Terms Of Electron Density Research Articles

Effects of magnetic field configurations on the minimized ECR ion thrusters for micro-Newton and wide-range operations

Space-based gravitational wave detection missions require precise thrusts over a wide-range of 1–100 μN. In this study, the axial ring-cusp magnetic field configuration is used to design a miniature electron cyclotron resonance ion thruster with a radius of 5 mm. Two typical configurations, i.e., open-type and closed-type, are compared in terms of electron density, electron temperature, and thrust for micro-Newton and wide-range operations. The results show that the open-type achieves high performances owing to the high efficiency of absorption of input microwave power. The lower limit of the mass flow rate in the electron cyclotron resonance (ECR) discharge is expanded to a very low value of 3 × 10−2 sccm to achieve 1 μN in the open-type. The thrust in the open-type could be tuned in a wide-range of 1–119 μN, meeting the requirement.

Arcing in ambient air triggered by pulsed x-ray radiation

The generation of arcs in air at atmospheric pressure induced by static voltage and triggered by x-ray pulses is analyzed. A static voltage is set between a cathode and an anode, and the arcing process is triggered by irradiating the air gap of a pin-to-plane switch with an x-ray photon pulse in the MeV range. This x-ray pulse produces a weakly ionized non-equilibrium air plasma (called the pre-plasma), which reduces the breakdown threshold. The influence of this pulsed x-ray on the arcing process is analyzed. The reduction of the breakdown voltage has been quantified, and for low static voltages, the creation of a sheath that is responsible for a delay in the arcing process is highlighted. Electrical measurements (currents and voltages) and optical emission spectroscopy have been performed to characterize the arcs in terms of electron density, temperature, and electric conductivity. A good agreement between measurements and 3D Maxwell calculations is achieved, which allows us to determine the electric conductivity of the arc in both self-triggered and x-ray-triggered regimes.

Preferred conformations of osmium cluster in terms of electron density

In this article, we propose to use AlteQ quantum free orbital method to determine preferred conformers of osmium-containing complexes. The study is based on the conformational analysis of a triosmium cluster with a morpholine fragment [(μ-H)(μ-Cl)Os3{η1-C(CH3)N(CH2CH2)2O}(CO)9]. 3D electron density maps were computed for each conformer of the cluster along with its environment in the crystal. The “cluster-environment” complementarity was assessed for each conformer based on the determination of relationships between the parameters of the electronic structures, which in turn are determined by the nature of intermolecular interactions. Free versions of the AlteQ for Windows and Linux are available at https://www.chemosophia.com.

The Dual Descriptor Reveals the Janus-Faced Behaviour of Diiodine.

The Janus–faced ligand behavior of diiodine (I2) was evidenced after applying the dual descriptor (DD or second-order Fukui function), thus providing additional support to the work performed by Rogachev and Hoffmann in 2013. Along with its capacity to reveal sites susceptible to undergo attacks simultaneously of nucleophilic and electrophilic types, another advantage of DD lies in being an orbital-free descriptor. That means it is based only upon total electron densities when written in its most accurate operational formula. This quality is not exclusive of DD because when Fukui functions are written in terms of electron densities instead of densities of frontier molecular orbitals, they become orbital-free descriptors too. Furthermore, the present work is an application of the generalized operational formula of the dual descriptor published in 2016 that takes into account any possible degeneracy in frontier molecular orbitals. As a proof about capabilities of DD, the possible sites for a favorable interaction between I2 with two organometallic compounds [Rh2(O2CCF3)4] and [(C8H11N2)Pt (CH3)] were correctly revealed by overlapping the biggest lobe for receiving nucleophilic attacks of one molecule with the biggest lobe for receiving electrophilic attacks of the other molecule, so allowing to predict the same coordination modes as experimentally known: linear “end–on” for the [(C8H11N2)Pt (CH3)]…I2, and bent “end–on” for the [Rh2(O2CCF3)4]…I2 interactions.

