Low-frequency Field Research Articles

Rapid Ascent of Hollow Particles in Water Induced by an Electric Field

A novel method has been proposed to induce rapid upward movement of colloidal particles with a density lower than water by applying an electric field of several V/mm in water. This phenomenon, known as the Electrically Induced Rapid Sedimentation (ERS) effect, marks the first occurrence of ‘rapid upward movement of colloidal particles’ within the scope of this phenomenon. Focusing on hollow particles, an investigation of the ERS effect was conducted through transmittance measurement. The hollow particles in water showed a drastic increase in ascending velocity through the application of an electric field. The ascending velocity raised when increasing the electric field strength. Utilizing a quasi-DC electric field (an extremely low-frequency AC electric field), aggregate structures were captured for the first time.

Physical factors in medical rehabilitation of children with damage to the capsulal-ligating apparatus of the knee joint

Pathology of the knee joint in children is a pressing problem in pediatric traumatology, orthopedics and pediatrics. The frequency of injuries to the knee joint is determined by the complexity of its structure, biomechanical features with a high probability of overload. At the same time, intra-articular injuries in children and adolescents, accounting for up to 7% in the structure of inpatient pathology, are the cause of pronounced functional disorders of the lower limb and the risk of developing post-traumatic osteoarthritis.
 Currently, physical factors are widely used at various stages of medical rehabilitation of children with damage to the capsular-ligamentous apparatus of the knee joint. The conducted studies have established the effectiveness of using local air cryotherapy in the early postoperative period, characterized by a pronounced anti-edematous, analgesic effect. Early regression of pain and elimination of microcirculatory disorders in the area of injury as a result of a course of pulsed low-frequency magnetic therapy at various stages of medical rehabilitation of children with damage to the capsular-ligamentous apparatus of the knee joint have been recorded. The beneficial effect of a pulsed low-frequency electrostatic field on indicators of orthopedic status, and thermography indicators in the area of injury in children with knee joint injuries has been established. Data were obtained on more pronounced regression of pain, earlier restoration of range of motion in the damaged joint and relief of signs of post-traumatic synovitis with the complex use of a pulsed low-frequency electrostatic field and robotic mechanotherapy in children with damage to the capsular ligamentous apparatus of the knee joint. The obtained clinical and functional results are of great importance for injuries of the knee joint with the risk of contractures in the postoperative period.

Informativity of the method of correlation adaptometry for assessing the severity of the corrective effect of combined use therapeutic physical factors on the example of metabolic syndrome

BACKGROUND: Evaluation of the effectiveness of the use of therapeutic physical factors using the method of correlation adaptometry is based on the effect of increasing the number of severity of correlation dependencies between the parameters characterizing the functional state of the body under the action of a stressor.
 AIM: Evaluation of the effectiveness of the combined use of transcranial magnetotherapy and a pulsed low-frequency electrostatic field in patients with metabolic syndrome using the method of correlation adaptometry.
 MATERIALS AND METHODS: The study involved 100 patients with a diagnosis of metabolic syndrome established in accordance with clinical guidelines. All patients were divided into four groups of 25 by simple fixed randomization. Patients in the control group received a placebo effect (imitation of physiotherapeutic effects with the device turned off) for 10 days of observation, in comparison group 1 ― exposure to a low-frequency electrostatic field, in comparison group 2 ― transcranial magnetotherapy with a traveling magnetic field, in the main group ― exposure to a pulsed electrostatic field in combination with transcranial magnetotherapy. The objectification of the effects of physiotherapy (evaluation of functional, biochemical and hormonal parameters) was based on a two-stage examination (before and after a course of treatment).
 RESULTS: Correlation adaptometry was based on the results of correlation analysis using a correlation matrix of variables characterizing the condition of patients after course correction. For each of the four groups of patients, 28 correlation coefficients were determined. For each group, 378 correlation coefficients were calculated, presented as the weight of the correlation graph. Additionally, the indicator of the average adaptive correlation was calculated. It is shown that the use of therapeutic physical factors is accompanied by a decrease in the weight of the correlation graph, which indicates the severity of the clinical effect due to the sanogenetic action of physiofactors. The most pronounced decrease was noted in the group of combined physiotherapy. Correlation analysis between the parameters of the average adaptive correlation and the integral coefficient of therapy efficiency showed that there is a strong, negative significant relationship between the HOMA insulin resistance index and the Quetelet index, chosen as the most informative variables.
 CONCLUSION: It is concluded that the method of correlation adaptometry is highly informative in assessing the effectiveness of using a pulsed low-frequency electrostatic field, transcranial magnetotherapy and their combined effects in patients with metabolic syndrome. A decrease in the indicator of the average adaptive correlation indicates an increase in the functional reserves of the system, the patterns of which are changes in certain estimated parameters that are not related to each other.

