Plane Wave Model Research Articles

Infrared‐Transparent Semiconductor Membranes for Electromagnetic Interference Shielding of Millimeter Waves

AbstractIt is demonstrated that single‐crystalline and highly doped GaAs membranes are excellent candidates for realizing infrared‐transparent shields of electromagnetic interference at millimeter frequencies. Measured optical transmittance spectra for the semiconductor membranes show resonant features between 750 and 2500 nm, with a 100% maximum transmittance. The shielding effectiveness of the membranes is extracted from measured scattering parameters between 65 and 85 GHz. Selected GaAs membranes and membranes/polyamide films exhibit shielding effectiveness ranging from 22 to 40 dB, which are suitable values to ensure the safe operation of infrared devices for commercial applications. Theoretical calculations based on a plane wave model show that the interplay of primary reflection and multiple internal reflections of the radio‐frequency waves results in broadband shielding capabilities of the membrane between 10 and 300 GHz.

SBS suppression in fiber amplifiers with a broadband seed.

We present a scalar, time-dependent, plane-wave model for stimulated Brillouin scattering (SBS) within a fiber amplifier having a seed linewidth comparable to, or greater than, the Brillouin frequency shift. The broadband model introduces the existence of a backward anti-Stokes wave, in addition to the Stokes wave present in the narrowband model. The model also incorporates a Fresnel reflection within the fiber or at the exit face. In the absence of Fresnel reflections, the SBS threshold increases linearly with seed linewidth, up to linewidths of at least three times the Brillouin frequency shift. In the presence of Fresnel reflections that seed the Stokes wave, the threshold increases sub-linearly, which agrees with previously reported experimental results. For non-zero reflections and modulation formats with very compact spectra, the threshold can decrease with bandwidth in the region 16-24 GHz due to seeding of the Stokes wave.

Probing the Molecular and Macroscopic Structure of Solid Solutions by Dynamic Nuclear Polarization (DNP) Enhanced 13C and 15N Solid-State NMR Spectroscopy.

Crystallization is a widely used purification technique in the manufacture of active pharmaceutical ingredients (APIs) and precursor molecules. However, when impurities and desired compounds have similar molecular structures, separation by crystallization may become challenging. In such cases, some impurities may form crystalline solid solutions with the desired product during recrystallization. Understanding the molecular structure of these recrystallized solid solutions is crucial to devise methods for effective purification. Unfortunately, there are limited analytical techniques that provide insights into the molecular structure or spatial distribution of impurities that are incorporated within recrystallized products. In this study, we investigated model solid solutions formed by recrystallizing salicylic acid (SA) in the presence of anthranilic acid (AA). These two molecules are known to form crystalline solid solutions due to their similar molecular structures. To overcome challenges associated with the long 1H longitudinal relaxation times (T1(1H)) of SA and AA, we employed dynamic nuclear polarization (DNP) and 15N isotope enrichment to enable solid-state NMR experiments. Results of solid-state NMR experiments and DFT calculations revealed that SA and AA are homogeneously alloyed as a solid solution. Heteronuclear correlation (HETCOR) experiments and plane-wave DFT structural models provide further evidence of the molecular-level interactions between SA and AA. This research provides valuable insights into the molecular structure of recrystallized solid solutions, contributing to the development of effective purification strategies and an understanding of the physicochemical properties of solid solutions.

