Structure of the TRPV1 ion channel determined by electron cryo-microscopy

PubMed Central

Liao, Maofu; Cao, Erhu; Julius, David; Cheng, Yifan

2014-01-01

Transient receptor potential (TRP) channels are sensors for a wide range of cellular and environmental signals, but elucidating how these channels respond to physical and chemical stimuli has been hampered by a lack of detailed structural information. Here, we exploit advances in electron cryo-microscopy to determine the structure of a mammalian TRP channel, TRPV1, at 3.4Å resolution, breaking the side-chain resolution barrier for membrane proteins without crystallization. Like voltage-gated channels, TRPV1 exhibits four-fold symmetry around a central ion pathway formed by transmembrane helices S5–S6 and the intervening pore loop, which is flanked by S1–S4 voltage sensor-like domains. TRPV1 has a wide extracellular ‘mouth’ with short selectivity filter. The conserved ‘TRP domain’ interacts with the S4–S5 linker, consistent with its contribution to allosteric modulation. Subunit organization is facilitated by interactions among cytoplasmic domains, including N-terminal ankyrin repeats. These observations provide a structural blueprint for understanding unique aspects of TRP channel function. PMID:24305160

Overview of electron crystallography of membrane proteins: crystallization and screening strategies using negative stain electron microscopy.

PubMed

Nannenga, Brent L; Iadanza, Matthew G; Vollmar, Breanna S; Gonen, Tamir

2013-01-01

Electron cryomicroscopy, or cryoEM, is an emerging technique for studying the three-dimensional structures of proteins and large macromolecular machines. Electron crystallography is a branch of cryoEM in which structures of proteins can be studied at resolutions that rival those achieved by X-ray crystallography. Electron crystallography employs two-dimensional crystals of a membrane protein embedded within a lipid bilayer. The key to a successful electron crystallographic experiment is the crystallization, or reconstitution, of the protein of interest. This unit describes ways in which protein can be expressed, purified, and reconstituted into well-ordered two-dimensional crystals. A protocol is also provided for negative stain electron microscopy as a tool for screening crystallization trials. When large and well-ordered crystals are obtained, the structures of both protein and its surrounding membrane can be determined to atomic resolution.

Controlling protein adsorption on graphene for cryo-EM using low-energy hydrogen plasmas

PubMed Central

Russo, Christopher J.; Passmore, Lori A.

2014-01-01

Despite its many favorable properties as a sample support for biological electron microscopy, graphene is not widely used because its hydrophobicity precludes reliable protein deposition. We describe a method to modify graphene using a low-energy hydrogen plasma, which reduces hydrophobicity without degrading the graphene lattice. We show that the use of plasma-treated graphene enables better control of protein distribution in ice for electron cryo-microscopy and improved image quality by reducing radiation-induced sample motion. PMID:24747813

A Versatile High-Vacuum Cryo-transfer System for Cryo-microscopy and Analytics

PubMed Central

Tacke, Sebastian; Krzyzanek, Vladislav; Nüsse, Harald; Wepf, Roger Albert; Klingauf, Jürgen; Reichelt, Rudolf

2016-01-01

Cryogenic microscopy methods have gained increasing popularity, as they offer an unaltered view on the architecture of biological specimens. As a prerequisite, samples must be handled under cryogenic conditions below their recrystallization temperature, and contamination during sample transfer and handling must be prevented. We present a high-vacuum cryo-transfer system that streamlines the entire handling of frozen-hydrated samples from the vitrification process to low temperature imaging for scanning transmission electron microscopy and transmission electron microscopy. A template for cryo-electron microscopy and multimodal cryo-imaging approaches with numerous sample transfer steps is presented. PMID:26910419

Site-Specific Biomolecule Labeling with Gold Clusters

PubMed Central

Ackerson, Christopher J.; Powell, Richard D.; Hainfeld, James F.

2013-01-01

Site-specific labeling of biomolecules in vitro with gold clusters can enhance the information content of electron cryomicroscopy experiments. This chapter provides a practical overview of well-established techniques for forming biomolecule/gold cluster conjugates. Three bioconjugation chemistries are covered: Linker-mediated bioconjugation, direct gold–biomolecule bonding, and coordination-mediated bonding of nickel(II) nitrilotriacetic acid (NTA)-derivatized gold clusters to polyhistidine (His)-tagged proteins. PMID:20887859

Introduction to electron crystallography.

PubMed

Kühlbrandt, Werner

2013-01-01

From the earliest work on regular arrays in negative stain, electron crystallography has contributed greatly to our understanding of the structure and function of biological macromolecules. The development of electron cryo-microscopy (cryo-EM) then lead to the first groundbreaking atomic models of the membrane proteins bacteriorhodopsin and light harvesting complex II within lipid bilayers. Key contributions towards cryo-EM and electron crystallography methods included specimen preparation and vitrification, liquid-helium cooling, data collection, and image processing. These methods are now applied almost routinely to both membrane and soluble proteins. Here we outline the advances and the breakthroughs that paved the way towards high-resolution structures by electron crystallography, both in terms of methods development and biological milestones.

Site-specific biomolecule labeling with gold clusters.

PubMed

Ackerson, Christopher J; Powell, Richard D; Hainfeld, James F

2010-01-01

Site-specific labeling of biomolecules in vitro with gold clusters can enhance the information content of electron cryomicroscopy experiments. This chapter provides a practical overview of well-established techniques for forming biomolecule/gold cluster conjugates. Three bioconjugation chemistries are covered: linker-mediated bioconjugation, direct gold-biomolecule bonding, and coordination-mediated bonding of nickel(II) nitrilotriacetic acid (NTA)-derivatized gold clusters to polyhistidine (His)-tagged proteins. Copyright © 2010 Elsevier Inc. All rights reserved.

The Structural Architecture of an Infectious Mammalian Prion Using Electron Cryomicroscopy.

PubMed

Vázquez-Fernández, Ester; Vos, Matthijn R; Afanasyev, Pavel; Cebey, Lino; Sevillano, Alejandro M; Vidal, Enric; Rosa, Isaac; Renault, Ludovic; Ramos, Adriana; Peters, Peter J; Fernández, José Jesús; van Heel, Marin; Young, Howard S; Requena, Jesús R; Wille, Holger

2016-09-01

The structure of the infectious prion protein (PrPSc), which is responsible for Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy, has escaped all attempts at elucidation due to its insolubility and propensity to aggregate. PrPSc replicates by converting the non-infectious, cellular prion protein (PrPC) into the misfolded, infectious conformer through an unknown mechanism. PrPSc and its N-terminally truncated variant, PrP 27-30, aggregate into amorphous aggregates, 2D crystals, and amyloid fibrils. The structure of these infectious conformers is essential to understanding prion replication and the development of structure-based therapeutic interventions. Here we used the repetitive organization inherent to GPI-anchorless PrP 27-30 amyloid fibrils to analyze their structure via electron cryomicroscopy. Fourier-transform analyses of averaged fibril segments indicate a repeating unit of 19.1 Å. 3D reconstructions of these fibrils revealed two distinct protofilaments, and, together with a molecular volume of 18,990 Å3, predicted the height of each PrP 27-30 molecule as ~17.7 Å. Together, the data indicate a four-rung β-solenoid structure as a key feature for the architecture of infectious mammalian prions. Furthermore, they allow to formulate a molecular mechanism for the replication of prions. Knowledge of the prion structure will provide important insights into the self-propagation mechanisms of protein misfolding.

Seeing tobacco mosaic virus through direct electron detectors

PubMed Central

Fromm, Simon A.; Bharat, Tanmay A.M.; Jakobi, Arjen J.; Hagen, Wim J.H.; Sachse, Carsten

2015-01-01

With the introduction of direct electron detectors (DED) to the field of electron cryo-microscopy, a wave of atomic-resolution structures has become available. As the new detectors still require comparative characterization, we have used tobacco mosaic virus (TMV) as a test specimen to study the quality of 3D image reconstructions from data recorded on the two direct electron detector cameras, K2 Summit and Falcon II. Using DED movie frames, we explored related image-processing aspects and compared the performance of micrograph-based and segment-based motion correction approaches. In addition, we investigated the effect of dose deposition on the atomic-resolution structure of TMV and show that radiation damage affects negative carboxyl chains first in a side-chain specific manner. Finally, using 450,000 asymmetric units and limiting the effects of radiation damage, we determined a high-resolution cryo-EM map at 3.35 Å resolution. Here, we provide a comparative case study of highly ordered TMV recorded on different direct electron detectors to establish recording and processing conditions that enable structure determination up to 3.2 Å in resolution using cryo-EM. PMID:25528571

Comparison of optimal performance at 300 keV of three direct electron detectors for use in low dose electron microscopy

PubMed Central

McMullan, G.; Faruqi, A.R.; Clare, D.; Henderson, R.

2014-01-01

Low dose electron imaging applications such as electron cryo-microscopy are now benefitting from the improved performance and flexibility of recently introduced electron imaging detectors in which electrons are directly incident on backthinned CMOS sensors. There are currently three commercially available detectors of this type: the Direct Electron DE-20, the FEI Falcon II and the Gatan K2 Summit. These have different characteristics and so it is important to compare their imaging properties carefully with a view to optimise how each is used. Results at 300 keV for both the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are presented. Of these, the DQE is the most important in the study of radiation sensitive samples where detector performance is crucial. We find that all three detectors have a better DQE than film. The K2 Summit has the best DQE at low spatial frequencies but with increasing spatial frequency its DQE falls below that of the Falcon II. PMID:25194828

EMHP: an accurate automated hole masking algorithm for single-particle cryo-EM image processing.

PubMed

Berndsen, Zachary; Bowman, Charles; Jang, Haerin; Ward, Andrew B

2017-12-01

The Electron Microscopy Hole Punch (EMHP) is a streamlined suite of tools for quick assessment, sorting and hole masking of electron micrographs. With recent advances in single-particle electron cryo-microscopy (cryo-EM) data processing allowing for the rapid determination of protein structures using a smaller computational footprint, we saw the need for a fast and simple tool for data pre-processing that could run independent of existing high-performance computing (HPC) infrastructures. EMHP provides a data preprocessing platform in a small package that requires minimal python dependencies to function. https://www.bitbucket.org/chazbot/emhp Apache 2.0 License. bowman@scripps.edu. Supplementary data are available at Bioinformatics online. © The Author(s) 2017. Published by Oxford University Press.

On the state of crystallography at the dawn of the electron microscopy revolution.

PubMed

Higgins, Matthew K; Lea, Susan M

2017-10-01

While protein crystallography has, for many years, been the most used method for structural analysis of macromolecular complexes, remarkable recent advances in high-resolution electron cryo-microscopy led to suggestions that 'the revolution will not be crystallised'. Here we highlight the current success rate, speed and ease of modern crystallographic structure determination and some recent triumphs of both 'classical' crystallography and the use of X-ray free electron lasers. We also outline fundamental differences between structure determination using X-ray crystallography and electron microscopy. We suggest that crystallography will continue to co-exist with electron microscopy as part of an integrated array of methods, allowing structural biologists to focus on fundamental biological questions rather than being constrained by the methods available. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Tilt-Pair Analysis of Images from a Range of Different Specimens in Single-Particle Electron Cryomicroscopy

PubMed Central

Henderson, Richard; Chen, Shaoxia; Chen, James Z.; Grigorieff, Nikolaus; Passmore, Lori A.; Ciccarelli, Luciano; Rubinstein, John L.; Crowther, R. Anthony; Stewart, Phoebe L.; Rosenthal, Peter B.

2011-01-01

The comparison of a pair of electron microscope images recorded at different specimen tilt angles provides a powerful approach for evaluating the quality of images, image-processing procedures, or three-dimensional structures. Here, we analyze tilt-pair images recorded from a range of specimens with different symmetries and molecular masses and show how the analysis can produce valuable information not easily obtained otherwise. We show that the accuracy of orientation determination of individual single particles depends on molecular mass, as expected theoretically since the information in each particle image increases with molecular mass. The angular uncertainty is less than 1° for particles of high molecular mass (∼ 50 MDa), several degrees for particles in the range 1–5 MDa, and tens of degrees for particles below 1 MDa. Orientational uncertainty may be the major contributor to the effective temperature factor (B-factor) describing contrast loss and therefore the maximum resolution of a structure determination. We also made two unexpected observations. Single particles that are known to be flexible showed a wider spread in orientation accuracy, and the orientations of the largest particles examined changed by several degrees during typical low-dose exposures. Smaller particles presumably also reorient during the exposure; hence, specimen movement is a second major factor that limits resolution. Tilt pairs thus enable assessment of orientation accuracy, map quality, specimen motion, and conformational heterogeneity. A convincing tilt-pair parameter plot, where 60% of the particles show a single cluster around the expected tilt axis and tilt angle, provides confidence in a structure determined using electron cryomicroscopy. PMID:21939668

Cryo-EM structures of the TMEM16A calcium-activated chloride channel.

PubMed

Dang, Shangyu; Feng, Shengjie; Tien, Jason; Peters, Christian J; Bulkley, David; Lolicato, Marco; Zhao, Jianhua; Zuberbühler, Kathrin; Ye, Wenlei; Qi, Lijun; Chen, Tingxu; Craik, Charles S; Jan, Yuh Nung; Minor, Daniel L; Cheng, Yifan; Jan, Lily Yeh

2017-12-21

Calcium-activated chloride channels (CaCCs) encoded by TMEM16A control neuronal signalling, smooth muscle contraction, airway and exocrine gland secretion, and rhythmic movements of the gastrointestinal system. To understand how CaCCs mediate and control anion permeation to fulfil these physiological functions, knowledge of the mammalian TMEM16A structure and identification of its pore-lining residues are essential. TMEM16A forms a dimer with two pores. Previous CaCC structural analyses have relied on homology modelling of a homologue (nhTMEM16) from the fungus Nectria haematococca that functions primarily as a lipid scramblase, as well as subnanometre-resolution electron cryo-microscopy. Here we present de novo atomic structures of the transmembrane domains of mouse TMEM16A in nanodiscs and in lauryl maltose neopentyl glycol as determined by single-particle electron cryo-microscopy. These structures reveal the ion permeation pore and represent different functional states. The structure in lauryl maltose neopentyl glycol has one Ca 2+ ion resolved within each monomer with a constricted pore; this is likely to correspond to a closed state, because a CaCC with a single Ca 2+ occupancy requires membrane depolarization in order to open (C.J.P. et al., manuscript submitted). The structure in nanodiscs has two Ca 2+ ions per monomer and its pore is in a closed conformation; this probably reflects channel rundown, which is the gradual loss of channel activity that follows prolonged CaCC activation in 1 mM Ca 2+ . Our mutagenesis and electrophysiological studies, prompted by analyses of the structures, identified ten residues distributed along the pore that interact with permeant anions and affect anion selectivity, as well as seven pore-lining residues that cluster near pore constrictions and regulate channel gating. Together, these results clarify the basis of CaCC anion conduction.

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

Electron cryomicroscopy structure of a membrane-anchored mitochondrial AAA protease.

PubMed

Lee, Sukyeong; Augustin, Steffen; Tatsuta, Takashi; Gerdes, Florian; Langer, Thomas; Tsai, Francis T F

2011-02-11

FtsH-related AAA proteases are conserved membrane-anchored, ATP-dependent molecular machines, which mediate the processing and turnover of soluble and membrane-embedded proteins in eubacteria, mitochondria, and chloroplasts. Homo- and hetero-oligomeric proteolytic complexes exist, which are composed of homologous subunits harboring an ATPase domain of the AAA family and an H41 metallopeptidase domain. Mutations in subunits of mitochondrial m-AAA proteases have been associated with different neurodegenerative disorders in human, raising questions on the functional differences between homo- and hetero-oligomeric AAA proteases. Here, we have analyzed the hetero-oligomeric yeast m-AAA protease composed of homologous Yta10 and Yta12 subunits. We combined genetic and structural approaches to define the molecular determinants for oligomer assembly and to assess functional similarities between Yta10 and Yta12. We demonstrate that replacement of only two amino acid residues within the metallopeptidase domain of Yta12 allows its assembly into homo-oligomeric complexes. To provide a molecular explanation, we determined the 12 Å resolution structure of the intact yeast m-AAA protease with its transmembrane domains by electron cryomicroscopy (cryo-EM) and atomic structure fitting. The full-length m-AAA protease has a bipartite structure and is a hexamer in solution. We found that residues in Yta12, which facilitate homo-oligomerization when mutated, are located at the interface between neighboring protomers in the hexamer ring. Notably, the transmembrane and intermembrane space domains are separated from the main body, creating a passage on the matrix side, which is wide enough to accommodate unfolded but not folded polypeptides. These results suggest a mechanism regarding how proteins are recognized and degraded by m-AAA proteases.

Specimen preparation for high-resolution cryo-EM

PubMed Central

Passmore, Lori A.; Russo, Christopher J.

2016-01-01

Imaging a material with electrons at near-atomic resolution requires a thin specimen that is stable in the vacuum of the transmission electron microscope. For biological samples, this comprises a thin layer of frozen aqueous solution containing the biomolecular complex of interest. The process of preparing a high-quality specimen is often the limiting step in the determination of structures by single-particle electron cryomicroscopy (cryo-EM). Here we describe a systematic approach for going from a purified biomolecular complex in aqueous solution to high-resolution electron micrographs that are suitable for 3D structure determination. This includes a series of protocols for the preparation of vitrified specimens on various specimen supports, including all-gold and graphene. We also describe techniques for troubleshooting when a preparation fails to yield suitable specimens, and common mistakes to avoid during each part of the process. Finally, we include recommendations for obtaining the highest quality micrographs from prepared specimens with current microscope, detector and support technology. PMID:27572723

The Enigma of the Respiratory Chain Supercomplex.

PubMed

Milenkovic, Dusanka; Blaza, James N; Larsson, Nils-Göran; Hirst, Judy

2017-04-04

Respiratory chain dysfunction plays an important role in human disease and aging. It is now well established that the individual respiratory complexes can be organized into supercomplexes, and structures for these macromolecular assemblies, determined by electron cryo-microscopy, have been described recently. Nevertheless, the reason why supercomplexes exist remains an enigma. The widely held view that they enhance catalysis by channeling substrates is challenged by both structural and biophysical information. Here, we evaluate and discuss data and hypotheses on the structures, roles, and assembly of respiratory-chain supercomplexes and propose a future research agenda to address unanswered questions. Copyright © 2017. Published by Elsevier Inc.

Hybrid fluorescence and electron cryo-microscopy for simultaneous electron and photon imaging.

PubMed

Iijima, Hirofumi; Fukuda, Yoshiyuki; Arai, Yoshihiro; Terakawa, Susumu; Yamamoto, Naoki; Nagayama, Kuniaki

2014-01-01

Integration of fluorescence light and transmission electron microscopy into the same device would represent an important advance in correlative microscopy, which traditionally involves two separate microscopes for imaging. To achieve such integration, the primary technical challenge that must be solved regards how to arrange two objective lenses used for light and electron microscopy in such a manner that they can properly focus on a single specimen. To address this issue, both lateral displacement of the specimen between two lenses and specimen rotation have been proposed. Such movement of the specimen allows sequential collection of two kinds of microscopic images of a single target, but prevents simultaneous imaging. This shortcoming has been made up by using a simple optical device, a reflection mirror. Here, we present an approach toward the versatile integration of fluorescence and electron microscopy for simultaneous imaging. The potential of simultaneous hybrid microscopy was demonstrated by fluorescence and electron sequential imaging of a fluorescent protein expressed in cells and cathodoluminescence imaging of fluorescent beads. Copyright © 2013 Elsevier Inc. All rights reserved.

Beam-induced motion correction for sub-megadalton cryo-EM particles.

PubMed

Scheres, Sjors Hw

2014-08-13

In electron cryo-microscopy (cryo-EM), the electron beam that is used for imaging also causes the sample to move. This motion blurs the images and limits the resolution attainable by single-particle analysis. In a previous Research article (Bai et al., 2013) we showed that correcting for this motion by processing movies from fast direct-electron detectors allowed structure determination to near-atomic resolution from 35,000 ribosome particles. In this Research advance article, we show that an improved movie processing algorithm is applicable to a much wider range of specimens. The new algorithm estimates straight movement tracks by considering multiple particles that are close to each other in the field of view, and models the fall-off of high-resolution information content by radiation damage in a dose-dependent manner. Application of the new algorithm to four data sets illustrates its potential for significantly improving cryo-EM structures, even for particles that are smaller than 200 kDa. Copyright © 2014, Scheres.

Paired β-sheet structure of an Aβ(1-40) amyloid fibril revealed by electron microscopy

PubMed Central

Sachse, Carsten; Fändrich, Marcus; Grigorieff, Nikolaus

2008-01-01

Alzheimer's disease is a neurodegenerative disorder that is characterized by the cerebral deposition of amyloid fibrils formed by Aβ peptide. Despite their prevalence in Alzheimer's and other neurodegenerative diseases, important details of the structure of amyloid fibrils remain unknown. Here, we present a three-dimensional structure of a mature amyloid fibril formed by Aβ(1-40) peptide, determined by electron cryomicroscopy at ≈8-Å resolution. The fibril consists of two protofilaments, each containing ≈5-nm-long regions of β-sheet structure. A local twofold symmetry within each region suggests that pairs of β-sheets are formed from equivalent parts of two Aβ(1-40) peptides contained in each protofilament. The pairing occurs via tightly packed interfaces, reminiscent of recently reported steric zipper structures. However, unlike these previous structures, the β-sheet pairing is observed within an amyloid fibril and includes significantly longer amino acid sequences. PMID:18483195

Atomic Structure of the Cystic Fibrosis Transmembrane Conductance Regulator.

PubMed

Zhang, Zhe; Chen, Jue

2016-12-01

The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel evolved from the ATP-binding cassette (ABC) transporter family. In this study, we determined the structure of zebrafish CFTR in the absence of ATP by electron cryo-microscopy to 3.7 Å resolution. Human and zebrafish CFTR share 55% sequence identity, and 42 of the 46 cystic-fibrosis-causing missense mutational sites are identical. In CFTR, we observe a large anion conduction pathway lined by numerous positively charged residues. A single gate near the extracellular surface closes the channel. The regulatory domain, dephosphorylated, is located in the intracellular opening between the two nucleotide-binding domains (NBDs), preventing NBD dimerization and channel opening. The structure also reveals why many cystic-fibrosis-causing mutations would lead to defects either in folding, ion conduction, or gating and suggests new avenues for therapeutic intervention. Copyright © 2016 Elsevier Inc. All rights reserved.

A novel lipoprotein nanoparticle system for membrane proteins

PubMed Central

Frauenfeld, Jens; Löving, Robin; Armache, Jean-Paul; Sonnen, Andreas; Guettou, Fatma; Moberg, Per; Zhu, Lin; Jegerschöld, Caroline; Flayhan, Ali; Briggs, John A.G.; Garoff, Henrik; Löw, Christian; Cheng, Yifan; Nordlund, Pär

2016-01-01

Membrane proteins are of outstanding importance in biology, drug discovery and vaccination. A common limiting factor in research and applications involving membrane proteins is the ability to solubilize and stabilize membrane proteins. Although detergents represent the major means for solubilizing membrane proteins, they are often associated with protein instability and poor applicability in structural and biophysical studies. Here, we present a novel lipoprotein nanoparticle system that allows for the reconstitution of membrane proteins into a lipid environment that is stabilized by a scaffold of Saposin proteins. We showcase the applicability of the method on two purified membrane protein complexes as well as the direct solubilization and nanoparticle-incorporation of a viral membrane protein complex from the virus membrane. We also demonstrate that this lipid nanoparticle methodology facilitates high-resolution structural studies of membrane proteins in a lipid environment by single-particle electron cryo-microscopy (cryo-EM) and allows for the stabilization of the HIV-envelope glycoprotein in a functional state. PMID:26950744

Direct imaging detectors for electron microscopy

NASA Astrophysics Data System (ADS)

Faruqi, A. R.; McMullan, G.

2018-01-01

Electronic detectors used for imaging in electron microscopy are reviewed in this paper. Much of the detector technology is based on the developments in microelectronics, which have allowed the design of direct detectors with fine pixels, fast readout and which are sufficiently radiation hard for practical use. Detectors included in this review are hybrid pixel detectors, monolithic active pixel sensors based on CMOS technology and pnCCDs, which share one important feature: they are all direct imaging detectors, relying on directly converting energy in a semiconductor. Traditional methods of recording images in the electron microscope such as film and CCDs, are mentioned briefly along with a more detailed description of direct electronic detectors. Many applications benefit from the use of direct electron detectors and a few examples are mentioned in the text. In recent years one of the most dramatic advances in structural biology has been in the deployment of the new backthinned CMOS direct detectors to attain near-atomic resolution molecular structures with electron cryo-microscopy (cryo-EM). The development of direct detectors, along with a number of other parallel advances, has seen a very significant amount of new information being recorded in the images, which was not previously possible-and this forms the main emphasis of the review.

Detection of isolated protein-bound metal ions by single-particle cryo-STEM.

PubMed

Elad, Nadav; Bellapadrona, Giuliano; Houben, Lothar; Sagi, Irit; Elbaum, Michael

2017-10-17

Metal ions play essential roles in many aspects of biological chemistry. Detecting their presence and location in proteins and cells is important for understanding biological function. Conventional structural methods such as X-ray crystallography and cryo-transmission electron microscopy can identify metal atoms on protein only if the protein structure is solved to atomic resolution. We demonstrate here the detection of isolated atoms of Zn and Fe on ferritin, using cryogenic annular dark-field scanning transmission electron microscopy (cryo-STEM) coupled with single-particle 3D reconstructions. Zn atoms are found in a pattern that matches precisely their location at the ferroxidase sites determined earlier by X-ray crystallography. By contrast, the Fe distribution is smeared along an arc corresponding to the proposed path from the ferroxidase sites to the mineral nucleation sites along the twofold axes. In this case the single-particle reconstruction is interpreted as a probability distribution function based on the average of individual locations. These results establish conditions for detection of isolated metal atoms in the broader context of electron cryo-microscopy and tomography.

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.

Detection of isolated protein-bound metal ions by single-particle cryo-STEM

PubMed Central

Elad, Nadav; Bellapadrona, Giuliano; Houben, Lothar; Sagi, Irit; Elbaum, Michael

2017-01-01

Metal ions play essential roles in many aspects of biological chemistry. Detecting their presence and location in proteins and cells is important for understanding biological function. Conventional structural methods such as X-ray crystallography and cryo-transmission electron microscopy can identify metal atoms on protein only if the protein structure is solved to atomic resolution. We demonstrate here the detection of isolated atoms of Zn and Fe on ferritin, using cryogenic annular dark-field scanning transmission electron microscopy (cryo-STEM) coupled with single-particle 3D reconstructions. Zn atoms are found in a pattern that matches precisely their location at the ferroxidase sites determined earlier by X-ray crystallography. By contrast, the Fe distribution is smeared along an arc corresponding to the proposed path from the ferroxidase sites to the mineral nucleation sites along the twofold axes. In this case the single-particle reconstruction is interpreted as a probability distribution function based on the average of individual locations. These results establish conditions for detection of isolated metal atoms in the broader context of electron cryo-microscopy and tomography. PMID:28973937

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.

cisTEM, user-friendly software for single-particle image processing.

PubMed

Grant, Timothy; Rohou, Alexis; Grigorieff, Nikolaus

2018-03-07

We have developed new open-source software called cis TEM (computational imaging system for transmission electron microscopy) for the processing of data for high-resolution electron cryo-microscopy and single-particle averaging. cis TEM features a graphical user interface that is used to submit jobs, monitor their progress, and display results. It implements a full processing pipeline including movie processing, image defocus determination, automatic particle picking, 2D classification, ab-initio 3D map generation from random parameters, 3D classification, and high-resolution refinement and reconstruction. Some of these steps implement newly-developed algorithms; others were adapted from previously published algorithms. The software is optimized to enable processing of typical datasets (2000 micrographs, 200 k - 300 k particles) on a high-end, CPU-based workstation in half a day or less, comparable to GPU-accelerated processing. Jobs can also be scheduled on large computer clusters using flexible run profiles that can be adapted for most computing environments. cis TEM is available for download from cistem.org. © 2018, Grant et al.

Asynchronous data acquisition and on-the-fly analysis of dose fractionated cryoEM images by UCSFImage

PubMed Central

Li, Xueming; Zheng, Shawn; Agard, David A.; Cheng, Yifan

2015-01-01

Newly developed direct electron detection cameras have a high image output frame rate that enables recording dose fractionated image stacks of frozen hydrated biological samples by electron cryomicroscopy (cryoEM). Such novel image acquisition schemes provide opportunities to analyze cryoEM data in ways that were previously impossible. The file size of a dose fractionated image stack is 20 ~ 60 times larger than that of a single image. Thus, efficient data acquisition and on-the-fly analysis of a large number of dose-fractionated image stacks become a serious challenge to any cryoEM data acquisition system. We have developed a computer-assisted system, named UCSFImage4, for semi-automated cryo-EM image acquisition that implements an asynchronous data acquisition scheme. This facilitates efficient acquisition, on-the-fly motion correction, and CTF analysis of dose fractionated image stacks with a total time of ~60 seconds/exposure. Here we report the technical details and configuration of this system. PMID:26370395

cisTEM, user-friendly software for single-particle image processing

PubMed Central

2018-01-01

We have developed new open-source software called cisTEM (computational imaging system for transmission electron microscopy) for the processing of data for high-resolution electron cryo-microscopy and single-particle averaging. cisTEM features a graphical user interface that is used to submit jobs, monitor their progress, and display results. It implements a full processing pipeline including movie processing, image defocus determination, automatic particle picking, 2D classification, ab-initio 3D map generation from random parameters, 3D classification, and high-resolution refinement and reconstruction. Some of these steps implement newly-developed algorithms; others were adapted from previously published algorithms. The software is optimized to enable processing of typical datasets (2000 micrographs, 200 k – 300 k particles) on a high-end, CPU-based workstation in half a day or less, comparable to GPU-accelerated processing. Jobs can also be scheduled on large computer clusters using flexible run profiles that can be adapted for most computing environments. cisTEM is available for download from cistem.org. PMID:29513216

Structural Plasticity of Helical Nanotubes Based on Coiled-Coil Assemblies

DOE PAGES

Egelman, Edward H.; Xu, C.; DiMaio, F.; ...

2015-01-22

Numerous instances can be seen in evolution in which protein quaternary structures have diverged while the sequences of the building blocks have remained fairly conserved. However, the path through which such divergence has taken place is usually not known. We have designed two synthetic 29-residue α-helical peptides, based on the coiled-coil structural motif, that spontaneously self-assemble into helical nanotubes in vitro. Using electron cryomicroscopy with a newly available direct electron detection capability, we can achieve near-atomic resolution of these thin structures. We show how conservative changes of only one or two amino acids result in dramatic changes in quaternary structure,more » in which the assemblies can be switched between two very different forms. This system provides a framework for understanding how small sequence changes in evolution can translate into very large changes in supramolecular structure, a phenomenon that may have significant implications for the de novo design of synthetic peptide assemblies.« less

Recent developments in the CCP-EM software suite.

PubMed

Burnley, Tom; Palmer, Colin M; Winn, Martyn

2017-06-01

As part of its remit to provide computational support to the cryo-EM community, the Collaborative Computational Project for Electron cryo-Microscopy (CCP-EM) has produced a software framework which enables easy access to a range of programs and utilities. The resulting software suite incorporates contributions from different collaborators by encapsulating them in Python task wrappers, which are then made accessible via a user-friendly graphical user interface as well as a command-line interface suitable for scripting. The framework includes tools for project and data management. An overview of the design of the framework is given, together with a survey of the functionality at different levels. The current CCP-EM suite has particular strength in the building and refinement of atomic models into cryo-EM reconstructions, which is described in detail.

Virus Assembly and Maturation

NASA Astrophysics Data System (ADS)

Johnson, John E.

2004-03-01

We use two techniques to look at three-dimensional virus structure: electron cryomicroscopy (cryoEM) and X-ray crystallography. Figure 1 is a gallery of virus particles whose structures Timothy Baker, one of my former colleagues at Purdue University, used cryoEM to determine. It illustrates the variety of sizes of icosahedral virus particles. The largest virus particle on this slide is the Herpes simplex virus, around 1200Å in diameter; the smallest we examined was around 250Å in diameter. Viruses bear their genomic information either as positive-sense DNA and RNA, double-strand DNA, double-strand RNA, or negative-strand RNA. Viruses utilize the various structure and function "tactics" seen throughout cell biology to replicate at high levels. Many of the biological principles that we consider general were in fact discovered in the context of viruses ...

Recent developments in the CCP-EM software suite

PubMed Central

Burnley, Tom

2017-01-01

As part of its remit to provide computational support to the cryo-EM community, the Collaborative Computational Project for Electron cryo-Microscopy (CCP-EM) has produced a software framework which enables easy access to a range of programs and utilities. The resulting software suite incorporates contributions from different collaborators by encapsulating them in Python task wrappers, which are then made accessible via a user-friendly graphical user interface as well as a command-line interface suitable for scripting. The framework includes tools for project and data management. An overview of the design of the framework is given, together with a survey of the functionality at different levels. The current CCP-EM suite has particular strength in the building and refinement of atomic models into cryo-EM reconstructions, which is described in detail. PMID:28580908

Rapid amyloid fiber formation from the fast-folding WW domain FBP28.

PubMed

Ferguson, Neil; Berriman, John; Petrovich, Miriana; Sharpe, Timothy D; Finch, John T; Fersht, Alan R

2003-08-19

The WW domains are small proteins that contain a three-stranded, antiparallel beta-sheet. The 40-residue murine FBP28 WW domain rapidly formed twirling ribbon-like fibrils at physiological temperature and pH, with morphology typical of amyloid fibrils. These ribbons were unusually wide and well ordered, making them highly suitable for structural studies. Their x-ray and electron-diffraction patterns displayed the characteristic amyloid fiber 0.47-nm reflection of the cross-beta diffraction signature. Both conventional and electron cryomicroscopy showed clearly that the ribbons were composed of many 2.5-nm-wide subfilaments that ran parallel to the long axis of the fiber. There was a region of lower density along the center of each filament. Lateral association of these filaments generated twisted, often interlinked, sheets up to 40 nm wide and many microns in length. The pitch of the helix varied from 60 to 320 nm, depending on the width of the ribbon. The wild-type FBP28 fibers were formed under conditions in which multiexponential folding kinetics is observed in other studies and which was attributed to a change in the mechanism of folding. It is more likely that those phases result from initial events in the off-pathway aggregation observed here.

Structure of the RZZ complex and molecular basis of its interaction with Spindly

PubMed Central

Mosalaganti, Shyamal; Keller, Jenny; Altenfeld, Anika; Rombaut, Pascaline; Petrovic, Arsen; Wohlgemuth, Sabine; Müller, Franziska; Herzog, Franz; Waldmann, Herbert

2017-01-01

Kinetochores are macromolecular assemblies that connect chromosomes to spindle microtubules (MTs) during mitosis. The metazoan-specific ≈800-kD ROD–Zwilch–ZW10 (RZZ) complex builds a fibrous corona that assembles on mitotic kinetochores before MT attachment to promote chromosome alignment and robust spindle assembly checkpoint signaling. In this study, we combine biochemical reconstitutions, single-particle electron cryomicroscopy, cross-linking mass spectrometry, and structural modeling to build a complete model of human RZZ. We find that RZZ is structurally related to self-assembling cytosolic coat scaffolds that mediate membrane cargo trafficking, including Clathrin, Sec13–Sec31, and αβ’ε-COP. We show that Spindly, a dynein adaptor, is related to BicD2 and binds RZZ directly in a farnesylation-dependent but membrane-independent manner. Through a targeted chemical biology approach, we identify ROD as the Spindly farnesyl receptor. Our results suggest that RZZ is dynein’s cargo at human kinetochores. PMID:28320825

Present and future of membrane protein structure determination by electron crystallography.

PubMed

Ubarretxena-Belandia, Iban; Stokes, David L

2010-01-01

Membrane proteins are critical to cell physiology, playing roles in signaling, trafficking, transport, adhesion, and recognition. Despite their relative abundance in the proteome and their prevalence as targets of therapeutic drugs, structural information about membrane proteins is in short supply. This chapter describes the use of electron crystallography as a tool for determining membrane protein structures. Electron crystallography offers distinct advantages relative to the alternatives of X-ray crystallography and NMR spectroscopy. Namely, membrane proteins are placed in their native membranous environment, which is likely to favor a native conformation and allow changes in conformation in response to physiological ligands. Nevertheless, there are significant logistical challenges in finding appropriate conditions for inducing membrane proteins to form two-dimensional arrays within the membrane and in using electron cryo-microscopy to collect the data required for structure determination. A number of developments are described for high-throughput screening of crystallization trials and for automated imaging of crystals with the electron microscope. These tools are critical for exploring the necessary range of factors governing the crystallization process. There have also been recent software developments to facilitate the process of structure determination. However, further innovations in the algorithms used for processing images and electron diffraction are necessary to improve throughput and to make electron crystallography truly viable as a method for determining atomic structures of membrane proteins. Copyright © 2010 Elsevier Inc. All rights reserved.

Present and future of membrane protein structure determination by electron crystallography

PubMed Central

Ubarretxena-Belandia, Iban; Stokes, David L.

2011-01-01

Membrane proteins are critical to cell physiology, playing roles in signaling, trafficking, transport, adhesion, and recognition. Despite their relative abundance in the proteome and their prevalence as targets of therapeutic drugs, structural information about membrane proteins is in short supply. This review describes the use of electron crystallography as a tool for determining membrane protein structures. Electron crystallography offers distinct advantages relative to the alternatives of X-ray crystallography and NMR spectroscopy. Namely, membrane proteins are placed in their native membranous environment, which is likely to favor a native conformation and allow changes in conformation in response to physiological ligands. Nevertheless, there are significant logistical challenges in finding appropriate conditions for inducing membrane proteins to form two-dimensional arrays within the membrane and in using electron cryo-microscopy to collect the data required for structure determination. A number of developments are described for high-throughput screening of crystallization trials and for automated imaging of crystals with the electron microscope. These tools are critical for exploring the necessary range of factors governing the crystallization process. There have also been recent software developments to facilitate the process of structure determination. However, further innovations in the algorithms used for processing images and electron diffraction are necessary to improve throughput and to make electron crystallography truly viable as a method for determining atomic structures of membrane proteins. PMID:21115172

Unfolding the mechanism of the AAA+ unfoldase VAT by a combined cryo-EM, solution NMR study.

PubMed

Huang, Rui; Ripstein, Zev A; Augustyniak, Rafal; Lazniewski, Michal; Ginalski, Krzysztof; Kay, Lewis E; Rubinstein, John L

2016-07-19

The AAA+ (ATPases associated with a variety of cellular activities) enzymes play critical roles in a variety of homeostatic processes in all kingdoms of life. Valosin-containing protein-like ATPase of Thermoplasma acidophilum (VAT), the archaeal homolog of the ubiquitous AAA+ protein Cdc48/p97, functions in concert with the 20S proteasome by unfolding substrates and passing them on for degradation. Here, we present electron cryomicroscopy (cryo-EM) maps showing that VAT undergoes large conformational rearrangements during its ATP hydrolysis cycle that differ dramatically from the conformational states observed for Cdc48/p97. We validate key features of the model with biochemical and solution methyl-transverse relaxation optimized spectroscopY (TROSY) NMR experiments and suggest a mechanism for coupling the energy of nucleotide hydrolysis to substrate unfolding. These findings illustrate the unique complementarity between cryo-EM and solution NMR for studies of molecular machines, showing that the structural properties of VAT, as well as the population distributions of conformers, are similar in the frozen specimens used for cryo-EM and in the solution phase where NMR spectra are recorded.

Structure of the transporter associated with antigen processing trapped by herpes simplex virus

PubMed Central

Oldham, Michael L; Grigorieff, Nikolaus; Chen, Jue

2016-01-01

The transporter associated with antigen processing (TAP) is an ATP-binding cassette (ABC) transporter essential to cellular immunity against viral infection. Some persistent viruses have evolved strategies to inhibit TAP so that they may go undetected by the immune system. The herpes simplex virus for example evades immune surveillance by blocking peptide transport with a small viral protein ICP47. In this study, we determined the structure of human TAP bound to ICP47 by electron cryo-microscopy (cryo-EM) to 4.0 Å. The structure shows that ICP47 traps TAP in an inactive conformation distinct from the normal transport cycle. The specificity and potency of ICP47 inhibition result from contacts between the tip of the helical hairpin and the apex of the transmembrane cavity. This work provides a clear molecular description of immune evasion by a persistent virus. It also establishes the molecular structure of TAP to facilitate mechanistic studies of the antigen presentation process. DOI: http://dx.doi.org/10.7554/eLife.21829.001 PMID:27935481

Architecture of eukaryotic mRNA 3′-end processing machinery

PubMed Central

Hill, Chris H.; Easter, Ashley D.; Emsley, Paul; Degliesposti, Gianluca; Gordiyenko, Yuliya; Santhanam, Balaji; Wolf, Jana; Wiederhold, Katrin; Dornan, Gillian L.; Skehel, Mark; Robinson, Carol V.; Passmore, Lori A.

2018-01-01

Newly transcribed eukaryotic precursor messenger RNAs (pre-mRNAs) are processed at their 3′ ends by the ~1-megadalton multiprotein cleavage and polyadenylation factor (CPF). CPF cleaves pre-mRNAs, adds a polyadenylate tail, and triggers transcription termination, but it is unclear how its various enzymes are coordinated and assembled. Here, we show that the nuclease, polymerase, and phosphatase activities of yeast CPF are organized into three modules. Using electron cryomicroscopy, we determined a 3.5-angstrom-resolution structure of the ~200-kilodalton polymerase module. This revealed four β propellers, in an assembly markedly similar to those of other protein complexes that bind nucleic acid. Combined with in vitro reconstitution experiments, our data show that the polymerase module brings together factors required for specific and efficient polyadenylation, to help coordinate mRNA 3′-end processing. PMID:29074584

Automating tasks in protein structure determination with the clipper python module.

PubMed

McNicholas, Stuart; Croll, Tristan; Burnley, Tom; Palmer, Colin M; Hoh, Soon Wen; Jenkins, Huw T; Dodson, Eleanor; Cowtan, Kevin; Agirre, Jon

2018-01-01

Scripting programming languages provide the fastest means of prototyping complex functionality. Those with a syntax and grammar resembling human language also greatly enhance the maintainability of the produced source code. Furthermore, the combination of a powerful, machine-independent scripting language with binary libraries tailored for each computer architecture allows programs to break free from the tight boundaries of efficiency traditionally associated with scripts. In the present work, we describe how an efficient C++ crystallographic library such as Clipper can be wrapped, adapted and generalized for use in both crystallographic and electron cryo-microscopy applications, scripted with the Python language. We shall also place an emphasis on best practices in automation, illustrating how this can be achieved with this new Python module. © 2017 The Authors Protein Science published by Wiley Periodicals, Inc. on behalf of The Protein Society.

Single-molecule analysis of a molecular disassemblase reveals the mechanism of Hsc70-driven clathrin uncoating

PubMed Central

Böcking, Till; Aguet, François; Harrison, Stephen C.; Kirchhausen, Tomas

2010-01-01

Heat shock cognate protein 70 (Hsc70) supports remodeling of protein complexes -- for example, disassembly of clathrin coats on endocytic coated vesicles. To understand how a simple ATP driven molecular clamp catalyzes a large-scale disassembly reaction, we have used single-particle fluorescence imaging to track the dynamics of Hsc70 and its clathrin substrate in real time. Hsc70 accumulates to a critical level, determined by kinetic modeling to be one Hsc70 for every two functional attachment sites; rapid, all-or-none uncoating then ensues. We propose that Hsc70 traps conformational distortions, seen previously by electron cryomicroscopy, in the vicinity of each occupied site and that accumulation of local strains destabilises the clathrin lattice. Capture of conformational fluctuations may be a general mechanism for chaperone-driven disassembly of protein complexes. PMID:21278753

Sparse and incomplete factorial matrices to screen membrane protein 2D crystallization

PubMed Central

Lasala, R.; Coudray, N.; Abdine, A.; Zhang, Z.; Lopez-Redondo, M.; Kirshenbaum, R.; Alexopoulos, J.; Zolnai, Z.; Stokes, D.L.; Ubarretxena-Belandia, I.

2014-01-01

Electron crystallography is well suited for studying the structure of membrane proteins in their native lipid bilayer environment. This technique relies on electron cryomicroscopy of two-dimensional (2D) crystals, grown generally by reconstitution of purified membrane proteins into proteoliposomes under conditions favoring the formation of well-ordered lattices. Growing these crystals presents one of the major hurdles in the application of this technique. To identify conditions favoring crystallization a wide range of factors that can lead to a vast matrix of possible reagent combinations must be screened. However, in 2D crystallization these factors have traditionally been surveyed in a relatively limited fashion. To address this problem we carried out a detailed analysis of published 2D crystallization conditions for 12 β-barrel and 138 α-helical membrane proteins. From this analysis we identified the most successful conditions and applied them in the design of new sparse and incomplete factorial matrices to screen membrane protein 2D crystallization. Using these matrices we have run 19 crystallization screens for 16 different membrane proteins totaling over 1,300 individual crystallization conditions. Six membrane proteins have yielded diffracting 2D crystals suitable for structure determination, indicating that these new matrices show promise to accelerate the success rate of membrane protein 2D crystallization. PMID:25478971

Cryo-electron microscopy structure of human peroxiredoxin-3 filament reveals the assembly of a putative chaperone.

PubMed

Radjainia, Mazdak; Venugopal, Hariprasad; Desfosses, Ambroise; Phillips, Amy J; Yewdall, N Amy; Hampton, Mark B; Gerrard, Juliet A; Mitra, Alok K

2015-05-05

Peroxiredoxins (Prxs) are a ubiquitous class of thiol-dependent peroxidases that play an important role in the protection and response of cells to oxidative stress. The catalytic unit of typical 2-Cys Prxs are homodimers, which can self-associate to form complex assemblies that are hypothesized to have signaling and chaperone activity. Mitochondrial Prx3 forms dodecameric toroids, which can further stack to form filaments, the so-called high-molecular-weight (HMW) form that has putative holdase activity. We used single-particle analysis and helical processing of electron cryomicroscopy images of human Prx3 filaments induced by low pH to generate a ∼7-Å resolution 3D structure of the HMW form, the first such structure for a 2-Cys Prx. The pseudo-atomic model reveals interactions that promote the stacking of the toroids and shows that unlike previously reported data, the structure can accommodate a partially folded C terminus. The HMW filament lumen displays hydrophobic patches, which we hypothesize bestow holdase activity. Copyright © 2015 Elsevier Ltd. All rights reserved.

Detailed Analysis of the Binding Mode of Vanilloids to Transient Receptor Potential Vanilloid Type I (TRPV1) by a Mutational and Computational Study

PubMed Central

Mori, Yoshikazu; Ogawa, Kazuo; Warabi, Eiji; Yamamoto, Masahiro; Hirokawa, Takatsugu

2016-01-01

Transient receptor potential vanilloid type 1 (TRPV1) is a non-selective cation channel and a multimodal sensor protein. Since the precise structure of TRPV1 was obtained by electron cryo-microscopy, the binding mode of representative agonists such as capsaicin and resiniferatoxin (RTX) has been extensively characterized; however, detailed information on the binding mode of other vanilloids remains lacking. In this study, mutational analysis of human TRPV1 was performed, and four agonists (capsaicin, RTX, [6]-shogaol and [6]-gingerol) were used to identify amino acid residues involved in ligand binding and/or modulation of proton sensitivity. The detailed binding mode of each ligand was then simulated by computational analysis. As a result, three amino acids (L518, F591 and L670) were newly identified as being involved in ligand binding and/or modulation of proton sensitivity. In addition, in silico docking simulation and a subsequent mutational study suggested that [6]-gingerol might bind to and activate TRPV1 in a unique manner. These results provide novel insights into the binding mode of various vanilloids to the channel and will be helpful in developing a TRPV1 modulator. PMID:27606946

The dynamic assembly of distinct RNA polymerase I complexes modulates rDNA transcription.

PubMed

Torreira, Eva; Louro, Jaime Alegrio; Pazos, Irene; González-Polo, Noelia; Gil-Carton, David; Duran, Ana Garcia; Tosi, Sébastien; Gallego, Oriol; Calvo, Olga; Fernández-Tornero, Carlos

2017-03-06

Cell growth requires synthesis of ribosomal RNA by RNA polymerase I (Pol I). Binding of initiation factor Rrn3 activates Pol I, fostering recruitment to ribosomal DNA promoters. This fundamental process must be precisely regulated to satisfy cell needs at any time. We present in vivo evidence that, when growth is arrested by nutrient deprivation, cells induce rapid clearance of Pol I-Rrn3 complexes, followed by the assembly of inactive Pol I homodimers. This dual repressive mechanism reverts upon nutrient addition, thus restoring cell growth. Moreover, Pol I dimers also form after inhibition of either ribosome biogenesis or protein synthesis. Our mutational analysis, based on the electron cryomicroscopy structures of monomeric Pol I alone and in complex with Rrn3, underscores the central role of subunits A43 and A14 in the regulation of differential Pol I complexes assembly and subsequent promoter association.

Processing of Cryo-EM Movie Data.

PubMed

Ripstein, Z A; Rubinstein, J L

2016-01-01

Direct detector device (DDD) cameras dramatically enhance the capabilities of electron cryomicroscopy (cryo-EM) due to their improved detective quantum efficiency (DQE) relative to other detectors. DDDs use semiconductor technology that allows micrographs to be recorded as movies rather than integrated individual exposures. Movies from DDDs improve cryo-EM in another, more surprising, way. DDD movies revealed beam-induced specimen movement as a major source of image degradation and provide a way to partially correct the problem by aligning frames or regions of frames to account for this specimen movement. In this chapter, we use a self-consistent mathematical notation to explain, compare, and contrast several of the most popular existing algorithms for computationally correcting specimen movement in DDD movies. We conclude by discussing future developments in algorithms for processing DDD movies that would extend the capabilities of cryo-EM even further. © 2016 Elsevier Inc. All rights reserved.

Structure of a Bacterial Dynamin-like Protein Lipid Tube Provides a Mechanism For Assembly and Membrane Curving

PubMed Central

Low, Harry H.; Sachse, Carsten; Amos, Linda A.; Löwe, Jan

2009-01-01

Summary Proteins of the dynamin superfamily mediate membrane fission, fusion, and restructuring events by polymerizing upon lipid bilayers and forcing regions of high curvature. In this work, we show the electron cryomicroscopy reconstruction of a bacterial dynamin-like protein (BDLP) helical filament decorating a lipid tube at ∼11 Å resolution. We fitted the BDLP crystal structure and produced a molecular model for the entire filament. The BDLP GTPase domain dimerizes and forms the tube surface, the GTPase effector domain (GED) mediates self-assembly, and the paddle region contacts the lipids and promotes curvature. Association of BDLP with GMPPNP and lipid induces radical, large-scale conformational changes affecting polymerization. Nucleotide hydrolysis seems therefore to be coupled to polymer disassembly and dissociation from lipid, rather than membrane restructuring. Observed structural similarities with rat dynamin 1 suggest that our results have broad implication for other dynamin family members. PMID:20064379

Structure and conformational states of the bovine mitochondrial ATP synthase by cryo-EM.

PubMed

Zhou, Anna; Rohou, Alexis; Schep, Daniel G; Bason, John V; Montgomery, Martin G; Walker, John E; Grigorieff, Nikolaus; Rubinstein, John L

2015-10-06

Adenosine triphosphate (ATP), the chemical energy currency of biology, is synthesized in eukaryotic cells primarily by the mitochondrial ATP synthase. ATP synthases operate by a rotary catalytic mechanism where proton translocation through the membrane-inserted FO region is coupled to ATP synthesis in the catalytic F1 region via rotation of a central rotor subcomplex. We report here single particle electron cryomicroscopy (cryo-EM) analysis of the bovine mitochondrial ATP synthase. Combining cryo-EM data with bioinformatic analysis allowed us to determine the fold of the a subunit, suggesting a proton translocation path through the FO region that involves both the a and b subunits. 3D classification of images revealed seven distinct states of the enzyme that show different modes of bending and twisting in the intact ATP synthase. Rotational fluctuations of the c8-ring within the FO region support a Brownian ratchet mechanism for proton-translocation-driven rotation in ATP synthases.

Accurate model annotation of a near-atomic resolution cryo-EM map

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

Hryc, Corey F.; Chen, Dong-Hua; Afonine, Pavel V.

Electron cryomicroscopy (cryo-EM) has been used to determine the atomic coordinates (models) from density maps of biological assemblies. These models can be assessed by their overall fit to the experimental data and stereochemical information. However, these models do not annotate the actual density values of the atoms nor their positional uncertainty. Here, we introduce a computational procedure to derive an atomic model from a cryo- EM map with annotated metadata. The accuracy of such a model is validated by a faithful replication of the experimental cryo-EM map computed using the coordinates and associated metadata. The functional interpretation of any structuralmore » features in the model and its utilization for future studies can be made in the context of its measure of uncertainty. We applied this protocol to the 3.3-Å map of the mature P22 bacteriophage capsid, a large and complex macromolecular assembly. With this protocol, we identify and annotate previously undescribed molecular interactions between capsid subunits that are crucial to maintain stability in the absence of cementing proteins or cross-linking, as occur in other bacteriophages.« less

Architecture of the ring formed by the tubulin homologue FtsZ in bacterial cell division

PubMed Central

Szwedziak, Piotr; Wang, Qing; Bharat, Tanmay A M; Tsim, Matthew; Löwe, Jan

2014-01-01

Membrane constriction is a prerequisite for cell division. The most common membrane constriction system in prokaryotes is based on the tubulin homologue FtsZ, whose filaments in E. coli are anchored to the membrane by FtsA and enable the formation of the Z-ring and divisome. The precise architecture of the FtsZ ring has remained enigmatic. In this study, we report three-dimensional arrangements of FtsZ and FtsA filaments in C. crescentus and E. coli cells and inside constricting liposomes by means of electron cryomicroscopy and cryotomography. In vivo and in vitro, the Z-ring is composed of a small, single-layered band of filaments parallel to the membrane, creating a continuous ring through lateral filament contacts. Visualisation of the in vitro reconstituted constrictions as well as a complete tracing of the helical paths of the filaments with a molecular model favour a mechanism of FtsZ-based membrane constriction that is likely to be accompanied by filament sliding. DOI: http://dx.doi.org/10.7554/eLife.04601.001 PMID:25490152

Accurate model annotation of a near-atomic resolution cryo-EM map.

PubMed

Hryc, Corey F; Chen, Dong-Hua; Afonine, Pavel V; Jakana, Joanita; Wang, Zhao; Haase-Pettingell, Cameron; Jiang, Wen; Adams, Paul D; King, Jonathan A; Schmid, Michael F; Chiu, Wah

2017-03-21

Electron cryomicroscopy (cryo-EM) has been used to determine the atomic coordinates (models) from density maps of biological assemblies. These models can be assessed by their overall fit to the experimental data and stereochemical information. However, these models do not annotate the actual density values of the atoms nor their positional uncertainty. Here, we introduce a computational procedure to derive an atomic model from a cryo-EM map with annotated metadata. The accuracy of such a model is validated by a faithful replication of the experimental cryo-EM map computed using the coordinates and associated metadata. The functional interpretation of any structural features in the model and its utilization for future studies can be made in the context of its measure of uncertainty. We applied this protocol to the 3.3-Å map of the mature P22 bacteriophage capsid, a large and complex macromolecular assembly. With this protocol, we identify and annotate previously undescribed molecular interactions between capsid subunits that are crucial to maintain stability in the absence of cementing proteins or cross-linking, as occur in other bacteriophages.

Accurate model annotation of a near-atomic resolution cryo-EM map

PubMed Central

Hryc, Corey F.; Chen, Dong-Hua; Afonine, Pavel V.; Jakana, Joanita; Wang, Zhao; Haase-Pettingell, Cameron; Jiang, Wen; Adams, Paul D.; King, Jonathan A.; Schmid, Michael F.; Chiu, Wah

2017-01-01

Electron cryomicroscopy (cryo-EM) has been used to determine the atomic coordinates (models) from density maps of biological assemblies. These models can be assessed by their overall fit to the experimental data and stereochemical information. However, these models do not annotate the actual density values of the atoms nor their positional uncertainty. Here, we introduce a computational procedure to derive an atomic model from a cryo-EM map with annotated metadata. The accuracy of such a model is validated by a faithful replication of the experimental cryo-EM map computed using the coordinates and associated metadata. The functional interpretation of any structural features in the model and its utilization for future studies can be made in the context of its measure of uncertainty. We applied this protocol to the 3.3-Å map of the mature P22 bacteriophage capsid, a large and complex macromolecular assembly. With this protocol, we identify and annotate previously undescribed molecular interactions between capsid subunits that are crucial to maintain stability in the absence of cementing proteins or cross-linking, as occur in other bacteriophages. PMID:28270620

Accurate model annotation of a near-atomic resolution cryo-EM map

DOE PAGES

Hryc, Corey F.; Chen, Dong-Hua; Afonine, Pavel V.; ...

2017-03-07

Electron cryomicroscopy (cryo-EM) has been used to determine the atomic coordinates (models) from density maps of biological assemblies. These models can be assessed by their overall fit to the experimental data and stereochemical information. However, these models do not annotate the actual density values of the atoms nor their positional uncertainty. Here, we introduce a computational procedure to derive an atomic model from a cryo- EM map with annotated metadata. The accuracy of such a model is validated by a faithful replication of the experimental cryo-EM map computed using the coordinates and associated metadata. The functional interpretation of any structuralmore » features in the model and its utilization for future studies can be made in the context of its measure of uncertainty. We applied this protocol to the 3.3-Å map of the mature P22 bacteriophage capsid, a large and complex macromolecular assembly. With this protocol, we identify and annotate previously undescribed molecular interactions between capsid subunits that are crucial to maintain stability in the absence of cementing proteins or cross-linking, as occur in other bacteriophages.« less

Unfolding the mechanism of the AAA+ unfoldase VAT by a combined cryo-EM, solution NMR study

PubMed Central

Huang, Rui; Ripstein, Zev A.; Augustyniak, Rafal; Lazniewski, Michal; Ginalski, Krzysztof; Kay, Lewis E.; Rubinstein, John L.

2016-01-01

The AAA+ (ATPases associated with a variety of cellular activities) enzymes play critical roles in a variety of homeostatic processes in all kingdoms of life. Valosin-containing protein-like ATPase of Thermoplasma acidophilum (VAT), the archaeal homolog of the ubiquitous AAA+ protein Cdc48/p97, functions in concert with the 20S proteasome by unfolding substrates and passing them on for degradation. Here, we present electron cryomicroscopy (cryo-EM) maps showing that VAT undergoes large conformational rearrangements during its ATP hydrolysis cycle that differ dramatically from the conformational states observed for Cdc48/p97. We validate key features of the model with biochemical and solution methyl-transverse relaxation optimized spectroscopY (TROSY) NMR experiments and suggest a mechanism for coupling the energy of nucleotide hydrolysis to substrate unfolding. These findings illustrate the unique complementarity between cryo-EM and solution NMR for studies of molecular machines, showing that the structural properties of VAT, as well as the population distributions of conformers, are similar in the frozen specimens used for cryo-EM and in the solution phase where NMR spectra are recorded. PMID:27402735

Tuning porosity and radial mechanical properties of DNA origami nanotubes via crossover design

NASA Astrophysics Data System (ADS)

Ma, Zhipeng; Kawai, Kentaro; Hirai, Yoshikazu; Tsuchiya, Toshiyuki; Tabata, Osamu

2017-06-01

DNA origami nanotubes are utilized as structural platforms for the fabrication of various micro/nanosystems for drug delivery, optical or biological sensing, and even nanoscale robots. Their radial structural and mechanical properties, which play a crucial role in the effective use of micro/nanosystems, have not been fully studied. In particular, the effects of crossovers, which are basic structures for rationally assembling double-stranded DNA (dsDNA) helices into a nanotube configuration, have not yet been characterized experimentally. To investigate the effects of crossovers on the porosity and the radial mechanical properties of DNA origami nanotubes, we fabricated a DNA origami nanotube with varied crossover designs along the nanotube axis. The radial geometry of the DNA origami nanotube is experimentally characterized by both atomic force microscopy (AFM) and electron cryomicroscopy (cryo-EM). Moreover, the radial mechanical properties of the DNA origami nanotube including the radial modulus are directly measured by force-distance-based AFM. These measurements reveal that the porosity and the radial modulus of DNA origami nanotubes can be tuned by adjusting the crossover design, which enables the optimal design and construction of DNA origami nanostructures for various applications.

Benchmarking the stability of human detergent-solubilised voltage-gated sodium channels for structural studies using eel as a reference

PubMed Central

Slowik, Daria; Henderson, Richard

2015-01-01

With the ultimate goal of detailed structural analysis of mammalian and particularly human voltage-gated sodium channels (VGSCs), we have investigated the relative stability of human and rat VGSCs and compared them with electric eel VGSC. We found that NaV1.3 from rat was the most stable after detergent solubilisation. The order of stability was rNaV1.3 > hNaV1.2 > hNaV1.1 > hNaV1.6 > hNaV1.3 > hNaV1.4. However, a comparison with the VGSC from Electrophorus electricus, which is most similar to NaV1.4, shows that the eel VGSC is considerably more stable in detergent than the human VGSCs examined. We conclude that current methods of structural analysis, such as single particle electron cryomicroscopy (cryoEM), may be most usefully targeted to eel VGSC or rNaV1.3, but that structural analysis on the full spectrum of VGSCs, by methods that require greater stability such as crystallisation and X-ray crystallography, will require further stabilisation of the channel. PMID:25838126

The ability of the Antarctic nematode Panagrolaimus davidi to survive intracellular freezing is dependent upon nutritional status.

PubMed

Raymond, Mélianie R; Wharton, David A

2013-02-01

The Antarctic nematode Panagrolaimus davidi is the best documented example of an animal surviving intracellular freezing and the only animal so far shown to survive such freezing throughout its tissues. However, a recent study found that after exposure to a freezing stress that produced intracellular freezing in a proportion of nematodes, the resulting survival levels could be explained if those nematodes that froze intracellularly had died. We have thus re-examined the survival of intracellular freezing in this nematode. The ability to survive a freezing exposure that is likely to produce intracellular freezing (freezing at -10 °C) declines with culture age. In cultures that are fed regularly, the ability to survive freezing at -10 °C increases, but in starved cultures freezing survival declines. Survival of intracellular freezing in fed cultures was confirmed using cryomicroscopy, staining of cells with vital dyes and by freeze substitution and transmission electron microscopy. We have thus confirmed that P. davidi can survive intracellular freezing and shown that this ability is dependent upon them being well fed. The effect of culture conditions on the nutrient status of the nematodes should thus be an important factor in the design of experiments.

