Frequency Mixing Research Articles

Frequency curves of high and low flows in intermittent river basins for hydrological analysis and hydraulic design

Upper and lower percentiles of Flow Duration Curves (FDCs) of daily streamflow data were investigated to develop frequency curves. Upper percentiles with exceedance probability of 1, 5 and 10% (Q1, Q5, Q10) were used for high flows, and lower percentiles with non-exceedance probability of 10, 5 and 1% (Q90, Q95, Q99) for low flows. Median value (Q50) was covered to represent the average conditions of streamflow. A mixed frequency analysis based on the total probability theorem taking zero values into account was applied for the lower percentiles of FDC. Case studies were performed for three intermittent Streamflow Gauging Stations (SGSs) from Kucuk Menderes River Basin in western Turkey. An overall assessment of results shows that the best-fit probability distribution function does not change from one SGS to another considerably for low flows while each SGS has its own probability distribution function for high flows. Upper and lower percentiles, and median value were calculated at various return periods by using the identified probability distribution functions. The calculated values were plotted in the form of frequency curves of high flow percentiles and low flow percentiles. The frequency curves have a practically significant potential use in hydrological analysis, water resources management and hydraulic design under high and low flow conditions. They are yet open to further development for regionalization and their applicability can be extended to ungauged sites in river basins.

Unleashing the Potential of Mixed Frequency Data: Measuring Risk with Dynamic Tail Index Regression Model

Unleashing the Potential of Mixed Frequency Data: Measuring Risk with Dynamic Tail Index Regression Model

Gas mixing and double frequency operation of the permanent magnet quadrupole minimum-B electron cyclotron resonance ion source CUBE-ECRIS

CUBE-ECRIS is a recently commissioned permanent magnet electron cyclotron resonance (ECR) ion source developed at the university of Jyväskylä accelerator laboratory. The special features of the new ion source design include an unconventional quadrupole minimum-B magnetic field structure and a slit beam extraction system necessitated by the line-shaped plasma loss fluxes. Gas mixing and double frequency operation are widely used methods to optimize high charge state ion production of conventional ECR ion sources. The work presented here demonstrates the applicability of these methods for boosting the high charge state beam currents of argon, krypton and xenon extracted from CUBE-ECRIS. Oxygen and helium were used as mixing gases and microwave frequencies between 10 and 11 GHz were used for single and double frequency operation. Gas mixing has a strong impact on the high charge state beam currents. For example, the highest observed charge state increased from 15+ to 19+ for krypton and from 16+ to 23+ for xenon with oxygen gas mixing. Double frequency operation provides an additional performance improvement, for example the currents of argon 9+ and 11+ beams, produced with gas mixing, increased 30% and 100% in double frequency operation at the same total power.

