High-Level ab initio electronic structure calculations of Water Clusters (H2O)16 and (H2O)17: a new global minimum for (H2O)16

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

Yoo, Soohaeng; Apra, Edoardo; Zeng, Xiao Cheng

The lowest-energy structures of water clusters (H2O)16 and (H2O)17 were revisited at the MP2 and CCSD(T) levels of theory. A new global minimum structure for (H2O)16 was found at the MP2 and CCSD(T) levels of theory and the effect of zero-point energy corrections on the relative stability of the low-lying minimum energy structures was assessed. For (H2O)17 the CCSD(T) calculations confirm the previously found at the MP2 level of theory "interior" arrangement (fully coordinated water molecule inside a spherical cluster) as the global minimum.

High-Level ab-initio Electronic Structure Calculations of Water Clusters (H2O)16 and (H2O)17 : a New Global Minimum for (H2O)16

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

Yoo, Soohaeng; Apra, Edoardo; Zeng, X.C.

The lowest-energy structures of water clusters (H2O)16 and (H2O)17 were revisited at the MP2 and CCSD(T) levels of theory. A new global minimum structure for (H2O)16 was found at both the MP2 and CCSD(T) levels of theory, and the effect of zero-point energy corrections on the relative stability of the low-lying minimum energy structures was assessed. For (H2O)17, the CCSD(T) calculations confirm the previously found at the MP2 level of theory interior arrangement (fully coordinated water molecule inside a spherical cluster) as the global minimum

Observation of collisionless heating of low energy electrons in low pressure inductively coupled argon plasmas

NASA Astrophysics Data System (ADS)

Lee, Min-Hyong; Lee, Hyo-Chang; Chung, Chin-Wook

2008-12-01

Collisionless heating of low energy electrons was observed in low pressure argon rf-biased inductively coupled plasmas (ICPs) by measurement of the electron energy distribution function (EEDF). When only capacitive power (bias) was supplied, the EEDF in the discharge was a bi-Maxwellian distribution with two electron groups. It was found that the low energy electrons were heated up significantly even with a little inductive power (<20 W) even when the discharge was in E mode. Due to the low gas pressure and low temperature of low energy electrons (close to the energy of the Ramsauer minimum), the collisional heating of low energy electrons appears to be negligible. Therefore, this effective heating of the low energy electrons showed a direct experimental evidence of the collisionless heating by inductive field. The significant heating of low energy electrons in E mode indicates that collisionless heating in the skin layer is an important electron heating mechanism of low pressure ICP even when the discharge is in E mode.

Multistate metadynamics for automatic exploration of conical intersections

NASA Astrophysics Data System (ADS)

Lindner, Joachim O.; Röhr, Merle I. S.; Mitrić, Roland

2018-05-01

We introduce multistate metadynamics for automatic exploration of conical intersection seams between adiabatic Born-Oppenheimer potential energy surfaces in molecular systems. By choosing the energy gap between the electronic states as a collective variable the metadynamics drives the system from an arbitrary ground-state configuration toward the intersection seam. Upon reaching the seam, the multistate electronic Hamiltonian is extended by introducing biasing potentials into the off-diagonal elements, and the molecular dynamics is continued on a modified potential energy surface obtained by diagonalization of the latter. The off-diagonal bias serves to locally open the energy gap and push the system to the next intersection point. In this way, the conical intersection energy landscape can be explored, identifying minimum energy crossing points and the barriers separating them. We illustrate the method on the example of furan, a prototype organic molecule exhibiting rich photophysics. The multistate metadynamics reveals plateaus on the conical intersection energy landscape from which the minimum energy crossing points with characteristic geometries can be extracted. The method can be combined with the broad spectrum of electronic structure methods and represents a generally applicable tool for the exploration of photophysics and photochemistry in complex molecules and materials.

A vortex line for K-shell ionization of a carbon atom by electron impact

NASA Astrophysics Data System (ADS)

Ward, S. J.; Macek, J. H.

2014-10-01

We obtained using the Coulomb-Born approximation a deep minimum in the TDCS for K-shell ionization of a carbon atom by electron impact for the electron ejected in the scattering plane. The minimum is obtained for the kinematics of the energy of incident electron Ei = 1801.2 eV, the scattering angle θf = 4°, the energy of the ejected electron Ek = 5 . 5 eV, and the angle for the ejected electron θk = 239°. This minimum is due to a vortex in the velocity field. At the position of the vortex, the nodal lines of Re [ T ] and Im [ T ] intersect. We decomposed the CB1 T-matrix into its multipole components for the kinematics of a vortex, taking the z'-axis parallel to the direction of the momentum transfer vector. The m = +/- 1 dipole components are necessary to obtain a vortex. We also considered the electron to be ejected out of the scattering plane and obtained the positions of the vortex for different values of the y-component of momentum of the ejected electron, ky. We constructed the vortex line for the kinematics of Ei = 1801.2 eV and θf = 4°. S.J.W. and J.H.M. acknowledge support from NSF under Grant No. PHYS- 0968638 and from D.O.E. under Grant Number DE-FG02-02ER15283, respectively.

Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s

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

Kurnosov, Arkady A.; Rubtsov, Igor V.; Maksymov, Andrii O.

2016-07-21

We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so that they can participate only in the transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to themore » atomic mass. For the same reason, the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Theory predictions are consistent with the time-dependent density functional theory calculations. Molecular systems for experimental evaluation of the predictions are proposed.« less

Pre-main Sequence Evolution and the Hydrogen-Burning Minimum Mass

NASA Astrophysics Data System (ADS)

Nakano, Takenori

There is a lower limit to the mass of the main-sequence stars (the hydrogen-burning minimum mass) below which the stars cannot replenish the energy lost from their surfaces with the energy released by the hydrogen burning in their cores. This is caused by the electron degeneracy in the stars which suppresses the increase of the central temperature with contraction. To find out the lower limit we need the accurate knowledge of the pre-main sequence evolution of very low-mass stars in which the effect of electron degeneracy is important. We review how Hayashi and Nakano (1963) carried out the first determination of this limit.

Cavity Born-Oppenheimer Approximation for Correlated Electron-Nuclear-Photon Systems.

PubMed

Flick, Johannes; Appel, Heiko; Ruggenthaler, Michael; Rubio, Angel

2017-04-11

In this work, we illustrate the recently introduced concept of the cavity Born-Oppenheimer approximation [ Flick et al. PNAS 2017 , 10.1073/pnas.1615509114 ] for correlated electron-nuclear-photon problems in detail. We demonstrate how an expansion in terms of conditional electronic and photon-nuclear wave functions accurately describes eigenstates of strongly correlated light-matter systems. For a GaAs quantum ring model in resonance with a photon mode we highlight how the ground-state electronic potential-energy surface changes the usual harmonic potential of the free photon mode to a dressed mode with a double-well structure. This change is accompanied by a splitting of the electronic ground-state density. For a model where the photon mode is in resonance with a vibrational transition, we observe in the excited-state electronic potential-energy surface a splitting from a single minimum to a double minimum. Furthermore, for a time-dependent setup, we show how the dynamics in correlated light-matter systems can be understood in terms of population transfer between potential energy surfaces. This work at the interface of quantum chemistry and quantum optics paves the way for the full ab initio description of matter-photon systems.

Theoretical analysis of the time-resolved binary (e, 2e) binding energy spectra on three-body photodissociation of acetone at 195 nm

NASA Astrophysics Data System (ADS)

Yamazaki, M.; Nakayama, S.; Zhu, C. Y.; Takahashi, M.

2017-11-01

We report on theoretical progress in time-resolved (e, 2e) electron momentum spectroscopy of photodissociation dynamics of the deuterated acetone molecule at 195 nm. We have examined the predicted minimum energy reaction path to investigate whether associated (e, 2e) calculations meet the experimental results. A noticeable difference between the experiment and calculations has been found at around binding energy of 10 eV, suggesting that the observed difference may originate, at least partly, in ever-unconsidered non-minimum energy paths.

Multi-heme cytochromes provide a pathway for survival in energy-limited environments

PubMed Central

Deng, Xiao; Dohmae, Naoshi; Nealson, Kenneth H.; Hashimoto, Kazuhito; Okamoto, Akihiro

2018-01-01

Bacterial reduction of oxidized sulfur species (OSS) is critical for energy production in anaerobic marine subsurfaces. In organic-poor sediments, H2 has been considered as a major energy source for bacterial respiration. We identified outer-membrane cytochromes (OMCs) that are broadly conserved in sediment OSS-respiring bacteria and enable cells to directly use electrons from insoluble minerals via extracellular electron transport. Biochemical, transcriptomic, and microscopic analyses revealed that the identified OMCs were highly expressed on the surface of cells and nanofilaments in response to electron donor limitation. This electron uptake mechanism provides sufficient but minimum energy to drive the reduction of sulfate and other OSS. These results suggest a widespread mechanism for survival of OSS-respiring bacteria via electron uptake from solid minerals in energy-poor marine sediments. PMID:29464208

Dispersive effects from a comparison of electron and positron scattering from

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

Paul Gueye; M. Bernheim; J. F. Danel

1998-05-01

Dispersive effects have been investigated by comparing elastic scattering of electrons and positrons from {sup 12}C at the Saclay Linear Accelerator. The results demonstrate that dispersive effects at energies of 262 MeV and 450 MeV are less than 2% below the first diffraction minimum [0.95 < q{sub eff} (fm{sup -1}) < 1.66] in agreement with the prediction of Friar and Rosen. At the position of this minimum (q{sub eff} = 1.84 fm{sup -1}), the deviation between the positron scattering cross section and the cross section derived from the electron results is -44% {+-} 30%.

An Empirical Model of Radiation Belt Electron Pitch Angle Distributions Based On Van Allen Probes Measurements

NASA Astrophysics Data System (ADS)

Zhao, H.; Friedel, R. H. W.; Chen, Y.; Reeves, G. D.; Baker, D. N.; Li, X.; Jaynes, A. N.; Kanekal, S. G.; Claudepierre, S. G.; Fennell, J. F.; Blake, J. B.; Spence, H. E.

2018-05-01

Based on over 4 years of Van Allen Probes measurements, an empirical model of radiation belt electron equatorial pitch angle distribution (PAD) is constructed. The model, developed by fitting electron PADs with Legendre polynomials, provides the statistical PADs as a function of L-shell (L = 1-6), magnetic local time, electron energy ( 30 keV to 5.2 MeV), and geomagnetic activity (represented by the Dst index) and is also the first empirical PAD model in the inner belt and slot region. For megaelectron volt electrons, model results show more significant day-night PAD asymmetry of electrons with higher energies and during disturbed times, which is caused by geomagnetic field configuration and flux radial gradient changes. Steeper PADs with higher fluxes around 90° pitch angle and lower fluxes at lower pitch angles for higher-energy electrons and during active times are also present, which could be due to electromagnetic ion cyclotron wave scattering. For hundreds of kiloelectron volt electrons, cap PADs are generally present in the slot region during quiet times and their energy-dependent features are consistent with hiss wave scattering, while during active times, cap PADs are less significant especially at outer part of slot region, which could be due to the complex energizing and transport processes. The 90°-minimum PADs are persistently present in the inner belt and appear in the slot region during active times, and minima at 90° pitch angle are more significant for electrons with higher energies, which could be a critical evidence in identifying the underlying physical processes responsible for the formation of 90°-minimum PADs.

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

Optical properties of InAs/GaAs quantum dot superlattice structures

NASA Astrophysics Data System (ADS)

Imran, Ali; Jiang, Jianliang; Eric, Deborah; Zahid, M. Noaman; Yousaf, M.; Shah, Z. H.

2018-06-01

Quantum dot (QD) structure has potential applications in modern highly efficient optoelectronic devices due to their band-tuning. The device dimensions have been miniatured with increased efficiencies by virtue of this discovery. In this research, we have presented modified analytical and simulation results of InAs/GaAs QD superlattice (QDSL). We have applied tight binding model for the investigation of ground state energies using timeindependent Schrödinger equation (SE) with effective mass approximation. It has been investigated that the electron energies are confined due to wave function delocalization in closely coupled QD structures. The minimum ground state energy can be obtained by increasing the periodicity and decreasing the barrier layer thickness. We have calculated electronics and optical properties which includes ground state energies, transition energies, density of states (DOS), absorption coefficient and refractive index, which can be tuned by structure modification. In our results, the minimum ground state energy of QDSL is achieved to be 0.25 eV with a maximum period of 10 QDs. The minimum band to band and band to continuum transition energies are 63 meV and 130 meV with 2 nm barrier layer thickness respectively. The absorption coefficient of our proposed QDSL model is found to be maximum 1.2 × 104 cm-1 and can be used for highly sensitive infrared detector and high efficiency solar cells.

Investigation of the electronic, magnetic and optical properties of newest carbon allotrope

NASA Astrophysics Data System (ADS)

Kazemi, Samira; Moradian, Rostam

2018-05-01

We investigate triple properties of monolayer pentagon graphene that include electronic, magnetic and optical properties based on density functional theory (DFT). Our results show that in the electronic and magnetic properties this structure with a direct energy gap of about 2.2 eV along Γ - Γ direction and total magnetic moment of 0.0013 μB per unit cell is almost a non-magnetic semiconductor. Also, its optical properties show that if this allotrope used in solar cell technology, its efficiency in the low energy will be better, because, in the range of energy, its loss energy function and reflectivity will be minimum.

Probing the global potential energy minimum of (CH2O)2: THz absorption spectrum of (CH2O)2 in solid neon and para-hydrogen.

PubMed

Andersen, J; Voute, A; Mihrin, D; Heimdal, J; Berg, R W; Torsson, M; Wugt Larsen, R

2017-06-28

The true global potential energy minimum configuration of the formaldehyde dimer (CH 2 O) 2 , including the presence of a single or a double weak intermolecular CH⋯O hydrogen bond motif, has been a long-standing subject among both experimentalists and theoreticians as two different energy minima conformations of C s and C 2h symmetry have almost identical energies. The present work demonstrates how the class of large-amplitude hydrogen bond vibrational motion probed in the THz region provides excellent direct spectroscopic observables for these weak intermolecular CH⋯O hydrogen bond motifs. The combination of concentration dependency measurements, observed isotopic spectral shifts associated with H/D substitutions and dedicated annealing procedures, enables the unambiguous assignment of three large-amplitude infrared active hydrogen bond vibrational modes for the non-planar C s configuration of (CH 2 O) 2 embedded in cryogenic neon and enriched para-hydrogen matrices. A (semi)-empirical value for the change of vibrational zero-point energy of 5.5 ± 0.3 kJ mol -1 is proposed for the dimerization process. These THz spectroscopic observations are complemented by CCSD(T)-F12/aug-cc-pV5Z (electronic energies) and MP2/aug-cc-pVQZ (force fields) electronic structure calculations yielding a (semi)-empirical value of 13.7 ± 0.3 kJ mol -1 for the dissociation energy D 0 of this global potential energy minimum.

Probing the global potential energy minimum of (CH2O)2: THz absorption spectrum of (CH2O)2 in solid neon and para-hydrogen

NASA Astrophysics Data System (ADS)

Andersen, J.; Voute, A.; Mihrin, D.; Heimdal, J.; Berg, R. W.; Torsson, M.; Wugt Larsen, R.

2017-06-01

The true global potential energy minimum configuration of the formaldehyde dimer (CH2O)2, including the presence of a single or a double weak intermolecular CH⋯O hydrogen bond motif, has been a long-standing subject among both experimentalists and theoreticians as two different energy minima conformations of Cs and C2h symmetry have almost identical energies. The present work demonstrates how the class of large-amplitude hydrogen bond vibrational motion probed in the THz region provides excellent direct spectroscopic observables for these weak intermolecular CH⋯O hydrogen bond motifs. The combination of concentration dependency measurements, observed isotopic spectral shifts associated with H/D substitutions and dedicated annealing procedures, enables the unambiguous assignment of three large-amplitude infrared active hydrogen bond vibrational modes for the non-planar Cs configuration of (CH2O)2 embedded in cryogenic neon and enriched para-hydrogen matrices. A (semi)-empirical value for the change of vibrational zero-point energy of 5.5 ± 0.3 kJ mol-1 is proposed for the dimerization process. These THz spectroscopic observations are complemented by CCSD(T)-F12/aug-cc-pV5Z (electronic energies) and MP2/aug-cc-pVQZ (force fields) electronic structure calculations yielding a (semi)-empirical value of 13.7 ± 0.3 kJ mol-1 for the dissociation energy D0 of this global potential energy minimum.

The Energy Spectrum of Solar Energetic Electrons

NASA Astrophysics Data System (ADS)

Wang, L.; Yang, L.; Krucker, S.; Wimmer-Schweingruber, R. F.; Bale, S. D.

2015-12-01

Here we present a statistical survey of the energy spectrum of solar energetic electron events (SEEs) observed by the WIND 3DP instrument from 1995 though 2014. For SEEs with the minimum energy below 10 keV and the maximum energy above 100 keV, ~85% (~2%) have a double-power-law energy spectrum with a steepening (hardening) above the break energy, while ~13% have a single-power-law energy spectrum at all energies. The average spectral index is ~2.4 below the energy break and is ~4.0 above the energy break. For SEEs detected only at energies <10 keV (>20 keV), they generally show a single-power-law spectrum with the average index of ~3.0 (~3.3). The spectrum of SEEs detected only below 10 keV appears to get harder with increasing solar activity, but the spectrum of SEEs with higher-energy electrons shows no clear correlation with solar activity. We will also investigate whether the observed energy spectrum of SEEs at 1 AU mainly reflects the electron acceleration at the Sun or the electron transport in the interplanetary medium.

Plasma Relaxation and Topological Aspects in Electron Magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, Bhimsen

2016-10-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient and turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve therefore in the same way as potential vorticity lines in 2D hydrodynamics.

Plasma relaxation and topological aspects in electron magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, B. K.

2016-07-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient α turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve, therefore, in the same way as potential vorticity lines in 2D hydrodynamics.

Modification of mesospheric OH and O3 during a measured highly relativistic electron precipitation event

NASA Technical Reports Server (NTRS)

Goldberg, R. A.; Jackman, C. H.; Backer, D. N.; Herrero, F. A.

1994-01-01

Highly relativistic electron precipitation events (HRE's) can provide a major source of energy affecting mesospheric constituents and ionization. Based on satellite data, these events are most pronounced near the minimum of the solar sunspot cycle, increasing in intensity, spectral hardness, and frequency of occurrence as the solar cycle declines. Since such events can be sustained up to several days, their integrated effect in the mesosphere can dominate over those of other energy sources such as relativistic electron precipitation events (REP's) and auroral precipitation. The energy deposition data to be discussed and analyzed were obtained by rocket at Poker Flat, Alaska, in May 1990 during a modest HRE observed at midday near the peak of the sunspot cycle. Using a NASA two dimensional model, significant enhancement of OH and depletion of O3 at 75 +/- 10 km altitude from the measured radiation are found. Estimates of enhanced effects were made for more intense HRE events, as might be expected during solar minimum. By causing O3 depletion, the electron precipitation can also regulate the penetration of solar UV radiation, which could affect the thermal properties of the mesosphere.

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.

Electron-impact electronic-state excitation of para-benzoquinone

NASA Astrophysics Data System (ADS)

Jones, D. B.; da Costa, R. F.; Kossoski, F.; Varella, M. T. do N.; Bettega, M. H. F.; Ferreira da Silva, F.; Limão-Vieira, P.; García, G.; Lima, M. A. P.; White, R. D.; Brunger, M. J.

2018-03-01

Angle resolved electron energy loss spectra (EELS) for para-benzoquinone (C6H4O2) have been recorded for incident electron energies of 20, 30, and 40 eV. Measured differential cross sections (DCSs) for electronic band features, composed of a combination of energetically unresolved electronic states, are subsequently derived from those EELS. Where possible, the obtained DCSs are compared with those calculated using the Schwinger multichannel method with pseudopotentials. These calculations were performed using a minimum orbital basis single configuration interaction framework at the static exchange plus polarisation level. Here, quite reasonable agreement between the experimental cross sections and the theoretical cross sections for the summation of unresolved states was observed.

Electron affinities and ionization energies of Cu and Ag delafossite compounds: A hybrid functional study

NASA Astrophysics Data System (ADS)

Miao, Mao-Sheng; Yarbro, Sam; Barton, Phillip T.; Seshadri, Ram

2014-01-01

Using density functional theory with a hybrid functional, we calculate the ionization energies and electron affinities of a series of delafossite compounds (AMO2: A =Cu, Ag; M =B, Al, Ga, In, Sc). The alignments of the valence band maximum and the conduction band minimum, which directly relate to the ionization energies and electron affinities, were obtained by calculations of supercell slab models constructed in a nonpolar orientation. Our calculations reveal that the ionization energy decreases with an increasing atomic number of group-III elements, and thus suggest an improved p-type doping propensity for heavier compounds. For keeping both a low ionization energy and a band gap of sufficient size, CuScO2 is superior to the Cu-based group-III delafossites. By analyzing the electronic structures, we demonstrate that the compositional trend of the ionization energies and electron affinities is the result of a combined effect of d-band broadening due to Cu(Ag)-Cu(Ag) coupling and a repositioning of the d-band center.

Electron tunneling spectroscopy study of electrically active traps in AlGaN/GaN high electron mobility transistors

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

Yang, Jie, E-mail: jie.yang@yale.edu; Cui, Sharon; Ma, T. P.

2013-11-25

We investigate the energy levels of electron traps in AlGaN/GaN high electron mobility transistors by the use of electron tunneling spectroscopy. Detailed analysis of a typical spectrum, obtained in a wide gate bias range and with both bias polarities, suggests the existence of electron traps both in the bulk of AlGaN and at the AlGaN/GaN interface. The energy levels of the electron traps have been determined to lie within a 0.5 eV band below the conduction band minimum of AlGaN, and there is strong evidence suggesting that these traps contribute to Frenkel-Poole conduction through the AlGaN barrier.

Quiet-Time Suprathermal (˜0.1 - 200 keV) Electrons in the Solar Wind

NASA Astrophysics Data System (ADS)

Wang, Linghua; Yang, Liu; Tao, Jiawei; Zong, Qiugang; Li, Gang; Wimmer-Schweingruber, Robert; He, Jiansen; Tu, Chuanyi; Bale, Stuart

2017-04-01

We present a statistical survey of the energy spectrum of solar wind suprathermal (˜0.1-200 keV) electrons measured by the WIND 3DP instrument at 1 AU during quiet times at the minimum and maximum of solar cycles 23 and 24. The observed energy spectrum of both (beaming) strahl and (isotropic) halo electrons at ˜0.1-1.5 keV generally fits to a Kappa distribution function with an index κ and effective temperature Teff, while the observed energy spectrum of nearly isotropic superhalo electrons at ˜20-200 keV generally fits to a power-law function, J ˜ E-β. We find a strong positive correlation between κ and Teff for both strahl and halo electrons, and a strong positive correlation between the strahl density and halo density. In both solar cycles, κ is larger at solar minimum than at solar maximum for both strahl and halo electrons. For the superhalo population, the spectral index β ranges from ˜1.6 to ˜3.7 and the integrated density nsup ranges from 10-8 cm-3 to 10-5 cm-3, with no clear association with the sunspot number. In solar cycle 23 (24), the distribution of β has a broad maximum between 2.4 and 2.8 (2.0 and 2.4). All the strahl, halo and superhalo populations show no obvious correlation with the solar wind core population. These results reflect the nature of the generation of solar wind suprathermal electrons.

Electron-exchange and quantum screening effects on the Thomson scattering process in quantum Fermi plasmas

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

Lee, Gyeong Won; Jung, Young-Dae; Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180-3590

2013-06-15

The influence of the electron-exchange and quantum screening on the Thomson scattering process is investigated in degenerate quantum Fermi plasmas. The Thomson scattering cross section in quantum plasmas is obtained by the plasma dielectric function and fluctuation-dissipation theorem as a function of the electron-exchange parameter, Fermi energy, plasmon energy, and wave number. It is shown that the electron-exchange effect enhances the Thomson scattering cross section in quantum plasmas. It is also shown that the differential Thomson scattering cross section has a minimum at the scattering angle Θ=π/2. It is also found that the Thomson scattering cross section increases with anmore » increase of the Fermi energy. In addition, the Thomson scattering cross section is found to be decreased with increasing plasmon energy.« less

Dehydrogenation of benzene on Pt(111) surface

NASA Astrophysics Data System (ADS)

Gao, W.; Zheng, W. T.; Jiang, Q.

2008-10-01

The dehydrogenation of benzene on Pt(111) surface is studied by ab initio density functional theory. The minimum energy pathways for benzene dehydrogenation are found with the nudge elastic band method including several factors of the associated barriers, reactive energies, intermediates, and transient states. The results show that there are two possible parallel minimum energy pathways on the Pt(111) surface. Moreover, the tilting angle of the H atom in benzene can be taken as an index for the actual barrier of dehydrogenation. In addition, the properties of dehydrogenation radicals on the Pt(111) surface are explored through their adsorption energy, adsorption geometry, and electronic structure on the surface. The vibrational frequencies of the dehydrogenation radicals derived from the calculations are in agreement with literature data.

Dehydrogenation of benzene on Pt(111) surface.

PubMed

Gao, W; Zheng, W T; Jiang, Q

2008-10-28

The dehydrogenation of benzene on Pt(111) surface is studied by ab initio density functional theory. The minimum energy pathways for benzene dehydrogenation are found with the nudge elastic band method including several factors of the associated barriers, reactive energies, intermediates, and transient states. The results show that there are two possible parallel minimum energy pathways on the Pt(111) surface. Moreover, the tilting angle of the H atom in benzene can be taken as an index for the actual barrier of dehydrogenation. In addition, the properties of dehydrogenation radicals on the Pt(111) surface are explored through their adsorption energy, adsorption geometry, and electronic structure on the surface. The vibrational frequencies of the dehydrogenation radicals derived from the calculations are in agreement with literature data.

A Simple ab initio Model for the Hydrated Electron that Matches Experiment

PubMed Central

Kumar, Anil; Walker, Jonathan A.; Bartels, David M.; Sevilla, Michael D.

2015-01-01

Since its discovery over 50 years ago, the “structure” and properties of the hydrated electron has been a subject for wonderment and also fierce debate. In the present work we seriously explore a minimal model for the aqueous electron, consisting of a small water anion cluster embedded in a polarized continuum, using several levels of ab initio calculation and basis set. The minimum energy zero “Kelvin” structure found for any 4-water (or larger) anion cluster, at any post-Hartree-Fock theory level, is very similar to a recently reported embedded-DFT-in-classical-water-MD simulation (UMJ: Uhlig, Marsalek, and Jungwirth, Journal of Physical Chemistry Letters 2012, 3, 3071-5), with four OH bonds oriented toward the maximum charge density in a small central “void”. The minimum calculation with just four water molecules does a remarkably good job of reproducing the resonance Raman properties, the radius of gyration derived from the optical spectrum, the vertical detachment energy, and the hydration free energy. For the first time we also successfully calculate the EPR g-factor and (low temperature ice) hyperfine couplings. The simple tetrahedral anion cluster model conforms very well to experiment, suggesting it does in fact represent the dominant structural motif of the hydrated electron. PMID:26275103

Inner reorganization limiting electron transfer controlled hydrogen bonding: intra- vs. intermolecular effects.

PubMed

Martínez-González, Eduardo; Frontana, Carlos

2014-05-07

In this work, experimental evidence of the influence of the electron transfer kinetics during electron transfer controlled hydrogen bonding between anion radicals of metronidazole and ornidazole, derivatives of 5-nitro-imidazole, and 1,3-diethylurea as the hydrogen bond donor, is presented. Analysis of the variations of voltammetric EpIcvs. log KB[DH], where KB is the binding constant, allowed us to determine the values of the binding constant and also the electron transfer rate k, confirmed by experiments obtained at different scan rates. Electronic structure calculations at the BHandHLYP/6-311++G(2d,2p) level for metronidazole, including the solvent effect by the Cramer/Truhlar model, suggested that the minimum energy conformer is stabilized by intramolecular hydrogen bonding. In this structure, the inner reorganization energy, λi,j, contributes significantly (0.5 eV) to the total reorganization energy of electron transfer, thus leading to a diminishment of the experimental k.

Energy, angular and spatial distributions of primary electrons inside photoconducting materials for digital mammography: Monte Carlo simulation studies.

PubMed

Sakellaris, T; Spyrou, G; Tzanakos, G; Panayiotakis, G

2007-11-07

Materials such as a-Se, a-As(2)Se(3), GaSe, GaAs, Ge, CdTe, CdZnTe, Cd(0.8)Zn(0.2)Te, ZnTe, PbO, TlBr, PbI(2) and HgI(2) are potential candidates as photoconductors in direct detectors for digital mammography. The x-ray induced primary electrons inside a photoconductor's bulk comprise the initial signal that propagates and forms the final signal (image) on the detector's electrodes. An already developed model for a-Se has been properly extended to simulate the primary electron production in the materials mentioned. Primary electron characteristics, such as their energy, angular and spatial distributions that strongly influence the characteristics of the final image, were studied for both monoenergetic and polyenergetic x-ray spectra in the mammographic energy range. The characteristic feature in the electron energy distributions for PbI(2) and HgI(2) is the atomic deexcitation peaks, whereas for the rest of the materials their shape can also be influenced by the electrons produced from primary photons. The electrons have a small tendency to be forward ejected whereas they prefer to be ejected perpendicular (theta = pi/2) to the incident beam's axis and at two lobes around phi = 0 and phi = pi. At practical mammographic energies (15-40 keV) a-Se, a-As(2)Se(3) and Ge have the minimum azimuthal uniformity whereas CdZnTe, Cd(0.8)Zn(0.2)Te and CdTe the maximum one. The spatial distributions for a-Se, a-As(2)Se(3), GaSe, GaAs, Ge, PbO and TlBr are almost independent of the polyenergetic spectrum, while those for CdTe, CdZnTe, Cd(0.8)Zn(0.2)Te, ZnTe, PbI(2) and HgI(2) have a spectrum dependence. In the practical mammographic energy range and at this primitive stage of primary electron production, a-Se has the best inherent spatial resolution as compared to the rest of the photoconductors. PbO has the minimum bulk space in which electrons can be produced whereas CdTe has the maximum one.

New Ways of Treating Data for Diatomic Molecule 'shelf' and Double-Minimum States

NASA Astrophysics Data System (ADS)

Le Roy, Robert J.; Tao, Jason; Khanna, Shirin; Pashov, Asen; Tellinghuisen, Joel

2017-06-01

Electronic states whose potential energy functions have 'shelf' or double-minimum shapes have always presented special challenges because, as functions of vibrational quantum number, the vibrational energies/spacings and inertial rotational constants either have an abrupt change of character with discontinuous slope, or past a given point, become completely chaotic. The present work shows that a `traditional' methodology developed for deep `regular' single-well potentials can also provide accurate `parameter-fit' descriptions of the v-dependence of the vibrational energies and rotational constants of shelf-state potentials that allow a conventional RKR calculation of their Potential energy functions. It is also shown that a merging of Pashov's uniquely flexible 'spline point-wise' potential function representation with Le Roy's `Morse/Long-Range' (MLR) analytic functional form which automatically incorporates the correct theoretically known long-range form, yields an analytic function that incorporates most of the advantages of both approaches. An illustrative application of this method to data to a double-minimum state of Na_2 will be described.

A New Potential Energy Surface for N+O2: Is There an NOO Minimum?

NASA Technical Reports Server (NTRS)

Walch, Stephen P.

1995-01-01

We report a new calculation of the N+02 potential energy surface using complete active space self-consistent field internally contracted configuration interaction with the Dunning correlation consistent basis sets. The peroxy isomer of N02 is found to be a very shallow minimum separated from NO+O by a barrier of only 0.3 kcal/mol (excluding zero-point effects). The entrance channel barrier height is estimated to be 8.6 kcal/mol for ICCI+Q calculations correlating all but the Ols and N1s electrons with a cc-p VQZ basis set.

The drift-diffusion interpretation of the electron current within the organic semiconductor characterized by the bulk single energy trap level

NASA Astrophysics Data System (ADS)

Cvikl, B.

2010-01-01

The closed solution for the internal electric field and the total charge density derived in the drift-diffusion approximation for the model of a single layer organic semiconductor structure characterized by the bulk shallow single trap-charge energy level is presented. The solutions for two examples of electric field boundary conditions are tested on room temperature current density-voltage data of the electron conducting aluminum/tris(8-hydroxyquinoline aluminum/calcium structure [W. Brütting et al., Synth. Met. 122, 99 (2001)] for which jexp∝Va3.4, within the interval of bias 0.4 V≤Va≤7. In each case investigated the apparent electron mobility determined at given bias is distributed within a given, finite interval of values. The bias dependence of the logarithm of their lower limit, i.e., their minimum values, is found to be in each case, to a good approximation, proportional to the square root of the applied electric field. On account of the bias dependence as incorporated in the minimum value of the apparent electron mobility the spatial distribution of the organic bulk electric field as well as the total charge density turn out to be bias independent. The first case investigated is based on the boundary condition of zero electric field at the electron injection interface. It is shown that for minimum valued apparent mobilities, the strong but finite accumulation of electrons close to the anode is obtained, which characterize the inverted space charge limited current (SCLC) effect. The second example refers to the internal electric field allowing for self-adjustment of its boundary values. The total electron charge density is than found typically to be of U shape, which may, depending on the parameters, peak at both or at either Alq3 boundary. It is this example in which the proper SCLC effect is consequently predicted. In each of the above two cases, the calculations predict the minimum values of the electron apparent mobility, which substantially exceed the corresponding published measurements. For this reason the effect of the drift term alone is additionally investigated. On the basis of the published empirical electron mobilities and the diffusion term revoked, it is shown that the steady state electron current density within the Al/Alq3 (97 nm)/Ca single layer organic structure may well be pictured within the drift-only interpretation of the charge carriers within the Alq3 organic characterized by the single (shallow) trap energy level. In order to arrive at this result, it is necessary that the nonzero electric field, calculated to exist at the electron injecting Alq3/Ca boundary, is to be appropriately accounted for in the computation.

