Formation Of Mixed Layer Research Articles

Modelling of 13CH4 injection experiments with graphite and tungsten test limiters in TEXTOR using the coupled code ERO-SDTrimSP

The 3D Monte-Carlo code ERO, which calculates erosion processes, impurity transport and deposition, has been coupled to the Monte-Carlo code SDTrimSP to simulate material mixing processes in wall components more precisely. SDTrimSP calculates the transport of ions in solids by means of the binary collision approximation. It keeps track of the depth dependent material concentration caused by implantation of projectiles in the solid. Modelling with the coupled code ERO-SDTrimSP is compared with dedicated TEXTOR experiments, in which the formation of mixed surface layers has been studied. In these experiments, methane 13CH4 was injected through graphite and tungsten spherical limiters during plasma exposure and the local redeposition probability was measured post mortem by surface analysis. A significant difference in the carbon 13C deposition efficiency, i.e. the ratio of the locally deposited to the injected amount of 13C, between graphite and tungsten was found, 4% for graphite and 0.3% for tungsten. Modelling of these experiments with ERO-SDTrimSP reproduces the clear substrate dependence with about 2% deposition efficiency on graphite and less than 0.5% on tungsten in good agreement with the experiment. The reason for the substrate dependence is partly explained by the higher physical sputtering yield of a thin carbon film on top of a tungsten substrate compared with a graphite substrate. Surface roughness of the materials has been identified to be another important parameter for the interpretation of the results.

Effect of Mesoscale Eddies on Subtropical Mode Water Variability from the Kuroshio Extension System Study (KESS)

Abstract Forty-eight profiling floats have been deployed in the Kuroshio Extension (KE) region since May 2004 as part of the Kuroshio Extension System Study (KESS) project. By combining the float temperature–salinity measurements with satellite altimetry data, this study investigates the role played by mesoscale eddies in controlling the property changes in North Pacific Subtropical Mode Water (STMW). Following a 3-yr period of low eddy activity in 2002–04, the KE showed a transition to a high eddy kinetic energy state in 2005. This transition is the result of delayed oceanic response to the 2002 shift in the basin-scale surface wind forcing in connection with the Pacific decadal oscillation. The high eddy kinetic energy state of the KE is characterized by successive shedding of strong cold-core rings into the recirculation gyre, resulting from the interaction of the KE jet with the Shatsky Rise or the preexisting cutoff rings. By transporting northern-origin, high-potential-vorticity (PV) KE water into the recirculation gyre, the enhanced eddy activity affects STMW in two ways: first, it hinders the formation of deep winter mixed layer (hence the source for STMW) by modifying the upper-ocean stratification and, second, it provides a direct high-PV source to mix with the surrounding low-PV STMW. The eddies’ influence upon STMW is observed to be both significant in magnitude and efficient in time. Relative to 2004, the PV signal in the core of STMW was reduced by one-half in 2005, and this weakening of STMW’s intensity occurred within a period of less than 7 months. This result supports recent findings by the authors based on historical temperature data that the variability in STMW formation depends more sensitively on the dynamic state of the KE than on the overlying atmospheric conditions.

The Impact of Surface Heat Flux and Wind on Thermal Stratification in Portage Lake, Michigan

Portage Lake is situated near the center of the Keweenaw Peninsula and is connected to Lake Superior via lengthy (> 7 km) navigation channels. Using moored thermistor records and meteorological data, we examine how changes in lake stratification are related to surface winds and heat flux. Frequent episodes of full water column mixing are observed throughout the summer. Convective mixing through surface cooling appears to be an important agent responsible for these events, as all occur during cold air outbreaks and when the net heat flux is directed out of the lake (negative). However, wind-induced mixing is also implicated in contributing to some vertical mixing events, as evidenced by two events initiated during a period of strong winds and declining, but not yet negative, heat fluxes. Our analysis indicates that each time the water column restratifies, it tends to become more susceptible to convectively-driven overturn during cold air outbreaks. This tendency is quantified by the estimated time over which surface cooling due to a specified set of conditions, characteristic of a cold air outbreak, would reduce the temperature contrast between the upper and lower layers by half. This time declines by more than an order of magnitude for successive restratification events observed in the summer of 1999. Our analysis also reveals successive formation and dissolution of a diurnal surface mixed layer in an otherwise homogeneous water column during a 10-day period of August 1999. This is attributed to the combination of relatively light winds and negative daily net heat fluxes.

