Fourier Transform Analysis Research Articles

Interplay between Forced Convection and Electroconvection during the Overlimiting Ion Transport through Anion-Exchange Membranes: A Fourier Transform Analysis of Membrane Voltage Drops

Electrodialysis (ED) applications have expanded in recent years and new modes of operation are being investigated. Operation at overlimiting currents involves the phenomenon of electroconvection, which is associated with the generation of vortices. These vortices accelerate the process of solution mixing, making it possible to increase the transport of ions across the membranes. In this work, frequency analysis is applied to investigate the interaction between different parameters on the development of electroconvection near anion-exchange membranes, which would provide a basis for the development of ED systems with favored electroconvection. Chronopotentiometric curves are registered and Fast Fourier Transform analysis is carried out to study the amplitude of the transmembrane voltage oscillations. Diverse behaviors are detected as a function of the level of forced convection and current density. The synergistic combination of forced convection and overlimiting currents leads to an increase in the signal amplitude, which is especially noticeable at frequencies around 0.1 Hz. Fast Fourier Transform analysis allows identifying, for a given system, the conditions that lead to a transition between stable and chaotic electroconvection modes.

Characterizing an Optically Induced Sub-micrometer Gigahertz Acoustic Wave in a Silicon Thin Plate.

Optically induced GHz-THz guided acoustic waves have been intensively studied because of the potential to realize noninvasive and noncontact material inspection. Although the generation of photoinduced guided acoustic waves utilizing nanostructures, such as ultrathin plates, nanowires, and materials interfaces, is being established, experimental characterization of these acoustic waves in consideration of the finite size effect has been difficult due to the lack of experimental methods with nm × ps resolution. Here we experimentally observe the sub-micrometer guided acoustic waves in a nanofabricated ultrathin silicon plate by ultrafast transmission electron microscopy with nm × ps precision. We successfully characterize the excited guided acoustic wave in frequency-wavenumber space by applying Fourier-transformation analysis on the bright-field movie. These results suggest the great potential of ultrafast transmission electron microscopy to characterize the acoustic modes realized in various nanostructures.

Integrated geophysical approach for ore exploration: Case study of Sidi Bou Aouane–Khadhkhadha Pb–Zn province – Northern Tunisia

AbstractWe carried out an integrated interpretation of available geophysical data (gravity and electrical data) in Sidi Bou Aouane–Khadhkhadha Pb–Zn province, located in a Neogene basin south of the Alpine thrust‐belt front in northern Tunisia. The interpretive approach of gravity data was done based on the Fourier transformation and spectral analysis to extract the residual component. Furthermore, edge enhancement techniques (tilt angle, total horizontal derivative) were applied to image the underlying lineaments in the study area. The computed gravity maps reveal multiple NE–SW hidden faults considered potential mineralization targets, referring to geological information. Detrital formations, known as containers of disseminated Pb–Zn mineralization, are expressed by low gravity responses. Resistivity and chargeability 3D inversion was conducted concurrently through on an iterative approach based on the conventional least‐squares algorithm and “incomplete Gauss‐Newton” as an optimization method. The initial model was defined based on drill‐hole data and geological knowledge. Inverted resistivity confirms the basin architecture expressed by gravity data. The combined interpretation of inverted resistivity and chargeability correlated to borehole and outcrops allows the definition of different electrical ranges associated to different lithologies and mineralization type and contents. A new potential target, expressing the same electrical signature of mineralization, is evidenced northward Khadhkhadha old mine. In addition, a potential copper concentration area was proven based on its electrical responses south Sidi Bou Aouane mine. 2.5D gravity modelling supports the evidenced interpreted target. The revealed results provided evidence for future interpretations of further geological structures, along with evaluations of mineral resources.