Seizures and Post-Ictal Respiratory Recovery in Kcnj16−/− Sprague-Dawley Rats

Epilepsy is a common neurological disorder (3.5 million in the US), of which ~1/3 continue to experience repeated seizures failing to benefit from anti-seizure medication. Poor seizure control puts patients with drug-resistant epilepsies at increased risk of Sudden Unexpected Death in Epilepsy (SUDEP), which is thought to result from severe post-ictal cardiorespiratory suppression. We’ve previously shown that Salt-Sensitive (SS) rats lacking 18 base pairs in the Kcnj16 gene (SS Kcnj16−/−), corresponding to a 6 amino acid (AA163-168) deletion in the second TM domain of Kir5.1, are susceptible to audiogenic seizures. Repeated seizures (1/day for 10 days) in this rat model resulted in ictal apnea, post-ictal respiratory suppression, diminished chemoreflexes, and high spontaneous mortality (PMID: 33232300). Here we generated additional Kcnj16−/− mutants on the outbred Sprague Dawley (SD Kcnj16−/−) genetic background to test the hypothesis that Kcnj16 mutations (T64I substitution; AA64-68 deletion (M7), and AA64-81 deletion (M8)) in the first TM domain of Kir5.1 causes: 1) audiogenic seizures, 2) progressive exacerbation of post-ictal ventilatory dysfunction, and 3) seizure-induced mortality. Ventilation (whole-body plethysmography) and seizure severity (Racine Score; HD video) were measured in male and female SD Kcnj16−/− rats for 20 minutes (min; baseline (BL)) before exposure to an auditory stimulus (2 min) and for 20 min of recovery. Mixed frequency white noise (WN) or a 10 kHz tone (85-95 dB) reproducibly elicited generalized tonic-clonic seizures (GTCSs) in all three SD mutants (T64I, M7, and M8). In SD Kcnj16−/− rats (T64I n=2, M7 n=3, M8 n=7, wild type n=2), 1 seizure/day for 10 days led to ictal apneas and transient post-ictal respiratory changes along with increases in body temperature (+1°C) following seizures, where breath frequency initially decreased (-25% of BL) before increasing (+40%) at 5 min post-stimulus and normalizing by 20 min. Tidal volume increased ~+80% from BL in the first 5 min and returned to BL by 20 min post-ictal. Minute ventilation was decreased (-10%) from BL within 1 min, increased to +60% by 5 minutes and returned to BL within 20 min post-stimulus. In contrast to previous SS Kcnj16−/− rat data, SD Kcnj16−/− rat post-ictal breathing patterns were unchanged across the 10-day seizure protocol, and we observed 100% survival. Our preliminary data suggests that Kcnj16 mutations at multiple sites can elicit the audiogenic seizure phenotype, but that SD Kcnj16−/− mutant rats appear resistant to repeated seizure-induced post-ictal ventilatory dysfunction and mortality — i.e. a potentially useful SUDEP-resistant model of repeated seizures. Funded by NIH HL122358. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Nowcasting Vietnam's Export Growth with Mixed Frequency Data

Purpose: The primary objective of this study is to investigate and employ a practical and meaningful nowcasting model to predict Vietnam's export growth based on factors of export supply and demand alongside relevant financial indicators. Theoretical Framework: This study employs the concepts and theories of nowcasting model with mixed frequency data to create the conceptual framework. Methodology: This study employs four commonly-used models in nowcasting: the bridge equation model (BEQ), Bayesian VAR model (BVAR), mixed frequency vector autoregressive model (MFVAR), and mixed data sampling regression (MIDAS). Findings: According to the experimental findings, the mixed frequency data models outperformed the models utilizing the same frequency data in nowcasting Vietnam's export growth. Additionally, this model demonstrated effectiveness in instantaneous and short-term forecasting. MIDAS emerged as the most suitable choice for nowcasting Vietnam's export growth among the models examined. Implication of Research: using data with mixed frequency along with corrresponding methods is the good way for nowcasting. Originality/Value: This study used macroeconomics factors to nowcast the export growth in Vietnam. It applied four different models including BEQ, BVAR, MFVAR, and MIDAS. The study reveals the roles of data and the potential capability in nowcasting of MIDAS model.

Experimental study on opto-acoustic nonlinear frequency-mixing technique with separated basic temperature

Different from the traditional frequency-mixing technique which employs a contacting transducer, the laser-induced acoustic nonlinear frequency-mixing detection technique utilizes a laser source to instigate crack motion and generate acoustic waves. Thus, apart from the temperature oscillation induced by the pump laser, the “basic temperature” originating from the probe laser can also influence the crack. This additional variable complicates the contact state of the crack, yielding a more diverse range of nonlinear acoustic signal attributes. In light of this, our study enhances the conventional opto-acoustic nonlinear frequency mixing experimental setup by integrating an independent heating laser beam. This modification isolates the impact of the “basic temperature” on crack width while also dialing down the probe laser power to mitigate its thermal effects. To amplify the sensitivity of crack detection, we deliberated on the optimal laser source parameters for this setup. Consequently, our revamped system, paired with fine-tuned parameters, captures nonlinear acoustic signals with an enriched feature set. This investigation can provide support for the non-contact opto-acoustic nonlinear frequency mixing technique in the detection and evaluation of micro-cracks.