Iterative addition of parallel non-local effects to full wave ICRF finite element models in axisymmetric tokamak plasmas

The current response of a hot magnetized plasma to a radio-frequency wave is non-local, turning the electromagnetic wave equation into an integro-differential equation. Non-local physics gives rise to wave physics and absorption processes not observed in local media. Furthermore, non-local physics alters wave propagation and absorption properties of the plasma. In this work, an iterative method that accounts for parallel non-local effects in 2D axisymmetric tokamak plasmas is developed, implemented, and verified. The iterative method is based on the finite element method and Fourier decomposition, with the advantage that this numerical scheme can describe non-local effects while using a high-fidelity antenna and wall representation, as well as limiting memory usage. The proposed method is implemented in the existing full wave solver FEMIC and applied to a minority heating scenario in ITER to quantify how parallel non-local physics affect wave propagation and dissipation in the ion cyclotron range of frequencies (ICRF). The effects are then compared to a reduced local plane wave model, both verifying the physics implemented in the model, as well as estimating how well a local plane wave approximation performs in scenarios with high single pass damping. Finally, the new version of FEMIC is benchmarked against the ICRF code TORIC.

Wavelet Analysis of Differential TEC Measurements Obtained Using LOFAR

AbstractRadio interferometers used to make astronomical observations, such as the LOw Frequency ARray (LOFAR), experience distortions imposed upon the received signal due to the ionosphere as well as those from instrumental errors. Calibration using a well‐characterized radio source can be used to mitigate these effects and produce more accurate images of astronomical sources, and the calibration process provides measurements of ionospheric conditions over a wide range of length scales. The basic ionospheric measurement this provides is differential Total Electron Content (TEC, the integral of electron density along the line of sight). Differential TEC measurements made using LOFAR have a precision of <1 mTECu and therefore enable investigation of ionospheric disturbances which may be undetectable to many other methods. We demonstrate an approach to identify ionospheric waves from these data using a wavelet transform and a simple plane wave model. The noise spectra are robustly characterized to provide uncertainty estimates for the fitted parameters. An example is shown in which this method identifies a wave with an amplitude an order of magnitude below those reported using Global Navigation Systems Satellite TEC measurements. Artificially generated data are used to test the accuracy of the method and establish the range of wavelengths which can be detected using this method with LOFAR data. This technique will enable the use of a large and mostly unexplored data set to study traveling ionospheric disturbances over Europe.

Experimental study of granular particle stacks’ circumferential edge-constraint effect and the level- and time-dependent acoustical behavior

Granular materials, such as activated carbon, have shown advantages in absorbing low-frequency sounds, but they also exhibit significant nonlinearities. In this article, three unique types of granular particle stacks’ acoustical behavior are described and experimentally analyzed. First, when measuring the sound absorption spectra of particle stacks with varying depths and sample holder sizes, it was found that the frictional interaction with the tube circumferential wall can significantly affect the measurements, and a 1-D plane-wave acoustical model is only valid when the sample is thin. Secondly, when granular samples were tested with increasing excitation levels, the results indicated a decreased modulus and an increased damping. By further varying excitation’s level and bandwidth, a fluid-displacement-related metric was identified to describe this behavior. Thirdly, when measuring particle stacks over a longer period, the stack’s resonance peak gradually shifts to a higher frequency as the sample consolidates. This frequency shift was proportional to log(Time).

Theoretical and experimental study of the optoelectronic, thermodynamic and vibrational properties of the nanostructure of m-WO3

Tungsten trioxide (WO3), an n-type semiconductor, has attracted attention due to its diversity of properties, such as catalytic activity, gas sensing capabilities, photochromic behavior, and its ability to absorb both ultraviolet and visible light. This study aimed to investigate the monoclinic phase of the synthesized WO3 (m-WO3) through a combination of computational and experimental studies. We present the results of a theoretical investigation on m-WO3 using first-principles calculations (ab initio) and the pseudopotential model of plane waves. The Density Functional Theory (DFT) was employed, utilizing both the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) to account for exchange potential and correlation effects. Structural properties, electron band structure, electron density of states, and optical properties (reflectivity and optical absorption) were computed for the optimized nanostructure at its lowest energy state. A comparison between the calculated lattice parameters and theoretical/experimental results revealed a good agreement. Furthermore, the thermodynamic potentials and specific heat at the constant volume of the nanostructure were calculated. Infrared (IR) and Raman spectra within the frequency range of 0–1000 cm−1 were estimated and assigned, and the results were compared with experimental data and demonstrated good agreement with the literature.