Refraction-reflection of electrons at lateral metallic interfaces

NASA Astrophysics Data System (ADS)

Kher-Elden, M. A.; El-Fattah, Z. M. Abd; Yassin, O.; El-Okr, M. M.

2017-11-01

Electron boundary element method (EBEM) has been employed to simulate electron refraction at the lateral interface between two homogenous metals featuring surface states characterized by isotropic constant energy surfaces. A decent agreement was achieved between the real-space EBEM simulations and the wave-space analysis obtained from electron plane wave expansion (EPWE) method. Calculations were performed for three different electron energies, being -0.05, -0.15, and -0.25 eV, where the reference energy is set to -0.4 eV, i.e., the band minimum of the Cu(111) surface state. For an interface separating two metals with the same effective mass (0.41 me) and a potential difference of 0.2 eV, we demonstrate that electrons with the first two energies exhibit refraction at the interface, following the Snell's law, and total internal reflections occur beyond energy-dependent critical angles, whereas for the third electron energy, a total internal reflection occurs at all incident angles. These findings were used to simulate optical elements such as convex lenses and possible guiding through perfect electron mirrors, in contrast to Bragg-based guiding. Given the varieties of possible means of manipulating the dispersion parameters via surface adsorbates and thin-film growth, the degree of electron refraction-reflection at metallic interfaces could be precisely tuned.

Experimental Potential Energy Curve for the 43 Π Electronic State of NaCs

NASA Astrophysics Data System (ADS)

Steely, Andrew; Cooper, Hannah; Zain, Hareem; Whipp, Ciara; Faust, Carl; Kortyna, Andrew; Huennekens, John

2017-04-01

We present results from experimental studies of the 43 Π electronic state of the NaCs molecule. This electronic state is interesting in that its potential energy curve likely exhibits a double minimum. As a result, interference effects are observed in the resolved bound-free fluorescence spectra. The optical-optical double resonance method was used to obtain Doppler-free excitation spectra for the 43 Π state. This dataset of measured level energies was expanded largely by observing fluorescence from levels populated by collisions. To aid in level assignments, simulations of resolved bound-free fluorescence spectra were calculated using the BCONT program (R. J. Le Roy, University of Waterloo). Spectroscopic constants were determined to summarize data belonging to inner well, outer well, and above barrier regions of the electronic state. Current work focuses on using the IPA method to construct an experimental potential energy curve. Work supported by NSF and Susquehanna University.

Tandem betatron

DOEpatents

Keinigs, Rhonald K.

1992-01-01

Two betatrons are provided in tandem for alternately accelerating an electron beam to avoid the single flux swing limitation of conventional betatrons and to accelerate the electron beam to high energies. The electron beam is accelerated in a first betatron during a period of increasing magnetic flux. The eletron beam is extracted from the first betatron as a peak magnetic flux is reached and then injected into a second betatron at a time of minimum magnetic flux in the second betatron. The cycle may be repeated until the desired electron beam energy is obtained. In one embodiment, the second betatron is axially offset from the first betatron to provide for electron beam injection directly at the axial location of the beam orbit in the second betatron.

Electron affinity of perhalogenated benzenes: A theoretical DFT study

NASA Astrophysics Data System (ADS)

Volatron, François; Roche, Cécile

2007-10-01

The potential energy surfaces (PES) of unsubstituted and perhalogenated benzene anions ( CX6-, X = F, Cl, Br, and I) were explored by means of DFT-B3LYP calculations. In the F and Cl cases seven extrema were located and characterized. In the Br and I cases only one minimum and two extrema were found. In each case the minimum was recomputed at the CCSD(T) level. The electron affinities of C 6X 6 were calculated (ZPE included). The results obtained agree well with the experimental determinations when available. The values obtained in the X = Br and the X = I cases are expected to be valuable predictions.

Molecular electrostatics for probing lone pair-π interactions.

PubMed

Mohan, Neetha; Suresh, Cherumuttathu H; Kumar, Anmol; Gadre, Shridhar R

2013-11-14

An electrostatics-based approach has been proposed for probing the weak interactions between lone pair containing molecules and π deficient molecular systems. For electron-rich molecules, the negative minima in molecular electrostatic potential (MESP) topography give the location of electron localization and the MESP value at the minimum (Vmin) quantifies the electron-rich character of that region. Interactive behavior of a lone pair bearing molecule with electron deficient π-systems, such as hexafluorobenzene, 1,3,5-trinitrobenzene, 2,4,6-trifluoro-1,3,5-triazine and 1,2,4,5-tetracyanobenzene explored within DFT brings out good correlation of the lone pair-π interaction energy (E(int)) with the Vmin value of the electron-rich system. Such interaction is found to be portrayed well with the Electrostatic Potential for Intermolecular Complexation (EPIC) model. On the basis of the precise location of MESP minimum, a prediction for the orientation of a lone pair bearing molecule with an electron deficient π-system is possible in the majority of the cases studied.

Potential energy function for CH3+CH3 ⇆ C2H6: Attributes of the minimum energy path

NASA Astrophysics Data System (ADS)

Robertson, S. H.; Wardlaw, D. M.; Hirst, D. M.

1993-11-01

The region of the potential energy surface for the title reaction in the vicinity of its minimum energy path has been predicted from the analysis of ab initio electronic energy calculations. The ab initio procedure employs a 6-31G** basis set and a configuration interaction calculation which uses the orbitals obtained in a generalized valence bond calculation. Calculated equilibrium properties of ethane and of isolated methyl radical are compared to existing theoretical and experimental results. The reaction coordinate is represented by the carbon-carbon interatomic distance. The following attributes are reported as a function of this distance and fit to functional forms which smoothly interpolate between reactant and product values of each attribute: the minimum energy path potential, the minimum energy path geometry, normal mode frequencies for vibrational motion orthogonal to the reaction coordinate, a torsional potential, and a fundamental anharmonic frequency for local mode, out-of-plane CH3 bending (umbrella motion). The best representation is provided by a three-parameter modified Morse function for the minimum energy path potential and a two-parameter hyperbolic tangent switching function for all other attributes. A poorer but simpler representation, which may be satisfactory for selected applications, is provided by a standard Morse function and a one-parameter exponential switching function. Previous applications of the exponential switching function to estimate the reaction coordinate dependence of the frequencies and geometry of this system have assumed the same value of the range parameter α for each property and have taken α to be less than or equal to the ``standard'' value of 1.0 Å-1. Based on the present analysis this is incorrect: The α values depend on the property and range from ˜1.2 to ˜1.8 Å-1.

Early experience in using and 18 Me V linear accelerator for mycosis fungoides at Howard University Hospital.

PubMed

Kumar, P P; Henschke, K; Mandal, K P; Nibhanupudy, J R; Patel, I S

1977-04-01

This paper describes the problems and solutions in using 18 MeV linear accelerator, with minimum 6 MeV electron capability, for total skin irradiation for mycosis fungoides. The 6 MeV electron energy can be degraded to acceptable electron energy of 3.2 MeV by interposing a plexiglass sheet of 9.6 mm in the beam. To minimize the bremsstrahlung, the degrading plexiglass should be kept away from the machine head. A wide area with uniform dose distribution over single plane can be achieved by using dual fields but homogenous dose distribution over irregular body surface cannot be achieved mainly because of self-shielding. The nails and the ocular lens can be easily shielded from the low energy electrons with 1.5 mm lead shield.

New analytical model for the ozone electronic ground state potential surface and accurate ab initio vibrational predictions at high energy range.

PubMed

Tyuterev, Vladimir G; Kochanov, Roman V; Tashkun, Sergey A; Holka, Filip; Szalay, Péter G

2013-10-07

An accurate description of the complicated shape of the potential energy surface (PES) and that of the highly excited vibration states is of crucial importance for various unsolved issues in the spectroscopy and dynamics of ozone and remains a challenge for the theory. In this work a new analytical representation is proposed for the PES of the ground electronic state of the ozone molecule in the range covering the main potential well and the transition state towards the dissociation. This model accounts for particular features specific to the ozone PES for large variations of nuclear displacements along the minimum energy path. The impact of the shape of the PES near the transition state (existence of the "reef structure") on vibration energy levels was studied for the first time. The major purpose of this work was to provide accurate theoretical predictions for ozone vibrational band centres at the energy range near the dissociation threshold, which would be helpful for understanding the very complicated high-resolution spectra and its analyses currently in progress. Extended ab initio electronic structure calculations were carried out enabling the determination of the parameters of a minimum energy path PES model resulting in a new set of theoretical vibrational levels of ozone. A comparison with recent high-resolution spectroscopic data on the vibrational levels gives the root-mean-square deviations below 1 cm(-1) for ozone band centres up to 90% of the dissociation energy. New ab initio vibrational predictions represent a significant improvement with respect to all previously available calculations.

Nanotechnology and clean energy: sustainable utilization and supply of critical materials

NASA Astrophysics Data System (ADS)

Fromer, Neil A.; Diallo, Mamadou S.

2013-11-01

Advances in nanoscale science and engineering suggest that many of the current problems involving the sustainable utilization and supply of critical materials in clean and renewable energy technologies could be addressed using (i) nanostructured materials with enhanced electronic, optical, magnetic and catalytic properties and (ii) nanotechnology-based separation materials and systems that can recover critical materials from non-traditional sources including mine tailings, industrial wastewater and electronic wastes with minimum environmental impact. This article discusses the utilization of nanotechnology to improve or achieve materials sustainability for energy generation, conversion and storage. We highlight recent advances and discuss opportunities of utilizing nanotechnology to address materials sustainability for clean and renewable energy technologies.

Unusual structures of MgF5- superhalogen anion

NASA Astrophysics Data System (ADS)

Anusiewicz, Iwona; Skurski, Piotr

2007-05-01

The vertical electron detachment energies (VDE) of three MgF5- anions were calculated at the outer valence Green function level with the 6-311 + G(3df) basis sets. This species was found to form unusual geometrical structures each of which corresponds to an anionic state exhibiting superhalogen nature. The global minimum structure was described as a system in which two central magnesium atoms are linked via symmetrical triangle formed by three fluorine atoms. Extremely large electron binding energies of these anions (exceeding 8.5 eV in all cases) were predicted and discussed.

Z-Pinch Plasma Neutron Sources

DTIC Science & Technology

2006-03-24

deuterium into 9 to 14 keV (around 10 keV), which is well in the fusion energy range we are interested in. To make plasma radiation sources work, we...showing the 1-D dynamics of the pinch plasma implosion, temperature, fusion energy production and deposition for the conditions of shot Z1422. The minimum...histories of ion and electron temperatures, fusion energy production and energy deposition in ID RMHD run modeling deuterium shot Z1422. In our simulations

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

NASA Technical Reports Server (NTRS)

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

Ammonia-water cation and ammonia dimer cation.

PubMed

Kim, Hahn; Lee, Han Myoung

2009-06-25

We have investigated the structure, interaction energy, electronic properties, and IR spectra of the ammonia-water cation (NH(3)H(2)O)(+) using density functional theory (DFT) and high-level ab initio theory. The ammonia-water cation has three minimum-energy structures of (a) H(2)NH(+)...OH(2), (b) H(3)N(+)...OH(2), and (c) H(3)NH(+)...OH. The lowest-energy structure is (a), followed by (c) and (b). The ammonia dimer cation has two minimum-energy structures [the lowest H(3)NH(+)...NH(2) structure and the second lowest (H(3)N...NH(3))(+) structure]. The minimum transition barrier for the interconversion between (a), (b), and (c) is approximately 6 kcal/mol. Most DFT calculations with various functionals, except a few cases, overstabilize the N...O and N...N binding, predicting different structures from Moller-Plesset second-order perturbation (MP2) theory and the most reliable complete basis set (CBS) limit of coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. Thus, the validity test of the DFT functionals for these ionized molecular systems would be of importance.

Uncertainty of the potential curve minimum for diatomic molecules extrapolated from Dunham type coefficients

NASA Astrophysics Data System (ADS)

Ilieva, T.; Iliev, I.; Pashov, A.

2016-12-01

In the traditional description of electronic states of diatomic molecules by means of molecular constants or Dunham coefficients, one of the important fitting parameters is the value of the zero point energy - the minimum of the potential curve or the energy of the lowest vibrational-rotational level - E00 . Their values are almost always the result of an extrapolation and it may be difficult to estimate their uncertainties, because they are connected not only with the uncertainty of the experimental data, but also with the distribution of experimentally observed energy levels and the particular realization of set of Dunham coefficients. This paper presents a comprehensive analysis based on Monte Carlo simulations, which aims to demonstrate the influence of all these factors on the uncertainty of the extrapolated minimum of the potential energy curve U (Re) and the value of E00 . The very good extrapolation properties of the Dunham coefficients are quantitatively confirmed and it is shown that for a proper estimate of the uncertainties, the ambiguity in the composition of the Dunham coefficients should be taken into account.

Competition between quasi-planar and cage-like structures in the B29- cluster: photoelectron spectroscopy and ab initio calculations.

PubMed

Li, Hai-Ru; Jian, Tian; Li, Wei-Li; Miao, Chang-Qing; Wang, Ying-Jin; Chen, Qiang; Luo, Xue-Mei; Wang, Kang; Zhai, Hua-Jin; Li, Si-Dian; Wang, Lai-Sheng

2016-10-26

Size-selected boron clusters have been found to be predominantly planar or quasi-planar (2D) in the small size regime with the appearance of three-dimensional (3D) borospherene cages of larger sizes. A seashell-like B 28 - cluster was previously shown to be the smallest borospherene, which competes with a quasi-planar isomer for the global minimum. Here we report a study on the structures and bonding of the B 29 - and B 29 clusters using photoelectron spectroscopy (PES) and first-principles calculations and demonstrate the continued competition between the 2D and borospherene structures. The PES spectrum of B 29 - displays a complex pattern with evidence of low-lying isomers. Global-minimum searches and extensive theoretical calculations revealed a complicated potential energy surface for B 29 - with five low-lying isomers, among which the lowest three were shown to contribute to the experimental spectrum. A 3D seashell-like C s (2, 1 A') isomer, featuring two heptagons on the waist and one octagon at the bottom, is the global minimum for B 29 - , followed by a 2D C 1 (3, 1 A) isomer with a hexagonal hole and a stingray-shaped 2D C s (1, 1 A') isomer with a pentagonal hole. However, by taking into account the entropic effects, the stingray-shaped isomer 1 was shown to be the lowest in energy at room temperature and was found to dominate the PES spectrum. Isomers 2 and 3, which have lower electron binding energies, were also found to be present in the experiment. Chemical bonding analyses showed that isomer 1 is an all-boron analogue of benzo[ghi]fluoranthene (C 18 H 10 ), whereas the borospherene isomer 2 possesses 18π electrons, conforming to the 2(N + 1) 2 electron counting rule for spherical aromaticity. For the B 29 neutral cluster, the seashell-like borospherene isomer is the global minimum, significantly lower in energy than the stingray-shaped quasi-planar structure.

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

Nogueira, C. P. S. M.; Guimarães, J. G.

In this paper, an auto-associative neural network using single-electron tunneling (SET) devices is proposed and simulated at low temperature. The nanoelectronic auto-associative network is able to converge to a stable state, previously stored during training. The recognition of the pattern involves decreasing the energy of the input state until it achieves a point of local minimum energy, which corresponds to one of the stored patterns.

Evaluation of Noninvasive Measurement Methods and Systems for Application in Vital Signs Detection. Part 1. Literature Review.

DTIC Science & Technology

1986-03-01

radiations from the body in the infrared spectrum of light energy provides a passive, noninvasive method of measuring and recording a subject’s relative... a minimum during each test. In transmission radiography, dosage (or dose rate) is a measure of the * energy of the applied radiation . X-ray energy is... a function of frequency (E *hi) and is expressed in electron volts

The effect of photoelectrons on boom-satellite potential differences during electron beam ejection

NASA Technical Reports Server (NTRS)

Lai, Shu T.; Cohen, Herbert A.; Aggson, Thomas L.; Mcneil, William J.

1987-01-01

Data taken on the SCATHA satellite at geosynchronous altitudes during periods of electron beam ejection in sunlight showed that the potential difference between an electrically isolated boom and the satellite main body was a function of beam current, energy, and boom-sun angle. The potential difference decreased as the boom area illuminated by the sun increased; the maximum and minimum potential differences were measured when minimum and maximum boom areas, respectively, were exposed to the sun. It is shown that photoelectrons, created on the boom, could be engulfed in the electrostatic field of the highly charged satellite main body. Theoretical calculations made using a simple current balance model showed that these electrons could provide a substantial discharging current to the main body and cause the observed variations in the potential difference between the main body and the booms.

Variation of Radiation Belt Content Indices and total electron energy During Magnetic Storms Based On Van Allen Probe Observations

NASA Astrophysics Data System (ADS)

Xiong, Y.; Xie, L.; Chen, L.; Pu, Z.

2017-12-01

We investigate the variability of the RBC indices and total electron energy for varying energies within outer belt during 42 isolate magnetic storms based on the electron flux data from MagEIS and REPT onboard Van Allen Probe-A spacecraft. Van Allan Probes travel throughout the entire radiation belt twice during each orbit, providing an excellent opportunity to measure the electron's pitch angle distributions near the magnetic equatorial plane which is essential to calculate the RBC index accurately. Instead of assuming an isotropic electron pitch angle distribution which is widely used in previous studies, we develop a new and reliable technique to infer the equatorial pitch angle distributions based on the off-equator measurements. The statistic results show that the total electron energy in outer belt increase in 80% storms and has a positive correlation with median value of AE during recovery phase and minimum -Dst. The possibility of observing RBC depletion increase at high energies. The upper limit energy of RBC enhancement has a positive correlation with median value of AE and Vsw during recovery phase and a negative correlation with median value of Nsw during storm, which is consist of the balance of acceleration by chorus waves and loss by EMIC waves.

Theoretical Study of Tautomerization Reactions for the Ground and First Excited Electronic States of Adenine

NASA Technical Reports Server (NTRS)

Salter, Latasha M.; Chaban, Galina M.; Kwak, Dochan (Technical Monitor)

2002-01-01

Geometrical structures and energetic properties for different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest singlet excited state potential energy surfaces are studied. Four tautomeric forms are considered, and their energetic order is found to be different on the ground and the excited state potential energy surfaces. Minimum energy reaction paths are obtained for hydrogen atom transfer (tautomerization) reactions in the ground and the lowest excited electronic states. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic states, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. This tautomerization process should become possible in the presence of water or other polar solvent molecules and should play an important role in the photochemistry of adenine.

Production of metals and compounds by radiation chemistry

NASA Technical Reports Server (NTRS)

Marsik, S. J.; Philipp, W. H.

1969-01-01

Preparation of metals and compounds by radiation induced chemical reactions involves irradiation of metal salt solutions with high energy electrons. This technique offers a method for the preparation of high purity metals with minimum contamination from the container material or the cover gas.

On energetic prerequisites of attracting electrons

NASA Astrophysics Data System (ADS)

Sundholm, Dage

2014-06-01

The internal reorganization energy and the zero-point vibrational energy (ZPE) of fractionally charged molecules embedded in molecular materials are discussed. The theory for isolated open quantum systems is taken as the starting point. It is shown that for isolated molecules the internal reorganization-energy function and its slope, i.e., the chemical potential of an open molecular system are monotonically decreasing functions with respect to increasing amount of negative excess charge (q) in the range of q = [0, 1]. Calculations of the ZPE for fractionally charged molecules show that the ZPE may have a minimum for fractional occupation. The calculations show that the internal reorganization energy and changes in the ZPE are of the same order of magnitude with different behavior as a function of the excess charge. The sum of the contributions might favor molecules with fractional occupation of the molecular units and partial delocalization of the excess electrons in solid-state materials also when considering Coulomb repulsion between the excess electrons. The fractional electrons are then coherently distributed on many molecules of the solid-state material forming a condensate of attracting electrons, which is crucial for the superconducting state.

On energetic prerequisites of attracting electrons.

PubMed

Sundholm, Dage

2014-06-21

The internal reorganization energy and the zero-point vibrational energy (ZPE) of fractionally charged molecules embedded in molecular materials are discussed. The theory for isolated open quantum systems is taken as the starting point. It is shown that for isolated molecules the internal reorganization-energy function and its slope, i.e., the chemical potential of an open molecular system are monotonically decreasing functions with respect to increasing amount of negative excess charge (q) in the range of q = [0, 1]. Calculations of the ZPE for fractionally charged molecules show that the ZPE may have a minimum for fractional occupation. The calculations show that the internal reorganization energy and changes in the ZPE are of the same order of magnitude with different behavior as a function of the excess charge. The sum of the contributions might favor molecules with fractional occupation of the molecular units and partial delocalization of the excess electrons in solid-state materials also when considering Coulomb repulsion between the excess electrons. The fractional electrons are then coherently distributed on many molecules of the solid-state material forming a condensate of attracting electrons, which is crucial for the superconducting state.

The multifarious temporal variations of low energy, relativistic cosmic ray electrons

NASA Technical Reports Server (NTRS)

Mcdonald, F. B.; Cline, T. L.; Simnett, G. M.

1972-01-01

A detailed examination is made of the intensity variations of 3 - 12 MeV interplanetary electrons. The data used are from the cosmic ray experiment flown on the IMP solar minimum through to the onset of the present solar maximum (i.e., from December 1963 through August 1969). A morphology for the intensity changes is tentatively proposed which includes solar flare-associated events, solar co-rotating increases, Forbush decreases, and quiet-time increases, as well as the long term eleven-year variation. It is contended that the electron component observed both during quiescent times and during quiet-time increases are galactic in origin. The quiet-time increases represent a completely new phenomenon that appears to be unique to the low energy electron population. During a quiet-time increase the electron intensity is enhanced by a factor of 3 to 5 over a period of days, and, in general, these periods anti-correlate with low-energy solar particle events. Qualitatively, their amplitude diminishes with increasing solar activity.

Multifarious temporal variations of low-energy relativistic cosmic-ray electrons.

NASA Technical Reports Server (NTRS)

Mcdonald, F. B.; Cline, T. L.; Simnett, G. M.

1972-01-01

Detailed examination of the intensity variations of 3- to 12-MeV interplanetary electrons. The data are from the Goddard cosmic-ray experiment on the Imp satellites and cover the period from just before the last solar minimum through the onset of the present solar maximum (i.e., from December 1963 through August 1969). A morphology for the intensity changes is tentatively proposed that includes solar-flare-associated events, solar co-rotating increases, Forbush decreases, quiet-time increases, and the long-term 11-year variation. It is contended that the electron components observed both during quiescent times and during quiet-time increases are galactic in origin. The quiet-time increases represent a completely new phenomenon that appears to be unique to the low-energy electron population. During a quiet-time increase the electron intensity is enhanced by a factor of 3 to 5 over a period of days, and, in general, these periods anticorrelate with low-energy solar particle events. Qualitatively, their amplitude diminishes with increasing solar activity.

A Novel Intrinsic Interface State Controlled by Atomic Stacking Sequence at Interfaces of SiC/SiO2.

PubMed

Matsushita, Yu-Ichiro; Oshiyama, Atsushi

2017-10-11

On the basis of ab initio total-energy electronic-structure calculations, we find that electron states localized at the SiC/SiO 2 interface emerge in the energy region between 0.3 eV below and 1.2 eV above the bulk conduction-band minimum (CBM) of SiC, being sensitive to the sequence of atomic bilayers in SiC near the interface. These new interface states unrecognized in the past are due to the peculiar characteristics of the CBM states that are distributed along the crystallographic channels. We also find that the electron doping modifies the energetics among the different stacking structures. Implication for performance of electron devices fabricated on different SiC surfaces is discussed.

Ultralow-power electronics for biomedical applications.

PubMed

Chandrakasan, Anantha P; Verma, Naveen; Daly, Denis C

2008-01-01

The electronics of a general biomedical device consist of energy delivery, analog-to-digital conversion, signal processing, and communication subsystems. Each of these blocks must be designed for minimum energy consumption. Specific design techniques, such as aggressive voltage scaling, dynamic power-performance management, and energy-efficient signaling, must be employed to adhere to the stringent energy constraint. The constraint itself is set by the energy source, so energy harvesting holds tremendous promise toward enabling sophisticated systems without straining user lifestyle. Further, once harvested, efficient delivery of the low-energy levels, as well as robust operation in the aggressive low-power modes, requires careful understanding and treatment of the specific design limitations that dominate this realm. We outline the performance and power constraints of biomedical devices, and present circuit techniques to achieve complete systems operating down to power levels of microwatts. In all cases, approaches that leverage advanced technology trends are emphasized.

Construction of exchange-correlation functionals through interpolation between the non-interacting and the strong-correlation limit

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

Zhou, Yongxi; Ernzerhof, Matthias, E-mail: Matthias.Ernzerhof@UMontreal.ca; Bahmann, Hilke

Drawing on the adiabatic connection of density functional theory, exchange-correlation functionals of Kohn-Sham density functional theory are constructed which interpolate between the extreme limits of the electron-electron interaction strength. The first limit is the non-interacting one, where there is only exchange. The second limit is the strong correlated one, characterized as the minimum of the electron-electron repulsion energy. The exchange-correlation energy in the strong-correlation limit is approximated through a model for the exchange-correlation hole that is referred to as nonlocal-radius model [L. O. Wagner and P. Gori-Giorgi, Phys. Rev. A 90, 052512 (2014)]. Using the non-interacting and strong-correlated extremes, variousmore » interpolation schemes are presented that yield new approximations to the adiabatic connection and thus to the exchange-correlation energy. Some of them rely on empiricism while others do not. Several of the proposed approximations yield the exact exchange-correlation energy for one-electron systems where local and semi-local approximations often fail badly. Other proposed approximations generalize existing global hybrids by using a fraction of the exchange-correlation energy in the strong-correlation limit to replace an equal fraction of the semi-local approximation to the exchange-correlation energy in the strong-correlation limit. The performance of the proposed approximations is evaluated for molecular atomization energies, total atomic energies, and ionization potentials.« less

Quantum chemical study of methane oxidation species

NASA Technical Reports Server (NTRS)

Jackels, C. F.

1984-01-01

Work completed on the 2A1 excited state and low-lying dissociative states of the methoxy radical is reported. A manuscript was prepared that reports the characterization of the 2A1 electronic state, the excitation energies and Franck-Condon factors for the 2A1 - 2E system, and the energies of intersection between the 2A1 state and the nearby dissociative states. The minimum excitation energy needed for predissociation of methoxy is predicted along with the corresponding implications for atmospheric chemistry.

Conceptual DFT analysis of the fragility spectra of atoms along the minimum energy reaction coordinate.

PubMed

Ordon, Piotr; Komorowski, Ludwik; Jedrzejewski, Mateusz

2017-10-07

Theoretical justification has been provided to the method for monitoring the sequence of chemical bonds' rearrangement along a reaction path, by tracing the evolution of the diagonal elements of the Hessian matrix. Relations between the divergences of Hellman-Feynman forces and the energy and electron density derivatives have been demonstrated. By the proof presented on the grounds of the conceptual density functional theory formalism, the spectral amplitude observed on the atomic fragility spectra [L. Komorowski et al., Phys. Chem. Chem. Phys. 18, 32658 (2016)] reflects selectively the electron density modifications in bonds of an atom. In fact the spectral peaks for an atom reveal changes of the electron density occurring with bonds creation, breaking, or varying with the reaction progress.

Conceptual DFT analysis of the fragility spectra of atoms along the minimum energy reaction coordinate

NASA Astrophysics Data System (ADS)

Ordon, Piotr; Komorowski, Ludwik; Jedrzejewski, Mateusz

2017-10-01

Theoretical justification has been provided to the method for monitoring the sequence of chemical bonds' rearrangement along a reaction path, by tracing the evolution of the diagonal elements of the Hessian matrix. Relations between the divergences of Hellman-Feynman forces and the energy and electron density derivatives have been demonstrated. By the proof presented on the grounds of the conceptual density functional theory formalism, the spectral amplitude observed on the atomic fragility spectra [L. Komorowski et al., Phys. Chem. Chem. Phys. 18, 32658 (2016)] reflects selectively the electron density modifications in bonds of an atom. In fact the spectral peaks for an atom reveal changes of the electron density occurring with bonds creation, breaking, or varying with the reaction progress.

Satellite sweeping of electrons at Neptune and Uranus

NASA Technical Reports Server (NTRS)

Cooper, John F.

1990-01-01

Knowledge of satellite sweeping parameters at Neptune and Uranus, and of their functional dependences on particle energy and pitch angle, can be critical in the proper identification of parent absorbers for observed absorption signatures in regions where OTD (offset, tilted dipole) models are valid representations of the measured magnetic fields. In this paper, critical electron energies are calculated for longitudinal drift resonance, snowplow (i.e., strong) absorption, leapfrog, and corkscrew effects, using a reduced version of OTD that neglects nonaxial dipole offsets. Earlier analytic work on sweeping rates is extended to give the radial dependence of these rates within the minimum-L region and to set limits on diffusion of electrons with the simplifying approximation that leapfrog effects are ignored.

Theoretical and experimental differential cross sections for electron impact excitation of the electronic bands of furfural

NASA Astrophysics Data System (ADS)

Jones, D. B.; Neves, R. F. C.; Lopes, M. C. A.; da Costa, R. F.; do N. Varella, M. T.; Bettega, M. H. F.; Lima, M. A. P.; García, G.; Limão-Vieira, P.; Brunger, M. J.

2016-03-01

We report results from a joint experimental and theoretical investigation into electron scattering from the important industrial species furfural (C5H4O2). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C5H4O2. The measurements were carried out at energies in the range 20-40 eV, and for scattered-electron angles between 10° and 90°. The energy resolution of those experiments was typically ˜80 meV. Corresponding Schwinger multichannel method with pseudo-potential calculations, for energies between 6-50 eV and with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were undertaken at the static exchange plus polarisation-level using a minimum orbital basis for single configuration interaction (MOB-SCI) approach. Agreement between the measured and calculated DCSs was qualitatively quite good, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOB-SCI. The role of multichannel coupling on the computed electronic-state DCSs is also explored in some detail.

Electronic structure and molecular dynamics of Na2Li

NASA Astrophysics Data System (ADS)

Malcolm, Nathaniel O. J.; McDouall, Joseph J. W.

Following the first report (Mile, B., Sillman, P. D., Yacob, A. R. and Howard, J. A., 1996, J. chem. Soc. Dalton Trans , 653) of the EPR spectrum of the mixed alkali-metal trimer Na2Li a detailed study has been made of the electronic structure and structural dynamics of this species. Two isomeric forms have been found: one of the type, Na-Li-Na, of C , symmetry and another, Li-Na-Na, of C symmetry. Also, there are two linear saddle points which correspond to 'inversion' transition structures, and a saddle point of C symmetry which connects the two minima. A molecular dynamics investigation of these species shows that, at the temperature of the reported experiments (170 K), the C minimum is not 'static', but undergoes quite rapid inversion. At higher temperatures the C minimum converts to the C form, but by a mechanism very different from that suggested by minimum energy path considerations. 2 2v s s 2v 2v s

Combined gradient projection/single component artificial force induced reaction (GP/SC-AFIR) method for an efficient search of minimum energy conical intersection (MECI) geometries

NASA Astrophysics Data System (ADS)

Harabuchi, Yu; Taketsugu, Tetsuya; Maeda, Satoshi

2017-04-01

We report a new approach to search for structures of minimum energy conical intersection (MECIs) automatically. Gradient projection (GP) method and single component artificial force induced reaction (SC-AFIR) method were combined in the present approach. As case studies, MECIs of benzene and naphthalene between their ground and first excited singlet electronic states (S0/S1-MECIs) were explored. All S0/S1-MECIs reported previously were obtained automatically. Furthermore, the number of force calculations was reduced compared to the one required in the previous search. Improved convergence in a step in which various geometrical displacements are induced by SC-AFIR would contribute to the cost reduction.

Landscape of an exact energy functional

NASA Astrophysics Data System (ADS)

Cohen, Aron J.; Mori-Sánchez, Paula

2016-04-01

One of the great challenges of electronic structure theory is the quest for the exact functional of density functional theory. Its existence is proven, but it is a complicated multivariable functional that is almost impossible to conceptualize. In this paper the asymmetric two-site Hubbard model is studied, which has a two-dimensional universe of density matrices. The exact functional becomes a simple function of two variables whose three-dimensional energy landscape can be visualized and explored. A walk on this unique landscape, tilted to an angle defined by the one-electron Hamiltonian, gives a valley whose minimum is the exact total energy. This is contrasted with the landscape of some approximate functionals, explaining their failure for electron transfer in the strongly correlated limit. We show concrete examples of pure-state density matrices that are not v representable due to the underlying nonconvex nature of the energy landscape. The exact functional is calculated for all numbers of electrons, including fractional, allowing the derivative discontinuity to be visualized and understood. The fundamental gap for all possible systems is obtained solely from the derivatives of the exact functional.

