Backscattering Analysis Research Articles

Heterogeneity in texture and crystal fabric of intensely hydrated ultramylonitic peridotites along a transform fault, Southwest Indian Ridge

Microstructures and olivine crystal fabrics were studied in amphibole-bearing peridotite samples obtained from the Marion Fracture Zone of the Southwest Indian Ridge by dredge D19 of the 1984 PROTEA Expedition Leg 5 cruise of the RV Melville. The peridotites show various textures ranging from extremely fine-grained well-layered ultramylonites to heterogeneously strained tectonites. Electron back-scatter diffraction analyses revealed that olivine crystal-preferred orientations (CPOs), which are developed primarily in coarse granular peridotites in the mantle, become weaker with an increasing degree of grain-size reduction from coarser to finer grains, for both porphyroclastic and matrix olivine grains. However, two well-layered ultramylonites are characterized by bimodal CPOs of (010)[001] (B type) and (001)[100] (E type) or a strong maximum of [010] normal to the foliation and girdle patterns of both [100] and [001] on the foliation plane (i.e., an axial [010] pattern or AG type). Moreover, spinel grains within these well-layered ultramylonites have not only been broken down to form olivine and amphibole by hydrous reactions, but have also been fractured and their fragments pulled apart in the fine-grained matrix. These features indicate that shear deformation occurred as increasing stress under hydrous conditions during the final stage of deformation, which enabled the local occurrence of low-temperature plastic deformation, resulting in the development of a CPO and a foliation within the ultramylonites.

Brillouin backscattering analysis in recent generation of telecom optical fibers

This paper reports on examination of the latest generation of telecom optical fibers for the Brillouin backscattering strain sensor application. Over 30 fibers from 5 different manufactures have been tested in terms of their ability to create a stable and accurate strain sensor. It has been proved that fibers that belong to the same standard, according to ITU-T (International Telecommunication Union), and even if provided by one manufacturer, demonstrate fundamentally different Brillouin backscattering response. It has been shown that unimodal Brillouin spectrum cannot be treated as the main parameter for fiber selection. In order to achieve accurate and reproducible results of strain measurement, it is necessary to perform initial examination of the fibers over the range of laser pulse width.

Austempering of PM HSS ASP2030 for improved fracture toughness

This study presents the fracture toughness improvement of the powder metallurgical high speed steel ASP2030 by replacing the martensitic matrix with a bainitic one. For this purpose, the fracture toughness of the steel is compared in both the austempered and marquenched states. The heat treatment of the samples was carried out by austenitizing in the range of 1150–1185 °C followed by either austempering at 235 °C or marquenching processes. Triple tempering at 560 °C for 2 h was also performed on all specimens. Fracture toughness measurements were performed on circumferentially notched tensile specimens. The microstructural features of the specimens were investigated using X-ray diffraction, optical and electron microscopy, and electron backscatter analysis. The results showed that the fracture toughness is sensitive to small changes in austenitizing temperature at both heat treatment conditions. By increasing the austenitizing temperature from 1150 to 1170 °C, the fracture toughness increases and then decreases with a further increase in temperature to 1185 °C. The results suggest that the changes in fracture toughness are due to the simultaneous effects of the volume fraction of undissolved carbides and the lattice microstrain values at different austenitizing temperatures. It can be concluded that the fracture toughness increases when the martensitic matrix is replaced by a bainitic structure. This improvement is related to finer bainitic laths width and also to the larger spacing between the particles of the undissolved carbides.

Microstructural Evolution of Cantilever Wire Probe after Touch-Down Fatigue Cycles for Power Semi-Conductor Wafer Testing

As fatigue fracture occurs in the bending area of the wire probe of the probe card owing to fatigue load during the touch-down (T/D) test, the development of wire probe materials with improved fatigue properties according to the wire materials is required. In this study, Tungsten (W), Rhenium-Tungsten (ReW), Beryllium-Copper (BeCu), and P7 (Palladium - Silver - Copper alloy, Pd-Ag-Cu) alloy were used to measure the tensile strength of the cantilever wire which was utilized for testing the electrical property of power semiconductor wafers used in the probe card. Additionally, the fatigue characteristics and microstructure changes of the wire were analyzed according to the T/D fatigue test using a scanning electron microscope, and electron back-scattered diffraction analysis was used for comparative analysis. In W and ReW wire probes with high initial yield strength, the misorientation angle due to grain elongation was smaller than that of P7. Accordingly, the grain deformation due to strain generation was small, whereas in materials with low initial yield strength, the misorientation angle was smaller. However, the amount of strain generated by grain orientation deformation was large. Therefore, under long-term T/D test conditions, it is assumed that ReW, W, and BeCu wire materials, which generate less deformation after long-term use than those with high initial strength, are superior to P7 materials.

