Frequency Shift Research Articles

Structural Characterization of Pyruvic Acid Dimers Formed inside Helium Nanodroplets by Infrared Spectroscopy and Ab Initio Study.

The structural arrangements of α-keto acid complexes hold significant interest across various fields of chemistry such as enzyme modeling, drug design, or polymer blending. Herein, we report mass-selective infrared (IR) spectra of pyruvic acid monomers and dimers in the range 1720-1820 cm-1 recorded in helium nanodroplets at 0.37 K. The monomer features IR bands at 1807.1 and 1734.5 cm-1, which are assigned to the carboxylic and ketonic C═O stretching vibrations, respectively. Furthermore, the pyruvic acid dimers generated inside the helium nanodroplets are characterized by carboxylic and ketonic C═O stretch vibrations appearing at 1799.2 and 1737.0 cm-1, respectively. This frequency shift of ±7 cm-1 for both C═O stretching bands from the monomer to the dimer demonstrates that the structural motif of the monomer is maintained upon dimer aggregation in helium nanodroplets. The structural assignments were supported by a comparison of the MP2/aug-cc-pVDZ-predicted harmonic vibrational spectra at the C═O stretching region with the experiments. The global minimum monomer structure with an intramolecular hydrogen bond and its dimer stabilized by both inter- and intramolecular hydrogen bonding interactions reproduce the experimental spectra from the monomer and dimer. This assigned dimer structure lies ca.11 kJ/mol above the corresponding global minimum and is favored in helium nanodroplets due to the long-range realignment of molecules via dipole-dipole interaction, followed by short-range stabilization upon intermolecular hydrogen bond formation. The barrier for reconfiguration of the precooled monomer conformer leading to the formation of the most stable dimer structure is around 58 kJ/mol, which is infeasible at 0.37 K.

Bimodal Absorber Frequencies Shift Induced by the Coupling of Bright and Dark Modes

In this paper, we demonstrate that the absorption frequencies of the bimodal absorber shift with the coupling strength of the bright and dark modes. The coupling between the bright mode and the dark mode can acquire electromagnetically induced transparency, we obtain the analytical relationship between the absorbing frequencies, the resonant frequencies, losses of the bright mode and dark mode, and the coupling strength between two modes by combining the coupled mode theory with the interference theory. As the coupling strength between the bright mode and the dark mode decreases, the two absorption peaks gradually move closer to each other, inversely, they will move away from each other. The simulation employs three distinct metasurface structures with coupling of the bright and dark modes, thereby verifying the generality of the theoretical findings.

High‐Speed and Long‐Distance Spin‐Wave Propagation in Spinel γ‐Fe2O3 Epitaxial Thin Films

AbstractIn spin wave (SW) devices, the modulation of SWs for computational units is necessary, imposing extremely high demands on material systems. In this study, high‐quality epitaxial‐grown spinel γ‐Fe2O3 thin films on conductive Nb‐doped SrTiO3 substrates, achieving fast‐speed, high‐frequency, and long‐distance SW propagation in this ferrimagnetic material, are developed. A novel two‐step film growth technique using pulsed laser deposition is proposed and optimized, and the damping constant, exchange stiffness, and anisotropies of γ‐Fe2O3 are determined. Compared to reported semiconductor magnetic materials, these epitaxial‐grown γ‐Fe2O3 thin films exhibit a significantly lower damping constant of 10−2, representing a substantial advancement. Using finite‐difference calculations, SW propagation is simulated, and vital information on transmission distance and dispersion curves is obtained. Experimental results show excellent agreement with these simulations. By applying a voltage to both sides of the conducting substrate, current across the film and SW device, resulting in the frequency shift of the SWs, is generated. These results demonstrate that high‐quality γ‐Fe2O3 films developed through the two‐step growth method can efficiently propagate SWs, offering possibilities for various modulation methods in SW‐based computing devices. This study positions spinel γ‐Fe2O3 as a promising ferrimagnetic candidate for future applications in efficient SW modulation within computational systems.

Probing the Effects of Size and Charge on the Monohydration and Dihydration of SiF5- and SiF62- via Comparisons with BF4- and PF6.

