Low-frequency Field Research Articles

Desorption characteristic of oil from sludge surfaces under low-frequency ultrasound

Oil and solids in oily sludge have complex composition and exhibit strong interaction, which both make difficult the oil removal. In this paper, experiments focused on oil/solid property analysis and oil removal have been conducted to determine desorption characteristics of oily sludge in low-frequency ultrasonic fields. Polar components have a high fraction of heteroatoms that form strong van der Waals forces and hydrogen bonds with solid particles. In comparison to nonpolar, polar components were found to be less desorbed from solid surfaces in the ultrasonic field. Metals in kaolinite had strong electrostatic interactions with carboxylic acid in oil. In addition, porous structure of kaolinite increased the re-adsorption probability of oil. In comparison to quartzite, kaolinite showed lower oil removal efficiency. Therefore, higher acoustic intensity with shorter treatment time was found to be effective for oily sludge with high content of polar components and kaolinite at constant energy.

Prediction of combustion promotion effect of high/low-frequency AC electric fields based on machine learning method

Electric field-assisted combustion has become a trend in the past several decades. The effects of low-frequency and high-frequency AC electric fields on the flame propagation and combustion process of CH4-N2-O2 lean burning flame are compared experimentally, and different machine learning methods are applied to predict the flame propagation and combustion characteristics in this research. The experimental results show that both the fields can affect the flame significantly in the electric field direction, while the flame front under a low-frequency field is more stable. The promotion effect of the fields on the average flame propagation speed is in the same order, and the high-frequency fields increase the combustion pressure and pressure rise rate more than the low-frequency one. Support vector machine and artificial neural network are used to establish the correlation model of the average flame propagation and combustion pressure, respectively. It is found that the generation ability and the prediction performance of the models are very impressive and reliable. The correlation coefficient of each model established by SVM method is over 0.998, and the values of MAPE and Theil IC are below 1.093% and 0.007, respectively. The calculation speed of the ANN model is much higher than that of the SVM one. Besides, the results of the SVM method are more deterministic than that of the ANN method. Present work illustrates that machine learning methods provide time-saving research approaches for the forecasting of the flame propagation and combustion characteristic parameters in the electric field-assisted combustion field.

Study on Electromagnetic Radiation Characteristics Based on HTS Maglev Levitation Test Line

As a new type of magnetic levitation train with the characteristics of self-stabilization and self-suspension, high-temperature superconducting magnetic levitation has developed to the test line research stage. In order to promote the rapid development of high-temperature superconducting magnetic levitation train engineering, and the main electromagnetic radiation sources are clarified by analyzing their working principles and structures. Then Ansoft Maxwell EM was used to build a 3D magnetic levitation train electromagnetic environment simulation model to simulate and predict the electromagnetic radiation characteristics of the magnetic levitation train system. Finally, a field EMF test was carried out to verify and assess the impact on the EM environment in the system. The results show that the permanent magnet track on the ground and the synchronous linear motor are the primary electromagnetic radiation sources, and the generated fields are mainly low-frequency fields and static magnetic fields. The low-frequency magnetic field inside the train decreases with the increase of frequency and is partially shielded by the carriage; The static magnetic field cannot be weakened by the carriage, and the static magnetic field inside the car decreases with the increase of height. All types of electromagnetic fields are far below the requirements of the relevant electromagnetic environmental standard limits, and have no effect on the electromagnetic radiation safety of the personnel inside the train and the surrounding environment; In considering of the special people who have pacemakers, static magnetic field suppression measures are studied, and the results show that the trains with high magnetic permeability permalloy as the shielding layer at the bottom of the vehicle greatly lower the static magnetic field within the train.

Abstract 4573: Evaluation of tumor treating fields (TTFields) effects at 200 kHz on a glioblastoma, an anaplastic ependymoma and an oligodendroglioma sample in a patient-derived ex vivo organoid model