Arctic Tundra Land Cover Classification on the Beaufort Coast Using the Kennaugh Element Framework on Dual-Polarimetric TerraSAR-X Imagery

Arctic tundra landscapes are highly complex and are rapidly changing due to the warming climate. Datasets that document the spatial and temporal variability of the landscape are needed to monitor the rapid changes. Synthetic Aperture Radar (SAR) imagery is specifically suitable for monitoring the Arctic, as SAR, unlike optical remote sensing, can provide time series regardless of weather and illumination conditions. This study examines the potential of seasonal backscatter mechanisms in Arctic tundra environments for improving land cover classification purposes by using a time series of HH/HV TerraSAR-X (TSX) imagery. A Random Forest (RF) classification was applied on multi-temporal Sigma Nought intensity and multi-temporal Kennaugh matrix element data. The backscatter analysis revealed clear differences in the polarimetric response of water, soil, and vegetation, while backscatter signal variations within different vegetation classes were more nuanced. The RF models showed that land cover classes could be distinguished with 92.4% accuracy for the Kennaugh element data, compared to 57.7% accuracy for the Sigma Nought intensity data. Texture predictors, while improving the classification accuracy on the one hand, degraded the spatial resolution of the land cover product. The Kennaugh elements derived from TSX winter acquisitions were most important for the RF model, followed by the Kennaugh elements derived from summer and autumn acquisitions. The results of this study demonstrate that multi-temporal Kennaugh elements derived from dual-polarized X-band imagery are a powerful tool for Arctic tundra land cover mapping.

Polycaprolactone and polycaprolactone triol blends to obtain a stable liquid nanotechnological formulation: synthesis, characterization and in vitro – in vivo taste masking evaluation

The use of polymeric blends is a potential strategy to obtain novel nanotechnological formulations aiming at drug delivery systems. Saquinavir, an antiretroviral drug, was chosen as a model drug for the development of new stable liquid formulations with unpleasant taste masking properties. Three formulations containing different polymeric ratios (1:3, 1:1 and 3:1) were prepared and properly characterized by particle size distribution, zeta potential, pH, drug content and encapsulation efficiency measurements. The stability was verified by monitoring the zeta potential, particle size distribution, polydispersity index and drug content by 90 days. The light backscattering analysis was used to early identify possible phenomena of instability in the formulations. The in vitro drug release and saquinavir cytotoxicity were evaluated. The in vitro and in vivo taste masking properties were studied using an electronic tongue and a human sensory panel. All formulations presented nanometric sizes around 200 nm and encapsulation efficiency above 99%. The parameters evaluated for stability remained constant throughout 90 days. The in vitro tests showed a controlled drug release and absence of toxic effects on human T lymphocytes. The electronic tongue experiment showed taste differences for all formulations in comparison to drug solutions, with a more pronounced difference for the formulation with higher polycaprolactone content (3:1). This formulation was chosen for in vivo sensory panel evaluation which results corroborated the electronic tongue experiments. In conclusion, the polymer blend nanoformulation developed herein showed the promising application to incorporate drugs aiming at pharmaceutical taste-masking properties.

Simultaneous velocity and concentration profiling of nuclear waste suspensions in pipe flow, using ultrasonic Doppler and backscatter analysis

