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26 pages, 3677 KiB  
Article
Application of Pseudoinfectious Viruses in Transient Gene Expression in Mammalian Cells: Combining Efficient Expression with Regulatory Compliance
by Gulzat Zauatbayeva, Tolganay Kulatay, Bakytkali Ingirbay, Zhanar Shakhmanova, Viktoriya Keyer, Mikhail Zaripov, Maral Zhumabekova and Alexandr V. Shustov
Biomolecules 2025, 15(2), 274; https://doi.org/10.3390/biom15020274 (registering DOI) - 13 Feb 2025
Abstract
Transient gene expression (TGE) is commonly employed for protein production, but its reliance on plasmid transfection makes it challenging to scale up. In this paper, an alternative TGE method is presented, utilizing pseudoinfectious alphavirus as an expression vector. Pseudoinfectious viruses (PIV) and a [...] Read more.
Transient gene expression (TGE) is commonly employed for protein production, but its reliance on plasmid transfection makes it challenging to scale up. In this paper, an alternative TGE method is presented, utilizing pseudoinfectious alphavirus as an expression vector. Pseudoinfectious viruses (PIV) and a replicable helper construct were derived from the genome of the Venezuelan equine encephalitis virus. The PIV carries a mutant capsid protein that prevents packaging into infectious particles, while the replicable helper encodes a wild-type capsid protein but lacks other viral structural proteins. Although PIV and the helper cannot independently spread infection, their combination results in increased titers in cell cultures, enabling easier scale-up of producing cultures. The PIV-driven production of a model protein outperforms that of alphavirus replicon vectors or simple plasmid vectors. Another described feature of the expression system is the modification to immobilized metal affinity chromatography (IMAC), allowing purification of His-tagged recombinant proteins from a conditioned medium in the presence of substances that can strip metal from the IMAC columns. The PIV-based expression system allows for the production of milligram quantities of recombinant proteins in static cultures, without the need for complex equipment such as bioreactors, and complies with regulatory requirements due to its distinction from common recombinant viruses. Full article
(This article belongs to the Section Synthetic Biology and Bioengineering)
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Figure 1

Figure 1
<p>Schematic of creating DNA-launched molecular infectious clones for RNA-genomes. Molecular designs of alphaviral replicons and packaging helpers. (<b>a</b>) The genome organization of Venezuelan equine encephalitis virus (VEEV) and cloning it into a plasmid (molecular infectious clone) suitable to infect cells with autonomously replicating RNA using DNA-transfection. (<b>b</b>) The VEErepGS replicon lacks genes encoding the viral structural proteins and has a heterologous gene cassette cloned under the control of the subgenomic promoter. (<b>c</b>) The VEErepGS.nsP2mut replicon is different from VEErepGS only in that VEErepGS.nsP2mut has mutation Q739L in the nsP2 gene. (<b>d</b>) Defective helper DH-delC has a large deletion in the genes for non-structural proteins (labeled del_nsP). The helper is incapable of autonomous replication. A capsid protein gene also has a deletion, which removes amino acid residues (a.a.) 82-111. Genes for spike proteins are without modifications. (<b>e</b>) Comparison of a deletion-containing capsid protein (in DH-delC) and wild-type capsid protein from VEEV (TC-83). Matching residues are shown as dots, missing residues as dashes. Stars indicate the numbered a.a. residues. Non-homologous Leu residue is a product of translation of the restriction site AAGCTT (Lys-Leu). (<b>f</b>) Defective helper DH-delE has the del_nsP deletion and all genes for spike proteins deleted. A gene for capsid protein is wild-type (TC-83) and is terminated with an engineered TGA codon. (<b>g</b>) A simple expression vector, which is a plasmid in which the GFP-2A-SEAP gene cassette is placed downstream of the CMV promoter. Symbols: Viral genes are shown as open boxes. The heterologous gene cassette GFP-2A-SEAP is shown as gray boxes (GFP, SEAP) and a filled (2A-peptide) box. Black arrow on line with the genome is the cytomegalovirus (CMV) promoter. Antigenomic ribozyme of hepatitis D virus (Rz) and transcriptional termination/polyadenylation signal (TT-PolyA) are labeled. Arrow above diagrams show subgenomic promoter. Inscriptions: nsP (nonstructural proteins), C-E3-E2-6k-E1 (structural proteins), 5′UTR and 3′UTR (untranslated regions), An (oligo-adenine stretch), SP (subgenomic promoter) GFP (green fluorescent protein), SEAP (human placental secretory alkaline phosphatase), FMDV 2A (foot-and-mouth disease virus autoprotease 2A), 10xHis (histidine tag), del_nsP (deletion in nonstructural genes), delC (deletion in the capsid gene), delE (deletion of spike protein genes), Q739L (Gln to Leu substitution in nsP2).</p>
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<p>Comparison of the wild-type capsid protein (from VEEV TC-83) and two mutant variants incapable of RNA packaging. Only the first 150 a.a. of the capsid protein are shown. TC-83, wild type. Cmut1, mutant variant having substitutions in the N-terminal part (RNA-binding domain), which reduces the RNA binding. Positively charged residues are replaced with neutral-charge residues. Cmut2, mutant variant with a different set of substitutions. Subdomains in the N-terminal part of the protein are shown (SD1-SD4) in accordance with [<a href="#B27-biomolecules-15-00274" class="html-bibr">27</a>]. Nuclear export signal (NES), nuclear localization signal (NLS) and the connecting peptide are involved in the cytopathic action of the wild-type capsid protein (labeled). Identical residues are depicted as dots. Stars indicate the a.a. numbered at every 10 residues. Numbering of residues is given above Cwt line.</p>
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<p>Titers of infectious particles (packaged replicons), photographs of producing cultures and SEAP levels obtained with the replicon vectors and a simple-expression plasmid. (<b>a</b>) Packaging of replicons into replicon particles was achieved by transfecting cell cultures with DREPs and helpers. The titers are shown for wild-type-nsP2 and mutant nsP2 (Q739L) replicons. Statistical significance: * (<span class="html-italic">p</span> &lt; 0.05), *** (<span class="html-italic">p</span> &lt; 0.001). (<b>b</b>) Pictures of HEK293FT cells infected with replicons VEErepGS (wild-type replicase) or VEErepGS.nsp2mut (nsP2 mutant). Fluorescence of GFP+ cells was photographed using the same exposure time. (<b>c</b>) Time course of the SEAP production in cultures infected with replicon particles using high MOI. HEK293FT cells produced more SEAP than BHK-21, and the wild-type replicon produced more than the mutant replicon. <span class="html-italic">Y</span>-axis, optical densities (ODs) obtained in the SEAP test. <span class="html-italic">X</span>-axis, time after infection. (<b>d</b>) Comparison of replicon vector-infected cultures, and cultures transfected with an expression plasmid, for the levels of produced recombinant protein. <span class="html-italic">Y</span>-axis, results of the SEAP test. <span class="html-italic">X</span>-axis, time after infection or transfection. Shown are means and SDs.</p>
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<p>Overview of pseudoinfectious viruses and the replicable packaging helper. (<b>a</b>) A PIV is based on the VEEV genome. The capsid protein in PIV is a mutant incapable of encapsidating genomic RNA. Clusters of mutations in the N-terminal part of the capsid protein, specifically Cmut1 and Cmut2, are denoted with stars *** and **, respectively. A second copy of subgenomic promoter (SP) is present in the PIV genome. Gene cassette GFP-2A-SEAP is cloned under the control of SP1 and structural protein genes (including mutant C) are under the control of SP2. The two PIVs are different depending on the version of the mutant capsid protein. (<b>b</b>) Replicable helper RH-piv has complete genes for replicase nsP1-nsP4 as well as cis-acting sequences 5′UTR and 3′UTR. Only the capsid protein gene (wild-type) is present in the helper in the structural genes region. Symbols are the same as in <a href="#biomolecules-15-00274-f001" class="html-fig">Figure 1</a>.</p>
