Local Energy Spectrum Research Articles

Cooperative Spectrum Sensing Algorithm Based on Eigenvalue Fusion

A novel algorithm is introduced to improve collaborative spectrum sensing under low cognitive capabilities and insufficient signal-to-noise ratio. The algorithm is based on the difference of random matrix eigenvalues and uses the theory of random eigenvalues and the extreme distribution of the minimum eigenvalue. It makes use of the average, both arithmetic and geometric, as well as the minimum and maximum values of eigenvalues as the detection metric. It calculates the fusion power parameter through local energy spectrum sensing. Simulation results demonstrate that the algorithm outperforms the DMM algorithm and the NMME algorithm under users with low cognitive capabilities and Insufficient signal-to-noise ratio, making it more suitable for low signal-to-noise ratio environments.

Probing dark matter axions using the hyperfine structure splitting of hydrogen atoms

QCD axions can be a substantial part of dark matter if their mass ma∼10−5 eV. Since the axions were created by the misalignment mechanism, their local energy spectrum density is large. Consequently, the axion-induced atomic transition rate is enhanced if the atomic energy gap matches the axion mass. The hyperfine splitting between the spin 0 singlet ground state and the spin 1 triplet state of hydrogen is 0.59×10−5 eV, which is close to the preferred mass of dark matter axions. With an energy gap adjustment by applying a weak Zeeman magnetic field, dark matter axions can induce atomic hydrogen transitions. Furthermore, because the total spins of the hydrogen triplet and singlet differ, the axion-induced transitions are detectable by a Stern–Gerlach apparatus or a sensitive magnetic field detector. A potential realization of the proposed scheme can be similar to existing hydrogen masers.

Energy Spectra and Vorticity Dynamics in a Two-Layer Shallow Water Ocean Model

Abstract The dynamically adaptive WAVETRISK-OCEAN global model is used to solve one- and two-layer shallow water ocean models of wind-driven western boundary current (WBC) turbulence. When the submesoscale is resolved, both the one-layer simulation and the barotropic mode of the two-layer simulations have an energy spectrum with a power law of −3, while the baroclinic mode has a power law of −5/3 to −2 for a Munk boundary layer. This is consistent with the theoretical prediction for the power laws of the barotropic and baroclinic (buoyancy variance) cascades in surface quasigeostrophic turbulence. The baroclinic mode has about 20% of the energy of the barotropic mode in this case. When a Munk–Stommel boundary layer dominates, both the baroclinic and barotropic modes have a power law of −3. Local energy spectrum analysis reveals that the midlatitude and equatorial jets have different energy spectra and contribute differently to the global energy spectrum. We have therefore shown that adding a single baroclinic mode qualitatively changes WBC turbulence, introducing an energy spectrum component typical of what occurs in stratified three-dimensional ocean flows. This suggests that the first baroclinic mode may be primarily responsible for the submesoscale turbulence energy spectrum of the oceans. Adding more vertical layers, and therefore more baroclinic modes, could strengthen the first baroclinic mode, producing a dual cascade spectrum (−5/3, −3) or (−3, −5/3) similar to that predicted by quasigeostrophic and surface quasigeostrophic models, respectively. Significance Statement This research investigates how wind energy is transferred from the largest ocean scales (thousands of kilometers) to the small turbulence scales (a few kilometers or less). We do this by using an idealized model that includes the simplest representation of density stratification. Our main finding is that this simple model captures an essential feature of the energy transfer process. Future work will compare our results to those obtained using ocean models with more realistic stratifications.

