Evolution Of Spectra Research Articles

Near-infrared-terahertz hyper-Raman spectroscopy of an excited silicon surface.

We recorded the hyper-Raman spectra resulting from the interaction of a near-infrared (near-IR) picosecond pulse and a terahertz (THz) ultrashort pulse at the surface of a (111) silicon sample. A simple model is proposed to analyze the evolution of the hyper-Raman spectra vs the time delay between the near-IR and THz pulses. It links the hyper-Raman spectra to the multi-phonon absorption in silicon. This approach makes it possible to demonstrate that, during carrier generation by the near-IR pulse, the two-phonon and three-phonon absorption bands are enhanced in modes involving optical phonons. This process results from the very rapid and strong population of the optical phonons induced by the photo-generated hot carriers. It occurs over a few hundreds of femtoseconds and lasts throughout the duration of the near-IR pulse.

Evolution mapping II: describing statistics of the non-linear cosmic velocity field.

Abstract We extend the evolution mapping approach, introduced in the first paper of this series to describe non-linear matter density fluctuations, to statistics of the cosmic velocity field. This framework classifies cosmological parameters into shape parameters, which determine the shape of the linear matter power spectrum, PL(k, z), and evolution parameters, which control its amplitude at any redshift. Evolution mapping leverages the fact that density fluctuations in cosmologies with identical shape parameters but different evolution parameters exhibit similar non-linear evolutions when expressed as a function of clustering amplitude. We analyse a suite of N-body simulations sharing identical shape parameters but spanning a wide range of evolution parameters. Using a method for estimating the volume-weighted velocity field based on the Voronoi tesselation of simulation particles, we study the non-linear evolution of the velocity divergence power spectrum, Pθθ(k), and its cross-power spectrum with the density field, Pδθ(k). We demonstrate that the evolution mapping relation applies accurately to Pθθ(k) and Pδθ(k). While this breaks down in the strongly non-linear regime, deviations can be modelled in terms of differences in the suppression factor, g(a) = D(a)/a, similar to those for the density field. Such modelling describes the differences in Pθθ(k) between models with the same linear clustering amplitude to better than 1percnt accuracy at all scales and redshifts considered. Evolution mapping simplifies the description of the cosmological dependence of non-linear density and velocity statistics, streamlining the sampling of large cosmological parameter spaces for cosmological analysis.

The magicity, the radii of neutron orbits 1<i>f</i><sub>7/2</sub>, 2<i>p</i><sub>3/2</sub> and halo-like structure of <sup>52,54</sup>Ca nuclei

The evolution of neutron single-particle spectra of isotones with N = 32 and 34 new magic neutron numbers in the region 16 ≤ Z ≤ 32 was calculated in the dispersive optical model. It was shown that the minimum of the difference between the Fermi energy and the half-sum of the energy levels of the last predominantly occupied state and the first predominantly unoccupied state is achieved in the magic isotones with N = 32 and 34. The calculated root-mean-square radius of the neutron halo-like state 2p3/2 in double magic 52Ca nucleus exceeded the radius of the underlying 1f7/2 state by 0.8 fm. It is consistent with the recent experimental data and theoretical predictions that explain ‟unexpectedly” large root-mean-square charge radius of this nucleus.

The evolution of micro-photoluminescence spectra of PECVD diamond microcrystals along the vertical growth direction and their dependence on CH4 concentration

The changes in the shape of micro-photoluminescence spectra of PECVD diamond micro-crystal measured, depending on the position of the excitation laser spot along the crystallite height, were analyzed. It was ascertained that the processes of SiV defect formation non-monotonically depend on the distance from the Si substrate. At the distances of 2–20 μm the concentration of SiV defects increases, then at distances larger than 20 μm the number of SiV defects decreases. The concentration of NV− and NV0 defects monotonically increases with the distance from the Si substrate. The predomination of SiV defect formation at the beginning stages of the crystal growth is explained by the substantial concentration of carbon vacancies required for their formation. With the increase in the distance from the substrate, the crystalline perfection increases, the concentration of carbon vacancies decreases and the processes of NV− and NV0 defect formation dominate. The increase in CH4 fraction within 0.75–6 % leads to the increase in the volume fraction of graphite-like carbon, which is the good diffusion channel for Si atoms from the substrate into the plasma. Therefore, the concentration of SiV, NV−, and NV0 defects on the surface of the crystal depends on the volume fraction of graphite-like carbon defined by CH4 content.