Correlative Super-Resolution Microscopy: New Dimensions and New Opportunities.

PubMed

Hauser, Meghan; Wojcik, Michal; Kim, Doory; Mahmoudi, Morteza; Li, Wan; Xu, Ke

2017-06-14

Correlative microscopy, the integration of two or more microscopy techniques performed on the same sample, produces results that emphasize the strengths of each technique while offsetting their individual weaknesses. Light microscopy has historically been a central method in correlative microscopy due to its widespread availability, compatibility with hydrated and live biological samples, and excellent molecular specificity through fluorescence labeling. However, conventional light microscopy can only achieve a resolution of ∼300 nm, undercutting its advantages in correlations with higher-resolution methods. The rise of super-resolution microscopy (SRM) over the past decade has drastically improved the resolution of light microscopy to ∼10 nm, thus creating exciting new opportunities and challenges for correlative microscopy. Here we review how these challenges are addressed to effectively correlate SRM with other microscopy techniques, including light microscopy, electron microscopy, cryomicroscopy, atomic force microscopy, and various forms of spectroscopy. Though we emphasize biological studies, we also discuss the application of correlative SRM to materials characterization and single-molecule reactions. Finally, we point out current limitations and discuss possible future improvements and advances. We thus demonstrate how a correlative approach adds new dimensions of information and provides new opportunities in the fast-growing field of SRM.

Structure of the MacAB-TolC ABC-type tripartite multidrug efflux pump

PubMed Central

Llabrés, Salomé; Neuberger, Arthur; Blaza, James N.; Bai, Xiao-chen; Okada, Ui; Murakami, Satoshi; van Veen, Hendrik W.; Zachariae, Ulrich; Scheres, Sjors H.W.; Luisi, Ben F.

2017-01-01

The MacA-MacB-TolC assembly of Escherichia coli is a transmembrane machine that spans the cell envelope and actively extrudes substrates, including macrolide antibiotics and polypeptide virulence factors. These transport processes are energized by the ATPase MacB, a member of the ATP-binding cassette (ABC) superfamily. We present an electron cryo-microscopy structure of the ABC-type tripartite assembly at near-atomic resolution. A hexamer of the periplasmic protein MacA bridges between a TolC trimer in the outer membrane and a MacB dimer in the inner membrane, generating a quaternary structure with a central channel for substrate translocation. A gating ring found in MacA is proposed to act as a one-way valve in substrate transport. The MacB structure features an atypical transmembrane domain (TMD) with a closely packed dimer interface and a periplasmic opening that is the likely portal for substrate entry from the periplasm, with subsequent displacement through an allosteric transport mechanism. PMID:28504659

Structure of a AAA+ unfoldase in the process of unfolding substrate

PubMed Central

Ripstein, Zev A; Huang, Rui; Augustyniak, Rafal; Kay, Lewis E; Rubinstein, John L

2017-01-01

AAA+ unfoldases are thought to unfold substrate through the central pore of their hexameric structures, but how this process occurs is not known. VAT, the Thermoplasma acidophilum homologue of eukaryotic CDC48/p97, works in conjunction with the proteasome to degrade misfolded or damaged proteins. We show that in the presence of ATP, VAT with its regulatory N-terminal domains removed unfolds other VAT complexes as substrate. We captured images of this transient process by electron cryomicroscopy (cryo-EM) to reveal the structure of the substrate-bound intermediate. Substrate binding breaks the six-fold symmetry of the complex, allowing five of the six VAT subunits to constrict into a tight helix that grips an ~80 Å stretch of unfolded protein. The structure suggests a processive hand-over-hand unfolding mechanism, where each VAT subunit releases the substrate in turn before re-engaging further along the target protein, thereby unfolding it. DOI: http://dx.doi.org/10.7554/eLife.25754.001 PMID:28390173

Structure of the bacterial flagellar hook and implication for the molecular universal joint mechanism.

PubMed

Samatey, Fadel A; Matsunami, Hideyuki; Imada, Katsumi; Nagashima, Shigehiro; Shaikh, Tanvir R; Thomas, Dennis R; Chen, James Z; Derosier, David J; Kitao, Akio; Namba, Keiichi

2004-10-28

The bacterial flagellum is a motile organelle, and the flagellar hook is a short, highly curved tubular structure that connects the flagellar motor to the long filament acting as a helical propeller. The hook is made of about 120 copies of a single protein, FlgE, and its function as a nano-sized universal joint is essential for dynamic and efficient bacterial motility and taxis. It transmits the motor torque to the helical propeller over a wide range of its orientation for swimming and tumbling. Here we report a partial atomic model of the hook obtained by X-ray crystallography of FlgE31, a major proteolytic fragment of FlgE lacking unfolded terminal regions, and by electron cryomicroscopy and three-dimensional helical image reconstruction of the hook. The model reveals the intricate molecular interactions and a plausible switching mechanism for the hook to be flexible in bending but rigid against twisting for its universal joint function.

Structure of the polycystic kidney disease TRP channel Polycystin-2 (PC2).

PubMed

Grieben, Mariana; Pike, Ashley C W; Shintre, Chitra A; Venturi, Elisa; El-Ajouz, Sam; Tessitore, Annamaria; Shrestha, Leela; Mukhopadhyay, Shubhashish; Mahajan, Pravin; Chalk, Rod; Burgess-Brown, Nicola A; Sitsapesan, Rebecca; Huiskonen, Juha T; Carpenter, Elisabeth P

2017-02-01

Mutations in either polycystin-1 (PC1 or PKD1) or polycystin-2 (PC2, PKD2 or TRPP1) cause autosomal-dominant polycystic kidney disease (ADPKD) through unknown mechanisms. Here we present the structure of human PC2 in a closed conformation, solved by electron cryomicroscopy at 4.2-Å resolution. The structure reveals a novel polycystin-specific 'tetragonal opening for polycystins' (TOP) domain tightly bound to the top of a classic transient receptor potential (TRP) channel structure. The TOP domain is formed from two extensions to the voltage-sensor-like domain (VSLD); it covers the channel's endoplasmic reticulum lumen or extracellular surface and encloses an upper vestibule, above the pore filter, without blocking the ion-conduction pathway. The TOP-domain fold is conserved among the polycystins, including the homologous channel-like region of PC1, and is the site of a cluster of ADPKD-associated missense variants. Extensive contacts among the TOP-domain subunits, the pore and the VSLD provide ample scope for regulation through physical and chemical stimuli.

Worldwide Protein Data Bank validation information: usage and trends.

PubMed

Smart, Oliver S; Horský, Vladimír; Gore, Swanand; Svobodová Vařeková, Radka; Bendová, Veronika; Kleywegt, Gerard J; Velankar, Sameer

2018-03-01

Realising the importance of assessing the quality of the biomolecular structures deposited in the Protein Data Bank (PDB), the Worldwide Protein Data Bank (wwPDB) partners established Validation Task Forces to obtain advice on the methods and standards to be used to validate structures determined by X-ray crystallography, nuclear magnetic resonance spectroscopy and three-dimensional electron cryo-microscopy. The resulting wwPDB validation pipeline is an integral part of the wwPDB OneDep deposition, biocuration and validation system. The wwPDB Validation Service webserver (https://validate.wwpdb.org) can be used to perform checks prior to deposition. Here, it is shown how validation metrics can be combined to produce an overall score that allows the ranking of macromolecular structures and domains in search results. The ValTrends DB database provides users with a convenient way to access and analyse validation information and other properties of X-ray crystal structures in the PDB, including investigating trends in and correlations between different structure properties and validation metrics.

Worldwide Protein Data Bank validation information: usage and trends

PubMed Central

Horský, Vladimír; Gore, Swanand; Svobodová Vařeková, Radka; Bendová, Veronika

2018-01-01

Realising the importance of assessing the quality of the biomolecular structures deposited in the Protein Data Bank (PDB), the Worldwide Protein Data Bank (wwPDB) partners established Validation Task Forces to obtain advice on the methods and standards to be used to validate structures determined by X-ray crystallography, nuclear magnetic resonance spectroscopy and three-dimensional electron cryo-microscopy. The resulting wwPDB validation pipeline is an integral part of the wwPDB OneDep deposition, biocuration and validation system. The wwPDB Validation Service webserver (https://validate.wwpdb.org) can be used to perform checks prior to deposition. Here, it is shown how validation metrics can be combined to produce an overall score that allows the ranking of macromolecular structures and domains in search results. The ValTrendsDB database provides users with a convenient way to access and analyse validation information and other properties of X-ray crystal structures in the PDB, including investigating trends in and correlations between different structure properties and validation metrics. PMID:29533231

Resolution of ab initio shapes determined from small-angle scattering.

PubMed

Tuukkanen, Anne T; Kleywegt, Gerard J; Svergun, Dmitri I

2016-11-01

Spatial resolution is an important characteristic of structural models, and the authors of structures determined by X-ray crystallography or electron cryo-microscopy always provide the resolution upon publication and deposition. Small-angle scattering of X-rays or neutrons (SAS) has recently become a mainstream structural method providing the overall three-dimensional structures of proteins, nucleic acids and complexes in solution. However, no quantitative resolution measure is available for SAS-derived models, which significantly hampers their validation and further use. Here, a method is derived for resolution assessment for ab initio shape reconstruction from scattering data. The inherent variability of the ab initio shapes is utilized and it is demonstrated how their average Fourier shell correlation function is related to the model resolution. The method is validated against simulated data for proteins with known high-resolution structures and its efficiency is demonstrated in applications to experimental data. It is proposed that henceforth the resolution be reported in publications and depositions of ab initio SAS models.

Resolution of ab initio shapes determined from small-angle scattering

PubMed Central

Tuukkanen, Anne T.; Kleywegt, Gerard J.; Svergun, Dmitri I.

2016-01-01

Spatial resolution is an important characteristic of structural models, and the authors of structures determined by X-ray crystallography or electron cryo-microscopy always provide the resolution upon publication and deposition. Small-angle scattering of X-rays or neutrons (SAS) has recently become a mainstream structural method providing the overall three-dimensional structures of proteins, nucleic acids and complexes in solution. However, no quantitative resolution measure is available for SAS-derived models, which significantly hampers their validation and further use. Here, a method is derived for resolution assessment for ab initio shape reconstruction from scattering data. The inherent variability of the ab initio shapes is utilized and it is demonstrated how their average Fourier shell correlation function is related to the model resolution. The method is validated against simulated data for proteins with known high-resolution structures and its efficiency is demonstrated in applications to experimental data. It is proposed that henceforth the resolution be reported in publications and depositions of ab initio SAS models. PMID:27840683

Four-stranded mini microtubules formed by Prosthecobacter BtubAB show dynamic instability.

PubMed

Deng, Xian; Fink, Gero; Bharat, Tanmay A M; He, Shaoda; Kureisaite-Ciziene, Danguole; Löwe, Jan

2017-07-18

Microtubules, the dynamic, yet stiff hollow tubes built from αβ-tubulin protein heterodimers, are thought to be present only in eukaryotic cells. Here, we report a 3.6-Å helical reconstruction electron cryomicroscopy structure of four-stranded mini microtubules formed by bacterial tubulin-like Prosthecobacter dejongeii BtubAB proteins. Despite their much smaller diameter, mini microtubules share many key structural features with eukaryotic microtubules, such as an M-loop, alternating subunits, and a seam that breaks overall helical symmetry. Using in vitro total internal reflection fluorescence microscopy, we show that bacterial mini microtubules treadmill and display dynamic instability, another hallmark of eukaryotic microtubules. The third protein in the btub gene cluster, BtubC, previously known as "bacterial kinesin light chain," binds along protofilaments every 8 nm, inhibits BtubAB mini microtubule catastrophe, and increases rescue. Our work reveals that some bacteria contain regulated and dynamic cytomotive microtubule systems that were once thought to be only useful in much larger and sophisticated eukaryotic cells.

Structure of the Deactive State of Mammalian Respiratory Complex I.

PubMed

Blaza, James N; Vinothkumar, Kutti R; Hirst, Judy

2018-02-06

Complex I (NADH:ubiquinone oxidoreductase) is central to energy metabolism in mammalian mitochondria. It couples NADH oxidation by ubiquinone to proton transport across the energy-conserving inner membrane, catalyzing respiration and driving ATP synthesis. In the absence of substrates, active complex I gradually enters a pronounced resting or deactive state. The active-deactive transition occurs during ischemia and is crucial for controlling how respiration recovers upon reperfusion. Here, we set a highly active preparation of Bos taurus complex I into the biochemically defined deactive state, and used single-particle electron cryomicroscopy to determine its structure to 4.1 Å resolution. We show that the deactive state arises when critical structural elements that form the ubiquinone-binding site become disordered, and we propose reactivation is induced when substrate binding to the NADH-reduced enzyme templates their reordering. Our structure both rationalizes biochemical data on the deactive state and offers new insights into its physiological and cellular roles. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Validation of cryo-EM structure of IP₃R1 channel.

PubMed

Murray, Stephen C; Flanagan, John; Popova, Olga B; Chiu, Wah; Ludtke, Steven J; Serysheva, Irina I

2013-06-04

About a decade ago, three electron cryomicroscopy (cryo-EM) single-particle reconstructions of IP3R1 were reported at low resolution. It was disturbing that these structures bore little similarity to one another, even at the level of quaternary structure. Recently, we published an improved structure of IP3R1 at ∼1 nm resolution. However, this structure did not bear any resemblance to any of the three previously published structures, leading to the question of why the structure should be considered more reliable than the original three. Here, we apply several methods, including class-average/map comparisons, tilt-pair validation, and use of multiple refinement software packages, to give strong evidence for the reliability of our recent structure. The map resolution and feature resolvability are assessed with the gold standard criterion. This approach is generally applicable to assessing the validity of cryo-EM maps of other molecular machines. Copyright © 2013 Elsevier Ltd. All rights reserved.

Structure of a eukaryotic cyclic nucleotide-gated channel

PubMed Central

Li, Minghui; Zhou, Xiaoyuan; Wang, Shu; Michailidis, Ioannis; Gong, Ye; Su, Deyuan; Li, Huan; Li, Xueming; Yang, Jian

2018-01-01

Summary Cyclic nucleotide-gated (CNG) channels are essential for vision and olfaction. They belong to the voltage-gated ion channel superfamily but their activities are controlled by intracellular cyclic nucleotides instead of transmembrane voltage. Here we report a 3.5 Å-resolution single-particle electron cryomicroscopy structure of a CNG channel from C. elegans in the cGMP-bound open state. The channel has an unusual voltage-sensor-like domain (VSLD), accounting for its deficient voltage dependence. A C-terminal linker connecting S6 and the cyclic nucleotide-binding domain interacts directly with both the VSLD and pore domain, forming a gating ring that couples conformational changes triggered by cyclic nucleotide binding to the gate. The selectivity filter is lined by the carboxylate side chains of a functionally important glutamate and three rings of backbone carbonyls. This structure provides a new framework for understanding mechanisms of ion permeation, gating and channelopathy of CNG channels and cyclic nucleotide modulation of related channels. PMID:28099415

Structure of the TRPA1 ion channel suggests regulatory mechanisms

PubMed Central

Paulsen, Candice E.; Armache, Jean-Paul; Gao, Yuan; Cheng, Yifan; Julius, David

2015-01-01

The TRPA1 ion channel (a.k.a the ‘wasabi receptor’) is a detector of noxious chemical agents encountered in our environment or produced endogenously during tissue injury or drug metabolism. These include a broad class of electrophiles that activate the channel through covalent protein modification. TRPA1 antagonists hold potential for treating neurogenic inflammatory conditions provoked or exacerbated by irritant exposure. Despite compelling reasons to understand TRPA1 function, structural mechanisms underlying channel regulation remain obscure. Here, we use single-particle electron cryo-microscopy to determine the structure of full-length human TRPA1 to ~4Å resolution in the presence of pharmacophores, including a potent antagonist. A number of unexpected features are revealed, including an extensive coiled-coil assembly domain stabilized by polyphosphate co-factors and a highly integrated nexus that converges on an unpredicted TRP-like allosteric domain. These findings provide novel insights into mechanisms of TRPA1 regulation, and establish a blueprint for structure-based design of analgesic and anti-inflammatory agents. PMID:25855297

Structure and conformational states of the bovine mitochondrial ATP synthase by cryo-EM

PubMed Central

Zhou, Anna; Rohou, Alexis; Schep, Daniel G; Bason, John V; Montgomery, Martin G; Walker, John E; Grigorieff, Nikolaus; Rubinstein, John L

2015-01-01

Adenosine triphosphate (ATP), the chemical energy currency of biology, is synthesized in eukaryotic cells primarily by the mitochondrial ATP synthase. ATP synthases operate by a rotary catalytic mechanism where proton translocation through the membrane-inserted FO region is coupled to ATP synthesis in the catalytic F1 region via rotation of a central rotor subcomplex. We report here single particle electron cryomicroscopy (cryo-EM) analysis of the bovine mitochondrial ATP synthase. Combining cryo-EM data with bioinformatic analysis allowed us to determine the fold of the a subunit, suggesting a proton translocation path through the FO region that involves both the a and b subunits. 3D classification of images revealed seven distinct states of the enzyme that show different modes of bending and twisting in the intact ATP synthase. Rotational fluctuations of the c8-ring within the FO region support a Brownian ratchet mechanism for proton-translocation-driven rotation in ATP synthases. DOI: http://dx.doi.org/10.7554/eLife.10180.001 PMID:26439008

Structure of the skeletal muscle calcium release channel activated with Ca2+ and AMP-PCP.

PubMed Central

Serysheva, I I; Schatz, M; van Heel, M; Chiu, W; Hamilton, S L

1999-01-01

The functional state of the skeletal muscle Ca2+ release channel is modulated by a number of endogenous molecules during excitation-contraction. Using electron cryomicroscopy and angular reconstitution techniques, we determined the three-dimensional (3D) structure of the skeletal muscle Ca2+ release channel activated by a nonhydrolyzable analog of ATP in the presence of Ca2+. These ligands together produce almost maximum activation of the channel and drive the channel population toward a predominately open state. The resulting 30-A 3D reconstruction reveals long-range conformational changes in the cytoplasmic region that might affect the interaction of the Ca2+ release channel with the t-tubule voltage sensor. In addition, a central opening and mass movements, detected in the transmembrane domain of both the Ca(2+)- and the Ca2+/nucleotide-activated channels, suggest a mechanism for channel opening similar to opening-closing of the iris in a camera diaphragm. PMID:10512814

Freezing-induced cellular and membrane dehydration in the presence of cryoprotective agents.

PubMed

Akhoondi, Maryam; Oldenhof, Harriëtte; Sieme, Harald; Wolkers, Willem F

2012-09-01

FTIR and cryomicroscopy have been used to study mouse embryonic fibroblast cells (3T3) during freezing in the absence and presence of DMSO and glycerol. The results show that cell volume changes as observed by cryomicroscopy typically end at temperatures above -15°C, whereas membrane phase changes may continue until temperatures as low as -30°C. This implies that cellular dehydration precedes dehydration of the bound water surrounding the phospholipid head groups. Both DMSO and glycerol increase the membrane hydraulic permeability at subzero temperature and reduce the activation energy for water transport. Cryoprotective agents facilitate dehydration to continue at low subzero temperatures thereby decreasing the incidence of intracellular ice formation. The increased subzero membrane hydraulic permeability likely plays an important role in the cryoprotective action of DMSO and glycerol. In the presence of DMSO water permeability was found to be greater compared to that in the presence of glycerol. Two temperature regimes were identified in an Arrhenius plot of the membrane hydraulic permeability. The activation energy for water transport at temperature ranging from 0 to -10°C was found to be greater than that below -10°C. The non-linear Arrhenius behavior of Lp has been implemented in the water transport model to simulate cell volume changes during freezing. At a cooling rate of 1°C min(-1), ∼5% of the initial osmotically active water volume is trapped inside the cells at -30°C.

High-resolution noise substitution to measure overfitting and validate resolution in 3D structure determination by single particle electron cryomicroscopy.

PubMed

Chen, Shaoxia; McMullan, Greg; Faruqi, Abdul R; Murshudov, Garib N; Short, Judith M; Scheres, Sjors H W; Henderson, Richard

2013-12-01

Three-dimensional (3D) structure determination by single particle electron cryomicroscopy (cryoEM) involves the calculation of an initial 3D model, followed by extensive iterative improvement of the orientation determination of the individual particle images and the resulting 3D map. Because there is much more noise than signal at high resolution in the images, this creates the possibility of noise reinforcement in the 3D map, which can give a false impression of the resolution attained. The balance between signal and noise in the final map at its limiting resolution depends on the image processing procedure and is not easily predicted. There is a growing awareness in the cryoEM community of how to avoid such over-fitting and over-estimation of resolution. Equally, there has been a reluctance to use the two principal methods of avoidance because they give lower resolution estimates, which some people believe are too pessimistic. Here we describe a simple test that is compatible with any image processing protocol. The test allows measurement of the amount of signal and the amount of noise from overfitting that is present in the final 3D map. We have applied the method to two different sets of cryoEM images of the enzyme beta-galactosidase using several image processing packages. Our procedure involves substituting the Fourier components of the initial particle image stack beyond a chosen resolution by either the Fourier components from an adjacent area of background, or by simple randomisation of the phases of the particle structure factors. This substituted noise thus has the same spectral power distribution as the original data. Comparison of the Fourier Shell Correlation (FSC) plots from the 3D map obtained using the experimental data with that from the same data with high-resolution noise (HR-noise) substituted allows an unambiguous measurement of the amount of overfitting and an accompanying resolution assessment. A simple formula can be used to calculate an unbiased FSC from the two curves, even when a substantial amount of overfitting is present. The approach is software independent. The user is therefore completely free to use any established method or novel combination of methods, provided the HR-noise test is carried out in parallel. Applying this procedure to cryoEM images of beta-galactosidase shows how overfitting varies greatly depending on the procedure, but in the best case shows no overfitting and a resolution of ~6 Å. (382 words). © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy.

PubMed

McMullan, G; Vinothkumar, K R; Henderson, R

2015-11-01

We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å(2) for every incident 300 keV e(-)/Å(2). The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e(-)/Å(2) per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

The host outer membrane proteins OmpA and OmpC are associated with the Shigella phage Sf6 virion

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

Zhao Haiyan, E-mail: zhaohy@ku.ed; Sequeira, Reuben D., E-mail: sequen@ku.ed; Galeva, Nadezhda A., E-mail: galeva@ku.ed

2011-01-20

Assembly of dsDNA bacteriophage is a precisely programmed process. Potential roles of host cell components in phage assembly haven't been well understood. It was previously reported that two unidentified proteins were present in bacteriophage Sf6 virion (Casjens et al, 2004, J.Mol.Biol. 339, 379-394, Fig. 2A). Using tandem mass spectrometry, we have identified the two proteins as outer membrane proteins (OMPs) OmpA and OmpC from its host Shigella flexneri. The transmission electron cryo-microscopy structure of Sf6 shows significant density at specific sites at the phage capsid inner surface. This density fit well with the characteristic beta-barrel domains of OMPs, thus maymore » be due to the two host proteins. Locations of this density suggest a role in Sf6 morphogenesis reminiscent of phage-encoded cementing proteins. These data indicate a new, OMP-related phage:host linkage, adding to previous knowledge that some lambdoid bacteriophage genomes contain OmpC-like genes that express phage-encoded porins in the lysogenic state.« less

Modeling protein structure at near atomic resolutions with Gorgon.

PubMed

Baker, Matthew L; Abeysinghe, Sasakthi S; Schuh, Stephen; Coleman, Ross A; Abrams, Austin; Marsh, Michael P; Hryc, Corey F; Ruths, Troy; Chiu, Wah; Ju, Tao

2011-05-01

Electron cryo-microscopy (cryo-EM) has played an increasingly important role in elucidating the structure and function of macromolecular assemblies in near native solution conditions. Typically, however, only non-atomic resolution reconstructions have been obtained for these large complexes, necessitating computational tools for integrating and extracting structural details. With recent advances in cryo-EM, maps at near-atomic resolutions have been achieved for several macromolecular assemblies from which models have been manually constructed. In this work, we describe a new interactive modeling toolkit called Gorgon targeted at intermediate to near-atomic resolution density maps (10-3.5 Å), particularly from cryo-EM. Gorgon's de novo modeling procedure couples sequence-based secondary structure prediction with feature detection and geometric modeling techniques to generate initial protein backbone models. Beyond model building, Gorgon is an extensible interactive visualization platform with a variety of computational tools for annotating a wide variety of 3D volumes. Examples from cryo-EM maps of Rotavirus and Rice Dwarf Virus are used to demonstrate its applicability to modeling protein structure. Copyright © 2011 Elsevier Inc. All rights reserved.

Structures of closed and open conformations of dimeric human ATM

PubMed Central

Baretić, Domagoj; Pollard, Hannah K.; Fisher, David I.; Johnson, Christopher M.; Santhanam, Balaji; Truman, Caroline M.; Kouba, Tomas; Fersht, Alan R.; Phillips, Christopher; Williams, Roger L.

2017-01-01

ATM (ataxia-telangiectasia mutated) is a phosphatidylinositol 3-kinase–related protein kinase (PIKK) best known for its role in DNA damage response. ATM also functions in oxidative stress response, insulin signaling, and neurogenesis. Our electron cryomicroscopy (cryo-EM) suggests that human ATM is in a dynamic equilibrium between closed and open dimers. In the closed state, the PIKK regulatory domain blocks the peptide substrate–binding site, suggesting that this conformation may represent an inactive or basally active enzyme. The active site is held in this closed conformation by interaction with a long helical hairpin in the TRD3 (tetratricopeptide repeats domain 3) domain of the symmetry-related molecule. The open dimer has two protomers with only a limited contact interface, and it lacks the intermolecular interactions that block the peptide-binding site in the closed dimer. This suggests that the open conformation may be more active. The ATM structure shows the detailed topology of the regulator-interacting N-terminal helical solenoid. The ATM conformational dynamics shown by the structures represent an important step in understanding the enzyme regulation. PMID:28508083

Structural Insights into the Niemann-Pick C1 (NPC1)-Mediated Cholesterol Transfer and Ebola Infection.

PubMed

Gong, Xin; Qian, Hongwu; Zhou, Xinhui; Wu, Jianping; Wan, Tao; Cao, Pingping; Huang, Weiyun; Zhao, Xin; Wang, Xudong; Wang, Peiyi; Shi, Yi; Gao, George F; Zhou, Qiang; Yan, Nieng

2016-06-02

Niemann-Pick disease type C (NPC) is associated with mutations in NPC1 and NPC2, whose gene products are key players in the endosomal/lysosomal egress of low-density lipoprotein-derived cholesterol. NPC1 is also the intracellular receptor for Ebola virus (EBOV). Here, we present a 4.4 Å structure of full-length human NPC1 and a low-resolution reconstruction of NPC1 in complex with the cleaved glycoprotein (GPcl) of EBOV, both determined by single-particle electron cryomicroscopy. NPC1 contains 13 transmembrane segments (TMs) and three distinct lumenal domains A (also designated NTD), C, and I. TMs 2-13 exhibit a typical resistance-nodulation-cell division fold, among which TMs 3-7 constitute the sterol-sensing domain conserved in several proteins involved in cholesterol metabolism and signaling. A trimeric EBOV-GPcl binds to one NPC1 monomer through the domain C. Our structural and biochemical characterizations provide an important framework for mechanistic understanding of NPC1-mediated intracellular cholesterol trafficking and Ebola virus infection. Copyright © 2016 Elsevier Inc. All rights reserved.

Cofilin Changes the Twist of F-Actin: Implications for Actin Filament Dynamics and Cellular Function

PubMed Central

McGough, Amy; Pope, Brian; Chiu, Wah; Weeds, Alan

1997-01-01

Cofilin is an actin depolymerizing protein found widely distributed in animals and plants. We have used electron cryomicroscopy and helical reconstruction to identify its binding site on actin filaments. Cofilin binds filamentous (F)-actin cooperatively by bridging two longitudinally associated actin subunits. The binding site is centered axially at subdomain 2 of the lower actin subunit and radially at the cleft between subdomains 1 and 3 of the upper actin subunit. Our work has revealed a totally unexpected (and unique) property of cofilin, namely, its ability to change filament twist. As a consequence of this change in twist, filaments decorated with cofilin have much shorter ‘actin crossovers' (∼75% of those normally observed in F-actin structures). Although their binding sites are distinct, cofilin and phalloidin do not bind simultaneously to F-actin. This is the first demonstration of a protein that excludes another actin-binding molecule by changing filament twist. Alteration of F-actin structure by cofilin/ADF appears to be a novel mechanism through which the actin cytoskeleton may be regulated or remodeled. PMID:9265645

The R403Q Myosin Mutation Implicated in Familial Hypertrophic Cardiomyopathy Causes Disorder at the Actomyosin Interface

PubMed Central

Volkmann, Niels; Lui, HongJun; Hazelwood, Larnele; Trybus, Kathleen M.; Lowey, Susan; Hanein, Dorit

2007-01-01

Background Mutations in virtually all of the proteins comprising the cardiac muscle sarcomere have been implicated in causing Familial Hypertrophic Cardiomyopathy (FHC). Mutations in the β-myosin heavy chain (MHC) remain among the most common causes of FHC, with the widely studied R403Q mutation resulting in an especially severe clinical prognosis. In vitro functional studies of cardiac myosin containing the R403Q mutation have revealed significant changes in enzymatic and mechanical properties compared to wild-type myosin. It has been proposed that these molecular changes must trigger events that ultimately lead to the clinical phenotype. Principal Findings Here we examine the structural consequences of the R403Q mutation in a recombinant smooth muscle myosin subfragment (S1), whose kinetic features have much in common with slow β-MHC. We obtained three-dimensional reconstructions of wild-type and R403Q smooth muscle S1 bound to actin filaments in the presence (ADP) and absence (apo) of nucleotide by electron cryomicroscopy and image analysis. We observed that the mutant S1 was attached to actin at highly variable angles compared to wild-type reconstructions, suggesting a severe disruption of the actin-myosin interaction at the interface. Significance These results provide structural evidence that disarray at the molecular level may be linked to the histopathological myocyte disarray characteristic of the diseased state. PMID:17987111

Estimating loop length from CryoEM images at medium resolutions.

PubMed

McKnight, Andrew; Si, Dong; Al Nasr, Kamal; Chernikov, Andrey; Chrisochoides, Nikos; He, Jing

2013-01-01

De novo protein modeling approaches utilize 3-dimensional (3D) images derived from electron cryomicroscopy (CryoEM) experiments. The skeleton connecting two secondary structures such as α-helices represent the loop in the 3D image. The accuracy of the skeleton and of the detected secondary structures are critical in De novo modeling. It is important to measure the length along the skeleton accurately since the length can be used as a constraint in modeling the protein. We have developed a novel computational geometric approach to derive a simplified curve in order to estimate the loop length along the skeleton. The method was tested using fifty simulated density images of helix-loop-helix segments of atomic structures and eighteen experimentally derived density data from Electron Microscopy Data Bank (EMDB). The test using simulated density maps shows that it is possible to estimate within 0.5 Å of the expected length for 48 of the 50 cases. The experiments, involving eighteen experimentally derived CryoEM images, show that twelve cases have error within 2 Å. The tests using both simulated and experimentally derived images show that it is possible for our proposed method to estimate the loop length along the skeleton if the secondary structure elements, such as α-helices, can be detected accurately, and there is a continuous skeleton linking the α-helices.

Binding of Capsaicin to the TRPV1 Ion Channel.

PubMed

Darré, Leonardo; Domene, Carmen

2015-12-07

Transient receptor potential (TRP) ion channels constitute a notable family of cation channels involved in the ability of an organisms to detect noxious mechanical, thermal, and chemical stimuli that give rise to the perception of pain, taste, and changes in temperature. One of the most experimentally studied agonist of TRP channels is capsaicin, which is responsible for the burning sensation produced when chili pepper is in contact with organic tissues. Thus, understanding how this molecule interacts and regulates TRP channels is essential to high impact pharmacological applications, particularly those related to pain treatment. The recent publication of a three-dimensional structure of the vanilloid receptor 1 (TRPV1) in the absence and presence of capsaicin from single particle electron cryomicroscopy experiments provides the opportunity to explore these questions at the atomic level. In the present work, molecular docking and unbiased and biased molecular dynamics simulations were employed to generate a structural model of the capsaicin-channel complex. In addition, the standard free energy of binding was estimated using alchemical transformations coupled with conformational, translational, and orientational restraints on the ligand. Key binding modes consistent with previous experimental data are identified, and subtle but essential dynamical features of the binding site are characterized. These observations shed some light into how TRPV1 interacts with capsaicin, and may help to refine design parameters for new TRPV1 antagonists, and potentially guide further developments of TRP channel modulators.

The Amphipathic Helix of Adenovirus Capsid Protein VI Contributes to Penton Release and Postentry Sorting

PubMed Central

Martinez, Ruben; Schellenberger, Pascale; Vasishtan, Daven; Aknin, Cindy; Austin, Sisley; Dacheux, Denis; Rayne, Fabienne; Siebert, Alistair; Ruzsics, Zsolt; Gruenewald, Kay

2014-01-01

ABSTRACT Nuclear delivery of the adenoviral genome requires that the capsid cross the limiting membrane of the endocytic compartment and traverse the cytosol to reach the nucleus. This endosomal escape is initiated upon internalization and involves a highly coordinated process of partial disassembly of the entering capsid to release the membrane lytic internal capsid protein VI. Using wild-type and protein VI-mutated human adenovirus serotype 5 (HAdV-C5), we show that capsid stability and membrane rupture are major determinants of entry-related sorting of incoming adenovirus virions. Furthermore, by using electron cryomicroscopy, as well as penton- and protein VI-specific antibodies, we show that the amphipathic helix of protein VI contributes to capsid stability by preventing premature disassembly and deployment of pentons and protein VI. Thus, the helix has a dual function in maintaining the metastable state of the capsid by preventing premature disassembly and mediating efficient membrane lysis to evade lysosomal targeting. Based on these findings and structural data from cryo-electron microscopy, we suggest a refined disassembly mechanism upon entry. IMPORTANCE In this study, we show the intricate connection of adenovirus particle stability and the entry-dependent release of the membrane-lytic capsid protein VI required for endosomal escape. We show that the amphipathic helix of the adenovirus internal protein VI is required to stabilize pentons in the particle while coinciding with penton release upon entry and that release of protein VI mediates membrane lysis, thereby preventing lysosomal sorting. We suggest that this dual functionality of protein VI ensures an optimal disassembly process by balancing the metastable state of the mature adenovirus particle. PMID:25473051

Design principles and applications of a cooled CCD camera for electron microscopy.

PubMed

Faruqi, A R

1998-01-01

Cooled CCD cameras offer a number of advantages in recording electron microscope images with CCDs rather than film which include: immediate availability of the image in a digital format suitable for further computer processing, high dynamic range, excellent linearity and a high detective quantum efficiency for recording electrons. In one important respect however, film has superior properties: the spatial resolution of CCD detectors tested so far (in terms of point spread function or modulation transfer function) are inferior to film and a great deal of our effort has been spent in designing detectors with improved spatial resolution. Various instrumental contributions to spatial resolution have been analysed and in this paper we discuss the contribution of the phosphor-fibre optics system in this measurement. We have evaluated the performance of a number of detector components and parameters, e.g. different phosphors (and a scintillator), optical coupling with lens or fibre optics with various demagnification factors, to improve the detector performance. The camera described in this paper, which is based on this analysis, uses a tapered fibre optics coupling between the phosphor and the CCD and is installed on a Philips CM12 electron microscope equipped to perform cryo-microscopy. The main use of the camera so far has been in recording electron diffraction patterns from two dimensional crystals of bacteriorhodopsin--from wild type and from different trapped states during the photocycle. As one example of the type of data obtained with the CCD camera a two dimensional Fourier projection map from the trapped O-state is also included. With faster computers, it will soon be possible to undertake this type of work on an on-line basis. Also, with improvements in detector size and resolution, CCD detectors, already ideal for diffraction, will be able to compete with film in the recording of high resolution images.

DeepPicker: A deep learning approach for fully automated particle picking in cryo-EM.

PubMed

Wang, Feng; Gong, Huichao; Liu, Gaochao; Li, Meijing; Yan, Chuangye; Xia, Tian; Li, Xueming; Zeng, Jianyang

2016-09-01

Particle picking is a time-consuming step in single-particle analysis and often requires significant interventions from users, which has become a bottleneck for future automated electron cryo-microscopy (cryo-EM). Here we report a deep learning framework, called DeepPicker, to address this problem and fill the current gaps toward a fully automated cryo-EM pipeline. DeepPicker employs a novel cross-molecule training strategy to capture common features of particles from previously-analyzed micrographs, and thus does not require any human intervention during particle picking. Tests on the recently-published cryo-EM data of three complexes have demonstrated that our deep learning based scheme can successfully accomplish the human-level particle picking process and identify a sufficient number of particles that are comparable to those picked manually by human experts. These results indicate that DeepPicker can provide a practically useful tool to significantly reduce the time and manual effort spent in single-particle analysis and thus greatly facilitate high-resolution cryo-EM structure determination. DeepPicker is released as an open-source program, which can be downloaded from https://github.com/nejyeah/DeepPicker-python. Copyright © 2016 Elsevier Inc. All rights reserved.

A structural mechanism for bacterial autotransporter glycosylation by a dodecameric heptosyltransferase family

PubMed Central

Yao, Qing; Lu, Qiuhe; Wan, Xiaobo; Song, Feng; Xu, Yue; Hu, Mo; Zamyatina, Alla; Liu, Xiaoyun; Huang, Niu; Zhu, Ping; Shao, Feng

2014-01-01

A large group of bacterial virulence autotransporters including AIDA-I from diffusely adhering E. coli (DAEC) and TibA from enterotoxigenic E. coli (ETEC) require hyperglycosylation for functioning. Here we demonstrate that TibC from ETEC harbors a heptosyltransferase activity on TibA and AIDA-I, defining a large family of bacterial autotransporter heptosyltransferases (BAHTs). The crystal structure of TibC reveals a characteristic ring-shape dodecamer. The protomer features an N-terminal β-barrel, a catalytic domain, a β-hairpin thumb, and a unique iron-finger motif. The iron-finger motif contributes to back-to-back dimerization; six dimers form the ring through β-hairpin thumb-mediated hand-in-hand contact. The structure of ADP-D-glycero-β-D-manno-heptose (ADP-D,D-heptose)-bound TibC reveals a sugar transfer mechanism and also the ligand stereoselectivity determinant. Electron-cryomicroscopy analyses uncover a TibC–TibA dodecamer/hexamer assembly with two enzyme molecules binding to one TibA substrate. The complex structure also highlights a high efficient hyperglycosylation of six autotransporter substrates simultaneously by the dodecamer enzyme complex. DOI: http://dx.doi.org/10.7554/eLife.03714.001 PMID:25310236

Structure of clathrin coat with bound Hsc70 and auxilin: mechanism of Hsc70-facilitated disassembly

PubMed Central

Xing, Yi; Böcking, Till; Wolf, Matthias; Grigorieff, Nikolaus; Kirchhausen, Tomas; Harrison, Stephen C

2010-01-01

The chaperone Hsc70 drives the clathrin assembly–disassembly cycle forward by stimulating dissociation of a clathrin lattice. A J-domain containing co-chaperone, auxilin, associates with a freshly budded clathrin-coated vesicle, or with an in vitro assembled clathrin coat, and recruits Hsc70 to its specific heavy-chain-binding site. We have determined by electron cryomicroscopy (cryoEM), at about 11 Å resolution, the structure of a clathrin coat (in the D6-barrel form) with specifically bound Hsc70 and auxilin. The Hsc70 binds a previously analysed site near the C-terminus of the heavy chain, with a stoichiometry of about one per three-fold vertex. Its binding is accompanied by a distortion of the clathrin lattice, detected by a change in the axial ratio of the D6 barrel. We propose that when Hsc70, recruited to a position close to its target by the auxilin J-domain, splits ATP, it clamps firmly onto its heavy-chain site and locks in place a transient fluctuation. Accumulation of the local strain thus imposed at multiple vertices can then lead to disassembly. PMID:20033059

Conformational changes accompany activation of reovirus RNA-dependent RNA transcription

PubMed Central

Mendez, Israel I.; Weiner, Scott G.; She, Yi-Min; Yeager, Mark; Coombs, Kevin M.

2009-01-01

Many critical biologic processes involve dynamic interactions between proteins and nucleic acids. Such dynamic processes are often difficult to delineate by conventional static methods. For example, while a variety of nucleic acid polymerase structures have been determined at atomic resolution, the details of how some multi-protein transcriptase complexes actively produce mRNA, as well as conformational changes associated with activation of such complexes, remain poorly understood. The mammalian reovirus innermost capsid (core) manifests all enzymatic activities necessary to produce mRNA from each of the 10 encased double-stranded RNA genes. We used rapid freezing and electron cryo-microscopy to trap and visualize transcriptionally active reovirus core particles and compared them to inactive core images. Rod-like density centered within actively transcribing core spike channels was attributed to exiting nascent mRNA. Comparative radial density plots of active and inactive core particles identified several structural changes in both internal and external regions of the icosahedral core capsid. Inactive and transcriptionally active cores were partially digested with trypsin and identities of initial tryptic peptides determined by mass spectrometry. Differentially-digested peptides, which also suggest transcription-associated conformational changes, were placed within the known 3-dimensional structures of major core proteins. PMID:18321727

Ensemble cryo-EM uncovers inchworm-like translocation of a viral IRES through the ribosome

PubMed Central

Abeyrathne, Priyanka D; Koh, Cha San; Grant, Timothy; Grigorieff, Nikolaus; Korostelev, Andrei A

2016-01-01

Internal ribosome entry sites (IRESs) mediate cap-independent translation of viral mRNAs. Using electron cryo-microscopy of a single specimen, we present five ribosome structures formed with the Taura syndrome virus IRES and translocase eEF2•GTP bound with sordarin. The structures suggest a trajectory of IRES translocation, required for translation initiation, and provide an unprecedented view of eEF2 dynamics. The IRES rearranges from extended to bent to extended conformations. This inchworm-like movement is coupled with ribosomal inter-subunit rotation and 40S head swivel. eEF2, attached to the 60S subunit, slides along the rotating 40S subunit to enter the A site. Its diphthamide-bearing tip at domain IV separates the tRNA-mRNA-like pseudoknot I (PKI) of the IRES from the decoding center. This unlocks 40S domains, facilitating head swivel and biasing IRES translocation via hitherto-elusive intermediates with PKI captured between the A and P sites. The structures suggest missing links in our understanding of tRNA translocation. DOI: http://dx.doi.org/10.7554/eLife.14874.001 PMID:27159452

The RNF168 paralog RNF169 defines a new class of ubiquitylated histone reader involved in the response to DNA damage

PubMed Central

Kitevski-LeBlanc, Julianne; Fradet-Turcotte, Amélie; Portella, Guillem; Yuwen, Tairan; Panier, Stephanie; Duan, Shili; Canny, Marella D; van Ingen, Hugo; Arrowsmith, Cheryl H; Rubinstein, John L; Vendruscolo, Michele; Durocher, Daniel; Kay, Lewis E

2017-01-01

Site-specific histone ubiquitylation plays a central role in orchestrating the response to DNA double-strand breaks (DSBs). DSBs elicit a cascade of events controlled by the ubiquitin ligase RNF168, which promotes the accumulation of repair factors such as 53BP1 and BRCA1 on the chromatin flanking the break site. RNF168 also promotes its own accumulation, and that of its paralog RNF169, but how they recognize ubiquitylated chromatin is unknown. Using methyl-TROSY solution NMR spectroscopy and molecular dynamics simulations, we present an atomic resolution model of human RNF169 binding to a ubiquitylated nucleosome, and validate it by electron cryomicroscopy. We establish that RNF169 binds to ubiquitylated H2A-Lys13/Lys15 in a manner that involves its canonical ubiquitin-binding helix and a pair of arginine-rich motifs that interact with the nucleosome acidic patch. This three-pronged interaction mechanism is distinct from that by which 53BP1 binds to ubiquitylated H2A-Lys15 highlighting the diversity in site-specific recognition of ubiquitylated nucleosomes. DOI: http://dx.doi.org/10.7554/eLife.23872.001 PMID:28406400

Acetylcholine-Binding Protein in the Hemolymph of the Planorbid Snail Biomphalaria glabrata Is a Pentagonal Dodecahedron (60 Subunits)

PubMed Central

Kapetanopoulos, Katharina; Braukmann, Sandra; Gebauer, Wolfgang; Tenzer, Stefan; Markl, Jürgen

2012-01-01

Nicotinic acetylcholine receptors (nAChR) play important neurophysiological roles and are of considerable medical relevance. They have been studied extensively, greatly facilitated by the gastropod acetylcholine-binding proteins (AChBP) which represent soluble structural and functional homologues of the ligand-binding domain of nAChR. All these proteins are ring-like pentamers. Here we report that AChBP exists in the hemolymph of the planorbid snail Biomphalaria glabrata (vector of the schistosomiasis parasite) as a regular pentagonal dodecahedron, 22 nm in diameter (12 pentamers, 60 active sites). We sequenced and recombinantly expressed two ∼25 kDa polypeptides (BgAChBP1 and BgAChBP2) with a specific active site, N-glycan site and disulfide bridge variation. We also provide the exon/intron structures. Recombinant BgAChBP1 formed pentamers and dodecahedra, recombinant BgAChBP2 formed pentamers and probably disulfide-bridged di-pentamers, but not dodecahedra. Three-dimensional electron cryo-microscopy (3D-EM) yielded a 3D reconstruction of the dodecahedron with a resolution of 6 Å. Homology models of the pentamers docked to the 6 Å structure revealed opportunities for chemical bonding at the inter-pentamer interfaces. Definition of the ligand-binding pocket and the gating C-loop in the 6 Å structure suggests that 3D-EM might lead to the identification of functional states in the BgAChBP dodecahedron. PMID:22916297

Renaissance of morphological studies: the examination of functional structures in living animal organs using the in vivo cryotechnique.

PubMed

Ohno, Shinichi; Saitoh, Yurika; Ohno, Nobuhiko; Terada, Nobuo

2017-01-01

Medical and biological scientists wish to understand the in vivo structures of the cells and tissues that make up living animal organs, as well as the locations of their molecular components. Recently, the live imaging of animal cells and tissues with fluorescence-labeled proteins produced via gene manipulation has become increasingly common. Therefore, it is important to ensure that findings derived from histological or immunohistochemical tissue sections of living animal organs are compatible with those obtained from live images of the same organs, which can be assessed using recently developed digital imaging techniques. Over the past two decades, we have performed immunohistochemical and morphological studies of the cells and tissues in living animal organs using a novel in vivo cryotechnique. The use of a specially designed liquid cryogen system with or without a cryoknife during this cryotechnique solved the technical problems that inevitably arise during the conventional preparation methods employed prior to light or electron microscopic examinations. Our in vivo cryotechnique has been found to be extremely useful for arresting transient physiological processes in cells and tissues and for maintaining their functional components-such as rapidly changing signaling molecules, membrane channels, or receptors-in situ. The purpose of the present review is to describe the basic mechanism underlying cryotechniques and the significance of our in vivo cryotechnique. In addition, it describes various morphological or immunohistochemical findings, observations made using quantum dots, and a Raman cryomicroscopy-based method for assessing oxygen saturation in the erythrocytes flowing through intestinal tissues.

Alignment of cryo-EM movies of individual particles by optimization of image translations.

PubMed

Rubinstein, John L; Brubaker, Marcus A

2015-11-01

Direct detector device (DDD) cameras have revolutionized single particle electron cryomicroscopy (cryo-EM). In addition to an improved camera detective quantum efficiency, acquisition of DDD movies allows for correction of movement of the specimen, due to both instabilities in the microscope specimen stage and electron beam-induced movement. Unlike specimen stage drift, beam-induced movement is not always homogeneous within an image. Local correlation in the trajectories of nearby particles suggests that beam-induced motion is due to deformation of the ice layer. Algorithms have already been described that can correct movement for large regions of frames and for >1 MDa protein particles. Another algorithm allows individual <1 MDa protein particle trajectories to be estimated, but requires rolling averages to be calculated from frames and fits linear trajectories for particles. Here we describe an algorithm that allows for individual <1 MDa particle images to be aligned without frame averaging or linear trajectories. The algorithm maximizes the overall correlation of the shifted frames with the sum of the shifted frames. The optimum in this single objective function is found efficiently by making use of analytically calculated derivatives of the function. To smooth estimates of particle trajectories, rapid changes in particle positions between frames are penalized in the objective function and weighted averaging of nearby trajectories ensures local correlation in trajectories. This individual particle motion correction, in combination with weighting of Fourier components to account for increasing radiation damage in later frames, can be used to improve 3-D maps from single particle cryo-EM. Copyright © 2015 Elsevier Inc. All rights reserved.

Structure of the rabbit ryanodine receptor RyR1 at near-atomic resolution

PubMed Central

Wu, Jianping; Li, Zhangqiang; Xie, Tian; Peng, Wei; Yin, Changcheng; Li, Xueming; Scheres, Sjors H.W.; Shi, Yigong; Yan, Nieng

2014-01-01

The ryanodine receptors (RyRs) are high-conductance intracellular Ca2+ channels that play a pivotal role in the excitation-contraction coupling of skeletal and cardiac muscles. RyRs are the largest known ion channels, with a homotetrameric organization and approximately 5000 residues in each protomer. Here we report the structure of the rabbit RyR1 in complex with its modulator FKBP12 at an overall resolution of 3.8 Å, determined by single-particle electron cryo-microscopy. Three previously uncharacterized domains, named Central, Handle, and Helical domains, display the armadillo repeat fold. These domains, together with the amino-terminal domain, constitute a network of superhelical scaffold for binding and propagation of conformational changes. The channel domain exhibits the voltage-gated ion channel superfamily fold with distinct features. A negative charge-enriched hairpin loop connecting S5 and the pore helix is positioned above the entrance to the selectivity filter vestibule. The four elongated S6 segments form a right-handed helical bundle that closes the pore at the cytoplasmic border of the membrane. Allosteric regulation of the pore by the cytoplasmic domains is mediated through extensive interactions between the Central domains and the channel domain. These structural features explain high ion conductance by RyRs and the long-range allosteric regulation of channel activities. PMID:25517095

Evolutionary tabu search strategies for the simultaneous registration of multiple atomic structures in cryo-EM reconstructions.

PubMed

Rusu, Mirabela; Birmanns, Stefan

2010-04-01

A structural characterization of multi-component cellular assemblies is essential to explain the mechanisms governing biological function. Macromolecular architectures may be revealed by integrating information collected from various biophysical sources - for instance, by interpreting low-resolution electron cryomicroscopy reconstructions in relation to the crystal structures of the constituent fragments. A simultaneous registration of multiple components is beneficial when building atomic models as it introduces additional spatial constraints to facilitate the native placement inside the map. The high-dimensional nature of such a search problem prevents the exhaustive exploration of all possible solutions. Here we introduce a novel method based on genetic algorithms, for the efficient exploration of the multi-body registration search space. The classic scheme of a genetic algorithm was enhanced with new genetic operations, tabu search and parallel computing strategies and validated on a benchmark of synthetic and experimental cryo-EM datasets. Even at a low level of detail, for example 35-40 A, the technique successfully registered multiple component biomolecules, measuring accuracies within one order of magnitude of the nominal resolutions of the maps. The algorithm was implemented using the Sculptor molecular modeling framework, which also provides a user-friendly graphical interface and enables an instantaneous, visual exploration of intermediate solutions. (c) 2009 Elsevier Inc. All rights reserved.

Solving the Secondary Structure Matching Problem in Cryo-EM De Novo Modeling Using a Constrained K-Shortest Path Graph Algorithm.

PubMed

Al Nasr, Kamal; Ranjan, Desh; Zubair, Mohammad; Chen, Lin; He, Jing

2014-01-01

Electron cryomicroscopy is becoming a major experimental technique in solving the structures of large molecular assemblies. More and more three-dimensional images have been obtained at the medium resolutions between 5 and 10 Å. At this resolution range, major α-helices can be detected as cylindrical sticks and β-sheets can be detected as plain-like regions. A critical question in de novo modeling from cryo-EM images is to determine the match between the detected secondary structures from the image and those on the protein sequence. We formulate this matching problem into a constrained graph problem and present an O(Δ(2)N(2)2(N)) algorithm to this NP-Hard problem. The algorithm incorporates the dynamic programming approach into a constrained K-shortest path algorithm. Our method, DP-TOSS, has been tested using α-proteins with maximum 33 helices and α-β proteins up to five helices and 12 β-strands. The correct match was ranked within the top 35 for 19 of the 20 α-proteins and all nine α-β proteins tested. The results demonstrate that DP-TOSS improves accuracy, time and memory space in deriving the topologies of the secondary structure elements for proteins with a large number of secondary structures and a complex skeleton.

Structural characterization of ribosome recruitment and translocation by type IV IRES.

PubMed

Murray, Jason; Savva, Christos G; Shin, Byung-Sik; Dever, Thomas E; Ramakrishnan, V; Fernández, Israel S

2016-05-09

Viral mRNA sequences with a type IV IRES are able to initiate translation without any host initiation factors. Initial recruitment of the small ribosomal subunit as well as two translocation steps before the first peptidyl transfer are essential for the initiation of translation by these mRNAs. Using electron cryomicroscopy (cryo-EM) we have structurally characterized at high resolution how the Cricket Paralysis Virus Internal Ribosomal Entry Site (CrPV-IRES) binds the small ribosomal subunit (40S) and the translocation intermediate stabilized by elongation factor 2 (eEF2). The CrPV-IRES restricts tvhe otherwise flexible 40S head to a conformation compatible with binding the large ribosomal subunit (60S). Once the 60S is recruited, the binary CrPV-IRES/80S complex oscillates between canonical and rotated states (Fernández et al., 2014; Koh et al., 2014), as seen for pre-translocation complexes with tRNAs. Elongation factor eEF2 with a GTP analog stabilizes the ribosome-IRES complex in a rotated state with an extra ~3 degrees of rotation. Key residues in domain IV of eEF2 interact with pseudoknot I (PKI) of the CrPV-IRES stabilizing it in a conformation reminiscent of a hybrid tRNA state. The structure explains how diphthamide, a eukaryotic and archaeal specific post-translational modification of a histidine residue of eEF2, is involved in translocation.

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.

Dynamic and Geometric Analyses of Nudaurelia capensis ωVirus Maturation Reveal the Energy Landscape of Particle Transitions

PubMed Central

Tang, Jinghua; Kearney, Bradley M.; Wang, Qiu; Doerschuk, Peter C.; Baker, Timothy S.; Johnson, John E.

2014-01-01

Quasi-equivalent viruses that infect animals and bacteria require a maturation process in which particles transition from initially assembled procapsids to infectious virions. Nudaurelia capensis ω virus (NωV) is a T=4, eukaryotic, ssRNA virus that has proved to be an excellent model system for studying the mechanisms of viral maturation. Structures of NωV procapsids (diam. = 480 Å), a maturation intermediate (410 Å), and the mature virion (410 Å) were determined by electron cryo-microscopy and three-dimensional image reconstruction (cryoEM). The cryoEM density for each particle type was analyzed with a recently developed Maximum Likelihood Variance (MLV) method for characterizing microstates occupied in the ensemble of particles used for the reconstructions. The procapsid and the mature capsid had overall low variance (i.e. uniform particle populations) while the maturation intermediate (that had not undergone post-assembly autocatalytic cleavage) had roughly 2-4 times the variance of the first two particles. Without maturation cleavage the particles assume a variety of microstates, as the frustrated subunits cannot reach a minimum energy configuration. Geometric analyses of subunit coordinates provided a quantitative description of the particle reorganization during maturation. Superposition of the four quasi-equivalent subunits in the procapsid had an average root mean square deviation (RMSD) of 3Å while the mature particle had an RMSD of 11Å, showing that the subunits differentiate from near equivalent environments in the procapsid to strikingly non-equivalent environments during maturation. Autocatalytic cleavage is clearly required for the reorganized mature particle to reach the minimum energy state required for stability and infectivity. PMID:24591180

Dynamic and geometric analyses of Nudaurelia capensis ω virus maturation reveal the energy landscape of particle transitions.

PubMed

Tang, Jinghua; Kearney, Bradley M; Wang, Qiu; Doerschuk, Peter C; Baker, Timothy S; Johnson, John E

2014-04-01

Quasi-equivalent viruses that infect animals and bacteria require a maturation process in which particles transition from initially assembled procapsids to infectious virions. Nudaurelia capensis ω virus (NωV) is a T = 4, eukaryotic, single-stranded ribonucleic acid virus that has proved to be an excellent model system for studying the mechanisms of viral maturation. Structures of NωV procapsids (diameter = 480 Å), a maturation intermediate (410 Å), and the mature virion (410 Å) were determined by electron cryo-microscopy and three-dimensional image reconstruction (cryoEM). The cryoEM density for each particle type was analyzed with a recently developed maximum likelihood variance (MLV) method for characterizing microstates occupied in the ensemble of particles used for the reconstructions. The procapsid and the mature capsid had overall low variance (i.e., uniform particle populations) while the maturation intermediate (that had not undergone post-assembly autocatalytic cleavage) had roughly two to four times the variance of the first two particles. Without maturation cleavage, the particles assume a variety of microstates, as the frustrated subunits cannot reach a minimum energy configuration. Geometric analyses of subunit coordinates provided a quantitative description of the particle reorganization during maturation. Superposition of the four quasi-equivalent subunits in the procapsid had an average root mean square deviation (RMSD) of 3 Å while the mature particle had an RMSD of 11 Å, showing that the subunits differentiate from near equivalent environments in the procapsid to strikingly non-equivalent environments during maturation. Autocatalytic cleavage is clearly required for the reorganized mature particle to reach the minimum energy state required for stability and infectivity. Copyright © 2014 John Wiley & Sons, Ltd.

Atomic model for the membrane-embedded VO motor of a eukaryotic V-ATPase.

PubMed

Mazhab-Jafari, Mohammad T; Rohou, Alexis; Schmidt, Carla; Bueler, Stephanie A; Benlekbir, Samir; Robinson, Carol V; Rubinstein, John L

2016-11-03

Vacuolar-type ATPases (V-ATPases) are ATP-powered proton pumps involved in processes such as endocytosis, lysosomal degradation, secondary transport, TOR signalling, and osteoclast and kidney function. ATP hydrolysis in the soluble catalytic V 1 region drives proton translocation through the membrane-embedded V O region via rotation of a rotor subcomplex. Variability in the structure of the intact enzyme has prevented construction of an atomic model for the membrane-embedded motor of any rotary ATPase. We induced dissociation and auto-inhibition of the V 1 and V O regions of the V-ATPase by starving the yeast Saccharomyces cerevisiae, allowing us to obtain a ~3.9-Å resolution electron cryomicroscopy map of the V O complex and build atomic models for the majority of its subunits. The analysis reveals the structures of subunits ac 8 c'c″de and a protein that we identify and propose to be a new subunit (subunit f). A large cavity between subunit a and the c-ring creates a cytoplasmic half-channel for protons. The c-ring has an asymmetric distribution of proton-carrying Glu residues, with the Glu residue of subunit c″ interacting with Arg735 of subunit a. The structure suggests sequential protonation and deprotonation of the c-ring, with ATP-hydrolysis-driven rotation causing protonation of a Glu residue at the cytoplasmic half-channel and subsequent deprotonation of a Glu residue at a luminal half-channel.

Structural characterization of ribosome recruitment and translocation by type IV IRES

PubMed Central

Murray, Jason; Savva, Christos G; Shin, Byung-Sik; Dever, Thomas E; Ramakrishnan, V; Fernández, Israel S

2016-01-01

Viral mRNA sequences with a type IV IRES are able to initiate translation without any host initiation factors. Initial recruitment of the small ribosomal subunit as well as two translocation steps before the first peptidyl transfer are essential for the initiation of translation by these mRNAs. Using electron cryomicroscopy (cryo-EM) we have structurally characterized at high resolution how the Cricket Paralysis Virus Internal Ribosomal Entry Site (CrPV-IRES) binds the small ribosomal subunit (40S) and the translocation intermediate stabilized by elongation factor 2 (eEF2). The CrPV-IRES restricts the otherwise flexible 40S head to a conformation compatible with binding the large ribosomal subunit (60S). Once the 60S is recruited, the binary CrPV-IRES/80S complex oscillates between canonical and rotated states (Fernández et al., 2014; Koh et al., 2014), as seen for pre-translocation complexes with tRNAs. Elongation factor eEF2 with a GTP analog stabilizes the ribosome-IRES complex in a rotated state with an extra ~3 degrees of rotation. Key residues in domain IV of eEF2 interact with pseudoknot I (PKI) of the CrPV-IRES stabilizing it in a conformation reminiscent of a hybrid tRNA state. The structure explains how diphthamide, a eukaryotic and archaeal specific post-translational modification of a histidine residue of eEF2, is involved in translocation. DOI: http://dx.doi.org/10.7554/eLife.13567.001 PMID:27159451

Devitrification and recrystallization of nanoparticle-containing glycerol and PEG-600 solutions.

PubMed

Lv, Fukou; Liu, Baolin; Li, Weijie; Jaganathan, Ganesh K

2014-02-01

Nanoparticles in solution offer unique electrical, mechanical and thermal properties due to their physical presence and interaction with the state of dispersion. This work is aimed to study the effects of hydroxyapatite (HA) nanoparticles on the devitrification and recrystallization events of two important cryoprotective solutions used in cell and tissue preservation namely glycerol (60%w/w) and PEG-600 (50%w/w). HA nanoparticles (20, 40 or 60 nm) were incorporated into solutions at the content of 0.1% or 0.5%(w/w), and were studied by differential scanning calorimeter (DSC) and cryomicroscopy. The presence of nanoparticles does not change the glass transition temperatures and melting temperatures of quenched solutions, but significantly affects the behavior of devitrification and recrystallization upon warming. Cryomicroscopic investigation showed the complex interactions among solution type, nanoparticle size and nanoparticle content, which apparently influence ice crystal growth or recrystallization in the quenched dispersions. These findings have significant implications for biomaterial cryopreservation, cryosurgery, and food manufacturing. The complexity of ice crystal growth kinetics in nanoparticle-containing dispersions remains to be poorly understood at the moment. Copyright © 2013 Elsevier Inc. All rights reserved.

