Frequency-dependent Effects Research Articles

Statistical Analysis of Graph-Theoretic Indices to Study EEG-TMS Connectivity in Patients With Depression.

AimThe objective of this work was to demonstrate the usefulness of a novel statistical method to study the impact of transcranial magnetic stimulation (TMS) on brain connectivity in patients with depression using different stimulation protocols, i.e., 1 Hz repetitive TMS over the right dorsolateral prefrontal cortex (DLPFC) (protocol G1), 10 Hz repetitive TMS over the left DLPFC (G2), and intermittent theta burst stimulation (iTBS) consisting of three 50 Hz burst bundle repeated at 5 Hz frequency (G3).MethodsElectroencephalography (EEG) connectivity analysis was performed using Directed Transfer Function (DTF) and a set of 21 indices based on graph theory. The statistical analysis of graph-theoretic indices consisted of a combination of the k-NN rule, the leave-one-out method, and a statistical test using a 2 × 2 contingency table.ResultsOur new statistical approach allowed for selection of the best set of graph-based indices derived from DTF, and for differentiation between conditions (i.e., before and after TMS) and between TMS protocols. The effects of TMS was found to differ based on frequency band.ConclusionA set of four brain asymmetry measures were particularly useful to study protocol- and frequency-dependent effects of TMS on brain connectivity.SignificanceThe new approach would allow for better evaluation of the therapeutic effects of TMS and choice of the most appropriate stimulation protocol.

A Study in Frequency-dependent Effects on Precision Pulsar Timing Parameters with the Pulsar Signal Simulator

Abstract In this paper we introduce a new python package, the Pulsar Signal Simulator, or psrsigsim, which is designed to simulate a pulsar signal from emission at the pulsar, through the interstellar medium, to observation by a radio telescope, and digitization in a standard data format. We use psrsigsim to simulate observations of three millisecond pulsars, PSRs J1744–1134, B1855+09, and B1953+29, to explore the covariances between frequency-dependent parameters, such as variations in the dispersion measure (DM), pulse profile evolution with frequency, and pulse scatter broadening. We show that psrsigsim can produce realistic simulated data and can accurately recover the parameters injected into the data. We also find that while there are covariances when fitting DM variations and frequency-dependent parameters, they have little effect on timing precision. Our simulations also show that time-variable scattering delays decrease the accuracy and increase the variability of the recovered DM and frequency-dependent parameters. Despite this, our simulations also show that the time-variable scattering delays have little impact on the rms of the timing residuals. This suggests that the variability seen in recovered DMs, when time-variable scattering delays are present, is due to a covariance between the two parameters, with the DM modeling out the additional scattering delays.

Online and offline effects of transcranial alternating current stimulation of the primary motor cortex

Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique that allows interaction with endogenous cortical oscillatory rhythms by means of external sinusoidal potentials. The physiological mechanisms underlying tACS effects are still under debate. Whereas online (e.g., ongoing) tACS over the motor cortex induces robust state-, phase- and frequency-dependent effects on cortical excitability, the offline effects (i.e. after-effects) of tACS are less clear. Here, we explored online and offline effects of tACS in two single-blind, sham-controlled experiments. In both experiments we used neuronavigated transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) as a probe to index changes of cortical excitability and delivered M1 tACS at 10 Hz (alpha), 20 Hz (beta) and sham (30 s of low-frequency transcranial random noise stimulation; tRNS). Corticospinal excitability was measured by single pulse TMS-induced motor evoked potentials (MEPs). tACS was delivered online in Experiment 1 and offline in Experiment 2. In Experiment 1, the increase of MEPs size was maximal with the 20 Hz stimulation, however in Experiment 2 neither the 10 Hz nor the 20 Hz stimulation induced tACS offline effects. These findings support the idea that tACS affects cortical excitability only during online application, at least when delivered on the scalp overlying M1, thereby contributing to the development of effective protocols that can be applied to clinical populations.

