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Search Results (536)

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Keywords = visible-near-infrared spectroscopy

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18 pages, 1927 KiB  
Article
Exploring Microelement Fertilization and Visible–Near-Infrared Spectroscopy for Enhanced Productivity in Capsicum annuum and Cyprinus carpio Aquaponic Systems
by Ivaylo Sirakov, Stefka Stoyanova, Katya Velichkova, Desislava Slavcheva-Sirakova, Elitsa Valkova, Dimitar Yorgov, Petya Veleva and Stefka Atanassova
Plants 2024, 13(24), 3566; https://doi.org/10.3390/plants13243566 - 20 Dec 2024
Viewed by 358
Abstract
This study explores the effects of varying exposure times of microelement fertilization on hydrochemical parameters, plant growth, and nutrient content in an aquaponic system cultivating Capsicum annuum L. (pepper) with Cyprinus carpio (Common carp L.). It also investigates the potential of visible–near-infrared [...] Read more.
This study explores the effects of varying exposure times of microelement fertilization on hydrochemical parameters, plant growth, and nutrient content in an aquaponic system cultivating Capsicum annuum L. (pepper) with Cyprinus carpio (Common carp L.). It also investigates the potential of visible–near-infrared (VIS-NIR) spectroscopy to differentiate between treated plants based on their spectral characteristics. The findings aim to enhance the understanding of microelement dynamics in aquaponics and optimize the use of VIS-NIR spectroscopy for nutrient and stress detection in crops. The effects of microelement exposure on the growth and health of Cyprinus carpio (Common carp L.) in an aquaponic system are investigated, demonstrating a 100% survival rate and optimal growth performance. The findings suggest that microelement treatments, when applied within safe limits, can enhance system productivity without compromising fish health. Concerning hydrochemical parameters, conductivity remained stable, with values ranging from 271.66 to 297.66 μS/cm, while pH and dissolved oxygen levels were within optimal ranges for aquaponic systems. Ammonia nitrogen levels decreased significantly in treated variants, suggesting improved water quality, while nitrate and orthophosphate reductions indicated an enhanced plant nutrient uptake. The findings underscore the importance of managing water chemistry to maintain a balanced and productive aquaponic system. The increase in root length observed in treatments 2 and 6 suggests that certain microelement exposure times may enhance root development, with treatment 6 showing the longest roots (58.33 cm). Despite this, treatment 2 had a lower biomass (61.2 g), indicating that root growth did not necessarily translate into increased plant weight, possibly due to energy being directed towards root development over fruit production. In contrast, treatment 6 showed both the greatest root length and the highest weight (133.4 g), suggesting a positive correlation between root development and fruit biomass. Yield data revealed that treatment 4 produced the highest yield (0.144 g), suggesting an optimal exposure time before nutrient imbalances negatively impact growth. These results highlight the complexity of microelement exposure in aquaponic systems, emphasizing the importance of fine-tuning exposure times to balance root growth, biomass, and yield for optimal plant development. The spectral characteristics of the visible–near-infrared region of pepper plants treated with microelements revealed subtle differences, particularly in the green (534–555 nm) and red edge (680–750 nm) regions. SIMCA models successfully classified control and treated plants with a misclassification rate of only 1.6%, highlighting the effectiveness of the spectral data for plant differentiation. Key wavelengths for distinguishing plant classes were 468 nm, 537 nm, 687 nm, 728 nm, and 969 nm, which were closely related to plant pigment content and nutrient status. These findings suggest that spectral analysis can be a valuable tool for the non-destructive assessment of plant health and nutrient status. Full article
(This article belongs to the Special Issue Macronutrients and Micronutrients in Plant Growth and Development)
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<p>Average root length, weight, and yield of cultivated pepper.</p>
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<p>Average reflectance spectra of pepper leaves in the visible–short wave NIR region.</p>
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<p>Discriminating power plot of SIMCA models for the discrimination of control of differently treated pepper plants.</p>
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<p>Schematic of experimental aquaponic system. (A) Fish tanks, (B) mechanical filter, (C) biofilter, (D) sump, and (E) plant section. Black arrows show the path of water.</p>
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<p>Image of experimental greenhouse used in current trial.</p>
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13 pages, 3343 KiB  
Article
Raman, MIR, VNIR, and LIBS Spectra of Szomolnokite, Rozenite, and Melanterite: Martian Implications
by Xiai Zhuo, Ruize Zhang, Erbin Shi, Jiahui Liu and Zongcheng Ling
Universe 2024, 10(12), 462; https://doi.org/10.3390/universe10120462 - 19 Dec 2024
Viewed by 279
Abstract
Different sulfates (Ca-, Mg, and Fe- sulfates) have been extensively detected on the Martian surface. As one of the Martian sulfates, the presence of ferrous sulfates will provide valuable clues about the redox environment, hydrological processes, and climatic history of ancient Mars. In [...] Read more.
Different sulfates (Ca-, Mg, and Fe- sulfates) have been extensively detected on the Martian surface. As one of the Martian sulfates, the presence of ferrous sulfates will provide valuable clues about the redox environment, hydrological processes, and climatic history of ancient Mars. In this study, three hydrated ferrous sulfates were prepared in the laboratory by heating dehydration reactions. These samples were analyzed using X-ray Diffraction (XRD) to confirm their phase and homogeneity. Subsequently, Raman, mid-infrared (MIR) spectra, visible near-infrared (VNIR) spectra, and laser-induced breakdown spectroscopy (LIBS) were measured and analyzed. The results demonstrate that the spectra of three hydrated ferrous sulfates exhibit distinctive features (e.g., the v1 and v3 features of SO42 tetrahedra in their Raman and MIR spectra) that can offer new insights for identifying different ferrous sulfates on Mars and aid in the interpretation of in-situ data collected by instruments such as the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC), SuperCam, and ChemCam, etc. Full article
(This article belongs to the Section Planetary Sciences)
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<p>Crystal structures of (<b>a</b>) FeSO<sub>4</sub>⋅H<sub>2</sub>O, (<b>b</b>) FeSO4⋅4H<sub>2</sub>O, and (<b>c</b>) FeSO<sub>4</sub>⋅7H<sub>2</sub>O.</p>
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<p>The XRD pattern of three hydrated ferrous sulfates.</p>
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<p>The Raman spectra of three hydrated ferrous sulfates.</p>
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<p>The MIR spectra of three hydrated ferrous sulfates.</p>
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<p>The VNIR spectra of three hydrated ferrous sulfates.</p>
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<p>The laser-induced breakdown spectroscopy (LIBS) spectra of three hydrated ferrous sulfates were obtained from (<b>a</b>) the Earth environment and (<b>b</b>) Mars-like conditions.</p>
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11 pages, 2922 KiB  
Article
The Trace-Element Characteristics of Chrysoberyl: Insights from Compositional and Spectroscopic Analyses
by Linling Dong, Yimiao Liu, Xinxin Gao and Ren Lu
Minerals 2024, 14(12), 1280; https://doi.org/10.3390/min14121280 - 17 Dec 2024
Viewed by 276
Abstract
To characterize the trace-element characteristics of chrysoberyl, we studied twenty-six chrysoberyl samples from various localities by using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS), photoluminescence (PL), and ultraviolet–visible–near-infrared (UV–Vis–NIR) spectroscopy. Chemical analysis has confirmed the existence of trace elements, including Fe, Ti, [...] Read more.