Computational Fluid Dynamics analysis of a jet-induced attrition

• Analyzed gas jet penetration in packed bed and particle entrainment into the jets. • Reconstructed collision energy spectra from statistical kinetic theory-based approach. • Calculated local attrition rate using first moment of local collision energy spectra. • Evaluated steady state attrition of grid jet attrition device. • Discussed published jet-induced attrition mechanisms and proposed an additional one. The flow dynamics, collisional behavior and attrition rates of a grid jet attrition unit are computationally investigated using a kinetic theory-based approach. Profiles of the flow statistical properties are presented and discussed to describe the jet dynamics. Attrition behavior and rates are analyzed from the local reconstruction of the collision energy spectra. The commonly used jet-induced attrition mechanisms which involve the entrainment of the particles into the jet followed by their acceleration and collision at the jet tip is reproduced by the CFD calculations in this work. Supported by the local attrition rates, it is shown that the shear-based collisions around the jets, due to counter-current particle axial motions, are an additional jet-induced mechanism generating more fines than at the jet tips.

Numerical investigation of turbulent features past different mechanical aortic valves

Flow through mechanical aortic valves (MAVs) has been constantly associated to higher haemolysis and platelet activation levels with respect to native valves, due to non-physiologic haemodynamic features. Both computational and experimental investigations have correlated the blood damage to augmented levels of turbulent stress downstream of MAVs. This study provides a computational estimation, drawn from high-resolution direct numerical simulations, of turbulent and fluctuating viscous stresses in three different MAV configurations, at subsequent stages of the cardiac cycle. The configurations comprise a St. Judes Medical Regent valve (SJMV), a Lapeyre-Triflo FURTIVA valve (LTFV) with three leaflets, and a SJMV with vortex generators (VGs). Non-standard configurations are expected to mitigate the mean stress level on blood constituents reducing the turbulent production. Computations are carried out by means of a finite-difference flow solver with a direct-forcing immersed boundary technique to handle fixed and moving bodies. The VGs are found to provide instabilities which corrupt the Kármán-like vortex shedding downstream of the leaflets, reducing the intensity of turbulent kinetic energy at the peak flow rate, thus lowering the local Reynolds shear stress. Conversely, the LTFV configuration provides comparable haemodynamic performance at peak flow rate but further reduced stress level in the deceleration phase. These interpretations are supported by probability density distributions from three-dimensional fields, and further corroborated by a pointwise mapping of the Taylor length scale and local energy spectra. The outcomes of this study might potentially be exploited to improve the design of new-generation MAVs, with the aim of decreasing the risk of thromboembolic complications.

Long Term Neutron Activation in JET DD Operation

In the 2019 C38 Deuterium-Deuterium campaign at JET several different ITER-relevant materials and dosimetry foils were irradiated in a specially designed long-term irradiation station located inside the vacuum vessel with the purpose of testing the activation of ITER materials by fusion neutrons. The samples were exposed to a neutron fluence of 1.9E14 n/cm2 during JET discharges performed in the experimental campaign over a period of 5 months. Gamma ray spectroscopy measurements were performed on irradiated samples to determine the activation of different long-lived isotopes in the samples. Monte Carlo computational analysis was performed to support the experiment by using the measured neutron yield and irradiation time. In this paper we focus on the computational analysis of the dosimetry foils that are used in order to measure the local neutron energy spectrum and flux. The foils were chosen to cover different neutron energies: thus Yttrium and some of the Nickel and Cobalt reactions were used to determine the Deuterium-Tritium fusion fraction, while Scandium and Iron and some of the Nickel and Cobalt reactions were used for comparison of the computed activity with the experimental measurements. The obtained C/E values show a reasonably good agreement between calculated and measured activity, thus validating the computational methodology and providing the basis for the analysis of the ITER-relevant materials and future experiments performed at JET in the Deuterium-Tritium campaign.