This study systematically examines the interactions of the trigonal bipyramidal silicon pentafluoride and octahedral silicon hexafluoride anions with either one or two water molecules, (SiF5-(H2O)n and SiF62-(H2O)n, respectively, where n = 1, 2). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed using the CCSD(T) ab initio method with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for Si, O, and F; denoted as haTZ). Two monohydrate and six dihydrate minima have been identified for the SiF5-(H2O)n systems, whereas one monohydrate and five dihydrate minima have been identified for the SiF62-(H2O)n systems. Both monohydrated anions have a minimum in which the water molecule adopts a symmetric double ionic hydrogen bond (DIHB) motif with C2v symmetry. However, a second unique monohydrate minimum has been identified for SiF5- in which the water molecule adopts an asymmetric DIHB motif along the edge of the trigonal bipyramidal anion between one axial and one equatorial F atom. This Cs structure is more than 2 kcal mol-1 lower in energy than the C2v local minimum at the CCSD(T)/haTZ level of theory. While the interactions between the solvent and ionic solute are quite strong for the monohydrated anions (electronic dissociation energies of ≈12 and ≈24 kcal mol-1 for the SiF5-(H2O)1 and SiF62-(H2O)1 global minima, respectively), these values are nearly perfectly doubled for the dihydrates, with the lowest-energy SiF5-(H2O)2 and SiF62-(H2O)2 minima exhibiting dissociation energies of ≈24 and ≈47 kcal mol-1, respectively. Structures that form hydrogen bonds between the solvating water molecules also exhibit the largest shifts in the harmonic OH stretching frequencies for the waters of hydration. These shifts can exceed -100 cm-1 for the SiF5-(H2O)2 minimum and -300 cm-1 for the SiF62-(H2O)2 minimum relative to an isolated H2O molecule at the CCSD(T)/haTZ level of theory. This work also corrects the OH stretching frequency shifts for two dihydrate minima of PF6- that were previously erroneously reported ( J. Phys. Chem. A 2020, 124, 8744-8752, DOI: 10.1021/acs.jpca.0c06466).

Across two continents: The genomic basis of environmental adaptation in house mice (Mus musculus domesticus) from the Americas.

Replicated clines across environmental gradients can be strong evidence of adaptation. House mice (Mus musculus domesticus) were introduced to the Americas by European colonizers and are now widely distributed from Tierra del Fuego to Alaska. Multiple aspects of climate, such as temperature, vary predictably across latitude in the Americas. Past studies of North American populations across latitudinal gradients provided evidence of environmental adaptation in traits related to body size, metabolism, and behavior and identified candidate genes using selection scans. Here, we investigate genomic signals of environmental adaptation on a second continent, South America, and ask whether there is evidence of parallel adaptation across multiple latitudinal transects in the Americas. We first identified loci across the genome showing signatures of selection related to climatic variation in mice sampled across a latitudinal transect in South America, accounting for neutral population structure. Consistent with previous results, most candidate SNPs were in putatively regulatory regions. Genes that contained the most extreme outliers relate to traits such as body weight or size, metabolism, immunity, fat, eye function, and the cardiovascular system. We then compared these results with the results of analyses of published data from two transects in North America. While most candidate genes were unique to individual transects, we found significant overlap among candidate genes identified independently in the three transects. These genes are diverse, with functions relating to metabolism, immunity, cardiac function, and circadian rhythm, among others. We also found parallel shifts in allele frequency in candidate genes across latitudinal gradients. Finally, combining data from all three transects, we identified several genes associated with variation in body weight. Overall, our results provide strong evidence of shared responses to selection and identify genes that likely underlie recent environmental adaptation in house mice across North and South America.

Fully Breaking Entanglement of Multiple Harmonics for Space- and Frequency-Division Multiplexing Wireless Applications via Space-Time-Coding Metasurface.