To characterize the trace-element characteristics of chrysoberyl, we studied twenty-six chrysoberyl samples from various localities by using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS), photoluminescence (PL), and ultraviolet–visible–near-infrared (UV–Vis–NIR) spectroscopy. Chemical analysis has confirmed the existence of trace elements, including Fe, Ti, Ga, Sn, B, Cr, and V. The phenomenon of ionic isomorphic substitution frequently occurs at lattice sites within chrysoberyl. Notably, the isomorphic substitution of Al3+ in octahedral sites is significant, with the primary substituting elements being Fe, Ti, Cr, V, Ga, and Sn. The PL spectra of chrysoberyl samples exhibit sharp peaks at 678 and 680 nm, which are attributed to Cr3+, even in samples in which the Cr concentration is below the detection limit of LA-ICP-MS. This demonstrates the high-sensitivity feature of PL spectroscopy. The UV–Vis–NIR spectra of chrysoberyl samples consistently exhibit a band at 440 nm, and strong double narrow bands near 367 nm and 375 nm are observed. These spectral features are associated with Fe3+ chromophores—specifically, Fe3+-Fe3+ pairs or clusters and Fe3+ ions, respectively. By combining LA–ICP–MS analysis and PL mapping on a sample exhibiting color zoning, it has been found that the darker sections contain a higher concentration of Cr compared to the lighter sections, while the concentrations of other elements remain largely consistent. In other words, subtle variations in Cr concentration may be the underlying cause of color zoning in chrysoberyl. Full article
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<p>Rough and polished chrysoberyl samples from various localities: (<b>A</b>) Myanmar; (<b>B</b>) Sri Lanka; (<b>C</b>) Tanzania; (<b>D</b>) India; (<b>E</b>) Brazil.</p>
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<p>The photoluminescence spectra of chrysoberyl samples. The spectral directions are in the same orientation. (<b>A</b>) Increasing Cr concentration; (<b>B</b>) Cr concentrations below the detection limit of LA-ICP-MS.</p>
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<p>The UV–Vis–NIR spectra of chrysoberyl samples. The spectral directions are in the same orientation.</p>
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<p>The elemental ternary plots illustrate the relationships between chemical composition and origins. (<b>A</b>) The Fe-Ti-Sn diagram; (<b>B</b>) The Fe-Ti-Ga diagram; (<b>C</b>) The Fe-Ga-Sn diagram; (<b>D</b>) The B-V-Cr diagram.</p>
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<p>An approximate linear negative correlation between the content of Al and the content of octahedral-site substituting metal ions (Me<sup>n+</sup>). The dashed line represents the linear fit for the content of Al and Me<sup>n+</sup>.</p>
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<p>The relationship between trace elements and Me<sup>n+</sup> concentration in chrysoberyl samples. (<b>A</b>) The relationship between Me<sup>n+</sup> and Fe. The dashed line represents the linear fit for the content of Fe and Me<sup>n+</sup>; (<b>B</b>) the relationship between Me<sup>n+</sup> and Ti. The dashed line is the approximation of the content of Ti and Me<sup>n+</sup>.</p>
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<p>The UV–Vis–NIR spectra of chrysoberyl sample S3. CIE L*a*b* coordinates of color circles here are calculated under D65 light for a 1 cm wafer thickness to demonstrate color features of chrysoberyl at the different sections of the zoning.</p>
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<p>Laser PL mapping of chrysoberyl sample S3: (<b>A</b>) at 678 nm; (<b>B</b>) at 680 nm; (<b>C</b>) schematic diagram of the test area.</p>
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19 pages, 4353 KiB  
Article
Fusarium Wilt of Banana Latency and Onset Detection Based on Visible/Near Infrared Spectral Technology
by Cuiling Li, Dandan Xiang, Shuo Yang, Xiu Wang and Chunyu Li
Agronomy 2024, 14(12), 2994; https://doi.org/10.3390/agronomy14122994 - 16 Dec 2024
Viewed by 364
Abstract
Fusarium wilt of banana is a soil-borne vascular disease caused by Fusarium oxysporum f. sp. cubense. The rapid and accurate detection of this disease is of great significance to controlling its spread. The research objective was to explore rapid banana Fusarium wilt [...] Read more.
Fusarium wilt of banana is a soil-borne vascular disease caused by Fusarium oxysporum f. sp. cubense. The rapid and accurate detection of this disease is of great significance to controlling its spread. The research objective was to explore rapid banana Fusarium wilt latency and onset detection methods and establish a disease severity grading model. Visible/near-infrared spectroscopy analysis combined with machine learning methods were used for the rapid in vivo detection of banana Fusarium wilt. A portable visible/near-infrared spectrum acquisition system was constructed to collect the spectra data of banana Fusarium wilt leaves representing five different disease grades, totaling 106 leaf samples which were randomly divided into a training set with 80 samples and a test set with 26 samples. Different data preprocessing methods were utilized, and Fisher discriminant analysis (FDA), an extreme learning machine (ELM), and a one-dimensional convolutional neural network (1D-CNN) were used to establish the classification models of the disease grades. The classification accuracies of the FDA, ELM, and 1D-CNN models reached 0.891, 0.989, and 0.904, respectively. The results showed that the proposed visible/near infrared spectroscopy detection method could realize the detection of the incubation period of banana Fusarium wilt and the classification of the disease severity and could be a favorable tool for the field diagnosis of banana Fusarium wilt. Full article
(This article belongs to the Section Pest and Disease Management)
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<p>Structure schematic diagram of the visible/near-infrared spectrum acquisition system.</p>
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<p>Internal structure diagram of the portable mainframe.</p>
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<p>Spectral data acquisition and the red dot on the left image represents the site where the symptom was observed and the spectral data were taken.</p>
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<p>Original reflectance spectrum of banana leaf samples. G0, G1, G2, G3, and G4 represent disease “Grade 0”, “Grade 1”, “Grade 2”, “Grade 3”, and “Grade 4”, respectively.</p>
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<p>Average original reflectance spectral curves of banana leaves for the five disease grades.</p>
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<p>The 1D-CNN network structure of the banana Fusarium wilt disease grading model.</p>
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<p>Reflectance spectra curves after pretreatment with SG smoothing method.</p>
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<p>Score coefficient curves of the first principal component PC1 based on the original spectral data.</p>
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<p>The 3D distribution of PC1, PC2, and PC3 based on the original spectral data.</p>
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<p>Disease grade classification results on test set of FD-MSC-SG-FDA model. G0, G1, G2, G3, and G4 represent disease “Grade 0”, “Grade 1”, “Grade 2”, “Grade 3”, and “Grade 4”, respectively.</p>
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<p>Influence of the number of hidden layer neurons on the MSC-SG-ELM model.</p>
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<p>Disease grade classification results of MSC-SG-ELM model on test set. G0, G1, G2, G3, and G4 represent disease Grade 0, Grade 1, Grade 2, Grade 3, and Grade 4, respectively.</p>
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<p>Loss values of the test set at different learning rates, each color represents a learning rate.</p>
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<p>Accuracies of the training set and test set at different learning rates, each color represents a learning rate.</p>
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<p>Loss values and accuracies when the learning rate was 0.01.</p>
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22 pages, 6302 KiB  
Article
Field Grading of Longan SSC via Vis-NIR and Improved BP Neural Network
by Jun Li, Meiqi Zhang, Kaixuan Wu, Hengxu Chen, Zhe Ma, Juan Xia and Guangwen Huang
Agriculture 2024, 14(12), 2297; https://doi.org/10.3390/agriculture14122297 - 14 Dec 2024
Viewed by 533
Abstract
Soluble solids content (SSC) measurements are crucial for managing longan production and post-harvest handling. However, most traditional SSC detection methods are destructive, cumbersome, and unsuitable for field applications. This study proposes a novel field detection model (Brix-back propagation neural network, Brix-BPNN), designed for [...] Read more.
Soluble solids content (SSC) measurements are crucial for managing longan production and post-harvest handling. However, most traditional SSC detection methods are destructive, cumbersome, and unsuitable for field applications. This study proposes a novel field detection model (Brix-back propagation neural network, Brix-BPNN), designed for longan SSC grading based on an improved BP neural network. Initially, nine preprocessing methods were combined with six classification algorithms to develop the longan SSC grading prediction model. Among these, the model preprocessed with Savitzky–Golay smoothing and the first derivative (SG-D1) demonstrated a 7.02% improvement in accuracy compared to the original spectral model. Subsequently, the BP network structure was refined, and the competitive adaptive reweighted sampling (CARS) algorithm was employed for feature wavelength extraction. The results show that the improved Brix-BPNN model, integrated with the CARS, achieves the highest prediction performance, with a 2.84% increase in classification accuracy relative to the original BPNN model. Additionally, the number of wavelengths is reduced by 92% compared to the full spectrum, making this model both lightweight and efficient for rapid field detection. Furthermore, a portable detection device based on visible-near-infrared (Vis-NIR) spectroscopy was developed for longan SSC grading, achieving a prediction accuracy of 83.33% and enabling fast, nondestructive testing in field conditions. Full article
(This article belongs to the Section Digital Agriculture)
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<p>Block diagram of the hardware system structure.</p>
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<p>Perspective view of the device.</p>
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<p>Physical drawing of the device: (<b>a</b>) internal structure of the device; (<b>b</b>) overall view of the device.</p>
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<p>Spectral collection points.</p>
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<p>Overall structures of the BPNN and Brix-BPNN.</p>
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<p>Structural diagram of the ECA-Brix attention mechanism.</p>
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<p>H-swish and ReLU activation functions.</p>
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<p>Max pooling process for longan spectral data.</p>
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<p>Original spectral curves.</p>
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<p>Average spectral curves of the three SSC grades.</p>
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<p>Feature wavelength selection of longan SSC based on the SPA algorithm: (<b>a</b>) RMSE variation of the model; (<b>b</b>) optimal feature wavelength selected by SPA.</p>
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<p>Feature wavelength selection of longan SSC based on the SPA algorithm: (<b>a</b>) RMSE variation of the model; (<b>b</b>) optimal feature wavelength selected by SPA.</p>
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<p>Feature wavelength selection of longan SSC based on the CARS algorithm: (<b>a</b>) number of sample variables; (<b>b</b>) RMSECV.</p>
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<p>Feature wavelength selection of longan SSC based on the CARS algorithm: (<b>a</b>) number of sample variables; (<b>b</b>) RMSECV.</p>
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<p>Statistical chart of the true and predicted labels for the SSC grade of the test samples.</p>
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13 pages, 2174 KiB  
Article
Leveraging Femtosecond Laser Ablation for Tunable Near-Infrared Optical Properties in MoS2-Gold Nanocomposites
by Ilya A. Zavidovskiy, Ilya V. Martynov, Daniil I. Tselikov, Alexander V. Syuy, Anton A. Popov, Sergey M. Novikov, Andrei V. Kabashin, Aleksey V. Arsenin, Gleb I. Tselikov, Valentyn S. Volkov and Alexey D. Bolshakov
Nanomaterials 2024, 14(23), 1961; https://doi.org/10.3390/nano14231961 - 6 Dec 2024
Viewed by 622
Abstract
Transition metal dichalcogenides (TMDCs), particularly molybdenum disulfide (MoS2), have gained significant attention in the field of optoelectronics and photonics due to their unique electronic and optical properties. The integration of TMDCs with plasmonic materials allows to tailor the optical response and [...] Read more.
