Determination Of Electron Density Research Articles

On the determination of ionospheric electron density profiles using multi-frequency riometry

Abstract. Radio wave absorption in the ionosphere is a function of electron density, collision frequency, radio wave polarisation, magnetic field and radio wave frequency. Several studies have used multi-frequency measurements of cosmic radio noise absorption to determine electron density profiles. Using the framework of statistical inverse problems, we investigated if an electron density altitude profile can be determined by using multi-frequency, dual-polarisation measurements. It was found that the altitude profile cannot be uniquely determined from a “complete” measurement of radio wave absorption for all frequencies and two polarisation modes. This implies that accurate electron density profile measurements cannot be ascertained using multi-frequency riometer data alone and that the reconstruction requires a strong additional a priori assumption of the electron density profile, such as a parameterised model for the ionisation source. Nevertheless, the spectral index of the absorption could be used to determine if there is a significant component of hard precipitation that ionises the lower part of the D region, but it is not possible to infer the altitude distribution uniquely with this technique alone.

Effective Atomic Number and Electron Density Determination for Fricke Gel Dosimeters Using Different Methods.

The effective atomic number and electron density of some Fricke gel dosimeters were calculated for photon interaction in the energy range from 10 keV to 1000 MeV using Auto-Zeff, direct and power law methods. The results are presented relative to those of water to allow direct comparison. It is found, that the effective atomic numbers and effective electron densities calculated with the Auto-Zeff and direct methods, demonstrates a good agreement in the energy interval extending from 0.1 MeV to 10 MeV. For effective atomic number relative to water, Ferrous Agarose Xylenol gel showed better water equivalence with difference up to 0.3%, while FX-PVA-GTA and Ferrous Xylenol Gelatin gels showed differences up to 2.26% and 2.25%, respectively.

Stark broadening parameters of Ar II and Ar III lines: Comparison of semiclassical calculations

For many applications, the semiclassical, theoretical calculations of Stark broadening parameters of isolated non-hydrogenic ion lines proved useful and reasonably accurate for plasma electron density determination. Several attempts were carried out to improve the calculation procedure of Stark broadening parameters and, in this way, to increase the accuracy of laboratory and astrophysical plasmas and opacity calculations. In this work for the test ions, we selected singly and doubly ionized argon lines. These ions are chosen for several reasons. First, among several studies, there are detailed Ar II calculations by Griem and coworkers, Hamdi et al., and by Blagojević and Konjević for singly and Hamdi et al.for doubly ionized argon lines. These large sets of data facilitate the extension of our work on improving semiclassical calculations. Second, argon gas applications as a plasma matrix are numerous, and reliable plasma diagnostics are of utmost importance for determining electron density, one of the essential plasma parameters for plasma modeling.

ESTIMATION OF THE ROLE OF RADIATION IN THE PLASMA OF ELECTRIC ARC DISCHARGE BETWEEN Cu-C COMPOSITES

This work is devoted to investigation of the radiation in the plasma of electric arc discharge between Cu-C composite electrodes and estimation of its contribution during the determination of electron density from the energy balance equation (Elenbaas-Heller). The contribution of radiation energy in heat transfer is estimated as well. The calculation is carried out based on the preliminary experimentally obtained radial distribution of plasma temperature. For the correct solution of the energy balance equation, a Gaussian approximation of the plasma temperature profile is used. Estimation of the total current was used as a criterion for the need to take into account the radiation in the diagnostics of electric arc plasma.

Inferring Jovian Electron Densities Using Plasma Wave Spectra Obtained by the Juno/Waves Instrument

AbstractThe Waves instrument onboard the Juno spacecraft has plasma wave‐measuring capabilities using a single electric dipole antenna and a uniaxial magnetic search coil. Together, these simultaneously measure electric and magnetic field spectral densities in the frequency range 50 Hz–20 kHz, above which only electric field spectral densities are measured up to 41 MHz. A major objective of the Juno mission is to explore Jupiter's high‐latitude magnetosphere and ionosphere. One of the key contributions of the Waves instrument is the determination of electron densities from plasma wave spectra. Given the very high magnetic field strengths near Juno's perijove passes, established techniques cannot be utilized to infer electron densities since such highly magnetized space plasma conditions have not previously been met in planetary missions. By revisiting theoretical treatments of plasma waves, we describe a novel method to determine electron densities from plasma wave spectra that is unique to the near‐Jupiter region. In the absence of the commonly observed upper hybrid resonance frequency in high‐density space plasmas (e.g., the vicinities of Io, Ganymede, Enceladus, and the near‐Earth environment), we achieve this by identifying emission cutoffs at the lower hybrid frequency and electron plasma frequency. Further, we discuss the development of the process and tools for identifying and digitizing appropriate resonance and cutoff frequencies.

