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Keywords = cubic phase signal

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27 pages, 2813 KiB  
Article
Study of Optical Solitons and Quasi-Periodic Behaviour for the Fractional Cubic Quintic Nonlinear Pulse Propagation Model
by Lotfi Jlali, Syed T. R. Rizvi, Sana Shabbir and Aly R. Seadawy
Mathematics 2025, 13(13), 2117; https://doi.org/10.3390/math13132117 - 28 Jun 2025
Viewed by 213
Abstract
This study explores analytical soliton solutions for the cubic–quintic time-fractional nonlinear non-paraxial pulse transmission model. This versatile model finds numerous uses in fiber optic communication, nonlinear optics, and optical signal processing. The strength of the quintic and cubic nonlinear components plays a crucial [...] Read more.
This study explores analytical soliton solutions for the cubic–quintic time-fractional nonlinear non-paraxial pulse transmission model. This versatile model finds numerous uses in fiber optic communication, nonlinear optics, and optical signal processing. The strength of the quintic and cubic nonlinear components plays a crucial role in nonlinear processes, such as self-phase modulation, self-focusing, and wave combining. The fractional nonlinear Schrödinger equation (FNLSE) facilitates precise control over the dynamic properties of optical solitons. Exact and methodical solutions include those involving trigonometric functions, Jacobian elliptical functions (JEFs), and the transformation of JEFs into solitary wave (SW) solutions. This study reveals that various soliton solutions, such as periodic, rational, kink, and SW solitons, are identified using the complete discrimination polynomial methods (CDSPM). The concepts of chaos and bifurcation serve as the framework for investigating the system qualitatively. We explore various techniques for detecting chaos, including three-dimensional and two-dimensional graphs, time-series analysis, and Poincarè maps. A sensitivity analysis is performed utilizing a variety of initial conditions. Full article
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20 pages, 7585 KiB  
Article
The Research on Path Planning Method for Detecting Automotive Steering Knuckles Based on Phased Array Ultrasound Point Cloud
by Yihao Mao, Jun Tu, Huizhen Wang, Yangfan Zhou, Qiao Wu, Xu Zhang and Xiaochun Song
Sensors 2025, 25(9), 2907; https://doi.org/10.3390/s25092907 - 4 May 2025
Viewed by 449
Abstract
To address the challenges of automatic detection caused by the variation of surface normal vectors in automotive steering knuckles, an automatic detection method based on ultrasonic phased array technology is herein proposed. First, a point cloud model of the workpiece was constructed using [...] Read more.
To address the challenges of automatic detection caused by the variation of surface normal vectors in automotive steering knuckles, an automatic detection method based on ultrasonic phased array technology is herein proposed. First, a point cloud model of the workpiece was constructed using ultrasonic distance measurement, and Gaussian-weighted principal component analysis was used to estimate the normal vectors of the point cloud. By utilizing the normal vectors, water layer thickness during detection, and the incident angle of the sound beam, the probe pose information corresponding to the detection point was precisely calculated, ensuring the stability of the sound beam incident angle during the detection process. At the same time, in the trajectory planning process, piecewise cubic Hermite interpolation was used to optimize the detection trajectory, ensuring continuity during probe movement. Finally, an automatic detection system was set up to test a steering knuckle specimen with surface circumferential cracks. The results show that the point cloud data of the steering knuckle specimen, obtained using phased array ultrasound, had a relative measurement error controlled within 1.4%, and the error between the calculated probe angle and the theoretical angle did not exceed 0.5°. The probe trajectory derived from these data effectively improved the B-scan image quality during the automatic detection of the steering knuckle and increased the defect signal amplitude by 5.6 dB, demonstrating the effectiveness of this method in the automatic detection of automotive steering knuckles. Full article
(This article belongs to the Section Physical Sensors)
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13 pages, 3845 KiB  
Article
Ultra-Compact Multimode Micro-Racetrack Resonator Based on Cubic Spline Curves
by Zhen Li, Chuang Cheng, Xin Fu and Lin Yang
Photonics 2025, 12(4), 326; https://doi.org/10.3390/photonics12040326 - 31 Mar 2025
Viewed by 466
Abstract
Micro-racetrack resonators have become one of the key components for realizing signal processing, generation, and integration in microwave photonics, owing to their high Q factor, compact footprint, and tunability. However, most of the reported micro-racetrack resonators are confined to the single-mode regime. In [...] Read more.
