Fraction Of Total Area Research Articles

Evidence of atrial mechanical dysfunction by acoustic quantification in abnormal relaxation and restrictive filling patterns of diastolic dysfunction in patients with coronary artery disease.

This study made use of acoustic quantification (AQ) to investigate if left atrial (LA) mechanical function was impaired in patients with diastolic dysfunction, which might not be detected by conventional Doppler echocardiography. One hundred and ten patients with coronary artery disease (mean age 65+/-11 years, 80% male) underwent echocardiography prospectively while AQ was performed using harmonic imaging at the apical four-chamber view to evaluate LA function. By Doppler echocardiography, left ventricular (LV) diastolic dysfunction in the form of abnormal relaxation pattern (ARP) was present in 84, pseudonormal (PN) in nine and restrictive filling pattern (RFP) in 10 patients. LA mechanical dysfunction with impaired total fractional area change (FAC) of </=20% was present in 17/19 (89%) patients in the RFP/PN group, but was observed in 27/84 (32%) patients with ARP. Despite identical diastolic Doppler indices between patients with ARP with preserved (n=57) and impaired total FAC, the latter group had significantly lower LV ejection fraction (P<0.001), larger LV volumes (P<0.05 and 0.002, respectively), as well as larger LA area (P<0.001) and lower LA peak emptying and filling rates (both P=0.001). In contrast, there was no difference in nearly all of the parameters of LA function, LV systolic function and LV volume between patients with RFP/PN and ARP with FAC </=20%. Both active and passive LA pump functions were impaired in patients with RFP/PN or ARP with FAC </=20%. LA mechanical dysfunction was found to be present in one-third of the patients with ARP of diastolic dysfunction despite a high MV-A. It was also present in almost all the patients with RFP/PN pattern of diastolic dysfunction. Therefore, AQ may provide information on atrial mechanical function complementary to that of Doppler echocardiography.

A new model for the fracture energy budget of phreatomagmatic explosions

The fragmentation of magma and of the hosting country rocks is a major process in explosive eruptions. It is important to quantify the mechanical energy needed for fragmentation in order to assess the physical processes of this volcanic phenomenon. This paper presents a method to calculate the fragmentation energy of country rock using granulometry data of a typical phreatomagmatic Eifel maar volcano explosion. The total fracture area of country rock fragments in one tephra layer was quantified and related to the critical fragmentation energy of these country rocks. The rock parameters critical shear stress and critical fragmentation energy were determined experimentally, whereas the pre-volcanic crack inventory was measured in the field. The paper concludes with the calculation of the energy balance (i.e. partitioning of thermal energy into kinetical energy and mechanical energy of the fragmentation) of one Eifel maar volcanic explosion.

Mitochondrial distribution and glycogen dynamics suggest diffusion constraints in muscle fibers of the blue crab, Callinectes sapidus.

The scaling of mitochondrial distribution, citrate synthase activity, and post-contractile glycogen recovery was examined in muscle fibers of the blue crab, Callinectes sapidus. The fast-twitch muscle fibers of C. sapidus can reach extremely large dimensions, which may impose constraints on aerobic metabolic processes. However, muscle cells from small crabs are not giant, meaning that during development muscle fibers cross and greatly exceed the surface area to volume (SAV) and diffusion threshold that is adhered to by the cells of most organisms. Cell diameters in the smallest size class were approximately 100 microm, while the largest size class had cell diameters in excess of 500 microm. In the smallest cells, the fractional area of subsarcolemmal and intermyofibrillar mitochondria was similar. However, in the largest cells, mitochondria were almost exclusively subsarcolemmal. Total fractional area of mitochondria was highest in the largest cells due to a proliferation of subsarcolemmal mitochondria. In contrast, citrate synthase activity decreased as cell size increased. Following burst contractile activity, glycogen concentrations decreased significantly and remained depressed for several hours in muscle comprised of giant cells, consistent with previous findings that anaerobic glycogenolysis fuels certain components of post-contractile recovery. However, in muscle composed of the smallest muscle cells, glycogen levels did not decrease significantly following burst activity. While normal scaling of aerobic metabolism would predict a slower aerobic recovery in larger animals, the present results suggest that cellular organization, SAV, and intracellular diffusion distances also impose constraints on aerobic processes in C. sapidus.

