Estimation Of Electron Density Research Articles

Properties of Electron Distributions in the Martian Space Environment

AbstractElectron and magnetic field measurements from the Mars atmosphere and volatile environment (MAVEN) mission are utilized to study the interaction between Mars and the solar wind. Instruments like the solar wind electron analyzer (SWEA) aboard MAVEN measure properties of the electron environment over a broad range of electron energies. Measurements at low electron energies include contributions from spacecraft photoelectrons and secondary electrons that must be accounted for to accurately characterize the environment. We developed an algorithm to identify and remove secondary electron contamination to improve estimates of electron densities and temperature. We then compiled global maps of average electron density, temperature, and temperature anisotropy under different conditions, considering quasi‐parallel and quasi‐perpendicular bow shocks and upstream solar wind Alfven Mach number. Higher temperature anisotropy is observed for quasi‐perpendicular shock crossings, as expected. We find significant electron temperature anisotropy upstream of the bow shock for quasi‐perpendicular shock crossings, suggesting a heating mechanism, such as that provided by electromagnetic waves. We analyzed the influence of hi and low Alfven Mach number conditions and found the electron plasma beta to be the only electron property significantly affected. We studied the relationship between the electron distribution function and the generation of instabilities and conclude that the upstream Alfven Mach number influences the stability of electron distributions in the Martian environment.

The First Atmospheric Radio Occultation Profiles From a GPS Receiver in Geostationary Orbit

This paper will present the first radio occultation (RO) electron density profiles of Earth’s atmosphere generated from a Global Positioning System (GPS) receiver in Geostationary orbit. The GPS receivers on the GOES-16 (R) and GOES-17 (S) satellites track GPS signals propagated through the Earth’s atmosphere and can be used to estimate electron density profiles. Radio occultation profiles from geosynchronous orbit holds the potential to generate unique temporal and spatial atmospheric measurements complementary to those from ground and low Earth orbit space based receivers, including limb observations of the upper atmosphere at altitudes above traditional low Earth orbiting RO satellites. This paper will present details of the GOES satellite GPS receivers and the limitations and challenges in generating RO profiles with its current hardware and software configuration. Following, the temporal and geo-spatial coverage for each of the GOES satellites will be presented, quantifying the frequency and number of GPS signals tracked down to sufficiently low enough altitudes to provide useful atmospheric information. Next, the data processing required to generate excess phase and electron density profiles will be described and demonstrated using two examples of GOES profiles. Subsequently, these two example GOES RO profiles will be compared to and calibrated with an ionospheric model, compared with co-located profiles from the low Earth orbit COSMIC-2 constellation and a ground based ionosonde.

Investigations on the effect of target angle on the stagnation layer of colliding laser produced plasmas of aluminum and silicon

The temporal and spatial characteristics of two colliding laser produced plasmas are investigated over a range of flat to wedge-shaped targets for aluminum and silicon. Fast-gated visible photography was used to investigate how the length and width of the stagnation evolved over timescales from 300 to 500 ns with filters used to help to separate the emission from neutral and higher ionization states. The velocity of the stagnation layer was measured to be in the range of 3.8–6.6×106 cm/s. The length of the stagnation layer was observed to increase as the wedge angle decreased from 180° to 80°. Time-resolved spectra were also recorded, which helped to reveal the dominant ion stage in a given time interval. Based on this analysis, the longest and most homogenous stagnation layers appear to be comprised of mostly neutral and singly ionized species. Line widths were used to estimate electron densities of 1×1017cm−3 and temperatures of 1.9–2.1 eV, which remained fairly constant over the timescales observed. The analysis suggests that there is significant collisional reheating of the stagnation layer followed by radiative recombination and that the stagnation layer dynamics are not sensitive to small changes in mass.