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<p>Titers of infectious particles (pseudoinfectious viruses, PIVs). Levels of the recombinant protein in cells cultures infected with PIV. (<b>a</b>) Packaging cultures (PIV + RH-piv helper) are expected to generate a mixture of two types of infectious particles: one containing the PIV genome and the other containing the helper genome. The method used to quantify infectious particles is based on counting GFP+ cells, which specifically measures the PIV-containing particles. Separate cultures were transfected with only PIV vectors (no helper) to measure the residual capacity of the PIVs to produce infectious particles. The horizontal dotted line represents the detection limit. (<b>b</b>) Production of the recombinant protein SEAP in PIV expression vector-infected cells cultures. Triplicate sets of cultures were infected with the PIV using different MOIs given in the figure legend. <span class="html-italic">Y</span>-axis, optical density in the SEAP test. <span class="html-italic">X</span>-axis, time after infection. Graphs show means and SDs.</p>
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<p>Production of the recombinant protein in cell cultures bearing expression RNA vectors (replicons, PIV) or a simple expression plasmid. (<b>a</b>) Expression analysis by the levels of SEAP produced by expression vectors: PIV, replicons, and a simple expression plasmid. Alphavirus genome-based constructs are PIV (pseudoinfectious virus with mutant capsid protein variant Cmut1), VEErepGS (replicon with wild-type replicase), VEErepGS.nsp2mut (replicon, nsP2-mutant). Simple expression plasmid is pCMV-GFP-SEAP. Producing cultures were obtained by particles infection (MOI 25 FFU/cell for the PIV and replicons), or DNA-transfection using CaPi for the simple vector. Expression media were collected on day 2 after infection or transfection. PC, positive control (commercially available SEAP, 1 unit in the same reaction conditions as other samples). NC, negative control (medium from naïve cells). <span class="html-italic">Y</span>-axis, optical density in the SEAP test. Plotted are means and SDs. (<b>b</b>) Photograph of one reaction plate from SEAP test used to measure the levels shown in panel (<b>a</b>). Two replicates were assayed on the presented plate (# is the replicate number). Aliquots of samples of expression media were loaded in row A of the test plate. Other rows contain dilutions of contents in row A as indicated at the left of the photograph.</p>
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<p>Finding optimal nickel ion concentration and SEAP purification. (<b>a</b>) Finding optimal concentration of Ni<sup>2+</sup> to add to supplemented chromatographic feed to prevent Ni<sup>2+</sup> leaching from IMAC resin. Activity of SEAP in eluates is shown. (<b>b</b>) SDS-PAGE with samples collected during SEAP purification from culture medium. F1,f2, fractions eluted in 250 mM imidazole. W1,w2, material washed from IMAC resin (two successive washes) with 50 mM imidazole. St, material collected upon stripping resin with 50 mM EDTA. Feed, conditioned medium. M, molecular mass marker. Bands of SEAP and BSA labeled with right-pointing triangles. (<b>c</b>) Western blot with anti-His-tag antibody. F1, sample from panel (<b>a</b>). Bands of molecular mass marker (M) remain visible on the membrane.</p>
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<p>Approach for recombinant protein production using pseudoinfectious viral vectors.</p>
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14 pages, 1658 KiB  
Article
Development of an AI Model for Predicting Methacholine Bronchial Provocation Test Results Using Spirometry
by SangJee Park, Yehyeon Yi, Seon-Sook Han, Tae-Hoon Kim, So Jeong Kim, Young Soon Yoon, Suhyun Kim, Hyo Jin Lee and Yeonjeong Heo
Diagnostics 2025, 15(4), 449; https://doi.org/10.3390/diagnostics15040449 (registering DOI) - 12 Feb 2025
Abstract
Background/Objectives: The methacholine bronchial provocation test (MBPT) is a diagnostic test frequently used to evaluate airway hyper-reactivity. MBPT is essential for diagnosing asthma; however, it can be time-consuming and resource-intensive. This study aimed to develop an artificial intelligence (AI) model to predict [...] Read more.
Background/Objectives: The methacholine bronchial provocation test (MBPT) is a diagnostic test frequently used to evaluate airway hyper-reactivity. MBPT is essential for diagnosing asthma; however, it can be time-consuming and resource-intensive. This study aimed to develop an artificial intelligence (AI) model to predict the MBPT results using forced expiratory volume in one second (FEV1) and bronchodilator test measurements from spirometry. Methods: a dataset of spirometry measurements, including Pre- and Post-bronchodilator FEV1, was used to train and validate the model. Results: Among the evaluated models, the multilayer perceptron (MLP) achieved the highest area under the curve (AUC) of 0.701 (95% CI: 0.676–0.725), accuracy of 0.758, and an F1-score of 0.853. Logistic regression (LR) and a support vector machine (SVM) demonstrated comparable performance with AUC values of 0.688, while random forest (RF) and extreme gradient boost (XGBoost) achieved slightly lower AUC values of 0.669 and 0.672, respectively. Feature importance analysis of the MLP model identified key contributing features, including Pre-FEF25–75 (%), Pre-FVC (L), Post FEV1/FVC, Change-FEV1 (L), and Change-FEF25–75 (%), providing insight into the interpretability and clinical applicability of the model. Conclusions: These results highlight the potential of the model to utilize readily available spirometry data, particularly FEV1 and bronchodilator responses, to accurately predict MBPT results. Our findings suggest that AI-based prediction can improve asthma diagnostic workflows by minimizing the reliance on MBPT and enabling faster and more accessible assessments. Full article
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<p>Flowchart of the data preprocessing.</p>
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<p>Receiver operating characteristic curve of MLP model with stratified K-fold (K = 5) cross validation.</p>
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<p>Feature importance of the input variables in the MLP model.</p>
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<p>Feature importance of the input variables in the various other models: (<b>a</b>) logistic regression, (<b>b</b>) random forest, (<b>c</b>) SVM, and (<b>d</b>) XGBoost.</p>
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<p>Feature importance of the input variables in the various other models: (<b>a</b>) logistic regression, (<b>b</b>) random forest, (<b>c</b>) SVM, and (<b>d</b>) XGBoost.</p>
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27 pages, 10700 KiB  
Article
Rice Yield Prediction Using Spectral and Textural Indices Derived from UAV Imagery and Machine Learning Models in Lambayeque, Peru
by Javier Quille-Mamani, Lia Ramos-Fernández, José Huanuqueño-Murillo, David Quispe-Tito, Lena Cruz-Villacorta, Edwin Pino-Vargas, Lisveth Flores del Pino, Elizabeth Heros-Aguilar and Luis Ángel Ruiz
Remote Sens. 2025, 17(4), 632; https://doi.org/10.3390/rs17040632 - 12 Feb 2025
Abstract
Predicting rice yield accurately is crucial for enhancing farming practices and securing food supplies. This research aims to estimate rice yield in Peru’s Lambayeque region by utilizing spectral and textural indices derived from unmanned aerial vehicle (UAV) imagery, which offers a cost-effective alternative [...] Read more.
