Harmonic Research Articles

High-harmonic Plasma Emission Induced by Electron Beams in Weakly Magnetized Plasmas

Electromagnetic radiation at higher harmonics of the plasma frequency (ω ∼ n ω pe, n > 2) has been occasionally observed in type II and type III solar radio bursts, yet the underlying mechanism remains undetermined. Here we present two-dimensional fully kinetic electromagnetic particle-in-cell simulations with high spectral resolution to investigate the beam-driven plasma emission process in weakly magnetized plasmas of typical coronal conditions. We focused on the generation mechanisms of high-harmonic emission. We found that a larger beam velocity (u d ) favors the generation of the higher-harmonic emission. The emissions grow later for higher harmonics and decrease in intensity by ∼2 orders of magnitude for each jump of the harmonic number. The second and third harmonic (H2 and H3) emissions get closer in intensity with larger u d . We also show that (1) the H3 emission is mainly generated via the coalescence of the H2 emission with the Langmuir waves, i.e., H2 + L → H3, wherein the coalescence with the forward-propagating beam-Langmuir wave leads to the forward-propagating H3, and coalescence with the backward-propagating Langmuir wave leads to the backward-propagating H3; and (2) the H4 emission mainly arises from the coalescence of the H3 emission with the forward- (backward-)propagating Langmuir wave, in terms of H3 + L → H4.

A Preliminary Timing Analysis of two Intermediate Polars: UU Col and Swift J0939.7-3224

We present the preliminary timing analysis of confirmed intermediate polar UU Col and possible intermediate polar Swift J0939.7-3224 in the optical band with the help of long-term, high-cadence continuous photometry from Transiting Exoplanet Survey Satellite (TESS). For UU Col, we revise previously reported orbital and spin periods as 3.464 ± 0.005 h and 863.74 ± 0.08 s, respectively. Using the second harmonic of the beat frequency, the beat period is estimated as ∼928 s. These findings indicate that UU Col is a disc-fed dominated disc-overflow accretor. For J0939, we establish the spin period as 2671.8 ± 0.8 s and refine the provisionally suggested orbital period as 8.49 ± 0.03 h. The absence of beat frequency in J0939 signifies that it might be a pure disc-fed accretor; however, an X-ray study of this source will help to understand its true nature.

Systematic analysis of electronic barrier heights and widths for concerted proton transfer in cyclic hydrogen bonded clusters: (HF)n, (HCl)n and (H2O)n where n = 3, 4, 5.

The MP2 and CCSD(T) methods are paired with correlation consistent basis sets as large as aug-cc-pVQZ to optimize the structures of the cyclic minima for (HF)n, (HCl)n and (H2O)n where n = 3-5, as well as the corresponding transition states (TSs) for concerted proton transfer (CPT). MP2 and CCSD(T) harmonic vibrational frequencies confirm the nature of each minimum and TS. Both conventional and explicitly correlated CCSD(T) computations are employed to assess the electronic dissociation energies and barrier heights for CPT near the complete basis (CBS) limit for all 9 clusters. Results for (HF)n are consistent with prior studies identifying Cnh and Dnh point group symmetry for the minima and TSs, respectively. Our computations also confirm that CPT proceeds through Cs TS structures for the C1 minima of (H2O)3 and (H2O)5, whereas the process goes through a TS with D2d symmetry for the S4 global minimum of (H2O)4. This work corroborates earlier findings that the minima for (HCl)3, (HCl)4 and (HCl)5 have C3h, S4 and C1 point group symmetry, respectively, and that the Cnh structures are not minima for n = 4 and 5. Moreover, our computations show the TSs for CPT in (HCl)3, (HCl)4 and (HCl)5 have D3h, D2d, and C2 point group symmetry, respectively. At the CCSD(T) CBS limit, (HF)4 and (HF)5 have the smallest electronic barrier heights for CPT (≈15 kcal mol-1 for both), followed by the HF trimer (≈21 kcal mol-1). The barriers are appreciably higher for the other clusters (around 27 kcal mol-1 for (H2O)4 and (HCl)3; roughly 30 kcal mol-1 for (H2O)3, (H2O)5 and (HCl)4; up to 38 kcal mol-1 for (HCl)5). At the CBS limit, MP2 significantly underestimates the CCSD(T) barrier heights (e.g., by ca. 2, 4 and 7 kcal mol-1 for the pentamers of HF, H2O and HCl, respectively), whereas CCSD overestimates these barriers by roughly the same magnitude. Scaling the barrier heights and dissociation energies by the number of fragments in the cluster reveals strong linear relationships between the two quantities and with the magnitudes of the imaginary vibrational frequency for the TSs.