Long-term variations of the sea level on the western coast of the Antarctic Peninsula

The aim of the study is to analyze seasonal and interannual changes in sea level on the western coast of the Antarctic Peninsula. Objects of study are seasonal and interannual variability of sea level, air temperature, pressure at sea level, precipitation in the period 1960–2018 at the Faraday/Akademik Vernadsky station, which was considered as representative site for the Antarctic Peninsula. Statistical methods of study were used, including estimates of linear trends of time series using the nonparametric Sen’s estimator of slope. The Mann-Kendall test was used to assess the significance of the slope of the trend. Time variability analysis was performed using wavelet analysis. Using the MATrix LABoratory (MATLAB) software package, squared of wavelet coefficients were calculated depending on the scale and shift or scalograms that characterize the local energy spectrum, and scalegrams calculated by averaging the scalograms by time shifts. The Morlet wavelet transformations were used. The results of the calculations showed that the trend of sea level at the Faraday/ Akademik Vernadsky station in the period 1960—2018, according to observations and correction on glacial isostatic adjustment of the crust is in the range from 3.05 to 3.45 mm/year, which is significantly higher than the global trend of 2.1 mm/year. Sea level scalograms allow estimating time-averaged periods and amplitudes of the coefficients for each season. In the austral winter and spring characteristic periods were 4—6 years, whereas the summer and autumn periods are characterized by 6–8 years, as well as by the highest amplitudes of the coefficients. All seasons are characterized by the appearance of a weakly pronounced period of about 4 years. The presence of peaks in the scalegrams at 6–8 and 3–4 years confirms the relationship of atmospheric and oceanic processes in West Antarctica to the natural variations of the ocean-atmosphere system, such as the Southern Annular Mode and El Nino-Southern Oscillation, which varies with typical 3–4 and 6–8 year periods. It was concluded that, unlike air temperature, the sea level trend is relatively weakly depends on the season, with the exception of autumn, when sea level trend is three times smaller than the average value. At the same time, the air temperature trend is the largest in the austral winter and the lowest in the summer.

Spatially localized multi-scale energy transfer in turbulent premixed combustion

A three-dimensional wavelet multi-resolution analysis of direct numerical simulations of a turbulent premixed flame is performed in order to investigate the spatially localized spectral transfer of kinetic energy across scales in the vicinity of the flame front. A formulation is developed that addresses the compressible spectral dynamics of the kinetic energy in wavelet space. The wavelet basis enables the examination of local energy spectra, along with inter-scale and subfilter-scale (SFS) cumulative energy fluxes across a scale cutoff, all quantities being available either unconditioned or conditioned on the local instantaneous value of the progress variable across the flame brush. The results include the quantification of mean spectral values and associated spatial variabilities. The energy spectra undergo, in most locations in the flame brush, a precipitous drop that starts at scales of the same order as the characteristic flame scale and continues to smaller scales, even though the corresponding decrease of the mean spectra is much more gradual. The mean convective inter-scale flux indicates that convection increases the energy of small scales, although it does so in a non-conservative manner due to the high aspect ratio of the grid, which limits the maximum scale level that can be used in the wavelet transform, and to the non-periodic boundary conditions, which exchange energy through surface forces, as explicitly elucidated by the formulation. The mean pressure-gradient inter-scale flux extracts energy from intermediate scales of the same order as the characteristic flame scale, and injects energy in the smaller and larger scales. The local SFS-cumulative contribution of the convective and pressure-gradient mechanisms of energy transfer across a given cutoff scale imposed by a wavelet filter is analysed. The local SFS-cumulative energy flux is such that the subfilter scales upstream from the flame always receive energy on average. Conversely, within the flame brush, energy is drained on average from the subfilter scales by convective and pressure-gradient effects most intensely when the filter cutoff is larger than the characteristic flame scale.

Multifractal metal in a disordered Josephson junctions array

We report the results of the numerical study of the non-dissipative quantum Josephson junction chain with the focus on the statistics of many-body wave functions and local energy spectra. The disorder in this chain is due to the random offset charges. This chain is one of the simplest physical systems to study many-body localization. We show that the system may exhibit three distinct regimes: insulating, characterized by the full localization of many-body wavefunctions, fully delocalized (metallic) one characterized by the wavefunctions that take all the available phase volume and the intermediate regime in which the volume taken by the wavefunction scales as a non-trivial power of the full Hilbert space volume. In the intermediate, non-ergodic regime the Thouless conductance (generalized to many-body problem) does not change as a function of the chain length indicating a failure of the conventional single-parameter scaling theory of localization transition. The local spectra in this regime display the fractal structure in the energy space which is related with the fractal structure of wave functions in the Hilbert space. A simple theory of fractality of local spectra is proposed and a new scaling relationship between fractal dimensions in the Hilbert and energy space is suggested and numerically tested.

