Frequency Separation Research Articles

Utilizing parametric instabilities to diagnose edge density fluctuations in TCV

Abstract Two-plasmon decay instabilities (TPDIs) are a class of parametric instabilities where a gyrotron beam, polarized in X-mode, decays nonlinearly into two upper hybrid waves at approximately half frequency. Here, we present the design of a simple radiometer that was installed at Tokamak á configuration variable to diagnose TPDIs as well as a novel technique that was used to calibrate the radiometer using thermal electron cyclotron emissions. We show examples of measured radiation from TPDIs that occur when the gyrotron beam intersects blob filaments in the scrape-off layer and demonstrate that the frequency separation of the TPDI daughter waves can be used to assess the densities of the blob filaments. This technique could be utilized to diagnose density fluctuations due to both blobs, ELMs, and rotating magnetic islands.

Numerical and experimental examination of performance curve instabilities of a centrifugal fan

Abstract This paper investigates the performance curve instability of centrifugal fans used in industrial applications such as sintering or pelletizing plants. The study focuses on experimental and numerical analyses of the fan’s performance curve during operation. Model measurements of an optimized fan reveal instabilities in the characteristic curve around 73 % and 42 % of the volume flow at best efficiency point (Q/Qref) resulting in a sudden drop in pressure coefficient and the onset of low-frequency noise emission. Numerical investigations using ANSYS CFX predict the flow pattern accurately. Excellent agreement is observed between measured and calculated data for flow conditions, with deviations below 1 % in pressure coefficient. Notably, the calculated instability range occurs earlier at lower flow rates, leading to a 6 % shift in the data. The flow exhibits a detachment zone on the blade suction side and a complete blockage of a single impeller passage, corresponding to the pressure drop in the performance curve. Further investigations reveal that rotor-stator interaction causes the abrupt impeller rotating stall phenomena, significantly impacting pressure generation at lower flow rates. A FFT analysis confirms the presence of rotating stall, with its dominant frequency observed and multiple harmonics. The comparison of separation frequency with existing literature supports the assumption that rotating stall is the cause of the instability.

Benchmarking the spectroscopic masses of 249 evolved stars using asteroseismology with TESS

Abstract One way to understand planet formation is through studying the correlations between planet occurrence rates and stellar mass. However, measuring stellar mass in the red giant regime is very difficult. In particular, the spectroscopic masses of certain evolved stars, often referred to as ”retired A-stars”, have been questioned in the literature. Efforts to resolve this mass controversy using spectroscopy, interferometry and asteroseismology have so far been inconclusive. A recent ensemble study found a mass-dependent mass offset, but the result was based on only 16 stars. With NASA’s Transiting Exoplanet Survey Satellite (TESS), we expand the investigation of the mass discrepancy to a total of 92 low-luminosity stars, synonymous with the retired A-stars. We measure their characteristic oscillation frequency, νmax, and the large frequency separation, Δν, from their TESS photometric time series. Using these measurements and asteroseismic scaling relations, we derive asteroseismic masses and compare them with spectroscopic masses from five surveys, to comprehensively study the alleged mass-dependent mass offset. We find a mass offset between spectroscopy and seismology that increases with stellar mass. However, we note that adopting the seismic mass scale does not have a significant effect on the planet occurrence-mass-metallicity correlation for the so-called retired A-stars. We also report seismic measurements and masses for 157 higher luminosity giants (mostly helium-core-burning) from the spectroscopic surveys.

Periodically correlated time series and the Variable Bandpass Periodic Block Bootstrap.

This research introduces a novel approach to resampling periodically correlated time series using bandpass filters for frequency separation called the Variable Bandpass Periodic Block Bootstrap and then examines the significant advantages of this new method. While bootstrapping allows estimation of a statistic's sampling distribution by resampling the original data with replacement, and block bootstrapping is a model-free resampling strategy for correlated time series data, both fail to preserve correlations in periodically correlated time series. Existing extensions of the block bootstrap help preserve the correlation structures of periodically correlated processes but suffer from flaws and inefficiencies. Analyses of time series data containing cyclic, seasonal, or periodically correlated principal components often seen in annual, daily, or other cyclostationary processes benefit from separating these components. The Variable Bandpass Periodic Block Bootstrap uses bandpass filters to separate a periodically correlated component from interference such as noise at other uncorrelated frequencies. A simulation study is presented, demonstrating near universal improvements obtained from the Variable Bandpass Periodic Block Bootstrap when compared with prior block bootstrapping methods for periodically correlated time series.

