Variation Of Electron Density Research Articles

Generation of equatorial plasma bubble after the 2022 Tonga volcanic eruption

Equatorial plasma bubbles are a phenomenon of plasma density depletion with small-scale density irregularities, normally observed in the equatorial ionosphere. This phenomenon, which impacts satellite-based communications, was observed in the Asia-Pacific region after the largest-on-record January 15, 2022 eruption of the Tonga volcano. We used satellite and ground-based ionospheric observations to demonstrate that an air pressure wave triggered by the Tonga volcanic eruption could cause the emergence of an equatorial plasma bubble. The most prominent observation result shows a sudden increase of electron density and height of the ionosphere several ten minutes to hours before the initial arrival of the air pressure wave in the lower atmosphere. The propagation speed of ionospheric electron density variations was ~ 480–540 m/s, whose speed was higher than that of a Lamb wave (~315 m/s) in the troposphere. The electron density variations started larger in the Northern Hemisphere than in the Southern Hemisphere. The fast response of the ionosphere could be caused by an instantaneous transmission of the electric field to the magnetic conjugate ionosphere along the magnetic field lines. After the ionospheric perturbations, electron density depletion appeared in the equatorial and low-latitude ionosphere and extended at least up to ±25° in geomagnetic latitude.

Satellite-based electron density background definition at mid-latitudes and comparison with IRI-2016 model under different solar conditions

A new method to define a background for the ionospheric electron density (Ne) is proposed, making use of mid-latitude measurements under different solar conditions from the Langmuir Probes onboard CHAMP and three identical Swarm satellites. In particular, CHAMP measurements during the years 2004 and 2009, and Swarm observations during 2016 and 2017 have been considered in the 15°-wide latitudinal belt from 35°N to 50°N, and from 0° to 360° in longitude. CHAMP/Swarm in-situ Ne measurements have been then used to check and compare this new defined background with the one computed directly from IRI-2016 Ne output at satellite altitude. The distributions of the relative deviations between the two backgrounds, and of positive and negative anomalies (i.e., Ne variations from each background greater than 30%) with respect to the geomagnetic activity levels have been evaluated under each investigated condition, namely year/satellite, season, night-time or noon hours. Results of this comparison highlight a general overestimation of Ne from IRI during noon hours, while a better agreement between the two backgrounds is found during night-time. However, an underestimation of IRI with respect to Swarm-derived background is found for 2017 data. Finally, the analysis of 2004 plasma data suggests that the IRI-2016 model can be used as a background during periods characterized by high levels of geomagnetic activity. Due to the difficulties to construct a background for satellite data, the proposed method can be considered an useful tool for analyses of electron density variations at the heights of the satellites in Low Earth Orbits (LEO).

DFT potentials from a chemical perspective: Anatomy of electron (de)localization in molecules and crystals.

We introduce a fermionic potential, , as a comprehensive measure of electron (de)localization in atomic-molecular systems. Unlike other common descriptors as ELF, LOL, etc., it characterizes all physical effects responsible for (de)localization of electrons, namely: an exchange hole depth, its tendency to change, a sensitivity of an exchange correlation hidden in a pair density and kinetic potential to local variations in electron density. Wells in the distribution correspond to the domains of maximum electron localization, while the potential's barriers prevent delocalization of electrons through them. It also estimates bond orders and successfully reveals the impact of chemical modifications or environmental effects on the delocalization of electrons in molecules and crystals. The components provide a unique opportunity to compare the influence of the mentioned physical effects on electron (de)localization. This merges physical and chemical views of electron delocalization using functions appearing in density functional theory.