Benchmark ab initio characterization of the multi-channel Cl + CH3X [X = F, Cl, Br, I] reactive potential energy surfaces.

We determine benchmark geometries and relative energies for the stationary points of the Cl + CH3X [X = F, Cl, Br, I] reactions. We consider four possible reaction pathways: hydrogen abstraction, hydrogen substitution, halogen abstraction, and halogen substitution, where the substitution processes can proceed via either Walden inversion or front-side attack. We perform geometry optimizations and obtain harmonic vibrational frequencies at the explicitly-correlated UCCSD(T)-F12b/aug-cc-pVTZ level of theory, followed by UCCSD(T)-F12b/aug-cc-pVQZ single-point computations to make finite-basis-set error negligible. To reach chemical (<1 kcal mol-1), or even subchemical (<0.5 kcal mol-1) accuracy, we include core-correlation, scalar relativistic, post-(T), spin-orbit-splitting and zero-point-energy contributions, as well, in the relative energies of all the stationary points. Our benchmark 0 K reaction enthalpies are compared to available experimental results and show good agreement. The stationary-point structures and energetics are interpreted in terms of Hammond's postulate and used to make predictions related to the dynamical behavior of these reactive systems.

The impact of solvation on the structure and electric field strength in Li+GlyGly complexes.

To scrutinise the impact of electric fields on the structure and vibrations of biomolecules in the presence of water, we study the sequential solvation of lithium diglycine up to three water molecules with cryogenic infrared action spectroscopy. Conformer-specific IR-IR spectroscopy and H2O/D2O isotopic substitution experiments provide most of the information required to decipher the structure of the observed conformers. Additional confirmation is provided by scaled harmonic vibrational frequency calculations using MP2 and DFT. The first water molecule is shown to bind to the Li+ ion, which weakens the electric field experienced by the peptide and as a consequence, also the strength of an internal NH⋯NH2 hydrogen bond in the diglycine backbone. The strength of this hydrogen bond decreases approximately linearly with the number of water molecules as a result of the decreasing electric field strength and coincides with an increase in the number of conformers observed in our spectra. The addition of two water molecules is already sufficient to change the preferred conformation of the peptide backbone, allowing for Li+ coordination to the lone pair of the terminal amine group.

Wavefunction theory and density functional theory analysis of ground and excited electronic states of TaB and WB.

Several low-lying electronic states of TaB and WB molecules were studied using ab initio multireference configuration interaction (MRCI), Davidson corrected MRCI (MRCI+Q), and coupled cluster singles doubles and perturbative triples [CCSD(T)] methods. Their full potential energy curves (PECs), equilibrium electron configurations, equilibrium bond distances (res), dissociation energies (Des), excitation energies (Tes), harmonic vibrational frequencies (ωes), and anharmonicities (ωexes) are reported. The MRCI dipole moment curves (DMCs) of the first 5 electronic states of both TaB and WB are also reported and the equilibrium dipole moment (μ) values are compared with the CCSD(T) μ values. The most stable 13Π (1σ22σ23σ11π3) and 15Δ (1σ22σ23σ11π21δ1) electronic states of TaB lie close in energy with ∼62 kcal mol-1De with respect to the Ta(4F) + B(2P) asymptote. However, spin-orbit coupling effects make the 15Δ0+ state the true ground state of TaB. The ground electronic state of WB (16Π) has the 1σ22σ13σ11π31δ2 electron configuration and is followed by the excited 16Σ+ and 14Δ states. Finally, the MRCI De, re, ωe, and ωexe values of the 13Π state of TaB and 16Π and 14Δ states of WB are used to assess the density functional theory (DFT) errors on a series of exchange-correlation functionals that span multiple-rungs of the Jacob's ladder of density functional approximations (DFA).

Fulminic acid: a quasibent spectacle.

