Effect of different modalities of transcranial magnetic stimulation on Parkinson's patients cognitive impairment and long-term effectiveness: a systematic review and network meta-analysis

Objective

This study used network Meta-analysis to compare the effects of different transcranial magnetic stimulation (TMS) modalities on the effectiveness and long-term validity of improving cognitive function in Parkinson's patients.

Methods

Computer searches of the Cochrane Library, PubMed, Web of Science, Embass, CNKI and Wanfang Data were conducted to collect randomized controlled clinical studies on TMS to improve cognitive function in Parkinson's patients published from the time of library construction to December 2023.

Results

A total of 22 studies and 1,473 patients were included, comprising 5 interventions: high frequency repetitive transcranial magnetic stimulation (HF-rTMS), low frequency repetitive transcranial magnetic stimulation (LF-rTMS), intermittent theta burst stimulation (iTBS), sham stimulation and conventional rehabilitation therapy (CRT). Network Meta-analysis showed that the ranking results of different TMS intervention modalities in terms of MoCA scores were: HF-rTMS > LF-rTMS > iTBS > sham > CRT, the ranking results of different TMS intervention modalities in terms of MMSE scores were: HF-rTMS > LF-rTMS > sham > CRT. The effect of TMS on improving Parkinsonian cognitive function lasted for 1 month compared to the no-stimulation group.

Conclusion

TMS has some long-term sustained effects on improving cognitive function in Parkinson's patients. HF-rTMS is more effective in improving cognitive function in Parkinson's patients.Systematic review registration: https://www.crd.york.ac.uk/PROSPERO, identifier: CRD42023463958.

Regulation Dipole Moments of N-Doped Graphene Coordinated with FePc Toward Highly Efficient Microwave Absorption Performance in C Band

The development of composites with highly efficient microwave absorption (MA) performance deeply depends on polarization loss, which can be induced by charge redistribution. Considering the fact that polarization centers can be easily obtained in graphene, herein, iron phthalocyanine (FePc) is used as polarization site to coordinate with nitrogen-doped graphene (FePc/N-rGO) to optimize MA performance comprehensively. The factors influencing MA properties focus on the interaction between FePc and N-rGO, and the change of dipole moments. The density functional theory (DFT) results demonstrated that FePc has strong interaction with N defect sites in graphene. The charge loss for FePc and charge accumulation for N-rGO occurred, leading to great increase of dipole moment, and the increased dipole moment can be acted as a descriptor to evaluate the enhanced polarization loss. Due to high charge redistribution capacity of N defect sites and FePc polarization centers, the FePc/N-rGO showed excellent MA properties in C band, and the minimum reflection loss value can reach -49.3 dB at 5.4 GHz with thickness of 3.8 mm. In addition, the fabric loaded with FePc/N-rGO showed good heat dissipation property. This work opens the door to the development of MA performance bound to polarization site with dipole moment.

NaxSb Alloy-Based Low-Frequency Mechanical Energy Harvesters for Virtual Taste Sensations

Batteries can be activated by external mechanical force and generate current, enabling a smart class of electrochemical-mechanical strain energy harvesters therefrom. Here, we have developed a NaxSb alloy-based harvester that is able to electrochemically convert low-frequency bending or pressing mechanical energy into electrical energy. The device is designed as a flexible symmetric cell incorporating two sodiated antimony nanoflake electrodes, whose peak power and energy output are more than twice those of other sodium-alloyed electrochemical-mechanical strain energy harvesters reported. We demonstrate that the open-circuit voltage of the device is an asymptotic function of the curvature radius in the bending mode and a linear function of pressure in the pressing mode. Taking advantage of the tunability of voltage, we present a new technology that simulates various tastes by releasing low-voltage electrical signals from the harvester. This technology can not only help people with impaired taste but also be integrated into a virtual reality system to create immersive taste experiences.

A Low-Cost, Tabletop LOD-EPR System for Nondestructive Quantification of Iron Oxide Nanoparticles in Tissues

Iron oxide nanoparticles (IONPs) have wide utility in applications from drug delivery to the rewarming of cryopreserved tissues. Due to the complex behavior of IONPs (e.g., uneven particle distribution and aggregation), further developments and clinical translation can be accelerated by having access to a noninvasive method for tissue IONP quantification. Currently, there is no low-cost method to nondestructively track IONPs in tissues across a wide range of concentrations. This work describes the performance of a low-cost, tabletop, longitudinally detected electron paramagnetic resonance (LOD-EPR) system to address this issue in the field of cryopreservation, which utilizes IONPs for rewarming of rat kidneys. A low-cost LOD-EPR system is realized via simultaneous transmit and receive using MHz continuous-wave transverse excitation with kHz modulation, which is longitudinally detected at the modulation frequency to provide both geometric and frequency isolation. The accuracy of LOD-EPR for IONP quantification is compared with NMR relaxometry. Solution measurements show excellent linearity (R2 > 0.99) versus Fe concentration for both measurements on EMG308 (a commercial nanoparticle), silica-coated EMG308, and PEG-coated EMG308 in water. The LOD-EPR signal intensity and NMR longitudinal relaxation rate constant (R1) of water are affected by particle coating, solution viscosity, and particle aggregation. R1 remains linear but with a reduced slope when in cryoprotective agent (CPA) solution, whereas the LOD-EPR signal is relatively insensitive to this. R1 does not correlate well with Fe concentration in rat kidney sections (R2 = 0.3487), while LOD-EPR does (R2 = 0.8276), with a linear regression closely matching that observed in solution and CPA.

Boosting Conductive Loss and Magnetic Coupling Based on "Size Modulation Engineering" toward Lower-Frequency Microwave Absorption

The rational design of absorber size is a promising strategy for obtaining excellent electromagnetic wave (EMW) absorption performance. However, achieving controllable tuning of the material size through simple methods is challenging and the associated EMW attenuation mechanisms are still unclear. In this study, the sizes of metal-organic frameworks (MOFs) are successfully tailored by changing the growth time and the molar ratio of iron (Fe)/organic ligands. The lateral and vertical lengths of MOFs vary in the range of 200 nm to 2 µm and 100 nm to 1 µm, respectively. Both experiments and simulations confirm that the decrease of MOF size favors the formation of more conductive networks, which is beneficial for improving the conductivity loss. Meanwhile, the micromagnetic simulation reveals that the magnetic coupling can be effectively enhanced by the decrease of MOF size, which is conducive to the improvement of magnetic loss, especially in low-frequency range. The reflection loss of Fe-based MOFs with optimized size reaches -46.4 dB at 6.2 GHz with an effective absorption bandwidth of 3.1 GHz. This work illustrates the important role of size effect in EMW dissipation and provides an effective strategy for enhancing the low-frequency EMW absorption performance.

Biological effects of electromagnetic fields on insects: a systematic review and meta-analysis

Worldwide, insects are declining at an alarming rate. Among other causes, the use of pesticides and modern agricultural practices play a major role in this. Cumulative effects of multiple low-dose toxins and the distribution of toxicants in nature have only started to be investigated in a methodical way. Existing research indicates another factor of anthropogenic origin that could have subtle harmful effects: the increasingly frequent use of electromagnetic fields (EMF) from man-made technologies. This systematic review summarizes the results of studies investigating the toxicity of electromagnetic fields in insects. The main objective of this review is to weigh the evidence regarding detrimental effects on insects from the increasing technological infrastructure, with a particular focus on power lines and the cellular network. The next generation of mobile communication technologies, 5G, is being deployed - without having been tested in respect of potential toxic effects. With humanity's quest for pervasiveness of technology, even modest effects of electromagnetic fields on organisms could eventually reach a saturation level that can no longer be ignored. An overview of reported effects and biological mechanisms of exposure to electromagnetic fields, which addresses new findings in cell biology, is included. Biological effects of non-thermal EMF on insects are clearly proven in the laboratory, but only partly in the field, thus the wider ecological implications are still unknown. There is a need for more field studies, but extrapolating from the laboratory, as is common practice in ecotoxicology, already warrants increasing the threat level of environmental EMF impact on insects.