Predicting rice yield accurately is crucial for enhancing farming practices and securing food supplies. This research aims to estimate rice yield in Peru’s Lambayeque region by utilizing spectral and textural indices derived from unmanned aerial vehicle (UAV) imagery, which offers a cost-effective alternative to traditional approaches. UAV data collection in commercial areas involved seven flights in 2022 and ten in 2023, focusing on key growth stages such as flowering, milk, and dough, each showing significant predictive capability. Vegetation indices like NDVI, SP, DVI, NDRE, GNDVI, and EVI2, along with textural features from the gray-level co-occurrence matrix (GLCM) such as ENE, ENT, COR, IDM, CON, SA, and VAR, were combined to form a comprehensive dataset for model training. Among the machine learning models tested, including Multiple Linear Regression (MLR), Support Vector Machines (SVR), and Random Forest (RF), MLR demonstrated high reliability for annual data with an R2 of 0.69 during the flowering and milk stages, and an R2 of 0.78 for the dough stage in 2022. The RF model excelled in the combined analysis of 2022–2023 data, achieving an R2 of 0.58 for the dough stage, all confirmed through cross-validation. Integrating spectral and textural data from UAV imagery enhances early yield prediction, aiding precision agriculture and informed decision-making in rice management. These results emphasize the need to incorporate climate variables to refine predictions under diverse environmental conditions, offering a scalable solution to improve agricultural management and market planning. Full article
(This article belongs to the Special Issue Perspectives of Remote Sensing for Precision Agriculture)
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<p>Study area: (<b>a</b>) geographical location of Peru; (<b>b</b>) Lambayeque region; and (<b>c</b>) commercial zones: Caballito, García, Santa Julia, Totora, and Zapote.</p>
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<p>Meteorological variables recorded during the rice growing season in 2022 and 2023: (<b>a</b>) maximum temperature (°C), minimum temperature (°C), and precipitation (mm); (<b>b</b>) relative humidity (%) and wind speed (m s<sup>−1</sup>). These data were collected at the automatic weather station of INIA-Vista Florida.</p>
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<p>(<b>a</b>) Flights carried out in the commercial areas; (<b>b</b>) phenology of the Capoteña variety according to days post sowing (DPS).</p>
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<p>Flow diagram of the methodology followed in this study.</p>
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<p>Flight platform and sensors. (<b>a</b>) DJI Matric 300 RTK, (<b>b</b>) Micasense RedEdge-MX multispectral sensor, and (<b>c</b>) Parrot Sequoia multispectral sensor, together with their respective calibration panels.</p>
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<p>Rice yield data in tons per hectare (t ha<sup>−1</sup>) in commercial fields of Ferreñafe for the years 2022 and 2023.</p>
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<p>Coefficient of determination (R<sup>2</sup>) of vegetation indices (VIs) and textural indices (TIs) in relation to measured rice yield during phenological stages. (<b>a</b>) Number of plots evaluated for each phenological stage in 2022 and 2023. (<b>b</b>) Distribution of R<sup>2</sup> values across phenological stages for 2022 and 2023.</p>
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<p>The optimal results from Sequential Feature Selection for Multiple Linear Regression (MLR) and Support Vector Regression (SVR) models using vegetation indices (VIs), texture indices (TIs), and their combination (VIs + TIs) across the flowering (<b>a</b>,<b>d</b>,<b>g</b>), milk (<b>b</b>,<b>e</b>,<b>h</b>), and dough (<b>c</b>,<b>f</b>,<b>i</b>) stages for the years 2022 (<b>a</b>–<b>c</b>), 2023 (<b>d</b>–<b>f</b>), and the combined period of 2022–2023 (<b>g</b>–<b>i</b>).</p>
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<p>Predicted versus measured grain yield for Multiple Linear Regression (MLR) and Support Vector Regression (SVR) models using vegetation indices (VIs), texture indices (TIs), and their combination (VIs + TIs) across the flowering (<b>a</b>,<b>d</b>,<b>g</b>), milk (<b>b</b>,<b>e</b>,<b>h</b>), and dough (<b>c</b>,<b>f</b>,<b>i</b>) stages for the years 2022 (<b>a</b>–<b>c</b>), 2023 (<b>d</b>–<b>f</b>), and the combined period 2022–2023 (<b>g</b>–<b>i</b>).</p>
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<p>Random Forest (RF) model for rice yield estimation during the flowering stage (2022–2023) using vegetation (VIs) and textural indices (TIs): (<b>a</b>) out-of-bag error (OOB), (<b>b</b>) variable selection via LOOCV (RMSE), and (<b>c</b>) predictor importance.</p>
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<p>Random Forest (RF) model for rice yield estimation during the milk stage (2022–2023) using vegetation (VIs) and textural indices (TIs): (<b>a</b>) out-of-bag error (OOB), (<b>b</b>) variable selection via LOOCV (RMSE), and (<b>c</b>) predictor importance.</p>
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<p>Random Forest (RF) model for rice yield estimation during the dough stage (2022–2023) using vegetation (VIs) and textural indices (TIs): (<b>a</b>) out-of-bag error (OOB), (<b>b</b>) variable selection via LOOCV (RMSE), and (<b>c</b>) predictor importance.</p>
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<p>Predicted versus measured grain yield for Random Forest (RF) models using vegetation indices (VIs), texture indices (TIs), and their combination (VIs + TIs) across the flowering (<b>a</b>,<b>d</b>,<b>g</b>), milk (<b>b</b>,<b>e</b>,<b>h</b>), and dough (<b>c</b>,<b>f</b>,<b>i</b>) stages for the years 2022 (<b>a</b>–<b>c</b>), 2023 (<b>d</b>–<b>f</b>), and the combined period 2022–2023 (<b>g</b>–<b>i</b>).</p>
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31 pages, 966 KiB  
Review
Functional Roles and Host Interactions of Orthoflavivirus Non-Structural Proteins During Replication
by Meghan K. Donaldson, Levi A. Zanders and Joyce Jose
Pathogens 2025, 14(2), 184; https://doi.org/10.3390/pathogens14020184 - 12 Feb 2025
Abstract
Orthoflavivirus, a genus encompassing arthropod-borne, positive-sense, single-stranded RNA viruses in the Flaviviridae family, represents clinically relevant viruses that pose significant threats to human and animal health worldwide. With warming climates and persistent urbanization, arthropod vectors and the viruses they transmit continue to [...] Read more.