Fulminic acid (HCNO) played a critical role in the early development of organic chemistry, and chemists have sought to discern the structure and characteristics of this molecule and its isomers for over 200 years. The mercurial nature of the extremely flat H-C-N bending potential of fulminic acid, with a nearly vanishing harmonic vibrational frequency at linearity, remains enigmatic and refractory to electronic structure theory, as dramatic variation with both orbital basis set and electron correlation method is witnessed. To solve this problem using rigorous electronic wavefunction methods, we have employed focal point analyses (FPA) to ascertain the ab initio limit of optimized linear and bent geometries, corresponding vibrational frequencies, and the HCN + O(3P) → HCNO reaction energy. Electron correlation treatments as extensive as CCSDT(Q), CCSDTQ(P), and even CCSDTQP(H) were employed, and complete basis set (CBS) extrapolations were performed using the cc-pCVXZ (X = 4-6) basis sets. Core electron correlation, scalar relativistic effects (MVD1), and diagonal Born-Oppenheimer corrections (DBOC) were all included and found to contribute significantly in determining whether vibrationless HCNO is linear or bent. At the all-electron (AE) CCSD(T)/CBS level, HCNO is a linear molecule with ω5(H-C-N bend) = 120 cm-1. However, composite AE-CCSDT(Q)/CBS computations give an imaginary frequency (51i cm-1) at the linear optimized geometry, leading to an equilibrium structure with an H-C-N angle of 173.9°. Finally, at the AE-CCSDTQ(P)/CBS level, HCNO is once again linear with ω5 = 45 cm-1, and inclusion of both MVD1 and DBOC effects yields ω5 = 32 cm-1. A host of other topics has also been investigated for fulminic acid, including the dependence of re and ωi predictions on a variety of CBS extrapolation formulas, the question of multireference character, the N-O bond energy and enthalpy of formation, and issues that give rise to the quasibent appellation.

Synthesis, spectroscopic, crystal structure and Hirshfeld surface analysis and DFT calculations of (E)-N-(2,6-dichlorophenyl)-1-(5-nitro-2-(piperidin-1-yl)phenyl) methanamine

In this study, experimental methods X-ray single crystal analysis, UV-vis spectroscopy and FT-IR spectroscopy, and theoretical methods Density Functional Theory (DFT) were used to study the structure of the new Schiff base (E)-N-(2,6-dichlorophenyl)-1-(5-nitro-2-(piperidin-1-yl)phenyl) methanamine. Theoretical calculations of the title compound and FT-IR harmonic vibration frequencies were carried out using B3LYP methods with the 6-31G(d,p) basis set. The optical properties have been studied by DFT calculation and the experimental UV-Vis spectrum presents its contribution to the HOMO-LUMO boundary. The molecular electrostatic potential map (MEP-ESP), analysis of frontier molecular orbitals (FMO), and determination of thermodynamic properties for the title compound were conducted using identical levels of theory. Besides, the structural state and crystal packing of the title compound were analyzed using molecular structure, Hirshfeld surfaces, interactions energies, energy frameworks and electrophilicity-based charge transfer (ECT) with DNA bases.

Design and Implementation of C-Band Frequency Synthesizer Using LMX2592 IC

The paper presents the design scheme and implementation of a PLL-based-frequency synthesizer using LMX2592 IC. The frequency synthesizer have vital role in the development of up-converter and down-converter equipments. Therefore, on the RT-Duroid RO4350 substrate, a low phase noise and stable carrier generator is designed and implemented. Graphical User Interface (GUI) &amp; LAN based programming is developed to easily change the synthesizer frequency. The control system analysis using root locus and bode plot is presented for system stability.The experimental results representing the performance parameters, like frequency range, frequency step size, output power, phase noise, carrier stability, harmonics, and spurious, etc., are also presented in the paper. The analysis of spurious and phase noise performance at near integer boundary conditions are done by changing loop bandwidth and phase margin.

To simple waves and small-amplitude perturbations in radiation gasodynamics

The paper analyzes one-dimensional simple waves and small-amplitude perturbations in radiating and scattering gray gas. The governing equation of radiation acoustics describing the dynamics of simple waves is derived. The conditions of radiation-thermal dissipation and radiation resistance force are introduced into this equation to describe the propagation with dissipation and attenuation of various radiation perturbation waves. The phenomenological approximate Whitham method is used to investigate non-equilibrium wave phenomena in radiative medium. This method is an effective way to analyze fundamental modes when more than one velocity appears in the governing equation. The use of this method is demonstrated in this paper by considering the evolution of one-dimensional harmonic waves caused by a short-wave initial perturbation of the equilibrium state of the radiating and scattering medium. Analytical solutions are obtained for all wave modes, which allow us to interpret their physical meaning. These solutions can be, in particular, an additional test for radiative hydrodynamic codes operating in the radiative acoustics regime. The presented approach may be useful in detailing higher-order numerical Godunov schemes for radiation acoustics problems.