Multi-Frequency Noise Reduction Method for Underwater Radiated Noise of Autonomous Underwater Vehicles

The multi-frequency noisy vibration of an autonomous underwater vehicle (AUV) is a significant factor affecting the performance of shear probes mounted on the head of AUVs. Many efforts have been made to suppress mechanical radiation noise; however, conventional noise reduction methods have their limitations, such as mode mixing. In order to extract thorough information from the aliasing modes and achieve multi-frequency mode targeted correction, a multi-frequency noise reduction method is proposed, based on secondary decomposition and the multi-mode coherence correction algorithm. Weak impulses in aliasing shear mode are enhanced, and mixing frequencies are isolated for thorough decomposition. Noisy mechanical vibrations in the shear modes are eliminated with the use of the acceleration modes along the identical central frequency series. The denoised modes are used to reconstruct the cleaned shear signal, and the updated spectra are aligned with the standard Nasmyth spectrum. Compared with the raw profiles, the variation in the dissipation rate estimated from the corrected shear is reduced by more than an order of magnitude.

Scattering matrix for chiral harmonic generation and frequency mixing in nonlinear metasurfaces

We generalize the concept of optical scattering matrix (S-matrix) to characterize harmonic generation and frequency mixing in planar metasurfaces in the limit of undepleted pump approximation. We show that the symmetry properties of such nonlinear S-matrix are determined by the metasurface symmetries at the macroscopic and microscopic scale. We demonstrate that for description of degenerate frequency mixing processes such as optical harmonic generation, the multidimensional S-matrix can be replaced with a reduced two-dimensional S-matrix. We show that for metasurfaces possessing specific point group symmetries, the selection rules determining the transformation of the reduced nonlinear S-matrix are simplified substantially and can be expressed in a compact form. We apply the developed approach to analyze chiral harmonic generation in nonlinear metasurfaces with various symmetries including rotational, inversion, in-plane mirror, and out-of-plane mirror symmetries. For each of those symmetries, we confirm the results of the developed analysis by full-wave numerical calculations. We believe our results provide a new paradigm for engineering nonlinear optical properties of metasurfaces which may find applications in active and nonlinear optics, biosensing, and quantum information processing.

Mixed Variable Parameter Energy Storage-Assisted Frequency Support Strategy

With the continuous increase in the installed capacity of new energy systems, the impact of power shocks on grid frequency is becoming more significant, seriously affecting the stability of the grid and thermal power units. For this reason, a mixed variable parameter energy storage-assisted frequency support control method is proposed. This method introduces an integral control mode based on the existing control mode and forms a co-ordinated control mode. The impact of the switching point of the mixed control mode is analyzed, and a new mode switching method is used. The model adjusts the frequency regulation parameters according to the different states of the grid frequency, making the frequency regulation more efficient. Finally, a frequency regulation model that integrates various improvement methods is built, and a 10 min continuous load disturbance is applied to compare and verify the frequency regulation performance of the model as a whole. The results indicate that the proposed control method can significantly improve the quality of grid frequency regulation, reduce the frequency deviation amplitude to 0.00096 p.u., reduce the participation time of thermal power units to 190.8393 s, and reduce the peak output to 0.1934 MW, demonstrating its engineering feasibility.