Complex magnox ponds at Sellafield retain hydroxide-based sludge with unknown physicochemical properties. The sludge is a corroded form of magnesium-based fuel cladding used in first generation magnox reactors. Long term storage and open-air aqueous conditions are major contributors to corrosion. Waste needs to be transported to interim storage using engineered pipelines. Remote in situ characterisation of sludge was achieved using a non-invasive ultrasonic velocity profiler (UVP). The UVP uses raw velocity and echo amplitude to extract velocity and acoustic profiles. Profiles are used to understand effect of particle size and concentration on attenuation. Spherical glass particles with two size distributions of known acoustic behaviour were analysed to establish acoustic profiles. 4MHz frequency transducers were mounted in-line on engineered pipelines, 90 deg and 135 deg to flow. Data were extracted from in situ transducers for validation and non-contact probes were utilised to prove data could be collected safely without exposure. Flow rate was varied to ensure full developed flow before analysis. Profiles extracted from concentration arrays were analysed to understand particle segregation in horizontal pipe arrangements and attenuation. Remote in-line characterisation allows safe analysis, whilst in-line characterisation saves time and money. Moving forward, complex non-defined nuclear simulants will be analysed to investigate the UVP's limitations.

Increased epithelial backscatter: A novel finding in subclinical and clinical keratoconus

To assess alterations in backscatter from the corneal epithelium, anterior stroma and lens surface in eyes with subclinical, mild and moderate keratoconus (KC). In this single-centre, cross-sectional study involving 24 eyes with subclinical KC, 107 eyes with manifest KC (mild=40 and moderate=67 eyes) and 90 controls, line densitometry was performed with Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) to obtain simultaneous backscatter values for the corneal epithelium, anterior stroma and anterior lens surface. Backscatter values and Pentacam parameters were used in subsequent statistical analyses. Eyes with subclinical, mild and moderate KC had similar epithelial and stromal backscatter (P > 0.05) that was significantly increased compared with the controls (P < 0.05). Although anterior lens surface backscatter did not differ between the control and KC groups (P > 0.05), it was significantly higher in the mild and moderate KC groups than in the subclinical KC group (P < 0.05). In the KC group (n=131) epithelial backscatter was strongly correlated with stromal backscatter (r=0.911, P < 0.0001). Increased epithelial backscatter and a strong correlation with anterior stromal backscatter in the KC groups were consistent with the epithelium-stroma interaction involved in KC pathogenesis. Single-point backscatter analysis can be used with point clouds to construct epithelial and stromal backscatter maps in Pentacam to aid the detection of KC as a novel feature.

Acoustic Backscatter and Attenuation Due to River Fine Sediments: Experimental Evaluation of Models and Inversion Methods

AbstractThe hydroacoustic monitoring of suspended sediment concentration (SSC) in rivers is based on the inversion of backscatter and attenuation models. To evaluate such models, acoustic backscatter and attenuation were measured from a homogeneous suspension of fine river sediments (clay) in a laboratory tank at various concentrations in the range 1–18 g/l. Agreement between the modeled and measured acoustic backscatter and attenuation values was found to be relatively poor. The results are highly sensitive to particle size and shape which come with large measurement uncertainties and they can be significantly improved by adjusting plausible particle parameters. Various inversion methods combining single or multiple frequencies, analysis of backscatter and/or attenuation, spherical or oblate shape hypothesis for particles and fixed or estimated lognormal grain size distribution are tested. The most promising inversion methods using both backscatter and attenuation information led to accurate SSC estimates.

Theoretical analysis of backscattering in hollow-core antiresonant fibers

We present a theoretical analysis into the fundamental physical mechanisms contributing to backscattering in hollow-core antiresonant fibers. We consider Rayleigh scattering originating from the hollow regions of the fiber, which may be filled with gases, Rayleigh scattering from within the glass membranes, as well as the contribution from scattering at the glass surfaces. We derive expressions for the backscattering coefficient into any specified guided mode for an arbitrary excitation. These lead to general scaling relations with the core size and wavelength, which are found to be the key parameters for backscattering, regardless of the exact antiresonant geometry. For a nested antiresonant hollow-core fiber with a core diameter of 35 µm, the only antiresonant fiber geometry for which the experimental data are available in the literature, we find that the surface-scattering limited backscattering coefficient of the fundamental mode into itself is nearly 40 dB below that of a single mode fiber, in good agreement with recently published measurements.

Detection of Subclinical Keratoconus With a Validated Alternative Method to Corneal Densitometry.