Two‐Photon Pumped Single‐Mode Lasing in CsPbBr3 Perovskite Microwire

AbstractAchieving high‐quality, frequency‐upconversion single‐mode lasing output is an important requirement for developing new nonlinear optoelectronic devices, such as on‐chip optical communication, nonlinear optical switches, and optical parametric amplifiers. Here, an individual CsPbBr3 microwire prepared by the anti‐solvent method is served as both gain media and microresonator to achieve two‐photon pumped frequency upconversion single‐mode lasing with the side‐mode suppression ratio of 18 dB. Meanwhile, the refractive index of orthorhombic perovskite is theoretically calculated based on first principles, and determining its square whispering‐gallery oscillation type by combining with the plane wave model and the steady‐state oscillation conditions of laser. The extracted exciton binding energy of 33.15 meV higher than the thermal ionization energy of room temperature (≈26 meV) suggests that the as‐grown CsPbBr3 microwires possess the capacity to achieve two‐photon pumped lasing output, as well further gaining deeper insights into the role of exciton‐phonon coupling in light emission.

New Clues about light sterile neutrinos: preference for models with damping effects in global fits

This article reports global fits of short-baseline neutrino data to oscillation models involving light sterile neutrinos. In the commonly-used 3+1 plane wave model, there is a well-known 4.9σ tension between data sets sensitive to appearance versus disappearance of neutrinos. We find that models that damp the oscillation prediction for the reactor data sets, especially at low energy, substantially improve the fits and reduce the tension. We consider two such scenarios. The first scenario introduces the quantum mechanical wavepacket effect that accounts for the source size in reactor experiments into the 3+1 model. We find that inclusion of the wavepacket effect greatly improves the overall fit compared to a three-neutrino model by ∆χ2/dof = 61.1/4 (7.1σ improvement) with best-fit ∆m2 = 1.4 eV2 and wavepacket length of 67 fm. The internal tension is reduced to 3.4σ. If reactor-data only is fit, then the wavepacket preferred length is 91 fm (> 20 fm at 99% CL). The second model introduces oscillations involving sterile flavor and allows the decay of the heaviest, mostly sterile mass state, ν4. This model introduces a damping term similar to the wavepacket effect, but across all experiments. Compared to a three-neutrino fit, this has a ∆χ2/dof = 60.6/4 (7σ improvement) with preferred ∆m2 = 1.4 eV2 and decay Γ = 0.35 eV. The internal tension is reduced to 3.7σ.For many years, the reactor event rates have been observed to have structure that deviates from prediction. Community discussion has focused on an excess compared to prediction observed at 5 MeV; however, other deviations are apparent. This structure has L dependence that is well-fit by the damped models. Before assuming this points to new physics, we urge closer examination of systematic effects that could lead to this L dependence.

ArrayNet: A Combined Seismic Phase Classification and Back-Azimuth Regression Neural Network for Array Processing Pipelines

ABSTRACT Array processing is an integral part of automatic seismic event detection pipelines for measuring apparent velocity and backazimuth of seismic arrivals. Both quantities are usually measured under the plane-wave assumption, and are essential to classify the phase type and to determine the direction toward the event epicenter. However, structural inhomogeneities can lead to deviations from the plane-wave model, which must be taken into account for phase classification and back-azimuth estimation. We suggest a combined classification and regression neural network, which we call ArrayNet, to determine the phase type and backazimuth directly from the arrival-time differences between all combinations of stations of a given seismic array without assuming a plane-wave model. ArrayNet is trained using regional P- and S-wave arrivals of over 30,000 seismic events from reviewed regional bulletins in northern Europe from the past three decades. ArrayNet models are generated and trained for each of the ARCES, FINES, and SPITS seismic arrays. We observe excellent performance for the seismic phase classification (up to 99% accuracy), and the derived back-azimuth residuals are significantly improved in comparison with traditional array processing results using the plane-wave assumption. The SPITS array in Svalbard exhibits particular issues when it comes to array processing in the form of high apparent seismic velocities and a multitude of frost quake signals inside the array, and we show how our new approach better handles these obstacles. Furthermore, we demonstrate the performance of ArrayNet on 20 months of continuous phase detections from the ARCES array and investigate the results for a selection of regional seismic events of interest. Our results demonstrate that automatic event detection at seismic arrays can be further enhanced using a machine learning approach that takes advantage of the unique array data recorded at these stations.

