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"Optical reflectance"
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Line-Field Confocal Optical Coherence Tomography: A New Tool for the Differentiation between Nevi and Melanomas?
Until now, the clinical differentiation between a nevus and a melanoma is still challenging in some cases. Line-field confocal optical coherence tomography (LC-OCT) is a new tool with the aim to change that. The aim of the study was to evaluate LC-OCT for the discrimination between nevi and melanomas. A total of 84 melanocytic lesions were examined with LC-OCT and 36 were also imaged with RCM. The observers recorded the diagnoses, and the presence or absence of the 18 most common imaging parameters for melanocytic lesions, nevi, and melanomas in the LC-OCT images. Their confidence in diagnosis and the image quality of LC-OCT and RCM were evaluated. The most useful criteria, the sensitivity and specificity of LC-OCT vs. RCM vs. histology, to differentiate a (dysplastic) nevus from a melanoma were analyzed. Good image quality correlated with better diagnostic performance (Spearman correlation: 0.4). LC-OCT had a 93% sensitivity and 100% specificity compared to RCM (93% sensitivity, 95% specificity) for diagnosing a melanoma (vs. all types of nevi). No difference in performance between RCM and LC-OCT was observed (McNemar’s p value = 1). Both devices falsely diagnosed dysplastic nevi as non-dysplastic (43% sensitivity for dysplastic nevus diagnosis). The most significant criteria for diagnosing a melanoma with LC-OCT were irregular honeycombed patterns (92% occurrence rate; 31.7 odds ratio (OR)), the presence of pagetoid spread (89% occurrence rate; 23.6 OR) and the absence of dermal nests (23% occurrence rate, 0.02 OR). In conclusion LC-OCT is useful for the discrimination between melanomas and nevi.
Journal Article
Analysis of the Impact of Metal Coatings on the Optical and Tribological Properties of Polymethyl Methacrylate Polymers
Polymethyl methacrylate (PMMA) is widely used in optical windows and protective glazing; however, its low reflectance and limited surface durability constrain its deployment in reflective optical assemblies. Here, nanoscale silver (Ag) layers were deposited on PMMA by direct-current sputtering (2–6 min) and analyzed by X-ray diffraction (XRD), the Fourier-transform infrared spectroscopy (FTIR), Atomic force microscopy (AFM), and UV–visible spectroscopy (UV-Vis) to link early-stage film growth to optical performance. XRD verified FCC-Ag formation, while FTIR indicated negligible modification of the PMMA chemical structure. AFM revealed pronounced topographical evolution with sputtering time, with the mean grain diameter and RMS roughness increasing by approximately 456% and 1123%, respectively, at the longest deposition time. UV-Vis measurements showed that reflectance increased from ≤30% for pristine PMMA to >90% after coating (at least a threefold increase), accompanied by an ~82% reduction in visible transmittance at 550 nm. These results demonstrate that sputtering time provides a single, scalable control knob to convert PMMA from a transparent window into a highly reflective metal-polymer hybrid suitable for protective mirrors and other high-end optical components.
Journal Article
Thermal maturity assessment of organic matter in the Precambrian–Lower Paleozoic high-over matured marine shale reservoirs: A review
Thermal maturity is one of key parameters for source rock evaluation, which affects not only the effectiveness of hydrocarbon generation and the properties of hydrocarbon but also the formation, evolution and extinction of organic matter-hosted pores in shale reservoirs. Thus, accurate assessment of thermal maturity is of great significance to the evaluation of conventional source rocks and gas-bearing properties of unconventional shale reservoirs. However, thermal maturity assessment of the Precambrian–Lower Paleozoic marine shale deposits has been challenging for several decades. On one hand, the widely used gold standard-vitrinite reflectance (VRo) cannot be used for maturity assessment due to the absence of vitrinite in the pre-Devonian strata. On the other hand, traditional organic geochemistry approaches (e.g., Tmax, biomarkers) cannot be used for maturity assessment of marine shale deposits at the high-over matured stages. In this review, four groups of macerals, including solid bitumen, vitrinite-like maceral, zooclasts and liptinite, can be identified in the Precambrian–Lower Paleozoic sediments, and optical characteristics and origins of these macerals have been summarized. Furthermore, various proxies of thermal maturity assessment are systematically investigated, providing potential solutions for accurate assessment of thermal maturity of the Precambrian–Lower Paleozoic high-over matured marine shale reservoirs. However, accurate identification of different macerals (e.g., solid bitumen, vitrinite-like maceral, graptolite) is still challenged, and moreover, the use of optical reflectance of these macerals is hindered due to optical anisotropies and various conversion relationships that converted their reflectance to equivalent vitrinite reflectance (EqVRo). In addition, Raman spectrometry is a rapid and non-destructive approach to evaluate thermal maturity of organic matter, and several Raman parameters, including FWHM-G, RBS and ID/IG ratio, can be used as the reliable maturity indicators, which overcome the influence of optical anisotropy on the optical indicators. Nevertheless, the application of Raman spectroscopy has been limited due to the lack of uniform test standards (e.g., experimental conditions) and peak fitting methods. In a word, every maturity proxy has its suitable range of application and limitations, so a variety of maturity indicators are essential to comprehensively evaluate thermal maturity of organic matter.
