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Sample records for additional electron density

  1. Visualization of electronic density

    DOE PAGESBeta

    Grosso, Bastien; Cooper, Valentino R.; Pine, Polina; Hashibon, Adham; Yaish, Yuval; Adler, Joan

    2015-04-22

    An atom’s volume depends on its electronic density. Although this density can only be evaluated exactly for hydrogen-like atoms, there are many excellent numerical algorithms and packages to calculate it for other materials. 3D visualization of charge density is challenging, especially when several molecular/atomic levels are intertwined in space. We explore several approaches to 3D charge density visualization, including the extension of an anaglyphic stereo visualization application based on the AViz package to larger structures such as nanotubes. We will describe motivations and potential applications of these tools for answering interesting questions about nanotube properties.

  2. Functionalisation of graphene by edge-halogenation and radical addition using polycyclic aromatic hydrocarbon models: edge electron density-binding energy relationship

    NASA Astrophysics Data System (ADS)

    Yadav, Amarjeet; Mishra, P. C.

    2015-04-01

    Structures and properties of functionalised graphene were investigated using several derivatives of some small polycyclic aromatic hydrocarbons (PAHs) taken as finite size models employing unrestricted density functional theory. The functionalisation reactions included fluorination or chlorination of all the edge carbon sites, addition of H, F or Cl atom, OH or OOH group at the different sites and addition of OH or OOH group at the different sites of the edge-halogenated PAHs. σ-inductive effects of fluorine and chlorine in the edge-fluorinated and edge-chlorinated PAHs, respectively, were found to affect electron density and molecular electrostatic potential (MEP) distributions significantly. σ-holes were located at the MEP surfaces along the CH and CCl bonds of the unmodified and edge-chlorinated PAHs, respectively. The H and F atoms and the OH group were found to add to all the carbon sites of PAHs exothermically, while addition of the Cl atom and the OOH group was found to be exothermic at a few carbon sites and endothermic at the other carbon sites. Enhanced electron densities at the edge carbon sites of the PAHs and binding energies of adducts of H and F atoms and the OH group at these sites were found to be linearly correlated.

  3. Visualization of electronic density

    NASA Astrophysics Data System (ADS)

    Grosso, Bastien; Cooper, Valentino R.; Pine, Polina; Hashibon, Adham; Yaish, Yuval; Adler, Joan

    2015-10-01

    The spatial volume occupied by an atom depends on its electronic density. Although this density can only be evaluated exactly for hydrogen-like atoms, there are many excellent algorithms and packages to calculate it numerically for other materials. Three-dimensional visualization of charge density is challenging, especially when several molecular/atomic levels are intertwined in space. In this paper, we explore several approaches to this, including the extension of an anaglyphic stereo visualization application based on the AViz package for hydrogen atoms and simple molecules to larger structures such as nanotubes. We will describe motivations and potential applications of these tools for answering interesting physical questions about nanotube properties.

  4. Interstellar Electron Density Spectra

    NASA Astrophysics Data System (ADS)

    Lambert, Hendrick Clark

    This study concerns the investigation of the form of the wavenumber spectrum of the Galactic electron density fluctuations through an examination of the scattering of the radio pulses emitted by pulsars as they propagate through the diffuse ionized interstellar gas. A widely used model for the electron density spectrum is based on the simple power-law: Pne(q)∝ q-β, where β = 11/3 is usually assumed, corresponding to Kolmogorov's turbulence spectrum. The simple Kolmogorov model provides satisfactory agreement for observations along many lines of sight; however, major inconsistencies remain. The inconsistencies suggest that an increase in the ratio of the power between the high (10-8[ m]-1≤ q<=10-7[ m]-1) and low (10-13[ m]-1≤ q<=10-12[ m]-1) wavenumbers is needed. This enhancement in the ratio can in turn be achieved by either including an inner scale, corresponding to a dissipation scale for the turbulent cascade, in the Kolmogorov spectrum or by considering steeper spectra. Spectra with spectral exponents β > 4 have been in general rejected based on observations of pulsar refractive scintillations. The special case of β = 4 has been given little attention and is analyzed in detail. Physically, this 'β = 4' model corresponds to the random distribution, both in location and orientation, of discrete objects with relatively sharp boundaries across the line of sight. An outer scale is included in the model to account for the average size of such objects. We compare the predictions of the inner-scale and β = 4 models both with published observations and observations we made as part of this investigation. We conclude that the form of the wavenumber spectrum is dependent on the line of sight. We propose a composite spectrum featuring a uniform background turbulence in presence of randomly distributed discrete objects, as modeled by the β = model.

  5. Effect of Ni and Pd Addition on Mechanical, Thermodynamic, and Electronic Properties of AuSn4-Based Intermetallics: A Density Functional Investigation

    NASA Astrophysics Data System (ADS)

    Tian, Yali; Zhou, Wei; Wu, Ping

    2016-05-01

    The effects of Ni and Pd addition on the mechanical, thermodynamic, and electronic properties of AuSn4-based intermetallic compounds (IMCs) have been investigated by first-principles calculations to reveal the essence of Au embrittlement. Three kinds of doped (namely Ni-doped, Pd-doped, and Ni/Pd-codoped) IMCs are considered in this work. The polycrystalline elastic properties are deduced from single-crystal elastic constants. It is found that the doped systems together with nondoped AuSn4 are all ductile phases. For Ni-doped AuSn4, the modulus, hardness, brittleness, Debye temperature, and minimum thermal conductivity increase with the Ni fraction, but this is not the case for the Pd-doped material, since Au0.75Pd0.25Sn4 is the more brittle phase. For Au0.5Pd0.25Ni0.25Sn4, the mechanical, thermodynamic, and electronic properties are similar to those of Au0.5Pd0.5Sn4.

  6. Effect of Ni and Pd Addition on Mechanical, Thermodynamic, and Electronic Properties of AuSn4-Based Intermetallics: A Density Functional Investigation

    NASA Astrophysics Data System (ADS)

    Tian, Yali; Zhou, Wei; Wu, Ping

    2016-08-01

    The effects of Ni and Pd addition on the mechanical, thermodynamic, and electronic properties of AuSn4-based intermetallic compounds (IMCs) have been investigated by first-principles calculations to reveal the essence of Au embrittlement. Three kinds of doped (namely Ni-doped, Pd-doped, and Ni/Pd-codoped) IMCs are considered in this work. The polycrystalline elastic properties are deduced from single-crystal elastic constants. It is found that the doped systems together with nondoped AuSn4 are all ductile phases. For Ni-doped AuSn4, the modulus, hardness, brittleness, Debye temperature, and minimum thermal conductivity increase with the Ni fraction, but this is not the case for the Pd-doped material, since Au0.75Pd0.25Sn4 is the more brittle phase. For Au0.5Pd0.25Ni0.25Sn4, the mechanical, thermodynamic, and electronic properties are similar to those of Au0.5Pd0.5Sn4.

  7. Teaching Chemistry with Electron Density Models

    NASA Astrophysics Data System (ADS)

    Shusterman, Gwendolyn P.; Shusterman, Alan J.

    1997-07-01

    Linus Pauling once said that a topic must satisfy two criteria before it can be taught to students. First, students must be able to assimilate the topic within a reasonable amount of time. Second, the topic must be relevant to the educational needs and interests of the students. Unfortunately, the standard general chemistry textbook presentation of "electronic structure theory", set as it is in the language of molecular orbitals, has a difficult time satisfying either criterion. Many of the quantum mechanical aspects of molecular orbitals are too difficult for most beginning students to appreciate, much less master, and the few applications that are presented in the typical textbook are too limited in scope to excite much student interest. This article describes a powerful new method for teaching students about electronic structure and its relevance to chemical phenomena. This method, which we have developed and used for several years in general chemistry (G.P.S.) and organic chemistry (A.J.S.) courses, relies on computer-generated three-dimensional models of electron density distributions, and largely satisfies Pauling's two criteria. Students find electron density models easy to understand and use, and because these models are easily applied to a broad range of topics, they successfully convey to students the importance of electronic structure. In addition, when students finally learn about orbital concepts they are better prepared because they already have a well-developed three-dimensional picture of electronic structure to fall back on. We note in this regard that the types of models we use have found widespread, rigorous application in chemical research (1, 2), so students who understand and use electron density models do not need to "unlearn" anything before progressing to more advanced theories.

  8. Electron (charge) density studies of cellulose models

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Introductory material first describes electron density approaches and demonstrates visualization of electron lone pairs and bonding as concentrations of electron density. Then it focuses on the application of Bader’s Quantum Theory of Atoms-in-Molecules (AIM) to cellulose models. The purpose of the ...

  9. Electron density studies of methyl cellobioside

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Experimental X-ray diffraction crystallography determines the variations in electron density that result from the periodic array of atoms in a crystal. Normally, the positions and type of atom are determined from the electron density based on an approximation that the atoms are spherical. However, t...

  10. The mapping of electronic energy distributions using experimental electron density.

    PubMed

    Tsirelson, Vladimir G

    2002-08-01

    It is demonstrated that the approximate kinetic energy density calculated using the second-order gradient expansion with parameters of the multipole model fitted to experimental structure factors reproduces the main features of this quantity in a molecular or crystal position space. The use of the local virial theorem provides an appropriate derivation of approximate potential energy density and electronic energy density from the experimental (model) electron density and its derivatives. Consideration of these functions is not restricted by the critical points in the electron density and provides a comprehensive characterization of bonding in molecules and crystals. PMID:12149553

  11. Electron density measurements in highly electronegative plasmas

    NASA Astrophysics Data System (ADS)

    Rafalskyi, D.; Lafleur, T.; Aanesland, A.

    2016-08-01

    In this paper we present experimental measurements of the electron density in very electronegative ‘ion–ion’ Ar–SF6 plasmas where previous investigations using Langmuir probes have observed electronegativities of up to 5000. The electron density is measured using a short matched dipole probe technique that provides a tolerance better than  ±2 · 1013 m‑3. The results demonstrate that the electron density in the low pressure plasma source (which contains a magnetic filter) can be reduced to around 2.7 · 1013 m‑3 with a corresponding plasma electronegativity of about 4000; close to that from fluid simulation predictions. The highest electronegativity, and lowest electron density, is achieved with a pure SF6 plasma, while adding only 6% SF6 to Ar allows the electronegativity to be increased from 0 to a few hundred with a corresponding decrease in the electron density by more than a thousand. The impedance probe based on a short matched dipole appears to be a practical diagnostic that can be used for independent measurements of the electron density in very electronegative plasmas, and opens up the possibility to further investigate and optimize electronegative plasma sources.

  12. Wavelet analysis of electron-density maps.

    PubMed

    Main, P; Wilson, J

    2000-05-01

    The wavelet transform is a powerful technique in signal processing and image analysis and it is shown here that wavelet analysis of low-resolution electron-density maps has the potential to increase their resolution. Like Fourier analysis, wavelet analysis expresses the image (electron density) in terms of a set of orthogonal functions. In the case of the Fourier transform, these functions are sines and cosines and each one contributes to the whole of the image. In contrast, the wavelet functions (simply called wavelets) can be quite localized and may only contribute to a small part of the image. This gives control over the amount of detail added to the map as the resolution increases. The mathematical details are outlined and an algorithm which achieves a resolution increase from 10 to 7 A using a knowledge of the wavelet-coefficient histograms, electron-density histogram and the observed structure amplitudes is described. These histograms are calculated from the electron density of known structures, but it seems likely that the histograms can be predicted, just as electron-density histograms are at high resolution. The results show that the wavelet coefficients contain the information necessary to increase the resolution of electron-density maps. PMID:10771431

  13. Theoretical study of lithium ionic conductors by electronic stress tensor density and electronic kinetic energy density.

    PubMed

    Nozaki, Hiroo; Fujii, Yosuke; Ichikawa, Kazuhide; Watanabe, Taku; Aihara, Yuichi; Tachibana, Akitomo

    2016-07-01

    We analyze the electronic structure of lithium ionic conductors, Li3PO4 and Li3PS4, using the electronic stress tensor density and kinetic energy density with special focus on the ionic bonds among them. We find that, as long as we examine the pattern of the eigenvalues of the electronic stress tensor density, we cannot distinguish between the ionic bonds and bonds among metalloid atoms. We then show that they can be distinguished by looking at the morphology of the electronic interface, the zero surface of the electronic kinetic energy density. © 2016 Wiley Periodicals, Inc. PMID:27232445

  14. Absolute Measurement of Electron Cloud Density

    SciTech Connect

    Covo, M K; Molvik, A W; Cohen, R H; Friedman, A; Seidl, P A; Logan, G; Bieniosek, F; Baca, D; Vay, J; Orlando, E; Vujic, J L

    2007-06-21

    Beam interaction with background gas and walls produces ubiquitous clouds of stray electrons that frequently limit the performance of particle accelerator and storage rings. Counterintuitively we obtained the electron cloud accumulation by measuring the expelled ions that are originated from the beam-background gas interaction, rather than by measuring electrons that reach the walls. The kinetic ion energy measured with a retarding field analyzer (RFA) maps the depressed beam space-charge potential and provides the dynamic electron cloud density. Clearing electrode current measurements give the static electron cloud background that complements and corroborates with the RFA measurements, providing an absolute measurement of electron cloud density during a 5 {micro}s duration beam pulse in a drift region of the magnetic transport section of the High-Current Experiment (HCX) at LBNL.

  15. Electron density measurement by differential interferometry

    SciTech Connect

    Ding, W. X.; Brower, D. L.; Deng, B. H.; Yates, T.

    2006-10-15

    A novel differential interferometer is being developed to measure the electron density gradient and its fluctuations. Two separate laser beams with slight spatial offset and frequency difference are coupled into a single mixer making a heterodyne measurement of the phase difference which is <1% of the total phase change experienced by each beam separately. This measure of the differential phase is made at multiple spatial points and can be inverted directly to provide the local density distribution.

  16. A Robust High Current Density Electron Gun

    NASA Astrophysics Data System (ADS)

    Mako, F.; Peter, W.; Shiloh, J.; Len, L. K.

    1996-11-01

    Proof-of-principle experiments are proposed to validate a new concept for a robust, high-current density Pierce electron gun (RPG) for use in klystrons and high brightness electron sources for accelerators. This rugged, long-life electron gun avoids the difficulties associated with plasma cathodes, thermionic emitters, and field emission cathodes. The RPG concept employs the emission of secondary electrons in a transmission mode as opposed to the conventional mode of reflection, i.e., electrons exit from the back face of a thin negative electron affinity (NEA) material, and in the same direction as the incident beam. Current amplification through one stage of a NEA material could be over 50 times. The amplification is accomplished in one or more stages consisting of one primary emitter and one or more secondary emitters. The primary emitter is a low current density robust emitter (e.g., thoriated tungsten). The secondary emitters are thin NEA electrodes which emit secondary electrons in the same direction as the incident beam. Specific application is targeted for a klystron gun to be used by SLAC with a cold cathode at 30-40 amps/cm^2 output from the secondary emission stage, a ~2 μs pulse length, and ~200 pulses/second.

  17. Density functional for ternary non-additive hard sphere mixtures.

    PubMed

    Schmidt, Matthias

    2011-10-19

    Based on fundamental measure theory, a Helmholtz free energy density functional for three-component mixtures of hard spheres with general, non-additive interaction distances is constructed. The functional constitutes a generalization of the previously given theory for binary non-additive mixtures. The diagrammatic structure of the spatial integrals in both functionals is of star-like (or tree-like) topology. The ternary diagrams possess a higher degree of complexity than the binary diagrams. Results for partial pair correlation functions, obtained via the Ornstein-Zernike route from the second functional derivatives of the excess free energy functional, agree well with Monte Carlo simulation data. PMID:21946780

  18. Electron Density Profiles of the Topside Ionosphere

    NASA Technical Reports Server (NTRS)

    Huang, Xue-Qin; Reinsch, Bodo W.; Bilitza, Dieter; Benson, Robert F.

    2002-01-01

    The existing uncertainties about the electron density profiles in the topside ionosphere, i.e., in the height region from h,F2 to - 2000 km, require the search for new data sources. The ISIS and Alouette topside sounder satellites from the sixties to the eighties recorded millions of ionograms but most were not analyzed in terms of electron density profiles. In recent years an effort started to digitize the analog recordings to prepare the ionograms for computerized analysis. As of November 2001 about 350000 ionograms have been digitized from the original 7-track analog tapes. These data are available in binary and CDF format from the anonymous ftp site of the National Space Science Data Center. A search site and browse capabilities on CDAWeb assist the scientific usage of these data. All information and access links can be found at http://nssdc.gsfc.nasa.gov/space/isis/isis- status.htm1. This paper describes the ISIS data restoration effort and shows how the digital ionograms are automatically processed into electron density profiles from satellite orbit altitude (1400 km for ISIS-2) down to the F peak. Because of the large volume of data an automated processing algorithm is imperative. The TOPside Ionogram Scaler with True height algorithm TOPIST software developed for this task is successfully scaling - 70% of the ionograms. An <> is available to manually scale the more difficult ionograms. The automated processing of the digitized ISIS ionograms is now underway, producing a much-needed database of topside electron density profiles for ionospheric modeling covering more than one solar cycle.

  19. Electronic structure and electron momentum density in TiSi

    NASA Astrophysics Data System (ADS)

    Ghaleb, A. M.; Mohammad, F. M.; Sahariya, Jagrati; Sharma, Mukesh; Ahuja, B. L.

    2013-03-01

    We report the electron momentum density in titanium monosilicide using 241Am Compton spectrometer. Experimental Compton profile has been compared with the theoretical profiles computed using linear combination of atomic orbitals (LCAO). The energy bands, density of states and Fermi surface structures of TiSi are reported using the LCAO and the full potential linearized augmented plane wave methods. Theoretical anisotropies in directional Compton profiles are interpreted in terms of energy bands. To confirm the conducting behavior, we also report the real space analysis of experimental Compton profile of TiSi.

  20. Correlated quantum transport of density wave electrons.

    PubMed

    Miller, J H; Wijesinghe, A I; Tang, Z; Guloy, A M

    2012-01-20

    Recently observed Aharonov-Bohm quantum interference of the period h/2e in charge density wave rings strongly suggests that correlated density wave electron transport is a cooperative quantum phenomenon. The picture discussed here posits that quantum solitons nucleate and transport current above a Coulomb blockade threshold field. We propose a field-dependent tunneling matrix element and use the Schrödinger equation, viewed as an emergent classical equation as in Feynman's treatment of Josephson tunneling, to compute the evolving macrostate amplitudes, finding excellent quantitative agreement with voltage oscillations and current-voltage characteristics in NbSe(3). A proposed phase diagram shows the conditions favoring soliton nucleation versus classical depinning. PMID:22400766

  1. Modeling Ionosphere Environments: Creating an ISS Electron Density Tool

    NASA Technical Reports Server (NTRS)

    Gurgew, Danielle N.; Minow, Joseph I.

    2011-01-01

    The International Space Station (ISS) maintains an altitude typically between 300 km and 400 km in low Earth orbit (LEO) which itself is situated in the Earth's ionosphere. The ionosphere is a region of partially ionized gas (plasma) formed by the photoionization of neutral atoms and molecules in the upper atmosphere of Earth. It is important to understand what electron density the spacecraft is/will be operating in because the ionized gas along the ISS orbit interacts with the electrical power system resulting in charging of the vehicle. One instrument that is already operational onboard the ISS with a goal of monitoring electron density, electron temperature, and ISS floating potential is the Floating Potential Measurement Unit (FPMU). Although this tool is a valuable addition to the ISS, there are limitations concerning the data collection periods. The FPMU uses the Ku band communication frequency to transmit data from orbit. Use of this band for FPMU data runs is often terminated due to necessary observation of higher priority Extravehicular Activities (EVAs) and other operations on ISS. Thus, large gaps are present in FPMU data. The purpose of this study is to solve the issue of missing environmental data by implementing a secondary electron density data source, derived from the COSMIC satellite constellation, to create a model of ISS orbital environments. Extrapolating data specific to ISS orbital altitudes, we model the ionospheric electron density along the ISS orbit track to supply a set of data when the FPMU is unavailable. This computer model also provides an additional new source of electron density data that is used to confirm FPMU is operating correctly and supplements the original environmental data taken by FPMU.

  2. Electron Density Calibration for Radiotherapy Treatment Planning

    SciTech Connect

    Herrera-Martinez, F.; Rodriguez-Villafuerte, M.; Martinez-Davalos, A.; Ruiz-Trejo, C.; Celis-Lopez, M. A.; Larraga-Gutierrez, J. M.; Garcia-Garduno, A.

    2006-09-08

    Computed tomography (CT) images are used as basic input data for most modern radiosurgery treatment planning systems (TPS). CT data not only provide anatomic information to delineate target volumes, but also allow the introduction of corrections for tissue inhomogeneities into dose calculations during the treatment planning procedure. These corrections involve the determination of a relationship between tissue electron density ({rho}e) and their corresponding Hounsfield Units (HU). In this work, an elemental analysis of different commercial tissue equivalent materials using Scanning Electron Microscopy was carried out to characterize their chemical composition. The tissue equivalent materials were chosen to ensure a large range of {rho}e to be included in the CT scanner calibration. A phantom was designed and constructed with these materials to simulate the size of a human head.

  3. Symmetry measures of the electron density.

    PubMed

    Casanova, David; Alemany, Pere; Alvarez, Santiago

    2010-10-01

    In this communication we define electronic symmetry operation and symmetry group measures, eSOM and eSGM, respectively, develop the basic algorithms to obtain them, and give some examples of the possible applications of these new computational tools. These new symmetry measures based on the electron density have been tested in an analysis of (a) the inversion symmetry for heteronuclear diatomic molecules, for the eclipsed and staggered conformations of ethane and tetrafluoroethane, and for a series of octahedral sulfur halides; (b) the reflection symmetry of three different conformers of tetrafluoroethene; and (c) the loss of C(6) symmetry along the B(2u) distortion mode of benzene and an analysis of rotational symmetry for different six-member ring heterocycles. PMID:20652983

  4. Electron Density Calibration for Radiotherapy Treatment Planning

    NASA Astrophysics Data System (ADS)

    Herrera-Martínez, F.; Rodríguez-Villafuerte, M.; Martínez-Dávalos, A.; Ruiz-Trejo, C.; Celis-López, M. A.; Lárraga-Gutiérrez, J. M.; García-Garduño, A.

    2006-09-01

    Computed tomography (CT) images are used as basic input data for most modern radiosurgery treatment planning systems (TPS). CT data not only provide anatomic information to delineate target volumes, but also allow the introduction of corrections for tissue inhomogeneities into dose calculations during the treatment planning procedure. These corrections involve the determination of a relationship between tissue electron density (ρe) and their corresponding Hounsfield Units (HU). In this work, an elemental analysis of different commercial tissue equivalent materials using Scanning Electron Microscopy was carried out to characterize their chemical composition. The tissue equivalent materials were chosen to ensure a large range of ρe to be included in the CT scanner calibration. A phantom was designed and constructed with these materials to simulate the size of a human head.

  5. Reanalysis of relativistic electron phase space density

    NASA Astrophysics Data System (ADS)

    Shprits, Yuri; Chen, Yue; Kondrashov, Dmitri

    In this study we perform a reanalysis of the sparse relativistic electron data using a relatively simple one-dimensional radial diffusion model and a Kalman filtering approach. The results of the reanalysis clearly show pronounced peaks in the electron phase space density (PSD), which can not be explained by the variations in the outer boundary, and can only be produced by a local acceleration processes. The location of the innovation vector shows that local acceleration is most efficient at L* = 5.5. To verify that our results are not affected by the limitations of the satellite orbit and coverage, we performed an "identical twin" experiments with synthetic data specified only at the locations for which CRRES observations are available. Our results indicate that the model with data assimilation can accurately reproduce the underlying structure of the PSD even when data is sparse.

  6. Electron density measurements for plasma adaptive optics

    NASA Astrophysics Data System (ADS)

    Neiswander, Brian W.

    Over the past 40 years, there has been growing interest in both laser communications and directed energy weapons that operate from moving aircraft. As a laser beam propagates from an aircraft in flight, it passes through boundary layers, turbulence, and shear layers in the near-region of the aircraft. These fluid instabilities cause strong density gradients which adversely affect the transmission of laser energy to a target. Adaptive optics provides corrective measures for this problem but current technology cannot respond quickly enough to be useful for high speed flight conditions. This research investigated the use of plasma as a medium for adaptive optics for aero-optics applications. When a laser beam passes through plasma, its phase is shifted proportionally to the electron density and gas heating within the plasma. As a result, plasma can be utilized as a dynamically controllable optical medium. Experiments were carried out using a cylindrical dielectric barrier discharge plasma chamber which generated a sub-atmospheric pressure, low-temperature plasma. An electrostatic model of this design was developed and revealed an important design constraint relating to the geometry of the chamber. Optical diagnostic techniques were used to characterize the plasma discharge. Single-wavelength interferometric experiments were performed and demonstrated up to 1.5 microns of optical path difference (OPD) in a 633 nm laser beam. Dual-wavelength interferometry was used to obtain time-resolved profiles of the plasma electron density and gas heating inside the plasma chamber. Furthermore, a new multi-wavelength infrared diagnostic technique was developed and proof-of-concept simulations were conducted to demonstrate the system's capabilities.

  7. Analysis of the IMAGE RPI electron density data and CHAMP plasmasphere electron density reconstructions with focus on plasmasphere modelling

    NASA Astrophysics Data System (ADS)

    Gerzen, T.; Feltens, J.; Jakowski, N.; Galkin, I.; Reinisch, B.; Zandbergen, R.

    2016-09-01

    The electron density of the topside ionosphere and the plasmasphere contributes essentially to the overall Total Electron Content (TEC) budget affecting Global Navigation Satellite Systems (GNSS) signals. The plasmasphere can cause half or even more of the GNSS range error budget due to ionospheric propagation errors. This paper presents a comparative study of different plasmasphere and topside ionosphere data aiming at establishing an appropriate database for plasmasphere modelling. We analyze electron density profiles along the geomagnetic field lines derived from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite/Radio Plasma Imager (RPI) records of remote plasma sounding with radio waves. We compare these RPI profiles with 2D reconstructions of the topside ionosphere and plasmasphere electron density derived from GNSS based TEC measurements onboard the Challenging Minisatellite Payload (CHAMP) satellite. Most of the coincidences between IMAGE profiles and CHAMP reconstructions are detected in the region with L-shell between 2 and 5. In general the CHAMP reconstructed electron densities are below the IMAGE profile densities, with median of the CHAMP minus IMAGE residuals around -588 cm-3. Additionally, a comparison is made with electron densities derived from passive radio wave RPI measurements onboard the IMAGE satellite. Over the available 2001-2005 period of IMAGE measurements, the considered combined data from the active and passive RPI operations cover the region within a latitude range of ±60°N, all longitudes, and an L-shell ranging from 1.2 to 15. In the coincidence regions (mainly 2 ⩽ L ⩽ 4), we check the agreement between available active and passive RPI data. The comparison shows that the measurements are well correlated, with a median residual of ∼52 cm-3. The RMS and STD values of the relative residuals are around 22% and 21% respectively. In summary, the results encourage the application of IMAGE RPI data for

  8. Extreme atmospheric electron densities created by extensive air showers

    NASA Astrophysics Data System (ADS)

    Rutjes, Casper; Camporeale, Enrico; Ebert, Ute; Buitink, Stijn; Scholten, Olaf; Trinh, Gia

    2016-04-01

    A sufficient density of free electrons and strong electric fields are the basic requirements to start any electrical discharge. In the context of thunderstorm discharges it has become clear that in addition droplets and or ice particles are required to enhance the electric field to values above breakdown. In our recent study [1] we have shown that these three ingredients have to interplay to allow for lightning inception, triggered by an extensive air shower event. The extensive air showers are a very stochastic natural phenomenon, creating highly coherent bursts of extreme electron density in our atmosphere. Predicting these electron density bursts accurately one has to take the uncertainty of the input variables into account. To this end we use uncertainty quantification methods, like in [2], to post-process our detailed Monte Carlo extensive air shower simulations, done with the CORSIKA [3] software package, which provides an efficient and elegant way to determine the distribution of the atmospheric electron density enhancements. We will present the latest results. [1] Dubinova, A., Rutjes, C., Ebert, E., Buitink, S., Scholten, O., and Trinh, G. T. N. "Prediction of Lightning Inception by Large Ice Particles and Extensive Air Showers." PRL 115 015002 (2015) [2] G.J.A. Loeven, J.A.S. Witteveen, H. Bijl, Probabilistic collocation: an efficient nonintrusive approach for arbitrarily distributed parametric uncertainties, 45th AIAA Aerospace Sciences Meeting, Reno, Nevada, 2007, AIAA-2007-317 [3] Heck, Dieter, et al. CORSIKA: A Monte Carlo code to simulate extensive air showers. No. FZKA-6019. 1998.

  9. Imaginary time density-density correlations for two-dimensional electron gases at high density

    SciTech Connect

    Motta, M.; Galli, D. E.; Moroni, S.; Vitali, E.

    2015-10-28

    We evaluate imaginary time density-density correlation functions for two-dimensional homogeneous electron gases of up to 42 particles in the continuum using the phaseless auxiliary field quantum Monte Carlo method. We use periodic boundary conditions and up to 300 plane waves as basis set elements. We show that such methodology, once equipped with suitable numerical stabilization techniques necessary to deal with exponentials, products, and inversions of large matrices, gives access to the calculation of imaginary time correlation functions for medium-sized systems. We discuss the numerical stabilization techniques and the computational complexity of the methodology and we present the limitations related to the size of the systems on a quantitative basis. We perform the inverse Laplace transform of the obtained density-density correlation functions, assessing the ability of the phaseless auxiliary field quantum Monte Carlo method to evaluate dynamical properties of medium-sized homogeneous fermion systems.

  10. FUSION++: A New Data Assimilative Model for Electron Density Forecasting

    NASA Astrophysics Data System (ADS)

    Bust, G. S.; Comberiate, J.; Paxton, L. J.; Kelly, M.; Datta-Barua, S.

    2014-12-01

    There is a continuing need within the operational space weather community, both civilian and military, for accurate, robust data assimilative specifications and forecasts of the global electron density field, as well as derived RF application product specifications and forecasts obtained from the electron density field. The spatial scales of interest range from a hundred to a few thousand kilometers horizontally (synoptic large scale structuring) and meters to kilometers (small scale structuring that cause scintillations). RF space weather applications affected by electron density variability on these scales include navigation, communication and geo-location of RF frequencies ranging from 100's of Hz to GHz. For many of these applications, the necessary forecast time periods range from nowcasts to 1-3 hours. For more "mission planning" applications, necessary forecast times can range from hours to days. In this paper we present a new ionosphere-thermosphere (IT) specification and forecast model being developed at JHU/APL based upon the well-known data assimilation algorithms Ionospheric Data Assimilation Four Dimensional (IDA4D) and Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE). This new forecast model, "Forward Update Simple IONosphere model Plus IDA4D Plus EMPIRE (FUSION++), ingests data from observations related to electron density, winds, electric fields and neutral composition and provides improved specification and forecast of electron density. In addition, the new model provides improved specification of winds, electric fields and composition. We will present a short overview and derivation of the methodology behind FUSION++, some preliminary results using real observational sources, example derived RF application products such as HF bi-static propagation, and initial comparisons with independent data sources for validation.

  11. Electron density measurement of cesium seeded negative ion source by surface wave probe

    SciTech Connect

    Kisaki, M.; Tsumori, K.; Nakano, H.; Ikeda, K.; Osakabe, M.; Nagaoka, K.; Shibuya, M.; Sato, M.; Sekiguchi, H.; Komada, S.; Kondo, T.; Hayashi, H.; Asano, E.; Takeiri, Y.; Kaneko, O.

    2012-02-15

    Electron density measurements of a large-scaled negative ion source were carried out with a surface wave probe. By comparison of the electron densities determined with the surface wave probe and a Langmuir probe, it was confirmed that the surface wave probe is highly available for diagnostic of the electron density in H{sup -} ion sources. In addition, it was found that the ratio of the electron density to the H{sup -} ion density dramatically decreases with increase of a bias voltage and the H{sup -} ions become dominant negative particles at the bias voltage of more than 6 V.

  12. Metastable atom probe for measuring electron beam density profiles

    NASA Technical Reports Server (NTRS)

    Lockhart, J. M.; Zorn, J. C.

    1972-01-01

    Metastable atom probe was developed for measuring current density in electron beam as function of two arbitrary coordinates, with spatial resolution better than 0.5 mm. Probe shows effects of space charge, magnetic fields, and other factors which influence electron current density, but operates with such low beam densities that introduced perturbation is very small.

  13. Electron density distributions in the high-latitude magnetosphere

    NASA Technical Reports Server (NTRS)

    Persoon, Ann M.

    1988-01-01

    Electron density profiles were constructed to study the plasma density depletions in the nightside auroral zone and the density variations with increasing altitude in the polar cap, using electric field spectrum measurements from the plasma wave instrument on DE-1. Sharply defined regions of depleted plasma densities were commonly observed on nightside auroral field lines, in which electron densities were strongly depleted in relation to the adjacent plasmaspheric and polar densities, forming a low-density cavity at about 70 deg invariant latitude. A correlation was found between low auroral plasma densities, upflowing ion distributions, and an energetic precipitating electron population, indicating that electron density depletions in the nightside auroral zone are directly associated with auroral acceleration processes.

  14. An Overview of Ionospheric Electron Density Variations over Istanbul

    NASA Astrophysics Data System (ADS)

    Kaymaz, Zerefsan; Türk Katircioglu, Filiz; Ceren Moral, Aysegul; Emine Ceren Kalafatoglu Eyiguler, R. A..; Zabotin, Nikolai

    2016-07-01

    This study will present the temporal variations in electron density measured in Istanbul (42, 29) using Dynasonde observations. Dynasonde is a type of ionosonde that can measure the dynamics of the ionosphere. Istanbul Dynasonde was established in October 2012 and collecting data since then. The NeXtYZ software have been used to convert ionospheric signals into ionospheric data. In this study, among 72 outputs of ionospheric parameters, electron density, and critical frequency for F2 layer, and TEC have been studied to reveal the ionospheric variations over Istanbul. Statistics for seasonal, monthly and daily variations were obtained by scanning thorough about two years of ionograms. Four types of temporal variability were determined depending on the season and the time of the day. Gravity waves were detected very clearly in the ionograms at this mid-latitude station. In addition, magnetic substorm signatures on the electron density are clearly noticeable and are seen both positive and negative phases. In this talk we will give an overview of the results based on the first two years of the Dynasonde operation in Istanbul.

  15. Electronic Flux Density beyond the Born-Oppenheimer Approximation.

    PubMed

    Schild, Axel; Agostini, Federica; Gross, E K U

    2016-05-19

    In the Born-Oppenheimer approximation, the electronic wave function is typically real-valued and hence the electronic flux density (current density) seems to vanish. This is unfortunate for chemistry, because it precludes the possibility to monitor the electronic motion associated with the nuclear motion during chemical rearrangements from a Born-Oppenheimer simulation of the process. We study an electronic flux density obtained from a correction to the electronic wave function. This correction is derived via nuclear velocity perturbation theory applied in the framework of the exact factorization of electrons and nuclei. To compute the correction, only the ground state potential energy surface and the electronic wave function are needed. For a model system, we demonstrate that this electronic flux density approximates the true one very well, for coherent tunneling dynamics as well as for over-the-barrier scattering, and already for mass ratios between electrons and nuclei that are much larger than the true mass ratios. PMID:26878256

  16. Prediction of crystal densities of organic explosives by group additivity

    SciTech Connect

    Stine, J R

    1981-08-01

    The molar volume of crystalline organic compound is assumed to be a linear combination of its constituent volumes. Compounds consisting only of the elements hydrogen, carbon, nitrogen, oxygen, and fluorine are considered. The constituent volumes are taken to be the volumes of atoms in particular bonding environments and are evaluated from a large set of crystallographic data. The predicted density has an expected error of about 3%. These results are applied to a large number of explosives compounds.

  17. Additivity, density fluctuations, and nonequilibrium thermodynamics for active Brownian particles

    NASA Astrophysics Data System (ADS)

    Chakraborti, Subhadip; Mishra, Shradha; Pradhan, Punyabrata

    2016-05-01

    Using an additivity property, we study particle-number fluctuations in a system of interacting self-propelled particles, called active Brownian particles (ABPs), which consists of repulsive disks with random self-propulsion velocities. From a fluctuation-response relation, a direct consequence of additivity, we formulate a thermodynamic theory which captures the previously observed features of nonequilibrium phase transition in the ABPs from a homogeneous fluid phase to an inhomogeneous phase of coexisting gas and liquid. We substantiate the predictions of additivity by analytically calculating the subsystem particle-number distributions in the homogeneous fluid phase away from criticality where analytically obtained distributions are compatible with simulations in the ABPs.

  18. Seismo-ionospheric coupling appearing as equatorial electron density enhancements observed via DEMETER electron density measurements

    NASA Astrophysics Data System (ADS)

    Ryu, K.; Lee, E.; Chae, J. S.; Parrot, M.; Pulinets, S.

    2014-10-01

    We report the processes and results of statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite over a period of 6 years (2005-2010), in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the equatorial ionization anomaly (EIA) intensity indices, which represent relative equatorial electron density increase, were performed for each region. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 5.0 in the low-latitude region can accompany observable precursory and concurrent EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling is consistent with our observation, and the possibility of earthquake prediction using the EIA intensity variation is discussed.

  19. Ionospheric E-region electron density and neutral atmosphere variations

    NASA Technical Reports Server (NTRS)

    Stick, T. L.

    1976-01-01

    Electron density deviations from a basic variation with the solar zenith angle were investigated. A model study was conducted in which the effects of changes in neutral and relative densities of atomic and molecular oxygen on calculated electron densities were compared with incoherent scatter measurements in the height range 100-117 km at Arecibo, Puerto Rico. The feasibility of determining tides in the neutral atmosphere from electron density profiles was studied. It was determined that variations in phase between the density and temperature variation and the comparable magnitudes of their components make it appear improbable that the useful information on tidal modes can be obtained in this way.

  20. Probing Electron Dynamics with the Laplacian of the Momentum Density

    SciTech Connect

    Sukumar, N.; MacDougall, Preston J.; Levit, M. Creon

    2012-09-24

    This chapter in the above-titled monograph presents topological analysis of the Laplacian of the electron momentum density in organic molecules. It relates topological features in this distribution to chemical and physical properties, particularly aromaticity and electron transport.

  1. Momentum-space properties from coordinate-space electron density

    SciTech Connect

    Harbola, Manoj K.; Zope, Rajendra R.; Kshirsagar, Anjali; Pathak, Rajeev K.

    2005-05-22

    Electron density and electron momentum density, while independently tractable experimentally, bear no direct connection without going through the many-electron wave function. However, invoking a variant of the constrained-search formulation of density-functional theory, we develop a general scheme (valid for arbitrary external potentials) yielding decent momentum-space properties, starting exclusively from the coordinate-space electron density. A numerical illustration of the scheme is provided for the closed-shell atomic systems He, Be, and Ne in their ground state and for 1s{sup 1} 2s{sup 1} singlet electronic excited state for helium by calculating the Compton profiles and the expectation values derived from given coordinate-space electron densities.

  2. Charge density waves in strongly correlated electron systems.

    PubMed

    Chen, Chih-Wei; Choe, Jesse; Morosan, E

    2016-08-01

    Strong electron correlations are at the heart of many physical phenomena of current interest to the condensed matter community. Here we present a survey of the mechanisms underlying such correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions. The focus is on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity. In addition to reviewing the CDW mechanisms in 1D, 2D, and 3D systems, we pay particular attention to the prevalence of this state in two particular classes of compounds, the high temperature superconductors (cuprates) and the layered transition metal dichalcogenides. The possibilities for quantum criticality resulting from the competition between magnetic fluctuations and electronic instabilities (CDW, unconventional superconductivity) are also discussed. PMID:27376547

  3. Charge density waves in strongly correlated electron systems

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Wei; Choe, Jesse; Morosan, E.

    2016-08-01

    Strong electron correlations are at the heart of many physical phenomena of current interest to the condensed matter community. Here we present a survey of the mechanisms underlying such correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions. The focus is on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity. In addition to reviewing the CDW mechanisms in 1D, 2D, and 3D systems, we pay particular attention to the prevalence of this state in two particular classes of compounds, the high temperature superconductors (cuprates) and the layered transition metal dichalcogenides. The possibilities for quantum criticality resulting from the competition between magnetic fluctuations and electronic instabilities (CDW, unconventional superconductivity) are also discussed.

  4. Sub-additivity in Electron Emission from GaAs

    NASA Astrophysics Data System (ADS)

    Brunkow, Evan; Clayburn, Nathan; Becker, Maria; Jones, Eric; Batelaan, Herman; Gay, Timothy

    2016-05-01

    When two spatially-overlapped laser pulses (775 nm center wavelength, 75 fs duration) are incident on an untreated <100> GaAs crystal surface, the electron emission rate depends on the temporal separation between the two pulses. We have shown that for delays between 0.2 and 1000ps, the emission rate is ``sub-additive'', i.e., is lower than when the beams have separation >> 1 ns. We believe the cause of this sub-additivity is an increase in reflectance and transmittance due to electrons occupying the excited state of the GaAs. We are now able to manipulate the magnitude of the sub-additivity by changing the number of electrons that are in the excited state. Sub-additivity is not observed with tungsten tip surfaces which have no excited state. Funded by NSF PHY-1505794, EPSCoR IIIA-1430519, and NSF 1306565 (HB).

  5. Ligand identification using electron-density mapcorrelations

    SciTech Connect

    Terwilliger, Thomas C.; Adams, Paul D.; Moriarty, Nigel W.; Cohn,Judith D.

    2006-12-01

    A procedure for the identification of ligands bound incrystal structuresof macromolecules is described. Two characteristics ofthe density corresponding to a ligand are used in the identificationprocedure. One is the correlation of the ligand density with each of aset of test ligands after optimization of the fit of that ligand to thedensity. The other is the correlation of a fingerprint of the densitywith the fingerprint of model density for each possible ligand. Thefingerprints consist of an ordered list of correlations of each the testligands with the density. The two characteristics are scored using aZ-score approach in which the correlations are normalized to the mean andstandard deviation of correlations found for a variety of mismatchedligand-density pairs, so that the Z scores are related to the probabilityof observing a particular value of the correlation by chance. Theprocedure was tested with a set of 200 of the most commonly found ligandsin the Protein Data Bank, collectively representing 57 percent of allligands in the Protein Data Bank. Using a combination of these twocharacteristics of ligand density, ranked lists of ligand identificationswere made for representative (F-o-F-c) exp(i phi(c)) difference densityfrom entries in the Protein Data Bank. In 48 percent of the 200 cases,the correct ligand was at the top of the ranked list of ligands. Thisapproach may be useful in identification of unknown ligands in newmacromolecular structures as well as in the identification of whichligands in a mixture have bound to a macromolecule.

  6. The experimental electron density in polymorphs A and B of the anti-ulcer drug famotidine

    NASA Astrophysics Data System (ADS)

    Overgaard, J.; Hibbs, D. E.

    2004-09-01

    A multipole description of the electron-density distribution in the two polymorphs of famotidine is given. The electrostatic potential shown on the molecular surfaces provides additional information on molecular reactivity.

  7. Electron density depletions in the nightside auroral zone

    NASA Technical Reports Server (NTRS)

    Persoon, A. M.; Gurnett, D. A.; Peterson, W. K.; Waite, J. H., Jr.; Burch, J. L.; Green, J. L.

    1988-01-01

    Dynamics Explorer 1 measurements are used to investigate regions of low electron density in the nightside auroral zone. Sharply defined regions of low electron density are found in auroral zone crossings from the predusk hours until the early morning hours at all radial distances up to at least 4.6 earth radii. Densities in the auroral cavity are shown to fall to values below 0.3/cu cm. Within the auroral cavity, electron-density-profile variations of a factor of 2 or more on spatial scales of tens of kilometers are found, and the electron plasma frequency to electron cyclotron frequency ratios are 0.02-0.4. The results suggest associations between the density depletions in the nightside auroral zone and auroral acceleration processes.

  8. Electron and ion densities in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.; Langer, W. D.

    1974-01-01

    A quantitative theory of ionization in diffuse clouds is developed which includes H(+) charge exchange with O. Dissociative charge exchange of He(+) with H2 plays an important role in the densities of H(+) and He(+). The abundance of HD is also discussed.

  9. Gutzwiller density functional theory for correlated electron systems

    SciTech Connect

    Ho, K. M.; Schmalian, J.; Wang, C. Z.

    2008-02-04

    We develop a density functional theory (DFT) and formalism for correlated electron systems by taking as reference an interacting electron system that has a ground state wave function which exactly obeys the Gutzwiller approximation for all one-particle operators. The solution of the many-electron problem is mapped onto the self-consistent solution of a set of single-particle Schroedinger equations, analogously to standard DFT-local density approximation calculations.

  10. Measurement of electron density using reactance cutoff probe

    NASA Astrophysics Data System (ADS)

    You, K. H.; You, S. J.; Kim, D. W.; Na, B. K.; Seo, B. H.; Kim, J. H.; Seong, D. J.; Chang, H. Y.

    2016-05-01

    This paper proposes a new measurement method of electron density using the reactance spectrum of the plasma in the cutoff probe system instead of the transmission spectrum. The highly accurate reactance spectrum of the plasma-cutoff probe system, as expected from previous circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], was measured using the full two-port error correction and automatic port extension methods of the network analyzer. The electron density can be obtained from the analysis of the measured reactance spectrum, based on circuit modeling. According to the circuit simulation results, the reactance cutoff probe can measure the electron density more precisely than the previous cutoff probe at low densities or at higher pressure. The obtained results for the electron density are presented and discussed for a wide range of experimental conditions, and this method is compared with previous methods (a cutoff probe using the transmission spectrum and a single Langmuir probe).

  11. Ionospheric Electron Density during Magnetically Active Times over Istanbul

    NASA Astrophysics Data System (ADS)

    Naz Erbaş, Bute; Kaymaz, Zerefsan; Ceren Moral, Aysegul; Emine Ceren Kalafatoglu Eyiguler, R. A..

    2016-07-01

    In this study, we analyze electron density variations over Istanbul using Dynasonde observations during the magnetically active times. In order to perform statistical analyses, we first determined magnetic storms and magnetospheric substorm intervals from October 2012 to October 2015 using Kyoto's magnetic index data. Corresponding ionospheric parameters, such as critical frequency of F2 region (foF2), maximum electron density height (hmF2), total electron density (TEC) etc. were retrieved from Dynasonde data base at Istanbul Technical University's Space Weather Laboratory. To understand the behavior of electron density during the magnetically active times, we remove the background quiet time variations first and then quantify the anomalies. In this presentation, we will report results from our preliminary analyses from the selected cases corresponding to the strong magnetic storms. Initial results show lower electron densities at noon times and higher electron densities in the late afternoon toward sunset times when compared to the electron densities of magnetically quiet times. We also compare the results with IRI and TIEGCM ionospheric models in order to understand the physical and dynamical causes of these variations. During the presentation we will also discuss the role of these changes during the magnetically active times on the GPS communications through ionosphere.

  12. Atomic electron affinities and the role of symmetry between electron addition and subtraction in a corrected Koopmans approach.

    PubMed

    Teale, A M; De Proft, F; Geerlings, P; Tozer, D J

    2014-07-28

    The essential aspects of zero-temperature grand-canonical ensemble density-functional theory are reviewed in the context of spin-density-functional theory and are used to highlight the assumption of symmetry between electron addition and subtraction that underlies the corrected Koopmans approach of Tozer and De Proft (TDP) for computing electron affinities. The issue of symmetry is then investigated in a systematic study of atomic electron affinities, comparing TDP affinities with those from a conventional Koopmans evaluation and electronic energy differences. Although it cannot compete with affinities determined from energy differences, the TDP expression yields results that are a significant improvement over those from the conventional Koopmans expression. Key insight into the results from both expressions is provided by an analysis of plots of the electronic energy as a function of the number of electrons, which highlight the extent of symmetry between addition and subtraction. The accuracy of the TDP affinities is closely related to the nature of the orbitals involved in the electron addition and subtraction, being particularly poor in cases where there is a change in principal quantum number, but relatively accurate within a single manifold of orbitals. The analysis is then extended to a consideration of the ground state Mulliken electronegativity and chemical hardness. The findings further emphasize the key role of symmetry in determining the quality of the results. PMID:24406854

  13. Modification of ionospheric electron density by dust suspension

    NASA Astrophysics Data System (ADS)

    Srivastava, Sweta; Mishra, Rashmi; Singh Sodha, Mahendra

    2016-05-01

    On the basis of a dynamic analysis the effectiveness of dust suspension for the reduction and enhancement of electron density in the E-layer of the ionosphere has been investigated in this paper. The analysis is based on the modelling of the E-layer as the Chapman α layer (validated earlier); the electron/ion production function, arrived at by Chapman and effective electron temperature-dependent electron–ion recombination coefficients in agreement with observations have been used. The balance of the charge on the particles and the number/energy balance of the constituents have been taken into account. The following is the physics of the change in electron density in the ionosphere by the suspension of dust. First, the dust provides a source (emission) and sink (accretion) of electrons. Second, the dust emits photoelectrons with energies much higher than those of ambient electrons, which enhances the electron temperature, leading to a reduced electron–ion recombination coefficient, and thus to a higher electron density. An interplay of these processes and the natural processes of electron production/annihilation determines the electron density and temperature in the dust suspension in the ionosphere. The numerical results, corresponding to suspension of dust of silicate (high work function) and Cs coated bronze (low work function) in the E-layer at 105 \\text{km} are presented and discussed.

  14. Picosecond imaging of low-density plasmas by electron deflectometry.

    PubMed

    Centurion, M; Reckenthaeler, P; Krausz, F; Fill, E E

    2009-02-15

    We have imaged optical-field ionized plasmas with electron densities as low as 10(13) cm(-3) on a picosecond timescale using ultrashort electron pulses. Electric fields generated by the separation of charges are imprinted on a 20 keV probe electron pulse and reveal a cloud of electrons expanding away from a positively charged plasma core. Our method allows for a direct measurement of the electron energy required to escape the plasma and the total charge. Simulations reproduce the main features of the experiment and allow determination of the energy of the electrons. PMID:19373367

  15. A determination of the current density in electron beams

    NASA Technical Reports Server (NTRS)

    Beil, R. J.

    1982-01-01

    Current gathering rotating probe techniques were used to examine the envelope shape and power density profile of electron beams used in electron beam welding devices. The electron power density contours which determine the shape of the weld vapor cavity, penetration, and local heat distribution were considered. A mathematical analysis consistent with a rotating probe technique necessary to determine the current density distribution (assumed symmetrically radial) in a cross-section of the beam is provided. An explanation of the experimental technique for obtaining data, a BASIC language computer program to determine the current density from the data, and a study indicating the level of confidence to be associated with results obtained are also provided. An example of the application of the analysis to some experimental electron beam data is included.

  16. Upgrading electron temperature and electron density diagnostic diagrams of forbidden line emission

    NASA Astrophysics Data System (ADS)

    Proxauf, B.; Öttl, S.; Kimeswenger, S.

    2014-01-01

    Context. Diagnostic diagrams of forbidden lines have been a useful tool for observers for many decades now. They are used to obtain information on the basic physical properties of thin gaseous nebulae. Some diagnostic diagrams are in wavelength domains that were difficult to apply either due to missing wavelength coverage or the low resolution of older spectrographs. Furthermore, most of the diagrams were calculated using just the species involved as a single atom gas, although several are affected by well-known fluorescence mechanisms as well. Additionally, the atomic data have improved up to the present time. Aims: The aim of this work is to recalculate well-known, but also sparsely used, unnoted diagnostics diagrams. The new diagrams provide observers with modern, easy-to-use recipes for determining electron temperature and densities. Methods: The new diagnostic diagrams were calculated using large grids of parameter space in the photoionization code CLOUDY. For a given basic parameter (e.g., electron density or temperature), the solutions with cooling-heating-equilibrium were chosen to derive the diagnostic diagrams. Empirical numerical functions were fitted to provide formulas usable in, e.g., data reduction pipelines. Results: The resulting diagrams differ significantly from those used up to now and will improve thermodynamic calculations. To our knowledge, detailed, directly applicable fit formulas are given for the first time, leading to the calculation of electron temperature or density from the line ratios.

  17. Electron Densities Near Io from Galileo Plasma Wave Observations

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.; Persoon, A. M.; Kurth, W. S.; Roux, A.; Bolton, S. J.

    2001-01-01

    This paper presents an overview of electron densities obtained near Io from the Galileo plasma wave instrument during the first four flybys of Io. These flybys were Io, which was a downstream wake pass that occurred on December 7, 1995; I24, which was an upstream pass that occurred on October 11, 1999; I25, which was a south polar pass that occurred on November 26, 1999; and I27, which was an upstream pass that occurred on February 22, 2000. Two methods were used to measure the electron density. The first was based on the frequency of upper hybrid resonance emissions, and the second was based on the low-frequency cutoff of electromagnetic radiation at the electron plasma frequency. For three of the flybys, Io, I25, and I27, large density enhancements were observed near the closest approach to Io. The peak electron densities ranged from 2.1 to 6.8 x 10(exp 4) per cubic centimeters. These densities are consistent with previous radio occultation measurements of Io's ionosphere. No density enhancement was observed during the I24 flyby, most likely because the spacecraft trajectory passed too far upstream to penetrate Io's ionosphere. During two of the flybys, I25 and I27, abrupt step-like changes were observed at the outer boundaries of the region of enhanced electron density. Comparisons with magnetic field models and energetic particle measurements show that the abrupt density steps occur as the spacecraft penetrated the boundary of the Io flux tube, with the region of high plasma density on the inside of the flux tube. Most likely the enhanced electron density within the Io flux tube is associated with magnetic field lines that are frozen to Io by the high conductivity of Io's atmosphere, thereby enhancing the escape of plasma along the magnetic field lines that pass through Io's ionosphere.

  18. Electron density profile description in the international reference ionosphere

    NASA Technical Reports Server (NTRS)

    Rawer, K.; Bilitza, D.

    1989-01-01

    Problems encountered during efforts to reformulate the IRI description of the electron density profile are examined. Consideration is given to Booker's (1979) proposal that the unique, analytic profile functions should cover the entire ionospheric height range. The IRI topside model is reviewed and the electron density profile of the middle and lower ionosphere are discussed. Rawer's (1983) procedure for combining the topside, middle, and lower ionospheric profiles into one analytic profile is reviewed.

  19. Electron density profile description in the international reference ionosphere

    NASA Astrophysics Data System (ADS)

    Rawer, K.; Bilitza, D.

    1989-10-01

    Problems encountered during efforts to reformulate the IRI description of the electron density profile are examined. Consideration is given to Booker's (1979) proposal that the unique, analytic profile functions should cover the entire ionospheric height range. The IRI topside model is reviewed and the electron density profile of the middle and lower ionosphere are discussed. Rawer's (1983) procedure for combining the topside, middle, and lower ionospheric profiles into one analytic profile is reviewed.

  20. Electron correlation in solids via density embedding theory

    SciTech Connect

    Bulik, Ireneusz W.; Chen, Weibing; Scuseria, Gustavo E.

    2014-08-07

    Density matrix embedding theory [G. Knizia and G. K.-L. Chan, Phys. Rev. Lett. 109, 186404 (2012)] and density embedding theory [I. W. Bulik, G. E. Scuseria, and J. Dukelsky, Phys. Rev. B 89, 035140 (2014)] have recently been introduced for model lattice Hamiltonians and molecular systems. In the present work, the formalism is extended to the ab initio description of infinite systems. An appropriate definition of the impurity Hamiltonian for such systems is presented and demonstrated in cases of 1, 2, and 3 dimensions, using coupled cluster theory as the impurity solver. Additionally, we discuss the challenges related to disentanglement of fragment and bath states. The current approach yields results comparable to coupled cluster calculations of infinite systems even when using a single unit cell as the fragment. The theory is formulated in the basis of Wannier functions but it does not require separate localization of unoccupied bands. The embedding scheme presented here is a promising way of employing highly accurate electronic structure methods for extended systems at a fraction of their original computational cost.

  1. Evidence of Electron Density Enhancements at Enceladus' Apoapsis

    NASA Astrophysics Data System (ADS)

    Persoon, A. M.; Gurnett, D. A.; Kurth, W. S.; Hospodarsky, G. B.; Groene, J. B.

    2015-12-01

    Enceladus' plumes are the dominant source of plasma in Saturn's magnetosphere. Icy particles and water vapor are vented into the inner magnetosphere through fissures in Enceladus' southern polar region. These fissures are subjected to tidal stresses that vary as Enceladus moves in a slightly eccentric orbit around Saturn. Plume activity is greatest when tidal stress is minimal. This occurs when Enceladus is farthest away from Saturn in its orbit (the Enceladus apoapsis). This study will show temporal variations in the electron density distribution that correlate with the position of Enceladus in its orbit around Saturn, with strong density enhancements in the vicinity of Enceladus when the moon is near apoapsis. Equatorial electron density measurements derived from the upper hybrid resonance frequency from the Cassini Radio and Plasma Wave Science (RPWS) experiment are used to illustrate these electron density enhancements.

  2. Tomography of the ionospheric electron density with geostatistical inversion

    NASA Astrophysics Data System (ADS)

    Minkwitz, D.; van den Boogaart, K. G.; Gerzen, T.; Hoque, M.

    2015-08-01

    In relation to satellite applications like global navigation satellite systems (GNSS) and remote sensing, the electron density distribution of the ionosphere has significant influence on trans-ionospheric radio signal propagation. In this paper, we develop a novel ionospheric tomography approach providing the estimation of the electron density's spatial covariance and based on a best linear unbiased estimator of the 3-D electron density. Therefore a non-stationary and anisotropic covariance model is set up and its parameters are determined within a maximum-likelihood approach incorporating GNSS total electron content measurements and the NeQuick model as background. As a first assessment this 3-D simple kriging approach is applied to a part of Europe. We illustrate the estimated covariance model revealing the different correlation lengths in latitude and longitude direction and its non-stationarity. Furthermore, we show promising improvements of the reconstructed electron densities compared to the background model through the validation of the ionosondes Rome, Italy (RO041), and Dourbes, Belgium (DB049), with electron density profiles for 1 day.

  3. Electron trapping and acceleration across a parabolic plasma density profile.

    PubMed

    Kim, J U; Hafz, N; Suk, H

    2004-02-01

    It is known that as a laser wakefield passes through a downward density transition in a plasma some portion of the background electrons are trapped in the laser wakefield and the trapped electrons are accelerated to relativistic high energies over a very short distance. In this study, by using a two-dimensional (2D) particle-in-cell (PIC) simulation, we suggest an experimental scheme that can manipulate electron trapping and acceleration across a parabolic plasma density channel, which is easier to produce and more feasible to apply to the laser wakefield acceleration experiments. In this study, 2D PIC simulation results for the physical characteristics of the electron bunches that are emitted from the parabolic density plasma channel are reported in great detail. PMID:14995568

  4. Electron density and gas density measurements in a millimeter-wave discharge

    NASA Astrophysics Data System (ADS)

    Schaub, S. C.; Hummelt, J. S.; Guss, W. C.; Shapiro, M. A.; Temkin, R. J.

    2016-08-01

    Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 μs long at 110 GHz and 2.2 μs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal to the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.

  5. Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

    SciTech Connect

    Ruiz Ruiz, J.; White, A. E.; Ren, Y.; Guttenfelder, W.; Kaye, S. M.; Leblanc, B. P.; Mazzucato, E.; Lee, K. C.; Domier, C. W.; Smith, D. R.; Yuh, H.

    2015-12-15

    Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, k{sub ⊥}ρ{sub e} ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which is shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.

  6. Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

    NASA Astrophysics Data System (ADS)

    Ruiz Ruiz, J.; Ren, Y.; Guttenfelder, W.; White, A. E.; Kaye, S. M.; Leblanc, B. P.; Mazzucato, E.; Lee, K. C.; Domier, C. W.; Smith, D. R.; Yuh, H.

    2015-12-01

    Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, kρe ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which is shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.

  7. Density-shear instability in electron magneto-hydrodynamics

    SciTech Connect

    Wood, T. S. Hollerbach, R.; Lyutikov, M.

    2014-05-15

    We discuss a novel instability in inertia-less electron magneto-hydrodynamics (EMHD), which arises from a combination of electron velocity shear and electron density gradients. The unstable modes have a lengthscale longer than the transverse density scale, and a growth-rate of the order of the inverse Hall timescale. We suggest that this density-shear instability may be of importance in magnetic reconnection regions on scales smaller than the ion skin depth, and in neutron star crusts. We demonstrate that the so-called Hall drift instability, previously argued to be relevant in neutron star crusts, is a resistive tearing instability rather than an instability of the Hall term itself. We argue that the density-shear instability is of greater significance in neutron stars than the tearing instability, because it generally has a faster growth-rate and is less sensitive to geometry and boundary conditions. We prove that, for uniform electron density, EMHD is “at least as stable” as regular, incompressible MHD, in the sense that any field configuration that is stable in MHD is also stable in EMHD. We present a connection between the density-shear instability in EMHD and the magneto-buoyancy instability in anelastic MHD.

  8. Non-additive response of larval ringed salamanders to intraspecific density.

    PubMed

    Ousterhout, Brittany H; Semlitsch, Raymond D

    2016-04-01

    Conditions experienced in early developmental stages can have long-term consequences for individual fitness. High intraspecific density during the natal period can affect juvenile and eventually adult growth rates, metabolism, immune function, survival, and fecundity. Despite the important ecological and evolutionary effects of early developmental density, the form of the relationship between natal density and resulting juvenile phenotype is poorly understood. To test competing hypotheses explaining responses to intraspecific density, we experimentally manipulated the initial larval density of ringed salamanders (Ambystoma annulatum), a pond-breeding amphibian, over 11 densities. We modeled the functional form of the relationship between natal density and juvenile traits, and compared the relative support for the various hypotheses based on their goodness of fit. These functional form models were then used to parameterize a simple simulation model of population growth. Our data support non-additive density dependence and presents an alternate hypothesis to additive density dependence, self-thinning and Allee effects in larval amphibians. We posit that ringed salamander larvae may be under selective pressure for tolerance to high density and increased efficiency in resource utilization. Additionally, we demonstrate that models of population dynamics are sensitive to assumptions of the functional form of density dependence. PMID:26683834

  9. Additions and Improvements to the FLASH Code for Simulating High Energy Density Physics Experiments

    NASA Astrophysics Data System (ADS)

    Lamb, D. Q.; Daley, C.; Dubey, A.; Fatenejad, M.; Flocke, N.; Graziani, C.; Lee, D.; Tzeferacos, P.; Weide, K.

