinity upper layer. The winter mixed layer depth was typically about 50-60m, and the spring phytoplankton bloom peaked in late April. In Atlantic and Arctic Waters the winter mixed layer depths were much greater, typically about 175-250m. Due to the requirement for thermal stratification, the phytoplankton build-ups there were slower and the peaks were delayed until late May. Seasonal development of mixed layer depths, nutrient consumption and chlorophyll was similar for the Atlantic and Arctic areas. Young Calanus copepodites of the first new generation in Coastal Water peaked in early May, preceding the peak in Atlantic Water by about 2weeks, and that in Arctic Water by about 6weeks. While the young G 1 cohorts in Coastal and Atlantic waters coincided rather well in time with the phytoplankton blooms, the timing of the cohort in Arctic Water was delayed compared to the phytoplankton. Two or more Calanus generations in Coastal Water, and two generations in Atlantic Water were observed. Only one generation was found in Arctic Water, where scarce autumn data precludes evaluation of a possible second generation. © 2012 Elsevier Ltd.

  7. Structure and deuterium retention properties of tungsten layers deposited by plasma sputtering in a mixed atmosphere of D2 and He

    Science.gov (United States)

    Tang, X. H.; Shi, L. Q.; O'Connor, D. J.; King, B.

    2014-03-01

    The influence of the deposition conditions on the surface morphology, crystal structure and deuterium retention of the tungsten layers formed by rf magnetron plasma sputtering in mixed atmosphere of D2, He and Ar, has been carried out. Helium containing deuterated tungsten layers (named He-WDx) on Cu/Si substrate demonstrate serious film damages with zones of cracks, fractures, flaking-off and large surface blisters. However, these kinds of damages do not happen on the He-WDx layers performed on mechanically polished polycrystalline Cu substrates because of larger surface roughness of the substrates. The crystal structure of the W layer greatly changes with the additional He in the layer, and large amounts of defects resulting in lattice expansion and X-diffraction peak broadening were produced in the W crystal. He in the W layer has direct impacts on D retention. Both D and He concentrations vary simultaneously with He fraction, attached negative bias and substrate temperature.

  8. Corrosion in supercritical fluids

    Energy Technology Data Exchange (ETDEWEB)

    Propp, W.A.; Carleson, T.E.; Wai, Chen M.; Taylor, P.R.; Daehling, K.W.; Huang, Shaoping; Abdel-Latif, M.

    1996-05-01

    Integrated studies were carried out in the areas of corrosion, thermodynamic modeling, and electrochemistry under pressure and temperature conditions appropriate for potential applications of supercritical fluid (SCF) extractive metallurgy. Carbon dioxide and water were the primary fluids studied. Modifiers were used in some tests; these consisted of 1 wt% water and 10 wt% methanol for carbon dioxide and of sulfuric acid, sodium sulfate, ammonium sulfate, and ammonium nitrate at concentrations ranging from 0.00517 to 0.010 M for the aqueous fluids. The materials studied were Types 304 and 316 (UNS S30400 and S31600) stainless steel, iron, and AISI-SAE 1080 (UNS G10800) carbon steel. The thermodynamic modeling consisted of development of a personal computer-based program for generating Pourbaix diagrams at supercritical conditions in aqueous systems. As part of the model, a general method for extrapolating entropies and related thermodynamic properties from ambient to SCF conditions was developed. The experimental work was used as a tool to evaluate the predictions of the model for these systems. The model predicted a general loss of passivation in iron-based alloys at SCF conditions that was consistent with experimentally measured corrosion rates and open circuit potentials. For carbon-dioxide-based SCFs, measured corrosion rates were low, indicating that carbon steel would be suitable for use with unmodified carbon dioxide, while Type 304 stainless steel would be suitable for use with water or methanol as modifiers.

  9. Atomic-Resolution Visualization of Distinctive Chemical Mixing Behavior of Ni, Co and Mn with Li in Layered Lithium Transition-Metal Oxide Cathode Materials

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Pengfei [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Zheng, Jianming [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lv, Dongping [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wei, Yi [Peking Univ., Beijing (China); Zheng, Jiaxin [Peking Univ., Beijing (China); Wang, Zhiguo [Univ. of Electronic Science and Technology of China, Chengdu (China); Kuppan, Saravanan [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Yu, Jianguo [Idaho National Lab. (INL), Idaho Falls, ID (United States); Luo, Langli [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Edwards, Danny J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Olszta, Matthew J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Amine, Khalil [Argonne National Lab. (ANL), Argonne, IL (United States); Liu, Jun [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Xiao, Jie [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Pan, Feng [Peking Univ., Beijing (China); Chen, Guoying [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Zhang, Jiguang [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wang, Chong M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2015-07-06

    Capacity and voltage fading of layer structured cathode based on lithium transition metal oxide is closely related to the lattice position and migration behavior of the transition metal ions. However, it is scarcely clear about the behavior of each of these transition metal ions. We report direct atomic resolution visualization of interatomic layer mixing of transition metal (Ni, Co, Mn) and lithium ions in layer structured oxide cathodes for lithium ion batteries. Using chemical imaging with aberration corrected scanning transmission electron microscope (STEM) and DFT calculations, we discovered that in the layered cathodes, Mn and Co tend to reside almost exclusively at the lattice site of transition metal (TM) layer in the structure or little interlayer mixing with Li. In contrast, Ni shows high degree of interlayer mixing with Li. The fraction of Ni ions reside in the Li layer followed a near linear dependence on total Ni concentration before reaching saturation. The observed distinctively different behavior of Ni with respect to Co and Mn provides new insights on both capacity and voltage fade in this class of cathode materials based on lithium and TM oxides, therefore providing scientific basis for selective tailoring of oxide cathode materials for enhanced performance.

  10. The open-ocean sensible heat flux and its significance for Arctic boundary layer mixing during early fall

    Science.gov (United States)

    Ganeshan, Manisha; Wu, Dong L.

    2016-10-01

    The increasing ice-free area during late summer has transformed the Arctic to a climate system with more dynamic boundary layer (BL) clouds and seasonal sea ice growth. The open-ocean sensible heat flux, a crucial mechanism of excessive ocean heat loss to the atmosphere during the fall freeze season, is speculated to play an important role in the recently observed cloud cover increase and BL instability. However, lack of observations and understanding of the resilience of the proposed mechanisms, especially in relation to meteorological and interannual variability, has left a poorly constrained BL parameterization scheme in Arctic climate models. In this study, we use multi-year Japanese cruise-ship observations from R/V Mirai over the open Arctic Ocean to characterize the surface sensible heat flux (SSHF) during early fall and investigate its contribution to BL turbulence. It is found that mixing by SSHF is favored during episodes of high surface wind speed and is also influenced by the prevailing cloud regime. The deepest BLs and maximum ocean-atmosphere temperature difference are observed during cold air advection (associated with the stratocumulus regime), yet, contrary to previous speculation, the efficiency of sensible heat exchange is low. On the other hand, the SSHF contributes significantly to BL mixing during the uplift (low pressure) followed by the highly stable (stratus) regime. Overall, it can explain ˜ 10 % of the open-ocean BL height variability, whereas cloud-driven (moisture and radiative) mechanisms appear to be the other dominant source of convective turbulence. Nevertheless, there is strong interannual variability in the relationship between the SSHF and the BL height which can be intensified by the changing occurrence of Arctic climate patterns, such as positive surface wind speed anomalies and more frequent conditions of uplift. This study highlights the need for comprehensive BL observations like the R/V Mirai for better understanding and

  11. The Open-Ocean Sensible Heat Flux and Its Significance for Arctic Boundary Layer Mixing During Early Fall

    Science.gov (United States)

    Ganeshan, Manisha; Wu, Dongliang

    2016-01-01

    The increasing ice-free area during late summer has transformed the Arctic to a climate system with more dynamic boundary layer (BL) clouds and seasonal sea ice growth. The open-ocean sensible heat flux, a crucial mechanism of excessive ocean heat loss to the atmosphere during the fall freeze season, is speculated to play an important role in the recently observed cloud cover increase and BL instability. However, lack of observations and understanding of the resilience of the proposed mechanisms, especially in relation to meteorological and interannual variability, has left a poorly constrained BL parameterization scheme in Arctic climate models. In this study, we use multiyear Japanese cruise-ship observations from RV Mirai over the open Arctic Ocean to characterize the surface sensible heat flux (SSHF) during early fall and investigate its contribution to BL turbulence. It is found that mixing by SSHF is favored during episodes of high surface wind speed and is also influenced by the prevailing cloud regime. The deepest BLs and maximum ocean-atmosphere temperature difference are observed during cold air advection (associated with the stratocumulus regime), yet, contrary to previous speculation, the efficiency of sensible heat exchange is low. On the other hand, the SSHF contributes significantly to BL mixing during the uplift (low pressure) followed by the highly stable (stratus) regime. Overall, it can explain 10 of the open ocean BL height variability, whereas cloud-driven (moisture and radiative) mechanisms appear to be the other dominant source of convective turbulence. Nevertheless, there is strong interannual variability in the relationship between the SSHF and the BL height which can be intensified by the changing occurrence of Arctic climate patterns, such as positive surface wind speed anomalies and more frequent conditions of uplift. This study highlights the need for comprehensive BL observations like the RV Mirai for better understanding and

  12. Evolution of anthropogenic pollution at the top of the regional mixed layer in the central Mexico plateau

    Science.gov (United States)

    Baumgardner, D.; Grutter, M.; Allan, J.; Ochoa, C.; Rappenglueck, B.; Russell, L. M.; Arnott, P.

    2009-01-01

    The concentrations of gases and properties of aerosol particles have been measured at the mountain site of Altzomoni approximately equidistant from Mexico City, Puebla and Cuernavaca, at an altitude of 4010 m. At this location there is a diurnal transition from local to regional mixed layer air whose properties depend on prevailing winds and larger scale circulation. Three days during March 2006 have been evaluated during which time the synoptic scale air flow was from the east, southeast and southwest. In general the properties of gases and particles were similar when the regional mixed layer (RML) was below the research site, regardless of the direction of flow. When the RML reached the site, the highest concentrations of CO, O3 and aerosol particles were from the east, decreasing as the flow shifted to the southeast then to the southwest. The maximum concentration of condensation nuclei (CN) was greater than 25×10-3 when winds were from the east. The highest mass concentrations of organic matter (OM), sulfate (SO4-), and Nitrate (NO3+ were 80, 4 and 8 μg m-3, at standard temperature and pressure in air from the east. The mass concentration of OM in the RML was greater than 70% of the total mass, regardless of the air mass origin. This compares to less than the 60% that has been reported for Mexico City. At night, the mass fraction of sulfate went up by a factor of ten from the daytime value when air arrived from the east. The relationship between the CO and OM suggests that the majority of the daytime OM is from biomass burning and at night it is from wood burning. Whereas the maximum CO at Altzomoni, 0.35 ppm, was approximately one tenth of the CO measured at the same time in the center of Mexico City, the maximum O3 of 120 ppb was approximately the same as in the city. The maximum nighttime values of O3 was 60 ppb, indicating the presence of residual pollution. From these results we conclude that even though Mexico City is the second most populated city in

  13. Evolution of Anthropogenic Pollution at the Top of the Regional Mixed Layer of the Central Mexico Plateau

    Science.gov (United States)

    Baumgardner, D.; Grutter, M.; Allan, J.; Ochoa, C.; Rappenglueck, B.; Russell, L. M.

    2009-04-01

    The concentrations of gases and properties of aerosol particles have been measured at the mountain site of Altzomoni approximately equidistant from Mexico City, Puebla and Cuernavaca, at an altitude of 4010 m. At this location there is a diurnal transition from local to regional mixed layer air whose properties depend on prevailing winds and larger scale circulation. Three days during March, 2006 have been evaluated during which time the synoptic scale air flow was from the east, southeast and southwest. In general the properties of gases and particles were similar when the regional mixed layer (RML) was below the research site, regardless of the direction of flow. When the RML reached the site, the highest concentrations of CO, O3 and aerosol particles were from the east, decreasing as the flow shifted to the southeast then to the southwest. The maximum concentration of condensation nuclei (CN) was greater than 25,000 cm-3 when winds were from the east. The highest mass concentrations of organic matter (OM), sulfate (SO4--), and Nitrate (NO3+) were 80, 4 and 8 μg m-3, at standard temperature and pressure in air from the east. The mass concentration of OM in the RML was greater than 70% of the total mass, regardless of the air mass origin. This compares to less than the 60% that has been reported for Mexico City. At night, the mass fraction of sulfate went up by a factor of ten from the daytime value when air arrived from the east. The relationship between the CO and OM suggests that the majority of the daytime OM is from biomass burning and at night it is from wood burning. Whereas the maximum CO at Altzomoni, 0.35 ppm, was approximately one tenth of the CO measured at the same time in the center of Mexico City, the maximum O3 of 120 ppb was approximately the same as in the city. The nighttime values of O3 was 60 ppb, indicating the presence of residual pollution. From these results we conclude that even though Mexico City is the second most populated city in the

  14. Formation of stable nanocomposite clays from small peptides reacted with montmorillonite and illite-smectite mixed layer clays

    Science.gov (United States)

    Block, K. A.; Katz, A.; LeBlanc, J.; Peña, S.; Gottlieb, P.