Experimental investigation of hybrid energy sharing strategy for multi-source electric vehicle

This paper deals with a current topic addressing the issue of energy management. Adequate energy management consists of finding the best harmony between different sources intended to supply the vehicle to satisfy the power required by the traction motor while ensuring good performances. Energy management strategy makes it possible to find the adequate distribution of the energy flow between power source elements by generating power references to be given by each source to satisfy the required power while respecting the constraints on these sources. In this context, a new energy management strategy based on the combination of flatness theory and the frequency separation principle is developed. This strategy determines the powers that the energy sources must supply and provides power source references based on their dynamics, imposing constraints to be taken into account. This novel hybrid strategy is applied to a hybrid vehicle configuration that uses a fuel cell as the primary source with a hybrid storage device (supercapacitor and battery). The implementation using dSPACE DS1005 will be presented to demonstrate the effectiveness of the proposed strategy.

A study on develop the High-Performance Wide - Band LNA for use with IEEE frequency

In this research, a low-noise amplifier (LNA) with uniform growth, silent operation, and absolutely brilliant uniformity is suggested to be utilized in bandwidth transmitters, with a comparative channel capacity (RBW) of 110%. To enhance extended the reach, researchers present a cascode with dual feedbacks and a wide bandpass (BPDWB) matching network formed from bias and parasitic characteristics. The techniques for constructing a corresponding networking are also shown, and measurements indicate that the channel's resonance frequency is a great pairing for the required resistance in the range from through 3.5 GHz. Resistance matched precision and efficiency in prediction are both boosted by the envisaged BPDWB networks. Paper presents a low amplifiers (LNA) in 0.25 m GaAs father made high mobility electrons semiconductor (GaAs pHEMT) developers and researchers NF0.55 at mhz. Additionally, for the range of frequency of 8.5-20 MHz, overall bit error rate (NF) is somewhere between 2.19 to 3.23 dB, while another NF maximum (vase: internet: mia2bf00852: mia2bf00852-math-0012) varied between 1.55 - 2.91 db. At top of just that, a two-tone test with a frequency separation of 50 MHz demonstrates that the suggested LNA may accomplish high IIP3 of 0.96 frequency range.

Effective dynamic energy management algorithm for grid-interactive microgrid with hybrid energy storage system

Microgrids offer an optimistic solution for delivering electricity to remote regions and incorporating renewable energy into existing power systems. However, the energy balance between generation and consumption remains a significant challenge in microgrid setups. This research presents an adaptive energy management approach for grid-interactive microgrids. The DC microgrid is established by combining solar PV with a battery-supercapacitor (SC) hybrid energy storage system (HESS). The proposed approach integrates the frequency separation strategy with a rule-based algorithm to ensure optimal power sharing among sources while maintaining the safe operation of storage units. Specifically, the battery meets steady-state energy demands, the SC addresses transient power requirements, and the grid support is tailored to system needs. The method employs the dq reference frame technique to control the grid inverter (VSC). The key merits include efficient power allocation, fast regulation of the DC link voltage irrespective of load or generation variations, seamless transition between scenarios, and introduction of a straightforward battery state of charge (SOC)-based coefficient for allocating power between the battery and the grid while enhancing the power quality within the grid. Moreover, safety measures prevent the SC from overcharging, the battery from high current, overcharging, and deep discharging, potentially extending their lifespan. Validation and implementation of the method are conducted using MATLAB/Simulink.

Optical properties of cylindrical topological photonic crystal heterostructures

This paper uses a modified transfer matrix method to investigate the optical properties of a cylindrical topological photonic crystal heterostructure composed of two cylindrical photonic crystals. Topological photonic crystals are novel structures with topological edge states capable of field confinement and robust propagation. Numerical results showed that when the sum of the phases of the reflection coefficients of the two cylindrical photonic crystals is zero, a topological edge state occurs inside their overlapping band gaps. In the linear regime, the peak frequency of the topological edge states undergoes a redshift as the incidence angle increases. An increase in the incidence angle leads to a decrease (increase) in the Full width at half maximum of the E-polarized (H-polarized) topological edge states. As the incidence angle increases, the frequency separation between the E-polarized and H-polarized topological edge states increases, causing the cylindrical heterostructure to work as a polarizer. The performance of the cylindrical topological photonic crystal heterostructure as a polarizer is evaluated in the linear and nonlinear regimes. We showed that the peak frequency of the topological edge states undergoes a redshift irrespective of their polarization state as the intensity of the input light increases. We found that the structure has a good performance in the nonlinear regime due to the higher displacement in E-polarized topological edge states compared to H-polarized topological edge states. The findings of this paper might be beneficial in the construction of polarization-maintaining optical fiber, which has specific applications in telecommunications, fiber optic sensing, interferometry, and quantum key distribution.

