Fuzzy generalized fast marching method for 3D segmentation of brain structures

The aim of this work is to develop a new model for segmentation of brain structures in medical brain MR images. Brain segmentation is a challenging task due to the complex anatomical structure of brain structures as well as intensity nonuniformity, partial volume effects and noise. Generally the structures of interest are of relatively complicated size and have significant shape variations, the structures boundaries may be blurry or even missing, and the surrounding background is full of irrelevant edges. Segmentation methods based on fuzzy models have been developed to overcome the uncertainty caused by these effects. In this study, we propose a robust and accurate brain structures segmentation method based on a combination of fuzzy model and deformable model. Our method breaks up into two great parts. Initially, a preliminary stage allows to construct the various information maps, in particular a fuzzy map, used as a principal information source, constructed using the Fuzzy C‐means method (FCM). Then, a deformable model implemented with the generalized fast marching method (GFMM), evolves toward the structure to be segmented, under the action of a normal force defined from these information maps. In this sense, we used a powerful evolution function based on a fuzzy model, adapted for brain structures. Two extensions of our general method are presented in this work. The first extension concerns the addition of an edge map to the fuzzy model and the use of some rules adapted to the segmentation process. The second extension consists of the use of several models evolving simultaneously to segment several structures. Extensive experiments are conducted on both simulated and real brain MRI datasets. Our proposed approach shows promising and achieves significant improvements with respect to several state‐of‐the‐art methods and with the three practical segmentation techniques widely used in neuroimaging studies, namely SPM, FSL, and Freesurfer.     

Semi-empirical calibration of the IEM backscattering model using radar images and moisture and roughness field measurements

Estimating surface parameters by radar-image inversion requires the use of well-calibrated backscattering models. None of the existing models is capable of correctly simulating scatterometer or satellite radar data. We propose a semi-empirical calibration of the Integral Equation Model (IEM) backscattering model in order to better reproduce the radar backscattering coefficient over bare agricultural soils. As correlation length is not only the least accurate but also the most difficult to measure of the parameters required in the models, we propose that it be replaced by a calibration parameter that would be estimated empirically from experimental databases of radar images and field measurements. This calibration was carried out using a number of radar configurations with different incidence angles, polarization configurations, and radar frequencies. Using several databases, the relationship between the calibration parameter and the surface roughness was determined for each radar configuration. In addition, the effect of the correlation function shape on IEM performance was studied using the three correlation functions (exponential, fractal, and Gaussian). The calibrated version of the IEM was then validated using another independent set of experimental data. The results show good agreement between the backscattering coefficient provided by the radar systems and that simulated by the calibrated version of the IEM. This calibrated version of the IEM can be used in inversion procedures to retrieve surface roughness and/or moisture values from radar images.     

Assessment of the ASAR sensor radiometric quality in comparison to ERS‐2 and RADARSAT‐1 SAR data

The estimation of geophysical parameters from Synthetic Aperture Radar (SAR) data necessitates well‐calibrated sensors with good radiometric precision. In this paper, the radiometric calibration of the new Advanced Synthetic Aperture Radar (ASAR‐ENVISAT) sensor was assessed by comparing ASAR data with ERS‐2 and RADARSAT‐1 SAR data. By analysing the difference between radar signals of forest stands, the results show differences of varying importance between the ASAR on the one hand, and the ERS‐2 and the RADARSAT‐1 on the other. For recent data acquired at the end of 2005, the difference varies from ?0.72 to +0.72 dB, with temporal variations that can reach 1.1 dB. For older data acquired in 2003 and 2004, we observe a sharp decrease in the radar signal in the range direction, which can attain 3.5 dB. The use of revised calibration constants provided recently by the European Space Agency (ESA) significantly improves the results of the radiometric calibration, where the difference between the ASAR and the other SARs will be lower than 0.5 dB.     

Potential of ASAR/ENVISAT for the characterization of soil surface parameters over bare agricultural fields

The objective of this investigation is to analyze the sensitivity of ASAR (Advanced Synthetic Aperture Radar) data to soil surface parameters (surface roughness and soil moisture) over bare fields, at various polarizations (HH, HV, and VV) and incidence angles (20°-43°). The relationships between backscattering coefficients and soil parameters were examined by means of 16 ASAR images and several field campaigns. We have found that HH and HV polarizations are more sensitive than VV polarization to surface roughness. The results also show that the radar signal is more sensitive to surface roughness at high incidence angle (43°). However, the dynamics of the radar signal as a function of soil roughness are weak for root mean square (rms) surface heights between 0.5 cm and 3.56 cm (only 3 dB for HH polarization and 43° incidence angle). The estimation of soil moisture is optimal at low and medium incidence angles (20°-37°). The backscattering coefficient is more sensitive to volumetric soil moisture in HH polarization than in HV polarization. In fact, the results show that the depolarization ratio σ_HH⁰/σ_HV⁰ is weakly dependent on the roughness condition, whatever the radar incidence. On the other hand, we observe a linear relationship between the ratio σ_HH⁰/σ_HV⁰ and the soil moisture. The backscattering coefficient ratio between a low and a high incidence angle decreases with the rms surface height, and minimizes the effect of the soil moisture.     

