Enhanced Electron Density Research Articles

Влияние подсветки на квантовое время жизни в селективно-легированных одиночных GaAs квантовых ямах с короткопериодными AlAs/GaAs-сверхрешеточными барьерами

Impact of illumination on high-mobility dense 2D electron gas in selectively doped single GaAs quantum well with short-period AlAs/GaAs superlattice barriers at T = 4.2 K in magnetic fields B < 2 T has been studied. It was demonstrated that illumination at low temperatures gives rise to enhancement of electron density, mobility and quantum lifetime in studied heterostructures. The enhancement of quantum lifetime after illumination for single GaAs quantum well with modulated superlattice doping had been explained as consequence of decrease in effective concentration of remote ionized donors.

Ionospheric Modulation by EMIC Wave‐Driven Proton Precipitation: Observations and Simulations

AbstractProtons of tens of keV can be resonantly scattered by electromagnetic ion cyclotron (EMIC) waves excited in the magnetosphere, resulting in proton precipitation down to the upper atmosphere. In this study, we report for the first time the ionospheric height‐dependent ionization in response to EMIC‐associated isolated proton aurora (IPA) using simultaneous space‐borne and ground‐based measurements. On 06 March 2019, the Polar Orbiting Environmental Satellites observed significant proton precipitation in the dusk sector (MLT ∼ 19), while ground‐based magnetometers detected a clear signature of EMIC waves. Meanwhile, the conjugated all sky imager captured an IPA and the nearby Poker Flat incoherent scatter radar (PFISR) showed enhanced electron density in the E region, suggesting a potential consequence of the EMIC wave‐driven proton precipitation. The Global Airglow model simulations confirmed the dominant impact of proton precipitation on the ionosphere and agreed well with PFISR observations. This study confirmed physical links from the magnetosphere to the ionosphere through EMIC‐driven proton precipitation.

Callisto's Atmosphere: First Evidence for H2 and Constraints on H2O

AbstractWe explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope from sublimated H2O and radiolytically produced H2 using the Direct Simulation Monte Carlo method. The spatial morphology of this corona produced via photoelectron and magnetospheric electron‐impact‐induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near‐surface O2 component. Our results indicate that sublimated H2O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark nonice or ice‐poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H2 component can reproduce the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by Galileo's plasma‐wave instrument, providing the first evidence of H2 in Callisto's atmosphere. The range of H2 surface densities explored, under a variety of conditions, that are consistent with these observations is ∼(0.4–1) × 108 cm−3. The simulated H2 escape rates and estimated lifetimes suggest that Callisto has a neutral H2 torus. We also place a rough upper limit on the peak H2O number density (≲108 cm−3), column density (≲1015 cm−2), and sublimation flux (≲1012 cm−2 s−1), all of which are 1–2 orders of magnitude less than that assumed in previous models. Finally, we discuss the implications of these results, as well as how they compare to Europa and Ganymede.

Disturbances of electron density in the high latitude upper (F-region) ionosphere induced by X-mode HF pump waves from EISCAT UHF radar observations

The paper presents experimental results concerning disturbances of electron density in the high latitude ionosphere F-region, induced by powerfulHF radio waves (pump waves) with extraordinary (X-mode) polarization. The experiments were carried out at the EISCAT/Heating facility at Tromsø, Norway. The EISCAT UHF incoherent scatter radar (ISR), running at 930 MHz, co-located with a heating facility, was used to detect the disturbances of electron density. In the course of the experiments, the X-mode HF pump waves radiated into the F-region towards the magnetic zenith at different pump frequencies and ratios of the pump frequency to the critical frequency of the F2 layer.The effective radiated power was ERP = 360–820 MW. An increase in electron densities was found in a wide altitude range, giving rise to field-aligned ducts with enhanced electron density. The features and behavior of the ducts were investigated. It was revealed that the ducts are formed under quiet background geophysical conditions in a wide altitude range up to the upper altitude limit of EISCAT ISR measurements, when the pump frequencies were both below and above the critical frequency of the F2 layer (fH ≤ foF2 or fH > foF2). A plausible formation mechanism of the ducts is discussed.