Real‐Time Measurements of Photonic Microchips with Femtometer‐Scale Spectral Precision and Ultrahigh Sensitivity

AbstractPhotonic integrated circuits (PICs) are enabling breakthroughs in several areas, including quantum computing, neuromorphic processors, wearable devices, and more. Nevertheless, existing PIC measurement methods lack the spectral precision, speed, and sensitivity required for refining current applications and exploring new frontiers such as point‐of‐care or wearable biosensors. Here, the “sweeping optical frequency mixing method (SOHO)” is presented, surpassing traditional PIC measurement methods with real‐time operation, 30 dB higher sensitivity, and over 100 times better spectral resolution. Leveraging the frequency mixing process with a sweeping laser, SOHO excels in simplicity, eliminating the need for advanced optical components and additional calibration procedures. Its superior performance is demonstrated on ultrahigh‐quality factor (Q) fiber‐loop resonators (Q = 46 × 106), as well as microresonators, realized on a new optical waveguide platform. An experimental spectral resolution of 19.1 femtometers is demonstrated using an 85‐meter‐long unbalanced fiber Mach Zehnder Interferometer, constrained by noise resulting from the extended fiber length, while the theoretical resolution is calculated to be 6.2 femtometers, limited by the linewidth of the reference laser. With its excellent performance metrics, SOHO has the potential to become a vital measurement tool in photonics, excelling in high‐speed and high‐resolution measurements of weak optical signals.

Pricing VIX futures with mixed frequency macroeconomic information

This paper develops a new mixed frequency macro affine stochastic volatility (MacroSV) model and presents a closed-form formula for pricing VIX futures. In our model, the variance is decomposed into long-run and short-run components and the long-run component is driven by the macroeconomic variables. The result from the Monte Carlo experiment shows that the new model outperforms the benchmark model in terms of VIX futures pricing. The results of MacroSV-type models suggest that there is a significant relationship between the volatility and macroeconomic variables. The in-sample forecast results indicate that the models with mixed frequency macroeconomic information outperform the benchmark Heston model. For the out-of-sample pricing, the MacroSV model with the economic information of PPI for the United States has an improvement of 16% over the Heston model.

Phase-locked dual-frequency microwave signal generation in an optoelectronic oscillator based on frequency mixing mutual injection

An approach to generating stable phase-locked dual-frequency microwave signals is proposed and demonstrated based on a dual-passband optoelectronic oscillator (OEO). Mode gain competition is broken by employing frequency mixing mutual injection effect to realize phase locking between the two oscillation signals, which is achieved by applying a single-tone signal to a microwave mixer in the OEO cavity. In addition, a dual-loop configuration with balanced detection is utilized to ensure a high side mode suppression ratio (SMSR) and ultra-low phase noise, which also enhances the stability of the generated signal. In the experiment, a phase-locked dual-frequency microwave signal at 9.9982 GHz and 10.1155 GHz is generated by using the proposed OEO scheme. The SMSR and the phase noise are 75 dB and –141 dBc/Hz@10 kHz, respectively. Additionally, the Allan deviation of the generated signal is in the order of 10−11@1 s. These parameters are superior to those based on the same OEO but with a single-loop configuration, which are also compared in detail.

High-power, narrow linewidth solid-state deep ultraviolet laser generation at 193 nm by frequency mixing in LBO crystals

High-power, narrow linewidth solid-state deep ultraviolet laser generation at 193 nm by frequency mixing in LBO crystals

Azimuthal modulation of light propagation through 1DPCs via efficient nonlinear frequency mixing

The present study aims to investigate the transmitted and reflected light beams from a one-dimensional defect photonic crystal (1DPC) composed of a three-level ladder-type quantum system. The lower leg of the ladder scheme is driven by a weaker probe beam, while the upper leg is driven by a stronger control beam. Unlike natural atoms, this type of model with broken symmetry permits the generation of a sum-frequency signal beam between the majority of higher and lower quantum states, resulting in the formation of a cyclic closed-loop arrangement for the interaction between light and matter. The Laguerre Gaussian (LG) field with strong coupling and a weak probe light interact with the quantum system. A new weak signal light is produced as a result of the system’s symmetric breakdown, and the medium becomes azimuthal dependent. We investigate the spatial dependence of the transmitted and reflected light from a defect 1DPC by using azimuthal modulation of the LG light. Additionally, we will discuss how the absorption spectrum’s spatial modulation varies with winding numbers. We discover that in certain regions, the gain can be realized without population inversion under certain specified parametric parameters.