Beam-beam interaction study of medium energy eRHIC

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

Hao,Y.; Litvinenko, V. N.; Ptitsyn, V.

Medium Energy eRHIC (MeRHIC), the first stage design of eRHIC, includes a multi-pass ERL that provides 4GeV high quality electron beam to collide with the ion beam of RHIC. It delivers a minimum luminosity of 10{sup 32} cm{sup -2}s{sup -1}. Beam-beam effects present one of major factors limiting the luminosity of colliders. In this paper, both beam-beam effects on the electron beam and the proton beam in MeRHIC are investigated. The beam-beam interaction can induce a head-tail type instability of the proton beam referred to as the kink instability. Thus, beam stability conditions should be established to avoid proton beammore » loss. Also, the electron beam transverse disruption by collisions has to be evaluated to ensure that the beam quality is good enough for the energy recovery pass. The relation of proton beam stability, electron disruption and consequential luminosity are carried out after thorough discussion.« less

π-Stacking, C-H/π, and halogen bonding interactions in bromobenzene and mixed bromobenzene-benzene clusters.

PubMed

Reid, Scott A; Nyambo, Silver; Muzangwa, Lloyd; Uhler, Brandon

2013-12-19

Noncovalent interactions play an important role in many chemical and biochemical processes. Building upon our recent study of the homoclusters of chlorobenzene, where π-π stacking and CH/π interactions were identified as the most important binding motifs, in this work we present a study of bromobenzene (PhBr) and mixed bromobenzene-benzene clusters. Electronic spectra in the region of the PhBr monomer S0-S1 (ππ*) transition were obtained using resonant two-photon ionization (R2PI) methods combined with time-of-flight mass analysis. As previously found for related systems, the PhBr cluster spectra show a broad feature whose center is red-shifted from the monomer absorption, and electronic structure calculations indicate the presence of multiple isomers and Franck-Condon activity in low-frequency intermolecular modes. Calculations at the M06-2X/aug-cc-pVDZ level find in total eight minimum energy structures for the PhBr dimer: four π-stacked structures differing in the relative orientation of the Br atoms (denoted D1-D4), one T-shaped structure (D5), and three halogen bonded structures (D6-D8). The calculated binding energies of these complexes, corrected for basis set superposition error (BSSE) and zero-point energy (ZPE), are in the range of -6 to -24 kJ/mol. Time-dependent density functional theory (TDDFT) calculations predict that these isomers absorb over a range that is roughly consistent with the breadth of the experimental spectrum. To examine the influence of dipole-dipole interaction, R2PI spectra were also obtained for the mixed PhBr···benzene dimer, where the spectral congestion is reduced and clear vibrational structure is observed. This structure is well-simulated by Franck-Condon calculations that incorporate the lowest frequency intermolecular modes. Calculations find four minimum energy structures for the mixed dimer and predict that the binding energy of the global minimum is reduced by ~30% relative to the global minimum PhBr dimer structure.

Doping Induced Structural Stability and Electronic Properties of GaN Nanotubes

PubMed Central

Khan, Mohammad Irfan; Tyagi, Neha; Swaroop Khare, Purnima

2014-01-01

The present paper discusses the effect of manganese doping on the structural stability and electronic band gap of chiral (2, 1), armchair (3, 3), and zigzag ((6, 0) and (10, 0)) single walled GaN nanotube by using density functional theory based Atomistix Toolkit (ATK) Virtual NanoLab (VNL). The structural stability has been analyzed in terms of minimum ground state total energy, binding, and formation energy. As an effect of Mn doping (1–4 atoms), all the GaN nanotubes taken into consideration show semiconducting to metallic transition first and after certain level of Mn doping changes its trend. PMID:24707225

Generalized variational approach to Kim-Gordon electron gas theory for ionic crystals

NASA Astrophysics Data System (ADS)

Ivanov, O. V.; Maksimov, E. G.

1996-01-01

The generalized approach to the Kim-Gordon electron gas model is proposed. The total density of a crystal is considered as a superposition of densities of individual overlapping ions. The possible distortions of individual ion densities are calculated in the presence of some auxiliary external potentials. The real values of these distortions are calculated by a variational method from the minimum total energy of a crystal. The proper prescription of the ion self-energy with a distorted density is given using the method elaborated in the nonequilibrium thermodynamics. Some examples of the calculation for phonon frequencies are presented and demonstrate a good agreement with experimental data.

Conical intersections of free energy surfaces in solution: Effect of electron correlation on a protonated Schiff base in methanol solution

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

Mori, Toshifumi; Nakano, Katsuhiro; Kato, Shigeki

2010-08-14

The minimum energy conical intersection (MECI) optimization method with taking account of the dynamic electron correlation effect [T. Mori and S. Kato, Chem. Phys. Lett. 476, 97 (2009)] is extended to locate the MECI of nonequilibrium free energy surfaces in solution. A multistate electronic perturbation theory is introduced into the nonequilibrium free energy formula, which is defined as a function of solute and solvation coordinates. The analytical free energy gradient and interstate coupling vectors are derived, and are applied to locate MECIs in solution. The present method is applied to study the cis-trans photoisomerization reaction of a protonated Schiff basemore » molecule (PSB3) in methanol (MeOH) solution. It is found that the effect of dynamic electron correlation largely lowers the energy of S{sub 1} state. We also show that the solvation effect strongly stabilizes the MECI obtained by twisting the terminal C=N bond to become accessible in MeOH solution, whereas the conical intersection is found to be unstable in gas phase. The present study indicates that both electron correlation and solvation effects are important in the photoisomerization reaction of PSB3. The effect of counterion is also examined, and seems to be rather small in solution. The structures of free energy surfaces around MECIs are also discussed.« less

Computational conformational antimicrobial analysis developing mechanomolecular theory for polymer biomaterials in materials science and engineering

NASA Astrophysics Data System (ADS)

Petersen, Richard C.

2014-03-01

Single-bond rotations or pyramidal inversions tend to either hide or expose relative energies that exist for atoms with nonbonding lone-pair electrons. Availability of lone-pair electrons depends on overall molecular electron distributions and differences in the immediate polarity of the surrounding pico/nanoenvironment. Stereochemistry three-dimensional aspects of molecules provide insight into conformations through single-bond rotations with associated lone-pair electrons on oxygen atoms in addition to pyramidal inversions with nitrogen atoms. When electrons are protected, potential energy is sheltered toward an energy minimum value to compatibilize molecularly with nonpolar environments. When electrons are exposed, maximum energy is available toward polar environment interactions. Computational conformational analysis software calculated energy profiles that exist during specific oxygen ether single-bond rotations with easy-to-visualize three-dimensional models for the trichlorinated bisaromatic ether triclosan antimicrobial polymer additive. As shown, fluctuating alternating bond rotations can produce complex interactions between molecules to provide entanglement strength for polymer toughness or alternatively disrupt weak secondary bonds of attraction to lower resin viscosity for new additive properties with nonpolar triclosan as a hydrophobic toughening/wetting agent. Further, bond rotations involving lone-pair electrons by a molecule at a nonpolar-hydrocarbon-membrane/polar-biologic-fluid interface might become sufficiently unstable to provide free mechanomolecular energies to disrupt weaker microbial membranes, for membrane transport of molecules into cells, provide cell signaling/recognition/defense and also generate enzyme mixing to speed reactions.

On energetic prerequisites of attracting electrons

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

Sundholm, Dage

The internal reorganization energy and the zero-point vibrational energy (ZPE) of fractionally charged molecules embedded in molecular materials are discussed. The theory for isolated open quantum systems is taken as the starting point. It is shown that for isolated molecules the internal reorganization-energy function and its slope, i.e., the chemical potential of an open molecular system are monotonically decreasing functions with respect to increasing amount of negative excess charge (q) in the range of q = [0, 1]. Calculations of the ZPE for fractionally charged molecules show that the ZPE may have a minimum for fractional occupation. The calculations showmore » that the internal reorganization energy and changes in the ZPE are of the same order of magnitude with different behavior as a function of the excess charge. The sum of the contributions might favor molecules with fractional occupation of the molecular units and partial delocalization of the excess electrons in solid-state materials also when considering Coulomb repulsion between the excess electrons. The fractional electrons are then coherently distributed on many molecules of the solid-state material forming a condensate of attracting electrons, which is crucial for the superconducting state.« less

Heating a plasma by a broadband stream of fast electrons: Fast ignition, shock ignition, and Gbar shock wave applications

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

Gus’kov, S. Yu., E-mail: guskov@sci.lebedev.ru; Nicolai, Ph.; Ribeyre, X.

2015-09-15

An exact analytic solution is found for the steady-state distribution function of fast electrons with an arbitrary initial spectrum irradiating a planar low-Z plasma with an arbitrary density distribution. The solution is applied to study the heating of a material by fast electrons of different spectra such as a monoenergetic spectrum, a step-like distribution in a given energy range, and a Maxwellian spectrum, which is inherent in laser-produced fast electrons. The heating of shock- and fast-ignited precompressed inertial confinement fusion (ICF) targets as well as the heating of a target designed to generate a Gbar shock wave for equation ofmore » state (EOS) experiments by laser-produced fast electrons with a Maxwellian spectrum is investigated. A relation is established between the energies of two groups of Maxwellian fast electrons, which are responsible for generation of a shock wave and heating the upstream material (preheating). The minimum energy of the fast and shock igniting beams as well as of the beam for a Gbar shock wave generation increases with the spectral width of the electron distribution.« less

Competition Between Radial Loss and EMIC Wave Scattering of MeV Electrons During Strong CME-shock Driven Storms

NASA Astrophysics Data System (ADS)

Hudson, M. K.; Jaynes, A. N.; Li, Z.; Malaspina, D.; Millan, R. M.; Patel, M.; Qin, M.; Shen, X.; Wiltberger, M. J.

2017-12-01

The two strongest storms of Solar Cycle 24, 17 March and 22 June 2015, provide a contrast between magnetospheric response to CME-shocks at equinox and solstice. The 17 March CME-shock initiated storm produced a stronger ring current response with Dst = - 223 nT, while the 22 June CME-shock initiated storm reached a minimum Dst = - 204 nT. The Van Allen Probes ECT instrument measured a dropout in flux for both events which can be characterized by magnetopause loss at higher L values prior to strong recovery1. However, rapid loss is seen at L 3 for the June storm at high energies with maximum drop in the 5.2 MeV channel of the REPT instrument coincident with the observation of EMIC waves in the H+ band by the EMFISIS wave instrument. The rapid time scale of loss can be determined from the 65 minute delay in passage of the Probe A relative to the Probe B spacecraft. The distinct behavior of lower energy electrons at higher L values has been modeled with MHD-test particle simulations, while the rapid loss of higher energy electrons is examined in terms of the minimum resonant energy criterion for EMIC wave scattering, and compared with the timescale for loss due to EMIC wave scattering which has been modeled for other storm events.2 1Baker, D. N., et al. (2016), Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015, J. Geophys. Res. Space Physics, 121, 6647-6660, doi:10.1002/2016JA022502. 2Li, Z., et al. (2014), Investigation of EMIC wave scattering as the cause for the BARREL 17 January 2013 relativistic electron precipitation event: A quantitative comparison of simulation with observations, Geophys. Res. Lett., 41, 8722-8729, doi:10.1002/2014GL062273.

Analysis of Nuclear Propagation Effects Utilizing Wideband Satellite Data.

DTIC Science & Technology

1981-04-01

integrated phase spectral energy on scales shorter than - 30 km. Like the TEC, the standard deviation of phase depends on the effective thickness of...Vila, P., "Etude Experimentale de L’Anomalie lonospherique Equatoriale en Afrique en Periode de Minimum Solaire ," Annales de Geophysique, Vol. 22, No...AFRDSP AT[: OP 65 ATTN: AFRDSS 82 DEPARTMENT OF THE AIR FORCE (Continued) DEPARTMENT OF ENERGY CONTRACTORS Electronic Systems Div EG&U, Inc Air force

Electronic effects on melting: Comparison of aluminum cluster anions and cations

NASA Astrophysics Data System (ADS)

Starace, Anne K.; Neal, Colleen M.; Cao, Baopeng; Jarrold, Martin F.; Aguado, Andrés; López, José M.

2009-07-01

Heat capacities have been measured as a function of temperature for aluminum cluster anions with 35-70 atoms. Melting temperatures and latent heats are determined from peaks in the heat capacities; cohesive energies are obtained for solid clusters from the latent heats and dissociation energies determined for liquid clusters. The melting temperatures, latent heats, and cohesive energies for the aluminum cluster anions are compared to previous measurements for the corresponding cations. Density functional theory calculations have been performed to identify the global minimum energy geometries for the cluster anions. The lowest energy geometries fall into four main families: distorted decahedral fragments, fcc fragments, fcc fragments with stacking faults, and "disordered" roughly spherical structures. The comparison of the cohesive energies for the lowest energy geometries with the measured values allows us to interpret the size variation in the latent heats. Both geometric and electronic shell closings contribute to the variations in the cohesive energies (and latent heats), but structural changes appear to be mainly responsible for the large variations in the melting temperatures with cluster size. The significant charge dependence of the latent heats found for some cluster sizes indicates that the electronic structure can change substantially when the cluster melts.

Refined energetic ordering for sulphate-water (n = 3-6) clusters using high-level electronic structure calculations

NASA Astrophysics Data System (ADS)

Lambrecht, Daniel S.; McCaslin, Laura; Xantheas, Sotiris S.; Epifanovsky, Evgeny; Head-Gordon, Martin

2012-10-01

This work reports refinements of the energetic ordering of the known low-energy structures of sulphate-water clusters ? (n = 3-6) using high-level electronic structure methods. Coupled cluster singles and doubles with perturbative triples (CCSD(T)) is used in combination with an estimate of basis set effects up to the complete basis set limit using second-order Møller-Plesset theory. Harmonic zero-point energy (ZPE), included at the B3LYP/6-311 + + G(3df,3pd) level, was found to have a significant effect on the energetic ordering. In fact, we show that the energetic ordering is a result of a delicate balance between the electronic and vibrational energies. Limitations of the ZPE calculations, both due to electronic structure errors, and use of the harmonic approximation, probably constitute the largest remaining errors. Due to the often small energy differences between cluster isomers, and the significant role of ZPE, deuteration can alter the relative energies of low-lying structures, and, when it is applied in conjunction with calculated harmonic ZPEs, even alters the global minimum for n = 5. Experiments on deuterated clusters, as well as more sophisticated vibrational calculations, may therefore be quite interesting.

Simulation of the energy distribution of relativistic electron precipitation caused by quasi-linear interactions with EMIC waves.

PubMed

Li, Zan; Millan, Robyn M; Hudson, Mary K

2013-12-01

[1]Previous studies on electromagnetic ion cyclotron (EMIC) waves as a possible cause of relativistic electron precipitation (REP) mainly focus on the time evolution of the trapped electron flux. However, directly measured by balloons and many satellites is the precipitating flux as well as its dependence on both time and energy. Therefore, to better understand whether pitch angle scattering by EMIC waves is an important radiation belt electron loss mechanism and whether quasi-linear theory is a sufficient theoretical treatment, we simulate the quasi-linear wave-particle interactions for a range of parameters and generate energy spectra, laying the foundation for modeling specific events that can be compared with balloon and spacecraft observations. We show that the REP energy spectrum has a peaked structure, with a lower cutoff at the minimum resonant energy. The peak moves with time toward higher energies and the spectrum flattens. The precipitating flux, on the other hand, first rapidly increases and then gradually decreases. We also show that increasing wave frequency can lead to the occurrence of a second peak. In both single- and double-peak cases, increasing wave frequency, cold plasma density or decreasing background magnetic field strength lowers the energies of the peak(s) and causes the precipitation to increase at low energies and decrease at high energies at the start of the precipitation.

The structure of high-temperature solar flare plasma in non-thermal flare models

NASA Technical Reports Server (NTRS)

Emslie, A. G.

1985-01-01

Analytic differential emission measure distributions have been derived for coronal plasma in flare loops heated both by collisions of high-energy suprathermal electrons with background plasma, and by ohmic heating by the beam-normalizing return current. For low densities, reverse current heating predominates, while for higher densities collisional heating predominates. There is thus a minimum peak temperature in an electron-heated loop. In contrast to previous approximate analyses, it is found that a stable reverse current can dominate the heating rate in a flare loop, especially in the low corona. Two 'scaling laws' are found which relate the peak temperature in the loop to the suprathermal electron flux. These laws are testable observationally and constitute a new diagnostic procedure for examining modes of energy transport in flaring loops.

Electronic Structure of Two-Dimensional Hydrocarbon Networks of sp2 and sp3 C Atoms

NASA Astrophysics Data System (ADS)

Fujii, Yasumaru; Maruyama, Mina; Wakabayashi, Katsunori; Nakada, Kyoko; Okada, Susumu

2018-03-01

Based on density functional theory with the generalized gradient approximation, we have investigated the geometric and electronic structures of two-dimensional hexagonal covalent networks consisting of oligoacenes and fourfold coordinated hydrocarbon atoms, which are alternately arranged in a hexagonal manner. All networks were semiconductors with a finite energy gap at the Γ point, which monotonically decreased with the increase of the oligoacene length. As a result of a Kagome network of oligoacene connected through sp3 C atoms, the networks possess peculiar electron states in their valence and conduction bands, which consist of a flat dispersion band and a Dirac cone. The total energy of the networks depends on the oligoacene length and has a minimum for the network comprising naphthalene.

Use of density functional theory method to calculate structures of neutral carbon clusters C{sub n} (3 ≤ n ≤ 24) and study their variability of structural forms

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

Yen, T. W.; Lai, S. K., E-mail: sklai@coll.phy.ncu.edu.tw

2015-02-28

In this work, we present modifications to the well-known basin hopping (BH) optimization algorithm [D. J. Wales and J. P. Doye, J. Phys. Chem. A 101, 5111 (1997)] by incorporating in it the unique and specific nature of interactions among valence electrons and ions in carbon atoms through calculating the cluster’s total energy by the density functional tight-binding (DFTB) theory, using it to find the lowest energy structures of carbon clusters and, from these optimized atomic and electronic structures, studying their varied forms of topological transitions, which include a linear chain, a monocyclic to a polycyclic ring, and a fullerene/cage-likemore » geometry. In this modified BH (MBH) algorithm, we define a spatial volume within which the cluster’s lowest energy structure is to be searched, and introduce in addition a cut-and-splice genetic operator to increase the searching performance of the energy minimum than the original BH technique. The present MBH/DFTB algorithm is, therefore, characteristically distinguishable from the original BH technique commonly applied to nonmetallic and metallic clusters, technically more thorough and natural in describing the intricate couplings between valence electrons and ions in a carbon cluster, and thus theoretically sound in putting these two charged components on an equal footing. The proposed modified minimization algorithm should be more appropriate, accurate, and precise in the description of a carbon cluster. We evaluate the present algorithm, its energy-minimum searching in particular, by its optimization robustness. Specifically, we first check the MBH/DFTB technique for two representative carbon clusters of larger size, i.e., C{sub 60} and C{sub 72} against the popular cut-and-splice approach [D. M. Deaven and K. M. Ho, Phys. Rev. Lett. 75, 288 (1995)] that normally is combined with the genetic algorithm method for finding the cluster’s energy minimum, before employing it to investigate carbon clusters in the size range C{sub 3}-C{sub 24} studying their topological transitions. An effort was also made to compare our MBH/DFTB and its re-optimized results carried out by full density functional theory (DFT) calculations with some early DFT-based studies.« less

Dynamic Electron Correlation Effects on the Ground State Potential Energy Surface of a Retinal Chromophore Model.

PubMed

Gozem, Samer; Huntress, Mark; Schapiro, Igor; Lindh, Roland; Granovsky, Alexander A; Angeli, Celestino; Olivucci, Massimo

2012-11-13

The ground state potential energy surface of the retinal chromophore of visual pigments (e.g., bovine rhodopsin) features a low-lying conical intersection surrounded by regions with variable charge-transfer and diradical electronic structures. This implies that dynamic electron correlation may have a large effect on the shape of the force fields driving its reactivity. To investigate this effect, we focus on mapping the potential energy for three paths located along the ground state CASSCF potential energy surface of the penta-2,4-dieniminium cation taken as a minimal model of the retinal chromophore. The first path spans the bond length alternation coordinate and intercepts a conical intersection point. The other two are minimum energy paths along two distinct but kinetically competitive thermal isomerization coordinates. We show that the effect of introducing the missing dynamic electron correlation variationally (with MRCISD) and perturbatively (with the CASPT2, NEVPT2, and XMCQDPT2 methods) leads, invariably, to a stabilization of the regions with charge transfer character and to a significant reshaping of the reference CASSCF potential energy surface and suggesting a change in the dominating isomerization mechanism. The possible impact of such a correction on the photoisomerization of the retinal chromophore is discussed.

Absolute vibrational numbering from isotope shifts in fragmentary spectroscopic data

NASA Astrophysics Data System (ADS)

Pashov, A.; Kowalczyk, P.; Jastrzebski, W.

2018-05-01

We discuss application of the isotope effect to establish the absolute vibrational numbering in electronic states of diatomic molecules. This is illustrated by examples of states with potential energy curves of both regular and irregular shape, with one or two potential minima. The minimum number of spectroscopic data (either term values or spectral line positions) necessary to provide a unique numbering is considered. We show that at favourable conditions just four term energies (or spectral lines) in one isotopologue and one term energy in the other suffice.

Phase inversion and frequency doubling of reflection high-energy electron diffraction intensity oscillations in the layer-by-layer growth of complex oxides

NASA Astrophysics Data System (ADS)

Mao, Zhangwen; Guo, Wei; Ji, Dianxiang; Zhang, Tianwei; Gu, Chenyi; Tang, Chao; Gu, Zhengbin; Nie*, Yuefeng; Pan, Xiaoqing

In situ reflection high-energy electron diffraction (RHEED) and its intensity oscillations are extremely important for the growth of epitaxial thin films with atomic precision. The RHEED intensity oscillations of complex oxides are, however, rather complicated and a general model is still lacking. Here, we report the unusual phase inversion and frequency doubling of RHEED intensity oscillations observed in the layer-by-layer growth of SrTiO3 using oxide molecular beam epitaxy. In contacts to the common understanding that the maximum(minimum) intensity occurs at SrO(TiO2) termination, respectively, we found that both maximum or minimum intensities can occur at SrO, TiO2, or even incomplete terminations depending on the incident angle of the electron beam, which raises a fundamental question if one can rely on the RHEED intensity oscillations to precisely control the growth of thin films. A general model including surface roughness and termination dependent mean inner potential qualitatively explains the observed phenomena, and provides the answer to the question how to prepare atomically and chemically precise surface/interfaces using RHEED oscillations for complex oxides. We thank National Basic Research Program of China (No. 11574135, 2015CB654901) and the National Thousand-Young-Talents Program.

Ground and excited states of vanadium hydroxide isomers and their cations, VOH0,+ and HVO0,+

NASA Astrophysics Data System (ADS)

Miliordos, Evangelos; Harrison, James F.; Hunt, Katharine L. C.

2013-03-01

Employing correlation consistent basis sets of quadruple-zeta quality and applying both multireference configuration interaction and single-reference coupled cluster methodologies, we studied the electronic and geometrical structure of the [V,O,H]0,+ species. The electronic structure of HVO0,+ is explained by considering a hydrogen atom approaching VO0,+, while VOH0,+ molecules are viewed in terms of the interaction of V+,2+ with OH-. The potential energy curves for H-VO0,+ and V0,+-OH have been constructed as functions of the distance between the interacting subunits, and the potential energy curves have also been determined as functions of the H-V-O angle. For the stationary points that we have located, we report energies, geometries, harmonic frequencies, and dipole moments. We find that the most stable bent HVO0,+ structure is lower in energy than any of the linear HVO0,+ structures. Similarly, the most stable state of bent VOH is lower in energy than the linear structures, but linear VOH+ is lower in energy than bent VOH+. The global minimum on the potential energy surface for the neutral species is the tilde{X}^3A″ state of bent HVO, although the tilde{X}^5A″ state of bent VOH is less than 5 kcal/mol higher in energy. The global minimum on the potential surface for the cation is the tilde{X}^4Σ ^- state of linear VOH+, with bent VOH+ and bent HVO+ both more than 10 kcal/mol higher in energy. For the neutral species, the bent geometries exhibit significantly higher dipole moments than the linear structures.

A surface hopping algorithm for nonadiabatic minimum energy path calculations.

PubMed

Schapiro, Igor; Roca-Sanjuán, Daniel; Lindh, Roland; Olivucci, Massimo

2015-02-15

The article introduces a robust algorithm for the computation of minimum energy paths transiting along regions of near-to or degeneracy of adiabatic states. The method facilitates studies of excited state reactivity involving weakly avoided crossings and conical intersections. Based on the analysis of the change in the multiconfigurational wave function the algorithm takes the decision whether the optimization should continue following the same electronic state or switch to a different state. This algorithm helps to overcome convergence difficulties near degeneracies. The implementation in the MOLCAS quantum chemistry package is discussed. To demonstrate the utility of the proposed procedure four examples of application are provided: thymine, asulam, 1,2-dioxetane, and a three-double-bond model of the 11-cis-retinal protonated Schiff base. © 2015 Wiley Periodicals, Inc.

Searches for cosmic-ray electron anisotropies with the Fermi Large Area Telescope

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

Ackermann, M.; Ajello, M.; Bechtol, K.

The Large Area Telescope on board the Fermi satellite (Fermi LAT) detected more than 1.6x10{sup 6} cosmic-ray electrons/positrons with energies above 60 GeV during its first year of operation. The arrival directions of these events were searched for anisotropies of angular scale extending from {approx}10 deg. up to 90 deg., and of minimum energy extending from 60 GeV up to 480 GeV. Two independent techniques were used to search for anisotropies, both resulting in null results. Upper limits on the degree of the anisotropy were set that depended on the analyzed energy range and on the anisotropy's angular scale. Themore » upper limits for a dipole anisotropy ranged from {approx}0.5% to {approx}10%.« less

Searches for cosmic-ray electron anisotropies with the Fermi Large Area Telescope

DOE PAGES

Ackermann, M.

2010-11-01

The Large Area Telescope on board the Fermi satellite (Fermi LAT) detected more than 1.6 × 10 6 cosmic-ray electrons/positrons with energies above 60 GeV during its first year of operation. The arrival directions of these events were searched for anisotropies of angular scale extending from ~ 10 ° up to 90°, and of minimum energy extending from 60 GeV up to 480 GeV. Two independent techniques were used to search for anisotropies, both resulting in null results. Upper limits on the degree of the anisotropy were set that depended on the analyzed energy range and on the anisotropy’s angularmore » scale. The upper limits for a dipole anisotropy ranged from ~ 0.5 % to ~ 10 % .« less

The thermoluminescence response of doped SiO2 optical fibres subjected to photon and electron irradiations.

PubMed

Hashim, S; Al-Ahbabi, S; Bradley, D A; Webb, M; Jeynes, C; Ramli, A T; Wagiran, H

2009-03-01

Modern linear accelerators, the predominant teletherapy machine in major radiotherapy centres worldwide, provide multiple electron and photon beam energies. To obtain reasonable treatment times, intense electron beam currents are achievable. In association with this capability, there is considerable demand to validate patient dose using systems of dosimetry offering characteristics that include good spatial resolution, high precision and accuracy. Present interest is in the thermoluminescence response and dosimetric utility of commercially available doped optical fibres. The important parameter for obtaining the highest TL yield during this study is to know the dopant concentration of the SiO2 fibre because during the production of the optical fibres, the dopants tend to diffuse. To achieve this aim, proton-induced X-ray emission (PIXE), which has no depth resolution but can unambiguously identify elements and analyse for trace elements with detection limits approaching microg/g, was used. For Al-doped fibres, the dopant concentration in the range 0.98-2.93 mol% have been estimated, with equivalent range for Ge-doped fibres being 0.53-0.71 mol%. In making central-axis irradiation measurements a solid water phantom was used. For 6-MV photons and electron energies in the range 6, 9 and 12 MeV, a source to surface distance of 100 cm was used, with a dose rate of 400 cGy/min for photons and electrons. The TL measurements show a linear dose-response over the delivered range of absorbed dose from 1 to 4 Gy. Fading was found to be minimal, less than 10% over five days subsequent to irradiation. The minimum detectable dose for 6-MV photons was found to be 4, 30 and 900 microGy for TLD-100 chips, Ge- and Al-doped fibres, respectively. For 6-, 9- and 12-MeV electron energies, the minimum detectable dose were in the range 3-5, 30-50 and 800-1400 microGy for TLD-100 chip, Ge-doped and Al-doped fibres, respectively.

Universality of Electron Distributions in Extensive Air Showers

NASA Astrophysics Data System (ADS)

Śmiałkowski, Andrzej; Giller, Maria

2018-02-01

Based on extensive air shower simulations, it is shown that electron distributions with respect to two angles determining the electron direction at a given shower age, for a fixed electron energy and lateral distance, are universal. This means that the distributions do not depend on the primary particle energy or mass (thus, neither on the interaction model), shower zenith angle, or shower to shower fluctuations, if they are taken at the same shower age. Together with previous work showing the universality of the distributions of the electron energy, lateral distance (integrated over angles), and angle (integrated over lateral distance) for fixed electron energy, this paper completes a full universal description of the electron states at various shower ages. Analytical parametrizations of the full electron states are given. It is also shown that some distributions can be described by a number of variables smaller than five, with the new ones being products of old ones raised to some power. The accuracy of the present parametrization is sufficiently good to apply to showers with a primary energy uncertainty of 14% (as is the case at the Pierre Auger Observatory). The shower fluctuations in the chosen bins of the multidimensional variable space are about 6%, determining the minimum uncertainty needed for the parametrization of the universal distributions. An analytical way of estimating the effect of the geomagnetic field is given. Thanks to the universality of the electron distribution in any shower, a new method of shower reconstruction can be worked out from the data from observatories using the fluorescence technique. The light fluxes (both fluorescence and Cherenkov) for any shower age can be exactly predicted for a shower with any primary energy and shower maximum depth, so that the two quantities can be obtained by best fitting the predictions to the measurements.

Ground and excited states of CaSH through electron propagator calculations

NASA Astrophysics Data System (ADS)

Ortiz, J. V.

1990-05-01

Electron propagator calculations of electron affinities of CaSH + produce ground and excited state energies at the optimized, C s minimum of the neutral ground state and at a C ∞v geometry. Feynman-Dyson amplitudes (FDAs) describe the distribution of the least bound electron in various states. The neutral ground state differs from the cation by the occupation of a one-electron state dominated by Ca s functions. Described by FDAs with Ca-S π pseudosymmetry, corresponding excited states have unpaired electrons in orbitals displaying interference between Ca p and d functions. Above these lies a σ pseudosymmetry FDA with principal contributions from Ca d functions. Two FDAs with σ pseudosymmetry follow. Higher excited states exhibit considerable delocalization onto S.

Electron Heat Flux in Pressure Balance Structures at Ulysses

NASA Technical Reports Server (NTRS)

Yamauchi, Yohei; Suess, Steven T.; Sakurai, Takashi; Whitaker, Ann F. (Technical Monitor)

2001-01-01

Pressure balance structures (PBSs) are a common feature in the high-latitude solar wind near solar minimum. Rom previous studies, PBSs are believed to be remnants of coronal plumes and be related to network activity such as magnetic reconnection in the photosphere. We investigated the magnetic structures of the PBSs, applying a minimum variance analysis to Ulysses/Magnetometer data. At 2001 AGU Spring meeting, we reported that PBSs have structures like current sheets or plasmoids, and suggested that they are associated with network activity at the base of polar plumes. In this paper, we have analyzed high-energy electron data at Ulysses/SWOOPS to see whether bi-directional electron flow exists and confirm the conclusions more precisely. As a result, although most events show a typical flux directed away from the Sun, we have obtained evidence that some PBSs show bi-directional electron flux and others show an isotropic distribution of electron pitch angles. The evidence shows that plasmoids are flowing away from the Sun, changing their flow direction dynamically in a way not caused by Alfven waves. From this, we have concluded that PBSs are generated due to network activity at the base of polar plumes and their magnetic structures axe current sheets or plasmoids.

Elastic collisions of low-energy electrons with SiY4 (Y = Cl, Br, I) molecules

NASA Astrophysics Data System (ADS)

Bettega, M. H. F.

2011-11-01

We employed the Schwinger multichannel method to compute elastic integral, differential, and momentum transfer cross sections for low-energy electron collisions with SiY4 (Y = Cl, Br, I) molecules. The calculations were carried out in the static-exchange and static-exchange plus polarization approximations for energies up to 10 eV. The elastic integral cross section for SiCl4 and SiBr4, computed in the static-exchange plus polarization approximation, shows two shape resonances belonging to the T2 and E symmetries of the Td group, and for SiI4 shows one shape resonance belonging to the E symmetry of the Td group. The present results agree well in shape with experimental total cross sections. The positions of the resonances observed in the calculated integral cross sections are also in agreement with the experimental positions. We have found the presence of a virtual state for SiCl4 and a Ramsauer-Townsend minimum for SiI4 at 0.5 eV. The present results show that the proper inclusion of polarization effects is crucial in order to correctly describe the resonance spectra of these molecules and also to identify a Ramsauer-Townsend minimum for SiI4 and a virtual state for SiCl4.

