Spectral Energy Density Research Articles

A directional spectrum evolution model for ship noise.

A radiation transport equation that describes the spatiotemporal evolution of the directional spectrum of underwater acoustic noise is presented and applied to ship noise. A ray-based algorithm is used to solve the transport equation and numerically simulate the evolution of the directional noise spectrum produced by a passing ship. The model described accounts for the transient and highly episodic nature of shipping noise, the strong anisotropy of the radiated shipping noise, the directional dependence of the resulting acoustic field, and the critical angle dependence of bottom-reflected energy. The model predicts time histories of sound pressure level and directional spectral energy density at distant locations if the ship track and the ship's radiated noise power are known. Simulations are shown to be in qualitatively good agreement with observations.

Fault branch determination method based on the amplitude information of the first wave head of the initial traveling wave of the fault

In order to solve the difficult problem of fault branch determination in multi-branch distribution networks, the transmission characteristics of fault traveling waves in the distribution line are analyzed. The variation law of fault traveling wave amplitude with fault distance and frequency is deduced theoretically, and the reasons for the difficult determination of fault branch in the distribution line are revealed. A fault branch determination method based on the energy spectral density of the amplitude of the first wave head of the fault initial traveling wave is proposed. The reference node and the reference end of distribution networks are defined. The ratio of the intrinsic amplitude matrix to the real fault matrix before offline is calculated. The fault branch determination matrix is established to realize the reliable determination of the fault branch. PSCAD is used to build a 10 kV multi-dominant network model to simulate various fault conditions to verify the fault branch determination method. The simulation results show that the method can effectively identify the fault branch and has strong reliability.

Origin of Ultralow Thermal Conductivity in Metal Halide Perovskites.

Resulting from their remarkable structure-property relationships, metal halide perovskites have garnered tremendous attention in recent years for a plethora of applications. For instance, their ultralow thermal conductivities make them promising candidates for thermoelectric and thermal barrier coating applications. It is widely accepted that the "guest" cations inside the metal halide framework act as "rattlers", which gives rise to strong intrinsic phonon resistances, thus explaining the structure-property relationship dictating their ultralow thermal conductivities. In contrast, through systematic atomistic simulations, we show that this conventionally accepted "rattling" behavior is not the mechanism dictating the ultralow thermal conductivities in metal halide perovskites. Instead, we show that the ultralow thermal conductivities in these materials mainly originate from the strongly anharmonic and mechanically soft metal halide framework. By comparing the thermal transport properties of the prototypical fully inorganic CsPbI3 and an empty PbI6 framework, we show that the addition of Cs+ ions inside the nanocages leads to an enhancement in thermal conductivity through vibrational hardening of the framework. Our extensive spectral energy density calculations show that the Cs+ ions have well-defined phase relations with the lattice dynamics of the "host" framework resulting in additional pathways for heat conduction, which is in disagreement with the description of the individual "rattling" of guests inside the framework that has been widely assumed to dictate their ultralow thermal conductivities. Furthermore, we show that an efficient strategy to control the heat transfer efficacy in these materials is through the manipulation of the framework anharmonicity achieved via strain and octahedral tilting. Our work provides the fundamental insights into the lattice dynamics that dictate heat transfer in these novel materials, which will ultimately help guide their further advancement in the next-generation of electronics such as in thermoelectric and photovoltaic applications.

Application of Transcranial Magnetic Stimulation with Electroencephalography in the Evaluation of Brain Function Changes after Stroke.