Performance analysis of multi-hop low earth orbit satellite network over mixed RF/FSO links

Low earth orbit satellite (LEOS) communication has emerged as a promising technology to achieve global coverage, while further reducing the end-to-end latency by establishing communication link between LEOSs. In this paper, we analyze the performance of multi-hop LEOS network in terms of bit error rate (BER) and outage probability over mixed radio frequency (RF)/free space optical (FSO) links where RF link is used for the link between ground terminal and LEOS and FSO link is used for establishing inter-satellite links (ISLs). The derived closed-form results are confirmed via Monte Carlo simulations and we show the effect of the number of satellite hops on outage probability and average BER performance by comparing scenarios both with and without ISLs.

Indirect estimation of the monthly transport turnover indicator in Italy

The paper discusses the results of a selection of a set of monthly indicators to be used as predictors of the quarterly index of Italian service turnover. A mixed frequency approach based on sparse temporal disaggregation is used, which outperforms the classical methods of the Chow and Lin family, allowing both a high number of regressors by the LASSO method and stable estimates. The application refers to the turnover in transport, a sector strongly affected in 2020 by the dramatic movements due to the COVID-19 pandemic and the resurgence of inflation at the end of 2021. The monthly indicators are selected from 143 time series: 56 series of business surveys in transport about both the climate and frequency of the answers; 18 series from Assaeroporti about both passengers and cargo flights split by national and international routes; 69 series of monthly turnover in industry split by both sector of economic activity and reference market. The sample spans the months from January 2010 to December 2021 for both seasonally adjusted and unadjusted data. Several aspects of the estimation are considered: the stability of selected indicators over the quarters 2017–2021; their forecasting performance; the reliability of the estimates in terms of their monthly pattern.

Key Contributors to Signal Generation in Frequency Mixing Magnetic Detection (FMMD): An In Silico Study.

Frequency mixing magnetic detection (FMMD) is a sensitive and selective technique to detect magnetic nanoparticles (MNPs) serving as probes for binding biological targets. Its principle relies on the nonlinear magnetic relaxation dynamics of a particle ensemble interacting with a dual frequency external magnetic field. In order to increase its sensitivity, lower its limit of detection and overall improve its applicability in biosensing, matching combinations of external field parameters and internal particle properties are being sought to advance FMMD. In this study, we systematically probe the aforementioned interaction with coupled Néel-Brownian dynamic relaxation simulations to examine how key MNP properties as well as applied field parameters affect the frequency mixing signal generation. It is found that the core size of MNPs dominates their nonlinear magnetic response, with the strongest contributions from the largest particles. The drive field amplitude dominates the shape of the field-dependent response, whereas effective anisotropy and hydrodynamic size of the particles only weakly influence the signal generation in FMMD. For tailoring the MNP properties and parameters of the setup towards optimal FMMD signal generation, our findings suggest choosing large particles of core sizes dC>25 nm with narrow size distributions (σ<0.1) to minimize the required drive field amplitude. This allows potential improvements of FMMD as a stand-alone application, as well as advances in magnetic particle imaging, hyperthermia and magnetic immunoassays.

Nowcasting the Russian economy macroeconomic indicators under uncertainty: Does taking into account the news sentiment help?