Synthetic CT Generation From Multi-Sequence MR Images for Head and Neck MRI-Only Radiotherapy via Cycle-Consistent Generative Adversarial Network

Synthetic CT (sCT) generation with MR image plays an essential role in MR-only radiotherapy, which can be used for electron density estimation and dose calculation in treatment planning. Currently, the reliability of deep learning-based methods for sCT generation depends on two aspects: the MR-CT registration errors, which can eliminate by a cycle-consistent generative adversarial network (CycleGAN) with unpaired training data, and the different anatomy information and contract divergence of various tissue in different sequences MRI which will significantly affect the nonlinear mapping of MR-CT. The purpose of this study is to investigate the effect of different sequence MRI by evaluating the image quality of corresponded sCTs.Multi-sequence MR images (T1, T2, T1C) and plan CT images of 151 patients with nasopharyngeal carcinoma were acquired on the same day in the radiation treatment position. 126 cases were randomly selected as the training set with the same preprocessing. Three unsupervised CycleGAN-based models were respectively trained with different sequence MRI with Architecture, which consists of 2 ResUnet-based generators and 2 Patch-GAN-based discriminators. The remaining 25 CT-MR cases with non-rigid registration were selected as the independent paired testing set. The mean error (ME) and mean absolute error (MAE) between plan CT and sCT of each model were used to measure the CT value estimation accuracy, which was calculated within air (Hounsfield Unit, HU < 100), soft tissue (-100 < HU < 150), bone (HU > 150) and whole body, respectively. Structural similarity index (SSIM) was applied to evaluate the similarity between error (plan CT and sCT.The MEs calculated between plan CT and T1, T2, T1C-based sCT images, were (-0.62 ± 3.06) vs. (-1.81 ± 3.13) vs. (0.13 ± 2.56) within air, (154.92 ± 87.93) vs. (173.27 ± 97.62) vs. (262.78 ± 91.74) within soft tissue, (1363.99 ± 294.94) vs. (337.21 ± 50.4) vs. (661.63 ± 168.43) within bone, (22.12 ± 29.47) vs. (17.05 ± 10.51) vs. (35.28 ± 20.75) within the whole body. The MAEs correspondingly were (4.49 ± 3.13) vs. (4.6 ± 3.47) vs. (4.6 ± 3.47) within air, (186.41 ± 61.75) vs. (197.33 ± 58.62) vs. (293.56 ± 72.72) within soft tissue, (186.41 ± 61.75) vs. (197.33 ± 58.62) vs. (293.56 ± 72.72) within bone, (31.28 ± 28.1) vs. (27.64 ± 10.41) vs. (42.6 ± 23.82) within the whole body. The quantitative analysis between T1, T2, T1C-sCTs indicates that the T1C based generated model achieves higher accuracy than the other models in nasopharyngeal carcinoma.The T1C MRI can provide sufficient anatomy information and tissue contract in synthetic CT prediction of head and neck region, which offers a substantial potential for density estimation and dose calculation in radiotherapy. The generation method and evaluation will investigate synthetic CT prediction with more complex tissue in various body parts.

Evaluation of Fe XIV Intensity Ratio for Electron Density Diagnostics by Laboratory Measurements

The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.

A Review of Voxel-Based Computerized Ionospheric Tomography with GNSS Ground Receivers

Ionized by solar radiation, the ionosphere causes a phase rotation or time delay to trans-ionospheric radio waves. Reconstruction of ionospheric electron density profiles with global navigation satellite system (GNSS) observations has become an indispensable technique for various purposes ranging from space physics studies to radio applications. This paper conducts a comprehensive review on the development of voxel-based computerized ionospheric tomography (CIT) in the last 30 years. A brief introduction is given in chronological order starting from the first report of CIT with simulation to the newly proposed voxel-based algorithms for ionospheric event analysis. The statement of the tomographic geometry and voxel models are outlined with the ill-posed and ill-conditioned nature of CIT addressed. With the additional information from other instrumental observations or initial models supplemented to make the coefficient matrix less ill-conditioned, equation constructions are categorized into constraints, virtual data assimilation and multi-source observation fusion. Then, the paper classifies and assesses the voxel-based CIT algorithms of the algebraic method, statistical approach and artificial neural networks for equation solving or electron density estimation. The advantages and limitations of the algorithms are also pointed out. Moreover, the paper illustrates the representative height profiles and two-dimensional images of ionospheric electron densities from CIT. Ionospheric disturbances studied with CIT are presented. It also demonstrates how the CIT benefits ionospheric correction and ionospheric monitoring. Finally, some suggestions are provided for further research about voxel-based CIT.

