Digital Image Analysis Techniques Research Articles

Changes in fractal dimension during aggregation

Experiments were performed to evaluate temporal changes in the fractal dimension of aggregates formed during flocculation of an initially monodisperse suspension of latex microspheres. Particle size distributions and aggregate geometrical information at different mixing times were obtained using a non-intrusive optical sampling and digital image analysis technique, under variable conditions of mixing speed, coagulant (alum) dose and particle concentration. Pixel resolution required to determine aggregate size and geometric measures including the fractal dimension is discussed and a quantitative measure of accuracy is developed. The two-dimensional fractal dimension was found to range from 1.94 to 1.48, corresponding to aggregates that are either relatively compact or loosely structured, respectively. Changes in fractal dimension are explained using a conceptual model, which describes changes in fractal dimension associated with aggregate growth and changes in aggregate structure. For aggregation of an initially monodisperse suspension, the fractal dimension was found to decrease over time in the initial stages of floc formation.

Strain Distribution within Geosynthetic-Reinforced Slopes

Geosynthetic-reinforced slopes are conventionally designed using methods based on limit equilibrium. In order to estimate the factor of safety against internal stability using these methods, the distribution of the reinforcement peak tensile forces with height must be assumed. A linear distribution of reinforcement peak tension with height, with zero tension at the crest and maximum peak tension at the toe of the structure, has often been assumed. Although this assumption may be appropriate for the design of vertical geosynthetic-reinforced walls, little evidence has been collected so far justifying this distribution for the design of geosynthetic-reinforced slopes. A combination of centrifuge testing and digital image analysis is undertaken in order to obtain the strain distribution within geosynthetic-reinforced slopes under prefailure conditions. Specifically, digital image analysis techniques are used to determine the displacement distribution along reinforcement layers in reduced-scale models subjected to increasing g levels. A sigmoid function was useful to fit raw displacement data and estimate the strain distribution along reinforcement layers. Analysis of reinforcement strain results shows that the location of the reinforcement maximum peak strain does not occur near the toe of the structure, but was located approximately at midheight of the reinforced slopes, at the point along the critical failure surface directly below the crest of the slope. The pattern of reinforcement peak strain with height obtained for prefailure conditions is similar to that obtained for failure conditions. The estimated factor of safety is found to be a good indicator of the magnitude of the reinforcement maximum peak strain for geosynthetic-reinforced slopes built with different configurations.

Foliar and tuber assessment of late blight (Phytophthora infestans (Mont.) de Bary) reaction in cultivated potato (Solanum tuberosum L.)

Host plant resistance is an important component to the management of potato late blight,Phytophthora infestans (Mont.) de Bary. Assessment of potato lines (Solanum tuberosum L.) with various levels of resistance toP. infestans (US8, A2 genotype) were evaluated in field trials, greenhouse controlled environment chambers and inoculated tuber reactions. Five lines (AWN86514-2, B0692-4, B0718-3, Jacqueline Lee, and B0288-17) with strong foliar resistance to late blight were identified in these inoculated field trials. Greenhouse controlled environment chamber studies allowed resistant and susceptible lines to be distinguished, but the 1998 greenhouse results did not correlate well with field data. Four lines (A084275-3, Bzura, MSG007-1, and MSG297-4RD) evaluated by a digital image analysis technique demonstrated tuber resistance based upon average reflective index values in the inoculated tuber studies. Tuber resistance did not correlate with field foliar resistance. Based upon these results, field assessment of foliar reaction toP. infestans provides the best measure for assessing late blight resistance in potato. Tuber resistance to late blight can be identified among lines with varying levels of foliar resistance.

Interrelationships among angiogenesis, proliferation, and apoptosis in the tumor microenvironment during N-methyl-N-nitrosourea androgen-induced prostate carcinogenesis in rats.

