Average Electron Density Research Articles

Vibrational kinetics in repetitively pulsed atmospheric pressure nitrogen discharges: average-power-dependent switching behaviour

Characterisation of the vibrational kinetics in nitrogen-based plasmas at atmospheric pressure is crucial for understanding the wider plasma chemistry, which is important for a variety of biomedical, agricultural and chemical processing applications. In this study, a 0-dimensional plasma chemical-kinetics model has been used to investigate vibrational kinetics in repetitively pulsed, atmospheric pressure plasmas operating in pure nitrogen, under application-relevant conditions (average plasma powers of 0.23–4.50 W, frequencies of 1–10 kHz, and peak pulse powers of 23–450 W). Simulations predict that vibrationally excited state production is dominated by electron-impact processes at lower average plasma powers. When the average plasma power increases beyond a certain limit, due to increased pulse frequency or peak pulse power, there is a switch in behaviour, and production of vibrationally excited states becomes dominated by vibrational energy transfer processes (vibration–vibration (V–V) and vibration–translation (V–T) reactions). At this point, the population of vibrational levels up to increases significantly, as a result of V–V reactions causing vibrational up-pumping. At average plasma powers close to where the switching behaviour occurs, there is potential to control the energy efficiency of vibrational state production, as small increases in energy deposition result in large increases in vibrational state densities. Subsequent pathways analysis reveals that energy in the vibrational states can also influence the wider reaction chemistry through vibrational–electronic (V–E) linking reactions (N + N N + N and N + N N + N), which result in increased Penning ionisation and an increased average electron density. Overall, this study investigates the potential for delineating the processes by which electronically and vibrationally excited species are produced in nitrogen plasmas. Therefore, potential routes by which nitrogen-containing plasma sources could be tailored, both in terms of chemical composition and energy efficiency, are highlighted.

Quantum and Classical Evaluations of Carboxylic Acid Bioisosteres: From Capped Moieties to a Drug Molecule.

Using the Quantum Theory of Atoms in Molecules, the average electron density (AED) tool was developed and employed to quantitatively evaluate the similarities between bioisosteric moieties in drug design. Bioisosteric replacements are valuable in drug molecules to fine-tune their pharmacokinetic and pharmacodynamic properties while maintaining their biological activity. This study was performed on non-classical bioisosteres of carboxylic acid. It was found that the AED of a given bioisostere is generally transferable, within less than 5% difference, irrespective of its environment. It was shown that the AED tool succeeds at depicting not only the similarities of bioisosteric groups but also at highlighting, as counter examples, the differences in non-bioisosteric groups. For the first time, the AED was used to evaluate bioisosterism in an FDA-approved drug molecule, furosemide, and in five analogues of this medicine. In one of the analogues, non-bioisosteric moieties were exchanged, and in four of the analogues, carboxylic acid was replaced with either furan or sulfonamide, and vice versa. It was also found that irrespective of the pH, the AED tool consistently reproduced experimental predictions. The distinct power of the AED tool in quantitatively and precisely measuring the similarity among bioisosteric groups is contrasted with the relatively ambiguous bioisosteric evaluations through the classical qualitative electrostatic potential (ESP) maps. The ESP maps were demonstrated to fail, even qualitatively, in depicting the similarities, in some cases.

Numerical simulation on the characteristics of a micro-hollow cathode discharge with external surface of the cathode covered by a dielectric layer

Being able to generate a plasma denser than that in the usual micro-hollow cathode discharge (MHCD) device, a MHCD with the cathode outer surface covered by a dielectric layer has been numerically simulated in atmospheric pressure helium with a two-dimensional fluid model in this paper. Results indicate that before reaching a steady state, the covered MHCD sequentially undergoes three phases. In the initial phase, a strong discharge and a weak discharge appear in the vicinities of the cathode and the anode, respectively. Then, a positive streamer propagates along the axis from the anode to the cathode. After that, the entire gap between the two electrodes is filled with discharges. In addition, the evolution of averaged densities is given for various species. Moreover, voltage and current curves are compared for the covered and uncovered MHCDs in the steady state. As expected, the covered MHCD has an averaged electron density higher than that of the uncovered MHCD in the steady state. These results are helpful in generating an atmospheric pressure plasma with high electron density, which is important for the extensive applications of MHCD.