An Electron Density Model of the D‐ and E‐Region Ionosphere for Transionospheric VLF Propagation

AbstractTerrestrial Very‐Low‐Frequency (VLF) energy from both lightning discharges and radio transmitters has a role in affecting the energetic electrons in the Van Allen radiation belts, but quantification of these effects is particularly difficult, largely due to the collisional damping experienced in the highly variable electron density in the D‐ and E‐region ionosphere. The Faraday International Reference Ionosphere (FIRI) model was specifically developed by combining lower‐ionosphere chemistry modeling with in situ rocket measurements, and represents to date the most reliable source of electron density profiles for the lower ionosphere. As a full‐resolution empirical model, FIRI is not well suited to D‐ and E‐region ionosphere inversion, and its applicability in transionospheric VLF simulation and in remote sensing of the lower ionosphere is limited. Motivated by how subionospheric VLF remote sensing has been aided by the Wait and Spies (WS) profile (Wait &amp; Spies, 1964), in this study, we parameterize the FIRI profiles and extend the WS profile to the E‐region ionosphere by introducing two new parameters: the knee altitude hk and the sharpness parameter for the E‐region ionosphere βE. Using this modified WS profile, we calculate the expected signals at different receiver locations from the NAA, NPM, and NWC transmitters under the full range of possible ionospheric conditions. We also describe and validate a method about how these results can be readily used to translate VLF measurements into estimates of the lower ionosphere electron density. Moreover, we use this method to evaluate the sensitivity of different ground receiver locations in lower‐ionosphere remote sensing.

Estimation of electron density and temperature in an argon rotating gliding arc using optical and electrical measurements

This work reports average electron temperature (Te) and electron density (ne) of an atmospheric argon rotating gliding arc (RGA), operated in glow-type mode, under transitional and turbulent flows. Both Te and ne were calculated near the shortest (δ) and longest (Δ) gap between the electrodes, by two different methods using two separate measurements: (1) optical emission spectroscopy (OES) and (2) physical–electrical. Te calculated from (a) collisional radiative model (CRM) (OES) and (b) BOLSIG+ [physical–electrical, reduced electric field (ENo) as input], differed each other by 16%–26% at δ and 6% at Δ. Te was maximum at δ (&amp;gt;2 eV) and minimum near Δ (1.6–1.7 eV). Similarly, the ENo was maximum near the δ (5–8 Td) and minimum near Δ, reaching an asymptotic value (1 Td). By benchmarking Te from CRM, the expected ENo near δ was corrected to 3 Td. The calculated CRM intensity agreed well with that of the measured for most of the emission lines indicating a well optimized model. The average ne near δ and Δ from Stark broadening (OES) was 4.8–8.0×1021 m−3, which is an order higher than the ne calculated through current density (physical–electrical). Te and ne were not affected by gas flow, attributed to the glow-type mode operation. To the best of authors’ knowledge, this work reports for the first time (a) an optimized CRM for RGAs (fine-structure resolved), (b) the poly-diagnostic approach to estimate plasma parameters, and (c) the validation of ENo calculated using physical–electrical measurements.

The Estimation of D‐Region Electron Densities From Trans‐Ionospheric Very Low Frequency Signals

AbstractDue to the relatively low ionization levels present in the D‐region of the ionosphere (60–90 km), few reliable methods exist for estimating electron densities at this altitude. Very Low Frequency (VLF, 3–30 kHz) radio waves, unlike higher frequency waves used for similar remote sensing applications, are sensitive to these low ionization levels. Much past work has addressed the estimation of D‐region electron densities using ground‐based measurements of signals originating from VLF transmitters or atmospheric lightning. We introduce a new technique for the estimation of ionospheric D‐region electron densities using satellite observations of trans‐ionospheric VLF signals originating from high‐powered VLF transmitters. Although most of the energy radiated from these transmitters is confined to sub‐ionospheric propagation modes, a small fraction penetrates the ionosphere in a right‐hand circularly polarized “whistler mode” which has been observed by many satellites. We show that the modal interference pattern previously observed enables the estimation of the electron density profile in the D‐region from a single satellite pass. Using data from the DEMETER experiment, each collection is compared with results from a validated theoretical model to select a best‐fit D‐region electron density profile. Results show expected seasonal variations and are consistent with rocket observations. Although the D‐region electron density estimates derived with this technique are shown to exhibit long‐term seasonal variations consistent with rocket and ground‐based observations, it is important to note that validation of these results remains difficult due to the lack of other techniques for continuously sensing the D‐region.