Deep learning for the detection of machining vibration chatter

Most of the work on chatter detection is based on laboratory machining tests, thus without the constraints of noise, the variety of situations to be managed in the industry, and the uncertainties on the parameters (sensor position, tool engagement, and sometimes even spindle rotation frequency). This work presents an approach first based on mechanical skills first to identify the optimal signal processing, then based on deep learning to automatically detect the phenomenon of chatter in machining. To do so, we use input images from the Fast Fourier Transform analysis of a vibration signal from the machining of an Alstom industrial railway system. The FFT images are first cropped in height to perform a renormalization of the signal scale. This renormalization step eliminates a bias regularly observed in the literature, which did not eliminate a simple correlation with signal amplitude because chatter is often, but not always, associated with stronger vibrations. Deep learning extracted features from the image data by exploiting pre-trained deep neural networks such as VGG16 and ResNet50. The data is derived from an industrial vibration signal (with noise, a not ideally placed sensors, and uncertainties on process parameters), which was very poorly represented in the literature. It is shown that by depleting the signal (renormalized amplitude and absence of information on the rotation speed), the model obtains a good result (an accuracy of 99% in the training and validation phases), which had never been done in the literature. In addition, since a part of the test dataset is similar to the training dataset, the proposed model obtains an accuracy of 98.82%. The robustness is proved by adding another test dataset containing noisy and more or less ambiguous images to be classified. The model still manages to detect these cases from its training of unambiguous cases, showing that the obtained generalization is efficient with an accuracy of 73.71%.

A Fabry–Perot Sensor with Cascaded Polymer Films Based on Vernier Effect for Simultaneous Measurement of Relative Humidity and Temperature

In this paper, fiber sensor based on Vernier effect for simultaneous measurement of relative humidity (RH) and temperature is proposed. The sensor is fabricated by coating two kinds of ultraviolet (UV) glue with different refractive indexes (RI) and thicknesses on the end face of a fiber patch cord. The thicknesses of two films are controlled to generate the Vernier effect. The inner film is formed by a cured lower-RI UV glue. The exterior film is formed by a cured higher-RI UV glue, of which thickness is much thinner than the inner film. Through the analysis of the Fast Fourier Transform (FFT) of the reflective spectrum, the Vernier effect is formed by the inner lower-RI polymer cavity and the cavity composed of both polymer films. By calibrating the RH and temperature response of two peaks on the envelope of the reflection spectrum, simultaneous measurements of RH and temperature are realized by solving a set of quadratic equations. Experimental results show that the highest RH and temperature sensitivities of the sensor are 387.3 pm/%RH (in 20%RH to 90%RH) and -533.0 pm/°C (in 15 °C to 40 °C), respectively. The sensor has merits of low cost, simple fabrication, and high sensitivity, which makes it very attractive for applications that need to simultaneously monitor these two parameters.

Optimising the Performance of CO2-Cured Alkali-Activated Aluminosilicate Industrial By-Products as Precursors

Three industrial aluminosilicate wastes were studied as precursors to produce alkali-activated concrete: (i) electric arc furnace slag, (ii) municipal solid waste incineration bottom ashes, and (iii) waste glass rejects. These were characterized via X-ray diffraction and fluorescence, laser particle size distribution, thermogravimetric, and Fourier-transform infrared analyses. Distinctive combinations of anhydrous sodium hydroxide and sodium silicate solution were tried by varying the Na2O/binder ratio (8%, 10%, 12%, 14%) and SiO2/Na2O ratio (0, 0.5, 1.0, 1.5) to find the optimum solution for maximized mechanical performance. Specimens were produced and subjected to a three-step curing process: (1) 24 h thermal curing (70 °C), (2) followed by 21 days of dry curing in a climatic chamber (~21 °C, 65% RH), and (3) ending with a 7-day carbonation curing stage (5 ± 0.2% CO2; 65 ± 10% RH). Compressive and flexural strength tests were performed, to ascertain the mix with the best mechanical performance. The precursors showed reasonable bonding capabilities, thus suggesting some reactivity when alkali-activated due to the presence of amorphous phases. Mixes with slag and glass showed compressive strengths of almost 40 MPa. Most mixes required a higher Na2O/binder ratio for maximized performance, even though, contrary to expectations, the opposite was observed for the SiO2/Na2O ratio.