Nb@Ge13/14]3−: New Family Members of Ge‐Based Intermetalloid Clusters

During the past two decades, single-atom-centered medium-sized germanium clusters [M@Gen ] (M=transition metals, n>12) have been extensively explored, both from theoretical perspectives and experimental gas-phase syntheses. However, the actual structural arrangements of the Ge13 and Ge14 endohedral cages are still ambiguous and have long remained an unresolved problem for experimental implementation. In this work, we successfully synthesize 13-/14-vertex Ge clusters [Nb@Ge13 ]3- (1) and [Nb@Ge14 ]3- (2), which are structurally characterized and exhibit unprecedented topologies, neither classical deltahedra nor 3-connected polyhedral structures. Theoretical analysis indicates that the major stabilization of the Ge backbones arises due to the substantial interaction of Ge 4p-AOs with the endohedral Nb 4d-AOs through three/four-center two-electron bonds with an enhanced electron density accumulated over the shortest Nb-Ge13 contact in 1. Low occupancies of the direct two-center two-electron (2c-2e) Nb-Ge and Ge-Ge σ bonds point to a considerable degree of electron delocalization over the Ge cages revealing their electron deficiency.

Extension of the Electron Density Enhancement From Middle to High Latitudes Observed by Swarm‐A in Summer of the Southern Hemisphere

AbstractThe major causal mechanism for the eastward contraction of the electron density (Ne) enhancement associated with the southern Midlatitude Summer Nighttime Anomaly (MSNA) was attributed to the thermospheric neutral wind at the middle geomagnetic latitude in the fixed local time coordinate. In the study, the Ne and horizontal cross‐track ion drifts observed by the Swarm‐A satellite at 462 km altitude show that the horizontal drifts can drive the Ne enhancement of the southern MSNA in the local summer of the Southern Hemisphere. Both the eastward and westward ion drifts transport the enhancement from the middle to the high geomagnetic latitudes, which results in the enhancement evolving at all the longitudes in the whole day.

Estimation Model of Global Ionospheric Irregularities: An Artificial Intelligence Approach

AbstractThe ionospheric sporadic E layer, the ionospheric irregularities of enhanced electron density, appears in the Earth's ionosphere at altitudes between 90 and 120 km, which supports the real‐world radio communication needs of many sectors reliant on ionosphere‐dependent decision‐making. The prediction of the occurrence of sporadic E layers has been extremely difficult due to the highly complex behavior. Conventional numerical methods are limited because of the inability to extract high‐level information from data. Deep learning is a powerful tool for mining latent features from data, which can theoretically avoid assumptions constraining physical methods. Inspired by feature extraction, we applied deep learning to explore latent relationships between mapping observable lower atmospheric data and ionospheric data from limited observations. The proposed model was trained with high‐resolution ERA5 data during 1 January 2007–30 August 2018 as input and corresponding ionospheric sporadic E data collected from COSMIC RO measurements as output. The results show that the model can learn complex relevance as bridges connecting the input and the desired output and obtain excellent performance and generalization capability by applying multiple evaluation criteria. Additionally, we established several model architecture training methods to explore the performance of the model with different input data. The statistic results show that model inference performance is proportional to the abundance of input information and is impacted by intraseasonal variability. The inference capability of the model achieves the best performance in the June–August (JJA) and December–February (DJF) seasons, which is the exact period of sporadic E layer significant occurrence, although different models are evaluated.

Disturbance Neutral Winds Effects on the Ionospheric Strip‐Like Bulge at Lower‐Middle Latitudes

