Frequency Selectivity Research Articles

Theoretical study of the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH

The coordination environment of Cu (the coordination number and arrangement of surface atoms) plays an important role in CO2 hydrogenation to CH3OH. Compared with the extensive studies of the effects of coordination number, the comprehensive effects of coordination number and arrangement of surface atoms were seldom explored in literature. To unravel the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH, the adsorption and reaction behaviors of H2 and CO2 on Cu(111), (100), (110) and (211) with different coordination numbers and arrangement of surface Cu were systematically calculated by density functional theory (DFT) and kinetic Monte Carlo (kMC) simulation. It was found that the adsorption energies of intermediates in CO2 hydrogenation on Cu surfaces increase with the decrease of coordination number. When the Cu coordination numbers are similar, the charge density on the open surface derived from the different atom arrangement becomes larger and leads to stronger interaction with intermediates than that on the compact one. DFT calculation and kMC simulation indicate that methanol formation pathway follows CO2*→HCOO*→HCOOH*→H2COOH*→H2CO*→CH3O*→CH3OH* on four Cu facets; CO formation is via CO2 direct dissociation on Cu(111), (100) and (110) but COOH* dissociation on (211). The low-coordinated surface Cu with more openness on Cu(211) is the highly active site for CO2 hydrogenation to CH3OH with high turnover of frequency (3.71 × 10−4 s−1) and high selectivity (87.17 %) at 600 K, PCO2 = 7.5 atm and PH2 = 22.5 atm, which is much higher than those on Cu(111), (100) and (110). This work unravels the effects of coordination environment on CO2 hydrogenation at the molecular level and provides an important insight into the design and development of catalysts with high performance in CO2 hydrogenation to CH3OH.

Verification of Outer Hair Cell Motor Protein, Prestin, as a Serological Biomarker for Mouse Cochlear Damage.

The motor protein prestin, found in the inner ear's outer hair cells (OHCs), is responsible for high sensitivity and sharp frequency selectivity in mammalian hearing. Some studies have suggested that prestin could be a serological biomarker for cochlear damage, as OHCs are highly vulnerable to damage from various sources. However, the reported data are inconsistent and lack appropriate negative controls. To investigate whether prestin can be used as a serological biomarker for cochlear damage or stress, we measured prestin quantities in the bloodstreams of mice using ELISA kits from different companies. Wildtype (WT) mice were exposed to different ototoxic treatments, including noise exposure and ototoxic reagents that rapidly kill OHCs. Prestin-knockout (KO) mice were used as a negative control. Our data show that some ELISA kits were not able to detect prestin specifically. The ELISA kit that could detect the prestin protein from cochlear homogenates failed to detect prestin in the bloodstream, despite there being significant damage to OHCs in the cochleae. Furthermore, the optical densities of the serum samples, which correlate to prestin quantities, were significantly influenced by hemolysis in the samples. In conclusion, Prestin from OHCs is not a sensitive and reliable serological biomarker for detecting cochlear damage in mice using ELISA.

Versatile design of tunable Faraday rotator for terahertz band using graphene-InSb-graphene and 1D photonic crystal

A Faraday rotator, composed of graphene-InSb-graphene as magnetic floor and Si- SiO2 materials as the non-magnetic floor is designed to operate at 10 THz frequency, promising for realizing future communication devices. The height of the dielectric layers significantly influences the selection of the resonance frequency. Additionally, the structure can be tuned to operate at a desired frequency thanks to the adjustable surface conductivity of graphene. The findings reveal that variations in the strength of the applied magnetic field intricately modulate the Faraday rotation (FR) and subsequently alter the transmission spectrum. Specifically, values exceeding 40 degrees of FR and a transmission rate of 50% were attainedwhen the magnetic field strength (B) was set at 2 Tesla. Finally, we have proposed a design process for a Faraday rotator that can operate at any arbitrary frequency in the THz band. This innovative design has the potential to introduce a novel approach in ultrathin magneto-optical nanophotonic devices, enabling the realization of polarization rotators characterized by elevated transmittance and reduced reliance on applied static magnetic fields within the THz band.