    2015-11-01

    FLASH is an open source, finite-volume Eulerian, spatially adaptive radiation hydrodynamics and magnetohydrodynamics code that incorporates capabilities for a broad range of physical processes, performs well on a wide range of computer architectures, and has a broad user base. Extensive capabilities have been added to FLASH to make it an open toolset for the academic high energy density physics (HEDP) community. We summarize these capabilities, with particular emphasis on recent additions and improvements. These include advancements in the optical ray tracing laser package, with methods such as bi-cubic 2D and tri-cubic 3D interpolation of electron number density, adaptive stepping and 2nd-, 3rd-, and 4th-order Runge-Kutta integration methods. Moreover, we showcase the simulated magnetic field diagnostic capabilities of the code, including induction coils, Faraday rotation, and proton radiography. We also describe several collaborations with the National Laboratories and the academic community in which FLASH has been used to simulate HEDP experiments. This work was supported in part at the University of Chicago by the DOE NNSA ASC through the Argonne Institute for Computing in Science under field work proposal 57789; and the NSF under grant PHY-0903997.

  10. Measuring ionospheric electron density using the plasma frequency probe

    SciTech Connect

    Jensen, M.D.; Baker, K.D. )

    1992-02-01

    During the past decade, the plasma frequency probe (PFP) has evolved into an accurate, proven method of measuring electron density in the ionosphere above about 90 km. The instrument uses an electrically short antenna mounted on a sounding rocket that is immersed in the plasma and notes the frequency where the antenna impedance is large and nonreactive. This frequency is closely related to the plasma frequency, which is a direct function of free electron concentration. The probe uses phase-locked loop technology to follow a changing electron density. Several sections of the plasma frequency probe circuitry are unique, especially the voltage-controlled oscillator that uses both an electronically tuned capacitor and inductor to give the wide tuning range needed for electron density measurements. The results from two recent sounding rocket flights (Thunderstorm II and CRIT II) under vastly different plasma conditions demonstrate the capabilities of the PFP and show the importance of in situ electron density measurements of understanding plasma processes. 9 refs.

  11. Proton cooling in ultracold low-density electron gas

    NASA Astrophysics Data System (ADS)

    Bobrov, A. A.; Bronin, S. Y.; Manykin, E. A.; Zelener, B. B.; Zelener, B. V.; Khikhlukha, D. R.

    2015-11-01

    A sole proton energy loss processes in an electron gas and the dependence of these processes on temperature and magnetic field are studied using molecular dynamics techniques in present work. It appears that for electron temperatures less than 100 K many body collisions affect the proton energy loss and these collisions must be taken into account. The influence of a strong magnetic field on the relaxation processes is also considered in this work. Calculations were performed for electron densities 10 cm-3, magnetic field 1-3 Tesla, electron temperatures 10-50 K, initial proton energies 100-10000 K.

  12. Edge chlorination of hexa-peri-hexabenzocoronene investigated by density functional theory and vibrational spectroscopy† †Electronic supplementary information (ESI) available: Description and animations of the vibrational normal modes of HBC and HBC-Cl discussed in the text. See DOI: 10.1039/c5cp07755a Click here for additional data file. Click here for additional data file.

    PubMed Central

    Maghsoumi, Ali; Narita, Akimitsu; Dong, Renhao; Feng, Xinliang; Castiglioni, Chiara

    2016-01-01

    We investigate the molecular structure and vibrational properties of perchlorinated hexa-peri-hexabenzocoronene (HBC-Cl) by density functional theory (DFT) calculations and IR and Raman spectroscopy, in comparison to the parent HBC. The theoretical and experimental IR and Raman spectra demonstrated very good agreement, elucidating a number of vibrational modes corresponding to the observed peaks. Compared with the parent HBC, the edge chlorination significantly alters the planarity of the molecule. Nevertheless, the results indicated that such structural distortion does not significantly impair the π-conjugation of such polycyclic aromatic hydrocarbons. PMID:26912311

  13. Addition reaction of alkyl radical to C60 fullerene: Density functional theory study

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto; Kawabata, Hiroshi

    2016-02-01

    Functionalized fullerenes are known as a high-performance molecules. In this study, the alkyl-functionalized fullerenes (denoted by R-C60) have been investigated by means of the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of fullerene. Also, the reaction mechanism of alkyl radicals with C60 was investigated. The methyl, ethyl, propyl, and butyl radicals (denoted by n = 1-4, where n means the number of carbon atoms in the alkyl radical) were examined as alkyl radicals. The DFT calculation showed that the alkyl radical binds to the carbon atom of C60 at the on-top site, and a strong C-C single bond is formed. The binding energies of alkyl radicals to C60 were distributed in the range of 31.8-35.1 kcal mol-1 at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists before alkyl addition, the barrier heights were calculated to be 2.1-2.8 kcal mol-1. The electronic states of R-C60 complexes were discussed on the basis of the theoretical results.

  14. Rocket radio measurement of electron density in the nighttime ionosphere

    NASA Technical Reports Server (NTRS)

    Gilchrist, B. E.; Smith, L. G.

    1979-01-01

    One experimental technique based on the Faraday rotation effect of radio waves is presented for measuring electron density in the nighttime ionosphere at midlatitudes. High frequency linearly-polarized radio signals were transmitted to a linearly-polarized receiving system located in a spinning rocket moving through the ionosphere. Faraday rotation was observed in the reference plane of the rocket as a change in frequency of the detected receiver output. The frequency change was measured and the information was used to obtain electron density data. System performance was evaluated and some sources of error were identified. The data obtained was useful in calibrating a Langmuir probe experiment for electron density values of 100/cu cm and greater. Data from two rocket flights are presented to illustrate the experiment.

  15. Electron density spatial profiles of the DCP source

    NASA Astrophysics Data System (ADS)

    Zander, Andrew T.; Miller, Myron H.

    Electron densities are measured in the high current, analytical and intervening zones of a DCP whose operating parameters are systematically varied. Detailed Ne distribution profiles are obtained for various sleeve flow, nebulizer flow, arc current and matrix concentration regimes. Flowing argon is found to establish a thermal pinch in the high current zone and to steepen gradients in plasmas employed for spectrochemical analysis. The distinctive electron density distributions in the DCP are more sensitive to modulation of gas flow variables than to changes in arc current. Magnetic pressure has no discernible role in pinch formation. Electron densities in spectroscopic regions are minimally affected by easily ionized or other matrix constituents at usual analytical concentrations.

  16. Ionospheric electron density profile estimation using commercial AM broadcast signals

    NASA Astrophysics Data System (ADS)

    Yu, De; Ma, Hong; Cheng, Li; Li, Yang; Zhang, Yufeng; Chen, Wenjun

    2015-08-01

    A new method for estimating the bottom electron density profile by using commercial AM broadcast signals as non-cooperative signals is presented in this paper. Without requiring any dedicated transmitters, the required input data are the measured elevation angles of signals transmitted from the known locations of broadcast stations. The input data are inverted for the QPS model parameters depicting the electron density profile of the signal's reflection area by using a probabilistic inversion technique. This method has been validated on synthesized data and used with the real data provided by an HF direction-finding system situated near the city of Wuhan. The estimated parameters obtained by the proposed method have been compared with vertical ionosonde data and have been used to locate the Shijiazhuang broadcast station. The simulation and experimental results indicate that the proposed ionospheric sounding method is feasible for obtaining useful electron density profiles.

  17. Electron temperature and density relationships in coronal mass ejections

    NASA Technical Reports Server (NTRS)

    Hammond, C. M.; Phillips, J. L.; Balogh, A.

    1995-01-01

    We examine 10 coronal mass ejections from the in-ecliptic portion of the Ulysses mission. Five of these CMEs are magnetic clouds. In each case we observe an inverse relationship between electron temperature and density. For protons this relationship is less clear. Earlier work has shown a similar inverse relationship for electrons inside magnetic clouds and interpreted it to mean that the polytropic index governing the expansion of electrons is less than unity. This requires electrons to be heated as the CME expands. We offer an alternative view that the inverse relationship between electron temperature and density is caused by more rapid cooling of the denser plasma through collisions. More rapid cooling of denser plasma has been shown for 1 AU measurements in the solar wind. As evidence for this hypothesis we show that the denser plasma inside the CMEs tends to be more isotropic indicating a different history of collisions for the dense plasma. Thus, although the electron temperature inside CMEs consistently shows an inverse correlation with the density, this is not an indication of the polytropic index of the plasma but instead supports the idea of collisional modification of the electrons during their transit from the sun.

  18. Electron density in the cusp ionosphere: increase or depletion?

    NASA Astrophysics Data System (ADS)

    Pitout, Frédéric; Blelly, Pierre-Louis

    2003-07-01

    Radar observations indicate that the electron density may decrease significantly in the cusp ionosphere, despite the intense precipitation of low-energy electrons originating from the magnetosheath. We have modeled the ionospheric footprints of the cusp and mantle regions, and we focus on the two rival processes acting pro and con the electron density build-up in those regions of intense precipitation, which also happened to be regions of strong electric field. On one hand, the precipitation provides the ionosphere with electrons; on the other hand, the strong electric field heats up the ion population, stimulating the production of NO+. A fraction of the NO+ produced then feeds the electron-consuming chemical reaction NO+ + e- -> NO in the F1-region, although this reaction is not favored in presence of a high electron temperature. We investigate various combinations of E-field and initial electron densities. Our simulations clearly show that the overall result depends on the origin of the flux tube, which eventually opens in the cusp region. We interpret our results in terms of seasonal effects, IMF-By and MLT dependence.

  19. Optimal-transport formulation of electronic density-functional theory

    NASA Astrophysics Data System (ADS)

    Buttazzo, Giuseppe; De Pascale, Luigi; Gori-Giorgi, Paola

    2012-06-01

    The most challenging scenario for Kohn-Sham density-functional theory, that is, when the electrons move relatively slowly trying to avoid each other as much as possible because of their repulsion (strong-interaction limit), is reformulated here as an optimal transport (or mass transportation theory) problem, a well-established field of mathematics and economics. In practice, we show that to solve the problem of finding the minimum possible internal repulsion energy for N electrons in a given density ρ(r) is equivalent to find the optimal way of transporting N-1 times the density ρ into itself, with the cost function given by the Coulomb repulsion. We use this link to set the strong-interaction limit of density-functional theory on firm ground and to discuss the potential practical aspects of this reformulation.

  20. Electron densities and the excitation of CN in molecular clouds

    NASA Technical Reports Server (NTRS)

    Black, John H.; Van Dishoeck, Ewine F.

    1991-01-01

    In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds.

  1. Measuring the electron density, temperature, and electronegativity in electron beam-generated plasmas produced in argon/SF6 mixtures

    NASA Astrophysics Data System (ADS)

    Boris, D. R.; Fernsler, R. F.; Walton, S. G.

    2015-04-01

    This paper presents measurements of electron density (ne0), electron temperature (Te), and electronegativity (α) in electron beam-generated plasmas produced in mixtures of argon and SF6 using Langmuir probes and plasma resonance spectroscopy. Langmuir probe measurements are analyzed using a model capable of handling multi-component plasmas with both positive and negative ions. Verification of the model is provided through plasma frequency resonance measurements of ne0. The results suggest a simple approach to ascertaining α in negative-ion-containing plasmas using Langmuir probes alone. In addition, modest amounts of SF6 are shown to produce sharp increases in both Te and α in electron beam generated plasmas.

  2. Electron density and plasma dynamics of a colliding plasma experiment

    NASA Astrophysics Data System (ADS)

    Wiechula, J.; Schönlein, A.; Iberler, M.; Hock, C.; Manegold, T.; Bohlender, B.; Jacoby, J.

    2016-07-01

    We present experimental results of two head-on colliding plasma sheaths accelerated by pulsed-power-driven coaxial plasma accelerators. The measurements have been performed in a small vacuum chamber with a neutral-gas prefill of ArH2 at gas pressures between 17 Pa and 400 Pa and load voltages between 4 kV and 9 kV. As the plasma sheaths collide, the electron density is significantly increased. The electron density reaches maximum values of ≈8 ṡ 1015 cm-3 for a single accelerated plasma and a maximum value of ≈2.6 ṡ 1016 cm-3 for the plasma collision. Overall a raise of the plasma density by a factor of 1.3 to 3.8 has been achieved. A scaling behavior has been derived from the values of the electron density which shows a disproportionately high increase of the electron density of the collisional case for higher applied voltages in comparison to a single accelerated plasma. Sequences of the plasma collision have been taken, using a fast framing camera to study the plasma dynamics. These sequences indicate a maximum collision velocity of 34 km/s.

  3. Shock-wave-based density down ramp for electron injection

    NASA Astrophysics Data System (ADS)

    Wang, Chunmei; Li, Ji; Sun, Jun; Luo, Xisheng

    2012-02-01

    We demonstrate a sharp density transition for electron injection in laser wakefield acceleration through numerical study. This density transition is generated by a detached shock wave induced by a cylinder inserted into a supersonic helium gas flow. In a Mach 1.5 flow, the scale length of the density transition Lgrad can approximately equal to plasma wavelength λp at the shock front, and can be further reduced with an increase of the flow Mach number. A density down ramp with Lgrad≥λp can reduce the phase velocity of the wakefield and lower the energy threshold for the electrons to be trapped. Moreover, the quality of the accelerated beam may be greatly improved by precisely controlling of Lgrad to be one λp. For an even sharper density down ramp with Lgrad≪λp, the oscillating electrons in the plasma wave will up shift their phase when crossing the ramp, therefore a fraction of the electrons are injected into the accelerating field. For this injection mechanism, there is no threshold requirement for the pump laser intensity to reach wave breaking, which is a big advantage as compared with other injection mechanisms.

  4. Reconstruction of the ionospheric electron density by geostatistical inversion

    NASA Astrophysics Data System (ADS)

    Minkwitz, David; van den Boogaart, Karl Gerald; Hoque, Mainul; Gerzen, Tatjana

    2015-04-01

    The ionosphere is the upper part of the atmosphere where sufficient free electrons exist to affect the propagation of radio waves. Typically, the ionosphere extends from about 50 - 1000 km and its morphology is mainly driven by solar radiation, particle precipitation and charge exchange. Due to the strong ionospheric impact on many applications dealing with trans-ionospheric signals such as Global Navigation Satellite Systems (GNSS) positioning, navigation and remote sensing, the demand for a highly accurate reconstruction of the electron density is ever increasing. Within the Helmholtz Alliance project "Remote Sensing and Earth System Dynamics" (EDA) the utilization of the upcoming radar mission TanDEM-L and its related products are prepared. The TanDEM-L mission will operate in L-band with a wavelength of approximately 24 cm and aims at an improved understanding of environmental processes and ecosystem change, e.g. earthquakes, volcanos, glaciers, soil moisture and carbon cycle. Since its lower frequency compared to the X-band (3 cm) and C-band (5 cm) radar missions, the influence of the ionosphere will increase and might lead to a significant degradation of the radar image quality if no correction is applied. Consequently, our interest is the reconstruction of the ionospheric electron density in order to mitigate the ionospheric delay. Following the ionosphere's behaviour we establish a non-stationary and anisotropic spatial covariance model of the electron density separated into a vertical and horizontal component. In order to estimate the model's parameters we chose a maximum likelihood approach. This approach incorporates GNSS total electron content measurements, representing integral measurements of the electron density between satellite to receiver ray paths, and the NeQuick model as a non-stationary trend. Based on a multivariate normal distribution the spatial covariance model parameters are optimized and afterwards the 3D electron density can be

  5. Image of electron densities from line and plane projections

    NASA Astrophysics Data System (ADS)

    Kontrym-Sznajd, G.; Samsel-Czekała, M.; Biasini, M.

    2008-04-01

    We compare Fourier transforms with orthogonal polynomials techniques applied in reconstructing three-dimensional electron-positron momentum densities from two-dimensional angular correlation of annihilation radiation (2D-ACAR) spectra and electron momentum densities from one-dimensional Compton profiles (1D-CP). In the case of Fourier transforms, we show results for two different algorithms: filtered back projection and Fourier-Bessel method. These techniques are presented for 2D-ACAR spectra in Y, ErGa3 and model profiles.

  6. Statistical quality indicators for electron-density maps

    SciTech Connect

    Tickle, Ian J.

    2012-04-01

    A likelihood-based metric for scoring the local agreement of a structure model with the observed electron density is described. The commonly used validation metrics for the local agreement of a structure model with the observed electron density, namely the real-space R (RSR) and the real-space correlation coefficient (RSCC), are reviewed. It is argued that the primary goal of all validation techniques is to verify the accuracy of the model, since precision is an inherent property of the crystal and the data. It is demonstrated that the principal weakness of both of the above metrics is their inability to distinguish the accuracy of the model from its precision. Furthermore, neither of these metrics in their usual implementation indicate the statistical significance of the result. The statistical properties of electron-density maps are reviewed and an improved alternative likelihood-based metric is suggested. This leads naturally to a χ{sup 2} significance test of the difference density using the real-space difference density Z score (RSZD). This is a metric purely of the local model accuracy, as required for effective model validation and structure optimization by practising crystallographers prior to submission of a structure model to the PDB. A new real-space observed density Z score (RSZO) is also proposed; this is a metric purely of the model precision, as a substitute for other precision metrics such as the B factor.

  7. The exact density functional for two electrons in one dimension

    NASA Astrophysics Data System (ADS)

    Cohen, Aron; Mori-Sanchez, Paula

    The exact universal density functional F [ ρ ] is calculated for real space two-electron densities in one dimension ρ (x) with a soft-Coulomb interaction. It is calculated by the Levy constrained search F [ ρ ] =minΨ-->ρ < Ψ | \\Tcirc +\\Vcircee | Ψ > over wavefunctions of a two-dimensional Hilbert space Ψ (x1 ,x2) --> ρ (x1) and can be directly visualized. We do an approximate constrained search via density matrices and a direct approximation to natural orbitals. This allows us to make an accurate approximation to the exact functional that is calculated using a search over potentials. We investigate the exact functional and the performance of many approximations on some of the most challenging electronic structure in two-electron systems, from strongly-correlated electron transfer to the description of a localized-delocalized transition. The exact Kohn-Sham potential, vs (x) , and exact Kohn-Sham eigenvalues, ɛi, are calculated and this allows us to discuss the band-gap problem versus the perspective of the exact density functional F [ ρ ] for all numbers of electrons. We calculate the derivative discontinuity of the exact functional in an example of a Mott-Insulator, one-dimensional stretched H2.

  8. Electron temperature and density measurements of laser induced germanium plasma

    NASA Astrophysics Data System (ADS)

    Shakeel, Hira; Arshad, Saboohi; Haq, S. U.; Nadeem, Ali

    2016-05-01

    The germanium plasma produced by the fundamental harmonics (1064 nm) of Nd:YAG laser in single and double pulse configurations have been studied spectroscopically. The plasma is characterized by measuring the electron temperature using the Boltzmann plot method for neutral and ionized species and electron number density as a function of laser irradiance, ambient pressure, and distance from the target surface. It is observed that the plasma parameters have an increasing trend with laser irradiance (9-33 GW/cm2) and with ambient pressure (8-250 mbar). However, a decreasing trend is observed along the plume length up to 4.5 mm. The electron temperature and electron number density are also determined using a double pulse configuration, and their behavior at fixed energy ratio and different interpulse delays is discussed.

  9. Spatial electron density and electric field strength measurements in microwave cavity experiments

    NASA Technical Reports Server (NTRS)

    Peters, M.; Whitehair, S.; Asmussen, J.; Kerber, H.; Rogers, J.

    1984-01-01

    Measurements of electron density and electric field strength have been made in an argon plasma contained in a resonant microwave cavity at 2.45 GHz. Spatial measurements of electron density, n sub e, are correlated with fluorescence observations of the discharge. Measurements of n sub e were made with Stark broadening and compared with n sub e calculated from measured plasma conductivity. Additional measurements of n sub e as a function of pressure and in mixtures of argon and oxygen are presented for pressures from 10 Torr to 1 atm. Measurements in flowing gases and in static systems are presented. In addition, limitations of these measurements are identified.

  10. Spatial electron density and electric field strength measurements in microwave cavity experiments

    NASA Technical Reports Server (NTRS)

    Peters, M.; Rogers, J.; Whitehair, S.; Asmussen, J.; Kerber, R.

    1984-01-01

    Measurements of electron density and electric field strength have been made in an argon plasma contained in a resonant microwave cavity at 2.45 GHz. Spatial measurements of electron density, n sub e, are correlated with fluorescence observations of the discharge. Measurements of n sub e were made with Stark broadening and compared with n sub 3 calculated from measured plasma conductivity. Additional measurements of n sub 3 as a function of pressure and in mixtures of argon and oxygen are presented for pressures from 10 Torr to 1 atm. Measurements in flowing gases and in static systems are presented. In addition, limitations of these measurements are identified.

  11. NUCLEOPHILIC ADDITION TO ACTIVATED DOUBLE BONDS: PREDICTION OF REACTIVITY FROM THE LAPLACIAN OF CHARGE DENSITY

    EPA Science Inventory

    The reactivities of a series of molecules in a Michael addition reaction are analyzed on the basis of properties expressed in the Laplacian of the charge density distribution. he charge densities of structurally optimized acrylic acid (AA), methacrylic acid (MAA), acrylonitrile (...

  12. Assessing the effect of electron density in photon dose calculations

    SciTech Connect

    Seco, J.; Evans, P. M.

    2006-02-15

    Photon dose calculation algorithms (such as the pencil beam and collapsed cone, CC) model the attenuation of a primary photon beam in media other than water, by using pathlength scaling based on the relative mass density of the media to water. In this study, we assess if differences in the electron density between the water and media, with different atomic composition, can influence the accuracy of conventional photon dose calculations algorithms. A comparison is performed between an electron-density scaling method and the standard mass-density scaling method for (i) tissues present in the human body (such as bone, muscle, etc.), and for (ii) water-equivalent plastics, used in radiotherapy dosimetry and quality assurance. We demonstrate that the important material property that should be taken into account by photon dose algorithms is the electron density, and not the mass density. The mass-density scaling method is shown to overestimate, relative to electron-density predictions, the primary photon fluence for tissues in the human body and water-equivalent plastics, where 6%-7% and 10% differences were observed respectively for bone and air. However, in the case of patients, differences are expected to be smaller due to the large complexity of a treatment plan and of the patient anatomy and atomic composition and of the smaller thickness of bone/air that incident photon beams of a treatment plan may have to traverse. Differences have also been observed for conventional dose algorithms, such as CC, where an overestimate of the lung dose occurs, when irradiating lung tumors. The incorrect lung dose can be attributed to the incorrect modeling of the photon beam attenuation through the rib cage (thickness of 2-3 cm in bone upstream of the lung tumor) and through the lung and the oversimplified modeling of electron transport in convolution algorithms. In the present study, the overestimation of the primary photon fluence, using the mass-density scaling method, was shown

  13. Determination of Plasma Electron Density from Optical Measurements

    NASA Astrophysics Data System (ADS)

    Neiswander, Brian; Matlis, Eric; Corke, Thomas

    2009-11-01

    Plasma has been shown to be effective in many flow control applications, but now may also find use in adaptive optics. Plasma's index of refraction is coupled with it's electron density which may be adjusted for adaptive control. An experimental setup to verify the relation between plasma electron density, pressure, and voltage is presented. A non-thermal DBD plasma cell is created by evacuating air and applying a voltage potential between two conducting glass slides. Plasma forms in the chamber between the glass and the applied voltage potential controls the electron density. A HeNe laser is passed through the plasma cell and then focused onto a duo-lateral position sensing device (PSD). The plasma cell is oriented at an angle to the laser's beam and so changes in the plasma's index of refraction produce lateral translations in the beam position. Differences in the PSD output with and without plasma provides for the calculation of the electron density averaged over the beam spot area. The data from this experiment will be used to further develop an adaptive plasma lens for wavefront aberration corrections.

  14. Probabilistic Fatigue Life Analysis of High Density Electronics Packaging

    NASA Technical Reports Server (NTRS)

    Moore, N. R.; Kolawa, E. A.; Sutharshana, S.; Newlin, L. E.; Creager, M.

    1996-01-01

    The fatigue of thin film metal interconnections in high density electronics packaging subjected to thermal cycling has been evaluated using a probabilistic fracture mechanics methodology. This probabilistic methodology includes characterization of thin film stress using an experimentally calibrated finite element model and simulation of flaw growth in the thin films using a stochastic crack growth model.

  15. FMCW Reflectometry for Electron Density Measurements on LTX

    NASA Astrophysics Data System (ADS)

    Kubota, S.; Nguyen, X. V.; Peebles, W. A.; Majeski, R.; Kaita, R.

    2012-10-01

    An FMCW (frequency-modulated continuous-wave) reflectometer is being developed and installed on the Lithium Tokamak Experiment (LTX). The initial system will have two channels covering 13.5--33 GHz for (O-mode) electron density measurements in the range of 0.2-1.3x10^13 cm-3. The reflectometer is designed to provide electron density profile measurements for fueling studies using the molecular cluster injector (MCI), the supersonic gas injector (SGI), as well as external gas puffing. The ultrafast time resolution >=4 μs allows tracking of both the fast evolution of the density profile as well as fluctuations. A future third channel will extend the frequency range to 53 GHz for coverage up to 3.5x10^13 cm-3. The system design, along with simulations using ray tracing and 2-D full-wave codes showing the measurement capabilities and data as available, will be presented.

  16. Fast electronic resistance switching involving hidden charge density wave states

    PubMed Central

    Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.

    2016-01-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T–TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483

  17. Fast electronic resistance switching involving hidden charge density wave states

    NASA Astrophysics Data System (ADS)

    Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.

    2016-05-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states.

  18. Fast electronic resistance switching involving hidden charge density wave states.

    PubMed

    Vaskivskyi, I; Mihailovic, I A; Brazovskii, S; Gospodaric, J; Mertelj, T; Svetin, D; Sutar, P; Mihailovic, D

    2016-01-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483

  19. Mapping neutral, ion, and electron number densities within laser-ablated plasma plumes

    NASA Astrophysics Data System (ADS)

    Weaver, I.; Doyle, Liam A.; Martin, G. W.; Riley, Dave; Lamb, M. J.; Graham, William G.; Morrow, Tom; Lewis, Ciaran L. S.

    1998-05-01

    Spatially and temporally varying neutral, ion and electron number densities have been mapped out within laser ablated plasma plumes expanding into vacuum. Ablation of a magnesium target was performed using a KrF laser, 30 ns pulse duration and 248 nm wavelength. During the initial stage of plasma expansion (t electron number densities, for laser power densities on target in the range 1.3 - 3.0 X 108 W/cm2. Later in the plasma expansion (t equals 1 microsecond(s) ) simultaneous absorption and laser induced fluorescence spectroscopy has been used to determine 3D neutral and ion number densities, for a power density equal to 6.7 X 107 W/cm2. Two distinct regions within the plume were identified. One is a fast component (approximately 106 cm-1) consisting of ions and neutrals with maximum number densities observed to be approximately 30 and 4 X 1012 cm-3 respectively, and the second consists of slow moving neutral material at a number density of up to 1015 cm-3. Additionally a Langmuir probe has been used to obtain ion and electron number densities at very late times in the plasma expansion (1 microsecond(s) density on target equal to 6 X 108 W/cm2. Two regions within the plume with different velocities were observed. Within a fast component (approximately 3 X 106 cms-1) electron and ion number densities of the order 5 X 1012 cm-3 were observed and within the second slower component (approximately 106 cms-1) electron and ion number densities of the order 1 - 2 X 1013 cm-3 were determined.

  20. Differentiability of Lieb functional in electronic density functional theory

    NASA Astrophysics Data System (ADS)

    Lammert, Paul E.

    A solid understanding of the Lieb functional FL is important because of its centrality in the foundations of electronic density functional theory. A basic question is whether directional derivatives of FL at an ensemble-V-representable density are given by (minus) the potential. A widely accepted purported proof that FL is Gâteaux differentiable at EV-representable densities would say, ?yes.? But that proof is fallacious, as shown here. FL is not Gâteaux differentiable in the normal sense, nor is it continuous. By means of a constructive approach, however, we are able to show that the derivative of FL at an EV-representable density ?0 in the direction of ?1 is given by the potential if ?0 and ?1 are everywhere strictly greater than zero, and they and the ground state wave function have square integrable derivatives through second order.

  1. Collimated fast electron beam generation in critical density plasma

    SciTech Connect

    Iwawaki, T. Habara, H.; Morita, K.; Tanaka, K. A.; Baton, S.; Fuchs, J.; Chen, S.; Nakatsutsumi, M.; Rousseaux, C.; Filippi, F.; Nazarov, W.

    2014-11-15

    Significantly collimated fast electron beam with a divergence angle 10° (FWHM) is observed when an ultra-intense laser pulse (I = 10{sup 14 }W/cm{sup 2}, 300 fs) irradiates a uniform critical density plasma. The uniform plasma is created through the ionization of an ultra-low density (5 mg/c.c.) plastic foam by X-ray burst from the interaction of intense laser (I = 10{sup 14 }W/cm{sup 2}, 600 ps) with a thin Cu foil. 2D Particle-In-Cell (PIC) simulation well reproduces the collimated electron beam with a strong magnetic field in the region of the laser pulse propagation. To understand the physical mechanism of the collimation, we calculate energetic electron motion in the magnetic field obtained from the 2D PIC simulation. As the results, the strong magnetic field (300 MG) collimates electrons with energy over a few MeV. This collimation mechanism may attract attention in many applications such as electron acceleration, electron microscope and fast ignition of laser fusion.

  2. C library for topological study of the electronic charge density.

    PubMed

    Vega, David; Aray, Yosslen; Rodríguez, Jesús

    2012-12-01

    The topological study of the electronic charge density is useful to obtain information about the kinds of bonds (ionic or covalent) and the atom charges on a molecule or crystal. For this study, it is necessary to calculate, at every space point, the electronic density and its electronic density derivatives values up to second order. In this work, a grid-based method for these calculations is described. The library, implemented for three dimensions, is based on a multidimensional Lagrange interpolation in a regular grid; by differentiating the resulting polynomial, the gradient vector, the Hessian matrix and the Laplacian formulas were obtained for every space point. More complex functions such as the Newton-Raphson method (to find the critical points, where the gradient is null) and the Cash-Karp Runge-Kutta method (used to make the gradient paths) were programmed. As in some crystals, the unit cell has angles different from 90°, the described library includes linear transformations to correct the gradient and Hessian when the grid is distorted (inclined). Functions were also developed to handle grid containing files (grd from DMol® program, CUBE from Gaussian® program and CHGCAR from VASP® program). Each one of these files contains the data for a molecular or crystal electronic property (such as charge density, spin density, electrostatic potential, and others) in a three-dimensional (3D) grid. The library can be adapted to make the topological study in any regular 3D grid by modifying the code of these functions. PMID:22865338

  3. Nearly degenerate electron distributions and superluminal radiation densities

    NASA Astrophysics Data System (ADS)

    Tomaschitz, Roman

    2010-02-01

    Polylogarithmic fugacity expansions of the partition function, the caloric and thermal equations of state, and the specific heat of fermionic power-law distributions are derived in the nearly degenerate low-temperature/high-density quantum regime. The spectral functions of an ultra-relativistic electron plasma are obtained by averaging the tachyonic radiation densities of inertial electrons with Fermi power-laws, whose entropy is shown to be extensive and stable. The averaged radiation densities are put to test by performing tachyonic cascade fits to the γ-ray spectrum of the TeV blazar Markarian 421 in a low and high emission state. Estimates of the thermal electron plasma in this active galactic nucleus are extracted from the spectral fits, such as temperature, number count, and internal energy. The tachyonic cascades reproduce the quiescent as well as a burst spectrum of the blazar obtained with imaging atmospheric Cherenkov detectors. Double-logarithmic plots of the differential tachyon flux exhibit intrinsic spectral curvature, caused by the Boltzmann factor of the electron gas.

  4. Statistical quality indicators for electron-density maps

    PubMed Central

    Tickle, Ian J.

    2012-01-01

    The commonly used validation metrics for the local agreement of a structure model with the observed electron density, namely the real-space R (RSR) and the real-space correlation coefficient (RSCC), are reviewed. It is argued that the primary goal of all validation techniques is to verify the accuracy of the model, since precision is an inherent property of the crystal and the data. It is demonstrated that the principal weakness of both of the above metrics is their inability to distinguish the accuracy of the model from its precision. Furthermore, neither of these metrics in their usual implementation indicate the statistical significance of the result. The statistical properties of electron-density maps are reviewed and an improved alternative likelihood-based metric is suggested. This leads naturally to a χ2 significance test of the difference density using the real-space difference density Z score (RSZD). This is a metric purely of the local model accuracy, as required for effective model validation and structure optimization by practising crystallographers prior to submission of a structure model to the PDB. A new real-space observed density Z score (RSZO) is also proposed; this is a metric purely of the model precision, as a substitute for other precision metrics such as the B factor. PMID:22505266

  5. Assisted assignment of ligands corresponding to unknown electron density.

    SciTech Connect

    Binkowski, T. A.; Cuff, M.; Nocek, B.; Chang, C.; Joachimiak, A.; Biosciences Division

    2010-01-03

    A semi-automated computational procedure to assist in the identification of bound ligands from unknown electron density has been developed. The atomic surface surrounding the density blob is compared to a library of three-dimensional ligand binding surfaces extracted from the Protein Data Bank (PDB). Ligands corresponding to surfaces which share physicochemical texture and geometric shape similarities are considered for assignment. The method is benchmarked against a set of well represented ligands from the PDB, in which we show that we can identify the correct ligand based on the corresponding binding surface. Finally, we apply the method during model building and refinement stages from structural genomics targets in which unknown density blobs were discovered. A semi-automated computational method is described which aims to assist crystallographers with assigning the identity of a ligand corresponding to unknown electron density. Using shape and physicochemical similarity assessments between the protein surface surrounding the density and a database of known ligand binding surfaces, a plausible list of candidate ligands are identified for consideration. The method is validated against highly observed ligands from the Protein Data Bank and results are shown from its use in a high-throughput structural genomics pipeline.

  6. Coupled-channels quantum theory of electronic flux density in electronically adiabatic processes: fundamentals.

    PubMed

    Diestler, D J

    2012-03-22

    The Born-Oppenheimer (BO) description of electronically adiabatic molecular processes predicts a vanishing electronic flux density (j(e)), =1/2∫dR[Δ(b) (x;R) - Δ(a) (x;R)] even though the electrons certainly move in response to the movement of the nuclei. This article, the first of a pair, proposes a quantum-mechanical "coupled-channels" (CC) theory that allows the approximate extraction of j(e) from the electronically adiabatic BO wave function . The CC theory is detailed for H(2)(+), in which case j(e) can be resolved into components associated with two channels α (=a,b), each of which corresponds to the "collision" of an "internal" atom α (proton a or b plus electron) with the other nucleus β (proton b or a). The dynamical role of the electron, which accommodates itself instantaneously to the motion of the nuclei, is submerged in effective electronic probability (population) densities, Δ(α), associated with each channel (α). The Δ(α) densities are determined by the (time-independent) BO electronic energy eigenfunction, which depends parametrically on the configuration of the nuclei, the motion of which is governed by the usual BO nuclear Schrödinger equation. Intuitively appealing formal expressions for the electronic flux density are derived for H(2)(+). PMID:22103768

  7. Electronic properties of solids excited with intermediate laser power densities

    NASA Astrophysics Data System (ADS)

    Sirotti, Fausto; Tempo Beamline Team

    Intermediate laser power density up to about 100 GW/cm2 is below the surface damage threshold is currently used to induce modification in the physical properties on short time scales. The absorption of a short laser pulse induces non-equilibrium electronic distributions followed by lattice-mediated equilibrium taking place only in the picosecond range. The role of the hot electrons is particularly important in several domains as for example fast magnetization and demagnetization processes, laser induced phase transitions, charge density waves. Angular resolved photoelectron spectroscopy measuring directly energy and momentum of electrons is the most adapted tool to study the electronic excitations at short time scales during and after fast laser excitations. The main technical problem is the space charge created by the pumping laser pulse. I will present angular resolved multiphoton photoemission results obtained with 800 nm laser pulses showing how space charge electrons emitted during fast demagnetization processes can be measured. Unable enter Affiliation: CNRS-SOLEIL Synchrotron L'Orme des Merisiers , Saint Aubin 91192 Gif sur Yvette France.

  8. Driving Plasmaspheric Electron Density Simulations During Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    De Pascuale, S.; Kletzing, C.; Jordanova, V.; Goldstein, J.; Wygant, J. R.; Thaller, S. A.

    2015-12-01

    We test global convection electric field models driving plasmaspheric electron density simulations (RAM-CPL) during geomagnetic storms with in situ measurements provided by the Van Allen Probes (RBSP). RAM-CPL is the cold plasma component of the ring-current atmosphere interactions suite (RAM-SCB) and describes the evolution of plasma density in the magnetic equatorial plane near Earth. Geomagnetic events observed by the RBSP satellites in different magnetic local time (MLT) sectors enable a comparison of local asymmetries in the input electric field and output densities of these simulations. Using a fluid MHD approach, RAM-CPL reproduces core plasmaspheric densities (L<4) to less than 1 order of magnitude difference. Approximately 80% of plasmapause crossings, defined by a low-density threshold, are reproduced to within a mean radial difference of 0.6 L. RAM-CPL, in conjunction with a best-fit driver, can be used in other studies as an asset to predict density conditions in locations distant from RBSP orbits of interest.

  9. Electron density dependence of impedance probe plasma potential measurements

    NASA Astrophysics Data System (ADS)

    Walker, D. N.; Blackwell, D. D.; Amatucci, W. E.

    2015-08-01

    In earlier works, we used spheres of various sizes as impedance probes in demonstrating a method of determining plasma potential, φp, when the probe radius is much larger than the Debye length, λD. The basis of the method in those works [Walker et al., Phys. Plasmas 13, 032108 (2006); ibid. 15, 123506 (2008); ibid. 17, 113503 (2010)] relies on applying a small amplitude signal of fixed frequency to a probe in a plasma and, through network analyzer-based measurements, determining the complex reflection coefficient, Γ, for varying probe bias, Vb. The frequency range of the applied signal is restricted to avoid sheath resonant effects and ion contributions such that ωpi ≪ ω ≪ ωpe, where ωpi is the ion plasma frequency and ωpe is the electron plasma frequency. For a given frequency and applied bias, both Re(Zac) and Im(Zac) are available from Γ. When Re(Zac) is plotted versus Vb, a minimum predicted by theory occurs at φp [Walker et al., Phys. Plasmas 17, 113503 (2010)]. In addition, Im(Zac) appears at, or very near, a maximum at φp. As ne decreases and the sheath expands, the minimum becomes harder to discern. The purpose of this work is to demonstrate that when using network analyzer-based measurements, Γ itself and Im(Zac) and their derivatives are useful as accompanying indicators to Re(Zac) in these difficult cases. We note the difficulties encountered by the most commonly used plasma diagnostic, the Langmuir probe. Spherical probe data is mainly used in this work, although we present limited data for a cylinder and a disk. To demonstrate the effect of lowered density as a function of probe geometry, we compare the cylinder and disk using only the indicator Re(Zac).

  10. Excess electrons in ice: a density functional theory study.

    PubMed

    Bhattacharya, Somesh Kr; Inam, Fakharul; Scandolo, Sandro

    2014-02-21

    We present a density functional theory study of the localization of excess electrons in the bulk and on the surface of crystalline and amorphous water ice. We analyze the initial stages of electron solvation in crystalline and amorphous ice. In the case of crystalline ice we find that excess electrons favor surface states over bulk states, even when the latter are localized at defect sites. In contrast, in amorphous ice excess electrons find it equally favorable to localize in bulk and in surface states which we attribute to the preexisting precursor states in the disordered structure. In all cases excess electrons are found to occupy the vacuum regions of the molecular network. The electron localization in the bulk of amorphous ice is assisted by its distorted hydrogen bonding network as opposed to the crystalline phase. Although qualitative, our results provide a simple interpretation of the large differences observed in the dynamics and localization of excess electrons in crystalline and amorphous ice films on metals. PMID:24401958

  11. Excitations and benchmark ensemble density functional theory for two electrons

    SciTech Connect

    Pribram-Jones, Aurora; Burke, Kieron; Yang, Zeng-hui; Ullrich, Carsten A.; Trail, John R.; Needs, Richard J.

    2014-05-14

    A new method for extracting ensemble Kohn-Sham potentials from accurate excited state densities is applied to a variety of two-electron systems, exploring the behavior of exact ensemble density functional theory. The issue of separating the Hartree energy and the choice of degenerate eigenstates is explored. A new approximation, spin eigenstate Hartree-exchange, is derived. Exact conditions that are proven include the signs of the correlation energy components and the asymptotic behavior of the potential for small weights of the excited states. Many energy components are given as a function of the weights for two electrons in a one-dimensional flat box, in a box with a large barrier to create charge transfer excitations, in a three-dimensional harmonic well (Hooke's atom), and for the He atom singlet-triplet ensemble, singlet-triplet-singlet ensemble, and triplet bi-ensemble.

  12. Electron density fluctuations in a disturbed ionospheric environment

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Ganguli, G.

    1988-01-01

    Electron density fluctuations in the earth's ionosphere can adversely affect SDIO systems which involve electromagnetic wave propagation, e.g., laser beams. This is particularly true for severely disturbed ionospheric conditions produced by high-altitude nuclear explosions (HANEs). This paper briefly describes, in general terms, the HANE environment and the various plasma instabilities which could generate small-scale electron density irregularities. As an example, an analysis of a single instability, the lower-hybrid-drift instability, which is likely to be excited in the ionosphere following a high altitude burst. Both the linear and nonlinear behavior of this instability are discussed. It is shown how these results can be applied to potential SDIO laser systems in a HANE environment.

  13. Fuzzy electron density fragments in macromolecular quantum chemistry, combinatorial quantum chemistry, functional group analysis, and shape-activity relations.

    PubMed

    Mezey, Paul G

    2014-09-16

    Conspectus Just as complete molecules have no boundaries and have "fuzzy" electron density clouds approaching zero density exponentially at large distances from the nearest nucleus, a physically justified choice for electron density fragments exhibits similar behavior. Whereas fuzzy electron densities, just as any fuzzy object, such as a thicker cloud on a foggy day, do not lend themselves to easy visualization, one may partially overcome this by using isocontours. Whereas a faithful representation of the complete fuzzy density would need infinitely many such isocontours, nevertheless, by choosing a selected few, one can still obtain a limited pictorial representation. Clearly, such images are of limited value, and one better relies on more complete mathematical representations, using, for example, density matrices of fuzzy fragment densities. A fuzzy density fragmentation can be obtained in an exactly additive way, using the output from any of the common quantum chemical computational techniques, such as Hartree-Fock, MP2, and various density functional approaches. Such "fuzzy" electron density fragments properly represented have proven to be useful in a rather wide range of applications, for example, (a) using them as additive building blocks leading to efficient linear scaling macromolecular quantum chemistry computational techniques, (b) the study of quantum chemical functional groups, (c) using approximate fuzzy fragment information as allowed by the holographic electron density theorem, (d) the study of correlations between local shape and activity, including through-bond and through-space components of interactions between parts of molecules and relations between local molecular shape and substituent effects, (e) using them as tools of density matrix extrapolation in conformational changes, (f) physically valid averaging and statistical distribution of several local electron densities of common stoichiometry, useful in electron density databank mining, for

  14. New Data on the Topside Electron Density Distribution

    NASA Technical Reports Server (NTRS)

    Huang, Xue-Qin; Reinisch, Bodo; Bilitza, Dieter; Benson, Robert F.

    2001-01-01

    The existing uncertainties about the electron density profiles in the topside ionosphere, i.e., in the height region from hmF2 to approx. 2000 km, require the search for new data sources. The ISIS and Alouette topside sounder satellites from the sixties to the eighties recorded millions of ionograms and most were not analyzed in terms of electron density profiles. In recent years an effort started to digitize the analog recordings to prepare the ionograms for computerized analysis. As of November 2001 about 350,000 ionograms have been digitized from the original 7-track analog tapes. These data are available in binary and CDF format from the anonymous ftp site of the National Space Science Data Center. A search site and browse capabilities on CDAWeb assist the scientific usage of these data. All information and access links can be found at http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html. This paper describes the ISIS data restoration effort and shows how the digital ionograms are automatically processed into electron density profiles from satellite orbit altitude (1400 km for ISIS-2) down to the F peak. Because of the large volume of data an automated processing algorithm is imperative. The automatic topside ionogram scaler with true height algorithm TOPIST software developed for this task is successfully scaling approx.70 % of the ionograms. An 'editing process' is available to manually scale the more difficult ionograms. The automated processing of the digitized ISIS ionograms is now underway, producing a much-needed database of topside electron density profiles for ionospheric modeling covering more than one solar cycle. The ISIS data restoration efforts are supported through NASA's Applied Systems and Information Research Program.

  15. Plasma actuator electron density measurement using microwave perturbation method

    SciTech Connect

    Mirhosseini, Farid; Colpitts, Bruce

    2014-07-21

    A cylindrical dielectric barrier discharge plasma under five different pressures is generated in an evacuated glass tube. This plasma volume is located at the center of a rectangular copper waveguide cavity, where the electric field is maximum for the first mode and the magnetic field is very close to zero. The microwave perturbation method is used to measure electron density and plasma frequency for these five pressures. Simulations by a commercial microwave simulator are comparable to the experimental results.

  16. Fe XXI as an electron density diagnostic in solar flares

    NASA Technical Reports Server (NTRS)

    Mason, H. E.; Doschek, G. A.; Feldman, U.; Bhatia, A. K.

    1979-01-01

    Atomic data have been calculated for Fe XXI, and the theoretical intensity ratios for many transitions are tabulated. Fe XXI lines in wavelength regions 1-25 A, 90-200 A, and 300-2500 A are discussed with reference to presently available solar and laboratory spectra. It is found that Fe XXI is an excellent density diagnostic for solar-flare and tokamak plasmas, when densities are in the range from 10 to the 11th to 10 to the 15th per cu cm. The theoretical calculations are applied to flare spectra obtained from OSO 5, and an electron density of less than 10 to the 13th per cu cm is deduced for a temperature of 10,000,000 K. The results are somewhat ambiguous in several cases because of the limited spectral and temporal resolution of these earlier spectrometers. However, the calculations will be important for forthcoming solar projects, such as the Solar Maximum Mission.

  17. A unifying probabilistic Bayesian approach to derive electron density from MRI for radiation therapy treatment planning.

    PubMed

    Gudur, Madhu Sudhan Reddy; Hara, Wendy; Le, Quynh-Thu; Wang, Lei; Xing, Lei; Li, Ruijiang

    2014-11-01

    MRI significantly improves the accuracy and reliability of target delineation in radiation therapy for certain tumors due to its superior soft tissue contrast compared to CT. A treatment planning process with MRI as the sole imaging modality will eliminate systematic CT/MRI co-registration errors, reduce cost and radiation exposure, and simplify clinical workflow. However, MRI lacks the key electron density information necessary for accurate dose calculation and generating reference images for patient setup. The purpose of this work is to develop a unifying method to derive electron density from standard T1-weighted MRI. We propose to combine both intensity and geometry information into a unifying probabilistic Bayesian framework for electron density mapping. For each voxel, we compute two conditional probability density functions (PDFs) of electron density given its: (1) T1-weighted MRI intensity, and (2) geometry in a reference anatomy, obtained by deformable image registration between the MRI of the atlas and test patient. The two conditional PDFs containing intensity and geometry information are combined into a unifying posterior PDF, whose mean value corresponds to the optimal electron density value under the mean-square error criterion. We evaluated the algorithm's accuracy of electron density mapping and its ability to detect bone in the head for eight patients, using an additional patient as the atlas or template. Mean absolute HU error between the estimated and true CT, as well as receiver operating characteristics for bone detection (HU > 200) were calculated. The performance was compared with a global intensity approach based on T1 and no density correction (set whole head to water). The proposed technique significantly reduced the errors in electron density estimation, with a mean absolute HU error of 126, compared with 139 for deformable registration (p = 2  ×  10(-4)), 283 for the intensity approach (p = 2  ×  10(-6)) and 282 without density

  18. A unifying probabilistic Bayesian approach to derive electron density from MRI for radiation therapy treatment planning

    NASA Astrophysics Data System (ADS)

    Sudhan Reddy Gudur, Madhu; Hara, Wendy; Le, Quynh-Thu; Wang, Lei; Xing, Lei; Li, Ruijiang

    2014-11-01

    MRI significantly improves the accuracy and reliability of target delineation in radiation therapy for certain tumors due to its superior soft tissue contrast compared to CT. A treatment planning process with MRI as the sole imaging modality will eliminate systematic CT/MRI co-registration errors, reduce cost and radiation exposure, and simplify clinical workflow. However, MRI lacks the key electron density information necessary for accurate dose calculation and generating reference images for patient setup. The purpose of this work is to develop a unifying method to derive electron density from standard T1-weighted MRI. We propose to combine both intensity and geometry information into a unifying probabilistic Bayesian framework for electron density mapping. For each voxel, we compute two conditional probability density functions (PDFs) of electron density given its: (1) T1-weighted MRI intensity, and (2) geometry in a reference anatomy, obtained by deformable image registration between the MRI of the atlas and test patient. The two conditional PDFs containing intensity and geometry information are combined into a unifying posterior PDF, whose mean value corresponds to the optimal electron density value under the mean-square error criterion. We evaluated the algorithm’s accuracy of electron density mapping and its ability to detect bone in the head for eight patients, using an additional patient as the atlas or template. Mean absolute HU error between the estimated and true CT, as well as receiver operating characteristics for bone detection (HU > 200) were calculated. The performance was compared with a global intensity approach based on T1 and no density correction (set whole head to water). The proposed technique significantly reduced the errors in electron density estimation, with a mean absolute HU error of 126, compared with 139 for deformable registration (p = 2  ×  10-4), 283 for the intensity approach (p = 2  ×  10-6) and 282 without density

  19. Weather Effects on the D-region Electron Density

    NASA Astrophysics Data System (ADS)

    Eccles, V.; Rice, D.; Sojka, J. J.; Hunsucker, R. D.; Raitt, W. J.

    2009-05-01

    Studies of D-region ionization are complicated by the low electron densities and the altitude range involved. The D-region bottom-side densities are less than 100 cm-3 and the D-region altitudes are inaccessible to most in-situ measurements. Available methods, such as sounding rockets and incoherent scatter radar, can provide detailed profiles for specific times and locations, but mesoscale characterization of D-region weather effects is difficult to obtain. Specifically the horizontal structuring of these densities and to which drivers they are most sensitive is unclear. The response of the D-region to solar inputs, background radiation sources, and wind transport from high latitudes needs to be better understood to improve both our understanding and modeling efforts. The Agile beacon monitor network measures signal strength from radio beacons from three important frequency ranges. The measurements in three frequency ranges, VLF (3-30kHz), LF (30-300 kHz), and HF (0.3-30 MHz), cooperatively help define the D region more precisely. The daytime D-region is perhaps best known for absorption of frequencies below 30 MHz. Measurements of radio signal absorption are useful in describing the D-region response to solar flares and the winter absorption anomaly. Description of the D- region bottom-side and nighttime D-region density requires a different methodology. VLF and LF propagation analysis is sensitive to densities in the 0.1 to 10 cm-3 range. Networks of receivers over these frequency ranges provide an approach for observing the horizontal spatial distribution of the lower D-region density. The D-region electron densities may be inferred by interpreting signal levels at VLF, LF, and HF using D-region models and propagation analysis. This paper describes how the model electron density profiles are modified to include weather effects. Variations are observed in day and night data even during the quietest solar conditions; some variations are consistent with

  20. Low-Density Steels: The Effect of Al Addition on Microstructure and Properties

    NASA Astrophysics Data System (ADS)

    Pramanik, Sudipta; Suwas, Satyam

    2014-09-01

    Density reduction of automotive steels is needed to reduce fuel consumption, thereby reducing greenhouse gas emissions. Aluminum addition has been found to be effective in making steels lighter. Such an addition does not change the crystal structure of the material. Steels modified with aluminum possess higher strength with very little compromise in ductility. In this work, different compositions of Fe-Al systems have been studied so that the desired properties of the material remain within the limit. A density reduction of approximately 10% has been achieved. The specific strength of optimal Fe-Al alloys is higher than conventional steels such as ultra-low-carbon steels.

  1. Simulations of Electron Density Perturbations in a Gas Discharge

    NASA Astrophysics Data System (ADS)

    Caplinger, James; Sotnikov, Vladimir; Main, Daniel

    2015-11-01

    Beginning with the idealized case of the Pierce diode, a series of particle-in-cell (PIC) simulations are conducted in order to characterize density perturbations in a laboratory gas discharge. This work is conducted to support future experimental investigations into electromagnetic scattering off of electron density perturbations excited by plasma flows. As a first step, 2D PIC simulations were conducted for the Pierce diode case, which is a simple model that exploits instabilities of a monochromatic electron beam between two grounded electrodes. These results were compared to the standard analytical solution. Departing from this idealized case we will include in the simulations electron-neutral collisions, particle creation from ionization, as well as an electric field generated by biased electrodes. A parameter study of electric field strength and collision frequency will be performed for values approaching the Pierce diode as well as extending to cases of expected laboratory parameters. If we can extract physical density spectra from simulations with parameters approaching experimental values, it may be possible to analyze electromagnetic scattering characteristics.

  2. Cutoff probe using Fourier analysis for electron density measurement

    NASA Astrophysics Data System (ADS)

    Na, Byung-Keun; You, Kwang-Ho; Kim, Dae-Woong; Chang, Hong-Young; You, Shin-Jae; Kim, Jung-Hyung

    2012-01-01

    This paper proposes a new method for cutoff probe using a nanosecond impulse generator and an oscilloscope, instead of a network analyzer. The nanosecond impulse generator supplies a radiating signal of broadband frequency spectrum simultaneously without frequency sweeping, while frequency sweeping method is used by a network analyzer in a previous method. The transmission spectrum (S21) was obtained through a Fourier analysis of the transmitted impulse signal detected by the oscilloscope and was used to measure the electron density. The results showed that the transmission frequency spectrum and the electron density obtained with a new method are very close to those obtained with a previous method using a network analyzer. And also, only 15 ns long signal was necessary for spectrum reconstruction. These results were also compared to the Langmuir probe's measurements with satisfactory results. This method is expected to provide not only fast measurement of absolute electron density, but also function in other diagnostic situations where a network analyzer would be used (a hairpin probe and an impedance probe) by replacing the network analyzer with a nanosecond impulse generator and an oscilloscope.

  3. Total electron content and F-region electron density distribution near the magnetic equator in India

    NASA Technical Reports Server (NTRS)

    Rastogi, R. G.; Sethia, G.; Chandra, H.; Deshpande, M. R.; Davies, K.; Murthy, B. S.

    1979-01-01

    Total electron content derived from the group delay measurements of ATS-6 radio beacons received at Ootacamund (India) are compared with the electron-density vs height distributions derived from the ionosonde data of the nearby station Kodaikanal. The daily variation of equivalent vertical total electron content does not show the midday bite out which is so prominently present in the corresponding daily variation of the maximum F-region electron density. The topside electron content continues to increase from sunrise to a maximum value around 1500 LT, while the bottomside electron content reaches a maximum value around 0500 LT. Daily variations of these as well as other parameters, e.g. the vertical slab thickness, the bottomside semi-thickness, the height of the F2 peak have been also studied for a geomagnetically quiet and a disturbed day.

  4. Edge Stabilized Ribbon (ESR); Stress, Dislocation Density and Electronic Performance

    NASA Technical Reports Server (NTRS)

    Sachs, E. M.

    1984-01-01

    The edge stabilized ribbon (ESR) silicon ribbon was grown in widths of 1, 2.2 and 4.0 inches at speeds ranging from .6 to 7 in/min, which result in ribbon thicknesses of 5 to 400 microns. One of the primary problems remaining in ESR growth is that of thermally induced mechanical stresses. This problem is manifested as ribbon with a high degree of residual stress or as ribbon with buckled ribbon. Thermal stresses result in a high dislocation density in the grown material, resulting in compromised electronic performance. Improvements in ribbon flatness were accomplished by modification of the ribbon cooling profile. Ribbon flatness and other experimental observations of ESR ribbon are discussed. Laser scanner measurements show a good correlation between diffusion length and dislocation density which indicates that the high dislocation densities are the primary cause of the poor current performance of ESR materials. Dislocation densities were reduced and improved electronic performance resulted. Laser scanner data on new and old material are presented.

  5. Ray tracing technique for global 3-D modeling of ionospheric electron density using GNSS measurements

    NASA Astrophysics Data System (ADS)

    Alizadeh, Mohamad Mahdi; Schuh, Harald; Schmidt, Michael

    2015-06-01

    For space geodetic techniques, operating in microwave band, ionosphere is a dispersive medium; thus, signals traveling through this medium are in the first approximation, affected proportional to the inverse of the square of their frequencies. This effect allows gaining information about the parameters of the ionosphere in terms of total electron content (TEC) or the electron density (Ne). Making use of this phenomenon, space geodetic techniques have turned into a capable tool for studying the ionosphere in the last decades. Up to now, two-dimensional (2-D) models of Vertical TEC (VTEC) have been widely developed and used by different communities; however, due to the fact that these models provide information about the integral of the whole electron content along the vertical or slant raypath, these maps are not useful when information about the ionosphere at different altitude is required. This paper presents a recent study which aims at developing a global 3-D model of the electron density, using measurements from Global Navigation Satellite Systems and by applying the ray tracing technique to the upper atmosphere. The developed modeling approach represents the horizontal variations of the electron density, with two sets of spherical harmonic expansions of degree and order 15. The height dependency of the electron density is represented by a multilayered Chapman profile function for the bottomside and topside ionosphere, and an appropriate model for the plasmasphere. In addition to the geodetic applications of the developed models, within this study, the 3-D models of electron density can include geophysical parameters like maximum electron density and its corresponding height. High-resolution modeling of these parameters allows an improved geophysical interpretation, which is essential in all studies of the upper atmosphere, space weather, and for the solar-terrestrial environment.

  6. Electron-density measurements in hohlraums using soft-x-ray deflectometry

    SciTech Connect

    Decker, C.D.; London, R.A.; Harte, J.A.; Powers, L.V.; Trebes, J.E.

    1998-05-01

    This paper presents design calculations for experiments that measure electron densities of laser heated hohlraums with soft-x-ray moir{acute e} deflectometry. Hydrodynamical simulations of the hohlraums are analyzed to obtain deflection angles of the probing beam and x-ray emission from the hohlraum. The deflection angles and resulting moir{acute e} fringe shifts and fringe contrast are predicted to be sufficient to infer electron-density gradients from measurements. In addition, the self-emission is found to be much lower than that of the probing laser beam, giving a good signal-to-noise ratio. In conclusion, moir{acute e} deflectometry with soft-x-ray lasers has the potential to give valuable information about the electron density in laser driven hohlraums. {copyright} {ital 1998} {ital The American Physical Society}

  7. Electron density power spectrum in the local interstellar medium

    NASA Technical Reports Server (NTRS)

    Armstrong, J. W.; Rickett, B. J.; Spangler, S. R.

    1995-01-01

    Interstellar scintillation (ISS), fluctuations in the amplitude and phase of radio waves caused by scattering in the interstellar medium, is important as a diagnostic of interstellar plasma turbulence. ISS is also of interest because it is noise for other radio astronomical observations. The unifying concern is the power spectrum of the interstellar electron density. Here we use ISS observations through the nearby (less than or approximately =1 kpc) (ISM) to estimate the spectrum. From measurements of angular broadening of pulsars and extragalactic sources, decorrelation bandwidth of pulsars, refractive steering of features in pulsar dynamic spectra, dispersion measured fluctuations of pulsars, and refractive scintillation index measurements, we construct a composite structure function that is approximately power law over 2 x 10(exp 6) m less than scale less than 10(exp 13) m. The data are consistent with the structure function having a logarithmic slope versus baseline less than 2; thus there is a meaningful connection between scales in the radiowave fluctuation field and the scales in the electron density field causing the scattering. The data give an upper limit to the inner scale, l(sub o) less than or approximately 10(exp 8) m and are consistent with much smaller values. We construct a composite electron density spectrum that is approximately power law over at least the approximately = 5 decade wavenumber range 10(exp -13)/m less than wavenumber less than 10(exp -8)/m and that may extend to higher wavenumbers. The average spectral index of electron density over this wavenumber range is approximately = 3.7, very close to the value expected for a Kolmogorov process. The outer scale size, L(sub o), must be greater than or approximately = 10(exp 13) m (determined from dispersion measure fluctuations). When the ISS data are combined with measurements of differential Faraday rotation angle, and gradients in the average electron density, constraints can be put on the

  8. Kinetic and electron-electron energies for convex sums of ground state densities with degeneracies and fractional electron number

    SciTech Connect

    Levy, Mel E-mail: mlevy@tulane.edu; Anderson, James S. M.; Zadeh, Farnaz Heidar; Ayers, Paul W. E-mail: mlevy@tulane.edu

    2014-05-14

    Properties of exact density functionals provide useful constraints for the development of new approximate functionals. This paper focuses on convex sums of ground-level densities. It is observed that the electronic kinetic energy of a convex sum of degenerate ground-level densities is equal to the convex sum of the kinetic energies of the individual degenerate densities. (The same type of relationship holds also for the electron-electron repulsion energy.) This extends a known property of the Levy-Valone Ensemble Constrained-Search and the Lieb Legendre-Transform refomulations of the Hohenberg-Kohn functional to the individual components of the functional. Moreover, we observe that the kinetic and electron-repulsion results also apply to densities with fractional electron number (even if there are no degeneracies), and we close with an analogous point-wise property involving the external potential. Examples where different degenerate states have different kinetic energy and electron-nuclear attraction energy are given; consequently, individual components of the ground state electronic energy can change abruptly when the molecular geometry changes. These discontinuities are predicted to be ubiquitous at conical intersections, complicating the development of universally applicable density-functional approximations.

  9. Observed Variations of O5+ Velocity Distributions with Electron Density

    NASA Astrophysics Data System (ADS)

    Kohl, J. L.; Cranmer, S. R.; Frazin, R. A.; Miralles, M.; Strachan, L.

    2001-05-01

    The Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO satellite has been used to measure the line profiles of O~VI 103.2 and 103.7 nm versus heliographic height in a variety of coronal holes and streamers during the period from 1996 to 2001. Those observations have been used to derive velocity distributions in the line-of-sight direction, which is typically perpendicular to the apparent magnetic field direction. In the case of polar coronal holes at solar minimum, the electron density is the smallest observed and the most-probable speed is the largest observed reaching values as high as 500 km/s at the largest heights. The O5+ most-probable speed is much larger than the hydrogen speed in those structures. The ratio of O5+ to hydrogen most-probable speeds increases with height. In contrast, the O5+ values are much smaller than those of hydrogen at the base of high-latitude streamers and never reach the hydrogen values at any observed height. The electron density in those structures is much greater than in the solar minimum coronal holes. Other structures have intermediate values of the electron density and O5+ most-probable speeds. In general, the O5+ most-probable speed and its ratio to the hydrogen value seem to decrease with increasing density. This apparent observational correlation may be related to thermalization from higher collision rates or it might be related to the physical process that causes the extreme O5+ perpendicular heating. This work is supported by NASA under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by PRODEX (Swiss Contribution).

