scholarly journals Automatic reconstruction of polycrystalline ice microstructure from image analysis: application to the EPICA ice core at Dome Concordia, Antarctica

1999 ◽  
Vol 45 (151) ◽  
pp. 547-554 ◽  
Author(s):  
Michel Gay ◽  
Jerome Weiss
Keyword(s):  
Preliminary Analysis ◽  
Structural Parameters ◽  
Ice Core ◽  
Grain Morphology ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Thin Sections ◽  
Polycrystalline Ice ◽  
Analysis Application ◽  
The Mean

AbstractA digital image-processing approach is proposed which allows the extraction of two-dimensional polycrystalline ice microstructure (grain boundaries) from thin sections observed between cross-polarisers. It is based on image segmentation of colour images. The method is applied to the preliminary analysis of the shallow ( Holocene) ice of the European Project for Ice Coring in Antarctica (EPICA) ice core at Dome Concordia. Structural parameters, such as the mean cross-sectional area, shape anisotropy and grain morphology, are obtained. The interest and limitations of this automatic procedure are discussed.

scholarly journals Automatic reconstruction of polycrystalline ice microstructure from image analysis: application to the EPICA ice core at Dome Concordia, Antarctica

1999 ◽  
Vol 45 (151) ◽  
pp. 547-554 ◽  
Author(s):  
Michel Gay ◽  
Jerome Weiss
Keyword(s):  
Preliminary Analysis ◽  
Structural Parameters ◽  
Ice Core ◽  
Grain Morphology ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Thin Sections ◽  
Polycrystalline Ice ◽  
Analysis Application ◽  
The Mean

AbstractA digital image-processing approach is proposed which allows the extraction of two-dimensional polycrystalline ice microstructure (grain boundaries) from thin sections observed between cross-polarisers. It is based on image segmentation of colour images. The method is applied to the preliminary analysis of the shallow ( Holocene) ice of the European Project for Ice Coring in Antarctica (EPICA) ice core at Dome Concordia. Structural parameters, such as the mean cross-sectional area, shape anisotropy and grain morphology, are obtained. The interest and limitations of this automatic procedure are discussed.

scholarly journals Determination of the Mean Number of Bonds per snow grain And of the Dependence of the Tensile Strength of Snow on Stereological Parameters

1978 ◽  
Vol 20 (83) ◽  
pp. 329-341 ◽  
Author(s):  
H. Gubler
Keyword(s):  
Tensile Strength ◽  
Density Distribution ◽  
Structural Parameters ◽  
Theoretical Density ◽  
Thin Sections ◽  
Distribution Parameters ◽  
The Mean ◽  
Fundamental Units ◽  
Effective Distribution

AbstractA theoretical density distribution of the Dumber of bonds per grain as a function of the mean number of bonds per grain is derived from the assumption of randomness and isotropy of grain and grain-bond location and orientation. The knowledge of the theoretical density distribution allows the determination of the effective distribution parameters from section planes or thin sections. The concept of the fundamental unit to describe the strength of snow is introduced. Structural parameters developed on the basis of the fundamental units show improved correlations with the tensile strength.

scholarly journals Measurement of snow density and microstructure using computed tomography

2002 ◽  
Vol 48 (161) ◽  
pp. 312-316 ◽  
Author(s):  
Chris C. Lundy ◽  
Michael Q. Edens ◽  
Robert L. Brown
Keyword(s):  
Computed Tomography ◽  
Plane Surface ◽  
Ct Images ◽  
Two Dimensional ◽  
Ct Scanner ◽  
Cross Sectional ◽  
Thin Sections ◽  
Kinetic Growth ◽  
Similar Images ◽  
Non Destructive