Cryo-EM Structure of the Mechanotransduction Channel NOMPC

PubMed Central

Jin, Peng; Bulkley, David; Guo, Yanmeng; Zhang, Wei; Guo, Zhenhao; Huynh, Walter; Wu, Shenping; Meltzer, Shan; Cheng, Tong; Jan, Lily Yeh; Jan, Yuh-Nung; Cheng, Yifan

2017-01-01

Mechanosensory transduction for senses such as proprioception, touch, balance, acceleration, hearing and pain relies on mechanotransduction channels, which convert mechanical stimuli into electrical signals in specialized sensory cells1. How force gates mechanotransduction channels is a central question in the field, for which there are two major models. One is the membrane-tension model: force applied to the membrane generates a change in membrane tension that is sufficient to gate the channel, as in the case of bacterial MscL channel and certain eukaryotic potassium channels2-5. The other is the tether model: force is transmitted via a tether to gate the channel. Recent study suggests that NOMPC, a mechanotransduction channel that mediates hearing and touch sensation in Drosophila, is gated by tethering of its ankyrin repeat (AR) domain to microtubules of the cytoskeleton6. Thus, a goal of studying NOMPC is to reveal the underlying mechanism of force induced gating, which could serve as a paradigm of the tether model. NOMPC, a Transient Receptor Potential (TRP) channel and the founding member of the TRPN sub-family7, fulfills all the criteria for a bona fide mechanotransduction channel1,8, and is important for a variety of mechanosensation-related behaviors such as locomotion, touch and sound sensation across different species including C. elegans9, Drosophila8,10-11 and zebrafish12. NOMPC has 29 ARs, the largest number among TRP channels. They are implicated as tether to convey force from cytoskeleton to the channel, thus to mediate mechanosensation6,13-15. A key question is how the long AR domain is organized as a tether that can trigger channel gating. Here we present a de novo atomic structure of NOMPC determined by single particle electron cryo-microscopy (cryo-EM), and discuss how its architecture could provide a means to convey mechanical force to generating an electrical signal within a cell. PMID:28658211

Impact of Buffer, Protein Concentration and Sucrose Addition on the Aggregation and Particle Formation during Freezing and Thawing.

PubMed

Hauptmann, Astrid; Podgoršek, Katja; Kuzman, Drago; Srčič, Stanko; Hoelzl, Georg; Loerting, Thomas

2018-03-19

This study addresses the effect of freezing and thawing on a therapeutic monoclonal antibody (mAb) solution and the corresponding buffer formulation. Particle formation, crystallization behaviour, morphology changes and cryo-concentration effects were studied after varying the freezing and thawing rates, buffer formulation and protein concentration. The impact of undergoing multiple freeze/thaw (FT)-cycles at controlled and uncontrolled temperature rates on mAb solutions was investigated in terms of particle formation. Physicochemical characteristics were analysed by Differential Scanning Calorimetry whereas morphology changes are visualized by cryomicroscopy measurements. Micro Flow Imaging, Archimedes and Dynamic Light Scattering were used to investigate particle formation. Data retrieved in the present study emphasizes the damage caused by multiple FT-cyles and the need for sucrose as a cryoprotectant preventing cold-crystallization specifically at high protein concentrations. Low protein concentrations cause an increase of micron particle formation. Low freezing rates lead to a decreased particle number with increased particle diameter. The overall goal of this research is to gain a better understanding of the freezing and thawing behaviour of mAb solutions with the ultimate aim to optimize this process step by reducing the unwanted particle formation, which also includes protein aggregates.

Optimal noise reduction in 3D reconstructions of single particles using a volume-normalized filter

PubMed Central

Sindelar, Charles V.; Grigorieff, Nikolaus

2012-01-01

The high noise level found in single-particle electron cryo-microscopy (cryo-EM) image data presents a special challenge for three-dimensional (3D) reconstruction of the imaged molecules. The spectral signal-to-noise ratio (SSNR) and related Fourier shell correlation (FSC) functions are commonly used to assess and mitigate the noise-generated error in the reconstruction. Calculation of the SSNR and FSC usually includes the noise in the solvent region surrounding the particle and therefore does not accurately reflect the signal in the particle density itself. Here we show that the SSNR in a reconstructed 3D particle map is linearly proportional to the fractional volume occupied by the particle. Using this relationship, we devise a novel filter (the “single-particle Wiener filter”) to minimize the error in a reconstructed particle map, if the particle volume is known. Moreover, we show how to approximate this filter even when the volume of the particle is not known, by optimizing the signal within a representative interior region of the particle. We show that the new filter improves on previously proposed error-reduction schemes, including the conventional Wiener filter as well as figure-of-merit weighting, and quantify the relationship between all of these methods by theoretical analysis as well as numeric evaluation of both simulated and experimentally collected data. The single-particle Wiener filter is applicable across a broad range of existing 3D reconstruction techniques, but is particularly well suited to the Fourier inversion method, leading to an efficient and accurate implementation. PMID:22613568

The structures of cytosolic and plastid-located glutamine synthetases from Medicago truncatula reveal a common and dynamic architecture

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

Torreira, Eva; Seabra, Ana Rita; Marriott, Hazel

The experimental models of dicotyledonous cytoplasmic and plastid-located glutamine synthetases unveil a conserved eukaryotic-type decameric architecture, with subtle structural differences in M. truncatula isoenzymes that account for their distinct herbicide resistance. The first step of nitrogen assimilation in higher plants, the energy-driven incorporation of ammonia into glutamate, is catalyzed by glutamine synthetase. This central process yields the readily metabolizable glutamine, which in turn is at the basis of all subsequent biosynthesis of nitrogenous compounds. The essential role performed by glutamine synthetase makes it a prime target for herbicidal compounds, but also a suitable intervention point for the improvement of cropmore » yields. Although the majority of crop plants are dicotyledonous, little is known about the structural organization of glutamine synthetase in these organisms and about the functional differences between the different isoforms. Here, the structural characterization of two glutamine synthetase isoforms from the model legume Medicago truncatula is reported: the crystallographic structure of cytoplasmic GSII-1a and an electron cryomicroscopy reconstruction of plastid-located GSII-2a. Together, these structural models unveil a decameric organization of dicotyledonous glutamine synthetase, with two pentameric rings weakly connected by inter-ring loops. Moreover, rearrangement of these dynamic loops changes the relative orientation of the rings, suggesting a zipper-like mechanism for their assembly into a decameric enzyme. Finally, the atomic structure of M. truncatula GSII-1a provides important insights into the structural determinants of herbicide resistance in this family of enzymes, opening new avenues for the development of herbicide-resistant plants.« less

Biological and physicochemical characterization of a serum- and xeno-free chemically defined cryopreservation procedure for adult human progenitor cells.

PubMed

Zeisberger, Steffen M; Schulz, Julia C; Mairhofer, Mario; Ponsaerts, Peter; Wouters, Guy; Doerr, Daniel; Katsen-Globa, Alisa; Ehrbar, Martin; Hescheler, Jurgen; Hoerstrup, Simon P; Zisch, Andreas H; Kolbus, Andrea; Zimmermann, Heiko

2011-01-01

While therapeutic cell transplantations using progenitor cells are increasingly evolving towards phase I and II clinical trials and chemically defined cell culture is established, standardization in biobanking is still in the stage of infancy. In this study, the EU FP6-funded CRYSTAL (CRYo-banking of Stem cells for human Therapeutic AppLication) consortium aimed to validate novel Standard Operating Procedures (SOPs) to perform and validate xeno-free and chemically defined cryopreservation of human progenitor cells and to reduce the amount of the potentially toxic cryoprotectant additive (CPA) dimethyl sulfoxide (DMSO). To achieve this goal, three human adult progenitor and stem cell populations-umbilical cord blood (UCB)-derived erythroid cells (UCB-ECs), UCB-derived endothelial colony forming cells (UCB-ECFCs), and adipose tissue (AT)-derived mesenchymal stromal cells (AT-MSCs)-were cryopreserved in chemically defined medium supplemented with 10% or 5% DMSO. Cell recovery, cell repopulation, and functionality were evaluated postthaw in comparison to cryopreservation in standard fetal bovine serum (FBS)-containing freezing medium. Even with a reduction of the DMSO CPA to 5%, postthaw cell count and viability assays indicated no overall significant difference versus standard cryomedium. Additionally, to compare cellular morphology/membrane integrity and ice crystal formation during cryopreservation, multiphoton laser-scanning cryomicroscopy (cryo-MPLSM) and scanning electron microscopy (SEM) were used. Neither cryo-MPLSM nor SEM indicated differences in membrane integrity for the tested cell populations under various conditions. Moreover, no influence was observed on functional properties of the cells following cryopreservation in chemically defined freezing medium, except for UCB-ECs, which showed a significantly reduced differentiation capacity after cryopreservation in chemically defined medium supplemented with 5% DMSO. In summary, these results demonstrate the feasibility and robustness of standardized xeno-free cryopreservation of different human progenitor cells and encourage their use even more in the field of tissue-engineering and regenerative medicine.

Spontaneous formation of nanometer scale tubular vesicles in aqueous mixtures of lipid and block copolymer amphiphiles.

PubMed

Lim, Seng Koon; Wong, Andrew S W; de Hoog, Hans-Peter M; Rangamani, Padmini; Parikh, Atul N; Nallani, Madhavan; Sandin, Sara; Liedberg, Bo

2017-02-08

Many common amphiphiles self-assemble in water to produce heterogeneous populations of discrete and symmetric but polydisperse and multilamellar vesicles isolating the encapsulated aqueous core from the surrounding bulk. But when mixtures of amphiphiles of vastly different elastic properties co-assemble, their non-uniform molecular organization can stabilize lower symmetries and produce novel shapes. Here, using high resolution electron cryomicroscopy and tomography, we identify the spontaneous formation of a membrane morphology consisting of unilamellar tubular vesicles in dilute aqueous solutions of binary mixtures of two different amphiphiles of vastly different origins. Our results show that aqueous phase mixtures of a fluid-phase phospholipid and an amphiphilic block copolymer spontaneously assume a bimodal polymorphic character in a composition dependent manner: over a broad range of compositions (15-85 mol% polymer component), a tubular morphology co-exists with spherical vesicles. Strikingly, in the vicinity of equimolar compositions, an exclusively tubular morphology (L t ; diameter, ∼15 nm; length, >1 μm; core, ∼2.0 nm; wall, ∼5-6 nm) emerges in an apparent steady state. Theory suggests that the spontaneous stabilization of cylindrical vesicles, unaided by extraneous forces, requires a significant spontaneous bilayer curvature, which in turn necessitates a strongly asymmetric membrane composition. We confirm that such dramatic compositional asymmetry is indeed produced spontaneously in aqueous mixtures of a lipid and polymer through two independent biochemical assays - (1) reduction in the quenching of fluorophore-labeled lipids and (2) inhibition in the activity of externally added lipid-hydrolyzing phospholipase A2, resulting in a significant enrichment of the polymer component in the outer leaflet. Taken together, these results illustrate the coupling of the membrane shape with local composition through spontaneous curvature generation under conditions of asymmetric distribution of mixtures of disparate amphiphiles.

C Terminus of Infectious Bursal Disease Virus Major Capsid Protein VP2 Is Involved in Definition of the T Number for Capsid Assembly

PubMed Central

Castón, José R.; Martínez-Torrecuadrada, Jorge L.; Maraver, Antonio; Lombardo, Eleuterio; Rodríguez, José F.; Casal, J. Ignacio; Carrascosa, José L.

2001-01-01

Infectious bursal disease virus (IBDV), a member of the Birnaviridae family, is a double-stranded RNA virus. The IBDV capsid is formed by two major structural proteins, VP2 and VP3, which assemble to form a T=13 markedly nonspherical capsid. During viral infection, VP2 is initially synthesized as a precursor, called VPX, whose C end is proteolytically processed to the mature form during capsid assembly. We have computed three-dimensional maps of IBDV capsid and virus-like particles built up by VP2 alone by using electron cryomicroscopy and image-processing techniques. The IBDV single-shelled capsid is characterized by the presence of 260 protruding trimers on the outer surface. Five classes of trimers can be distinguished according to their different local environments. When VP2 is expressed alone in insect cells, dodecahedral particles form spontaneously; these may be assembled into larger, fragile icosahedral capsids built up by 12 dodecahedral capsids. Each dodecahedral capsid is an empty T=1 shell composed of 20 trimeric clusters of VP2. Structural comparison between IBDV capsids and capsids consisting of VP2 alone allowed the determination of the major capsid protein locations and the interactions between them. Whereas VP2 forms the outer protruding trimers, VP3 is found as trimers on the inner surface and may be responsible for stabilizing functions. Since elimination of the C-terminal region of VPX is correlated with the assembly of T=1 capsids, this domain might be involved (either alone or in cooperation with VP3) in the induction of different conformations of VP2 during capsid morphogenesis. PMID:11602723

Combined approaches to flexible fitting and assessment in virus capsids undergoing conformational change☆

PubMed Central

Pandurangan, Arun Prasad; Shakeel, Shabih; Butcher, Sarah Jane; Topf, Maya

2014-01-01

Fitting of atomic components into electron cryo-microscopy (cryoEM) density maps is routinely used to understand the structure and function of macromolecular machines. Many fitting methods have been developed, but a standard protocol for successful fitting and assessment of fitted models has yet to be agreed upon among the experts in the field. Here, we created and tested a protocol that highlights important issues related to homology modelling, density map segmentation, rigid and flexible fitting, as well as the assessment of fits. As part of it, we use two different flexible fitting methods (Flex-EM and iMODfit) and demonstrate how combining the analysis of multiple fits and model assessment could result in an improved model. The protocol is applied to the case of the mature and empty capsids of Coxsackievirus A7 (CAV7) by flexibly fitting homology models into the corresponding cryoEM density maps at 8.2 and 6.1 Å resolution. As a result, and due to the improved homology models (derived from recently solved crystal structures of a close homolog – EV71 capsid – in mature and empty forms), the final models present an improvement over previously published models. In close agreement with the capsid expansion observed in the EV71 structures, the new CAV7 models reveal that the expansion is accompanied by ∼5° counterclockwise rotation of the asymmetric unit, predominantly contributed by the capsid protein VP1. The protocol could be applied not only to viral capsids but also to many other complexes characterised by a combination of atomic structure modelling and cryoEM density fitting. PMID:24333899

Structure of a human cap-dependent 48S translation pre-initiation complex

PubMed Central

Eliseev, Boris; Yeramala, Lahari; Leitner, Alexander; Karuppasamy, Manikandan; Raimondeau, Etienne; Huard, Karine; Alkalaeva, Elena; Aebersold, Ruedi

2018-01-01

Abstract Eukaryotic translation initiation is tightly regulated, requiring a set of conserved initiation factors (eIFs). Translation of a capped mRNA depends on the trimeric eIF4F complex and eIF4B to load the mRNA onto the 43S pre-initiation complex comprising 40S and initiation factors 1, 1A, 2, 3 and 5 as well as initiator-tRNA. Binding of the mRNA is followed by mRNA scanning in the 48S pre-initiation complex, until a start codon is recognised. Here, we use a reconstituted system to prepare human 48S complexes assembled on capped mRNA in the presence of eIF4B and eIF4F. The highly purified h-48S complexes are used for cross-linking/mass spectrometry, revealing the protein interaction network in this complex. We report the electron cryo-microscopy structure of the h-48S complex at 6.3 Å resolution. While the majority of eIF4B and eIF4F appear to be flexible with respect to the ribosome, additional density is detected at the entrance of the 40S mRNA channel which we attribute to the RNA-recognition motif of eIF4B. The eight core subunits of eIF3 are bound at the 40S solvent-exposed side, as well as the subunits eIF3d, eIF3b and eIF3i. elF2 and initiator-tRNA bound to the start codon are present at the 40S intersubunit side. This cryo-EM structure represents a molecular snap-shot revealing the h-48S complex following start codon recognition. PMID:29401259

Molecular basis for the binding and modulation of V-ATPase by a bacterial effector protein

PubMed Central

Alvarez, Claudia P.; Bueler, Stephanie A.; Xu, Caishuang; Boniecki, Michal T.; Kanelis, Voula; Rubinstein, John L.

2017-01-01

Intracellular pathogenic bacteria evade the immune response by replicating within host cells. Legionella pneumophila, the causative agent of Legionnaires’ Disease, makes use of numerous effector proteins to construct a niche supportive of its replication within phagocytic cells. The L. pneumophila effector SidK was identified in a screen for proteins that reduce the activity of the proton pumping vacuolar-type ATPases (V-ATPases) when expressed in the yeast Saccharomyces cerevisae. SidK is secreted by L. pneumophila in the early stages of infection and by binding to and inhibiting the V-ATPase, SidK reduces phagosomal acidification and promotes survival of the bacterium inside macrophages. We determined crystal structures of the N-terminal region of SidK at 2.3 Å resolution and used single particle electron cryomicroscopy (cryo-EM) to determine structures of V-ATPase:SidK complexes at ~6.8 Å resolution. SidK is a flexible and elongated protein composed of an α-helical region that interacts with subunit A of the V-ATPase and a second region of unknown function that is flexibly-tethered to the first. SidK binds V-ATPase strongly by interacting via two α-helical bundles at its N terminus with subunit A. In vitro activity assays show that SidK does not inhibit the V-ATPase completely, but reduces its activity by ~40%, consistent with the partial V-ATPase deficiency phenotype its expression causes in yeast. The cryo-EM analysis shows that SidK reduces the flexibility of the A-subunit that is in the ‘open’ conformation. Fluorescence experiments indicate that SidK binding decreases the affinity of V-ATPase for a fluorescent analogue of ATP. Together, these results reveal the structural basis for the fine-tuning of V-ATPase activity by SidK. PMID:28570695

Rotavirus architecture at subnanometer resolution.

PubMed

Li, Zongli; Baker, Matthew L; Jiang, Wen; Estes, Mary K; Prasad, B V Venkataram

2009-02-01

Rotavirus, a nonturreted member of the Reoviridae, is the causative agent of severe infantile diarrhea. The double-stranded RNA genome encodes six structural proteins that make up the triple-layer particle. X-ray crystallography has elucidated the structure of one of these capsid proteins, VP6, and two domains from VP4, the spike protein. Complementing this work, electron cryomicroscopy (cryoEM) has provided relatively low-resolution structures for the triple-layer capsid in several biochemical states. However, a complete, high-resolution structural model of rotavirus remains unresolved. Combining new structural analysis techniques with the subnanometer-resolution cryoEM structure of rotavirus, we now provide a more detailed structural model for the major capsid proteins and their interactions within the triple-layer particle. Through a series of intersubunit interactions, the spike protein (VP4) adopts a dimeric appearance above the capsid surface, while forming a trimeric base anchored inside one of the three types of aqueous channels between VP7 and VP6 capsid layers. While the trimeric base suggests the presence of three VP4 molecules in one spike, only hints of the third molecule are observed above the capsid surface. Beyond their interactions with VP4, the interactions between VP6 and VP7 subunits could also be readily identified. In the innermost T=1 layer composed of VP2, visualization of the secondary structure elements allowed us to identify the polypeptide fold for VP2 and examine the complex network of interactions between this layer and the T=13 VP6 layer. This integrated structural approach has resulted in a relatively high-resolution structural model for the complete, infectious structure of rotavirus, as well as revealing the subtle nuances required for maintaining interactions in such a large macromolecular assembly.

Root xylem embolisms and refilling. Relation To water potentials of soil, roots, and leaves, and osmotic potentials of root xylem Sap

PubMed

McCully

1999-03-01

Embolism and refilling of vessels was monitored directly by cryomicroscopy of field-grown corn (Zea mays L.) roots. To test the reliability of an earlier study showing embolism refilling in roots at negative leaf water potentials, embolisms were counted, and root water potentials (Psiroot) and osmotic potentials of exuded xylem sap from the same roots were measured by isopiestic psychrometry. All vessels were full at dawn (Psiroot -0.1 MPa). Embolisms were first seen in late metaxylem vessels at 8 AM. Embolized late metaxylem vessels peaked at 50% at 10 AM (Psiroot -0.1 MPa), fell to 44% by 12 PM (Psiroot -0.23 MPa), then dropped steadily to zero by early evening (Psiroot -0.28 MPa). Transpiration was highest (8.5 μg cm-2 s-1) between 12 and 2 PM when the percentage of vessels embolized was falling. Embolized vessels were refilled by liquid moving through their lateral walls. Xylem sap was very low in solutes. The mechanism of vessel refilling, when Psiroot is negative, requires further investigation. Daily embolism and refilling in roots of well-watered plants is a normal occurrence and may be a component of an important hydraulic signaling mechanism between roots and shoots.

Structure of FcRY, an avian immunoglobulin receptor related to mammalian mannose receptors, and its complex with IgY

PubMed Central

He, Yongning; Bjorkman, Pamela J.

2011-01-01

Fc receptors transport maternal antibodies across epithelial cell barriers to passively immunize newborns. FcRY, the functional counterpart of mammalian FcRn (a major histocompatibility complex homolog), transfers IgY across the avian yolk sac, and represents a new class of Fc receptor related to the mammalian mannose receptor family. FcRY and FcRn bind immunoglobulins at pH ≤6.5, but not pH ≥7, allowing receptor–ligand association inside intracellular vesicles and release at the pH of blood. We obtained structures of monomeric and dimeric FcRY and an FcRY–IgY complex and explored FcRY's pH-dependent binding mechanism using electron cryomicroscopy (cryoEM) and small-angle X-ray scattering. The cryoEM structure of FcRY at pH 6 revealed a compact double-ring “head,” in which the N-terminal cysteine-rich and fibronectin II domains were folded back to contact C-type lectin-like domains 1–6, and a “tail” comprising C-type lectin-like domains 7–8. Conformational changes at pH 8 created a more elongated structure that cannot bind IgY. CryoEM reconstruction of FcRY dimers at pH 6 and small-angle X-ray scattering analysis at both pH values confirmed both structures. The cryoEM structure of the FcRY–IgY revealed symmetric binding of two FcRY heads to the dimeric FcY, each head contacting the CH4 domain of one FcY chain. FcRY shares structural properties with mannose receptor family members, including a head and tail domain organization, multimerization that may regulate ligand binding, and pH-dependent conformational changes. Our results facilitate understanding of immune recognition by the structurally related mannose receptor family and comparison of diverse methods of Ig transport across evolution. PMID:21746914

Structure of the F–actin–tropomyosin complex

PubMed Central

von der Ecken, Julian; Müller, Mirco; Lehman, William; Manstein, Dietmar J.; Penczek, Pawel A.; Raunser, Stefan

2015-01-01

Filamentous actin (F-actin) is the major protein of muscle thin filaments, and actin microfilaments are the main component of the eukaryotic cytoskeleton. Mutations in different actin isoforms lead to early-onset autosomal dominant non-syndromic hearing loss1, familial thoracic aortic aneurysms and dissections2, and multiple variations of myopathies3. In striated muscle fibres, the binding of myosin motors to actin filaments is mainly regulated by tropomyosin and troponin4,5. Tropomyosin also binds to F-actin in smooth muscle and in non-muscle cells and stabilizes and regulates the filaments there in the absence of troponin6. Although crystal structures for monomeric actin (G-actin) are available7, a high-resolution structure of F-actin is still missing, hampering our understanding of how disease-causing mutations affect the function of thin muscle filaments and microfilaments. Here we report the three-dimensional structure of F-actin at a resolution of 3.7 ångstroms in complex with tropomyosin at a resolution of 6.5ångstroms, determined by electron cryomicroscopy. The structure reveals that the D-loop is ordered and acts as a central region for hydrophobic and electrostatic interactions that stabilize the F-actin filament. We clearly identify the density corresponding to ADP and Mg2+ and explain the possible effect of prominent disease-causing mutants. A comparison of F-actin with G-actin reveals the conformational changes during filament formation and identifies the D-loop as their key mediator. We also confirm that negatively charged tropomyosin interacts with a positively charged groove on F-actin. Comparison of the position of tropomyosin in F-actin–tropomyosin with its position in our previously determined actin–tropomyosin–myosin structure8 reveals a myosin-induced transition of tropomyosin. Our results allow us to understand the role of individual mutations in the genesis of actin- and tropomyosin-related diseases and will serve as a strong foundation for the targeted development of drugs. PMID:25470062

Selectivity filters and cysteine-rich extracellular loops in voltage-gated sodium, calcium, and NALCN channels

PubMed Central

Stephens, Robert F.; Guan, W.; Zhorov, Boris S.; Spafford, J. David

2015-01-01

How nature discriminates sodium from calcium ions in eukaryotic channels has been difficult to resolve because they contain four homologous, but markedly different repeat domains. We glean clues from analyzing the changing pore region in sodium, calcium and NALCN channels, from single-cell eukaryotes to mammals. Alternative splicing in invertebrate homologs provides insights into different structural features underlying calcium and sodium selectivity. NALCN generates alternative ion selectivity with splicing that changes the high field strength (HFS) site at the narrowest level of the hourglass shaped pore where the selectivity filter is located. Alternative splicing creates NALCN isoforms, in which the HFS site has a ring of glutamates contributed by all four repeat domains (EEEE), or three glutamates and a lysine residue in the third (EEKE) or second (EKEE) position. Alternative splicing provides sodium and/or calcium selectivity in T-type channels with extracellular loops between S5 and P-helices (S5P) of different lengths that contain three or five cysteines. All eukaryotic channels have a set of eight core cysteines in extracellular regions, but the T-type channels have an infusion of 4–12 extra cysteines in extracellular regions. The pattern of conservation suggests a possible pairing of long loops in Domains I and III, which are bridged with core cysteines in NALCN, Cav, and Nav channels, and pairing of shorter loops in Domains II and IV in T-type channel through disulfide bonds involving T-type specific cysteines. Extracellular turrets of increasing lengths in potassium channels (Kir2.2, hERG, and K2P1) contribute to a changing landscape above the pore selectivity filter that can limit drug access and serve as an ion pre-filter before ions reach the pore selectivity filter below. Pairing of extended loops likely contributes to the large extracellular appendage as seen in single particle electron cryo-microscopy images of the eel Nav1 channel. PMID:26042044

Intercellular ice propagation: experimental evidence for ice growth through membrane pores.

PubMed Central

Acker, J P; Elliott, J A; McGann, L E

2001-01-01

Propagation of intracellular ice between cells significantly increases the prevalence of intracellular ice in confluent monolayers and tissues. It has been proposed that gap junctions facilitate ice propagation between cells. This study develops an equation for capillary freezing-point depression to determine the effect of temperature on the equilibrium radius of an ice crystal sufficiently small to grow through gap junctions. Convection cryomicroscopy and video image analysis were used to examine the incidence and pattern of intracellular ice formation (IIF) in the confluent monolayers of cell lines that do (MDCK) and do not (V-79W) form gap junctions. The effect of gap junctions on intracellular ice propagation was strongly temperature-dependent. For cells with gap junctions, IIF occurred in a directed wave-like pattern in 100% of the cells below -3 degrees C. At temperatures above -3 degrees C, there was a marked drop in the incidence of IIF, with isolated individual cells initially freezing randomly throughout the sample. This random pattern of IIF was also observed in the V-79W monolayers and in MDCK monolayers treated to prevent gap junction formation. The significant change in the low temperature behavior of confluent MDCK monolayers at -3 degrees C is likely the result of the inhibition of gap junction-facilitated ice propagation, and supports the theory that gap junctions facilitate ice nucleation between cells. PMID:11509353

Structural, Mechanistic, and Antigenic Characterization of the Human Astrovirus Capsid

PubMed Central

York, Royce L.; Yousefi, Payam A.; Bogdanoff, Walter; Haile, Sara; Tripathi, Sarvind

2015-01-01

ABSTRACT Human astroviruses (HAstVs) are nonenveloped, positive-sense, single-stranded RNA viruses that are a leading cause of viral gastroenteritis. HAstV particles display T=3 icosahedral symmetry formed by 180 copies of the capsid protein (CP), which undergoes proteolytic maturation to generate infectious HAstV particles. Little is known about the molecular features that govern HAstV particle assembly, maturation, infectivity, and immunogenicity. Here we report the crystal structures of the two main structural domains of the HAstV CP: the core domain at 2.60-Å resolution and the spike domain at 0.95-Å resolution. Fitting of these structures into the previously determined 25-Å-resolution electron cryomicroscopy density maps of HAstV allowed us to characterize the molecular features on the surfaces of immature and mature T=3 HAstV particles. The highly electropositive inner surface of HAstV supports a model in which interaction of the HAstV CP core with viral RNA is a driving force in T=3 HAstV particle formation. Additionally, mapping of conserved residues onto the HAstV CP core and spike domains in the context of the immature and mature HAstV particles revealed dramatic changes to the exposure of conserved residues during virus maturation. Indeed, we show that antibodies raised against mature HAstV have reactivity to both the HAstV CP core and spike domains, revealing for the first time that the CP core domain is antigenic. Together, these data provide new molecular insights into HAstV that have practical applications for the development of vaccines and antiviral therapies. IMPORTANCE Astroviruses are a leading cause of viral diarrhea in young children, immunocompromised individuals, and the elderly. Despite the prevalence of astroviruses, little is known at the molecular level about how the astrovirus particle assembles and is converted into an infectious, mature virus. In this paper, we describe the high-resolution structures of the two main astrovirus capsid proteins. Fitting these structures into previously determined low-resolution maps of astrovirus allowed us to characterize the molecular surfaces of immature and mature astroviruses. Our studies provide the first evidence that astroviruses undergo viral RNA-dependent assembly. We also provide new insight into the molecular mechanisms that lead to astrovirus maturation and infectivity. Finally, we show that both capsid proteins contribute to the adaptive immune response against astrovirus. Together, these studies will help to guide the development of vaccines and antiviral drugs targeting astrovirus. PMID:26656707

Ice nucleating agents allow embryo freezing without manual seeding.

PubMed

Teixeira, Magda; Buff, Samuel; Desnos, Hugo; Loiseau, Céline; Bruyère, Pierre; Joly, Thierry; Commin, Loris

2017-12-01

Embryo slow freezing protocols include a nucleation induction step called manual seeding. This step is time consuming, manipulator dependent and hard to standardize. It requires access to samples, which is not always possible within the configuration of systems, such as differential scanning calorimeters or cryomicroscopes. Ice nucleation can be induced by other methods, e.g., by the use of ice nucleating agents. Snomax is a commercial preparation of inactivated proteins extracted from Pseudomonas syringae. The aim of our study was to investigate if Snomax can be an alternative to manual seeding in the slow freezing of mouse embryos. The influence of Snomax on the pH and osmolality of the freezing medium was evaluated. In vitro development (blastocyst formation and hatching rates) of fresh embryos exposed to Snomax and embryo cryopreserved with and without Snomax was assessed. The mitochondrial activity of frozen-thawed blastocysts was assessed by JC-1 fluorescent staining. Snomax didn't alter the physicochemical properties of the freezing medium, and did not affect embryo development of fresh embryos. After cryopreservation, the substitution of manual seeding by the ice nucleating agent (INA) Snomax did not affect embryo development or embryo mitochondrial activity. In conclusion, Snomax seems to be an effective ice nucleating agent for the slow freezing of mouse embryos. Snomax can also be a valuable alternative to manual seeding in research protocols in which manual seeding cannot be performed (i.e., differential scanning calorimetry and cryomicroscopy). Copyright © 2017 Elsevier Inc. All rights reserved.

Chromophore orientation in bacteriorhodopsin determined from the angular dependence of deuterium nuclear magnetic resonance spectra of oriented purple membranes.

PubMed

Moltke, S; Nevzorov, A A; Sakai, N; Wallat, I; Job, C; Nakanishi, K; Heyn, M P; Brown, M F

1998-08-25

The orientation of prosthetic groups in membrane proteins is of considerable importance in understanding their functional role in energy conversion, signal transduction, and ion transport. In this work, the orientation of the retinylidene chromophore of bacteriorhodopsin (bR) was investigated using 2H NMR spectroscopy. Bacteriorhodopsin was regenerated with all-trans-retinal stereospecifically deuterated in one of the geminal methyl groups on C1 of the cyclohexene ring. A highly oriented sample, which is needed to obtain individual bond orientations from 2H NMR, was prepared by forming hydrated lamellar films of purple membranes on glass slides. A Monte Carlo method was developed to accurately simulate the 2H NMR line shape due to the distribution of bond angles and the orientational disorder of the membranes. The number of free parameters in the line shape simulation was reduced by independent measurements of the intrinsic line width (1.6 kHz from T2e experiments) and the effective quadrupolar coupling constant (38. 8-39.8 kHz from analysis of the line shape of a powder-type sample). The angle between the C1-(1R)-1-CD3 bond and the purple membrane normal was determined with high accuracy from the simultaneous analysis of a series of 2H NMR spectra recorded at different inclinations of the uniaxially oriented sample in the magnetic field at 20 and -50 degrees C. The value of 68.7 +/- 2.0 degrees in dark-adapted bR was used, together with the previously determined angle of the C5-CD3 bond, to calculate the possible orientations of the cyclohexene ring in the membrane. The solutions obtained from 2H NMR were then combined with additional constraints from linear dichroism and electron cryomicroscopy to obtain the allowed orientations of retinal in the noncentrosymmetric membrane structure. The combined data indicate that the methyl groups on the polyene chain point toward the cytoplasmic side of the membrane and the N-H bond of the Schiff base to the extracellular side, i.e., toward the side of proton release in the pump pathway.

High post-thaw survival of ram sperm after partial freeze-drying.

PubMed

Arav, Amir; Idda, Antonella; Nieddu, Stefano Mario; Natan, Yehudit; Ledda, Sergio

2018-03-14

Recrystallization damages occur when a frozen sample is held at high subzero temperatures and when the warming process is too slow. In this work, ram semen diluted in two different concentrations of sugar solutions (Lyo A consisted of 0.4 M sorbitol and 0.25 M trehalose, and the second, Lyo B composed of 0.26 M sorbitol and 0.165 M trehalose) in egg yolk and Tris medium were compared after freezing 10 μL samples to: (1) - 10, - 25, and - 35 °C and thawing. (2) Freezing to - 10 and - 25 °C, holding for 1 h and then thawing, and (3) freezing to - 10 and - 25 °C and drying for 1 h at these temperatures at a vacuum of 80 mTorr, prior thawing. For drying, we used a new freeze-drying apparatus (Darya, FertileSafe, Israel) having a condensation temperature below - 110 °C and a vacuum pressure of 10-100 mTorr that is reached in less than 10s. Results showed that samples in Lyo B solution frozen at - 25 °C had significantly higher sperm motility in partially freeze-dried samples than frozen samples (46.6 ± 2.8% vs 1.2 ± 2.5%, P < 0.001). Moreover, partially dried samples in Lyo B showed higher motility than Lyo A at - 25 °C (46.6 ± 2.8% vs 35 ± 4%). Cryomicroscopy and low-temperature/low-pressure environmental scanning electronic microscope demonstrated that the amount of the ice crystals present in partially dried samples was lower than in the frozen samples. Holding the sperm at high subzero temperatures is necessary for the primary drying of cells during the freeze-drying process. Rapid freeze-drying can be achieved using this new device, which enables to reduce recrystallization damages.

Calorimetric determination of inhibition of ice crystal growth by antifreeze protein in hydroxyethyl starch solutions.

PubMed Central

Hansen, T N; Carpenter, J F

1993-01-01

Differential scanning calorimetry and cryomicroscopy were used to investigate the effects of type I antifreeze protein (AFP) from winter flounder on 58% solutions of hydroxyethyl starch. The glass, devitrification, and melt transitions noted during rewarming were unaffected by 100 micrograms/ml AFP. Isothermal annealing experiments were undertaken to detect the effects of AFP-induced inhibition of ice crystal growth using calorimetry. A premelt endothermic peak was detected during warming after the annealing procedure. Increasing the duration or the temperature of the annealing for the temperature range from -28 and -18 degrees C resulted in a gradual increase in the enthalpy of the premelt endotherm. This transition was unaffected by 100 micrograms/ml AFP. Annealing between -18 and -10 degrees C resulted in a gradual decrease in the premelt peak enthalpy. This process was inhibited by 100 micrograms/ml AFP. Cryomicroscopic examination of the samples revealed that AFP inhibited ice recrystallization during isothermal annealing at -10 degrees C. Annealing at lower temperatures resulted in minimal ice recrystallization and no visible effect of AFP. Thus, the 100 micrograms/ml AFP to have a detectable influence on thermal events in the calorimeter, conditions must be used that result in significant ice growth without AFP and visible inhibition of this process by AFP. Images FIGURE 8 PMID:7690257

Recombinant Dendroides canadensis antifreeze proteins as potential ingredients in cryopreservation solutions.

PubMed

Halwani, Dina O; Brockbank, Kelvin G M; Duman, John G; Campbell, Lia H

2014-06-01

Expanding cryopreservation methods to include a wider range of cell types, such as those sensitive to freezing, is needed for maintaining the viability of cell-based regenerative medicine products. Conventional cryopreservation protocols, which include use of cryoprotectants such as dimethylsulfoxide (Me2SO), have not prevented ice-induced damage to cell and tissue matrices during freezing. A family of antifreeze proteins (AFPs) produced in the larvae of the beetle, Dendroides canadensis allow this insect to survive subzero temperatures as low as -26°C. This study is an assessment of the effect of the four hemolymph D. canadensis AFPs (DAFPs) on the supercooling (nucleating) temperature, ice structure patterns and viability of the A10 cell line derived from the thoracic aorta of embryonic rat. Cryoprotectant solution cocktails containing combinations of DAFPs in concentrations ranging from 0 to 3mg/mL in Unisol base mixed with 1M Me2SO were first evaluated by cryomicroscopy. Combining multiple DAFPs demonstrated significant supercooling point depressing activity (∼9°C) when compared to single DAFPs and/or conventional 1M Me2SO control solutions. Concentrations of DAFPs as low as 1 μg/mL were sufficient to trigger this effect. In addition, significantly improved A10 smooth muscle cell viability was observed in cryopreservation experiments with low DAFP-6 and DAFP-2 concentrations in combination with Me2SO. No significant improvement in viability was observed with either DAFP-1 or DAFP-4. Low and effective DAFP concentrations are advantageous because they minimize concerns regarding cell cytotoxicity and manufacturing cost. These findings support the potential of incorporating DAFPs in solutions used to cryopreserve cells and tissues. Copyright © 2014 Elsevier Inc. All rights reserved.

Effects of Intercellular Junction Protein Expression on Intracellular Ice Formation in Mouse Insulinoma Cells

PubMed Central

Higgins, Adam Z.; Karlsson, Jens O.M.

2013-01-01

The development of cryopreservation procedures for tissues has proven to be difficult in part because cells within tissue are more susceptible to intracellular ice formation (IIF) than are isolated cells. In particular, previous studies suggest that cell-cell interactions increase the likelihood of IIF by enabling propagation of ice between neighboring cells, a process thought to be mediated by gap junction channels. In this study, we investigated the effects of cell-cell interactions on IIF using three genetically modified strains of the mouse insulinoma cell line MIN6, each of which expressed key intercellular junction proteins (connexin-36, E-cadherin, and occludin) at different levels. High-speed video cryomicroscopy was used to visualize the freezing process in pairs of adherent cells, revealing that the initial IIF event in a given cell pair was correlated with a hitherto unrecognized precursor phenomenon: penetration of extracellular ice into paracellular spaces at the cell-cell interface. Such paracellular ice penetration occurred in the majority of cell pairs observed, and typically preceded and colocalized with the IIF initiation events. Paracellular ice penetration was generally not observed at temperatures >−5.65°C, which is consistent with a penetration mechanism via defects in tight-junction barriers at the cell-cell interface. Although the maximum temperature of paracellular penetration was similar for all four cell strains, genetically modified cells exhibited a significantly higher frequency of ice penetration and a higher mean IIF temperature than did wild-type cells. A four-state Markov chain model was used to quantify the rate constants of the paracellular ice penetration process, the penetration-associated IIF initiation process, and the intercellular ice propagation process. In the initial stages of freezing (>−15°C), junction protein expression appeared to only have a modest effect on the kinetics of propagative IIF, and even cell strains lacking the gap junction protein connexin-36 exhibited nonnegligible ice propagation rates. PMID:24209845

Performance of a kinetic model for intracellular ice formation based on the extent of supercooling.

PubMed

Pitt, R E; Chandrasekaran, M; Parks, J E

1992-06-01

Cryomicroscopy was used to study the incidence of intracellular ice formation (IIF) in protoplasts isolated from rye (Secale cereale) leaves during subfreezing isothermal periods and in in vitro mature bovine oocytes during cooling at constant rates. IIF in protoplasts occurred at random times during isothermal periods, and the kinetics of IIF were faster as isothermal temperature decreased. Mean IIF times decreased from approximately 1700 s at -4.0 degrees C to less than 1 s at -18.5 degrees C. Total incidence of IIF after 200 s increased from 4% at -4.0 degrees C to near 100% at -15.5 degrees C. IIF behavior in protoplasts was qualitatively similar to that for Drosophila melanogaster embryos over the same temperature ranges (Myers et al., Cryobiology 26, 472-484, 1989), but the kinetics of IIF were about five times faster in protoplasts. IIF observations in linear cooling of bovine oocytes indicated a median IIF temperature of -11 degrees C at 16 degrees C/min and total incidences of 97%, 50%, and 19% at 16, 8, and 4 degrees C/min, respectively. A stochastic model of IIF was developed which preserved certain features of an earlier model (Pitt et al. Cryobiology 28, 72-86, 1991), namely Weibull behavior in IIF temperatures during rapid linear cooling, but with a departure from the concept of a supercooling tolerance. Instead, the new model uses the osmotic state of the cell, represented by the extent of supercooling, as the independent variable governing the kinetics of IIF. Two kinetic parameters are needed for the model: a scale factor tau 0 dictating the sensitivity to supercooling, and an exponent rho dictating the strength of time dependency. The model was fit to the data presented in this study as well as those from Myers et al. and Pitt et al. for D. melanogaster embryos with and without cryoprotectant, and from Toner et al. (Cryobiology 28, 55-71, 1991) for mouse oocytes. In protoplasts, D. melanogaster embryos, and mouse oocytes, the parameters were estimated from IIF times in the early stages of isothermal periods, while the osmotic state of the cell was relatively constant. In bovine oocytes, the parameters were estimated from linear cooling data. Without further calibration, the model was used to predict total IIF incidence under different cooling regimes. For protoplasts, D. melanogaster embryos, and bovine oocytes, the model's predictions were quite accurate compared to the actual data. In mouse oocytes, adjustment of the hydraulic permeability coefficient (Lp) at 0 degree C was required to yield realistic behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemical and charge transfer studies on interfaces of a conjugated polymer and ITO

NASA Astrophysics Data System (ADS)

David, Tanya M. S.; Arasho, Wondwosson; Smith, O'Neil; Hong, Kunlun; Bonner, Carl; Sun, Sam-Shajing

2017-08-01

Conjugated oligomers and polymers are very attractive for potential future plastic electronic and opto-electronic device applications such as plastic photo detectors and solar cells, thermoelectric devices, field effect transistors, and light emitting diodes. Understanding and optimizing charge transport between an active polymer layer and conductive substrate is critical to the optimization of polymer based electronic and opto-electronic devices. This study focused on the design, synthesis, self-assembly, and electron transfers and transports of a phosphonic acid end-functionalized polyphenylenevinylene (PPV) that was covalently attached and self-assembled onto an Indium Tin Oxide (ITO) substrate. This study demonstrated how atomic force microscopy (AFM) can be an effective characterization technique in conjunction with conventional electron transfer methods, including cyclic voltammetry (CV), towards determining electron transfer rates in polymer and polymer/conductor interface systems. This study found that the electron transfer rates of covalently attached and self-assembled films were much faster than the spin coated films. The knowledge from this study can be very useful for designing potential polymer based electronic and opto-electronic thin film devices.

Effects of Electron Scattering at Metal-Nonmetal Interfaces on Electron-Phonon Equilibration in Gold Films

DTIC Science & Technology

2009-01-26

dielectrics is a major concern in thermal boundary conductance studies . This aspect of energy transfer has been extensively studied and modeled on long...electron-phonon coupling in the particle. There have been only a small number of studies looking at electron-phonon relaxation around interfaces in thin...film systems. These studies avoid complications due to nanopar- ticle geometries i.e., capillary modes on determining the electron-phonon-interfacial

Monte Carlo study of electron relaxation in graphene with spin polarized, degenerate electron gas in presence of electron-electron scattering

NASA Astrophysics Data System (ADS)

Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek

2017-12-01

The Monte Carlo simulation method is applied to study the relaxation of excited electrons in monolayer graphene. The presence of spin polarized background electrons population, with density corresponding to highly degenerate conditions is assumed. Formulas of electron-electron scattering rates, which properly account for electrons presence in two energetically degenerate, inequivalent valleys in this material are presented. The electron relaxation process can be divided into two phases: thermalization and cooling, which can be clearly distinguished when examining the standard deviation of electron energy distribution. The influence of the exchange effect in interactions between electrons with parallel spins is shown to be important only in transient conditions, especially during the thermalization phase.

Modulated Electron Emission by Scattering-Interference of Primary Electrons

NASA Astrophysics Data System (ADS)

Valeri, Sergio; di Bona, Alessandro

We review the effects of scattering-interference of the primary, exciting beam on the electron emission from ordered atomic arrays. The yield of elastically and inelastically backscattered electrons, Auger electrons and secondary electrons shows a marked dependence on the incidence angle of primary electrons. Both the similarity and the relative importance of processes experienced by incident and excident electrons are discussed. We also present recent studies of electron focusing and defocusing along atomic chains. The interplay between these two processes determines the in-depth profile of the primary electron intensity anisotropy. Finally, the potential for surface-structural studies and limits for quantitative analysis are discussed, in comparison with the Auger electron diffraction (AED) and photoelectron diffraction (PD) techniques.

The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors

PubMed Central

Thorman, Rachel M; Kumar T. P., Ragesh; Fairbrother, D Howard

2015-01-01

Summary Focused electron beam induced deposition (FEBID) is a single-step, direct-write nanofabrication technique capable of writing three-dimensional metal-containing nanoscale structures on surfaces using electron-induced reactions of organometallic precursors. Currently FEBID is, however, limited in resolution due to deposition outside the area of the primary electron beam and in metal purity due to incomplete precursor decomposition. Both limitations are likely in part caused by reactions of precursor molecules with low-energy (<100 eV) secondary electrons generated by interactions of the primary beam with the substrate. These low-energy electrons are abundant both inside and outside the area of the primary electron beam and are associated with reactions causing incomplete ligand dissociation from FEBID precursors. As it is not possible to directly study the effects of secondary electrons in situ in FEBID, other means must be used to elucidate their role. In this context, gas phase studies can obtain well-resolved information on low-energy electron-induced reactions with FEBID precursors by studying isolated molecules interacting with single electrons of well-defined energy. In contrast, ultra-high vacuum surface studies on adsorbed precursor molecules can provide information on surface speciation and identify species desorbing from a substrate during electron irradiation under conditions more representative of FEBID. Comparing gas phase and surface science studies allows for insight into the primary deposition mechanisms for individual precursors; ideally, this information can be used to design future FEBID precursors and optimize deposition conditions. In this review, we give a summary of different low-energy electron-induced fragmentation processes that can be initiated by the secondary electrons generated in FEBID, specifically, dissociative electron attachment, dissociative ionization, neutral dissociation, and dipolar dissociation, emphasizing the different nature and energy dependence of each process. We then explore the value of studying these processes through comparative gas phase and surface studies for four commonly-used FEBID precursors: MeCpPtMe3, Pt(PF3)4, Co(CO)3NO, and W(CO)6. Through these case studies, it is evident that this combination of studies can provide valuable insight into potential mechanisms governing deposit formation in FEBID. Although further experiments and new approaches are needed, these studies are an important stepping-stone toward better understanding the fundamental physics behind the deposition process and establishing design criteria for optimized FEBID precursors. PMID:26665061

The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors.

PubMed

Thorman, Rachel M; Kumar T P, Ragesh; Fairbrother, D Howard; Ingólfsson, Oddur

2015-01-01

Focused electron beam induced deposition (FEBID) is a single-step, direct-write nanofabrication technique capable of writing three-dimensional metal-containing nanoscale structures on surfaces using electron-induced reactions of organometallic precursors. Currently FEBID is, however, limited in resolution due to deposition outside the area of the primary electron beam and in metal purity due to incomplete precursor decomposition. Both limitations are likely in part caused by reactions of precursor molecules with low-energy (<100 eV) secondary electrons generated by interactions of the primary beam with the substrate. These low-energy electrons are abundant both inside and outside the area of the primary electron beam and are associated with reactions causing incomplete ligand dissociation from FEBID precursors. As it is not possible to directly study the effects of secondary electrons in situ in FEBID, other means must be used to elucidate their role. In this context, gas phase studies can obtain well-resolved information on low-energy electron-induced reactions with FEBID precursors by studying isolated molecules interacting with single electrons of well-defined energy. In contrast, ultra-high vacuum surface studies on adsorbed precursor molecules can provide information on surface speciation and identify species desorbing from a substrate during electron irradiation under conditions more representative of FEBID. Comparing gas phase and surface science studies allows for insight into the primary deposition mechanisms for individual precursors; ideally, this information can be used to design future FEBID precursors and optimize deposition conditions. In this review, we give a summary of different low-energy electron-induced fragmentation processes that can be initiated by the secondary electrons generated in FEBID, specifically, dissociative electron attachment, dissociative ionization, neutral dissociation, and dipolar dissociation, emphasizing the different nature and energy dependence of each process. We then explore the value of studying these processes through comparative gas phase and surface studies for four commonly-used FEBID precursors: MeCpPtMe3, Pt(PF3)4, Co(CO)3NO, and W(CO)6. Through these case studies, it is evident that this combination of studies can provide valuable insight into potential mechanisms governing deposit formation in FEBID. Although further experiments and new approaches are needed, these studies are an important stepping-stone toward better understanding the fundamental physics behind the deposition process and establishing design criteria for optimized FEBID precursors.

77 FR 12312 - Electronic Submission of Nonclinical Study Data; Notice of Pilot Project

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-29

...] Electronic Submission of Nonclinical Study Data; Notice of Pilot Project AGENCY: Food and Drug Administration... the electronic submission of nonclinical study data using the Standard for Exchange of Nonclinical Data (SEND), a new electronic data standard format, which can be used to support review activity...

Numerical study on characteristics of radio-frequency discharge at atmospheric pressure in argon with small admixtures of oxygen

NASA Astrophysics Data System (ADS)

Wang, Yinan; Liu, Yue

2017-07-01

In this paper, a 1D fluid model is developed to study the characteristics of a discharge in argon with small admixtures of oxygen at atmospheric pressure. This model consists of a series of equations, including continuity equations for electrons, positive ions, negative ions and neutral particles, the energy equation, and the Poisson equation for electric potential. Special attention has been paid to the electron energy dissipation and the mechanisms of electron heating, while the admixture of oxygen is in the range of 0.1%-0.6%. It is found that when the oxygen-to-argon ratio grows, the discharge is obviously divided into three stages: electron growth, electron reduction and the electron remaining unchanged. Furthermore, the cycle-averaged electric field, electron temperature, electron Ohmic heating, electron collisionless heating, electron energy dissipation and the net electron production are also studied in detail, and when the oxygen-to-argon ratio is relatively larger (R = 0.6%), double value peaks of electron Ohmic heating appear in the sheath. According to the results of the numerical simulation, various oxygen-to-argon ratios result in different amounts of electron energy dissipation and electron heating.

Changes to Workflow and Process Measures in the PICU During Transition From Semi to Full Electronic Health Record.

PubMed

Salib, Mina; Hoffmann, Raymond G; Dasgupta, Mahua; Zimmerman, Haydee; Hanson, Sheila

2015-10-01

Studies showing the changes in workflow during transition from semi to full electronic medical records are lacking. This objective study is to identify the changes in workflow in the PICU during transition from semi to full electronic health record. Prospective observational study. Children's Hospital of Wisconsin Institutional Review Board waived the need for approval so this study was institutional review board exempt. This study measured clinical workflow variables at a 72-bed PICU during different phases of transition to a full electronic health record, which occurred on November 4, 2012. Phases of electronic health record transition were defined as follows: pre-electronic health record (baseline data prior to transition to full electronic health record), transition phase (3 wk after electronic health record), and stabilization (6 mo after electronic health record). Data were analyzed for the three phases using Mann-Whitney U test with a two-sided p value of less than 0.05 considered significant. Seventy-two bed PICU. All patients in the PICU were included during the study periods. Five hundred and sixty-four patients with 2,355 patient days were evaluated in the three phases. Duration of rounds decreased from a median of 9 minutes per patient pre--electronic health record to 7 minutes per patient post electronic health record. Time to final note decreased from 2.06 days pre--electronic health record to 0.5 days post electronic health record. Time to first medication administration after admission also decreased from 33 minutes pre--electronic health record and 7 minutes post electronic health record. Time to Time to medication reconciliation was significantly higher pre-electronic health record than post electronic health record and percent of medication reconciliation completion was significantly lower pre--electronic health record than post electronic health record and percent of medication reconciliation completion was significantly higher pre--electronic health record than. There was no significant change in time between placement of discharge order and physical transfer from the unit [corrected].changes clinical workflow in a PICU with decreased duration of rounds, time to final note, time to medication administration, and time to medication reconciliation completion. There was no change in the duration from medical to physical transfer.

Negative ions of polyatomic molecules.

PubMed Central

Christophorou, L G

1980-01-01

In this paper general concepts relating to, and recent advances in, the study of negative ions of polyatomic molecules area discussed with emphasis on halocarbons. The topics dealt with in the paper are as follows: basic electron attachment processes, modes of electron capture by molecules, short-lived transient negative ions, dissociative electron attachment to ground-state molecules and to "hot" molecules (effects of temperature on electron attachment), parent negative ions, effect of density, nature, and state of the medium on electron attachment, electron attachment to electronically excited molecules, the binding of attached electrons to molecules ("electron affinity"), and the basic and the applied significance of negative-ion studies. PMID:7428744

A scanning electron microscopy study of the macro-crystalline structure of 2-(2,4-dinitrobenzyl) pyridine

NASA Technical Reports Server (NTRS)

Ware, Jacqueline; Hammond, Ernest C., Jr.

1989-01-01

The compound, 2-(2,4-dinitrobenzyl) pyridine, was synthesized in the laboratory; an introductory level electron microscopy study of the macro-crystalline structure was conducted using the scanning electron microscope (SEM). The structure of these crystals was compared with the macrostructure of the crystal of 2-(2,4-dinitrobenzyl) pyridinium bromide, the hydrobromic salt of the compound which was also synthesized in the laboratory. A scanning electron microscopy crystal study was combined with a study of the principle of the electron microscope.

Soluble fullerene derivatives: The effect of electronic structure on transistor performance and air stability

NASA Astrophysics Data System (ADS)

Ball, James M.; Bouwer, Ricardo K. M.; Kooistra, Floris B.; Frost, Jarvist M.; Qi, Yabing; Domingo, Ester Buchaca; Smith, Jeremy; de Leeuw, Dago M.; Hummelen, Jan C.; Nelson, Jenny; Kahn, Antoine; Stingelin, Natalie; Bradley, Donal D. C.; Anthopoulos, Thomas D.

2011-07-01

The family of soluble fullerene derivatives comprises a widely studied group of electron transporting molecules for use in organic electronic and optoelectronic devices. For electronic applications, electron transporting (n-channel) materials are required for implementation into organic complementary logic circuit architectures. To date, few soluble candidate materials have been studied that fulfill the stringent requirements of high carrier mobility and air stability. Here we present a study of three soluble fullerenes with varying electron affinity to assess the impact of electronic structure on device performance and air stability. Through theoretical and experimental analysis of the electronic structure, characterization of thin-film structure, and characterization of transistor device properties we find that the air stability of the present series of fullerenes not only depends on the absolute electron affinity of the semiconductor but also on the disorder within the thin-film.

The electronic structure of VO in its ground and electronically excited states: A combined matrix isolation and quantum chemical (MRCI) study

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

Hübner, Olaf; Hornung, Julius; Himmel, Hans-Jörg, E-mail: hans-jorg.himmel@aci.uni-heidelberg.de

2015-07-14

The electronic ground and excited states of the vanadium monoxide (VO) molecule were studied in detail. Electronic absorption spectra for the molecule isolated in Ne matrices complement the previous gas-phase spectra. A thorough quantum chemical (multi-reference configuration interaction) study essentially confirms the assignment and characterization of the electronic excitations observed for VO in the gas-phase and in Ne matrices and allows the clarification of open issues. It provides a complete overview over the electronically excited states up to about 3 eV of this archetypical compound.

Correlated Light and Electron Microscopy/Electron Tomography of Mitochondria In Situ

PubMed Central

Perkins, Guy A.; Sun, Mei G.; Frey, Terrence G.

2009-01-01

Three-dimensional light microscopy and three-dimensional electron microscopy (electron tomography) separately provide very powerful tools to study cellular structure and physiology, including the structure and physiology of mitochondria. Fluorescence microscopy allows one to study processes in live cells with specific labels and stains that follow the movement of labeled proteins and changes within cellular compartments but does not have sufficient resolution to define the ultrastructure of intracellular organelles such as mitochondria. Electron microscopy and electron tomography provide the highest resolution currently available to study mitochondrial ultrastructure but cannot follow processes in living cells. We describe the combination of these two techniques in which fluorescence confocal microscopy is used to study structural and physiologic changes in mitochondria within apoptotic HeLa cells to define the apoptotic timeframe. Cells can then be selected at various stages of the apoptotic timeframe for examination at higher resolution by electron microscopy and electron tomography. This is a form of “virtual” 4-dimensional electron microscopy that has revealed interesting structural changes in the mitochondria of HeLa cells during apoptosis. The same techniques can be applied, with modification, to study other dynamic processes within cells in other experimental contexts. PMID:19348881

Safety Assessment of Electronic Cigarettes and Their Relationship with Cardiovascular Disease

PubMed Central

Zhang, Guangwei; Zhang, Kai; Hou, Rui; Xing, Chunli; Yu, Qi; Liu, Enqi

2018-01-01

Smoking leads to the occurrence and development of a variety of diseases. Most importantly, it is an independent risk factor of cardiovascular atherosclerosis. In recent years, electronic cigarettes have become a popular alternative to traditional cigarettes, since modern micro-electronic techniques provide the possibility of simulating the process of traditional smoking. Additionally, it is convenient and fashionable. Nevertheless, comments about the safety of electronic cigarettes remain controversial. Although the research about electronic cigarettes increased exponentially, there has been no systematic study of its safety. The aim of the current study is to review the literature reports about the safety of electronic cigarettes, and to understand their hazards and disadvantages. It was found that most of the current research about electronic cigarettes comprises short-term and in vitro studies. There are few reports of in vivo and long-term studies. Notably, the level of harmful components such as volatile organic compounds, tobacco-specific nitrosamines and heavy metals in electronic cigarettes are even higher than in traditional cigarettes. Therefore, the harm of electronic cigarettes should not be underestimated. In conclusion, the question of whether electronic cigarettes are a safe and sufficient substitute for traditional smoking needs further investigation. PMID:29304018

Spin-electron acoustic soliton and exchange interaction in separate spin evolution quantum plasmas

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

Andreev, Pavel A., E-mail: andreevpa@physics.msu.ru

Separate spin evolution quantum hydrodynamics is generalized to include the Coulomb exchange interaction, which is considered as interaction between the spin-down electrons being in quantum states occupied by one electron. The generalized model is applied to study the non-linear spin-electron acoustic waves. Existence of the spin-electron acoustic soliton is demonstrated. Contributions of concentration, spin polarization, and exchange interaction to the properties of the spin electron acoustic soliton are studied.

Theoretical investigation of the electronic structure of a substituted nickel phthalocyanine

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

Kaur, Prabhjot, E-mail: prabhphysics@gmail.com; Sachdeva, Ritika; Singh, Sukhwinder

2016-05-23

The optimized geometry and electronic structure of an organic compound nickel phthalocyanine tetrasulfonic acid tetra sodium salt have been investigated using density functional theory. We have also optimized the structure of nickel phthalocyanine tetrasulfonic acid tetra sodium salt in dimethyl sulfoxide to study effects of solvent on the electronic structure and transitions. Experimentally, the electronic transitions have been studied using UV-VIS spectroscopic technique. It is observed that the electronic transitions obtained from the theoretical studies generally agree with the experiment.

Diffusive transport of energetic electrons in the solar corona: X-ray and radio diagnostics

NASA Astrophysics Data System (ADS)

Musset, S.; Kontar, E. P.; Vilmer, N.

2018-02-01

Context. Imaging spectroscopy in X-rays with RHESSI provides the possibility to investigate the spatial evolution of X-ray emitting electron distribution and therefore, to study transport effects on energetic electrons during solar flares. Aims: We study the energy dependence of the scattering mean free path of energetic electrons in the solar corona. Methods: We used imaging spectroscopy with RHESSI to study the evolution of energetic electrons distribution in various parts of the magnetic loop during the 2004 May 21 flare. We compared these observations with the radio observations of the gyrosynchrotron radiation of the same flare and with the predictions of a diffusive transport model. Results: X-ray analysis shows a trapping of energetic electrons in the corona and a spectral hardening of the energetic electron distribution between the top of the loop and the footpoints. Coronal trapping of electrons is stronger for radio-emitting electrons than for X-ray-emitting electrons. These observations can be explained by a diffusive transport model. Conclusions: We show that the combination of X-ray and radio diagnostics is a powerful tool to study electron transport in the solar corona in different energy domains. We show that the diffusive transport model can explain our observations, and in the range 25-500 keV, the scattering mean free path of electrons decreases with electron energy. We can estimate for the first time the scattering mean free path dependence on energy in the corona.

Development of an electron-ion coincidence apparatus for molecular-frame electron energy loss spectroscopy studies

NASA Astrophysics Data System (ADS)

Watanabe, Noboru; Hirayama, Tsukasa; Yamada, So; Takahashi, Masahiko

2018-04-01

We report details of an electron-ion coincidence apparatus, which has been developed for molecular-frame electron energy loss spectroscopy studies. The apparatus is mainly composed of a pulsed electron gun, an energy-dispersive electron spectrometer, and an ion momentum imaging spectrometer. Molecular-orientation dependence of the high-energy electron scattering cross section can be examined by conducting measurements of vector correlation between the momenta of the scattered electron and fragment ion. Background due to false coincidences is significantly reduced by introducing a pulsed electron beam and pulsing scheme of ion extraction. The experimental setup has been tested by measuring the inner-shell excitation of N2 at an incident electron energy of 1.5 keV and a scattering angle of 10.2°.

Electron-electron interaction in ion-atom collisions studied by projectile state-resolved Auger-electron spectroscopy

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

Dohyung Lee.