Comparison of measurement methods of room sound energy for sound insulation performance evaluation at low frequencies

In the field measurement of acoustic performances, such as sound insulation and floor impact sound insulation, sound pressure level is usually measured to find the sound energy in a closed space. However, the sound pressure level at low frequencies such as the 63 Hz band depends on the measurement position due to the influence of the room eigenmodes, which leads to large uncertainties of the measured average sound pressure levels in rooms. In this study, several measurement methods of sound energy were applied to the low-frequency sound field of a mock-up room that simulates a source room in an RC apartment. Along with the standard sound pressure level measurement, the low-frequency procedure according to ISO 16283 series and acoustic energy density measurement using the combined particle velocity-pressure sensor were conducted, and their accuracies were evaluated based on the average sound pressure obtained by the grid-point measurement over the entire room.

High-order Bragg forward scattering and frequency shift of low-frequency underwater acoustic field by moving rough sea surface

Acoustic scattering modulation caused by an undulating sea surface on the space–time dimension seriously affects underwater detection and target recognition. Herein, underwater acoustic scattering modulation from a moving rough sea surface is studied based on integral equation and parabolic equation. And with the principles of grating and constructive interference, the mechanism of this acoustic scattering modulation is explained. The periodicity of the interference of moving rough sea surface will lead to the interference of the scattering field at a series of discrete angles, which will form comb-like and frequency-shift characteristics on the intensity and the frequency spectrum of the acoustic scattering field, respectively, which is a high-order Bragg scattering phenomenon. Unlike the conventional Doppler effect, the frequency shifts of the Bragg scattering phenomenon are multiples of the undulating sea surface frequency and are independent of the incident sound wave frequency. Therefore, even if a low-frequency underwater acoustic field is incident, it will produce obvious frequency shifts. Moreover, under the action of ideal sinusoidal waves, swells, fully grown wind waves, unsteady wind waves, or mixed waves, different moving rough sea surfaces create different acoustic scattering processes and possess different frequency shift characteristics. For the swell wave, which tends to be a single harmonic wave, the moving rough sea surface produces more obvious high-order scattering and frequency shifts. The same phenomena are observed on the sea surface under fully grown wind waves, however, the frequency shift slightly offsets the multiple peak frequencies of the wind wave spectrum. Comparing with the swell and fully-grown wind waves, the acoustic scattering and frequency shift are not obvious for the sea surface under unsteady wind waves.

Effectiveness of Physiotherapy Methods in Medical Rehabilitation of Patients with Shoulder and Scapular Pain Syndrome in a Sanatorium: a Randomized Clinical Study