PurposeTo enhance the current standards of subclinical keratoconus screening based on the statistical modeling of the pixel intensity distribution of Scheimpflug images.MethodsScheimpflug corneal tomographies corresponding to 25 corneal meridians of 60 participants were retrospectively collected and divided into three groups: controls (20 eyes), subclinical keratoconus (20 eyes), and clinical keratoconus (20 eyes). Only right eyes were selected. After corneal segmentation, pixel intensities of the stromal tissue were statistically modeled using a Weibull probability density function from which parameter α (pixel brightness) was derived. Further, data were transformed to polar coordinates, smoothed, and interpolated to build a map of the corneal α parameter. The discriminative power of the method was analyzed using receiver operating characteristic curves.ResultsThe proposed platform-independent method achieved a higher performance in discriminating subclinical keratoconus from control eyes (90.0% sensitivity, 95.0% specificity, 0.97 area under the curve [AUC]) than the standard method (Belin–Ambrósio enhanced ectasia display), which uses only corneal morphometry (85.0% sensitivity, 85.0% specificity, 0.80 AUC).ConclusionsAnalysis of light backscatter at the cornea successfully discriminates subclinical keratoconus from control eyes, upgrading the results previously reported in the literature.Translational RelevanceThe proposed methodology has the potential to support clinicians in the detection of keratoconus before showing clinical signs.

Substructure induced dendrite-fragmentation during thermomechanical processing of as-cast Mg-Sn-Li-Zn alloy

The present work deals with emphasizing the role of substructure development in fragmentation of the cast structure in Mg-Sn-0.3Li-3Zn alloy during thermomechanical processing. In this respect, a new micro-mechanism and a conceptual model were proposed for dendrite fragmentation, which was supported by 3D-tomography, electron back scattered diffraction, and angle selective back-scattered imaging analyses. Balancing of the dihedral angle of the non-equilibrium triple junctions led to the formation of grooves at the dendrite arms, followed by penetration of α-Mg matrix through the grooves and finally resulted in fragmentation of the specified dendrite arm. In fact, despite the conventional expectation regarding the high contribution of brittle fracture and shearing in fragmentation of the dendrites at low temperature regime, it was observed that the substructure development in a medium-to-high stacking fault energy material greatly participated in thermally-activated disintegration of the dendritic cast-structure.

Growth patterns in early childhood and cardiovascular structure and function at 4 years old: A prospective cohort study

Background and aimsChildhood overweight and obesity are lifetime risk factors for cardiovascular disease but the relationship between dynamic body mass index (BMI) change and cardiovascular structure and function in early childhood remains unclear. Methods and resultsThis cohort study consisted 525 participants with 6 distinct representative growth patterns to examine the associations between BMI growth patterns and subsequent cardiovascular structure and function at age 4. BMIs were obtained at birth, 2 and 4 years old. Cardiovascular assessments were performed, including blood pressure (BP), cardiac geometric parameters, left ventricular (LV) function, speckle-tracking, integrated backscatter analysis and carotid intima-media thickness. Compared to the stable normal BMI pattern, children with the stable overweight (OW) pattern had significantly greater LV anatomic parameters in fully adjusted models. Children with the catch-up (CU) pattern revealed a uniform trend and had poorer strain. LV diameters and integrated backscatter signals were larger for those with BMI gain and lose pattern. Children with BMI lose pattern showed improved tendency involving LV mass index and BP. Both OW and CU patterns were associated with high systolic BP [odds ratio (95% CI): OW: 3.67 (1.08, 12.47); CU: 4.24 (1.75, 10.28)]. Compared to static BMI measurements at birth, 2 and 4 years old, dynamic BMI growth patterns were more predictive of cardiovascular structure and function at 4. ConclusionsChildren with overweight-related BMI growth patterns in early childhood experienced undesirable cardiovascular functional or structural changes as early as 4 years old, indicating that early intervention is needed and potentially beneficial.

Effect of ZrB2 addition on microstructure evolution and mechanical properties of 93 wt.% tungsten heavy alloys