The 700 ks Chandra Spiderweb Field

Aims. We present the X-ray imaging and spectral analysis of the diffuse emission around the radio galaxy J1140-2629 (the Spiderweb galaxy) at z = 2.16 and of its nuclear emission, based on a deep (700 ks) Chandra observation. Methods. We obtained a robust characterization of the unresolved nuclear emission, and carefully computed the contamination in the surrounding regions due to the wings of the instrument point spread function. Then, we quantified the extended emission within a radius of 12 arcsec. We used the Jansky Very Large Array radio image to identify the regions overlapping the jets, and performed X-ray spectral analysis separately in the jet regions and in the complementary area. Results. We find that the Spiderweb galaxy hosts a mildly absorbed quasar, showing a modest yet significant spectral and flux variability on a timescale of ∼1 year (observed frame). We find that the emission in the jet regions is well described by a power law with a spectral index of Γ ∼ 2 − 2.5, and it is consistent with inverse-Compton upscattering of the cosmic microwave background photons by the relativistic electrons. We also find a roughly symmetric, diffuse emission within a radius of ∼100 kpc centered on the Spiderweb galaxy. This emission, which is not associated with the jets, is significantly softer and consistent with thermal bremsstrahlung from a hot intracluster medium (ICM) with a temperature of kT = 2.0−0.4+0.7 keV, and a metallicity of Z < 1.6 Z⊙ at 1σ c.l. The average electron density within 100 kpc is ne = (1.51 ± 0.24 ± 0.14) × 10−2 cm−3, corresponding to an upper limit for the total ICM mass of ≤(1.76 ± 0.30 ± 0.17) × 1012 M⊙ (where error bars are 1σ statistical and systematic, respectively). The rest-frame luminosity L0.5 − 10 keV = (2.0 ± 0.5) × 1044 erg s−1 is about a factor of 2 higher than the extrapolated L − T relation for massive clusters, but still consistent within the scatter. If we apply hydrostatic equilibrium to the ICM, we measure a total gravitational mass M(<100 kpc) = (1.5−0.3+0.5) × 1013 M⊙ and, extrapolating at larger radii, we estimate a total mass M500 = (3.2−0.6+1.1) × 1013 M⊙ within a radius of r500 = (220 ± 30) kpc. Conclusions. We conclude that the Spiderweb protocluster shows significant diffuse emission within a radius of 12 arcsec, whose major contribution is provided by inverse-Compton scattering associated with the radio jets. Outside the jet regions, we also identified thermal emission within a radius of ∼100 kpc, revealing the presence of hot, diffuse baryons that may represent the embryonic virialized halo of the forming cluster.

Applying Thomson scattering to diagnosing turbulent density and velocity fluctuations in a gas-puff z-pinch

The electron plasma wave feature (EPW) in the time-resolved Thomson scattering spectrum is used to obtain the local electron density in imploding high energy density gas-puff z-pinch plasmas. The optical setup was optimized to allow the relatively weak EPW feature obtained from 1 MA imploding neon gas-puff z-pinches to be seen above the continuum emission as well as the brighter ion acoustic wave (IAW) feature. Using a frequency-doubled Nd:YLF laser (E = 10 J, λ = 526.5 nm, Δt= 2.3 ns, spot size ∼ 250 μm) and two visible light streak cameras, we determined the average electron density in the imploding plasma sheath 40 ns prior to stagnation to be ne=2.5×1018/cm3. At pinch time, it reached ne=1.7×1019/cm3. The electron temperature during implosion measured via the IAW (approximately 50 eV) was four times lower than the implosion electron temperature measured via the EPW (approximately 200 eV), assuming that neither feature is affected by turbulent fluctuations in the plasma. In order for the electron temperatures inferred from the EPW and IAW spectral features to be self-consistent, we find that it is necessary to include velocity fluctuations in the analysis of the IAW feature peaks and corresponding density fluctuation in the peak widths of the EPW feature.

