Structures In Mixing Layer Research Articles

New phyllosilicate types in a carbonaceous chondrite matrix

CARBONACEOUS chondrites provide valuable information as they are the least altered examples of early Solar System material1. The matrix constitutes a major proportion of carbonaceous chondrites. Despite many past attempts, unambiguous identification of the minerals in the matrix has not been totally successful2. This is mainly due to the extremely fine-grained nature of the matrix phases. Recently, progress in the characterisation of these phases has been made by electron diffraction studies3,4. We present here the direct observation, by high resolution imaging, of phases in carbonaceous chondrite matrices. We used ion-thinned sections from the Murchison C2(M) meteorite for transmission electron microscopy. The Murchison matrix contains both ordered and disordered inter-growths of serpentine-like and brucite-like layers. Such mixed-layer structures are new types of layer silicates. © 1979 Nature Publishing Group.

Observations of a Rain-Formed Mixed Layer

The structure and dynamics of a rain-formed mixed layer (ML) are studied using hourly STD and profiling current meter casts. Because the fluid beneath the rain-formed ML was vertically homogeneous, the ML buoyancy g′ and horizontal velocity difference δV were easily observable as the ML depth h increased by entrainment from 7 to 18 m in a period of 8 h. The overall Richardson number of the mixed layer g′(h + d/2)/δV2 ≈ 0.7 during that period, where d is the thickness of the transition layer at the base of the ML. The entrainment rate was consistent with that of a laboratory surface half-jet (Ellison and Turner, 1959). The transition layer thickness was an appreciable fraction of the ML thickness, roughly d ≈ h/3. The density profile through the transition layer was linear and symmetric, and the overall Richardson number of the transition layer g′d/δV2 ≈ 1/4.

Measurements of the growth rate and structure in plane turbulent mixing layers

Mean velocity and turbulent intensity measurements are reported for five different plane turbulent mixing layers, each with a different velocity ratio. These experiments confirm that increasing free-stream turbulence causes increases in the growth rate and in the Reynolds stresses. Cross-correlation measurements with time delay made in the mixing layer with the lowest free-stream turbulence level show that the large-eddy structure had length scales in the two cross-stream directions which were roughly equal, unlike the results reported by Brown & Roshko (1974) and others. Further measurements showed that a vortex-street wake existed immediately downstream of the splitter plate and that transition occurred in the wake flow rather than in a normal laminar mixing layer. This is thought to have prevented the Brown–Roshko structures from forming. Comparison of the growth rate observed in this case with other measured results suggests that the essential or effective turbulent structure in mixing layers is independent both of velocity ratio and of the degree of two-dimensionality which exists in the largest scales of turbulence.

Influence of wave dispersion on vortex pairing in a jet

The geometry of large-scale structures in the turbulent mixing layer of a moderate Reynolds number jet is deduced from measurements of the fluctuating pressure in the hydrodynamic near field. The structures are rings of concentrated vorticity that distort with downstream distance until statistical axisymmetry disappears. The rings are spaced quasi-periodically and coalesce with each other, producing larger spacings. Statistical and flow-visualization techniques are applied to free and forced jets over a range of Reynolds numbers from 5000 to 50000 to demonstrate that rings of a given spacing do not coalesce with each other until they are far enough downstream that the local mixing layer has attained some critical thickness which scales with the wavelength of the vortex pair. Wave dispersion is evaluated as a plausible mechanism for localizing the coalescences. The central feature of the model is the observation that a shear layer is dispersive to wavelengths much longer than its thickness and non-dispersive to shorter waves.

Effect of free-stream turbulence on large structure in turbulent mixing layers

Flow-visualization investigations and correlation measurements show that the essentially two-dimensional structures which dominated the turbulent mixing layer of Brown & Roshko (1974) are formed only if the free-stream turbulence is low. If free-stream disturbances are significant, as is likely in most practical cases, including a mixing layer entraining ‘still air’ from the surroundings, three-dimensionality develops at an early stage in transition. Other recent experiments strongly suggest that the Brown-Roshko structure will not form if the initial mixing layer is turbulent or subject to instability modes other than spanwise vortices. Therefore the Brown-Roshko structure will be rare in practice. The alternative large structure in a mixing layer, found by several workers, is intense, but fully three-dimensional and thus less orderly than the Brown-Roshko structure.The balance of evidence suggests that if the Brown-Roshko structure does appear it will eventually relax into the alternative fully three-dimensional form: the Kármán vortex street behind a bluff body provides a precedent for slow development of three-dimensionality. However the Brown-Roshko structure, if formed, may well relax so slowly as to be identifiable for the full length of a practical flow.

