Inhomogeneous Electron Density Research Articles

Investigating the Drivers of Electron Temperature Variations in H ii Regions with Keck-KCWI and VLT-MUSE

H ii region electron temperatures are a critical ingredient in metallicity determinations, and recent observations have revealed systematic variations in the temperatures measured using different ions. We present electron temperatures (T e ) measured using the optical auroral lines ([N ii]λ5756, [O ii]λ λ7320, 7330, [S ii]λ λ4069, 4076, [O iii]λ4363, and [S iii]λ6312) for a sample of H ii regions in seven nearby galaxies. We use observations from the Physics at High Angular resolution in Nearby Galaxies survey (PHANGS) obtained with integral field spectrographs on Keck (Keck Cosmic Web Imager) and the Very Large Telescope (Multi-Unit Spectroscopic Explorer). We compare the different T e measurements with H ii region and ISM environmental properties such as electron density, ionization parameter, molecular gas velocity dispersion, and stellar association/cluster mass and age obtained from PHANGS. We find that the temperatures from [O ii] and [S ii] are likely overestimated due to the presence of electron density inhomogeneities in H ii regions. We measure high [O iii] temperatures in a subset of regions with high molecular gas velocity dispersion and low ionization parameter, which may be explained by the presence of low-velocity shocks. In agreement with previous studies, the T e–T e between [N ii] and [S iii] temperatures have the lowest observed scatter and follow predictions from photoionization modeling, which suggests that these tracers reflect H ii region temperatures across the various ionization zones better than [O ii], [S ii], and [O iii].

Energy losses of highly charged Arq+ ions during grazing incidence on tungsten surfaces

In this study, we investigate the energy loss of highly charged ions interacting with various tungsten surfaces. The analysis primarily focuses on elucidating the impact of electron density distributions on energy loss of ions. Furthermore, we explore the correlation between surface azimuthal angles and energy loss under both uniform and inhomogeneous electron density distributions. Utilizing the classical over-the-barrier model (COBM), simulations involving trajectory calculations, energy loss, charge-exchange processes, and surface electron distributions, etc., were performed. Remarkably, the significant influence of axial channeling of surfaces on ion energy loss is observed. For the comparison of ion energy loss under uniform and inhomogeneous electron density distributions, the results reveal a more pronounced effect of electron density inhomogeneity on ion energy loss at higher energy-loss values. Additionally, the calculated energy-loss spectra of Ar16+ ions grazing on graphite surfaces show reasonable agreement with experimental data. These findings are crucial for understanding the surface structure of crystals.

Disentangling patchy reionization signatures from primordial gravitational waves using CMB E-mode and B-mode polarization

ABSTRACT The detection of large angular scale B mode in the cosmic microwave background (CMB) polarization signal will open a direct window into not only the primary CMB anisotropies caused by the primordial gravitational waves (PGW) originating in the epoch of inflation, but also the secondary anisotropies imprinted during the epoch of cosmic reionization. The existence of patchiness in the electron density during reionization produces a unique distortion in the CMB B-mode polarization, which can be distinguished from the PGW signal with the aid of spatial frequency modes. In this work, we employ an EB estimator by combining E-mode and B-mode polarization for the τ power spectrum signal generated in a photon-conserving seminumerical reionization model called SCRIPT. We developed a Bayesian framework for the joint detection of the PGW and reionization signal from CMB observations and show the efficacy of this technique for upcoming CMB experiments. We find that, for our model, the τ power spectrum signal effectively tracks the inhomogeneous electron density field, allowing for robust constraints on the patchy B-mode signal. Further, our results indicate that employing the EB estimator for the τ signal will facilitate ground-based CMB-S4 to detect the patchy B-mode signal at approximately ≥2σ confidence level, while observations with space-based PICO will improve this detection to ≥3σ going as high as ≥7σ for extreme reionization models. These findings not only highlight the future potential of these experiments to provide an improved picture of the reionization process but also have important implications towards an unbiased measurement of r.