Based on transcranial magnetic stimulation (TMS) with electroencephalography technology, this study analyzed the rehabilitation mechanism of patients' motor function reconstruction and nerve remodeling after stroke. It revealed the function of the cerebral cortex network at a deeper level and established a set of prognostic marker evaluation indicators for the reconstruction of motor function after stroke. Twenty-one patients treated at the Beijing Rehabilitation Hospital of Capital Medical University because of ischemic stroke in the territory supplied by the middle cerebral artery were selected as the experimental group. Neurophysiological evaluation, motor function evaluation, and clinical evaluation were performed 30 and 180 d after the onset of ischemic stroke. In the control group, neurophysiological evaluation was also performed as a reference index to evaluate the changes in cortical patterns after stroke. The brain topographic map showed the changes in energy or power spectral density (PSD) at 1,000 ms after stimulation as compared with before stimulation, but no difference was detected in these patients. The time-frequency analysis showed that when the left primary motor cortex (M1) area was stimulated using TMS, the PSD values of the left and right M1 and posterior occipital cortex areas produced an 8-40 Hz wave band in patients S1-S11. There was no significant energy change in patients S12-S16. For patients with different injury types, degrees of injury, and different onset periods, individualized intervention methods should be adopted. The evaluation methods should be as diverse as possible, and the rehabilitation effects of patients should be assessed from multiple perspectives to avoid the limitations of single factors. Possible mechanism: After brain injury, the nervous system can change its structure and function through different ways and maintain it for a certain period of time. This plasticity change will change with the course of the disease.

A conservative Galerkin solver for the quasilinear diffusion model in magnetized plasmas

The quasilinear theory describes the resonant interaction between particles and waves with two coupled equations: one for the evolution of the particle probability density function (pdf), the other for the wave spectral energy density (sed). In this paper, we propose a conservative Galerkin scheme for the quasilinear model in three-dimensional momentum space and three-dimensional spectral space, with cylindrical symmetry.We construct an unconditionally conservative weak form, and propose a discretization that preserves the unconditional conservation property, by “unconditional” we mean that conservation is independent of the singular transition probability. The discrete operators, combined with a consistent quadrature rule, will preserve all the conservation laws rigorously. The technique we propose is quite general: it works for both relativistic and non-relativistic systems, for both magnetized and unmagnetized plasmas, and even for problems with time-dependent dispersion relations.We represent the particle pdf by continuous basis functions, and use discontinuous basis functions for the wave sed, thus enabling the application of a positivity-preserving technique. The marching simplex algorithm, which was initially designed for computer graphics, is adopted for numerical integration on the resonance manifold. We introduce a semi-implicit time discretization, and discuss the stability condition. In addition, we present numerical examples with a “bump on tail” initial configuration, showing that the particle-wave interaction results in a strong anisotropic diffusion effect on the particle pdf.

Quantitative analysis method for extraordinary optical transmission of thin microcavity by the catastrophic theory

Extraordinary optical transmission (EOT) can be regarded as a phase transition process based on the variation of the aperture of the thin microcavity by the published results. Considering that the catastrophe theory could describe quantitatively any phase transition process, a novel method is proposed to analyze the EOT transition quantitatively based on a cusp catastrophic model with dimensionless analysis. The quantitative relationship of transmitted energy spectral density is fully obtained, which is also related to the aperture radius and incident electromagnetic frequency. Furthermore, from this method, a quantum transition factor is derived strictly to describe the EOT transition process, which can be divided into wave region, wave-particle duality region and quantum region with the factor increasing from 0 to 1, and Bethe's aperture theory stating that transmission is proportional to is only one of our special cases in the wave region. Finally, the influence of the aperture and the frequency of incident wave on the EOT transmittance is analysed, and the catastrophic model is verified by previous experiments. The novel method of transition analysis provides a new insight into the EOT.

Quantum-quasiclassical analysis of center-of-mass nonseparability in hydrogen atom stimulated by strong laser fields *

We have developed a quantum-quasiclassical computational scheme for quantitative treating of the nonseparable quantum–classical dynamics of the 6D hydrogen atom in a strong laser pulse. In this approach, the electron is treated quantum mechanically and the center-of-mass (CM) motion classically. Thus, the Schrödinger equation for the electron and the classical Hamilton equations for the CM variables, nonseparable due to relativistic effects stimulated by strong laser fields, are integrated simultaneously. In this approach, it is natural to investigate the idea of using the CM- velocity spectroscopy as a classical ‘build-up’ set up for detecting the internal electron quantum dynamics. We have performed such an analysis using the hydrogen atom in linearly polarized laser fields as an example and found a strong correlation between the CM kinetic energy distribution after a laser pulse and the spectral density of electron kinetic energy. This shows that it is possible to detect the quantum dynamics of an electron by measuring the distribution of the CM kinetic energy.