AbstractIn the past, two-dimensional images of internal snow structure have been obtained through plane surface sections or thin sections. These techniques are time-consuming and necessarily destroy the snow specimen. Computed tomography (CT) allows similar images to be obtained, but in a more efficient and non-destructive manner. To demonstrate the methodology, a CT scanner was used to obtain cross-sectional images over time of a snow sample undergoing kinetic-growth metamorphism. Densities calculated from the CT images correlated well to density measured using a traditional method. A procedure was developed that allows the CT image to be converted to binary in an objective manner. Employing innovative stereological software, the microstructural properties (grain diameter, bond diameter, neck length and intercept length) of the snow were then measured from the two-dimensional CT images. The presented methodology provides significant improvements over previous techniques, requiring less time and labor to obtain high-quality microstructural data.

scholarly journals Shallow-ice microstructure at Dome Concordia, Antarctica

2000 ◽  
Vol 30 ◽  
pp. 8-12 ◽  
Author(s):  
Laurent Arnaud ◽  
Jérôme Weiss ◽  
Michel Gay ◽  
Paul Duval
Keyword(s):  
Crystal Size ◽  
Accumulation Rate ◽  
Ice Core ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Size Distributions ◽  
Thin Sections ◽  
Crystal Size Distributions ◽  
Size Profile ◽  
The Mean

AbstractThe shallow-ice microstructure at Dome Concordia, Antarctica, has been studied between 100 m and 580 m. An original digital-image-processing technique has been specially developed to extract ice microstructure (grain boundaries) from thin sections prepared during the two first scientific EPICA field seasons (1997/98 and 1998/99). Using this, not only the mean crystal size, but also crystal-size distributions and shape anisotropy were determined. The mean crystal-size profile as well as crystal-size distributions reveal normal grain growth up to 430 m. Between 430 m and 500 m, a marked decrease of crystal size is observed and compared with a similar trend obtained in the "old" Dome C ice core formerly associated with the Holocene/Last Glacial transition (Duval and Lorius, 1980). This seems to indicate a slightly lower accumulation rate (by <10%) at Dome C. The shapes of the crystal-size distributions, though very similar, do evolve with depth and seem to be sensitive to climatic changes. An increasing flattening of crystal shape is observed with depth. This allowed estimation of the vertical strain rate in the shallow part of the ice sheet.

scholarly journals Determination of the Mean Number of Bonds per snow grain And of the Dependence of the Tensile Strength of Snow on Stereological Parameters

1978 ◽  
Vol 20 (83) ◽  
pp. 329-341 ◽  
Author(s):  
H. Gubler
Keyword(s):  
Tensile Strength ◽  
Density Distribution ◽  
Structural Parameters ◽  
Theoretical Density ◽  
Thin Sections ◽  
Distribution Parameters ◽  
The Mean ◽  
Fundamental Units ◽  
Effective Distribution

AbstractA theoretical density distribution of the Dumber of bonds per grain as a function of the mean number of bonds per grain is derived from the assumption of randomness and isotropy of grain and grain-bond location and orientation. The knowledge of the theoretical density distribution allows the determination of the effective distribution parameters from section planes or thin sections. The concept of the fundamental unit to describe the strength of snow is introduced. Structural parameters developed on the basis of the fundamental units show improved correlations with the tensile strength.

scholarly journals Ice Structure and Crystal Fabrics of the 2200 M Ice Core at Vostok Station, Antarctica

1988 ◽  
Vol 10 ◽  
pp. 223-223
Author(s):  
N.I. Barkov ◽  
V.Ya. Lipenkov ◽  
V.N. Petrov
Keyword(s):  
Ice Core ◽  
Three Dimensional ◽  
Air Bubbles ◽  
The Core ◽  
Polycrystalline Ice ◽  
Vostok Station ◽  
Dimensional Parameters ◽  
The Mean ◽  
Ice Fabrics

Both the ice structure and the ice fabric along the 2200 m ice core at Vostok Station were investigated during the 25th, 29th and 30th Soviet Antarctic Expeditions.Several kinds of three-dimensional parameters of polycrystalline ice were measured, e.g. the mean diameter and size distribution of ice crystals and air bubbles, and specific volumeThe variation in most of these parameters along the core reflects not only the process of metamorphism in ice but also changes in the environmental conditions at the surface. The causes of these variations are discussed, in order to estimate the possibility of a paleoclimatic interpretation.The evolution of c-axis fabrics with depth is discussed in relation to the ice-deformation conditions.A comparison of ice fabrics at Vostok, Byrd Station and Camp Century shows that similar mechanisms cause the reorientation of crystals. The role of temperature in fabric development is discussed.