In this paper the following models are compared: restricted and unrestricted MIDAS-models (mixed data sampling models), MFBVAR-model (mixed frequency Bayesian vector autoregression), Linear model with regularization (MIDAS_L1-, MIDAS_L2and MIDAS_PC-model) and dynamic factor model. The results are compared with classical autoregression as a benchmark. Production indices for different industries and indicators characterizing Russian GDP and its components, energy prices and PMI of Russia and its main trading partners, as well as indicators derived from the analysis of sentiment of news articles published by a number of major media and blogs are used as explanatory variables. The paper also proposes a method of rapid assessment of the current state of the economy based on data for the first or first two months of the quarter in question only. The use of this approach in combination with news sentiment analysis allows to draw conclusions about current economic situation extremely rapidly. Models’ accuracy is assessed by cross-validation for periods before and after the Q2 2022, the significance of the effect of adding news variables is assessed using the Diebold—Mariano test. When testing during the crisis period (starting from the Q1 2022), the addition of news variables leads to an increase in accuracy for 45% of the models considered, and the average improvement (reduction in the average absolute error) was 1.39 points (the reduction in MAE for the science-based GDP growth rates of Russia is 0.64 p.p.). At the same time, in a calmer (pre-sanction) period, the advantage of news is less noticeable: an increase in accuracy was recorded in 30% of cases with an average decrease in error of 1.54 points (the decrease in MAE for Russia’s GDP growth rate is 0.26 p.p.), and the change accuracy of science data when adding variables reflecting the news background turns out to be statistically insignificant. Thus, the use of news sentiment is not a “silver bullet” in the task of nowcasting Russian GDP, but in times of crisis it can serve as a good and, importantly, very operative indicator of the state of the economy and can be used in conjunction with more traditional explanatory variables.

Theoretical analysis of perturbative high harmonic wave mixing from plasma surfaces

High harmonic generation modulated by a weakly perturbing laser field enables new wave mixing frequency components, thus allowing in-situ spatiotemporal measurements and wavefront control of attosecond optical pulses. However, perturbative high harmonic wave mixing from plasma surfaces has not been investigated extensively. In this study, we theoretically analyze the plasma high harmonic generation process in the relativistic regime modulated by a perturbing laser field with an arbitrary frequency. New wave mixing frequency components satisfying the conservation laws of photon energy and momentum are observed. The wave mixing component intensities adhere to a power law for the perturbating laser photon number as the perturbing laser intensity increases, thereby revealing perturbative behaviors in the nonperturbative, extremely nonlinear optical process of high harmonic generation. Detailed studies reveal the polarization selection rule and physical mechanism of high harmonic wave mixing. The modulation of the relativistic factor or mass enhancement of electrons on the plasma surface by the perturbing laser field is believed to result in high harmonic wave mixing in the relativistic regime.

Nonlinear Frequency Mixing Ultrasound Imaging of Nanoscale Contrast Agents.

Nanoscale ultrasound contrast agents show promise as alternatives for diagnostics and therapies due to their enhanced stability and ability to traverse blood vessels. Nonetheless, their reduced size limits echogenicity. This study introduces an enhanced nanobubble frequency mixing ultrasound imaging method, by capitalizing on their nonlinear acoustic response to dual-frequency excitation. A single broadband transducer (L12-3v) controlled by a programmable ultrasound system was used to transmit a dual-frequency single-cycle wavefront. The frequency mixing effect enabled simultaneous transducer capture of nanobubble-generated sum and difference frequencies in real time without the need for additional hardware or post-processing, by substituting the single-frequency wavefront in a standard contrast harmonic pulse inversion imaging protocol, with the dual-frequency wavefront. Optimization experiments were conducted in tissue mimicking phantoms. Among the dual-frequency combinations that were tested, the highest contrast was obtained using 4&8 MHz. The nanobubble contrast improved with increased mechanical index, and achieved a maximal contrast improvement of 8.4 ± 0.5 dB compared to 4 MHz pulse inversion imaging. In imaging of a breast cancer tumor mouse model, after a systemic nanobubble injection, the contrast was improved by 3.4 ± 1.7, 4.8 ± 1.8, and 6.3 ± 1.6 dB for mechanical indices of 0.04, 0.08, and 0.1, respectively. Nonlinear frequency mixing significantly improved the nanobubble contrast, which facilitated their imaging in-vivo. This study offers a new avenue to enhance ultrasound imaging utilizing nanobubbles, potentially leading to advancements in other diagnostic applications.