The Production of Preferred Orientation in a Concentrated Dispersion of Elongated and Flattened Grains

Rees, A. I.

doi:10.1086/627343

Cited by 117 publications

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“…It has been found that the preferred orientation of ferromagnetic minerals in sedimentary rocks is controlled primarily by the hydrodynamic factors, while the geomagnetic field only influences grains smaller than 0.03 mm. The minimum susceptibility directions have been found to be perpendicular to the bedding under all the sedimentation regimes; small deviations have been recorded in the case of sedimentation on a slope, but for practical purposes they can be ignored (usually they are less than 10~ The experiments are reported in papers by Rees (1966Rees ( , 1968Rees ( , 1971, Hamilton (1967), Hamilton et al (1968 and Rees and Woodall (1975).…”

Section: Magnetic Anisotropy Of Sedimentary Rocksmentioning

confidence: 97%

Magnetic anisotropy of rocks and its application in geology and geophysics

Hrouda¹

1982

Geophysical Surveys

1,028

571

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Abstract. Magnetic anisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization. In massive ore it is due to processes associated with emplacement and consolidation of an ore body as well as to ductile deformation.Hence, it can be used as a tool of structural analysis for almost all rock types. Moreover, it can influence considerably the orientation of the remanent magnetization vector as well as the configuration of a magnetic anomaly over a magnetized body. For these reasons it should be investigated in palaeomagnetism and applied geophysics as well.

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Section: Magnetic Anisotropy Of Sedimentary Rocksmentioning

confidence: 97%

Magnetic anisotropy of rocks and its application in geology and geophysics

Hrouda¹

1982

Geophysical Surveys

1,028

571

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“…The detailed analysis of shape-fabric for features with different eccentricity displays a recurrent general increase of iso-orientation with increasing eccentricity. This is expected when particles of different shape are subjected to grain-to-grain interactions and dispersive pressure (Rees 1968). Elongated particles develop a flow-related orientation better than sub-spherical particles.…”

Section: Fabric In Pyroclastic Rock Samplesmentioning

confidence: 97%

Image analysis and circular statistics for shape-fabric analysis: applications to lithified ignimbrites

Capaccioni

Valentini

Rocchi

et al. 1997

Bulletin of Volcanology

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Computer-assisted image analysis can be successfully used to derive quantitative textural data on pyroclastic rock samples. This method provides a large number of different measurements such as grain size, particle shape and 2D orientation of particle main axes (directional-or shape-fabric) automatically and in a relatively short time. Orientation data reduction requires specific statistical tests, mainly devoted to defining the kind of particle distribution pattern, the possible occurrence of preferred particle orientation, the confidence interval of the mean direction and the degree of randomness with respect to pre-assigned theoretical frequency distributions. Data obtained from image analysis of seven lithified ignimbrite samples from the Vulsini Volcanic District (Central Italy) are used to test different statistics and to provide insight about directional fabrics. First, the possible occurrence of a significant deviation from a theoretical circular uniform distribution was evaluated by using the Rayleigh and Tukey x 2 tests. Then, the Kuiper test was performed to evaluate whether or not the observation fits with a unimodal, Von Mises-like theoretical frequency distribution. Finally, the confidence interval of mean direction was calculated. With the exception of one sample (FPD10), which showed a well-developed bimodality, all the analysed samples display significant anisotropic and unimodal distributions. The minimum number of measurements necessary to obtain reasonable variabilities of the calculated statistics and mean directions was evaluated by repeating random collections of the measured particles at increments of 100 particles for each sample. Although the observed variabilities depend largely on the pattern of distribution and an absolute minimum number cannot be stated, approximately 1500-2000 measurements are required in order to get meaningful mean directions for the analysed samples.

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“…It may be noted that large values of h correspond to a rapid transfer of heat between the phases (LTE) and small values of h gives rise to relatively strong LTNE effects. Although the porous medium is anisotropic, the preferential orientation of the grains constituting the medium renders it isotropic in the direction parallel to the stratification (Rees [16], Rice et al [17]). For this reason, the porous medium could be taken as being horizontally isotropic.…”

Section: Problem Formulationmentioning

confidence: 99%

Boundary and thermal non-equilibrium effects on convective instability in an anisotropic porous layer

Shivakumara

Lee

Mamatha³

et al. 2011

J Mech Sci Technol

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The effects of boundary and local thermal non-equilibrium on the criterion for the onset of convection in a sparsely packed horizontal anisotropic porous layer are investigated. A two-field temperature model each representing the solid and fluid phases separately is used and the flow in the porous medium is described by the Brinkman extended-Darcy model. The lower boundary is rigid, while the upper boundary is considered to be either rigid or free with fixed temperature conditions at the boundaries. The stability equations are solved numerically using the Galerkin method to extract the critical stability parameters. The influence of local thermal non-equilibrium, mechanical and thermal anisotropy parameters representing the fluid and solid phases is assessed on the stability characteristics of the system. The existing results are obtained as limiting cases from the present study.

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The Production of Preferred Orientation in a Concentrated Dispersion of Elongated and Flattened Grains

Cited by 117 publications

References 0 publications

Magnetic anisotropy of rocks and its application in geology and geophysics

Magnetic anisotropy of rocks and its application in geology and geophysics

Image analysis and circular statistics for shape-fabric analysis: applications to lithified ignimbrites

Boundary and thermal non-equilibrium effects on convective instability in an anisotropic porous layer

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