Competitive adsorption of polymers on metal nanoparticles

We investigate the effect of system properties and adsorption sequence on competitive adsorption of poly(methyl methacrylate) (PMMA) and polystyrene (PS) on narrowly polydispersed cobalt (Co) nanoparticles ( D ∼ 27 nm). The adsorbed layer composition is studied using thermo-gravimetric analysis (TGA). We find that adsorbed layers of PS are completely displaced by PMMA when the solvent is a common good solvent. An adsorbed layer of only PMMA is also obtained through competitive adsorption from a common good solvent. However, in a selective solvent that is poor for PS, sequential adsorption leads to the formation of mixed layers.

Effect of a hard supra-thick interlayer on adhesion of DLC film prepared with PBIID process

Diamond-like carbon (DLC) films were prepared on aluminum alloy (A5052) and tungsten-carbide (WC) substrates with plasma-based ion implantation and deposition (PBIID) using hydrocarbon gas. Adhesion strength of DLC film was increased by the formation of interfacial mixing layer by carbon ion implantation and the production of SiCx nanolayer on the substrate prior to DLC deposition. As DLC films on the softer substrate were broken easily because of large deformation of substrate by local loads, the hard and supra-thick interlayer of plasma-sprayed tungsten-carbide (WC) with the thickness of 100–200μm was produced to protect the softer substrate between the DLC film and the substrate. The scratch testing evaluation showed that the supra-thick WC interlayer improved remarkably the adhesion of DLC films on the aluminum alloy substrate and the thicker WC interlayer was more effective for improvement of adhesion.

Effect of Ion Implantation on DLC Preparation Using PBIID Process

This paper discusses the effects of ion implantation on a diamond-like carbon (DLC) preparation using a hybrid process of plasma-based ion implantation and deposition (PBIID) using superimposed RF and negative high-voltage pulses. Adhesion strength of a DLC film on A-5052 and SUS304 was enhanced by carbon ion implantation to substrate materials. Cross section of interface between the DLC film and substrate was observed by scanning transmission electron microscopy (STEM) and analyzed by energy dispersive X-ray spectroscopy (EDS). It was found that the amorphouslike mixing layer of graded carbon component and substrate materials was produced in the ion-implanted region of substrate and the oxide layer on the substrate surface was destroyed. Besides the reduction of residual stress in the DLC film, the formation of amorphouslike mixing layer and the destruction of oxide layer led to the enhancement in adhesion strength of the DLC film. Residual stress, sp3 fraction, hardness, density, and hydrogen content of the DLC films deposited from acetylene and toluene plasma have the variation with negative pulsed voltage for ion implantation

Formation and pathways of intermediate water in the Parallel Ocean Circulation Model's Southern Ocean

The formation mechanisms and pathways of intermediate water in the Southern Ocean are analyzed from output of a high‐resolution ocean general circulation model. Deep winter mixed layer formation in the Southern Ocean is diagnosed from the model results and is found to be mostly consistent with observations. Diapycnal water mass transformations by air‐sea fluxes and internal mixing are quantified and split into mean and eddy components. The diapycnal formation of the water masses that constitute the Antarctic intermediate water layer in the southeast Pacific is found to occur mainly in the western Pacific Ocean in this model. In winter, convection up to 900 m is found to set the potential vorticity characteristics of this layer. Eddy fluxes of heat and buoyancy play an important role in the formation of the intermediate waters by transferring water from the southern parts of the subtropical gyres into the Antarctic Circumpolar Current (ACC) and vice versa. The effects of eddy fluxes are found to vary significantly along the path of the ACC. They are strongly concentrated in the regions near the Agulhas Return Current in the Indian Ocean and the Brazil‐Malvinas Confluence in the Atlantic.