Harmonic generation and utilization are significant topics in nonlinear science. Although the progress in the microwave region has been expedited by the development of time-modulated metasurfaces, one major issue of these devices is the strong entanglement of multiple harmonics, leading to criticism of their use in frequency-division multiplexing (FDM) applications. Previous studies have attempted to overcome this limitation, but they suffer from designing complexity or insufficient controlling capability. Here a new space-time-coding metasurface (STCM) is proposed to independently and precisely synthesize not only the phases but also the amplitudes of various harmonics. This promising feature is successfully demonstrated in wireless space- and frequency-division multiplexing experiments, where modulated and unmodulated signals are simultaneously transmitted via different harmonics using a shared STCM. To illustrate the advantages, binary frequency shift keying (BFSK) and quadrature phase shift keying (QPSK) modulation schemes are respectively implemented. Behind the intriguing functionality, the mechanism of the space-time coding strategy and the analytical designing method are elaborated, which are validated numerically and experimentally. It is believed that the achievements can potentially propel the time-vary metasurfaces in the next-generation wireless applications.

Anti-IgG Doped Melanin Nanoparticles Functionalized Quartz Tuning Fork Immunosensors for Immunoglobulin G Detection: In Vitro and In Silico Study

The quartz tuning fork (QTF) is a promising instrument for biosensor applications due to its advanced properties such as high sensitivity to physical quantities, cost-effectiveness, frequency stability, and high-quality factor. Nevertheless, the fork’s small size and difficulty in modifying the prongs’ surfaces limit its wide use in experimental research. Our study presents the development of a QTF immunosensor composed of three active layers: biocompatible natural melanin nanoparticles (MNPs), glutaraldehyde (GLU), and anti-IgG layers, for the detection of immunoglobulin G (IgG). Frequency shifts of QTFs after MNP functionalization, GLU activation, and anti-IgG immobilization were measured with an Asensis QTF F-master device. Using QTF immunosensors that had been modified under optimum conditions, the performance of QTF immunosensors for IgG detection was evaluated. Accordingly, a finite element method (FEM)-based model was produced using the COMSOL Multiphysics software program (COMSOL License No. 2102058) to simulate the effect of deposited layers on the QTF resonance frequency. The experimental results, which demonstrated shifts in frequency with each layer during QTF surface functionalization, corroborated the simulation model predictions. A modelling error of 0.05% was observed for the MNP-functionalized QTF biosensor compared to experimental findings. This study validated a simulation model that demonstrates the advantages of a simulation-based approach to optimize QTF biosensors, thereby reducing the need for extensive laboratory work.

Terahertz Sensing Based on Floating Bilayer Metasurface with Toroidal Dipole Resonance Toward Ultra‐High Sensitivity

AbstractMetasurface structures have proven to be effective in enhancing terahertz sensing signals and can thus be used as sensors to improve terahertz detection sensitivity. However, the sensitivity is limited by the poor spatial overlap between the analytes and the local electric field of the metasurface. In this work, a novel design of a floating bilayer metasurface structure for terahertz sensing is proposed and investigated. This structure supports a sharp toroidal dipole resonance and can concentrate near‐field energy on the analyte and metal atoms rather than on the substrate surface by floating the metal atoms. Consequently, the sensitivity is significantly improved to as high as 362 GHz RIU−1; theoretically, this is approximately 2.6 times higher than that of the common metasurface. The ability of the floating bilayer metasurface to quantitatively detect chlorothalonil is experimentally demonstrated. The resonance peak shows a significant frequency shift of 7 GHz for a change of 0.0001 mg dL−1 in chlorothalonil concentration, reaching up to 86 GHz when the change in chlorothalonil concentration is 100 mg dL−1; this is approximately 6.6 times higher than that of the common metasurface. This work provides opportunities for metasurface to realize ultrasensitive sensing in the terahertz regime.

Frequency characteristics of collimated blue light generated by four-wave mixing in cesium vapor

The frequency evaluation of collimated blue light (CBL) generated by parametric four-wave mixing (FWM) in hot atomic vapor is presented. The cesium (133Cs) atoms are excited from the 6S1/2 ground state to 8S1/2 excited state with the 852 and 795 nm pump lasers, producing an optical field at 4.2 µm through an amplified spontaneous emission via population inversion on the 8S1/2 → 7P3/2 transition and the 456 nm CBL via FWM on the 7P3/2 → 6S1/2 transition. The frequency shift of 456 nm CBL has been measured by velocity-selective optical pumping spectral technique when the frequency of any one of two pumping lasers is tuned. The ratio of the frequency shift of 456 nm CBL to the two-photon frequency detuning of two pumping lasers is 0.8912, implying that the generated 4.2 µm light frequency is also correspondingly shifted.

Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures

Quantum magnonics investigates the quantum-mechanical properties of magnons, such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 μm-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total crystallographic anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultralow millikelvin temperatures, crucial for developing quantum magnonic devices.

Dynamically Tunable Half‐Ring Fano Resonator Based on Black Phosphorus

A tunable material black phosphorus (BP) terahertz (THz) half‐ring Fano resonator is proposed, exhibiting enhanced sensitivity, tunable frequency parameters, and the flexible sensing range. A half‐ring is positioned above the main channel, while a groove is excavated beneath it to produce the Fano resonance. The discrete mode of the half‐ring is coupled with the continuous mode of the groove, leading to a significantly enhanced sensitivity. This sensor can pick up subtle changes in the surrounding environment. Additionally, the incorporation of BP into the half‐ring positioned above the channel enables the flexible adjustment of the Fano resonator's resonant frequency. This adjustment is achieved through the manipulation of the electron doping concentration of the BP material. At the third‐order resonance around 5.81 THz, the frequency shift margin can reach 160 GHz. Adjusting the structural parameters of the Fano resonator, such as the radius of its outer ring, the distance of this ring to the main channel, and the groove's height, significantly affects its transmission spectrum. The Fano resonator demonstrates its considerable potential for applications in the field of integrated electronics. It not only provides an innovative design perspective, but also lays the foundation for the study of THz systems.

Dynamical states associated with the shift in whistling frequency in aeroacoustic system

Self-sustained aeroacoustic oscillations arising from the interactions between the hydrodynamic and acoustic fields are perceived as a whistle. Such whistling can lead to large amplitude acoustic oscillations that have disastrous consequences for engineering systems such as large segmented solid rocket motors and large gas pipelines. The whistling corresponds to the state of limit cycle oscillations (LCO) in dynamical systems theory. An aeroacoustic system exhibits different dynamical states when the bulk flow velocity is varied as a control parameter. Understanding the dynamical states and the transitions between them, as the control parameter is varied, is crucial in designing control strategies for such aeroacoustic oscillations. Previous studies have shown that as the control parameter varies, in an aeroacoustic system that has a flow through orifices, the whistling frequency shifts. We show that such a change in frequency occurs via three different scenarios— (1) direct transition between the two LCOs as an abrupt transition, (2) via a state of intermittency, and (3) via a state of aperiodicity. In the current aeroacoustic system, the abrupt transition between the LCOs is manifested as a bursting behaviour where the amplitude of the acoustic pressure fluctuations abruptly switches between the high and low-amplitude LCOs. Further, we show that the dynamical state and the transition between them during the frequency shift have a correlation with the magnitude of the frequency shift. Using recurrence theory we show that there is a change in the dynamical state of the system during the frequency shift. Further, we use synchronisation theory to investigate the coupled behaviour of the velocity (u′) and the acoustic pressure (p′) fluctuations during the different dynamical states. Our findings imply that u′ and p′ exhibit phase synchronisation (PS) during the state of LCO, corresponding to whistling. In contrast, u′ and p′ are desynchronised during the state of aperiodicity, corresponding to stable operation. Furthermore, the bursts of periodic oscillations during intermittency correspond to the phase-synchronised epochs of periodic u′ and p′, and the aperiodic epochs correspond to the desynchronised aperiodic u′ and p′.

Driving voltage frequency and electrode material effects on electromagnetic radiation of the surface dielectric barrier discharge in the air

The electrical discharges are, among others, accompanied by the emission of electromagnetic waves of various frequencies. We studied this emission for the surface dielectric barrier discharge in the air. We used the discharge with one strip-driven electrode and a sinusoidal driving voltage of frequencies 5 and 10 kHz. From the spectra of emitted waves in the frequency band up to 3 GHz, we found that this type of discharge emits the radiation of frequencies below 500 MHz. In this frequency band, we focused on the effect of the driving voltage frequency and driven electrode material on the spectra of these waves. It was found that emitted radiation is distributed in several packages of frequencies, and an increase in the driving voltage frequency or voltage increases the power level of emitted radiation. Compared with the radiation spectrum of the discharge with an aluminium-driven electrode in the spectrum of the discharge with the copper-driven electrode, new peaks of various power levels and the shift of certain radiation frequencies to lower values appear. To understand the underlying mechanism of the discharge electromagnetic waves emission, we focused on the correlation between the electric component of emitted EMWs and the discharge electrical parameters as a function of time and discharge voltage.Graphical abstract