INTRODUCTION. The high prevalence of shoulder pain syndrome (SPS) determines the relevance of the development of new comprehensive methods of rehabilitation of this category of patients.
 AIM. To evaluate the clinical effectiveness of shockwave therapy (SWT) and pulsed low-frequency electrostatic field (PLEF) in patients with SPS undergoing medical rehabilitation in a sanatorium-resort organization in comparison with traditional health resort treatment.
 MATERIALS AND METHODS. The comparative analysis of medical rehabilitation efficiency was carried out in 90 patients with SPS aged 31–68 years undergoing medical rehabilitation in the health resort complex “Vulan” — a clinical branch of National Medical Research Center for Rehabilitation and Balneology. All patients were divided into 3 groups of 30 persons each by the method of simple randomization. Group 1 patients (control) received traditional health resort treatment, including ozokeritotherapy, physical exercise therapy, electrotherapy with sinusoidal modulated currents and manual massage. Patients of the second group (comparison) received against the background of the above complex 3 SWT procedures on the shoulder joint once a week. Group 3 patients (main group) received, in addition to traditional treatments, 3 SWT and 8 field PLEF treatments administered every other day. The effectiveness of rehabilitation was evaluated according to the severity of pain syndrome (VAS scale), Swanson’s scale for the shoulder. Movement volume before and after rehabilitation was measured with an orthopedic angle gauge. Microcirculation state was assessed by laser Doppler flowmetry (LDF). Leukert scale was used to assess the state of well-being. The results of the study were assessed 18 days after the beginning of rehabil itation measures.
 RESULTS AND DISCUSSION. Patients who additionally received SWT and PLEF against the background of traditional health resort treatment noted a significant reduction in the severity of pain syndrome, while in the main group pain regression was noted earlier (on day 4–5), whereas in the comparison group the same results were obtained by the day 14th . In the control group, patients noted significant changes on the VAS scale only by the end of the rehabilitation course. On the Swanson scale, the most significant positive results were also obtained by the patients in the main group: the pain decreased on average 2.6-fold, the volume of active movements in the shoulder joint increased 2.7-fold, and activity in everyday life 1.9-fold. Statistical differences in the Swanson Scale scores with the comparison group were obtained with regard to pain syndrome and volume of active movements. When comparing with the control group, reliable differences were revealed in all Swanson’s scale indicators in both the main group and the comparison group. When studying the dynamics of microcirculation according to LDF data, it was noted that reliable changes in the main indices of the LDF-gram were revealed only in the groups that received innovative physical therapy interventions.
 CONCLUSION. Thus, the inclusion of modern physiotherapeutic techniques of SWT and PLEF into the program of health resort treatment of patients with SPS allows to increase significantly the efficiency of medical rehabilitation carried out in the sanatorium organization.

On the adiabatic approximation for the laser-dressed atom

The adiabatic approximation is analyzed for non-perturbative interaction of an atomic system with an intense low-frequency laser field. We find that the well-known adiabatic ansatz, which consists in using the DC-based Green’s and wave functions for an atom in the instantaneous AC field to calculate transition matrix elements, exceeds the level of accuracy of the adiabatic approximation and requires further theoretical revision. It is shown that the non-analyticity in the field strength of the DC-based Green’s and wave functions leads to violation of the adiabaticity constrains and the appearance of rapidly oscillating components in the transition matrix elements. We suggest an improved adiabatic approach utilizing the analytical parts in the DC-based Green’s and wave functions. We illustrate our revised adiabatic approach for analysis of atomic polarizability in two-component laser field with an intense infrared and perturbative extreme ultraviolet components within the zero-range potential model.

Mass Spectrometric Identification of Metabolites after Magnetic-Pulse Treatment of Infected Pyrus communis L. Microplants

The major goal of this study is to create a venue for further work on the effect of pulsed magnetic fields on plant metabolism. It deals with metabolite synthesis in the aforementioned conditions in microplants of Pyrus communis L. So far, there have been glimpses into the governing factors of plant biochemistry in vivo, and low-frequency pulsed magnestatic fields have been shown to induce additional electric currents in plant tissues, thus perturbing the value of cell membrane potential and causing the biosynthesis of new metabolites. In this study, sixty-seven metabolites synthesized in microplants within 3–72 h after treatment were identified and annotated. In total, thirty-one metabolites were produced. Magnetic-pulse treatment caused an 8.75-fold increase in the concentration of chlorogenic acid (RT = 8.33 ± 0.0197 min) in tissues and the perturbation of phenolic composition. Aucubin, which has antiviral and antistress biological activity, was identified as well. This study sheds light on the effect of magnetic fields on the biochemistry of low-molecular-weight metabolites of pear plants in vitro, thus providing in-depth metabolite analysis under optimized synthetic conditions. This study utilized high-resolution gas chromatography-mass spectrometry, metabolomics methods, stochastic dynamics mass spectrometry, quantum chemistry, and chemometrics, respectively. Stochastic dynamics uses the relationships between measurands and molecular structures of silylated carbohydrates, showing virtually identical mass spectra and comparable chemometrics parameters.