Physics-based acoustic inversion of sound velocity and attenuation in low-velocity marine sediments

Using data from the Yellow Sea, arrival times of the direct wave and surface/bottom reflections from explosive sources to a vertical hydrophone array are used to precisely determine each explosive source’s location, the source energy spectral density (SESD), and the water depth. Long-range propagation waveforms reveal modal dispersion: the ground wave, water wave, Airy phase, etc. There are two high-frequency (HF) groups of water waves. One propagates with the sound speed in the water below the thermocline, the other with a speed close to the sound speed in the water above the thermocline. The HF group arrival times offer a time reference for dispersion analyses, including the ground wave speed at the cutoff frequency and the group velocity at Airy frequency. Associated with a top layer oflow-velocity sediments (LVS), seafloor reflections have two pulses: one from the water-sediment interface, one from the sediment-basement interface; Long-range transmission loss (TL) exhibits abnormal peaks at selected frequencies. Above-mentioned physics characteristics and the SESD-normalized TL(r) and TL(f) in 50–5000 Hz range up to 27.6 km are used for observationally driven inferences of seafloor geo-acoustic parameters, such as the sound velocity and attenuation in the LVS layer, its thickness, the sound velocity in the basement, etc.

Generalized Impedance-based Transient Analysis for Multi-branched Pipeline Systems

Transient analysis of multi-branched pipeline systems is generalized by the development of an impedance method. Both open and closed boundaries of branched pipeline elements were implemented in the analytical development of a reservoir multi-branched pipeline valve system, in which impedance and transient responses performance were compared with those of conventional approaches. To address realistic boundary conditions along the branched element, a partially opened boundary condition was implemented in the impedance expression of the branched pipeline system. The performance of the generalized multi-branch impedance method was evaluated on a large water supply system with 10 minor branches from the actual system. The impact of the designated branches was evaluated using the pressure root-mean-square error (RMSE) and the energy spectral density difference between the original and skeletonized systems. Combinations of multiple branches for certain flow conditions were identified based on the holistic response for both the frequency and time domains. The proposed method can be a useful alternative to effectively address the skeletonization issue for pipeline systems with multi-branched elements.

Marginal stability constraint on runaway electron distribution

High-frequency kinetic instabilities of the strongly anisotropic runaway electrons (RE) can enhance the pitch-angle scattering of the runaways significantly. This wave-induced scattering can easily prevail over runaway scattering on high-Z impurities. In a steady state, collisional damping balances the kinetic drive of the unstable waves, keeping the RE distribution function at marginal stability. The marginal stability constraint limits the achievable RE densities and the shape of the RE distribution function. In this study, we consider whistler and compressional Alfvén waves as the primary source of enhanced elastic scattering of the runaways. By balancing the anomalous Doppler resonance drive with the collisional wave damping, we find the RE distribution function in the ultra-relativistic range of the phase space. We also derive an expression for the spectral energy density of the waves. We show that the power needed to compensate for the wave dissipation is negligible compared to the work of the electric field. The latter is in balance with the synchrotron losses of the runaway electrons.

SALT2 versus SALT3: updated model surfaces and their impacts on type Ia supernova cosmology

ABSTRACT For the past decade, SALT2 has been the most common model used to fit Type Ia supernova (SN Ia) light curves for dark energy analyses. Recently, the SALT3 model was released, which upgraded a number of model features but has not yet been used for measurements of dark energy. Here, we evaluate the impact of switching from SALT2 to SALT3 for a SN cosmology analysis. We train SALT2 and SALT3 on an identical training sample of 1083 well-calibrated Type Ia supernovae, ensuring that any differences found come from the underlying model framework. We publicly release the results of this training (the SALT ‘surfaces’). We then run a cosmology analysis on the public Dark Energy Survey 3-Yr Supernova data sample (DES-SN3YR), and on realistic simulations of those data. We provide the first estimate of the SN + CMB systematic uncertainty arising from the choice of SALT model framework (i.e. SALT2 versus SALT3), Δw = + 0.001 ± 0.005 – a negligible effect at the current level of dark energy analyses. We also find that the updated surfaces are less sensitive to photometric calibration uncertainties than previous SALT2 surfaces, with the average spectral energy density dispersion reduced by a factor of two over optical wavelengths. This offers an opportunity to reduce the contribution of calibration errors to SN cosmology uncertainty budgets.

