Dimensional Electron Density Research Articles

Three dimensional atomistic-scale electron density distribution analysis of ZnWO4: Sm phosphors

In this work, we demonstrate a study of three-dimensional atomic-scale electron density distribution analysis for Sm3+ doped ZnWO4 phosphors. The rare-earth element Sm3+ doped ZnWO4 with various concentrations synthesized via chemical precipitation technique were studied for understanding their photoluminescence properties and bonding characteristics. The density of the electrons along the bond path was determined and the parameters of electron density distribution analysis were correlated with the photoluminescence behavior of the synthesized materials. The present work paves a promising path to get efficient phosphor material for display and lighting applications.

Computer Aided Numerical Simulations of Current Induced Domain Wall in a Nanowire

Abstract This paper proposes the numerical simulations of soft modes of an magnetic domain wall induced by current in a compressed nanowire. We model the Hamiltonian of a nanowire by studying the variations of the parameters with spin-orbit coupling and axial magnetic field. We simulate the variation of chemical potential versus the density of states with spin orbit coupling energy along with Zeeman strength with respect to the energy density. Further we also study of tight binding parameter with spin-orbit coupling energy. Band structure of compressed nanowire is obtained along with simulation of three dimensional electron density and transmission and current density factors. Throughout the manuscript we investigate and make a experimental design of device physics, device characteristics and logical architecture of nanowire required to develop multiple-bit per single cell memory, utilized in high performance computing and vision systems. Using GPU accelerated Micromagnetic framework we simulate the stapled domain wall in a compressed region.

Variation in Coronal Activity from Solar Cycle 24 Minimum to Maximum Using Three-Dimensional Reconstructions of the Coronal Electron Density from STEREO/COR1

Three dimensional electron density distributions in the solar corona are reconstructed for 100 Carrington Rotations (CR 2054$-$2153) during 2007/03$-$2014/08 using the spherically symmetric method from polarized white-light observations with the STEREO/COR1. These three-dimensional electron density distributions are validated by comparison with similar density models derived using other methods such as tomography and a MHD model as well as using data from SOHO/LASCO-C2. Uncertainties in the estimated total mass of the global corona are analyzed based on differences between the density distributions for COR1-A and -B. Long-term variations of coronal activity in terms of the global and hemispheric average electron densities (equivalent to the total coronal mass) reveal a hemispheric asymmetry during the rising phase of Solar Cycle 24, with the northern hemisphere leading the southern hemisphere by a phase shift of 7$-$9 months. Using 14-CR (~13-month) running averages, the amplitudes of the variation in average electron density between Cycle 24 maximum and Cycle 23/24 minimum (called the modulation factors) are found to be in the range of 1.6$-$4.3. These modulation factors are latitudinally dependent, being largest in polar regions and smallest in the equatorial region. These modulation factors also show a hemispheric asymmetry, being somewhat larger in the southern hemisphere. The wavelet analysis shows that the short-term quasi-periodic oscillations during the rising and maximum phases of Cycle 24 have a dominant period of 7$-$8 months. In addition, it is found that the radial distribution of mean electron density for streamers at Cycle 24 maximum is only slightly larger (by ~30%) than at cycle minimum.

