Automated pinhole-aperture diagnostic for the current profiling of TWT electron beams

NASA Astrophysics Data System (ADS)

Wei, Yu-Xiang; Huang, Ming-Guang; Liu, Shu-Qing; Liu, Jin-Yue; Hao, Bao-Liang; Du, Chao-Hai; Liu, Pu-Kun

2013-02-01

The measurement system reported here is intended for use in determining the current density distribution of electron beams from Pierce guns for use in TWTs. The system was designed to automatically scan the cross section of the electron beam and collect the high-resolution data with a Faraday cup probe mounted on a multistage manipulator using the LabVIEW program. A 0.06 mm thick molybdenum plate with a pinhole and a Faraday cup mounted as a probe assembly was employed to sample the electron beam current with 0.5 µm space resolution. The thermal analysis of the probe with pulse beam heating was discussed. A 0.45 µP electron gun with the expected minimum beam radius 0.42 mm was measured and the three-dimensional current density distribution, beam envelope and phase space were presented.

Energy flux and characteristic energy of an elemental auroral structure

NASA Technical Reports Server (NTRS)

Lanchester, B. S.; Palmer, J. R.; Rees, M. H.; Lummerzheim, D.; Kaila, K.; Turunen, T.

1994-01-01

Electron density profiles acquired with the EISCAT radar at 0.2 s time resolution, together with TV images and photometric intensities, were used to study the characteristics of thin (less than 1 km) auroral arc structures that drifted through the field of view of the instruments. It is demonstrated that both high time and space resolution are essential for deriving the input parameters of the electron flux responsible for the elemental auroral structures. One such structure required a 400 mW/sq m (erg/sq cm s) downward energy flux carried by an 8 keV monochromatic electron flux equivalent to a current density of 50 micro Angstrom/sq m.

RCrane: semi-automated RNA model building.

PubMed

Keating, Kevin S; Pyle, Anna Marie

2012-08-01

RNA crystals typically diffract to much lower resolutions than protein crystals. This low-resolution diffraction results in unclear density maps, which cause considerable difficulties during the model-building process. These difficulties are exacerbated by the lack of computational tools for RNA modeling. Here, RCrane, a tool for the partially automated building of RNA into electron-density maps of low or intermediate resolution, is presented. This tool works within Coot, a common program for macromolecular model building. RCrane helps crystallographers to place phosphates and bases into electron density and then automatically predicts and builds the detailed all-atom structure of the traced nucleotides. RCrane then allows the crystallographer to review the newly built structure and select alternative backbone conformations where desired. This tool can also be used to automatically correct the backbone structure of previously built nucleotides. These automated corrections can fix incorrect sugar puckers, steric clashes and other structural problems.

An atomic model of brome mosaic virus using direct electron detection and real-space optimization.

PubMed

Wang, Zhao; Hryc, Corey F; Bammes, Benjamin; Afonine, Pavel V; Jakana, Joanita; Chen, Dong-Hua; Liu, Xiangan; Baker, Matthew L; Kao, Cheng; Ludtke, Steven J; Schmid, Michael F; Adams, Paul D; Chiu, Wah

2014-09-04

Advances in electron cryo-microscopy have enabled structure determination of macromolecules at near-atomic resolution. However, structure determination, even using de novo methods, remains susceptible to model bias and overfitting. Here we describe a complete workflow for data acquisition, image processing, all-atom modelling and validation of brome mosaic virus, an RNA virus. Data were collected with a direct electron detector in integrating mode and an exposure beyond the traditional radiation damage limit. The final density map has a resolution of 3.8 Å as assessed by two independent data sets and maps. We used the map to derive an all-atom model with a newly implemented real-space optimization protocol. The validity of the model was verified by its match with the density map and a previous model from X-ray crystallography, as well as the internal consistency of models from independent maps. This study demonstrates a practical approach to obtain a rigorously validated atomic resolution electron cryo-microscopy structure.

Electron Density Distribution Changes of Magnesiowüstite With Pressure

NASA Astrophysics Data System (ADS)

Diamond, M. R.; Popov, D.; Shen, G.; Jeanloz, R.

2017-12-01

Magnesiowüstite is one of the dominant minerals in the earth's lower mantle; its density and elasticity, substantially altered by its spin crossover, have direct consequence to interpreting deep-earth geophysical data. High-resolution single-crystal x-ray diffraction data can portray the 3-dimensional distribution of electron density through the Fourier transform of measured form factors. Here we present experimentally measured changes in electron density distribution of single-crystal (Mg.85,Fe.15)O as it goes through its iron(II) high-spin to low-spin electronic transition between about 40 and 60 GPa [Lin and Tsuchiya, 2008], in a diamond-anvil cell. As (Mg,Fe)O undergoes a pressure induced spin crossover (from high spin at low pressure to low spin at high pressure) due to overlap of its eg orbitals, the t2g orbitals become more pronounced to due a higher population of electrons, while the eg orbitals diminish. The spin splitting energy becomes increasingly unfavorable compared to the spin orbital pairing energy. By looking at the population of electrons at different directions in real space, we directly observe these changes in orbital occupation leading up to and during the spin crossover. Since high-Mg magnesiowüstite has a high symmetry structure at these pressure conditions, detecting relative changes in electron density distribution (comparing subsequent pressure steps) is feasible by collecting high resolution data offered by high-energy X rays and wide opening-angle diamond-anvil cells.

Shape information from a critical point analysis of calculated electron density maps: application to DNA-drug systems

NASA Astrophysics Data System (ADS)

Leherte, L.; Allen, F. H.; Vercauteren, D. P.

1995-04-01

A computational method is described for mapping the volume within the DNA double helix accessible to a groove-binding antibiotic, netropsin. Topological critical point analysis is used to locate maxima in electron density maps reconstructed from crystallographically determined atomic coordinates. The peaks obtained in this way are represented as ellipsoids with axes related to local curvature of the electron density function. Combining the ellipsoids produces a single electron density function which can be probed to estimate effective volumes of the interacting species. Close complementarity between host and ligand in this example shows the method to be a good representation of the electron density function at various resolutions; while at the atomic level the ellipsoid method gives results which are in close agreement with those from the conventional, spherical, van der Waals approach.

Shape information from a critical point analysis of calculated electron density maps: Application to DNA-drug systems

NASA Astrophysics Data System (ADS)

Leherte, Laurence; Allen, Frank H.

1994-06-01

A computational method is described for mapping the volume within the DNA double helix accessible to the groove-binding antibiotic netropsin. Topological critical point analysis is used to locate maxima in electron density maps reconstructed from crystallographically determined atomic coordinates. The peaks obtained in this way are represented as ellipsoids with axes related to local curvature of the electron density function. Combining the ellipsoids produces a single electron density function which can be probed to estimate effective volumes of the interacting species. Close complementarity between host and ligand in this example shows the method to give a good representation of the electron density function at various resolutions. At the atomic level, the ellipsoid method gives results which are in close agreement with those from the conventional spherical van der Waals approach.

Temporal Behavior of the Ionospheric Electron Density at Low Latitudes: First Glimpse

NASA Astrophysics Data System (ADS)

Gjerloev, J. W.; Humberset, B. K.; Gonzalez, S. A.; Garnett Marques Brum, C.

2013-12-01

In this paper we address the spatiotemporal characteristics of the electron density at 150 km altitude in the low latitude ionosphere above the Arecibo Observatory. We utilize a new pointing mode that allows us to probe the same volume in the ionosphere for a continuous period of approximately 25 min. or more. The ISR profiles have 150 m range resolution and samples have a 10-second time resolution; we probed 60 individual regions uniformly spaced in local times and covering the full 24 hours. For each time series we determine the total derivative of the electron density using a narrow Hanning bandpass filter that allow us to determine the variability at different frequencies. This is done for each of the 60 local time regions. We further compare to widely used static statistical models and test their underlying assumption: Dynamics can be ignored.

Platinum replica electron microscopy: Imaging the cytoskeleton globally and locally.

PubMed

Svitkina, Tatyana M

2017-05-01

Structural studies reveal how smaller components of a system work together as a whole. However, combining high resolution of details with full coverage of the whole is challenging. In cell biology, light microscopy can image many cells in their entirety, but at a lower resolution, whereas electron microscopy affords very high resolution, but usually at the expense of the sample size and coverage. Structural analyses of the cytoskeleton are especially demanding, because cytoskeletal networks are unresolvable by light microscopy due to their density and intricacy, whereas their proper preservation is a challenge for electron microscopy. Platinum replica electron microscopy can uniquely bridge the gap between the "comfort zones" of light and electron microscopy by allowing high resolution imaging of the cytoskeleton throughout the entire cell and in many cells in the population. This review describes the principles and applications of platinum replica electron microscopy for studies of the cytoskeleton. Copyright © 2017 Elsevier Ltd. All rights reserved.

Platinum Replica Electron Microscopy: Imaging the Cytoskeleton Globally and Locally

PubMed Central

SVITKINA, Tatyana M.

2017-01-01

Structural studies reveal how smaller components of a system work together as a whole. However, combining high resolution of details with full coverage of the whole is challenging. In cell biology, light microscopy can image many cells in their entirety, but at a lower resolution, whereas electron microscopy affords very high resolution, but usually at the expense of the sample size and coverage. Structural analyses of the cytoskeleton are especially demanding, because cytoskeletal networks are unresolvable by light microscopy due to their density and intricacy, whereas their proper preservation is a challenge for electron microscopy. Platinum replica electron microscopy can uniquely bridge the gap between the “comfort zones” of light and electron microscopy by allowing high resolution imaging of the cytoskeleton throughout the entire cell and in many cells in the population. This review describes the principles and applications of platinum replica electron microscopy for studies of the cytoskeleton. PMID:28323208

Coherent diffraction imaging analysis of shape-controlled nanoparticles with focused hard X-ray free-electron laser pulses.

PubMed

Takahashi, Yukio; Suzuki, Akihiro; Zettsu, Nobuyuki; Oroguchi, Tomotaka; Takayama, Yuki; Sekiguchi, Yuki; Kobayashi, Amane; Yamamoto, Masaki; Nakasako, Masayoshi

2013-01-01

We report the first demonstration of the coherent diffraction imaging analysis of nanoparticles using focused hard X-ray free-electron laser pulses, allowing us to analyze the size distribution of particles as well as the electron density projection of individual particles. We measured 1000 single-shot coherent X-ray diffraction patterns of shape-controlled Ag nanocubes and Au/Ag nanoboxes and estimated the edge length from the speckle size of the coherent diffraction patterns. We then reconstructed the two-dimensional electron density projection with sub-10 nm resolution from selected coherent diffraction patterns. This method enables the simultaneous analysis of the size distribution of synthesized nanoparticles and the structures of particles at nanoscale resolution to address correlations between individual structures of components and the statistical properties in heterogeneous systems such as nanoparticles and cells.

Regional 3-D ionospheric electron density specification on the basis of data assimilation of ground-based GNSS and radio occultation data

NASA Astrophysics Data System (ADS)

Aa, Ercha; Liu, Siqing; Huang, Wengeng; Shi, Liqin; Gong, Jiancun; Chen, Yanhong; Shen, Hua; Li, Jianyong

2016-06-01

In this paper, a regional 3-D ionospheric electron density specification over China and adjacent areas (70°E-140°E in longitude, 15°N-55°N in latitude, and 100-900 km in altitude) is developed on the basis of data assimilation technique. The International Reference Ionosphere (IRI) is used as a background model, and a three-dimensional variational technique is used to assimilate both the ground-based Global Navigation Satellite System (GNSS) observations from the Crustal Movement Observation Network of China (CMONOC) and International GNSS Service (IGS) and the ionospheric radio occultation (RO) data from FORMOSAT-3/COSMIC (F3/C) satellites. The regional 3-D gridded ionospheric electron densities can be generated with temporal resolution of 5 min in universal time, horizontal resolution of 2° × 2° in latitude and longitude, and vertical resolution of 20 km between 100 and 500 km and 50 km between 500 and 900 km. The data assimilation results are validated through extensive comparison with several sources of electron density information, including (1) ionospheric total electron content (TEC); (2) Abel-retrieved F3/C electron density profiles (EDPs); (3) ionosonde foF2 and bottomside EDPs; and (4) the Utah State University Global Assimilation of Ionospheric Measurements (USU-GAIM) under both geomagnetic quiet and disturbed conditions. The validation results show that the data assimilation procedure pushes the climatological IRI model toward the observation, and a general accuracy improvement of 15-30% can be expected. Thecomparisons also indicate that the data assimilation results are more close to the Center for Orbit Determination of Europe (CODE) TEC and Madrigal TEC products than USU-GAIM. These initial results might demonstrate the effectiveness of the data assimilation technique in improving specification of local ionospheric morphology.

Atomic-scale diffractive imaging of sub-cycle electron dynamics in condensed matter

PubMed Central

Yakovlev, Vladislav S.; Stockman, Mark I.; Krausz, Ferenc; Baum, Peter

2015-01-01

For interaction of light with condensed-matter systems, we show with simulations that ultrafast electron and X-ray diffraction can provide a time-dependent record of charge-density maps with sub-cycle and atomic-scale resolutions. Using graphene as an example material, we predict that diffraction can reveal localised atomic-scale origins of optical and electronic phenomena. In particular, we point out nontrivial relations between microscopic electric current and density in undoped graphene. PMID:26412407

Atomic-scale diffractive imaging of sub-cycle electron dynamics in condensed matter

DOE PAGES

Yakovlev, Vladislav S.; Stockman, Mark I.; Krausz, Ferenc; ...

2015-09-28

For interaction of light with condensed-matter systems, we show with simulations that ultrafast electron and X-ray diffraction can provide a time-dependent record of charge-density maps with sub-cycle and atomic-scale resolutions. Using graphene as an example material, we predict that diffraction can reveal localised atomic-scale origins of optical and electronic phenomena. Here, we point out nontrivial relations between microscopic electric current and density in undoped graphene.

Macromolecular refinement by model morphing using non-atomic parameterizations.

PubMed

Cowtan, Kevin; Agirre, Jon

2018-02-01

Refinement is a critical step in the determination of a model which explains the crystallographic observations and thus best accounts for the missing phase components. The scattering density is usually described in terms of atomic parameters; however, in macromolecular crystallography the resolution of the data is generally insufficient to determine the values of these parameters for individual atoms. Stereochemical and geometric restraints are used to provide additional information, but produce interrelationships between parameters which slow convergence, resulting in longer refinement times. An alternative approach is proposed in which parameters are not attached to atoms, but to regions of the electron-density map. These parameters can move the density or change the local temperature factor to better explain the structure factors. Varying the size of the region which determines the parameters at a particular position in the map allows the method to be applied at different resolutions without the use of restraints. Potential applications include initial refinement of molecular-replacement models with domain motions, and potentially the use of electron density from other sources such as electron cryo-microscopy (cryo-EM) as the refinement model.

X-ray imaging spectroscopic diagnostics on Nike

NASA Astrophysics Data System (ADS)

Aglitskiy, Y.; Karasik, M.; Serlin, V.; Weaver, J. L.; Oh, J.; Obenschain, S. P.; Ralchenko, Yu.

2017-10-01

Electron temperature and density diagnostics of the laser plasma produced within the focal spot of the NRL's Nike laser are being explored with the help of X-ray imaging spectroscopy. Spectra of He-like and H-like ions were taken by Nike focusing spectrometers in a range of lower (1.8 kev, Si XIV) and higher (6.7 kev, Fe XXV) x-ray energies. Data that were obtained with spatial resolution were translated into the temperature and density as functions of distance from the target. As an example electron density was determined from He-like satellites to Ly-alpha in Si XIV. The dielectronic satellites with intensity ratios that are sensitive to collisional transfer of population between different triplet groups of double-excited states 2l2l' in Si XIII were observed with high spatial and spectral resolution Lineouts taken at different axial distances from the planar Si target show changing spectral shapes due to the different electron densities as determined by supporting non-LTE simulations. These shapes are relatively insensitive to the plasma temperature which was measured using different spectral lines. This work was supported by the US DOE/NNSA.

High-resolution electron microscope observation of voids in amorphous Ge.

NASA Technical Reports Server (NTRS)

Donovan, T. M.; Heinemann, K.

1971-01-01

Electron micrographs have been obtained which clearly show the existence of a void network in amorphous Ge films formed at substrate temperatures of 25 and 150 C, and the absence of a void network in films formed at higher substrate temperatures of 200 and 250 C. These results correlate quite well with density measurements and predictions of void densities by indirect methods.

Fabrication method of two-photon luminescent organic nano-architectures using electron-beam irradiation

NASA Astrophysics Data System (ADS)

Kamura, Yoshio; Imura, Kohei

2018-06-01

Optical recording on organic thin films with a high spatial resolution is promising for high-density optical memories, optical computing, and security systems. The spatial resolution of the optical recording is limited by the diffraction of light. Electrons can be focused to a nanometer-sized spot, providing the potential for achieving better resolution. In conventional electron-beam lithography, however, optical tuning of the fabricated structures is limited mostly to metals and semiconductors rather than organic materials. In this article, we report a fabrication method of luminescent organic architectures using a focused electron beam. We optimized the fabrication conditions of the electron beam to generate chemical species showing visible photoluminescence via two-photon near-infrared excitations. We utilized this fabrication method to draw nanoscale optical architectures on a polystyrene thin film.

An Electron Density Source-Function Study of DNA Base Pairs in Their Neutral and Ionized Ground States†.

PubMed

Gatti, Carlo; Macetti, Giovanni; Boyd, Russell J; Matta, Chérif F

2018-07-05

The source function (SF) decomposes the electron density at any point into contributions from all other points in the molecule, complex, or crystal. The SF "illuminates" those regions in a molecule that most contribute to the electron density at a point of reference. When this point of reference is the bond critical point (BCP), a commonly used surrogate of chemical bonding, then the SF analysis at an atomic resolution within the framework of Bader's Quantum Theory of Atoms in Molecules returns the contribution of each atom in the system to the electron density at that BCP. The SF is used to locate the important regions that control the hydrogen bonds in both Watson-Crick (WC) DNA dimers (adenine:thymine (AT) and guanine:cytosine (GC)) which are studied in their neutral and their singly ionized (radical cationic and anionic) ground states. The atomic contributions to the electron density at the BCPs of the hydrogen bonds in the two dimers are found to be delocalized to various extents. Surprisingly, gaining or loosing an electron has similar net effects on some hydrogen bonds concealing subtle compensations traced to atomic sources contributions. Coarser levels of resolutions (groups, rings, and/or monomers-in-dimers) reveal that distant groups and rings often have non-negligible effects especially on the weaker hydrogen bonds such as the third weak CH⋅⋅⋅O hydrogen bond in AT. Interestingly, neither the purine nor the pyrimidine in the neutral or ionized forms dominate any given hydrogen bond despite that the former has more atoms that can act as source or sink for the density at its BCP. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

Electron momentum density and Compton profile by a semi-empirical approach

NASA Astrophysics Data System (ADS)

Aguiar, Julio C.; Mitnik, Darío; Di Rocco, Héctor O.

2015-08-01

Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi-Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron-electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects. We tested the approach for all metals with Z=3-50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments.

Anharmonic Thermal Oscillations of the Electron Momentum Distribution in Lithium Fluoride

NASA Astrophysics Data System (ADS)

Erba, A.; Maul, J.; Itou, M.; Dovesi, R.; Sakurai, Y.

2015-09-01

Anharmonic thermal effects on the electron momentum distribution of a lithium fluoride single crystal are experimentally measured through high-resolution Compton scattering and theoretically modeled with ab initio simulations, beyond the harmonic approximation to the lattice potential, explicitly accounting for thermal expansion. Directional Compton profiles are measured at two different temperatures, 10 and 300 K, with a high momentum space resolution (0.10 a.u. in full width at half maximum), using synchrotron radiation. The effect of temperature on measured directional Compton profiles is clearly revealed by oscillations extending almost up to |p |=4 a .u . , which perfectly match those predicted from quantum-mechanical simulations. The wave-function-based Hartree-Fock method and three classes of the Kohn-Sham density functional theory (local-density, generalized-gradient, and hybrid approximations) are adopted. The lattice thermal expansion, as described with the quasiharmonic approach, is found to entirely account for the effect of temperature on the electron momentum density within the experimental accuracy.

Spatial Resolution in Scanning Electron Microscopy and Scanning Transmission Electron Microscopy Without a Specimen Vacuum Chamber.

PubMed

Nguyen, Kayla X; Holtz, Megan E; Richmond-Decker, Justin; Muller, David A

2016-08-01

A long-standing goal of electron microscopy has been the high-resolution characterization of specimens in their native environment. However, electron optics require high vacuum to maintain an unscattered and focused probe, a challenge for specimens requiring atmospheric or liquid environments. Here, we use an electron-transparent window at the base of a scanning electron microscope's objective lens to separate column vacuum from the specimen, enabling imaging under ambient conditions, without a specimen vacuum chamber. We demonstrate in-air imaging of specimens at nanoscale resolution using backscattered scanning electron microscopy (airSEM) and scanning transmission electron microscopy. We explore resolution and contrast using Monte Carlo simulations and analytical models. We find that nanometer-scale resolution can be obtained at gas path lengths up to 400 μm, although contrast drops with increasing gas path length. As the electron-transparent window scatters considerably more than gas at our operating conditions, we observe that the densities and thicknesses of the electron-transparent window are the dominant limiting factors for image contrast at lower operating voltages. By enabling a variety of detector configurations, the airSEM is applicable to a wide range of environmental experiments including the imaging of hydrated biological specimens and in situ chemical and electrochemical processes.

Spatial Resolution in Scanning Electron Microscopy and Scanning Transmission Electron Microscopy Without a Specimen Vacuum Chamber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Kayla X.; Holtz, Megan E.; Richmond-Decker, Justin

2016-07-25

Abstract A long-standing goal of electron microscopy has been the high-resolution characterization of specimens in their native environment. However, electron optics require high vacuum to maintain an unscattered and focused probe, a challenge for specimens requiring atmospheric or liquid environments. Here, we use an electron-transparent window at the base of a scanning electron microscope’s objective lens to separate column vacuum from the specimen, enabling imaging under ambient conditions, without a specimen vacuum chamber. We demonstrate in-air imaging of specimens at nanoscale resolution using backscattered scanning electron microscopy (airSEM) and scanning transmission electron microscopy. We explore resolution and contrast using Montemore » Carlo simulations and analytical models. We find that nanometer-scale resolution can be obtained at gas path lengths up to 400μm, although contrast drops with increasing gas path length. As the electron-transparent window scatters considerably more than gas at our operating conditions, we observe that the densities and thicknesses of the electron-transparent window are the dominant limiting factors for image contrast at lower operating voltages. By enabling a variety of detector configurations, the airSEM is applicable to a wide range of environmental experiments including the imaging of hydrated biological specimens andin situchemical and electrochemical processes.« less

High-resolution Compton scattering study of the electron momentum density in Al

NASA Astrophysics Data System (ADS)

Ohata, T.; Itou, M.; Matsumoto, I.; Sakurai, Y.; Kawata, H.; Shiotani, N.; Kaprzyk, S.; Mijnarends, P. E.; Bansil, A.

2000-12-01

We report high-resolution Compton profiles (CP's) of Al along the three principal symmetry directions at a photon energy of 59.38 keV, together with corresponding highly accurate theoretical profiles obtained within the local-density approximation (LDA) based band-theory framework. A good accord between theory and experiment is found with respect to the overall shapes of the CP's and their first and second derivatives, as well as the anisotropies in the CP's defined as differences between pairs of various CP's. There are, however, discrepancies in that, in comparison to the LDA predictions, the measured profiles are lower at low momenta, show a Fermi cutoff that is broader, and display a tail that is higher at momenta above the Fermi momentum. A number of simple model calculations are carried out in order to gain insight into the nature of the underlying 3D momentum density in Al and the role of the Fermi surface in inducing fine structure in the CP's. The present results when compared with those on Li show clearly that the size of discrepancies between theoretical and experimental CP's is markedly smaller in Al than in Li. This indicates that, with increasing electron density, the conventional picture of the electron gas becomes more representative of the momentum density and that shortcomings of the LDA framework in describing the electron correlation effects become less important.

Comparison of an Atomic Model and Its Cryo-EM Image at the Central Axis of a Helix

PubMed Central

He, Jing; Zeil, Stephanie; Hallak, Hussam; McKaig, Kele; Kovacs, Julio; Wriggers, Willy

2016-01-01

Cryo-electron microscopy (cryo-EM) is an important biophysical technique that produces three-dimensional (3D) density maps at different resolutions. Because more and more models are being produced from cryo-EM density maps, validation of the models is becoming important. We propose a method for measuring local agreement between a model and the density map using the central axis of the helix. This method was tested using 19 helices from cryo-EM density maps between 5.5 Å and 7.2 Å resolution and 94 helices from simulated density maps. This method distinguished most of the well-fitting helices, although challenges exist for shorter helices. PMID:27280059

ATOMIC RESOLUTION CRYO ELECTRON MICROSCOPY OF MACROMOLECULAR COMPLEXES

PubMed Central

ZHOU, Z. HONG

2013-01-01

Single-particle cryo electron microscopy (cryoEM) is a technique for determining three-dimensional (3D) structures from projection images of molecular complexes preserved in their “native,” noncrystalline state. Recently, atomic or near-atomic resolution structures of several viruses and protein assemblies have been determined by single-particle cryoEM, allowing ab initio atomic model building by following the amino acid side chains or nucleic acid bases identifiable in their cryoEM density maps. In particular, these cryoEM structures have revealed extended arms contributing to molecular interactions that are otherwise not resolved by the conventional structural method of X-ray crystallography at similar resolutions. High-resolution cryoEM requires careful consideration of a number of factors, including proper sample preparation to ensure structural homogeneity, optimal configuration of electron imaging conditions to record high-resolution cryoEM images, accurate determination of image parameters to correct image distortions, efficient refinement and computation to reconstruct a 3D density map, and finally appropriate choice of modeling tools to construct atomic models for functional interpretation. This progress illustrates the power of cryoEM and ushers it into the arsenal of structural biology, alongside conventional techniques of X-ray crystallography and NMR, as a major tool (and sometimes the preferred one) for the studies of molecular interactions in supramolecular assemblies or machines. PMID:21501817

2D electron density profile measurement in tokamak by laser-accelerated ion-beam probe.

PubMed

Chen, Y H; Yang, X Y; Lin, C; Wang, L; Xu, M; Wang, X G; Xiao, C J

2014-11-01

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.

Phase contrast in high resolution electron microscopy

DOEpatents

Rose, H.H.

1975-09-23

This patent relates to a device for developing a phase contrast signal for a scanning transmission electron microscope. The lens system of the microscope is operated in a condition of defocus so that predictable alternate concentric regions of high and low electron density exist in the cone of illumination. Two phase detectors are placed beneath the object inside the cone of illumination, with the first detector having the form of a zone plate, each of its rings covering alternate regions of either higher or lower electron density. The second detector is so configured that it covers the regions of electron density not covered by the first detector. Each detector measures the number of electrons incident thereon and the signal developed by the first detector is subtracted from the signal developed by the record detector to provide a phase contrast signal. (auth)

Rocket measurements of electron density irregularities during MAC/SINE

NASA Technical Reports Server (NTRS)

Ulwick, J. C.

1989-01-01

Four Super Arcas rockets were launched at the Andoya Rocket Range, Norway, as part of the MAC/SINE campaign to measure electron density irregularities with high spatial resolution in the cold summer polar mesosphere. They were launched as part of two salvos: the turbulent/gravity wave salvo (3 rockets) and the EISCAT/SOUSY radar salvo (one rocket). In both salvos meteorological rockets, measuring temperature and winds, were also launched and the SOUSY radar, located near the launch site, measured mesospheric turbulence. Electron density irregularities and strong gradients were measured by the rocket probes in the region of most intense backscatter observed by the radar. The electron density profiles (8 to 4 on ascent and 4 on descent) show very different characteristics in the peak scattering region and show marked spatial and temporal variability. These data are intercompared and discussed.

Electron temperature and heat load measurements in the COMPASS divertor using the new system of probes

NASA Astrophysics Data System (ADS)

Adamek, J.; Seidl, J.; Horacek, J.; Komm, M.; Eich, T.; Panek, R.; Cavalier, J.; Devitre, A.; Peterka, M.; Vondracek, P.; Stöckel, J.; Sestak, D.; Grover, O.; Bilkova, P.; Böhm, P.; Varju, J.; Havranek, A.; Weinzettl, V.; Lovell, J.; Dimitrova, M.; Mitosinkova, K.; Dejarnac, R.; Hron, M.; The COMPASS Team; The EUROfusion MST1 Team

2017-11-01

A new system of probes was recently installed in the divertor of tokamak COMPASS in order to investigate the ELM energy density with high spatial and temporal resolution. The new system consists of two arrays of rooftop-shaped Langmuir probes (LPs) used to measure the floating potential or the ion saturation current density and one array of Ball-pen probes (BPPs) used to measure the plasma potential with a spatial resolution of ~3.5 mm. The combination of floating BPPs and LPs yields the electron temperature with microsecond temporal resolution. We report on the design of the new divertor probe arrays and first results of electron temperature profile measurements in ELMy H-mode and L-mode. We also present comparative measurements of the parallel heat flux using the new probe arrays and fast infrared termography (IR) data during L-mode with excellent agreement between both techniques using a heat power transmission coefficient γ  =  7. The ELM energy density {{\\varepsilon }\\parallel } was measured during a set of NBI assisted ELMy H-mode discharges. The peak values of {{\\varepsilon }\\parallel } were compared with those predicted by model and with experimental data from JET, AUG and MAST with a good agreement.

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.

High-resolution angle-resolved photoemission study of electronic structure and charge-density wave formation in HoTe3

NASA Astrophysics Data System (ADS)

Liu, Guodong; Wang, Chenlu; Zhang, Yan; Hu, Bingfeng; Mou, Daixiang; Yu, Li; Zhao, Lin; Zhou, Xingjiang; Wang, Nanlin; Chen, Chuangtian; Xu, Zuyan

We performed high-resolution angle-resolved photoemission spectroscopy (ARPES) measurement on high quality crystal of HoTe3, an intriguing quasi-two-dimensional rare-earth-element tritelluride charge-density-wave (CDW) compound. The main features of the electronic structure in this compound are established by employing a quasi-CW laser (7eV) and a helium discharging lamp (21.22 eV) as excitation light sources. It reveals many bands back folded according to the CDW periodicity and two incommensurate CDW gaps created by perpendicular Fermi surface (FS) nesting vectors. A large gap is found to open in well nested regions of the Fermi surface sheets, whereas other Fermi surface sections with poor nesting remain ungapped. In particular, some peculiar features are identified by using our ultra-high resolution and bulk sensitive laser-ARPES.

Active control of bright electron beams with RF optics for femtosecond microscopy

DOE PAGES

Williams, J.; Zhou, F.; Sun, T.; ...

2017-08-01

A frontier challenge in implementing femtosecond electron microscopy is to gain precise optical control of intense beams to mitigate collective space charge effects for significantly improving the throughput. In this paper, we explore the flexible uses of an RF cavity as a longitudinal lens in a high-intensity beam column for condensing the electron beams both temporally and spectrally, relevant to the design of ultrafast electron microscopy. Through the introduction of a novel atomic grating approach for characterization of electron bunch phase space and control optics, we elucidate the principles for predicting and controlling the phase space dynamics to reach optimalmore » compressions at various electron densities and generating conditions. We provide strategies to identify high-brightness modes, achieving ~100 fs and ~1 eV resolutions with 10 6 electrons per bunch, and establish the scaling of performance for different bunch charges. These results benchmark the sensitivity and resolution from the fundamental beam brightness perspective and also validate the adaptive optics concept to enable delicate control of the density-dependent phase space structures to optimize the performance, including delivering ultrashort, monochromatic, high-dose, or coherent electron bunches.« less

Active control of bright electron beams with RF optics for femtosecond microscopy

PubMed Central

Williams, J.; Zhou, F.; Sun, T.; Tao, Z.; Chang, K.; Makino, K.; Berz, M.; Duxbury, P. M.; Ruan, C.-Y.

2017-01-01

A frontier challenge in implementing femtosecond electron microscopy is to gain precise optical control of intense beams to mitigate collective space charge effects for significantly improving the throughput. Here, we explore the flexible uses of an RF cavity as a longitudinal lens in a high-intensity beam column for condensing the electron beams both temporally and spectrally, relevant to the design of ultrafast electron microscopy. Through the introduction of a novel atomic grating approach for characterization of electron bunch phase space and control optics, we elucidate the principles for predicting and controlling the phase space dynamics to reach optimal compressions at various electron densities and generating conditions. We provide strategies to identify high-brightness modes, achieving ∼100 fs and ∼1 eV resolutions with 106 electrons per bunch, and establish the scaling of performance for different bunch charges. These results benchmark the sensitivity and resolution from the fundamental beam brightness perspective and also validate the adaptive optics concept to enable delicate control of the density-dependent phase space structures to optimize the performance, including delivering ultrashort, monochromatic, high-dose, or coherent electron bunches. PMID:28868325

Densely packed beta-structure at the protein-lipid interface of porin is revealed by high-resolution cryo-electron microscopy.

PubMed

Sass, H J; Büldt, G; Beckmann, E; Zemlin, F; van Heel, M; Zeitler, E; Rosenbusch, J P; Dorset, D L; Massalski, A

1989-09-05

Porin is an integral membrane protein that forms channels across the outer membrane of Escherichia coli. Electron microscopic studies of negatively stained two-dimensional porin crystals have shown three stain accumulations per porin trimer, revealing the locations of pores spanning the membrane. In this study, reconstituted porin lattices embedded in glucose were investigated using the low-dose technique on a cryo-electron microscope equipped with a helium-cooled superconducting objective lens. The specimen temperature was maintained at 5 K to yield an improved microscopic and specimen stability. Under these conditions, we obtained for the first time electron diffraction patterns from porin lattices to a resolution of 3.2 A and images showing optical diffraction up to a resolution of 4.9 A. Applying correlation averaging techniques to the digitized micrographs, we were able to reconstruct projected images of the porin trimer to a resolution of up to 3.5 A. In the final projection maps, amplitudes from electron diffraction and phases from these images were combined. The predominant feature is a high-density narrow band (about 6 A in thickness) that delineates the outer perimeter of the trimer. Since the molecule consists of almost exclusively beta-sheet structure, as revealed by spectroscopic data, we conclude that this band is a cylindrical beta-pleated sheet crossing the membrane nearly perpendicularly to its plane. Another intriguing finding is a low-density area (about 70 A2) situated in the centre of the trimer.

A new method for determining the plasma electron density using three-color interferometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arakawa, Hiroyuki; Kawano, Yasunori; Itami, Kiyoshi

2012-06-15

A new method for determining the plasma electron density using the fractional fringes on three-color interferometer is proposed. Integrated phase shift on each interferometer is derived without using the temporal history of the fractional fringes. The dependence on the fringe resolution and the electrical noise are simulated on the wavelengths of CO{sub 2} laser. Short-time integrations of the fractional fringes enhance the reliability of this method.

In Situ Observation of Intermittent Dissipation at Kinetic Scales in the Earth's Magnetosheath

NASA Astrophysics Data System (ADS)

Chasapis, Alexandros; Matthaeus, W. H.; Parashar, T. N.; Wan, M.; Haggerty, C. C.; Pollock, C. J.; Giles, B. L.; Paterson, W. R.; Dorelli, J.; Gershman, D. J.; Torbert, R. B.; Russell, C. T.; Lindqvist, P.-A.; Khotyaintsev, Y.; Moore, T. E.; Ergun, R. E.; Burch, J. L.

2018-03-01

We present a study of signatures of energy dissipation at kinetic scales in plasma turbulence based on observations by the Magnetospheric Multiscale mission (MMS) in the Earth’s magnetosheath. Using several intervals, and taking advantage of the high-resolution instrumentation on board MMS, we compute and discuss several statistical measures of coherent structures and heating associated with electrons, at previously unattainable scales in space and time. We use the multi-spacecraft Partial Variance of Increments (PVI) technique to study the intermittent structure of the magnetic field. Furthermore, we examine a measure of dissipation and its behavior with respect to the PVI as well as the current density. Additionally, we analyze the evolution of the anisotropic electron temperature and non-Maxwellian features of the particle distribution function. From these diagnostics emerges strong statistical evidence that electrons are preferentially heated in subproton-scale regions of strong electric current density, and this heating is preferentially in the parallel direction relative to the local magnetic field. Accordingly, the conversion of magnetic energy into electron kinetic energy occurs more strongly in regions of stronger current density, a finding consistent with several kinetic plasma simulation studies and hinted at by prior studies using lower resolution Cluster observations.

The energy balance and pressure in the solar transition zone for network and active region features

NASA Technical Reports Server (NTRS)

Nicolas, K. R.; Bartoe, J.-D. F.; Brueckner, G. E.; Vanhoosier, M. E.

1979-01-01

The electron pressure and energy balance in the solar transition zone are determined for about 125 network and active region features on the basis of high spectral and spatial resolution extreme ultraviolet spectra. Si III line intensity ratios obtained from the Naval Research Laboratory high-resolution telescope and spectrograph during a rocket flight are used as diagnostics of electron density and pressure for solar features near 3.5 x 10 to the 4th K. Observed ratios are compared with the calculated dependence of the 1301 A/1312 A and 1301 A/1296 A line intensity ratios on electron density, temperature and pressure. Electron densities ranging from 2 x 10 to the 10th/cu cm to 10 to the 12th/cu cm and active region pressures from 3 x 10 to the 15th to 10 to the 16th/cu cm K are obtained. Energy balance calculations reveal the balance of the divergence of the conductive flux and turbulent energy dissipation by radiative energy losses in a plane-parallel homogeneous transition zone (fill factor of 1), and an energy source requirement for a cylindrical zone geometry (fill factor less than 0.04).

Simultaneous imaging electron- and ion-feature Thomson scattering measurements of radiatively heated Xe.

PubMed

Pollock, B B; Meinecke, J; Kuschel, S; Ross, J S; Shaw, J L; Stoafer, C; Divol, L; Tynan, G R; Glenzer, S H

2012-10-01

Uniform density and temperature Xe plasmas have been produced over >4 mm scale-lengths using x-rays generated in a cylindrical Pb cavity. The cavity is 750 μm in depth and diameter, and is heated by a 300 J, 2 ns square, 1054 nm laser pulse focused to a spot size of 200 μm at the cavity entrance. The plasma is characterized by simultaneous imaging Thomson scattering measurements from both the electron and ion scattering features. The electron feature measurement determines the spatial electron density and temperature profile, and using these parameters as constraints in the ion feature analysis allows an accurate determination of the charge state of the Xe ions. The Thomson scattering probe beam is 40 J, 200 ps, and 527 nm, and is focused to a 100 μm spot size at the entrance of the Pb cavity. Each system has a spatial resolution of 25 μm, a temporal resolution of 200 ps (as determined by the probe duration), and a spectral resolution of 2 nm for the electron feature system and 0.025 nm for the ion feature system. The experiment is performed in a Xe filled target chamber at a neutral pressure of 3-10 Torr, and the x-rays produced in the Pb ionize and heat the Xe to a charge state of 20±4 at up to 200 eV electron temperatures.

Faraday-effect polarimeter-interferometer system for current density measurement on EAST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, H. Q.; Jie, Y. X., E-mail: yx-jie@ipp.ac.cn; Zou, Z. Y.

2014-11-15

A multichannel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retro-reflectors are mounted in the inside wall for the double-pass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. Initial calibration indicates the electron line-integrated density resolution is less than 5 × 10{sup 16} m{sup −2} (∼2°), and the Faraday rotation angle rms phase noise is <0.1°.

Evidence for anisotropic dielectric properties of monoclinic hafnia using valence electron energy-loss spectroscopy in high-resolution transmission electron microscopy and ab initio time-dependent density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guedj, C.; CEA, LETI, MINATEC Campus, F-38054 Grenoble; Hung, L.

2014-12-01

The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO{sub 2}) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO{sub 2}, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO{sub 2} may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectricmore » permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.« less

Resolution-of-identity stochastic time-dependent configuration interaction for dissipative electron dynamics in strong fields.

PubMed

Klinkusch, Stefan; Tremblay, Jean Christophe

2016-05-14

In this contribution, we introduce a method for simulating dissipative, ultrafast many-electron dynamics in intense laser fields. The method is based on the norm-conserving stochastic unraveling of the dissipative Liouville-von Neumann equation in its Lindblad form. The N-electron wave functions sampling the density matrix are represented in the basis of singly excited configuration state functions. The interaction with an external laser field is treated variationally and the response of the electronic density is included to all orders in this basis. The coupling to an external environment is included via relaxation operators inducing transition between the configuration state functions. Single electron ionization is represented by irreversible transition operators from the ionizing states to an auxiliary continuum state. The method finds its efficiency in the representation of the operators in the interaction picture, where the resolution-of-identity is used to reduce the size of the Hamiltonian eigenstate basis. The zeroth-order eigenstates can be obtained either at the configuration interaction singles level or from a time-dependent density functional theory reference calculation. The latter offers an alternative to explicitly time-dependent density functional theory which has the advantage of remaining strictly valid for strong field excitations while improving the description of the correlation as compared to configuration interaction singles. The method is tested on a well-characterized toy system, the excitation of the low-lying charge transfer state in LiCN.

Ultrashort megaelectronvolt positron beam generation based on laser-accelerated electrons

NASA Astrophysics Data System (ADS)

Xu, Tongjun; Shen, Baifei; Xu, Jiancai; Li, Shun; Yu, Yong; Li, Jinfeng; Lu, Xiaoming; Wang, Cheng; Wang, Xinliang; Liang, Xiaoyan; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan

2016-03-01

Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron-positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8 × 1021 s-1, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy.

Thermal imaging diagnostics of high-current electron beams.

PubMed

Pushkarev, A; Kholodnaya, G; Sazonov, R; Ponomarev, D

2012-10-01

The thermal imaging diagnostics of measuring pulsed electron beam energy density is presented. It provides control of the electron energy spectrum and a measure of the density distribution of the electron beam cross section, the spatial distribution of electrons with energies in the selected range, and the total energy of the electron beam. The diagnostics is based on the thermal imager registration of the imaging electron beam thermal print in a material with low bulk density and low thermal conductivity. Testing of the thermal imaging diagnostics has been conducted on a pulsed electron accelerator TEU-500. The energy of the electrons was 300-500 keV, the density of the electron current was 0.1-0.4 kA/cm(2), the duration of the pulse (at half-height) was 60 ns, and the energy in the pulse was up to 100 J. To register the thermal print, a thermal imager Fluke-Ti10 was used. Testing showed that the sensitivity of a typical thermal imager provides the registration of a pulsed electron beam heat pattern within one pulse with energy density over 0.1 J/cm(2) (or with current density over 10 A/cm(2), pulse duration of 60 ns and electron energy of 400 keV) with the spatial resolution of 0.9-1 mm. In contrast to the method of using radiosensitive (dosimetric) materials, thermal imaging diagnostics does not require either expensive consumables, or plenty of processing time.

Crystallization, dehydration and experimental phasing of WbdD, a bifunctional kinase and methyltransferase from Escherichia coli O9a

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagelueken, Gregor; Huang, Hexian; Harlos, Karl

2012-10-01

The optimization of WbdD crystals using a novel dehydration protocol and experimental phasing at 3.5 Å resolution by cross-crystal averaging followed by molecular replacement of electron density into a non-isomorphous 3.0 Å resolution native data set are reported. WbdD is a bifunctional kinase/methyltransferase that is responsible for regulation of lipopolysaccharide O antigen polysaccharide chain length in Escherichia coli serotype O9a. Solving the crystal structure of this protein proved to be a challenge because the available crystals belonging to space group I23 only diffracted to low resolution (>95% of the crystals diffracted to resolution lower than 4 Å and most onlymore » to 8 Å) and were non-isomorphous, with changes in unit-cell dimensions of greater than 10%. Data from a serendipitously found single native crystal that diffracted to 3.0 Å resolution were non-isomorphous with a lower (3.5 Å) resolution selenomethionine data set. Here, a strategy for improving poor (3.5 Å resolution) initial phases by density modification and cross-crystal averaging with an additional 4.2 Å resolution data set to build a crude model of WbdD is desribed. Using this crude model as a mask to cut out the 3.5 Å resolution electron density yielded a successful molecular-replacement solution of the 3.0 Å resolution data set. The resulting map was used to build a complete model of WbdD. The hydration status of individual crystals appears to underpin the variable diffraction quality of WbdD crystals. After the initial structure had been solved, methods to control the hydration status of WbdD were developed and it was thus possible to routinely obtain high-resolution diffraction (to better than 2.5 Å resolution). This novel and facile crystal-dehydration protocol may be useful for similar challenging situations.« less

Validated near-atomic resolution structure of bacteriophage epsilon15 derived from cryo-EM and modeling

PubMed Central

Baker, Matthew L.; Hryc, Corey F.; Zhang, Qinfen; Wu, Weimin; Jakana, Joanita; Haase-Pettingell, Cameron; Afonine, Pavel V.; Adams, Paul D.; King, Jonathan A.; Jiang, Wen; Chiu, Wah

2013-01-01

High-resolution structures of viruses have made important contributions to modern structural biology. Bacteriophages, the most diverse and abundant organisms on earth, replicate and infect all bacteria and archaea, making them excellent potential alternatives to antibiotics and therapies for multidrug-resistant bacteria. Here, we improved upon our previous electron cryomicroscopy structure of Salmonella bacteriophage epsilon15, achieving a resolution sufficient to determine the tertiary structures of both gp7 and gp10 protein subunits that form the T = 7 icosahedral lattice. This study utilizes recently established best practice for near-atomic to high-resolution (3–5 Å) electron cryomicroscopy data evaluation. The resolution and reliability of the density map were cross-validated by multiple reconstructions from truly independent data sets, whereas the models of the individual protein subunits were validated adopting the best practices from X-ray crystallography. Some sidechain densities are clearly resolved and show the subunit–subunit interactions within and across the capsomeres that are required to stabilize the virus. The presence of the canonical phage and jellyroll viral protein folds, gp7 and gp10, respectively, in the same virus suggests that epsilon15 may have emerged more recently relative to other bacteriophages. PMID:23840063

On macromolecular refinement at subatomic resolution with interatomic scatterers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afonine, Pavel V., E-mail: pafonine@lbl.gov; Grosse-Kunstleve, Ralf W.; Adams, Paul D.

2007-11-01

Modelling deformation electron density using interatomic scatters is simpler than multipolar methods, produces comparable results at subatomic resolution and can easily be applied to macromolecules. A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than ∼1.0 Å) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8–1.0 Å, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented bymore » additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.« less

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

DOE PAGES

Valdivia, M. P.; Stutman, D.; Stoeckl, C.; ...

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 × 10 23 cm ₋3more » in a 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

Electron-density descriptors as predictors in quantitative structure--activity/property relationships and drug design.

PubMed

Matta, Chérif F; Arabi, Alya A

2011-06-01

The use of electron density-based molecular descriptors in drug research, particularly in quantitative structure--activity relationships/quantitative structure--property relationships studies, is reviewed. The exposition starts by a discussion of molecular similarity and transferability in terms of the underlying electron density, which leads to a qualitative introduction to the quantum theory of atoms in molecules (QTAIM). The starting point of QTAIM is the topological analysis of the molecular electron-density distributions to extract atomic and bond properties that characterize every atom and bond in the molecule. These atomic and bond properties have considerable potential as bases for the construction of robust quantitative structure--activity/property relationships models as shown by selected examples in this review. QTAIM is applicable to the electron density calculated from quantum-chemical calculations and/or that obtained from ultra-high resolution x-ray diffraction experiments followed by nonspherical refinement. Atomic and bond properties are introduced followed by examples of application of each of these two families of descriptors. The review ends with a study whereby the molecular electrostatic potential, uniquely determined by the density, is used in conjunction with atomic properties to elucidate the reasons for the biological similarity of bioisosteres.

Time-resolved serial crystallography captures high-resolution intermediates of photoactive yellow protein

DOE PAGES

Tenboer, Jason; Basu, Shibom; Zatsepin, Nadia; ...

2014-12-05

We report that serial femtosecond crystallography using ultrashort pulses from X-ray Free Electron Lasers (XFELs) offers the possibility to study light-triggered dynamics of biomolecules. Using microcrystals of the blue light photoreceptor, photoactive yellow protein, as a model system, we present high resolution, time-resolved difference electron density maps of excellent quality with strong features, which allow the determination of structures of reaction intermediates to 1.6 Å resolution. These results open the way to the study of reversible and non-reversible biological reactions on time scales as short as femtoseconds under conditions which maximize the extent of reaction initiation throughout the crystal.

High-spatial-resolution electron density measurement by Langmuir probe for multi-point observations using tiny spacecraft

NASA Astrophysics Data System (ADS)

Hoang, H.; Røed, K.; Bekkeng, T. A.; Trondsen, E.; Clausen, L. B. N.; Miloch, W. J.; Moen, J. I.

2017-11-01

A method for evaluating electron density using a single fixed-bias Langmuir probe is presented. The technique allows for high-spatio-temporal resolution electron density measurements, which can be effectively carried out by tiny spacecraft for multi-point observations in the ionosphere. The results are compared with the multi-needle Langmuir probe system, which is a scientific instrument developed at the University of Oslo comprising four fixed-bias cylindrical probes that allow small-scale plasma density structures to be characterized in the ionosphere. The technique proposed in this paper can comply with the requirements of future small-sized spacecraft, where the cost-effectiveness, limited space available on the craft, low power consumption and capacity for data-links need to be addressed. The first experimental results in both the plasma laboratory and space confirm the efficiency of the new approach. Moreover, detailed analyses on two challenging issues when deploying the DC Langmuir probe on a tiny spacecraft, which are the limited conductive area of the spacecraft and probe surface contamination, are presented in the paper. It is demonstrated that the limited conductive area, depending on applications, can either be of no concern for the experiment or can be resolved by mitigation methods. Surface contamination has a small impact on the performance of the developed probe.

Simultaneous imaging electron- and ion-feature Thomson scattering measurements of radiatively heated Xe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pollock, B. B.; University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093; Meinecke, J.

2012-10-15

Uniform density and temperature Xe plasmas have been produced over >4 mm scale-lengths using x-rays generated in a cylindrical Pb cavity. The cavity is 750 {mu}m in depth and diameter, and is heated by a 300 J, 2 ns square, 1054 nm laser pulse focused to a spot size of 200 {mu}m at the cavity entrance. The plasma is characterized by simultaneous imaging Thomson scattering measurements from both the electron and ion scattering features. The electron feature measurement determines the spatial electron density and temperature profile, and using these parameters as constraints in the ion feature analysis allows an accuratemore » determination of the charge state of the Xe ions. The Thomson scattering probe beam is 40 J, 200 ps, and 527 nm, and is focused to a 100 {mu}m spot size at the entrance of the Pb cavity. Each system has a spatial resolution of 25 {mu}m, a temporal resolution of 200 ps (as determined by the probe duration), and a spectral resolution of 2 nm for the electron feature system and 0.025 nm for the ion feature system. The experiment is performed in a Xe filled target chamber at a neutral pressure of 3-10 Torr, and the x-rays produced in the Pb ionize and heat the Xe to a charge state of 20{+-}4 at up to 200 eV electron temperatures.« less

Tools for Model Building and Optimization into Near-Atomic Resolution Electron Cryo-Microscopy Density Maps.

PubMed

DiMaio, F; Chiu, W

2016-01-01

Electron cryo-microscopy (cryoEM) has advanced dramatically to become a viable tool for high-resolution structural biology research. The ultimate outcome of a cryoEM study is an atomic model of a macromolecule or its complex with interacting partners. This chapter describes a variety of algorithms and software to build a de novo model based on the cryoEM 3D density map, to optimize the model with the best stereochemistry restraints and finally to validate the model with proper protocols. The full process of atomic structure determination from a cryoEM map is described. The tools outlined in this chapter should prove extremely valuable in revealing atomic interactions guided by cryoEM data. © 2016 Elsevier Inc. All rights reserved.

Three-dimensional multi-fluid simulations of Titan's interaction with Saturn's magnetosphere: Comparisons with Cassini's T55 flyby

NASA Astrophysics Data System (ADS)

Snowden, D.; Winglee, R.

2013-08-01

We describe a new multi-fluid model of Titan's interaction with Saturn's magnetosphere that includes finer resolution in Titan's ionosphere, photoionization, electron-impact ionization, dissociative recombination, and ion-neutral coupling in the momentum and energy equations. We compare simulation results to data from Cassini's T55 flyby to show that including magnetospheric electron-impact ionization in Titan's nightside ionosphere is necessary to calculate electron densities, electron temperatures, and ion velocities that are consistent with Cassini observations. However, similar to other studies, we find that the electron-impact ionization rate calculated by the model needs to be significantly reduced to produce an electron density that is in agreement with the observations. We also find that an upstream plasma flow with significant components northward and radially outward from Saturn is needed to reproduce the gradual increase in electron density observed during the ingress portion of T55. This suggests that Titan was in a nonideal environment with a plasma flow oriented away from the direction of corotation during T55 and likely during the subsequent flybys T56, T57, T58, and T59 when similar electron density enhancements were seen on the inbound portion of Cassini's trajectory.

Development of a Nomarski-type multi-frame interferometer as a time and space resolving diagnostics for the free electron density of laser-generated plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boerner, M.; Frank, A.; Pelka, A.

2012-04-15

This article reports on the development and set-up of a Nomarski-type multi-frame interferometer as a time and space resolving diagnostics of the free electron density in laser-generated plasma. The interferometer allows the recording of a series of 4 images within 6 ns of a single laser-plasma interaction. For the setup presented here, the minimal accessible free electron density is 5 x 10{sup 18} cm{sup -3}, the maximal one is 2 x 10{sup 20} cm{sup -3}. Furthermore, it provides a resolution of the electron density in space of 50 {mu}m and in time of 0.5 ns for one image with amore » customizable magnification in space for each of the 4 images. The electron density was evaluated from the interferograms using an Abel inversion algorithm. The functionality of the system was proven during first experiments and the experimental results are presented and discussed. A ray tracing procedure was realized to verify the interferometry pictures taken. In particular, the experimental results are compared to simulations and show excellent agreement, providing a conclusive picture of the evolution of the electron density distribution.« less

Two-Dimensional Electron Density Measurement of Positive Streamer Discharge in Atmospheric-Pressure Air

NASA Astrophysics Data System (ADS)

Inada, Yuki; Ono, Ryo; Kumada, Akiko; Hidaka, Kunihiko; Maeyama, Mitsuaki

2016-09-01

The electron density of streamer discharges propagating in atmospheric-pressure air is crucially important for systematic understanding of the production mechanisms of reactive species utilized in wide ranging applications such as medical treatment, plasma-assisted ignition and combustion, ozone production and environmental pollutant processing. However, electron density measurement during the propagation of the atmospheric-pressure streamers is extremely difficult by using the conventional localized type measurement systems due to the streamer initiation jitters and the irreproducibility in the discharge paths. In order to overcome the difficulties, single-shot two-dimensional electron density measurement was conducted by using a Shack-Hartmann type laser wavefront sensor. The Shack-Hartmann sensor with a temporal resolution of 2 ns was applied to pulsed positive streamer discharges generated in an air gap between pin-to-plate electrodes. The electron density a few ns after the streamer initiation was 7*1021m-3 and uniformly distributed along the streamer channel. The electron density and its distribution profile were compared with a previous study simulating similar streamers, demonstrating good agreement. This work was supported in part by JKA and its promotion funds from KEIRIN RACE. The authors like to thank Mr. Kazuaki Ogura and Mr. Kaiho Aono of The University of Tokyo for their support during this work.

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.

Electric field imaging of single atoms

PubMed Central

Shibata, Naoya; Seki, Takehito; Sánchez-Santolino, Gabriel; Findlay, Scott D.; Kohno, Yuji; Matsumoto, Takao; Ishikawa, Ryo; Ikuhara, Yuichi

2017-01-01

In scanning transmission electron microscopy (STEM), single atoms can be imaged by detecting electrons scattered through high angles using post-specimen, annular-type detectors. Recently, it has been shown that the atomic-scale electric field of both the positive atomic nuclei and the surrounding negative electrons within crystalline materials can be probed by atomic-resolution differential phase contrast STEM. Here we demonstrate the real-space imaging of the (projected) atomic electric field distribution inside single Au atoms, using sub-Å spatial resolution STEM combined with a high-speed segmented detector. We directly visualize that the electric field distribution (blurred by the sub-Å size electron probe) drastically changes within the single Au atom in a shape that relates to the spatial variation of total charge density within the atom. Atomic-resolution electric field mapping with single-atom sensitivity enables us to examine their detailed internal and boundary structures. PMID:28555629

Correcting pervasive errors in RNA crystallography through enumerative structure prediction.

PubMed

Chou, Fang-Chieh; Sripakdeevong, Parin; Dibrov, Sergey M; Hermann, Thomas; Das, Rhiju

2013-01-01

Three-dimensional RNA models fitted into crystallographic density maps exhibit pervasive conformational ambiguities, geometric errors and steric clashes. To address these problems, we present enumerative real-space refinement assisted by electron density under Rosetta (ERRASER), coupled to Python-based hierarchical environment for integrated 'xtallography' (PHENIX) diffraction-based refinement. On 24 data sets, ERRASER automatically corrects the majority of MolProbity-assessed errors, improves the average R(free) factor, resolves functionally important discrepancies in noncanonical structure and refines low-resolution models to better match higher-resolution models.

Photoemission and Photoabsorption Investigation of the Electronic Structure of Ytterbium Doped Strontium Fluoroapatite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, A J; van Buuren, T; Bostedt, C

X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure was used to evaluate the density of occupied states of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy (XAS) at the Yb 4d (N{sub 4,5}-edge), Sr 3d (M{sub 4,5}-edge), P 2p (L{sub 2,3}-edge), F 1s and O 1s (K-edges) absorption edges. These results provide the first measurements of the electronic structure and surface chemistry of this material.

Using cryoEM Reconstruction and Phase Extension to Determine Crystal Structure of Bacteriophage $${\\Phi}$$6 Major Capsid Protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nemecek, Daniel; Plevka, Pavel; Boura, Evzen

2013-11-29

Bacteriophagemore » $${\\Phi}$$6 is a double-stranded RNA virus that has been extensively studied as a model organism. In this paper we describe structure determination of $${\\Phi}$$6 major capsid protein P1. The protein crystallized in base centered orthorhombic space group C2221. Matthews’s coefficient indicated that the crystals contain from four to seven P1 subunits in the crystallographic asymmetric unit. The self-rotation function had shown presence of fivefold axes of non-crystallographic symmetry in the crystals. Thus, electron density map corresponding to a P1 pentamer was excised from a previously determined cryoEM reconstruction of the $${\\Phi}$$6 procapsid at 7 Å resolution and used as a model for molecular replacement. The phases for reflections at higher than 7 Å resolution were obtained by phase extension employing the fivefold non-crystallographic symmetry present in the crystal. Lastly, the averaged 3.6 Å-resolution electron density map was of sufficient quality to allow model building.« less

Goniometer-based femtosecond crystallography with X-ray free electron lasers

DOE PAGES

Cohen, Aina E.; Soltis, S. Michael; González, Ana; ...

2014-10-31

The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiation-sensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-Å resolution electron density map. With smaller crystals, high-density grids were usedmore » to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β 2-adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources.« less

Goniometer-based femtosecond crystallography with X-ray free electron lasers

PubMed Central

Cohen, Aina E.; Soltis, S. Michael; González, Ana; Aguila, Laura; Alonso-Mori, Roberto; Barnes, Christopher O.; Baxter, Elizabeth L.; Brehmer, Winnie; Brewster, Aaron S.; Brunger, Axel T.; Calero, Guillermo; Chang, Joseph F.; Chollet, Matthieu; Ehrensberger, Paul; Eriksson, Thomas L.; Feng, Yiping; Hattne, Johan; Hedman, Britt; Hollenbeck, Michael; Holton, James M.; Keable, Stephen; Kobilka, Brian K.; Kovaleva, Elena G.; Kruse, Andrew C.; Lemke, Henrik T.; Lin, Guowu; Lyubimov, Artem Y.; Manglik, Aashish; Mathews, Irimpan I.; McPhillips, Scott E.; Nelson, Silke; Peters, John W.; Sauter, Nicholas K.; Smith, Clyde A.; Song, Jinhu; Stevenson, Hilary P.; Tsai, Yingssu; Uervirojnangkoorn, Monarin; Vinetsky, Vladimir; Wakatsuki, Soichi; Weis, William I.; Zadvornyy, Oleg A.; Zeldin, Oliver B.; Zhu, Diling; Hodgson, Keith O.

2014-01-01

The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiation-sensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-Å resolution electron density map. For smaller crystals, high-density grids were used to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β2-adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources. PMID:25362050

Resolution-of-identity stochastic time-dependent configuration interaction for dissipative electron dynamics in strong fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klinkusch, Stefan; Tremblay, Jean Christophe

In this contribution, we introduce a method for simulating dissipative, ultrafast many-electron dynamics in intense laser fields. The method is based on the norm-conserving stochastic unraveling of the dissipative Liouville-von Neumann equation in its Lindblad form. The N-electron wave functions sampling the density matrix are represented in the basis of singly excited configuration state functions. The interaction with an external laser field is treated variationally and the response of the electronic density is included to all orders in this basis. The coupling to an external environment is included via relaxation operators inducing transition between the configuration state functions. Single electronmore » ionization is represented by irreversible transition operators from the ionizing states to an auxiliary continuum state. The method finds its efficiency in the representation of the operators in the interaction picture, where the resolution-of-identity is used to reduce the size of the Hamiltonian eigenstate basis. The zeroth-order eigenstates can be obtained either at the configuration interaction singles level or from a time-dependent density functional theory reference calculation. The latter offers an alternative to explicitly time-dependent density functional theory which has the advantage of remaining strictly valid for strong field excitations while improving the description of the correlation as compared to configuration interaction singles. The method is tested on a well-characterized toy system, the excitation of the low-lying charge transfer state in LiCN.« less

Compact microwave imaging system to measure spatial distribution of plasma density

NASA Astrophysics Data System (ADS)

Ito, H.; Oba, R.; Yugami, N.; Nishida, Y.

2004-10-01

We have developed an advanced microwave interferometric system operating in the K band (18-27 GHz) with the use of a fan-shaped microwave based on a heterodyne detection system for measuring the spatial distribution of the plasma density. In order to make a simple, low-cost, and compact microwave interferometer with better spatial resolution, a microwave scattering technique by a microstrip antenna array is employed. Experimental results show that the imaging system with the microstrip antenna array can have finer spatial resolution than one with the diode antenna array and reconstruct a good spatially resolved image of the finite size dielectric phantoms placed between the horn antenna and the micro strip antenna array. The precise two-dimensional electron density distribution of the cylindrical plasma produced by an electron cyclotron resonance has been observed. As a result, the present imaging system is more suitable for a two- or three-dimensional display of the objects or stationary plasmas and it is possible to realize a compact microwave imaging system.

Direct Detection Electron Energy-Loss Spectroscopy: A Method to Push the Limits of Resolution and Sensitivity.

PubMed

Hart, James L; Lang, Andrew C; Leff, Asher C; Longo, Paolo; Trevor, Colin; Twesten, Ray D; Taheri, Mitra L

2017-08-15

In many cases, electron counting with direct detection sensors offers improved resolution, lower noise, and higher pixel density compared to conventional, indirect detection sensors for electron microscopy applications. Direct detection technology has previously been utilized, with great success, for imaging and diffraction, but potential advantages for spectroscopy remain unexplored. Here we compare the performance of a direct detection sensor operated in counting mode and an indirect detection sensor (scintillator/fiber-optic/CCD) for electron energy-loss spectroscopy. Clear improvements in measured detective quantum efficiency and combined energy resolution/energy field-of-view are offered by counting mode direct detection, showing promise for efficient spectrum imaging, low-dose mapping of beam-sensitive specimens, trace element analysis, and time-resolved spectroscopy. Despite the limited counting rate imposed by the readout electronics, we show that both core-loss and low-loss spectral acquisition are practical. These developments will benefit biologists, chemists, physicists, and materials scientists alike.

Influence of Atmospheric Pressure and Composition on LIBS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hatch, Jeremy J.; Scott, Jill R.; Effenberger, A. J. Jr.

2014-03-01

Most LIBS experiments are conducted at standard atmospheric pressure in air. However, there are LIBS studies that vary the pressure and composition of the gas. These studies have provided insights into fundamentals of the mechanisms that lead to the emission and methods for improving the quality of LIBS spectra. These atmospheric studies are difficult because the effects of pressure and gas composition and interconnected, making interpretation of the results difficult. The influence of pressures below and above 760 Torr have been explored. Performing LIBS on a surface at reduced pressures (<760 Torr) can result in enhanced spectra due to highermore » resolution, increased intensity, improved signal-to-noise (S/N), and increased ablation. Lower pressures produce increased resolution because the line width in LIBS spectra is predominantly due to Stark and Doppler broadening. Stark broadening is primarily caused from collisions between electrons and atoms, while Doppler broadening is proportional to the plasma temperature. Close examination using a high resolution spectrometer reveals that spectra show significant peak broadening and self-absorption as pressures increase, especially for pressures >760 Torr. During LIBS plasma expansion, energy is lost to the surrounding atmosphere, which reduces the lifetime of the laser plasma. Therefore, reducing the pressure increases the lifetime of the plasma, allowing more light from the laser plasma to be collected; thus, increasing the observed signal intensity. However, if pressures are too low (<10 Torr), then there is a steep drop in LIBS spectral intensity. This loss in intensity is mostly due to a disordered plasma that results from the lack of sufficient atmosphere to provide adequate confinement. At reduced pressures, the plasma expands into a less dense atmosphere, which results in a less dense shock wave. The reduced density in the shock wave results in reduced plasma shielding, allowing more photons to reach the sample. Increasing the number of photons interacting with the sample surface results in increased ablation, which can lead to increased intensity. The composition of the background gas has been shown to greatly influence the observed LIBS spectra by altering the plasma temperature, electron density, mass removal, and plasma shielding that impact the emission intensity and peak resolution. It has been reported that atmospheric Ar results in the highest plasma temperature and electron density, while a He atmosphere results in the lowest plasma temperatures and electron density. Studying temporal data, it was also found that Ar had the slowest decay of both electron density and plasma temperature, while He had the fastest decay in both parameters. The higher plasma temperature and electron density results in an increase in line broadenin, or poor resolution, for Ar compared to He. A rapidly developing LIBS plasma with a sufficient amount of electrons can absorb a significant portion of the laser pulse through inverse Bremsstahlung. Ar (15.8 eV ) is more easily ionized than He (24.4 eV). The breakdown threshold for He at 760 Torr is approximately 3 times greater than Ar and approximately 5 times greater at 100 Torr. The lower breakdown threshold in Ar, compared to He, creates an environment favorable for plasma shielding, which reduces sample vaporization and leads to a weaker LIBS signal.« less

Analysis of polarization in hydrogen bonded complexes: An asymptotic projection approach

NASA Astrophysics Data System (ADS)

Drici, Nedjoua

2018-03-01

The asymptotic projection technique is used to investigate the polarization effect that arises from the interaction between the relaxed, and frozen monomeric charge densities of a set of neutral and charged hydrogen bonded complexes. The AP technique based on the resolution of the original Kohn-Sham equations can give an acceptable qualitative description of the polarization effect in neutral complexes. The significant overlap of the electron densities, in charged and π-conjugated complexes, impose further development of a new functional, describing the coupling between constrained and non-constrained electron densities within the AP technique to provide an accurate representation of the polarization effect.

Talbot-Lau x-ray deflectometry phase-retrieval methods for electron density diagnostics in high-energy density experiments.

