Frequency-dependent Response Research Articles

Frequency-Dependent Antioxidant Responses in HT-1080 Human Fibrosarcoma Cells Exposed to Weak Radio Frequency Fields.

This study explores the complex relationship between radio frequency (RF) exposure and cancer cells, focusing on the HT-1080 human fibrosarcoma cell line. We investigated the modulation of reactive oxygen species (ROS) and key antioxidant enzymes, including superoxide dismutase (SOD), peroxidase, and glutathione (GSH), as well as mitochondrial superoxide levels and cell viability. Exposure to RF fields in the 2-5 MHz range at very weak intensities (20 nT) over 4 days resulted in distinct, frequency-specific cellular effects. Significant increases in SOD and GSH levels were observed at 4 and 4.5 MHz, accompanied by reduced mitochondrial superoxide levels and enhanced cell viability, suggesting improved mitochondrial function. In contrast, lower frequencies like 2.5 MHz induced oxidative stress, evidenced by GSH depletion and increased mitochondrial superoxide levels. The findings demonstrate that cancer cells exhibit frequency-specific sensitivity to RF fields even at intensities significantly below current safety standards, highlighting the need to reassess exposure limits. Additionally, our analysis of the radical pair mechanism (RPM) offers deeper insight into RF-induced cellular responses. The modulation of ROS and antioxidant enzyme activities is significant for cancer treatment and has broader implications for age-related diseases, where oxidative stress is a central factor in cellular degeneration. The findings propose that RF fields may serve as a therapeutic tool to selectively modulate oxidative stress and mitochondrial function in cancer cells, with antioxidants playing a key role in mitigating potential adverse effects.

Joint phase control in metasurfaces for optical convolution operations

Combining the propagation and geometric phases in a metasurface facilitates the independent control of multiple parameters of the light field. However, the geometric phase often displays a random distribution, making it difficult to observe directly. We introduce a frequency-dependent phase response: at frequency f1, there is a superposition of the geometric and propagation phases, whereas at frequency f2, the propagation phase remains constant, and only the geometric phase is applied. The superposition can be interpreted as a convolution process in far-field Fraunhofer diffraction, enabling convolution metasurface devices to generate complex orbital angular momentum beams array and patterned array. Notably, the geometric phase aligns with the characteristic distribution of orbital angular momentum beams, allowing direct observation of the loaded geometric phase. These findings open what we believe to be new avenues for manipulating and calculating complex vector optical fields, optical information coding, controlling light-matter interactions, and enhancing optical communication.

Dielectric and Shear-Mechanical "Humps" in the Nonlinear Response of Polar Glassformers.

Many glassformers display electrorheological effects and a pronounced maximum in their frequency dependent nonlinear dielectric response. The latter so-called "hump" feature was often linked to correlated-particle motions and, so far, was not explored in the large-perturbation mechanical response of viscous liquids. To first clarify the electro-viscoelastic coupling in the linear domain, using the modified Gemant, DiMarzio, and Bishop model, it is demonstrated how the small-amplitude shear mechanical response of S-methoxy-PC, a derivative of propylene carbonate, can be related to its complex dielectric permittivity. Then, in the nonlinear regime, a "hump" feature is identified in the rheological third-order shear modulus of S-methoxy-PC and of another polar glassformer, propylene glycol. Thus, the observation of a "hump" in the cubic response of viscous liquids does not necessarily rely on the application of electrical fields.

Reflection of Storm Surge and Tides in Convergent Estuaries With Dams, the Case of Charleston, USA