Abstract TTFields are alternating electric fields of low intensity (1-3 V/cm) and intermediate frequency (100-500 kHz), which are effective and approved for the treatment of glioblastoma (GBM) using 200 kHz frequency. However, there is a lack of ex vivo models to evaluate effects on patients’ tumor biology or to screen patients for treatment efficacy. Therefore, we adapted patient-derived three-dimensional GBM tissue culture models to be compatible with TTFields application and recently published the feasibility of such an approach (Nickl, et al., 2022, doi: 10.3390/cancers14215177). Here, we applied one of those models, i.e. tumor-organoids cultured as microtumors on murine organotypic hippocampal slice cultures (OHSCs), to additional brain tumor entities, namely a sample of an anaplastic ependymoma (AE) patient and an oligodendroglioma patient. Organoids were generated from fresh intra-operatively obtained tumor tissue and cultured for 2 weeks. OHSCs were prepared by slicing the brains of mice 5-8 days postpartum to sections with a thickness of 350 µm using a vibratome, and culturing them for 2 weeks as well. Subsequently, organoids were placed onto the OHSCs. The inovitro™ laboratory research system was used for TTFields administration at 200 kHz and 1.5 V/cm for 72 h. Microtumor growth was evaluated on fluorescence images. Viable organoids formed from the GBM, AE and oligodendroglioma sample and grew to microtumors when placed onto OHSCs. Application of TTFields at 200 kHz led to a significant decrease of microtumor size of the GBM and AE (both p<0.0001), but not the oligodendroglioma sample. This proof-of-principle investigation proved that the application of patient-derived organoids cultured on OHSCs is feasible to investigate the effects of TTFields on different kinds of brain tumors. To our knowledge, this is the first evaluation of TTFields efficacy on patient derived AE and oligodendroglioma tissue cultures. While TTFields at 200 kHz led to a decrease in the microtumor size of the AE sample, the non-responsiveness of the oligodendroglioma sample may be due to different inter-patient sensitivity to TTFields or a suboptimal TTFields frequency. Citation Format: Vera Nickl, Ellina Schulz, Ellaine Salvador, Laureen Trautmann, Leopold Diener, Almuth F. Kessler, Camelia M. Monoranu, Ralf-Ingo Ernestus, Mario Löhr, Carsten Hagemann. Evaluation of tumor treating fields (TTFields) effects at 200 kHz on a glioblastoma, an anaplastic ependymoma and an oligodendroglioma sample in a patient-derived ex vivo organoid model. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4573.

Measuring and assessing the effects of extremely low-frequency electromagnetic fields (ELF-EMF) on blood parameters and liver enzymes of personnel working in high voltage power stations in a petrochemical industry

IntroductionExposure to electric and magnetic fields (EMF) is a phenomenon that has always been present. In the last two decades, there have been numerous worries about the possible effects of extremely low-frequency (ELF) fields on human health. Consequently, this study aims to measure and evaluate the effect of ELF fields on blood parameters and liver enzymes of personnel working in high-voltage power stations in the petrochemical industry. MethodsThis cross-sectional, descriptive-analytical study was done in a petrochemical industry in southern Iran in 2021. Two groups of 50 people were selected to attain the research goals and classify jobs with the risk of exposure to extremely low-frequency electromagnetic fields (ELF-EMF) and the time spent on work. One group was exposed to ELF-EMF, and the other was regarded as the control group. Electromagnetic fields were measured using the HI-3604 device and the standard method of IEEE 1994-644. The workers' demographic data, blood parameters, and liver enzymes were also obtained from the workers’ medical records. The course of changes in each of the blood parameters and liver enzymes and demographic variables in the control and case groups were then examined. In the last stage, the effect of the electric field and magnetic field on the blood parameters and liver enzymes of the two control and subject groups was conducted using the multiple regression model. ResultsThe measured points in all stations are 200, and the minimum and maximum values of the magnetic field was 0.8 and 2019 mG, respectively. The minimum and maximum values of the electric field intensity was 0.003 and 215 V/m, respectively. The average results of the demographic variables and blood and liver indices in the control and case groups from 2018 to 2020 revealed that the average variables were not significantly different in the case and control groups (p-value>0.05). Moreover, workers' exposure to ELF-EMF was below the permissible limit. ConclusionBased on the results of the present study, ELF-EMF does not have any significant effects on demographic factors, blood parameters, and liver enzymes.

Simulating dielectric spectra: A demonstration of the direct electric field method and a new model for the nonlinear dielectric response.

We demonstrate a method to compute the dielectric spectra of fluids in molecular dynamics (MD) by directly applying electric fields to the simulation. We obtain spectra from MD simulations with low magnitude electric fields (≈0.01 V/Å) in agreement with spectra from the fluctuation-dissipation method for water and acetonitrile. We examine this method's trade-off between noise at low field magnitudes and the nonlinearity of the response at higher field magnitudes. We then apply the Booth equation to describe the nonlinear response of both fluids at low frequency (0.1GHz) and high field magnitude (up to 0.5 V/Å). We develop a model of the frequency-dependent nonlinear response by combining the Booth description of the static nonlinear dielectric response of fluids with the frequency-dependent linear dielectric response of the Debye model. We find good agreement between our model and the MD simulations of the nonlinear dielectric response for both acetonitrile and water.