Micro-racetrack resonators have become one of the key components for realizing signal processing, generation, and integration in microwave photonics, owing to their high Q factor, compact footprint, and tunability. However, most of the reported micro-racetrack resonators are confined to the single-mode regime. In this paper, we designed an ultra-compact multimode micro-racetrack resonator (MMRR) based on shape-optimized multimode waveguide bends (MWBs). Cubic spline curves were used to represent the MWB boundary and adjoint methods were utilized for inverse optimization, achieving an effective radius of 8 μm. Asymmetric directional couplers (ADCs) were designed to independently couple three modes into a multimode micro-racetrack, according to phase-matching conditions and transmission analysis. The MMRR was successfully fabricated on a commercial platform using a 193 nm dry lithography process. The device exhibited high loaded Q factors of 2.3 × 105, 4.1 × 104, and 2.9 × 104, and large free spectral ranges (FSRs) of 5.4, 4.7, and 4.2 nm for TE0, TE1, and TE2 modes, with about a 19 × 55 μm2 footprint. Full article
(This article belongs to the Special Issue Recent Advancement in Microwave Photonics)
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15 pages, 4626 KiB  
Article
Structural, Morphological and Thermoluminescence Properties of Mn-Doped Zinc Zirconate (ZnZrO3) Phosphors
by Habtamu F. Etefa and Francis B. Dejene
Appl. Sci. 2025, 15(7), 3761; https://doi.org/10.3390/app15073761 - 29 Mar 2025
Cited by 1 | Viewed by 468
Abstract
We investigated the thermoluminescence (TL) properties of Mn-doped zinc zirconate (ZnZrO3:Mn) phosphors under beta (β) radiation. SEM revealed morphological changes with varying levels of Mn doping (0–5%), while XRD confirmed a pure cubic phase. Mn doping introduced luminescent centers, enhancing emission [...] Read more.
We investigated the thermoluminescence (TL) properties of Mn-doped zinc zirconate (ZnZrO3:Mn) phosphors under beta (β) radiation. SEM revealed morphological changes with varying levels of Mn doping (0–5%), while XRD confirmed a pure cubic phase. Mn doping introduced luminescent centers, enhancing emission efficiency. Mn2+ ions facilitated green/red emissions (4T16A1), while Mn4+ contributed to deep-red emissions (2E → 4A₂), making the material suitable for optoelectronic applications. Compared to conventional phosphors, ZnZrO3:Mn exhibited superior thermal stability, enhanced luminescence, and tunable emissions. The TL dose−response showed a systematic peak shift to higher temperatures with increasing radiation dose, confirming its potential for use in accurate dosimetry. The TL glow curves displayed primary (349 K) and secondary (473 K) peaks that were influenced by heating-rate variations, which led to peak shifts and increased intensity. An innovative thermal-cleaning approach (110–336 °C) refined luminescence by stabilizing deeper traps while erasing shallow-trap signals. This combined effect of Mn doping and thermal treatment optimized ZnZrO3 phosphors’ structural, optical, and TL properties. These findings provide insights into their potential use in radiation dosimetry and display technologies, offering a new strategy for future perspective luminescent materials Full article
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17 pages, 2514 KiB  
Article
A Water Environment-Based Simulated Method for Ultrasonic Testing of Slag Inclusion Weld Defects Based on Improved VMD
by Jing Zhang, Guocai Zhang, Zijie Chen, Hailin Zou, Shuai Xue, Jianjie Deng and Jianqing Li
Sensors 2024, 24(13), 4199; https://doi.org/10.3390/s24134199 - 28 Jun 2024
Viewed by 1501
Abstract
The identification of slag inclusion defects in welds is of the utmost importance in guaranteeing the integrity, safety, and prolonged service life of welded structures. Most research focuses on different kinds of weld defects, but branch research on categories of slag inclusion material [...] Read more.