Overcoming Periodic Stripe Noise in Infrared Linear Array Images: The Fourier-Assisted Correlative Denoising Method

Infrared linear array detectors frequently experience vertical, low-frequency, and periodic stripe noise during imaging, stemming from electro-mechanical interference. Unlike conventional periodic disturbances, this interference showcases long periodicities and is uniquely columnar in orientation. Its presence, especially within the low-frequency domain, renders conventional filtering techniques ineffective and, at times, detrimental to image quality. Addressing this challenge, we introduce Fourier-Assisted Correlative Denoising (FACD), a correlation-centric denoising approach tailored for such unique interference patterns. This mechanism begins with the capture of a pure background image, inclusive of periodic noise, during the non-uniform correction phase of the infrared detector. Leveraging the noise's frequency domain attributes, we extract a one-dimensional single-cycle noise signal. The infrared image is subsequently segmented into parts, and using the detected noise periodicity, the one-dimensional signals for each segment are computed. By leveraging the correlation between these signals and the benchmark one-dimensional noise pattern, we ascertain the noise profile within each segment. This profile is then employed for spatial domain denoising across the entire image frame. Empirical assessments confirm that the FACD outperforms contemporary denoising techniques by augmenting the peak signal-to-noise ratio by approximately 2.5 dB, underscoring its superior robustness. Furthermore, in light of its specificity to this noise model, FACD rapidly denoises high-resolution real infrared linear array scans, thus meeting the stringent real-time and resolution imperatives of advanced infrared linear array scanning apparatuses.

Sphygmomanometer Dynamic Pressure Measurement Using a Condenser Microphone

There is a worldwide need to improve blood pressure (BP) measurement error in order to correctly diagnose hypertension. Cardiovascular diseases cause 17.9 million deaths annually and are a substantial monetary strain on healthcare. The current measurement uncertainty of 3 mmHg should be improved upon. Dynamic pressure measurement standards are lacking or non-existing. In this study we propose a novel method of measuring air pressure inside the sphygmomanometer tubing during BP measurement using a condenser microphone. We designed, built, and tested a system that uses a radiofrequency (RF) modulation method to convert changes in capacitance of a condenser microphone into pressure signals. We tested the RF microphone with a low-frequency (LF) sound source, BP simulator and using a piezoresistive pressure sensor as a reference. Necessary tests were conducted to assess the uncertainty budget of the system. The RF microphone prototype has a working frequency range from 0.5 Hz to 280 Hz in the pressure range from 0 to 300 mmHg. The total expanded uncertainty (k = 2, p = 95.5%) of the RF microphone was 4.32 mmHg. The proposed method could establish traceability of BP measuring devices to acoustic standards described in IEC 61094-2 and could also be used in forming dynamic BP standards.

Modulation of Motor Awareness: A Transcranial Magnetic Stimulation Study in the Healthy Brain

Previous studies on the mechanisms underlying willed actions reported that the premotor cortex may be involved in the construction of motor awareness. However, its exact role is still under investigation. Here, we investigated the role of the dorsal premotor cortex (PMd) in motor awareness by modulating its activity applying inhibitory rTMS to PMd, before a specific motor awareness task (under three conditions: without stimulation, after rTMS and after Sham stimulation). During the task, subjects had to trace straight lines to a given target, receiving visual feedback of the line trajectories on a computer screen. Crucially, in most trials, the trajectories on the screen were deviated, and to produce straight lines, subjects had to correct their movements towards the opposite direction. After each trial, participants were asked to judge whether the line seen on the computer screen corresponded to the line actually drawn. Results show that participants in the No Stimulation condition did not recognize the perturbation until 14 degrees of deviation. Importantly, active, but not Sham, rTMS significantly modulated motor awareness, decreasing the amplitude of the angle at which participants became aware of the trajectory correction. These results suggest that PMd plays a crucial role in action self-monitoring.

Structural and Electromagnetic Signatures of Anatase and Rutile NTs and Sheets in Three Different Water Models under Different Temperature Conditions

Experimental studies of TiO2 nanotubes have been conducted for nearly three decades and have revealed the remarkable advantages of this material. Research based on computer simulations is much rarer, with research using density functional theory (DFT) being the most significant in this field. It should be noted, however, that this approach has significant limitations when studying the macroscopic properties of nanostructures such as nanosheets and nanotubes. An alternative with great potential has emerged: classical molecular dynamics simulations (MD). MD Simulations offer the possibility to study macroscopic properties such as the density of phonon states (PDOS), power spectra, infrared spectrum, water absorption and others. From this point of view, the present study focuses on the distinction between the phases of anatase and rutile TiO2. The LAMMPS package is used to study both the structural properties by applying the radial distribution function (RDF) and the electromagnetic properties of these phases. Our efforts are focused on exploring the effect of temperature on the vibrational properties of TiO2 anatase nanotubes and an in-depth analysis of how the phononic softening phenomenon affects TiO2 nanostructures to improve the fundamental understanding in different dimensions and morphological configurations. A careful evaluation of the stability of TiO2 nanolamines and nanotubes at different temperatures is performed, as well as the adsorption of water on the nanosurface of TiO2, using three different water models.

Unlocking potential: low frequency subthalamic nucleus stimulation enhances executive function in Parkinson's disease patients with postural instability/gait disturbance

Postural instability/gait disturbance (PIGD) is very common in advanced Parkinson's disease, and associated with cognitive dysfunction. Research suggests that low frequency (5-12 Hz) subthalamic nucleus-deep brain stimulation (STN-DBS) could improve cognition in patients with Parkinson's disease (PD). However, the clinical effectiveness of low frequency stimulation in PIGD patients has not been explored. This study was designed in a double-blinded randomized cross-over manner, aimed to verify the effect of low frequency STN-DBS on cognition of PIGD patients. Twenty-nine PIGD patients with STN-DBS were tested for cognitive at off (no stimulation), low frequency (5 Hz), and high frequency (130 Hz) stimulation. Neuropsychological tests included the Stroop Color-Word Test (SCWT), Verbal fluency test, Symbol Digital Switch Test, Digital Span Test, and Benton Judgment of Line Orientation test. For conflict resolution of executive function, low frequency stimulation significantly decreased the completion time of SCWT-C (p = 0.001) and Stroop interference effect (p < 0.001) compared to high frequency stimulation. However, no significant differences among stimulation states were found for other cognitive tests. Here we show, low frequency STN-DBS improved conflict resolution of executive function compared to high frequency. Our results demonstrated the possibility of expanding the treatment coverage of DBS to cognitive function in PIGD, which will facilitate integration of low frequency stimulation into future DBS programming.

Nanolayered Ceramic-Confined Graphene Aerogel with Conformal Heterointerfaces for Low-Frequency Microwave Absorption

Graphene-based aerogels have garnered considerable attention for their lightweight and efficient microwave absorption (MA) properties; however, optimizing the relationship between impedance matching and attenuation capability at low frequencies remains a challenge. In this study, a three-dimensional (3D) silicon carbonitride (SiCN) nanoceramic-coated graphene aerogel with conformal heterogeneous interfaces is constructed by precursor infiltration and pyrolysis to optimize MA performance at low frequencies. Thanks to the enhanced impedance matching and significant interfacial polarization of the two-dimensional sandwiched SiCN/graphene/SiCN cell walls and multiple scattering occurring within the 3D porous skeleton, the aerogel achieves a minimum reflection loss of -57.9 dB at an ultralow frequency of 4.92 GHz (C-band) and a broad bandwidth of 5.0 GHz at an ultralow thickness of 1.7 mm. The strategy developed here provides a method for enhancing dielectric polarization loss in graphene aerogels by the joint optimization of interfacial polarization and impedance matching, inspiring the design of high-performance graphene-based materials for low-frequency MA.