Exploring intermolecular interactions in some halogen substituted formyl coumarins and their DFT studies

The present manuscript describes an in-depth analysis of various interactions present in the crystal structure of formyl coumarins using Crystal explorer 17.0. Element based interactions were quantified by the decomposition of generated 3D surfaces into 2D fingerprint regions. DFT methods were used to explore electrostatic parameters, global and local reactivity descriptors. Electrophilicity based charge transfer (ECT) analysis was done to explore the probability of charge transfer between formyl coumarins and DNA base pairs. The reactivity and selectivity of different formyl coumarins have been accessed using Fukui functions in their reduced form. Non-bonding orbital (NBO) analysis revealed the presence of various hyperconjugative interactions and their stabilization energy in formyl coumarins. Non-linear optical properties are presented in terms of first order hyperpolarizibility (β0), where maximum β0 is observed for C4 (1.64 × 10-30esu.) which is found to be 2 times greater than that of p-nitroaniline. Molecular electrostatic potential (MEP) plots are mapped in terms of electron density.

A Tomographic Method for the Reconstruction of the Plasmasphere Based on COSMIC/ FORMOSAT-3 Data

A tomographic method has been developed for reconstructing the topside ionospheric and plasmaspheric electron density distribution using total electron content (TEC) measurements from global positioning system (GPS) receivers aboard the constellation observing system for meteorology, ionosphere, and climate&#x002F;Formosa Satellite Mission 3 (COSMIC&#x002F;FORMOSAT-3). Since the COSMIC&#x002F;FORMOSAT-3 constellation has an orbit altitude of about 800 km, the integral TEC measurements obtained from the topside GPS navigation data are rather small and imposed relevant challenges to obtaining stable electron density reconstructions. However, the developed method can represent the natural variability of the plasma ambient in terms of latitude, altitude, solar activity, season, and local time when analyzing electron density reconstructions during 2008&#x2013;2013. The method employs independent spatial grids for satellite rising and setting geometries and imposes a set of constraints to stabilize the solution in the presence of noise and ill-conditioned geometry. We further consider background ionosphere and plasmasphere models for electron density initialization and filling data gaps. The quality assessment using TEC and <i>in-situ</i> electron density measurements has shown that the proposed method performs better than the background model, with improvements of about 26&#x0025; in TEC and 20&#x0025; in terms of electron density. Our investigation also reveals the necessity of more accurate background electron density representations and precise TEC measurements in order to have better plasmaspheric specifications at high altitudes.

A Comparison of the Topside Electron Density Measured by the Swarm Satellites and Incoherent Scatter Radars Over Resolute Bay, Canada

AbstractElectron density measured at high latitudes by the Swarm satellites is compared with the measurements by the RISR incoherent scatter radars as the satellites fly by the radars' field of views near Resolute Bay, Canada between 2014 and 2019. More than 200 satellite passes crossing multiple radar beams are considered. Overall, the Swarm‐based electron densities are smaller than those measured by the radars by ∼30%. The values are closer to one another at electron densities between and , corresponding to plasma frequencies between 1.5 and 3.5 MHz. Swarm‐measured values are getting progressively smaller than those measured by radars at larger electron densities/plasma frequencies. For the entire range of measured electron densities, the slope of the best fit linear line to the data expressed in terms of electron density is ∼0.62 and offset is . Stronger differences between the instruments were found for observations at nighttime and dawn.

Topside Ionosphere and Plasmasphere Modelling Using GNSS Radio Occultation and POD Data

A 3D-model approach has been developed to describe the electron density of the topside ionosphere and plasmasphere based on Global Navigation Satellite System (GNSS) measurements onboard low Earth orbit satellites. Electron density profiles derived from ionospheric Radio Occultation (RO) data are extrapolated to the upper ionosphere and plasmasphere based on a linear Vary-Chap function and Total Electron Content (TEC) measurements. A final update is then obtained by applying tomographic algorithms to the slant TEC measurements. Since the background specification is created with RO data, the proposed approach does not require using any external ionospheric/plasmaspheric model to adapt to the most recent data distributions. We assessed the model accuracy in 2013 and 2018 using independent TEC data, in situ electron density measurements, and ionosondes. A systematic better specification was obtained in comparison to NeQuick, with improvements around 15% in terms of electron density at 800 km, 26% at the top-most region (above 10,000 km) and 26% to 55% in terms of TEC, depending on the solar activity level. Our investigation shows that the developed model follows a known variation of electron density with respect to geographic/geomagnetic latitude, altitude, solar activity level, season, and local time, revealing the approach as a practical and useful tool for describing topside ionosphere and plasmasphere using satellite-based GNSS data.