Method for Two-Stage Radar Measurement of the Blade Repetition Rate of a Propeller-Driven Aircraft

Introduction. Radar images of aircraft propellers can significantly improve the quality of their recognition and protection against simulating interference. Such images can be obtained using algorithms based on an inverse antenna aperture synthesis. A key factor determining the quality of image acquisition is the accuracy of the rotor blade rotation frequency measurement. In 2019, a method for measuring the blade repetition rate was proposed, which is based on convolution of the "secondary" signal modulation spectrum while simultaneously eliminating the influence of the Doppler frequency of the signal reflected from the aircraft body. In sequential analysis, the number of cycles is determined by the ratio of the maximum blade repetition rate (hundreds of hertz) to the discrete frequency shift (thousandths of hertz). In this case, to solve the measurement problem, the required number of cycles should be hundreds of thousands, which is expensive in terms of practical implementation.Aim. Development of a two-stage method for measuring the blade repetition rate, which allows the number of signal convolution cycles to be reduced by hundreds of times.Materials and methods. The proposed method is aimed at implementing adaptation circuits to an a priori unknown rotor speed of an aircraft, which can be determined based on the blade rotation frequency. The method involves measuring the blade frequency in two stages: a rough measurement of the blade frequency rate followed by its accurate measurement within the limits of the maximum errors of the rough measurement.Results. A method for a two-stage measurement of the blade repetition rate as applied to the construction of radar images of aircraft propellers is proposed. The feasibility of the method is illustrated by the example of a signal reflected from a Mi-8 helicopter. The requirements to the measurement error of the blade repetition rate and to the frequency analysis step at the precise measurement stage are formulated. The requirement to the repetition rate of probing signals is substantiated, the fulfillment of which ensures an unambiguous restoration of the spectrum of "secondary" modulation of the signal reflected from the blades of a propeller-driven aircraft.Conclusion. The developed method for a two-stage measurement of the blade repetition rate ensures the adaptation of algorithms for constructing radar images of aircraft propellers to their rotation frequency.

Large eddy simulation and linear stability analysis of active sway control for wind turbine array wake

The convective instability of wind turbine wakes allows specific upstream forcing to amplify downstream, leading to increased wake meandering and replenishment, thereby providing a theoretical basis for active wake control. In this study, the active sway control—a strategy previously proven to enhance wake recovery at the single wind turbine level—is analyzed at the turbine array level. The similarity and differences between individual turbine wakes and the wake array are analyzed using large eddy simulations and linear stability analysis, considering both uniform and turbulent inflow conditions. For cases with uniform inflow, large eddy simulations reveal significant meandering motion in the wake array induced by active sway control at a motion amplitude of 1% rotor diameter, consistent with previous studies of standalone wind turbine wakes. Nevertheless, the sensitive frequency for the wake array extends down to St = 0.125 below the limit of St > 0.2 for a single wake, and the optimal control frequency for the standalone turbine wake becomes suboptimal for the array. Linear stability analysis reveals the underlying mechanism of this frequency shift as changes in the shear-layer instability due to the overlap of upstream and downstream wakes and is capable to provide fast estimation of optimal control frequencies. When inflow turbulence intensity increases, the gain of active sway control is reduced, underscoring the importance of low-turbulence environment for successfully implementing the active sway control. The reduction in wake response is captured by the linear stability analysis if the base flow accounts for the faster wake expansion caused by inflow turbulence.