Multimodal Local Resonators for Low-Frequency Amelioration of Acoustic Black Holes

Acoustic black holes (ABHs) are effective at suppressing vibrations at high frequencies, but their performance at low frequencies is limited. This paper aims to improve the low-frequency performance of ABH plates through the design of a metamaterial acoustic black hole (MMABH) plate. The MMABH plate consists of a double-layer ABH plate with a set of periodic local resonators installed between the layers. The resonators are tuned to the low-frequency peak points of the ABH plate, which are identified using finite element analysis. To dissipate vibration energy, the beams of the resonators are covered with damping layers. A modal analysis of the MMABH plate is performed, confirming its damping effect over a wide frequency band, especially at low frequencies.

Lightweight Co3O4/CC Composites with High Microwave Absorption Performance

With the rapid development of electronic and communication technology for military radars, the demand for microwave-absorbing materials in the low-frequency range with thin layers is growing. In this study, flexible Co₃O₄/CC (carbon cloth) composites derived from Co-MOFs (metal-organic frameworks) and CC are prepared using hydrothermal and thermal treatment processes. The flexible precursors of the Co-MOFs/CC samples are calcined with different calcination temperatures, for which the material structure, dielectric properties, and microwave absorption performance are changed. With the increases in calcination temperature, the minimum reflection loss of the corresponding Co₃O₄/CC composites gradually moves to the lower frequency with a thinner thickness. In addition, the Co₃O₄/CC composites with the 25 wt% filler loading ratio exhibit the minimum reflection loss (RL) of -46.59 dB at 6.24 GHz with a 4.2 mm thickness. When the thickness is 3.70 mm, the effective absorption bandwidth is 3.04 GHz from 5.84 to 8.88 GHz. This study not only proves that the Co₃O₄/CC composite is an outstanding microwave-absorbing material with better flexibility but also provides useful inspiration for research on wideband microwave absorption materials below 10 GHz.

Low Frequency Attenuation Characteristics of Two-Dimensional Hollow Scatterer Locally Resonant Phonon Crystals

The finite element method (FEM) was applied to study the low frequency band gap characteristics of a designed phonon crystal plate formed by embedding a hollow lead cylinder coated with silicone rubber into four epoxy resin short connecting plates. The energy band structure, transmission loss and displacement field were analyzed. Compared to the band gap characteristics of three traditional phonon crystal plates, namely, the square connecting plate adhesive structure, embedded structure and fine short connecting plate adhesive structure, the phonon crystal plate of the short connecting plate structure with a wrapping layer was more likely to generate low frequency broadband. The vibration mode of the displacement vector field was observed, and the mechanism of band gap formation was explained based on the spring mass model. By discussing the effects of the width of the connecting plate, the inner and outer radii and height of the scatterer on the first complete band gap, it indicated that the narrower the width of the connecting plate, the smaller the thickness; the smaller the inner radius of the scatterer, the larger the outer radius; and the higher the height, the more conducive it is to the expansion of the band gap.

Research on an Optimized Quarter-Wavelength Resonator-Based Triboelectric Nanogenerator for Efficient Low-Frequency Acoustic Energy Harvesting

Sound wave is an extensively existing mechanical wave, especially in marine and industrial plants where low-frequency acoustic waves are ubiquitous. The effective collection and utilization of sound waves provide a fresh new approach to supply power for the distributed nodes of the rapidly developing Internet of Things technology. In this paper, a novel acoustic triboelectric nanogenerator (QWR-TENG) was proposed for efficient low-frequency acoustic energy harvesting. QWR-TENG consisted of a quarter-wavelength resonant tube, a uniformly perforated aluminum film, an FEP membrane, and a conductive carbon nanotube coating. Simulation and experimental studies showed that QWR-TENG has two resonance peaks in the low-frequency range, which effectively extends the response bandwidth of acoustic-electrical conversion. The structural optimized QWR-TENG has excellent electrical output performance, and the maximum output voltage, short-circuit current and transferred charge are 255 V, 67 μA, and 153 nC, respectively, under the acoustic frequency of 90 Hz and sound pressure level of 100 dB. On this basis, a conical energy concentrator was introduced to the entrance of the acoustic tube, and a composite quarter-wavelength resonator-based triboelectric nanogenerator (CQWR-TENG) was designed to further enhance the electrical output. Results showed that the maximum output power and the power density per unit pressure of CQWR-TENG reached 13.47 mW and 2.27 WPa^-1m^-2, respectively. Application demonstrations indicated that QWR/CQWR-TENG has good capacitor charging performance and is expected to realize power supply for distributed sensor nodes and other small electrical devices.

Molecular Epidemiology of SARS-CoV-2 during Five COVID-19 Waves and the Significance of Low-Frequency Lineages

SARS-CoV-2 lineages and variants of concern (VOC) have gained more efficient transmission and immune evasion properties with time. We describe the circulation of VOCs in South Africa and the potential role of low-frequency lineages on the emergence of future lineages. Whole genome sequencing was performed on SARS-CoV-2 samples from South Africa. Sequences were analysed with Nextstrain pangolin tools and Stanford University Coronavirus Antiviral & Resistance Database. In 2020, 24 lineages were detected, with B.1 (3%; 8/278), B.1.1 (16%; 45/278), B.1.1.348 (3%; 8/278), B.1.1.52 (5%; 13/278), C.1 (13%; 37/278) and C.2 (2%; 6/278) circulating during the first wave. Beta emerged late in 2020, dominating the second wave of infection. B.1 and B.1.1 continued to circulate at low frequencies in 2021 and B.1.1 re-emerged in 2022. Beta was outcompeted by Delta in 2021, which was thereafter outcompeted by Omicron sub-lineages during the 4th and 5th waves in 2022. Several significant mutations identified in VOCs were also detected in low-frequency lineages, including S68F (E protein); I82T (M protein); P13L, R203K and G204R/K (N protein); R126S (ORF3a); P323L (RdRp); and N501Y, E484K, D614G, H655Y and N679K (S protein). Low-frequency variants, together with VOCs circulating, may lead to convergence and the emergence of future lineages that may increase transmissibility, infectivity and escape vaccine-induced or natural host immunity.

Nonlinear Energy Harvesting by Piezoelectric Bionic 'M' Shape Generating Beam Featured in Reducing Stress Concentration

Inspired by the flapping wings of seagulls during flight, a new low-cost, magnet-free, bistable piezoelectric energy harvester is proposed to obtain energy from low-frequency vibration and convert it into electrical energy and reduce fatigue damage caused by stress concentration. In order to optimize the power generation efficiency of this energy harvesting, finite element analysis and experimental tests were carried out. The results of finite element analysis and experimental results are in good agreement, and the superior performance in improving stress concentration of the energy harvester compared to the previous parabolic (bow-shaped) one using bistable technology was quantitatively analyzed using finite element simulation, with a maximum stress reduction of 32.34%. The experimental results showed that under optimal operating conditions, the maximum open-circuit voltage of the harvester was 11.5 V, and the maximum output power was 73 μW. These results indicate that this is a promising strategy, which provides a reference for collecting vibrational energy in low-frequency environments.

A Bio-Inspired Bistable Piezoelectric Structure for Low-Frequency Energy Harvesting Applied to Reduce Stress Concentration

Inspired by the two typical movement stages in the wingbeat cycle of a seagull in flight, a bio-inspired bistable wing-flapping energy harvester is proposed in this paper to effectively convert low-frequency, low-amplitude and random vibrations into electricity. The movement process of this harvester is analyzed, and it is found that it can significantly alleviate the shortcomings of stress concentration in previous energy harvester structures. A power-generating beam composed of a 301 steel sheet and a PVDF (polyvinylidene difluoride) piezoelectric sheet with imposed limit constraints is then modeled, tested and evaluated. The energy harvesting performance of the model at low frequencies (1-20 Hz) is experimentally examined, where the maximum open-circuit output voltage of the model reaches 11,500 mV at 18 Hz. With a 47 kΩ external resistance of the circuit, the peak output power of the circuit reaches its maximum state of 0.734 mW (18 Hz). When a full bridge circuit is employed to convert AC to DC, the 470 μF capacitor connected to it reaches 3000 mV at peak voltage after 380 s of charging.