Information content and temporal structure of face selective local field potentials frequency bands in IT cortex.

Sensory stimulation triggers synchronized bioelectrical activity in the brain across various frequencies. This study delves into network-level activities, specifically focusing on local field potentials as a neural signature of visual category representation. Specifically, we studied the role of different local field potential frequency oscillation bands in visual stimulus category representation by presenting images of faces and objects to three monkeys while recording local field potential from inferior temporal cortex. We found category selective local field potential responses mainly for animate, but not inanimate, objects. Notably, face-selective local field potential responses were evident across all tested frequency bands, manifesting in both enhanced (above mean baseline activity) and suppressed (below mean baseline activity) local field potential powers. We observed four different local field potential response profiles based on frequency bands and face selective excitatory and suppressive responses. Low-frequency local field potential bands (1-30Hz) were more prodominstaly suppressed by face stimulation than the high-frequency (30-170Hz) local field potential bands. Furthermore, the low-frequency local field potentials conveyed less face category informtion than the high-frequency local field potential in both enhansive and suppressive conditions. Furthermore, we observed a negative correlation between face/object d-prime values in all the tested local field potential frequency bands and the anterior-posterior position of the recording sites. In addition, the power of low-frequency local field potential systematically declined across inferior temporal anterior-posterior positions, whereas high-frequency local field potential did not exhibit such a pattern. In general, for most of the above-mentioned findings somewhat similar results were observed for body, but not, other stimulus categories. The observed findings suggest that a balance of face selective excitation and inhibition across time and cortical space shape face category selectivity in inferior temporal cortex.

Study on VLF Electric Field Anomalies Caused by Seismic Activity on the Western Coast of the Pacific Rim

In order to explore the correlation between earthquakes and ionospheric very low-frequency (VLF) electric field disturbances, this article uses VLF data observed by the China Earthquake Electromagnetic Satellite (CSES) to analyze very low-frequency signals before and after earthquakes from January 2019 to March 2023 in terms of the amplitude and signal-to-noise ratio of electric field power spectrum disturbances. Taking 73 earthquakes with a magnitude of 6.0 or higher occurring in the Circum-Pacific seismic belt as an example, comprehensive research on the VLF electric field disturbance phenomenon caused by strong earthquakes is conducted, considering both the earthquake location and source mechanism. The research results indicate the following: (1) there is a strong correlation between earthquakes with a magnitude of 6.0 or above and abnormal disturbances in the VLF electric field, which often occur within 20 days before the earthquake and within 800 km from the epicenter. (2) From the perspective of earthquake-prone areas, the VLF electric field anomalies observed before earthquakes in the Ryukyu Islands of the Taiwan region exhibit small and concentrated field fluctuations, while the Taiwan Philippines region exhibits larger field fluctuations and more dispersed fluctuations. The discovery of this correlation between seismic ionospheric phenomena and seismic activity provides a new and effective approach to earthquake monitoring, which can be used for earthquake prediction, early warning, and disaster prevention and reduction work.

Role of nuclear dynamics in high harmonic generation redshift of H2 +

The detailed spectral and temporal structures of high-order harmonic generation (HHG) have provided us with a wealth of information about the highly nonlinear response of atoms, molecules, and electronic structures to intense low-frequency laser fields. In this study, we aim to investigate the underlying physics behind the molecular high harmonic spectra redshift beyond the Born–Oppenheimer approximation for and its isotopes with numerical simulations of the time-dependent Schrödinger equation. One widely recognized phenomenon is the occurrence of a spectral redshift at the trailing edge of a laser pulse. However, our findings reveal that even when driven by a sinusoidal laser pulse without a falling edge, the HHG redshift appears and highlights that the observed spectral redshift is not solely due to the declining intensity of the laser pulse. We show that it is a direct consequence of the decrease in ionization energy during the transition from recombination time to ionization time within wave packets at short internuclear distances. Interestingly, our results also demonstrate how a sinusoidal laser pulse without a rising part can disrupt the standard picture of redshift in literatures in the past. This finding suggests that there are additional factors influencing the redshift mechanism beyond just the trailing edge of the laser pulse. These phenomena are elucidated through the analysis of the dynamics of the nuclear wave packet. Our study provides valuable insights into the complex dynamics of HHG processes and sheds light on how different laser pulse characteristics can influence spectral redshifts and harmonic generation in molecular systems.