This dissertation addresses the problem of dynamic electron-electron interactions in fast ion-atom collisions using projectile Auger electron spectroscopy. The study was carried out by measuring high-resolution projectile KKL Auger electron spectra as a function of projectile energy for the various collision systems of 0.25-2 MeV/u O{sup q+} and F{sup q+} incident on H{sub 2} and He targets. The electrons were detected in the beam direction, where the kinematic broadening is minimized. A zero-degree tandem electron spectrometer system, was developed and showed the versatility of zero-degree measurements of collisionally-produced atomic states. The zero-degree binary encounter electrons (BEe), quasifree target electrons ionizedmore » by the projectiles in head-on collisions, were observed as a strong background in the KLL Auger electron spectrum. They were studied by treating the target ionization as 180{degree} Rutherford elastic scattering in the projectile frame, and resulted in a validity test of the impulse approximation (IA) and a way to determine the spectrometer efficiency. An anomalous q-dependence, in which the zero-degree BEe yields increase with decreasing projectile charge state (q), was observed. State-resolved KLL Auger cross sections were determined by using the BEe normalization and thus the cross section of the electron-electron interactions such as resonant transfer-excitation (RTE), electron-electron excitation (eeE), and electron-electron ionization (eeI) were determined. Projectile 2l capture with 1s {yields} 2p excitation by the captured target electron was observed as an RTE process with Li-like and He-like projectiles and the measured RTEA (RTE followed by Auger decay) cross sections showed good agreement with an RTE-IA treatment and RTE alignment theory.« less

The interaction of low-energy electrons with fructose molecules

NASA Astrophysics Data System (ADS)

Chernyshova, I. V.; Kontrosh, E. E.; Markush, P. P.; Shpenik, O. B.

2017-11-01

Using a hypocycloidal electronic spectrometer, the interactions of low energy electrons (0-8.50 eV) with fructose molecules, namely, electron scattering and dissociative attachment, are studied. The results of these studies showed that the fragmentation of fructose molecules occurs effectively even at an electron energy close to zero. In the total electron-scattering cross section by molecules, resonance features (at energies 3.10 and 5.00 eV) were first observed near the formation thresholds of light ion fragments OH- and H-. The correlation of the features observed in the cross sections of electron scattering and dissociative attachment is analyzed.

The electronic properties of potassium doped copper-phthalocyanine studied by electron energy-loss spectroscopy.

PubMed

Flatz, K; Grobosch, M; Knupfer, M

2007-06-07

The authors have studied the electronic structure of potassium doped copper-phthalocyanine using electron energy-loss spectroscopy. The evolution of the loss function indicates the formation of distinct KxCuPc phases. Taking into account the C1s and K2p core level excitations and recent results by Giovanelli et al. [J. Chem. Phys. 126, 044709 (2007)], they conclude that these are K2CuPc and K4CuPc. They discuss the changes in the electronic excitations upon doping on the basis of the molecular electronic levels and the presence of electronic correlations.

Modified Monte Carlo method for study of electron transport in degenerate electron gas in the presence of electron-electron interactions, application to graphene

NASA Astrophysics Data System (ADS)

Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek

2017-07-01

Standard computational methods used to take account of the Pauli Exclusion Principle into Monte Carlo (MC) simulations of electron transport in semiconductors may give unphysical results in low field regime, where obtained electron distribution function takes values exceeding unity. Modified algorithms were already proposed and allow to correctly account for electron scattering on phonons or impurities. Present paper extends this approach and proposes improved simulation scheme allowing including Pauli exclusion principle for electron-electron (e-e) scattering into MC simulations. Simulations with significantly reduced computational cost recreate correct values of the electron distribution function. Proposed algorithm is applied to study transport properties of degenerate electrons in graphene with e-e interactions. This required adapting the treatment of e-e scattering in the case of linear band dispersion relation. Hence, this part of the simulation algorithm is described in details.

Study of Electron Polarization Dynamics in the JLEIC at Jlab

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

Lin, Fanglei; Derbenev, Yaroslav; Morozov, Vasiliy

The design of an electron polarization scheme in the Jefferson Lab Electron-Ion Collider (JLEIC) aims to attain a high longitudinal electron polarization (over 70%) at collision points as required by the nuclear physics program. Comprehensive strategies for achieving this goal have been considered and developed including injection of highly polarized electrons from CEBAF, mechanisms for manipulation and preservation of the polarization in the JLEIC collider ring and measurement of the electron polarization. In particular, maintaining a sufficiently long polarization lifetime is crucial for accumulation of adequate experimental statistics. The chosen electron polarization configuration, based on the unique figure-8 geometry ofmore » the ring, removes the electron spin-tune energy dependence. This significantly simplifies the control of the electron polarization and suppresses the synchrotron sideband resonances. This paper reports recent studies and simulations of the electron polarization dynamics in the JLEIC electron collider ring.« less

Advanced Electron Holography Applied to Electromagnetic Field Study in Materials Science.

PubMed

Shindo, Daisuke; Tanigaki, Toshiaki; Park, Hyun Soon

2017-07-01

Advances and applications of electron holography to the study of electromagnetic fields in various functional materials are presented. In particular, the development of split-illumination electron holography, which introduces a biprism in the illumination system of a holography electron microscope, enables highly accurate observations of electromagnetic fields and the expansion of the observable area. First, the charge distributions on insulating materials were studied by using split-illumination electron holography and including a mask in the illumination system. Second, the three-dimensional spin configurations of skyrmion lattices in a helimagnet were visualized by using a high-voltage holography electron microscope. Third, the pinning of the magnetic flux lines in a high-temperature superconductor YBa 2 Cu 3 O 7-y was analyzed by combining electron holography and scanning ion microscopy. Finally, the dynamic accumulation and collective motions of electrons around insulating biomaterial surfaces were observed by utilizing the amplitude reconstruction processes of electron holography. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Technology as friend or foe? Do electronic health records increase burnout?

PubMed

Ehrenfeld, Jesse M; Wanderer, Jonathan P

2018-06-01

To summarize recent relevant studies regarding the use of electronic health records and physician burnout. Recently acquired knowledge regarding the relationship between electronic health record use, professional satisfaction, burnout, and desire to leave clinical practice are discussed. Adoption of electronic health records has increased across the United States and worldwide. Although electronic health records have many benefits, there is growing concern about the adverse consequences of their use on physician satisfaction and burnout. Poor usability, incongruent workflows, and the addition of clerical tasks to physician documentation requirements have been previously highlighted as ongoing concerns with electronic health record adoption. In multiple recent studies, electronic health records have been shown to decrease professional satisfaction, increase burnout, and the likelihood that a physician will reduce or leave clinical practice. One interventional study demonstrated a positive effect of a dedicated electronic health record entry clerk on physicians working in an outpatient practice.

Electron dynamics surrounding the X line in asymmetric magnetic reconnection

NASA Astrophysics Data System (ADS)

Zenitani, S.; Hasegawa, H.; Nagai, T.

2017-12-01

Electron dynamics surrounding the X line in magnetopause-type asymmetric reconnection is investigated using a two-dimensional particle-in-cell simulation. We study electron properties of three characteristic regions in the vicinity of the X line. The fluid properties, velocity distribution functions (VDFs), and orbits are studied and cross-compared. On the magnetospheric side of the X line, the normal electric field enhances the electron meandering motion from the magnetosheath side. The motion leads to a crescent-shaped component in the electron VDF, in agreement with recent studies. On the magnetosheath side of the X line, the magnetic field line is so stretched in the third dimension that its curvature radius is comparable with typical electron Larmor radius. The electron motion becomes nonadiabatic, and therefore the electron idealness is no longer expected to hold. Around the middle of the outflow regions, the electron nonidealness is coincident with the region of the nonadiabatic motion. Finally, we introduce a finite-time mixing fraction (FTMF) to evaluate electron mixing. The FTMF marks the magnetospheric side of the X line, where the nonideal energy dissipation occurs.

The Extent to Which Electronic Technology Education Is Meeting Employment Needs of Industry.

ERIC Educational Resources Information Center

Wamble, Jack D.

A study compared the perceptions of electronic technology education teachers and employers in the electronics industry regarding the competencies graduates need for employment in the industry. The study population consisted of 27 state institutions with electronics technology programs in Arkansas, Missouri, Kansas, Oklahoma, Illinois, Kentucky,…

Effect of electron-electron scattering on the conductance of a quantum wire studied with the Boltzman transport equation

NASA Astrophysics Data System (ADS)

Lyo, S. K.; Huang, Danhong

2006-05-01

Electron-electron scattering conserves total momentum and does not dissipate momentum directly in a low-density system where the umklapp process is forbidden. However, it can still affect the conductance through the energy relaxation of the electrons. We show here that this effect can be studied with arbitrary accuracy in a multisublevel one-dimensional (1D) single quantum wire system in the presence of roughness and phonon scattering using a formally exact solution of the Boltzmann transport equation. The intrasubband electron-electron scattering is found to yield no net effect on the transport of electrons in 1D with only one sublevel occupied. For a system with a multilevel occupation, however, we find a significant effect of intersublevel electron-electron scattering on the temperature and density dependence of the resistance at low temperatures.

Electronic self-monitoring of mood using IT platforms in adult patients with bipolar disorder: A systematic review of the validity and evidence.

PubMed

Faurholt-Jepsen, Maria; Munkholm, Klaus; Frost, Mads; Bardram, Jakob E; Kessing, Lars Vedel

2016-01-15

Various paper-based mood charting instruments are used in the monitoring of symptoms in bipolar disorder. During recent years an increasing number of electronic self-monitoring tools have been developed. The objectives of this systematic review were 1) to evaluate the validity of electronic self-monitoring tools as a method of evaluating mood compared to clinical rating scales for depression and mania and 2) to investigate the effect of electronic self-monitoring tools on clinically relevant outcomes in bipolar disorder. A systematic review of the scientific literature, reported according to the Preferred Reporting items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines was conducted. MEDLINE, Embase, PsycINFO and The Cochrane Library were searched and supplemented by hand search of reference lists. Databases were searched for 1) studies on electronic self-monitoring tools in patients with bipolar disorder reporting on validity of electronically self-reported mood ratings compared to clinical rating scales for depression and mania and 2) randomized controlled trials (RCT) evaluating electronic mood self-monitoring tools in patients with bipolar disorder. A total of 13 published articles were included. Seven articles were RCTs and six were longitudinal studies. Electronic self-monitoring of mood was considered valid compared to clinical rating scales for depression in six out of six studies, and in two out of seven studies compared to clinical rating scales for mania. The included RCTs primarily investigated the effect of heterogeneous electronically delivered interventions; none of the RCTs investigated the sole effect of electronic mood self-monitoring tools. Methodological issues with risk of bias at different levels limited the evidence in the majority of studies. Electronic self-monitoring of mood in depression appears to be a valid measure of mood in contrast to self-monitoring of mood in mania. There are yet few studies on the effect of electronic self-monitoring of mood in bipolar disorder. The evidence of electronic self-monitoring is limited by methodological issues and by a lack of RCTs. Although the idea of electronic self-monitoring of mood seems appealing, studies using rigorous methodology investigating the beneficial as well as possible harmful effects of electronic self-monitoring are needed.

Two-Electron Transfer Pathways.

PubMed

Lin, Jiaxing; Balamurugan, D; Zhang, Peng; Skourtis, Spiros S; Beratan, David N

2015-06-18

The frontiers of electron-transfer chemistry demand that we develop theoretical frameworks to describe the delivery of multiple electrons, atoms, and ions in molecular systems. When electrons move over long distances through high barriers, where the probability for thermal population of oxidized or reduced bridge-localized states is very small, the electrons will tunnel from the donor (D) to acceptor (A), facilitated by bridge-mediated superexchange interactions. If the stable donor and acceptor redox states on D and A differ by two electrons, it is possible that the electrons will propagate coherently from D to A. While structure-function relations for single-electron superexchange in molecules are well established, strategies to manipulate the coherent flow of multiple electrons are largely unknown. In contrast to one-electron superexchange, two-electron superexchange involves both one- and two-electron virtual intermediate states, the number of virtual intermediates increases very rapidly with system size, and multiple classes of pathways interfere with one another. In the study described here, we developed simple superexchange models for two-electron transfer. We explored how the bridge structure and energetics influence multielectron superexchange, and we compared two-electron superexchange interactions to single-electron superexchange. Multielectron superexchange introduces interference between singly and doubly oxidized (or reduced) bridge virtual states, so that even simple linear donor-bridge-acceptor systems have pathway topologies that resemble those seen for one-electron superexchange through bridges with multiple parallel pathways. The simple model systems studied here exhibit a richness that is amenable to experimental exploration by manipulating the multiple pathways, pathway crosstalk, and changes in the number of donor and acceptor species. The features that emerge from these studies may assist in developing new strategies to deliver multiple electrons in condensed-phase redox systems, including multiple-electron redox species, multimetallic/multielectron redox catalysts, and multiexciton excited states.

Michel electron reconstruction using cosmic-ray data from the MicroBooNE LArTPC

NASA Astrophysics Data System (ADS)

Acciarri, R.; Adams, C.; An, R.; Anthony, J.; Asaadi, J.; Auger, M.; Bagby, L.; Balasubramanian, S.; Baller, B.; Barnes, C.; Barr, G.; Bass, M.; Bay, F.; Bishai, M.; Blake, A.; Bolton, T.; Bugel, L.; Camilleri, L.; Caratelli, D.; Carls, B.; Castillo Fernandez, R.; Cavanna, F.; Chen, H.; Church, E.; Cianci, D.; Cohen, E.; Collin, G. H.; Conrad, J. M.; Convery, M.; Crespo-Anadón, J. I.; Del Tutto, M.; Devitt, D.; Dytman, S.; Eberly, B.; Ereditato, A.; Escudero Sanchez, L.; Esquivel, J.; Fleming, B. T.; Foreman, W.; Furmanski, A. P.; Garcia-Gamez, D.; Garvey, G. T.; Genty, V.; Goeldi, D.; Gollapinni, S.; Graf, N.; Gramellini, E.; Greenlee, H.; Grosso, R.; Guenette, R.; Hackenburg, A.; Hamilton, P.; Hen, O.; Hewes, J.; Hill, C.; Ho, J.; Horton-Smith, G.; Huang, E.-C.; James, C.; de Vries, J. Jan; Jen, C.-M.; Jiang, L.; Johnson, R. A.; Joshi, J.; Jostlein, H.; Kaleko, D.; Karagiorgi, G.; Ketchum, W.; Kirby, B.; Kirby, M.; Kobilarcik, T.; Kreslo, I.; Laube, A.; Li, Y.; Lister, A.; Littlejohn, B. R.; Lockwitz, S.; Lorca, D.; Louis, W. C.; Luethi, M.; Lundberg, B.; Luo, X.; Marchionni, A.; Mariani, C.; Marshall, J.; Martinez Caicedo, D. A.; Meddage, V.; Miceli, T.; Mills, G. B.; Moon, J.; Mooney, M.; Moore, C. D.; Mousseau, J.; Murrells, R.; Naples, D.; Nienaber, P.; Nowak, J.; Palamara, O.; Paolone, V.; Papavassiliou, V.; Pate, S. F.; Pavlovic, Z.; Piasetzky, E.; Porzio, D.; Pulliam, G.; Qian, X.; Raaf, J. L.; Rafique, A.; Rochester, L.; von Rohr, C. Rudolf; Russell, B.; Schmitz, D. W.; Schukraft, A.; Seligman, W.; Shaevitz, M. H.; Sinclair, J.; Snider, E. L.; Soderberg, M.; Söldner-Rembold, S.; Soleti, S. R.; Spentzouris, P.; Spitz, J.; St. John, J.; Strauss, T.; Sutton, K. A.; Szelc, A. M.; Tagg, N.; Terao, K.; Thomson, M.; Toups, M.; Tsai, Y.-T.; Tufanli, S.; Usher, T.; Van de Water, R. G.; Viren, B.; Weber, M.; Wickremasinghe, D. A.; Wolbers, S.; Wongjirad, T.; Woodruff, K.; Yang, T.; Yates, L.; Zeller, G. P.; Zennamo, J.; Zhang, C.

2017-09-01

The MicroBooNE liquid argon time projection chamber (LArTPC) has been taking data at Fermilab since 2015 collecting, in addition to neutrino beam, cosmic-ray muons. Results are presented on the reconstruction of Michel electrons produced by the decay at rest of cosmic-ray muons. Michel electrons are abundantly produced in the TPC, and given their well known energy spectrum can be used to study MicroBooNE's detector response to low-energy electrons (electrons with energies up to ~ 50 MeV). We describe the fully-automated algorithm developed to reconstruct Michel electrons, with which a sample of ~ 14,000 Michel electron candidates is obtained. Most of this article is dedicated to studying the impact of radiative photons produced by Michel electrons on the accuracy and resolution of their energy measurement. In this energy range, ionization and bremsstrahlung photon production contribute similarly to electron energy loss in argon, leading to a complex electron topology in the TPC. By profiling the performance of the reconstruction algorithm on simulation we show that the ability to identify and include energy deposited by radiative photons leads to a significant improvement in the energy measurement of low-energy electrons. The fractional energy resolution we measure improves from over 30% to ~ 20% when we attempt to include radiative photons in the reconstruction. These studies are relevant to a large number of analyses which aim to study neutrinos by measuring electrons produced by νe interactions over a broad energy range.

Michel Electron Reconstruction Using Cosmic-Ray Data from the MicroBooNE LArTPC

DOE PAGES

Acciarri, R.

2017-09-14

The MicroBooNE liquid argon time projection chamber (LArTPC) has been taking data at Fermilab since 2015 collecting, in addition to neutrino beam, cosmic-ray muons. Results are presented on the reconstruction of Michel electrons produced by the decay at rest of cosmic-ray muons. Michel electrons are abundantly produced in the TPC, and given their well known energy spectrum can be used to study MicroBooNE's detector response to low-energy electrons (electrons with energies up to ~50 MeV). We describe the fully-automated algorithm developed to reconstruct Michel electrons, with which a sample of ~14,000 Michel electron candidates is obtained. Most of this article is dedicated to studying the impact of radiative photons produced by Michel electrons on the accuracy and resolution of their energy measurement. In this energy range, ionization and bremsstrahlung photon production contribute similarly to electron energy loss in argon, leading to a complex electron topology in the TPC. By profiling the performance of the reconstruction algorithm on simulation we show that the ability to identify and include energy deposited by radiative photons leads to a significant improvement in the energy measurement of low-energy electrons. The fractional energy resolution we measure improves from over 30% to ~20% when we attempt to include radiative photons in the reconstruction. These studies are relevant to a large number of analyses which aim to study neutrinos by measuring electrons produced bymore » $$\

Simulation studies for operating electron beam ion trap at very low energy for disentangling edge plasma spectra

NASA Astrophysics Data System (ADS)

Jin, Xuelong; Fei, Zejie; Xiao, Jun; Lu, Di; Hutton, Roger; Zou, Yaming

2012-07-01

Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with a beam transmission above 57% for the SH-PermEBIT. Ar and W spectra were measured from the SH-PermEBIT at the apparent electron beam energies (read from the voltage difference between the electron gun cathode and the central drift tube) of 60 eV and 1200 eV, respectively. The spectra are shown in this paper.

Study of ring influence and electronic response to proton transfer reactions. Reaction electronic flux analysis.

PubMed

Herrera, Barbara

2011-05-01

In this article, a theoretical study of 1-5 proton transfers is presented. Two model systems which represent 1-5 proton transfer, 3-hidroxy-2-propenimine and salicyldenaniline have been studied as shown in Fig. 1. For this purpose, a DFT/B3LYP/6-311+G**, reaction force and reaction electronic flux analysis is made. The obtained results indicate that both proton transfers exhibit energetic and electronic differences emphasizing the role of the neighbor ring and the impact of conjugation on electronic properties.

77 FR 9945 - Draft Guidance for Industry on Providing Submissions in Electronic Format-Standardized Study Data...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-21

...] Draft Guidance for Industry on Providing Submissions in Electronic Format--Standardized Study Data... Submissions in Electronic Format--Standardized Study Data.'' This draft guidance establishes FDA's recommendation that sponsors and applicants submit nonclinical and clinical study data in a standardized...

Electron transfer and conformational change in complexes of trimethylamine dehydrogenase and electron transferring flavoprotein.

PubMed

Jones, Matthew; Talfournier, Francois; Bobrov, Anton; Grossmann, J Günter; Vekshin, Nikolai; Sutcliffe, Michael J; Scrutton, Nigel S

2002-03-08

The trimethylamine dehydrogenase-electron transferring flavoprotein (TMADH.ETF) electron transfer complex has been studied by fluorescence and absorption spectroscopies. These studies indicate that a series of conformational changes occur during the assembly of the TMADH.ETF electron transfer complex and that the kinetics of assembly observed with mutant TMADH (Y442F/L/G) or ETF (alpha R237A) complexes are much slower than are the corresponding rates of electron transfer in these complexes. This suggests that electron transfer does not occur in the thermodynamically most favorable state (which takes too long to form), but that one or more metastable states (which are formed more rapidly) are competent in transferring electrons from TMADH to ETF. Additionally, fluorescence spectroscopy studies of the TMADH.ETF complex indicate that ETF undergoes a stable conformational change (termed structural imprinting) when it interacts transiently with TMADH to form a second, distinct, structural form. The mutant complexes compromise imprinting of ETF, indicating a dependence on the native interactions present in the wild-type complex. The imprinted form of semiquinone ETF exhibits an enhanced rate of electron transfer to the artificial electron acceptor, ferricenium. Overall molecular conformations as probed by small-angle x-ray scattering studies are indistinguishable for imprinted and non-imprinted ETF, suggesting that changes in structure likely involve confined reorganizations within the vicinity of the FAD. Our results indicate a series of conformational events occur during the assembly of the TMADH.ETF electron transfer complex, and that the properties of electron transfer proteins can be affected lastingly by transient interaction with their physiological redox partners. This may have significant implications for our understanding of biological electron transfer reactions in vivo, because ETF encounters TMADH at all times in the cell. Our studies suggest that caution needs to be exercised in extrapolating the properties of in vitro interprotein electron transfer reactions to those occurring in vivo.

Application of Life Cycle Assessment on Electronic Waste Management: A Review.

PubMed

Xue, Mianqiang; Xu, Zhenming

2017-04-01

Electronic waste is a rich source of both valuable materials and toxic substances. Management of electronic waste is one of the biggest challenges of current worldwide concern. As an effective and prevailing environmental management tool, life cycle assessment can evaluate the environmental performance of electronic waste management activities. Quite a few scientific literatures reporting life cycle assessment of electronic waste management with significant outcomes have been recently published. This paper reviewed the trends, characteristics, research gaps, and challenges of these studies providing detailed information for practitioners involved in electronic waste management. The results showed that life cycle assessment studies were most carried out in Europe, followed by Asia and North America. The research subject of the studies mainly includes monitors, waste printed circuit boards, mobile phones, computers, printers, batteries, toys, dishwashers, and light-emitting diodes. CML was the most widely used life cycle impact assessment method in life cycle assessment studies on electronic waste management, followed by EI99. Furthermore, 40% of the reviewed studies combined with other environmental tools, including life cycle cost, material flow analysis, multi-criteria decision analysis, emergy analysis, and hazard assessment which came to more comprehensive conclusions from different aspects. The research gaps and challenges including uneven distribution of life cycle assessment studies, life cycle impact assessment methods selection, comparison of the results, and uncertainty of the life cycle assessment studies were examined. Although life cycle assessment of electronic waste management facing challenges, their results will play more and more important role in electronic waste management practices.

Application of Life Cycle Assessment on Electronic Waste Management: A Review

NASA Astrophysics Data System (ADS)

Xue, Mianqiang; Xu, Zhenming

2017-04-01

Electronic waste is a rich source of both valuable materials and toxic substances. Management of electronic waste is one of the biggest challenges of current worldwide concern. As an effective and prevailing environmental management tool, life cycle assessment can evaluate the environmental performance of electronic waste management activities. Quite a few scientific literatures reporting life cycle assessment of electronic waste management with significant outcomes have been recently published. This paper reviewed the trends, characteristics, research gaps, and challenges of these studies providing detailed information for practitioners involved in electronic waste management. The results showed that life cycle assessment studies were most carried out in Europe, followed by Asia and North America. The research subject of the studies mainly includes monitors, waste printed circuit boards, mobile phones, computers, printers, batteries, toys, dishwashers, and light-emitting diodes. CML was the most widely used life cycle impact assessment method in life cycle assessment studies on electronic waste management, followed by EI99. Furthermore, 40% of the reviewed studies combined with other environmental tools, including life cycle cost, material flow analysis, multi-criteria decision analysis, emergy analysis, and hazard assessment which came to more comprehensive conclusions from different aspects. The research gaps and challenges including uneven distribution of life cycle assessment studies, life cycle impact assessment methods selection, comparison of the results, and uncertainty of the life cycle assessment studies were examined. Although life cycle assessment of electronic waste management facing challenges, their results will play more and more important role in electronic waste management practices.

Low-energy electron-induced reactions in condensed matter

NASA Astrophysics Data System (ADS)

Arumainayagam, Christopher R.; Lee, Hsiao-Lu; Nelson, Rachel B.; Haines, David R.; Gunawardane, Richard P.

2010-01-01

The goal of this review is to discuss post-irradiation analysis of low-energy (≤50 eV) electron-induced processes in nanoscale thin films. Because electron-induced surface reactions in monolayer adsorbates have been extensively reviewed, we will instead focus on low-energy electron-induced reactions in multilayer adsorbates. The latter studies, involving nanoscale thin films, serve to elucidate the pivotal role that the low-energy electron-induced reactions play in high-energy radiation-induced chemical reactions in condensed matter. Although electron-stimulated desorption (ESD) experiments conducted during irradiation have yielded vital information relevant to primary or initial electron-induced processes, we wish to demonstrate in this review that analyzing the products following low-energy electron irradiation can provide new insights into radiation chemistry. This review presents studies of electron-induced reactions in nanoscale films of molecular species such as oxygen, nitrogen trifluoride, water, alkanes, alcohols, aldehydes, ketones, carboxylic acids, nitriles, halocarbons, alkane and phenyl thiols, thiophenes, ferrocene, amino acids, nucleotides, and DNA using post-irradiation techniques such as temperature-programmed desorption (TPD), reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), gel electrophoresis, and microarray fluorescence. Post-irradiation temperature-programmed desorption, in particular, has been shown to be useful in identifying labile radiolysis products as demonstrated by the first identification of methoxymethanol as a reaction product of methanol radiolysis. Results of post-irradiation studies have been used not only to identify radiolysis products, but also to determine the dynamics of electron-induced reactions. For example, studies of the radiolysis yield as a function of incident electron energy have shown that dissociative electron attachment plays an important role in the electron-induced single strand breaks in DNA leading to mutagenic damage. Studies such as these not only provide insight into the fundamentals of electron-molecule interactions in the condensed phase but also may provide information valuable to (a) furthering cost-efficient destruction of hazardous chemicals, (b) understanding the electron-induced decomposition of feed gases used in the plasma processing of semiconductor devices, (c) clarifying the role, if any, of low-energy electrons, produced by cosmic rays, contributing to the formation of the ozone hole by interacting with halocarbons and producing Cl atoms, (d) illuminating the dynamics of electron-induced oligomerization and/or polymerization, and (e) explicating the astrochemistry of icy grains.

Electronic health records to facilitate clinical research.

PubMed

Cowie, Martin R; Blomster, Juuso I; Curtis, Lesley H; Duclaux, Sylvie; Ford, Ian; Fritz, Fleur; Goldman, Samantha; Janmohamed, Salim; Kreuzer, Jörg; Leenay, Mark; Michel, Alexander; Ong, Seleen; Pell, Jill P; Southworth, Mary Ross; Stough, Wendy Gattis; Thoenes, Martin; Zannad, Faiez; Zalewski, Andrew

2017-01-01

Electronic health records (EHRs) provide opportunities to enhance patient care, embed performance measures in clinical practice, and facilitate clinical research. Concerns have been raised about the increasing recruitment challenges in trials, burdensome and obtrusive data collection, and uncertain generalizability of the results. Leveraging electronic health records to counterbalance these trends is an area of intense interest. The initial applications of electronic health records, as the primary data source is envisioned for observational studies, embedded pragmatic or post-marketing registry-based randomized studies, or comparative effectiveness studies. Advancing this approach to randomized clinical trials, electronic health records may potentially be used to assess study feasibility, to facilitate patient recruitment, and streamline data collection at baseline and follow-up. Ensuring data security and privacy, overcoming the challenges associated with linking diverse systems and maintaining infrastructure for repeat use of high quality data, are some of the challenges associated with using electronic health records in clinical research. Collaboration between academia, industry, regulatory bodies, policy makers, patients, and electronic health record vendors is critical for the greater use of electronic health records in clinical research. This manuscript identifies the key steps required to advance the role of electronic health records in cardiovascular clinical research.

Electron screening and its effects on big-bang nucleosynthesis

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

Wang Biao; Bertulani, C. A.; Balantekin, A. B.

We study the effects of electron screening on nuclear reaction rates occurring during the big-bang nucleosynthesis epoch. The sensitivity of the predicted elemental abundances on electron screening is studied in detail. It is shown that electron screening does not produce noticeable results in the abundances unless the traditional Debye-Hueckel model for the treatment of electron screening in stellar environments is enhanced by several orders of magnitude. This work rules out electron screening as a relevant ingredient to big-bang nucleosynthesis, confirming a previous study [see Itoh et al., Astrophys. J. 488, 507 (1997)] and ruling out exotic possibilities for the treatmentmore » of screening beyond the mean-field theoretical approach.« less

A Copmarative Review of Electronic Prescription Systems: Lessons Learned from Developed Countries

PubMed Central

Samadbeik, Mahnaz; Ahmadi, Maryam; Sadoughi, Farahnaz; Garavand, Ali

2017-01-01

This review study aimed to compare the electronic prescription systems in five selected countries (Denmark, Finland, Sweden, England, and the United States). Compared developed countries were selected by the identified selection process from the countries that have electronic prescription systems. Required data were collected by searching the valid databases, most widely used search engines, and visiting websites related to the national electronic prescription system of each country and also sending E-mails to the related organizations using specifically designed data collection forms. The findings showed that the electronic prescription system was used at the national, state, local, and area levels in the studied countries and covered the whole prescription process or part of it. There were capabilities of creating electronic prescription, decision support, electronically transmitting prescriptions from prescriber systems to the pharmacies, retrieving the electronic prescription at the pharmacy, electronic refilling prescriptions in all studied countries. The patient, prescriber, and dispenser were main human actors, as well as the prescribing and dispensing providers were main system actors of the Electronic Prescription Service. The selected countries have accurate, regular, and systematic plans to use electronic prescription system, and health ministry of these countries was responsible for coordinating and leading the electronic health. It is suggested to use experiences and programs of the leading countries to design and develop the electronic prescription systems. PMID:28331859

Transmission electron microscope studies of extraterrestrial materials

NASA Technical Reports Server (NTRS)

Keller, Lindsay P.

1995-01-01

Transmission Electron Microscopy, X-Ray spectrometry and electron-energy-loss spectroscopy are used to analyse carbon in interplanetary dust particles. Optical micrographs are shown depicting cross sections of the dust particles embedded in sulphur. Selected-area electron diffraction patterns are shown. Transmission Electron Microscope specimens of lunar soil were prepared using two methods: ion-milling and ultramicrotomy. A combination of high resolution TEM imaging and electron diffraction is used to characterize the opaque assemblages. The opaque assemblages analyzed in this study are dominated by ilmenite with lesser rutile and spinel exsolutions, and traces of Fe metal.

Development of a highly-sensitive Penning ionization electron spectrometer using the magnetic bottle effect

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

Ota, Masahiro; Ishiguro, Yuki; Nakajima, Yutaro

2016-02-01

This paper reports on a highly-sensitive retarding-type electron spectrometer for a continuous source of electrons, in which the electron collection efficiency is increased by utilizing the magnetic bottle effect. This study demonstrates an application to Penning ionization electron spectroscopy using collisional ionization with metastable He*(2{sup 3}S) atoms. Technical details and performances of the instrument are presented. This spectrometer can be used for studies of functional molecules and assemblies, and exterior electron densities are expected to be selectively observed by the Penning ionization.

REVIEWS OF TOPICAL PROBLEMS: lonization and quenching of excited atoms with the production of fast electrons

NASA Astrophysics Data System (ADS)

Kolokolov, N. B.; Blagoev, A. B.

1993-03-01

Studies of reactions involving excited atoms, which result in the release of electrons with energies exceeding the mean plasma electron energy, are reviewed. Particular attention is devoted to plasma electron spectroscopy (PES) which combines the advantages of studies of elementary plasma processes with those of traditional electron spectroscopy. Data obtained by investigating the following reactions are reported: chemoionization with the participation of two excited inert-gas atoms, Penning ionization of atoms and molecules by metastable helium atoms, and electron quenching of excited inert-gas atoms and mercury atoms. The effect of processes in which fast electrons are emitted on plasma properties is discussed.

Electron transfer complex between nitrous oxide reductase and cytochrome c552 from Pseudomonas nautica: kinetic, nuclear magnetic resonance, and docking studies.

PubMed

Dell'acqua, Simone; Pauleta, Sofia R; Monzani, Enrico; Pereira, Alice S; Casella, Luigi; Moura, José J G; Moura, Isabel

2008-10-14

The multicopper enzyme nitrous oxide reductase (N 2OR) catalyzes the final step of denitrification, the two-electron reduction of N 2O to N 2. This enzyme is a functional homodimer containing two different multicopper sites: CuA and CuZ. CuA is a binuclear copper site that transfers electrons to the tetranuclear copper sulfide CuZ, the catalytic site. In this study, Pseudomonas nautica cytochrome c 552 was identified as the physiological electron donor. The kinetic data show differences when physiological and artificial electron donors are compared [cytochrome vs methylviologen (MV)]. In the presence of cytochrome c 552, the reaction rate is dependent on the ET reaction and independent of the N 2O concentration. With MV, electron donation is faster than substrate reduction. From the study of cytochrome c 552 concentration dependence, we estimate the following kinetic parameters: K m c 552 = 50.2 +/- 9.0 muM and V max c 552 = 1.8 +/- 0.6 units/mg. The N 2O concentration dependence indicates a K mN 2 O of 14.0 +/- 2.9 muM using MV as the electron donor. The pH effect on the kinetic parameters is different when MV or cytochrome c 552 is used as the electron donor (p K a = 6.6 or 8.3, respectively). The kinetic study also revealed the hydrophobic nature of the interaction, and direct electron transfer studies showed that CuA is the center that receives electrons from the physiological electron donor. The formation of the electron transfer complex was observed by (1)H NMR protein-protein titrations and was modeled with a molecular docking program (BiGGER). The proposed docked complexes corroborated the ET studies giving a large number of solutions in which cytochrome c 552 is placed near a hydrophobic patch located around the CuA center.

Observation of autoionization in O 2 by an electron-electron coincidence method

NASA Astrophysics Data System (ADS)

Doering, J. P.; Yang, J.; Cooper, J. W.

1995-01-01

A strong transition to an autoionizing stata has been observed in O 2 at 16.83 ± 0.11 eV by means of a new electron-electron conincidence method. The method uses the fact that electrons arising from autoionizing states appear at a constant energy loss corresponding to the excitation energy of the autoionizing state rather than at a constant ionization potential as do electrons produced by direct ionization. Comparison of the present data with previous photoionization studies suggests that the autoionizing O 2 state is the same state deduced to be responsible for abnormal vibrational intensities in the O 2+X 2Πg ground state when 16.85 eV Ne(I) photons are used. These electron-electron coincidence experiments provide a direct new method for the study of autoionization produced by electron impact.

Electron-Impact Ionization and Dissociative Ionization of Biomolecules

NASA Technical Reports Server (NTRS)

Huo, Winifred M.; Chaban, Galina M.; Dateo, Christopher E.

2006-01-01

It is well recognized that secondary electrons play an important role in radiation damage to humans. Particularly important is the damage of DNA by electrons, potentially leading to mutagenesis. Molecular-level study of electron interaction with DNA provides information on the damage pathways and dominant mechanisms. Our study of electron-impact ionization of DNA fragments uses the improved binary-encounter dipole model and covers DNA bases, sugar phosphate backbone, and nucleotides. An additivity principle is observed. For example, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3(sup prime)- and C5 (sup prime)-deoxyribose-phospate cross sections, differing by less than 5%. Investigation of tandem double lesion initiated by electron-impact dissociative ionization of guanine, followed by proton reaction with the cytosine in the Watson-Crick pair, is currently being studied to see if tandem double lesion can be initiated by electron impact. Up to now only OH-induced tandem double lesion has been studied.

Study of electrostatic electron cyclotron parallel flow velocity shear instability in the magnetosphere of Saturn

NASA Astrophysics Data System (ADS)

Kandpal, Praveen; Pandey, R. S.

2018-05-01

In the present paper, the study of electrostatic electron cyclotron parallel flow velocity shear instability in presence of perpendicular inhomogeneous DC electric field has been carried out in the magnetosphere of Saturn. Dimensionless growth rate variation of electron cyclotron waves has been observed with respect to k⊥ ρe for various plasma parameters. Effect of velocity shear scale length (Ae), inhomogeneity (P/a), the ratio of ion to electron temperature (Ti/Te) and density gradient (ɛnρe) on the growth of electron cyclotron waves in the inner magnetosphere of Saturn has been studied and analyzed. The mathematical formulation and computation of dispersion relation and growth rate have been done by using the method of characteristic solution and kinetic approach. This theoretical analysis has been done taking the relevant data from the Cassini spacecraft in the inner magnetosphere of Saturn. We have considered ambient magnetic field data and other relevant data for this study at the radial distance of ˜4.82-5.00 Rs. In our study velocity shear and ion to electron temperature ratio have been observed to be the major sources of free energy for the electron cyclotron instability. The inhomogeneity of electric field caused a small noticeable impact on the growth rate of electrostatic electron cyclotron instability. Density gradient has been observed playing stabilizing effect on electron cyclotron instability.

Electron Transport and Nonlinear Optical Properties of Substituted Aryldimesityl Boranes: A DFT Study

PubMed Central

Pandith, Altaf Hussain; Islam, Nasarul

2014-01-01

A comprehensive theoretical study was carried out on a series of aryldimesityl borane (DMB) derivatives using Density Functional theory. Optimized geometries and electronic parameters like electron affinity, reorganization energy, frontiers molecular contours, polarizability and hyperpolarizability have been calculated by employing B3PW91/6-311++G (d, p) level of theory. Our results show that the Hammett function and geometrical parameters correlates well with the reorganization energies and hyperpolarizability for the series of DMB derivatives studied in this work. The orbital energy study reveals that the electron releasing substituents increase the LUMO energies and electron withdrawing substituents decrease the LUMO energies, reflecting the electron transport character of aryldimesityl borane derivatives. From frontier molecular orbitals diagram it is evident that mesityl rings act as the donor, while the phenylene and Boron atom appear as acceptors in these systems. The calculated hyperpolarizability of secondary amine derivative of DMB is 40 times higher than DMB (1). The electronic excitation contributions to the hyperpolarizability studied by using TDDFT calculation shows that hyperpolarizability correlates well with dipole moment in ground and excited state and excitation energy in terms of the two-level model. Thus the results of these calculations can be helpful in designing the DMB derivatives for efficient electron transport and nonlinear optical material by appropriate substitution with electron releasing or withdrawing substituents on phenyl ring of DMB system. PMID:25479382

Electronic prompts significantly increase response rates to postal questionnaires: a randomized trial within a randomized trial and meta-analysis.

PubMed

Clark, Laura; Ronaldson, Sarah; Dyson, Lisa; Hewitt, Catherine; Torgerson, David; Adamson, Joy

2015-12-01

To assess the effectiveness of sending electronic prompts to randomized controlled trial participants to return study questionnaires. A "trial within a trial" embedded within a study determining the effectiveness of chronic obstructive pulmonary disease (DOC) screening on smoking cessation. Those participants taking part in DOC who provided a mobile phone number and/or an electronic mail address were randomized to either receive an electronic prompt or no electronic prompt to return a study questionnaire. The results were combined with two previous studies in a meta-analysis. A total of 437 participants were randomized: 226 to the electronic prompt group and 211 to the control group. A total of 285 (65.2%) participants returned the follow-up questionnaire: 157 (69.5%) in the electronic prompt group and 128 (60.7%) in the control group [difference 8.8%; 95% confidence interval (CI): -0.11%, 17.7%; P = 0.05]. The mean time to response was 23 days in the electronic prompt group and 33 days in the control group (hazard ratio = 1.27; 95% CI: 1.105, 1.47). The meta-analysis of all three studies showed an increase in response rate of 7.1% (95% CI: 0.8%, 13.3%). The use of electronic prompts increased response rates and reduces the time to response. Copyright © 2015 Elsevier Inc. All rights reserved.

[Anaerobic reduction of humus/Fe (III) and electron transport mechanism of Fontibacter sp. SgZ-2].

PubMed

Ma, Chen; Yang, Gui-qin; Lu, Qin; Zhou, Shun-gui

2014-09-01

Humus and Fe(III) respiration are important extracellular respiration metabolism. Electron transport pathway is the key issue of extracellular respiration. To understand the electron transport properties and the environmental behavior of a novel Fe(III)- reducing bacterium, Fontibacter sp. SgZ-2, capacities of anaerobic humus/Fe(III) reduction and electron transport mechanisms with four electron acceptors were investigated in this study. The results of anaerobic batch experiments indicated that strain SgZ-2 had the ability to reduce humus analog [ 9,10-anthraquinone-2,6-disulfonic acid (AQDS) and 9,10-anthraquinone-2-sulfonic acid (AQS)], humic acids (HA), soluble Fe(III) (Fe-EDTA and Fe-citrate) and Fe(III) oxides [hydrous ferric oxide (HFO)]. Fermentative sugars (glucose and sucrose) were the most effective electron donors in the humus/Fe(III) reduction by strain SgZ-2. Additionally, differences of electron carrier participating in the process of electron transport with different electron acceptors (i. e. , oxygen, AQS, Fe-EDTA and HFO) were investigated using respiratory inhibitors. The results suggested that similar respiratory chain components were involved in the reducing process of oxygen and Fe-EDTA, including dehydrogenase, quinones and cytochromes b-c. In comparison, only dehydrogenase was found to participate in the reduction of AQS and HFO. In conclusion, different electron transport pathways may be employed by strain SgZ-2 between insoluble and soluble electron acceptors or among soluble electron acceptors. Preliminary models of electron transport pathway with four electron acceptors were proposed for strain SgZ-2, and the study of electron transport mechanism was explored to the genus Fontibacter. All the results from this study are expected to help understand the electron transport properties and the environmental behavior of the genus Fontibacter.

Fractional conductance oscillations in quantum rings: wave packet picture of transport in a few-electron system.

PubMed

Chwiej, T; Szafran, B

2013-04-17

We study electron transfer across a two-terminal quantum ring using a time-dependent description of the scattering process. For the considered scattering event the quantum ring is initially charged with one or two electrons, with another electron incident to the ring from the input channel. We study the electron transfer probability (T) as a function of the external magnetic field. We determine the periodicity of T for a varied number of electrons confined within the ring. For that purpose we develop a method to describe the wave packet dynamics for a few electrons participating in the scattering process, taking into full account the electron-electron correlations. We find that electron transfer across the quantum ring initially charged by a single electron acquires a distinct periodicity of half of the magnetic flux quantum (Φ0/2), corresponding to the formation of a transient two-electron state inside the ring. In the case of a three-electron scattering problem with two electrons initially occupying the ring, a period of Φ0/3 for T is formed in the limit of thin channels. The effect of disorder present in the confinement potential of the ring is also discussed.

Ab Initio Study of Electronic Excitation Effects on SrTiO 3

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

Zhao, Shijun; Zhang, Yanwen; Weber, William J.

Interaction of energetic ions or lasers with solids often induces electronic excitations that may modify material properties significantly. In this study, effects of electronic excitations on strontium titanate SrTiO 3 (STO) are investigated based on first-principles calculations. The lattice structure, electronic properties, lattice vibrational frequencies, and dynamical stabilities are studied in detail. The results suggest that electronic excitation induces charge redistribution that is mainly observed in Ti–O bonds. The electronic band gap increases with increasing electronic excitation, as excitation mainly induces depopulation of Ti 3d states. Phonon analysis indicates that there is a large phonon band gap induced by electronicmore » excitation because of the changes in the vibrational properties of Ti and O atoms. In addition, a new peak appears in the phonon density of states with imaginary frequencies, an indication of lattice instability. Further dynamics simulations confirm that STO undergoes transition to an amorphous structure under strong electronic excitations. In conclusion, the optical properties of STO under electronic excitation are consistent with the evolution of atomic and electronic structures, which suggests a possibility to probe the properties of STO in nonequilibrium state using optical measurement.« less

Ab Initio Study of Electronic Excitation Effects on SrTiO 3

DOE PAGES

Zhao, Shijun; Zhang, Yanwen; Weber, William J.

2017-11-14

Interaction of energetic ions or lasers with solids often induces electronic excitations that may modify material properties significantly. In this study, effects of electronic excitations on strontium titanate SrTiO 3 (STO) are investigated based on first-principles calculations. The lattice structure, electronic properties, lattice vibrational frequencies, and dynamical stabilities are studied in detail. The results suggest that electronic excitation induces charge redistribution that is mainly observed in Ti–O bonds. The electronic band gap increases with increasing electronic excitation, as excitation mainly induces depopulation of Ti 3d states. Phonon analysis indicates that there is a large phonon band gap induced by electronicmore » excitation because of the changes in the vibrational properties of Ti and O atoms. In addition, a new peak appears in the phonon density of states with imaginary frequencies, an indication of lattice instability. Further dynamics simulations confirm that STO undergoes transition to an amorphous structure under strong electronic excitations. In conclusion, the optical properties of STO under electronic excitation are consistent with the evolution of atomic and electronic structures, which suggests a possibility to probe the properties of STO in nonequilibrium state using optical measurement.« less

Electron and ion dynamics study of iron in warm dense matter regime by time-resolved XAS measurements and from first-principles

NASA Astrophysics Data System (ADS)

Ogitsu, T.; Fernandez-Paãella, A.; Correa, A.; Engelhorn, K.; Barbrel, B.; Prendergast, D. G.; Pemmaraju, D.; Beckwith, M.; Kraus, D.; Hamel, S.; Cho, B. I.; Jin, L.; Wong, J.; Heinman, P.; Collins, G. W.; Falcone, R.; Ping, Y.

2016-10-01

We present a study of the electron-phonon coupling of warm dense iron upon femtosecond laser excitation by time-resolved x-ray absorption near edge spectroscopy (XANES). The dynamics of iron in electron-ion non-equilibrium conditions was studied using ab-initio density-functional-theory (DFT) simulations combined with the Two Temperature Model (TTM) where spatial inhomogeneity of electron (and ion) temperature(s) due to short ballistic electron transport length in iron was explicitly taken into consideration. Detailed comparison between our simulation results and experiments indicates that the ion temperature dependence on specific heat and on electron-phonon coupling also plays a relevant role in modeling the relaxation dynamics of electrons and ions. These results are the first experimental evidence of the suppression of the electron-phonon coupling factor of a transition metal at electron temperatures ranging 5000- 10000 K. This work was performed under DOE contract DE-AC52-07NA27344 with support from OFES Early Career program and LLNL LDRD program.

Influence of pressure and volume on superconductivity in Mg1-xAlxB2 and Mg(B1-yCy)2

NASA Astrophysics Data System (ADS)

Sharma, Roopam; Singh, Namita; Khenata, R.; Varshney, Dinesh

2018-05-01

A quantitative analysis of observed parameters is studied that influences superconducting state in Al (C) doped MgB2. The three square well model with three interactions namely, the Coulomb the electron-phonon and the electron- charge fluctuations is based on indirect-exchange Cooper pairing of electrons (quasiparticles) via adhoc attractive charge fluctuations apart from phonons. The relevant energy gap expressions are solved. The indirect-exchange formalism provides a unique set of electronic parameters [electron-phonon (λσσph), electron-charge fluctuations (λσσpl), electron-electron (μσσ) and Coulomb screening parameter (μσσ*)] which, in particular, reproduce the dependence of Tc on Al (C) doping concentration and pressure P. Also, the variation in slope dTc/dP with increased Al (C) substitution (0 ≤ x ≤ 0.5)(0 ≤ y ≤ 0.125) is studied. Moreover, variation of dlnTc/dV Å-3 as a function of electron-phonon coupling strength and as a function of Coulomb screening parameter is studied.

A Randomized Controlled Trial of an Electronic Informed Consent Process

PubMed Central

Rothwell, Erin; Wong, Bob; Rose, Nancy C.; Anderson, Rebecca; Fedor, Beth; Stark, Louisa A.; Botkin, Jeffrey R.

2018-01-01

A pilot study assessed an electronic informed consent model within a randomized controlled trial (RCT). Participants who were recruited for the parent RCT project were randomly selected and randomized to either an electronic consent group (n = 32) or a simplified paper-based consent group (n = 30). Results from the electronic consent group reported significantly higher understanding of the purpose of the study, alternatives to participation, and who to contact if they had questions or concerns about the study. However, participants in the paper-based control group reported higher mean scores on some survey items. This research suggests that an electronic informed consent presentation may improve participant understanding for some aspects of a research study. PMID:25747685

A Validity and Reliability Study of the Basic Electronics Skills Self-Efficacy Scale (BESS)

ERIC Educational Resources Information Center

Korkmaz, Ö.; Korkmaz, M. K.

2016-01-01

The aim of this study is to improve a measurement tool to evaluate the self-efficacy of Electrical-Electronics Engineering students through their basic electronics skills. The sample group is composed of 124 Electrical-Electronics engineering students. The validity of the scale is analyzed with two different methods through factor analysis and…

Electronic properties of diphenyl-s-tetrazine and some related oligomers. An spectroscopic and theoretical study

NASA Astrophysics Data System (ADS)

Moral, Mónica; García, Gregorio; Peñas, Antonio; Garzón, Andrés; Granadino-Roldán, José M.; Melguizo, Manuel; Fernández-Gómez, Manuel

2012-10-01

This work presents a theoretical and spectroscopic study on the electronic and structural properties of the diphenyl-s-tetrazine molecule (Ph2Tz) and some oligomeric derivatives. Ph2Tz was synthesized through a variation of Pinner-type reaction which uses N-acetylcysteine as catalyst. Insight into the structure and electronic properties of the title compound was obtained through IR, Raman, UV-Vis spectra in different solvents, and theoretical calculations. Theoretical studies have been extended to different n-mers derivatives up to an ideal molecular wire through the oligomeric approximation, predicting this way electronic properties such as LUMO energy levels, electron affinity and reorganization energy in order to assess their possible applications in molecular electronics.

Opportunities and challenges in integrating electronic health records into undergraduate medical education: a national survey of clerkship directors.

PubMed

Hammoud, Maya M; Margo, Katherine; Christner, Jennifer G; Fisher, Jonathan; Fischer, Shira H; Pangaro, Louis N

2012-01-01

Few studies have reported on the utilization and the effect of electronic health records on the education of medical students. The purpose of this study was to describe the current use of electronic health records by medical students in the United States and explore the opportunities and challenges of integrating electronic health records into daily teaching of medical students. A survey with 24 questions regarding the use of electronic health records by medical students was developed by the Alliance for Clinical Educators and sent to clerkship directors across the United States. Both quantitative and qualitative responses were collected and analyzed to determine current access to and use of electronic health records by medical students. This study found that an estimated 64% of programs currently allow student use of electronic health records, of which only two thirds allowed students to write notes within the electronic record. Overall, clerkship directors' opinions on the effects of electronic health records on medical student education were neutral, and despite acknowledging many advantages to electronic health records, there were many concerns raised regarding their use in education. Medical students are using electronic health records at higher rates than physicians in practice. Although this is overall reassuring, educators have to be cautious about the limitations being placed on student's documentation in electronic health records as this can potentially have consequences on their training, and they need to explore ways to maximize the benefits of electronic health records in medical education.

Quality and accuracy of electronic pre-anesthesia evaluation forms.

PubMed

Almeshari, Meshari; Khalifa, Mohamed; El-Metwally, Ashraf; Househ, Mowafa; Alanazi, Abdullah

2018-07-01

Paper-based forms have been widely used to document patient health information for anesthesia; however, hospitals are now switching to electronic patient file documentation for anesthesia. The aim of this study is to compare the quality of paper-based and electronic pre-anesthesia assessment forms. The research conducted in this study was quasi-experimental using a pretest-posttest design without a control group. The study was conducted at King Abdulaziz Medical City, Riyadh (KAMC-RD) during November 2015. Paper-based forms were converted into electronic forms, and the paper-based pre-anesthesia forms were used during the first two weeks of the data collection period while electronic forms were completed in the last two weeks. The quality of each (electronic vs. paper) was evaluated with respect to missing items, errors, and unreadable items. The sample size included all 15 anesthetists working in the pre-anesthesia clinic at KAMC-RD. The anesthetists completed 25 pre-anesthesia forms daily during a five-day week schedule. A total of 500 patient forms were completed during the study (250 paper-based and 250 electronic forms). Anesthetists' satisfaction with the electronic pre-anesthesia form was also measured using a questionnaire. The electronic form shows significantly higher quality in all assessment categories (missing items, errors, and unreadable items; X² (2, N = 500) = 171.64, p < 0.001). The satisfaction survey found 81.65% of the anesthetists were satisfied with the electronic pre-anesthesia form for all questions. Our study demonstrates that the electronic pre-anesthesia form has better data quality, meets the expectations of anesthetists and aids to decrease missing key preoperative information. This type of approach is imperative for the safety of perioperative patients. Copyright © 2018. Published by Elsevier B.V.

Wigner distributions for an electron

NASA Astrophysics Data System (ADS)

Kumar, Narinder; Mondal, Chandan

2018-06-01

We study the Wigner distributions for a physical electron, which reveal the multidimensional images of the electron. The physical electron is considered as a composite system of a bare electron and photon. The Wigner distributions for unpolarized, longitudinally polarized and transversely polarized electron are presented in transverse momentum plane as well as in impact-parameter plane. The spin-spin correlations between the bare electron and the physical electron are discussed. We also evaluate all the leading twist generalized transverse momentum distributions (GTMDs) for electron.

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.

[Study of the effect of heat source separation distance on plasma physical properties in laser-pulsed GMAW hybrid welding based on spectral diagnosis technique].

PubMed

Liao, Wei; Hua, Xue-Ming; Zhang, Wang; Li, Fang

2014-05-01

In the present paper, the authors calculated the plasma's peak electron temperatures under different heat source separation distance in laser- pulse GMAW hybrid welding based on Boltzmann spectrometry. Plasma's peak electron densities under the corresponding conditions were also calculated by using the Stark width of the plasma spectrum. Combined with high-speed photography, the effect of heat source separation distance on electron temperature and electron density was studied. The results show that with the increase in heat source separation distance, the electron temperatures and electron densities of laser plasma did not changed significantly. However, the electron temperatures of are plasma decreased, and the electron densities of are plasma first increased and then decreased.

Cluster/Peace Electrons Velocity Distribution Function: Modeling the Strahl in the Solar Wind

NASA Technical Reports Server (NTRS)

Figueroa-Vinas, Adolfo; Gurgiolo, Chris; Goldstein, Melvyn L.

2008-01-01

We present a study of kinetic properties of the strahl electron velocity distribution functions (VDF's) in the solar wind. These are used to investigate the pitch-angle scattering and stability of the population to interactions with electromagnetic (whistler) fluctuations. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer. Our study focuses on the mechanisms that control and regulate the pitch-angle and stability of strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the electron heat-flux and temperature anisotropy. The goal is to check whether the strahl electrons are constrained by some instability (e.g., the whistler instability), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by fitting the VDF's to a spectral spherical harmonic model from which the moments are derived directly from the model coefficients.

Learning English with Electronic Textbooks on Tablet PCs

ERIC Educational Resources Information Center

Lin, Chih-cheng

2017-01-01

Previous studies on electronic textbooks were all survey studies of college students in the U.S.A. Their main findings revealed that using electronic textbooks and using print textbooks showed no statistical differences in learning achievements. As mobile devices became popular in classrooms, the present study was intended to confirm the…

Experimental Studies on Electronic Portfolios in Turkey: A Literature Review

ERIC Educational Resources Information Center

Alan, Selahattin; Sünbül, Ali Murat

2015-01-01

In this study, a literature review was conducted about an individual's selected efforts, products stored in electronic format, and electronic portfolios that reflect the development and capacity of multimedia systems. In this context, relevant experimental studies performed in Turkey are collected to show e-portfolio application forms, their…

Beta electron fluxes inside a magnetic plasma cavern: Calculation and comparison with experiment

NASA Astrophysics Data System (ADS)

Stupitskii, E. L.; Smirnov, E. V.; Kulikova, N. A.

2010-12-01

We study the possibility of electrostatic blanking of beta electrons in the expanding spherical blob of a radioactive plasma in a rarefied ionosphere. From numerical studies on the dynamics of beta electrons departing a cavern, we obtain the form of a function that determines the portion of departing electrons and calculate the flux density of beta electrons inside the cavern in relation to the Starfish Prime nuclear blast. We show that the flux density of electrons in geomagnetic flux tubes and inside the cavern depend on a correct allowance for the quantity of beta electrons returning to the cavern. On the basis of a physical analysis, we determine the approximate criterion for the return of electrons from a geomagnetic flux tube to the cavern. We compare calculation results in terms of the flux density of beta electrons inside the cavern with the recently published experimental results from operation Starfish Prime.

An Overview of Recent Studies in Junior College Electrical-Electronics Curriculum.

ERIC Educational Resources Information Center

Williams, Harry E.

This brief paper discusses in some detail several recent studies of electrical-electronics curricula at the junior college level and presents a 22-item bibliography of studies in this area. Comments based on the findings of the studies include: (1) A method of instruction, particulary applicable to the field of electronics education, seems to be…

Simulation study of interactions of Space Shuttle-generated electron beams with ambient plasmas

NASA Technical Reports Server (NTRS)

Lin, Chin S.

1992-01-01

This report summarizes results obtained through the support of NASA Grant NAGW-1936. The objective of this report is to conduct large scale simulations of electron beams injected into space. The topics covered include the following: (1) simulation of radial expansion of an injected electron beam; (2) simulations of the active injections of electron beams; (3) parameter study of electron beam injection into an ionospheric plasma; and (4) magnetosheath-ionospheric plasma interactions in the cusp.

The Development of a Framework for and a Model Teaching-Learning System in Electronics Technology for the Elementary School.

ERIC Educational Resources Information Center

Inaba, Lawrence Akio

Developing a rationale and a structure of knowledge as the basis for an instructional system in electronics technology and designing and developing a packaged instructional system in electronics technology for the sixth grade is the two-fold purpose of this study. The study identifies electronics technology within the broad framework of industrial…

A theoretical study of structural, opto-electronic and nonlinear properties of arylboroxine derivatives

NASA Astrophysics Data System (ADS)

Islam, Nasarul; Pandith, Altaf Hussain

2018-01-01

Density functional theory at CAM-B3LYP/6-311G++ (2d, 2p) level was employed to study the Triphenylboroxine derivatives ( TB) containing electron donating and electron substituents, for their charge transfer and nonlinear optical properties. The results reveal that electron donating groups facilitate the rapid electron injection as compared to unsubstituted TB. It was observed that upon substitution with electron donating groups, the TB derivatives show an increased double bond character in the B3-C18 bond indicating an increase in the degree of conjugation. The Frontier molecular orbital studies indicate that highest occupied molecular orbitals of the neutral molecules delocalize primarily over the three phenyl rings and bridging oxygen atoms, whereas the lowest unoccupied molecular orbitals localize largely on the two phenyl rings and the boron atoms. Further, the TD-DFT studies indicate that the maximum absorption band results from the electron transitions from the initial states that are contributed by the HOMO and HOMO-1 to the final states that are mainly contributed by the LUMOs. In addition, we have observed that the introduction of electron donating group to the TB-7 leads to more active nonlinear performance.

Study of the electronic structure of electron accepting cyano-films: TCNQversusTCNE.

PubMed

Capitán, Maria J; Álvarez, Jesús; Navio, Cristina

2018-04-18

In this article, we perform systematic research on the electronic structure of two closely related organic electron acceptor molecules (TCNQ and TCNE), which are of technological interest due to their outstanding electronic properties. These studies have been performed from the experimental point of view by the use electron spectroscopies (XPS and UPS) and supported theoretically by the use of ab-initio DFT calculations. The cross-check between both molecules allows us to identify the characteristic electronic features of each part of the molecules and their contribution to the final electronic structure. We can describe the nature of the band gap of these materials, and we relate this with the appearance of the shake-up features in the core level spectra. A band bending and energy gap reduction of the aforementioned electronic structure in contact with a metal surface are seen in the experimental results as well in the theoretical calculations. This behavior implies that the TCNQ thin film accepts electrons from the metal substrate becoming a Schottky n-junction.

Feasibility study for mega-electron-volt electron beam tomography.

PubMed

Hampel, U; Bärtling, Y; Hoppe, D; Kuksanov, N; Fadeev, S; Salimov, R

2012-09-01

Electron beam tomography is a promising imaging modality for the study of fast technical processes. But for many technical objects of interest x rays of several hundreds of keV energy are required to achieve sufficient material penetration. In this article we report on a feasibility study for fast electron beam computed tomography with a 1 MeV electron beam. The experimental setup comprises an electrostatic accelerator with beam optics, transmission target, and a single x-ray detector. We employed an inverse fan-beam tomography approach with radiographic projections being generated from the linearly moving x-ray source. Angular projections were obtained by rotating the object.

Microelectronics in Japan

NASA Astrophysics Data System (ADS)

Boulton, William R.

1995-02-01

The purpose of this JTEC study is to evaluate Japan's electronic manufacturing and packaging capabilities within the context of global economic competition. To carry out this study, the JTEC panel evaluated the framework of the Japanese consumer electronics industry and various technological and organizational factors that are likely to determine who will win and lose in the marketplace. This study begins with a brief overview of the electronics industry, especially as it operates in Japan today. Succeeding chapters examine the electronics infrastructure in Japan and take an in-depth look at the central issues of product development in order to identify those parameters that will determine future directions for electronic packaging technologies.

Microelectronics in Japan

NASA Technical Reports Server (NTRS)

Boulton, William R.

1995-01-01

The purpose of this JTEC study is to evaluate Japan's electronic manufacturing and packaging capabilities within the context of global economic competition. To carry out this study, the JTEC panel evaluated the framework of the Japanese consumer electronics industry and various technological and organizational factors that are likely to determine who will win and lose in the marketplace. This study begins with a brief overview of the electronics industry, especially as it operates in Japan today. Succeeding chapters examine the electronics infrastructure in Japan and take an in-depth look at the central issues of product development in order to identify those parameters that will determine future directions for electronic packaging technologies.