    2015-12-01

    Understanding how organic compounds interact with clay minerals and which functional groups result in the strongest bonds is pivotal to achieving a better understanding of how mineral composition affects the residence time of carbon and nitrogen in soils. In this work, we describe how small peptides derived from tryptone casein digest are dissolved and suspended with clay minerals to examine the nature of OM adsorption to mineral surfaces and the resulting effect on clay mineral structure. XRD analyses indicate that peptides intercalation results in expansion of the d001 spacing of montmorillonite (Mt) and the smectite component of a 70-30 illite-smectite mixed layer clay (I-S) and poorer crystallinity overall as a result of exfoliation of tactoids. Peptide adsorption is concentration-dependent, however, surface adsorption appears to mediate interlayer adsorption in Mt reaching a maximum of 16% of the mass of the organoclay complex, indicating that at a critical concentration, peptide intercalation will supersede surface adsorption resulting in a more stable attachment. In I-S the degree of surface adsorption and intercalation is proportional to concentration, however, surface adsorption is not a priming mechanism for interlayer adsorption. Thermogravimetric analysis of the organoclay complexes determined by TGA coupled to GC-MS indicate that the most prominent product species measured was 1-(1-Trimethylsiloxyethenyl)-3-trimethylsiloxy-benzene, likely from tryptophan monomer decomposition. The compound was detected over a broad temperature range, greater than 300 oC, during pyrolysis and suggests a carbon-silicon covalent bond formed between the peptide and tetrahedral layers in the clay. An additional silicon-bearing VOC detected at lower pyrolysis temperature by GC was N,N-Diethyl-1-(trimethylsilyl)-9,10-didehydroergoline-8-carboxamide, likely derived from a lysine-bearing peptide derivative. We hypothesize that hydrophobic (non-ionic) peptides react with silanol

  15. Effect of Strong Acid Functional Groups on Electrode Rise Potential in Capacitive Mixing by Double Layer Expansion

    KAUST Repository

    Hatzell, Marta C.

    2014-12-02

    © 2014 American Chemical Society. The amount of salinity-gradient energy that can be obtained through capacitive mixing based on double layer expansion depends on the extent the electric double layer (EDL) is altered in a low salt concentration (LC) electrolyte (e.g., river water). We show that the electrode-rise potential, which is a measure of the EDL perturbation process, was significantly (P = 10-5) correlated to the concentration of strong acid surface functional groups using five types of activated carbon. Electrodes with the lowest concentration of strong acids (0.05 mmol g-1) had a positive rise potential of 59 ± 4 mV in the LC solution, whereas the carbon with the highest concentration (0.36 mmol g-1) had a negative rise potential (-31 ± 5 mV). Chemical oxidation of a carbon (YP50) using nitric acid decreased the electrode rise potential from 46 ± 2 mV (unaltered) to -6 ± 0.5 mV (oxidized), producing a whole cell potential (53 ± 1.7 mV) that was 4.4 times larger than that obtained with identical electrode materials (from 12 ± 1 mV). Changes in the EDL were linked to the behavior of specific ions in a LC solution using molecular dynamics and metadynamics simulations. The EDL expanded in the LC solution when a carbon surface (pristine graphene) lacked strong acid functional groups, producing a positive-rise potential at the electrode. In contrast, the EDL was compressed for an oxidized surface (graphene oxide), producing a negative-rise electrode potential. These results established the linkage between rise potentials and specific surface functional groups (strong acids) and demonstrated on a molecular scale changes in the EDL using oxidized or pristine carbons.

  16. ENGINEERING BULLETIN: SUPERCRITICAL WATER OXIDATION

    Science.gov (United States)

    This engineering bulletin presents a description and status of supercritical water oxidation technology, a summary of recent performance tests, and the current applicability of this emerging technology. This information is provided to assist remedial project managers, contractors...

  17. Characterization of Organic Thin Film Solar Cells of PCDTBT : PC71BM Prepared by Different Mixing Ratio and Effect of Hole Transport Layer

    Directory of Open Access Journals (Sweden)

    Vijay Srinivasan Murugesan

    2015-01-01

    Full Text Available The organic thin film solar cells (OTFSCs have been successfully fabricated using PCDTBT : PC71BM with different mixing ratios (1 : 1 to 1 : 8 and the influence of hole transport layer thickness (PEDOT : PSS. The active layers with different mixing ratios of PCDTBT : PC71BM have been fabricated using o-dichlorobenzene (o-DCB. The surface morphology of the active layers and PEDOT : PSS layer with different thicknesses were characterized by AFM analysis. Here, we report that the OTFSCs with high performance have been optimized with 1 : 4 ratios of PCDTBT : PC71BM. The power conversion efficiency (PCE = 5.17% of the solar cells was significantly improved by changing thickness of PEDOT : PSS layer. The thickness of the PEDOT : PSS layer was found to be of significant importance; the thickness of the PEDOT : PSS layer at 45 nm (higher spin speed 5000 rpm shows higher short circuit current density (Jsc and lower series resistance (Rs and higher PCE.

  18. ASSESSING THE IMPACT OF WIND SPEED AND MIXING-LAYER HEIGHT ON AIR QUALITY IN KRAKOW (POLAND IN THE YEARS 2014-2015

    Directory of Open Access Journals (Sweden)

    Robert OLENIACZ

    2016-05-01

    Full Text Available The paper discusses the role of wind speed and mixing-layer height in shaping the levels of pollutant concentrations in the air of Krakow (Southern Poland. The hourly averaged measurements of concentrations of selected air pollutants and wind speed values from the period of 2014-2015, recorded at two of the air quality monitoring stations within Krakow (both industrial and urban background were used for this purpose. Temporal variability of mixing-layer height in the area of the monitoring stations was determined using numerical modelling with the CALMET model and the measurements derived from, i.a., two upper air stations. It was found that wind speed and mixing-layer height are in at least moderate agreement with the concentration values for some pollutants. For PM10, PM2.5, NO2, NOx, CO and C6H6 correlation coefficient is of negative value, which indicates that the low wind speed and low mixing-layer height may be the dominant reason for elevated concentrations of these substances in the air, especially in the winter months. Moderate but positive correlation was found between O3 concentrations and analysed meteorological parameters, proving that the availability of appropriate precursors and their inflow from the neighbouring areas have an important role in the formation of tropospheric ozone. On the other hand, in case of SO2, a weak both positive and negative correlation coefficient was obtained, depending on the period and location of the station concerned.

  19. Bacterial communities of surface mixed layer in the Pacific sector of the western Arctic Ocean during sea-ice melting.

    Science.gov (United States)

    Han, Dukki; Kang, Ilnam; Ha, Ho Kyung; Kim, Hyun Cheol; Kim, Ok-Sun; Lee, Bang Yong; Cho, Jang-Cheon; Hur, Hor-Gil; Lee, Yoo Kyung

    2014-01-01

    From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1) surface seawater, (2) ice core, and (3) melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting.

  20. Bacterial communities of surface mixed layer in the Pacific sector of the western Arctic Ocean during sea-ice melting.

    Directory of Open Access Journals (Sweden)

    Dukki Han

    Full Text Available From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1 surface seawater, (2 ice core, and (3 melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting.

  1. Application of exciplex in the fabrication of white organic light emitting devices with mixed fluorescent and phosphorescent layers

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Dan; Duan, Yahui; Yang, Yongqiang [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science & Engineering, Jilin University, Changchun 130012 (China); Hu, Nan [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science & Engineering, Jilin University, Changchun 130012 (China); Changchun University of Science and Technology, Changchun 130012 (China); Wang, Xiao [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science & Engineering, Jilin University, Changchun 130012 (China); Sun, Fengbo [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science & Engineering, Jilin University, Changchun 130012 (China); Changchun University of Science and Technology, Changchun 130012 (China); Duan, Yu, E-mail: duanyu@jlu.edu.cn [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science & Engineering, Jilin University, Changchun 130012 (China)

    2015-10-15

    In this study, a highly efficient fluorescent/phosphorescent white organic light-emitting device (WOLED) was fabricated using exciplex light emission. The hole-transport material 4,4',4''-tris(N-carbazolyl)triphenylamine (TCTA), and electron-transport material, 4,7-diphenyl-1,10-phenanthroline (Bphen), were mixed to afford a blue-emitting exciplex. The WOLED was fabricated with a yellow phosphorescent dye, Ir(III) bis(4-phenylthieno [3,2-c] pyridinato-N,C{sup 2'}) acetylacetonate (PO-01), combined with the exciplex. In this structure, the energy can be efficiently transferred from the blend layer to the yellow phosphorescent dye, thus improving the efficiency of the utilization of the triplet exciton. The maximum power efficiency of the WOLED reached a value 9.03 lm/W with an external quantum efficiency of 4.3%. The Commission Internationale de I'Eclairage (CIE) color coordinates (x,y) of the device were from (0.39, 0.45) to (0.27, 0.31), with a voltage range of 4–9 V. - Highlights: • An exciplex/phosphorescence hybrid white OLED was fabricated for the first time with blue/orange complementary emitters. • By using exciplex as the blue emitter, non-radiative triplet-states on the exciplex can be harvested for light-emission by transferring them to low triplet-state phosphors.

  2. The three-dimensional evolution of a plane mixing layer. Part 1: The Kelvin-Helmholtz roll-up

    Science.gov (United States)

    Rogers, Michael M.; Moser, Robert D.

    1991-01-01

    The Kelvin Helmholtz roll up of three dimensional, temporally evolving, plane mixing layers were simulated numerically. All simulations were begun from a few low wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity profile. The spanwise disturbance wavelength was taken to be less than or equal to the streamwise wavelength associated with the Kelvin Helmholtz roll up. A standard set of clean structures develop in most of the simulations. The spanwise vorticity rolls up into a corrugated spanwise roller, with vortex stretching creating strong spanwise vorticity in a cup shaped region at the vends of the roller. Predominantly streamwise rib vortices develop in the braid region between the rollers. For sufficiently strong initial three dimensional disturbances, these ribs collapse into compact axisymmetric vortices. The rib vortex lines connect to neighboring ribs and are kinked in the opposite direction of the roller vortex lines. Because of this, these two sets of vortex lines remain distinct. For certain initial conditions, persistent ribs do not develop. In such cases the development of significant three dimensionality is delayed. When the initial three dimensional disturbance energy is about equal to, or less than, the two dimensional fundamental disturbance energy, the evolution of the three dimensional disturbance is nearly linear (with respect to the mean and the two dimensional disturbances), at least until the first Kelvin Helmholtz roll up is completed.

  3. From mixed to three-layer core/shell PtCu nanoparticles: ligand-induced surface segregation to enhance electrocatalytic activity.

    Science.gov (United States)

    Dai, Changqing; Yang, Yang; Zhao, Zheng; Fisher, Adrian; Liu, Zhiping; Cheng, Daojian

    2017-07-06

    Core-shell segregated bimetallic nanoparticles (NPs) exhibit increased enhanced catalytic performance compared to that of mixed bimetallic NPs. Here, we report a simple, yet efficient, one-pot synthetic strategy to synthesize uniform three-layer core/shell PtCu NPs by adding benzyl ether (BE) in the synthesis process of mixed PtCu NPs. In comparison with commercial Pt/C and also mixed PtCu NPs, the three-layer core/shell PtCu NPs exhibit superior activity in catalyzing the oxygen reduction reaction (ORR), formic acid oxidation reaction (FAOR), methanol oxidation reaction (MOR), and ethanol oxidation reaction (EOR), mainly due to the ligand (BE)-induced surface segregation of Pt on the surface of the NPs.

  4. Supercritical fluid technology

    Energy Technology Data Exchange (ETDEWEB)

    Penninger, J.M.L.; McHugh, M.A.; Radosz, M.; Krukonis, V.J.