Orthoflavivirus, a genus encompassing arthropod-borne, positive-sense, single-stranded RNA viruses in the Flaviviridae family, represents clinically relevant viruses that pose significant threats to human and animal health worldwide. With warming climates and persistent urbanization, arthropod vectors and the viruses they transmit continue to widen their geographic distribution, expanding endemic zones. Flaviviruses such as dengue virus, Zika virus, West Nile virus, and tick-borne encephalitis virus cause debilitating and fatal infections globally. In 2024, the World Health Organization and the Pan American Health Organization declared the current dengue situation a Multi-Country Grade 3 Outbreak, the highest level. FDA-approved treatment options for diseases caused by flaviviruses are limited or non-existent, and vaccines are suboptimal for many flaviviruses. Understanding the molecular characteristics of the flavivirus life cycle, virus-host interactions, and resulting pathogenesis in various cells and model systems is critical for developing effective therapeutic intervention strategies. This review will focus on the virus-host interactions of mosquito- and tick-borne flaviviruses from the virus replication and assembly perspective, emphasizing the interplay between viral non-structural proteins and host pathways that are hijacked for their advantage. Highlighting interaction pathways, including innate immunity, intracellular movement, and membrane modification, emphasizes the need for rigorous and targeted antiviral research and development against these re-emerging viruses. Full article
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<p>Representation of the flavivirus genome organization and known full-length protein crystal structures. (<b>A</b>) ZIKV genomic RNA structure with predicted 5′ and 3′ UTR structures. (<b>B</b>) Polyprotein organization. (<b>C</b>) Polyprotein topology across the ER membrane with indicated viral and host protease cleavage sites [<a href="#B18-pathogens-14-00184" class="html-bibr">18</a>]. (<b>D</b>) ZIKV NS1 (PDB: 5GS6) dimeric crystal structure solved through X-ray crystallography with each monomer separately colored. (<b>E</b>) DENV NS2B-3 (PDB: 5YVW) monomer crystal structure solved through X-ray crystallography with the NS2B peptide colored in red and NS3 in blue. (<b>F</b>) ZIKV NS5 (PDB: 5TMH) structure solved through X-ray crystallography.</p>
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23 pages, 1967 KiB  
Article
Machine Learning to Forecast Airborne Parietaria Pollen in the North-West of the Iberian Peninsula
by Gonzalo Astray, Rubén Amigo Fernández, María Fernández-González, Duarte A. Dias-Lorenzo, Guillermo Guada and Francisco Javier Rodríguez-Rajo
Sustainability 2025, 17(4), 1528; https://doi.org/10.3390/su17041528 - 12 Feb 2025
Abstract
Pollen forecasting models are helpful tools to predict environmental processes and allergenic risk events. Parietaria belongs to the Urticaceae family, and due to its high-level pollen production, is responsible for many cases of severe pollinosis reactions. This research aims to develop different machine [...] Read more.
Pollen forecasting models are helpful tools to predict environmental processes and allergenic risk events. Parietaria belongs to the Urticaceae family, and due to its high-level pollen production, is responsible for many cases of severe pollinosis reactions. This research aims to develop different machine learning models such as the random forest—RF, support vector machine—SVM, and artificial neural network—ANN models, to predict Parietaria pollen concentrations in the atmosphere of northwest Spain using 24 years of data from 1999 to 2022. The results obtained show an increase in the duration and intensity of the Parietaria main pollen season in the Mediterranean region (Ourense). Machine learning models exhibited their capacity to forecast Parietaria pollen concentrations at one, two, and three days ahead. The best selected models presented high correlation coefficients between 0.713 and 0.859, with root mean squared errors between 5.55 and 7.66 pollen grains·m−3 for the testing phase. The models developed could be improved by increasing the number of years, studying other hyperparameter ranges, or analyzing different data distributions. Full article
(This article belongs to the Section Pollution Prevention, Mitigation and Sustainability)
29 pages, 465 KiB  
Review
Fighting Strategies Against Chagas’ Disease: A Review
by Andrea Hernández-Flores, Debora Elías-Díaz, Bernadeth Cubillo-Cervantes, Carlos N. Ibarra-Cerdeña, David Morán, Audrey Arnal and Andrea Chaves
Pathogens 2025, 14(2), 183; https://doi.org/10.3390/pathogens14020183 - 12 Feb 2025
Abstract
Chagas disease, caused by Trypanosoma cruzi, remains a significant public health challenge, particularly in Latin America, where it is one of the most neglected diseases and is primarily transmitted by triatomine insects. The disease exhibits complexity due to its diverse transmission routes, [...] Read more.
Chagas disease, caused by Trypanosoma cruzi, remains a significant public health challenge, particularly in Latin America, where it is one of the most neglected diseases and is primarily transmitted by triatomine insects. The disease exhibits complexity due to its diverse transmission routes, including vectorial and non-vectorial mechanisms such as blood transfusions and congenital transmission. Effective monitoring and control strategies are critical to mitigating its impact. This review focuses on current monitoring and control efforts, emphasizing the importance of enhanced surveillance systems, improved risk assessments, and integrated vector control programs. Surveillance plays a pivotal role in early detection and timely intervention, particularly in endemic regions, while vector control remains central to reducing transmission. Moreover, the development of novel diagnostic tools, treatments, and vaccines is a crucial step in advancing control efforts. This review also highlights the involvement of local governments, international organizations, and civil society in executing these strategies, stressing the need for sustained political commitment to ensure the success of public health programs. By addressing key challenges in monitoring, control, and prevention, this review aims to provide insights and recommendations to further global efforts in reducing the burden of Chagas disease. Full article
21 pages, 455 KiB  
Article
Advancing Fault Detection in Distribution Networks with a Real-Time Approach Using Robust RVFLN
by Cem Haydaroğlu, Heybet Kılıç, Bilal Gümüş and Mahmut Temel Özdemir
Appl. Sci. 2025, 15(4), 1908; https://doi.org/10.3390/app15041908 - 12 Feb 2025
Abstract
In this paper, the fault type and location of high-impedance short-circuit faults, which are difficult to detect in distribution networks, are determined in real time using the Real-Time Digital Simulator (RTDS). In this study, an IEEE 39-bar system model is created using the [...] Read more.
In this paper, the fault type and location of high-impedance short-circuit faults, which are difficult to detect in distribution networks, are determined in real time using the Real-Time Digital Simulator (RTDS). In this study, an IEEE 39-bar system model is created using the Real-Time Simulation Software Package (RSCAD). In this model, a short-circuit fault is generated at different fault impedance values. For high-impedance short-circuit fault detection, 14 feature vectors are created. Six of these feature vectors are newly developed, and it is found that these six new feature vectors contribute 10% to the detection of hard-to-detect high-impedance short-circuit faults. We propose a data-driven online algorithm for fault type and location detection based on robust regularized random vector function networks (ORR-RVFLNs). Moreover, the robustness of the model is improved by adding a certain amount of noise to the detected short-circuit fault data. In this study, the method ORR-RVFLN for the 39-bus system IEEE detects the average error type for all error impedances, with 92.2% success for the data with noise added. In this study, the fault location is shown to be more than 90% accurate for distances greater than 400 m. Full article
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<p>RVFLN algorithm.</p>
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<p>Single-busbar transmission line model.</p>
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<p>IEEE 39-busbar model.</p>
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<p>ORR-RVFLN detection rate on data with no noise added.</p>
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<p>ORR-RVFLN detection rate on data with procedural noise.</p>
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15 pages, 306 KiB  
Review
Current Tick Control Strategies and Prospects for Using Nanotechnology as an Efficient Alternative—A Review
by Rafaela Regina Fantatto, João Vitor Carvalho Constantini, Flávio Augusto Sanches Politi, Rodrigo Sorrechia, Camila Cristina Baccetti Medeiros, Marcela Tavares Luiz, Gervásio Henrique Bechara, Ana Carolina de Souza Chagas, Marlus Chorilli and Rosemeire Cristina Linhari Rodrigues Pietro
Vet. Sci. 2025, 12(2), 163; https://doi.org/10.3390/vetsci12020163 - 12 Feb 2025
Abstract
Ticks pose significant challenges to public and veterinary health, acting as vectors of several diseases that affect animals and humans. Traditional chemical control methods, such as pyrethroids and organophosphates, have led to increasing resistance and environmental contamination, highlighting the need and urgency for [...] Read more.