Simulation and Experimental Study of a Piezoelectric Stack Energy Harvester for Railway Track Vibrations

As one of the most important modes of transportation, the safety of running trains and railway tracks is significant. It is essential to power sensors that detect and track health in remote areas. The vibration energy of the track structure is enormous, stable, and not limited by weather factors such as the sun and wind. A new type of arch beam piezoelectric stack energy harvester for railway systems is studied in this paper. Through simulation analyses and experimental verification of the energy harvester, the influences of external resistance, load, pre-stress, and load frequency on the energy harvesting performance of the piezoelectric energy harvester are discussed. When the frequency is less than 6 Hz, the energy capture efficiency is greatly affected by the frequency. When the frequency exceeds 6 Hz, the frequency has little effect and the load dramatically affects the energy capture efficiency. The pre-stress has little effect on the energy capture efficiency, but there is an optimal value at 4.5 kN. The energy harvester has an output power of 193 mW, a weight of 912 g, and the energy density can reach 211.8 μW/g. These results can provide a reference for subsequent experiments in the actual environment.

Optimized Weight Low-Frequency Search Coil Magnetometer for Ground-Airborne Frequency Domain Electromagnetic Method

The vertical component magnetic field signal in the ground-airborne frequency domain electromagnetic (GAFDEM) method is detected by the air coil sensor, which is parallel to the ground. Unfortunately, the air coil sensor has low sensitivity in the low-frequency band, making it challenging to detect effective low-frequency signals and causing low accuracy and large error for interpreted deep apparent resistivity in actual detection. This work develops an optimized weight magnetic core coil sensor for GAFDEM. The cupped flux concentrator is used in the sensor to reduce the weight of the sensor while maintaining the magnetic gathering capacity of the core coil. The winding of the core coil is optimized to resemble the shape of a rugby ball, taking full advantage of the magnetic gathering capacity at the core center. Laboratory and field experiment results show that the developed optimized weight magnetic core coil sensor for the GAFDEM method is highly sensitive in the low-frequency band. Therefore, the detection results at depth are more accurate compared with those obtained using existing air coil sensors.

Investigation of transient machining in the cortical bone drilling process by conventional and axial vibration-assisted drilling methods

A temperature exceeding the safety threshold and excessive drilling force occurring during bone drilling may lead to irreversible damage to bone tissue and postoperative complications. Previous studies have shown that vibration-assisted drilling methods could have lower temperatures and drilling forces than those of the conventional drilling method; we hypothesized that the main reason for these reductions stems from the differences in the transient machining processes between conventional and vibration-assisted drilling methods. To investigate these differences, comparative experiments and two-dimensional finite element models were performed and developed. The differences in the transient machining processes were verified by experimentation and clearly exhibited by the finite element models. Compared with the steady cutting process that produced continuous-spiral chips in the conventional drilling method, transient machining in the low-frequency vibration-assisted drilling method was a periodically dynamic cutting-separation process that produced uniform petal chips with specific settings of drilling and vibration parameters. Moreover, the transient machining process in the ultrasonic vibration-assisted drilling method was transformed into a combined action with high-speed impact and negative rake angle cutting processes; this action produced a large proportion of powdery chips. Therefore, it could be concluded that the superposed axial vibration significantly changed the transient machining process and radically changed the mechanical state and thermal environment; these changes were the main reason for the apparent differences in the drilling performance levels.

A Novel Bird-Shape Broadband Piezoelectric Energy Harvester for Low Frequency Vibrations

This work presents a novel bird-shaped broadband piezoelectric energy harvester based on a two-DOF crossed beam for low-frequency environmental vibrations. The harvester features a cantilever mounted on a double-hinged beam, whose rotating motions effectively diminish its natural frequencies. Numerical simulation based on the finite element method is conducted to analyze the modal shapes and the harmonic response of the proposed harvester. Prototypes are fabricated and experiments are carried out by a testing system, whose results indicate a good agreement with the simulation. The multi-frequency energy harvesting is achieved at the first-, second-, and fifth-order resonances. In particular, the proposed harvester demonstrates the remarkable output characteristics of 9.53 mW and 1.83 mW at frequencies as low as 19.23 HZ and 45.38 Hz, which are superior to the majority of existing energy harvesters. Besides, the influences of key parameters on the harvesting performance are experimentally investigated to optimize the environmental adaptability of the harvester. This work provides a new perspective for efficiently harvesting the low-frequency vibration energy, which can be utilized for supplying power to electronic devices.

Design and Experimental Investigation of an Ultra-Low Frequency, Low-Intensity, and Multidirectional Piezoelectric Energy Harvester with Liquid as the Energy-Capture Medium

Traditional piezoelectric vibration energy harvesters (PVEHs) usually adopt a rigid energy-capture structure, which can achieve efficient energy harvesting in single-directional, high-frequency, and high-intensity vibration environments. However, efficient harvesting with the use of low-frequency, low-intensity, and multidirectional vibration energy remains a challenge for existing harvesters. To tackle this problem, we proposed a PVEH with liquid as the energy-capture medium. Our previous research verified that this set up can show a good energy harvesting performance under low-frequency, low-intensity, and horizontal multidirectional vibration excitation. In this paper, we further studied the possibility of vertical multidirectional energy harvesting using this device, as well as the influence of several important parameters (rope margin, liquid level height, and floating block shape) on the output performance. The results showed that the proposed PVEH can realize energy harvesting in three-dimensional space and that the output characteristic is adjustable.

A Central Spiral Split Rectangular-Shaped Metamaterial Absorber Surrounded by Polarization-Insensitive Ring Resonator for S-Band Applications

This paper reports a central spiral split-rectangular-shaped metamaterial absorber surrounded by a polarization-insensitive ring resonator for s-band applications. The rated absorption is 99.9% at 3.1 GHz when using a three-layer structure where the top and ground are made of copper and the center dielectric material is a commonly used FR-4 substrate. The central split gaps have an impact on the unit cell by increasing high absorption, and an adequate electric field is apparent in the outer split ring gap. At 3.1 GHz, the permittivity and permeability are negative and positive, respectively, so the proposed unit cell acts as an epsilon negative (ENG) metamaterial absorber. In a further analysis, Roger4450B was used as a substrate and obtained excellent absorption rates of 99.382%, 99.383%, 99.91%, and 95.17% at 1.44, 3.96, 4.205, and 5.025 GHz, respectively, in the S- and C-band regions. This unit cell acts as a single negative metamaterial (SNG) absorber at all resonance frequencies. The S₁₁ and S₂₁ parameters for FR-4 and Rogers4450B were simulated while keeping the polarization angle (θ and φ) at 15, 30, 45, 60, 75, and 90 degrees to measure, permittivity, permeability, reflective index, absorption, and reflection. The values of the reflective index are near zero. Near-zero reflective indexes (NZRI) are widely used in antenna gain propagation. The unit cell fabricated for the FR-4 substrate attained 99.9% absorption. S-band values in the range of (2-4) GHz can be applied for low-frequency radar detection.

The Efficiency of Hearing Protective Devices against Occupational Low Frequency Noise in Comparison to the New Subjective Suggested Method

Backround

Noise is one of the most important occupational and environmental health hazards. Exposure to loud noise can cause irrevocable hearing damage and loss of hearing. The aim of this study was to determine the efficiency of two samples of earmuff and earplug in low frequency noise reduction in comparison to subjective method.