    1985-01-01

    This book presents the state-of-the-art in the science and technology of supercritical fluid (scf) processing. Current research as described in the book, focuses on developments in equations of state for binary and multicomponent mixtures (including polymer solutions), solubility measurements at near-critical conditions, measurements of critical properties of binary mixtures and their correlation with equations of state. Progress in thermodynamics, coupled with advances in the design and construction of high pressure equipment, has opened up a wide avenue of commercial application (e.g. decaffeination of coffee beans, extractions of flavours and spices, purification of pharmaceutical products, separations of polymeric materials, deodorization and deacidification of vegetable oils, fractionation of fatty acids, coal liquefaction, wood delignitication, etc.)

  5. Tensiometry and dilational rheology of mixed β-lactoglobulin/ionic surfactant adsorption layers at water/air and water/hexane interfaces.

    Science.gov (United States)

    Dan, Abhijit; Gochev, Georgi; Miller, Reinhard

    2015-07-01

    Oscillating drop tensiometry was applied to study adsorbed interfacial layers at water/air and water/hexane interfaces formed from mixed solutions of β-lactoglobulin (BLG, 1 μM in 10 mM buffer, pH 7 - negative net charge) and the anionic surfactant SDS or the cationic DoTAB. The interfacial pressure Π and the dilational viscoelasticity modulus |E| of the mixed layers were measured for mixtures of varying surfactant concentrations. The double capillary technique was employed which enables exchange of the protein solution in the drop bulk by surfactant solution (sequential adsorption) or by pure buffer (washing out). The first protocol allows probing the influence of the surfactant on a pre-adsorbed protein layer thus studying the protein/surfactant interactions at the interface. The second protocol gives access to the residual values of Π and |E| measured after the washing out procedure thus bringing information about the process of protein desorption. The DoTAB/BLG complexes exhibit higher surface activity and higher resistance to desorption in comparison with those for the SDS/BLG complexes due to hydrophobization via electrostatic binding of surfactant molecules. The neutral DoTAB/BLG complexes achieve maximum elastic response of the mixed layer. Mixed BLG/surfactant layers at the water/oil interface are found to reach higher surface pressure and lower maximum dilational elasticity than those at the water/air surface. The sequential adsorption mode experiments and the desorption study reveal that binding of DoTAB to pre-adsorbed BLG globules is somehow restricted at the water/air surface in comparison with the case of complex formation in the solution bulk and subsequently adsorbed at the water/air surface. Maximum elasticity is achieved with washed out layers obtained after simultaneous adsorption, i.e. isolation of the most surface active DoTAB/BLG complex. These specific effects are much less pronounced at the W/H interface.

  6. The impact of tidal mixing at the Kuril Straits on the North Pacific: Part 2, Thermohaline adjustment of the intermediate layer

    Science.gov (United States)

    Toyoda, T.; Nakamura, T.; Ishikawa, Y.; Awaji, T.

    2003-04-01

    Recent studies show the importance of strong mixing at the Kuril Straits in freshning the intermediate layer to supply the low salinity water required for the production of the North Pacific Intermediate Water (NPIW) which is distributed over the entire subtropical gyre [Talley, 1991]. Nakamura et al.(2000; 2003) indicate that the strong vertical mixing is driven by a swift tidal flow and suggest that it has the ability to change the fluxes of potential vorticity (PV) and other water properties from the Okhotsk Sea to the North Pacific. Such an effect of tidal mixing at the western boundary is expected to affect the subarctic circulation based on the ventilated thermocline theory [Pedlosky, 1996], as well as the subsurface circulation in the subtropical region. In order to assess the impacts of tidal mixing at the Kurils on the circulation of the North Pacifc, a set of experiments are performed using a global ocean general circulation model. The Okhotsk Sea water flowing into the intermediate layer of the North Pacific becomes colder and fresher at the Kurils by strong vertical mixing. This enhances the supply of low PV water to the North Pacific intermediate layer, particulalrly in spring. Our analysis shows that the dynamical adjustment to the western boundary mixing is conducted by both Kelvin and Rossby waves of 2nd and higher modes. The Kelvin waves propagate along the coast against the Kuroshio current, and split into two components: one propagating along the equator and the other passing through the Indonesian Archipelago. On the other hands, since the higher-mode Rossby waves are affected by the mean flow field, the waves move eastward. This feature differs from the classical thermohaline adjustment proccess of the deep layer (e.g., Kawase 1987), which takes into account the role of Kelvin waves alone in the eastward spreading. The propagation of both types of waves significantly modifies the circulation of the North Pacific intermediate layer

  7. Processing of polyolefin blends in supercritical propane solution

    Science.gov (United States)

    Han, Suh Joon

    New polymer blending methods are developed and studied by processing polyolefins in supercritical propane in this research. Polypropylene and ethylene copolymers were dissolved in supercritical propane, and processed via various paths and reactions, i.e., RESS (rapid expansion of supercritical solution), ICSS (isobaric crystallization from supercritical solution), and thermoplastic vulcanizate (TPV) formation. Each process resulted in a unique morphology of polyolefin blends. The effect of polyolefin microstructure on the solution behavior in supercritical propane was investigated, and the relationship between the morphology of the polyolefin blends and processing paths in supercritical propane solutions was established. To understand the thermodynamic properties of polyolefins in bulk and solutions, the solubility parameter was estimated by measurement of the internal pressure from the experimental P-V-T data for polyolefins in the melt state. As the short chain branch content in the ethylene copolymers increased, the internal pressure decreased. The cloud-point pressures of binary polymer solutions in propane decreased as the extent of short chain branching increased in the ethylene copolymers. At the same degree of branching, the cloud-point pressure decreased slightly with increasing branch length. The cloud-point pressures of a ternary polymer solution in the pressure-temperature phase diagrams were higher than those of binary polymer solutions at the same composition (indicating poorer solubility). Microfibers and microparticles (10 ˜ 50 mum diameter) were precipitated from the RESS process while microcellular foams were obtained from the ICSS process. The phase domains of the ethylene-butene (EB) copolymer in the polypropylene from the RESS process were smaller for highly branched EB copolymer. The surface morphology of ethylene copolymers in the microcelluar foams was also changed by increasing the branch content from microparticles to a viscous layer. New

  8. Nanotechnology and supercritical fluids | Hamidreza | Journal of ...

    African Journals Online (AJOL)

    Several techniques have been proposed to produce nanomaterials using ... of the supercritical based techniques applied to the production of nanoparticles materials. Keywords: Supercritical fluids; Nanoparticles; SCF technology; RESS; SAS.

  9. Consistent Large-Eddy Simulation of a Temporal Mixing Layer Laden with Evaporating Drops. Part 2; A Posteriori Modelling

    Science.gov (United States)

    Leboissertier, Anthony; Okong'O, Nora; Bellan, Josette

    2005-01-01

    Large-eddy simulation (LES) is conducted of a three-dimensional temporal mixing layer whose lower stream is initially laden with liquid drops which may evaporate during the simulation. The gas-phase equations are written in an Eulerian frame for two perfect gas species (carrier gas and vapour emanating from the drops), while the liquid-phase equations are written in a Lagrangian frame. The effect of drop evaporation on the gas phase is considered through mass, species, momentum and energy source terms. The drop evolution is modelled using physical drops, or using computational drops to represent the physical drops. Simulations are performed using various LES models previously assessed on a database obtained from direct numerical simulations (DNS). These LES models are for: (i) the subgrid-scale (SGS) fluxes and (ii) the filtered source terms (FSTs) based on computational drops. The LES, which are compared to filtered-and-coarsened (FC) DNS results at the coarser LES grid, are conducted with 64 times fewer grid points than the DNS, and up to 64 times fewer computational than physical drops. It is found that both constant-coefficient and dynamic Smagorinsky SGS-flux models, though numerically stable, are overly dissipative and damp generated small-resolved-scale (SRS) turbulent structures. Although the global growth and mixing predictions of LES using Smagorinsky models are in good agreement with the FC-DNS, the spatial distributions of the drops differ significantly. In contrast, the constant-coefficient scale-similarity model and the dynamic gradient model perform well in predicting most flow features, with the latter model having the advantage of not requiring a priori calibration of the model coefficient. The ability of the dynamic models to determine the model coefficient during LES is found to be essential since the constant-coefficient gradient model, although more accurate than the Smagorinsky model, is not consistently numerically stable despite using DNS

  10. Evolution of anthropogenic pollution at the top of the regional mixed layer in the central Mexico plateau

    Directory of Open Access Journals (Sweden)

    D. Baumgardner

    2009-01-01

    Full Text Available The concentrations of gases and properties of aerosol particles have been measured at the mountain site of Altzomoni approximately equidistant from Mexico City, Puebla and Cuernavaca, at an altitude of 4010 m. At this location there is a diurnal transition from local to regional mixed layer air whose properties depend on prevailing winds and larger scale circulation. Three days during March 2006 have been evaluated during which time the synoptic scale air flow was from the east, southeast and southwest. In general the properties of gases and particles were similar when the regional mixed layer (RML was below the research site, regardless of the direction of flow. When the RML reached the site, the highest concentrations of CO, O3 and aerosol particles were from the east, decreasing as the flow shifted to the southeast then to the southwest. The maximum concentration of condensation nuclei (CN was greater than 25×10−3 when winds were from the east. The highest mass concentrations of organic matter (OM, sulfate (SO4, and Nitrate (NO3+ were 80, 4 and 8 μg m−3, at standard temperature and pressure in air from the east. The mass concentration of OM in the RML was greater than 70% of the total mass, regardless of the air mass origin. This compares to less than the 60% that has been reported for Mexico City.

    At night, the mass fraction of sulfate went up by a factor of ten from the daytime value when air arrived from the east. The relationship between the CO and OM suggests that the majority of the daytime OM is from biomass burning and at night it is from wood burning.

    Whereas the maximum CO at Altzomoni, 0.35 ppm, was approximately one tenth of the CO measured at the same time in the center of Mexico City, the maximum O3 of 120 ppb was approximately the same as in the city. The maximum nighttime values of O3 was 60 ppb

  11. OCR - The 3 Layered Approach for Classification and Identification of Telugu Hand Written Mixed Consonants and Conjunct Consonants by Using Advanced Fuzzy Logic Controller

    Directory of Open Access Journals (Sweden)

    B.Rama

    2016-04-01

    Full Text Available Optical Character recognition is the method of digi talization of hand and type written or printed text into machine-encoded form and is super fluity of the various applications of envision of human’s life. In present human life OCR has bee n successfully using in finance, legal, banking, health care and home need appliances. Ind ia is a multi cultural, literature and traditional scripted country. Telugu is the souther n Indian language, it is a syllabic language, symbol script represents a complete syllable and fo rmed with the conjunct mixed consonants in their representation. Recognition of mixed conjunct consonants is critical than the normal consonants, because of their variation in written s trokes, conjunct maxing with pre and post level of consonants. This paper proposes the layere d approach methodology to recognize the characters, conjunct consonants, mixed- conjunct co nsonants and expressed the efficient classification of the hand written and printed conj unct consonants. This paper implements the Advanced Fuzzy Logic system controller to take the text in the form of written or printed, collected the text images from the scanned file, di gital camera, Processing the Image with Examine the high intensity of images based on the q uality ration, Extract the image characters depends on the quality then check the character ori entation and alignment then to check the character thickness, base and print ration. The inp ut image characters can classify into the two ways, first way represents the normal consonants an d the second way represents conjunct consonants. Digitalized image text divided into th ree layers, the middle layer represents normal consonants and the top and bottom layer represents mixed conjunct consonants. Here recognition process starts from middle layer, and t hen it continues to check the top and bottom layers. The recognition process treat as conjunct c onsonants when it can detect any symbolic characters in top and

  12. Laminar mixed convection boundary layer flow induced by a permeable surface stretched with prescribed skin friction boundary conditions

    Directory of Open Access Journals (Sweden)

    Mohamed Ali

    2015-09-01

    Full Text Available The mixed laminar boundary layer flow and heat transfer on a permeable stretched surface moving with prescribed skin friction are studied. Three major cases, which correspond to complete similarity solutions, are considered. The cases are combinations of power law indices n and m representing temperature and skin friction distributions, respectively. The first case (n = 0, m = 0.5 corresponds to isothermal stretched surface with skin friction at the surface scales as x 1/4. The second case (n = 1, m = 1 is a linear temperature and skin friction distribution along the vertical stretched surface. The third case (n = −1, m = 0 represents inverse temperature variation along the surface with prescribed skin friction of the order of x −1/2. Similarity solutions are obtained for the surface stretched in a stagnant air with Prandtl number = 0.72. The effect of suction/injection velocity (fw and the buoyancy parameter (λ is studied in detail. The results show that the heat transfer coefficient along the surface is enhanced for assisting flow (λ > 0 at any value of fw for the first and second cases, while it is reduced for the third case. However, the opposite is true for the opposing flow (λ < 0. Furthermore, suction enhances the heat transfer coefficient, whereas injection degrades it at any fixed λ for the first and second prescribed skin friction boundary conditions, and the opposite is true for the third case.

