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Area Distribution (area + distribution)

Distribution by Scientific Domains

Life Sciences	25%

Selected Abstracts

Discussion of landslide self-organized criticality and the initiation of debris flow

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2007
Chen Chien-Yuan
Abstract The study contains descriptions of landslides and debris flows in a small upland catchment in Taiwan between 1986 and 2004. This catchment, the Chushui Creek, is situated near the epicentre of the 1999 M7·6 Chi-Chi earthquake. This is an area with high background erosion rate. The Chi-Chi earthquake caused a sharp increase in the rate of mass wasting in the epicentral area, and the data presented in this study illustrates the geomorphic change associated with the earthquake. The measurements of the geometry of the trunk stream of the Chushui catchment also show its change due to the impact of a strong typhoon in 1996. Two channel reaches that were affected by separate debris flows during this event were identified. Each reach has three sections: scour, transfer and deposition. Cross profiles of these sections show a systematic change from V-shaped bedrock channel in the scour areas to flat-floored channel in the transfer and deposition areas. Debris flows also occurred on other occasions in this channel, and their frequency has increased since the 1999 earthquake. In addition, this study contains precise geographic and statistical descriptions of the landslides triggered by three typhoons and an earthquake that affected the catchment since 1996. The total landslide area is measured for different time intervals, and a marked increase in landslide incidence is found after the 1999 earthquake. Frequency,area plots of the 126 landslides in the catchment indicate a power-law scaling with an exponent of about -1·5 of these quantities, as has been observed in other studies. We propose that a link exists between landslide frequency,area distributions and initialization of debris flow in the catchment. It may be classified as a self-organized criticality process with a critical frequency,area distribution for the landslide population. In this case, the landslide frequency,area distribution is useful in quantifying the severity of the trigger and the contribution of landslides to debris flow. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Channel head location and characteristics using digital elevation models

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2006
G. R. Hancock
Abstract The drainage network is the conduit through which much surface water and sediment are routed within a catchment. In a catchment, the position of where hillslopes begin and channels end has long been considered the position of transition between diffusive processes upslope and the more incisive fluvial processes downslope. Consequently, understanding channel head location is an important issue in understanding catchment hydrology and geomorphology. This study examines channel head position and characteristics in a catchment in Arnhem Land, Northern Territory, Australia. In this study the position of channel heads was mapped within the catchment and plotted on a reliable digital elevation model of the catchment. It was found that the majority of channel heads have relatively small source areas and that graphical catchment descriptors, such as the area,slope relationship and cumulative area distribution, can provide reliable measures of the field position of the heads of first-order streams and the transition from hillslope to channel. The area,slope relationship and cumulative area distribution are also shown to be good tools for determining digital elevation model grid size which can capture hillslope detail and the transition from hillslope to channel. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Testing of the SIBERIA landscape evolution model using the Tin Camp Creek, Northern Territory, Australia, field catchment

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2002
G. R. Hancock
Abstract The SIBERIA landscape evolution model was used to simulate the geomorphic development of the Tin Camp Creek natural catchment over geological time. Measured hydrology, erosion and geomorphic data were used to calibrate the SIBERIA model, which was then used to make independent predictions of the landform geomorphology of the study site. The catchment, located in the Northern Territory, Australia is relatively untouched by Europeans so the hydrological and erosion processes that shaped the area can be assumed to be the same today as they have been in the past, subject to the caveats regarding long-term climate fluctuation. A qualitative, or visual comparison between the natural and simulated catchments indicates that SIBERIA can match hillslope length and hillslope profile of the natural catchments. A comparison of geomorphic and hydrological statistics such as the hypsometric curve, width function, cumulative area distribution and area,slope relationship indicates that SIBERIA can model the geomorphology of the selected Tin Camp Creek catchments. Copyright 2002 © Environmental Research Institute of the Supervising Scientist, Commonwealth of Australia. [source]

Epifluorescence microscopy and image analysis of high-level polycyclic aromatic hydrocarbon contamination in soils