Local Time Distribution and Activity Dependence of Extreme Electron Densities in the Auroral D‐Region as an Image of Energy‐Dependent Energetic Electron Precipitation

AbstractStudying the episodes with the most elevated electron density (Ne) values provides valuable information about spatial distribution and drivers of intense energetic electron (EE) precipitation, which has important space weather implications. By combining EISCAT‐Tromso UHF observations in different modes made in 2001–2021, we survey Ne occurrences and study statistical properties of EE precipitation, producing the highest 10% and 1% of Ne values at the altitudes between 100 and 75 km (corresponding to EE energies of ∼20–∼200 keV). We found that the highest Ne values occur in the nightside‐morning local time sector at the altitudes 90–100 km and in the morning‐noon sector at low altitudes (75–85 km). Although this bimodal pattern could partly be contributed by the suppressed Ne in the dark ionosphere, by analyzing measurements in the twilight conditions at all MLTs together with published patterns of EE precipitation, we argue that a dominance of pre‐noon maximum at low altitudes reflects the enhanced precipitation of >100 keV electrons in this local time sector. At all altitudes (especially below 90 km), the appearance of the highest Ne values favors enhanced auroral activity and shows a strong correlation with fast solar wind (V > 550 km/s) events. These properties mimic the well‐known driving characteristics of energetic electrons. From the correlation of Ne with integral magnetic activity indexes we found that the memory of preceding magnetic activity increases with decreasing altitude, reaching roughly one day at H = 75 km. We discuss the advantages of exploring Ne data at specific altitudes (compared to direct measurements of EE precipitation) to investigate statistically the effects of specific precipitated energy components and the evolution of EE energy spectra.

Analysis of rogue wave in the mid-infrared supercontinuum under femtosecond weak seed pulse conditions based on deep learning

The generation process of rogue wave (RW) is affected by noise, which is an unstable state, and the existence of RW will reduce the stability of mid-infrared supercontinuum. However, the process of studying RW requires a large amount of data simulation and statistics, and traditional methods are time-consuming and inefficient. Therefore, this paper adopts long short-term memory (LSTM) neural network to obtain the spectrum information after transmission for a certain distance according to the waveform information of the incident pulse. The results show that the LSTM neural network structure can train and predict the peak power, time deviation information, time intensity evolution and spectrum evolution of RW after 10 cm propagation with only changing the number of internal units. And it performs well on both large and small data sets.

Information geometry and parameter sensitivity of non-Hermitian Hamiltonians

Information geometry is the application of differential geometry in statistics, where the Fisher-Rao metric serves as the Riemannian metric on the statistical manifold, providing an intrinsic property for parameter sensitivity. In this paper, we explore the application of information geometry in the realm of non-Hermitian quantum systems, focusing on the Fisher-Rao metric as a measure of parameter sensitivity. We approximate the Lindblad master equation for non-Hermitian Hamiltonians to analyze the temporal evolution of the quantum geometric metric. Utilizing the quantum spin Ising model with an imaginary magnetic field as an exemplar, we investigate the energy spectrum and geometric metric evolution within PT-symmetry Hamiltonians. We demonstrate that the detrimental effects of dissipation can be counteracted by introducing a control Hamiltonian, leading to improved accuracy in parameter estimation. Our work provides insights into the role of quantum control in mitigating dissipative impacts and enhancing the precision of quantum metrological tasks.

Decay of magnetohydrodynamic turbulence in the expanding solar wind: WIND observations

We have studied the decay of turbulence in the solar wind. Fluctuations carried by the expanding wind are naturally damped because of flux conservation, slowing down the development of a turbulent cascade. The latter also damps fluctuations but results in plasma heating. We analyzed time series of the velocity and magnetic field ($ v $ and $ B $, respectively) obtained by the WIND spacecraft at 1 au. Fluctuations were recast in terms of the Elsasser variables, $ z v B rho $, with rho being the average density, and their second- and third-order structure functions were used to evaluate the Politano-Pouquet relation, modified to account for the effect of expansion. We find that expansion plays a major role in the Alfv\'enic stream, those for which $z_+ z_-$. In such a stream, expansion damping and turbulence damping act, respectively, on large and small scales for $z_+$, and also balance each other. Instead, $z_-$ is only subject to a weak turbulent damping because expansion is a negligible loss at large scales and a weak source at inertial range scales. These properties are in qualitative agreement with the observed evolution of energy spectra that is described by a double power law separated by a break that sweeps toward lower frequencies for increasing heliocentric distances. However, the data at 1 au indicate that injection by sweeping is not enough to sustain the turbulent cascade. We derived approximate decay laws of energy with distance that suggest possible solutions for the inconsistency: in our analysis, we either overestimated the cascade of $z_ or missed an additional injection mechanism; for example, velocity shear among streams.