In this study, 93 wt.% tungsten heavy alloys reinforced with highly uniform and dispersed ZrO2 particles were successfully manufactured by powder metallurgy method. In order to fabricate fine-grained tungsten heavy alloys with outstanding performances, ultrafine 93W-4.9Ni-2.1Fe composite powder fabricated using a two-step reduction approach was selected as raw material. Microstructure and mechanical properties were experimentally examined to investigate the influence of ZrB2 addition. Meanwhile, transmission electron microscope and energy spectral analysis identified that ZrO2 particles were generated through the reaction between ZrB2 and oxygen from the grain boundaries. The ultimate tensile strength, elongation, and hardness of 93W-0.75ZrB2 alloys could reach to 963 ± 16 MPa, 18.4 ± 1.3% and 387.6 ± 4.4 HV, respectively, benefitted from the combination of fine-grained strengthening and oxide dispersion strengthening mechanisms. The W grains without observable texture were homogeneously distributed in the γ matrix phase based on electron back-scattered diffraction analysis. Moreover, it was determined that the main fracture types of 93W-ZrB2 alloys were W grain cleavage failure and ductile matrix rupture, closely related to the ZrB2 content in alloys. The current work provided a possible method for purifying the boundaries and enhancing the strength and elongation of W-Ni-Fe alloys simultaneously.

Restoration of the radio frequency ion source of the 5.5 MV CN-Van de Graaff accelerator at IFUNAM

The 5.5 MV CN-Van de Graaff (VDG) accelerator was first installed and operated in the early 50's at Rice University (Houston, TX) and it was donated to IFUNAM (“Instituto de Física, Universidad Nacional Autónoma de México”) in 1984 and started a new life in 1988. At the end of 2017, the ion source was severely damaged. Several power supplies were destroyed. In this article we describe the process of restoring the VDG terminal. A number of power supplies were redesigned, built, tested and mounted in the Terminal. As a result of the work carried out during most of 2019, the VDG accelerator is now operational and we show data from the Rutherford Backscattering (RBS) analysis of a platinum coated silicon slab using the first proton and α beams. Electronic diagrams of all supplies in their new configuration are provided for the benefit of this kind of RF-Ion sources users still numerous.

Texture evolution in platinum: the role of non-octahedral slip

ABSTRACT An anomalous deformation texture evolution has been observed in high-stacking-fault-energy pure platinum during cold rolling. A maximum of 98% thickness reduction, equivalent to a true strain of 3.9, was imposed. The evolution of texture observed during rolling is characterised as sluggish and the starting texture was retained up to very large rolling strains. The evolution of a characteristic rolling texture and its strengthening was dramatic and observed only after 95% thickness reduction. The retarded evolution of texture in platinum is explained by the activity of an unusual non-octahedral slip system. To understand the contribution of non-octahedral slip systems towards texture evolution, visco-plastic self-consistent simulation was carried out. The simulation results show that the activation of {100}<011> non-octahedral slip system slows down the evolution of final texture. Detailed electron back-scatter diffraction microstructural analysis was carried out to understand the deformation mechanisms and its influence on delayed texture evolution.

Morphological and Compositional Studies on Al/Ti/TiN/Si, Al/TiN/Si, Al/W/Si, Al/WN/Si Systems to Test the Diffusion Barrier Properties of Nanoscale-Thick Layers between Al and Si.

In this work, an investigation of the properties of nanoscale-thick Ti/TiN, TiN, W, WN layers as diffusion barriers between Si and Al is carried out in view of Si-based electronic applications. Heat treatments were performed on the samples to activate interdiffusion between Si and Al. Changing annealing time and temperature, each sample was morphologically characterized by scanning electron microscopy and atomic force microscopy and compositionally characterized by Rutherford backscattering analysis. The aim is to evaluate the efficiency of the layers as diffusion barriers between Si and Al and, at the same time, to evaluate the surface morphological changes upon annealing processes.

Sentinel-1 Backscatter Analysis and Radiative Transfer Modeling of Dense Winter Wheat Time Series