  10. Reduction of electron density in a plasma by injection of liquids

    NASA Technical Reports Server (NTRS)

    Sodha, M. S.; Evans, J. S.

    1974-01-01

    In this paper, the authors have investigated the physics of various processes relevant to the reduction of electron density in a plasma by addition of water droplets; two processes have in particular been analyzed in some detail, viz, the electron attachment to charged dielectric droplets and the emission of negative ions by vaporization from these droplets. The results of these analyses have been applied to a study of the kinetics of reduction of electron density and charging of droplets in an initially overionized plasma, after addition of water droplets. A number of simplifying assumptions including uniform size and charge on droplets and negligible change in the radius of the droplet due to evaporation have been made.

  11. Equation satisfied by the energy-density functional for electron-electron mutual Coulomb repulsion

    SciTech Connect

    Joubert, Daniel P.

    2011-10-15

    It is shown that the electron-electron mutual Coulomb repulsion energy-density functional V{sub ee}{sup {gamma}}[{rho}] satisfies the equationV{sub ee}{sup {gamma}}[{rho}{sub N}{sup 1}]-V{sub ee}{sup {gamma}}[{rho}{sub N-1}{sup {gamma}}]={integral}d{sup 3}r({delta}V{sub ee}{sup {gamma}}[{rho}{sub N}{sup 1}]/{delta}{rho}{sub N}{sup 1}(r))[{rho}{sub N}{sup 1}(r)-{rho}{sub N-1}{sup {gamma}}(r)], where {rho}{sub N}{sup 1}(r) and {rho}{sub N-1}{sup {gamma}}(r) are N-electron and (N-1)-electron densities determined from the same adiabatic scaled external potential of the N-electron system at coupling strength {gamma}.

  12. Effects Of Radiation On Electronics-Additional References

    NASA Technical Reports Server (NTRS)

    Bouquet, Frank L.

    1988-01-01

    Bibliography abstracts summarizing literature on effects of radiation on new electronic devices. This and second volume cover years 1984 and 1985. Third volume, covers 1982 and 1983 (previously published).

  13. Estimations of electron densities and temperatures in He-3 dominated plasmas. [in nuclear pumped lasers

    NASA Technical Reports Server (NTRS)

    Depaola, B. D.; Marcum, S. D.; Wrench, H. K.; Whitten, B. L.; Wells, W. E.

    1979-01-01

    It is very useful to have a method of estimation for electron temperature and electron densities in nuclear pumped plasmas because measurements of such quantities are very difficult. This paper describes a method, based on rate equation analysis of the ionized species in the plasma and the electron energy balance. In addition to the ionized species, certain neutral species must also be calculated. Examples are given for pure helium and a mixture of helium and argon. In the HeAr case, He(+), He2(+), He/2 3S/, Ar(+), Ar2(+), and excited Ar are evaluated.

  14. Electron Densities and Alkali Atoms in Exoplanet Atmospheres

    NASA Astrophysics Data System (ADS)

    Lavvas, P.; Koskinen, T.; Yelle, R. V.

    2014-11-01

    We describe a detailed study on the properties of alkali atoms in extrasolar giant planets, and specifically focus on their role in generating the atmospheric free electron densities, as well as their impact on the transit depth observations. We focus our study on the case of HD 209458b, and we show that photoionization produces a large electron density in the middle atmosphere that is about two orders of magnitude larger than the density anticipated from thermal ionization. Our purely photochemical calculations, though, result in a much larger transit depth for K than observed for this planet. This result does not change even if the roles of molecular chemistry and excited state chemistry are considered for the alkali atoms. In contrast, the model results for the case of exoplanet XO-2b are in good agreement with the available observations. Given these results we discuss other possible scenarios, such as changes in the elemental abundances, changes in the temperature profiles, and the possible presence of clouds, which could potentially explain the observed HD 209458b alkali properties. We find that most of these scenarios cannot explain the observations, with the exception of a heterogeneous source (i.e., clouds or aerosols) under specific conditions, but we also note the discrepancies among the available observations.

  15. Electron densities and alkali atoms in exoplanet atmospheres

    SciTech Connect

    Lavvas, P.; Koskinen, T.; Yelle, R. V.

    2014-11-20

    We describe a detailed study on the properties of alkali atoms in extrasolar giant planets, and specifically focus on their role in generating the atmospheric free electron densities, as well as their impact on the transit depth observations. We focus our study on the case of HD 209458b, and we show that photoionization produces a large electron density in the middle atmosphere that is about two orders of magnitude larger than the density anticipated from thermal ionization. Our purely photochemical calculations, though, result in a much larger transit depth for K than observed for this planet. This result does not change even if the roles of molecular chemistry and excited state chemistry are considered for the alkali atoms. In contrast, the model results for the case of exoplanet XO-2b are in good agreement with the available observations. Given these results we discuss other possible scenarios, such as changes in the elemental abundances, changes in the temperature profiles, and the possible presence of clouds, which could potentially explain the observed HD 209458b alkali properties. We find that most of these scenarios cannot explain the observations, with the exception of a heterogeneous source (i.e., clouds or aerosols) under specific conditions, but we also note the discrepancies among the available observations.

  16. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    SciTech Connect

    Bajaj, Sanyam Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang; Reza, Shahed; Chumbes, Eduardo M.; Khurgin, Jacob; Rajan, Siddharth

    2015-10-12

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10{sup 7 }cm/s at a low sheet charge density of 7.8 × 10{sup 11 }cm{sup −2}. An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

  17. Ionospheric mapping functions based on electron density fields

    NASA Astrophysics Data System (ADS)

    Zus, Florian; Deng, Zhiguo; Heise, Stefan; Wickert, Jens

    2016-04-01

    We developed an ionospheric Mapping Function (MF) for the Global Navigation Satellite System (GNSS) which is based on the electron density field of the International Reference Ionosphere (IRI). The station specific MF utilizes a look-up table which contains a set of ray-traced ionospheric delays. Hence, unlike the simple MFs that are currently in use, the developed MF depends on the time, location, elevation and azimuth angle. Ray-bending is taken into account, which implies that the MF depends on the carrier frequency as well. This frequency dependency of the MF can be readily used to examine higher-order ionospheric effects due to ray-bending. We compare the proposed MF with the so-called single layer model MF and find significant differences in particular around the equatorial anomaly. In so-far as the proposed MF is based on a realistic electron density field (IRI) our comparison shows the potential error of the single-layer model MF in practice. We conclude that the developed MF concept might be valuable in the GNSS Total Electron Content estimation. The frequency dependency of the MF can be used to mitigate higher-order ionospheric effects.

  18. Electron density measurements during the NLC-91 campaign

    NASA Technical Reports Server (NTRS)

    Ulwick, J. C.; Kelley, Michael C.; Alcala, C.

    1994-01-01

    A Super Arcas rocket, MISTI B, containing DC and RF probes, was launched as a part of the PMSE (Polar Mesosphere Summer Echoes) Salvo during the NLC-91 (Noctilucent Cloud) campaign to measure electron density irregularities with high spatial resolution. Measurements of large and small scale structures in the electron density were made on rocket ascent and descent at the altitudes of 86.5 and 88.5 +/- 0.5 km corresponding to the two altitudes of strongest backscatter recorded by the nearby CUPRI (Cornell University Portable Radar Interferometer) radar. Power spectra of the fluctuations shows two different structuring and scattering mechanisms exist at altitudes only 1 km apart. Since the rocket apogee was 89 km, the rocket was in the height range 88.5 +/- 0.5 km for 30 seconds giving an unusual measurement of horizontal structure over a distance of 5.5 km. Using the simultaneous DC and RF probe measurements of electron depletions and sharp gradient in the lower layer, the role of aerosols in creating these depletions and gradients is speculated upon.

  19. Automated Processing of ISIS Topside Ionograms into Electron Density Profiles

    NASA Technical Reports Server (NTRS)

    Reinisch, bodo W.; Huang, Xueqin; Bilitza, Dieter; Hills, H. Kent

    2004-01-01

    Modeling of the topside ionosphere has for the most part relied on just a few years of data from topside sounder satellites. The widely used Bent et al. (1972) model, for example, is based on only 50,000 Alouette 1 profiles. The International Reference Ionosphere (IRI) (Bilitza, 1990, 2001) uses an analytical description of the graphs and tables provided by Bent et al. (1972). The Alouette 1, 2 and ISIS 1, 2 topside sounder satellites of the sixties and seventies were ahead of their times in terms of the sheer volume of data obtained and in terms of the computer and software requirements for data analysis. As a result, only a small percentage of the collected topside ionograms was converted into electron density profiles. Recently, a NASA-funded data restoration project has undertaken and is continuing the process of digitizing the Alouette/ISIS ionograms from the analog 7-track tapes. Our project involves the automated processing of these digital ionograms into electron density profiles. The project accomplished a set of important goals that will have a major impact on understanding and modeling of the topside ionosphere: (1) The TOPside Ionogram Scaling and True height inversion (TOPIST) software was developed for the automated scaling and inversion of topside ionograms. (2) The TOPIST software was applied to the over 300,000 ISIS-2 topside ionograms that had been digitized in the fkamework of a separate AISRP project (PI: R.F. Benson). (3) The new TOPIST-produced database of global electron density profiles for the topside ionosphere were made publicly available through NASA s National Space Science Data Center (NSSDC) ftp archive at . (4) Earlier Alouette 1,2 and ISIS 1, 2 data sets of electron density profiles from manual scaling of selected sets of ionograms were converted fiom a highly-compressed binary format into a user-friendly ASCII format and made publicly available through nssdcftp.gsfc.nasa.gov. The new database for the topside

  20. Electron density and electron temperature measurement in a bi-Maxwellian electron distribution using a derivative method of Langmuir probes

    SciTech Connect

    Choi, Ikjin; Chung, ChinWook; Youn Moon, Se

    2013-08-15

    In plasma diagnostics with a single Langmuir probe, the electron temperature T{sub e} is usually obtained from the slope of the logarithm of the electron current or from the electron energy probability functions of current (I)-voltage (V) curve. Recently, Chen [F. F. Chen, Phys. Plasmas 8, 3029 (2001)] suggested a derivative analysis method to obtain T{sub e} by the ratio between the probe current and the derivative of the probe current at a plasma potential where the ion current becomes zero. Based on this method, electron temperatures and electron densities were measured and compared with those from the electron energy distribution function (EEDF) measurement in Maxwellian and bi-Maxwellian electron distribution conditions. In a bi-Maxwellian electron distribution, we found the electron temperature T{sub e} obtained from the method is always lower than the effective temperatures T{sub eff} derived from EEDFs. The theoretical analysis for this is presented.

  1. On the asymptotic improvement of supervised learning by utilizing additional unlabeled samples - Normal mixture density case

    NASA Technical Reports Server (NTRS)

    Shahshahani, Behzad M.; Landgrebe, David A.

    1992-01-01

    The effect of additional unlabeled samples in improving the supervised learning process is studied in this paper. Three learning processes. supervised, unsupervised, and combined supervised-unsupervised, are compared by studying the asymptotic behavior of the estimates obtained under each process. Upper and lower bounds on the asymptotic covariance matrices are derived. It is shown that under a normal mixture density assumption for the probability density function of the feature space, the combined supervised-unsupervised learning is always superior to the supervised learning in achieving better estimates. Experimental results are provided to verify the theoretical concepts.

  2. Deriving large electron temperatures and small electron densities with the Cassini Langmuir probe at Saturn

    NASA Astrophysics Data System (ADS)

    Garnier, Philippe; Wahlund, Jan-Erik; Holmberg, Mika; Lewis, Geraint; Schippers, Patricia; Rochel Grimald, Sandrine; Gurnett, Donald; Coates, Andrew; Dandouras, Iannis; Waite, Hunter

    2014-05-01

    The Langmuir Probes (LPs) are commonly used to investigate the cold plasma characteristics in planetary ionospheres/magnetospheres. The LPs performances are limited to low temperatures (i.e. below 5-10 eV at Saturn) and large densities (above several particles/cm3). A strong sensitivity of the Cassini LP measurements to energetic electrons (hundreds eV) may however be observed at Saturn in the L Shell range L=6-10 RS. These electrons impact the surface of the probe and generate a detectable current of secondary electrons. We investigate the influence of such electrons on the current-voltage (I-V) characteristics (for negative potentials), and manage to reproduce the observations with a reasonable precision through empirical and theoretical methods. Conversely, the modelling allows us to derive useful information about the energetic electrons from the LP observations : some information about their pitch angle anisotropy (if combined with the data from a single CAPS ELS anode), as well as an estimate of the electron temperature (in the range 100-300 eV) and of the electron density (above 0.1 particles/cm3). This enlarges the LP measurements capabilities when the influence of the energetic electrons is large (essentially near L=6-10 RS at Saturn). We finally show that a significant influence of the energetic electrons (larger than the contribution of thermal ions) is also expected in various plasma environments of the Solar System, such as at Jupiter (i.e near Ganymede, Europa, Callisto and Io), or even at Earth (in the plasmasheet, the magnetosheath or in plasma cavities). Large electron temperatures and small electron densities could potentially be derived in these environments, which may be of interest for Langmuir Probes in the Earth magnetosphere or onboard the future JUICE mission at Jupiter.

  3. Electron density dependence of impedance probe plasma potential measurements

    SciTech Connect

    Walker, D. N.; Blackwell, D. D.; Amatucci, W. E.

    2015-08-15

    In earlier works, we used spheres of various sizes as impedance probes in demonstrating a method of determining plasma potential, φ{sub p}, when the probe radius is much larger than the Debye length, λ{sub D}. The basis of the method in those works [Walker et al., Phys. Plasmas 13, 032108 (2006); ibid. 15, 123506 (2008); ibid. 17, 113503 (2010)] relies on applying a small amplitude signal of fixed frequency to a probe in a plasma and, through network analyzer-based measurements, determining the complex reflection coefficient, Γ, for varying probe bias, V{sub b}. The frequency range of the applied signal is restricted to avoid sheath resonant effects and ion contributions such that ω{sub pi} ≪ ω ≪ ω{sub pe}, where ω{sub pi} is the ion plasma frequency and ω{sub pe} is the electron plasma frequency. For a given frequency and applied bias, both Re(Z{sub ac}) and Im(Z{sub ac}) are available from Γ. When Re(Z{sub ac}) is plotted versus V{sub b}, a minimum predicted by theory occurs at φ{sub p} [Walker et al., Phys. Plasmas 17, 113503 (2010)]. In addition, Im(Z{sub ac}) appears at, or very near, a maximum at φ{sub p}. As n{sub e} decreases and the sheath expands, the minimum becomes harder to discern. The purpose of this work is to demonstrate that when using network analyzer-based measurements, Γ itself and Im(Z{sub ac}) and their derivatives are useful as accompanying indicators to Re(Z{sub ac}) in these difficult cases. We note the difficulties encountered by the most commonly used plasma diagnostic, the Langmuir probe. Spherical probe data is mainly used in this work, although we present limited data for a cylinder and a disk. To demonstrate the effect of lowered density as a function of probe geometry, we compare the cylinder and disk using only the indicator Re(Z{sub ac})

  4. Momentum distribution function of the electron gas at metallic densities

    NASA Astrophysics Data System (ADS)

    Takada, Yasutami; Yasuhara, H.

    1991-10-01

    The momentum distribution function n(k) of the electron gas is calculated in the effective-potential-expansion method at metallic densities. The recently established self-consistency relation between n(k) and the correlation energy [Y. Takada and T. Kita, J. Phys. Soc. Jpn. 60, 25 (1991)] is employed to check the accuracy of our results. This check shows that the effective-potential-expansion method provides probably the exact and at least more accurate results of n(k) than all the other methods that have given n(k) thus far.

  5. The electron density in clouds of turbulent interstellar plasma

    NASA Astrophysics Data System (ADS)

    Pynzar', A. V.

    2016-03-01

    The dependence of the emission measure on the dispersion measure due to the Galactic background has been derived for 120 directions in the Galaxy. This analysis has yielded the mean electron density, effective thickness of the electron layer, and the volume filling factor of the clouds of ionized gas along the line of sight. The pulsar J1745-2900, which lies in a direction close to the direction toward the center of the Galaxy, is located at least 100 pc closer to the observer than the source Sgr A* along the line of sight. The scatter-broadened angular size of J1745-2900 is determined by the turbulent medium in the Sagittarius Arm.

  6. Electron temperature and density probe for small aeronomy satellites.

    PubMed

    Oyama, K-I; Hsu, Y W; Jiang, G S; Chen, W H; Cheng, C Z; Fang, H K; Liu, W T

    2015-08-01

    A compact and low power consumption instrument for measuring the electron density and temperature in the ionosphere has been developed by modifying the previously developed Electron Temperature Probe (ETP). A circuit block which controls frequency of the sinusoidal signal is added to the ETP so that the instrument can measure both T(e) in low frequency mode and N(e) in high frequency mode from the floating potential shift of the electrode. The floating potential shift shows a minimum at the upper hybrid resonance frequency (f(UHR)). The instrument which is named "TeNeP" can be used for tiny satellites which do not have enough conductive surface area for conventional DC Langmuir probe measurements. The instrument also eliminates the serious problems associated with the contamination of satellite surface as well as the sensor electrode. PMID:26329217

  7. Electron temperature and density probe for small aeronomy satellites

    SciTech Connect

    Oyama, K.-I.; Hsu, Y. W.; Jiang, G. S.; Chen, W. H.; Liu, W. T.; Cheng, C. Z.; Fang, H. K.

    2015-08-15

    A compact and low power consumption instrument for measuring the electron density and temperature in the ionosphere has been developed by modifying the previously developed Electron Temperature Probe (ETP). A circuit block which controls frequency of the sinusoidal signal is added to the ETP so that the instrument can measure both T{sub e} in low frequency mode and N{sub e} in high frequency mode from the floating potential shift of the electrode. The floating potential shift shows a minimum at the upper hybrid resonance frequency (f{sub UHR}). The instrument which is named “TeNeP” can be used for tiny satellites which do not have enough conductive surface area for conventional DC Langmuir probe measurements. The instrument also eliminates the serious problems associated with the contamination of satellite surface as well as the sensor electrode.

  8. Equatorial electron energy and number densities in the Jovian magnetosphere

    NASA Technical Reports Server (NTRS)

    Luthey, J. L.

    1972-01-01

    A synchrotron model with a Maxwellian energy distribution of the form e to the (-E/E sub 0) power is used in a comparison with spatially resolved radio interferometric measurements of the Jovian emission. The observations of the decimeter radiation as a function of equatorial distance at 10.4 and 21 cm wavelength were reduced to source emission/cc of source electrons in each of 16 concentric rings. The peak energies for isotropically distributed electrons exceeded the maximum energy for flat orbiting electrons, and the peaks were generally located from 2.25 to 3 Jupiter radii. Beyond 3 radii, the order of magnitude on number density became a sensitive function of pitch angle distribution. The total equatorial intensities at 75 cm wavelength were computed for (E sub 0)(r) and n(r) at different values of B sub 0. The radiative half life for electrons of initial energy E sub 0 in a dipole field was calculated and found to be nearly constant at one year or less for altitudes at and below the position in peak energy.

  9. The effective density of randomly moving electrons and related characteristics of materials with degenerate electron gas

    SciTech Connect

    Palenskis, V.

    2014-04-15

    Interpretation of the conductivity of metals, of superconductors in the normal state and of semiconductors with highly degenerate electron gas remains a significant issue if consideration is based on the classical statistics. This study is addressed to the characterization of the effective density of randomly moving electrons and to the evaluation of carrier diffusion coefficient, mobility, and other parameters by generalization of the widely published experimental results. The generalized expressions have been derived for various kinetic parameters attributed to the non-degenerate and degenerate electron gas, by analyzing a random motion of the single type carriers in homogeneous materials. The values of the most important kinetic parameters for different metals are also systematized and discussed. It has been proved that Einstein's relation between the diffusion coefficient and the drift mobility of electrons is held for any level of degeneracy if the effective density of randomly moving carriers is properly taken into account.

  10. Communication: Investigation of the electron momentum density distribution of nanodiamonds by electron energy-loss spectroscopy.

    PubMed

    Feng, Zhenbao; Yang, Bing; Lin, Yangming; Su, Dangsheng

    2015-12-01

    The electron momentum distribution of detonation nanodiamonds (DND) was investigated by recording electron energy-loss spectra at large momentum transfer in the transmission electron microscope (TEM), which is known as electron Compton scattering from solid (ECOSS). Compton profile of diamond film obtained by ECOSS was found in good agreement with prior photon experimental measurement and theoretical calculation that for bulk diamond. Compared to the diamond film, the valence Compton profile of DND was found to be narrower, which indicates a more delocalization of the ground-state charge density for the latter. Combining with other TEM characterizations such as high-resolution transmission electron spectroscopy, diffraction, and energy dispersive X-ray spectroscopy measurements, ECOSS was shown to be a great potential technique to study ground-state electronic properties of nanomaterials. PMID:26646862

  11. Communication: Investigation of the electron momentum density distribution of nanodiamonds by electron energy-loss spectroscopy

    SciTech Connect

    Feng, Zhenbao; Yang, Bing; Lin, Yangming; Su, Dangsheng

    2015-12-07

    The electron momentum distribution of detonation nanodiamonds (DND) was investigated by recording electron energy-loss spectra at large momentum transfer in the transmission electron microscope (TEM), which is known as electron Compton scattering from solid (ECOSS). Compton profile of diamond film obtained by ECOSS was found in good agreement with prior photon experimental measurement and theoretical calculation that for bulk diamond. Compared to the diamond film, the valence Compton profile of DND was found to be narrower, which indicates a more delocalization of the ground-state charge density for the latter. Combining with other TEM characterizations such as high-resolution transmission electron spectroscopy, diffraction, and energy dispersive X-ray spectroscopy measurements, ECOSS was shown to be a great potential technique to study ground-state electronic properties of nanomaterials.

  12. Interchange Stability at Saturn and the role of electron density

    NASA Astrophysics Data System (ADS)

    Hospodarsky, George; Kennelly, Timothy; Thomsen, Michelle; Persoon, Ann; Gurnett, Donald; Kurth, William

    2015-04-01

    Interchange events, where "injections" of hotter, less dense plasma move inward to return the magnetic flux carried outward by the colder, more dense plasma are common in rapidly rotating magnetospheres. The Cassini spacecraft detects these injections on almost every orbit of Saturn that encounters the inner and middle (<15 Rs) magnetosphere. Significant changes often occur in the number of injection events and the location they are detected (L shell) between inbound and outbound passes on a given Cassini orbit. Furthermore, differences are observed between consecutive orbits for the same local time sampling. Similar variations between inbound and outbound passes, and between orbits have been observed in the electron density values measured by Cassini. We examine the relationship between the observed electron plasma density and characteristics of the injection events as detected by the Cassini Plasma Spectrometer (CAPS) and Magnetospheric Imaging Instrument (MIMI) for a series of near equatorial orbits between L of about 4.5 to 10 with the inbound primarily in the midnight sector and the outbound in the noon sector.

  13. Measurement of the electron density in Transient Spark discharge

    NASA Astrophysics Data System (ADS)

    Janda, Mário; Martišovitš, Viktor; Hensel, Karol; Dvonč, Lukáš; Machala, Zdenko

    2014-12-01

    This paper presents our measurements of the electron density in a streamer-to-spark transition discharge, which is named transient spark (TS), in atmospheric pressure air. Despite the dc applied voltage, TS has a pulsed character with short (˜10-100 ns) high current (>1 A) pulses, with a repetition frequency on the order of kHz. The electron density ne ˜ 1017 cm-3 at maximum is reached in TS with repetition frequencies below ˜3 kHz, using relatively low power delivered to the plasma (0.2-3 W). The temporal evolution of ne was estimated from the resistance of the plasma discharge, which was obtained by a detailed analysis of the electric circuit representing the TS and the discharge diameter measurements using a fast intensified charge-coupled device (iCCD) camera. This estimate was compared with ne calculated from the measured Stark broadening of several atomic lines: Hα, N at 746 nm, and O triplet at 777 nm. Good agreement was obtained, although the method based on the plasma resistance is sensitive to an accurate determination of the discharge diameter. We have found that this method is also limited for strongly ionized plasmas. On the other hand, a lower ne detection limit can be obtained by this method than from the Stark broadening of atomic lines.

  14. One-electron reduced density matrices of strongly correlated harmonium atoms

    SciTech Connect

    Cioslowski, Jerzy

    2015-03-21

    Explicit asymptotic expressions are derived for the reduced one-electron density matrices (the 1-matrices) of strongly correlated two- and three-electron harmonium atoms in the ground and first excited states. These expressions, which are valid at the limit of small confinement strength ω, yield electron densities and kinetic energies in agreement with the published values. In addition, they reveal the ω{sup 5/6} asymptotic scaling of the exchange components of the electron-electron repulsion energies that differs from the ω{sup 2/3} scaling of their Coulomb and correlation counterparts. The natural orbitals of the totally symmetric ground state of the two-electron harmonium atom are found to possess collective occupancies that follow a mixed power/Gaussian dependence on the angular momentum in variance with the simple power-law prediction of Hill’s asymptotics. Providing rigorous constraints on energies as functionals of 1-matrices, these results are expected to facilitate development of approximate implementations of the density matrix functional theory and ensure their proper description of strongly correlated systems.

  15. High Energy Density Additives for Hybrid Fuel Rockets to Improve Performance and Enhance Safety

    NASA Technical Reports Server (NTRS)

    Jaffe, Richard L.

    2014-01-01

    We propose a conceptual study of prototype strained hydrocarbon molecules as high energy density additives for hybrid rocket fuels to boost the performance of these rockets without compromising safety and reliability. Use of these additives could extend the range of applications for which hybrid rockets become an attractive alternative to conventional solid or liquid fuel rockets. The objectives of the study were to confirm and quantify the high enthalpy of these strained molecules and to assess improvement in rocket performance that would be expected if these additives were blended with conventional fuels. We confirmed the chemical properties (including enthalpy) of these additives. However, the predicted improvement in rocket performance was too small to make this a useful strategy for boosting hybrid rocket performance.

  16. Tapanuli Organoclay Addition Into Linear Low Density Polyethylene-Pineapple Fiber Composites

    SciTech Connect

    Adawiyah, Robiatul; Juwono, Ariadne L.; Roseno, Seto

    2010-12-23

    Linear low density polyethylene-Tapanuli organoclay-pineapple fiber composites were succesfully synthesized by a melt intercalation method. The clay was modified as an organoclay by a cation exchange reaction using hexadecyl trimethyl ammonium bromide (HDTMABr) surfactant. The X-ray diffraction results of the organoclay exhibited a higher basal spacing of 1.87 nm compared to the unmodified clay of 1.46 nm. The composite tensile strength was enhanced up to 46.4% with the 1 wt% organoclay addition. Both tensile and flexural moduli increased up to 150.6% and 43% with the 3 wt% organoclay addition to the composites. However, the flexural strength of the composites was not improved with the organoclay addition. The addition of organoclay has also decreased the heat deflection temperature of the composites.

  17. Tapanuli Organoclay Addition Into Linear Low Density Polyethylene-Pineapple Fiber Composites

    NASA Astrophysics Data System (ADS)

    Adawiyah, Robiatul; Juwono, Ariadne L.; Roseno, Seto

    2010-12-01

    Linear low density polyethylene-Tapanuli organoclay-pineapple fiber composites were succesfully synthesized by a melt intercalation method. The clay was modified as an organoclay by a cation exchange reaction using hexadecyl trimethyl ammonium bromide (HDTMABr) surfactant. The X-ray diffraction results of the organoclay exhibited a higher basal spacing of 1.87 nm compared to the unmodified clay of 1.46 nm. The composite tensile strength was enhanced up to 46.4% with the 1 wt% organoclay addition. Both tensile and flexural moduli increased up to 150.6% and 43% with the 3 wt% organoclay addition to the composites. However, the flexural strength of the composites was not improved with the organoclay addition. The addition of organoclay has also decreased the heat deflection temperature of the composites.

  18. Next Generation Orthopaedic Implants by Additive Manufacturing Using Electron Beam Melting

    PubMed Central

    Murr, Lawrence E.; Gaytan, Sara M.; Martinez, Edwin; Medina, Frank; Wicker, Ryan B.

    2012-01-01

    This paper presents some examples of knee and hip implant components containing porous structures and fabricated in monolithic forms utilizing electron beam melting (EBM). In addition, utilizing stiffness or relative stiffness versus relative density design plots for open-cellular structures (mesh and foam components) of Ti-6Al-4V and Co-29Cr-6Mo alloy fabricated by EBM, it is demonstrated that stiffness-compatible implants can be fabricated for optimal stress shielding for bone regimes as well as bone cell ingrowth. Implications for the fabrication of patient-specific, monolithic, multifunctional orthopaedic implants using EBM are described along with microstructures and mechanical properties characteristic of both Ti-6Al-4V and Co-29Cr-6Mo alloy prototypes, including both solid and open-cellular prototypes manufactured by additive manufacturing (AM) using EBM. PMID:22956957

  19. Dymalloy: A composite substrate for high power density electronic components

    SciTech Connect

    Kerns, J.A.; Colella, N.J.; Makowiecki, D.; Davidson, H.L.

    1995-06-29

    High power density electronic components such as fast microprocessors and power semiconductors must operate below the maximum rated device junction temperature to ensure reliability. function temperatures are determined by the amount of heat generated and the thermal resistance from junction to the ambient thermal environment. Two of the Largest contributions to this thermal resistance are the die attach interface and the package base. A decrease in these resistances can allow increased component packing density in MCMs, reduction of heat sink volume in tightly packed systems, enable the use of higher performance circuit components, and improve reliability. The substrate for high power density devices is the primary thermal link between the junctions and the heat sink. Present high power multichip modules and single chip packages use substrate materials such as silicon nitride or copper tungsten that have thermal conductivity in the range of 200 W/mK. We have developed Dymalloy, a copper-diamond composite, that has a thermal conductivity of 420 W/mK and an adjustable coefficient of thermal expansion, nominally 5.5 ppm/C at 25 C, compatible with silicon and gallium arsenide. Because of the matched coefficient of thermal expansion it is possible to use low thermal resistance hard die attach methods. Dymalloy is a composite material made using micron size Type I diamond powder that has a published thermal conductivity of 600 to 1000 W/mK in a metal matrix that has a thermal conductivity of 350 W/mK. The region of chemical bonding between the matrix material and diamond is limited to approximately 1000 A to maintain a high effective thermal conductivity for the composite. The material may be fabricated in near net shapes. Besides having exceptional thermal properties, the mechanical properties of this material also make it an attractive candidate as an electronic component substrate material.

  20. Regioselectivity of radical additions to substituted alkenes: insight from conceptual density functional theory.

    PubMed

    De Vleeschouwer, Freija; Jaque, Pablo; Geerlings, Paul; Toro-Labbé, Alejandro; De Proft, Frank

    2010-08-01

    Radical additions to substituted alkenes are among the most important reactions in radical chemistry. Nonetheless, there is still some controversy in the literature about the factors that affect the rate and regioselectivity in these addition reactions. In this paper, the orientation of (nucleophilic) radical additions to electron-rich, -neutral, and -poor monosubstituted substrates (11 reactions in total) is investigated through the use of chemical concepts and reactivity descriptors. The regioselectivity of the addition of nucleophilic radicals on electron-rich and -neutral alkenes is thermodynamically controlled. An excellent correlation of 94% is found between the differences in activation barriers and in product stabilities (unsubstituted versus substituted site attack). Polar effects at the initial stage of the reaction play a significant role when electron-poor substrates are considered, lowering the extent of regioselectivity toward the unsubstituted sites, as predicted from the stability differences. This is nicely confirmed through an analysis for each of the 11 reactions using the spin-polarized dual descriptor, matching electrophilic and nucleophilic regions. PMID:20614876

  1. Electronic and structural properties of ultrathin tungsten nanowires and nanotubes by density functional theory calculation

    SciTech Connect

    Sun, Shih-Jye; Lin, Ken-Huang; Li, Jia-Yun; Ju, Shin-Pon

    2014-10-07

    The simulated annealing basin-hopping method incorporating the penalty function was used to predict the lowest-energy structures for ultrathin tungsten nanowires and nanotubes of different sizes. These predicted structures indicate that tungsten one-dimensional structures at this small scale do not possess B.C.C. configuration as in bulk tungsten material. In order to analyze the relationship between multi-shell geometries and electronic transfer, the electronic and structural properties of tungsten wires and tubes including partial density of state and band structures which were determined and analyzed by quantum chemistry calculations. In addition, in order to understand the application feasibility of these nanowires and tubes on nano-devices such as field emitters or chemical catalysts, the electronic stability of these ultrathin tungsten nanowires was also investigated by density functional theory calculations.

  2. Surface electron density models for accurate ab initio molecular dynamics with electronic friction

    NASA Astrophysics Data System (ADS)

    Novko, D.; Blanco-Rey, M.; Alducin, M.; Juaristi, J. I.

    2016-06-01

    Ab initio molecular dynamics with electronic friction (AIMDEF) is a valuable methodology to study the interaction of atomic particles with metal surfaces. This method, in which the effect of low-energy electron-hole (e-h) pair excitations is treated within the local density friction approximation (LDFA) [Juaristi et al., Phys. Rev. Lett. 100, 116102 (2008), 10.1103/PhysRevLett.100.116102], can provide an accurate description of both e-h pair and phonon excitations. In practice, its applicability becomes a complicated task in those situations of substantial surface atoms displacements because the LDFA requires the knowledge at each integration step of the bare surface electron density. In this work, we propose three different methods of calculating on-the-fly the electron density of the distorted surface and we discuss their suitability under typical surface distortions. The investigated methods are used in AIMDEF simulations for three illustrative adsorption cases, namely, dissociated H2 on Pd(100), N on Ag(111), and N2 on Fe(110). Our AIMDEF calculations performed with the three approaches highlight the importance of going beyond the frozen surface density to accurately describe the energy released into e-h pair excitations in case of large surface atom displacements.

  3. Electron delocalization and electron density of small polycyclic aromatic hydrocarbons in singlet excited states.

    PubMed

    Estévez-Fregoso, Mar; Hernández-Trujillo, Jesús

    2016-04-28

    The four lowest singlet electronic states of benzene, the acenes from naphthalene to pentacene, phenanthrene and pyrene were studied by means of theoretical methods. Their vertical excitation energies from the ground electronic states were computed at the CASPT2 approximation. As an attempt to explain the trends observed in the excitation energies, several descriptors based on the electron density were used and the similarity of these molecules with their ground state counterparts was analyzed. It was found that the changes of the topological properties at the C-C bond critical points do not explain the decreasing trends for the excitation energies with the increase of the number of rings, in part because the small changes that take place in the electron density occur above and below the molecular plane. A similarity index based on electron delocalization between quantum topological atoms was defined to compare a molecule in two different electronic states. It was found that, mainly for the acenes, this index goes in line with the excitation energies to the first excited state. Implications of the changes in electron delocalization on the aromatic character of these molecules are also discussed. In general, local aromaticity decreases upon excitation. PMID:26795361

  4. Electron density profiles in the plasmasphere and trough

    NASA Astrophysics Data System (ADS)

    Laakso, H.; Masson, A.

    The plasmasphere is a manifestation of an ionospheric ion outflow that corotates with the Earth's magnetic field. This region has been studied for several decades but we still have lack of good empirical model for it. Since year 1996, the Polar satellite has passed through the inner magnetosphere more than 5,000 times, crossing the plasmapause region more than 15,000 times (sometimes four times per 18-hr orbit). Using the electron densities provided by the EFI experiment, we study statistically the density variation at L = 3-12 shells. With a power law fitting, we determine the plasmapause (PP) location and thickness, and the power law index of density slope in the plasmasphere and trough region. All characteristics reveal strong and interesting variations with MLT and Kp. The average PP location moves from L = 5 to L = 3.5 with increasing Kp. For any Kp, however, the MLT dependence is clear; both dawn- and duskside show particularly interesting activity. The PP thickness decreases with increasing Kp from 0.7 L to 0.1 L. Particularly on the nightside the plasmapause becomes very steep during increasing geomagnetic activity. On the dayside the PP thickness tends to remain always quite large (0.4-0.8 L). The trough power law index k (density is proportional to L-k) shows strong behavior with both MLT and Kp; for instance, in the post-midnight sector k decreases from 5 to 3 with increasing Kp whereas in the pre-midnight sector the change occurs between 4 and 3. Near noon k is 2.5 for all Kp conditions.

  5. Theoretical polarization-dependent X-ray spectra of Be-like Fe calculated for different electron beam densities

    NASA Astrophysics Data System (ADS)

    Shlyaptseva, Alla; Mancini, Roberto

    1998-05-01

    We study theoretically the polarization properties of X-ray spectra of Be-like Fe ions excited through resonant capture by an electron beam with different electron densities. Our previous work in this area was related to the study of polarization of dielectronic satellite lines of Fe ions excited by a low-density electron beam. (A.S. Shlyaptseva, R.C. Mancini, P. Neill, P. Beiersdorfer, J.R. Crespo López-Urrutia, and K. Widmann, Phys. Rev. A, 57), 888 (1998) Here we extend our work to the case of higher-density electron beams. As the density of the electron beam increases, new channels of electron capture appear. Thus the atomic and polarization characteristics of the satellite lines change. Moreover, additional X-ray satellite lines will appear. Using the density matrix formalism, we calculate the polarization characteristics and polarization-dependent spectra of dielectronic satellite lines of Be-like Fe produced at different energies and densities of the electron beam. We compare the results of the present work with our previous ones for low-density electron beams. These results are relevant to the identification of X-ray polarization-dependent spectral features and for X-ray line polarization spectroscopy.

  6. Additives

    NASA Technical Reports Server (NTRS)

    Smalheer, C. V.

    1973-01-01

    The chemistry of lubricant additives is discussed to show what the additives are chemically and what functions they perform in the lubrication of various kinds of equipment. Current theories regarding the mode of action of lubricant additives are presented. The additive groups discussed include the following: (1) detergents and dispersants, (2) corrosion inhibitors, (3) antioxidants, (4) viscosity index improvers, (5) pour point depressants, and (6) antifouling agents.

  7. Laser-driven electron acceleration in a plasma channel with an additional electric field

    NASA Astrophysics Data System (ADS)

    Cheng, Li-Hong; Xue, Ju-Kui; Liu, Jie

    2016-05-01

    We examine the electron acceleration in a two-dimensional plasma channel under the action of a laser field and an additional static electric field. We propose to design an appropriate additional electric field (its direction and location), in order to launch the electron onto an energetic trajectory. We find that the electron acceleration strongly depends on the coupled effects of the laser polarization, the direction, and location of the additional electric field. The additional electric field affects the electron dynamics by changing the dephasing rate. Particularly, a suitably designed additional electric field leads to a considerable energy gain from the laser pulse after the interaction with the additional electric field. The electron energy gain from the laser with the additional electric field can be much higher than that without the additional electric field. This engineering provides a possible means for producing high energetic electrons.

  8. Density gradient free electron collisionally excited x-ray laser

    DOEpatents

    Campbell, E.M.; Rosen, M.D.

    1984-11-29

    An operational x-ray laser is provided that amplifies 3p-3s transition x-ray radiation along an approximately linear path. The x-ray laser is driven by a high power optical laser. The driving line focused optical laser beam illuminates a free-standing thin foil that may be associated with a substrate for improved structural integrity. This illumination produces a generally cylindrically shaped plasma having an essentially uniform electron density and temperature, that exists over a long period of time, and provides the x-ray laser gain medium. The x-ray laser may be driven by more than one optical laser beam. The x-ray laser has been successfully demonstrated to function in a series of experimental tests.

  9. Density gradient free electron collisionally excited X-ray laser

    DOEpatents

    Campbell, Edward M.; Rosen, Mordecai D.

    1989-01-01

    An operational X-ray laser (30) is provided that amplifies 3p-3s transition X-ray radiation along an approximately linear path. The X-ray laser (30) is driven by a high power optical laser. The driving line focused optical laser beam (32) illuminates a free-standing thin foil (34) that may be associated with a substrate (36) for improved structural integrity. This illumination produces a generally cylindrically shaped plasma having an essentially uniform electron density and temperature, that exists over a long period of time, and provides the X-ray laser gain medium. The X-ray laser (30) may be driven by more than one optical laser beam (32, 44). The X-ray laser (30) has been successfully demonstrated to function in a series of experimental tests.

  10. Electronic properties of graphene nanoribbons: A density functional investigation

    SciTech Connect

    Kumar, Sandeep Sharma, Hitesh

    2015-05-15

    Density functional theory calculations have been performed on graphene nano ribbons (GNRs) to investigate the electronic properties as a function of chirality, size and hydrogenation on the edges. The calculations were performed on GNRs with armchair and zigzag configurations with 28, 34, 36, 40, 50, 56, 62, 66 carbon atoms. The structural stability of AGNR and ZGNR increases with the size of nanoribbon where as hydrogenation of GNR tends to lowers their structural stability. All GNRs considered have shown semiconducting behavior with HOMO-LUMO gap decreasing with the increase in the GNR size. The hydrogenation of GNR decreases its HOMO-LUMO gap significantly. The results are in agreement with the available experimental and theoretical results.

  11. The measurement of electron density in a rocket motor plume

    NASA Astrophysics Data System (ADS)

    Cooper, David A.; Frederick, Robert A.

    1993-06-01

    This paper discusses the development of a diagnostic technique to measure the electron density in a rocket motor plume in order to characterize and rank solid rocket propellants based on their propensity to attenuate the communication signal to a missile. Three techniques were originally investigated as possible low-cost approaches that could be used for plume comparisons as a function of propellant. These approaches consisted of Langmuir probes, electromagnetic coils, and focused microwave probes. The focused microwave probe concept was considered the most appropriate technique to implement for the research to be conducted. The complete design and analysis of a focused microwave probe system operating at 17 GHz was conducted and the selection to determine this operating frequency discussed. Initial estimates of general uncertainty analysis suggest very good results are obtainable using a F-4 lens system and horn diameter of 17 in. for the 17 GHz frequency.

  12. A multichannel interferometer for electron density measurements in COMPASS

    NASA Astrophysics Data System (ADS)

    Edlington, Trevor; Wylde, Richard

    1992-10-01

    A compact seven channel interferometer has been designed and built to measure electron density profiles in the COMPASS (compact assembly) tokamak. Two far-infrared (FIR) laser cavities are optically pumped with a single continuous-wave CO2 laser, generating two similar beams at λ=433 μm with a small, tunable difference frequency (0.5-1.0 MHz). The COMPASS facility incorporates a complex set of poloidal field coils close to the vacuum vessel as well as a versatile set of close coupled ``helical'' resonant magnetic perturbation windings which severely restrict diagnostic access. As a result a novel approach to the optical circuit has been necessary. Wire grid polarizers are used to divide the laser power equally between channels and to overlay probing and local oscillator beams after the probe beams have made a double pass through the plasma. Gaussian beam-mode optics is used to minimize the size of the optical components.

  13. Electronic density fluctuation associated to coherent plasmon excitations

    NASA Astrophysics Data System (ADS)

    Gervasoni, Juana; Segui, Silvina; Arista, Nestor

    2011-10-01

    In this work we analyze, in the frame of the coherent states, the fluctuation of the electronic collective modes associated with the wake potential generated by an external particle of charge Ze. This perturbation is described as coherent states of plasmons spatially localized in an average distance of the order of the velocity of the projectile divided by the plasmon frequency of the material. One of the most important features is that in all the cases, for different trajectories of the external particle, and for different structures of the material, the fluctuations are not negligible. In particular, we observe that due to the importance of the surface in nanostructured materials, the fluctuation of density is very sensitive to their geometry and composition, fact that must have taken into account for the nanodevices designs. In this work we analyze, in the frame of the coherent states, the fluctuation of the electronic collective modes associated with the wake potential generated by an external particle of charge Ze. This perturbation is described as coherent states of plasmons spatially localized in an average distance of the order of the velocity of the projectile divided by the plasmon frequency of the material. One of the most important features is that in all the cases, for different trajectories of the external particle, and for different structures of the material, the fluctuations are not negligible. In particular, we observe that due to the importance of the surface in nanostructured materials, the fluctuation of density is very sensitive to their geometry and composition, fact that must have taken into account for the nanodevices designs. Acknowledgements to CNEA and CONICET, Argentina.

  14. Coherent electron beam density modulator for driving X-ray free electron lasers

    NASA Astrophysics Data System (ADS)

    Novokhatski, A.; Decker, F.-J.; Hettel, B.; Nosochkov, Yu.; Sullivan, M.

    2015-02-01

    We propose a new compact scheme for a Free Electron Laser with more coherent properties for the X-ray beam. Higher FEL performance would be achieved using a train of electron bunches initially accelerated in a linear accelerator. Similar to the RF klystron concept, we propose developing an X-ray FEL which consists of two parts: an X-ray self-seeding electron beam density modulator and an output set of undulators. A density modulator consists of a low-Q X-ray cavity and an undulator, which is placed between the cavity mirrors. We use this undulator as a very high gain amplifier, which compensates the amplitude loss due to monochromatic X-ray reflections from the mirrors. Following the X-ray cavity, the density modulated electron beam is separated from the X-ray beam and then enters the output set of undulators. The frequency spectrum of the final X-ray beam is determined mainly by the bandwidth of the reflected elements in the X-ray cavity.

  15. Effect of electron density on cutoff frequency of III-N HFETs

    NASA Astrophysics Data System (ADS)

    Matulionis, Arvydas; Morkoç, Hadis

    2014-03-01

    Advances in frequency performance of heterostructure field-effect transistors (HFETs) are discussed in terms of dissipative processes. The conditions for fastest dissipation coincide reasonably well with those for fastest operation and slowest device degradation. The correlation has its genesis in dissipation of the hot-phonon heat accumulated by non-equilibrium optical phonons launched by hot electrons. The hot-phonon heat causes defect formation and additional electron scattering in a different manner as compared with the effects due to conventional heat accumulated by acoustic phonons. The desirable ultrafast conversion of hot phonons into acoustic phonons is assisted by plasmons as demonstrated through measurement of hot-phonon lifetime. Signatures of plasmons have been also resolved in hot-electron transport, transistor frequency performance, phase noise, and device reliability. The plasmon-assisted ultrafast dissipation of hot-phonon heat explains the known necessity for application a stronger negative gate bias to a channel with higher as-grown electron density.

  16. Dayside electron density structures organised by the Martian crustal magnetic fields

    NASA Astrophysics Data System (ADS)

    Dieval, C.; Wild, J. A.; Morgan, D. D.; Andrews, D. J.; Gurnett, D. A.

    2015-12-01

    The Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard Mars Express is able to detect remotely the Martian topside electron densities down to the main ionospheric peak. In the ionospheric mode it transmits a sequence of pulses in the frequency range 0.1 to 5.5 MHz and measures the delay of reception of the reflected signals returned by the ionospheric plasma layers below the spacecraft. Previous studies using MARSIS have investigated localized electron density structures in the dayside Martian ionosphere, located in areas of typically near-vertical or oblique orientation of the Martian crustal magnetic fields. These crustal fields are remnants of the now extinct global Martian dipole magnetic field, with the strongest fields in the Southern hemisphere reaching up to |B| > 200 nT at altitudes of 400 km. These density structures are often detected as apparent upwellings above the surrounding ideally horizontally stratified ionosphere. Previous studies searched the density structures at a fixed sounding frequency of 1.9 MHz (equivalent to a plasma density of 4.47·104 cm-3), which is a typical frequency at which they are detected. In addition, these studies did not account for the signal dispersion due to the propagation through the ionosphere, which causes larger time delays for receiving the radar echoes, and therefore an underestimation of the altitude of these structures. In the present work we propose to use a statistical dataset of such density structures detected on the dayside of Mars by MARSIS in areas of oblique crustal fields, to determine the interval of densities for which the structures are found to make apparent upwellings. Then we use the corresponding electron density profiles corrected for signal dispersion, to determine the real altitudes of the density structures, their vertical extent and their plasma scale heights compared to the surrounding ionosphere. These new informations give critical hints for uncovering their origins

  17. Radioactinide Additions to the Electronic Gamma-ray Spectrum Catalogue

    SciTech Connect

    R.J. Gehrke; J.R. Davidson; P.J. Taylor; R.G. Helmer; J.W. Mandler

    2001-05-01

    With the completion of a CD ROM version of the original R. L. HEATH''s Gamma-ray Spectrum Catalogue, it became obvious that a number of radionuclides are missing which are important to various fields of nuclear science and technology. With a large amount of transuranic waste awaiting permanent disposal across the Department of Energy (DOE) complex and the need for its assay in order to dispose of it, it was decided that the addition of the radioactinides encountered in transuranic waste should be the first priority. In response to this need, the spectra of 233U, 235U, 238U, 237Np, 238Pu, 239Pu, 240Pu, 241Pu, 242Pu, 241Am and 243Am have been acquired with modern Ge detectors, and prepared for graphics presentation along with the parent and progeny decay chains and decay schemes. The associated tables of -ray energies and emission probabilities have been downloaded from the Evaluated Nuclear Structure Data file (ENSDF) database. This information is being incorporated into the Gamma-Ray Spectrometry Center Web Site at http://id.inel.gov/gamma

  18. Nighttime E-region Electron Density Profiles Measured During the EQUIS II Campaign at Kwajalein Atoll

    NASA Astrophysics Data System (ADS)

    Rowland, D. E.; Pfaff, R. F.; Fourre, R.; Kudeki, E.; Steigies, C. T.; Chau, K.; Sarango, M.

    2005-05-01

    The EQUIS II nighttime E-region rocket and radar measurements were made in order to improve our understanding of the electrodynamics associated with density gradients, neutral wind shear, and enhanced electric fields that develop post-sunset in the near-equatorial region. Four rocket experiments were launched on two separate nights in September, 2004 from Kwajalein Atoll (9.4° N, 167.5° E), while simultaneous E-region radar observations were made with the ALTAIR radar. The focus of this presentation are the electron density profiles measured by two instrumented rockets as they passed through the unstable region on the upleg and downleg. Each rocket used two Langmuir probes and an impedance probe of a new design to measure both the absolute electron density and small-scale density fluctuations with spatial scales on the order of one meter. The impedance probe returned measurements from 7 kHz to 4 MHz, using a new design that excited the plasma using a pseudo-white-noise generator, allowing for an altitude resolution of approximately 40 meters. These impedance curves allow determination of the electron density from the identification of the upper hybrid frequency. In addition, evidence is presented that the impedance probe observed the lower-frequency "series" resonance which is dependent on the electron temperature. Data from the Langmuir probes, a beacon experiment, and the impedance probe are compared and the resulting density profiles are examined to estimate their contribution to the observed electric field irregularities via the gradient-drift and other instabilities.

  19. Measurement of the electron density in a microwave plasma torch at atmospheric pressure

    SciTech Connect

    Zhang Qing; Zhang Guixin; Wang Liming; Wang Xinxin; Wang Shumin; Chen Yan

    2009-11-16

    The electron density in a microwave plasma torch at atmospheric pressure was measured with a Mach-Zehnder interferometer. The electron density is on the order of 10{sup 17}/cm{sup 3}, one order higher than that deduced from the Stark broadening of spectral lines, and increases with the increase in the microwave power. The spatial distribution of the electron density was obtained. The highest electron density locates at the symmetrical axis of the plasma torch and decreases radially. It was found that the electron density fluctuates within a range of 0.3 with the time under the same experimental conditions.

  20. First test of BNL electron beam ion source with high current density electron beam

    SciTech Connect

    Pikin, Alexander Alessi, James G. Beebe, Edward N.; Shornikov, Andrey; Mertzig, Robert; Wenander, Fredrik; Scrivens, Richard

    2015-01-09

    A new electron gun with electrostatic compression has been installed at the Electron Beam Ion Source (EBIS) Test Stand at BNL. This is a collaborative effort by BNL and CERN teams with a common goal to study an EBIS with electron beam current up to 10 A, current density up to 10,000 A/cm{sup 2} and energy more than 50 keV. Intensive and pure beams of heavy highly charged ions with mass-to-charge ratio < 4.5 are requested by many heavy ion research facilities including NASA Space Radiation Laboratory (NSRL) at BNL and HIE-ISOLDE at CERN. With a multiampere electron gun, the EBIS should be capable of delivering highly charged ions for both RHIC facility applications at BNL and for ISOLDE experiments at CERN. Details of the electron gun simulations and design, and the Test EBIS electrostatic and magnetostatic structures with the new electron gun are presented. The experimental results of the electron beam transmission are given.

  1. 36 CFR 1236.24 - What are the additional requirements for managing unstructured electronic records?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 36 Parks, Forests, and Public Property 3 2010-07-01 2010-07-01 false What are the additional requirements for managing unstructured electronic records? 1236.24 Section 1236.24 Parks, Forests, and Public... Additional Requirements for Electronic Records § 1236.24 What are the additional requirements for...

  2. 36 CFR 1236.24 - What are the additional requirements for managing unstructured electronic records?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 36 Parks, Forests, and Public Property 3 2011-07-01 2011-07-01 false What are the additional requirements for managing unstructured electronic records? 1236.24 Section 1236.24 Parks, Forests, and Public... Additional Requirements for Electronic Records § 1236.24 What are the additional requirements for...

  3. 36 CFR 1236.24 - What are the additional requirements for managing unstructured electronic records?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 36 Parks, Forests, and Public Property 3 2014-07-01 2014-07-01 false What are the additional requirements for managing unstructured electronic records? 1236.24 Section 1236.24 Parks, Forests, and Public... Additional Requirements for Electronic Records § 1236.24 What are the additional requirements for...

  4. 36 CFR 1236.24 - What are the additional requirements for managing unstructured electronic records?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 36 Parks, Forests, and Public Property 3 2013-07-01 2012-07-01 true What are the additional requirements for managing unstructured electronic records? 1236.24 Section 1236.24 Parks, Forests, and Public... Additional Requirements for Electronic Records § 1236.24 What are the additional requirements for...

  5. 36 CFR 1236.24 - What are the additional requirements for managing unstructured electronic records?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 36 Parks, Forests, and Public Property 3 2012-07-01 2012-07-01 false What are the additional requirements for managing unstructured electronic records? 1236.24 Section 1236.24 Parks, Forests, and Public... Additional Requirements for Electronic Records § 1236.24 What are the additional requirements for...

  6. Diagnostics principle of microwave cut-off probe for measuring absolute electron density

    SciTech Connect

    Jun, Hyun-Su

    2014-08-15

    A generalized diagnostics principle of microwave cut-off probe is presented with a full analytical solution. In previous studies on the microwave cut-off measurement of weakly ionized plasmas, the cut-off frequency ω{sub c} of a given electron density is assumed to be equal to the plasma frequency ω{sub p} and is predicted using electromagnetic simulation or electric circuit model analysis. However, for specific plasma conditions such as highly collisional plasma and a very narrow probe tip gap, it has been found that ω{sub c} and ω{sub p} are not equal. To resolve this problem, a generalized diagnostics principle is proposed by analytically solving the microwave cut-off condition Re[ε{sub r,eff}(ω = ω{sub c})] = 0. In addition, characteristics of the microwave cut-off condition are theoretically tested for correct measurement of the absolute electron density.

  7. Pauling bond strength, bond length and electron density distribution

    SciTech Connect

    Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.; Iversen, Bo B.; Spackman, M. A.

    2014-01-18

    A power law regression equation, = 1.46(<ρ(rc)>/r)-0.19, connecting the average experimental bond lengths, , with the average accumulation of the electron density at the bond critical point, <ρ(rc)>, between bonded metal M and oxygen atoms, determined at ambient conditions for oxide crystals, where r is the row number of the M atom, is similar to the regression equation R(M-O) = 1.39(ρ(rc)/r)-0.21 determined for three perovskite crystals for pressures as high as 80 GPa. The two equations are also comparable with those, = 1.43(/r)-0.21, determined for a large number of oxide crystals at ambient conditions and = 1.39(/r)-0.22, determined for geometry optimized hydroxyacid molecules, that connect the bond lengths to the average Pauling electrostatic bond strength, , for the M-O bonded interactions. On the basis of the correspondence between the two sets of equations connecting ρ(rc) and the Pauling bond strength s with bond length, it appears that Pauling’s simple definition of bond strength closely mimics the accumulation of the electron density between bonded pairs of atoms. The similarity of the expressions for the crystals and molecules is compelling evidence that the M-O bonded interactions for the crystals and molecules 2 containing the same bonded interactions are comparable. Similar expressions, connecting bond lengths and bond strength, have also been found to hold for fluoride, nitride and sulfide molecules and crystals. The Brown-Shannon bond valence, σ, power law expression σ = [R1/(R(M-O)]N that has found wide use in crystal chemistry, is shown to be connected to a more universal expression determined for oxides and the perovskites, <ρ(rc)> = r[(1.41)/]4.76, demonstrating that the bond valence for a bonded interaction is likewise closely connected to the accumulation of the electron density between the bonded atoms. Unlike the Brown-Shannon expression, it is universal in that it holds for the M

  8. The Influence of Energetic Electrons on the Cassini Langmuir Probe at Saturn : Deriving Large Electron Temperatures and Small Electron Densities

    NASA Astrophysics Data System (ADS)

    Garnier, P.; Wahlund, J.; Holmberg, M.; Lewis, G.; Schippers, P.; Thomsen, M. F.; Rochel Grimald, S.; Gurnett, D. A.; Coates, A. J.; Dandouras, I. S.; Waite, J. H.

    2013-12-01

    The Langmuir probes (LPs) are commonly used to investigate the cold plasma characteristics in planetary ionospheres/magnetospheres. The LPs performances are limited to low temperatures (i.e. below 5-10 eV at Saturn) and large densities (above several particles/cm3). A strong sensitivity of the Cassini LP measurements to energetic electrons (hundreds eV) may however be observed at Saturn in the L Shell range L=6-10 RS. These electrons impact the surface of the probe and generate a detectable current of secondary electrons. We investigated the influence of such electrons on the current-voltage (I-V) characteristics (for negative potentials), showing that both the DC level and slope of the I-V curve are modified. The influence of energetic electrons may be interpreted in terms of the critical and anticritical temperatures concept that is important for spacecraft charging studies. Estimations of the maximum secondary yield value for the LP surface are obtained without using laboratory measurements. Empirical and theoretical methods were developed to reproduce the influence of the energetic electrons with a reasonable precision. Conversely, this modelling allows us to derive useful information about the energetic electrons from the LP observations : some information about their pitch angle anisotropy (if combined with the data from a single CAPS ELS anode), as well as an estimate of the electron temperature (in the range 100-300 eV) and of the electron density (above 0.1 particles/cm3). This enlarges the LP measurements capabilities when the influence of the energetic electrons is large (essentially near L=6-10 RS at Saturn). The understanding of this influence may be used for other missions using Langmuir probes, such as the future missions JUICE at Jupiter, BepiColombo at Mercury, or even the probes in the Earth magnetosphere.

  9. A restoration model of distorted electron density in wave-cutoff probe measurement

    SciTech Connect

    Jun, Hyun-Su Lee, Yun-Seong

    2014-02-15

    This study investigates the problem of electron density distortion and how the density can be restored in a wave-cutoff probe. Despite recent plasma diagnostics research using a wave-cutoff probe, the problem of electron density distortion caused by plasma conditions has not been resolved. Experimental results indicate that electron density measured using the wave-cutoff method is highly susceptible to variations in the probe tip gap. This electron density distortion is caused by the bulk plasma disturbance between probe tips, and it must be removed for calculating the absolute electron density. To do this, a detailed analytic model was developed using the power balance equation near probe tips. This model demonstrates the characteristics of plasma distortion in wave-cutoff probe measurement and successfully restored the absolute value of electron density with varying probe tip gaps.

  10. Modeling of free electronic state density in hydrogenic plasmas based on nearest neighbor approximation

    SciTech Connect

    Nishikawa, Takeshi

    2014-07-15

    Most conventional atomic models in a plasma do not treat the effect of the plasma on the free-electron state density. Using a nearest neighbor approximation, the state densities in hydrogenic plasmas for both bound and free electrons were evaluated and the effect of the plasma on the atomic model (especially for the state density of the free electron) was studied. The model evaluates the electron-state densities using the potential distribution formed by the superposition of the Coulomb potentials of two ions. The potential from one ion perturbs the electronic state density on the other. Using this new model, one can evaluate the free-state density without making any ad-hoc assumptions. The resulting contours of the average ionization degree, given as a function of the plasma temperature and density, are shifted slightly to lower temperatures because of the effect of the increasing free-state density.

  11. Exploring the temporally resolved electron density evolution in extreme ultra-violet induced plasmas

    NASA Astrophysics Data System (ADS)

    van der Horst, R. M.; Beckers, J.; Nijdam, S.; Kroesen, G. M. W.

    2014-07-01

    We measured the electron density in an extreme ultra-violet (EUV) induced plasma. This is achieved in a low-pressure argon plasma by using a method called microwave cavity resonance spectroscopy. The measured electron density just after the EUV pulse is 2.6 × 1016 m-3. This is in good agreement with a theoretical prediction from photo-ionization, which yields a density of 4.5 × 1016 m-3. After the EUV pulse the density slightly increases due to electron impact ionization. The plasma (i.e. electron density) decays in tens of microseconds.

  12. Enhanced modified faraday cup for determination of power density distribution of electron beams

    DOEpatents

    Elmer, John W.; Teruya, Alan T.

    2001-01-01

    An improved tomographic technique for determining the power distribution of an electron or ion beam using electron beam profile data acquired by an enhanced modified Faraday cup to create an image of the current density in high and low power ion or electron beams. A refractory metal disk with a number of radially extending slits, one slit being about twice the width of the other slits, is placed above a Faraday cup. The electron or ion beam is swept in a circular pattern so that its path crosses each slit in a perpendicular manner, thus acquiring all the data needed for a reconstruction in one circular sweep. The enlarged slit enables orientation of the beam profile with respect to the coordinates of the welding chamber. A second disk having slits therein is positioned below the first slit disk and inside of the Faraday cup and provides a shield to eliminate the majority of secondary electrons and ions from leaving the Faraday cup. Also, a ring is located below the second slit disk to help minimize the amount of secondary electrons and ions from being produced. In addition, a beam trap is located in the Faraday cup to provide even more containment of the electron or ion beam when full beam current is being examined through the center hole of the modified Faraday cup.

  13. Device and method for electron beam heating of a high density plasma

    DOEpatents

    Thode, L.E.

    A device and method for relativistic electron beam heating of a high density plasma in a small localized region are described. A relativistic electron beam generator produces a high voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10/sup 17/ to 10/sup 20/.

  14. Electronic structures of hydrogen functionalized carbon nanotube: Density functional theory (DFT) study

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto; Iyama, Tetsuji; Kawabata, Hiroshi

    2016-05-01

    Electronic structures and formation mechanism of hydrogen functionalized carbon nanotube (CNT) have been investigated by means of density functional theory (DFT) method. The mechanism of hydrogen addition reaction to the CNT surface was also investigated. Pure and boron-nitrogen (BN) substituted CNT (denoted by CNT and BN-CNT, respectively) were examined as the carbon nanotubes. It was found that the additions of hydrogen atom to B (boron atom) and C (carbon atom) sites of BN-CNT proceed without activation barrier, whereas the hydrogenation of N (nitrogen atom) site needs the activation energy. The electronic states of hydrogen functionalized CNT and BN-CNT were discussed on the basis of theoretical results.