How electron delocalization influences the electron-withdrawing properties of isomeric benzobischalcogenadiazoles

The fermionic potential and delocalization indices for benzo-bis-1,2,5-chalcogenadiazoles reveal inhomogeneous electron delocalization in their benzene ring, which results in compactly localized lone electron pairs on the chalcogen atoms. These features of (de)localization are rooted in a local increase in the kinetic component of the electron correlation, which expresses the Fermi hole variability and the kinetic potential response to electron density variations in the benzene ring of benzobis-1,2,5-chalcogenadiazoles. This explains their better electron-withdrawing properties compared to benzobis-1,2,3-chalcogenadiazoles

A three-dimensional stochastic structure model derived from high-resolution isolated equatorial plasma bubble simulations

Ionospheric structure is characterized by the space–time variation of electron density. However, our understanding of the physical processes that initiate and sustain intermediate-scale structure development does not relate directly to statistical measures that characterize the structure. Consequently, high-resolution physics-based equatorial plasma bubble simulations are essential for identifying systematic relations between statistical structure measures and the underlying physics that initiates and sustains the structure evolution. An earlier paper summarized the analysis of simulated equatorial plasma bubble (EPB) structure initiated with a quasi-periodic bottom-side perturbation that generated five plasma bubbles. The results are representative of real environments. However, the association of the structure development with individual EPBs was difficult to ascertain. This paper summarizes the analysis of new results from single isolated EPB realizations with varying parameters that affect the structure development. The evolution of the single isolated EPB realizations reveal what we have identified as a canonical structure evolution pattern manifest in the space–time development of four quantitative spectral parameters. The onset of structure occurs when the plasma bubble penetrates the F-region peak. The parameter evolution from the initiation point have a fish-like appearance. The three-dimensional structure model can be used to interpret in situ and remote diagnostic measurements as well as predicting the deleterious effects of propagation disturbances on satellite communication, navigation, and surveillance systems.Graphical

Strain Effects in Twisted Spiral Antimonene.

Van der Waals (vdW) layered materials exhibit fruitful novel physical properties. The energy band of such materials depends strongly on their structures, and a tremendous variation in their physical properties can be deduced from a tiny change in inter-layer spacing, twist angle, or in-plane strain. In this work, a kind of vdW layered material of spiral antimonene is constructed, and the strain effects in the material are studied. The spiral antimonene is grown on a germanium (Ge) substrate and is induced by a helical dislocation penetrating through few atomic-layers of antimonene (β-phase). The as-grown spiral is intrinsically strained, and the lattice distortion is found to be pinned around the dislocation. Both spontaneous inter-layer twist and in-plane anisotropic strain are observed in scanning tunneling microscope (STM) measurements. The strain in the spiral antimonene can be significantly modified by STM tip interaction, leading to a variation in the surface electronic density of states (DOS) and a large modification in the work function of up to a few hundreds of millielectron-volts (meV). Those strain effects are expected to have potential applications in building up novel piezoelectric devices.

Annual and semi-annual variations of electron density in the topside ionosphere observed by CSES

In this paper, based on the observations from Langmuir probe (LAP) onboard the China Seismo-Electromagnetic Satellite (CSES), the annual/semi-annual variations of electron density (Ne) measured at 02:00 and 14:00 local time (LT) in the topside ionosphere have been analyzed. Results indicated that the Ne exhibits an amplification-linear-saturation with the increase of P10.7 in the daytime, while roughly linear in the nighttime. The annual/semi-annual variations of CSES Ne at around 500 km are found by morphological analysis and Morlet wavelet analysis, with dominant period of 187 days and 374 days. The annual components of longitude-averaged Ne dominate at most magnetic latitudes (Mlats) with maxima around the June solstices in the northern hemisphere and the December solstice in the southern hemisphere (except for the northern hemisphere in the nighttime), while the semi-annual variation dominates at the magnetic equator and low magnetic latitudes with two maxima at equinoxes. The Ne dominant period is characterized by a transition from semi-annual variation at the equator and low magnetic latitudes regions to annual variation at the middle magnetic latitudes region. The annual/semi-annual variations of Ne observed by CSES satellite show a consistent performance with previous studies, and have complemented the ionospheric characteristics at 500 km altitude, especially in the nighttime.

