The retina provides a window to study the pathophysiology of cerebrovascular diseases. Pathological retinal microvascular changes may reflect microangiopathic processes in the brain. Recent advances in optical imaging techniques have enabled imaging of the retinal microvasculature at the capillary level, and the generation of high-resolution, non-invasive capillary perfusion maps (nCPMs) with the Retinal Function Imager (RFI). However, the lack of quantitative analyses of the nCPMs may limit the wider application of the method in clinical research. The goal of this project was to demonstrate the feasibility of automated segmentation and fractal analysis of nCPMs. We took two nCPMs of each subject in a group of 6 healthy volunteers and used our segmentation algorithm to do the automated segmentation for monofractal and multifractal analyses. The monofractal dimension was 1.885 ± 0.020, and the multifractal dimension was 1.876 ± 0.010 (P =0.108). The coefficient of repeatability was 0.070 for monofractal analysis and 0.026 for multifractal analysis. This study demonstrated that the automatic segmentation of nCPMs is feasible for fractal analyses. Both monofractal and multifractal analyses yielded similar results. The quantitative analyses of microvasculature at the capillary level may open up a new era for studying the microvascular diseases such as cerebral small vessel disease.

The algorithm seemed to be feasible for automatically segmenting the CCT and ET in OCT images using these tested OCT devices. The segmented results were equivalent to that obtained with the manual method.

Fractal analysis measures the complexity of geometric structures. The aim of this study was to evaluate the feasibility and accuracy of fractal analysis in liver fibrosis. A total of 77 rats were included: 10 sham, 46 with fibrosis secondary to bile duct ligation (BDL), and 21 with fibrosis due to CCl 4 intoxication. Measurements included the fractal dimension of Kolmogorov (D k ), histologic lesions, the area of fibrosis by image analysis, liver hydroxyproline content, messenger RNA fibronectin, serum hyaluronate level, and portal pressure. Fibrotic rats were given placebo, octreotide, or O 2 -vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO). Intraobserver agreement of D k was excellent with the intraclass (ic) correlation coefficient r ic ‫؍‬ 0.91 (P < .0001) as well as the interobserver agreement with r ic ‫؍‬ 0.88 (P < .001). D k was correlated with other measurements or markers of fibrosis: the area of fibrosis (r ‫؍‬ 0.75; P < .0001), hydroxyproline content (r ‫؍‬ 0.51; P < .001), serum hyaluronate level (r ‫؍‬ 0.52; P < .001), and portal pressure (r ‫؍‬ 0.52; P < .01). D k was significantly different between the 2 models of fibrosis (P < .0001), unlike the area of fibrosis, and this relationship was independent of other histologic lesions. The significant decrease in fibrosis observed with octreotide or V-PYRRO/NO was similarly reflected by D k or the area of fibrosis. The diagnostic accuracy for the fibrosis model was 97% with the 5 main measurements or markers of fibrosis studied, with D k isolated at the first step by stepwise analysis. In conclusion, fractal analysis is suitable for analyzing liver fibrosis and has excellent reproducibility. This is the only quantitative morphometric method that can discriminate among the models of fibrosis and is sensitive enough to detect pharmacologically induced changes in liver fibrosis. (HEPATOLOGY 2002;36:840-849.)

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Research on sheath expansion is critical to the understanding of the dielectric recovery process in a vacuum interrupter after interruption of vacuum arcs. In this paper, we investigated how residual plasma affects breakdown in the sheath expansion period after the current zero. To simulate sheath expansion and breakdown, we developed a fully kinetic particle-in-cell Monte Carlo collision model with one spatial dimension and three velocity dimensions. The model accounted for various collisions, including ionization, excitation, elastic collisions, charge exchange, and momentum exchange, and we added an external circuit to the model to make the calculations self-consistent. The existence of metal vapor slowed the sheath expansion in the gap and caused high electric field formation in front of the cathode surface. The initial residual plasma, which was at sufficiently low density, seemed to have a limited impact on breakdown, and the metal vapor dominated the breakdown in this case. Additionally, the breakdown probability was sensitive to the initial plasma density if the value exceeded a specific threshold, and plasma at sufficiently high density could mean that breakdown would occur more easily. We found that if the simulation does not take the residual plasma into account, it could overestimate the critical value of the metal vapor density, which is always used to describe the boundary of breakdown after interruption of vacuum arcs. We discussed the breakdown mechanism in sheath expansion, and the breakdown is determined by a combination of metal vapor, residual plasma, and the electric field in front of the cathode surface.

Abstract:The scaling effect correction of retrieved parameters is an essential and difficult issue in analysis and application of remote sensing information. Based on fractal theory, this paper developed a scaling transfer model to correct the scaling effect of the leaf area index (LAI) estimated from coarse spatial resolution image. As the key parameter of the proposed model, the information fractal dimension (D) of the up-scaling pixel was calculated by establishing the double logarithmic linear relationship between D-2 and the normalized difference vegetation index (NDVI) standard deviation (σ NDV I ) of the up-scaling pixel. Based on the calculated D and the fractal relationship between the exact LAI and the approximated LAI estimated from the coarse resolution pixel, a LAI scaling transfer model was established. Finally, the model accuracy in correcting the scaling effect was discussed. Results indicated that the D increases with increasing σ NDV I , and the D-2 was highly linearly correlated with σ NDV I on the double logarithmic coordinate axis. The scaling transfer model corrected the scaling effect of LAI with a maximum value of root-mean-square error (RMSE) of 0.011. The maximum absolute correction error (ACE) and relative correction error (RCE) were only 0.108% and 8.56%, respectively. The spatial heterogeneity was the primary cause resulting in the scaling effect and the key influencing factor of correction effect. The results indicated that the developed method based on fractal theory could effectively correct the scaling effect of LAI estimated from the heterogeneous pixels.

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The objective of this paper is to determine how the high-voltage discharging metal vapour deposited on the nearby ceramic inner surface influences the breakdowns of gaps between centre shield and end shield in vacuum interrupters. Two types of shield materials were selected, namely copper and stainless steel. The end curvature radius of the shield was 3 mm. The distance between the shields could adjust manually from 4 to 8 mm. The distance between the shields and ceramic was 3.5 mm. The negative polarity standard lightning impulse voltage (12/50 μs) was repeated for 900 operations based on an up-and-down method. The experimental results illustrated that the metal deposition layer on the inner surface of the ceramic envelope significantly influenced the breakdown voltage of the shield gaps. At a shield gap distance of d ¼ 4 mm, the breakdown voltage of the shield gap increased from an initial lower voltage to the saturation voltage by approximately 200 operations. Then, the breakdown voltage decreased to a lower voltage range during only 50 operations, and the breakdown voltage maintained at this lower voltage range until the end of 900 operations. Furthermore, as the shield gap distance increased from d ¼ 4 to 6 mm and 8 mm, the breakdown voltage also maintained at this lower voltage range. A metal deposition layer was formed on the inner surface of ceramic by repetitive application of the lightning impulse voltage. To analyse the influence of the metal deposition layer, the electric field distributions were calculated for the original vacuum interrupter and the vacuum interrupter with the metal deposition layer on the ceramic inner surface. The simulation results suggested that the metal deposition layer took part in the breakdown path between the shield gaps and deteriorated the insulation performance.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.