AbstractDuring the geomagnetic storm on 3–6 November 2021, the in‐situ plasma density and the gridded total electron content (TEC) maps registered a persistent presence of the strip‐like bulges (electron density enhancement, also known as the shoulders in previous literatures) at lower‐middle latitudes. The observed strip‐like bulge resided in the Pacific‐America‐Atlantic sector and lasted from 07:00 UT on 4 November to 20:00 UT on 6 November. For the first time, the temporal evolution of the 2‐D strip‐like bulge was recorded by gridded TEC maps, though observations were limited over the North American continents. The TEC maps showed a continuous shrinking of the nightside midlatitude plasma band structure right before the presence of the narrow strip‐like bulge. Simultaneous measurements from the Ionospheric Connection Explorer satellite (ICON) revealed an equatorward turning of the field‐aligned ion transportation driven by the disturbance equatorward neutral winds. However, the enhanced fountain effect at low latitudes was not observed during the entire formation phase of the strip‐like bulge. We propose that the storm‐induced enhanced equatorward thermospheric neutral winds push the plasma equatorward along the field lines, and the plasma band structure was developed into the strip‐like bulge. In addition, the ion composition of both the plasma band structure and the strip‐like bulges are dominated by H+, and the maintenance of the strip‐like bulge could be due to the compensation of the downward plasmaspheric content flux.

Analysis of Electron Precipitation and Ionospheric Density Enhancements Due To Hiss Using Incoherent Scatter Radar and Arase Observations

AbstractPlasmaspheric hiss can cause energetic electron precipitation from the magnetosphere to the Earth's upper atmosphere and affect the ionospheric electron density profiles. In this study, we use Arase satellite measurements in the dayside plasmasphere to model the electron precipitation and the resultant ionospheric response, and compare the results to the electron density measured by the Poker Flat Incoherent Scatter Radar (PFISR). We analyzed two close conjunction events between Arase and PFISR at L ∼ 6 in the afternoon sector, when Arase was in the outer plasmasphere and traveled into the plasmaspheric plumes. Modest or strong hiss waves were observed with amplitudes higher than 50 pT during both events. Quasilinear modeling suggests that the hiss waves could cause intense electron precipitation ranging from several keV to several hundred keV energies. The electron density profiles at 60–90 km modeled by the Boulder Electron Radiation to Ionization (BERI) model suggest significant electron density enhancements due to the precipitating electrons. PFISR simultaneously observed electron density enhancements during both events, and provided evidence for the electron precipitation at altitudes down to <70 km. The temporal modulation of hiss caused the modulated density profiles in BERI modeling, but was not evident in PFISR observations. The modeled altitude profiles of the perturbed electron density overall agree with PFISR observation. At altitudes below 75 km, the modeled electron densities are lower than the observation, suggesting additional high energy electron precipitation possibly due to low frequency (<50 Hz) waves or hiss wave powers ducted to high latitudes.

Ionospheric Nighttime Enhancements in the Equatorial Region as Revealed by the Beidou Geostationary TEC Observations

AbstractIonospheric electron density enhancement at nighttime has been widely studied in the past decades. However, the mechanisms of this anomalous nighttime enhancement are not fully understood. In this study, we took advantage of the fidelity of geostationary total electron contents (GEO TECs) combined with the observations from three equatorial ionosondes to examine the morphology of equatorial ionospheric nighttime enhancements in the Asian‐Australian sector. The equatorial ionospheric nighttime enhancements from GEO TECs during 2016–2018 can be characterized by three categories. Each of these categories showed similar seasonal variations, with the maximal occurrence in the equinoxes. Interestingly, there was a strong correlation between the pre‐reversal enhancement (PRE) of the eastward equatorial electric field and these three types of equatorial ionospheric nighttime enhancements that were mostly accompanied by PRE inferred from foF2 and h'F2 from ionograms around dusk. Nevertheless, the formations of equatorial ionospheric nighttime enhancements could be associated with other factors, such as the equatorial electric fields and neutral winds, as well as associated plasma transports. This study provides a new perspective to explore the variations and the underlying physical processes of ionospheric nighttime enhancements.

Dual‐Atomic Catalysts Deduced from d−π Conjugated Metal−Organic Frameworks for Efficient Oxygen Evolution Reaction