Three-dimensional ionospheric tomography based on compressed sensing

The insufficient number of low-elevation observations is a limitation of the three-dimensional ionospheric computer tomography (CT) based on the global navigation satellite system (GNSS). To solve this problem, accurate prior information on the regional ionosphere must be obtained. However, it is difficult to explicitly and accurately express prior ionospheric information. This study uses compressed sensing (CS) for ionospheric tomography for the first time. Specifically, the electron density obtained from the international reference ionosphere is used to build a dictionary to fully integrate the prior information into the dictionary. Then, the electron density is reconstructed by using the compressive sampling matching pursuit method. Subsequently, the GNSS data of China (Region I) and Europe (Region II) were utilized to validate this proposed method, and the results are compared with ionosonde observations. The mean and standard deviation (SD) of the difference with respect to the ionosonde result are 41 and 22 km, respectively. The mean and SD of relative deviation were 16% and 9%, respectively. In Region II, the mean and SD of the deviation between the reversed peak electron density and the result of the ionosonde were 1.9 × 1010 m−3 and 8.1 × 1010 m−3, respectively. The mean and SD of the relative deviation were 3% and 13%, respectively. The mean and SD of the peak height deviation were 33 and 19 km, and the mean and SD of the relative deviation were 11% and 7%. The electron density distribution and variation in these two regions showed a local time dependence, and the horizontal gradient of the electron density in the latitude was greater than that in the longitude. Moreover, CT by CS is efficient, taking about 6 s per inversion based on an desktop computer with 16 GB RAM and Intel (R) Core (TM) i7-8700 CPU.

Probing the Local Environment of Active Sites during 2-Propanol Oxidation to Acetone on the Co3O4 (001) Surface: Insights from First-Principles O K-Edge XANES Spectroscopy

We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic structure of the active sites on the Co3O4 (001) surface during 2-propanol oxidation to acetone in humid conditions. In the gas phase, the O K-edge spectra of 2-propanol and acetone, as well that of 2-propoxide considered as a reaction intermediate, present no pre-edge peaks. Upon 2-propanol adsorption at the Co site of the Co3O4 (001) surface, the O K-edge spectrum presents a distinct peak preceded by a bump in the pre-edge region, both due to dipole transitions from O 1s to 2p states hybridized with Co 3d empty states. The formation of 2-propoxide leads to two distinct pre-edge peaks due to the increase of 3d empty states. A further increment of these pre-edge peaks is observed when acetone is formed and is rather ascribed to the new contributions of carbon 2p empty states in the transitions occurring in the pre-edge region. The changes observed in the pre-edge peak along the oxidation were correlated to the electronic configuration and hybridization of the cobalt atom directly bonded to alcohol. The variation of electron densities was also monitored for all surface cobalt atoms including the ones on which molecular water and dissociated water are adsorbed. The PDOS analysis and crystal field theory showed that adsorption of 2-propanol and molecular water on the surface does not change the oxidation state of +3, while surface cobalt atoms bonded to OH groups have an oxidation state of +4. The 3d Löwdin charges analysis shows pronounced cooperative effects between both Co sites during the last oxidation step which corresponds to the decomposition of 2-propoxide to acetone.

Investigation of the Topside Ionosphere over Cyprus and Russia Using Swarm Data

Using the topside electron density (Ne) measurements recorded over Cyprus and Russia, we investigate the latitudinal variation in the topside electron density during the interval 2014–2020, encompassing a period of high-to-low solar activity. The selected topside electron density dataset employed in this study is based on the in situ Langmuir probe data on board the European Space Agency (ESA) Swarm satellites, in the vicinity of the three Digisonde stations in Nicosia (35.14°N, 33.2°E), Moscow (55.5°N, 37.3°E) and Saint Petersburg (60.0°N, 30.7°E). Our investigation demonstrates that the ratio Ne_Swarm/NmF2 between the coincident Ne_Swarm and the Digisonde NmF2 observations is higher than one on various occasions over Nicosia during the nighttime, which is not the case over Moscow and Saint Petersburg, signifying a discrepancy feature of the electron density at Swarm altitudes which depends not only on the solar activity and time of day but also on the latitude.