Effects of the ground-electrode temperature on the plasma physicochemical processes and biological inactivation functions involved in surface dielectric barrier discharge

In this work, a surface dielectric barrier discharge (SDBD) device coupled with power electronics technology was designed for precise control of the ground-electrode temperature to investigate the dynamic behavior of the physicochemical processes and biological inactivation functions involved in SDBD plasma. It was found that an increase of the electrode temperature from 30 to 210 °C reduced the breakdown voltage and increased the current pulse amplitude because the reduced electric field strength and average electron density of the SDBD plasma were consistently enhanced. The change in the plasma-chemistry mode (O3-dominant to NO x -dominant) was more sensitive to the ground-electrode temperature than that of the power density and gas temperature. O3 in the gas and liquid phases could not be detected at electrode temperatures above 90 °C, and the NO x mode almost immediately occurred after the plasma was turned on for ground-electrode temperatures of ⩾180 °C. The increase in the electrode temperature increased the acidity of the plasma-activated water and, more importantly, short-lived reactive species OH and NO were detected at electrode temperatures ⩾120 °C in the case of aqueous solutions treated directly with SDBD plasma. The biological inactivation function of the SDBD plasma, i.e. for bacterial suspensions and tumor cell cultures, was improved by about three orders of magnitude and 40% at the optimal electrode temperatures of 180 °C and 120 °C, respectively. This is an important breakthrough for development of SDBD-based biomedical devices for specific purposes on a commercial level by regulating the plasma chemistry through the ground-electrode temperature, overcoming the limitations of chamber heating and compressed air supply.

Evaluating Synthetic CT Calculation Accuracy in a 1.5 T MR-Linac Clinical Workflow

<h3>Purpose/Objective(s)</h3> The adapt to shape (ATS) workflow of 1.5 T MR-Linac 1.5 allows plan adaptation according to the new patient anatomy with a plan optimization on daily magnetic resonance imaging (MRI)-based synthetic computed tomography (syCT). This study evaluates the effectiveness of introducing into the clinical workflow a per/patient assessment of the minimum expected dosimetric errors associated with an MRI-based syCT adapted plan. <h3>Materials/Methods</h3> 55 patients treated at 1.5T MR-Linac in different tumors sites were consecutively included in this study. Each patient underwent CT and MR simulation scans for treatment plan preparation. The patient's target and organs at risk (OARs) were contoured in a treatment planning system, and a reference CT plan was generated using eight to twelve individual beam angles; the plan contains electronic density (ED) bulk assignment information i.e., the contours to use in the ATS workflow, and their corresponding average ED, the priority of each contour respect to density assignment in case of contour overlaps. To assess the dosimetric error made by using ATS procedure, for each patient the plan was recalculated on ideal syCT obtained from the reference CT by forcing the drawn contours to the average ED as indicated on the reference CT plan. Targets and OARs dose-volume histogram (DVH) of the CT and syCT plans and the dose distributions using gamma analysis 3%-3mm and 2%2mm criteria, were compared. <h3>Results</h3> For the dose distribution on syCT and CT, the average pass rate of gamma analysis using the 3%/3 mm and 2%/2 mm criteria were higher than 99% and 98%, for 47 patients out of 55; similarly targets and OARs DVH dose differences remained below 1%. For the remaining 8 patients, the source of discrepancy was investigated, and the CT reference plan was reworked to decrease the dosimetric differences on the syCT plan; the results obtained are shown in Table 1. <h3>Conclusion</h3> The accuracy of the plan adaptation on MR-based syCT may be affected by several factors. The inclusion of a per-patient assessment in the clinical workflow allows monitoring and possible optimization before the start of the radiotherapy course.