PubMed

Valdivia, Maria Pia; Stutman, Dan; Stoeckl, Christian; Mileham, Chad; Begishev, Ildar A; Bromage, Jake; Regan, Sean P

2018-01-10

Talbot-Lau x-ray interferometry uses incoherent x-ray sources to measure refraction index changes in matter. These measurements can provide accurate electron density mapping through phase retrieval. An adaptation of the interferometer has been developed in order to meet the specific requirements of high-energy density experiments. This adaptation is known as a moiré deflectometer, which allows for single-shot capabilities in the form of interferometric fringe patterns. The moiré x-ray deflectometry technique requires a set of object and reference images in order to provide electron density maps, which can be costly in the high-energy density environment. In particular, synthetic reference phase images obtained ex situ through a phase-scan procedure, can provide a feasible solution. To test this procedure, an object phase map was retrieved from a single-shot moiré image obtained from a plasma-produced x-ray source. A reference phase map was then obtained from phase-stepping measurements using a continuous x-ray tube source in a small laboratory setting. The two phase maps were used to retrieve an electron density map. A comparison of the moiré and phase-stepping phase-retrieval methods was performed to evaluate single-exposure plasma electron density mapping for high-energy density and other transient plasma experiments. It was found that a combination of phase-retrieval methods can deliver accurate refraction angle mapping. Once x-ray backlighter quality is optimized, the ex situ method is expected to deliver electron density mapping with improved resolution. The steps necessary for improved diagnostic performance are discussed.

Challenges in quantitative crystallographic characterization of 3D thin films by ACOM-TEM.

PubMed

Kobler, A; Kübel, C

2017-02-01

Automated crystal orientation mapping for transmission electron microscopy (ACOM-TEM) has become an easy to use method for the investigation of crystalline materials and complements other TEM methods by adding local crystallographic information over large areas. It fills the gap between high resolution electron microscopy and electron back scatter diffraction in terms of spatial resolution. Recent investigations showed that spot diffraction ACOM-TEM is a quantitative method with respect to sample parameters like grain size, twin density, orientation density and others. It can even be used in combination with in-situ tensile or thermal testing. However, there are limitations of the current method. In this paper we discuss some of the challenges and discuss solutions, e.g. we present an ambiguity filter that reduces the number of pixels with a '180° ambiguity problem'. For that an ACOM-TEM tilt series of nanocrystalline Pd thin films with overlapping crystallites was acquired and analyzed. Copyright © 2017. Published by Elsevier B.V.

New Thomson scattering diagnostic on RFX-mod.

PubMed

Alfier, A; Pasqualotto, R

2007-01-01

This article describes the completely renovated Thomson scattering (TS) diagnostic employed in the modified Reversed Field eXperiment (RFX-mod) since it restarted operation in 2005. The system measures plasma electron temperature and density profiles along an equatorial diameter, measuring in 84 positions with 7 mm spatial resolution. The custom built Nd:YLF laser produces a burst of 10 pulses at 50 Hz with energy of 3 J, providing ten profile measurements in a plasma discharge of about 300 ms duration. An optical delay system accommodates three scattering volumes in each of the 28 interference filter spectrometers. Avalanche photodiodes detect the Thomson scattering signals and allow them to be recorded by means of waveform digitizers. Electron temperature is obtained using an alternative relative calibration method, based on the use of a supercontinuum light source. Rotational Raman scattering in nitrogen has supplied the absolute calibration for the electron density measurements. During RFX-mod experimental campaigns in 2005, the TS diagnostic has demonstrated its performance, routinely providing reliable high resolution profiles.

Laboratory calibration of density-dependent lines in the extreme ultraviolet spectral region

NASA Astrophysics Data System (ADS)

Lepson, J. K.; Beiersdorfer, P.; Gu, M. F.; Desai, P.; Bitter, M.; Roquemore, L.; Reinke, M. L.

2012-05-01

We have been making spectral measurements in the extreme ultraviolet (EUV) from different laboratory sources in order to investigate the electron density dependence of various astrophysically important emission lines and to test the atomic models underlying the diagnostic line ratios. The measurement are being performed at the Livermore EBIT-I electron beam ion trap, the National Spherical Torus Experiment (NSTX) at Princeton, and the Alcator C-Mod tokamak at the Massachusetts Institute of Technology, which together span an electron density of four orders of magnitude and which allow us to test the various models at high and low density limits. Here we present measurements of Fe XXII and Ar XIV, which include new data from an ultra high resolution (λ/Δλ >4000) spectrometer at the EBIT-I facility. We found good agreement between the measurements and modeling calculations for Fe XXII, but poorer agreement for Ar XIV.

Experimental determination of spin-dependent electron density by joint refinement of X-ray and polarized neutron diffraction data.

PubMed

Deutsch, Maxime; Claiser, Nicolas; Pillet, Sébastien; Chumakov, Yurii; Becker, Pierre; Gillet, Jean Michel; Gillon, Béatrice; Lecomte, Claude; Souhassou, Mohamed

2012-11-01

New crystallographic tools were developed to access a more precise description of the spin-dependent electron density of magnetic crystals. The method combines experimental information coming from high-resolution X-ray diffraction (XRD) and polarized neutron diffraction (PND) in a unified model. A new algorithm that allows for a simultaneous refinement of the charge- and spin-density parameters against XRD and PND data is described. The resulting software MOLLYNX is based on the well known Hansen-Coppens multipolar model, and makes it possible to differentiate the electron spins. This algorithm is validated and demonstrated with a molecular crystal formed by a bimetallic chain, MnCu(pba)(H(2)O)(3)·2H(2)O, for which XRD and PND data are available. The joint refinement provides a more detailed description of the spin density than the refinement from PND data alone.

Mapping atomic motions with ultrabright electrons: towards fundamental limits in space-time resolution.

PubMed

Manz, Stephanie; Casandruc, Albert; Zhang, Dongfang; Zhong, Yinpeng; Loch, Rolf A; Marx, Alexander; Hasegawa, Taisuke; Liu, Lai Chung; Bayesteh, Shima; Delsim-Hashemi, Hossein; Hoffmann, Matthias; Felber, Matthias; Hachmann, Max; Mayet, Frank; Hirscht, Julian; Keskin, Sercan; Hada, Masaki; Epp, Sascha W; Flöttmann, Klaus; Miller, R J Dwayne

2015-01-01

The long held objective of directly observing atomic motions during the defining moments of chemistry has been achieved based on ultrabright electron sources that have given rise to a new field of atomically resolved structural dynamics. This class of experiments requires not only simultaneous sub-atomic spatial resolution with temporal resolution on the 100 femtosecond time scale but also has brightness requirements approaching single shot atomic resolution conditions. The brightness condition is in recognition that chemistry leads generally to irreversible changes in structure during the experimental conditions and that the nanoscale thin samples needed for electron structural probes pose upper limits to the available sample or "film" for atomic movies. Even in the case of reversible systems, the degree of excitation and thermal effects require the brightest sources possible for a given space-time resolution to observe the structural changes above background. Further progress in the field, particularly to the study of biological systems and solution reaction chemistry, requires increased brightness and spatial coherence, as well as an ability to tune the electron scattering cross-section to meet sample constraints. The electron bunch density or intensity depends directly on the magnitude of the extraction field for photoemitted electron sources and electron energy distribution in the transverse and longitudinal planes of electron propagation. This work examines the fundamental limits to optimizing these parameters based on relativistic electron sources using re-bunching cavity concepts that are now capable of achieving 10 femtosecond time scale resolution to capture the fastest nuclear motions. This analysis is given for both diffraction and real space imaging of structural dynamics in which there are several orders of magnitude higher space-time resolution with diffraction methods. The first experimental results from the Relativistic Electron Gun for Atomic Exploration (REGAE) are given that show the significantly reduced multiple electron scattering problem in this regime, which opens up micron scale systems, notably solution phase chemistry, to atomically resolved structural dynamics.

Transferability of electronic structure of four energetic materials by using single crystal and high resolution X-ray diffraction experiments

NASA Astrophysics Data System (ADS)

Chen, Yu-Sheng

The electronic structures of four energetic materials, trinitrodiazapentalene (C6H3N5O6, TNDAP), beta-1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (C4H8N8O8, beta-HMX), 1,3,3-trinitroazetidine (C3H4N4O6, TNAZ), and hexahydro-1,3,5-trinitro-1,3,5-s-triazine (C3H6N6O6, RDX), have been analyzed using Hansen-Coppens multipole refinements, using high resolution X-ray diffraction data collected at low temperature, as well as from theoretical calculated structure factors from the solid state phase using density functional theory (DFT), plus B3LYP level theory, and the 6-31G* basis set. However, when comparing both the deformation density and the electrostatic potentials from the theoretical results in TNDAP and TNAZ, they disagree with the experimental results. Therefore, those results have been deposited in appendices A4 and A6, for future reference. In HMX and RDX the theoretical results are in good agreement with experimental results. The physical properties derived from the electronic structure in these four energetic materials, such as multipole populations, the values of the electron density and its Laplacian of the electron density at the bond critical points, have also been calculated using "Atoms in Molecules" (AIM) theory both from the solid state phase calculation, and the experiment, as well as directly calculated from the free molecule in the gas phase. The electron density and the magnitude of its Laplacian from the gas phase are always larger than for the solid state phase calculation and the experiment. This may be due to the packing effect. The transferability of the experimental electronic structure of the NO 2 groups from HMX to TNDAP, TNAZ and RDX are also presented here. Even though the major populated multipoles are robust (small e.s.d.'s), these are few in number, compared with other lower populated multipoles for which the populations span a larger range. Since the deformation electron density distributions are reconstructed using linear combinations of the multipoles, it is necessary to give more degrees of freedom in the refinements. Therefore, those electron density distributions which have a wider range of the multipole populations should not be fixed in the refinements. Utilizing the same coordinate system setup in the multipole refinements of the functional groups, this system can be used as a starting point for solving the charge distribution of a larger system.

Pioneer Venus Data Analysis

NASA Technical Reports Server (NTRS)

Jones, Douglas E.

1996-01-01

Analysis and interpretation of data from the Orbiter Retarding Potential Analyzer (ORPA) onboard the Pioneer Venus Orbiter is reported. By comparing ORPA data to proton data from the Orbiter Plasma Analyzer (OPA), it was found that the ORPA suprathermal electron densities taken outside the Venusian ionopause represent solar wind electron densities, thus allowing the high resolution study of Venus bow shocks using both magnetic field and solar wind electron data. A preliminary analysis of 366 bow shock penetrations was completed using the solar wind electron data as determined from ORPA suprathermal electron densities and temperatures, resulting in an estimate of the extent to which mass loading pickup of O+ (UV ionized O atoms flowing out of the Venus atmosphere) upstream of the Venus obstacle occurred. The pickup of O+ averaged 9.95%, ranging from 0.78% to 23.63%. Detailed results are reported in two attached theses: (1) Comparison of ORPA Suprathermal Electron and OPA Solar Wind Proton Data from the Pioneer Venus Orbiter and (2) Pioneer Venus Orbiter Retarding Potential Analyzer Observations of the Electron Component of the Solar Wind, and of the Venus Bow Shock and Magnetosheath.

Calculation of characteristics of compressed gaseous xenon gamma-ray detectors

NASA Astrophysics Data System (ADS)

Komarov, V. B.; Dmitrenko, V. V.; Ulin, S. E.; Uteshev, Z. M.

1992-12-01

Energy resolution and pulse distribution of a compressed gaseous xenon cylindrical detector were calculated. The analytical calculation took into account gamma-ray energy, fluctuation of electron-ion pairs, electron distribution, recombination, and H excess. The calculation was performed for a xenon density less than 0.6 g/cm and H excess less than 2 percent.

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

DOE PAGES

Kapetanakis, Myron; Zhou, Wu; Oxley, Mark P.; ...

2015-09-25

Photon-based spectroscopies have played a central role in exploring the electronic properties of crystalline solids and thin films. They are a powerful tool for probing the electronic properties of nanostructures, but they are limited by lack of spatial resolution. On the other hand, electron-based spectroscopies, e.g., electron energy loss spectroscopy (EELS), are now capable of subangstrom spatial resolution. Core-loss EELS, a spatially resolved analog of x-ray absorption, has been used extensively in the study of inhomogeneous complex systems. In this paper, we demonstrate that low-loss EELS in an aberration-corrected scanning transmission electron microscope, which probes low-energy excitations, combined with amore » theoretical framework for simulating and analyzing the spectra, is a powerful tool to probe low-energy electron excitations with atomic-scale resolution. The theoretical component of the method combines density functional theory–based calculations of the excitations with dynamical scattering theory for the electron beam. We apply the method to monolayer graphene in order to demonstrate that atomic-scale contrast is inherent in low-loss EELS even in a perfectly periodic structure. The method is a complement to optical spectroscopy as it probes transitions entailing momentum transfer. The theoretical analysis identifies the spatial and orbital origins of excitations, holding the promise of ultimately becoming a powerful probe of the structure and electronic properties of individual point and extended defects in both crystals and inhomogeneous complex nanostructures. The method can be extended to probe magnetic and vibrational properties with atomic resolution.« less

Method for Estimating the Charge Density Distribution on a Dielectric Surface.

PubMed

Nakashima, Takuya; Suhara, Hiroyuki; Murata, Hidekazu; Shimoyama, Hiroshi

2017-06-01

High-quality color output from digital photocopiers and laser printers is in strong demand, motivating attempts to achieve fine dot reproducibility and stability. The resolution of a digital photocopier depends on the charge density distribution on the organic photoconductor surface; however, directly measuring the charge density distribution is impossible. In this study, we propose a new electron optical instrument that can rapidly measure the electrostatic latent image on an organic photoconductor surface, which is a dielectric surface, as well as a novel method to quantitatively estimate the charge density distribution on a dielectric surface by combining experimental data obtained from the apparatus via a computer simulation. In the computer simulation, an improved three-dimensional boundary charge density method (BCM) is used for electric field analysis in the vicinity of the dielectric material with a charge density distribution. This method enables us to estimate the profile and quantity of the charge density distribution on a dielectric surface with a resolution of the order of microns. Furthermore, the surface potential on the dielectric surface can be immediately calculated using the obtained charge density. This method enables the relation between the charge pattern on the organic photoconductor surface and toner particle behavior to be studied; an understanding regarding the same may lead to the development of a new generation of higher resolution photocopiers.

Temperature and density evolution during decay in a 2.45 GHz hydrogen electron cyclotron resonance plasma: off-resonant and resonant cases.

PubMed

Cortázar, O D; Megía-Macías, A; Vizcaíno-de-Julián, A

2013-09-01

Time resolved electron temperature and density measurements during the decay stage in a hydrogen electron cyclotron resonance (ECR) plasma are presented for a resonance and off-resonance magnetic field configurations. The measurements are conducted on a ECR plasma generator excited at 2.45 GHz denominated test-bench for ion-sources plasma studies at ESS Bilbao. The plasma parameters evolution is studied by Langmuir probe diagnostic with synchronized sample technique developed for repetitive pulsed plasmas with a temporal resolution of 200 ns in typical decay processes of about 40 μs. An afterglow transient is clearly observed in the reflected microwave power signal from the plasma. Simultaneously, the electron temperature evolution shows rebounding peaks that may be related to the interplay between density drop and microwave coupling with deep impact on the Electron Energy Distribution Function. The correlation of such structures with the plasma absorbed power and the coupling quality is also reported.

2D imaging X-ray diagnostic for measuring the current density distribution in a wide-area electron beam produced in a multiaperture diode with plasma cathode

NASA Astrophysics Data System (ADS)

Kurkuchekov, V.; Kandaurov, I.; Trunev, Y.

2018-05-01

A simple and inexpensive X-ray diagnostic tool was designed for measuring the cross-sectional current density distribution in a low-relativistic pulsed electron beam produced in a source based on an arc-discharge plasma cathode and multiaperture diode-type electron optical system. The beam parameters were as follows: Uacc = 50–110 kV, Ibeam = 20–100 A, τbeam = 0.1–0.3 ms. The beam effective diameter was ca. 7 cm. Based on a pinhole camera, the diagnostic allows one to obtain a 2D profile of electron beam flux distribution on a flat metal target in a single shot. The linearity of the diagnostic system response to the electron flux density was established experimentally. Spatial resolution of the diagnostic was also estimated in special test experiments. The optimal choice of the main components of the diagnostic technique is discussed.

Combining image processing and modeling to generate traces of beta-strands from cryo-EM density images of beta-barrels.

PubMed

Si, Dong; He, Jing

2014-01-01

Electron cryo-microscopy (Cryo-EM) technique produces 3-dimensional (3D) density images of proteins. When resolution of the images is not high enough to resolve the molecular details, it is challenging for image processing methods to enhance the molecular features. β-barrel is a particular structure feature that is formed by multiple β-strands in a barrel shape. There is no existing method to derive β-strands from the 3D image of a β-barrel at medium resolutions. We propose a new method, StrandRoller, to generate a small set of possible β-traces from the density images at medium resolutions of 5-10Å. StrandRoller has been tested using eleven β-barrel images simulated to 10Å resolution and one image isolated from the experimentally derived cryo-EM density image at 6.7Å resolution. StrandRoller was able to detect 81.84% of the β-strands with an overall 1.5Å 2-way distance between the detected and the observed β-traces, if the best of fifteen detections is considered. Our results suggest that it is possible to derive a small set of possible β-traces from the β-barrel cryo-EM image at medium resolutions even when no separation of the β-strands is visible in the images.

Synthesis of metal nanoparticle and patterning in polymeric films induced by electron beam

NASA Astrophysics Data System (ADS)

Yamamoto, Hiroki; Kozawa, Takahiro; Tagawa, Seiichi; Marignier, Jean-Louis; Mostafavi, Mehran; Belloni, Jacqueline

2018-03-01

Using an electron beam, thin polymeric films loaded with metal nanoparticles of silver were prepared by a one-step irradiation-induced reduction of the metal ions embedded in the polymer. The metal nanoparticles were observed by either optical absorption or microscopy. The mechanism of the reduction of metal ions and of the polymer crosslinking were deduced from the average absorbance measurements. In view of realizing specific patterns of high resolution using the electron beam, electron beam produces 200 nm wide lines that can be separated by unexposed spaces of adjustable width, where precursors were dissolved. The resolution of the electron beam has been exploited to demonstrate the achievement of nanopatterning on polymer films using a direct-writing process. This method supplies interesting applications such as masks, replicas, or imprint molds of improved density and contrast.

High speed FPGA-based Phasemeter for the far-infrared laser interferometers on EAST

NASA Astrophysics Data System (ADS)

Yao, Y.; Liu, H.; Zou, Z.; Li, W.; Lian, H.; Jie, Y.

2017-12-01

The far-infrared laser-based HCN interferometer and POlarimeter/INTerferometer\\break (POINT) system are important diagnostics for plasma density measurement on EAST tokamak. Both HCN and POINT provide high spatial and temporal resolution of electron density measurement and used for plasma density feedback control. The density is calculated by measuring the real-time phase difference between the reference beams and the probe beams. For long-pulse operations on EAST, the calculation of density has to meet the requirements of Real-Time and high precision. In this paper, a Phasemeter for far-infrared laser-based interferometers will be introduced. The FPGA-based Phasemeter leverages fast ADCs to obtain the three-frequency signals from VDI planar-diode Mixers, and realizes digital filters and an FFT algorithm in FPGA to provide real-time, high precision electron density output. Implementation of the Phasemeter will be helpful for the future plasma real-time feedback control in long-pulse discharge.

The conceptual design of high temporal resolution HCN interferometry for atmospheric pressure air plasmas

NASA Astrophysics Data System (ADS)

Zhang, J. B.; Liu, H. Q.; Jie, Y. X.; Wei, X. C.; Hu, L. Q.

2018-01-01

A heterodyne interferometer operating at the frequency f = 890 GHz has been designed for measuring the electron density of atmospheric pressure air plasmas, it's density range is from 1015 to 3×1019 m-3 and the pressure range is from 1 Pa to 20 kPa. The system is configured as a Mach\

Layout and results from the initial operation of the high-resolution x-ray imaging crystal spectrometer on the Large Helical Device.

PubMed

Pablant, N A; Bitter, M; Delgado-Aparicio, L; Goto, M; Hill, K W; Lazerson, S; Morita, S; Roquemore, A L; Gates, D; Monticello, D; Nielson, H; Reiman, A; Reinke, M; Rice, J E; Yamada, H

2012-08-01

First results of ion and electron temperature profile measurements from the x-ray imaging crystal spectrometer (XICS) diagnostic on the Large Helical Device (LHD) are presented. This diagnostic system has been operational since the beginning of the 2011 LHD experimental campaign and is the first application of the XICS diagnostic technique to helical plasma geometry. The XICS diagnostic provides measurements of ion and electron temperature profiles in LHD with a spatial resolution of 2 cm and a maximum time resolution of 5 ms (typically 20 ms). Ion temperature profiles from the XICS diagnostic are possible under conditions where charge exchange recombination spectroscopy (CXRS) is not possible (high density) or is perturbative to the plasma (low density or radio frequency heated plasmas). Measurements are made by using a spherically bent crystal to provide a spectrally resolved 1D image of the plasma from line integrated emission of helium-like Ar(16 +). The final hardware design and configuration are detailed along with the calibration procedures. Line-integrated ion and electron temperature measurements are presented, and the measurement accuracy is discussed. Finally central temperature measurements from the XICS system are compared to measurements from the Thomson scattering and CXRS systems, showing excellent agreement.

Ultrashort megaelectronvolt positron beam generation based on laser-accelerated electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Tongjun; Shen, Baifei, E-mail: bfshen@mail.shcnc.ac.cn; Xu, Jiancai, E-mail: jcxu@siom.ac.cn

Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron–positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8 × 10{sup 21} s{sup −1}, thus allows specific studies of fast kinetics in millimeter-thick materials withmore » a high time resolution and exhibits potential for applications in positron annihilation spectroscopy.« less

Tomographic reconstruction of ionospheric electron density during the storm of 5-6 August 2011 using multi-source data

PubMed Central

Tang, Jun; Yao, Yibin; Zhang, Liang; Kong, Jian

2015-01-01

The insufficiency of data is the essential reason for ill-posed problem existed in computerized ionospheric tomography (CIT) technique. Therefore, the method of integrating multi-source data is proposed. Currently, the multiple satellite navigation systems and various ionospheric observing instruments provide abundant data which can be employed to reconstruct ionospheric electron density (IED). In order to improve the vertical resolution of IED, we do research on IED reconstruction by integration of ground-based GPS data, occultation data from the LEO satellite, satellite altimetry data from Jason-1 and Jason-2 and ionosonde data. We used the CIT results to compare with incoherent scatter radar (ISR) observations, and found that the multi-source data fusion was effective and reliable to reconstruct electron density, showing its superiority than CIT with GPS data alone. PMID:26266764

Tomographic reconstruction of ionospheric electron density during the storm of 5-6 August 2011 using multi-source data.

PubMed

Tang, Jun; Yao, Yibin; Zhang, Liang; Kong, Jian

2015-08-12

The insufficiency of data is the essential reason for ill-posed problem existed in computerized ionospheric tomography (CIT) technique. Therefore, the method of integrating multi-source data is proposed. Currently, the multiple satellite navigation systems and various ionospheric observing instruments provide abundant data which can be employed to reconstruct ionospheric electron density (IED). In order to improve the vertical resolution of IED, we do research on IED reconstruction by integration of ground-based GPS data, occultation data from the LEO satellite, satellite altimetry data from Jason-1 and Jason-2 and ionosonde data. We used the CIT results to compare with incoherent scatter radar (ISR) observations, and found that the multi-source data fusion was effective and reliable to reconstruct electron density, showing its superiority than CIT with GPS data alone.

High resolution measurements of nightside ion troughs at Venus - Evidence of electrodynamic perturbations

NASA Technical Reports Server (NTRS)

Taylor, H. A., Jr.; Grebowsky, J. M.; Mayr, H. G.; Niemann, H. B.; Brace, L. H.; Cloutier, P. A.; Daniell, R. E., Jr.; Coulson, J. T.

1982-01-01

The Bennett rf ion mass spectrometer of the Pioneer Venus Orbiter was expressly designed to provide variable temporal resolution for measurements of thermal ion composition and density. The Explore-Adapt mode is used to obtain priority for measuring the most prominent ion species; in the 2/16 configuration, the two dominant ions within the available range of 16 species are selectively sampled at the highest rate of 0.2 sec/sample. The high-resolution measurements are combined with independent observations from the magnetic field, neutral mass spectrometer, and electron temperature experiments in investigating sharply structured troughs in the low-altitude nightside ion concentrations. The results suggest a close correlation between the structure in the ion distributions and the structured configuration of the magnetic field that is draped about the planet. In the regions of the ion depletions, sharp fluctuations in electron temperature and anomalous increases in the density of neutral gases suggest that the ion depletion may be associated with dynamic perturbation in the ion and neutral flows and/or local joule heating.

Understanding Intense Laser Interactions with Solid Density Plasma

DTIC Science & Technology

2017-01-04

obtain the time-dependent diffraction efficiency. Further improvements may lead to femtosecond temporal resolution, with negligible pump-probe jitter...with negligible pump-probe jitter being possible with future laser- wakefield-accelerator ultrafast-electron-diffraction schemes. Distribution

The Mesoscale Ionospheric Simulation Testbed (MIST) Regional Data Assimilation Model (Invited)

NASA Astrophysics Data System (ADS)

Comberiate, J.; Kelly, M. A.; Miller, E.; Paxton, L.

2013-12-01

The Mesoscale Ionospheric Simulation Testbed (MIST) provides a regional nowcast and forecast of electron density values and has sufficient resolution to include equatorial plasma bubbles. The SSUSI instrument on the DMSP F18 satellite has high-resolution nightly observations of plasma bubbles at 8 PM local time throughout the current solar maximum. MIST can assimilate SSUSI UV observations, GPS TEC measurements, and SCINDA S4 readings simultaneously into a single scintillation map over a region of interest. MIST also models ionospheric physics to provide a short-term UHF scintillation forecast based on assimilated data. We will present examples of electron density and scintillation maps from MIST. We will also discuss the potential to predict scintillation occurrence up to 6 hours in advance using observations of the equatorial arcs from SSUSI observations at 5:30 PM local time on the DMSP F17 satellite.

Influence of the cytoplasmic domains of aquaporin-4 on water conduction and array formation.

PubMed

Mitsuma, Tadanori; Tani, Kazutoshi; Hiroaki, Yoko; Kamegawa, Akiko; Suzuki, Hiroshi; Hibino, Hiroshi; Kurachi, Yoshihisa; Fujiyoshi, Yoshinori

2010-10-01

Phosphorylation of Ser180 in cytoplasmic loop D has been shown to reduce the water permeability of aquaporin (AQP) 4, the predominant water channel in the brain. However, when the structure of the S180D mutant (AQP4M23S180D), which was generated to mimic phosphorylated Ser180, was determined to 2.8 Å resolution using electron diffraction patterns, it showed no significant differences from the structure of the wild-type channel. High-resolution density maps usually do not resolve protein regions that are only partially ordered, but these can sometimes be seen in lower-resolution density maps calculated from electron micrographs. We therefore used images of two-dimensional crystals and determined the structure of AQP4M23S180D at 10 A resolution. The features of the 10-A density map are consistent with those of the previously determined atomic model; in particular, there were no indications of any obstruction near the cytoplasmic pore entrance. In addition, water conductance measurements, both in vitro and in vivo, show the same water permeability for wild-type and mutant AQP4M23, suggesting that the S180D mutation neither reduces water conduction through a conformational change nor reduces water conduction by interacting with a protein that would obstruct the cytoplasmic channel entrance. Finally, the 10-A map shows a cytoplasmic density in between four adjacent tetramers that most likely represents the association of four N termini. This finding supports the critical role of the N terminus of AQP4 in the stabilization of orthogonal arrays, as well as their interference through lipid modification of cysteine residues in the longer N-terminal isoform. Copyright © 2010 Elsevier Ltd. All rights reserved.

Micro-computed tomography: Applications for high-resolution skeletal density determinations: An example using annually banded crustose coralline algae

NASA Astrophysics Data System (ADS)

Chan, P.; Halfar, J.; Norley, C. J. D.; Pollmann, S. I.; Adey, W.; Holdsworth, D. W.

2017-09-01

Warming and acidification of the world's oceans are expected to have widespread consequences for marine biodiversity and ecosystem functioning. However, due to the relatively short record of instrumental observations, one has to rely upon geochemical and physical proxy information stored in biomineralized shells and skeletons of calcareous marine organisms as in situ recorders of past environments. Of particular interest is the response of marine calcifiers to ocean acidification through the examination of structural growth characteristics. Here we demonstrate the application of micro-computed tomography (micro-CT) for three-dimensional visualization and analysis of growth, skeletal density, and calcification in a slow-growing, annually banded crustose coralline alga Clathromorphum nereostratum (increment width ˜380 µm). X-ray images and time series of skeletal density were generated at 20 µm resolution and rebinned to 40, 60, 80, and 100 µm for comparison in a sensitivity analysis. Calcification rates were subsequently calculated as the product of density and growth (linear extension). While both skeletal density and calcification rates do not significantly differ at varying spatial resolutions (the latter being strongly influenced by growth rates), clear visualization of micron-scale growth features and the quantification of structural changes on subannual time scales requires higher scanning resolutions. In the present study, imaging at 20 µm resolution reveals seasonal cycles in density that correspond to summer/winter variations in skeletal structure observed using scanning electron microscopy (SEM). Micro-CT is a fast, nondestructive, and high-resolution technique for structural and morphometric analyses of temporally banded paleoclimate archives, particularly those that exhibit slow or compressed growth or micron-scale structures.

Rapid temporal evolution of radiation from non-thermal electrons in solar flares

NASA Technical Reports Server (NTRS)

Lu, Edward T.; Petrosian, Vahe

1987-01-01

Solutions of the time dependent Fokker-Planck equation was found for accelerated electrons undergoing Coulomb collisions in a magnetized, fully ionized plasma. An exact solution was found for arbitrary pitch angle and energy distribution in a uniform background plasma. Then, for an inhomogeneous plasma, a solution was found for particles with small pitch angles. These solutions were used to calculate the temporal evolution of bremsstrahlung x-rays from short bursts of nonthermal electron beams, and these spectra were compared with observed high time resolution spectra of short timescale solar hard x-ray bursts. It is shown that the observed softening in time of the spectra rules out a homogeneous background and therefore the possibility of electrons being confined to the corona either because of converging magnetic field or high densities. The inhomogeneous solution was also applied to a model with constant coronal density and exponentially rising chromospheric density. The spectra are shown to be consistent with that produced by a collimated beam of electrons accelerated in the corona with certain given conditions. These conditions could be violated if large pitch angle electrons are present.

Characterization of twin boundaries in an Fe–17.5Mn–0.56C twinning induced plasticity steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patterson, Erin E., E-mail: erin.diedrich@yahoo.com; Field, David P., E-mail: dfield@wsu.edu; Zhang, Yudong, E-mail: yudong.zhang@univ-metz.fr

2013-11-15

A twinning-induced plasticity steel of composition Fe–17.5 wt.% Mn–0.56 wt.% C–1.39 wt.% Al–0.24 wt.% Si was analyzed for the purpose of characterizing the relationship between tensile strain and deformation twinning. Tensile samples achieved a maximum of 0.46 true strain at failure, and a maximum ultimate tensile strength of 1599 MPa. Electron backscatter diffraction (EBSD) analysis showed that the grain orientation rotated heavily to < 111 > parallel to the tensile axis above 0.3 true strain. Sigma 3 misorientations, as identified by EBSD orientation measurements, and using the image quality maps were used to quantify the number of twins present inmore » the scanned areas of the samples. The image quality method yielded a distinct positive correlation between the twin area density and deformation, but the orientation measurements were unreliable in quantifying twin density in these structures. Quantitative analysis of the twin fraction is limited from orientation information because of the poor spatial resolution of EBSD in relation to the twin thickness. The EBSD orientation maps created for a thin foil sample showed some improvement in the resolution of the twins, but not enough to be significant. Measurements of the twins in the transmission electron microscopy micrographs yielded an average thickness of 23 nm, which is near the resolution capabilities of EBSD on this material for the instrumentation used. Electron channeling contrast imaging performed on one bulk tensile specimen of 0.34 true strain, using a method of controlled diffraction, yielded several images of twinning, dislocation structures and strain fields. A twin thickness of 66 nm was measured by the same method used for the transmission electron microscopy measurement. It is apparent that the results obtain by electron channeling contrast imaging were better than those by EBSD but did not capture all information on the twin boundaries such as was observed by transmission electron microscopy. - Highlights: • Performed tensile tests to assess mechanical performance of TWIP alloy • Analyzed tensile specimens using EBSD, TEM, and ECCI • EBSD showed that most twinning occurred at or near the < 111 >//TA orientation. • EBSD, TEM and ECCI were used to measure average twin density. • Compared spatial resolution of EBSD, ECCI and TEM for the instrumentation used.« less

Symmetry and electronic structure of noble-metal nanoparticles and the role of relativity.

PubMed

Häkkinen, Hannu; Moseler, Michael; Kostko, Oleg; Morgner, Nina; Hoffmann, Margarita Astruc; von Issendorff, Bernd

2004-08-27

We present high resolution UV-photoelectron spectra of cold mass selected Cun-, Agn-, and Aun- with n=53-58. The observed electron density of states is not the expected simple electron shell structure, but is strongly influenced by electron-lattice interactions. Only Cu55- and Ag55- exhibit highly degenerate states. This is a direct consequence of their icosahedral symmetry, as is confirmed by density functional theory calculations. Neighboring sizes exhibit perturbed electronic structures, as they are formed by removal or addition of atoms to the icosahedron and therefore have lower symmetries. Gold clusters in the same size range show completely different spectra with almost no degeneracy, which indicates that they have structures of much lower symmetry. This behavior is related to strong relativistic bonding effects in gold, as demonstrated by ab initio calculations for Au55-.

Imaging of the outer valence orbitals of CO by electron momentum spectroscopy — Comparison with high level MRSD-CI and DFT calculations

NASA Astrophysics Data System (ADS)

Fan, X. W.; Chen, X. J.; Zhou, S. J.; Zheng, Y.; Brion, C. E.; Frey, R.; Davidson, E. R.

1997-09-01

A newly constructed energy dispersive multichannel electron momentum spectrometer has been used to image the electron density of the outer valence orbitals of CO with high precision. Binding energy spectra are obtained at a coincidence energy resolution of 1.2 eV fwhm. The measured electron density profiles in momentum space for the outer valence orbitals of CO are compared with cross sections calculated using SCF wavefunctions with basis sets of varying complexity up to near-Hartree-Fock limit in quality. The effects of correlation and electronic relaxation on the calculated momentum profiles are investigated using large MRSD-CI calculations of the full ion-neutral overlap distributions, as well as large basis set DFT calculations with local and non-local (gradient corrected) functionals.

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

NASA Astrophysics Data System (ADS)

Lu, Chao; Jiang, Tao; Liu, Shengguang; Wang, Rui; Zhao, Lingrong; Zhu, Pengfei; Liu, Yaqi; Xu, Jun; Yu, Dapeng; Wan, Weishi; Zhu, Yimei; Xiang, Dao; Zhang, Jie

2018-03-01

An accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ˜3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10-19 s m, about 2 orders of magnitude higher than that achieved with state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.

xMDFF: molecular dynamics flexible fitting of low-resolution X-ray structures.

PubMed

McGreevy, Ryan; Singharoy, Abhishek; Li, Qufei; Zhang, Jingfen; Xu, Dong; Perozo, Eduardo; Schulten, Klaus

2014-09-01

X-ray crystallography remains the most dominant method for solving atomic structures. However, for relatively large systems, the availability of only medium-to-low-resolution diffraction data often limits the determination of all-atom details. A new molecular dynamics flexible fitting (MDFF)-based approach, xMDFF, for determining structures from such low-resolution crystallographic data is reported. xMDFF employs a real-space refinement scheme that flexibly fits atomic models into an iteratively updating electron-density map. It addresses significant large-scale deformations of the initial model to fit the low-resolution density, as tested with synthetic low-resolution maps of D-ribose-binding protein. xMDFF has been successfully applied to re-refine six low-resolution protein structures of varying sizes that had already been submitted to the Protein Data Bank. Finally, via systematic refinement of a series of data from 3.6 to 7 Å resolution, xMDFF refinements together with electrophysiology experiments were used to validate the first all-atom structure of the voltage-sensing protein Ci-VSP.

High-resolution neutron and X-ray diffraction room-temperature studies of an H-FABP-oleic acid complex: study of the internal water cluster and ligand binding by a transferred multipolar electron-density distribution.

PubMed

Howard, E I; Guillot, B; Blakeley, M P; Haertlein, M; Moulin, M; Mitschler, A; Cousido-Siah, A; Fadel, F; Valsecchi, W M; Tomizaki, Takashi; Petrova, T; Claudot, J; Podjarny, A

2016-03-01

Crystal diffraction data of heart fatty acid binding protein (H-FABP) in complex with oleic acid were measured at room temperature with high-resolution X-ray and neutron protein crystallography (0.98 and 1.90 Å resolution, respectively). These data provided very detailed information about the cluster of water molecules and the bound oleic acid in the H-FABP large internal cavity. The jointly refined X-ray/neutron structure of H-FABP was complemented by a transferred multipolar electron-density distribution using the parameters of the ELMAMII library. The resulting electron density allowed a precise determination of the electrostatic potential in the fatty acid (FA) binding pocket. Bader's quantum theory of atoms in molecules was then used to study interactions involving the internal water molecules, the FA and the protein. This approach showed H⋯H contacts of the FA with highly conserved hydrophobic residues known to play a role in the stabilization of long-chain FAs in the binding cavity. The determination of water hydrogen (deuterium) positions allowed the analysis of the orientation and electrostatic properties of the water molecules in the very ordered cluster. As a result, a significant alignment of the permanent dipoles of the water molecules with the protein electrostatic field was observed. This can be related to the dielectric properties of hydration layers around proteins, where the shielding of electrostatic interactions depends directly on the rotational degrees of freedom of the water molecules in the interface.

Investigation of an electronic image enhancer for radiographs

NASA Technical Reports Server (NTRS)

Vary, A.

1972-01-01

Radiographs of nuclear and aerospace components were studied with a closed-circuit television system to determine the advantages of electronic enhancement in radiographic nondestructive evaluation. The radiographic images were examined on a television monitor under various degrees of magnification and enhancement. The enhancement was accomplished by generating a video signal whose amplitude is proportional to the rate of change of density. Points, lines, edges, and other density variations that are faintly registered in the original image are rendered in sharp relief. Examples of the applications of this mode of enhancement are discussed together with the system's dynamic response and resolution.

Investigation of an electronic image enhancer for radiographs.

NASA Technical Reports Server (NTRS)

Vary, A.

1972-01-01

Radiographs of nuclear and aerospace components were studied with a closed-circuit television system to determine the advantages of electronic enhancement in radiographic nondestructive evaluation. The radiographic images were examined on a television monitor under various degrees of magnification and enhancement. The enhancement was accomplished by generating a video signal whose amplitude is proportional to the rate of change of density. Points, lines, edges, and other density variations that are faintly registered in the original image are rendered in sharp relief. Examples of the applications of this mode of enhancement are discussed together with the system's dynamic response and resolution.

Fully Hydrated Yeast Cells Imaged with Electron Microscopy

PubMed Central

Peckys, Diana B.; Mazur, Peter; Gould, Kathleen L.; de Jonge, Niels

2011-01-01

We demonstrate electron microscopy of fully hydrated eukaryotic cells with nanometer resolution. Living Schizosaccaromyces pombe cells were loaded in a microfluidic chamber and imaged in liquid with scanning transmission electron microscopy (STEM). The native intracellular (ultra)structures of wild-type cells and three different mutants were studied without prior labeling, fixation, or staining. The STEM images revealed various intracellular components that were identified on the basis of their shape, size, location, and mass density. The maximal achieved spatial resolution in this initial study was 32 ± 8 nm, an order of magnitude better than achievable with light microscopy on pristine cells. Light-microscopy images of the same samples were correlated with the corresponding electron-microscopy images. Achieving synergy between the capabilities of light and electron microscopy, we anticipate that liquid STEM will be broadly applied to explore the ultrastructure of live cells. PMID:21575587

Fully hydrated yeast cells imaged with electron microscopy.

PubMed

Peckys, Diana B; Mazur, Peter; Gould, Kathleen L; de Jonge, Niels

2011-05-18

We demonstrate electron microscopy of fully hydrated eukaryotic cells with nanometer resolution. Living Schizosaccharomyces pombe cells were loaded in a microfluidic chamber and imaged in liquid with scanning transmission electron microscopy (STEM). The native intracellular (ultra)structures of wild-type cells and three different mutants were studied without prior labeling, fixation, or staining. The STEM images revealed various intracellular components that were identified on the basis of their shape, size, location, and mass density. The maximal achieved spatial resolution in this initial study was 32 ± 8 nm, an order of magnitude better than achievable with light microscopy on pristine cells. Light-microscopy images of the same samples were correlated with the corresponding electron-microscopy images. Achieving synergy between the capabilities of light and electron microscopy, we anticipate that liquid STEM will be broadly applied to explore the ultrastructure of live cells. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

High time resolution measurements of rocket potential changes induced by electron beam emission

NASA Technical Reports Server (NTRS)

Raitt, W. J.; Myers, N. B.; Williamson, P. R.; Banks, P. M.; Kawashima, N.

1984-01-01

The transient charging and photon emission from the vacuum chamber testing of the Cooperative High Altitude Rocket Gun Experiment are studied. Graphs of the mother-daughter voltage versus time and high time resolution data related to the return current to the vehicle are examined. It is observed that for average sounding rocket densities of 10 to the -6th torr the slope of the voltage rise of the rocket begins to flatten 40 microsec after the onset of electron beam emission, and for higher gas pressure the rocket reaches a maximum voltage of 25 or 30 microsec after the onset of electron beam emission. The data reveal that the return current mechanism for the higher gas pressure is through the sheath.

Atomic modeling of cryo-electron microscopy reconstructions--joint refinement of model and imaging parameters.

PubMed

Chapman, Michael S; Trzynka, Andrew; Chapman, Brynmor K

2013-04-01

When refining the fit of component atomic structures into electron microscopic reconstructions, use of a resolution-dependent atomic density function makes it possible to jointly optimize the atomic model and imaging parameters of the microscope. Atomic density is calculated by one-dimensional Fourier transform of atomic form factors convoluted with a microscope envelope correction and a low-pass filter, allowing refinement of imaging parameters such as resolution, by optimizing the agreement of calculated and experimental maps. A similar approach allows refinement of atomic displacement parameters, providing indications of molecular flexibility even at low resolution. A modest improvement in atomic coordinates is possible following optimization of these additional parameters. Methods have been implemented in a Python program that can be used in stand-alone mode for rigid-group refinement, or embedded in other optimizers for flexible refinement with stereochemical restraints. The approach is demonstrated with refinements of virus and chaperonin structures at resolutions of 9 through 4.5 Å, representing regimes where rigid-group and fully flexible parameterizations are appropriate. Through comparisons to known crystal structures, flexible fitting by RSRef is shown to be an improvement relative to other methods and to generate models with all-atom rms accuracies of 1.5-2.5 Å at resolutions of 4.5-6 Å. Copyright © 2013 Elsevier Inc. All rights reserved.

Influence of grid resolution in fluid-model simulation of nanosecond dielectric barrier discharge plasma actuator

NASA Astrophysics Data System (ADS)

Hua, Weizhuo; Fukagata, Koji

2018-04-01

Two-dimensional numerical simulation of a surface dielectric barrier discharge (SDBD) plasma actuator, driven by a nanosecond voltage pulse, is conducted. A special focus is laid upon the influence of grid resolution on the computational result. It is found that the computational result is not very sensitive to the streamwise grid spacing, whereas the wall-normal grid spacing has a critical influence. In particular, the computed propagation velocity changes discontinuously around the wall-normal grid spacing about 2 μm due to a qualitative change of discharge structure. The present result suggests that a computational grid finer than that was used in most of previous studies is required to correctly capture the structure and dynamics of streamer: when a positive nanosecond voltage pulse is applied to the upper electrode, a streamer forms in the vicinity of upper electrode and propagates along the dielectric surface with a maximum propagation velocity of 2 × 108 cm/s, and a gap with low electron and ion density (i.e., plasma sheath) exists between the streamer and dielectric surface. Difference between the results obtained using the finer and the coarser grid is discussed in detail in terms of the electron transport at a position near the surface. When the finer grid is used, the low electron density near the surface is caused by the absence of ionization avalanche: in that region, the electrons generated by ionization is compensated by drift-diffusion flux. In contrast, when the coarser grid is used, underestimated drift-diffusion flux cannot compensate the electrons generated by ionization, and it leads to an incorrect increase of electron density.

Iterative model building, structure refinement and density modification with the PHENIX AutoBuild wizard.

PubMed

Terwilliger, Thomas C; Grosse-Kunstleve, Ralf W; Afonine, Pavel V; Moriarty, Nigel W; Zwart, Peter H; Hung, Li Wei; Read, Randy J; Adams, Paul D

2008-01-01

The PHENIX AutoBuild wizard is a highly automated tool for iterative model building, structure refinement and density modification using RESOLVE model building, RESOLVE statistical density modification and phenix.refine structure refinement. Recent advances in the AutoBuild wizard and phenix.refine include automated detection and application of NCS from models as they are built, extensive model-completion algorithms and automated solvent-molecule picking. Model-completion algorithms in the AutoBuild wizard include loop building, crossovers between chains in different models of a structure and side-chain optimization. The AutoBuild wizard has been applied to a set of 48 structures at resolutions ranging from 1.1 to 3.2 A, resulting in a mean R factor of 0.24 and a mean free R factor of 0.29. The R factor of the final model is dependent on the quality of the starting electron density and is relatively independent of resolution.

A temporally and spatially resolved electron density diagnostic method for the edge plasma based on Stark broadening

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zafar, A., E-mail: zafara@ornl.gov; Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830; Martin, E. H.

2016-11-15

An electron density diagnostic (≥10{sup 10} cm{sup −3}) capable of high temporal (ms) and spatial (mm) resolution is currently under development at Oak Ridge National Laboratory. The diagnostic is based on measuring the Stark broadened, Doppler-free spectral line profile of the n = 6–2 hydrogen Balmer series transition. The profile is then fit to a fully quantum mechanical model including the appropriate electric and magnetic field operators. The quasi-static approach used to calculate the Doppler-free spectral line profile is outlined here and the results from the model are presented for H-δ spectra for electron densities of 10{sup 10}–10{sup 13} cm{supmore » −3}. The profile shows complex behavior due to the interaction between the magnetic substates of the atom.« less

First measurement of time evolution of electron temperature profiles with Nd:YAG Thomson scattering system on Heliotron J.

PubMed

Kenmochi, N; Minami, T; Takahashi, C; Tei, S; Mizuuchi, T; Kobayashi, S; Nagasaki, K; Nakamura, Y; Okada, H; Kado, S; Yamamoto, S; Ohshima, S; Konoshima, S; Shi, N; Zang, L; Ohtani, Y; Kasajima, K; Sano, F

2014-11-01

A Nd:YAG Thomson scattering system has been developed for Heliotron J. The system consists of two 550 mJ 50 Hz lasers, large collection optics, and 25 radial channel (∼1 cm spatial resolution) interference polychromators. This measurement system achieves a S/N ratio of ∼50 for low-density plasma (ne ∼ 0.5 × 10(19) m(-3)). A time evolution of electron temperature profiles was measured with this system for a high-intensity gas-puff (HIGP) fueling neutral-beam-injection plasma. The peripheral temperature of the higher-density phase after HIGP recovers to the low-density pre-HIGP level, suggesting that improving particle transport in the HIGP plasma may be possible.

Computational methods for constructing protein structure models from 3D electron microscopy maps.

PubMed

Esquivel-Rodríguez, Juan; Kihara, Daisuke

2013-10-01

Protein structure determination by cryo-electron microscopy (EM) has made significant progress in the past decades. Resolutions of EM maps have been improving as evidenced by recently reported structures that are solved at high resolutions close to 3Å. Computational methods play a key role in interpreting EM data. Among many computational procedures applied to an EM map to obtain protein structure information, in this article we focus on reviewing computational methods that model protein three-dimensional (3D) structures from a 3D EM density map that is constructed from two-dimensional (2D) maps. The computational methods we discuss range from de novo methods, which identify structural elements in an EM map, to structure fitting methods, where known high resolution structures are fit into a low-resolution EM map. A list of available computational tools is also provided. Copyright © 2013 Elsevier Inc. All rights reserved.

New computational tools for H/D determination in macromolecular structures from neutron data.

PubMed

Siliqi, Dritan; Caliandro, Rocco; Carrozzini, Benedetta; Cascarano, Giovanni Luca; Mazzone, Annamaria

2010-11-01

Two new computational methods dedicated to neutron crystallography, called n-FreeLunch and DNDM-NDM, have been developed and successfully tested. The aim in developing these methods is to determine hydrogen and deuterium positions in macromolecular structures by using information from neutron density maps. Of particular interest is resolving cases in which the geometrically predicted hydrogen or deuterium positions are ambiguous. The methods are an evolution of approaches that are already applied in X-ray crystallography: extrapolation beyond the observed resolution (known as the FreeLunch procedure) and a difference electron-density modification (DEDM) technique combined with the electron-density modification (EDM) tool (known as DEDM-EDM). It is shown that the two methods are complementary to each other and are effective in finding the positions of H and D atoms in neutron density maps.

Study of high resolution x-ray spectrometer concepts for NIF experiments

NASA Astrophysics Data System (ADS)

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; Efthimion, P.; Gao, L.; Maddox, J.; Pablant, N. A.; Beiersdorfer, P.; Chen, H.; Coppari, F.; Ma, T.; Nora, R.; Scott, H.; Schneider, M.; Mancini, R.

2015-11-01

Options have been investigated for DIM-insertable (Diagnostic Instrument Manipulator) high resolution (E/ ΔE ~ 3000 - 5000) Bragg crystal x-ray spectrometers for experiments on the NIF. Of interest are time integrated Cu K- and Ta L-edge absorption spectra and time resolved Kr He- β emission from compressed symcaps for inference of electron temperature from dielectronic satellites and electron density from Stark broadening. Cylindrical and conical von Hamos, Johann, and advanced high throughput designs have been studied. Predicted x-ray intensities, spectrometer throughputs, spectral resolution, and spatial focusing properties, as well as lab evaluations of some spectrometer candidates will be presented. Performed under the auspices of the US DOE by PPPL under contract DE-AC02-09CH11466 and by LLNL under contract DE-AC52-07NA27344.

A large area high resolution imaging detector for fast atom diffraction

NASA Astrophysics Data System (ADS)

Lupone, Sylvain; Soulisse, Pierre; Roncin, Philippe

2018-07-01

We describe a high resolution imaging detector based on a single 80 mm micro-channel-plate (MCP) and a phosphor screen mounted on a UHV flange of only 100 mm inner diameter. It relies on standard components and we describe its performance with one or two MCPs. A resolution of 80 μm rms is observed on the beam profile. At low count rate, individual impact can be pinpointed with few μm accuracy but the resolution is probably limited by the MCP channel diameter. The detector has been used to record the diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD), a technique probing the electronic density of the topmost layer only. The detector was also used to record the scattering profile during azimuthal scan of the crystal to produce triangulation curves revealing the surface crystallographic directions of molecular layers. It should also be compatible with reflection high energy electron (RHEED) experiment when fragile surfaces require a low exposure to the electron beam. The discussions on the mode of operation specific to diffraction experiments apply also to commercial detectors.

Observations Of Planetary Nebula NGC 3242 Using STIS From HST19 GO 12600

NASA Astrophysics Data System (ADS)

Miller, Timothy R.; Dufour, Reginald J.; Henry, Richard B. C.; Kwitter, Karen B.; Shaw, Richard A.; Balick, Bruce; Corradi, Romano

2014-06-01

During HST Cycle 19, we obtained long-slit spectra using STIS of the planetary nebula NGC 3242 with higher spatial resolution than previously published. The full wavelength range is around 1100-10200Å, covering many nebular lines for determining numerous ionic abundances and electron densities and temperatures. In this work, we first analyze the low- and moderate-resolution UV emission lines of carbon, nitrogen and oxygen. In particular, the resolved lines of C_III] 1907 and C_III] 1909 have yielded a direct measurement of one of the dominant ionic species for carbon and a determination of the density occupied by doubly-ionized carbon and other similar ions. Next, the spatial emission profile of these lines reveals variations in the inferred density along the line of sight from about 2800-11500 cm-3, compared with a value ~3800 cm-3, when averaged over the entire slit. Similarly, the electron temperature is around 12000K for the entire slit and ranges from about 11400-14000K when the slit is divided into smaller sub-regions. Lastly, these sub-regions of the nebula have been modeled in detail with the photoionization code CLOUDY. This modeling will assess the density profile that produces the observed density variation, reproduce the temperature fluctuations, and constrain the central star temperature. We acknowledge the gracious support from HST and the University of Oklahoma.

Estimate of size distribution of charged MSPs measured in situ in winter during the WADIS-2 sounding rocket campaign

NASA Astrophysics Data System (ADS)

Asmus, Heiner; Staszak, Tristan; Strelnikov, Boris; Lübken, Franz-Josef; Friedrich, Martin; Rapp, Markus

2017-08-01

We present results of in situ measurements of mesosphere-lower thermosphere dusty-plasma densities including electrons, positive ions and charged aerosols conducted during the WADIS-2 sounding rocket campaign. The neutral air density was also measured, allowing for robust derivation of turbulence energy dissipation rates. A unique feature of these measurements is that they were done in a true common volume and with high spatial resolution. This allows for a reliable derivation of mean sizes and a size distribution function for the charged meteor smoke particles (MSPs). The mean particle radius derived from Schmidt numbers obtained from electron density fluctuations was ˜ 0.56 nm. We assumed a lognormal size distribution of the charged meteor smoke particles and derived the distribution width of 1.66 based on in situ-measured densities of different plasma constituents. We found that layers of enhanced meteor smoke particles' density measured by the particle detector coincide with enhanced Schmidt numbers obtained from the electron and neutral density fluctuations. Thus, we found that large particles with sizes > 1 nm were stratified in layers of ˜ 1 km thickness and lying some kilometers apart from each other.

Femtosecond Electron Wave Packet Propagation and Diffraction: Towards Making the ``Molecular Movie"

NASA Astrophysics Data System (ADS)

Miller, R. J. Dwayne

2003-03-01

Time-resolved electron diffraction harbors great promise for achieving atomic resolution of the fastest chemical processes. The generation of sufficiently short electron pulses to achieve this real time view of a chemical reaction has been limited by problems in maintaining short electron pulses with realistic electron densities to the sample. The propagation dynamics of femtosecond electron packets in the drift region of a photoelectron gun are investigated with an N-body numerical simulation and mean-field model. This analyis shows that the redistribution of electrons inside the packet, arising from space-charge and dispersion contributions, changes the pulse envelope and leads to the development of a spatially linear axial velocity distribution. These results have been used in the design of femtosecond photoelectron guns with higher time resolution and novel electron-optical methods of pulse characterization that are approaching 100 fs timescales. Time-resolved diffraction studies with electron pulses of approximately 500 femtoseconds have focused on solid-liquid phase transitions under far from equilibrium conditions. This work gives a microscopic description of the melting process and illustrates the promise of atomically resolving transition state processes.

Dependence of the Energy Resolution of a Hemispherical Semiconductor Detector on the Bias Voltage

NASA Astrophysics Data System (ADS)

Samedov, V. V.

2017-12-01

It is shown that the series expansion of the amplitude and variance of the hemispherical semiconductor detector signal in inverse bias voltage allows finding the Fano factor, the product of electron lifetime and mobility, the degree of inhomogeneity of the trap density in the semiconductor material, and the relative variance of the electronic channel gain. An important advantage of the proposed method is that it is independent of the electronic channel gain and noise.

Surface determination through atomically resolved secondary-electron imaging

PubMed Central

Ciston, J.; Brown, H. G.; D'Alfonso, A. J.; Koirala, P.; Ophus, C.; Lin, Y.; Suzuki, Y.; Inada, H.; Zhu, Y.; Allen, L. J.; Marks, L. D.

2015-01-01

Unique determination of the atomic structure of technologically relevant surfaces is often limited by both a need for homogeneous crystals and ambiguity of registration between the surface and bulk. Atomically resolved secondary-electron imaging is extremely sensitive to this registration and is compatible with faceted nanomaterials, but has not been previously utilized for surface structure determination. Here we report a detailed experimental atomic-resolution secondary-electron microscopy analysis of the c(6 × 2) reconstruction on strontium titanate (001) coupled with careful simulation of secondary-electron images, density functional theory calculations and surface monolayer-sensitive aberration-corrected plan-view high-resolution transmission electron microscopy. Our work reveals several unexpected findings, including an amended registry of the surface on the bulk and strontium atoms with unusual seven-fold coordination within a typically high surface coverage of square pyramidal TiO5 units. Dielectric screening is found to play a critical role in attenuating secondary-electron generation processes from valence orbitals. PMID:26082275

Surface determination through atomically resolved secondary-electron imaging

DOE PAGES

Ciston, J.; Brown, H. G.; D’Alfonso, A. J.; ...

2015-06-17

We report that unique determination of the atomic structure of technologically relevant surfaces is often limited by both a need for homogeneous crystals and ambiguity of registration between the surface and bulk. Atomically resolved secondary-electron imaging is extremely sensitive to this registration and is compatible with faceted nanomaterials, but has not been previously utilized for surface structure determination. Here we show a detailed experimental atomic-resolution secondary-electron microscopy analysis of the c(6 x 2) reconstruction on strontium titanate (001) coupled with careful simulation of secondary-electron images, density functional theory calculations and surface monolayer-sensitive aberration-corrected plan-view high-resolution transmission electron microscopy. Our workmore » reveals several unexpected findings, including an amended registry of the surface on the bulk and strontium atoms with unusual seven-fold coordination within a typically high surface coverage of square pyramidal TiO 5 units. Lastly, dielectric screening is found to play a critical role in attenuating secondary-electron generation processes from valence orbitals.« less

Sub-millisecond electron density profile measurement at the JET tokamak with the fast lithium beam emission spectroscopy system

NASA Astrophysics Data System (ADS)

Réfy, D. I.; Brix, M.; Gomes, R.; Tál, B.; Zoletnik, S.; Dunai, D.; Kocsis, G.; Kálvin, S.; Szabolics, T.; JET Contributors

2018-04-01

Diagnostic alkali atom (e.g., lithium) beams are routinely used to diagnose magnetically confined plasmas, namely, to measure the plasma electron density profile in the edge and the scrape off layer region. A light splitting optics system was installed into the observation system of the lithium beam emission spectroscopy diagnostic at the Joint European Torus (JET) tokamak, which allows simultaneous measurement of the beam light emission with a spectrometer and a fast avalanche photodiode (APD) camera. The spectrometer measurement allows density profile reconstruction with ˜10 ms time resolution, absolute position calculation from the Doppler shift, spectral background subtraction as well as relative intensity calibration of the channels for each discharge. The APD system is capable of measuring light intensities on the microsecond time scale. However ˜100 μs integration is needed to have an acceptable signal to noise ratio due to moderate light levels. Fast modulation of the beam up to 30 kHz is implemented which allows background subtraction on the 100 μs time scale. The measurement covers the 0.9 < ρpol < 1.1 range with 6-10 mm optical resolution at the measurement location which translates to 3-5 mm radial resolution at the midplane due to flux expansion. An automated routine has been developed which performs the background subtraction, the relative calibration, and the comprehensive error calculation, runs a Bayesian density reconstruction code, and loads results to the JET database. The paper demonstrates the capability of the APD system by analyzing fast phenomena like pellet injection and edge localized modes.

Quantification of dislocation nucleation stress in TiN through high-resolution in situ indentation experiments and first principles calculations

DOE PAGES

Li, N.; Yadav, S. K.; Liu, X. -Y.; ...

2015-11-05

Using the in situ indentation of TiN in a high-resolution transmission electron microscope, the nucleation of full as well as partial dislocations has been observed from {001} and {111} surfaces, respectively. The critical elastic strains associated with the nucleation of the dislocations were analyzed from the recorded atomic displacements, and the nucleation stresses corresponding to the measured critical strains were computed using density functional theory. The resolved shear stress was estimated to be 13.8 GPa for the partial dislocation 1/6 <110> {111} and 6.7 GPa for the full dislocation ½ <110> {110}. Moreover, such an approach of quantifying nucleation stressesmore » for defects via in situ high-resolution experiment coupled with density functional theory calculation may be applied to other unit processes.« less

Accurate Nanoscale Crystallography in Real-Space Using Scanning Transmission Electron Microscopy.

PubMed

Dycus, J Houston; Harris, Joshua S; Sang, Xiahan; Fancher, Chris M; Findlay, Scott D; Oni, Adedapo A; Chan, Tsung-Ta E; Koch, Carl C; Jones, Jacob L; Allen, Leslie J; Irving, Douglas L; LeBeau, James M

2015-08-01

Here, we report reproducible and accurate measurement of crystallographic parameters using scanning transmission electron microscopy. This is made possible by removing drift and residual scan distortion. We demonstrate real-space lattice parameter measurements with <0.1% error for complex-layered chalcogenides Bi2Te3, Bi2Se3, and a Bi2Te2.7Se0.3 nanostructured alloy. Pairing the technique with atomic resolution spectroscopy, we connect local structure with chemistry and bonding. Combining these results with density functional theory, we show that the incorporation of Se into Bi2Te3 causes charge redistribution that anomalously increases the van der Waals gap between building blocks of the layered structure. The results show that atomic resolution imaging with electrons can accurately and robustly quantify crystallography at the nanoscale.

New data processing for multichannel FIR laser interferometer

NASA Astrophysics Data System (ADS)

Jun-Ben, Chen; Xiang, Gao

1989-10-01

Usually, both the probing and reference signals received by LATGS detectors of FIR interferometer pass through hardware phase discriminator and the output phase difference--hence the electron line densities is collected for analysis and display with a computerized data acquisition system(DAS). In this paper, a new numerical method for computing the phase difference in software has been developed instead of hardware phase discriminator, the temporal resolution and stability is improved. An asymmetrical Abel inversion is applied to processing the data from a seven-channel FIR HCN laser interferometer and the space-time distributions of plasma electron density in the HT-6M tokamak are derived.

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.

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Chao; Jiang, Tao; Liu, Shengguang

Here, an accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ~3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10 –19 sm, about 2 orders of magnitude higher than that achieved withmore » state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.« less

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

DOE PAGES

Lu, Chao; Jiang, Tao; Liu, Shengguang; ...

2018-03-12

Here, an accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ~3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10 –19 sm, about 2 orders of magnitude higher than that achieved withmore » state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.« less

Importance of conduction electron correlation in a Kondo lattice, Ce₂CoSi₃.

PubMed

Patil, Swapnil; Pandey, Sudhir K; Medicherla, V R R; Singh, R S; Bindu, R; Sampathkumaran, E V; Maiti, Kalobaran

2010-06-30

Kondo systems are usually described by the interaction of the correlation induced local moments with the highly itinerant conduction electrons. Here, we study the role of electron correlations among conduction electrons in the electronic structure of a Kondo lattice compound, Ce₂CoSi₃, using high resolution photoemission spectroscopy and ab initio band structure calculations, where Co 3d electrons contribute in the conduction band. High energy resolution employed in the measurements helped to reveal the signatures of Ce 4f states derived Kondo resonance features at the Fermi level and the dominance of Co 3d contributions at higher binding energies in the conduction band. The lineshape of the experimental Co 3d band is found to be significantly different from that obtained from the band structure calculations within the local density approximations, LDA. Consideration of electron-electron Coulomb repulsion, U, among Co 3d electrons within the LDA + U method leads to a better representation of experimental results. The signature of an electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. These results clearly demonstrate the importance of the electron correlation among conduction electrons in deriving the microscopic description of such Kondo systems.

Isotope analysis in the transmission electron microscope.

PubMed

Susi, Toma; Hofer, Christoph; Argentero, Giacomo; Leuthner, Gregor T; Pennycook, Timothy J; Mangler, Clemens; Meyer, Jannik C; Kotakoski, Jani

2016-10-10

The Ångström-sized probe of the scanning transmission electron microscope can visualize and collect spectra from single atoms. This can unambiguously resolve the chemical structure of materials, but not their isotopic composition. Here we differentiate between two isotopes of the same element by quantifying how likely the energetic imaging electrons are to eject atoms. First, we measure the displacement probability in graphene grown from either 12 C or 13 C and describe the process using a quantum mechanical model of lattice vibrations coupled with density functional theory simulations. We then test our spatial resolution in a mixed sample by ejecting individual atoms from nanoscale areas spanning an interface region that is far from atomically sharp, mapping the isotope concentration with a precision better than 20%. Although we use a scanning instrument, our method may be applicable to any atomic resolution transmission electron microscope and to other low-dimensional materials.

Method for local temperature measurement in a nanoreactor for in situ high-resolution electron microscopy.

PubMed

Vendelbo, S B; Kooyman, P J; Creemer, J F; Morana, B; Mele, L; Dona, P; Nelissen, B J; Helveg, S

2013-10-01

In situ high-resolution transmission electron microscopy (TEM) of solids under reactive gas conditions can be facilitated by microelectromechanical system devices called nanoreactors. These nanoreactors are windowed cells containing nanoliter volumes of gas at ambient pressures and elevated temperatures. However, due to the high spatial confinement of the reaction environment, traditional methods for measuring process parameters, such as the local temperature, are difficult to apply. To address this issue, we devise an electron energy loss spectroscopy (EELS) method that probes the local temperature of the reaction volume under inspection by the electron beam. The local gas density, as measured using quantitative EELS, is combined with the inherent relation between gas density and temperature, as described by the ideal gas law, to obtain the local temperature. Using this method we determined the temperature gradient in a nanoreactor in situ, while the average, global temperature was monitored by a traditional measurement of the electrical resistivity of the heater. The local gas temperatures had a maximum of 56 °C deviation from the global heater values under the applied conditions. The local temperatures, obtained with the proposed method, are in good agreement with predictions from an analytical model. Copyright © 2013 Elsevier B.V. All rights reserved.