A novel filtering patch antenna with high selectivity and wide out‐of‐band suppression

AbstractIn this study, a novel filtering patch antenna with high selectivity and wide out‐of‐band suppression is presented. The antenna consists of a square patch, a metal ground and a feeding line, and four radiation nulls are introduced out of the passband. By designing the stepped feeding line with metal vias, two radiation nulls are introduced out of the passband. A U‐shaped slot is etched on the ground, and a third radiation null is produced. A lowpass filter, integrated into the feeding line, results in the fourth radiation null and the harmonic suppression response. By introducing these structures, the antenna achieves satisfactory frequency selectivity and bilateral wide harmonic suppressions. The proposed design is verified by the simulation and measurement results. Measured impedance bandwidth is 15% (3.33–3.87 GHz), which can perfectly cover the 5G‐N78 band, and measured peak gain can reach 9.0 dBi. The measured edge roll‐off rates in the lower and upper sidebands are 232 and 139 dB/GHz, respectively.

Limitations in human auditory spectral analysis at high frequencies.

Humans are adept at identifying spectral patterns, such as vowels, in different rooms, at different sound levels, or produced by different talkers. How this feat is achieved remains poorly understood. Two psychoacoustic analogs of spectral pattern recognition are spectral profile analysis and spectrotemporal ripple direction discrimination. This study tested whether pattern-recognition abilities observed previously at low frequencies are also observed at extended high frequencies. At low frequencies (center frequency ∼500 Hz), listeners were able to achieve accurate profile-analysis thresholds, consistent with prior literature. However, at extended high frequencies (center frequency ∼10 kHz), listeners' profile-analysis thresholds were either unmeasurable or could not be distinguished from performance based on overall loudness cues. A similar pattern of results was observed with spectral ripple discrimination, where performance was again considerably better at low than at high frequencies. Collectively, these results suggest a severe deficit in listeners' ability to analyze patterns of intensity across frequency in the extended high-frequency region that cannot be accounted for by cochlear frequency selectivity. One interpretation is that the auditory system is not optimized to analyze such fine-grained across-frequency profiles at extended high frequencies, as they are not typically informative for everyday sounds.

Wide‐angle band‐pass FSS with high‐frequency selectivity based on SIW cavity technology

AbstractThis work proposes and investigates a wide‐angle band‐pass frequency selective surface (FSS) with two sharp sidebands. The presented FSS element is made up of three metallic layers and two substrate layers in between, which are surrounded by a substrate‐integrated waveguide (SIW) cavity. The top metallic layer is identical to the bottom layer, composed of a square patch etched with a hexagonal groove, while the middle layer is a similar patch but with rectangular notch edges. This structure achieves a second‐order band‐pass response with highly frequency selectivity on either side of the passband. At the same time, this FSS demonstrates excellent stability for both transverse electric and transverse magnetic polarizations with incident angles between 0° and 60°. The electric current and field distributions are demonstrated for deep analysis. Furthermore, an equivalent circuit model is developed to further understand the operating mechanisms. To verify the validity of the design, we construct a prototype of the SIW‐based FSS (SIW‐FSS) and measured it. There is a fair degree of agreement between the measured and simulated results. Finally, we loaded it onto the horn antenna and tested its application in filtering antennas.

Screening for optimal parameters for modified pharyngeal electrical stimulation for the treatment of dysphagia after stroke in rats