Theoretical Study of a Porous Silicon Cavity Based on Second Harmonic Waves Formed by Ferroelectric Crystals for Wide Range Multiphysical and Chemical Measurement

Theoretical Study of a Porous Silicon Cavity Based on Second Harmonic Waves Formed by Ferroelectric Crystals for Wide Range Multiphysical and Chemical Measurement

A novel model of nonlocal photoacoustic and plasmaelastic heated by laser pulsed excitation of nanoscale semiconductor medium

The study takes into account the diffusion of photo-excited carriers in the presence of a laser pulse and theoretically investigates photoacoustic wave propagation in the thermoelastic domain. In a nonlocality medium, the phenomena of thermomechanical and acoustic wave interaction are considered. Thermoelasticity, photothermal, and photoacoustic theories provide the controlling formulas. Photoacoustic waves are not dependent on electron–phonon or electron–hole thermalization processes; rather, they are produced by thermoelastic stress resulting from the temperature increase induced by the laser. The optical, elastic, and thermoelastic characteristics of nanoscale semiconductor materials are taken into account and photoacoustic signals are predicted by solving a thermal diffusion issue and a thermoelastic problem in combination. The mathematical model can be solved using the harmonic wave approach. By obtaining numerical solutions, all the physical fields of the physical domain, such as thermal, acoustic, mechanical, and carrier density diffusion, as well as displacements and temperatures, can be derived. The influences of nonlocal parameters, thermal delay, and laser pulse effect are investigated and compared using two- and three-dimensional visual representations, corresponding to two-dimensions and three-dimensions domains, respectively.

Harmonic Frequency Enhanced Direction of Arrival Estimation Using Non-Uniform Linear Arrays

Harmonic Frequency Enhanced Direction of Arrival Estimation Using Non-Uniform Linear Arrays

A Low-Phase-Noise VCO With Common-Mode Resonance Expansion and Intrinsic Differential 2nd-Harmonic Output Based on a Single Three-Coil Transformer

In this article, we propose a voltage-controlled oscillator (VCO) with a single three-coil transformer, featuring a common-mode (CM) resonance expansion and intrinsic differential 2nd harmonic output. In addition to a conventional transformer-based class-F resonator, an internal third coil is added to manipulate the CM response. On one hand, it expands the CM resonance bandwidth, eliminating the need for manual harmonic tuning to align the 2nd harmonic resonance. On the other hand, it creates a simultaneous wideband differential response at the 2nd harmonic frequency, therefore, the power consumption of the extra frequency doubler can be saved. Using the proposed stacked 8-shape inductor topology, the third coil can be placed inside the class-F transformer without consuming an extra chip area. Fabricated in a 65-nm CMOS process, the measured tuning range of the proposed VCO is 21.1%, from 12.3 to 15.2 GHz. The proposed VCO achieves a peak phase noise (PN) performance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 118.0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 111.9 dBc/Hz at 1 MHz offset for fundamental frequency and 2nd harmonic, respectively, the corresponding peak figure-of-merit (FoM) of which is 190.4 and 190.1 dBc/Hz, respectively. The VCO consumes a power of 8.4–9.6 mW, while occupying a small area of 0.06 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}$</tex-math> </inline-formula> thanks to the stacked 8-shape inductor topology.

Modelling bulk and surface characteristics of cubic CeO2, Gd2O3, and gadolinium-doped ceria using a partial charge framework.

The development and characterization of materials for solid oxide fuel cells (SOFC) is an important step towards sustainable energy technologies. This present study models cubic CeO2, Gd2O3, and gadolinium-doped ceria (GDC) using newly constructed interaction potentials based on a partial atom charge framework. The interaction model was validated by comparing the structural properties with experimental reference data, which were found to be in good agreement. Validation of the potential model was conducted considering the surface stability of CeO2 and Gd2O3. Additionally, the accuracy of the novel potential model was assessed by comparing the oxygen diffusion coefficient in GDCn (n = 4-15) and the associated activation energy. The results demonstrate that the novel potential model is capable of describing the oxygen diffusion in GDC. In addition, this study compares the vibrational properties of the bulk with density functional theory (DFT) calculations, using a harmonic frequency analysis that avoids the need for computationally expensive quantum mechanical molecular dynamics (QM MD) simulations. The potential is compatible with a reactive water model, thus providing a framework for the simulation of solid-liquid interfaces.