Empirical mode decomposition and power spectrum filtering for detection of frequency channels related to multi-scale geochemical anomalies: Metal exploration targeting in Moalleman district, NE Iran

Geochemical anomaly patterns for metal exploration targeting usually reveal non-stationarity due mainly to the non-linear synthesis of ore-forming processes. The spectrum–area (S–A) multifractal filtering and the bidimensional empirical mode decomposition (BEMD) are robust methodologies for detecting geochemical anomalies with different scaling properties. The former portrays the generalized scale invariance characteristics of a geochemical image in the two-dimensional Fourier frequency domain. It relies on estimating scaling exponents of power-law functions in the spectral energy density plane to design filter functions that amplify a geochemical signal in specific frequency channels. The BEMD decomposes a geochemical image into a number of bidimensional intrinsic mode functions (BIMFs). It represents the spatial–frequency–energy distribution of a given image that suits non-stationary geochemical signals arising from non-linear Earth systems. This paper gauges the relevance of BEMD and S–A in signalizing frequency channels that correspond to regional- and local-scale geochemical anomalies through a comparative experiment in the Moalleman district, NE Iran. The BEMD filtered the multi-element anomaly map adaptively into a set of BIMFs (BIMF1, BIMF2, and BIMF3) and a residual signal, in order of decreasing frequency, yielding geochemical patterns with scaling characteristics from local to regional. The S–A model filtered the multi-element anomaly map into very high, high, and low frequency channels that characterize noise signatures and geochemical anomalies associated with local and regional ore-forming processes, respectively. The results indicate that the high frequency channel derived from the BEMD filtering (i.e., BIMF1) can portray more effectively local-scale metal-vectoring anomalies distributed at/around ore-controlling faults/fractures. However, the low frequency channel yielded by S–A filtering has enhanced effectively geochemical anomaly architectures that were developed through regional metallogenesis. Therefore, we considered the local-scale geochemical anomalies (i.e., BIMF1) to delimit metal-vectoring targets, whereby four exploration priorities were defined as new areas for further metal prospecting within the study area.

Event Horizon and Environs (ETHER): A Curated Database for EHT and ngEHT Targets and Science

The next generation Event Horizon Telescope (ngEHT) will observe multiple supermassive black hole (SMBH) candidates down to a few tens of mJy, and profoundly transform our understanding of the local SMBH population. Given the impossibility of large-area high-resolution millimeter surveys, multi-frequency spectral energy densities (SEDs), and models are required to both identify source samples tailored to specific science goals, and to predict the feasibility of detection of individual interesting sources. Here, we present the Event Horizon and Environs (ETHER) source and SED model database whose primary use is to enable the selection and optimization of targets for EHT and ngEHT science. The living ETHER database currently consolidates 1.6 million black hole mass estimates, ∼15,500 milliarcsec-scale radio fluxes, ∼14,000 hard X-ray fluxes (expected to grow by factor ≳40 with the eROSITA data release) and SED information as obtained from catalogs and database queries, the literature, and our own new observations. Jet and accretion flow models are fit to individual SEDs in an automated way in order to predict the ngEHT observable fluxes from the jet base and accretion inflow. The database can be filtered by parameters or cross matched to a user source list, with the automated SED fitting models optionally fine tuned by the user. We have identified an initial ngEHT ‘gold sample’ for jet base studies and potentially black hole shadows; this sample will grow significantly in the coming years. While the ngEHT requires and will best exploit the ETHER database, six (eleven) ETHER sources have already been observed (scheduled) with the EHT in 2022 (2023), and the database has wide ranging applications in galaxy and black hole mass evolution studies.