Statistical Characteristics of the Temporal Spectrum of Scattered Radiation in the Equatorial Ionosphere

On the basis of the solution of the space-time characteristic system by the method of geometric optics using symbolic calculations, analytical and numerical simulation of the propagation of the ordinary and extraordinary radio waves in the conducting equatorial ionospheric plasma was made considering the anisotropy of plasma irregularities and non-stationary nature of propagation medium. Broadening of the spectrum and the displacement of its maximum contain velocity of a turbulent plasma flow and parameters characterizing anisotropic plasmonic structures. Statistical moments of both radio waves do not depend on the absorption sign and are valid for both active and absorptive random media. Temporal pulsations and conductivity of a turbulent ionospheric plasma have an influence on the evaluation of the spectrum-varying propagation distances travelling by these waves. The new double-humped effect in the temporal spectrum has been revealed for the ordinary wave varying anisotropy coefficient and dip angle of stretched plasmonic structures. From a theoretical point of view, the algorithms developed in this work allow effective modelling of the propagation of both radio signals in the equatorial conductive ionospheric plasma, considering the external magnetic field, inhomogeneities of electron density in-homogeneities, as well as non-stationary.

Using microwave refraction to determine local inhomogeneities of a rotating plasma

Abstract To determine the local inhomogeneities of a rotating plasma, the method based on microwave refraction was used. The method is based on spectral and correlation analysis of the reflected signals from the rotating plasma layer at normal and inclined microwave incidence. This method allowed us to determine local inhomogeneities of plasma electron density, angles of azimuthal displacement of grooves, and its angular frequency of rotation. Using an additional 4th horn antenna, in contrast to previous works, it was possible to find and analyze two regions with azimuthal inhomogeneities in the rotating plasma. Analysis of the reflected signals shows the presence of four grooves, and the angular frequency of rotation ω = 1.16 × 104 rad/s was also determined.

Исследование отражения плоской электромагнитной волны от неоднородного плазменного слоя, расположенного на идеально проводящей плоскости

A method for numerical modelling of the reflection of an electromagnetic wave from a planar plasma layer with an inhomogeneous electron density of particles covered of an ideally conducting plane is proposed in the work. The frequency responses of wave reflection coefficients modules are calculated for various incidence angles and electron density profiles of carriers using the differential sweep method. The paper shows that in the region of plasma resonance the plasma layer with a parabolic profile of charge carrier concentration has the lowest reflection level. The effect of the effective frequency of electron collisions in an inhomogeneous plasma layer on the reflection level was studied in this work.

Anomalous electronic energy losses in protons passing through Gd thin films

We report a theoretical analysis of recent data on the unexpectedly high electronic energy loss protons in a polycrystalline gadolinium target. These results led the authors of this data to conclude that the free electron model used to analyse these results fails. In this work we provide a quantitative explanation of the experimental results, using an approach based on density functional theory within the framework of the free electron gas model. We performed semi-classical trajectory simulations (SCTS) and employ the local-density-approximation model (LDA), using an inhomogeneous electron density distribution and the polycrystalline character of Gd samples. The good agreement obtained, delineates the need of considering a realistic description of a particle trajectory and the effective electron density ‘seen’ along it, whose description remains within a FEG model.

Mechanism of near-forward scattering driven photon acceleration in the interaction between an intense laser and under-dense plasmas

The mechanism of photon acceleration driven by the near-forward scattering (NFS) in the interaction between an intense laser and under-dense plasmas is studied by particle-in-cell (PIC) simulation. This mechanism utilizes tunneling ionization effect to stimulate electron plasma waves when the intense laser pulse propagates in under-dense plasmas. The electron plasma density is inhomogeneous both in longitudinal and transverse direction. In the longitudinal direction, a steep ionized electron density front is generated by incident laser ionizing the helium gas. Around the ionization front, the incident laser interacts with electron plasma waves, thus generating the first kind of NFS waves. Compared with the frequency of laser, the frequency of NFS wave increases. This is the first characteristic peak in the frequency spectrum. In the transverse direction, the electron plasma waves have different phase velocities, which makes the incident laser pulse undergo NFS process and upshift its frequency. This is the second characteristic peak in the frequency spectrum. Owing to the fact that the electron density inhomogeneity is much larger than the electron density perturbation of electron plasma wave, the scattering model and dispersion relationships, which are based on perturbation theory like stimulated Raman scattering, are no longer applicable to this case. Our further study shows that the incident laser, electron density plasma waves and NFS waves still satisfy the energy conservation and momentum conservation that is, they still satisfy the three-wave coupling relationship of momentum and energy conservation under the condition of heterogeneous density, thus explaining the appearance of two characteristic peaks in the frequency spectrum and their growth in the wave-vector space. This study has significant reference to the spectrum evolution when the intense laser pulse propagates in under-dense plasma.