Individual age and connective tissue lipofuscin in the hard clam Eurhomalea exalbida

In the hard clam Eurhomalea exalbida, autofluorescent granules were detected in high concentrations in the connective tissue around the intestine and in other tissues. Autofluorescence combined with Sudan black B and PAS positive reactions suggested that these granules were lipofuscin-like. The concentration of this material in the connective tissue (CT) around the intestine was quantified by image analysis and expressed as total area fraction occupied by lipofuscin granules. Lipofuscin concentration was distinctly better related with individual age as determined from stable isotope-validated shell growth bands than with any morphometric parameter. This relationship was described best by a Gompertz model: Lipofuscin t =24.79e−e −0.029(Age t−58.578) ( N=38; r nl 2=0.882). Age was predicted from lipofuscin CT concentration by a von Bertalanffy model: Age t=68.00(1−e −0.146(Lipofuscin t +0.028) ) 0.664 ( N=38; r nl 2=0.933). Our findings suggest that lipofuscin CT concentration in E. exalbida is a function of individual age. If this holds true for bivalves in general, lipofuscin may be a suitable proxy for age in species with less clear shell growth band patterns.

An extreme-value approach to detect clumping and an application to tropical forest gap-mosaic dynamics

Although forest tree pattern-dynamics has long been a focus for ecological theory, many aspects of basic analysis remain problematic. This paper describes, examines and illustrates an ‘extreme-value’ approach to clump detection. Simulations demonstrate that the approach, though simple, is sensitive and well suited to identifying aggregation, even in small data sets. The test is complementary to the χ2 approach and significantly outperforms it when high-density clusters form a relatively small fraction of the total area. This difference holds true as density declines, though the power of both tests decreases and the χ2 test eventually fails. Though powerful, the extreme-value tests are slightly conservative. The approach is adaptable to other null distributions and applications. An illustration uses tree data from a Ugandan forest plot with records from 1939 to 1992. One plausible explanation for observed stem increases in this plot is an unusually high incidence of large tree-fall events. Evidence for this is sought through spatial localization of various stem populations. Chi-square tests detect non-random density patterns in the populations that comprise ‘all stems &gt; 10 cm diameter recorded in the 1992 survey’, and ‘all recruits in 1976’. In the extreme-value test three populations are found to be clumped, these are ‘pioneers &gt; 10 cm diameter recorded in the 1992 survey’, ‘all recruits in 1992’ and again ‘all recruits in 1976’. These patterns, particularly the pioneer trees and stem recruitment, signal a ‘gap-dynamic process’ of tree regeneration. Despite this, the trends observed in the Ugandan plot appear unlikely to be caused by tree-falls alone. Various technical and ecological aspects of the extreme-value approach and tree spatial analyses are discussed.

Inversion of net ecosystem CO2 flux measurements for estimation of canopy PAR absorption