7T wollastonite from Fuka, Okayama Prefecture

A 7T wollastonite was found at Fuka, Okayama Prefecture. Based on film intensity data, its stacking sequence has been found as (TTGTGTG). Here, T represents a (100) slab of wollastonite which is in continuous position with respect to the preceding one, and G a slab displaced by b⁄2. The structure may be regarded as a mixed-layer structure composed of three 2M and one 1T. The structure gave R=0.13 for 65 hk0 reflexions observed. The lattice constants are a=54.3±0.3 A, b=7.30±0.03 A, c=7.08±0.03 A, α=90.0±0.2°, β=95.5±0.2°, and γ=92.1±0.2°.

Structure determination of a mixed-layer bismuth titanate, Bi7Ti4NbO21, by super-high-resolution electron microscopy

The crystal structure of a bismuth titanate, Bi7Ti4NbO21, was determined on the basis of super-high- resolution images, taken by a recently constructed 1000 kV electron microscope, in which each cation site was approximately defined. It was found that the crystal has a mixed-layer structure, i.e. Bi4Ti3O12 and Bi3TiNbO9-like layers are alternately intergrown. The symmetry is orthorhombic with space group I2cm. The lattice parameters are a = 5.45, b = 5.42 and c = 58.1 Å. That the periodicity along c is twice that expected from a simple intergrowth can be accounted for by the rotation of octahedra. The lattice defects found are discussed in terms of twinning of the crystal.

Structure and heat energy budget of mixed layer capped by inversion during the period of polar outbreak over Kuroshio region : NINOMIYA K. and T. AKIYAMA, 1976. J. met. Soc. Japan, (2) 54 (3): 160–174

Structure and heat energy budget of mixed layer capped by inversion during the period of polar outbreak over Kuroshio region : NINOMIYA K. and T. AKIYAMA, 1976. J. met. Soc. Japan, (2) 54 (3): 160–174

Nickel- and chromium-bearing clay minerals in quartz magnesite rock at Izumma, Shizuoka Prefecture, Japan.

Nickel- and chromium-bearing clay minerals occur in quartz-magnesite rock which is an alteration product of serpentinite in the Sambagawa metamorphic terrane at Izumma, Shizuoka Prefecture. They are classified into two varieties on the basis of their mineralogical properties: Variety A occurs as aggregates each about 50μm long and up to 20μm wide in pore spaces between quartz grains of the quartz-magnesite rock. The aggregates consisting of very fine-grained crystals are rich in Cr2O3 and NiO. Of considerable interest is the fact that the contents of Cr2O3 and NiO vary from aggregate to aggregate (4.18-7.40% Cr2O3 and 3.28-27.9% NiO). Judging from the experimental results, this variety is considered to be smectite with abundant potassium in its interlayer positions. Variety B occurs as infillings in small fissures existing especially in the marginal part of the quartz-magnesite rock. The material is poor in Cr2O3 and NiO contents (0.05-0.35% Cr2O3 and 0.05-0.44% NiO) and is considerably homogeneous. This variety is considered to be a smectite with a basal reflection at 11 A which splits with ethylene glycol probably suggesting a mixed-layer structure. Variety A is considered to have been produced by the action of a chromium- and nickel-rich hydrothermal solution trapped in minor pore spaces between quartz grains of the quartz-magnesite rock, while Variety B, which is poorer in chromium and nickel than Variety A, was produced from a mobile hydrothermal solution with smaller amounts of chromium and nickel. There is a possibility that the development of the latter variety is intimately related to a lower temperature of water during secondary alteration processes.