AbstractConvergent estuaries have been shortened by dam‐like structures worldwide. Here, we evaluate 31 long‐term water level stations and use a semi‐analytical tide model to investigate how landward‐funneling and a dam influence tidal and storm surge propagation in the greater Charleston Harbor region, South Carolina, where three rivers meet: the Ashley, Cooper, and Wando. Results show that the phase speed and amplification of the principal tidal harmonic (M2) is larger than other long waves such as storm surge (∼1–4 days) and setup‐setdown (∼4–10 days). Further landward, all waves attenuate, but, as they approach the dam on the Cooper River, a frequency dependent response in amplitude and phase progression occurs. A semi‐analytical tidal model shows that funneling and the presence of a dam amplify tidal waves through wave interference from partial and full reflection, respectively. The different phase progressions of the reflected waves interact with the incident wave to increase or decrease the summed overall wave amplitude. Using a friction‐convergence parameter space, we demonstrate that dominant tides in 23 estuaries and the tidal, storm surge, and setup‐setdown waves in the Cooper River can be delineated into three regimes that describe landward amplification or attenuation associated with funneling, a dam, or both. The regime of each tidal constituent is consistent but can change with the duration and height of each storm surge event; dam associated wave interference can attenuate long‐duration events, while the most intense events (short duration, high water) are amplified by dams more than funneling and greatly increase flood exposure.

High internal phase Pickering emulsion solely stabilized by low-content chitosan: Insight into relations between network microstructures and rheological properties

Nano-sized and well-dispersed chitosan particles (CSPs) are prepared by adjusting pH towards pKa of chitosan (CS) aqueous solutions. The prepared CSPs are able to stabilize high internal phase Pickering emulsions (HIPPEs) with low CSP contents, at minimum of 0.2 wt% CSP stabilizing a maximum of 85 % oil phase fraction in a near-neutral environment. It is clarified by microscopy, small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS) measurements that CSPs act as Pickering particle emulsifiers to form a network immobilizing oil droplets in HIPPEs. Using power-law analysis on SAOS results, the solid-like but frequency-dependent rheological response is attributed to the physical connection among CSPs, while the overshoot of the loss modulus in LAOS test is assigned to the featured resistance of networks to the applied large deformation. The oil phase fraction, CSP concentration, temperature and ionic strength are found to be key factors for the rheological behavior and emulsion stability. This work is expected to guide the design and processing of HIPPE stabilized solely by polysaccharides.

Pulse generators for enhanced magnetomotive ultrasound: Toward a cost-effective imaging for tissue characterization.

Magnetomotive ultrasound (MMUS) stands out as a promising and effective ultrasound-based method for detecting magnetic nanoparticles (MNPs) within tissues. This innovative technique relies on the precise estimation of micrometric displacements induced by the interaction of an external magnetic field with MNPs. Pulsed MMUS has emerged as a strategic alternative to address limitations associated with harmonic excitation, such as heat generation in amplifiers and coils, frequency-dependent tissue mechanical responses, and prolonged magnetic field rise times. Despite the growing interest in MMUS, the devices conventionally employed to excite the coil are not specifically tailored to generate intense magnetic fields while minimizing interference with the transient behavior of induced displacements. To bridge this gap, our work introduces the design and fabrication of two pulse generators: one based on a capacitor-discharge circuit and the other on a resonant-inverter circuit. We evaluated the performance of these pulse generators by considering parameters such as the magnetic field generated, rise and fall times, and their ability to supply sustained current for varied pulse widths across different pulse repetition frequencies. Furthermore, we carried out a practical MMUS implementation using tissue-mimicking phantoms, demonstrating the capability of both devices to achieve magnetic fields of up to 1T and average displacements of 25 µm within the phantom. In addition, we estimated the shear wave velocity, effective shear modulus, and their temperature-dependent variations. Our findings highlight the versatility and efficacy of the proposed pulse generators and emphasize their potential as low-cost platforms for theranostic applications, enabling the assessment of targeted entities within biological tissues.

Viscoelasticity of diverse biological samples quantified by Acoustic Force Microrheology (AFMR)

In the context of soft matter and cellular mechanics, microrheology - the use of micron-sized particles to probe the frequency-dependent viscoelastic response of materials – is widely used to shed light onto the mechanics and dynamics of molecular structures. Here we present the implementation of active microrheology in an Acoustic Force Spectroscopy setup (AFMR), which combines multiplexing with the possibility of probing a wide range of forces ( ~ pN to ~nN) and frequencies (0.01–100 Hz). To demonstrate the potential of this approach, we perform active microrheology on biological samples of increasing complexity and stiffness: collagen gels, red blood cells (RBCs), and human fibroblasts, spanning a viscoelastic modulus range of five orders of magnitude. We show that AFMR can successfully quantify viscoelastic properties by probing many beads with high single-particle precision and reproducibility. Finally, we demonstrate that AFMR to map local sample heterogeneities as well as detect cellular responses to drugs.