Nanoscale femtosecond imaging of transient hot solid density plasmas with elemental and charge state sensitivity using resonant coherent diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kluge, T., E-mail: t.kluge@hzdr.de; Bussmann, M.; Huang, L. G., E-mail: lingen.huang@hzdr.de

Here, we propose to exploit the low energy bandwidth, small wavelength, and penetration power of ultrashort pulses from XFELs for resonant Small Angle Scattering (SAXS) on plasma structures in laser excited plasmas. Small angle scattering allows to detect nanoscale density fluctuations in forward scattering direction. Typically, the SAXS signal from laser excited plasmas is expected to be dominated by the free electron distribution. We propose that the ionic scattering signal becomes visible when the X-ray energy is in resonance with an electron transition between two bound states (resonant coherent X-ray diffraction). In this case, the scattering cross-section dramatically increases somore » that the signal of X-ray scattering from ions silhouettes against the free electron scattering background which allows to measure the opacity and derived quantities with high spatial and temporal resolution, being fundamentally limited only by the X-ray wavelength and timing. Deriving quantities such as ion spatial distribution, charge state distribution, and plasma temperature with such high spatial and temporal resolution will make a vast number of processes in shortpulse laser-solid interaction accessible for direct experimental observation, e.g., hole-boring and shock propagation, filamentation and instability dynamics, electron transport, heating, and ultrafast ionization dynamics.« less

Global 3-D ionospheric electron density reanalysis based on multisource data assimilation

NASA Astrophysics Data System (ADS)

Yue, Xinan; Schreiner, William S.; Kuo, Ying-Hwa; Hunt, Douglas C.; Wang, Wenbin; Solomon, Stanley C.; Burns, Alan G.; Bilitza, Dieter; Liu, Jann-Yenq; Wan, Weixing; Wickert, Jens

2012-09-01

We report preliminary results of a global 3-D ionospheric electron density reanalysis demonstration study during 2002-2011 based on multisource data assimilation. The monthly global ionospheric electron density reanalysis has been done by assimilating the quiet days ionospheric data into a data assimilation model constructed using the International Reference Ionosphere (IRI) 2007 model and a Kalman filter technique. These data include global navigation satellite system (GNSS) observations of ionospheric total electron content (TEC) from ground-based stations, ionospheric radio occultations by CHAMP, GRACE, COSMIC, SAC-C, Metop-A, and the TerraSAR-X satellites, and Jason-1 and 2 altimeter TEC measurements. The output of the reanalysis are 3-D gridded ionospheric electron densities with temporal and spatial resolutions of 1 h in universal time, 5° in latitude, 10° in longitude, and ˜30 km in altitude. The climatological features of the reanalysis results, such as solar activity dependence, seasonal variations, and the global morphology of the ionosphere, agree well with those in the empirical models and observations. The global electron content derived from the international GNSS service global ionospheric maps, the observed electron density profiles from the Poker Flat Incoherent Scatter Radar during 2007-2010, and foF2 observed by the global ionosonde network during 2002-2011 are used to validate the reanalysis method. All comparisons show that the reanalysis have smaller deviations and biases than the IRI-2007 predictions. Especially after April 2006 when the six COSMIC satellites were launched, the reanalysis shows significant improvement over the IRI predictions. The obvious overestimation of the low-latitude ionospheric F region densities by the IRI model during the 23/24 solar minimum is corrected well by the reanalysis. The potential application and improvements of the reanalysis are also discussed.

Characterization of spatially resolved high resolution x-ray spectrometers for HEDP and light-source experiments

NASA Astrophysics Data System (ADS)

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; Efthimion, P.; Pablant, N.; Lu, J.; Beiersdorfer, P.; Chen, H.; Magee, E.

2014-10-01

A high resolution 1D imaging x-ray spectrometer concept comprising a spherically bent crystal and a 2D pixelated detector is being optimized for diagnostics of small sources such as high energy density physics (HEDP) and synchrotron radiation or x-ray free electron laser experiments. This instrument is used on tokamak experiments for measurement of spatial profiles of Doppler ion temperature and plasma flow velocity, as well as electron temperature. Laboratory measurements demonstrate a resolving power, E/ ΔE of 10,000 and spatial resolution better than 10 μm. Good performance is obtained for Bragg angles ranging from 23 to 63 degrees. Initial tests of the instrument on HEDP plasmas are being performed with a goal of developing spatially resolved ion and electron temperature diagnostics. This work was performed under the auspices of the US DOE by PPPL under Contract DE-AC02-09CH11466 and by LLNL under Contract DE-AC52-07NA27344.

Harmonic analysis of the ionospheric electron densities retrieved from FORMOSAT-3/COSMIC radio occultation measurements

NASA Astrophysics Data System (ADS)

Masoumi, S.; Safari, A.; Sharifi, M.; Sam Khaniani, A.

2011-12-01

In order to investigate regular variations of the ionosphere, the least-squares harmonic estimation is applied to the time series of ionospheric electron densities in the region of Iran derived from about five years of Global Positioning System Radio Occultation (GPS RO) observations by FORMOSAT-3/COSMIC satellites. Although the obtained results are slightly different from the expected ones due to the low horizontal resolution of RO measurements, high vertical resolution of the observations enables us to detect not only the Total Electron Content (TEC) variations, but also periodic patterns of electron densities in different altitudes of the ionosphere. Dominant diurnal and annual signals, together with their Fourier series decompositions, and also periods close to 27 days are obtained, which is consistent with the previous analyses on TEC. In the equatorial anomaly band, the annual component is weaker than its Fourier decomposition periods. In particular, the semiannual period dominates the annual component, which is probably due to the effect of geomagnetic field. By the investigation of the frequencies at different local times, the semiannual signal is more significant than the annual one in the daytime, while the annual frequency is dominant at night. By the detection of the phases of the components, it is revealed that the annual signal has its maximum in summer at high altitudes, and in winter at lower altitudes. This suggests the effect of neutral compositions in the lower atmosphere. Further, the semiannual component peaks around equinox during the day, while its maximum mostly occurs in solstice at night. Since RO measurements can be used to derive TEC along the signal path between a GPS satellite and a receiver, study on the potentiality of using these observations for the prediction of electron densities and its application to the ionospheric correction of the single frequency receivers is suggested.

First measurement of time evolution of electron temperature profiles with Nd:YAG Thomson scattering system on Heliotron J

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenmochi, N., E-mail: kemmchi.naoki.62r@st.kyoto-u.ac.jp; Tei, S.; Zang, L.

2014-11-15

A Nd:YAG Thomson scattering system has been developed for Heliotron J. The system consists of two 550 mJ 50 Hz lasers, large collection optics, and 25 radial channel (∼1 cm spatial resolution) interference polychromators. This measurement system achieves a S/N ratio of ∼50 for low-density plasma (n{sub e} ∼ 0.5 × 10{sup 19} m{sup −3}). A time evolution of electron temperature profiles was measured with this system for a high-intensity gas-puff (HIGP) fueling neutral-beam-injection plasma. The peripheral temperature of the higher-density phase after HIGP recovers to the low-density pre-HIGP level, suggesting that improving particle transport in the HIGP plasma maymore » be possible.« less

Monte Carlo Approach for Estimating Density and Atomic Number From Dual-Energy Computed Tomography Images of Carbonate Rocks

NASA Astrophysics Data System (ADS)

Victor, Rodolfo A.; Prodanović, Maša.; Torres-Verdín, Carlos

2017-12-01

We develop a new Monte Carlo-based inversion method for estimating electron density and effective atomic number from 3-D dual-energy computed tomography (CT) core scans. The method accounts for uncertainties in X-ray attenuation coefficients resulting from the polychromatic nature of X-ray beam sources of medical and industrial scanners, in addition to delivering uncertainty estimates of inversion products. Estimation of electron density and effective atomic number from CT core scans enables direct deterministic or statistical correlations with salient rock properties for improved petrophysical evaluation; this condition is specifically important in media such as vuggy carbonates where CT resolution better captures core heterogeneity that dominates fluid flow properties. Verification tests of the inversion method performed on a set of highly heterogeneous carbonate cores yield very good agreement with in situ borehole measurements of density and photoelectric factor.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wojciech, Blachucki

This work treats of the high energy resolution off-resonant X-ray spectroscopy (HEROS) method of determining the density of unoccupied electronic states in the vicinity of the absorption edge. HEROS is an alternative to the existing X-ray absorption spectroscopy (XAS) methods and opens the way for new studies not achievable before.

Comment on: Polar Plumes and Fine-scale Coronal Structures - On the Interpretation of Coronal Radio Sounding Data by Patzold and Bird

NASA Technical Reports Server (NTRS)

Woo, R.; Habbal, S. R.

1998-01-01

Radio occultation measurements, which probe electron density over a wide dynamic range with high sensitivity and high spatial and temporal resolution reveal a solar corona permeated by a hierarchy of filamentary structures.

Development of inorganic resists for electron beam lithography: Novel materials and simulations

NASA Astrophysics Data System (ADS)

Jeyakumar, Augustin

Electron beam lithography is gaining widespread utilization as the semiconductor industry progresses towards both advanced optical and non-optical lithographic technologies for high resolution patterning. The current resist technologies are based on organic systems that are imaged most commonly through chain scission, networking, or a chemically amplified polarity change in the material. Alternative resists based on inorganic systems were developed and characterized in this research for high resolution electron beam lithography and their interactions with incident electrons were investigated using Monte Carlo simulations. A novel inorganic resist imaging scheme was developed using metal-organic precursors which decompose to form metal oxides upon electron beam irradiation that can serve as inorganic hard masks for hybrid bilayer inorganic-organic imaging systems and also as directly patternable high resolution metal oxide structures. The electron beam imaging properties of these metal-organic materials were correlated to the precursor structure by studying effects such as interactions between high atomic number species and the incident electrons. Optimal single and multicomponent precursors were designed for utilization as viable inorganic resist materials for sub-50nm patterning in electron beam lithography. The electron beam imaging characteristics of the most widely used inorganic resist material, hydrogen silsesquioxane (HSQ), was also enhanced using a dual processing imaging approach with thermal curing as well as a sensitizer catalyzed imaging approach. The interaction between incident electrons and the high atomic number species contained in these inorganic resists was also studied using Monte Carlo simulations. The resolution attainable using inorganic systems as compared to organic systems can be greater for accelerating voltages greater than 50 keV due to minimized lateral scattering in the high density inorganic systems. The effects of loading nanoparticles in an electron beam resist was also investigated using a newly developed hybrid Monte Carlo approach that accounts for multiple components in a solid film. The resolution of the nanocomposite resist process was found to degrade with increasing nanoparticle loading. Finally, the electron beam patterning of self-assembled monolayers, which were found to primarily utilize backscattered electrons from the high atomic number substrate materials to form images, was also investigated and characterized. It was found that backscattered electrons limit the resolution attainable at low incident electron energies.

Using the Flipchem Photochemistry Model When Fitting Incoherent Scatter Radar Data

NASA Astrophysics Data System (ADS)

Reimer, A. S.; Varney, R. H.

2017-12-01

The North face Resolute Bay Incoherent Scatter Radar (RISR-N) routinely images the dynamics of the polar ionosphere, providing measurements of the plasma density, electron temperature, ion temperature, and line of sight velocity with seconds to minutes time resolution. RISR-N does not directly measure ionospheric parameters, but backscattered signals, recording them as voltage samples. Using signal processing techniques, radar autocorrelation functions (ACF) are estimated from the voltage samples. A model of the signal ACF is then fitted to the ACF using non-linear least-squares techniques to obtain the best-fit ionospheric parameters. The signal model, and therefore the fitted parameters, depend on the ionospheric ion composition that is used [e.g. Zettergren et. al. (2010), Zou et. al. (2017)].The software used to process RISR-N ACF data includes the "flipchem" model, which is an ion photochemistry model developed by Richards [2011] that was adapted from the Field LineInterhemispheric Plasma (FLIP) model. Flipchem requires neutral densities, neutral temperatures, electron density, ion temperature, electron temperature, solar zenith angle, and F10.7 as inputs to compute ion densities, which are input to the signal model. A description of how the flipchem model is used in RISR-N fitting software will be presented. Additionally, a statistical comparison of the fitted electron density, ion temperature, electron temperature, and velocity obtained using a flipchem ionosphere, a pure O+ ionosphere, and a Chapman O+ ionosphere will be presented. The comparison covers nearly two years of RISR-N data (April 2015 - December 2016). Richards, P. G. (2011), Reexamination of ionospheric photochemistry, J. Geophys. Res., 116, A08307, doi:10.1029/2011JA016613.Zettergren, M., Semeter, J., Burnett, B., Oliver, W., Heinselman, C., Blelly, P.-L., and Diaz, M.: Dynamic variability in F-region ionospheric composition at auroral arc boundaries, Ann. Geophys., 28, 651-664, https://doi.org/10.5194/angeo-28-651-2010, 2010.Zou, S., D. Ozturk, R. Varney, and A. Reimer (2017), Effects of sudden commencement on the ionosphere: PFISR observations and global MHD simulation, Geophys. Res. Lett., 44, 3047-3058, doi:10.1002/2017GL072678.

High-Resolution Infrared and Electron-Diffraction Studies of Trimethylenecyclopropane ([3]-Radialene)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wright, Corey; Holmes, Joshua; Nibler, Joseph W.

2013-05-16

Combined high-resolution spectroscopic, electron-diffraction, and quantum theoretical methods are particularly advantageous for small molecules of high symmetry and can yield accurate structures that reveal subtle effects of electron delocalization on molecular bonds. The smallest of the radialene compounds, trimethylenecyclopropane, [3]-radialene, has been synthesized and examined in the gas phase by these methods. The first high-resolution infrared spectra have been obtained for this molecule of D3h symmetry, leading to an accurate B0 rotational constant value of 0.1378629(8) cm-1, within 0.5% of the value obtained from electronic structure calculations (density functional theory (DFT) B3LYP/cc-pVTZ). This result is employed in an analysis ofmore » electron-diffraction data to obtain the rz bond lengths (in Å): C-H = 1.072 (17), C-C = 1.437 (4), and C=C = 1.330 (4). The analysis does not lead to an accurate value of the HCH angle; however, from comparisons of theoretical and experimental angles for similar compounds, the theoretical prediction of 117.5° is believed to be reliable to within 2°. The effect of electron delocalization in radialene is to reduce the single C-C bond length by 0.07 Å compared to that in cyclopropane.« less

On the nature of Ni···Ni interaction in a model dimeric Ni complex.

PubMed

Kamiński, Radosław; Herbaczyńska, Beata; Srebro, Monika; Pietrzykowski, Antoni; Michalak, Artur; Jerzykiewicz, Lucjan B; Woźniak, Krzysztof

2011-06-07

A new dinuclear complex (NiC(5)H(4)SiMe(2)CHCH(2))(2) (2) was prepared by reacting nickelocene derivative [(C(5)H(4)SiMe(2)CH=CH(2))(2)Ni] (1) with methyllithium (MeLi). Good quality crystals were subjected to a high-resolution X-ray measurement. Subsequent multipole refinement yielded accurate description of electron density distribution. Detailed inspection of experimental electron density in Ni···Ni contact revealed that the nickel atoms are bonded and significant deformation of the metal valence shell is related to different populations of the d-orbitals. The existence of the Ni···Ni bond path explains the lack of unpaired electrons in the complex due to a possible exchange channel.

Electrical and physical characterizations of the effects of oxynitridation and wet oxidation at the interface of SiO2/4H-SiC(0001) and (000\\bar{1})

NASA Astrophysics Data System (ADS)

Shiomi, Hiromu; Kitai, Hidenori; Tsujimura, Masatoshi; Kiuchi, Yuji; Nakata, Daisuke; Ono, Shuichi; Kojima, Kazutoshi; Fukuda, Kenji; Sakamoto, Kunihiro; Yamasaki, Kimiyohi; Okumura, Hajime

2016-04-01

The effects of oxynitridation and wet oxidation at the interface of SiO2/4H-SiC(0001) and (000\\bar{1}) were investigated using both electrical and physical characterization methods. Hall measurements and split capacitance-voltage (C-V) measurements revealed that the difference in field-effect mobility between wet oxide and dry oxynitride interfaces was mainly attributed to the ratio of the mobile electron density to the total induced electron density. The surface states close to the conduction band edge causing a significant trapping of inversion carriers were also evaluated. High-resolution Rutherford backscattering spectroscopy (HR-RBS) analysis and high-resolution elastic recoil detection analysis (HR-ERDA) were employed to show the nanometer-scale compositional profile of the SiC-MOS interfaces for the first time. These analyses, together with cathode luminescence (CL) spectroscopy and transmission electron microscopy (TEM), suggested that the deviations of stoichiometry and roughness at the interface defined the effects of oxynitridation and wet oxidation at the interface of SiO2/4H-SiC(0001) and (000\\bar{1}).

The Electron Density Features Revealed by the GNSS-Based Radio Tomography in the Different Latitudinal and Longitudinal Sectors of the Ionosphere

NASA Astrophysics Data System (ADS)

Andreeva, Elena; Tereshchenko, Evgeniy; Nazarenko, Marina; Nesterov, Ivan; Kozharin, Maksim; Padokhin, Artem; Tumanova, Yulia

2016-04-01

The ionospheric radio tomography is an efficient method for electron density imaging in the different geographical regions of the world under different space weather conditions. The input for the satellite-based ionospheric radio tomography is provided by the signals that are transmitted from the navigational satellites and recorded by the chains or networks of ground receivers. The low-orbiting (LO) radio tomography employs the 150/400 MHz radio transmissions from the Earth's orbiters (like the Russian Tsikada/Parus and American Transit) flying at a height of ~1000 km above the Earth in the nearly polar orbits. The phases of the signals from a moving satellite which are recorded by the chains of ground receivers oriented along the satellite path form the families of linear integrals of electron density along the satellite-receiver rays that are used as the input data for LORT. The LO tomographic inversion of these data by phase difference method yields the 2D distributions of the ionospheric plasma in the vertical plane containing the receiving chain and the satellite path. LORT provides vertical resolution of 20-30 km and horizontal resolution of 30-40 km. The high-orbiting (HO) radio tomography employs the radio transmissions from the GPS/GLONASS satellites and enables 4D imaging of the ionosphere (3 spatial coordinates and time). HORT has a much wider spatial coverage (almost worldwide) and provides continuous time series of the reconstructions. However, the spatial resolution of HORT is lower (~100 km horizontally with a time step 60-20 min). In the regions with dense receiving networks (Europe, USA, Alaska, Japan), the resolution can be increased to 30-50 km with a time interval of 30-10 min. To date, the extensive RT data collected from the existing RT chains and networks enable a thorough analysis of both the regular and sporadic ionospheric features which are observed systematically or appear spontaneously, whose origin is fairly well understood or requires a dedicated study. We present the examples of the both types of the structures. We show a collection of different ionospheric structures under different space weather conditions: the ionization troughs, with their widely varying shapes, depths, positions, and internal distributions of plasma; isolated spots of the increased or decreased electron density, sharp wall-like density gradients, blobs, wavelike disturbances on different spatiotemporal scales etc. We demonstrate the series of the local isolated irregularities which are observed during both the quiet and disturbed days. We show the examples of the ionospheric plasma distributions strikingly varying during the geomagnetic storms. Some of the RT data are compared to the independent observations by the ionosondes. We also present the examples of RT images comparison with the UV spectroscopy data.

Electron beam patterning for writing of positively charged gold colloidal nanoparticles

NASA Astrophysics Data System (ADS)

Zafri, Hadar; Azougi, Jonathan; Girshevitz, Olga; Zalevsky, Zeev; Zitoun, David

2018-02-01

Synthesis at the nanoscale has progressed at a very fast pace during the last decades. The main challenge today lies in precise localization to achieve efficient nanofabrication of devices. In the present work, we report on a novel method for the patterning of gold metallic nanoparticles into nanostructures on a silicon-on-insulator (SOI) wafer. The fabrication makes use of relatively accessible equipment, a scanning electron microscope (SEM), and wet chemical synthesis. The electron beam implants electrons into the insulating material, which further anchors the positively charged Au nanoparticles by electrostatic attraction. The novel fabrication method was applied to several substrates useful in microelectronics to add plasmonic particles. The resolution and surface density of the deposition were tuned, respectively, by the electron energy (acceleration voltage) and the dose of electronic irradiation. We easily achieved the smallest written feature of 68 ± 18 nm on SOI, and the technique can be extended to any positively charged nanoparticles, while the resolution is in principle limited by the particle size distribution and the scattering of the electrons in the substrate. [Figure not available: see fulltext.

Extracting the redox orbitals in Li battery materials with high-resolution x-ray compton scattering spectroscopy.

PubMed

Suzuki, K; Barbiellini, B; Orikasa, Y; Go, N; Sakurai, H; Kaprzyk, S; Itou, M; Yamamoto, K; Uchimoto, Y; Wang, Yung Jui; Hafiz, H; Bansil, A; Sakurai, Y

2015-02-27

We present an incisive spectroscopic technique for directly probing redox orbitals based on bulk electron momentum density measurements via high-resolution x-ray Compton scattering. Application of our method to spinel Li_{x}Mn_{2}O_{4}, a lithium ion battery cathode material, is discussed. The orbital involved in the lithium insertion and extraction process is shown to mainly be the oxygen 2p orbital. Moreover, the manganese 3d states are shown to experience spatial delocalization involving 0.16±0.05 electrons per Mn site during the battery operation. Our analysis provides a clear understanding of the fundamental redox process involved in the working of a lithium ion battery.

Suprathermal plasma analyzer for the measurement of low-energy electron distribution in the ionosphere.

PubMed

Shimoyama, M; Oyama, K-I; Abe, T; Yau, A W

2011-07-01

It is commonly believed that an energy transfer from thermal to suprathermal electrons (

Evaluation of Multi-Channel ADCs for Gamma-Ray Spectroscopy

NASA Astrophysics Data System (ADS)

Tan, Hui; Hennig, Wolfgang; Walby, Mark D.; Breus, Dimitry; Harris, Jackson

2013-04-01

As nuclear physicists increasingly design large scale experiments with hundreds or thousands of detector channels, there are growing needs for high density readout electronics with good timing and energy resolution that at the same time offer lower cost per channel compared to existing commercial solutions. Recent improvements in the design of commercial analog to digital converters (ADCs) have resulted in a variety of multi-channel ADCs that are natural choice for designing such high density readout modules. However, multi-channel ADCs typically are designed for medical imaging/ultrasound applications and therefore are not rated for their spectroscopic characteristics. In this work, we evaluated the gamma-ray spectroscopic performance of several multi-channel ADCs, including their energy resolution, nonlinearity, and timing resolution. Some of these ADCs demonstrated excellent energy resolution, 2.66% FWHM at 662 keV with a LaBr3 or 1.78 keV FWHM at 1332.5 keV with a high purity germanium (HPGe) detector, and sub-nanosecond timing resolution with LaBr 3. We present results from these measurements to illustrate their suitability for gamma-ray spectroscopy.

X-ray structure determination using low-resolution electron microscopy maps for molecular replacement

DOE PAGES

Jackson, Ryan N.; McCoy, Airlie J.; Terwilliger, Thomas C.; ...

2015-07-30

Structures of multi-subunit macromolecular machines are primarily determined by either electron microscopy (EM) or X-ray crystallography. In many cases, a structure for a complex can be obtained at low resolution (at a coarse level of detail) with EM and at higher resolution (with finer detail) by X-ray crystallography. The integration of these two structural techniques is becoming increasingly important for generating atomic models of macromolecular complexes. A low-resolution EM image can be a powerful tool for obtaining the "phase" information that is missing from an X-ray crystallography experiment, however integration of EM and X-ray diffraction data has been technically challenging.more » Here we show a step-by-step protocol that explains how low-resolution EM maps can be placed in the crystallographic unit cell by molecular replacement, and how initial phases computed from the placed EM density are extended to high resolution by averaging maps over non-crystallographic symmetry. As the resolution gap between EM and Xray crystallography continues to narrow, the use of EM maps to help with X-ray crystal structure determination, as described in this protocol, will become increasingly effective.« less

Adiabatic electron thermal pressure fluctuations in tokamak plasmas.

PubMed

Meier, M A; Bengtson, R D; Hallock, G A; Wootton, A J

2001-08-20

Electron thermal pressure fluctuations measured in the edge plasma of the Texas Experimental Tokamak Upgrade are a fundamental component of plasma turbulence on both sides of the velocity shear layer. The ratio of specific heats, estimated from fluctuations in electron temperature and electron number density measured simultaneously at the same electrode, indicates that observed fluctuations are adiabatic. The observations are made by means of a novel Langmuir probe technique, the time domain triple-probe method, which concurrently measures multiple plasma properties at each of two electrodes with the temporal and the spatial resolution required to estimate thermodynamic properties in a turbulent plasma.

Disorder and defects are not intrinsic to boron carbide

NASA Astrophysics Data System (ADS)

Mondal, Swastik; Bykova, Elena; Dey, Somnath; Ali, Sk Imran; Dubrovinskaia, Natalia; Dubrovinsky, Leonid; Parakhonskiy, Gleb; van Smaalen, Sander

2016-01-01

A unique combination of useful properties in boron-carbide, such as extreme hardness, excellent fracture toughness, a low density, a high melting point, thermoelectricity, semi-conducting behavior, catalytic activity and a remarkably good chemical stability, makes it an ideal material for a wide range of technological applications. Explaining these properties in terms of chemical bonding has remained a major challenge in boron chemistry. Here we report the synthesis of fully ordered, stoichiometric boron-carbide B13C2 by high-pressure-high-temperature techniques. Our experimental electron-density study using high-resolution single-crystal synchrotron X-ray diffraction data conclusively demonstrates that disorder and defects are not intrinsic to boron carbide, contrary to what was hitherto supposed. A detailed analysis of the electron density distribution reveals charge transfer between structural units in B13C2 and a new type of electron-deficient bond with formally unpaired electrons on the C-B-C group in B13C2. Unprecedented bonding features contribute to the fundamental chemistry and materials science of boron compounds that is of great interest for understanding structure-property relationships and development of novel functional materials.

Measurements of density dependent intensity ratios of extreme ultraviolet line emission from Fe X, XI, and XII

NASA Astrophysics Data System (ADS)

Shimizu, Erina; Ali, Safdar; Tsuda, Takashi; Sakaue, Hiroyuki A.; Kato, Daiji; Murakami, Izumi; Hara, Hirohisa; Watanabe, Tetsuya; Nakamura, Nobuyuki

2017-05-01

We report high-resolution density dependent intensity ratio measurements for middle charge states of iron in the extreme ultraviolet (EUV) spectral wavelength range of 160-200 Å. The measurements were performed at the Tokyo EBIT laboratory by employing a flat-field grazing incidence spectrometer installed on a low energy compact electron beam ion trap. The intensity ratios for several line pairs stemming from Fe X, Fe XI and Fe XII were extracted from spectra collected at the electron beam energies of 340 and 400 eV by varying the beam current between 7.5 and 12 mA at each energy. In addition, the effective electron densities were obtained experimentally by imaging the electron beam profile and ion cloud size with a pinhole camera and visible spectrometer, respectively. In this paper, the experimental results are compared with previous data from the literature and with the present calculations performed using a collisional-radiative model. Our experimental results show a rather good agreement with the calculations and previous reported results.

Structural and electron charge density studies of a nonlinear optical compound 4,4 di-methyl amino cyano biphenyl

NASA Astrophysics Data System (ADS)

Naima, Boubegra; Abdelkader, Chouaih; Mokhtaria, Drissi; Fodil, Hamzaoui

2014-01-01

The 4,4 dimethyl amino cyano biphenyl crystal (DMACB) is characterized by its nonlinear activity. The intra molecular charge transfer of this molecule results mainly from the electronic transmission of the electro-acceptor (cyano) and electro-donor (di-methyl-amino) groups. An accurate electron density distribution around the molecule has been calculated based on a high-resolution X-ray diffraction study. The data were collected at 123 K using graphite-monochromated Mo K α radiation to sin(β)/λ = 1.24 Å-1. The integrated intensities of 13796 reflections were measured and reduced to 6501 independent reflections with I >= 3σ(I). The crystal structure was refined using the experimental model of Hansen and Coppens (1978). The crystal structure has been validated and deposited at the Cambridge Crystallographic Data Centre with the deposition number CCDC 876507. In this article, we present the thermal motion and the structural analysis obtained from the least-square refinement based on F2 and the electron density distribution obtained from the multipolar model.

STM on Gate-Tunable Graphene

NASA Astrophysics Data System (ADS)

Zhang, Yuanbo

2009-03-01

We have successfully performed atomically-resolved scanning tunneling microscopy and spectroscopy (STS) on mechanically exfoliated graphene samples having tunable back-gates. We have discovered that the tunneling spectra of graphene flakes display an unexpected gap-like feature that is pinned to the Fermi level for different gate voltages, and which coexists with another depression in density-of-states that moves with gate voltage. Extensive tests and careful analysis show that the gap-feature is due to phonon-assisted inelastic tunneling, and the depression directly marks the location of the graphene Dirac point. Using tunneling spectroscopy as a new tool, we further probe the local energetic variations of the graphene charge neutral point (Dirac point) to map out spatial electron density inhomogeneities in graphene. Such measurements are two orders of magnitude higher in resolution than previous experiments, and they can be directly correlated with nanometer scale topographic features. Based on our observation of energy-dependent periodic electronic interference patterns, our measurements also reveal the nature of impurity scattering of Dirac fermions in graphene. These results are significant for understanding the sources of electron density inhomogeneity and electron scattering in graphene, and the microscopic causes of graphene electron mobility.

Quasi-optical design for systems to diagnose the electron temperature and density fluctuations on EAST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Qifo; Liu, Yong; Zhao, Hailin, E-mail: zhaohailin@ipp.ac.cn

A system to simultaneously diagnose the electron temperature and density fluctuations is proposed for Experimental Advanced Superconducting Tokamak device. This system includes a common quasi-optical antenna, a correlation electron cyclotron emission (CECE) system that is used to measure the electron temperature fluctuations and a Doppler backscattering (DBS) system that is used to measure the electron density fluctuations. The frequency range of the proposed CECE system is 108-120 GHz, and this corresponds to a radial coverage of normalized radius ((R − R{sub 0})/a, R{sub 0} = 1850 mm, a = 450 mm) from 0.2 to 0.67 for the plasma operation withmore » a toroidal magnetic field of 2.26 T. This paper focuses on the design of the quasi-optical antenna and aims at optimizing the poloidal resolution for different frequency bands. An optimum result gives the beam radius for the CECE system of 13-15 mm and this corresponds to a wave number range of k{sub θ} < 2.4 cm{sup −1}. The beam radius is 20-30 mm for V band (50-75 GHz) and 15-20 mm for W band (75-110 GHz).« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Migunov, V., E-mail: v.migunov@fz-juelich.de; Dunin-Borkowski, R. E.; London, A.

The one-dimensional charge density distribution along an electrically biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holography in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge density distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional electricmore » field and electrostatic potential around the needle with ∼10 nm spatial resolution, without needing to consider either the influence of the perturbed reference wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge density in a material using electron holography in the presence of additional contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness.« less

Iterative model building, structure refinement and density modification with the PHENIX AutoBuild wizard

PubMed Central

Terwilliger, Thomas C.; Grosse-Kunstleve, Ralf W.; Afonine, Pavel V.; Moriarty, Nigel W.; Zwart, Peter H.; Hung, Li-Wei; Read, Randy J.; Adams, Paul D.

2008-01-01

The PHENIX AutoBuild wizard is a highly automated tool for iterative model building, structure refinement and density modification using RESOLVE model building, RESOLVE statistical density modification and phenix.refine structure refinement. Recent advances in the AutoBuild wizard and phenix.refine include automated detection and application of NCS from models as they are built, extensive model-completion algorithms and automated solvent-molecule picking. Model-completion algorithms in the AutoBuild wizard include loop building, crossovers between chains in different models of a structure and side-chain optimization. The AutoBuild wizard has been applied to a set of 48 structures at resolutions ranging from 1.1 to 3.2 Å, resulting in a mean R factor of 0.24 and a mean free R factor of 0.29. The R factor of the final model is dependent on the quality of the starting electron density and is relatively independent of resolution. PMID:18094468

A comparative study on the experimentally derived electron densities of three protease inhibitor model compounds.

PubMed

Grabowsky, Simon; Pfeuffer, Thomas; Morgenroth, Wolfgang; Paulmann, Carsten; Schirmeister, Tanja; Luger, Peter

2008-07-07

In order to contribute to a rational design of optimised protease inhibitors which can covalently block the nucleophilic amino acids of the proteases' active sites, we have chosen three model compounds (aziridine , oxirane and acceptor-substituted olefin ) for the examination of their electron-density distribution. Therefore, high-resolution low temperature (9, 27 and 100 K) X-ray diffraction experiments on single-crystals were carried out with synchrotron and conventional X-radiation. It could be shown by the analysis of the electron density using mainly Bader's Theory of Atoms in Molecules, Volkov's EPMM method for interaction energies, electrostatic potentials and Gatti's Source Function that aziridine is most suitable for drug design in this field. A regioselective nucleophilic attack at carbon atom C1 could be predicted and even hints about the reaction's stereoselectivity could be obtained. Moreover, the comparison between two data sets of aziridine (conventional X-ray source vs. synchrotron radiation) gave an estimate concerning the reproducibility of the quantitative results.

TEMPy: a Python library for assessment of three-dimensional electron microscopy density fits.

PubMed

Farabella, Irene; Vasishtan, Daven; Joseph, Agnel Praveen; Pandurangan, Arun Prasad; Sahota, Harpal; Topf, Maya

2015-08-01

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.

Energy-Filtered High-Resolution Electron Microscopy for Quantitative Solid State Structure Determination

DTIC Science & Technology

1997-01-01

is given by [19]: vP = e Ïne /(m0««0) , where e is the elementary charge, m0 is the electron rest mass, ne is the density of free electrons, and...and energy filtering systems. Fig. 8. EELS spectra acquired from a Ni/Ti multilayer specimen when the elctron beam is positioned at (a) Ti and (b) Ni...332 (1991). [11] T. Tanji, K. Urata, K. Ishizuka, Q. Ru, and A. Tonomura, Ultramicroscopy 49, 259–264 (1993). [12] D. E . Newbury, Microscopy: The Key

Ultrafast molecular processes mapped by femtosecond x-ray diffraction

NASA Astrophysics Data System (ADS)

Elsaesser, Thomas

2012-02-01

X-ray diffraction with a femtosecond time resolution allows for mapping photoinduced structural dynamics on the length scale of a chemical bond and in the time domain of atomic and molecular motion. In a pump-probe approach, a femtosecond excitation pulse induces structural changes which are probed by diffracting a femtosecond hard x-ray pulse from the excited sample. The transient angular positions and intensities of diffraction peaks give insight into the momentary atomic or molecular positions and into the distribution of electronic charge density. The simultaneous measurement of changes on different diffraction peaks is essential for determining atom positions and charge density maps with high accuracy. Recent progress in the generation of ultrashort hard x-ray pulses (Cu Kα, wavelength λ=0.154 nm) in laser-driven plasma sources has led to the implementation of the powder diffraction and the rotating crystal method with a time resolution of 100 fs. In this contribution, we report new results from powder diffraction studies of molecular materials. A first series of experiments gives evidence of a so far unknown concerted transfer of electrons and protons in ammonium sulfate [(NH4)2SO4], a centrosymmetric structure. Charge transfer from the sulfate groups results in the sub-100 fs generation of a confined electron channel along the c-axis of the unit cell which is stabilized by transferring protons from the adjacent ammonium groups into the channel. Time-dependent charge density maps display a periodic modulation of the channel's charge density by low-frequency lattice motions with a concerted electron and proton motion between the channel and the initial proton binding site. A second study addresses atomic rearrangements and charge dislocations in the non-centrosymmetric potassium dihydrogen phosphate [KH2PO4, KDP]. Photoexcitation generates coherent low-frequency motions along the LO and TO phonon coordinates, leaving the average atomic positions unchanged. The time-dependent maps of electron density demonstrate a concomitant oscillatory relocation of electronic charge with a spatial amplitude of the order of a chemical bond length, two orders of magnitude larger than the vibrational amplitudes. The coherent phonon motions drive the charge relocation, similar to a soft mode driven phase transition between the ferro- and paraelectric phase of KDP.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Los Alamos National Laboratory, Mailstop M888, Los Alamos, NM 87545, USA; Lawrence Berkeley National Laboratory, One Cyclotron Road, Building 64R0121, Berkeley, CA 94720, USA; Department of Haematology, University of Cambridge, Cambridge CB2 0XY, England

The PHENIX AutoBuild Wizard is a highly automated tool for iterative model-building, structure refinement and density modification using RESOLVE or TEXTAL model-building, RESOLVE statistical density modification, and phenix.refine structure refinement. Recent advances in the AutoBuild Wizard and phenix.refine include automated detection and application of NCS from models as they are built, extensive model completion algorithms, and automated solvent molecule picking. Model completion algorithms in the AutoBuild Wizard include loop-building, crossovers between chains in different models of a structure, and side-chain optimization. The AutoBuild Wizard has been applied to a set of 48 structures at resolutions ranging from 1.1 {angstrom} tomore » 3.2 {angstrom}, resulting in a mean R-factor of 0.24 and a mean free R factor of 0.29. The R-factor of the final model is dependent on the quality of the starting electron density, and relatively independent of resolution.« less

Iterative projection algorithms for ab initio phasing in virus crystallography.

PubMed

Lo, Victor L; Kingston, Richard L; Millane, Rick P

2016-12-01

Iterative projection algorithms are proposed as a tool for ab initio phasing in virus crystallography. The good global convergence properties of these algorithms, coupled with the spherical shape and high structural redundancy of icosahedral viruses, allows high resolution phases to be determined with no initial phase information. This approach is demonstrated by determining the electron density of a virus crystal with 5-fold non-crystallographic symmetry, starting with only a spherical shell envelope. The electron density obtained is sufficiently accurate for model building. The results indicate that iterative projection algorithms should be routinely applicable in virus crystallography, without the need for ancillary phase information. Copyright © 2016 Elsevier Inc. All rights reserved.

Improvement of density resolution in short-pulse hard x-ray radiographic imaging using detector stacks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borm, B.; Gärtner, F.; Khaghani, D.

2016-09-15

We demonstrate that stacking several imaging plates (IPs) constitutes an easy method to increase hard x-ray detection efficiency. Used to record x-ray radiographic images produced by an intense-laser driven hard x-ray backlighter source, the IP stacks resulted in a significant improvement of the radiograph density resolution. We attribute this to the higher quantum efficiency of the combined detectors, leading to a reduced photon noise. Electron-photon transport simulations of the interaction processes in the detector reproduce the observed contrast improvement. Increasing the detection efficiency to enhance radiographic imaging capabilities is equally effective as increasing the x-ray source yield, e.g., by amore » larger drive laser energy.« less

Unambiguous determination of H-atom positions: comparing results from neutron and high-resolution X-ray crystallography.

PubMed

Gardberg, Anna S; Del Castillo, Alexis Rae; Weiss, Kevin L; Meilleur, Flora; Blakeley, Matthew P; Myles, Dean A A

2010-05-01

The locations of H atoms in biological structures can be difficult to determine using X-ray diffraction methods. Neutron diffraction offers a relatively greater scattering magnitude from H and D atoms. Here, 1.65 A resolution neutron diffraction studies of fully perdeuterated and selectively CH(3)-protonated perdeuterated crystals of Pyrococcus furiosus rubredoxin (D-rubredoxin and HD-rubredoxin, respectively) at room temperature (RT) are described, as well as 1.1 A resolution X-ray diffraction studies of the same protein at both RT and 100 K. The two techniques are quantitatively compared in terms of their power to directly provide atomic positions for D atoms and analyze the role played by atomic thermal motion by computing the sigma level at the D-atom coordinate in simulated-annealing composite D-OMIT maps. It is shown that 1.65 A resolution RT neutron data for perdeuterated rubredoxin are approximately 8 times more likely overall to provide high-confidence positions for D atoms than 1.1 A resolution X-ray data at 100 K or RT. At or above the 1.0sigma level, the joint X-ray/neutron (XN) structures define 342/378 (90%) and 291/365 (80%) of the D-atom positions for D-rubredoxin and HD-rubredoxin, respectively. The X-ray-only 1.1 A resolution 100 K structures determine only 19/388 (5%) and 8/388 (2%) of the D-atom positions above the 1.0sigma level for D-rubredoxin and HD-rubredoxin, respectively. Furthermore, the improved model obtained from joint XN refinement yielded improved electron-density maps, permitting the location of more D atoms than electron-density maps from models refined against X-ray data only.

Ultrafast X-Ray Absorption Spectroscopy of Isochorically Heated Warm Dense Matter

NASA Astrophysics Data System (ADS)

Engelhorn, Kyle Craig

This dissertation will present a series of new tools, together with new techniques, focused on the understanding of warm and dense matter. We report on the development of a high time resolution and high detection efficiency x-ray camera. The camera is integrated with a short pulse laser and an x-ray beamline at the Advanced Light Source synchrotron. This provides an instrument for single shot, broadband x-ray absorption spectroscopy of warm and dense matter with 2 picosecond time resolution. Warm and dense matter is created by isochorically heating samples of known density with an ultrafast optical laser pulse, and X-ray absorption spectroscopy probes the unoccupied electronic density of states before the onset of hydrodynamic expansion and electron-ion equilibrium is reached. Measured spectra from a variety of materials are compared with first principle molecular dynamics and density functional theory calculations. In heated silicon dioxide spectra, two novel pre-edge features are observed, a peak below the band gap and absorption within the band gap, while a reduction was observed in the features above the edge. From consideration of the calculated spectra, the peak below the gap is attributed to valence electrons that have been promoted to the conduction band, the absorption within the gap is attributed to broken Si-O bonds, and the reduction above the edge is attributed to an elevated ionic temperature. In heated copper spectra, a time-dependent shift and broadening of the absorption edge are observed, consistent with and elevated electron temperature. The temporal evolution of the electronic temperature is accurately determined by fitting the measured spectra with calculated spectra. The electron-ion equilibration is studied with a two-temperature model. In heated nickel spectra, a shift of the absorption edge is observed. This shift is found to be inconsistent with calculated spectra and independent of incident laser fluence. A shift of the chemical potential is applied to the calculated spectra to obtain satisfactory agreement with measured spectra.

Measurement of the dynamic charge response of materials using low-energy, momentum-resolved electron energy-loss spectroscopy (M-EELS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Husain, Ali A.; Mitrano, Matteo; Rak, Melinda S.

One of the most fundamental properties of an interacting electron system is its frequency- and wave-vector-dependent density response function, χ(q,ω). The imaginary part, χ"(q,ω), defines the fundamental bosonic charge excitations of the system, exhibiting peaks wherever collective modes are present. χ quantifies the electronic compressibility of a material, its response to external fields, its ability to screen charge, and its tendency to form charge density waves. Unfortunately, there has never been a fully momentum-resolved means to measure χ(q,ω) at the meV energy scale relevant to modern electronic materials. Here, we demonstrate a way to measure χ with quantitative momentum resolutionmore » by applying alignment techniques from x-ray and neutron scattering to surface high-resolution electron energy-loss spectroscopy (HR-EELS). This approach, which we refer to here as M-EELS" allows direct measurement of χ"(q,ω) with meV resolution while controlling the momentum with an accuracy better than a percent of a typical Brillouin zone. We apply this technique to finite-{\\bf q} excitations in the optimally-doped high temperature superconductor, Bi 2Sr 2CaCu 2O 8+x (Bi2212), which exhibits several phonons potentially relevant to dispersion anomalies observed in ARPES and STM experiments. In conclusion, our study defines a path to studying the long-sought collective charge modes in quantum materials at the meV scale and with full momentum control.« less

Measurement of the dynamic charge response of materials using low-energy, momentum-resolved electron energy-loss spectroscopy (M-EELS)

DOE PAGES

Husain, Ali A.; Mitrano, Matteo; Rak, Melinda S.; ...

2017-10-06

One of the most fundamental properties of an interacting electron system is its frequency- and wave-vector-dependent density response function, χ(q,ω). The imaginary part, χ"(q,ω), defines the fundamental bosonic charge excitations of the system, exhibiting peaks wherever collective modes are present. χ quantifies the electronic compressibility of a material, its response to external fields, its ability to screen charge, and its tendency to form charge density waves. Unfortunately, there has never been a fully momentum-resolved means to measure χ(q,ω) at the meV energy scale relevant to modern electronic materials. Here, we demonstrate a way to measure χ with quantitative momentum resolutionmore » by applying alignment techniques from x-ray and neutron scattering to surface high-resolution electron energy-loss spectroscopy (HR-EELS). This approach, which we refer to here as M-EELS" allows direct measurement of χ"(q,ω) with meV resolution while controlling the momentum with an accuracy better than a percent of a typical Brillouin zone. We apply this technique to finite-{\\bf q} excitations in the optimally-doped high temperature superconductor, Bi 2Sr 2CaCu 2O 8+x (Bi2212), which exhibits several phonons potentially relevant to dispersion anomalies observed in ARPES and STM experiments. In conclusion, our study defines a path to studying the long-sought collective charge modes in quantum materials at the meV scale and with full momentum control.« less

Large Time Projection Chambers for Rare Event Detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heffner, M

The Time Projection Chamber (TPC) concept [add ref to TPC section] has been applied to many projects outside of particle physics and the accelerator based experiments where it was initially developed. TPCs in non-accelerator particle physics experiments are principally focused on rare event detection (e.g. neutrino and darkmater experiments) and the physics of these experiments can place dramatically different constraints on the TPC design (only extensions to the traditional TPCs are discussed here). The drift gas, or liquid, is usually the target or matter under observation and due to very low signal rates a TPC with the largest active massmore » is desired. The large mass complicates particle tracking of short and sometimes very low energy particles. Other special design issues include, efficient light collection, background rejection, internal triggering and optimal energy resolution. Backgrounds from gamma-rays and neutrons are significant design issues in the construction of these TPCs. They are generally placed deep underground to shield from cosmogenic particles and surrounded with shielding to reduce radiation from the local surroundings. The construction materials have to be carefully screened for radiopurity as they are in close contact with the active mass and can be a signification source of background events. The TPC excels in reducing this internal background because the mass inside the fieldcage forms one monolithic volume from which fiducial cuts can be made ex post facto to isolate quiet drift mass, and can be circulated and purified to a very high level. Self shielding in these large mass systems can be significant and the effect improves with density. The liquid phase TPC can obtain a high density at low pressure which results in very good self-shielding and compact installation with a lightweight containment. The down sides are the need for cryogenics, slower charge drift, tracks shorter than the typical electron diffusion, lower energy resolution (e.g. xenon) and limited charge readout options. Slower charge drift requires long electron lifetimes placing strict limits on the oxygen and other impurities with high electron affinity. A significant variation of the liquid phase TPC, that improves the charge readout, is the dual-phase TPC where a gas phase layer is formed above the liquid into which the drifting electrons are extracted and amplified, typically with electroluminescence. The successful transfer of electrons through the phase boundary requires careful control of its position and setting up an appropriate electric field. A high pressure gas phase TPC has no cryogenics and density is easily optimized for the signal, but a large heavy pressure vessel is required. Although shelf shielding is reduced, it can in some cases approach that of the liquid phase; in xenon at 50atm the density is about half that of water or about 1/6 of liquid xenon. A significant feature of high pressure xenon gas is the energy resolution. Below a density of about 0.5g/cc the intrinsic resolution is only a few times that of high purity germanium. A neutrino-less double beta decay (0{nu}2{beta}) TPC operated below this density limit could enjoy excellent energy resolution and maintain particle tracking for background rejection. An observable interaction with the TPC results in a charged particle that travels in the drift matter exciting and ionizing the atoms until the initial energy is converted into ionization, scintillation, or heat with relatively large fluctuations around a mean distribution. Rare event TPCs can be designed to detect scintillation light as well as charge to exploit the anti-correlation to improve energy resolution and/or signal to noise. An electric drift field separates the electrons and positive ions from the ionization although the separation is not complete and some electrons are captured, exciting atoms and releasing more light than the primary excitation alone. The average partition between the scintillation and ionization can be manipulated to increase the ionization (at a loss of scintillation) by a number of methods such as, increasing the strength of the electric field up to a saturation of the ionization yield, increasing the temperature to enhance the diffusion of the ionized electrons, and adding dopants such as triethylamine that can be photoionized by the scintillation photons releasing more ionization. Scintillation light is typically collected with photomultiplier tubes (PMTs) and avalanche photo diodes (APDs) although any fast (compared to the ionization drift speed) light collector capable of detecting the typically UV photons, maintaining high radiopurity and perhaps withstanding pressure would work. CCDs are slow and therefore only record 2 dimensions integrating over the time direction, some of which can be recovered with a few PMTs.« less

Kinetic-scale fluctuations resolved with the Fast Plasma Investigation on NASA's Magnetospheric Multiscale mission.

NASA Astrophysics Data System (ADS)

Gershman, D. J.; Figueroa-Vinas, A.; Dorelli, J.; Goldstein, M. L.; Shuster, J. R.; Avanov, L. A.; Boardsen, S. A.; Stawarz, J. E.; Schwartz, S. J.; Schiff, C.; Lavraud, B.; Saito, Y.; Paterson, W. R.; Giles, B. L.; Pollock, C. J.; Strangeway, R. J.; Russell, C. T.; Torbert, R. B.; Moore, T. E.; Burch, J. L.

2017-12-01

Measurements from the Fast Plasma Investigation (FPI) on NASA's Magnetospheric Multiscale (MMS) mission have enabled unprecedented analyses of kinetic-scale plasma physics. FPI regularly provides estimates of current density and pressure gradients of sufficient accuracy to evaluate the relative contribution of terms in plasma equations of motion. In addition, high-resolution three-dimensional velocity distribution functions of both ions and electrons provide new insights into kinetic-scale processes. As an example, for a monochromatic kinetic Alfven wave (KAW) we find non-zero, but out-of-phase parallel current density and electric field fluctuations, providing direct confirmation of the conservative energy exchange between the wave field and particles. In addition, we use fluctuations in current density and magnetic field to calculate the perpendicular and parallel wavelengths of the KAW. Furthermore, examination of the electron velocity distribution inside the KAW reveals a population of electrons non-linearly trapped in the kinetic-scale magnetic mirror formed between successive wave peaks. These electrons not only contribute to the wave's parallel electric field but also account for over half of the density fluctuations within the wave, supplying an unexpected mechanism for maintaining quasi-neutrality in a KAW. Finally, we demonstrate that the employed wave vector determination technique is also applicable to broadband fluctuations found in Earth's turbulent magnetosheath.

Dual wavelength imaging of a scrape-off layer in an advanced beam-driven field-reversed configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osin, D.; Schindler, T., E-mail: dosin@trialphaenergy.com

2016-11-15

A dual wavelength imaging system has been developed and installed on C-2U to capture 2D images of a He jet in the Scrape-Off Layer (SOL) of an advanced beam-driven Field-Reversed Configuration (FRC) plasma. The system was designed to optically split two identical images and pass them through 1 nm FWHM filters. Dual wavelength images are focused adjacent on a large format CCD chip and recorded simultaneously with a time resolution down to 10 μs using a gated micro-channel plate. The relatively compact optical system images a 10 cm plasma region with a spatial resolution of 0.2 cm and can bemore » used in a harsh environment with high electro-magnetic noise and high magnetic field. The dual wavelength imaging system provides 2D images of either electron density or temperature by observing spectral line pairs emitted by He jet atoms in the SOL. A large field of view, combined with good space and time resolution of the imaging system, allows visualization of macro-flows in the SOL. First 2D images of the electron density and temperature observed in the SOL of the C-2U FRC are presented.« less

Developments in the CCP4 molecular-graphics project.

PubMed

Potterton, Liz; McNicholas, Stuart; Krissinel, Eugene; Gruber, Jan; Cowtan, Kevin; Emsley, Paul; Murshudov, Garib N; Cohen, Serge; Perrakis, Anastassis; Noble, Martin

2004-12-01

Progress towards structure determination that is both high-throughput and high-value is dependent on the development of integrated and automatic tools for electron-density map interpretation and for the analysis of the resulting atomic models. Advances in map-interpretation algorithms are extending the resolution regime in which fully automatic tools can work reliably, but at present human intervention is required to interpret poor regions of macromolecular electron density, particularly where crystallographic data is only available to modest resolution [for example, I/sigma(I) < 2.0 for minimum resolution 2.5 A]. In such cases, a set of manual and semi-manual model-building molecular-graphics tools is needed. At the same time, converting the knowledge encapsulated in a molecular structure into understanding is dependent upon visualization tools, which must be able to communicate that understanding to others by means of both static and dynamic representations. CCP4 mg is a program designed to meet these needs in a way that is closely integrated with the ongoing development of CCP4 as a program suite suitable for both low- and high-intervention computational structural biology. As well as providing a carefully designed user interface to advanced algorithms of model building and analysis, CCP4 mg is intended to present a graphical toolkit to developers of novel algorithms in these fields.

Quantitative analysis of intermolecular interactions in orthorhombic rubrene

DOE PAGES

Hathwar, Venkatesha R.; Sist, Mattia; Jørgensen, Mads R. V.; ...

2015-08-14

Rubrene is one of the most studied organic semiconductors to date due to its high charge carrier mobility which makes it a potentially applicable compound in modern electronic devices. Previous electronic device characterizations and first principles theoretical calculations assigned the semiconducting properties of rubrene to the presence of a large overlap of the extended π-conjugated core between molecules. We present here the electron density distribution in rubrene at 20 K and at 100 K obtained using a combination of high-resolution X-ray and neutron diffraction data. The topology of the electron density and energies of intermolecular interactions are studied quantitatively. Specifically,more » the presence of C π...C πinteractions between neighbouring tetracene backbones of the rubrene molecules is experimentally confirmed from a topological analysis of the electron density, Non-Covalent Interaction (NCI) analysis and the calculated interaction energy of molecular dimers. A significant contribution to the lattice energy of the crystal is provided by H—H interactions. The electron density features of H—H bonding, and the interaction energy of molecular dimers connected by H—H interaction clearly demonstrate an importance of these weak interactions in the stabilization of the crystal structure. Finally, the quantitative nature of the intermolecular interactions is virtually unchanged between 20 K and 100 K suggesting that any changes in carrier transport at these low temperatures would have a different origin. The obtained experimental results are further supported by theoretical calculations.« less

Differentiation and Characterization of Excitatory and Inhibitory Synapses by Cryo-electron Tomography and Correlative Microscopy

PubMed Central

Sun, Rong; Zhang, Bin; Qi, Lei; Shivakoti, Sakar; Tian, Chong-Li; Lau, Pak-Ming

2018-01-01

As key functional units in neural circuits, different types of neuronal synapses play distinct roles in brain information processing, learning, and memory. Synaptic abnormalities are believed to underlie various neurological and psychiatric disorders. Here, by combining cryo-electron tomography and cryo-correlative light and electron microscopy, we distinguished intact excitatory and inhibitory synapses of cultured hippocampal neurons, and visualized the in situ 3D organization of synaptic organelles and macromolecules in their native state. Quantitative analyses of >100 synaptic tomograms reveal that excitatory synapses contain a mesh-like postsynaptic density (PSD) with thickness ranging from 20 to 50 nm. In contrast, the PSD in inhibitory synapses assumes a thin sheet-like structure ∼12 nm from the postsynaptic membrane. On the presynaptic side, spherical synaptic vesicles (SVs) of 25–60 nm diameter and discus-shaped ellipsoidal SVs of various sizes coexist in both synaptic types, with more ellipsoidal ones in inhibitory synapses. High-resolution tomograms obtained using a Volta phase plate and electron filtering and counting reveal glutamate receptor-like and GABAA receptor-like structures that interact with putative scaffolding and adhesion molecules, reflecting details of receptor anchoring and PSD organization. These results provide an updated view of the ultrastructure of excitatory and inhibitory synapses, and demonstrate the potential of our approach to gain insight into the organizational principles of cellular architecture underlying distinct synaptic functions. SIGNIFICANCE STATEMENT To understand functional properties of neuronal synapses, it is desirable to analyze their structure at molecular resolution. We have developed an integrative approach combining cryo-electron tomography and correlative fluorescence microscopy to visualize 3D ultrastructural features of intact excitatory and inhibitory synapses in their native state. Our approach shows that inhibitory synapses contain uniform thin sheet-like postsynaptic densities (PSDs), while excitatory synapses contain previously known mesh-like PSDs. We discovered “discus-shaped” ellipsoidal synaptic vesicles, and their distributions along with regular spherical vesicles in synaptic types are characterized. High-resolution tomograms further allowed identification of putative neurotransmitter receptors and their heterogeneous interaction with synaptic scaffolding proteins. The specificity and resolution of our approach enables precise in situ analysis of ultrastructural organization underlying distinct synaptic functions. PMID:29311144

A sensitive EUV Schwarzschild microscope for plasma studies with sub-micrometer resolution

DOE PAGES

Zastrau, U.; Rodel, C.; Nakatsutsumi, M.; ...

2018-02-05

We present an extreme ultraviolet (EUV) microscope using a Schwarzschild objective which is optimized for single-shot sub-micrometer imaging of laser-plasma targets. The microscope has been designed and constructed for imaging the scattering from an EUV-heated solid-density hydrogen jet. Here, imaging of a cryogenic hydrogen target was demonstrated using single pulses of the free-electron laser in Hamburg (FLASH) free-electron laser at a wavelength of 13.5 nm. In a single exposure, we observe a hydrogen jet with ice fragments with a spatial resolution in the sub-micrometer range. In situ EUV imaging is expected to enable novel experimental capabilities for warm dense mattermore » studies of micrometer-sized samples in laser-plasma experiments.« less

A sensitive EUV Schwarzschild microscope for plasma studies with sub-micrometer resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zastrau, U.; Rodel, C.; Nakatsutsumi, M.

We present an extreme ultraviolet (EUV) microscope using a Schwarzschild objective which is optimized for single-shot sub-micrometer imaging of laser-plasma targets. The microscope has been designed and constructed for imaging the scattering from an EUV-heated solid-density hydrogen jet. Here, imaging of a cryogenic hydrogen target was demonstrated using single pulses of the free-electron laser in Hamburg (FLASH) free-electron laser at a wavelength of 13.5 nm. In a single exposure, we observe a hydrogen jet with ice fragments with a spatial resolution in the sub-micrometer range. In situ EUV imaging is expected to enable novel experimental capabilities for warm dense mattermore » studies of micrometer-sized samples in laser-plasma experiments.« less

An iterative three-dimensional electron density imaging algorithm using uncollimated compton scattered x rays from a polyenergetic primary pencil beam.

PubMed

Van Uytven, Eric; Pistorius, Stephen; Gordon, Richard

2007-01-01

X-ray film-screen mammography is currently the gold standard for detecting breast cancer. However, one disadvantage is that it projects a three-dimensional (3D) object onto a two-dimensional (2D) image, reducing contrast between small lesions and layers of normal tissue. Another limitation is its reduced sensitivity in women with mammographically dense breasts. Computed tomography (CT) produces a 3D image yet has had a limited role in mammography due to its relatively high dose, low resolution, and low contrast. As a first step towards implementing quantitative 3D mammography, which may improve the ability to detect and specify breast tumors, we have developed an analytical technique that can use Compton scatter to obtain 3D information of an object from a single projection. Imaging material with a pencil beam of polychromatic x rays produces a characteristic scattered photon spectrum at each point on the detector plane. A comparable distribution may be calculated using a known incident x-ray energy spectrum, beam shape, and an initial estimate of the object's 3D mass attenuation and electron density. Our iterative minimization algorithm changes the initially arbitrary electron density voxel matrix to reduce regular differences between the analytically predicted and experimentally measured spectra at each point on the detector plane. The simulated electron density converges to that of the object as the differences are minimized. The reconstruction algorithm has been validated using simulated data produced by the EGSnrc Monte Carlo code system. We applied the imaging algorithm to a cylindrically symmetric breast tissue phantom containing multiple inhomogeneities. A preliminary ROC analysis scores greater than 0.96, which indicate that under the described simplifying conditions, this approach shows promise in identifying and localizing inhomogeneities which simulate 0.5 mm calcifications with an image voxel resolution of 0.25 cm and at a dose comparable to mammography.

Navigating 3D electron microscopy maps with EM-SURFER.

PubMed

Esquivel-Rodríguez, Juan; Xiong, Yi; Han, Xusi; Guang, Shuomeng; Christoffer, Charles; Kihara, Daisuke

2015-05-30

The Electron Microscopy DataBank (EMDB) is growing rapidly, accumulating biological structural data obtained mainly by electron microscopy and tomography, which are emerging techniques for determining large biomolecular complex and subcellular structures. Together with the Protein Data Bank (PDB), EMDB is becoming a fundamental resource of the tertiary structures of biological macromolecules. To take full advantage of this indispensable resource, the ability to search the database by structural similarity is essential. However, unlike high-resolution structures stored in PDB, methods for comparing low-resolution electron microscopy (EM) density maps in EMDB are not well established. We developed a computational method for efficiently searching low-resolution EM maps. The method uses a compact fingerprint representation of EM maps based on the 3D Zernike descriptor, which is derived from a mathematical series expansion for EM maps that are considered as 3D functions. The method is implemented in a web server named EM-SURFER, which allows users to search against the entire EMDB in real-time. EM-SURFER compares the global shapes of EM maps. Examples of search results from different types of query structures are discussed. We developed EM-SURFER, which retrieves structurally relevant matches for query EM maps from EMDB within seconds. The unique capability of EM-SURFER to detect 3D shape similarity of low-resolution EM maps should prove invaluable in structural biology.

Measurement of atomic electric fields and charge densities from average momentum transfers using scanning transmission electron microscopy.

PubMed

Müller-Caspary, Knut; Krause, Florian F; Grieb, Tim; Löffler, Stefan; Schowalter, Marco; Béché, Armand; Galioit, Vincent; Marquardt, Dennis; Zweck, Josef; Schattschneider, Peter; Verbeeck, Johan; Rosenauer, Andreas

2017-07-01

This study sheds light on the prerequisites, possibilities, limitations and interpretation of high-resolution differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM). We draw particular attention to the well-established DPC technique based on segmented annular detectors and its relation to recent developments based on pixelated detectors. These employ the expectation value of the momentum transfer as a reliable measure of the angular deflection of the STEM beam induced by an electric field in the specimen. The influence of scattering and propagation of electrons within the specimen is initially discussed separately and then treated in terms of a two-state channeling theory. A detailed simulation study of GaN is presented as a function of specimen thickness and bonding. It is found that bonding effects are rather detectable implicitly, e.g., by characteristics of the momentum flux in areas between the atoms than by directly mapping electric fields and charge densities. For strontium titanate, experimental charge densities are compared with simulations and discussed with respect to experimental artifacts such as scan noise. Finally, we consider practical issues such as figures of merit for spatial and momentum resolution, minimum electron dose, and the mapping of larger-scale, built-in electric fields by virtue of data averaged over a crystal unit cell. We find that the latter is possible for crystals with an inversion center. Concerning the optimal detector design, this study indicates that a sampling of 5mrad per pixel is sufficient in typical applications, corresponding to approximately 10×10 available pixels. Copyright © 2016 Elsevier B.V. All rights reserved.

Electron Flux Models for Different Energies at Geostationary Orbit

NASA Technical Reports Server (NTRS)

Boynton, R. J.; Balikhin, M. A.; Sibeck, D. G.; Walker, S. N.; Billings, S. A.; Ganushkina, N.

2016-01-01

Forecast models were derived for energetic electrons at all energy ranges sampled by the third-generation Geostationary Operational Environmental Satellites (GOES). These models were based on Multi-Input Single-Output Nonlinear Autoregressive Moving Average with Exogenous inputs methodologies. The model inputs include the solar wind velocity, density and pressure, the fraction of time that the interplanetary magnetic field (IMF) was southward, the IMF contribution of a solar wind-magnetosphere coupling function proposed by Boynton et al. (2011b), and the Dst index. As such, this study has deduced five new 1 h resolution models for the low-energy electrons measured by GOES (30-50 keV, 50-100 keV, 100-200 keV, 200-350 keV, and 350-600 keV) and extended the existing >800 keV and >2 MeV Geostationary Earth Orbit electron fluxes models to forecast at a 1 h resolution. All of these models were shown to provide accurate forecasts, with prediction efficiencies ranging between 66.9% and 82.3%.

Rotary ATPases

PubMed Central

Stewart, Alastair G.; Sobti, Meghna; Harvey, Richard P.; Stock, Daniela

2013-01-01

Rotary ATPases are molecular rotary motors involved in biological energy conversion. They either synthesize or hydrolyze the universal biological energy carrier adenosine triphosphate. Recent work has elucidated the general architecture and subunit compositions of all three sub-types of rotary ATPases. Composite models of the intact F-, V- and A-type ATPases have been constructed by fitting high-resolution X-ray structures of individual subunits or sub-complexes into low-resolution electron densities of the intact enzymes derived from electron cryo-microscopy. Electron cryo-tomography has provided new insights into the supra-molecular arrangement of eukaryotic ATP synthases within mitochondria and mass-spectrometry has started to identify specifically bound lipids presumed to be essential for function. Taken together these molecular snapshots show that nano-scale rotary engines have much in common with basic design principles of man made machines from the function of individual “machine elements” to the requirement of the right “fuel” and “oil” for different types of motors. PMID:23369889

Scalable Sub-micron Patterning of Organic Materials Toward High Density Soft Electronics.

PubMed

Kim, Jaekyun; Kim, Myung-Gil; Kim, Jaehyun; Jo, Sangho; Kang, Jingu; Jo, Jeong-Wan; Lee, Woobin; Hwang, Chahwan; Moon, Juhyuk; Yang, Lin; Kim, Yun-Hi; Noh, Yong-Young; Jaung, Jae Yun; Kim, Yong-Hoon; Park, Sung Kyu

2015-09-28

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. In this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. The successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics.

Scalable Sub-micron Patterning of Organic Materials Toward High Density Soft Electronics

NASA Astrophysics Data System (ADS)

Kim, Jaekyun; Kim, Myung-Gil; Kim, Jaehyun; Jo, Sangho; Kang, Jingu; Jo, Jeong-Wan; Lee, Woobin; Hwang, Chahwan; Moon, Juhyuk; Yang, Lin; Kim, Yun-Hi; Noh, Yong-Young; Yun Jaung, Jae; Kim, Yong-Hoon; Kyu Park, Sung

2015-09-01

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. In this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. The successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics.

Carbohydrate binding sites in a pancreatic alpha-amylase-substrate complex, derived from X-ray structure analysis at 2.1 A resolution.

PubMed Central

Qian, M.; Haser, R.; Payan, F.

1995-01-01

The X-ray structure analysis of a crystal of pig pancreatic alpha-amylase (PPA, EC 3.2.1.1.) that was soaked with the substrate maltopentaose showed electron density corresponding to two independent carbohydrate recognition sites on the surface of the molecule. Both binding sites are distinct from the active site described in detail in our previous high-resolution study of a complex between PPA and a carbohydrate inhibitor (Qian M, Buisson G, Duée E, Haser H, Payan F, 1994, Biochemistry 33:6284-6294). One of the binding sites previously identified in a 5-A-resolution electron density map, lies at a distance of 20 A from the active site cleft and can accommodate two glucose units. The second affinity site for sugar units is located close to the calcium binding site. The crystal structure of the maltopentaose complex was refined at 2.1 A resolution, to an R-factor of 17.5%, with an RMS deviation in bond distances of 0.007 A. The model includes all 496 residues of the enzyme, 1 calcium ion, 1 chloride ion, 425 water molecules, and 3 bound sugar rings. The binding sites are characterized and described in detail. The present complex structure provides the evidence of an increased stability of the structure upon interaction with the substrate and allows identification of an N-terminal pyrrolidonecarboxylic acid in PPA. PMID:7613472

Great Lakes Region Morphology and Impacts of March 17, 2015 SED Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Heine, T.; Moldwin, M.; Zou, S.

2015-12-01

Under quiet geomagnetic conditions, the mid-latitude ionosphere is relatively uniform with little spatial variation in electron density. However, during intense geomagnetic storms, density gradients associated with Storm Enhanced Density (SED) plumes and Sub-auroral Polarization Streams (SAPS) can move across the dayside mid-latitude ionosphere producing small spatial scale density structure that may be connected to ionospheric scintillation. The evolution of the SED plume during the March 17, 2015 "St. Patrick's Day Storm" is investigated using aggregated data from high resolution GPS receivers at the University of Michigan and throughout the Great Lakes region. Structural density features in the SED gradient can be observed and compared to GPS scintillation measurements—providing insight into the physical mechanisms behind ionospheric scintillation.

Electron-stimulated purification of platinum nanostructures grown via focused electron beam induced deposition.

PubMed

Lewis, Brett B; Stanford, Michael G; Fowlkes, Jason D; Lester, Kevin; Plank, Harald; Rack, Philip D

2015-01-01

Platinum-carbon nanostructures deposited via electron beam induced deposition from MeCpPt(IV)Me3 are purified during a post-deposition electron exposure treatment in a localized oxygen ambient at room temperature. Time-dependent studies demonstrate that the process occurs from the top-down. Electron beam energy and current studies demonstrate that the process is controlled by a confluence of the electron energy loss and oxygen concentration. Furthermore, the experimental results are modeled as a 2nd order reaction which is dependent on both the electron energy loss density and the oxygen concentration. In addition to purification, the post-deposition electron stimulated oxygen purification process enhances the resolution of the EBID process due to the isotropic carbon removal from the as-deposited materials which produces high-fidelity shape retention.