Large eddy simulation of the turbulent round jet dynamics

Large Eddy Simulation (LES) of turbulent free round jet submerged in water has been performed at Reynolds number Re = 25 000. LES results are compared against the PIV measurements data for the same flow configuration. The processes of the mixing layer formation in the jet initial region and its evolution down-stream have been studied with the analysts of turbulent power spectra. The effect of the subgrid Smagorinsky model coefficient Cs on the jet hydrodynamics has been studied.

Dynamic erosion and deposition on carbon and tungsten due to simultaneous bombardment with deuterium and beryllium ions in plasmas

The erosion and redeposition processes of carbon (C) and tungsten (W) exposed to high-fluence deuterium (D) plasmas containing beryllium (Be) impurity are investigated by computer simulations. At high-fluence (>10 25 m −2), fluence-independent sputtering yields of C, W and the deposited Be, as well as the Be deposition rate (erosion rate) are obtained for both C and W. With increasing plasma temperature, a transition from Be deposition to W erosion occurs similarly to the case of C deposition on W [3,9], but the transition temperature is lower as a result of stronger sputtering of the deposited Be. At the Be plasma concentration of less than ∼4%, a balance between the incident and released Be is reached for both C and W at the plasma temperature of more than ∼10 eV due to the formation of Be-W and Be-C mixed layers. The dependence of the transition temperature on the Be plasma concentration and the plasma fluence is calculated.

Mixing Layer Formation near the Tropopause Due to Gravity Wave–Critical Level Interactions in a Cloud-Resolving Model

Abstract A plausible mechanism for the formation of mixing layers in the lower stratosphere above regions of tropical convection is demonstrated numerically using high-resolution, two-dimensional (2D), anelastic, nonlinear, cloud-resolving simulations. One noteworthy point is that the mixing layer simulated in this study is free of anvil clouds and well above the cloud anvil top located in the upper troposphere. Hence, the present mechanism is complementary to the well-known process by which overshooting cloud turrets causes mixing within stratospheric anvil clouds. The paper is organized as a case study verifying the proposed mechanism using atmospheric soundings obtained during the Central Equatorial Pacific Experiment (CEPEX), when several such mixing layers, devoid of anvil clouds, had been observed. The basic dynamical ingredient of the present mechanism is (quasi stationary) gravity wave–critical level interactions, occurring in association with a reversal of stratospheric westerlies to easterlies below the tropopause region. The robustness of the results is shown through simulations at different resolutions. The insensitivity of the qualitative results to the details of the subgrid scheme is also evinced through further simulations with and without subgrid mixing terms. From Lagrangian reconstruction of (passive) ozone fields, it is shown that the mixing layer is formed kinematically through advection by the resolved-scale (nonlinear) velocity field.

Abyssal monitoring of upper ocean processes

The transition from the early surface-reflected to near-surface-refracted waves is associated with a triplication pattern of arrivals which is very sensitive to upper ocean processes, including mixed layer formation, spicy fronts and internal waves. The pattern is well sampled at surface-conjugate depths (3 to 5 km). Deep and relatively short vertical arrays operating in the still, uniform abyssal environment are an attractive alternative to shallow in situ measurements.

DLC coating of a few microns in thickness on three-dimensional substrates

Uniform coating of the thick diamond-like carbon (DLC) on three-dimensional substrates was studied using a hybrid process of plasma-based ion implantation and deposition (PBIID). In the PBIID system, an RF pulse for plasma generation and a negative high-voltage pulse for ion implantation were supplied to a substrate through a single electrical feedthrough. Then the high-density plasma was produced along the substrate, leading to the formation of uniform coating film and the ion implantation on three-dimensional substrates. Ion implantation by PBII technique served to the reduction in compressive residual stress of DLC film and the formation of mixing layer between the DLC film and the substrate. As a result, the thick and good-adhesive DLC film with more than a few μm in thickness was almost uniformly prepared on the surface of cylindrical pipe, triangle prism, and trench structure. The deposition rate was approximately 1 μm/h using the toluene as a precursor gas. The hardness of the DLC films was found to be about 12 GPa by nano-indentation method.