Nonlinear dielectric response in glass formers: Restoring forces and avoided spin-glass criticality.

Experimental measurements of nonlinear dielectric response in glass formers like supercooled glycerol or propylene carbonate have been interpreted as providing evidence for a growing thermodynamic length scale when lowering temperature. A heuristic picture based on coherently flipping "superdipoles" with disordered internal structure has been argued to capture the essence of the experimentally reported behavior, pointing to the key role of effectively disordered interactions in structural glasses. We test these ideas by devising an explicit one-dimensional model of interacting spins incorporating both the spin-glass spirit of the superdipole argument and the necessary long-time decorrelation of structural disorder, encoded here in a slow dynamics of the coupling constants. The frequency-dependent third-order response of the model qualitatively reproduces the typical humped shape reported in experiments. The temperature dependence of the maximum value is also qualitatively reproduced. In contrast, the humped shape of the third-order response is not reproduced by a simple kinetically constrained spin model with noninteracting spins. To rationalize these results, we propose a two-length-scale scenario by distinguishing between the characteristic length of dynamical heterogeneities and a rigidity length that accounts for the local tendency of spins to flip coherently as a block, in the presence of interactions. We show that both length scales are identical in the kinetically constrained spin model, while they have significantly different dynamics in the model of interacting spins.

About Cosmic Microwave Background Radiation (CMBR)

Because the CMBR follows the PLANCK's radiation law more or less exactly, it should, because of the indistinguishability of individual photons, apply to a whatever black emitter. Therefrom arises the guess, that the existence of an upper cut- off frequency of the vacuum could be the cause for the decrease in the upper frequency range. Since the lower-frequent share of the curve correlates with the frequency response of an oscillating circuit with the Qfactor ½, it is examined, whether it succeeds to approximate the Planck curve by multi-plication of the initial curve with the dynamic, time- dependent frequency response of the above-mentioned model. Reason of the time-dependence is the expansion of the universe. This work is based on a model published in [1]. It is shown, that the PLANCK graph can be approximated by application of the cumulative frequency response given by the model, upon the spectrum of an oscillatory circuit with the Q-factor ½. Furthermore, the progression of frequency, energy and entropy is analysed. The results point out, that origin and progression of the CMBR have elapsed in a totally different manner than generally assumed. Because photons behaved like neutrinos immediately after BB they did not interact with other matter then. Thus, we can exactly calculate back to 8.08·10–106s instead of 379,000 years after BB. Section 6 has been reworked.

A compact circuit-based metasurface for enhancing magnetic resonance imaging

Herein, we propose a compact 0.36 T MRI-enhancing circuit-based metasurface working at its third order mode. Different from most MRI-enhancing metasurface designs which exploit the fundamental mode with the highest enhancement, our choice is a trade-off between the enhancement and homogeneity. The metasurface is organized with capacitively-loaded metal wires where the capacitors decrease the electric length of the wires thus enabling a deep subwavelength scale. The working frequency of metasurface is tuned to the Larmor frequency, contributing to the redistribution of transmitted field. Full-wave simulations based on CST Microwave Studio compare the magnetic field in a mimicked MRI environment with and without the metasurface. The utilization of metasurface leads to a field enhancement ratio of 9.36-fold over a 28 × 28 cm2 area at 2 cm height while exceeding unity till almost 12 cm. Meanwhile, the variation of the quasi-homogenous magnetic field is less than 1/3 over a relatively large area. The impact of metasurface is further demonstrated by simulations with a head bio-model to evaluate the transmitted field strength and electromagnetic energy absorption. A preliminary measuring experiment is also conducted to validate the special mode pattern. The proposed metasurface effectively enhances the transmitted efficiency thus can be employed in clinical MRI to enhance imaging quality or reduce the input power. Moreover, this design paradigm is compatible with other enhancing approaches due to the nonmagnetic inclusions and frequency-dependent response and can be adapted for higher-field MRI systems by adjusting the length of metal wires and the value of loaded capacitors.