A Numerical Simulation of a Low-Temperature Argon Plasma Jet

A plasma jet at atmospheric pressure using a dielectric barrier discharge (DBD) can be very useful in the biomedical field. In this article, a numerical simulation of such plasma jet operating in argon gas and launched in the open air was developed using COMSOL Multiphysics software. Three coupled models are considered in this study. A hydrodynamic investigation is conducted and the dilution of argon in air is considered an initial value in the plasma model. An electrostatic study is developed in order to preview the initial electric field. Finally, a plasma study is carried out and discussed in terms of electron density, electric field distribution, and plasma length. This study is validated by comparing the results to those measured in a similar system in the literature. The results are in good agreement with the literature and correspond to the physics of the plasma jet.

A Thermophysical Perspective of the Inter-relationship between Debye Temperature and Electron Density

A comprehensive thermophysical analysis of the linkage between the Debye temperature θD and electron density ne has been presented. Assuming that the Debye cut-off frequency ωD is related to the effective oscillation frequency ω of screened ion cores of a metallic material, a simple analytical relationship could be established between θD, bonding electron density ne, and materials density ρm. Alternately, it is possible to establish a consistent set of electron density n e values using θD, which in the case of pure metals is shown to exhibit a linear scaling with Miedema’s thermochemical electron density n e M values. The temperature, pressure, and composition dependencies of θD are addressed uniformly in terms of isobaric and isothermal volume variations of ne; besides, invoking the subregular solution formalism for expressing composition-induced molar volume variation simple approximations for melting temperature Tm and vibrational entropy $$ S_{T}^{\text{o}} $$ have been suggested in terms of electron density. Estimates of θD, $$ S_{298}^{\text{o}} $$ , and average sound velocity have been obtained for metastable bcc U1−xZrx solid solution.

A chemical interpretation of protein electron density maps in the worldwide protein data bank.

High-quality three-dimensional structural data is of great value for the functional interpretation of biomacromolecules, especially proteins; however, structural quality varies greatly across the entries in the worldwide Protein Data Bank (wwPDB). Since 2008, the wwPDB has required the inclusion of structure factors with the deposition of x-ray crystallographic structures to support the independent evaluation of structures with respect to the underlying experimental data used to derive those structures. However, interpreting the discrepancies between the structural model and its underlying electron density data is difficult, since derived sigma-scaled electron density maps use arbitrary electron density units which are inconsistent between maps from different wwPDB entries. Therefore, we have developed a method that converts electron density values from sigma-scaled electron density maps into units of electrons. With this conversion, we have developed new methods that can evaluate specific regions of an x-ray crystallographic structure with respect to a physicochemical interpretation of its corresponding electron density map. We have systematically compared all deposited x-ray crystallographic protein models in the wwPDB with their underlying electron density maps, if available, and characterized the electron density in terms of expected numbers of electrons based on the structural model. The methods generated coherent evaluation metrics throughout all PDB entries with associated electron density data, which are consistent with visualization software that would normally be used for manual quality assessment. To our knowledge, this is the first attempt to derive units of electrons directly from electron density maps without the aid of the underlying structure factors. These new metrics are biochemically-informative and can be extremely useful for filtering out low-quality structural regions from inclusion into systematic analyses that span large numbers of PDB entries. Furthermore, these new metrics will improve the ability of non-crystallographers to evaluate regions of interest within PDB entries, since only the PDB structure and the associated electron density maps are needed. These new methods are available as a well-documented Python package on GitHub and the Python Package Index under a modified Clear BSD open source license.