Differential cross sections for the electron impact ionization of Ar (3 p) atoms for equal energy final state electrons

NASA Astrophysics Data System (ADS)

Purohit, Ghanshyam; Singh, Prithvi

2017-06-01

The electron-impact ionization of inert gases for asymmetric final state energy sharing conditions has been studied in detail. However, there have been relatively few studies examining equal energy final state electrons. We report in this communication the results of triple differential cross sections (TDCSs) for electron impact ionization of Ar (3 p) for equal energy sharing of the outgoing electrons. We calculate TDCS in the modified distorted wave Born approximation (DWBA) formalism including post collision interaction (PCI) and polarization potential. We compare the results of our calculation with available measurements [Phys. Rev. A 87, 022712 (2013)]. We study the effect of PCI, target polarization on the trends of TDCS for the single ionization of Ar (3 p) targets.

A randomized controlled trial of an electronic informed consent process.

PubMed

Rothwell, Erin; Wong, Bob; Rose, Nancy C; Anderson, Rebecca; Fedor, Beth; Stark, Louisa A; Botkin, Jeffrey R

2014-12-01

A pilot study assessed an electronic informed consent model within a randomized controlled trial (RCT). Participants who were recruited for the parent RCT project were randomly selected and randomized to either an electronic consent group (n = 32) or a simplified paper-based consent group (n = 30). Results from the electronic consent group reported significantly higher understanding of the purpose of the study, alternatives to participation, and who to contact if they had questions or concerns about the study. However, participants in the paper-based control group reported higher mean scores on some survey items. This research suggests that an electronic informed consent presentation may improve participant understanding for some aspects of a research study. © The Author(s) 2014.

Dynamics and reactivity of trapped electrons on supported ice crystallites.

PubMed

Stähler, Julia; Gahl, Cornelius; Wolf, Martin

2012-01-17

The solvation dynamics and reactivity of localized excess electrons in aqueous environments have attracted great attention in many areas of physics, chemistry, and biology. This manifold attraction results from the importance of water as a solvent in nature as well as from the key role of low-energy electrons in many chemical reactions. One prominent example is the electron-induced dissociation of chlorofluorocarbons (CFCs). Low-energy electrons are also critical in the radiation chemistry that occurs in nuclear reactors. Excess electrons in an aqueous environment are localized and stabilized by the local rearrangement of the surrounding water dipoles. Such solvated or hydrated electrons are known to play an important role in systems such as biochemical reactions and atmospheric chemistry. Despite numerous studies over many years, little is known about the microscopic details of these electron-induced chemical processes, and interest in the fundamental processes involved in the reactivity of trapped electrons continues. In this Account, we present a surface science study of the dynamics and reactivity of such localized low-energy electrons at D(2)O crystallites that are supported by a Ru(001) single crystal metal surface. This approach enables us to investigate the generation and relaxation dynamics as well as dissociative electron attachment (DEA) reaction of excess electrons under well-defined conditions. They are generated by photoexcitation in the metal template and transferred to trapping sites at the vacuum interface of crystalline D(2)O islands. In these traps, the electrons are effectively decoupled from the electronic states of the metal template, leading to extraordinarily long excited state lifetimes on the order of minutes. Using these long-lived, low-energy electrons, we study the DEA to CFCl(3) that is coadsorbed at very low concentrations (∼10(12) cm(-2)). Using rate equations and direct measurement of the change of surface dipole moment, we estimated the electron surface density for DEA, yielding cross sections that are orders of magnitude higher than the electron density measured in the gas phase.

(Charge separation in photoredox reactions). Informal annual technical progress report, October 1, 1981-October 1, 1982. [N,N,N',N'tetramethylbenzidine

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

Kevan, L.

1982-10-21

During this period work has focused on the structural aspects of photoinduced charge separation in micellar media with initial forays into vesicular media. The primary techniques utilized are electron spin resonance and electron spin echo spectrometry. The analysis of electron spin echo modulation gives a unique handle on very weak hyperfine interactions thus providing a new structural tool for this general problem. Electron spin resonance and electron spin echo studies of the photoionization of N,N,N',N'tetramethylbenzidine (TMB) to give the cation radical have been carried out in anionic, cationic and nonionic micellar solutions frozen to 77/sup 0/K. The photoionization efficiency ofmore » TMB has also been studied in micelles with varying alkyl chain lengths of the surfactant. Stearic acid nitroxide spin probes have also been used to determine some structural aspects of the location of the neutral TMB molecule in anionic micelles before photoionization. The nitroxide work in which the nitroxide is acting as an electron acceptor also shows that a suitable electron acceptor can be located within the micellar structure. The effect of inorganic solutes on the efficiency of the photoionization of TMB in frozen micelles has also been studied. A series of electron scavenger studies have been initiated to study the effect on TMB photoionization efficiency. Electron spin echo detection of laser photogenerated TMB cation in liquid sodium dodecyl sulfate solutions at room temperature has recently been observed.« less

eV-TEM: Transmission electron microscopy in a low energy cathode lens instrument.

PubMed

Geelen, Daniël; Thete, Aniket; Schaff, Oliver; Kaiser, Alexander; van der Molen, Sense Jan; Tromp, Rudolf

2015-12-01

We are developing a transmission electron microscope that operates at extremely low electron energies, 0-40 eV. We call this technique eV-TEM. Its feasibility is based on the fact that at very low electron energies the number of energy loss pathways decreases. Hence, the electron inelastic mean free path increases dramatically. eV-TEM will enable us to study elastic and inelastic interactions of electrons with thin samples. With the recent development of aberration correction in cathode lens instruments, a spatial resolution of a few nm appears within range, even for these very low electron energies. Such resolution will be highly relevant to study biological samples such as proteins and cell membranes. The low electron energies minimize adverse effects due to radiation damage. Copyright © 2015. Published by Elsevier B.V.

Study of local currents in low dimension materials using complex injecting potentials

NASA Astrophysics Data System (ADS)

He, Shenglai; Covington, Cody; Varga, Kálmán

2018-04-01

A complex potential is constructed to inject electrons into the conduction band, mimicking electron currents in nanoscale systems. The injected electrons are time propagated until a steady state is reached. The local current density can then be calculated to show the path of the conducting electrons on an atomistic level. The method allows for the calculation of the current density vectors within the medium as a function of energy of the conducting electron. Using this method, we investigate the electron pathway of graphene nanoribbons in various structures, molecular junctions, and black phosphorus nanoribbons. By analyzing the current flow through the structures, we find strong dependence on the structural geometry and the energy of the injected electrons. This method may be of general use in the study of nano-electronic materials and interfaces.

Theoretical study on the spectroscopic and third-order nonlinear optical properties of two-dimensional charge-transfer pyrazine derivatives

NASA Astrophysics Data System (ADS)

Li, Haipeng; Zhang, Yi; Bi, Zetong; Xu, Runfeng; Li, Mingxue; Shen, Xiaopeng; Tang, Gang; Han, Kui

2017-12-01

In this paper, density functional theory method was employed to study the electronic absorption spectrum and electronic static second hyperpolarisability of X-shaped pyrazine derivatives with two-dimensional charge-transfer structures. Computational results show that the push-pull electron abilities of the substituent groups and the length of the conjugated chains affect the electronic spectrum and static second hyperpolarisability of the pyrazine derivatives. As the push-pull electron abilities of the substituent groups or the length of the conjugated chains increases, the frontier molecular orbital energy gap decreases, resulting in increased second hyperpolarisability and redshift of the electronic absorption bands. The electronic absorption spectra of the pyrazine derivatives maintain good transparency in the blue light band. The electronic static second hyperpolarisability exhibits a linear relationship to the frontier molecular orbital energy gap. Particularly, increasing/decreasing the push-pull electron abilities of the substituent groups considerably affect the static second hyperpolarisability in long conjugated systems, which is important to the modulation of molecular organic nonlinear optical (NLO) properties. The studied pyrazine derivatives show large third-order NLO response and good transparency in the blue light band and are thus promising candidates as NLO materials for photonics applications.

Evaluation of Electronic and Paper Textual Glosses on Second Language Vocabulary Learning and Reading Comprehension

ERIC Educational Resources Information Center

Lee, Ho; Lee, Hansol; Lee, Jang Ho

2016-01-01

Second language studies have supported the use of glossing for enhancing vocabulary learning. Along with technological developments, an increasing number of studies have examined electronic textual glossing in computer-assisted environments, yet only a small number of studies have compared electronic glossing to its traditional paper counterpart.…

Prototype electronic stethoscope vs. conventional stethoscope for auscultation of heart sounds.

PubMed

Kelmenson, Daniel A; Heath, Janae K; Ball, Stephanie A; Kaafarani, Haytham M A; Baker, Elisabeth M; Yeh, Daniel D; Bittner, Edward A; Eikermann, Matthias; Lee, Jarone

2014-08-01

In an effort to decrease the spread of hospital-acquired infections, many hospitals currently use disposable plastic stethoscopes in patient rooms. As an alternative, this study examines a prototype electronic stethoscope that does not break the isolation barrier between clinician and patient and may also improve the diagnostic accuracy of the stethoscope exam. This study aimed to investigate whether the new prototype electronic stethoscope improved auscultation of heart sounds compared to the standard conventional isolation stethoscope. In a controlled, non-blinded, cross-over study, clinicians were randomized to identify heart sounds with both the prototype electronic stethoscope and a conventional stethoscope. The primary outcome was the score on a 10-question heart sound identification test. In total, 41 clinicians completed the study. Subjects performed significantly better in the identification of heart sounds when using the prototype electronic stethoscope (median = 9 [7-10] vs. 8 [6-9] points, p value <0.0001). Subjects also significantly preferred the prototype electronic stethoscope. Clinicians using a new prototype electronic stethoscope achieved greater accuracy in identification of heart sounds and also universally favoured the new device, compared to the conventional stethoscope.

Protection of DNA against low-energy electrons by amino acids: a first-principles molecular dynamics study.

PubMed

Gu, Bin; Smyth, Maeve; Kohanoff, Jorge

2014-11-28

Using first-principles molecular dynamics simulations, we have investigated the notion that amino acids can play a protective role when DNA is exposed to excess electrons produced by ionizing radiation. In this study we focus on the interaction of glycine with the DNA nucleobase thymine. We studied thymine-glycine dimers and a condensed phase model consisting of one thymine molecule solvated in amorphous glycine. Our results show that the amino acid acts as a protective agent for the nucleobase in two ways. If the excess electron is initially captured by the thymine, then a proton is transferred in a barrier-less way from a neighboring hydrogen-bonded glycine. This stabilizes the excess electron by reducing the net partial charge on the thymine. In the second mechanism the excess electron is captured by a glycine, which acts as a electron scavenger that prevents electron localization in DNA. Both these mechanisms introduce obstacles to further reactions of the excess electron within a DNA strand, e.g. by raising the free energy barrier associated with strand breaks.

Electronic monitoring of patient adherence to oral antihypertensive medical treatment: a systematic review.

PubMed

Christensen, Arne; Osterberg, Lars G; Hansen, Ebba Holme

2009-08-01

Poor patient adherence is often the reason for suboptimal blood pressure control. Electronic monitoring is one method of assessing adherence. The aim was to systematically review the literature on electronic monitoring of patient adherence to self-administered oral antihypertensive medications. We searched the Pubmed, Embase, Cinahl and Psychinfo databases and websites of suppliers of electronic monitoring devices. The quality of the studies was assessed according to the quality criteria proposed by Haynes et al. Sixty-two articles were included; three met the criteria proposed by Haynes et al. and nine reported the use of electronic adherence monitoring for feedback interventions. Adherence rates were generally high, whereas average study quality was low with a recent tendency towards improved quality. One study detected investigator fraud based on electronic monitoring data. Use of electronic monitoring of patient adherence according to the quality criteria proposed by Haynes et al. has been rather limited during the past two decades. Electronic monitoring has mainly been used as a measurement tool, but it seems to have the potential to significantly improve blood pressure control as well and should be used more widely.

Status of Plasma Electron Hose Instability Studies in FACET

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

Adli, Erik; /U. Oslo; England, Robert Joel

In the FACET plasma-wakefield acceleration experiment a dense 23 GeV electron beam will interact with lithium and cesium plasmas, leading to plasma ion-channel formation. The interaction between the electron beam and the plasma sheath-electrons may lead to a fast growing electron hose instability. By using optics dispersion knobs to induce a controlled z-x tilt along the beam entering the plasma, we investigate the transverse behavior of the beam in the plasma as function of the tilt. We seek to quantify limits on the instability in order to further explore potential limitations on future plasma wakefield accelerators due to the electronmore » hose instability. The FACET plasma-wakefield experiment at SLAC will study beam driven plasma wakefield acceleration. A dense 23 GeV electron beam will interact with lithium or cesium plasma, leading to plasma ion-channel formation. The interaction between the electron beam and the plasma sheath-electrons drives the electron hose instability, as first studied by Whittum. While Ref. [2] indicates the possibility of a large instability growth rate for typical beam and plasma parameters, other studies including have shown that several physical effects may mitigate the hosing growth rate substantially. So far there has been no quantitative benchmarking of experimentally observed hosing in previous experiments. At FACET we aim to perform such benchmarking by for example inducing a controlled z-x tilt along the beamentering the plasma, and observing the transverse behavior of the beam in the plasma as function. The long-term objective of these studies is to quantify potential limitations on future plasma wakefield accelerators due to the electron hose instability.« less

Auditing The Completeness and Legibility of Computerized Radiological Request Forms.

PubMed

Al Muallem, Yahya; Al Dogether, Majed; Househ, Mowafa; Saddik, Basema

2017-11-04

Certain Saudi healthcare organizations transfer outpatients to medical imaging departments for radiological examinations in a manual process that relies on the use of paper-based forms. With the increased implementation of electronic medical records in Saudi Hospitals, little is known about the completeness and legibility of information captured in  electronic-based medical imaging forms. The purpose of this study is to audit the completeness and legibility of medical imaging paper-based forms in comparison with electronic-based medical imaging forms. As a secondary objective, we also examined the number of errors found on the forms.An observational retrospective cross-sectional study was utilized to audit the completeness and legibility of both paper and electronic forms collected between March 1 and May 15, 2015. The study measured the association among categorical variables using Chi-Square analysis. The results of this investigation show a significant association between form completion and type of record (i.e., paper vs. electronic) where electronic-based systems were found to be more complete than paper-based records. Electrnoic based records were also found to improve form legibility, promote user adherence to complete the forms and minimize entry errors. In conclusion, electronic-based medical imaging forms are more complete and legible than paper based forms. Future studies should evaluate other hospitals and compare both legibility and completeness of electronic-based medical imaging forms and conduct usability evaluation studies with users to explore the impacts of system design on both completeness and legibility of electronic forms, in general, but more specifically, electronic-based medical imaging forms.

Electron energy distribution function in the divertor region of the COMPASS tokamak during neutral beam injection heating

NASA Astrophysics Data System (ADS)

Hasan, E.; Dimitrova, M.; Havlicek, J.; Mitošinková, K.; Stöckel, J.; Varju, J.; Popov, Tsv K.; Komm, M.; Dejarnac, R.; Hacek, P.; Panek, R.; the COMPASS Team

2018-02-01

This paper presents the results from swept probe measurements in the divertor region of the COMPASS tokamak in D-shaped, L-mode discharges, with toroidal magnetic field BT = 1.15 T, plasma current Ip = 180 kA and line-average electron densities varying from 2 to 8×1019 m-3. Using neutral beam injection heating, the electron energy distribution function is studied before and during the application of the beam. The current-voltage characteristics data are processed using the first-derivative probe technique. This technique allows one to evaluate the plasma potential and the real electron energy distribution function (respectively, the electron temperatures and densities). At the low average electron density of 2×1019 m-3, the electron energy distribution function is bi-Maxwellian with a low-energy electron population with temperatures 4-6 eV and a high-energy electron group 12-25 eV. As the line-average electron density is increased, the electron temperatures decrease. At line-average electron densities above 7×1019 m-3, the electron energy distribution function is found to be Maxwellian with a temperature of 6-8.5 eV. The effect of the neutral beam injection heating power in the divertor region is also studied.

Oxidation of Carbon Nanotubes in an Ionizing Environment.

PubMed

Koh, Ai Leen; Gidcumb, Emily; Zhou, Otto; Sinclair, Robert

2016-02-10

In this work, we present systematic studies on how an illuminating electron beam which ionizes molecular gas species can influence the mechanism of carbon nanotube oxidation in an environmental transmission electron microscope (ETEM). We found that preferential attack of the nanotube tips is much more prevalent than for oxidation in a molecular gas environment. We establish the cumulative electron doses required to damage carbon nanotubes from 80 keV electron beam irradiation in gas versus in high vacuum. Our results provide guidelines for the electron doses required to study carbon nanotubes within or without a gas environment, to determine or ameliorate the influence of the imaging electron beam. This work has important implications for in situ studies as well as for the oxidation of carbon nanotubes in an ionizing environment such as that occurring during field emission.

Experimental and DFT Studies of the Electron-Withdrawing Ability of Perfluoroalkyl (R F) Groups: Electron Affinities of PAH(R F) n Increase Significantly with Increasing R F Chain Length

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

San, Long K.; Spisak, Sarah N.; Dubceac, Cristina

Two series of aromatic compounds with perfluoroalkyl (RF) groups of increasing length, 1,3,5,7-naphthalene(RF)4 and 1,3,5,7,9-corannulene(RF)5, have been prepared and their electronic properties studied by low-temperature PES (i.e., gas-phase electron affinity (EA) measurements). These and many related compounds were also studied by DFT calculations. The data demonstrate unambiguously that the electron-withdrawing ability of RF substituents increases significantly and uniformly from CF3 to C2F5 to n-C3F7 to n-C4F9.

Experimental and DFT Studies of the Electron-Withdrawing Ability of Perfluoroalkyl (R-F) Groups: Electron Affinities of PAH(R-F)(n) Increase Significantly with Increasing R-F Chain Length

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

San, Long K.; Spisak, Sarah N.; Dubceac, Cristina

2018-01-26

Two series of aromatic compounds with perfluoroalkyl (RF) groups of increasing length, 1,3,5,7-naphthalene(RF)4 and 1,3,5,7,9-corannulene(RF)5, have been prepared and their electronic properties studied by low-temperature PES (i.e., gas-phase electron affinity (EA) measurements). These and many related compounds were also studied by DFT calculations. The data demonstrate unambiguously that the electron-withdrawing ability of RF substituents increases significantly and uniformly from CF3 to C2F5 to n-C3F7 to n-C4F9.

Numerical studies of electron dynamics in oblique quasi-perpendicular collisionless shock waves

NASA Technical Reports Server (NTRS)

Liewer, P. C.; Decyk, V. K.; Dawson, J. M.; Lembege, B.

1991-01-01

Linear and nonlinear electron damping of the whistler precursor wave train to low Mach number quasi-perpendicular oblique shocks is studied using a one-dimensional electromagnetic plasma simulation code with particle electrons and ions. In some parameter regimes, electrons are observed to trap along the magnetic field lines in the potential of the whistler precursor wave train. This trapping can lead to significant electron heating in front of the shock for low beta(e). Use of a 64-processor hypercube concurrent computer has enabled long runs using realistic mass ratios in the full particle in-cell code and thus simulate shock parameter regimes and phenomena not previously studied numerically.

High pressure and synchrotron radiation studies of solid state electronic instabilities

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

Pifer, J.H.; Croft, M.C.

This report discusses Eu and General Valence Instabilities; Ce Problem: L{sub 3} Spectroscopy Emphasis; Bulk Property Emphasis; Transition Metal Compound Electronic Structure; Electronic Structure-Phonon Coupling Studies; High Temperature Superconductivity and Oxide Materials; and Novel Materials Collaboration with Chemistry.

Photoinduced Bimolecular Electron Transfer in Ionic Liquids: Cationic Electron Donors

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

Wu, Boning; Liang, Min; Zmich, Nicole

Recently, we have reported a systematic study of photoinduced electron-transfer reactions in ionic liquid solvents using neutral and anionic electron donors and a series of cyano-substituted anthracene acceptors [Wu, B.; Maroncelli, M.; Castner, E. W., Jr.Photoinduced Bimolecular Electron Transfer in Ionic Liquids. J. Am. Chem. Soc.139, 2017, 14568]. In this paper, we report complementary results for a cationic class of 1-alkyl-4-dimethylaminopyridinium electron donors. Reductive quenching of cyano-substituted anthracene fluorophores by these cationic quenchers is studied in solutions of acetonitrile and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Varying the length of the alkyl chain permits tuning of the quencher diffusivities in solution.more » The observed quenching kinetics are interpreted using a diffusion-reaction analysis. Finally, together with results from the prior study, these results show that the intrinsic electron-transfer rate constant does not depend on the quencher charge in this family of reactions.« less

Photoinduced Bimolecular Electron Transfer in Ionic Liquids: Cationic Electron Donors

DOE PAGES

Wu, Boning; Liang, Min; Zmich, Nicole; ...

2018-01-29

Recently, we have reported a systematic study of photoinduced electron-transfer reactions in ionic liquid solvents using neutral and anionic electron donors and a series of cyano-substituted anthracene acceptors [Wu, B.; Maroncelli, M.; Castner, E. W., Jr.Photoinduced Bimolecular Electron Transfer in Ionic Liquids. J. Am. Chem. Soc.139, 2017, 14568]. In this paper, we report complementary results for a cationic class of 1-alkyl-4-dimethylaminopyridinium electron donors. Reductive quenching of cyano-substituted anthracene fluorophores by these cationic quenchers is studied in solutions of acetonitrile and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Varying the length of the alkyl chain permits tuning of the quencher diffusivities in solution.more » The observed quenching kinetics are interpreted using a diffusion-reaction analysis. Finally, together with results from the prior study, these results show that the intrinsic electron-transfer rate constant does not depend on the quencher charge in this family of reactions.« less

Advances in positron and electron scattering*

NASA Astrophysics Data System (ADS)

Limão-Vieira, Paulo; García, Gustavo; Krishnakumar, E.; Petrović, Zoran; Sullivan, James; Tanuma, Hajime

2016-10-01

The topical issue on Advances in Positron and Electron Scattering" combines contributions from POSMOL 2015 together with others devoted to celebrate the unprecedented scientific careers of our loyal colleagues and trusted friends Steve Buckman (Australian National University, Australia) and Michael Allan (University of Fribourg, Switzerland) on the occasion of their retirements. POSMOL 2015, the XVIII International Workshop on Low-Energy Positron and Positronium Physics and the XIX International Symposium on Electron-Molecule Collisions and Swarms, was held at Universidade NOVA de Lisboa, Lisboa, Portugal, from 17-20 July 2015. The international workshop and symposium allowed to achieve a very privileged forum of sharing and developing our scientific expertise on current aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and related topics, as well as electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent developments in the study of swarms are also fully addressed.

ELECTRON AS A FUNDAMENTAL ELEMENTARY PARTICLE. PART I

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

Kakinuma, U.

1962-12-01

Elementary particles may be nothing but an electron existing under a certain condition, or a group of electrons that are formed to a certain combined state. Therefore, the knowledge of the electron structure is the starting point of our investigation about matter. To obtain the structure, the electron in an absolutely statical state is considered first and is studied by use of the gage- transformation defined in a modified way. This leads to the discovery oi a revised expression for the electromagnetic energy-tensor inside the electron as well as the wave equation for the electron formally similar to the Schrodingermore » equation for the hydrogen atom. However, our wave equation is interpreted as indicating the mode of energy distribution in the electron. To linearize the wave equation, a complex Riemannian geometry has been developed with results promising to be serviceable for further studies. (auth)« less

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

Electron crystallography and aquaporins.

PubMed

Schenk, Andreas D; Hite, Richard K; Engel, Andreas; Fujiyoshi, Yoshinori; Walz, Thomas

2010-01-01

Electron crystallography of two-dimensional (2D) crystals can provide information on the structure of membrane proteins at near-atomic resolution. Originally developed and used to determine the structure of bacteriorhodopsin (bR), electron crystallography has recently been applied to elucidate the structure of aquaporins (AQPs), a family of membrane proteins that form pores mostly for water but also other solutes. While electron crystallography has made major contributions to our understanding of the structure and function of AQPs, structural studies on AQPs, in turn, have fostered a number of technical developments in electron crystallography. In this contribution, we summarize the insights electron crystallography has provided into the biology of AQPs, and describe technical advancements in electron crystallography that were driven by structural studies on AQP 2D crystals. In addition, we discuss some of the lessons that were learned from electron crystallographic work on AQPs. Copyright © 2010 Elsevier Inc. All rights reserved.

[Study on the distribution of plasma parameters in electrodeless lamp using emission spectrometry].

PubMed

Wang, Chang-Quan; Zhang, Gui-Xin; Wang, Xin-Xin; Shao, Ming-Song; Dong, Jin-Yang; Wang, Zan-Ji

2011-09-01

Electrodeless lamp in pear shape was ignited using inductively coupled discharge setup and Ar-Hg mixtures as working gas. The changes in electronic temperature and density with axial and radial positions at 5 s of igniting were studied by means of emission spectrometry. The changes in electronic temperature were obtained according to the Ar line intensity ratio of 425.9 nm/ 750.4 nm. And the variations in electronic density were analyzed using 750.4 nm line intensity. It was found that plasma electronic temperature and density is various at different axial or radial positions. The electronic temperatures first increase, then decrease, and then increase quickly, and finally decline. While the electronic density firstly increase quickly, the decrease, and then rise slowly and finally decline again with axial distance increasing. With radial distance increasing, electronic temperature increases to a stable area, then continues to rise, while electronic density decreases.

Average stopping powers for electron and photon sources for radiobiological modeling and microdosimetric applications

NASA Astrophysics Data System (ADS)

Vassiliev, Oleg N.; Kry, Stephen F.; Grosshans, David R.; Mohan, Radhe

2018-03-01

This study concerns calculation of the average electronic stopping power for photon and electron sources. It addresses two problems that have not yet been fully resolved. The first is defining the electron spectrum used for averaging in a way that is most suitable for radiobiological modeling. We define it as the spectrum of electrons entering the sensitive to radiation volume (SV) within the cell nucleus, at the moment they enter the SV. For this spectrum we derive a formula that combines linearly the fluence spectrum and the source spectrum. The latter is the distribution of initial energies of electrons produced by a source. Previous studies used either the fluence or source spectra, but not both, thereby neglecting a part of the complete spectrum. Our derived formula reduces to these two prior methods in the case of high and low energy sources, respectively. The second problem is extending electron spectra to low energies. Previous studies used an energy cut-off on the order of 1 keV. However, as we show, even for high energy sources, such as 60Co, electrons with energies below 1 keV contribute about 30% to the dose. In this study all the spectra were calculated with Geant4-DNA code and a cut-off energy of only 11 eV. We present formulas for calculating frequency- and dose-average stopping powers, numerical results for several important electron and photon sources, and tables with all the data needed to use our formulas for arbitrary electron and photon sources producing electrons with initial energies up to  ∼1 MeV.

User-Centered Design, Experience, and Usability of an Electronic Consent User Interface to Facilitate Informed Decision-Making in an HIV Clinic.

PubMed

Ramos, S Raquel

2017-11-01

Health information exchange is the electronic accessibility and transferability of patient medical records across various healthcare settings and providers. In some states, patients have to formally give consent to allow their medical records to be electronically shared. The purpose of this study was to apply a novel user-centered, multistep, multiframework approach to design and test an electronic consent user interface, so patients with HIV can make more informed decisions about electronically sharing their health information. This study consisted of two steps. Step 1 was a cross-sectional, descriptive, qualitative study that used user-centric design interviews to create the user interface. This informed Step 2. Step 2 consisted of a one group posttest to examine perceptions of usefulness, ease of use, preference, and comprehension of a health information exchange electronic consent user interface. More than half of the study population had college experience, but challenges remained with overall comprehension regarding consent. The user interface was not independently successful, suggesting that in addition to an electronic consent user interface, human interaction may also be necessary to address the complexities associated with consenting to electronically share health information. Comprehension is key factor in the ability to make informed decisions.

Electronic structures of GaAs/AlxGa1-xAs quantum double rings

PubMed Central

Xia, Jian-Bai

2006-01-01

In the framework of effective mass envelope function theory, the electronic structures of GaAs/AlxGa1-xAs quantum double rings (QDRs) are studied. Our model can be used to calculate the electronic structures of quantum wells, wires, dots, and the single ring. In calculations, the effects due to the different effective masses of electrons and holes in GaAs and AlxGa1-xAs and the valence band mixing are considered. The energy levels of electrons and holes are calculated for different shapes of QDRs. The calculated results are useful in designing and fabricating the interrelated photoelectric devices. The single electron states presented here are useful for the study of the electron correlations and the effects of magnetic fields in QDRs.

Transport of secondary electrons and reactive species in ion tracks

NASA Astrophysics Data System (ADS)

Surdutovich, Eugene; Solov'yov, Andrey V.

2015-08-01

The transport of reactive species brought about by ions traversing tissue-like medium is analysed analytically. Secondary electrons ejected by ions are capable of ionizing other molecules; the transport of these generations of electrons is studied using the random walk approximation until these electrons remain ballistic. Then, the distribution of solvated electrons produced as a result of interaction of low-energy electrons with water molecules is obtained. The radial distribution of energy loss by ions and secondary electrons to the medium yields the initial radial dose distribution, which can be used as initial conditions for the predicted shock waves. The formation, diffusion, and chemical evolution of hydroxyl radicals in liquid water are studied as well. COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy.

Electron-beam generated porous dextran gels: experimental and quantum chemical studies.

PubMed

Naumov, Sergej; Knolle, Wolfgang; Becher, Jana; Schnabelrauch, Matthias; Reichelt, Senta

2014-06-01

The aim of this work was to investigate the reaction mechanism of electron-beam generated macroporous dextran cryogels by quantum chemical calculation and electron paramagnetic resonance measurements. Electron-beam radiation was used to initiate the cross-linking reaction of methacrylated dextran in semifrozen aqueous solutions. The pore morphology of the resulting cryogels was visualized by scanning electron microscopy. Quantum chemical calculations and electron paramagnetic resonance studies provided information on the most probable reaction pathway and the chain growth radicals. The most probable reaction pathway was a ring opening reaction and the addition of a C-atom to the double-bond of the methacrylated dextran molecule. First detailed quantum chemical calculation on the reaction mechanism of electron-beam initiated cross-linking reaction of methacrylated dextran are presented.

Electron string phenomenon: physics and use

NASA Astrophysics Data System (ADS)

Donets, Evgeny D.

2004-01-01

Electron string phenomenon arises as a result of phase transition of a state of multiply reflected electron beam to this new discovered state of one component electron plasma and can be easily observed in the reflex mode of EBIS operation. The transition goes via a strong instability, which causes considerable electron energy spread, which in its turn suppresses the instability. Electron string state is a stationary state of hot pure electron plasma, which is heated by injected electron beam and cooled because of electron loses. Electron string is quiet in broad regions of experimental parameters, so that it is used for confinement and ionization of positive ions by electron impact to highly charge states similar to electron beams in EBIS. Application of electron strings instead of electron beams for ion production allows to save about 99% of electric power of electron beam and simultaneously to improve reliability of an ion source considerably. The JINR EBIS `Krion-2' in the string mode of operation is used for production of N7+, Ar16+ and Fe24+ ion beams and their acceleration to relativistic energies on the facility of the JINR super conducting one turn injection synchrotron `Nuklotron'. The tubular electron string possibly can exist and it is under study now theoretically and experiments are prepared now. Estimations show that a Tubular Electron String Ion Source (TESIS) could have up to three orders of magnitude higher ion output then a Linear one (LESIS). In frames of nuclear astrophysics electron strings can be used for research of fusion nuclear reactions at low energies in conditions when both beam and target nuclei do not carry orbital electrons. The project NARITA — Nuclear Astrophysics Researches in an Ion Trap Apparatus is proposed. Polarization effects also can be studied.

The low-lying electronic excitations in long polyenes: A PPP-MRD-CI study

NASA Astrophysics Data System (ADS)

Tavan, Paul; Schulten, Klaus

1986-12-01

A correct description of the electronic excitations in polyenes demands that electron correlation is accounted for correctly. Very large expansions are necessary including many-electron configurations with at least one, two, three, and four electrons promoted from the Hartree-Fock ground state. The enormous size of such expansions had prohibited accurate computations of the spectra for polyenes with more than ten π electrons. We present a multireference double excitation configuration interaction method (MRD-CI) which allows such computations for polyenes with up to 16 π electrons. We employ a Pariser-Parr-Pople (PPP) model Hamiltonian. For short polyenes with up to ten π electrons our calculations reproduce the excitation energies resulting from full-CI calculations. We extend our calculations to study the low-lying electronic excitations of the longer polyenes, in particular, the gap between the first optically forbidden and the first optically allowed excited singlet state. The size of this gap is shown to depend strongly on the degree of bond alternation and on the dielectric shielding of the Coulomb repulsion between the π electrons.

A Statitstical Study of Energetic Electron Phase Space Density with RBSP and BD-IES Data

NASA Astrophysics Data System (ADS)

Chen, X.; Zong, Q.; Zhou, X.; Zou, H.; Wang, Y.

2017-12-01

We present a statistical study of energetic electron phase space density (PSD) with combined observations from the Magnetic Electron Ion Spectrometer (MagEIS) instruments onboard the Van Allen Probes and the Image Electron Spectrometer (BD-IES) onboard an inclined geosynchronous orbit satellite. The electron PSD as a function of the adiabatic invariants is derived using one year data (Nov. 2015 to Oct. 2016) of these instruments. The orbits of the satellites cover a wide range of L-shells, allowing for the distribution of electron PSD throughout the radiation belt (L* 1 to 10). A persistent peak of energetic electron ( 30 to 1000 MeV/G) PSD is unambiguously identified at L* 5.5, which may help to understand the role of local acceleration and radial diffusion in the dynamics of energetic electrons. In addition, the electron PSD shows a power-law distribution with the exponent varying from about -2 to -4 depending on L*. The variance of electron PSD during storm and substorm activities indicating by SYMH and AE indices are also discussed.

An Overview of Electron Acceptors in Microbial Fuel Cells

PubMed Central

Ucar, Deniz; Zhang, Yifeng; Angelidaki, Irini

2017-01-01

Microbial fuel cells (MFC) have recently received increasing attention due to their promising potential in sustainable wastewater treatment and contaminant removal. In general, contaminants can be removed either as an electron donor via microbial catalyzed oxidization at the anode or removed at the cathode as electron acceptors through reduction. Some contaminants can also function as electron mediators at the anode or cathode. While previous studies have done a thorough assessment of electron donors, cathodic electron acceptors and mediators have not been as well described. Oxygen is widely used as an electron acceptor due to its high oxidation potential and ready availability. Recent studies, however, have begun to assess the use of different electron acceptors because of the (1) diversity of redox potential, (2) needs of alternative and more efficient cathode reaction, and (3) expanding of MFC based technologies in different areas. The aim of this review was to evaluate the performance and applicability of various electron acceptors and mediators used in MFCs. This review also evaluated the corresponding performance, advantages and disadvantages, and future potential applications of select electron acceptors (e.g., nitrate, iron, copper, perchlorate) and mediators. PMID:28469607

New Advancements in the Study of the Uniform Electron Gas with Full Configuration Interaction Quantum Monte Carlo

NASA Astrophysics Data System (ADS)

Ruggeri, Michele; Luo, Hongjun; Alavi, Ali

Full Configuration Interaction Quantum Monte Carlo (FCIQMC) is able to give remarkably accurate results in the study of atoms and molecules. The study of the uniform electron gas (UEG) on the other hand has proven to be much harder, particularly in the low density regime. The source of this difficulty comes from the strong interparticle correlations that arise at low density, and essentially forbid the study of the electron gas in proximity of Wigner crystallization. We extend a previous study on the three dimensional electron gas computing the energy of a fully polarized gas for N=27 electrons at high and medium density (rS = 0 . 5 to 5 . 0). We show that even when dealing with a polarized UEG the computational cost of the study of systems with rS > 5 . 0 is prohibitive; in order to deal with correlations and to extend the density range that to be studied we introduce a basis of localized states and an effective transcorrelated Hamiltonian.

A study on the anisole-water complex by molecular beam-electronic spectroscopy and molecular mechanics calculations.

PubMed

Becucci, M; Pietraperzia, G; Pasquini, M; Piani, G; Zoppi, A; Chelli, R; Castellucci, E; Demtroeder, W

2004-03-22

An experimental and theoretical study is made on the anisole-water complex. It is the first van der Waals complex studied by high resolution electronic spectroscopy in which the water is seen acting as an acid. Vibronically and rotationally resolved electronic spectroscopy experiments and molecular mechanics calculations are used to elucidate the structure of the complex in the ground and first electronic excited state. Some internal dynamics in the system is revealed by high resolution spectroscopy. (c) 2004 American Institute of Physics

Electronic, thermoelectric and transport properties of cesium cadmium trifluoride: A DFT study

NASA Astrophysics Data System (ADS)

Abraham, Jisha Annie; Pagare, G.; Sanyal, Sankar P.

2018-04-01

The full potential linearized augmented plane wave method based on density functional theory is employed to investigate the electronic structure of CsCdF3. The electronic properties of this compound have been studied from the band structure plot and density of states. The presence of indirect energy gap reveals its insulating nature. Using constant relaxation time, the electrical conductivity, electronic thermal conductivity, Seebeck coefficient and figure of merit are calculated by using Boltzmann transport theory. We have also studied the temperature dependence of thermoelectric properties of this compound.

Electron transport in furfural: dependence of the electron ranges on the cross sections and the energy loss distribution functions

NASA Astrophysics Data System (ADS)

Ellis-Gibbings, L.; Krupa, K.; Colmenares, R.; Blanco, F.; Muńoz, A.; Mendes, M.; Ferreira da Silva, F.; Limá Vieira, P.; Jones, D. B.; Brunger, M. J.; García, G.

2016-09-01

Recent theoretical and experimental studies have provided a complete set of differential and integral electron scattering cross section data from furfural over a broad energy range. The energy loss distribution functions have been determined in this study by averaging electron energy loss spectra for different incident energies and scattering angles. All these data have been used as input parameters for an event by event Monte Carlo simulation procedure to obtain the electron energy deposition patterns and electron ranges in liquid furfural. The dependence of these results on the input cross sections is then analysed to determine the uncertainty of the simulated values.

Electronic tracking for people with dementia: an exploratory study of the ethical issues experienced by carers in making decisions about usage.

PubMed

White, Eleanor Bantry; Montgomery, Paul

2014-03-01

Electronic tracking through GPS (global positioning system) is being used to monitor and locate people with dementia who are vulnerable to becoming lost. Through a review of the literature and an original study, this article examined ethical issues associated with use in a domestic setting. The qualitative study consisted of in-depth interviews with 10 carers who were using electronic tracking. The study explored the values, beliefs and contextual factors that motivated carers to use electronic tracking. It examined the extent of involvement of the person with dementia in decision-making and it explored the various ethical dilemmas encountered by carers when introducing the tracking system. As an issue that emerged from the interviews, specific attention was paid to exploring covert usage. From the study findings, recommendations have been made for research and practice about the use of electronic tracking in dementia care.

Electronic toll collection/electronic screening interoperability pilot project : final report synthesis

DOT National Transportation Integrated Search

2005-12-02

In 1998, ITS America established a Blue Ribbon Panel on electronic commerce to study the convergence of transportation and electronic payment systems. Panel members included senior managers from government, toll agencies, motor carrier industry, and ...

Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

PubMed

Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

2014-07-22

Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films.

STUDIES OF A FREE ELECTRON LASER DRIVEN BY A LASER-PLASMA ACCELERATOR

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

Montgomery, A.; Schroeder, C.; Fawley, W.

A free electron laser (FEL) uses an undulator, a set of alternating magnets producing a periodic magnetic fi eld, to stimulate emission of coherent radiation from a relativistic electron beam. The Lasers, Optical Accelerator Systems Integrated Studies (LOASIS) group at Lawrence Berkeley National Laboratory (LBNL) will use an innovative laserplasma wakefi eld accelerator to produce an electron beam to drive a proposed FEL. In order to optimize the FEL performance, the dependence on electron beam and undulator parameters must be understood. Numerical modeling of the FEL using the simulation code GINGER predicts the experimental results for given input parameters. Amongmore » the parameters studied were electron beam energy spread, emittance, and mismatch with the undulator focusing. Vacuum-chamber wakefi elds were also simulated to study their effect on FEL performance. Energy spread was found to be the most infl uential factor, with output FEL radiation power sharply decreasing for relative energy spreads greater than 0.33%. Vacuum chamber wakefi elds and beam mismatch had little effect on the simulated LOASIS FEL at the currents considered. This study concludes that continued improvement of the laser-plasma wakefi eld accelerator electron beam will allow the LOASIS FEL to operate in an optimal regime, producing high-quality XUV and x-ray pulses.« less

Experimental Studies of Lateral Electron Transport in Gallium Arsenide-Aluminum Gallium Arsenide Heterostructures.

DTIC Science & Technology

1982-12-01

AD-A125 858 EXPERIMENTAL STUDIES OF LATERAL ELECTRON TRANSPORT IN 1/3 GALLIUM ARSENIDE-RL..(U) ILLINOIS UNIV AT URBANA COORDINATED SCIENCE LAB N R...EXPERIMENTAL STUDIES OF LATERALXILECTRON TRANSPORT ,:g IN GALLIUM ARSENIDE -ALUMINUM GALLIUM ARSENIDE- -HETEROSTRUCTURES APRVE O PUBLICRLEAS.DSRBUINULMTE. 2...EXPERIMENTAL STUDIES OF LATERAL ELECTRON TRANSPORT IN GALLIUM ARSENIDE-ALUMINUM GALLIUM ARSENIDE Technical Report R-975 HETEROSTRUCTURES 6. PERFORMING ONG

Ultrastructural Study of Some Pollen Grains of Prairie Flowers

ERIC Educational Resources Information Center

Kozar, Frank

1973-01-01

Discusses the importance of the electron microscope, and in particular the scanning electron microscope, in studying the surface topography, sectional substructures, and patterns of development of pollen grains. The production, dispersal methods, and structure of pollen grains are described and illustrated with numerous electron micrographs. (JR)

Simulation studies of plasma waves in the electron foreshock - The generation of Langmuir waves by a gentle bump-on-tail electron distribution

NASA Technical Reports Server (NTRS)

Dum, C. T.

1990-01-01

Particle simulation experiments were used to study the basic physical ingredients needed for building a global model of foreshock wave phenomena. In particular, the generation of Langmuir waves by a gentle bump-on-tail electron distribution is analyzed. It is shown that, with appropriately designed simulations experiments, quasi-linear theory can be quantitatively verified for parameters corresponding to the electron foreshock.

The Relationship Between Magnet Designation, Electronic Health Record Adoption, and Medicare Meaningful Use Payments.

PubMed

Lippincott, Christine; Foronda, Cynthia; Zdanowicz, Martin; McCabe, Brian E; Ambrosia, Todd

2017-08-01

The objective of this study was to examine the relationship between nursing excellence and electronic health record adoption. Of 6582 US hospitals, 4939 were eligible for the Medicare Electronic Health Record Incentive Program, and 6419 were eligible for evaluation on the HIMSS Analytics Electronic Medical Record Adoption Model. Of 399 Magnet hospitals, 330 were eligible for the Medicare Electronic Health Record Incentive Program, and 393 were eligible for evaluation in the HIMSS Analytics Electronic Medical Record Adoption Model. Meaningful use attestation was defined as receipt of a Medicare Electronic Health Record Incentive Program payment. The adoption electronic health record was defined as Level 6 and/or 7 on the HIMSS Analytics Electronic Medical Record Adoption Model. Logistic regression showed that Magnet-designated hospitals were more likely attest to Meaningful Use than non-Magnet hospitals (odds ratio = 3.58, P < .001) and were more likely to adopt electronic health records than non-Magnet hospitals (Level 6 only: odds ratio = 3.68, P < .001; Level 6 or 7: odds ratio = 4.02, P < .001). This study suggested a positive relationship between Magnet status and electronic health record use, which involves earning financial incentives for successful adoption. Continued investigation is needed to examine the relationships between the quality of nursing care, electronic health record usage, financial implications, and patient outcomes.

Electron density inversed by plasma lines induced by suprathermal electron in the ionospheric modification experiment

NASA Astrophysics Data System (ADS)

Wang, Xiang; Zhou, Chen

2018-05-01

Incoherent scatter radar (ISR) is the most powerful ground-based measurement facility to study the ionosphere. The plasma lines are not routinely detected by the incoherent scatter radar due to the low intensity, which falls below the measured spectral noise level of the incoherent scatter radar. The plasma lines are occasionally enhanced by suprathermal electrons through the Landau damping process and detectable to the incoherent scatter radar. In this study, by using the European Incoherent Scatter Association (EISCAT) UHF incoherent scatter radar, the experiment observation presents that the enhanced plasma lines were observed. These plasma lines were considered as manifest of the suprathermal electrons generated by the high-frequency heating wave during the ionospheric modification. The electron density profile is also obtained from the enhanced plasma lines. This study can be a promising technique for obtaining the accurate electron density during ionospheric modification experiment.

Laser ablation under different electron heat conduction models in inertial confinement fusion

NASA Astrophysics Data System (ADS)

Li, Shuanggui; Ren, Guoli; Huo, Wen Yi

2018-06-01

In this paper, we study the influence of three different electron heat conduction models on the laser ablation of gold plane target. Different from previous studies, we concentrate on the plasma conditions, the conversion efficiency from laser into soft x rays and the scaling relation of mass ablation, which are relevant to hohlraum physics study in indirect drive inertial confinement fusion. We find that the simulated electron temperature in corona region is sensitive to the electron heat conduction models. For different electron heat conduction models, there are obvious differences in magnitude and spatial profile of electron temperature. For the flux limit model, the calculated conversion efficiency is sensitive to flux limiters. In the laser ablation of gold, most of the laser energies are converted into x rays. So the scaling relation of mass ablation rate is quite different from that of low Z materials.

Cubic Calorimeter for High-Energy Electrons in Ultra-Long Ballooning

NASA Technical Reports Server (NTRS)

Moiseev, Alexander A.; Mitchell, John W.; Ormes, Jonathan F.; Streitmatter, Robert E.

2003-01-01

The concept and optimization study of a balloon-borne instrument to study high-energy (from 100 GeV to 5 TeV) cosmic ray electrons will be presented. This energy range of electrons is very interesting for the study of cosmic ray propagation and the search for the nearby sources of high-energy electrons. The instrument is based on a cubic design that allows the detection from all sides. Proton rejection is provided by stringent track analysis, which allows defining when an electron shower is exhausted while the hadron shower continues development. The collecting power of a nominal balloon-borne instrument using this concept will be over 2 square meters sr. This will provide approximately 3,000 electron events above 500 GeV for 3-month long ULDB flight. This instrument will also be capable of detecting sharp features in the high energy gamma-ray spectrum such as gamma-ray lines originating from the dark matter annihilation.

Investigation, study and practice of optoelectronic MOOCs

NASA Astrophysics Data System (ADS)

Shi, Jianhua; Liu, Wei; Lei, Bing; Yao, Tianfu; Fu, Sihua

2017-08-01

MOOC(Massive Open Online Course) is a new teaching model that has been springing up since 2012. The typical characters are short teaching video, massive learners, flexible place and time to study, etc. Although MOOC is very popular now, opto-electronic MOOCs are not much enough to meet the need of online learners. In this paper, the phylogeny, the current situation and the characters of MOOC were described, the most famous MOOCs' websites, such as Udacity, Coursera, edX, Chinese College MOOC, xuetangx, were introduced, the opto-electronic MOOCs come from these famous MOOCs' website were investigated extensively and studied deeply, the "Application of Opto-electronic Technology MOOC" which was established by our group is introduced, and some conclusions are obtained. These conclusions can give some suggestions to the online learners who are interested in opto-electronic and the teachers who are teaching the opto-electronic curriculums. The preparation of "Opto-electronic Technology MOOC" is described in short.

Optimization of equipment for electron radiation processing

NASA Astrophysics Data System (ADS)

Tartz, M.; Hartmann, E.; Lenk, M.; Mehnert, R.

1999-05-01

In the course of the last decade, IOM Leipzig has developed low-energy electron accelerators for electron beam curing of polymer coatings and printing inks. In order to optimize the electron irradiation field, electron optical calculations have been carried out using the commercially available EGUN code. The present study outlines the design of the diode-type low-energy electron accelerators LEA and EBOGEN, taking into account the electron optical effects of secondary components such as the retaining rods installed in the cathode assembly.

One-electron propagation in Fermi, Pasta, Ulam disordered chains with Gaussian acoustic pulse pumping

NASA Astrophysics Data System (ADS)

Silva, L. D. Da; Dos Santos, J. L. L.; Ranciaro Neto, A.; Sales, M. O.; de Moura, F. A. B. F.

In this work, we consider a one-electron moving on a Fermi, Pasta, Ulam disordered chain under effect of electron-phonon interaction and a Gaussian acoustic pulse pumping. We describe electronic dynamics using quantum mechanics formalism and the nonlinear atomic vibrations using standard classical physics. Solving numerical equations related to coupled quantum/classical behavior of this system, we study electronic propagation properties. Our calculations suggest that the acoustic pumping associated with the electron-lattice interaction promote a sub-diffusive electronic dynamics.

A Feasibility Study of Computer Assisted Instruction in US Army Basic Electronics Training. Final Report.

ERIC Educational Resources Information Center

International Business Machines Corp., Gaithersburg, MD. Federal Systems Div.

A study of computer-assisted instruction (CAI) for US Army basic electronics training at the US Army Signal Center and School establishes the feasibility of CAI as a training technique. Three aspects of CAI are considered: effectiveness, efficiency, and applicability of CAI to basic electronics training. The study explores the effectiveness of the…

Managing complex research datasets using electronic tools: A meta-analysis exemplar

PubMed Central

Brown, Sharon A.; Martin, Ellen E.; Garcia, Theresa J.; Winter, Mary A.; García, Alexandra A.; Brown, Adama; Cuevas, Heather E.; Sumlin, Lisa L.

2013-01-01

Meta-analyses of broad scope and complexity require investigators to organize many study documents and manage communication among several research staff. Commercially available electronic tools, e.g., EndNote, Adobe Acrobat Pro, Blackboard, Excel, and IBM SPSS Statistics (SPSS), are useful for organizing and tracking the meta-analytic process, as well as enhancing communication among research team members. The purpose of this paper is to describe the electronic processes we designed, using commercially available software, for an extensive quantitative model-testing meta-analysis we are conducting. Specific electronic tools improved the efficiency of (a) locating and screening studies, (b) screening and organizing studies and other project documents, (c) extracting data from primary studies, (d) checking data accuracy and analyses, and (e) communication among team members. The major limitation in designing and implementing a fully electronic system for meta-analysis was the requisite upfront time to: decide on which electronic tools to use, determine how these tools would be employed, develop clear guidelines for their use, and train members of the research team. The electronic process described here has been useful in streamlining the process of conducting this complex meta-analysis and enhancing communication and sharing documents among research team members. PMID:23681256

Managing complex research datasets using electronic tools: a meta-analysis exemplar.

PubMed

Brown, Sharon A; Martin, Ellen E; Garcia, Theresa J; Winter, Mary A; García, Alexandra A; Brown, Adama; Cuevas, Heather E; Sumlin, Lisa L

2013-06-01

Meta-analyses of broad scope and complexity require investigators to organize many study documents and manage communication among several research staff. Commercially available electronic tools, for example, EndNote, Adobe Acrobat Pro, Blackboard, Excel, and IBM SPSS Statistics (SPSS), are useful for organizing and tracking the meta-analytic process as well as enhancing communication among research team members. The purpose of this article is to describe the electronic processes designed, using commercially available software, for an extensive, quantitative model-testing meta-analysis. Specific electronic tools improved the efficiency of (a) locating and screening studies, (b) screening and organizing studies and other project documents, (c) extracting data from primary studies, (d) checking data accuracy and analyses, and (e) communication among team members. The major limitation in designing and implementing a fully electronic system for meta-analysis was the requisite upfront time to decide on which electronic tools to use, determine how these tools would be used, develop clear guidelines for their use, and train members of the research team. The electronic process described here has been useful in streamlining the process of conducting this complex meta-analysis and enhancing communication and sharing documents among research team members.

Electron microscopy methods in studies of cultural heritage sites

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

Vasiliev, A. L., E-mail: a.vasiliev56@gmail.com; Kovalchuk, M. V.; Yatsishina, E. B.

The history of the development and application of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray microanalysis (EDXMA) in studies of cultural heritage sites is considered. In fact, investigations based on these methods began when electron microscopes became a commercial product. Currently, these methods, being developed and improved, help solve many historical enigmas. To date, electron microscopy combined with microanalysis makes it possible to investigate any object, from parchment and wooden articles to pigments, tools, and objects of art. Studies by these methods have revealed that some articles were made by ancient masters using ancient “nanotechnologies”; hence,more » their comprehensive analysis calls for the latest achievements in the corresponding instrumental methods and sample preparation techniques.« less

Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study

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

Xiao, Haiyan Y.; Weber, William J.; Zhang, Yanwen

2015-02-09

In this study, the response of titanate pyrochlores (A 2Ti 2O 7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O 2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization inmore » titanate pyrochlores under laser, electron and ion irradiations.« less

Electronic whiteboards: review of the literature.

PubMed

Randell, Rebecca; Greenhalgh, Joanne; Wyatt, Jeremy; Gardner, Peter; Pearman, Alan; Honey, Stephanie; Dowding, Dawn

2015-01-01

Electronic whiteboards are being introduced into hospitals to communicate real-time patient information instantly to staff. This paper provides a preliminary review of the current state of evidence for the effect of electronic whiteboards on care processes and patient outcomes. A literature search was performed for the dates 1996 to 2014 on MEDLINE, EMBASE, IEEE Xplore, Science Direct, and the ACM Digital Library. Thirteen papers, describing 11 studies, meeting the inclusion criteria were identified. The majority of studies took place in the Emergency Department. While studies looked at the impact of electronic whiteboards on the process of care, there is an absence of evidence concerning impact on patient outcomes. There is a need for robust research measuring the impact of electronic whiteboards on inpatient care.

Electron microscopy methods in studies of cultural heritage sites

NASA Astrophysics Data System (ADS)

Vasiliev, A. L.; Kovalchuk, M. V.; Yatsishina, E. B.

2016-11-01

The history of the development and application of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray microanalysis (EDXMA) in studies of cultural heritage sites is considered. In fact, investigations based on these methods began when electron microscopes became a commercial product. Currently, these methods, being developed and improved, help solve many historical enigmas. To date, electron microscopy combined with microanalysis makes it possible to investigate any object, from parchment and wooden articles to pigments, tools, and objects of art. Studies by these methods have revealed that some articles were made by ancient masters using ancient "nanotechnologies"; hence, their comprehensive analysis calls for the latest achievements in the corresponding instrumental methods and sample preparation techniques.

Theoretical research program to study transition metal trimers and embedded clusters

NASA Technical Reports Server (NTRS)

Walch, S. P.

1984-01-01

Small transition metal clusters were studied at a high level of approximation, including all the valence electrons in the calculation and extensive electron correlation, in order to understand the electronic structure of these small metal clusters. By comparison of dimers, trimers, and possibly higher clusters, the information obtained was used to provide insights into the electronic structure of bulk transition metals. Small metal clusters are currently of considerable experimental interest and some information is becomming available both from matrix electron spin resonance studies and from gas phase spectroscopy. Collaboration between theorists and experimentalists is thus expected to be especially profitable at this time since there is some experimental information which can serve to guide the theoretical work.

Generation of low-emittance electron beams in electrostatic accelerators for FEL applications

NASA Astrophysics Data System (ADS)

Chen, Teng; Elias, Luis R.

1995-02-01

This paper reports results of transverse emittance studies and beam propagation in electrostatic accelerators for free electron laser applications. In particular, we discuss emittance growth analysis of a low current electron beam system consisting of a miniature thermoionic electron gun and a National Electrostatics Accelerator (NEC) tube. The emittance growth phenomenon is discussed in terms of thermal effects in the electron gun cathode and aberrations produced by field gradient changes occurring inside the electron gun and throughout the accelerator tube. A method of reducing aberrations using a magnetic solenoidal field is described. Analysis of electron beam emittance was done with the EGUN code. Beam propagation along the accelerator tube was studied using a cylindrically symmetric beam envelope equation that included beam self-fields and the external accelerator fields which were derived from POISSON simulations.

Curie temperature behavior in half-metallic ferromagnetic double perovskites within the electronic correlation picture

NASA Astrophysics Data System (ADS)

Estrada, F.; Guzmán, E. J.; Navarro, O.; Avignon, M.

2018-05-01

The half-metallic ferromagnetic compound Sr2FeMoO6 is considered a fundamental material to understand the role of electronic parameters controlling the half-metallic ground state and high Curie temperature in double perovskite. We present an electronic approach using the Green's function technique and the renormalization perturbation expansion method to study the thermodynamical properties of double perovskites. The model is based on a correlated electron picture with localized Fe spins and conduction electrons interacting with the local spins via a double-exchange-type mechanism. Electron correlations within the conduction band are also included in order to study the Curie temperature TC. Our results show an increases of TC by increasing the carrier density in La-doped Sr2FeMoO6 compounds in contrast to the case of uncorrelated itinerant electrons.

Recent progress on beam stability study in the PSR

NASA Astrophysics Data System (ADS)

Wang, Tai-Sen F.; Channell, Paul J.; Cooper, Richard K.; Fitzgerald, Daniel H.; Hardek, Tom; Hutson, Richard; Jason, Andrew J.; Macek, Robert J.; Plum, Michael A.; Wilkinson, Carol

A fast transverse instability has been observed in the Los Alamos Proton Storage Ring (PSR) when the injected beam intensity reaches more than 2 (times) 10(exp 13) protons per pulse. Understanding the cause and control of this instability has taken on new importance as the neutron-scattering community considers the next generation of accelerator-driven spallation-neutron sources, which call for peak-proton intensities of 10(exp 14) per pulse or higher. Previous observations and theoretical studies indicate that the instability in the PSR is most likely driven by electrons trapped within the proton beam. Recent studies using an experimental electron-clearing system and voltage-biased pinger-electrodes for electron clearing and collection support this hypothesis. Experiments have also been performed to study the instability threshold when varying the electron production rate. Theoretical studies include a computer simulation of a simplified model for the e -- p instability and the investigation of possible electron confinement in the ring-element magnetic fields. This paper reports some recent results from these studies.

Students' Use of Electronic Support Tools in Mathematics

ERIC Educational Resources Information Center

Crawford, Lindy; Higgins, Kristina N.; Huscroft-D'Angelo, Jacqueline N.; Hall, Lindsay

2016-01-01

This study investigated students' use of electronic support tools within a computer-based mathematics program. Electronic support tools are tools, such as hyperlinks or calculators, available within many computer-based instructional programs. A convenience sample of 73 students in grades 4-6 was selected to participate in the study. Students…

High pressure and synchrotron radiation studies of solid state electronic instabilities. Final technial report, May 1, 1984--April 1987

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

Pifer, J.H.; Croft, M.C.

This report discusses Eu and General Valence Instabilities; Ce Problem: L{sub 3} Spectroscopy Emphasis; Bulk Property Emphasis; Transition Metal Compound Electronic Structure; Electronic Structure-Phonon Coupling Studies; High Temperature Superconductivity and Oxide Materials; and Novel Materials Collaboration with Chemistry.

Electronic Information Resources in Undergraduate Education: An Exploratory Study of Opportunities for Student Learning and Independence.

ERIC Educational Resources Information Center

McDowell, Liz

2002-01-01

This qualitative interview-based study examines lecturer perspectives on the roles of electronic information resources in undergraduate education. Highlights include electronic academic libraries; changes toward more constructivist approaches to learning; information quality on the Web; plagiarism; information use; information literacy; and…

Employers' Perceptions of the Benefits of Employment Electronic Portfolios

ERIC Educational Resources Information Center

Leahy, Ronda L.; Filiatrault, Ariana

2017-01-01

The purpose of this study was to examine employers' perceptions of the effectiveness of employment electronic portfolios (ePortfolios) when evaluating potential job candidates. For the purpose of this study, ePortfolios were defined as a collection of electronic files that demonstrates one's qualifications, abilities, and experiences that are…

Educators' Perspectives on Having Been Cyber Harassed: A Phenomenological Study

ERIC Educational Resources Information Center

Davenport, Paula M.

2014-01-01

The abuse of individuals through electronic means, typically of students by other students, has been researched extensively. The electronic abuse of other individuals through electronic means has received a dearth of research attention. The purpose of this qualitative transcendental phenomenological study was to explore, describe, and expand the…

Attachment 1 : appendices : electronic toll collection/electronic screening interoperability pilot project, supplement to the final report

DOT National Transportation Integrated Search

2005-07-29

In 1998, ITS America established a Blue Ribbon Panel on electronic commerce to study the convergence of transportation and electronic payment systems. Panel members included senior managers from government, toll agencies, motor carrier industry, and ...

Electron (charge) density studies of cellulose models

USDA-ARS?s Scientific Manuscript database

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

Preliminary Study of a Hybrid Helicon-ECR Plasma Source

NASA Astrophysics Data System (ADS)

M. Hala, A.; Oksuz, L.; Ximing, Zhu

2016-08-01

A new type of hybrid discharge is experimentally investigated in this work. A helicon source and an electron cyclotron resonance (ECR) source were combined to produce plasma. As a preliminary study of this type of plasma, the optical emission spectroscopy (OES) method was used to obtain values of electron temperature and density under a series of typical conditions. Generally, it was observed that the electron temperature decreases and the electron density increases as the pressure increased. When increasing the applied power at a certain pressure, the average electron density at certain positions in the discharge does not increase significantly possibly due to the high degree of neutral depletion. Electron temperature increased with power in the hybrid mode. Possible mechanisms of these preliminary observations are discussed.

Relationship between electronic properties and drug activity of seven quinoxaline compounds: A DFT study

NASA Astrophysics Data System (ADS)

Behzadi, Hadi; Roonasi, Payman; Assle taghipour, Khatoon; van der Spoel, David; Manzetti, Sergio

2015-07-01

The quantum chemical calculations at the DFT/B3LYP level of theory were carried out on seven quinoxaline compounds, which have been synthesized as anti-Mycobacterium tuberculosis agents. Three conformers were optimized for each compound and the lowest energy structure was found and used in further calculations. The electronic properties including EHOMO, ELUMO and related parameters as well as electron density around oxygen and nitrogen atoms were calculated for each compound. The relationship between the calculated electronic parameters and biological activity of the studied compounds were investigated. Six similar quinoxaline derivatives with possible more drug activity were suggested based on the calculated electronic descriptors. A mechanism was proposed and discussed based on the calculated electronic parameters and bond dissociation energies.