Combined application of pulsed low-frequency electrostatic field and robotic mechanotherapy for damage to capsular ligamentous apparatus of the knee joint in children (Methodological recommendations, SAHI MSPC MRRSM MHD. 2022. - 19 p.).

Pathology of the knee joint in children is an urgent problem in pediatric traumatology, orthopedics and pediatrics. Features of the anatomical structure of the knee joint, its functioning, high static and dynamic loads determine the frequency of injuries of this localization (up to 25% among all injuries of the musculoskeletal system).

Interference Pattern Anomaly of an Acoustic Field Induced by Bottom Elasticity in Shallow Water

This paper reports the interference pattern of an acoustic field in the 100–300 Hz frequency band observed in a shallow water experiment. Assuming there is a conventional fluid sea bottom, the observed interference pattern is first demonstrated to potentially be abnormal, as a measured waveguide invariant of 1.03 corresponding to the 200–300 Hz frequency band could indicate that the bottom sound speed is relatively high, which is inconsistent with another observation from the interference pattern that the sound field is dominated by only one mode if the frequency is lower than 150 Hz. The numerical analysis shows that, owing to the high bottom sound speed, the third mode can still strongly interfere with the first mode at a frequency of 150 Hz, at least. Accordingly, a dual-layer sea bottom model consisting of a fluid sediment layer and an underlying half-space elastic substrate was proposed to interpret the observed anomaly. The results reveal that the acoustic leakage attenuation due to the elastic substrate plays a major role in the observed dominance of one mode in the sound field occurring below a frequency of 150 Hz. Therefore, the deep bottom’s elasticity may have a significant impact on the interference characteristics of low-frequency acoustic fields in shallow water under certain conditions.

Bistability of prefrontal states gates access to consciousness

Access of sensory information to consciousness has been linked to the ignition of content-specific representations in association cortices. How does ignition interact with intrinsic cortical state fluctuations to give rise to conscious perception? We addressed this question in the prefrontal cortex (PFC) by combining multi-electrode recordings with a binocular rivalry (BR) paradigm inducing spontaneously driven changes in the content of consciousness, inferred from the reflexive optokinetic nystagmus (OKN) pattern. We find that fluctuations between low-frequency (LF, 1-9Hz) and beta (∼20-40Hz) local field potentials (LFPs) reflect competition between spontaneous updates and stability of conscious contents, respectively. Both LF and beta events were locally modulated. The phase of the former locked differentially to the competing populations just before a spontaneous transition while the latter synchronized the neuronal ensemble coding the consciously perceived content. These results suggest that prefrontal state fluctuations gate conscious perception by mediating internal states that facilitate perceptual update and stability.

Research and Application of Low Frequency and High Amplitude Depressurization Technology in Yi 59 Block

Yi 59 block as the main block of Changchun, With the deepening of water injection development, Unstable water quality, measure, Influence of factors such as operation, increase in cumulative amount, Water injection pressure increased year by year, High pressure under injection problem increasingly significant, 19-year injection-production ratio drops to 1, Seriously restricting block development, Urgent governance. This article from the reservoir physical properties—source control—Start with daily management, the mechanism of reservoir blockage is analyzed, Preliminary demonstration of low frequency high amplitude depressurization injection enhancement technology, indoor evaluation, Field Application and Parameter Optimization, Effective management of under-injection wells, Achieved block smooth water injection, Great application prospect.

A Low-Frequency Unidirectional Underwater Acoustic Transducer

A unidirectional underwater acoustic transducer has the advantage of narrower beam width. In the low-frequency field, a single transducer is usually omnidirectional because its dimension is much smaller than the wavelength of the sound waves. Here, a low-frequency unidirectional underwater acoustic transducer, the Single-Sided Radiation Flextensional Transducer (SSR FT), which is driven by a stack with the longitudinal vibration, was designed by the finite-element method. The vibration mode of the transducer was first studied and analyzed. Then, an underwater harmonic response analysis of the transducer was conducted. We found that the second resonance, corresponding to the fourth vibration mode, could be unidirectional based on a specific s br, which is the ratio of r b (the radius of the tail mass) to l maj (the inner length of the semi-major axis of the radiation surface). Finally, the effect of s br on the vibration velocity and directivity of the SSR FT was investigated. We established that the vibration velocity amplitude and phase of the shell were different at the same vibration mode but at different s br, which resulted in different directivity.