About the Propagation of RSDN‐20 “Alpha” Signals in the Earth‐Ionosphere Waveguide During Geomagnetic Disturbances

AbstractThe paper presents the results of the modeling of VLF radio waves propagation in horizontally inhomogeneous region of the high‐latitude Earth‐ionosphere waveguide during different types of the geomagnetic disturbances. The frequencies of the model source of signal correspond to the frequencies of the long‐distance navigation radio system RSDN‐20 “Alpha” constantly broadcasting in the VLF range in the Russian Federation. It is considered the geomagnetic storm on 24 January 2012 and geomagnetic substorm on 11 December 2015. Electron density profiles and collision rates of electrons with neutrals are taken from the measurements of EISCAT radar in Tromso and EISCAT 42m radar on Svalbard. The numerical experiments were conducted with a highly horizontally inhomogeneous electron density in the ionosphere. It is shown that the amplitudes and phases of the VLF signals at these frequencies show a noticeable reaction to changes in the ionospheric parameters during the considered geomagnetic disturbances. Calculations show that changes in amplitude of RSDN‐20 “Alpha” signals caused by the action of the Earth's magnetic field and horizontal inhomogeneities depend on the direction of signal propagation relative to the Earth's magnetic field vector and cannot be reversed if the direction of propagation changes to the opposite. The results of the numerical experiment were compared with the corresponding characteristics of the RSDN‐20 signals calculated from the observations of electromagnetic signals at the Lovozero observatory for the case on 11 December 2015.

Effects of an inhomogeneous electron density distribution on the hydrogen distribution in TiZrTaNbAl multi-principal element alloys

A body-centered cubic equiatomic TiZrTaNbAl multi-principal element alloy (MPEA) with elemental fluctuations was investigated to further understand the relationship between the microstructure and hydrogen distribution. In this study, a composition dependence of the hydrogen distribution was observed in the TiZrTaNbAl MPEA. An inhomogeneous electron density distribution of the MPEA was revealed by advanced differential phase-contrast scanning electron microscopy (DPC-STEM) for the first time. The results showed that the electron density has a significant effect on the hydrogen distribution in TiZrTaNbAl MPEAs. This work provides new insight into the design of materials with high hydrogen storage capacity and high hydrogen embrittlement resistance.

Characteristics of Vacuolar Inclusions in Coelastrella rubescens Namsu R1 Green Microalgae Cells in Low- and High-Intensity Light

Coelastrella rubescens Kaufnerová & Eliás (Chlorophyceae) is a green, single-celled algae that lives in the terrestrial-air environment. Under stress conditions, its cells go into a state characterized by low photosynthetic activity and high content of reserve lipids and secondary carotenoids. For the first time, a comparative morphological, ultrastructural, and elemental analysis of vacuolar inclusions in the C. rubescens NAMSU R1 strain when cultivated on a mineral medium under conditions of low and high (causing stress) light intensity. Microalgae cells stained with the fluorescent dye DAPI showed signs of the presence of polyphosphates. Polarization microscopy in cells of C. rubescens has identified structures capable of refracting polarized light, which is typical of crystals. Cell analysis of C. rubescens with the transmission electron microscopy (TEM) method revealed the presence of various vacuoles with heterogeneous contents (autophagic bodies, crystalloids, and rounded globules of inhomogeneous electron density). With the exception of autophagic bodies noted in cells only in bright light, these inclusions were characteristic of microalgae cells, regardless of the intensity of illumination. The elemental composition of vacuolar inclusions was characterized by TEM in combination with energy-dispersive X-ray spectroscopy: the predominant content of nitrogen, phosphorus, or both elements simultaneously was established in them. The potential physiological role of C. rubescens vacuolar inclusions is discussed.