Bladder and bowel responses to lumbosacral epidural stimulation in uninjured and transected anesthetized rats

Spinal cord epidural stimulation (scES) mapping at L5-S1 was performed to identify parameters for bladder and bowel inhibition and/or contraction. Using spinally intact and chronic transected rats of both sexes in acute urethane-anesthetized terminal preparations, scES was systematically applied using a modified Specify 5–6–5 (Medtronic) electrode during bladder filling/emptying cycles while recording bladder and colorectal pressures and external urethral and anal sphincter electromyography activity. The results indicate frequency-dependent effects on void volume, micturition, bowel peristalsis, and sphincter activity just above visualized movement threshold intensities that differed depending upon neurological intactness, with some sex-dependent differences. Thereafter, a custom-designed miniature 15-electrode array designed for greater selectivity was tested and exhibited the same frequency-dependent urinary effects over a much smaller surface area without any concurrent movements. Thus, select activation of autonomic nervous system circuitries with scES is a promising neuromodulation approach for expedient translation to individuals with SCI and potentially other neurologic disorders.

Enhanced Phase Estimation for Long-Haul Multi-Carrier Systems Using a Dual-Reference Subcarrier Approach

Multi-subcarrier (MSC) modulation is recently standing out as a notable new feature in the latest generations of high-speed coherent optical transceivers, providing distinctive advantages over legacy single-carrier systems. However, the transition from single-carrier to MSC modulation still requires significant optimization of digital signal processing subsystems, in order to maximize the inherent potential of subcarrier multiplexing. In this article, the penalty associated with the usage of carrier phase estimation (CPE) methods inherited from single-carrier systems is quantitatively studied and the need for enhanced MSC-tailored solutions is evidenced. A novel pilot-based joint-subcarrier CPE method based on a dual-reference subcarrier (DRS) approach is described and numerically assessed. The proposed DRS-CPE exploits the frequency-dependent walk-off effect imposed by chromatic dispersion (CD) to enable the separation of phase noise processes incurred by the transmitter and local oscillator lasers, thereby allowing to effectively apply joint-subcarrier CPE independently of the symbol-rate per subcarrier. Our numerical results demonstrate that the proposed DRS-CPE enables to operate with near-optimum performance at symbol-rates per subcarrier as low as 1 Gbaud over ultra-long-haul distances.

Frequency-Dependent Effects on Bladder Reflex by Saphenous Nerve Stimulation and a Possible Action Mechanism of Tibial Nerve Stimulation in Cats.

PurposeThe present study determined the effects of saphenous nerve stimulation (SNS) at different stimulation frequencies on bladder reflex and explored a possible action mechanism of tibial nerve stimulation (TNS) on bladder activity in cats.MethodsTwo bipolar nerve cuff electrodes were implanted on the saphenous nerve and the contralateral tibial nerve in 13 cats, respectively. Multiple cystometrograms were obtained to determine the effects of single SNS at different frequencies and that of combined SNS and TNS on the micturition reflex by infusing normal saline.ResultsSNS at 1 Hz significantly reduced the bladder capacity (BC) to 59.8%±7.7% and 59.3%±5.8% of the control level at the intensity threshold (T) and 2T, respectively (P<0.05), while that at 20 Hz significantly increased the BC to 130.6%±4.2% of the control level at 6T (P<0.05). The TNS and SNS at 20 Hz did not significantly change the BCs at 1T (P>0.05), while combined stimulation at 1T significantly increased the BC to 122.7%±1.9% of the control level and induced an inhibitory effect which was similar to that TNS at 2T.ConclusionsThe current study revealed that SNS reduced and increased BC depending on different stimulation frequencies. The combined SNS and TNS maximized the clinical efficacy at a low intensity. Also, SNS may be a potential therapeutic mechanism of TNS.

Evaluation Method of the Vibration Reduction Effect Considering the Real Load- and Frequency-Dependent Stiffness of Slab-Track Mats.