Temporal variability in transmission spectra of H2-dominated exoplanets: The influence of thermal evolution and stellar irradiation on atmospheric composition

Planets and their host stars undergo evolutionary changes over time, resulting in variations in internal temperature and incoming radiation, which significantly impact the temperature structure and composition of their atmospheres. These evolving conditions give rise to distinctive features in planetary spectra that are observable only during specific stages of planetary evolution. We aim to understand how the composition of planets with H2-dominated atmospheres changes over longer timescales due to their thermal evolution. We also investigate time-dependent features in the transmission spectra. These features could provide insights in both the formation and evolution of these gaseous planets, as well as the timescales of these changes, enabling us to study the potential variability of exoplanets over time. We evolve a ∼0.04 MJup and ∼0.45 MJup planet around a 1.0 M⊙ and 1.3 M⊙ star respectively for 109.5 years. In both systems, the planets are considered at semi-major axes of 0.1 AU and 1.0 AU. The star-planet systems are evolved by making use of Modules for Experiments in Stellar Astrophysics (MESA). The temperature–pressure profiles are obtained at selected time-steps using an analytical approximation based on the internal and irradiation temperature of the planet at each time step. We then use VULCAN, a photochemical kinetics code, to see how the composition changes with time in the atmosphere due to the thermal evolution of the planets. By making use of the radiative transfer code petitRADTrans, we also simulate the evolution of the transmission spectra of the planets to find potential time-dependent spectral features. Our findings show a prominent change in the CO2 feature at ∼4.3μm. For the 0.45 MJup case, this feature is visible in the pre-main-sequence phase of the host star, regardless of orbital distance from the host star. In the case of the ∼0.04 MJup planet, this CO2 feature is visible until t ≤ 106 years, and then it reappears after t ≥ 108 years when the planet is 0.1 AU away the host star. The CH4 features at ∼3.3μm and ∼7.5μm are only time-dependent when the planet is located at 0.1 AU from the host star and experiences high irradiation since the high temperature at early stages favoured CO2 over CH4. When the planet is 1.0 AU away from its host star, the CH4 features are always visible regardless of the mass and hence internal temperature of the planet.

Observation of tungsten emission spectra up to W46+ ions in the Large Helical Device and contribution to the study of high-Z impurity transport in fusion plasmas

Spectroscopic studies of emissions released from tungsten ions combined with a pellet injection technique have been conducted in Large Helical Device for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. The spectral intensities of W5+, W24+–W28+, W37+, W38+, W41+–W43+, W45+, and W46+ emission lines were measured simultaneously over a wide wavelength range from x-ray to visible. Time evolutions of the various tungsten line spectra indicate that the tungsten confinement time depends on the electron density of the plasma and is long in high density plasmas, on the order of seconds, and short in low density plasmas, on the order of sub-seconds. When the confinement time was long, the tungsten ions remained in the plasma until the end of the discharge, changing their dominant charge with the change in electron temperature. When the confinement time was short, the tungsten ions rapidly decreased in all charge states and disappeared. Space-resolved EUV and visible spectroscopy measurements have revealed that tungsten ions stayed in the core region of the plasma with changing their dominant charge state depending on the electron temperature in the discharges with the long confinement time. Detailed analysis of soft x-ray emission suggested that the confinement time increases with density and becomes saturated when the central electron density exceeds 2 × 1013 cm−3.

Alocasia Indica Assisted Green Synthesis of Metallic Cu Nanoparticles for Enhanced Antimicrobial Activities

In the past several years, the widespread utility of copper nanoparticles (CuNPs) has spurred global interest in streamlining synthesis methodologies. Notably, this study introduces an environmentally conscious strategy for synthesizing CuNPs using the extract of Alocasia indica. Employing a chemical reduction process, A. indica, abundant in phenolics and flavonoids, acts as a potent reducing agent. The nanoparticles (NPs) synthesized by A. indica have been carefully characterized by Ultraviolet–Visible (UV–Viz) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) analysis and antimicrobial analysis. UV testing, spanning wave length, elucidates light absorption attributed to the newly formed CuNPs by showcasing a surface plasmonic resonance peak at 204 nm. The evolution of the FTIR spectrum of the produced CuNPs confirms the presence of diverse biomolecules. TEM delineates the synthesis of irregularly shaped particles. Elemental composition analysis via EDX identifies the presence of various elements, including C, O, Al, Cl, K and Cu, with detailed insights into their mass percentages, standard deviations, atom percentages and characteristic X-ray energy levels. The successful synthesis of CuNPs is validated by XRD, which reveals characteristic copper peaks at 2[Formula: see text] = [Formula: see text], [Formula: see text] and [Formula: see text]. The synthesized NP showed 98.99% inhibition against Staphylococcus aureus and 99.99% inhibition against Escherichia coli. This research presents an easy, economical and ecologically friendly process for producing CuNPs utilizing A. indica extracts.