  15. Electron momentum density, band structure, and structural properties of SrS

    SciTech Connect

    Sharma, G.; Munjal, N.; Vyas, V.; Kumar, R.; Sharma, B. K.; Joshi, K. B.

    2013-10-15

    The electron momentum density, the electronic band structure, and the structural properties of SrS are presented in this paper. The isotropic Compton profile, anisotropies in the directional Compton profiles, the electronic band structure and density of states are calculated using the ab initio periodic linear combination of atomic orbitals method with the CRYSTAL06 code. Structural parameters of SrS-lattice constants and bulk moduli in the B1 and B2 phases-are computed together with the transition pressure. The computed parameters are well in agreement with earlier investigations. To compare the calculated isotropic Compton profile, measurement on polycrystalline SrS is performed using 5Ci-{sup 241}Am Compton spectrometer. Additionally, charge transfer is studied by means of the Compton profiles computed from the ionic model. The nature of bonding in the isovalent SrS and SrO compounds is compared on the basis of equal-valenceelectron-density profiles and the bonding in SrS is found to be more covalent than in SrO.

  16. DAMQT: A package for the analysis of electron density in molecules

    NASA Astrophysics Data System (ADS)

    López, Rafael; Rico, Jaime Fernández; Ramírez, Guillermo; Ema, Ignacio; Zorrilla, David

    2009-09-01

    DAMQT is a package for the analysis of the electron density in molecules and the fast computation of the density, density deformations, electrostatic potential and field, and Hellmann-Feynman forces. The method is based on the partition of the electron density into atomic fragments by means of a least deformation criterion. Each atomic fragment of the density is expanded in regular spherical harmonics times radial factors, which are piecewise represented in terms of analytical functions. This representation is used for the fast evaluation of the electrostatic potential and field generated by the electron density and nuclei, as well as for the computation of the Hellmann-Feynman forces on the nuclei. An analysis of the atomic and molecular deformations of the density can be also carried out, yielding a picture that connects with several concepts of the empirical structural chemistry. Program summaryProgram title: DAMQT1.0 Catalogue identifier: AEDL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDL_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GPLv3 No. of lines in distributed program, including test data, etc.: 278 356 No. of bytes in distributed program, including test data, etc.: 31 065 317 Distribution format: tar.gz Programming language: Fortran90 and C++ Computer: Any Operating system: Linux, Windows (Xp, Vista) RAM: 190 Mbytes Classification: 16.1 External routines: Trolltech's Qt (4.3 or higher) ( http://www.qtsoftware.com/products), OpenGL (1.1 or higher) ( http://www.opengl.org/), GLUT 3.7 ( http://www.opengl.org/resources/libraries/glut/). Nature of problem: Analysis of the molecular electron density and density deformations, including fast evaluation of electrostatic potential, electric field and Hellmann-Feynman forces on nuclei. Solution method: The method of Deformed Atoms in Molecules, reported elsewhere [1], is used for partitioning the molecular electron density

  17. Nanosecond Enhancements of the Atmospheric Electron Density by Extensive Air Showers

    NASA Astrophysics Data System (ADS)

    Rutjes, C.; Camporeale, E.; Ebert, U.; Buitink, S.; Scholten, O.; Trinh, G. T. N.; Witteveen, J.

    2015-12-01

    As is well known a sufficient density of free electrons and strong electric fields are the basic requirements to start any electrical discharge. In the context of thunderstorm discharges it has become clear that in addition droplets and or ice particles are required to enhance the electric field to values above breakdown. In our recent study [1] we have shown that these three ingredients have to interplay to allow for lightning inception, triggered by an extensive air shower event. The extensive air showers are a very stochastic natural phenomenon, creating highly coherent sub-nanosecond enhancements of the atmospheric electron density. Predicting these electron density enhancements accurately one has to take the uncertainty of the input variables into account. For this study we use the initial energy, inclination and altitude of first interaction, which will influence the evolution of the shower significantly. To this end, we use the stochastic collocation method, [2] to post-process our detailed Monte Carlo extensive air shower simulations, done with the CORSIKA [3] software package, which provides an efficient and elegant way to determine the distribution of the atmospheric electron density enhancements. [1] Dubinova, A., Rutjes, C., Ebert, E., Buitink, S., Scholten, O., and Trinh, G. T. N. "Prediction of Lightning Inception by Large Ice Particles and Extensive Air Showers." PRL 115 015002 (2015)[2] G.J.A. Loeven, J.A.S. Witteveen, H. Bijl, Probabilistic collocation: an efficient nonintrusive approach for arbitrarily distributed parametric uncertainties, 45th AIAA Aerospace Sciences Meeting, Reno, Nevada, 2007, AIAA-2007-317[3] Heck, Dieter, et al. CORSIKA: A Monte Carlo code to simulate extensive air showers. No. FZKA-6019. 1998.

  18. Talbot-Lau X-ray Deflectometer electron density diagnostic for laser and pulsed power high energy density plasma experiments

    DOE PAGESBeta

    Valdivia, M. P.; Stutman, D.; Stoeckl, C.; Mileham, C.; Begishev, I.; Theobald, W.; Bromage, J.; Regan, S. P.; Klein, S. R.; Munoz-Cordoves, G.; et al

    2016-04-21

    Talbot-Lau X-ray Deflectometry has been developed as an electron density diagnostic for High Energy Density plasmas. The technique can deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single Moiré image. An 8 keV Talbot-Lau interferometer was deployed using laser and x-pinch backlighters. Grating survival and electron density mapping was demonstrated for 25-29 J, 8-30 ps laser pulses using copper foil targets. Moire pattern formation and grating survival was also observed using a copper x-pinch driven at 400 kA, ~1 kA/ns. Lastly, these results demonstrate the potential of TXD as an electron density diagnostic for HED plasmas.

  19. Possible cause of enhancement of electron temperature in high electron density region in the dayside ionosphere

    NASA Astrophysics Data System (ADS)

    Kakinami, Yoshihiro; Watanabe, Shigeto

    2016-07-01

    When neutral atmosphere is ionized by solar EUV, energetic electrons named photoelectrons are emitted. The photoelectrons are primary heat source of electrons in the ionosphere in the daytime. The heating rate of electron by photoelectron is proportion to 0.97 power of electron density (Ne) while the heated electron is cooled through the Column collision with ions, the rate of which rate is square of Ne. Therefore, electron temperature (Te) decreases and approach ion temperature (Ti) with increase of Ne. Ions are also cooled through the collision with neutral spices. Finally, these temperatures (Te, Ti and Tn) show very similar values in high Ne region. However, Te enhancement with increase of Ne is found in the satellite observation at 600 km in the daytime ionosphere [Kakinami et al., 2011]. Similar Ti variation is also found around the magnetic dip equator [Kakinami et al., 2014]. One possible cause of the enhancement of Te is enhacement of Tn with increase Ne because both Ne and Tn increase with increase of solar irradiance flux, F10.7 [Lei et al., 2007]. However, since such the enhancements of Te are seen in any F10.7, it is hard to explain the phenomenon. In this paper, we present correlation between Te (Ti) and Ne obtained by the Incoherent Scatter radar at Jicamarca. The similar correlation, namely positive correlation of Te (Ti) with Ne in high Ne region are found above 300 km. Using the observations and Tn and neutral density calculated with MSIS, the Column collision cooling with ions, and inelastic collision cooling with neutral spices for electron are shown. The heat conduction along the magnetic field line is also estimated by using IRI model. Using these information, we discuss possible cause of the enhancement of Te in the high Ne region. References Kakinami et al. (2011), J. Geophys. Res., doi:10.1029/2011JA016905. Kakinami et al. (2014), J. Geophys. Res., 119, doi:10.1002/2014JA020302. Lei et al.(2007), J. Geophys. Res., doi:10.1029/2006JA012041.

  20. Comparing two iteration algorithms of Broyden electron density mixing through an atomic electronic structure computation

    NASA Astrophysics Data System (ADS)

    Man-Hong, Zhang

    2016-05-01

    By performing the electronic structure computation of a Si atom, we compare two iteration algorithms of Broyden electron density mixing in the literature. One was proposed by Johnson and implemented in the well-known VASP code. The other was given by Eyert. We solve the Kohn-Sham equation by using a conventional outward/inward integration of the differential equation and then connect two parts of solutions at the classical turning points, which is different from the method of the matrix eigenvalue solution as used in the VASP code. Compared to Johnson’s algorithm, the one proposed by Eyert needs fewer total iteration numbers. Project supported by the National Natural Science Foundation of China (Grant No. 61176080).

  1. Local ionospheric electron density reconstruction from simultaneous ground-based GNSS and ionosonde measurements

    NASA Astrophysics Data System (ADS)

    Stankov, S. M.; Warnant, R.; Stegen, K.

    2009-04-01

    entire altitude range is a straightforward process. As a by-product of the described procedure, the value of the ionospheric slab thickness can be easily computed. To be able to provide forecast, additional information about the current solar and geomagnetic activity is needed. For the purpose, observations available in real time -- at the Royal Institute of Meteorology (RMI), the Royal Observatory of Belgium (ROB), and the US National Oceanic and Atmospheric Administration (NOAA) -- are used. Recently, a new hybrid model for estimating and predicting the local magnetic index K has been developed. This hybrid model has the advantage of using both, ground-based (geomagnetic field components) and space-based (solar wind parameters) measurements, which results in more reliable estimates of the level of geomagnetic activity - current and future. The described reconstruction procedure has been tested on actual measurements at the RMI Dourbes Geophysics Centre (coordinates: 50.1N, 4.6E) where a GPS receiver is collocated with a digital ionosonde (code: DB049, type: Lowell DGS 256). Currently, the nominal time resolution between two consecutive reconstructions is set to 15 minutes with a forecast horizon for each reconstruction of up to 60 minutes. Several applications are envisaged. For example, the ionospheric propagation delays can be estimated and corrected much easier if the electron density profile is available at a nearby location on a real-time basis. Also, both the input data and the reconstruction results can be used for validation purposes in ionospheric models, maps, and services. Recent studies suggest that such ionospheric monitoring systems can help research/services related to aircraft navigation, e.g. for development of the ‘ionospheric threat' methodology.

  2. Measurement of a density profile of a hot-electron plasma in RT-1 with three-chord interferometry

    NASA Astrophysics Data System (ADS)

    Saitoh, H.; Yano, Y.; Yoshida, Z.; Nishiura, M.; Morikawa, J.; Kawazura, Y.; Nogami, T.; Yamasaki, M.

    2015-02-01

    The electron density profile of a plasma in a magnetospheric dipole field configuration was measured with a multi-chord interferometry including a relativistic correction. In order to improve the accuracy of density reconstruction, a 75 GHz interferometer was installed at a vertical chord of the Ring Trap 1 (RT-1) device in addition to previously installed ones at tangential and another vertical chords. The density profile was calculated by using the data of three-chord interferometry including relativistic effects for a plasma consisting of hot and cold electrons generated by electron cyclotron resonance heating (ECH). The results clearly showed the effects of density peaking and magnetic mirror trapping in a strongly inhomogeneous dipole magnetic field.

  3. Measurement of a density profile of a hot-electron plasma in RT-1 with three-chord interferometry

    SciTech Connect

    Saitoh, H.; Yano, Y.; Yoshida, Z.; Nishiura, M.; Morikawa, J.; Kawazura, Y.; Nogami, T.; Yamasaki, M.

    2015-02-15

    The electron density profile of a plasma in a magnetospheric dipole field configuration was measured with a multi-chord interferometry including a relativistic correction. In order to improve the accuracy of density reconstruction, a 75 GHz interferometer was installed at a vertical chord of the Ring Trap 1 (RT-1) device in addition to previously installed ones at tangential and another vertical chords. The density profile was calculated by using the data of three-chord interferometry including relativistic effects for a plasma consisting of hot and cold electrons generated by electron cyclotron resonance heating (ECH). The results clearly showed the effects of density peaking and magnetic mirror trapping in a strongly inhomogeneous dipole magnetic field.

  4. Quasimonoenergetic collimated electron beams from a laser wakefield acceleration in low density pure nitrogen

    SciTech Connect

    Tao, Mengze; Hafz, Nasr A. M. Li, Song; Mirzaie, Mohammad; Elsied, Ahmed M. M.; Ge, Xulei; Liu, Feng; Sokollik, Thomas; Sheng, Zhengming; Zhang, Jie; Chen, Liming

    2014-07-15

    A laser wakefield acceleration (LWFA) experiment is performed using 30 TW, 30 fs, and 800 nm laser pulses, focused onto pure nitrogen plasma having relatively low densities in the range of 0.8×10{sup 18} cm{sup −3} to 2.7×10{sup 18} cm{sup −3}. Electron beams having a low divergence of ∼3  mrad (full-width at half-maximum) and quasi-monoenergetic peak energies of ∼105  MeV are achieved over 4-mm interaction length. The total electron beam charge reached to 2 nC, however, only 1%–2% of this (tens of pC) had energies >35 MeV. We tried different conditions to optimize the electron beam acceleration; our experiment verifies that lower nitrogen plasma densities are generating electron beams with high quality in terms of divergence, charge, pointing stability, and maximum energy. In addition, if LWFA is to be widely used as a basis for compact particle accelerators in the future, therefore, from the economic and safety points of view we propose the use of nitrogen gas rather than helium or hydrogen.

  5. Competition between excitonic charge and spin density waves: Influence of electron-phonon and Hund's rule couplings

    NASA Astrophysics Data System (ADS)

    Kaneko, Tatsuya; Zenker, Bernd; Fehske, Holger; Ohta, Yukinori

    2015-09-01

    We analyze the stability of excitonic ground states in the two-band Hubbard model with additional electron-phonon and Hund's rule couplings using a combination of mean-field and variational cluster approaches. We show that both the interband Coulomb interaction and the electron-phonon interaction will cooperatively stabilize a charge density wave (CDW) state which typifies an "excitonic" CDW if predominantly triggered by the effective interorbital electron-hole attraction or a "phononic" CDW if mostly caused by the coupling to the lattice degrees of freedom. By contrast, the Hund's rule coupling promotes an excitonic spin density wave. We determine the transition between excitonic charge and spin density waves and comment on a fixation of the phase of the excitonic order parameter that would prevent the formation of a superfluid condensate of excitons. The implications for exciton condensation in several material classes with strongly correlated electrons are discussed.

  6. Transportation of high-current ion and electron beams in the accelerator drift gap in the presence of an additional electron background

    NASA Astrophysics Data System (ADS)

    Karas', V. I.; Kornilov, E. A.; Manuilenko, O. V.; Tarakanov, V. P.; Fedorovskaya, O. V.

    2015-12-01

    The dynamics of a high-current ion beam propagating in the drift gap of a linear induction accelerator with collective focusing is studied using 3D numerical simulations in the framework of the full system of the Vlasov-Maxwell equations (code KARAT). The ion beam is neutralized by a comoving electron beam in the current density and, partially, in space charge, since the velocities of electrons and ions differ substantially. The dynamics of the high-current ion beam is investigated for different versions of additional neutralization of its space charge. It is established that, for a given configuration of the magnetic field and in the presence of a specially programmed injection of additional electrons from the boundary opposite to the ion injection boundary, the angular divergence of the ion beam almost vanishes, whereas the current of the ion beam at the exit from the accelerator drift gap changes insignificantly and the beam remains almost monoenergetic.

  7. Transportation of high-current ion and electron beams in the accelerator drift gap in the presence of an additional electron background

    SciTech Connect

    Karas’, V. I. Kornilov, E. A.; Manuilenko, O. V.; Tarakanov, V. P.; Fedorovskaya, O. V.

    2015-12-15

    The dynamics of a high-current ion beam propagating in the drift gap of a linear induction accelerator with collective focusing is studied using 3D numerical simulations in the framework of the full system of the Vlasov–Maxwell equations (code KARAT). The ion beam is neutralized by a comoving electron beam in the current density and, partially, in space charge, since the velocities of electrons and ions differ substantially. The dynamics of the high-current ion beam is investigated for different versions of additional neutralization of its space charge. It is established that, for a given configuration of the magnetic field and in the presence of a specially programmed injection of additional electrons from the boundary opposite to the ion injection boundary, the angular divergence of the ion beam almost vanishes, whereas the current of the ion beam at the exit from the accelerator drift gap changes insignificantly and the beam remains almost monoenergetic.

  8. Ligand identification using electron-density map correlations

    SciTech Connect

    Terwilliger, Thomas C.; Adams, Paul D.; Moriarty, Nigel W.; Cohn, Judith D.

    2007-01-01

    An automated ligand-fitting procedure is applied to (F{sub o} − F{sub c})exp(iϕ{sub c}) difference density for 200 commonly found ligands from macromolecular structures in the Protein Data Bank to identify ligands from density maps. A procedure for the identification of ligands bound in crystal structures of macromolecules is described. Two characteristics of the density corresponding to a ligand are used in the identification procedure. One is the correlation of the ligand density with each of a set of test ligands after optimization of the fit of that ligand to the density. The other is the correlation of a fingerprint of the density with the fingerprint of model density for each possible ligand. The fingerprints consist of an ordered list of correlations of each the test ligands with the density. The two characteristics are scored using a Z-score approach in which the correlations are normalized to the mean and standard deviation of correlations found for a variety of mismatched ligand-density pairs, so that the Z scores are related to the probability of observing a particular value of the correlation by chance. The procedure was tested with a set of 200 of the most commonly found ligands in the Protein Data Bank, collectively representing 57% of all ligands in the Protein Data Bank. Using a combination of these two characteristics of ligand density, ranked lists of ligand identifications were made for representative (F{sub o} − F{sub c})exp(iϕ{sub c}) difference density from entries in the Protein Data Bank. In 48% of the 200 cases, the correct ligand was at the top of the ranked list of ligands. This approach may be useful in identification of unknown ligands in new macromolecular structures as well as in the identification of which ligands in a mixture have bound to a macromolecule.

  9. Density functional theory study of the effects of alloying additions on sulfur adsorption on nickel surfaces

    NASA Astrophysics Data System (ADS)

    Malyi, Oleksandr I.; Chen, Zhong; Kulish, Vadym V.; Bai, Kewu; Wu, Ping

    2013-01-01

    Reactions of hydrogen sulfide (H2S) with Nickel/Ytrria-doped zirconia (Ni/YDZ) anode materials might cause degradation of the performance of solid oxide fuel cells when S containing fuels are used. In this paper, we employ density functional theory to investigate S adsorption on metal (M)-doped and undoped Ni(0 0 1) and Ni(1 1 1) surfaces. Based on the performed calculations, we analyze the effects of 12 alloying additions (Ag, Au, Al, Bi, Cd, Co, Cu, Fe, Sn, Sb, V, and Zn) on the temperature of transition between clean (S atoms do not adsorb on the surfaces) and contaminated (S atoms can adsorb on the surfaces spontaneously) M-doped Ni surfaces for different concentrations of H2S in the fuel. Predicted results are consistent with many experimental studies relevant to S poisoning of both Ni/YDZ and M-doped Ni/YDZ anode materials. This study is important to understand S poisoning phenomena and to develop new S tolerant anode materials.

  10. Density functional theory for d- and f-electron materials and compounds

    DOE PAGESBeta

    Mattson, Ann E.; Wills, John M.

    2016-02-12

    Here, the fundamental requirements for a computationally tractable Density Functional Theory-based method for relativistic f- and (nonrelativistic) d-electron materials and compounds are presented. The need for basing the Kohn–Sham equations on the Dirac equation is discussed. The full Dirac scheme needs exchange-correlation functionals in terms of four-currents, but ordinary functionals, using charge density and spin-magnetization, can be used in an approximate Dirac treatment. The construction of a functional that includes the additional confinement physics needed for these materials is illustrated using the subsystem-functional scheme. If future studies show that a full Dirac, four-current based, exchange-correlation functional is needed, the subsystemmore » functional scheme is one of the few schemes that can still be used for constructing functional approximations.« less

  11. Atomic charges, dipole moments, and Fukui functions using the Hirshfeld partitioning of the electron density.

    PubMed

    De Proft, F; Van Alsenoy, C; Peeters, A; Langenaeker, W; Geerlings, P

    2002-09-01

    In the Hirshfeld partitioning of the electron density, the molecular electron density is decomposed in atomic contributions, proportional to the weight of the isolated atom density in the promolecule density, constructed by superimposing the isolated atom electron densities placed on the positions the atoms have in the molecule. A maximal conservation of the information of the isolated atoms in the atoms-in-molecules is thereby secured. Atomic charges, atomic dipole moments, and Fukui functions resulting from the Hirshfeld partitioning of the electron density are computed for a large series of molecules. In a representative set of organic and hypervalent molecules, they are compared with other commonly used population analysis methods. The expected bond polarities are recovered, but the charges are much smaller compared to other methods. Condensed Fukui functions for a large number of molecules, undergoing an electrophilic or a nucleophilic attack, are computed and compared with the HOMO and LUMO densities, integrated over the Hirshfeld atoms in molecules. PMID:12116389

  12. Geometrically necessary dislocation densities in olivine obtained using high-angular resolution electron backscatter diffraction.

    PubMed

    Wallis, David; Hansen, Lars N; Ben Britton, T; Wilkinson, Angus J

    2016-09-01

    Dislocations in geological minerals are fundamental to the creep processes that control large-scale geodynamic phenomena. However, techniques to quantify their densities, distributions, and types over critical subgrain to polycrystal length scales are limited. The recent advent of high-angular resolution electron backscatter diffraction (HR-EBSD), based on diffraction pattern cross-correlation, offers a powerful new approach that has been utilised to analyse dislocation densities in the materials sciences. In particular, HR-EBSD yields significantly better angular resolution (<0.01°) than conventional EBSD (~0.5°), allowing very low dislocation densities to be analysed. We develop the application of HR-EBSD to olivine, the dominant mineral in Earth's upper mantle by testing (1) different inversion methods for estimating geometrically necessary dislocation (GND) densities, (2) the sensitivity of the method under a range of data acquisition settings, and (3) the ability of the technique to resolve a variety of olivine dislocation structures. The relatively low crystal symmetry (orthorhombic) and few slip systems in olivine result in well constrained GND density estimates. The GND density noise floor is inversely proportional to map step size, such that datasets can be optimised for analysing either short wavelength, high density structures (e.g. subgrain boundaries) or long wavelength, low amplitude orientation gradients. Comparison to conventional images of decorated dislocations demonstrates that HR-EBSD can characterise the dislocation distribution and reveal additional structure not captured by the decoration technique. HR-EBSD therefore provides a highly effective method for analysing dislocations in olivine and determining their role in accommodating macroscopic deformation. PMID:27337604

  13. 3D Distribution of the Coronal Electron Density and its Evolution with Solar Cycle

    NASA Astrophysics Data System (ADS)

    Wang, Tongjiang; Reginald, Nelson Leslie; Davila, Joseph M.; St. Cyr, Orville Chris

    2016-05-01

    The variability of the solar white-light corona and its connection to the solar activity has been studied for more than a half century. It is widely accepted that the temporal variation of the total radiance of the K-corona follows the solar cycle pattern (e.g., correlated with sunspot number). However, the origin of this variation and its relationships with regard to coronal mass ejections and the solar wind are yet to be clearly understood. We know that the COR1-A and –B instruments onboard the STEREO spacecraft have continued to perform high-cadence (5 min) polarized brightness measurements from two different vantage points over a long period of time that encompasses the solar minimum of Solar Cycle 23 to the solar maximum of Solar Cycle 24. This extended period of polarized brightness measurements can now be used to reconstruct 3D electron density distributions of the corona between the heliocentric heights of 1.5-4.0 solar radii. In this study we have constructed the 3D coronal density models for 100 Carrington rotations (CRs) from 2007 to 2014 using the spherically symmetric inversion (SSI) method. The validity of these 3D density models is verified by comparing with similar 3D density models created by other means such as tomography, MHD modeling, and 2D density distributions inverted from the polarized brightness images from LASCO/C2 instrument onboard the SOHO spacecraft. When examining the causes for the temporal variation of the global electron content we find that its increase from the solar minimum to maximum depends on changes to both the total area and mean density of coronal streamers. We also find that the global and hemispheric electron contents show quasi-periodic variations with a period of 8-9 CRs during the ascending and maximum phases of Solar Cycle 24 through wavelet analysis. In addition, we also explore any obvious relationships between temporal variation of the global electron content with the photospheric magnetic flux, total mass of

  14. Measurements of electron density profiles using an angular filter refractometer

    SciTech Connect

    Haberberger, D. Ivancic, S.; Hu, S. X.; Boni, R.; Barczys, M.; Craxton, R. S.; Froula, D. H.

    2014-05-15

    A novel diagnostic technique, angular filter refractometry (AFR), has been developed to characterize high-density, long-scale-length plasmas relevant to high-energy-density physics experiments. AFR measures plasma densities up to 10{sup 21} cm{sup −3} with a 263-nm probe laser and is used to study the plasma expansion from CH foil and spherical targets that are irradiated with ∼9 kJ of ultraviolet (351-nm) laser energy in a 2-ns pulse. The data elucidate the temporal evolution of the plasma profile for the CH planar targets and the dependence of the plasma profile on target radius for CH spheres.

  15. Field-aligned electron density irregularities near 500 km Equator to polar cap topside sounder observations

    NASA Technical Reports Server (NTRS)

    Benson, R. F.

    1985-01-01

    In addition to spread F, evidence for field-aligned electron density irregularities is commonly observed on Alouette 2 topside sounder ionograms recorded near perigee (500 km). This evidence is provided by distinctive signal returns from sounder-generated Z mode waves. At low latitudes these waves become guided in wave ducts caused by field-aligned electron density irregularities and give rise to strong long-duration echoes. At high latitudes, extending well into the polar cap, these Z mode waves (and stimulated electrostatic waves at the plasma frequency) produce a series of vertical bars on the ionogram display as the satellite traverses discrete field-aligned density structures. The radio frequency (RF) noise environment to be expected in the 400 to 500 km altitude region from low to high latitudes was examined by analyzing perigee Alouette 2 topside sounder data. All observed noise bands were scaled on nearly 200 topside sounder ionograms recorded near perigee at low, mid, and high latitude telemetry stations. The minimum and maximum frequencies of each noise band were entered into a data base or computer analysis. The signals of primary interest in the perigee study were found to be sounder-generated.

  16. Formation and nonlinear dynamics of the squeezed state of a helical electron beam with additional deceleration

    NASA Astrophysics Data System (ADS)

    Egorov, E. N.; Koronovskii, A. A.; Kurkin, S. A.; Hramov, A. E.

    2013-11-01

    Results of numerical simulations and analysis of the formation and nonlinear dynamics of the squeezed state of a helical electron beam in a vircator with a magnetron injection gun as an electron source and with additional electron deceleration are presented. The ranges of control parameters where the squeezed state can form in such a system are revealed, and specific features of the system dynamics are analyzed. It is shown that the formation of a squeezed state of a nonrelativistic helical electron beam in a system with electron deceleration is accompanied by low-frequency longitudinal dynamics of the space charge.

  17. Formation and nonlinear dynamics of the squeezed state of a helical electron beam with additional deceleration

    SciTech Connect

    Egorov, E. N. Koronovskii, A. A.; Kurkin, S. A.; Hramov, A. E.

    2013-11-15

    Results of numerical simulations and analysis of the formation and nonlinear dynamics of the squeezed state of a helical electron beam in a vircator with a magnetron injection gun as an electron source and with additional electron deceleration are presented. The ranges of control parameters where the squeezed state can form in such a system are revealed, and specific features of the system dynamics are analyzed. It is shown that the formation of a squeezed state of a nonrelativistic helical electron beam in a system with electron deceleration is accompanied by low-frequency longitudinal dynamics of the space charge.

  18. High-energy-density electron beam from interaction of two successive laser pulses with subcritical-density plasma

    NASA Astrophysics Data System (ADS)

    Wang, J. W.; Yu, W.; Yu, M. Y.; Xu, H.; Ju, J. J.; Luan, S. X.; Murakami, M.; Zepf, M.; Rykovanov, S.

    2016-02-01

    It is shown by particle-in-cell simulations that a narrow electron beam with high energy and charge density can be generated in a subcritical-density plasma by two consecutive laser pulses. Although the first laser pulse dissipates rapidly, the second pulse can propagate for a long distance in the thin wake channel created by the first pulse and can further accelerate the preaccelerated electrons therein. Given that the second pulse also self-focuses, the resulting electron beam has a narrow waist and high charge and energy densities. Such beams are useful for enhancing the target-back space-charge field in target normal sheath acceleration of ions and bremsstrahlung sources, among others.

  19. Additive effects of electronic and nuclear energy losses in irradiation-induced amorphization of zircon

    SciTech Connect

    Zarkadoula, Eva; Toulemonde, Marcel; Weber, William J.

    2015-12-28

    We used a combination of ion cascades and the unified thermal spike model to study the electronic effects from 800 keV Kr and Xe ion irradiation in zircon. We compared the damage production for four cases: (a) due to ion cascades alone, (b) due to ion cascades with the electronic energy loss activated as a friction term, (c) due to the thermal spike from the combined electronic and nuclear energy losses, and (d) due to ion cascades with electronic stopping and the electron-phonon interactions superimposed. We found that taking the electronic energy loss out as a friction term results in reduced damage, while the electronic electron-phonon interactions have additive impact on the final damage created per ion.

  20. Additive effects of electronic and nuclear energy loss in irradiation-induced amorphization of zircon

    SciTech Connect

    Zarkadoula, Eva; Toulemonde, Marcel; Weber, William J.

    2015-12-29

    We used a combination of ion cascades and the unified thermal spike model to study the electronic effects from 800 keV Kr and Xe ion irradiation in zircon. We compared the damage production for four cases: (a) due to ion cascades alone, (b) due to ion cascades with the electronic energy loss activated as a friction term, (c) due to the thermal spike from the combined electronic and nuclear energy losses, and (d) due to ion cascades with electronic stopping and the electron-phonon interactions superimposed. As a result, we found that taking the electronic energy loss out as a friction term results in reduced damage, while the electronic electron-phonon interactions have additive impact on the final damage created per ion.

  1. Additive effects of electronic and nuclear energy loss in irradiation-induced amorphization of zircon

    DOE PAGESBeta

    Zarkadoula, Eva; Toulemonde, Marcel; Weber, William J.

    2015-12-29

    We used a combination of ion cascades and the unified thermal spike model to study the electronic effects from 800 keV Kr and Xe ion irradiation in zircon. We compared the damage production for four cases: (a) due to ion cascades alone, (b) due to ion cascades with the electronic energy loss activated as a friction term, (c) due to the thermal spike from the combined electronic and nuclear energy losses, and (d) due to ion cascades with electronic stopping and the electron-phonon interactions superimposed. As a result, we found that taking the electronic energy loss out as a frictionmore » term results in reduced damage, while the electronic electron-phonon interactions have additive impact on the final damage created per ion.« less

  2. Electron correlation in the interacting quantum atoms partition via coupled-cluster lagrangian densities.

    PubMed

    Holguín-Gallego, Fernando José; Chávez-Calvillo, Rodrigo; García-Revilla, Marco; Francisco, Evelio; Pendás, Ángel Martín; Rocha-Rinza, Tomás

    2016-07-15

    The electronic energy partition established by the Interacting Quantum Atoms (IQA) approach is an important method of wavefunction analyses which has yielded valuable insights about different phenomena in physical chemistry. Most of the IQA applications have relied upon approximations, which do not include either dynamical correlation (DC) such as Hartree-Fock (HF) or external DC like CASSCF theory. Recently, DC was included in the IQA method by means of HF/Coupled-Cluster (CC) transition densities (Chávez-Calvillo et al., Comput. Theory Chem. 2015, 1053, 90). Despite the potential utility of this approach, it has a few drawbacks, for example, it is not consistent with the calculation of CC properties different from the total electronic energy. To improve this situation, we have implemented the IQA energy partition based on CC Lagrangian one- and two-electron orbital density matrices. The development presented in this article is tested and illustrated with the H2 , LiH, H2 O, H2 S, N2 , and CO molecules for which the IQA results obtained under the consideration of (i) the CC Lagrangian, (ii) HF/CC transition densities, and (iii) HF are critically analyzed and compared. Additionally, the effect of the DC in the different components of the electronic energy in the formation of the T-shaped (H2 )2 van der Waals cluster and the bimolecular nucleophilic substitution between F(-) and CH3 F is examined. We anticipate that the approach put forward in this article will provide new understandings on subjects in physical chemistry wherein DC plays a crucial role like molecular interactions along with chemical bonding and reactivity. © 2016 Wiley Periodicals, Inc. PMID:27237084

  3. Using tomography of GPS TEC to routinely determine ionospheric average electron density profiles

    NASA Astrophysics Data System (ADS)

    Yizengaw, E.; Moldwin, M. B.; Dyson, P. L.; Essex, E. A.

    2007-03-01

    This paper introduces a technique that calculates average electron density (Ne) profiles over a wide geographic area of coverage, using tomographic ionospheric Ne profiles. These Ne profiles, which can provide information of the Ne distribution up to global positioning system (GPS) orbiting altitude (with the coordination of space-based GPS tomographic profiles), can be incorporated into the next generation of the international reference ionosphere (IRI) model. An additional advantage of tomography is that it enables accurate modeling of the topside ionosphere. By applying the tomographic reconstruction approach to ground-based GPS slant total electron content (STEC), we calculate 3-h average Ne profiles over a wide region. Since it uses real measurement data, tomographic average Ne profiles describe the ionosphere during quiet and disturbed periods. The computed average Ne profiles are compared with IRI model profiles and average Ne profiles obtained from ground-based ionosondes.

  4. Density matrix embedding theory for interacting electron-phonon systems

    NASA Astrophysics Data System (ADS)

    Sandhoefer, Barbara; Chan, Garnet Kin-Lic

    2016-08-01

    We describe the extension of the density matrix embedding theory framework to coupled interacting fermion-boson systems. This provides a frequency-independent, entanglement embedding formalism to treat bulk fermion-boson problems. We illustrate the concepts within the context of the one-dimensional Hubbard-Holstein model, where the phonon bath states are obtained from the Schmidt decomposition of a self-consistently adjusted coherent state. We benchmark our results against accurate density matrix renormalization group calculations.

  5. Ion acceleration enhanced by additional neutralizing electrons in a magnetically expanding double layer plasma

    SciTech Connect

    Takahashi, Kazunori; Fujiwara, Tamiya

    2010-10-15

    Electrons neutralizing an ion beam are additionally supplied to a magnetically expanding double layer (DL) plasma from the downstream side of the DL. The rf power and the argon gas pressure are maintained at 200 W and 55 mPa, respectively, and the source magnetic field is varied in the range of about 70-550 G. It is observed that the ion beam energy corresponding to the DL potential drop increases up to 30 eV with an increase in the magnetic field when supplying the additional electrons, while it saturates at 20 eV for the case of the absence of the additional electrons. The supplied electrons are believed to be an energy source for the DL such that increasing the magnetic field is able to increase the potential drop beyond the limit found in the absence of the supplied electrons.

  6. Discharge dynamics and plasma density recovery by on/off switches of additional gas

    NASA Astrophysics Data System (ADS)

    Lee, Hyo-Chang; Kwon, Deuk-Chul; Oh, SeungJu; Kang, Hyun-Ju; Kim, Yu-Sin; Chung, Chin-Wook

    2016-06-01

    Measurement of the plasma density is investigated to study plasma dynamics by adding reactive gas (O2) or rare gas (He) in Ar plasmas. When the O2 or He gas is added, plasma density is suddenly decreased, while the plasma density recovers slowly with gas off. It is found that the recovery time is strongly dependent on the gas flow rate, and it can be explained by effect of gas residence time. When the He gas is off in the Ar plasma, the plasma density is overshot compared to the case of the O2 gas pulsing due to enhanced ionizations by metastable atoms. Analysis and calculation for correlation between the plasma density dynamics and the gas pulsing are also presented in detail.

  7. Electron density distribution in the organic superconductor (TMTSF)/sub 2/AsF/sub 6/

    SciTech Connect

    Wudl, F.; Nalewajek, D.; Troup, J.M.; Extine, M.W.

    1983-10-28

    Excellent crystals of (TMTSF)/sub 2/AsF/sub 6/ (TMTSF, tetramethyltetraselenafulvalene) were employed to obtain x-ray diffraction data for a determination of the electron density distribution in this organic superconductor. Electron density was observed between molecules in a stack of donors of an organic metal and between certain interstack selenium atoms of these donors.

  8. Concept for using laser beams to measure electron density in plasmas

    NASA Technical Reports Server (NTRS)

    Longo, S. E.

    1966-01-01

    Concept is proposed for using laser beams as a means of measuring electron density at various points in flame or plasma exhausts. Measurement of the electron density is obtained by detecting reflected waves in the plasma that were activated by the laser.

  9. Synopsis of D- and E-region electron densities during the energy budget campaign

    NASA Technical Reports Server (NTRS)

    Friedrich, M.; Baker, K. D.; Brekke, A.; Dickinson, P. H. G.; Dumbs, A.; Grandal, B.; Thrane, E. V.; Smith, L. G.; Torkar, K. M.

    1982-01-01

    Electron density profiles from ground-based and rocket-borne measurements conducted at three sites in northern Scandinavia under various degrees of geophysical disturbances are presented. These data are checked against an instantaneous picture of the ionospheric absorption obtained via the dense riometer network. A map of the riometer absorption and measured electron densities over Scandinavia is given.

  10. Density matrix renormalization group with efficient dynamical electron correlation through range separation

    SciTech Connect

    Hedegård, Erik Donovan Knecht, Stefan; Reiher, Markus; Kielberg, Jesper Skau; Jensen, Hans Jørgen Aagaard

    2015-06-14

    We present a new hybrid multiconfigurational method based on the concept of range-separation that combines the density matrix renormalization group approach with density functional theory. This new method is designed for the simultaneous description of dynamical and static electron-correlation effects in multiconfigurational electronic structure problems.

  11. The forbidden S II electron density distribution over the planetary nebula NGC 7009

    NASA Astrophysics Data System (ADS)

    Meaburn, J.; Walsh, J. R.

    1981-08-01

    Electron densities have been measured from [S ii] 6716/6731 A line ratios for a grid of points over the surface of the planetary nebula NGC 7009 using a photon counting detector. The radial dependence of the electron density has been modelled, and the relationship provides possible evidence that the planetary nebula shell is driven by a strong stellar wind

  12. Materials for high-density electronic packaging and interconnection

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Electronic packaging and interconnections are the elements that today limit the ultimate performance of advanced electronic systems. Materials in use today and those becoming available are critically examined to ascertain what actions are needed for U.S. industry to compete favorably in the world market for advanced electronics. Materials and processes are discussed in terms of the final properties achievable and systems design compatibility. Weak points in the domestic industrial capability, including technical, industrial philosophy, and political, are identified. Recommendations are presented for actions that could help U.S. industry regain its former leadership position in advanced semiconductor systems production.

  13. Exploiting the spatial locality of electron correlation within the parametric two-electron reduced-density-matrix method

    NASA Astrophysics Data System (ADS)

    DePrince, A. Eugene; Mazziotti, David A.

    2010-01-01

    The parametric variational two-electron reduced-density-matrix (2-RDM) method is applied to computing electronic correlation energies of medium-to-large molecular systems by exploiting the spatial locality of electron correlation within the framework of the cluster-in-molecule (CIM) approximation [S. Li et al., J. Comput. Chem. 23, 238 (2002); J. Chem. Phys. 125, 074109 (2006)]. The 2-RDMs of individual molecular fragments within a molecule are determined, and selected portions of these 2-RDMs are recombined to yield an accurate approximation to the correlation energy of the entire molecule. In addition to extending CIM to the parametric 2-RDM method, we (i) suggest a more systematic selection of atomic-orbital domains than that presented in previous CIM studies and (ii) generalize the CIM method for open-shell quantum systems. The resulting method is tested with a series of polyacetylene molecules, water clusters, and diazobenzene derivatives in minimal and nonminimal basis sets. Calculations show that the computational cost of the method scales linearly with system size. We also compute hydrogen-abstraction energies for a series of hydroxyurea derivatives. Abstraction of hydrogen from hydroxyurea is thought to be a key step in its treatment of sickle cell anemia; the design of hydroxyurea derivatives that oxidize more rapidly is one approach to devising more effective treatments.

  14. Electron-pair densities in position and momentum spaces for multi-determinant wavefunctions

    NASA Astrophysics Data System (ADS)

    Koga, Toshikatsu; Matsuyama, Hisashi

    1998-09-01

    The electronic intracule (relative motion) and extracule (centre-of-mass motion) densities are electron-pair densities which characterize the motion of a pair of electrons in atoms and molecules. A unified method is presented for the evaluation of these electron-pair densities in both position and momentum spaces for wavefunctions expressed as linear combinations of Slater determinants. Detailed expressions are developed for atomic systems where angular integrations can be performed analytically. Interesting relations between atomic intracule and extracule densities and between their moments are discussed. An illustrative application of the results is given for the 0953-4075/31/17/005/img1 and 0953-4075/31/17/005/img2 states of the helium atom, and the first calculations are reported for the singlet-triplet differences in the extracule densities and in the momentum-space intracule density.

  15. Ionospheric electron density irregularities observed by satellite-to-satellite, dual-frequency, low-low Doppler tracking link

    NASA Technical Reports Server (NTRS)

    Estes, R. D.; Grossi, M. D.

    1984-01-01

    A low-low, satellite-to-satellite, dual-frequency, Doppler tracking experiment was performed. The data are analyzed here for irregularities in electron density at the altitude of 212 km. The differential Doppler data with the relative motion term removed are integrated to obtain a representation of the electron density variation along the satellite path. Well-known large-scale features such as the equatorial geomagnetic anomaly and day/night ionization level differences are clearly observed in the integrated data. The larger crest of the morning geomagnetic anomaly is seen to occur in the southern (winter) hemisphere in agreement with previous observations. In addition, a sharp peak in the electron density at the day-to-night transition point is observed in two consecutive revolutions. This effect may be due to the previously postulated atmospheric shock wave generated by supersonic motion of the terminator.

  16. Measurement of electron density by Stark broadening in an ablative pulsed plasma thruster

    SciTech Connect

    Liu Feng; Nie Zongfu; Xu Xu; Zhou Qianhong; Li Linsen; Liang Rongqing

    2008-09-15

    Electron density was measured by Stark broadening in an ablative pulsed plasma thruster. The asymmetrical deconvolution is used to obtain Stark broadening. The result shows that the electron density in the discharge channel is 2.534x10{sup 22} m{sup -3} when the discharge energy is 5 J and the measured electron temperature is 18 000 K, and it is in excellent agreement with other experimental and theoretical data. The electron density in the discharge channel increases very minimally with increasing discharge energy.

  17. Device and method for electron beam heating of a high density plasma

    DOEpatents

    Thode, Lester E.

    1981-01-01

    A device and method for relativistic electron beam heating of a high density plasma in a small localized region. A relativistic electron beam generator produces a high voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target plasma is ionized prior to application of the electron beam by means of a laser or other preionization source. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high density target plasma causing the relativistic electron beam to efficiently deposit its energy into a small localized region within the high density plasma target.

  18. High density electronic circuit and process for making

    DOEpatents

    Morgan, William P.

    1999-01-01

    High density circuits with posts that protrude beyond one surface of a substrate to provide easy mounting of devices such as integrated circuits. The posts also provide stress relief to accommodate differential thermal expansion. The process allows high interconnect density with fewer alignment restrictions and less wasted circuit area than previous processes. The resulting substrates can be test platforms for die testing and for multi-chip module substrate testing. The test platform can contain active components and emulate realistic operational conditions, replacing shorts/opens net testing.

  19. High density electronic circuit and process for making

    DOEpatents

    Morgan, W.P.

    1999-06-29

    High density circuits with posts that protrude beyond one surface of a substrate to provide easy mounting of devices such as integrated circuits are disclosed. The posts also provide stress relief to accommodate differential thermal expansion. The process allows high interconnect density with fewer alignment restrictions and less wasted circuit area than previous processes. The resulting substrates can be test platforms for die testing and for multi-chip module substrate testing. The test platform can contain active components and emulate realistic operational conditions, replacing shorts/opens net testing. 8 figs.

  20. Longitudinal and Hemispheric Variations of Nighttime E-Layer Electron Density in the Auroral Zone

    NASA Astrophysics Data System (ADS)

    Luan, X.; Wang, W.; Dou, X.; Burns, A. G.; Yue, X.

    2014-12-01

    The longitudinal patterns of nighttime E layer electron density in the auroral zone are analyzed in both hemispheres using COSMIC observation under quiet and solar minimum conditions. These l patterns are compared with the variations of particle precipitating energy flux from TIMED/GUVI under similar geophysical conditions, and also the solar radiation source of the auroral E layer are discussed. Our main conclusions are: (1) the nighttime maximum E-layer electron density presents pronounced longitudinal variations in the auroral zone, which depends on seasons and hemispheres. In local winter of both hemispheres and in northern equinox, maximum electron density is located in most western sectors within magnetic longitudes of 120-360°E. In local summer of both hemispheres and in southern equinox, greater the electron density occurs in a wide longitudinal sector centered at 0°E. (2) Hemispheric asymmetry occurs in auroral E layer electron density in all seasons, including equinox. In local winter, the maximum density of the northern hemisphere is much higher than that of southern hemisphere. In equinox, the longitudinal patterns of the electron density are out of phase between the two hemispheres. (3) The effects of the auroral precipitation are dominant in building the E layer electron density in the auroral zone for all seasons, except in southern summer in sector of 300-90°E MLON, where strong solar radiation takes place.

  1. Simulation of electron beam from two strip electron guns and control of power density by rotation of gun

    NASA Astrophysics Data System (ADS)

    Sahu, G. K.; Baruah, S.; Thakur, K. B.

    2012-11-01

    Electron beam is preferably used for large scale evaporation of refractory materials. Material evaporation from a long and narrow source providing a well collimated wedge shaped atomic beam has applications in isotopic purification of metals relevant to nuclear industry. The electron beam from an electron gun with strip type filament provides a linear heating source. However, the high power density of the electron beam can lead to turbulence of the melt pool and undesirable splashing of molten metal. For obtaining quiet surface evaporation, the linear electron beam is generally scanned along its length. To further reduce the power density to maintain quiet evaporation the width of the vapour source can be controlled by rotating the electron gun on its plane, thereby scanning an inclined beam over the molten pool. The rotation of gun has further advantages. When multiple strip type electron guns are used for scaling up evaporation length, a dark zone appears between two beams due to physical separation of adjacent guns. This dark zone can be reduced by rotating the gun and thereby bringing two adjacent beams closer. The paper presented here provides the simulation results of the electron beam trajectory and incident power density originating from two strip electron guns by using in-house developed code. The effect of electron gun rotation on the electron beam trajectory and power density is studied. The simulation result is experimentally verified with the image of molten pool and heat affected zone taken after experiment. This technique can be gainfully utilized in controlling the time averaged power density of the electron beam and obtaining quiet evaporation from the metal molten pool.

  2. Studies of improved electron confinement in low density L-mode National Spherical Torus Experiment discharges

    SciTech Connect

    Stutman, D.; Finkenthal, M.; Tritz, K.; Redi, M. H.; Kaye, S. M.; Bell, M. G.; Bell, R. E.; LeBlanc, B. P.; Hill, K. W.; Medley, S. S.; Menard, J. E.; Rewoldt, G.; Wang, W. X.; Synakowski, E. J.; Levinton, F.; Kubota, S.; Bourdelle, C.; Dorland, W.; The NSTX Team

    2006-09-15

    Electron transport is rapid in most National Spherical Torus Experiment, M. Ono et al., Nucl. Fusion 40, 557 (2000) beam heated plasmas. A regime of improved electron confinement is nevertheless observed in low density L-mode (''low-confinement'') discharges heated by early beam injection. Experiments were performed in this regime to study the role of the current profile on thermal transport. Variations in the magnetic shear profile were produced by changing the current ramp rate and onset of neutral beam heating. An increased electron temperature gradient and local minimum in the electron thermal diffusivity were observed at early times in plasmas with the fastest current ramp and earliest beam injection. In addition, an increased ion temperature gradient associated with a region of reduced ion transport is observed at slightly larger radii. Ultrasoft x-ray measurements of double-tearing magnetohydrodynamic activity, together with current diffusion calculations, point to the existence of negative magnetic shear in the core of these plasmas. Discharges with slower current ramp and delayed beam onset, which are estimated to have more monotonic q-profiles, do not exhibit regions of reduced transport. The results are discussed in the light of the initial linear microstability assessment of these plasmas, which suggests that the growth rate of all instabilities, including microtearing modes, can be reduced by negative or low magnetic shear in the temperature gradient region. Several puzzles arising from the present experiments are also highlighted.

  3. High-energy-density electron jet generation from an opening gold cone filled with near-critical-density plasma

    SciTech Connect

    Yu, T. P. Shao, F. Q.; Zou, D. B.; Ge, Z. Y.; Zhang, G. B.; Wang, W. Q.; Li, X. H.; Liu, J. X.; Ouyang, J. M.; Yu, W.; Luan, S. X.; Wang, J. W.; Wong, A. Y.

    2015-01-14

    By using two-dimensional particle-in-cell simulations, we propose a scheme for strong coupling of a petawatt laser with an opening gold cone filled with near-critical-density plasmas. When relevant parameters are properly chosen, most laser energy can be fully deposited inside the cone with only 10% leaving the tip opening. Due to the asymmetric ponderomotive acceleration by the strongly decayed laser pulse, high-energy-density electrons with net laser energy gain are accumulated inside the cone, which then stream out of the tip opening continuously, like a jet. The jet electrons are fully relativistic, with speeds around 0.98−0.998 c and densities at 10{sup 20}/cm{sup 3} level. The jet can keep for a long time over 200 fs, which may have diverse applications in practice.

  4. Role of density gradient driven trapped electron mode turbulence in the H-mode inner core with electron heating

    NASA Astrophysics Data System (ADS)

    Ernst, D. R.; Burrell, K. H.; Guttenfelder, W.; Rhodes, T. L.; Dimits, A. M.; Bravenec, R.; Grierson, B. A.; Holland, C.; Lohr, J.; Marinoni, A.; McKee, G. R.; Petty, C. C.; Rost, J. C.; Schmitz, L.; Wang, G.; Zemedkun, S.; Zeng, L.

    2016-05-01

    A series of DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] low torque quiescent H-mode experiments show that density gradient driven trapped electron mode (DGTEM) turbulence dominates the inner core of H-mode plasmas during strong electron cyclotron heating (ECH). Adding 3.4 MW ECH doubles Te/Ti from 0.5 to 1.0, which halves the linear DGTEM critical density gradient, locally reducing density peaking, while transport in all channels displays extreme stiffness in the density gradient. This suggests that fusion α-heating may degrade inner core confinement in H-mode plasmas with moderate density peaking and low collisionality, with equal electron and ion temperatures, key conditions expected in burning plasmas. Gyrokinetic simulations using GYRO [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] (and GENE [Jenko et al., Phys. Plasmas 7, 1904 (2000)]) closely match not only particle, energy, and momentum fluxes but also density fluctuation spectra from Doppler backscattering (DBS), with and without ECH. Inner core DBS density fluctuations display discrete frequencies with adjacent toroidal mode numbers, which we identify as DGTEMs. GS2 [Dorland et al., Phys. Rev. Lett. 85, 5579 (2000)] predictions show the DGTEM can be suppressed, to avoid degradation with electron heating, by broadening the current density profile to attain q0>qmin>1 .

  5. Decay of the electron number density in the nitrogen afterglow using a hairpin resonator probe

    NASA Astrophysics Data System (ADS)

    Siefert, Nicholas S.; Ganguly, Biswa N.; Sands, Brian L.; Hebner, Greg A.

    2006-08-01

    A hairpin resonator was used to measure the electron number density in the afterglow of a nitrogen glow discharge (p=0.25-0.75Torr). Electron number densities were measured using a time-dependent approach similar to the approach used by Spencer et al. [J. Phys. D 20, 923 (1987)]. The decay time of the electron number density was used to determine the electron temperature in the afterglow, assuming a loss of electrons via ambipolar diffusion to the walls. The electron temperature in the near afterglow remained between 0.4 and 0.6eV, depending on pressure. This confirms the work by Guerra et al. [IEEE Trans. Plasma. Sci. 31, 542 (2003)], who demonstrated experimentally and numerically that the electron temperature stays significantly above room temperature via superelastic collisions with highly vibrationally excited ground state molecules and metastables, such as AΣu+3.

  6. Electron density measurement of inductively coupled plasmas by terahertz time-domain spectroscopy (THz-TDS)

    SciTech Connect

    Ando, Ayumi; Kurose, Tomoko; Kitano, Katsuhisa; Hamaguchi, Satoshi; Reymond, Vivien; Kitahara, Hideaki; Takano, Keisuke; Hangyo, Masanori; Tani, Masahiko

    2011-10-01

    The electron densities of argon inductively coupled plasmas were measured by terahertz time-domain spectroscopy (THz-TDS). At a low pressure, the electron densities were also measured with a Langmuir-type double probe and the validity of THz-TDS electron-density measurement in a plasma has been corroborated. As the input radio-frequency (RF) power increases, the plasma density and gas temperature increase, which makes the probe measurement less reliable or even impossible, due to the large heat load to the probe surface. On the contrary, the THz-TDS measurement is unaffected by the gas temperature and becomes more reliable due to the higher electron density at higher input power for plasma generation.

  7. Depth profile characterization technique for electron density in GaN films by infrared reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Kamijoh, Takaaki; Ma, Bei; Morita, Ken; Ishitani, Yoshihiro

    2016-05-01

    Infrared reflectance spectroscopy is a noncontact measurement method for carrier density and mobility. In this article, the model determination procedure of layer-type nonuniform electron distribution is investigated, since the spectrum fitting hitherto has been conducted on the basis of a multilayer model defined in advance. A simplified case of a high-electron-density GaN layer embedded in a GaN matrix is mainly studied. The following procedure is found to be applicable. The first step is the determination of the high-density layer position in the vicinity of the surface, in the middle region, or in the vicinity of the interface. This is followed by the specification of the sheet electron density and the layer thickness of the high-density region. It is found that this procedure is also applicable to the characterization of two-dimensional electron gases in the vicinity of AlGaN/GaN heterointerfaces.

  8. Electron-electron cusp condition and asymptotic behavior for the Pauli potential in pair density functional theory.

    PubMed

    Nagy, A; Amovilli, C

    2008-03-21

    In the ground state, the pair density n can be determined by solving a single auxiliary equation of a two-particle problem. Electron-electron cusp condition and asymptotic behavior for the Pauli potential of the effective potential of the two-particle equation are presented. PMID:18361562

  9. Comparison of F-region electron density observations by satellite radio tomography and incoherent scatter methods

    NASA Astrophysics Data System (ADS)

    Nygrén, T.; Markkanen, M.; Lehtinen, M.; Tereshchenko, E. D.; Khudukon, B. Z.; Evstafiev, O. V.; Pollari, P.

    1996-12-01

    In November 1995 a campaign of satellite radiotomography supported by the EISCAT incoherent scatter radar and several other instruments was arranged in Scandinavia. A chain of four satellite receivers extending from the north of Norway to the south of Finland was installed approximately along a geomagnetic meridian. The receivers carried out difference Doppler measurements using signals from satellites flying along the chain. The EISCAT UHF radar was simultaneously operational with its beam swinging either in geomagnetic or in geographic meridional plane. With this experimental set-up latitudinal scans of F-region electron density are obtained both from the radar observations and by tomographic inversion of the phase observations given by the difference Doppler experiment. This paper shows the first results of the campaign and compares the electron densities given by the two methods. Acknowledgements. This work has been supported by the UK Particle-Physics and Astronomy Research Council. The assistance of the director and staff of the EISCAT Scientific Association, the staff of the Norsk Polarinstitutt and the director and staff of the Swedish Institute of Space Physics is gratefully acknowledged. In addition the authors would like to thank Professor Evgeny Tereshchenko of the Polar Geophysical Institute in Mumansk, Russia and Dr Tuomo Nygrén of the University of Oulu, Finland for provision of data from EISCAT special program time during the November 1995 campaign. Topical Editor D. Alcaydé thanks E. J. Fremouw and another referee for their help in evaluating this paper.--> Correspondence to: I. K. Walker-->

  10. Many-electron expansion: A density functional hierarchy for strongly correlated systems

    NASA Astrophysics Data System (ADS)

    Zhu, Tianyu; de Silva, Piotr; van Aggelen, Helen; Van Voorhis, Troy

    2016-05-01

    Density functional theory (DFT) is the de facto method for the electronic structure of weakly correlated systems. But for strongly correlated materials, common density functional approximations break down. Here, we derive a many-electron expansion (MEE) in DFT that accounts for successive one-, two-, three-, ... particle interactions within the system. To compute the correction terms, the density is first decomposed into a sum of localized, nodeless one-electron densities (ρi). These one-electron densities are used to construct relevant two- (ρi+ρj ), three- (ρi+ρj+ρk ), ... electron densities. Numerically exact results for these few-particle densities can then be used to correct an approximate density functional via any of several many-body expansions. We show that the resulting hierarchy gives accurate results for several important model systems: the Hubbard and Peierls-Hubbard models in 1D and the pure Hubbard model in 2D. We further show that the method is numerically convergent for strongly correlated systems: applying successively higher order corrections leads to systematic improvement of the results. MEE thus provides a hierarchy of density functional approximations that applies to both weakly and strongly correlated systems.

  11. The effects of a multidensity plasma on ultraviolet spectroscopic electron density diagnostics

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.

    1984-01-01

    Spectroscopic electron density diagnostics have been developed for interpretation of UV, EUV, and X-ray emission line spectra of solar and other astrophysical plasmas, and tokamak plasmas. In principle, accurate electron densities can be determined. However, in practice, a number of difficulties arise with respect to the determination of very accurate electron densities in the 1100-3000 A region. The present study has the objective to investigate one of these difficulties, taking into account the effect on line ratios produced by a source composed of several regions of substantially different densities, all at the same temperature. The study is in particular concerned with a source in which small high density knots are embedded in low-density plasma. Attention is given to line ratios involving the O IV multiplet near 1400 A, obtained from the spectrum of a surge observed outside the solar limb.

  12. Curly arrows meet electron density transfers in chemical reaction mechanisms: from electron localization function (ELF) analysis to valence-shell electron-pair repulsion (VSEPR) inspired interpretation.

    PubMed

    Andrés, Juan; Berski, Sławomir; Silvi, Bernard

    2016-07-01

    Probing the electron density transfers during a chemical reaction can provide important insights, making possible to understand and control chemical reactions. This aim has required extensions of the relationships between the traditional chemical concepts and the quantum mechanical ones. The present work examines the detailed chemical insights that have been generated through 100 years of work worldwide on G. N. Lewis's ground breaking paper on The Atom and the Molecule (Lewis, G. N. The Atom and the Molecule, J. Am. Chem. Soc. 1916, 38, 762-785), with a focus on how the determination of reaction mechanisms can be reached applying the bonding evolution theory (BET), emphasizing how curly arrows meet electron density transfers in chemical reaction mechanisms and how the Lewis structure can be recovered. BET that combines the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT) provides a powerful tool providing insight into molecular mechanisms of chemical rearrangements. In agreement with physical laws and quantum theoretical insights, BET can be considered as an appropriate tool to tackle chemical reactivity with a wide range of possible applications. Likewise, the present approach retrieves the classical curly arrows used to describe the rearrangements of chemical bonds for a given reaction mechanism, providing detailed physical grounds for this type of representation. The ideas underlying the valence-shell-electron pair-repulsion (VSEPR) model applied to non-equilibrium geometries provide simple chemical explanations of density transfers. For a given geometry around a central atom, the arrangement of the electronic domain may comply or not with the VSEPR rules according with the valence shell population of the considered atom. A deformation yields arrangements which are either VSEPR defective (at least a domain is missing to match the VSEPR arrangement corresponding to the geometry of the ligands), VSEPR compliant

  13. Electron-positron momentum density in TTF-TCNQ

    NASA Astrophysics Data System (ADS)

    Ishibashi, Shoji; Manuel, Alfred A.; Hoffmann, Ludger; Bechgaard, Klaus

    1997-01-01

    We present measurements of the positron two-dimensional angular correlation of annihilation radiation (2D-ACAR) in TTF-TCNQ. We report also theoretical simulations of the 2D-ACAR in which the electron wave functions were expressed as TTF or TCNQ molecular orbitals obtained from self-consistent quantum chemical calculations. The positron wave function was calculated taking the charge transfer from TTF to TCNQ as a parameter. The best agreement with the experiment is obtained for a charge transfer of 0.7 electrons from the TTF to the TCNQ molecules. This is larger than the value of 0.55 obtained from a study of the Kohn anomaly. We investigate also the shape and position of the Fermi surface and conclude that a simple planar Fermi surface is consistent with our measurements.

  14. Quantitative electron density characterization of soft tissue substitute plastic materials using grating-based x-ray phase-contrast imaging

    SciTech Connect

    Sarapata, A.; Chabior, M.; Zanette, I.; Pfeiffer, F.; Cozzini, C.; Sperl, J. I.; Bequé, D.; Langner, O.; Coman, J.; Ruiz-Yaniz, M.

    2014-10-15

    Many scientific research areas rely on accurate electron density characterization of various materials. For instance in X-ray optics and radiation therapy, there is a need for a fast and reliable technique to quantitatively characterize samples for electron density. We present how a precise measurement of electron density can be performed using an X-ray phase-contrast grating interferometer in a radiographic mode of a homogenous sample in a controlled geometry. A batch of various plastic materials was characterized quantitatively and compared with calculated results. We found that the measured electron densities closely match theoretical values. The technique yields comparable results between a monochromatic and a polychromatic X-ray source. Measured electron densities can be further used to design dedicated X-ray phase contrast phantoms and the additional information on small angle scattering should be taken into account in order to exclude unsuitable materials.

  15. Quantitative electron density characterization of soft tissue substitute plastic materials using grating-based x-ray phase-contrast imaging.

    PubMed

    Sarapata, A; Chabior, M; Cozzini, C; Sperl, J I; Bequé, D; Langner, O; Coman, J; Zanette, I; Ruiz-Yaniz, M; Pfeiffer, F

    2014-10-01

    Many scientific research areas rely on accurate electron density characterization of various materials. For instance in X-ray optics and radiation therapy, there is a need for a fast and reliable technique to quantitatively characterize samples for electron density. We present how a precise measurement of electron density can be performed using an X-ray phase-contrast grating interferometer in a radiographic mode of a homogenous sample in a controlled geometry. A batch of various plastic materials was characterized quantitatively and compared with calculated results. We found that the measured electron densities closely match theoretical values. The technique yields comparable results between a monochromatic and a polychromatic X-ray source. Measured electron densities can be further used to design dedicated X-ray phase contrast phantoms and the additional information on small angle scattering should be taken into account in order to exclude unsuitable materials. PMID:25362404

  16. Quantitative electron density characterization of soft tissue substitute plastic materials using grating-based x-ray phase-contrast imaging

    NASA Astrophysics Data System (ADS)

    Sarapata, A.; Chabior, M.; Cozzini, C.; Sperl, J. I.; Bequé, D.; Langner, O.; Coman, J.; Zanette, I.; Ruiz-Yaniz, M.; Pfeiffer, F.