Nonlinear optical conductivity resulting from the local energy spectrum at the M point in graphene

Based on the tight-binding model we construct a nonlinear Hamiltonian to describe the effective electric system around the $M$ point for the single layer graphene. The local energy spectrum at the $M$ point is approximated by the perfect hyperbolic geometry, and the modification by the screening effect from the substrate is taken into account. With the method based on the concept of the Floquet states and quasienergies (FSQ) we investigate the third order nonlinear conductivity ${\ensuremath{\sigma}}_{3}(\ensuremath{\omega}),\phantom{\rule{0.16em}{0ex}}{\ensuremath{\sigma}}_{3}(3\ensuremath{\omega})$ for the different frequency ranges, respectively, in which only the $\ensuremath{\pi}\ensuremath{-}{\ensuremath{\pi}}^{*}$ bands are involved. A positive cusplike peak arises at $\ensuremath{\hbar}\ensuremath{\omega}={\ensuremath{\varepsilon}}_{\mathrm{gap}}(\text{M})/3$ for ${\ensuremath{\sigma}}_{3}(3\ensuremath{\omega})$ which originates from the three-photon processes. Also, there is a peak at ${\ensuremath{\varepsilon}}_{\mathrm{gap}}(\text{M})/2$ for ${\ensuremath{\sigma}}_{3}(\ensuremath{\omega})$ resulting from two-photon-resonant processes. The analysis of the pole processes indicates that a self-energy-like term transition process plays a role in the nonlinear optical response, and the different transition processes interact with each other during the response to the external field. These interactions can be influenced by the polarization of the external field.

Vibration Signature Analysis Of A Chipped Spur Gear Tooth

Signal processing is a widely applied tool for condition monitoring of rotating machinery. These techniques are thus utilized extensively to process experimental signals. However, hypothesis about data and computational efforts often restrict the application of some techniques. The empirical mode decomposition (EMD) and Hilbert spectrum allows to overcome these limitations. This paper applies this method to vibration signal analysis for localised gear fault diagnosis. Considering that the gear fault vibration signal generate both the amplitude and frequency demodulated signals, the EMD could exactly decompose these demodulated signals into a number of intrinsic mode functions (IMFs), each of which can be amplitude-demodulated or frequency-demodulated component, the frequency families could be separated effectively from the gear vibration signal by applying EMD to the gear vibration signal. Furthermore, when fault occurs in gears, the energy of the gear vibration signal would change correspondingly, whilst the local Hilbert energy spectrum can exactly provide the energy distribution of the signal in certain frequency range with the change of the time and frequency. Thus, the fault information of the gear vibration signal can be extracted effectively from the local Hilbert energy spectrum.

Local and nonlocal energy spectra of superfluidHe3turbulence

Below the phase transition temperature $Tc \simeq 10^{-3}$K He-3B has a mixture of normal and superfluid components. Turbulence in this material is carried predominantly by the superfluid component. We explore the statistical properties of this quantum turbulence, stressing the differences from the better known classical counterpart. To this aim we study the time-honored Hall-Vinen-Bekarevich-Khalatnikov coarse-grained equations of superfluid turbulence. We combine pseudo-spectral direct numerical simulations with analytic considerations based on an integral closure for the energy flux. We avoid the assumption of locality of the energy transfer which was used previously in both analytic and numerical studies of the superfluid He-3B turbulence. For T<0.37 Tc, with relatively weak mutual friction, we confirm the previously found "subcritical" energy spectrum E(k), given by a superposition of two power laws that can be approximated as $E(k)~ k^{-x}$ with an apparent scaling exponent 5/3 <x(k)< 3. For T>0.37 Tc and with strong mutual friction, we observed numerically and confirmed analytically the scale-invariant spectrum $E(k)~ k^{-x}$ with a (k-independent) exponent x > 3 that gradually increases with the temperature and reaches a value $x\simeq 9$ for $T\approx 0.72 Tc$. In the near-critical regimes we discover a strong enhancement of intermittency which exceeds by an order of magnitude the corresponding level in classical hydrodynamic turbulence.