Proliferation, apoptosis and angiogenesis are critical biologic processes altered during carcinogenesis. Surrogate biomarkers of these processes represent potential intermediate endpoints for short-term intervention studies with preventive and therapeutic agents. We examined the interrelationships among these processes during prostate carcinogenesis induced by N-methyl-N-nitrosourea (MNU) in male Wistar-Unilever rats. Immunohistochemical and digital image analysis techniques were used to evaluate the proliferation index, the apoptotic index and microvessel density (MVD) in tissue representing stages of prostate carcinogenesis. The proliferation index in the normal glandular epithelium of the prostate is lower than that observed in hyperplastic foci and atypical hyperplasia (P < 0.01) and is further increased in carcinoma (P < 0.01). Apoptosis in the normal prostate epithelium or hyperplastic lesions is lower than in adenocarcinoma (P < 0.01). In parallel to proliferation index, MVD increases as prostate cancer progresses. As tumors enlarge, we observed a predictable change in biomarker expression within the tumor microenvironment. We examined prostate tumors vertical line 1 cm in diameter and biomarker expression was quantified within the peripheral (outer 1-2 mm), central (perinecrotic) and intermediate (remaining) areas of each tumor. The proliferation index is higher (P < 0.01) in the intermediate area than either in the peripheral area or central area. Similarly, the vascular density in the intermediate area is higher (P < 0.01) than either in the peripheral or central area. The apoptotic index is higher (P < 0.05) in the central perinecrotic core than that in either the intermediate or the peripheral area. In conclusion, we observe that angiogenesis, proliferation and apoptosis are linked biological processes predictably altered temporally and spatially during prostate carcinogenesis in the MNU model. These biomarker changes are similar to those reported in human prostate carcinogenesis and represent potential biomarkers for the assessment of dietary, chemopreventive and therapeutic agents.

The Use of Remote Sensing and Landscape Metrics to Describe Structures and Changes in Urban Land Uses

Remote sensing technology has great potential for acquisition of detailed and accurate land-use information for management and planning of urban regions. However, the determination of land-use data with high geometric and thematic accuracy is generally limited by the availability of adequate remote sensing data, in terms of spatial and temporal resolution, and digital image analysis techniques. This study introduces a methodology using information on image spatial form—landscape metrics—to describe urban land-use structures and land-cover changes that result from urban growth. The analysis is based on spatial analysis of land-cover structures mapped from digitally classified aerial photographs of the urban region Santa Barbara, CA. Landscape metrics were calculated for segmented areas of homogeneous urban land use to allow a further characterization of the land use of these areas. The results show a useful separation and characterization of three urban land-use types: commercial development, high-density residential, and low-density residential. Several important structural land-cover features were identified for this study. These were: the dominant general land cover (built up or vegetation), the housing density, the mean structure and plot size, and the spatial aggregation of built-up areas. For two test areas in the Santa Barbara region, changes (urban growth) in the urban spatial land-use structure can be described and quantified with landscape metrics. In order to discriminate more accurately between the three land-cover types of interest, the landscape metrics were further refined into what are termed ‘landscape metric signatures’ for the land-use categories. The analysis shows the importance of the spatial measurements as second-order image information that can contribute to more detailed mapping of urban areas and towards a more accurate characterization of spatial urban growth pattern.

Experimental and Data Analysis Techniques Used for High Strain Rate Tests on Cohesionless Soil

Abstract Experimental methods used to subject drained triaxial compression axisymmetric test specimens composed of cohesionless soils to very high strain rates and analyze the resulting data are presented. Included is the use of a custom gravity drop-frame loading system to generate the high strain rates and a custom square triaxial cell to minimize optical distortion. Methods to collect and analyze the experimental results are also presented. High-speed film photography, coupled with digital image analysis techniques, are used to capture specimen deformations. Experimental issues such as image analysis of specimens, optical corrections, time synchronization of photographic images with data acquisition, inertial effects, global versus local strain measurements, axisymmetric shape of the specimen during deformation, and membrane compliance are examined by analyzing test results that were performed at high strain rates.

Fractal analysis of eroded surfaces by digital image processing

Jet impingement erosion test rig has been used to erode titanium alloy specimens (Ti–4Al–4V). Eroded surface profiles have been obtained by vertical sectioning method for light microscopy observation. Mixed fractals have been measured from profile images by a digital image processing and analysis technique. The use of this technique allows glimpsing a quantitative correlation among material properties, fractal surface topography and erosion phenomena.