Transition metal dichalcogenides (TMDCs), particularly molybdenum disulfide (MoS2), have gained significant attention in the field of optoelectronics and photonics due to their unique electronic and optical properties. The integration of TMDCs with plasmonic materials allows to tailor the optical response and offers significant advantages for photonic applications. This study presents a novel approach to synthesize MoS2-Au nanocomposites utilizing femtosecond laser ablation in liquid to achieve tunable optical properties in the near-infrared (NIR) region. By adjusting ablation and fragmentation protocols, we successfully synthesize various core–shell and core–shell–satellite nanoparticle composites, such as MoS2/MoSxOy, MoSxOy/Au, and MoS2/MoSxOy/Au. UV-visible absorption spectroscopy unveils considerable changes in the optical response of the particles depending on the fabrication regime due to structural modifications. Hybrid nanoparticles exhibit enhanced photothermal properties when subjected to NIR-I laser irradiation, demonstrating potential benefits for selective photothermal therapy. Our findings underscore that the engineered nanocomposites not only facilitate green synthesis but also pave the way for tailored therapeutic applications, highlighting their role as promising candidates in the field of nanophotonics and cancer treatment. Full article
(This article belongs to the Special Issue Optical Composites, Nanophotonics and Metamaterials)
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<p>Schematic representation of the one-, two-, and three-step processes as well as solution mixing for the synthesis of pristine and hybrid MoS<sub>2</sub>/Au NPs.</p>
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<p>TEM characterization of one-step synthesized NPs. (<b>a</b>,<b>d</b>) TEM images of the ablated MoS<sub>2</sub> (<b>a</b>) and Au (<b>d</b>) NPs. Scale bar, 50 nm. (<b>b</b>,<b>e</b>) Size distributions of MoS<sub>2</sub> (<b>b</b>) and Au (<b>e</b>) NPs. (<b>c</b>,<b>f</b>) SAED patterns of MoS<sub>2</sub> (<b>c</b>) and Au (<b>f</b>) NPs.</p>
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<p>Characterization of two- and three-step synthesized NPs and Raman spectroscopy data. TEM images of (<b>a</b>) “Au in MoS<sub>2</sub>”, (<b>b</b>)“MoS<sub>2</sub> in Au”, and (<b>c</b>) “MoS<sub>2</sub>:Au co-fragmented” NPs. Scale bar, 50 nm. Size distributions of (<b>d</b>) “Au in MoS<sub>2</sub>”, (<b>e</b>) “MoS<sub>2</sub> in Au”, and (<b>f</b>) “MoS<sub>2</sub>:Au co-fragmented” NPs. Turquoise bars represent Au NPs, while orange bars represent MoS<sub>2</sub>-based NPs. (<b>g</b>) Raman spectra of the NPs. Violet, brown- and green-colored numbers indicate the positions of the peaks related to MoS<sub>2</sub>, MoS<sub>x</sub>O<sub>y</sub>, and MoO<sub>x</sub>, respectively. Inset shows the magnified low-intensity peaks of the MoS<sub>2</sub> sample.</p>
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<p>High-angle annular dark-field imaging (upper left panels) and EDX maps of “MoS<sub>2</sub>” (<b>a</b>), “MoS<sub>2</sub> in Au” (<b>b</b>), and “Au in MoS<sub>2</sub>” (<b>c</b>) NPs. Scale bar, 20 nm.</p>
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<p>Optical absorption and photoheating. (<b>a</b>) UV-visible extinction spectra. Red dotted line indicates the photoheating laser wavelength. (<b>b</b>–<b>g</b>) Photoheating dynamics. ΔT<sub>max</sub> and PCE notations indicate the values of maximum temperature increases observed throughout the heating and photothermal conversion efficiencies. The plots are presented in the following order: (<b>b</b>) MoS2, (<b>c</b>) Au, (<b>d</b>) MoS<sub>2</sub> in Au, (<b>e</b>) Au in MoS<sub>2</sub>, (<b>f</b>) MoS<sub>2</sub>:Au co-fragmented, (<b>g</b>) MoS<sub>2</sub>+Au.</p>
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11 pages, 2365 KiB  
Article
Non-Destructive Detection of Pesticide-Treated Baby Leaf Lettuce During Production and Post-Harvest Storage Using Visible and Near-Infrared Spectroscopy
by Dimitrios S. Kasampalis, Pavlos I. Tsouvaltzis and Anastasios S. Siomos
Sensors 2024, 24(23), 7547; https://doi.org/10.3390/s24237547 - 26 Nov 2024
Viewed by 446
Abstract
The market demand for baby leaf lettuce is constantly increasing, while safety has become one of the most important traits in determining consumer preference driven by human health hazards concerns. In this study, the performance of visible and near-infrared (vis/NIR) spectroscopy was tested [...] Read more.
The market demand for baby leaf lettuce is constantly increasing, while safety has become one of the most important traits in determining consumer preference driven by human health hazards concerns. In this study, the performance of visible and near-infrared (vis/NIR) spectroscopy was tested in discriminating pesticide-free against pesticide-treated lettuce plants. Two commercial fungicides (mancozeb and fosetyl-al) and two insecticides (deltamethrin and imidacloprid) were applied as spray solutions at the recommended rates on baby leaf lettuce plants. Untreated-control plants were sprayed with water. Reflectance data in the wavelength range 400–2500 nm were captured on leaf samples until harvest on the 10th day upon pesticide application, as well as after 4 and 8 days during post-harvest storage at 5 °C. In addition, biochemical components in leaf tissue were also determined during storage, such as antioxidant enzymes’ activities (peroxidase [POD], catalase [CAT], and ascorbate peroxidase [APX]), along with malondialdehyde [MDA] and hydrogen peroxide [H2O2] content. Partial least square discriminant analysis (PLSDA) combined with feature-selection techniques was implemented, in order to classify baby lettuce tissue into pesticide-free or pesticide-treated ones. The genetic algorithm (GA) and the variable importance in projection (VIP) scores identified eleven distinct regions and nine specific wavelengths that exhibited the most significant effect in the detection models, with most of them in the near-infrared region of the electromagnetic spectrum. According to the results, the classification accuracy of discriminating pesticide-treated against non-treated lettuce leaves ranged from 94% to 99% in both pre-harvest and post-harvest periods. Although there were no significant differences in enzyme activities or H2O2, the MDA content in pesticide-treated tissue was greater than in untreated ones, implying that the chemical spray application probably induced a stress response in the plant that was disclosed with the reflected energy. In conclusion, vis/NIR spectroscopy appears as a promising, reliable, rapid, and non-destructive tool in distinguishing pesticide-free from pesticide-treated lettuce products. Full article
(This article belongs to the Section Chemical Sensors)
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<p>Classification rate (%) of pesticide-free and pesticide-treated baby lettuce leaves based on reflectance spectra data (340–2500 nm) within each day of pre-harvest production or postharvet storage, as well as average means for the whole period upon pooling the data of all individual days.</p>
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<p>Spectra reflectance (%) of pesticide-free (blue line) and pesticide-treated (red line) baby lettuce leaves in the vis-NIR part (340–2500 nm) as average means for the whole period upon pooling the data captured in all individual days. The eleven green areas represent the parts of the spectrum that exhibited the most significant effect on the partial least squares discrimination analysis classifier and were detected using the genetic algorithm (GA).</p>
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<p>The variable importance in projection scores (VIP) in the vis/NIR part (340–2500 nm), which represents the individual effect of each wavelength on the partial least squares discrimination analysis classifier. The vertical green lines correspond to the wavelengths with the highest VIP scores. The red dot line corresponds to the lowest limit above which a wavelength exhibits a significant effect in the discriminant analysis algorithm.</p>
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<p>Classification rate (%) of pesticide-free and pesticide-treated baby lettuce leaves based on the reflectance spectra data at 377, 517, 689, 959, 994, 1361, 1390, 1875, and 2177 nm that were selected using the VIP scores analysis, within each day of pre-harvest production or post-harvest storage, as well as average for the whole period upon pooling the data captured in all individual days.</p>
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8 pages, 3430 KiB  
Communication
Fano Resonance-Associated Plasmonic Circular Dichroism in a Multiple-Dipole Interaction Born–Kuhn Model
by Wanlu Bian, Guodong Zhu, Fengcai Ma, Tongtong Zhu and Yurui Fang
Sensors 2024, 24(23), 7517; https://doi.org/10.3390/s24237517 - 25 Nov 2024
Viewed by 444
Abstract
Plasmon chirality has garnered significant interest in sensing application due to its strong electromagnetic field localization and highly tunable optical properties. Understanding the effects of mode coupling in chiral structures on chiral optical activity is particularly important for advancing this field. In this [...] Read more.