Pharyngeal electrical stimulation (PES), a novel noninvasive peripheral nerve stimulation technique, can effectively improve neurogenic dysphagia and increase the safety and effectiveness of swallowing in the clinic. However, the lack of animal models for dysphagia has limited the mechanistic research on PES, which affects its wide application. Therefore, determining optimal parameters for PES in rats is needed to enable mechanistic studies. Modified PES (mPES), which has different waves and pulse widths from PES, was used; in previous studies mPES was found to have a neurological mechanism like that of PES. A poststroke dysphagia (PSD) model was established, and rats with dysphagia were grouped into three different intensities (0.1 mA, 0.5 mA, and 1 mA) for the selection of optimal intensity and three different frequencies (1 Hz, 2 Hz, and 5 Hz) for the selection of optimal frequency based on a stimulation duration of 10 min in the clinic. A Videofluroscopic Swallow Screen (VFSS) was used to assess swallowing function in rats before and after mPES treatment. The results showed that the 1 mA group had better swallowing function (p < 0.05) than the model group. Compared with the model group, the 1 Hz and 5 Hz groups had the same improvement in swallowing function (p < 0.05). However, the increase in excitatory signals in the sensorimotor cortex was more pronounced in the 5 Hz group than in the other frequency stimulation groups (p < 0.05). Combining the clinical findings with the above results, we concluded that the optimal stimulation parameter for mPES in rats is “frequency: 5 Hz, current intensity: 1 mA for 10 min/day”, which provides a basis for future basic experimental studies of mPES in animals.

Exploring deeper groundwater in a dolomite aquifer using telluric electric frequency selection method geophysical approach

Several Telluric Electric Frequency Selection Method (TEFSM) geophysical equipment is now available for groundwater exploration. However, case studies on its application in different hydrogeological settings are limited. This study investigates the TEFSM geophysical approach's application to identify groundwater potential sites for drilling production boreholes in a dolomite aquifer in South Africa. Field tests comprised geophysical surveys using the TEFSM approach to collect vertical and horizontal electrical potential difference profile data from four sites. Evaluation of the potential difference profile data before borehole drilling indicated that two sites had groundwater potential. Two sites were therefore prepared for drilling. Corroboration of the survey data and drilling lithology show that the TEFSM investigated up to 230 m depth and delineated the thickness of the dolomite aquifer from 170 m to 210 m. The dolomite aquifer was delineated based on low EPD contrast ranging from 0.042 to 0.083 mV. The ability of the TEFSM to delineate the dolomite aquifer at a depth of 170–210 m highlights the technical capability of the approach in exploring deeper aquifers that are important to meet the rising demand for freshwater. More research is necessary to establish the EPD ranges of aquifer lithology in different hydrogeological settings. It will assist in the interpretation of the data by field practitioners to optimise the application of this TEFSM technology in groundwater investigations.

An ultra-thin tri-functional coding metasurface based on frequency and polarization selection

An ultra-thin tri-functional coding metasurface based on frequency and polarization selection

Tunable band-stop fiber filter based on laser-induced graphene metamaterial in THz frequency

As an important device in the application of terahertz (THz) technology, a THz filter has broad application prospects in the fields of THz communication, imaging, and sensing. In this paper, a THz filter based on grating structure laser-induced graphene (LIG)/ side polishing terahertz fiber composite structure is proposed. In the experiment, we achieved the maximum Q factor of 23.83 at the central resonant frequency of 0.715 THz. By modifying the grating structure, a tunable operational span of 269 GHz was achieved, along with a tunable range of 21 GHz through laser stimulation. In testing, we found that LIG materials prepared with circular filling are more sensitive to relatively high-power pump lasers, while LIG samples prepared with line filling exhibit better linear response to laser power. Furthermore, the compact and highly integrated nature of the device suggests its broad potential utility in the realm of THz frequency selection.

Criticality and chaos in auditory and vestibular sensing

The auditory and vestibular systems exhibit remarkable sensitivity of detection, responding to deflections on the order of angstroms, even in the presence of biological noise. The auditory system exhibits high temporal acuity and frequency selectivity, allowing us to make sense of the acoustic world around us. As the acoustic signals of interest span many orders of magnitude in both amplitude and frequency, this system relies heavily on nonlinearities and power-law scaling. The vestibular system, which detects ground-borne vibrations and creates the sense of balance, exhibits highly sensitive, broadband detection. It likewise requires high temporal acuity so as to allow us to maintain balance while in motion. The behavior of these sensory systems has been extensively studied in the context of dynamical systems theory, with many empirical phenomena described by critical dynamics. Other phenomena have been explained by systems in the chaotic regime, where weak perturbations drastically impact the future state of the system. Using a Hopf oscillator as a simple numerical model for a sensory element in these systems, we explore the intersection of the two types of dynamical phenomena. We identify the relative tradeoffs between different detection metrics, and propose that, for both types of sensory systems, the instabilities giving rise to chaotic dynamics improve signal detection.