Investigation of micromechanics and relaxation spectrum evolution in multiple recycled asphalt binders

Investigation of micromechanics and relaxation spectrum evolution in multiple recycled asphalt binders

Evolution of QPOs in GX 339–4 and EXO 1846–031 with Insight-HXMT and NICER

We conduct a spectral and timing analysis of GX 339−4 and EXO 1846−031 with the aim of studying the evolution of type-C quasiperiodic oscillations (QPOs) with spectral parameters. The high-cadence data from Insight-HXMT and NICER allow us to track the evolution of QPOs and spectra simultaneously. Type-C QPOs appear at the end of the low–hard state and/or the hard–intermediate state. Our results reveal that the QPO frequency is closely related to the inner disk radius and mass accretion rate in the two sources. This correlation aligns well with the dynamic frequency model of a truncated disk.

Flux Density Stability and Temporal Changes in the Spectra of Millisecond Pulsars Using the GMRT

This paper presents an investigation of the spectral properties of 10 millisecond pulsars (MSPs) discovered by the uGMRT, observed from 2017 to 2023 using band 3 (300–500 MHz) and 4 (550–750 MHz) of the uGMRT. For these MSPs, we have reported a range of spectral indices from ∼0 to −4.8, while averaging the full observing band and all the observing epochs. For every MSP, we calculated the mean flux density across 7–8 subbands, each with approximately 25 MHz bandwidth spanning band 3 and band 4. We computed their modulation indices as well as average and maximum-to-median flux density within each subband. Using the temporal variations of the flux density we calculated the refractive scintillation timescales and estimated a structure function with a time lag for eight MSPs in the sample. We note a significant temporal evolution of the in-band spectra, classified into three categories based on the nature of the best-fit power-law spectra, having single positive spectral indices, multiple broken power laws, and single negative spectral indices. Additionally, indications of a low-frequency turnover and temporal variations of the turnover frequency (to the extent that turnover was observed for some of the epochs while not seen for the rest) were noted for all the MSPs. To the best of our knowledge, this is the first systematic investigation probing temporal changes in MSP spectra as well as in the turnover frequency. Future exploration with dense monitoring combined with the modeling of spectra can provide vital insight into the intrinsic emission properties of MSPs and interstellar medium properties.

Investigation of the structural and microstructural properties of copper and tantalum substituted BiMeVOx compounds with enhanced oxygen ion conductivity: Bi4V2-xCux/2Tax/2O11-3x/4 (0.1≤ x ≤ 0.5)

In this study, the objective was to improve the performance of bismuth vanadium oxide Bi4V2O11 by synthesizing double substituted compounds using copper ions Cu2+ and tantalum ions Ta5+. Bi4V2-xCux/2Tax/2O11-3x/4 (0.1 ≤ x ≤ 0.5) polycrystalline samples of were prepared via the solid-state route. XRD patterns measured at room temperature revealed the stabilization of the monoclinic α-Bi4V2O11 type structure for x = 0.1 and the tetragonal γ or γ' -Bi4V2O11 for x > 0.2. This result has been confirmed by thermogravimetric analysis (DTA), FT-IR spectroscopy and Raman scattering measurements. The influence of the composition on the microstructure and grain size of the prepared samples was explored through dilatometric study, density measurements, and scanning electron microscopy (SEM). Thermal Raman spectra evolution was also investigated. The temperature-dependent Raman spectroscopy analysis of the compound α-BiCuTaVOx (x = 0.1) demonstrated variations in the position, intensity, and width of the Raman mode around 850 cm−1, indicating temperature-assisted structural modifications. One defining feature of the tetragonal-dominated phase of the BiMeVOx systems is the increasing merging of the weak band at 930 cm−1 with the dominating band at 850 cm−1. This behavior was also observed for our samples. The V–O bond lengths were calculated using an empirical relation based on the diatomic approximation. Electrochemical impedance spectroscopy (EIS) was used to investigate the changes in electrical conductivity with the substitution rate across the temperature range of 300–720 °C. The sample with x = 0.3 exhibited the highest electrical conductivity at both high and low temperatures. However, the optimal substitution rate to achieve the best conductivity in this series of copper and tantalum-substituted BiCuTaVOx was found to be x = 0.3 (σ = 4 × 10−3 S cm−1 at 600 °C).