Sleep and use of electronic devices in adolescence: results from a large population-based study

PubMed Central

Hysing, Mari; Pallesen, Ståle; Stormark, Kjell Morten; Jakobsen, Reidar; Lundervold, Astri J; Sivertsen, Børge

2015-01-01

Objectives Adolescents spend increasingly more time on electronic devices, and sleep deficiency rising in adolescents constitutes a major public health concern. The aim of the present study was to investigate daytime screen use and use of electronic devices before bedtime in relation to sleep. Design A large cross-sectional population-based survey study from 2012, the youth@hordaland study, in Hordaland County in Norway. Setting Cross-sectional general community-based study. Participants 9846 adolescents from three age cohorts aged 16–19. The main independent variables were type and frequency of electronic devices at bedtime and hours of screen-time during leisure time. Outcomes Sleep variables calculated based on self-report including bedtime, rise time, time in bed, sleep duration, sleep onset latency and wake after sleep onset. Results Adolescents spent a large amount of time during the day and at bedtime using electronic devices. Daytime and bedtime use of electronic devices were both related to sleep measures, with an increased risk of short sleep duration, long sleep onset latency and increased sleep deficiency. A dose–response relationship emerged between sleep duration and use of electronic devices, exemplified by the association between PC use and risk of less than 5 h of sleep (OR=2.70, 95% CI 2.14 to 3.39), and comparable lower odds for 7–8 h of sleep (OR=1.64, 95% CI 1.38 to 1.96). Conclusions Use of electronic devices is frequent in adolescence, during the day as well as at bedtime. The results demonstrate a negative relation between use of technology and sleep, suggesting that recommendations on healthy media use could include restrictions on electronic devices. PMID:25643702

RF Design of a High Average Beam-Power SRF Electron Source

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

Sipahi, Nihan; Biedron, Sandra; Gonin, Ivan

2016-06-01

There is a significant interest in developing high-average power electron sources, particularly in the area of electron sources integrated with Superconducting Radio Frequency (SRF) systems. For these systems, the electron gun and cathode parts are critical components for stable intensity and high-average powers. In this initial design study, we will present the design of a 9-cell accelerator cavity having a frequency of 1.3 GHz and the corresponding field optimization studies.

Rat Phantom Depth Dose Studies in Electron, X-ray, Gamma-Ray, and Reactor Radiation Fields

DTIC Science & Technology

1986-12-01

i©™D©/^ ^1[P@^T Rat phantom depth dose studies in electron , Xrayf gamma-ray, and reactor radiation fields M. Dooley D. M. Eagleson G. H. Zeman...energy electrons , bremsstrahlung, and mixed neutron/gamma radiation fields are sometimes used in radiobiological experiments employing rats. This report...have revealed differing sensitivities of experimental animals that have been exposed to cobalt-60 photons, high-energy electrons , high-energy X rays

Electron beam induced light emission

NASA Astrophysics Data System (ADS)

Ulrich, A.; Heindl, T.; Krücken, R.; Morozov, A.; Skrobol, C.; Wieser, J.

2009-08-01

Electron beams with a particle energy of typically 12keV are used for collisional excitation of dense gases. The electrons are sent through ceramic membranes of only 300nm thickness into gas targets. Excimer light emission from the pure rare gases and from gas mixtures are studied for the development of brilliant VUV and UV light sources. The application of the technology for gas kinetic studies is described and its potential for building very small electron beam pumped lasers is discussed.

Catalysis of Nuclear Reactions by Electrons

NASA Astrophysics Data System (ADS)

Lipoglavšek, Matej

2018-01-01

Electron screening enhances nuclear reaction cross sections at low energies. We studied the nuclear reaction 1H(19F,αγ)16O in inverse kinematics in different solid hydrogen targets. Measured resonance strengths differed by up to a factor of 10 in different targets. We also studied the 2H(p,γ)3He fusion reaction and observed electrons emitted as reaction products instead of γ rays. In this case electron screening greatly enhances internal conversion probability.

Fluid and hybrid models for streamers

NASA Astrophysics Data System (ADS)

Bonaventura, Zdeněk

2016-09-01

Streamers are contracted ionizing waves with self-generated field enhancement that propagate into a low-ionized medium exposed to high electric field leaving filamentary trails of plasma behind. The widely used model to study streamer dynamics is based on drift-diffusion equations for electrons and ions, assuming local field approximation, coupled with Poisson's equation. For problems where presence of energetic electrons become important a fluid approach needs to be extended by a particle model, accompanied also with Monte Carlo Collision technique, that takes care of motion of these electrons. A combined fluid-particle approach is used to study an influence of surface emission processes on a fast-pulsed dielectric barrier discharge in air at atmospheric pressure. It is found that fluid-only model predicts substantially faster reignition dynamics compared to coupled fluid-particle model. Furthermore, a hybrid model can be created in which the population of electrons is divided in the energy space into two distinct groups: (1) low energy `bulk' electrons that are treated with fluid model, and (2) high energy `beam' electrons, followed as particles. The hybrid model is then capable not only to deal with streamer discharges in laboratory conditions, but also allows us to study electron acceleration in streamer zone of lighting leaders. There, the production of fast electrons from streamers is investigated, since these (runaway) electrons act as seeds for the relativistic runaway electron avalanche (RREA) mechanism, important for high-energy atmospheric physics phenomena. Results suggest that high energy electrons effect the streamer propagation, namely the velocity, the peak electric field, and thus also the production rate of runaway electrons. This work has been supported by the Czech Science Foundation research project 15-04023S.

Study of the Effects of the Electric Field on Charging Measurements on Individual Micron-size Dust Grains by Secondary Electron Emissions

NASA Technical Reports Server (NTRS)

Tankosic, D.; Abbas, M. M.

2013-01-01

The dust charging by electron impact is an important dust charging process in Astrophysical, Planetary, and the Lunar environments. Low energy electrons are reflected or stick to the grains charging the dust grains negatively. At sufficiently high energies electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Available theoretical models for the calculation of SEE yield applicable for neutral, planar or bulk surfaces are generally based on Sternglass Equation. However, viable models for charging of individual dust grains do not exist at the present time. Therefore, the SEE yields have to be obtained by some experimental methods at the present time. We have conducted experimental studies on charging of individual micron size dust grains in simulated space environments using an electrodynamic balance (EDB) facility at NASA-MSFC. The results of our extensive laboratory study of charging of individual micron-size dust grains by low energy electron impact indicate that the SEE by electron impact is a very complex process expected to be substantially different from the bulk materials. It was found that the incident electrons may lead to positive or negative charging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration. In this paper we give a more elaborate discussion about the possible effects of the AC field in the EDB on dust charging measurements by comparing the secondary electron emission time-period (tau (sub em) (s/e)) with the time-period (tau (sub ac) (ms)) of the AC field cycle in the EDB that we have briefly addressed in our previous publication.

Are low income patients receiving the benefits of electronic health records? A statewide survey.

PubMed

Butler, Matthew J; Harootunian, Gevork; Johnson, William G

2013-06-01

There are concerns that physicians serving low-income, Medicaid patients, in the United States are less likely to adopt electronic health records and, if so, that Medicaid patients will be denied the benefits from electronic health record use. This study seeks to determine whether physicians treating Medicaid patients were less likely to have adopted electronic health records. Physician surveys completed during physicians' license renewal process in Arizona were merged with the physician licensing data and Medicaid administrative claims data. Survey responses were received from 50.7 percent (6,780 out of 13,380) of all physicians practicing in Arizona. Physician survey responses were used to identify whether the physician used electronic health records and the degree to which the physician exchanged electronic health records with other health-care providers. Medicaid claims data were used to identify which physicians provided health care to Medicaid beneficiaries. The primary outcome of interest was whether Medicaid providers were more or less likely to have adopted electronic health records. Logistic regression analysis was used to estimate average marginal effects. In multivariate analysis, physicians with 20 or more Medicaid patients during the survey cycle were 4.1 percent more likely to use an electronic health record and 5.2 percent more likely to be able to transmit electronic health records to at least one health-care provider outside of their practice. These effects increase in magnitude when the analysis is restricted to solo practice physicians This is the first study to find a pro-Medicaid gap in electronic health record adoption suggesting that the low income patients served by Arizona's Health Care Cost Containment System are not at a disadvantage with regard to electronic health record access and that Arizona's model of promoting electronic health record adoption merits further study.

Electronic health record use, intensity of hospital care, and patient outcomes.

PubMed

Blecker, Saul; Goldfeld, Keith; Park, Naeun; Shine, Daniel; Austrian, Jonathan S; Braithwaite, R Scott; Radford, Martha J; Gourevitch, Marc N

2014-03-01

Previous studies have suggested that weekend hospital care is inferior to weekday care and that this difference may be related to diminished care intensity. The purpose of this study was to determine whether a metric for measuring intensity of hospital care based on use of the electronic health record was associated with patient-level outcomes. We performed a cohort study of hospitalizations at an academic medical center. Intensity of care was defined as the hourly number of provider accessions of the electronic health record, termed "electronic health record interactions." Hospitalizations were categorized on the basis of the mean difference in electronic health record interactions between the first Friday and the first Saturday of hospitalization. We used regression models to determine the association of these categories with patient outcomes after adjusting for covariates. Electronic health record interactions decreased from Friday to Saturday in 77% of the 9051 hospitalizations included in the study. Compared with hospitalizations with no change in Friday to Saturday electronic health record interactions, the relative lengths of stay for hospitalizations with a small, moderate, and large decrease in electronic health record interactions were 1.05 (95% confidence interval [CI], 1.00-1.10), 1.11 (95% CI, 1.05-1.17), and 1.25 (95% CI, 1.15-1.35), respectively. Although a large decrease in electronic health record interactions was associated with in-hospital mortality, these findings were not significant after risk adjustment (odds ratio 1.74, 95% CI, 0.93-3.25). Intensity of inpatient care, measured by electronic health record interactions, significantly diminished from Friday to Saturday, and this decrease was associated with length of stay. Hospitals should consider monitoring and correcting temporal fluctuations in care intensity. Copyright © 2014 Elsevier Inc. All rights reserved.

Solar Wind Strahl Observations and Their Implication to the Core-Halo Formation due to Scattering

NASA Technical Reports Server (NTRS)

Vinas, Adolfo F.

2011-01-01

A study of the kinetic properties of the strahl electron velocity distribution functions (VDF?s) in the solar wind is presented. This study focuses on the mechanisms that control and regulate the electron VDF?s and the stability of the strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the strahl-electron density, temperature anisotropy, and electron heat-flux. These parameters are used to investigate the stability of the strahl population. The analysis check for whether the strahl electrons are constrained by some instability (e.g., the whistler or KAW instabilities), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by modeling of the 3D-VDF?s from which the moments properties of the various populations are obtained. The results of this study have profound implication on the current hypothesis about the probable formation of the solar wind halo electrons produced from the scattering of the strahl population. This hypothesis is strengthened by direct observations of the strahl electrons being scattered into the core-halo in an isolated event. The observation implies that the scattering of the strahl is not a continuous process but occurs in bursts in regions where conditions for wave growth providing the scattering are optimum. Sometimes, observations indicate that the strahl component is anisotropic (Tper/Tpal approx. 2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism, however this condition is not always observed. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer.

Use of Electronic Versus Print Textbooks by Chilean Dental Students: A National Survey.

PubMed

Aravena, Pedro Christian; Schulz, Karen; Parra, Annemarie; Perez-Rojas, Francisco; Rosas, Cristian; Cartes-Velásquez, Ricardo

2017-03-01

Electronic textbooks have become available in recent decades as replacements or alternatives for print versions. The aim of this descriptive cross-sectional study was to evaluate the use of electronic versus print textbooks by Chilean dental students. The target population was students from 14 Chilean dental schools. The questionnaire was adapted and translated to Spanish from a previous survey used in a similar study. It consisted of the following variables: preferred type, type used, frequency of use, source, electronic devices used to read, and disposal after use. The use of textbooks was analyzed and compared by gender and course (p≤0.05). The final sample consisted of 3,256 students (21.38±2.5 years of age, 50.8% women). Most of the participants reported using both types of texts, with most (63.9%) preferring print over electronic texts, including significantly more women (p<0.001) and first-year students (p<0.001). Most of the participants (82.8%), more women (p<0.001), and with variations over years of study (p<0.001) reported that they printed out their electronic texts, and 91.8% kept their printed material. Most of the students used electronic books on a daily basis (47.3%) or at least twice a week (30.7%). The main source of electronic textbooks was the Internet (43.8%). A personal computer was the most widely used device for reading electronic texts (95.0%), followed by a cell phone (46.4%) and a tablet (24.5%). Overall, these Chilean dental students preferred print over electronic textbooks, despite having available electronic devices.

Syringe-Injectable Electronics with a Plug-and-Play Input/Output Interface.

PubMed

Schuhmann, Thomas G; Yao, Jun; Hong, Guosong; Fu, Tian-Ming; Lieber, Charles M

2017-09-13

Syringe-injectable mesh electronics represent a new paradigm for brain science and neural prosthetics by virtue of the stable seamless integration of the electronics with neural tissues, a consequence of the macroporous mesh electronics structure with all size features similar to or less than individual neurons and tissue-like flexibility. These same properties, however, make input/output (I/O) connection to measurement electronics challenging, and work to-date has required methods that could be difficult to implement by the life sciences community. Here we present a new syringe-injectable mesh electronics design with plug-and-play I/O interfacing that is rapid, scalable, and user-friendly to nonexperts. The basic design tapers the ultraflexible mesh electronics to a narrow stem that routes all of the device/electrode interconnects to I/O pads that are inserted into a standard zero insertion force (ZIF) connector. Studies show that the entire plug-and-play mesh electronics can be delivered through capillary needles with precise targeting using microliter-scale injection volumes similar to the standard mesh electronics design. Electrical characterization of mesh electronics containing platinum (Pt) electrodes and silicon (Si) nanowire field-effect transistors (NW-FETs) demonstrates the ability to interface arbitrary devices with a contact resistance of only 3 Ω. Finally, in vivo injection into mice required only minutes for I/O connection and yielded expected local field potential (LFP) recordings from a compact head-stage compatible with chronic studies. Our results substantially lower barriers for use by new investigators and open the door for increasingly sophisticated and multifunctional mesh electronics designs for both basic and translational studies.

Electronic case report forms and electronic data capture within clinical trials and pharmacoepidemiology.

PubMed

Rorie, David A; Flynn, Robert W V; Grieve, Kerr; Doney, Alexander; Mackenzie, Isla; MacDonald, Thomas M; Rogers, Amy

2017-09-01

Researchers in clinical and pharmacoepidemiology fields have adopted information technology (IT) and electronic data capture, but these remain underused despite the benefits. This review discusses electronic case report forms and electronic data capture, specifically within pharmacoepidemiology and clinical research. The review used PubMed and the Institute of Electrical and Electronic Engineers library. Search terms used were agreed by the authors and documented. PubMed is medical and health based, whereas Institute of Electrical and Electronic Engineers is technology based. The review focuses on electronic case report forms and electronic data capture, but briefly considers other relevant topics; consent, ethics and security. There were 1126 papers found using the search terms. Manual filtering and reviewing of abstracts further condensed this number to 136 relevant manuscripts. The papers were further categorized: 17 contained study data; 40 observational data; 27 anecdotal data; 47 covering methodology or design of systems; one case study; one literature review; two feasibility studies; and one cost analysis. Electronic case report forms, electronic data capture and IT in general are viewed with enthusiasm and are seen as a cost-effective means of improving research efficiency, educating participants and improving trial recruitment, provided concerns about how data will be protected from misuse can be addressed. Clear operational guidelines and best practises are key for healthcare providers, and researchers adopting IT, and further work is needed on improving integration of new technologies with current systems. A robust method of evaluation for technical innovation is required. © 2017 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.

Electronic case report forms and electronic data capture within clinical trials and pharmacoepidemiology

PubMed Central

Flynn, Robert W. V.; Grieve, Kerr; Doney, Alexander; Mackenzie, Isla; MacDonald, Thomas M.; Rogers, Amy

2017-01-01

Aims Researchers in clinical and pharmacoepidemiology fields have adopted information technology (IT) and electronic data capture, but these remain underused despite the benefits. This review discusses electronic case report forms and electronic data capture, specifically within pharmacoepidemiology and clinical research. Methods The review used PubMed and the Institute of Electrical and Electronic Engineers library. Search terms used were agreed by the authors and documented. PubMed is medical and health based, whereas Institute of Electrical and Electronic Engineers is technology based. The review focuses on electronic case report forms and electronic data capture, but briefly considers other relevant topics; consent, ethics and security. Results There were 1126 papers found using the search terms. Manual filtering and reviewing of abstracts further condensed this number to 136 relevant manuscripts. The papers were further categorized: 17 contained study data; 40 observational data; 27 anecdotal data; 47 covering methodology or design of systems; one case study; one literature review; two feasibility studies; and one cost analysis. Conclusion Electronic case report forms, electronic data capture and IT in general are viewed with enthusiasm and are seen as a cost‐effective means of improving research efficiency, educating participants and improving trial recruitment, provided concerns about how data will be protected from misuse can be addressed. Clear operational guidelines and best practises are key for healthcare providers, and researchers adopting IT, and further work is needed on improving integration of new technologies with current systems. A robust method of evaluation for technical innovation is required. PMID:28276585

A 20-liter test stand with gas purification for liquid argon research

DOE PAGES

Li, Y.; Thorn, C.; Tang, W.; ...

2016-06-06

Here, we describe the design of a 20-liter test stand constructed to study fundamental properties of liquid argon (LAr). Moreover, this system utilizes a simple, cost-effective gas argon (GAr) purification to achieve high purity, which is necessary to study electron transport properties in LAr. An electron drift stack with up to 25 cm length is constructed to study electron drift, diffusion, and attachment at various electric fields. Finally, a gold photocathode and a pulsed laser are used as a bright electron source. The operational performance of this system is reported.

A 20-liter test stand with gas purification for liquid argon research

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

Li, Y.; Thorn, C.; Tang, W.

Here, we describe the design of a 20-liter test stand constructed to study fundamental properties of liquid argon (LAr). Moreover, this system utilizes a simple, cost-effective gas argon (GAr) purification to achieve high purity, which is necessary to study electron transport properties in LAr. An electron drift stack with up to 25 cm length is constructed to study electron drift, diffusion, and attachment at various electric fields. Finally, a gold photocathode and a pulsed laser are used as a bright electron source. The operational performance of this system is reported.

Theoretical studies of electronically excited states

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

Besley, Nicholas A.

2014-10-06

Time-dependent density functional theory is the most widely used quantum chemical method for studying molecules in electronically excited states. However, excited states can also be computed within Kohn-Sham density functional theory by exploiting methods that converge the self-consistent field equations to give excited state solutions. The usefulness of single reference self-consistent field based approaches for studying excited states is demonstrated by considering the calculation of several types of spectroscopy including the infrared spectroscopy of molecules in an electronically excited state, the rovibrational spectrum of the NO-Ar complex, core electron binding energies and the emission spectroscopy of BODIPY in water.

Electronic Submissions of Pesticide Applications

EPA Pesticide Factsheets

Applications for pesticide registration can be submitted electronically, including forms, studies, and draft product labeling. Applicants need not submit multiple electronic copies of any pieces of their applications.

Attosecond Spectroscopy Probing Electron Correlation Dynamics

NASA Astrophysics Data System (ADS)

Winney, Alexander H.

Electrons are the driving force behind every chemical reaction. The exchange, ionization, or even relaxation of electrons is behind every bond broken or formed. According to the Bohr model of the atom, it takes an electron 150 as to orbit a proton[6]. With this as a unit time scale for an electron, it is clear that a pulse duration of several femtoseconds will not be sufficient to understanding electron dynamics. Our work demonstrates both technical and scientific achievements that push the boundaries of attosecond dynamics. TDSE studies show that amplification the yield of high harmonic generation (HHG) may be possible with transverse confinement of the electron. XUV-pump-XUV-probe shows that the yield of APT train can be sufficient for 2-photon double ionization studies. A zero dead-time detection system allows for the measurement of state-resolved double ionization for the first time. Exploiting attosecond angular streaking[7] probes sequential and non-sequential double ionization via electron-electron correlations with attosecond time resolution. Finally, using recoil frame momentum correlation, the fast dissociation of CH 3I reveals important orbital ionization dynamics of non-dissociative & dissociative, single & double ionization.

Structural changes induced by lattice-electron interactions: SiO2 stishovite and FeTiO3 ilmenite.

PubMed

Yamanaka, Takamitsu

2005-09-01

The bright source and highly collimated beam of synchrotron radiation offers many advantages for single-crystal structure analysis under non-ambient conditions. The structure changes induced by the lattice-electron interaction under high pressure have been investigated using a diamond anvil pressure cell. The pressure dependence of electron density distributions around atoms is elucidated by a single-crystal diffraction study using deformation electron density analysis and the maximum entropy method. In order to understand the bonding electrons under pressure, diffraction intensity measurements of FeTiO3 ilmenite and gamma-SiO2 stishovite single crystals at high pressures were made using synchrotron radiation. Both diffraction studies describe the electron density distribution including bonding electrons and provide the effective charge of the cations. In both cases the valence electrons are more localized around the cations with increasing pressure. This is consistent with molecular orbital calculations, proving that the bonding electron density becomes smaller with pressure. The thermal displacement parameters of both samples are reduced with increasing pressure.

Investigation of mid-latitude electron density enhancement using total electron content measurements and FORMOSAT-3/COSMIC electron density profiles

NASA Astrophysics Data System (ADS)

Rajesh, P. K.; Nanan, Balan; Liu, Jann-Yenq; Lin, Charles C. H.; Chang, S. Y.; Chen, Chia-Hung

This study investigates the mid-latitude electron density enhancement (MEDE) using global ionospheric map (GIM) total electron content (TEC) measurements and FORMOSAT-3/COSMIC (F3/C) electron density profiles. Diurnal, seasonal, latitudinal, and solar activity variations in the occurrence and strength of MEDE are examined using global GIM TEC data in the years 2002 and 2009. The results show that MEDE occurrence is pronounced during 2200-0400 LT, the feature also appears during day. The strength of MEDE maximizes around 0400 LT, and is very weak during daytime. The occurrence and strength show significant longitude dependence, and vary with season and solar activity. Concurrent F3/C electron density profiles also reveal enhancement of the peak electron density and total electron content. Further studies are carried out by examining the role of neutral wind in re-organizing the plasma using SAMI2 and HWM93 models. The results indicate that meridional neutral wind could cause the plasma to converge over mid-latitudes, and thus support in maintaining the enhancement.

Transport properties of a quantum dot and a quantum ring in series

NASA Astrophysics Data System (ADS)

Seo, Minky; Chung, Yunchul

2018-01-01

The decoherence mechanism of an electron interferometer is studied by using a serial quantum dot and ring device. By coupling a quantum dot to a quantum ring (closed-loop electron interferometer), we were able to observe both Coulomb oscillations and Aharonov-Bohm interference simultaneously. The coupled device behaves like an ordinary double quantum dot at zero magnetic field while the conductance of the Coulomb blockade peak is modulated by the electron interference at finite magnetic fields. By injecting one electron at a time (by exploiting the sequential tunneling of a quantum dot) into the interferometer, we were able to study the visibility of the electron interference at non-zero bias voltage. The visibility was found to decay rapidly as the electron energy was increased, which was consistent with the recently reported result for an electron interferometer. However, the lobe pattern and the sudden phase jump became less prominent. These results imply that the lobe pattern and the phase jump in an electron interferometer may be due to electron interactions inside the interferometer, as is predicted by the theory.

Seeing Atoms and Molecules in Action with an Electron 'Eye' | Berkeley Lab

Science.gov Websites

, also called "electron guns," that can drive advanced X-ray lasers known as "free form of X-ray light. Free-electron lasers have opened new frontiers in studying materials and chemistry that you can look at with an X-ray free-electron laser, but with an electron eye." He added, "

Excess electrons in ice: a density functional theory study.

PubMed

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

2014-02-21

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

Multicomponent Time-Dependent Density Functional Theory: Proton and Electron Excitation Energies.

PubMed

Yang, Yang; Culpitt, Tanner; Hammes-Schiffer, Sharon

2018-04-05

The quantum mechanical treatment of both electrons and protons in the calculation of excited state properties is critical for describing nonadiabatic processes such as photoinduced proton-coupled electron transfer. Multicomponent density functional theory enables the consistent quantum mechanical treatment of more than one type of particle and has been implemented previously for studying ground state molecular properties within the nuclear-electronic orbital (NEO) framework, where all electrons and specified protons are treated quantum mechanically. To enable the study of excited state molecular properties, herein the linear response multicomponent time-dependent density functional theory (TDDFT) is derived and implemented within the NEO framework. Initial applications to FHF - and HCN illustrate that NEO-TDDFT provides accurate proton and electron excitation energies within a single calculation. As its computational cost is similar to that of conventional electronic TDDFT, the NEO-TDDFT approach is promising for diverse applications, particularly nonadiabatic proton transfer reactions, which may exhibit mixed electron-proton vibronic excitations.

Studying electron-PAG interactions using electron-induced fluorescence

NASA Astrophysics Data System (ADS)

Narasimhan, Amrit; Grzeskowiak, Steven; Ostrander, Jonathan; Schad, Jonathon; Rebeyev, Eliran; Neisser, Mark; Ocola, Leonidas E.; Denbeaux, Gregory; Brainard, Robert L.

2016-03-01

In extreme ultraviolet (EUV) lithography, 92 eV photons are used to expose photoresists. Typical EUV resists are organic-based and chemically amplified using photoacid generators (PAGs). Upon exposure, PAGs produce acids which catalyze reactions that result in changes in solubility. In EUV lithography, photo- and secondary electrons (energies of 10- 80 eV) play a large role in PAG acid-production. Several mechanisms for electron-PAG interactions (e.g. electron trapping, and hole-initiated chemistry) have been proposed. The aim of this study is to explore another mechanism - internal excitation - in which a bound PAG electron can be excited by receiving energy from another energetic electron, causing a reaction that produces acid. This paper explores the mechanism of internal excitation through the analogous process of electron-induced fluorescence, in which an electron loses energy by transferring that energy to a molecule and that molecule emits a photon rather than decomposing. We will show and quantify electron-induced fluorescence of several fluorophores in polymer films to mimic resist materials, and use this information to refine our proposed mechanism. Relationships between the molecular structure of fluorophores and fluorescent quantum yield may aid in the development of novel PAGs for EUV lithography.

A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

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

Lewis, Nicholas H. C.; Dong, Hui; Oliver, Thomas A. A.

2015-09-28

Two dimensional electronic spectroscopy has proven to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derivemore » response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale.« less

A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

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

Lewis, Nicholas H. C.; Dong, Hui; Oliver, Thomas A. A.

2015-09-28

Two dimensional electronic spectroscopy has proved to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derivemore » response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale.« less

A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy.

PubMed

Lewis, Nicholas H C; Dong, Hui; Oliver, Thomas A A; Fleming, Graham R

2015-09-28

Two dimensional electronic spectroscopy has proved to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derive response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale.

Print versus electronic journals: a preliminary investigation into the effect of journal format on research processes*

PubMed Central

Sathe, Nila A.; Grady, Jenifer L.; Giuse, Nunzia B.

2002-01-01

Purpose: To begin investigating the impact of electronic journals on research processes such as information seeking, the authors conducted a pilot journal-use study to test the hypothesis that patrons use print and electronic journals differently. Methodology: We placed fifteen high-use print titles also available in electronic format behind the circulation desk; patrons were asked to complete a survey upon requesting a journal. We also conducted a parallel survey of patrons using library computers. Both surveys asked patrons to identify themselves by user category and queried them about their journal use. Results: During the month-long study, patrons completed sixty-nine surveys of electronic and ninety surveys of print journal use. Results analysis indicated that fellows, students, and residents preferred electronic journals, and faculty preferred print journals. Patrons used print journals for reading articles and scanning contents; they employed electronic journals for printing articles and checking references. Users considered electronic journals easier to access and search than print journals; however, they reported that print journals had higher quality text and figures. Discussion/Conclusion: This study is an introductory step in examining how electronic journals affect research processes. Our data revealed that there were distinct preferences in format among categories. In addition to collection management implications for libraries, these data also have implications for publishers and educators; current electronic formats do not facilitate all types of uses and thus may be changing learning patterns as well. PMID:11999183

Electron-phonon coupling in graphene placed between magnetic Li and Si layers on cobalt

NASA Astrophysics Data System (ADS)

Usachov, Dmitry Yu.; Fedorov, Alexander V.; Vilkov, Oleg Yu.; Ogorodnikov, Ilya I.; Kuznetsov, Mikhail V.; Grüneis, Alexander; Laubschat, Clemens; Vyalikh, Denis V.

2018-02-01

Using angle-resolved photoemission spectroscopy (ARPES), we study the electronic structure and electron-phonon coupling in a Li-doped graphene monolayer decoupled from the Co(0001) substrate by intercalation of silicon. Based on the photoelectron diffraction measurements, we disclose the structural properties of the Si/Co interface. Our density functional theory calculations demonstrate that in the studied Li/graphene/Si/Co system the magnetism of Co substrate induces notable magnetic moments on Li and Si atoms. At the same time graphene remains almost nonmagnetic and clamped between two magnetically active atomic layers with antiparallel magnetizations. ARPES maps of the graphene Fermi surface reveal strong electron doping, which may lead to superconductivity mediated by electron-phonon coupling (EPC). Analysis of the spectral function of photoelectrons reveals apparent anisotropy of EPC in the k space. These properties make the studied system tempting for studying the relation between superconductivity and magnetism in two-dimensional materials.

Electron Energetics in the Martian Dayside Ionosphere: Model Comparisons with MAVEN Data

NASA Technical Reports Server (NTRS)

Sakai, Shotaro; Andersson, Laila; Cravens, Thomas E.; Mitchell, David L.; Mazelle, Christian; Rahmati, Ali; Fowler, Christopher M.; Bougher, Stephen W.; Thiemann, Edward M. B.; Epavier, Francis G.;

Analysis of microscopic parameters of surface charging in polymer caused by defocused electron beam irradiation.

PubMed

Liu, Jing; Zhang, Hai-Bo

2014-12-01

The relationship between microscopic parameters and polymer charging caused by defocused electron beam irradiation is investigated using a dynamic scattering-transport model. The dynamic charging process of an irradiated polymer using a defocused 30 keV electron beam is conducted. In this study, the space charge distribution with a 30 keV non-penetrating e-beam is negative and supported by some existing experimental data. The internal potential is negative, but relatively high near the surface, and it decreases to a maximum negative value at z=6 μm and finally tend to 0 at the bottom of film. The leakage current and the surface potential behave similarly, and the secondary electron and leakage currents follow the charging equilibrium condition. The surface potential decreases with increasing beam current density, trap concentration, capture cross section, film thickness and electron-hole recombination rate, but with decreasing electron mobility and electron energy. The total charge density increases with increasing beam current density, trap concentration, capture cross section, film thickness and electron-hole recombination rate, but with decreasing electron mobility and electron energy. This study shows a comprehensive analysis of microscopic factors of surface charging characteristics in an electron-based surface microscopy and analysis. Copyright © 2014 Elsevier Ltd. All rights reserved.

Can Electron-Rich Oxygen (O2-) Withdraw Electrons from Metal Centers? A DFT Study on Oxoanion-Caged Polyoxometalates.

PubMed

Takazaki, Aki; Eda, Kazuo; Osakai, Toshiyuki; Nakajima, Takahito

2017-10-12

The answer to the question "Can electron-rich oxygen (O 2- ) withdraw electrons from metal centers?" is seemingly simple, but how the electron population on the M atom behaves when the O-M distance changes is a matter of controversy. A case study has been conducted for Keggin-type polyoxometalate (POM) complexes, and the first-principles electronic structure calculations were carried out not only for real POM species but also for "hypothetical" ones whose heteroatom was replaced with a point charge. From the results of natural population analysis, it was proven that even an electron-rich O 2- , owing to its larger electronegativity as a neutral atom, withdraws electrons when electron redistribution occurs by the change of the bond length. In the case where O 2- coexists with a cation having a large positive charge (e.g., P 5+ (O 2- ) 4 = [PO 4 ] 3- ), the gross electron population (GEP) on the M atom seemingly increases as the O atom comes closer, but this increment in GEP is not due to the role of the O atom but due to a Coulombic effect of the positive charge located on the cation. Furthermore, it was suggested that not GEP but net electron population (NEP) should be responsible for the redox properties.

Rapid contrast evaluation method based on affinity beads and backscattered electron imaging for the screening of electron stains.

PubMed

Kaku, Hiroki; Inoue, Kanako; Muranaka, Yoshinori; Park, Pyoyun; Ikeda, Kenichi

2015-10-01

Uranyl salts are toxic and radioactive; therefore, several studies have been conducted to screen for substitutes of electron stains. In this regard, the contrast evaluation process is time consuming and the results obtained are inconsistent. In this study, we developed a novel contrast evaluation method using affinity beads and a backscattered electron image (BSEI), obtained using scanning electron microscopy. The contrast ratios of BSEI in each electron stain treatment were correlated with those of transmission electron microscopic images. The affinity beads bound to cell components independently. Protein and DNA samples were enhanced by image contrast treated with electron stains; however, this was not observed for sugars. Protein-conjugated beads showed an additive effect of image contrast when double-stained with lead. However, additive effect of double staining was not observed in DNA-conjugated beads. The varying chemical properties of oligopeptides showed differences in image contrast when treated with each electron stain. This BSEI-based evaluation method not only enables screening for alternate electron stains, but also helps analyze the underlying mechanisms of electron staining of cellular structures. © The Author 2015. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

One-Electron Reduction of Penicillins in Relation to the Oxidative Stress Phenomenon

PubMed Central

Szabó, László; Tóth, Tünde; Takács, Erzsébet; Wojnárovits, László

2015-01-01

Certain bactericidal antibiotics target mitochondrial components and, due to the leakage of electrons from the electron transport chain, one-electron reduction might occur that can lead to intermediates passing the electron to suitable acceptors. This study aimed at investigating the one-electron reduction mechanism of selected penicillin derivatives using pulse radiolysis techniques. Penicillins can accommodate the electron on each of their carbonyl carbon. Ketyl radicals are thus produced, which are reducing agents with possibility to interact with suitable biomolecules. A detailed mechanism of the reduction is reported. PMID:26690427

Electron irradiation induced effects on the physico-chemical properties of L-Arginine Maleate Dihydrate (LAMD) single crystals

NASA Astrophysics Data System (ADS)

Thomas, Prince; Dhole, S. D.; Joseph, Ginson P.

2018-07-01

Single crystals of L-Arginine Maleate Dihydrate (LAMD) have been synthesized by slow solvent evaporation technique and irradiated with 6 MeV electrons at fluences of 0.5 ×1015e /cm2 , 1.0 ×1015e /cm2 and 1.5 ×1015e /cm2 . The Powder X-ray Diffraction (PXRD) studies showed that the intensity of the diffraction peaks of the Electron Beam (EB) irradiated crystals decreases with irradiation fluence. The electron irradiation induced effects on the optical parameters such as cut-off wavelength, band gap, Urbach energy and refractive index have been studied and the results are tabulated. The electronic parameters such as valence electron plasma energy, ℏωp , Penn gap, Ep , Fermi energy, EF and Electronic polarizability, α for pure and irradiated LAMD crystals are calculated. The electrical and thermal properties of the pure and irradiated LAMD crystals are also investigated.

Engineering the electronic structure of graphene superlattices via Fermi velocity modulation

NASA Astrophysics Data System (ADS)

Lima, Jonas R. F.

2017-01-01

Graphene superlattices have attracted much research interest in the last years, since it is possible to manipulate the electronic properties of graphene in these structures. It has been verified that extra Dirac points appear in the electronic structure of the system. The electronic structure in the vicinity of these points has been studied for a gapless and gapped graphene superlattice and for a graphene superlattice with a spatially modulated energy gap. In each case a different behavior was obtained. In this work we show that via Fermi velocity engineering it is possible to tune the electronic properties of a graphene superlattice to match all the previous cases studied. We also obtained new features of the system never observed before, reveling that the electronic structure of graphene is very sensitive to the modulation of the Fermi velocity. The results obtained here are relevant for the development of novel graphene-based electronic devices.

First principles studies of electron tunneling in proteins

PubMed Central

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

2014-01-01

A first principles study of electronic tunneling along the chain of seven Fe/S clusters in respiratory complex I, a key enzyme in the respiratory electron transport chain, is described. The broken-symmetry states of the Fe/S metal clusters calculated at both DFT and semi-empirical ZINDO levels were utilized to examine both the extremely weak electronic couplings between Fe/S clusters and the tunneling pathways, which provide a detailed atomistic-level description of the charge transfer process in the protein. One-electron tunneling approximation was found to hold within a reasonable accuracy, with only a moderate induced polarization of the core electrons. The method is demonstrated to be able to calculate accurately the coupling matrix elements as small as 10−4 cm−1. A distinct signature of the wave properties of electrons is observed as quantum interferences of multiple tunneling pathways. PMID:25383312

Coupled study by TEM/EELS and STM/STS of electronic properties of C- and CN-nanotubes

NASA Astrophysics Data System (ADS)

Lin, Hong; Lagoute, Jérôme; Repain, Vincent; Chacon, Cyril; Girard, Yann; Lauret, Jean-Sébastien; Arenal, Raul; Ducastelle, François; Rousset, Sylvie; Loiseau, Annick

2011-12-01

Carbon nanotubes are the focus of considerable research efforts due to their fascinating physical properties. They provide an excellent model system for the study of one-dimensional materials and molecular electronics. The chirality of nanotubes can lead to very different electronic behaviour, either metallic or semiconducting. Their electronic spectrum consists of a series of Van Hove singularities defining a bandgap for semiconducting tubes and molecular orbitals at the corresponding energies. A promising way to tune the nanotubes electronic properties for future applications is to use doping by heteroatoms. Here we report on the experimental investigation of the role of many-body interactions in nanotube bandgaps, the visualization in direct space of the molecular orbitals of nanotubes and the properties of nitrogen doped nanotubes using scanning tunneling microscopy and transmission electron microscopy as well as electron energy loss spectroscopy.

Analysis of proton and electron spectrometer data from OGO-5 spacecraft

NASA Technical Reports Server (NTRS)

Pomerantz, M. A.

1975-01-01

The interaction between the geomagnetic and interplanetary magnetic fields is studied through its effects upon the intensities of solar electrons reaching the polar caps during times of strongly anisotropic electron fluxes in the magnetosheath. During the particle event of November 18, 1968, electrons of solar origin were observed outside the magnetopause with detectors aboard OGO-5. Correlative studies of these satellite observations and concurrent measurements by riometers and ionospheric forward scatter systems in both polar regions revealed that the initial stage of the associated polar cap absorption event is attributable to the arrival of solar electrons. Evidence of a north-south asymmetry in the solar electron flux, at a time when the interplanetary magnetic field vector was nearly parallel with the ecliptic plane, supports an open magnetospheric model. The analysis indicates that an anisotropic electron flux may be isotropized at the magnetopause before propagating into the polar regions.

Electron acoustic solitary waves in a magnetized plasma with nonthermal electrons and an electron beam

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

Singh, S. V., E-mail: satyavir@iigs.iigm.res.in; Lakhina, G. S., E-mail: lakhina@iigs.iigm.res.in; University of the Western Cape, Belville

2016-08-15

A theoretical investigation is carried out to study the obliquely propagating electron acoustic solitary waves having nonthermal hot electrons, cold and beam electrons, and ions in a magnetized plasma. We have employed reductive perturbation theory to derive the Korteweg-de-Vries-Zakharov-Kuznetsov (KdV-ZK) equation describing the nonlinear evolution of these waves. The two-dimensional plane wave solution of KdV-ZK equation is analyzed to study the effects of nonthermal and beam electrons on the characteristics of the solitons. Theoretical results predict negative potential solitary structures. We emphasize that the inclusion of finite temperature effects reduces the soliton amplitudes and the width of the solitons increasesmore » by an increase in the obliquity of the wave propagation. The numerical analysis is presented for the parameters corresponding to the observations of “burst a” event by Viking satellite on the auroral field lines.« less

Runaway electrons in tokamaks

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

Liu, Chang

The generation of runaway electrons is a complex and important phenomenon that impacts many areas of plasma physics. Due to the decrease of electron collision frequency with increasing velocity, electrons under strong electric field can experience unlimited “runaway” acceleration. In tokamaks, runaway electrons can be produced in disruptions, due to the strong inductive electric field formed as the thermal energy of plasma gets rapidly lost. This population of runaway electrons can undergo an exponential growth, denoted the runaway electron avalanche, due to hard collisions between relativistic runaway electrons and low energy electrons. It is predicted that in a large tokamakmore » device like the International Thermonuclear Experimental Reactor (ITER), a runway electron beam generated in a disruption event can potentially cause severe damage to the device, which poses a significant challenge for ITER to achieve its mission. It is therefore extremely important to seek an effective mitigation mechanism for runaway electrons. Experimental efforts have been made to study the properties of runaway electrons in tokamaks, including their generation, diffusion, and radiation. In order to understand these experimental results, extensive theoretical and simulation studies of runaway electron physics are required. The main topic of this thesis is to study the wave particle interaction associated with runaway electron beams in tokamaks. The runaway electrons can emit and absorb electromagnetic waves through resonances, and can be diffused in momentum space by the waves. Initially, we address the Cherenkov radiation of runaway electrons, which originates from the polarization of the plasma medium. The energy and momentum loss of the Cherenkov radiation can be modeled by adding a correction to the Coulomb logarithm in the collisional drag force. Subsequently, we address pitch angle scattering caused by normal modes in the plasma, which are driven unstable by the anisotropicity of the runaway electron beam. The fluctuating electromagnetic fields are found to act as a seed for the unstable normal modes. Numerical simulations show that the pitch angle scattering effect from the normal modes, mainly whistler waves, can be significantly larger than that from collisional pitch angle scattering. Finally, we present a synthetic diagnostic tool we developed to calculate the electron cyclotron emission (ECE) from the runaway electrons, and successfully reproduce the prompt growth of the ECE signal observed in DIII-D quiescent runaway electron (QRE) experiments. Within the thesis, we also present the application of the adjoint method to runaway electron research, and show the calculations of the runaway probability function (RPF) and the expected loss time (ELT). These calculations not only help depict the dynamics of runaway electrons in momentum space, but also can be used to efficiently calculate experimentally relevant quantities such as the critical electric field for runaway electron avalanche and the avalanche growth rate.« less

Molecular Electron Density Theory: A Modern View of Reactivity in Organic Chemistry.

PubMed

Domingo, Luis R

2016-09-30

A new theory for the study of the reactivity in Organic Chemistry, named Molecular Electron Density Theory (MEDT), is proposed herein. MEDT is based on the idea that while the electron density distribution at the ground state is responsible for physical and chemical molecular properties, as proposed by the Density Functional Theory (DFT), the capability for changes in electron density is responsible for molecular reactivity. Within MEDT, the reactivity in Organic Chemistry is studied through a rigorous quantum chemical analysis of the changes of the electron density as well as the energies associated with these changes along the reaction path in order to understand experimental outcomes. Studies performed using MEDT allow establishing a modern rationalisation and to gain insight into molecular mechanisms and reactivity in Organic Chemistry.

Effect of Single-Electron Interface Trapping in Decanano MOSFETs: A 3D Atomistic Simulation Study

NASA Technical Reports Server (NTRS)

Asenov, Asen; Balasubramaniam, R.; Brown, A. R.; Davies, J. H.

2000-01-01

We study the effect of trapping/detrapping of a single-electron in interface states in the channel of n-type MOSFETs with decanano dimensions using 3D atomistic simulation techniques. In order to highlight the basic dependencies, the simulations are carried out initially assuming continuous doping charge, and discrete localized charge only for the trapped electron. The dependence of the random telegraph signal (RTS) amplitudes on the device dimensions and on the position of the trapped charge in the channel are studied in detail. Later, in full-scale, atomistic simulations assuming discrete charge for both randomly placed dopants and the trapped electron, we highlight the importance of current percolation and of traps with strategic position where the trapped electron blocks a dominant current path.

Double photoionization of atoms

NASA Astrophysics Data System (ADS)

Wiedenhoeft, Marco

2003-10-01

Double photoionization studies of atoms and molecules are new state-of-the-art studies providing a deeper knowledge of multi-electron excitations. This type of work advances the understanding of many-body problems. Double photoionization of atoms is of great interest to learn about electron-electron correlation and relaxation effects in atoms and molecules. In order to study double photoionization processes, a new electron-electron coincidence apparatus was built to carry out the measurements. I will present the apparatus I built as well as the results of the measurement of the triply-differential-cross-section (TDCS) for the predicted interference and Post-Collision-Interaction (PCI) effects in the Xenon N5O2,3 O2,3 Auger decay after 4d5/2 photoionization. Furthermore I present measurements for direct double photoionization of Helium at various photon energies.

Electron Energy Loss Spectral Imaging of TiC Formed by Supernovae: A Scanning Transmission Electron Microscopy Study of Grain Formation and Alteration Mechanisms

NASA Astrophysics Data System (ADS)

Daulton, T. L.; Bernatowicz, T. J.; Croat, T. K.

2012-03-01

Micrometer-sized spherules of graphite formed by supernovae contain numerous TiC and Fe-Ni subgrains. These subgrains often have disordered surface rims. The mechanism(s) of rim formation on these subgrains is studied by transmission electron microscopy.

Impact of Electronic Portfolios on Prospective Teachers' Participation, Motivation, and Autonomous Learning

ERIC Educational Resources Information Center

Gámiz-Sánchez, Vanesa-María; Gallego-Arrufat, María-Jesús; Crisol-Moya, Emilio

2016-01-01

This study explores the impact of electronic portfolios on undergraduate learning in higher education. Based on a descriptive study, it analyses the prospective teacher's perception of use of these tools (electronic portfolio in Moodle-Mahara, in the institutional environment of a university in southern Europe), examining the variables…

The Efficacy of Electronic Books in Fostering Kindergarten Children's Emergent Story Understanding

ERIC Educational Resources Information Center

de Jong, Maria T.; Bus, Adriana G.

2004-01-01

A counterbalanced, within-subjects design was carried out to study the efficacy of electronic books in fostering kindergarten children's emergent story understanding. The study compared effects of children's independent reading of stories electronically with effects of printed books read aloud by adults. Participants were 18 four- to five-year-old…

Problems in Learning of Electronic Filing at Vocational School in Yogyakarta Special Region, Indonesia

ERIC Educational Resources Information Center

Sutirman; Muhyadi; Surjono, Herman Dwi

2017-01-01

This study aims to investigate the learning implementation of electronic filing and problems faced by teachers in learning implementing of electronic filing. This study is a descriptive research with qualitative approach. Collecting data used interview and documentation techniques. The research subjects consisted of 29 teachers who teach Filing…

"Clickers" and Metacognition: How Do Electronic Response Devices ("Clickers") Influence Student Metacognition?

ERIC Educational Resources Information Center

Manke-Brady, Melanie

2012-01-01

The purpose of this study was to examine whether electronic response systems influence student metacognitions in large lecture settings, and how metacognitive processes are influenced. Moreover, this study compared electronic response systems with a low technology system and sought to establish whether differences exist in how the two response…

A Laboratory Study of the Charging/Discharging Mechanisms of a Dust Particle Exposed to an Electron Beam

NASA Technical Reports Server (NTRS)

Venturini, C. C.; Spann, J. F.; Comfort, R. H.

1999-01-01

The interaction of micron sized particles or "dust particles" with different space and planetary environments has become an important area of research. One particular area of interest is how dust particles interact with plasmas. Studies have shown that charged dust particles immersed in plasmas can alter plasma characteristics, while ions and electrons in plasmas can affect a particle's potential and thereby, its interaction with other particles. The basis for understanding these phenomena is the charging mechanisms of the dust particle, specifically, how the particle's charge and characteristics are affected when exposed to ions and electrons. At NASA Marshall Space Flight Center, a laboratory experiment has been developed to study the interaction of dust particles with electrons. Using a unique laboratory technique known as electrodynamic suspension, a single charged particle is suspended in a modified quadrupole trap. Once suspended, the particle is then exposed to an electron beam to study the charging/discharging mechanisms due to collisions of energetic electrons. The change in the particle's charge, approximations of the charging/discharging currents, and the charging/discharging yield are calculated.

Ultra high vacuum test setup for electron gun

NASA Astrophysics Data System (ADS)

Pandiyar, M. L.; Prasad, M.; Jain, S. K.; Kumar, R.; Hannurkar, P. R.

2008-05-01

Ultra High Vacuum (UHV) test setup for electron gun testing has been developed. The development of next generation light sources and accelerators require development of klystron as a radio frequency power source, and in turn electron gun. This UHV electron gun test setup can be used to test the electron guns ranging from high average current, quasi-continuous wave to high peak current, single pulse etc. An electron gun has been designed, fabricated, assembled and tested for insulation up to 80 kV under the programme to develop high power klystron for future accelerators. Further testing includes the electron emission parameters characterization of the cathode, as it determines the development of a reliable and efficient electron gun with high electron emission current and high life time as well. This needs a clean ultra high vacuum to study these parameters particularly at high emission current. The cathode emission current, work function and vapour pressure of cathode surface material at high temperature studies will further help in design and development of high power electron gun The UHV electron gun test setup consists of Turbo Molecular Pump (TMP), Sputter Ion Pump (SIP), pressure gauge, high voltage and cathode power supplies, current measurement device, solenoid magnet and its power supply, residual gas analyser etc. The ultimate vacuum less than 2×10-9 mbar was achieved. This paper describes the UHV test setup for electron gun testing.

Monte Carlo simulations of secondary electron emission due to ion beam milling

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

Mahady, Kyle; Tan, Shida; Greenzweig, Yuval

We present a Monte Carlo simulation study of secondary electron emission resulting from focused ion beam milling of a copper target. The basis of this study is a simulation code which simulates ion induced excitation and emission of secondary electrons, in addition to simulating focused ion beam sputtering and milling. This combination of features permits the simulation of the interaction between secondary electron emission, and the evolving target geometry as the ion beam sputters material. Previous ion induced SE Monte Carlo simulation methods have been restricted to predefined target geometries, while the dynamic target in the presented simulations makes thismore » study relevant to image formation in ion microscopy, and chemically assisted ion beam etching, where the relationship between sputtering, and its effects on secondary electron emission, is important. We focus on a copper target, and validate our simulation against experimental data for a range of: noble gas ions, ion energies, ion/substrate angles and the energy distribution of the secondary electrons. We then provide a detailed account of the emission of secondary electrons resulting from ion beam milling; we quantify both the evolution of the yield as high aspect ratio valleys are milled, as well as the emission of electrons within these valleys that do not escape the target, but which are important to the secondary electron contribution to chemically assisted ion induced etching.« less

Study of variations in structural, optical parameters and bulk etch rate of CR-39 polymer due to electron irradiation

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

Sahoo, G. S.; Joshi, D. S.; Tripathy, S. P., E-mail: sam.tripathy@gmail.com, E-mail: tripathy@barc.gov.in

2016-07-14

In this work, electron induced modifications on the bulk etch rate, structural and optical parameters of CR-39 polymer were studied using gravimetric, FTIR (Fourier Transform Infrared) and UV–vis (Ultraviolet–Visible) techniques, respectively. CR-39 samples were irradiated with 10 MeV electron beam for different durations to have the absorbed doses of 1, 10, 550, 5500, 16 500, and 55 000 kGy. From the FTIR analysis, the peak intensities at different bands were found to be changing with electron dose. A few peaks were observed to shift at high electron doses. From the UV-vis analysis, the optical band gaps for both direct and indirect transitions weremore » found to be decreasing with the increase in electron dose whereas the opacity, number of carbon atoms in conjugation length, and the number of carbon atoms per cluster were found to be increasing. The bulk etch rate was observed to be increasing with the electron dose. The primary objective of this investigation was to study the response of CR-39 to high electron doses and to determine a suitable pre-irradiation condition. The results indicated that, the CR-39 pre-irradiated with electrons can have better sensitivity and thus can be potentially applied for neutron dosimetry.« less

Investigation of the surface sensitivity of positron-annihilation-induced Auger-electron spectroscopy

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

Mehl, D.R.

1990-01-01

The first surface sensitivity studies of positron-annihilation-induced Auger-electron spectroscopy (PAES) are presented. Preliminary measurements on polycrystalline Al with adsorbates indicate that PAES is more selective of the surface than conventional electron-induced Auger electron spectroscopy (EAES). PAES and EAES studies of well-defined overlayer-metal systems of Cu(110)+S and Cu(110)+Cs verify that PAES is selective of the top atomic layer. This surface selectivity is accounted for by theoretical calculations which indicate that the positron surface state is displaced away from the substrate by the over-layer, decreasing the annihilation rate of positrons with substrate core electrons.

Determination of electron-nucleus collisions geometry with forward neutrons

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

Zheng, L.; Aschenauer, E.; Lee, J. H.

2014-12-29

There are a large number of physics programs one can explore in electron-nucleus collisions at a future electron-ion collider. Collision geometry is very important in these studies, while the measurement for an event-by-event geometric control is rarely discussed in the prior deep-inelastic scattering experiments off a nucleus. This paper seeks to provide some detailed studies on the potential of tagging collision geometries through forward neutron multiplicity measurements with a zero degree calorimeter. As a result, this type of geometry handle, if achieved, can be extremely beneficial in constraining nuclear effects for the electron-nucleus program at an electron-ion collider.

A study of electrically active traps in AlGaN/GaN high electron mobility transistor

NASA Astrophysics Data System (ADS)

Yang, Jie; Cui, Sharon; Ma, T. P.; Hung, Ting-Hsiang; Nath, Digbijoy; Krishnamoorthy, Sriram; Rajan, Siddharth

2013-10-01

We have studied electron conduction mechanisms and the associated roles of the electrically active traps in the AlGaN layer of an AlGaN/GaN high electron mobility transistor structure. By fitting the temperature dependent I-V (Current-Voltage) curves to the Frenkel-Poole theory, we have identified two discrete trap energy levels. Multiple traces of I-V measurements and constant-current injection experiment all confirm that the main role of the traps in the AlGaN layer is to enhance the current flowing through the AlGaN barrier by trap-assisted electron conduction without causing electron trapping.

Theoretical study of the effect of ionospheric return currents on the electron temperature

NASA Technical Reports Server (NTRS)

Schunk, R. W.; Sojka, J. J.; Bowline, M. D.

1987-01-01

A time-dependent, three-dimensional model of the high-altitude ionosphere is presently used to study the effects of field-aligned ionospheric return currents on auroral electron temperatures for different seasonal and solar cycle conditions, as well as for different upper boundary heat fluxes. The average, large scale, return current densities, which are a few microamps/sq m, are too small to affect auroral electron temperatures. The thermoelectric effect exhibits a pronounced solar cycle and seasonal dependence, and its heat transport corresponds to an upward flow of electron energy which can be either a source or sink of electron energy depending on altitude and geophysical conditions.

Study of inelastic e-Cd and e-Zn collisions

NASA Astrophysics Data System (ADS)

Piwinski, Mariusz; Klosowski, Lukasz; Dziczek, Darek; Chwirot, Stanislaw

2016-09-01

Electron-photon coincidence experiments are well known for providing more detailed information about electron-atom collision than any other technique. The Electron Impact Coherence Parameters (EICP) values obtained in such studies deliver the most complete characterization of the inelastic collision and allow for a verification of proposed theoretical models. We present the results of Stokes and EICP parameters characterising electronic excitation of the lowest singlet P-state of cadmium and zinc atoms for various collision energies. The experiments were performed using electron-photon coincidence technique in the coherence analysis version. The obtained data are presented and compared with existing CCC and RDWA theoretical predictions.

An electro-optical and electron injection study of benzothiazole-based squaraine dyes as efficient dye-sensitized solar cell materials: a first principles study.

PubMed

Al-Fahdan, Najat Saeed; Asiri, Abdullah M; Irfan, Ahmad; Basaif, Salem A; El-Shishtawy, Reda M

2014-12-01

Squaraine dyes have attracted significant attention in many areas of daily life from biomedical imaging to semiconducting materials. Moreover, these dyes are used as photoactive materials in the field of solar cells. In the present study, we investigated the structural, electronic, photophysical, and charge transport properties of six benzothiazole-based squaraine dyes (Cis-SQ1-Cis-SQ3 and Trans-SQ1-Trans-SQ3). The effect of electron donating (-OCH3) and electron withdrawing (-COOH) groups was investigated intensively. Ground state geometry and frequency calculations were performed by applying density functional theory (DFT) at B3LYP/6-31G** level of theory. Absorption spectra were computed in chloroform at the time-dependent DFT/B3LYP/6-31G** level of theory. The driving force of electron injection (ΔG (inject)), relative driving force of electron injection (ΔG r (inject)), electronic coupling constants (|VRP|) and light harvesting efficiency (LHE) of all six compounds were calculated and compared with previously studied sensitizers. The ΔG (inject), ΔG r (inject) and |VRP| of all six compounds revealed that these sensitizers would be efficient dye-sensitized solar cell materials. Cis/Trans-SQ3 exhibited superior LHE as compared to other derivatives. The Cis/Trans geometric effect was studied and discussed with regard to electro-optical and charge transport properties.

Data Documentation for Navy Civilian Manpower Study,

DTIC Science & Technology

1986-09-01

Engineering 0830 Mechanical Engineer 0840 Nuclear Engineering 0850 Electrical Engineering 0855 Electronics Engineering 0856 Electronics ...OCCUPATIONAL LEVEL (DONOL) CODES DONOL code Title 1060 Engineering Drafting 1061 Electronics Technician w 1062 Engineering Technician 1063 Industrial...Architect 2314 Electrical Engineer 2315 Electronic Engineer 2316 Industrial Engineer 2317 Mechanical Engineer 2318

Electron and photon identification in the D0 experiment

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

Abazov, V. M.; Abbott, B.; Acharya, B. S.

2014-06-01

The electron and photon reconstruction and identification algorithms used by the D0 Collaboration at the Fermilab Tevatron collider are described. The determination of the electron energy scale and resolution is presented. Studies of the performance of the electron and photon reconstruction and identification are summarized.

A Case Study in E-Journal Developments: The Scandinavian Position.

ERIC Educational Resources Information Center

Joa, Harald

1997-01-01

Provides an overview of peer-reviewed scientific and scholarly electronic journals in Scandinavia from a publisher's point of view. Discusses the electronic journals market in Scandinavia, international electronic publishing, the Institute for Scientific Information's Electronic Library Project, the one-stop shopping concept, and copyright and…

Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices

DTIC Science & Technology

2015-06-01

either Co– or MnSi– initiated films on c(4x4) GaAs. Studies using x - ray photoemission spectroscopy (XPS), STM/STS, and transmission electron microscopy...Co– or MnSi– initiated films on c(4x4) GaAs. Studies using x - ray photoemission spectroscopy (XPS), STM/STS, and transmission electron microscopy (TEM...diagram of the Palmstrøm lab in-situ growth and char- acterization setup, with 6 MBE growth chambers, 3 scanning probe microscopes, an x - ray

Feasibility study of common electronic equipment for shuttle sortie experiment payloads

NASA Technical Reports Server (NTRS)

1974-01-01

A study was conducted to determine the feasibility of using standardized electronic equipment on the space shuttle vehicle in an effort to reduce the cost estimates. The standards for Nuclear Instrument Modules (NIM) and CAMAC electronic equipment are presented and described. It was determined that the CAMAC electronic equipment was more suitable for use with the space shuttle systems. Specific applications of the CAMAC equipment are analyzed. Illustrations of the equipment and circuit diagrams of the subsystems are provided.

Electron drift velocity and mobility in graphene

NASA Astrophysics Data System (ADS)

Dong, Hai-Ming; Duan, Yi-Feng; Huang, Fei; Liu, Jin-Long

2018-04-01

We present a theoretical study of the electric transport properties of graphene-substrate systems. The drift velocity, mobility, and temperature of the electrons are self-consistently determined using the Boltzmann equilibrium equations. It is revealed that the electronic transport exhibits a distinctly nonlinear behavior. A very high mobility is achieved with the increase of the electric fields increase. The electron velocity is not completely saturated with the increase of the electric field. The temperature of the hot electrons depends quasi-linearly on the electric field. In addition, we show that the electron velocity, mobility, and electron temperature are sensitive to the electron density. These findings could be employed for the application of graphene for high-field nano-electronic devices.

Advanced Accelerators: Particle, Photon and Plasma Wave Interactions

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

Williams, Ronald L.

2017-06-29

The overall objective of this project was to study the acceleration of electrons to very high energies over very short distances based on trapping slowly moving electrons in the fast moving potential wells of large amplitude plasma waves, which have relativistic phase velocities. These relativistic plasma waves, or wakefields, are the basis of table-top accelerators that have been shown to accelerate electrons to the same high energies as kilometer-length linear particle colliders operating using traditional decades-old acceleration techniques. The accelerating electrostatic fields of the relativistic plasma wave accelerators can be as large as GigaVolts/meter, and our goal was to studymore » techniques for remotely measuring these large fields by injecting low energy probe electron beams across the plasma wave and measuring the beam’s deflection. Our method of study was via computer simulations, and these results suggested that the deflection of the probe electron beam was directly proportional to the amplitude of the plasma wave. This is the basis of a proposed diagnostic technique, and numerous studies were performed to determine the effects of changing the electron beam, plasma wave and laser beam parameters. Further simulation studies included copropagating laser beams with the relativistic plasma waves. New interesting results came out of these studies including the prediction that very small scale electron beam bunching occurs, and an anomalous line focusing of the electron beam occurs under certain conditions. These studies were summarized in the dissertation of a graduate student who obtained the Ph.D. in physics. This past research program has motivated ideas for further research to corroborate these results using particle-in-cell simulation tools which will help design a test-of-concept experiment in our laboratory and a scaled up version for testing at a major wakefield accelerator facility.« less

Investigation of viability of plant tissue in the environmental scanning electron microscopy.