Ignition threshold for non-Maxwellian plasmas

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

Hay, Michael J., E-mail: hay@princeton.edu; Fisch, Nathaniel J.; Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543

2015-11-15

An optically thin p-{sup 11}B plasma loses more energy to bremsstrahlung than it gains from fusion reactions, unless the ion temperature can be elevated above the electron temperature. In thermal plasmas, the temperature differences required are possible in small Coulomb logarithm regimes, characterized by high density and low temperature. Ignition could be reached more easily if the fusion reactivity can be improved with nonthermal ion distributions. To establish an upper bound for the potential utility of a nonthermal distribution, we consider a monoenergetic beam with particle energy selected to maximize the beam-thermal reactivity. Comparing deuterium-tritium (DT) and p-{sup 11}B, themore » minimum Lawson criteria and minimum ρR required for inertial confinement fusion (ICF) volume ignition are calculated with and without the nonthermal feature. It turns out that channeling fusion alpha energy to maintain such a beam facilitates ignition at lower densities and ρR, improves reactivity at constant pressure, and could be used to remove helium ash. On the other hand, the reactivity gains that could be realized in DT plasmas are significant, the excess electron density in p-{sup 11}B plasmas increases the recirculated power cost to maintain a nonthermal feature and thereby constrains its utility to ash removal.« less

DFT study of gases adsorption on sharp tip nano-catalysts surface for green fertilizer synthesis

NASA Astrophysics Data System (ADS)

Yahya, Noorhana; Irfan, Muhammad; Shafie, Afza; Soleimani, Hassan; Alqasem, Bilal; Rehman, Zia Ur; Qureshi, Saima

2016-11-01

The energy minimization and spin modifications of sorbates with sorbents in magnetic induction method (MIM) play a vital role in yield of fertilizer. Hence, in this article the focus of study is the interaction of sorbates/reactants (H2, N2 and CO2) in term of average total adsorption energies, average isosteric heats of adsorption energies, magnetic moments, band gaps energies and spin modifications over identical cone tips nanocatalyst (sorbents) of Fe2O3, Fe3O4 (magnetic), CuO and Al2O3 (non-magnetic) for green nano-fertilizer synthesis. Study of adsorption energy, band structures and density of states of reactants with sorbents are purely classical and quantum mechanical based concepts that are vividly illustrated and supported by ADSORPTION LOCATOR and Cambridge Seriel Total Energy Package (CASTEP) modules following classical and first principle DFT simulation study respectively. Maximum values of total average energies, total average adsorption energies and average adsorption energies of H2, N2 and CO2 molecules are reported as -14.688 kcal/mol, -13.444 kcal/mol, -3.130 kcal/mol, - kcal/mol and -6.348 kcal/mol over Al2O3 cone tips respectively and minimum over magnetic cone tips. Whereas, the maximum and average minimum values of average isosteric heats of adsorption energies of H2, N2 and CO2 molecules are figured out to be 3.081 kcal/mol, 4.842 kcal/mol and 6.848 kcal/mol, 0.988 kcal/mol, 1.554 kcal/mol and 2.236 kcal/mol over aluminum oxide and Fe3O4 cone tips respectively. In addition to the adsorption of reactants over identical cone sorbents the maximum and minimum values of net spin, electrons and number of bands for magnetite and aluminum oxide cone structures are attributed to 82 and zero, 260 and 196, 206 and 118 for Fe3O4 and Al2O3 cones respectively. Maximum and least observed values of band gap energies are figured out to be 0.188 eV and 0.018 eV with Al2O3 and Fe3O4 cone structures respectively. Ultimately, with the adsorption of reactants an identical increment of 14 electrons each in up and down spins is resulted.

Organic semiconductor density of states controls the energy level alignment at electrode interfaces

PubMed Central

Oehzelt, Martin; Koch, Norbert; Heimel, Georg

2014-01-01

Minimizing charge carrier injection barriers and extraction losses at interfaces between organic semiconductors and metallic electrodes is critical for optimizing the performance of organic (opto-) electronic devices. Here, we implement a detailed electrostatic model, capable of reproducing the alignment between the electrode Fermi energy and the transport states in the organic semiconductor both qualitatively and quantitatively. Covering the full phenomenological range of interfacial energy level alignment regimes within a single, consistent framework and continuously connecting the limiting cases described by previously proposed models allows us to resolve conflicting views in the literature. Our results highlight the density of states in the organic semiconductor as a key factor. Its shape and, in particular, the energy distribution of electronic states tailing into the fundamental gap is found to determine both the minimum value of practically achievable injection barriers as well as their spatial profile, ranging from abrupt interface dipoles to extended band-bending regions. PMID:24938867

Electron self-energy in a homogeneous magnetic field

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

Gepraegs, R.; Riffert, H.; Herold, H.

1994-05-15

A relativistic calculation of the electron self-energy in a strong homogeneous magnetic field is presented, and the final expressions are calculated numerically for the Landau levels [ital N]=0,1,2,3 and both spin projections ([sigma]=[plus minus]1). For a given [ital N][gt]0 the energy of the spin-up state ([sigma]=+1) increases monotonically, but the spin-down ([sigma]=[minus]1) energy is negative for small fields, shows a minimum, and then increases for large fields; a crossing of levels appears for [ital N][gt]0. The total decay rates for these states are also obtained, as well as the spin-flip transition probability for ([ital N]=1, [sigma]=+1)[r arrow]([ital N]=1, [sigma]=[minus]1). Itmore » turns out that this transition rate is extremely small compared to the usual cyclotron emission rates.« less

Proton and Electron Threshold Energy Measurements for Extravehicular Activity Space Suits. Chapter 2

NASA Technical Reports Server (NTRS)

Moyers, M. F.; Nelson, G. D.; Saganti, P. B.

2003-01-01

Construction of ISS will require more than 1000 hours of EVA. Outside of ISS during EVA, astronauts and cosmonauts are likely to be exposed to a large fluence of electrons and protons. Development of radiation protection guidelines requires the determination of the minimum energy of electrons and protons that penetrate the suits at various locations. Measurements of the water-equivalent thickness of both US. and Russian EVA suits were obtained by performing CT scans. Specific regions of interest of the suits were further evaluated using a differential range shift technique. This technique involved measuring thickness ionization curves for 6-MeV electron and 155-MeV proton beams with ionization chambers using a constant source-to-detector distance. The thicknesses were obtained by stacking polystyrene slabs immediately upstream of the detector. The thicknesses of the 50% ionizations relative to the maximum ionizations were determined. The detectors were then placed within the suit and the stack thickness adjusted until the 50% ionization was reestablished. The difference in thickness between the 50% thicknesses was then used with standard range-energy tables to determine the threshold energy for penetration. This report provides a detailed description of the experimental arrangement and results.

Solar wind ∼0.1-1.5 keV electrons at quiet times

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

Tao, Jiawei; Wang, Linghua, E-mail: wanglhwang@gmail.com; Zong, Qiugang

2016-03-25

We present a statistical survey of the energy spectrum of solar wind suprathermal (∼0.1-1.5 keV) electrons measured by the WIND 3-D Plasma & Energetic Particle (3DP) instrument at 1 AU during quiet times at the minimum and maximum of solar cycles 23 and 24. Firstly, we separate strahl (beaming) electrons and halo (isotropic) electrons based on their features in pitch angle distributions. Secondly, we fit the observed energy spectrum of both the strahl and halo electrons at ∼0.1-1.5 keV to a Kappa distribution function with an index κ, effective temperature T{sub eff} and density n{sub 0}. We also integrate themore » the measurements over ∼0.1-1.5 keV to obtain the average electron energy E{sub avg} of the strahl and halo. We find a strong positive correlation between κ and T{sub eff} for both the strahl and halo, possibly reflecting the nature of the generation of these suprathermal electrons. Among the 245 selected samples, ∼68% have the halo κ smaller than the strahl κ, while ∼50% have the halo E{sub h} larger than the strahl E{sub s}.« less

Energy consumption program: A computer model simulating energy loads in buildings

NASA Technical Reports Server (NTRS)

Stoller, F. W.; Lansing, F. L.; Chai, V. W.; Higgins, S.

1978-01-01

The JPL energy consumption computer program developed as a useful tool in the on-going building modification studies in the DSN energy conservation project is described. The program simulates building heating and cooling loads and computes thermal and electric energy consumption and cost. The accuracy of computations are not sacrificed, however, since the results lie within + or - 10 percent margin compared to those read from energy meters. The program is carefully structured to reduce both user's time and running cost by asking minimum information from the user and reducing many internal time-consuming computational loops. Many unique features were added to handle two-level electronics control rooms not found in any other program.

Uniform electron gases. III. Low-density gases on three-dimensional spheres.

PubMed

Agboola, Davids; Knol, Anneke L; Gill, Peter M W; Loos, Pierre-François

2015-08-28

By combining variational Monte Carlo (VMC) and complete-basis-set limit Hartree-Fock (HF) calculations, we have obtained near-exact correlation energies for low-density same-spin electrons on a three-dimensional sphere (3-sphere), i.e., the surface of a four-dimensional ball. In the VMC calculations, we compare the efficacies of two types of one-electron basis functions for these strongly correlated systems and analyze the energy convergence with respect to the quality of the Jastrow factor. The HF calculations employ spherical Gaussian functions (SGFs) which are the curved-space analogs of Cartesian Gaussian functions. At low densities, the electrons become relatively localized into Wigner crystals, and the natural SGF centers are found by solving the Thomson problem (i.e., the minimum-energy arrangement of n point charges) on the 3-sphere for various values of n. We have found 11 special values of n whose Thomson sites are equivalent. Three of these are the vertices of four-dimensional Platonic solids - the hyper-tetrahedron (n = 5), the hyper-octahedron (n = 8), and the 24-cell (n = 24) - and a fourth is a highly symmetric structure (n = 13) which has not previously been reported. By calculating the harmonic frequencies of the electrons around their equilibrium positions, we also find the first-order vibrational corrections to the Thomson energy.

Electron acceleration by surface plasma waves in double metal surface structure

NASA Astrophysics Data System (ADS)

Liu, C. S.; Kumar, Gagan; Singh, D. B.; Tripathi, V. K.

2007-12-01

Two parallel metal sheets, separated by a vacuum region, support a surface plasma wave whose amplitude is maximum on the two parallel interfaces and minimum in the middle. This mode can be excited by a laser using a glass prism. An electron beam launched into the middle region experiences a longitudinal ponderomotive force due to the surface plasma wave and gets accelerated to velocities of the order of phase velocity of the surface wave. The scheme is viable to achieve beams of tens of keV energy. In the case of a surface plasma wave excited on a single metal-vacuum interface, the field gradient normal to the interface pushes the electrons away from the high field region, limiting the acceleration process. The acceleration energy thus achieved is in agreement with the experimental observations.

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

Junay, A.; Guézo, S., E-mail: sophie.guezo@univ-rennes1.fr; Turban, P.

We study structural and electronic inhomogeneities in Metal—Organic Molecular monoLayer (OML)—semiconductor interfaces at the sub-nanometer scale by means of in situ Ballistic Electron Emission Microscopy (BEEM). BEEM imaging of Au/1-hexadecanethiols/GaAs(001) heterostructures reveals the evolution of pinholes density as a function of the thickness of the metallic top-contact. Using BEEM in spectroscopic mode in non-short-circuited areas, local electronic fingerprints (barrier height values and corresponding spectral weights) reveal a low-energy tunneling regime through the insulating organic monolayer. At higher energies, BEEM evidences new conduction channels, associated with hot-electron injection in the empty molecular orbitals of the OML. Corresponding band diagrams at buriedmore » interfaces can be thus locally described. The energy position of GaAs conduction band minimum in the heterostructure is observed to evolve as a function of the thickness of the deposited metal, and coherently with size-dependent electrostatic effects under the molecular patches. Such BEEM analysis provides a quantitative diagnosis on metallic top-contact formation on organic molecular monolayer and appears as a relevant characterization for its optimization.« less

Langmuir Probe Measurements in an Inductively Coupled Ar/CF4 Plasmas

NASA Technical Reports Server (NTRS)

Rao, M. V. V. S.; Meyyappan, M.; Sharma, S. P.; Arnold, James O. (Technical Monitor)

2000-01-01

Technological advancement in the microelectronics industry requires an understanding of the physical and chemical processes occurring in plasmas of fluorocarbon gases, such as carbon tetrafluoride (CF4) which is commonly used as an etchant, and their mixtures to optimize various operating parameters. In this paper we report data on electron number density (ne), electron temperature'(Te), electron energy distribution function (EEDF), mean electron energy, ion number density (ni), and plasma potential (Vp) measured by using Langmuir probe in an inductively coupled 13.56 MHz radio frequency plasmas generated in 50%Ar:50%CF4 mixture in the GEC cell. The probe data were recorded at various radial positions providing radial profiles of these plasma parameters at 10-50 mTorr pressures and 200 W and 300 W of RF power. Present measurements indicate that the electron and ion number densities increase with increase in pressure and power. Whereas the plasma potential and electron temperature decrease with increase in pressure, and they weakly depend on RF power. The radial profiles exhibit that the electron and ion number densities and the plasma potential peak at the center of the plasma with an exponential fall away from it, while the electron temperature has a minimum at the center and it increases steadily towards the electrode edge. The EEDFs have a characteristic drop near the low energy end at all pressures and pressures and their shapes represent non-Maxwellian plasma and exhibit more like Druyvesteyn energy distribution.v

Linking the micro and macro: L-H transition dynamics and threshold physics

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

Malkov, M. A., E-mail: mmalkov@ucsd.edu; Diamond, P. H.; Miki, K.

2015-03-15

The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density P{sub thr} (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in P{sub thr} (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions.more » Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in P{sub thr} (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by an increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.« less

On the electrodynamics of moving particles in a quasi flat spacetime with Lorentz violation and its cosmological implications

NASA Astrophysics Data System (ADS)

Cruz, Cláudio Nassif

2016-06-01

This research aims to develop a new approach towards a consistent coupling of electromagnetic and gravitational fields, by using an electron that couples with a weak gravitational potential by means of its electromagnetic field. To accomplish this, we must first build a new model which provides the electromagnetic nature of both the mass and the energy of the electron, and which is implemented with the idea of γ-photon decay into an electron-positron pair. After this, we place the electron (or positron) in the presence of a weak gravitational potential given in the intergalactic medium, so that its electromagnetic field undergoes a very small perturbation, thus leading to a slight increase in the field’s electromagnetic energy density. This perturbation takes place by means of a tiny coupling constant ξ because gravity is a very weak interaction compared with the electromagnetic one. Thus, we realize that ξ is a new dimensionless universal constant, which reminds us of the fine structure constant α; however, ξ is much smaller than α because ξ takes into account gravity, i.e. ξ ∝G. We find ξ = V/c≅1.5302 × 10-22, where c is the speed of light and V ∝G(≅4.5876 × 10-14m/s) is a universal minimum speed that represents the lowest limit of speed for any particle. Such a minimum speed, unattainable by particles, represents a preferred reference frame associated with a background field that breaks the Lorentz symmetry. The metric of the flat spacetime shall include the presence of a uniform vacuum energy density, which leads to a negative pressure at cosmological scales (cosmological anti-gravity). The tiny values of the cosmological constant and the vacuum energy density will be successfully obtained in agreement with the observational data.

Novel hole transport materials for organic light emitting devices

NASA Astrophysics Data System (ADS)

Shi, Jianmin; Forsythe, Eric; Morton, David

2008-08-01

Organic electronic devices generally have a layered structure with organic materials sandwiched between an anode and a cathode, such organic electronic devices of organic light-emitting diode (OLED), organic photovoltaic (OPV), organic thin-film transistor (OTFT). There are many advantages of these organic electronic devices as compared to silicon-based devices. However, one of key challenge for an organic electronic device is to minimize the charge injection barrier from electrodes to organic materials and improve the charge transport mobility. In order to overcome these circumstances, there are many approaches including, designing organic materials with minimum energy barriers and improving charge transport mobility. Ideally organic materials or complex with Ohmic contact will be the most desired.

Electronic structures and geometries of the XF{sub 3} (X = Cl, Br, I, At) fluorides

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

Sergentu, Dumitru-Claudiu; CEISAM, UMR CNRS 6230, Université de Nantes, 2 Rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3; Amaouch, Mohamed

The potential energy surfaces of the group 17 XF{sub 3} (X = Cl, Br, I, At) fluorides have been investigated for the first time with multiconfigurational wave function theory approaches. In agreement with experiment, bent T-shaped C{sub 2v} structures are computed for ClF{sub 3}, BrF{sub 3}, and IF{sub 3}, while we predict that an average D{sub 3h} structure would be experimentally observed for AtF{sub 3}. Electron correlation and scalar relativistic effects strongly reduce the energy difference between the D{sub 3h} geometry and the C{sub 2v} one, along the XF{sub 3} series, and in the X = At case, spin-orbit couplingmore » also slightly reduces this energy difference. AtF{sub 3} is a borderline system where the D{sub 3h} structure becomes a minimum, i.e., the pseudo-Jahn-Teller effect is inhibited since electron correlation and scalar-relativistic effects create small energy barriers leading to the global C{sub 2v} minima, although both types of effects interfere.« less

New chemical sources of energy: A theoretical study

NASA Astrophysics Data System (ADS)

Chaban, Galina

The research presented in this dissertation employs methods of quantum chemistry for the search of highly energetic chemical compounds that can have applications as possible energy sources. The areas of research include: (1) improvement of orbital optimization methods for different types of wavefunctions which leads to substantial savings of computer time and memory; (2) predicting new high energy isomers for singlet and triplet states of Nsb3F and their kinetic stability with respect to isomerisation and dissociation reactions; (3) estimation of minimum energy reaction paths for dissociation reactions of high energy isomers of Nsb2Osb2 including potential energy barriers and minimum energy crossing points between the closest singlet and triplet states; (4) investigation of thermodynamic and kinetic stability of Van der Waals complexes M-Hsb2 (M = Li, Be, B, C, Na, Mg, Al, Si) that can play an important role in improvement of energetic properties of hydrogen based rocket fuels; (5) mapping of the potential energy surface for AlHsb2 compound in the region of crossing between sp2Bsb2 and sp2Asb1 electronic states and predicting the kinetic stability of Al complex, which suggests that Al may be among the promising candidates for inclusion into solid hydrogen for the purpose of energy storage.

Optimal algorithm to improve the calculation accuracy of energy deposition for betavoltaic MEMS batteries design

NASA Astrophysics Data System (ADS)

Li, Sui-xian; Chen, Haiyang; Sun, Min; Cheng, Zaijun

2009-11-01

Aimed at improving the calculation accuracy when calculating the energy deposition of electrons traveling in solids, a method we call optimal subdivision number searching algorithm is proposed. When treating the energy deposition of electrons traveling in solids, large calculation errors are found, we are conscious of that it is the result of dividing and summing when calculating the integral. Based on the results of former research, we propose a further subdividing and summing method. For β particles with the energy in the entire spectrum span, the energy data is set only to be the integral multiple of keV, and the subdivision number is set to be from 1 to 30, then the energy deposition calculation error collections are obtained. Searching for the minimum error in the collections, we can obtain the corresponding energy and subdivision number pairs, as well as the optimal subdivision number. The method is carried out in four kinds of solid materials, Al, Si, Ni and Au to calculate energy deposition. The result shows that the calculation error is reduced by one order with the improved algorithm.

Considerations for NSLS-II Synchrotron Radiation Protection When Operating Damping Wigglers at Low Machine Energy

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

Seletskiy, S.; Podobedov, B.

2015-12-30

The NSLS-II storage ring vacuum chamber, including frontends (FE) and beamlines (BL), is protected from possible damage from synchrotron radiation (SR) emitted from insertion devices (IDs) by a dedicated active interlock system (AIS). The system monitors electron beam position and angle and triggers a beam dump if the beam orbit is outside of the active interlock envelope (AIE). The AIE was calculated under the assumptions of 3 GeV beam energy and ID gaps set to their minimum operating values (i.e. “fully closed”). Recently it was proposed to perform machine studies that would ramp the stored beam energy significantly below themore » nominal operational value of 3 GeV. These studies may potentially include the use of NSLS-II damping wigglers (DWs) for electron beam emittance reduction and control.« less

Quasiparticle and hybrid density functional methods in defect studies: An application to the nitrogen vacancy in GaN

NASA Astrophysics Data System (ADS)

Lewis, D. K.; Matsubara, M.; Bellotti, E.; Sharifzadeh, S.

2017-12-01

Defects in semiconductors can play a vital role in the performance of electronic devices, with native defects often dominating the electronic properties of the semiconductor. Understanding the relationship between structural defects and electronic function will be central to the design of new high-performance materials. In particular, it is necessary to quantitatively understand the energy and lifetime of electronic states associated with the defect. Here, we apply first-principles density functional theory (DFT) and many-body perturbation theory within the GW approximation to understand the nature and energy of the defect states associated with a charged nitrogen vacancy on the electronic properties of gallium nitride (GaN), as a model of a well-studied and important wide gap semiconductor grown with defects. We systematically investigate the sources of error associated with the GW approximation and the role of the underlying atomic structure on the predicted defect state energies. Additionally, analysis of the computed electronic density of states (DOS) reveals that there is one occupied defect state 0.2 eV below the valence band maximum and three unoccupied defect states at energy of 0.2-0.4 eV above the conduction band minimum, suggesting that this defect in the +1 charge state will not behave as a carrier trap. Furthermore, we compare the character and energy of the defect state obtained from GW and DFT using the HSE approximate density functional and find excellent agreement. This systematic study provides a more complete understanding of how to obtain quantitative defect energy states in bulk semiconductors.

Efficient Geometry Minimization and Transition Structure Optimization Using Interpolated Potential Energy Surfaces and Iteratively Updated Hessians.

PubMed

Zheng, Jingjing; Frisch, Michael J

2017-12-12

An efficient geometry optimization algorithm based on interpolated potential energy surfaces with iteratively updated Hessians is presented in this work. At each step of geometry optimization (including both minimization and transition structure search), an interpolated potential energy surface is properly constructed by using the previously calculated information (energies, gradients, and Hessians/updated Hessians), and Hessians of the two latest geometries are updated in an iterative manner. The optimized minimum or transition structure on the interpolated surface is used for the starting geometry of the next geometry optimization step. The cost of searching the minimum or transition structure on the interpolated surface and iteratively updating Hessians is usually negligible compared with most electronic structure single gradient calculations. These interpolated potential energy surfaces are often better representations of the true potential energy surface in a broader range than a local quadratic approximation that is usually used in most geometry optimization algorithms. Tests on a series of large and floppy molecules and transition structures both in gas phase and in solutions show that the new algorithm can significantly improve the optimization efficiency by using the iteratively updated Hessians and optimizations on interpolated surfaces.

Negative space charge effects in photon-enhanced thermionic emission solar converters

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

Segev, G.; Weisman, D.; Rosenwaks, Y.

2015-07-06

In thermionic energy converters, electrons in the gap between electrodes form a negative space charge and inhibit the emission of additional electrons, causing a significant reduction in conversion efficiency. However, in Photon Enhanced Thermionic Emission (PETE) solar energy converters, electrons that are reflected by the electric field in the gap return to the cathode with energy above the conduction band minimum. These electrons first occupy the conduction band from which they can be reemitted. This form of electron recycling makes PETE converters less susceptible to negative space charge loss. While the negative space charge effect was studied extensively in thermionicmore » converters, modeling its effect in PETE converters does not account for important issues such as this form of electron recycling, nor the cathode thermal energy balance. Here, we investigate the space charge effect in PETE solar converters accounting for electron recycling, with full coupling of the cathode and gap models, and addressing conservation of both electric and thermal energy. The analysis shows that the negative space charge loss is lower than previously reported, allowing somewhat larger gaps compared to previous predictions. For a converter with a specific gap, there is an optimal solar flux concentration. The optimal solar flux concentration, the cathode temperature, and the efficiency all increase with smaller gaps. For example, for a gap of 3 μm the maximum efficiency is 38% and the optimal flux concentration is 628, while for a gap of 5 μm the maximum efficiency is 31% and optimal flux concentration is 163.« less

Relativistic Shear Flow between Electron-Ion and Electron-Positron Plasmas and Astrophysical Applications

NASA Astrophysics Data System (ADS)

Liang, Edison; Fu, Wen; Böttcher, Markus

2017-10-01

We present particle-in-cell simulation results of relativistic shear boundary layers between electron-ion and electron-positron plasmas and discuss their potential applications to astrophysics. Specifically, we find that in the case of a fast electron-positron spine surrounded by a slow-moving or stationary electron-ion sheath, lepton acceleration proceeds in a highly anisotropic manner due to electromagnetic fields created at the shear interface. While the highest-energy leptons still produce a beaming pattern (as seen in the quasi-stationary frame of the sheath) of order 1/Γ, where Γ is the bulk Lorentz factor of the spine, for lower-energy particles, the beaming is much less pronounced. This is in stark contrast to the case of pure electron-ion shear layers, in which anisotropic particle acceleration leads to significantly narrower beaming patterns than 1/Γ for the highest-energy particles. In either case, shear-layer acceleration is expected to produce strongly angle-dependent lepton (hence, emanating radiation) spectra, with a significantly harder spectrum in the forward direction than viewed from larger off-axis angles, much beyond the regular Doppler boosting effect from a co-moving isotropic lepton distribution. This may solve the problem of the need for high (and apparently arbitrarily chosen) minimum Lorentz factors of radiating electrons, often plaguing current blazar and GRB jet modeling efforts.

(The AMY experiment)

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

Not Available

1989-01-01

The AMY experiment is one of three major experiments at TRISTAN which is studying the states the matter produced in electron positron annihilations in the center of mass energy range of 50--65GeV. It provides information between the lower energy facilities such as PEP and PETRA and the new facilities SLC and LEP which are designed to operate in the region of the Z{sup 0} mass near 90GeV. In the region of the AMY experiment, interaction cross sections are near their minimum of about 100pb, making it difficult to acquire large data samples during typical running cycles. This last year hasmore » seen an accumulation of about 10--{minus}12pb{sup {minus}1} of integrated luminosity in the energy range from 58 to 61.7GeV. Despite this limited data sample, the AMY experiment has been extremely active in attempting to extract the minimum amount of information from the data. Some of the most significant results are discussed in this paper. 9 refs.« less

The structure, energetics, and nature of the chemical bonding of phenylthiol adsorbed on the Au(111) surface: implications for density-functional calculations of molecular-electronic conduction.

PubMed

Bilić, Ante; Reimers, Jeffrey R; Hush, Noel S

2005-03-01

The adsorption of phenylthiol on the Au(111) surface is modeled using Perdew and Wang density-functional calculations. Both direct molecular physisorption and dissociative chemisorption via S-H bond cleavage are considered as well as dimerization to form disulfides. For the major observed product, the chemisorbed thiol, an extensive potential-energy surface is produced as a function of both the azimuthal orientation of the adsorbate and the linear translation of the adsorbate through the key fcc, hcp, bridge, and top binding sites. Key structures are characterized, the lowest-energy one being a broad minimum of tilted orientation ranging from the bridge structure halfway towards the fcc one. The vertically oriented threefold binding sites, often assumed to dominate molecular electronics measurements, are identified as transition states at low coverage but become favored in dense monolayers. A similar surface is also produced for chemisorption of phenylthiol on Ag(111); this displays significant qualitative differences, consistent with the qualitatively different observed structures for thiol chemisorption on Ag and Au. Full contours of the minimum potential energy as a function of sulfur translation over the crystal face are described, from which the barrier to diffusion is deduced to be 5.8 kcal mol(-1), indicating that the potential-energy surface has low corrugation. The calculated bond lengths, adsorbate charge and spin density, and the density of electronic states all indicate that, at all sulfur locations, the adsorbate can be regarded as a thiyl species that forms a net single covalent bond to the surface of strength 31 kcal mol(-1). No detectable thiolate character is predicted, however, contrary to experimental results for alkyl thiols that indicate up to 20%-30% thiolate involvement. This effect is attributed to the asymptotic-potential error of all modern density functionals that becomes manifest through a 3-4 eV error in the lineup of the adsorbate and substrate bands. Significant implications are described for density-functional calculations of through-molecule electron transport in molecular electronics.

Statistical properties of radiation power levels from a high-gain free-electron laser at and beyond saturation

NASA Astrophysics Data System (ADS)

Schroeder, C. B.; Fawley, W. M.; Esarey, E.

2003-07-01

We investigate the statistical properties (e.g., shot-to-shot power fluctuations) of the radiation from a high-gain free-electron laser (FEL) operating in the nonlinear regime. We consider the case of an FEL amplifier reaching saturation whose shot-to-shot fluctuations in input radiation power follow a gamma distribution. We analyze the corresponding output power fluctuations at and beyond saturation, including beam energy spread effects, and find that there are well-characterized values of undulator length for which the fluctuations reach a minimum.

Simulation of the electromagnetic field in a cylindrical cavity of an ECR ions source

NASA Astrophysics Data System (ADS)

Estupiñán, A.; Orozco, E. A.; Dugar-Zhabon, V. D.; Murillo Acevedo, M. T.

2017-12-01

Now there are numerous sources for multicharged ions production, each being designed for certain science or technological objectives. Electron cyclotron resonance ion sources (ECRIS) are best suited for designing heavy ion accelerators of very high energies, because they can generate multicharged ion beams at relatively great intensities. In these sources, plasma heating and its confinement are effected predominantly in minimum-B magnetic traps, this type of magnetic trap consist of two current coils used for the longitudinal magnetic confinement and a hexapole system around the cavity to generate a transversal confinement of the plasma. In an ECRIS, the electron cyclotron frequency and the microwave frequency are maintained equal on a quasi-ellipsoidal surface localized in the trap volume. It is crucial to heat electrons to energies sufficient to ionize K- and L-levels of heavy atoms. In this work, we present the preliminary numerical results concerning the space distribution of TE 111 microwave field in a cylindrical cavity. The 3D microwave field is calculated by solving the Maxwell equations through the Yee’s method. The magnetic field of minimum-B configuration is determined using the Biot-Savart law. The parameters of the magnetic system are that which guarantee the ECR surface location in a zone of a reasonably high microwave tension. Additionally, the accuracy of electric and magnetic fields calculations are checked.

Insights into geometries, stabilities, electronic structures, reactivity descriptors, and magnetic properties of bimetallic Nim Cun-m (m = 1, 2; n = 3-13) clusters: Comparison with pure copper clusters.

PubMed

Singh, Raman K; Iwasa, Takeshi; Taketsugu, Tetsuya

2018-05-25

A long-range corrected density functional theory (LC-DFT) was applied to study the geometric structures, relative stabilities, electronic structures, reactivity descriptors and magnetic properties of the bimetallic NiCu n -1 and Ni 2 Cu n -2 (n = 3-13) clusters, obtained by doping one or two Ni atoms to the lowest energy structures of Cu n , followed by geometry optimizations. The optimized geometries revealed that the lowest energy structures of the NiCu n -1 and Ni 2 Cu n -2 clusters favor the Ni atom(s) situated at the most highly coordinated position of the host copper clusters. The averaged binding energy, the fragmentation energies and the second-order energy differences signified that the Ni doped clusters can continue to gain an energy during the growth process. The electronic structures revealed that the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies of the LC-DFT are reliable and can be used to predict the vertical ionization potential and the vertical electron affinity of the systems. The reactivity descriptors such as the chemical potential, chemical hardness and electrophilic power, and the reactivity principle such as the minimum polarizability principle are operative for characterizing and rationalizing the electronic structures of these clusters. Moreover, doping of Ni atoms into the copper clusters carry most of the total spin magnetic moment. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

Influence of Fröhlich polaron coupling on renormalized electron bands in polar semiconductors: Results for zinc-blende GaN

NASA Astrophysics Data System (ADS)

Nery, Jean Paul; Allen, Philip B.

2016-09-01

We develop a simple method to study the zero-point and thermally renormalized electron energy ɛk n(T ) for k n the conduction band minimum or valence maximum in polar semiconductors. We use the adiabatic approximation, including an imaginary broadening parameter i δ to suppress noise in the density-functional integrations. The finite δ also eliminates the polar divergence which is an artifact of the adiabatic approximation. Nonadiabatic Fröhlich polaron methods then provide analytic expressions for the missing part of the contribution of the problematic optical phonon mode. We use this to correct the renormalization obtained from the adiabatic approximation. Test calculations are done for zinc-blende GaN for an 18 ×18 ×18 integration grid. The Fröhlich correction is of order -0.02 eV for the zero-point energy shift of the conduction band minimum, and +0.03 eV for the valence band maximum; the correction to renormalization of the 3.28 eV gap is -0.05 eV, a significant fraction of the total zero point renormalization of -0.15 eV.

Measurements of the ambient photoelectron spectrum from Atmosphere Explorer. I - AE-E measurements below 300 km during solar minimum conditions. II - AE-E measurements from 300 to 1000 km during solar minimum conditions

NASA Technical Reports Server (NTRS)

Lee, J. S.; Doering, J. P.; Potemra, T. A.; Brace, L. H.

1980-01-01

A study is presented of the ambient photoelectron spectrum below 300 km which includes 500 AE-E orbits observed from Dec. 13, 1975 to Feb. 24, 1976. The daytime photoelectron spectrum from 1 to 100 eV was illustrated by several spectra; high resolution 10-32 eV spectra show the widths of the photoelectron lines and the variation of the linewidth and intensity with altitude. The photoelectron flux below 300 km is constant over a period of several months; the photoelectron lines between 20 and 30 eV are very sharp when the total plasma density is low, but broaden at high altitudes as the plasma density builds up during the day. The photo-electron flux above 300 km had an intensity and energy spectrum characteristic of the 250-300 km region only in the presence of low plasma density at the satellite altitude. The flux at high altitudes was extremely variable 3 h after sunrise as a result of attenuation and energy loss to thermal plasma along the path of escaping electrons.