Palaeosecular variation of the Earth's magnetic field during the last 10000 years based on the annually laminated sediment of Lake Nautäjarvi, central Finland

A palaeomagnetic study of the Lake Nautajärvi sediment sequence in central Finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for Holocene stratigraphic correlation and age control. Based on x-ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the Lake Nautajärvi varve sequence, which covers nearly 10000 years with an estimated counting error of less than ±1% and a mean sedimentation rate of 0.66 mm yr-1. We reconstructed a record of the palaeomagnetic secular variation (PSV) of the Earth's magnetic field in this nearly 7 m long section of clastic-organic varves. Mineral magnetic measurements indicated that pseudosingle-domain magnetite is the major carrier of the remanence. PSV shows many of the familiar features of declination and inclination that have previously been recorded in northern Europe. In addition, the Lake Nautajärvi record contains a continuous record of relative palaeointensity.

Prolonged calcium transients and myocardial remodelling in early experimental uraemia.

Cardiovascular disease is the most common cause of premature death in patients with end-stage renal disease, possibly due to a specific 'uraemic cardiomyopathy'. This study was designed to investigate the cardiac changes induced by a moderate impairment of renal function in a model of uraemia. Male Wistar rats (n=11) were rendered uraemic by 5/6 nephrectomy or sham operated (n=11). After 4 weeks, cardiac dimensions were measured from fixed tissue sections using a digital image analysis technique. In parallel groups of animals, cardiac myocytes were isolated and studied for evidence of functional changes attributable to uraemia. After steady-state field stimulation at 0.5 Hz, intracellular Ca(2+) handling (using Fura-2) was investigated. Up to 20 consecutive transients were averaged as the extracellular Ca(2+) was increased. The 5/6 nephrectomy group had a 75% reduction in glomerular filtration rate, and a 2- to 3-fold increase in serum urea and creatinine compared with sham-operated control animals (P<0.0001). However, the blood pressure was found to be similar in each group. Histology of the intact hearts (five pairs) showed a significant increase in tissue cross-sectional area (14%; P<0.04), cross-sectional area of the left ventricle (22%; P<0.04), and a significant increase in left ventricular wall thickness (15%; P<0.03). In the single cardiac cell study, under basal conditions (1-2 mM extra-cellular Ca(2+)) no significant differences in intracellular Ca(2+) were observed, but in high extracellular Ca(2+) the uraemic cells were slower to return to diastolic intracellular Ca(2+) levels (P<0.05). The data provide evidence of altered myocardial structure and function in early experimental uraemia. The changes described are consistent with concentric hypertrophy of the left ventricle, which occurs in the absence of hypertension.

Questioning the evidence for Earth's oldest fossils

Structures resembling remarkably preserved bacterial and cyanobacterial microfossils from about 3,465-million-year-old Apex cherts of the Warrawoona Group in Western Australia currently provide the oldest morphological evidence for life on Earth and have been taken to support an early beginning for oxygen-producing photosynthesis. Eleven species of filamentous prokaryote, distinguished by shape and geometry, have been put forward as meeting the criteria required of authentic Archaean microfossils, and contrast with other microfossils dismissed as either unreliable or unreproducible. These structures are nearly a billion years older than putative cyanobacterial biomarkers, genomic arguments for cyanobacteria, an oxygenic atmosphere and any comparably diverse suite of microfossils. Here we report new research on the type and re-collected material, involving mapping, optical and electron microscopy, digital image analysis, micro-Raman spectroscopy and other geochemical techniques. We reinterpret the purported microfossil-like structure as secondary artefacts formed from amorphous graphite within multiple generations of metalliferous hydrothermal vein chert and volcanic glass. Although there is no support for primary biological morphology, a Fischer--Tropsch-type synthesis of carbon compounds and carbon isotopic fractionation is inferred for one of the oldest known hydrothermal systems on Earth.

Analysis of evaporating thick liquid films on solids

The diffusion-controlled evaporation of small circular volatile liquid films from solid surfaces was monitored by employing video microscopy from a plan view and then applying digital image analysis techniques. The decrease of the liquid-solid contact area of these films during the last stages of the evaporation was found to be linear with time. This paper presents experimental results of four organic liquid films (n-nonane, n-octane, toluene, n-butanol) on three substrates poly(methyl methacrylate), poly(ethylene terephthalate) (Mylar), and glass. The linear decreases of the surface areas of hanging drops from a polypropylene fiber for the same liquids were also monitored using both plan and side view video cameras for comparison. Analyses of optically recorded liquid film and drop shapes were carried out and a diffusion model depending on the presence or absence of the substrate was developed. By combining the experimental area decrease of a spherical drop due to the diffusion-controlled evaporation with that of a small spherical cap shaped liquid film resting on a solid surface, it is possible to calculate the small contact angles (less than 10°) of the wetting thick liquid films on solids. The relationship between film evaporation rate and the solid-liquid interfacial interactions is also discussed.