Molecular structure, QTAIM and bonding character of cation–π interactions of mono- and divalent metal cations (Li+, Na+, K+, Be2+, Mg2+ and Ca2+) with drug of acetaminophen

The molecular modeling analysis via density functional theory (DFT) calculations is performed on all the formed complexes from interaction between mono- and divalent metal cations (Li+, Na+, K+, Be2+, Mg2+ and Ca2+) with acetaminophen. The interaction energies are calculated by M06-2X method in the gas phase and the solution. The obtained structures are analyzed by topological parameters in terms of electron density (ρ) and its Laplacian (∇2ρ) at the bond critical point (BCP) using the atoms in molecules (AIM) methodology. The evaluated results from calculations suggest that the strongest interaction and the highest electron density at BCP are related to the Be2+ complex. In addition, the natural bond orbital (NBO) analysis is performed to investigate the charge distribution in the related complexes. The MEP (molecular electrostatic potential) is given the visual representation of the chemically active sites and comparative reactivity of atoms. Finally, the quantum molecular descriptors such as energy gap, electronic chemical potential, global hardness and electrophilicity index are calculated to evaluate the electronic properties, stability and reactivity of the analyzed complexes.

Experimental, DFT dimeric modeling and AIM study of H-bond-mediated composite vibrational structure of Chelidonic acid

The composite vibrational structure near 3650–3200 and 3000–2400 cm−1 in the observed IR absorption spectrum of Chelidonic acid has been explained in terms of intra- and inter-molecular −O−H∙∙∙O H-bonding attributed to monomer and dimer species computed at B3LYP/6–311++G(d,p) level. Three of the six dimer species derived out of ten monomeric components have shown both intra- and inter-molecular H-bonding. Vibrational modes of the monomer and dimer species are satisfactorily identified with the observed IR and Raman bands including frequency shifts associated with the H-bondings. The H-bond interactions in the monomer and dimer species have been characterized in terms of electron density, ρ(r), its Laplacian, ∇2ρ(r) and potential energy density at the O∙∙∙H bond critical points (BCPs) based on the Atoms in Molecules (AIM) theory. The attractive (van der Waals, H-bonds) and repulsive steric clash (SC) interactions are explained using computed reduced density gradient values from the noncovalent interaction (NCI) method. The AIM analysis confirms the presence of the intra- and inter-molecular H-bondings in the monomer/dimer species. The natural bond orbital (NBO) analysis of the natural charges and stabilization energy of the H-bonds for the dimer species further points to the stronger inter-than intra-molecular H-bonding.

Effect of Nitrogen Addition on Electron Density and Temperature of Cascaded Arc Argon Discharge Plasma Diagnosed by Laser Thomson Scattering

The electron density and electron temperature of the recombining argon plasma from a cascaded arc discharge source were measured by the laser Thomson scattering approach. In this paper, a small amount of nitrogen gas was introduced into the argon discharge source. The addition of the nitrogen gas was applied to investigate the change of the plasma parameters in terms of electron density and temperature. The measurements showed that the electron density dropped by 2 orders of magnitude at 10% nitrogen gas addition compared with no nitrogen addition. The dissociative recombination following the charge transfer between atomic ions and nitrogen molecules was responsible for the decrease of electron density. In addition, with the increase of nitrogen gas addition, the measurements indicated that the electron temperature first increased to a maximum and then decreased. This was due to that the superelastic collision between the electrons and the highly excited vibrational nitrogen molecules could heat the electrons leading to the increase of electron temperature while the electron-vibrational energy transfer by electron–nitrogen molecules impact excitation resulted in that electron temperature decreased due to electrons’ kinetic energy losing processes.