Real time 3‐D electron density reconstruction over Europe by using TaD profiler

AbstractThe TaD (Topside Sounder Model (TSM)‐assisted Digisonde) profiler, developed on the basis of the Topside Sounder Model (TSM), provides vertical electron density profiles (EDP) over Digisondes from the bottomside ionosphere up to Global Navigation Satellite Systems (GNSS) orbit heights. TaD EDP uses the Digisonde bottomside profile and extends it above the F2 layer peak, representing O+ distribution by α‐Chapman formula and H+ distribution by a single exponent. Topside scale height HT and transition height hT are taken from TSM, while the plasmasphere scale height Hp is defined as a function of HT. All profile parameters are adjusted to the current conditions comparing the profile integral with the GNSS vertical total electron content (TEC) retrieved from the European Reference Frame (EUREF) maps. To expand to three dimensions (3‐D), European maps of foF2 and hmF2 are produced, based on Digisonde data, with spatial resolution 1°×1° in latitude and longitude, and TaD profiles are calculated at each grid node. Electron density (ED) at any point of the 3‐D space is obtained by linear interpolation of TaD parameters between neighbor nodes. Samples of two dimensional (2‐D) electron density distribution (EDD) at different cross sections of the 3‐D space between 200 km and 1150 km over the mapping area are presented, along with distributions of the electron density along various raypaths of GNSS signals. The modeled 3‐D EDD is compared with vertical (vTEC) and slant (sTEC) TEC parameters calculated from individual GNSS receivers. The model error (relative deviation of model from the data), based on 6780 data values, is 10% for sTEC and 6% for vTEC.

Achievement of a short term three dimensional electron density mapping of the ionosphere in the European sector: Comparisons with the IRI model for quiet-moderate geomagnetic-ionospheric conditions

In this paper will be described the procedure followed for the achievement of a short term three dimensional (3-D) electron density mapping of the ionosphere in the European area.It consists of three main steps: (1) foF2 and M(3000)F2 short-term forecasts, (foF2STF) and (M3000F2STF), are calculated at 12 ionospheric observatories scattered in the European area; (2) the values of foF2STF and M3000F2STF on a grid of equi-spaced points, (foF2STF,GP) and (M3000F2STF,GP), are calculated by means of an appropriate interpolation algorithm by using the foF2STF and M3000F2STF data; (3) foF2STF,GP and M3000F2STF,GP data ingestion into the IRI model is employed to produce a short term 3-D electron density mapping (ST-3D-M) of the ionosphere.The electron density profiles provided by the ST-3D-M and IRI models, were compared with the electron density profiles autoscaled by the Automatic Real-Time Ionogram Scaler with True-height (ARTIST) system, which are here considered as the truth profiles. The results of these comparisons, shown for a certain number of epochs during quiet-moderate geomagnetic-ionospheric conditions, in the truth-sites of Athens (38○.0′N, 23○.5′E), Chilton (51○.5′N, −0○.6′W), Dourbes (50○.1′ N, 4○.6′E), Pruhonice (50○.0′N, 14○.6′E), Rome (41○.9′N, 12○.5′E), and Tortosa (40○.8′N, 0○.5′E), indicate that the ST-3D-M as forecasting tool can be considered generally reliable.

Minimizing NeQuick TEC prediction error via data ingestion at three African equatorial stations

NeQuick model is a three dimensional and time dependent ionospheric electron density model that gives as output electron density profile N(h) and via integration the slant TEC (sTEC) for any particular locations on the globe. The model requires as input solar ionizing index in addition to the coordinates of the ray points. The index being used as a proxy to the EUV which is responsible for the ionization of the upper atmosphere is either the smoothed sunspot numbers (R12) or the 10.7 cm solar radio noise flux (F10.7 ). The closer the values of the proxy index to the EUV value, the better the performance of the NeQuick model. We have therefore investigated the improvement of NeQuick via optimization of the F10.7 index using GPS sTEC derived data from three stations in the equatorial region of the African sector. In order to achieve this, the root mean square of the difference between the modeled and the observed sTEC values were calculated for a range of values of F10.7, and via optimization, the effective F10.7 index (i.e. the one that gives the minimum root mean square error or the one that minimizes the error between the observed and the modeled) was obtained for a particular day and for a particular station. The value obtained (i.e. F10.7 effective ), which is a station based value, is then used as ionization index into the NeQuick model for the next two consecutive days. The results obtained showed an improvement in the model performance for these two days although that of the first day, in most cases, is better than that of the second day.