Quantifying the heterogeneity impact of risk factors on regional bicycle crash frequency: A hybrid approach of clustering and random parameter model

The existence of internal and external heterogeneity has been established by numerous studies across various fields, including transportation and safety analysis. The findings from these studies underscore the complexity of crash data and the multifaceted nature of risk factors involved in accidents. However, most studies consider the effects of unobserved heterogeneity from one perspective −- either within clusters (internal) or between clusters (external) −- and do not investigate the biases from both simultaneously on crash frequency analysis. To fill this gap, this study proposes a hybrid approach combining latent class cluster analysis with the random parameter negative binomial regression model (LCA-RPNB) to explore the association between risk factors and bicycle crash frequency. First, the bicycle crash data is categorized into three clusters using LCA based on crash features such as gender, trip purposes, weather, and light conditions. Then, the separated crash frequency models for different clusters and the overall model are developed based on RPNB using regional factors of crash locations as independent variables and the crash frequency of different clusters respectively as dependent variables. The hybrid approach enables a comprehensive examination of internal and external heterogeneities among bicycle crash frequency factors simultaneously. Results suggest that the proposed hybrid approach exhibits superior fitting and predictive performance compared to the model only considers the effects of unobserved heterogeneity from one perspective with the lower values of Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), Mean Absolute Error (MAE) and Root Mean Squared Error (RMSE). This approach can help policymakers and urban planners to design more effective safety interventions by understanding the distinct needs of different bicyclist clusters and the specific factors that contribute to crash risk in each group.

Modeling compact objects with quark matter and dark energy: A comparative study of the radial oscillation modes of HESS J1731-347 and PSR J0740+6620

We model the massive pulsar J0740+6620 and the light HESS J1731-347 compact object assuming (i) quark matter and (ii) dark energy stars. Within Einstein’s General Relativity, and assuming objects made of isotropic matter, we adopt analytic equations-of-state for both matter contents. Although the inner composition of the objects is very different in each case, both equations-of-state imply qualitatively very similar mass-to-radius relationships. We compute the spectra of radial equations for all four cases and the corresponding wave functions as well as the large frequency separations. A comparison between the different matter contents is made as well.

Doping Profile Meter for Semiconductor Structures

ABSTRACT A measuring device designed to gauge the distribution of electrically charged impurities within strongly asymmetric p – n junctions, Schottky barriers, and metal – insulator – semiconductor structures, employs the capacitance – voltage method. This device is controlled by a personal computer through a microcontroller. The coordinates of the concentration profile points are determined through a simultaneous selection of signals proportional to the concentration and its spatial coordinate, achieved by the selective hardware separation of information frequencies from a polyharmonic voltage. This process occurs in a structure installed in the negative-feedback circuit of the operational amplifier. The entire profiling process takes 30 seconds. It boasts a depth resolution of 15 angstroms (equivalent to 3‒4 atomic layers of the crystal lattice) at an impurity concentration of 5 × 1017 cm−3, with a maximum measured concentration of 5 × 1018 cm−3. The dimensions of the measuring device are 180 × 120 × 50 mm. The study presents examples of its practical applications.

Effects of Fallen Posidonia Oceanica Seagrass Leaves on Wave Energy at Sandy Beaches

Posidonia Oceanica (PO) is an endemic marine plant in the Mediterranean Sea. In an experimental study conducted in the Eastern Mediterranean, the effects of natural PO leaves on reducing the height of incident waves impacting a beach were measured. The transmission coefficient (Kt) was found to vary between 0.73 and 0.94, which is equivalent to a wave height decay of 6–27%. The results show that in their natural environment, free-floating dead PO leaves dissipate incoming wave energy and have the capacity to protect beaches against erosion. Further analysis in separate frequency bands showed that waves with periods between 4.5–6.2 s were more sensitive to PO leaves in terms of energy dissipation. The transmission coefficient for medium-period waves, calculated using the medium-frequency part of the wave spectrum, delivered a maximum transmission coefficient of 0.5, corresponding to a 50% decay in wave height due to PO leaves.

MAGPIE: An interactive tool for visualizing and analyzing protein-ligand interactions.