イオンプラズマ複合プロセスによる低融点亜鉛合金へのDLC成膜と評価

A 3 µm thick DLC film of sufficient-adhesion was prepared on a zinc-alloy (Zn-4Al-3Cu) of low melting point (372°C) by a hybrid process of plasma-based ion implantation and deposition using hydrocarbon gases such as CH4, C2H2 and C7H8. In this process, an RF (13.56 MHz, 3 kW) pulse for plasma generation and a negative high-voltage pulse for ion implantation were supplied to a work-piece through a single electrical feed-through. As the work-piece itself was used for RF antenna for plasma generation, the high-density pulsed plasma was produced around the work-piece. Ion implantation with the negative high-voltage pulse (-10--20 kV, 2-4 µs and 1-4 kHz) led to the reduction in compressive residual stress of DLC film and the formation of mixing layer, resulting in the thick DLC film with a 3 µm in thickness on the Zn-alloy.

Role of convection in winter mixed layer formation in the Gulf of Maine, February 1987

Moored hourly observations of temperature and salinity from the Wilkinson Basin in the western Gulf of Maine, augmented with gulf‐wide hydrography surveys, document the winter mixed layer evolution between 4 and 18 February, 1987. Wind stresses and air‐sea heat fluxes were estimated from the Gulf of Maine (44005) National Data Buoy Center buoy winds and temperatures using bulk formulae. During the study period, a pair of strong cooling episodes due to offshore (southeastward) winds bracketed an even stronger cooling event due to a strong northeasterly storm. The 0–165 m water column cooled during the study period. Heat budgets based on the observations show that local air‐sea heat loss could only explain cooling in the upper 35–60 m of the Wilkinson water column. Lateral advection must have caused the deeper cooling. The Price, Weller and Pinkel [PWP] one‐dimensional bulk mixed layer model [Price et al., 1986], forced with observed surface fluxes, exhibited a mixed layer that deepened from about 60 m to 120 m during the initial stages of the nor'easter in general accordance with observation. Diagnostic PWP model experiments showed that convective overturning was required to produce the observed mixed layer depth of 120 m. Direct wind mixing alone could deepen the model mixed layer to only about 80 m. However, the model property profiles produced by a 10‐day PWP model run differed significantly from observations, which reflected advection effects. Observed hydrographic property distributions combined with horizontal velocity estimates from a Dartmouth linear, three‐dimensional, finite‐element circulation model of the Gulf (FUNDY5) help to explain differences between the PWP model and observations in terms of lateral advection in the upper 65 m. The observed cooling between 65 m and 165 m must be related to advection.

Intermolecular interactions in the binary systems of cationic and nonionic surfactants

The micellization of the mixtures of cationic (cetyltrimethylammonium bromide, cetylpyridinium bromide) and nonionic (Triton X-100) surfactants at various content of components in aqueous solutions, as well as the adsorption of surfactants at the air/solution interface were studied. The effect of negative deviation from the ideality was discovered during the formation of mixed micelles and adsorption layers. Various theoretical approaches to the quantitative description of mixed systems were compared within the framework of the model of pseudophase separation. The parameters of intermolecular interaction in mixed micelles and adsorption layers, excess free energies of micellization and adsorption, compositions of micelles and adsorption layers were calculated. It was shown that the use of various theoretical approaches for the analysis of interactions in surfactant mixtures leads to close numerical results. It was shown that the composition of mixed micelles and adsorption layers, as well as the parameters of intermolecular interaction and the excess free energy depend on the relative content and molecular structure of surfactants (mixture components).

Wave breaking and critical levels for propagating inertio‐gravity waves in the lower stratosphere

AbstractThis paper analyses and interprets the formation of mixed layers due to propagating inertio‐gravity waves observed during the Fronts and Atlantic Storm‐Track EXperiment. The data used are high‐vertical‐resolution soundings launched from different sites located in the North Atlantic sector. In agreement with other studies, attributing the origin of the inertio‐gravity waves to the adjustment of the jet stream near fronts, the largest waves observed are often located in the vicinity of and above frontal bands. The amplitude of these waves is large enough that they give rise to narrow mixed layers. By a detailed analysis of the waves' characteristics, we can distinguish whether such a mixing is favoured by the presence of an inertia‐critical level, where |Ω|=f, or results from wave‐induced convective instability occurring far from critical levels. Here, Ω is the wave intrinsic frequency and f is the Coriolis parameter. These observations highlight the importance of inertio‐gravity waves in the vertical exchanges that occur in the stratosphere. Copyright © 2002 Royal Meteorological Society