Maximum Entropy Method Applied in the Experimental Visualization of Electron Density Distributions in BiFeO3

The BiFeO3 is a largely studied compound with magnetoeletric coupling at room temperature. This is due its potential technological applications that can be directly used in advanced technologies. BiFeO3 is an oxide with perovskite structure and R3c space group (rhombohedral symmetry). In this work, synchrotron radiation X-ray powder diffraction data was used to obtain a detailed description of BiFeO3 crystal structure. Thereafter, experimental electron density distribution calculations were obtained using by the maximum entropy method (MEM) statistical approach. The ionic/covalent nature of the bonding and the interaction between the ions are clearly revealed by constructing electron density maps. The Fe3+-O2− and Bi3+-O2− bonding were studied in 1 and 2 dimensional electron density distributions. Due the high resolution of the obtained maps, it can be regarded as the most precise electron density distributions seen inside the material.

Nanoscale strain mapping in battery nanostructures

Coherent x-ray diffraction imaging is used to map the local three dimensional strain inhomogeneity and electron density distribution of two individual LiNi0.5Mn1.5O4−δ cathode nanoparticles in both ex-situ and in-situ environments. Our reconstructed images revealed a maximum strain of 0.4%. We observed different variations in strain inhomogeneity due to multiple competing effects. The compressive/tensile component of the strain is connected to the local lithium content and, on the surface, interpreted in terms of a local Jahn-Teller distortion of Mn3+. Finally, the measured strain distributions are discussed in terms of their impact on competing theoretical models of the lithiation process.

Titin-Based Modulation of Sarcomere Structure as Revealed by Equatorial X-Ray Diffraction

Myofilament Length Dependent Activation (LDA) is the cellular mechanism underlying the Frank-Starling Law of the Heart. LDA is defined as an increase in force for a given amount of calcium when the muscle is stretched to a longer sarcomere length. Despite its physiological importance, the sensor that underlies LDA is not known. To address this issue we use X-ray diffraction of intact twitching rat papillary muscle where muscle initially at maximum sarcomere length (Lmax) is quickly released to slack length (Slack). X-ray patterns are taken is a 10 ms window just prior to force generation.Previous analyses of the data did not support the hypothesis that there was a radially outward movement of myosin heads at Lmax requiring some other explanation. The equatorial portion of our X-ray patterns show 5 pairs of well-resolved diffraction spots from the 1,0 to the 3, 0 equatorial reflection. This allowed calculation of two dimensional electron density maps (ED maps) comparing Lmax and Slack from both wild type rats and mutant rats with exceptionally long titin (J Mol Cell Cardiol. 44:983-91 2008) where the passive tension generated at Lmax, as well as LDA, is much reduced. Difference ED maps (Lmax-Slack) from WT rats indicate a better localization of both thick and thin filaments at Lmax plus the existence of bridging density joining the thick and thin filaments at Lmax and not at slack. In difference ED maps from the titin mutant rats, the bridging structures are absent and only the thick filaments appeared better localized. These results support a model where a small number of crossbridges transmit titin-based strain from the thick filament to the thin filament as part of the mechanism of LDA. Supported by NIH R01HL075494 and 9 P41 GM103622.

Quantum oscillations of nonlinear response in electron systems with variable density

Quantum oscillations of dissipative resistance are observed in response to electric current applied to a GaAs quantum well with variable two dimensional electron density placed in quantizing magnetic fields. At a fixed magnetic field, the period of the current induced oscillations depends linearly on the electron density. The observed behavior is in accord with a recently proposed model that considers the DC bias-induced spatial re-population of Landau levels as the origin of the resistance oscillations. It indicates the important role of the electron screening in the vicinity of the quantum well, which significantly enhances the nonlinear response.

A Theoretical Estimation of the Charge Density Distribution in the Diluted Magnetic Semiconductors of Si<sub>1-x</sub>M<sub>x</sub> and Ge<sub>1-x</sub>M<sub>x </sub>(M = V, Mn, Co)

An effort has been made to understand the charge density distribution of the Si and Ge based diluted magnetic semiconductors. A theoretical analysis has been done on the variation of charge densities when the semiconductors Si and Ge are doped with the transition metal atoms of V, Mn and Co with different concentrations of x (0.02, 0.04, 0.06, 0.08, and 0.10), in Si1-xMx and Ge1-xMx. Two dimensional electron density contour maps have been plotted for all the compositions studied in this work. The theoretical mid bond densities were found out for the compounds which can be taken as the reference values for comparison of the experimental values of the same compositions.