Wheeltracking Fatigue Simulation of Bituminous Mixtures

ABSTRACT In order to better simulate the dynamic effects of a rolling wheel travelling over an asphalt pavement, and to better understand the initiation and growth of cracks in bituminous pavement layers, a wheeltracking fatigue simulation facility was developed. This experimental facility permitted the testing of large slab specimens (305×305×50mm) using dynamic wheel loadings. The slab specimens were supported on a soft elastomeric foundation that simulated overlay behaviour on top of a weak pavement structure. Digital photography and image analysis techniques were utilised to monitor the initiation and propagation of fatigue cracks on the bottom of these slabs. Two standard Irish mixtures, a Dense Base Course Macadam (DBC) and Hot Rolled Asphalt (HRA), were evaluated with the fatigue simulation facility. Crack damage was seen to initiate on the bottom face of the slab specimen in a direction parallel to the direction of wheel travel. These cracks would interconnect to form a full width crack that propa...

The effect of a tibial baseplate undersurface peripheral lip on cement penetration in total knee arthroplasty

Many total knee arthroplasty (TKA) tibial baseplates have a peripheral lip or cement pocket theoretically to increase cement penetration by decreasing edge escape of the cement squeeze film on baseplate impaction. We reviewed 177 consecutive TKAs (89 nonlipped and 87 lipped baseplates) performed by a single surgeon, using the same third-generation tibial cementation techniques. Cement penetration patterns of the lateral 12 mm of proximal tibia were examined by a semiautomatic computerized digital image analysis technique. Penetration in the lipped baseplate was double that of the nonlipped baseplate at the component's lateral edge (P<.05) and continued to be statistically significantly greater to 4 mm from edge. From 5 to 7 mm, the difference was no longer statistically significant, and from 8 to 12 mm, the penetration was equal.

Quantitative characterization of spatial arrangement of shrinkage and gas (air) pores in cast magnesium alloys

Pressure die-cast magnesium (Mg) alloys contain both shrinkage and gas (air) microporosity. Characterization of shrinkage and (gas) air microporosity is essential for understanding microstructure–properties correlations in these alloys. In this contribution, a recently reported digital image analysis (DIA) technique has been further developed to separately quantify and characterize the attributes of shrinkage and air microporosity in AM series of cast Mg alloys. The image analysis procedure is utilized to measure the nearest-neighbor distributions of the shrinkage and gas (air) pores, and to quantify the clustering tendency of the pores. A new affinity parameter is defined to characterize the affinity of gas (air) pores to shrinkage pores and vice versa. The affinity parameters are computed from the same image analysis data.

Instantaneous bubble velocity measurements using digital image analysis

Recently the author of this paper presented an application of image-processing techniques to identify and to measure the parameters of the bubble in bubbly flow.1 In this paper, a new technique—a noninvasive measurement, using digital image analysis techniques, based on multiframe record to measure the instantaneous bubble rise velocity—is presented.

Wheeltracking Fatigue Simulation of Bituminous Mixtures

ABSTRACT In order to better simulate the dynamic effects of a rolling wheel travelling over an asphalt pavement, and to better understand the initiation and growth of cracks in bituminous pavement layers, a wheeltracking fatigue simulation facility was developed. This experimental facility permitted the testing of large slab specimens (305×305×50mm) using dynamic wheel loadings. The slab specimens were supported on a soft elastomeric foundation that simulated overlay behaviour on top of a weak pavement structure. Digital photography and image analysis techniques were utilised to monitor the initiation and propagation of fatigue cracks on the bottom of these slabs. Two standard Irish mixtures, a Dense Base Course Macadam (DBC) and Hot Rolled Asphalt (HRA), were evaluated with the fatigue simulation facility. Crack damage was seen to initiate on the bottom face of the slab specimen in a direction parallel to the direction of wheel travel. These cracks would interconnect to form a full width crack that propagated through the depth of the slab. Under similar loading conditions the DBC mix had significant lower fatigue strength (two orders of magnitude).