The purpose of this research was to investigate and improve the accuracy of the existing slab-track mat (STM) specifications in the evaluation of the vibration reduction effect. The static nonlinearity and dynamic mechanical characteristics of three types of STMs were tested, and then a modified fractional derivative Poynting–Thomson (FDPT) model was used to characterize the preload and frequency dependence. A modified vehicle–floating slab track (FST) coupled dynamic model was established to analyze the actual insertion loss. The insertion loss error evaluated by the frequency-dependent tangent stiffness increased with the increase in STM nonlinearity, and the error obtained by the third preload tangent stiffness was usually greater than that of the second preload. Compared with the secant stiffness, the second preload frequency-dependent tangent stiffness was more suitable for evaluating STMs with high-static–low-dynamics (HSLD) stiffness. In order to reflect the frequency dependence effect and facilitate engineering applications, it is recommended that second preload tangent stiffness corresponding to the natural frequency of the FST be used for evaluation. Furthermore, the insertion loss of the STMs with monotonically increased stiffness decreased as the axle load increased, and the opposite was true for the STMs with monotonically decreased stiffness. The vibration isolation efficiency of the STMs with HSLD stiffness was both stable and better than that of the STMs with monotonic stiffness.

Damping of gravitational waves in 2-2-holes

A 2-2-hole is an explicit realization of a horizonless object that can still very closely resemble a BH. An ordinary relativistic gas can serve as the matter source for the 2-2-hole solution of quadratic gravity, and this leads to a calculable area-law entropy. Here we show that it also leads to an estimate of the damping of a gravitational wave as it travels to the center of the 2-2-hole and back out again. We identify two frequency dependent effects that greatly diminish the damping. Spinning 2-2-hole solutions are not known, but we are still able to consider some spin dependent effects. The frequency and spin dependence of the damping helps to determine the possible echo resonance signal from the rotating remnants of merger events. It also controls the fate of the ergoregion instability.

A Correlation Between Electric Fields That Target the Cell Membrane Potential and Dividing HeLa Cancer Cell Growth Inhibition.

Clinical studies show that low intensity (single V/cm), intermediate-frequency (100kHz-300kHz) electric fields inhibit the growth of cancer cells, while the mechanism is not yet understood. We examine the hypothesis that electric fields modify the cell membrane potential of dividing cancer cells in a way that correlates with cells growth inhibition. A Schwan based mathematical model calculates the changes in HeLa cells membrane potential due to single V/cm electric fields and frequencies from 0.1 to 1MHz. An experimental study examines the effect of these electric fields on the inhibition of HeLa cells growth in an incubator. The theoretical calculation shows that the effects of these electric fields on cell membrane potential decrease with an increase in frequency. The HeLa cells experiments verified the inhibitory effect of these fields on cell growth. The inhibitory effect is decreasing with an increase in frequency, in a way that is similar to the frequency dependent effect of these fields on the cell membrane potential. The superposition of the theoretical results and the experimental results suggest a correlation between the effect of these fields on the cell membrane potential and inhibition of cancer cell growth. It should be emphasized that correlations do not prove causality, however, they suggest an area for future research. These findings have value for the understanding of the mechanisms of cancer cells growth inhibition with electric fields and suggest an interesting area of research on the interaction between electromagnetic fields and cancer cells.

The frequency-dependent effect of electrical fields on the mobility of intracellular vesicles in astrocytes

Slow-wave sleep, defined by low frequency (<4 Hz) electrical brain activity, is a basic brain function affecting metabolite clearance and memory consolidation. The origin of low-frequency activity is related to cortical up and down states, but the underlying cellular mechanism of how low-frequency activities affect metabolite clearance and memory consolidation has remained elusive. We applied electrical stimulation with voltages comparable to in vivo sleep recordings over a range of frequencies to cultured glial astrocytes while monitored the trafficking of GFP-tagged intracellular vesicles using total internal reflection fluorescence microscopy (TIRFM). We found that during low frequency (2 Hz) electrical stimulation the mobility of intracellular vesicle increased more than 20%, but remained unchanged under intermediate (20 Hz) or higher (200 Hz) frequency stimulation. We demonstrated a frequency-dependent effect of electrical stimulation on the mobility of astrocytic intracellular vesicles. We suggest a novel mechanism of brain modulation that electrical signals in the lower range frequencies embedded in brainwaves modulate the functionality of astrocytes for brain homeostasis and memory consolidation. The finding suggests a physiological mechanism whereby endogenous low-frequency brain oscillations enhance astrocytic function that may underlie some of the benefits of slow-wave sleep and highlights possible medical device approach for treating neurological diseases.