Ticks pose significant challenges to public and veterinary health, acting as vectors of several diseases that affect animals and humans. Traditional chemical control methods, such as pyrethroids and organophosphates, have led to increasing resistance and environmental contamination, highlighting the need and urgency for alternative strategies. This review explores contemporary approaches to tick control, emphasizing plant-derived acaricides and their integration with nanotechnology. Plant extracts, known for their acaricidal properties, disrupt several biological processes in ticks, reducing reproduction and survival rates. The advent of nanotechnology offers promising advances in increasing the efficacy of these natural extracts. Nanoparticles add properties to the systems where they act by improving the stability, bioavailability, and targeted delivery of plant-derived compounds, potentially overcoming the limitations of traditional acaricides. This synthesis of current knowledge highlights the potential of combining plant extracts with nanotechnology to develop sustainable and effective tick control solutions, addressing issues of acaricide resistance as well as environmental concerns. The review also identifies research gaps and suggests directions for future studies to optimize the application of nanotechnology in tick management. Full article
(This article belongs to the Section Veterinary Physiology, Pharmacology, and Toxicology)
28 pages, 6815 KiB  
Article
ZSM Framework for Autonomous Security Service Level Agreement Life-Cycle Management in B5G Networks
by Rodrigo Asensio-Garriga, Alejandro Molina Zarca, Jordi Ortiz, Ana Hermosilla, Hugo Ramón Pascual, Antonio Pastor and Antonio Skarmeta
Future Internet 2025, 17(2), 86; https://doi.org/10.3390/fi17020086 - 12 Feb 2025
Abstract
In the rapidly evolving landscape of telecommunications, the integration of commercial 5G solutions and the rise of edge computing have reshaped service delivery, emphasizing the customization of requirements through network slices. However, the heterogeneity of devices and technologies in 5G and beyond networks [...] Read more.
In the rapidly evolving landscape of telecommunications, the integration of commercial 5G solutions and the rise of edge computing have reshaped service delivery, emphasizing the customization of requirements through network slices. However, the heterogeneity of devices and technologies in 5G and beyond networks poses significant challenges, particularly in terms of security management. Addressing this complexity, our work adopts the Zero-touch network and Service Management (ZSM) reference architecture to enable end-to-end automation of security and service management in Beyond 5G networks. This paper introduces the ZSM-based framework, which harnesses software-defined networking, network function virtualization, end-to-end slicing, and orchestration paradigms to autonomously enforce and preserve security service level agreements (SSLAs) across multiple domains that make up a 5G network. The framework autonomously manages end-to-end security slices through intent-driven closed loops at various logical levels, ensuring compliance with ETSI end-to-end network slice management standards for 5G communication services. The paper elaborates with an SSLA-triggered use case comprising two phases: proactive, wherein the framework deploys and configures an end-to-end security slice tailored to the security service level agreement specifications, and reactive, where machine learning-trained security mechanisms autonomously detect and mitigate novel beyond 5G attacks exploiting open-sourced 5G core threat vectors. Finally, the results of the implementation and validation are presented, demonstrating the practical application of this research. Interestingly, these research results have been integrated into the ETSI ZSM Proof of Concept #6: ’Security SLA Assurance in 5G Network Slices’, highlighting the relevance and impact of the study in the real world. Full article
29 pages, 11552 KiB  
Article
Characterization of High-Speed Steels—Experimental Data and Their Evaluation Supported by Machine Learning Algorithms
by Manfred Wiessner and Ernst Gamsjäger
Metals 2025, 15(2), 194; https://doi.org/10.3390/met15020194 - 12 Feb 2025
Abstract
X-ray diffractograms of high-speed steels are analyzed using machine learning algorithms to accurately classify various heat treatments. These differently heat-treated steel samples are also investigated by dilatometric analysis and by metallographic analysis in order to label the samples accordingly. Both agglomerative hierarchical clustering [...] Read more.
X-ray diffractograms of high-speed steels are analyzed using machine learning algorithms to accurately classify various heat treatments. These differently heat-treated steel samples are also investigated by dilatometric analysis and by metallographic analysis in order to label the samples accordingly. Both agglomerative hierarchical clustering and t-distributed stochastic neighbor embedding are employed to automatically classify preprocessed X-ray datasets. The clusters obtained by this procedure agree well with the labeled data. By supervised learning via a support vector machine, hyperplanes are constructed that allow separating the clusters from each other based on the X-ray measurements. The exactness of these hyperplanes is analyzed by cross-validation. The machine learning algorithms used in this work are valuable tools to separate different microstructures based on their diffractograms. It is demonstrated that the separation of martensitic, bainitic, and pearlitic microstructures is possible based on the diffractograms only by means of machine learning algorithms, while the same problem is error-prone when looking at the diffractograms only. Full article
26 pages, 1498 KiB  
Article
Enhancing Software Sustainability: Leveraging Large Language Models to Evaluate Security Requirements Fulfillment in Requirements Engineering
by Ahmad F. Subahi
Systems 2025, 13(2), 114; https://doi.org/10.3390/systems13020114 - 12 Feb 2025
Abstract
In the digital era, cybersecurity is integral for preserving national security, digital privacy, and social sustainability. This research emphasizes the role of non-functional equirements (NFRs) in developing secure software systems that enhance societal wellbeing by ensuring data protection, user privacy, and system robustness. [...] Read more.
In the digital era, cybersecurity is integral for preserving national security, digital privacy, and social sustainability. This research emphasizes the role of non-functional equirements (NFRs) in developing secure software systems that enhance societal wellbeing by ensuring data protection, user privacy, and system robustness. Specifically, this study introduces a proof-of-concept approach by leveraging machine learning (ML) models to classify NFRs and identify security-related issues early in the software development lifecycle. Two experiments were conducted to assess the effectiveness of different models for binary and multi-class classification tasks. In Experiment 1, BERT-based models and artificial neural networks (ANNs) were fine-tuned to classify NFRs into security and non-security categories using a dataset of 803 statements. BERT-based models outperformed ANNs, achieving higher accuracy, precision, recall, and ROC-AUC scores, with hyperparameter tuning further enhancing the results. Experiment 2 assessed logistic regression (LR), a support vector machine (SVM), and XGBoost for the multi-class classification of security-related NFRs into seven categories. The SVM and XGBoost showed strong performance, achieving high precision and recall in specific categories. The findings demonstrate the effectiveness of advanced ML models in automating NFR classification, improving software security, and supporting social sustainability. Future work will explore hybrid approaches to enhance scalability and accuracy. Full article
(This article belongs to the Section Systems Engineering)
17 pages, 5757 KiB  
Article
Neural Network-Assisted DPD of Wideband PA Nonlinearity for Sub-Nyquist Sampling Systems
by Mengqiu Liu, Xining Yang, Jian Gao, Sen Cao, Guisheng Liao, Gaopan Hou and Dawei Gao
Sensors 2025, 25(4), 1106; https://doi.org/10.3390/s25041106 - 12 Feb 2025
Abstract
The design of conventional digital predistortion (DPD) requires an analogue-to-digital converter (ADC) with a sampling frequency that is multiple times the signal bandwidth, which is extremely challenging for sub-Nyquist sampling systems with undersampled signals. To address this, this paper proposes a neural network [...] Read more.