Plasmon chirality has garnered significant interest in sensing application due to its strong electromagnetic field localization and highly tunable optical properties. Understanding the effects of mode coupling in chiral structures on chiral optical activity is particularly important for advancing this field. In this work, we numerically investigate the circular dichroism (CD) of elliptical nanodisk dimers arranged in an up-and-down configuration with a specific rotation angle. By adjusting the inter-particle distance and geometric parameters, we introduce the coupling between dipole and electric hexapole modes, forming an extended Born–Kuhn model that achieves strong CD. Our findings show that the coupling of dipole modes with electric hexapole modes in elliptical nanodisks can also show obvious Fano resonance and a strong CD effect, and the structure with the largest Fano asymmetry factor shows the highest CD. In addition, CD spectroscopy is highly sensitive to changes in the refractive index of the surrounding medium, especially in the visible and near-infrared regions, highlighting its potential for application in high-sensitivity refractive index sensors. Full article
(This article belongs to the Section Optical Sensors)
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<p>Born–Kuhn model composed of two nanodisks. (<b>a</b>) Structure scheme, R<sub>1</sub> = 100 nm, R<sub>2</sub> = 22.5 nm, R<sub>3</sub> = 50 nm, R<sub>4</sub> = 400 nm, the thickness of the two particles H is 50 nm, the gap g between the upper and lower is 50 nm, the angle is 120°, and the light incident is perpendicular to the cross plane of the two nanodisks. (<b>b</b>) The extinction cross-section of individual nanodisks. The insets show the charge distributions of the nanodisks at the resonance wavelength of 800 nm. (<b>c</b>) The extinction cross-section of the structure excited by LCP and RCP. The insets show the surface charge distributions at the corresponding peaks. (<b>d</b>) CD spectrum.</p>
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<p>(<b>a</b>) Extinction cross-section of a dimer composed of small dimers. (<b>b</b>) The nano-configuration of a dimer composed of two large particles. CPL excites the extinction cross-section of the two large particles. (<b>c</b>) The extinction CD spectrum and the charge distribution of the upper and lower particles after excitation of the corresponding formant. (<b>d</b>) The extinction CD spectrum and the charge distribution of the upper and lower particles after the LCP and RCP formant excitation.</p>
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<p>(<b>a</b>) The extinction cross-section and the corresponding CD spectrum for the distance <span class="html-italic">g</span> between the two particles at 40nm, and the illustration shows the charge distribution at the corresponding resonance. (<b>b</b>) <span class="html-italic">g</span> = 30 nm. (<b>c</b>) <span class="html-italic">g</span> = 20 nm. (<b>d</b>) <span class="html-italic">g</span> = 10 nm.</p>
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<p>(<b>a</b>) The central dot of the small nanodisk overlaps with the vertex of the large nanodisk. (<b>b</b>) The vertex of the left end of the small nanodisk overlaps with the vertex of the large nanodisk. (<b>c</b>) The center point of the small nanodisk overlaps with the middle of the center point and the vertex of the large nanodisk. (<b>d</b>) The vertex of the right end of the small nanodisk overlaps with the vertex of the large nanodisk.</p>
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<p>(<b>a</b>) The CD spectrum after the surrounding medium environment n increased from 1.1 to 1.4. (<b>b</b>) The CD spectrum when the angle between the two particles increased from 10° to 80°.</p>
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18 pages, 3885 KiB  
Article
Investigation of Wettability, Thermal Stability, and Solar Behavior of Composite Films Based on Thermoplastic Polyurethane and Barium Titanate Nanoparticles
by Dilayda Kanmaz, Rumeysa Celen, Esra Karaca and Gizem Manasoglu
Polymers 2024, 16(23), 3259; https://doi.org/10.3390/polym16233259 - 23 Nov 2024
Viewed by 455
Abstract
Herein, composite films were produced by incorporating different amounts (1, 3, 5, and 7%) of barium titanate nanoparticles into the thermoplastic polyurethane matrix using a solution casting method. This study examined the impact of the presence and concentration of a barium titanate additive [...] Read more.
Herein, composite films were produced by incorporating different amounts (1, 3, 5, and 7%) of barium titanate nanoparticles into the thermoplastic polyurethane matrix using a solution casting method. This study examined the impact of the presence and concentration of a barium titanate additive on morphologic properties, mechanical performance, thermal stability, solar behavior, and wettability of produced film samples. The films were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, scanning electron microscope, ultraviolet-visible near-infrared spectrophotometer, water contact angle, and tensile strength measurements. In the present study, the mass loss of samples containing 7% barium titanate was 24% lower than that of the pure polyurethane reference. The increase of barium titanate rate added to polyurethane enhanced the solar reflectance property of the films, including the near-infrared region. As a prominent result, the transmittance value decreased significantly compared to the reference in the ultraviolet region, and it dropped to 3% for the highest additive concentration. The contact angle values of polyurethane films increased by 11–40% depending on the barium titanate addition ratio. The nano additive also positively affected the mechanical performance of the reference polyurethane film by slightly increasing the tensile strength values. Full article
(This article belongs to the Special Issue Advances in Functional Polyurethane and Composites)
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<p>Solution casting process: (<b>a</b>) Film applicator; (<b>b</b>) Casting of the polymer solution; (<b>c</b>) Production of the film; (<b>d</b>) Removal of the solvent; (<b>e</b>) Drying of the film.</p>
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<p>SEM micrographs of pure polyurethane film (<b>a</b>) and polyurethane films containing 1% (<b>b</b>), 3% (<b>c</b>), 5% (<b>d</b>), and 7% (<b>e</b>) barium titanate additive.</p>
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<p>FTIR spectra of barium titanate powder (BT), pure polyurethane film (BT0), and barium titanate-added polyurethane films (BT1–BT7) at wavelength ranges of (<b>a</b>) 4000–400 cm<sup>−1</sup> and (<b>b</b>) 600–400 cm<sup>−1</sup>.</p>
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<p>DSC curves of barium titanate powder (BT), pure polyurethane film (BT0), and barium titanate-added polyurethane films (BT1–BT7).</p>
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<p>TGA curves of barium titanate powder (BT), pure polyurethane film (BT0), and barium titanate-added polyurethane films (BT1–BT7).</p>
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<p>Contact angle values of pure polyurethane and barium titanate-added polyurethane films.</p>
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<p>Transmittance spectra of polyurethane films added with barium titanate at different concentrations. (<b>a</b>) Ultraviolet region; (<b>b</b>) entire spectrum scanned.</p>
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<p>Reflectance spectra of polyurethane films added with barium titanate at different concentrations. (<b>a</b>) Near-infrared region; (<b>b</b>) ultraviolet region and entire spectrum scanned.</p>
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<p>Absorbance spectra of polyurethane films added with barium titanate at different concentrations. (<b>a</b>) Ultraviolet region; (<b>b</b>) entire spectrum scanned.</p>
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<p>Tensile strength results of pure polyurethane and barium titanate-added polyurethane films.</p>
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17 pages, 2380 KiB  
Article
Nondestructive Detection of Litchi Stem Borers Using Multi-Sensor Data Fusion
by Zikun Zhao, Sai Xu, Huazhong Lu, Xin Liang, Hongli Feng and Wenjing Li
Agronomy 2024, 14(11), 2691; https://doi.org/10.3390/agronomy14112691 - 15 Nov 2024
Viewed by 461
Abstract
To enhance lychee quality assessment and address inconsistencies in post-harvest pest detection, this study presents a multi-source fusion approach combining hyperspectral imaging, X-ray imaging, and visible/near-infrared (Vis/NIR) spectroscopy. Traditional single-sensor methods are limited in detecting pest damage, particularly in lychees with complex skins, [...] Read more.