Optical frequency shifted FMCW Lidar system for unambiguous measurement of distance and velocity

A new frequency-modulated continuous-wave (FMCW) Lidar system is proposed to measure distance and velocity unambiguously by using a frequency-shifted probe light. The optical frequency shift is induced by an acousto-optic modulator (AOM). The generated beat signal is up converted to high frequency, sparing sufficient RF bandwidth to avoid signal aliasing caused by high Doppler frequency shifts. The aliasing-free beat signal thus can be used to extract distance and velocity information unambiguously. Here, we experimentally demonstrated real-time measurement on a disk spinning up to 26.43 m/s at 1.267 m away. The precision of the measured distance and velocity are 16 mm and 0.037 m/s respectively. Furthermore, the proposed scheme is capable of discriminating the direction of rotation based on a single Fast Fourier Transform analysis. In addition, we apply a free space circulator to the system to weaken the mirror-scattered signals and thus to achieve continuous measurement of beats signal over wide frequency range. Finally, a three-dimensional image of the spinning disk is reconstructed.

The Study of Cu(II) Adsorption onto Synthetically Modified Geopolymers

The study of Cu(II) from aqueous solutions using the adsorption process on synthetically modified geopolymers was performed under static conditions. Three geopolymers (based on metaphase of Serbian clay, metaphase of German clay and metaphase of German clay plus 10% of carbon cloth) were used. The geopolymers were made by condensing a mixture of metaphases and alkali activator solution at a fixed ratio at room temperature and then at a temperature of 60 °C in a dry oven. Then, the geopolymer samples were pre-crashed to a fixed-radius size. Their properties were characterized by X-ray diffractometry (XRD), Diffuse Reflectance Infrared Fourier Transform (DRIFT) analysis and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). Adsorption experiments were carried out under batch process as a function of the dose, concentration of metal, and contact time. The uptake of Cu(II) was rapid, and it increased with increasing metal concentration. The sorption percentage decreased with increasing concentration of Cu(II). The equilibrium adsorption capacity of geopolymers was measured and extrapolated using more isotherms. The data fit very well the linear Langmuir isotherm model. The pseudo-second-order kinetic model can well describe the adsorption behavior of Cu(II) ions with geopolymers samples. These results show that used geopolymers hold great potential to remove Cu(II) from industrial wastewater.

Determination of output current THD of multilevel inverter by ANN

In recent years, the use of multi-level inverters in power electronics applications has been increasing. The most important advantage of the multi-level inverter circuits compared to the classical two-level topology is that the output voltage is closer to the sinusoidal waveform, operating at a lower switching frequency and high efficiency. Also, low Total Harmonic Distortion (THD) current waveforms occur at the output of multi-level inverter circuits. In this study, a three-phase five-level cascaded inverter is designed by simulating it in MATLAB-Simulink. It is aimed to predict the THDi value of the load current of the inverter. By changing the parameters such as switching frequency, modulation index and load value in the designed multi-level inverter circuit, a dataset is produced for the THDi value of the load current by Fast Fourier Transform (FFT) analysis with MATLAB-Simulink. The generated dataset is used in the training and testing phase of the Artificial Neural Network (ANN) system, which is an artificial intelligence technique. Thus, the THDi value of the load current is estimated. In this way, estimating the parameter determines the inverter circuit with the least THDi before the experimental implementation. At the final estimation phase, the average percent error (APE) value of the current value for the test is obtained as 0.5177 % and 0.5718 %, respectively.

Influence of nanoparticle additives on vibration characteristics in fluid film lubricated journal bearing using real time analysis

The rotating machineries in the power plant undergo through the vibrations during the working and create the severe effects such as whirl instability. In this work, vibration phenomenon is taken into consideration in the plain journal bearing used in the steam power plant. Three grades of Mobil lubricants (DTE 24, DTE 25, and DTE 26) are considered during the study. TiO2 nanoparticle additives are considered during the study as a lubricant additive to examine the vibration induced in the journal bearings. Titanium dioxide nanoparticles (TiO2, 0.5 wt%) of size 40 nm are considered as a lubricant additive to enhance the properties of the lubricants. An experimental approach is presented in this work by opting Fast Fourier Transform (FFT) analyzer. The signals captured by FFT analyzer are then processed on data acquisition software. Comparative analysis is carried out for three different lubricants with and without adding titanium dioxide (TiO2) nanoparticle additives to examine the vibration characteristics of journal bearings. Vibration characteristics such as accelerometer and acoustic pressure in the bearing are measured at speeds ranging from 500 rpm. to 1000 rpm at constant load of 1000 N on the hydrodynamic journal bearing. The purpose of this study is to find out the influence of titanium dioxide as an additive on the vibration characteristics of the journal bearing such as variation in vibration and noise generated in the hydrodynamic journal bearing.