LabVIEW-FPGA-Based Real-Time Data Acquisition System for ADITYA-U Heterodyne Interferometry

Microwave interferometry has been used extensively for plasma diagnostics in tokamak for real-time electron density measurements. Real-time density measurement is an indispensable part of advanced tokamaks, as it can be used as feedback to control the plasma operation. In this article, we report the development of the phase extraction method in a heterodyne interferometer for real-time density estimation using a field-programmable gate array (FPGA). FPGA provides parallel processing, minimum control delay, more efficient processing architecture, and jitter-free synchronization between different control layers. Digital CORDIC algorithm is used for the estimation of the phase between two arms of the interferometer. A LabVIEW program is developed for the FPGA target and host controller to acquire the data and estimate electron density in real time, which can be used for feedback purpose by regulating the amount of gas injection using piezoelectric valve that requires a high voltage (~100 V) for about 1 ms. The delay in generating the feedback signal is proportional to the sampling speed (100 kHz) of the analog signal. In this work, line-averaged electron density measurement using digital signal processing (DSP) and LabVIEW-FPGA technology is presented. The developed interferometer and data acquisition (DAQ) system installed on ADITYA-U tokamak can measure the electron density in the range of $1 \times 10^{18} - 1 \times 10^{20}\,\,\text{m}^{-3}$ . The algorithm used for the estimation of phase difference is validated using a conventional arctan method. The developed reconfigurable FPGA-based DAQ system uses low power, has a reconfigurable hardware structure for fast real-time signal processing, and can be easily upgraded.

Measurement of the free electron line density in a spherical theta-pinch plasma target by single wavelength interferometry

A single wavelength heterodyne interferometer has been set up to investigate the free electron density integrated axially along the line of sight (line density) in a theta-pinch plasma to determine its applicability as a plasma target for ion beam stripping. The maximal line density reached in this experiment was cm−2 at 80 Pa and 20 kV. The findings demonstrate the pulsed character of the line density and its increase by raising the load voltage and the working gas pressure. Additionally, the results were compared with spectroscopic free electron density estimations, which were carried out by H-line broadening and peak separation. The time behavior of the line density indicates that its peak value is delayed by about 10 µs compared to the spectroscopic results. This effect is due to the formation of an extended, magnetically compressed plasma column in the vicinity of the current maximum, although the highest volumetric free electron density is reached near the current zero crossing. Since the line density is an essential parameter in describing the stripping capabilities of the plasma target, the interferometric diagnostic is superior to a spectroscopic diagnostic, because it directly provides integrated values along the line of sight. Furthermore, the measurements of the line density in this experiment partially show nonphysical negative values, which is due to gaseous effects and residual shot vibrations.

Modification of Martian Ionosphere

To partially meet the communication requirements in Mars, low-frequency ground-to-ground communication is likely to be used in the future and hence, it is desirable to increase electron density in the Martian ionosphere. As a convenient means to this, we have proposed and explored the production of high electron density regions in the Martian atmosphere in daytime by suspension of low work function dust, specifically Cs-coated bronze in the atmosphere. Equations of the kinetics of the dusty air in sunlight have been introduced and a numerical estimate of the daytime electron density at 60-100 km heights has been obtained as a function of the dust parameters. Photoelectric emission from dust and accretion of electrons and ions on dust particles play the key role in getting the desired electron density at high altitudes (60-100 km). A discussion of the numerical results has been given with conclusions.