Translational PK/PD and the first-in-human dose selection of a PD1/IL15: an engineered recombinant targeted cytokine for cancer immunotherapy.

Interleukin 15 (IL-15) is a potential anticancer agent and numerous engineered IL-15 agonists are currently under clinical investigation. Selective targeting of IL-15 to specific lymphocytes may enhance therapeutic effects while helping to minimize toxicities. We designed and built a heterodimeric targeted cytokine (TaCk) that consists of an anti-programmed cell death 1 receptor antibody (anti-PD-1) and an engineered IL-15. This "PD1/IL15" selectively delivers IL-15 signaling to lymphocytes expressing PD-1. We then investigated the pharmacokinetic (PK) and pharmacodynamic (PD) effects of PD1/IL15 TaCk on immune cell subsets in cynomolgus monkeys after single and repeat intravenous dose administrations. We used these results to determine the first-in-human (FIH) dose and dosing frequency for early clinical trials. The PD1/IL15 TaCk exhibited a nonlinear multiphasic PK profile, while the untargeted isotype control TaCk, containing an anti-respiratory syncytial virus antibody (RSV/IL15), showed linear and dose proportional PK. The PD1/IL15 TaCk also displayed a considerably prolonged PK (half-life range ∼1.0-4.1 days) compared to wild-type IL-15 (half-life ∼1.1h), which led to an enhanced cell expansion PD response. The PD was dose-dependent, durable, and selective for PD-1+ lymphocytes. Notably, the dose- and time-dependent PK was attributed to dynamic TMDD resulting from test article-induced lymphocyte expansion upon repeat administration. The recommended first-in-human (FIH) dose of PD1/IL15 TaCk is 0.003mg/kg, determined based on a minimum anticipated biological effect level (MABEL) approach utilizing a combination of in vitro and preclinical in vivo data. This work provides insight into the complex PK/PD relationship of PD1/IL15 TaCk in monkeys and informs the recommended starting dose and dosing frequency selection to support clinical evaluation of this novel targeted cytokine.

Efficient minimum blind area model for system and interference uncertainty

AbstractIn the anti‐interference of broadband communication radio, interference cancellation performance is seriously affected by the uncertainty of the working frequency selection of the communication system and the direction of hostile interference. The closed‐form solution of the interference cancellation weight value and the signal‐to‐interference noise ratio after the cancellation are derived and simplified to clarify the factors affecting interference cancellation quality. Then, the efficient blind area criterion is established for the low computational complexity in view of cancellation quality, which combines the radio communication index and anti‐interference demand index. Based on this criterion, the minimum blind area model is proposed for robust performance. The experimental results in the auxiliary antenna spacing optimisation are consistent with the theoretical analysis, verifying the effectiveness of the proposed model in dealing with uncertain communication frequency and interference direction. It is very promising in communication interference cancellation.

Development of a Tetherless Bioimpedance Device That Uses Morphologic Changes to Predict Blood Flow Restrictions Mimicking Peripheral Artery Disease Progression.

A tetherless multi-targeted bioimpedance device was designed, modeled, built, and tested for measuring arterial pulse and, using morphological analysis, its potential for monitoring blood flow restrictions that mimic Peripheral Artery Disease (PAD) was assessed across multiple peripheral arteries. Specifically, we first developed a small form factor, tetherless, bioimpedance device, based on high-frequency structure simulator (HFSS) simulations. After designing and building the device we then tested it in vivo on human subjects on multiple arteries and found that we did not need to modify the gain on the device compared to the bench top system. Further, it was found that changes in the morphology of the bioimpedance signal over time, depicted through the ratio of the first and second harmonic in the signal frequency, could be used to predict blood flow restrictions that mimic peripheral artery disease (PAD). The HFSS simulations helped guide the modulation frequency selection and the placement of the bioimpedance electrodes. We built the device and compared it to two commercially available bioimpedance devices and it was shown to demonstrate a distinct advantage in its multi-target capability, enabling more accurate pulse measurements from different arteries without the need for tuning the circuit for each artery. Comparing the ratio of the 1st and 2nd harmonics as a function of the blood flow restriction, the two commercial devices showed a maximum error across arteries of between 22% and 27% depending on the measurement location, whereas our system consistently displayed a stable value of just below 4%. With this system, there is the potential for comprehensive and personalized medical examinations for PAD at the point of care (POC).