Excitation and enhancement of wakefield by beating of two laser beams in a preformed plasma channel: An analytical study

We investigate analytically the nonlinear interaction of two beating laser beams with plasma by considering electron density inhomogeneity in the axial and radial directions. We apply the fluid model coupled with Maxwell equations to obtain a nonlinear equation for studying the plasma wave. We solve this nonlinear equation using the hypergeometric and Airy functions and present the damping and outgoing wave solutions. Our results show that the longitudinal and transverse wakefields generated in the preformed density-ramped plasma channel are much stronger than the inhomogeneous plasma with density-ramped profile.

Theoretically Modeling Photoionized Regions with Fractal Geometry in Three Dimensions

We create a photoionization model embedded in the turbulent interstellar medium (ISM) by using the state-of-the-art Messenger Monte Carlo MAPPINGS V code (M3) in conjunction with the CMFGEN stellar atmosphere model. We show that the turbulent ISM causes the inhomogeneity of electron temperature and density within the nebula. The fluctuation in the turbulent ISM creates complex ionization structures seen in nearby nebulae. The inhomogeneous density distribution within the nebula creates a significant scatter on the spatially resolved standard optical diagnostic diagrams, which cannot be represented by the spherical constant-density photoionization model. We analyze the dependence of different optical emission lines on the complexity of nebular geometry, finding that the emission lines residing on the nebular boundary are highly sensitive to the complexity of nebular geometry, while the emission lines produced throughout the nebula are sensitive to the density distribution of the ISM within the nebula. Our fractal photoionization model demonstrates that a complex nebular geometry is required for the accurate modeling of H ii regions and emission-line galaxies, especially for the high-redshift galaxies, where the ISM is highly turbulent based on increasing observational evidence.

The free electron model and the electronic energy losses of protons at low velocities interacting with polycrystalline tantalum

In this letter, we report experimental data and theoretical work on the electronic energy loss and energy loss straggling of protons transmitted through self-supported thin films of tantalum in a polycrystalline tetragonal phase . Low-energy protons with energies below 10 keV and Ta films with nominal thickness of 6, 9 and 12 nm are used. The aim of this work is to understand the unexpected values of the Ta stopping power for low-energy proton backscattering reported recently, which are far from the prediction of the standard free electron gas model and semi-empirical approaches. This had led the authors to conclude the failure of the free electron model. Our transmission measurements confirm these experimental results. In this work, a qualitative discussion and quantitative explanation of our experimental results is given, using an approach based on the density functional theory within the framework of the free electron gas (FEG) model. We performed semiclassical deterministic trajectory simulations and employ the local density approximation model, using an inhomogeneous electron density distribution and the polycrystalline character of Ta samples.

Inhomogeneous plasma electron density inversion based on Bayesian regularization neural network

Electron density is one of the most important parameters for characterizing plasma properties, so obtaining accurate electron density is a prerequisite for studying the interaction between plasma and the electromagnetic waves. This paper presents the effects of different electron densities on the electric field distribution of a microstrip antenna with a center frequency of 2.45 GHz. Then, on the basis of the integrated model of plasma and the microstrip antenna, the Bayesian regularization neural network (BRNN) is used to retrieve the electron density of inhomogeneous plasma. Furthermore, the performance of the proposed approach is evaluated and analyzed by comparison with Levenberg–Marquardt (LM) and Scaled Conjugate Gradient (SCG) neural networks. The results show that the BRNN provides better performance than LM and SCG neural networks to retrieve plasma electron density based on the electric field intensity at fewer spatial positions. The accurate distribution of the electron density of inhomogeneous plasma can be obtained using BRNN. In addition, the greater the range variation of electron density, the greater the relative inversion error. This study provides an important theoretical basis for the diagnosis of electron density for inhomogeneous plasma in experiments.