  13. Detailed characteristics of drop-laden mixing layers: Large eddy simulation predictions compared to direct numerical simulation

    Science.gov (United States)

    Okong'o, Nora; Leboissetier, Anthony; Bellan, Josette

    2008-10-01

    Results are compared from direct numerical simulation (DNS) and large eddy simulation (LES) of a temporal mixing layer laden with evaporating drops to assess the ability of LES to reproduce detailed characteristics of DNS. The LES used computational drops, each of which represented eight physical drops, and a reduced flow field resolution using a grid spacing four times larger than that of the DNS. The LES also used models for the filtered source terms, which express the coupling of the drops with the flow, and for the unresolved subgrid-scale (SGS) fluxes of species mass, momentum, and enthalpy. The LESs were conducted using one of three different SGS-flux models: dynamic-coefficient gradient (GRD), dynamic-coefficient Smagorinsky (SMD), and constant-coefficient scale similarity (SSC). The comparison of the LES with the filtered-and-coarsened (FC) DNS considered detailed aspects of the flow that are of interest in ignition or full combustion. All LESs captured the largest-scale vortex, the global amount of vapor emanating from the drops, and the overall size distribution of the drops. All LESs tended to underpredict the global amount of irreversible entropy production (dissipation). The SMD model was found unable to capture either the global or local vorticity variation and had minimal small-scale activity in dynamic and thermodynamic variables compared to the FC-DNS. The SMD model was also deficient in predicting the spatial distribution of drops and of the dissipation. In contrast, the GRD and SSC models did mimic the small-scale activity of the FC-DNS and the spatial distribution of drops and of the dissipation. Therefore, the GRD and SSC models are recommended, while the SMD model seems inappropriate for combustion or other problems where the local activity must be predicted.

  14. Alteration of the size distributions and mixing states of black carbon through transport in the boundary layer in east Asia

    Science.gov (United States)

    Miyakawa, Takuma; Oshima, Naga; Taketani, Fumikazu; Komazaki, Yuichi; Yoshino, Ayako; Takami, Akinori; Kondo, Yutaka; Kanaya, Yugo

    2017-05-01

    Ground-based measurements of black carbon (BC) were performed near an industrial source region in the early summer of 2014 and at a remote island in Japan in the spring of 2015. Here, we report the temporal variations in the transport, size distributions, and mixing states of the BC-containing particles. These particles were characterized using a continuous soot monitoring system, a single particle soot photometer, and an aerosol chemical speciation monitor. The effects of aging on the growth of BC-containing particles were examined by comparing the ground-based observations between the near-source and remote island sites. Secondary formation of sulfate and organic aerosols strongly affected the increases in BC coating (i.e., enhancement of cloud condensation nuclei activity) with air mass aging from the source to the outflow regions. The effects of wet removal on BC microphysics were elucidated by classifying the continental outflow air masses depending on the enhancement ratios of BC to CO (ΔBC / ΔCO), which were used as an indicator of the transport efficiency of BC. It was found that ΔBC / ΔCO ratios were controlled mainly by the wet removal during transport in the planetary boundary layer (PBL) on the timescale of 1-2 days. The meteorological conditions and backward trajectory analyses suggested that air masses strongly affected by wet removal originated mainly from a region in southern China (20-35° N) in the spring of 2015. Removal of large and thickly coated BC-containing particles was detected in the air masses that were substantially affected by the wet removal in the PBL, as predicted by Köhler theory. The size and water solubility of BC-containing particles in the PBL can be altered by the wet removal as well as the condensation of non-BC materials.

  15. Dynamic transition in supercritical iron.

    Science.gov (United States)

    Fomin, Yu D; Ryzhov, V N; Tsiok, E N; Brazhkin, V V; Trachenko, K

    2014-11-26

    Recent advance in understanding the supercritical state posits the existence of a new line above the critical point separating two physically distinct states of matter: rigid liquid and non-rigid gas-like fluid. The location of this line, the Frenkel line, remains unknown for important real systems. Here, we map the Frenkel line on the phase diagram of supercritical iron using molecular dynamics simulations. On the basis of our data, we propose a general recipe to locate the Frenkel line for any system, the recipe that importantly does not involve system-specific detailed calculations and relies on the knowledge of the melting line only. We further discuss the relationship between the Frenkel line and the metal-insulator transition in supercritical liquid metals. Our results enable predicting the state of supercritical iron in several conditions of interest. In particular, we predict that liquid iron in the Jupiter core is in the "rigid liquid" state and is highly conducting. We finally analyse the evolution of iron conductivity in the core of smaller planets such as Earth and Venus as well as exoplanets: as planets cool off, the supercritical core undergoes the transition to the rigid-liquid conducting state at the Frenkel line.

  16. Supercritical Fluid Reactions for Coal Processing

    Energy Technology Data Exchange (ETDEWEB)

    Charles A. Eckert

    1997-11-01

    Exciting opportunities exist for the application of supercritical fluid (SCF) reactions for the pre-treatment of coal. Utilizing reactants which resemble the organic nitrogen containing components of coal, we developed a method to tailor chemical reactions in supercritical fluid solvents for the specific application of coal denitrogenation. The tautomeric equilibrium of a Schiff base was chosen as one model system and was investigated in supercritical ethane and cosolvent modified supercritical ethane. The Diels-Alder reaction of anthracene and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) was selected as a second model system, and it was investigated in supercritical carbon dioxide.

  17. Assessment of hurricane's effect on the upper mixed layer of the southwestern Mexican Pacific during ENSO 1997-1998: in situ and satellite observations

    Directory of Open Access Journals (Sweden)

    Raúl Aguirre-Gómez

    2015-03-01

    Full Text Available Using data from closely spaced CTD profiles and satellite imagery we investigated the effect of hurricane Rick on the sea surface temperature (SST and the upper mixed layer of the southwestern Mexican Pacific coast. Effects of ENSO 1997-1998 in this region are also discussed by analysing SST maps. Coincident hydrographic measurements were carried out during an oceanographic campaign over the area in November 1997. Results revealed an increment of SST between 3 to 4°C above the climatological mean temperature (25° ± 2°C, in the Mexican Tropical Pacific, during ENSO. In situ measurements show instabilities in the upper mixed layer after the pass of the hurricane in oceanic areas. Satellite and historical databases enabled interpretation and analyses of ENSO's effect on the southwest coast of Mexico.

  18. Efficient and Air-Stable Mixed-Cation Lead Mixed-Halide Perovskite Solar Cells with n-Doped Organic Electron Extraction Layers.

    Science.gov (United States)

    Wang, Zhiping; McMeekin, David P; Sakai, Nobuya; van Reenen, Stephan; Wojciechowski, Konrad; Patel, Jay B; Johnston, Michael B; Snaith, Henry J

    2017-02-01

    Air-stable doping of the n-type fullerene layer in an n-i-p planar heterojunction perovskite device is capable of enhancing device efficiency and improving device stability. Employing a (HC(NH2 )2 )0.83 Cs0.17 Pb(I0.6 Br0.4 )3 perovskite as the photoactive layer, glass-glass laminated devices are reported, which sustain 80% of their "post burn-in" efficiency over 3400 h under full sun illumination in ambient conditions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Grain size, morphometry and mineralogy of airborne input in the Canary basin: evidence of iron particle retention in the mixed layer

    Directory of Open Access Journals (Sweden)

    Alfredo Jaramillo-Vélez

    2016-09-01

    Full Text Available Aeolian dust plays an important role in climate and ocean processes. Particularly, Saharan dust deposition is of importance in the Canary Current due to its content of iron minerals, which are fertilizers of the ocean. In this work, dust particles are characterized mainly by granulometry, morphometry and mineralogy, using image processing and scanning northern Mauritania and the Western Sahara. The concentration of terrigenous material was measured in three environments: the atmosphere (300 m above sea level, the mixed layer at 10 m depth, and 150 m depth. Samples were collected before and during the dust events, thus allowing the effect of Saharan dust inputs in the water column to be assessed. The dominant grain size was coarse silt. Dominant minerals were iron oxy-hydroxides, silicates and Ca-Mg carbonates. A relative increase of iron mineral particles (hematite and goethite was detected in the mixed layer, reflecting a higher permanence of iron in the water column despite the greater relative density of these minerals in comparison with the other minerals. This higher iron particle permanence does not appear to be explained by physical processes. The retention of this metal by colloids or microorganisms is suggested to explain its long residence time in the mixed layer.

  20. Radiation Effect on Mixed Convection Boundary Layer Flow of a Viscoelastic Fluid over a Horizontal Circular Cylinder with Constant Heat Flux

    Directory of Open Access Journals (Sweden)

    Hussain Ahmad

    2016-01-01

    Full Text Available In the present article, radiation effect on mixed convection boundary layer flow of a viscoelastic fluid over a horizontal circular cylinder with constant heat flux has been numerically analyzed. The governing boundary layer equations are transformed to dimensionless nonlinear partial differential equations. The equations are solved numerically by using Keller-box method. The computed results are in excellent agreement with the previous studies. Skin friction coefficient and Nusselt number are emphasized specifically. These quantities are displayed against the curvature parameter. The effects of pertinent parameters involved in the problem namely effective Prandtl number and mixed convection parameter on skin friction coefficient and Nusselt number are shown through graphs and table. Boundary layer separation points are also calculated with and without radiation and a comparison is shown. The presence of radiation helps to decrease or increase the skin friction coefficient for the negative or positive values of the mixed convection parameter accordingly. The decrease in value of effective Prandtl number helps to increase the value of skin friction coefficient and Nusselt number for viscoelastic fluids.

  1. Role of the ocean mixed layer processes in the response of the North Pacific winter SST and MLD to global warming in CGCMs

    Energy Technology Data Exchange (ETDEWEB)

    Yim, Bo Young; Noh, Yign [Yonsei University, Department of Atmospheric Sciences, Global Environmental Laboratory, Seoul (Korea, Republic of); Yeh, Sang-Wook [Hanyang University, Department of Environmental Marine Science, Ansan (Korea, Republic of)

    2012-03-15

    It is investigated how the changes of winter sea surface temperature (SST) and mixed layer depth (MLD) under climate change projections are predicted differently in the North Pacific depending on the coupled general circulation models (CGCMs), and how they are related to the dynamical property of the simulated ocean mixed layer. For this purpose the dataset from eleven CGCMs reported to IPCC's AR4 are used, while detailed analysis is given to the MRI and MIROC models. Analysis of the CGCM data reveals that the increase of SST and the decrease of MLD in response to global warming tend to be smaller for the CGCM in which the ratio of ocean heat transport (OHT) to surface heat flux (SHF), R (=OHT/SHF), is larger in the heat budget of the mixed layer. The negative correlation is found between the changes of OHT and SHF under global warming, which may weaken the response to global warming in the CGCM with larger R. It is also found that the models with low horizontal resolution tend to give broader western boundary currents, larger R, and the smaller changes of SST and MLD under global warming. (orig.)

  2. Solubility of solids in supercritical fluids using equations of state — excess Gibbs free energy models

    OpenAIRE

    Verotti Filho, C.; Costa, Glória Meyberg Nunes

    1996-01-01

    p. 351–355 Solubilities of several organic solids in four supercritical fluids are calculated with Soave and Peng-Robinson equations of state, incorporating excess Gibbs free energy into the mixing rules, with Heidemann-Kokal, Wong-Sandler and MHV2 procedures. Three excess Gibbs free energy models are used in the mixing rules: NRTL, UNiQUAC and UNIFAC. Furthermore, a comparison between these mixing rules and conventional two-binary-parameter form and modification of the excluded volume par...

  3. The ASTAR 2007 April 14 haze layer: The radiative effect of an aged and internally mixed aerosol in the Arctic

    Science.gov (United States)

    Engvall, A.-C.; Ström, J.; Tunved, P.; Schlager, H.; Minikin, A.