    2014-10-01

    Many scientific research areas rely on accurate electron density characterization of various materials. For instance in X-ray optics and radiation therapy, there is a need for a fast and reliable technique to quantitatively characterize samples for electron density. We present how a precise measurement of electron density can be performed using an X-ray phase-contrast grating interferometer in a radiographic mode of a homogenous sample in a controlled geometry. A batch of various plastic materials was characterized quantitatively and compared with calculated results. We found that the measured electron densities closely match theoretical values. The technique yields comparable results between a monochromatic and a polychromatic X-ray source. Measured electron densities can be further used to design dedicated X-ray phase contrast phantoms and the additional information on small angle scattering should be taken into account in order to exclude unsuitable materials.

  17. Statistical Averages of F-Layer Electron Density, Electron Temperature and Ion Temperature Over Millstone Hill

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Holt, J. M.; Goncharenko, L.

    2001-12-01

    All Millstone Hill incoherent scatter radar data collected since 1978 are available through the Madrigal Database at MIT Haystack Observatory. A set of empirical models for basic and derived incoherent scatter parameters, including electron density Ne, electron and ion temperatures Te and Ti, electric field and parallel ion drift is being developed from this extensive dataset. Such models of the average behavior of key ionosphere-thermosphere (IT) parameters, based on long term accumulated data, are important for space weather studies not only in terms of quantitative descriptions of the IT system but also in terms of clarifying several outstanding scientific problems. This paper presents Ne, Te and Ti averages in the ionospheric F-layer from which local empirical models can be generated. We sort every parameter measured locally into bins. The binning parameters are local time (0000-2400 LT), the day of year (season), and altitude (150-1000 km). Each data point belongs to a certain bin and has corresponding solar flux index F107 and geomagnetic index Ap. For each bin, a multiple regression is performed for a function including (1) the constant term, (2) linear effect terms of F107 and (3) Ap, and (4) the F107 and Ap cross effect term, to give a set of fitting coefficients, such that our model of bin averages is keyed to F107 and Ap. The deviations of actual data from the model represent the remaining day-to-day variability. We will present the data distribution of each bin and discuss the main features of our averages and models.

  18. An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics

    NASA Astrophysics Data System (ADS)

    Valdivia, M. P.; Stutman, D.; Stoeckl, C.; Theobald, W.; Mileham, C.; Begishev, I. A.; Bromage, J.; Regan, S. P.

    2016-02-01

    X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 1023 cm-3 in a low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of <8%. The 50 ± 15 μm spatial resolution achieved across the full field of view was found to be limited by the x-ray source-size, similar to conventional radiography.

  19. An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics

    DOE PAGESBeta

    Valdivia, M. P.; Stutman, D.; Stoeckl, C.; Theobald, W.; Mileham, C.; Begishev, I. A.; Bromage, J.; Regan, S. P.

    2016-02-10

    X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 1023 cm₋3 in amore » low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of <8%. We found the 50 ± 15 μm spatial resolution achieved across the full field of view was limited by the x-ray source-size, similar to conventional radiography.« less

  20. An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics.

    PubMed

    Valdivia, M P; Stutman, D; Stoeckl, C; Theobald, W; Mileham, C; Begishev, I A; Bromage, J; Regan, S P

    2016-02-01

    X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 10(23) cm(-3) in a low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of <8%. The 50 ± 15 μm spatial resolution achieved across the full field of view was found to be limited by the x-ray source-size, similar to conventional radiography. PMID:26931847

  1. Sheath Effects on Electron Density Measurements in Frequency Shift Probe and their Application to Electron Temperature Measurements

    NASA Astrophysics Data System (ADS)

    Nakamura, Keiji; Zhang, Qi; Sugai, Hideo

    2009-10-01

    Technologies of plasma monitoring are important for accurate plasma control. We have developed a frequency shift probe, and the probe enables us to measure an electron density from variation of resonance frequency of the probe head similarly to the hairpin probe. A plane structure of the probe head make it possible to minimizes disturbance to the processing plasma, and the probe is applicable to a reactive polymer-deposition plasmas since the polymer has no significant effects on the resonance frequency. The electron density is usually obtained from a plasma-induced shift of the probe resonance frequency, however influences of a sheath around the probe should been considered for more precise density measurements. In this work, sheath effects on the frequency shift probe were investigated, and the frequency shift probe was applied to measure a electron temperature using the sheath effects. As the sheath thickness increased, the resonance frequency decreased, and the sheath effect is enhanced depending on probe structure. Since the sheath width is proportional to Debye length, the probe resonance frequency depends on electron density and electron temperature, suggesting that resonance frequencies obtained in two probes having different sheath dependence gives an unique solution of the density and temperature of electrons.

  2. [Determination of electron density in atmospheric pressure radio frequency dielectric barrier discharges by Stark broadening].

    PubMed

    Li, Sen; Liu, Zhong-wei; Chen, Qiang; Liu, Fu-ping; Wang, Zheng-duo; Yang, Li-zhen

    2012-01-01

    The use of high frequency power to generate plasma at atmospheric pressure is a relatively new development. An apparatus of atmospheric pressure radio frequency dielectric barrier discharge was constructed. Plasma emission based measurement of electron density in discharge columns from Stark broadening Ar is discribed. The spacial profile of electron density was studied. In the middle of the discharge column, as the input power increases from 138 to 248 W, the electron density rises from 4.038 x 10(21) m(-3) to 4.75 x 10(21) m(-3). PMID:22497121

  3. Numerical solution for Nagumo's equation for the electron density in photorefractive materials

    NASA Astrophysics Data System (ADS)

    Magaña, Fernando

    2005-03-01

    We study the distribution of the electron density in a photorefractive material, using a set of nonlinear partial differential equations, that describes the physical response of photorefractive systems under inhomogeneous ilumination based on the band transport model, proposed by Kukhtarev et al. (Ferroelectrics, vol. 22, 949 (1979)). Assuming that the electron density only depends of x coordinate and taking a constant external electric field E in the same x coordinate we find that the electron density obeys a Nagumo's equation whose solution is soliton type.

  4. Relationship between electron density and effective densities of body tissues for stopping, scattering, and nuclear interactions of proton and ion beams

    SciTech Connect

    Kanematsu, Nobuyuki; Inaniwa, Taku; Koba, Yusuke

    2012-02-15

    Purpose: In treatment planning of charged-particle radiotherapy, patient heterogeneity is conventionally modeled as variable-density water converted from CT images to best reproduce the stopping power, which may lead to inaccuracies in the handling of multiple scattering and nuclear interactions. Although similar conversions can be defined for these individual interactions, they would be valid only for specific CT systems and would require additional tasks for clinical application. This study aims to improve the practicality of the interaction-specific heterogeneity correction. Methods: The authors calculated the electron densities and effective densities for stopping power, multiple scattering, and nuclear interactions of protons and ions, using the standard elemental-composition data for body tissues to construct the invariant conversion functions. The authors also simulated a proton beam in a lung-like geometry and a carbon-ion beam in a prostate-like geometry to demonstrate the procedure and the effects of the interaction-specific heterogeneity correction. Results: Strong correlations were observed between the electron density and the respective effective densities, with which the authors formulated polyline conversion functions. Their effects amounted to 10% differences in multiple-scattering angle and nuclear interaction mean free path for bones compared to those in the conventional heterogeneity correction. Although their realistic effect on patient dose distributions would be generally small, it could be at the level of a few percent when a carbon-ion beam traverses a large bone. Conclusions: The present conversion functions are invariant and may be incorporated in treatment planning systems with a common function relating CT number to electron density. This will enable improved beam dose calculation while minimizing initial setup and quality management of the user's specific system.

  5. Wavefront-sensor-based electron density measurements for laser-plasma accelerators

    SciTech Connect

    Plateau, Guillaume; Matlis, Nicholas; Geddes, Cameron; Gonsalves, Anthony; Shiraishi, Satomi; Lin, Chen; van Mourik, Reinier; Leemans, Wim

    2010-02-20

    Characterization of the electron density in laser produced plasmas is presented using direct wavefront analysis of a probe laser beam. The performance of a laser-driven plasma-wakefield accelerator depends on the plasma wavelength, hence on the electron density. Density measurements using a conventional folded-wave interferometer and using a commercial wavefront sensor are compared for different regimes of the laser-plasma accelerator. It is shown that direct wavefront measurements agree with interferometric measurements and, because of the robustness of the compact commercial device, have greater phase sensitivity, straightforward analysis, improving shot-to-shot plasma-density diagnostics.

  6. Simultaneous measurement of core electron temperature and density fluctuations during electron cyclotron heating on DIII-D

    SciTech Connect

    White, A. E.; Schmitz, L.; Peebles, W. A.; Rhodes, T. L.; Carter, T. A.; McKee, G. R.; Shafer, M. W.; Staebler, G. M.; Burrell, K. H.; DeBoo, J. C.; Prater, R.

    2010-02-15

    New measurements show that long-wavelength (k{sub t}hetarho{sub s}<0.5) electron temperature fluctuations can play an important role in determining electron thermal transport in low-confinement mode (L-mode) tokamak plasmas. In neutral beam-heated L-mode tokamak plasmas, electron thermal transport and the amplitude of long-wavelength electron temperature fluctuations both increase in cases where local electron cyclotron heating (ECH) is used to modify the plasma profiles. In contrast, the amplitude of simultaneously measured long-wavelength density fluctuations does not significantly increase. Linear stability analysis indicates that the ratio of the trapped electron mode (TEM) to ion temperature gradient (ITG) mode growth rates increases in the cases with ECH. The increased importance of the TEM drive relative to the ITG mode drive in the cases with ECH may be associated with the increases in electron thermal transport and electron temperature fluctuations.

  7. An improved inversion for FORMOSAT-3/COSMIC ionosphere electron density profiles

    NASA Astrophysics Data System (ADS)

    Pedatella, N. M.; Yue, X.; Schreiner, W. S.

    2015-10-01

    An improved method to retrieve electron density profiles from Global Positioning System (GPS) radio occultation (RO) data is presented and applied to Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations. The improved inversion uses a monthly grid of COSMIC F region peak densities (NmF2), which are obtained via the standard Abel inversion, to aid the Abel inversion by providing information on the horizontal gradients in the ionosphere. This lessens the impact of ionospheric gradients on the retrieval of GPS RO electron density profiles, reducing the dominant error source in the standard Abel inversion. Results are presented that demonstrate the NmF2 aided retrieval significantly improves the quality of the COSMIC electron density profiles. Improvements are most notable at E region altitudes, where the improved inversion reduces the artificial plasma cave that is generated by the Abel inversion spherical symmetry assumption at low latitudes during the daytime. Occurrence of unphysical negative electron densities at E region altitudes is also reduced. Furthermore, the NmF2 aided inversion has a positive impact at F region altitudes, where it results in a more distinct equatorial ionization anomaly. COSMIC electron density profiles inverted using our new approach are currently available through the University Corporation for Atmospheric Research COSMIC Data Analysis and Archive Center. Owing to the significant improvement in the results, COSMIC data users are encouraged to use electron density profiles based on the improved inversion rather than those inverted by the standard Abel inversion.

  8. Photocurrent enhancement in nonpolar liquids by the addition of electron scavengers

    SciTech Connect

    Howell, G.A.; Lee, K.; Tweeten, D.W.; Lipsky, S.

    1988-07-14

    The photocurrent from anthracene, triphenylamine, and N,N,N',N'-tetramethyl-p-phenylenediamine excited above their ionization thresholds in liquid n-pentane or n-hexane is found to be enhanced by the addition of low concentrations (/approx lt/0.02 M) of the electron scavengers perfluoromethylcyclohexane or perfluorodecalin. The enhancement is not observed in solvents of higher electron mobility (e.g.,. cyclohexane, isooctane, etc.) or for scavengers of lower electron affinity (e.g., n-perfluorohexane). For the solute naphthalene, no enhancement is observed under any conditions. The effects of excitation energy and applied electric field strength are reported.

  9. Mixed-Color Multiphoton Transitions as Additional Quantum Channels for Electron Photoemission

    NASA Astrophysics Data System (ADS)

    Huang, Wayne; Becker, Maria; Beck, Joshua; Batelaan, Herman

    2016-05-01

    We demonstrate mixed-color electron photoemission from tungsten nanotips. In the experiment, second-harmonic photons were introduced to modify the multiphoton emission process. A twofold increase in quantum efficiency results from the opening up of an additional three-photon quantum channel. The super-additive photoelectron signal can be controlled by input power, field polarization, and pulse overlap. The results of our study provide new prospects for quantum photonics, multiphoton microscopy, and spin-polarized electron sources. We acknowledge supports from NSF, Grant Number 1306565, 1430519. NSF Grant Number 1306565, 1430519.

  10. Electronic states of aryl radical functionalized graphenes: Density functional theory study

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto; Kawabata, Hiroshi

    2016-06-01

    Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz) n (n = 1–4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR–(Bz) n (n = 1–4) showed that the aryl radical binds to the carbon atom of GR, and a C–C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol‑1 at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol‑1. The electronic states of GR–(Bz) n were examined on the basis of theoretical results.

  11. Experimental confirmation of calculated phases and electron density profile for wet native collagen.

    PubMed Central

    Stinson, R H; Bartlett, M W; Kurg, T; Sweeny, P R; Hendricks, R W

    1979-01-01

    An experimental procedure is developed to phase the reflections obtained in x-ray diffraction investigations of collagen in native wet tendons. Phosphotungstic acid was used for isomorphous addition in phase determination and was located by electron microscopy. Structure factors (with phases) were obtained from the electron microscopy data for the heavy metal. Structure-factor magnitudes for collagen with and without the heavy metal were obtained from the x-ray diffraction data. The first 10 orders were investigated. Standard Argand diagrams provided two solutions for each of these, except the weak sixth order. In each case, one of the two possible solutions agrees well with the phases proposed on theoretical grounds by Hulmes et al. The present results suggest that their other proposed phases are probably correct. An electron density profile along the unit cell of the fibril is presented that shows a distinct step, as expected on the basis of the hole-overlap model. The overlap region is 48% of the length of the unit cell. Images FIGURE 2 PMID:262416

  12. A new version of the NeQuick ionosphere electron density model

    NASA Astrophysics Data System (ADS)

    Nava, B.; Coïsson, P.; Radicella, S. M.

    2008-12-01

    NeQuick is a three-dimensional and time dependent ionospheric electron density model developed at the Aeronomy and Radiopropagation Laboratory of the Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy and at the Institute for Geophysics, Astrophysics and Meteorology of the University of Graz, Austria. It is a quick-run model particularly tailored for trans-ionospheric applications that allows one to calculate the electron concentration at any given location in the ionosphere and thus the total electron content (TEC) along any ground-to-satellite ray-path by means of numerical integration. Taking advantage of the increasing amount of available data, the model formulation is continuously updated to improve NeQuick capabilities to provide representations of the ionosphere at global scales. Recently, major changes have been introduced in the model topside formulation and important modifications have also been introduced in the bottomside description. In addition, specific revisions have been applied to the computer package associated to NeQuick in order to improve its computational efficiency. It has therefore been considered appropriate to finalize all the model developments in a new version of the NeQuick. In the present work the main features of NeQuick 2 are illustrated and some results related to validation tests are reported.

  13. Excitation of surface plasma waves by a density modulated electron beam at a conductor-dusty plasma interface

    SciTech Connect

    Gupta, Ruby; Sharma, Suresh C.; Prakash, Ved

    2011-05-15

    A density modulated electron beam propagating through a conductor-dusty plasma interface drives electromagnetic surface plasma waves (SPWs) to instability via Cerenkov and cyclotron interaction. The SPWs propagate across an external magnetic field parallel to the interface. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the typical parameters of the SPWs. The frequency and the growth rate of the unstable wave instability increase with the relative density of negatively charged dust grains {delta} (= n{sub io}/n{sub eo}, where n{sub io} is the ion plasma density and n{sub eo} is the electron plasma density). The phase velocity of the unstable waves also increases with {delta}. In addition, the growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and square root of beam density in fast cyclotron interaction. Moreover, the dispersion relation of SPWs has been retrieved in the absence of the modulated beam and without dust grains.

  14. Determination of free electron density in sequentially doped InxGa1-xAs by Raman spectroscopy.

    PubMed

    Kort, Kenneth R; Hung, P Y; Loh, Wei-Yip; Bersuker, Gennadi; Banerjee, Sarbajit

    2015-01-01

    The advent and exponential growth of mobile computing has spurred greater emphasis on the adoption of III-V compound semiconductors in device architectures. The introduction of high charge carrier densities within InxGa1-xAs and the development of metrologies to quantitate the extent of doping have thus emerged as an urgent imperative. As an amphoteric dopant, Si begins to occupy anionic sites at high concentrations, thereby limiting the maximum carrier density that can be obtained upon Si doping of III-V semiconductors. Here, we present Raman results on sequentially doped In0.53Ga0.47As wherein sulfur monolayer doping is used to introduce additional carrier density to Si-doped samples. The sequential doping of Si and S allows for high carrier concentrations of up to 1.3 × 10(19) cm(-3) to be achieved without damaging the III-V lattice. The coupling of the plasmon in the doped samples to the longitudinal optic phonons allows Raman spectroscopy to serve as an excellent probe of the extent of dopant activation, charge carrier density, and the surface depletion region. In particular, the energy position of a high-frequency coupled mode (HFCM) that is detected above 400 cm(-1) is used to extract the free electron density in these samples. The extracted free electron densities are well correlated with measured sheet resistance values and the carrier densities deduced from Hall measurements. PMID:25588191

  15. Communication: Near-locality of exchange and correlation density functionals for 1- and 2-electron systems.

    PubMed

    Sun, Jianwei; Perdew, John P; Yang, Zenghui; Peng, Haowei

    2016-05-21

    The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin density approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound. PMID:27208927

  16. Communication: Near-locality of exchange and correlation density functionals for 1- and 2-electron systems

    NASA Astrophysics Data System (ADS)

    Sun, Jianwei; Perdew, John P.; Yang, Zenghui; Peng, Haowei

    2016-05-01

    The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin density approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound.

  17. Measurement of free electron density during photon irradiation

    NASA Astrophysics Data System (ADS)

    Barnett, Frank M.

    To disrupt molecules and therefore make them and their accompanying biological cells inactive, it is generally necessary to create more than one ionization within the molecule. This study is to use an electron linear accelerator to generate high energy photons, which then irradiate macroscopic volumes of animal cells in a measurement enclosure. During irradiation the conductivity of the volume will be measured, and at the end of irradiation, the decay of conductivity will be measured as a function of time. In order to obtain accurate timing of the cessation of radiation, a timing device has been constructed. It will be tested prior to the start of the measurements. The purpose of this study is to establish whether photon irradiation delivered in short, high intensity bursts, would be more effective in destroying malignant cells by producing multiple ionization within molecules of the cell.

  18. High Energy Density Science with Ultrarelativistic Electron Beams

    NASA Astrophysics Data System (ADS)

    Joshi, Chan

    2001-10-01

    An intense, high-energy electron or positron beam can have focused intensities rivaling those of today's most powerful lasers. For example, the 5 ps (FWHM), 50 GeV beam at the Stanford Linear Accelerator Center at 1 kA and focused to a 3 micron rms spot size gives intensities of > 10^20 W/cm^2 at a repetition rate of 10 Hz. Unlike a ps or fs laser pulse, the particle beam can readily bore through several mm of steel due to the rigidity of its flux component. However, the same particle beam can be manipulated quite strongly by a plasma that is a million times less dense than air! This is because of the incredibly strong collective fields induced in the plasma by the Coulomb force of the beam. The collective fields in turn react back onto the beam leading to many clearly-observable phenomena. The beam can be: (1) deflected leading focusing, defocusing, or even steering of the beam; (2) undulated causing the emission of spontaneous betatron x-ray radiation and; (3) accelerated or de-accelerated by the plasma fields. Using the 28.5 GeV electron and positron beams from the SLAC linac we have carried out a series of experiments that demonstrate clearly the above mentioned effects. The results are compared with theoretical predictions and 3D, one-to-one PIC code simulations using the code OSIRIS. These phenomena may have practical application in future technologies including optical elements in particle beam lines, synchrotron light sources, and ultra-high gradient accelerators.

  19. High energy density plasma science with an ultrarelativistic electron beam

    NASA Astrophysics Data System (ADS)

    Joshi, C.; Blue, B.; Clayton, C. E.; Dodd, E.; Huang, C.; Marsh, K. A.; Mori, W. B.; Wang, S.; Hogan, M. J.; O'Connell, C.; Siemann, R.; Watz, D.; Muggli, P.; Katsouleas, T.; Lee, S.

    2002-05-01

    An intense, high-energy electron or positron beam can have focused intensities rivaling those of today's most powerful laser beams. For example, the 5 ps (full-width, half-maximum), 50 GeV beam at the Stanford Linear Accelerator Center (SLAC) at 1 kA and focused to a 3 micron rms spot size gives intensities of >1020 W/cm-2 at a repetition rate of >10 Hz. Unlike a ps or fs laser pulse which interacts with the surface of a solid target, the particle beam can readily tunnel through tens of cm of steel. However, the same particle beam can be manipulated quite effectively by a plasma that is a million times less dense than air! This is because of the incredibly strong collective fields induced in the plasma by the Coulomb force of the beam. The collective fields in turn react back onto the beam leading to many clearly observable phenomena. The beam paraticles can be: (1) Deflected leading to focusing, defocusing, or even steering of the beam; (2) undulated causing the emission of spontaneous betatron x-ray radiation and; (3) accelerated or decelerated by the plasma fields. Using the 28.5 GeV electron beam from the SLAC linac a series of experiments have been carried out that demonstrate clearly many of the above mentioned effects. The results can be compared with theoretical predictions and with two-dimensional and three-dimensional, one-to-one, particle-in-cell code simulations. These phenomena may have practical applications in future technologies including optical elements in particle beam lines, synchrotron light sources, and ultrahigh gradient accelerators.

  20. Lowest Π-Π* electronic transitions in linear and two-dimensional polycyclic aromatic hydrocarbons: enhanced electron density edge effect

    NASA Astrophysics Data System (ADS)

    Yadav, Amarjeet; Mishra, P. C.

    2014-04-01

    Polycyclic aromatic hydrocarbons (PAHs) form an important class of molecules as they are ubiquitous, pollute air and cause severe health problems. Lowest vertical π-π* singlet-singlet or triplet-triplet excitation energies and corresponding oscillator strengths were studied for several linear and two-dimensional PAHs employing time-dependent density functional theory. Excited-state electron density, molecular electrostatic potential (MEP) and spin density distributions in the PAHs, along with ground-state chemical hardness, were also studied. It has been found that, generally, excitation energies and oscillator strengths decrease with increase in PAH size, and excitation energies and chemical hardness are strongly linearly correlated. Enhanced electron density edge effect, which was found to occur in the ground states of the molecules, continues to hold in their excited states also. A strong similarity between the ground and π-π* excited-state MEP maps suggests that σ electrons are the main contributors to the enhanced electron density at the edges. Due to their strong electronic absorption transitions in the visible and infrared regions, the PAHs can be used for harnessing solar energy efficiently.

  1. Time-dependent density-functional tight-binding method with the third-order expansion of electron density

    SciTech Connect

    Nishimoto, Yoshio

    2015-09-07

    We develop a formalism for the calculation of excitation energies and excited state gradients for the self-consistent-charge density-functional tight-binding method with the third-order contributions of a Taylor series of the density functional theory energy with respect to the fluctuation of electron density (time-dependent density-functional tight-binding (TD-DFTB3)). The formulation of the excitation energy is based on the existing time-dependent density functional theory and the older TD-DFTB2 formulae. The analytical gradient is computed by solving Z-vector equations, and it requires one to calculate the third-order derivative of the total energy with respect to density matrix elements due to the inclusion of the third-order contributions. The comparison of adiabatic excitation energies for selected small and medium-size molecules using the TD-DFTB2 and TD-DFTB3 methods shows that the inclusion of the third-order contributions does not affect excitation energies significantly. A different set of parameters, which are optimized for DFTB3, slightly improves the prediction of adiabatic excitation energies statistically. The application of TD-DFTB for the prediction of absorption and fluorescence energies of cresyl violet demonstrates that TD-DFTB3 reproduced the experimental fluorescence energy quite well.

  2. Time-dependent density-functional tight-binding method with the third-order expansion of electron density.

    PubMed

    Nishimoto, Yoshio

    2015-09-01

    We develop a formalism for the calculation of excitation energies and excited state gradients for the self-consistent-charge density-functional tight-binding method with the third-order contributions of a Taylor series of the density functional theory energy with respect to the fluctuation of electron density (time-dependent density-functional tight-binding (TD-DFTB3)). The formulation of the excitation energy is based on the existing time-dependent density functional theory and the older TD-DFTB2 formulae. The analytical gradient is computed by solving Z-vector equations, and it requires one to calculate the third-order derivative of the total energy with respect to density matrix elements due to the inclusion of the third-order contributions. The comparison of adiabatic excitation energies for selected small and medium-size molecules using the TD-DFTB2 and TD-DFTB3 methods shows that the inclusion of the third-order contributions does not affect excitation energies significantly. A different set of parameters, which are optimized for DFTB3, slightly improves the prediction of adiabatic excitation energies statistically. The application of TD-DFTB for the prediction of absorption and fluorescence energies of cresyl violet demonstrates that TD-DFTB3 reproduced the experimental fluorescence energy quite well. PMID:26342360

  3. Automated determination of electron density from electric field measurements on the Van Allen Probes spacecraft

    NASA Astrophysics Data System (ADS)

    Zhelavskaya, Irina; Kurth, William; Spasojevic, Maria; Shprits, Yuri

    2016-07-01

    We present the Neural-network-based Upper-hybrid Resonance Determination (NURD) algorithm for automatic inference of the electron number density from plasma wave measurements made onboard NASA's Van Allen Probes mission. A feedforward neural network is developed to determine the upper hybrid resonance frequency, f_{uhr}, from electric field measurements, which is then used to calculate the electron number density. In previous missions, the plasma resonance bands were manually identified, and there have been few attempts to do robust, routine automated detections. We describe the design and implementation of the algorithm and perform an initial analysis of the resulting electron number density distribution obtained by applying NURD to 2.5 years of data collected with the EMFISIS instrumentation suite of the Van Allen Probes mission. Densities obtained by NURD are compared to those obtained by another recently developed automated technique and also to an existing empirical plasmasphere and trough density model.

  4. Electron Density Measurements in UV-Preionized XeCl and CO2 Laser Gas Mixtures

    NASA Astrophysics Data System (ADS)

    Takagi, Shigeyuki; Sato, Saburo; Goto, Tatsumi

    1989-11-01

    A Langmuir probe technique has been used to measure electron densities and temperatures in UV-preionized XeCl excimer and CO2 laser gas mixtures in a laser tube. For this experiment, only pin electrodes (preionization sparks) were operated with no discharge between the main electrodes. The measured electron densities were about 108 cm-3 in both the excimer and CO2 laser gases, compared with 1010 cm-3 in pure He gas. The electron density was found to increase due to the proximity of the main electrodes. The coefficients of absorption for excimer and CO2 laser gas were obtained from the characteristics of the electron densities vs the distance from the UV source. Based on the absorption coefficient for XeCl, 0.9 cm-1 atm-1, we propose pin-electrode arrangements for spatially uniform preionization.

  5. High energy density capacitors for power electronic applications using nano-structure multilayer technology

    SciTech Connect

    Barbee, T.W. Jr.; Johnson, G.W.

    1995-09-01

    Power electronics applications are currently limited by capacitor size and performance. Only incremental improvements are anticipated in existing capacitor technologies, while significant performance advances are required in energy density and overall performance to meet the technical needs of the applications which are important for U.S. economic competitiveness. One application, the Power Electronic Building Block (PEBB), promises a second electronics revolution in power electronic design. High energy density capacitors with excellent electrical thermal and mechanical performance represent an enabling technology in the PEBB concept. We propose a continuing program to research and develop LLNL`s nano-structure multilayer technologies for making high voltage, high energy density capacitors. Our controlled deposition techniques are capable of synthesizing extraordinarily smooth sub-micron thick layers of dielectric and conductor materials. We have demonstrated that, with this technology, high voltage capacitors with an order of magnitude improvement in energy density are achievable.

  6. Comparisons of ionospheric electron density distributions reconstructed by GPS computerized tomography, backscatter ionograms, and vertical ionograms

    NASA Astrophysics Data System (ADS)

    Zhou, Chen; Lei, Yong; Li, Bofeng; An, Jiachun; Zhu, Peng; Jiang, Chunhua; Zhao, Zhengyu; Zhang, Yuannong; Ni, Binbin; Wang, Zemin; Zhou, Xuhua

    2015-12-01

    Global Positioning System (GPS) computerized ionosphere tomography (CIT) and ionospheric sky wave ground backscatter radar are both capable of measuring the large-scale, two-dimensional (2-D) distributions of ionospheric electron density (IED). Here we report the spatial and temporal electron density results obtained by GPS CIT and backscatter ionogram (BSI) inversion for three individual experiments. Both the GPS CIT and BSI inversion techniques demonstrate the capability and the consistency of reconstructing large-scale IED distributions. To validate the results, electron density profiles obtained from GPS CIT and BSI inversion are quantitatively compared to the vertical ionosonde data, which clearly manifests that both methods output accurate information of ionopsheric electron density and thereby provide reliable approaches to ionospheric soundings. Our study can improve current understanding of the capability and insufficiency of these two methods on the large-scale IED reconstruction.

  7. Self-Energy Correction to Momentum-Density Distribution of Positron-Electron Pairs

    NASA Astrophysics Data System (ADS)

    Tang, Z.; Nagai, Y.; Inoue, K.; Toyama, T.; Chiba, T.; Saito, M.; Hasegawa, M.

    2005-03-01

    Positron two-dimensional angular correlation of annihilation radiation (2D ACAR), i.e., the 2D projection of the electron momentum densities sampled by positron, in Si is employed to verify the prediction of the density functional theory within the local-density approximation (LDA). Carefully conducted test shows that the LDA introduces small but definite discrepancies to the 2D-ACAR anisotropies. Self-energy calculation using the GW method indicates that density-fluctuation contributes anisotropic momentum-density correction and thus improves the agreement between theory and experiment. These results provide valuable annotations to the arguments concerning the accuracy and validity of the LDA and GW schemes.

  8. Acceleration of high charge density electron beams in the SLAC linac

    SciTech Connect

    Sheppard, J.C.; Clendenin, J.E.; Jobe, R.K.; Lueth, V.G.; Millich, A.; Ross, M.C.; Seeman, J.T.; Stiening, R.F.

    1984-01-01

    The SLAC Linear Collider (SLC) will require both electron and positron beams of very high charge density and low emittance to be accelerated to about 50 GeV in the SLAC 3-km linac. The linac is in the process of being improved to meet this requirement. The program to accelerate an electron beam of high charge density through the first third of the SLC linac is described and the experimental results are discussed. 7 references, 5 figures.

  9. The first in situ electron temperature and density measurements of the Martian nightside ionosphere

    NASA Astrophysics Data System (ADS)

    Fowler, C. M.; Andersson, L.; Ergun, R. E.; Morooka, M.; Delory, G.; Andrews, D. J.; Lillis, Robert J.; McEnulty, T.; Weber, T. D.; Chamandy, T. M.; Eriksson, A. I.; Mitchell, D. L.; Mazelle, C.; Jakosky, B. M.

    2015-11-01

    The first in situ nightside electron density and temperature profiles at Mars are presented as functions of altitude and local time (LT) from the Langmuir Probe and Waves (LPW) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft. LPW is able to measure densities as low as ˜100 cm-3, a factor of up to 10 or greater improvement over previous measurements. Above 200 km, near-vertical density profiles of a few hundred cubic centimeters were observed for almost all nightside LT, with the lowest densities and highest temperatures observed postmidnight. Density peaks of a few thousand cubic centimeters were observed below 200 km at all nightside LT. The lowest temperatures were observed below 180 km and approach the neutral atmospheric temperature. One-dimensional modeling demonstrates that precipitating electrons were able to sustain the observed nightside ionospheric densities below 200 km.

  10. Generalization of the Kohn-Sham system that can represent arbitrary one-electron density matrices

    NASA Astrophysics Data System (ADS)

    van Dam, Hubertus J. J.

    2016-05-01

    Density functional theory is currently the most widely applied method in electronic structure theory. The Kohn-Sham method, based on a fictitious system of noninteracting particles, is the workhorse of the theory. The particular form of the Kohn-Sham wave function admits only idempotent one-electron density matrices whereas wave functions of correlated electrons in post-Hartree-Fock methods invariably have fractional occupation numbers. Here we show that by generalizing the orbital concept and introducing a suitable dot product as well as a probability density, a noninteracting system can be chosen that can represent the one-electron density matrix of any system, even one with fractional occupation numbers. This fictitious system ensures that the exact electron density is accessible within density functional theory. It can also serve as the basis for reduced density matrix functional theory. Moreover, to aid the analysis of the results the orbitals may be assigned energies from a mean-field Hamiltonian. This produces energy levels that are akin to Hartree-Fock orbital energies such that conventional analyses based on Koopmans' theorem are available. Finally, this system is convenient in formalisms that depend on creation and annihilation operators as they are trivially applied to single-determinant wave functions.

  11. Generalization of the Kohn-Sham system that can represent arbitrary one-electron density matrices

    DOE PAGESBeta

    Hubertus J. J. van Dam

    2016-05-23

    Density functional theory is currently the most widely applied method in electronic structure theory. The Kohn-Sham method, based on a fictitious system of noninteracting particles, is the workhorse of the theory. The particular form of the Kohn-Sham wave function admits only idempotent one-electron density matrices whereas wave functions of correlated electrons in post-Hartree-Fock methods invariably have fractional occupation numbers. Here we show that by generalizing the orbital concept and introducing a suitable dot product as well as a probability density, a noninteracting system can be chosen that can represent the one-electron density matrix of any system, even one with fractionalmore » occupation numbers. This fictitious system ensures that the exact electron density is accessible within density functional theory. It can also serve as the basis for reduced density matrix functional theory. Moreover, to aid the analysis of the results the orbitals may be assigned energies from a mean-field Hamiltonian. This produces energy levels that are akin to Hartree-Fock orbital energies such that conventional analyses based on Koopmans' theorem are available. Lastly, this system is convenient in formalisms that depend on creation and annihilation operators as they are trivially applied to single-determinant wave functions.« less

  12. Temporal-spatial modeling of electron density enhancement due to successive lightning strokes

    NASA Astrophysics Data System (ADS)

    Lay, Erin H.; Rodger, Craig J.; Holzworth, Robert H.; Cho, Mengu; Thomas, Jeremy N.

    2010-11-01

    We report results on the temporal-spatial modeling of electron density enhancement due to successive lightning strokes. Stroke rates based on World-Wide Lightning Location Network measurements are used as input to an axisymmetric Finite Difference Time Domain model that describes the effect of lightning electromagnetic pulses (EMP) on the ionosphere. Each successive EMP pulse interacts with a modified background ionosphere due to the previous pulses, resulting in a nonlinear electron density perturbation over time that eventually reaches a limiting value. The qualitative ionospheric response to successive EMPs is presented in 2-D, axisymmetric space. Results from this study show that the nonlinear electron density perturbations due to successive lightning strokes must be taken into account and varies with altitude. The limiting maximum electron density is reached earlier in time for higher altitudes, and the most significant effect occurs at 88 km. The limiting modeled electron density profile in the 83-91 km altitude range does not depend on the initial electron density.

  13. Localized electron heating and downstream density rise in expanding helicon plasma

    NASA Astrophysics Data System (ADS)

    Ghosh, Soumen; Barada, Kshitish; Chattopadhyay, Prabal; Ghosh, Joydeep; Bora, Dhiraj

    2015-11-01

    Localized electron heating and downstream density rise have been observed in presence of diverging magnetic fields in a linear expanding helicon plasma system. Axial wave field measurement shows the presence of damped helicon waves with standing wave character folded into it even at low densities (1016 m-3) . Helicon wavelength is just about twice the antenna length and the phase velocity (vp) is almost equal to the speed required for electron impact ionization. Observations advocate the Landau damping heating by the helicon waves, particularly in our low density plasma. Electron heating, confined away from the antenna centre, strongly indicates a source of local power absorption, occurring due to damped helicon waves. Further downstream from the location of electron heating, a density peak is observed. Location of both electron heating and density peaking can be varied by changing the axial magnetic field topology. A comprehensive discussion regarding the cause behind both the localized electron heating and downstream density rise will be discussed in this presentation.

  14. Analysis of the enhanced negative correlation between electron density and electron temperature related to earthquakes

    NASA Astrophysics Data System (ADS)

    Shen, X. H.; Zhang, X.; Liu, J.; Zhao, S. F.; Yuan, G. P.

    2015-04-01

    Ionospheric perturbations in plasma parameters have been observed before large earthquakes, but the correlation between different parameters has been less studied in previous research. The present study is focused on the relationship between electron density (Ne) and temperature (Te) observed by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite during local nighttime, in which a positive correlation has been revealed near the equator and a weak correlation at mid- and low latitudes over both hemispheres. Based on this normal background analysis, the negative correlation with the lowest percent in all Ne and Te points is studied before and after large earthquakes at mid- and low latitudes. The multiparameter observations exhibited typical synchronous disturbances before the Chile M8.8 earthquake in 2010 and the Pu'er M6.4 in 2007, and Te varied inversely with Ne over the epicentral areas. Moreover, statistical analysis has been done by selecting the orbits at a distance of 1000 km and ±7 days before and after the global earthquakes. Enhanced negative correlation coefficients lower than -0.5 between Ne and Te are found in 42% of points to be connected with earthquakes. The correlation median values at different seismic levels show a clear decrease with earthquakes larger than 7. Finally, the electric-field-coupling model is discussed; furthermore, a digital simulation has been carried out by SAMI2 (Sami2 is Another Model of the Ionosphere), which illustrates that the external electric field in the ionosphere can strengthen the negative correlation in Ne and Te at a lower latitude relative to the disturbed source due to the effects of the geomagnetic field. Although seismic activity is not the only source to cause the inverse Ne-Te variations, the present results demonstrate one possibly useful tool in seismo-electromagnetic anomaly differentiation, and a comprehensive analysis with multiple parameters helps to

  15. Density Gradient Stabilization of Electron Temperature Gradient Driven Turbulence in a Spherical Tokamak

    SciTech Connect

    Ren, Y; Mazzucato, E; Guttenfelder, W; Bell, R E; Domier, C W; LeBlanc, B P; Lee, K C; Luhmann Jr, N C; Smith, D R

    2011-03-21

    In this letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k⊥ρs ≤10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of two decrease in the plasma effective thermal diffusivity.

  16. Density gradient stabilization of electron temperature gradient driven turbulence in a spherical tokamak.

    PubMed

    Ren, Y; Kaye, S M; Mazzucato, E; Guttenfelder, W; Bell, R E; Domier, C W; LeBlanc, B P; Lee, K C; Luhmann, N C; Smith, D R; Yuh, H

    2011-04-22

    In this Letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k(⊥)ρ(s) ≲ 10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of 2 decrease in the plasma effective thermal diffusivity. PMID:21599377

  17. Path Integrals for Electronic Densities, Reactivity Indices, and Localization Functions in Quantum Systems

    PubMed Central

    Putz, Mihai V.

    2009-01-01

    The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr’s quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions – all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems. PMID:20087467

  18. Chemical bonding in view of electron charge density and kinetic energy density descriptors.

    PubMed

    Jacobsen, Heiko

    2009-05-01

    Stalke's dilemma, stating that different chemical interpretations are obtained when one and the same density is interpreted either by means of natural bond orbital (NBO) and subsequent natural resonance theory (NRT) application or by the quantum theory of atoms in molecules (QTAIM), is reinvestigated. It is shown that within the framework of QTAIM, the question as to whether for a given molecule two atoms are bonded or not is only meaningful in the context of a well-defined reference geometry. The localized-orbital-locator (LOL) is applied to map out patterns in covalent bonding interaction, and produces results that are consistent for a variety of reference geometries. Furthermore, LOL interpretations are in accord with NBO/NRT, and assist in an interpretation in terms of covalent bonding. PMID:19090572

  19. Thermodiffusion of high-density electron-hole plasmas in semiconductors

    SciTech Connect

    Mahler, G.; Maier, G.; Forchel, A.; Laurich, B.; Sanwald, H.; Schmid, W.

    1981-12-21

    The spatial distributions of temperature and density in electron-hole plasmas in surface-excited semiconductors are investigated with use of linear irreversible thermodynamics and a microscopic plasma theory. Above a certain threshold the density distribution is dominated by a characteristic density, which increases with temperature. Experimental results for Ge, unstressed Si, and Si under high uniaxial stress are in agreement with the theory.

  20. A new method for determining the plasma electron density using optical frequency comb interferometer

    SciTech Connect

    Arakawa, Hiroyuki Tojo, Hiroshi; Sasao, Hajime; Kawano, Yasunori; Itami, Kiyoshi

    2014-04-15

    A new method of plasma electron density measurement using interferometric phases (fractional fringes) of an optical frequency comb interferometer is proposed. Using the characteristics of the optical frequency comb laser, high density measurement can be achieved without fringe counting errors. Simulations show that the short wavelength and wide wavelength range of the laser source and low noise in interferometric phases measurements are effective to reduce ambiguity of measured density.

  1. Covalent addition of chitosan to graphene sheets: Density functional theory explorations of quadrupole coupling constants

    NASA Astrophysics Data System (ADS)

    Mokhtari, Ali; Harismah, Kun; Mirzaei, Mahmoud

    2015-12-01

    Density functional theory (DFT) calculations have been performed to detect the stabilities and properties of chitosan-functionalized graphene and graphene-oxide structures (G-Chit and GO-Chit). The model systems with two different sizes of sheets have been optimized and the molecular and atomic properties have been evaluated for them. The results indicated that investigated G-Chit and GO-Chit structures could be considered as stable structures but with different properties. The properties for GO and GO-Chit structures are almost similar; however, they are different from the original G and G-Chit structures. The results also indicated that the properties could be also size-dependent, in which different molecular and atomic properties have been observed for the investigate G sheets.

  2. Electron density measurements in a pulse-repetitive microwave discharge in air

    SciTech Connect

    Nikolic, M.; Popovic, S.; Vuskovic, L.; Herring, G. C.; Exton, R. J.

    2011-12-01

    We have developed a technique for absolute measurements of electron density in pulse-repetitive microwave discharges in air. The technique is based on the time-resolved absolute intensity of a nitrogen spectral band belonging to the Second Positive System, the kinetic model and the detailed particle balance of the N{sub 2}C{sup 3}{Pi}{sub u} ({nu} = 0) state. This new approach bridges the gap between two existing electron density measurement methods (Langmuir probe and Stark broadening). The electron density is obtained from the time-dependent rate equation for the population of N{sub 2}C{sup 3}{Pi}{sub u} ({nu} = 0) using recorded waveforms of the absolute C{sup 3}{Pi}{sub u}{yields}B{sup 3}{Pi}{sub g} (0-0) band intensity, the forward and reflected microwave power density. Measured electron density waveforms using numerical and approximated analytical methods are presented for the case of pulse repetitive planar surface microwave discharge at the aperture of a horn antenna covered with alumina ceramic plate. The discharge was generated in air at 11.8 Torr with a X-band microwave generator using 3.5 {mu}s microwave pulses at peak power of 210 kW. In this case, we were able to time resolve the electron density within a single 3.5 {mu}s pulse. We obtained (9.0 {+-} 0.6) x 10{sup 13} cm{sup -3} for the peak and (5.0 {+-} 0.6) x 10{sup 13} cm{sup -3} for the pulse-average electron density. The technique presents a convenient, non-intrusive diagnostic method for local, time-defined measurements of electron density in short duration discharges near atmospheric pressures.

  3. The effect of additives on charge decay in electron-beam charged polypropylene films

    NASA Astrophysics Data System (ADS)

    Hillenbrand, J; Motz, T; Sessler, G M; Zhang, X; Behrendt, N; von Salis-Soglio, C; Erhard, D P; Altstädt, V; Schmidt, H-W

    2009-03-01

    The charge decay in isotactic polypropylene (i-PP) films of 50 µm thickness, containing three kinds of additives, namely a trisamide, a bisamide and a fluorinated compound, with concentrations in the range 0.004-1 wt% was studied. Compression molding was used to produce the films. The samples were either surface-charged by a corona method or volume-charged by mono-energetic electron beams of different energies, having penetration depths up to 6 µm. In all cases, surface potentials of about 200 V were chosen. After charging the films, the decay of the surface potential was studied either by an isothermal discharge method at 90 °C or by thermally stimulated discharge measurements. The results show a dependence of the decay rate on the kind of additive used, on additive concentration and on the energy of the injected charges. In particular, for samples with fluorinated additives, the stability of the surface potential decreases markedly with increasing electron energy, while such a dependence is very weak for samples containing the bisamide additive and does not exist at all for samples with the trisamide additive. These observations are tentatively explained by the radiation-induced generation of relatively mobile negative ions originating from the bisamide and fluorinated additives.

  4. Generation of High-Density Electrons Based on Plasma Grating Induced Bragg Diffraction in Air

    SciTech Connect

    Shi Liping; Li Wenxue; Wang Yongdong; Lu Xin; Ding Liang'en; Zeng Heping

    2011-08-26

    Efficient nonlinear Bragg diffraction was observed as an intense infrared femtosecond pulse was focused on a plasma grating induced by interference between two ultraviolet femtosecond laser pulses in air. The preformed electrons inside the plasma grating were accelerated by subsequent intense infrared laser pulses, inducing further collisional ionization and significantly enhancing the local electron density.

  5. The topological features of the intracule density of the uniform electron gas

    NASA Astrophysics Data System (ADS)

    Fradera, X.; Sarasola, C.; Ugalde, J. M.; Boyd, R. J.

    1999-05-01

    The Laplacian of the self-consistent-field radial intracule density of the uniform electron gas has been analyzed. It reaches its absolute maximum at the electron-electron coalescence point with a value of 0.3 ρ2, where ρ is the electron charge density. Then, it decreases as the interlectronic distance increases and has an attenuated oscillatory decay at larger distances. Further examination of this function yields an onion-like representation of the spatial structure of the uniform electron gas from the viewpoint of an arbitrary reference electron. Our calculations demonstrate that the radius of the first layer is 13.069 rs and the remaining layers obey a simple relationship with respect to the layer number with a separation of 6.065 rs between adjacent layers.

  6. Role of Density Gradient Driven Trapped Electron Modes in the H-Mode Inner Core with Electron Heating

    NASA Astrophysics Data System (ADS)

    Ernst, D.

    2015-11-01

    We present new experiments and nonlinear gyrokinetic simulations showing that density gradient driven TEM (DGTEM) turbulence dominates the inner core of H-Mode plasmas during strong electron heating. Thus α-heating may degrade inner core confinement in H-Mode plasmas with moderate density peaking. These DIII-D low torque quiescent H-mode experiments were designed to study DGTEM turbulence. Gyrokinetic simulations using GYRO (and GENE) closely match not only particle, energy, and momentum fluxes, but also density fluctuation spectra, with and without ECH. Adding 3.4 MW ECH doubles Te /Ti from 0.5 to 1.0, which halves the linear TEM critical density gradient, locally flattening the density profile. Density fluctuations from Doppler backscattering (DBS) intensify near ρ = 0.3 during ECH, displaying a band of coherent fluctuations with adjacent toroidal mode numbers. GYRO closely reproduces the DBS spectrum and its change in shape and intensity with ECH, identifying these as coherent TEMs. Prior to ECH, parallel flow shear lowers the effective nonlinear DGTEM critical density gradient 50%, but is negligible during ECH, when transport displays extreme stiffness in the density gradient. GS2 predictions show the DGTEM can be suppressed, to avoid degradation with electron heating, by broadening the current density profile to attain q0 >qmin > 1 . A related experiment in the same regime varied the electron temperature gradient in the outer half-radius (ρ ~ 0 . 65) using ECH, revealing spatially coherent 2D mode structures in the Te fluctuations measured by ECE imaging. Fourier analysis with modulated ECH finds a threshold in Te profile stiffness. Supported by the US DOE under DE-FC02-08ER54966 and DE-FC02-04ER54698.

  7. Validation of Ionosonde Electron Density Reconstruction Algorithms with IONOLAB-RAY in Central Europe

    NASA Astrophysics Data System (ADS)

    Gok, Gokhan; Mosna, Zbysek; Arikan, Feza; Arikan, Orhan; Erdem, Esra

    2016-07-01

    Ionospheric observation is essentially accomplished by specialized radar systems called ionosondes. The time delay between the transmitted and received signals versus frequency is measured by the ionosondes and the received signals are processed to generate ionogram plots, which show the time delay or reflection height of signals with respect to transmitted frequency. The critical frequencies of ionospheric layers and virtual heights, that provide useful information about ionospheric structurecan be extracted from ionograms . Ionograms also indicate the amount of variability or disturbances in the ionosphere. With special inversion algorithms and tomographical methods, electron density profiles can also be estimated from the ionograms. Although structural pictures of ionosphere in the vertical direction can be observed from ionosonde measurements, some errors may arise due to inaccuracies that arise from signal propagation, modeling, data processing and tomographic reconstruction algorithms. Recently IONOLAB group (www.ionolab.org) developed a new algorithm for effective and accurate extraction of ionospheric parameters and reconstruction of electron density profile from ionograms. The electron density reconstruction algorithm applies advanced optimization techniques to calculate parameters of any existing analytical function which defines electron density with respect to height using ionogram measurement data. The process of reconstructing electron density with respect to height is known as the ionogram scaling or true height analysis. IONOLAB-RAY algorithm is a tool to investigate the propagation path and parameters of HF wave in the ionosphere. The algorithm models the wave propagation using ray representation under geometrical optics approximation. In the algorithm , the structural ionospheric characteristics arerepresented as realistically as possible including anisotropicity, inhomogenity and time dependence in 3-D voxel structure. The algorithm is also used

  8. Influence of DE3 tide on the equinoctial asymmetry of the zonal mean ionospheric electron density

    NASA Astrophysics Data System (ADS)

    Ren, Zhipeng; Wan, Weixing; Xiong, Jiangang; Liu, Libo

    2014-12-01

    Through respectively adding September DE3 tide and March DE3 tide at the low boundary of Global Coupled Ionosphere-Thermosphere-Electrodynamics Model, Institute of Geology and Geophysics, Chinese Academy of Sciences (GCITEM-IGGCAS), we simulate the influence of DE3 tide on the equinoctial asymmetry of the zonal mean ionospheric electron density. The influence of DE3 tide on the equinoctial asymmetry of the zonal mean electron density varies with latitude, altitude, and solar activity level. Compared with the density driven by the September DE3 tide, the March DE3 tide mainly decreases the lower ionospheric zonal mean electron density and mainly increases the electron density at higher ionosphere. In the low-latitude ionosphere, DE3 tide drives an equatorial ionization anomaly (EIA) structure at higher ionosphere in the relative difference of zonal mean electron density, which suggests that DE3 tide affects the longitudinal mean equatorial vertical E × B plasma drifts. Although the lower ionospheric equinoctial asymmetry driven by DE3 tide mainly decreases with the increase of solar activity, the asymmetry at higher ionosphere mainly increases with solar activity. However, EIA in equinoctial asymmetry mainly decreases with the increase of solar activity.

  9. Dispersion relations of electron density fluctuations in a Hall thruster plasma, observed by collective light scattering

    SciTech Connect

    Tsikata, S.; Pisarev, V.; Gresillon, D. M.; Lemoine, N.

    2009-03-15

    Kinetic models and numerical simulations of E-vectorxB-vector plasma discharges predict microfluctuations at the scales of the electron cyclotron drift radius and the ion plasma frequency. With the help of a specially designed collective scattering device, the first experimental observations of small-scale electron density fluctuations inside the plasma volume are obtained, and observed in the expected ranges of spatial and time scales. The anisotropy, dispersion relations, form factor, amplitude, and spatial distribution of these electron density fluctuations are described and compared to theoretical expectations.

  10. Reorientation of the Stripe Phase of 2D Electrons by a Minute Density Modulation

    NASA Astrophysics Data System (ADS)

    Mueed, M. A.; Hossain, Md. Shafayat; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.

    2016-08-01

    Interacting two-dimensional electrons confined in a GaAs quantum well exhibit isotropic transport when the Fermi level resides in the first excited (N =1 ) Landau level. Adding an in-plane magnetic field (B||) typically leads to an anisotropic, stripelike (nematic) phase of electrons with the stripes oriented perpendicular to the B|| direction. Our experimental data reveal how a periodic density modulation, induced by a surface strain grating from strips of negative electron-beam resist, competes against the B||-induced orientational order of the stripe phase. Even a minute (<0.25 %) density modulation is sufficient to reorient the stripes along the direction of the surface grating.

  11. To What Extent are "Atoms in Molecules" Structures of Hydrocarbons Reproducible from the Promolecule Electron Densities?

    PubMed

    Keyvani, Zahra Alimohammadi; Shahbazian, Shant; Zahedi, Mansour

    2016-03-24

    The "atoms in molecules" structures of 225 unsubstituted hydrocarbons are derived from both the optimized and the promolecule electron densities. A comparative analysis demonstrates that the molecular graphs derived from these two types of electron densities at the same geometry are equivalent for almost 90 % of the hydrocarbons containing the same number and types of critical points. For the remaining 10 % of molecules, it is demonstrated that by inducing small perturbations, through the variation of the used basis set or slight changes in the used geometry, the emerging molecular graphs from both densities are also equivalent. Interestingly, the (3, -1) critical point between two "non-bonded" hydrogen atoms, which triggered "H-H bonding" controversy is also observed in the promolecule densities of certain hydrocarbons. Evidently, the topology of the electron density is not dictated by chemical bonds or strong interactions and deformations induced by the interactions of atoms in molecules have a quite marginal role, virtually null, in shaping the general traits of the topology of molecular electron densities of the studied hydrocarbons, whereas the key factor is the underlying atomic densities. PMID:26914604

  12. Measurement of power density distribution and beam waist simulation for electron beam

    NASA Astrophysics Data System (ADS)

    Shen, Chunlong; Peng, Yong; Wang, Kehong; Zhou, Qi

    2013-02-01

    The study aims to measure the power density distribution of the electron beam (EB) for further estimating its characteristics. A compact device combining deflection signal controller and current signal acquisition circuit of the EB was built. A software modelling framework was developed to investigate structural parameters of the electron beam. With an iterative algorithm, the functional relationship between the electron beam power and its power density was solved and the corresponding contour map of power density distribution was plotted through isoline tracking approach. The power density distribution of various layers of cross-section beam was reconstructed for beam volume by direct volume rendering technique. The further simulation of beam waist with all-known marching cubes algorithm reveals the evolution of spatial appearance and geometry measurement principle was explained in detail. The study provides an evaluation of promising to replace the traditional idea of EB spatial characteristics.

  13. Analysis of hydrogen-bond interaction potentials from the electron density: Integration of NCI regions

    PubMed Central

    Contreras-García, Julia; Yang, Weitao; Johnson, Erin R.

    2013-01-01

    Hydrogen bonds are of crucial relevance to many problems in chemistry biology and materials science. The recently-developed NCI (Non-Covalent Interactions) index enables real-space visualization of both attractive (van der Waals and hydrogen-bonding) and repulsive (steric) interactions based on properties of the electron density It is thus an optimal index to describe the interplay of stabilizing and de-stabilizing contributions that determine stable minima on hydrogen-bonding potential-energy surfaces (PESs). In the framework of density-functional theory energetics are completely determined by the electron density Consequently NCI will be shown to allow quantitative treatment of hydrogen-bond energetics. The evolution of NCI regions along a PES follows a well-behaved pattern which, upon integration of the electron density is capable of mimicking conventional hydrogen-bond interatomic potentials. PMID:21786796

  14. Effect of q-nonextensive parameter and saturation time on electron density steepening in electron-positron-ion plasmas

    SciTech Connect

    Hashemzadeh, M.

    2015-11-15

    The effect of q-nonextensive parameter and saturation time on the electron density steepening in electron-positron-ion plasmas is studied by particle in cell method. Phase space diagrams show that the size of the holes, and consequently, the number of trapped particles strongly depends on the q-parameter and saturation time. Furthermore, the mechanism of the instability and exchange of energy between electron-positron and electric field is explained by the profiles of the energy density. Moreover, it is found that the q-parameter, saturation time, and electron and positron velocities affect the nonlinear evolution of the electron density which leads to the steepening of its structure. The q-nonextensive parameter or degree of nonextensivity is the relation between temperature gradient and potential energy of the system. Therefore, the deviation of q-parameter from unity indicates the degree of inhomogeneity of temperature or deviation from equilibrium. Finally, using the kinetic theory, a generalized q-dispersion relation is presented for electron-positron-ion plasma systems. It is found that the simulation results in the linear regime are in good agreement with the growth rate results obtained by the kinetic theory.

  15. Effect of Powder Reuse Times on Additive Manufacturing of Ti-6Al-4V by Selective Electron Beam Melting

    NASA Astrophysics Data System (ADS)

    Tang, H. P.; Qian, M.; Liu, N.; Zhang, X. Z.; Yang, G. Y.; Wang, J.

    2015-03-01

    An advantage of the powder-bed-based metal additive manufacturing (AM) processes is that the powder can be reused. The powder reuse or recycling times directly affect the affordability of the additively manufactured parts, especially for the AM of titanium parts. This study examines the influence of powder reuse times on the characteristics of Ti-6Al-4V powder, including powder composition, particle size distribution (PSD), apparent density, tap density, flowability, and particle morphology. In addition, tensile samples were manufactured and evaluated with respect to powder reuse times and sample locations in the powder bed. The following findings were made from reusing the same batch of powder 21 times for AM by selective electron beam melting: (i) the oxygen (O) content increased progressively with increasing reuse times but both the Al content and the V content remained generally stable (a small decrease only); (ii) the powder became less spherical with increasing reuse times and some particles showed noticeable distortion and rough surfaces after being reused 16 times; (iii) the PSD became narrower and few satellite particles were observed after 11 times of reuse; (iv) reused powder showed improved flowability; and (v) reused powder showed no measurable undesired influence on the AM process and the samples exhibited highly consistent tensile properties, irrespective of their locations in the powder bed. The implications of these findings were discussed.

  16. Additive Manufacturing of Multifunctional Components Using High Density Carbon Nanotube Yarn Filaments

    NASA Technical Reports Server (NTRS)

    Gardner, John M.; Sauti, Godfrey; Kim, Jae-Woo; Cano, Roberto J.; Wincheski, Russell A.; Stelter, Christopher J.; Grimsley, Brian W.; Working, Dennis C.; Siochi, Emilie J.

    2016-01-01

    Additive manufacturing allows for design freedom and part complexity not currently attainable using traditional manufacturing technologies. Fused Filament Fabrication (FFF), for example, can yield novel component geometries and functionalities because the method provides a high level of control over material placement and processing conditions. This is achievable by extrusion of a preprocessed filament feedstock material along a predetermined path. However if fabrication of a multifunctional part relies only on conventional filament materials, it will require a different material for each unique functionality printed into the part. Carbon nanotubes (CNTs) are an attractive material for many applications due to their high specific strength as well as good electrical and thermal conductivity. The presence of this set of properties in a single material presents an opportunity to use one material to achieve multifunctionality in an additively manufactured part. This paper describes a recently developed method for processing continuous CNT yarn filaments into three-dimensional articles, and summarizes the mechanical, electrical, and sensing performance of the components fabricated in this way.

  17. Comparison study between coherent echoes at VHF range and electron density estimated by Ionosphere Model for Auroral Zone

    NASA Astrophysics Data System (ADS)

    Nishiyama, Takanori; Nakamura, Takuji; Tsutsumi, Masaki; Tanaka, Yoshi; Nishimura, Koji; Sato, Kaoru; Tomikawa, Yoshihiro; Kohma, Masashi

    2016-07-01

    Polar Mesosphere Winter Echo (PMWE) is known as back scatter echo from 55 to 85 km in the mesosphere, and it has been observed by MST and IS radar in polar region during non-summer period. Since density of free electrons as scatterer is low in the dark mesosphere during winter, it is suggested that PMWE requires strong ionization of neutral atmosphere associated with Energetic Particles Precipitations (EPPs) during Solar Proton Events [Kirkwood et al., 2002] or during geomagnetically disturbed periods [Nishiyama et al., 2015]. However, studies on relationship between occurrence of PMWE and background electron density has been limited yet [Lübken et al., 2006], partly because the PMWE occurrence rate is known to be quite low (2.9%) [Zeller et al., 2006]. The PANSY (Program of the Antarctic Syowa MST/IS) radar, which is the largest MST radar in Antarctica, observed many PMWE events since it has started mesosphere observations in June 2012. We established an application method of the PANSY radar as riometer, which makes it possible to estimate Cosmic Noise Absorptions (CNA) as proxy of relative variations on background electron density. In addition, electron density profiles from 60 to 150 km altitude are calculated by Ionospheric Model for the Auroral Zone (IMAZ) [McKinnell and Friedrich, 2007] and CNA estimated by the PANSY radar. In this presentation, we would like to focus on strong PMWE during two big geomagnetic storm events, St. Patrick's Day and the Summer Solstice 2015 Event, in order to compare observed PMWE characteristics to model background electron density. On March 19 and 22, recovery phase of St. Patrick's Day Storm, sudden PMWE intensification was detected near 60 km by the PANSY radar. At the same time, strong Cosmic Noise Absorptions (CNA) of 0.8 dB and 1.0 dB were measured, respectively. However, calculated electron density profiles did not show high electron density at the altitude where the PMWE intensification were observed. On June 22, the

  18. The evolution of electron density and temperature distributions in the topside ionosphere during magnetic storms

    NASA Technical Reports Server (NTRS)

    Cole, K. D.; Findlay, J. A.

    1974-01-01

    The latitudinal distributions of electron density and temperature during geomagnetic storms in the mid-latitude topside ionosphere are observed to change in a manner than can be related to the evolution of ring current particle populations. The region of auroral precipitation is characterized by correlated increases in electron temperature and density. Equatorwards of this region, there is a broad belt of elevated electron temperatures and depressed electron densities which is usually much broader than any stable auroral red arc distinguishable from the ground, but which is nevertheless the same basic physical phenomenon. The changes of position of this belt can be related to prior bursts of geomagnetic activity and injection of ring current particles into the magnetosphere.

  19. Comparison between GPS radio occultation electron densities and in situ satellite observations

    NASA Astrophysics Data System (ADS)

    Pedatella, N. M.; Yue, X.; Schreiner, W. S.