Cosmological model-independent constraints on the baryon fraction in the IGM from fast radio bursts and supernovae data

Fast Radio Bursts (FRBs) are millisecond-duration radio transients with an observed dispersion measure (DM) greater than the expected Milky Way contribution, which suggests that such events are of extragalactic origin. Although some models have been proposed to explain the physics of the pulse, the mechanism behind the FRBs emission is still unknown. From FRBs data with known host galaxies, the redshift is directly measured and can be combined with estimates of the DM to constrain the cosmological parameters, such as the baryon number density and the Hubble constant. However, the poor knowledge of the fraction of baryonic mass in the intergalactic medium (f_{IGM}) and its degeneracy with the cosmological parameters impose limits on the cosmological application of FRBs. In this work we present a cosmological model-independent method to determine the evolution of f_{IGM} combining the latest FRBs observations with localized host galaxy and current supernovae data. We consider constant and time-dependent f_{IGM} parameterizations and show, through a Bayesian model selection analysis, that a conclusive answer about the time-evolution of f_{IGM} depend strongly on the DM fluctuations due to the spatial variation in cosmic electron density (delta ). In particular, our analysis show that the evidence varies from strong (in favor of a growing evolution of f_{IGM} with redshift) to inconclusive, as larger values of delta are considered.

Elucidating the phase behavior of ternary model membrane mixtures containing halogenated cholesterol analogues.

Cellular plasma membranes exhibit nanoscale lateral lipid heterogeneity, a feature that is thought to be central to their functionality. However, only a few biophysical methods are capable of detecting domains at sub-micron length scales. We recently showed that cryogenic electron microscopy (cryo-EM) can directly image phase separation in extruded liposomes due to its ability to resolve the intrinsic thickness and electron density differences of ordered and disordered phases. However, the contrast between these phases is poor compared to conventional fluorescence microscopy and is thus both a limiting factor and a focal point for optimization. Because the fundamental source of contrast is the spatial variation in electron density within the bilayer, lipid modifications aimed at selectively increasing the electron density of one phase might enhance the ability to resolve coexisting phases. To this end, we make use of a model membrane mixture of DPPC/DOPC/cholesterol, in which one hydrogen of the methyl group on the steroid ring of cholesterol is replaced by an electron-rich halogen atom. We use a variety of biophysical techniques including confocal fluorescence microscopy, FRET, and cryo-EM to examine phase behavior as a function of composition and temperature. We find that cryo-EM image contrast is increased in liposomes containing halogenated cholesterol as expected. However, the phase behavior of these mixtures is altered compared to mixtures containing native cholesterol providing a cautionary note that halogenated cholesterol has biophysical effects beyond increasing electron density.

Singular spectrum analysis and modeling of the temporal variations of the global ionospheric F2-layer peak electron density retrieved from COSMIC radio occultation measurements

The singular spectrum analysis (SSA) is a relatively new method for decomposing time series into separable and interpretable series (i.e., trend, periodic, and irregular components). Here, the ionospheric variability in the peak electron density (NmF2) observations provided by FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation measurements during 2009–2019, which completely covers solar-cycle 24, was examined using the nonparametric method (SSA). This study identified different temporal patterns inherent in the COSMIC data, which can be employed to reconstruct/model noise-free time series. Based on a proper choice of SSA parameters, it was observed that SSA can be employed to extract various components of these datasets. Additionally, the results showed that the slowly varying component (trend) was largely influenced by solar activity and closely followed the behavior of the sunspot cycle. The SSA method demonstrated seasonal patterns (the semiannual component). Based on the patterns, the reconstructed series for each of the selected components were separately modeled with a corresponding fit function using the 10.7 cm solar proxy, which prior be smoothed by Spline fitting. It was observed that the polynomial function efficiently modeled the trend component with R2 = 0.95, while the harmonic function adequately represented the semiannual component with R2 = 0.97. To validate the proposed model, the data were estimated for the time interval from January 2020 to August 2022, which represented the ascending phase of the ongoing solar-cycle 25. The results revealed that the modeled data correlated with the observed COSMIC-2 data with a high correlation coefficient (0.95). These findings indicate that the underlying model can effectively describe the behavior of the electron density during the investigated period, and the SSA method is particularly powerful for analyzing nonstationary time series and capable of identifying sub-time series (trends along with seasonal periodic components).