Methods

All the procedures of the work were done using the simulated human ear canal and the required microphone in the eardrum. At the octave frequencies, that is 31.5 and 63.5, 125, 250, 500, 1000, 2000, 4000, and 8000 Hz, and intensities of 85-90 dB, one stage was done by using the individual's subjective response relative to the received sound before and after using the ear protector.

Results

The sound levels before and after the protection were significantly different in both the model and humans (P < 0.05). However, at 315 Hz frequency, the rate of attenuation is increased by 4 dB after placing the earplug and 14 dB after placing the earmuff, showing a reduction of 18 dB.

Conclusions

This study verifies the increasing protection by simultaneous application of earplugs and earmuffs. Because of the laboratory evaluation of ear protectors, it is possible not to justify the proficiency of ear protectors in a subjective method.

Analysis and Suppression of Thermal Magnetic Noise of Ferrite in the SERF Co-Magnetometer

The ferrite magnetic shield is widely used in ultra-high-sensitivity atomic sensors because of its low noise characteristics. However, its noise level varies with temperature and affects the performance of the spin-exchange relaxation-free (SERF) co-magnetometer. Therefore, it is necessary to analyze and suppress the thermal magnetic noise. In this paper, the thermal magnetic noise model of a ferrite magnetic shield is established, and the thermal magnetic noise of ferrite is calculated more accurately by testing the low-frequency complex permeability at different temperatures. A temperature suppression method based on the improved heat dissipation efficiency of the ferrite magnetic shield is also proposed. The magnetic noise of the ferrite is reduced by 46.7%. The experiment is basically consistent with the theory. The sensitivity of the co-magnetometer is decreased significantly, from 1.21 × 10-5°/s/Hz1/2 to 7.02 × 10-6°/s/Hz1/2 at 1 Hz. The experimental results demonstrate the effectiveness of the proposed method. In addition, the study is also helpful for evaluating the thermal magnetic noise of other materials.

Acute neuromuscular and hormonal responses to 20% vs 40% velocity-loss in males and females before and after 8 weeks of velocity-loss resistance training

NEW FINDINGS

What is the central question of this study? Do males and females differ in fatiguability during dynamic loadings, and what are the acute neuromuscular and hormonal responses to 20% versus 40% velocity-loss resistance loadings? How does an 8-week velocity-loss resistance training period modify acute neuromuscular and hormonal responses in males and females? What is the main finding and its importance? Utilizing resistance training methods that regulate the within-set fatigue limit, males appeared to be more susceptible to fatigue than females before the training period. This between-sex difference was diminished after training. The predominant mechanisms of fatigue from 20% and 40% velocity-based resistance training appears to be within the musculature.

ABSTRACT

Scientific examination of velocity-based resistance training (VBRT) has increased recently, but how males and females respond to different VBRT protocols or how these acute responses are modified after a period of training is unknown. Habitually resistance-trained males and females followed either a 20% or 40% velocity-loss program for 8 weeks. Acute squat loading tests (5 sets, 70% 1-RM load, 3 minutes rest) were performed before and after the training period. Tests of maximum neuromuscular performance and blood sampling were conducted prior to, within 10 minutes of completion (POST) and 24 hours after each acute loading test. Testing included countermovement jump, resting femoral nerve electrical stimulation, and bilateral isometric leg press. Blood samples were analysed for whole-blood lactate, serum testosterone, cortisol, growth hormone and creatine kinase concentrations. Countermovement jump height, maximum isometric bilateral leg press force, and force from 10 Hz doublet decreased in all groups at POST after 20% and 40% velocity-loss. Only males showed reduced force from 100 Hz doublet and voluntary force over 100 ms at POST before training. 40% velocity-loss led to increased blood lactate and growth hormone responses before training in both males and females. After training, more systematic and equivalent responses in force over 100 ms, force from 100 Hz doublet and blood lactate were observed regardless of sex/VBRT protocol. Overall, acute responses were greater from 40% VBRT and males were more susceptible to acute loss in force production capacity before the training period. These VBRT protocol- and sex-related differences were diminished after training. This article is protected by copyright. All rights reserved.

Study on Microwave Absorption Performance Enhancement of Metamaterial/Honeycomb Sandwich Composites in the Low Frequency Band

With the rapid development of electronic technology and modern radar detection system, there is increasingly urgent demand for microwave absorbing composites working efficiently in the low frequency range (e.g., 1−2 GHz). In this work, a type of metamaterial/honeycomb sandwich composite (MHSC) was proposed and fabricated, which exhibited a light weight structure and excellent wave-absorbing performance in the low frequency band. The relationship between the wave-absorbing properties and the design parameters of the composite, such as the thickness of the wave-transmitting skin, the thickness and dielectric properties of the wave-absorbing honeycomb, was systematically investigated. The electromagnetic coupling interference between the honeycomb absorber and metamaterial resonator proved to be a crucial factor that affects synergistic wave-absorbing performance in the low-frequency band. Under the rational design, the incorporation of subwavelength-sized phase-gradient metamaterial units in the composite can significantly improve low-frequency wave-absorbing performance for greater than 5 dB (an increment larger than 100%); and the obtained MHSC exhibits averaged reflectivity (Ra) less than −10 dB in the low frequency band of 1−2 GHz as well as outstanding performance (Ra < −14.6 dB) over an extremely wide frequency range (1−18 GHz). The MHSC reported in this study could be a promising candidate for the key material in high-performance radar stealth and other related applications.

Case Report: Low-Frequency Repetitive Transcranial Magnetic Stimulation to Dorsolateral Prefrontal Cortex and Auditory Cortex in a Patient With Tinnitus and Depression

Repetitive transcranial magnetic stimulation (rTMS) has been widely used as a promising therapy for tinnitus. However, the exact target and stimulation sequence of rTMS that is most effective for treating tinnitus remains unclear. Here, we report a case of a 62-year-old man with treatment-refractory tinnitus and depression whose symptoms markedly improved after undergoing low-frequency rTMS over the right-side dorsolateral prefrontal cortex and left auditory cortex area. Our report indicates that low-frequency rTMS treatment that stimulates multiple brain regions sequentially is feasible and may clinically benefit patients with tinnitus and depression.

Effect of Concave Stave on Class I Barrel-Stave Flextensional Transducer

To meet the requirements of low frequency, high power, small size and light weight, a type of Class I barrel-stave flextensional transducer employing improved concave stave is presented. As the key component of flextensional transducer, concave stave plays an important role in vibrating efficiently to radiate acoustic energy. The structure of concave stave has a great effect on its behavior. In this paper, the main parameters of concave stave are discussed, especially the effect of radius on flextensional transducer. Both concave stave and transducer are analyzed through finite element method, including mechanical transformation behavior of concave stave and performances of flextensional transducer. On the basis of finite element design, five prototypes employing concave staves with different radii are manufactured and measured. The simulations and tests reveal that concave stave can affect performances of flextensional transducer. A larger radius of concave stave will result in a greater amplification of vibration and a lower resonance frequency of transducer. This can be a feasible way to optimize the resonance frequency or source level of flextensional transducer through adjusting the radius of concave stave in a small range. According to the electrical and acoustical tests, our Class I barrel-stave flextensional transducer is capable of being used as underwater low-frequency small-size projector.

Design, Manufacture and Test of Piezoelectric Cantilever-Beam Energy Harvesters with Hollow Structures

This article presents a single-crystal piezoelectric energy harvester (PEH) with a trapezoidal hollow hole that can obtain high energy density at low frequency. Harvesters with a hollow structure were fabricated through a series of manufacturing processes such as thermocompression bonding, screen printing and laser cutting. Finite element analysis (FEA) and experimental results showed that using low modulus brass instead of stainless steel as the PEH substrate enhances the voltage output of the device, and the hollow design greatly increases the overall stress level and power density. In addition, the developed PEH with a trapezoidal hole obtained the best output performance; when the acceleration, resonance frequency and matched load resistance were 0.5 g, 56.3 Hz and 114 kΩ, respectively, the peak voltage was 17 V and the power density was 2.52 mW/cm³. Meanwhile, compared with the unhollowed device, the peak voltage and maximum power density of the proposed PEH were increased by 30.7% and 24.4%, respectively, and the resonance frequency was reduced by 7%. This study verified the feasibility of the optimized design through simulation and experimental comparison.