Implementation and experimental evaluation of Mega-voltage fan-beam CT using a linear accelerator

BackgroundMega-voltage fan-beam Computed Tomography (MV-FBCT) holds potential in accurate determination of relative electron density (RED) and proton stopping power ratio (SPR) but is not widely available.ObjectiveTo demonstrate the feasibility of MV-FBCT using a medical linear accelerator (LINAC) with a 2.5 MV imaging beam, an electronic portal imaging device (EPID) and multileaf collimators (MLCs).MethodsMLCs were used to collimate MV beam along z direction to enable a 1 cm width fan-beam. Projection data were acquired within one gantry rotation and preprocessed with in-house developed artifact correction algorithms before the reconstruction. MV-FBCT data were acquired at two dose levels: 30 and 60 monitor units (MUs). A Catphan 604 phantom was used to evaluate basic image quality. A head-sized CIRS phantom with three configurations of tissue-mimicking inserts was scanned and MV-FBCT Hounsfield unit (HU) to RED calibration was established for each insert configuration using linear regression. The determination coefficient ({R}^{2}) was used to gauge the accuracy of HU-RED calibration. Results were compared with baseline single-energy kilo-voltage treatment planning CT (TP-CT) HU-RED calibration which represented the current standard clinical practice.ResultsThe in-house artifact correction algorithms effectively suppressed ring artifact, cupping artifact, and CT number bias in MV-FBCT. Compared to TP-CT, MV-FBCT was able to improve the prediction accuracy of the HU-RED calibration curve for all three configurations of insert materials, with {R}^{2} > 0.9994 and {R}^{2} < 0.9990 for MV-FBCT and TP-CT HU-RED calibration curves of soft-tissue inserts, respectively. The measured mean CT numbers of blood-iodine mixture inserts in TP-CT drastically deviated from the fitted values but not in MV-FBCT. Reducing the radiation level from 60 to 30 MU did not decrease the prediction accuracy of the MV-FBCT HU-RED calibration curve.ConclusionWe demonstrated the feasibility of MV-FBCT and its potential in providing more accurate RED estimation.

The Influence of Solar X-ray Flares on SAR Meteorology: The Determination of the Wet Component of the Tropospheric Phase Delay and Precipitable Water Vapor

In this work, we study the impact of high-energy radiation induced by solar X-ray flares on the determination of the temporal change in precipitable water vapor (ΔPWV) as estimated using the synthetic aperture radar (SAR) meteorology technique. As recent research shows, this radiation can significantly affect the ionospheric D-region and induces errors in the estimation of the total electron content (TEC) by the applied models. Consequently, these errors are reflected in the determination of the phase delay and in many different types of measurements and models, including calculations of meteorological parameters based on SAR observations. The goal of this study is to quantify the impact of solar X-ray flares on the estimation of ΔPWV and provide an estimate of errors induced if the vertical total electron content (VTEC) is obtained by single layer models (SLM) or multiple layer models (MLM) (these models do not include ionosphere properties below the altitude of 90 km as input parameters and cannot provide information about local disturbances in the D-region). The performed analysis is based on a known procedure for the determination of the D-region electron density (and, consequently, the vertical total electron content in the D-region (VTECD)) using ionospheric observations by very low frequency (VLF) radio waves. The main result indicates that if the D-region, perturbed by medium-sized and intense X-ray flares, is not modeled, errors occur in the determination of ΔPWV. This study emphasizes the need for improved MLMs for the estimation of the TEC, including observational data at D-region altitudes during medium-sized and intense X-ray flare events.

Quick-look estimates of ionospheric properties from radio occultation data

Radio occultations are commonly used to determine vertical profiles of ionospheric electron density from measurements of frequency. “Frequency residuals” are important intermediate data products in radio occultation experiments. Frequency residuals are defined as the difference between observed and predicted values of the received frequency, where the predicted frequency includes all effects except refraction at the target object. However, relationships between properties of a vertical profile of ionospheric electron density and properties of time series of frequency residuals are not widely known by the broad community of scientists who may work with frequency residuals. Here we illustrate and explain how properties of a vertical profile of ionospheric electron density affect time series of frequency residuals. We also develop four quantitative relationships between electron density values and frequency residuals. These provide predictions for the topside plasma scale height, topside electron densities, peak altitude, and peak electron density that can be generated directly from a set of frequency residuals without the need to implement the full Abel transform analysis that is usually required to determine electron densities from frequency residuals. They can also be generated prior to the implementation of a high-quality baseline correction, to which the Abel transform analysis is sensitive. The development of these predictions assumed that the ionosphere has an exponential topside and a Chapman-like peak. These predictions are successfully tested on two-way radio occultation observations from the MAVEN Radio Occultation Science Experiment (ROSE) at Mars.

