Determination Of Electron Density Research Articles

New Insights into the Catalytic Activity of Cobalt Orthophosphate Co3 (PO4 )2 from Charge Density Analysis.

An extensive characterization of Co3(PO4)2 was performed by topological analysis according to Bader‘s Quantum Theory of Atoms in Molecules from the experimentally and theoretically determined electron density. This study sheds light on the reactivity of cobalt orthophosphate as a solid‐state heterogeneous oxidative‐dehydration and ‐dehydrogenation catalyst. Various faces of the bulk catalyst were identified as possible reactive sites given their topological properties. The charge accumulations and depletions around the two independent five‐ and sixfold‐coordinated cobalt atoms, found in the topological analysis, are correlated to the orientation and population of the d‐orbitals. It is shown that the (011) face has the best structural features for catalysis. Fivefold‐coordinated ions in close proximity to advantageously oriented vacant coordination sites and electron depletions suit the oxygen lone pairs of the reactant, mainly for chemisorption. This is confirmed both from the multipole refinement as well as from density functional theory calculations. Nearby basic phosphate ions are readily available for C−H activation.

Experimental Determination of Electronic Density and Temperature in Water-Confined Plasmas Generated by Laser Shock Processing

In this work, diagnoses of laser-induced plasmas were performed in several Laser Shock Processing (LSP) experiments using the Balmer Hα-line (656.27 nm) and several Mg II spectral lines. A Q-switched laser of Nd:YAG was focused on aluminum samples (Al2024-T351) in LSP experiments. Two methods were used to diagnose the plasma. The first method, which required two different experiments, was the standard for establishing the electronic temperature through the use of a Boltzmann Plot with spectral lines of Mg II and self-absorption correction. The Stark width of the Balmer Hα-line was used to determine the electron density in each of the cases studied. The second method had lower accuracy, but only required an experimental determination. Two parameters, the electronic temperature and the electron density, were obtained with the aid of the Hα-line in a single data acquisition process. The order of magnitude of the temperature obtained from this last method was sufficiently close to the value obtained by the standard method (within a factor lower than 2.0), which is considered to be important in order to allow for its possible use in industrial conditions.

Multipole electron densities and atomic displacement parameters in urea from accurate powder X-ray diffraction.

Electron density determination based on structure factors obtained through powder X-ray diffraction has so far been limited to high-symmetry inorganic solids. This limit is challenged by determining high-quality structure factors for crystalline urea using a bespoke vacuum diffractometer with imaging plates. This allows the collection of data of sufficient quality to model the electron density of a molecular system using the multipole method. The structure factors, refined parameters as well as chemical bonding features are compared with results from the high-quality synchrotron single-crystal study by Birkedal et al. [Acta Cryst. (2004), A60, 371-381] demonstrating that powder X-ray diffraction potentially provides a viable alternative for electron density determination in simple molecular crystals where high-quality single crystals are not available.

Evaluation of emission contributions from charge-exchange between the excited states of deuterium with He+ during diagnostic of thermal helium gas beam injection and laser-induced fluorescence

Emission contributions from charge-exchange of excited deuterium (n = 2, 3) with He+ are evaluated in a 1-D kinetic collisional radiative model in order to analyze their effects on the Thermal Helium Beam (THB) line-ratio diagnostic on ASDEX Upgrade and Laser Induced Fluorescence (LIF) He I density measurements in ITER. Recent charge-exchange calculations show that cross sections from excited deuterium (n = 2, 3) with He+ are over 4-orders of magnitude higher than those from the ground state (n = 1) and occur at very low energies where they are more likely to interact with the thermal He+ ions introduced by ionization of the diagnostic helium gas-puff injection. Higher densities of excited deuterium are typically present in the Scrape-Off Layer (SOL), divertor, and edge regions of tokamaks, where the LIF and THB helium diagnostics are typically used for nHeI and simultaneous determination of electron temperatures and densities and where contributions from charge-exchange emission may offset these values if not taken into account. The analysis presented in this work shows that due to the higher density of deuterium in the ground rather than in excited states and the divergent behavior of deuterium and He+ density profiles along the SOL and edge regions, the deuterium-He+ charge-exchange contributions to the helium puff emission are 3-orders of magnitude lower than those from electron-impact excitation. Similar plasma conditions are expected in the ITER divertor, with the exception that in the area near the strike-points and targets, the electron temperature is not high enough to excite from the ground state but deuterium, electron, and He+ densities are high enough to dominate the emission from charge-exchange and recombination. These findings strengthen the assumption made in the present line-ratio model that helium emission from gas-puff into plasma is mainly dominated by electron-excitation. It is also shown that, in general, charge-exchange helium emission is 2-orders of magnitude higher than the emission due to recombination. These findings suggest the importance of including charge-exchange processes as a source of neutrals in ionic fractional abundance calculations in plasmas and helium-ash transport modeling in fusion reactors.