Quantitative tools to compile and analyze biomolecular interactions among chemically diverse binding partners would improve therapeutic design and aid in studying molecular evolution. Here we present Mapping Areas of Genetic Parsimony In Epitopes (MAGPIE), a publicly available software package for simultaneously visualizing and analyzing thousands of interactions between a single protein or small molecule ligand (the "target") and all of its protein binding partners ("binders"). MAGPIE generates an interactive three-dimensional visualization from a set of protein complex structures that share the target ligand, as well as sequence logo-style amino acid frequency graphs that show all the amino acids from the set of protein binders that interact with user-defined target ligand positions or chemical groups. MAGPIE highlights all the salt bridge and hydrogen bond interactions made by the target in the visualization and as separate amino acid frequency graphs. Finally, MAGPIE collates the most common target-binder interactions as a list of "hotspots," which can be used to analyze trends or guide the de novo design of protein binders. As an example of the utility of the program, we used MAGPIE to probe how different antibody fragments bind a viral antigen; how a common metabolite binds diverse protein partners; and how two ligands bind orthologs of a well-conserved glycolytic enzyme for a detailed understanding of evolutionarily conserved interactions involved in its activation and inhibition. MAGPIE is implemented in Python 3 and freely available at https://github.com/glasgowlab/MAGPIE, along with sample datasets, usage examples, and helper scripts to prepare input structures.

Quantum Big-Bounce as a phenomenology of RQM in the Mini-superspace

We investigate the emergence of a quantum Big-Bounce in the context of an isotropic Universe, filled by a self-interacting scalar field, which plays the role of a physical clock. The bouncing cosmology is the result of a scattering process, driven by the scalar field potential, which presence breaks down the frequency separation of the Wheeler-DeWitt equation, treated in strict analogy to a relativistic quantum system. Differently from previous analyses, we consider a really perturbative self-interaction potential, affecting the dynamics in a finite range of the time labeled by the scalar clock (and in particular we remove the divergent character previously allowed). The main result of the present analysis is that, when the Relativistic Quantum Mechanics formalism is properly implemented in the Mini-superspace analogy, the probability amplitude for the bounce is, both in the standard and polymerized case, characterized by a maximum in correspondence of the quasi-classical condition of a Universe minimum volume.

Improved Effectiveness of Vane-Type Vortex Generators for Incident Shock-Induced Separation

An experimental investigation is conducted to improve the control effectiveness of an array of vane-type vortex generators (VG) implemented 6 δ upstream of an incident shock-induced separation generated using a 14-deg wedge in a Mach 2.05 flow. Initially, the effect of an array of rectangular vanes (RRV) is studied by varying the vane 1) chord to height (c/h)=7.2, 4.2, 2) angle α=24, 20, 18, and 16 deg, 3) height to boundary-layer thickness (h/δ)=0.75, 0.5, 0.3, and 0.2, and 4) interdevice spacing to height (s/h)=12, 9.5, 7.5, 6.5, 5.7, 5.5, and 5.0. Similar tests were also performed for ramp vanes (RV) with α=24 deg. Due to inherent design differences, an RRV device generates a larger region of vortex influence relative to an RV device. Therefore, reducing s/h significantly reduces the extent of uncontrolled separation regions between neighboring VGs that improves their separation control capability. The best performing RRV devices with vane height h/δ=0.5, h/δ=0.3, and h/δ=0.2 show maximum reduction in separation extent of nearly 80, 74, and 70%, respectively, relative to no control. The equivalent RV devices, however, show much reduced control effectiveness. All controls exhibit a shift in the dominant separation frequency to higher values, indicating a reduction in the overall extent of separation.

Anisotropic dark energy stars within vanishing complexity factor formalism: Hydrostatic equilibrium, radial oscillations, and observational implications

We investigate the structure and radial oscillations of anisotropic compact stars composed of dark energy, using the vanishing complexity factor formalism within general relativity. This novel approach establishes a direct link between the energy density and anisotropic factor, providing a robust framework for studying these exotic stellar objects. Employing an Extended Chaplygin Gas equation of state, we numerically compute interior solutions for both isotropic and anisotropic stars, revealing distinct differences in their properties. Additionally, we examine the oscillation modes and frequencies of these stars, highlighting the impact of anisotropy on their pulsational behaviour. Our results reveal distinct differences in the stellar properties, such as the metric potentials, pressure, speed of sound, and relativistic adiabatic index, between the two cases. Furthermore, we calculate the large frequency separation for the fundamental and first excited modes, offering insights relevant for future asteroseismology studies. Our findings shed light on the complex interplay of gravity, matter, and anisotropy in compact stars, providing a new perspective on dark energy's role in their structure and dynamics.