Mixed-layer mica-chlorite in very low-grade metaclastites from the Malàguide Complex (Betic Cordilleras, Spain)

AbstractMixed-layered phyllosilicates with composition intermediate between mica and chlorite were identified in very low-grade metaclastites from the Malàguide Complex (Betic Cordilleras, Spain), and studied by X-ray diffraction, and transmission and analytical electron microscopy. They occur both as small grains in the rock matrix, and associated with muscovitechlorite stacks. Transmission electron microscope observations revealed a transition from chlorite to ordered 1:1 interstratifications through complex 1:2 and 1:3 interstratifications. Analytical electron microscopy data indicate a composition slightly different from the sum of discrete trioctahedral chlorite and dioctahedral mica. The types of layer transitions suggest that mixed-layer formation included two main processes: (1) the replacement of a brucite sheet by a cation sheet in the chlorite structure; and (2) the precipitation of mica-like layers between the chlorite layers. The strongest diffraction lines in oriented X-ray patterns are: 12.60 Å (002), 7.98 Å (003), 4.82 Å (005) and 3.48 Å (007).

Mathematical model for predictive control of the bell-less top charging system of a blast furnace

Abstract Modern blast furnaces use bell-less top systems for the charging of the solid feed into the furnace. The complete potential of the charging system for distributing the material in the furnace cross-section in any desired profile can be achieved only by using a suitable charge distribution model. By considering the flow of different types of solid particles like iron ore, sinter and coke through the bin and rotating chute, equations have been developed for the particle trajectories. The formation of the ring shaped hill of material by the accumulation of the falling material has been modeled considering the angle of repose, rolling and layer penetration. These relationships have been combined with appropriate corrections for the burden descent and the mixed layer formation to develop the overall geometry of the stock line. The burden charge model has been used in an optimization routine to determine the best charging pattern to transit from an existing stock line geometry to a new geometry. The models have been tested in an operating furnace and incorporated in a supervisory control system.

Effects of atmospheric conditions on mechanical mixed layer formation and wear behaviour in A356–15 vol.-%SiCp composite

Dry sliding wear tests have been carried out on A356–15 vol.-%SiCp metal matrix composite to evaluate the effects of argon and oxygen atmospheres on mechanical mixed layer (MML) formation and wear behaviour. The wear rate of the composite under an oxygen atmosphere is higher by one order of magnitude than that under an argon atmosphere. The formation of the MML depends strongly on the atmospheric conditions. The MML formed under argon is found to be more stable and results in a lower wear rate within the parametric regime, compared with that formed under an oxygen atmosphere. The mechanism of material removal under an argon atmosphere is by delamination. Under the oxygen atmosphere the MML is highly unstable, and material removal is by severe two and three body abrasion at low load and low sliding velocity. At high load and high sliding velocity, the material removal mechanism is by delamination.

Formation of mixed layers and compounds on beryllium due to C + and CO + bombardment

Compound formation on a clean beryllium single crystal (0 0 0 1) during bombardment with 5 keV C + and 3 and 5 keV CO + ions is studied by means of in situ X-ray photoelectron spectroscopy (XPS). In combination with in situ Rutherford backscattering analysis (RBS), TRIDYN computer simulation, and measurements of the weight change of the sample due to the bombardment, models for the sample composition changes and erosion mechanisms are derived for both ion species. In the case of C + bombardment a carbon layer builds up on top of the beryllium. The transition region from pure beryllium to pure carbon consists partly of Be 2C and the beryllium erosion stops as the covering carbon layer develops. During CO + bombardment a deposition/erosion equilibrium is established. After initial C and O accumulation, the beryllium substrate is covered by a ternary mixture layer of about 10 nm thickness containing BeO, elementary carbon and C–O compounds. Be 2C is present only at low fluences and before the equilibrium is established. The erosion of beryllium proceeds and a chemical erosion process limits the deposited amounts of carbon and oxygen via emission of CO.