Changes in the concentration of mesospheric O3 and OH during a highly relativistic electron precipitation event

NASA Astrophysics Data System (ADS)

Goldberg, R. A.; Jackman, C. H.; Baker, D. N.; Herrero, F. A.

Highly relativistic electron precipitation events (HREs) can provide a major source of energy affecting ionization levels and minor constituents in the mesosphere. Based on satellite data, these events are most pronounced during the minimum of the solar sunspot cycle, increasing in intensity, spectral hardness and frequency of occurrence as solar activity declines. Furthermore, although the precipitating flux is modulated diurnally in local time, the noontime maximum is very broad, exceeding several hours. Since such events can be sustained up to several days, their integrated effect in the mesosphere can dominate over those of other external sources such as relativistic electron precipitation events (REPs) and auroral precipitation. In this work, the effects of HRE relativistic electrons on the neutral minor constituents OH and O3 are modeled during a modest HRE, to estimate their anticipated impact on mesospheric heating and dynamics. The data to be discussed and analyzed were obtained by rocket at Poker Flat, Alaska on May 13, 1990 during an HRE observed at midday near the peak of the sunspot cycle. Solid state detectors were used to measure the electron fluxes and their energy spectra. An x-ray scintillator was included to measure bremsstrahlung x-rays produced by energetic electrons impacting the upper atmosphere; however, these were found to make a negligible contribution to the energy deposition during this particular HRE event. Hence, the energy deposition produced by the highly relativistic electrons dominated within the mesosphere and was used exclusively to infer changes in the middle atmospheric minor constituent abundances. By employing a two-dimensional photochemical model developed for this region at Goddard Space Fight Center, it has been found that for this event, peak modifications in the neutral minor species occurred near 80 km. A maximum enhancement for OH was calculated to be over 40% at the latitude of the launch site, which in turn induced a maximum depletion of O3 in excess of 30%. Since this particular HRE occurred near solar maximum, it was of modest intensity and spectral hardness, parameters which could grow significantly as solar minimum is approached. Estimates of mesospheric OH enhancement and O3 depletion have also been made for more intense HRE events, as might be expected during the declining phase of the solar cycle. The findings imply that the energy deposition from highly relativistic electrons during more intense HREs could modulate the concentration of important minor species within the mesosphere to much higher levels than estimated for the observed HRE. By causing O3 destruction, the electron precipitation can also modify the penetration depth of solar UV radiation, which may affect thermal properties of the mesosphere to depths approaching 60 km.

Analysis of vibrational, structural, and electronic properties of rivastigmine by density functional theory

NASA Astrophysics Data System (ADS)

Prasad, O.; Sinha, L.; Misra, N.; Narayan, V.; Kumar, N.; Kumar, A.

2010-09-01

The present work deals with the structural, electronic, and vibrational analysis of rivastigmine. Rivastigmine, an antidementia medicament, is credited with significant therapeutic effects on the cognitive, functional, and behavioural problems that are commonly associated with Alzheimer’s dementia. For rivastigmine, a number of minimum energy conformations are possible. The geometry of twelve possible conformers has been analyzed and the most stable conformer was further optimized at a higher basis set. The electronic properties and vibrational frequencies were then calculated using a density functional theory at the B3LYP level with the 6-311+G(d, p) basis set. The different molecular surfaces have also been drawn to understand the activity of the molecule. A narrower frontier orbital energy gap in rivastigmine makes it softer and more reactive than water and dimethylfuran. The calculated value of the dipole moment is 2.58 debye.

Scattered electrons in microscopy and microanalysis

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

Ottensmeyer, F.P.

The use of scattered electrons alone for direct imaging of biological specimens makes it possible to obtain structural information at atomic and near-atomic spatial resolutions of 0.3 to 0.5 nanometer. While this is not as good as the resolution possible with x-ray crystallography, such an approach provides structural information rapidly on individual macromolecules that have not been, and possibly cannot be, crystallized. Analysis of the spectrum of energies of scattered electrons and imaging of the latter with characteristic energy bands within the spectrum produces a powerful new technique of atomic microanalysis. This technique, which has a spatial resolution of aboutmore » 0.5 nanometer and a minimum detection sensitivity of about 50 atoms of phosphorus, is especially useful for light atom analysis and appears to have applications in molecular biology, cell biology, histology, pathology, botany, and many other fields.« less

Scattered electrons in microscopy and microanalysis

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

Ottensmeyer, F.P.

The use of scattered electrons alone for direct imaging of biological specimens makes it possible to obtain structural information at atomic and near-atomic spatial resolutions of 0.3 to 0.5 nanometer. While this is not as good as the resolution possible with x-ray crystallography, such an approach provides structural information rapidly on individual macromolecules that have not been, and possibly cannot be, crystallized. Analysis of the spectrum of energies of scattered electrons and imaging of the latter with characteristic energy bands within the spectrum produce a powerful new technique of atomic microanalysis. This technique, which has a spatial resolution of aboutmore » 0.5 nanometer and a minimum detection sensitivity of about 50 atoms of phosphorus, is especially useful for light atom analysis and appears to have applications in molecular biology, cell biology, histology, pathology, botany, and many other fields.« less

Nearly metastable rhombohedral phases of bcc metals

NASA Astrophysics Data System (ADS)

Mehl, Michael J.; Finkenstadt, Daniel

2008-02-01

The energy E(c/a) for a bcc element stretched along its [001] axis (the Bain path) has a minimum at c/a=1 , a maximum at c/a=2 , and an elastically unstable local minimum at c/a>2 . An alternative path connecting the bcc and fcc structures is the rhombohedral lattice. The primitive lattice has R3¯m symmetry, with the angle α changing from 109.4° (bcc), to 90° (simple cubic), to 60 ° (fcc). We study this path for the non-magnetic bcc transition metals (V, Nb, Mo, Ta, and W) using both all-electron linearized augmented plane wave and projector augmented wave VASP codes. Except for Ta, the energy E(α) has a local maximum at α=60° , with local minima near 55° and 70° , the latter having lower energy, suggesting the possibility of a metastable rhombohedral state for these materials. We first examine the elastic stability of the 70° minimum structure, and determine that only W is elastically stable in this structure, with the smallest eigenvalue of the elastic tensor at 4GPa . We then consider the possibility that tungsten is actually metastable in this structure by looking at its vibrational and third-order elastic stability.

The statistics of relativistic electron pitch angle distribution in the Earth's radiation belt based on the Van Allen Probes measurements

NASA Astrophysics Data System (ADS)

Zhao, H.; Freidel, R. H. W.; Chen, Y.; Henderson, M. G.; Kanekal, S. G.; Baker, D. N.; Spence, H. E.; Reeves, G. D.

2015-12-01

The relativistic electron pitch angle distribution (PAD) is an important characteristic of radiation belt electrons, which can give information on source or loss processes in a specific region. Using data from MagEIS and REPT instruments onboard the Van Allen Probes, a statistical survey of relativistic electron pitch angle distribution (PAD) is performed. By fitting relativistic electron PADs to Legendre polynomials, an empirical model of PADs as a function of L (from 1.4 to 6), MLT, electron energy (~100 keV - 5 MeV), and geomagnetic activity is developed and many intriguing features are found. In the outer radiation belt, an unexpected dawn/dusk asymmetry of ultra-relativistic electrons is found during quiet times, with the asymmetry becoming stronger at higher energies and at higher L shells. This may indicate the existence of physical processes acting on the relativistic electrons on the order of drift period, or be a signature of the partial ring current. In the inner belt and slot region, 100s of keV pitch angle distributions with minima at 90° are shown to be persistent in the inner belt and appears in the slot region during storm times. The model also shows clear energy dependence and L shell dependence of 90°-minimum pitch angle distribution. On the other hand, the head-and-shoulder pitch angle distributions are found during quiet times in the slot region, and the energy, L shell and geomagnetic activity dependence of those PADs are consistent with the wave-particle interaction caused by hiss waves.

Electron affinity and surface states of GaN m -plane facets: Implication for electronic self-passivation

NASA Astrophysics Data System (ADS)

Portz, V.; Schnedler, M.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.

2018-03-01

The electron affinity and surface states are of utmost importance for designing the potential landscape within (heterojunction) nanowires and hence for tuning conductivity and carrier lifetimes. Therefore, we determined for stoichiometric nonpolar GaN (10 1 ¯0 ) m -plane facets, i.e., the dominating sidewalls of GaN nanowires, the electron affinity to 4.06 ±0.07 eV and the energy of the empty Ga-derived surface state in the band gap to 0.99 ±0.08 eV below the conduction band minimum using scanning tunneling spectroscopy. These values imply that the potential landscape within GaN nanowires is defined by a surface state-induced Fermi-level pinning, creating an upward band bending at the sidewall facets, which provides an electronic passivation.

Boltzmann transport properties of ultra thin-layer of h-CX monolayers

NASA Astrophysics Data System (ADS)

Kansara, Shivam; Gupta, Sanjeev K.; Sonvane, Yogesh

2018-04-01

Structural, electronic and thermoelectric properties of monolayer h-CX (X= Al, As, B, Bi, Ga, In, P, N, Sb and Tl) have been computed using density functional theory (DFT). The structural, electronic band structure, phonon dispersion curves and thermoelectric properties have been investigated. h-CGa and h-CTl show the periodically lattice vibrations and h-CB and h-CIn show small imaginary ZA frequencies. Thermoelectric properties are obtained using BoltzTrap code with the constant relaxation time (τ) approximation such as electronic, thermal and electrical conductivity calculated for various temperatures. The results indicate that h-CGa, h-CIn, h-CTl and h-CAl have direct band gaps with minimum electronic thermal and electrical conductivity while h-CB and h-CN show the high electronic thermal and electrical conductivity with highest cohesive energy.

Uniform electron gases. III. Low-density gases on three-dimensional spheres

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

Agboola, Davids; Knol, Anneke L.; Gill, Peter M. W., E-mail: peter.gill@anu.edu.au

2015-08-28

By combining variational Monte Carlo (VMC) and complete-basis-set limit Hartree-Fock (HF) calculations, we have obtained near-exact correlation energies for low-density same-spin electrons on a three-dimensional sphere (3-sphere), i.e., the surface of a four-dimensional ball. In the VMC calculations, we compare the efficacies of two types of one-electron basis functions for these strongly correlated systems and analyze the energy convergence with respect to the quality of the Jastrow factor. The HF calculations employ spherical Gaussian functions (SGFs) which are the curved-space analogs of Cartesian Gaussian functions. At low densities, the electrons become relatively localized into Wigner crystals, and the natural SGFmore » centers are found by solving the Thomson problem (i.e., the minimum-energy arrangement of n point charges) on the 3-sphere for various values of n. We have found 11 special values of n whose Thomson sites are equivalent. Three of these are the vertices of four-dimensional Platonic solids — the hyper-tetrahedron (n = 5), the hyper-octahedron (n = 8), and the 24-cell (n = 24) — and a fourth is a highly symmetric structure (n = 13) which has not previously been reported. By calculating the harmonic frequencies of the electrons around their equilibrium positions, we also find the first-order vibrational corrections to the Thomson energy.« less

Parameterized study of the ionospheric modification associated with sun-aligned polar cap arcs

NASA Technical Reports Server (NTRS)

Crain, D. J.; Sojka, J. J.; Schunk, R. W.; Zhu, L.

1993-01-01

The local ionospheric modification that is due to a generalized steady state solar aligned (SA) arc structure is addressed. For a representative set of SA arc parameters which includes both convection and precipitation, emphasis is placed on the modification by SA polar cap arcs upon the F region electron density and the height integrated conductivity. At low fluxes and low characteristic energies, SA polar cap arcs have the most pronounced relative effect at F region altitudes in darkness for winter solar minimum conditions. The absolute enhancement in summer solar minimum and winter solar maximum is equivalent to that of winter solar minimum, but the higher ambient densities make the relative enhancement less. The TEC enhancement associated with an SA arc may be used to indicate the degree of plasma cross flow across the arc.

Energies of the X- and L-valleys in In{sub 0.53}Ga{sub 0.47}As from electronic structure calculations

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

Greene-Diniz, Gabriel; Greer, J. C.; Fischetti, M. V.

2016-02-07

Several theoretical electronic structure methods are applied to study the relative energies of the minima of the X- and L-conduction-band satellite valleys of In{sub x}Ga{sub 1−x}As with x = 0.53. This III-V semiconductor is a contender as a replacement for silicon in high-performance n-type metal-oxide-semiconductor transistors. The energy of the low-lying valleys relative to the conduction-band edge governs the population of channel carriers as the transistor is brought into inversion, hence determining current drive and switching properties at gate voltages above threshold. The calculations indicate that the position of the L- and X-valley minima are ∼1 eV and ∼1.2 eV, respectively, higher in energymore » with respect to the conduction-band minimum at the Γ-point.« less

Vibronic coupling and selectivity of vibrational excitation in the negative ion resonances of ozone

NASA Astrophysics Data System (ADS)

Allan, Michael; Popovic̀, Duška B.

1997-04-01

A recent experimental paper reported two shape resonances in electron impact on ozone, A 1 and B 2, both causing vibrational excitation with a distinct pattern of selectivity. The present Letter attempts to rationalize this selectivity using approximate potential curves, calculated for the A 1 and B 2 resonances by adding the SCF energy of neutral ozone to electron attachment energies calculated from ab initio virtual orbital energies using the Koopmans' theorem and an empirical scaling relation. The slopes of the curves explain the efficient excitation of the symmetric stretch by both resonances and the lack of the bending excitation by the B 2 resonance. The A 1 and B 2 resonances are strongly coupled by the b 2 antisymmetric stretch vibration, causing a double minimum on the lower surface. Nonadiabatic effects caused by the strong vibronic coupling explain the observed excitation of the antisymmetric stretch vibration.

Overall Traveling-Wave-Tube Efficiency Improved By Optimized Multistage Depressed Collector Design

NASA Technical Reports Server (NTRS)

Vaden, Karl R.

2002-01-01

Depressed Collector Design The microwave traveling wave tube (TWT) is used widely for space communications and high-power airborne transmitting sources. One of the most important features in designing a TWT is overall efficiency. Yet, overall TWT efficiency is strongly dependent on the efficiency of the electron beam collector, particularly for high values of collector efficiency. For these reasons, the NASA Glenn Research Center developed an optimization algorithm based on simulated annealing to quickly design highly efficient multistage depressed collectors (MDC's). Simulated annealing is a strategy for solving highly nonlinear combinatorial optimization problems. Its major advantage over other methods is its ability to avoid becoming trapped in local minima. Simulated annealing is based on an analogy to statistical thermodynamics, specifically the physical process of annealing: heating a material to a temperature that permits many atomic rearrangements and then cooling it carefully and slowly, until it freezes into a strong, minimum-energy crystalline structure. This minimum energy crystal corresponds to the optimal solution of a mathematical optimization problem. The TWT used as a baseline for optimization was the 32-GHz, 10-W, helical TWT developed for the Cassini mission to Saturn. The method of collector analysis and design used was a 2-1/2-dimensional computational procedure that employs two types of codes, a large signal analysis code and an electron trajectory code. The large signal analysis code produces the spatial, energetic, and temporal distributions of the spent beam entering the MDC. An electron trajectory code uses the resultant data to perform the actual collector analysis. The MDC was optimized for maximum MDC efficiency and minimum final kinetic energy of all collected electrons (to reduce heat transfer). The preceding figure shows the geometric and electrical configuration of an optimized collector with an efficiency of 93.8 percent. The results show the improvement in collector efficiency from 89.7 to 93.8 percent, resulting in an increase of three overall efficiency points. In addition, the time to design a highly efficient MDC was reduced from a month to a few days. All work was done in-house at Glenn for the High Rate Data Delivery Program. Future plans include optimizing the MDC and TWT interaction circuit in tandem to further improve overall TWT efficiency.

Ab initio R-matrix calculations of e+-molecule scattering

NASA Technical Reports Server (NTRS)

Danby, Grahame; Tennyson, Jonathan

1990-01-01

The adaptation of the molecular R-matrix method, originally developed for electron-molecule collision studies, to positron scattering is discussed. Ab initio R-matrix calculations are presented for collisions of low energy positrons with a number of diatomic systems including H2, HF and N2. Differential elastic cross sections for positron-H2 show a minimum at about 45 deg for collision energies between 0.3 and 0.5 Ryd. The calculations predict a bound state of positronHF. Calculations on inelastic processes in N2 and O2 are also discussed.

Can the cosmic x ray and gamma ray background be due to reflection of a steep power law spectrum and Compton scattering by relativistic electrons?

NASA Technical Reports Server (NTRS)

Zycki, Piotr T.; Zdziarski, Andrzej A.; Svensson, Roland

1991-01-01

We reconsider the recent model for the origin in the cosmic X-ray and gamma-ray background by Rogers and Field. The background in the model is due to an unresolved population of AGNs. An individual AGN spectrum contains three components: a power law with the energy index of alpha = 1.1, an enhanced reflection component, and a component from Compton scattering by relativistic electrons with a low energy cutoff at some minimum Lorentz factor, gamma(sub min) much greater than 1. The MeV bump seen in the gamma-ray background is then explained by inverse Compton emission by the electrons. We show that the model does not reproduce the shape of the observed X-ray and gamma-ray background below 10 MeV and that it overproduces the background at larger energies. Furthermore, we find the assumptions made for the Compton component to be physically inconsistent. Relaxing the inconsistent assumptions leads to model spectra even more different from that of the observed cosmic background. Thus, we can reject the hypothesis that the high-energy cosmic background is due to the described model.

Complete-active-space second-order perturbation theory (CASPT2//CASSCF) study of the dissociative electron attachment in canonical DNA nucleobases caused by low-energy electrons (0-3 eV)

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

Francés-Monerris, Antonio; Segarra-Martí, Javier; Merchán, Manuela

Low-energy (0-3 eV) ballistic electrons originated during the irradiation of biological material can interact with DNA/RNA nucleobases yielding transient-anion species which undergo decompositions. Since the discovery that these reactions can eventually lead to strand breaking of the DNA chains, great efforts have been dedicated to their study. The main fragmentation at the 0-3 eV energy range is the ejection of a hydrogen atom from the specific nitrogen positions. In the present study, the methodological approach introduced in a previous work on uracil [I. González-Ramírez et al., J. Chem. Theory Comput. 8, 2769-2776 (2012)] is employed to study the DNA canonicalmore » nucleobases fragmentations of N–H bonds induced by low-energy electrons. The approach is based on minimum energy path and linear interpolation of internal coordinates computations along the N–H dissociation channels carried out at the complete-active-space self-consistent field//complete-active-space second-order perturbation theory level. On the basis of the calculated theoretical quantities, new assignations for the adenine and cytosine anion yield curves are provided. In addition, the π{sub 1}{sup −} and π{sub 2}{sup −} states of the pyrimidine nucleobases are expected to produce the temporary anions at electron energies close to 1 and 2 eV, respectively. Finally, the present theoretical results do not allow to discard neither the dipole-bound nor the valence-bound mechanisms in the range of energies explored, suggesting that both possibilities may coexist in the experiments carried out with the isolated nucleobases.« less

Complete-active-space second-order perturbation theory (CASPT2//CASSCF) study of the dissociative electron attachment in canonical DNA nucleobases caused by low-energy electrons (0-3 eV).

PubMed

Francés-Monerris, Antonio; Segarra-Martí, Javier; Merchán, Manuela; Roca-Sanjuán, Daniel

2015-12-07

Low-energy (0-3 eV) ballistic electrons originated during the irradiation of biological material can interact with DNA/RNA nucleobases yielding transient-anion species which undergo decompositions. Since the discovery that these reactions can eventually lead to strand breaking of the DNA chains, great efforts have been dedicated to their study. The main fragmentation at the 0-3 eV energy range is the ejection of a hydrogen atom from the specific nitrogen positions. In the present study, the methodological approach introduced in a previous work on uracil [I. González-Ramírez et al., J. Chem. Theory Comput. 8, 2769-2776 (2012)] is employed to study the DNA canonical nucleobases fragmentations of N-H bonds induced by low-energy electrons. The approach is based on minimum energy path and linear interpolation of internal coordinates computations along the N-H dissociation channels carried out at the complete-active-space self-consistent field//complete-active-space second-order perturbation theory level. On the basis of the calculated theoretical quantities, new assignations for the adenine and cytosine anion yield curves are provided. In addition, the π1 (-) and π2 (-) states of the pyrimidine nucleobases are expected to produce the temporary anions at electron energies close to 1 and 2 eV, respectively. Finally, the present theoretical results do not allow to discard neither the dipole-bound nor the valence-bound mechanisms in the range of energies explored, suggesting that both possibilities may coexist in the experiments carried out with the isolated nucleobases.

Complete-active-space second-order perturbation theory (CASPT2//CASSCF) study of the dissociative electron attachment in canonical DNA nucleobases caused by low-energy electrons (0-3 eV)

NASA Astrophysics Data System (ADS)

Francés-Monerris, Antonio; Segarra-Martí, Javier; Merchán, Manuela; Roca-Sanjuán, Daniel

2015-12-01

Low-energy (0-3 eV) ballistic electrons originated during the irradiation of biological material can interact with DNA/RNA nucleobases yielding transient-anion species which undergo decompositions. Since the discovery that these reactions can eventually lead to strand breaking of the DNA chains, great efforts have been dedicated to their study. The main fragmentation at the 0-3 eV energy range is the ejection of a hydrogen atom from the specific nitrogen positions. In the present study, the methodological approach introduced in a previous work on uracil [I. González-Ramírez et al., J. Chem. Theory Comput. 8, 2769-2776 (2012)] is employed to study the DNA canonical nucleobases fragmentations of N-H bonds induced by low-energy electrons. The approach is based on minimum energy path and linear interpolation of internal coordinates computations along the N-H dissociation channels carried out at the complete-active-space self-consistent field//complete-active-space second-order perturbation theory level. On the basis of the calculated theoretical quantities, new assignations for the adenine and cytosine anion yield curves are provided. In addition, the π1- and π2- states of the pyrimidine nucleobases are expected to produce the temporary anions at electron energies close to 1 and 2 eV, respectively. Finally, the present theoretical results do not allow to discard neither the dipole-bound nor the valence-bound mechanisms in the range of energies explored, suggesting that both possibilities may coexist in the experiments carried out with the isolated nucleobases.

An ab initio study of the C3(+) cation using multireference methods

NASA Technical Reports Server (NTRS)

Taylor, Peter R.; Martin, J. M. L.; Francois, J. P.; Gijbels, R.

1991-01-01

The energy difference between the linear 2 sigma(sup +, sub u) and cyclic 2B(sub 2) structures of C3(+) has been investigated using large (5s3p2d1f) basis sets and multireference electron correlation treatments, including complete active space self consistent fields (CASSCF), multireference configuration interaction (MRCI), and averaged coupled-pair functional (ACPF) methods, as well as the single-reference quadratic configuration interaction (QCISD(T)) method. Our best estimate, including a correction for basis set incompleteness, is that the linear form lies above the cyclic from by 5.2(+1.5 to -1.0) kcal/mol. The 2 sigma(sup +, sub u) state is probably not a transition state, but a local minimum. Reliable computation of the cyclic/linear energy difference in C3(+) is extremely demanding of the electron correlation treatment used: of the single-reference methods previously considered, CCSD(T) and QCISD(T) perform best. The MRCI + Q(0.01)/(4s2p1d) energy separation of 1.68 kcal/mol should provide a comparison standard for other electron correlation methods applied to this system.

First-principles study of the effect of functional groups on polyaniline backbone

PubMed Central

Chen, X. P.; Jiang, J. K.; Liang, Q. H.; Yang, N.; Ye, H. Y.; Cai, M.; Shen, L.; Yang, D. G.; Ren, T. L.

2015-01-01

We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone. Analyses of the obtained energy barriers, reaction energies and minimum energy paths indicate that the chemical reactivity of the polyaniline derivatives is significantly enhanced by protonic acid doping of the substituted materials. Further study of the density of states at the Fermi level, band gap, HOMO and LUMO shows that both the unprotonated and protonated states of these polyanilines are altered to different degrees depending on the functional group. We also note that changes in both the chemical and electronic properties are very sensitive to the polarity and size of the functional group. It is worth noting that these changes do not substantially alter the inherent chemical and electronic properties of polyaniline. Our results demonstrate that introducing different functional groups on a polymer backbone is an effective approach to obtain tailored conductive polymers with desirable properties while retaining their intrinsic properties, such as conductivity. PMID:26584671

Absolute laser-intensity measurement and online monitor calibration using a calorimeter at a soft X-ray free-electron laser beamline in SACLA

NASA Astrophysics Data System (ADS)

Tanaka, Takahiro; Kato, Masahiro; Saito, Norio; Owada, Shigeki; Tono, Kensuke; Yabashi, Makina; Ishikawa, Tetsuya

2018-06-01

This paper reports measurement of the absolute intensity of free-electron laser (FEL) and calibration of online intensity monitors for a brand-new FEL beamline BL1 at SPring-8 Angstrom Compact free-electron LAser (SACLA) in Japan. To measure the absolute intensity of FEL, we used a room-temperature calorimeter originally developed for FELs in the hard X-ray range. By using the calorimeter, we calibrated online intensity monitors of BL1, gas monitors (GMs), based on the photoionization of argon gas, in the photon energy range from 25 eV to 150 eV. A good correlation between signals obtained from the calorimeter and GMs was observed in the pulse energy range from 1 μJ to 100 μJ, where the upper limit is nearly equal to the maximum pulse energy at BL1. Moreover, the calibration result of the GMs, measured in terms of the spectral responsivity, demonstrates a characteristic photon-energy dependence owing to the occurrence of the Cooper minimum in the total ionization cross-section of argon gas. These results validate the feasibility of employing the room-temperature calorimeter in the measurement of absolute intensity of FELs over the specified photon energy range.

Cyber warfare and electronic warfare integration in the operational environment of the future: cyber electronic warfare

NASA Astrophysics Data System (ADS)

Askin, Osman; Irmak, Riza; Avsever, Mustafa

2015-05-01

For the states with advanced technology, effective use of electronic warfare and cyber warfare will be the main determining factor of winning a war in the future's operational environment. The developed states will be able to finalize the struggles they have entered with a minimum of human casualties and minimum cost thanks to high-tech. Considering the increasing number of world economic problems, the development of human rights and humanitarian law it is easy to understand the importance of minimum cost and minimum loss of human. In this paper, cyber warfare and electronic warfare concepts are examined in conjunction with the historical development and the relationship between them is explained. Finally, assessments were carried out about the use of cyber electronic warfare in the coming years.

Tungsten Ditelluride: a layered semimetal.

PubMed

Lee, Chia-Hui; Silva, Eduardo Cruz; Calderin, Lazaro; Nguyen, Minh An T; Hollander, Matthew J; Bersch, Brian; Mallouk, Thomas E; Robinson, Joshua A

2015-06-12

Tungsten ditelluride (WTe2) is a transition metal dichalcogenide (TMD) with physical and electronic properties that make it attractive for a variety of electronic applications. Although WTe2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We experimentally and theoretically investigate the structure, dynamics and electronic properties of WTe2, and verify that WTe2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like transport. Our findings unambiguously confirm the metallic nature of WTe2, introduce new information about the Raman modes of Td-WTe2, and demonstrate that Td-WTe2 is readily oxidized via environmental exposure. Finally, these findings confirm that, in its thermodynamically favored Td form, the utilization of WTe2 in electronic device architectures such as field effect transistors may need to be reevaluated.

10 CFR 440.16 - Minimum program requirements.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 10 Energy 3 2014-01-01 2014-01-01 false Minimum program requirements. 440.16 Section 440.16 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION WEATHERIZATION ASSISTANCE FOR LOW-INCOME PERSONS § 440.16 Minimum...) Families with children; (4) High residential energy users; and (5) Households with a high energy burden. (c...

10 CFR 440.16 - Minimum program requirements.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 10 Energy 3 2012-01-01 2012-01-01 false Minimum program requirements. 440.16 Section 440.16 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION WEATHERIZATION ASSISTANCE FOR LOW-INCOME PERSONS § 440.16 Minimum...) Families with children; (4) High residential energy users; and (5) Households with a high energy burden. (c...

10 CFR 440.16 - Minimum program requirements.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 10 Energy 3 2013-01-01 2013-01-01 false Minimum program requirements. 440.16 Section 440.16 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION WEATHERIZATION ASSISTANCE FOR LOW-INCOME PERSONS § 440.16 Minimum...) Families with children; (4) High residential energy users; and (5) Households with a high energy burden. (c...

Simulation of ASTROD I test mass charging due to solar energetic particles and interplanetary electrons

NASA Astrophysics Data System (ADS)

Liu, L.; Dong, Y.; Bao, G.; Ni, W.-T.; Shaul, D. N. A.

2010-01-01

As ASTROD I travels through space, its test mass will accrue charge due to exposure of the spacecraft to high-energy particles. This test mass charge will result in Coulomb forces between the test mass and the surrounding electrodes. In earlier work, we have used the GEANT 4 toolkit to simulate charging of the ASTROD test mass due to cosmic-ray protons of energies between 0.1 and 1000 GeV at solar maximum and at solar minimum. Here we use GEANT 4 to simulate the charging process due to solar energetic particle events and interplanetary electrons. We then estimate the test mass acceleration noise due to these fluxes. The predicted charging rates range from 2247 e+/s to 47,055 e+/s, at peak intensity, for the four largest SEP events in September and October 1989. Although the noise due to charging exceeds the ASTROD I budget for the two larger events, it can be suppressed through continuous discharging. The acceleration noise during the two small events is well below the design target. The charging rate of the ASTROD I test mass due to interplanetary electrons in this simulation is about -11% of the cosmic-ray protons at solar minimum, and over -37% at solar maximum. In addition to the Monte Carlo uncertainty, an error of ±30% in the net charging rates should be added to account for uncertainties in the spectra, physics models and geometry implementations.

Relative electronic and free energies of octane's unique conformations

NASA Astrophysics Data System (ADS)

Kirschner, Karl N.; Heiden, Wolfgang; Reith, Dirk

2017-06-01

This study reports the geometries and electronic energies of n-octane's unique conformations using perturbation methods that best mimic CCSD(T) results. In total, the fully optimised minima of n-butane (2 conformations), n-pentane (4 conformations), n-hexane (12 conformations) and n-octane (96 conformations) were investigated at several different theory levels and basis sets. We find that DF-MP2.5/aug-cc-pVTZ is in very good agreement with the more expensive CCSD(T) results. At this level, we can clearly confirm the 96 stable minima which were previously found using a reparameterised density functional theory (DFT). Excellent agreement was found between their DFT results and our DF-MP2.5 perturbation results. Subsequent Gibbs free energy calculations, using scaled MP2/aug-cc-pVTZ zero-point vibrational energy and frequencies, indicate a significant temperature dependency of the relative energies, with a change in the predicted global minimum. The results of this work will be important for future computational investigations of fuel-related octane reactions and for optimisation of molecular force fields (e.g. lipids).

Wave-driven butterfly distribution of Van Allen belt relativistic electrons.

PubMed

Xiao, Fuliang; Yang, Chang; Su, Zhenpeng; Zhou, Qinghua; He, Zhaoguo; He, Yihua; Baker, D N; Spence, H E; Funsten, H O; Blake, J B

2015-10-05

Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day-night asymmetry in Earth's magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28 June 2013 geomagnetic storm. Simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution. The current provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons.

Performance of a neutron spectrometer based on a PIN diode.

PubMed

Agosteo, S; D'Angelo, G; Fazzi, A; Para, A Foglio; Pola, A; Ventura, L; Zotto, P

2005-01-01

The neutron spectrometer discussed in this work consists of a PIN diode coupled with a polyethylene converter. Neutrons are detected through the energy deposited by recoil-protons in silicon. The maximum detectable energy is -6 MeV and is imposed by the thickness of the fully depleted layer (300 microm for the present device). The minimum detectable energy which can be assessed with pulse-shape discrimination (PSD) is -0.9 MeV. PSD is performed with a crossover method and setting the diode in the 'reverse-injection' configuration (i.e. with the N+ layer adjacent to the converter). This configuration provides longer collection times for the electron-hole pairs generated by the recoil-protons. The limited interval of detectable energies restricts the application of this spectrometer to low-energy neutron fields, such as the ones which can be produced at facilities hosting low-energy ion accelerators. The capacity to reproduce continuous neutron spectra was investigated by optimising the electronic chain for pulse-shape discrimination. In particular, the spectrometer was irradiated with neutrons that were generated by striking a thick beryllium target with protons of several energies and the measured spectra were compared with data taken from the literature.

RDX geometries, excited states, and revised energy ordering of conformers via MP2 and CCSD(T) methodologies: insights into decomposition mechanism.

PubMed

Molt, Robert W; Watson, Thomas; Lotrich, Victor F; Bartlett, Rodney J

2011-02-10

The geometries, harmonic frequencies, elec-tronic excitation levels, and energetic orderings of various conformers of RDX have been computed at the ab initio MP2 and CCSD(T) levels, providing more reliable results than have been previously obtained. We observe that the various local minimum-energy conformers are all competitive for being the absolute minimum and that, at reasonable temperatures, several conformers will appreciably contribute to the population of RDX. As a result, we have concluded that any mechanistic study to investigate thermal decomposition can reasonably begin from any one of the cyclohexane conformers of RDX. As such, it is necessary to consider the transition states for each RDX conformer to gauge what the activation energy is. Homolytic bond dissociation has long been speculated to be critical to detonation; we report here the most accurate estimates of homolytic BDEs yet calculated, likely to be accurate within 3 kcal mol(-1). The differences in energy for homolytic BDEs among all the possible RDR conformers are again small, such that most all of the conformers can reasonably be speculated as the next step in the mechanism starting from the RDR radical.