    2009-04-01

    the mixing state of the aerosol in the size range between 17 and 239 nm obtained from a volatility DMPS (V-DMPS). Information about the light-absorbing properties of the aerosol was obtained from a custom-built particle soot absorption photometer (PSAP), which provided the particle light-absorption coefficient sp at a wavelength of 525 nm. From this we estimated the black carbon mass concentration (BC, ng m-3) by using the commonly employed specific absorption coefficient 10 m2 g-1 [Petzold, et al., 1997]. As a part of the quality control, an intercomparison was made with measurements from the Zeppelin station (474 m.a.s.l.) at Ny-Ålesund [Ström, et al., 2003; Engvall, et al., 2008]. This indicated good agreement between the airborne and the ground-based size-distribution results for particles of diameter smaller than approximately 200 nm. To investigate the radiative effects of the enhanced aerosol layer a one-dimensional radiation model was used to simulate the amplified heating rate (K day-1). The calculations were based on in-situ measurements of the input variables, viz. relative humidity (RH), temperature (T), pressure (p), aerosol size distribution, and the scattering and absorption properties of the aerosols, for more details see [Treffeisen, et al., 2007]. CONCLUSIONS Transport of pollutants from the mid-latitudes into the Arctic free troposphere may give rise to a heating rate within the plume of up to 1.3 K day-1, dependent on the properties of the plume and the surface albedo. The surface properties, in this study ice/snow covered or ice-free ocean, are of importance since the latter case with a low albedo shows a 25-30% decrease of the heating rate compared to the snow/ice case. These results can be compared to those obtained by [Treffeisen, et al., 2007], who estimated a heating rate of 1.7 K day-1 at an altitude of 0.5 km based on the observed concentrations of particles, soot, and aerosol scattering during the highest pollution event ever recorded

  4. The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

    Science.gov (United States)

    Ding, Jianning; Li, Yan; Hu, Hongwei; Bai, Li; Zhang, Shuai; Yuan, Ningyi

    2013-01-01

    High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO2 nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO2 DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO2 electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO2 nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6 wt.% rutile) TiO2 nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3 mA cm-2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO2 nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.

  5. The implementation of a MiXed Layer model (MXL, v1.0) for the dynamics of the atmospheric boundary layer in the Modular Earth Submodel System (MESSy)

    Science.gov (United States)

    Janssen, R. H. H.; Pozzer, A.

    2014-10-01

    We present a new submodel for the Modular Earth Submodel System (MESSy): the MiXed Layer (MXL) model for the diurnal dynamics of the convective boundary layer, including explicit representations of entrainment and surface fluxes. Through the MESSy interface, MXL is coupled with modules that represent other processes relevant to chemistry in the atmospheric boundary layer (ABL). In combination, these provide a computationally inexpensive tool that is ideally suited for the analysis of field data, for evaluating new parametrizations for 3-D models, and for performing systematic sensitivity analyses. A case study for the DOMINO campaign in Southern Spain is shown to demonstrate the use and performance of MXL/MESSy in reproducing and analysing field observations.

  6. Removing Solids From Supercritical Water

    Science.gov (United States)

    Hong, Glenn T.

    1992-01-01

    Apparatus removes precipitated inorganic salts and other solids in water-recycling process. Designed for use with oxidation in supercritical water which treats wastes and yields nearly pure water. Heating coils and insulation around vessel keep it hot. Locking bracket seals vessel but allows it to be easily opened for replacement of filled canisters.

  7. Supercritical multicomponent solvent coal extraction

    Science.gov (United States)

    Corcoran, W. H.; Fong, W. S.; Pichaichanarong, P.; Chan, P. C. F.; Lawson, D. D. (Inventor)

    1983-01-01

    The yield of organic extract from the supercritical extraction of coal with larger diameter organic solvents such as toluene is increased by use of a minor amount of from 0.1 to 10% by weight of a second solvent such as methanol having a molecular diameter significantly smaller than the average pore diameter of the coal.

  8. Initial instability of round liquid jet at subcritical and supercritical environments

    Energy Technology Data Exchange (ETDEWEB)

    Muthukumaran, C. K.; Vaidyanathan, Aravind, E-mail: aravind7@iist.ac.in [Department of Aerospace Engineering, Indian Institute of Space Science and Technology, Trivandrum, Kerala 695547 (India)

    2016-07-15

    In the present experimental work, the behavior of laminar liquid jet in its own vapor as well as supercritical fluid environment is conducted. Also the study of liquid jet injection into nitrogen (N{sub 2}) environment is carried out at supercritical conditions. It is expected that the injected liquid jet would undergo thermodynamic transition to the chamber condition and this would alter the behavior of the injected jet. Moreover at such conditions there is a strong dependence between thermodynamic and fluid dynamic processes. Thus the thermodynamic transition has its effect on the initial instability as well as the breakup nature of the injected liquid jet. In the present study, the interfacial disturbance wavelength, breakup characteristics, and mixing behavior are analysed for the fluoroketone liquid jet that is injected into N{sub 2} environment as well as into its own vapor at subcritical to supercritical conditions. It is observed that at subcritical chamber conditions, the injected liquid jet exhibits classical liquid jet characteristics with Rayleigh breakup at lower Weber number and Taylor breakup at higher Weber number for both N{sub 2} and its own environment. At supercritical chamber conditions with its own environment, the injected liquid jet undergoes sudden thermodynamic transition to chamber conditions and single phase mixing characteristics is observed. However, the supercritical chamber conditions with N{sub 2} as ambient fluid does not have significant effect on the thermodynamic transition of the injected liquid jet.

  9. Initial instability of round liquid jet at subcritical and supercritical environments

    Science.gov (United States)

    Muthukumaran, C. K.; Vaidyanathan, Aravind

    2016-07-01

    In the present experimental work, the behavior of laminar liquid jet in its own vapor as well as supercritical fluid environment is conducted. Also the study of liquid jet injection into nitrogen (N2) environment is carried out at supercritical conditions. It is expected that the injected liquid jet would undergo thermodynamic transition to the chamber condition and this would alter the behavior of the injected jet. Moreover at such conditions there is a strong dependence between thermodynamic and fluid dynamic processes. Thus the thermodynamic transition has its effect on the initial instability as well as the breakup nature of the injected liquid jet. In the present study, the interfacial disturbance wavelength, breakup characteristics, and mixing behavior are analysed for the fluoroketone liquid jet that is injected into N2 environment as well as into its own vapor at subcritical to supercritical conditions. It is observed that at subcritical chamber conditions, the injected liquid jet exhibits classical liquid jet characteristics with Rayleigh breakup at lower Weber number and Taylor breakup at higher Weber number for both N2 and its own environment. At supercritical chamber conditions with its own environment, the injected liquid jet undergoes sudden thermodynamic transition to chamber conditions and single phase mixing characteristics is observed. However, the supercritical chamber conditions with N2 as ambient fluid does not have significant effect on the thermodynamic transition of the injected liquid jet.

  10. The influence of the UV irradiation intensity on photocatalytic activity of ZnAl layered double hydroxides and derived mixed oxides

    Directory of Open Access Journals (Sweden)

    Hadnađev-Kostić Milica S.

    2012-01-01

    Full Text Available Layered double hydroxides (LDHs have been studied to a great extent as environmental-friendly complex materials that can be used as photocatalysts or photocatalyst supports. ZnAl layered double hydroxides and their derived mixed oxides were chosen for the investigation of photocatalytic performances in correlation with the UV intensities measured in the South Pannonia region. Low supersaturation coprecipitation method was used for the ZnAl LDH synthesis. For the characterization of LDH and thermal treated samples powder X-ray diffraction (XRD, scanning electron microscopy (SEM, electron dispersive spectroscopy (EDS, nitrogen adsorption-desorption were used. The decomposition of azodye, methylene blue was chosen as photocatalytic test reaction. The study showed that the ZnAl mixed oxide obtained by thermal decomposition of ZnAl LDH has stable activity in the broader UV light irradiation range characterizing the selected region. Photocatalytic activity could be mainly attributed to the ZnO phase, detected both in LDH and thermally treated samples. The study showed that the ZnAl mixed oxide obtained by the calcination of ZnAl LDH has a stable activity within the measured UV light irradiation range; whereas the parent ZnAl LDH catalyst did not perform satisfactory when low UV irradiation intensity is implied.

  11. Effects of aggregates on mixed adsorption layers of poly(ethylene imine) and sodium dodecyl sulfate at the air/liquid interface.

    Science.gov (United States)

    Tonigold, Katrin; Varga, Imre; Nylander, Tommy; Campbell, Richard A

    2009-04-07

    We have exploited the spatial and kinetic resolution of ellipsometry to monitor the lateral movement of inhomogeneous patches of material in mixed adsorption layers of poly(ethylene imine) and sodium dodecyl sulfate at the air/liquid interface. We show that the choice of sample preparation methods can have a profound effect on the state of the interface for chemically equivalent samples. The extent of aggregation in the bulk solution on relevant time scales is affected by specific details of the polymer/surfactant mixing process, which produces varying numbers of aggregates that can become trapped in the interfacial layer, resulting in an enhanced and fluctuating ellipsometry signal. It can be beneficial to apply the surface-cleaning method of aspiration prior to physical measurements to remove trapped aggregates through the creation of a fresh interface. At low pH, the ellipsometry signal of samples prepared with surface cleaning is remarkably constant over a factor of >500 in the bulk composition below charge equivalence, which is discussed in terms of possible adsorption mechanisms. At high pH, through observing temporal fluctuations in the ellipsometry signal of samples prepared with surface cleaning, we reveal two important processes: there is the spontaneous adsorption of aggregates > 0.2 microm in diameter into the interfacial layer, and with time there is the fusion of smaller aggregates to generate new large surface aggregates. We attribute the favorability of the adsorption and fusion processes at high pH to reduced electrostatic barriers resulting from the low surface charge density of the aggregates. It is inappropriate in this case to consider the interface to comprise a homogeneous adsorption layer that is in dynamic equilibrium with the bulk solution. Our work shows that it can be helpful to consider whether there are macroscopic particles embedded in molecular layers at the air/liquid interface for systems where there is prior knowledge of

  12. A new first-order turbulence mixing model for the stable atmospheric boundary-layer: development and testing in large-eddy and single column models

    Science.gov (United States)

    Huang, J.; Bou-Zeid, E.; Golaz, J.

    2011-12-01

    Parameterization of the stably-stratified atmospheric boundary-layer is of crucial importance to different aspects of numerical weather prediction at regional scales and climate modeling at global scales, such as land-surface temperature forecasts, fog and frost prediction, and polar climate. It is well-known that most operational climate models require excessive turbulence mixing of the stable boundary-layer to prevent decoupling of the atmospheric component from the land component under strong stability, but the performance of such a model is unlikely to be satisfactory under weakly and moderately stable conditions. In this study we develop and test a general turbulence mixing model of the stable boundary-layer which works under different stabilities and for steady as well as unsteady conditions. A-priori large-eddy simulation (LES) tests are presented to motivate and verify the new parameterization. Subsequently, an assessment of this model using the GFDL single-column model (SCM) is performed. Idealized test cases including continuously varying stability, as well as stability discontinuity, are used to test the new SCM against LES results. A good match of mean and flux profiles is found when the new parameterization is used, while other traditional first-order turbulence models using the concept of stability function perform poorly. SCM spatial resolution is also found to have little impact on the performance of the new turbulence closure, but temporal resolution is important and a numerical stability criterion based on the model time step is presented.

  13. Universal scaling behavior of supercritical matter

    CERN Document Server

    Bolmatov, Dima; Trachenko, K

    2013-01-01

    Properties of supercritical fluids have been of enduring interest since the critical phenomena were discovered by Cagniard de la Tour in 1822, stimulating fundamental theoretical work and development of experimental techniques. Here, we study the thermodynamic properties of the supercritical state, and discover that specific heat shows a crossover between two different dynamic regimes of the low-temperature rigid liquid and high-temperature non-rigid supercritical fluid. We formulate a theory of heat capacity above the crossover, and find good agreement between calculated and experimental data for rare-gas supercritical liquids (Ne, Ar, Kr and Xe) with no free fitting parameters. We derive the relationship between scaling exponents of heat capacity and viscosity in the supercritical region, and show that these exponents exhibit universality. The universality is explained by the universal temperature behavior of the maximal length of the longitudinal phonons that can exist in the supercritical system and that ...