AbstractThe fractional absorption of photosynthetically active radiation (fPAR) is frequently a key variable in models describing terrestrial ecosystem–atmosphere interactions, carbon uptake, growth and biogeochemistry. We present a novel approach to the estimation of the fraction of incident photosynthetically active radiation absorbed by the photosynthetic components of a plant canopy (fChl). The method uses micrometeorological measurements of CO2 flux and incident radiation to estimate light response parameters from which canopy structure is deduced. Data from two Ameriflux sites in Oklahoma, a tallgrass prairie site and a wheat site, are used to derive 7‐day moving average estimates of fChl during three years (1997–1999). The inverse estimates are compared to long‐term field measurements of PAR absorption. Good correlations are obtained when the field‐measured fPAR is scaled by an estimate of the green fraction of total leaf area, although the inverse technique tends to be lower in value than the field measurements.The inverse estimates of fChl using CO2 flux measurements are different from measurements of fPAR that might be made by other, more direct, techniques. However, because the inverse estimates are based on observed canopy CO2 uptake, they might be considered more biologically relevant than direct measurements that are affected by non‐physiologically active components of the canopy. With the increasing number of eddy covariance sites around the world the technique provides the opportunity to examine seasonal and inter‐annual variation in canopy structure and light harvesting capacity at individual sites. Furthermore, the inverse fChl provide a new source of data for development and testing of fPAR retrieval using remote sensing. New remote sensing algorithms, or adjustments to existing algorithms, might thus become better conditioned to ‘biologically significant’ light absorption than currently possible.

Temperature- and pressure-dependent transient analysis of single component permeation through nanoporous carbon membranes

Using a transient analysis of permeation, i.e. the time lag method, as a function of temperature and pressure, it is shown that each of the parameters needed to fully evaluate adsorption and diffusion can be obtained in situ. These experiments were conducted on a supported tubular nanoporous carbon membrane, 5.1 cm 2 in area and prepared by ultrasonic deposition of poly(furfuryl alcohol) onto a porous stainless steel support. The permeation experiments were conducted at temperatures ranging from 25 to 225°C and over a range of pressures from 100 to 700 kPa. Under these conditions the fluxes ranged from 10 −7 to 10 −4 mol/m 2/s with permeances ranging between 10 −12 and 10 −9 mol/m 2/s/Pa. Heats of adsorption were found to be 2.5, 2.21, 3.05 and 2.52 kcal/mol for N 2, O 2, Ar and CO 2, respectively, and generally lower than those reported for granular nanoporous carbons. The apparent activation barriers to diffusion were also found to be low at 2.06, 5.87, 4.12, 5.89 and 2.19 kcal/mol for He, N 2, O 2, Ar and CO 2. These results point to the presence of two parallel pathways for transport — the major one through the nanopores but a second through a few defect pores. Assumed to be on the order of 50 nm in diameter, these defects were calculated to represent a total area fraction of 3.43×10 −9.

Overexpression of Cu2+/Zn2+ superoxide dismutase protects against early diabetic glomerular injury in transgenic mice.

Ex vivo and in vitro observations implicate superoxide as a mediator of cell injury in diabetes, but in vivo evidence is lacking. In the current studies, parameters of glomerular injury were examined in hemizygous nondiabetic transgenic mice (SOD) and streptozotocin-diabetic (D) transgenic mice (D-SOD), which overexpress human cytoplasmic Cu2+/Zn2+ superoxide dismutase (SOD-1), and in corresponding wild-type littermates (WT, D-WT) after 4 months of diabetes. In both SOD and D-SOD mice, renal cortical SOD-1 activity was twofold higher than values in the WT mice; blood glucose and glycosylated hemoglobin (GHb) levels did not differ in the two diabetic groups. Urinary albumin excretion, fractional albumin clearance, urinary transforming growth factor-beta (TGF-beta) excretion, glomerular volume, glomerular content of immunoreactive TGF-beta, and collagen alpha1 (IV) and renal cortical malondialdehyde (MDA) levels were significantly higher in D-WT mice compared with corresponding values in D-SOD mice. Glomerular volume, glomerular content of TGF-beta and collagen IV, renal cortical MDA, and urinary excretion of TGF-beta in D-SOD mice did not differ significantly from corresponding values in either the nondiabetic SOD or WT mice. In separate groups of mice studied after 8 months of diabetes, mesangial matrix area, calculated as a fraction of total glomerular tuft area, and plasma creatinine were significantly higher in D-WT but not in D-SOD mice, compared with corresponding values in the nondiabetic mice. In vitro infection of mesangial cells (MC) with a recombinant adenovirus encoding human SOD-1 increased SOD-1 activity threefold over control cells and prevented the reduction of aconitase activity, an index of cellular superoxide, and the increase in collagen synthesis that otherwise occurred in control MC in response to culture with 300 or 500 mg/dl glucose. Thus, increases in cellular SOD-1 activity attenuate diabetic renal injury in vivo and also prevent stimulation of MC matrix protein synthesis induced in vitro by high glucose.