PubMed

Zheng, Tao; Waldron, K W; Donald, Athene M

2009-11-01

The advantages of environmental scanning electron microscopy (ESEM) make it a suitable technique for studying plant tissue in its native state. There have been few studies on the effects of ESEM environment and beam damage on the viability of plant tissue. A simple plant tissue, Allium cepa (onion) upper epidermal tissue was taken as the model for study. The change of moisture content of samples was studied at different relative humidities. Working with the electron beam on, viability tests were conducted for samples after exposure in the ESEM under different operating conditions to investigate the effect of electron beam dose on the viability of samples. The results suggested that without the electron beam, the ESEM chamber itself can prevent the loss of initial moisture if its relative humidity is maintained above 90%. With the electron beam on, the viability of Allium cepa (onion) cells depends both on the beam accelerating voltage and the electron dose/unit area hitting the sample. The dose can be controlled by several of the ESEM instrumental parameters. The detailed process of beam damage on cuticle-down and cuticle-up samples was investigated and compared. The results indicate that cuticular adhesion to the cell wall is relatively weak, but highly resistant to electron beam damage. Systematic study on the effect of ESEM operation parameters has been done. Results qualitatively support the intuitive expectations, but demonstrate quantitatively that Allium cepa epidermal cells are able to be kept in a hydrated and viable state under relevant operation condition inside ESEM, providing a basis for further in situ experiments on plant tissues.

Progress in Fast Ignition Studies with Electrons and Protons

NASA Astrophysics Data System (ADS)

MacKinnon, A. J.; Akli, K. U.; Bartal, T.; Beg, F. N.; Chawla, S.; Chen, C. D.; Chen, H.; Chen, S.; Chowdhury, E.; Fedosejevs, R.; Freeman, R. R.; Hey, D.; Higginson, D.; Key, M. H.; King, J. A.; Link, A.; Ma, T.; MacPhee, A. G.; Offermann, D.; Ovchinnikov, V.; Pasley, J.; Patel, P. K.; Ping, Y.; Schumacher, D. W.; Stephens, R. B.; Tsui, Y. Y.; Wei, M. S.; Van Woerkom, L. D.

2009-09-01

Isochoric heating of inertially confined fusion plasmas by laser driven MeV electrons or protons is an area of great topical interest in the inertial confinement fusion community, particularly with respect to the fast ignition (FI) concept for initiating burn in a fusion capsule. In order to investigate critical aspects needed for a FI point design, experiments were performed to study 1) laser-to-electrons or protons conversion issues and 2) laser-cone interactions including prepulse effects. A large suite of diagnostics was utilized to study these important parameters. Using cone—wire surrogate targets it is found that pre-pulse levels on medium scale lasers such as Titan at Lawrence Livermore National Laboratory produce long scale length plasmas that strongly effect coupling of the laser to FI relevant electrons inside cones. The cone wall thickness also affects coupling to the wire. Conversion efficiency to protons has also been measured and modeled as a function of target thickness, material. Conclusions from the proton and electron source experiments will be presented. Recent advances in modeling electron transport and innovative target designs for reducing igniter energy and increasing gain curves will also be discussed. In conclusion, a program of study will be presented based on understanding the fundamental physics of the electron or proton source relevant to FI.

Standardizing terminology and definitions of medication adherence and persistence in research employing electronic databases.

PubMed

Raebel, Marsha A; Schmittdiel, Julie; Karter, Andrew J; Konieczny, Jennifer L; Steiner, John F

2013-08-01

To propose a unifying set of definitions for prescription adherence research utilizing electronic health record prescribing databases, prescription dispensing databases, and pharmacy claims databases and to provide a conceptual framework to operationalize these definitions consistently across studies. We reviewed recent literature to identify definitions in electronic database studies of prescription-filling patterns for chronic oral medications. We then develop a conceptual model and propose standardized terminology and definitions to describe prescription-filling behavior from electronic databases. The conceptual model we propose defines 2 separate constructs: medication adherence and persistence. We define primary and secondary adherence as distinct subtypes of adherence. Metrics for estimating secondary adherence are discussed and critiqued, including a newer metric (New Prescription Medication Gap measure) that enables estimation of both primary and secondary adherence. Terminology currently used in prescription adherence research employing electronic databases lacks consistency. We propose a clear, consistent, broadly applicable conceptual model and terminology for such studies. The model and definitions facilitate research utilizing electronic medication prescribing, dispensing, and/or claims databases and encompasses the entire continuum of prescription-filling behavior. Employing conceptually clear and consistent terminology to define medication adherence and persistence will facilitate future comparative effectiveness research and meta-analytic studies that utilize electronic prescription and dispensing records.

Study of clusters using negative ion photodetachment spectroscopy

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

Zhao, Yuexing

1995-12-01

The weak van der Waals interaction between an open-shell halogen atom and a closed-shell atom or molecule has been investigated using zero electron kinetic energy (ZEKE) spectroscopy. This technique is also applied to study the low-lying electronic states in GaAs and GaAs -. In addition, the spectroscopy and electron detachment dynamics of several small carbon cluster anions are studied using resonant multiphoton detachment spectroscopy.

Waste electrical and electronic equipment management and Basel Convention compliance in Brazil, Russia, India, China and South Africa (BRICS) nations.

PubMed

Ghosh, Sadhan Kumar; Debnath, Biswajit; Baidya, Rahul; De, Debashree; Li, Jinhui; Ghosh, Sannidhya Kumar; Zheng, Lixia; Awasthi, Abhishek Kumar; Liubarskaia, Maria A; Ogola, Jason S; Tavares, André Neiva

2016-08-01

Brazil, Russia, India, China and South Africa (BRICS) nations account for one-quarter of the world's land area, having more than 40% of the world's population, and only one-quarter of the world gross national income. Hence the study and review of waste electrical and electronic equipment management systems in BRICS nations is of relevance. It has been observed from the literature that there are studies available comparing two or three country's waste electrical and electronic equipment status, while the study encompassing the BRICS nations considering in a single framework is scant. The purpose of this study is to analyse the existing waste electrical and electronic equipment management systems and status of compliance to Basel convention in the BRICS nations, noting possible lessons from matured systems, such as those in the European Union EU) and USA. The study introduced a novel framework for a waste electrical and electronic equipment management system that may be adopted in BRICS nations and revealed that BRICS countries have many similar types of challenges. The study also identified some significant gaps with respect to the management systems and trans-boundary movement of waste electrical and electronic equipment, which may attract researchers for further research. © The Author(s) 2016.

Millisecond resolution electron fluxes from the Cluster satellites: Calibrated EDI ambient electron data

NASA Astrophysics Data System (ADS)

Förster, Matthias; Rashev, Mikhail; Haaland, Stein

2017-04-01

The Electron Drift Instrument (EDI) onboard Cluster can measure 500 eV and 1 keV electron fluxes with high time resolution during passive operation phases in its Ambient Electron (AE) mode. Data from this mode is available in the Cluster Science Archive since October 2004 with a cadence of 16 Hz in the normal mode or 128 Hz for burst mode telemetry intervals. The fluxes are recorded at pitch angles of 0, 90, and 180 degrees. This paper describes the calibration and validation of these measurements. The high resolution AE data allow precise temporal and spatial diagnostics of magnetospheric boundaries and will be used for case studies and statistical studies of low energy electron fluxes in the near-Earth space. We show examples of applications.

The Diffusion of Electronic Text among University Students and Faculty: A Strategy for Laboratory Research. Monograph Number One of the Electronic Text Monograph Series.

ERIC Educational Resources Information Center

Dozier, David M.

This monograph defines and describes research in the study of adoption of electronic text services in higher education institutions. Electronic text here includes text and graphic information encoded and transmitted via broadcast, signal, or cable, under user control. It places the diffusion of electronic text in higher education within the…

Electronic Commerce: A National Performance Review Initiative.

DTIC Science & Technology

1995-09-01

This study of the National Information Infrastructure (NII) was conducted as part of IDA’s Central Research Program. Electronic commerce is one of... commerce is nothing more than conducting business via electronic means. An outgrowth of the NPR, the electronic commerce initiative, commits the...private, and public sectors are committed to implementing electronic commerce throughout the United States. The objective ol this paper is to enhance

Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles

PubMed Central

Tvrdy, Kevin; Frantsuzov, Pavel A.; Kamat, Prashant V.

2011-01-01

Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO2, TiO2, and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO2) were not the same as those which showed the highest photocurrent (TiO2). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency. PMID:21149685

Electronic Health in Perspective of Healthcare Managers: A Qualitative Study in South of Iran

PubMed Central

BASTANI, Peivand; ABOLHASANI, Nazanin; SHAARBAFCHIZADEH, Nasrin

2014-01-01

Abstract Background The important role of electronic health as well as importance of health care systems awareness and readiness may lead to develop the essential infrastructures for electronic health especially in developing countries. This study aims to investigate goals, gains, applications, challenges and other important issues related to success performance of electronic health. Method This research proposed a grounded theory in a qualitative design and a purposive sampling was used to select participants which consisted of 28 hospital managers and staff field managers working in deputy of health and curative affairs of Medical Science Universities in south of Iran. Semi structured interviews were conducted using a topic guide and intended themes derived from the results using Max QDA software during five steps. Results Nine themes through interviewees” viewpoints were made up as followed: Electronic health definition, necessity and importance of electronic health, electronic health advantages, relationship between electronic health and internet, physicians” opposition to electronic health, prerequisites for electronic health, solutions for applying electronic health plan, factors affecting electronic health acceptance in society and electronic health system challenges. Conclusion It seems that there are good circumstances in the south medical universities about settlement and implementations of electronic health and their managers are aware of its advantages, importance and necessities. The present findings implicate that these organizations should consider the user friendly and probable resistances of the present clients, in this regard it is suggested that the used technology must be accepted by users, having standard base, inexpensive and simple enough while less vulnerable in response to changes. PMID:26110152

Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles.

PubMed

Tvrdy, Kevin; Frantsuzov, Pavel A; Kamat, Prashant V

2011-01-04

Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO(2), TiO(2), and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO(2)) were not the same as those which showed the highest photocurrent (TiO(2)). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency.

Electronic Health in Perspective of Healthcare Managers: A Qualitative Study in South of Iran.

PubMed

Bastani, Peivand; Abolhasani, Nazanin; Shaarbafchizadeh, Nasrin

2014-06-01

The important role of electronic health as well as importance of health care systems awareness and readiness may lead to develop the essential infrastructures for electronic health especially in developing countries. This study aims to investigate goals, gains, applications, challenges and other important issues related to success performance of electronic health. This research proposed a grounded theory in a qualitative design and a purposive sampling was used to select participants which consisted of 28 hospital managers and staff field managers working in deputy of health and curative affairs of Medical Science Universities in south of Iran. Semi structured interviews were conducted using a topic guide and intended themes derived from the results using Max QDA software during five steps. Nine themes through interviewees" viewpoints were made up as followed: Electronic health definition, necessity and importance of electronic health, electronic health advantages, relationship between electronic health and internet, physicians" opposition to electronic health, prerequisites for electronic health, solutions for applying electronic health plan, factors affecting electronic health acceptance in society and electronic health system challenges. It seems that there are good circumstances in the south medical universities about settlement and implementations of electronic health and their managers are aware of its advantages, importance and necessities. The present findings implicate that these organizations should consider the user friendly and probable resistances of the present clients, in this regard it is suggested that the used technology must be accepted by users, having standard base, inexpensive and simple enough while less vulnerable in response to changes.

An Educational Laboratory for Digital Control and Rapid Prototyping of Power Electronic Circuits

ERIC Educational Resources Information Center

Choi, Sanghun; Saeedifard, M.

2012-01-01

This paper describes a new educational power electronics laboratory that was developed primarily to reinforce experimentally the fundamental concepts presented in a power electronics course. The developed laboratory combines theoretical design, simulation studies, digital control, fabrication, and verification of power-electronic circuits based on…

Electronic Computer Aided Design. Its Application in FE.

ERIC Educational Resources Information Center

Further Education Unit, London (England).

A study was conducted at the Electronics Industrial Unit at the Dorset Institute of Higher Education to investigate the feasibility of incorporating computer-aided design (CAD) in electrical and electronic courses. The aim was to investigate the application of CAD to electrical and electronic systems; the extent to which industrial developments…

Math for Electronics; Industrial Electronics 1: 9323.04.

ERIC Educational Resources Information Center

Dade County Public Schools, Miami, FL.

This curriculum guide is designed for the student interested in preparing for vocational electronics and related fields of electricity, emphasizing the mathematics necessary for an indepth study of electronics. Included in the course content are goals, specific block objectives, basic algebra, powers of 10, the slide rule, basic trigonometry…

Influence of mitochondrial efficiency on beef lean color stability

USDA-ARS?s Scientific Manuscript database

Loss of electrons in the electron transport chain has been implicated as a source of variation in feed efficiency of meat producing animals. The present study was conducted to evaluate the effects of electron loss during electron transport on beef lean color stability. Beef carcasses (n = 91) were...

Use of electronic cigarettes among Romanian university students: a cross-sectional study.

PubMed

Lotrean, Lucia Maria

2015-04-11

Because electronic cigarettes are relatively new, data on usage patterns and factors which influence them are sparse. Hence, this study aims at assessing awareness, beliefs about electronic cigarettes and experimentation with them among university students from Romania- a country where the sales and marketing of these products are widespread. Secondly, correlates of electronic cigarette experimentation will also be investigated. A cross-sectional study was performed by means of anonymous questionnaires among 480 students, aged 19-24, from Cluj-Napoca, Romania, between April-May 2013. The results show that 92.5% of the students have heard about e-cigarettes; out of these, one quarter (53.3% of the smokers, 25% of the ex-smokers, 5.5% of the non-smokers) have tried electronic cigarettes at least once during lifetime. The results of the multinomial logistic regression point out that the correlates of electronic cigarette experimentation were: male gender, being a smoker of traditional cigarettes, having friends who experimented with electronic cigarettes, having stronger beliefs that electronic cigarettes could help them quit smoking and being less convinced that they are used only by smokers. The explained variance was 59%. The results underline the importance of addressing the issue of e-cigarette use through health education programs and regulatory interventions, since e-cigarettes are a reality faced by the Romanian youth.

The value of structured data elements from electronic health records for identifying subjects for primary care clinical trials.

PubMed

Ateya, Mohammad B; Delaney, Brendan C; Speedie, Stuart M

2016-01-11

An increasing number of clinical trials are conducted in primary care settings. Making better use of existing data in the electronic health records to identify eligible subjects can improve efficiency of such studies. Our study aims to quantify the proportion of eligibility criteria that can be addressed with data in electronic health records and to compare the content of eligibility criteria in primary care with previous work. Eligibility criteria were extracted from primary care studies downloaded from the UK Clinical Research Network Study Portfolio. Criteria were broken into elemental statements. Two expert independent raters classified each statement based on whether or not structured data items in the electronic health record can be used to determine if the statement was true for a specific patient. Disagreements in classification were discussed until 100 % agreement was reached. Statements were also classified based on content and the percentages of each category were compared to two similar studies reported in the literature. Eligibility criteria were retrieved from 228 studies and decomposed into 2619 criteria elemental statements. 74 % of the criteria elemental statements were considered likely associated with structured data in an electronic health record. 79 % of the studies had at least 60 % of their criteria statements addressable with structured data likely to be present in an electronic health record. Based on clinical content, most frequent categories were: "disease, symptom, and sign", "therapy or surgery", and "medication" (36 %, 13 %, and 10 % of total criteria statements respectively). We also identified new criteria categories related to provider and caregiver attributes (2.6 % and 1 % of total criteria statements respectively). Electronic health records readily contain much of the data needed to assess patients' eligibility for clinical trials enrollment. Eligibility criteria content categories identified by our study can be incorporated as data elements in electronic health records to facilitate their integration with clinical trial management systems.

Statistical investigation of the efficiency of EMIC waves in precipitating relativistic electrons

NASA Astrophysics Data System (ADS)

Hudson, M. K.; Qin, M.; Millan, R. M.; Woodger, L. A.; Shekhar, S.

2017-12-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed as an effective way to scatter relativistic electrons into the atmospheric loss cone. In our study, however, among the total 399 coincidence events when NOAA satellites goes through the region of EMIC wave activity, only 103 are associated with Relativistic Electron Precipitation (REP) events, which indicates that the link between EMIC waves and relativistic electrons is much weaker than expected. Most of the studies so far have been focused on the He+ band EMIC waves, and H+ band EMIC waves have been regarded as less important to the precipitation of electrons. In our study, we demonstrate that among the 103 EMIC wave events detected by Van Allen Probes that are in close conjunction with relativistic electron precipitation observed by POES satellites, the occurrence rate of H+ and He+ band EMIC waves coincident with REP is comparable, suggesting closer examination of the range of ΔL and ΔMLT used to determine coincidence between Van Allen Probes EMIC waves and POES precipitation observation.

Computational Study of Primary Electrons in the Cusp Region of an Ion Engine's Discharge Chamber

NASA Technical Reports Server (NTRS)

Stueber, Thomas J. (Technical Monitor); Deshpande, Shirin S.; Mahalingam, Sudhakar; Menart, James A.

2004-01-01

In this work a computer code called PRIMA is used to study the motion of primary electrons in the magnetic cusp region of the discharge chamber of an ion engine. Even though the amount of wall area covered by the cusps is very small, the cusp regions are important because prior computational analyses have indicated that most primary electrons leave the discharge chamber through the cusps. The analysis presented here focuses on the cusp region only. The affects of the shape and size of the cusp region on primary electron travel are studied as well as the angle and location at which the electron enters the cusp region. These affects are quantified using the confinement length and the number density distributions of the primary electrons. In addition to these results comparisons of the results from PRIMA are made to experimental results for a cylindrical discharge chamber with two magnetic rings. These comparisons indicate the validity of the computer code called PRIMA.

Density functional theory studies on the structures and electronic communication of meso-ferrocenylporphyrins: long range orbital coupling via porphyrin core.

PubMed

Zhang, Lijuan; Qi, Dongdong; Zhang, Yuexing; Bian, Yongzhong; Jiang, Jianzhuang

2011-02-01

The molecular and electronic structures together with the electronic absorption spectra of a series of metal free meso-ferrocenylporphyrins, namely 5-ferrocenylporphyrin (1), 5,10-diferrocenylporphyrin (2), 5,15-diferrocenylporphyrin (3), 5,10,15-triferrocenylporphyrin (4), and 5,10,15,20-tetraferrocenylporphyrin (5) have been studied with the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. For the purpose of comparative studies, metal free porphyrin without any ferrocenyl group (0) and isolated ferrocene (6) were also calculated. The effects of the number and position of meso-attached ferrocenyl substituents on their molecular and electronic structures, atomic charges, molecular orbitals, and electronic absorption spectra of 1-5 were systematically investigated. The orbital coupling is investigated in detail, explaining well the long range coupling of ferrocenyl substituents connected via porphyrin core and the systematic change in the electronic absorption spectra of porphyrin compounds. Copyright © 2010 Elsevier Inc. All rights reserved.

Preliminary Mechanical Design Study of the Hollow Electron Lens for HL-LHC

NASA Astrophysics Data System (ADS)

Zanoni, Carlo; Gobbi, Giorgia; Perini, Diego; Stancari, Giulio

2017-07-01

A Hollow Electron Lens (HEL) has been proposed in order to improve performance of halo control and collimation in the Large Hadron Collider in view of its High Luminosity upgrade (HL-LHC). The concept is based on a hollow beam of electrons that travels around the protons for a few meters. The electron beam is produced by a cathode and then guided by a strong magnetic field. The first step of the design is the definition of the magnetic field that drives the electron trajectories. The estimation of such trajectories by means of a dedicated MATLAB tool is presented. The influence of the main geometrical and electrical parameters is analyzed and discussed. Then, the main mechanical design choices for the solenoids, cryostats gun and collector are described. The aim of this paper is to provide an overview of the feasibility study of the Electron Lens for LHC. The methods used in this study also serve as examples for future mechanical and integration designs of similar devices.

Preliminary Mechanical Design Study of the Hollow Electron Lens for HL-LHC

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

Zanoni, Carlo; Gobbi, Giorgia; Perini, Diego

A Hollow Electron Lens (HEL) has been proposed in order to improve performance of halo control and collimation in the Large Hadron Collider in view of its High Luminosity upgrade (HL-LHC). The concept is based on a hollow beam of electrons that travels around the protons for a few meters. The electron beam is produced by a cathode and then guided by a strong magnetic field. The first step of the design is the definition of the magnetic field that drives the electron trajectories. The estimation of such trajectories by means of a dedicated MATLAB tool is presented. The influencemore » of the main geometrical and electrical parameters is analyzed and discussed. Then, the main mechanical design choices for the solenoids, cryostats gun and collector are described. The aim of this paper is to provide an overview of the feasibility study of the Electron Lens for LHC. The methods used in this study also serve as examples for future mechanical and integration designs of similar devices.« less

Electron Emission in Highly Charged Ion-Atom Collisions

NASA Astrophysics Data System (ADS)

Liao, Chunlei

1995-01-01

This dissertation addresses the problem of electron emission in highly charged ion-atom collisions. The study is carried out by measuring doubly differential cross sections (DDCS) of emitted electrons for projectiles ranging from fluorine up to gold at ejection angles (theta _{L}) from 0^circ to 70^circ with respect to the beam direction. Prominent features are a very strong forward peaked angular distribution of emitted electrons and the appearance of strong diffraction structures in the binary encounter electron (BEe) region for projectiles heavier than chlorine. This is in clear contradiction to the results found with fluorine projectiles, where the BEe production increases slightly with increasing theta_{L} and no structure is observed in the BEe region. Both can be understood in the impulse approximation as elastic scattering of quasi free target electrons in the projectile potential. Our measurements also show that the violation of q ^2 scaling of the DDCS previously established for 0^circ electron spectra persists for all emission angles and almost all electron energies. In ion-atom collisions, besides electrons from target, electrons from projectile ionization are also presented in the emitted electron spectra. Using electron-projectile coincidence technique, different collision channels can be separated. In order to eliminate the speculations of contributions from projectile related capture and loss channels, coincidence studies of diffraction structures are initiated. In the 0^circ electron spectrum of 0.3 MeV/u I^{6+} impacting on H_2, strong autoionization peaks are observed on the shoulders of the cusp peak. The energies of these autoionization lines in the projectile rest frame are determined by high-resolution electron spectroscopy, and collision mechanism is probed by electron-charge state selected projectile coincidence technique.

Radiobiological Effectiveness of Ultrashort Laser-Driven Electron Bunches: Micronucleus Frequency, Telomere Shortening and Cell Viability.

PubMed

Andreassi, Maria Grazia; Borghini, Andrea; Pulignani, Silvia; Baffigi, Federica; Fulgentini, Lorenzo; Koester, Petra; Cresci, Monica; Vecoli, Cecilia; Lamia, Debora; Russo, Giorgio; Panetta, Daniele; Tripodi, Maria; Gizzi, Leonida A; Labate, Luca

2016-09-01

Laser-driven electron accelerators are capable of producing high-energy electron bunches in shorter distances than conventional radiofrequency accelerators. To date, our knowledge of the radiobiological effects in cells exposed to electrons using a laser-plasma accelerator is still very limited. In this study, we compared the dose-response curves for micronucleus (MN) frequency and telomere length in peripheral blood lymphocytes exposed to laser-driven electron pulse and X-ray radiations. Additionally, we evaluated the effects on cell survival of in vitro tumor cells after exposure to laser-driven electron pulse compared to electron beams produced by a conventional radiofrequency accelerator used for intraoperative radiation therapy. Blood samples from two different donors were exposed to six radiation doses ranging from 0 to 2 Gy. Relative biological effectiveness (RBE) for micronucleus induction was calculated from the alpha coefficients for electrons compared to X rays (RBE = alpha laser/alpha X rays). Cell viability was monitored in the OVCAR-3 ovarian cancer cell line using trypan blue exclusion assay at day 3, 5 and 7 postirradiation (2, 4, 6, 8 and 10 Gy). The RBE values obtained by comparing the alpha values were 1.3 and 1.2 for the two donors. Mean telomere length was also found to be reduced in a significant dose-dependent manner after irradiation with both electrons and X rays in both donors studied. Our findings showed a radiobiological response as mirrored by the induction of micronuclei and shortening of telomere as well as by the reduction of cell survival in blood samples and cancer cells exposed in vitro to laser-generated electron bunches. Additional studies are needed to improve preclinical validation of the radiobiological characteristics and efficacy of laser-driven electron accelerators in the future.

Using Electronic Portfolio to Promote Professional Learning Community for Pre-Service Early Childhood Teachers at Alquds University

ERIC Educational Resources Information Center

Khales, Buad

2016-01-01

The present study aims to explore whether the electronic portfolio can influence pre-service teachers' education and to examine how professional learning communities develop through electronic portfolios. To achieve this, twenty-four student-teachers taking a course in early childhood education at Al-Quds University participated in a study to…

Effects of Electronic Reading Environments' Structure on L2 Reading Comprehension

ERIC Educational Resources Information Center

Al-Seghayer, Khalid

2017-01-01

This study examines the effects of an electronic reading environment's structure on second language (L2) reading comprehension. In particular, this study explores whether clarifying the underlying structure of an electronic text, along with the ways in which its units or nodes are organized and interrelated results in better comprehension as well…

Virtual Lab to Develop Achievement in Electronic Circuits for Hearing-Impaired Students

ERIC Educational Resources Information Center

Baladoh, S. M.; Elgamal, A. F.; Abas, H. A.

2017-01-01

This paper aims to report and discuss the use of a virtual lab for developing achievement in electronic circuits for hearing-impaired students. Results from a number of studies have proved that the virtual lab allowed students to build and test a wide variety of electronic circuits. The present study was implemented to investigate the…

Internet User and Electronic Journals Perception: An Inservice Science Teacher Study

ERIC Educational Resources Information Center

Nuangchalerm, Prasart

2010-01-01

The growth and diversity of electronic academic journals had been widely distributed. It can be made our beliefs that future electronic scholarly journals will be different from their print antecedents and that both will fill a different niche of user, and will be necessary for the growth of any field knowledge. This study aims to investigate…

Research and Assessment of Learning Environments through Photoelicitation: Graduate Student Perceptions of Electronics Manufacturing in India

ERIC Educational Resources Information Center

Berdanier, Catherine G. P.; Cox, Monica F.

2015-01-01

This research studies the positive and negative perceptions of graduate students from the United States studying issues of sustainable electronics and electronics manufacturing in India as part of a National Science Foundation Integrative Graduate Education and Research Traineeship (IGERT) curriculum. The purpose of this paper is to discuss the…

Just Five More Minutes Please: Electronic Media Use, Sleep and Behaviour in Young Children

ERIC Educational Resources Information Center

Séguin, Daniel; Klimek, Victoria

2016-01-01

This study explored the relationship between electronic media use, sleep and behaviour in preschool-aged children between the ages of three and five years. The primary hypothesis of this study was that excessive electronic media use (>2 hours a day) would positively correlate with sleep patterns (in particular, disturbances) and negative…

Electron kinetics in capacitively coupled plasmas modulated by electron injection

NASA Astrophysics Data System (ADS)

Zhang, Ya; Peng, Yanli; Innocenti, Maria Elena; Jiang, Wei; Wang, Hong-yu; Lapenta, Giovanni

2017-09-01

The controlling effect of an electron injection on the electron energy distribution function (EEDF) and on the energetic electron flux, in a capacitive radio-frequency argon plasma, is studied using a one-dimensional particle-in-cell/Monte Carlo collisions model. The input power of the electron beam is as small as several tens of Watts with laboratory achievable emission currents and energies. With the electron injection, the electron temperature decreases but with a significant high energy tail. The electron density, electron temperature in the sheath, and electron heating rate increase with the increasing emission energy. This is attributed to the extra heating of the energetic electrons in the EEDF tail. The non-equilibrium EEDF is obtained for strong non-local distributions of the electric field, electron heating rate, excitation, and ionization rate, indicating the discharge has transited from a volume heating (α-mode dominated) into a sheath heating (γ-mode dominated) type. In addition, the electron injection not only modifies the self-bias voltage, but also enhances the electron flux that can reach the electrodes. Moreover, the relative population of energetic electrons significantly increases with the electron injection compared to that without the electron injection, relevant for modifying the gas and surface chemistry reactions.

Effect of EMIC Wave Normal Angle Distribution on Relativistic Electron Scattering

NASA Technical Reports Server (NTRS)

Gamayunov, K. V.; Khazanov, G. V.

2006-01-01

The flux level of outer-zone relativistic electrons (above 1 MeV) is extremely variable during geomagnetic storms, and controlled by a competition between acceleration and loss. Precipitation of these electrons due to resonant pitch-angle scattering by electromagnetic ion cyclotron (EMIC) waves is considered one of the major loss mechanisms. This mechanism was suggested in early theoretical studies more than three decades ago. However, direct experimental evidence of the wave role in relativistic electrons precipitation is difficult to obtain because of lack of concurrent measurements of precipitating electrons at low altitudes and the waves in a magnetically conjugate equatorial region. Recently, the data from balloon-borne X-ray instruments provided indirect but strong evidence on an efficiency of the EMIC wave induced loss for the outer-zone relativistic electrons. These observations stimulated theoretical studies that, particularly, demonstrated that EMIC wave induced pitch-angle diffusion of MeV electrons can operate in the strong diffusion limit and this mechanism can compete with relativistic electron depletion caused by the Dst effect during the initial and main phases of storm. Although an effectiveness of relativistic electron scattering by EMIC waves depends strongly on the wave spectral properties, the most favorable assumptions regarding wave characteristics has been made in all previous theoretical studies. Particularly, only quasi field-aligned EMIC waves have been considered as a driver for relativistic electron loss. At the same time, there is growing experimental and theoretical evidence that these waves can be highly oblique; EMIC wave energy can occupy not only the region of generation, i.e. the region of small wave normal angles, but also the entire wave normal angle region, and even only the region near 90 degrees. The latter can dramatically change he effectiveness of relativistic electron scattering by EMIC waves. In the present study, we calculate the pitch-angle diffusion coefficients using the typical wave normal distributions obtained from our self-consistent ring current-EMIC wave model, and try to quantify the effect of EMIC wave normal angle characteristics on relativistic electron scattering.

Electronic journal access: how does it affect the print subscription price?*

PubMed Central

Chen, Frances L.; Wrynn, Paul; Rieke, Judith L.

2001-01-01

Objective: This study examined the rates of print journal subscription price increases according to the type of available electronic access. The types of access included: electronic priced separately from the print, combination print with “free online” access, and aggregated, defined here as electronic access purchased as part of a collection. The percentages of print price increases were compared to each other and to that for titles available only in print. The authors were not aware of prior objective research in this area. Methods: The authors analyzed the percentage print price increases of 300 journals over a five-year time period. The titles were grouped according to type of available electronic access. The median and mean percentage print price increases were calculated and plotted for all titles within each group. Results: Using both the median and the mean to look at the percentage print price increases over five years, it was obvious that print prices for journals with electronic access exceeded journals that did not offer an electronic option. Electronic priced separately averaged 3% to 5% higher than print only titles using both measures. Combination print with “free online” access had higher increases from 1996 to 1999, but, in 2000, their percentage increases were about the same as print only titles. The rate of price increases for aggregated titles consistently went down over the past five years. Journals with no electronic option showed the lowest percentage rates of print price increase. Conclusions: The authors' findings reveal that the increases of print prices for their sample of titles were higher if a type of electronic access was offered. According to the results of this study, aggregated collections currently represent the electronic option whose percentage price increase for print prices was lowest. However, the uneven fluctuations in rates of subscription prices revealed that the pricing of journals with electronic access is still evolving. More study is recommended to see if the trends observed in this study are sustained over a longer time period. PMID:11837258

Adapting practice-based intervention research to electronic environments: opportunities and complexities at two institutions.

PubMed

Stille, Christopher J; Lockhart, Steven A; Maertens, Julie A; Madden, Christi A; Darden, Paul M

2015-01-01

Primary care practice-based research has become more complex with increased use of electronic health records (EHRs). Little has been reported about changes in study planning and execution that are required as practices change from paper-based to electronic-based environments. We describe the evolution of a pediatric practice-based intervention study as it was adapted for use in the electronic environment, to enable other practice-based researchers to plan efficient, effective studies. We adapted a paper-based pediatric office-level intervention to enhance parent-provider communication about subspecialty referrals for use in two practice-based research networks (PBRNs) with partially and fully electronic environments. We documented the process of adaptation and its effect on study feasibility and efficiency, resource use, and administrative and regulatory complexities, as the study was implemented in the two networks. Considerable time and money was required to adapt the paper-based study to the electronic environment, requiring extra meetings with institutional EHR-, regulatory-, and administrative teams, and increased practice training. Institutional unfamiliarity with using EHRs in practice-based research, and the consequent need to develop new policies, were major contributors to delays. Adapting intervention tools to the EHR and minimizing practice disruptions was challenging, but resulted in several efficiencies as compared with a paper-based project. In particular, recruitment and tracking of subjects and data collection were easier and more efficient. Practice-based intervention research in an electronic environment adds considerable cost and time at the outset of a study, especially for centers unfamiliar with such research. Efficiencies generated have the potential of easing the work of study enrollment, subject tracking, and data collection.

Academic impact of a public electronic health database: bibliometric analysis of studies using the general practice research database.

PubMed

Chen, Yu-Chun; Wu, Jau-Ching; Haschler, Ingo; Majeed, Azeem; Chen, Tzeng-Ji; Wetter, Thomas

2011-01-01

Studies that use electronic health databases as research material are getting popular but the influence of a single electronic health database had not been well investigated yet. The United Kingdom's General Practice Research Database (GPRD) is one of the few electronic health databases publicly available to academic researchers. This study analyzed studies that used GPRD to demonstrate the scientific production and academic impact by a single public health database. A total of 749 studies published between 1995 and 2009 with 'General Practice Research Database' as their topics, defined as GPRD studies, were extracted from Web of Science. By the end of 2009, the GPRD had attracted 1251 authors from 22 countries and been used extensively in 749 studies published in 193 journals across 58 study fields. Each GPRD study was cited 2.7 times by successive studies. Moreover, the total number of GPRD studies increased rapidly, and it is expected to reach 1500 by 2015, twice the number accumulated till the end of 2009. Since 17 of the most prolific authors (1.4% of all authors) contributed nearly half (47.9%) of GPRD studies, success in conducting GPRD studies may accumulate. The GPRD was used mainly in, but not limited to, the three study fields of "Pharmacology and Pharmacy", "General and Internal Medicine", and "Public, Environmental and Occupational Health". The UK and United States were the two most active regions of GPRD studies. One-third of GRPD studies were internationally co-authored. A public electronic health database such as the GPRD will promote scientific production in many ways. Data owners of electronic health databases at a national level should consider how to reduce access barriers and to make data more available for research.

Provider-to-Provider Electronic Communication in the Era of Meaningful Use: A Review of the Evidence

PubMed Central

Walsh, Colin; Siegler, Eugenia L; Cheston, Erin; O'Donnell, Heather; Collins, Sarah; Stein, Daniel; Vawdrey, David K.; Stetson, Peter D.

2014-01-01

Background Electronic communication between providers occurs daily in clinical practice but has not been well studied. Purpose To assess the impact of provider-to-provider electronic communication tools on communication and healthcare outcomes through literature review. Data sources OVID Medline, Pubmed, Google Scholar, CINAHL, and Academic Search Premier. Study Selection Publication in English language peer-reviewed journals. Studies provided quantitative provider-to-provider communication data, provider satisfaction statistics, or EHR communication data. Data Extraction Literature review. Data Synthesis Two reviewers conducted the title review to determine eligible studies from initial search results. Three reviewers independently reviewed titles, abstracts, and full text (where appropriate) against inclusion and exclusion criteria. Limitations Small number of eligible studies; few described trial design (20%). Homogeneous provider-type (physicians). English-only studies. Conclusions Of twenty-five included studies, all focused on physicians; most were observational (68%). Most (60%) described electronic specialist referral tools. Although overall use has been measured, there were no studies of the effectiveness of intra-EHR messaging. Literature describing the effectiveness of provider-to-provider electronic communications is sparse and narrow in scope. Complex care, such as that envisioned for the Patient Centered Medical Home, necessitates further research. PMID:24101544

Health-oriented electronic oral health record: development and evaluation.

PubMed

Wongsapai, Mansuang; Suebnukarn, Siriwan; Rajchagool, Sunsanee; Beach, Daryl; Kawaguchi, Sachiko

2014-06-01

This study aims to develop and evaluate a new Health-oriented Electronic Oral Health Record that implements the health-oriented status and intervention index. The index takes the principles of holistic oral healthcare and applies them to the design and implementation of the Health-oriented Electronic Oral Health Record. We designed an experiment using focus groups and a consensus (Delphi process) method to develop a new health-oriented status and intervention index and graphical user interface. A comparative intervention study with qualitative and quantitative methods was used to compare an existing Electronic Oral Health Record to the Health-oriented Electronic Oral Health Record, focusing on dentist satisfaction, accuracy, and completeness of oral health status recording. The study was conducted by the dental staff of the Inter-country Center for Oral Health collaborative hospitals in Thailand. Overall, the user satisfaction questionnaire had a positive response to the Health-oriented Electronic Oral Health Record. The dentists found it easy to use and were generally satisfied with the impact on their work, oral health services, and surveillance. The dentists were significantly satisfied with the Health-oriented Electronic Oral Health Record compared to the existing Electronic Oral Health Record (p < 0.001). The accuracy and completeness values of the oral health information recorded using the Health-oriented Electronic Oral Health Record were 97.15 and 93.74 percent, respectively. This research concludes that the Health-oriented Electronic Oral Health Record satisfied many dentists, provided benefits to holistic oral healthcare, and facilitated the planning, managing, and evaluation of the healthcare delivery system.

#Vapelife: An Exploratory Study of Electronic Cigarette Use and Promotion on Instagram.

PubMed

Laestadius, Linnea I; Wahl, Megan M; Cho, Young I

2016-10-14

The growth of social networking services has enabled the sharing of electronic cigarette opinions and experiences via user-generated content. This exploratory study analyzed electronic cigarette content found on the visual social networking service, Instagram, in order to highlight public health challenges created by this content and support understanding of electronic cigarette promotion and usage. A qualitative content analysis was performed on Instagram posts made with the hashtags #ecig or #vape in October 2014. Images, text, and hashtags from 85 posts (43 #ecig, 42 #vape) were analyzed. In addition, the total number of posts made with eight key electronic cigarette hashtags was recorded at four points between March 2014 and October 2015. The total number of #vape posts on Instagram grew by 4,163,274 during the study period, while #ecig posts increased by 741,916. Of the posts examined in-depth, corporate users made up over half of posts. No posts were critical of electronic cigarettes. Few mentioned electronic cigarettes in the context of health benefits. No posts included major brands, and mod style electronic cigarettes were mentioned or depicted in over half of posts. A majority of posts included hashtags expressing vaping identity and community. In addition, users mentioned novel practices such as sub-ohming. Conclusions/Importance: Instagram users in our sample characterized electronic cigarettes primarily as novel devices rather than equivalents to cigarettes. Further, hashtag communities and identities appear to be forming around vaping. Future research should consider the public health implications of these hashtags, as well as novel electronic cigarette practices.

Diabetes quality of care and outpatient utilization associated with electronic patient-provider messaging: a cross-sectional analysis.

PubMed

Harris, Lynne T; Haneuse, Sebastien J; Martin, Diane P; Ralston, James D

2009-07-01

To test the hypothesis that electronic patient-provider messaging is associated with high care quality for diabetes and lower outpatient utilization. We conducted a cross-sectional analysis of electronic patient-provider messaging over a 15-month period between 1 January 2004 and 31 March 2005. The study was set at Group Health Cooperative--a consumer-governed, nonprofit health care system that operates in Washington and Idaho. Participants included all patients aged >or=18 years with a diagnosis of diabetes. In addition to usual care, all patients had the option to use electronic messaging to communicate with their care providers. The primary outcome measures were diabetes-related quality-of-care indicators (A1C, blood pressure, and LDL cholesterol) and outpatient visits (primary care, specialty care, and emergency). Nineteen percent of patients with diabetes used electronic messaging to communicate with their care providers during the study period (n = 2,924) (overall study cohort: 15,427 subjects). In multivariate models, frequent use of electronic messaging was associated with A1C <7% (relative risk [RR] 1.36 [95% CI 1.16-1.58]). Contrary to our hypothesis, frequent use of electronic messaging was also associated with a higher rate of outpatient visits (1.39 [1.26-1.53]). Frequent use of electronic secure messaging is associated with better glycemic control and increased outpatient utilization. Electronic patient-provider communication may represent one strategy to meet the health care needs of this unique population. More research is necessary to assess the effect of electronic messaging on care quality and utilization.

Relativistic electron precipitation during geomagnetic storm time in the years 2006-2010

NASA Astrophysics Data System (ADS)

Glesnes Ødegaard, Linn-Kristine; Nesse Tyssøy, Hilde; Sandanger, Marit irene; Stadsnes, Johan; Søraas, Finn

2015-04-01

The processes leading to acceleration or loss of relativistic electrons in the magnetosphere during geomagnetic storm time have yet to be fully understood, and whether a geomagnetic storm will lead to enhanced or depleted fluxes of relativistic electrons can not be known in advance. Relativistic Electron Precipitation (REP) can penetrate deep into the atmosphere and influence composition and dynamics. To study the effect of REP upon the atmosphere, the energy and intensity of the electrons need to be accurately represented. We use satellite measurements of electrons with energies E>300 keV and E>1000 keV to study the behaviour of these electron populations during geomagnetic storms. We use the MEPED detectors on board the POES satellites NOAA-17, NOAA-18, MetOp-02 and NOAA-19, where the vertical telescope measures precipitated flux, and the horizontal telescope trapped flux at satellite altitude (ca 850 km). Using a newly developed technique, we can derive the flux of electrons depositing their energy in the atmosphere from the pair of detectors on each satellite. 75 isolated storms were identified in the period 2006-2010. The storms include both typical CME driven storms, and weak long duration storms driven by CIRs. Each storm was divided into pre-storm phase, main phase and recovery phase, and the flux of relativistic electrons was monitored through the storms. By combining the measurements from several satellites, we obtain a close to global view of the relativistic electron fluxes, enabling us to study the relationship between the REP and different geomagnetic indices and solar wind drivers.

Vanderbilt free-electron-laser project in biomedical and materials research. Annual report, 1 February 1987-31 January 1988

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

Haglund, R.F.; Tolk, N.H.

The Medical Free Electron Laser Program was awarded to develop, construct and operate a free-electron laser facility dedicated to biomedical and materials studies, with particular emphases on: fundamental studies of absorption and localization of electromagnetic energy on and near material surfaces, especially through electronic and other selective, non-statistical processes; non-thermal photon-materials interactions (e.g., electronic bond-breaking or vibrational energy transfer) in physical and biological materials as well as in long-wavelength biopolymer dynamics; development of FEL-based methods to study drug action and to characterize biomolecular properties and metabolic processes in biomembranes; clinical applications in otolaryngology, neurosurgery, ophthalmology and radiology stressing the usemore » of the laser for selective laser-tissue, laser-cellular and laser-molecule interactions in both therapeutic and diagnostic modalities.« less

Synthesis and electronic properties of nanophase semiconductor materials

NASA Astrophysics Data System (ADS)

Sailor, Michael J.

1993-05-01

The objective of the research effort is to understand and learn to control the morphologic and electronic properties of electrodeposited nanophase semiconductors. The initial work has focused on electrodeposition of nanophase CdSe, using a sequential monolayer deposition technique that we are developing. We are currently extending the synthesis phase of this project into silicon, silicon carbide, and phosphor materials. This work also encompasses studying semiconductor electrodeposition into materials with restricted dimensions, such as microporous alumina and porous silicon membranes. By growing films with very small grain sizes, we hope to produce and study materials that display unusual electronic or luminescent effects. We are primarily interested in the electronic properties of the II-VI and group IV materials, for potential applications in nanoscale electronics and optical detector technologies. The phosphors are being studied for their potential as efficient high-resolution display materials.

Positron annihilation induced Auger electron spectroscopy

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

Weiss, A.

1991-02-01

A review is given on the results of PAES (positron annihilation induced Auger Electron Spectroscopy) studies to data, with a concentration on those results obtained at the University of Texas at Arlington. Low energy positions, trapped in a surface localized state annihilate with core electrons resulting in the emission of Auger electrons. The advantages of PEAS include: (i) the elimination of the very large secondary electron background, and (ii) increased surface selectivity. (AIP)

Electron cloud generation and trapping in a quadrupole magnet at the Los Alamos proton storage ring

NASA Astrophysics Data System (ADS)

Macek, Robert J.; Browman, Andrew A.; Ledford, John E.; Borden, Michael J.; O'Hara, James F.; McCrady, Rodney C.; Rybarcyk, Lawrence J.; Spickermann, Thomas; Zaugg, Thomas J.; Pivi, Mauro T. F.

2008-01-01

Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR) have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the “prompt” electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the “swept” electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100μs. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the quadrupole.

Binding of two-electron metastable states in semiconductor quantum dots under a magnetic field

NASA Astrophysics Data System (ADS)

Garagiola, Mariano; Pont, Federico M.; Osenda, Omar

2018-04-01

Applying a strong enough magnetic field results in the binding of few-electron resonant states. The mechanism was proposed many years ago but its verification in laboratory conditions is far more recent. In this work we study the binding of two-electron resonant states. The electrons are confined in a cylindrical quantum dot which is embedded in a semiconductor wire. The geometry considered is similar to the one used in actual experimental setups. The low-energy two-electron spectrum is calculated numerically from an effective-mass approximation Hamiltonian modelling the system. Methods for binding threshold calculations in systems with one and two electrons are thoroughly studied; in particular, we use quantum information quantities to assess when the strong lateral confinement approximation can be used to obtain reliable low-energy spectra. For simplicity, only cases without bound states in the absence of an external field are considered. Under these conditions, the binding threshold for the one-electron case is given by the lowest Landau energy level. Moreover, the energy of the one-electron bounded resonance can be used to obtain the two-electron binding threshold. It is shown that for realistic values of the two-electron model parameters it is feasible to bind resonances with field strengths of a few tens of tesla.

Theoretical Study of Ultrafast Electron Injection into a Dye/TiO2 System in Dye-Sensitized Solar Cells

NASA Astrophysics Data System (ADS)

Lin, Chundan; Xia, Qide; Li, Kuan; Li, Juan; Yang, Zhenqing

2018-06-01

The ultrafast injection of excited electrons in dye/TiO2 system plays a critical role, which determines the device's efficiency in large part. In this work, we studied the geometrical structures and electronic properties of a dye/TiO2 composite system for dye-sensitized solar cells (DSSCs) by using density functional theory, and we analyzed the mechanism of ultrafast electron injection with emphasis on the power conversion efficiency. The results show that the dye SPL103/TiO2 (101) surface is more stable than dye SPL101. The electron injection driving force of SPL103/TiO2 (101) is 3.55 times that of SPL101, indicating that SPL103/TiO2 (101) has a strong ability to transfer electrons. SPL103 and SPL101/TiO2 (101) both have fast electron transfer processes, and especially the electron injection time of SPL103/TiO2 (101) is only 1.875 fs. The results of this work are expected to provide a new understanding of the mechanism of electron injection in dyes/TiO2 systems for use in highly effective DSSCs.

Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study

PubMed Central

Xiao, H. Y.; Weber, W. J.; Zhang, Y.; Zu, X. T.; Li, S.

2015-01-01

The response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser, electron and ion irradiations. PMID:25660219

Single electron counting using a dual MCP assembly

NASA Astrophysics Data System (ADS)

Yang, Yuzhen; Liu, Shulin; Zhao, Tianchi; Yan, Baojun; Wang, Peiliang; Yu, Yang; Lei, Xiangcui; Yang, Luping; Wen, Kaile; Qi, Ming; Heng, Yuekun

2016-09-01

The gain, pulse height resolution and peak-to-valley ratio of single electrons detected by using a Chevron configured Microchannel Plate (MCP) assembly are studied. The two MCPs are separated by a 280 μm gap and are biased by four electrodes. The purpose of the study is to determine the optimum bias voltage arrangements for single electron counting. By comparing the results of various bias voltage combinations, we conclude that good performance for the electron counting can be achieved by operating the MCP assembly in saturation mode. In addition, by applying a small reverse bias voltage across the gap while adjusting the bias voltages of the MCPs, optimum performance of electron counting can be obtained.

Electron beam irradiation processing for industrial and medical applications

NASA Astrophysics Data System (ADS)

Ozer, Zehra Nur

2017-09-01

In recent years, electron beam processing has been widely used for medical and industrial applications. Electron beam accelerators are reliable and durable equipments that can produce ionizing radiation when it is needed for a particular commercial use. On the industrial scale, accelerators are used to generate electrons in between 0.1-100 MeV energy range. These accelerators are used mainly in plastics, automotive, wire and electric cables, semiconductors, health care, aerospace and environmental industries, as well as numerous researches. This study presents the current applications of electron beam processing in medicine and industry. Also planned study of a design for such a system in the energy range of 200-300 keV is introduced.

A long way to the electrode: how do Geobacter cells transport their electrons?

PubMed

Bonanni, Pablo Sebastián; Schrott, Germán David; Busalmen, Juan Pablo

2012-12-01

The mechanism of electron transport in Geobacter sulfurreducens biofilms is a topic under intense study and debate. Although some proteins were found to be essential for current production, the specific role that each one plays in electron transport to the electrode remains to be elucidated and a consensus on the mechanism of electron transport has not been reached. In the present paper, to understand the state of the art in the topic, electron transport from inside of the cell to the electrode in Geobacter sulfurreducens biofilms is analysed, reviewing genetic studies, biofilm conductivity assays and electrochemical and spectro-electrochemical experiments. Furthermore, crucial data still required to achieve a deeper understanding are highlighted.

Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study.

PubMed

Xiao, H Y; Weber, W J; Zhang, Y; Zu, X T; Li, S

2015-02-09

The response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser, electron and ion irradiations.

Spectrum bandwidth narrowing of Thomson scattering X-rays with energy chirped electron beams from laser wakefield acceleration

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

Xu, Tong; Chen, Min, E-mail: minchen@sjtu.edu.cn; Li, Fei-Yu

2014-01-06

We study incoherent Thomson scattering between an ultrashort laser pulse and an electron beam accelerated from a laser wakefield. The energy chirp effects of the accelerated electron beam on the final radiation spectrum bandwidth are investigated. It is found that the scattered X-ray radiation has the minimum spectrum width and highest intensity as electrons are accelerated up to around the dephasing point. Furthermore, it is proposed that the electron acceleration process inside the wakefield can be studied by use of 90° Thomson scattering. The dephasing position and beam energy chirp can be deduced from the intensity and bandwidth of themore » scattered radiation.« less

Synthesis and CV Studies of Dithiol-terminated Metal Terpyridine Complexes

NASA Technical Reports Server (NTRS)

Asano, Sylvia; Fan, Wendy; Ng, Hou-Tee; Han, Jie; Meyyappan, M.

2003-01-01

Transition metal coordination complexes possess unique electronic structures that should be a good model for studying electronic transport behavior at a molecular level. The discrete, multiple redox states, low redox potential and the superb ability to establish contact with other molecular and electronic components by coordination chemistry have made this a subject of investigation for their possible application as active electronic components in molecular devices. We present the synthesis and electrochemical characterization of 4'-thioacetylphenyl-2'2:6',2"-terpyridine iron(II) complex and compare it with a model bis-terpyridine iron(II) complex by cyclic voltammetry. With the use of different working electrodes, the behavior of these complexes show different electron transfer rates.

Electronic bullying among middle school students.

PubMed

Kowalski, Robin M; Limber, Susan P

2007-12-01

Electronic communications technologies are affording children and adolescents new means of bullying one another. Referred to as electronic bullying, cyberbullying, or online social cruelty, this phenomenon includes bullying through e-mail, instant messaging, in a chat room, on a website, or through digital messages or images sent to a cell phone. The present study examined the prevalence of electronic bullying among middle school students. A total of 3,767 middle school students in grades 6, 7, and 8 who attend six elementary and middle schools in the southeastern and northwestern United States completed a questionnaire, consisting of the Olweus Bully/Victim Questionnaire and 23 questions developed for this study that examined participants' experiences with electronic bullying, as both victims and perpetrators. Of the students, 11% that they had been electronically bullied at least once in the last couple of months (victims only); 7% indicated that they were bully/victims; and 4% had electronically bullied someone else at least once in the previous couple of months (bullies only). The most common methods for electronic bullying (as reported by both victims and perpetrators) involved the use of instant messaging, chat rooms, and e-mail. Importantly, close to half of the electronic bully victims reported not knowing the perpetrator's identity. Electronic bullying represents a problem of significant magnitude. As children's use of electronic communications technologies is unlikely to wane in coming years, continued attention to electronic bullying is critical. Implications of these findings for youth, parents, and educators are discussed.

Electronic structure of strongly reduced (1 ‾ 1 1) surface of monoclinic HfO2

NASA Astrophysics Data System (ADS)

Cheng, YingXing; Zhu, Linggang; Ying, Yile; Zhou, Jian; Sun, Zhimei

2018-07-01

Material surface is playing an increasingly important role in electronic devices as their size down to nanoscale. Here, by first-principles calculations we studied the surface oxygen-vacancies (Vos) induced electronic-structure variation of HfO2 , in order to explore its potential applications in surface-controlled electronic devices. Firstly, it is found that single Vo tends to segregate onto the surface and attracts each other as they form pairs, making the formation of vacancies-contained functional surface possible. Then extensive Vo-chains whose formation/rupture can represent the high/low conductivity state are constructed. The electronic states induced by the Vos remain localized in the band-gap region for most of the Vo-chains studied here. A transition to a metallic conductance is found in metastable Vo-chain with formation energy increased by 0.25 eV per Vo. Moreover, we highlight the significance of the Hubbard U correction for density functional theory when studying the electronic-structure based conductance in the oxides. By comprehensive calculations, we find a conductivity-stability dilemma of the Vo-chains, providing guideline for understanding and designing the electronic devices based on HfO2 surface.

The existence of electron-acoustic shock waves and their interactions in a non-Maxwellian plasma with q-nonextensive distributed electrons

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

Han, Jiu-Ning; He, Yong-Lin; Han, Zhen-Hai

2013-07-15

We present a theoretical investigation for the nonlinear interaction between electron-acoustic shock waves in a nonextensive two-electron plasma. The interaction is governed by a pair of Korteweg-de Vries-Burgers equations. We focus on studying the colliding effects on the propagation of shock waves, more specifically, we have studied the effects of plasma parameters, i.e., the nonextensive parameter q, the “hot” to “cold” electron number density ratio α, and the normalized electron kinematic viscosity η{sub 0} on the trajectory changes (phase shifts) of shock waves. It is found that there are trajectory changes (phase shifts) for both colliding shock waves in themore » present plasma system. We also noted that the nonlinearity has no decisive effect on the trajectory changes, the occurrence of trajectory changes may be due to the combined role played by the dispersion and dissipation of the nonlinear structure. Our theoretical study may be beneficial to understand the propagation and interaction of nonlinear electrostatic waves and may brings a possibility to develop the nonlinear theory of electron-acoustic waves in astrophysical plasma systems.« less

Parametric study of transport beam lines for electron beams accelerated by laser-plasma interaction

NASA Astrophysics Data System (ADS)

Scisciò, M.; Lancia, L.; Migliorati, M.; Mostacci, A.; Palumbo, L.; Papaphilippou, Y.; Antici, P.

2016-03-01

In the last decade, laser-plasma acceleration of high-energy electrons has attracted strong attention in different fields. Electrons with maximum energies in the GeV range can be laser-accelerated within a few cm using multi-hundreds terawatt (TW) lasers, yielding to very high beam currents at the source (electron bunches with up to tens-hundreds of pC in a few fs). While initially the challenge was to increase the maximum achievable electron energy, today strong effort is put in the control and usability of these laser-generated beams that still lack of some features in order to be used for applications where currently conventional, radio-frequency (RF) based, electron beam lines represent the most common and efficient solution. Several improvements have been suggested for this purpose, some of them acting directly on the plasma source, some using beam shaping tools located downstream. Concerning the latter, several studies have suggested the use of conventional accelerator magnetic devices (such as quadrupoles and solenoids) as an easy implementable solution when the laser-plasma accelerated beam requires optimization. In this paper, we report on a parametric study related to the transport of electron beams accelerated by laser-plasma interaction, using conventional accelerator elements and tools. We focus on both, high energy electron beams in the GeV range, as produced on petawatt (PW) class laser systems, and on lower energy electron beams in the hundreds of MeV range, as nowadays routinely obtained on commercially available multi-hundred TW laser systems. For both scenarios, our study allows understanding what are the crucial parameters that enable laser-plasma accelerators to compete with conventional ones and allow for a beam transport. We show that suitable working points require a tradeoff-combination between low beam divergence and narrow energy spread.

A spherical electron cloud hopping model for studying product branching ratios of dissociative recombination.

PubMed

Yu, Hua-Gen

2008-05-21

A spherical electron cloud hopping (SECH) model is proposed to study the product branching ratios of dissociative recombination (DR) of polyatomic systems. In this model, the fast electron-captured process is treated as an instantaneous hopping of a cloud of uniform spherical fractional point charges onto a target M+q ion (or molecule). The sum of point charges (-1) simulates the incident electron. The sphere radius is determined by a critical distance (Rc eM) between the incoming electron (e-) and the target, at which the potential energy of the e(-)-M+q system is equal to that of the electron-captured molecule M+q(-1) in a symmetry-allowed electronic state with the same structure as M(+q). During the hopping procedure, the excess energies of electron association reaction are dispersed in the kinetic energies of M+q(-1) atoms to conserve total energy. The kinetic energies are adjusted by linearly adding atomic momenta in the direction of driving forces induced by the scattering electron. The nuclear dynamics of the resultant M+q(-1) molecule are studied by using a direct ab initio dynamics method on the adiabatic potential energy surface of M+q(-1), or together with extra adiabatic surface(s) of M+q(-1). For the latter case, the "fewest switches" surface hopping algorithm of Tully was adapted to deal with the nonadiabaticity in trajectory propagations. The SECH model has been applied to study the DR of both CH+ and H3O+(H2O)2. The theoretical results are consistent with the experiment. It was found that water molecules play an important role in determining the product branching ratios of the molecular cluster ion.

Specular Reflectivity and Hot-Electron Generation in High-Contrast Relativistic Laser-Plasma Interactions

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

Kemp, Gregory Elijah

2013-01-01

Ultra-intense laser (> 1018 W/cm2) interactions with matter are capable of producing relativistic electrons which have a variety of applications in state-of-the-art scientific and medical research conducted at universities and national laboratories across the world. Control of various aspects of these hot-electron distributions is highly desired to optimize a particular outcome. Hot-electron generation in low-contrast interactions, where significant amounts of under-dense pre-plasma are present, can be plagued by highly non-linear relativistic laser-plasma instabilities and quasi-static magnetic field generation, often resulting in less than desirable and predictable electron source characteristics. High-contrast interactions offer more controlled interactions but often at the costmore » of overall lower coupling and increased sensitivity to initial target conditions. An experiment studying the differences in hot-electron generation between high and low-contrast pulse interactions with solid density targets was performed on the Titan laser platform at the Jupiter Laser Facility at Lawrence Livermore National Laboratory in Livermore, CA. To date, these hot-electrons generated in the laboratory are not directly observable at the source of the interaction. Instead, indirect studies are performed using state-of-the-art simulations, constrained by the various experimental measurements. These measurements, more-often-than-not, rely on secondary processes generated by the transport of these electrons through the solid density materials which can susceptible to a variety instabilities and target material/geometry effects. Although often neglected in these types of studies, the specularly reflected light can provide invaluable insight as it is directly influenced by the interaction. In this thesis, I address the use of (personally obtained) experimental specular reflectivity measurements to indirectly study hot-electron generation in the context of high-contrast, relativistic laser-plasma interactions.« less

Discovering the Puzzling Behaviour of Electrons with the Grimaldi-Young Experiment

ERIC Educational Resources Information Center

Matteucci, Giorgio; Castaneda, Roman; Serna, Samuel; Medina, Francisco; Garcia-Sucerquia, Jorge

2010-01-01

An experiment analogous to that devised by Grimaldi and subsequently repeated by Young to study the nature of light has been realized with electrons. Following the Grimaldi and Young line of thought, an original approach is presented to introduce undergraduate physics students to the wave behaviour of electrons. An electron microscope equipped…

Utilzing Networked Computer Workstations To Conduct Electronic Focus Groups.

ERIC Educational Resources Information Center

Lowery, Catherine; Franklin, Kathy K.

Researchers at the University of Arkansas at Little Rock conducted a study of faculty attitudes about the use of technology in the college classroom using electronic focus group sessions. This paper examines the electronic focus group data collection procedure. The electronic sessions were conducted in a decision-support center on campus with 13…

Inter-professional electronic documents and child health: a study of persisting non-electronic communication in the use of electronic documents.

PubMed

Saario, Sirpa; Hall, Christopher; Peckover, Sue

2012-12-01

Information and communication technologies are widely used in health and social care settings to replace previous means of record keeping, assessment and communication. Commentary on the strengths and weaknesses of such systems abound, thus it is useful to examine how they are used in practice. This article draws on findings from two separate studies, conducted between 2005 and 2007, which examined how child health and welfare professionals use electronic documents in Finland and England. Known respectively as Miranda and CAF, these systems are different in terms of structure and function but in their everyday use common features are identified, notably the continued use of and reliance on non-electronic means of communication. Based on interviews with professionals, three forms of non-electronic communication are described: alternative records, phone calls and letters, which facilitate the sharing of the electronic record. Finally, the electronic documents are further analysed as potential boundary objects which aim to create common understanding between sites and professionals. Copyright © 2012 Elsevier Ltd. All rights reserved.

Simulations of the temporal and spatial resolution for a compact time-resolved electron diffractometer

NASA Astrophysics Data System (ADS)

Robinson, Matthew S.; Lane, Paul D.; Wann, Derek A.

2016-02-01

A novel compact electron gun for use in time-resolved gas electron diffraction experiments has recently been designed and commissioned. In this paper we present and discuss the extensive simulations that were performed to underpin the design in terms of the spatial and temporal qualities of the pulsed electron beam created by the ionisation of a gold photocathode using a femtosecond laser. The response of the electron pulses to a solenoid lens used to focus the electron beam has also been studied. The simulated results show that focussing the electron beam affects the overall spatial and temporal resolution of the experiment in a variety of ways, and that factors that improve the resolution of one parameter can often have a negative effect on the other. A balance must, therefore, be achieved between spatial and temporal resolution. The optimal experimental time resolution for the apparatus is predicted to be 416 fs for studies of gas-phase species, while the predicted spatial resolution of better than 2 nm-1 compares well with traditional time-averaged electron diffraction set-ups.

Solvent as electron donor: Donor/acceptor electronic coupling is a dynamical variable

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

Castner, E.W. Jr.; Kennedy, D.; Cave, R.J.