Current and future trends in clay mineralogy—a review

AbstractProgress in science is not a linear function of time but resembles more closely a sigmoidal process in which new trends depend on the nucleation of new ideas and the re-activation of older studies. New and improved instruments, particularly electron microscopes and microprobes, infrared spectrometers and atomic absorption analysers have been the nucleating agents for many new lines of investigation. The interdisciplinary nature of clay mineralogy makes communication between different areas of study very important and the clay mineral societies have an important part to play in this respect.In the future, renewed efforts to obtain a convenient and reliable method of quantitative mineral analysis are likely to be made. Crystal structure analysis will be directed increasingly towards the study of order and disorder in cation distributions, layer charges, and layer stacking arrangements. Studies of domain structures in layer silicates will continue, and further refinements in mixed-layer structure analysis can be expected. Infrared spectroscopic analysis will increasingly become a major tool. The study of clay mineral synthesis and alteration in nature and in the laboratory shows signs of important re-activation. Clay-organic studies are developing in many directions.

Electron microdiffraction study of the superperiodicity of mixed-layer structures

Electron microdiffraction study of the superperiodicity of mixed-layer structures

寒気吹出時における黒潮海域の混合層•逆転層の構造と熱収支状況

寒気吹出時における黒潮海域の混合層•逆転層の構造と熱収支状況

The Intradiurnal Temperature Variation in the Upper Ocean Layer

Abstract An experiment to investigate the structure of the oceanic mixed layer was conducted between 28 September and 14 October, 1971, at 21N and between 66 and 67W aboard the NOAA Discoverer. During the experiment a quartz thermometer system capable of measuring temperature changes to within 0.001C was deployed from a surface buoy. Time-series temperature data were obtained from 10, 20, 30, 40 and 50 m depths and digitally recorded with a sampling interval of 1.1 min. This paper presents the results of an analysis of the temperature fluctuations in the mixed layer at selected levels for a three-day period characterized by fair weather conditions. STD measurements indicate there were no observable changes in salinity during this period. The observations show downward propagation of the diurnal heat wave at a rate of about 5 m hr−1 resulting in a turbulent exchange coefficient for the diurnal cycle of the order of 100 cm2 sec−1. During the heating portion of the cycle, which occurs during the day, the mix...

On density effects and large structure in turbulent mixing layers

Plane turbulent mixing between two streams of different gases (especially nitrogen and helium) was studied in a novel apparatus. Spark shadow pictures showed that, for all ratios of densities in the two streams, the mixing layer is dominated by large coherent structures. High-speed movies showed that these convect at nearly constant speed, and increase their size and spacing discontinuously by amalgamation with neighbouring ones. The pictures and measurements of density fluctuations suggest that turbulent mixing and entrainment is a process of entanglement on the scale of the large structures; some statistical properties of the latter are used to obtain an estimate of entrainment rates. Large changes of the density ratio across the mixing layer were found to have a relatively small effect on the spreading angle; it is concluded that the strong effects, which are observed when one stream is supersonic, are due to compressibility effects, not density effects, as has been generally supposed.

Investigation of the projections of the electron density on the z axis of micas with different degrees of hydration

Experimental results show that the height of the potassium maximum of the z projection of the electron density is correlated with the degree of hydration of micas. It is demonstrated that this can be explained not only by the displacement of potassium from the geometrical center of the interlayer gap but also by the appearance of mixed layer structures with layers containing different amounts of water in the intermediate packet.

Clay Minerals of the Green River Formation (Eocene) of Wyoming

X-ray analyses indicate that illite, smectite, loughlinite (Na20.3MgO. 6SIO2.8H20) and chlorite are present in the < 2/zm fraction of the lacustrine Green River Formation (Eocene) of Wyoming. Material amorphous to X-rays and random mixed-layer structures are present in subordinate amounts. Individual crystals vary from pure, well-ordered structures to poorly crystallized forms. Illite is ubiquitous, occurring in all the samples studied. It is generally associated with other clay minerals but frequently occurs as the only clay mineral found in the 'oil shales'. Smectite is present in all three members of the Green River Formation, but its presence frequently shows an inverse relationship to both analcime and loughlinite. Loughlinite is restricted to the saline facies of the Wilkins Peak Member. Chlorite occurs only in the silty and sandy beds of the Tipton Shale Member. The distribution of random mixed-layer structures and amorphous material is irregular. Several independent lines of evidence favour an in situ origin for many of the clay minerals reported in this investigation. The 'oil shales', which are in most cases varved, kerogenous, dolomitic marls, have a variable clay mineral composition. There is a marked tendency, however, for illite to be the dominant or the only clay mineral present. Apparently the geochemical conditions favouring the accumulation of the oil shales also favoured in situ generation of illite.