MO-FG-204-01: Improved Noise Suppression for Dual-Energy CT Through Entropy Minimization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrongolo, M; Zhu, L

2015-06-15

Purpose: In dual energy CT (DECT), noise amplification during signal decomposition significantly limits the utility of basis material images. Since clinically relevant objects contain a limited number of materials, we propose to suppress noise for DECT based on image entropy minimization. An adaptive weighting scheme is employed during noise suppression to improve decomposition accuracy with limited effect on spatial resolution and image texture preservation. Methods: From decomposed images, we first generate a 2D plot of scattered data points, using basis material densities as coordinates. Data points representing the same material generate a highly asymmetric cluster. We orient an axis bymore » minimizing the entropy in a 1D histogram of these points projected onto the axis. To suppress noise, we replace pixel values of decomposed images with center-of-mass values in the direction perpendicular to the optimal axis. To limit errors due to cluster overlap, we weight each data point’s contribution based on its high and low energy CT values and location within the image. The proposed method’s performance is assessed on physical phantom studies. Electron density is used as the quality metric for decomposition accuracy. Our results are compared to those without noise suppression and with a recently developed iterative method. Results: The proposed method reduces noise standard deviations of the decomposed images by at least one order of magnitude. On the Catphan phantom, this method greatly preserves the spatial resolution and texture of the CT images and limits induced error in measured electron density to below 1.2%. In the head phantom study, the proposed method performs the best in retaining fine, intricate structures. Conclusion: The entropy minimization based algorithm with adaptive weighting substantially reduces DECT noise while preserving image spatial resolution and texture. Future investigations will include extensive investigations on material decomposition accuracy that go beyond the current electron density calculations. This work was supported in part by the National Institutes of Health (NIH) under Grant Number R21 EB012700.« less

Development of a low energy electron spectrometer for SCOPE

NASA Astrophysics Data System (ADS)

Tominaga, Y.; Saito, Y.; Yokota, S.

2010-12-01

We are newly developing an electrostatic analyzer which measures low energy electrons for the future satellite mission SCOPE (cross Scale COupling in the Plasma universE). The main purpose of the SCOPE mission is to understand the cross scale coupling between macroscopic MHD scale phenom- ena and microscopic ion and electron scale phenomena. In order to understand the dynamics of plasma in such small scales, we need to observe the plasma with an analyzer which has high time resolutions. In the Earth's magnetosphere, typical timescale of plasma cyclotron frequency is ~10 sec (ions) and ~ 10 msec (electrons). In order to conduct electron-scale observations, an analyzer which has a very high time resolution(~ 10 msec) is necessary for the experiment. So far, we decided a design of the analyzer. The analyzer has three nested spherical/toroidal deflectors, which enables us to measure two different energies simultaneously and shorten the time resolution of the experiment. In order to obtain 3D velocity distribution functions of electrons, the analyzer must have 4-pi steradian field of view. We will install 8 sets of the analyzers on the satellite. Using all these analyzers we will secure 4-pi str fov at the same time. In the experiment, we plan to measure electrons from 10 eV to 22.5 keV with 32 steps. Given that the sampling time of the experiment is 0.5 msec, it takes about 8 msec to measure the whole energy range, then the time resolution of the experiment is 8 msec. The energy and angular resolution of the inner analyzer is 0.23 and 16 degrees, respectively, and that of the outer analyzer is 0.17 and 11.5 degrees, respectively. To measure enough electrons within the sampling time, the analyzer is designed to have geometrical factors (sensitivities) of 7.5e-3 (inner analyzer) and 1.0e-2 (outer analyzer) cm-2 str-1, respectively. However, it is not apparent that these characteristics of the analyzer is really appropriate for the experiment. And there are some operational problems which we have to consider and resolve. In this study, we ... 1.confirm that the analyzer we designed has characteristics appropriate for the experiment and it can measure the 3D distribution function and velocity moments of electrons. 2.estimate how the non-uniformity of the analyzer's efficiency affects the velocity moments. 3.estimate how spin motion of the satellite affects the velocity moments. Assuming Maxwellian electron distribution function with known density, bulk velocity, and temperature, we calculated the counts that the analyzer will measure taking into account the characteristic of the analyzer. Using these counts, we calculated the distribution function and velocity moments, and compared the results with the assumed density, bulk velocity and temperature in order to see the precision of the experiment. From these calculations we found that ... 1.the characteristics of the analyzer are good enough to measure the velocity moments of electrons with an error less than several percent. 2.the non-uniformity of the efficiency of the analyzers will severely affect the bulk velocity of electrons. 3.we should have special observation modes (to change the time resolution or energy range) which depends on the observation area.

Structure of a designed, right-handed coiled-coil tetramer containing all biological amino acids

PubMed Central

Sales, Mark; Plecs, Joseph J.; Holton, James M.; Alber, Tom

2007-01-01

The previous design of an unprecedented family of two-, three-, and four-helical, right-handed coiled coils utilized nonbiological amino acids to efficiently pack spaces in the oligomer cores. Here we show that a stable, right-handed parallel tetrameric coiled coil, called RH4B, can be designed entirely using biological amino acids. The X-ray crystal structure of RH4B was determined to 1.1 Å resolution using a designed metal binding site to coordinate a single Yb2+ ion per 33-amino acid polypeptide chain. The resulting experimental phases were particularly accurate, and the experimental electron density map provided an especially clear, unbiased view of the molecule. The RH4B structure closely matched the design, with equivalent core rotamers and an overall root-mean-square deviation for the N-terminal repeat of the tetramer of 0.24 Å. The clarity and resolution of the electron density map, however, revealed alternate rotamers and structural differences between the three sequence repeats in the molecule. These results suggest that the RH4B structure populates an unanticipated variety of structures. PMID:17766380

Structure of a designed, right-handed coiled-coil tetramer containing all biological amino acids.

PubMed

Sales, Mark; Plecs, Joseph J; Holton, James M; Alber, Tom

2007-10-01

The previous design of an unprecedented family of two-, three-, and four-helical, right-handed coiled coils utilized nonbiological amino acids to efficiently pack spaces in the oligomer cores. Here we show that a stable, right-handed parallel tetrameric coiled coil, called RH4B, can be designed entirely using biological amino acids. The X-ray crystal structure of RH4B was determined to 1.1 Angstrom resolution using a designed metal binding site to coordinate a single Yb(2+) ion per 33-amino acid polypeptide chain. The resulting experimental phases were particularly accurate, and the experimental electron density map provided an especially clear, unbiased view of the molecule. The RH4B structure closely matched the design, with equivalent core rotamers and an overall root-mean-square deviation for the N-terminal repeat of the tetramer of 0.24 Angstrom. The clarity and resolution of the electron density map, however, revealed alternate rotamers and structural differences between the three sequence repeats in the molecule. These results suggest that the RH4B structure populates an unanticipated variety of structures.

Crystallization and preliminary X-ray analysis of the inducible lysine decarboxylase from Escherichia coli

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexopoulos, Eftichia; Department of Medical Biophysics, University of Toronto, Division of Cancer Genomics and Proteomics, Ontario Cancer Institute, Toronto Medical Discovery Tower, 101 College Street, Toronto, Ontario M5G 1L7; Kanjee, Usheer

2008-08-01

The structure of the decameric inducible lysine decarboxylase from E. coli was determined by SIRAS using a hexatantalum dodecabromide (Ta{sub 6}Br{sub 12}{sup 2+}) derivative. Model building and refinement are under way. The decameric inducible lysine decarboxylase (LdcI) from Escherichia coli has been crystallized in space groups C2 and C222{sub 1}; the Ta{sub 6}Br{sub 12}{sup 2+} cluster was used to derivatize the C2 crystals. The method of single isomorphous replacement with anomalous scattering (SIRAS) as implemented in SHELXD was used to solve the Ta{sub 6}Br{sub 12}{sup 2+}-derivatized structure to 5 Å resolution. Many of the Ta{sub 6}Br{sub 12}{sup 2+}-binding sites hadmore » twofold and fivefold noncrystallographic symmetry. Taking advantage of this feature, phase modification was performed in DM. The electron-density map of LdcI displays many features in agreement with the low-resolution negative-stain electron-density map [Snider et al. (2006 ▶), J. Biol. Chem.281, 1532–1546].« less

Criteria to Extract High-Quality Protein Data Bank Subsets for Structure Users.

PubMed

Carugo, Oliviero; Djinović-Carugo, Kristina

2016-01-01

It is often necessary to build subsets of the Protein Data Bank to extract structural trends and average values. For this purpose it is mandatory that the subsets are non-redundant and of high quality. The first problem can be solved relatively easily at the sequence level or at the structural level. The second, on the contrary, needs special attention. It is not sufficient, in fact, to consider the crystallographic resolution and other feature must be taken into account: the absence of strings of residues from the electron density maps and from the files deposited in the Protein Data Bank; the B-factor values; the appropriate validation of the structural models; the quality of the electron density maps, which is not uniform; and the temperature of the diffraction experiments. More stringent criteria produce smaller subsets, which can be enlarged with more tolerant selection criteria. The incessant growth of the Protein Data Bank and especially of the number of high-resolution structures is allowing the use of more stringent selection criteria, with a consequent improvement of the quality of the subsets of the Protein Data Bank.

A computerized Langmuir probe system

NASA Astrophysics Data System (ADS)

Pilling, L. S.; Bydder, E. L.; Carnegie, D. A.

2003-07-01

For low pressure plasmas it is important to record entire single or double Langmuir probe characteristics accurately. For plasmas with a depleted high energy tail, the accuracy of the recorded ion current plays a critical role in determining the electron temperature. Even for high density Maxwellian distributions, it is necessary to accurately model the ion current to obtain the correct electron density. Since the electron and ion current saturation values are, at best, orders of magnitude apart, a single current sensing resistor cannot provide the required resolution to accurately record these values. We present an automated, personal computer based data acquisition system for the determination of fundamental plasma properties in low pressure plasmas. The system is designed for single and double Langmuir probes, whose characteristics can be recorded over a bias voltage range of ±70 V with 12 bit resolution. The current flowing through the probes can be recorded within the range of 5 nA-100 mA. The use of a transimpedance amplifier for current sensing eliminates the requirement for traditional current sensing resistors and hence the need to correct the raw data. The large current recording range is realized through the use of a real time gain switching system in the negative feedback loop of the transimpedance amplifier.

Estimate of the Coulomb correlation energy in CeAg2Ge2 from inverse photoemission and high resolution photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Banik, Soma; Arya, A.; Bendounan, Azzedine; Maniraj, M.; Thamizhavel, A.; Vobornik, I.; Dhar, S. K.; Deb, S. K.

2014-08-01

The occupied and the unoccupied electronic structure of CeAg2Ge2 single crystal has been studied using high resolution photoemission and inverse photoemission spectroscopy, respectively. High resolution photoemission reveals the clear signature of Ce 4f states in the occupied electronic structure which was not observed clearly in our earlier studies. The Coulomb correlation energy in this system has been determined experimentally from the position of the 4f states above and below the Fermi level. Theoretically, the correlation energy has been determined by using the first principles density functional calculations within the generalized gradient approximations taking into account the strong intra-atomic (on-site) interaction Hubbard Ueff term. The calculated valence band shows minor changes in the spectral shape with increasing Ueff due to the fact that the density of Ce 4f state is narrow in the occupied part and is hybridized with the Ce 5d, Ag 4d and Ge 4p states. On the other hand, substantial changes are observed in the spectral shape of the calculated conduction band with increasing Ueff since the density of Ce 4f state is very large in the unoccupied part, compared to other states. The estimated value of correlation energy for CeAg2Ge2 from the experiment and the theory is ≈ 4.2 eV. The resonant photoemission data are analyzed in the framework of the single-impurity Anderson model which further confirms the presence of the Coulomb correlation energy and small hybridization in this system.

Differential localization of SAP102 and PSD-95 is revealed in hippocampal spines using super-resolution light microscopy.

PubMed

Zheng, Chan-Ying; Wang, Ya-Xia; Kachar, Bechara; Petralia, Ronald S

2011-01-01

Synapse-associated protein 102 (SAP102) and postsynaptic density 95 (PSD-95) are two major cytoskeleton proteins in the postsynaptic density (PSD). Both of them belong to the membrane-associated guanylate kinase (MAGUK) family, which clusters and anchors glutamate receptors and other proteins at synapses. In our previous study, we found that SAP102 and PSD-95 have different distributions, using combined light/electron microscopy (LM/EM) methods.1 Here, we double labeled endogenous SAP102 and PSD-95 in mature hippocampal neurons, and then took images by two different kinds of super resolution microscopy-Stimulated Emission Depletion microscopy (STED) and DeltaVision OMX 3D super resolution microscopy. We found that our 2D and 3D super resolution data were consistent with our previous LM/EM data, showing significant differences in the localization of SAP102 and PSD-95 in spines: SAP102 is distributed in both the PSD and cytoplasm of spines, while PSD-95 is concentrated only in the PSD area. These results indicate functional differences between SAP102 and PSD-95 in synaptic organization and plasticity.

CheckDen, a program to compute quantum molecular properties on spatial grids.

PubMed

Pacios, Luis F; Fernandez, Alberto

2009-09-01

CheckDen, a program to compute quantum molecular properties on a variety of spatial grids is presented. The program reads as unique input wavefunction files written by standard quantum packages and calculates the electron density rho(r), promolecule and density difference function, gradient of rho(r), Laplacian of rho(r), information entropy, electrostatic potential, kinetic energy densities G(r) and K(r), electron localization function (ELF), and localized orbital locator (LOL) function. These properties can be calculated on a wide range of one-, two-, and three-dimensional grids that can be processed by widely used graphics programs to render high-resolution images. CheckDen offers also other options as extracting separate atom contributions to the property computed, converting grid output data into CUBE and OpenDX volumetric data formats, and perform arithmetic combinations with grid files in all the recognized formats.

Nanoscale temperature mapping in operating microelectronic devices

DOE PAGES

Mecklenburg, Matthew; Hubbard, William A.; White, E. R.; ...

2015-02-05

We report that modern microelectronic devices have nanoscale features that dissipate power nonuniformly, but fundamental physical limits frustrate efforts to detect the resulting temperature gradients. Contact thermometers disturb the temperature of a small system, while radiation thermometers struggle to beat the diffraction limit. Exploiting the same physics as Fahrenheit’s glass-bulb thermometer, we mapped the thermal expansion of Joule-heated, 80-nanometer-thick aluminum wires by precisely measuring changes in density. With a scanning transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS), we quantified the local density via the energy of aluminum’s bulk plasmon. Rescaling density to temperature yields maps with amore » statistical precision of 3 kelvin/hertz ₋1/2, an accuracy of 10%, and nanometer-scale resolution. Lastly, many common metals and semiconductors have sufficiently sharp plasmon resonances to serve as their own thermometers.« less

Itinerant density wave instabilities at classical and quantum critical points

DOE PAGES

Feng, Yejun; van Wezel, Jasper; Wang, Jiyang; ...

2015-07-27

Charge ordering in metals is a fundamental instability of the electron sea, occurring in a host of materials and often linked to other collective ground states such as superconductivity. What is difficult to parse, however, is whether the charge order originates among the itinerant electrons or whether it arises from the ionic lattice. Here in this study we employ high-resolution X-ray diffraction, combined with high-pressure and low-temperature techniques and theoretical modelling, to trace the evolution of the ordering wavevector Q in charge and spin density wave systems at the approach to both thermal and quantum phase transitions. The non-monotonic behaviourmore » of Q with pressure and the limiting sinusoidal form of the density wave point to the dominant role of the itinerant instability in the vicinity of the critical points, with little influence from the lattice. Fluctuations rather than disorder seem to disrupt coherence.« less

Extending the reanalysis to the ionosphere based on ground and LEO based GNSS observations

NASA Astrophysics Data System (ADS)

Yue, X.; Schreiner, W. S.; Kuo, Y.

2012-12-01

We report preliminary results of a global 3-D ionospheric electron density reanalysis during 2002-2011 based on multi-source data assimilation. The monthly global ionospheric electron density reanalysis has been done by assimilating the quiet days ionospheric data into a data assimilation model constructed using the International Reference Ionosphere (IRI) 2007 model and a Kalman filter technique. These data include global navigation satellite system (GNSS) observations of ionospheric total electron content (TEC) from ground based stations, ionospheric radio occultations by CHAMP, GRACE, COSMIC, SAC-C, Metop-A, and the TerraSAR-X satellites, and Jason-1 and 2 altimeter TEC measurements. The output of the reanalysis are 3-D gridded ionospheric electron densities with temporal and spatial resolutions of 1 hr in universal time, 5o in latitude, 10o in longitude, and ~ 30 km in altitude. The climatological features of the reanalysis results, such as solar activity dependence, seasonal variations, and the global morphology of the ionosphere, agree well with those in the empirical models and observations. The global electron content (GEC) derived from the international GNSS service (IGS) global ionospheric maps (GIM), the observed electron density profiles from the Poker Flat Incoherent Scatter Radar (PFISR) during 2007-2010, and foF2 observed by the global ionosonde network during 2002-2011 are used to validate the reanalysis method. All comparisons show that the reanalysis have smaller deviations and biases than the IRI-2007 predictions. Especially after April 2006 when the six COSMIC satellites were launched, the reanalysis shows significant improvement over the IRI predictions. The obvious overestimation of the low-latitude ionospheric F-region densities by the IRI model during the 23/24 solar minimum is corrected well by the reanalysis. The potential application and improvements of the reanalysis are also discussed.

Higher-Resolution Structure of the Human Insulin Receptor Ectodomain: Multi-Modal Inclusion of the Insert Domain.

PubMed

Croll, Tristan I; Smith, Brian J; Margetts, Mai B; Whittaker, Jonathan; Weiss, Michael A; Ward, Colin W; Lawrence, Michael C

2016-03-01

Insulin receptor (IR) signaling is critical to controlling nutrient uptake and metabolism. However, only a low-resolution (3.8 Å) structure currently exists for the IR ectodomain, with some segments ill-defined or unmodeled due to disorder. Here, we revise this structure using new diffraction data to 3.3 Å resolution that allow improved modeling of the N-linked glycans, the first and third fibronectin type III domains, and the insert domain. A novel haptic interactive molecular dynamics strategy was used to aid fitting to low-resolution electron density maps. The resulting model provides a foundation for investigation of structural transitions in IR upon ligand binding. Copyright © 2016 Elsevier Ltd. All rights reserved.

Multidimensional Attosecond Resonant X-Ray Spectroscopy of Molecules: Lessons from the Optical Regime

PubMed Central

Mukamel, Shaul; Healion, Daniel; Zhang, Yu; Biggs, Jason D.

2013-01-01

New free-electron laser and high-harmonic generation X-ray light sources are capable of supplying pulses short and intense enough to perform resonant nonlinear time-resolved experiments in molecules. Valence-electron motions can be triggered impulsively by core excitations and monitored with high temporal and spatial resolution. We discuss possible experiments that employ attosecond X-ray pulses to probe the quantum coherence and correlations of valence electrons and holes, rather than the charge density alone, building on the analogy with existing studies of vibrational motions using femtosecond techniques in the visible regime. PMID:23245522

Qualification and implementation of line ratio spectroscopy on helium as plasma edge diagnostic at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Griener, M.; Muñoz Burgos, J. M.; Cavedon, M.; Birkenmeier, G.; Dux, R.; Kurzan, B.; Schmitz, O.; Sieglin, B.; Stroth, U.; Viezzer, E.; Wolfrum, E.; the ASDEX Upgrade Team

2018-02-01

A new thermal helium beam diagnostic has been implemented as plasma edge diagnostic at the ASDEX Upgrade (AUG) tokamak. The helium beam is built to measure the electron density n e and temperature T e simultaneously with high spatial and temporal resolution in order to investigate steady-state as well as fast transport processes in the plasma edge region. For the thermal helium beam emission line ratio spectroscopy, neutral helium is locally injected into the plasma by a piezo valve. This enabled the measurement of the line resolved emission intensities of seven He I lines for different plasma scenarios in AUG. The different line ratios can be used together with a collisional-radiative model (CRM) to reconstruct the underlying electron temperature and density. Ratios from the same spin species are used for the electron density reconstruction, whereas spin mixed ratios are sensitive to electron temperature changes. The different line ratios as well as different CRMs are tested for their suitability for diagnostic applications. Furthermore their consistency in calculating identical parameters is validated and the resulting profiles are compared to other available diagnostics at AUG.

Real-space identification of intermolecular bonding with atomic force microscopy.

PubMed

Zhang, Jun; Chen, Pengcheng; Yuan, Bingkai; Ji, Wei; Cheng, Zhihai; Qiu, Xiaohui

2013-11-01

We report a real-space visualization of the formation of hydrogen bonding in 8-hydroxyquinoline (8-hq) molecular assemblies on a Cu(111) substrate, using noncontact atomic force microscopy (NC-AFM). The atomically resolved molecular structures enable a precise determination of the characteristics of hydrogen bonding networks, including the bonding sites, orientations, and lengths. The observation of bond contrast was interpreted by ab initio density functional calculations, which indicated the electron density contribution from the hybridized electronic state of the hydrogen bond. Intermolecular coordination between the dehydrogenated 8-hq and Cu adatoms was also revealed by the submolecular resolution AFM characterization. The direct identification of local bonding configurations by NC-AFM would facilitate detailed investigations of intermolecular interactions in complex molecules with multiple active sites.

A wide range real-time synchronous demodulation system for the dispersion interferometer on HL-2M

NASA Astrophysics Data System (ADS)

Wu, Tongyu; Zhang, Wei; Yin, Zejie

2017-09-01

A real-time synchronous demodulation system has been developed for the dispersion interferometer on a HL-2M tokamak. The system is based on the phase extraction method which uses a ratio of modulation amplitudes. A high-performance field programmable gate array with pipeline process capabilities is used to realize the real time synchronous demodulation algorithm. A fringe jump correction algorithm is applied to follow the fast density changes of the plasma. By using the Peripheral Component Interconnect Express protocol, the electronics can perform real-time density feedback with a temporal resolution of 100 ns. Some experimental results presented show that the electronics can obtain a wide measurement range of 2.28 × 1022 m-2 with high precision.

Band Gap Tuning in 2D Layered Materials by Angular Rotation.

PubMed

Polanco-Gonzalez, Javier; Carranco-Rodríguez, Jesús Alfredo; Enríquez-Carrejo, José L; Mani-Gonzalez, Pierre G; Domínguez-Esquivel, José Manuel; Ramos, Manuel

2017-02-08

We present a series of computer-assisted high-resolution transmission electron (HRTEM) simulations to determine Moiré patters by induced twisting effects between slabs at rotational angles of 3°, 5°, 8°, and 16°, for molybdenum disulfide, graphene, tungsten disulfide, and tungsten selenide layered materials. In order to investigate the electronic structure, a series of numerical simulations using density functional methods (DFT) methods was completed using Cambridge serial total energy package (CASTEP) with a generalized gradient approximation to determine both the band structure and density of states on honeycomb-like new superlattices. Our results indicated metallic transitions when the rotation approached 8° with respect to each other laminates for most of the two-dimensional systems that were analyzed.

Band Gap Tuning in 2D Layered Materials by Angular Rotation

PubMed Central

Polanco-Gonzalez, Javier; Carranco-Rodríguez, Jesús Alfredo; Enríquez-Carrejo, José L.; Mani-Gonzalez, Pierre G.; Domínguez-Esquivel, José Manuel; Ramos, Manuel

2017-01-01

We present a series of computer-assisted high-resolution transmission electron (HRTEM) simulations to determine Moiré patters by induced twisting effects between slabs at rotational angles of 3°, 5°, 8°, and 16°, for molybdenum disulfide, graphene, tungsten disulfide, and tungsten selenide layered materials. In order to investigate the electronic structure, a series of numerical simulations using density functional methods (DFT) methods was completed using Cambridge serial total energy package (CASTEP) with a generalized gradient approximation to determine both the band structure and density of states on honeycomb-like new superlattices. Our results indicated metallic transitions when the rotation approached 8° with respect to each other laminates for most of the two-dimensional systems that were analyzed. PMID:28772507

Study of electronic structure and Compton profiles of transition metal diborides

NASA Astrophysics Data System (ADS)

Bhatt, Samir; Heda, N. L.; Kumar, Kishor; Ahuja, B. L.

2017-08-01

We report Compton profiles (CPs) of transition metal diborides (MB2; M= Ti and Zr) using a 740 GBq 137Cs Compton spectrometer measured at an intermediate resolution of 0.34 a.u. To validate the experimental momentum densities, we have employed the linear combination of atomic orbitals (LCAO) method to compute the theoretical CPs along with the energy bands, density of states (DOS) and Mulliken's population response. The LCAO computations have been performed in the frame work of density functional theory (DFT) and hybridization of Hartree-Fock and DFT (namely B3LYP and PBE0). For both the diborides, the CPs based on revised Perdew-Burke-Ernzerhof exchange and correlation functions (DFT-PBESol) lead to a better agreement with the experimental momentum densities than other reported approximations. Energy bands, DOS and real space analysis of CPs confirm a metallic-like character of both the borides. Further, a comparison of DFT-PBESol and experimental data on equal-valence-electron-density scale shows more ionicity in ZrB2 than that in TiB2, which is also supported by the Mulliken's population based charge transfer data.

Tracking of an electron beam through the solar corona with LOFAR

NASA Astrophysics Data System (ADS)

Mann, G.; Breitling, F.; Vocks, C.; Aurass, H.; Steinmetz, M.; Strassmeier, K. G.; Bisi, M. M.; Fallows, R. A.; Gallagher, P.; Kerdraon, A.; Mackinnon, A.; Magdalenic, J.; Rucker, H.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, M. J.; Bernardi, G.; Best, P.; Bîrzan, L.; Bonafede, A.; Broderick, J. W.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Corstanje, A.; Gasperin, F. de; Geus, E. de; Deller, A.; Duscha, S.; Eislöffel, J.; Engels, D.; Falcke, H.; Fender, R.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.; Gunst, A. W.; van Haarlem, M.; Hassall, T. E.; Heald, G.; Hessels, J. W. T.; Hoeft, M.; Hörandel, J.; Horneffer, A.; Juette, E.; Karastergiou, A.; Klijn, W. F. A.; Kondratiev, V. I.; Kramer, M.; Kuniyoshi, M.; Kuper, G.; Maat, P.; Markoff, S.; McFadden, R.; McKay-Bukowski, D.; McKean, J. P.; Mulcahy, D. D.; Munk, H.; Nelles, A.; Norden, M. J.; Orru, E.; Paas, H.; Pandey-Pommier, M.; Pandey, V. N.; Pizzo, R.; Polatidis, A. G.; Rafferty, D.; Reich, W.; Röttgering, H.; Scaife, A. M. M.; Schwarz, D. J.; Serylak, M.; Sluman, J.; Smirnov, O.; Stappers, B. W.; Tagger, M.; Tang, Y.; Tasse, C.; ter Veen, S.; Thoudam, S.; Toribio, M. C.; Vermeulen, R.; van Weeren, R. J.; Wise, M. W.; Wucknitz, O.; Yatawatta, S.; Zarka, P.; Zensus, J. A.

2018-03-01

The Sun's activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983).

On the properties of synchrotron-like X-ray emission from laser wakefield accelerated electron beams

NASA Astrophysics Data System (ADS)

McGuffey, C.; Schumaker, W.; Matsuoka, T.; Chvykov, V.; Dollar, F.; Kalintchenko, G.; Kneip, S.; Najmudin, Z.; Mangles, S. P. D.; Vargas, M.; Yanovsky, V.; Maksimchuk, A.; Thomas, A. G. R.; Krushelnick, K.

2018-04-01

The electric and magnetic fields responsible for electron acceleration in a Laser Wakefield Accelerator (LWFA) also cause electrons to radiate x-ray photons. Such x-ray pulses have several desirable properties including short duration and being well collimated with tunable high energy. We measure the scaling of this x-ray source experimentally up to laser powers greater than 100 TW. An increase in laser power allows electron trapping at a lower density as well as with an increased trapped charge. These effects resulted in an x-ray fluence that was measured to increase non-linearly with laser power. The fluence of x-rays was also compared with that produced from K-α emission resulting from a solid target interaction for the same energy laser pulse. The flux was shown to be comparable, but the LWFA x-rays had a significantly smaller source size. This indicates that such a source may be useful as a backlighter for probing high energy density plasmas with ultrafast temporal resolution.

The O IV and S IV intercombination lines in solar and stellar ultraviolet spectra

NASA Technical Reports Server (NTRS)

Cook, J. W.; Keenan, F. P.; Dufton, P. L.; Kingston, A. E.; Pradhan, A. K.; Zhang, H. L.; Doyle, J. G.; Hayes, M. A.

1995-01-01

New calculations of O IV electron density diagnostic emission-line ratios involving the 1399.8, 1401.2, 1404.8, and 14076.4 A transitions are presented. A comparison of these calculations with observational data from a quiet solar region, a sunspot, and an active region obtained with the High Resolution Telescope and Spectrograph (HRTS), two flares observed with the SO82B spectrograph on board Skylab, and Hubble Space Telescope (HST) observations by the Goddard High Resolution Spectrograph (GHRS) of Capella, gives good results using the ratio R(sub 1) = I(1407.4 A)/I(1401.2 A). However, the electron density obtained using the ratio R(sub 2) = I(1407.4 A)/I(1404.8 A) is often an order of magnitude smaller. The O IV 1404.8 A line is blended with the S IV 1404.8 A line, and we investigate whether this ratio may still be used as a density diagnostic if the S IV 1406.1 A line intensity is used to correct for the presence of S IV 1404.8 A, using previous S IV calculations by Dufton et al. We still find systematic differences compared to density determinations from line ratios that do not involve the O IV 1404.8 A line, which we suggest are due to errors in earlier theoretical calculations of the S IV atomic data, and also possibly to previously unconsidered fluorescent pumping of the upper level of the S IV 1404.8 A transition.

High-Resolution Crystal Structures of Protein Helices Reconciled with Three-Centered Hydrogen Bonds and Multipole Electrostatics

PubMed Central

Kuster, Daniel J.; Liu, Chengyu; Fang, Zheng; Ponder, Jay W.; Marshall, Garland R.

2015-01-01

Theoretical and experimental evidence for non-linear hydrogen bonds in protein helices is ubiquitous. In particular, amide three-centered hydrogen bonds are common features of helices in high-resolution crystal structures of proteins. These high-resolution structures (1.0 to 1.5 Å nominal crystallographic resolution) position backbone atoms without significant bias from modeling constraints and identify Φ = -62°, ψ = -43 as the consensus backbone torsional angles of protein helices. These torsional angles preserve the atomic positions of α-β carbons of the classic Pauling α-helix while allowing the amide carbonyls to form bifurcated hydrogen bonds as first suggested by Némethy et al. in 1967. Molecular dynamics simulations of a capped 12-residue oligoalanine in water with AMOEBA (Atomic Multipole Optimized Energetics for Biomolecular Applications), a second-generation force field that includes multipole electrostatics and polarizability, reproduces the experimentally observed high-resolution helical conformation and correctly reorients the amide-bond carbonyls into bifurcated hydrogen bonds. This simple modification of backbone torsional angles reconciles experimental and theoretical views to provide a unified view of amide three-centered hydrogen bonds as crucial components of protein helices. The reason why they have been overlooked by structural biologists depends on the small crankshaft-like changes in orientation of the amide bond that allows maintenance of the overall helical parameters (helix pitch (p) and residues per turn (n)). The Pauling 3.613 α-helix fits the high-resolution experimental data with the minor exception of the amide-carbonyl electron density, but the previously associated backbone torsional angles (Φ, Ψ) needed slight modification to be reconciled with three-atom centered H-bonds and multipole electrostatics. Thus, a new standard helix, the 3.613/10-, Némethy- or N-helix, is proposed. Due to the use of constraints from monopole force fields and assumed secondary structures used in low-resolution refinement of electron density of proteins, such structures in the PDB often show linear hydrogen bonding. PMID:25894612

High-resolution crystal structures of protein helices reconciled with three-centered hydrogen bonds and multipole electrostatics.

PubMed

Kuster, Daniel J; Liu, Chengyu; Fang, Zheng; Ponder, Jay W; Marshall, Garland R

2015-01-01

Theoretical and experimental evidence for non-linear hydrogen bonds in protein helices is ubiquitous. In particular, amide three-centered hydrogen bonds are common features of helices in high-resolution crystal structures of proteins. These high-resolution structures (1.0 to 1.5 Å nominal crystallographic resolution) position backbone atoms without significant bias from modeling constraints and identify Φ = -62°, ψ = -43 as the consensus backbone torsional angles of protein helices. These torsional angles preserve the atomic positions of α-β carbons of the classic Pauling α-helix while allowing the amide carbonyls to form bifurcated hydrogen bonds as first suggested by Némethy et al. in 1967. Molecular dynamics simulations of a capped 12-residue oligoalanine in water with AMOEBA (Atomic Multipole Optimized Energetics for Biomolecular Applications), a second-generation force field that includes multipole electrostatics and polarizability, reproduces the experimentally observed high-resolution helical conformation and correctly reorients the amide-bond carbonyls into bifurcated hydrogen bonds. This simple modification of backbone torsional angles reconciles experimental and theoretical views to provide a unified view of amide three-centered hydrogen bonds as crucial components of protein helices. The reason why they have been overlooked by structural biologists depends on the small crankshaft-like changes in orientation of the amide bond that allows maintenance of the overall helical parameters (helix pitch (p) and residues per turn (n)). The Pauling 3.6(13) α-helix fits the high-resolution experimental data with the minor exception of the amide-carbonyl electron density, but the previously associated backbone torsional angles (Φ, Ψ) needed slight modification to be reconciled with three-atom centered H-bonds and multipole electrostatics. Thus, a new standard helix, the 3.6(13/10)-, Némethy- or N-helix, is proposed. Due to the use of constraints from monopole force fields and assumed secondary structures used in low-resolution refinement of electron density of proteins, such structures in the PDB often show linear hydrogen bonding.

Estimation of the Total Electron Content of the Martian Ionosphere using Radar Sounder Surface Echoes

NASA Technical Reports Server (NTRS)

Safaeinili, Ali; Kofman, Wlodek; Mouginot, Jeremie; Gim, Yonggyu; Herique, Alain; Ivanov, Anton B.; Plaut, Jeffrey J.; Picardi, Giovanni

2007-01-01

The Martian ionosphere's local total electron content (TEC) and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet. We report the global distribution of the TEC by analyzing more than 750,000 echoes of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). This is the first direct measurement of the TEC of the Martian ionosphere. The technique used in this paper is a novel 'transmission-mode' sounding of the ionosphere of Mars in contrast to the Active Ionospheric Sounding experiment (AIS) on MARSIS, which generally operates in the reflection mode. This technique yields a global map of the TEC for the Martian ionosphere. The radar transmits a wideband chirp signal that travels through the ionosphere before and after being reflected from the surface. The received waves are attenuated, delayed and dispersed, depending on the electron density in the column directly below the spacecraft. In the process of correcting the radar signal, we are able to estimate the TEC and its global distribution with an unprecedented resolution of about 0.1 deg in latitude (5 km footprint). The mapping of the relative geographical variations in the estimated nightside TEC data reveals an intricate web of high electron density regions that correspond to regions where crustal magnetic field lines are connected to the solar wind. Our data demonstrates that these regions are generally but not exclusively associated with areas that have magnetic field lines perpendicular to the surface of Mars. As a result, the global TEC map provides a high-resolution view of where the Martian crustal magnetic field is connected to the solar wind. We also provide an estimate of the neutral atmospheric scale height near the ionospheric peak and observe temporal fluctuations in peak electron density related to solar activity.

Joint small-angle X-ray and neutron scattering data analysis of asymmetric lipid vesicles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eicher, Barbara; Heberle, Frederick A.; Marquardt, Drew T.

2017-02-28

Low- and high-resolution models describing the internal transbilayer structure of asymmetric lipid vesicles have been developed. These models can be used for the joint analysis of small-angle neutron and X-ray scattering data. The models describe the underlying scattering length density/electron density profiles either in terms of slabs or through the so-called scattering density profile, previously applied to symmetric lipid vesicles. Both models yield structural details of asymmetric membranes, such as the individual area per lipid, and the hydrocarbon thickness of the inner and outer bilayer leaflets. The scattering density profile model, however, comes at a cost of increased computational effortmore » but results in greater structural resolution, showing a slightly lower packing of lipids in the outer bilayer leaflet of ~120 nm diameter palmitoyloleoyl phosphatidylcholine (POPC) vesicles, compared to the inner leaflet. Here, analysis of asymmetric dipalmitoyl phosphatidylcholine/POPC vesicles did not reveal evidence of transbilayer coupling between the inner and outer leaflets at 323 K, i.e.above the melting transition temperature of the two lipids.« less

Brickworx builds recurrent RNA and DNA structural motifs into medium- and low-resolution electron-density maps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chojnowski, Grzegorz, E-mail: gchojnowski@genesilico.pl; Waleń, Tomasz; University of Warsaw, Banacha 2, 02-097 Warsaw

2015-03-01

A computer program that builds crystal structure models of nucleic acid molecules is presented. Brickworx is a computer program that builds crystal structure models of nucleic acid molecules using recurrent motifs including double-stranded helices. In a first step, the program searches for electron-density peaks that may correspond to phosphate groups; it may also take into account phosphate-group positions provided by the user. Subsequently, comparing the three-dimensional patterns of the P atoms with a database of nucleic acid fragments, it finds the matching positions of the double-stranded helical motifs (A-RNA or B-DNA) in the unit cell. If the target structure ismore » RNA, the helical fragments are further extended with recurrent RNA motifs from a fragment library that contains single-stranded segments. Finally, the matched motifs are merged and refined in real space to find the most likely conformations, including a fit of the sequence to the electron-density map. The Brickworx program is available for download and as a web server at http://iimcb.genesilico.pl/brickworx.« less

Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states.

PubMed

Moerland, Robert J; Weppelman, I Gerward C; Garming, Mathijs W H; Kruit, Pieter; Hoogenboom, Jacob P

2016-10-17

We show cathodoluminescence-based time-resolved electron beam spectroscopy in order to directly probe the spontaneous emission decay rate that is modified by the local density of states in a nanoscale environment. In contrast to dedicated laser-triggered electron-microscopy setups, we use commercial hardware in a standard SEM, which allows us to easily switch from pulsed to continuous operation of the SEM. Electron pulses of 80-90 ps duration are generated by conjugate blanking of a high-brightness electron beam, which allows probing emitters within a large range of decay rates. Moreover, we simultaneously attain a resolution better than λ/10, which ensures details at deep-subwavelength scales can be retrieved. As a proof-of-principle, we employ the pulsed electron beam to spatially measure excited-state lifetime modifications in a phosphor material across the edge of an aluminum half-plane, coated on top of the phosphor. The measured emission dynamics can be directly related to the structure of the sample by recording photon arrival histograms together with the secondary-electron signal. Our results show that time-resolved electron cathodoluminescence spectroscopy is a powerful tool of choice for nanophotonics, within reach of a large audience.

Electron Temperature Gradient Scale Measurements in ICRF Heated Plasmas at Alcator C-Mod

NASA Astrophysics Data System (ADS)

Houshmandyar, Saeid; Phillips, Perry E.; Rowan, William L.; Howard, Nathaniel T.; Greenwald, Martin

2016-10-01

It is generally believed that the temperature gradient is a driving mechanism for the turbulent transport in hot and magnetically confined plasmas. A feature of many anomalous transport models is the critical threshold value (LC) for the gradient scale length, above which both the turbulence and the heat transport increases. This threshold is also predicted by the recent multi-scale gyrokinetic simulations, which are focused on addressing the electron (and ion) heat transport in tokamaks. Recently, we have established an accurate technique (BT-jog) to directly measure the electron temperature gradient scale length (LTe =Te / ∇T) profile, using a high-spatial resolution radiometer-based electron cyclotron emission (ECE) diagnostic. For the work presented here, electrons are heated by ion cyclotron range of frequencies (ICRF) through minority heating in L-mode plasmas at different power levels, TRANSP runs determine the electron heat fluxes and the scale lengths are measured through the BT-jog technique. Furthermore, the experiment is extended for different plasma current and electron densities by which the parametric dependence of LC on magnetic shear, safety factor and density will be investigated. This work is supported by U.S. DoE OFES, under Award No. DE-FG03-96ER-54373.

High throughput, detailed, cell-specific neuroanatomy of dendritic spines using microinjection and confocal microscopy

PubMed Central

Dumitriu, Dani; Rodriguez, Alfredo; Morrison, John H.

2012-01-01

Morphological features such as size, shape and density of dendritic spines have been shown to reflect important synaptic functional attributes and potential for plasticity. Here we describe in detail a protocol for obtaining detailed morphometric analysis of spines using microinjection of fluorescent dyes, high resolution confocal microscopy, deconvolution and image analysis using NeuronStudio. Recent technical advancements include better preservation of tissue resulting in prolonged ability to microinject, and algorithmic improvements that compensate for the residual Z-smear inherent in all optical imaging. Confocal imaging parameters were probed systematically for the identification of both optimal resolution as well as highest efficiency. When combined, our methods yield size and density measurements comparable to serial section transmission electron microscopy in a fraction of the time. An experiment containing 3 experimental groups with 8 subjects in each can take as little as one month if optimized for speed, or approximately 4 to 5 months if the highest resolution and morphometric detail is sought. PMID:21886104

The hydration structure at yttria-stabilized cubic zirconia (110)-water interface with sub-Ångström resolution

DOE PAGES

Hou, Binyang; Kim, Seunghyun; Kim, Taeho; ...

2016-06-15

The interfacial hydration structure of yttria-stabilized cubic zirconia (110) surface in contact with water was determined with ~0.5 Å resolution by high-resolution X-ray reflectivity measurement. The terminal layer shows a reduced electron density compared to the following substrate lattice layers, which indicates there are additional defects generated by metal depletion as well as intrinsic oxygen vacancies, both of which are apparently filled by water species. Above this top surface layer, two additional adsorbed layers are observed forming a characteristic interfacial hydration structure. The first adsorbed layer shows abnormally high density as pure water and likely includes metal species, whereas themore » second layer consists of pure water. The observed interfacial hydration structure seems responsible for local equilibration of the defective surface in water and eventually regulating the long-term degradation processes. As a result, the multitude of water interactions with the zirconia surface results in the complex but highly ordered interfacial structure constituting the reaction front.« less

Current density tensors

NASA Astrophysics Data System (ADS)

Lazzeretti, Paolo

2018-04-01

It is shown that nonsymmetric second-rank current density tensors, related to the current densities induced by magnetic fields and nuclear magnetic dipole moments, are fundamental properties of a molecule. Together with magnetizability, nuclear magnetic shielding, and nuclear spin-spin coupling, they completely characterize its response to magnetic perturbations. Gauge invariance, resolution into isotropic, deviatoric, and antisymmetric parts, and contributions of current density tensors to magnetic properties are discussed. The components of the second-rank tensor properties are rationalized via relationships explicitly connecting them to the direction of the induced current density vectors and to the components of the current density tensors. The contribution of the deviatoric part to the average value of magnetizability, nuclear shielding, and nuclear spin-spin coupling, uniquely determined by the antisymmetric part of current density tensors, vanishes identically. The physical meaning of isotropic and anisotropic invariants of current density tensors has been investigated, and the connection between anisotropy magnitude and electron delocalization has been discussed.

A statistical survey of heat input parameters into the cusp thermosphere

NASA Astrophysics Data System (ADS)

Moen, J. I.; Skjaeveland, A.; Carlson, H. C.

2017-12-01

Based on three winters of observational data, we present those ionosphere parameters deemed most critical to realistic space weather ionosphere and thermosphere representation and prediction, in regions impacted by variability in the cusp. The CHAMP spacecraft revealed large variability in cusp thermosphere densities, measuring frequent satellite drag enhancements, up to doublings. The community recognizes a clear need for more realistic representation of plasma flows and electron densities near the cusp. Existing average-value models produce order of magnitude errors in these parameters, resulting in large under estimations of predicted drag. We fill this knowledge gap with statistics-based specification of these key parameters over their range of observed values. The EISCAT Svalbard Radar (ESR) tracks plasma flow Vi , electron density Ne, and electron, ion temperatures Te, Ti , with consecutive 2-3 minute windshield-wipe scans of 1000x500 km areas. This allows mapping the maximum Ti of a large area within or near the cusp with high temporal resolution. In magnetic field-aligned mode the radar can measure high-resolution profiles of these plasma parameters. By deriving statistics for Ne and Ti , we enable derivation of thermosphere heating deposition under background and frictional-drag-dominated magnetic reconnection conditions. We separate our Ne and Ti profiles into quiescent and enhanced states, which are not closely correlated due to the spatial structure of the reconnection foot point. Use of our data-based parameter inputs can make order of magnitude corrections to input data driving thermosphere models, enabling removal of previous two fold drag errors.

Xenon-plasma-light low-energy ultrahigh-resolution photoemission study of Co(S1-xSex)2 (x=0.075)

NASA Astrophysics Data System (ADS)

Sato, Takafumi; Souma, Seigo; Sugawara, Katsuaki; Nakayama, Kosuke; Raj, Satyabrata; Hiraka, Haruhiro; Takahashi, Takashi

2007-09-01

We have performed low-energy ultrahigh-resolution photoemission spectroscopy on Co(S1-xSex)2 (x=0.075) to elucidate the bulk electronic states responsible for the ferromagnetic transition. By using a newly developed plasma-driven low-energy xenon (Xe) discharge lamp (hν=8.436eV) , we clearly observed a sharp quasiparticle peak at the Fermi level together with the remarkable temperature dependence of the electron density of states across the transition temperature. Comparison with the experimental result by the HeIα resonance line (hν=21.218eV) indicates that the sharp quasiparticle is of bulk origin and is produced by the Fermi-level crossing of the Co 3d eg↓ subband.

Time-dependent analysis of visible helium line-ratios for electron temperature and density diagnostic using synthetic simulations on NSTX-U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muñoz Burgos, J. M.; Barbui, T.; Schmitz, O.

Helium line-ratios for electron temperature (T e) and density (n e) plasma diagnostic in the Scrape-Off-Layer (SOL) and Edge regions of tokamaks are widely used. Due to their intensities and proximity of wavelengths, the singlet 667.8 and 728.1 nm, and triplet 706.5 nm visible lines have been typically preferred. Time-dependency of the triplet line (706.5 nm) has been previously analyzed in detail by including transient effects on line-ratios during gas-puff diagnostic applications. In this work, several line-ratio combinations within each of the two spin systems are analyzed with the purpose of eliminating transient effects to extend the application of thismore » powerful diagnostic to high temporal resolution characterization of plasmas. The analysis is done using synthetic emission modeling and diagnostic for low electron density NSTX SOL plasma conditions by several visible lines. Quasi-static equilibrium, and time-dependent models are employed to evaluate transient effects of the atomic population levels that may affect the derived electron temperatures and densities as the helium gas-puff penetrates the plasma. Ultimately, the analysis of a wider range of spectral lines will help to extend this powerful diagnostic to experiments where the wavelength range of the measured spectra may be constrained either by limitations of the spectrometer, or by other conflicting lines from different ions.« less

Time-dependent analysis of visible helium line-ratios for electron temperature and density diagnostic using synthetic simulations on NSTX-U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muñoz Burgos, J. M., E-mail: jmunozbu@pppl.gov; Stutman, D.; Tritz, K.

Helium line-ratios for electron temperature (T{sub e}) and density (n{sub e}) plasma diagnostic in the Scrape-Off-Layer (SOL) and edge regions of tokamaks are widely used. Due to their intensities and proximity of wavelengths, the singlet, 667.8 and 728.1 nm, and triplet, 706.5 nm, visible lines have been typically preferred. Time-dependency of the triplet line (706.5 nm) has been previously analyzed in detail by including transient effects on line-ratios during gas-puff diagnostic applications. In this work, several line-ratio combinations within each of the two spin systems are analyzed with the purpose of eliminating transient effects to extend the application of thismore » powerful diagnostic to high temporal resolution characterization of plasmas. The analysis is done using synthetic emission modeling and diagnostic for low electron density NSTX SOL plasma conditions by several visible lines. Quasi-static equilibrium and time-dependent models are employed to evaluate transient effects of the atomic population levels that may affect the derived electron temperatures and densities as the helium gas-puff penetrates the plasma. The analysis of a wider range of spectral lines will help to extend this powerful diagnostic to experiments where the wavelength range of the measured spectra may be constrained either by limitations of the spectrometer or by other conflicting lines from different ions.« less

Time-dependent analysis of visible helium line-ratios for electron temperature and density diagnostic using synthetic simulations on NSTX-U

DOE PAGES

Muñoz Burgos, J. M.; Barbui, T.; Schmitz, O.; ...

2016-07-11

Helium line-ratios for electron temperature (T e) and density (n e) plasma diagnostic in the Scrape-Off-Layer (SOL) and Edge regions of tokamaks are widely used. Due to their intensities and proximity of wavelengths, the singlet 667.8 and 728.1 nm, and triplet 706.5 nm visible lines have been typically preferred. Time-dependency of the triplet line (706.5 nm) has been previously analyzed in detail by including transient effects on line-ratios during gas-puff diagnostic applications. In this work, several line-ratio combinations within each of the two spin systems are analyzed with the purpose of eliminating transient effects to extend the application of thismore » powerful diagnostic to high temporal resolution characterization of plasmas. The analysis is done using synthetic emission modeling and diagnostic for low electron density NSTX SOL plasma conditions by several visible lines. Quasi-static equilibrium, and time-dependent models are employed to evaluate transient effects of the atomic population levels that may affect the derived electron temperatures and densities as the helium gas-puff penetrates the plasma. Ultimately, the analysis of a wider range of spectral lines will help to extend this powerful diagnostic to experiments where the wavelength range of the measured spectra may be constrained either by limitations of the spectrometer, or by other conflicting lines from different ions.« less

Enhanced tunable narrow-band THz emission from laser-modulated electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiang, D.; Stupakov, G.; /SLAC

2009-06-19

We propose and analyze a scheme to generate enhanced narrow-band terahertz (THz) radiation through down-conversion of the frequency of optical lasers using laser-modulated electron beams. In the scheme the electron beam is first energy modulated by two lasers with wave numbers k{sub 1} and k2, respectively. After passing through a dispersion section, the energy modulation is converted to density modulation. Due to the nonlinear conversion process, the beam will have density modulation at wave number k = nk{sub 1} + mk{sub 2}, where n and m are positive or negative integers. By properly choosing the parameters for the lasers andmore » dispersion section, one can generate density modulation at THz frequency in the beam using optical lasers. This density-modulated beam can be used to generate powerful narrow-band THz radiation. Since the THz radiation is in tight synchronization with the lasers, it should provide a high temporal resolution for the optical-pump THz-probe experiments. The central frequency of the THz radiation can be easily tuned by varying the wavelength of the two lasers and the energy chirp of the electron beam. The proposed scheme is in principle able to generate intense narrow-band THz radiation covering the whole THz range and offers a promising way towards the tunable intense narrow-band THz sources.« less

UHF Radar observations at HAARP with HF pump frequencies near electron gyro-harmonics and associated ionospheric effects

NASA Astrophysics Data System (ADS)

Watkins, Brenton; Fallen, Christopher; Secan, James

Results for HF modification experiments at the HAARP facility in Alaska are presented for experiments with the HF pump frequency near third and fourth electron gyro-harmonics. A UHF diagnostic radar with range resolution of 600 m was used to determine time-dependent altitudes of scattering from plasma turbulence during heating experiments. Experiments were conducted with multiple HF frequencies stepped by 20 kHz above and below the gyro-harmonic values. During times of HF heating the HAARP facility has sufficient power to enhance large-scale ionospheric densities in the lower ionosphere (about 150-200 km altitude) and also in the topside ionosphere (above about 350 km). In the lower ionosphere, time-dependent decreases of the altitude of radar scatter result from electron density enhancements. The effects are substantially different even for relatively small frequency steps of 20 kHz. In all cases the time-varying altitude decrease of radar scatter stops about 5-10 km below the gyro-harmonic altitude that is frequency dependent; we infer that electron density enhancements stop at this altitude where the radar signals stop decreasing with altitude. Experiments with corresponding total electron content (TEC) data show that for HF interaction altitudes above about 170 km there is substantial topside electron density increases due to upward electron thermal conduction. For lower altitudes of HF interaction the majority of the thermal energy is transferred to the neutral gas and no significant topside density increases are observed. By selecting an appropriate HF frequency a little greater than the gyro-harmonic value we have demonstrated that the ionospheric response to HF heating is a self-oscillating mode where the HF interaction altitude moves up and down with a period of several minutes. If the interaction region is above about 170 km this also produces a continuously enhanced topside electron density and upward plasma flux. Experiments using an FM scan with the HF frequency increasing near the gyro-harmonic value were conducted. The FM scan rate was sufficiently slow that the electron density was approximately in an equilibrium state. For these experiments the altitude of the HF interaction follows a near straight line downward parallel to the altitude-dependent gyro-harmonic level.

Measurement of neoclassically predicted edge current density at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Dunne, M. G.; McCarthy, P. J.; Wolfrum, E.; Fischer, R.; Giannone, L.; Burckhart, A.; the ASDEX Upgrade Team

2012-12-01

Experimental confirmation of neoclassically predicted edge current density in an ELMy H-mode plasma is presented. Current density analysis using the CLISTE equilibrium code is outlined and the rationale for accuracy of the reconstructions is explained. Sample profiles and time traces from analysis of data at ASDEX Upgrade are presented. A high time resolution is possible due to the use of an ELM-synchronization technique. Additionally, the flux-surface-averaged current density is calculated using a neoclassical approach. Results from these two separate methods are then compared and are found to validate the theoretical formula. Finally, several discharges are compared as part of a fuelling study, showing that the size and width of the edge current density peak at the low-field side can be explained by the electron density and temperature drives and their respective collisionality modifications.

The structure and thermal motion of the B800-850 LH2 complex from Rps.acidophila at 2.0A resolution and 100K: new structural features and functionally relevant motions.

PubMed

Papiz, Miroslav Z; Prince, Steve M; Howard, Tina; Cogdell, Richard J; Isaacs, Neil W

2003-03-07

The structure at 100K of integral membrane light-harvesting complex II (LH2) from Rhodopseudomonas acidophila strain 10050 has been refined to 2.0A resolution. The electron density has been significantly improved, compared to the 2.5A resolution map, by high resolution data, cryo-cooling and translation, libration, screw (TLS) refinement. The electron density reveals a second carotenoid molecule, the last five C-terminal residues of the alpha-chain and a carboxy modified alpha-Met1 which forms the ligand of the B800 bacteriochlorophyll. TLS refinement has enabled the characterisation of displacements between molecules in the complex. B850 bacteriochlorophyll molecules are arranged in a ring of 18 pigments composed of nine approximate dimers. These pigments are strongly coupled and at their equilibrium positions the excited state dipole interaction energies, within and between dimers, are approximately 370cm(-1) and 280cm(-1), respectively. This difference in coupling energy is similar in magnitude to changes in interaction energies arising from the pigment displacements described by TLS tensors. The displacements appear to be non-random in nature and appear to be designed to optimise the modulation of pigment energy interactions. This is the first time that LH2 pigment displacements have been quantified experimentally. The calculated energy changes indicate that there may be significant contributions to inter-pigment energy interactions from molecular displacements and these may be of importance to photosynthetic energy transfer.

Measurements of hot electrons in the Extrap T1 reversed-field pinch

NASA Astrophysics Data System (ADS)

Welander, A.; Bergsåker, H.

1998-02-01

The presence of an anisotropic energetic electron population in the edge region is a characteristic feature of reversed-field pinch (RFP) plasmas. In the Extrap T1 RFP, the anisotropic, parallel heat flux in the edge region measured by calorimetry was typically several hundred 0741-3335/40/2/011/img1. To gain more insight into the origin of the hot electron component and to achieve time resolution of the hot electron flow during the discharge, a target probe with a soft x-ray monitor was designed, calibrated and implemented. The x-ray emission from the target was measured with a surface barrier detector covered with a set of different x-ray filters to achieve energy resolution. A calibration in the range 0.5-2 keV electron energy was performed on the same target and detector assembly using a 0741-3335/40/2/011/img2 cathode electron gun. The calibration data are interpolated and extrapolated numerically. A directional asymmetry of more than a factor of 100 for the higher energy electrons is observed. The hot electrons are estimated to constitute 10% of the total electron density at the edge and their energy distribution is approximated by a half-Maxwellian with a temperature slightly higher than the central electron temperature. Scalings with plasma current, as well as correlations with local 0741-3335/40/2/011/img3 measurements and radial dependences, are presented.

Characterization of high density SiPM non-linearity and energy resolution for prompt gamma imaging applications

NASA Astrophysics Data System (ADS)

Regazzoni, V.; Acerbi, F.; Cozzi, G.; Ferri, A.; Fiorini, C.; Paternoster, G.; Piemonte, C.; Rucatti, D.; Zappalà, G.; Zorzi, N.; Gola, A.

2017-07-01

Fondazione Bruno Kessler (FBK) (Trento, Italy) has recently introduced High Density (HD) and Ultra High-Density (UHD) SiPMs, featuring very small micro-cell pitch. The high cell density is a very important factor to improve the linearity of the SiPM in high-dynamic-range applications, such as the scintillation light readout in high-energy gamma-ray spectroscopy and in prompt gamma imaging for proton therapy. The energy resolution at high energies is a trade-off between the excess noise factor caused by the non-linearity of the SiPM and the photon detection efficiency of the detector. To study these effects, we developed a new setup that simulates the LYSO light emission in response to gamma photons up to 30 MeV, using a pulsed light source. We measured the non-linearity and energy resolution vs. energy of the FBK RGB-HD e RGB-UHD SiPM technologies. We considered five different cell sizes, ranging from 10 μm up to 25 μm. With the UHD technology we were able to observe a remarkable reduction of the SiPM non-linearity, less than 5% at 5 MeV with 10 μm cells, which should be compared to a non-linearity of 50% with 25 μm-cell HD-SiPMs. With the same setup, we also measured the different components of the energy resolution (intrinsic, statistical, detector and electronic noise) vs. cell size, over-voltage and energy and we separated the different sources of excess noise factor.

Electronic band structure and charge density wave transition in quasi-2D KMo6O17 purple bronze

NASA Astrophysics Data System (ADS)

Valbuena, M. A.; Avila, J.; Vyalikh, D. V.; Guyot, H.; Laubschat, C.; Molodtsov, S. L.; Asensio, M. C.

2008-03-01

High resolution angle-resolved photoemission of quasi-2D KMo6O17 purple bronze has been performed in the range from room temperature to 130 K, slightly above the charge density wave (CDW) transition (Tc = 110 K), and down to 35 K (well below Tc). In this paper we report a detailed study of how electronic band structure is affected by this transition driven by the hidden nesting scenario. The expected spectroscopic fingerprints of the CDW phase transition have been found and discussed according to the hidden one dimension and the development of a quasi-commensurate CDW. The excellent agreement between theory and our experimental results makes of potassium purple bronze a reference system for studying this type of instabilities.

High-speed digital holography for neutral gas and electron density imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Granstedt, E. M., E-mail: egranstedt@gmail.com; Thomas, C. E.; Kaita, R.

2016-05-15

An instrument was developed using digital holographic reconstruction of the wavefront from a CO{sub 2} laser imaged on a high-speed commercial IR camera. An acousto-optic modulator is used to generate 1–25 μs pulses from a continuous-wave CO{sub 2} laser, both to limit the average power at the detector and also to freeze motion from sub-interframe time scales. Extensive effort was made to characterize and eliminate noise from vibrations and second-surface reflections. Mismatch of the reference and object beam curvature initially contributed substantially to vibrational noise, but was mitigated through careful positioning of identical imaging lenses. Vibrational mode amplitudes were successfullymore » reduced to ≲1 nm for frequencies ≳50 Hz, and the inter-frame noise across the 128 × 128 pixel window which is typically used is ≲2.5 nm. To demonstrate the capabilities of the system, a piezo-electric valve and a reducing-expanding nozzle were used to generate a super-sonic gas jet which was imaged with high spatial resolution (better than 0.8 lp/mm) at high speed. Abel inversions were performed on the phase images to produce 2-D images of localized gas density. This system could also be used for high spatial and temporal resolution measurements of plasma electron density or surface deformations.« less

Atomic resolution chemical bond analysis of oxygen in La2CuO4

NASA Astrophysics Data System (ADS)

Haruta, M.; Nagai, T.; Lugg, N. R.; Neish, M. J.; Nagao, M.; Kurashima, K.; Allen, L. J.; Mizoguchi, T.; Kimoto, K.

2013-08-01

The distorted CuO6 octahedron in La2CuO4 was studied using aberration-corrected scanning transmission electron microscopy at atomic resolution. The near-edge structure in the oxygen K-edge electron energy-loss spectrum was recorded as a function of the position of the electron probe. After background subtraction, the measured spectrum image was processed using a recently developed inversion process to remove the mixing of signals on the atomic columns due to elastic and thermal scattering. The spectra were then compared with first-principles band structure calculations based on the local-density approximation plus on-site Coulomb repulsion (LDA + U) approach. In this article, we describe in detail not only anisotropic chemical bonding of the oxygen 2p state with the Cu 3d state but also with the Cu 4p and La 5d/4f states. Furthermore, it was found that buckling of the CuO2 plane was also detectable at the atomic resolution oxygen K-edge. Lastly, it was found that the effects of core-hole in the O K-edge were strongly dependent on the nature of the local chemical bonding, in particular, whether it is ionic or covalent.

Aberration-Corrected Electron Beam Lithography at the One Nanometer Length Scale

DOE PAGES

Manfrinato, Vitor R.; Stein, Aaron; Zhang, Lihua; ...

2017-04-18

Patterning materials efficiently at the smallest length scales has been a longstanding challenge in nanotechnology. Electron-beam lithography (EBL) is the primary method for patterning arbitrary features, but EBL has not reliably provided sub-4 nm patterns. The few competing techniques that have achieved this resolution are orders of magnitude slower than EBL. In this work, we employed an aberration-corrected scanning transmission electron microscope for lithography to achieve unprecedented resolution. Here we show aberration-corrected EBL at the one nanometer length scale using poly(methyl methacrylate) (PMMA) and have produced both the smallest isolated feature in any conventional resist (1.7 ± 0.5 nm) andmore » the highest density patterns in PMMA (10.7 nm pitch for negative-tone and 17.5 nm pitch for positive-tone PMMA). We also demonstrate pattern transfer from the resist to semiconductor and metallic materials at the sub-5 nm scale. These results indicate that polymer-based nanofabrication can achieve feature sizes comparable to the Kuhn length of PMMA and ten times smaller than its radius of gyration. Use of aberration-corrected EBL will increase the resolution, speed, and complexity in nanomaterial fabrication.« less

Scalable Sub-micron Patterning of Organic Materials Toward High Density Soft Electronics

PubMed Central

Kim, Jaekyun; Kim, Myung-Gil; Kim, Jaehyun; Jo, Sangho; Kang, Jingu; Jo, Jeong-Wan; Lee, Woobin; Hwang, Chahwan; Moon, Juhyuk; Yang, Lin; Kim, Yun-Hi; Noh, Yong-Young; Yun Jaung, Jae; Kim, Yong-Hoon; Kyu Park, Sung

2015-01-01

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. In this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. The successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics. PMID:26411932

Scalable sub-micron patterning of organic materials toward high density soft electronics

DOE PAGES

Kim, Jaekyun; Kim, Myung -Gil; Kim, Jaehyun; ...

2015-09-28

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. Inmore » this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. As a result, the successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics.« less

Rocket measurements of mesospheric ionization irregularities

NASA Technical Reports Server (NTRS)

Stoltzfus, R. B.; Bowhill, S. A.

1985-01-01

The Langmuir probe technique for measurement of electron concentration in the mesosphere is capable of excellent altitude resolution, of order 1 m. Measurements from nine daytime rocket flights carrying an electron density fine structure experiment frequently show small scale ionization structures in the altitude region 70 to 90 km. The irregularities are believed to be the result of turbulent advection of ions and electrons. The fine structure experiment flown by the University of Illinois is described and methods of analyzing the collected data is presented. Theories of homogeneous, isotropic turbulence are reviewed. Power spectra of the measured irregularities are calculated and compared to spectra predicted by turbulence theories.

Digital holographic interferometry employing Fresnel transform reconstruction for the study of flow shear stabilized Z-pinch plasmas.

PubMed

Ross, M P; Shumlak, U

2016-10-01

The ZaP-HD flow Z-pinch project provides a platform to explore how shear flow stabilized Z-pinches could scale to high-energy-density plasma (plasma with pressures exceeding 1 Mbar) and fusion reactor conditions. The Z-pinch is a linear plasma confinement geometry in which the plasma carries axial electric current and is confined by its self-induced magnetic field. ZaP-HD generates shear stabilized, axisymmetric Z-pinches with stable lifetimes approaching 60 μs. The goal of the project is to increase the plasma density and temperature compared to the previous ZaP project by compressing the plasma to smaller radii (≈1 mm). Radial and axial plasma electron density structure is measured using digital holographic interferometry (DHI), which provides the necessary fine spatial resolution. ZaP-HD's DHI system uses a 2 ns Nd:YAG laser pulse with a second harmonic generator (λ = 532 nm) to produce holograms recorded by a Nikon D3200 digital camera. The holograms are numerically reconstructed with the Fresnel transform reconstruction method to obtain the phase shift caused by the interaction of the laser beam with the plasma. This provides a two-dimensional map of line-integrated electron density, which can be Abel inverted to determine the local number density. The DHI resolves line-integrated densities down to 3 × 10 20 m -2 with spatial resolution near 10 μm. This paper presents the first application of Fresnel transform reconstruction as an analysis technique for a plasma diagnostic, and it analyzes the method's accuracy through study of synthetic data. It then presents an Abel inversion procedure that utilizes data on both sides of a Z-pinch local number density profile to maximize profile symmetry. Error estimation and Abel inversion are applied to the measured data.

Bottom-up formation of robust gold carbide

PubMed Central

Westenfelder, Benedikt; Biskupek, Johannes; Meyer, Jannik C.; Kurasch, Simon; Lin, Xiaohang; Scholz, Ferdinand; Gross, Axel; Kaiser, Ute

2015-01-01

A new phenomenon of structural reorganization is discovered and characterized for a gold-carbon system by in-situ atomic-resolution imaging at temperatures up to 1300 K. Here, a graphene sheet serves in three ways, as a quasi transparent substrate for aberration-corrected high-resolution transmission electron microscopy, as an in-situ heater, and as carbon supplier. The sheet has been decorated with gold nanoislands beforehand. During electron irradiation at 80 kV and at elevated temperatures, the accumulation of gold atoms has been observed on defective graphene sites or edges as well as at the facets of gold nanocrystals. Both resulted in clustering, forming unusual crystalline structures. Their lattice parameters and surface termination differ significantly from standard gold nanocrystals. The experimental data, supported by electron energy loss spectroscopy and density-functional theory calculations, suggests that isolated gold and carbon atoms form – under conditions of heat and electron irradiation – a novel type of compound crystal, Au-C in zincblende structure. The novel material is metastable, but surprisingly robust, even under annealing condition. PMID:25772348

A study of optical scattering methods in laboratory plasma diagnosis

NASA Technical Reports Server (NTRS)

Phipps, C. R., Jr.

1972-01-01

Electron velocity distributions are deduced along axes parallel and perpendicular to the magnetic field in a pulsed, linear Penning discharge in hydrogen by means of a laser Thomson scattering experiment. Results obtained are numerical averages of many individual measurements made at specific space-time points in the plasma evolution. Because of the high resolution in k-space and the relatively low maximum electron density 2 x 10 to the 13th power/cu cm, special techniques were required to obtain measurable scattering signals. These techniques are discussed and experimental results are presented.