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

Pederson, Mark R.; Baruah, Tunna; Basurto, Luis

We have applied a recently developed method to incorporate the self-interaction correction through Fermi orbitals to Mg-porphyrin, C{sub 60}, and pentacene molecules. The Fermi-Löwdin orbitals are localized and unitarily invariant to the Kohn-Sham orbitals from which they are constructed. The self-interaction-corrected energy is obtained variationally leading to an optimum set of Fermi-Löwdin orbitals (orthonormalized Fermi orbitals) that gives the minimum energy. A Fermi orbital, by definition, is dependent on a certain point which is referred to as the descriptor position. The degree to which the initial choice of descriptor positions influences the variational approach to the minimum and the complexitymore » of the energy landscape as a function of Fermi-orbital descriptors is examined in detail for Mg-porphyrin. The applications presented here also demonstrate that the method can be applied to larger molecular systems containing a few hundred electrons. The atomization energy of the C{sub 60} molecule within the Fermi-Löwdin-orbital self-interaction-correction approach is significantly improved compared to local density approximation in the Perdew-Wang 92 functional and generalized gradient approximation of Perdew-Burke-Ernzerhof functionals. The eigenvalues of the highest occupied molecular orbitals show qualitative improvement.« less

Self-interaction corrections applied to Mg-porphyrin, C60, and pentacene molecules

NASA Astrophysics Data System (ADS)

Pederson, Mark R.; Baruah, Tunna; Kao, Der-you; Basurto, Luis

2016-04-01

We have applied a recently developed method to incorporate the self-interaction correction through Fermi orbitals to Mg-porphyrin, C60, and pentacene molecules. The Fermi-Löwdin orbitals are localized and unitarily invariant to the Kohn-Sham orbitals from which they are constructed. The self-interaction-corrected energy is obtained variationally leading to an optimum set of Fermi-Löwdin orbitals (orthonormalized Fermi orbitals) that gives the minimum energy. A Fermi orbital, by definition, is dependent on a certain point which is referred to as the descriptor position. The degree to which the initial choice of descriptor positions influences the variational approach to the minimum and the complexity of the energy landscape as a function of Fermi-orbital descriptors is examined in detail for Mg-porphyrin. The applications presented here also demonstrate that the method can be applied to larger molecular systems containing a few hundred electrons. The atomization energy of the C60 molecule within the Fermi-Löwdin-orbital self-interaction-correction approach is significantly improved compared to local density approximation in the Perdew-Wang 92 functional and generalized gradient approximation of Perdew-Burke-Ernzerhof functionals. The eigenvalues of the highest occupied molecular orbitals show qualitative improvement.

ESR dosimeter material properties of phenols compound exposed to radiotherapeutic electron beams

NASA Astrophysics Data System (ADS)

Gallo, Salvatore; Iacoviello, Giuseppina; Bartolotta, Antonio; Dondi, Daniele; Panzeca, Salvatore; Marrale, Maurizio

2017-09-01

There is a need for a sensitive dosimeter using Electron Spin Resonance spectroscopy for use in medical applications, since non-destructive read-out and dose archival could be achieved with this method. This work reports a systematic ESR investigation of IRGANOX ® 1076 exposed to clinical electron beams produced by a LINAC used for radiation therapy treatments. Recently, dosimetric features of this material were investigated for irradiation with 60Co γ -photons and neutrons in both pellet and film shape and have been found promising thanks to their high efficiency of radiation-matter energy transfer and radical stability at room temperature. Here the analysis of the dosimetric features of these ESR dosimeters exposed to clinical electron beams at energies of 7, 10 and 14 MeV, is described in terms of dependence on microwave power and modulation amplitude, response on dose, dependence on beam type, detection limits, and signal stability after irradiation. The analysis of the ESR signal as function of absorbed dose highlights that the response of this material is linear in the dose range investigated (1-13 Gy) and is independent of the beam energy. The minimum detectable dose is found to be smaller than 1 Gy. Comparison of electron stopping power values of these dosimeters with those of water and soft tissue highlights equivalence of the response to electron beams in the energy range considered. The signal intensity was monitored for 40 days after irradiation and for all energies considered and it shows negligible variations in the first 500 h after irradiation whereas after 1100 h the signal decay is only of about 4%. In conclusion, it is found that phenolic compounds possess good dosimetric features which make it useful as a sensitive dosimeter for medical applications.

Plasmon excitations with a semi-integer angular momentum.

PubMed

Mendonça, J T; Serbeto, A; Vieira, J

2018-05-18

We provide an explicit model for a spin-1/2 quasi-particle, based on the superposition of plasmon excitations in a quantum plasmas with intrinsic orbital angular momentum. Such quasi-particle solutions can show remarkable similarities with single electrons moving in vacuum: they have spin-1/2, a finite rest mass, and a quantum dispersion. We also show that these quasi-particle solutions satisfy a criterium of energy minimum.

Global optimization of small bimetallic Pd-Co binary nanoalloy clusters: a genetic algorithm approach at the DFT level.

PubMed

Aslan, Mikail; Davis, Jack B A; Johnston, Roy L

2016-03-07

The global optimisation of small bimetallic PdCo binary nanoalloys are systematically investigated using the Birmingham Cluster Genetic Algorithm (BCGA). The effect of size and composition on the structures, stability, magnetic and electronic properties including the binding energies, second finite difference energies and mixing energies of Pd-Co binary nanoalloys are discussed. A detailed analysis of Pd-Co structural motifs and segregation effects is also presented. The maximal mixing energy corresponds to Pd atom compositions for which the number of mixed Pd-Co bonds is maximised. Global minimum clusters are distinguished from transition states by vibrational frequency analysis. HOMO-LUMO gap, electric dipole moment and vibrational frequency analyses are made to enable correlation with future experiments.

KF post-deposition treatment of industrial Cu(In, Ga)(S, Se) 2 thin-film surfaces: Modifying the chemical and electronic structure

DOE PAGES

Mezher, Michelle; Mansfield, Lorelle M.; Horsley, Kimberly; ...

2017-08-14

The chemical and electronic structures of industrial chalcopyrite photovoltaic absorbers after KF post-deposition treatment (KF-PDT) are investigated using electron spectroscopies to probe the occupied and unoccupied electronic states. In contrast to a variety of recent publications on the impact of KF-PDT, this study focuses on industrial Cu(In,Ga)(S,Se) 2 absorbers that also contain sulfur at the surface. We find that the KF-PDT removes surface adsorbates and oxides and also observe a change in the S/Se ratio. Furthermore, the KF-PDT leads to a Cu reduction at the surface but to a much lower degree than the strongly Cu-depleted or even Cu-free surfacesmore » reported for (non-industrial) sulfur-free Cu(In,Ga)Se 2 absorbers. Furthermore, the valence band maximum at the surface is found at a lower energy compared to the untreated absorber, and the conduction band minimum is found at a higher energy, overall revealing a widening of the bandgap in the surface region.« less

KF post-deposition treatment of industrial Cu(In, Ga)(S, Se) 2 thin-film surfaces: Modifying the chemical and electronic structure

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

Mezher, Michelle; Mansfield, Lorelle M.; Horsley, Kimberly

The chemical and electronic structures of industrial chalcopyrite photovoltaic absorbers after KF post-deposition treatment (KF-PDT) are investigated using electron spectroscopies to probe the occupied and unoccupied electronic states. In contrast to a variety of recent publications on the impact of KF-PDT, this study focuses on industrial Cu(In,Ga)(S,Se) 2 absorbers that also contain sulfur at the surface. We find that the KF-PDT removes surface adsorbates and oxides and also observe a change in the S/Se ratio. Furthermore, the KF-PDT leads to a Cu reduction at the surface but to a much lower degree than the strongly Cu-depleted or even Cu-free surfacesmore » reported for (non-industrial) sulfur-free Cu(In,Ga)Se 2 absorbers. Furthermore, the valence band maximum at the surface is found at a lower energy compared to the untreated absorber, and the conduction band minimum is found at a higher energy, overall revealing a widening of the bandgap in the surface region.« less

Variation of mechanical and thermal properties of the thermoplastics reinforced with natural fibers by electron beam processing

NASA Astrophysics Data System (ADS)

Kim, Sok Won; Oh, Seungmin; Lee, Kyuse

2007-11-01

With restrictions for environmental protection being strengthened, the thermoplastics reinforced with natural fibers (NFs) such as jute, kenaf, flax, etc., appeared as an automobile interior material instead of the chemical plastics. Regardless of many advantages, one shortcoming is the deformation after being formed in high temperature of about 200 °C, caused by the poor adhesion between the natural fibers and thermoplastics. Also, the energy saving in connection with car air-conditioning becomes very important. In this study, the thermal conductivity, tensile strength, and deformation of several kinds of thermoplastic composites composing of 50% polypropylene (PP) and 50% natural fiber irradiated by the electron beam (energy: 0.5 MeV, dose: 0-20 kGy) were measured. The length and thickness of PP and NF are 80±10 mm and 40-120 μm, respectively. The results show that the thermal conductivity and the tensile strength changed and became minimum when the dose of electron beam is 10 kGy, and the deformation after the thermal cycle were reduced by the electron beam.

Cooled window for X-rays or charged particles

DOEpatents

Logan, Clinton M.

1996-01-01

A window that provides good structural integrity and a very high capacity for removal of the heat deposited by x-rays, electrons, or ions, with minimum attenuation of the desired beam. The window is cooled by providing microchannels therein through which a coolant is pumped. For example, the window may be made of silicon with etched microchannels therein and covered by a silicon member. A window made of silicon with a total thickness of 520 .mu.m transmits 96% of the x-rays at an energy of 60 keV, and the transmission is higher than 90% for higher energy photons.

New generation of Cherenkov counters

NASA Astrophysics Data System (ADS)

Giomataris, Y.; Charpak, G.; Peskov, V.; Sauli, F.

1992-12-01

Experimental results with a parallel plate avalanche chamber (PPAC) having a CsI photocathode and pad array readout are reported. High gains in excess of 10 5 have been obtained with He gas at atmospheric pressure and traces of CH 4 or CF 4 quencher. Such light gas mixtures extend the transparency for the Cherenkov light to the extreme UV region and allow detector operation with very low sensitivity to the ionization produced by minimum ionizing particles. A hadron blind detector (HBD) is discussed which exploits the broad photon energy bandwidth (≈ 10 eV) and the high Cherenkov threshold ( pπ = 15 GeV). This fast detector, since it has a good spatial resolution, can be used at the future Large Hadron Collider (LHC) or the Superconductivity Super Collider (SSC) either as an efficient electron tagger, rejecting hadrons faking electrons in the calorimeter, or as a pretracker giving fast electron and high-energy muon signature and momentum estimation. Other potential applications in the domain of Cherenkov light detection are also discussed.

Ablation driven by hot electrons generated during the ignitor laser pulse in shock ignition

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

Piriz, A. R.; Rodriguez Prieto, G.; Tahir, N. A.

2012-12-15

An analytical model for the ablation driven by hot electrons is presented. The hot electrons are assumed to be generated during the high intensity laser spike used to produce the ignitor shock wave in the shock ignition driven inertial fusion concept, and to carry on the absorbed laser energy in its totality. Efficient energy coupling requires to keep the critical surface sufficiently close to the ablation front and this goal can be achieved for high laser intensities provided that the laser wavelength is short enough. Scaling laws for the ablation pressure and the other relevant magnitudes of the ablation cloudmore » are found in terms of the laser and target parameters. The effect of the preformed plasma assembled by the compression pulse, previous to the ignitor, is also discussed. It is found that a minimum ratio between the compression and the ignitor pulses would be necessary for the adequate matching of the corresponding scale lengths.« less

Method and apparatus for detecting dilute concentrations of radioactive xenon in samples of xenon extracted from the atmosphere

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

Warburton, William K.; Hennig, Wolfgang G.

A method and apparatus for measuring the concentrations of radioxenon isotopes in a gaseous sample wherein the sample cell is surrounded by N sub-detectors that are sensitive to both electrons and to photons from radioxenon decays. Signal processing electronics are provided that can detect events within the sub-detectors, measure their energies, determine whether they arise from electrons or photons, and detect coincidences between events within the same or different sub-detectors. The energies of detected two or three event coincidences are recorded as points in associated two or three-dimensional histograms. Counts within regions of interest in the histograms are then usedmore » to compute estimates of the radioxenon isotope concentrations. The method achieves lower backgrounds and lower minimum detectable concentrations by using smaller detector crystals, eliminating interference between double and triple coincidence decay branches, and segregating double coincidences within the same sub-detector from those occurring between different sub-detectors.« less

Anode optimization for miniature electronic brachytherapy X-ray sources using Monte Carlo and computational fluid dynamic codes

PubMed Central

Khajeh, Masoud; Safigholi, Habib

2015-01-01

A miniature X-ray source has been optimized for electronic brachytherapy. The cooling fluid for this device is water. Unlike the radionuclide brachytherapy sources, this source is able to operate at variable voltages and currents to match the dose with the tumor depth. First, Monte Carlo (MC) optimization was performed on the tungsten target-buffer thickness layers versus energy such that the minimum X-ray attenuation occurred. Second optimization was done on the selection of the anode shape based on the Monte Carlo in water TG-43U1 anisotropy function. This optimization was carried out to get the dose anisotropy functions closer to unity at any angle from 0° to 170°. Three anode shapes including cylindrical, spherical, and conical were considered. Moreover, by Computational Fluid Dynamic (CFD) code the optimal target-buffer shape and different nozzle shapes for electronic brachytherapy were evaluated. The characterization criteria of the CFD were the minimum temperature on the anode shape, cooling water, and pressure loss from inlet to outlet. The optimal anode was conical in shape with a conical nozzle. Finally, the TG-43U1 parameters of the optimal source were compared with the literature. PMID:26966563

Ag/CuO nanoparticles prepared from a novel trinuclear compound [Cu(Imdz)4(Ag(CN)2)2] (Imdz = imidazole) by a pyrolysis display excellent antimicrobial activity

NASA Astrophysics Data System (ADS)

Adhikary, Jaydeep; Das, Balaram; Chatterjee, Sourav; Dash, Sandeep Kumar; Chattopadhyay, Sourav; Roy, Somenath; Chen, Jeng-Wei; Chattopadhyay, Tanmay

2016-06-01

One copper and two silver containing one hetero tri-nuclear precursor compound [Cu(Imdz)4(Ag(CN)2)2] (1) (Imdz = Imidazole) has been synthesized and characterized by single crystal X-ray diffraction. Simple pyrolysis of the complex at 550 °C for 4 h afforded Ag/CuO nanoparticles (NPs). The synthesized nanoparticles were characterized by ultraviolet-visible (UV-Vis), Fourier transform infrared (FT-IR), X-ray powder diffraction (XRPD), dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and X-ray photo electron spectroscopy (XPS). Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) have been employed as model microbial species to study the anti-microbial activity of the synthesized NPs. The NPs showed potent anti-microbial activity evidenced from the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values. Very high level of cell uptake and then generation of reactive oxygen species (ROS) are the origin of such strong antimicrobial activity for the NPs. However, the cytotoxicity level of the NPs towards normal human cell is very low.

Chemistry of Aviation Fuels

NASA Technical Reports Server (NTRS)

Knepper, Bryan; Hwang, Soon Muk; DeWitt, Kenneth J.

2004-01-01

Minimum ignition energies of various methanol/air mixtures were measured in a temperature controlled constant volume combustion vessel using a spark ignition method with a spark gap distance of 2 mm. The minimum ignition energies decrease rapidly as the mixture composition (equivalence ratio, Phi) changes from lean to stoichiometric, reach a minimum value, and then increase rather slowly with Phi. The minimum of the minimum ignition energy (MIE) and the corresponding mixture composition were determined to be 0.137 mJ and Phi = 1.16, a slightly rich mixture. The variation of minimum ignition energy with respect to the mixture composition is explained in terms of changes in reaction chemistry.

Investigation of energy deposited by femtosecond electron transfer in collisions using hydrated ion nanocalorimetry.

PubMed

Holm, Anne I S; Donald, William A; Hvelplund, Preben; Larsen, Mikkel K; Nielsen, Steen Brøndsted; Williams, Evan R

2008-10-30

Ion nanocalorimetry is used to investigate the internal energy deposited into M (2+)(H 2O) n , M = Mg ( n = 3-11) and Ca ( n = 3-33), upon 100 keV collisions with a Cs or Ne atom target gas. Dissociation occurs by loss of water molecules from the precursor (charge retention) or by capture of an electron to form a reduced precursor (charge reduction) that can dissociate either by loss of a H atom accompanied by water molecule loss or by exclusively loss of water molecules. Formation of bare CaOH (+) and Ca (+) by these two respective dissociation pathways occurs for clusters with n up to 33 and 17, respectively. From the threshold dissociation energies for the loss of water molecules from the reduced clusters, obtained from binding energies calculated using a discrete implementation of the Thomson liquid drop model and from quantum chemistry, estimates of the internal energy deposition can be obtained. These values can be used to establish a lower limit to the maximum and average energy deposition. Not taking into account effects of a kinetic shift, over 16 eV can be deposited into Ca (2+)(H 2O) 33, the minimum energy necessary to form bare CaOH (+) from the reduced precursor. The electron capture efficiency is at least a factor of 40 greater for collisions of Ca (2+)(H 2O) 9 with Cs than with Ne, reflecting the lower ionization energy of Cs (3.9 eV) compared to Ne (21.6 eV). The branching ratio of the two electron capture dissociation pathways differs significantly for these two target gases, but the distributions of water molecules lost from the reduced precursors are similar. These results suggest that the ionization energy of the target gas has a large effect on the electron capture efficiency, but relatively little effect on the internal energy deposited into the ion. However, the different branching ratios suggest that different electronic excited states may be accessed in the reduced precursor upon collisions with these two different target gases.

Modelling of Electron and Proton Beams in a White-light Solar Flare

NASA Astrophysics Data System (ADS)

Milligan, R. O.; Procházka, O.; Reid, A.; Allred, J. C.; Mathioudakis, M.

2017-12-01

Observations of an X1 class WL solar flare on 2014 June 11 showed a surprisingly weak emission in both higher order Balmer and Lyman lines and continua. The flare was observed by RHESSI but low energy cut-off of non-thermal component was indeterminable due to the unusually hard electron spectrum (delta = 3). An estimate of power in non-thermal electron beams together with an area of WL emission observed by HMI yielded to an upper and lower estimate of flux 1E9 and 3E10 erg/cm2/s, respectively. We performed a grid of models using a radiative hydrodynamic code RADYN in order to compare synthetic spectra with observations. For low energy cut-off we chose a range from 20 to 120 keV with a step of 20 keV and delta parameter equal to 3. Electron beam-driven models show that higher low energy cut-off is more likely to produce an absorption Balmer line profile, if the total energy flux remains relatively low. On the other hand a detectable rise of HMI continuum (617 nm) lays a lower limit on the beam flux. Proton beam-driven models with equivalent fluxes indicate a greater penetration depth, while the Balmer lines reveal significantly weaker emission. Atmospheric temperature profiles show that for higher values of low energy cut-off the energy of the beam is deposited lower in chromosphere or even in temperature minimum region. This finding suggests, that suppressed hydrogen emission can indicate a formation of white-light continuum below chromosphere.

Charge transfer excitons and image potential states on organic semiconductor surfaces

NASA Astrophysics Data System (ADS)

Yang, Qingxin; Muntwiler, Matthias; Zhu, X.-Y.

2009-09-01

We report two types of excited electronic states on organic semiconductor surfaces: image potential states (IPS) and charge transfer excitons (CTE). In the former, an excited electron is localized in the surface-normal direction by the image potential and delocalized in the surface plane. In the latter, the electron is localized in all directions by both the image potential and the Coulomb potential from a photogenerated hole on an organic molecule. We use crystalline pentacene and tetracene surfaces as model systems, and time- and angle-resolved two-photon photoemission spectroscopy to probe the energetics and dynamics of both the IPS and the CTE states. On either pentacene or tetracene surfaces, we observe delocalized image bands and a series of CT excitons with binding energies <0.5eV below the image-band minimum. The binding energies of these CT excitons agree well with solutions to the atomic-H-like Schrödinger equation based on the image potential and the electron-hole Coulomb potential. We hypothesize that the formation of CT excitons should be general to the surfaces of organic semiconductors where the relatively narrow valance-band width facilitates the localization of the hole and the low dielectric constant ensures strong electron-hole attraction.

Minimum energy control and optimal-satisfactory control of Boolean control network

NASA Astrophysics Data System (ADS)

Li, Fangfei; Lu, Xiwen

2013-12-01

In the literatures, to transfer the Boolean control network from the initial state to the desired state, the expenditure of energy has been rarely considered. Motivated by this, this Letter investigates the minimum energy control and optimal-satisfactory control of Boolean control network. Based on the semi-tensor product of matrices and Floyd's algorithm, minimum energy, constrained minimum energy and optimal-satisfactory control design for Boolean control network are given respectively. A numerical example is presented to illustrate the efficiency of the obtained results.

A 5 nW Quasi-Linear CMOS Hot-Electron Injector for Self-Powered Monitoring of Biomechanical Strain Variations.

PubMed

Zhou, Liang; Abraham, Adam C; Tang, Simon Y; Chakrabartty, Shantanu

2016-12-01

Piezoelectricity-driven hot-electron injectors (p-HEI) are used for self-powered monitoring of mechanical activity in biomechanical implants and structures. Previously reported p-HEI devices operate by harvesting energy from a piezoelectric transducer to generate current and voltage references which are then used for initiating and controlling the process of hot-electron injection. As a result, the minimum energy required to activate the device is limited by the power requirements of the reference circuits. In this paper we present a p-HEI device that operates by directly exploiting the self-limiting capability of an energy transducer when driving the process of hot-electron injection in a pMOS floating-gate transistor. As a result, the p-HEI device can activate itself at input power levels less than 5 nW. Using a prototype fabricated in a 0.5- [Formula: see text] bulk CMOS process we validate the functionality of the proposed injector and show that for a fixed input power, its dynamics is quasi-linear with respect to time. The paper also presents measurement results using a cadaver phantom where the fabricated p-HEI device has been integrated with a piezoelectric transducer and is used for self-powered monitoring of mechanical activity.

HREM study of irradiation damage in human dental enamel crystals.

PubMed

Brès, E F; Hutchison, J L; Senger, B; Voegel, J C; Frank, R M

1991-06-01

Several phenomena have been observed during the examination of human dental enamel crystals (mainly constituted by hydroxyapatite (OHAP] by high-resolution electron microscopy (HREM) at 300 and 400 keV: orientation-dependent damage in the form of mass loss from voids or uniform destruction of crystal structure, beam-induced diffusion creating outgrowths at the crystal surfaces, recrystallization of the bulk crystal and crystallization of the inorganic components of the matrix surrounding the crystals. These beam-induced crystals have the CaO structure. The phenomena observed are most likely due to various electron-crystal interaction mechanisms (ballistic knock-on damage, electronic excitations, temperature rise, etc.). In this paper, the contribution of the ballistic process to the phenomena observed is discussed. The quantitative description of the knock-on collisions rests on the McKinley-Feshbach cross-section formula. The minimum ion displacement energies which appear in this expression have been estimated on the basis of the electrostatic ion binding energies, and the covalent bond energies if required. It is shown that hydroxyl, calcium and oxygen ions can effectively be displaced by the incident 300 and 400 keV electrons. Thus, the formation of CaO crystals by the combination of calcium and oxygen ions diffusing from their initial sites inside the OHAP lattice can tentatively be explained.

Analysis of boron carbides' electronic structure

NASA Technical Reports Server (NTRS)

Howard, Iris A.; Beckel, Charles L.

1986-01-01

The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

Tungsten Ditelluride: a layered semimetal

PubMed Central

Lee, Chia-Hui; Silva, Eduardo Cruz; Calderin, Lazaro; Nguyen, Minh An T.; Hollander, Matthew J.; Bersch, Brian; Mallouk, Thomas E.; Robinson, Joshua A.

2015-01-01

Tungsten ditelluride (WTe2) is a transition metal dichalcogenide (TMD) with physical and electronic properties that make it attractive for a variety of electronic applications. Although WTe2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We experimentally and theoretically investigate the structure, dynamics and electronic properties of WTe2, and verify that WTe2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like transport. Our findings unambiguously confirm the metallic nature of WTe2, introduce new information about the Raman modes of Td-WTe2, and demonstrate that Td-WTe2 is readily oxidized via environmental exposure. Finally, these findings confirm that, in its thermodynamically favored Td form, the utilization of WTe2 in electronic device architectures such as field effect transistors may need to be reevaluated. PMID:26066766

Prompt Acceleration of Magnetospheric Electrons to Ultrarelativistic Energies by the 17 March 2015 Interplanetary Shock

NASA Technical Reports Server (NTRS)

Kanekal, S. G.; Baker, D. N.; Fennell, J. F.; Jones, A.; Schiller, Q.; Richardson, I.G.; Li, X.; Turner, D. L.; Califf, S.; Claudepierre, S. G.;

10 CFR 862.6 - Voluntary minimum altitude.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 10 Energy 4 2011-01-01 2011-01-01 false Voluntary minimum altitude. 862.6 Section 862.6 Energy DEPARTMENT OF ENERGY RESTRICTIONS ON AIRCRAFT LANDING AND AIR DELIVERY AT DEPARTMENT OF ENERGY NUCLEAR SITES... designated site. Applicable FAA prohibitions or restrictions take precedence over this voluntary minimum...

Accurate bond energies of hydrocarbons from complete basis set extrapolated multi-reference singles and doubles configuration interaction.

PubMed

Oyeyemi, Victor B; Pavone, Michele; Carter, Emily A

2011-12-09

Quantum chemistry has become one of the most reliable tools for characterizing the thermochemical underpinnings of reactions, such as bond dissociation energies (BDEs). The accurate prediction of these particular properties (BDEs) are challenging for ab initio methods based on perturbative corrections or coupled cluster expansions of the single-determinant Hartree-Fock wave function: the processes of bond breaking and forming are inherently multi-configurational and require an accurate description of non-dynamical electron correlation. To this end, we present a systematic ab initio approach for computing BDEs that is based on three components: 1) multi-reference single and double excitation configuration interaction (MRSDCI) for the electronic energies; 2) a two-parameter scheme for extrapolating MRSDCI energies to the complete basis set limit; and 3) DFT-B3LYP calculations of minimum-energy structures and vibrational frequencies to account for zero point energy and thermal corrections. We validated our methodology against a set of reliable experimental BDE values of CC and CH bonds of hydrocarbons. The goal of chemical accuracy is achieved, on average, without applying any empirical corrections to the MRSDCI electronic energies. We then use this composite scheme to make predictions of BDEs in a large number of hydrocarbon molecules for which there are no experimental data, so as to provide needed thermochemical estimates for fuel molecules. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A recoil-proton spectrometer based on a p-i-n diode implementing pulse-shape discrimination.

PubMed

Agosteo, S; D'Angelo, G; Fazzi, A; Foglio Para, A; Pola, A; Ventura, L; Zotto, P

2004-01-01

A recoil-proton spectrometer was created by coupling a p-i-n diode with a polyethylene converter. The maximum detectable energy, imposed by the thickness of the totally depleted layer, is approximately 6 MeV. The minimum detectable energy is limited by the contribution of secondary electrons generated by photons in the detector assembly. This limit is approximately 1.5 MeV at full-depletion voltage and was decreased using pulse-shape discrimination. The diode was set up in the 'reverse-injection' configuration (i.e. with the N+ layer adjacent to the converter). This configuration provides longer collection times for the electron-hole pairs generated by the recoil-protons. The pulse-shape discrimination was based on the zero-crossing time of bipolar signals from a (CR)2-(RC)2 filter. The detector was characterised using monoenergetic neutrons generated in the Van De Graaff CN accelerator at the INFN-Laboratori Nazionali di Legnaro. The energy limit for discrimination proved to be approximately 900 keV.

INVERSE COMPTON SCATTERING MODEL FOR X-RAY EMISSION OF THE GAMMA-RAY BINARY LS 5039

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

Yamaguchi, M. S.; Takahara, F.

2012-12-20

We propose a model for the gamma-ray binary LS 5039 in which the X-ray emission is due to the inverse Compton (IC) process instead of the synchrotron radiation. Although the synchrotron model has been discussed in previous studies, it requires a strong magnetic field which leads to a severe suppression of the TeV gamma-ray flux in conflict with H.E.S.S. observations. In this paper, we calculate the IC emission by low energy electrons ({gamma}{sub e} {approx}< 10{sup 3}) in the Thomson regime. We find that IC emission of the low energy electrons can explain the X-ray flux and spectrum observed withmore » Suzaku if the minimum Lorentz factor of injected electrons {gamma}{sub min} is around 10{sup 3}. In addition, we show that the Suzaku light curve is well reproduced if {gamma}{sub min} varies in proportion to the Fermi flux when the distribution function of injected electrons at higher energies is fixed. We conclude that the emission from LS 5039 is well explained by the model with the IC emission from electrons whose injection properties are dependent on the orbital phase. Since the X-ray flux is primarily determined by the total number of cooling electrons, this conclusion is rather robust, although some mismatches between the model and observations at the GeV band remain in the present formulation.« less

Microstability Properties of the Local Minimum | B | Regime in Pegasus

NASA Astrophysics Data System (ADS)

Smith, David R.; Bongard, M. W.; Fonck, R. J.; Reusch, J. A.; Rhodes, A. T.

2017-10-01

A local minimum | B | region, or ``magnetic well,'' was recently observed in the low-aspect-ratio Pegasus device in high- β scenarios with strong edge current peaking. The ∇B reversal within the magnetic well alters particle drifts, orbits, fast ion losses, and instability drives. Here, we report on the microstability properties of the magnetic well region with calculations from the GENE gyrokinetic code. In particular, we explore the dependence on magnetic well depth and the role of electromagnetic effects. Preliminary results from local electromagnetic calculations indicate unstable electron modes exist in the magnetic well region. Connections to NSTX-U and MAST-U operational scenarios are also discussed. Finally, probe measurements of electrostatic and magnetic fluctuations in the Pegasus magnetic well region are presented in Ref. 3. This material is based upon work supported by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Award Number DE-SC0001288 and DE-FG02-96ER54375.

Electronic structure and vibrational analysis of AHA⋯HX complexes

NASA Astrophysics Data System (ADS)

Joshi, Kaustubh A.; Gejji, Shridhar P.

2005-10-01

Electronic structures of the binary complexes of acetohydroxamic acid (AHA) and hydrogen halides, HX (X = F, Cl, Br) have been investigated using the second order perturbation theory. In the lowest energy structure of AHA⋯HF complex, hydrogen fluoride acts as a proton-donor with carbonyl oxygen and simultaneously as a proton-acceptor with the hydroxyl group. For chloro- and bromo-substituted derivatives, however, the lowest minimum possesses hydrogen-bonded interactions with the carbonyl oxygen in addition to those from the methyl proton of AHA. Frequency shifts of NH and CN stretching vibrations enable one to distinguish different conformers of AHA⋯HX complexes.

On Directly Solving SCHRÖDINGER Equation for H+2 Ion by Genetic Algorithm

NASA Astrophysics Data System (ADS)

Saha, Rajendra; Bhattacharyya, S. P.

Schrödinger equation (SE) is sought to be solved directly for the ground state of H+2 ion by invoking genetic algorithm (GA). In one approach the internuclear distance (R) is kept fixed, the corresponding electronic SE for H+2 is solved by GA at each R and the full potential energy curve (PEC) is constructed. The minimum of the PEC is then located giving Ve and Re. Alternatively, Ve and Re are located in a single run by allowing R to vary simultaneously while solving the electronic SE by genetic algorithm. The performance patterns of the two strategies are compared.

Numerical study of electronic impact and radiation in sonoluminescence

NASA Astrophysics Data System (ADS)

Xu, Ning; Wang, Long; Hu, Xiwei

1998-02-01

A hydrodynamic simulation of pure argon single-bubble sonoluminescence including electron collisional ionization, recombination, and radiative energy loss has been performed. We find that near the moment that the bubble reaches its minimum radius the atoms inside a very thin layer around the origin of the bubble are strongly ionized, and the light emission occurs nearly simultaneously. Therefore we conclude that multiple ionization and recombination, which mainly occur in the thin layer of plasma, play a dramatically important role in the noble gas sonoluminescence. We also find that the temperature and the intensity of luminescence are not so high as those predicted by previous models, which consider only neutral gases.

10 CFR 862.6 - Voluntary minimum altitude.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 10 Energy 4 2010-01-01 2010-01-01 false Voluntary minimum altitude. 862.6 Section 862.6 Energy DEPARTMENT OF ENERGY RESTRICTIONS ON AIRCRAFT LANDING AND AIR DELIVERY AT DEPARTMENT OF ENERGY NUCLEAR SITES § 862.6 Voluntary minimum altitude. In addition to complying with all applicable FAA prohibitions or...