Modeling of a Rope-Driven Piezoelectric Vibration Energy Harvester for Low-Frequency and Wideband Energy Harvesting

In this work, a mechanical model of a rope-driven piezoelectric vibration energy harvester (PVEH) for low-frequency and wideband energy harvesting was presented. The rope-driven PVEH consisting of one low-frequency driving beam (LFDB) and one high-frequency generating beam (HFGB) connected with a rope was modeled as two mass-spring-damper suspension systems and a massless spring, which can be used to predict the dynamic motion of the LFDB and HFGB. Using this model, the effects of multiple parameters including excitation acceleration, rope margin and rope stiffness in the performance of the PVEH have been investigated systematically by numerical simulation and experiments. The results show a reasonable agreement between the simulation and experimental study, which demonstrates the validity of the proposed model of rope-driven PVEH. It was also found that the performance of the PVEH can be adjusted conveniently by only changing rope margin or stiffness. The dynamic mechanical model of the rope-driven PVEH built in this paper can be used to the further device design or optimization.

Research and Fabrication of Broadband Ring Flextensional Underwater Transducer

At present, high-speed underwater acoustic communication requires underwater transducers with the characteristics of low frequency and broadband. The low-frequency transducers also are expected to be low-frequency directional for realization of point-to-point communication. In order to achieve the above targets, this paper proposes a new type of flextensional transducer which is constructed of double mosaic piezoelectric ceramic rings and spherical cap metal shells. The transducer realizes broadband transmission by means of the coupling between radial vibration of the piezoelectric rings and high-order flexural vibration of the spherical cap metal shells. The low-frequency directional transmission of the transducer is realized by using excitation signals with different amplitude and phase on two mosaic piezoelectric rings. The relationship between transmitting voltage response (TVR), resonance frequency and structural parameters of the transducer is analyzed by finite element software COMSOL. The broadband performance of the transducer is also optimized. On this basis, the low-frequency directivity of the transducer is further analyzed and the ratio of the excitation signals of the two piezoelectric rings is obtained. Finally, a prototype of the broadband ring flextensional underwater transducer is fabricated according to the results of simulation. The electroacoustic performance of the transducer is tested in an anechoic water tank. Experimental results show that the maximum TVR of the transducer is 147.2 dB and the operation bandwidth is 1.5–4 kHz, which means that the transducer has good low-frequency, broadband transmission capability. Meanwhile, cardioid directivity is obtained at 1.4 kHz and low-frequency directivity is realized.

Physiological and Behavioral Responses to Vocalization Playback in Mice

In mice, the caller’s production of social vocalizations has been extensively studied but the effect of these vocalizations on the listener is less understood, with playback studies to date utilizing one vocalization category or listeners of one sex. This study examines how several categories of mouse vocalizations affect listeners of both sexes to better understand the communicative functions of these vocal categories. We examined physiological and behavioral responses of male and female CBA/CaJ mice to playback of four social vocalization categories: ultrasonic vocalizations (USVs), low-frequency harmonic calls, mid-frequency vocalizations, and noisy calls. Based on the conditions under which these calls are emitted, we hypothesized that playback of these vocal categories would have differential effects on the listeners. In females, playback of all four vocalization categories increased stress hormone levels (corticosterone), but only the non-USV categories increased corticosterone in males. The magnitude of corticosterone increase in non-USV trials was greater in females than in males. In open field tests, all four vocal categories decreased central ambulation in males and females, indicating an increase in anxiety-related behavior. Further, we found that the proportions of USVs emitted by subjects, but not their overall calling rates, were affected by playback of some vocal categories, suggesting that vocalization categories have different communication content. These results show that, even in the absence of behavioral and acoustic contextual features, each vocal category evokes physiological and behavioral responses in mice, with some differences in responses as a function of the listener’s sex and playback signal. These findings suggest that at least some of the vocal categories have distinct communicative functions.

Pudendal Nerve Block by Low-Frequency (≤1 kHz) Biphasic Electrical Stimulation

OBJECTIVES

To test the hypothesis that poststimulation block of nerve conduction can be achieved by low-frequency (≤1 kHz) biphasic stimulation (LFBS).

MATERIALS AND METHODS

A tripolar cuff electrode was placed around the pudendal nerve in cats to deliver LFBS (1 kHz, 500 Hz, and 100 Hz). Two bipolar hook electrodes were placed central and distal to the cuff electrode to induce external urethral sphincter (EUS) contractions. A catheter was inserted into the urethra to record EUS contraction pressure. Pudendal nerve block by LFBS was confirmed by the failure of the central hook electrode stimulation to induce EUS contractions, while the distal hook electrode stimulation still induced contractions.

RESULTS

Pudendal nerve conduction was completely blocked by LFBS at different frequencies (1 kHz, 500 Hz, and 100 Hz) after terminating LFBS. The post-LFBS block induced at the minimal stimulation intensity and duration was fully reversible within the same time period (10-15 min on average) for the three frequencies. However, the stimulation duration to induce block significantly (p < 0.05) increased from 23 ± 8 sec to 95 ± 14 sec when frequency increased from 100 Hz to 1 kHz.

CONCLUSION

This study discovered that LFBS (≤1 kHz), like high-frequency (≥5 kHz) biphasic stimulation (HFBS), can induce poststimulation block. The result provides support for the theory that biphasic stimulation waveforms block axonal conduction by changing intracellular and extracellular ion concentrations. The post-LFBS block provides the opportunity to develop new neuromodulation devices for clinical applications where initial nerve firing is acceptable.

An Area-Efficient and Highly Linear Reconfigurable Continuous-Time Filter for Biomedical Sensor Applications

This paper proposes a compact, high-linearity, and reconfigurable continuous-time filter with a wide frequency-tuning capability for biopotential conditioning. It uses an active filter topology and a new operational-transconductance-amplifier (OTA)-based current-steering (CS) integrator. Consequently, a large time constant τ, good linearity, and linear bandwidth tuning could be achieved in the presented filter with a small silicon area. The proposed filter has a reconfigurable structure that can be operated as a low-pass filter (LPF) or a notch filter (NF) for different purposes. Based on the novel topology, the filter can be readily implemented monolithically and a prototype circuit was fabricated in the 0.18 μm standard complementary-metal–oxide–semiconductor (CMOS) process. It occupied a small area of 0.068 mm² and consumed 25 μW from a 1.8 V supply. Measurement results show that the cutoff frequency of the LPF could be linearly tuned from 0.05 Hz to 300 Hz and the total-harmonic-distortion (THD) was less than −76 dB for a 2 Hz, 200 mVpp sine input. The input-referred noises were 5.5 μVrms and 6.4 μVrms for the LPF and NF, respectively. A comparison with conventional designs reveals that the proposed design achieved the lowest harmonic distortion and smallest on-chip capacitor. Moreover, its ultra-low cutoff frequency and relatively linear frequency tuning capability make it an attractive solution as an analog front-end for biopotential acquisitions.