Determination of the test-samples electron density via dual energy computer tomography

In this work we determines electron density using data obtained via CT scanner with one radiation source operating in two modes: with 80 kV and 120 kV voltage. We perform tomography study of calibration phantom with predetermined electron densities. Single linear relationship between energy-subtracted Hounsfield unit and relative electron density is determined. Using determined relationship the relative electron densities of phantom calibration samples is calculated. The comparison of calculated and nominal values proves the possibility of the samples relative electron density determination using energy-subtracted Hounsfield unit with error less than 2%.

Electronic structure of Schiff-base peroxo{2,2'-[1,2-phenyl-enebis(nitrilo-methanylyl-idene)]bis-(6-meth-oxy-phenolato)}titanium(IV) monohydrate: a possible model structure of the reaction center for the theoretical study of hemoglobin.

An extensive characterization of [Ti(C22H18N2O6)]·H2O was performed by topological analysis according to Bader's quantum theory of atoms in molecules (QTAIM) from the experimentally (multipole model) and theoretically (DFT) determined electron density. To the best of our knowledge, this study is the first example of an experimental electronic structure of a coordination compound in which a peroxo anion is bonded to a 3d central atom. The titanium coordination polyhedron could be described as a deformed tetrahedral pyramid if the midpoint of the peroxide O-O bond (side-on mode) is considered to be in the quasi-apical position. According to the multipole model (MM) results, the titanium atom has a positive QTAIM charge of 2.05 e- which does not correspond to the formal Ti (IV) oxidation state. On the other hand, the peroxo oxygen atoms O(1) and O(2) have MM QTAIM charges of -0.27 and -0.12, respectively. This asymmetric charge density distribution on the peroxo oxygens is in agreement with the distorted orientation of the O2 moiety with respect to the titanium atom. Despite the fact that the overall MM charge of the O2 moiety is more remote from the formal -2 charge than from neutral O2, the O-O distance remains close to that in the peroxo O2 2- anion. In the case of DFT results, the titanium atom charge is also found to be close to +2, the O2 x- moiety charge is around -1, the optimized O-O distance is shorter by only ca 0.04 Å than the experimental value of 1.5005 (16) Å, and the DFT d-populations on titanium are found to be lower than the experimental MM value. This study is the first experimental electronic structure of a transition metal peroxo complex.

Multipole electron densities and structural parameters from synchrotron powder X-ray diffraction data obtained with a MYTHEN detector system (OHGI).

Powder X-ray diffraction has some inherent advantages over traditional single-crystal X-ray diffraction in accurately determining electron densities and structural parameters due to the lower requirements for sample crystallinity, simpler corrections and measurement simultaneity. For some simple inorganic materials, it has been shown that these advantages can compensate for disadvantages such as peak overlap and error-prone background subtraction. Although it is challenging to extend powder X-ray diffraction-based electron-density studies to organic materials with significant peak overlap, previous results using a dedicated vacuum diffractometer with a large image-plate camera (AVID) demonstrated that it can be done. However, the vacuum setup with the off-line detector system was found to prohibit a widespread use. Fast microstrip detectors, which have been employed at a number of powder diffraction beamlines, have the potential to facilitate electron-density studies. Nevertheless, no electron-density studies even for materials with slight peak overlap have been performed with microstrip detectors. One of the most critical problems has been a difference in sensitivity between microstrip channels, which substantially defines the dynamic range of a detector. Recently, a robust approach to this problem has been developed and applied to a total scattering measurement system (OHGI) with 15 MYTHEN microstrip modules. In the present study, synchrotron powder X-ray diffraction data obtained with OHGI are evaulated in terms of multipole electron densities and structural parameters (atomic positions and displacement parameters). These results show that, even without a dedicated setup and perfect samples, electron-density modelling can be carried out on high-quality powder X-ray diffraction data. However, it was also found that the required prior information about the sample prohibits widespread use of the method. With the presently obtainable data quality, electron densities of molecular crystals in general are not reliably obtained from powder data, but it is an excellent, possibly superior, alternative to single-crystal measurements for small-unit-cell inorganic solids. If aspherical atomic scattering factors can be obtained from other means (multipole databases, theoretical calculations), then atomic positions (including for hydrogen) and anisotropic atomic displacement parameters (non-hydrogen atoms) of excellent accuracy can be refined from synchrotron powder X-ray diffraction data on organic crystals.