Transformation of Sericite into an Interstratified Mineral

AbstractSericite was K-depleted with molten LiNO3. The sample was changed into an interstratified structure in the presence of a small amount of LiNO3 after prolonged treatment, and in the presence of a considerable amount of LiNO3 a similar structure was formed after about 3 hr of reaction. In the case of the presence of the proper amount of NaCl, a mixed-layer structure was easily obtained by treatment for a long period of time with a considerable amount of molten LiNO3.The interstratified mineral had a basal spacing of 22 Å–23·3 Å which was expanded to 25 Å–27·6 Å by treatment with ethylene glycol.

Crystallography of the Hexagonal Ferrites

The hexagonal ferrites form an unusual group of complex, ferrimagnetic oxides embodying some 60 known crystal structures. These include phases for which the structural unit cell is larger than that in any known inorganic materials. The various hexagonal ferrite modifications fall into two distinct structural series, each formed by the ordered interlayering (stacking) of two discrete building blocks; these blocks stack along the c crystallographic axis in varying ratios and varying permutations to form strictly coherent, reproducible crystal structures. This mixed-layering aspect of the hexagonal ferrites permits direct, visual observation of the sequence of their subunit-cell stacking elements, after etching, by means of electron microscopy. The sequence of stacked blocks in such structures constitutes the only information lacking for a complete, three-dimensional structure determination. Direct access to this information provides an immediate, unique solution of the crystal structure problem in each case and thereby avoids the dilemmas of a classical diffraction approach to such large unit cells. Ferrite structures with hexagonal c dimensions of 1455 and 1577 angstroms have been uniquely solved by direct electron microscopic readout of surface etch features. One must exercise caution, however, in generalizing these findings to other materials. The method is successful in the case of the hexagonal ferrites because these are mixed-layer structures, wherein the building blocks react at different rates to a specific etchant. Mixed-layer systems are not uncommon in crystallography, and it is likely that similar techniques can be developed for other such materials. Regardless of the validity of this prognosis, however, it is quite evident that high-resolution replica electron microscopy is a most promising tool for the direct observation of surface structure on an ultramicro scale. During the studies reported here replica resolution capability was improved to about 10 angstroms; final resolution is limited by the particle size of the platinum shadowing material. Careful control of experimental conditions during replica preparation or an alternate choice of shadowing material, or both, might reasonably improve the resolution by a factor of 2. This resolution is within the range of most unit cell dimensions and approaches interatomic distances in solid-state materials. The potential of such an experimental capability needs no elaboration.

'Salt-biscuits'; a special growth structure of NaCl in salt sediments of the Tuz Goelue ('Salt Lake'), Turkey

ABSTRACT X-ray analyses indicate that illite, montmorillonite, and chlorite are abundant in the less-than-2-µ fraction of the Tipton Shale Member of the lacustrine Green River Formation (Eocene). Material amorphous to X-rays and mixed-layer structures are present in subordinate amounts. These minerals have been known to occur in rocks of lacustrine origin, but this investigation shows a general correlation between lithology and clay mineral suite. An illite suite is restricted to the to the argillaceous and analcimic tuffs near the top of the member. A chlorite-illite suite is found only in the coarser clastics developed in the middle of the member, and a montmorillonite-illite suite is restricted to the montmorillonitie tuffs and oil shales at the base of the member. Source rock and dia enetic alteration account for the distributional pattern.

Lidar applications in air pollution research and control.

The fundamental capabilities and limitations of the lidar (laser radar) in observing particulate concentrations in the atmosphere are discussed. The advantages of the lidar technique stem from its ability to obtain measurements remotely and at a high density in space and time. The quantitative application of the technique is limited by the accuracies with which: (1) the separate effects upon the return signal of back-scatter and attenuation may be identified; and (2) the optical parameters may be related to the characteristics of the aerosol. The main areas of utility for lidar in air pollution research and control are: (1) to observe the structure and height of mixing layers; (2) to measure the transport and diffusion of plumes or clouds of particulates; and (3) to remotely determine smoke-plume opacity. These applications are briefly reviewed and exemplified.