Measurement uncertainty analysis of sound intensity using double-coupler calibration system

Currently, sound intensity instrument calibrations consist of a paired microphone phase and pressure calibrations, and the general uncertainty analysis focuses on how to calculate and express the uncertainty in the pressure lever and phase difference. However, no guidance for intensity level uncertainty is available. A significant barrier is the requirement to develop a measurement model that constitutes a relationship between the output quantities and input quantities, known to be the paired microphone pressure levels and phase difference. The Beijing Aerospace Institute of Metrology and Measurement Technology (AIM) is addressing this issue using a double-coupler calibration system, which is the incentive for the systematic evaluation of the associated measurement uncertainty in this study. A set of methodologies based on the plane-wave model is developed for estimating intensity and particle velocity uncertainty for sound intensity instruments.

Bayesian selection of plane-wave decomposition models.

Plane-wave decompositions, whereby a measured sound field is described as a superposition of plane waves, are central to many applications in acoustics and audio engineering. This letter applies a Bayesian probabilistic inference framework to the plane wave decomposition problem and examines the Deviance Information Criterion (DIC) for selecting the optimum number of waves in the decomposition. The framework learns the model directly from the data and, as such, adapts to the wavefield under study. The DIC is applied to data measured in two reverberant sound fields (highly-reverberant and lightly-damped) to determine the simplest models providing the preferred fit to the data.

Influence of orifice thickness and chamfer on broadband noise in a water circuit

An incompressible large-eddy simulation (LES) is used to predict broadband noise generation by an orifice in a water circuit. Flow conditions are chosen in order to avoid cavitation. The model’s results are compared to measured wall pressure fluctuations for three orifices: a thin sharp-square-edge orifice, a thick sharp-square-edge orifice and a thick narrower orifice with an upstream chamfer. Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulations (LES) fail to reproduce the steady-flow drag coefficient of the thick sharp-edge orifice and of the upstream-chamfered orifice. Large differences are found in the steady-flow drag coefficient of different samples of the thick orifice. An edge-tone like instability is observed in the near-field pressure fluctuations of one of the thick sharp-square-edge orifices, which does not appear in the other samples and is suppressed by the upstream chamfer. However, there are only minor differences in far-field radiated sound for these thick sharp-edged orifices. A plane-wave model with acoustic source from the LES predicts the power spectral density (PSD) of the acoustic pressures within a factor 3. At low Strouhal numbers (based on the orifice diameter and the cross-sectional averaged velocity in the orifice) the thin orifice behaves similarly to the thicker strongly chamfered orifices, with thin central cylindrical section. At higher Strouhal numbers the measured and predicted acoustic-pressure fluctuations due to these orifices are two orders of magnitude lower than those of thick orifices with sharp square edges. As orifices are used for the control of the flow distribution through complex water-cooling networks, the good results for thick chamfered narrow orifices call for a further study to find shapes that minimize the sound production at constant static pressure drop.