Orientation-dependent imaging of electronically excited quantum dots

NASA Astrophysics Data System (ADS)

Nguyen, Duc; Goings, Joshua J.; Nguyen, Huy A.; Lyding, Joseph; Li, Xiaosong; Gruebele, Martin

2018-02-01

We previously demonstrated that we can image electronic excitations of quantum dots by single-molecule absorption scanning tunneling microscopy (SMA-STM). With this technique, a modulated laser beam periodically saturates an electronic transition of a single nanoparticle, and the resulting tunneling current modulation ΔI(x0, y0) maps out the SMA-STM image. In this paper, we first derive the basic theory to calculate ΔI(x0, y0) in the one-electron approximation. For near-resonant tunneling through an empty orbital "i" of the nanostructure, the SMA-STM signal is approximately proportional to the electron density |φi) (x0,y0)|

Orientation-dependent imaging of electronically excited quantum dots.

PubMed

Nguyen, Duc; Goings, Joshua J; Nguyen, Huy A; Lyding, Joseph; Li, Xiaosong; Gruebele, Martin

2018-02-14

We previously demonstrated that we can image electronic excitations of quantum dots by single-molecule absorption scanning tunneling microscopy (SMA-STM). With this technique, a modulated laser beam periodically saturates an electronic transition of a single nanoparticle, and the resulting tunneling current modulation ΔI(x 0 , y 0 ) maps out the SMA-STM image. In this paper, we first derive the basic theory to calculate ΔI(x 0 , y 0 ) in the one-electron approximation. For near-resonant tunneling through an empty orbital "i" of the nanostructure, the SMA-STM signal is approximately proportional to the electron density φ i x 0 ,y 0 2 of the excited orbital in the tunneling region. Thus, the SMA-STM signal is approximated by an orbital density map (ODM) of the resonantly excited orbital at energy E i . The situation is more complex for correlated electron motion, but either way a slice through the excited electronic state structure in the tunneling region is imaged. We then show experimentally that we can nudge quantum dots on the surface and roll them, thus imaging excited state electronic structure of a single quantum dot at different orientations. We use density functional theory to model ODMs at various orientations, for qualitative comparison with the SMA-STM experiment. The model demonstrates that our experimentally observed signal monitors excited states, localized by defects near the surface of an individual quantum dot. The sub-nanometer super-resolution imaging technique demonstrated here could become useful for mapping out the three-dimensional structure of excited states localized by defects within nanomaterials.

Review of GaN-based devices for terahertz operation

NASA Astrophysics Data System (ADS)

Ahi, Kiarash

2017-09-01

GaN provides the highest electron saturation velocity, breakdown voltage, operation temperature, and thus the highest combined frequency-power performance among commonly used semiconductors. The industrial need for compact, economical, high-resolution, and high-power terahertz (THz) imaging and spectroscopy systems are promoting the utilization of GaN for implementing the next generation of THz systems. As it is reviewed, the mentioned characteristics of GaN together with its capabilities of providing high two-dimensional election densities and large longitudinal optical phonon of ˜90 meV make it one of the most promising semiconductor materials for the future of the THz emitters, detectors, mixers, and frequency multiplicators. GaN-based devices have shown capabilities of operation in the upper THz frequency band of 5 to 12 THz with relatively high photon densities in room temperature. As a result, THz imaging and spectroscopy systems with high resolution and deep depth of penetration can be realized through utilizing GaN-based devices. A comprehensive review of the history and the state of the art of GaN-based electronic devices, including plasma heterostructure field-effect transistors, negative differential resistances, hetero-dimensional Schottky diodes, impact avalanche transit times, quantum-cascade lasers, high electron mobility transistors, Gunn diodes, and tera field-effect transistors together with their impact on the future of THz imaging and spectroscopy systems is provided.

Differentiation and Characterization of Excitatory and Inhibitory Synapses by Cryo-electron Tomography and Correlative Microscopy.

PubMed

Tao, Chang-Lu; Liu, Yun-Tao; Sun, Rong; Zhang, Bin; Qi, Lei; Shivakoti, Sakar; Tian, Chong-Li; Zhang, Peijun; Lau, Pak-Ming; Zhou, Z Hong; Bi, Guo-Qiang

2018-02-07

As key functional units in neural circuits, different types of neuronal synapses play distinct roles in brain information processing, learning, and memory. Synaptic abnormalities are believed to underlie various neurological and psychiatric disorders. Here, by combining cryo-electron tomography and cryo-correlative light and electron microscopy, we distinguished intact excitatory and inhibitory synapses of cultured hippocampal neurons, and visualized the in situ 3D organization of synaptic organelles and macromolecules in their native state. Quantitative analyses of >100 synaptic tomograms reveal that excitatory synapses contain a mesh-like postsynaptic density (PSD) with thickness ranging from 20 to 50 nm. In contrast, the PSD in inhibitory synapses assumes a thin sheet-like structure ∼12 nm from the postsynaptic membrane. On the presynaptic side, spherical synaptic vesicles (SVs) of 25-60 nm diameter and discus-shaped ellipsoidal SVs of various sizes coexist in both synaptic types, with more ellipsoidal ones in inhibitory synapses. High-resolution tomograms obtained using a Volta phase plate and electron filtering and counting reveal glutamate receptor-like and GABA A receptor-like structures that interact with putative scaffolding and adhesion molecules, reflecting details of receptor anchoring and PSD organization. These results provide an updated view of the ultrastructure of excitatory and inhibitory synapses, and demonstrate the potential of our approach to gain insight into the organizational principles of cellular architecture underlying distinct synaptic functions. SIGNIFICANCE STATEMENT To understand functional properties of neuronal synapses, it is desirable to analyze their structure at molecular resolution. We have developed an integrative approach combining cryo-electron tomography and correlative fluorescence microscopy to visualize 3D ultrastructural features of intact excitatory and inhibitory synapses in their native state. Our approach shows that inhibitory synapses contain uniform thin sheet-like postsynaptic densities (PSDs), while excitatory synapses contain previously known mesh-like PSDs. We discovered "discus-shaped" ellipsoidal synaptic vesicles, and their distributions along with regular spherical vesicles in synaptic types are characterized. High-resolution tomograms further allowed identification of putative neurotransmitter receptors and their heterogeneous interaction with synaptic scaffolding proteins. The specificity and resolution of our approach enables precise in situ analysis of ultrastructural organization underlying distinct synaptic functions. Copyright © 2018 Tao, Liu et al.

Herschel Galactic Plane Survey of [NII] Fine Structure Emission

NASA Astrophysics Data System (ADS)

Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.; Pineda, Jorge L.

2015-12-01

We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10-8-10-7 Wm-2 sr-1 level over the range -60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointing is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10-50 cm-3 with an average value of 29 cm-3 and N+ column densities 1016-1017 cm-2. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.

Transverse Space-Charge Field-Induced Plasma Dynamics for Ultraintense Electron-Beam Characterization

NASA Astrophysics Data System (ADS)

Tarkeshian, R.; Vay, J. L.; Lehe, R.; Schroeder, C. B.; Esarey, E. H.; Feurer, T.; Leemans, W. P.

2018-04-01

Similarly to laser or x-ray beams, the interaction of sufficiently intense particle beams with neutral gases will result in the creation of plasma. In contrast to photon-based ionization, the strong unipolar field of a particle beam can generate a plasma where the electron population receives a large initial momentum kick and escapes, leaving behind unshielded ions. Measuring the properties of the ensuing Coulomb exploding ions—such as their kinetic energy distribution, yield, and spatial distribution—can provide information about the peak electric fields that are achieved in the electron beams. Particle-in-cell simulations and analytical models are presented for high-brightness electron beams of a few femtoseconds or even hundreds of attoseconds, and transverse beam sizes on the micron scale, as generated by today's free electron lasers. Different density regimes for the utilization as a potential diagnostics are explored, and the fundamental differences in plasma dynamical behavior for e-beam or photon-based ionization are highlighted. By measuring the dynamics of field-induced ions for different gas and beam densities, a lower bound on the beam charge density can be obtained in a single shot and in a noninvasive way. The exponential dependency of the ionization yield on the beam properties can provide unprecedented spatial and temporal resolution, at the submicrometer and subfemtosecond scales, respectively, offering a practical and powerful approach to characterizing beams from accelerators at the frontiers of performance.

Ultrahigh Energy Density in SrTiO3 Film Capacitors.

PubMed

Hou, Chuangming; Huang, Weichuan; Zhao, Wenbo; Zhang, Dalong; Yin, Yuewei; Li, Xiaoguang

2017-06-21

Solid-state dielectric film capacitors with high-energy-storage density will further promote advanced electronic devices and electrical power systems toward miniaturization, lightweight, and integration. In this study, the influence of interface and thickness on energy storage properties of SrTiO 3 (STO) films grown on La 0.67 Sr 0.33 MnO 3 (LSMO) electrode are systematically studied. The cross-sectional high resolution transmission electron microscopy reveals an ion interdiffusion layer and oxygen vacancies at the STO/LSMO interface. The capacitors show good frequency stability and increased dielectric constant with increasing STO thickness (410-710 nm). The breakdown strength (E b ) increases with decreasing STO thickness and reaches 6.8 MV/cm. Interestingly, the E b under positive field is enhanced significantly and an ultrahigh energy density up to 307 J/cm 3 with a high efficiency of 89% is realized. The enhanced E b may be related to the modulation of local electric field and redistribution of oxygen vacancies at the STO/LSMO interface. Our results should be helpful for potential strategies to design devices with ultrahigh energy density.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Jiusheng; van den Bedem, Henry; Brunger, Axel T.

Calmodulin (CaM) is the primary calcium signaling protein in eukaryotes and has been extensively studied using various biophysical techniques. Prior crystal structures have noted the presence of ambiguous electron density in both hydrophobic binding pockets of Ca 2+-CaM, but no assignment of these features has been made. In addition, Ca 2+-CaM samples many conformational substates in the crystal and accurately modeling the full range of this functionally important disorder is challenging. In order to characterize these features in a minimally biased manner, a 1.0 Å resolution single-wavelength anomalous diffraction data set was measured for selenomethionine-substituted Ca 2+-CaM. Density-modified electron-density mapsmore » enabled the accurate assignment of Ca 2+-CaM main-chain and side-chain disorder. These experimental maps also substantiate complex disorder models that were automatically built using low-contour features of model-phased electron density. Furthermore, experimental electron-density maps reveal that 2-methyl-2,4-pentanediol (MPD) is present in the C-terminal domain, mediates a lattice contact between N-terminal domains and may occupy the N-terminal binding pocket. The majority of the crystal structures of target-free Ca 2+-CaM have been derived from crystals grown using MPD as a precipitant, and thus MPD is likely to be bound in functionally critical regions of Ca 2+-CaM in most of these structures. The adventitious binding of MPD helps to explain differences between the Ca 2+-CaM crystal and solution structures and is likely to favor more open conformations of the EF-hands in the crystal.« less

Phenomenological plasmon broadening and relation to the dispersion

NASA Astrophysics Data System (ADS)

Hobbiger, Raphael; Drachta, Jürgen T.; Kreil, Dominik; Böhm, Helga M.

2017-02-01

Pragmatic ways of including lifetime broadening of collective modes in the electron liquid are critically compared. Special focus lies on the impact of the damping parameter onto the dispersion. It is quantitatively exemplified for the two-dimensional case, for both, the charge ('sheet'-)plasmon and the spin-density plasmon. The predicted deviations fall within the resolution limits of advanced techniques.

2.2 Å resolution cryo-EM structure of β-galactosidase in complex with a cell-permeant inhibitor.

PubMed

Bartesaghi, Alberto; Merk, Alan; Banerjee, Soojay; Matthies, Doreen; Wu, Xiongwu; Milne, Jacqueline L S; Subramaniam, Sriram

2015-06-05

Cryo-electron microscopy (cryo-EM) is rapidly emerging as a powerful tool for protein structure determination at high resolution. Here we report the structure of a complex between Escherichia coli β-galactosidase and the cell-permeant inhibitor phenylethyl β-D-thiogalactopyranoside (PETG), determined by cryo-EM at an average resolution of ~2.2 angstroms (Å). Besides the PETG ligand, we identified densities in the map for ~800 water molecules and for magnesium and sodium ions. Although it is likely that continued advances in detector technology may further enhance resolution, our findings demonstrate that preparation of specimens of adequate quality and intrinsic protein flexibility, rather than imaging or image-processing technologies, now represent the major bottlenecks to routinely achieving resolutions close to 2 Å using single-particle cryo-EM. Copyright © 2015, American Association for the Advancement of Science.

PFISR GPS tracking mode for researching high-latitude ionospheric electron density gradients associated with GPS scintillation

NASA Astrophysics Data System (ADS)

Loucks, D. C.; Palo, S. E.; Pilinski, M.; Crowley, G.; Azeem, S. I.; Hampton, D. L.

2016-12-01

Ionospheric behavior in the high-latitudes can significantly impact Ultra High Frequency (UHF) signals in the 300 MHz to 3 GHz band, resulting in degradation of Global Positioning System (GPS) position solutions and satellite communications interruptions. To address these operational concerns, a need arises to identify and understand the ionospheric structure that leads to disturbed conditions in the Arctic. Structures in the high-latitude ionosphere are known to change on the order of seconds or less, can be decameters to kilometers in scale, and elongate across magnetic field lines at auroral latitudes. Nominal operations at Poker Flat Incoherent Scatter Radar (PFISR) give temporal resolution on the order of minutes, and range resolution on the order of tens of kilometers, while specialized GPS receivers available for ionospheric sensing have a 100Hz observation sampling rate. One of these, ASTRA's Connected Autonomous Space Environment Sensor (CASES) is used for this study. We have developed a new GPS scintillation tracking mode for PFISR to address open scientific questions regarding temporal and spatial electron density gradients. The mode will be described, a number of experimental campaigns will be analyzed, and results and lessons learned will be presented.

Swift heavy ion track formation in Gd2Zr2-xTixO7 pyrochlore: Effect of electronic energy loss

NASA Astrophysics Data System (ADS)

Lang, Maik; Toulemonde, Marcel; Zhang, Jiaming; Zhang, Fuxiang; Tracy, Cameron L.; Lian, Jie; Wang, Zhongwu; Weber, William J.; Severin, Daniel; Bender, Markus; Trautmann, Christina; Ewing, Rodney C.

2014-10-01

The morphology of swift heavy ion tracks in the Gd2Zr2-xTixO7 pyrochlore system has been investigated as a function of the variation in chemical composition and electronic energy loss, dE/dx, over a range of energetic ions: 58Ni, 101Ru, 129Xe, 181Ta, 197Au, 208Pb, and 238U of 11.1 MeV/u specific energy. Bright-field transmission electron microscopy, synchrotron X-ray diffraction, and Raman spectroscopy reveal an increasing degree of amorphization with increasing Ti-content and dE/dx. The size and morphology of individual ion tracks in Gd2Ti2O7 were characterized by high-resolution transmission electron microscopy revealing a core-shell structure with an outer defect-fluorite dominated shell at low dE/dx to predominantly amorphous tracks at high dE/dx. Inelastic thermal-spike calculations have been used together with atomic-scale characterization of ion tracks in Gd2Ti2O7 by high resolution transmission electron microscopy to deduce critical energy densities for the complex core-shell morphologies induced by ions of different dE/dx.

Atomic-resolution characterization of the effects of CdCl2 treatment on poly-crystalline CdTe thin films

NASA Astrophysics Data System (ADS)

Paulauskas, T.; Buurma, C.; Colegrove, E.; Guo, Z.; Sivananthan, S.; Chan, M. K. Y.; Klie, R. F.

2014-08-01

Poly-crystalline CdTe thin films on glass are used in commercial solar-cell superstrate devices. It is well known that post-deposition annealing of the CdTe thin films in a CdCl2 environment significantly increases the device performance, but a fundamental understanding of the effects of such annealing has not been achieved. In this Letter, we report a change in the stoichiometry across twin boundaries in CdTe and propose that native point defects alone cannot account for this variation. Upon annealing in CdCl2, we find that the stoichiometry is restored. Our experimental measurements using atomic-resolution high-angle annular dark field imaging, electron energy-loss spectroscopy, and energy dispersive X-ray spectroscopy in a scanning transmission electron microscope are supported by first-principles density functional theory calculations.

Electron-stimulated purification of platinum nanostructures grown via focused electron beam induced deposition

DOE PAGES

Lewis, Brett B.; Stanford, Michael G.; Fowlkes, Jason D.; ...

2015-04-08

In this paper, platinum–carbon nanostructures deposited via electron beam induced deposition from MeCpPt(IV)Me 3 are purified during a post-deposition electron exposure treatment in a localized oxygen ambient at room temperature. Time-dependent studies demonstrate that the process occurs from the top–down. Electron beam energy and current studies demonstrate that the process is controlled by a confluence of the electron energy loss and oxygen concentration. Furthermore, the experimental results are modeled as a 2nd order reaction which is dependent on both the electron energy loss density and the oxygen concentration. Finally, in addition to purification, the post-deposition electron stimulated oxygen purification processmore » enhances the resolution of the EBID process due to the isotropic carbon removal from the as-deposited materials which produces high-fidelity shape retention.« less

Conceptual Design of Electron-Beam Generated Plasma Tools

NASA Astrophysics Data System (ADS)

Agarwal, Ankur; Rauf, Shahid; Dorf, Leonid; Collins, Ken; Boris, David; Walton, Scott

2015-09-01

Realization of the next generation of high-density nanostructured devices is predicated on etching features with atomic layer resolution, no damage and high selectivity. High energy electron beams generate plasmas with unique features that make them attractive for applications requiring monolayer precision. In these plasmas, high energy beam electrons ionize the background gas and the resultant daughter electrons cool to low temperatures via collisions with gas molecules and lack of any accelerating fields. For example, an electron temperature of <0.6 eV with densities comparable to conventional plasma sources can be obtained in molecular gases. The chemistry in such plasmas can significantly differ from RF plasmas as the ions/radicals are produced primarily by beam electrons rather than those in the tail of a low energy distribution. In this work, we will discuss the conceptual design of an electron beam based plasma processing system. Plasma properties will be discussed for Ar, Ar/N2, and O2 plasmas using a computational plasma model, and comparisons made to experiments. The fluid plasma model is coupled to a Monte Carlo kinetic model for beam electrons which considers gas phase collisions and the effect of electric and magnetic fields on electron motion. The impact of critical operating parameters such as magnetic field, beam energy, and gas pressure on plasma characteristics in electron-beam plasma processing systems will be discussed. Partially supported by the NRL base program.

Control of Wigner localization and electron cavity effects in near-field emission spectra of In(Ga)P/GaInP quantum-dot structures

NASA Astrophysics Data System (ADS)

Mintairov, A. M.; Kapaldo, J.; Merz, J. L.; Rouvimov, S.; Lebedev, D. V.; Kalyuzhnyy, N. A.; Mintairov, S. A.; Belyaev, K. G.; Rakhlin, M. V.; Toropov, A. A.; Brunkov, P. N.; Vlasov, A. S.; Zadiranov, Yu. M.; Blundell, S. A.; Mozharov, A. M.; Mukhin, I.; Yakimov, M.; Oktyabrsky, S.; Shelaev, A. V.; Bykov, V. A.

2018-05-01

Structural and emission properties of few-electron In(Ga)P/GaInP quantum dots (QDs) representing natural Wigner molecules (WM) and whispering gallery mode (WGM) electron (e ) cavities have been investigated. QD structures were grown using self-organized metal-organic vapor phase epitaxy and deposition from ˜3 to 7 monolayers of InP at 700 °C. Using atomic force microscopy, transmission electron microscopy, near-field scanning optical microscopy (NSOM), and μ -photoluminescence (μ -PL) spectra we obtained In(Ga)P/GaInP QDs having lateral size 80-180 nm, height 5-30 nm, Ga content 0.0-0.4, density 2 -10 μm-2 , and electron population up to 20 and demonstrated control of their density and size distribution. Using high-spatial-resolution low-temperature PL spectra, NSOM imaging, and calculations of charge density distributions we observed Wigner localization and e -cavity effects for a series of dots having quantum confinement ℏ ω0=0.5 -6 meV . We used these data together with time-resolved PL measurements to clarify the effect of Coulomb interaction and WM formation on emission spectra of few-electron QDs. We present direct observation of 2 e , 6 e , and 9 e WMs; 2 e and 4 e WGMs; and Fabry-Perot e modes and establish conditions of e -WGM-cavity formation in these QDs.

Three-dimensional structure of basal body triplet revealed by electron cryo-tomography

PubMed Central

Li, Sam; Fernandez, Jose-Jesus; Marshall, Wallace F; Agard, David A

2012-01-01

Basal bodies and centrioles play central roles in microtubule (MT)-organizing centres within many eukaryotes. They share a barrel-shaped cylindrical structure composed of nine MT triplet blades. Here, we report the structure of the basal body triplet at 33 Å resolution obtained by electron cryo-tomography and 3D subtomogram averaging. By fitting the atomic structure of tubulin into the EM density, we built a pseudo-atomic model of the tubulin protofilaments at the core of the triplet. The 3D density map reveals additional densities that represent non-tubulin proteins attached to the triplet, including a large inner circular structure in the basal body lumen, which functions as a scaffold to stabilize the entire basal body barrel. We found clear longitudinal structural variations along the basal body, suggesting a sequential and coordinated assembly mechanism. We propose a model in which δ-tubulin and other components participate in the assembly of the basal body. PMID:22157822

A Pair Production Telescope for Medium-Energy Gamma-Ray Polarimetry

NASA Technical Reports Server (NTRS)

Hunter, Stanley D.; Bloser, Peter F.; Depaola, Gerardo; Dion, Michael P.; DeNolfo, Georgia A.; Hanu, Andrei; Iparraguirre, Marcos; Legere, Jason; Longo, Francesco; McConnell, Mark L.;

Conduction at domain walls in oxide multiferroics

NASA Astrophysics Data System (ADS)

Seidel, J.; Martin, L. W.; He, Q.; Zhan, Q.; Chu, Y.-H.; Rother, A.; Hawkridge, M. E.; Maksymovych, P.; Yu, P.; Gajek, M.; Balke, N.; Kalinin, S. V.; Gemming, S.; Wang, F.; Catalan, G.; Scott, J. F.; Spaldin, N. A.; Orenstein, J.; Ramesh, R.

2009-03-01

Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO3. The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features.

Conduction at domain walls in oxide multiferroics.

PubMed

Seidel, J; Martin, L W; He, Q; Zhan, Q; Chu, Y-H; Rother, A; Hawkridge, M E; Maksymovych, P; Yu, P; Gajek, M; Balke, N; Kalinin, S V; Gemming, S; Wang, F; Catalan, G; Scott, J F; Spaldin, N A; Orenstein, J; Ramesh, R

2009-03-01

Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO(3). The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features.

Monitoring long-range electron transfer pathways in proteins by stimulated attosecond broadband X-ray Raman spectroscopy

DOE PAGES

Zhang, Yu; Biggs, Jason D.; Govind, Niranjan; ...

2014-10-09

In this study, long-range electron transfer (ET) plays a key role in many biological energy conversion and synthesis processes. We show that nonlinear spectroscopy with attosecond X-ray pulses provides a real time movie of the evolving oxidation states and electron densities around atoms, and can probe these processes with high spatial and temporal resolution. This is demonstrated in a simulation study of the stimulated X-ray Raman (SXRS) signals in Re-modified azurin, which had long served as a benchmark for long-range ET in proteins. Nonlinear SXRS signals are sensitive to the local electronic structure and should offer a novel window formore » long-range ET.« less

Digital direct electron imaging of energy-filtered electron backscatter diffraction patterns

NASA Astrophysics Data System (ADS)

Vespucci, S.; Winkelmann, A.; Naresh-Kumar, G.; Mingard, K. P.; Maneuski, D.; Edwards, P. R.; Day, A. P.; O'Shea, V.; Trager-Cowan, C.

2015-11-01

Electron backscatter diffraction is a scanning electron microscopy technique used to obtain crystallographic information on materials. It allows the nondestructive mapping of crystal structure, texture, and strain with a lateral and depth resolution on the order of tens of nanometers. Electron backscatter diffraction patterns (EBSPs) are presently acquired using a detector comprising a scintillator coupled to a digital camera, and the crystallographic information obtainable is limited by the conversion of electrons to photons and then back to electrons again. In this article we will report the direct acquisition of energy-filtered EBSPs using a digital complementary metal-oxide-semiconductor hybrid pixel detector, Timepix. We show results from a range of samples with different mass and density, namely diamond, silicon, and GaN. Direct electron detection allows the acquisition of EBSPs at lower (≤5 keV) electron beam energies. This results in a reduction in the depth and lateral extension of the volume of the specimen contributing to the pattern and will lead to a significant improvement in lateral and depth resolution. Direct electron detection together with energy filtering (electrons having energy below a specific value are excluded) also leads to an improvement in spatial resolution but in addition provides an unprecedented increase in the detail in the acquired EBSPs. An increase in contrast and higher-order diffraction features are observed. In addition, excess-deficiency effects appear to be suppressed on energy filtering. This allows the fundamental physics of pattern formation to be interrogated and will enable a step change in the use of electron backscatter diffraction (EBSD) for crystal phase identification and the mapping of strain. The enhancement in the contrast in high-pass energy-filtered EBSD patterns is found to be stronger for lighter, less dense materials. The improved contrast for such materials will enable the application of the EBSD technique to be expanded to materials for which conventional EBSD analysis is not presently practicable.

First principles study of NH3 adsorption on carbon nanowires

NASA Astrophysics Data System (ADS)

Tapia, Jorge-Alejandro; Sanchez, Alvaro-Daniel; Acosta, Cesar; Canto, Gabriel

2009-03-01

Recently has been reported a new type of one-dimensional carbon structures. Carbon nanowires formed by a linear carbon-atom chain inside an armchair (5,5) carbon nanotube has been observed using high-resolution transmission electron microscopy. Theoretical and experimental studies of the NH3 adsorption in the carbon nanotubes report changes in the electronic properties of the carbon nanotubes. In the present work we have studied the electronic and structure properties of carbon nanowires (chain@SWCNT) when NH3 atoms are adsorbed. We used the Density Functional Theory and the calculations where performed by the pseudopotentials LCAO method (SIESTA code) and the Generalized Gradient Approximation (GGA) for the exchange-correlation potential. We have analyzed the changes in the atomic structure and density of states (DOS). We found that the electronic character of the carbon chain of the chain@SWCNT system, can be modulate by NH3 adsorption. This research was supported by SEP under Grant No. PROMEP/103.5/07/2595 and the Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grants No. 82497 and 60534.

Coherent X-Ray Diffraction Imaging of Chloroplasts from Cyanidioschyzon merolae by Using X-Ray Free Electron Laser.

PubMed

Takayama, Yuki; Inui, Yayoi; Sekiguchi, Yuki; Kobayashi, Amane; Oroguchi, Tomotaka; Yamamoto, Masaki; Matsunaga, Sachihiro; Nakasako, Masayoshi

2015-07-01

Coherent X-ray diffraction imaging (CXDI) is a lens-less technique for visualizing the structures of non-crystalline particles with the dimensions of submicrometer to micrometer at a resolution of several tens of nanometers. We conducted cryogenic CXDI experiments at 66 K to visualize the internal structures of frozen-hydrated chloroplasts of Cyanidioschyzon merolae using X-ray free electron laser (XFEL) as a coherent X-ray source. Chloroplast dispersed specimen disks at a number density of 7/(10×10 µm(2)) were flash-cooled with liquid ethane without staining, sectioning or chemical labeling. Chloroplasts are destroyed at atomic level immediately after the diffraction by XFEL pulses. Thus, diffraction patterns with a good signal-to-noise ratio from single chloroplasts were selected from many diffraction patterns collected through scanning specimen disks to provide fresh specimens into the irradiation area. The electron density maps of single chloroplasts projected along the direction of the incident X-ray beam were reconstructed by using the iterative phase-retrieval method and multivariate analyses. The electron density map at a resolution of 70 nm appeared as a C-shape. In addition, the fluorescence image of proteins stained with Flamingo™ dye also appeared as a C-shape as did the autofluorescence from Chl. The similar images suggest that the thylakoid membranes with an abundance of proteins distribute along the outer membranes of chloroplasts. To confirm the present results statistically, a number of projection structures must be accumulated through high-throughput data collection in the near future. Based on the results, we discuss the feasibility of XFEL-CXDI experiments in the structural analyses of cellular organelles. © The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Preliminary neutron and X-ray crystallographic studies of equine cyanomethemoglobin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovalevsky, A.Y.; Fisher, S.Z.; Seaver, S.

2010-08-18

Room-temperature and 100 K X-ray and room-temperature neutron diffraction data have been measured from equine cyanomethemoglobin to 1.7 {angstrom} resolution using a home source, to 1.6 {angstrom} resolution on NE-CAT at the Advanced Photon Source and to 2.0 {angstrom} resolution on the PCS at Los Alamos Neutron Science Center, respectively. The cyanomethemoglobin is in the R state and preliminary room-temperature electron and neutron scattering density maps clearly show the protonation states of potential Bohr groups. Interestingly, a water molecule that is in the vicinity of the heme group and coordinated to the distal histidine appears to be expelled from thismore » site in the low-temperature structure.« less

High Temporal and Spatial Resolution Global GPS TEC Observations of the 2015 St. Patrick Day Storm

NASA Astrophysics Data System (ADS)

Vierinen, J.

2015-12-01

High spatiotemperal resolution global GPS TEC measurements of the 2015 St. Patrick's day storm are presented. The high resolution data is useful, as it clearly shows the high latitude convection patterns, the equatorward progression of the auroral region, the tongue of ionization, as well as the increased electron density in the equatorial anomaly region. The measurements are compared with high power large aperture radar and passive radar measurements of coherent and incoherent scatter at Millstone Hill. Regions of fast convection identified in the GPS TEC data are found to coincide with coherent scatter in both radar data. Convection velocities determined from GPS TEC are compared with those obtained from incoherent scatter radar measurements.

Measurements of mass attenuation coefficient, effective atomic number and electron density of some amino acids

NASA Astrophysics Data System (ADS)

Kore, Prashant S.; Pawar, Pravina P.

2014-05-01

The mass attenuation coefficients of some amino acids, such as DL-aspartic acid-LR(C4H7NO4), L-glutamine (C4H10N2O3), creatine monohydrate LR(C4H9N3O2H2O), creatinine hydrochloride (C4H7N3O·HCl) L-asparagine monohydrate(C4H9N3O2H2O), L-methionine LR(C5H11NO2S), were measured at 122, 356, 511, 662, 1170, 1275 and 1330 keV photon energies using a well-collimated narrow beam good geometry set-up. The gamma-rays were detected using NaI (Tl) scintillation detection system with a resolution of 0.101785 at 662 keV. The attenuation coefficient data were then used to obtain the effective atomic numbers (Zeff), and effective electron densities (Neff) of amino acids. It was observed that the effective atomic number (Zeff) and effective electron densities (Neff) initially decrease and tend to be almost constant as a function of gamma-ray energy. Zeff and Neff experimental values showed good agreement with the theoretical values with less than 1% error for amino acids.

Doppler measurements of the ionosphere on the occasion of the Apollo-Soyuz test project. Part 1: Computer simulation of ionospheric-induced Doppler shifts

NASA Technical Reports Server (NTRS)

Grossi, M. D.; Gay, R. H.

1975-01-01

A computer simulation of the ionospheric experiment of the Apollo-Soyuz Test Project (ASTP) was performed. ASTP is the first example of USA/USSR cooperation in space and is scheduled for summer 1975. The experiment consists of performing dual-frequency Doppler measurements (at 162 and 324 MHz) between the Apollo Command Service Module (CSM) and the ASTP Docking Module (DM), both orbiting at 221-km height and at a relative distance of 300 km. The computer simulation showed that, with the Doppler measurement resolution of approximately 3 mHz provided by the instrumentation (in 10-sec integration time), ionospheric-induced Doppler shifts will be measurable accurately at all times, with some rare exceptions occurring when the radio path crosses regions of minimum ionospheric density. The computer simulation evaluated the ability of the experiment to measure changes of columnar electron content between CSM and DM (from which horizontal gradients of electron density at 221-km height can be obtained) and to measure variations in DM-to-ground columnar content (from which an averaged columnar content and the electron density at the DM can be deduced, under some simplifying assumptions).

On the transferability of electron density in binary vanadium borides VB, V3B4 and VB2.

PubMed

Terlan, Bürgehan; Akselrud, Lev; Baranov, Alexey I; Borrmann, Horst; Grin, Yuri

2015-12-01

Binary vanadium borides are suitable model systems for a systematic analysis of the transferability concept in intermetallic compounds due to chemical intergrowth in their crystal structures. In order to underline this structural relationship, topological properties of the electron density in VB, V3B4 and VB2 reconstructed from high-resolution single-crystal X-ray diffraction data as well as derived from quantum chemical calculations, are analysed in terms of Bader's Quantum Theory of Atoms in Molecules [Bader (1990). Atoms in Molecules: A Quantum Theory, 1st ed. Oxford: Clarendon Press]. The compounds VB, V3B4 and VB2 are characterized by a charge transfer from the metal to boron together with two predominant atomic interactions, the shared covalent B-B interactions and the polar covalent B-M interactions. The resembling features of the crystal structures are well reflected by the respective B-B interatomic distances as well as by ρ(r) values at the B-B bond critical points. The latter decrease with an increase in the corresponding interatomic distances. The B-B bonds show transferable electron density properties at bond critical points depending on the respective bond distances.

Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers

DOE PAGES

Kluge, T.; Rödel, C.; Rödel, M.; ...

2017-10-23

In this paper, we study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibilitymore » of the method. Finally, we present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system.« less

Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kluge, T.; Rödel, C.; Rödel, M.

In this paper, we study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibilitymore » of the method. Finally, we present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system.« less

3D tomography of midlatitude sporadic-E in Japan from GNSS-TEC data

NASA Astrophysics Data System (ADS)

Muafiry, Ihsan Naufal; Heki, Kosuke; Maeda, Jun

2018-03-01

We studied ionospheric irregularities caused by midlatitude sporadic-E ( Es) in Japan using ionospheric total electron content (TEC) data from a dense GNSS array, GEONET, with a 3D (three-dimensional) tomography technique. Es is a thin layer of unusually high ionization that appears at altitudes of 100 km. Here, we studied five cases of Es irregularities in 2010 and 2012, also reported in previous studies, over the Kanto and Kyushu Districts. We used slant TEC residuals as the input and estimated the number of electron density anomalies of more than 2000 small blocks with dimensions of 20-30 km covering a horizontal region of 300 × 500 km. We applied a continuity constraint to stabilize the solution and performed several different resolution tests with synthetic data to assess the accuracy of the results. The tomography results showed that positive electron density anomalies occurred at the E region height, and the morphology and dynamics were consistent with those reported by earlier studies.

Chorus Waves Modulation of Langmuir Waves in the Radiation Belts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jinxing; Bortnik, Jacob; An, Xin

Using high-resolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, rising-tone whistler-mode chorus emissions exhibit a one-to-one correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E || component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermalmore » electrons via Landau resonance, and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. As a result, this microscale interaction between chorus waves and high frequency electrostatic waves provides a new insight into the nonlinear wave-particle interaction process.« less

Chorus Waves Modulation of Langmuir Waves in the Radiation Belts

DOE PAGES

Li, Jinxing; Bortnik, Jacob; An, Xin; ...

2017-11-20

Using high-resolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, rising-tone whistler-mode chorus emissions exhibit a one-to-one correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E || component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermalmore » electrons via Landau resonance, and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. As a result, this microscale interaction between chorus waves and high frequency electrostatic waves provides a new insight into the nonlinear wave-particle interaction process.« less

High-yield, ultrafast, surface plasmon-enhanced, Au nanorod optical field electron emitter arrays.

PubMed

Hobbs, Richard G; Yang, Yujia; Fallahi, Arya; Keathley, Philip D; De Leo, Eva; Kärtner, Franz X; Graves, William S; Berggren, Karl K

2014-11-25

Here we demonstrate the design, fabrication, and characterization of ultrafast, surface-plasmon enhanced Au nanorod optical field emitter arrays. We present a quantitative study of electron emission from Au nanorod arrays fabricated by high-resolution electron-beam lithography and excited by 35 fs pulses of 800 nm light. We present accurate models for both the optical field enhancement of Au nanorods within high-density arrays, and electron emission from those nanorods. We have also studied the effects of surface plasmon damping induced by metallic interface layers at the substrate/nanorod interface on near-field enhancement and electron emission. We have identified the peak optical field at which the electron emission mechanism transitions from a 3-photon absorption mechanism to strong-field tunneling emission. Moreover, we have investigated the effects of nanorod array density on nanorod charge yield, including measurement of space-charge effects. The Au nanorod photocathodes presented in this work display 100-1000 times higher conversion efficiency relative to previously reported UV triggered emission from planar Au photocathodes. Consequently, the Au nanorod arrays triggered by ultrafast pulses of 800 nm light in this work may outperform equivalent UV-triggered Au photocathodes, while also offering nanostructuring of the electron pulse produced from such a cathode, which is of interest for X-ray free-electron laser (XFEL) development where nanostructured electron pulses may facilitate more efficient and brighter XFEL radiation.

Use of noncrystallographic symmetry for automated model building at medium to low resolution.

PubMed

Wiegels, Tim; Lamzin, Victor S

2012-04-01

A novel method is presented for the automatic detection of noncrystallographic symmetry (NCS) in macromolecular crystal structure determination which does not require the derivation of molecular masks or the segmentation of density. It was found that throughout structure determination the NCS-related parts may be differently pronounced in the electron density. This often results in the modelling of molecular fragments of variable length and accuracy, especially during automated model-building procedures. These fragments were used to identify NCS relations in order to aid automated model building and refinement. In a number of test cases higher completeness and greater accuracy of the obtained structures were achieved, specifically at a crystallographic resolution of 2.3 Å or poorer. In the best case, the method allowed the building of up to 15% more residues automatically and a tripling of the average length of the built fragments.

Compression of high-density 0.16 pC electron bunches through high field gradients for ultrafast single shot electron diffraction: The Compact RF Gun

PubMed Central

Daoud, Hazem; Floettmann, Klaus; Dwayne Miller, R. J.

2017-01-01

We present an RF gun design for single shot ultrafast electron diffraction experiments that can produce sub-100 fs high-charge electron bunches in the 130 keV energy range. Our simulations show that our proposed half-cell RF cavity is capable of producing 137 keV, 27 fs rms (60 fs FWHM), 106 electron bunches with an rms spot size of 276 μm and a transverse coherence length of 2.0 nm. The required operation power is 9.2 kW, significantly lower than conventional rf cavity designs and a key design feature. This electron source further relies on high electric field gradients at the cathode to simultaneously accelerate and compress the electron bunch to open up new space-time resolution domains for atomically resolved dynamics. PMID:28428973

A dominant electron trap in molecular beam epitaxial InAlN lattice-matched to GaN

NASA Astrophysics Data System (ADS)

Pandey, Ayush; Bhattacharya, Aniruddha; Cheng, Shaobo; Botton, Gianluigi A.; Mi, Zetian; Bhattacharya, Pallab

2018-04-01

Deep levels in lattice-matched undoped and Si-doped InAlN/GaN grown by plasma-assisted molecular beam epitaxy have been identified and characterized by capacitance and photocapacitance measurements. From x-ray diffraction, reflectance measurements, electron energy loss spectroscopy and high-resolution transmission electron microscopy it is evident that the material has two distinct phases with different compositions. These correspond to In compositions of 18.1% and 25.8%, with corresponding bandgaps of 4.6 eV and 4.1 eV, respectively. The lower bandgap material is present as columnar microstructures in the form of quantum wires. A dominant electron trap with an activation energy of 0.293  ±  0.01 eV, a small capture cross-section of (1.54  ±  0.25)  ×  10-18 cm2, and density increasing linearly with Si doping density is identified in all the samples. The characteristics of the electron trap and variation of diode capacitance are discussed in the context of carrier dynamics involving the dominant trap level and the quantum wires.

Conformable actively multiplexed high-density surface electrode array for brain interfacing

DOEpatents

Rogers, John; Kim, Dae-Hyeong; Litt, Brian; Viventi, Jonathan

2015-01-13

Provided are methods and devices for interfacing with brain tissue, specifically for monitoring and/or actuation of spatio-temporal electrical waveforms. The device is conformable having a high electrode density and high spatial and temporal resolution. A conformable substrate supports a conformable electronic circuit and a barrier layer. Electrodes are positioned to provide electrical contact with a brain tissue. A controller monitors or actuates the electrodes, thereby interfacing with the brain tissue. In an aspect, methods are provided to monitor or actuate spatio-temporal electrical waveform over large brain surface areas by any of the devices disclosed herein.

Effects of Digitization and JPEG Compression on Land Cover Classification Using Astronaut-Acquired Orbital Photographs

NASA Technical Reports Server (NTRS)

Robinson, Julie A.; Webb, Edward L.; Evangelista, Arlene

2000-01-01

Studies that utilize astronaut-acquired orbital photographs for visual or digital classification require high-quality data to ensure accuracy. The majority of images available must be digitized from film and electronically transferred to scientific users. This study examined the effect of scanning spatial resolution (1200, 2400 pixels per inch [21.2 and 10.6 microns/pixel]), scanning density range option (Auto, Full) and compression ratio (non-lossy [TIFF], and lossy JPEG 10:1, 46:1, 83:1) on digital classification results of an orbital photograph from the NASA - Johnson Space Center archive. Qualitative results suggested that 1200 ppi was acceptable for visual interpretive uses for major land cover types. Moreover, Auto scanning density range was superior to Full density range. Quantitative assessment of the processing steps indicated that, while 2400 ppi scanning spatial resolution resulted in more classified polygons as well as a substantially greater proportion of polygons < 0.2 ha, overall agreement between 1200 ppi and 2400 ppi was quite high. JPEG compression up to approximately 46:1 also did not appear to have a major impact on quantitative classification characteristics. We conclude that both 1200 and 2400 ppi scanning resolutions are acceptable options for this level of land cover classification, as well as a compression ratio at or below approximately 46:1. Auto range density should always be used during scanning because it acquires more of the information from the film. The particular combination of scanning spatial resolution and compression level will require a case-by-case decision and will depend upon memory capabilities, analytical objectives and the spatial properties of the objects in the image.

Vertically grown nanowire crystals of dibenzotetrathienocoronene (DBTTC) on large-area graphene

DOE PAGES

Kim, B.; Chiu, C. -Y.; Kang, S. J.; ...

2016-06-01

Here we demonstrate controlled growth of vertical organic crystal nanowires on single layer graphene. Using Scanning Electron Microscopy (SEM), high-resolution transition electron microscopy (TEM), and Grazing Incidence X-ray Diffraction (GIXD), we probe the microstructure and morphology of dibenzotetrathienocoronene (DBTTC) nanowires epitaxially grown on graphene. The investigation is performed at both the ensemble and single nanowire level, and as function of growth parameters, providing insight of and control over the formation mechanism. Finally, the size, density and height of the nanowires can be tuned via growth conditions, opening new avenues for tailoring three-dimensional (3-D) nanostructured architectures for organic electronics with improvedmore » functional performance.« less

Electrical conduction at domain walls in multiferroic BiFeO3

NASA Astrophysics Data System (ADS)

Seidel, Jan; Martin, Lane; He, Qing; Zhan, Qian; Chu, Ying-Hao; Rother, Axel; Hawkridge, Michael; Maksymovych, Peter; Yu, Pu; Gajek, Martin; Balke, Nina; Kalinin, Sergei; Gemming, Sybille; Wang, Feng; Catalán, Gustau; Scott, James; Spaldin, Nicola; Orenstein, Joseph; Ramesh, Ramamoorthy

2009-03-01

We report the observation of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. The origin and nature of the observed conductivity is probed using a combination of conductive atomic force microscopy, high resolution transmission electron microscopy and first-principles density functional computations. We show that a structurally driven change in both the electrostatic potential and local electronic structure (i.e., a decrease in band gap) at the domain wall leads to the observed electrical conductivity. We estimate the conductivity in the wall to be several orders of magnitude higher than for the bulk material. Additionally we demonstrate the potential for device applications of such conducting nanoscale features.

Organic Power Electronics: Transistor Operation in the kA/cm2 Regime

PubMed Central

Klinger, Markus P.; Fischer, Axel; Kaschura, Felix; Widmer, Johannes; Kheradmand-Boroujeni, Bahman; Ellinger, Frank; Leo, Karl

2017-01-01

In spite of interesting features as flexibility, organic thin-film transistors have commercially lagged behind due to the low mobilities of organic semiconductors associated with hopping transport. Furthermore, organic transistors usually have much larger channel lengths than their inorganic counterparts since high-resolution structuring is not available in low-cost production schemes. Here, we present an organic permeable-base transistor (OPBT) which, despite extremely simple processing without any high-resolution structuring, achieve a performance beyond what has so far been possible using organic semiconductors. With current densities above 1 kA cm−2 and switching speeds towards 100 MHz, they open the field of organic power electronics. Finding the physical limits and an effective mobility of only 0.06 cm2 V−1 s−1, this OPBT device architecture has much more potential if new materials optimized for its geometry will be developed. PMID:28303924

Phonon spectrum of single-crystalline FeSe probed by high-resolution electron energy-loss spectroscopy

NASA Astrophysics Data System (ADS)

Zakeri, Khalil; Engelhardt, Tobias; Le Tacon, Matthieu; Wolf, Thomas

2018-06-01

Utilizing high-resolution electron energy-loss spectroscopy (HREELS) we measure the phonon frequencies of β-FeSe(001), cleaved under ultra-high vacuum conditions. At the zone center (Γ bar-point) three prominent loss features are observed at loss energies of about ≃ 20.5 and 25.6 and 40 meV. Based on the scattering selection rules we assign the observed loss features to the A1g, B1g, and A2u phonon modes of β-FeSe(001). The experimentally measured phonon frequencies do not agree with the results of density functional based calculations in which a nonmagnetic, a checkerboard or a strip antiferromagnetic order is assumed for β-FeSe(001). Our measurements suggest that, similar to the other Fe-based materials, magnetism has a profound impact on the lattice dynamics of β-FeSe(001).

High resolution X-ray spectra of solar flares. V - Interpretation of inner-shell transitions in Fe XX-Fe XXIII

NASA Technical Reports Server (NTRS)

Doschek, G. A.; Feldman, U.; Cowan, R. D.

1981-01-01

The paper examines high-resolution solar flare iron line spectra recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval Research Laboratory on an Air Force spacecraft launched on 1979 February 24. The emission line spectrum is due to inner-shell transitions in the ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line intensities obtained by methods discussed by Merts, Cowan, and Magee (1976), electron temperatures as a function of time for two large class X flares are derived. These temperatures are deduced from intensities of lines of Fe XXII, Fe XXIII, and Fe XXIV. The determination of the differential emission measure between about 12-million and 20-million K using these temperatures is considered. The possibility of determining electron densities in flare and tokamak plasmas using the inner-shell spectra of Fe XXI and Fe XX is discussed.

Flexible Organic Electronics for Use in Neural Sensing

PubMed Central

Bink, Hank; Lai, Yuming; Saudari, Sangameshwar R.; Helfer, Brian; Viventi, Jonathan; Van der Spiegel, Jan; Litt, Brian; Kagan, Cherie

2016-01-01

Recent research in brain-machine interfaces and devices to treat neurological disease indicate that important network activity exists at temporal and spatial scales beyond the resolution of existing implantable devices. High density, active electrode arrays hold great promise in enabling high-resolution interface with the brain to access and influence this network activity. Integrating flexible electronic devices directly at the neural interface can enable thousands of multiplexed electrodes to be connected using many fewer wires. Active electrode arrays have been demonstrated using flexible, inorganic silicon transistors. However, these approaches may be limited in their ability to be cost-effectively scaled to large array sizes (8×8 cm). Here we show amplifiers built using flexible organic transistors with sufficient performance for neural signal recording. We also demonstrate a pathway for a fully integrated, amplified and multiplexed electrode array built from these devices. PMID:22255558

Crystallization and preliminary X-ray analysis of the inducible lysine decarboxylase from Escherichia coli

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexopoulos, E.; Kanjee, U.; Snider, J.

2010-02-11

The decameric inducible lysine decarboxylase (LdcI) from Escherichia coli has been crystallized in space groups C2 and C222{sub 1}; the Ta{sub 6}Br{sub 12}{sup 2+} cluster was used to derivatize the C2 crystals. The method of single isomorphous replacement with anomalous scattering (SIRAS) as implemented in SHELXD was used to solve the Ta{sub 6}Br{sub 12}{sup 2+}-derivatized structure to 5 {angstrom} resolution. Many of the Ta{sub 6}Br{sub 12}{sup 2+}-binding sites had twofold and fivefold noncrystallographic symmetry. Taking advantage of this feature, phase modification was performed in DM. The electron-density map of LdcI displays many features in agreement with the low-resolution negative-stain electron-densitymore » map [Snider et al. (2006), J. Biol. Chem. 281, 1532-1546].« less

Organic Power Electronics: Transistor Operation in the kA/cm2 Regime.

PubMed

Klinger, Markus P; Fischer, Axel; Kaschura, Felix; Widmer, Johannes; Kheradmand-Boroujeni, Bahman; Ellinger, Frank; Leo, Karl

2017-03-17

In spite of interesting features as flexibility, organic thin-film transistors have commercially lagged behind due to the low mobilities of organic semiconductors associated with hopping transport. Furthermore, organic transistors usually have much larger channel lengths than their inorganic counterparts since high-resolution structuring is not available in low-cost production schemes. Here, we present an organic permeable-base transistor (OPBT) which, despite extremely simple processing without any high-resolution structuring, achieve a performance beyond what has so far been possible using organic semiconductors. With current densities above 1 kA cm -2 and switching speeds towards 100 MHz, they open the field of organic power electronics. Finding the physical limits and an effective mobility of only 0.06 cm 2  V -1  s -1 , this OPBT device architecture has much more potential if new materials optimized for its geometry will be developed.

Unraveling orbital hybridization of triplet emitters at the metal-organic interface.

PubMed

Ewen, Pascal R; Sanning, Jan; Doltsinis, Nikos L; Mauro, Matteo; Strassert, Cristian A; Wegner, Daniel

2013-12-27

We have investigated the structural and electronic properties of phosphorescent planar platinum(II) complexes at the interface of Au(111) with submolecular resolution using combined scanning tunneling microscopy and spectroscopy as well as density functional theory. Our analysis shows that molecule-substrate coupling and lateral intermolecular interactions are weak. While the ligand orbitals remain essentially unchanged upon contact with the substrate, we found modified electronic behavior at the Pt atom due to local hybridization and charge transfer to the substrate. Thus, this novel class of phosphorescent molecules exhibits well-defined and tunable interaction with its local environment.

Interpretation of monoclinic hafnia valence electron energy-loss spectra by time-dependent density functional theory

NASA Astrophysics Data System (ADS)

Hung, L.; Guedj, C.; Bernier, N.; Blaise, P.; Olevano, V.; Sottile, F.

2016-04-01

We present the valence electron energy-loss spectrum and the dielectric function of monoclinic hafnia (m -HfO2) obtained from time-dependent density-functional theory (TDDFT) predictions and compared to energy-filtered spectroscopic imaging measurements in a high-resolution transmission-electron microscope. Fermi's golden rule density-functional theory (DFT) calculations can capture the qualitative features of the energy-loss spectrum, but we find that TDDFT, which accounts for local-field effects, provides nearly quantitative agreement with experiment. Using the DFT density of states and TDDFT dielectric functions, we characterize the excitations that result in the m -HfO2 energy-loss spectrum. The sole plasmon occurs between 13 and 16 eV, although the peaks ˜28 and above 40 eV are also due to collective excitations. We furthermore elaborate on the first-principles techniques used, their accuracy, and remaining discrepancies among spectra. More specifically, we assess the influence of Hf semicore electrons (5 p and 4 f ) on the energy-loss spectrum, and find that the inclusion of transitions from the 4 f band damps the energy-loss intensity in the region above 13 eV. We study the impact of many-body effects in a DFT framework using the adiabatic local-density approximation (ALDA) exchange-correlation kernel, as well as from a many-body perspective using "scissors operators" matched to an ab initio G W calculation to account for self-energy corrections. These results demonstrate some cancellation of errors between self-energy and excitonic effects, even for excitations from the Hf 4 f shell. We also simulate the dispersion with increasing momentum transfer for plasmon and collective excitation peaks.

Development of a high resolution x-ray spectrometer for the National Ignition Facility (NIF)

DOE PAGES

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; ...

2016-09-28

A high resolution (E/ΔE = 1200-1800) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in National Ignition Facility experiments. The instrument will be a diagnostic instrument manipulator positioned cassette designed mainly to infer electron density in compressed capsules from Stark broadening of the helium-β (1s 2-1s3p) lines of krypton and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and focus (1) the Kr Heβ complex and (2) the Heα (1s 2-1s2p) and Lyα (1s-2p) complexes onto a streak camera photocathode for time resolved measurement, and a third cylindrical or conicalmore » crystal will focus the full Heα to Heβ spectral range onto an image plate to provide a time integrated calibration spectrum. Calculations of source x-ray intensity, spectrometer throughput, and spectral resolution are presented. Furthermore, details of the conical-crystal focusing properties as well as the status of the instrumental design are also presented.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manfrinato, Vitor R.; Stein, Aaron; Zhang, Lihua

Patterning materials efficiently at the smallest length scales has been a longstanding challenge in nanotechnology. Electron-beam lithography (EBL) is the primary method for patterning arbitrary features, but EBL has not reliably provided sub-4 nm patterns. The few competing techniques that have achieved this resolution are orders of magnitude slower than EBL. In this work, we employed an aberration-corrected scanning transmission electron microscope for lithography to achieve unprecedented resolution. Here we show aberration-corrected EBL at the one nanometer length scale using poly(methyl methacrylate) (PMMA) and have produced both the smallest isolated feature in any conventional resist (1.7 ± 0.5 nm) andmore » the highest density patterns in PMMA (10.7 nm pitch for negative-tone and 17.5 nm pitch for positive-tone PMMA). We also demonstrate pattern transfer from the resist to semiconductor and metallic materials at the sub-5 nm scale. These results indicate that polymer-based nanofabrication can achieve feature sizes comparable to the Kuhn length of PMMA and ten times smaller than its radius of gyration. Use of aberration-corrected EBL will increase the resolution, speed, and complexity in nanomaterial fabrication.« less

Development of a high resolution x-ray spectrometer for the National Ignition Facility (NIF).

PubMed

Hill, K W; Bitter, M; Delgado-Aparicio, L; Efthimion, P C; Ellis, R; Gao, L; Maddox, J; Pablant, N A; Schneider, M B; Chen, H; Ayers, S; Kauffman, R L; MacPhee, A G; Beiersdorfer, P; Bettencourt, R; Ma, T; Nora, R C; Scott, H A; Thorn, D B; Kilkenny, J D; Nelson, D; Shoup, M; Maron, Y

2016-11-01

A high resolution (E/ΔE = 1200-1800) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in National Ignition Facility experiments. The instrument will be a diagnostic instrument manipulator positioned cassette designed mainly to infer electron density in compressed capsules from Stark broadening of the helium-β (1s 2 -1s3p) lines of krypton and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and focus (1) the Kr Heβ complex and (2) the Heα (1s 2 -1s2p) and Lyα (1s-2p) complexes onto a streak camera photocathode for time resolved measurement, and a third cylindrical or conical crystal will focus the full Heα to Heβ spectral range onto an image plate to provide a time integrated calibration spectrum. Calculations of source x-ray intensity, spectrometer throughput, and spectral resolution are presented. Details of the conical-crystal focusing properties as well as the status of the instrumental design are also presented.

Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy

PubMed Central

König, Thomas; Simon, Georg H; Heinke, Lars; Lichtenstein, Leonid

2011-01-01

Summary Surfaces of thin oxide films were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001) and line defects in aluminum oxide on NiAl(110), respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM) and the electronic structure by scanning tunneling spectroscopy (STS). On magnesium oxide, different color centers, i.e., F0, F+, F2+ and divacancies, have different effects on the contact potential. These differences enabled classification and unambiguous differentiation by KPFM. True atomic resolution shows the topography at line defects in aluminum oxide. At these domain boundaries, STS and KPFM verify F2+-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide films beyond imaging the topography of the surface atoms. PMID:21977410

Fast front-end electronics for semiconductor tracking detectors: Trends and perspectives

NASA Astrophysics Data System (ADS)

Rivetti, Angelo

2014-11-01

In the past few years, extensive research efforts pursued by both the industry and the academia have lead to major improvements in the performance of Analog to Digital Converters (ADCs) and Time to Digital Converters (TDCs). ADCs achieving 8-10 bit resolution, 50-100 MHz conversion frequency and less than 1 mW power consumption are the today's standard, while TDCs have reached sub-picosecond time resolution. These results have been made possible by architectural upgrades combined with the use of ultra deep submicron CMOS technologies with minimum feature size of 130 nm or smaller. Front-end ASICs in which a prompt digitization is followed by signal conditioning in the digital domain can now be envisaged also within the tight power budget typically available in high density tracking systems. Furthermore, tracking detectors embedding high resolution timing capabilities are gaining interest. In the paper, ADC's and TDC's developments which are of particular relevance for the design front-end electronics for semiconductor trackers are discussed along with the benefits and challenges of exploiting such high performance building blocks in implementing the next generation of ASICs for high granularity particle detectors.

Ultrafast large-amplitude relocation of electronic charge in ionic crystals

PubMed Central

Zamponi, Flavio; Rothhardt, Philip; Stingl, Johannes; Woerner, Michael; Elsaesser, Thomas

2012-01-01

The interplay of vibrational motion and electronic charge relocation in an ionic hydrogen-bonded crystal is mapped by X-ray powder diffraction with a 100 fs time resolution. Photoexcitation of the prototype material KH2PO4 induces coherent low-frequency motions of the PO4 tetrahedra in the electronically excited state of the crystal while the average atomic positions remain unchanged. Time-dependent maps of electron density derived from the diffraction data demonstrate an oscillatory relocation of electronic charge with a spatial amplitude two orders of magnitude larger than the underlying vibrational lattice motions. Coherent longitudinal optical and tranverse optical phonon motions that dephase on a time scale of several picoseconds, drive the charge relocation, similar to a soft (transverse optical) mode driven phase transition between the ferro- and paraelectric phase of KH2PO4. PMID:22431621

On Spatial Structuring of the F2 Layer Studied by the Satellite Radio Sounding of the Ionosphere Disturbed by High-Power HF Radio Waves

NASA Astrophysics Data System (ADS)

Tereshchenko, E. D.; Turyansky, V. A.; Khudukon, B. Z.; Yurik, R. Yu.; Frolov, V. L.

2018-01-01

We present the results of studying the characteristics of the artificial plasma structures excited in the ionospheric F2 region modified by high-power HF radio waves. The experiments were carried out at the Sura heating facility using satellite radio sounding of the ionosphere. The plasma density profile was reconstructed with the highest possible spatial resolution for today, about 4 km. In a direction close to the magnetic zenith of the pump wave, the following phenomena were observed: the formation of a cavity with a 15% lower plasma density at the altitudes of the F2 layer and below; the formation of an area with plasma density increased by 12% at altitudes greater than 400 km. With a long-term quasiperiodic impact of the pump wave on the ionosphere, wavy large-scale electron-density perturbations (the meridional scale λx ≈ 130 km and the vertical scale λz ≈ 440 km) are also formed above the Sura facility. These perturbations can be due to the plasma density modulation by an artificial acoustic-gravity wave with a period of 10.6 m, which was formed by the heat source inside a large-scale cavity with low plasma density; there is generation of the electron density irregularities for the electrons with ΔNe/Ne ≈ 3% in the form of layers having the sizes 10-12 km along and about 24 km across the geomagnetic field, which are found both below and above the F2-layer maximum. The mechanisms of the formation of these plasma structures are discussed.

Opposite Latitudinal Dependence of the Premidnight and Postmidnight Oscillations in the Electron Density of Midlatitude F Layer

NASA Astrophysics Data System (ADS)

Chen, Gang; Wang, Jin; Zhang, Shaodong; Deng, Zhongxin; Zhong, Dingkun; Wu, Chen; Jin, Han; Li, Yaxian

2018-01-01

The dense observation points of the oblique-incidence ionosonde network in North China make it possible to discover the ionospheric regional variations with relatively high spatial resolution. The ionosonde network and the Beijing digisonde are used to investigate the ionospheric nighttime oscillations in January and February 2011. The electron density enhancements occurring before and after midnight present the obvious opposite latitudinal dependence in the time-latitude maps, which are composed by the differential critical frequency of F2 layer. The premidnight enhancements (PRMEs) appeared earlier in the north and then moved to south. The postmidnight enhancements (POMEs) did the opposite. The data analysis shows that the PRME was a part of the large-scale traveling ionospheric disturbance (LSTID), which may be produced by gravity waves. The southward propagation of the LSTIDs is considered to form the positive latitudinal dependence of the wave peaks and troughs. The postmidnight F layer oscillation was composed by a single enhancement and a single decline following it. The westward electric field-induced E × B drift, which pushed the F layer to lower altitudes with higher recombination loss, was most likely to compress the plasma and produce the POMEs. Along with the continuously dropping of the layer, the recombination loss exceeded the density increase due to the compression effect and then the electron density decline appeared.

Novel aspects of direct laser acceleration of relativistic electrons

NASA Astrophysics Data System (ADS)

Arefiev, Alexey

2015-11-01

Production of energetic electrons is a keystone aspect of ultraintense laser-plasma interactions that underpins a variety of topics and applications, including fast ignition inertial confinement fusion and compact particle and radiation sources. There is a wide range of electron acceleration regimes that depend on the duration of the laser pulse and the plasma density. This talk focuses on the regime in which the plasma is significantly underdense and the laser pulse duration is longer than the electron response time, so that, in contrast to the wakefield acceleration regime, the pulse creates a quasi-static channel in the electron density. Such a regime is of particular interest, since it can naturally arise in experiments with solid density targets where the pre-pulse of an ultraintense laser produces an extended sub-critical pre-plasma. This talk examines the impact of several key factors on electron acceleration by the laser pulse and the resulting electron energy gain. A detailed consideration is given to the role played by: (1) the static longitudinal electric field, (2) the static transverse electric field, (3) the electron injection into the laser pulse, (4) the electromagnetic dispersion, and (5) the static longitudinal magnetic field. It is shown that all of these factors lead, under conditions outlined in the talk, to a considerable electron energy gain that greatly exceeds the ponderomotive limit. The static fields do not directly transfer substantial energy to electrons. Instead, they alter the longitudinal dephasing between the electrons and the laser pulse, which then allows the electrons to gain extra energy from the pulse. The talk will also outline a time-resolution criterion that must be satisfied in order to correctly reproduce these effects in particle-in-cell simulations. Supported by AFOSR Contract No. FA9550-14-1-0045, National Nuclear Security Administration Contract No. DE-FC52-08NA28512, and US Department of Energy Contract No. DE-FG02-04ER54742.

A method to estimate statistical errors of properties derived from charge-density modelling

PubMed Central

Lecomte, Claude

2018-01-01

Estimating uncertainties of property values derived from a charge-density model is not straightforward. A methodology, based on calculation of sample standard deviations (SSD) of properties using randomly deviating charge-density models, is proposed with the MoPro software. The parameter shifts applied in the deviating models are generated in order to respect the variance–covariance matrix issued from the least-squares refinement. This ‘SSD methodology’ procedure can be applied to estimate uncertainties of any property related to a charge-density model obtained by least-squares fitting. This includes topological properties such as critical point coordinates, electron density, Laplacian and ellipticity at critical points and charges integrated over atomic basins. Errors on electrostatic potentials and interaction energies are also available now through this procedure. The method is exemplified with the charge density of compound (E)-5-phenylpent-1-enylboronic acid, refined at 0.45 Å resolution. The procedure is implemented in the freely available MoPro program dedicated to charge-density refinement and modelling. PMID:29724964

Low-dose patterning of platinum nanoclusters on carbon nanotubes by focused-electron-beam-induced deposition as studied by TEM

PubMed Central

Bittencourt, Carla; Bals, Sara; Van Tendeloo, Gustaaf

2013-01-01

Summary Focused-electron-beam-induced deposition (FEBID) is used as a direct-write approach to decorate ultrasmall Pt nanoclusters on carbon nanotubes at selected sites in a straightforward maskless manner. The as-deposited nanostructures are studied by transmission electron microscopy (TEM) in 2D and 3D, demonstrating that the Pt nanoclusters are well-dispersed, covering the selected areas of the CNT surface completely. The ability of FEBID to graft nanoclusters on multiple sides, through an electron-transparent target within one step, is unique as a physical deposition method. Using high-resolution TEM we have shown that the CNT structure can be well preserved thanks to the low dose used in FEBID. By tuning the electron-beam parameters, the density and distribution of the nanoclusters can be controlled. The purity of as-deposited nanoclusters can be improved by low-energy electron irradiation at room temperature. PMID:23399584

Millimeter-wave imaging diagnostics systems on the EAST tokamak (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Y. L.; Xie, J. L., E-mail: jlxie@ustc.edu.cn; Yu, C. X.

2016-11-15

Millimeter-wave imaging diagnostics, with large poloidal span and wide radial range, have been developed on the EAST tokamak for visualization of 2D electron temperature and density fluctuations. A 384 channel (24 poloidal × 16 radial) Electron Cyclotron Emission Imaging (ECEI) system in F-band (90-140 GHz) was installed on the EAST tokamak in 2012 to provide 2D electron temperature fluctuation images with high spatial and temporal resolution. A co-located Microwave Imaging Reflectometry (MIR) will be installed for imaging of density fluctuations by December 2016. This “4th generation” MIR system has eight independent frequency illumination beams in W-band (75-110 GHz) driven bymore » fast tuning synthesizers and active multipliers. Both of these advanced millimeter-wave imaging diagnostic systems have applied the latest techniques. A novel design philosophy “general optics structure” has been employed for the design of the ECEI and MIR receiver optics with large aperture. The extended radial and poloidal coverage of ECEI on EAST is made possible by innovations in the design of front-end optics. The front-end optical structures of the two imaging diagnostics, ECEI and MIR, have been integrated into a compact system, including the ECEI receiver and MIR transmitter and receiver. Two imaging systems share the same mid-plane port for simultaneous, co-located 2D fluctuation measurements of electron density and temperature. An intelligent remote-control is utilized in the MIR electronics systems to maintain focusing at the desired radial region even with density variations by remotely tuning the probe frequencies in about 200 μs. A similar intelligent technique has also been applied on the ECEI IF system, with remote configuration of the attenuations for each channel.« less

Millimeter-wave imaging diagnostics systems on the EAST tokamak (invited)

NASA Astrophysics Data System (ADS)

Zhu, Y. L.; Xie, J. L.; Yu, C. X.; Zhao, Z. L.; Gao, B. X.; Chen, D. X.; Liu, W. D.; Liao, W.; Qu, C. M.; Luo, C.; Hu, X.; Spear, A. G.; Luhmann, N. C.; Domier, C. W.; Chen, M.; Ren, X.; Tobias, B. J.