The physical properties and evolution of the interacting system AM 1204−292

ABSTRACT We investigate interaction effects in the stellar and gas kinematics, stellar population, and ionized gas properties of the interacting galaxy pair AM 1204−292,composed of NGC 4105 and NGC 4106. The data consist of long-slit spectra in the range 3000–7050 Å. The massive E3 galaxy NGC 4105 presents a flat stellar velocity profile, while the ionized gas is in strong rotation, suggesting an external origin. Its companion, NGC 4106, shows asymmetries in the radial velocity field, likely due to the interaction. The dynamics of the interacting pair were modelled using the P-Gadget3 treepm/sph code, from which we show that the system has just passed the first perigalacticum, which triggered an outbreak of star formation, currently at full maximum. We characterized the stellar population properties using the stellar population synthesis code starlight and, on average, both galaxies are predominantly composed of old stellar populations. NGC 4105 has a slightly negative age gradient, comparable with that of the most massive elliptical galaxies, but a steeper metallicity gradient. The SB0 galaxy NGC 4106 presents smaller radial variations in both age and metallicity in comparison with intermediate-mass early-type galaxies. These gradients have not been disturbed by interaction, since the star formation happened very recently and was not extensive in mass. Electron density estimates for the pair are systematically higher than those obtained in isolated galaxies. The central O/H abundances were obtained from photoionization models in combination with emission-line ratios, which resulted in 12 + log(O/H) = 9.03 ± 0.02 and 12 + log(O/H) = 8.69 ± 0.05 for NGC 4105 and NGC 4106, respectively.

Quantitative positron emission tomography imaging in the presence of iodinated contrast media using electron density quantifications from dual-energy computed tomography.

As preparation for future positron emission tomography (PET)/dual-energy computed tomography (DECT)T imaging modality and new possible clinical applications, the study aimed to evaluate the utility of clinically available spectral results from a DECT system for improving attenuation corrections of PET acquisitions in the presence of iodinated contrast media. The dependence of the accuracy of PET quantification values, reconstructed with conventional and spectral-based attenuation corrections, was examined as a function of the amount of iodine content and x-ray radiation exposure. Measurements were performed on commercial PET/CT and DECT systems, using a semi-anthropomorphic phantom with seven centrifuge tubes in its bore. Five different configurations of tube contents were scanned by both PET/CT and DECT. With the aim of mimicking clinically observed concentrations, in all phantom configurations the center tube contained a high concentration of radionuclide while the peripheral tubes contained a lower concentration of radionuclide. Iodine content was incrementally increased between phantom configurations by replacing iodine-free tubes with tubes that contained the original radionuclide concentration within a 10mg/ml iodine dilution. DECT-based attenuation correction maps were generated by scaling electron density spectral results into corresponding 511keV photon linear attenuation coefficients. Mean SUV values obtained from the nominal PET reconstruction, using conventional CT images as input for the attenuation correction, demonstrate a monotonic increase of 8.6% when the water and radionuclide mixtures were replaced by iodine, water, and radionuclide (same level of activity) mixture. Mean SUV values obtained from the DECT-based reconstruction, in which the attenuation correction utilizes electron density values as input, demonstrate different, more stable behavior across all iodine insert configurations, with a standard deviation to mean ratio of less than 1%. This observed behavior was independent of the area size used for measurement. A minor radiation dose dependency of the electron density values (below 0.5%) was observed. This resulted in consistent (iodine independent) PET quantification behavior, which persisted even at the lowest radiation dose levels tested in our experiment, that is, 25% of the radiation dose utilized for CT acquisition in the clinical PET/CT protocol. Utilization of DECT-generated electron density estimations for attenuation correction benefit PET quantification consistency in the presence of iodine and at nominal and low DECT radiation exposure levels. The ability to correctly account for iodinated contrast media in PET acquisitions will allow the development of new clinical applications that rely on the quantitative capabilities of spectral CT technologies and modern PET systems.