Electric field induced negative capacitance in semiconducting polymer

Electric field dependent capacitance and dielectric loss in poly(3-hexylthiophene) are measured by precision capacitance bridge. Carrier mobility and density are estimated from fits to current–voltage and capacitance data. The capacitance varies largely at lower frequency, and it decreases at higher electric fields. The negative capacitance at low frequency and high field is due to the negative phase angle between the dipole field and the ac signal. The intrinsic carrier density is calculated from fits to the Mott–Schottky equation, and this is consistent with I–V data analysis. At higher frequency, the carriers do not follow the ac signal and their density drops; and the flatband potential increases mainly due to the build-in potentials within ordered and amorphous regions in the sample.

Phonon-driven intra-exciton Rabi oscillations in CsPbBr3 halide perovskites

Coupling electromagnetic radiation with matter, e.g., by resonant light fields in external optical cavities, is highly promising for tailoring the optoelectronic properties of functional materials on the nanoscale. Here, we demonstrate that even internal fields induced by coherent lattice motions can be used to control the transient excitonic optical response in CsPbBr3 halide perovskite crystals. Upon resonant photoexcitation, two-dimensional electronic spectroscopy reveals an excitonic peak structure oscillating persistently with a 100-fs period for up to ~2 ps which does not match the frequency of any phonon modes of the crystals. Only at later times, beyond 2 ps, two low-frequency phonons of the lead-bromide lattice dominate the dynamics. We rationalize these findings by an unusual exciton-phonon coupling inducing off-resonant 100-fs Rabi oscillations between 1s and 2p excitons driven by the low-frequency phonons. As such, prevailing models for the electron-phonon coupling in halide perovskites are insufficient to explain these results. We propose the coupling of characteristic low-frequency phonon fields to intra-excitonic transitions in halide perovskites as the key to control the anharmonic response of these materials in order to establish new routes for enhancing their optoelectronic properties.

The impact of persistent anomalous precipitation in Southwest China caused by low-frequency atmospheric disturbances in different latitudes and altitudes

Previous studies have pointed out that persistent abnormal precipitation is closely related to atmospheric low-frequency oscillation, and Southwest China can be affected by low-frequency oscillation in different latitudes and altitudes. Therefore, it is necessary to study the relationship between persistent abnormal precipitation in Southwest China and low-frequency oscillation. In this study, the characteristics of atmospheric low-frequency oscillation in different latitudes and altitudes affecting persistent extreme precipitation in Southwest China were discussed by synthetic analysis and Butterworth filtering with precipitation data from meteorological stations and NCEP/NCAR reanalysis data, and the configuration relationship of low-frequency systems in three-dimensional space was shown. The results showed the following: 1) in the low-frequency circulation field, the Ural Mountains, east of Lake Baikal, the Sea of Okhotsk (Japan), the Western Pacific subtropical high control area, the South China Sea, the Indian Peninsula, and the Bay of Bengal were the key areas affecting precipitation; 2) oscillation could better reflect the original circulation characteristics at all latitudes of each layer, and on a period of oscillation of 15–30 days, it will affect precipitation at all altitudes and latitudes; and 3) at the lower level, different low-frequency cyclones and anticyclones moved to the mid-latitude and converged in different forms in the precipitation area. In the middle layer, the low-frequency high-pressure and low-pressure centers in the middle and high latitudes moved southward, finally forming a circulation situation of the high west and low east. At the upper level, the rainy area was controlled by low-frequency anticyclones and divergence centers from different regions, forming a high-altitude divergence field. The results can provide a theoretical basis for forecasting the extended period of persistent heavy rain in Southwest China.

Theoretical modeling and analysis of a quasi-zero-stiffness vibration isolator equipped with extensible and axially magnetized negative stiffness modules

Quasi-zero-stiffness (QZS) isolation systems have demonstrated good performance in low-frequency vibration isolation fields. However, the existing QZS isolation systems with traditional negative stiffness elements cannot support high payloads under miniaturization and simplification. To give some beneficial insights into high loading capacity, optimized structure, and good vibration isolation performance, a novel axially magnetized negative stiffness module (MNSM) is proposed based on the concepts of modularity and expansibility. Concretely, an axially magnetized negative stiffness unit (MNSU) is designed as the fundamental building block of MNSM, and the proposed MNSM can be composed of different axially magnetized negative stiffness units (MNSUs) for diversified requirements. To effectively investigate the characteristics of the MNSU, a computationally high efficient equivalent surface current method is developed. As a result, two types of MNSUs with optimized parameters are achieved, and their design procedures are presented respectively. To verify the benefits of the MNSMs, the designed QZS isolator is theoretically modeled and solved with the average method and then verified through the Runge–Kutta method. Through analyzing the isolation systems with MNSMs under different nonlinearities and dynamic parameters, the results indicate that the proposed MNSMs can endow the QZS vibration isolator with a lower resonant frequency, a wider isolation frequency range, and a smaller transmissibility. Additionally, it is also demonstrated that there is an inverse relationship between the complexity of the MNSM structure and the sensitivity of the isolation system.