Revealing the EMIC Wave Frequency Differences in the Ionosphere via Coordinated Observations: A Case Study

AbstractWe study electromagnetic ion cyclotron (EMIC) waves based on observations from the ionosphere, magnetosphere, and ground during a geomagnetic storm recovery phase on 28 August 2018. In this case, multiple ducting EMIC waves in the ionosphere show higher frequencies in the post‐midnight than those in the pre‐midnight. Ionospheric EMIC wave frequency differences in magnetic local time (MLT) are consistent with MLT frequency differences in the equatorial magnetosphere, which are mainly caused by different background magnetic field at different L‐shells. Moreover, we report the first observation of frequency range selections in ionospheric ducting EMIC waves and find that frequency selections depend on the magnetic field intensity in the main part of the ionospheric waveguide, with higher frequency corresponding to larger magnetic field. This study reveals the important role of background magnetic field in regulating ducting EMIC wave frequencies in the ionosphere.

Psilocybin decreases neural responsiveness and increases functional connectivity while preserving pure-tone frequency selectivity in mouse auditory cortex.

Psilocybin is a serotonergic psychedelic believed to have therapeutic potential for neuropsychiatric conditions. Despite well-documented prevalence of perceptual alterations, hallucinations, and synesthesia associated with psychedelic experiences, little is known about how psilocybin affects sensory cortex or alters the activity of neurons in awake animals. To investigate, we conducted two-photon imaging experiments in auditory cortex of awake mice and collected video of free-roaming mouse behavior, both at baseline and during psilocybin treatment. In comparison with pre-dose neural activity, a 2 mg/kg ip dose of psilocybin initially increased the amplitude of neural responses to sound. Thirty minutes post-dose, behavioral activity and neural response amplitudes decreased, yet functional connectivity increased. In contrast, control mice given intraperitoneal saline injections showed no significant changes in either neural or behavioral activity across conditions. Notably, neuronal stimulus selectivity remained stable during psilocybin treatment, for both tonotopic cortical maps and single-cell pure-tone frequency tuning curves. Our results mirror similar findings regarding the effects of serotonergic psychedelics in visual cortex and suggest that psilocybin modulates the balance of intrinsic versus stimulus-driven influences on neural activity in auditory cortex.NEW & NOTEWORTHY Recent studies have shown promising therapeutic potential for psychedelics in treating neuropsychiatric conditions. Musical experience during psilocybin-assisted therapy is predictive of treatment outcome, yet little is known about how psilocybin affects auditory processing. Here, we conducted two-photon imaging experiments in auditory cortex of awake mice that received a dose of psilocybin. Our results suggest that psilocybin modulates the roles of intrinsic neural activity versus stimulus-driven influences on auditory perception.

Frequency-selective acoustic micromanipulation platform

Acoustic micromanipulation methods offer versatile tools ranging from lab-on-chip diagnostic platforms to mobile microrobots. Acoustically oscillating bubble-powered microsystems are gaining increased attention owing to their low cost and convenient operation. To date, no studies have reported on the controllability of the driving frequency on acoustic micromanipulation platforms using Helmholtz resonators. Here, we introduce a Helmholtz resonant cavity into a bubble-powered microsystem to reveal the function of the oscillation modes and frequency selectivity. The Su–Schrieffer–Heeger (SSH) model was utilized to construct a topological interfacial state and bubble-powered working location. We experimentally observed that the microparticles were captured by the oscillation bubble and underwent orbital rotation at the topological frequency. However, the microparticles were tightly bound close to the oscillation bubble area when the driving frequency was outside the topological frequency range. Our acoustic micromanipulation platform implements multiple microparticle manipulation modes based on frequency selectivity that are independent of optical or magnetic properties, which can enrich the micromanipulation toolbox and exhibit enormous application potential in the biomedical field.