    2015-06-01

    Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Positioning System (GPS) radio occultation (RO) electron densities are compared with collocated in situ observations from the CHAllenging Minisatellite Payload (CHAMP) and Communications/Navigation Outage Forecasting System (C/NOFS) satellites. The comparison is restricted to observations occurring within 2° latitude and longitude and 15 min local time. The in situ observations occur at altitudes of ˜300-800 km, and the results of the present study represent the first global comparison of COSMIC electron densities at altitudes ranging from near the F region peak to the topside ionosphere. The correlation coefficient between the COSMIC and in situ observations is greater than 0.90, indicating an overall good agreement between GPS RO electron densities and CHAMP and C/NOFS satellite observations. Furthermore, when averaged over all latitudes and local times, we find a near-zero mean bias and root-mean-square difference of typically less than ±30% between the COSMIC electron densities and collocated in situ observations. The overall good agreement demonstrates that the COSMIC GPS RO observations provide an accurate measure of electron density in the topside ionosphere. The results also reveal a systematic structure to the error in the equatorial and low-latitude daytime ionosphere. This structure is related to the equatorial ionization anomaly and is consistent with the error introduced by the Abel inversion spherical symmetry assumption used to retrieve the COSMIC electron density profiles. The present study thus provides direct observational evidence of the Abel inversion error on GPS RO electron densities.

  20. Photochemical response of the nighttime mesosphere to electric field heating—Onset of electron density enhancements

    NASA Astrophysics Data System (ADS)

    Kotovsky, D. A.; Moore, R. C.

    2016-05-01

    Onsets of electron density enhancements in the upper nighttime mesosphere produced by electric field heating of electrons are examined using a photochemical model that accounts for 29 dynamic species via a set of 156 reactions. Physical mechanisms are identified which result in electron density enhancements that continuously increase for up to several seconds after electric field heating, establishing the conditions under which early VLF scattering is either "fast" (<20 ms) or slower (>20 ms, including "slow," ≥500 ms). During heating, O- ions are produced by heterolysis, e- + O2 → e- + O- + O+, and dissociative attachment, e-+ O2 → O- + O. Following heating, a significant proportion of O- ions associatively detach with molecular oxygen, O- + O2 → O3 + e-, and atomic oxygen, O- + O → O2 + e-. If enough O- ions are produced during heating such that O- detachment exceeds electron loss (predominantly attachment, e- + O3 → O2- + O, and/or electron-ion recombination), electron densities will continue to increase after heating has ended. Consequently, the total risetime of electron density enhancements produced by electric field heating is controlled by the duration of the electric field heating and (in some cases) the effects of O- detachment following heating.

  1. Effect of crosslink density on some properties of electron beam-irradiated styrene-butadiene rubber

    NASA Astrophysics Data System (ADS)

    Wang, Qingguo; Wang, Fenlan; Cheng, Kuo

    2009-11-01

    Crosslink densities of electron beam (EB)-irradiated styrene-butadiene rubber (SBR) samples were measured by using a novel magnetic resonance crosslink density spectrometer (MRCDS). With 1,1,1-trimethylolpropane triacrylate (TMPTA) loading increasing, the crosslink density of EB-irradiated SBR increases up to a certain level, and then decreases in the irradiation dose range 50-200 kGy. Tensile strength, elongation at break, thermal stability and pyrolysis products of the EB-irradiated SBR samples with different crosslink densities were also studied in this paper.

  2. Distribution of E/N and N/e/ in a cross-flow electric discharge laser. [electric field to neutral gas density and electron number density

    NASA Technical Reports Server (NTRS)

    Dunning, J. W., Jr.; Lancashire, R. B.; Manista, E. J.

    1976-01-01

    Measurements have been conducted of the effect of the convection of ions and electrons on the discharge characteristics in a large scale laser. The results are presented for one particular distribution of ballast resistance. Values of electric field, current density, input power density, ratio of electric field to neutral gas density (E/N), and electron number density were calculated on the basis of measurements of the discharge properties. In a number of graphs, the E/N ratio, current density, power density, and electron density are plotted as a function of row number (downstream position) with total discharge current and gas velocity as parameters. From the dependence of the current distribution on the total current, it appears that the electron production in the first two rows significantly affects the current flowing in the succeeding rows.

  3. Ionosphere variability during the 2009 SSW: Influence of the lunar semidiurnal tide and mechanisms producing electron density variability

    NASA Astrophysics Data System (ADS)

    Pedatella, N. M.; Liu, H.-L.; Sassi, F.; Lei, J.; Chau, J. L.; Zhang, X.

    2014-05-01

    To investigate ionosphere variability during the 2009 sudden stratosphere warming (SSW), we present simulation results that combine the Whole Atmosphere Community Climate Model Extended version and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM). The simulations reveal notable enhancements in both the migrating semidiurnal solar (SW2) and lunar (M2) tides during the SSW. The SW2 and M2 amplitudes reach ˜50 m s-1 and ˜40 m s-1, respectively, in zonal wind at E region altitudes. The dramatic increase in the M2 at these altitudes influences the dynamo generation of electric fields, and the importance of the M2 on the ionosphere variability during the 2009 SSW is demonstrated by comparing simulations with and without the M2. TIME-GCM simulations that incorporate the M2 are found to be in good agreement with Jicamarca Incoherent Scatter Radar vertical plasma drifts and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations of the maximum F region electron density. The agreement with observations is worse if the M2 is not included in the simulation, demonstrating that the lunar tide is an important contributor to the ionosphere variability during the 2009 SSW. We additionally investigate sources of the F region electron density variability during the SSW. The primary driver of the electron density variability is changes in electric fields. Changes in meridional neutral winds and thermosphere composition are found to also contribute to the electron density variability during the 2009 SSW. The electron density variability for the 2009 SSW is therefore not solely due to variability in electric fields as previously thought.

  4. Structural, elastic, electronic, and thermodynamic properties of MgAgSb investigated by density functional theory

    NASA Astrophysics Data System (ADS)

    Wang, Jun-Fei; Fu, Xiao-Nan; Zhang, Xiao-Dong; Wang, Jun-Tao; Li, Xiao-Dong; Jiang, Zhen-Yi

    2016-08-01

    The structural, elastic, electronic, and thermodynamic properties of thermoelectric material MgAgSb in γ,β,α phases are studied with first-principles calculations based on density functional theory. The optimized lattice constants accord well with the experimental data. According to the calculated total energy of the three phases, the phase transition order is determined from α to γ phase with cooling, which is in agreement with the experimental result. The physical properties such as elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and anisotropy factor are also discussed and analyzed, which indicates that the three structures are mechanically stable and each has a ductile feature. The Debye temperature is deduced from the elastic properties. The total density of states (TDOS) and partial density of states (PDOS) of the three phases are investigated. The TDOS results show that the γ phase is most stable with a pseudogap near the Fermi level, and the PDOS analysis indicates that the conduction band of the three phases is composed mostly of Mg-3s, Ag-4d, and Sb-5p. In addition, the changes of the free energy, entropy, specific heat, thermal expansion of γ-MgAgSb with temperature are obtained successfully. The obtained results above are important parameters for further experimental and theoretical tuning of doped MgAgSb as a thermoelectric material at high temperature. Project supported by the National Natural Science Foundation of China (Grant No. 11504088), the Fund from Henan University of Technology, China (Grant Nos. 2014YWQN08 and 2013JCYJ12), the Natural Science Fund from the Henan Provincial Education Department, China (Grant No. 16A140027), the Natural Science Foundation of Shaanxi Province of China (Grant Nos. 2013JQ1018 and 15JK1759), and the Science Foundation of Northwest University of China (Grant No. 14NW23).

  5. Decay of Bloch oscillations in the charge-density-wave ordered phase of an all electronic charge density wave state

    NASA Astrophysics Data System (ADS)

    Matveev, Oleg; Shvaika, Andrij; Devereaux, Thomas; Freericks, James

    The charge-density-wave phase of the Falicov-Kimball model displays a number of anomalous behavior including the appearance of subgap density of states as the temperature increases. These subgap states should have a significant impact on transport properties, particularly the nonlinear response of the system to a large dc electric field. Using the Kadanoff-Baym-Keldysh formalism, we employ nonequilibrium dynamical mean-field theory to exactly solve for this nonlinear response. We examine both the current and the order parameter of the conduction electrons as the ordered system is driven by a dc electric field. Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, Lviv, Ukraine.

  6. Bayesian spatiotemporal analysis of zero-inflated biological population density data by a delta-normal spatiotemporal additive model.

    PubMed

    Arcuti, Simona; Pollice, Alessio; Ribecco, Nunziata; D'Onghia, Gianfranco

    2016-03-01

    We evaluate the spatiotemporal changes in the density of a particular species of crustacean known as deep-water rose shrimp, Parapenaeus longirostris, based on biological sample data collected during trawl surveys carried out from 1995 to 2006 as part of the international project MEDITS (MEDiterranean International Trawl Surveys). As is the case for many biological variables, density data are continuous and characterized by unusually large amounts of zeros, accompanied by a skewed distribution of the remaining values. Here we analyze the normalized density data by a Bayesian delta-normal semiparametric additive model including the effects of covariates, using penalized regression with low-rank thin-plate splines for nonlinear spatial and temporal effects. Modeling the zero and nonzero values by two joint processes, as we propose in this work, allows to obtain great flexibility and easily handling of complex likelihood functions, avoiding inaccurate statistical inferences due to misclassification of the high proportion of exact zeros in the model. Bayesian model estimation is obtained by Markov chain Monte Carlo simulations, suitably specifying the complex likelihood function of the zero-inflated density data. The study highlights relevant nonlinear spatial and temporal effects and the influence of the annual Mediterranean oscillations index and of the sea surface temperature on the distribution of the deep-water rose shrimp density. PMID:26418888

  7. Properties of Inconel 625 Mesh Structures Grown by Electron Beam Additive Manufacturing

    SciTech Connect

    List III, Frederick Alyious; Dehoff, Ryan R; Lowe, Larry E; Sames, William J

    2014-01-01

    Relationships between electron beam parameters (beam current, beam speed, and beam focus) and physical properties (mass, diameter, elastic modulus, and yield strength) have been investigated for Inconel 625 mesh cubes fabricated using an additive manufacturing technology based on electron beam melting. The elastic modulus and yield strength of the mesh cubes have been systematically varied by approximately a factor of ten by changing the electron beam parameters. Simple models have been used to understand better these relationships. Structural anisotropies of the mesh associated with the layered build architecture have been observed and may contribute, along with microstructural anisotropies, to the anisotropic mechanical properties of the mesh. Knowledge of this kind is likely applicable to other metal and alloy systems and is essential to rapidly realize the full potential of this burgeoning technology.

  8. Density functional theory studies of electron interaction with DNA: can zero eV electrons induce strand breaks?

    PubMed

    Li, Xifeng; Sevilla, Michael D; Sanche, Léon

    2003-11-12

    The discovery of DNA strand breaks induced by low energy secondary electrons sparks a necessity to elucidate the mechanism. Through theoretical studies based on a sugar-phosphate-sugar model that mimics a backbone section of the DNA strand, it is found that bond cleavages at 3' or 5'C-O sites after addition of an electron are possible with a ca. 10 kcal/mol activation barrier. Moreover, the potential energy surfaces show that dissociation at both sites is highly favorable thermodynamically. Although the phosphate group in DNA is not a favored site for electron attachment because of competitive electron transfer to the bases, any electrons which attach to phosphates on first encounter may induce strand breaks even when the electron energy is near zero eV. These findings have profound implication as low energy secondary electrons are abundantly generated in all types of ionization radiation. PMID:14599198

  9. Uniform electron gases. II. The generalized local density approximation in one dimension

    SciTech Connect

    Loos, Pierre-François Ball, Caleb J.; Gill, Peter M. W.

    2014-05-14

    We introduce a generalization (gLDA) of the traditional Local Density Approximation (LDA) within density functional theory. The gLDA uses both the one-electron Seitz radius r{sub s} and a two-electron hole curvature parameter η at each point in space. The gLDA reduces to the LDA when applied to the infinite homogeneous electron gas but, unlike the LDA, it is also exact for finite uniform electron gases on spheres. We present an explicit gLDA functional for the correlation energy of electrons that are confined to a one-dimensional space and compare its accuracy with LDA, second- and third-order Møller-Plesset perturbation energies, and exact calculations for a variety of inhomogeneous systems.

  10. Electron density and temperature of gas-temperature-dependent cryoplasma jet

    SciTech Connect

    Noma, Yuri; Hyuk Choi, Jai; Muneoka, Hitoshi; Terashima, Kazuo

    2011-03-01

    A microsize cryoplasma jet was developed and analyzed at plasma gas temperatures ranging from room temperature down to 5 K. Experimental results obtained from optical emission spectroscopy and current-voltage measurements indicate that the average electron density and electron temperature of the cryoplasma jet depend on the gas temperature. In particular, the electron temperature in the cryoplasma starts to decrease rapidly near 60 K from about 13 eV at 60 K to 2 eV at 5 K, while the electron density increases from about 10{sup 9} to approximately 10{sup 12} cm{sup -3} from room temperature to 5 K. This phenomenon induces an increase in the Coulomb interaction between electrons, which can be explained by the virial equation of state.

  11. Influence of modifying additives on the electronic state of supported palladium

    NASA Astrophysics Data System (ADS)

    Pestryakov, A. N.; Lunin, V. V.; Fuentes, S.; Bogdanchikova, N.; Barrera, A.

    2003-01-01

    The influence of modifying additives of Ce, Zr, La and Cs oxides on the electronic state of palladium supported on γ-Al 2O 3 has been studied by IR-spectroscopy of adsorbed CO, diffuse reflectance UV-visible spectroscopy, X-ray diffraction (XRD) and H 2 chemisorption. The modified supports have been prepared using impregnation, coprecipitation and sol-gel methods. It is established that Ce and Zr oxide additives increase the effective charge of palladium ions whereas La and Cs oxides lower it. The effect of metal-support interaction is stronger in samples prepared by sol-gel than by coprecipitation

  12. Electron density modulation in an asymmetric bipolar pulsed dc magnetron discharge

    SciTech Connect

    Karkari, S. K.; Ellingboe, A. R.; Gaman, C.; Swindells, I.; Bradley, J. W.

    2007-09-15

    This paper investigates the spatial and temporal variation in plasma electron density over a region between 5 and 10 cm above the race-track region of a pulsed magnetron sputtering target. The pulse operation is performed using an asymmetric bipolar pulsed dc power supply, which provides a sequence of large negative ''on-phase'' voltage (-350 V) and a small positive ''reverse-phase'' voltage (+10 V) for 55% of the pulse duration (10 {mu}s). The electron density is measured using a floating microwave hairpin resonance probe. The results show electron expulsion from the target in the initial on phase, which propagates with a characteristic speed exceeding the ion thermal speed. In the steady state on phase, a consistent higher density is observed. A quantitative model has been developed to explain the resultant density drops in the initial on phase. While in the reverse phase, we observed an anomalous growth in density at a specific location from the target (d>7 cm). The mechanism behind the increase in electron density has been attributed to the modulation in spatial plasma potential, which was measured earlier in the same apparatus using a floating emissive probe [J. W. Bradley et al., Plasma Sources Sci. Technol. 13, 189 (2004)].

  13. [Research on electron density in DC needle-plate corona discharge at atmospheric pressure].

    PubMed

    Liu, Zhi-Qiang; Guo, Wei; Liu, Tao-Tao; Wu, Wen-Shuo; Liu, Shu-Min

    2013-11-01

    Using needle-plate discharge device, corona discharge experiment was done in the atmosphere. Through photo of spot size of light-emitting area, the relationship between the voltage and thickness of corona layer was discussed. When the distance between tip and plate is fixed, the thickness of corona layer increases with the increase in voltage; when the voltage is fixed, the thickness of corona layer decreases with the increase in the distance between tip and plate. As spectral intensity of N2 (C3pi(u)) (337.1 nm)reflects high energy electron density, it was measured with emission spectrometry. The results show that high energy electron density is the biggest near the needle tip and the relationship between high energy electron density and voltage is basically linear increasing. Fixing voltage, high energy electron density decreases with the increase in the distance between tip and plate. When the voltage and the distance between tip and plate are fixed, the high energy electron density increases with the decrease in the curvature radius of needle tip. These results are of great importance for the study of plasma parameters of corona discharge. PMID:24555347

  14. Analysis of density effects in plasmas and their influence on electron-impact cross sections

    NASA Astrophysics Data System (ADS)

    Belkhiri, M.; Poirier, M.

    2014-12-01

    Density effects in plasmas are analyzed using a Thomas-Fermi approach for free electrons. First, scaling properties are determined for the free-electron potential and density. For hydrogen-like ions, the first two terms of an analytical expansion of this potential as a function of the plasma coupling parameter are obtained. In such ions, from these properties and numerical calculations, a simple analytical fit is proposed for the plasma potential, which holds for any electron density, temperature, and atomic number, at least assuming that Maxwell-Boltzmann statistics is applicable. This allows one to analyze perturbatively the influence of the plasma potential on energies, wave functions, transition rates, and electron-impact collision rates for single-electron ions. Second, plasmas with an arbitrary charge state are considered, using a modified version of the Flexible Atomic Code (FAC) package with a plasma potential based on a Thomas-Fermi approach. Various methods for the collision cross-section calculations are reviewed. The influence of plasma density on these cross sections is analyzed in detail. Moreover, it is demonstrated that, in a given transition, the radiative and collisional-excitation rates are differently affected by the plasma density. Some analytical expressions are proposed for hydrogen-like ions in the limit where the Born or Lotz approximation applies and are compared to the numerical results from the FAC.

  15. Temporal-spatial modeling of non-linear electron density enhancement due to successive lightning strokes

    NASA Astrophysics Data System (ADS)

    Lay, E. H.; Holzworth, R. H.; Cho, M.; Rodger, C. J.; Thomas, J. N.

    2008-12-01

    We report results on the temporal-spatial modeling of non-linear electron density enhancement due to successive lightning strokes using World Wide Lightning Location Network (WWLLN) data to experimentally describe the rate of large lightning strokes. The WWLLN provides real-time lightning locations globally by measuring the very low frequency (VLF) radiation emanating from lightning discharges. These WWLLN stroke rates are used as input to an axi-symmetric FDTD model that describes the non-linear effect of lightning electromagnetic pulses (EMP) on the ionosphere. This non-linear effect results from accumulating electron density modifications due to the interaction of the EMP from multiple successive lightning strokes with the lower ionosphere. Further studies must be completed to narrow uncertainties in the model, but the qualitative ionospheric response to successive EMPs is presented in two-dimensional, axi-symmetric space. Results from this study show that the non-linear effect of lightning EMP due to successive lightning strokes must be taken into account and varies with altitude. The limiting maximum electron density is reached earlier in time for higher altitudes, and the most significant effect occurs at 88 km. The limiting maximum modeled electron density profile in the 83- to 91-km altitude range does not depend on the initial electron density.

  16. Field-aligned Electron Density Measurements and Comparison with Diffusive Equilibrium Models

    NASA Astrophysics Data System (ADS)

    Ozhogin, P.; Song, P.; Tu, J.; Reinisch, B. W.

    2012-12-01

    The diffusive equilibrium model describes the electron and ion densities along the magnetic field line in the plasmasphere and has been widely used in, for example, ray tracing and pitch-angle scattering calculations. It is based on the hydrostatic equilibrium with the electrostatic force that acts on ions and electrons along geomagnetic field lines while there is actually no motion or diffusion of the plasma involved. The model requires multiple input parameters: electron density and ion composition (H+, He+, O+) at a base level for a magnetic field line in the ionosphere, and the (electron or ion) temperature in the plasmasphere. It has been recognized that these input parameters have to be flexible from one field line to another so that the model output does not contradict some known observed relationship. However, while the flexibility provides the possibility to fit any individual observed density distribution which is measured across many different field lines, the model prediction becomes questionable along a single field line. Since the plasma density measurements along a single field line were not available until recently, the validity of the diffusive equilibrium models has not been verified independently. This study is to investigate both qualitatively and quantitatively whether the fundamental functional form of the diffusive equilibrium model can be useful and consistent with a large database of field-aligned electron density distributions from the radio plasma imager (RPI) instrument onboard the IMAGE satellite.

  17. Observations and Modeling of the Nighttime Electron Density Enhancement in the Mid-latitude Ionosphere

    NASA Astrophysics Data System (ADS)

    Chen, C.; Saito, A.; Lin, C.; Huba, J. D.; Liu, J. G.

    2010-12-01

    In this study, we compare the observational data from FORMOSAT-3/COSMIC and theoretical model results performed by SAMI2 (Sami2 is Another Model of the Ionosphere) for studying the longitudinal structure of the Mid-latitude Summer Nighttime Anomaly (MSNA). In order to study the occurrence of the nighttime electron density enhancement, we defined MSNA index by the ratio of the difference of the nighttime and daytime electron densities. The observational results by the FORMOSAT-3/COSMIC satellites show that there are three obvious nighttime electron density enhancement areas around South American, European, and Northeast Asian regions during local summer. The SAMI2 model can also successfully reproduce the ionospheric MSNA structure during local summer on both hemispheres, except for Northeast Asian region. This difference between observation and model simulation may be caused by the difference between the neutral wind model and the real winds. The physical mechanisms for the longitudinal structure of the MSNA are investigated in the different model conditions. Results show that the equatorward meridional neutral winds can drive the electron density up to a higher altitude along the magnetic field lines and the longer plasma production rate by solar EUV at higher latitudes in the summer time can provide the electron density source in the nighttime ionosphere. We concluded that the combination effect by the neutral wind and the plasma production rate play the important role of the MSNA longitudinal structure.

  18. A density-temperature description of the outer electron radiation belt during geomagnetic storms

    SciTech Connect

    Borovsky, Joseph E; Cayton, Thomas E; Denton, Michael H

    2009-01-01

    Electron flux measurements from 7 satellites in geosynchronous orbit from 1990-2007 are fit with relativistic bi-Maxwellians, yielding a number density n and temperature T description of the outer electron radiation belt. For 54.5 spacecraft years of measurements the median value ofn is 3.7x10-4 cm-3 and the median value ofT is 142 keY. General statistical properties of n, T, and the 1.1-1.5 MeV flux J are investigated, including local-time and solar-cycle dependencies. Using superposed-epoch analysis triggered on storm onset, the evolution of the outer electron radiation belt through high-speed-steam-driven storms is investigated. The number density decay during the calm before the storm is seen, relativistic-electron dropouts and recoveries from dropout are investigated, and the heating of the outer electron radiation belt during storms is examined. Using four different triggers (SSCs, southward-IMF CME sheaths, southward-IMF magnetic clouds, and minimum Dst), CME-driven storms are analyzed with superposed-epoch techniques. For CME-driven storms an absence of a density decay prior to storm onset is found, the compression of the outer electron radiation belt at time of SSC is analyzed, the number-density increase and temperature decrease during storm main phase is seen, and the increase in density and temperature during storm recovery phase is observed. Differences are found between the density-temperature and the flux descriptions, with more information for analysis being available in the density-temperature description.

  19. Electron-radiation effects on the ac and dc electrical properties and unpaired electron densities of three aerospace polymers

    NASA Technical Reports Server (NTRS)

    Long, Sheila Ann T.; Long, Edward R., Jr.; Ries, Heidi R.; Harries, Wynford L.

    1986-01-01

    The effects of gigarad-level total absorbed doses from 1-MeV electrons on the post-irradiation alternating-current (ac) and direct-current (dc) electrical properties and the unpaired electron densities have been studied for Kapton, Ultem, and Mylar. The unpaired electron densities (determined from electron paramagnetic resonance spectroscopy) and the dc electrical conductivities of the irradiated materials were monitored as functions of time following the exposures to determine their decay characteristics at room temperature. The elevated-temperature ac electrical dissipations of the Ultem and Mylar were affected by the radiation. The dc conductivity of the Kapton increased by five orders of magnitude, while the dc conductivities of the Ultem and Mylar increased by less than an order of magnitude, due to the radiation. The observed radiation-generated changes in the ac electrical dissipations are explained in terms of known radiation-generated changes in the molecular structures of the three materials. A preliminary model relating the dc electrical conductivity and the unpaired electron density in the Kapton is proposed.

  20. Electron-radiation effects on the ac and dc electrical properties and unpaired electron densities of three aerospace polymers

    NASA Astrophysics Data System (ADS)

    Long, Sheila Ann T.; Long, Edward R., Jr.; Ries, Heidi R.; Harries, Wynford L.

    1986-12-01

    The effects of gigarad-level total absorbed doses from 1-MeV electrons on the post-irradiation alternating-current (ac) and direct-current (dc) electrical properties and the unpaired electron densities have been studied for Kapton, Ultem, and Mylar. The unpaired electron densities (determined from electron paramagnetic resonance spectroscopy) and the dc electrical conductivities of the irradiated materials were monitored as functions of time following the exposures to determine their decay characteristics at room temperature. The elevated-temperature ac electrical dissipations of the Ultem and Mylar were affected by the radiation. The dc conductivity of the Kapton increased by five orders of magnitude, while the dc conductivities of the Ultem and Mylar increased by less than an order of magnitude, due to the radiation. The observed radiation-generated changes in the ac electrical dissipations are explained in terms of known radiation-generated changes in the molecular structures of the three materials. A preliminary model relating the dc electrical conductivity and the unpaired electron density in the Kapton is proposed.

  1. The electron localization as the information content of the conditional pair density

    NASA Astrophysics Data System (ADS)

    Urbina, Andres S.; Torres, F. Javier; Rincon, Luis

    2016-06-01

    In the present work, the information gained by an electron for "knowing" about the position of another electron with the same spin is calculated using the Kullback-Leibler divergence (DKL) between the same-spin conditional pair probability density and the marginal probability. DKL is proposed as an electron localization measurement, based on the observation that regions of the space with high information gain can be associated with strong correlated localized electrons. Taking into consideration the scaling of DKL with the number of σ-spin electrons of a system (Nσ), the quantity χ = (Nσ - 1) DKLfcut is introduced as a general descriptor that allows the quantification of the electron localization in the space. fcut is defined such that it goes smoothly to zero for negligible densities. χ is computed for a selection of atomic and molecular systems in order to test its capability to determine the region in space where electrons are localized. As a general conclusion, χ is able to explain the electron structure of molecules on the basis of chemical grounds with a high degree of success and to produce a clear differentiation of the localization of electrons that can be traced to the fluctuation in the average number of electrons in these regions.

  2. The electron localization as the information content of the conditional pair density.

    PubMed

    Urbina, Andres S; Torres, F Javier; Rincon, Luis

    2016-06-28

    In the present work, the information gained by an electron for "knowing" about the position of another electron with the same spin is calculated using the Kullback-Leibler divergence (DKL) between the same-spin conditional pair probability density and the marginal probability. DKL is proposed as an electron localization measurement, based on the observation that regions of the space with high information gain can be associated with strong correlated localized electrons. Taking into consideration the scaling of DKL with the number of σ-spin electrons of a system (N(σ)), the quantity χ = (N(σ) - 1) DKLfcut is introduced as a general descriptor that allows the quantification of the electron localization in the space. fcut is defined such that it goes smoothly to zero for negligible densities. χ is computed for a selection of atomic and molecular systems in order to test its capability to determine the region in space where electrons are localized. As a general conclusion, χ is able to explain the electron structure of molecules on the basis of chemical grounds with a high degree of success and to produce a clear differentiation of the localization of electrons that can be traced to the fluctuation in the average number of electrons in these regions. PMID:27369494

  3. Measurements of the Electron Cloud Density in the PEP-II Low Energy Ring

    SciTech Connect

    Byrd, J.; De Santis, S.; Sonnad, K.; Caspers, F.; Kroyer, T.; Krasnykh, A.; Pivi, M.; /SLAC

    2012-04-10

    Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave that is independently excited and transmitted over a section of the accelerator. We infer the absolute phase shift with relatively high accuracy from the phase modulation of the transmission due to the modulation of the electron cloud density from a gap in the positively charged beam. We have used this technique for the first time to measure the average electron cloud density over a 50 m straight section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center. We have also measured the variation of the density by using low field solenoid magnets to control the electrons.

  4. Early time evolution of negative ion clouds and electron density depletions produced during electron attachment chemical release experiments

    NASA Technical Reports Server (NTRS)

    Scales, W. A.; Bernhardt, P. A.; Ganguli, G.

    1994-01-01

    Two-dimensional electrostatic particle-in-cell simulations are used to study the early time evolution of electron depletions and negative ion clouds produced during electron attachment chemical releases in the ionosphere. The simulation model considers the evolution in the plane perpendicular to the magnetic field and a three-species plasma that contains electrons, positive ions, and also heavy negative ions that result as a by-product of the electron attachment reaction. The early time evolution (less than the negative ion cyclotron period) of the system shows that a negative charge surplus initially develops outside of the depletion boundary as the heavy negative ions move across the boundary. The electrons are initially restricted from moving into the depletion due to the magnetic field. An inhomogenous electric field develops across the boundary layer due to this charge separation. A highly sheared electron flow velocity develops in the depletion boundary due to E x B and Delta-N x B drifts that result from electron density gradients and this inhomogenous electric field. Structure eventually develops in the depletion boundary layer due to low-frequency electrostatic waves that have growth times shorter than the negative ion cyclotron period. It is proposed that these waves are most likely produced by the electron-ion hybrid instability that results from sufficiently large shears in the electron flow velocity.

  5. Application of seamless vertical profiles for use in the topside electron density modeling

    NASA Astrophysics Data System (ADS)

    Triskova, L.; Galkin, I.; Truhlik, V.; Reinisch, B. W.

    Modeling of the topside electron (ion) density profiles, usually done within the Booker formalism, greatly benefits from the recently introduced representation by the Chapman function with continuously varying scale height, dubbed a vary-Chap function. The vary-Chap function is capable of producing smooth and seamless altitude dependences from a variety of previously developed empirical models. This paper presents a successful project of using the vary-Chap function to obtain a seamless representation of the electron density profiles based on three global models; the IRI (International Reference Ionosphere) for the bottomside ionosphere and an empirical topside electron density model and an empirical upper transition height model. The results show the advantage of the proposed method and its potential for implementation in the IRI.

  6. An efficient method for computing the QTAIM topology of a scalar field: the electron density case.

    PubMed

    Rodríguez, Juan I

    2013-03-30

    An efficient method for computing the quantum theory of atoms in molecules (QTAIM) topology of the electron density (or other scalar field) is presented. A modified Newton-Raphson algorithm was implemented for finding the critical points (CP) of the electron density. Bond paths were constructed with the second-order Runge-Kutta method. Vectorization of the present algorithm makes it to scale linearly with the system size. The parallel efficiency decreases with the number of processors (from 70% to 50%) with an average of 54%. The accuracy and performance of the method are demonstrated by computing the QTAIM topology of the electron density of a series of representative molecules. Our results show that our algorithm might allow to apply QTAIM analysis to large systems (carbon nanotubes, polymers, fullerenes) considered unreachable until now. PMID:23175458

  7. Electron beam manipulation, injection and acceleration in plasma wakefield accelerators by optically generated plasma density spikes

    NASA Astrophysics Data System (ADS)

    Wittig, Georg; Karger, Oliver S.; Knetsch, Alexander; Xi, Yunfeng; Deng, Aihua; Rosenzweig, James B.; Bruhwiler, David L.; Smith, Jonathan; Sheng, Zheng-Ming; Jaroszynski, Dino A.; Manahan, Grace G.; Hidding, Bernhard

    2016-09-01

    We discuss considerations regarding a novel and robust scheme for optically triggered electron bunch generation in plasma wakefield accelerators [1]. In this technique, a transversely propagating focused laser pulse ignites a quasi-stationary plasma column before the arrival of the plasma wake. This localized plasma density enhancement or optical "plasma torch" distorts the blowout during the arrival of the electron drive bunch and modifies the electron trajectories, resulting in controlled injection. By changing the gas density, and the laser pulse parameters such as beam waist and intensity, and by moving the focal point of the laser pulse, the shape of the plasma torch, and therefore the generated trailing beam, can be tuned easily. The proposed method is much more flexible and faster in generating gas density transitions when compared to hydrodynamics-based methods, and it accommodates experimentalists needs as it is a purely optical process and straightforward to implement.

  8. Propagation of terahertz waves in an atmospheric pressure microplasma with Epstein electron density profile

    SciTech Connect

    Yuan Chengxun; Zhou Zhongxiang; Zhang, Jingwen W.; Sun Hongguo; Wang He; Du Yanwei; Xiang Xiaoli

    2011-03-15

    Propagation properties of terahertz (THz) waves in a bounded atmospheric-pressure microplasma (AMP) are analyzed in this study. A modified Epstein profile model is used to simulate the electron density distribution caused by the plasma sheaths. By introducing the dielectric constant of a Drude-Lorentz model and using the method of dividing the plasma into a series of subslabs with uniform electron density, the coefficients of power reflection, transmission, and absorption are derived for a bounded microplasma structure. The effects of size of microplasma, electron density profile, and collision frequency on the propagation of THz waves are analyzed numerically. The results indicate that the propagation of THz waves in AMPs depend greatly on the above three parameters. It is demonstrated that the THz wave can play an important role in AMPs diagnostics; meanwhile, the AMP can be used as a novel potential tool to control THz wave propagation.

  9. Radial Electron Temperature and Density Measurements Using Thomson Scattering System in GAMMA 10/PDX

    NASA Astrophysics Data System (ADS)

    Yoshikawa, M.; Ohta, K.; Wang, X.; Chikatsu, M.; Kohagura, J.; Shima, Y.; Sakamoto, M.; Imai, T.; Nakashima, Y.; Yasuhara, R.; Yamada, I.; Funaba, H.; Minami, T.

    2015-11-01

    A Thomson scattering (TS) system in GAMMA 10/PDX has been developed for the measurement of radial profiles of electron temperature and density in a single plasma and laser shot. The TS system has a large solid angle optical collection system and high-sensitivity signal detection system. The TS signals are obtained using four-channel high-speed digital oscilloscopes controlled by a Windows PC. We designed the acquisition program for six oscilloscopes to obtain 10-Hz TS signals in a single plasma shot, following which the time-dependent electron temperatures and densities can be determined. Moreover, in order to obtain larger TS signal intensity in the edge region, we added a second collection mirror. The radial electron temperatures and densities at six radial positions in GAMMA 10/PDX were successfully obtained.

  10. Measuring the Density of a Molecular Cluster Injector via Visible Emission from an Electron Beam

    SciTech Connect

    Lundberg, D. P.; Kaita, R.; Majeski, R. M.; Stotler, D. P.

    2010-06-28

    A method to measure the density distribution of a dense hydrogen gas jet is pre- sented. A Mach 5.5 nozzle is cooled to 80K to form a flow capable of molecular cluster formation. A 250V, 10mA electron beam collides with the jet and produces Hα emission that is viewed by a fast camera. The high density of the jet, several 1016cm-3, results in substantial electron depletion, which attenuates the Hα emission. The attenuated emission measurement, combined with a simplified electron-molecule collision model, allows us to determine the molecular density profile via a simple iterative calculation.

  11. Likelihood-based modification of experimental crystal structure electron density maps

    DOEpatents

    Terwilliger, Thomas C.

    2005-04-16

    A maximum-likelihood method for improves an electron density map of an experimental crystal structure. A likelihood of a set of structure factors {F.sub.h } is formed for the experimental crystal structure as (1) the likelihood of having obtained an observed set of structure factors {F.sub.h.sup.OBS } if structure factor set {F.sub.h } was correct, and (2) the likelihood that an electron density map resulting from {F.sub.h } is consistent with selected prior knowledge about the experimental crystal structure. The set of structure factors {F.sub.h } is then adjusted to maximize the likelihood of {F.sub.h } for the experimental crystal structure. An improved electron density map is constructed with the maximized structure factors.

  12. Measurement of the electron density in a subatmospheric dielectric barrier discharge by spectral line shape

    SciTech Connect

    Dong Lifang; Qi Yuyan; Liu Weiyuan; Fan Weili

    2009-07-01

    The electron density in a subatmospheric dielectric barrier discharge by using argon spectral line shape is measured for the first time. With the gas pressure increasing in the range of 1x10{sup 4} Pa-6x10{sup 4} Pa, the line profiles of argon 696.54 nm are measured. An asymmetrical deconvolution procedure is applied to separate the Gaussian and Lorentzian profile from the measured spectral line. The gas temperature is estimated by using rotational temperature of N{sub 2}{sup +}. By subtracting the van der Waals broadening and partial Lorentzian instrumental broadening from the Lorentzian broadening, the Stark broadening is obtained and used to estimate the electron density. It is found that the electron density in dielectric barrier discharge increases with the increase in gas pressure.

  13. Improvement of retrieved FORMOSAT-3/COSMIC electron densities validated by ionospheric sounder measurements at Jicamarca

    NASA Astrophysics Data System (ADS)

    Aragon-Angel, A.; Liou, Y.-A.; Lee, C.-C.; Reinisch, B. W.; HernáNdez-Pajares, M.; Juan, M.; Sanz, J.

    2011-10-01

    Inversion techniques applied to GPS-LEO radio occultation data allow the retrieval of accurate and worldwide-distributed refractivity profiles, which, in the case of the ionosphere, can be converted into electron densities providing information regarding the electron content distribution in this atmospheric region. In order to guarantee the accuracy of the electron density retrievals, two key points should be taken into account: the horizontal gradients of the electronic distribution and the topside electron content above the LEO orbit. The deployment in April 2006 of the satellite Constellation Observing System for Meteorology Ionosphere and Climate (FORMOSAT-3/COSMIC), carrying GPS receivers on board, provides valuable radio occultation data with global and almost uniform coverage overcoming the sparsity of data from previous LEO missions (for instance, GPS/MET, CHAMP, and SAC-C). This is also one of the main limitations of other sources providing direct observations, such as ionosondes. In this study, the improved Abel transform inversion is used to analyze derived ionospheric electron density profiles of the whole year 2007 in a scenario with very high electron density gradients: The neighboring area of Jicamarca (76.9°W, 12°S, dip latitude: 1°N), Perú, located at very low latitude and close to the geomagnetic equator, and the influence of the Appleton-Hartree equatorial anomaly (Davies, 1990). Moreover, different strategies to account for the topside electron content in the occultation data inversion are compared and discussed, taking advantage of the availability of FORMOSAT-3/COSMIC data sets and manually calibrated measurements from Jicamarca DPS. Statistical results show that for the current scenario the improvements are only about 10%, evidencing that the lack of colocation is one important source of error for the classical Abel inversion. Implications with respect to the plasmaspheric contribution have been derived from this data set analysis, in

  14. Determination of Kohn-Sham effective potentials from electron densities using the differential virial theorem.

    PubMed

    Ryabinkin, Ilya G; Staroverov, Viktor N

    2012-10-28

    We present an accurate method for constructing the Kohn-Sham effective potential corresponding to a given electron density in one-dimensional and spherically symmetric systems. The method is based on the differential virial theorem--an exact relation between the effective potential, the electron density, and the kinetic energy density. A distinctive feature of the proposed technique is that it employs a size-consistent bosonic reference potential to ensure the correct asymptotic behavior of the resulting Kohn-Sham potential. We describe a practical implementation of our method and use it to obtain high-quality exchange-correlation and correlation potentials of the neon and argon atoms from ab initio densities generated in large Slater- and Gaussian-type basis sets. PMID:23126701

  15. The effect of iron vapor on electron density of hyperbaric arc plasma

    SciTech Connect

    Ogawa, Yoji

    1993-12-31

    In the hyperbaric arc welding, the arc characteristics are very strongly affected by the local density of iron vapor, because of its lower ionization potential compared with those of the components of shielding gas for hyperbaric welding such as argon and helium. The set of Saha-Eggert equations which include the ionization of iron vapor is solved from the assumption of local thermodynamic equilibrium. Particle densities of argon-helium mixed shielding gas which is contaminated by iron vapor are calculated for temperatures between 3,000 and 30,000 K and pressures between 0.1 and 100 atmospheres (0.01 and 10 MPa). The results show that electron densities at relatively low temperature are increased by iron vapor, and the amount is directly proportional to the square root of contaminated coefficient of iron vapor in the shielding gas. The effect of component ratios of argon and helium on electron densities is also considered in detail.

  16. Discussion of the reliability of electron densities and energies interpreted from data and limits on the proton energy and density

    NASA Technical Reports Server (NTRS)

    Beard, D. B.

    1972-01-01

    Analysis of radio observations of Jupiter were changed to take into account the antenna resolution. A dipole magnetic field with a surface equatorial value of 7 gauss is assumed. The electron temperature is found to increase for r 2.5 Jupiter radii with decreasing r as 1/r cubed, reaching a peak of about 100 MeV at r = 2.5 Jupiter radii. For r 2.5 Jupiter radii, the electron temperature goes as r to the 6th power because of energy lost to radiation. The consequences of making an upper estimate on the proton flux by assuming the magnetic field is loaded with all the energetic protons it can hold are described. The upper limits of proton energy, density, flux, and energy flux are calculated for 1, 2, 2.5, 3, and 6 Jupiter radii. The proton energy and velocity estimates are considered to be fairly reliable; the upper limit to the number density is probably much higher than actuality.

  17. Electron density and temperature profile diagnostics for C-2 field reversed configuration plasmas

    SciTech Connect

    Deng, B. H.; Kinley, J. S.; Schroeder, J.

    2012-10-15

    The 9-point Thomson scattering diagnostic system for the C-2 field reversed configuration plasmas is improved and the measured electron temperature profiles are consistent with theoretical expectations. Rayleigh scattering revealed a finite line width of the ruby laser emission, which complicates density calibration. Taking advantage of the plasma wobble motion, density profile reconstruction accuracy from the 6-chord two-color CO{sub 2}/HeNe interferometer data is improved.

  18. Tomography of the Galactic free electron density with the Square Kilometer Array

    NASA Astrophysics Data System (ADS)

    Greiner, M.; Schnitzeler, D. H. F. M.; Enßlin, T. A.

    2016-05-01

    We present a new algorithm for reconstructing the Galactic free electron density from pulsar dispersion measures. The algorithm performs a nonparametric tomography for a density field with an arbitrary amount of degrees of freedom. It is based on approximating the Galactic free electron density as the product of a profile function with a statistically isotropic and homogeneous log-normal field. Under this approximation the algorithm generates a map of the free electron density as well as an uncertainty estimate without the need of information about the power spectrum. The uncertainties of the pulsar distances are treated consistently by an iterative procedure. We tested the algorithm using the NE2001 model with modified fluctuations as a Galaxy model, pulsar populations generated from the Lorimer population model, and mock observations emulating the upcoming Square Kilometer Array (SKA). We show the quality of the reconstruction for mock data sets containing between 1000 and 10 000 pulsars with distance uncertainties of up to 25%. Our results show that with the SKA nonparametric tomography of the Galactic free electron density becomes feasible, but the quality of the reconstruction is very sensitive to the distance uncertainties.

  19. Feedback control of plasma electron density and ion energy in an inductively coupled plasma etcher

    SciTech Connect

    Lin Chaung; Leou, K.-C.; Huang, H.-M.; Hsieh, C.-H.

    2009-01-15

    Here the authors report the development of a fuzzy logic based feedback control of the plasma electron density and ion energy for high density plasma etch process. The plasma electron density was measured using their recently developed transmission line microstrip microwave interferometer mounted on the chamber wall, and the rf voltage was measured by a commercial impedance meter connected to the wafer stage. The actuators were two 13.56 MHz rf power generators which provided the inductively coupled plasma power and bias power, respectively. The control system adopted the fuzzy logic control algorithm to reduce frequent actuator action resulting from measurement noise. The experimental results show that the first wafer effect can be eliminated using closed-loop control for both poly-Si and HfO{sub 2} etching. In particular, for the HfO2 etch, the controlled variables in this work were much more effective than the previous one where ion current was controlled, instead of the electron density. However, the pressure disturbance effect cannot be reduced using plasma electron density feedback.

  20. Modelling the experimental electron density: only the synergy of various approaches can tackle the new challenges

    PubMed Central

    Macchi, Piero; Gillet, Jean-Michel; Taulelle, Francis; Campo, Javier; Claiser, Nicolas; Lecomte, Claude

    2015-01-01

    Electron density is a fundamental quantity that enables understanding of the chemical bonding in a molecule or in a solid and the chemical/physical property of a material. Because electrons have a charge and a spin, two kinds of electron densities are available. Moreover, because electron distribution can be described in momentum or in position space, charge and spin density have two definitions and they can be observed through Bragg (for the position space) or Compton (for the momentum space) diffraction experiments, using X-rays (charge density) or polarized neutrons (spin density). In recent years, we have witnessed many advances in this field, stimulated by the increased power of experimental techniques. However, an accurate modelling is still necessary to determine the desired functions from the acquired data. The improved accuracy of measurements and the possibility to combine information from different experimental techniques require even more flexibility of the models. In this short review, we analyse some of the most important topics that have emerged in the recent literature, especially the most thought-provoking at the recent IUCr general meeting in Montreal. PMID:26175903

  1. Simultaneous measurement of electron temperature and density by a line pair method in the RFP plasma

    NASA Astrophysics Data System (ADS)

    Watanabe, Masayuki; Shimizu, S.; Ogawa, H.; Shinohara, T.

    2009-11-01

    A line-pair-method has been applied for a simultaneous measurement of the electron temperature and density in ATRAS RFP plasma. Three helium spectrum lines (668nm, 706nm, 728nm) were measured during the discharge at the same time and the electron temperature and density is estimated by using a Collision-Radiation model. To get the signal of the helium impunity line from the RFP discharge, the RFP plasma in the hydrogen gas with a few mixed helium gas was formed. In the typical ATRAS RFP discharge of the plasma current of 60kA, the electron temperature was approximately 50-150 eV and the electron density is the order of 10^18 m-3. During the discharge, the change of the temperature and density are mutually related and this correlation was the almost reverse phase. The periodically change of the temperature and density were also observed. This change synchronizes with a periodically increase of the averaged toroidal magnetic field, which is caused by the toroidal rotation of the increase of the toroidal magnetic field. This rotation, which is deeply related with dynamo effect, makes the plasma energy lose and particles also diffuse toward the plasma edge. As a result, the recycling of the particle and energy are occurred at the same time.

  2. The secondary electron emission yield of muscovite mica: Charging kinetics and current density effects

    NASA Astrophysics Data System (ADS)

    Blaise, G.; Pesty, F.; Garoche, P.

    2009-02-01

    Using a dedicated scanning electron microscope, operating in the spot mode, the charging properties of muscovite mica have been studied in the energy range of 100-8000 eV. The intrinsic yield curve σ0(E), representing the variation of the yield of the uncharged material with the energy E, has been established: the maximum value of the yield is 3.92 at E =300 eV and the two crossovers corresponding to σ0(E)=1 are, respectively, at energies EI<100 eV and EII=4850 eV. At a given energy and under a low current density J ≤100 nA/cm2, the yield varies with the electron fluence from its intrinsic value σ0 up to the value corresponding to the self-regulated regime for which σ =1. This variation is independent of J. The fluence dependence of the yield σ(D ) is due to the internal field produced by the accumulation of charges that blocks the emission when the charging is positive and enhances it when it is negative. At room temperature, the relaxation time of stored charges is estimated to be of the order of 250 s for holes and 150 s for electrons. Three current density effects have been observed when J ≥400 nA/cm2. (i) The variation of σ(D ) with the fluence D depends on J. (ii) Negative charging is obtained at high current density in the energy range (EI, EII) where the material is normally positively charged at low current density. (iii) Electron exoemission (bursts of electrons) is produced at low energy when the net stored charge is positive. The interpretation of the current density effect on σ(D ) is based on the high rate of charging, the effect relative to negative charging is due to the expansion of the electron distribution, while the exoemission effect is due to the collective relaxation process of electrons.

  3. [The reconstruction of welding arc 3D electron density distribution based on Stark broadening].

    PubMed

    Zhang, Wang; Hua, Xue-Ming; Pan, Cheng-Gang; Li, Fang; Wang, Min

    2012-10-01

    The three-dimensional electron density is very important for welding arc quality control. In the present paper, Side-on characteristic line profile was collected by a spectrometer, and the lateral experimental data were approximated by a polynomial fitting. By applying an Abel inversion technique, the authors obtained the radial intensity distribution at each wavelength and thus constructed a profile for the radial positions. The Fourier transform was used to separate the Lorentz linear from the spectrum reconstructed, thus got the accurate Stark width. And we calculated the electronic density three-dimensional distribution of the TIG welding are plasma. PMID:23285847

  4. Employing homogeneity properties of density functionals to determine the total electronic energy

    NASA Astrophysics Data System (ADS)

    Morrison, Robert C.; Parr, Robert G.

    1996-05-01

    The exchange-correlation energy is calculated from expressions for (Exc+Tc)/2 and (Exc-Tc)/2. The expression for Exc+Tc is known exactly. The expression for Exc-Tc is not known exactly and we approximate Gxc-Tc, where Gxc=Exc+J/N, by assuming that it is a functional that is homogeneous of degree 1 in the electron density and that Tc is homogeneous of degree 0 in the electron density. The resulting formula for the total energy reduces the average of the errors in the Parr and Ghosh

    [Phys. Rev. A 51, 3564 (1995)]
    approximation by about one-half.

  5. Spatio-temporal dynamics of electron density in femtosecond laser microplasma of gases

    NASA Astrophysics Data System (ADS)

    Bukin, V. V.; Garnov, S. V.; Strelkov, V. V.; Shirokikh, T. V.; Sychev, D. K.

    2009-06-01

    The formation and evolution of femtosecond laser plasma produced in microvolumes of gases at different pressures upon their multiply ionization by high intensity pulses of fundamental and second harmonics of a Ti:sapphire laser is studied. The interferometric technique for precise ultrafast optical diagnostics of such plasma was applied. The numerical technique of interferogram processing and reconstruction of instant spatial distribution of refractive index and free electron density in laser-induced plasma applied for this proposes is described. The spatiotemporal distribution of the refractive index and free electron density were studied with a spatial resolution of ˜1 μ m and a temporal resolution of ˜70 fs.

  6. High-current density, high-brightness electron beams from large-area lanthanum hexaboride cathodes

    NASA Astrophysics Data System (ADS)

    Loschialpo, P.; Kapetanakos, C. A.

    1987-12-01

    Large (approx. 5 cm) diameter lanthanum hexaboride (LaB6) cathodes operated at 10 kV have produced 1 to 5 micro electron pulses with current density between 10 and 20 A/sq cm. Normalized beam brightness, has been consistently measured. To obtain this high current density, the LaB6 cathodes have been heated to temperatures between approximately 1600 to 1800 C. Very uniform temperature profiles are obtained by applying a carefully tailored electron bombardment heating power distribution. These measurements have been made between pressure .000001 to .00001 Torr, i.e., under much less demanding vacuum conditions than that required by conventional dispenser type cathodes.

  7. Critical density for Landau damping in a two-electron-component plasma

    SciTech Connect

    Rupp, Constantin F.; López, Rodrigo A.; Araneda, Jaime A.

    2015-10-15

    The asymptotic evolution of an initial perturbation in a collisionless two-electron-component plasma with different temperatures is studied numerically. The transition between linear and nonlinear damping regimes is determined by slowly varying the density of the secondary electron-component using high-resolution Vlasov-Poisson simulations. It is shown that, for fixed amplitude perturbations, this transition behaves as a critical phenomenon with time scales and field amplitudes exhibiting power-law dependencies on the threshold density, similar to the critical amplitude behavior in a single-component plasma.

  8. Validation of plasmasphere electron density reconstructions derived from data on board CHAMP by IMAGE/RPI data

    NASA Astrophysics Data System (ADS)

    Gerzen, T.; Feltens, J.; Jakowski, N.; Galkin, I.; Denton, R.; Reinisch, B.; Zandbergen, R.

    2015-01-01

    Plasmaspheric electron content is, beyond the ionosphere as major source, a significant contributor to the overall TEC budget affecting GNSS signals. The plasmasphere can induce half or more of the GNSS range errors caused by atmospheric electrical charges, in particular at nighttime. At DLR Neustrelitz, Germany, GPS measurements recorded onboard the LEO satellite CHAMP were used to reconstruct the topside electron density distribution (ionosphere and plasmasphere) up to GPS altitude, applying a model-based assimilation technique. In this paper, the potential of these CHAMP topside reconstructions for analyzing space weather related changes in the geo-plasma is investigated. For this purpose, comparisons are made between the CHAMP reconstructed profiles and electron densities derived from passive radio wave observations by the IMAGE RPI instrument for years 2001 till 2005. The comparison results indicate that an improvement, compared to the electron density of a background model, can be achieved by CHAMP data assimilation. The improvement is especially visible in the L-shell region below 3, which contributes notably to the GNSS signal delays. However, for the region around the plasmapause, systematical electron density underestimations of the background model w.r.t. the IMAGE data are detected. The rather limited CHAMP data coverage and the degraded observation geometry at these high altitudes seem to be not sufficient for complete compensation of this underestimation during the assimilation procedure. The results presented in this paper demonstrate the strengths of LEO TEC data assimilation, but at the same time illustrate the necessity to improve the modeling of the plasmasphere region above 4 ER L-shell distances. Furthermore, they reveal the need of additional data to establish an appropriate data base for the modeling of the complete plasmasphere.

  9. Electron mobility in very low density GaN/AlGaN/GaN heterostructures

    SciTech Connect

    Manfra, M.J.; Baldwin, K.W.; Sergent, A.M.; Molnar, R.J.; Caissie, J.

    2004-09-06

    We report on the transport properties of a tunable two-dimensional electron gas (2DEG) confined at the lower interface of a GaN/Al{sub 0.06}Ga{sub 0.94}N/GaN heterostructure grown by plasma-assisted molecular beam epitaxy on semi-insulating GaN templates prepared by hydride vapor phase epitaxy. Using an insulated gate Hall bar structure, the electron density is continuously tuned from {approx}2x10{sup 12} down to 1.5x10{sup 11} cm{sup -2}. At T=300 mK, the 2DEG displays a maximum mobility of 80 000 cm{sup 2}/V s at a sheet density of 1.75x10{sup 12} cm{sup -2}. At low densities, the mobility exhibits a power law dependence on density -{mu}{approx}n{sub e}{sup {alpha}}, with {alpha}{approx}1.0, over the range of 2x10{sup 11}-1x10{sup 12} cm{sup -2}. In this density regime, the mobility is no longer limited by alloy scattering and long-range Coulomb scattering dominates. We discuss the dominant scattering mechanisms that presently limit low temperature mobility at electron densities below 1x10{sup 12} cm{sup -2}.

  10. Exploring the electron density in plasma induced by EUV radiation: I. Experimental study in hydrogen

    NASA Astrophysics Data System (ADS)

    van der Horst, R. M.; Beckers, J.; Osorio, E. A.; Astakhov, D. I.; Goedheer, W. J.; Lee, C. J.; Ivanov, V. V.; Krivtsum, V. M.; Koshelev, K. N.; Lopaev, D. V.; Bijkerk, F.; Banine, V. Y.

    2016-04-01

    Plasmas induced by EUV radiation are unique since they are created without the need of any discharge. Moreover, it is essential to characterize these plasmas to understand and predict their long term impact on highly delicate optics in EUV lithography tools. In this paper we study plasmas induced by 13.5 nm EUV radiation in hydrogen gas. The electron density is measured temporally resolved using a non-invasive technique known as microwave cavity resonance spectroscopy. The influence of the EUV pulse energy and gas pressure on the temporal evolution of the electron density has been explored over a parameter range relevant for industry. Our experimental results show that the maximum electron density is in the order of 1014 m-3 and depends linearly on the EUV pulse energy. Furthermore, the maximum electron density depends quadratically on the pressure; the linear term is caused by photoionization and the quadratic term by subsequent electron impact ionization. The decay of the plasma is governed by ambipolar diffusion and, hence, becomes slower at elevated pressures. Similarities and differences of the same processes in argon are highlighted in this paper.

  11. Dynamics of the spatial electron density distribution of EUV-induced plasmas

    NASA Astrophysics Data System (ADS)

    van der Horst, R. M.; Beckers, J.; Osorio, E. A.; Banine, V. Y.

    2015-11-01

    We studied the temporal evolution of the electron density distribution in a low pressure pulsed plasma induced by high energy extreme ultraviolet (EUV) photons using microwave cavity resonance spectroscopy (MCRS). In principle, MCRS only provides space averaged information about the electron density. However, we demonstrate here the possibility to obtain spatial information by combining multiple resonant modes. It is shown that EUV-induced plasmas, albeit being a rather exotic plasma, can be explained by known plasma physical laws and processes. Two stages of plasma behaviour are observed: first the electron density distribution contracts, after which it expands. It is shown that the contraction is due to cooling of the electrons. The moment when the density distribution starts to expand is related to the inertia of the ions. After tens of microseconds, the electrons reached the wall of the cavity. The speed of this expansion is dependent on the gas pressure and can be divided into two regimes. It is shown that the acoustic dominated regime the expansion speed is independent of the gas pressure and that in the diffusion dominated regime the expansion depends reciprocal on the gas pressure.

  12. Exploring the electron density in plasmas induced by extreme ultraviolet radiation in argon

    NASA Astrophysics Data System (ADS)

    van der Horst, R. M.; Beckers, J.; Osorio, E. A.; Banine, V. Y.

    2015-07-01

    The new generation of lithography tools use high energy EUV radiation which ionizes the present background gas due to photoionization. To predict and understand the long term impact on the highly delicate mirrors, it is essential to characterize these kinds of EUV-induced plasmas. We measured the electron density evolution in argon gas during and just after irradiation by a short pulse of EUV light at 13.5 nm by applying microwave cavity resonance spectroscopy. Dependencies on EUV pulse energy and gas pressure have been explored over a range relevant for industrial applications. Our experimental results show that the maximum reached electron density depends linearly on pulse energy. A quadratic dependence caused by photoionization and subsequent electron impact ionization by free electrons is found from experiments where the gas pressure is varied. This is demonstrated by our theoretical estimates presented in this manuscript as well.

  13. Effective electron displacements: A tool for time-dependent density functional theory computational spectroscopy

    SciTech Connect

    Guido, Ciro A. Cortona, Pietro; Adamo, Carlo; Institut Universitaire de France, 103 Bd Saint-Michel, F-75005 Paris

    2014-03-14

    We extend our previous definition of the metric Δr for electronic excitations in the framework of the time-dependent density functional theory [C. A. Guido, P. Cortona, B. Mennucci, and C. Adamo, J. Chem. Theory Comput. 9, 3118 (2013)], by including a measure of the difference of electronic position variances in passing from occupied to virtual orbitals. This new definition, called Γ, permits applications in those situations where the Δr-index is not helpful: transitions in centrosymmetric systems and Rydberg excitations. The Γ-metric is then extended by using the Natural Transition Orbitals, thus providing an intuitive picture of how locally the electron density changes during the electronic transitions. Furthermore, the Γ values give insight about the functional performances in reproducing different type of transitions, and allow one to define a “confidence radius” for GGA and hybrid functionals.

  14. Highly collimated monoenergetic target-surface electron acceleration in near-critical-density plasmas

    SciTech Connect

    Mao, J. Y.; Chen, L. M.; Huang, K.; Ma, Y.; Zhao, J. R.; Yan, W. C.; Ma, J. L.; Wei, Z. Y.; Li, D. Z.; Aeschlimann, M.; Zhang, J.

    2015-03-30

    Optimized-quality monoenergetic target surface electron beams at MeV level with low normalized emittance (0.03π mm mrad) and high charge (30 pC) per shot have been obtained from 3 TW laser-solid interactions at a grazing incidence. The 2-Dimension particle-in-cell simulations suggest that electrons are wake-field accelerated in a large-scale, near-critical-density preplasma. It reveals that a bubble-like structure as an accelerating cavity appears in the near-critical-density plasma region and travels along the target surface. A bunch of electrons are pinched transversely and accelerated longitudinally by the wake field in the bubble. The outstanding normalized emittance and monochromaticity of such highly collimated surface electron beams could make it an ideal beam for fast ignition or may serve as an injector in traditional accelerators.

  15. Monte Carlo modeling of electron density in hypersonic rarefied gas flows

    SciTech Connect

    Fan, Jin; Zhang, Yuhuai; Jiang, Jianzheng

    2014-12-09

    The electron density distribution around a vehicle employed in the RAM-C II flight test is calculated with the DSMC method. To resolve the mole fraction of electrons which is several orders lower than those of the primary species in the free stream, an algorithm named as trace species separation (TSS) is utilized. The TSS algorithm solves the primary and trace species separately, which is similar to the DSMC overlay techniques; however it generates new simulated molecules of trace species, such as ions and electrons in each cell, basing on the ionization and recombination rates directly, which differs from the DSMC overlay techniques based on probabilistic models. The electron density distributions computed by TSS agree well with the flight data measured in the RAM-C II test along a decent trajectory at three altitudes 81km, 76km, and 71km.

  16. Electron density compression and oscillating effects on laser energy absorption in overdense plasma targets.

    PubMed

    Ge, Z Y; Zhuo, H B; Yu, W; Yang, X H; Yu, T P; Li, X H; Zou, D B; Ma, Y Y; Yin, Y; Shao, F Q; Peng, X J

    2014-03-01

    An analytical model for energy absorption during the interaction of an ultrashort, ultraintense laser with an overdense plasma is proposed. Both the compression effect of the electron density profile and the oscillation of the electron plasma surface are self-consistently included, which exhibit significant influences on the laser energy absorption. Based on our model, the general scaling law of the compression effect depending on laser strength and initial density is derived, and the temporal variation of the laser absorption due to the boundary oscillating effect is presented. It is found that due to the oscillation of the electron plasma surface, the laser absorption rate will vibrate periodically at ω or 2ω frequency for the p-polarized and s-polarized laser, respectively. The effect of plasma collision on the laser absorption has also been investigated, which shows a considerable rise in absorption with increasing electron-ion collision frequency for both polarizations. PMID:24730955

  17. Numerical solution of the compressible Navier-Stokes equations using density gradients as additional dependent variables. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Kwon, J. H.

    1977-01-01

    Numerical solution of two dimensional, time dependent, compressible viscous Navier-Stokes equations about arbitrary bodies was treated using density gradients as additional dependent variables. Thus, six dependent variables were computed with the SOR iteration method. Besides formulation for pressure gradient terms, a formulation for computing the body density was presented. To approximate the governing equations, an implicit finite difference method was employed. In computing the solution for the flow about a circular cylinder, a problem arose near the wall at both stagnation points. Thus, computations with various conditions were tried to examine the problem. Also, computations with and without formulations are compared. The flow variables were computed on 37 by 40 field first, then on an 81 by 40 field.