Scanning tunneling microscopy of a graphene layer placed on a micro structured substrate

The features of the surface topography and the local energy spectrum of the graphene layer placed on a two-dimensional array of GaN pyramids are studied using scanning tunneling microscopy and local tunneling spectroscopy. This structure can be used as a test structure for the application of graphene as a flexible conductive transparent electrode in optoelectronics. Sagging of a graphene layer in the space between pyramids is found and the sagging value is estimated to be about 20% of the pyramid height of 1.1 μm. Local energy spectra show the change of the graphene electron energy spectrum due to the mechanical stress at sagging.

Photoionization of neutral atoms by X waves carrying orbital angular momentum

In contrast to plane waves, twisted or vortex beams have a complex spatial structure. Both their intensity and energy flow vary within the wave front. Beyond that, polychromatic vortex beams, such as $X$ waves, have a spatially dependent energy distribution. We propose a method to measure this (local) energy spectrum. The method is based on the measurement of the energy distribution of photoelectrons from alkali-metal atoms. On the basis of our fully relativistic calculations, we argue that even ensembles of atoms can be used to probe the local energy spectrum of short twisted pulses.

GALACTIC COSMIC RAYS IN THE LOCAL INTERSTELLAR MEDIUM: VOYAGER 1 OBSERVATIONS AND MODEL RESULTS.

Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3 MeV nuc-1 and electrons down to 2.7 MeV. The H and He spectra have the same energy dependence between 3 and 346 MeV nuc-1, with a broad maximum in the 10-50 MeV nuc-1 range and a H/He ratio of 12.2 ± 0.9. The peak H intensity is ~15 times that observed at 1 AU, and the observed local interstellar gradient of 3-346 MeV H is -0.009 ± 0.055% AU-1, consistent with models having no local interstellar gradient. The energy spectrum of electrons (e - + e +) with 2.7-74 MeV is consistent with E -1.30±0.05 and exceeds the H intensity at energies below ~50 MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with >3 MeV nuc-1 and electrons with >3 MeV is 0.83-1.02 eV cm-3 and the ionization rate of atomic H is in the range of 1.51-1.64 × 10-17 s-1. This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy cosmic rays or the presence of a suprathermal tail on the energy spectrum at much lower energies. The propagation model fits also provide improved estimates of the elemental abundances in the source of Galactic cosmic rays.

Interpretation of Voyager 1 data on low energy cosmic rays in galactic wind model

The local interstellar energy spectra of galactic cosmic rays down to a few MeV/nucleon were directly measured in the experiment on the board of the Voyager 1 spacecraft. We suggest interpretation of these data based on our models of cosmic ray acceleration in supernova remnants and the diffusion in galactic wind where diffusion coefficient is determined by the cosmic ray streaming instability. The dependence of wind velocity on distance above the Galactic disk is determined.

Dynamics of the wave turbulence spectrum in vibrating plates: A numerical investigation using a conservative finite difference scheme

The dynamics of the local kinetic energy spectrum of an elastic plate vibrating in a wave turbulence (WT) regime is investigated with a finite difference, energy-conserving scheme. The numerical method allows the simulation of pointwise forcing together with realistic boundary conditions, a set-up which is close to experimental conditions. In the absence of damping, the framework of non-stationary wave turbulence is used. Numerical simulations show the presence of a front propagating to high frequencies, leaving a steady spectrum in its wake. Self-similar dynamics of the spectra are found with and without periodic external forcing. For the periodic forcing, the mean injected power is found to be constant, and the frequency at the cascade front evolves linearly with time resulting in a increase of the total energy. For the free turbulence, the energy contained in the cascade remains constant while the frequency front increases as t1/3. These self-similar solutions are found to be in accordance with the kinetic equation derived from the von Kármán plate equations. The effect of the pointwise forcing is observable and introduces a steeper slope at low frequencies, as compared to the unforced case. The presence of a realistic geometric imperfection of the plate is found to have no effect on the global properties of the spectra dynamics. The steeper slope brought by the external forcing is shown to be still observable in a more realistic case where damping is added.