A direct measurement method of quantum relaxation time.

The quantum relaxation time of electrons in condensed matters is an important physical property, but its direct measurement has been elusive for a century. Here, we report a breakthrough that allows direct determination of quantum relaxation time at zero and non-zero frequencies using optical measurement. Through dielectric loss function, we connect bound electron effects to the physical parameters of plasma resonance and find an extra term of quantum relaxation time from inelastic scattering between bound electrons and conduction electrons at non-zero frequencies. We demonstrate here that the frequency-dependent inelastic polarization effect of bound electrons is the dominant contribution to quantum relaxation time of conduction electrons at optical frequencies, and the elastic polarization effect of bound electrons also dramatically changes the plasma resonance frequency through effective screening to charge carriers.

Effect of frequency dependence on the seismic performance of linear viscoelastic base-isolated structures

The purpose is to address two issues arising from the frequency dependence of viscoelastic (VE) isolation bearings implemented in base-isolated structures (BIS): (i) how the frequency dependence affects the structural response; and (ii) which method is appropriate for the VE BIS. Effects of the frequency dependence on the absolute acceleration transmissibility are analyzed based on a two-degree-of-freedom system. Three generic algorithms: (i) constant-parameter approximation (CPA), (ii) mode superposition iteration, and (iii) modified rational polynomial approximate (RPA) are used to calculate the seismic responses. Effects of the frequency dependence on the seismic responses of the VE BIS subjected to the historic earthquakes are numerically analyzed through a five-story frame structure. The results show that the frequency dependence of the stiffness can broaden the absolute acceleration transmissibility curve of the VE BIS. The seismic responses in general are underestimated when the frequency dependence is not well considered, and the response errors are influenced by the frequency dependence, excitation characteristics and structural dynamic property. The RPA method takes into account the frequency dependence of VE isolation bearings completely through the rational polynomial model. The CPA and mode superposition iteration methods can only consider frequency dependence effect partially, and the mode superposition iteration method performs better.

Electromagnetic transient modeling of grounding electrodes buried in frequency dependent soil with variable water content

The increasing demand for electricity over the past few decades has been continuously urging for more reliable power systems. Power transmission line networks, due to their vast physical dimensions, are the most critical components of a complex power system concerning the direct lightning strike. Grounding systems are widely used to mitigate the transient overvoltages for the protection of electrical component and human safety. The goal of this paper is to investigate the effect of frequency dependence of soil electrical parameters on the performance of vertical and horizontal grounding electrodes subjected to direct lightning strike, considering a variable water content of soil. Four soil models that take into account the variation of soil water content are reviewed and compared. The numerical simulations are performed using a full-wave electromagnetic model based on the Finite Element Method (FEM) in the frequency range from 1 kHz to 5 MHz and applying different soil models with varying water content. Then, electromagnetic transient (EMT) compatible equivalent circuits of grounding electrodes are developed using Fast Relaxed Vector Fitting (FRVF). Typical first and subsequent return stroke current waveforms measured at two different locations are adopted. The results of this paper demonstrate the importance of considering the variation of soil water content in the transient response of grounding electrodes. Simulation results demonstrate that the frequency dependence of the soil parameters lead to a decrease of the potential rise of the grounding electrodes compared to the case where the soil parameters are assumed constant. The effect of soil water content on the grounding performance is also shown to be dependent on the soil type, value of soil water content, and length of electrode.

Analysis of Organic Light-Emitting Diode SPICE Models with Constant or Voltage-Dependent Components.

A simplified OLED SPICE model with two resistors and two capacitors that have constant or voltagedependent (VD) values is proposed. Our model includes physical characteristics such as voltage and frequency dependency and agrees well with measurements. In this paper, we analyze the OLED frequency dependency effects and RC delay properties by controlling model parameters for DC, AC, and transient conditions. Importantly, we found that a model with constant parameters is simple and is accurate enough. Based on our simulation results, we suggest a new guideline for an OLED SPICE circuit model and simulation target.