Dual-Feature Frequency Component Compression Method for Accelerating Reconstruction in Magnetic Particle Imaging

The frequency component compression method (FCCM) has been widely used in magnetic particle imaging (MPI) technology to improve reconstruction efficiency. This method can reduce the reconstruction time by using the signal-to-noise ratio (SNR) feature to remove high noise frequency components. To further accelerate the reconstruction, a dual-feature frequency component compression method (DF-FCCM) was developed herein. A new energy spectral density (ESD) feature was introduced to describe the noise level of measurement signal. By using the SNR feature and the ESD feature, the DF-FCCM can select valuable frequency components that contain low noise both in the measurement signal and the system matrix. The reconstruction time can be reduced by using fewer frequency components that contain more valuable information. The efficiency and the robustness of the proposed method was validated through extensive simulation experiments. Further real experiments based on the OpenMPI data set verified that the DF-FCCM can be applied in real MPI reconstruction. Compared to the previous SNR-FCCM, the DF-FCCM can achieve similar or better reconstruction quality by using 25% reconstruction time. The proposed method can efficiently improve the reconstruction efficiency and potential to improve the online MPI imaging, which is essential for pre-clinical and clinical applications.

Mechanism of amorphous-like thermal conductivity in binary oxide Yb<sub>3</sub>TaO<sub>7</sub>

The materials with low thermal conductivity (<i>κ</i>) are both fundamentally interesting and technologically important in applications relevant to thermal energy conversion and thermal management, such as thermoelectric conversion devices, thermal barrier coatings, and thermal storage. Therefore, understanding the physical mechanisms of glass-like heat conduction in crystalline materials is essential for the development and design of low-<i>κ</i> materials. In this work, the microscopic phonon mechanism of glass-like low <i>κ</i> in binary simple crystal Yb<sub>3</sub>TaO<sub>7</sub> with fluorite structure is investigated by using the equilibrium molecular dynamics, phonon spectral energy density, and lattice dynamics. Meanwhile, the weberite-structured Yb<sub>3</sub>TaO<sub>7</sub> is also mentioned for comparison. The calculated <i>κ</i> indicates that fluorite Yb<sub>3</sub>TaO<sub>7</sub> has a glass-like low <i>κ</i> while weberite Yb<sub>3</sub>TaO<sub>7</sub> has a crystal <i>κ</i>. Such a low <i>κ</i> in fluorite Yb<sub>3</sub>TaO<sub>7</sub> is mainly due to the large difference in interatomic force between O-Yb and O-Ta. This different atomic bonding can significantly soften the phonon mode and thus limit phonon transport. To further describe the microscopic phonon thermal conduction, the single-channel model based on the phonon gas model is first used to calculate the total <i>κ</i>. However, the single-channel model significantly underestimates the <i>κ</i>, suggesting the presence of non-normal phonons in Yb<sub>3</sub>TaO<sub>7</sub>. Based on this, vibrational mode decomposition is conducted throughout the entire phonon spectrum of fluorite- and weberite-type Yb<sub>3</sub>TaO<sub>7</sub>. It is found that most modes in fluorite Yb<sub>3</sub>TaO<sub>7</sub> fall in the Ioffe–Regel regime and exhibit a strongly diffusive nature. Such diffusive modes cannot be described by the phonon gas model. Based on the decomposed phonon modes, the dual-channel model involving diffusive mode and propagating mode is used to describe the phonon thermal conduction, by which the obtained results accord well with the experimental values. The vast majority (> 90%) of heat in fluorite Yb<sub>3</sub>TaO<sub>7</sub> is found to be transported by diffusive modes rather than propagating modes. Consequently, the <i>κ</i> of fluorite Yb<sub>3</sub>TaO<sub>7</sub> increases with temperature rising, exhibiting a unique glass-like nature. In particular, contrary to conventional wisdom, the optical phonon mode in fluorite Yb<sub>3</sub>TaO<sub>7</sub> plays a significant or even decisive role in thermal conduction, which could serve as a new physical factor to adjust <i>κ</i> in solid materials. Overall, the new understanding of the link between chemical bonding and glass-like <i>κ</i> can contribute to the development and design of low-<i>κ</i> materials.