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2006
J. Chadwick Roper
Abstract Interactions between polycyclic aromatic hydrocarbons (PAHs) and soil are an important determinant of their chemical availability and transport. Laboratory examination of microscale PAH,soil interaction is limited by the availability of methods for particle-scale observation. Inverted epifluorescence microscopy, combined with digital photography and computer image analysis, was evaluated for specificity and linearity using dissolved PAHs. A pyrene filter (excitation wavelength, 360,400 nm; emission wavelength, 450,520 nm) gave nonspecific PAH fluorescence, and bias for fluoranthene, benzo[b]fluoranthene, benzo[g, h, i]perylene, and benz[a]anthracene was quantified in comparison to that for pyrene. Concentrations ranging from 1 to 10 mM for anthracene, fluoranthene, and pyrene and from 1 to 50 mM for naphthalene produced a linear response with low interpixel variability. Liquid-phase analyses validated use of the technique for the descriptive analysis of PAH distribution in solid samples, but liquid-phase calibration was not quantitative for spiked or field-contaminated soils. The mean luminance for three field soils was proportional to the values predicted from their chemically measured concentrations and to values from spiked, aged, uncontaminated materials. Image analysis of laboratory- and field-contaminated samples determined the area distribution of fluorescent intensity and the size of fluorescent areas exceeding a threshold luminance. These qualitative descriptions of the microscale spatial distribution of PAH contamination are presented as potential endpoints for future research on biogeochemical interactions in heavily contaminated solids. [source]

The use of digital elevation models in the identification and characterization of catchments over different grid scales

HYDROLOGICAL PROCESSES, Issue 9 2005
Dr G. R. Hancock
Abstract This study examines the ability of well-known hydrological and geomorphological descriptors and statistics to differentiate between catchments with spatially varying geology, size and shape subject to the same climate in the Northern Territory, Australia. The effect of digital elevation model grid resolution on these statistics is also examined. Results demonstrate that catchment descriptors such as the area,slope relationship, cumulative area distribution and hypsometric curve can differentiate between catchments with different geology and resultant morphology, but catchment network statistics are insensitive to differences in geology. Examination of the effects of digital elevation model grid scale demonstrates that while considerable catchment information can be gained at digital elevation grids greater than 10 m by 10 m, hillslope and hydrological detail can be lost. Geomorphic descriptors such as the area,slope relationship, cumulative area distribution, width function and Strahler statistics were shown to be sensitive to digital elevation model grid scale, but the hypsometric curve was not. Consequently, caution is needed when deciding on an appropriate grid resolution as well as the interpretation and analysis of catchment properties at grid scales greater than that for optimal hillslope and area aggregation definition. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Radon track imaging in CR-39 plastic detectors using confocal scanning laser microscopy

JOURNAL OF MICROSCOPY, Issue 3 2005
N. PETFORD
Summary Confocal scanning laser microscopy (CSLM) has been used to provide the first images of radon track populations in two external CR-39 plastic detectors. Measurements of variables including track area distribution and estimates of the angle of track inclination (dip) derived from surface CSLM sections are presented. CSLM depth slices, combined with three-dimensional (3D) visualization techniques, provide a new, non-destructive way of examining the 2D and 3D geometry of the etched tracks within solid-state nuclear track detectors that may prove useful in complementing existing optical microscopy methods. [source]

Population estimation of human embryonic stem cell cultures

BIOTECHNOLOGY PROGRESS, Issue 2 2010
Thomas Thurnherr
Abstract Traditionally, the population of human embryonic stem cell (hESC) culture is estimated through haemacytometer counts, which include harvesting the cells and manually analyzing a fraction of an entire population. Obviously, through this highly invasive method, it is not possible to preserve any spatial information on the cell population. The goal of this study is to identify a fast and consistent method for in situ automated hESC population estimation to quantitatively estimate the cell growth. Therefore, cell cultures were fixed, stained, and their nuclei imaged through high-resolution microscopy, and the images were processed with different image analysis techniques. The proposed method first identifies signal and background by computing an image specific threshold for image segmentation. By applying a morphological operator (watershed), we split most physically overlapping nuclei, leading to a pixel area distribution of isolated signal areas on the image. On the basis of this distribution, we derive a nucleus area model, describing the distribution of the area of cell debris, single nuclei, and small groups of connected nuclei. Through the model, we can give a quantitative estimation of the population. The focus of this study is on low-density human embryonic stem cell populations; hence cultures were measured at days 2,3 after seeding. Compared with manual cell counts, the automatic method achieved higher accuracy with <6% error. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source]