Time-dependent diffusion in undulating thin fibers: Impact on axon diameter estimation

Diffusion MRI may enable non-invasive mapping of axonal microstructure. Most approaches infer axon diameters from effects of time-dependent diffusion on the diffusion-weighted MR signal by modeling axons as straight cylinders. Axons do not, however, propagate in straight trajectories, and so far the impact of the axonal trajectory on diameter estimation has been insufficiently investigated. Here, we employ a toy model of axons, which we refer to as the undulating thin fiber model, to analyze the impact of undulating trajectories on the time dependence of diffusion. We study time-dependent diffusion in the frequency domain and characterize the diffusion spectrum by its height, width, and low-frequency behavior (power law exponent). Results show that microscopic orientation dispersion of the thin fibers is the main parameter that determines the characteristics of the diffusion spectra. At lower frequencies (longer diffusion times), straight cylinders and undulating thin fibers can have virtually identical spectra. If the straight-cylinder assumption is used to interpret data from undulating thin axons, the diameter is overestimated by an amount proportional to the undulation amplitude and microscopic orientation dispersion of the fibers. At higher frequencies (shorter diffusion times), spectra from cylinders and undulating thin fibers differ. The low-frequency behavior of the spectra from the undulating thin fibers may also differ from that of cylinders, because the power law exponent of undulating fibers can reach values below 2 for experimentally relevant frequency ranges. In conclusion, we argue that the non-straight nature of axonal trajectories should not be overlooked when analyzing and interpreting diffusion MRI data.

Extremely Low Frequency Magnetic Fields Do Not Affect LTP-Like Plasticity in Healthy Humans

Introduction

Several studies explored the biological effects of extremely low-frequency magnetic fields (ELF-MFs) in vitro, reporting the induction of functional changes in neuronal activity. In particular, ELF-MFs can influence synaptic plasticity both in vitro and in animal models but some studies reported an increase in long-term potentiation (LTP) whereas others suggested its reduction. However, no specific study has investigated such effect on humans.

Aims

To evaluate whether ELF-MFs affect the propensity of the human cortex to undergo LTP-like plasticity.

Methods

We designed a randomized, single-blind, sham-controlled, cross-over study on 10 healthy subjects. Cortical plasticity was induced by intermittent theta burst stimulation (iTBS) before and after 45-min ELF-MFs (75 Hz; 1.8 mT) or sham exposure and was estimated by measuring the changes of motor evoked potentials (MEP) amplitude before and after each iTBS.

Results

No adverse events were reported. No significant effects of ELF-MFs on cortical plasticity were found.

Conclusion

Whole-brain exposure to ELF-MFs (75 Hz; 1.8 mT) is safe and does not seem to significantly affect LTP-like plasticity in human motor cortex.

Identifying Clinically and Functionally Distinct Groups Among Healthy Controls and First Episode Psychosis Patients by Clustering on EEG Patterns

OBJECTIVE

The mismatch negativity (MMN) is considered as a promising biomarker that can inform future therapeutic studies. However, there is a large variability among patients with first episode psychosis (FEP). Also, most studies report a single electrode site and on comparing case-control group differences. Few have taken advantage of the full wealth of multi-channel EEG signals to examine observable patterns. None, to our knowledge, have used machine learning (ML) approaches to investigate neurophysiological derived subgroups with distinct cognitive and functional outcome characteristics. In this study, we applied ML to empirically stratify individuals into homogeneous subgroups based on multi-channel MMN data. We then characterized the functional, cognitive, and clinical profiles of these neurobiologically derived subgroups. We also explored the underlying low frequency range responses (delta, theta, alpha) during MMN.

METHODS

Clinical, neurocognitive, functioning data of 33 healthy controls and 20 FEP patients were collected. 90% of the patients had 6-month follow-up data. Neurocognition, social cognition, and functioning measures were assessed using the NCCB Cognitive Battery, the Awareness of Social Inference Test, UCSD Performance-Based Skills Assessment, and Multnomah Community Ability Scale. Symptom severity was collected using the PANSS. MMN amplitude and single-trial derived low frequency activity across 24 frontocentral channels were used as main variables in the ML k-means clustering analyses.

RESULTS

We found a consistent pattern of two distinctive subgroups. We labeled them as "better functioning" and "poorer functioning" clusters, respectively. Each subgroup can be mapped onto either better or poorer clinical, cognitive, and functioning profiles. Also, we identified two subgroups of patients: one showed improved MMN and one showed worsening of MMN over time. Patients with improved MMN had better follow-up clinical, cognitive, and functioning profile than those with worsening MMN. Among the low frequency bands, delta frequency appeared to be the most relevant to the observed MMN responses in all individuals. However, higher delta responses were not necessarily associated with a better functioning profile, suggesting that delta frequency alone may not be useful in clinical characterization.

CONCLUSIONS

The ML approach could be a robust tool to explore heterogeneity and facilitate the identification of neurobiological homogeneous subgroups in FEP.

Research on the Cascade-Connected Transducer with Multi-Segment Used in the Acoustic Telemetry System while Drilling

The electroacoustic transducer with the performances of low frequency, small size, and high power is desired in the application of the acoustic telemetry system while drilling. In order to fulfill the severe requirements, a novel cascade-connected transducer with multi-segment is developed. The essential framework of such a transducer is to add the cross-beams in the multi-segment cascade-connected arrangement, based on the fundamental configuration of the longitudinal transducer. The flexural vibrations of cross-beams help the transducer to present the appropriate coupling between longitudinal and flexural vibrations, which provide many benefits in keeping the advantages of the longitudinal transducer and lowering the resonance frequency. It is the finite element method to be used for simulating the mode shapes of the cascade-connected transducer, especially the behavior of the cross-beams, and some performances of transducer are also predicted. Several prototypes of cascade-connected transducers with different segments are manufactured. Their related tests show a good agreement with the finite element simulations and analyses. Their characteristics of low frequency, small size, light weight, and high power are attractive for the transmitting or receiving application in the acoustic telemetry system while drilling.

Extended Subaperture Imaging Method for Airborne Low Frequency Ultrawideband SAR Data

The subaperture processing is one of the essential strategies for low frequency ultrawideband synthetic aperture radar (LF UWB SAR) imaging, especially for the real-time LF UWB SAR imaging because it can improve the parallelization of the imaging algorithm. However, due to the longer synthetic aperture of LF UWB SAR, the traditional subaperture imaging encounters an azimuth ambiguities problem, which severely degrades the focused quality of the imaging results. In this paper, the reason for the presence of azimuth ambiguities in the LF UWB SAR subaperture imaging and its influence on image quality is first analyzed in theory. Then, an extended subaperture imaging method based on the extension of subaperture length before Range Cell Migration Correction (RCMC) was proposed. By lengthening the subaperture length, the azimuth ambiguities are effectively eliminated. Finally, the extended part of subaperture is wiped off before the azimuth compression (AC), and the LF UWB SAR image of high focused quality is obtained. The correctness of the theory analysis and the effectiveness of the proposed method have been validated through simulated and real LF UWB SAR data.

Virtual Loudspeaker Effect of Graphene-Based Hybrid Material To Improve Low-Frequency Acoustic Performance

Closed-box loudspeaker systems (CBLSSs) are compact and simple air-suspension loudspeaker systems, and their low-frequency responses are determined by two fundamental parameters: resonance frequency and total damping. Recently, electronic devices have come to require more compact designs, so the volumes of loudspeaker should be reduced. However, a small loudspeaker cannot retain sufficient acoustic space, resulting in poor low-frequency acoustic performance. Herein, we investigated acoustic characterization of the CBLSS with different filling materials such as thermally expanded graphene oxide (TEGO), activated carbon, graphene platelets, and melamine foam (MF). Upon the powder-based test, the resonance frequency of the loudspeaker decreased and resulted in a volume increasing effect inside of the loudspeaker. The TEGO shows almost double volume increase rate, compared to other particle-based filling materials. Employing hybrid filling material that consists of TEGO in an MF cage (TEGO@MF), the volume increase rate of the novel loudspeaker was over 24% at 300 cc. Because of the high adsorptive characteristics and thermal properties of TEGO, the acoustic performance in the low-frequency domain was clearly enhanced, despite the reduced mass loading. Furthermore, these properties were observed to be highly effective for enhancing the low-frequency acoustic performance of the larger loudspeaker, achieving a volume increase rate of 49.5% in a 700 cc enclosure.