A reduction in near-field hydroacoustic flow noise using shark skin-inspired surfaces

Recent studies have demonstrated improved hydrodynamic performance for hydrofoils and uncrewed underwater vehicles (UUVs) using passive surface geometries such as riblets and shark skin-inspired denticles. However, little is known about the impact of added surface roughness on the production of flow-induced noise, a critical design consideration for UUVs in sensitive environments. We present here experimental results of near-field hydroacoustic noise measurements for boundary layer flow over smooth and bioinspired denticle-covered surfaces. A 3 in. wide and 10 in. long segment of staggered denticles was fabricated in-house using photopolymer 3D printing, and flow and acoustic measurements were made in a custom-built flow channel using particle image velocimetry (PIV) and miniature hydrophones. Comparing acoustic power spectra over flat and denticle-covered plates, we find both a scale- and frequency-dependent response in radiated noise. At low flow speeds (Re ∼ 20,000), the denticle surface shows a 20 dB enhancement in radiated noise at frequencies below 1000 Hz, but no change at higher frequencies. While at high flow speeds (Re ∼ 60 000), the denticle surface reduces radiated noise by ∼10 dB for frequencies between 4000 and 8000 Hz. Analysis of PIV data will elucidate the flow physics responsible for these effects. [Work sponsored by Office of Naval Research.]

Neuromorphic auditory classification based on a single dynamical electrochemical memristor

Designing compact computing hardware and systems is highly desired for resource-restricted edge computing applications. Utilizing the rich dynamics in a physical device for computing is a unique approach in creating complex functionalities with miniaturized footprint. In this work, we developed a dynamical electrochemical memristor from a static memristor by replacing the gate material. The dynamical device possessed short-term fading dynamics and exhibited distinct frequency-dependent responses to varying input signals, enabling its use as a single device-based frequency classifier. Simulation showed that the device responses to different frequency components in a mixed-frequency signal were additive with nonlinear attenuation at higher frequency, providing a guideline in designing the system to process complex signals. We used a rate-coding scheme to convert real world auditory recordings into fixed amplitude spike trains to decouple amplitude-based information and frequency-based information and was able to demonstrate auditory classification of different animals. The work provides a new building block for temporal information processing.

Analyzing Temperature – Dependent Structural Changes and Frequency Response of a Ferroelectric Nanocomposite Based on Triglycine Sulfate with Oxidized Multiwalled Carbon Nanotubes

The present work is a continuing study on anomalous properties of the ferroelectric nanocomposite from triglycine sulfate (TGS) and oxidized multiwalled carbon nanotubes (OMWCNT). In this study, the nature of frequency response in a region of 102–107 Hz at low temperatures (63–273 K) will be clarified by analyzing structural changes when reducing temperature. It was found that the interaction between TGS and OMWCNT inhibited the switching of SO4 - groups, leading to a significant increase in relaxation time, activation energies and coercive fields. Consequently, the domain – wall freezing occurred at higher temperatures than those in pure TGS.

Stochastic Syncing in Sinusoidally Driven Atomic Orbital Memory.