2016-11-01

Millimeter-wave imaging diagnostics, with large poloidal span and wide radial range, have been developed on the EAST tokamak for visualization of 2D electron temperature and density fluctuations. A 384 channel (24 poloidal × 16 radial) Electron Cyclotron Emission Imaging (ECEI) system in F-band (90-140 GHz) was installed on the EAST tokamak in 2012 to provide 2D electron temperature fluctuation images with high spatial and temporal resolution. A co-located Microwave Imaging Reflectometry (MIR) will be installed for imaging of density fluctuations by December 2016. This "4th generation" MIR system has eight independent frequency illumination beams in W-band (75-110 GHz) driven by fast tuning synthesizers and active multipliers. Both of these advanced millimeter-wave imaging diagnostic systems have applied the latest techniques. A novel design philosophy "general optics structure" has been employed for the design of the ECEI and MIR receiver optics with large aperture. The extended radial and poloidal coverage of ECEI on EAST is made possible by innovations in the design of front-end optics. The front-end optical structures of the two imaging diagnostics, ECEI and MIR, have been integrated into a compact system, including the ECEI receiver and MIR transmitter and receiver. Two imaging systems share the same mid-plane port for simultaneous, co-located 2D fluctuation measurements of electron density and temperature. An intelligent remote-control is utilized in the MIR electronics systems to maintain focusing at the desired radial region even with density variations by remotely tuning the probe frequencies in about 200 μs. A similar intelligent technique has also been applied on the ECEI IF system, with remote configuration of the attenuations for each channel.

Resolution Measurement from a Single Reconstructed Cryo-EM Density Map with Multiscale Spectral Analysis.

PubMed

Yang, Yu-Jiao; Wang, Shuai; Zhang, Biao; Shen, Hong-Bin

2018-06-25

As a relatively new technology to solve the three-dimensional (3D) structure of a protein or protein complex, single-particle reconstruction (SPR) of cryogenic electron microscopy (cryo-EM) images shows much superiority and is in a rapidly developing stage. Resolution measurement in SPR, which evaluates the quality of a reconstructed 3D density map, plays a critical role in promoting methodology development of SPR and structural biology. Because there is no benchmark map in the generation of a new structure, how to realize the resolution estimation of a new map is still an open problem. Existing approaches try to generate a hypothetical benchmark map by reconstructing two 3D models from two halves of the original 2D images for cross-reference, which may result in a premature estimation with a half-data model. In this paper, we report a new self-reference-based resolution estimation protocol, called SRes, that requires only a single reconstructed 3D map. The core idea of SRes is to perform a multiscale spectral analysis (MSSA) on the map through multiple size-variable masks segmenting the map. The MSSA-derived multiscale spectral signal-to-noise ratios (mSSNRs) reveal that their corresponding estimated resolutions will show a cliff jump phenomenon, indicating a significant change in the SSNR properties. The critical point on the cliff borderline is demonstrated to be the right estimator for the resolution of the map.

CrowdPhase: crowdsourcing the phase problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jorda, Julien; Sawaya, Michael R.; Yeates, Todd O., E-mail: yeates@mbi.ucla.edu

The idea of attacking the phase problem by crowdsourcing is introduced. Using an interactive, multi-player, web-based system, participants work simultaneously to select phase sets that correspond to better electron-density maps in order to solve low-resolution phasing problems. The human mind innately excels at some complex tasks that are difficult to solve using computers alone. For complex problems amenable to parallelization, strategies can be developed to exploit human intelligence in a collective form: such approaches are sometimes referred to as ‘crowdsourcing’. Here, a first attempt at a crowdsourced approach for low-resolution ab initio phasing in macromolecular crystallography is proposed. A collaborativemore » online game named CrowdPhase was designed, which relies on a human-powered genetic algorithm, where players control the selection mechanism during the evolutionary process. The algorithm starts from a population of ‘individuals’, each with a random genetic makeup, in this case a map prepared from a random set of phases, and tries to cause the population to evolve towards individuals with better phases based on Darwinian survival of the fittest. Players apply their pattern-recognition capabilities to evaluate the electron-density maps generated from these sets of phases and to select the fittest individuals. A user-friendly interface, a training stage and a competitive scoring system foster a network of well trained players who can guide the genetic algorithm towards better solutions from generation to generation via gameplay. CrowdPhase was applied to two synthetic low-resolution phasing puzzles and it was shown that players could successfully obtain phase sets in the 30° phase error range and corresponding molecular envelopes showing agreement with the low-resolution models. The successful preliminary studies suggest that with further development the crowdsourcing approach could fill a gap in current crystallographic methods by making it possible to extract meaningful information in cases where limited resolution might otherwise prevent initial phasing.« less

Theoretical and material studies of thin-film electroluminescent devices

NASA Technical Reports Server (NTRS)

Summers, C. J.

1989-01-01

Thin-film electroluminescent (TFEL) devices are studied for a possible means of achieving a high resolution, light weight, compact video display panel for computer terminals or television screens. The performance of TFEL devices depends upon the probability of an electron impact exciting a luminescent center which in turn depends upon the density of centers present in the semiconductor layer, the possibility of an electron achieving the impact excitation threshold energy, and the collision cross section itself. Efficiency of such a device is presently very poor. It can best be improved by increasing the number of hot electrons capable of impact exciting a center. Hot electron distributions and a method for increasing the efficiency and brightness of TFEL devices (with the additional advantage of low voltage direct current operation) are investigated.

Charge Redistribution in the β-NAPHTHOL-WATER Complex as Measured by High Resolution Stark Spectroscopy in the Gas Phase.

NASA Astrophysics Data System (ADS)

Fleisher, Adam J.; Pratt, David W.; Cembran, Alessandro; Gao, Jiali

2010-06-01

The extensively studied photoacid β-naphthol exhibits a large decrease in pKa upon irradiation with ultraviolet light, in the condensed phase. β-naphthol is almost 10 million times more acidic in the excited electronic state, compared to the ground state. Motivated by this fact, we report here the measurement of the electronic dipole moments of the β-naphthol-water complex in both electronic states, from which estimates of the charge transfer from solute to solvent in both states will be made. Comparisons to ab initio and density functional theory calculations will also be reported. N. Mataga and T. Kubota, Molecular Interactions and Electronic Spectra (Marcel Dekker, New York, 1970). Y. Mo, J. Gao, S.D. Peyerimhoff, J. Chem. Phys. 112, 5530 (2000).

Inherently-Forced Tensile Strain in Nanodiamond-Derived Onion-like Carbon: Consequences in Defect-Induced Electrochemical Activation

PubMed Central

Ko, Young-Jin; Cho, Jung-Min; Kim, Inho; Jeong, Doo Seok; Lee, Kyeong-Seok; Park, Jong-Keuk; Baik, Young-Joon; Choi, Heon-Jin; Lee, Seung-Cheol; Lee, Wook-Seong

2016-01-01

We analyzed the nanodiamond-derived onion-like carbon (OLC) as function of synthesis temperature (1000~1400 °C), by high-resolution electron microscopy, electron energy loss spectroscopy, visible-Raman spectroscopy, ultraviolet photoemission spectroscopy, impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The temperature dependences of the obtained properties (averaged particle size, tensile strain, defect density, density of states, electron transfer kinetics, and electrochemical oxidation current) unanimously coincided: they initially increased and saturated at 1200 °C. It was attributed to the inherent tensile strains arising from (1) the volume expansion associated with the layer-wise diamond-to-graphite transformation of the core, which caused forced dilation of the outer shells during their thermal synthesis; (2) the extreme curvature of the shells. The former origin was dominant over the latter at the outermost shell, of which the relevant evolution in defect density, DOS and electron transfer kinetics determined the electrochemical performances. In detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) using the OLC as electrode, their oxidation peak currents were enhanced by factors of 15~60 with annealing temperature. Their limit of detection and the linear range of detection, in the post-treatment-free condition, were as excellent as those of the nano-carbon electrodes post-treated by Pt-decoration, N-doping, plasma, or polymer. PMID:27032957

The Focusing Optics X-ray Solar Imager (FOXSI)

NASA Astrophysics Data System (ADS)

Krucker, S.

2011-12-01

The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA Low Cost Access to Space sounding rocket payload that will launch in early 2012. A larger sensitivity and dynamic range than currently available are needed in order to image faint X-rays from electron beams in the tenuous corona, particularly those near the coronal acceleration region and those that escape into interplanetary space. FOXSI combines nested, grazing-incidence replicated optics with double-sided silicon strip detectors to achieve a dynamic range of >100 and a sensitivity 100 times that of RHESSI. Advances in the fabrication and assembly of the optics at the NASA Marshall Space Flight Center provide a spatial resolution of 8 arcseconds (FWHM), while the silicon detectors, developed by the Astro-H team at ISAS/JAXA, offer an energy resolution of 0.4 keV. FOXSI's first flight will conduct a search for nonthermal electrons in the quiet Sun, possibly related to nanoflares. FOXSI will serve as a pathfinder for future space-based solar hard X-ray spectroscopic imagers, which will be able to image nonthermal electrons in flare acceleration sites and provide quantitative measurements such as energy spectra, densities, and energy content in accelerated electrons.

The Focusing Optics X-ray Solar Imager

NASA Astrophysics Data System (ADS)

Glesener, Lindsay; Krucker, S.; Christe, S.; Ramsey, B.; Ishikawa, S.; Takahashi, T.; Saito, S.

2011-05-01

The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA Low Cost Access to Space sounding rocket payload that will launch in late 2011. A larger sensitivity and dynamic range than currently available are needed in order to image faint X-rays from electron beams in the tenuous corona, particularly those near any coronal acceleration region and those that escape into interplanetary space. FOXSI combines fast-replication, nested, grazing-incidence optics with double-sided silicon strip detectors to achieve a dynamic range of >100 and a sensitivity 100 times that of RHESSI. Advances in the fabrication and assembly of the optics at the NASA Marshall Space Flight Center provide a spatial resolution of 8 arcseconds, while the silicon detectors, developed by the Astro-H team at ISAS/JAXA, offer an energy resolution of 0.5 keV. FOXSI's first flight will be used to conduct a search for X-ray emission from nonthermal electron beams in quiet Sun nanoflares. In addition, FOXSI will serve as a pathfinder for future space-based solar hard X-ray spectroscopic imagers, which will be able to image nonthermal electrons in flare acceleration sites and provide quantitative measurements such as energy spectra, densities, and energy content in accelerated electrons.

Inelastic Tunneling Spectroscopy of Alkanethiol Molecules: High-Resolution Spectroscopy and Theoretical Simulations

NASA Astrophysics Data System (ADS)

Okabayashi, Norio; Paulsson, Magnus; Ueba, Hiromu; Konda, Youhei; Komeda, Tadahiro

2010-02-01

We investigate inelastic electron tunneling spectroscopy (IETS) for alkanethiol self-assembled monolayers (SAM) with a scanning tunneling microscope and compare it to first-principles calculations. Using a combination of partial deuteration of the molecule and high-resolution measurements, we identify and differentiate between methyl (CH3) and methylene (CH2) groups and their symmetric and asymmetric C-H stretch modes. The calculations agree quantitatively with the measured IETS in producing the weight of the symmetric and asymmetric C-H stretch modes while the methylene stretch mode is largely underestimated. We further show that inelastic intermolecular scattering is important in the SAM by plotting the theoretical current densities.

Space-resolved measurements of neutrons and ions emitted by a plasma focus

NASA Astrophysics Data System (ADS)

Jaeger, U.

1980-05-01

Space-resolved measurements of neutrons and of accelerated charged particles emitted by a plasma focus device are presented. The neutron source was measured with one and two dimensional paraffin collimators. The spatial resolution is 5 mn along the axis and the radius, with a time resolution of 10 ns. In order to make quantitative statements about the neutron yield, neutron scattering, absorption, and nuclear reactions were taken into account. Part of the neutron measurement was carried out together with time and space resolved measurements of the electron density to study possible correlations between n sub e and y sub n.

In situ data collection and structure refinement from microcapillary protein crystallization

PubMed Central

Yadav, Maneesh K.; Gerdts, Cory J.; Sanishvili, Ruslan; Smith, Ward W.; Roach, L. Spencer; Ismagilov, Rustem F.; Kuhn, Peter; Stevens, Raymond C.

2007-01-01

In situ X-ray data collection has the potential to eliminate the challenging task of mounting and cryocooling often fragile protein crystals, reducing a major bottleneck in the structure determination process. An apparatus used to grow protein crystals in capillaries and to compare the background X-ray scattering of the components, including thin-walled glass capillaries against Teflon, and various fluorocarbon oils against each other, is described. Using thaumatin as a test case at 1.8 Å resolution, this study demonstrates that high-resolution electron density maps and refined models can be obtained from in situ diffraction of crystals grown in microcapillaries. PMID:17468785

Relationship between large horizontal electric fields and auroral arc elements

NASA Astrophysics Data System (ADS)

Lanchester, B. S.; Kailá, K.; McCrea, I. W.

1996-03-01

High time resolution optical measurements in the magnetic zenith are compared with European Incoherent Scatter (EISCAT) field-aligned measurements of electron density at 0.2-s resolution and with horizontal electric field measurements made at 278 km with resolution of 9 s. In one event, 20 min after a spectacular auroral breakup, a system of narrow and active arc elements moved southward into the magnetic zenith, where it remained for several minutes. During a 30-s interval of activity in a narrow arc element very close to the radar beam, the electric field vectors at 3-s resolution were found to be extremely large (up to 400 mVm-1) and to point toward the bright optical features in the arc, which moved along its length. It is proposed that the large electric fields are short-lived and are directly associated with the particle precipitation that causes the bright features in auroral arc elements.

Wide-aperture aspherical lens for high-resolution terahertz imaging

NASA Astrophysics Data System (ADS)

Chernomyrdin, Nikita V.; Frolov, Maxim E.; Lebedev, Sergey P.; Reshetov, Igor V.; Spektor, Igor E.; Tolstoguzov, Viktor L.; Karasik, Valeriy E.; Khorokhorov, Alexei M.; Koshelev, Kirill I.; Schadko, Aleksander O.; Yurchenko, Stanislav O.; Zaytsev, Kirill I.

2017-01-01

In this paper, we introduce wide-aperture aspherical lens for high-resolution terahertz (THz) imaging. The lens has been designed and analyzed by numerical methods of geometrical optics and electrodynamics. It has been made of high-density polyethylene by shaping at computer-controlled lathe and characterized using a continuous-wave THz imaging setup based on a backward-wave oscillator and Golay detector. The concept of image contrast has been implemented to estimate image quality. According to the experimental data, the lens allows resolving two points spaced at 0.95λ distance with a contrast of 15%. To highlight high resolution in the THz images, the wide-aperture lens has been employed for studying printed electronic circuit board containing sub-wavelength-scale elements. The observed results justify the high efficiency of the proposed lens design.

Comparing an Atomic Model or Structure to a Corresponding Cryo-electron Microscopy Image at the Central Axis of a Helix.

PubMed

Zeil, Stephanie; Kovacs, Julio; Wriggers, Willy; He, Jing

2017-01-01

Three-dimensional density maps of biological specimens from cryo-electron microscopy (cryo-EM) can be interpreted in the form of atomic models that are modeled into the density, or they can be compared to known atomic structures. When the central axis of a helix is detectable in a cryo-EM density map, it is possible to quantify the agreement between this central axis and a central axis calculated from the atomic model or structure. We propose a novel arc-length association method to compare the two axes reliably. This method was applied to 79 helices in simulated density maps and six case studies using cryo-EM maps at 6.4-7.7 Å resolution. The arc-length association method is then compared to three existing measures that evaluate the separation of two helical axes: a two-way distance between point sets, the length difference between two axes, and the individual amino acid detection accuracy. The results show that our proposed method sensitively distinguishes lateral and longitudinal discrepancies between the two axes, which makes the method particularly suitable for the systematic investigation of cryo-EM map-model pairs.

Comparing an Atomic Model or Structure to a Corresponding Cryo-electron Microscopy Image at the Central Axis of a Helix

PubMed Central

Zeil, Stephanie; Kovacs, Julio; Wriggers, Willy

2017-01-01

Abstract Three-dimensional density maps of biological specimens from cryo-electron microscopy (cryo-EM) can be interpreted in the form of atomic models that are modeled into the density, or they can be compared to known atomic structures. When the central axis of a helix is detectable in a cryo-EM density map, it is possible to quantify the agreement between this central axis and a central axis calculated from the atomic model or structure. We propose a novel arc-length association method to compare the two axes reliably. This method was applied to 79 helices in simulated density maps and six case studies using cryo-EM maps at 6.4–7.7 Å resolution. The arc-length association method is then compared to three existing measures that evaluate the separation of two helical axes: a two-way distance between point sets, the length difference between two axes, and the individual amino acid detection accuracy. The results show that our proposed method sensitively distinguishes lateral and longitudinal discrepancies between the two axes, which makes the method particularly suitable for the systematic investigation of cryo-EM map–model pairs. PMID:27936925

Electronic and mechanical improvement of the receiving terminal of a free-space microwave power transmission system

NASA Technical Reports Server (NTRS)

Brown, W. C.

1977-01-01

Significant advancements were made in a number of areas: improved efficiency of basic receiving element at low power density levels, improved resolution and confidence in efficiency measurements mathematical modelling and computer simulation of the receiving element and the design, construction, and testing of an environmentally protected two-plane construction suitable for low cost, highly automated construction of large receiving arrays.

Oil-free hyaluronic acid matrix for serial femtosecond crystallography

NASA Astrophysics Data System (ADS)

Sugahara, Michihiro; Song, Changyong; Suzuki, Mamoru; Masuda, Tetsuya; Inoue, Shigeyuki; Nakane, Takanori; Yumoto, Fumiaki; Nango, Eriko; Tanaka, Rie; Tono, Kensuke; Joti, Yasumasa; Kameshima, Takashi; Hatsui, Takaki; Yabashi, Makina; Nureki, Osamu; Numata, Keiji; Iwata, So

2016-04-01

The grease matrix was originally introduced as a microcrystal-carrier for serial femtosecond crystallography and has been expanded to applications for various types of proteins, including membrane proteins. However, the grease-based matrix has limited application for oil-sensitive proteins. Here we introduce a grease-free, water-based hyaluronic acid matrix. Applications for proteinase K and lysozyme proteins were able to produce electron density maps at 2.3-Å resolution.

Visualization of Space-Time Ambiguities to be Explored by NASA GEC Mission with a Critique of Synthesized Measurements for Different GEC Mission Scenarios

NASA Technical Reports Server (NTRS)

Sojka, Jan J.

2003-01-01

The Grant supported research addressing the question of how the NASA Solar Terrestrial Probes (STP) Mission called Geospace electrodynamics Connections (GEC) will resolve space-time structures as well as collect sufficient information to solve the coupled thermosphere-ionosphere- magnetosphere dynamics and electrodynamics. The approach adopted was to develop a high resolution in both space and time model of the ionosphere-thermosphere (I-T) over altitudes relevant to GEC, especially the deep-dipping phase. This I-T model was driven by a high- resolution model of magnetospheric-ionospheric (M-I) coupling electrodynamics. Such a model contains all the key parameters to be measured by GEC instrumentation, which in turn are the required parameters to resolve present-day problems in describing the energy and momentum coupling between the ionosphere-magnetosphere and ionosphere-thermosphere. This model database has been successfully created for one geophysical condition; winter, solar maximum with disturbed geophysical conditions, specifically a substorm. Using this data set, visualizations (movies) were created to contrast dynamics of the different measurable parameters. Specifically, the rapidly varying magnetospheric E and auroral electron precipitation versus the slower varying ionospheric F-region electron density, but rapidly responding E-region density.

Variations of Strahl Properties with Fast and Slow Solar Wind

NASA Technical Reports Server (NTRS)

Figueroa-Vinas, Adolfo; Goldstein, Melvyn L.; Gurgiolo, Chris

2008-01-01

The interplanetary solar wind electron velocity distribution function generally shows three different populations. Two of the components, the core and halo, have been the most intensively analyzed and modeled populations using different theoretical models. The third component, the strahl, is usually seen at higher energies, is confined in pitch-angle, is highly field-aligned and skew. This population has been more difficult to identify and to model in the solar wind. In this work we make use of the high angular, energy and time resolution and three-dimensional data of the Cluster/PEACE electron spectrometer to identify and analyze this component in the ambient solar wind during high and slow speed solar wind. The moment density and fluid velocity have been computed by a semi-numerical integration method. The variations of solar wind density and drift velocity with the general build solar wind speed could provide some insight into the source, origin, and evolution of the strahl.

Electronic signatures of dimerization in IrTe2

NASA Astrophysics Data System (ADS)

Dai, Jixia; Wu, Weida; Oh, Yoon Seok; Cheong, S.-W.; Yang, J. J.

2014-03-01

Recently, the mysterious phase transition around Tc ~ 260 K in IrTe2 has been intensively studied. A structural supermodulation with q =1/5 was identified below Tc. A variety of microscopic mechanisms have been proposed to account for this transition, including charge-density wave due to Fermi surface nesting, Te p-orbital driven structure instability, anionic depolymerization, ionic dimerization, and so on. However, there has not been an unified picture on the nature of this transition. To address this issue, we have performed low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) experiments on IrTe2 and IrTe2-xSex. Our STM data clearly shows a strong bias dependence in both topography and local density of states (STS) maps. High resolution spectroscopic data further confirms the stripe-like electronic states modulation, which provides insight to the ionic dimerization revealed by X-ray diffraction.

Identifying the 630 nm auroral arc emission height: A comparison of the triangulation, FAC profile, and electron density methods

NASA Astrophysics Data System (ADS)

Megan Gillies, D.; Knudsen, D.; Donovan, E.; Jackel, B.; Gillies, R.; Spanswick, E.

2017-08-01

We present a comprehensive survey of 630 nm (red-line) emission discrete auroral arcs using the newly deployed Redline Emission Geospace Observatory. In this study we discuss the need for observations of 630 nm aurora and issues with the large-altitude range of the red-line aurora. We compare field-aligned currents (FACs) measured by the Swarm constellation of satellites with the location of 10 red-line (630 nm) auroral arcs observed by all-sky imagers (ASIs) and find that a characteristic emission height of 200 km applied to the ASI maps gives optimal agreement between the two observations. We also compare the new FAC method against the traditional triangulation method using pairs of all-sky imagers (ASIs), and against electron density profiles obtained from the Resolute Bay Incoherent Scatter Radar-Canadian radar, both of which are consistent with a characteristic emission height of 200 km.

Reflectometry diagnostics on TCV

NASA Astrophysics Data System (ADS)

Molina Cabrera, Pedro; Coda, Stefano; Porte, Laurie; Offeddu, Nicola; Tcv Team

2017-10-01

Both profile reflectometer and Doppler back-scattering (DBS) diagnostics are being developed for the TCV Tokamak using a steerable quasi-optical launcher and universal polarizers. First results will be presented. A pulse reflectometer is being developed to complement Thomson Scattering measurements of electron density, greatly increasing temporal resolution and also effectively enabling fluctuation measurements. Pulse reflectometry consists of sending short pulses of varying frequency and measuring the roundtrip group-delay with precise chronometers. A fast arbitrary waveform generator is used as a pulse source feeding frequency multipliers that bring the pulses to V-band. A DBS diagnostic is currently operational in TCV. DBS may be used to infer the perpendicular velocity and wave number spectrum of electron density fluctuations in the 3-15 cm-1 wave-number range. Off-the-shelf transceiver modules, originally used for VNA measurements, are being used in a Doppler radar configuration. See author list of S. Coda et al., 2017 Nucl. Fusion 57 102011.

Models of SOL transport and their relation to scaling of the divertor heat flux width in DIII-D

DOE PAGES

Makowski, M. A.; Lasnier, C. J.; Leonard, A. W.; ...

2014-10-06

Strong support for the critical pressure gradient model for the heat flux width has been obtained, in that the measured separatrix pressure gradient lies below and scales similarly to the pressure gradient limit obtained from the ideal, infinite-n stability codes, BALOO and 2DX, in all cases that have been examined. Predictions of a heuristic drift model for the heat flux width are also in qualitative agreement with the measurements. We obtained these results by using an improved high rep-rate and higher edge spatial resolution Thomson scattering system on DIII-D to measure the upstream electron temperature and density profiles. In ordermore » to compare theory and experiment, profiles of density, temperature, and pressure for both electrons and ions are needed as well values of these quantitities at the separatrix. We also developed a simple method to identify a proxy for the separatrix.« less

Quantification of the Conditioning Phase in Cooled Pixelated TlBr Detectors

NASA Astrophysics Data System (ADS)

Koehler, Will; He, Zhong; O'Neal, Sean; Yang, Hao; Kim, Hadong; Cirignano, Leonard; Shah, Kanai

2015-08-01

Thallium-bromide (TlBr) is currently under investigation as an alternative room-temperature semiconductor gamma-ray spectrometer due to its favorable material properties (large bandgap, high atomic numbers, and high density). Previous work has shown that 5 mm thick pixelated TlBr detectors can achieve sub-1% FWHM energy resolution at 662 keV for single-pixel events. These results are limited to - 20° C operation where detector performance is stable. During the first one to five days of applied bias at - 20° C, many TlBr detectors undergo a conditioning phase, where the energy resolution improves and the depth-dependent electron drift velocity stabilizes. In this work, the spectroscopic performance, drift velocity, and freed electron concentrations of multiple 5 mm thick pixelated TlBr detectors are monitored throughout the conditioning phase. Additionally, conditioning is performed twice on the same detector at different times to show that improvement mechanisms relax when the detector is stored without bias. We conclude that the improved spectroscopy results from internal electric field stabilization and uniformity caused by fewer trapped electrons.

Shedding light on cell compartmentation in the candidate phylum Poribacteria by high resolution visualisation and transcriptional profiling

NASA Astrophysics Data System (ADS)

Jahn, Martin T.; Markert, Sebastian M.; Ryu, Taewoo; Ravasi, Timothy; Stigloher, Christian; Hentschel, Ute; Moitinho-Silva, Lucas

2016-10-01

Assigning functions to uncultivated environmental microorganisms continues to be a challenging endeavour. Here, we present a new microscopy protocol for fluorescence in situ hybridisation-correlative light and electron microscopy (FISH-CLEM) that enabled, to our knowledge for the first time, the identification of single cells within their complex microenvironment at electron microscopy resolution. Members of the candidate phylum Poribacteria, common and uncultivated symbionts of marine sponges, were used towards this goal. Cellular 3D reconstructions revealed bipolar, spherical granules of low electron density, which likely represent carbon reserves. Poribacterial activity profiles were retrieved from prokaryotic enriched sponge metatranscriptomes using simulation-based optimised mapping. We observed high transcriptional activity for proteins related to bacterial microcompartments (BMC) and we resolved their subcellular localisation by combining FISH-CLEM with immunohistochemistry (IHC) on ultra-thin sponge tissue sections. In terms of functional relevance, we propose that the BMC-A region may be involved in 1,2-propanediol degradation. The FISH-IHC-CLEM approach was proven an effective toolkit to combine -omics approaches with functional studies and it should be widely applicable in environmental microbiology.

Genetically targeted 3D visualisation of Drosophila neurons under Electron Microscopy and X-Ray Microscopy using miniSOG

PubMed Central

Ng, Julian; Browning, Alyssa; Lechner, Lorenz; Terada, Masako; Howard, Gillian; Jefferis, Gregory S. X. E.

2016-01-01

Large dimension, high-resolution imaging is important for neural circuit visualisation as neurons have both long- and short-range patterns: from axons and dendrites to the numerous synapses at terminal endings. Electron Microscopy (EM) is the favoured approach for synaptic resolution imaging but how such structures can be segmented from high-density images within large volume datasets remains challenging. Fluorescent probes are widely used to localise synapses, identify cell-types and in tracing studies. The equivalent EM approach would benefit visualising such labelled structures from within sub-cellular, cellular, tissue and neuroanatomical contexts. Here we developed genetically-encoded, electron-dense markers using miniSOG. We demonstrate their ability in 1) labelling cellular sub-compartments of genetically-targeted neurons, 2) generating contrast under different EM modalities, and 3) segmenting labelled structures from EM volumes using computer-assisted strategies. We also tested non-destructive X-ray imaging on whole Drosophila brains to evaluate contrast staining. This enabled us to target specific regions for EM volume acquisition. PMID:27958322

High-resolution multi-MeV x-ray radiography using relativistic laser-solid interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Courtois, C.; Compant La Fontaine, A.; Barbotin, M.

2011-02-15

When high intensity ({>=}10{sup 19} W cm{sup -2}) laser light interacts with matter, multi-MeV electrons are produced. These electrons can be utilized to generate a MeV bremsstrahlung x-ray emission spectrum as they propagate into a high-Z solid target positioned behind the interaction area. The short duration (<10 ps) and the small diameter (<500 {mu}m) of the x-ray pulse combined with the MeV x-ray spectrum offers an interesting alternative to conventional bremsstrahlung x-ray sources based on an electron accelerator used to radiograph dense, rapidly moving objects. In experiments at the Omega EP laser, a multi-MeV x-ray source is characterized consistently withmore » number of independent diagnostics. An unfiltered x-ray dose of approximately 2 rad in air at 1 m and a source diameter of less than 350 {mu}m are inferred. Radiography of a complex and high area density (up to 61 g/cm{sup 2}) object is then performed with few hundred microns spatial resolution.« less

Interlaced zone plate optics for hard X-ray imaging in the 10 nm range

DOE PAGES

Mohacsi, Istvan; Vartiainen, Ismo; Rosner, Benedikt; ...

2017-03-08

Multi-keV X-ray microscopy has been particularly successful in bridging the resolution gap between optical and electron microscopy. However, resolutions below 20 nm are still considered challenging, as high throughput direct imaging methods are limited by the availability of suitable optical elements. In order to bridge this gap, we present a new type of Fresnel zone plate lenses aimed at the sub-20 and the sub-10 nm resolution range. By extending the concept of double-sided zone plate stacking, we demonstrate the doubling of the effective line density and thus the resolution and provide large aperture, single- chip optical devices with 15 andmore » 7 nm smallest zone widths. The detailed characterization of these lenses shows excellent optical properties with focal spots down to 7.8 nm. Furthermore, beyond wave front characterization, the zone plates also excel in typical imaging scenarios, verifying their resolution close to their diffraction limited optical performance.« less

Interlaced zone plate optics for hard X-ray imaging in the 10 nm range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohacsi, Istvan; Vartiainen, Ismo; Rosner, Benedikt

Multi-keV X-ray microscopy has been particularly successful in bridging the resolution gap between optical and electron microscopy. However, resolutions below 20 nm are still considered challenging, as high throughput direct imaging methods are limited by the availability of suitable optical elements. In order to bridge this gap, we present a new type of Fresnel zone plate lenses aimed at the sub-20 and the sub-10 nm resolution range. By extending the concept of double-sided zone plate stacking, we demonstrate the doubling of the effective line density and thus the resolution and provide large aperture, single- chip optical devices with 15 andmore » 7 nm smallest zone widths. The detailed characterization of these lenses shows excellent optical properties with focal spots down to 7.8 nm. Furthermore, beyond wave front characterization, the zone plates also excel in typical imaging scenarios, verifying their resolution close to their diffraction limited optical performance.« less

Interlaced zone plate optics for hard X-ray imaging in the 10 nm range

PubMed Central

Mohacsi, Istvan; Vartiainen, Ismo; Rösner, Benedikt; Guizar-Sicairos, Manuel; Guzenko, Vitaliy A.; McNulty, Ian; Winarski, Robert; Holt, Martin V.; David, Christian

2017-01-01

Multi-keV X-ray microscopy has been particularly successful in bridging the resolution gap between optical and electron microscopy. However, resolutions below 20 nm are still considered challenging, as high throughput direct imaging methods are limited by the availability of suitable optical elements. In order to bridge this gap, we present a new type of Fresnel zone plate lenses aimed at the sub-20 and the sub-10 nm resolution range. By extending the concept of double-sided zone plate stacking, we demonstrate the doubling of the effective line density and thus the resolution and provide large aperture, singlechip optical devices with 15 and 7 nm smallest zone widths. The detailed characterization of these lenses shows excellent optical properties with focal spots down to 7.8 nm. Beyond wave front characterization, the zone plates also excel in typical imaging scenarios, verifying their resolution close to their diffraction limited optical performance.

Interlaced zone plate optics for hard X-ray imaging in the 10 nm range

NASA Astrophysics Data System (ADS)

Mohacsi, Istvan; Vartiainen, Ismo; Rösner, Benedikt; Guizar-Sicairos, Manuel; Guzenko, Vitaliy A.; McNulty, Ian; Winarski, Robert; Holt, Martin V.; David, Christian

2017-03-01

Multi-keV X-ray microscopy has been particularly successful in bridging the resolution gap between optical and electron microscopy. However, resolutions below 20 nm are still considered challenging, as high throughput direct imaging methods are limited by the availability of suitable optical elements. In order to bridge this gap, we present a new type of Fresnel zone plate lenses aimed at the sub-20 and the sub-10 nm resolution range. By extending the concept of double-sided zone plate stacking, we demonstrate the doubling of the effective line density and thus the resolution and provide large aperture, singlechip optical devices with 15 and 7 nm smallest zone widths. The detailed characterization of these lenses shows excellent optical properties with focal spots down to 7.8 nm. Beyond wave front characterization, the zone plates also excel in typical imaging scenarios, verifying their resolution close to their diffraction limited optical performance.

Measuring the Autocorrelation Function of Nanoscale Three-Dimensional Density Distribution in Individual Cells Using Scanning Transmission Electron Microscopy, Atomic Force Microscopy, and a New Deconvolution Algorithm.

PubMed

Li, Yue; Zhang, Di; Capoglu, Ilker; Hujsak, Karl A; Damania, Dhwanil; Cherkezyan, Lusik; Roth, Eric; Bleher, Reiner; Wu, Jinsong S; Subramanian, Hariharan; Dravid, Vinayak P; Backman, Vadim

2017-06-01

Essentially all biological processes are highly dependent on the nanoscale architecture of the cellular components where these processes take place. Statistical measures, such as the autocorrelation function (ACF) of the three-dimensional (3D) mass-density distribution, are widely used to characterize cellular nanostructure. However, conventional methods of reconstruction of the deterministic 3D mass-density distribution, from which these statistical measures can be calculated, have been inadequate for thick biological structures, such as whole cells, due to the conflict between the need for nanoscale resolution and its inverse relationship with thickness after conventional tomographic reconstruction. To tackle the problem, we have developed a robust method to calculate the ACF of the 3D mass-density distribution without tomography. Assuming the biological mass distribution is isotropic, our method allows for accurate statistical characterization of the 3D mass-density distribution by ACF with two data sets: a single projection image by scanning transmission electron microscopy and a thickness map by atomic force microscopy. Here we present validation of the ACF reconstruction algorithm, as well as its application to calculate the statistics of the 3D distribution of mass-density in a region containing the nucleus of an entire mammalian cell. This method may provide important insights into architectural changes that accompany cellular processes.

Measuring the Autocorrelation Function of Nanoscale Three-Dimensional Density Distribution in Individual Cells Using Scanning Transmission Electron Microscopy, Atomic Force Microscopy, and a New Deconvolution Algorithm

PubMed Central

Li, Yue; Zhang, Di; Capoglu, Ilker; Hujsak, Karl A.; Damania, Dhwanil; Cherkezyan, Lusik; Roth, Eric; Bleher, Reiner; Wu, Jinsong S.; Subramanian, Hariharan; Dravid, Vinayak P.; Backman, Vadim

2018-01-01

Essentially all biological processes are highly dependent on the nanoscale architecture of the cellular components where these processes take place. Statistical measures, such as the autocorrelation function (ACF) of the three-dimensional (3D) mass–density distribution, are widely used to characterize cellular nanostructure. However, conventional methods of reconstruction of the deterministic 3D mass–density distribution, from which these statistical measures can be calculated, have been inadequate for thick biological structures, such as whole cells, due to the conflict between the need for nanoscale resolution and its inverse relationship with thickness after conventional tomographic reconstruction. To tackle the problem, we have developed a robust method to calculate the ACF of the 3D mass–density distribution without tomography. Assuming the biological mass distribution is isotropic, our method allows for accurate statistical characterization of the 3D mass–density distribution by ACF with two data sets: a single projection image by scanning transmission electron microscopy and a thickness map by atomic force microscopy. Here we present validation of the ACF reconstruction algorithm, as well as its application to calculate the statistics of the 3D distribution of mass–density in a region containing the nucleus of an entire mammalian cell. This method may provide important insights into architectural changes that accompany cellular processes. PMID:28416035

Super-resolution biomolecular crystallography with low-resolution data.

PubMed

Schröder, Gunnar F; Levitt, Michael; Brunger, Axel T

2010-04-22

X-ray diffraction plays a pivotal role in the understanding of biological systems by revealing atomic structures of proteins, nucleic acids and their complexes, with much recent interest in very large assemblies like the ribosome. As crystals of such large assemblies often diffract weakly (resolution worse than 4 A), we need methods that work at such low resolution. In macromolecular assemblies, some of the components may be known at high resolution, whereas others are unknown: current refinement methods fail as they require a high-resolution starting structure for the entire complex. Determining the structure of such complexes, which are often of key biological importance, should be possible in principle as the number of independent diffraction intensities at a resolution better than 5 A generally exceeds the number of degrees of freedom. Here we introduce a method that adds specific information from known homologous structures but allows global and local deformations of these homology models. Our approach uses the observation that local protein structure tends to be conserved as sequence and function evolve. Cross-validation with R(free) (the free R-factor) determines the optimum deformation and influence of the homology model. For test cases at 3.5-5 A resolution with known structures at high resolution, our method gives significant improvements over conventional refinement in the model as monitored by coordinate accuracy, the definition of secondary structure and the quality of electron density maps. For re-refinements of a representative set of 19 low-resolution crystal structures from the Protein Data Bank, we find similar improvements. Thus, a structure derived from low-resolution diffraction data can have quality similar to a high-resolution structure. Our method is applicable to the study of weakly diffracting crystals using X-ray micro-diffraction as well as data from new X-ray light sources. Use of homology information is not restricted to X-ray crystallography and cryo-electron microscopy: as optical imaging advances to subnanometre resolution, it can use similar tools.

Ionospheric model-observation comparisons: E layer at Arecibo Incorporation of SDO-EVE solar irradiances

NASA Astrophysics Data System (ADS)

Sojka, Jan J.; Jensen, Joseph B.; David, Michael; Schunk, Robert W.; Woods, Tom; Eparvier, Frank; Sulzer, Michael P.; Gonzalez, Sixto A.; Eccles, J. Vincent

2014-05-01

This study evaluates how the new irradiance observations from the NASA Solar Dynamics Observatory (SDO) Extreme Ultraviolet Variability Experiment (EVE) can, with its high spectral resolution and 10 s cadence, improve the modeling of the E region. To demonstrate this a campaign combining EVE observations with that of the NSF Arecibo incoherent scatter radar (ISR) was conducted. The ISR provides E region electron density observations with high-altitude resolution, 300 m, and absolute densities using the plasma line technique. Two independent ionospheric models were used, the Utah State University Time-Dependent Ionospheric Model (TDIM) and Space Environment Corporation's Data-Driven D Region (DDDR) model. Each used the same EVE irradiance spectrum binned at 1 nm resolution from 0.1 to 106 nm. At the E region peak the modeled TDIM density is 20% lower and that of the DDDR is 6% higher than observed. These differences could correspond to a 36% lower (TDIM) and 12% higher (DDDR) production rate if the differences were entirely attributed to the solar irradiance source. The detailed profile shapes that included the E region altitude and that of the valley region were only qualitatively similar to observations. Differences on the order of a neutral-scale height were present. Neither model captured a distinct dawn to dusk tilt in the E region peak altitude. A model sensitivity study demonstrated how future improved spectral resolution of the 0.1 to 7 nm irradiance could account for some of these model shortcomings although other relevant processes are also poorly modeled.

Bragg-cell receiver study

NASA Technical Reports Server (NTRS)

Wilson, Lonnie A.

1987-01-01

Bragg-cell receivers are employed in specialized Electronic Warfare (EW) applications for the measurement of frequency. Bragg-cell receiver characteristics are fully characterized for simple RF emitter signals. This receiver is early in its development cycle when compared to the IFM receiver. Functional mathematical models are derived and presented in this report for the Bragg-cell receiver. Theoretical analysis is presented and digital computer signal processing results are presented for the Bragg-cell receiver. Probability density function analysis are performed for output frequency. Probability density function distributions are observed to depart from assumed distributions for wideband and complex RF signals. This analysis is significant for high resolution and fine grain EW Bragg-cell receiver systems.

Improved Estimation of Electron Temperature from Rocket-borne Impedance Probes

NASA Astrophysics Data System (ADS)

Rowland, D. E.; Wolfinger, K.; Stamm, J. D.

2017-12-01

The impedance probe technique is a well known method for determining high accuracy measurements of electron number density in the Earth's ionosphere. We present analysis of impedance probe data from several sounding rockets at low, mid-, and auroral latitudes, including high cadence estimates of the electron temperature, derived from analytical fits to the antenna impedance curves. These estimates compare favorably with independent estimates from Langmuir Probes, but at much higher temporal and spatial resolution, providing a capability to resolve small-scale temperature fluctuations. We also present some considerations for the design of impedance probes, including assessment of the effects of resonance damping due to rocket motion, effects of wake and spin modulation, and aspect angle to the magnetic field.

Implementation of a multichannel soft x-ray diagnostic for electron temperature measurements in TJ-II high-density plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baiao, D.; Varandas, C.; Medina, F.

2012-10-15

Based on the multi-foil technique, a multichannel soft x-ray diagnostic for electron temperature measurements has been recently implemented in the TJ-II stellarator. The diagnostic system is composed by four photodiodes arrays with beryllium filters of different thickness. An in-vacuum amplifier board is coupled to each array, aiming at preventing induced noise currents. The Thomson scattering and the vacuum ultraviolet survey diagnostics are used for assessing plasma profiles and composition, being the analysis carried out with the radiation code IONEQ. The electron temperature is determined through the different signal-pair ratios with temporal and spatial resolution. The design and preliminary results frommore » the diagnostic are presented.« less

High resolution energy analyzer for broad ion beam characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kanarov, V.; Hayes, A.; Yevtukhov, R.

2008-09-15

Characterization of the ion energy distribution function (IEDF) of low energy high current density ion beams by conventional retarding field and deflection type energy analyzers is limited due to finite ion beam emittance and beam space charge spreading inside the analyzer. These deficiencies are, to a large extent, overcome with the recent development of the variable-focusing retarding field energy analyzer (RFEA), which has a cylindrical focusing electrode preceding the planar retarding grid. The principal concept of this analyzer is conversion of a divergent charged particle beam into a quasiparallel beam before analyzing it by the planar retarding field. This allowsmore » analysis of the beam particle total kinetic energy distribution with greatly improved energy resolution. Whereas this concept was first applied to analyze 5-10 keV pulsed electron beams, the present authors have adapted it to analyze the energy distribution of a low energy ({<=}1 KeV) broad ion beam. In this paper we describe the RFEA design, which was modified from the original, mainly as required by the specifics of broad ion beam energy analysis, and the device experimental characterization and modeling results. Among the modifications, an orifice electrode placed in front of the RFEA provides better spatial resolution of the broad ion beam ion optics emission region and reduces the beam plasma density in the vicinity of analyzer entry. An electron repeller grid placed in front of the RFEA collector was found critical for suppressing secondary electrons, both those incoming to the collector and those released from its surface, and improved energy spectrum measurement repeatability and accuracy. The use of finer mesh single- and double-grid retarding structures reduces the retarding grid lens effect and improves the analyzer energy resolution and accuracy of the measured spectrum mean energy. However, additional analyzer component and configuration improvements did not further change the analyzed IEDF shape or mean energy value. This led us to conclude that the optimized analyzer construction provides an energy resolution considerably narrower than the investigated ion beam energy spectrum full width at half maximum, and the derived energy spectrum is an objective and accurate representation of the analyzed broad ion beam energy distribution characteristics. A quantitative study of the focusing voltage and retarding grid field effects based on the experimental data and modeling results have supported this conclusion.« less

Electronic structure of the heavy-fermion caged compound Ce 3 Pd 20 X 6 ( X = Si, Ge ) studied by density functional theory and photoelectron spectroscopy

DOE PAGES

Yamaoka, Hitoshi; Schwier, Eike F.; Arita, Masashi; ...

2015-03-30

The electronic structure of Ce₃Pd₂₀X₆ (X = Si, Ge) has been studied using detailed density functional theory (DFT) calculations and high-resolution photoelectron spectroscopy (PES) measurements. The orbital decomposition of the electronic structure by DFT calculations indicates that Ce atoms at the (8c) site surrounded by 16 Pd atoms have a more localized nature and a tendency to be magnetic. Ce atoms in the (4a) site surrounded by 12 Pd and 6 X atoms, on the other, show only a negligible magnetic moment. In the photoemission valence-band spectra we observe a strong f⁰ (Ce⁴⁺) component with a small fraction of f¹more » (Ce³⁺) component. The spectral weight of f¹ component near the Fermi level Ce₃Pd₂₀Si₆ is stronger than that for Ce₃Pd₂₀Ge₆ at the 4d-4f resonance, suggesting stronger c-f hybridization in the former. This may hint to the origin of the large electronic specific coefficient of Ce₃Pd₂₀Si₆ compared to Ce₃Pd₂₀Ge₆.« less

First principles study of hydrogen adsorption on carbon nanowires.

NASA Astrophysics Data System (ADS)

Tapia, Alejandro; Aguilera, Luis; Murrieta, Gabriel; de Coss, Romeo

2007-03-01

Recently has been reported a new type of one-dimensional carbon structures. Carbon nanowires formed by a linear carbon-atom chain inside an armchair (5,5) carbon nanotube has been observed using high-resolution transmission electron microscopy. In the present work we have studied the changes in the electronic structure of a carbon nanowires and (5,5) single-walled carbon nanotubes (SWCN) when a hydrogen atom is adsorbed. We used the Density Functional Theory and the calculations where performed by the pseudopotentials LCAO method (SIESTA code) and the Generalized Gradient Approximation (GGA) for the exchange-correlation potential. We have analyzed the changes in the atomic structure, density of states (LDOS), and the local orbital population. We found charge transfer from the nanotube to the linear chain and the hydrogen atom, the electronic character of the chain and nanotube sub-systems in chain@SWCN is the same that in the corresponding isolated systems, chain or SWCN. But the hydrogen adsorption produced changes in the atomic estructure and the electronic properties. This research was supported by PRIORI-UADY under Grant No. FING-05-004 and Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grants No. 43830-F and 49985-J.

Photon mass attenuation coefficients, effective atomic numbers and electron densities of some thermoluminescent dosimetric compounds

NASA Astrophysics Data System (ADS)

Gowda, Shivalinge; Krishnaveni, S.; Yashoda, T.; Umesh, T. K.; Gowda, Ramakrishna

2004-09-01

Photon mass attenuation coefficients of some thermoluminescent dosimetric (TLD) compounds, such as LiF, CaCO_3, CaSO_4, CaSO_4\\cdot2H_2O, SrSO_4, CdSO_4, BaSO_4, C_4H_6BaO_4 and 3CdSO_4\\cdot8H_2O were determined at 279.2, 320.07, 514.0, 661.6, 1115.5, 1173.2 and 1332.5 keV in a well-collimated narrow beam good geometry set-up using a high resolution, hyper pure germanium detector. The attenuation coefficient data were then used to compute the effective atomic number and the electron density of TLD compounds. The interpolation of total attenuation cross-sections of photons of energy E in elements of atomic number Z was performed using the logarithmic regression analysis of the data measured by the authors and reported earlier. The best-fit coefficients so obtained in the photon energy range of 279.2 to 320.07 keV, 514.0 to 661.6 keV and 1115.5 to 1332.5 keV by a piece-wise interpolation method were then used to find the effective atomic number and electron density of the compounds. These values are found to be in agreement with other available published values.

HERSCHEL GALACTIC PLANE SURVEY OF [N ii] FINE STRUCTURE EMISSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.

2015-12-01

We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10{sup −8}–10{sup −7} Wm{sup −2} sr{sup −1} level over the range –60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointingmore » is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10–50 cm{sup −3} with an average value of 29 cm{sup −3} and N{sup +} column densities 10{sup 16}–10{sup 17} cm{sup −2}. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.« less

The Inversion of Ionospheric/plasmaspheric Electron Density From GPS Beacon Observations

NASA Astrophysics Data System (ADS)

Zou, Y. H.; Xu, J. S.; Ma, S. Y.

It is a space-time 4-D tomography to reconstruct ionospheric/ plasmaspheric elec- tron density, Ne, from ground-based GPS beacon measurements. The mathematical foundation of such inversion is studied in this paper and some simulation results of reconstruction for GPS network observation are presented. Assuming reasonably a power law dependence of NE on time with an index number of 1-3 during one ob- servational time of GPS (60-90min.), 4-D inversion in consideration is reduced to a 3-D cone-beam tomography with incomplete projections. To see clearly the effects of the incompleteness on the quality of reconstruction for 3-D condition, we deduced theoretically the formulae of 3-D parallel-beam tomography. After establishing the mathematical basis, we adopt linear temporal dependence of NE and voxel elemental functions to perform simulation of NE reconstruction with the help of IRI90 model. Reasonable time-dependent 3-D images of ionosphere/ plasmasphere electron density distributions are obtained when taking proper layout of the GPS network and allowing variable resolutions in vertical.

Small-scale structure of O2(+) and proton hydrates in a Noctilucent Cloud and polar mesospheric summer echo of August 9/10 1991 above Kiruna

NASA Technical Reports Server (NTRS)

Balsiger, F.; Kopp, E.; Friedrich, M.; Torkar, K. M.; Walchli, U.

1993-01-01

A novel mass spectrometer designed to measure simultaneously positive ion composition in the mesosphere, was successfully launched during the NLC-91 project. Instruments supporting the mass spectrometer were a probed to measure both electrons and positive ions as well as a wave propagation experiment. The location of the Noctilucent Clouds (NLC) was determined by a particle impact sensor to detect secondary electrons and ions from the impact of NLC particle. The density of proton hydrates and of the related total ions is depleted in the NLC region at 83 km. An improved detection limit of 5 x 10(exp 4)/cu m for positive ions and improved height resolution revealed for the first time large gradients in the O2(+), H(+)(H2O)2 and H(+)(H2O)6 densities within a small height range of the order of 50 m. Such gradients at the altitude of NLC and Polar Mesospheric Summer Echoes (PMSE) are associated with strong variability of mesospheric water vapor, temperature and neutral air density.

Crystallization and preliminary X-ray diffraction analysis of mouse galectin-4 N-terminal carbohydrate recognition domain in complex with lactose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krejčiříková, Veronika; Fábry, Milan; Marková, Vladimíra

2008-07-01

Mouse galectin-4 carbohydrate binding domain was overexpressed in E. coli and crystallized in the presence of lactose. The crystals belong to tetragonal space group P42{sub 1}2 and diffraction data were collected to 2.1 Å resolution. Galectin-4 is thought to play a role in the process of tumour conversion of cells of the alimentary tract and the breast tissue; however, its exact function remains unknown. With the aim of elucidating the structural basis of mouse galectin-4 (mGal-4) binding specificity, we have undertaken X-ray analysis of the N-terminal domain, CRD1, of mGal-4 in complex with lactose (the basic building block of knownmore » galectin-4 carbohydrate ligands). Crystals of CRD1 in complex with lactose were obtained using vapour-diffusion techniques. The crystals belong to tetragonal space group P42{sub 1}2 with unit-cell parameters a = 91.1, b = 91.16, c = 57.10 Å and preliminary X-ray diffraction data were collected to 3.2 Å resolution. An optimized crystallization procedure and cryocooling protocol allowed us to extend resolution to 2.1 Å. Structure refinement is currently under way; the initial electron-density maps clearly show non-protein electron density in the vicinity of the carbohydrate binding site, indicating the presence of one lactose molecule. The structure will help to improve understanding of the binding specificity and function of the potential colon cancer marker galectin-4.« less

Well-Known Mediators of Selective Oxidation with Unknown Electronic Structure: Metal-Free Generation and EPR Study of Imide-N-oxyl Radicals.

PubMed

Krylov, Igor B; Kompanets, Mykhailo O; Novikova, Katerina V; Opeida, Iosip O; Kushch, Olga V; Shelimov, Boris N; Nikishin, Gennady I; Levitsky, Dmitri O; Terent'ev, Alexander O

2016-01-14

Nitroxyl radicals are widely used in chemistry, materials sciences, and biology. Imide-N-oxyl radicals are subclass of unique nitroxyl radicals that proved to be useful catalysts and mediators of selective oxidation and CH-functionalization. An efficient metal-free method was developed for the generation of imide-N-oxyl radicals from N-hydroxyimides at room temperature by the reaction with (diacetoxyiodo)benzene. The method allows for the production of high concentrations of free radicals and provides high resolution of their EPR spectra exhibiting the superhyperfine structure from benzene ring protons distant from the radical center. An analysis of the spectra shows that, regardless of the electronic effects of the substituents in the benzene ring, the superhyperfine coupling constant of an unpaired electron with the distant protons at positions 4 and 5 of the aromatic system is substantially greater than that with the protons at positions 3 and 6 that are closer to the N-oxyl radical center. This is indicative of an unusual character of the spin density distribution of the unpaired electron in substituted phthalimide-N-oxyl radicals. Understanding of the nature of the electron density distribution in imide-N-oxyl radicals may be useful for the development of commercial mediators of oxidation based on N-hydroxyimides.

Growth process, characterization, and modeling of electronic properties of coupled InAsSbP nanostructures

NASA Astrophysics Data System (ADS)

Marquardt, Oliver; Hickel, Tilmann; Neugebauer, Jörg; Gambaryan, Karen M.; Aroutiounian, Vladimir M.

2011-08-01

Quaternary III-V InAsSbP quantum dots (QDs) have been grown in the form of cooperative InAsSb/InAsP structures using a modified version of the liquid phase epitaxy. High resolution scanning electron microscopy, atomic force microscopy, and Fourier-transform infrared spectrometry were used to investigate these so-called nano-camomiles, mainly consisting of a central InAsSb QD surrounded by six InAsP-QDs, that shall be referred to as leaves in the following. The observed QDs average density ranges from 0.8 to 2 × 109 cm-2, with heights and widths dimensions from 2 to 20 nm and 5 to 45 nm, respectively. The average density of the leaves is equal to (6-10) × 109 cm-2 with dimensions of approx. 5 to 40 nm in width and depth. To achieve a first basic understanding of the electronic properties, we have modeled these novel nanostructures using second-order continuum elasticity theory and an eight-band k .p model to calculate the electronic structure. Our calculations found a clear localization of hole states in the central InAsSb dot. The localization of electron states, however, was found to be weak and might thus be easily influenced by external electric fields or strain.

Direct in situ observation of the electron-driven synthesis of Ag filaments on α-Ag2WO4 crystals

PubMed Central

Longo, E.; Cavalcante, L. S.; Volanti, D. P.; Gouveia, A. F.; Longo, V. M.; Varela, J. A.; Orlandi, M. O.; Andrés, J.

2013-01-01

In this letter, we report, for the first time, the real-time in situ nucleation and growth of Ag filaments on α-Ag2WO4 crystals driven by an accelerated electron beam from an electronic microscope under high vacuum. We employed several techniques to characterise the material in depth. By using these techniques combined with first-principles modelling based on density functional theory, a mechanism for the Ag filament formation followed by a subsequent growth process from the nano- to micro-scale was proposed. In general, we have shown that an accelerated electron beam from an electronic microscope under high vacuum enables in situ visualisation of Ag filaments with subnanometer resolution and offers great potential for addressing many fundamental issues in materials science, chemistry, physics and other fields of science. PMID:23591807

Electronic Structure of Ytterbium-Doped Strontium Fluoroapatite: Photoemission and Photoabsorption Investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, Art J.; Van Buuren, Tony W.; Bostedt, C

X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium-doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure and Sr 3d, P 2p and 2s, Yb 4d and 4p, F 1s and O 1s core lines were used to evaluate the surface and near surface chemistry of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy (XAS) at the Yb 4d (N4,5-edge), Sr 3d (M4,5-edge), P 2p (L2,3-edge), F 1s and O 1s (K-edges) absorption edges. These results provide themore » first measurements of the electronic structure and surface chemistry of this material.« less

Sensing magnetic flux density of artificial neurons with a MEMS device.

PubMed

Tapia, Jesus A; Herrera-May, Agustin L; García-Ramírez, Pedro J; Martinez-Castillo, Jaime; Figueras, Eduard; Flores, Amira; Manjarrez, Elías

2011-04-01

We describe a simple procedure to characterize a magnetic field sensor based on microelectromechanical systems (MEMS) technology, which exploits the Lorentz force principle. This sensor is designed to detect, in future applications, the spiking activity of neurons or muscle cells. This procedure is based on the well-known capability that a magnetic MEMS device can be used to sense a small magnetic flux density. In this work, an electronic neuron (FitzHugh-Nagumo) is used to generate controlled spike-like magnetic fields. We show that the magnetic flux density generated by the hardware of this neuron can be detected with a new MEMS magnetic field sensor. This microdevice has a compact resonant structure (700 × 600 × 5 μm) integrated by an array of silicon beams and p-type piezoresistive sensing elements, which need an easy fabrication process. The proposed microsensor has a resolution of 80 nT, a sensitivity of 1.2 V.T(-1), a resonant frequency of 13.87 kHz, low power consumption (2.05 mW), quality factor of 93 at atmospheric pressure, and requires a simple signal processing circuit. The importance of our study is twofold. First, because the artificial neuron can generate well-controlled magnetic flux density, we suggest it could be used to analyze the resolution and performance of different magnetic field sensors intended for neurobiological applications. Second, the introduced MEMS magnetic field sensor may be used as a prototype to develop new high-resolution biomedical microdevices to sense magnetic fields from cardiac tissue, nerves, spinal cord, or the brain.

Measurement of plasma densities by dual frequency multichannel boxcar THz time domain spectroscopy

NASA Astrophysics Data System (ADS)

Meier, St. M.; Tsankov, Ts V.; Luggenhölscher, D.; Czarnetzki, U.

2017-06-01

In this paper we show the development and the application of the terahertz time domain spectroscopy (THz TDS) diagnostic technique for the determination of plasma densities in low-pressure discharges. A commercially available system was modified to reach a better signal-to-noise ratio. For that the THz emitter and the detection method were changed and a fast lock-in amplifier was used to reach 38 MHz lock-in frequency. These modifications in a combination with the novel method of dual frequency multichannel boxcar embedded as a feature in the lock-in amplifier allowed us to make also time-resolved measurements. The temporal resolution can potentially go down to 100 ps and is limited only by the spectral range that needs to be recovered for the measurement of low electron densities. Further, the cause of artefacts found in all THz TDS based systems, but not understood until now, is identified and explained. As an application the electron densities in inductively coupled plasmas sustained in a magnetic multi-cusp chamber are determined. Results from steady-state discharges in noble gases (He, Ne, Ar, Kr, Xe) and time-resolved measurements in pulsed discharges in Ar and Ne are presented. The technique is benchmarked against microwave interferometry with good agreement in the applicability range of both techniques. The THz TDS performs reliably also in much denser plasmas where standard microwave interferometry fails. The lower limit for the technique is at a line-integrated electron density of 1012 cm-2, corresponding to about 1011 cm-3 for typical plasma dimensions.

Lithium electrodeposition dynamics in aprotic electrolyte observed in situ via transmission electron microscopy

DOE PAGES

Leenheer, Andrew Jay; Jungjohann, Katherine Leigh; Zavadil, Kevin Robert; ...

2015-03-18

Electrodeposited metallic lithium is an ideal negative battery electrode, but nonuniform microstructure evolution during cycling leads to degradation and safety issues. A better understanding of the Li plating and stripping processes is needed to enable practical Li-metal batteries. Here we use a custom microfabricated, sealed liquid cell for in situ scanning transmission electron microscopy (STEM) to image the first few cycles of lithium electrodeposition/dissolution in liquid aprotic electrolyte at submicron resolution. Cycling at current densities from 1 to 25 mA/cm 2 leads to variations in grain structure, with higher current densities giving a more needle-like, higher surface area deposit. Themore » effect of the electron beam was explored, and it was found that, even with minimal beam exposure, beam-induced surface film formation could alter the Li microstructure. The electrochemical dissolution was seen to initiate from isolated points on grains rather than uniformly across the Li surface, due to the stabilizing solid electrolyte interphase surface film. As a result, we discuss the implications for operando STEM liquid-cell imaging and Li-battery applications.« less

High-resolution structure of the Shigella type-III secretion needle by solid-state NMR and cryo-electron microscopy

NASA Astrophysics Data System (ADS)

Demers, Jean-Philippe; Habenstein, Birgit; Loquet, Antoine; Kumar Vasa, Suresh; Giller, Karin; Becker, Stefan; Baker, David; Lange, Adam; Sgourakis, Nikolaos G.

2014-09-01

We introduce a general hybrid approach for determining the structures of supramolecular assemblies. Cryo-electron microscopy (cryo-EM) data define the overall envelope of the assembly and rigid-body orientation of the subunits while solid-state nuclear magnetic resonance (ssNMR) chemical shifts and distance constraints define the local secondary structure, protein fold and inter-subunit interactions. Finally, Rosetta structure calculations provide a general framework to integrate the different sources of structural information. Combining a 7.7-Å cryo-EM density map and 996 ssNMR distance constraints, the structure of the type-III secretion system needle of Shigella flexneri is determined to a precision of 0.4 Å. The calculated structures are cross-validated using an independent data set of 691 ssNMR constraints and scanning transmission electron microscopy measurements. The hybrid model resolves the conformation of the non-conserved N terminus, which occupies a protrusion in the cryo-EM density, and reveals conserved pore residues forming a continuous pattern of electrostatic interactions, thereby suggesting a mechanism for effector protein translocation.

Computational prediction of atomic structures of helical membrane proteins aided by EM maps.

PubMed

Kovacs, Julio A; Yeager, Mark; Abagyan, Ruben

2007-09-15

Integral membrane proteins pose a major challenge for protein-structure prediction because only approximately 100 high-resolution structures are available currently, thereby impeding the development of rules or empirical potentials to predict the packing of transmembrane alpha-helices. However, when an intermediate-resolution electron microscopy (EM) map is available, it can be used to provide restraints which, in combination with a suitable computational protocol, make structure prediction feasible. In this work we present such a protocol, which proceeds in three stages: 1), generation of an ensemble of alpha-helices by flexible fitting into each of the density rods in the low-resolution EM map, spanning a range of rotational angles around the main helical axes and translational shifts along the density rods; 2), fast optimization of side chains and scoring of the resulting conformations; and 3), refinement of the lowest-scoring conformations with internal coordinate mechanics, by optimizing the van der Waals, electrostatics, hydrogen bonding, torsional, and solvation energy contributions. In addition, our method implements a penalty term through a so-called tethering map, derived from the EM map, which restrains the positions of the alpha-helices. The protocol was validated on three test cases: GpA, KcsA, and MscL.

Electronic properties of Fe3O4: LCAO calculations and Compton spectroscopy

NASA Astrophysics Data System (ADS)

Panwar, Kalpana; Tiwari, Shailja; Heda, N. L.

2018-04-01

We report the Compton profile (CP) measurements of Fe3O4 using 100 mCi241Am Compton spectrometer at momentum resolution of 0.55 a.u. The experimental CP has been compared with the linear combination of atomic orbitals (LCAO) data within density functional theory (DFT). The local density and generalized gradient approximation (LDA and GGA, respectively) have been used under the framework of DFT scheme. It is found that the DFT-GGA scheme gives the better agreement than to DFT-LDA. In addition, we have also computed the M ulliken's population (M P) and density of states (DOS) using the DFT scheme. M P data predicts the charge transfer from Fe to O atoms while DOS have confirmed the half metallic character of the compound.

Variation of mesospheric ozone during the highly relativistic electron event in May 1992 as measured by the High Resolution Doppler Imager instrument on UARS

NASA Astrophysics Data System (ADS)

Pesnell, W. Dean; Goldberg, Richard A.; Jackman, Charles H.; Chenette, D. L.; Gaines, E. E.

2000-10-01

Highly relativistic electron precipitation events (HREs) include long-lived enhancements of the flux of electrons with E>1MeV into the Earth's atmosphere. HREs also contain increased fluxes of electrons with energies above 100 keV that have been predicted to cause large depletions of mesospheric ozone. For some of the measured instantaneous values of the electron fluxes during the HRE of May 1992, relative depletions greater than 22% were predicted to occur between altitudes of 55 and 80 km, where HOx reactions cause local minima in both the ozone number density and mixing ratio altitude profiles. These ozone depletions should follow the horizontal distribution of the electron precipitation, having a distinct boundary equatorward of the L=3 magnetic shell. To search for these effects, we have analyzed ozone data from the High Resolution Doppler Imager (HRDI) instrument on UARS. Owing to the multiple, off-track viewing angles of HRDI, observations in the region affected by the electrons are taken at similar local solar times before, during, and after the electron flux increase. Our analysis limits the relative ozone depletion to values <10% during the very intense May 1992 HRE. We do observe decreases in the ozone mixing ratio at several points in the diurnal cycle that may be associated with the transport of water vapor into the mesosphere during May 1992. This masking of the precipitating electron effects by the seasonal variations in water vapor can complicate the detection of those effects.

Design of a dispersion interferometer combined with a polarimeter to increase the electron density measurement reliability on ITER

NASA Astrophysics Data System (ADS)

Akiyama, T.; Sirinelli, A.; Watts, C.; Shigin, P.; Vayakis, G.; Walsh, M.

2016-11-01

A dispersion interferometer is a reliable density measurement system and is being designed as a complementary density diagnostic on ITER. The dispersion interferometer is inherently insensitive to mechanical vibrations, and a combined polarimeter with the same line of sight can correct fringe jump errors. A proof of the principle of the CO2 laser dispersion interferometer combined with the PEM polarimeter was recently conducted, where the phase shift and the polarization angle were successfully measured simultaneously. Standard deviations of the line-average density and the polarization angle measurements over 1 s are 9 × 1016 m-2 and 0.19°, respectively, with a time constant of 100 μs. Drifts of the zero point, which determine the resolution in steady-state operation, correspond to 0.25% and 1% of the phase shift and the Faraday rotation angle expected on ITER.

Design of a dispersion interferometer combined with a polarimeter to increase the electron density measurement reliability on ITER.

PubMed

Akiyama, T; Sirinelli, A; Watts, C; Shigin, P; Vayakis, G; Walsh, M

2016-11-01

A dispersion interferometer is a reliable density measurement system and is being designed as a complementary density diagnostic on ITER. The dispersion interferometer is inherently insensitive to mechanical vibrations, and a combined polarimeter with the same line of sight can correct fringe jump errors. A proof of the principle of the CO 2 laser dispersion interferometer combined with the PEM polarimeter was recently conducted, where the phase shift and the polarization angle were successfully measured simultaneously. Standard deviations of the line-average density and the polarization angle measurements over 1 s are 9 × 10 16 m -2 and 0.19°, respectively, with a time constant of 100 μs. Drifts of the zero point, which determine the resolution in steady-state operation, correspond to 0.25% and 1% of the phase shift and the Faraday rotation angle expected on ITER.