The Effect of Background Gas on the Excitation Temperature and Electron Number Density of Basalt Plasma Induced by 10.6 Micron Laser Radiation

Time-integrated optical emission spectroscopy was applied for the analysis of emission spectra, and determination of electron densities and excitation temperatures of basalt plasma induced by 10.6 micron laser radiation. The plasma was studied in air, argon and carbon dioxide, under pressure of 10, 50, and 100 mbar. The plasma emission intensity was found to be strongly dependent on the nature of the ambient gas and its pressure. The highest emission intensities and signal to noise ratios were obtained in argon. Depending on the composition and pressure of the surrounding atmosphere, the values of plasma temperature varied between 14,400 K (air at 10 mbar) and 17,100 K (carbon dioxide at 100 mbar). Similarly, the electron number density varied between 3 × 1016 cm−3 (10 mbar air) and 1.6 × 1017 cm−3 (100 mbar CO2). The observed behavior was correlated with the properties of the studied gases, in particular, their mass, thermal conductivity and ionization energy, and the role of the ambient gas in controlling the efficiency of laser-target coupling, laser-plasma interaction and plasma shielding.

Electron Density Profiles in the Upper Ionosphere of Mars From 11 Years of MARSIS Data: Variability Due to Seasons, Solar Cycle, and Crustal Magnetic Fields

AbstractThe Mars Advanced Radar for Subsurface and Ionosphere Sounding on board the Mars Express spacecraft measures the frequency of local plasma oscillations, which can be used to determine electron densities local to the spacecraft. This paper provides an overview of electron densities in the upper Martian ionosphere, obtained by investigating over 400,000 ionograms, during the course of about 11 years, corresponding to a full solar cycle. The data cover wide latitude and longitude ranges, 180° of solar zenith angle (SZA), and altitudes from about 250 to 1,550 km. The electron density profiles show large fluctuations within each orbit and also for any given altitude and SZA range. However, the median electron density is almost constant on the dayside at a fixed altitude range, with the exception of a dip at around 30° SZA, at altitudes between 300 and 600 km. A sudden drop in density is observed as the terminator is approached from the dayside. For a fixed SZA range, the median electron density decreases exponentially with increasing altitude. The high‐altitude scale height is composed of two exponential functions of SZA joined near the ionospheric terminator. The e‐folding height changes between 45 and 214 km from the subsolar point up to 120°, corresponding to effective temperatures between about 165 and 780 K. Solar activity has a clear effect on the median electron densities above 500 km and on e‐folding height. The median electron density is higher during northern winters, as well as above regions of strong crustal fields on the dayside.

Determination of effective atomic numbers and electron densities for some synthesized triazoles from the measured total mass attenuation coefficients at different energies

The effective atomic numbers and electron densities of some synthesized triazoles were determined using the experimental values of total mass attenuation coefficients at 13.93, 17.77, 26.34, and 59.54 keV photon energies. The measurements were performed in a transmission geometry that consists of a Si(Li) detector, an 241Am point source and a target. The measured results were compared with two different theoretical results. The measured results are generally consistent with the theoretical results. It is observed that the measured parameters depend on the photon energy, weighted contributions of the individual atoms within the triazoles, atom number in the triazoles, and chemical composition of triazoles. Also, the effective electron density increases linearly with increasing effective atomic number.

Development of a Method to Determine Electron Density and Effective Atomic Number of High Atomic Number Solid Materials Using Dual-Energy Computed Tomography.

Aim:This study aims to develop a method using dual-energy computed tomography (DECT) to determine the effective atomic number and electron density of substances.Materials and Methods:Ten chemical substances of pure analytical grade were obtained from various manufacturers. These chemicals were pelletized using a hydraulic press. These pellets were scanned using DECT. A relation was obtained for the pellet's atomic number and electron density with their CT number or Hounsfield unit (HU) values. Calibration coefficients were determined. Five new chemical pellets were scanned, and their effective atomic number and electron densities were determined using the calibration coefficients to test the efficacy of the calibration method.Results:The results obtained for effective atomic number and electron density from the HU number of DECT images were within ±5% and ±3%, respectively, of their actual values.Conclusions:DECT can be used as an effective tool for determining the effective atomic number and electron density of high atomic number substance.