To enhance lychee quality assessment and address inconsistencies in post-harvest pest detection, this study presents a multi-source fusion approach combining hyperspectral imaging, X-ray imaging, and visible/near-infrared (Vis/NIR) spectroscopy. Traditional single-sensor methods are limited in detecting pest damage, particularly in lychees with complex skins, as they often fail to capture both external and internal fruit characteristics. By integrating multiple sensors, our approach overcomes these limitations, offering a more accurate and robust detection system. Significant differences were observed between pest-free and infested lychees. Pest-free lychees exhibited higher hardness, soluble sugars (11% higher in flesh, 7% higher in peel), vitamin C (50% higher in flesh, 2% higher in peel), polyphenols, anthocyanins, and ORAC values (26%, 9%, and 14% higher, respectively). The Vis/NIR data processed with SG+SNV+CARS yielded a partial least squares regression (PLSR) model with an R2 of 0.82, an RMSE of 0.18, and accuracy of 89.22%. The hyperspectral model, using SG+MSC+SPA, achieved an R2 of 0.69, an RMSE of 0.23, and 81.74% accuracy, while the X-ray method with support vector regression (SVR) reached an R2 of 0.69, an RMSE of 0.22, and 76.25% accuracy. Through feature-level fusion, Recursive Feature Elimination with Cross-Validation (RFECV), and dimensionality reduction using PCA, we optimized hyperparameters and developed a Random Forest model. This model achieved 92.39% accuracy in pest detection, outperforming the individual methods by 3.17%, 10.25%, and 16.14%, respectively. The multi-source fusion approach also improved the overall accuracy by 4.79%, highlighting the critical role of sensor fusion in enhancing pest detection and supporting the development of automated non-destructive systems for lychee stem borer detection. Full article
(This article belongs to the Section Precision and Digital Agriculture)
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<p>Schematic diagram of the visible/near-infrared spectroscopy acquisition device.</p>
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<p>Schematic diagram of the hyperspectral imaging acquisition device.</p>
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<p>Schematic diagram of the X-ray image acquisition system.</p>
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<p>Multi-source information fusion flowchart.</p>
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<p>(<b>a</b>) Raw visible/near-infrared spectrum, (<b>b</b>) visible/near-infrared spectrum after SG+SNV preprocessing.</p>
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<p>(<b>a</b>) Raw hyperspectral spectrum, (<b>b</b>) hyperspectral spectrum after SG+MSC preprocessing.</p>
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<p>PCA classification of grayscale values in X-ray imaging feature regions for stem-borer-infested and non-infested fruit.</p>
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<p>(<b>a</b>) Litchi fruit without pests, (<b>b</b>) litchi fruit with pests.</p>
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48 pages, 9198 KiB  
Review
Illuminating Malaria: Spectroscopy’s Vital Role in Diagnosis and Research
by Bayden R. Wood, John A. Adegoke, Thulya Chakkumpulakkal Puthan Veettil, Ankit Dodla, Keith Dias, Neha Mehlawat, Callum Gassner, Victoria Stock, Sarika Joshi, Magdalena Giergiel, Diana E. Bedolla and Philip Heraud
Spectrosc. J. 2024, 2(4), 216-263; https://doi.org/10.3390/spectroscj2040015 - 15 Nov 2024
Viewed by 876
Abstract
Spectroscopic techniques have emerged as crucial tools in the field of malaria research, offering immense potential for improved diagnosis and enhanced understanding of the disease. This review article pays tribute to the pioneering contributions of Professor Henry Mantsch in the realm of clinical [...] Read more.
Spectroscopic techniques have emerged as crucial tools in the field of malaria research, offering immense potential for improved diagnosis and enhanced understanding of the disease. This review article pays tribute to the pioneering contributions of Professor Henry Mantsch in the realm of clinical biospectroscopy, by comprehensively exploring the diverse applications of spectroscopic methods in malaria research. From the identification of reliable biomarkers to the development of innovative diagnostic approaches, spectroscopic techniques spanning the ultraviolet to far-infrared regions have played a pivotal role in advancing our knowledge of malaria. This review will highlight the multifaceted ways in which spectroscopy has contributed to the field, with a particular emphasis on its impact on diagnostic advancements and drug research. By leveraging the minimally invasive and highly accurate nature of spectroscopic techniques, researchers have made significant strides in improving the detection and monitoring of malaria parasites. These advancements hold the promise of enhancing patient outcomes and aiding in the global efforts towards the eradication of this devastating disease. Full article
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Graphical abstract

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<p>Asexual and sexual phases of the malaria parasite in RBC. After sporozoites enter the bloodstream, they travel to the liver, where they invade hepatocytes and develop into schizonts, each containing thousands of merozoites. These merozoites are then released and invade erythrocytes, initiating the intraerythrocytic asexual phase. During this phase, the parasites grow and divide within the food vacuole, progressing through three distinct morphological stages: ring, trophozoite, and schizont. When schizonts rupture, they release merozoites, continuing the erythrocytic cycle. Some merozoites, instead of replicating, differentiate into male and female gametocytes capable of transmission to mosquitoes. The digestion of hemoglobin by the parasite leads to the accumulation of Hz. In the circulation, only ring-stage parasites and late-stage gametocytes are observed. Reproduced with permission from the Royal Society of Chemistry [<a href="#B7-spectroscj-02-00015" class="html-bibr">7</a>].</p>
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<p>Hematin and β-hematin structure. (<b>A</b>) Schematic representation of hematin, the monomeric precursor of β-hematin. (<b>B</b>) Structure and packing arrangement of β-hematin (synthetic malaria pigment) viewed along the c-axis. Some (h,k,l) planes are indicated. Reprinted with permission from the American Chemical Society [<a href="#B19-spectroscj-02-00015" class="html-bibr">19</a>].</p>
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<p>Raman excitation wavelength measurements recorded of β-hematin. The asterisks (*) highlight the bands enhanced relative to the other excitation wavelengths at 830 nm. Reproduced with permission from the American Chemical Society [<a href="#B20-spectroscj-02-00015" class="html-bibr">20</a>].</p>
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<p>(<b>A</b>) FTIR spectrum of β-hematin. (<b>B</b>) FTIR spectrum of hemozoin extracted from malaria trophozoites. Reproduced with permission from the American Chemical Society [<a href="#B20-spectroscj-02-00015" class="html-bibr">20</a>].</p>
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<p>Absorbance spectra recorded during the acidification of hemin to form β-hematin. Reproduced with permission from the American Chemical Society [<a href="#B20-spectroscj-02-00015" class="html-bibr">20</a>].</p>
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<p>Representative second derivative spectra, (<b>a</b>) β-hematin (green), (<b>b</b>) dry hemozoin isolated from infected red blood cells (red), (<b>c</b>) dry crystalline hemozoin purchased from Invivogen (blue). Reproduced with permission from the American Chemical Society [<a href="#B5-spectroscj-02-00015" class="html-bibr">5</a>].</p>
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<p>FTIR averaged normalized spectra of the C-H stretching region and fingerprint region from the Australian Synchrotron of RBCs (control) and the three stages of the parasitic life cycle (ring, trophozoite, and schizont) within a fixed RBC. Standard deviation spectra are shown below each spectrum for both spectral regions. Reproduced with permission from the American Chemical Society [<a href="#B31-spectroscj-02-00015" class="html-bibr">31</a>].</p>
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<p>(<b>A</b>) Visible image of the thick film of malaria-infected RBCs. (<b>B</b>) Partial dark-field effect visible micrograph highlighting the trophozoites. (<b>C</b>) Chemical map of the area outlined by the red square (ROI) in (<b>B</b>), generated by integrating the region between 1680 and 1620 cm<sup>−1</sup>, with lighter colors indicating hemozoin deposits within the trophozoites. (<b>D</b>) UHCA of ROI using D-values algorithm in the range of 1700–1300 cm<sup>−1</sup> revealing two clusters: Blue cluster, hemozoin, and red cluster, hemoglobin. (<b>E</b>) UHCA of ROI showing five clusters where the pink cluster spectrum is like hemozoin in the late-stage trophozoites, while green and grey clusters represent a mix of hemoglobin and hemozoin. The light blue cluster corresponds well with the hemoglobin present within RBCs, along with red cluster present as submicron dots (300 nm) corresponding to the hemozoin throughout the stages of <span class="html-italic">P. falciparum</span> life cycle. (<b>F</b>) Mean spectra corresponding to each cluster shown in (<b>E</b>). Reproduced with permission from the Royal Society of Chemistry [<a href="#B68-spectroscj-02-00015" class="html-bibr">68</a>].</p>
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<p>Raman acoustic levitation spectroscopy (RALS). (<b>A</b>) A droplet of isolated red blood cells levitated using a piezo-electric transducer and reflective plate. (<b>B</b>) Schematic showing acoustic levitator coupled to a Raman microscope using a right-angled adaptor. (<b>C</b>) Spectra of trophozoite lysate from lysed red blood cells (<b>top</b>) and micro-Raman spectrum of hemozoin (<b>bottom</b>). Reproduced with permission from the Royal Society of Chemistry [<a href="#B69-spectroscj-02-00015" class="html-bibr">69</a>].</p>