Low-Frequency Oscillations for Nonlocal Neuronal Coupling in Shared Intentionality Before and After Birth: Toward the Origin of Perception

The theoretical study observes literature to understand whether or not low-frequency oscillations can simultaneously alter the excitability of neurons from peripheral nervous subsystems in different individuals to provide Shared Intentionality in recipients (e.g., fetuses and newborns) and what are the attributes of ecological context for Shared Intentionality. To grasp the perception of objects during environmental learning at the onset of cognition, a fetus needs exogenous factors that could stimulate her nervous system to choose the relevant sensory stimulus. Low-frequency brain oscillations can cause the nonlocal coupling of neurons in peripheral and central nervous subsystems that provide subliminal perception. An external low-frequency oscillator and the proximity of individuals can stimulate the coordination of their heart rates and modulate neuronal excitability. External low-frequency oscillations can increase the cognitive performance of the subjects. The characteristics of this pulsed low-frequency field are oscillations with 400 and 700 nm wavelengths alternately with the pulsed frequency ranging from 1 to 1.6 Hz. This theoretical work contributes to knowledge about nonlocal neuronal coupling in different organisms that can appear due to low-frequency oscillations. The significance of the article is that it explains the neurophysiological processes occurring during Shared Intentionality - one of the central issues in understanding the cognitive development of young children, as the conventional view in cognitive sciences argues. The article's impact is a proposal of the universal mechanism of nonlocal neuronal coupling in shaping the embryonal nervous system in animals of all species, which opens new directions for research on the origin of perception of objects.

Low-frequency electric fields at smartphone surface

Mobile phones, tablets, and other devices with capacitive touchscreens are ubiquitous in modern society. Consequently, the battery health of such devices along with the potential public health impacts of their typical use is of high importance. Here, we investigate the AC electric field present near the touchscreen surface during device charging. Using a Trifield TF2 meter for magnitude and a Faraday pickup coil for frequency, we study the AC electric field at the surface of an Apple iPhone 8 mobile phone in the 0–200 kHz range, well below the uplink/downlink bands used for cellular signals. We find the addition of the frequency content throughout this range and with integrated magnitude of the order of 500 V/m rms under certain phone charging conditions. Our findings suggest that the field is being generated by the lithium-ion battery. We note also that these AC electric fields are not present when the device is charged from a portable power bank.

A Hyperflexible Electrode Array for Long-Term Recording and Decoding of Intraspinal Neuronal Activity.

Neural interfaces for stable access to the spinal cord (SC) electrical activity can benefit patients with motor dysfunctions. Invasive high-density electrodes can directly extract signals from SC neuronal populations that can be used for the facilitation, adjustment, and reconstruction of motor actions. However, developing neural interfaces that can achieve high channel counts and long-term intraspinal recording remains technically challenging. Here, a biocompatible SC hyperflexible electrode array (SHEA) with an ultrathin structure that minimizes mechanical mismatch between the interface and SC tissue and enables stable single-unit recording for more than 2 months in mice is demonstrated. These results show that SHEA maintains stable impedance, signal-to-noise ratio, single-unit yield, and spike amplitude after implantation into mouse SC. Gait analysis and histology show that SHEA implantation induces negligible behavioral effects and Inflammation. Additionally, multi-unit signals recorded from the SC ventral horn can predict the mouse's movement trajectory with a high decoding coefficient of up to 0.95. Moreover, during step cycles, it is found that the neural trajectory of spikes and low-frequency local field potential (LFP) signal exhibits periodic geometry patterns. Thus, SHEA can offer an efficient and reliable SC neural interface for monitoring and potentially modulating SC neuronal activity associated with motor dysfunctions.