Asymptotics of Zero Oscillations and the Spectral Energy Density of Equilibrium Radiation in a Nonideal Plasma

Asymptotics of Zero Oscillations and the Spectral Energy Density of Equilibrium Radiation in a Nonideal Plasma

Gravitational wave stochastic background in reduced Horndeski theories

We generalize to reduced Horndeski theories of gravity, where gravitational waves (GWs) travel at the speed of light, the expression of a statistically homogeneous and unpolarized stochastic gravitational wave background (SGWB) signal measured as the correlation between the individual signals detected by two interferometers in arbitrary configurations. We also discuss some results found in the literature regarding cosmological distances in modified theories, namely, the simultaneous validity of a duality distance relation for GW signals and of the coincidence between the gravitational wave luminosity distance, based on the energy flux, and the distance inferred from the wave amplitude. This discussion allows us to conclude that the spectral energy density per unit solid angle of an astrophysical SGWB signal has the same functional dependency with the luminosity of each emitting source as in General Relativity (GR). Using the generalized expression of the GW energy-momentum tensor and the modified propagation law for the tensor modes, we conclude that the energy density of a SGWB maintains the same functional relation with the scale factor as in GR, provided that the modified theory coincides with GR in a given hypersurface of constant time. However, the relation between the detected signal and the spectral energy density is changed by the global factor $G_4(\varphi(t_0))$, thus potentially serving as a probe for modified gravity theories.

Ionization Waves, Propagating in Opposite Directions, as in Red Sprites

The paper is devoted to the study of a pulsed streamer discharge, similar to that in the Earth’s upper atmosphere. An experimental setup providing the formation of two ionization waves propagating in opposite directions from a region filled with a plasma formed by the capacitive discharge in low-pressure atmospheric air was created. In a physical experiment, the process of propagation of red ionization waves (streamers) was simulated. It was established that the average propagation velocities of their fronts correspond to those of red sprites. This was shown as a result of spectral studies that at air pressures of 0.4-3 Torr, the radiation color radiation observed visually and captured on an integral photograph from the region of passage of ionization waves is determined by the spectral transitions of the first positive system (FPS) of nitrogen molecules, similar to what occurs for red sprites. In this case, the spectral energy density of radiation in the most intense band of the second positive system (SPS) of the nitrogen molecule with a wavelength of 337.13 nm is an order of magnitude or higher than that in the most intense band of the FPS with the wavelength of 775.32 nm. Using the emission spectra and methods of optical emission spectroscopy (OES), the main parameters of the discharge plasma are estimated. Thus, the created setup makes it possible to simulate the process of the formation of red sprites propagating in opposite directions under laboratory conditions.

A new look at the infrared properties of z ∼ 5 galaxies

ABSTRACT Recent Atacama Large Millimeter Array large surveys unveiled the presence of significant dust continuum emission in star-forming galaxies at z > 4. Unfortunately, such large programs – i.e. ALPINE (z ∼ 5) and REBELS (z ∼ 7) – only provide us with a single far-infrared (FIR) continuum data point for their individual targets. Therefore, high-z galaxies FIR spectral energy densities (SEDs) remain mostly unconstrained, hinging on an assumption for their dust temperature (Td) in the SED fitting procedure. This introduces uncertainties in the inferred dust masses (Md), infrared luminosities (LIR), and obscured star formation rate (SFR) fraction at z > 4. In this work, we use a method that allows us to constrain Td with a single-band measurement by combining the 158 $\mu$m continuum information with the overlying [C ii emission line. We analyse the 21 [C ii and FIR continuum-detected z ∼ 5 galaxies in ALPINE, finding a range of Td = 25–60 K and Md = 0.6–25.1 × 107 M⊙. Given the measured stellar masses of ALPINE galaxies, the inferred dust yields are around Md/M⋆ = (0.2–8) × 10−3, consistent with theoretical dust-production constraints. We find that eight out of the 21 ALPINE galaxies have LIR ≥ 1012 L⊙, comparable to ultraluminous IR galaxies (ULIRGs). Relying on ultraviolet-to-optical SED fitting, the SFR was underestimated by up to two orders of magnitude in four of these eight ULIRGs-like galaxies. We conclude that these four peculiar sources should be characterized by a two-phase interstellar medium structure with ‘spatially segregated’ FIR and ultraviolet emitting regions.

Cosmological Singularity as an Informational Seed for Everything

Mathematical problem of encoding of the universe quantum state in the cosmological singularity is considered using a free and massless scalar .eld as a prototype of matter. Two di.erent but coherent approaches to this issue are presented. The expression for the scalar particles' spectral energy density, which is initially encoded at the singularity, is deduced. An informational aspect of the problem is discussed.