  14. Influence of Dynamics and Chemistry on the Diurnal Variation of VOCs in the Planetary Boundary Layer above a Mixed Forest Canopy in the Southeastern United States

    Science.gov (United States)

    Guenther, A. B.; Su, L.; Patton, E. G.; Vila-Guerau Arellano, J.; Mak, J. E.

    2014-12-01

    The planetary boundary layer (PBL) is a region of inherent interest because reactive VOCs emitted from the forest canopy are mixed with the residual and free tropospheric air masses, oxidized, and/or otherwise removed in this region. The characterization of diurnal variation of VOCs in the PBL is limited due to the lack of appropriate sampling platforms that are able to probe all the regions of interest: from the surface to the entrainment zone. Here we present the application of the Whole Air Sample Profiler (WASP) system during the 2013 Southeast Atmosphere Study (SAS) campaign. A total of 41 research flights (RFs) were carried out during the 2013 SAS campaign between June 1 and June 14 over the Alabama Aquatic Biodiversity Center (AABC) site and the SEARCH site. During each RF, ambient air sampling started from 50-100 m above the canopy top and stopped at ~1200 m above the mean sea level (a.m.s.l). The air samples were subsequently analyzed by using a proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). Here we analyze the vertical profiles and averaged diurnal variation of the mixing ratios of several reactive VOC species, including isoprene, the sum of monoterpenes, and first generation oxidation products of isoprene: methyl vinyl ketone and methacrolein (MVK+MACR). A MiXed Layer Chemistry (MXLCH) model, guided by the meteorological and chemical observations during the SAS campaign, is used to study the influence of boundary layer dynamics and new isoprene oxidation mechanism on the diurnal variation of major biogenic VOCs emitted from the forest canopy. The new scheme includes OH recycling through two pathways under low-NOx regime: (1) hydroxyl peroxy radicals (HOC5H8OO•; ISOPO2) unimolecular isomerization, and (2) ISOPO2+HO2. The model is able to reproduce the evolution of the boundary layer dynamics (including potential temperature, and boundary layer height) during the selected simulation dates. Based on the model results, budget

  15. Pulsed discharge plasmas in supercritical carbon dioxide

    OpenAIRE

    Kiyan, Tsuyoshi; Uemura, A.; Tanaka, K.; Zhang, C. H.; Namihira, Takao; Sakugawa, Takashi; Katsuki, Sunao; Akiyama, Hidenori; Roy, B.C.; Sasaki, M.; Goto, M.; キヤン, ツヨシ; ナミヒラ, タカオ; サクガワ, タカシ; カツキ, スナオ

    2005-01-01

    In recent years, several studies about electrical discharge plasma in supercritical carbon dioxide (CO2) have been carried out. One of the unique characteristics of supercritical fluid is a large density fluctuation near the critical point that can result in marked dramatic changes of thermal conductivity. Therefore, the electrical discharge plasma produced in supercritical fluid has unique features and reactions unlike those of normal plasma produced in gas phase. In our experiments, two typ...

  16. Mixed Convection Boundary-layer Flow of a Nanofluid Near Stagnation-point on a Vertical Plate with Effects of Buoyancy Assisting and Opposing Flows

    Directory of Open Access Journals (Sweden)

    Hossein Tamim

    2013-07-01

    Full Text Available In this study, the steady laminar mixed convection boundary layer flow of a nanofluid near the stagnation-point on a vertical plate with prescribed surface temperature is investigated. Here, both assisting and opposing flows are considered and studied. Using appropriate transformations, the system of partial differential equations is transformed into an ordinary differential system of two equations, which is solved numerically by shooting method, coupled with Runge-Kutta scheme. Three different types of nanoparticles, namely copper Cu, alumina Al2O3 and titania TiO2 with water as the base fluid are considered. Numerical results are obtained for the skin-friction coefficient and Nusselt number as well as for the velocity and temperature profiles for some values of the governing parameters, namely, the nanoparticle volume fraction parameter &Phiand mixed convection parameter &lambda It is found that the highest rate of heat transfer occurs in the mixed convection with assisting flow while the lowest one occurs in the mixed convection with opposing flow. Moreover, the skin friction coefficient and the heat transfer rate at the surface are highest for copper–water nanofluid compared to the alumina–water and titania–water nanofluids.

  17. Unsteady laminar mixed convection boundary layer flow near a vertical wedge due to oscillations in the free-stream and surface temperature

    Directory of Open Access Journals (Sweden)

    Roy N.C.

    2016-02-01

    Full Text Available The unsteady laminar boundary layer characteristics of mixed convection flow past a vertical wedge have been investigated numerically. The free-stream velocity and surface temperature are assumed to be oscillating in the magnitude but not in the direction of the oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the straightforward finite difference method for the entire frequency range, and the extended series solution for low frequency range and the asymptotic series expansion method for high frequency range. The results demonstrate the effects of the Richardson number, Ri, introduced to quantify the influence of mixed convection and the Prandtl number, Pr, on the amplitudes and phase angles of the skin friction and heat transfer. In addition, the effects of these parameters are examined in terms of the transient skin friction and heat transfer.

  18. Mechanisms controlling primary and new production in a global ecosystem model – Part I: The role of the large-scale upper mixed layer variability

    Directory of Open Access Journals (Sweden)

    E. E. Popova

    2006-07-01

    Full Text Available A global general circulation model coupled to a simple six-compartment ecosystem model is used to study the extent to which global variability in primary and export production can be realistically predicted on the basis of advanced parameterizations of upper mixed layer physics, without recourse to introducing extra complexity in model biology. The ''K profile parameterization'' (KPP scheme employed, combined with 6-hourly external forcing, is able to capture short-term periodic and episodic events such as diurnal cycling and storm-induced deepening. The model realistically reproduces various features of global ecosystem dynamics that have been problematic in previous global modelling studies, using a single generic parameter set. The realistic simulation of deep convection in the North Atlantic, and lack of it in the North Pacific and Southern Oceans, leads to good predictions of chlorophyll and primary production in these contrasting areas. Realistic levels of primary production are predicted in the oligotrophic gyres due to high frequency external forcing of the upper mixed layer (accompanying paper Popova et al., 2006 and novel parameterizations of zooplankton excretion. Good agreement is shown between model and observations at various JFOFS time series sites: BATS, KERFIX, Papa and station India. One exception is that the high zooplankton grazing rates required to maintain low chlorophyll in high-nutrient low-chlorophyll and oligotrophic systems lessened agreement between model and data in the northern North Atlantic, where mesozooplankton with lower grazing rates may be dominant. The model is therefore not globally robust in the sense that additional parameterizations were needed to realistically simulate ecosystem dynamics in the North Atlantic. Nevertheless, the work emphasises the need to pay particular attention to the parameterization of mixed layer physics in global ocean ecosystem modelling as a prerequisite to

  19. Solubility in supercritical solvents: A comparison of theory and simulation

    Science.gov (United States)

    Tomberli, Bruno Luca

    1998-12-01

    Solubility at supercritical conditions is studied using thermodynamics and statistical mechanics. The Redlich- Kwong equation of state, virial equation of state and fluctuation theory are used to predict the chemical potential for pure and mixed Lennard-Jones fluids. Where literature results are unavailable, Monte Carlo simulations employing the Widom particle insertion method are also carried out to determine the chemical potential at the same conditions. Several methods are shown to achieve an accuracy on the order of five percent. Based on the success of these theories, qualitative studies of cavity-interaction contributions to the chemical potential and the effect of clustering in supercritical solvation are conducted. Finally, fluctuation theory is shown to be the only available method suitable for ab initio calculations of the chemical potential involving anisotropic potentials. A suitable potential for naphthalene-carbon dioxide systems is developed from existing multi-site exp-6-1 potentials and predictions of the chemical potential of infinitely- dilute naphthalene in supercritical carbon dioxide are made as an example of a possible application of this method.

  20. Numerical solution on mixed convection boundary layer flow past a horizontal circular cylinder in a Jeffrey fluid with constant heat flux

    Science.gov (United States)

    Zokri, S. M.; Arifin, N. S.; Mohamed, M. K. A.; Salleh, M. Z.; Kasim, A. R. M.; Mohammad, N. F.

    2017-08-01

    This paper discusses the viscous dissipation effect with constant heat flux on the mixed convection boundary layer flow past a horizontal circular cylinder in a Jeffrey fluid. The transformed partial differential equations are solved numerically by using the well-tested, flexible, implicit and unconditionally stable Keller-box method. Numerical results for the velocity and temperature profiles are attained in the form of graph for different values of parameters such as Prandtl number, ratio of relaxation to retardation times and Deborah number. It is found that the velocity profile is noticeably decreased with an increase in Deborah number while the temperature profile is slightly increased.

  1. Effects of the chemical reaction and heat generation or absorption on a mixed convection boundary layer flow over a vertical stretching sheet with nonuniform slot mass transfer

    Science.gov (United States)

    Samyuktha, N.; Ravindran, R.; Ganapathirao, M.

    2017-01-01

    An analysis is performed to study the effects of the chemical reaction and heat generation or absorption on a steady mixed convection boundary layer flow over a vertical stretching sheet with nonuniform slot mass transfer. The governing boundary layer equations with boundary conditions are transformed into the dimensionless form by a group of nonsimilar transformations. Nonsimilar solutions are obtained numerically by solving the coupled nonlinear partial differential equations using the quasi-linearization technique combined with an implicit finite difference scheme. The numerical computations are carried out for different values of dimensionless parameters to display the distributions of the velocity, temperature, concentration, local skin friction coefficient, local Nusselt number, and local Sherwood number. The results obtained indicate that the local Nusselt and Sherwood numbers increase with nonuniform slot suction, but nonuniform slot injection produces the opposite effect. The local Nusselt number decreases with heat generation and increases with heat absorption.

  2. A computer program for the calculation of the flow field including boundary layer effects for mixed-compression inlets at angle of attack

    Science.gov (United States)

    Vadyak, J.; Hoffman, J. D.

    1982-01-01

    A computer program was developed which is capable of calculating the flow field in the supersonic portion of a mixed compression aircraft inlet operating at angle of attack. The supersonic core flow is computed using a second-order three dimensional method-of-characteristics algorithm. The bow shock and the internal shock train are treated discretely using a three dimensional shock fitting procedure. The boundary layer flows are computed using a second-order implicit finite difference method. The shock wave-boundary layer interaction is computed using an integral formulation. The general structure of the computer program is discussed, and a brief description of each subroutine is given. All program input parameters are defined, and a brief discussion on interpretation of the output is provided. A number of sample cases, complete with data listings, are provided.

  3. Lipidomics by Supercritical Fluid Chromatography

    Directory of Open Access Journals (Sweden)

    Laurent Laboureur

    2015-06-01

    Full Text Available This review enlightens the role of supercritical fluid chromatography (SFC in the field of lipid analysis. SFC has been popular in the late 1980s and 1990s before almost disappearing due to the commercial success of liquid chromatography (LC. It is only 20 years later that a regain of interest appeared when new commercial instruments were introduced. As SFC is fully compatible with the injection of extracts in pure organic solvent, this technique is perfectly suitable for lipid analysis and can be coupled with either highly universal (UV or evaporative light scattering or highly specific (mass spectrometry detection methods. A short history of the use of supercritical fluids as mobile phase for the separation oflipids will be introduced first. Then, the advantages and drawbacks of SFC are discussed for each class of lipids (fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, prenols, polyketides defined by the LIPID MAPS consortium.

  4. Lipidomics by Supercritical Fluid Chromatography

    Science.gov (United States)

    Laboureur, Laurent; Ollero, Mario; Touboul, David

    2015-01-01

    This review enlightens the role of supercritical fluid chromatography (SFC) in the field of lipid analysis. SFC has been popular in the late 1980s and 1990s before almost disappearing due to the commercial success of liquid chromatography (LC). It is only 20 years later that a regain of interest appeared when new commercial instruments were introduced. As SFC is fully compatible with the injection of extracts in pure organic solvent, this technique is perfectly suitable for lipid analysis and can be coupled with either highly universal (UV or evaporative light scattering) or highly specific (mass spectrometry) detection methods. A short history of the use of supercritical fluids as mobile phase for the separation oflipids will be introduced first. Then, the advantages and drawbacks of SFC are discussed for each class of lipids (fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, prenols, polyketides) defined by the LIPID MAPS consortium. PMID:26090714

  5. Nanostructure Neutron Converter Layer Development

    Science.gov (United States)

    Park, Cheol (Inventor); Sauti, Godfrey (Inventor); Kang, Jin Ho (Inventor); Lowther, Sharon E. (Inventor); Thibeault, Sheila A. (Inventor); Bryant, Robert G. (Inventor)

    2016-01-01

    Methods for making a neutron converter layer are provided. The various embodiment methods enable the formation of a single layer neutron converter material. The single layer neutron converter material formed according to the various embodiments may have a high neutron absorption cross section, tailored resistivity providing a good electric field penetration with submicron particles, and a high secondary electron emission coefficient. In an embodiment method a neutron converter layer may be formed by sequential supercritical fluid metallization of a porous nanostructure aerogel or polyimide film. In another embodiment method a neutron converter layer may be formed by simultaneous supercritical fluid metallization of a porous nanostructure aerogel or polyimide film. In a further embodiment method a neutron converter layer may be formed by in-situ metalized aerogel nanostructure development.