Improving the clinical workflow of a MR-Linac by dosimetric evaluation of synthetic CT.

Adaptive radiotherapy performed on the daily magnetic resonance imaging (MRI) is an option to improve the treatment quality. In the adapt-to-shape workflow of 1.5-T MR-Linac, the contours of structures are adjusted on the basis of patient daily MRI, and the adapted plan is recalculated on the MRI-based synthetic computed tomography (syCT) generated by bulk density assignment. Because dosimetric accuracy of this strategy is a priority and requires evaluation, this study aims to explore the usefulness of adding an assessment of dosimetric errors associated with recalculation on syCT to the clinical workflow. Sixty-one patients, with various tumor sites, treated using a 1.5-T MR-Linac were included in this study. In Monaco V5.4, the target and organs at risk (OARs) were contoured, and a reference CT plan that contains information about the outlined contours, their average electron density (ED), and the priority of ED assignment was generated. To evaluate the dosimetric error of syCT caused by the inherent approximation within bulk density assignment, the reference CT plan was recalculated on the syCT obtained from the reference CT by forcing all contoured structures to their mean ED defined on the reference plan. The dose–volume histogram (DVH) and dose distribution of the CT and syCT plan were compared. The causes of dosimetric discrepancies were investigated, and the reference plan was reworked to minimize errors if needed. For 54 patients, gamma analysis of the dose distribution on syCT and CT show a median pass rate of 99.7% and 98.5% with the criteria of 3%/3 mm and 2%/2 mm, respectively. DVH difference of targets and OARs remained less than 1.5% or 1 Gy. For the remaining patients, factors (i.e., inappropriate ED assignments) influenced the dosimetric agreement of the syCT vs. CT reference DVH by up to 21%. The causes of the errors were promptly identified, and the DVH dosimetry was realigned except for two lung treatments for which a significant discrepancy remained. The recalculation on the syCT obtained from the planning CT is a powerful tool to assess and decrease the minimal error committed during the adaptive plan on the MRI-based syCT.

Low power degradation of perfluorooctane sulfonate (PFOS) in water using a nanosecond pulsed atmospheric pressure plasma

The prevalence and persistence of perfluoroalkyl substances (PFAS) has led to significant concerns over the damage they can have on human health and the environment, particularly when they contaminate bodies of water. In this work, a plasma driven with high-voltage (20 kV) pulses of varying duration (50–400 ns) and frequency (0.5–10 kHz) is investigated for degrading perfluorooctane sulfonate (PFOS) in water. The concentration of PFOS in solution decreased with repeated passes through the reactor. Increasing the power consumption of the plasma, either by increasing the pulse width or the frequency, improved the rate of PFOS loss but decreased the energy efficiency. For instance, reducing the frequency of the pulse from 10 kHz to 500 Hz decreased the power consumption by over an order of magnitude while requiring about twice as much time to reduce 50% of the PFOS signal. Time-averaged emission spectroscopy showed that increasing the frequency decreased the average electron density of the plasma while infrared measurements indicate only a modest increase to the temperature of the reactor. In contrast, increasing the pulse width from 50 ns to 400 ns did not have a significant impact on the average electron density or the reactor temperature. Spectroscopy revealed the presence of photons with energies >5 eV which could contribute to PFOS loss. This work shows that the main factor determining PFOS loss is the contact time between the plasma reactor and the solution, which implies the most energy efficient operating parameters for PFOS degradation comes from minimizing the duration and frequency of the high-voltage pulses to reduce power consumption.