Estimating water use by sugar maple trees: considerations when using heat-pulse methods in trees with deep functional sapwood.

Accurate estimates of sapwood properties (including radial depth of functional xylem and wood water content) are critical when using the heat pulse velocity (HPV) technique to estimate tree water use. Errors in estimating the volumetric water content (V(h)) of the sapwood, especially in tree species with a large proportion of sapwood, can cause significant errors in the calculations ofsap velocity and sap flow through tree boles. Scaling to the whole-stand level greatly inflates these errors. We determined the effects of season, tree size and radial wood depth on V(h) of wood cores removed from Acer saccharum Marsh. trees throughout 3 years in upstate New York. We also determined the effects of variation in V(h) on sap velocity and sap flow calculations based on HPV data collected from sap flow gauges inserted at four depths. In addition, we compared two modifications of Hatton's weighted average technique, the zero-step and zero-average methods, for determining sap velocity and sap flow at depths beyond those penetrated by the sap flow gauges. Parameter V(h) varied significantly with time of year (DOY), tree size (S), and radial wood depth (RD), and there were significant DOY x S and DOY x RD interactions. Use of a mean whole-tree V(h) value resulted in differences ranging from -6 to +47% for both sap velocity and sap flow for individual sapwood annuli compared with use of the V(h) value determined at the specific depth where a probe was placed. Whole-tree sap flow was 7% higher when calculated on the basis of the individual V(h) value compared with the mean whole-tree V(h) value. Calculated total sap flow for a tree with a DBH of 48.8 cm was 13 and 19% less using the zero-step and the zero-average velocity techniques, respectively, than the value obtained with Hatton's weighted average technique. Smaller differences among the three methods were observed for a tree with a DBH of 24.4 cm. We conclude that, for Acer saccharum: (1) mean V(h) changes significantly during the year and can range from nearly 50% during winter and early spring, to 20% during the growing season;(2) large trees have a significantly greater V(h) than small trees; (3) overall, V(h) decreases and then increases significantly with radial wood depth, suggesting that radial water movement and storage are highly dynamic; and (4) V(h) estimates can vary greatly and influence subsequent water use calculations depending on whether an average or an individual V(h) value for a wood core is used. For large diameter trees in which sapwood comprises a large fraction of total stem cross-sectional area (where sap flow gauges cannot be inserted across the entire cross-sectional area), the zero-average modification of Hatton's weighted average method reduces the potential for large errors in whole-tree and landscape water balance estimates based on the HPV method.

HYDRODEMETALLATION CATALYST PELLETS WITH NONUNIFORM RADIAL PORE SIZE DISTRIBUTION

Hydrodemetallation catalysts typically become inactive by pore mouth plugging, leaving a portion of the catalyst in the interior unutilized. By designing the pore size distribution so as to accommodate larger amount of metal deposit, improved performance can be attained. In this work the effect of nonuniform radial pore size distribution on catalyst performance is explored theoretically. Under the constraints of fixed total internal surface area and local void fraction, it is shown that catalysts with linear radial pore size distribution have larger metal deposit capacity. Furthermore, plugging of the pore mouth is delayed and therefore catalyst lifetime also increases.

Immunohistochemical video-microdensitometry of myocardial collagen type I and type III.