Evolution of the Secondary Electron Spectrum during Cosmic-Ray Discharge in the Universe

We recently found that streaming cosmic rays (CRs) induce a resistive electric field that can accelerate secondary electrons produced by CR ionization. In this work, we study the evolution of the energy spectrum of secondary electrons by numerically solving the one-dimensional Boltzmann equation and Ohm’s law. We show that the accelerated secondary electrons further ionize a gas, that is, an electron avalanche occurs, resulting in increased ionization and excitation of the gas. Although the resistive electric field becomes weaker than the one before the CR discharge, the weak resistive electric field weakly accelerates the secondary electrons. The quasi-steady state is almost independent of the initial resistive electric field but depends on the electron fraction in the gas. The resistive electric field in the quasi-steady state is larger for the higher electron fraction, which makes the number of secondary electrons that can ionize the gas larger, resulting in a higher ionization rate. The CR discharge could explain the high ionization rate that is observed in some molecular clouds.

Temporal evolution of absorption spectra for diisopropyl methylphosphonate at high temperatures in a shock tube

Absorption spectra and cross-sections of Diisopropyl Methylphosphonate (DIMP) are measured in argon at temperatures of 600–1250 K in a shock tube using rapid scanning, broadband absorption spectroscopy. Measurements are obtained at approximately 2.3 kHz with each complete scan of the 925–1350 wavenumber band taking 90 microseconds. This technique enables spectra behind incident and reflected shocks to be obtained in a single test. In addition, multiple spectra are obtained behind the reflected shock during the test time. A significant reduction in absorption cross section with temperature is observed, and the spectra taken during the test time show no decomposition or significant changes, suggesting that vibrational equilibrium is achieved.

Multiwavelength Modeling for the Shallow Decay Phase of Gamma-Ray Burst Afterglows

We simulate the emission in the shallow decay phase of gamma-ray burst afterglows using a time-dependent code. We test four models: the energy injection model, evolving the injection efficiency of nonthermal electrons, evolving the amplification of the magnetic field, and the wind model with a relatively low bulk Lorentz factor. All of the four models can reproduce the typical X-ray afterglow lightcurve. The spectral shape depends on not only the parameter values at the time corresponding to the observer time but also the past evolution of the parameters. The model differences appear in the evolution of the broadband spectrum, especially in the inverse Compton component. Future gamma-ray observations with imaging atmospheric Cherenkov telescopes such as the Cherenkov Telescope Array will reveal the mechanism of the shallow decay phase.

Studying the evolution of the power spectra of acoustic radiation during the destruction of a solid body

Studying the evolution of the power spectra of acoustic radiation during the destruction of a solid body

Observation of the Infrared-Induced Structural Change in the Microscopic Hydrogen Bond Network of Phenol-Methanol Cluster Cations in a Cold-Ion Trap.

To gain insight into microscopic hydrogen bond networks, we measured ultraviolet photodissociation (UVPD) spectra of the phenol-methanol 1:3 cluster cation, [PhOH(MeOH)3]+ trapped in a variable temperature ion trap. At low temperatures, an isomer with a ring-type hydrogen bond structure dominates, whereas at higher temperatures the chain-type isomers become dominant due to the flexibility of their hydrogen bond structures. We also found a clear temperature dependence of the spectral features, such as band position and width. In addition to the above measurement, we observed the infrared (IR) induced isomerization of [PhOH(MeOH)3]+ to study the dynamical aspects of hydrogen bond networks. We succeeded in observing IR-induced isomerization from the ring to chain forms of [PhOH(MeOH)3]+ at low temperature. The isomerization was clearly identified as a change in the UVPD spectra. The time evolution of the UVPD spectra after IR excitation indicated that the IR-induced isomerization occurs within a nanosecond. The chain-type isomers produced by the IR-induced isomerization are then converted back to the ring-type form by collisions with cold He buffer gas in the trap. This backward isomerization proceeds with a time constant of 100 μs under our experimental conditions. In this study, we evaluated the temperatures of the chain isomers during the backward isomerization on the basis of the spectral features.