A Velocity Measurement Method Based on Charge Induction.

In this paper, based on the principle of charge induction, a new velocity measurement method is proposed. A moving target generates a low-frequency electric field, which can be induced with an electrode and detection frontend. Velocity measurements are achieved by placing two electrodes at a fixed distance to detect the characteristic times. Firstly, the electric field generated by the moving target is modeled, and the theoretical output of the detection frontend is obtained via a simulation of the target passing by a single electrode. Then, according to the theoretical output, the velocity measurement simulation results of double electrodes are given for various driving conditions, such as a single vehicle driving in a single lane, a single vehicle changing lanes, two vehicles driving close together, and a multiple-vehicle situation. Finally, the above driving conditions are experimentally verified in sunny weather, windy and rainy weather, and a night environment.

A bistable cholesteric liquid crystal film stabilized by a liquid-crystalline epoxy/thiol compound-based polymer.

Bistable cholesteric liquid crystals have promising application prospects in various fields, such as smart windows and displays. However, the long-term stability of two individual states is not easy to achieve, hindering their practical use. In this research, the bistable feature was enhanced by constructing a microsphere-type polymer with a liquid-crystalline epoxy/thiol monomer in negative dielectric anisotropic cholesteric liquid crystals. Spectroscopic and optical examinations revealed that either the transparent planar state or the opaque focal conic state can be maintained without the aid of an external field. Moreover, they can be switched to each other by applying a high- or low-frequency electric field. Further, factors such as the chemical structure of thiol compounds, curing temperature and curing time were investigated to explore their influences on the micro morphology of the polymer and thereby the electro-optical properties. In addition, the frequency-dependent driving scheme was analysed. Finally, bistable switching was demonstrated using an optimized sample. This energy-efficient bistable film shines light on future applications in smart windows, photonic paper and other electro-optical devices.

A low-frequency acoustic sensing scheme based on cladding mode of large-angle tilted fiber Bragg grating

A novel low frequency acoustic sensor based on the cladding mode of large-angle tilted fiber Bragg grating (TFBG) is proposed and verified in this work. It mainly uses the characteristic that the coupling mode of the core and cladding mode in TFBG is easy to change when the TFBG experiences micro-bend, which will finally causes a dramatic drift in the spectrum. By combining a large-angle TFBG with the designed polyethylene terephthalate (PET) transducer diaphragm and cavity structure, an effective low-frequency acoustic sensing system is obtained in this work. Under the action of applied acoustic wave, the transducer membrane will have periodic vibrations, which will makes the fixed TFBG dynamically bend, directly leading to a wavelength shift of the cladding mode spectrum. The experimental results show that the sensing system can achieve high-sensitivity acoustic detection in a frequency range of 45–220 Hz, and a maximum acoustic pressure sensitivity of 115.88 mV/Pa at 54 Hz. Moreover, the minimum detection sound pressure can achieve 539.2 μPa/Hz<sup>1/2</sup>@54 Hz. Therefore, the sensor has the advantages of high sensitivity, good repeatability, simple structure, easy processing, etc. It has a great development prospect in the low-frequency acoustic detection related application fields.

Reference Standard of Low-Frequency Electric Field Strength With Electrical Traceability

Reference Standard of Low-Frequency Electric Field Strength With Electrical Traceability

Диэлектрическо-спектроскопическая сепарация характеристик механизмов проводимости в нанкристаллическх пленках AgI

The study of the frequency dependence of the components of the complex permittivity of thin (100 nm) nanocrystal silver iodide (AgI) films revealed the presence of two different types of relaxation processes, sharply differing in their relaxation times: tau1<<tau2. It is established that the small relaxation time of tau1 is the time of formation of a stable configuration of the internal electric field when the external high-frequency sinusoidal electric field is shielded by a system of free conduction electrons. On the contrary, a long relaxation time of tau2 characterizes the process of shielding a low-frequency external field by a system of quasi-free silver ions. It is shown that the temperature dependence of the numerical value of tau1(T) has a thermal hysteresis with a loop, the position of the heating and cooling branches of which coincides with the temperature region of the forward and reverse phase transitions in the AgI film: semiconductor-superionic and superionic-semi-conductor. The results of calculating the parameters of dielectric spectra in the framework of Debye theory are presented, demonstrating good agreement with the parameters of the proposed electrical circuit of the film sample calculated by the complex impedance method