Collagen is an essential part of the cardiac interstitium. Collagen subtypes, their location, total amount and the architecture of the fibrillar network are of functional importance. Architecture in terms of density of the fibrillar network is assumed to be reflected by the intensity of immunohistochemical staining of collagen. The aim of this study was to evaluate a video-based microdensitometric method for quantifying density expressed as absorbance of collagen subtypes I and III stained with an indirect immunoperoxidase method in myectomy specimens of patients with hypertrophic obstructive cardiomyopathy. Various factors influencing the immunohistochemical staining product and the technical properties of the image analysis system were investigated. Linearity between collagen concentration and the absorbance of the immunohistochemical staining product was demonstrated for collagen I using a dot-blot technique. Immunohistochemical collagen staining and density measurement were easily reproducible. The cardiac disability of the patients was assessed according to the New York Heart Association (NYHA) criteria. There was a significant increase in collagen type I density with higher NYHA class, whereas no significant association was found for total collagen area fraction. Thus, video-based microdensitometry gives further insight into the structural remodelling of myocardial collagens and reveals their significance in the process of heart failure in hypertrophic cardiomyopathy.

放電焼結の基礎と応用 放電プラズマ焼結法によって作製した遷移金属炭化物分散Ｍｏ焼結合金の低温破断挙動

In order to improve both fracture strength and ductility at low temperature, fine-grained sintered molybdenum alloys dispersed with 0.8mol% TaC or 1.6mol% TiC were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The mixtures of fine molybdenum powder with grains measuring 20nm in diameter and carbide particles which were prepared by MA, were sintered at 1870K for 300s under 49MPa by SPS. The sintered alloys had relative densities of over 99% and grain sizes of approximately 2-5μm. The low-temperature fracture strength and ductility were evaluated by a three-point bending test at 77K to 360K. The results were compared with those for sintered alloys dispersed with 0.4-1.6mol% TaC or TiC which were prepared by MA and hot isostatic pressing (HIP). The following results were obtained.(1) Both low-temperature fracture strength and ductility increased by dispersion of carbides. This result was the same as those obtained from sintered alloys prepared by MA and HIP.(2) The alloy dispersed with TaC had a low dutile-to-brittle transiton temperature of 157K and a high fracture strength of 1860MPa at the temperature.(3) High fracture strength of the present alloy was attributed to both carbide dispersion and grain refining, though the former effect was much effective.(4) The alloy dispersed with TaC exhibited mostly intergranular fracture mode. The intergranular fracture area comprised 70% of the total fracture area. In contrast, the alloy dispersed with TiC exhibited a mixed mode of intergranular and transgranular fracture. The intergranular fracture area comprised 50%.

2-D Meso-Analysis of Two-Phase Materials with Microinclusions Exhibiting Transformation Plasticity.

The microcracking behaviors of two-phase materials with microinclusions exhibiting transformation plasticity are analyzed by using the two-dimensional meso-analysis method. Numerical studies have been conducted for some aspects of transformation-induced plasticity which is observed in Zirconia toughened ceramics. Irreversible strains and macro, stress-strain relationship due to dilatational transformation have been simulated under tensile loading condition. R-curve behaviors and microcracking patterns considering the mismatch between matrix and inclusions and the transformation plasticity of second-phase particles have been discussed under model-I loading condition. Influences of the total area fraction and the size of second-phase particles have also been studied through the calculated results.

Metabolic adaptation to fat-supplemented diet by the thoroughbred horse.

Following 10 weeks of fat supplementation a group of aerobically trained thoroughbred horses exhibited a significant decrease in postprandial plasma triacylglycerol concentration. This decrease was associated with a mean 50% increase in plasma total lipase activity following pentosan polysulfate administration and an increase in postprandial plasma cholesterol concentration. A significant increase in the activity of muscle citrate synthase (EC 4.1.3.7), expressed as a ratio to the total fractional area occupied by type I and type IIa muscle fibres, was also observed. No significant change in the concentration of resting muscle glycogen or triacylglycerol occurred as a result of fat supplementation. These results suggest that there was improved management of the fat load and that the triacylglycerol-clearing capacity of the horses was increased as a result of fat supplementation. It is suggested that the increase in plasma total lipase activity following pentosan polysulfate administration may have reflected an increase in muscle lipoprotein lipase (EC 3.1.1.34) activity, which would increase the capacity of muscle for free fatty acid uptake from circulating triacylglycerol-rich plasma lipoproteins. Fat supplementation may also enhance the oxidative capacity of muscle, as suggested by the significant increase in muscle citrate synthase and the trend towards an increase in beta-hydroxyacyl CoA dehydrogenase (EC 1.1.1.35) following 10 weeks of fat supplementation.