Estimation and Uncertainties of Profiles and Equilibria for Fusion Modeling Codes

The results of transport modeling codes, e.g., GENE for the plasma core or SOLPS-ITER for the plasma edge, depend critically on reliable profile and equilibrium estimates. The propagation of uncertainties (UP) of input quantities to the results of modeling codes, e.g., power and particle exhaust and plasma stability, is frequently neglected because of the costs of running the codes as well as because of the missing uncertainty quantification of input quantities. The situation becomes even more cumbersome if profile gradients and their uncertainties are of major concern for transport analyses. Two different techniques are presented to estimate profiles, profile gradients, their uncertainties, and candidate profiles for UP in modeling codes. Markov Chain Monte Carlo sampling of the posterior probability density of an integrated data analysis approach is applied to estimate electron density and temperature profiles. Nonstationary Gaussian process regression is applied to estimate ion temperature and angular velocity profiles. Both methods provide in a natural way profile gradients, profile logarithmic gradients, and their uncertainties. Modeling codes benefit also from reliable equilibrium reconstructions and quantification of the uncertainty of various equilibrium parameters. For the analysis of diagnostics data, the position and uncertainty of flux surfaces as well as of the magnetic axis are important. For plasma transport and stability codes, the estimation of uncertainties of current and q-profiles is presented. For plasma edge codes the position of the separatrix contour and its uncertainty at various poloidal positions is of primary interest especially if steep profile gradients are present. Examples of uncertainties and their sources in magnetic scalar quantities, profiles, and separatrix contours are shown.

3‐D Tomography of the Ionospheric Anomalies Immediately Before and After the 2011 Tohoku‐Oki (Mw9.0) Earthquake

AbstractA dense network of ground global navigation satellite system receivers detected ionospheric total electron content (TEC) changes starting ~40 min before the 2011 Tohoku‐oki (Mw9.0) earthquake around the ruptured fault, together with the long‐lasting postseismic TEC drop. In this paper, we robustly estimate three‐dimensional (3‐D) distribution of both preseismic and postseismic ionospheric anomalies of the 2011 Tohoku‐oki earthquake by tomographic inversions of electron density anomalies. We set up &gt;6,000 blocks, as large as 1.0° (east‐west) × 0.9° (north‐south) × 60 km (vertical), over the Japanese Islands, the Sea of Japan, and the Korean Peninsula, up to 870 km altitude. By using TEC anomalies of pairs exceeding ~1,300 stations and eight satellites obtained using reference curves, we estimated electron density anomalies within individual blocks. The results showed that the preseismic and postseismic anomalies do not overlap in space. The preseismic anomalies are composed of low (~300 km height) positive and high (~600 km height) negative anomalies. They occurred above the land of NE Japan without extending offshore, suggesting its origin related to surface electric charges. On the other hand, the postseismic electron depletion occurred offshore above the region where large coseismic uplift took place. These results demonstrate that the preseismic and postseismic ionospheric anomalies are independent not only temporarily but also spatially and certainly in underlying physical mechanisms. We propose a simple model to explain how surface charges redistribute ionospheric electrons to make the observed preseismic electron density anomalies.

Electron density and effective atomic number estimation in a maximum a posteriori framework for dual-energy computed tomography.

The stoichiometric calibration method for dual-energy CT (DECT) proposed by Bourque et al. (Phys Med Biol. 59:2059; 2014), which provides estimators of the electron density and the effective atomic number, is adapted to a maximum a posteriori (MAP) framework to increase the model's robustness to noise and biases in CT data, specifically for human tissues. Robust physical parameter estimation from noisy DECT scans is required to maximize the precision of quantities used for radiotherapy treatment planning such as the proton stopping power (SPR). Estimation of electron density and effective atomic number is performed by constraining their variation to the natural range of values expected for human tissues, while maximizing attenuation data fidelity. The MAP framework is first compared against the original method using theoretical CT numbers with Gaussian noise. The quantitative accuracy of the MAP framework is then validated experimentally on the Gammex 467 phantom. Then, using two clinical datasets, the advantages of the approach are experimentally evaluated, qualitatively, and quantitatively. The theoretical study shows that the root-mean-square error on the electron density, the effective atomic number and the SPR are, respectively, reduced from 2.3 to 1.5, 5.7 to 3.2 and 2.8 to 1.7% with the adapted framework, when analyzing soft tissues and bone together. The experimental validation study shows that the standard deviation in Gammex inserts can be reduced, on average, by factors of 1.4 (electron density), 2.7 (effective atomic number), and 1.9 (SPR), while the quantitative accuracy of the three physical parameters is preserved, on average. Evaluation on clinical datasets show apparent noise reduction in maps of all estimated physical quantities, and suggests that the MAP framework has increased robustness to beam hardening and photon starvation artifacts. Mean values for the electron density, the effective atomic number, and the SPR averaged in four uniform regions of interest (brain, muscle, adipose, and cranium), respectively, differ by 0.7, 1.8, and 0.9% between both frameworks. The standard deviation in the same regions of interest is also reduced, on average, by factors of 1.8, 6.6, and 3.2 with the MAP framework. Differences in mean value and standard deviations are statistically significant. Theoretical and experimental results suggest that the MAP framework produces more accurate and precise estimates of the electron density and SPR. Thus, the present approach limits the propagation of noise in DECT attenuation data to radiotherapy-related parameters maps such as the SPR and the electron density. Using a MAP framework with DECT for radiotherapy treatment planning can help maximizing the precision of dose calculation. The method also provides more precise estimates of the effective atomic number. The MAP methodology is presented in a general way such that it can be adapted to any DECT image-based tissue characterization method.