  18. All-electron time-dependent density functional theory with finite elements: time-propagation approach.

    PubMed

    Lehtovaara, Lauri; Havu, Ville; Puska, Martti

    2011-10-21

    We present an all-electron method for time-dependent density functional theory which employs hierarchical nonuniform finite-element bases and the time-propagation approach. The method is capable of treating linear and nonlinear response of valence and core electrons to an external field. We also introduce (i) a preconditioner for the propagation equation, (ii) a stable way to implement absorbing boundary conditions, and (iii) a new kind of absorbing boundary condition inspired by perfectly matched layers. PMID:22029294

  19. Squeezed states of electrons and transitions of the density of states

    NASA Technical Reports Server (NTRS)

    Lee, Seung Joo; Um, Chung IN

    1993-01-01

    Electron systems which have low dimensional properties have been constructed by squeezing the motion in zero, one, or two-directions. An isolated quantum dot is modeled by a potential box with delta-profiled, penetrable potential walls embedded in a large outer box with infinitely high potential walls which represent the world function with respect to vacuum. We show the smooth crossover of the density of states from the three-dimensional to the quasi-zero dimensional electron gas.

  20. 2D electron density profile measurement in tokamak by laser-accelerated ion-beam probe

    SciTech Connect

    Chen, Y. H.; Yang, X. Y.; Lin, C. E-mail: cjxiao@pku.edu.cn; Wang, X. G.; Xiao, C. J. E-mail: cjxiao@pku.edu.cn; Wang, L.; Xu, M.

    2014-11-15

    A new concept of Heavy Ion Beam Probe (HIBP) diagnostic has been proposed, of which the key is to replace the electrostatic accelerator of traditional HIBP by a laser-driven ion accelerator. Due to the large energy spread of ions, the laser-accelerated HIBP can measure the two-dimensional (2D) electron density profile of tokamak plasma. In a preliminary simulation, a 2D density profile was reconstructed with a spatial resolution of about 2 cm, and with the error below 15% in the core region. Diagnostics of 2D density fluctuation is also discussed.

  1. Tailoring the core electron density in modulation-doped core‑multi-shell nanowires

    NASA Astrophysics Data System (ADS)

    Buscemi, Fabrizio; Royo, Miquel; Goldoni, Guido; Bertoni, Andrea

    2016-05-01

    We show how a proper radial modulation of the composition of core-multi-shell nanowires (NWs) critically enhances the control of the free-carrier density in the high-mobility core with respect to core‑single-shell structures, thus overcoming the technological difficulty of fine tuning the remote doping density. We calculate the electron population of the different NW layers as a function of the doping density and of several geometrical parameters by means of a self-consistent Schrödinger–Poisson approach: free carriers tend to localize in the outer shell and screen the core from the electric field of the dopants.

  2. Microwave Transmission Measurements of the Electron Cloud Density In The Positron Ring of PEP-II

    SciTech Connect

    Pivi, M.T.F.; Krasnykh, A.K; Byrd, J.; Santis, S.De; Sonnad, K.G.; Caspers, F.; Kroyer, T.; /CERN

    2008-07-03

    Clouds of electrons in the vacuum chambers of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We applied a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a straight section of the accelerator. The modulation in the wave transmission which appear to increase in depth when the clearing solenoids are switched off, seem to be directly correlated to the electron cloud density in the section. Furthermore, we expect a larger phase shift of a wave transmitted through magnetic dipole field regions if the transmitted wave couples with the gyration motion of the electrons. We have used this technique to measure the average electron cloud density (ECD) specifically for the first time in magnetic field regions of a new 4-dipole chicane in the positron ring of the PEP-II collider at SLAC. In this paper we present and discuss the measurements taken in the Low Energy Ring (LER) between 2006 and 2008.

  3. Microwave Transmission Measurements of the Electron Cloud density In the Positron Ring of PEP-II

    SciTech Connect

    Pivi, Mauro T.F.; Krasnykh, Anatoly K.; Byrd, John; De Santis, Stefano; Sonnaad, Kiran G.; Caspers, Fritz; Kroyer, Tom

    2008-06-18

    Clouds of electrons in the vacuum chambers of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electrons clouds over substantial lengths of the beam pipe. We applied a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a straight section of the accelerator. The modulation in the wave transmission which appears to increase in depth when the clearing solenoids are switched off, seem to be directly correlated to the electron cloud density in the section. Furthermore, we expect a larger phase shift of a wave transmitted through magnetic dipole field regionsif the transmitted wave couples with the gyration motion of the electrons. We have used this technique to measure the average electron cloud density (ECD) specifically for the first time in magnetic field regions of a new 4-dipole chicane in the positron ring of the PEP-II collider at SLAC. In this paper we present and discuss the measurements taken in the Low Energy Ring (LER) between 2006 and 2008.

  4. Development and application of diagnostic instrumentation for measurement of electron density and conductivity

    SciTech Connect

    Bauman, L.E.

    1990-05-01

    The purpose of this contract was to assemble and demonstrate in the laboratory a Faraday rotation system for measurement of electron density and conductivity, with the intent to produce a system suitable for diagnostic support of the development of pulsed, space-based magnetohydrodynamic (MHD) power systems. Two system configurations were tested: (1) a rotating polarizer and (2) a beam splitting polarizer. Due to the short path length plasma produced in the laboratory flame, the long wavelength 496 {mu}m methyl fluoride laser line was used and only the more sensitive rotating polarizer configuration was used for the demonstration experiments. Electron number densities from 2 {times} 10{sup 19} to 9 {times} 10{sup 19} were measured with good agreement to statistical equilibrium (Saha) calculations using emission absorption-measured flame temperatures and neutral seed atom number seed atom nuclear densities. The electron collision frequencies were measured by transmission measurements. Combining these two measurements gave measured electron conductivities of between 4 and 12 mohs/m. These results compared reasonably well with those found with an electron collision frequency model combined with chemical equilibrium calculations and the emission absorption measurements. Ellipticity measurements of electron collision frequency were not possible due to the short path length of the laboratory plasma. 46 refs., 25 figs., 9 tabs.

  5. Statistical studies of electron density around lunar wake boundary derived from WFC observation onboard KAGUYA

    NASA Astrophysics Data System (ADS)

    Kasahara, Y.; Kanatani, K.; Goto, Y.; Hashimoto, K.; Omura, Y.; Kumamoto, A.; Ono, T.; Nishino, M. N.; Saito, Y.; Tsunakawa, H.

    2011-12-01

    The waveform capture (WFC) [1,2] onboard KAGUYA measured two components of electric wave signals detected by the two orthogonal 30 m tip-to-tip antennas from 100Hz to 1MHz during the mission period of KAGUYA from November, 2007 to June 2009. By taking advantage of a moon orbiter, the WFC was expected to measure plasma waves related to solar wind-moon interaction, mini-magnetospheres caused by magnetic anomaly on the lunar surface, and radio emissions to be observed from the moon. Because the moon is basically non-magnetized, the solar wind particles directly hit the lunar surface and a plasma cavity called the "lunar wake" is created behind the moon. We investigated electron density profile around the terminator of the moon from the local plasma frequency obtained by WFC. Because our measurement is a direct method measuring the local plasma frequency, we expect absolute density can be derived. KAGUYA experienced encounters with the lunar wake every 2 hours at an altitude of ~100km in the nominal mission, we first analyzed electron density statistically when KAGUYA was located in the solar wind comparing with the data from WIND. Using these observation data, we constructed an electron density model around the lunar wake boundary region. We also report several interesting feature in the profile such as asymmetric structure depending on the direction of interplanetary magnetic field (IMF). KAGUYA was descended to the 50 km altitude and was descended again down to 10-30km in lower altitude (perilune). Electron density in the lower altitude region is also studied using the data obtained in the extended mission. We found electron density slightly increases in the lower altitude region. [1] Y. Kasahara et al., Earth, Planets and Space, 60, 341-351, 2008. [2] T. Ono et al., Space Science Review, doi:10.1007/s11214-010-9673-8, 2010.

  6. Martian electron density profiles retrieved from Mars Express dual-frequency radio occultation measurements

    NASA Astrophysics Data System (ADS)

    Zhang, S. J.; Cui, J.; Guo, P.; Li, J. L.; Ping, J. S.; Jian, N. C.; Zhang, K. F.

    2015-05-01

    The S- and X-band dual-frequency Doppler radio occultation observations obtained by the Mars Express Radio Science (MaRS) experiments are reduced in this study. A total of 414 Martian electron density profiles are retrieved covering the period from DOY 93 2004 to DOY 304 2012. These observations are well distributed over both longitude and latitude, with Sun-Mars distance varying from 1.38 AU to 1.67 AU, the solar zenith angle (SZA) ranging from 52 ° to 122 ° . Due to the improved vertical resolution for the MaRS experiments, the vertical structures of the retrieved profiles appear to be more complicated than those revealed by early radio occultation experiments. Dayside electron density profiles have primary peaks (M2) typically around 130 km and secondary peaks (M1) around 110 km. Nightside electron density profiles are highly variable, many of which do not have double layer structures. Both the dayside and nightside electron density profiles reveal some atypical features such as topside layering above M2 and bottom-side layering below M1. The former likely represent the plasma fluctuations in response to the solar wind (SW) interactions with the Martian ionosphere, whereas the latter is thought to be induced by the meteoric influx. We fit the peak electron density of profiles up to terminator with a simple power relation (Nm =N0 Chk (χ) ) , with the best-fit subsolar peak electron density being N0 = (1.499 ± 0.002) ×105cm-3 , and the best-fit power index being k = 0.513 ± 0.001 . The measured total electron content (TEC) is obtained by integrating the observed electron density profile vertically from 50 km to 400 km, which is then compared with the ideal TEC computed from the one-layer Chapman model. We find that the one-layer Chapman model can generally underestimate the measured TEC up to ∼ 0.1 TECU (1TECU = 1.0 ×1016m-2) for 55 °

  7. Radial Electron Momentum Densities of Colloidal CdSe Nanocrystals Determined by Positron Beam Analysis

    SciTech Connect

    Denison, A B; Meulenberg, R; Eijt, S W H; Van Veen, A; Mijnarends, P E; Barbiellini, B; Bansil, A; Fischer, C; Weber, M H; Lynn, K G

    2003-07-31

    We present depth-resolved positron 2D angular correlation of annihilation radiation (2DACAR) experiments on CdSe quantum dots in the diameter range from 2.5 to 6 nm, deposited as micrometer thin layers. The average radial distribution of the valence electron momentum density (EMD) of CdSe quantum dots has been extracted, which reveals a systematic dependence upon particle size. The quantum confinement related changes and their size scaling observable at the Jones zone momentum of {approx}0.8 a.u. seem to agree with the previous coincidence Doppler study. In addition, the average radial EMD shows an increase in the low-momentum range (<0.6 a.u.) and a reduction in the high-momentum range (>1.6 a.u.) with respect to that measured on a bulk CdSe single crystal. Possible origins of these are described. First-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method were performed to gain a better insight.

  8. Vibronic properties of organic semiconductors based on phthalocyanine complexes with asymmetrically distributed electron density

    SciTech Connect

    Belogorokhov, I. A.; Martishov, M. N.; Mamichev, D. A.; Dronov, M. A.; Pushkarev, V. E.; Ryabchikov, Yu. V.; Forsh, P. A.; Tomilova, L. G.; Khokhlov, D. R.

    2010-06-15

    This study is concerned with the optical properties of organic semiconductors based on lanthanide (III) biphthalocyanine and triphthalocyanine complexes with asymmetrically distributed electron density. The {sup Cl}PcLu{sup tBu}Pc biphthalocyanine and {sup Cl}PcEu{sup Bu}PcLu{sup Bu}Pc triphthalocyanine solid films ({sup Cl}Pc = 2, 3, 9, 10, 16, 17, 23, 24-octachlorophthalocyaninate, {sup tBu}Pc = 2(3), 9(10), 16(17), 23(24)-tetra- tretbutylphthalocyani-nate, {sup Bu}Pc = 2, 3, 9, 10, 16, 17, 23, 24-octabutylphthalo cyaninate) are fabricated, and their transmittance spectra in the middle infrared region are studied. Analysis of the transmittance spectra shows that the addition of complexity to phthalocyanine molecules yields some changes in the spectra. Specifically, the isoindole group can exhibit vibronic properties in the form of four absorption lines in the range 1400-1450 cm{sup -1}. New absorption lines that may be due to chlorine-carbon bonds are observed in the far-infrared region.

  9. Electron Density Measurements of a Field-Reversed Configuration Using Fiber Probe Interferometry

    NASA Astrophysics Data System (ADS)

    Camacho, J. F.; Lynn, A. G.; Ruden, E. L.

    2010-11-01

    A HeNe laser interferometer operating at 632.8 nm with two single-mode optical fiber probe beams has been assembled to measure time history of the line-integrated electron density of a field-reversed configuration (FRC) for a magnetized target fusion (MTF) experiment. Our system features probe path lengths many times longer than the reference paths. We have performed simultaneous measurements along two diameters at different axial locations. During plasma formation, translation, and capture tests, the lower probe monitored the formation region, while the upper probe monitored the capture region corresponding to the location of an imploding cylindrical aluminum liner driven by the Shiva Star capacitor bank to compress and heat the FRC plasma. For the actual imploding liner experiment, the upper chord was moved to monitor the translating FRC at the entrance to the liner region. Results from the formation, translation, and capture tests as well as an actual imploding liner experiment will be presented. In addition, interferometer visibility measurements and other factors establishing the viability of our design will be discussed.

  10. Simulation of Electron Cloud Density Distributions in RHIC Dipoles at Injection and Transition and Estimates for Scrubbing Times

    SciTech Connect

    He,P.; Blaskiewicz, M.; Fischer, W.

    2009-01-02

    In this report we summarize electron-cloud simulations for the RHIC dipole regions at injection and transition to estimate if scrubbing over practical time scales at injection would reduce the electron cloud density at transition to significantly lower values. The lower electron cloud density at transition will allow for an increase in the ion intensity.

  11. Electron density profile measurements at a self-focusing ion beam with high current density and low energy extracted through concave electrodes

    SciTech Connect

    Fujiwara, Y. Nakamiya, A.; Sakakita, H.; Hirano, Y.; Kiyama, S.; Koguchi, H.

    2014-02-15

    The self-focusing phenomenon has been observed in a high current density and low energy ion beam. In order to study the mechanism of this phenomenon, a special designed double probe to measure the electron density and temperature is installed into the chamber where the high current density ion beam is injected. Electron density profile is successfully measured without the influence of the ion beam components. Estimated electron temperature and density are ∼0.9 eV and ∼8 × 10{sup 8} cm{sup −3} at the center of ion beam cross section, respectively. It was found that a large amount of electrons are spontaneously accumulated in the ion beam line in the case of self-forcing state.

  12. Amplification of current density modulation in a FEL with an infinite electron beam

    SciTech Connect

    Wang, G.; Litvinenko, V.N.; Webb, S.D.

    2011-03-28

    We show that the paraxial field equation for a free electron laser (FEL) in an infinitely wide electron beam with {kappa}-2 energy distribution can be reduced to a fourth ordinary differential equation (ODE). Its solution for arbitrary initial phase space density modulation has been derived in the wave-vector domain. For initial current modulation with Gaussian profile, close form solutions are obtained in space-time domain. In developing an analytical model for a FEL-based coherent electron cooling system, an infinite electron beam has been assumed for the modulation and correction processes. While the assumption has its limitation, it allows for an analytical close form solution to be obtained, which is essential for investigating the underlying scaling law, benchmarking the simulation codes and understanding the fundamental physics. 1D theory was previously applied to model a CeC FEL amplifier. However, the theory ignores diffraction effects and does not provide the transverse profile of the amplified electron density modulation. On the other hand, 3D theories developed for a finite electron beam usually have solutions expanded over infinite number of modes determined by the specific transverse boundary conditions. Unless the mode with the largest growth rate substantially dominates other modes, both evaluation and extracting scaling laws can be complicated. Furthermore, it is also preferable to have an analytical FEL model with assumptions consistent with the other two sections of a CeC system. Recently, we developed the FEL theory in an infinitely wide electron beam with {kappa}-1 (Lorentzian) energy distribution. Close form solutions have been obtained for the amplified current modulation initiated by an external electric field with various spatial-profiles. In this work, we extend the theory into {kappa}-2 energy distribution and study the evolution of current density induced by an initial density modulation.

  13. Excitation density distribution in electron-beam-pumped ZnSe semiconductor lasers

    SciTech Connect

    Donskoi, E N; Zalyalov, A N; Petrushin, O N; Savel'ev, Yu A; Tarasov, M D; Shigaev, Yu S; Zhdanova, E V; Zverev, M M; Peregudov, D V; Ivanov, S V; Sedova, I V; Sorokin, S V

    2008-12-31

    The spatial density distribution of the absorbed energy in ZnSe semiconductor lasers excited by electrons with energies from 2 keV to 1 MeV is calculated by the Monte-Carlo method. Approximate analytic expressions determining the absorbed energy of electrons in ZnSe are presented. The pump power threshold in a semiconductor quantum-well ZnSe structure is experimentally determined. The lasing threshold in such structures is estimated as a function of the electron energy. (active media)

  14. Thermalization time of noble metal nanoparticles: effects of the electron density profile

    NASA Astrophysics Data System (ADS)

    López-Bastidas, C.

    2012-02-01

    The lack of d-electron screening in the s-electron spill-out region at the surface of Ag nanoparticles increases the electron-electron interaction in this region compared to the bulk. Therefore when comparing the electron-electron interaction contribution to the thermalization time of nanoparticles of varying radius, smaller particles thermalize faster due to the increased surface to bulk ratio. One aspect which has not been addressed is the effect of the spatial distribution of charge at the surface of the nanoparticle. In this work it is shown that the size dependence of the thermalization time is very sensitive to the surface density profile. The electron thermalization time of conduction electrons in noble metal nanoparticles as a function of the radius is calculated. The sensitivity of the scattering rate to the spatial distribution of charge at the surface of the nanostructure is analyzed using several model surface profiles. The change in surface charge distribution via charging or coating of the nanospheres is shown to be a tool for control and probing of the ultra-fast electron-electron dynamics in metallic nanoparticles.

  15. Proton and Electron Additions to Iron (II) Dinitrogen Complexes Containing Pendant Amines

    SciTech Connect

    Heiden, Zachariah M.; Chen, Shentan; Labios, Liezel AN; Bullock, R. Morris; Walter, Eric D.; Tyson, Elizabeth L.; Mock, Michael T.

    2014-03-10

    We describe a single site cis-(H)FeII-N2 complex, generated by the protonation of an iron-carbon bond of a "reduced" iron complex, that models key aspects of proposed protonated intermediates of the E4 state of nitrogenase. The influence on N2 binding from the addition of protons to the pendant amine sites in the second coordination sphere is described. Furthermore, the addition of electrons to the protonated complexes results in H2 loss. The mechanism of H2 loss is explored to draw a parallel to the origin of H2 loss (homolytic or heterolytic) and the nature of N2 coordination in intermediates of the E4 state of nitrogenase.

  16. Optimal control of the electronic current density: Application to one- and two-dimensional one-electron systems

    SciTech Connect

    Kammerlander, David; Marques, Miguel A. L.; Castro, Alberto

    2011-04-15

    Quantum optimal control theory is a powerful tool for engineering quantum systems subject to external fields such as the ones created by intense lasers. The formulation relies on a suitable definition for a target functional, that translates the intended physical objective to a mathematical form. We propose the use of target functionals defined in terms of the one-particle density and its current. A strong motivation for this is the possibility of using time-dependent density-functional theory for the description of the system dynamics. We exemplify this idea by defining an objective functional that on one hand attempts a large overlap with a target density and on the other hand minimizes the current. The latter requirement leads to optimized states with increased stability, which we prove with a few examples of one- and two-dimensional one-electron systems.

  17. A new interferometry-based electron density fluctuation diagnostic on Alcator C-Moda)

    NASA Astrophysics Data System (ADS)

    Kasten, C. P.; Irby, J. H.; Murray, R.; White, A. E.; Pace, D. C.

    2012-10-01

    The two-color interferometry diagnostic on the Alcator C-Mod tokamak has been upgraded to measure fluctuations in the electron density and density gradient for turbulence and transport studies. Diagnostic features and capabilities are described. In differential mode, fast phase demodulation electronics detect the relative phase change between ten adjacent, radially-separated (ΔR = 1.2 cm, adjustable), vertical-viewing chords, which allows for measurement of the line-integrated electron density gradient. The system can be configured to detect the absolute phase shift of each chord by comparison to a local oscillator, measuring the line-integrated density. Each chord is sensitive to density fluctuations with kR < 20.3 cm-1 and is digitized at up to 10 MS/s, resolving aspects of ion temperature gradient-driven modes and other long-wavelength turbulence. Data from C-Mod discharges is presented, including observations of the quasi-coherent mode in enhanced D-alpha H-mode plasmas and the weakly coherent mode in I-mode.

  18. Plasma devices to guide and collimate a high density of MeV electrons.

    PubMed

    Kodama, R; Sentoku, Y; Chen, Z L; Kumar, G R; Hatchett, S P; Toyama, Y; Cowan, T E; Freeman, R R; Fuchs, J; Izawa, Y; Key, M H; Kitagawa, Y; Kondo, K; Matsuoka, T; Nakamura, H; Nakatsutsumi, M; Norreys, P A; Norimatsu, T; Snavely, R A; Stephens, R B; Tampo, M; Tanaka, K A; Yabuuchi, T

    2004-12-23

    The development of ultra-intense lasers has facilitated new studies in laboratory astrophysics and high-density nuclear science, including laser fusion. Such research relies on the efficient generation of enormous numbers of high-energy charged particles. For example, laser-matter interactions at petawatt (10(15) W) power levels can create pulses of MeV electrons with current densities as large as 10(12) A cm(-2). However, the divergence of these particle beams usually reduces the current density to a few times 10(6) A cm(-2) at distances of the order of centimetres from the source. The invention of devices that can direct such intense, pulsed energetic beams will revolutionize their applications. Here we report high-conductivity devices consisting of transient plasmas that increase the energy density of MeV electrons generated in laser-matter interactions by more than one order of magnitude. A plasma fibre created on a hollow-cone target guides and collimates electrons in a manner akin to the control of light by an optical fibre and collimator. Such plasma devices hold promise for applications using high energy-density particles and should trigger growth in charged particle optics. PMID:15616556

  19. Three-dimensional electron density along the WSA and MSNA latitudes probed by FORMOSAT-3/COSMIC

    NASA Astrophysics Data System (ADS)

    Chang, F. Y.; Liu, J. Y.; Chang, L. C.; Lin, C. H.; Chen, C. H.

    2015-09-01

    In this paper, we employ electron density profiles derived by the GPS radio occultation experiment aboard the FORMOSAT-3/COSMIC (F3/C) satellites to examine the electron density on geographic latitudes of 40° to 80° in the Southern hemisphere and 30° to 60° in the Northern hemisphere at various global fixed local times from February 2009 to January 2010. The results reveal that an eastward shift of a single-peak plasma density feature occurs along the Weddell Sea Anomaly (WSA) latitudes, while a double-peak plasma density feature appears along the northern Mid-latitude Summer Nighttime Anomaly (MSNA) latitudes. A cross-comparison between three-dimensional F3/C electron density and HWM93 simulation confirms that the magnetic meridional effect and vertical effect caused by neutral winds exhibit the eastward shifts. Furthermore, we find that the eastward shift of the peaks when viewed as a function of local time suggests that they could be interpreted as being comprised of different tidal components with distinct zonal phase velocities in local time.

  20. Extreme density-driven delocalization error for a model solvated-electron system

    SciTech Connect

    Johnson, Erin R. Otero-de-la-Roza, A. Dale, Stephen G.

    2013-11-14

    Delocalization (or charge-transfer) error is one of the scarce but spectacular failures of density-functional theory. It is particularly apparent in extensively delocalized molecules, and manifests in the calculation of bandgaps, reaction barriers, and dissociation limits. Even though delocalization error is always present in the self-consistent electron density, the differences from reference densities are often quite subtle and the error tends to be driven by the exchange-correlation energy expression. In this article, we propose a model system (the Kevan model) where approximate density functionals predict dramatically different charge distributions because of delocalization error. The model system consists of an electron trapped in a water hexamer and is a finite representation of an experimentally observed class of solids: electrides. The Kevan model is of fundamental interest because it allows the estimation of charge transfer error without recourse to fractional charge calculations, but our results are also relevant in the context of the modeling of confined electrons in density-functional theory.

  1. Raman calibration of the HT-7 yttrium aluminum garnet Thomson scattering for electron density measurements

    SciTech Connect

    Zang Qing; Zhao Junyu; Gao Xiang; Shi Lingwei; Zhang Tao; Xi Xiaoqi; Yang Li; Hu Qingsheng; Sajjad, S.

    2007-11-15

    A multipulse neodym doped yttrium aluminum garnet laser Thomson scattering system calibrated by the anti-Stokes rotational Raman scattering from nitrogen gas had been developed in the HT-7 superconducting Tokmak. By virtue of this system, measured electron density results of the plasma were obtained. The results showed good repeatability and its total uncertainty was estimated to be {+-}18%.

  2. Partial-reflection studies of D-region winter variability. [electron density measurements

    NASA Technical Reports Server (NTRS)

    Denny, B. W.; Bowhill, S. A.

    1973-01-01

    D-region electron densities were measured from December, 1972, to July, 1973, at Urbana, Illinois (latitude 40.2N) using the partial-reflection technique. During the winter, electron densities at altitudes of 72, 76.5, and 81 km show cyclical changes with a period of about 5 days that are highly correlated between these altitudes, suggesting that the mechanism responsible for the winter anomaly in D-region ionization applies throughout this height region. From January 13 to February 3, a pronounced wave-like variation occurred in the partial-reflection measurements, apparently associated with a major stratospheric warming that developed in that period. During the same time period, a traveling periodic variation is observed in the 10-mb height; it is highly correlated with the partial-reflection measurements. Electron density enhancements occur approximately at the same time as increases in the 10-mb height. Comparison of AL and A3 absorption measurements with electron density measurements below 82 km indicates that the winter anomaly in D-region ionization is divided into two types. Type 1, above about 82 km, extends horizontally for about 200 km while type 2, below about 82 km, extends for a horizontal scale of at least 1000 km.

  3. Time Evolution of the Electron and Ar* Metastable Atom Densities in Pulsed Plasmas

    SciTech Connect

    Sikimic, Brankica; Stefanovic, Ilija; Winter, Joerg; Denysenko, Igor; Sadeghic, Nader

    2011-11-29

    Metastable and electron densities of pulsed argon plasma containing nano-sized particles were measured by the means of Laser Absorption Spectroscopy and Microwave Interferometry, respectively. Laser Induced Fluorescence was probing the Ar* metastable axial distribution during one dust growing cycle. The experimental results of the dust-free and dusty plasma afterglow were compared to the results obtained by a global model.

  4. Charge density stabilised local electron spin pair states in insulating polymers

    SciTech Connect

    Serra, S.; Dissado, L. A.

    2014-12-14

    A model is presented that addresses the energy stability of localized electron states in insulating polymers with respect to delocalized free electron-like states at variable charge densities. The model was derived using an effective Hamiltonian for the total energy of electrons trapped in large polarons and spin-paired bipolarons, which includes the electrostatic interaction between charges that occurs when the charge density exceeds the infinite dilution limit. The phase diagram of the various electronic states with respect to the charge density is derived using parameters determined from experimental data for polyethylene, and it is found that a phase transition from excess charge in the form of stable polarons to a stable state of bipolarons with charge = 2 and spin number S = 0 is predicted for a charge density between 0.2 C/m{sup 3} and ∼2 C/m{sup 3}. This transition is consistent with a change from low mobility charge transport to charge transport in the form of pulses with a mobility orders of magnitude higher that has been observed in several insulating polymers.

  5. Relative electron density determination using a physics based parameterization of photon interactions in medical DECT.

    PubMed

    van Abbema, Joanne K; van Goethem, Marc-Jan; Greuter, Marcel J W; van der Schaaf, Arjen; Brandenburg, Sytze; van der Graaf, Emiel R

    2015-05-01

    Radiotherapy and particle therapy treatment planning require accurate knowledge of the electron density and elemental composition of the tissues in the beam path to predict the local dose deposition. We describe a method for the analysis of dual energy computed tomography (DECT) images that provides the electron densities and effective atomic numbers of tissues. The CT measurement process is modelled by system weighting functions, which apply an energy dependent weighting to the parameterization of the total cross section for photon interactions with matter. This detailed parameterization is based on the theoretical analysis of Jackson and Hawkes and deviates, at most, 0.3% from the tabulated NIST values for the elements H to Zn. To account for beam hardening in the object as present in the CT image we implemented an iterative process employing a local weighting function, derived from the method proposed by Heismann and Balda. With this method effective atomic numbers between 1 and 30 can be determined. The method has been experimentally validated on a commercially available tissue characterization phantom with 16 inserts made of tissue substitutes and aluminium that has been scanned on a dual source CT system with tube potentials of 100 kV and 140 kV using a clinical scan protocol. Relative electron densities of all tissue substitutes have been determined with accuracy better than 1%. The presented DECT analysis method thus provides high accuracy electron densities and effective atomic numbers for radiotherapy and especially particle therapy treatment planning. PMID:25905890

  6. Relative electron density determination using a physics based parameterization of photon interactions in medical DECT

    NASA Astrophysics Data System (ADS)

    van Abbema, Joanne K.; van Goethem, Marc-Jan; Greuter, Marcel J. W.; van der Schaaf, Arjen; Brandenburg, Sytze; van der Graaf, Emiel R.

    2015-05-01

    Radiotherapy and particle therapy treatment planning require accurate knowledge of the electron density and elemental composition of the tissues in the beam path to predict the local dose deposition. We describe a method for the analysis of dual energy computed tomography (DECT) images that provides the electron densities and effective atomic numbers of tissues. The CT measurement process is modelled by system weighting functions, which apply an energy dependent weighting to the parameterization of the total cross section for photon interactions with matter. This detailed parameterization is based on the theoretical analysis of Jackson and Hawkes and deviates, at most, 0.3% from the tabulated NIST values for the elements H to Zn. To account for beam hardening in the object as present in the CT image we implemented an iterative process employing a local weighting function, derived from the method proposed by Heismann and Balda. With this method effective atomic numbers between 1 and 30 can be determined. The method has been experimentally validated on a commercially available tissue characterization phantom with 16 inserts made of tissue substitutes and aluminium that has been scanned on a dual source CT system with tube potentials of 100 kV and 140 kV using a clinical scan protocol. Relative electron densities of all tissue substitutes have been determined with accuracy better than 1%. The presented DECT analysis method thus provides high accuracy electron densities and effective atomic numbers for radiotherapy and especially particle therapy treatment planning.

  7. Performance of a local electron density trigger to select extensive air showers at sea level

    NASA Technical Reports Server (NTRS)

    Abbas, T.; Madani, J.; Ashton, F.

    1985-01-01

    Time coincident voltage pulses in the two closely space (1.6m) plastic scintillators were recorded. Most of the recorded events are expeted to be due to electrons in cosmic ray showers whose core fall at some distance from the detectors. This result is confirmed from a measurement of the frequency distribution of the recorded density ratios of the two scintillators.

  8. Direct evaluation via forced oscillation method of the electronic state density of sizable clusters.

    PubMed

    Conte, R; Arrighini, G P; Guidotti, C

    2007-01-30

    Metal clusters described in the framework of a simple tight binding model have been studied. Application of a dynamical approach (FOM), jointly with efficient storage of the sparse Hamiltonian matrix involved, is shown to allow direct evaluation of the electronic state density of sizable cubic-symmetry aggregates. PMID:17186475

  9. Density functional theory for low-energy electron-molecule scattering

    NASA Astrophysics Data System (ADS)

    Burke, Kieron; Wasserman, Adam

    2004-09-01

    Time-dependent density functional theory (TDDFT) is becoming popular as an approach to time-dependent electronic problems[1]. In the weak field regime, TDDFT predicts electronic transition frequencies and optical spectra of atoms, molecules, clusters, and solids, with an accuracy comparable to high-level wavefunction calculations at a fraction of the computational cost[2]. For large systems, TDDFT is the method of choice. Given the importance of correlation effects in low-energy electron-molecule scattering, extracting scattering amplitudes from TDDFT appears desirable. I will review this background, and outline how this can be done[3]. Detailed results will be shown by Wasserman in another talk. [1] Time-Dependent Density Functional Theory, M.A.L. Marques and E.K.U. Gross, Annu. Rev. Phys. Chem. 55, 427 (2004). [2] Time-dependent density functional theory in quantum chemistry, F. Furche and K. Burke, to appear in 1st vol. of Annu. Rev. of Computational Chemistry (2004) [3] Electron-molecule scattering from time-dependent density functional theory A. Wasserman, N.T. Maitra, and K. Burke, submitted (see http:dft.rutgers.edu/pubs/publist.html).

  10. A Method to Improve Electron Density Measurement of Cone-Beam CT Using Dual Energy Technique

    PubMed Central

    Men, Kuo; Dai, Jian-Rong; Li, Ming-Hui; Chen, Xin-Yuan; Zhang, Ke; Tian, Yuan; Huang, Peng; Xu, Ying-Jie

    2015-01-01

    Purpose. To develop a dual energy imaging method to improve the accuracy of electron density measurement with a cone-beam CT (CBCT) device. Materials and Methods. The imaging system is the XVI CBCT system on Elekta Synergy linac. Projection data were acquired with the high and low energy X-ray, respectively, to set up a basis material decomposition model. Virtual phantom simulation and phantoms experiments were carried out for quantitative evaluation of the method. Phantoms were also scanned twice with the high and low energy X-ray, respectively. The data were decomposed into projections of the two basis material coefficients according to the model set up earlier. The two sets of decomposed projections were used to reconstruct CBCT images of the basis material coefficients. Then, the images of electron densities were calculated with these CBCT images. Results. The difference between the calculated and theoretical values was within 2% and the correlation coefficient of them was about 1.0. The dual energy imaging method obtained more accurate electron density values and reduced the beam hardening artifacts obviously. Conclusion. A novel dual energy CBCT imaging method to calculate the electron densities was developed. It can acquire more accurate values and provide a platform potentially for dose calculation. PMID:26346510

  11. Quantum electrodynamical time-dependent density functional theory for many-electron systems on a lattice

    NASA Astrophysics Data System (ADS)

    Farzanehpour, Mehdi; Tokatly, Ilya; Nano-Bio Spectroscopy Group; ETSF Scientific Development Centre Team

    2015-03-01

    We present a rigorous formulation of the time-dependent density functional theory for interacting lattice electrons strongly coupled to cavity photons. We start with an example of one particle on a Hubbard dimer coupled to a single photonic mode, which is equivalent to the single mode spin-boson model or the quantum Rabi model. For this system we prove that the electron-photon wave function is a unique functional of the electronic density and the expectation value of the photonic coordinate, provided the initial state and the density satisfy a set of well defined conditions. Then we generalize the formalism to many interacting electrons on a lattice coupled to multiple photonic modes and prove the general mapping theorem. We also show that for a system evolving from the ground state of a lattice Hamiltonian any density with a continuous second time derivative is locally v-representable. Spanish Ministry of Economy and Competitiveness (Grant No. FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (Grant No. IT578-13), COST Actions CM1204 (XLIC) and MP1306 (EUSpec).

  12. YUP.SCX: Coaxing Atomic Models into Medium Resolution Electron Density Maps

    PubMed Central

    Tan, Robert K.-Z.; Devkota, Batsal; Harvey, Stephen C.

    2008-01-01

    The structures of large macromolecular complexes in different functional states can be determined by cryo-electron microscopy, which yields electron density maps of low to intermediate resolutions. The maps can be combined with high-resolution atomic structures of components of the complex, to produce a model for the complex that is more accurate than the formal resolution of the map. To this end, methods have been developed to dock atomic models into density maps rigidly or flexibly, and to refine a docked model so as to optimize the fit of the atomic model into the map. We have developed a new refinement method called YUP.SCX. The electron density map is converted into a component of the potential energy function to which terms for stereochemical restraints and volume exclusion are added. The potential energy function is then minimized (using simulated annealing) to yield a stereochemically-restrained atomic structure that fits into the electron density map optimally. We used this procedure to construct an atomic model of the 70S ribosome in the pre-accommodation state. Although some atoms are displaced by as much as 33 Å, they divide themselves into nearly rigid fragments along natural boundaries with smooth transitions between the fragments. PMID:18572416

  13. Measurements of the Electron Cloud Density in the PEP-II Low Energy Ring

    SciTech Connect

    Byrd, John; De Santis, Stefano; Sonnad, Kiran; Caspers, Fritz; Kroyer, Tom; Krasnykh, Anatoly; Pivi, Mauro

    2008-06-01

    Clouds of low energy electronsin the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energyelectron clouds over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave that is independently excited and transmitted over a section of the accelerator. We infer the absolute phase shift with relatively high accuracy from the phase modulation of the transmission due to the modulation of the electron cloud density from a gap in the positively charged beam. We have used this technique for the first time to measure the average electron cloud density over a 50 m straight section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center. We have also measured the variation of the density by using low field solenoid magnets to control the electrons.

  14. HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations

    SciTech Connect

    Alfred, F.

    1982-01-01

    HF-waves incident on an overdense (HF-frequency < penetration frequency) ionosphere are known to produce large scale electron density irregularities. It is predicted that similar irregularities are formed during underdense HF-modification. The propagation of UHF radio waves originating from radio stars will be affected by such irregularities in the ionosphere. The interest in a scintillation experiment is twofold. One may obtain information on the electron density irregularies and one may learn about the propagation of radio waves through such a perturbed medium. A thin screen (diffractive) theory is derived which allows to draw conclusons on the electron density irregularities from the intensity fluctuations measured on the ground if the phase perturbations are much less than one radian. Since radio stars suitable for scintillation measurements at UHF are very faint an antenna with a large collection area is required. The observations reported in this dissertation were performed with the 300m diameter spherical reflector of the Arecibo Observatory. Successful observations were performed at 430 MHz and at 1400 MHz. Intensity fluctuations at such high frequencies measured with a large antenna suffer severe filtering in the thin phase screen regime. The theory presented in this dissertation includes these filtering effects. Many observations agree with the predictions of that theory. Some observations indicate that refraction effects have to be included to explain the data. HF-induced electron density irregularities were only observed during overdense heating.

  15. F region electron density profile inversion from backscatter ionogram based on international reference ionosphere

    NASA Astrophysics Data System (ADS)

    Zhu, Peng; Zhou, Chen; Zhang, Yuannong; Yang, Guobin; Jiang, Chunhua; Sun, Hengqing; Cui, Xiao

    2015-07-01

    Ionospheric backscatter sounding transmits HF (3-30 MHz) radio wave obliquely into ionosphere and receives echoes backscattered from remote ground. Due to the focusing effect, the echoes form leading edge on the swept frequency backscatter ionogram (BSI). This kind of backscatter ionogram contains plentiful ionospheric information, such as electron density, radio wave propagation modes and maximum usage frequency (MUF). By inversion algorithm, the backscatter ionogram can provide two-dimensional electron density profile (EDP) down range. In this paper, we propose an ionospheric F2 region EDP inversion algorithm. By utilizing the F2 bottomside electron density profile represented by the International Reference Ionosphere (IRI) model and ray tracing techniques, this approach inverts the leading edge of the backscatter ionogram to two dimensional F region EDP. Results of validation experiments demonstrate that the inverted ionospheric EDPs show good agreement with the results of vertical ionosonde and provide reliable information of ionosphere. Thus the proposed inversion algorithm provide an effective and accurate method for achieving large scale and remote ionospheric electron density structure.

  16. Time-Dependent Electronic Populations in Fragment-Based Time-Dependent Density Functional Theory.

    PubMed

    Mosquera, Martín A; Wasserman, Adam

    2015-08-11

    Conceiving a molecule as being composed of smaller molecular fragments, or subunits, is one of the pillars of the chemical and physical sciences and leads to productive methods in quantum chemistry. Using a fragmentation scheme, efficient algorithms can be proposed to address problems in the description of chemical bond formation and breaking. We present a formally exact time-dependent density functional theory for the electronic dynamics of molecular fragments with a variable number of electrons. This new formalism is an extension of previous work [Phys. Rev. Lett. 111, 023001 (2013)]. We also introduce a stable density-inversion method that is applicable to time-dependent and ground-state density functional theories and their extensions, including those discussed in this work. PMID:26574438

  17. SOLAR NEUTRINO PHYSICS OSCILLATIONS: SENSITIVITY TO THE ELECTRONIC DENSITY IN THE SUN'S CORE

    SciTech Connect

    Lopes, Ilidio; Turck-Chieze, Sylvaine E-mail: ilopes@uevora.pt

    2013-03-01

    Solar neutrinos coming from different nuclear reactions are now detected with high statistics. Consequently, an accurate spectroscopic analysis of the neutrino fluxes arriving on Earth's detectors becomes available, in the context of neutrino oscillations. In this work, we explore the possibility of using this information to infer the radial profile of the electronic density in the solar core. So, we discuss the constraints on the Sun's density and chemical composition that can be determined from solar neutrino observations. This approach constitutes an independent and alternative diagnostic to the helioseismic investigations already done. The direct inversion method, which we propose to obtain the radial solar electronic density profile, is almost independent of the solar model.

  18. Distances for galactic planetary nebulae using mean forbidden O II doublet ratio electron densities

    NASA Astrophysics Data System (ADS)

    Kingsburgh, Robin L.; Barlow, M. J.

    1992-07-01

    Forbidden O II 3726, 3729-A double ratios and electron densities are presented for 68 galactic PN. For 45 of the objects, the doublet ratios represent integrations over the whole of the nebula. Calibrations recently derived from the Magellanic Cloud PN are used to derive distances for the majority of the nebulae. The typical forbidden O II density at the transition point between an optically thick and thin nebula is 4500/cu cm. An extensive comparison is made between the distances derived and previously published distances and distance scales. It is shown that the present distances, based on Magellanic Cloud calibrations, yield consistency with independent distance estimates. They also exhibit much greater self-consistency between central star masses derived from luminosity vs Teff comparisons on the one hand, and from absolute magnitude vs evolutionary age comparisons on the other. For the PN in this sample, rms electron densities, filling factors, and absolute radii are also derived.

  19. Simulation of AlGaN/GaN high-electron-mobility transistor gauge factor based on two-dimensional electron gas density and electron mobility

    NASA Astrophysics Data System (ADS)

    Chu, Min; Koehler, Andrew D.; Gupta, Amit; Nishida, Toshikazu; Thompson, Scott E.

    2010-11-01

    The gauge factor of AlGaN/GaN high-electron-mobility transistor was determined theoretically, considering the effect of stress on the two-dimensional electron gas (2DEG) sheet carrier density and electron mobility. Differences in the spontaneous and piezoelectric polarization between the AlGaN and GaN layers, with and without external mechanical stress, were investigated to calculate the stress-altered 2DEG density. Strain was incorporated into a sp3d5-sp3 empirical tight-binding model to obtain the change in electron effective masses under biaxial and uniaxial stress. The simulated longitudinal gauge factor (-7.9±5.2) is consistent with experimental results (-2.4±0.5) obtained from measurements eliminating parasitic charge trapping effects through continuous subbandgap optical excitation.

  20. Refluxed electrons direct laser acceleration in ultrahigh laser and relativistic critical density plasma interaction

    SciTech Connect

    Wang, J.; Zhao, Z. Q.; Zhu, B.; Zhang, Z. M.; Zhou, W. M.; Gu, Y. Q.; Cao, L. H.

    2015-01-15

    Refluxed electrons direct laser acceleration is proposed so as to generate a high-charge energetic electron beam. When a laser pulse is incident on a relativistic critical density target, the rising edge of the pulse heats the target and the sheath fields on the both sides of the target reflux some electrons inside the expanding target. These electrons can be trapped and accelerated due to the self-transparency and the negative longitudinal electrostatic field in the expanding target. Some of the electrons can be accelerated to energies exceeding the ponderomotive limit 1/2a{sub 0}{sup 2}mc{sup 2}. Effective temperature significantly above the ponderomotive scaling is observed. Furthermore, due to the limited expanding length, the laser propagating instabilities are suppressed in the interaction. Thus, high collimated beams with tens of μC charge can be generated.

  1. Bayesian modeling of JET Li-BES for edge electron density profiles using Gaussian processes

    NASA Astrophysics Data System (ADS)

    Kwak, Sehyun; Svensson, Jakob; Brix, Mathias; Ghim, Young-Chul; JET Contributors Collaboration

    2015-11-01

    A Bayesian model for the JET lithium beam emission spectroscopy (Li-BES) system has been developed to infer edge electron density profiles. The 26 spatial channels measure emission profiles with ~15 ms temporal resolution and ~1 cm spatial resolution. The lithium I (2p-2s) line radiation in an emission spectrum is calculated using a multi-state model, which expresses collisions between the neutral lithium beam atoms and the plasma particles as a set of differential equations. The emission spectrum is described in the model including photon and electronic noise, spectral line shapes, interference filter curves, and relative calibrations. This spectral modeling gets rid of the need of separate background measurements for calculating the intensity of the line radiation. Gaussian processes are applied to model both emission spectrum and edge electron density profile, and the electron temperature to calculate all the rate coefficients is obtained from the JET high resolution Thomson scattering (HRTS) system. The posterior distributions of the edge electron density profile are explored via the numerical technique and the Markov chain Monte Carlo (MCMC) samplings. See the Appendix of F. Romanelli et al., Proceedings of the 25th IAEA Fusion Energy Conference 2014, Saint Petersburg, Russia.

  2. Spherical-Harmonic Decomposition for Molecular Recognition in Electron-Density Maps

    PubMed Central

    DiMaio, Frank P.; Soni, Ameet B.; Phillips, George N.; Shavlik, Jude W.

    2008-01-01

    An important problem in high-throughput protein crystallography is constructing a protein model from an electron-density map. DiMaio et al. (2006) describe an automated approach to this otherwise time-consuming process. One important step involves searching the density map for many small protein fragments, or templates. The previous approach uses Fourier convolution to quickly compare some rotation of the template to the entire density map. We propose to instead use the spherical-harmonic decomposition of the template and of some region in the density map. In this new framework, we are able to eliminate areas of the map from the search process if they are unlikely to match to any templates. We design several “first-pass filters” for this elimination task, including one filter which uses a set of rotation-invariant descriptors (derived from the spherical-harmonic decomposition) of a sphere of density to train an accurate classifier. We show our new template-matching method improves accuracy and reduces running time, compared to our previous approach. Protein models constructed using this matching also show significant accuracy improvement. We extend our method to produce a structural-homology detection algorithm that, due to its use of electron-density maps, is more sensitive than sequence-only methods. PMID:19517990

  3. Improving accuracy of electron density measurement in the presence of metallic implants using orthovoltage computed tomography

    SciTech Connect

    Yang Ming; Virshup, Gary; Mohan, Radhe; Shaw, Chris C.; Zhu, X. Ronald; Dong Lei

    2008-05-15

    The goal of this study was to evaluate the improvement in electron density measurement and metal artifact reduction using orthovoltage computed tomography (OVCT) imaging compared with conventional kilovoltage CT (KVCT). For this study, a bench-top system was constructed with adjustable x-ray tube voltage up to 320 kVp. A commercial tissue-characterization phantom loaded with inserts of various human tissue substitutes was imaged using 125 kVp (KVCT) and 320 kVp (OVCT) x rays. Stoichiometric calibration was performed for both KVCT and OVCT imaging using the Schneider method. The metal inserts--titanium rods and aluminum rods--were used to study the impact of metal artifacts on the electron-density measurements both inside and outside the metal inserts. It was found that the relationships between Hounsfield units and relative electron densities (to water) were more predictable for OVCT than KVCT. Unlike KVCT, the stoichiometric calibration for OVCT was insensitive to the use of tissue substitutes for direct electron density calibration. OVCT was found to significantly reduce metal streak artifacts. Errors in electron-density measurements within uniform tissue substitutes were reduced from 42% (maximum) and 18% (root-mean-square) in KVCT to 12% and 2% in OVCT, respectively. Improvements were also observed inside the metal implants. For the detectors optimized for KVCT, the imaging dose is almost doubled for OVCT for the image quality comparable to KVCT. OVCT may be a good option for high-precision radiotherapy treatment planning, especially for patients with metal implants and especially for charged particle therapy, such as proton therapy.

  4. Assessment of precision in ionospheric electron density profiles retrieved by GPS radio occultations

    NASA Astrophysics Data System (ADS)

    Alexander, P.; de la Torre, A.; Hierro, R.; Llamedo, P.

    2014-12-01

    The Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) is a six satellite radio occultation mission that was launched in April 2006. The close proximity of these satellites during some months after launch provides a unique opportunity to evaluate the precision of Global Positioning System (GPS) radio occultation (RO) retrievals of ionospheric electron density from nearly collocated and simultaneous observations. RO data from 30 consecutive days during July and August 2006 are divided into ten groups in terms of daytime or nighttime and latitude. In all cases, the best precision values (about 1%) are found at the F peak height and they slightly degrade upwards. For all daytime groups, it is seen that electron density profiles above about 120 km height exhibit a substantial improvement in precision. Nighttime groups are rather diverse: in particular, the precision becomes better than 10% above different levels between 120 and 200 km height. Our overall results show that up to 100-200 km (depending on each group), the uncertainty associated with the precision is in the order of the measured electron density values. Even worse, the retrieved values tend sometimes to be negative. Although we cannot rely directly on electron density values at these altitudes, the shape of the profiles could be indicative of some ionospheric features (e.g. waves and sporadic E layers). Above 200 km, the profiles of precision are qualitatively quite independent from daytime or latitude. From all the nearly collocated pairs studied, only 49 exhibited a difference between line of sight angles of both RO at the F peak height larger than 10°. After analyzing them we find no clear indications of a significant representativeness error in electron density profiles due to the spherical assumption above 120 km height. Differences in precision between setting and rising GPS RO may be attributed to the modification of the processing algorithms applied to rising cases

  5. Electron scattering from 4He and Ne clusters: determination of the cluster density from the electronic surface barrier potential

    NASA Astrophysics Data System (ADS)

    Martini, K.; Toennies, J. P.; Winkler, C.

    1991-03-01

    A monoenergetic beam of electrons is scattered from a beam of 4He clusters. The angular distribution of the scattered electronically excited atoms and clusters is measured by an open Venetian-blind multiplier, which is rotatable in the plane of both beams. The threshold electron energy for excitation of the clusters shows a shift to higher energies with respect to the atom component by between 0.6 and 1.1 eV depending on the cluster source temperature T0 ( P0 = 20 bar in all experiments). The observed potential shift Eb is attributed to the surface barrier for penetration of the electrons into the cluster. From the known dependence of Eb on density the core densities of the helium clusters is estimated to vary between n = 1.2 × 10 22 cm -3 and n = 2.2 × 10 22 cm -3 for T0 = 14.9 and 11 K, respectively. The latter values agree with those for bulk liquid helium. For Ne clusters, Eb = 0.7 ± 0.3 eV independent of the source conditions.

  6. Importance of Relativistic Effects and Electron Correlation in Structure Factors and Electron Density of Diphenyl Mercury and Triphenyl Bismuth.

    PubMed

    Bučinský, Lukáš; Jayatilaka, Dylan; Grabowsky, Simon

    2016-08-25

    This study investigates the possibility of detecting relativistic effects and electron correlation in single-crystal X-ray diffraction experiments using the examples of diphenyl mercury (HgPh2) and triphenyl bismuth (BiPh3). In detail, the importance of electron correlation (ECORR), relativistic effects (REL) [distinguishing between total, scalar and spin-orbit (SO) coupling relativistic effects] and picture change error (PCE) on the theoretical electron density, its topology and its Laplacian using infinite order two component (IOTC) wave functions is discussed. This is to develop an understanding of the order of magnitude and shape of these different effects as they manifest in the electron density. Subsequently, the same effects are considered for the theoretical structure factors. It becomes clear that SO and PCE are negligible, but ECORR and scalar REL are important in low- and medium-order reflections on absolute and relative scales-not in the high-order region. As a further step, Hirshfeld atom refinement (HAR) and subsequent X-ray constrained wavefunction (XCW) fitting have been performed for the compound HgPh2 with various relativistic and nonrelativistic wave functions against the experimental structure factors. IOTC calculations of theoretical structure factors and relativistic HAR as well as relativistic XCW fitting are presented for the first time, accounting for both scalar and spin-orbit relativistic effects. PMID:27434184

  7. Dense Helical Electron Bunch Generation in Near-Critical Density Plasmas with Ultrarelativistic Laser Intensities

    PubMed Central

    Hu, Ronghao; Liu, Bin; Lu, Haiyang; Zhou, Meilin; Lin, Chen; Sheng, Zhengming; Chen, Chia-erh; He, Xiantu; Yan, Xueqing

    2015-01-01

    The mechanism for emergence of helical electron bunch(HEB) from an ultrarelativistic circularly polarized laser pulse propagating in near-critical density(NCD) plasma is investigated. Self-consistent three-dimensional(3D) Particle-in-Cell(PIC) simulations are performed to model all aspects of the laser plasma interaction including laser pulse evolution, electron and ion motions. At a laser intensity of 1022 W/cm2, the accelerated electrons have a broadband spectrum ranging from 300 MeV to 1.3 GeV, with the charge of 22 nano-Coulombs(nC) within a solid-angle of 0.14 Sr. Based on the simulation results, a phase-space dynamics model is developed to explain the helical density structure and the broadband energy spectrum. PMID:26503634

  8. Thomson scattering from near-solid density plasmas using soft x-ray free electron lasers

    SciTech Connect

    Holl, A; Bornath, T; Cao, L; Doppner, T; Dusterer, S; Forster, E; Fortmann, C; Glenzer, S H; Gregori, G; Laarmann, T; Meiwes-Broer, K H; Przystawik, A; Radcliffe, P; Redmer, R; Reinholz, H; Ropke, G; Thiele, R; Tiggesbaumker, J; Toleikis, S; Truong, N X; Tschentscher, T; Uschmann, I; Zastrau, U

    2006-11-21

    We propose a collective Thomson scattering experiment at the VUV free electron laser facility at DESY (FLASH) which aims to diagnose warm dense matter at near-solid density. The plasma region of interest marks the transition from an ideal plasma to a correlated and degenerate many-particle system and is of current interest, e.g. in ICF experiments or laboratory astrophysics. Plasma diagnostic of such plasmas is a longstanding issue. The collective electron plasma mode (plasmon) is revealed in a pump-probe scattering experiment using the high-brilliant radiation to probe the plasma. The distinctive scattering features allow to infer basic plasma properties. For plasmas in thermal equilibrium the electron density and temperature is determined from scattering off the plasmon mode.

  9. Density functional calculation of the structural and electronic properties of germanium quantum dots

    SciTech Connect

    Anas, M. M.; Gopir, G.

    2015-04-24

    We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.

  10. Power dependence of electron density at various pressures in inductively coupled plasmas

    SciTech Connect

    Kim, June Young; Kim, Dong-Hwan; Kim, Ju Ho; Jeon, Sang-Bum; Cho, Sung-Won; Chung, Chin-Wook

    2014-11-15

    Experimental observation of the electron density variation in inductively coupled plasmas with the electron energy probability function (EEPFs) was performed at various gas pressures at two RF powers (25 W and 200 W). The measured EEPFs at high power discharges (200 W) showed a Maxwellian distribution, while evolution of the EEPFs from a bi-Maxwellian distribution to a Druyvesteyn-like distribution was observed at low RF powers (25 W) with increasing pressure. A discrepancy of the electron density variation between the two RF powers was observed. This difference is explained by the modified collisional loss and the Bohm velocity from the EEPF of the bi-Maxwellian distribution and the Druyvesteyn–like distribution.

  11. Dense Helical Electron Bunch Generation in Near-Critical Density Plasmas with Ultrarelativistic Laser Intensities.

    PubMed

    Hu, Ronghao; Liu, Bin; Lu, Haiyang; Zhou, Meilin; Lin, Chen; Sheng, Zhengming; Chen, Chia-erh; He, Xiantu; Yan, Xueqing

    2015-01-01

    The mechanism for emergence of helical electron bunch(HEB) from an ultrarelativistic circularly polarized laser pulse propagating in near-critical density(NCD) plasma is investigated. Self-consistent three-dimensional(3D) Particle-in-Cell(PIC) simulations are performed to model all aspects of the laser plasma interaction including laser pulse evolution, electron and ion motions. At a laser intensity of 10(22) W/cm(2), the accelerated electrons have a broadband spectrum ranging from 300 MeV to 1.3 GeV, with the charge of 22 nano-Coulombs(nC) within a solid-angle of 0.14 Sr. Based on the simulation results, a phase-space dynamics model is developed to explain the helical density structure and the broadband energy spectrum. PMID:26503634

  12. Density Functional Theory of Structural and Electronic Properties of III-N Semiconductors

    SciTech Connect

    Guerel, H. Hakan; Akinci, Oezden; Uenlue, Hilmi

    2010-11-01

    In this wok, we present the density functional theory (DFT) calculations of cubic III-N based semiconductors by using the full potential linear augmented plane-wave method plus local orbitals as implemented in the WIEN2k code. Our aim is to predict the pressure effect on structural and electronic properties of III-N binaries and ternaries. Results are given for structural properties (e.g., lattice constant, elastic constants, bulk modulus, and its pressure derivative) and electronic properties (e.g., band structure, density of states, band gaps and band widths) of GaAs, GaN, AlN, and InN binaries and GaAsN ternaries. The proposed model uses GGA exchange-correlation potential to determine band gaps of semiconductors at {Gamma}, L and X high symmetry points of Brillouin zone. The results are found in good agreement with available experimental data for structural and electronic properties of these semiconductors.

  13. Electron density and temperature measurement by continuum radiation emitted from weakly ionized atmospheric pressure plasmas

    SciTech Connect

    Park, Sanghoo; Choe, Wonho; Youn Moon, Se; Park, Jaeyoung

    2014-02-24

    The electron-atom neutral bremsstrahlung continuum radiation emitted from weakly ionized plasmas is investigated for electron density and temperature diagnostics. The continuum spectrum in 450–1000 nm emitted from the argon atmospheric pressure plasma is found to be in excellent agreement with the neutral bremsstrahlung formula with the electron-atom momentum transfer cross-section given by Popović. In 280–450 nm, however, a large discrepancy between the measured and the neutral bremsstrahlung emissivities is observed. We find that without accounting for the radiative H{sub 2} dissociation continuum, the temperature, and density measurements would be largely wrong, so that it should be taken into account for accurate measurement.

  14. Nonlinear magnetic field dependence of spin polarization in high-density two-dimensional electron systems

    NASA Astrophysics Data System (ADS)

    Yang, K. F.; Liu, H. W.; Mishima, T. D.; Santos, M. B.; Nagase, K.; Hirayama, Y.

    2011-08-01

    The spin polarization (P) of high-density InSb two-dimensional electron systems (2DESs) has been measured using both parallel and tilted magnetic fields. P is found to exhibit a superlinear increase with the total field B. This P-B nonlinearity results in a difference in spin susceptibility between its real value χs and χgm~ m*g* (m* and g* are the effective mass and g factor, respectively) as routinely used in experiments. We demonstrate that such a P-B nonlinearity originates from the linearly P-dependent g* due to the exchange coupling of electrons rather than from the electron correlation as predicted for the low-density 2DES.

  15. Photochemical response of the nighttime mesosphere to electric field heating—Recovery of electron density enhancements

    NASA Astrophysics Data System (ADS)

    Kotovsky, D. A.; Moore, R. C.

    2016-02-01

    A photochemical model has been developed to examine the response of the nighttime mesosphere to electric field heating. Time dynamics of 29 chemical species are accounted for by a set of 156 reactions. Recovery dynamics of electron density enhancements are examined in detail, and the recovery timescales of VLF scattering resulting from the modeled conductivity changes are quantitatively estimated. Both typical recovery (up to 240 s) and long recovery (>300 s) timescales of early VLF scattering events are explainable in terms of the model results. Electron production and loss during recovery is determined by a small set of attachment, detachment, and recombination processes. Based on the model results, we conclude that long recovery VLF scattering proceeds from sufficiently large electron density enhancements that are controlled by slow recombination loss (i.e., when attachment loss is small or balanced by detachment).

  16. Density functional theory description of electronic properties of wurtzite zinc oxide

    NASA Astrophysics Data System (ADS)

    Franklin, L.; Ekuma, C. E.; Zhao, G. L.; Bagayoko, D.

    2013-05-01

    We report calculated, electronic properties of wurtzite zinc oxide (w-ZnO). We solved self-consistently the two inherently coupled equations of density functional theory (DFT), following the Bagayoko, Zhao, and Williams (BZW) method as enhanced by the work of Ekuma and Franklin (BZW-EF). We employed a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Most of the calculated, electronic properties of w-ZnO are in excellent agreement with experiment, including our zero temperature band gap of 3.39 eV and the electron effective mass. The doubly self-consistent approach utilized in this work points to the ability of theory to predict accurately key properties of semiconductors and hence to inform and to guide the design and fabrication of semiconductor-based devices.

  17. Electron density diagnostics for gaseous nebulae involving the O 4 intercombination lines near 1400 A

    NASA Technical Reports Server (NTRS)

    Keenan, F. P.; Conlon, E. S.; Bowden, D. A.; Feibelman, W. A.; Pradhan, Anil K.

    1992-01-01

    Theoretical O IV electron density sensitive emission line ratios, determined using electron impact excitation rates calculated with the R-matrix code, are presented for R(sub 1) = I(1407.4 A)/I(1401.2 A), R(sub 2) = I(1404.8 A)/I(1401.2A), R(sub 3) = I(1399.8 A)/(1401.2 A), and R(sub 4) = I(1397.2 A)/I(1401.2 A). The observed values of R(sub 1)-R(sub 4), measured from high resolution spectra obtained with the International Ultraviolet Explorer (IUE) satellite, lead to electron densities that are compatible, and which are also in good agreement with those deduced from line ratios in other species. This provides observational support for the accuracy of the atomic data adopted in the present calculations.

  18. Pairing and unpairing electron densities in organic systems: two-electron three center through space and through bonds interactions.

    PubMed

    Lobayan, Rosana M; Bochicchio, Roberto C

    2014-05-01

    Two-electron three-center bonding interactions in organic ions like methonium (CH5(+)), ethonium (C2H7(+)), and protonated alkanes n - C4H11(+) isomers (butonium cations) are described and characterized within the theoretical framework of the topological analysis of the electron density decomposition into its effectively paired and unpaired contributions. These interactions manifest in some of this type of systems as a concentration of unpaired electron cloud around the bond paths, in contrast to the well known paradigmatic boron hydrids in which it is not only concentrated close to the atomic nucleus and the bond paths but out of them and over the region defined by the involved atoms as a whole. This result permits to propose an attempt of classification for these interactions based in such manifestations. In the first type, it is called as interactions through bonds and in the second type as interactions through space type. PMID:24811636

  19. Upward shift of the vortex solid phase in high-temperature-superconducting wires through high density nanoparticle addition

    NASA Astrophysics Data System (ADS)

    Miura, Masashi; Maiorov, Boris; Balakirev, Fedor F.; Kato, Takeharu; Sato, Michio; Takagi, Yuji; Izumi, Teruo; Civale, Leonardo

    2016-02-01

    We show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO3 nanoparticles. (Y0.77,Gd0.23)Ba2Cu3Oy films were grown on metal substrates with different concentration of BaZrO3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO3 concentration, the nanoparticle size remains constant but the twin-boundary density increases. Up to the highest nanoparticle concentration (n ~ 1.3 × 1022/m3), the irreversibility field (Hirr) continues to increase with no sign of saturation up to 60 T, although the vortices vastly outnumber pinning centers. We find extremely high Hirr, namely Hirr = 30 T (H||45°) and 24 T (H||c) at 65 K and 58 T (H||45°) and 45 T (H||c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged.