A Thermodynamic Perspective of the Composition Dependence of Bulk Modulus in Terms of Electron Density and Molar Volume

The variation of bulk modulus with composition of alloy phases is a core issue in any thermodynamic theory of alloy formation. Though it emerges from fundamental theory that elastic property, especially the bulk modulus is crucially dependent on interstitial electron density (ρb) distribution and its variation with respect to alloy composition, a coherent thermodynamic treatment connecting bulk modulus with electron density together with its composition dependence, is still lacking. The present study addresses this issue for solid solution alloys. A phenomenological analysis of the composition dependence of bulk modulus (BT) of single phase alloys has been presented in terms of bonding charge density (ρb) and its corresponding change with atomic volume (V). This link is developed using the fundamental interrelationship existing between bulk modulus, electron density, and molar volume. The change in bonding charge density (Δρb) with composition (x) has been modeled using an exponential scaling relation with respect to the corresponding change in atomic volume (ΔV). This scaling relation is based on the concept of the universal binding energy relation, which in turn results in a simple exponential variation of bulk modulus with composition-induced change of atomic volume. It is also shown that a common functional representation namely, BT (V) ≈ Bo exp{C × (ΔV)}, can be obtained for the temperature, pressure, and composition dependence of bulk modulus in terms of corresponding changes in volume (ΔV). The constant C takes context-dependent meaning and values. The applicability of this exponential relation towards representing the effect of composition on bulk modulus has been satisfactorily demonstrated for many substitutional alloy systems.

Ionospheric Plasma Irregularities Characterized by the Swarm Satellites: Statistics at High Latitudes

AbstractThe polar ionosphere is often characterized by irregularities and fluctuations in the plasma density. We present a statistical study of ionospheric plasma irregularities based on the observations from the European Space Agency's Swarm mission. The in situ electron density obtained with the Langmuir probe and the total electron content from the onboard global positioning system receiver are used to detect ionospheric plasma irregularities. We derive the irregularity parameters from the electron density in terms of the rate of change of density index and electron density gradients. We also use the rate of change of total electron content index as the irregularity parameter based on the global positioning system data. The background electron density and plasma irregularities are closely controlled by the Earth's magnetic field, with averaged enhancements close to the magnetic poles. The climatological maps in magnetic latitude/magnetic local time coordinates show predominant plasma irregularities near the dayside cusp, polar cap, and nightside auroral oval. These irregularities may be associated with large‐scale plasma structures such as polar cap patches, auroral blobs, auroral particle precipitation, and the equatorward wall of the ionospheric trough. The spatial distributions of irregularities depend on the interplanetary magnetic field (IMF). By filtering the irregularity parameters according to IMF By, we find a clear asymmetry of the spatial distribution in the cusp and polar cap between the Northern (NH) and Southern Hemispheres (SH). For negative IMF By, irregularities are stronger in the dusk (dawn) sector in the NH (SH) and vice versa. This feature is in agreement with the high‐latitude ionospheric convection pattern that is regulated by the IMF By component. The plasma irregularities are also controlled by the solar activity within the current declining solar cycle. The irregularities in the SH polar cap show a seasonal variation with higher values from September to April, while the seasonal variation in the NH is only obvious around solar maximum during 2014–2015.

CO2 Complexes with Five-Membered Heterocycles: Structure, Topology, and Spectroscopic Characterization.

In a first step toward the rational design of macrocyclic structures optimized for CO2 capture, we systematically explored the potential of 30 five-membered aromatic heterocycles to establish coordinating complexes with this pollutant. The interactions between the two moieties were studied in several orientations, and the obtained complexes were analyzed in terms of electron density and vibrational fingerprint. The former is an aid to provide an in-depth knowledge of the interaction, whereas the latter should help to select structural motifs that have not only good complexation properties but also diagnostic spectroscopic signals.