Ground-Motion Attenuation, Stress Drop, and Directivity of Induced Events in the Groningen Gas Field by Spectral Inversion of Borehole Records

ABSTRACTProduction-induced earthquakes in the Groningen gas field caused damage to buildings and concerns for the population, the gas-field owner, and the local and national authorities and institutions. The largest event (ML=3.6) occurred in 2012 near Huizinge, and, despite the subsequent decision of the Dutch government to reduce the gas production in the following years, similar magnitude events occurred in 2018 and 2019 (ML=3.4). Thanks to the improvement of the local seismic networks in the last years, recent events provide a large number of recordings and an unprecedented opportunity to study the characteristics of induced earthquakes in the Groningen gas field and related ground motions.In this study, we exploit the S-wave Fourier amplitude spectra recorded by the 200 m depth borehole sensors of the G network from 2015 to 2019 to derive source and attenuation parameters for ML≥2 induced earthquakes. The borehole spectra are decomposed into source, attenuation, and site nonparametric functions, and parametric models are then adopted to determine moment magnitudes, corner frequencies, and stress drops of 21 events. Attenuation and source parameters are discussed and compared with previous estimates for the region. The impact of destructive interference of upgoing and downgoing waves at borehole depth on the derived parameters is also discussed and assessed to be minor.The analysis of the apparent source spectra reveals that several events show rupture directivity and provides clear observations of frequency-dependent directivity effects in induced earthquakes. The estimated rupture direction shows a good agreement with orientation of pre-existing faults within the reservoir. Our results confirm that rupture directivity is still an important factor for small-magnitude induced events, affecting the amplitude of recorded short-period response spectra and causing relevant spatial ground-motion variability.

Top Coating Anti-Erosion Performance Analysis in Wind Turbine Blades Depending on Relative Acoustic Impedance. Part 2: Material Characterization and Rain Erosion Testing Evaluation

Under droplet impingement, surface leading edge protection (LEP) coating materials for wind turbine blades develop high-rate transient pressure build-up and a subsequent relaxation in a range of strain rates. The stress-strain coating LEP behavior at a working frequency range depends on the specific LEP and on the material and operational conditions, as described in this research in a previous work. Wear fatigue failure analysis, based on the Springer model, requires coating and substrate speed of sound measurements as constant input material parameters. It considers a linear elastic response of the polymer subjected to drop impact loads, but does not account for the frequency dependent viscoelastic effects for the materials involved. The model has been widely used and validated in the literature for different liquid impact erosion problems. In this work, it is shown the appropriate definition of the viscoelastic materials properties with ultrasonic techniques. It is broadly used for developing precise measurements of the speed of sound in thin coatings and laminates. It also allows accurately evaluating elastic moduli and assessing mechanical properties at the high frequencies of interest. In the current work, an investigation into various LEP coating application cases have been undertaken and related with the rain erosion durability factors due to suitable material impedance definition. The proposed numerical procedures to predict wear surface erosion have been evaluated in comparison with the rain erosion testing, in order to identify suitable coating and composite substrate combinations. LEP erosion performance at rain erosion testing (RET) technique is used widely in the wind industry as the key metric, in an effort to assess the response of the varying material and operational parameters involved.

Effect of Channel Engineering on Quasi-Static Capacitance-Voltage Characteristics of Double-Gate MOSFET