The design of conventional digital predistortion (DPD) requires an analogue-to-digital converter (ADC) with a sampling frequency that is multiple times the signal bandwidth, which is extremely challenging for sub-Nyquist sampling systems with undersampled signals. To address this, this paper proposes a neural network (NN)-assisted wideband power amplifier (PA) DPD method for sub-Nyquist sampling systems, wherein a dual-stage architecture is designed to handle the ambiguity caused by subsampled communications signals. In the first stage, the time-delayed polynomial reconstruction method is employed to estimate the wideband DPD nonlinearity coarsely with the undersampled signals with limited pilots. In the second stage, an NN-based DPD method is proposed for the virtual training of the DPD, which learns the up-sampled DPD behavior by taking advantage of the pre-estimated DPD model and the input data signals, which reduces the length of the training sequence significantly and refines the DPD behavior efficiently. Simulation results demonstrate the efficacy of the proposed method in tackling the wideband PA nonlinearity and its ability to outperform the conventional method in terms of power spectrum, error vector magnitude, and bit error rate. Full article
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<p>A system block diagram of the sub-Nyquist sampling system.</p>
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<p>The structure of the proposed attention-based NN for virtual training.</p>
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<p>The structure of the attention-based NN proposed for virtual training.</p>
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<p>PSD performance of different methods at <math display="inline"><semantics> <mrow> <mi>S</mi> <mi>N</mi> <mi>R</mi> <mo>=</mo> <mn>15</mn> <mspace width="3.33333pt"/> <mi>dB</mi> </mrow> </semantics></math>.</p>
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<p>PSD performance of various DPD methods versus different SNRs: (<b>a</b>) PSD of PA output with TDMPR, (<b>b</b>) PSD of PA output with ARVTDNN, and (<b>c</b>) PSD of PA output with proposed NN-assisted DPD.</p>
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<p>Constellation diagrams at <math display="inline"><semantics> <mrow> <mi>S</mi> <mi>N</mi> <mi>R</mi> <mo>=</mo> <mn>15</mn> <mspace width="3.33333pt"/> <mi>dB</mi> </mrow> </semantics></math>: (<b>a</b>) ARVTDNN and (<b>b</b>) the proposed method.</p>
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<p>The EVM performance of various DPD methods versus different SNRs.</p>
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<p>The BER performance of various DPD methods versus different SNRs.</p>
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<p>PSD of PA output with the proposed NN-assisted DPD with different levels of temperature and humidity.</p>
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<p>Constellation diagrams at different temperature/humidity levels: (<b>a</b>) low temperature/low humidity, (<b>b</b>) mild temperature/mild humidity, and (<b>c</b>) high temperature/high humidity.</p>
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<p>Constellation diagrams at different temperature/humidity levels: (<b>a</b>) low temperature/low humidity, (<b>b</b>) mild temperature/mild humidity, and (<b>c</b>) high temperature/high humidity.</p>
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35 pages, 1361 KiB  
Article
Evaluating Machine Learning Algorithms for Financial Fraud Detection: Insights from Indonesia
by Cheng-Wen Lee, Mao-Wen Fu, Chin-Chuan Wang and Muh. Irfandy Azis
Mathematics 2025, 13(4), 600; https://doi.org/10.3390/math13040600 - 12 Feb 2025
Abstract
The study utilized Multiple Linear Regression along with advanced classification algorithms such as Logistic Regression, K-Nearest Neighbors (KNN), Support Vector Machine (SVM), Decision Tree, and Random Forest, to detect financial statement fraud. Model performance was evaluated using key metrics, including precision, recall, accuracy, [...] Read more.
The study utilized Multiple Linear Regression along with advanced classification algorithms such as Logistic Regression, K-Nearest Neighbors (KNN), Support Vector Machine (SVM), Decision Tree, and Random Forest, to detect financial statement fraud. Model performance was evaluated using key metrics, including precision, recall, accuracy, and F1-Score. The analysis also identified significant indicators of fraud, such as Accounts Receivable Turnover, Days Outstanding Accounts Receivable, Days Payables Outstanding, Logarithm of Gross Profit, Gross Profit Margin, Inventory to Sales Ratio, and Total Asset Turnover. Among the models, Random Forest emerged as the most effective algorithm, consistently outperforming others on both training and testing datasets. Logistic Regression and SVM demonstrated strong reliability, whereas KNN and Decision Tree faced overfitting challenges, limiting their practical application. These findings emphasize the critical need for enhanced fraud detection frameworks, leveraging machine learning algorithms like Random Forest to identify fraud patterns effectively. The study highlights the importance of strengthening internal controls, implementing targeted fraud detection measures, and promoting regulatory improvements to enhance transparency and financial accountability. Full article
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<p>Methodological Framework.</p>
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<p>The Logistic Regression Classification Confusion Matrix.</p>
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<p>The K-Nearest Neighbors Classification Confusion Matrix.</p>
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<p>The Support Vector Machine Classification Confusion Matrix.</p>
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<p>The Decision Tree Classification Confusion Matrix.</p>
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<p>The Random Forest Classification Confusion Matrix.</p>
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23 pages, 3549 KiB  
Article
Efavirenz Repurposing Challenges: A Novel Nanomicelle-Based Antiviral Therapy Against Mosquito-Borne Flaviviruses
by Sofía Maldonado, Pedro Fuentes, Ezequiel Bernabeu, Facundo Bertera, Javier Opezzo, Eduardo Lagomarsino, Hyun J. Lee, Fleming Martínez Rodríguez, Marcelo R. Choi, María Jimena Salgueiro, Elsa B. Damonte, Christian Höcht, Marcela A. Moretton, Claudia S. Sepúlveda and Diego A. Chiappetta
Pharmaceutics 2025, 17(2), 241; https://doi.org/10.3390/pharmaceutics17020241 - 12 Feb 2025
Abstract
Background/Objective: World Health Organization latest statistics state that 17% of infectious diseases are transmitted by vectors, causing more than 700,000 deaths each year. Particularly, dengue (DENV), Zika (ZIKV) and yellow fever (YFV) viral infections have generated international awareness due to their epidemic proportion [...] Read more.