2000-04-06

The authors combine analysis of measurements by femtosecond optical spectroscopy, computer simulations, and the generalized Mulliken-Hush (GMH) theory in the study of electron-transfer reactions and electron donor-acceptor interactions. The study focus is on ultrafast photoinduced electron-transfer reactions from aromatic amine solvent donors to excited-state acceptors. The experimental results from femtosecond dynamical measurements fall into three categories: six coumarin acceptors reductively quenched by N,N-dimethylaniline (DMA), eight electron-donating amine solvents reductively quenching coumarin 152 (7-(dimethylamino)-4-(trifluoromethyl)-coumarin), and reductive quenching dynamics of two coumarins by DMA as a function of dilution in the nonreactive solvents toluene and chlorobenzene. Applying a combination of molecular dynamicsmore » trajectories, semiempirical quantum mechanical calculations (of the relevant adiabatic electronic states), and GMH theory to the C152/DMA photoreaction, the authors calculate the electron donor/acceptor interaction parameter H{sub DA} at various time frames, H{sub DA} is strongly modulated by both inner-sphere and outer-sphere nuclear dynamics, leading us to conclude that H{sub DA} must be considered as a dynamical variable.« less

Interplay of hot electrons from localized and propagating plasmons.

PubMed

Hoang, Chung V; Hayashi, Koki; Ito, Yasuo; Gorai, Naoki; Allison, Giles; Shi, Xu; Sun, Quan; Cheng, Zhenzhou; Ueno, Kosei; Goda, Keisuke; Misawa, Hiroaki

2017-10-03

Plasmon-induced hot-electron generation has recently received considerable interest and has been studied to develop novel applications in optoelectronics, photovoltaics and green chemistry. Such hot electrons are typically generated from either localized plasmons in metal nanoparticles or propagating plasmons in patterned metal nanostructures. Here we simultaneously generate these heterogeneous plasmon-induced hot electrons and exploit their cooperative interplay in a single metal-semiconductor device to demonstrate, as an example, wavelength-controlled polarity-switchable photoconductivity. Specifically, the dual-plasmon device produces a net photocurrent whose polarity is determined by the balance in population and directionality between the hot electrons from localized and propagating plasmons. The current responsivity and polarity-switching wavelength of the device can be varied over the entire visible spectrum by tailoring the hot-electron interplay in various ways. This phenomenon may provide flexibility to manipulate the electrical output from light-matter interaction and offer opportunities for biosensors, long-distance communications, and photoconversion applications.Plasmon-induced hot electrons have potential applications spanning photodetection and photocatalysis. Here, Hoang et al. study the interplay between hot electrons generated by localized and propagating plasmons, and demonstrate wavelength-controlled polarity-switchable photoconductivity.

Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons

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

Hugenschmidt, Christoph; Legl, Stefan; Physik-Department E21, Technische Universitaet Muenchen, James-Franck-Strasse, 85748 Garching

2006-10-15

Positron annihilation induced Auger-electron spectroscopy (PAES) has several advantages over conventional Auger-electron spectroscopy such as extremely high surface sensitivity and outstanding signal-to-noise ratio at the Auger-transition energy. In order to benefit from these prominent features a low-energy positron beam of high intensity is required for surface sensitive PAES studies. In addition, an electron energy analyzer is required, which efficiently detects the Auger electrons with acceptable energy resolution. For this reason a novel time-of-flight (TOF) spectrometer has been developed at the intense positron source NEPOMUC that allows PAES studies within short measurement time. This TOF-PAES setup combines a trochoidal filter andmore » a flight tube in a Faraday cage in order to achieve an improved energy resolution of about 1 eV at high electron energies up to E{approx_equal}1000 eV. The electron flight time is the time between the annihilation radiation at the sample and when the electron hits a microchannel plate detector at the end of the flight tube.« less

Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons

NASA Astrophysics Data System (ADS)

Hugenschmidt, Christoph; Legl, Stefan

2006-10-01

Positron annihilation induced Auger-electron spectroscopy (PAES) has several advantages over conventional Auger-electron spectroscopy such as extremely high surface sensitivity and outstanding signal-to-noise ratio at the Auger-transition energy. In order to benefit from these prominent features a low-energy positron beam of high intensity is required for surface sensitive PAES studies. In addition, an electron energy analyzer is required, which efficiently detects the Auger electrons with acceptable energy resolution. For this reason a novel time-of-flight (TOF) spectrometer has been developed at the intense positron source NEPOMUC that allows PAES studies within short measurement time. This TOF-PAES setup combines a trochoidal filter and a flight tube in a Faraday cage in order to achieve an improved energy resolution of about 1eV at high electron energies up to E ≈1000eV. The electron flight time is the time between the annihilation radiation at the sample and when the electron hits a microchannel plate detector at the end of the flight tube.

Anomalous High-Energy Waterfall-Like Electronic Structure in 5 d Transition Metal Oxide Sr2IrO4 with a Strong Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Liu, Yan; Yu, Li; Jia, Xiaowen; Zhao, Jianzhou; Weng, Hongming; Peng, Yingying; Chen, Chaoyu; Xie, Zhuojin; Mou, Daixiang; He, Junfeng; Liu, Xu; Feng, Ya; Yi, Hemian; Zhao, Lin; Liu, Guodong; He, Shaolong; Dong, Xiaoli; Zhang, Jun; Xu, Zuyan; Chen, Chuangtian; Cao, Gang; Dai, Xi; Fang, Zhong; Zhou, X. J.

2015-08-01

The low energy electronic structure of Sr2IrO4 has been well studied and understood in terms of an effective Jeff = 1/2 Mott insulator model. However, little work has been done in studying its high energy electronic behaviors. Here we report a new observation of the anomalous high energy electronic structure in Sr2IrO4. By taking high-resolution angle-resolved photoemission measurements on Sr2IrO4 over a wide energy range, we have revealed for the first time that the high energy electronic structures show unusual nearly-vertical bands that extend over a large energy range. Such anomalous high energy behaviors resemble the high energy waterfall features observed in the cuprate superconductors. While strong electron correlation plays an important role in producing high energy waterfall features in the cuprate superconductors, the revelation of the high energy anomalies in Sr2IrO4, which exhibits strong spin-orbit coupling and a moderate electron correlation, points to an unknown and novel route in generating exotic electronic excitations.

Anomalous High-Energy Waterfall-Like Electronic Structure in 5 d Transition Metal Oxide Sr2IrO4 with a Strong Spin-Orbit Coupling.

PubMed

Liu, Yan; Yu, Li; Jia, Xiaowen; Zhao, Jianzhou; Weng, Hongming; Peng, Yingying; Chen, Chaoyu; Xie, Zhuojin; Mou, Daixiang; He, Junfeng; Liu, Xu; Feng, Ya; Yi, Hemian; Zhao, Lin; Liu, Guodong; He, Shaolong; Dong, Xiaoli; Zhang, Jun; Xu, Zuyan; Chen, Chuangtian; Cao, Gang; Dai, Xi; Fang, Zhong; Zhou, X J

2015-08-12

The low energy electronic structure of Sr2IrO4 has been well studied and understood in terms of an effective Jeff = 1/2 Mott insulator model. However, little work has been done in studying its high energy electronic behaviors. Here we report a new observation of the anomalous high energy electronic structure in Sr2IrO4. By taking high-resolution angle-resolved photoemission measurements on Sr2IrO4 over a wide energy range, we have revealed for the first time that the high energy electronic structures show unusual nearly-vertical bands that extend over a large energy range. Such anomalous high energy behaviors resemble the high energy waterfall features observed in the cuprate superconductors. While strong electron correlation plays an important role in producing high energy waterfall features in the cuprate superconductors, the revelation of the high energy anomalies in Sr2IrO4, which exhibits strong spin-orbit coupling and a moderate electron correlation, points to an unknown and novel route in generating exotic electronic excitations.

Electronic recorder study

DOT National Transportation Integrated Search

1998-06-01

Information on the current use of electronic recorders and opinions on mandatory electronic recorder use was obtained from truck and bus fleets and owner operators through the cooperation of several trucking industry associations. Due to the low resp...

A review of electronic journal acquisition, management, and use in health sciences libraries.

PubMed

Burrows, Suzetta

2006-01-01

The paper describes patterns of electronic journal usage in health sciences libraries during the past decade. The paper presents a case study, documenting the pattern of acquisition, management, and usage at the Louis Calder Memorial Library of the University of Miami Miller School of Medicine. Health sciences journals were early to offer electronic alternatives to print. As a result, health sciences libraries, their patrons, and the public at large were early to embrace the new versions and continue to embrace the significant changes in scholarly communication they enable. Although the patterns of electronic journals among health sciences libraries and other special and academic libraries have similarities, they also have differences. Broad studies of electronic journals in non-health sciences libraries have been published, but a retrospective review of electronic journals in health sciences libraries has not.

Photoinduced electron transfer between benzyloxy dendrimer phthalocyanine and benzoquinone

NASA Astrophysics Data System (ADS)

Zhang, Tiantian; Ma, Dongdong; Pan, Sujuan; Wu, Shijun; Jiang, Yufeng; Zeng, Di; Yang, Hongqin; Peng, Yiru

2016-10-01

Photo-induced electron transfer (PET) is an important and fundamental process in natural photosynthesis. To mimic such interesting PET process, a suitable donor and acceptor couple were properly chosen. Dendrimer phthalocyanines and their derivatives have emerged as promising materials for artificial photosynthesis systems. In this paper, the electron transfer between the light harvest dendrimer phthalocyanine (donor) and the 1,4-benzoquinone (acceptor) was studied by UV/Vis and fluorescence spectroscopic methods. It was found that fluorescence of phthalocyanine was quenched by benzoquinone (BQ) via excited state electron transfer, from the phthalocyanine to the BQ upon excitation at 610 nm. The Stern-Volmer constant (KSV) of electron transfer was calculated. Our study suggests that this dendritic phthalocyanine is an effective new electron donor and transmission complex and could be used as a potential artificial photosynthesis system.

The Experimental Study of Novel Pseudospark Hollow Cathode Plasma Electron Gun

NASA Astrophysics Data System (ADS)

Gu, Xiaowei; Meng, Lin; Sun, Yiqin; Yu, Xinhua

2008-11-01

The high-power microwave devices with plasma-filled have unique properties. One of the major problems associated with plasma-filled microwave sources is that ions from the plasma drift toward the gun regions of the tube. This bombardment is particularly dangerous for the gun, where high-energy ion impacts can damage the cathode surface and degrade its electron emission capabilities. One of the techniques investigated to mitigate this issue is to replace the material cathode with plasma cathode. Now, we study the novel electron gun (E-gun) that can be suitable for high power microwave device applications, adopting two forms of discharge channel, 1: a single hole channel, the structure can produce a solid electron beam; 2: porous holes channel, the structure can generate multiple electronic injection which is similar to the annular electron beam.

Radiation studies of optical and electronic components used in astronomical satellite studies

NASA Technical Reports Server (NTRS)

Becher, J.; Kernell, R. L.

1981-01-01

The synchronous orbit of the IUE carries the satellite through Earth's outer electron belt. A 40 mCi Sr90 source was used to simulate these electrons. A 5 mCi source of Co60 was used to simulate bremmstrahlung. A 10 MeV electron Linac and a 1.7 MeV electron Van de Graaf wer used to investigate the energy dependence of radiation effects and to perform radiations at a high flux rate. A 100 MeV proton cyclotron was used to simulate cosmic rays. Results are presented for three instrument systems of the IUE and measurements for specific components are reported. The three instrument systems were the ultraviolet converter, the fine error sensor (FES), and the SEC vidicon camera tube. The components were optical glasses, electronic components, silicon photodiodes, and UV window materials.

Electronic cigarettes. A position statement of the forum of international respiratory societies.

PubMed

Schraufnagel, Dean E; Blasi, Francesco; Drummond, M Bradley; Lam, David C L; Latif, Ehsan; Rosen, Mark J; Sansores, Raul; Van Zyl-Smit, Richard

2014-09-15

Awareness and usage of electronic cigarettes has exponentially increased during the last few years, especially among young people and women in some countries. The rapid acceptance of electronic cigarettes may be attributed in part to the perception created by marketing and the popular press that they are safer than combustible cigarettes. To alert and advise policy makers about electronic cigarettes and their potential hazards. Using The Union's position paper on electronic cigarettes as the starting template, the document was written using an iterative process. Portions of the manuscript have been taken directly from the position papers of participating societies. Because electronic cigarettes generate less tar and carcinogens than combustible cigarettes, use of electronic cigarettes may reduce disease caused by those components. However, the health risks of electronic cigarettes have not been adequately studied. Studies looking at whether electronic cigarettes can aid smoking cessation have had inconsistent results. Moreover, the availability of electronic cigarettes may have an overall adverse health impact by increasing initiation and reducing cessation of combustible nicotine delivery products. The health and safety claims regarding electronic nicotine delivery devices should be subject to evidentiary review. The potential benefits of electronic cigarettes to an individual smoker should be weighed against potential harm to the population of increased social acceptability of smoking and use of nicotine, the latter of which has addictive power and untoward effects. As a precaution, electronic nicotine delivery devices should be restricted or banned until more information about their safety is available. If they are allowed, they should be closely regulated as medicines or tobacco products.

Nongyrotropic electron orbits in collisionless magnetic reconnection

NASA Astrophysics Data System (ADS)

Zenitani, S.

2016-12-01

In order to study inner workings of magnetic reconnection, NASA has recently launched Magnetospheric MultiScale (MMS) spacecraft. It is expected to observe electron velocity distribution functions (VDFs) at high resolution in magnetotail reconnection sites in 2017. Since VDFs are outcomes of many particle orbits, it is important to understand the relation between electron orbits and VDFs. In this work, we study electron orbits and associated VDFs in the electron current layer in magnetic reconnection, by using a two-dimensional particle-in-cell (PIC) simulation. By analyzing millions of electron orbits, we discover several new orbits: (1) Figure-eight-shaped regular orbits inside the super-Alfvenic electron jet, (2) noncrossing Speiser orbits that do not cross the midplane, (3) noncrossing regular orbits on the jet flanks, and (4) nongyrotropic electrons in the downstream of the jet termination region. Properties of these orbits are organized by a theory on particle orbits (Buchner & Zelenyi 1989 JGR). The noncrossing orbits are mediated by the polarization electric field (Hall electric field E_z) near the midplane. These orbits can be understood as electrostatic extensions of the conventional theory. Properties of the super-Alfvenic electron jet are attributed to the traditional Speiser-orbit electrons. On the other hand, the noncrossing electrons are the majority in number density in the jet flanks. This raise a serious question to our present understanding of physics of collisionless magnetic reconnection, which only assumes crossing populations. We will also discuss spatial distribution of energetic electrons and observational signatures of noncrossing electrons. Reference: Zenitani & Nagai (2016), submitted to Phys. Plasmas.

Effect of electron irradiation dose on the performance of avalanche photodiode electron detectors

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

Kawauchi, Taizo; Wilde, Markus; Fukutani, Katsuyuki

2009-01-01

Avalanche photodiodes (APDs) are efficient detectors for electrons with energies below 100 keV. The damaging effects of 8 keV electron beam irradiation on the dark current and the output signal of the APD detector were investigated in this study. The APD dark current increases after electron doses exceeding 1.4x10{sup 13} cm{sup -2}. Preirradiation by high doses of 8 keV electrons further causes a deformation of the pulse height distribution of the APD output in the subsequent detection of low-flux electrons. This effect is particularly prominent when the energy of the detected electrons is lower than that of the damaging electrons.more » By comparing the experimental data with results of a simulation based on an electron trapping model, we conclude that the degradation of the APD performance is attributable to an enhancement of secondary-electron trapping at irradiation induced defects.« less

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

Bose, A; Gardel, EJ; Vidoudez, C

Oxidation-reduction reactions underlie energy generation in nearly all life forms. Although most organisms use soluble oxidants and reductants, some microbes can access solid-phase materials as electron-acceptors or -donors via extracellular electron transfer. Many studies have focused on the reduction of solid-phase oxidants. Far less is known about electron uptake via microbial extracellular electron transfer, and almost nothing is known about the associated mechanisms. Here we show that the iron-oxidizing photoautotroph Rhodopseudomonas palustris TIE-1 accepts electrons from a poised electrode, with carbon dioxide as the sole carbon source/electron acceptor. Both electron uptake and ruBisCo form I expression are stimulated by light.more » Electron uptake also occurs in the dark, uncoupled from photosynthesis. Notably, the pioABC operon, which encodes a protein system essential for photoautotrophic growth by ferrous iron oxidation, influences electron uptake. These data reveal a previously unknown metabolic versatility of photoferrotrophs to use extracellular electron transfer for electron uptake.« less

Electron heating and thermal relaxation of gold nanorods revealed by two-dimensional electronic spectroscopy.

PubMed

Lietard, Aude; Hsieh, Cho-Shuen; Rhee, Hanju; Cho, Minhaeng

2018-03-01

To elucidate the complex interplay between the size and shape of gold nanorods and their electronic, photothermal, and optical properties for molecular imaging, photothermal therapy, and optoelectronic devices, it is a prerequisite to characterize ultrafast electron dynamics in gold nanorods. Time-resolved transient absorption (TA) studies of plasmonic electrons in various nanostructures have revealed the time scales for electron heating, lattice vibrational excitation, and phonon relaxation processes in condensed phases. However, because linear spectroscopic and time-resolved TA signals are vulnerable to inhomogeneous line-broadening, pure dephasing and direct electron heating effects are difficult to observe. Here we show that femtosecond two-dimensional electronic spectroscopy, with its unprecedented time resolution and phase sensitivity, can be used to collect direct experimental evidence for ultrafast electron heating, anomalously strong coherent and transient electronic plasmonic responses, and homogenous dephasing processes resulting from electron-vibration couplings even for polydisperse gold nanorods.

Fabrication of ZnS nanoparticle chains on a protein template

PubMed Central

Hulleman, J.; Kim, S. M.; Tumkur, T.; Rochet, J.-C.; Stach, E.; Stanciu, L.

2011-01-01

In the present study, we have exploited the properties of a fibrillar protein for the template synthesis of zinc sulfide (ZnS) nanoparticle chains. The diameter of the ZnS nanoparticle chains was tuned in range of ~30 to ~165 nm by varying the process variables. The nanoparticle chains were characterized by field emission scanning electron microscopy, UV–Visible spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy. The effect of incubation temperature on the morphology of the nanoparticle chains was also studied. PMID:21804765

Electronic and Atomic Collisions. Abstracts of Contributed Papers. International Conference on the Physics of Electronic and atomic Collisions (14th) Held at Palo Alto, California in 1985,

DTIC Science & Technology

1985-01-01

Vukstich, A. M. Solomon Electron-Electron Coincidence Spectrometer for the Study of Relative Triple Differential 709 Cross Sections for Autoionizing...wavelengths depen~eat three- and four -photon ionization spectra v v ., v VVvVvVV (V of Bi and Bi (2) The ionizatign of"Bi2 is studied by various one &(I...the observed energetic protons must arise from at least four repulsive states. The lower energy group consists of protons arising from" . excitation

Modeling the process of interaction of 10 keV electrons with a plane dielectric surface

NASA Astrophysics Data System (ADS)

Vokhmyanina, Kristina; Sotnikova, Valentina; Sotnikov, Alexey; Kaplii, Anna; Nikulicheva, Tatyana; Kubankin, Alexandr; Kishin, Ivan

2018-05-01

The effect of guiding of charged particles by dielectric channels is of noticeable interest at the present time. The phenomenon is widely studied experimentally and theoretically but some points still need to be clarified. A previously developed model of interaction of fast electrons with dielectric surface at grazing incidence is used to study the independence of electron deflection on the value of electron beam current. The calculations were performed assuming a smooth dependence of the surface conductivity on the beam current in the 40-3000 nA range.

Fullerene Cyanation Does Not Always Increase Electron Affinity: Experimental and Theoretical Study

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

Clikeman, Tyler T.; Deng, Shihu; Popov, Alexey A.

2015-01-01

The electron affinities of C70 derivatives with trifluoromethyl, methyl and cyano groups were studied experimentally and theoretically using low-temperature photoelectron spectroscopy (LT PES) and density functional theory (DFT). The electronic effects of these functional groups were determined and found to be highly dependent on the addition patterns. Substitution of CF3 for CN for the same addition pattern increases the experimental electron affinity by 70 meV per substitution. The synthesis of a new fullerene derivative, C70(CF3)10(CN)2, is reported for the first time

Single-Molecule Interfacial Electron Transfer

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

Lu, H. Peter

This project is focused on the use of single-molecule high spatial and temporal resolved techniques to study molecular dynamics in condensed phase and at interfaces, especially, the complex reaction dynamics associated with electron and energy transfer rate processes. The complexity and inhomogeneity of the interfacial ET dynamics often present a major challenge for a molecular level comprehension of the intrinsically complex systems, which calls for both higher spatial and temporal resolutions at ultimate single-molecule and single-particle sensitivities. Combined single-molecule spectroscopy and electrochemical atomic force microscopy approaches are unique for heterogeneous and complex interfacial electron transfer systems because the static andmore » dynamic inhomogeneities can be identified and characterized by studying one molecule at a specific nanoscale surface site at a time. The goal of our project is to integrate and apply these spectroscopic imaging and topographic scanning techniques to measure the energy flow and electron flow between molecules and substrate surfaces as a function of surface site geometry and molecular structure. We have been primarily focusing on studying interfacial electron transfer under ambient condition and electrolyte solution involving both single crystal and colloidal TiO 2 and related substrates. The resulting molecular level understanding of the fundamental interfacial electron transfer processes will be important for developing efficient light harvesting systems and broadly applicable to problems in fundamental chemistry and physics. We have made significant advancement on deciphering the underlying mechanism of the complex and inhomogeneous interfacial electron transfer dynamics in dyesensitized TiO 2 nanoparticle systems that strongly involves with and regulated by molecule-surface interactions. We have studied interfacial electron transfer on TiO 2 nanoparticle surfaces by using ultrafast single-molecule spectroscopy and electrochemical AFM metal tip scanning microscopy, focusing on understanding the interfacial electron transfer dynamics at specific nanoscale electron transfer sites with high-spatially and temporally resolved topographic-and-spectroscopic characterization at individual molecule basis, characterizing single-molecule rate processes, reaction driving force, and molecule-substrate electronic coupling. One of the most significant characteristics of our new approach is that we are able to interrogate the complex interfacial electron transfer dynamics by actively pin-point energetic manipulation of the surface interaction and electronic couplings, beyond the conventional excitation and observation.« less

Charge transport in metal oxides: A theoretical study of hematite α-Fe2O3

NASA Astrophysics Data System (ADS)

Iordanova, N.; Dupuis, M.; Rosso, K. M.

2005-04-01

Transport of conduction electrons and holes through the lattice of α-Fe2O3 (hematite) is modeled as a valence alternation of iron cations using ab initio electronic structure calculations and electron transfer theory. Experimental studies have shown that the conductivity along the (001) basal plane is four orders of magnitude larger than the conductivity along the [001] direction. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e., the reorganization energy and the electronic coupling matrix element that enter Marcus' theory. The calculation of the electronic coupling followed the generalized Mulliken-Hush approach using the complete active space self-consistent field method. Our findings demonstrate an approximately three orders of magnitude anisotropy in both electron and hole mobility between directions perpendicular and parallel to the c axis, in good accord with experimental data. The anisotropy arises from the slowness of both electron and hole mobilities across basal oxygen planes relative to that within iron bilayers between basal oxygen planes. Interestingly, for elementary reaction steps along either of the directions considered, there is only less than one order of magnitude difference in mobility between electrons and holes, in contrast to accepted classical arguments. Our findings indicate that the most important quantity underlying mobility differences is the electronic coupling, albeit the reorganization energy contributes as well. The large values computed for the electronic coupling suggest that charge transport reactions in hematite are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron spin coupling within the Fe-Fe donor-acceptor pair, while the reorganization energy is essentially independent of the electron spin coupling.

Electron-transfer and acid-base properties of a two-electron oxidized form of quaterpyrrole that acts as both an electron donor and an acceptor.

PubMed

Zhang, Min; E, Wenbo; Ohkubo, Kei; Sanchez-Garcia, David; Yoon, Dae-Wi; Sessler, Jonathan L; Fukuzumi, Shunichi; Kadish, Karl M

2008-02-21

Electron-transfer interconversion between the four-electron oxidized form of a quaterpyrrole (abbreviated as P4 for four pyrroles) and the two-electron oxidized form (P4H2) as well as between P4H2 and its fully reduced form (P4H4) bearing analogous substituents in the alpha- and beta-pyrrolic positions was studied by means of cyclic voltammetry and UV-visible spectroelectrochemistry combined with ESR and laser flash photolysis measurements. The two-electron oxidized form, P4H2, acts as both an electron donor and an electron acceptor. The radical cation (P4H2*+) and radical anion (P4H2*-) are both produced by photoinduced electron transfer from dimeric 1-benzyl-1,4-dihydronicotinamide to P4H2, whereas the cation radical form of the compound is also produced by electron-transfer oxidation of P4H2 with [Ru(bpy)3]3+. The ESR spectra of P4H2*+ and P4H2*- were recorded at low temperature and exhibit spin delocalization over all four pyrrole units. Thus, the two-electron oxidized form of the quaterpyrrole (P4H2) displays redox and electronic features analogous to those seen in the case of porphyrins and may be considered as a simple, open-chain model of this well-studied tetrapyrrolic macrocycle. The dynamics of deprotonation from P4H2*+ and disproportionation of P4H2 were examined by laser flash photolysis measurements of photoinduced electron-transfer oxidation and reduction of P4H2, respectively.

Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

DOE PAGES

Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; ...

2015-09-21

The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. Moreover, in this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly,more » our Monte Carlo simulations reveal that the fast reduction with doping of the N eel T N and the structural T S transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Finally, our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. Our study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.« less

Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

NASA Astrophysics Data System (ADS)

Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

2015-09-01

The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (x z ,y z ,x y ) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. In this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations reveal that the fast reduction with doping of the Néel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. This study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.

Nonequilibrium, steady-state electron transport with N-representable density matrices from the anti-Hermitian contracted Schrödinger equation

NASA Astrophysics Data System (ADS)

Rothman, Adam E.; Mazziotti, David A.

2010-03-01

We study molecular conductivity for a one-electron, bath-molecule-bath model Hamiltonian. The primary quantum-mechanical variable is the one-electron reduced density matrix (1-RDM). By identifying similarities between the steady-state Liouville equation and the anti-Hermitian contracted Schrödinger equation (ACSE) [D. A. Mazziotti, Phys. Rev. A 75, 022505 (2007)], we develop a way of enforcing nonequilibrium, steady-state behavior in a time-independent theory. Our results illustrate the relationship between current and voltage in molecular junctions assuming that the total number of electrons under consideration can be fixed across all driving potentials. The impetus for this work is a recent study by Subotnik et al. that also uses the 1-RDM to study molecular conductivity under different assumptions regarding the total number of electrons [J. E. Subotnik et al., J. Chem. Phys. 130, 144105 (2009)]. Unlike calculations in the previous study, our calculations result in 1-RDMs that are fully N-representable. The present work maintains N-representability through a bath-bath mixing that is related to a time-independent relaxation of the baths in the absence of the molecule, as governed by the ACSE. A lack of N-representability can be important since it corresponds to occupying energy states in the molecule or baths with more than one electron or hole (the absence of an electron) in violation of the Pauli principle. For this reason the present work may serve as an important, albeit preliminary, step in designing a 2-RDM/ACSE method for studying steady-state molecular conductivity with an explicit treatment of electron correlation.

Evaluation of Arabic Language Learning Program for Non-Native Speakers in Saudi Electronic University According to Total Quality Standards

ERIC Educational Resources Information Center

Alowaydhi, Wafa Hafez

2016-01-01

The current study aimed at standardizing the program of learning Arabic for non-native speakers in Saudi Electronic University according to certain standards of total quality. To achieve its purpose, the study adopted the descriptive analytical method. The author prepared a measurement tool for evaluating the electronic learning programs in light…

Differential cross sections for electron impact excitation of the Herzberg pseudocontinuum of molecular oxygen

NASA Astrophysics Data System (ADS)

Green, M. A.; Maddern, T.; Brunger, M. J.; Campbell, L.; Cartwright, D. C.; Newell, W. R.; Teubner, P. J. O.

2002-09-01

We report differential cross sections (DCSs) for electron impact excitation of the sum (c1Σ u- + A'3 Δ u + A3 Σ u+) of the three states that constitute the Herzberg pseudocontinuum in O2. These DCSs were measured at seven incident electron energies in the range 9-20 eV and over the scattered electron angular range 10-90°. We note that this represents a far more detailed study than has hitherto previously been reported. In their review on electron-diatomic molecule scattering systems, Brunger and Buckman (Brunger M J and Buckman S J 2002 Phys. Rep. 357 215) clearly identified gaps in our knowledge for electron impact excitation of the Herzberg electronic states. The present study rectifies this situation and, additionally, seeks to stimulate theoreticians to extend their existing integral cross section calculations, for the c1 Σ u-, A'3 Δ u and A3 Σ u+ states, to the DCS-level.

The Effect of an Electronic SBAR Communication Tool on Documentation of Acute Events in the Pediatric Intensive Care Unit.

PubMed

Panesar, Rahul S; Albert, Ben; Messina, Catherine; Parker, Margaret

2016-01-01

The Situation, Background, Assessment, Recommendation (SBAR) handoff tool is designed to improve communication. The effects of integrating an electronic medical record (EMR) with a SBAR template are unclear. The research team hypothesizes that an electronic SBAR template improves documentation and communication between nurses and physicians. In all, 84 patient events were recorded from 542 admissions to the pediatric intensive care unit. Three time periods were studied: (a) paper documentation only, (b) electronic documentation, and (c) electronic documentation with an SBAR template. Documentation quality was assessed using a 4-point scoring system. The frequency of event notes increased progressively during the 3 study periods. Mean quality scores improved significantly from paper documentation to EMR free-text notes and to electronic SBAR-template notes, as did nurse and attending physician notification. The implementation of an electronic SBAR note is associated with more complete documentation and increased frequency of documentation of communication among nurses and physicians. © The Author(s) 2014.

Theoretical study on the electronic structures and phosphorescent properties of four Ir(III) complexes with different substituents on the ancillary ligand

NASA Astrophysics Data System (ADS)

Han, Deming; Shang, Xiaohong; Zhang, Gang; Zhao, Lihui

2013-12-01

The geometry structures, electronic structures, absorption and phosphorescent properties of four Ir(III) complexes {[(F2-ppy)2Ir(pta-X)], where F2-ppy = (2,4-difluoro)phenylpyridine; pta = pyridine-1,2,4-triazole; X = -CF3; -H; -CH3; -N(CH3)2}, are investigated using the density functional method. The results reveal that the electron-accepting group -CF3 has no obvious effect on absorption and emission properties, while the substitutive group -N(CH3)2 with strong electron-donating ability has obvious effect on the emission properties. The mobility of hole and electron were studied computationally based on the Marcus-Hush theory. Calculations of ionisation potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. We hope that this theoretical work can provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes.

Experimental and theoretical triple differential cross sections for electron-impact ionization of Ar (3p) for equal energy final state electrons

NASA Astrophysics Data System (ADS)

Amami, Sadek; Ozer, Zehra N.; Dogan, Mevlut; Yavuz, Murat; Varol, Onur; Madison, Don

2016-09-01

There have been several studies of electron-impact ionization of inert gases for asymmetric final state energy sharing and normally one electron has an energy significantly higher than the other. However, there have been relatively few studies examining equal energy final state electrons. Here we report experimental and theoretical triple differential cross sections for electron impact ionization of Ar (3p) for equal energy sharing of the outgoing electrons. Previous experimental results combined with some new measurements are compared with distorted wave born approximation (DWBA) results, DWBA results using the Ward-Macek (WM) approximation for the post collision interaction (PCI), and three-body distorted wave (3DW) which includes PCI without approximation. The results show that it is crucially important to include PCI in the calculation particularly for lower energies and that the WM approximation is valid only for high energies. The 3DW, on the other hand, is in reasonably good agreement with data down to fairly low energies.

Recording signs of deterioration in acute patients: The documentation of vital signs within electronic health records in patients who suffered in-hospital cardiac arrest.

PubMed

Stevenson, Jean E; Israelsson, Johan; Nilsson, Gunilla C; Petersson, Göran I; Bath, Peter A

2016-03-01

Vital sign documentation is crucial to detecting patient deterioration. Little is known about the documentation of vital signs in electronic health records. This study aimed to examine documentation of vital signs in electronic health records. We examined the vital signs documented in the electronic health records of patients who had suffered an in-hospital cardiac arrest and on whom cardiopulmonary resuscitation was attempted between 2007 and 2011 (n = 228), in a 372-bed district general hospital. We assessed the completeness of vital sign data compared to VitalPAC™ Early Warning Score and the location of vital signs within the electronic health records. There was a noticeable lack of completeness of vital signs. Vital signs were fragmented through various sections of the electronic health records. The study identified serious shortfalls in the representation of vital signs in the electronic health records, with consequential threats to patient safety. © The Author(s) 2014.

Evaluating the Role and Effects of Precipitation on Relativistic Electron Losses during Storms

NASA Astrophysics Data System (ADS)

Chen, Y.; Fu, X.

2016-12-01

Theoretic studies have suggested that during storm times various waves (e.g., whistler-mode chorus and electromagnetic ion cyclotron waves) can cause significant precipitation of relativistic ( MeV) electrons that are originally trapped inside the outer radiation belt. However, the role of precipitation and its quantitative contribution to the losses of outer-belt electrons remain open questions. In this study, we tackle these questions by systemically examining the latest wave and electron in-situ, simultaneous observations made at different altitudes by Van Allen Probes from near equator, NOAA POES at low Earth orbits near/across electron loss cone, and BARREL under the mesosphere. After calibrating with DEMTER observations, we first confirm and quantify the response of POES MEPED proton channels to MeV electrons. Next, we identify a list of precipitation events from BARREL and POES measurements, examine the temporal adn spatial relation between the two data sets, and estimate the intensities of electron precipitation with ascertained uncertainties. Then, from Van Allen Probes data, we select another list of dropout events during storms. By cross checking the above two lists, we are able to determine the causal relation between precipitation and dropouts through individual case as well as statistical studies so as to quantify the contributions from precipitation. This study mainly focuses on the relatively small L-shells with positive phase space density radial gradient in order to alleviate the impacts from outward radial diffusion and adiabatic effects. Based upon the recent discovery of cross-energy cross-pitch angle coherence, we pay particular attention to the cross-term diffusions which may account for the extra "loss" needed by observed MeV electron dropouts. Results from this observational study will advance our knowledge on the loss mechanism of outer-belt electrons, and thus lay down another stepping stone towards high-fidelity physics-based models for radiation belts.

Sleep and use of electronic devices in adolescence: results from a large population-based study.

PubMed

Hysing, Mari; Pallesen, Ståle; Stormark, Kjell Morten; Jakobsen, Reidar; Lundervold, Astri J; Sivertsen, Børge

2015-02-02

Adolescents spend increasingly more time on electronic devices, and sleep deficiency rising in adolescents constitutes a major public health concern. The aim of the present study was to investigate daytime screen use and use of electronic devices before bedtime in relation to sleep. A large cross-sectional population-based survey study from 2012, the youth@hordaland study, in Hordaland County in Norway. Cross-sectional general community-based study. 9846 adolescents from three age cohorts aged 16-19. The main independent variables were type and frequency of electronic devices at bedtime and hours of screen-time during leisure time. Sleep variables calculated based on self-report including bedtime, rise time, time in bed, sleep duration, sleep onset latency and wake after sleep onset. Adolescents spent a large amount of time during the day and at bedtime using electronic devices. Daytime and bedtime use of electronic devices were both related to sleep measures, with an increased risk of short sleep duration, long sleep onset latency and increased sleep deficiency. A dose-response relationship emerged between sleep duration and use of electronic devices, exemplified by the association between PC use and risk of less than 5 h of sleep (OR=2.70, 95% CI 2.14 to 3.39), and comparable lower odds for 7-8 h of sleep (OR=1.64, 95% CI 1.38 to 1.96). Use of electronic devices is frequent in adolescence, during the day as well as at bedtime. The results demonstrate a negative relation between use of technology and sleep, suggesting that recommendations on healthy media use could include restrictions on electronic devices. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Space Charge Effect in the Sheet and Solid Electron Beam

NASA Astrophysics Data System (ADS)

Song, Ho Young; Kim, Hyoung Suk; Ahn, Saeyoung

1998-11-01

We analyze the space charge effect of two different types of electron beam ; sheet and solid electron beam. Electron gun simulations are carried out using shadow and control grids for high and low perveance. Rectangular and cylindrical geometries are used for sheet and solid electron beam in planar and disk type cathode. The E-gun code is used to study the limiting current and space charge loading in each geometries.

STUDY BY AES AND EELS OF InP, InSb, InPO4 AND InxGa1-xAs SUBMITTED TO ELECTRON IRRADIATION

NASA Astrophysics Data System (ADS)

Ghaffour, M.; Abdellaoui, A.; Bouslama, M.; Ouerdane, A.; Al-Douri, Y.

2012-02-01

The surface of materials plays an important role in their technological applications. In the interest to study the stability of materials and their behavior, we irradiate them by the electrons by using the electron spectroscopy such as the Auger electron spectroscopy (AES) and the electron energy loss spectroscopy (EELS). These methods have proved their good sensitivity to study material surfaces. In this paper, we give some results about the effect of the electron beam irradiating the compounds InP, InSb, InPO4 and InxGa1-xAs. The III-V semiconductors InP and InSb seem to be sensitive to the electron irradiation. This breaks the chemical bonds between the element III and V which leads to an oxidation process at the surface. The AES and EELS spectroscopy are also used to characterize the oxide InPO4 whose thickness is about 10 Å grown on the substrate InP(100). The irradiation of the system InPO4/InP(100) by the electron beam of 5 keV energy leads to a structural change of the surface, so that there is breaking of chemical bonds between indium and phosphorus (In-P) and formation of new oxide other than InPO4. In this study we show an important result concerning the effect of the electron beam on the compound InxGa1-xAs by varying the parameter x to obtain In0.2Ga0.8As and In0.53Ga0.47As. It appears that the electron beam affects In0.2Ga0.8As too much in comparison with In0.53Ga0.47As. In the case of the irradiation of In0.2Ga0.8As, there is breaking of chemical bonds between indium and GaAs leading to formation of indium oxide associated to GaAs.

Compton interaction of free electrons with intense low frequency radiation

NASA Technical Reports Server (NTRS)

Illarionov, A. F.; Kompaneyets, D. A.

1978-01-01

Electron behavior in an intense low frequency radiation field, with induced Compton scattering as the primary mechanism of interaction, is investigated. Evolution of the electron energy spectrum is studied, and the equilibrium spectrum of relativistic electrons in a radiation field with high brightness temperature is found. The induced radiation pressure and heating rate of an electron gas are calculated. The direction of the induced pressure depends on the radiation spectrum. The form of spectrum, under the induced force can accelerate electrons to superrelativistic energies is found.

Experimental Search for a Heavy Electron

DOE R&D Accomplishments Database

Boley, C. D.; Elias, J. E.; Friedman, J. I.; Hartmann, G. C.; Kendall, H. W.; Kirk, P.N.; Sogard, M. R.; Van Speybroeck, L. P.; de Pagter, J. K.

1967-09-01

A search for a heavy electron of the type considered by Low and Blackmon has been made by studying the inelastic scattering of 5 BeV electrons from hydrogen. The search was made over a range of values of the mass of the heavy electron from 100 t0 1300 MeV. No evidence for such a particle was observed. Upper limits on the production cross sections were determined and employed to deducelimits on the values of the electron-photon-heavy electron coupling constant in Low and Blackmon=s theory.

Electron Solvation in Two Dimensions

NASA Astrophysics Data System (ADS)

Miller, A. D.; Bezel, I.; Gaffney, K. J.; Garrett-Roe, S.; Liu, S. H.; Szymanski, P.; Harris, C. B.

2002-08-01

Ultrafast two-photon photoemission has been used to study electron solvation at two-dimensional metal/polar-adsorbate interfaces. The molecular motion that causes the excess electron solvation is manifested as a dynamic shift in the electronic energy. Although the initially excited electron is delocalized in the plane of the interface, interactions with the adsorbate can lead to its localization. A method for determining the spatial extent of the localized electron in the plane of the interface has been developed. This spatial extent was measured to be on the order of a single adsorbate molecule.

Effect of Electronic Editing on Error Rate of Newspaper.

ERIC Educational Resources Information Center

Randall, Starr D.

1979-01-01

A study of a North Carolina newspaper indicates that newspapers using fully integrated electronic editing systems have fewer errors in spelling, punctuation, sentence construction, hyphenation, and typography than newspapers not using electronic editing. (GT)

Timelike Momenta In Quantum Electrodynamics

DOE R&D Accomplishments Database

Brodsky, S. J.; Ting, S. C. C.

1965-12-01

In this note we discuss the possibility of studying the quantum electrodynamics of timelike photon propagators in muon or electron pair production by incident high energy muon or electron beams from presently available proton or electron accelerators.

A Monte Carlo simulation code for calculating damage and particle transport in solids: The case for electron-bombarded solids for electron energies up to 900 MeV

NASA Astrophysics Data System (ADS)

Yan, Qiang; Shao, Lin

2017-03-01

Current popular Monte Carlo simulation codes for simulating electron bombardment in solids focus primarily on electron trajectories, instead of electron-induced displacements. Here we report a Monte Carol simulation code, DEEPER (damage creation and particle transport in matter), developed for calculating 3-D distributions of displacements produced by electrons of incident energies up to 900 MeV. Electron elastic scattering is calculated by using full-Mott cross sections for high accuracy, and primary-knock-on-atoms (PKAs)-induced damage cascades are modeled using ZBL potential. We compare and show large differences in 3-D distributions of displacements and electrons in electron-irradiated Fe. The distributions of total displacements are similar to that of PKAs at low electron energies. But they are substantially different for higher energy electrons due to the shifting of PKA energy spectra towards higher energies. The study is important to evaluate electron-induced radiation damage, for the applications using high flux electron beams to intentionally introduce defects and using an electron analysis beam for microstructural characterization of nuclear materials.

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

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

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

2015-12-28

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

Why do Electrons with "Anomalous Energies" appear in High-Pressure Gas Discharges?

NASA Astrophysics Data System (ADS)

Kozyrev, Andrey; Kozhevnikov, Vasily; Semeniuk, Natalia

2018-01-01

Experimental studies connected with runaway electron beams generation convincingly shows the existence of electrons with energies above the maximum voltage applied to the discharge gap. Such electrons are also known as electrons with "anomalous energies". We explain the presence of runaway electrons having so-called "anomalous energies" according to physical kinetics principles, namely, we describe the total ensemble of electrons with the distribution function. Its evolution obeys Boltzmann kinetic equation. The dynamics of self-consistent electromagnetic field is taken into the account by adding complete Maxwell's equation set to the resulting system of equations. The electrodynamic mechanism of the interaction of electrons with a travelling-wave electric field is analyzed in details. It is responsible for the appearance of electrons with high energies in real discharges.

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

DOE PAGES

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

2015-12-29

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

Structure of IgG and IgY molecules in ribosome-antibody complexes as studied by electron microscopy.

PubMed

Noll, F; Lutsch, G; Bielka, H

1982-03-01

The overall shape and dimensions of IgG (rabbit) and IgY (chicken) antibodies against ribosomal proteins have been studied in electron micrographs of ribosome-antibody complexes. The antibodies appear as Y-shaped molecules with an angle of about 90 degrees between their Fab arms. The length of one Fab arm amounts to about 10 nm. No differences between the IgG and IgY molecules could be detected electron microscopically. The data obtained on the shape of IgG and IgY correlate with those of earlier electron microscopic studies while the determined size of the Fab arms is in the range found by scattering methods.

Study of Microwave Radiation from the Electron Beam at the Telescope Array Site

NASA Astrophysics Data System (ADS)

Ikeda, Daisuke; Gaïor, Romain; Mase, Keiichi; Shin, Bokkyun; De Vries, Krijn; Yamamoto, Tokonatsu; Ishihara, Aya; Kuwabara, Takao; Yoshida, Shigeru; Shibata, Tatsunobu; Ohta, Izumi S.; Ogio, Shoichi; Fukushima, Masaki; Sagawa, Hiroyuki; Matthews, John N.; Thomson, Gordon B.; Hanson, Kael; Meures, Thomas; Murchadha, Aongus Ó.

The Telescope Array (TA) experiment installed the electron accelerator in order to calibrate the fluorescence detector by shooting 40 MeV electrons into the atmosphere. This accelerator also works to investigate the radio detection techniques used for the cosmic ray observations. Using this accelerator, four experimental groups have studied individual radio detection methods at different frequency bands ranging from 50 MHz to 12 GHz. All of these experiments have observed the microwave radiation from the electron beam itself. We have studied the radiation by combining all the measured results and constructed a model of this phenomena. Results of four experiments and model expectation are in good agreement within the systematic uncertainty.

Collaborative Research: Fundamental studies of plasma control using surface embedded electronic devices

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

Raja, Laxminarayan L.; PanneerChelvam, PremKumar; Levko, Dimtry

2016-02-26

The proposed study will investigate the effect of active electron injection of from electrode surfaces To the best of our knowledge, no such a study has ever been attempted even though it could lead to the formation of whole new classes of plasma based devices and systems. We are motivated by recent articles and simple theory which gives strong reason to believe that embedded electronic devices can be used to exert control over the SEE coefficient of semiconductor surfaces (and maybe other surface types as well). Furthermore, the research will explore how such sub-surface electronic devices can best be usedmore » to exert control over an associated plasma.« less

Low-energy electron point projection microscopy/diffraction study of suspended graphene

NASA Astrophysics Data System (ADS)

Hsu, Wei-Hao; Chang, Wei-Tse; Lin, Chun-Yueh; Chang, Mu-Tung; Hsieh, Chia-Tso; Wang, Chang-Ran; Lee, Wei-Li; Hwang, Ing-Shouh

2017-11-01

In this work, we present our study of suspended graphene with low-energy electrons based on a point projection microscopic/diffractive imaging technique. Both exfoliated and chemical vapor deposition (CVD) graphene samples were studied in an ultra-high vacuum chamber. This method allows imaging of individual adsorbates at the nanometer scale and characterizing graphene layers, graphene lattice orientations, ripples on graphene membranes, etc. We found that long-duration exposure to low-energy electron beams induced aggregation of adsorbates on graphene when the electron dose rate was above a certain level. We also discuss the potential of this technique to conduct coherent diffractive imaging for determining the atomic structures of biological molecules adsorbed on suspended graphene.

Geometry dependence of electron donating or accepting abilities of amine groups in 4,4‧-disulfanediylbis(methylene)dithiazol-2-amine: Pyramidal versus planar

NASA Astrophysics Data System (ADS)

Karabıyık, Hasan; Kırılmış, Cumhur; Karabıyık, Hande

2017-08-01

The molecular and crystal structure of the title compound in which two thiazole-2-amine rings are linked to each other by disulfide bridge (sbnd Csbnd Ssbnd Ssbnd Csbnd) were studied by single-crystal X-ray diffraction, FT-IR, NMR spectroscopy, quantum chemical calculations and topological analyses on the electron density. A novel synthesis route for the compounds having symmetrical disulfide bridge is reported. The most important result regarding the compound is about electron donating or accepting properties of the terminal amine groups. Planar amine group acts as an electron-donating group, while pyramidal amine behaves as electron-accepting group. This inference was confirmed by scrutiny of crystallographic geometry and quantum chemical studies. To ascertain underlying reasons for this fact, intermolecular interactions (Nsbnd H⋯N type H-bonds and Csbnd H···π interactions) were studied. These interactions involving aromatic thiazole rings are verified by topological electron density and Hirshfeld surface analyses. Intermolecular interactions do not have an effect on the differentiation in electron donating or accepting ability of amine groups, because both amine groups are involved in Nsbnd H⋯N type H-bonds. In methodological sense, it has been understood that Ehrenfest forces acting on electron density are useful theoretical probe to analyze intra-molecular charge transfer processes.

A Theoretical Approach to Electronic Prescription System: Lesson Learned from Literature Review

PubMed Central

Samadbeik, Mahnaz; Ahmadi, Maryam; Hosseini Asanjan, Seyed Masoud

2013-01-01

Context The tendency to use advanced technology in healthcare and the governmental policies have put forward electronic prescription. Electronic prescription is considered as the main solution to overcome the major drawbacks of the paper-based medication prescription, such as transcription errors. This study aims to provide practical information concerning electronic prescription system to a variety of stakeholders. Evidence Acquisition In this review study, PubMed, ISI Web of Science, Scopus, EMBASE databases, Iranian National Library Of Medicine (INLM) portal, Google Scholar, Google and Yahoo were searched for relevant English publications concerning the problems of paper-based prescription, and concept, features, levels, benefits, stakeholders and standards of electronic prescription system. Results There are many problems with the paper prescription system which, according to studies have jeopardized patients’ safety and negatively affected the outcomes of medication therapy. All of these problems are remedied through the implementation of e-prescriptions. Conclusions The sophistication of electronic prescription and integration with EHR will become a reality, if all its stakeholders collaborate in developing fast and secure electronic prescription systems. It is plausible that the required infrastructure should be provided for implementation of the national integrated electronic prescription systems in countries without the system. Given the barriers to the implementation and use, policymakers should consider multiple strategies and offer incentives to encourage e-prescription initiatives. This will result in widespread adoption of the system. PMID:24693376

The need for academic electronic health record systems in nurse education.

PubMed

Chung, Joohyun; Cho, Insook

2017-07-01

The nursing profession has been slow to incorporate information technology into formal nurse education and practice. The aim of this study was to identify the use of academic electronic health record systems in nurse education and to determine student and faculty perceptions of academic electronic health record systems in nurse education. A quantitative research design with supportive qualitative research was used to gather information on nursing students' perceptions and nursing faculty's perceptions of academic electronic health record systems in nurse education. Eighty-three participants (21 nursing faculty and 62 students), from 5 nursing schools, participated in the study. A purposive sample of 9 nursing faculty was recruited from one university in the Midwestern United States to provide qualitative data for the study. The researcher-designed surveys (completed by faculty and students) were used for quantitative data collection. Qualitative data was taken from interviews, which were transcribed verbatim for analysis. Students and faculty agreed that academic electronic health record systems could be useful for teaching students to think critically about nursing documentation. Quantitative and qualitative findings revealed that academic electronic health record systems regarding nursing documentation could help prepare students for the future of health information technology. Meaningful adoption of academic electronic health record systems will help in building the undergraduate nursing students' competence in nursing documentation with electronic health record systems. Copyright © 2017. Published by Elsevier Ltd.

Effect of the diffusion parameters on the observed γ-ray spectrum of sources and their contribution to the local all-electron spectrum: The EDGE code

NASA Astrophysics Data System (ADS)

López-Coto, R.; Hahn, J.; BenZvi, S.; Dingus, B.; Hinton, J.; Nisa, M. U.; Parsons, R. D.; Greus, F. Salesa; Zhang, H.; Zhou, H.

2018-11-01

The positron excess measured by PAMELA and AMS can only be explained if there is one or several sources injecting them. Moreover, at the highest energies, it requires the presence of nearby ( ∼ hundreds of parsecs) and middle age (maximum of ∼ hundreds of kyr) sources. Pulsars, as factories of electrons and positrons, are one of the proposed candidates to explain the origin of this excess. To calculate the contribution of these sources to the electron and positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma rays to the Earth), a code to treat the propagation of electrons and compute their diffusion from a central source with a flexible injection spectrum. Using this code, we can derive the source's gamma-ray spectrum, spatial extension, the all-electron density in space, the electron and positron flux reaching the Earth and the positron fraction measured at the Earth. We present in this paper the foundations of the code and study how different parameters affect the gamma-ray spectrum of a source and the electron flux measured at the Earth. We also studied the effect of several approximations usually performed in these studies. This code has been used to derive the results of the positron flux measured at the Earth in [1].

Study on field-aligned electrons with Cluster observation in the Earth's cusp

NASA Astrophysics Data System (ADS)

Shi, Jiankui; Torkar, Klaus; Cheng, Zhengwei

2017-04-01

Cusp region is very important to the solar wind-magnetosphere coupling. The solar wind particles, through the cusp, can directly entry into the magnetosphere and ionosphere, and transport the mass, momentum and energy. The gyrating charged particles with field-aligned velocity are significant to perform the transportation. In this study, data from Cluster observation are used to study the characteristics of field-aligned electrons (FAE's) including the downward and the upward FAEs in the cusp. We select FAE event to do analysis. The durations of the FAE event covered a wide range from 6 to 475 seconds. The FAE's were found to occur very commonly in a circumpolar zone in the polar region and the MLT and ILAT distributions showed that most of the FAE events were observed around the cusp (70-80°ILAT, 0900-1500MLT). With the FAE flux the contribution of the electrons to the Field-Aligned Current (FAC) is estimated and the result shows that the FAE was the main carrier to the FAC in the cusp. The physical mechanisms of the FAE are analyzed, namely that the downward electrons were mainly from the solar wind and the upward electrons may originated from accelerated ionospheric up-flowing electrons or mirrored solar wind electrons. The energy transportation into the magnetosphere by the solar wind electrons through the cusp is also investigated.

Characteristics of electron distributions observed during large amplitude whistler wave events in the magnetosphere

NASA Astrophysics Data System (ADS)

Wilson, L. B., III; Cattell, C. A.; Kellogg, P. J.; Goetz, K.; Wygant, J.; Breneman, A. W.; Kersten, K.

2010-12-01

We present a statistical study of the characteristics of electron distributions associated with large amplitude whistler waves inside the terrestrial magnetosphere using waveform capture data as an addition of the study by Kellogg et al., [2010b]. We identified three types of electron distributions observed simultaneously with the whistler waves including beam-like, beam/flattop, and anisotropic distributions. The whistlers exhibited different characteristics dependent upon the observed electron distributions. The majority of the waveforms observed in our study have f/fce ≤ 0.5 and are observed primarily in the radiation belts outside the plasmapause simultaneously with anisotropic electron distributions. We also present an example waveform capture of the largest magnetic field amplitude (≥ 8 nT pk-pk) whistler wave measured in the radiation belts. The majority of the largest amplitude whistlers occur during magnetically active periods (AE > 200 nT).

Polarization Studies for the eRHIC Electron Storage Ring

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

Gianfelice-Wendt, Eliana; Tepikian, S.

A hadron/lepton collider with polarized beams has been under consideration by the scientific community since some years, in the U.S. and Europe. Among the various proposals, those by JLAB and BNL with polarized electron and proton beams are currently under closer study in the U.S. Experimenters call for the simultaneous storage of electron bunches with both spin helicity. In the BNL based Ring-Ring design, electrons are stored at top energy in a ring to be accommodated in the existing RHIC tunnel. The transversely polarized electron beam is injected into the storage ring at variable energies, between 5 and 18 GeV.more » Polarization is brought into the longitudinal direction at the IP by a couple of spin rotators. In this paper results of first studies of the attainable beam polarization level and lifetime in the storage ring at 18 GeV are presented.« less

Study of ultrasonic attenuation in f-electron systems in the paramagnetic limit of Coulomb interaction

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

Shadangi, Asit Ku., E-mail: asitshad@iopb.res.in; Rout, G. C., E-mail: gcr@iopb.res.in

2015-05-15

We report here a microscopic model study of ultrasonic attenuation in f-electron systems based on Periodic Anderson Model in which Coulomb interaction is considered within a mean-field approximation for a weak interaction. The Phonon is coupled to the conduction band and f-electrons. The phonon Green's function is calculated by Zubarev's technique of the Green's function method. The temperature dependent ultrasonic attenuation co-efficient is calculated from the imaginary part of the phonon self-energy in the dynamic and long wave length limit. The f-electron occupation number is calculated self-consistently in paramagnetic limit of Coulomb interaction. The effect of the Coulomb interaction onmore » ultrasonic attenuation is studied by varying the phonon coupling parameters to the conduction and f-electrons, hybridization strength, the position of f-level and the Coulomb interaction Strength. Results are discussed on the basis of experimental results.« less

Jellium Hydride

NASA Astrophysics Data System (ADS)

Bonev, Stanimir; Ashcroft, Neil W.

2000-03-01

We have studied a system of protons (with compensating additional electrons) embedded in a previously neutral electron gas (the standard jellium problem) at densities corresponding to rs = 0.8 - 3.4. This expands on the study of a single proton in an interacting electron gas(C.O. Almbladh, U. von Barth, Z.D. Popovic, and M.J. Scott, Phys. Rev. B \\underline14), 2250 (1976), and in particular, it permits a detailed study of a proton pairing in a many-electron environment. Ab initio (LSDA) simulations show the appearance of a bond proton-pair at rs >= 3.2 and with a dimer length R ≈ 1.5 a_0. At larger separations, the preferred state is a pair of H^- - like ions, i.e. electrons are captured from jellium. This is in accordance with an analysis of the situation where the charge surrounding a proton is determined jointly by the cusp condition and linear response.

Characteristics of Electron Distributions Observed During Large Amplitude Whistler Wave Events in the Magnetosphere

NASA Technical Reports Server (NTRS)

Wilson, Lynn B., III

2010-01-01

We present a statistical study of the characteristics of electron distributions associated with large amplitude whistler waves inside the terrestrial magnetosphere using waveform capture data as an addition of the study by Kellogg et al., [2010b]. We identified three types of electron distributions observed simultaneously with the whistler waves including beam-like, beam/flattop, and anisotropic distributions. The whistlers exhibited different characteristics dependent upon the observed electron distributions. The majority of the waveforms observed in our study have f/fce < or = 0.5 and are observed primarily in the radiation belts outside the plasmapause simultaneously with anisotropic electron distributions. We also present an example waveform capture of the largest magnetic field amplitude (> or = 8 nT pk-pk) whistler wave measured in the radiation belts. The majority of the largest amplitude whistlers occur during magnetically active periods (AE > 200 nT).

Ultrafast electron transfer processes studied by pump-repump-probe spectroscopy.

PubMed

Fischer, Martin K; Gliserin, Alexander; Laubereau, Alfred; Iglev, Hristo

2011-03-01

The photodetachment of Br(-), I(-) and OH(-) in aqueous solution is studied by 2- and 3-pulse femtosecond spectroscopy. The UV excitation leads to fast electron separation followed by formation of a donor-electron pairs. An additional repump pulse is used for secondary excitation of the intermediates. The 3-pulse technique allows distinguishing the pair-intermediate from the fully separated electron. Using this method we observe a novel geminate recombination channel of .OH with adjacent hydrated electrons. The process leads to an ultrafast quenching (0.7 ps) of almost half the initial number of radicals. The phenomenon is not observed in Br(-) and I(-). Our results demonstrate the potential of the 3-pulse spectroscopy to elucidate the mechanism of ultrafast ET reactions. Photodetachment of aqueous anions studied by two- and three pulse spectroscopy. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Attosecond electron pulse trains and quantum state reconstruction in ultrafast transmission electron microscopy

NASA Astrophysics Data System (ADS)

Priebe, Katharina E.; Rathje, Christopher; Yalunin, Sergey V.; Hohage, Thorsten; Feist, Armin; Schäfer, Sascha; Ropers, Claus

2017-12-01

Ultrafast electron and X-ray imaging and spectroscopy are the basis for an ongoing revolution in the understanding of dynamical atomic-scale processes in matter. The underlying technology relies heavily on laser science for the generation and characterization of ever shorter pulses. Recent findings suggest that ultrafast electron microscopy with attosecond-structured wavefunctions may be feasible. However, such future technologies call for means to both prepare and fully analyse the corresponding free-electron quantum states. Here, we introduce a framework for the preparation, coherent manipulation and characterization of free-electron quantum states, experimentally demonstrating attosecond electron pulse trains. Phase-locked optical fields coherently control the electron wavefunction along the beam direction. We establish a new variant of quantum state tomography—`SQUIRRELS'—for free-electron ensembles. The ability to tailor and quantitatively map electron quantum states will promote the nanoscale study of electron-matter entanglement and new forms of ultrafast electron microscopy down to the attosecond regime.

Allosteric control of internal electron transfer in cytochrome cd1 nitrite reductase

PubMed Central

Farver, Ole; Kroneck, Peter M. H.; Zumft, Walter G.; Pecht, Israel

2003-01-01

Cytochrome cd1 nitrite reductase is a bifunctional multiheme enzyme catalyzing the one-electron reduction of nitrite to nitric oxide and the four-electron reduction of dioxygen to water. Kinetics and thermodynamics of the internal electron transfer process in the Pseudomonas stutzeri enzyme have been studied and found to be dominated by pronounced interactions between the c and the d1 hemes. The interactions are expressed both in dramatic changes in the internal electron-transfer rates between these sites and in marked cooperativity in their electron affinity. The results constitute a prime example of intraprotein control of the electron-transfer rates by allosteric interactions. PMID:12802018

Influence of the electron intrinsic magnetic moment on the transverse dielectric permittivity of degenerate electron gas

NASA Astrophysics Data System (ADS)

Maslov, S. A.; Bobrov, V. B.; Kirillin, A. V.; Trigger, S. A.

2018-01-01

Using the linear response theory, the transverse dielectric permittivity of a homogeneous and isotropic system of charged particles is considered. In the ideal gas approximation for the polarization function, an explicit analytical expression for the transverse permittivity of a degenerate electron plasma, which takes into account electron spin, is found. This result describes both the Landau diamagnetism and Pauli paramagnetism in electron plasma. The influence of the electron intrinsic magnetic moment on the spatial and frequency dispersion of the transverse dielectric permittivity of degenerate electron plasma is numerically studied, that is crucial for determining the optical characteristics of plasma.

Electrostatic potential barrier for electron emission at graphene edges induced by the nearly free electron states

NASA Astrophysics Data System (ADS)

Gao, Yanlin; Okada, Susumu

2017-05-01

Using the density functional theory, we studied the electronic structures of zigzag graphene nanoribbons with hydroxyl, H, ketone, aldehyde, or carboxyl terminations under a lateral electric field. The critical electric field for electron emission is proportional to the work function of the functionalized edges except the hydroxylated edge, which leads to the anomalous electric field outside the edge, owing to the electrons in the nearly free electron (NFE) state in the vacuum region. The strong electric field also causes a potential barrier for the electron emission from the H-terminated edge owing to the downward shift of the NFE state.

An Application of Fuzzy Theory to Technical Competency Analysis for the Entry-Level Electronic Technician.

ERIC Educational Resources Information Center

Chang, Liang-Te; And Others

A study was conducted to develop the electronic technical competencies of duty and task analysis by using a revised DACUM (Developing a Curriculum) method, a questionnaire survey, and a fuzzy synthesis operation. The revised DACUM process relied on inviting electronics trade professionals to analyze electronic technology for entry-level…