Asteroseismology of evolved stars in six star clusters observed by Kepler/K2

In this study, we have explored the frequency separations, Δν and δν02, the height and width of the oscillation power excess, HGauss and δνenv, as a function of the frequency of maximum power νmax by analyzing 187 evolved stars in six star clusters observed by the Kepler/K2 missions. We have also examined the asteroseismic relation in the Christensen-Dalsgaard diagram. Given the importance of scaling relations, the dependency of asteroseismic scaling relations on physical quantities must be verified to reduce systematic errors through the exploration of observational data obtained from various sources. In this context, the star cluster provides a valuable means to assess the age and metallicity. Focusing on evolved stars with 30μHz<νmax<220μHz, we have exploited the mass effect without the need for deriving the individual stellar mass. We have found that the considered relations appear to be associated with the age of star clusters, thereby the mass of the stars in a given evolutionary status for star clusters with different ages. By separately considering red giant branch stars and red clump stars, we have found that red clump stars appear more sensitive to the cluster age compared with red giant branch stars. It has been suggested that conclusions regarding the dependency of metallicity should be drawn with due care as outcomes are subject to how to treat metallicity. Finally, we conclude by briefly pointing out implications of our findings on asteroseismic inferences.

A Hybrid Beat Frequency Oscillation Suppression Strategy for DC Microgrids

In DC microgrids, parallel-connected power converters are commonly used to integrate distributed energy sources. However, interactions of power switching noises among these power converters could lead to large low-frequency beat frequency oscillations under certain conditions, which degrades system performance and reliability, especially for DC microgrids with parallel connected Boost converters. In this research, the output impedance model for multiple parallel-connected Boost converters is developed for beat frequency oscillation analysis, and then a hybrid method is proposed to address this issue. The proposed method includes separated switching frequency channels and additional line inductors. Experimental results validate the effectiveness of the proposed method.

A 4–8 GHz kinetic inductance traveling-wave parametric amplifier using four-wave mixing with near quantum-limited noise performance

Kinetic inductance traveling-wave parametric amplifiers (KI-TWPAs) have a wide instantaneous bandwidth with a near quantum-limited noise performance and a relatively high dynamic range. Because of this, they are suitable readout devices for cryogenic detectors and superconducting qubits and have a variety of applications in quantum sensing. This work discusses the design, fabrication, and performance of a KI-TWPA based on four-wave mixing in a NbTiN microstrip transmission line. This device amplifies a signal band from 4 to 8 GHz without contamination from image tones, which are produced in a separate higher frequency band. The 4–8 GHz band is commonly used to read out cryogenic detectors, such as microwave kinetic inductance detectors and Josephson junction-based qubits. We report a measured maximum gain of over 20 dB using four-wave mixing with a 1 dB gain compression point of −58 dBm at 15 dB of gain over that band. The bandwidth and peak gain are tunable by adjusting the pump-tone frequency and power. Using a Y-factor method, we measure an amplifier-added noise of 0.5 ≤ Nadded ≤ 1.5 photons from 4.5 to 8 GHz.

Design optimization and experimental verification of ultrasonic stack for micro hot embossing of polymers

Ultrasonic micro hot embossing (UMHE) is a prominent technique used in numerous sectors to produce micro parts since it is cheaper, faster, and more accurate. Amplitude uniformity is a crucial parameter in UMHE in order to manufacture micro parts with accurate dimensions and high-quality surfaces, even though limited research has been conducted on the uniformity of ultrasonic amplitude at the horn face during the embossing process. This paper presents an experimental and numerical study for designing an ultrasonic transducer and horn tailored to the micro hot embossing of polymer micro parts. A finite element (FE) simulation model combined with the Taguchi method has been developed to optimize the horn geometry and maximum amplitude uniformity. The Taguchi orthogonal array of 25 design runs has been generated and simulated using the developed FE modal analysis model, and then the optimized geometry was used to fabricate the horn. Applied torque and operating time calibrate and evaluate the transducer vibration characteristics. Experimental and simulation results revealed that the fabricated ultrasonic transducer and horn of a straight microfeature has a natural frequency of 28.8 kHz and has an 11 µm average peak-to-peak amplitude with 0.963 amplitude homogeneity along the microfeature face. The achieved frequency separation was greater than 0.85 kHz, whereas the gain ratio was 1.2. The design methodology developed in this paper showed great potential and has been numerically validated for various microfeature shapes across the horn face. Consequently, it can be applied to various ultrasonic applications beyond UMHE.