Preoperative Prediction of the Aggressiveness of Oral Tongue Squamous Cell Carcinoma with Quantitative Parameters from Dual-Energy Computed Tomography

ObjectivesTo determine whether quantitative parameters derived from dual-energy computed tomography (DECT) were predictive of the aggressiveness of oral tongue squamous cell carcinoma (OTSCC) including the pathologic stages, histologic differentiation, lymph node status, and perineural invasion (PNI).MethodsBetween August 2019 and March 2021, 93 patients (mean age, 54.6 ± 13.8 years; 66 men) with pathologically diagnosed OTSCC were enrolled in this prospective study. Preoperative DECT was performed and quantitative parameters (e.g., slope of the spectral Hounsfield unit curve [λHu], normalized iodine concentration [nIC], normalized effective atomic number [nZeff], and normalized electron density [nRho]) were measured on arterial phase (AP) and venous phase (VP) DECT imaging. Quantitative parameters from DECT were compared between patients with different pathologic stages, histologic differentiation, lymph node statuses, and perineural invasion statuses. Logistic regression analysis was utilized to assess independent parameters and the diagnostic performance was analyzed by the receiver operating characteristic curves (ROC).ResultsλHu and nIC in AP and λHu, nZeff, and nIC in VP were significantly lower in stage III–IV lesions than in stage I–II lesions (p < 0.001 to 0.024). λHu in VP was an independent predictor of tumor stage with an odds ratio (OR) of 0.29, and area under the curve (AUC) of 0.80. λHu and nIC were higher in well-differentiated lesions than in poorly differentiated lesions (p < 0.001 to 0.021). The nIC in VP was an independent predictor of histologic differentiation with OR of 0.31, and AUC of 0.78. λHu and nIC in VP were lower in OTSCCs with lymph node metastasis than those without metastasis (p < 0.001 to 0.005). λHu in VP was the independent predictor of lymph node status with OR of 0.42, and AUC of 0.74. No significant difference was found between OTSCCs without PNI and those with PNI in terms of the quantitative DECT parameters.ConclusionDECT can be a complementary means for the preoperative prediction of the aggressiveness of OTSCC.

Pulsed plasma flow diagnostics

This paper presents the results of optical and probe diagnostics of hydrogen plasma flow in a coaxial plasma accelerator. The triple probe and the Optosky ATP2000P linear spectrometer with a spectral range of 200-1100 nm were used for measuring the electron current and obtaining the hydrogen plasma emission spectrum. The individual spectral lines were observed using an M833 monochromator spectrometer with a spectral resolution of 0.024 nm. From the measured electron currents and emission spectrums, the electron densities in the flux of a hydrogen pulsed plasma were calculated. We used the Stark method of Hβ hydrogen line broadening for calculations of electron densities. The obtained experimental results from the probe and spectroscopic measurements of electron density correspond well. In this work, we also obtained the dependence of the electron density on the voltages applied to the capacitor bank. The electron density increases with increasing voltage, because of the increased energy applied to the discharge. The average electron densities in the plasma flux showed &nbsp;1.13&nbsp;∙&nbsp;1021 m-3, &nbsp;4.14&nbsp;∙&nbsp;1021 m-3, and &nbsp;5.57&nbsp;∙&nbsp;1021 m-3 at three values of voltages of 3 kV, 4 kV, and 5 kV, respectively.

Analysis of Information Entropies for He-Like Ions

The electronic structure, a special quality of an atomic or molecular system, is the major factor for further realization of physical results. However, in this paper, we present the topical issue of normalized electron density in position and momentum spaces, Shannon, Rényi, and Tsallis entropies to quantify the reach of electron delocalization for several atomic systems. Hartree-Fock-Roothaan (HFR) wave function is performed and considered for He-like ions using single-Zeta 𝛽-type orbital (βTOs) basis set to investigate the affecting of electron density and information entropies. The electron density maxima in position space are raised, and their positions move toward the nucleus as Z increases, in accordance with the increasing attractive force of the nucleus, and vice versa in momentum space. Shannon’s entropy has impacted the delocalization of the electron in different atomic systems. In the limit γ→1, both Rényi and Tsallis entropy results recover Shannon’s entropy value. Rényi and Tsallis entropies decrease by increasing γ. Indeed, the estimated results have been calculated via the Wolfram Mathematica program and have good agreement with the literature results. The obtained results may be a useful reference for future studies on theoretical information quantities. Doi: 10.28991/ESJ-2022-06-04-08 Full Text: PDF