AbstractA series of semiconductive cobalt‐based metal–organic framework (MOFs) are prepared in this work using 2,3,6,7,10,11‐hexaiminotriphenylene (HATP) as ligand and diverse metal ions as the second coordination centers (M = Mn, Ni, and Zn) (denoted as CoxM3‐x(HITP)2 MOFs). The series of bimetallic CoxM3‐x(HITP)2 MOFs exhibit ultrathin graphene‐like nanostructure, highly d–π conjugated network, large specific surface areas, and diverse metal coordination modes. Density functional theory calculations reveal the unique synergism between M (M = Mn, Ni, and Zn) and Co nodes, in which adjacent layers of M atoms can efficiently modulate the electron densities of Co atoms in Co3(HITP)2. As compared, CoxZn3‐x(HITP)2 MOF possesses substantially enhanced electron density around the Co atoms, dual‐metal atomic sites, and rich metal coordination modes, and exhibits superior electrochemical activity. Among them, CoxZn3‐x(HITP)2 displays the outperformed electrocatalytic performances of the oxygen evolution reaction (OER). Particularly, CoxZn3‐x(HITP)2 shows the lowest overpotential of 210 mV and good long‐term stability. This work develops an efficient strategy for designing and regulating atomically dispersed catalysts in conductive MOFs toward clean energy applications.

Two-dimensional conductive π-conjugated metal-organic frameworks as promising electrocatalysts for highly efficient hydrogen evolution reaction

Two-dimensional conductive π-conjugated metal-organic frameworks (2D c-MOFs), as a new promising electrocatalytic materials, have spurred great research interests, but the systematic research on the structure-property relationship of c-MOF-based electrocatalysts is scarcely reported. Herein we conduct a first-principles study on the screening of a family of 2D c-MOFs (TM3(HITN)2) as HER electrocatalysts, which are constructed by TM atoms and 2,3,8,9,14,15-hexaiminotrinaphthylene (HITN) functional groups. The data suggests that all these 2D TM3(HITN)2 possess metallic with good conductivity for electrochemical reactions due to their intrinsic π-electron conjugation and sufficient interaction between the TM atoms and the organic linkers. Through the complete computational screening, the Zr3(HITN)2 stands out because of its near-zero ΔG*H value and low activation energy barrier. Moreover, the distinguished HER performance of Zr3(HITN)2 can be attributed to the extremely enhanced electron density derived from the C-2p orbitals near the Fermi level accompanied by the size increase of the tri-dentated aromatic linkers. Hence, this study not only highlights a family of promising 2D c-MOF electrocatalysts toward HER, but also supplies a valuable insight on the design of novel and high-performance c-MOF-based materials for better electrocatalysis.

Explaining Solar Flare‐Induced Ionospheric Ion Upflow at Millstone Hill (42.6°N)

AbstractPrevious studies have shown that solar flares can significantly affect Earth's ionosphere and induce ion upflow with a magnitude of ∼110 m/s in the topside ionosphere (∼570 km) at Millstone Hill (42.61°N, 71.48°W). We use simulations from the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) and observations from Incoherent Scatter Radar (ISR) at Millstone Hill to reveal the mechanism of ionospheric ion upflow near the X9.3 flare peak (07:16 LT) on 6 September 2017. The ISR observed ionospheric upflow was captured by the TIEGCM in both magnitude and morphology. The term analysis of the F‐region ion continuity equation during the solar flare shows that the ambipolar diffusion enhancement is the main driver for the upflow in the topside ionosphere, while ion drifts caused by electric fields and neutral winds play a secondary role. Further decomposition of the ambipolar diffusive velocity illustrates that flare‐induced changes in the vertical plasma density gradient is responsible for ion upflow. The changes in the vertical plasma density gradient are mainly due to solar extreme ultraviolet (EUV, 15.5–79.8 nm) induced electron density and temperature enhancements at the F2‐region ionosphere with a minor and indirectly contribution from X‐ray (0–15.5 nm) and ultraviolet (UV, 79.8–102.7 nm).

Comparison of the tidal signatures in sporadic E and vertical ion convergence rate, using FORMOSAT-3/COSMIC radio occultation observations and GAIA model

Sporadic E or Es is a transient phenomenon where thin layers of enhanced electron density appear in the ionospheric E region (90–120 km altitude). The neutral wind shear caused by atmospheric tides can lead ions to converge vertically at E-region heights and form the Es layer. This research aims to determine the role of atmospheric solar and lunar tides in Es occurrence. For this purpose, radio occultation data of FORMOSAT-3/COSMIC have been used, which provide complete global coverage of Es events. Moreover, GAIA model simulations have been employed to evaluate the vertical ion convergence induced by solar tides. The results show both migrating and non-migrating solar tidal signatures and the semidiurnal migrating lunar tidal signature mainly in low and mid-latitude Es occurrence. The seasonal variation of the migrating solar tidal components of Es is in good agreement with those in the vertical ion convergence derived from GAIA at higher altitudes. Furthermore, some non-migrating components of solar tides, including semidiurnal westward wavenumbers 1 and 3 and diurnal eastward wavenumbers 2 and 3, also significantly affect the Es occurrence rate.Graphical