Investigation of the effect of vibration in the multi-objective optimization of dry turning of hardened steel

PurposeThis study aims to investigate the effect of vibration on ceramic tools under dry cutting conditions and find the optimum cutting condition for the hardened steel machining process in a computer numerical control (CNC) lathe machine.Design/methodology/approachIn this research, an integrated fuzzy TOPSIS-based Taguchi L9 optimization model has been applied for the multi-objective optimization (MOO) of the hard-turning responses. Additionally, the effect of vibration on the ceramic tool wear was investigated using Analysis of Variance (ANOVA) and Fast Fourier Transform (FFT).FindingsThe optimum cutting conditions for the multi-objective responses were obtained at 98 m/min cutting speed, 0.1 mm/rev feed rate and 0.2 mm depth of cut. According to the ANOVA of the input cutting parameters with respect to response variables, feed rate has the most significant impact (53.79%) on the control of response variables. From the vibration analysis, the feed rate, with a contribution of 34.74%, was shown to be the most significant process parameter influencing excessive vibration and consequent tool wear.Research limitations/implicationsThe MOO of response parameters at the optimum cutting parameter settings can significantly improve productivity in the dry turning of hardened steel and control over the input process parameters during machining.Originality/valueMost studies on optimizing responses in dry hard-turning performed in CNC lathe machines are based on single-objective optimization. Additionally, the effect of vibration on the ceramic tool during MOO of hard-turning has not been studied yet.

Methods for Reducing Subdivision Error within One Signal Period of Single-Field Scanning Absolute Linear Encoder

Optical encoders are widely used in accurate displacement measurement and motion-control technologies. Based on different measurement methods, optical encoders can be divided into absolute and incremental optical encoders. Absolute linear encoders are commonly used in advanced computer numerical control (CNC) machines. The subdivision error within one signal period (SDE) of the absolute linear encoder is vital to the positioning accuracy and low velocity control of CNC machines. In our paper, we study the working principle of the absolute linear encoder. We proposed two methods for reducing the SDE of the absolute linear encoder, a single-field scanning method based on the shutter-shaped Moiré fringe, as well as a method for suppressing harmonics through a phase shift of index grating. We established a SDE measuring device to determine the absolute linear encoder's SDE, which we measured using a constant-speed approach. With our proposed methods, the SDE was reduced from ±0.218 μm to ±0.135 μm, which is a decrease of 38.07%. Our fast Fourier transformation (FFT) analysis of the collected Moiré fringe signals demonstrated that the third-, fifth-, and seventh-order harmonics were effectively suppressed.

A review on the closed-loop strategy for speed control of BLDC motors

The advancements in the field of materials and force gadgets, coupled with the increased affordability of highperformance processors, have led to a widespread adoption of Brushless Direct Current (BLDC) motors across various industries. These applications range from household appliances to automotive, aerospace, and medical sectors. The widespread use of may be attributed to its manifold advantages over various types of engines, such as its superior efficiency, robust power output, extended operational lifespan, relatively quiet operation, and broader range of achievable speeds. Due to the increasing adoption of Brushless Direct Current (BLDC) motors in many real-life applications as a replacement for traditional motors, this paper aims to compile and evaluate a comprehensive list of control algorithms employed for BLDC motor control. This study discusses several ways for managing speed and current, including hysteresis band control, variable DC-link voltage control, and Pulse Width Modulation (PWM) control schemes. The optimization of Proportional-Integral-Derivative (PID) gains for these controlling techniques is achieved through the utilization of the particle swarm optimization (PSO) algorithm. By employing Fast Fourier Transform (FFT) analysis to examine the controller behavior through frequency analysis of the output signals and calculating the Total Harmonic Distortion (THD), a more advantageous control method may be determined.