Choroidal structural changes and choroidal vascularity index in patients with systemic hypertension

2021 ◽  
pp. 112067212110356
Author(s):  
Nazife Aşıkgarip ◽  
Emine Temel ◽  
Ahmet Kıvrak ◽  
Kemal Örnek
Keyword(s):  
Blood Pressure ◽  
Systolic Blood Pressure ◽  
Patient Group ◽  
Structural Changes ◽  
Structural Parameters ◽  
Systemic Hypertension ◽  
Cross Sectional ◽  
Treatment Naïve ◽  
The Mean ◽  
The Impact

Purpose: To assess the impact of systemic hypertension on the choroidal structure and choroidal vascularity index (CVI). Methods: This prospective cross-sectional study comprised 50 eyes of 50 treatment-naive hypertensive patients and 50 eyes of 50 healthy subjects. Choroidal thickness (CT) was measured in the subfoveal region, 1500 µm nasal to the fovea, and 1500 µm temporal to the fovea. Binarization of the enhanced depth-optical coherence tomography images was performed with Image-J software. The CT, choroidal area (CA), luminal area (LA), and CVI were compared statistically. Results: The mean subfoveal, nasal, and temporal CT were decreased in the patient group (p 0.003, 0.026, and 0.001, respectively). The mean CA, LA, and CVI were decreased in the patient group in comparison to controls ( p = 0.047, 0.009, and 0.016 respectively). The correlation between the subfoveal CT and systolic blood pressure was significant ( r = −0.450, p < 0.001). There was a significant correlation between the systolic blood pressure and CVI ( r = −0.401, p < 0.001). Conclusion: The significant decrease in the structural parameters and CVI show that choroid is affected in patients with treatment-naive hypertension.

scholarly journals Ice Structure and Crystal Fabrics of the 2200 M Ice Core at Vostok Station, Antarctica

1988 ◽  
Vol 10 ◽  
pp. 223 ◽  
Author(s):  
N.I. Barkov ◽  
V.Ya. Lipenkov ◽  
V.N. Petrov
Keyword(s):  
Ice Core ◽  
Three Dimensional ◽  
Air Bubbles ◽  
The Core ◽  
Polycrystalline Ice ◽  
Vostok Station ◽  
Dimensional Parameters ◽  
The Mean ◽  
Ice Fabrics

Both the ice structure and the ice fabric along the 2200 m ice core at Vostok Station were investigated during the 25th, 29th and 30th Soviet Antarctic Expeditions. Several kinds of three-dimensional parameters of polycrystalline ice were measured, e.g. the mean diameter and size distribution of ice crystals and air bubbles, and specific volume The variation in most of these parameters along the core reflects not only the process of metamorphism in ice but also changes in the environmental conditions at the surface. The causes of these variations are discussed, in order to estimate the possibility of a paleoclimatic interpretation. The evolution of c-axis fabrics with depth is discussed in relation to the ice-deformation conditions. A comparison of ice fabrics at Vostok, Byrd Station and Camp Century shows that similar mechanisms cause the reorientation of crystals. The role of temperature in fabric development is discussed.

scholarly journals Curvilinear Coordinate System for Mathematical Analysis of Inclined Buoyant Jets Using the Integral Method