Determination of bed voidage using water substitution and 3D magnetic resonance imaging, bed density and pressure drop in packed-bed reactors

Using a water substitution method to determine bed voidage, an independent relationship between bed height and bed voidage was observed for the trilobe (virgin and crushed) and cylindrical alumina supports. Typical bed voidage values of 0.49–0.51 (virgin trilobe). 0.46–0.52 (crushed trilobe) and 0.28–0.31 (cylindrical) were observed within 0.1 and 0.19 m i.d. columns. However, bed voidage values were approximately 6% larger in the 0.05 m i.d. column and could be attributed to a greater extent of wall zone voidage. Dense packing of the columns in all cases resulted in a decrease in bed voidage which had significant effects on bed density and column pressure drop. In addition to the water substitution measurements of bed voidage, three-dimensional magnetic resonance imaging (MRI) data were used in conjunction with digital image analysis techniques to obtain one-dimensional radial profiles of voidage from comparable alumina catalyst support material. Similar results and trends in voidage values between the water substitution method and those obtained from MRI data are evident. In all cases, the analysis of the MRI data yields voidage values that are consistently higher than those obtained from water substitution measurements.

Experiments on particle dispersion in a plane wake

Detailed experimental results are presented concerning the effects of vortex structures on the solid particle dispersion process in a plane wake. Previous numerical results have indicated that vortex structures in plane wakes can disperse intermediate Stokes number particles into highly organized patterns. The cross stream spatial dispersion values associated with these particles were computed to be several times greater than that associated with fluid elements. The major objective of this study was to obtain direct experimental results concerning the time dependent particle dispersion process in a plane wake. The experimental approach used in this work primarily involves laser sheet pulsed imaging of glass bead particles in a wake downstream of a blunt trailing edge. Two sizes of glass beads with nominal diameters of 10 and 30 μm were used as particles in an air flow. The associated Stokes numbers of the particles were 0.15 and 1.4. Digital image analysis techniques were employed to identify and determine particle locations and velocities. The results demonstrate that particle dispersion in plane wakes can produce highly organized patterns of particle concentrations. The particles at intermediate Stokes number are focused into sheet-like regions near the boundaries of the large scale vortex structures. In addition the spatial dispersion of the intermediate Stokes number particles was much larger than the smaller Stokes number particles. These experimental results strongly support previous numerical simulation findings.

ROAD MARKING ASSESSMENT USING DIGITAL IMAGE ANALYSIS.

This paper presents a systematic approach for the automated measurement of road marking wear (erosion) using digital video image analysis techniques. These techniques are used to digitize an image of the road surface and thereafter manipulate the image to obtain the extent of any road marking within the image. Simply, after digitization, a process known as image segmentation was used to analyse the image to ascertain the picture elements (pixels) within the image that were clearly road markings and those which were not. Subsequently, a further process, called image enhancement, was developed to remove misclassified pixels. Finally, a novel process (feature description) was used to compare the road marking with an ‘ideal’ to determine any erosion of the original road marking. The above system was tested on a set of images of road markings. The accuracy of this system in comparison to a manual method of assessing road marking erosion was investigated using statistical techniques. The results show clearly that the automated methodology is accurate and reliable.

Road marking assessment using digital image analysis

This paper presents a systematic approach for the automated measurement of road marking wear (erosion) using digital video image analysis techniques. These techniques are used to digitize an image of the road surface and thereafter manipulate the image to obtain the extent of any road marking within the image. Simply, after digitization, a process known as image segmentation was used to analyse the image to ascertain the picture elements (pixels) within the image that were clearly road markings and those which were not. Subsequently, a further process, called image enhancement, was developed to remove misclassified pixels. Finally, a novel process (feature description) was used to compare the road marking with an ‘ideal’ to determine any erosion of the original road marking. The above system was tested on a set of images of road markings. The accuracy of this system in comparison to a manual method of assessing road marking erosion was investigated using statistical techniques. The results show clearly that the automated methodology is accurate and reliable.