Analysis of how compliant layers and encapsulation affect power generated from piezoelectric stacked composites for bone healing medical devices

Use of piezoelectric materials to harvest energy from human motion is commonly investigated. Traditional piezoelectric materials are inefficient at low frequencies but composite structures can increase efficiency at these frequencies. Compliant layer adaptive composite stack (CLACS) is a new piezoelectric PZT (lead zirconate titanate) structure designed for orthopedic implants to use loads generated during walking to provide electrical stimulation for bone healing. The CLACS structure increases power efficiency and structural properties as compared to PZT alone. The purpose of this study was to investigate the effects of compliant layer and encapsulation thicknesses on strain-related parameters for CLACS predicted by finite element models. Percent changes in strain as compliant layer thickness increased were compared to percent changes in power experimentally produced by CLACS given similar geometries and loading conditions. Percent changes in PZT z-strain matched the trends for increases in experimental power, but was not directly proportional. PZT z-strain and radial strain increased as compliant layer and top and bottom encapsulation thickness increased. PZT z-strain and radial strain decreased as side encapsulation thickness increased for a normalized distributed force on the PZT. The overall goal of this study was to inform future design decisions regarding CLACS structures specifically for use in orthopedic implants.

Long-term intermittent low-frequency repetitive transcranial magnetic stimulation effectively controls seizures in two drug-free adolescent patients

Recently, repetitive transcranial magnetic stimulation (rTMS) has been widely used for treating neurological and psychiatric diseases. Low-frequency rTMS is used to effectively control the occurrence of seizures, including medication-refractory epilepsy and cortical dysplasia or neocortical epilepsy. However, there have been no reports on the effects of long-term rTMS on epilepsy. We observed the clinical effects of long-term rTMS in two drug-free adolescent epileptic patients with a preference for non-drug therapy. The two drug-free adolescent patients, who underwent intermittent low-frequency rTMS treatment for 36 weeks, obtained effective control of seizures (including episode and severity). However, a systematic study is required to confirm our observations.

Comparison of Physiological and Biochemical Autonomic Indices in Children with and without Autism Spectrum Disorders

Background and objectives: Autism Spectrum Disorder (ASD) is a complex neuro-developmental disorder and it has been suggested that symptoms of ASD are associated with neural networks that regulate the Autonomic Nervous System (ANS). However, the nature of autonomic atypicalities in ASDs remain largely unknown. Measures like Heart Rate Variability (HRV) and urinary Vanillylmandelic Acid (VMA) estimation are sensitive and non-invasive physiological and biochemical indicators of autonomic nervous activity. This study aimed to compare the physiological and biochemical autonomic indices in children with and without ASD. Materials and Methods: In this case-control study, 40 children with autism and 40 Typically Developing (TD) children were recruited. Measures of physiological autonomic index were assessed by the analysis of short term HRV, and the urinary levels of VMA estimation was used as a biochemical autonomic index. Results: Cardiac sympathetic activity assessed by Low Frequency (nu) of HRV was significantly higher in the ASD group in comparison with the TD group (p = 0.006). On the contrary, both the High Frequency (abs) and (nu) of HRV were found to be significantly lower in autistic children (p = 0.034 and p = 0.000) than controls. Autistic children also exhibited a significantly higher level (p = 0.049) of VMA concentration compared to TD children. Conclusion: The study concludes that children with ASD exhibit lower cardio-vagal activity as measured by HRV and increased sympathetic activity as assessed by urinary VMA compared to that of TD children. The core autistic symptoms exhibited by children with ASD could be due to the differences in baseline arousal or stress which might be associated with autonomic dysfunction. Further studies are needed to examine the association of this autonomic dysregulation with ASD symptoms and comorbidities.

A Low-Cost Electromagnetic Docking Guidance System for Micro Autonomous Underwater Vehicles

As important observational platforms for the Smart Ocean concept, autonomous underwater vehicles (AUVs) that perform long-term observation in fleets are beneficial because they provide large-scale sampling data with a sufficient spatiotemporal resolution. Therefore, a large number of low-cost micro AUVs with docking capability for power recharge and data transmission are essential. This study designed a low-cost electromagnetic docking guidance (EMDG) system for micro AUVs. The EMDG system is composed of a transmitter coil located on the dock and a three-axial search coil magnetometer acting as a receiver. The search coil magnetometer was optimized for small sizes while maintaining sufficient sensitivity. The signal conditioning and processing subsystem was designed to calculate the deflection angle (β) for docking guidance. Underwater docking tests showed that the system can detect the electromagnetic signal and successfully guide AUV docking. The AUV can still perform docking in extreme positions, which cannot be realized through normal optical or acoustic guidance. This study is the first to focus on the EM guidance system for low-cost micro AUVs. The search coil sensor in the AUV is inexpensive and compact so that the system can be equipped on a wide range of AUVs.

Using Root Cause Analysis and Occupational Safety Research to Prevent Child Sexual Abuse in Schools

Significant progress has been made in the past two decades understanding how child molesters gain access to children and molest them while manipulating others to not get caught. However, incidents of child sexual abuse in schools by educators, and by other children, continue. This manuscript suggests that a comprehensive solution involves two components: (1) using root cause analysis methodology to systematically identify and integrate repetitive causes; (2) to use the findings from voluminous occupational safety research focusing on low-frequency but high-intensity events. Additionally, this manuscript describes eight organizational operations and practices that may reduce the risk of sexual abuse of children by educators or peers in a school setting. These findings were based on existing recommendations and on root cause analysis of thousands of incidents in schools and other youth serving organizations. Finally, the manuscript discusses how a framework drawn from occupational safety research can help schools and other youth serving organizations create environments that will help to create safe environments. Authors have used both components in working with thousands of organizations including faith-based, independent, and urban independent school districts, youth development programs, social service agencies, camps and so on serving diverse populations in 11 countries.

Microporous and Flexible Framework Acoustic Metamaterials for Sound Attenuation and Contrast Agent Applications

The low-frequency (100-1250 Hz) acoustic properties of metal-organic framework (MOF) materials were examined in impedance tube experiments. The anomalously high sound transmission loss of HKUST-1, FeBTC, and MIL-53(Al) quantitatively demonstrated that these prototypical MOFs are absorptive acoustic metamaterials. To the best of our knowledge, this is the first example of MOFs that have been demonstrated to be acoustic metamaterials. Low-frequency acoustic dampening by subwavelength MOF metamaterials is likely due to sound dissipation and absorption facilitated by multiple internal reflections within the microporous framework structure. Modification of MIL-53(Al) with flexible organic linkers clarified that acoustic signatures of the MOFs may be tailored to add or alter certain diagnostic acoustic signatures. These results may be applied to the rational design of lightweight sound-insulating construction materials and acoustic contrast agents for subsurface mapping and monitoring applications at low frequency (100-1250 Hz).

Electromagnetic Analysis, Characterization and Discussion of Inductive Transmission Parameters for Titanium Based Housing Materials in Active Medical Implantable Devices

The growing demand for active medical implantable devices requires data and or power links between the implant and the outside world. Every implant has to be encapsulated from the body by a specific housing and one of the most common materials used is titanium or titanium alloy. Titanium thas the necessary properties in terms of mechanical and chemical stability and biocompatibility. However, its electrical conductivity presents a challenge for the electromagnetic transmission of data and power. The proposed paper presents a fast and practical method to determine the necessary transmission parameters for titanium encapsulated implants. Therefore, the basic transformer-transmission-model is used with measured or calculated key values for the inductances. Those are then expanded with correction factors to determine the behavior with the encapsulation. The correction factors are extracted from finite element method simulations. These also enable the analysis of the magnetic field distribution inside of the housing. The simulated transmission properties are very close to the measured values. Additionally, based on lumped elements and magnetic field distribution, the influential parameters are discussed in the paper. The parameter discussion describes how to enhance the transmitted power, data-rate or distance, or to reduce the size of the necessary coils. Finally, an example application demonstrates the usage of the methods.