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Aristeidis A. Bloutsos ◽  
Panayotis C. Yannopoulos
Keyword(s):  
Coordinate System ◽  
Integral Method ◽  
Two Dimensional ◽  
Mean Flow ◽  
Buoyant Jet ◽  
Cross Sectional ◽  
Buoyant Jets ◽  
Curvilinear Coordinate ◽  
The Mean ◽  
Cartesian Coordinate

The development of a local system of orthogonal curvilinear coordinates, which is appropriate to monitor the flow of an inclined buoyant jet with reference to the basic Cartesian coordinate system is presented. Such a system is necessary for the correct application of the integral method, since the well-known Gaussian profiles should be integrated on the cross-sectional area of inclined buoyant jet, where they are valid. This is the major advantage of the present work compared to all other integral methods using Cartesian coordinate systems. Consequently, the flow and mixing governing partial differential equations (PDE), i.e., continuity, momentum, buoyancy, and/or tracer conservation, are written in the local orthogonal curvilinear coordinate system and, then, the Reynolds substitution regarding mean and fluctuating components of all dependent variables is applied. After averaging with respect to time, the mean flow PDEs are taken, omitting second-order terms, as the dynamic pressure and molecular viscosity, compared to the mean flow and mixing contributions of turbulent terms. The latter are introduced through empirical coefficients. The Boussinesq’s approximation regarding small density differences is taken into consideration. The system of PDEs is closed by assuming known spreading coefficients along with Gaussian similarity profiles. The methodology is applied in the inclined two-dimensional buoyant jet; thus, PDEs are integrated on the jet cross-sectional area resulting in ordinary differential equations (ODE), which are appropriate to be solved by applying the 4th order Runge-Kutta algorithm coded in either FORTRAN or EXCEL. The numerical solution of ODEs, concerning trajectory of the inclined two-dimensional buoyant jet, as well as longitudinal variations of the mean axial velocity, mean concentration, minimum dilution, and entrainment velocity or entrainment coefficient, occurs quickly, saving computer memory and effort. The satisfactory agreement of results with experimental data available in the literature empowers the usefulness of the proposed methodology in inclined buoyant jets.

scholarly journals On the Rates of Growth of Grains and Crystals in South Polar Firn

1969 ◽  
Vol 8 (53) ◽  
pp. 241-252 ◽  
Author(s):  
Anthony J. Gow
Keyword(s):  
Crystal Growth ◽  
Cross Sections ◽  
Mean Annual Temperature ◽  
Growth Data ◽  
Cross Sectional ◽  
Thin Sections ◽  
The Mean ◽  
Image Position ◽  
Rates Of Growth ◽  
Strong Linear Relationship

The size of firn crystals as a function of age has been investigated in thin sections to a depth of 49 m at the South Pole. Grain cross-sections increased in size from 0.24 mm2 at 0.1 m depth to 0.63 mm2 at 10 m. Crystals, as distinct from grains, increased in size from 0.18 to 0.43 mm2 over the same interval, implying that grains are generally composed of just one or two crystals rather than several as is frequently contended. The mean crystal cross-section increased linearly with the age of the firn at a rate of 0.0006 mm2 year−1; in 388 year old firn at 49 m the crystal size measured 0.63 mm2. Analysis of crystal-growth data from other locations in Antarctica and Greenland also revealed a strong linear relationship between the mean cross-sectional arcas (D2) of crystals (in mm2) and their ages in years (t), i.e. . The fact that the temperature dependence of the crystal growth rate K can be expressed very satisfactorily in an equation of the form K = K0 exp (E/RT) confirms predictions that crystal growth in firn is essentially analogous to grain growth in metallic and ceramic sinters. An extrapolation of available data indicates that crystal growth rates in dry firn could be expected to vary by two orders of magnitude (0.0003 to 0.03 mm2 year−1) over the temperature range −60° to −15°C. A method of utilizing crystal growth-mean annual temperature data to determine accumulation rates in snow is demonstrated.

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