Background/Objective: World Health Organization latest statistics state that 17% of infectious diseases are transmitted by vectors, causing more than 700,000 deaths each year. Particularly, dengue (DENV), Zika (ZIKV) and yellow fever (YFV) viral infections have generated international awareness due to their epidemic proportion and risks of international spread. In this framework, the repositioning strategy of Efavirenz (EFV) represents a key clinical feature to improve different antiviral therapies. Therefore, the development of Soluplus®-based nanomicelles (NMs) loaded with EFV (10 mg/mL) for optimized oral pharmacotherapy against ZIKV, DENV and YFV infections was investigated. Methods: EFV-NMs were obtained by an acetone diffusion technique. Micellar size and in vitro micellar interaction with mucin were assessed by dynamic light scattering. In vitro cytocompatibility was investigated in A549 and Vero cells and micellar in vitro antiviral activity against ZIKV, DENV and YFV was evaluated. In vivo oral bioavailability and histological studies were assessed in Wistar rats. Results: EFV encapsulation within Soluplus® NMs increased the drug’s apparent aqueous solubility up to 4803-fold with a unimodal micellar size distribution and a micellar size of ~90 nm at 25 and 37 °C. Micellar in vitro interaction with mucin was also assessed in a pH range of 1.2–7.5 and its storage micellar physicochemical stability at 4 °C was confirmed over 2 years. In vitro cytocompatibility assays in A549 and Vero cells confirmed that EFV micellar dispersions resulted in safe nanoformulations. Interestingly, EFV-loaded NMs exhibited significantly higher in vitro antiviral activity compared with EFV solution for all the tested flaviviruses. In addition, the selectivity index (SI) values reveal that EFV-loaded NMs exhibited considerably more biological efficacy compared to EFV solution in A549 and Vero cell lines and for each viral infection (SI > 10). Further, the drug pharmacokinetics parameters were enhanced after the oral administration of EFV-loaded NMs, being biocompatible by not causing damage in the gastrointestinal segments. Conclusions: Overall, our EFV nanoformulation highlighted its potential as a novel drug delivery platform for optimized ZIKV, DENV and YFV antiviral therapy. Full article
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<p>EFV apparent aqueous solubility (S<sub>a</sub>) versus Soluplus<sup>®</sup> concentration (% <span class="html-italic">w</span>/<span class="html-italic">v</span>) in distilled water at 25 °C. Results are expressed as mean ± standard deviation (S.D.) (<span class="html-italic">n</span> = 3).</p>
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<p>(<b>A</b>) Micellar size and size distribution of drug-free NMs and (<b>B</b>) EFV-NMs. (<b>C</b>) Macroscopic aspect of micellar dispersions, in absence and presence of EFV, at 25 and 37 °C. (<b>D</b>) TEM micrographs of EFV-NMs. Red arrows point out NMs (scale bar: 200 nm).</p>
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<p>The particle size of the EFV-NMs in the absence and the presence of 0.025% <span class="html-italic">w</span>/<span class="html-italic">v</span> mucin in different simulated gastrointestinal fluids (pH 1.2, 6.8, 7.5 and 6.0).</p>
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<p>In vitro EFV release profiles from EFV-NMs and EFV suspension at 37 °C over 6 h. Data are means ± standard deviation (S.D.), <span class="html-italic">n</span> = 3.</p>
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<p>Cell viability of (<b>A</b>) A549 cells and (<b>B</b>) Vero cells after 48 h of treatment with EFV solution (10 mg/mL), drug-free NMs and EFV-NMs (10 mg/mL) (37 °C, 5% CO<sub>2</sub>). Data are means ± standard deviation (S.D.) (<span class="html-italic">n</span> = 3).</p>
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<p>Antiviral activity. A549 and Vero cells were infected with DENV-2, ZIKV or YFV (m.o.i. 0.1) in the absence of compound and after 1 h adsorption at 37 °C the inocula were removed and the cells were re-fed with MM containing, or not containing (VC), different concentrations of EFV and EFV-NMs. The antiviral activity of the compounds was determined at 48 h p.i.; supernatant cultures were harvested and the viral yields were determined by plaque assays. All determinations were performed in triplicate. The percentages of inhibition are presented as the mean ± SD obtained from three independent experiments.</p>
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<p>Viral titer inhibition. A549 and Vero cells were infected with DENV-2, ZIKV or YFV (m.o.i. 0.1) in the absence of compound and, after 1 h adsorption at 37 °C, re-fed with MM containing, or not containing (VC), a single concentration (10 µg/mL) of EFV, EFV-NMs or NMs. The antiviral activity of the compounds was determined after 48 h p.i.; supernatant cultures were harvested and the viral yields were determined by plaque assays. All determinations were performed in triplicate and the viral titer values are presented as the mean ± SD obtained from three independent experiments. <span class="html-italic">p</span>-values were determined using an ANOVA analysis followed by Dunnett’s post hoc test. Hashtag represents significant differences with respect to the treatments, asterisk represents significant differences with respect to the VC: * <span class="html-italic">p</span> &lt; 0.05; ##/** <span class="html-italic">p</span> &lt; 0.01; *** <span class="html-italic">p</span> &lt; 0.001; ####/**** <span class="html-italic">p</span> &lt; 0.0001.</p>
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<p>Representative images of hematoxylin and eosin (H&amp;E) staining of stomach, small and large intestine treated with (<b>A</b>) saline solution and (<b>B</b>) EFV-NMs (magnification: ×100; scale bar = 100 µm). Representative sections from three rats analyzed for each condition.</p>
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<p>The preparation of EFV-NMs employing an acetone displacement technique. The scheme was made in BioRender (<a href="https://biorender.com/" target="_blank">https://biorender.com/</a>, date accessed: 3 January 2025).</p>
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29 pages, 4553 KiB  
Article
Simultaneous Source Number Detection and DOA Estimation Using Deep Neural Network and K2-Means Clustering with Prior Knowledge
by Aifei Liu, Yuan Zhou, Zi Li, Yuxuan Xie, Cao Zeng and Zhiling Liu
Electronics 2025, 14(4), 713; https://doi.org/10.3390/electronics14040713 - 12 Feb 2025
Viewed by 55
Abstract
Source number detection and Direction-of-Arrival (DOA) estimation are usually addressed in two stages, leading to high computational load. This paper proposes a simple solution to efficiently estimate the source number and DOAs using deep neural network (DNN) and clustering, named DNN-C. By observing [...] Read more.
Source number detection and Direction-of-Arrival (DOA) estimation are usually addressed in two stages, leading to high computational load. This paper proposes a simple solution to efficiently estimate the source number and DOAs using deep neural network (DNN) and clustering, named DNN-C. By observing that sources in space are usually few, DNN-C uses a simple fully connected DNN to obtain a spatial spectrum. Then, the K2-means clustering is specially designed to extract the source information from the obtained spatial spectrum. In particular, to enable the proposed DNN-C with the ability to detect the mixed sources, we first develop a new strategy for training data generation, and provide a guideline for data balance setting. We then explore the prior knowledge of array signal processing and spatial spectrum to obtain a peak vector and propose to add a virtual peak into the peak vector, and thus transform the task of source detection as a binary clustering problem of noise and sources. Overall, DNN-C provides a lightweight solution to implement source number detection and DOA estimation simultaneously and efficiently. Its testing time is about 2 times less than the classical solution (i.e., minimum descriptive length and multiple signal classification, shortened as MDL-MUSIC) when the grid step is 1° Importantly, it is robust to nonuniform noise by nature and can identify the absence of sources. The effectiveness of DNN-C is verified by simulation results. Furthermore, the DNN-C model trained by simulated data shows its generalization to real data measured by a circular array of eight sensors. Full article
(This article belongs to the Section Circuit and Signal Processing)