The identification of slag inclusion defects in welds is of the utmost importance in guaranteeing the integrity, safety, and prolonged service life of welded structures. Most research focuses on different kinds of weld defects, but branch research on categories of slag inclusion material is limited and critical for safeguarding the quality of engineering and the well-being of personnel. To address this issue, we design a simulated method using ultrasonic testing to identify the inclusion of material categories in austenitic stainless steel. It is based on a simulated experiment in a water environment, and six categories of cubic specimens, including four metallic and two non-metallic materials, are selected to simulate the slag materials of the inclusion defects. Variational mode decomposition optimized by particle swarm optimization is employed for ultrasonic signals denoising. Moreover, the phase spectrum of the denoised signal is utilized to extract the phase characteristic of the echo signal from the water–slag specimen interface. The experimental results show that our method has the characteristics of appropriate decomposition and good denoising performance. Compared with famous signal denoising algorithms, the proposed method extracted the lowest number of intrinsic mode functions from the echo signal with the highest signal-to-noise ratio and lowest normalized cross-correlation among all of the comparative algorithms in signal denoising of weld slag inclusion defects. Finally, the phase spectrum can ascertain whether the slag inclusion is a thicker or thinner medium compared with the weld base material based on the half-wave loss existing or not in the echo signal phase. Full article
(This article belongs to the Special Issue Sensing and Imaging for Defect Detection)
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25 pages, 5632 KiB  
Article
Helical Gearbox Defect Detection with Machine Learning Using Regular Mesh Components and Sidebands
by Iulian Lupea, Mihaiela Lupea and Adrian Coroian
Sensors 2024, 24(11), 3337; https://doi.org/10.3390/s24113337 - 23 May 2024
Cited by 7 | Viewed by 2001
Abstract
The current paper presents helical gearbox defect detection models built from raw vibration signals measured using a triaxial accelerometer. Gear faults, such as localized pitting, localized wear on helical pinion tooth flanks, and low lubricant level, are under observation for three rotating velocities [...] Read more.
The current paper presents helical gearbox defect detection models built from raw vibration signals measured using a triaxial accelerometer. Gear faults, such as localized pitting, localized wear on helical pinion tooth flanks, and low lubricant level, are under observation for three rotating velocities of the actuator and three load levels at the speed reducer output. The emphasis is on the strong connection between the gear faults and the fundamental meshing frequency GMF, its harmonics, and the sidebands found in the vibration spectrum as an effect of the amplitude modulation (AM) and phase modulation (PM). Several sets of features representing powers on selected frequency bands or/and associated peak amplitudes from the vibration spectrum, and also, for comparison, time-domain and frequency-domain statistical feature sets, are proposed as predictors in the defect detection task. The best performing detection model, with a testing accuracy of 99.73%, is based on SVM (Support Vector Machine) with a cubic kernel, and the features used are the band powers associated with six GMF harmonics and two sideband pairs for all three accelerometer axes, regardless of the rotation velocities and the load levels. Full article
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22 pages, 1843 KiB  
Article
Long-Time Coherent Integration for the Spatial-Based Bistatic Radar Based on Dual-Scale Decomposition and Conditioned CPF
by Suqi Li, Yihan Wang, Yanfeng Liang and Bailu Wang
Remote Sens. 2024, 16(10), 1798; https://doi.org/10.3390/rs16101798 - 18 May 2024
Viewed by 1543
Abstract
This paper addresses the problem of weak maneuvering target detection in the space-based bistatic radar system through long-time coherent integration (LTCI). The space-based bistatic radar is vulnerable to the high-order range migration (RM) and Doppler frequency migration (DFM), since the target, the receiver [...] Read more.