GNSS blasting vibration monitoring and feature recognition method

Aiming at the problems of the current blasting vibration monitoring, such as unstable low-frequency performance, vulnerability to environmental interference, complex operation, and easily damaged, a new blasting vibration monitoring and feature recognition method of complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and multiscale permutation entropy (MPE) and singular spectrum analysis (SSA) is proposed based on global navigation satellite system (GNSS). Initially, a new method of GNSS blasting vibration monitoring is proposed according to the blasting environment and blasting characteristics, it can provide a new reference for GNSS technology to be used in blasting vibration monitoring. Then, signal simulation proved that the proposed feature recognition method can effectively remove the low-frequency and high-frequency background noise as well as trend items of blasting vibration signals and accurately extract the dominant frequency of vibration compared with the traditional processing methods. Finally, the proposed method is demonstrated by factory open blasting and tunnel excavation blasting compared with the monitoring results of the conventional blasting recorder, it can accurately recognize the characteristics of blasting initiation time, particle peak velocity (PPV), initiation period, and dominant frequency of vibration. The RMSE of PPVs is 0.086, and other errors are within 5%, which is highly consistent with the monitoring results of blasting recorder. The GNSS blasting vibration monitoring and feature recognition method can improve the low-frequency stability, field adaptability, simple operation, and information richness of blasting monitoring, which can provide a new approach for blasting monitoring; it can also be an important supplement to existing blasting monitoring methods.

An aeroengine fault diagnosis method using high-frequency acoustic coupling with rotating blade flow field

Utilizing high-frequency sound waves for aeroengine structure diagnosis has been established in previous works. However, exploring its potential in analyzing rotating blade flow fields remains an open area of research. In this study, we propose a non-invasive fault diagnosis method that couples high-frequency sound waves with rotating blade flow fields, performing mode detection of the coupled frequency. As a widely used noise detection technique, acoustic mode detection enables the extraction of spatial information from noise, providing essential insights for noise reduction design. Essentially, the flow-sound coupling arises from nonlinear interactions, wherein the characteristic low-frequency periodic flow is excited by the high-frequencyexternal sound source, generating new coupled acoustic sources that radiate and propagate inside the duct. Mode detection aids in understanding the location and spatial phase information of the coupled acoustic sources. Furthermore, through both simulations and experiments, we have established the connection between fault information and mode spectrum. Finally, we endeavor to employ a machine learning approach to build a fault diagnosis model. In summary, this method ingeniously superimposes low-frequency periodic flow field information onto high-frequency sound waves, achieving high-precision diagnosis of the rotating blade flow field.

Pre-Earthquake Ionospheric Anomalies of the Wenchuan Earthquake Studied with DEMETER Satellite

The pre-earthquake ionospheric anomalies in Wenchuan, China (21°-41°N, 93°-113°E) are studied and analyzed using the summer nighttime data from 2005 to 2008 measured by DEMETER (Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions) satellite detectors ICE (Internet Communications Engine), IAP (In Application Programming), and ISL (Interior Switching Link). In this paper, we take the 12 May 2008 Wenchuan earthquake as an example, use the spatial gridding method to construct the background field over the epicenter, analyze the background characteristics of very low frequency (VLF) electric field components, low-energy particle parameters, and plasma parameters, and define the perturbation intensity index of each parameter before the earthquake to extract each parameter anomaly in both space and time dimensions. The results show that the background values of some ionospheric parameters in the Wenchuan area are related to spatial distribution. Moreover, anomalous enhancement of low-frequency electric field power spectral density, H+ concentration, He+ concentration and ion concentration with different intensities and anomalous weakening of ion temperature were extracted in the fifteen days before the Wenchuan earthquake. After filtering the data to exclude external interference, such as solar activity, this paper concludes that there is some connection between these anomalies and the Wenchuan earthquake.