Beyond comparison: Brillouin microscopy and AFM-based indentation reveal divergent insights into the mechanical profile of the murine retina

Mechanical tissue properties increasingly serve as pivotal phenotypic characteristics that are subject to change during development or pathological progression. The quantification of such material properties often relies on physical contact between a load-applying probe and an exposed sample surface. For most tissues, meeting these requirements entails an invasive preparation, which poses the risk of yielding mechanical properties that do not portray the physiological state of a tissue within a functioning organism. Brillouin microscopy has emerged as a non-invasive, optical technique that enables the assessment of mechanical cell and tissue properties with high spatio-temporal resolution. In optically transparent specimens, it does not require animal sacrifice, tissue dissection or sectioning. However, the extent to which results obtained from Brillouin microscopy allow to infer conclusions about potential results obtained with a contact-based technique, and vice versa, is unclear. Sources for discrepancies include the varying characteristic temporal and spatial scales, the directionality of measurement, environmental factors, and mechanical moduli probed. In this work, we addressed those aspects by quantifying the mechanical properties of acutely dissected murine retinae using Brillouin microscopy and atomic force microscopy (AFM)-based indentation measurements. Our results show a distinct mechanical profile of the retinal layers with respect to the Brillouin frequency shift, the Brillouin linewidth and the apparent Young’s modulus. Contrary to previous reports, our findings do not support a simple correlative relationship between Brillouin frequency shift and apparent Young’s modulus. Additionally, the divergent sensitivities of Brillouin microscopy and AFM-indentation measurements to structural features, as visualized by transmission electron microscopy, to cross-linking or changes post mortem underscore the dangers of assuming interchangeability between the two methods. In conclusion, our study advocates for viewing Brillouin microscopy and AFM-based indentation measurements as complementary tools, discouraging direct comparisons a priori and suggesting their combined use for a more comprehensive understanding of tissue mechanical properties.

A level adjusted cochlear frequency-to-place map for estimating tonotopic frequency mismatch with a cochlear implant.

To provide a level-adjusted correction to the current standard relating anatomical cochlear place to characteristic frequency in humans, and to re-evaluate anatomical frequency mismatch in cochlear implant (CI) recipients considering this correction. It is hypothesized that a level-adjusted place-frequency function may represent a more accurate tonotopic benchmark for CIs in comparison to the current standard. The present analytical study compiled data from fifteen previous animal studies that reported iso-intensity responses from cochlear structures at different stimulation levels. Extracted outcome measures were characteristic frequencies and centroid-based best frequencies at 70 dB SPL input from 47 specimens spanning a broad range of cochlear locations. A simple relationship was used to transform these measures to human estimates of characteristic and best frequencies, and non-linear regression was applied to these estimates to determine how the standard human place-frequency function should be adjusted to reflect best frequency rather than characteristic frequency. The proposed level-adjusted correction was then compared to average place-frequency positions of commonly used CI devices when programmed with clinical settings. The present study showed that the best frequency at 70 dB SPL (BF70) tends to shift away from characteristic frequency (CF). The amount of shift was statistically significant (signed-rank test z = 5.143, p < 0.001), but the amount and direction of shift depended on cochlear location. At cochlear locations up to 600° from the base, BF70 shifted downwards in frequency relative to CF by about 4 semitones on average. Beyond 600° from the base, BF70 shifted upwards in frequency relative to CF by about 6 semitones on average. In terms of spread (90% prediction interval), the amount of shift between CF and BF70 varied from relatively no shift to nearly an octave of shift. With the new level-adjusted frequency-place function, the amount of anatomical frequency mismatch for devices programmed with standard of care settings is less extreme than originally thought, and may be nonexistent for all but the most apical electrodes. The present study validates the current standard for relating cochlear place to characteristic frequency, and introduces a level-adjusted correction for how best frequency shifts away from characteristic frequency at moderately loud stimulation levels. This correction may represent a more accurate tonotopic reference for CIs. To the extent that it does, its implementation may potentially enhance perceptual accommodation and speech understanding in CI users, thereby improving CI outcomes and contributing to advancements in the programming and clinical management of CIs.

Genome-Wide Allele Frequency Changes Reveal That Dynamic Metapopulations Evolve Differently.