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<p>Array signal model for a uniform linear array: <math display="inline"><semantics> <mrow> <msub> <mi>s</mi> <mi>k</mi> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <msub> <mi>θ</mi> <mi>k</mi> </msub> </semantics></math> are the waveform and DOA of the <span class="html-italic">k</span>-th sources, respectively; <span class="html-italic">d</span> is the distance between two adjacent sensors; the steering vector at <math display="inline"><semantics> <msub> <mi>θ</mi> <mi>k</mi> </msub> </semantics></math> is <math display="inline"><semantics> <mrow> <mi mathvariant="bold">a</mi> <mrow> <mo>(</mo> <msub> <mi>θ</mi> <mi>k</mi> </msub> <mo>)</mo> </mrow> <mo>=</mo> <mrow> <mo>[</mo> <mn>1</mn> <mspace width="1.em"/> <msup> <mi>e</mi> <mrow> <mi>j</mi> <mn>2</mn> <mi>π</mi> <mi>d</mi> <mi>s</mi> <mi>i</mi> <mi>n</mi> <msub> <mi>θ</mi> <mi>k</mi> </msub> <mo>/</mo> <mi>λ</mi> </mrow> </msup> <mo>⋯</mo> <msup> <mi>e</mi> <mrow> <mi>j</mi> <mn>2</mn> <mi>π</mi> <mrow> <mo>(</mo> <mi>M</mi> <mo>−</mo> <mn>1</mn> <mo>)</mo> </mrow> <mi>d</mi> <mi>s</mi> <mi>i</mi> <mi>n</mi> <msub> <mi>θ</mi> <mi>k</mi> </msub> <mo>/</mo> <mi>λ</mi> </mrow> </msup> <mo>]</mo> </mrow> </mrow> </semantics></math>; the received signal at the <span class="html-italic">m</span>-th sensor is <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </semantics></math>; and the received array signal vector is <math display="inline"><semantics> <mrow> <mi mathvariant="bold">r</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <msup> <mrow> <mo>[</mo> <msub> <mi>r</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>,</mo> <msub> <mi>r</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>,</mo> <mo>⋯</mo> <msub> <mi>r</mi> <mi>M</mi> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>]</mo> </mrow> <mi>T</mi> </msup> </mrow> </semantics></math>.</p>
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<p>Scheme of DNN-C.</p>
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<p>Structure of DNN; for the autoencoder, we define the size of each of the input and output layers as <math display="inline"><semantics> <mrow> <mover accent="true"> <mi>J</mi> <mo>˜</mo> </mover> <mo>=</mo> <mi>M</mi> <mrow> <mo>(</mo> <mi>M</mi> <mo>−</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </semantics></math> since the input vector <math display="inline"><semantics> <mi mathvariant="bold">x</mi> </semantics></math> has a size of <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>(</mo> <mi>M</mi> <mo>−</mo> <mn>1</mn> <mo>)</mo> </mrow> </semantics></math>. In addition, we denote that the number of each encoder and decoder has one hidden layer of which the size is <math display="inline"><semantics> <mrow> <mo>⌊</mo> <mstyle scriptlevel="0" displaystyle="true"> <mfrac> <mover accent="true"> <mi>J</mi> <mo>˜</mo> </mover> <mn>2</mn> </mfrac> </mstyle> <mo>⌋</mo> </mrow> </semantics></math>, and denote the number of spatial subregions as <span class="html-italic">p</span>. For each of the multi-layer classifiers after the autoencoder, the sizes of the two hidden layers are, respectively, <math display="inline"><semantics> <mrow> <mo>⌊</mo> <mstyle scriptlevel="0" displaystyle="true"> <mfrac> <mn>2</mn> <mn>3</mn> </mfrac> </mstyle> <mover accent="true"> <mi>J</mi> <mo>˜</mo> </mover> <mo>⌋</mo> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mo>⌊</mo> <mstyle scriptlevel="0" displaystyle="true"> <mfrac> <mn>4</mn> <mn>9</mn> </mfrac> </mstyle> <mover accent="true"> <mi>J</mi> <mo>˜</mo> </mover> <mo>⌋</mo> </mrow> </semantics></math>.</p>
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<p>Spatial spectrum of DNN for real data with a source of <math display="inline"><semantics> <mrow> <msub> <mi>θ</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>8</mn> <mo>°</mo> </mrow> </semantics></math> and an estimated SNR of 50 dB. The red cross corresponds to the true DOA of source (i.e., 8°).</p>
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<p>Spatial spectra of DNN-C under different virtual peaks in absence of sources; (<b>a</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math>; (<b>b</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.2</mn> </mrow> </semantics></math>; (<b>c</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.3</mn> </mrow> </semantics></math>; (<b>d</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.4</mn> </mrow> </semantics></math>.</p>
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<p>Spatial spectra of DNN-C under different virtual peaks in presence of two sources with DOAs of <math display="inline"><semantics> <mrow> <mo>(</mo> <msub> <mi>θ</mi> <mn>1</mn> </msub> <mo>=</mo> <mo>−</mo> <mn>40.1</mn> <mo>°</mo> <mo>,</mo> <msub> <mi>θ</mi> <mn>2</mn> </msub> <mo>=</mo> <mo>−</mo> <mn>28.2</mn> <mo>°</mo> <mo>)</mo> </mrow> </semantics></math>; (<b>a</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.3</mn> </mrow> </semantics></math>; (<b>b</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.4</mn> </mrow> </semantics></math>; (<b>c</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math>; (<b>d</b>) <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mrow> <mi>v</mi> <mi>i</mi> <mi>r</mi> </mrow> </msub> <mo>=</mo> <mn>0.6</mn> </mrow> </semantics></math>.</p>
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<p>Testing time for different methods.</p>
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<p>Performance versus number of snapshots when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) FAR of source number detection.</p>
Full article ">Figure 9
<p>Performance versus DOA of a single source; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
Full article ">Figure 10
<p>Performance versus SNR when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
Full article ">Figure 11
<p>Performance versus number of snapshots when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
Full article ">Figure 12
<p>Performance versus SNR when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
Full article ">Figure 13
<p>Performance versus DOA separation when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
Full article ">Figure 14
<p>Performance versus WNPR when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>S</mi> <mi>N</mi> <mi>R</mi> <mo>=</mo> <mo>−</mo> <mn>4</mn> </mrow> </semantics></math> dB, and <math display="inline"><semantics> <mrow> <mi>N</mi> <mo>=</mo> <mn>1000</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
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<p>Performance versus WNPR when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>S</mi> <mi>N</mi> <mi>R</mi> <mo>=</mo> <mo>−</mo> </mrow> </semantics></math>6 dB, and <math display="inline"><semantics> <mrow> <mi>N</mi> <mo>=</mo> <mn>100</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
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<p>Performance versus correlation coefficient when <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>; (<b>a</b>) PD of source number detection; (<b>b</b>) PMD of source number detection; (<b>c</b>) FAR of source number detection; (<b>d</b>) RMSE of DOA estimation based on the estimated number of sources.</p>
Full article ">Figure 17
<p>Spatial spectrum of DNN-C for real data with source of <math display="inline"><semantics> <mrow> <msub> <mi>θ</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>8</mn> <mo>°</mo> </mrow> </semantics></math> and an estimated SNR of 50 dB. The red dot with a red circle corresponds to the true DOA of source (i.e., 8°). The red dot with a black circle corresponds to the virtual peak.</p>
Full article ">Figure 18
<p>Normalized spatial spectra of conventional methods for real data with source of <math display="inline"><semantics> <mrow> <msub> <mi>θ</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>8</mn> <mo>°</mo> </mrow> </semantics></math> and an estimated SNR of 50 dB. The blue cross corresponds to the true DOA of source (i.e., 8°).</p>
Full article ">Figure 19
<p>Spatial spectrum of DNN-C for real data with source of <math display="inline"><semantics> <mrow> <msub> <mi>θ</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>8</mn> <mo>°</mo> </mrow> </semantics></math> and an estimated SNR of −10 dB; The red dot with a red circle corresponds to the true DOA of source (i.e., 8°). The red dot with a black circle corresponds to the virtual peak.</p>
Full article ">Figure 20
<p>Normalized spatial spectra of conventional methods for real data with source of <math display="inline"><semantics> <mrow> <msub> <mi>θ</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>8</mn> <mo>°</mo> </mrow> </semantics></math> and an estimated SNR of −10 dB. The blue cross corresponds to the true DOA of source (i.e., 8°).</p>
Full article ">Figure 21
<p>Spatial spectrum of DNN-C for real data in the absence of the source. The red dot with a black circle corresponds to the virtual peak.</p>
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