Sonic Bouquet: Decoding Cross-Modal Correspondences Between Timbre and Scent

The examination of cross-modal correspondences between auditory and olfactory senses opens up an intriguing perspective into the study of extra-musical meaning. In a behavioral experiment, musically trained participants were presented with 26 complex synthetic tones and 12 aromatic stimuli. Their task was to report potential associations between the two. The data analysis revealed that the majority of scents featured at least one association with a sound that was above chance. The salient acoustical correlates of basic aromatic categories could be summarized as follows: both fruity (e.g., cherry, melon, and pomegranate) and sour aromas exhibited a positive correlation with pitch. Fruity scents, in addition, were more likely to be associated with sounds featuring pronounced low harmonic partials (1st–4th), low noise content, low roughness, and a greater number of distinct pitches. Conversely, sour aromas were linked with stronger energy in the higher frequencies. Sweet scents correlated with sounds characterized by a lower spectral centroid, whereas aromas in the spicy/other category were associated with weak lower partials (fundamental frequency in particular) and stronger noisy components.

Seismic Beacon-A New Instrument for Detection of Changes in Rock Massif.

The seismic beacon is a new instrument that allows for the measurement of changes in a rock massif with high sensitivity. It is based on effects, which affect the propagation of harmonic seismic waves generated continuously with stable and precise frequency and amplitude. These seismic waves are registered by a system of seismic stations. The amplitude of the seismic signal is very small, and it is normally hidden in a seismic noise. Special techniques are applied to increase the signal-to-noise ratio. In 2020, the first prototype of the seismic beacon was constructed in a laboratory, and field tests were performed in 2022 and 2023. During the tests, the changes in spectral amplitude and phase of seismic waves were detected, which is interpreted as the changes in material properties. These measurements testified the basic functionality of the device. The seismic beacon has been developed primarily for the detection of critical stress before an earthquake, which is manifested by non-linear effects such as higher harmonics generation. In addition, it could be used, for example, in the detection of magma movements, groundwater level changes, changes in hydrocarbon saturation in rocks during the extraction of oil and natural gas, or the penetration of gases and liquids into the earth's crust.

Characteristics of common code conducted emission of multi-boost converters

One of the primary challenges faced when utilizing power converters such as a DC boost converter is electromagnetic interference (EMI) issues, one of which is common-mode (CM) noise. In order to mitigate the unwanted EMI from converters and design proper EMI filters, it is imperative to possess comprehensive insight into the characteristics of CM noise generated from the converters. This study presents the investigation regarding the characteristic of CM noise emitted by multi-boost converters when operated under varying duty cycle conditions. The research was conducted by measuring and analyzing the CM noise generated by three identical boost converters arranged in a parallel configuration. The result shows that the amplitude of each harmonic of CM noise generated by the multi-boost converters is 5 dB to 10 dB higher than CM noise from a single-boost converter. This is due to each converter being configured in the same conditions, producing a constructive interaction of the generated CM noise. Moreover, the duty cycle of pulse-width modulation (PWM) has a strong influence on the characteristic of the amplitude of each harmonic frequency. It is proven by the amplitude pattern of each harmonic of CM noise. Under duty cycle variations, the converters generate similar peaks and valley amplitude patterns as the Fourier transformation of the trapezoidal waveform used in the PWM setting.

Bicoherence Analysis of Oxygen Ion Cyclotron Harmonic Waves Observed by Van Allen Probes

AbstractBicoherence analysis is statistically performed for the oxygen ion cyclotron harmonic (OCH) waves observed by Van Allen Probes. While OCH waves and so‐called electromagnetic ion cyclotron harmonics have indistinguishable spectral characteristics in observation, they are believed to be excited by different mechanisms with the latter being suggested to arise from nonlinear wave‐wave coupling. Our result reveals that most of the OCH wave events have small bicoherence indices, so they are unlikely excited by wave‐wave coupling. The result is not much affected by the parameter choice in the bicoherence analysis, although increasing the subinterval length and/or reducing the subinterval overlap increases the chance of getting large bicoherence index values. Furthermore, the examination of two special events with large bicoherence indices shows that the observed phase relationship among different wave components does not align with the expectation from wave‐wave coupling. The events cannot be convincingly confirmed to be generated through wave‐wave coupling.

Analytic gradients for relativistic exact-two-component equation-of-motion coupled-cluster singles and doubles method.

A first implementation of analytic gradients for spinor-based relativistic equation-of-motion coupled-cluster singles and doubles method using an exact two-component Hamiltonian augmented with atomic mean-field spin-orbit integrals is reported. To demonstrate its applicability, we present calculations of equilibrium structures and harmonic vibrational frequencies for the electronic ground and excited states of the radium mono-amide molecule (RaNH2) and the radium mono-methoxide molecule (RaOCH3). Spin-orbit coupling is shown to quench Jahn-Teller effects in the first excited state of RaOCH3, resulting in a C3v equilibrium structure. The calculations also show that the radium atoms in these molecules serve as efficient optical cycling centers.