A convolutional plane wave model for sound field reconstruction

Spatial sound field interpolation relies on suitable models to conform to available measurements and predict the sound field in the domain of interest. A suitable model can be difficult to determine when the spatial domain of interest is large compared to the wavelength or when spherical and planar wavefronts are present or the sound field is complex, as in the near-field. To span such complex sound fields, the global reconstruction task can be partitioned into local subdomain problems. Previous studies have shown that partitioning approaches rely on sufficient measurements within each domain due to the higher number of model coefficients. This study proposes a joint analysis of all of the local subdomains while enforcing self-similarity between neighbouring partitions. More specifically, the coefficients of local plane wave representations are sought to have spatially smooth magnitudes. A convolutional model of the sound field in terms of plane wave filters is formulated and the inverse reconstruction problem is solved via the alternating direction method of multipliers. The experiments on simulated and measured sound fields suggest that the proposed method retains the flexibility of local models to conform to complex sound fields and also preserves the global structure to reconstruct from fewer measurements.

On the Legitimacy of Using Plane-Wave Model and Two-Component Measurement Systems when Performing MT Soundings in Polar Regions

On the Legitimacy of Using Plane-Wave Model and Two-Component Measurement Systems when Performing MT Soundings in Polar Regions

Dual-Hop Mixed FSO-VLC Underwater Wireless Communication Link

Underwater optical wireless communications (UOWCs) are promising and potential wireless carriers to envisage underwater phenomenal activities for various applications towards the futuristic 5G and beyond (5GB) wireless systems. The main challenges to deploy underwater applications are the physicochemical properties and strong turbulence channel conditions. In this regard, the end-to-end (E2E) performance analysis of a dual-hop mixed FSO/UVLC system under the intensity modulation/direct detection (IM/DD) technique in consideration of pulse amplitude modulation (PAM) scheme is investigated. Throughout this study, to tackle the issues of moderate-to-strong turbulence channel conditions, this work deploys the Gamma-Gamma (GG) distribution fading model and the links are designed by unifying plane wave models in the corresponding links, respectively. This investigation outperforms higher achievable data rate with minimal delay response and enhance network connectivity in real-time monitoring scenarios as compared with the traditional underwater wireless communication technologies. In more contrast, the probability distribution function (PDF), cumulative distribution function (CDF), and closed-form expression of the system are derived and presented in terms of Meijer-G function as well as Extended Generalized Bivariate Meijer-G Function (EGBMGF). The significant E2E performance metrics are obtained by employing the decode-and-forward (DF) relay protocol in hostile channel conditions. In aggregating this work, we combine the analytical expressions that present an efficient tool to depict the impact of channel parameters on the system. The simulation results are plausible of the system performance metrics as average BER (ABER) and outage probability <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(P_{out})$ </tex-math></inline-formula> in the presence of pointing and without pointing error events. Finally, in this work, we use the Monte-Carlo approach for the best fitting curves and validate the numerical expression yields simulation results.

Identification Approach of Arriving Wave Model Based on Likelihood Ratio Test With Different Sensor Noise Levels

Abstractk‐vector direction determined by propagation characteristics is crucial for understanding the global features of space plasma. Identifying the arriving wave model is a major factor in obtaining fast and accurate results in the direction finding of various plasma waves. If we can determine whether the observation data contain a significant natural wave or not, we can reduce the computational time for direction finding analysis by excluding noise‐only data. The conventional approach for identifying the arriving wave model assumes that all electromagnetic field sensors have same noise levels. However, the noise levels of electromagnetic field sensors on board scientific satellites can change owing to sensor degradation during long‐term instrument operation. Thus, the arriving wave model should be identified even when the noise levels of all electromagnetic field sensors are not equal. We proposed robustly identifying the arriving wave model by introducing a noise integration kernel that includes information about noise level ratios. Our proposed approach classifies a spectral matrix into three cases: noise model, single plane wave model, and multiple waves model. The proposed approach comprises the likelihood ratio test, and the identification result based on a statistical viewpoint. We conducted Monte Carlo simulations, and it was verified that the proposed approach can correctly derive the arriving wave model with high accuracy even with different sensor noise levels.