Study of the Soft and Hard X-Ray Emitted by APF Plasma Focus Device in Different Pressures

In this paper, an investigation on the X-rays emitted in different pressures by APF plasma focus devices using filtered PIN-diodes and fast plastic scintillation detector is reported. The highest X-ray emission was observed in the pressure of 1.6 torr and the behavior of X-ray intensities registered by different filters versus applied pressure were seemed to be similar. The X-ray angular distribution was bimodal, peaked approximately at ±18°. The intensity of X-rays decreased abruptly along the central axis of the device where the cylindrical plasma pinch was formed.     

The effects of modified zinc oxide nanoparticles on the mechanical/thermal properties of epoxy resin

Characterized by its strength, durability, and thermal properties, epoxy resin has been widely used as an adhesive, paint, and coating in many applications in the aerospace, civil and automotive industries. Despite this, the thermoset polymer resin has been known for its brittleness and low fracture resistance. This study focuses on the reinforcement of an epoxy resin system (diglycidyl ether of bisphenol A) with zinc oxide (ZnO) nanoparticles in their pristine form and a further modified form. The modification took place in two ways: coating with polydopamine (PDA) and covalently functionalizing them with (3-aminopropyl)triethoxysilane (APTES) and (3-glycidoxypropyl)trimethoxysilane (GPTMS). Therefore, four different types of nanoparticles were used: pristine ZnO, ZnO/PDA, ZnO/GPTMS, and ZnO/APTES aiming to improve the interfacial bonding between the polymeric matrix and the reinforcement. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, and scanning electron microscopy characterization and imaging techniques were used to prove that the ZnO nanoparticles were successfully modified prior to manufacturing the epoxy composites. While tensile testing showed that using pristine ZnO increases the composite's strength by 32.14%, the fracture toughness of the resin was improved by 9.40% when reinforced with ZnO functionalized with APTES. TGA showed that the addition of functionalized nanoparticles increases the material's degradation temperature by at most 7.31 ± 4.9°C using ZnO/APTES. Differential scanning calorimetry and dynamic mechanical analysis testing proved that the addition of any type of nanoparticles increases the resin's glass transition temperature by as much as 7.83°C (ZnO/APTES).     

The mechanical and thermal properties of graphitic carbon nitride (g-C3N4)-based epoxy composites

Numerous ways to reinforce epoxy resin and improve its thermomechanical properties have been attempted using organic and inorganic nanoparticles. In this paper, graphitic carbon nitride (g-C₃N₄) nanoparticles were synthesized and used to improve the mechanical properties and thermal stability of epoxy composites. The g-C₃N₄ was synthesized from cheap melamine powder using a simple one-step thermal treatment, then was used to reinforce the resin at different weight percentages (wt%). X-ray diffraction, scanning electron microscopy (SEM), and Fourier infrared spectroscopy were used to characterize the g-C₃N₄ and ensure its successful synthesis by studying the changes in its crystal structure, morphology, and chemical structure. The filler was dispersed in the resin using a combination of ultrasonication and high shear mixing. The results showed that the mechanical properties were optimum when 0.5 wt% g-C₃N₄ was used. The tensile strength and fracture toughness of the resulting epoxy composite improved by 21.8% and 77.3%, respectively. SEM was used to investigate the morphologies of cracks formed in epoxy composite specimens after the tensile testing. The SEM micrographs of the fracture surface showed a transition from a brittle to a rough morphology, signifying the enhancement in the composites' toughness. Thermogravimetric analysis showed a good improvement in degradation temperature of up to 8.86% while dynamic mechanical analysis showed that the incorporation of g-C₃N₄ did not affect the material's glass transition temperature.     

Investigation of Nitrogen HXR with Neon Admixture on the APF Plasma Focus

An investigation on the HXR emitted from APF plasma focus device operated with different volumetric ratios of nitrogen-neon (N₂:Ne) admixture working gas at different voltage-pressure limits is presented. The optimum pressures obtained at the applied voltages of 12, and 13 kV were 3.5 torr for percentage of (50:50) of (N₂:Ne) admixture and 3 torr for percentages of (75:25) and (90:10) in admixture and also for pure N₂, while at the voltage of 11 kV, the optimum pressures were 3 torr for percentage of (50:50) and 2.5 torr for percentages of (75:25), (90:10), and pure N₂. At each applied voltages of 11, 12, and 13 kV, with increasing percentage of N₂ in the (N₂:Ne) admixture, the intensity of HXR was found to increase where the low intensity was for percentage of (50:50) of (N₂:Ne) and the higher intensity was for pure N₂. The results illustrate that the voltage and the composition of working gas are effective parameters in the HXR emission from a plasma focus device.