A novel sulfonated aromatic polyimide synthesis and characterization: Energy calculations, QTAIM simulation study of the hydrated structure of one unit

AbstractA new type of sulfonated polyimide was synthesized from a one‐step polycondensation reaction with perylene‐3,4,9,10‐tetracarboxylic dianhydride and 4,4′‐diamino‐2,2′‐stilbenedisulfonic. Pure characterization of sulfonated polyimide (SPI) was performed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, thermogravimetric analysis, differential thermal gravimetric analysis, ultraviolet–visible spectroscopy, and solubility tests. Moreover, the SPI film was prepared by a thermal imidization step heating procedure. Furthermore, quantum chemical calculations of the synthesized SPI were investigated with density functional theory (DFT) and time‐dependent density functional theory. By calculating the frontiers molecular orbital energies of the obtained polyimide, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and the energy gap (Δ) values were found for the one structural unit and three structural units of SPI, respectively. Also, QTAIM was carried out based on the AIMAll program. With the increase in water molecules, the average electronic energy density (HBCP) value decreased according to the results of QTAIM. The SPI can be used as a potential membrane in fuel cells.

Spectroscopic and imaging observations of transient hot and cool loops by IRIS and SDO

ABSTRACT Coronal loops are the basic building blocks of the solar atmosphere and are observed on various length scales. However, their formation mechanism is still unclear. In this paper, we present spectroscopic and imaging observations of small-scale transients and the subsequent formation of transient loops. For this purpose, we have utilized the multiwavelength observations recorded by the Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS) slit-jaw imager (SJI), along with spectroscopic measurements provided by IRIS. For the photospheric magnetic field data, we obtained line-of-sight magnetogram data provided by the Helioseismic and Magnetic Imager (HMI). Small-scale transients are simultaneously observed with several EUV and UV passbands of AIA and IRIS/SJI. The HMI magnetogram provides evidence of negative flux cancellations beneath these transients. Differential emission measure (DEM) analysis shows that one of the transients attains temperatures up to 8 MK whereas another one only reaches 0.4 MK. These transients further lead to the formation of small-scale loops with similar temperature distributions, thus termed hot and cool loops respectively. During the course of events, the IRIS slit was rastering the region and thus provided spectroscopic measurements at both transients and associated loops. This enabled us to perform in-depth investigations of the hot and cool loops. Using a density-sensitive O iv line pair, we obtained average electron densities along the hot and cool loops to be 1011.2 and 1010.8 cm−3 respectively. Energy estimates suggest that flux cancellation could easily power the hot transient, while it is insufficient for the cool transient. Lifetime estimates and magnetic field extrapolation suggest the presence of small-scale and fine structures within these loops. The results provide crucial ingredients for the physics of loop formation and the thermodynamics involved.

Trapped Electron Effects in Transient Helium Sub-Nanosecond Atmospheric Microplasmas

For fast rising voltage in planar electrode geometry, it is shown that electrons can be trapped in a potential well between a reversed plasma-driven electric field and the applied electrode voltage. This trapping mechanism occurs in a subset of the inter-electrode gap and leads to increased average electron density in nanosecond discharges. There is a threshold ratio of the applied voltage to rise time for which the electrons experience a pendulum-like motion without any polarity change in the applied voltage. The fast rise time of the driven voltage leads to an enhanced trapped effect and augments the electron density of >5 eV energetic electrons, which can be exploited to produce excited chemical species and high plasma densities on nanosecond timescales.