This paper addresses the problem of weak maneuvering target detection in the space-based bistatic radar system through long-time coherent integration (LTCI). The space-based bistatic radar is vulnerable to the high-order range migration (RM) and Doppler frequency migration (DFM), since the target, the receiver and the transmitter all can play fast movement independently. To correct high- order RM and DFM, this usually involves joint high-dimensional parameter searching, incurring a large computational burden. In our previous work, a dual-scale (DS) decomposition of motion parameters was proposed, in which the optimal GRFT is conditionally decoupled into two cascade procedures called the modified generalized inverse Fourier transform (GIFT) and generalized Fourier transform (GFT), resulting in the DS-GRFT detector. However, even if the DS-GRFT detector preserves the superior performance and dramatically decreases the complexity, high-dimensional searching is still required. In this paper, by analyzing the structure of the DS-GRFT detector, we further designed a conditioned cubic phase function (CCPF) tailored to the range–slow-time signal after GIFT, breaking the joint high-dimensional searching into independent one-dimensional searching. Then, by connecting the proposed CCPF with the GIFT, we achieved a new LTCI detector called the DS-GIFT-CCPF detector, which obtained a significant computational cost reduction with acceptable performance loss, as demonstrated in numerical experiments. Full article
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13 pages, 2538 KiB  
Article
Simulation Method for the Impact of Atmospheric Wind Speed on Optical Signals in Satellite–Ground Laser Communication Links
by Wujisiguleng Zhao and Chunyi Chen
Photonics 2024, 11(5), 417; https://doi.org/10.3390/photonics11050417 - 30 Apr 2024
Cited by 1 | Viewed by 1663
Abstract
To analyze the intensity of atmospheric turbulence in a satellite–ground laser communication link, it is important to consider the effect of increased atmospheric turbulence caused by wind speed. Atmospheric turbulence causes a change in the refractive index, which negatively impacts the quality and [...] Read more.
To analyze the intensity of atmospheric turbulence in a satellite–ground laser communication link, it is important to consider the effect of increased atmospheric turbulence caused by wind speed. Atmospheric turbulence causes a change in the refractive index, which negatively impacts the quality and focusing ability of the laser beam by altering its phase front. To simulate the changes in amplitude and phase characteristics of laser beam propagation in atmospheric turbulence caused by wind speed, a transverse translation phase screen is used. To better understand and address the influence of atmospheric wind speed on the phase of optical signals in satellite–ground laser communication links, this paper proposes a Monte Carlo simulation method. This method utilizes the spatial and temporal variations in the refractive index in the atmosphere and integrates the principles of optical signal propagation in the atmosphere to simulate changes in the phase of optical signals under different wind speed conditions. By analyzing the variations in the received optical signal’s power, the Monte Carlo method is employed to simulate phase screens and logarithmic amplitude screens. Additionally, it models the probability density of the statistical behavior of received optical signal’s fluctuations, as well as the time autocorrelation coefficient of optical signals. This paper, under the coupling condition in satellite–ground laser communication links, conducted a Monte Carlo simulation experiment to analyze the characteristics of the optical signal’s fluctuations in the link and discovered that atmospheric wind speed affects the shape of the power spectral density model of the received optical signal. Increasing wind speed leads to a decrease in the time autocorrelation coefficient of the received optical signal and affects the coupling efficiency. The paper then used a cubic spline interpolation fitting method to verify the models of the power spectral density and the autocorrelation time coefficient of the optical signal. This provides a theoretical foundation and practical guidance for the optimization of satellite–ground laser communication systems. Full article
(This article belongs to the Section Optical Communication and Network)
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21 pages, 9215 KiB  
Article
Identifying System Non-Linearities by Fusing Signal Bispectral Signatures
by Georgia Koukiou
Electronics 2024, 13(7), 1287; https://doi.org/10.3390/electronics13071287 - 29 Mar 2024
Cited by 3 | Viewed by 1259
Abstract
Higher-order statistics investigate the phase relationships between frequency components, an aspect which cannot be treated using conventional spectral measures such as the power spectrum. Among the widely used higher-order statistics, the bispectrum ranks prominently. By delving into higher-order correlations, the bispectrum offers a [...] Read more.