SPFS: SNR peak-based frequency selection method to alleviate resolution degradation in MPI real-time imaging

Objective. The primary objective of this study is to address the reconstruction time challenge in magnetic particle imaging (MPI) by introducing a novel approach named SNR-peak-based frequency selection (SPFS). The focus is on improving spatial resolution without compromising reconstruction speed, thereby enhancing the clinical potential of MPI for real-time imaging. Approach. To overcome the trade-off between reconstruction time and spatial resolution in MPI, the researchers propose SPFS as an innovative frequency selection method. Unlike conventional SNR-based selection, SPFS prioritizes frequencies with signal-to-noise ratio (SNR) peaks that capture crucial system matrix information. This adaptability to varying quantities of selected frequencies enhances versatility in the reconstruction process. The study compares the spatial resolution of MPI reconstruction using both SNR-based and SPFS frequency selection methods, utilizing simulated and real device data. Main results. The research findings demonstrate that the SPFS approach substantially improves image resolution in MPI, especially when dealing with a limited number of frequency components. By focusing on SNR peaks associated with critical system matrix information, SPFS mitigates the spatial resolution degradation observed in conventional SNR-based selection methods. The study validates the effectiveness of SPFS through the assessment of MPI reconstruction spatial resolution using both simulated and real device data, highlighting its potential to address a critical limitation in the field. Significance. The introduction of SPFS represents a significant breakthrough in MPI technology. The method not only accelerates reconstruction time but also enhances spatial resolution, thus expanding the clinical potential of MPI for various applications. The improved real-time imaging capabilities of MPI, facilitated by SPFS, hold promise for advancements in drug delivery, plaque assessment, tumor treatment, cerebral perfusion evaluation, immunotherapy guidance, and in vivo cell tracking.

Selection of an Optimal Frequency for Offshore Wind Farms

Offshore wind power has attracted significant attention due to its high potential, capability for large-scale farms, and high capacity factor. However, it faces high investment costs and issues with subsea power transmission. Conventional high-voltage AC (HVAC) methods are limited by charging current, while high-voltage DC (HVDC) methods suffer from the high cost of power conversion stations. The low-frequency AC (LFAC) method mitigates the charging current through low-frequency operation and can reduce power conversion station costs. This paper aims to identify the economically optimal frequency by comparing the investment costs of LFAC systems at various frequencies. The components of LFAC, including transformers, offshore platforms, and cables, exhibit frequency-dependent characteristics. Lower frequencies result in an increased size and volume of transformers, leading to higher investment costs for offshore platforms. In contrast, cable charging currents and losses are proportional to frequency, causing the total cost to reach a minimum at a specific frequency. To determine the optimal frequency, simulations of investment costs for varying capacities and distances were conducted.

Yolk-shell electron-rich Ru@hollow pyridinic-N-doped carbon nanospheres with tunable shell thickness and ultrahigh surface area for biomass-derived levulinic acid hydrogenation under mild conditions

Aiming to efficiently upgrade renewable biomass-derived levulinic acid (LA) into γ-valerolactone (GVL), we have devised yolk-shell electron-rich Ru@hollow pyridinic-N-doped carbon nanospheres, featuring a tunable shell thickness (20−70 nm) and an ultrahigh surface area (4016 m2 g−1). Experimental and theoretical investigations reveal that the strategic formation of the yolk-shell structure and appropriate thinning of the carbon shell facilitate the generation of electron-rich Ru0 and a positive shift of the d-band center towards the Fermi level by increasing surface pyridinic-N species. These modifications suitably intensify Ru0−H interaction, promote reactant adsorption, stimulate electron transfer between active H and the CO group of LA, and ultimately reduce apparent activation energy. Consequently, a high LA turnover frequency (18733.4 h−1 at 30 °C) and GVL selectivity (99.9%), alongside excellent stability up to eight cycles, are achieved, markedly outperforming externally-supported analogues. These findings afford valuable insights into designing yolk-shell nanostructures for biomass upgrading through microenvironment engineering.