Universal energy relations and metal/ceramic interfaces

NASA Technical Reports Server (NTRS)

Smith, John R.; Schlosser, Herbert; Ferrante, John

1990-01-01

Known general relationships between pertinent variables are applied to investigate metal-ceramic interfaces. The adhesive energy is determined. The electronic exchange-correlation energy is found to be the dominant attractive term in the total energy. Results for the adhesive energy are obtained for junctions of all combinations of the low index surfaces of Al,Na, Mg, and Zn. This leads to a variety of curves, all with a single minimum of separation and equilibrium binding energy. Scaling results for 10 contacts fall closely onto a single curve, a universal energy relation for adhesion. The scaled chemisorption curves fall accurately on the same universal form that was found for adhesion. For the case of cohesion, all-first principle results are scaled and again all scaled curves for a variety of metals fall accurately on the universal form for adhesion and chemisorption. An intimate relationship between the energetics of solids and molecules is inferred.

Pulsed electron beam propagation in gases under pressure of 6.6 kPa in drift tube

NASA Astrophysics Data System (ADS)

Kholodnaya, G. E.; Sazonov, R. V.; Ponomarev, D. V.; Remnev, G. E.; Poloskov, A. V.

2017-02-01

This paper presents the results of an investigation of pulsed electron beam transport propagated in a drift tube filled with different gases (He, H2, N2, Ar, SF6, and CO2). The total pressure in the drift tube was 6.6 kPa. The experiments were carried out using a TEA-500 pulsed electron accelerator. The electron beam was propagated in the drift tube composed of two sections equipped with reverse current shunts. Under a pressure of 6.6 kPa, the maximum value of the electron beam charge closed on the walls of the drift tube was recorded when the beam was propagated in hydrogen and carbon dioxide. The minimum value of the electron beam charge closed on the walls of the drift tube was recorded for sulfur hexafluoride. The visualization of the pulsed electron beam energy losses onto the walls of the drift chamber was carried out using radiation-sensitive film.

Energy and IAQ Implications of Alternative Minimum Ventilation Rates in California Retail and School Buildings

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

Dutton, Spencer M.; Fisk, William J.

For a stand-alone retail building, a primary school, and a secondary school in each of the 16 California climate zones, the EnergyPlus building energy simulation model was used to estimate how minimum mechanical ventilation rates (VRs) affect energy use and indoor air concentrations of an indoor-generated contaminant. The modeling indicates large changes in heating energy use, but only moderate changes in total building energy use, as minimum VRs in the retail building are changed. For example, predicted state-wide heating energy consumption in the retail building decreases by more than 50% and total building energy consumption decreases by approximately 10% asmore » the minimum VR decreases from the Title 24 requirement to no mechanical ventilation. The primary and secondary schools have notably higher internal heat gains than in the retail building models, resulting in significantly reduced demand for heating. The school heating energy use was correspondingly less sensitive to changes in the minimum VR. The modeling indicates that minimum VRs influence HVAC energy and total energy use in schools by only a few percent. For both the retail building and the school buildings, minimum VRs substantially affected the predicted annual-average indoor concentrations of an indoor generated contaminant, with larger effects in schools. The shape of the curves relating contaminant concentrations with VRs illustrate the importance of avoiding particularly low VRs.« less

Molecules for materials: germanium hydride neutrals and anions. Molecular structures, electron affinities, and thermochemistry of GeHn/GeHn- (n = 0-4) and Ge2Hn/Ge2Hn(-) (n = 0-6).

PubMed

Li, Qian-Shu; Lü, Rui-Hua; Xie, Yaoming; Schaefer, Henry F

2002-12-01

The GeH(n) (n = 0-4) and Ge(2)H(n) (n = 0-6) systems have been studied systematically by five different density functional methods. The basis sets employed are of double-zeta plus polarization quality with additional s- and p-type diffuse functions, labeled DZP++. For each compound plausible energetically low-lying structures were optimized. The methods used have been calibrated against a comprehensive tabulation of experimental electron affinities (Chemical Reviews 102, 231, 2002). The geometries predicted in this work include yet unknown anionic species, such as Ge(2)H(-), Ge(2)H(2)(-), Ge(2)H(3)(-), Ge(2)H(4)(-), and Ge(2)H(5)(-). In general, the BHLYP method predicts the geometries closest to the few available experimental structures. A number of structures rather different from the analogous well-characterized hydrocarbon radicals and anions are predicted. For example, a vinylidene-like GeGeH(2) (-) structure is the global minimum of Ge(2)H(2) (-). For neutral Ge(2)H(4), a methylcarbene-like HGë-GeH(3) is neally degenerate with the trans-bent H(2)Ge=GeH(2) structure. For the Ge(2)H(4) (-) anion, the methylcarbene-like system is the global minimum. The three different neutral-anion energy differences reported in this research are: the adiabatic electron affinity (EA(ad)), the vertical electron affinity (EA(vert)), and the vertical detachment energy (VDE). For this family of molecules the B3LYP method appears to predict the most reliable electron affinities. The adiabatic electron affinities after the ZPVE correction are predicted to be 2.02 (Ge(2)), 2.05 (Ge(2)H), 1.25 (Ge(2)H(2)), 2.09 (Ge(2)H(3)), 1.71 (Ge(2)H(4)), 2.17 (Ge(2)H(5)), and -0.02 (Ge(2)H(6)) eV. We also reported the dissociation energies for the GeH(n) (n = 1-4) and Ge(2)H(n) (n = 1-6) systems, as well as those for their anionic counterparts. Our theoretical predictions provide strong motivation for the further experimental study of these important germanium hydrides. Copyright 2002 Wiley Periodicals, Inc.

Electronic and magnetic properties of small rhodium clusters

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

Soon, Yee Yeen; Yoon, Tiem Leong; Lim, Thong Leng

2015-04-24

We report a theoretical study of the electronic and magnetic properties of rhodium-atomic clusters. The lowest energy structures at the semi-empirical level of rhodium clusters are first obtained from a novel global-minimum search algorithm, known as PTMBHGA, where Gupta potential is used to describe the atomic interaction among the rhodium atoms. The structures are then re-optimized at the density functional theory (DFT) level with exchange-correlation energy approximated by Perdew-Burke-Ernzerhof generalized gradient approximation. For the purpose of calculating the magnetic moment of a given cluster, we calculate the optimized structure as a function of the spin multiplicity within the DFT framework.more » The resultant magnetic moments with the lowest energies so obtained allow us to work out the magnetic moment as a function of cluster size. Rhodium atomic clusters are found to display a unique variation in the magnetic moment as the cluster size varies. However, Rh{sub 4} and Rh{sub 6} are found to be nonmagnetic. Electronic structures of the magnetic ground-state structures are also investigated within the DFT framework. The results are compared against those based on different theoretical approaches available in the literature.« less

Excitation energies, photoionization cross sections, and asymmetry parameters of the methyl and silyl radicals.

PubMed

Velasco, A M; Lavín, C; Dolgounitcheva, O; Ortiz, J V

2014-08-21

Vertical excitation energies of the methyl and silyl radicals were inferred from ab initio electron propagator calculations on the electron affinities of CH3(+) and SiH3(+). Photoionization cross sections and angular distribution of photoelectrons for the outermost orbitals of both CH3 and SiH3 radicals have been obtained with the Molecular Quantum Defect Orbital method. The individual ionization cross sections corresponding to the Rydberg channels to which the excitation of the ground state's outermost electron gives rise are reported. Despite the relevance of methyl radical in atmospheric chemistry and combustion processes, only data for the photon energy range of 10-11 eV seem to be available. Good agreement has been found with experiment for photoionization cross section of this radical. To our knowledge, predictions of the above mentioned photoionization parameters on silyl radical are made here for the first time, and we are not aware of any reported experimental measurements. An analysis of our results reveals the presence of a Cooper minimum in the photoionization of the silyl radical. The adequacy of the two theoretical procedures employed in the present work is discussed.

Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

NASA Technical Reports Server (NTRS)

Chaban, Galina M.; Salter, Latasha M.; Kwak, Dochan (Technical Monitor)

2002-01-01

Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

Excitation energies, photoionization cross sections, and asymmetry parameters of the methyl and silyl radicals

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

Velasco, A. M.; Lavín, C., E-mail: clavin@qf.uva.es; Dolgounitcheva, O.

2014-08-21

Vertical excitation energies of the methyl and silyl radicals were inferred from ab initio electron propagator calculations on the electron affinities of CH{sub 3}{sup +} and SiH{sub 3}{sup +}. Photoionization cross sections and angular distribution of photoelectrons for the outermost orbitals of both CH{sub 3} and SiH{sub 3} radicals have been obtained with the Molecular Quantum Defect Orbital method. The individual ionization cross sections corresponding to the Rydberg channels to which the excitation of the ground state's outermost electron gives rise are reported. Despite the relevance of methyl radical in atmospheric chemistry and combustion processes, only data for the photonmore » energy range of 10–11 eV seem to be available. Good agreement has been found with experiment for photoionization cross section of this radical. To our knowledge, predictions of the above mentioned photoionization parameters on silyl radical are made here for the first time, and we are not aware of any reported experimental measurements. An analysis of our results reveals the presence of a Cooper minimum in the photoionization of the silyl radical. The adequacy of the two theoretical procedures employed in the present work is discussed.« less

Simple method for determining fullerene negative ion formation★

NASA Astrophysics Data System (ADS)

Felfli, Zineb; Msezane, Alfred Z.

2018-04-01

A robust potential wherein is embedded the crucial core-polarization interaction is used in the Regge-pole methodology to calculate low-energy electron elastic scattering total cross section for the C60 fullerene in the electron impact energy range 0.02 ≤ E ≤ 10.0 eV. The energy position of the characteristic dramatically sharp resonance appearing at the second Ramsauer-Townsend minimum of the total cross section representing stable C60 - fullerene negative ion formation agrees excellently with the measured electron affinity of C60 [Huang et al., J. Chem. Phys. 140, 224315 (2014)]. The benchmarked potential and the Regge-pole methodology are then used to calculate electron elastic scattering total cross sections for selected fullerenes, from C54 through C240. The total cross sections are found to be characterized generally by Ramsauer-Townsend minima, shape resonances and dramatically sharp resonances representing long-lived states of fullerene negative ion formation. For the total cross sections of C70, C76, C78, and C84 the agreement between the energy positions of the very sharp resonances and the measured electron affinities is outstanding. Additionally, we compare our extracted energy positions of the resultant fullerene anions from our calculated total cross sections of the C86, C90 and C92 fullerenes with the estimated electron affinities ≥3.0 eV by the experiment [Boltalina et al., Rapid Commun. Mass Spectrom. 7, 1009 (1993)]. Resonance energy positions of other fullerenes, including C180 and C240 are also obtained. Most of the total cross sections presented in this paper are the first and only; our novel approach is general and should be applicable to other fullerenes as well and complex heavy atoms, such as the lanthanide atoms. We conclude with a remark on the catalytic properties of the fullerenes through their negative ions.

Nanometres-resolution Kikuchi patterns from materials science specimens with transmission electron forward scatter diffraction in the scanning electron microscope.

PubMed

Brodusch, N; Demers, H; Gauvin, R

2013-04-01

A charge-coupled device camera of an electron backscattered diffraction system in a scanning electron microscope was positioned below a thin specimen and transmission Kikuchi patterns were collected. Contrary to electron backscattered diffraction, transmission electron forward scatter diffraction provides phase identification and orientation mapping at the nanoscale. The minimum Pd particle size for which a Kikuchi diffraction pattern was detected and indexed reliably was 5.6 nm. An orientation mapping resolution of 5 nm was measured at 30 kV. The resolution obtained with transmission electron forward scatter diffraction was of the same order of magnitude than that reported in electron nanodiffraction in the transmission electron microscope. An energy dispersive spectrometer X-ray map and a transmission electron forward scatter diffraction orientation map were acquired simultaneously. The high-resolution chemical, phase and orientation maps provided at once information on the chemical form, orientation and coherency of precipitates in an aluminium-lithium 2099 alloy. © 2013 The Authors Journal of Microscopy © 2013 Royal Microscopical Society.

Energy deposition and middle atmosphere electrodynamic response to a highly relativistic electron precipitation event

NASA Technical Reports Server (NTRS)

Goldberg, R. A.; Baker, D. N.; Herrero, F. A.; Mccarthy, S. P.; Twigg, P. A.; Croskey, C. L.; Hale, L. C.

1994-01-01

Rocket data have been used to evaluate the characteristics of precipitating relativistic electrons and their effects on the electrodynamic structure of the middle atmosphere. These data were obtained at Poker Flat, Alaska, on May 13 and 14, 1990, during a midday, highly relativistic electron (HRE) precipitation event. Solid state detectors were used to measure the electron fluxes and their energy spectra. An X ray scintillator was included on each flight to measure bremsstrahlung X rays produced by energetic electrons impacting on the upper atmosphere. However, these were found the be of negligible importance for this particular event. The energy deposition by the electrons has been determined from the flux measurements and compared with in situ measurements of the atmospheric electrical response. The electrodynamic measurements were obtained by the same rockets and additionally on May 13, with an accompanying rocket. The impact flux was highly irregular, containing short-lived bursts of relativistic electrons, mainly with energies below 0.5 MeV and with fluxes most enhanced between pitch angles of 0 deg - 20 deg. Although the geostationary counterpart of this measured event was considered to be of relatively low intensity and hardness, energy deposition peaked near 75 km with fluxes approaching an ion pair production rate in excess of 100/cu cm s. This exceeds peak fluxes in relativistic electron precipitation (REP) events as observed by us in numerous rocket soundings since 1976. Conductivity measurements from a blunt probe showed that negative electrical conductivities exceeded positive conductivities down to 50 km or lower, consistent with steady ionization by precipitating electrons above 1 MeV. These findings imply that the electrons from the outer radiation zone can modulate the electrical properties of the middle atmosphere to altitudes below 50 km. During the decline and activity minimum of the current solar cycle, we anticipate the occurence of similar events but with fluxes 1-2 orders of magnitude above that reported here, based on studies of earlier solar cycles (e.g., Baker et al., 1993).

Energy deposition and middle atmosphere electrodynamic response to a highly relativistic electron precipitation event

NASA Astrophysics Data System (ADS)

Goldberg, R. A.; Baker, D. N.; Herrero, F. A.; McCarthy, S. P.; Twigg, P. A.; Croskey, C. L.; Hale, L. C.

1994-10-01

Rocket data have been used to evaluate the characteristics of precipitating relativistic electrons and their effects on the electrodynamic structure of the middle atmosphere. These data were obtained at Poker Flat, Alaska, on May 13 and 14, 1990, during a midday, highly relativistic electron (HRE) precipitation event. Solid state detectors were used to measure the electron fluxes and their energy spectra. An X ray scintillator was included on each flight to measure bremsstrahlung X rays produced by energetic electrons impacting on the upper atmosphere. However, these were found the be of negligible importance for this particular event. The energy deposition by the electrons has been determined from the flux measurements and compared with in situ measurements of the atmospheric electrical response. The electrodynamic measurements were obtained by the same rockets and additionally on May 13, with an accompanying rocket. The impact flux was highly irregular, containing short-lived bursts of relativistic electrons, mainly with energies below 0.5 MeV and with fluxes most enhanced between pitch angles of 0 deg - 20 deg. Although the geostationary counterpart of this measured event was considered to be of relatively low intensity and hardness, energy deposition peaked near 75 km with fluxes approaching an ion pair production rate in excess of 100/cu cm s. This exceeds peak fluxes in relativistic electron precipitation (REP) events as observed by us in numerous rocket soundings since 1976. Conductivity measurements from a blunt probe showed that negative electrical conductivities exceeded positive conductivities down to 50 km or lower, consistent with steady ionization by precipitating electrons above 1 MeV. These findings imply that the electrons from the outer radiation zone can modulate the electrical properties of the middle atmosphere to altitudes below 50 km. During the decline and activity minimum of the current solar cycle, we anticipate the occurence of similar events but with fluxes 1-2 orders of magnitude above that reported here, based on studies of earlier solar cycles (e.g., Baker et al., 1993).

[Basic concepts of radiology physics].

PubMed

Gambini, D-J

2010-11-01

An x-ray tube mainly emits low-energy X-rays, with few maximum energy E₀ (equal in keV to the voltage U in kV) x-rays. Aluminium filtration (mandatory minimum thickness of 1.5 to 2.5 mm based on tube voltage) reduces soft X-rays and provides a mean energy equal to 2/3 E₀. The half value layer of a reference material characterizes the spectrum. X-ray attenuation in tissues is due to secondary electron interactions: photoelectric effect at low-energy, especially in dense materials with high Z number; compton effect at intermediate-energy, proportional to density. The optimization of acquisition parameters of a medically necessary examination is based on appropriate selection of the highest voltage (U in kV) providing the best contrast and lowest tube current (Q in mAs) providing a diagnostic image.

Multi-energy x-ray detector calibration for Te and impurity density (nZ) measurements of MCF plasmas

NASA Astrophysics Data System (ADS)

Maddox, J.; Pablant, N.; Efthimion, P.; Delgado-Aparicio, L.; Hill, K. W.; Bitter, M.; Reinke, M. L.; Rissi, M.; Donath, T.; Luethi, B.; Stratton, B.

2016-11-01

Soft x-ray detection with the new "multi-energy" PILATUS3 detector systems holds promise as a magnetically confined fusion (MCF) plasma diagnostic for ITER and beyond. The measured x-ray brightness can be used to determine impurity concentrations, electron temperatures, ne 2 Z eff products, and to probe the electron energy distribution. However, in order to be effective, these detectors which are really large arrays of detectors with photon energy gating capabilities must be precisely calibrated for each pixel. The energy-dependence of the detector response of the multi-energy PILATUS3 system with 100 K pixels has been measured at Dectris Laboratory. X-rays emitted from a tube under high voltage bombard various elements such that they emit x-ray lines from Zr-Lα to Ag-Kα between 1.8 and 22.16 keV. Each pixel on the PILATUS3 can be set to a minimum energy threshold in the range from 1.6 to 25 keV. This feature allows a single detector to be sensitive to a variety of x-ray energies, so that it is possible to sample the energy distribution of the x-ray continuum and line-emission. PILATUS3 can be configured for 1D or 2D imaging of MCF plasmas with typical spatial energy and temporal resolution of 1 cm, 0.6 keV, and 5 ms, respectively.

TIME DEPENDENCE OF THE e{sup −} FLUX MEASURED BY PAMELA DURING THE 2006 JULY–2009 DECEMBER SOLAR MINIMUM

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

Adriani, O.; Bongi, M.; Barbarino, G. C.

2015-09-10

Precision measurements of the electron component of cosmic radiation provide important information about the origin and propagation of cosmic rays in the Galaxy not accessible from the study of cosmic-ray nuclear components due to their differing diffusion and energy-loss processes. However, when measured near Earth, the effects of propagation and modulation of Galactic cosmic rays in the heliosphere, particularly significant for energies up to at least 30 GeV, must be properly taken into account. In this paper the electron (e{sup −}) spectra measured by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics down to 70 MeV from 2006 Julymore » to 2009 December over six-month time intervals are presented. Fluxes are compared with a state-of-the-art three-dimensional model of solar modulation that reproduces the observations remarkably well.« less

Interference of interchromophoric energy-transfer pathways in π-conjugated macrocycles

DOE PAGES

Alfonso Hernandez, Laura; Nelson, Tammie Renee; Gelin, Maxim F.; ...

2016-11-10

The interchromophoric energy-transfer pathways between weakly coupled units in a π-conjugated phenylene–ethynylene macrocycle and its half-ring analogue have been investigated using the nonadiabatic excited-state molecular dynamics approach. To track the flow of electronic transition density between macrocycle units, we formulate a transition density flux analysis adapted from the statistical minimum flow method previously developed to investigate vibrational energy flow. Following photoexcitation, transition density is primarily delocalized on two chromophore units and the system undergoes ultrafast energy transfer, creating a localized excited state on a single unit. In the macrocycle, distinct chromophore units donate transition density to a single acceptor unitmore » but do not interchange transition density among each other. We find that energy transfer in the macrocycle is slower than in the corresponding half ring because of the presence of multiple interfering energy-transfer pathways. Finally, simulation results are validated by modeling the fluorescence anisotropy decay.« less

Deactivation via ring opening: A quantum chemical study of the excited states of furan and comparison to thiophene

NASA Astrophysics Data System (ADS)

Gavrilov, Nemanja; Salzmann, Susanne; Marian, Christel M.

2008-06-01

Minimum nuclear arrangements of the ground and low-lying excited electronic states of furan were obtained by means of (time dependent) Kohn-Sham density functional theory. A combined density functional/multi-reference configuration interaction method (DFT/MRCI) was employed to compute the spectral properties at these points. Multiple minima were found on the first excited singlet (S 1) potential energy hypersurface with electronic structures S1, S2, S3 corresponding to the 1 1A 2 (π → 3s-Ryd), 1 1B 2 (π → π ∗), and 2 1A 1 (π → π ∗) states in the vertical absorption spectrum, respectively. In analogy to recently published studies in thiophene [S. Salzmann, M. Kleinschmidt, J. Tatchen, R. Weinkauf, C.M. Marian, Phys. Chem. Chem. Phys. 10 (2008) 380] a deactivation mechanism for electronically excited furan was detected that involves the opening of the pentacyclic ring. We found a nearly barrierless relaxation pathway from the Franck-Condon region along a C-O bond-breaking coordinate. Hereby the initially excited 1B 2 (π → π ∗) state undergoes a conical intersection with a 1B 1 (π → σ ∗) state. The system can return to the electronic ground state through a second conical intersection of the 1(π → σ ∗) state before the minimum of that B 1 state is reached.

Time Dependence of the Electron and Positron Components of the Cosmic Radiation Measured by the PAMELA Experiment between July 2006 and December 2015.

PubMed

Adriani, O; Barbarino, G C; Bazilevskaya, G A; Bellotti, R; Boezio, M; Bogomolov, E A; Bongi, M; Bonvicini, V; Bottai, S; Bruno, A; Cafagna, F; Campana, D; Carlson, P; Casolino, M; Castellini, G; De Santis, C; Di Felice, V; Galper, A M; Karelin, A V; Koldashov, S V; Koldobskiy, S A; Krutkov, S Y; Kvashnin, A N; Leonov, A; Malakhov, V; Marcelli, L; Martucci, M; Mayorov, A G; Menn, W; Mergé, M; Mikhailov, V V; Mocchiutti, E; Monaco, A; Mori, N; Munini, R; Osteria, G; Panico, B; Papini, P; Pearce, M; Picozza, P; Ricci, M; Ricciarini, S B; Simon, M; Sparvoli, R; Spillantini, P; Stozhkov, Y I; Vacchi, A; Vannuccini, E; Vasilyev, G I; Voronov, S A; Yurkin, Y T; Zampa, G; Zampa, N; Potgieter, M S; Vos, E E

2016-06-17

Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field.

Storm phase-partitioned rates and budgets of global Alfvénic energy deposition, electron precipitation, and ion outflow

NASA Astrophysics Data System (ADS)

Hatch, Spencer M.; LaBelle, James; Chaston, Christopher C.

2018-01-01

We review the role of Alfvén waves in magnetosphere-ionosphere coupling during geomagnetically active periods, and use three years of high-latitude FAST satellite observations of inertial Alfvén waves (IAWs) together with 55 years of tabulated measurements of the Dst index to answer the following questions: 1) How do global rates of IAW-related energy deposition, electron precipitation, and ion outflow during storm main phase and storm recovery phase compare with global rates during geomagnetically quiet periods? 2) What fraction of net IAW-related energy deposition, electron precipitation, and ion outflow is associated with storm main phase and storm recovery phase; that is, how are these budgets partitioned by storm phase? We find that during the period between October 1996 and November 1999, rates of IAW-related energy deposition, electron precipitation, and ion outflow during geomagnetically quiet periods are increased by factors of 4-5 during storm phases. We also find that ∼62-68% of the net Alfvénic energy deposition, electron precipitation, and ion outflow in the auroral ionosphere occurred during storm main and recovery phases, despite storm phases comprising only 31% of this period. In particular storm main phase, which comprised less than 14% of the three-year period, was associated with roughly a third of the total Alfvénic energy input and ion outflow in the auroral ionosphere. Measures of geomagnetic activity during the IAW study period fall near corresponding 55-year median values, from which we conclude that each storm phase is associated with a fraction of total Alfvénic energy, precipitation, and outflow budgets in the auroral ionosphere that is, in the long term, probably as great or greater than the fraction associated with geomagnetic quiescence for all times except possibly those when geomagnetic activity is protractedly weak, such as solar minimum. These results suggest that the budgets of IAW-related energy deposition, electron precipitation, and ion outflow are roughly equally partitioned by geomagnetic storm phase.

Electronic structure and reactivity of cobalt oxide dimers and their hexacarbonyl complexes: a density functional study.

PubMed

Uzunova, Ellie L; Mikosch, Hans

2012-03-29

The dimers of cobalt oxide (CoO)(2) with cyclic and open bent structure are studied with the B1LYP density functional; the ordering of states is validated by the CCSD(T) method. The D(2h)-symmetry rhombic dioxide Co(2)O(2) with antiferromagnetically ordered electrons on cobalt centers is the global minimum. The cyclic peroxide Co(2)(O(2)) with side-on-bonded dioxygen in (7)B(2) ground state is separated from the global minimum by an energy gap of 3.15 eV. The dioxide is highly reactive as indicated by the high value of proton affinity and chemical reactivity indices. The four-member ring structures are more stable than those with three-member ring or chain configuration. The thermodynamic stability toward dissociation to CoO increases upon carbonylation, whereas proton affinity and reactivity with release of molecular oxygen also increase. The global minimum of Co(2)O(2)(CO)(6) corresponds to a triplet state (3)A" with oxygen atoms shifted above the molecular plane of the rhombic dioxide Co(2)O(2). The SOMO-LUMO gap in the ground-state carbonylated dioxide is wider, compared to the same gap in the bare dicobalt dioxide. The peroxo-isomer Co(2)(O(2))(CO)(6) retains the planar Co(2)(O(2)) ring and is only stable in a high-spin state (7)A". The carbonylated clusters have increased reactivity in both redox and nucleophilic reactions, as a result of the increased electron density in the Co(2)O(2)-ring area.

Electromechanical flight control actuator, volume 1

NASA Technical Reports Server (NTRS)

1978-01-01

An electromechanical actuator was developed that will follow a proportional control command with minimum wasted energy to demonstrate the feasibility of meeting space vehicle actuator requirements using advanced electromechanical concepts. The approach was restricted to a four-channel redundant configuration. Each channel has independent drive and control electronics, a brushless electric motor with brake, and velocity and position feedback transducers. A differential gearbox sums the output velocities of the motors. Normally, two motors are active and the other two are braked.

HEOS-A2: Press kit

NASA Technical Reports Server (NTRS)

Allaway, H. G.; Kukowski, J.

1972-01-01

The characteristics of the HEOS-A2 satellite and its assigned mission are discussed. The spacecraft carries seven experiments to investigate the strength and direction of the magnetic fields encountered, the energy distribution of protons and electrons, the nature of the solar winds, detection of micrometeorites, and low frequency solar observations. The highly elliptical polar orbit required for this mission will have an apogee of 38 earth radii. The lifetime of the satellite is expected to be one year minimum.

Wave-driven butterfly distribution of Van Allen belt relativistic electrons

DOE PAGES

Xiao, Fuliang; Yang, Chang; Su, Zhenpeng; ...

2015-10-05

Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day–night asymmetry in Earth’s magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28more » June 2013 geomagnetic storm. In conclusion, simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution. Finally, the current provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons.« less

Wave-driven butterfly distribution of Van Allen belt relativistic electrons

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

Xiao, Fuliang; Yang, Chang; Su, Zhenpeng

Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day–night asymmetry in Earth’s magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28more » June 2013 geomagnetic storm. In conclusion, simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution. Finally, the current provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons.« less

Early stages of Cs adsorption mechanism for GaAs nanowire surface

NASA Astrophysics Data System (ADS)

Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu

2018-03-01

In this study, the adsorption mechanism of Cs adatoms on the (100) surface of GaAs nanowire with [0001] growth direction is investigated utilizing first principles method based on density function theory. The adsorption energy, work function, atomic structure and electronic property of clean surface and Cs-covered surfaces with different coverage are discussed. Results show that when only one Cs is adsorbed on the surface, the most favorable adsorption site is BGa-As. With increasing Cs coverage, work function gradually decreases and gets its minimum at 0.75 ML, then rises slightly when Cs coverage comes to 1 ML, indicating the existence of 'Cs-kill' phenomenon. According to further analysis, Cs activation process can effectively reduce the work function due to the formation of a downward band bending region and surface dipole moment directing from Cs adatom to the surface. As Cs coverage increases, the conduction band minimum and valence band maximum both shift towards lower energy side, contributed by the orbital hybridization between Cs-5s, Cs-5p states and Ga-4p, As-4s, As-4p states near Fermi level. The theoretical calculations and analysis in this study can improve the Cs activation technology for negative electron affinity optoelectronic devices based on GaAs nanowires, and also provide a reference for the further Cs/O or Cs/NF3 activation process.

Potential energy surfaces of the low-lying electronic states of the Li + LiCs system

NASA Astrophysics Data System (ADS)

Jasik, P.; Kilich, T.; Kozicki, J.; Sienkiewicz, J. E.

2018-03-01

Ab initio quantum chemistry calculations are performed for the mixed alkali triatomic system. Global minima of the ground and first excited doublet states of the trimer are found and Born-Oppenheimer potential energy surfaces of the Li atom interacting with the LiCs molecule were calculated for these states. The lithium atom is placed at various distances and bond angles from the lithium-caesium dimer. Three-body nonadditive forces of the Li2Cs molecule in the global minimum are investigated. Dimer-atom interactions are found to be strongly attractive and may be important in the experiments, particularly involving cold alkali polar dimers.

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

Bazante, Alexandre P., E-mail: abazante@chem.ufl.edu; Bartlett, Rodney J.; Davidson, E. R.

The benzene radical anion is studied with ab initio coupled-cluster theory in large basis sets. Unlike the usual assumption, we find that, at the level of theory investigated, the minimum energy geometry is non-planar with tetrahedral distortion at two opposite carbon atoms. The anion is well known for its instability to auto-ionization which poses computational challenges to determine its properties. Despite the importance of the benzene radical anion, the considerable attention it has received in the literature so far has failed to address the details of its structure and shape-resonance character at a high level of theory. Here, we examinemore » the dynamic Jahn-Teller effect and its impact on the anion potential energy surface. We find that a minimum energy geometry of C{sub 2} symmetry is located below one D{sub 2h} stationary point on a C{sub 2h} pseudo-rotation surface. The applicability of standard wave function methods to an unbound anion is assessed with the stabilization method. The isotropic hyperfine splitting constants (A{sub iso}) are computed and compared to data obtained from experimental electron spin resonance experiments. Satisfactory agreement with experiment is obtained with coupled-cluster theory and large basis sets such as cc-pCVQZ.« less

Observation of b 2 symmetry vibrational levels of the SO 2C 1B 2 state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants

DOE PAGES

Park, G. Barratt; Jiang, Jun; Saladrigas, Catherine A.; ...

2016-04-14

Here, the C 1B 2 state of SO 2 has a double-minimum potential in the antisymmetric stretch coordinate, such that the minimum energy geometry has nonequivalent SO bond lengths. However, low-lying levels with odd quanta of antisymmetric stretch (b 2 vibrational symmetry) have not previously been observed because transitions into these levels from the zero-point level of the X ~ state are vibronically forbidden. We use IR-UV double resonance to observe the b 2 vibrational levels of the C state below 1600 cm –1 of vibrational excitation. This enables a direct characterization of the vibrational level staggering that results frommore » the double-minimum potential. In addition, it allows us to deperturb the strong c-axis Coriolis interactions between levels of a 1 and b 2 vibrational symmetry, and to determine accurately the vibrational dependence of the rotational constants in the distorted C electronic state.« less

Observation of b 2 symmetry vibrational levels of the SO 2C 1B 2 state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants

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

Park, G. Barratt; Jiang, Jun; Saladrigas, Catherine A.

Here, the C 1B 2 state of SO 2 has a double-minimum potential in the antisymmetric stretch coordinate, such that the minimum energy geometry has nonequivalent SO bond lengths. However, low-lying levels with odd quanta of antisymmetric stretch (b 2 vibrational symmetry) have not previously been observed because transitions into these levels from the zero-point level of the X ~ state are vibronically forbidden. We use IR-UV double resonance to observe the b 2 vibrational levels of the C state below 1600 cm –1 of vibrational excitation. This enables a direct characterization of the vibrational level staggering that results frommore » the double-minimum potential. In addition, it allows us to deperturb the strong c-axis Coriolis interactions between levels of a 1 and b 2 vibrational symmetry, and to determine accurately the vibrational dependence of the rotational constants in the distorted C electronic state.« less

Quadratic String Method for Locating Instantons in Tunneling Splitting Calculations.

PubMed

Cvitaš, Marko T

2018-03-13

The ring-polymer instanton (RPI) method is an efficient technique for calculating approximate tunneling splittings in high-dimensional molecular systems. In the RPI method, tunneling splitting is evaluated from the properties of the minimum action path (MAP) connecting the symmetric wells, whereby the extensive sampling of the full potential energy surface of the exact quantum-dynamics methods is avoided. Nevertheless, the search for the MAP is usually the most time-consuming step in the standard numerical procedures. Recently, nudged elastic band (NEB) and string methods, originaly developed for locating minimum energy paths (MEPs), were adapted for the purpose of MAP finding with great efficiency gains [ J. Chem. Theory Comput. 2016 , 12 , 787 ]. In this work, we develop a new quadratic string method for locating instantons. The Euclidean action is minimized by propagating the initial guess (a path connecting two wells) over the quadratic potential energy surface approximated by means of updated Hessians. This allows the algorithm to take many minimization steps between the potential/gradient calls with further reductions in the computational effort, exploiting the smoothness of potential energy surface. The approach is general, as it uses Cartesian coordinates, and widely applicable, with computational effort of finding the instanton usually lower than that of determining the MEP. It can be combined with expensive potential energy surfaces or on-the-fly electronic-structure methods to explore a wide variety of molecular systems.