  6. Phase diagrams in mixed spin-3/2 and spin-2 Ising system with two alternative layers within the effective-field theory

    Institute of Scientific and Technical Information of China (English)

    Bayram Devirena; Yasin Polatb; Mustafa Keskinc

    2011-01-01

    The phase diagrams in the mixed spin-3/2 and spin-2 Ising system with two alternative layers on a honeycomb lattice are investigated and discussed by the use of the effective-field theory with correlations. The interaction of the nearest-neighbour spins of each layer is taken to be positive (ferromagnetic interaction) and the interaction of the adjacent spins of the nearest-neighbour layers is considered to be either positive or negative (ferromagnetic or antiferromagnetic interaction). The temperature dependence of the layer magnetizations of the system is examined to characterize the nature (continuous or discontinuous) of the phase transitions and obtain the phase transition temperatures. The system exhibits both second-and first-order phase transitions besides triple point (TP), critical end point (E), multicritical point (A), isolated critical point (C) and reentrant behaviour depending on the interaction parameters. We have also studied the temperature dependence of the total magnetization to find the compensation points,system. The phase diagrams are constructed in eight different planes and it is found that the system also presents the compensation phenomena depending on the sign of the bilinear exchange interactions.

  7. Nonlinear optics in Xe-filled hollow-core PCF in high pressure and supercritical regimes

    CERN Document Server

    Azhar, M; Travers, J C; Russell, P St J

    2013-01-01

    Supercritical Xe at 293 K offers a Kerr nonlinearity that can exceed that of fused silica while being free of Raman scattering. It also has a much higher optical damage threshold and a transparency window that extends from the UV to the infrared. We report the observation of nonlinear phenomena, such as self-phase modulation, in hollow-core photonic crystal fiber filled with supercritical Xe. In the subcritical regime, intermodal four-wave-mixing resulted in the generation of UV light in the HE12 mode. The normal dispersion of the fiber at high pressures means that spectral broadening can clearly obtained without influence from soliton effects or material damage.

  8. Implementing supercritical water oxidation technology in a lunar base environmental control/life support system

    Science.gov (United States)

    Meyer Sedej, M.

    1985-01-01

    A supercritical water oxidation system (SCWOS) offers several advantages for a lunar base environmental control/life support system (ECLSS) compared to an ECLSS based on Space Station technology. In supercritically heated water (630 K, 250 atm) organic materials mix freely with oxygen and undergo complete combustion. Inorganic salts lose solubility and precipitate out. Implementation of SCWOS can make an ECLSS more efficient and reliable by elimination of several subsystems and by reduction in potential losses of life support consumables. More complete closure of the total system reduces resupply requirements from the earth, a crucial cost item in maintaining a lunar base.

  9. Recuperative supercritical carbon dioxide cycle

    Science.gov (United States)

    Sonwane, Chandrashekhar; Sprouse, Kenneth M; Subbaraman, Ganesan; O'Connor, George M; Johnson, Gregory A

    2014-11-18

    A power plant includes a closed loop, supercritical carbon dioxide system (CLS-CO.sub.2 system). The CLS-CO.sub.2 system includes a turbine-generator and a high temperature recuperator (HTR) that is arranged to receive expanded carbon dioxide from the turbine-generator. The HTR includes a plurality of heat exchangers that define respective heat exchange areas. At least two of the heat exchangers have different heat exchange areas.

  10. Oxidation of Alloy 600 and Alloy 690: Experimentally Accelerated Study in Hydrogenated Supercritical Water

    Science.gov (United States)

    Moss, Tyler; Cao, Guoping; Was, Gary S.

    2017-04-01

    The objective of this study is to determine whether the oxidation of Alloys 600 and 690 in supercritical water occurs by the same mechanism in subcritical water. Coupons of Alloys 690 and 600 were exposed to hydrogenated subcritical and supercritical water from 633 K to 673 K (360 °C to 400 °C) and the oxidation behavior was observed. By all measures of oxide character and behavior, the oxidation process is the same above and below the supercritical line. Similar oxide morphologies, structures, and chemistries were observed for each alloy across the critical point, indicating that the oxidation mechanism is the same in both subcritical and supercritical water. Oxidation results in a multi-layer oxide structure composed of particles of NiO and NiFe2O4 formed by precipitation on the outer surface and a chromium-rich inner oxide layer formed by diffusion of oxygen to the metal-oxide interface. The inner oxide on Alloy 600 is less chromium rich than that observed on Alloy 690 and is accompanied by preferential oxidation of grain boundaries. The inner oxide on Alloy 690 initially forms by internal oxidation before a protective layer of chromium-rich MO is formed with Cr2O3 at the metal-oxide interface. Grain boundaries in Alloy 690 act as fast diffusion paths for chromium that forms a protective Cr2O3 layer at the surface, preventing grain boundary oxidation from occurring.

  11. Oxidation of Alloy 600 and Alloy 690: Experimentally Accelerated Study in Hydrogenated Supercritical Water

    Science.gov (United States)

    Moss, Tyler; Cao, Guoping; Was, Gary S.

    2017-02-01

    The objective of this study is to determine whether the oxidation of Alloys 600 and 690 in supercritical water occurs by the same mechanism in subcritical water. Coupons of Alloys 690 and 600 were exposed to hydrogenated subcritical and supercritical water from 633 K to 673 K (360 °C to 400 °C) and the oxidation behavior was observed. By all measures of oxide character and behavior, the oxidation process is the same above and below the supercritical line. Similar oxide morphologies, structures, and chemistries were observed for each alloy across the critical point, indicating that the oxidation mechanism is the same in both subcritical and supercritical water. Oxidation results in a multi-layer oxide structure composed of particles of NiO and NiFe2O4 formed by precipitation on the outer surface and a chromium-rich inner oxide layer formed by diffusion of oxygen to the metal-oxide interface. The inner oxide on Alloy 600 is less chromium rich than that observed on Alloy 690 and is accompanied by preferential oxidation of grain boundaries. The inner oxide on Alloy 690 initially forms by internal oxidation before a protective layer of chromium-rich MO is formed with Cr2O3 at the metal-oxide interface. Grain boundaries in Alloy 690 act as fast diffusion paths for chromium that forms a protective Cr2O3 layer at the surface, preventing grain boundary oxidation from occurring.

  12. Destruction of polyphasic systems in supercritical water reaction media; Etude de la destruction de systemes polyphasiques en milieu eau supercritique

    Energy Technology Data Exchange (ETDEWEB)

    Leybros, A.

    2009-12-15

    Spent ion exchange resins (IER) are, hence, radioactive process wastes for which there is no satisfactory industrial treatment. Supercritical water oxidation offers a viable alternative treatment to destroy the organic structure of resins by using supercritical water properties. The reactor used in Supercritical Fluids and Membranes Laboratory is a double shell stirred reactor. Total Organic Carbon reduction rates higher than 99% were obtained thanks to POSCEA2 experimental set-up when using a co-fuel, isopropyl alcohol. Influence of operating parameters was studied. A detailed reactional mechanism for cationic and anionic resins is created. For the solubilization of the particles in supercritical water, a mechanism has been created with the identified rate determining species and implemented into Fluent software through the EDC approach. Experimental temperature profiles are well represented by EDC model. Reaction rates are hence controlled by the chemical species mixing. (author)

  13. Supercritical Fluid Chromatography, Pressurized Liquid Extraction and Supercritical Fluid Extraction

    Energy Technology Data Exchange (ETDEWEB)

    Henry, Matthew C.; Yonker, Clement R.

    2006-06-15

    In this review we examine the related fields of supercritical fluid chromatography (SFC) and supercritical fluid extraction (SFE). We reviewed the published literature in the period from November 2003 to November 2005. Well over 300 papers were published in this period. This large body of work indicates continuing active growth of the field, but an exhaustive review is beyond the scope of this work. We have chosen to include a sampling of publications that best represent the continuing trends and new ideas in the field. In keeping with past reviews on this subject1, we have broadened our scope to include fluid systems operating at high temperature and pressure, but below the critical point. Various terms have been applied to this state: sub-critical fluid extraction, pressurized liquid extraction, and accelerated solvent extraction. The term accelerated solvent extraction has been used by instrument manufacturers to refer to this process, but we will use the more descriptive term pressurized liquid extraction (PLE) to refer to these systems. Most of the research in the field is of an “evolutionary” rather than “revolutionary” nature. As in the previous review period, applications papers make up a majority of the published work. Pharmaceutical applications continue to be a strong theme. Most of the pharmaceutical work has centered on preparative, rather than analytical, separations. Chiral separations are an exception, as analytical scale separations of chiral compounds are an area of intense interest. Food and natural products represent the next largest body of work. Major themes are the isolation and characterization of high-value added foodstuffs, fragrances, and flavor compounds from novel natural materials or agricultural by-products. The areas of food, natural products, and pharmaceutical separation science converge in the area of so-called nutraceuticals. These are typically high-value products, either sold alone or as part of a fortified food, that

  14. Supercritical Water Mixture (SCWM) Experiment

    Science.gov (United States)

    Hicks, Michael C.; Hegde, Uday G.

    2012-01-01

    The subject presentation, entitled, Supercritical Water Mixture (SCWM) Experiment, was presented at the International Space Station (ISS) Increment 33/34 Science Symposium. This presentation provides an overview of an international collaboration between NASA and CNES to study the behavior of a dilute aqueous solution of Na2SO4 (5% w) at near-critical conditions. The Supercritical Water Mixture (SCWM) investigation, serves as important precursor work for subsequent Supercritical Water Oxidation (SCWO) experiments. The SCWM investigation will be performed in DECLICs High Temperature Insert (HTI) for the purpose of studying critical fluid phenomena at high temperatures and pressures. The HTI includes a completely sealed and integrated test cell (i.e., Sample Cell Unit SCU) that will contain approximately 0.3 ml of the aqueous test solution. During the sequence of tests, scheduled to be performed in FY13, temperatures and pressures will be elevated to critical conditions (i.e., Tc = 374C and Pc = 22 MPa) in order to observe salt precipitation, precipitate agglomeration and precipitate transport in the presence of a temperature gradient without the influences of gravitational forces. This presentation provides an overview of the motivation for this work, a description of the DECLIC HTI hardware, the proposed test sequences, and a brief discussion of the scientific research objectives.

  15. Optical properties of mixed aerosol layers over Japan derived with multi-wavelength Mie-Raman lidar system

    Science.gov (United States)

    Hara, Yukari; Nishizawa, Tomoaki; Sugimoto, Nobuo; Matsui, Ichiro; Pan, Xiaole; Kobayashi, Hiroshi; Osada, Kazuo; Uno, Itsushi

    2017-02-01

    Mixing state of aerosols and optical properties including lidar ratio, particle depolarization ratio, and Ångström exponent were investigated at Fukuoka in western Japan using a multi-wavelength Mie-Raman lidar (MMRL), various aerosol mass-concentration measurements, and a polarization optical particle counter during Winter-Spring 2015. Aerosol extinction coefficient, backscatter coefficient, and depolarization at 355 and 532 nm and attenuated backscatter coefficient at 1064 nm are obtained from the MMRL measurements. Ten aerosol episodes were classified into three categories (air pollution, mineral dust, and marine aerosol) based on aerosol mass-concentration measurements in the fine-mode (particle diameter Dplidar ratio for air pollution was 57±4 sr at 355 nm and 53±8 sr at 532 nm with Ångström exponent of 1.4±0.5. For mineral dust, a slightly high averaged lidar ratio (50±7 sr at 355 nm and 54±9 sr at 532 nm) was obtained with relatively high Ångström exponent of 0.8±0.3 owing to contributions from fine-mode particles (PMf). The mean particle depolarization ratios of 13±8% at 355 nm and 16±6% at 532 nm also suggest mixing of mineral dust and anthropogenic fine-mode aerosols. The lowest lidar ratio was obtained for marine case. Classification of aerosol types using the lidar ratio and particle depolarization ratio was conducted based on the results obtained in this study. The classified aerosol types almost corresponded to aerosol category obtained by previous studies. We found no remarkable correlation between the fraction of black carbon and the lidar ratio: this might be due to the complexity of the mixing state among various aerosols. The obtained lidar ratio was rather correlated with the ratio of PMf to PM10, representing the mixing state of fine- and coarse-mode particles.