Longitudinal variations in the position and magnitude of the poleward wall of the ionospheric trough in the southern hemisphere

For the first time, joint variations with longitude in the position of the high-latitude ionosphere structures: equatorward boundary of auroral diffuse precipitation, poleward wall and minimum of subauroral (main) ionization trough were considered. The data from the CHAMP satellite in the southern winter hemisphere in the evening, midnight and morning sectors were used, as well as a model of the auroral diffuse precipitation. The average (for all longitudes) distance between the equatorward boundary of the auroral oval and poleward wall increases from 1° in the evening to 2.5° in the morning, and between the auroral oval and trough minimum from 3.5° to 6.5°, respectively. These values agree well with the estimates obtained using different methods in other experiments. The poleward wall and minimum of the trough experience synchronous variations with longitude, the distance between the auroral oval and trough changes with longitude because of the different character of the longitudinal effect. Unexpectedly stable longitudinal variations in the magnitude of the poleward wall were identified for the first time: magnitude changes 4 times in the evening, 6 times at midnight and 3 times in the morning. Longitudinal variations in the poleward wall magnitude at midnight are completely correlated with the diffuse precipitation flux, in the evening with the electron density at mid-latitudes, and in the morning the poleward wall is clearly associated with electron density variations on the dayside. These results confirm the known assumptions that at midnight the poleward wall is completely formed by diffuse precipitation, and in the morning the poleward wall is evidently determined by the transport of ionization from the dayside. In the evening, the influence of residual solar ionization was probably manifested. In this sector, at America-Atlantic longitudes, an equatorward minimum of electron density is often formed, which prevents accurate determination of the trough position. These cases require a deeper analysis. In the evening at longitudes of America and at midnight at longitudes of 30°-90°, neither the poleward wall nor minimum of the trough is sometimes formed at all. This unexpected result requires clarification of the trough formation mechanism.

Approaching PetaVolts per Meter Plasmonics Using Structured Semiconductors

A newly uncovered class of plasmons in the strongly excited limit opens access to unprecedented Petavolts per meter electromagnetic fields with wide-ranging, transformative impact. Unlike conventional plasmons, such plasmons are constituted by non-perturbative, large-amplitude oscillations of the ultradense, delocalized free electron Fermi gas inherent in conductive media. Here structured semiconductors doped to have an appropriate conduction electron density are introduced to tune the properties of the Fermi gas for matched excitation of large-amplitude plasmons using readily available electron beams which enables immediate experimental validation. Specifically, an electrostatic, surface “crunch-in” plasmon is collisionlessly excited by the beam launched inside a tube. Strong excitation due to matching results in relativistic oscillations of the electron gas and unravels unique phenomena. Relativistically induced ballistic electron transport comes about due to relativistic multifold increase in the mean free path and also leads to unconventional heat deposition beyond Ohm’s law. This explains the absence of observed damage or solid-plasma formation in past experiments on conductive samples interacting with electron bunches shorter than 10−13 seconds. Furthermore, relativistic momentum leads to copious tunneling of electron gas across the surface, which then crunches inside the tube. Relativistic effects along with large, localized electron density variations underlying these modes necessitate kinetic approach to theoretical and computational modeling. Kinetic model presented here demonstrates experimental viability of observing tens of gigavolts per meter plasmonic fields excited by matching readily available electron beams to plasmons in semiconductors with 1018cm−3 free electron density, and paves the way for Petavolts per meter plasmonics.

Decade-long Timing Study of the Black Widow Millisecond Pulsar J1544+4937

Results from 11 yr of radio timing for the eclipsing black widow millisecond pulsar (MSP) binary J1544+4937 is presented in this paper. We report a phase-connected timing model for this MSP, using observations with the Giant Metrewave Radio Telescope (GMRT) at multiple frequencies and with the Green Bank Telescope. This is the longest-duration timing study of any galactic-field MSP with the GMRT. While extending the timing baseline from the existing 1.5 yr to about a decade we report the first detection for a significant value of proper motion (μ T ∼ 10.14(5) mas yr−1) for this pulsar. Temporal variations of dispersion measure (ΔDM ∼ 10−3 pc cm−3) manifested by significant determination of first-, second-, and third-order dispersion measure (DM) derivatives are observed along the line of sight to the pulsar. We also noticed frequency-dependent DM variations of the order of 10−3 pc cm−3, which could arise due to spatial electron density variations in the interstellar medium. This study has revealed a secular variation of the orbital period for this MSP for the first time. We investigated possible causes and propose that variation in the gravitational quadrupole moment of the companion could be responsible for the observed temporal changes in the orbital period.