Local Structural Analysis of Al<sub>2</sub>O<sub>3</sub>, Cr:Al<sub>2</sub>O<sub>3</sub> and V:Al<sub>2</sub>O<sub>3</sub> Using Powder XRD

The electron density distribution and the local structure of aluminum oxide (Al2O3), chromium doped aluminum oxide (Cr:Al2O3) and vanadium doped aluminum oxide (V:Al2O3) have been studied. Powder X-ray data set of Al2O3 , Cr:Al2O3 and V:Al2O3 is analyzed in terms of cell parameters, thermal vibration parameters, 1D, 2D and 3 Dimensional electron density distributions. The bonding between the atoms using the maximum entropy method (MEM) and bond length distribution using pair distribution function (PDF) has been analyzed. The particle size of Al2O3 , Cr:Al2O3 and V:Al2O3 is also analyzed using XRD and SEM.

Molecular Structure of Type II Collagen

The naturally crystalline arrangement of collagen molecules within the fibrils of some tissues, allows the use of fiber diffraction methods for structural characterization. This method has the potential to give structural information about collagen type II with minimum interference from sample preparation and may give the opportunity to produce relatively detailed three-dimensional visualization of the fibrils sub-structure. Towards this end, experiments with Multiple Isomorphous Replacement (MIR) were carried out to so that a one-dimensional electron density map of native collagen structure may be determined. Several experiments were performed at the BioCAT facility at Argonne National Laboratory with variations of: sample holder designs, sample preparation procedures, heavy atoms for MIR, temperatures and setups for small and medium angle diffraction. Some more optimum combinations of these produced data of resolution 15 A or better in the axial direction. Using these data, a subsequent study that also made use of AFM and TEM techniques, revealed that the parameters of collagen type II fibrils from lamprey notochord are very similar if not the same as collagen type II fibrils in mammalian tissues: 30 nm in diameter, axial periodicity of 67 nm, amino acid charge distribution is the same. Analysis of the X-ray diffraction derived one dimensional electron density map showed that the telopeptides, which are crucial for fibrillogenesis and organization of collagen type II tissues, have a very specific folded conformation, reminiscent of that seen in the C-telopeptide of type I collagen. The folded telopeptide conformations provide a clear picture of the intermolecular crosslink locations within the contributing collagen monomers within the 67 nm D-period. This type of structural information is essential for understanding the mechanisms of tissue development and disease pathologies.

Radio occultation techniques for probing the ionosphere

GPS radio occultation measurements establish the basis for a new remote sensing technique for vertical profile information on the electron density of the entire ionosphere from satellite orbit heights down to the bottomside. No other profiling technique such as vertical sounding or incoherent scatter, unifies vertical profiling through the entire ionosphere with global coverage. Inversion methods are described both for vertical profiling as well as for tree dimensional electron density reconstructions of the ionosphere. In three dimensional electron density reconstructions using signals from Global Navigation Satellite Systems (GNSS), the Ionospheric Radio Occultation (IRO) measurements provide vertical information which is complementary to the information obtained by ground based measurements. Assessment of achievable accuracy and spatial resolution are addressed by simulation studies. IRO measurements have been carried out onboard the German CHAMP satellite since 11 April 2001 on a routine basis. Assuming a spherically layered ionosphere, up to about 150 Electron Density Profiles (EDPs) per day are retrieved within a latency of 3 h. Validation results obtained by using independent data sources are reported. The validation with vertical sounding data in mid-latitudes indicates a small positive bias in the plasma frequency of up to about 0.5 MHz throughout the entire profile. Averages of the numerous EDPs show wellknown ionospheric phenomena such as the equatorial anomaly, the winter anomaly and the expansion of the profile with increasing solar energy input. It is concluded that CHAMP-IRO measurements have the potential to establish global data sets of vertical electron density profiles for developing and improving global ionospheric models and to provide operational space weather information.