Extremely low barrier activation of methane on spin-polarized ferryl ion [FeO]2+ at the four-membered ring of zeolite

The Panov's α-O center in ZSM-5 zeolite revealing extraordinary activity in the oxidation of methane to methanol has been a subject of intense experimental and theoretical studies. Consensus on the structure and the origin of α-O superactivity seems to be achieved only in that α-O represents the ferryl group [FeO]2+ (bound by four lattice oxo sites) in cation-exchange position at some zeolite ring containing two framework Al atoms. Among rings with various sizes only three ones (four-, five-, and six-membered) can provide the ferryl ion with the necessary four number of oxo ligands (in the “plane” of ring) at reasonable Fe-O distance of about 2.0 Å. The six-membered ring is considered as the most probable one due to the 29Si MAS NMR data on Al pairs distribution on zeolite rings. However, the six-membered model in ZSM-5 has not been checked on behalf of the possibility of axial Fe-O coordination along Fe and terminal oxygen axis. By means of plane-wave DFT modeling, the present work shows that this coordination in fact takes place for six-membered ring unlike the four- and five-membered ones in which the Fe cation appears well above the plane of ring making the axial coupling impossible. Therefore, by known strong negative effect of axial oxo ligand on the ferryl species oxidizing activity, the six-membered model has to be discarded. Instead, a model of [FeO]2+ at four- or five-membered ring is to be put forward. In this work the four-membered model is shown to form the oxyl ground state Fe(III)–O• with the radical-like β-spin polarized oxygen. Calculated barrier of hydrogen abstraction from methane on this center is as low as 1.7 kcal/mol. The obtained prediction opens a way for other reactions to be probed on this center, particularly, the condensation of methane and oxidative dehydrogenation of hydrocarbons at low temperatures.

Nonlinear Breit-Wheeler pair production in collisions of bremsstrahlung γ quanta and a tightly focused laser pulse

Experimental efforts toward the detection of the nonperturbative strong-field regime of the Breit-Wheeler pair creation process plan to combine incoherent sources of GeV $\gamma$ quanta and the coherent fields of tightly focussed optical laser pulses. This endeavour calls for a theoretical understanding of how the pair yields depend on the applied laser field profile. We provide estimates for the number of produced pairs in a setup where the high-energy radiation is generated via bremsstrahlung. Attention is paid to the role of the transversal and longitudinal focussing of the laser field, along with the incorporation of a Gaussian pulse envelope. We compare our corresponding results with predictions from plane-wave models and determine the parameters of focused laser pulses which maximize the pair yield at fixed pulse energy. Besides, the impact of various super-Gaussian profiles for the laser pulse envelope and its transverse shape is discussed.

Optoelectronic and thermodynamic properties, infrared and Raman spectra of NbO2 and Nb2O5 from DFT formalism

All Niobium(Nb)-based materials have been widely investigated in recent decades due to a series of special applications in the high-tech industry, namely, in the aerospace sectors, for example, as metallic superalloys and, also, in the electro-electronic in which they are used as microcapacitors. We report the results of a theoretical study of the Niobium Dioxide (NbO2) and Niobium Pentoxide (Nb2O5) which is based on the ab initio plane-wave pseudo-potential model from Density Functional Theory (DFT), within both the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA), for the exchange and correlation potential. The structural properties, the electronic band structure, the electronic density of states, the reflectivity and the optical absorption are calculated from the nanostructures optimized at their lowest energy levels and, the comparison reveals good agreement of the calculated lattice parameters with theoretical and experimental results. An indirect bandgap E(ZΓ) was obtained within the GGA and LDA approximations of calculation for both NbO2 and Nb2O5. In addition, the optical absorptions and the reflectivities were shown to be sensitive to the plane of polarization of the incident light in the range of ultraviolet radiation to visible spectrum. The theoretical peaks of the infrared (IR) and Raman spectra in the frequency range of 0–1000 cm−1 was estimated and assigned, considering the norm-conserved pseudopotentials. The thermodynamic potentials, the specific heat at constant volume of the nanostructures are also calculated, which dependence on the temperature are specified.