Low-latitude plasma blobs above Africa: Exploiting GOLD and multi-satellite in situ measurements

Low-latitude plasma blobs are localized density enhancements of electron density that are occasionally observed in the night-time tropical ionosphere. Two-dimensional (2D) imaging of this phenomenon has been rare and frequently restricted to Central/South America, which is densely covered with ground-based airglow imagers and Global Navigation Satellite System (GNSS) receivers. In Africa, on the contrary, no 2D image of a blob has been reported. Here we present two low-latitude blob events above Africa, one in the Northern summer and the other in winter, in the 2-dimensional Far-UltraViolet (FUV) images from the Global-scale Observations of the Limb and Disk (GOLD) mission. Additionally, multiple satellites (four spacecraft per event) on the Low-Earth-Orbit (LEO) encountered the blob events, some within the GOLD images and some outside. The LEO data support the robustness of GOLD observations and bridge time gaps between the consecutive images. Properties of the two blob events above Africa generally support the conclusions in a previous case study for Central/South America. Plasma therein exhibited higher O+ fraction and faster ion flow toward outer L-shells than the ambient. The blobs were conjugate to locally intensified Equatorial Ionization Anomaly crests without conspicuous equatorward-westward propagation. Our results demonstrate the usefulness of GOLD and multiple LEO satellites in monitoring the ionosphere above Africa, which is a fascinating laboratory of low-latitude electrodynamics but still waiting for more observatories to be deployed.

Satellite In Situ Electron Density Observations of the Midlatitude Storm Enhanced Density on the Noon Meridional Plane in the F Region During the 20 November 2003 Magnetic Storm

AbstractIonospheric storm enhanced density (SED) has been extensively investigated using total electron content deduced from GPS ground and satellite‐borne receivers. However, dayside in situ electron density measurements have not been analyzed in detail for SEDs yet. We report in situ electron density measurements of a SED event in the Northern Hemisphere (NH) at the noon meridian plane measured by the Challenging Minisatellite Payload (CHAMP) polar‐orbiting satellite at about 390 km altitude during the 20 November 2003 magnetic storm. The CHAMP satellite measurements render rare documentation about the dayside SED's life cycle at a fixed magnetic local time (MLT) through multiple passes. Solar wind drivers triggered the SED onset and controlled its lifecycle through its growth and retreat phases. The SED electron density enhancement extended from the equatorial ionization anomaly to the noon cusp. The midlatitude electron density increased to a maximum at the end of the growth phase. Afterward, the dayside SED region retreated gradually to lower magnetic latitudes. The observations showed a hemisphere asymmetry, with the NH electron density exhibiting a more significant enhancement. The simulations using the Thermosphere Ionosphere Electrodynamic General Circulation model show a good agreement with the CHAMP observations. The simulations indicate that the dayside midlatitude electron density enhancement has a complicated dependence on vertical ion drift, neutral wind, magnetic latitude, MLT, and the height of the F2 layer. Finally, we discuss the notion of using the mean cross‐polar cap electric field as a proxy for assessing the effects of solar wind drivers on producing midlatitude electron density enhancement.