  16. Large-eddy simulation of trans- and supercritical injection

    Science.gov (United States)

    Müller, H.; Niedermeier, C. A.; Jarczyk, M.; Pfitzner, M.; Hickel, S.; Adams, N. A.

    2016-07-01

    In a joint effort to develop a robust numerical tool for the simulation of injection, mixing, and combustion in liquid rocket engines at high pressure, a real-gas thermodynamics model has been implemented into two computational fluid dynamics (CFD) codes, the density-based INCA and a pressure-based version of OpenFOAM. As a part of the validation process, both codes have been used to perform large-eddy simulations (LES) of trans- and supercritical nitrogen injection. Despite the different code architecture and the different subgrid scale turbulence modeling strategy, both codes yield similar results. The agreement with the available experimental data is good.

  17. Length scales in cryogenic injection at supercritical pressure

    Energy Technology Data Exchange (ETDEWEB)

    Branam, R.; Mayer, W. [German Aerospace Center, DLR Lampoldshausen, 74239 Hardthausen (Germany)

    2002-09-01

    Length scales provide some understanding of the injection of cryogenic propellants in rocket chambers on mixing efficiency, which translates to burning efficiency and performance. This project uses supercritical cryogenic nitrogen to look at high-density core flows such as those of coaxial injectors used in rocket engines. The investigation considers test conditions from 4.0 to 6.0 MPa chamber pressure at two injection velocities and temperatures. Experimental data taken by using shadowgraph images provides a means of characterizing turbulent flow structures using a two-point correlation method to determine length scales and structure shapes. The experimental results are compared to computational models. (orig.)

  18. Improving the Performances of Random Copolymer Based Organic Solar Cells by Adjusting the Film Features of Active Layers Using Mixed Solvents

    Directory of Open Access Journals (Sweden)

    Xiangwei Zhu

    2015-12-01

    Full Text Available A novel random copolymer based on donor–acceptor type polymers containing benzodithiophene and dithienosilole as donors and benzothiazole and diketopyrrolopyrrole as acceptors was designed and synthesized by Stille copolymerization, and their optical, electrochemical, charge transport, and photovoltaic properties were investigated. This copolymer with high molecular weight exhibited broad and strong absorption covering the spectra range from 500 to 800 nm with absorption maxima at around 750 nm, which would be very conducive to obtaining large short-circuits current densities. Unlike the general approach using single solvent to prepare the active layer film, mixed solvents were introduced to change the film feature and improve the morphology of the active layer, which lead to a significant improvement of the power conversion efficiency. These results indicate that constructing random copolymer with multiple donor and acceptor monomers and choosing proper mixed solvents to change the characteristics of the film is a very promising way for manufacturing organic solar cells with large current density and high power conversion efficiency.

  19. Simulation of wind-induced near-inertial oscillations in a mixed layer near the east coast of Korea in the East/Japan Sea

    Institute of Scientific and Technical Information of China (English)

    NAM SungHyun; PARK Young-Gyu

    2013-01-01

    Using a simple damped slab model, it was possible to show that a local wind induced 88%(15 of 17) of the near-inertial oscillations (NIO) observed in the mixed layer near the east coast of Korea from 1999 to 2004. The model, however, overestimated the energy level in about two-thirds of the simulated cases, because the slab model was forced with winds whose characteristic period was shorter than the damping time scale of the model at 1.5 d. At the observation site, due to typhoons and orographic effects, high-frequency wind forcing is quite common, as is the overestimation of the energy level in the slab model results. In short, a simple slab model with a damping time-scale of about 1.5 d would be enough to show that the local wind was the main energy source of the near-inertial energy in this area, but the model could not be used to accurately estimate the amount of the work done by the wind to the mixed layer.

  20. The broad H-alpha, [O III] line wings in stellar supercluster A of NGC2363 and the turbulent mixing layer hypothesis

    CERN Document Server

    Binette, Luc; Ubeda, Leonardo; Raga, Alejandro C; Robert, Carmelle; Krongold, Yair

    2009-01-01

    Context. SuperclusterA in the extragalactic HII region NGC2363 is remarkable for the hypersonic gas seen as faint extended broad emission lines with a full width zero intensity of 7000km/s. Aims. We explore the possibility that the observed broad profiles are the result of the interaction of a high velocity cluster wind with dense photoionized clumps. Methods. The geometry considered is that of near static photoionized condensations at the surface of which turbulent mixing layers arise as a result of the interaction with the hot wind. The approximative treatment of turbulence is carried out using the mixing length approach of Canto & Raga. The code mappings Ic is used to derive the mean quantities describing the flow and to compute the line emissivities within the turbulent layers. The velocity projection in three dimensions of the line sources is carried out analytically. Results. A fast entraining wind of up to ~4300km/s appears to be required to reproduce the faint wings of the broad H-alpha and [O III...

  1. MHD mixed convective boundary layer flow of a nanofluid through a porous medium due to an exponentially stretching sheet

    KAUST Repository

    Ferdows, M.

    2012-01-01

    Magnetohydrodynamic (MHD) boundary layer flow of a nanofluid over an exponentially stretching sheet was studied. The governing boundary layer equations are reduced into ordinary differential equations by a similarity transformation. The transformed equations are solved numerically using the Nactsheim-Swigert shooting technique together with Runge-Kutta six-order iteration schemes. The effects of the governing parameters on the flow field and heat transfer characteristics were obtained and discussed. The numerical solutions for the wall skin friction coefficient, the heat and mass transfer coefficient, and the velocity, temperature, and concentration profiles are computed, analyzed, and discussed graphically. Comparison with previously published work is performed and excellent agreement is observed. 2012 M. Ferdows et al.

  2. MHD Mixed Convective Boundary Layer Flow of a Nanofluid through a Porous Medium due to an Exponentially Stretching Sheet

    Directory of Open Access Journals (Sweden)

    M. Ferdows

    2012-01-01

    Full Text Available Magnetohydrodynamic (MHD boundary layer flow of a nanofluid over an exponentially stretching sheet was studied. The governing boundary layer equations are reduced into ordinary differential equations by a similarity transformation. The transformed equations are solved numerically using the Nactsheim-Swigert shooting technique together with Runge-Kutta six-order iteration schemes. The effects of the governing parameters on the flow field and heat transfer characteristics were obtained and discussed. The numerical solutions for the wall skin friction coefficient, the heat and mass transfer coefficient, and the velocity, temperature, and concentration profiles are computed, analyzed, and discussed graphically. Comparison with previously published work is performed and excellent agreement is observed.

  3. INTEGRATED SUPERCRITICAL FLUID EXTRACTION AND BIOPROCESSING

    Directory of Open Access Journals (Sweden)

    Owen Catchpole

    2012-01-01

    Full Text Available Supercritical fluids are increasingly being used and promoted at a laboratory and pilot scale to produce high value, natural bioactives from biologically based raw materials. Supercritical CO2 is overwhelmingly the solvent of choice for these operations, but is largely limited to the processing of dry raw materials and the extraction of low polarity, low molecular weight compounds. The use of co-solvents and the use of alternative ‘near-critical’ extraction fluids such as dimethyl ether show potential to mitigate these limitations. Commercialisation of new supercritical extraction processes has arguably been limited because the supercritical extraction process has been developed in isolation of other processing steps necessary to achieve a successful product. This study reviews recent developments in integrated processing that incorporate the use of supercritical fluids for bioseparations and in particular process schemes that produce high value natural bioactives. Integrated processes include prior operation (fermentation, extraction, enzyme pre-treatment, physical fractionation or size reduction followed by supercritical extraction or fractionation and processes in which operations are carried out in situ in supercritical fluids (supercritical chromatography, enzymatic conversion, precipitation and coating of solutes. The use of co-solvents and alternative extraction solvents in these processes is discussed. Prospects for future developments are also discussed.

  4. Study on elution ability of salicylic acid on ion exchange resins in supercritical carbon dioxide

    Institute of Scientific and Technical Information of China (English)

    Ping YUAN; Jianguo CAI; Junjie GONG; Xiu DENG

    2009-01-01

    The elution ability of salicylic acid on ion exchange resins in supercritical carbon dioxide has been studied. Some factors influencing elution recovery,including entrainer, temperature, pressure and the flow rate of supercritical fluid CO2 are discussed in this work.The addition of a small amount of entrainer, such as ethanol, triethanolamine and their mixture to supercritical CO2 can cause dramatic effects on the elution ability. The results show that the salicylic acid can be only slightly eluted from the resin with supercritical CO2 alone with temperatures ranging from 307.15 to 323.15K and pressures ranging from 10 to 30MPa. Meanwhile, with the same T, P conditions, 40.58% and 73.08% salicylic acid can be eluted from the ion exchange resin with ethanol and ethanol + triethanolamine as the entrainer, respec-tively. An improved PR equation of state with VDWl mixing rules is used to calculate the elution recovery of salicylic acid in supercritical CO2 and the results agree well with the experimental data.

  5. Fixed Bed Adsorption of Drugs on Silica Aerogel from Supercritical Carbon Dioxide Solutions

    Directory of Open Access Journals (Sweden)

    Giuseppe Caputo

    2013-01-01

    Full Text Available Supercritical adsorption coupled with the high adsorption capacity of silica aerogel allows the preparation of a new kind of delivery systems of poor water soluble drugs. In order to overcome drawbacks of conventional techniques where the use of liquid solvents can cause the fracture of aerogel porous structure, in this work a new adsorption process of drugs from a supercritical mixture is proposed. Adsorption takes place from a fluid solution of the drug in supercritical CO2 and ethanol as cosolvent. A fixed bed adsorption plant has been developed to allow fast mixing of fluid phase and effective contact in the adsorption column. The use of ethanol as cosolvent allows to overcome the limitation of supercritical adsorption due to low solubility of many drugs in supercritical CO2. Adsorption isotherms were measured for one-model substance, nimesulide, at 40°C, and breakthrough curve was experimentally obtained. The drug loading of the drug into silica aerogel was up to 9 wt%. The drug composite was characterized using scanning electron microscopy, and release kinetics of the adsorbed drug were also evaluated by in vitro dissolution tests. The dissolution of nimesulide from loaded aerogel is much faster than dissolution of crystalline nimesulide. Around 80% of nimesulide dissolves from the aerogel within 6 minutes, whereas dissolving 80% of the crystalline drug takes about 90 min.

  6. Winter ocean-ice interactions under thin sea ice observed by IAOOS platforms during N-ICE2015: Salty surface mixed layer and active basal melt

    Science.gov (United States)

    Koenig, Zoé; Provost, Christine; Villacieros-Robineau, Nicolas; Sennéchael, Nathalie; Meyer, Amelie

    2016-10-01

    IAOOS (Ice Atmosphere Arctic Ocean Observing System) platforms, measuring physical parameters at the atmosphere-snow-ice-ocean interface deployed as part of the N-ICE2015 campaign, provide new insights on winter conditions North of Svalbard. The three regions crossed during the drifts, the Nansen Basin, the Sofia Deep, and the Svalbard northern continental slope featured distinct hydrographic properties and ice-ocean exchanges. In the Nansen Basin, the quiescent warm layer was capped by a stepped halocline (60 and 110 m) and a deep thermocline (110 m). Ice was forming and the winter mixed layer salinity was larger by ˜0.1 g/kg than previously observed. Over the Svalbard continental slope, the Atlantic Water (AW) was very shallow (20 m from the surface) and extended offshore from the 500 m isobath by a distance of about 70 km, sank along the slope (40 m from the surface) and probably shed eddies into the Sofia Deep. In the Sofia Deep, relatively warm waters of Atlantic origin extended from 90 m downward. Resulting from different pathways, these waters had a wide range of hydrographic characteristics. Sea-ice melt was widespread over the Svalbard continental slope and ocean-to-ice heat fluxes reached values of 400 W m-2 (mean of ˜150 W m-2 over the continental slope). Sea-ice melt events were associated with nea