Automatic Electron Density Determination by Using a Convolutional Neural Network

In this study, we developed a technique for automatically determining upper hybrid resonance (UHR) frequencies using a convolutional neural network (CNN) to derive the electron density along the orbit of the Arase satellite. We used three CNN models (AlexNet, VGG16 and ResNet) to determine the UHR frequencies without additional features based on an expert's knowledge. We also reproduced the multi-layer perceptron (MLP) model that had been used for the Van Allen probes mission, which requires observed electric field spectra and additional five features (i.e., decimal logarithm of electron cyclotron frequency (log 10 f ce ), L-value, geomagnetic index (K p ), magnetic local time, and frequency bin with the highest power spectral density from the electric field spectra (fbin max )). We confirmed that the proposed method using CNN more accurately determined the UHR frequencies than did the conventional method. The mean absolute error (MAE) of the VGG16 model was 3.478 bins when the input vector comprised both the observed electric field spectrum and the additional five features. In contrast, the MAE of the conventional method was 5.986 bins (72.1% worse). Moreover, we confirmed that the proposed method achieves a high accuracy regardless of the use of the additional five features (the MAE of the ResNet model was 3.664 bins when excluding the additional five features). This suggests that the feature map of the ResNet model acquired a representation ability beyond the five features.

Effective Atomic Number and Electron Density Determination of Some Amino Acids by Using Scattering Intensity Ratio of 59.54 keV Gamma Rays

In this study the specific atomic arguments have been determined for F-Glycine (C2H5O2N), Alenine (L, D) (C3H7O2N), Leucine (L, D) (C6H13O2N), L-Proline (C5H9O2N) amino acids. The calculation procedure of the experimental values of atomic parameters was carried out by using scattering intensity ratios of γ-rays. These γ-rays were obtained from 5 Ci 241Am annular radioactive source. In traditional studies, these arguments were determined by transmission technique. The scattered γ-rays were counted by using an HPGe semiconductor detector. Our detecting system was connected to a separate amplifier and an Accuspec card. Theoretical values of related atomic parameters for amino acid targets were calculated and cross checked with our experiential values. Our deliberated values are in good concordance with theoretical calculations.

Vapor density and electron density determination during high-current anode phenomena in vacuum arcs

This paper presents time and space resolved results of spectroscopic measurements in a vacuum circuit breaker experiment during high-current anode modes, i.e., anode spot type 1, anode spot type 2, and anode plume. Excited state densities for Cu I, Cu II, and Cu III transitions are determined during anode spot type 1 and type 2 as well as for the anode plume. Temporal evolution of excited state densities and Cu neutral gas densities are also determined during anode spot type 1 and type 2, which show that the Cu density in front of the anode during anode spot type 2 is about 6 times higher compared to anode spot type 1. Electron densities are also determined during both types of anode spot using Stark broadening. The electron densities during anode spot type 2 are remarkably higher than during anode spot type 1.

The Hβ line dip shift measurements in wide range of plasma electron density

In this paper, we present experimental shift results of the dip of the Balmer Hβ line emitted from three plasma sources. The use of different sources enabled the measurements to be carried out under a wide range of plasma conditions. The electron density was in the range of (0.17–6.56) × 1023 m−3 and electron temperature in the range of 10,100–33,000 K. For higher electron densities, the measured dip shift shows a nonlinear dependence on the electron density. It is shown that this nonlinearity is the consequence of the asymmetry of the Hβ line. The correlation between the measured dip shift and Hβ line halfwidths shows that the dip shift can be used for plasma electron density determination. This can be useful in cases when the Hβ spectrum cannot be fully covered by the spectral apparatus.

Libraries of Extremely Localized Molecular Orbitals. 3. Construction and Preliminary Assessment of the New Databanks.