Journal Article
Proximal Active Optical Sensing Operational Improvement for Research Using the CropCircle ACS-470, Implications for Measurement of Normalized Difference Vegetation Index (NDVI)
Active radiometric reflectance is useful to determine plant characteristics in field conditions. However, the physics of silicone diode-based sensing are temperature sensitive, where a change in temperature affects photoconductive resistance. High-throughput plant phenotyping (HTPP) is a modern approach using sensors often mounted to proximal based platforms for spatiotemporal measurements of field grown plants. Yet HTPP systems and their sensors are subject to the temperature extremes where plants are grown, and this may affect overall performance and accuracy. The purpose of this study was to characterize the only customizable proximal active reflectance sensor available for HTPP research, including a 10 °C increase in temperature during sensor warmup and in field conditions, and to suggest an operational use approach for researchers. Sensor performance was measured at 1.2 m using large titanium-dioxide white painted field normalization reference panels and the expected detector unity values as well as sensor body temperatures were recorded. The white panel reference measurements illustrated that individual filtered sensor detectors subjected to the same thermal change can behave differently. Across 361 observations of all filtered detectors before and after field collections where temperature changed by more than one degree, values changed an average of 0.24% per 1 °C. Recommendations based on years of sensor control data and plant field phenotyping agricultural research are provided to support ACS-470 researchers by using white panel normalization and sensor temperature stabilization.
Journal Article
Investigation on Microstructure Evolution and Visible-Infrared Property of Vacuum-Heat-Treated TiN Film
TiN films were prepared by direct current (DC) reactive magnetron sputtering technique and then vacuum-heat-treated at different temperatures (400, 600 and 800 °C) for 3600 s to improve their properties through increasing the crystallinity and eliminating the lattice defects of the films. Optical properties in the visible-infrared region of TiN films after vacuum heat treatment were investigated. Results revealed that optical reflectance of TiN films first increased and then decreased after the vacuum heat treatment. The reflectance of all the films was below 14%. With the heat treatment temperature rising from 400 to 600 °C, infrared emissivity of TiN films first dropped and then went up at 800 °C. As the heat treatment temperature was 600 °C, the infrared emissivity of TiN films could be reduced to 0.488 and was the lowest. Results showed that vacuum heat treatment could reduce the infrared emissivity of TiN films.
Journal Article
Magnetic Control of Optical Reflectance from Metallic Thin Film Using Surface Plasmon Resonance and Faraday Rotation
We demonstrate magnetic control of optical reflectance with no ferromagnetic material via combining the Faraday rotation and the surface plasmon resonance (SPR) in a Kretschman configuration under magnetic fields < 0.5 T. The SPR produces the polarization sensitive reflectance from the Au or Ag thin film coated on a N-BK7 prism in which the Faraday rotation occurs. The gold (Au) or silver (Ag) metal film as a plasmonic film somewhat acts as an incident angle-dependent reflection polarizer that can sensitively sense the polarization change induced by the Faraday rotation that occurs in a prism. We find that combination of Faraday rotation and the surface plasmon can induce a significant magnetic modulation of reflectance normalized with respect to that obtained with no magnetic fields at a specific incident angle of light. The magnetic control of optical reflectance presented may find an application in polarizer-free photonic devices with no ferromagnetic material for magneto-optical modulation.
Journal Article
Analysis of Perovskite Solar Cell Degradation over Time Using NIR Spectroscopy—A Novel Approach
In recent years, there has been a dynamic development of photovoltaic materials based on perovskite structures. Solar cells based on perovskite materials are characterised by a relatively high price/performance ratio. Achieving stability at elevated temperatures has remained one of the greatest challenges in the perovskite solar cell research community. However, significant progress in this field has been made by utilising different compositional engineering routes for the fabrication of perovskite semiconductors such as triple cation-based perovskite structures. In this work, a new approach for the rapid analysis of the changes occurring in time in perovskite structures was developed. We implemented a quick and inexpensive method of estimating the ageing of perovskite structures based on an express diagnosis of light reflection in the near-infrared region. The possibility of using optical reflectance in the NIR range (900–1700 nm) to observe the ageing of perovskite structures over time was investigated, and changes in optical reflectance spectra of original perovskite solar cell structures during one month after PSC production were monitored. The ratio of characteristic pikes in the reflection spectra was determined, and statistical analysis by the two-dimensional correlation spectroscopy (2D-COS) method was performed. This method allowed correctly detecting critical points in thermal ageing over time.
Journal Article
Strong Modulations of Optical Reflectance in Tapered Core–Shell Nanowires
Random assemblies of vertically aligned core–shell GaAs–AlGaAs nanowires displayed an optical response dominated by strong oscillations of the reflected light as a function of the incident angle. In particular, angle-resolved specular reflectance measurements showed the occurrence of periodic modulations in the polarization-resolved spectra of reflected light for a surprisingly wide range of incident angles. Numerical simulations allowed for identifying the geometrical features of the core–shell nanowires leading to the observed oscillatory effects in terms of core and shell thickness as well as the tapering of the nanostructure. The present results indicate that randomly displaced ensembles of nanoscale heterostructures made of III–V semiconductors can operate as optical metamirrors, with potential for sensing applications.
Journal Article
Correlation between structural properties and iridescent colors of cellulose nanocrystalline films
We investigate the effect of shear flow applied during the drying of aqueous suspension of cellulose nanocrystals on optical reflective properties and structural characteristics of the resulting solidified films. Shear flow can significantly improve internal structural homogeneity of the films, while its effect on optical reflective properties is relatively minor. The measured width of the selective reflection peak is an order of magnitude larger than expected for an ideal helically modulated structure, which reflects a distribution of pitch values and possibly also of regimes of distorted helical modulation. We attribute these imperfections to the broad size distribution of the cellulose nanocrystals.
Journal Article