Fine control of lattice thermal conductivity in low-dimensional materials

Optimal regulation of lattice thermal conductivity in low-dimensional materials is fundamental to obtain highly efficient miniaturized devices. To this aim, we use quantum-mechanical based analyses to understand how atomic type and structural geometry determine electron density and lattice dynamic features ruling the thermal conduction. As a case study, we consider layered van der Waals transition metal dichalcogenides with a finite number of layers. We find that a large thermal conductivity is realized when the atomic bonds display highly covalent character, promoting fast motions of the cations in correspondence of the low-frequency phonon band. Such an effect is the result of the entangled electronic and phonon features, which are captured by the covalency and cophonicity metric. The investigation protocol that we present has general applicability and can be used to design novel thermal low-dimensional materials irrespective of the kind of atomic topology and chemical composition.

An Iterative Method for Computed Tomography Machine Calibration: Attenuation and Dual-Energy Computed Tomography Inversion from the Hounsfield Numbers

Introduction: Photoelectric effect and X-ray scattering determine the attenuation coefficient of materials in diagnostic radiology. This manuscript presents an iterative gradient search method to separate the contributions to attenuation from these two independent sources. This issue assumes importance due to two reasons, including 1) Electron density determination of scanned materials and 2) correct dose calculation in diagnostic radiology. Material and Methods: A special water-filled phantom which was custom-built for simultaneous scanning of 12 samples was used in the current study. Attenuation coefficient equations were iteratively solved to calculate the contributions from x-ray scattering and photoelectric effects. Results: Data converged after five iterations (within 1%). Error in the attenuation coefficient was measured at ±3%. Conclusion: As evidenced by the obtained results, this method can be used to determine the Compton and photoelectric contributions with sufficient accuracy. Moreover, the inversion of Dual- Energy computed tomography (DECT) data for finding electron density and effective atomic number of materials also presents satisfactory results.

Electron density measurement using a partially covered hairpin resonator in an inductively coupled plasma.

Hairpin probes are used to determine electron densities via measuring the shift of the resonant frequency of the probe structure when immersed in a plasma. This manuscript presents new developments in hairpin probe hardware and theory that have enabled measurements in a high electron density plasma, up to approximately 1012 cm-3, corresponding to a plasma frequency of about 9 GHz. Hardware developments include the use of both quarter-wavelength and three-quarter-wavelength partially covered hairpin probes in a transmission mode together with an easily reproducible implementation of the associated microwave electronics using commercial off-the-shelf components. The three-quarter-wavelength structure is operated at its second harmonic with the purpose of measuring higher electron densities. New theory developments for interpreting the probe measurements include the use of a transmission line model to find an accurate relationship between the resonant frequency of the probe and the electron density, including effects of partially covering the probes with epoxy. Measurements are taken in an inductively coupled plasma sustained in argon at pressures below 50 mTorr. Results are compared with Langmuir probe and interferometry measurements.

Incoherent and Collective Thomson Scattering for the Determination of Electron and Ion Properties in Low-Temperature Plasma

In this lecture an overview of applications of incoherent Thomson scattering (TS) as well as collective Thomson scattering (CTS) will be given. These are the most accurate methods for measuring the electron and ion properties, because the method is direct and non-intrusive. A CTS system based on the fundamental wavelength of a seeded Nd:YAG laser, being developed for the high density, low-temperature plasma of the linear plasma generator Magnum-PSI will be described also. The small Debye length of dense low temperature plasma enables application of CTS at relatively short laser wavelength. The combination of this CTS system and existing incoherent TS system enables determination of electron density and temperature as well as ion temperature and plasma velocity of the near surface plasma. In this lecture, the theoretical background and experimental challenges of the work will be given along with some examples that demonstrate the capabilities of such systems.

Ionized outflows in local luminous AGN: what are the real densities and outflow rates?