Local structure of the thermoelectric material Mg 2Si using XRD

The electron density distribution and local structure of the high temperature thermoelectric material Mg 2Si have been studied and analyzed. Powder X-ray data of Mg 2Si is analyzed in terms of local structure, thermal vibration parameters, 1D, 2D and 3 dimensional electron density distributions. The bonding between the atoms has been studied using maximum entropy method (MEM) and the bond-length distribution using pair distribution function (PDF).

Visualization of Magnetic Surfaces during Current Ramp-Up Phase Using Thermal Lithium Sheet Beam in CPD

Two dimensional electron density profile measurement has been performed in the spherical tokamak CPD (Compact PWI experimental Device) using Li sheet beam imaging technique. The topological change from the open magnetic field line configuration to the closed one is visualized by this technique. The plasma current can be driven by RF waves itself in a weak mirror configuration and a clear change is observed in plasma boundary as well as magnetic field topology associated with the transition of the current from low (∼1 kA) to high (∼3 kA) value.

Effect of reaction time on the composition of graphite bis(trifluoromethanesulfonyl)imide

Graphite intercalation compounds (GICs) of composition CxN(SO2CF3)2·δF are prepared under ambient conditions in 48% hydrofluoric acid, using K2MnF6 as an oxidizing reagent. The stage 2 GIC product structures are determined using powder XRD and modeled by fitting one dimensional electron density profiles. A new digestion method followed by selective fluoride electrode elemental analyses allows the determination of free fluoride within products, and the compositional x and δ parameters are determined for reaction times from 0.25 to 500h.

Positron annihilation study for cadmium (electronic structure and enhancement effect)

AbstractThe three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW), linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were argued in view of positron wave function in Cd.

Sounding of the topside ionosphere/plasmasphere based on GPS measurements from CHAMP: Initial results

Beside the GPS radio occultation measurements of the troposphere and ionosphere, the CHAMP satellite tracks presently up to 8 GPS satellites simultaneously for navigation. The received dual frequency GPS signals provide valuable information on the ionization state of the topside ionosphere and plasmasphere. This paper briefly describes a new developed model assisted technique to improve the three dimensional electron density estimation above the CHAMP orbit from these GPS measurements. Application of this assimilation algorithm provides a 2‐D electron density slice of the ionosphere/plasmasphere system within the CHAMP orbit plane from the CHAMP altitude up to GPS orbit heights. We estimate the accuracy of the GPS TEC calibration and perform a first validation by comparing the retrieved electron density of the ionosphere/plasmasphere slice at CHAMP altitude to simultaneous electron density measurements of the Langmuir Probe onboard CHAMP.

The physical structure of the planetary nebula NGC 6781

The planetary nebula NGC 6781 was imaged in major optical emission lines. These lines allow us to construct maps of the projected, two dimensional Balmer decrement, electron density, electron temperature, ionization and abundance structure. The average electron density, determined from the (S ii) lines, is500 cm 3 , while the electron temperature distribution, determined from the (N ii) lines, is flat at 10 000 K. The Balmer decrement map shows that there are variations in extinction between the north and south areas of the planetary nebula. The higher extinction observed to the north of the central star is probably caused by dust spatially associated with CO emission at blue{shifted velocities. The (N ii) image reveals the known optical halo, at a flux level of0.2% of the strong shell emission in the east, but now the angular extent of 216 00 190 00 is much larger than previous measurements. The halo is also present in (O iii), where we measure an extent of 190 00 162 00 .T he ionization maps indicate substantial ionization along the caps of the ellipsoid as well as in the halo. The maps also show a sharp decrease in ionization along the outer edge of the shell in the west and the east, south{east. The typical log abundances measured for He, N, O and S are 10.97, 8.14, 8.72 and 6.90, respectively.