Stochastically fluctuating multiwell systems are a promising route toward physical implementations of energy-based machine learning and neuromorphic hardware. One of the challenges is finding tunable material platforms that exhibit such multiwell behavior and understanding how complex dynamic input signals influence their stochastic response. One such platform is the recently discovered atomic Boltzmann machine, where each stochastic unit is represented by a binary orbital memory state of an individual atom. Here, we investigate the stochastic response of binary orbital memory states to sinusoidal input voltages. Using scanning tunneling microscopy, we investigated orbital memory derived from individual Fe and Co atoms on black phosphorus. We quantify the state residence times as a function of various input parameters such as frequency, amplitude, and offset voltage. The state residence times for both species, when driven by a sinusoidal signal, exhibit synchronization that can be quantitatively modeled by a Poisson process based on the switching rates in the absence of a sinusoidal signal. For individual Fe atoms, we also observe a frequency-dependent response of the state favorability, which can be tuned by the input parameters. In contrast to Fe, there is no significant frequency dependence in the state favorability for individual Co atoms. Based on the Poisson model, the difference in the response of the state favorability can be traced to the difference in the voltage-dependent switching rates of the two different species. This platform provides a tunable way to induce population changes in stochastic systems and provides a foundation toward understanding driven stochastic multiwell systems.

Quantitative prediction of the fracture scale based on frequency-dependent S-wave splitting

The development of natural fractures has a significant impact on underground reservoirs and leads to seismic anisotropy. Furthermore, the scale of natural fractures directly affects oil and gas preservation, hydraulic fracture construction, and the production development of shale reservoirs. The S-wave anisotropy is a frequency-dependent parameter and the change in S-wave anisotropy with frequency is a function of the fracture scale. We develop an innovative method for predicting the fracture scale quantitatively using frequency-dependent S-wave anisotropy. The quantitative relationship between different fracture scales and the frequency-dependent response of the S-wave splitting (SWS) anisotropy can be obtained using a dynamic rock-physics model. The frequency-dependent S-wave anisotropy is calculated via SWS analysis in the frequency domain, after which this quantitative relationship and the calculated frequency-dependent response are used to establish an objective function for the inversion of the fracture scale at different depths using the least-squares algorithm. We synthesize data under ideal conditions, test our method, apply our method to field data, and find that the quantitative prediction method of the fracture scale yielded reasonable prediction results. The S-wave anisotropy is calculated based on the SWS analysis from the horizontal components of the upgoing wavefields of the field vertical seismic profile. We compare the fracture scale calculated from logging data using our method, and the results obtained indicate that this method can successfully predict the fracture scale quantitatively.

A Closed-Form Expression for the Frequency-Dependent Microwave Responsivity of Transistors Based on the I–V Curve and S-Parameters

A Closed-Form Expression for the Frequency-Dependent Microwave Responsivity of Transistors Based on the <i>I</i>–<i>V</i> Curve and S-Parameters

Comparing the Perceived Intensity of Vibrotacitle Cues Scaled Based on Inherent Dynamic Range.

Wearable devices increasingly incorporate vibrotactile feedback notifications to users, which are limited by the frequency-dependent response characteristics of the low-cost actuators that they employ. To increase the range and type of information that can be conveyed to users via vibration feedback, it is crucial to understand user perception of vibration cue intensity across the narrow range of frequencies that these actuators operate. In this paper, we quantify user perception of vibration cues conveyed via a linear resonant actuator embedded in a bracelet interface using two psychophysical experiments. We also experimentally determine the frequency response characteristics of the wearable device. We then compare user perceived intensity of vibration cues delivered by the bracelet when the cues undergo frequency-specific amplitude modulation based on user perception compared to modulation based on the experimental or manufacturer-reported characterization of the actuator dynamic response. For applications in which designers rely on user perception of cue amplitudes across frequencies to be equivalent, it is recommended that a perceptual calibration experiment be conducted to determine appropriate modulation factors. For applications in which only relative perceived amplitudes are important, basing amplitude modulation factors on manufacturer data or experimentally determined dynamic response characteristics of the wearable device should be sufficient.

Frequency-Dependent Quadratic Response Properties and Two-Photon Absorption from Relativistic Equation-of-Motion Coupled Cluster Theory.