The fast and reliable determination of wave functions and electron densities of macromolecules has been one of the goals of theoretical chemistry for a long time, and in this context, several linear scaling techniques have been successfully devised over the years. Different approaches have been adopted to tackle this problem, and one of them exploits the fact that, according to the traditional chemical perception, molecules can be seen as constituted of recurring units (e.g., functional groups) with well-defined chemical features. This has led to the development of methods in which the global wave functions or electron densities of macromolecules are obtained by simply transferring density matrices or fuzzy electron densities associated with molecular fragments. In this context, we propose an alternative strategy that aims at quickly reconstructing wave functions and electron densities of proteins through the transfer of extremely localized molecular orbitals (ELMOs), which are orbitals strictly localized on small molecular units and, for this reason, easily transferable from molecule to molecule. To accomplish this task we have constructed original libraries of ELMOs that cover all the possible elementary fragments of the 20 natural amino acids in all their possible protonation states and forms. Our preliminary test calculations have shown that, compared to more traditional methods of quantum chemistry, the transfers from the novel ELMO databanks allow to obtain wave function and electron densities of large polypeptides and proteins at a significantly reduced computational cost. Furthermore, notwithstanding expected discrepancies, the obtained electron distributions and electrostatic potentials are in very good agreement with those obtained at Hartree-Fock and density functional theory (DFT) levels. Therefore, the results encourage to use the new libraries as alternatives to the popular pseudoatom-databases of crystallography in the refinement of crystallographic structures of macromolecules. In particular, in this context, we have already envisaged the coupling of the ELMO databanks with the promising Hirshfeld atom refinement technique to extend the applicability of the latter to very large systems.

Time-resolved and multiple-angle Thomson scattering on gas-puff Z-Pinch plasmas at pinch time.

A 526.5 nm Thomson scattering diagnostic laser enables probing of the plasma conditions of neon gas-puff z-pinch implosions with temporal resolution. Splitting the laser into two 2.5 J pulses, both 2.3 ns in duration and separated by 4 ns, allows observation of sub-nanosecond time-resolved spectra for a total time of 7 ns. Collection optics were set at 90° and 30° to the laser, observing the same on-axis scattering volume with a radial extent of 0.4 mm. The spectra from both angles were collected by using the same streak camera, using a coupling system that allowed us to obtain temporal, spectral, and angular resolution in the same image. By comparing the ion-acoustic spectra from the two angles, we determined electron temperature and a range of possible electron densities. Measurements made in the 1-3 ns period before pinch time show best fit (determined by a least-squares method) electron densities of around 2 × 1019 cm-3, increasing to 1.5 × 1020 cm-3 in the 3 ns following the start of the x-ray burst (t = 0 ns) from the pinch. The electron temperature increases from 300 eV to 500 eV at t = 0 ns before decreasing to below 300 eV after pinch time. With the present parameters (probe beam, collection angles, and electron temperature and density), this diagnostic method is too insensitive to electron density to provide more than a constraint on that parameter. Plasma regimes in which this technique could determine electron density with some precision are calculated.

Building Fluorinated Hybrid Crystals: Understanding the Role of Noncovalent Interactions

Noncovalent interactions play a key role in functional materials. Metal–organofluorine interactions are of special interest because they directly affect the structure and reactivity of hybrid fluorinated materials. In-depth understanding and modulating of these interactions would enable the rational design of functional materials from fundamental chemical principles. In this work, we propose a computational approach that enables a comprehensive and quantitative characterization of noncovalent interactions (NCIs) in hybrid fluorinated crystals. Our approach couples dispersion-corrected density functional theory to NCI analysis. Additionally, we determine electron densities at bond critical points and identify electrostatic interactions using a simple electrostatic model. The versatility of this approach to probe a wide range of NCIs is demonstrated for a series of four bimetallic fluorinated crystals incorporating alkali–manganese(II) pairs and trifluoroacetato ligands. Noncovalent interactions in these hy...

Synthetic helium beam diagnostic and underlying atomic data

We report on synthetic helium beam emission spectroscopy (BES) in fusion edge plasmas, as enabled by the 3D kinetic (neutral particle) transport code EIRENE. We also review and upgrade the underlying atomic helium data base, resorting to the most recent version of the Goto–Fujimoto collisional-radiative code and a recommended and publicly exposed reference cross section data set from an internationally coordinated (IAEA) evaluation activity. On the example of the Wendelstein 7-X (W7-X) stellarator, we use both the upgraded transport code and data base to simulate the penetration of and radiation from thermal helium used for BES in the island divertor region. This allows to evaluate the applicability of the diagnostic in different plasma backgrounds, simulated with the 3D edge plasma Monte Carlo code EMC3-EIRENE, and with different levels of refinement of underlying atomic data. The sensitivity of the diagnostic to the atomic data set—which is crucial for a quantitative determination of electron density and temperature profiles—is investigated and discussed, as well as the effects of p-He beam widening and correlated line-of-sight integration.

Погрешности определения электронной концентрации при решении обратной задачи радиопросвечивания дневной ионосферы Венеры.