Systematic control of α-Fe2O3 crystal growth direction for improved electrochemical performance of lithium-ion battery anodes

α-Fe2O3 nanomaterials with an elongated nanorod morphology exhibiting superior electrochemical performance were obtained through hydrothermal synthesis assisted by diamine derivatives as shape-controlling agents (SCAs) for application as anodes in lithium-ion batteries (LIBs). The physicochemical characteristics were investigated via XRD and FESEM, revealing well-crystallized α-Fe2O3 with adjustable nanorod lengths between 240 and 400 nm and aspect ratios in the range from 2.6 to 5.7. The electrochemical performance was evaluated by cyclic voltammetry and charge–discharge measurements. A SCA test series, including ethylenediamine, 1,2-diaminopropane, 2,3-diaminobutane, and N-methylethylenediamine, was implemented in terms of the impact on the nanorod aspect ratio. Varied substituents on the vicinal diamine structure were examined towards an optimized reaction center in terms of electron density and steric hindrance. Possible interaction mechanisms of the diamine derivatives with ferric species and the correlation between the aspect ratio and electrochemical performance are discussed. Intermediate-sized α-Fe2O3 nanorods with length/aspect ratios of ≈240 nm/≈2.6 and ≈280 nm/≈3.0 were found to have excellent electrochemical characteristics with reversible discharge capacities of 1086 and 1072 mAh g−1 at 0.1 C after 50 cycles.

Structural analysis, solvent effects and intramolecular interactions in rilpivirine: A new non-nucleoside reverse transcriptase inhibitor for HIV treatment

The intramolecular hydrogen bonding in rilpivirine has been evaluated by density functional theory (DFT) calculations. All possible conformers of the corresponding compound were fully optimized at B3LYP/6-311++G(d,p) level using the Gaussian 09 program package. From 22 different obtained conformers, the most stable one were R5 and R8 in the gas phase and aqueous solution, respectively. Those could be stabilized by steric and electronic effects and the intramolecular hydrogen bonding. The solvent effects on the electronic and structural properties were investigated using the Tomasi's polarized continuum model. The conceptual DFT based reactivity and stability descriptors, chemical potential, hardness, electrophilicity index, energy gap and also total energies and dipole moments were calculated. The topological properties of the electron density distributions for CH⋯N and CH⋯C intramolecular hydrogen bond bridges were analyzed in terms of electron density (ρ) and its Laplacian (∇2ρ) at the bond and ring critical points from Bather's quantum theory of atoms in molecules. Results show that the CH⋯N and CH⋯C bonds show low electron density and non-covalent characteristics (∇2ρ (BCP)>0) while CH and CO have covalent character (∇2ρ(BCP)<0). Charge density distributions and chemical reactive sites of studied conformers have been obtained by molecular electrostatic potential surface. The theoretical calculations for rilpivirine conformers in aqueous solution were also performed at the same level of theory. Calculated data indicate that the order of stability of rilpivirine conformers in water is different to their stability order in the gas phase.

Effects of the major sudden stratospheric warming event of 2009 on the subionospheric very low frequency/low frequency radio signals

AbstractThis paper presents effects of the major sudden stratospheric warming (SSW) event of 2009 on the subionospheric very low frequency/low frequency (VLF/LF) radio signals propagating in the Earth‐ionosphere waveguide. Signal amplitudes from four transmitters received by VLF/LF radio networks of Germany and Japan corresponding to the major SSW event are investigated for possible anomalies and atmospheric influence on the high‐ to middle‐latitude ionosphere. Significant anomalous increase or decrease of nighttime and daytime amplitudes of VLF/LF signals by ∼3–5 dB during the SSW event have been found for all propagation paths associated with stratospheric temperature rise at 10 hPa level. Increase or decrease in VLF/LF amplitudes during daytime and nighttime is actually due to the modification of the lower ionospheric boundary conditions in terms of electron density and electron‐neutral collision frequency profiles and associated modal interference effects between the different propagating waveguide modes during the SSW period. TIMED/SABER mission data are also used to investigate the upper mesospheric conditions over the VLF/LF propagation path during the same time period. We observe a decrease in neutral temperature and an increase in pressure at the height of 75–80 km around the peak time of the event. VLF/LF anomalies are correlated and in phase with the stratospheric temperature and mesospheric pressure variation, while minimum of mesospheric cooling shows a 2–3 day delay with maximum VLF/LF anomalies. Simulations of VLF/LF diurnal variation are performed using the well‐known Long Wave Propagating Capability (LWPC) code within the Earth‐ionosphere waveguide to explain the VLF/LF anomalies qualitatively.