We present the implementation of quadratic response theory based upon the relativistic equation-of-motion coupled cluster method. We showcase our implementation, whose generality allows us to consider both time-dependent and time-independent electric and magnetic perturbations, by considering the static and frequency-dependent hyperpolarizability of hydrogen halides (HX, X = F-At), providing comprehensive insights into their electronic response characteristics. Additionally, we evaluated the Verdet constant for noble gases Xe and Rn and discussed the relative importance of relativistic and electron correlation effects for these magneto-optical properties. Finally, we calculate the two-photon absorption cross sections of transition [ns1S0 → (n + 1)s1S0] of Ga+ and In+, which are suggested as candidates for new ion clocks. As our implementation allows for the use of nonrelativistic Hamiltonians as well, we have compared our EOM-QRCC results to the QR-CC implementation in the DALTON code and show that the differences between CC and EOMCC response are in general smaller than 5% for the properties considered. Collectively, the results underscore the versatility of our implementation and its potential as a benchmark tool for other approximated models, such as density functional theory for higher-order properties.

Ion-Mediated Recombination Dynamics in Perovskite-Based Memory Light-Emitting Diodes for Neuromorphic Control Systems.

Neuromorphic devices can help perform memory-heavy tasks more efficiently due to the co-localization of memory and computing. In biological systems, fast dynamics are necessary for rapid communication, while slow dynamics aid in the amplification of signals over noise and regulatory processes such as adaptation- such dual dynamics are key for neuromorphic control systems. Halide perovskites exhibit much more complex phenomena than conventional semiconductors due to their coupled ionic, electronic, and optical properties which result in modulatable drift, diffusion of ions, carriers, and radiative recombination dynamics. This is exploited to engineer a dual-emitter tandem device with the requisite dual slow-fast dynamics. Here, a perovskite-organic tandem light-emitting diode (LED) capable of modulating its emission spectrum and intensity owing to the ion-mediated recombination zone modulation between the green-emitting quasi-2D perovskite layer and the red-emitting organic layer is introduced. Frequency-dependent response and high dynamic range memory of emission intensity and spectra in a LED are demonstrated. Utilizing the emissive read-out, image contrast enhancement as a neuromorphic pre-processing step to improve pattern recognition capabilities is illustrated. As proof of concept using the device's slow-fast dynamics, an inhibition of the return mechanism is physically emulated.

Temperature and frequency dependent response of electrical conduction and dielectric relaxation mechanism in CuCr2O4 tetragonally distorted spinel chromite

Herein, the polycrystalline CuCr2O4 (CCO) electro-ceramic was prepared via the sol-gel self-combustion route. The X-ray powder diffraction analysis at room temperature revealed that the CCO chromite was synthesized in a single phase tetragonally distorted normal spinel structure with I41/amd space group. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigated the polycrystalline nature of the compound. The microstructural analysis by field emission scanning electron microscopy (FESEM) explored the surface morphology of micron-sized grains (Gs) distinguished by well-pronounced grain boundaries (GBs) available for electrical response of the material. The color mapping images of elements by energy-dispersive X-ray spectroscopy (EDS) divulged the homogeneous distribution of elements in the compound. The surface chemistry of the compound was studied by X-ray photoelectron spectroscopy (XPS). This information helped in understanding the electronic states of the ions contributing to the electrical networks and mechanisms responsible for the charge transport within the CCO system. The dielectric relaxation and electrical transport properties were analyzed using complex impedance spectroscopy (CIS) over the experimental range of frequency and temperature from 40 Hz to 1 MHz and 243–493 K, respectively. The experimental complex impedance data were analyzed by RGQGRGBQGB equivalent circuit model which resolved the electro-active contributions of bulk and interface of the CCO spinel to its electrical dynamics. The dispersion in AC conductivity was explained by Jonscher's double power law which provided evidence of small polaron hopping (SPH) as a dominant transport mechanism governing electrical conduction in the compound. The temperature-dependent DC conductivity pattern exhibited an Arrhenius-like behavior that followed Mott and Davis's model of SPH. The analysis of complex electrical modulus M*(ω,T) professed the localized and de-localized movements of the charge carriers. The dielectric permittivity response of CCO followed Havriliak-Negami (HN) phenomenology that divulged the existence of non-Debye type dielectric relaxation processes. The interfacial polarization was observed to be accountable for the dispersion in dielectric loss spectra.