Robust and Remote Photoplethysmography Based on Smartphone Imaging of the Human Palm

Arrhythmia is a marked symptom of many cardiovascular diseases (CVDs). Fast and accurate measurement of heart rate (HR) can lead to prompt detection of arrhythmia, which could be potentially life-threatening. However, it remains a challenge to robustly and remotely measure HR due to the typically changing ambient conditions surrounding human subjects. In this study, we propose a method to accurately measure human HR by simply using a smartphone camera. We use three special approaches for HR estimation. Firstly, we fuse the raw data by subtracting G channel from R channel to enhance the heartbeat signal from video data. Secondly, instead of the entire palm, we select a region of interest (ROI) from the palm for heart rate detection based on signal-to-noise ratio (SNR) maps, which reduces the proportion of the weak signal area. Thirdly, after applying Fast Fourier Transform (FFT) analyses of the time-series data from the video, we set an interval threshold based on the heart rate range to accurately determine heart rate. With a reference HR value measured by electrocardiography (ECG), the detection rate of the proposed method is 95.84% (overall result from 30 test subjects) when used for measurement at an ambient light intensity of 150 lux within a distance of 4.5 meters. The method’s strong adaptability to changing ambient conditions and ease of implementation makes it applicable to many scenarios, such as homes of the elderly, classrooms, and other public spaces.

Ionospheric Variability over the Brazilian Equatorial Region during the Minima Solar Cycles 1996 and 2009: Comparison between Observational Data and the IRI Model

The behavior of the Brazilian equatorial ionosphere during the solar minimum periods, 1996 and 2009, which cover the solar cycles 22/23 and 23/24, respectively, is investigated. For this, the F2 layer critical frequency (foF2) and peak height (hmF2) registered by a Digisonde operated at São Luis (2.33° S; 44° W) are carefully analyzed. The results show that the seasonal mean values of the foF2 and the hmF2 in the equinoxes and winter during 2009 were lower than in 1996. In the summer, an anomalous response to solar variability was observed. In this case, the hmF2 in 2009 is higher than in 1996 during a specific daytime interval. Besides that, it was verified that the prereversal enhancement of the zonal electric field (PRE) during the equinoxes in 2009 occurred a few minutes earlier than in 1996. Additionally, a Fast Fourier Transform (FFT) analysis was used to investigate the impacts of solar atmospheric tides (amplitude, diurnal, semidiurnal, and terdiurnal modes) on foF2 and hmF2 parameters with respect to its seasonality. Significant differences were observed between their values during the two minima, mainly in the amplitude of hmF2, which was higher in 1996 than in 2009 for all days analyzed. Moreover, the seasonality in the diurnal and semidiurnal modes for both periods presented an annual variability, while the terdiurnal mode exhibited annual and semiannual components. The results are compared with the International Reference Ionosphere (IRI) model, and the main differences between the observation and the model results are discussed in this work.

Evaluation of various properties of gypsum particleboards reinforced with olivine mineral

In this study, it was investigated some properties of gypsum particleboards which is produced with olivine mineral. Wood particles were added as reinforcement in different proportions (70% and 30%) to two types of plasterboard. The effects of inorganic olivine mineral added to these two types of boards were evaluated in terms of their physical and mechanical properties, thermal conductivity, and combustion behaviour. Subsequently, tests were carried to determine their water absorption, thickness swelling, internal bonding, bending strength, modulus of elasticity, thermal conductivity, and combustion performance. The properties of the boards were then examined using Fourier-transform infrared spectroscopy and thermogravimetric analysis. The Fourier-transform infrared analysis revealed the typical traces of cellulose, hemicellulose, and lignin in the wood material, traces of gypsum as the binder, and varying traces of olivine, according to the additive ratio, were also observed. Thermal analysis determined the positive contribution of olivine to the basic stability of both types of boards. It can be concluded that olivine, when added in different proportions, is a suitable reinforcement material for improving the technical properties of gypsum particleboard.

Multistep Transformation from Amorphous and Nonporous Fullerenols to Highly Crystalline Microporous Materials.

The structural and morphological properties of fullerenols upon exposure to heat treatment have yet to be understood. Herein, the temperature-driven structural and morphological evolutions of fullerenols C60 (OH) and C70 (OH) were investigated. In situ spectroscopic techniques, such as variable-temperature X-ray diffraction and coupled thermogravimetric Fourier-transform infrared analysis, were used to elucidate the structural transformation mechanism of fullerenols. Both fullerenols underwent four-step structural transformation upon heating and cooling, including amorphous-to-crystalline transition, thermal expansion, structural compression, and new crystal formation. Compared to the initially nonporous amorphous fullerenol, the crystalline product exhibited microporosity with a surface area of 114 m2 g-1 and demonstrated CO2 sorption capability. These findings show the potential of fullerene derivatives as adsorbents.