Higher-order statistics investigate the phase relationships between frequency components, an aspect which cannot be treated using conventional spectral measures such as the power spectrum. Among the widely used higher-order statistics, the bispectrum ranks prominently. By delving into higher-order correlations, the bispectrum offers a means of extracting additional merits and insights from frequency coupling, enhancing our understanding of complex signal interactions. This analytical approach overcomes the limitations of traditional methods, providing a more comprehensive view of the complex relationships within the frequency domain. In this paper, the extensive use of the bispectrum in various scientific and technical areas is firstly emphasized by presenting very recent applications. The main scope of this work is to investigate the consequences of various non-linearities in the creation of phase couplings. Specifically, the quadratic, the cubic and the logarithmic non-linearities are examined. In addition, simple recommendations are given on how the underlying nonlinearity could be detected. The total approach is novel, considering the capability to distinguish from the bispectral content if two non-linearities are simultaneously present. Full article
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13 pages, 3609 KiB  
Article
Crystallization of Ethylene Plant Hormone Receptor—Screening for Structure
by Buket Rüffer, Yvonne Thielmann, Moritz Lemke, Alexander Minges and Georg Groth
Biomolecules 2024, 14(3), 375; https://doi.org/10.3390/biom14030375 - 20 Mar 2024
Cited by 2 | Viewed by 2561
Abstract
The plant hormone ethylene is a key regulator of plant growth, development, and stress adaptation. Many ethylene-related responses, such as abscission, seed germination, or ripening, are of great importance to global agriculture. Ethylene perception and response are mediated by a family of integral [...] Read more.
The plant hormone ethylene is a key regulator of plant growth, development, and stress adaptation. Many ethylene-related responses, such as abscission, seed germination, or ripening, are of great importance to global agriculture. Ethylene perception and response are mediated by a family of integral membrane receptors (ETRs), which form dimers and higher-order oligomers in their functional state as determined by the binding of Cu(I), a cofactor to their transmembrane helices in the ER-Golgi endomembrane system. The molecular structure and signaling mechanism of the membrane-integral sensor domain are still unknown. In this article, we report on the crystallization of transmembrane (TM) and membrane-adjacent domains of plant ethylene receptors by Lipidic Cubic Phase (LCP) technology using vapor diffusion in meso crystallization. The TM domain of ethylene receptors ETR1 and ETR2, which is expressed in E. coli in high quantities and purity, was successfully crystallized using the LCP approach with different lipids, lipid mixtures, and additives. From our extensive screening of 9216 conditions, crystals were obtained from identical crystallization conditions for ETR1 (aa 1-316) and ETR2 (aa 1-186), diffracting at a medium–high resolution of 2–4 Å. However, data quality was poor and not sufficient for data processing or further structure determination due to rotational blur and high mosaicity. Metal ion loading and inhibitory peptides were explored to improve crystallization. The addition of Zn(II) increased the number of well-formed crystals, while the addition of ripening inhibitory peptide NIP improved crystal morphology. However, despite these improvements, further optimization of crystallization conditions is needed to obtain well-diffracting, highly-ordered crystals for high-resolution structural determination. Overcoming these challenges will represent a major breakthrough in structurally determining plant ethylene receptors and promote an understanding of the molecular mechanisms of ethylene signaling. Full article
(This article belongs to the Special Issue Recent Insights into Metal Binding Proteins)
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11 pages, 468 KiB  
Review
Overlapping Receptor-Based Pathogenic Cascades in Degenerative Disease: Implications Ranging from Tumor Targeting to Aging and Dementia Therapeutics
by Joseph S. D’Arrigo
Int. J. Transl. Med. 2024, 4(1), 152-162; https://doi.org/10.3390/ijtm4010008 - 6 Feb 2024
Viewed by 1413
Abstract
Previous research has already shown that apolipoprotein (apo)A-I is adsorbed from the bloodstream onto the surface of certain colloidal lipid particles after the intravenous injection of such colloidal nanocarriers. As a result, various blood–brain barrier (BBB) scavenger receptors are targeted by these (apoA-I-coated) [...] Read more.