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<p>(<b>A</b>) <span class="html-italic">Graphium weiskei</span> butterfly wings. (<b>B</b>) Schematic cross-sectional view of a gold-coated wing showing typical chitinous conical protrusion dimensions and spacings based on SEM images. (<b>C</b>–<b>F</b>) SEM images of chitinous nano-structured conical arrays found on the wings of the <span class="html-italic">G. weiskei</span> butterfly. (<b>C</b>,<b>D</b>) SEM images acquired after deposition with <span class="html-italic">P. falciparum</span>-infected RBC lysate. (<b>E</b>,<b>F</b>) Control butterfly wings without lysate deposition. (<b>G</b>–<b>I</b>) SERS spectra of 0.0005%, 0.005%, and 0% (control) malarial-infected RBC lysate, respectively. (<b>J</b>) Conventional Raman spectrum of hemozoin at 785 nm. Reproduced with permission from the Royal Society of Chemistry [<a href="#B81-spectroscj-02-00015" class="html-bibr">81</a>].</p>
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<p>(<b>A</b>) <span class="html-italic">Graphium weiskei</span> butterfly wings. (<b>B</b>) Schematic cross-sectional view of a gold-coated wing showing typical chitinous conical protrusion dimensions and spacings based on SEM images. (<b>C</b>–<b>F</b>) SEM images of chitinous nano-structured conical arrays found on the wings of the <span class="html-italic">G. weiskei</span> butterfly. (<b>C</b>,<b>D</b>) SEM images acquired after deposition with <span class="html-italic">P. falciparum</span>-infected RBC lysate. (<b>E</b>,<b>F</b>) Control butterfly wings without lysate deposition. (<b>G</b>–<b>I</b>) SERS spectra of 0.0005%, 0.005%, and 0% (control) malarial-infected RBC lysate, respectively. (<b>J</b>) Conventional Raman spectrum of hemozoin at 785 nm. Reproduced with permission from the Royal Society of Chemistry [<a href="#B81-spectroscj-02-00015" class="html-bibr">81</a>].</p>
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<p>Infrared images of trophozoites inside infected erythrocytes. (<b>a</b>) Three-dimensional representation of an infected and an uninfected cell. (<b>b</b>) False color images of 6 erythrocytes infected with trophozoites and their visible images. Color scale corresponding to the integration area underneath each spectrum (pixel). Reproduced with permission from the Royal Society of Chemistry [<a href="#B93-spectroscj-02-00015" class="html-bibr">93</a>].</p>
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<p>A diagram of the instrumentation and operation of an O-PTIR microscope (Photothermal Inc., Santa Barbara, CA, USA). This figure is from an open-access article distributed under the terms of the Creative Commons CC-BY license [<a href="#B109-spectroscj-02-00015" class="html-bibr">109</a>].</p>
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<p>Trends in miniaturization of near-infrared spectrometers. This article containing this figure is distributed under the terms of the Creative Commons Attribution-Non-commercial 4.0 License [<a href="#B119-spectroscj-02-00015" class="html-bibr">119</a>].</p>
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<p>Scanning of mice and blood spots using NIRS. Panel (<b>A</b>,<b>B</b>) illustrate how mice were held and non-invasively scanned. Panel (<b>C</b>) illustrates scanning of dry blood spots on the slides. Panel (<b>D</b>) shows the resultant raw spectral signatures from various body parts of a mouse and spectral signatures from blood spots. The figure is from an open-access article distributed under the terms of the Creative Commons Attribution License [<a href="#B131-spectroscj-02-00015" class="html-bibr">131</a>].</p>
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<p>Partial least squares regression plots for malaria-diluted samples ranging from (<b>A</b>) 6% to 0.00001%, (<b>B</b>) 0.1% to 0.00001%, where the actual parasitemia plotted on the <span class="html-italic">x</span>-axis and the predicted parasitemia on the <span class="html-italic">y</span>-axis. (<b>C</b>) PCA Score plots (PC1 vs. PC2) for 6% to 0.00001% range. (<b>D</b>) Comparison between control samples and those with the lowest parasitemia (0.000001%). Reproduced with permission from the American Chemical Society [<a href="#B5-spectroscj-02-00015" class="html-bibr">5</a>].</p>
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<p>The image illustrates PCA applied to visible spectra of single cells. (<b>A</b>) A 3D scores plot for various RBC samples (control, rings, trophozoites, schizonts), demonstrating clear separation of control RBCs from infected cells along PC 2. (<b>B</b>) The PC1 loadings plot, highlighting significant positive and negative loadings. (<b>C</b>) The PC2 loadings plot. (<b>D</b>) A 3D scores plot comparing RBCs infected with rings (R) and trophozoites (T). (<b>E</b>) Schizonts (S) and trophozoites (T). (<b>F</b>) Rings (R) and schizonts (S). (<b>G</b>–<b>I</b>) Presents the computed confusion matrices (CM) that illustrate the accuracy of the SVM models developed in this study. (<b>G</b>) Shows multiclass models, including datasets from control, rings, schizonts, and trophozoites. Panels (<b>B</b>–<b>D</b>) display binary classifications comparing infected classes with the control: (<b>B</b>) control vs. trophozoites, (<b>C</b>) control vs. rings, and (<b>D</b>) control vs. schizonts. The numbers in each class indicate the spectra count used for testing. Reproduced with permission from the American Chemical Society [<a href="#B6-spectroscj-02-00015" class="html-bibr">6</a>].</p>
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<p>Analysis of IR and Raman spectra from a single isolated red blood cell (RBC). For the IR analysis: (<b>a</b>) An unsupervised hierarchical cluster analysis (UHCA) cluster image was generated, and (<b>b</b>) shows a visible image of a Giemsa-stained cell. For the Raman analysis: (<b>c</b>) presents the UHCA cluster image, and (<b>d</b>,<b>e</b>) the average spectra for each cluster were displayed for the IR and Raman analysis, respectively, while (<b>f</b>) displays the integration map of the Raman band for hemozoin, in the range of 1629–1599 cm<sup>−1</sup>, using baselines set at 1585–1575 cm<sup>−1</sup> and 1652–1643 cm<sup>−1</sup>. The Raman spectra provided precise localization of hemozoin bands, which was not possible to identify directly in the IR spectra of the RBC. Note the colors of the spectra match the classes in the UHCA maps. Reproduced with permission from Elsevier [<a href="#B94-spectroscj-02-00015" class="html-bibr">94</a>].</p>
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<p>(<b>A</b>–<b>C</b>) PLS-R results for WB samples spiked with R-staged parasites. PLS-R predicted versus reference plots for the higher parasitemia models (1–0.25%) are shown for: (<b>A</b>) the lower wavelength range (200–700 nm), (<b>B</b>) the higher wavelength range (1000–2500 nm), and (<b>C</b>) the entire wavelength range (200–2500 nm). (<b>D</b>) The PLS regression vector for the lower parasitemia models highlights key marker bands associated with both infected and control aqueous blood. Reproduced with permission from the American Chemical Society [<a href="#B132-spectroscj-02-00015" class="html-bibr">132</a>].</p>
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<p>AFM-IR imaging of a <span class="html-italic">P. falciparum</span> trophozoite inside a red blood cell. (<b>a</b>) AFM topography. (<b>b</b>) AFM deflection map showing the location of the points where spectra were measured, inside (blue) and outside (red) of the protrusion. (<b>c</b>,<b>d</b>) Spectra measured from the signal of the IR intensity peak (V) showing different bands for the red and blue spots in the 1450–950 and 1800–1450 cm<sup>−1</sup> regions, respectively. (<b>e</b>,<b>f</b>) IR peak maps obtained at 1207 and 1660 cm<sup>−1</sup>, respectively. (<b>g</b>,<b>h</b>) Score and loading plots from the PCA applied to the 3100–2800 cm<sup>−1</sup> region. Replicated from [<a href="#B156-spectroscj-02-00015" class="html-bibr">156</a>].</p>
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<p>(<b>A</b>–<b>C</b>) AFM images recorded of sectioned cells prior to TERS acquisition. (<b>A</b>) A 30 × 30 μm AFM image recorded of a population of infected red blood cells showing a potential cell target highlighted by the blue square. (<b>B</b>) A high-resolution image of the cell highlighted in (<b>A</b>) showing hemozoin crystals aligned in the digestive vacuole. (<b>C</b>) An even higher resolution AFM image of the digestive vacuole of the parasite showing single crystals of hemozoin that can be selectively targeted with the TERS active tip. (<b>D</b>) TERS spectrum recorded of the edge of a hemozoin crystal. The spectrum was recorded with a laser power of 600 μW and exposure time of 5 s. (<b>E</b>) After recording a spectrum, the tip was retracted by several micrometers, and a further spectrum recorded to ensure the tip had not been contaminated by the sample. (<b>F</b>) Surface-enhanced Raman spectrum recorded of β-hematin prepared using SERS active Ag-particles. Spectra were recorded using a 532 nm laser and 10 s acquisition time. (<b>G</b>) Resonance Raman spectrum of β-hematin recorded at 532 nm with 10 s acquisition time. Reproduced with permission from the American Chemical Society [<a href="#B157-spectroscj-02-00015" class="html-bibr">157</a>].</p>
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<p>A partial least squares discriminant analysis (PLS-DA) prediction plot showing the classification of either malaria positive (&lt;0.5) or negative (&gt;0.5); spectra color-coded malaria positive (red) or negative (green) by PCR. (<b>B</b>) Same as in (<b>A</b>), except support vector machine (SVM) learning is used for the classification. (<b>C</b>) Receiver operating characteristic (ROC) curves showing the diagnostic of the PLS-DA and SVM classification. (<b>D</b>) ROC curve for data where samples were assigned positive- and negative, based on PCR versus randomized models. (<b>E</b>) Average spectra over the three spectral ranges used for PLS-DA classification. Superimposed is a color code showing the regression loadings for malaria positive (“warm colors”) or negative (“cool colors”) classification for each absorbance value. This figure is reproduced from an open-access article published by Biomedical Central (BMC), a part of Springer Nature [<a href="#B57-spectroscj-02-00015" class="html-bibr">57</a>].</p>
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13 pages, 8022 KiB  
Article
On the Effect of Randomly Oriented Grain Growth on the Structure of Aluminum Thin Films Deposited via Magnetron Sputtering
by Vagelis Karoutsos, Nikoletta Florini, Nikolaos C. Diamantopoulos, Christina Balourda, George P. Dimitrakopulos, Nikolaos Bouropoulos and Panagiotis Poulopoulos
Coatings 2024, 14(11), 1441; https://doi.org/10.3390/coatings14111441 - 13 Nov 2024
Viewed by 697
Abstract
The microstructure of aluminum thin films, including the grain morphology and surface roughness, are key parameters for improving the thermal or electrical properties and optical reflectance of films. The first step in optimizing these parameters is a thorough understanding of the grain growth [...] Read more.