A Structural Alternative to Chronosequence Analysis for Uneven-Aged Northern Hardwood Forests

Structural changes over time in forests of shade-tolerant species are difficult to study because these stands are often broadly uneven-aged and not suitable for traditional chronosequence analysis. Yet because of past disturbances of variable intensity and frequency, there is often substantial structural variation among stands of a given site quality class. In this study, diameter distributions from 70 primary northern hardwood stands were analyzed to determine if certain structural indices might allow placement of stands in a developmental sequence. Modal stand diameter and the fraction of total overstory crown area in large trees (> 46 cm dbh) were among the most useful measures for distinguishing stages of development. Modal diameter ranged from 10 cm to 62 cm for stands on good sites. Correlations between diameter and age were highly significant (P < 0.0001) for the three principal species on all three site quality classes, suggesting that stands with a greater proportion of large trees are generally in a later stage of development. Stands with < 45% of the crown area in large trees have predominantly unimodal size distributions. As modal stand diameter increases, the shape of the size distribution changes from positively skewed to nearly symmetric. As the proportion of crown area in large trees exceeds 45% and the ratio of crown area in large to mature (26-45 cm dbh) trees exceeds 1.5, the form of the size distribution changes to multimodal, irregular, or descending monotonic.

Estimation of microscopic rubbing alignment parameters

Abstract We report an examination of the cloth-rubbing process, widely used to effect liquid crystal alignment, from a simplified microscopic perspective. We define strength of rubbing by the average applied force per rubbing fibre (approximately 11-22μN under our conditions, assuming all fibres passing the surface make contact), and extent of rubbing by the fraction of total surface area contacted during the process. Fibre-surface microscopic contact widths estimated from atomic force microscopy images of rubbed alignment polymer surfaces were in the range 10-500 nm. Taking 100 nm as an average value, we show that the entire alignment surface may be contacted several times during a typical rubbing process. Fibre-surface contact shear stresses can approach the GPa range, several orders of magnitude greater than the macroscopic rubbing pressure.

Joining of single-crystalline molybdenum and carbon-ceramics by using palladium and palladium-silver alloy as brazing metal

In order to develop a material for the first wall and the protection wall of a fusion reactor, brazing of dissimilar materials such as single-crystalline molybdenum an carbon-ceramics was performed by using palladium and palladium-silver alloy as the brazing metal. Fracture strength of the brazed joint was evaluated by the bend tests at room temperature and the embrittlement of the brazed joint was investigated in terms of fractography and EPMA and EDX analysis. The results are summarized as follows: 1. (1) fracture strength of the brazed joint was 34–94 MPa and much lower than that of the bulk carbon-ceramics or that of the brazed joint between molybdenum single crystals; 2. (2) crack generated from the Mo-rich phase in the vicinity of the interface between the brazed layer and the carbon-ceramics and then propagated alternatively through the brazed layer or the carbon-ceramics; 3. (3) the higher the fracture strength of the brazed joint was, the smaller was the ratio of the Mo-rich and Pd-rich regions to the total fracture area.