Погрешности определения электронной концентрации при решении обратной задачи радиопросвечивания дневной ионосферы Венеры.

Assessment of electron density effects on dose calculation and optimisation accuracy for nasopharynx, for MRI only treatment planning.

Computed tomography (CT) is the gold standard for radiotherapy simulation and treatment planning, providing spatial accuracy, bony anatomy definition and electron density information for dose calculations. Magnetic resonance imaging (MRI) has been introduced in radiotherapy to improve visualisation of anatomy for accurate target definition and contouring, however lacks electron density information required for dose calculations, with various methods used to overcome this. The aim of this work is to assess the impact on dose calculation accuracy and optimisation results of different approaches to determine electron density, as could be used in MRI only treatment planning for nasopharyngeal datasets with VMAT treatment plans. Volumetric modulated arc therapy (VMAT) plans were created for 10 retrospective head and neck (H&N) nasopharyngeal patients. The VMAT plans were generated on the gold standard dataset, the original CT scan. Data sets with no density correction (water equivalent) and two different sets of bulk density correction for bone/air/tissue applied separately were generated for these patients and the VMAT plans were recalculated for each case. Plans were also reoptimised on these data sets, and recalculated. Optimisation error was assessed through equivalent uniform dose (EUD) differences. Additionally, point dose comparison, dose volume histogram (DVH) analysis and gamma analysis of dose were used to assess dose calculation error. The dose calculation error on average was an increase in EUD whereas the optimisation error on average was a reduction in EUD compared to the original plan for all datasets aside from the bone only override dataset where bone was set to 1.61g/cm3. For the optimisation error, the largest mean absolute error (MAE) was 1.88Gy EUD for the PTV, and 2.21Gy EUD for the brainstem, for the reoptimisation completed on the air only overridden dataset, and recalculated on the original. Bulk density corrections for bone and air provide dose calculations within 3% of the original treatment plans. Optimisation errors have the potential to be greater than dose calculation errors if incorrect density corrections are utilized. Electron density correction using a bulk density approach achieves dose calculation uncertainties within 3%, however more advanced approaches, such as a voxel based approach, may improve accuracy and should be considered.

Measurement of Electron Density from Stark-Broadened Spectral Lines Appearing in Silver Nanomaterial Plasma

This work communicates results from optical emission spectroscopy following laser-induced optical breakdown at or near nanomaterial. Selected atomic lines of silver are evaluated for a consistent determination of electron density. Comparisons are presented with Balmer series hydrogen results. Measurements free of self-absorption effects are of particular interest. For several silver lines, asymmetries are observed in the recorded line profiles. Electron densities of interest range from 0.5 to 3 × 1017 cm−3 for five nanosecond Q-switched Nd:YAG radiation at wavelengths of 1064 nm, 532 nm, and 355 nm and for selected silver emission lines including 328.06 nm, 338.28 nm, 768.7 nm, and 827.3 nm and the hydrogen alpha Balmer series line at 656.3 nm. Line asymmetries are presented for the 328.06-nm and 338.28-nm Ag I lines that are measured following generation of the plasma due to multiple photon absorption. This work explores electron density variations for different irradiance levels and reports spectral line asymmetry of resonance lines for different laser fluence levels.

Characterization of a novel microwave plasma sheet source operated at atmospheric pressure

Typically, microwave plasma sources (MPSs) operated at atmospheric pressure deliver plasmas in the common form of flames or cylindrical columns. In contrast to that, in this paper, a novel MPS (recently patented by us) for generating a new type of plasma in the form of a plasma sheet, which is sustained within a dielectric flat cuboid box, is presented. It is waveguide based, operated at a frequency of 2.45 GHz and in argon at atmospheric pressure. The plasma sheet consists of many filaments, typical of a microwave argon plasma. The MPS is described and analyzed in terms of optical emission spectroscopy, simulation of the electric field distributions in the MPS and numerical modeling of the working gas flow. Depending on the argon flow rate and absorbed microwave power, the determined electron density and rotational temperatures of OH radicals ranged from 3.6 × 1014 to 5.6 × 1014 cm−3 and from 800–1250 K, respectively. Numerical simulations have confirmed that the dimensions of the box are chosen correctly to ensure a sufficiently homogeneous distribution of the gas flow velocity field. The calculated electromagnetic field distributions in the MPS with plasma have shown that the device is well matched to the feeding line. The relative simplicity of the presented plasma source and industrially convenient plasma shape make it attractive for practical applications in the surface treatment of various materials.