The quasi-static capacitance–voltage (QSCV) characteristics of 10-nm-gate-length double-gate N-type metal–oxide–semiconductor field-effect transistors (NMOSFETs) with Si, Ge, InAs, $$ {\hbox{In}}_{0.53} {\hbox{Ga}}_{0.47} {\hbox{As}} $$ , and GaAs as channel materials are studied and simulated using Silvaco ATLAS three-dimensional (3D) technology computer-aided design (TCAD) software. The QSCV approach offers the advantage of immunity against frequency dependence effects and the ability to measure small capacitances in the 100 fF range. In this device, we consider the self-consistent solution of Schrodinger’s equation with Poisson’s equation. The splitting of the conduction band into multiple subbands is considered, while there is no doping in the channel region. The effects of metal gate electrode engineering, channel engineering (Si, Ge, GaAs, $$ {\hbox{In}}_{0.53} {\hbox{Ga}}_{0.47} {\hbox{As}} $$ , and InAs), and different channel thicknesses with $$ \left( {{\hbox{Al}}_{2} {\hbox{O}}_{3} } \right) $$ as gate oxide having thickness of 0.8 nm on the QSCV characteristics are studied. A comparison of the QSCV characteristics is carried out for the above-mentioned channel materials, revealing a significant reduction in the inversion-mode QSCV characteristics for all the materials due to quantization that results in a decrease in the overall gate-to-channel capacitance and hence increases the threshold voltage of the MOS device. The QSCV characteristics are also useful to measure the oxide thickness, flat-band voltage, threshold voltage, maximum depletion region thickness, charge distribution in the dielectric, interface trap charge, and interface states between the channel and gate oxide before device fabrication.

Reheat flames response to entropy waves

Sequential combustion architectures rely on auto-ignition flame stabilization in the second stage combustor. Due to the exponential temperature dependence of the ignition delay time the second stage flames can respond to hot spots generated by unsteady first stage combustion. In this paper, the auto-ignition flame response is investigated by extending an existing analytical model for acoustic waves so that it also accounts for entropy waves. Explicit expressions for the flame transfer functions and linear to non-linear transition thresholds are derived. Results for different operating conditions, forcing amplitudes and frequencies are discussed. For this, three computational domains of increasing complexity are considered for model validation: a 2D duct, a 3D backward facing step, and finally a full-scale Ansaldo Energia GT26 sequential combustor. Unsteady Reynold-averaged Navier–Stokes as well as large-eddy simulations are performed. Acoustic and entropic contributions of the flame response are separated by means of system identification techniques. Finally, non-linear flame transfer functions are identified. It is observed that the gains linearly increase with the excitation frequency and non-linear, frequency dependent effects are observed already for small amplitude levels of excitation.

Frequency-Dependent Light Stimulation Effects on Performance During Vigilance Tasks on a Laptop.

Students, office workers, or other computer and mobile device users can suffer from decrements in alertness or productivity, but many intervention methods on these can be too distracting or even affect daily routines. Using heart rate (HR) to determine a fast and slow target frequency at which to oscillate light brightness stimulation on a laptop, thirty-six participants joined a cognitive task where we hypothesized that fast frequency stimulation would increase alertness and decrease relaxation, while slow frequency stimulation would have the opposite effects. We found that slow frequency stimulation produces a statistically significant delay in response time, users react more slowly (3.8e2 ± 5.5e1 ms), when compared to the no stimulation (3.7e2 ± 4.1e1 ms) (p = 9.0e-3) conditions. The (Slow - No Stimulation) response time (1.7e1 ± 2.7e2 ms) produced a statistically significant delay in response time versus the (Fast - No Stimulation) response time (-0.74 ± 2.4e1 ms) (p = .016). These delays due to slow stimulation occurred without influencing accuracy or subjective sleepiness ratings. We observed that frequency-dependent light stimulation can potentially influence HRV metrics such as the mean normal-to-normal intervals and mean HR. Future work will target breathing rate to determine light stimulation oscillations as we further investigate the potential of using the slow-frequency domain to unobtrusively influence user performance and physiology.

Non-equilibrium magnetic properties in bimorphic phases of ErIr3

In this work, we report the successful synthesis of a polycrystalline, binary compound ErIr3, forming a macroscopic coexistence of two different cubic structures (AuBe5-type and AuCu3-type). The magnetic properties of two polymorphs could be distinguished by means of different measurement techniques. The detailed study of dc magnetization and heat capacity behaviour confirm that the phase with the cubic AuBe5-type structure orders ferromagnetically below 5.2 K, while the AuCu3-type phase remains paramagnetic down to 2.5 K. The presence of a glassy state in this compound is manifested in the frequency dependent ac susceptibility measurement, magnetic relaxation and magnetic memory effect.