Investigation of mechanism of anode plasma formation in ion diode with dielectric anode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pushkarev, A., E-mail: aipush@mail.ru

The results of investigation of the anode plasma formation in a diode with a passive anode in magnetic insulation mode are presented. The experiments have been conducted using the BIPPAB-450 ion accelerator (350–400 kV, 6–8 kA, 80 ns) with a focusing conical diode with B{sub r} external magnetic field (a barrel diode). For analysis of plasma formation at the anode and the distribution of the ions beam energy density, infrared imaging diagnostics (spatial resolution of 1–2 mm) is used. For analysis of the ion beam composition, time-of-flight diagnostics (temporal resolution of 1 ns) were used. Our studies have shown that when the magnetic induction inmore » the A-C gap is much larger than the critical value, the ion beam energy density is close to the one-dimensional Child-Langmuir limit on the entire working surface of the diode. Formation of anode plasma takes place only by the flashover of the dielectric anode surface. In this mode, the ion beam consists primarily of singly ionized carbon ions, and the delay of the start of formation of the anode plasma is 10–15 ns. By reducing the magnetic induction in the A-C gap to a value close to the critical one, the ion beam energy density is 3–6 times higher than that calculated by the one-dimensional Child-Langmuir limit, but the energy density of the ion beam is non-uniform in cross-section. In this mode, the anode plasma formation occurs due to ionization of the anode material with accelerated electrons. In this mode, also, the delay in the start of the formation of the anode plasma is much smaller and the degree of ionization of carbon ions is higher. In all modes occurred effective suppression of the electronic component of the total current, and the diode impedance was 20–30 times higher than the values calculated for the mode without magnetic insulation of the electrons. The divergence of the ion beam was 4.5°–6°.« less

Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Alina, D.; Alves, M. I. R.; Armitage-Caplan, C.; Arnaud, M.; Arzoumanian, D.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Burigana, C.; Butler, R. C.; Cardoso, J.-F.; Catalano, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Christensen, P. R.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Gouveia Dal Pino, E. M.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Donzelli, S.; Doré, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Ferrière, K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Galeotta, S.; Ganga, K.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Guillet, V.; Hansen, F. K.; Harrison, D. L.; Helou, G.; Hernández-Monteagudo, C.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Magalhães, A. M.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Pasian, F.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pietrobon, D.; Plaszczynski, S.; Poidevin, F.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Savini, G.; Scott, D.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Zacchei, A.; Zonca, A.

2015-04-01

This paper presents an overview of the polarized sky as seen by Planck HFI at 353 GHz, which is the most sensitive Planck channel for dust polarization. We construct and analyse maps of dust polarization fraction and polarization angle at 1° resolution, taking into account noise bias and possible systematic effects. The sensitivity of the Planck HFI polarization measurements allows for the first time a mapping of Galactic dust polarized emission on large scales, including low column density regions. We find that the maximum observed dust polarization fraction is high (pmax = 19.8%), in particular in some regions of moderate hydrogen column density (NH < 2 × 1021 cm-2). The polarization fraction displays a large scatter at NH below a few 1021 cm-2. There is a general decrease in the dust polarization fraction with increasing column density above NH ≃ 1 × 1021 cm-2 and in particular a sharp drop above NH ≃ 1.5 × 1022 cm-2. We characterize the spatial structure of the polarization angle using the angle dispersion function. We find that the polarization angle is ordered over extended areas of several square degrees, separated by filamentary structures of high angle dispersion function. These appear as interfaces where the sky projection of the magnetic field changes abruptly without variations in the column density. The polarization fraction is found to be anti-correlated with the dispersion of polarization angles. These results suggest that, at the resolution of 1°, depolarization is due mainly to fluctuations in the magnetic field orientation along the line of sight, rather than to the loss of grain alignment in shielded regions. We also compare the polarization of thermal dust emission with that of synchrotron measured with Planck, low-frequency radio data, and Faraday rotation measurements toward extragalactic sources. These components bear resemblance along the Galactic plane and in some regions such as the Fan and North Polar Spur regions. The poor match observed in other regions shows, however, that dust, cosmic-ray electrons, and thermal electrons generally sample different parts of the line of sight. Appendices are available in electronic form at http://www.aanda.org

High Resolution Reconstruction of the Ionosphere for SAR Applications

NASA Astrophysics Data System (ADS)

Minkwitz, David; Gerzen, Tatjana; Hoque, Mainul

2014-05-01

Caused by ionosphere's strong impact on radio signal propagation, high resolution and highly accurate reconstructions of the ionosphere's electron density distribution are demanded for a large number of applications, e.g. to contribute to the mitigation of ionospheric effects on Synthetic Aperture Radar (SAR) measurements. As a new generation of remote sensing satellites the TanDEM-L radar mission is planned to improve the understanding and modelling ability of global environmental processes and ecosystem change. TanDEM-L will operate in L-band with a wavelength of approximately 24 cm enabling a stronger penetration capability compared to X-band (3 cm) or C-band (5 cm). But accompanied by the lower frequency of the TanDEM-L signals the influence of the ionosphere will increase. In particular small scale irregularities of the ionosphere might lead to electron density variations within the synthetic aperture length of the TanDEM-L satellite and in turn might result into blurring and azimuth pixel shifts. Hence the quality of the radar image worsens if the ionospheric effects are not mitigated. The Helmholtz Alliance project "Remote Sensing and Earth System Dynamics" (EDA) aims in the preparation of the HGF centres and the science community for the utilisation and integration of the TanDEM-L products into the study of the Earth's system. One significant point thereby is to cope with the mentioned ionospheric effects. Therefore different strategies towards achieving this objective are pursued: the mitigation of the ionospheric effects based on the radar data itself, the mitigation based on external information like global Total Electron Content (TEC) maps or reconstructions of the ionosphere and the combination of external information and radar data. In this presentation we describe the geostatistical approach chosen to analyse the behaviour of the ionosphere and to provide a high resolution 3D electron density reconstruction. As first step the horizontal structure of the ionosphere is studied in space and time on the base of ground-based TEC measurements in the European region. In order to determine the correlation of measurements at different locations or points of time the TEC measurements are subtracted by a base model to define a stationary random field. We outline the application of the NeQuick model and the final IGS TEC maps as background and show first results regarding the distribution and the stationarity of the resulting residuals. Moreover, the occurred problems and questions are discussed and finally an outlook towards the next modelling steps is presented.

Polarizable atomic multipole X-ray refinement: application to peptide crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnieders, Michael J.; Fenn, Timothy D.; Howard Hughes Medical Institute

2009-09-01

A method to accelerate the computation of structure factors from an electron density described by anisotropic and aspherical atomic form factors via fast Fourier transformation is described for the first time. Recent advances in computational chemistry have produced force fields based on a polarizable atomic multipole description of biomolecular electrostatics. In this work, the Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field is applied to restrained refinement of molecular models against X-ray diffraction data from peptide crystals. A new formalism is also developed to compute anisotropic and aspherical structure factors using fast Fourier transformation (FFT) of Cartesian Gaussianmore » multipoles. Relative to direct summation, the FFT approach can give a speedup of more than an order of magnitude for aspherical refinement of ultrahigh-resolution data sets. Use of a sublattice formalism makes the method highly parallelizable. Application of the Cartesian Gaussian multipole scattering model to a series of four peptide crystals using multipole coefficients from the AMOEBA force field demonstrates that AMOEBA systematically underestimates electron density at bond centers. For the trigonal and tetrahedral bonding geometries common in organic chemistry, an atomic multipole expansion through hexadecapole order is required to explain bond electron density. Alternatively, the addition of interatomic scattering (IAS) sites to the AMOEBA-based density captured bonding effects with fewer parameters. For a series of four peptide crystals, the AMOEBA–IAS model lowered R{sub free} by 20–40% relative to the original spherically symmetric scattering model.« less

X-ray diffraction measurement of cosolvent accessible volume in rhombohedral insulin crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soares, Alexei S.; Caspar, Donald L. D.

We report x-ray crystallographic measurement of the number of solvent electrons in the unit cell of a protein crystal equilibrated with aqueous solutions of different densities provides information about preferential hydration in the crystalline state. Room temperature and cryo-cooled rhombohedral insulin crystals were equilibrated with 1.2 M trehalose to study the effect of lowered water activity. The native and trehalose soaked crystals were isomorphous and had similar structures. Including all the low resolution data, the amplitudes of the structure factors were put on an absolute scale (in units of electrons per asymmetric unit) by constraining the integrated number of electronsmore » inside the envelope of the calculated protein density map to equal the number deduced from the atomic model. This procedure defines the value of F(0 0 0), the amplitude at the origin of the Fourier transform, which is equal to the total number of electrons in the asymmetric unit (i.e. protein plus solvent). Comparison of the F(0 0 0) values for three isomorphous pairs of room temperature insulin crystals, three with trehalose and three without trehalose, indicates that 75 ± 12 electrons per asymmetric unit were added to the crystal solvent when soaked in 1.2 M trehalose. If all the water in the crystal were available as solvent for the trehalose, 304 electrons would have been added. Thus, the co-solvent accessible volume is one quarter of the total water in the crystal. Finally, determination of the total number of electrons in a protein crystal is an essential first step for mapping the average density distribution of the disordered solvent.« less

X-ray diffraction measurement of cosolvent accessible volume in rhombohedral insulin crystals

DOE PAGES

Soares, Alexei S.; Caspar, Donald L. D.

2017-08-31

We report x-ray crystallographic measurement of the number of solvent electrons in the unit cell of a protein crystal equilibrated with aqueous solutions of different densities provides information about preferential hydration in the crystalline state. Room temperature and cryo-cooled rhombohedral insulin crystals were equilibrated with 1.2 M trehalose to study the effect of lowered water activity. The native and trehalose soaked crystals were isomorphous and had similar structures. Including all the low resolution data, the amplitudes of the structure factors were put on an absolute scale (in units of electrons per asymmetric unit) by constraining the integrated number of electronsmore » inside the envelope of the calculated protein density map to equal the number deduced from the atomic model. This procedure defines the value of F(0 0 0), the amplitude at the origin of the Fourier transform, which is equal to the total number of electrons in the asymmetric unit (i.e. protein plus solvent). Comparison of the F(0 0 0) values for three isomorphous pairs of room temperature insulin crystals, three with trehalose and three without trehalose, indicates that 75 ± 12 electrons per asymmetric unit were added to the crystal solvent when soaked in 1.2 M trehalose. If all the water in the crystal were available as solvent for the trehalose, 304 electrons would have been added. Thus, the co-solvent accessible volume is one quarter of the total water in the crystal. Finally, determination of the total number of electrons in a protein crystal is an essential first step for mapping the average density distribution of the disordered solvent.« less

Role of dislocations and carrier concentration in limiting the electron mobility of InN films grown by plasma assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Tangi, Malleswararao; De, Arpan; Shivaprasad, S. M.

2018-01-01

We report the molecular beam epitaxy growth of device quality InN films on GaN epilayer and nano-wall network (NWN) templates deposited on c-sapphire by varying the film thickness up to 1 μm. The careful experiments are directed towards obtaining high mobility InN layers having a low band gap with improved crystal quality. The dislocation density is quantified by using high resolution X-ray diffraction rocking curve broadening values of symmetric and asymmetric reflections, respectively. We observe that the dislocation density of the InN films grown on GaN NWN is less than that of the films grown on the GaN epilayer. This is attributed to the nanoepitaxial lateral overlayer growth (ELOG) process, where the presence of voids at the interface of InN/GaN NWN prevents the propagation of dislocation lines into the InN epilayers, thereby causing less defects in the overgrown InN films. Thus, this new adaptation of the nano-ELOG growth process enables us to prepare InN layers with high electron mobility. The obtained electron mobility of 2121 cm2/Vs for 1 μm thick InN/GaN NWN is comparable with the literature values of similar thickness InN films. Furthermore, in order to understand the reasons that limit electron mobility, the charge neutrality condition is employed to study the variation of electron mobility as a function of dislocation density and carrier concentration. Overall, this study provides a route to attaining improved crystal quality and electronic properties of InN films.

High-resolution imaging of a shock front in plastic by phase contrast imaging at LCLS

NASA Astrophysics Data System (ADS)

Beckwith, M.; Jiang, S.; Zhao, Y.; Schropp, A.; Fernandez-Panella, A.; Rinderknecht, H. G.; Wilks, S.; Fournier, K.; Galtier, E.; Xing, Z.; Granados, E.; Gamboa, E.; Glenzer, S. H.; Heimann, P.; Zastrau, U.; Cho, B. I.; Eggert, J. H.; Collins, G. W.; Ping, Y.

2017-10-01

Understanding the propagation of shock waves is important for many areas of high energy density physics, including inertial confinement fusion (ICF) and shock compression science. In order to probe the shock front structures in detail, a diagnostic capable of detecting both the small spatial and temporal changes in the material is required. Here we show the experiment using hard X-ray phase contrast imaging (PCI) to probe the shock wave propagation in polyimide with submicron spatial resolution. The experiment was performed at the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Lightsource (LCLS). PCI together with the femtosecond time scales of x-ray free electron lasers enables the imaging of optically opaque materials that undergo rapid temporal and spatial changes. The result reveals the evolution of the density profile with time. Work performed under DOE Contract No. DE-AC52-07NA27344 with support from OFES Early Career and LLNL LDRD program.

An overview of heavy-atom derivatization of protein crystals

PubMed Central

Pike, Ashley C. W.; Garman, Elspeth F.; Krojer, Tobias; von Delft, Frank; Carpenter, Elisabeth P.

2016-01-01

Heavy-atom derivatization is one of the oldest techniques for obtaining phase information for protein crystals and, although it is no longer the first choice, it remains a useful technique for obtaining phases for unknown structures and for low-resolution data sets. It is also valuable for confirming the chain trace in low-resolution electron-density maps. This overview provides a summary of the technique and is aimed at first-time users of the method. It includes guidelines on when to use it, which heavy atoms are most likely to work, how to prepare heavy-atom solutions, how to derivatize crystals and how to determine whether a crystal is in fact a derivative. PMID:26960118

Atomic and electronic structures of BaHfO3-doped TFA-MOD-derived YBa2Cu3O7-δ thin films

NASA Astrophysics Data System (ADS)

Molina-Luna, Leopoldo; Duerrschnabel, Michael; Turner, Stuart; Erbe, Manuela; Martinez, Gerardo T.; Van Aert, Sandra; Holzapfel, Bernhard; Van Tendeloo, Gustaaf

2015-11-01

Tailoring the properties of oxide-based nanocomposites is of great importance for a wide range of materials relevant for energy technology. YBa2Cu3O7-δ (YBCO) superconducting thin films containing nanosized BaHfO3 (BHO) particles yield a significant improvement of the magnetic flux pinning properties and a reduced anisotropy of the critical current density. These films were prepared by chemical solution deposition (CSD) on (100) SrTiO3 (STO) substrates yielding critical current densities up to 3.6 MA cm-2 at 77 K and self-field. Transport in-field J c measurements demonstrated a high pinning force maximum of around 6 GN/m3 for a sample annealed at T = 760 °C that has a doping of 12 mol% of BHO. This sample was investigated by scanning transmission electron microscopy (STEM) in combination with electron energy-loss spectroscopy (EELS) yielding strain and spectral maps. Spherical BHO nanoparticles of 15 nm in size were found in the matrix, whereas the particles at the interface were flat. A 2 nm diffusion layer containing Ti was found at the YBCO (BHO)/STO interface. Local lattice deformation mapping at the atomic scale revealed crystal defects induced by the presence of both sorts of BHO nanoparticles, which can act as pinning centers for magnetic flux lines. Two types of local lattice defects were identified and imaged: (i) misfit edge dislocations and (ii) Ba-Cu-Cu-Ba stacking faults (Y-248 intergrowths). The local electronic structure and charge transfer were probed by high energy resolution monochromated electron energy-loss spectroscopy. This technique made it possible to distinguish superconducting from non-superconducting areas in nanocomposite samples with atomic resolution in real space, allowing the identification of local pinning sites on the order of the coherence length of YBCO (˜1.5 nm) and the determination of 0.25 nm dislocation cores.

High-density stretchable microelectrode arrays: An integrated technology platform for neural and muscular surface interfacing

NASA Astrophysics Data System (ADS)

Guo, Liang

2011-12-01

Numerous applications in neuroscience research and neural prosthetics, such as retinal prostheses, spinal-cord surface stimulation for prosthetics, electrocorticogram (ECoG) recording for epilepsy detection, etc., involve electrical interaction with soft excitable tissues using a surface stimulation and/or recording approach. These applications require an interface that is able to set up electrical communications with a high throughput between electronics and the excitable tissue and that can dynamically conform to the shape of the soft tissue. Being a compliant and biocompatible material with mechanical impedance close to that of soft tissues, polydimethylsiloxane (PDMS) offers excellent potential as the substrate material for such neural interfaces. However, fabrication of electrical functionalities on PDMS has long been very challenging. This thesis work has successfully overcome many challenges associated with PDMS-based microfabrication and achieved an integrated technology platform for PDMS-based stretchable microelectrode arrays (sMEAs). This platform features a set of technological advances: (1) we have fabricated uniform current density profile microelectrodes as small as 10 mum in diameter; (2) we have patterned high-resolution (feature as small as 10 mum), high-density (pitch as small as 20 mum) thin-film gold interconnects on PDMS substrate; (3) we have developed a multilayer wiring interconnect technology within the PDMS substrate to further boost the achievable integration density of such sMEA; and (4) we have invented a bonding technology---via-bonding---to facilitate high-resolution, high-density integration of the sMEA with integrated circuits (ICs) to form a compact implant. Taken together, this platform provides a high-resolution, high-density integrated system solution for neural and muscular surface interfacing. sMEAs of example designs are evaluated through in vitro and in vivo experimentations on their biocompatibility, surface conformability, and surface recording/stimulation capabilities, with a focus on epimysial (i.e. on the surface of muscle) applications. Finally, as an example medical application, we investigate a prosthesis for unilateral vocal cord paralysis (UVCP) based on simultaneous multichannel epimysial recording and stimulation.

Structure and physical conditions in the Huygens region of the Orion nebula

NASA Astrophysics Data System (ADS)

O'Dell, C. R.; Ferland, G. J.; Peimbert, M.

2017-02-01

Hubble Space Telescope images, MUSE maps of emission lines, and an atlas of high velocity resolution emission-line spectra have been used to establish for the first time correlations of the electron temperature, electron density, radial velocity, turbulence, and orientation within the main ionization front of the nebula. From the study of the combined properties of multiple features, it is established that variations in the radial velocity are primarily caused by the photoevaporating ionization front being viewed at different angles. There is a progressive increase of the electron temperature and density with decreasing distance from the dominant ionizing star θ1 Ori C. The product of these characteristics (ne × Te) is the most relevant parameter in modelling a blister-type nebula like the Huygens region, where this quantity should vary with the surface brightness in Hα. Several lines of evidence indicate that small-scale structure and turbulence exist down to the level of our resolution of a few arcseconds. Although photoevaporative flow must contribute at some level to the well-known non-thermal broadening of the emission lines, comparison of quantitative predictions with the observed optical line widths indicates that it is not the major additive broadening component. Derivation of Te values for H+ from radio+optical and optical-only ionized hydrogen emission showed that this temperature is close to that derived from [N II] and that the transition from the well-known flat extinction curve which applies in the Huygens region to a more normal steep extinction curve occurs immediately outside of the Bright Bar feature of the nebula.

Gallium Arsenide detectors for X-ray and electron (beta particle) spectroscopy

NASA Astrophysics Data System (ADS)

Lioliou, G.; Barnett, A. M.

2016-11-01

Results characterizing GaAs p+-i-n+ mesa photodiodes with a 10 μm i layer for their spectral response under illumination of X-rays and beta particles are presented. A total of 22 devices, having diameters of 200 μm and 400 μm, were electrically characterized at room temperature. All devices showed comparable characteristics with a measured leakage current ranging from 4 nA/cm2 to 67 nA/cm2 at an internal electric field of 50 kV/cm. Their unintentionally doped i layers were found to be almost fully depleted at 0 V due to their low doping density. 55Fe X-ray spectra were obtained using one 200 μm diameter device and one 400 μm diameter device. The best energy resolution (FWHM at 5.9 keV) achieved was 625 eV using the 200 μm and 740 eV using the 400 μm diameter device, respectively. Noise analysis showed that the limiting factor for the energy resolution of the system was the dielectric noise; if this noise was eliminated by better design of the front end of the readout electronics, the achievable resolution would be 250 eV. 63Ni beta particle spectra obtained using the 200 μm diameter device showed the potential utility of these detectors for electron and beta particle detection. The development of semiconductor electron spectrometers is important particularly for space plasma physics; such devices may find use in future space missions to study the plasma environment of Jupiter and Europa and the predicted electron impact excitation of water vapor plumes from Europa hypothesized as a result of recent Hubble Space Telescope (HST) UV observations.

High-resolution photoelectron spectroscopy of TiO3H2-: Probing the TiO2- + H2O dissociative adduct

NASA Astrophysics Data System (ADS)

DeVine, Jessalyn A.; Abou Taka, Ali; Babin, Mark C.; Weichman, Marissa L.; Hratchian, Hrant P.; Neumark, Daniel M.

2018-06-01

Slow electron velocity-map imaging spectroscopy of cryogenically cooled TiO3H2- anions is used to probe the simplest titania/water reaction, TiO20/- + H2O. The resultant spectra show vibrationally resolved structure assigned to detachment from the cis-dihydroxide TiO(OH)2- geometry based on density functional theory calculations, demonstrating that for the reaction of the anionic TiO2- monomer with a single water molecule, the dissociative adduct (where the water is split) is energetically preferred over a molecularly adsorbed geometry. This work represents a significant improvement in resolution over previous measurements, yielding an electron affinity of 1.2529(4) eV as well as several vibrational frequencies for neutral TiO(OH)2. The energy resolution of the current results combined with photoelectron angular distributions reveals Herzberg-Teller coupling-induced transitions to Franck-Condon forbidden vibrational levels of the neutral ground state. A comparison to the previously measured spectrum of bare TiO2- indicates that reaction with water stabilizes neutral TiO2 more than the anion, providing insight into the fundamental chemical interactions between titania and water.

Time-Dependent Density Functional Theory for Open Systems and Its Applications.

PubMed

Chen, Shuguang; Kwok, YanHo; Chen, GuanHua

2018-02-20

Photovoltaic devices, electrochemical cells, catalysis processes, light emitting diodes, scanning tunneling microscopes, molecular electronics, and related devices have one thing in common: open quantum systems where energy and matter are not conserved. Traditionally quantum chemistry is confined to isolated and closed systems, while quantum dissipation theory studies open quantum systems. The key quantity in quantum dissipation theory is the reduced system density matrix. As the reduced system density matrix is an O(M! × M!) matrix, where M is the number of the particles of the system of interest, quantum dissipation theory can only be employed to simulate systems of a few particles or degrees of freedom. It is thus important to combine quantum chemistry and quantum dissipation theory so that realistic open quantum systems can be simulated from first-principles. We have developed a first-principles method to simulate the dynamics of open electronic systems, the time-dependent density functional theory for open systems (TDDFT-OS). Instead of the reduced system density matrix, the key quantity is the reduced single-electron density matrix, which is an N × N matrix where N is the number of the atomic bases of the system of interest. As the dimension of the key quantity is drastically reduced, the TDDFT-OS can thus be used to simulate the dynamics of realistic open electronic systems and efficient numerical algorithms have been developed. As an application, we apply the method to study how quantum interference develops in a molecular transistor in time domain. We include electron-phonon interaction in our simulation and show that quantum interference in the given system is robust against nuclear vibration not only in the steady state but also in the transient dynamics. As another application, by combining TDDFT-OS with Ehrenfest dynamics, we study current-induced dissociation of water molecules under scanning tunneling microscopy and follow its time dependent dynamics. Given the rapid development in ultrafast experiments with atomic resolution in recent years, time dependent simulation of open electronic systems will be useful to gain insight and understanding of such experiments. This Account will mainly focus on the practical aspects of the TDDFT-OS method, describing the numerical implementation and demonstrating the method with applications.

Charge density wave order in 1D mirror twin boundaries of single-layer MoSe 2

DOE PAGES

Barja, Sara; Wickenburg, Sebastian; Liu, Zhen-Fei; ...

2016-04-18

Here, We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe 2. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe 2 and MoS 2. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent densitymore » of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.« less

SPECTRE (www.noveltis.fr/spectre): a web Service for Ionospheric Products

NASA Astrophysics Data System (ADS)

Jeansou, E.; Crespon, F.; Garcia, R.; Helbert, J.; Moreaux, G.; Lognonne, P.

2005-12-01

The dense GPS networks developed for geodesic applications appear to be very efficient ionospheric sensors because of interaction between plasma and electromagnetic waves. Indeed, the dual frequency receivers provide data from which the Slant Total Electron Content (STEC) can be easily extracted to compute Vertical Total Electron Content (VTEC) maps. The SPECTRE project, Service and Products for ionospheric Electron Content and Tropospheric Refractivity over Europe, is currently a pre-operational service providing VTEC maps with high time and space resolution after 3 days time delay (http://www.noveltis.fr/spectre and http://ganymede.ipgp.jussieu.fr/spectre). This project is a part of SWENET, SpaceWeather European Network, initiated by the European Space Agency. The SPECTRE data products are useful for many applications. We will present these applications in term of interest for the scientific community with a special focus on spaceweather and transient ionospheric perturbations related to Earthquakes. Moreover, the pre-operational extensions of SPECTRE to the californian (SCIGN/BARD) and japanese (GEONET) dense GPS networks will be presented. Then the method of 3D tomography of the electron density from GPS data will be presented and its resolution discussed. The expected improvements of the 3D tomographic images by new tomographic reconstruction algorithms and by the advent of the Galileo system will conclude the presentation.

Femtosecond Snapshots of quantum mechanics at work in plasmonic nano-structures

NASA Astrophysics Data System (ADS)

Carbone, Fabrizio

Ultrafast Transmission Electron Microscopy enabled a new technique (Photon-Induced Near Field Electron Microscopy, PINEM), capable of controlling electromagnetic fields confined on the surface of nanostructures and image their properties with nm-resolution in direct space and fs resolution in time. In this presentation, we will show some recent results where the standing wave formed by the plasmonic field confined on the surface of one silver nano-wire was imaged together with its energy exchange with the imaging electrons. In these results, both the interference and the quantization of the plasmonic near field could be imaged simultaneously, revealing both a quantum and a classical aspect of the electromagnetic field in one snapshot. The implications of these results will be discussed, and we will also present new ideas and methodologies to go beyond such an experiment and image the interaction between single electrons and single plasmons. We will also show that shaping the electron density in a thin film via light pulses is possible by taking advantage of the plasmon-plasmon interference and the ability of light polarization to control the excitation of different plasmonic field geometries in ad hoc designed nanostructures. Movies of the propagation of plasmons will also be presented, providing insights into their speed, propagation losses and the effect of confinment. This work was supported by an ERC Grant USED.

Electronic Structure and Band Gap of Fullerenes on Tungsten Surfaces: Transition from a Semiconductor to a Metal Triggered by Annealing.

PubMed

Monazami, Ehsan; McClimon, John B; Rondinelli, James; Reinke, Petra

2016-12-21

The understanding and control of molecule-metal interfaces is critical to the performance of molecular electronics and photovoltaics devices. We present a study of the interface between C 60 and W, which is a carbide-forming transition metal. The complex solid-state reaction at the interface can be exploited to adjust the electronic properties of the molecule layer. Scanning tunneling microscopy/spectroscopy measurements demonstrate the progression of this reaction from wide band gap (>2.5 eV) to metallic molecular surface during annealing from 300 to 800 K. Differential conduction maps with 10 4 scanning tunneling spectra are used to quantify the transition in the density of states and the reduction of the band gap during annealing with nanometer spatial resolution. The electronic transition is spatially homogeneous, and the surface band gap can therefore be adjusted by a targeted annealing step. The modified molecules, which we call nanospheres, are quite resistant to ripening and coalescence, unlike any other metallic nanoparticle of the same size. Densely packed C 60 and isolated C 60 molecules show the same transition in electronic structure, which confirms that the transformation is controlled by the reaction at the C 60 -W interface. Density functional theory calculations are used to develop possible reaction pathways in agreement with experimentally observed electronic structure modulation. Control of the band gap by the choice of annealing temperature is a unique route to tailoring molecular-layer electronic properties.

Electron beam induced current in the high injection regime.

PubMed

Haney, Paul M; Yoon, Heayoung P; Koirala, Prakash; Collins, Robert W; Zhitenev, Nikolai B

2015-07-24

Electron beam induced current (EBIC) is a powerful technique which measures the charge collection efficiency of photovoltaics with sub-micron spatial resolution. The exciting electron beam results in a high generation rate density of electron-hole pairs, which may drive the system into nonlinear regimes. An analytic model is presented which describes the EBIC response when the total electron-hole pair generation rate exceeds the rate at which carriers are extracted by the photovoltaic cell, and charge accumulation and screening occur. The model provides a simple estimate of the onset of the high injection regime in terms of the material resistivity and thickness, and provides a straightforward way to predict the EBIC lineshape in the high injection regime. The model is verified by comparing its predictions to numerical simulations in one- and two-dimensions. Features of the experimental data, such as the magnitude and position of maximum collection efficiency versus electron beam current, are consistent with the three-dimensional model.

Laser-driven relativistic electron beam interaction with solid dielectric

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarkisov, G. S.; Ivanov, V. V.; Leblanc, P.

2012-07-30

The multi-frames shadowgraphy, interferometry and polarimetry diagnostics with sub-ps time resolution were used for an investigation of ionization wave dynamics inside a glass target induced by laser-driven relativistic electron beam. Experiments were done using the 50 TW Leopard laser at the UNR. For a laser flux of {approx}2 Multiplication-Sign 10{sup 18}W/cm{sup 2} a hemispherical ionization wave propagates at c/3. The maximum of the electron density inside the glass target is {approx}2 Multiplication-Sign 10{sup 19}cm{sup -3}. Magnetic and electric fields are less than {approx}15 kG and {approx}1 MV/cm, respectively. The electron temperature has a maximum of {approx}0.5 eV. 2D interference phasemore » shift shows the 'fountain effect' of electron beam. The very low ionization inside glass target {approx}0.1% suggests a fast recombination at the sub-ps time scale. 2D PIC-simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields.« less

Carbohydrate structure: the rocky road to automation.

PubMed

Agirre, Jon; Davies, Gideon J; Wilson, Keith S; Cowtan, Kevin D

2017-06-01

With the introduction of intuitive graphical software, structural biologists who are not experts in crystallography are now able to build complete protein or nucleic acid models rapidly. In contrast, carbohydrates are in a wholly different situation: scant automation exists, with manual building attempts being sometimes toppled by incorrect dictionaries or refinement problems. Sugars are the most stereochemically complex family of biomolecules and, as pyranose rings, have clear conformational preferences. Despite this, all refinement programs may produce high-energy conformations at medium to low resolution, without any support from the electron density. This problem renders the affected structures unusable in glyco-chemical terms. Bringing structural glycobiology up to 'protein standards' will require a total overhaul of the methodology. Time is of the essence, as the community is steadily increasing the production rate of glycoproteins, and electron cryo-microscopy has just started to image them in precisely that resolution range where crystallographic methods falter most. Copyright © 2016 Elsevier Ltd. All rights reserved.

Experimental evidence and structural modeling of nonstoichiometric (010) surfaces coexisting in hydroxyapatite nano-crystals.

PubMed

Ospina, C A; Terra, J; Ramirez, A J; Farina, M; Ellis, D E; Rossi, A M

2012-01-01

High-resolution transmission electron microscopy (HRTEM) and ab initio quantum-mechanical calculations of electronic structure were combined to investigate the structure of the hydroxyapatite (HA) (010) surface, which plays an important role in HA interactions with biological media. HA was synthesized by in vitro precipitation at 37°C. HRTEM images revealed thin elongated rod nanoparticles with preferential growth along the [001] direction and terminations parallel to the (010) plane. The focal series reconstruction (FSR) technique was applied to develop an atomic-scale structural model of the high-resolution images. The HRTEM simulations identified the coexistence of two structurally distinct terminations for (010) surfaces: a rather flat Ca(II)-terminated surface and a zig-zag structure with open OH channels. Density functional theory (DFT) was applied in a periodic slab plane-wave pseudopotential approach to refine details of atomic coordination and bond lengths of Ca(I) and Ca(II) sites in hydrated HA (010) surfaces, starting from the HRTEM model. Copyright © 2011 Elsevier B.V. All rights reserved.

Probing optical band gaps at the nanoscale in NiFe₂O₄ and CoFe₂O₄ epitaxial films by high resolution electron energy loss spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dileep, K.; Loukya, B.; Datta, R., E-mail: ranjan@jncasr.ac.in

2014-09-14

Nanoscale optical band gap variations in epitaxial thin films of two different spinel ferrites, i.e., NiFe₂O₄ (NFO) and CoFe₂O₄ (CFO), have been investigated by spatially resolved high resolution electron energy loss spectroscopy. Experimentally, both NFO and CFO show indirect/direct band gaps around 1.52 eV/2.74 and 2.3 eV, and 1.3 eV/2.31 eV, respectively, for the ideal inverse spinel configuration with considerable standard deviation in the band gap values for CFO due to various levels of deviation from the ideal inverse spinel structure. Direct probing of the regions in both the systems with tetrahedral A site cation vacancy, which is distinct frommore » the ideal inverse spinel configuration, shows significantly smaller band gap values. The experimental results are supported by the density functional theory based modified Becke-Johnson exchange correlation potential calculated band gap values for the different cation configurations.« less

Near-Atomic Resolution Structure of a Plant Geminivirus Determined by Electron Cryomicroscopy.

PubMed

Hipp, Katharina; Grimm, Clemens; Jeske, Holger; Böttcher, Bettina

2017-08-01

African cassava mosaic virus is a whitefly-transmitted geminivirus which forms unique twin particles of incomplete icosahedra that are joined at five-fold vertices, building an unusual waist. How its 22 capsomers interact within a half-capsid or across the waist is unknown thus far. Using electron cryo-microscopy and image processing, we determined the virion structure with a resolution of 4.2 Å and built an atomic model for its capsid protein. The inter-capsomer contacts mediated by the flexible N termini and loop regions differed within the half-capsids and at the waist, explaining partly the unusual twin structure. The tip of the pentameric capsomer is sealed by a plug formed by a turn region harboring the evolutionary conserved residue Y193. Basic amino acid residues inside the capsid form a positively charged pocket next to the five-fold axis of the capsomer suitable for binding DNA. Within this pocket, density most likely corresponding to DNA was resolved. Copyright © 2017 Elsevier Ltd. All rights reserved.

Regional application of multi-layer artificial neural networks in 3-D ionosphere tomography

NASA Astrophysics Data System (ADS)

Ghaffari Razin, Mir Reza; Voosoghi, Behzad

2016-08-01

Tomography is a very cost-effective method to study physical properties of the ionosphere. In this paper, residual minimization training neural network (RMTNN) is used in voxel-based tomography to reconstruct of 3-D ionosphere electron density with high spatial resolution. For numerical experiments, observations collected at 37 GPS stations from Iranian permanent GPS network (IPGN) are used. A smoothed TEC approach was used for absolute STEC recovery. To improve the vertical resolution, empirical orthogonal functions (EOFs) obtained from international reference ionosphere 2012 (IRI-2012) used as object function in training neural network. Ionosonde observations is used for validate reliability of the proposed method. Minimum relative error for RMTNN is 1.64% and maximum relative error is 15.61%. Also root mean square error (RMSE) of 0.17 × 1011 (electrons/m3) is computed for RMTNN which is less than RMSE of IRI2012. The results show that RMTNN has higher accuracy and compiles speed than other ionosphere reconstruction methods.

Development of a High Resolution X-Ray Spectrometer for the National Ignition Facility (NIF)

NASA Astrophysics Data System (ADS)

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; Efthimion, P. C.; Ellis, R.; Gao, L.; Maddox, J.; Pablant, N. A.; Schneider, M. B.; Chen, H.; Ayers, S.; Kauffman, R. L.; Macphee, A. G.; Beiersdorfer, P.; Ma, T.; Nora, R. C.; Scott, H. A.; Thorn, D. B.; Kilkenny, J. D.; Nelson, D.; Shoup, M., III; Maron, Y.

2016-10-01

A high resolution (E/ ΔE 2000) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in NIF experiments. The instrument will be a positioner insertable cassette designed to infer electron density in compressed capsules from Stark broadening of the helium- β (1s2-1s3p) lines of krypton, and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and sagittally focus (1) the Kr He β complex and (2) the He α and Ly α complexes onto a streak camera photocathode for time resolved measurement. A third cylindrical crystal will focus the full He α to He β spectrum onto an image plate for a time integrated calibration spectrum. Performance estimates and design status will be presented. Performed under the auspices of the US DOE by PPPL under contract DE-AC02-09CH11466 and by LLNL under contract DE-AC52-07NA27344.

Fitting Multimeric Protein Complexes into Electron Microscopy Maps Using 3D Zernike Descriptors

PubMed Central

Esquivel-Rodríguez, Juan; Kihara, Daisuke

2012-01-01

A novel computational method for fitting high-resolution structures of multiple proteins into a cryoelectron microscopy map is presented. The method named EMLZerD generates a pool of candidate multiple protein docking conformations of component proteins, which are later compared with a provided electron microscopy (EM) density map to select the ones that fit well into the EM map. The comparison of docking conformations and the EM map is performed using the 3D Zernike descriptor (3DZD), a mathematical series expansion of three-dimensional functions. The 3DZD provides a unified representation of the surface shape of multimeric protein complex models and EM maps, which allows a convenient, fast quantitative comparison of the three dimensional structural data. Out of 19 multimeric complexes tested, near native complex structures with a root mean square deviation of less than 2.5 Å were obtained for 14 cases while medium range resolution structures with correct topology were computed for the additional 5 cases. PMID:22417139

Fitting multimeric protein complexes into electron microscopy maps using 3D Zernike descriptors.

PubMed

Esquivel-Rodríguez, Juan; Kihara, Daisuke

2012-06-14

A novel computational method for fitting high-resolution structures of multiple proteins into a cryoelectron microscopy map is presented. The method named EMLZerD generates a pool of candidate multiple protein docking conformations of component proteins, which are later compared with a provided electron microscopy (EM) density map to select the ones that fit well into the EM map. The comparison of docking conformations and the EM map is performed using the 3D Zernike descriptor (3DZD), a mathematical series expansion of three-dimensional functions. The 3DZD provides a unified representation of the surface shape of multimeric protein complex models and EM maps, which allows a convenient, fast quantitative comparison of the three-dimensional structural data. Out of 19 multimeric complexes tested, near native complex structures with a root-mean-square deviation of less than 2.5 Å were obtained for 14 cases while medium range resolution structures with correct topology were computed for the additional 5 cases.

Fabrication of Si3N4 thin films on phynox alloy substrates for electronic applications

NASA Astrophysics Data System (ADS)

Shankernath, V.; Naidu, K. Lakshun; Krishna, M. Ghanashyam; Padmanabhan, K. A.

2018-04-01

Thin films of Si3N4 are deposited on Phynox alloy substrates using radio frequency magnetron sputtering. The thickness of the films was varied between 80-150 nm by increasing the duration of deposition from 1 to 3 h at a fixed power density and working pressure. X-ray diffraction patterns reveal that the Si3N4 films had crystallized inspite of the substrates not being heated during deposition. This was confirmed using selected area electron diffraction and high resolution transmission electron microscopy also. It is postulated that a low lattice misfit between Si3N4 and Phynox provides energetically favourable conditions for ambient temperature crystallization. The hardness of the films is of the order of 6 to 9 GPa.

Cathodochromic storage device

NASA Technical Reports Server (NTRS)

Bosomworth, D. R.; Moles, W. H.

1969-01-01

A memory and display device has been developed by combing a fast phosphor layer with a cathodochromic layer in a cathode ray tube. Images are stored as patterns of electron beam induced optical density in the cathodo-chromic material. The stored information is recovered by exciting the backing, fast phosphor layer with a constant current electron beam and detecting the emitted radiation which is modulated by absorption in the cathodochromic layer. The storage can be accomplished in one or more TV frames (1/30 sec each). More than 500 TV line resolution and close to 2:1 contrast ratio are possible. The information storage time in a dark environment is approximately 24 hours. A reconstituted (readout) electronic video signal can be generated continuously for times in excess of 10 minutes or periodically for several hours.

Ground-State Charge-Density Distribution in a Crystal of the Luminescent ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline.

PubMed

Jarzembska, Katarzyna N; Kamiński, Radosław; Durka, Krzysztof; Woźniak, Krzysztof

2018-05-10

This contribution is devoted to the first electron density studies of a luminescent oxyquinolinato boron complex in the solid state. ortho-Phenylenediboronic acid mixed with 8-hydroxyquinoline in dioxane forms high-quality single crystals via slow solvent evaporation, which allows successful high resolution data collection (sin θ/λ = 1.2 Å -1 ) and charge density distribution modeling. Particular attention has been paid to the boron-oxygen fragment connecting the two parts of the complex, and to the solvent species exhibiting anharmonic thermal motion. The experiment and theory compared rather well in terms of atomic charges and volumes, except for the boron centers. Boron atoms, as expected, constitute the most electron-deficient species in the complex molecule, whereas the neighboring oxygen and carbon atoms are the most significantly negatively charged ones. This part of the molecule appears to be very much involved in the charge transfer occurring between the acid fragment and oxyquinoline moiety leading to the observed fluorescence, as supported by the time-dependent density functional theory (TDDFT) results and the generated transition density maps. TDDFT calculations indicated that p-type atomic orbitals contributing to the HOMO-1, HOMO, and LUMO play the major role in the lowest energy transitions, and enabled further comparison with the charge density features, which is discussed in details. Furthermore, the results confirmed the known fact the Q ligand character is most important for the spectroscopic properties of this class of complexes.

Comparative Morphology of Mg+ and O+ Ions Made by the HIRAAS Experiment

NASA Astrophysics Data System (ADS)

Dymond, K.

2017-12-01

We present coincident observations of the spatial distribution of the Mg+ ion and O+ ions made by the High Resolution Airglow and Aurora Spectroscopy (HIRAAS) experiment that flew on the United States Air Force Advanced Research and Global Observing Satellite (ARGOS) mission during 1999-2002. The HIRAAS experiment featured two instruments that made coincident ultraviolet limb scan measurements viewing aft of the satellite. In the first year of mission operations, the Ionospheric Spectroscopy and Atmospheric Chemistry (ISAAC) instrument made observations of the Mg+ emission near 280 nm with a cadence of 100 s and altitude resolution of 5 km. The Low Resolution Airglow and Aurora Spectrograph (LORAAS) instrument made measurements of the 80-170 nm region of the Earth's airglow spectrum, including the 91.1 nm emission produced by radiative recombination of O+ and electrons, at 100 s cadence and 5 km altitude resolution. We use the recently developed Volume Emission Rate Tomography (VERT) technique to invert the UV measurements and produce the Mg+ and O+ ion distributions in the orbit plane of the satellite. We present our approach and comparisons of the distributions to each other and the International Reference Ionosphere model. Similar to previous metal ion density measurements, we see considerable variability over the globe with extended plumes of Mg+ ion density extending upward from 100 km to greater than 700 km and small compact layers. However, the O+ ion densities do not show similar structures, indicating that the Mg+ structures are likely driven by processes that act below the F-region ionosphere where O+ is a minor species. The global distribution of the Mg+ ions, which is related to the development of Sporadic-E, is of particular interest in this study.

Nano-size defects in arsenic-implanted HgCdTe films: a HRTEM study

NASA Astrophysics Data System (ADS)

Bonchyk, O. Yu.; Savytskyy, H. V.; Swiatek, Z.; Morgiel, Y.; Izhnin, I. I.; Voitsekhovskii, A. V.; Korotaev, A. G.; Mynbaev, K. D.; Fitsych, O. I.; Varavin, V. S.; Dvoretsky, S. A.; Marin, D. V.; Yakushev, M. V.

2018-02-01

Radiation damage and its transformation under annealing were studied with bright-field and high-resolution transmission electron microscopy for arsenic-implanted HgCdTe films with graded-gap surface layers. In addition to typical highly defective layers in as-implanted material, a 50 nm-thick sub-surface layer with very low defect density was observed. The main defects in other layers after implantation were dislocation loops, yet after arsenic activation annealing, the dominating defects were single dislocations. Transport (from depth to surface), transformation and annihilation of radiation-induced defects were observed as a result of annealing, with the depth with the maximum defect density decreasing from 110 to 40 nm.

Ionospheric TEC Weather Map Over South America

NASA Astrophysics Data System (ADS)

Takahashi, H.; Wrasse, C. M.; Denardini, C. M.; Pádua, M. B.; de Paula, E. R.; Costa, S. M. A.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. Galera; Ivo, A.; Sant'Anna, N.

2016-11-01

Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Contínuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total 140 sites, have been used. TECMAPs with a time resolution of 10 min are produced in 12 h time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1 TECU = 1016 el m-2 (TECU) <10) to the crest region (TECU > 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

High resolution Thomson scattering system for steady-state linear plasma sources

NASA Astrophysics Data System (ADS)

Lee, K. Y.; Lee, K. I.; Kim, J. H.; Lho, T.

2018-01-01

The high resolution Thomson scattering system with 63 points along a 25 mm line measures the radial electron temperature (Te) and its density (ne) in an argon plasma. By using a DC arc source with lanthanum hexaboride (LaB6) electrode, plasmas with electron temperature of over 5 eV and densities of 1.5 × 1019 m-3 have been measured. The system uses a frequency doubled (532 nm) Nd:YAG laser with 0.25 J/pulse at 20 Hz. The scattered light is collected and sent to a triple-grating spectrometer via optical-fibers, where images are recorded by an intensified charge coupled device (ICCD) camera. Although excellent in stray-light reduction, a disadvantage comes with its relatively low optical transmission and in sampling a tiny scattering volume. Thus requires accumulating multitude of images. In order to improve photon statistics, pixel binning in the ICCD camera as well as enlarging the intermediate slit-width inside the triple-grating spectrometer has been exploited. In addition, the ICCD camera capture images at 40 Hz while the laser is at 20 Hz. This operation mode allows us to alternate between background and scattering shot images. By image subtraction, influences from the plasma background are effectively taken out. Maximum likelihood estimation that uses a parameter sweep finds best fitting parameters Te and ne with the incoherent scattering spectrum.

High resolution Thomson scattering system for steady-state linear plasma sources.

PubMed

Lee, K Y; Lee, K I; Kim, J H; Lho, T

2018-01-01

The high resolution Thomson scattering system with 63 points along a 25 mm line measures the radial electron temperature (T e ) and its density (n e ) in an argon plasma. By using a DC arc source with lanthanum hexaboride (LaB 6 ) electrode, plasmas with electron temperature of over 5 eV and densities of 1.5 × 10 19 m -3 have been measured. The system uses a frequency doubled (532 nm) Nd:YAG laser with 0.25 J/pulse at 20 Hz. The scattered light is collected and sent to a triple-grating spectrometer via optical-fibers, where images are recorded by an intensified charge coupled device (ICCD) camera. Although excellent in stray-light reduction, a disadvantage comes with its relatively low optical transmission and in sampling a tiny scattering volume. Thus requires accumulating multitude of images. In order to improve photon statistics, pixel binning in the ICCD camera as well as enlarging the intermediate slit-width inside the triple-grating spectrometer has been exploited. In addition, the ICCD camera capture images at 40 Hz while the laser is at 20 Hz. This operation mode allows us to alternate between background and scattering shot images. By image subtraction, influences from the plasma background are effectively taken out. Maximum likelihood estimation that uses a parameter sweep finds best fitting parameters T e and n e with the incoherent scattering spectrum.

Statistical density modification using local pattern matching

DOEpatents

Terwilliger, Thomas C.

2007-01-23

A computer implemented method modifies an experimental electron density map. A set of selected known experimental and model electron density maps is provided and standard templates of electron density are created from the selected experimental and model electron density maps by clustering and averaging values of electron density in a spherical region about each point in a grid that defines each selected known experimental and model electron density maps. Histograms are also created from the selected experimental and model electron density maps that relate the value of electron density at the center of each of the spherical regions to a correlation coefficient of a density surrounding each corresponding grid point in each one of the standard templates. The standard templates and the histograms are applied to grid points on the experimental electron density map to form new estimates of electron density at each grid point in the experimental electron density map.

Imaging of current density distributions with a Nb weak-link scanning nano-SQUID microscope

PubMed Central

Shibata, Yusuke; Nomura, Shintaro; Kashiwaya, Hiromi; Kashiwaya, Satoshi; Ishiguro, Ryosuke; Takayanagi, Hideaki

2015-01-01

Superconducting quantum interference devices (SQUIDs) are accepted as one of the highest magnetic field sensitive probes. There are increasing demands to image local magnetic fields to explore spin properties and current density distributions in a two-dimensional layer of semiconductors or superconductors. Nano-SQUIDs have recently attracting much interest for high spatial resolution measurements in nanometer-scale samples. Whereas weak-link Dayem Josephson junction nano-SQUIDs are suitable to miniaturization, hysteresis in current-voltage (I-V) characteristics that is often observed in Dayem Josephson junction is not desirable for a scanning microscope. Here we report on our development of a weak-link nano-SQUIDs scanning microscope with small hysteresis in I-V curve and on reconstructions of two-dimensional current density vector in two-dimensional electron gas from measured magnetic field. PMID:26459874

Efficient evaluation of Coulomb integrals in a mixed Gaussian and plane-wave basis using the density fitting and Cholesky decomposition.

PubMed

Čársky, Petr; Čurík, Roman; Varga, Štefan

2012-03-21

The objective of this paper is to show that the density fitting (resolution of the identity approximation) can also be applied to Coulomb integrals of the type (k(1)(1)k(2)(1)|g(1)(2)g(2)(2)), where k and g symbols refer to plane-wave functions and gaussians, respectively. We have shown how to achieve the accuracy of these integrals that is needed in wave-function MO and density functional theory-type calculations using mixed Gaussian and plane-wave basis sets. The crucial issues for achieving such a high accuracy are application of constraints for conservation of the number electrons and components of the dipole moment, optimization of the auxiliary basis set, and elimination of round-off errors in the matrix inversion. © 2012 American Institute of Physics

Imaging of current density distributions with a Nb weak-link scanning nano-SQUID microscope

NASA Astrophysics Data System (ADS)

Shibata, Yusuke; Nomura, Shintaro; Kashiwaya, Hiromi; Kashiwaya, Satoshi; Ishiguro, Ryosuke; Takayanagi, Hideaki

2015-10-01

Superconducting quantum interference devices (SQUIDs) are accepted as one of the highest magnetic field sensitive probes. There are increasing demands to image local magnetic fields to explore spin properties and current density distributions in a two-dimensional layer of semiconductors or superconductors. Nano-SQUIDs have recently attracting much interest for high spatial resolution measurements in nanometer-scale samples. Whereas weak-link Dayem Josephson junction nano-SQUIDs are suitable to miniaturization, hysteresis in current-voltage (I-V) characteristics that is often observed in Dayem Josephson junction is not desirable for a scanning microscope. Here we report on our development of a weak-link nano-SQUIDs scanning microscope with small hysteresis in I-V curve and on reconstructions of two-dimensional current density vector in two-dimensional electron gas from measured magnetic field.

Jang Bogo Antarctic Ionosonde

NASA Astrophysics Data System (ADS)

Bullett, Terry; Jee, Geonhwa; Livingston, Robert; Kim, Jeong-Han; Zabotin, Nikolay; Lee, Chang-Sup; Grubb, Richard; Mabie, Justin; Kwon, Hyuck-Jin

2016-04-01

The Korean Polar Research Institute has established the Jang Bogo research station in Antarctica on Terra Nova Bay (74.62°S, 164.23°E). One of the space environment sensors installed in 2014 is a world class research ionosonde facility consisting of a Vertical Incidence Pulsed Ionospheric Radar (VIPIR) with Dynasonde signal processing. The VIPIR is an MF/HF radar oeprating from 0.5 to 25 MHz. The transmit antenna is a 36x75x75m dual vertical incidence log periodic design and the receive antenna is a 70x70m array of 8 orthogonal 4m active dipoles attached to 8 coherent digital receivers. Full resolution In-Phase and Quadrature data are recorded for post analysis. The low atmospheric noise and low interference combine with the high system performance to produce ionogram data of very high quality and allow measurements with high time resolution. The 2015 data were taken using the first generation VIPIR electronics on loan from Boulder. Antenna repairs and the installation of the second generation VIPIR electronics were completed at the end of 2015. Phase based Dynasonde analysis techniques are applied to the VIPIR data to perform echo detection and to derive electron density profiles and velocity vectors.

Synthesis and characterization of metal-dielectric composites with copper nanoparticles embedded in a glass matrix: A multitechnique approach

NASA Astrophysics Data System (ADS)

Lipinska-Kalita, Kristina E.; Krol, Denise M.; Hemley, Russell J.; Mariotto, Gino; Kalita, Patricia E.; Ohki, Yoshimichi

2005-09-01

The precipitation and growth of copper nanoparticles in an optically transparent aluminosilicate glass matrix was investigated. The size of particles in this heterophase glass-based composite was modified in a controlled manner by isothermal heat treatments. A multitechnique approach, consisting of Raman scattering spectroscopy, high-resolution transmission electron microscopy, x-ray diffraction technique, and optical absorption spectroscopy, has been used to study the nucleation and crystallization processes. Optical absorption spectroscopy revealed the presence of intense absorption bands attributed to oscillations of free electrons, known as the surface-plasmon resonance band of copper particles, and confirmed a gradual increase of the particles' mean size and density with annealing time. The Raman scattering on acoustical phonons from Cu quantum dots in the glass matrix measured for off-resonance conditions demonstrated the presence of intense, inhomogeneously broadened peaks that have been assigned to the confined acoustic eigenmodes of copper nanoparticles. The particle-size dependence of the acoustic peak energies and the relation between the size distribution and bandwidths of these peaks were derived. High-resolution transmission electron microscopy was used to monitor the nucleation of the nanoparticles and to estimate their mean size.

Structural Insights into High Density Lipoprotein: Old Models and New Facts

PubMed Central

Gogonea, Valentin

2016-01-01

The physiological link between circulating high density lipoprotein (HDL) levels and cardiovascular disease is well-documented, albeit its intricacies are not well-understood. An improved appreciation of HDL function and overall role in vascular health and disease requires at its foundation a better understanding of the lipoprotein's molecular structure, its formation, and its process of maturation through interactions with various plasma enzymes and cell receptors that intervene along the pathway of reverse cholesterol transport. This review focuses on summarizing recent developments in the field of lipid free apoA-I and HDL structure, with emphasis on new insights revealed by newly published nascent and spherical HDL models constructed by combining low resolution structures obtained from small angle neutron scattering (SANS) with contrast variation and geometrical constraints derived from hydrogen–deuterium exchange (HDX), crosslinking mass spectrometry, electron microscopy, Förster resonance energy transfer, and electron spin resonance. Recently published low resolution structures of nascent and spherical HDL obtained from SANS with contrast variation and isotopic labeling of apolipoprotein A-I (apoA-I) will be critically reviewed and discussed in terms of how they accommodate existing biophysical structural data from alternative approaches. The new low resolution structures revealed and also provided some answers to long standing questions concerning lipid organization and particle maturation of lipoproteins. The review will discuss the merits of newly proposed SANS based all atom models for nascent and spherical HDL, and compare them with accepted models. Finally, naturally occurring and bioengineered mutations in apoA-I, and their impact on HDL phenotype, are reviewed and discuss together with new therapeutics employed for restoring HDL function. PMID:26793109

Improving the accuracy of macromolecular structure refinement at 7 Å resolution.

PubMed

Brunger, Axel T; Adams, Paul D; Fromme, Petra; Fromme, Raimund; Levitt, Michael; Schröder, Gunnar F

2012-06-06

In X-ray crystallography, molecular replacement and subsequent refinement is challenging at low resolution. We compared refinement methods using synchrotron diffraction data of photosystem I at 7.4 Å resolution, starting from different initial models with increasing deviations from the known high-resolution structure. Standard refinement spoiled the initial models, moving them further away from the true structure and leading to high R(free)-values. In contrast, DEN refinement improved even the most distant starting model as judged by R(free), atomic root-mean-square differences to the true structure, significance of features not included in the initial model, and connectivity of electron density. The best protocol was DEN refinement with initial segmented rigid-body refinement. For the most distant initial model, the fraction of atoms within 2 Å of the true structure improved from 24% to 60%. We also found a significant correlation between R(free) values and the accuracy of the model, suggesting that R(free) is useful even at low resolution. Copyright © 2012 Elsevier Ltd. All rights reserved.

Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection

NASA Astrophysics Data System (ADS)

Nakamura, Takuma; Nakamura, Rumi; Haseagwa, Hiroshi

2016-03-01

Spatial dimensions of the detailed structures of the electron diffusion region in anti-parallel magnetic reconnection were analyzed based on two-dimensional fully kinetic particle-in-cell simulations. The electron diffusion region in this study is defined as the region where the positive reconnection electric field is sustained by the electron inertial and non-gyrotropic pressure components. Past kinetic studies demonstrated that the dimensions of the whole electron diffusion region and the inner non-gyrotropic region are scaled by the electron inertial length de and the width of the electron meandering motion, respectively. In this study, we successfully obtained more precise scalings of the dimensions of these two regions than the previous studies by performing simulations with sufficiently small grid spacing (1/16-1/8 de) and a sufficient number of particles (800 particles cell-1 on average) under different conditions changing the ion-to-electron mass ratio, the background density and the electron βe (temperature). The obtained scalings are adequately supported by some theories considering spatial variations of field and plasma parameters within the diffusion region. In the reconnection inflow direction, the dimensions of both regions are proportional to de based on the background density. Both dimensions also depend on βe based on the background values, but the dependence in the inner region ( ˜ 0.375th power) is larger than the whole region (0.125th power) reflecting the orbits of meandering and accelerated electrons within the inner region. In the outflow direction, almost only the non-gyrotropic component sustains the positive reconnection electric field. The dimension of this single-scale diffusion region is proportional to the ion-electron hybrid inertial length (dide)1/2 based on the background density and weakly depends on the background βe with the 0.25th power. These firm scalings allow us to predict observable dimensions in real space which are indeed in reasonable agreement with past in situ spacecraft observations in the Earth's magnetotail and have important implications for future observations with higher resolutions such as the NASA Magnetospheric Multiscale (MMS) mission.

Superior cycle performance and high reversible capacity of SnO2/graphene composite as an anode material for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Liu, Lilai; An, Maozhong; Yang, Peixia; Zhang, Jinqiu

2015-03-01

SnO2/graphene composite with superior cycle performance and high reversible capacity was prepared by a one-step microwave-hydrothermal method using a microwave reaction system. The SnO2/graphene composite was characterized by X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscope, X-ray photoelectron spectroscopy, transmission electron microscopy and high resolution transmission electron microscopy. The size of SnO2 grains deposited on graphene sheets is less than 3.5 nm. The SnO2/graphene composite exhibits high capacity and excellent electrochemical performance in lithium-ion batteries. The first discharge and charge capacities at a current density of 100 mA g-1 are 2213 and 1402 mA h g-1 with coulomb efficiencies of 63.35%. The discharge specific capacities remains 1359, 1228, 1090 and 1005 mA h g-1 after 100 cycles at current densities of 100, 300, 500 and 700 mA g-1, respectively. Even at a high current density of 1000 mA g-1, the first discharge and charge capacities are 1502 and 876 mA h g-1, and the discharge specific capacities remains 1057 and 677 mA h g-1 after 420 and 1000 cycles, respectively. The SnO2/graphene composite demonstrates a stable cycle performance and high reversible capacity for lithium storage.

Polaronic behavior in a weak-coupling superconductor.

PubMed

Swartz, Adrian G; Inoue, Hisashi; Merz, Tyler A; Hikita, Yasuyuki; Raghu, Srinivas; Devereaux, Thomas P; Johnston, Steven; Hwang, Harold Y

2018-02-13

The nature of superconductivity in the dilute semiconductor SrTiO 3 has remained an open question for more than 50 y. The extremely low carrier densities ([Formula: see text]-[Formula: see text] cm -3 ) at which superconductivity occurs suggest an unconventional origin of superconductivity outside of the adiabatic limit on which the Bardeen-Cooper-Schrieffer (BCS) and Migdal-Eliashberg (ME) theories are based. We take advantage of a newly developed method for engineering band alignments at oxide interfaces and access the electronic structure of Nb-doped SrTiO 3 , using high-resolution tunneling spectroscopy. We observe strong coupling to the highest-energy longitudinal optic (LO) phonon branch and estimate the doping evolution of the dimensionless electron-phonon interaction strength ([Formula: see text]). Upon cooling below the superconducting transition temperature ([Formula: see text]), we observe a single superconducting gap corresponding to the weak-coupling limit of BCS theory, indicating an order of magnitude smaller coupling ([Formula: see text]). These results suggest that despite the strong normal state interaction with electrons, the highest LO phonon does not provide a dominant contribution to pairing. They further demonstrate that SrTiO 3 is an ideal system to probe superconductivity over a wide range of carrier density, adiabatic parameter, and electron-phonon coupling strength.

Computation of the influence of scanning probe microscope (SPM) on quantum dot eigenstates and 2DEG potential

NASA Astrophysics Data System (ADS)

Stopa, Michael

2005-03-01

We calculate the electronic structure of GaAs-AlGaAs two-dimensional electron gas (2DEG) devices, such as quantum dots and quantum point contacts (QPCs) in the presence of a tip of a scanning probe microscope at some distance above the surface. The calculation employs standard density functional theory with exchange and correlation treated in the local density approximation. The position and voltage on the tip are varied and the conditions for depletion of the 2DEG are shown to compare favorably to experiment [1]. We show that the size of the depletion region created (by a negative tip voltage) is unexpectedly small due to focusing of the potential lines by the higher dielectric. We study the interaction of the tip with an isolated quantum dot that contains one or two electrons. The raster pattern of the difference between single particle energies reveals that the tip distorts the shape of the confining potential and suggests that excited state properties, if they can be measured experimentally, can contribute to the resolution of spatial information. [1] M.A. Topinka, R.M. Westervelt, E.J. Heller, ``http://meso.deas.harvard.edu/papers/Topinka, PT 56 12 (2003)'' (Imaging Electron Flow), Physics Today 56, 12 (2003).

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

The purpose of the LIEDR (Local Ionospheric Electron Density Reconstruction) system is to acquire and process data from simultaneous ground-based GNSS TEC and digital ionosonde measurements, and subsequently to deduce the vertical electron density distribution in the local ionosphere. LIEDR is primarily designed to operate in real time for service applications, and, if sufficient data from solar and geomagnetic observations are available, to provide short-term forecast as well. For research applications and further development of the system, a post-processing mode of operation is also envisaged. In essence, the reconstruction procedure consists in the following. The high-precision ionosonde measurements are used for directly obtaining the bottom part of the electron density profile. The ionospheric profiler for the lower side (i.e. below the density peak height, hmF2) is based on the Epstein layer functions using the known values of the critical frequencies, foF2 and foE, and the propagation factor, M3000F2. The corresponding bottom-side part of the total electron content is calculated from this profile and is then subtracted from the GPS TEC value in order to obtain the unknown portion of the TEC in the upper side (i.e. above the hmF2). Ionosonde data, together with the simultaneously-measured TEC and empirically obtained O+/H+ ion transition level values, are all required for the determination of the topside electron density scale height. The topside electron density is considered as a sum of the constituent oxygen and hydrogen ion densities with unknown vertical scale heights. The latter are calculated by solving a system of transcendental equations that arise from the incorporation of a suitable ionospheric profiler (Chapman, Epstein, or Exponential) into formulae describing ionospheric conditions (plasma quasi-neutrality, ion transition level). Once the topside scale heights are determined, the construction of the vertical electron density distribution in the 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.

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS2 Films.

PubMed

Precner, M; Polaković, T; Qiao, Qiao; Trainer, D J; Putilov, A V; Di Giorgio, C; Cone, I; Zhu, Y; Xi, X X; Iavarone, M; Karapetrov, G

2018-04-30

We report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS 2 films. Scanning tunneling microscopy, Kelvin probe force microscopy, and transmission electron microscopy were used to obtain high resolution images and quantitative measurements of the local density of states, work function and nature of defects in MoS 2 films. We track the evolution of defects that are formed under heating and electron beam irradiation. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the work function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally or e-beam activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS 2 . Even at equilibrium conditions, the work function and local density of states values are strongly affected near grain boundaries and edges. The results provide initial estimates of the thermal budgets available for reliable fabrication of MoS 2 -based integrated electronics and indicate the importance of defect control and layer passivation.

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS 2 Films

DOE PAGES

Precner, Marian; Polakovic, T.; Qiao, Qiao; ...

2018-04-30

Here, we report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS 2 films. Scanning tunneling microscopy, Kelvin probe force microscopy, and transmission electron microscopy were used to obtain high resolution images and quantitative measurements of the local density of states, work function and nature of defects in MoS 2 films. We track the evolution of defects that are formed under heating and electron beam irradiation. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the workmore » function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally or e-beam activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS 2. Even at equilibrium conditions, the work function and local density of states values are strongly affected near grain boundaries and edges. The results provide initial estimates of the thermal budgets available for reliable fabrication of MoS 2-based integrated electronics and indicate the importance of defect control and layer passivation.« less

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS 2 Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Precner, Marian; Polakovic, T.; Qiao, Qiao

Here, we report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS 2 films. Scanning tunneling microscopy, Kelvin probe force microscopy, and transmission electron microscopy were used to obtain high resolution images and quantitative measurements of the local density of states, work function and nature of defects in MoS 2 films. We track the evolution of defects that are formed under heating and electron beam irradiation. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the workmore » function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally or e-beam activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS 2. Even at equilibrium conditions, the work function and local density of states values are strongly affected near grain boundaries and edges. The results provide initial estimates of the thermal budgets available for reliable fabrication of MoS 2-based integrated electronics and indicate the importance of defect control and layer passivation.« less

On macromolecular refinement at subatomic resolution withinteratomic scatterers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afonine, Pavel V.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.

2007-11-09

A study of the accurate electron density distribution in molecular crystals at subatomic resolution, better than {approx} 1.0 {angstrom}, requires more detailed models than those based on independent spherical atoms. A tool conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8-1.0 {angstrom}, the number of experimental data is insufficient for the full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark datasets gave results comparable in quality withmore » results of multipolar refinement and superior of those for conventional models. Applications to several datasets of both small- and macro-molecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.« less

On macromolecular refinement at subatomic resolution with interatomic scatterers

PubMed Central

Afonine, Pavel V.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.; Lunin, Vladimir Y.; Urzhumtsev, Alexandre

2007-01-01

A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than ∼1.0 Å) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8–1.0 Å, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package. PMID:18007035

On macromolecular refinement at subatomic resolution with interatomic scatterers.

PubMed

Afonine, Pavel V; Grosse-Kunstleve, Ralf W; Adams, Paul D; Lunin, Vladimir Y; Urzhumtsev, Alexandre

2007-11-01

A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than approximately 1.0 A) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8-1.0 A, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.

Physics in Screening Environments

NASA Astrophysics Data System (ADS)

Certik, Ondrej

In the current study, we investigated atoms in screening environments like plasmas. It is common practice to extract physical data, such as temperature and electron densities, from plasma experiments. We present results that address inherent computational difficulties that arise when the screening approach is extended to include the interaction between the atomic electrons. We show that there may arise an ambiguity in the interpretation of physical properties, such as temperature and charge density, from experimental data due to the opposing effects of electron-nucleus screening and electron-electron screening. The focus of the work, however, is on the resolution of inherent computational challenges that appear in the computation of two-particle matrix elements. Those enter already at the Hartree-Fock level. Furthermore, as examples of post Hartree-Fock calculations, we show second-order Green's function results and many body perturbation theory results of second order. A self-contained derivation of all necessary equations has been included. The accuracy of the implementation of the method is established by comparing standard unscreened results for various atoms and molecules against literature for Hartree-Fock as well as Green's function and many body perturbation theory. The main results of the thesis are presented in the chapter called Screened Results, where the behavior of several atomic systems depending on electron-electron and electron-nucleus Debye screening was studied. The computer code that we have developed has been made available for anybody to use. Finally, we present and discuss results obtained for screened interactions. We also examine thoroughly the computational details of the calculations and particular implementations of the method.

Experimental and theoretical charge density studies at subatomic resolution.