Fast Monte Carlo simulation of DNA damage induction by Auger-electron emission

Purpose: A local damage model (LDM) was developed to estimate the biological efficiency of Auger-electron-emitting radionuclides.Materials and methods: The LDM required information on the local dose distribution, local energy spectrum, and clustered DNA damage yields in the cell nucleus. To apply the model, the nucleus was divided into concentric shells where each shell contributed its own local dose, energy spectrum, and damage yield. The local doses and energy spectra were computed using the PENELOPE (PENetration and Energy LOss of Positrons and Electrons) code. The DNA damage yields were estimated using the MCDS (Monte Carlo damage simulation) code.Results: For a typical 4-μm radius mammalian cell nucleus, the absorbed doses to the cell nucleus per unit cumulated activity, equal to 0.0065, 0.00418, 0.0028, 0.0027 and 0.0015 Gy Bq−1 s−1 for 125I, 119Sb, 123I, 111In and 99mTc, were within 6% difference with the MIRD (Medical Internal Radiation Dose) published data. The simulated total (simple and complex) single-strand break (SSB) and double-strand break (DSB) yields were in the same order, i.e., 125I > 119Sb > 123I > 111In > 99mTc. The agreement between present results and literature data for the DNA damage yields was generally good. More than 75% of the total SSB and DSB yields were contributed from regions within 2.5 μm of the nucleus center.Conclusions: The proposed methodology was computationally efficient and could be applied to other irradiation geometries such as cell clusters.

Reflection of solar wind protons on the Martian bow shock: Investigations by means of 3‐dimensional simulations

The reflection of solar wind protons on the Martian bow shock (BS) is investigated by means of three‐dimensional simulation models. A two steps approach is adopted to allow a detailed analysis of the reflected population. Firstly, the 3‐dimensional hybrid model of Modolo et al. (2005) is used to compute a stationary state of the interaction of the solar wind (SW) with Mars. Secondly, the motion of test particles is followed in the electromagnetic field computed by the hybrid simulation meanwhile detection criteria defined to identify reflected protons are applied. This study demonstrates some effects of the large curvature of a planetary BS on the structure of the foreshock. Reflected protons encounter the BS in a region encompassing parts of the quasi‐perpendicular and quasi‐parallel shocks, and exit the shock mainly from the quasi‐parallel region. The energy spectrum of all reflected protons extends from 0 to almost 15keV. A virtual omnidirectional detector (VOD) is used to compute the local omnidirectional flux of reflected protons at various locations upstream of the BS. Spatial variations of this omnidirectional flux indicate the location and spatial extent of the proton foreshock and demonstrate its shift, increasing with the distance downstream, in the direction opposite to the motional electric field of the SW. Local energy spectra computed from the VOD observations demonstrate the existence of an energy gradient along the direction of the convection electric field.

Measurement of an inverse Compton scattering source local spectrum using k-edge filters

X-ray sources based on the inverse Compton scattering process are attracting a growing interest among scientists, due to their extremely fast pulse, quasi-monochromatic spectrum, and relatively high intensity. The energy spectrum of the x-ray beam produced by inverse Compton scattering sources in a fixed observation direction is a quasi-monochromatic approximately Gaussian distribution. The mean value of this distribution varies with the scattering polar angle between the electron beam direction and the x-ray beam observation direction. Previous works reported experimental measurements of the mean energy as a function of the polar angle. This work introduces a method for the measurement of the whole local energy spectrum (i.e., the spectrum in a fixed observation direction) of the x-ray beam yielded by inverse Compton scattering sources, based on a k-edge filtering technique.