Fine structure of streamer-to-filament transition in high-pressure nanosecond surface dielectric barrier discharge

Abstract The fine structure of a streamer-to-filament transition in a single-shot high-voltage nanosecond surface dielectric barrier discharge in molecular nitrogen at pressure P = 6 bar was studied with the help of ICCD microimaging. An intermediate discharge structure, existing for only a few nanoseconds, was observed in the time interval between two discharge modes: streamer discharge, with a typical electron density of n e ∼ 1015 cm−3, and filamentary discharge, with n e ∼ 1019 cm−3. The structure was observed for both polarities of the high-voltage electrode. The structure can be briefly described as a stochastic appearance of thin channels propagating a bit faster than the main ionization front of merged surface streamers, transforming in a few nanoseconds in a bi-directional ionization wave. One wave, which we associate with a feather-like structure in optical emission, propagates further away from the high-voltage electrode, and another, a backward wave of emission, propagates back towards the edge of the high-voltage electrode. When the backward wave of emission almost reaches the high-voltage electrode, the filament appears. Plasma properties of the observed structure were studied to better understand the nature of a streamer-to-filament transition. Theoretical analysis suggests that the instability of a flat front of ionization wave (Laplacian instability) triggers the streamer-to-filament transition, and that a surface stem (a tiny region with enhanced electron density) should be in the origin of the bi-directional ionization wave.

Free zinc determines the formability of the vesicular dense core in diabetic beta cells.

During the progression of type 2 diabetes, total body zinc deficiency disrupts the formability of the electron-dense core in beta-cell vesicles, but the mechanism is unclear. Using fluorescence imaging, transmission electron microscopy and pharmacokinetics assays, we established a strong link between an increasing concentration of free zinc and the formability enhancement of the dense core electron density. Thus, our results highlight a mechanism by which zinc supplementation enhances the maturation of dense cores and restores the secretion of insulin in two diabetic mouse models both in vitro and in vivo. This study provides a potential research direction for investigating the etiology and nutrition of zinc in the management of type 2 diabetes.

C–O band structure modified broad spectral response carbon nitride with enhanced electron density in photocatalytic peroxymonosulfate activation for bisphenol pollutants removal

Here, a simple one-step calcination method uses glycolic acid (GA) and urea to synthesize C-O band structure modified carbon nitride with broad spectral response, which is used to construct a peroxymonosulfate/visible light (PMS/vis) system. The solid-state 13C NMR proved that C-O band structure was successfully introduced into the carbon nitride. Density functional theory (DFT) calculation show that the introduction of C-O band structure shortens the band gap of 0.05 g GA modified CN (0.05 GA-CN). Besides, Ultraviolet photoelectron spectroscopy (UPS) further illustrate that the 0.05 GA-CN has a higher charge density and promotes the degradation of pollutants. In PMS/vis system, 0.05 GA-CN can completely degrade bisphenol A (BPA) within 36 min. In addition, 0.05 GA-CN can also degrade bisphenol E (BPE) and bisphenol F (BPF). The cyclic voltammetry (CV) curve show that the introduction of C-O band structure enhances the activation ability of PMS. At the same time, 0.05 GA-CN/PMS has enhanced the activity of degrading BPA under blue light (450–462 nm), green light (510–520 nm) and red light (610–625 nm). This research provides a new method to synthesize carbon nitride with enhanced electron density for degradation of bisphenol pollutants in PMS/vis system.

1,3 Dialkylated Imidazolium Ionic Liquid Causes Interdigitated Domains in a Phospholipid Membrane.

Amphiphilic imidazolium-based ionic liquids (ILs) have proven their efficacy in altering the membrane integrity and dynamics. The present article investigates the phase-separated domains in a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane induced by 1,3 dialkylated imidazolium IL. Isotherm measurements on DPPC monolayers formed at the air-water interface have shown a decrease in the mean molecular area with the addition of this IL. The positive value of the excess Gibbs free energy of mixing indicates an unfavorable mixing of the IL into the lipid. This leads to IL-induced phase-separated domains in the multilayer of the lipid confirmed by the occurrence of two sets of equidistance peaks in the X-ray reflectivity data. The electron density profile along the surface normal obtained by the swelling method shows the bilayer thickness of the newly formed IL-rich phase to be substantially lower (∼34 Å) than the DPPC phase (∼45.8 Å). This IL-rich phase has been confirmed to be interdigitated, showing an enhanced electron density in the tail region due to the overlapping hydrocarbon chains. Differential scanning calorimetry measurements showed that the incorporation of IL enhances the fluidity of the lipid bilayer. Therefore, the study indicates the formation of an interdigitated phase with a lower order compared to the gel phase in the DPPC membrane supplemented with the IL.