Two important characteristics of metapopulations are extinction-(re)colonization dynamics and gene flow between subpopulations. These processes can cause strong shifts in genome-wide allele frequencies that are generally not observed in "classical" (large, stable, and panmictic) populations. Subpopulations founded by one or a few individuals, the so-called propagule model, are initially expected to show intermediate allele frequencies at polymorphic sites until natural selection and genetic drift drive allele frequencies toward a mutation-selection-drift equilibrium characterized by a negative exponential-like distribution of the site frequency spectrum. We followed changes in site frequency spectrum distribution in a natural metapopulation of the cyclically parthenogenetic pond-dwelling microcrustacean Daphnia magna using biannual pool-seq samples collected over a 5-yr period from 118 ponds occupied by subpopulations of known age. As expected under the propagule model, site frequency spectra in newly founded subpopulations trended toward intermediate allele frequencies and shifted toward right-skewed distributions as the populations aged. Immigration and subsequent hybrid vigor altered this dynamic. We show that the analysis of site frequency spectrum dynamics is a powerful approach to understand evolution in metapopulations. It allowed us to disentangle evolutionary processes occurring in a natural metapopulation, where many subpopulations evolve in parallel. Thereby, stochastic processes like founder and immigration events lead to a pattern of subpopulation divergence, while genetic drift leads to converging site frequency spectrum distributions in the persisting subpopulations. The observed processes are well explained by the propagule model and highlight that metapopulations evolve differently from classical populations.

Assessing the Impact of Climate Change on Global Crop Yields and Farming Practices

Climate change is recognized as one of the most pressing challenges of our time, with profound implications for global food security. This review article delves into the multifaceted impacts of climate change on crop yields and farming practices on a global scale. By synthesizing recent research findings, identifying key challenges and opportunities, and exploring adaptation strategies, this review provides a comprehensive analysis of the complex interplay between climate change and agriculture. The effects of climate change on agriculture are diverse and far reaching. Alterations in weather patterns, including shifts in temperature, precipitation, and frequency of extreme events, pose significant challenges to agricultural productivity and food security. These changes disrupt traditional farming practices, exacerbate water stress, soil erosion, and crop loss, and threaten the livelihoods of millions of farmers worldwide. Additionally, changes in pest and disease dynamics have further compounded the challenges faced by agricultural systems under pressure from climate variability. These challenges, there are opportunities for innovation and adaptation in the agricultural systems. This review highlights the potential of climate-smart agricultural practices such as crop diversification, conservation agriculture, and precision farming to enhance resilience and mitigate the impacts of climate change on crop yields. investments in climate-resilient crop varieties, improved water management techniques, and sustainable land management practices offer pathways for building adaptive capacities and ensuring food security in a changing climate. addressing the complex challenges of climate change adaptation in agriculture requires concerted action at multiple levels. This review emphasizes the importance of coordinated efforts among policymakers, researchers, farmers, and other stakeholders in developing and implementing effective adaptation strategies. Such strategies should be context-specific, socially equitable, and environmentally sustainable, considering the diverse needs and priorities of different regions and communities. This review underscores the urgent need for coordinated action to build resilient and sustainable food systems in the face of a changing climate. By synthesizing the latest research findings, identifying key challenges and opportunities, and exploring adaptation strategies, this review aims to inform policymakers, researchers, and practitioners about the imperative of addressing climate change’s impacts on agriculture. Only through collaborative and transformative action can we ensure food security for the present and future generations in a rapidly changing world.

Terahertz Sensing of L-Valine and L-Phenylalanine Solutions.

To detect and differentiate two essential amino acids (L-Valine and L-Phenylalanine) in the human body, a novel asymmetrically folded dual-aperture metal ring terahertz metasurface sensor was designed. A solvent mixture of water and glycerol with a volume ratio of 2:8 was proposed to reduce the absorption of terahertz waves by reducing the water content. A sample chamber with a controlled liquid thickness of 15 μm was fabricated. And a terahertz time-domain spectroscopy (THz-TDS) system, which is capable of horizontally positioning the samples, was assembled. The results of the sensing test revealed that as the concentration of valine solution varied from 0 to 20 mmol/L, the sensing resonance peak shifted from 1.39 THz to 1.58 THz with a concentration sensitivity of 9.98 GHz/mmol∗L-1. The resonance peak shift phenomenon in phenylalanine solution was less apparent. It is assumed that the coupling enhancement between the absorption peak position of solutes in the solution and the sensing peak position amplified the terahertz localized electric field resonance, which resulted in the increase in frequency shift. Therefore, it could be shown that the sensor has capabilities in performing the marker sensing detection of L-Valine.