Spatially resolved X-ray study of the mixed morphology SNR G359.1-0.5

ABSTRACT We present a detailed spatially resolved X-ray study of Chandra observations towards the central region of the supernova remnant (SNR) G359.1-0.5. We removed 168 point-like sources and performed an adaptive smoothing on the entire field-of-view of the Chandra ACIS-I observation. The images obtained show an extended X-ray emission below $4.0\, {\rm keV}$ that partially fills the interior of G359.1-0.5. In order to characterize the X-ray emission, we divide the emitting area into 10 different regions inside the remnant. We identify the presence of at least four emission lines that confirm the thin thermal plasma origin. All spectral regions are well fitted by a recombining plasma model (VRNEI) with an absorbing column density range from 1.5 to $2.1\times 10^{22}\, {\rm cm}^{-2}$, and electron temperatures from 0.14 to $0.19\, {\rm keV}$. We also calculated an average electron density of $0.7\, {\rm cm}^{-3}$, estimated an age of 2.8 × 104 yr for the remnant, which can be lower if the filling factor is considered, and an X-ray luminosity of $1.6 \times 10^{35} \, {\rm erg}\, {\rm s}^{-1}$. Finally, we show that the X-ray emission is morphologically anti-correlated with adjacent CO clouds interacting with the SNR. Our results favour that the recombining plasma inside G359.1-0.5 could be explained via adiabatic cooling.

Distances of galactic radio pulsars; first quadrant: −2° &amp;lt; ℓ &amp;lt; 90° and −2° &amp;lt; b &amp;lt; 2°

ABSTRACT Distance versus dispersion measure relations are constructed for Galactic radio pulsars in small solid angle intervals. The calculations are based on some basic criteria, as well as using the independent distance measurements of well examined pulsars for the first Galactic quadrant, including Galactic central directions. Values of average free electron density for these regions are derived from the fits to distance versus dispersion measure relations and checked for consistency and smoothness. The effects of plasma in the Galactic arms and within the central parts of the Galactic bulge region are also compared and discussed. Our adopted distances for the radio pulsars are compared with the ones given in some other models. Some basic results on distributions of the radio pulsars and the plasma are presented.

Monitoring Space Weather: Using Automated, Accurate Neural Network Based Whistler Segmentation for Whistler Inversion

AbstractIt is challenging, yet important, to measure the—ever‐changing—cold electron density in the plasmasphere. The cold electron density inside and outside of the plasmapause is a key parameter for radiation belt dynamics. One indirect measurement is through finding the velocity dispersion relation exhibited by lightning induced whistlers. The main difficulty of the method comes from low signal‐to‐noise ratios for most of the ground‐based whistler components. To provide accurate electron density and ‐shell measurements, whistler components need to be detectable in the noisy background, and their characteristics need to be reliably determined. For this reason, precise segmentation is needed on a spectrogram image. Here, we present a fully automated way to perform such an image segmentation by leveraging the power of convolutional neural networks, a state‐of‐the‐art method for computer vision tasks. Testing the proposed method against a manually, and semi‐manually segmented whistler data set achieved 10% relative electron density prediction error for 80% of the segmented whistler traces, while for the shell, the relative error is 5% for 90% of the cases. By segmenting more than 1 million additional real whistler traces from Rothera station Antarctica, logged over 9 years, seasonal changes in the average electron density were found. The variations match previously published findings, and confirm the capabilities of the image segmentation technique.

First principles studies on the electronic and contact properties of single layer 2H-MoS2/1T'-MX2 heterojunctions.