PubMed

Fischer, A; Tiana, D; Scherer, W; Batke, K; Eickerling, G; Svendsen, H; Bindzus, N; Iversen, B B

2011-11-17

Analysis of accurate experimental and theoretical structure factors of diamond and silicon reveals that the contraction of the core shell due to covalent bond formation causes significant perturbations of the total charge density that cannot be ignored in precise charge density studies. We outline that the nature and origin of core contraction/expansion and core polarization phenomena can be analyzed by experimental studies employing an extended Hansen-Coppens multipolar model. Omission or insufficient treatment of these subatomic charge density phenomena might yield erroneous thermal displacement parameters and high residual densities in multipolar refinements. Our detailed studies therefore suggest that the refinement of contraction/expansion and population parameters of all atomic shells is essential to the precise reconstruction of electron density distributions by a multipolar model. Furthermore, our results imply that also the polarization of the inner shells needs to be adopted, especially in cases where second row or even heavier elements are involved in covalent bonding. These theoretical studies are supported by direct multipolar refinements of X-ray powder diffraction data of diamond obtained from a third-generation synchrotron-radiation source (SPring-8, BL02B2).

Crystal step edges can trap electrons on the surfaces of n-type organic semiconductors.

PubMed

He, Tao; Wu, Yanfei; D'Avino, Gabriele; Schmidt, Elliot; Stolte, Matthias; Cornil, Jérôme; Beljonne, David; Ruden, P Paul; Würthner, Frank; Frisbie, C Daniel

2018-05-30

Understanding relationships between microstructure and electrical transport is an important goal for the materials science of organic semiconductors. Combining high-resolution surface potential mapping by scanning Kelvin probe microscopy (SKPM) with systematic field effect transport measurements, we show that step edges can trap electrons on the surfaces of single crystal organic semiconductors. n-type organic semiconductor crystals exhibiting positive step edge surface potentials display threshold voltages that increase and carrier mobilities that decrease with increasing step density, characteristic of trapping, whereas crystals that do not have positive step edge surface potentials do not have strongly step density dependent transport. A device model and microelectrostatics calculations suggest that trapping can be intrinsic to step edges for crystals of molecules with polar substituents. The results provide a unique example of a specific microstructure-charge trapping relationship and highlight the utility of surface potential imaging in combination with transport measurements as a productive strategy for uncovering microscopic structure-property relationships in organic semiconductors.

A new crystal form of Aspergillus oryzae catechol oxidase and evaluation of copper site structures in coupled binuclear copper enzymes.

PubMed

Penttinen, Leena; Rutanen, Chiara; Saloheimo, Markku; Kruus, Kristiina; Rouvinen, Juha; Hakulinen, Nina

2018-01-01

Coupled binuclear copper (CBC) enzymes have a conserved type 3 copper site that binds molecular oxygen to oxidize various mono- and diphenolic compounds. In this study, we found a new crystal form of catechol oxidase from Aspergillus oryzae (AoCO4) and solved two new structures from two different crystals at 1.8-Å and at 2.5-Å resolutions. These structures showed different copper site forms (met/deoxy and deoxy) and also differed from the copper site observed in the previously solved structure of AoCO4. We also analysed the electron density maps of all of the 56 CBC enzyme structures available in the protein data bank (PDB) and found that many of the published structures have vague copper sites. Some of the copper sites were then re-refined to find a better fit to the observed electron density. General problems in the refinement of metalloproteins and metal centres are discussed.

Induced Charge Fluctuations in Semiconductor Detectors with a Cylindrical Geometry

NASA Astrophysics Data System (ADS)

Samedov, Victor V.

2018-01-01

Now, compound semiconductors are very appealing for hard X-ray room-temperature detectors for medical and astrophysical applications. Despite the attractive properties of compound semiconductors, such as high atomic number, high density, wide band gap, low chemical reactivity and long-term stability, poor hole and electron mobility-lifetime products degrade the energy resolution of these detectors. The main objective of the present study is in development of a mathematical model of the process of the charge induction in a cylindrical geometry with accounting for the charge carrier trapping. The formulae for the moments of the distribution function of the induced charge and the formulae for the mean amplitude and the variance of the signal at the output of the semiconductor detector with a cylindrical geometry were derived. It was shown that the power series expansions of the detector amplitude and the variance in terms of the inverse bias voltage allow determining the Fano factor, electron mobility lifetime product, and the nonuniformity level of the trap density of the semiconductor material.

Nanoscale Electronic Structure of Cuprate Superconductors Investigated with Scanning Tunneling Spectroscopy

NASA Astrophysics Data System (ADS)

Williams, Tess Lawanna

Despite 25 years of intense research activity, high-temperature superconductors remain poorly understood, with the underlying pairing mechanism still unidentified. Efforts are complicated by the remarkably complex phase diagram, rich in energy-dependent charge and spin orders. In this thesis I describe the use of a Scanning Tunneling Microscope (STM) to study energy-dependent charge orders in Bi2-- yPbySr2CuO6+delta , a cuprate high-temperature superconductor. STM, a surface-sensitive probe used to map electronic structure with sub-meV energy resolution and sub-A spatial resolution, has contributed greatly to our current understanding of the cuprate high-temperature superconductors. However, STM data is acquired with a constant-current normalization condition. The measured differential conductance, g(x, y, V), is often taken to be proportional to the density of states at energy eV (where V is the voltage applied between tip and sample). In fact, due to the normalization condition, the measured g(x, y, V) is actually the quotient of the density of states at energy eV and the integrated density of states from the Fermi energy to eV. This unavoidable quotient may fold electronic structure from its true energy range into other energies. I discuss a new method to correct STM differential conductance spectra to remove the constant-current normalization condition. Using local work function measurements and the constant-current topograph, I create a map which does not suffer from the setpoint effect and contains a mixture of topographic information and properly normalized spectroscopic information. I apply this method to the extraction of the incommensurate charge modulation at q⃗˜34 2pa0 . I also extend the study of electronic nematic order, an atomic-lattice-periodic C4 → C2 symmetry breaking, from highly underdoped Bi2 Sr2CaCu2O 8+delta [28] to overdoped Bi2--yPb ySr2CuO6+/-delta. I find that the electronic nematic order parameter is robust to change of scan angle. I define and contrast three different electronic nematic orders with different phases with respect to the crystal. I discuss the effect of the choice of normalization and possible alternate explanations for the source of the calculated nematic order. Finally, I discuss a drift-correction technique, which removes picometer scale drift that is introduced into a spectral map by experimental imperfections, and characterize the optimal algorithm and potential artifacts that drift-correction may introduce.

Control of the π plasmon in a single layer graphene by charge doping

NASA Astrophysics Data System (ADS)

Shin, S. Y.; Kim, N. D.; Kim, J. G.; Kim, K. S.; Noh, D. Y.; Kim, Kwang S.; Chung, J. W.

2011-08-01

We report that the behavior of a low-energy π plasmon excitation in a single layer graphene (SLG) can be modified by doping external potassium (K) atoms, a feature demanded to realize the graphene plasmonics. Using high-resolution electron-energy-loss spectroscopy, we find that upon K-doping the π plasmon energy increases by 1.1 eV due to the K-induced electron density up to n = 7 × 1013 cm-2 in SLG. The four modified dispersions for different K-dopings, however, are found to merge into a single universal curve when plotted in the dimensionless coordinates indicating that the unique plasmonic character of SLG is preserved despite the K-dopings.

Temperature and Electron Density Diagnostics of a Candle-Flame Shaped Flare. Asymmetric Reconnection Evidence

NASA Astrophysics Data System (ADS)

Guidoni, Silvina E.; McKenzie, David E.; Longcope, Dana W.; Plowman, Joseph E.; Yoshimura, Keiji

2013-03-01

Candle-flame shaped flares are archetypical structures that represent indirect evidence of magnetic reconnection. For long-lived events, most of their observed features can be explained with the classic magnetic reconnection model of solar flares, the CSHKP model. A flare resembling 1992 Tsuneta's famous candle-flame flare occurred on January 28 2011; we present its temperature and electron density diagnostics. This flare was observed with Hinode/XRT, SDO/AIA, and STEREO (A)/EUVI, resulting in high resolution, broad temperature coverage, and stereoscopic views of this iconic structure. Our XRT filter-ratio temperature and density maps corroborate the general reconnection scenario. The high temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the post-flare arcade, a feature that has been observed in other long duration events. This tower is a localized density increase, as shown by our XRT electron density maps. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this tower-like structure. The XRT maps also reveal that reconnected loops that are successively connected at their tops to this tower develop a density increase in one of their legs that can reach over 2 times the density value of the other leg, giving the appearance of ``half-loops''. Their density is nevertheless still lower than at the tower. These jumps in density last longer than several acoustic transit times along the loops. We use STEREO images to show that the half-loop brightening is not a line-of- sight projection effect of the type suggested by Forbes and Acton (1996). This would indicate that asymmetric reconnection took place between loops originally belonging to systems with different magnetic field strengths, densities, and temperatures. We hypothesize that the heat generated by reconnection's slow shocks is then transferred to each leg of the loop at different rates. Therefore, the increase in electron density due to chromospheric evaporation is different in each leg. Thermal pressure balance between the legs is prevented by shocked plasma at the top of the loops. We also present preliminary results comparing a new fast DEM method that uses SDO/AIA data with the XRT filter ratio method. Both methods complement each other, they agree at the overlap between their instruments' temperature response functions (3-12 MK) while the SDO/AIA method works well at lower temperatures and the XRT one at higher temperatures.

Plasma potential and electron temperature evaluated by ball-pen and Langmuir probes in the COMPASS tokamak

NASA Astrophysics Data System (ADS)

Dimitrova, M.; Popov, Tsv K.; Adamek, J.; Kovačič, J.; Ivanova, P.; Hasan, E.; López-Bruna, D.; Seidl, J.; Vondráček, P.; Dejarnac, R.; Stöckel, J.; Imríšek, M.; Panek, R.; the COMPASS Team

2017-12-01

The radial distributions of the main plasma parameters in the scrape-off-layer of the COMPASS tokamak are measured during L-mode and H-mode regimes by using both Langmuir and ball-pen probes mounted on a horizontal reciprocating manipulator. The radial profile of the plasma potential derived previously from Langmuir probes data by using the first derivative probe technique is compared with data derived using ball-pen probes. A good agreement can be seen between the data acquired by the two techniques during the L-mode discharge and during the H-mode regime within the inter-ELM periods. In contrast with the first derivative probe technique, the ball-pen probe technique does not require a swept voltage and, therefore, the temporal resolution is only limited by the data acquisition system. In the electron temperature evaluation, in the far scrape-off layer and in the limiter shadow, where the electron energy distribution is Maxwellian, the results from both techniques match well. In the vicinity of the last closed flux surface, where the electron energy distribution function is bi-Maxwellian, the ball-pen probe technique results are in agreement with the high-temperature components of the electron distribution only. We also discuss the application of relatively large Langmuir probes placed in parallel and perpendicularly to the magnetic field lines to studying the main plasma parameters. The results obtained by the two types of the large probes agree well. They are compared with Thomson scattering data for electron temperatures and densities. The results for the electron densities are compared also with the results from ASTRA code calculation of the electron source due to the ionization of the neutrals by fast electrons and the origin of the bi-Maxwellian electron energy distribution function is briefly discussed.

The Empirical Canadian High Arctic Ionospheric Model (E-CHAIM): Bottomside Parameterization

NASA Astrophysics Data System (ADS)

Themens, D. R.; Jayachandran, P. T.

2017-12-01

It is well known that the International Reference Ionosphere (IRI) suffers reduced accuracy in its representation of monthly median ionospheric electron density at high latitudes. These inaccuracies are believed to stem, at least in part, from a historical lack of data from these regions. Now, roughly thirty and forty years after the development of the original URSI and CCIR foF2 maps, respectively, there exists a much larger dataset of high latitude observations of ionospheric electron density. These new measurements come in the form of new ionosonde deployments, such as those of the Canadian High Arctic Ionospheric Network, the CHAMP, GRACE, and COSMIC radio occultation missions, and the construction of the Poker Flat, Resolute, and EISCAT Incoherent Scatter Radar systems. These new datasets afford an opportunity to revise the IRI's representation of the high latitude ionosphere. Using a spherical cap harmonic expansion to represent horizontal and diurnal variability and a Fourier expansion in day of year to represent seasonal variations, we have developed a new model of the bottomside ionosphere's electron density for the high latitude ionosphere, above 50N geomagnetic latitude. For the peak heights of the E and F1 layers (hmE and hmF1, respectively), current standards use a constant value for hmE and either use a single-parameter model for hmF1 (IRI) or scale hmF1 with the F peak (NeQuick). For E-CHAIM, we have diverged from this convention to account for the greater variability seen in these characteristics at high latitudes, opting to use a full spherical harmonic model description for each of these characteristics. For the description of the bottomside vertical electron density profile, we present a single-layer model with altitude-varying scale height. The scale height function is taken as the sum three scale height layer functions anchored to the F2 peak, hmF1, and hmE. This parameterization successfully reproduces the structure of the various bottomside layers while ensuring that the resulting electron density profile is free of strong vertical gradient artifacts and is doubly differentiable.

Ionospheric response to 17 March 2013 geomagnetic storm identified by data assimilation result

NASA Astrophysics Data System (ADS)

Yue, Xinan; Zhao, Biqiang; Hu, Lianhuan; She, Chengli

2017-04-01

Based on slant total electron content (TEC) observations made by 10 satellites and 450 ground IGS GNSS stations, we constructed a 4-D ionospheric electron density reanalysis during the March 17, 2013 geomagnetic storm. Four main large-scale ionospheric disturbances are identified from reanalysis: (1) The positive storm during the initial phase; (2) The SED (storm enhanced density) structure in both northern and southern hemisphere; (3) The large positive storm in main phase; (4) The significant negative storm in middle and low latitude during recovery phase. We then run the NCAR-TIEGCM model with Heelis electric potential empirical model as polar input. The TIEGCM can reproduce 3 of 4 large-scale structures (except SED) very well. We then further analyzed the altitudinal variations of these large-scale disturbances and found several interesting things, such as the altitude variation of SED, the rotation of positive/negative storm phase with local time. Those structures could not be identified clearly by traditional used data sources, which either has no global coverage or no vertical resolution. The drivers such as neutral wind/density and electric field from TIEGCM simulations are also analyzed to self-consistently explain the identified disturbance features.

Large Scale Ionospheric Response During March 17, 2013 Geomagnetic Storm: Reanalysis Based on Multiple Satellites Observations and TIEGCM Simulations

NASA Astrophysics Data System (ADS)

Yue, X.; Wang, W.; Schreiner, W. S.; Kuo, Y. H.; Lei, J.; Liu, J.; Burns, A. G.; Zhang, Y.; Zhang, S.

2015-12-01

Based on slant total electron content (TEC) observations made by ~10 satellites and ~450 ground IGS GNSS stations, we constructed a 4-D ionospheric electron density reanalysis during the March 17, 2013 geomagnetic storm. Four main large-scale ionospheric disturbances are identified from reanalysis: (1) The positive storm during the initial phase; (2) The SED (storm enhanced density) structure in both northern and southern hemisphere; (3) The large positive storm in main phase; (4) The significant negative storm in middle and low latitude during recovery phase. We then run the NCAR-TIEGCM model with Heelis electric potential empirical model as polar input. The TIEGCM can reproduce 3 of 4 large-scale structures (except SED) very well. We then further analyzed the altitudinal variations of these large-scale disturbances and found several interesting things, such as the altitude variation of SED, the rotation of positive/negative storm phase with local time. Those structures could not be identified clearly by traditional used data sources, which either has no gloval coverage or no vertical resolution. The drivers such as neutral wind/density and electric field from TIEGCM simulations are also analyzed to self-consistantly explain the identified disturbance features.

Measurements of the ambient photoelectron spectrum from Atmosphere Explorer. I - AE-E measurements below 300 km during solar minimum conditions. II - AE-E measurements from 300 to 1000 km during solar minimum conditions

NASA Technical Reports Server (NTRS)

Lee, J. S.; Doering, J. P.; Potemra, T. A.; Brace, L. H.

1980-01-01

A study is presented of the ambient photoelectron spectrum below 300 km which includes 500 AE-E orbits observed from Dec. 13, 1975 to Feb. 24, 1976. The daytime photoelectron spectrum from 1 to 100 eV was illustrated by several spectra; high resolution 10-32 eV spectra show the widths of the photoelectron lines and the variation of the linewidth and intensity with altitude. The photoelectron flux below 300 km is constant over a period of several months; the photoelectron lines between 20 and 30 eV are very sharp when the total plasma density is low, but broaden at high altitudes as the plasma density builds up during the day. The photo-electron flux above 300 km had an intensity and energy spectrum characteristic of the 250-300 km region only in the presence of low plasma density at the satellite altitude. The flux at high altitudes was extremely variable 3 h after sunrise as a result of attenuation and energy loss to thermal plasma along the path of escaping electrons.

Crossed Ga2O3/SnO2 multiwire architecture: a local structure study with nanometer resolution.

PubMed

Martínez-Criado, Gema; Segura-Ruiz, Jaime; Chu, Manh-Hung; Tucoulou, Remi; López, Iñaki; Nogales, Emilio; Mendez, Bianchi; Piqueras, Javier

2014-10-08

Crossed nanowire structures are the basis for high-density integration of a variety of nanodevices. Owing to the critical role of nanowires intersections in creating hybrid architectures, it has become a challenge to investigate the local structure in crossing points in metal oxide nanowires. Thus, if intentionally grown crossed nanowires are well-patterned, an ideal model to study the junction is formed. By combining electron and synchrotron beam nanoprobes, we show here experimental evidence of the role of impurities in the coupling formation, structural modifications, and atomic site configuration based on crossed Ga2O3/SnO2 nanowires. Our experiment opens new avenues for further local structure studies with both nanometer resolution and elemental sensitivity.

Where Water Is Oxidized to Dioxygen: Structure of the Photosynthetic Mn4Ca Cluster

PubMed Central

Yano, Junko; Kern, Jan; Sauer, Kenneth; Latimer, Matthew J.; Pushkar, Yulia; Biesiadka, Jacek; Loll, Bernhard; Saenger, Wolfram; Messinger, Johannes; Zouni, Athina; Yachandra, Vittal K.

2014-01-01

The oxidation of water to dioxygen is catalyzed within photosystem II (PSII) by a Mn4Ca cluster, the structure of which remains elusive. Polarized extended x-ray absorption fine structure (EXAFS) measurements on PSII single crystals constrain the Mn4Ca cluster geometry to a set of three similar high-resolution structures. Combining polarized EXAFS and x-ray diffraction data, the cluster was placed within PSII, taking into account the overall trend of the electron density of the metal site and the putative ligands. The structure of the cluster from the present study is unlike either the 3.0 or 3.5 angstrom–resolution x-ray structures or other previously proposed models. PMID:17082458

Experimental observation of charge-shift bond in fluorite CaF2.

PubMed

Stachowicz, Marcin; Malinska, Maura; Parafiniuk, Jan; Woźniak, Krzysztof

2017-08-01

On the basis of a multipole refinement of single-crystal X-ray diffraction data collected using an Ag source at 90 K to a resolution of 1.63 Å -1 , a quantitative experimental charge density distribution has been obtained for fluorite (CaF 2 ). The atoms-in-molecules integrated experimental charges for Ca 2+ and F - ions are +1.40 e and -0.70 e, respectively. The derived electron-density distribution, maximum electron-density paths, interaction lines and bond critical points along Ca 2+ ...F - and F - ...F - contacts revealed the character of these interactions. The Ca 2+ ...F - interaction is clearly a closed shell and ionic in character. However, the F - ...F - interaction has properties associated with the recently recognized type of interaction referred to as `charge-shift' bonding. This conclusion is supported by the topology of the electron localization function and analysis of the quantum theory of atoms in molecules and crystals topological parameters. The Ca 2+ ...F - bonded radii - measured as distances from the centre of the ion to the critical point - are 1.21 Å for the Ca 2+ cation and 1.15 Å for the F - anion. These values are in a good agreement with the corresponding Shannon ionic radii. The F - ...F - bond path and bond critical point is also found in the CaF 2 crystal structure. According to the quantum theory of atoms in molecules and crystals, this interaction is attractive in character. This is additionally supported by the topology of non-covalent interactions based on the reduced density gradient.

Calibration of a High Resolution X-ray Spectrometer for High-Energy-Density Plasmas on NIF

NASA Astrophysics Data System (ADS)

Kraus, B.; Gao, L.; Hill, K. W.; Bitter, M.; Efthimion, P.; Schneider, M. B.; Chen, H.; Ayers, J.; Beiersdorfer, P.; Liedahl, D.; Macphee, A. G.; Thorn, D. B.; Bettencourt, R.; Kauffman, R.; Le, H.; Nelson, D.

2017-10-01

A high-resolution, DIM-based (Diagnostic Instrument Manipulator) x-ray crystal spectrometer has been calibrated for and deployed at the National Ignition Facility (NIF) to diagnose plasma conditions and mix in ignition capsules near stagnation times. Two conical crystals in the Hall geometry focus rays from the Kr He- α, Ly- α, and He- β complexes onto a streak camera for time-resolved spectra, in order to measure electron density and temperature by observing Stark broadening and relative intensities of dielectronic satellites. Signals from these two crystals are correlated with a third crystal that time-integrates the intervening energy range. The spectrometer has been absolutely calibrated using a microfocus x-ray source, an array of CCD and single-photon-counting detectors, and K- and L-absorption edge filters. Measurements of the integrated reflectivity, energy range, and energy resolution for each crystal will be presented. The implications of the calibration on signal levels from NIF implosions and x-ray filter choices will be discussed. This work was performed under the auspices of the U.S. DoE by Princeton Plasma Physics Laboratory under contract DE-AC02-09CH11466 and by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

Computational Prediction of Atomic Structures of Helical Membrane Proteins Aided by EM Maps

PubMed Central

Kovacs, Julio A.; Yeager, Mark; Abagyan, Ruben

2007-01-01

Integral membrane proteins pose a major challenge for protein-structure prediction because only ≈100 high-resolution structures are available currently, thereby impeding the development of rules or empirical potentials to predict the packing of transmembrane α-helices. However, when an intermediate-resolution electron microscopy (EM) map is available, it can be used to provide restraints which, in combination with a suitable computational protocol, make structure prediction feasible. In this work we present such a protocol, which proceeds in three stages: 1), generation of an ensemble of α-helices by flexible fitting into each of the density rods in the low-resolution EM map, spanning a range of rotational angles around the main helical axes and translational shifts along the density rods; 2), fast optimization of side chains and scoring of the resulting conformations; and 3), refinement of the lowest-scoring conformations with internal coordinate mechanics, by optimizing the van der Waals, electrostatics, hydrogen bonding, torsional, and solvation energy contributions. In addition, our method implements a penalty term through a so-called tethering map, derived from the EM map, which restrains the positions of the α-helices. The protocol was validated on three test cases: GpA, KcsA, and MscL. PMID:17496035

Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

PubMed Central

Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K. Y.; Klie, Robert F.; Kim, Moon J.

2016-01-01

Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis. PMID:27255415

Three-dimensional structural dynamics and fluctuations of DNA-nanogold conjugates by individual-particle electron tomography

NASA Astrophysics Data System (ADS)

Zhang, Lei; Lei, Dongsheng; Smith, Jessica M.; Zhang, Meng; Tong, Huimin; Zhang, Xing; Lu, Zhuoyang; Liu, Jiankang; Alivisatos, A. Paul; Ren, Gang

2016-03-01

DNA base pairing has been used for many years to direct the arrangement of inorganic nanocrystals into small groupings and arrays with tailored optical and electrical properties. The control of DNA-mediated assembly depends crucially on a better understanding of three-dimensional structure of DNA-nanocrystal-hybridized building blocks. Existing techniques do not allow for structural determination of these flexible and heterogeneous samples. Here we report cryo-electron microscopy and negative-staining electron tomography approaches to image, and three-dimensionally reconstruct a single DNA-nanogold conjugate, an 84-bp double-stranded DNA with two 5-nm nanogold particles for potential substrates in plasmon-coupling experiments. By individual-particle electron tomography reconstruction, we obtain 14 density maps at ~2-nm resolution. Using these maps as constraints, we derive 14 conformations of dsDNA by molecular dynamics simulations. The conformational variation is consistent with that from liquid solution, suggesting that individual-particle electron tomography could be an expected approach to study DNA-assembling and flexible protein structure and dynamics.

Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

DOE PAGES

Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; ...

2016-06-03

Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/ (110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocationmore » cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. In conclusion, this report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.« less

Rotational Spectra and Nuclear Quadrupole Coupling Constants of Iodoimidazoles

NASA Astrophysics Data System (ADS)

Cooper, Graham A.; Anderson, Cara J.; Medcraft, Chris; Legon, Anthony; Walker, Nick

2017-06-01

The microwave spectra of two isomers of iodoimidazole have been recorded and assigned with resolution of their nuclear quadrupole coupling constants. These constants have been analysed in terms of the conjugation between the lone pairs on the iodine atom and the aromatic π-bonding system, and the effect of this conjugation on the distribution of π-electron density in the ring. A comparison of these properties has been made between iodoimidazole and other 5- and 6-membered aromatic rings bonded to halogen atoms.

C60 and U ion irradiation of Gd 2Ti xZr 2-xO 7 pyrochlore

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jiaming; Toulemonde, Marcel; Lang, Maik

2015-08-01

Gd 2Ti xZr 2-xO 7 (x = 0 to 2) pyrochlore was irradiated by 30 MeV C 60 clusters, which provide an extremely high ionizing energy density. Here, high-resolution transmission electron microscopy revealed a complex ion-track structure in Gd 2Ti 2O 7 and Gd 2TiZrO 7, consisting of an amorphous core and a shell of a disordered, defect-fluorite structure.

A comparison of three regions of Puppis A

NASA Technical Reports Server (NTRS)

Fischbach, K. F.; Bateman, L. M.; Canizares, C. R.; Markert, T. H.; Saez, P. J.

1990-01-01

High resolution X-ray spectral observations of Puppis A were performed with the FPCS on the Einstein Observatory at three regions of the remnant: the shock front, the bright eastern knot, and the interior. Plasma diagnostics of lines from OVII and OVIII constrain the values of electron temperature, ionization timescale, and hydrogen column density. Results of the diagnostics for these three regions are compared. A nonequilibrium analysis of previously published fluxes of oxygen lines shows that the interior has not yet reached ionization equilibrium.

Use of Electronic Tag Data and Associated Analytical Tools to Identify and Predict Habitat Utilization of Marine Predators

DTIC Science & Technology

2013-09-30

fin, sperm and humpback whales). RESULTS The tracking data reveal that the California Current Large Marine Ecosystem (CCLME; Supplementary...within 1u31u grid cells. b, Density of large marine predators within the CCLME at a 0.25 º 30.25º resolution. The CCLME is a highly retentive area...sooty shearwaters). The retention with and attraction to the CCLME is consistent with the high productivity of this region that supports large

III-V compound semiconductor material characterization of microstructures and nanostructures on various optoelectronic devices with analytical transmission electron microscopy and high resolution electron microscopy

NASA Astrophysics Data System (ADS)

Zhou, Wei

Analytical Transmission Electron Microscopy (TEM) and High Resolution Electron Microscopy have been carried out to characterize microstructures and nanostructures in various III-V compound semiconductor devices by metalorganic chemical vapor deposition (MOCVD). The low-defect GaN nonplanar templates by lateral epitaxial overgrowth (LEO) has a trapezoidal cross-section with smooth (0001) and {112¯2} facets. Penetration of threading dislocations (TDs) beyond mask windows is observed in ordinary LEO substrates. In two-step LEO substrates, where TDs are engineered to bend 90° in the TD bending layer after the first LEO step, only perfect a-type dislocations with Burgers vector b = 1/3 <112¯0> are generated in the upper Post-bending layer with a density of ˜8 x 107cm-2. The demonstrated 3-dimensional dislocation spatial distribution in the LEO nonplanar substrate substantiates the dislocation reaction mechanism. Al0.07GaN/GaN superlattice can further decrease dislocations. InGaN QW thickness enhancement on top of GaN nonplanar templates has been verified to influence the optoelectronic properties significantly. Dense arrays of hexagonally ordered MOCVD-grown (In)(Ga)As nano-QDs by block copolymer nanolithography & selective area growth (SAG), approximately 20nm in diameter and 40nm apart with a density of 1011/cm 2, are perfect crystals by TEM. V-shaped defects and worse InAs growth uniformity have been observed in multiple layers of vertically coupled self-assembled InAs nanostructure arrays on strain-modulated GaAs substrates. TEM shows a smooth coalesced GaN surface with a thickness as thin as ˜200nm after Nano-LEO and a defect reduction of 70%-75%. The (In)GaAs 20 nm twist bonded compliant substrates have almost no compliant effect and higher dislocation density, but the 10nm compliant substrates are on the contrary. A 60nm oxygen-infiltrated crystallized transition layer is observed between the amorphous oxidized layer and the crystallized unoxidized aperture in Al xGa1-xAs wet lateral oxidation, potentially influencing the current confinement characteristic of the sub-micron oxide aperture. Almost no dislocation is aroused by the wet lateral oxidation of In0.52Al 0.48As in the InP microresonator waveguides. XTEM was performed to compare InP SAG regions with 10˜50mum masks, which shows the performance deterioration of laser threshold current densities in the case of 50mum mask results from high density of dislocations induced from the highly strained QW structures caused by the high enhancements.

High-resolution coherent x-ray diffraction imaging of metal-coated polymer microspheres.

PubMed

Skjønsfjell, Eirik T B; Kleiven, David; Patil, Nilesh; Chushkin, Yuriy; Zontone, Federico; Gibaud, Alain; Breiby, Dag W

2018-01-01

Coherent x-ray diffraction imaging (CXDI) is becoming an important 3D quantitative microscopy technique, allowing structural investigation of a wide range of delicate mesoscale samples that cannot be imaged by other techniques like electron microscopy. Here we report high-resolution 3D CXDI performed on spherical microcomposites consisting of a polymer core coated with a triple layer of nickel-gold-silica. These composites are of high interest to the microelectronics industry, where they are applied in conducting adhesives as fine-pitch electrical contacts-which requires an exceptional degree of uniformity and reproducibility. Experimental techniques that can assess the state of the composites non-destructively, preferably also while embedded in electronic chips, are thus in high demand. We demonstrate that using CXDI, all four different material components of the composite could be identified, with radii matching well to the nominal specifications of the manufacturer. Moreover, CXDI provided detailed maps of layer thicknesses, roughnesses, and defects such as holes, thus also facilitating cross-layer correlations. The side length of the voxels in the reconstruction, given by the experimental geometry, was 16 nm. The effective resolution enabled resolving even the thinnest coating layer of ∼20  nm nominal width. We discuss critically the influence of the weak phase approximation and the projection approximation on the reconstructed electron density estimates, demonstrating that the latter has to be employed. We conclude that CXDI has excellent potential as a metrology tool for microscale composites.

Weiss oscillations and particle-hole symmetry at the half-filled Landau level

NASA Astrophysics Data System (ADS)

Cheung, Alfred K. C.; Raghu, S.; Mulligan, Michael

2017-06-01

Particle-hole symmetry in the lowest Landau level of the two-dimensional electron gas requires the electrical Hall conductivity to equal ±e2/2 h at half filling. We study the consequences of weakly broken particle-hole symmetry for magnetoresistance oscillations about half filling in the presence of an applied periodic one-dimensional electrostatic potential using the Dirac composite fermion theory proposed by Son [Son, Phys. Rev. X 5, 031027 (2015), 10.1103/PhysRevX.5.031027]. At fixed electron density, the oscillation minima are asymmetrically biased towards higher magnetic fields, while at fixed magnetic field the oscillations occur symmetrically as the electron density is varied about half filling. We find an approximate "sum rule" obeyed for all pairs of oscillation minima that can be tested in experiment. The locations of the magnetoresistance oscillation minima for the composite fermion theory of Halperin, Lee, and Read (HLR) and its particle-hole conjugate agree exactly. Within the current experimental resolution, the locations of the oscillation minima produced by the Dirac composite fermion coincide with those of HLR. These results may indicate that all three composite fermion theories describe the same long-wavelength physics.

Triple-twin domains in Mg doped GaN wurtzite nanowires: structural and electronic properties of this zinc-blende-like stacking

NASA Astrophysics Data System (ADS)

Arbiol, Jordi; Estradé, Sònia; Prades, Joan D.; Cirera, Albert; Furtmayr, Florian; Stark, Christoph; Laufer, Andreas; Stutzmann, Martin; Eickhoff, Martin; Gass, Mhairi H.; Bleloch, Andrew L.; Peiró, Francesca; Morante, Joan R.

2009-04-01

We report on the effect of Mg doping on the properties of GaN nanowires grown by plasma assisted molecular beam epitaxy. The most significant feature is the presence of triple-twin domains, the density of which increases with increasing Mg concentration. The resulting high concentration of misplaced atoms gives rise to local changes in the crystal structure equivalent to the insertion of three non-relaxed zinc-blende (ZB) atomic cells, which result in quantum wells along the wurtzite (WZ) nanowire growth axis. High resolution electron energy loss spectra were obtained exactly on the twinned (zinc-blende) and wurtzite planes. These atomically resolved measurements, which allow us to identify modifications in the local density of states, revealed changes in the band to band electronic transition energy from 3.4 eV for wurtzite to 3.2 eV in the twinned lattice regions. These results are in good agreement with specific ab initio atomistic simulations and demonstrate that the redshift observed in previous photoluminescence analyses is directly related to the presence of these zinc-blende domains, opening up new possibilities for band-structure engineering.

Superior material qualities and transport properties of InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Ya-Chao, Zhang; Xiao-Wei, Zhou; Sheng-Rui, Xu; Da-Zheng, Chen; Zhi-Zhe, Wang; Xing, Wang; Jin-Feng, Zhang; Jin-Cheng, Zhang; Yue, Hao

2016-01-01

Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free InGaN channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 × 1013 cm-2 is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cm2/V·s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that InGaN channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional GaN channel heterostructure. The gratifying results imply that InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices. Project supported by the National Natural Science Foundation of China (Grant Nos. 61306017, 61334002, 61474086, and 11435010) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61306017).

Construction and validation of an atomic model for bacterial TSPO from electron microscopy density, evolutionary constraints, and biochemical and biophysical data.

PubMed

Hinsen, Konrad; Vaitinadapoule, Aurore; Ostuni, Mariano A; Etchebest, Catherine; Lacapere, Jean-Jacques

2015-02-01

The 18 kDa protein TSPO is a highly conserved transmembrane protein found in bacteria, yeast, animals and plants. TSPO is involved in a wide range of physiological functions, among which the transport of several molecules. The atomic structure of monomeric ligand-bound mouse TSPO in detergent has been published recently. A previously published low-resolution structure of Rhodobacter sphaeroides TSPO, obtained from tubular crystals with lipids and observed in cryo-electron microscopy, revealed an oligomeric structure without any ligand. We analyze this electron microscopy density in view of available biochemical and biophysical data, building a matching atomic model for the monomer and then the entire crystal. We compare its intra- and inter-molecular contacts with those predicted by amino acid covariation in TSPO proteins from evolutionary sequence analysis. The arrangement of the five transmembrane helices in a monomer of our model is different from that observed for the mouse TSPO. We analyze possible ligand binding sites for protoporphyrin, for the high-affinity ligand PK 11195, and for cholesterol in TSPO monomers and/or oligomers, and we discuss possible functional implications. Copyright © 2014 Elsevier B.V. All rights reserved.

Weiss oscillations and particle-hole symmetry at the half-filled Landau level

DOE PAGES

Cheung, Alfred K. C.; Raghu, S.; Mulligan, Michael

2017-06-15

Particle-hole symmetry in the lowest Landau level of the two-dimensional electron gas requires the electrical Hall conductivity to equal ± e 2/2h at half filling. Here, we study the consequences of weakly broken particle-hole symmetry for magnetoresistance oscillations about half filling in the presence of an applied periodic one-dimensional electrostatic potential using the Dirac composite fermion theory proposed by Son [Son, Phys. Rev. X 5, 031027 (2015)]. At fixed electron density, the oscillation minima are asymmetrically biased towards higher magnetic fields, while at fixed magnetic field the oscillations occur symmetrically as the electron density is varied about half filling. Wemore » find an approximate “sum rule” obeyed for all pairs of oscillation minima that can be tested in experiment. The locations of the magnetoresistance oscillation minima for the composite fermion theory of Halperin, Lee, and Read (HLR) and its particle-hole conjugate agree exactly. Within the current experimental resolution, the locations of the oscillation minima produced by the Dirac composite fermion coincide with those of HLR. These results may indicate that all three composite fermion theories describe the same long-wavelength physics.« less

Weiss oscillations and particle-hole symmetry at the half-filled Landau level

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheung, Alfred K. C.; Raghu, S.; Mulligan, Michael

Particle-hole symmetry in the lowest Landau level of the two-dimensional electron gas requires the electrical Hall conductivity to equal ± e 2/2h at half filling. Here, we study the consequences of weakly broken particle-hole symmetry for magnetoresistance oscillations about half filling in the presence of an applied periodic one-dimensional electrostatic potential using the Dirac composite fermion theory proposed by Son [Son, Phys. Rev. X 5, 031027 (2015)]. At fixed electron density, the oscillation minima are asymmetrically biased towards higher magnetic fields, while at fixed magnetic field the oscillations occur symmetrically as the electron density is varied about half filling. Wemore » find an approximate “sum rule” obeyed for all pairs of oscillation minima that can be tested in experiment. The locations of the magnetoresistance oscillation minima for the composite fermion theory of Halperin, Lee, and Read (HLR) and its particle-hole conjugate agree exactly. Within the current experimental resolution, the locations of the oscillation minima produced by the Dirac composite fermion coincide with those of HLR. These results may indicate that all three composite fermion theories describe the same long-wavelength physics.« less

Quantitative Assessment of CRAND Contribution to the Inner Belt Electron Intensity

NASA Astrophysics Data System (ADS)

Zhang, K.; Li, X.; Selesnick, R.; Schiller, Q. A.; Zhao, H.; Baker, D. N.; Temerin, M. A.

2017-12-01

Following the direct identification and measurements of Cosmic Ray Albedo Neutron Decay (CRAND) produced electrons near the inner edge of the inner belt by Colorado Student Space Weather Experiment (CSSWE)1, we extend the study by addressing more comprehensive questions: (1) what is the relative CRAND contribution to the inner belt compared with electrons injected from further out? (2) How does this relative contribution vary with geomagnetic activity and electron energy? (3) What is the solar cycle dependence of CRAND electrons? In order to answer the above questions, extended data of relativistic electrons in the inner belt are needed for a much longer time period and also finer energy resolution is required. Therefore, we will show results regarding the above questions based on data including other low Earth orbit measurements in addition to CSSWE, such as SAMPEX/PET, DEMETER/IDP, and PROBA-V/EPT. [1] Li, Xinlin, Richard Selesnick, Quintin Schiller, Kun Zhang, Hong Zhao, Daniel Baker, and Michael Temerin (2017), Direct detection of albedo neutron decay electrons at the inner edge of the radiation belt and determination of neutron density in near-Earth space, Nature, under review.

A multi-emitter fitting algorithm for potential live cell super-resolution imaging over a wide range of molecular densities.

PubMed

Takeshima, T; Takahashi, T; Yamashita, J; Okada, Y; Watanabe, S

2018-05-25

Multi-emitter fitting algorithms have been developed to improve the temporal resolution of single-molecule switching nanoscopy, but the molecular density range they can analyse is narrow and the computation required is intensive, significantly limiting their practical application. Here, we propose a computationally fast method, wedged template matching (WTM), an algorithm that uses a template matching technique to localise molecules at any overlapping molecular density from sparse to ultrahigh density with subdiffraction resolution. WTM achieves the localization of overlapping molecules at densities up to 600 molecules μm -2 with a high detection sensitivity and fast computational speed. WTM also shows localization precision comparable with that of DAOSTORM (an algorithm for high-density super-resolution microscopy), at densities up to 20 molecules μm -2 , and better than DAOSTORM at higher molecular densities. The application of WTM to a high-density biological sample image demonstrated that it resolved protein dynamics from live cell images with subdiffraction resolution and a temporal resolution of several hundred milliseconds or less through a significant reduction in the number of camera images required for a high-density reconstruction. WTM algorithm is a computationally fast, multi-emitter fitting algorithm that can analyse over a wide range of molecular densities. The algorithm is available through the website. https://doi.org/10.17632/bf3z6xpn5j.1. © 2018 The Authors. Journal of Microscopy published by JohnWiley & Sons Ltd on behalf of Royal Microscopical Society.

Radio-Tomographic Images of Post-midnight Equatorial Plasma Depletions

NASA Astrophysics Data System (ADS)

Hei, M. A.; Bernhardt, P. A.; Siefring, C. L.; Wilkens, M.; Huba, J. D.; Krall, J.; Valladares, C. E.; Heelis, R. A.; Hairston, M. R.; Coley, W. R.; Chau, J. L.

2013-12-01

For the first time, post-midnight equatorial plasma depletions (EPDs) have been imaged in the longitude-altitude plane using radio-tomography. High-resolution (~10 km × 10 km) electron-density reconstructions were created from total electron content (TEC) data using an array of receivers sited in Peru and the Multiplicative Algebraic Reconstruction Technique (MART) inversion algorithm. TEC data were obtained from the 150 and 400 MHz signals transmitted by the CERTO beacon on the C/NOFS satellite. In-situ electron density data from the C/NOFS CINDI instrument and electron density profiles from the UML Jicamarca ionosonde were used to generate an initial guess for the MART inversion, and also to constrain the inversion process. Observed EPDs had widths of 100-1000 km, spacings of 300-900 km, and often appeared 'pinched off' at the bottom. Well-developed EPDs appeared on an evening with a very small (4 m/s) Pre-Reversal-Enhancement (PRE), suggesting that postmidnight enhancements of the vertical plasma drift and/or seeding-induced uplifts (e.g. gravity waves) were responsible for driving the Rayleigh-Taylor Instability into the nonlinear regime on this night. On another night the Jicamarca ISR recorded postmidnight (~0230 LT) Eastward electric fields nearly twice as strong as the PRE fields seven hours earlier. These electric fields lifted the whole ionosphere, including embedded EPDs, over a longitude range ~14° wide. CINDI detected a dawn depletion in exactly the area where the reconstruction showed an uplifted EPD. Strong Equatorial Spread-F observed by the Jicamarca ionosonde during receiver observation times confirmed the presence of ionospheric irregularities.

Analysis of plasmaspheric plumes: CLUSTER and IMAGE observations and numerical simulations

NASA Technical Reports Server (NTRS)

Darouzet, Fabien; DeKeyser, Johan; Decreau, Pierrette; Gallagher, Dennis; Pierrard, Viviane; Lemaire, Joseph; Dandouras, Iannis; Matsui, Hiroshi; Dunlop, Malcolm; Andre, Mats

2005-01-01

Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles can be derived from the plasma frequency and/or from the spacecraft potential (note that the electron spectrometer is usually not operating inside the plasmasphere); ion velocity is also measured onboard these satellites (but ion density is not reliable because of instrumental limitations). The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 RE every 10 minutes; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations for 3 plume events and compare CLUSTER in-situ data (panel A) with global images of the plasmasphere obtained from IMAGE (panel B), and with numerical simulations for the formation of plumes based on a model that includes the interchange instability mechanism (panel C). In particular, we study the geometry and the orientation of plasmaspheric plumes by using a four-point analysis method, the spatial gradient. We also compare several aspects of their motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary observed by the wave experiment WHISPER on the four spacecraft, (ii) ion velocity derived from the ion spectrometer CIS onboard CLUSTER, (iii) drift velocity measured by the electron drift instrument ED1 onboard CLUSTER and (iv) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.

Topside correction of IRI by global modeling of ionospheric scale height using COSMIC radio occultation data

NASA Astrophysics Data System (ADS)

Wu, M. J.; Guo, P.; Fu, N. F.; Xu, T. L.; Xu, X. S.; Jin, H. L.; Hu, X. G.

2016-06-01

The ionosphere scale height is one of the most significant ionospheric parameters, which contains information about the ion and electron temperatures and dynamics in upper ionosphere. In this paper, an empirical orthogonal function (EOF) analysis method is applied to process all the ionospheric radio occultations of GPS/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) from the year 2007 to 2011 to reconstruct a global ionospheric scale height model. This monthly medium model has spatial resolution of 5° in geomagnetic latitude (-87.5° ~ 87.5°) and temporal resolution of 2 h in local time. EOF analysis preserves the characteristics of scale height quite well in the geomagnetic latitudinal, anural, seasonal, and diurnal variations. In comparison with COSMIC measurements of the year of 2012, the reconstructed model indicates a reasonable accuracy. In order to improve the topside model of International Reference Ionosphere (IRI), we attempted to adopt the scale height model in the Bent topside model by applying a scale factor q as an additional constraint. With the factor q functioning in the exponent profile of topside ionosphere, the IRI scale height should be forced equal to the precise COSMIC measurements. In this way, the IRI topside profile can be improved to get closer to the realistic density profiles. Internal quality check of this approach is carried out by comparing COSMIC realistic measurements and IRI with or without correction, respectively. In general, the initial IRI model overestimates the topside electron density to some extent, and with the correction introduced by COSMIC scale height model, the deviation of vertical total electron content (VTEC) between them is reduced. Furthermore, independent validation with Global Ionospheric Maps VTEC implies a reasonable improvement in the IRI VTEC with the topside model correction.

Observing Solar Radio Bursts from the Lunar Surface

NASA Technical Reports Server (NTRS)

MacDowall, R. J.; Lazio, T. J.; Bale, S. D.; Burns, J.; Gopalswamy, N.; Jones, D. L.; Kaiser, M. L.; Kasper, J.; Weiler, K. W.

2010-01-01

Locating low frequency radio observatories on the lunar surface has a number of advantages. Here, we describe the Radio Observatory for Lunar Sortie Science (ROLSS), a concept for a low frequency, radio imaging interferometric array designed to study particle acceleration in the corona and inner heliosphere. ROLSS would be deployed during an early lunar sortie or by a robotic rover as part of an unmanned landing. The prime science mission is to image type II and type III solar radio bursts with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Secondary science goals include constraining the density of the lunar ionosphere by searching for a low radio frequency cutoff of the solar radio emissions and constraining the low energy electron population in astrophysical sources. Furthermore, ROLSS serves a pathfinder function for larger lunar radio arrays. Key design requirements on ROLES include the operational frequency and angular resolution. The electron densities in the solar corona and inner heliosphere are such that the relevant emission occurs below 10 MHz, essentially unobservable from Earth's surface due to the terrestrial ionospheric cutoff. Resolving the potential sites of particle acceleration requires an instrument with an angular resolution of at least 2 deg, equivalent to a linear array size of approximately 500 meters. Operations would consist of data acquisition during the lunar day, with regular data downlinks. The major components of the ROLSS array are 3 antenna arms arranged in a Y shape, with a central electronics package (CEP). Each antenna arm is a linear strip of polyimide film (e.g., Kapton (TM)) on which 16 single polarization dipole antennas are located by depositing a conductor (e.g., silver). The arms also contain transmission lines for carrying the radio signals from the science antennas to the CEP.

High-Resolution Faraday Rotation and Electron-Phonon Coupling in Surface States of the Bulk-Insulating Topological Insulator Cu_{0.02}Bi_{2}Se_{3}.

PubMed

Wu, Liang; Tse, Wang-Kong; Brahlek, M; Morris, C M; Aguilar, R Valdés; Koirala, N; Oh, S; Armitage, N P

2015-11-20

We have utilized time-domain magnetoterahertz spectroscopy to investigate the low-frequency optical response of the topological insulator Cu_{0.02}Bi_{2}Se_{3} and Bi_{2}Se_{3} films. With both field and frequency dependence, such experiments give sufficient information to measure the mobility and carrier density of multiple conduction channels simultaneously. We observe sharp cyclotron resonances (CRs) in both materials. The small amount of Cu incorporated into the Cu_{0.02}Bi_{2}Se_{3} induces a true bulk insulator with only a single type of conduction with a total sheet carrier density of ~4.9×10^{12}/cm^{2} and mobility as high as 4000 cm^{2}/V·s. This is consistent with conduction from two virtually identical topological surface states (TSSs) on the top and bottom of the film with a chemical potential ~145 meV above the Dirac point and in the bulk gap. The CR broadens at high fields, an effect that we attribute to an electron-phonon interaction. This assignment is supported by an extended Drude model analysis of the zero-field Drude conductance. In contrast, in normal Bi_{2}Se_{3} films, two conduction channels were observed, and we developed a self-consistent analysis method to distinguish the dominant TSSs and coexisting trivial bulk or two-dimensional electron gas states. Our high-resolution Faraday rotation spectroscopy on Cu_{0.02}Bi_{2}Se_{3} paves the way for the observation of quantized Faraday rotation under experimentally achievable conditions to push the chemical potential in the lowest Landau level.

Arbitrarily shaped high-coherence electron bunches from cold atoms

NASA Astrophysics Data System (ADS)

McCulloch, A. J.; Sheludko, D. V.; Saliba, S. D.; Bell, S. C.; Junker, M.; Nugent, K. A.; Scholten, R. E.

2011-10-01

Ultrafast electron diffractive imaging of nanoscale objects such as biological molecules and defects in solid-state devices provides crucial information on structure and dynamic processes: for example, determination of the form and function of membrane proteins, vital for many key goals in modern biological science, including rational drug design. High brightness and high coherence are required to achieve the necessary spatial and temporal resolution, but have been limited by the thermal nature of conventional electron sources and by divergence due to repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that, if the electrons are shaped into ellipsoidal bunches with uniform density, the Coulomb explosion can be reversed using conventional optics, to deliver the maximum possible brightness at the target. Here we demonstrate arbitrary and real-time control of the shape of cold electron bunches extracted from laser-cooled atoms. The ability to dynamically shape the electron source itself and to observe this shape in the propagated electron bunch provides a remarkable experimental demonstration of the intrinsically high spatial coherence of a cold-atom electron source, and the potential for alleviation of electron-source brightness limitations due to Coulomb explosion.

Effect of screw threading dislocations and inverse domain boundaries in GaN on the shape of reciprocal-space maps.

PubMed

Barchuk, Mykhailo; Motylenko, Mykhaylo; Lukin, Gleb; Pätzold, Olf; Rafaja, David

2017-04-01

The microstructure of polar GaN layers, grown by upgraded high-temperature vapour phase epitaxy on [001]-oriented sapphire substrates, was studied by means of high-resolution X-ray diffraction and transmission electron microscopy. Systematic differences between reciprocal-space maps measured by X-ray diffraction and those which were simulated for different densities of threading dislocations revealed that threading dislocations are not the only microstructure defect in these GaN layers. Conventional dark-field transmission electron microscopy and convergent-beam electron diffraction detected vertical inversion domains as an additional microstructure feature. On a series of polar GaN layers with different proportions of threading dislocations and inversion domain boundaries, this contribution illustrates the capability and limitations of coplanar reciprocal-space mapping by X-ray diffraction to distinguish between these microstructure features.

Remote Sensing of Ionosphere by IONOLAB Group

NASA Astrophysics Data System (ADS)

Arikan, Feza

2016-07-01

Ionosphere is a temporally and spatially varying, dispersive, anisotropic and inhomogeneous medium that is characterized primarily by its electron density distribution. Electron density is a complex function of spatial and temporal variations of solar, geomagnetic, and seismic activities. Ionosphere is the main source of error for navigation and positioning systems and satellite communication. Therefore, characterization and constant monitoring of variability of the ionosphere is of utmost importance for the performance improvement of these systems. Since ionospheric electron density is not a directly measurable quantity, an important derivable parameter is the Total Electron Content (TEC), which is used widely to characterize the ionosphere. TEC is proportional to the total number of electrons on a line crossing the atmosphere. IONOLAB is a research group is formed by Hacettepe University, Bilkent University and Kastamonu University, Turkey gathered to handle the challenges of the ionosphere using state-of-the-art remote sensing and signal processing techniques. IONOLAB group provides unique space weather services of IONOLAB-TEC, International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model based IRI-Plas-MAP, IRI-Plas-STEC and Online IRI-Plas-2015 model at www.ionolab.org. IONOLAB group has been working for imaging and monitoring of ionospheric structure for the last 15 years. TEC is estimated from dual frequency GPS receivers as IONOLAB-TEC using IONOLAB-BIAS. For high spatio-temporal resolution 2-D imaging or mapping, IONOLAB-MAP algorithm is developed that uses automated Universal Kriging or Ordinary Kriging in which the experimental semivariogram is fitted to Matern Function with Particle Swarm Optimization (PSO). For 3-D imaging of ionosphere and 1-D vertical profiles of electron density, state-of-the-art IRI-Plas model based IONOLAB-CIT algorithm is developed for regional reconstruction that employs Kalman Filters for state/temporal transition. IONOLAB group contributes to remote sensing of upper atmosphere, ionosphere and plasmasphere with continuing TUBITAK projects. IONOLAB group is open to joint research and collaboration with researchers from all disciplines that investigate the challenges of ionosphere and space weather. This study is supported by TUBITAK 114E541, 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

Absolute atomic hydrogen densities in a radio frequency discharge measured by two-photon laser induced fluorescence imaging

NASA Astrophysics Data System (ADS)

Chérigier, L.; Czarnetzki, U.; Luggenhölscher, D.; Schulz-von der Gathen, V.; Döbele, H. F.

1999-01-01

Absolute atomic hydrogen densities were measured in the gaseous electronics conference reference cell parallel plate reactor by Doppler-free two-photon absorption laser induced fluorescence spectroscopy (TALIF) at λ=205 nm. The capacitively coupled radio frequency discharge was operated at 13.56 MHz in pure hydrogen under various input power and pressure conditions. The Doppler-free excitation technique with an unfocused laser beam together with imaging the fluorescence radiation by an intensified charge coupled device camera allows instantaneous spatial resolution along the radial direction. Absolute density calibration is obtained with the aid of a flow tube reactor and titration with NO2. The influence of spatial intensity inhomogenities along the laser beam and subsequent fluorescence are corrected by TALIF in xenon. A full mapping of the absolute density distribution between the electrodes was obtained. The detection limit for atomic hydrogen amounts to about 2×1018 m-3. The dissociation degree is of the order of a few percent.

Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D

DOE PAGES

Haskey, S. R.; Grierson, B. A.; Burrell, K. H.; ...

2016-09-26

Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region inmore » H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. Finally, these challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model. Published by AIP Publishing.« less

Measurement of heat load density profile on acceleration grid in MeV-class negative ion accelerator.

PubMed

Hiratsuka, Junichi; Hanada, Masaya; Kojima, Atsushi; Umeda, Naotaka; Kashiwagi, Mieko; Miyamoto, Kenji; Yoshida, Masafumi; Nishikiori, Ryo; Ichikawa, Masahiro; Watanabe, Kazuhiro; Tobari, Hiroyuki

2016-02-01

To understand the physics of the negative ion extraction/acceleration, the heat load density profile on the acceleration grid has been firstly measured in the ITER prototype accelerator where the negative ions are accelerated to 1 MeV with five acceleration stages. In order to clarify the profile, the peripheries around the apertures on the acceleration grid were separated into thermally insulated 34 blocks with thermocouples. The spatial resolution is as low as 3 mm and small enough to measure the tail of the beam profile with a beam diameter of ∼16 mm. It was found that there were two peaks of heat load density around the aperture. These two peaks were also clarified to be caused by the intercepted negative ions and secondary electrons from detailed investigation by changing the beam optics and gas density profile. This is the first experimental result, which is useful to understand the trajectories of these particles.

Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D.

PubMed

Haskey, S R; Grierson, B A; Burrell, K H; Chrystal, C; Groebner, R J; Kaplan, D H; Pablant, N A; Stagner, L

2016-11-01

Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region in H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. These challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model.

Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haskey, S. R.; Grierson, B. A.; Burrell, K. H.

Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region inmore » H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. Finally, these challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model. Published by AIP Publishing.« less

Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D

NASA Astrophysics Data System (ADS)

Haskey, S. R.; Grierson, B. A.; Burrell, K. H.; Chrystal, C.; Groebner, R. J.; Kaplan, D. H.; Pablant, N. A.; Stagner, L.

2016-11-01

Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region in H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. These challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model.

Probing mesoscopic crystals with electrons: One-step simultaneous inelastic and elastic scattering theory

NASA Astrophysics Data System (ADS)

Nazarov, Vladimir U.; Silkin, Vyacheslav M.; Krasovskii, Eugene E.

2017-12-01

Inelastic scattering of the medium-energy (˜10 -100 eV) electrons underlies the method of the high-resolution electron energy-loss spectroscopy (HREELS), which has been successfully used for decades to characterize pure and adsorbate-covered surfaces of solids. With the emergence of graphene and other quasi-two-dimensional (Q2D) crystals, HREELS could be expected to become the major experimental tool to study this class of materials. We, however, identify a critical flaw in the theoretical picture of the HREELS of Q2D crystals in the context of the inelastic scattering only ("energy-loss functions" formalism), in contrast to its justifiable use for bulk solids and surfaces. The shortcoming is the neglect of the elastic scattering, which we show is inseparable from the inelastic one, and which, affecting the spectra dramatically, must be taken into account for the meaningful interpretation of the experiment. With this motivation, using the time-dependent density functional theory for excitations, we build a theory of the simultaneous inelastic and elastic electron scattering at Q2D crystals. We apply this theory to HREELS of graphene, revealing an effect of the strongly coupled excitation of the π +σ plasmon and elastic diffraction resonances. Our results open a path to the theoretically interpretable study of the excitation processes in crystalline mesoscopic materials by means of HREELS, with its supreme resolution on the meV energy scale, which is far beyond the capacity of the now overwhelmingly used EELS in transmission electron microscopy.

Modeling of a sensitive time-of-flight flash LiDAR system

NASA Astrophysics Data System (ADS)

Fathipour, V.; Wheaton, S.; Johnson, W. E.; Mohseni, H.

2016-09-01

used for monitoring and profiling structures, range, velocity, vibration, and air turbulence. Remote sensing in the IR region has several advantages over the visible region, including higher transmitter energy while maintaining eye-safety requirements. Electron-injection detectors are a new class of detectors with high internal avalanche-free amplification together with an excess-noise-factor of unity. They have a cutoff wavelength of 1700 nm. Furthermore, they have an extremely low jitter. The detector operates in linear-mode and requires only bias voltage of a few volts. This together with the feedback stabilized gain mechanism, makes formation of large-format high pixel density electron-injection FPAs less challenging compared to other detector technologies such as avalanche photodetectors. These characteristics make electron-injection detectors an ideal choice for flash LiDAR application with mm scale resolution at longer ranges. Based on our experimentally measured device characteristics, a detailed theoretical LiDAR model was developed. In this model we compare the performance of the electron-injection detector with commercially available linear-mode InGaAs APD from (Hamamatsu G8931-20) as well as a p-i-n diode (Hamamatsu 11193 p-i-n). Flash LiDAR images obtained by our model, show the electron-injection detector array (of 100 x 100 element) achieves better resolution with higher signal-to-noise compared with both the InGaAs APD and the p-i-n array (of 100 x 100 element).

Electron Density and Two-Channel Neutron Emission Measurements in Steady-State Spherical Inertial-Electrostatically Confined Plasmas, with Review of the 1-D Kinetic Model

NASA Technical Reports Server (NTRS)

Dobson, Chris C.; Hrbud, Ivana

2004-01-01

Electron density measurements have been made in steady-state plasmas in a spherical inertial electrostatic confinement (IEC) discharge using microwave interferometry. Plasma cores interior to two cathodes, having diameters of 15 and 23 cm, respectively, were probed over a transverse range of 10 cm with a spatial resolution of about 1.4 cm for buffer gas pressures from 0.2 to 6 Pa in argon and deuterium. The transverse profiles are generally flat, in some cases with eccentric symmetric minima, and give mean densities of from approx. = 0.4 to 7x 10(exp 10)/cu cm, the density generally increasing with the neutral gas pressure. Numerical solutions of the 1-D Poisson equation for EC plasmas are reviewed and energy distribution functions are identified which give flat transverse profiles. These functions are used with the plasma approximation to obtain solutions which also give densities consistent with the measurements, and a double potential well solution is obtained which has minima qualitatively similar to those observed. Explicit consideration is given to the compatibility of the solutions interior and exterior to the cathode, and to grid transparency. Deuterium fusion neutron emission rates were also measured and found to be isotropic, to within the measurement error, over two simultaneous directions. Anisotropy was observed in residual emissions during operation with non-fusing hydrogen-1. The deuterium rates are consistent with predictions from the model.

Self-organized Sr leads to solid state twinning in nano-scaled eutectic Si phase

PubMed Central

Albu, M.; Pal, A.; Gspan, C.; Picu, R. C.; Hofer, F.; Kothleitner, G.

2016-01-01

A new mechanism for twin nucleation in the eutectic Al-Si alloy with trace Sr impurities is proposed. Observations made by sub-angstrom resolution scanning transmission electron microscopy and X-ray probing proved the presence of <110> Sr columns located preferentially at twin boundaries. Density functional theory simulations indicate that Sr atoms bind in the Si lattice only along the <110> direction, with preferential positions at first and second nearest neighbors for interstitial and substitutional Sr, respectively. Density functional theory total energy calculations confirm that twin nucleation at Sr columns is energetically favorable. Hence, twins may nucleate in Si precipitates after solidification, which provides a different perspective to the currently accepted mechanism which suggests twin formation during precipitate growth. PMID:27527789

Effect of Si, Mg, and Mg Zn doping on structural properties of a GaN layer grown by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Cho, H. K.; Lee, J. Y.; Kim, K. S.; Yang, G. M.

2001-12-01

We have studied the structural properties of undoped, Si-doped, Mg-doped, and Mg-Zn codoped GaN using high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy. When compared with undoped GaN, the dislocation density at the surface of the GaN layer decreases with Si doping and increases with Mg doping. In addition, we observed a reduction of dislocation density by codoping with Zn atoms in the Mg-doped GaN layer. The full width at half maximum of HRXRD shows that Si doping and Mg-Zn codoping improve the structural quality of the GaN layer as compared with undoped and Mg-doped GaN, respectively.

Picosecond Dynamics Of The GaAs (110) Surface Studied With Laser Photoemission

NASA Astrophysics Data System (ADS)

Haight, R.; Silberman, J. A.; Lilie, M. I.

1988-08-01

A novel laser system and detection scheme is described which has been developed to investigate the transient dynamics of photoexcited electrons at material surfaces and interfaces with photoemission. The excited carrier population on the surface of GaAs (110) and the related Cr/GaAs (110) surface has been studied with 1-2 picosecond time resolution. Studies reveal a rapid rise and fall of the photexcited carrier population at the clean semiconductor surface within 15 picoseconds of excitation. For times greater than 15 picoseconds the carrier density decays slowly. Studies of the photoexcited surface after deposition of small numbers of Cr atoms reveal a remarkable decrease in the carrier density observed at the surface for a coverage as low as .006 monolayer.

Self-organized Sr leads to solid state twinning in nano-scaled eutectic Si phase

NASA Astrophysics Data System (ADS)

Albu, M.; Pal, A.; Gspan, C.; Picu, R. C.; Hofer, F.; Kothleitner, G.

2016-08-01

A new mechanism for twin nucleation in the eutectic Al-Si alloy with trace Sr impurities is proposed. Observations made by sub-angstrom resolution scanning transmission electron microscopy and X-ray probing proved the presence of <110> Sr columns located preferentially at twin boundaries. Density functional theory simulations indicate that Sr atoms bind in the Si lattice only along the <110> direction, with preferential positions at first and second nearest neighbors for interstitial and substitutional Sr, respectively. Density functional theory total energy calculations confirm that twin nucleation at Sr columns is energetically favorable. Hence, twins may nucleate in Si precipitates after solidification, which provides a different perspective to the currently accepted mechanism which suggests twin formation during precipitate growth.

Band gap bowing in NixMg1−xO

PubMed Central

Niedermeier, Christian A.; Råsander, Mikael; Rhode, Sneha; Kachkanov, Vyacheslav; Zou, Bin; Alford, Neil; Moram, Michelle A.

2016-01-01

Epitaxial transparent oxide NixMg1−xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system. PMID:27503808

High-density carrier-accumulated and electrically stable oxide thin-film transistors from ion-gel gate dielectric

PubMed Central

Fujii, Mami N.; Ishikawa, Yasuaki; Miwa, Kazumoto; Okada, Hiromi; Uraoka, Yukiharu; Ono, Shimpei

2015-01-01

The use of indium–gallium–zinc oxide (IGZO) has paved the way for high-resolution uniform displays or integrated circuits with transparent and flexible devices. However, achieving highly reliable devices that use IGZO for low-temperature processes remains a technological challenge. We propose the use of IGZO thin-film transistors (TFTs) with an ionic-liquid gate dielectric in order to achieve high-density carrier-accumulated IGZO TFTs with high reliability, and we discuss a distinctive mechanism for the degradation of this organic–inorganic hybrid device under long-term electrical stress. Our results demonstrated that an ionic liquid or gel gate dielectric provides highly reliable and low-voltage operation with IGZO TFTs. Furthermore, high-density carrier accumulation helps improve the TFT characteristics and reliability, and it is highly relevant to the electronic phase control of oxide materials and the degradation mechanism for organic–inorganic hybrid devices. PMID:26677773

Determination of the density of surface states at the semiconductor-insulator interface in a metal-insulator-semiconductor structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gulyamov, G., E-mail: Gulyamov1949@rambler.ru; Sharibaev, N. U.

2011-02-15

The temporal dependence of thermal generation of electrons from occupied surface states at the semiconductor-insulator interface in a metal-insulator-semiconductor structure is studied. It is established that, at low temperatures, the derivative of the probability of depopulation of occupied surface states with respect to energy is represented by the Dirac {delta} function. It is shown that the density of states of a finite number of discrete energy levels under high-temperature measurements manifests itself as a continuous spectrum, whereas this spectrum appears discrete at low temperatures. A method for processing the continuous spectrum of the density of surface states is suggested thatmore » method makes it possible to determine the discrete energy spectrum. The obtained results may be conducive to an increase in resolution of the method of non-stationary spectroscopy of surface states.« less

High speed digital holography for density and fluctuation measurements (invited).

PubMed

Thomas, C E; Baylor, L R; Combs, S K; Meitner, S J; Rasmussen, D A; Granstedt, E M; Majeski, R P; Kaita, R

2010-10-01

The state of the art in electro-optics has advanced to the point where digital holographic acquisition of wavefronts is now possible. Holographic wavefront acquisition provides the phase of the wavefront at every measurement point. This can be done with accuracy on the order of a thousandth of a wavelength, given that there is sufficient care in the design of the system. At wave frequencies which are much greater than the plasma frequency, the plasma index of refraction is linearly proportional to the electron density and wavelength, and the measurement of the phase of a wavefront passing through the plasma gives the chord-integrated density directly for all points measured on the wavefront. High-speed infrared cameras (up to ∼40,000 fps at ∼64×4 pixels) with resolutions up to 640×512 pixels suitable for use with a CO(2) laser are readily available, if expensive.

High-density carrier-accumulated and electrically stable oxide thin-film transistors from ion-gel gate dielectric.

PubMed

Fujii, Mami N; Ishikawa, Yasuaki; Miwa, Kazumoto; Okada, Hiromi; Uraoka, Yukiharu; Ono, Shimpei

2015-12-18

The use of indium-gallium-zinc oxide (IGZO) has paved the way for high-resolution uniform displays or integrated circuits with transparent and flexible devices. However, achieving highly reliable devices that use IGZO for low-temperature processes remains a technological challenge. We propose the use of IGZO thin-film transistors (TFTs) with an ionic-liquid gate dielectric in order to achieve high-density carrier-accumulated IGZO TFTs with high reliability, and we discuss a distinctive mechanism for the degradation of this organic-inorganic hybrid device under long-term electrical stress. Our results demonstrated that an ionic liquid or gel gate dielectric provides highly reliable and low-voltage operation with IGZO TFTs. Furthermore, high-density carrier accumulation helps improve the TFT characteristics and reliability, and it is highly relevant to the electronic phase control of oxide materials and the degradation mechanism for organic-inorganic hybrid devices.