Previous research has already shown that apolipoprotein (apo)A-I is adsorbed from the bloodstream onto the surface of certain colloidal lipid particles after the intravenous injection of such colloidal nanocarriers. As a result, various blood–brain barrier (BBB) scavenger receptors are targeted by these (apoA-I-coated) colloidal nanocarriers. This targeted molecular interaction is mediated/facilitated by the adsorbed apoA-I, which is then followed by receptor-mediated endocytosis and subsequent transcytosis of the nanocarrier particles across the BBB. A multifunctional combination therapy is obtained by adding the appropriate drug(s) to these biomimetic (lipid cubic phase) nanocarriers. This therapeutic targets specific cell-surface scavenger receptors, primarily class B type I (SR-BI), and crosses the blood–brain barrier. The lipid contents of artificial biomimetic (nanoemulsion) nanocarrier particles and of naturally occurring high-density lipoproteins (HDL) have been shown to be similar, which enables these nanocarrier particles to partially imitate or simulate the known heterogeneity (i.e., subpopulations or subspecies) of HDL particles. Hence, colloidal drug nanocarriers have the potential to be used in the biomedical treatment of complicated medical conditions including dementia, as well as certain elements of aging. Widespread inflammation and oxidative stress—two processes that include several pathophysiological cascades—are brought on by dementia risk factors. More recent studies suggest that proinflammatory cytokines may be released in response to a prolonged inflammatory stimulus in the gut, for example through serum amyloid A (SAA). Therefore, pharmacologically targeting a major SAA receptor implicated in the SAA-mediated cell signaling processes that cause aging and/or cognitive decline, and ultimately Alzheimer’s disease or (late-onset) dementia, could be an effective preventive and therapeutic approach. Full article
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21 pages, 10332 KiB  
Article
A Comparative and Critical Analysis for In Vitro Cytotoxic Evaluation of Magneto-Crystalline Zinc Ferrite Nanoparticles Using MTT, Crystal Violet, LDH, and Apoptosis Assay
by Juan Luis de la Fuente-Jiménez, César Iván Rodríguez-Rivas, Irma Beatriz Mitre-Aguilar, Andrea Torres-Copado, Eric Alejandro García-López, José Herrera-Celis, María Goretti Arvizu-Espinosa, Marco Antonio Garza-Navarro, Luis Gerardo Arriaga, Janet Ledesma García, Domingo Ixcóatl García-Gutiérrez, Alejandro Zentella Dehesa, Ashutosh Sharma and Goldie Oza
Int. J. Mol. Sci. 2023, 24(16), 12860; https://doi.org/10.3390/ijms241612860 - 16 Aug 2023
Cited by 10 | Viewed by 3498
Abstract
Zinc ferrite nanoparticles (ZFO NPs) are a promising magneto-crystalline platform for nanomedicine-based cancer theranostics. ZFO NPs synthesized using co-precipitation method are characterized using different techniques. UV-visible spectroscopy exhibits absorption peaks specific for ZFO. Raman spectroscopy identifies Raman active, infrared active, and silent vibrational [...] Read more.