Construction of eight mixed-valence pentanuclear CuI4CuII clusters using ligands with inhomogeneous electron density distribution: synthesis, characterization and photothermal properties.

To enhance light absorption in the visible region for the utilization of sunlight, eight mixed-valence polynuclear CuI/CuII clusters have been synthesized for evaluating their photothermal conversion performance. They are fabricated considering the ligand's electron density distribution inhomogeneity using 1,2,3-triazole (3N) or tetrazole (4N) and different mono-phosphine ligands. We report here the synthesis, crystal structure, characterization, optical properties, and photothermal conversion performance of these clusters. X-ray crystal structures reveal that those pentanuclear clusters are neutral clusters with octahedrally-coordinated copper(II) ion being surrounded by four tetrahedrally coordinated copper(I) ions. Interestingly, with the introduction of the mixed-valence centers, these compounds show additional light absorption centers in 350-600 nm via the IVCT transition mechanism, compared with our previously reported Cu(II) compounds. These clusters show excellent photothermal conversion performance, with an average equilibrium temperature (∼60 °C) and a temperature increment (∼40 °C), which are also superior to Cu(II) complexes (the average equilibrium temperature ∼55 °C). This work proves that it is possible to design and prepare new polynuclear mixed-valence CuI/CuII clusters for achieving high-performance photothermal conversion materials.

Statistical Measurements of Dispersion Measure Fluctuations in Fast Radio Bursts

Abstract Extragalactic fast radio bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu & Zhang, but no clear correlation hinting toward large-scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM < 500 pc cm−3. A trend of nonconstant SF and nonzero correlation function (CF) at angular separations θ less than 10° is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at θ ≲ 10° can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of 100 Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.

Small-angle X-ray and neutron scattering

Small-angle scattering (SAS) is a technique that is able to probe the structural organization of matter and quantify its response to changes in external conditions. X-ray and neutron scattering profiles measured from bulk materials or materials deposited at surfaces arise from nanostructural inhomogeneities of electron or nuclear density. The analysis of SAS data from coherent scattering events provides information about the length scale distributions of material components. Samples for SAS studies may be prepared in situ or under near-native conditions and the measurements performed at various temperatures, pressures, flows, shears or stresses, and in a time-resolved fashion. In this Primer, we provide an overview of SAS, summarizing the types of instrument used, approaches for data collection and calibration, available data analysis methods, structural information that can be obtained using the method, and data depositories, standards and formats. Recent applications of SAS in structural biology and the soft-matter and hard-matter sciences are also discussed.

Correlating inhomogeneity in anionic electron density with hydrogen incorporation in Y5Si3 electrides

Correlating inhomogeneity in anionic electron density with hydrogen incorporation in Y₅Si₃ electrides

Analysis of Echo Characteristics of Spatially Inhomogeneous and Time-Varying Plasma Sheath

The “black barrier” phenomenon caused by plasma sheath during the reentry of a high-speed target will seriously affect the detection of radar echo by a ground monitoring station, which is not conducive to making corresponding adjustments to different situations in real-time. The echo reflects the information of the target’s position and speed, which is significant for real-time monitoring and effective strike. In this work, the effect of a high-speed target plasma sheath on electromagnetic wave echo characteristics was investigated by using the proposed spatially inhomogeneous and time-varying plasma sheath model. The Z-transform finite-difference time domain (Z-FDTD) method was adopted to calculate the time domain and frequency domain results of the echo in plasma sheaths with spatially inhomogeneous, uniform and spatially inhomogeneous and time-varying electron density distributions. The effects of different time-varying parameters and plasma parameters on the echo characteristics of the plasma sheath were analyzed. The results show that the reflected echo in spatially inhomogeneous and time-varying plasma is less than that of the other two. The magnitude of the reflected echo is proportional to the time-varying parameter peak coefficient and Gaussian width, and inversely proportional to the collision frequency and plasma thickness. The theoretical results provide important guidance for ground monitoring and anti-stealth.