The microstructure of aluminum thin films, including the grain morphology and surface roughness, are key parameters for improving the thermal or electrical properties and optical reflectance of films. The first step in optimizing these parameters is a thorough understanding of the grain growth mechanisms and film structure. To investigate these issues, thin aluminum films with thicknesses ranging from 25 to 280 nm were coated on SiOx/Si substrates at ambient temperature under high-vacuum conditions and a low argon pressure of 3 × 10−3 mbar (0.3 Pa) using the radio frequency magnetron sputtering method. Quantitative analyses of the surface roughness and nanograin characteristics were conducted using atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction. Changes in specular reflectance were measured using ultraviolet–visible and near-infrared spectroscopy. The low roughness values obtained from the AFM images resulted in high film reflectivity, even for thicker films. TEM and AFM results indicate monomodal, randomly oriented grain growth without a distinct columnar or spherical morphology. Using TEM cross-sectional images and the dependence of the grain size on the film thickness, we propose a grain growth mechanism based on the diffusion mobility of aluminum atoms through grain boundaries. Full article
(This article belongs to the Section Thin Films)
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<p>XRD pattern of the 280 nm thick Al film deposited on SiO<sub>x</sub>/Si.</p>
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<p>(<b>a</b>) Cross-sectional high-angle annular dark-field (HAADF) STEM image of the Al/Si heterostructure. (<b>b</b>) Corresponding layered image of EDS maps. The inset illustrates the interfacial region with the oxygen signal due to the SiO<sub>x</sub> interlayer.</p>
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<p>AFM images of the deposited Al films for the following samples: (<b>a</b>) ALM1, (<b>b</b>) ALM2, (<b>c</b>) ALM3, (<b>d</b>) ALM4, (<b>e</b>) ALM5, and (<b>f</b>) ALM6. All image dimensions are 1 × 1 μm<sup>2</sup>, except for image (<b>a</b>), whose dimensions are 500 × 500 nm<sup>2</sup>.</p>
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<p>Grain size distribution histograms corresponding to each AFM image in <a href="#coatings-14-01441-f003" class="html-fig">Figure 3</a>; d<sub>g</sub> denotes the mean grain size obtained by the Gaussian function fitted to each histogram.</p>
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<p>Measured average RMS roughness for the six film surfaces (<a href="#coatings-14-01441-t002" class="html-table">Table 2</a>) plotted as a function of film thickness.</p>
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<p>Reflectance spectra of two Al thin films with different thicknesses deposited on glass substrate.</p>
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<p>(<b>a</b>) Cross-sectional bright-field TEM image of a region of the Al/Si heterostructure obtained along the [1<math display="inline"><semantics> <mrow> <mover accent="true"> <mrow> <mn>1</mn> </mrow> <mo>¯</mo> </mover> </mrow> </semantics></math>0]Si zone axis of the substrate. SAED patterns obtained from the substrate and the Al film are given as insets. Reflections from diffracting planes are denoted on the SAED patterns. In the case of the Al film, its polycrystalline character yields a ring-type SAED pattern. (<b>b</b>) The 3D AFM surface image of the same film.</p>
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<p>(<b>a</b>) Cross-sectional bright field TEM image showing another region of the Al/Si heterostructure. (<b>b</b>,<b>c</b>) Corresponding dark field TEM images obtained with different reflections of the film, showing diffraction contrast from different crystallites. In (<b>b</b>), the arrows indicate smaller-sized crystallites near the heterointerface.</p>
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<p>(<b>a</b>) HRTEM image along the [1<math display="inline"><semantics> <mrow> <mover accent="true"> <mrow> <mn>1</mn> </mrow> <mo>¯</mo> </mover> </mrow> </semantics></math>0] zone axis of Si, showing in atomic resolution the polycrystalline Al epilayer grown on the Si substrate. Moiré fringes in the Al film are due to the overlap of grains along the projection direction. (<b>b</b>) GPA phase map illustrating the phase changes in the epilayer due to its polycrystalline structure. The inset is the corresponding diffractogram indicating the selected spatial periodicities close to 220 Si that were employed for creating the phase map.</p>
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<p>Measured average grain diameter obtained by distribution histograms of <a href="#coatings-14-01441-f003" class="html-fig">Figure 3</a> plotted as a function of film thickness.</p>
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17 pages, 5391 KiB  
Article
Nondestructive Identification of Internal Potato Defects Using Visible and Short-Wavelength Near-Infrared Spectral Analysis
by Dennis Semyalo, Yena Kim, Emmanuel Omia, Muhammad Akbar Andi Arief, Haeun Kim, Eun-Yeong Sim, Moon S. Kim, Insuck Baek and Byoung-Kwan Cho
Agriculture 2024, 14(11), 2014; https://doi.org/10.3390/agriculture14112014 - 8 Nov 2024
Viewed by 742
Abstract
Potatoes are a staple food crop consumed worldwide, with their significance extending from household kitchens to large-scale food processing industries. Their market value and quality are often compromised by various internal defects such as pythium, bruising, internal browning, hollow heart, gangrene, blackheart, internal [...] Read more.