Cell wall polysaccharides of endophytic Pseudomonas putida elicit defense against rice blast disease.

To characterize the functional role of extracellular polysaccharides and lipopolysaccharide extracted from endophytic Pseudomonas putida BP25 (PpBP25) against rice blast. We profiled the transcriptome of endobacterized rice seedlings using RNA-seq. Fluorescence imaging of interaction between Magnaporthe:: gfp and P. putida:: mCherry was performed on rice-phylloplane using Confocal Laser Scanning Microscopy (CLSM). Microbial polysaccharides, EPS and LPS extracted from PpBP25 were characterized using Fourier-transform infrared-spectroscopic analysis (FTIR). Biochemical assays, and gene expression analysis were conducted on EPS and LPS-treated rice seedlings. A detached-leaf assay was designed to test the blasticidal-effect of bacterial-endophyte, EPS and LPSon rice-phylloplane.PpBP25elicited defense in rice with a consequently altered seedling phenotype. Rice cultivar, Pusa Basmati-1, colonized by PpBP25 showed an altered transcriptome profile displaying a total of 110-downregulated and 68-upregulated genes (p<0.005) representing growth/development and defense pathways, respectively. CLSM of PpBP25 bacterized phylloplane showed reduced conidial-germination and mycelial-biomass of M. oryzae. To decipher the elicitor role of polysaccharides, we purified and characterized EPS and LPS using FTIR. Rice treated with the EPS and LPS showed root-growth inhibition -the phenotype of MAMP-triggered immunity. While the EPS showed blast suppressive activity at 1-20mg mL-1 (79.80-86.87% reduction over control), the LPS exhibited 78.0-79.8% reduction at 20-200µg mL-1on rice. Polysaccharides treated seedling showed elevated activities of peroxidase and polyphenol-oxidase activities, and total-phenols content. Treated plantlets showed up regulation of OsPR1.1, OsPR3, OsGLP3-3 OsZFP179, and Oshox24 as well as down regulation of OsACS6. We showed that P. putida and its cell-wall associated polysaccharides could elicit defense against rice blast.

Simultaneous local spectral, colorimetric, and topographic characterization of laser-induced colored stainless steel with low coherence interference microscopy

Laser marking is a well-established advanced technology for changing the color properties of an object. The spectral response or color information induced by the laser is generally measured with a spectrometer or an ellipsometer. These instruments only provide an average response over an area of a few thousand µm² at best. However, color laser marking is a local process that modifies the structure of the metal at a micrometer scale. In this work, we propose a technique for extracting simultaneously the 3D topography and the 2D spectral response from 460 nm to 900 nm, providing color information over this spectral range, in a single measurement. The proposed technique uses a low-coherence interference microscope to provide a laterally diffraction-limited measurement (∼1 µm) over a large field of view (up to 200 × 200 µm²) with the advantages of being rapid (<3 min) and contactless. Through the Fourier Transform analysis of the measured interferogram, a multimodal characterization (quantitative spectra, color (xy) and topography) of reflective samples can be achieved. Results obtained on laser-induced colored stainless steel are reported.

Fe2O3/diatomite materials as efficient photo-Fenton catalysts for ciprofloxacin removal.

In this study, we used Fe2O3/diatomite material system toward ciprofloxacin (CIP) photo-Fenton removal in water under visible light (vis) excitation. The characterization of Fe2O3/diatomite catalysts was determined by X-ray diffraction patterns, Fourier-transform infrared analysis, inductively coupled plasma mass spectrometry, and scanning electron microscopy. The photo-Fenton catalytic activity of the Fe2O3/diatomite was appraised by the removal efficiency of the CIP throughout the effect of the H2O2 with various parameters such as initial pH, catalyst amount, and H2O2 amount. The results indicate that 0.2 gL-1 Fe2O3/diatomite catalysts achieved the highest performance at approximately 90.03% with a 50 μL H2O2 concentration. Furthermore, the Fe2O3/diatomite catalysts have high stability, with over 80% CIP removed after five cycles. This study is inspired to develop a potential material for photo-Fenton degradation of antibiotics in wastewater.