Dielectric behaviour and dipole moment of binary mixtures containing certain amides in benzene

Certain polar amides(v) are dissolved in benzene, a nonpolar solvent(u) to prepare binary mixtures with different composition of the amides like acetanilide, N-N-dimethyl acetamide, N-methyl acetamide, acetamide and formamide. Static relative permittivity ɛ0uv , high frequency permittivity ɛ ∞uv for different weight fraction of polar solute at 30°C are determined. The dielectric behaviour of binary mixtures are investigated under electric field of low frequency by using the Debye model for polar liquids. Static dipole moment µs , dipole moment µv from conductivity measurements and µ t from bond angle and bond moment measurements are computed. The dipole moments are consequence of attractive interaction between the adjacent molecules in binary mixture due to variation of electron densities. Hydrogen bonding, associated charge distribution among the constituent molecules, changes in bond angle values are some of the factors that give rise to dipole moment of binary mixtures. Nearly equal and close values of µs , µv and µt proves the correctness of dielectric behaviour studies of amides- benzene binary mixtures.

Numerical simulation of gas production from Class III hydrate reservoirs using low-frequency electric heating-assisted depressurization with horizontal wells

The global clean energy shortage has become a significant concern along with environmental pollution caused by the burning of conventional fuels. Natural gas hydrates are considered to be a potential source of clean energy with vast resources widely distributed in permafrost and marine sediments. In order to improve the gas production efficiency from Class III hydrate reservoirs, an innovative production method using low-frequency electric heating-assisted depressurization with the dual-horizontal well mode is first proposed. This method takes advantage of the in-situ heat generated within the hydrate layer through a low-frequency electric field and the wide range of fluid flow and uniform heating of horizontal wells. To better understand the production mechanisms of the proposed method and evaluate its feasibility for increasing gas production, its production performance is analyzed in this work using numerical simulations. Based on the geological data of the Shenhu Area in the South China Sea, a numerical simulation model is first established. Then, the gas production and energy recovery performance are studied. Finally, the influence of production parameters on production performance is analyzed. The results show that additional heat input at the early stage of production can have a synergistic effect with depressurization in the gradient decreasing voltage heating mode, thus resulting in better production performance compared to the gradient increasing voltage and constant voltage modes. The maximum energy efficiency ratio can reach 17.65, which implies that the energy utilization efficiency of the proposed method has great potential for hydrate recovery. Horizontal wells have a larger wellbore contact area with the hydrate reservoir compared to vertical wells; therefore, they exhibit an expanded range of depressurization and hydrate dissociation. When the horizontal wells are positioned in the upper part of the hydrate layer, the negative impact caused by gravity can be reduced. Cumulative gas production increases with the initial voltage, but the energy efficiency ratio decreases, highlighting the need for optimizing the initial voltage. The proposed method and the findings of this work provide a useful reference for the efficient development of gas hydrate reservoirs.

Occupational exposure to electromagnetic fields from dental devices: A descriptive study

Abstract
 
 Objective: Electromagnetic Field sources which are widely used as part of the operating mechanism occupational exposure occurs with the electricity is generated, distributed or usage in the everyday environment. We aimed to obtain the Extremely Low Frequency-Magnetic Field exposure profile for dental health workers from electrical devices used in dentistry. 
 Methods: Measurements were performed while appliances under working conditions, 10 cm distance with the device for 6 minutes and for 7 days. The highest measured value in every 10 second was recorded. The mean ± SD of minimum and maximum Extremely Low Frequency-Magnetic Field for high-speed dental handpiece with LED, low-speed dental handpiece, model-trimming machine, automatic boil-out unit, steam machine, vacuum device, and polishing machine were recorded in milliGauss. 
 Results: The values which obtains from model-trimming machine and polishing machine were remarkable (809.17 ± 37.70 / 975.00 ± 10.27, 649.33 ± 201.37 / 1367.00 ± 32.17, respectively). Conclusion: The results show that periodic Electromagnetic Field exposure measurements should be conducted to obtain more detailed information about workplace exposures and sources.
 
 Keywords: Health, electromagnetic field, extremely low-frequency field, exposure, occupational