Potatoes are a staple food crop consumed worldwide, with their significance extending from household kitchens to large-scale food processing industries. Their market value and quality are often compromised by various internal defects such as pythium, bruising, internal browning, hollow heart, gangrene, blackheart, internal sprouting, and dry rot. This study aimed to classify internal-based defects and investigate the quantification of internal defective areas in potatoes using visible and short-wavelength near-infrared spectroscopy. The acquisition of the spectral data of potato tubers was performed using a spectrometer with a wavelength range of 400–1100 nm. The classification of internal-based defects was performed using partial least squares discriminant analysis (PLS-DA), while the quantification of the internal defective area was based on partial least squares regression (PLSR). The PLS-DA double cross-validation accuracy for the distinction between non-defective and all internally defective potatoes was 90.78%. The double cross-validation classification accuracy achieved for pythium, bruising, and non-defective categories was 91.03%. The internal defective area model based on PLSR achieved a correlation coefficient of double cross-validation of 0.91 and a root mean square error of double cross-validation of 0.85 cm2. This study makes a valuable contribution to advancing nondestructive techniques for evaluating internal defects in potatoes. Full article
(This article belongs to the Section Agricultural Product Quality and Safety)
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<p>Experimental field of potato tubers in Pyeongchang, Gangwon-do, South Korea.</p>
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<p>Top view of the inside of the spectral data acquisition chamber: light source (<b>A</b>), potato tuber (<b>B</b>), and cooling fan (<b>C</b>).</p>
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<p>Internal defects in potatoes: non-defective (<b>A</b>), pythium (<b>B</b>), dry rot (<b>C</b>), bruising (<b>D</b>), gangrene (<b>E</b>), blackheart (<b>F</b>), internal browning (<b>G</b>), hollow heart (<b>H</b>), and internal sprouting (<b>I</b>).</p>
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<p>A flow chart for the major steps performed during internal defect area determination. ROI is the region of interest.</p>
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<p>Mean spectra of each internal defect in potatoes.</p>
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<p>Calibration classification plot for sound (0) and defective potatoes (1). The numbers of observation spectra for total, sound, and defective potatoes were 341, 114, and 227, respectively.</p>
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<p>Double cross-validation classification plot for sound (0) and defective potatoes (1). The numbers of observation spectra for total, sound, and defective potatoes were 141, 47, and 94, respectively.</p>
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<p>Beta coefficient plot for the detection of sound and defective potatoes.</p>
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<p>Calibration classification plot for non-defective (0), bruising (1), and pythium (2) defective categories in potatoes. The numbers of observation spectra for total, non-defective, bruising, and pythium potato categories were 268, 168, 78, and 22, respectively.</p>
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<p>Double cross-validation classification plot for non-defective (0), bruising (1), and pythium (2) defect categories in potatoes. The numbers of observation spectra for total, non-defective, bruising, and pythium potato categories were 115, 72, 33, and 10, respectively.</p>
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<p>Beta coefficient plot for the classification of internal-based defect categories in potatoes.</p>
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<p>Calibration and double cross-validation plot for the internal defective area in potatoes. The number of observation spectra: n = 383. Rv is the correlation coefficient of double cross-validation.</p>
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<p>Beta coefficient plot for the internal defective area in potatoes.</p>
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10 pages, 4340 KiB  
Article
Study on the Thermal Control Performance of Mg-Li Alloy Micro-Arc Oxidation Coating in High-Temperature Environments
by Wentao Zhang, Shigang Xin, Qing Huang and Haiyang Jiao
Surfaces 2024, 7(4), 969-978; https://doi.org/10.3390/surfaces7040063 - 8 Nov 2024
Viewed by 784
Abstract
This paper reports on the successful preparation of a low absorption–emission thermal control coating on the surface of LAZ933 magnesium–lithium alloy using the micro-arc oxidation method. This study analyzed the microstructure, phase composition, and thermal control properties of the coating using Scanning Electron [...] Read more.
This paper reports on the successful preparation of a low absorption–emission thermal control coating on the surface of LAZ933 magnesium–lithium alloy using the micro-arc oxidation method. This study analyzed the microstructure, phase composition, and thermal control properties of the coating using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), UV–visible near-infrared spectroscopy (UV-VIS-NIR) and infrared emissivity measurements. The results indicate that the hemispherical emissivity of the coating remains unaffected with an increase in temperature and holding time, while the solar absorption ratio gradually increases. The thermal control performance of the coating after a high-temperature experiment was found to be related to the diffusion of the Li metal element in the magnesium lithium alloy matrix, as determined by X-ray photoelectron spectroscopy (XPS), flame graphite furnace atomic absorption spectrometry (GFAAS) and Glow Discharge Optical Emission Spectroscopy (GD-OES). As the holding time is extended, the coating structure gradually loosens under thermal stress. The Li metal element in the substrate diffuses outward and reacts with O2, H2O and CO2 in the air, forming LiO2, LiOH, Li2CO3 and other products. This reaction affects the coating’s solar absorption ratio in the end. Full article
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<p>Reflectance curves of the coating after different holding times.</p>
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<p>XRD spectra of coatings after different times at 200 °C.</p>
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<p>Surface topographies of the coatings after different high-temperature exposure times: (<b>a</b>) following 0 h of high temperature, (<b>b</b>) following 48 h of high temperature, (<b>c</b>) following 144 h of high temperature, and (<b>d</b>) following 288 h of high temperature.</p>
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<p>Cross-sectional topography of the coating after different high-temperature exposure times: (<b>a</b>) following 0 h of high temperature, (<b>b</b>) following 48 h of high temperature, (<b>c</b>) following 144 h of high temperature, and (<b>d</b>) following 288 h of high temperature.</p>
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<p>XPS spectra of the coating after different high-temperature exposure times: (<b>a</b>) Si 2p, (<b>b</b>) O 1s, (<b>c</b>) Mg 1s, and (<b>d</b>) Li 1s.</p>
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<p>Spectral test spectrum of glow power generation: (<b>a</b>) Mg, (<b>b</b>) Li, (<b>c</b>) Al, and (<b>d</b>) Zn.</p>
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18 pages, 5849 KiB  
Article
Rapid Classification of Sugarcane Nodes and Internodes Using Near-Infrared Spectroscopy and Machine Learning Techniques
by Siramet Veerasakulwat, Agustami Sitorus and Vasu Udompetaikul
Sensors 2024, 24(22), 7102; https://doi.org/10.3390/s24227102 - 5 Nov 2024
Viewed by 909
Abstract
Accurate and rapid discrimination between nodes and internodes in sugarcane is vital for automating planting processes, particularly for minimizing bud damage and optimizing planting material quality. This study investigates the potential of visible-shortwave near-infrared (Vis–SWNIR) spectroscopy (400–1000 nm) combined with machine learning for [...] Read more.
Accurate and rapid discrimination between nodes and internodes in sugarcane is vital for automating planting processes, particularly for minimizing bud damage and optimizing planting material quality. This study investigates the potential of visible-shortwave near-infrared (Vis–SWNIR) spectroscopy (400–1000 nm) combined with machine learning for this classification task. Spectral data were acquired from the sugarcane cultivar Khon Kaen 3 at multiple orientations, and various preprocessing techniques were employed to enhance spectral features. Three machine learning algorithms, linear discriminant analysis (LDA), K-Nearest Neighbors (KNNs), and artificial neural networks (ANNs), were evaluated for their classification performance. The results demonstrated high accuracy across all models, with ANN coupled with derivative preprocessing achieving an F1-score of 0.93 on both calibration and validation datasets, and 0.92 on an independent test set. This study underscores the feasibility of Vis–SWNIR spectroscopy and machine learning for rapid and precise node/internode classification, paving the way for automation in sugarcane billet preparation and other precision agriculture applications. Full article
(This article belongs to the Section Smart Agriculture)
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<p>Field sampling of sugarcane stalks for spectral analysis.</p>
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<p>Experimental setup for Vis–SWNIR spectral data acquisition from sugarcane stalks: (1) spectrometer, (2) light source, and (3) probe.</p>
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<p>Schematic representation of the node/internode scanning angles for spectral data acquisition.</p>
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<p>Schematic representation of machine learning algorithms used in this study. (<b>a</b>) Linear Discriminant Analysis (LDA), (<b>b</b>) k-Nearest Neighbors (KNN) and (<b>c</b>) Artificial Neural Network (ANN). In these diagrams, rectangles represent datasets, calculations, and models. Arrows indicate the flow of data.</p>
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<p>Schematic representation of machine learning algorithms used in this study. (<b>a</b>) Linear Discriminant Analysis (LDA), (<b>b</b>) k-Nearest Neighbors (KNN) and (<b>c</b>) Artificial Neural Network (ANN). In these diagrams, rectangles represent datasets, calculations, and models. Arrows indicate the flow of data.</p>
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<p>Overview of the node/internode classification model development process.</p>
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<p>Average Vis–SWNIR spectra of sugarcane nodes and internodes with ±1 standard deviation: (<b>a</b>) original, (<b>b</b>) MN, (<b>c</b>) Norm_L2, (<b>d</b>) Norm_inf, (<b>e</b>) MSC, (<b>f</b>) SNV, and (<b>g</b>) DL.</p>
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<p>Average Vis–SWNIR spectra of sugarcane nodes and internodes with ±1 standard deviation: (<b>a</b>) original, (<b>b</b>) MN, (<b>c</b>) Norm_L2, (<b>d</b>) Norm_inf, (<b>e</b>) MSC, (<b>f</b>) SNV, and (<b>g</b>) DL.</p>
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<p>Comparison of performance metrics of calibration and validation models for different preprocessing methods and machine learning algorithms: (<b>a</b>) node F1-score (calibration), (<b>b</b>) internode F1-score (calibration), (<b>c</b>) node F1-score (validation), (<b>d</b>) internode F1-score (validation), (<b>e</b>) model accuracy (calibration), and (<b>f</b>) model accuracy (validation).</p>
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<p>Comparison of performance metrics of external validation models for different preprocessing methods and machine learning algorithms: (<b>a</b>) node F1-score, (<b>b</b>) internode F1-score, and (<b>c</b>) model accuracy.</p>
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