Zinc ferrite nanoparticles (ZFO NPs) are a promising magneto-crystalline platform for nanomedicine-based cancer theranostics. ZFO NPs synthesized using co-precipitation method are characterized using different techniques. UV-visible spectroscopy exhibits absorption peaks specific for ZFO. Raman spectroscopy identifies Raman active, infrared active, and silent vibrational modes while Fourier transforms infrared spectroscopic (FTIR) spectra display IR active modes that confirm the presence of ZFO. X-ray diffraction pattern (XRD) exhibits the crystalline planes of single-phase ZFO with a face-centered cubic structure that coincides with the selected area electron diffraction pattern (SAED). The average particle size according to high-resolution transmission electron microscopy (HR-TEM) is 5.6 nm. X-ray photoelectron spectroscopy (XPS) signals confirm the chemical states of Fe, Zn, and O. A superconducting quantum interference device (SQUID) displays the magnetic response of ZFO NPs, showing a magnetic moment of 45.5 emu/gm at 70 kOe. These ZFO NPs were then employed for comparative cytotoxicity evaluation using MTT, crystal violet, and LDH assays on breast adenocarcinoma epithelial cell (MCF-7), triple-negative breast cancer lines (MDA-MB 231), and human embryonic kidney cell lines (HEK-293). Flow cytometric analysis of all the three cell lines were performed in various concentrations of ZFO NPs for automated cell counting and sorting based on live cells, cells entering in early or late apoptotic phase, as well as in the necrotic phase. This analysis confirmed that ZFO NPs are more cytotoxic towards triple-negative breast cancer cells (MDA-MB-231) as compared to breast adenocarcinoma cells (MCF-7) and normal cell lines (HEK-293), thus corroborating that ZFO can be exploited for cancer therapeutics. Full article
(This article belongs to the Special Issue New Perspectives of Colloids for Biological Applications)
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25 pages, 5912 KiB  
Article
Dependence of the Michelson Interferometer-Based Membrane-Less Optical Microphone–Photoacoustic Spectroscopy Gas-Sensing Method on the Fundamental Parameters of a Photoacoustic Gas Cell
by Shuchao Wang, Ali K. Yetisen, Kun Wang, Martin Jakobi and Alexander W. Koch
Photonics 2023, 10(8), 888; https://doi.org/10.3390/photonics10080888 - 1 Aug 2023
Cited by 2 | Viewed by 1596
Abstract
This article presents a mathematical model of the Michelson interferometer (MI)-based membrane-less optical microphone (MeoM)–photoacoustic spectroscopy (MeoM–PAS) method, which is also referred to as MI-based photoacoustic interferometry (PAI), for gas-sensing applications in complex and adverse environments, as it offers a completely static measurement [...] Read more.
This article presents a mathematical model of the Michelson interferometer (MI)-based membrane-less optical microphone (MeoM)–photoacoustic spectroscopy (MeoM–PAS) method, which is also referred to as MI-based photoacoustic interferometry (PAI), for gas-sensing applications in complex and adverse environments, as it offers a completely static measurement system and the separation of a photoacoustic (PA) gas cell from the measuring system. It also investigates the dependence of this method on the fundamental parameters of a cubical PA gas cell using axial PA signals. The results indicate that the phase of the method is a sine function of the distance between the two light beams and a power exponent of the cell length, the cell height, and the distance between the excitation source and the nearest light beam, under the condition that the PA gas cell is resonant and that the excitation source is at the position of the peak or valley of the PA signals. It is at its maximum when the distance between the two light beams is approximately half the wavelength of the PA signals under the same conditions. In addition, the dependence of a PA gas cell using non-axial PA signals is described under the conditions that the PA gas cell is resonant, which is consistent with the changing aforementioned parameters for the distance between the two light beams, the cell length and height, and the distance between the excitation source and the nearest light beam. Furthermore, the selection of five common materials (aluminum, brass, glass, quartz, and stainless steel) for the PA gas cell is discussed under the influence of temperature fluctuations outside the PA gas cell, noise inside and outside the PA gas cell, as well as thermal and viscous losses inside the PA gas cell. The results indicate that quartz and stainless steel are promising options. Finally, the parameters related to the sensitivity enhancement of the method are analyzed using mathematical models, where the sensitivity of the method can be theoretically enhanced by reducing the dimensions of the PA gas cell. Full article
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11 pages, 4242 KiB  
Article
Selective NO2 Detection of CaCu3Ti4O12 Ceramic Prepared by the Sol-Gel Technique and DRIFT Measurements to Elucidate the Gas Sensing Mechanism
by Rodrigo Espinoza-González, Josefa Caamaño, Ximena Castillo, Marcelo O. Orlandi, Anderson A. Felix, Marcos Flores, Adriana Blanco, Carmen Castro-Castillo and Francisco Gracia
Materials 2023, 16(9), 3390; https://doi.org/10.3390/ma16093390 - 26 Apr 2023
Cited by 4 | Viewed by 2286
Abstract
NO2 is one of the main greenhouse gases, which is mainly generated by the combustion of fossil fuels. In addition to its contribution to global warming, this gas is also directly dangerous to humans. The present work reports the structural and gas [...] Read more.