New Observations of Subarcsecond Photospheric Bright Points

We have used an interference filter centered at 4305 A within the bandhead of the CH radical (the 'G band') and real-time image selection at the Swedish Vacuum Solar Telescope on La Palma to produce very high contrast images of subarcsecond photospheric bright points at all locations on the solar disk. During the 6 day period of 1993 September 15-20 we observed active region NOAA 7581 from its appearance on the East limb to a near-disk-center position on September 20. A total of 1804 bright points were selected for analysis from the disk center image using feature extraction image processing techniques. The measured Full Width at Half Maximum (FWHM) distribution of the bright points in the image is lognormal with a modal value of 220 km (0 sec .30) and an average value of 250 km (0 sec .35). The smallest measured bright point diameter is 120 km (0 sec .17) and the largest is 600 km (O sec .69). Approximately 60% of the measured bright points are circular (eccentricity approx. 1.0), the average eccentricity is 1.5, and the maximum eccentricity corresponding to filigree in the image is 6.5. The peak contrast of the measured bright points is normally distributed. The contrast distribution variance is much greater than the measurement accuracy, indicating a large spread in intrinsic bright-point contrast. When referenced to an averaged 'quiet-Sun' area in the image, the modal contrast is 29% and the maximum value is 75%; when referenced to an average intergranular lane brightness in the image, the distribution has a modal value of 61% and a maximum of 119%. The bin-averaged contrast of G-band bright points is constant across the entire measured size range. The measured area of the bright points, corrected for pixelation and selection effects, covers about 1.8% of the total image area. Large pores and micropores occupy an additional 2% of the image area, implying a total area fraction of magnetic proxy features in the image of 3.8%. We discuss the implications of this area fraction measurement in the context of previously published measurements which show that typical active region plage has a magnetic filling factor on the order of 10% or greater. The results suggest that in the active region analyzed here, less than 50% of the small-scale magnetic flux tubes are demarcated by visible proxies such as bright points or pores.

Non-destructive measurement of leaf area in olive ( Olea europaea L.) trees using a gap inversion method

Leaf Area Index (LAI) data are required to characterise evaporation and assimilation rates from canopies. The LAI of a canopy of trees can be estimated from the transmittance of radiation at various angles. A commercial sensor for LAI determination (Plant Canopy Analyzer LI-COR LAI-2000) was tested for olive trees ( Olea europaea L.) during 1992 and 1993 in Cordoba, Spain. Plant leaf area of single olive trees was measured destructively and compared with indirect measurements with the PCA. A simulation model was constructed to test sampling strategies to determine plant area index (PAI) with the PCA in tree orchards. Plant areas and area densities of isolated olive trees in the field were accurately determined using the PCA. The PAI in arrays of young potted olive trees was also measured adequately. Measurements in an olive orchard and results of the simulation model of the PCA indicated that the PCA alone will underpredict PAI by around 30% in olive orchards or arrays of trees with similar geometry. Accurate PAI determination may be obtained in some cases by using the PCA to calculate the PA of single trees. Alternatively, PAI may be calculated as the weighted average of the maximum and minimum values of PAI in the orchard using the ground cover as a weighting factor. PAI estimates will be very close to LAI in olive orchards as the fraction of total area corresponding to leaves exceeds 90% in olive trees grown in the field.

The area coverage of geophysical fields as a function of sensor field-of-view

In many remote sensing studies of geophysical fields such as clouds, land cover, or sea ice characteristics, the fractional area coverage of the field in an image is estimated as the proportion of pixels that have the characteristic of interest (i.e., are part of the field) as determined by some thresholding operation. The effect of sensor field-of-view on this estimate is examined by modeling the unknown distribution of subpixel area fraction with the beta distribution, whose two parameters depend upon the true fractional area coverage, the pixel size, and the spatial structure of the geophysical field. Since it is often not possible to relate digital number, reflectance, or temperature to subpixel area fraction, the statistical models described are used to determine the effect of pixel size and thresholding operations on the estimate of area fraction for hypothetical geophysical fields. Examples are given for simulated cumuliform clouds and linear openings in sea ice, whose spatial structures are described by an exponential autocovariance function. It is shown that the rate and direction of change in total area fraction with changing pixel size depends on the true area fraction, the spatial structure, and the thresholding operation used.