Effects of Electron Density Variation of Active Sites in CO<sub>2</sub> Activation and Photoreduction: A Review

Effects of Electron Density Variation of Active Sites in CO<sub>2</sub> Activation and Photoreduction: A Review

Electron Density Variations in the Interstellar Medium and the Average Frequency Profile of a Scintle from Pulsar Scintillation Spectra

We observed the scintillation pattern of nine bright pulsars at 324 MHz and three at 1.68 GHz and analyzed the wavenumber spectrum, which is related to electron density variations of the plasma turbulence of the interstellar medium (ISM). For all pulsars the frequency section of the autocorrelation function (ACF) of the dynamic spectra to at least 45% of the maximum corresponds to predictions of scattering theories with a range of power-law exponents of the wavenumber spectrum of 3.56 ≤ α ≤ 3.97 with errors ≤0.05 and a mean with standard deviation of 3.76 ± 0.13. The range includes α = 3.67 for the Kolmogorov spectrum. Similar results, although with larger errors, were found from the Fourier transform of the ACFs down to ∼10−3 of the maximum. No clear case of a distinction between thin-screen and extended-medium scattering models was found. The average frequency profile of the scintles can be characterized for steep wavenumber spectra with α ≲ 4 by a cusp with a somewhat rounded peak. For flatter spectra, down to at least α ∼ 3.56 the cusp with its peak becomes more pronounced and its decay steepens. We discuss our findings in the context of the scattering characteristics of the ISM.

Electronic structures of zwitterionic and protonated forms of glycine betaine in water: Insights into solvent effects from ab initio simulations

Glycine betaine (GB), a naturally occurring osmolyte, has many biological functions and is used in food supplements, pharmaceuticals, and animal feed. GB usually exists as a zwitterion in aqueous solutions. Due to the hygroscopic property of GB, protonated form of GB, GBH+ (noted as GBH) is often used. In order to understand the hydration structures of GB and GBH at the atomic and electronic-structure level, a combination of ab initio molecular dynamics simulations and electronic structure calculations based on density functional theory (DFT), single-excitation configuration interaction method, and coupled-cluster ansatz was utilized. A hybrid explicit–implicit solvation model was used to elucidate solvent effects. Within the hybrid scheme, microsolvated structures of GB and GBH with up to 100 water molecules were obtained, showing that water molecules bind to GB and GBH in a dramatically different manner. By calculating the molecular electron-density distributions at PBE0-D4/def2-TZVP level, it shows that the variation of electron density for GB is more significant than GBH, suggesting that GB can interact with more water molecules than GBH. The interaction energies of GB–(H2O)n and GBH–(H2O)n systems (n = 1–6) at DLPNO-CCSD(T)/cc-pVQZ level highlight the difference from an energy point of view. Using the microsolvated structures of GB and GBH, the features of experimental K-edge spectra can be reproduced using the efficient PNO-ROCIS/B3LYP method, implying the reliability of the hybrid explicit–implicit solvation approach. The results suggest that complementary insights into the geometries and electronic structures of GB and GBH could be obtained through combined methods, which provides a methodological approach for understanding the hydration structures of zwitterionic and charged molecules.

How does electron exchange correlation influence reactivity of metallo-β-lactamase L1 against cephalosporin antibiotics

Cephalosporin hydrolysis by the metallo-β-lactamase L1 is a reaction where electron delocalization in the substrate-protein complex affects the reaction rate: the more cephalosporin lone pairs are localized on the N atom, the higher hydrolysis rates are. We show that high Fermi holevariability is responsible for the stipulation of the electron lone pairs’ localization.One-electron potentials reveal that higher lone pairs’ localization is expressed in the dominance of the static exchange correlation (reflected in theaverage Fermi hole depth) in theN atomvicinity. However, this dominance was found to be defined by the height of the kinetic exchange potential barriers (expressing the Fermi holevariability and the response of the exchange correlation hidden in the kinetic potential to electron density variations), rather than by the features of the static exchange correlation itself. The need to account both static and kinetic exchange correlations for the reliable description of the electron delocalization explains inapplicability of the simple geometric criteria for the chemical bonding study in the considered systems.