Constructed via in-plane heterojunction contacts between the semiconducting 2H phase (as the channel) and the metallic 1T' phase (as the electrode), two-dimensional (2D) transition metal dichalcogenide (TMD) field-effect transistors (FETs) have received much recent attention because they significantly reduce contact resistance. In this paper, ab initio quantum transport simulation is done to study and predict the electronic states and contact properties of the 2H-MoS2/1T'-MX2 (WS2, TaSe2, NbSe2, MoSe2, TaS2, and NbS2) in-plane heterojunctions. It is found that the interfacial states are not obvious and the fluctuation of the average electron density at the 1T'/2H phase boundary is small for all 2H-MoS2/1T'-MX2 heterojunctions. The average electrostatic potential differences (ΔV) are all negative, which is beneficial to promote the charge transfer from 1T'-MX2 to 2H-MoS2. Moreover, the p-type Schottky contact of the 2H-MoS2/1T'-MX2 heterojunctions is formed and the ΦSB,P values are 0.609 eV, 0.625 eV, 0.641 eV, 0.617 eV, 0.469 eV and 0.477 eV for 1T'-WS2, 1T'-TaSe2, 1T'-NbSe2, 1T'-MoSe2, 1T'-TaS2, and 1T'-NbS2, respectively. The results provide theoretical guidance for designing two-dimensional material devices.

One-dimensional simulation of Ar dielectric barrier discharge driven by combined rf/dc sources at atmospheric pressure

&lt;sec&gt;We present the dielectric barrier discharge (DBD) mechanism of argon (Ar) plasma driven by a combination of radio frequency (rf) voltage source and direct current (dc) voltage source at atmospheric pressure, based on one-dimensional self-consistent coupled fluid model. Using the finite element method (FEM) to numerically calculate the model, the average value of period average electron density varying with the average value of period average gas voltage in one rf period, and the variation of the minimum rf sustaining voltage are obtained under different dc voltages. In addition, the spatiotemporal distribution of the electron density and electron generation rate, the spatial distribution of electron temperature, and the time-domain variation of electron conduction current flowing to the dielectric are studied. The results show that the introduction of the dc voltage source has a significant effect on the rf discharge process of atmospheric pressure Ar gas, and the parameters of the plasma state are changed correspondingly. The discharge process is mainly controlled by the air gap voltage, and the dc voltage affects the gap voltage by changing the charge density on the dielectric surface. The minimum rf sustaining voltage &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;rf,min &lt;/sub&gt;first increases and then decreases with the increase of dc voltage. The amplitude of rf minimum sustaining discharge voltage is changed by the dc voltage. And when the amplitude is reached or exceeded, the discharge is controlled by the rf power supply.&lt;/sec&gt;&lt;sec&gt;On the one hand, in the &lt;i&gt;α&lt;/i&gt; mode, when the dc voltage is low, electrons are generated near the ground electrode. The electric field intensity in the ionization area is too small to maintain ionization. When the dc voltage is high, the sheath is formed, and electrons are generated near the rf sheaths on both sides and the boundary of the plasma region. In the γ mode, when the rf voltage amplitude is equal to or greater than the rf minimum sustain discharge voltage amplitude, i.e. &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;rf &lt;/sub&gt;≥ &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;rf,min&lt;/sub&gt;, the generation and distribution of electrons are almost unaffected by the dc voltage.&lt;/sec&gt;&lt;sec&gt;On the other hand, in the &lt;i&gt;α&lt;/i&gt; mode, the ionization cannot be sustained for the low dc voltage, resulting in the failure to form the main plasma area. Therefore, the electron temperature is generally high. Owing to the high electron density near the ground electrode, the electron temperature is higher. The electron density near the dielectric is less than that near the electrode, so the temperature is lower. When the dc voltage is getting larger, the sheath and the main plasma region are formed. The dc voltage significantly affects the electron temperature by controlling the sheath voltage and the length of the main plasma region.&lt;/sec&gt;&lt;sec&gt;Finally, in the α mode, the electron density near the medium is very low and the air gap voltage is negative for the low dc voltage. As a result, few electrons can reach the surface of the dielectric, and the conduction current of electrons flowing to the medium is very small. With the increase of the dc voltage, the electric field across air gap increases, and electrons, under the action of the electric field, flow from the dielectric surface. The sheath having formed, some speedy non-localization electrons that have reached the dielectric surface are reflected back to the sheath, resulting in a significant reduction in the number of electrons that can reach the dielectric surface.&lt;/sec&gt;