Characterization Of Dielectric Barrier Discharge (DBD) Produced In Air At Atmospheric Pressure And Its Application In Surface Modification Of High-Density Polyethylene (HDPE)

The low surface energy of HDPE limits its industrial uses as it is not suitable for printing and adhesion. The main aim of this work is to improve the wetting properties of high-density polyethylene (HDPE) using air dielectric barrier discharge (DBD) operating at the line frequency (50 Hz). The estimation of electron temperature and electron density has been done by electrical and optical methods. The surface roughness of the control and plasma treated polymer film is analysed by contact angle (CA) measurement, surface energy measurement and scanning electron microscope (SEM) analysis. The contact angle was found to be suppressed from 93.180±2.00 to 63.750±0.880 after 10s of plasma treatment which implied that the surface property had changed to a hydrophilic state caused by an increase in the surface roughness.

Comparison of SuperDARN peak electron density estimates based on elevation angle measurements to ionosonde and incoherent scatter radar measurements

Measurements of the electron density at the F region peak by the Canadian Advanced Digital Ionosonde (CADI) and the Resolute Incoherent Scatter Radar (RISR) are used to assess the quality of peak electron density estimates made from elevation angle measurements by the Super Dual Auroral Radar Network (SuperDARN) high-frequency radar at Rankin Inlet (RKN). All three instruments monitor the ionosphere near Resolute Bay. The CADI-RKN joint dataset comprises measurements between 2008 and 2017 while RISR-RKN dataset covers about 60 daylong events in 2016. Reasonable agreement between the RKN estimates and measurements by CADI and RISR is shown. Two minor discrepancies are discussed: RKN radar daytime peak electron density overestimation by ~ 10% and underestimation by up to 30% in other time sectors. In winter nighttime and dawn, cases were identified in which the RKN radar significantly overestimates the peak electron density. This occurs when the phase in the RKN interferometer measurements is incorrectly shifted by 2uppi , and this is most significant when electron densities are low. Statistical fitting to the joint data sets, split into four time sectors of a day, has been done and parameters of the fit have been determined. These allow slight adjustment of measured real-time RKN values to better reflect real peak electron densities in the ionosphere within its field of view.

Experimental Stark broadening parameters for singly ionized molybdenum spectral lines in near UV

This work is dedicated to Stark broadening of singly ionized Molybdenum spectral lines in UV spectrum. We present stark widths of 43 Mo II spectral lines in the wavelength range 275 to 376 nm measured at electron density of ≈ 1.5 × 1023 m−3 and electron temperature of ≈ 13000 K. A Laser Induced Plasma, employed as a radiation source, has a very rich spectrum in Mo II lines in UV region at the aforementioned plasma parameters. All spectra are recorded side on in the imaging mode of the ICCD camera and spectral lines are obtained applying inverse Abel transform. In cases of partially overlapping lines we apply a multi-peak fit procedure. Well isolated Mo I and Mo II spectral lines, not just from UV region, are used in Saha-Boltzmann method to estimate electron temperature and electron density. Width of well researched He I 388.86 nm line is employed as an independent check of electron density value. All Stark width results are presented normalized to 1 × 1023 m−3 electron density.