  20. Upward shift of the vortex solid phase in high-temperature-superconducting wires through high density nanoparticle addition.

    PubMed

    Miura, Masashi; Maiorov, Boris; Balakirev, Fedor F; Kato, Takeharu; Sato, Michio; Takagi, Yuji; Izumi, Teruo; Civale, Leonardo

    2016-01-01

    We show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO3 nanoparticles. (Y0.77,Gd0.23)Ba2Cu3Oy films were grown on metal substrates with different concentration of BaZrO3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO3 concentration, the nanoparticle size remains constant but the twin-boundary density increases. Up to the highest nanoparticle concentration (n ~ 1.3 × 10(22)/m(3)), the irreversibility field (Hirr) continues to increase with no sign of saturation up to 60 T, although the vortices vastly outnumber pinning centers. We find extremely high Hirr, namely Hirr = 30 T (H||45°) and 24 T (H||c) at 65 K and 58 T (H||45°) and 45 T (H||c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged. PMID:26853703

  1. Upward shift of the vortex solid phase in high-temperature-superconducting wires through high density nanoparticle addition

    PubMed Central

    Miura, Masashi; Maiorov, Boris; Balakirev, Fedor F.; Kato, Takeharu; Sato, Michio; Takagi, Yuji; Izumi, Teruo; Civale, Leonardo

    2016-01-01

    We show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO3 nanoparticles. (Y0.77,Gd0.23)Ba2Cu3Oy films were grown on metal substrates with different concentration of BaZrO3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO3 concentration, the nanoparticle size remains constant but the twin-boundary density increases. Up to the highest nanoparticle concentration (n ~ 1.3 × 1022/m3), the irreversibility field (Hirr) continues to increase with no sign of saturation up to 60 T, although the vortices vastly outnumber pinning centers. We find extremely high Hirr, namely Hirr = 30 T (H||45°) and 24 T (H||c) at 65 K and 58 T (H||45°) and 45 T (H||c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged. PMID:26853703

  2. Upward shift of the vortex solid phase in high-temperature-superconducting wires through high density nanoparticle addition

    DOE PAGESBeta

    Miura, Masashi; Maiorov, Boris; Balakirev, Fedor F.; Kato, Takeharu; Sato, Michio; Takagi, Yuji; Izumi, Teruo; Civale, Leonardo

    2016-02-08

    Here, we show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO3 nanoparticles. (Y0.77,Gd0.23)Ba2Cu3Oy films were grown on metal substrates with different concentration of BaZrO3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO3 concentration, the nanoparticle size remains constant but the twin-boundary density increases. Up to the highest nanoparticle concentration (n ~ 1.3 × 1022/m3), the irreversibility field (Hirr) continues to increase with no sign of saturation up to 60 T, although the vortices vastly outnumbermore » pinning centers. We find extremely high Hirr, namely Hirr = 30 T (H||45°) and 24 T (H||c) at 65 K and 58 T (H||45°) and 45 T (H||c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged.« less

  3. Validation of Spherically Symmetric Inversion by Use of a Tomographically Reconstructed Three-Dimensional Electron Density of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Wang, Tongjiang; Davila, Joseph M.

    2014-01-01

    Determining the coronal electron density by the inversion of white-light polarized brightness (pB) measurements by coronagraphs is a classic problem in solar physics. An inversion technique based on the spherically symmetric geometry (spherically symmetric inversion, SSI) was developed in the 1950s and has been widely applied to interpret various observations. However, to date there is no study of the uncertainty estimation of this method. We here present the detailed assessment of this method using a three-dimensional (3D) electron density in the corona from 1.5 to 4 solar radius as a model, which is reconstructed by a tomography method from STEREO/COR1 observations during the solar minimum in February 2008 (Carrington Rotation, CR 2066).We first show in theory and observation that the spherically symmetric polynomial approximation (SSPA) method and the Van de Hulst inversion technique are equivalent. Then we assess the SSPA method using synthesized pB images from the 3D density model, and find that the SSPA density values are close to the model inputs for the streamer core near the plane of the sky (POS) with differences generally smaller than about a factor of two; the former has the lower peak but extends more in both longitudinal and latitudinal directions than the latter. We estimate that the SSPA method may resolve the coronal density structure near the POS with angular resolution in longitude of about 50 deg. Our results confirm the suggestion that the SSI method is applicable to the solar minimum streamer (belt), as stated in some previous studies. In addition, we demonstrate that the SSPA method can be used to reconstruct the 3D coronal density, roughly in agreement with the reconstruction by tomography for a period of low solar activity (CR 2066). We suggest that the SSI method is complementary to the 3D tomographic technique in some cases, given that the development of the latter is still an ongoing research effort.

  4. Charge, current and spin densities of a two-electron system in Russell-Saunders spin-orbit coupled eigenstates

    NASA Astrophysics Data System (ADS)

    Ayuel, K.; de Châtel, P. F.; Amani, Salah

    2002-04-01

    Charge, current and spin densities are calculated for a two-electron system, maintaining the explicit form of the wave functions, in terms of Slater determinants. The two-electron Russell-Saunders spin-orbit coupled eigenstates | L, S, J, MJ> are expressed as four-component spinors, and the operators of the above densities as 4×4 matrices. The contributions of various one-electron states to these densities are identified.

  5. Dependence of Electron Density on Fermi Energy in N-Type Gallium Antimonide

    PubMed Central

    Bennett, Herbert S.; Hung, Howard

    2003-01-01

    The majority electron density as a function of the Fermi energy is calculated in zinc blende, n-type GaSb for donor densities between 1016 cm−3 and 1019 cm−3. These calculations solve the charge neutrality equation self-consistently for a four-band model (three conduction sub-bands at Γ, L, and X and one equivalent valence band at Γ) of GaSb. Our calculations assume parabolic densities of states and thus do not treat the density-of-states modifications due to high concentrations of dopants, many body effects, and non-parabolicity of the bands. Even with these assumptions, the results are important for interpreting optical measurements such as Raman measurements that are proposed as a nondestructive method for wafer acceptance tests.

  6. Effect of SiO2 and Al2O3 addition on the density, Tg and CTE of mixed alkali - alkaline earth borate glass

    NASA Astrophysics Data System (ADS)

    Deshpande, A. M.; Deshpande, V. K.

    2009-07-01

    Mixed alkali — alkaline earth borate glasses, with the addition of silica and alumina, have been studied for their density, Tg and CTE with a view of exploring the applicability of these glasses in glass to metal sealing applications. It has been observed that silica addition results in an increase in density and Tg while the alumina addition decreases the density and Tg. The variation in CTE exhibits minima with the addition of both, silica and alumina. An attempt is made here to explain the observed variations in the properties on the basis of different mass of the additives, number of non bridging oxygens (NBOs) and other changes in the glass network.

  7. Real-time electron density measurements from Cotton-Mouton effect in JET machine

    SciTech Connect

    Brombin, M.; Boboc, A.; Zabeo, L.

    2008-10-15

    Real-time density profile measurements are essential for advanced fusion tokamak operation and interferometry is a proven method for this task. Nevertheless, as a consequence of edge localized modes, pellet injections, fast density increases, or disruptions, the interferometer is subject to fringe jumps, which produce loss of the signal preventing reliable use of the measured density in a real-time feedback controller. An alternative method to measure the density is polarimetry based on the Cotton-Mouton effect, which is proportional to the line-integrated electron density. A new analysis approach has been implemented and tested to verify the reliability of the Cotton-Mouton measurements for a wide range of plasma parameters and to compare the density evaluated from polarimetry with that from interferometry. The density measurements based on polarimetry are going to be integrated in the real-time control system of JET since the difference with the interferometry is within one fringe for more than 90% of the cases.

  8. Evidence for density-gradient-driven trapped-electron modes in improved confinement RFP plasmas

    NASA Astrophysics Data System (ADS)

    Duff, James; Chapman, Brett; Sarff, John; Terry, Paul; Williams, Zach; Ding, Weixing; Brower, David; Parke, Eli

    2015-11-01

    Density fluctuations in the large-density-gradient region of improved-confinement MST RFP plasmas exhibit features characteristic of the trapped-electron-mode (TEM), strong evidence that drift wave turbulence emerges in RFP plasmas when magnetic transport is reduced. In standard RFP plasmas, core transport is governed by magnetic stochasticity stemming from current-driven tearing modes. Using inductive control, these tearing modes are reduced, improving confinement. The improved confinement is associated with substantial increases in the density and temperature gradients, and we present evidence for the onset of drift wave instability. Density fluctuations are measured with a multi-chord, laser-based interferometer. These fluctuations have wavenumbers kϕ *ρs <0.14, frequencies characteristic of drift waves (>50 kHz), and are clearly distinct from residual global tearing modes. Their amplitudes increase with the local density gradient, and require a critical density gradient. Gyrokinetic analysis provides supporting evidence of microinstability in these plasmas, in which the density-gradient-driven TEM is most unstable. The experimental threshold gradient is close to the predicted critical gradient for linear stability. Work supported by DOE.

  9. High-Altitude High-Latitude Electron-Density and Magnetic-Field Enhancements Observed during Magnetic Storms - Including the Storm of 17 April 2002

    NASA Technical Reports Server (NTRS)

    Benson, Robert F.; Bilitza, Dieter; Grebowsky, Joseph M.; Truhlik, Vladimir; Wang, Yongli; Reinisch, Bodo W.

    2009-01-01

    In addition to the spectacular remote measurements from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite [Burch, Space Sci. Rev., 2003], the Radio Plasma Imager (RPI) on IMAGE had the capability of making accurate magnetospheric local electron-density and magnetic-field determinations in addition to obtaining remote electron-density profiles [Reinisch et al., GRL, 2001; Benson et al., JGR, 2003]. These determinations were made using interleaved passive and active modes of operation of the RPI; the former were used to produce dynamic spectra and the latter to produce plasmagrams during active sounding. The plasmagrams of particular interest in this investigation were produced during the apogee (8 RE) portion of the IMAGE orbit when the RPI often operated in a high-resolution mode (300 Hz frequency steps) designed for accurate frequency measurements of sounder-stimulated plasma resonances. Here we present examples from 2001 and 2002, when the IMAGE apogee was at high latitudes, of large increase the electron density and magnetic-field intensity (relative to quiet control conditions) during magnetic storms. During the 17 April 2002 storm, the electron density increased by about a factor of 4 and the magnetic-field intensity increased by nearly a factor of 2. During the much larger storm of 31 March 2001, the RPI data presented in Osherovich et al. [2007] indicates that the electron density increased by about a factor of 10.

  10. Measurement of electron density transients in pulsed RF discharges using a frequency boxcar hairpin probe

    NASA Astrophysics Data System (ADS)

    Peterson, David; Coumou, David; Shannon, Steven

    2015-11-01

    Time resolved electron density measurements in pulsed RF discharges are shown using a hairpin resonance probe using low cost electronics, on par with normal Langmuir probe boxcar mode operation. Time resolution of 10 microseconds has been demonstrated. A signal generator produces the applied microwave frequency; the reflected waveform is passed through a directional coupler and filtered to remove the RF component. The signal is heterodyned with a frequency mixer and rectified to produce a DC signal read by an oscilloscope. At certain points during the pulse, the plasma density is such that the applied frequency is the same as the resonance frequency of the probe/plasma system, creating reflected signal dips. The applied microwave frequency is shifted in small increments in a frequency boxcar routine to determine the density as a function of time. A dc sheath correction is applied for the grounded probe, producing low cost, high fidelity, and highly reproducible electron density measurements. The measurements are made in both inductively and capacitively coupled systems, the latter driven by multiple frequencies where a subset of these frequencies are pulsed. Measurements are compared to previous published results, time resolved OES, and in-line measurement of plasma impedance. This work is supported by the NSF DOE partnership on plasma science, the NSF GOALI program, and MKS Instruments.

  11. Long-range density-matrix-functional theory: Application to a modified homogeneous electron gas

    SciTech Connect

    Pernal, Katarzyna

    2010-05-15

    We propose a method that employs functionals of the one-electron reduced density matrix (density matrix) to capture long-range effects of electron correlation. The complementary short-range regime is treated with density functionals. In an effort to find approximations for the long-range density-matrix functional, a modified power functional is applied to the homogeneous electron gas with Coulomb interactions replaced by their corresponding long-range counterparts. For the power {beta}=1/2 and the range-separation parameter {omega}=1/r{sub s}, the functional reproduces the correlation and the kinetic correlation energies with a remarkable accuracy for intermediate and large values of r{sub s}. Analysis of the Euler equation corresponding to this functional reveals correct r{sub s} expansion of the correlation energy in the limit of large r{sub s}. The first expansion coefficient is in very good agreement with that obtained from the modified Wigner-Seitz model.

  12. Validation of ISS Floating Potential Measurement Unit Electron Densities and Temperatures

    NASA Technical Reports Server (NTRS)

    Coffey, Victoria N.; Minow, Joseph I.; Parker, Linda N.; Bui, Them; Wright, Kenneth, Jr.; Koontz, Steven L.; Schneider, T.; Vaughn, J.; Craven, P.

    2007-01-01

    Validation of the Floating Potential Measurement Unit (FPMU) electron density and temperature measurements is an important step in the process of evaluating International Space Station spacecraft charging issues .including vehicle arcing and hazards to crew during extravehicular activities. The highest potentials observed on Space Station are due to the combined VxB effects on a large spacecraft and the collection of ionospheric electron and ion currents by the 160 V US solar array modules. Ionospheric electron environments are needed for input to the ISS spacecraft charging models used to predict the severity and frequency of occurrence of ISS charging hazards. Validation of these charging models requires comparing their predictions with measured FPMU values. Of course, the FPMU measurements themselves must also be validated independently for use in manned flight safety work. This presentation compares electron density and temperatures derived from the FPMU Langmuir probes and Plasma Impedance Probe against the independent density and temperature measurements from ultraviolet imagers, ground based incoherent scatter radar, and ionosonde sites.

  13. Variations of the ionospheric electron density during the Bhuj seismic event

    NASA Astrophysics Data System (ADS)

    Trigunait, A.; Parrot, M.; Pulinets, S.; Li, F.

    2004-12-01

    Ionospheric perturbations by natural geophysical activity, such as volcanic eruptions and earthquakes, have been studied since the great Alaskan earthquake in 1964. Measurements made from the ground show a variation of the critical frequency of the ionosphere layers before and after the shock. In this paper, we present an experimental investigation of the electron density variations around the time of the Bhuj earthquake in Gujarat, India. Several experiments have been used to survey the ionosphere. Measurements of fluctuations in the integrated electron density or TEC (Total Electron Content) between three satellites (TOPEX-POSEIDON, SPOT2, SPOT4) and the ground have been done using the DORIS beacons. TEC has been also evaluated from a ground-based station using GPS satellites, and finally, ionospheric data from a classical ionospheric sounder located close to the earthquake epicenter are utilized. Anomalous electron density variations are detected both in day and night times before the quake. The generation mechanism of these perturbations is explained by a modification of the electric field in the global electric circuit induced during the earthquake preparation.

  14. Coaxial wet-spun yarn supercapacitors for high-energy density and safe wearable electronics.

    PubMed

    Kou, Liang; Huang, Tieqi; Zheng, Bingna; Han, Yi; Zhao, Xiaoli; Gopalsamy, Karthikeyan; Sun, Haiyan; Gao, Chao

    2014-01-01

    Yarn supercapacitors have great potential in future portable and wearable electronics because of their tiny volume, flexibility and weavability. However, low-energy density limits their development in the area of wearable high-energy density devices. How to enhance their energy densities while retaining their high-power densities is a critical challenge for yarn supercapacitor development. Here we propose a coaxial wet-spinning assembly approach to continuously spin polyelectrolyte-wrapped graphene/carbon nanotube core-sheath fibres, which are used directly as safe electrodes to assembly two-ply yarn supercapacitors. The yarn supercapacitors using liquid and solid electrolytes show ultra-high capacitances of 269 and 177 mF cm(-2) and energy densities of 5.91 and 3.84 μWh cm(-2), respectively. A cloth supercapacitor superior to commercial capacitor is further interwoven from two individual 40-cm-long coaxial fibres. The combination of scalable coaxial wet-spinning technology and excellent performance of yarn supercapacitors paves the way to wearable and safe electronics. PMID:24786366

  15. Coaxial wet-spun yarn supercapacitors for high-energy density and safe wearable electronics

    PubMed Central

    Kou, Liang; Huang, Tieqi; Zheng, Bingna; Han, Yi; Zhao, Xiaoli; Gopalsamy, Karthikeyan; Sun, Haiyan; Gao, Chao

    2014-01-01

    Yarn supercapacitors have great potential in future portable and wearable electronics because of their tiny volume, flexibility and weavability. However, low-energy density limits their development in the area of wearable high-energy density devices. How to enhance their energy densities while retaining their high-power densities is a critical challenge for yarn supercapacitor development. Here we propose a coaxial wet-spinning assembly approach to continuously spin polyelectrolyte-wrapped graphene/carbon nanotube core-sheath fibres, which are used directly as safe electrodes to assembly two-ply yarn supercapacitors. The yarn supercapacitors using liquid and solid electrolytes show ultra-high capacitances of 269 and 177 mF cm−2 and energy densities of 5.91 and 3.84 μWh cm−2, respectively. A cloth supercapacitor superior to commercial capacitor is further interwoven from two individual 40-cm-long coaxial fibres. The combination of scalable coaxial wet-spinning technology and excellent performance of yarn supercapacitors paves the way to wearable and safe electronics. PMID:24786366

  16. Coaxial wet-spun yarn supercapacitors for high-energy density and safe wearable electronics

    NASA Astrophysics Data System (ADS)

    Kou, Liang; Huang, Tieqi; Zheng, Bingna; Han, Yi; Zhao, Xiaoli; Gopalsamy, Karthikeyan; Sun, Haiyan; Gao, Chao

    2014-05-01

    Yarn supercapacitors have great potential in future portable and wearable electronics because of their tiny volume, flexibility and weavability. However, low-energy density limits their development in the area of wearable high-energy density devices. How to enhance their energy densities while retaining their high-power densities is a critical challenge for yarn supercapacitor development. Here we propose a coaxial wet-spinning assembly approach to continuously spin polyelectrolyte-wrapped graphene/carbon nanotube core-sheath fibres, which are used directly as safe electrodes to assembly two-ply yarn supercapacitors. The yarn supercapacitors using liquid and solid electrolytes show ultra-high capacitances of 269 and 177 mF cm-2 and energy densities of 5.91 and 3.84 μWh cm-2, respectively. A cloth supercapacitor superior to commercial capacitor is further interwoven from two individual 40-cm-long coaxial fibres. The combination of scalable coaxial wet-spinning technology and excellent performance of yarn supercapacitors paves the way to wearable and safe electronics.

  17. Unequal density effect on static structure factor of coupled electron layers

    SciTech Connect

    Saini, L. K. Nayak, Mukesh G.

    2014-04-24

    In order to understand the ordered phase, if any, in a real coupled electron layers (CEL), there is a need to take into account the effect of unequal layer density. Such phase is confirmed by a strong peak in a static structure factor. With the aid of quantum/dynamical version of Singwi, Tosi, Land and Sjölander (so-called qSTLS) approximation, we have calculated the intra- and interlayer static structure factors, S{sub ll}(q) and S{sub 12}(q), over a wide range of density parameter r{sub sl} and interlayer spacing d. In our present study, the sharp peak in S{sub 22}(q) has been found at critical density with sufficiently lower interlayer spacing. Further, to find the resultant effect of unequal density on intra- and interlayer static structure factors, we have compared our results with that of the recent CEL system with equal layer density and isolated single electron layer.

  18. Experimental and Theoretical Electron Density Analysis of Copper Pyrazine Nitrate Quasi-Low-Dimensional Quantum Magnets.

    PubMed

    Dos Santos, Leonardo H R; Lanza, Arianna; Barton, Alyssa M; Brambleby, Jamie; Blackmore, William J A; Goddard, Paul A; Xiao, Fan; Williams, Robert C; Lancaster, Tom; Pratt, Francis L; Blundell, Stephen J; Singleton, John; Manson, Jamie L; Macchi, Piero

    2016-02-24

    The accurate electron density distribution and magnetic properties of two metal-organic polymeric magnets, the quasi-one-dimensional (1D) Cu(pyz)(NO3)2 and the quasi-two-dimensional (2D) [Cu(pyz)2(NO3)]NO3·H2O, have been investigated by high-resolution single-crystal X-ray diffraction and density functional theory calculations on the whole periodic systems and on selected fragments. Topological analyses, based on quantum theory of atoms in molecules, enabled the characterization of possible magnetic exchange pathways and the establishment of relationships between the electron (charge and spin) densities and the exchange-coupling constants. In both compounds, the experimentally observed antiferromagnetic coupling can be quantitatively explained by the Cu-Cu superexchange pathway mediated by the pyrazine bridging ligands, via a σ-type interaction. From topological analyses of experimental charge-density data, we show for the first time that the pyrazine tilt angle does not play a role in determining the strength of the magnetic interaction. Taken in combination with molecular orbital analysis and spin density calculations, we find a synergistic relationship between spin delocalization and spin polarization mechanisms and that both determine the bulk magnetic behavior of these Cu(II)-pyz coordination polymers. PMID:26811927

  19. Critic: a new program for the topological analysis of solid-state electron densities

    NASA Astrophysics Data System (ADS)

    Otero-de-la-Roza, A.; Blanco, M. A.; Pendás, A. Martín; Luaña, Víctor

    2009-01-01

    In this paper we introduce CRITIC, a new program for the topological analysis of the electron densities of crystalline solids. Two different versions of the code are provided, one adapted to the LAPW (Linear Augmented Plane Wave) density calculated by the WIEN2K package and the other to the ab initio Perturbed Ion ( aiPI) density calculated with the PI7 code. Using the converged ground state densities, CRITIC can locate their critical points, determine atomic basins and integrate properties within them, and generate several graphical representations which include topological atomic basins and primary bundles, contour maps of ρ and ∇ρ, vector maps of ∇ρ, chemical graphs, etc. Program summaryProgram title: CRITIC Catalogue identifier: AECB_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECB_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GPL, version 3 No. of lines in distributed program, including test data, etc.: 1 206 843 No. of bytes in distributed program, including test data, etc.: 12 648 065 Distribution format: tar.gz Programming language: FORTRAN 77 and 90 Computer: Any computer capable of compiling Fortran Operating system: Unix, GNU/Linux Classification: 7.3 Nature of problem: Topological analysis of the electron density in periodic solids. Solution method: The automatic localization of the electron density critical points is based on a recursive partitioning of the Wigner-Seitz cell into tetrahedra followed by a Newton search from significant points on each tetrahedra. Plotting of and integration on the atomic basins is currently based on a new implementation of Keith's promega algorithm. Running time: Variable, depending on the task. From seconds to a few minutes for the localization of critical points. Hours to days for the determination of the atomic basins shape and properties. Times correspond to a typical 2007 PC.

  20. Electron density and collision frequency of microwave resonant cavity produced discharges. [Progress report

    SciTech Connect

    McColl, W.; Brooks, C.; Brake, M.L.

    1992-12-31

    This progress report consists of an article, the abstract of which follows, and apparently the references and vita from a proposal. A review of perturbation diagnostics applied to microwave resonant cavity discharges is presented. The classical microwave perturbation technique examines the shift in the resonant frequency and cavity quality factor of the resonant cavity caused by low electron density discharges. However, modifications presented here allow the analysis to be applied to discharges with electron densities beyond the limit predicted by perturbation theory. An {open_quote}exact{close_quote} perturbation analysis is presented which models the discharge as a separate dielectric, thereby removing the restrictions on electron density imposed by the classical technique. The {open_quote}exact{close_quote} method also uses measurements of the shifts in the resonant conditions of the cavity. Thirdly, an electromagnetic analysis is presented which uses a characteristic equation, based upon Maxwell`s laws, and predicts the discharge conductivity based upon measurements of a complex axial wave number. By allowing the axial wave number of the electromagnetic fields to be complex, the fields are experimentally and theoretically shown to be spatially attenuated. The diagnostics are applied to continuous-wave microwave (2.45 GHz) discharges produced in an Asmussen resonant cavity. Double Langmuir probes, placed directly in the discharge at the point where the radial electric field is zero, act as a comparison with the analytic diagnostics. Microwave powers ranging from 30 to 100 watts produce helium and nitrogen discharges with pressures ranging from 0.5 to 6 torr. Analysis of the data predicts electron temperatures from 5 to 20 eV, electron densities from 10{sup 11} to 3 {times} 10{sup 12} cm{sup {minus}3}, and collision frequencies from 10{sup 9} to 10{sup 11} sec{sup {minus}1}.

  1. Validation of COSMIC radio occultation electron density profiles by incoherent scatter radar data

    NASA Astrophysics Data System (ADS)

    Cherniak, Iurii; Zakharenkova, Irina

    The COSMIC/FORMOSAT-3 is a joint US/Taiwan radio occultation mission consisting of six identical micro-satellites. Each microsatellite has a GPS Occultation Experiment payload to operate the ionospheric RO measurements. FS3/COSMIC data can make a positive impact on global ionosphere study providing essential information about height electron density distribu-tion. For correct using of the RO electron density profiles for geophysical analysis, modeling and other applications it is necessary to make validation of these data with electron density distributions obtained by another measurement techniques such as proven ground based facili-ties -ionosondes and IS radars. In fact as the ionosondes provide no direct information on the profile above the maximum electron density and the topside ionosonde profile is obtained by fitting a model to the peak electron density value, the COSMIC RO measurements can make an important contribution to the investigation of the topside part of the ionosphere. IS radars provide information about the whole electron density profile, so we can estimate the agreement of topside parts between two independent measurements. To validate the reliability of COS-MIC data we have used the ionospheric electron density profiles derived from IS radar located near Kharkiv, Ukraine (geographic coordinates: 49.6N, 36.3E, geomagnetic coordinates: 45.7N, 117.8E). The Kharkiv radar is a sole incoherent scatter facility on the middle latitudes of Eu-ropean region. The radar operates with 100-m zenith parabolic antenna at 158 MHz with peak transmitted power 2.0 MW. The Kharkiv IS radar is able to determine the heights-temporal distribution of ionosphere parameters in height range of 70-1500 km. At the ionosphere in-vestigation by incoherent scatter method there are directly measured the power spectrum (or autocorrelation function) of scattered signal. With using of rather complex procedure of the received signal processing it is possible to estimate the

  2. Persistent order due to transiently enhanced nesting in an electronically excited charge density wave

    PubMed Central

    Rettig, L.; Cortés, R.; Chu, J.-H.; Fisher, I. R.; Schmitt, F.; Moore, R. G.; Shen, Z.-X.; Kirchmann, P. S.; Wolf, M.; Bovensiepen, U.

    2016-01-01

    Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time- and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of the dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. Our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order. PMID:26804717

  3. Photoemission study of the electronic structure and charge density waves of Na₂Ti₂Sb₂O

    SciTech Connect

    Tan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L.

    2015-04-30

    The electronic structure of Na₂Ti₂Sb₂O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na₂Ti₂Sb₂O in the non-magnetic state, which indicates that there is no magnetic order in Na₂Ti₂Sb₂O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na₂Ti₂Sb₂O. Photon energy dependent ARPES results suggest that the electronic structure of Na₂Ti₂Sb₂O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV at 7 K, indicating that Na₂Ti₂Sb₂O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime. (author)

  4. A hybrid density functional study on the electron and hole trap states in anatase titanium dioxide.

    PubMed

    Yamamoto, Takenori; Ohno, Takahisa

    2012-01-14

    We present a theoretical study on electron and hole trap states in the bulk and (001) surface of anatase titanium dioxide using screened hybrid density functional calculations. In both the bulk and surface, calculations suggest that the neutral and ionized oxygen vacancies are possible electron traps. The doubly ionized oxygen vacancy is the most stable in the bulk, and is a candidate for a shallow donor in colorless anatase crystals. The hole trap states are localized at oxygen anions in both the bulk and surface. The self-trapped electron centered at a titanium cation cannot be produced in the bulk, but can be formed at the surface. The electron trap level at the surface oxygen vacancy is consistent with observations by photoelectron spectroscopy. The optical absorptions and luminescence in UV-irradiated anatase nanoparticles are found to come from the surface self-trapped hole and the surface oxygen vacancy. PMID:22127526

  5. Electron beam fluorescence system to measure gas density in impulse facilities

    NASA Technical Reports Server (NTRS)

    Hoppe, J. C.

    1974-01-01

    Very rapid measurements, ranging from a few microsecond to milliseconds in duration, characterize studies made in shock regions or behind them. A system to measure gas density under such conditions in a 15.24-cm (6-in.) expansion tube is described. The basic elements are an electron beam of moderate energy and high current capability, an optical detector, and the associated electronics and data readout equipment. A heated-cathode electron gun, capable of pulsed operation and delivering up to 200 milliamperes current, provides the source of electrons. Optics include a simple collector lens, aperture, collimator lens, filters, and a photomultiplier tube. The photomultiplier output signal was recorded by means of photographed oscilloscope traces for pulsed beam operation.

  6. Energies and densities of electrons confined in elliptical and ellipsoidal quantum dots.

    PubMed

    Halder, Avik; Kresin, Vitaly V

    2016-10-01

    We consider a droplet of electrons confined within an external harmonic potential well of elliptical or ellipsoidal shape, a geometry commonly encountered in work with semiconductor quantum dots and other nanoscale or mesoscale structures. For droplet sizes exceeding the effective Bohr radius, the dominant contribution to average system parameters in the Thomas-Fermi approximation comes from the potential energy terms, which allows us to derive expressions describing the electron droplet's shape and dimensions, its density, total and capacitive energy, and chemical potential. The analytical results are in very good agreement with experimental data and numerical calculations, and make it possible to follow the dependence of the properties of the system on its parameters (the total number of electrons, the axial ratios and curvatures of the confinement potential, and the dielectric constant of the material). An interesting feature is that the eccentricity of the electron droplet is not the same as that of its confining potential well. PMID:27502044

  7. Nano-structure multilayer technology fabrication of high energy density capacitors for the power electronic building book

    SciTech Connect

    Barbee, T.W.; Johnson, G.W.; Wagner, A.V.

    1997-10-21

    Commercially available capacitors do not meet the specifications of the Power Electronic Building Block (PEBB) concept. We have applied our propriety nanostructure multilayer materials technology to the fabrication of high density capacitors designed to remove this impediment to PEBB progress. Our nanostructure multilayer capacitors will also be enabling technology in many industrial and military applications. Examples include transient suppression (snubber capacitors), resonant circuits, and DC filtering in PEBB modules. Additionally, weapon applications require compact energy storage for detonators and pulsed-power systems. Commercial applications run the gamut from computers to lighting to communications. Steady progress over the last five years has brought us to the threshold of commercial manufacturability. We have demonstrated a working dielectric energy density of > 11 J/cm3 in 20 nF devices designed for 1 kV operation.

  8. Recent electron temperature and density results from the ATF Thomson scattering system

    SciTech Connect

    Rasmussen, D.A.; England, A.C.; Murakami, M.; Howe, H.C.; Clark, T.L.; Kindsfather, R.R.; Rayburn, T.M.; Stewart, K.A.; Rogers, P.S.; Bell, G.L.

    1989-01-01

    A spatial multipoint Thomson scattering system has been developed for the Advanced Toroidal Facility (ATF) torsatron. The system measures temperature and density at 15 vertical locations on a vertical chord for each laser shot (one per plasma discharge). By remotely relocating the laser beam and reconfiguring the viewing optics during a series of ATF discharges, a two-dimensional (2-D) electron temperature and density map of the plasma cross section can be obtained. Results obtained with this system during ATF operation in 1988 and early 1989 are presented. 7 refs., 6 figs.

  9. Structural and electronic properties of poly(vinyl alcohol) using density functional theory

    SciTech Connect

    Dabhi, Shweta Jha, Prafulla K.

    2014-04-24

    The first principles calculations have been carried out to investigate the structural, electronic band structure density of states along with the projected density of states for poly(vinyl alcohol). Our structural calculation suggests that the poly(vinyl alcohol) exhibits monoclinic structure. The calculated structural lattice parameters are in excellent agreement with available experimental values. The band structure calculations reveal that the direct and indirect band gaps are 5.55 eV and 5.363 eV respectively in accordance with experimental values.

  10. Local conditions for the Pauli potential in order to yield self-consistent electron densities exhibiting proper atomic shell structure

    NASA Astrophysics Data System (ADS)

    Finzel, Kati

    2016-01-01

    The local conditions for the Pauli potential that are necessary in order to yield self-consistent electron densities from orbital-free calculations are investigated for approximations that are expressed with the help of a local position variable. It is shown that those local conditions also apply when the Pauli potential is given in terms of the electron density. An explicit formula for the Ne atom is given, preserving the local conditions during the iterative procedure. The resulting orbital-free electron density exhibits proper shell structure behavior and is in close agreement with the Kohn-Sham electron density. This study demonstrates that it is possible to obtain self-consistent orbital-free electron densities with proper atomic shell structure from simple one-point approximations for the Pauli potential at local density level.

  11. Chemostat Studies of TCE-Dehalogenating Anaerobic Consortia under Excess and Limited Electron Donor Addition

    NASA Astrophysics Data System (ADS)

    Semprini, L.; Azizian, M.; Green, J.; Mayer-Blackwell, K.; Spormann, A. M.

    2015-12-01

    Two cultures - the Victoria Strain (VS) and the Evanite Strain (EV), enriched with the organohalide respiring bacteria Dehalococcoides mccartyi - were grown in chemostats for more than 4 years at a mean cell residence time of 50 days. The slow doubling rate represents growth likely experienced in the subsurface. The chemostats were fed formate as an electron donor and trichloroethene (TCE) as the terminal electron acceptor. Under excess formate conditions, stable operation was observed with respect to TCE transformation, steady-state hydrogen (H2) concentrations (40 nM), and the structure of the dehalogenating community. Both cultures completely transformed TCE to ethene, with minor amounts of vinyl chloride (VC) observed, along with acetate formation. When formate was limited, TCE was transformed incompletely to ethene (40-60%) and VC (60- 40%), and H2 concentrations ranged from 1 to 3 nM. The acetate concentration dropped below detection. Batch kinetic studies of TCE transformation with chemostat harvested cells found transformation rates of c-DCE and VC were greatly reduced when the cells were grown with limited formate. Upon increasing formate addition to the chemostats, from limited to excess, essentially complete transformation of TCE to ethene was achieved. The increase in formate was associated with an increase in H2 concentration and the production of acetate. Results of batch kinetic tests showed increases in transformation rates for TCE and c-DCE by factors of 3.5 and 2.5, respectively, while VC rates increased by factors of 33 to 500, over a six month period. Molecular analysis of chemostat samples is being performed to quantify the changes in copy numbers of reductase genes and to determine whether shifts in the strains of Dehalococcoides mccartyi where responsible for the observed rate increases. The results demonstrate the importance of electron donor supply for successful in-situ remediation.

  12. The variational two-electron reduced-density-matrix method for extended systems

    NASA Astrophysics Data System (ADS)

    Rubin, Nicholas C.

    In this thesis we develop the variational two-electron reduced-density-matrix method for extended systems. Extended systems are represented in two ways: i) lattice models describing the dominant valence electronic structure with periodic boundaries to account for their extended nature and ii) a crystalline-orbital basis built from atomic orbitals using the generalization of molecular orbital theory to polymers. The first part of this thesis (Ch. 3--4) examines the performance of the variational 2-RDM method on lattice systems with tunable electron correlation. The first of these systems is the classic Hubbard model with linear and ladder lattice topologies. Because electron correlation functions, such as charge- and spin-ordering, are linear functions of the 2-RDM, the difference in electronic structure between one- and quasi-one-dimensional systems is accurately characterized. The second model contains only two-body interactions and is unique among typical spin models in that it does not have a mean-field reference wave function. The ground state wave functions from all Hamiltonians in the model have the same 1-electron reduced density matrix; consequently, one-electron theories are largely inapplicable. The superconducting eta-pairing ground states make the model a unique tool for demonstrating the necessary N-representability in highly correlated environments. The second part of this thesis (Ch. 5--6) develops a formalism for modeling materials by solving the full Schrodinger equation. Crystalline-orbital Hartree-Fock provides a set of orbitals and integral tensors for the variational 2-RDM method. We demonstrate that time-reversal symmetry, which is implicitly included in position space electronic structure calculations, must be explicitly included as an N-representability constraint on the 2-RDM when using a momentum space basis. The necessity of these equality constraints is demonstrated by the accurate recovery of the binding energy of two polymers and the

  13. Emergent phenomena and magnetism in high-density electron gases in SrTiO3

    NASA Astrophysics Data System (ADS)

    Stemmer, Susanne

    2013-03-01

    GdTiO3/SrTiO3 interfaces grown by molecular beam epitaxy exhibit mobile carrier densities that are remarkably well predicted by the electrostatic requirements of the compensation of the polar discontinuity at the interface. Carrier densities are ~3x1014 cm-2, or ~0.5 electron per surface unit cell. By sandwiching few-unit-cell-thick SrTiO3 layers between GdTiO3, carrier concentrations in the SrTiO3 approach densities under which on-site Coulomb interactions may appear. By changing the width of the quantum well, the 3D electron density can be varied, which allows for a systematic study of interaction effects. In this presentation, we discuss evidence for short-range Coulomb interactions, and associated phenomena, in ultrathin, confined the SrTiO3 quantum wells containing extreme charge densities. We show that narrow SrTiO3 quantum wells exhibit ferromagnetism at low temperatures, as evidenced by a hysteresis in the magnetoresistance. The Curie temperature scales with the thickness of the SrTiO3 quantum well. We discuss evidence for on-site Mott-Hubbard-type correlation physics in the temperature-dependent transport in metallic quantum wells. With increasing 3D carrier densities we observe a correlation-induced mass enhancement, followed by a transition to a correlated insulator at the highest 3D densities. We also discuss the role of disorder in the insulating state. This work was done in collaboration with Pouya Moetakef, Clayton A. Jackson, Leon Balents, Jim Allen, Jimmy Williams and David Goldhaber-Gordon.

  14. Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory.

    PubMed

    Tait, E W; Ratcliff, L E; Payne, M C; Haynes, P D; Hine, N D M

    2016-05-18

    Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable. PMID:27094207

  15. Electron densities of bexarotene and disila-bexarotene from invariom application: a comparative study.

    PubMed

    Luger, Peter; Weber, Manuela; Hübschle, Christian; Tacke, Reinhold

    2013-04-14

    By the application of the invariom formalism, which provides aspherical atomic scattering factors, the electron densities of the RXR-selective retinoid agonists bexarotene (1a) and disila-bexarotene (1b) were derived from their known low resolution (d = 0.76 Å) crystal structures. The density distributions allowed us to make a comparison of the electronic properties of these pharmacologically relevant compounds. Differences were found to be restricted to relatively small regions in the terminal six-membered rings of the tetrahydronaphthalene and tetrahydrodisilanaphthalene fragments. In total, the replacement of two carbon atoms in 1a by silicon atoms (→1b) does neither influence the electronic structures nor the pharmacological properties (RXR receptor activation) significantly. It should be noted that the almost completely software supported invariom formalism can yield electronic information for biologically interacting systems with moderate effort. This offers interesting possibilities for drug research, in that steric and electronic information can be combined for the analysis of intermolecular recognition and interaction on an atomic scale. This approach is also valuable for the design and development of silicon-containing drugs using the carbon/silicon switch strategy. PMID:23429500

  16. Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory

    NASA Astrophysics Data System (ADS)

    Tait, E. W.; Ratcliff, L. E.; Payne, M. C.; Haynes, P. D.; Hine, N. D. M.

    2016-05-01

    Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable.

  17. Analysis of lithium driven electron density peaking in FTU liquid lithium limiter experiments

    NASA Astrophysics Data System (ADS)

    Szepesi, G.; Romanelli, M.; Militello, F.; Peeters, A. G.; Camenen, Y.; Casson, F. J.; Hornsby, W. A.; Snodin, A. P.; Wágner, D.; the FTU Team

    2013-03-01

    The impact of lithium impurities on the microstability and turbulent transport characteristics in the core of a typical FTU liquid lithium limiter (LLL) (Mazzitelli et al 2011 Nucl. Fusion 51 073006) discharge during the density ramp-up phase is studied. A non-linear gyrokinetic analysis performed with GKW (Peeters et al 2009 Comput. Phys. Commun. 180 2650) accompanied by a quasi-linear fluid analysis is presented. We show that a centrally peaked, high concentration lithium profile contributes to the electron peaking by reducing the outward electron flux, and that it leads to inward turbulent deuterium transport through ion flux separation.

  18. Charge density harmonics generation in free-electron relativistic parametric devices.

    PubMed

    Baccaro, S; Demartini, F; Ghigo, A

    1982-04-01

    A single-particle theory of the evolution of the harmonic content of a bunched beam in a relativistic optical klystron is reported. The equations of motion of the electrons in the dispersive-magnetic-drift space are solved analytically, including the effects of the energy and angular spreads of the beam. The theory enables one to predict the optical efficiency of a coherent relativistic scatterer designed for the generation of the third harmonics of the charge density wave (lambda(sc) = 1766 A) induced on the electron beam of the Frascati storage ring, Adone, with gamma = 1200. PMID:19710862

  19. Communication: Reduced density matrices in molecular systems: Grand-canonical electron states

    SciTech Connect

    Bochicchio, Roberto C.; Miranda-Quintana, Ramón A.; Rial, Diego

    2013-11-21

    Grand-canonical like descriptions of many electron atomic and molecular open systems which are characterized by a non-integer number of electrons are presented. Their associated reduced density matrices (RDMs) are obtained by introducing the contracting mapping for this type of distributions. It is shown that there is loss of information when connecting RDMs of different order by partial contractions. The energy convexity property of these systems simplifies the description. Consequently, this formulation opens the possibility to a new look for chemical descriptors such as chemical potential and reactivity among others. Examples are presented to discuss the theoretical aspects of this work.

  20. Electron affinities for rare gases and some actinides from local-spin-density-functional theory

    SciTech Connect

    Guo, Y.; Wrinn, M.C.; Whitehead, M.A. )

    1989-12-01

    The negative ions of the rare gases (He, Ne, Ar, Kr, Xe, and Rn) and some actinides (Pu, Am, Bk, Cf, and Es) have been calculated self-consistently by the generalized exchange local-spin-density-functional theory with self-interaction correction and correlation. The electron affinities were obtained as the differences between the statistical total energies of the negative ions and neutral atoms; the electron affinities were positive around several millirydbergs. Consequently, the negative ions are predicted stable for the rare gases and actinides.

  1. Field-aligned electron density irregularities near 500 km. Equator to polar cap topside sounder Z mode observations

    NASA Technical Reports Server (NTRS)

    Benson, R. F.

    1984-01-01

    In addition to spread F, evidence for field-aligned electron density irregularities is commonly observed on Alouette 2 topside sounder ionograms recorded near perigee (500 km). This evidence is provided by distinctive signal returns from sounder-generated Z mode waves. At low latitudes these waves become guided in wave ducts caused by field-aligned electron density irregularities and give rise to strong long-duration echoes. At high latitudes, extending well into the polar cap, these Z mode waves (and stimulated electrostatic waves at the plasma frequency) produce a series of vertical bars on the ionogram display as the satellite traverses discrete field-aligned density structures. The radio frequency (RF) noise environment to be expected in the 400 to 500 km altitude region from low to high latitudes was examined by analyzing perigee Alouette 2 topside sounder data. All observed noise bands were scaled on nearly 200 topside sounder ionograms recorded near perigee at low, mid, and high latitude telemetry stations. The minimum and maximum frequencies of each noise band were entered into a data base or compuer analysis. The signals of primary interest in the perigee study were found to be sounder-generated.

  2. Fast magnetic reconnection in low-density electron-positron plasmas

    SciTech Connect

    Bessho, Naoki; Bhattacharjee, A.

    2010-10-15

    Two-dimensional particle-in-cell simulations have been performed to study magnetic reconnection in low-density electron-positron plasmas without a guide magnetic field. Impulsive reconnection rates become of the order of unity when the background density is much smaller than 10% of the density in the initial current layer. It is demonstrated that the outflow speed is less than the upstream Alfven speed, and that the time derivative of the density must be taken into account in the definition of the reconnection rate. The reconnection electric fields in the low-density regime become much larger than the ones in the high-density regime, and it is possible to accelerate the particles to high energies more efficiently. The inertial term in the generalized Ohm's law is the most dominant term that supports a large reconnection electric field. An effective collisionless resistivity is produced and tracks the extension of the diffusion region in the late stage of the reconnection dynamics, and significant broadening of the diffusion region is observed. Because of the broadening of the diffusion region, no secondary islands, which have been considered to play a role to limit the diffusion region, are generated during the extension of the diffusion region in the outflow direction.

  3. Steep Electron Density Gradients in the Midlatitude Nighttime Ionosphere: Current Understanding and Future Directions

    NASA Astrophysics Data System (ADS)

    Makela, J. J.; Kelley, M. C.; Mathews, J. D.; Kintner, P. M.; Aponte, N.; Ledvina, B. M.; Nicolls, M. J.; Seker, I.

    2004-12-01

    The midlatitude nighttime ionosphere is generally considered to be a fairly quiet system. Indeed, when compared to the highly active low- and high-latitudes, this seems to be a valid description. However, observations in the 1990s, notably those conducted as part of the multi-instrument Combined Ionospheric Campaigns (CICs) carried out periodically from 1997 to 1999, have shown that disturbances can indeed occur in this region. For example, a relatively common feature seen in allsky images taken at 630.0 nm are bands of depleted intensity aligned from the northwest to southeast that propagate to the southwest (in the northern hemisphere). The general characteristics of these bands are now fairly well documented, as is the basic understanding of their underlying physics. The effects of these medium-scale traveling ionospheric disturbances, or electrobouyancy waves, is to produce gradients in the electron density and F-layer height. During quiet magnetic periods, these gradients are fairly small, of the order of a few TEC units. However, these structures seem to be amplified by high geomagnetic activity at which times the gradients can be of the order of 10 to 20 TEC units over distances as small as several 10s of kilometers. Although much was learned about these structures during the CICs of the late 1990s, there are still several unexplained features that warrant further investigation, notably their genesis region, Kp dependence, and effects (if any) on trans-ionospheric radio signals. We suggest the need for a new set of campaigns in the Caribbean to address these questions, modeled on the CICs but extending their spatial coverage and including additional instrumentation not available during the initial campaigns. It is only through such a comprehensive, multi-technique investigation that we will make further headway on understanding these phenomena.

  4. Existence of a virtual cathode close to a strongly electron emissive wall in low density plasmas

    NASA Astrophysics Data System (ADS)

    Tierno, S. P.; Donoso, J. M.; Domenech-Garret, J. L.; Conde, L.

    2016-01-01

    The interaction between an electron emissive wall, electrically biased in a plasma, is revisited through a simple fluid model. We search for realistic conditions of the existence of a non-monotonic plasma potential profile with a virtual cathode as it is observed in several experiments. We mainly focus our attention on thermionic emission related to the operation of emissive probes for plasma diagnostics, although most conclusions also apply to other electron emission processes. An extended Bohm criterion is derived involving the ratio between the two different electron densities at the potential minimum and at the background plasma. The model allows a phase-diagram analysis, which confirms the existence of the non-monotonic potential profiles with a virtual cathode. This analysis shows that the formation of the potential well critically depends on the emitted electron current and on the velocity at the sheath edge of cold ions flowing from the bulk plasma. As a consequence, a threshold value of the governing parameter is required, in accordance to the physical nature of the electron emission process. The latter is a threshold wall temperature in the case of thermionic electrons. Experimental evidence supports our numerical calculations of this threshold temperature. Besides this, the potential well becomes deeper with increasing electron emission, retaining a fraction of the released current which limits the extent of the bulk plasma perturbation. This noninvasive property would explain the reliable measurements of plasma potential by using the floating potential method of emissive probes operating in the so-called strong emission regime.

  5. Measurements of Electron Temperature and Density, in an AC Pulsed Oxygen Plasma Discharge

    NASA Astrophysics Data System (ADS)

    Yousif, Farook; Martinez, Horacio; Castillo, Fermin

    2007-06-01

    Emission and analytical spectroscopy was applied to investigate O2 plasma, which was generated by an AC discharge between 0.15 and 0.5 Torr pressure. For the diagnostic study, a double Langmuir probe was employed. The derivation of plasma parameters is based on a theoretical description of the double-probe current-voltage characterization in the Thick Sheath Limit (TSL) region [1]. Electron temperature of Te = 1.09 eV and an ion density of ni= 2.08 x 10^10 cm-3 were evaluated at 2 Torr. We present electron temperature and ion density as a function of the pressure at 3 different power discharge levels. Also we present emission spectroscopy in the wavelength range of 200-1100 nm as a function of the pressure. [1] J.D. Swift and J. R. Schwar, Electric Probes for Plasma Diagnostics (New York: Elsevier) 1971.

  6. Nonequilibrium atmospheric pressure plasma with ultrahigh electron density and high performance for glass surface cleaning

    SciTech Connect

    Iwasaki, Masahiro; Matsudaira, Yuto; Hori, Masaru; Inui, Hirotoshi; Kano, Hiroyuki; Yoshida, Naofumi; Ito, Masafumi

    2008-02-25

    We produced a nonequilibrium atmospheric pressure plasma by applying an alternative current between two electrodes. The gas temperature and electron density were evaluated using optical emission spectroscopy. It was found that the plasma had gas temperatures from 1800 to 2150 K and ultrahigh electron densities in the order of 10{sup 16} cm{sup -3}. A remarkably high oxygen radical concentration of 1.6x10{sup 15} cm{sup -3} was obtained at a 1% O{sub 2}/Ar gas flow rate of 15 slm (standard liters per minute). Contact angles below 10 deg. were obtained in the process of glass cleaning with a plasma exposure time of 23 ms.

  7. Deducing fast electron density changes in randomly orientated uncrystallized biomolecules in a pump-probe experiment.

    PubMed

    Pande, K; Schwander, P; Schmidt, M; Saldin, D K

    2014-07-17

    We propose a method for deducing time-resolved structural changes in uncrystallized biomolecules in solution. The method relies on measuring the angular correlations of the intensities, when averaged over a large number of diffraction patterns from randomly oriented biomolecules in solution in a liquid solvent. The experiment is somewhat like a pump-probe version of an experiment on small angle X-ray scattering, except that the data expected by the algorithm are not just the radial variation of the averaged intensities. The differences of these correlation functions as measured from a photoexcited and dark structure enable the direct calculation of the difference electron density with a knowledge of only the dark structure. We exploit a linear relation we derive between the difference in these correlation functions and the difference electron density, applicable for small structural changes. PMID:24914159

  8. F region electron density irregularity spectra near auroral acceleration and shear regions

    NASA Technical Reports Server (NTRS)

    Basu, S.; Basu, S.; Mackenzie, E.; Coley, W. R.; Hanson, W. B.; Lin, C. S.

    1984-01-01

    Two orbits of the Atmosphere Explorer D yielded data on F region electron irregularities in the high latitude ionosphere. Data were taken with a retarding potential analyzer, an ion drift meter, a low energy electron experiment and a photoelectron spectrometer. Auroral forms were simultaneously visually sighted by DMSP spacecraft. The irregularities were associated with auroral excitation and large structured flow regions. Steep spectra with one-dimensional spectral index values for wavelengths over 1 km were observed in the acceleration region. Large amplitude irregularities appeared in large structured flow regions and displayed shallow spectra, indicating the presence of large power spectral densities at scale lengths of about 100 m. It is suspected that large velocities or shears in the velocities in adjacent precipitation regions cause the F region density perturbations.

  9. van der Waals forces in density functional theory: Perturbational long-range electron-interaction corrections

    SciTech Connect

    Angyan, Janos G.; Gerber, Iann C.; Savin, Andreas; Toulouse, Julien

    2005-07-15

    Long-range exchange and correlation effects, responsible for the failure of currently used approximate density functionals in describing van der Waals forces, are taken into account explicitly after a separation of the electron-electron interaction in the Hamiltonian into short- and long-range components. We propose a 'range-separated hybrid' functional based on a local density approximation for the short-range exchange-correlation energy, combined with a long-range exact exchange energy. Long-range correlation effects are added by a second-order perturbational treatment. The resulting scheme is general and is particularly well adapted to describe van der Waals complexes, such as rare gas dimers.

  10. Simulations of nanocrystals under pressure: Combining electronic enthalpy and linear-scaling density-functional theory

    SciTech Connect

    Corsini, Niccolò R. C. Greco, Andrea; Haynes, Peter D.; Hine, Nicholas D. M.; Molteni, Carla

    2013-08-28

    We present an implementation in a linear-scaling density-functional theory code of an electronic enthalpy method, which has been found to be natural and efficient for the ab initio calculation of finite systems under hydrostatic pressure. Based on a definition of the system volume as that enclosed within an electronic density isosurface [M. Cococcioni, F. Mauri, G. Ceder, and N. Marzari, Phys. Rev. Lett.94, 145501 (2005)], it supports both geometry optimizations and molecular dynamics simulations. We introduce an approach for calibrating the parameters defining the volume in the context of geometry optimizations and discuss their significance. Results in good agreement with simulations using explicit solvents are obtained, validating our approach. Size-dependent pressure-induced structural transformations and variations in the energy gap of hydrogenated silicon nanocrystals are investigated, including one comparable in size to recent experiments. A detailed analysis of the polyamorphic transformations reveals three types of amorphous structures and their persistence on depressurization is assessed.

  11. Distributions of the ion temperature, ion pressure, and electron density over the current sheet surface

    NASA Astrophysics Data System (ADS)

    Kyrie, N. P.; Markov, V. S.; Frank, A. G.; Vasilkov, D. G.; Voronova, E. V.

    2016-06-01

    The distributions of the ion temperature, ion pressure, and electron density over the width (the major transverse dimension) of the current sheet have been studied for the first time. The current sheets were formed in discharges in argon and helium in 2D and 3D magnetic configurations. It is found that the temperature of argon ions in both 2D and 3D magnetic configurations is almost uniform over the sheet width and that argon ions are accelerated by the Ampère force. In contrast, the distributions of the electron density and the temperature of helium ions are found to be substantially nonuniform. As a result, in the 2D magnetic configuration, the ion pressure gradient across the sheet width makes a significant contribution (comparable with the Ampère force) to the acceleration of helium ions, whereas in the 3D magnetic configuration, the Ampère force is counterbalanced by the pressure gradient.

  12. Mars Global Surveyor Radio Science Electron Density Profiles: Interannual Variability and Implications for the Neutral Atmosphere

    NASA Technical Reports Server (NTRS)

    Bougher, S. W.; Engel, S.; Hinson, D. P.; Murphy, J. R.

    2003-01-01

    The Mars Global Surveyor (MGS) Radio Science (RS) experiment employs an ultrastable oscillator aboard the spacecraft. The signal from the oscillator to Earth is refracted by the Martian ionosphere, allowing retrieval of electron density profiles versus radius and geopotential. The present analysis is carried out on five sets of occultation measurements: (1) four obtained near northern summer solstice (Ls = 74-116, near aphelion) at high northern latitudes (64.7-77.6N), and (2) one set of profiles approaching equinox conditions (Ls = 135- 146) at high southern latitudes (64.7-69.1S). Electron density profiles (95 to 200 km) are examined over a narrow range of solar zenith angles (76.5-86.9 degrees) for local true solar times of (1) 3-4 hours and (2) 12.1 hours. Variations spanning 1-Martian year are specifically examined in the Northern hemisphere.

  13. Rocket Measurement of a Daytime Electron Density Profile up to 620 Kilometers

    NASA Technical Reports Server (NTRS)

    Jackson, J. E.; Bauer, S. J.

    1961-01-01

    On April 27, 1961 at 1502 EST a four-stage research rocket was fired from Wallops Island, Virginia, to measure the ionospheric electron density distribution by means of Seddon's CW propagation technique. This experimental technique is based upon the dispersive Doppler effect measured at two harmonically related frequencies, in this case f = 12.267 Mc and 6f = 73.6 Mc. The electron density profile measured above the peak of the F2 region is representative of a diffusive-equilibrium distribution in an isothermal ionosphere having a temperature of 1640 deg +/- 90 deg K. This result, when compared with satellite and other data, indicates that the upper ionosphere is in thermodynamic equilibrium.

  14. TEMPy: a Python library for assessment of three-dimensional electron microscopy density fits

    PubMed Central

    Farabella, Irene; Vasishtan, Daven; Joseph, Agnel Praveen; Pandurangan, Arun Prasad; Sahota, Harpal; Topf, Maya

    2015-01-01

    Three-dimensional electron microscopy is currently one of the most promising techniques used to study macromolecular assemblies. Rigid and flexible fitting of atomic models into density maps is often essential to gain further insights into the assemblies they represent. Currently, tools that facilitate the assessment of fitted atomic models and maps are needed. TEMPy (template and electron microscopy comparison using Python) is a toolkit designed for this purpose. The library includes a set of methods to assess density fits in intermediate-to-low resolution maps, both globally and locally. It also provides procedures for single-fit assessment, ensemble generation of fits, clustering, and multiple and consensus scoring, as well as plots and output files for visualization purposes to help the user in analysing rigid and flexible fits. The modular nature of TEMPy helps the integration of scoring and assessment of fits into large pipelines, making it a tool suitable for both novice and expert structural biologists. PMID:26306092

  15. Deducing fast electron density changes in randomly orientated uncrystallized biomolecules in a pump–probe experiment

    PubMed Central

    Pande, K.; Schwander, P.; Schmidt, M.; Saldin, D. K.

    2014-01-01

    We propose a method for deducing time-resolved structural changes in uncrystallized biomolecules in solution. The method relies on measuring the angular correlations of the intensities, when averaged over a large number of diffraction patterns from randomly oriented biomolecules in solution in a liquid solvent. The experiment is somewhat like a pump–probe version of an experiment on small angle X-ray scattering, except that the data expected by the algorithm are not just the radial variation of the averaged intensities. The differences of these correlation functions as measured from a photoexcited and dark structure enable the direct calculation of the difference electron density with a knowledge of only the dark structure. We exploit a linear relation we derive between the difference in these correlation functions and the difference electron density, applicable for small structural changes. PMID:24914159

  16. textbf{Tomography of Ionosphere electron density and its abnormity analysis during Wenchuan earthquake }

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoya; Xing, Nan

    2010-05-01

    A multiple-arc method and Kriging interpolation are applied to obtain VTEC as well as DCB using ground-based GPS data. Given by the time variation characteristics of VTEC and DCB, VTEC is calculated every 30 minutes as local variables, and DCB is calculated every day as global variables. Kriging method, taking the spatial information of VTEC into account, is useful to make VTEC more precise and stable. Meanwhile, based on 3-variable spline basis function, we expand electron density into a linear combination of a set of grid points. Tomography of Ionosphere electron density is made by MART. The results show the coherence with CHAMP occultation results. We applied these two ways to process the ground-based GPS data of Yangzi River Triangle Region in May, 2008 when the shocking earthquake happened in Wenchuan. A simple statistic analysis reveals the response of ionosphere to the earthquake and also the abnormal signal occurred before the earthquake.

  17. Sun Corona Electron Densities Derived from VLBI Sessions in 2011/2012

    NASA Astrophysics Data System (ADS)

    Soja, B.; Sun, J.; Heinkelmann, R.; Schuh, H.; Böhm, J.

    2013-08-01

    Twelve IVS R&D sessions in 2011/2012 primarily aimed to increase the sensitivity of VLBI to relativistic phenomena by including observations closer than 15 degrees to the heliocenter. These observations are also affected by the plasma of the Sun corona, a dispersive medium which is the target of our research presented here. Starting with the ionospheric delay corrections derived from two-frequency VLBI measurements, Sun corona electron densities were estimated together with other dispersive effects like instrumental biases and the Earth ionosphere. The results for the R&D sessions were analysed and compared with external information like Sunspot numbers and solar flux indices. The estimated electron densities show good agreement with previous models of the Sun corona obtained by various spacecraft missions.

  18. Electron-cyclotron wave scattering by edge density fluctuations in ITER

    SciTech Connect

    Tsironis, Christos; Peeters, Arthur G.; Isliker, Heinz; Chatziantonaki, Ioanna; Vlahos, Loukas; Strintzi, Dafni

    2009-11-15

    The effect of edge turbulence on the electron-cyclotron wave propagation in ITER is investigated with emphasis on wave scattering, beam broadening, and its influence on localized heating and current drive. A wave used for electron-cyclotron current drive (ECCD) must cross the edge of the plasma, where density fluctuations can be large enough to bring on wave scattering. The scattering angle due to the density fluctuations is small, but the beam propagates over a distance of several meters up to the resonance layer and even small angle scattering leads to a deviation of several centimeters at the deposition location. Since the localization of ECCD is crucial for the control of neoclassical tearing modes, this issue is of great importance to the ITER design. The wave scattering process is described on the basis of a Fokker-Planck equation, where the diffusion coefficient is calculated analytically as well as computed numerically using a ray tracing code.

  19. High-current density, high-brightness electron beams from large-area lanthanum hexaboride cathodes

    NASA Astrophysics Data System (ADS)

    Loschialpo, P.; Kapetanakos, C. A.

    1988-04-01

    Large diameter lanthanum hexaboride (LaB6) cathodes operated at 10 kV have produced 1-5-microsec electron pulses with current density between 10 and 20 A/sq cm. Normalized beam brightness, approximately 300,000 A/sq cm sq rad has been consistently measured. To obtain this high-current density, the LaB6 cathodes have been heated to temperatures between about 1600 and 1800 C. Very uniform temperature profiles are obtained by applying a carefully tailored electron bombardment heating power distribution. These measurements have been made between pressure 10 to the -6th to -10 to the -5th Torr, i.e., under much less demanding vacuum conditions than that required by conventional dispenser-type cathodes.

  20. Computational analysis of thermal-motion effects on the topological properties of the electron density.

    PubMed

    Michael, J Robert; Koritsanszky, Tibor

    2015-03-01

    The distributions of bond topological properties (BTPs) of the electron density upon thermal vibrations of the nuclei are computationally examined to estimate different statistical figures, especially uncertainties, of these properties. The statistical analysis is based on a large ensemble of BTPs of the electron densities for thermally perturbed nuclear geometries of the formamide molecule. Each bond critical point (BCP) is found to follow a normal distribution whose covariance correlates with the displacement amplitudes of the nuclei involved in the bond. The BTPs are found to be markedly affected not only by normal modes of the significant bond-stretching component but also by modes that involve mainly hydrogen-atom displacements. Their probability distribution function can be decently described by Gumbel-type functions of positive (negative) skewness for the bonds formed by non-hydrogen (hydrogen) atoms. PMID:25727872