NO2 is one of the main greenhouse gases, which is mainly generated by the combustion of fossil fuels. In addition to its contribution to global warming, this gas is also directly dangerous to humans. The present work reports the structural and gas sensing properties of the CaCu3Ti4O12 compound prepared by the sol-gel technique. Rietveld refinement confirmed the formation of the pseudo-cubic CaCu3Ti4O12 compound, with less than 4 wt% of the secondary phases. The microstructural and elemental composition analysis were carried out using scanning electron microscopy and X-ray energy dispersive spectroscopy, respectively, while the elemental oxidation states of the samples were determined by X-ray photoelectron spectroscopy. The gas sensing response of the samples was performed for different concentrations of NO2, H2, CO, C2H2 and C2H4 at temperatures between 100 and 300 °C. The materials exhibited selectivity for NO2, showing a greater sensor signal at 250 °C, which was correlated with the highest concentration of nitrite and nitrate species on the CCTO surface using DRIFT spectroscopy. Full article
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19 pages, 8760 KiB  
Article
A Novel Bistatic SAR Maritime Ship Target Imaging Algorithm Based on Cubic Phase Time-Scaled Transformation
by Qing Yang, Zhongyu Li, Junao Li, Hongyang An, Junjie Wu, Yiming Pi and Jianyu Yang
Remote Sens. 2023, 15(5), 1330; https://doi.org/10.3390/rs15051330 - 27 Feb 2023
Cited by 6 | Viewed by 1997
Abstract
Due to the advantages of flexible configuration, bistatic synthetic aperture radar (BiSAR) has the ability to effectively observe from various visual angles, such as forward view area and squint area, and has good anti-jamming characteristics. It can be applied to the surveillance of [...] Read more.
Due to the advantages of flexible configuration, bistatic synthetic aperture radar (BiSAR) has the ability to effectively observe from various visual angles, such as forward view area and squint area, and has good anti-jamming characteristics. It can be applied to the surveillance of ship targets on the sea and is gradually gaining an increasing amount of attention. However, for ship targets with complex motions on the sea surface, such as maneuvering targets or ship targets under high sea conditions, the high-order Doppler frequency of the scattering points is always spatial variation (related to the spatial position of scattering points), which poses a considerable challenge for the imaging of maritime ship targets in BiSAR. To resolve this problem, a BiSAR maritime ship target imaging algorithm based on cubic phase time-scaled transformation is proposed in this paper. First, through pre-processing of echo such as Doppler prefiltering and keystone transform, the translation compensation of the BiSAR maritime ship target is completed, and the scattering point energy is corrected to within one range unit. Then, the azimuth signal is modeled as a multi-component cubic phase signal. Based on the proposed cubic phase time-scaled transformation, the Doppler centroid, frequency rate, and third-order frequency of scattering points are estimated. Eventually, the BiSAR imaging of maritime ship targets is realized. This algorithm has excellent noise immunity and low cross-terms. The simulation leads to the verification of the validity of the proposed algorithm. Full article
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