This study evaluates a temporally dense VV-polarized Sentinel-1 C-band backscatter time series (revisit time of 1.5 days) for wheat fields near Munich (Germany). A dense time series consisting of images from different orbits (varying acquisition) is analyzed, and Radiative Transfer (RT)-based model combinations are adapted and evaluated with the use of radar backscatter. The model shortcomings are related to scattering mechanism changes throughout the growth period with the use of polarimetric decomposition. Furthermore, changes in the RT modeled backscatter results with spatial aggregation from the pixel to field scales are quantified and related to the sensitivity of the RT models, and their soil moisture output are quantified and related to changes in backscatter. Therefore, various (sub)sets of the dense Sentinel-1 time series are analyzed to relate and quantify the impact of the abovementioned points on the modeling results. The results indicate that the incidence angle is the main driver for backscatter differences between consecutive acquisitions with various recording scenarios. The influence of changing azimuth angles was found to be negligible. Further analyses of polarimetric entropy and scattering alpha angle using a dual polarimetric eigen-based decomposition show that scattering mechanisms change over time. The patterns analyzed in the entropy-alpha space indicate that scattering mechanism changes are mainly driven by the incidence angle and not by the azimuth angle. Besides the analysis of differences within the Sentinel-1 data, we analyze the capability of RT model approaches to capture the observed Sentinel-1 backscatter changes due to various acquisition geometries. For this, the surface models “Oh92” or “IEM_B” (Baghdadi’s version of the Integral Equation Method) are coupled with the canopy model “SSRT” (Single Scattering Radiative Transfer). To resolve the shortcomings of the RT model setup in handling varying incidence angles and therefore the backscatter changes observed between consecutive time steps of a dense winter wheat time series, an empirical calibration parameter (coef) influencing the transmissivity (T) is introduced. The results show that shortcomings of simplified RT model architectures caused by handling time series consisting of images with varied incidence angles can be at least partially compensated by including a calibration coefficient to parameterize the modeled transmissivity for the varying incidence angle scenarios individually.

Erosion and Corrosion Resistance Performance of Laser Metal Deposited High-Entropy Alloy Coatings at Hellisheidi Geothermal Site.

Geothermal process equipment and accessories are usually manufactured from low-alloy steels which offer affordability but increase the susceptibility of the materials to corrosion. Applying erosion-corrosion-resistant coatings to these components could represent an economical solution to the problem. In this work, testing of two newly developed laser metal deposited high-entropy alloy (LMD-HEA) coatings—CoCrFeNiMo0.85 and Al0.5CoCrFeNi, applied to carbon and stainless steels—was carried out at the Hellisheidi geothermal power plant. Tests in three different geothermal environments were performed at the Hellisheidi site: wellhead test at 194 °C and 14 bar, erosion test at 198 °C and 15 bar, and aerated test at 90 °C and 1 bar. Post-test microstructural characterization was performed via Scanning Eletron Microscope (SEM), Back-Scattered Electrons analysis (BSE), Energy Dispersive X-ray Spectroscopy (EDS), optical microscopy, and optical profilometry while erosion assessment was carried out using an image and chemical analysis. Both the CoCrFeNiMo0.85 and Al0.5CoCrFeNi coatings showed manufacturing defects (cracks) and were prone to corrosion damage. Results show that damage in the CoCrFeNiMo0.85-coated carbon steel can be induced by manufacturing defects in the coating. This was further confirmed by the excellent corrosion resistance performance of the CoCrFeNiMo0.85 coating deposited onto stainless steel, where no manufacturing cracks were observed.

Sensitivity Analysis of Sentinel-1 Backscatter to Oil Palm Plantations at Pluriannual Scale: A Case Study in Gabon, Africa

The present paper focuses on a sensitivity analysis of Sentinel-1 backscattering signatures from oil palm canopies cultivated in Gabon, Africa. We employed one Sentinel-1 image per year during the 2015–2021 period creating two separated time series for both the wet and dry seasons. The first images were almost simultaneously acquired to the initial growth stage of oil palm plants. The VH and VV backscattering signatures were analysed in terms of their corresponding statistics for each date and compared to the ones corresponding to tropical forests. The times series for the wet season showed that, in a time interval of 2–3 years after oil palm plantation, the VV/VH ratio in oil palm parcels increases above the one for forests. Backscattering and VV/VH ratio time series for the dry season exhibit similar patterns as for the wet season but with a more stable behaviour. The separability of oil palm and forest classes was also quantitatively addressed by means of the Jeffries–Matusita distance, which seems to point to the C-band VV/VH ratio as a potential candidate for discrimination between oil palms and natural forests, although further analysis must still be carried out. In addition, issues related to the effect of the number of samples in this particular scenario were also analysed. Overall, the outcomes presented here can contribute to the understanding of the radar signatures from this scenario and to potentially improve the accuracy of mapping techniques for this type of ecosystems by using remote sensing. Nevertheless, further research is still to be done as no classification method was performed due to the lack of the required geocoded reference map. In particular, a statistical assessment of the radar signatures should be carried out to statistically characterise the observed trends.