ABSTRACT We report on the determination of electron densities, and their impact on the outflow masses and rates, measured in the central few hundred parsecs of 11 local luminous active galaxies. We show that the peak of the integrated line emission in the active galactic nuclei (AGN) is significantly offset from the systemic velocity as traced by the stellar absorption features, indicating that the profiles are dominated by outflow. In contrast, matched inactive galaxies are characterized by a systemic peak and weaker outflow wing. We present three independent estimates of the electron density in these AGN, discussing the merits of the different methods. The electron density derived from the [S ii] doublet is significantly lower than that found with a method developed in the last decade using auroral and transauroral lines, as well as a recently introduced method based on the ionization parameter. The reason is that, for gas photoionized by an AGN, much of the [S ii] emission arises in an extended partially ionized zone where the implicit assumption that the electron density traces the hydrogen density is invalid. We propose ways to deal with this situation and we derive the associated outflow rates for ionized gas, which are in the range 0.001–0.5 M⊙ yr−1 for our AGN sample. We compare these outflow rates to the relation between $\dot{M}_{\rm out}$ and LAGN in the literature, and argue that it may need to be modified and rescaled towards lower mass outflow rates.

Adsorption of Organic Acids and Phosphate to an Iron (Oxyhydr)oxide Mineral: A Combined Experimental and Density Functional Theory Study.

The interaction of soil organic matter with mineral surfaces is a critical reaction involved in many ecosystem services, including stabilization of organic matter in the terrestrial carbon pool and bioavailability of plant nutrients. Using model organic acids typically present in soil solutions, this study couples laboratory adsorption studies with density functional theory (DFT) to provide physical insights into the nature of the chemical bonding between carboxylate functional groups and a model FeOOH cluster. Topological determination of electron density at bond critical points using quantum theory of atoms in molecules (QTAIM) analysis revealed that the presence of multiple bonding paths between the organic acid and the FeOOH cluster is essential in determining the competitive adsorption of organic acids and phosphate for FeOOH surface adsorption sites. The electron density and Laplacian parameter values from QTAIM indicated that the primary carboxylate-FeOOH bond was more ionic than covalent in nature. The experimental and computational results provide molecular-level evidence of the important role of electrostatic forces in the bonding between carboxylic acids and Fe-hydroxides. This knowledge may assist in the formulation of management studies to meet the challenges of maintaining ecosystems services in the face of a changing climate.

Plasma density determination by using hydrogen Balmer Hα spectral line with improved accuracy

In this paper, we demonstrate the use of hydrogen Balmer Hα spectral line for plasma electron density determination with a similar accuracy as is obtained by using the hydrogen Balmer Hβ spectral line. The reason for this is that Hβ often cannot be used for plasma electron density determination in many experiments. Theories that treat Hα line give different relation between halfwidth and electron density. The corresponding numerical procedure for the correction of electron density obtained from Hα line is established in this paper. For that purpose, experimental line profiles emitted from an electric wall stabilized dc and pulsed arc and laser produced plasma were used, as well as the experimental data available in the literature.

Extending SDP Modeling to the Inverted Hexagonal Phase

The SDP (Scattering Density Profile) technique was developed to model the X-ray and neutron scattering profiles of lipid bilayers. The lipids were divided up into coarse grained components, with the probability of a component being found at a given point in the bilayer represented by an appropriate function. Most of the lipid component probability densities were modeled as Gaussians, with the hydrocarbon tail region represented by an error function. Building on this powerful method developed by others, we have extended it to the inverted hexagonal phase. As the technique was originally developed for use for lipids with phosphatidylcholine head groups, we have also modified it for use with phosphatidylethanolamine head groups. We have been able to generate models whose Fourier components agree well with the amplitudes acquired from X-ray diffraction. Additionally, the Luzzati interface from the models is close to the experimentally determined electron density peak, as one would expect for these systems.

Doppler-free, laser saturated absorption profile of 414 nm helium line for plasma density measurements

In a recent publication [J. Quant. Spectrosc. Radiat. Transfer, 2019 230, 48], Zafar et al. have reported on the use of Doppler-free spectroscopy of helium 414 nm line for the determination of electron density in helium plasmas. This was done by fitting their experimentally obtained Doppler-free line profiles with spectral profiles constructed using a Stark broadening model. But in this model, authors have assumed a closed two-level system for the 21P-61D transition, an approximation which results in considering an order of magnitude smaller homogeneous spectral width for the 414 nm line. This assumption of Zafar et al. also leads to 3 orders of magnitude underestimated saturation factor of the line. In this work, we report the correct procedure for the reconstruction of Doppler-free 414 nm line profiles and apply it for the electron densities measurements, as considered in Zafar et al’s paper. It is concluded that the minimum electron densities measurable by this technique is in the range of 1 × 1018m−3, rendering questionable the possibility of measuring by this technique lower electron densities, which was reported in the above cited publication.