Origin of the 30 THz Emission Detected During the Solar Flare on 2012 March 13 at 17:20 UT

NASA Astrophysics Data System (ADS)

Trottet, G.; Raulin, J.-P.; Mackinnon, A.; Giménez de Castro, G.; Simões, P. J. A.; Cabezas, D.; de La Luz, V.; Luoni, M.; Kaufmann, P.

2015-10-01

Solar observations in the infrared domain can bring important clues on the response of the low solar atmosphere to primary energy released during flares. At present, the infrared continuum has been detected at 30 THz (10 μm) in only a few flares. SOL2012-03-13, which is one of these flares, has been presented and discussed in Kaufmann et al. ( Astrophys. J. 768, 134, 2013). No firm conclusions were drawn on the origin of the mid-infrared radiation. In this work we present a detailed multi-frequency analysis of the SOL2012-03-13 event, including observations at radio-millimeter and submillimeter wavelengths, in hard X-rays (HXR), gamma-rays (GR), Hα, and white light. The HXR/GR spectral analysis shows that SOL2012-03-13 is a GR line flare and allows estimating the numbers of and energy contents in electrons, protons, and α particles produced during the flare. The energy spectrum of the electrons producing the HXR/GR continuum is consistent with a broken power-law with an energy break at {˜} 800 keV. We show that the high-energy part (above {˜} 800 keV) of this distribution is responsible for the high-frequency radio emission ({>} 20 GHz) detected during the flare. By comparing the 30 THz emission expected from semi-empirical and time-independent models of the quiet and flare atmospheres, we find that most ({˜} 80 %) of the observed 30 THz radiation can be attributed to thermal free-free emission of an optically thin source. Using the F2 flare atmospheric model (Machado et al. in Astrophys. J. 242, 336, 1980), this thin source is found to be at temperatures T {˜} 8000 K and is located well above the minimum temperature region. We argue that the chromospheric heating, which results in 80 % of the 30 THz excess radiation, can be due to energy deposition by nonthermal flare-accelerated electrons, protons, and α particles. The remaining 20 % of the 30 THz excess emission is found to be radiated from an optically thick atmospheric layer at T {˜} 5000 K, below the temperature minimum region, where direct heating by nonthermal particles is insufficient to account for the observed infrared radiation.

Mean-field theory for multipole ordering in f-electron systems on the basis of a j-j coupling scheme

NASA Astrophysics Data System (ADS)

Yamamura, Ryosuke; Hotta, Takashi

2018-05-01

We develop a microscopic theory for multipole ordering, applicable to the system with plural numbers of f electrons per ion, from an itinerant picture on the basis of a j-j coupling scheme. For the purpose, by introducing the Γ8 Hubbard Hamiltonian as the minimum model to discuss the multipole ordering in f-electron systems, we describe the mean-field approximation in terms of the multipole operators. For the case of n = 2 , where n denotes the average f-electron number per ion, we analyze the model on a simple cubic lattice to obtain the multipole phase diagram. In particular, we find the order of non-Kramers Γ3 quadrupoles, O20 and O22 , with different ordering vectors. We attempt to explain the phase diagram from the discussion on the interaction energy.

Origins of Fermi-level pinning on GaN and InN polar and nonpolar surfaces

NASA Astrophysics Data System (ADS)

Segev, D.; Van de Walle, C. G.

2006-10-01

Using band structure and total energy methods, we study the atomic and electronic structures of the polar (+c and - c plane) and nonpolar (a and m plane) surfaces of GaN and InN. We identify two distinct microscopic origins for Fermi-level pinning on GaN and InN, depending on surface stoichiometry and surface polarity. At moderate Ga/N ratios unoccupied gallium dangling bonds pin the Fermi level on n-type GaN at 0.5 0.7 eV below the conduction-band minimum. Under highly Ga-rich conditions metallic Ga adlayers lead to Fermi-level pinning at 1.8 eV above the valence-band maximum. We also explain the source of the intrinsic electron accumulation that has been universally observed on polar InN surfaces. It is caused by In-In bonds leading to occupied surface states above the conduction-band minimum. We predict that such a charge accumulation will be absent on the nonpolar surfaces of InN, when prepared under specific conditions.

Band gap tuning of amorphous Al oxides by Zr alloying

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

Canulescu, S., E-mail: stec@fotonik.dtu.dk; Schou, J.; Jones, N. C.

2016-08-29

The optical band gap and electronic structure of amorphous Al-Zr mixed oxides with Zr content ranging from 4.8 to 21.9% were determined using vacuum ultraviolet and X-ray absorption spectroscopy. The light scattering by the nano-porous structure of alumina at low wavelengths was estimated based on the Mie scattering theory. The dependence of the optical band gap of the Al-Zr mixed oxides on the Zr content deviates from linearity and decreases from 7.3 eV for pure anodized Al{sub 2}O{sub 3} to 6.45 eV for Al-Zr mixed oxides with a Zr content of 21.9%. With increasing Zr content, the conduction band minimum changes non-linearlymore » as well. Fitting of the energy band gap values resulted in a bowing parameter of ∼2 eV. The band gap bowing of the mixed oxides is assigned to the presence of the Zr d-electron states localized below the conduction band minimum of anodized Al{sub 2}O{sub 3}.« less

The Multi-species Farley-Buneman Instability in the Solar Chromosphere

NASA Astrophysics Data System (ADS)

Madsen, Chad A.; Dimant, Yakov S.; Oppenheim, Meers M.; Fontenla, Juan M.

2014-03-01

Empirical models of the solar chromosphere show intense electron heating immediately above its temperature minimum. Mechanisms such as resistive dissipation and shock waves appear insufficient to account for the persistence and uniformity of this heating as inferred from both UV lines and continuum measurements. This paper further develops the theory of the Farley-Buneman instability (FBI) which could contribute substantially to this heating. It expands upon the single-ion theory presented by Fontenla by developing a multiple-ion-species approach that better models the diverse, metal-dominated ion plasma of the solar chromosphere. This analysis generates a linear dispersion relationship that predicts the critical electron drift velocity needed to trigger the instability. Using careful estimates of collision frequencies and a one-dimensional, semi-empirical model of the chromosphere, this new theory predicts that the instability may be triggered by velocities as low as 4 km s-1, well below the neutral acoustic speed. In the Earth's ionosphere, the FBI occurs frequently in situations where the instability trigger speed significantly exceeds the neutral acoustic speed. From this, we expect neutral flows rising from the photosphere to have enough energy to easily create electric fields and electron Hall drifts with sufficient amplitude to make the FBI common in the chromosphere. If so, this process will provide a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet Sun.

Study of spatial resolution of coordinate detectors based on Gas Electron Multipliers

NASA Astrophysics Data System (ADS)

Kudryavtsev, V. N.; Maltsev, T. V.; Shekhtman, L. I.

2017-02-01

Spatial resolution of GEM-based tracking detectors is determined in the simulation and measured in the experiments. The simulation includes GEANT4 implemented transport of high energy electrons with careful accounting of atomic relaxation processes including emission of fluorescent photons and Auger electrons and custom post-processing with accounting of diffusion, gas amplification fluctuations, distribution of signals on readout electrodes, electronics noise and particular algorithm of final coordinate calculation (center of gravity). The simulation demonstrates that the minimum of spatial resolution of about 10 μm can be achieved with a gas mixture of Ar -CO2 (75-25 %) at a strips pitch from 250 μm to 300 μm. At a larger pitch the resolution quickly degrades reaching 80-100 μm at a pitch of 460-500 μm. Spatial resolution of low-material triple-GEM detectors for the DEUTERON facility at the VEPP-3 storage ring is measured at the extracted beam facility of the VEPP-4 M collider. One-coordinate resolution of the DEUTERON detector is measured with electron beam of 500 MeV, 1 GeV and 3.5 GeV energies. The determined value of spatial resolution varies in the range from approximately 35 μm to 50 μm for orthogonal tracks in the experiments.

Green synthesis and characterization of Carica papaya leaf extract coated silver nanoparticles through X-ray diffraction, electron microscopy and evaluation of bactericidal properties

PubMed Central

Banala, Rajkiran Reddy; Nagati, Veera Babu; Karnati, Pratap Reddy

2015-01-01

The evolution of nanotechnology and the production of nanomedicine from various sources had proven to be of intense value in the field of biomedicine. The smaller size of nanoparticles is gaining importance in research for the treatment of various diseases. Moreover the production of nanoparticles is eco-friendly and cost effective. In the present study silver nanoparticles were synthesized from Carica papaya leaf extract (CPL) and characterized for their size and shape using scanning electron microscopy and transmission electron microscopy, respectively. Fourier transform infrared spectroscopy (FTIR), Energy dispersive X-ray spectroscopy (EDS/EDX) and X-ray diffraction spectroscopy (XRD) were conducted to determine the concentration of metal ions, the shape of molecules. The bactericidal activity was evaluated using Luria Bertani broth cultures and the minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) were estimated using turbidimetry. The data analysis showed size of 50–250 nm spherical shaped nanoparticles. The turbidimetry analysis showed MIC and MBC was >25 μg/mL against both Gram positive and Gram negative bacteria in Luria Bertani broth cultures. In summary the synthesized silver nanoparticles from CPL showed acceptable size and shape of nanoparticles and effective bactericidal activity. PMID:26288570

Green synthesis and characterization of Carica papaya leaf extract coated silver nanoparticles through X-ray diffraction, electron microscopy and evaluation of bactericidal properties.

PubMed

Banala, Rajkiran Reddy; Nagati, Veera Babu; Karnati, Pratap Reddy

2015-09-01

The evolution of nanotechnology and the production of nanomedicine from various sources had proven to be of intense value in the field of biomedicine. The smaller size of nanoparticles is gaining importance in research for the treatment of various diseases. Moreover the production of nanoparticles is eco-friendly and cost effective. In the present study silver nanoparticles were synthesized from Carica papaya leaf extract (CPL) and characterized for their size and shape using scanning electron microscopy and transmission electron microscopy, respectively. Fourier transform infrared spectroscopy (FTIR), Energy dispersive X-ray spectroscopy (EDS/EDX) and X-ray diffraction spectroscopy (XRD) were conducted to determine the concentration of metal ions, the shape of molecules. The bactericidal activity was evaluated using Luria Bertani broth cultures and the minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) were estimated using turbidimetry. The data analysis showed size of 50-250 nm spherical shaped nanoparticles. The turbidimetry analysis showed MIC and MBC was >25 μg/mL against both Gram positive and Gram negative bacteria in Luria Bertani broth cultures. In summary the synthesized silver nanoparticles from CPL showed acceptable size and shape of nanoparticles and effective bactericidal activity.

Electronic structure and magnetism of titanium substituted Cd3P2: An ab-initio study

NASA Astrophysics Data System (ADS)

Jaiganesh, G.; Jaya, S. Mathi

2018-05-01

Using the ab-initio computations that are based on the density functional theory, we have investigated the magnetism and electronic properties of one and two Ti atom substituted Cd3P2 compound. The magnetic stability of the substituted compounds was obtained by analyzing the minimum total energies in nonmagnetic, ferromagnetic and antiferromagnetic phases. Our results indicated the formation of magnetic order in one and two Ti atom substituted Cd3P2 as well as metallic characteristics in these systems. A significant value of the magnetic moment of Ti atom is observed from our calculations. We further find that the neighboring Cd and P atoms too acquire a small magnetic moment.

Highly Relativistic Electrons from UARS and Their Effect on Atmospheric Ozone

NASA Astrophysics Data System (ADS)

Pesnell, W. D.; Goldberg, R. A.; Jackman, C. H.; Chenette, D. L.; Gaines, E. E.

2001-12-01

In a study involving 5 of the instruments on UARS, we have investigated how fluxes of high-energy electrons could modify the chemistry of the upper stratosphere and mesosphere. Fluxes of high-energy electrons (E > 100~keV) have been predicted to deplete mesospheric ozone by 20% or more, and stratospheric ozone to a lesser degree. Precipitating fluxes of these electrons can increase by 1--2 orders of magnitude during highly relativistic electron (HRE) events, and often contain significant contributions from electrons with E > 1~MeV. This research has produced a database of differential electron energy spectra obtained during the decline of solar cycle 22. We have used this database to understand the radiation environment of low-Earth orbit. We will show how the HEPS data provides energy-dependent lifetimes for the energetic electrons and that elevated electron fluxes should be expected on any satellite mission lasting more than 1 week. Once the electron fluxes are known, the atmospheric effects can be predicted by model calculations and those predictions compared with composition measurements. For the instantaneous electron fluxes measured during a large May 1992 HRE, relative depletions of ozone greater than 15% were predicted to occur between altitudes of 60--80~km, where HO{}x reactions cause a local minimum in the ozone concentration. The chemical signature of an HRE would be ozone depletions in the region of enhanced flux, particularly within the magnetic L-shell limits of 3 < L < 4. Data from HEPS, CLAES, HALOE, HRDI, and MLS were combined to search for such effects during the May 1992 HRE. Mesospheric ozone measurements from HRDI and stratospheric ozone measurements by CLAES and MLS were searched for the predicted depletions. The seasonal evolution of water vapor was monitored with HALOE. Our analysis shows that between altitudes of 65--75 km the ozone mixing ratio was relatively constant within the overlapping local solar time bands during May 1992. Above 80--85 km, there was evidence of evolution through May 1992 and the HRE event.

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

Alfonso Hernandez, Laura; Nelson, Tammie Renee; Gelin, Maxim F.

The interchromophoric energy-transfer pathways between weakly coupled units in a π-conjugated phenylene–ethynylene macrocycle and its half-ring analogue have been investigated using the nonadiabatic excited-state molecular dynamics approach. To track the flow of electronic transition density between macrocycle units, we formulate a transition density flux analysis adapted from the statistical minimum flow method previously developed to investigate vibrational energy flow. Following photoexcitation, transition density is primarily delocalized on two chromophore units and the system undergoes ultrafast energy transfer, creating a localized excited state on a single unit. In the macrocycle, distinct chromophore units donate transition density to a single acceptor unitmore » but do not interchange transition density among each other. We find that energy transfer in the macrocycle is slower than in the corresponding half ring because of the presence of multiple interfering energy-transfer pathways. Finally, simulation results are validated by modeling the fluorescence anisotropy decay.« less

Theoretical studies on the possible sensitizers of DSSC: Nanocomposites of graphene quantum dot hybrid phthalocyanine/tetrabenzoporphyrin/tetrabenzotriazaporphyrins/cis-tetrabenzodiazaporphyrins/tetrabenzomonoazaporphyrins and their Cu-metallated macrocycles

NASA Astrophysics Data System (ADS)

Gao, Feng; Yang, Chuan-Lu; Wang, Mei-Shan; Ma, Xiao-Guang; Liu, Wen-Wang

2018-04-01

The feasibility of nanocomposites of cir-coronene graphene quantum dot (GQD) with phthalocyanine, tetrabenzoporphyrin, tetrabenzotriazaporphyrins, cis-tetrabenzodiazaporphyrins, tetrabenzomonoazaporphyrins and their Cu-metallated macrocycles as a sensitizer of dye-sensitized solar cells (DSSC) are investigated. Based on the first principles density functional theory (DFT), the geometrical structures of the separate GQD and 10 macrocycles, and their hybridized nanocomposites are fully optimized. The energy stabilities of the obtained structures are confirmed by harmonic frequency analysis. The optical absorptions of the optimized structures are calculated with time-dependent DFT. The feasibility of the nanocomposites as the sensitizer of DSSC is examined by the charge spatial separation, the electron transfer, the molecular orbital energy levels of the nanocomposites and the electrolyte, and the conduction band minimum of TiO2 electrode. The results demonstrate that all the nanocomposites have enhanced absorptions in the visible light range, and their molecular orbital energies satisfy the requirement of sensitizers. However, only two of the ten considered nanocomposites demonstrate significantly charge spatial separation. The GQD-Cu-TBP is identified as the most favorable candidate sensitizer of DSSC by the most enhanced in optical absorption, obvious charge spatial separation, suitable LUMO energy levels and driving force for electron transfer, and low recombination rate of electron and hole.

Autonomous Sensor Motes Employing Liquid-Bearing Rotary Stages

DTIC Science & Technology

2014-03-06

breaks off (Fig. 27d) as shown in the sudden change in force, indicating rotor pull off. The minimum of each curve indicates the maximum tensile load...configuration, with marks on the curves at the minimum energy positions are shown in Fig. 39. The minimum energy positions from Fig. 39are plotted as...rates between 5 and 17 Hz rotation rate plotted vs. rotor eccentricity. The minimum energy positions are indicated on each curve . 3.3 Discussion

Orientations of dendritic growth during solidification

NASA Astrophysics Data System (ADS)

Lee, Dong Nyung

2017-03-01

Dendrites are crystalline forms which grow far from the limit of stability of the plane front and adopt an orientation which is as close as possible to the heat flux direction. Dendritic growth orientations for cubic metals, bct Sn, and hcp Zn, can be controlled by thermal conductivity, Young's modulus, and surface energy. The control factors have been elaborated. Since the dendrite is a single crystal, its properties such as thermal conductivity that influences the heat flux direction, the minimum Young's modulus direction that influences the strain energy minimization, and the minimum surface energy plane that influences the crystal/liquid interface energy minimization have been proved to control the dendritic growth direction. The dendritic growth directions of cubic metals are determined by the minimum Young's modulus direction and/or axis direction of symmetry of the minimum crystal surface energy plane. The dendritic growth direction of bct Sn is determined by its maximum thermal conductivity direction and the minimum surface energy plane normal direction. The primary dendritic growth direction of hcp Zn is determined by its maximum thermal conductivity direction and the minimum surface energy plane normal direction and the secondary dendrite arm direction of hcp Zn is normal to the primary dendritic growth direction.

Ab initio based study of the ArO- photoelectron spectra: Selectivity of spin-orbit transitions

NASA Astrophysics Data System (ADS)

Buchachenko, A. A.; Jakowski, Jacek; Chałasiński, Grzegorz; Szczȩśniak, M. M.; Cybulski, S. M.

2000-04-01

A combined ab initio atoms-in-molecule approach was implemented to model the photoelectron spectra of the ArO- anion. The lowest adiabatic states of Σ and Π symmetry of ArO and ArO- were investigated using the fourth-order Møller-Plessett perturbation theory including bond functions. The total energies were dissected into electrostatic, exchange, induction, and dispersion components. The complex of Ar with atomic oxygen is only weakly bound, primarily by dispersion interaction. The Π state possesses a deeper minimum (Re=3.4Å,De=380μEh) than the Σ state (Re=3.8Å,De=220μEh). In contrast, the anion complex is fairly strongly bound, primarily by ion-induced dipole induction forces, and the Σ state possesses a deeper minimum at shorter interatomic distances (Re=3.02Å,De=3600μEh) than the Π state (Re=3.35Å,De=2400μEh). The Σ-Π splittings in both systems are mainly due to differences in the exchange repulsion terms. Atoms-in-molecule models were used to account for the spin-orbit interaction, and to generate adiabatic relativistic potentials and wave functions. Collisional properties, diffusion, and mobility coefficients of O and O- in Ar, and absolute total Ar+O scattering cross sections, were calculated and found to agree well with the available experimental data. The photoelectron spectra were simulated within vibronic model, and were found in excellent agreement with the experimental measurements. The bimodal electron kinetic energy distribution was shown to stem from the strong selectivity of spin-orbit transitions, which split into two dense groups, depending on the initial electronic state of the anion. The latter feature cannot be described without explicit consideration of electronic intensity factor.

Nonlinear simulations of peeling-ballooning modes with anomalous electron viscosity and their role in edge localized mode crashes

DOE PAGES

Xu, X. Q.; Dudson, B.; Snyder, P. B.; ...

2010-10-22

A minimum set of equations based on the peeling-ballooning (P-B) model with nonideal physics effects (diamagnetic drift, E×B drift, resistivity, and anomalous electron viscosity) is found to simulate pedestal collapse when using the new BOUT++ simulation code, developed in part from the original fluid edge code BOUT. Nonlinear simulations of P-B modes demonstrate that the P-B modes trigger magnetic reconnection, which leads to the pedestal collapse. With the addition of a model of the anomalous electron viscosity under the assumption that the electron viscosity is comparable to the anomalous electron thermal diffusivity, it is found from simulations using a realisticmore » high-Lundquist number that the pedestal collapse is limited to the edge region and the edge localized mode (ELM) size is about 5–10% of the pedestal stored energy. Furthermore, this is consistent with many observations of large ELMs.« less

Wavefunction Properties and Electronic Band Structures of High-Mobility Semiconductor Nanosheet MoS2

NASA Astrophysics Data System (ADS)

Baik, Seung Su; Lee, Hee Sung; Im, Seongil; Choi, Hyoung Joon; Ccsaemp Team; Edl Team

2014-03-01

Molybdenum disulfide (MoS2) nanosheet is regarded as one of the most promising alternatives to the current semiconductors due to its significant band-gap and electron-mobility enhancement upon exfoliating. To elucidate such thickness-dependent properties, we have studied the electronic band structures of bulk and monolayer MoS2 by using the first-principles density-functional method as implemented in the SIESTA code. Based on the wavefunction analyses at the conduction band minimum (CBM) points, we have investigated possible origins of mobility difference between bulk and monolayer MoS2. We provide formation energies of substitutional impurities at the Mo and S sites, and discuss feasible electron sources which may induce a significant difference in the carrier lifetime. This work was supported by NRF of Korea (Grant Nos. 2009-0079462 and 2011-0018306), Nano-Material Technology Development Program (2012M3a7B4034985), and KISTI supercomputing center (Project No. KSC-2013-C3-008). Center for Computational Studies of Advanced Electronic Material Properties.

First-principles investigation of the dissociation and coupling of methane on small copper clusters: Interplay of collision dynamics and geometric and electronic effects

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

Varghese, Jithin J.; Mushrif, Samir H., E-mail: shmushrif@ntu.edu.sg

Small metal clusters exhibit unique size and morphology dependent catalytic activity. The search for alternate minimum energy pathways and catalysts to transform methane to more useful chemicals and carbon nanomaterials led us to investigate collision induced dissociation of methane on small Cu clusters. We report here for the first time, the free energy barriers for the collision induced activation, dissociation, and coupling of methane on small Cu clusters (Cu{sub n} where n = 2–12) using ab initio molecular dynamics and metadynamics simulations. The collision induced activation of the stretching and bending vibrations of methane significantly reduces the free energy barriermore » for its dissociation. Increase in the cluster size reduces the barrier for dissociation of methane due to the corresponding increase in delocalisation of electron density within the cluster, as demonstrated using the electron localisation function topology analysis. This enables higher probability of favourable alignment of the C–H stretching vibration of methane towards regions of high electron density within the cluster and makes higher number of sites available for the chemisorption of CH{sub 3} and H upon dissociation. These characteristics contribute in lowering the barrier for dissociation of methane. Distortion and reorganisation of cluster geometry due to high temperature collision dynamics disturb electron delocalisation within them and increase the barrier for dissociation. Coupling reactions of CH{sub x} (x = 1–3) species and recombination of H with CH{sub x} have free energy barriers significantly lower than complete dehydrogenation of methane to carbon. Thus, competition favours the former reactions at high hydrogen saturation on the clusters.« less

Polarization effects in low-energy electron-CH4 elastic collisions in an exact exchange treatment

NASA Astrophysics Data System (ADS)

Jain, Ashok; Weatherford, C. A.; Thompson, D. G.; McNaughten, P.

1989-12-01

We have investigated the polarization effects in very-low-energy (below 1 eV) electron- CH4 collisions in an exact-exchange treatment. The two models of the parameter-free polarization potential are employed; one, the VpolJT potential, introduced by Jain and Thompson [J. Phys. B 15, L631 (1982)], is based on an approximate polarized-orbital method, and two, the correlation-polarization potential VpolCP, first proposed by O'Connel and Lane [Phys. Rev. A 27, 1893 (1983)], is given as a simple analytic form in terms of the charge density of the target. In this rather very low-energy region, the polarization effects play a decisive role, particularly in creating structure in the differential cross section (DCS) and producing the Ramsauer-Townsend minimum in the total cross section. Our DCS at 0.2, 0.4, and 0.6 eV are compared with recent measurements. We found that a local parameter-free approximation for the polarization potential is quite successful if it is determined under the polarized-orbital-type technique rather than based on the correlation-polarization approach.

Dosimetry for electron Intra-Operative RadioTherapy: Comparison of output factors obtained through alanine/EPR pellets, ionization chamber and Monte Carlo-GEANT4 simulations for IORT mobile dedicate accelerator

NASA Astrophysics Data System (ADS)

Marrale, Maurizio; Longo, Anna; Russo, Giorgio; Casarino, Carlo; Candiano, Giuliana; Gallo, Salvatore; Carlino, Antonio; Brai, Maria

2015-09-01

In this work a comparison between the response of alanine and Markus ionization chamber was carried out for measurements of the output factors (OF) of electron beams produced by a linear accelerator used for Intra-Operative Radiation Therapy (IORT). Output factors (OF) for conventional high-energy electron beams are normally measured using ionization chamber according to international dosimetry protocols. However, the electron beams used in IORT have characteristics of dose per pulse, energy spectrum and angular distribution quite different from beams usually used in external radiotherapy, so the direct application of international dosimetry protocols may introduce additional uncertainties in dosimetric determinations. The high dose per pulse could lead to an inaccuracy in dose measurements with ionization chamber, due to overestimation of ks recombination factor. Furthermore, the electron fields obtained with IORT-dedicated applicators have a wider energy spectrum and a wider angular distribution than the conventional fields, due to the presence of electrons scattered by the applicator's wall. For this reason, a dosimetry system should be characterized by a minimum dependence from the beam energy and from angle of incidence of electrons. This become particularly critical for small and bevelled applicators. All of these reasons lead to investigate the use of detectors different from the ionization chamber for measuring the OFs. Furthermore, the complete characterization of the radiation field could be accomplished also by the use of Monte Carlo simulations which allows to obtain detailed information on dose distributions. In this work we compare the output factors obtained by means of alanine dosimeters and Markus ionization chamber. The comparison is completed by the Monte Carlo calculations of OFs determined through the use of the Geant4 application "iort _ therapy" . The results are characterized by a good agreement of response of alanine pellets and Markus ionization chamber and Monte Carlo results (within about 3%) for both flat and bevelled applicators.

Implications of orbital hybridization on the electronic properties of doped quantum dots: the case of Cu:CdSe

NASA Astrophysics Data System (ADS)

Wright, Joshua T.; Forsythe, Kyle; Hutchins, Jamie; Meulenberg, Robert W.

2016-04-01

This paper investigates how chemical dopants affect the electronic properties of CdSe quantum dots (QDs) and why a model that incorporates the concepts of orbital hybridization must be used to understand these properties. Extended X-ray absorption fine structure spectroscopy measurements show that copper dopants in CdSe QDs occur primarily through a statistical doping mechanism. Ultraviolet photoemission spectroscopy (UPS) experiments provide a detailed insight on the valence band (VB) structure of doped and undoped QDs. Using UPS measurements, we are able to observe photoemission from the Cu d-levels above VB maximum of the QDs which allows a complete picture of the energy band landscape of these materials. This information provides insights into many of the physical properties of doped QDs, including the highly debated near-infrared photoluminescence in Cu doped CdSe QDs. We show that all our results point to a common theme of orbital hybridization in Cu doped CdSe QDs which leads to optically and electronically active states below the conduction band minimum. Our model is supported from current-voltage measurements of doped and undoped materials, which exhibit Schottky to Ohmic behavior with Cu doping, suggestive of a tuning of the lowest energy states near the Fermi level.This paper investigates how chemical dopants affect the electronic properties of CdSe quantum dots (QDs) and why a model that incorporates the concepts of orbital hybridization must be used to understand these properties. Extended X-ray absorption fine structure spectroscopy measurements show that copper dopants in CdSe QDs occur primarily through a statistical doping mechanism. Ultraviolet photoemission spectroscopy (UPS) experiments provide a detailed insight on the valence band (VB) structure of doped and undoped QDs. Using UPS measurements, we are able to observe photoemission from the Cu d-levels above VB maximum of the QDs which allows a complete picture of the energy band landscape of these materials. This information provides insights into many of the physical properties of doped QDs, including the highly debated near-infrared photoluminescence in Cu doped CdSe QDs. We show that all our results point to a common theme of orbital hybridization in Cu doped CdSe QDs which leads to optically and electronically active states below the conduction band minimum. Our model is supported from current-voltage measurements of doped and undoped materials, which exhibit Schottky to Ohmic behavior with Cu doping, suggestive of a tuning of the lowest energy states near the Fermi level. Electronic supplementary information (ESI) available: Thermogravimetric analysis and X-ray photoelectron spectroscopy of QD films. See DOI: 10.1039/C6NR00494F

The effect of tidal forces on the minimum energy configurations of the full three-body problem

NASA Astrophysics Data System (ADS)

Levine, Edward

We investigate the evolution of minimum energy configurations for the Full Three Body Problem (3BP). A stable ternary asteroid system will gradually become unstable due to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect and an unpredictable trajectory will ensue. Through the interaction of tidal torques, energy in the system will dissipate in the form of heat until a stable minimum energy configuration is reached. We present a simulation that describes the dynamical evolution of three bodies under the mutual effects of gravity and tidal torques. Simulations show that bodies do not get stuck in local minima and transition to the predicted minimum energy configuration.

Dependence of Mechanical and Thermal Properties of Thermoplastic Composites on Electron Beam Irradiation

NASA Astrophysics Data System (ADS)

Kim, Sok Won; Park, K.; Lee, S. H.; Kang, J. S.; Kang, K. H.

2007-06-01

Since the restrictions for environmental protection being strengthened, thermoplastics reinforced with natural fibers (NF’s), such as jute, kenaf, flax, etc. have appeared as alternatives to chemical plastics for automobile interior materials. In this study, the thermal conductivity, tensile strength, and deformation of several kinds of thermoplastic composites composed of 50% polypropylene (PP) and 50% natural fiber (NF) irradiated by an electron beam (energy: 0.5 MeV, dose: 0 20 kGy) were measured. The length and thickness of PP and NF are 80 ± 10 mm and 40 120 μm, respectively. The results show that the thermal conductivity and the tensile strength changed and became minimum, when the dose of the electron beam was 10 kGy. However, the effect of the dose on the deformation was not clear.

Influence of the inter-ion interaction on the phase diagrams of the 1D Falicov-Kimball system

NASA Astrophysics Data System (ADS)

Gajek, Z.; Lemański, R.

2004-05-01

A model of itinerant, spinless electrons interacting with ions via the on-site Coulomb potential U, modified by the inter-ionic nearest-neighbour interaction V, is studied on the one-dimensional infinite lattice. Only periodical configurations of the ions with a limited number of lattice sites in a unit cell and their mixtures are taken into account. Phases whose energies reach minimum values for given electron and ion chemical potentials are selected and depicted for a set of model parameters. Then the results are translated into the ion density-electron density canonical phase diagrams and summarized in the electrondensity-U plane. The diagrams clearly show how various kinds of charge ordering evolve with V, starting from V=0 case, that represents the standard Falicov-Kimball model discussed previously.

25 CFR 547.15 - What are the minimum technical standards for electronic data communications between system...

Code of Federal Regulations, 2010 CFR

2010-04-01

... WITH THE PLAY OF CLASS II GAMES § 547.15 What are the minimum technical standards for electronic data...) Player tracking information; (8) Download Packages; and (9) Any information that affects game outcome. (b...

25 CFR 547.15 - What are the minimum technical standards for electronic data communications between system...

Code of Federal Regulations, 2012 CFR

2012-04-01

... WITH THE PLAY OF CLASS II GAMES § 547.15 What are the minimum technical standards for electronic data...) Player tracking information; (8) Download Packages; and (9) Any information that affects game outcome. (b...

25 CFR 547.15 - What are the minimum technical standards for electronic data communications between system...

Code of Federal Regulations, 2011 CFR

2011-04-01

... WITH THE PLAY OF CLASS II GAMES § 547.15 What are the minimum technical standards for electronic data...) Player tracking information; (8) Download Packages; and (9) Any information that affects game outcome. (b...

Formation of hollow atoms above a surface

NASA Astrophysics Data System (ADS)

Briand, Jean Pierre; Phaneuf, Ronald; Terracol, Stephane; Xie, Zuqi

2012-06-01

Slow highly stripped ions approaching or penetrating surfaces are known to capture electrons into outer shells of the ions, leaving the innermost shells empty, and forming hollow atoms. Electron capture occurs above and below the surfaces. The existence of hollow atoms below surfaces e.g. Ar atoms whose K and L shells are empty, with all electrons lying in the M and N shells, was demonstrated in 1990 [1]. At nm above surfaces, the excited ions may not have enough time to decay before hitting the surfaces, and the formation of hollow atoms above surfaces has even been questioned [2]. To observe it, one must increase the time above the surface by decelerating the ions. We have for the first time decelerated O^7+ ions to energies as low as 1 eV/q, below the minimum energy gained by the ions due to the acceleration by their image charge. As expected, no ion backscattering (trampoline effect) above dielectric (Ge) was observed and at the lowest ion kinetic energies, most of the observed x-rays were found to be emitted by the ions after surface contact. [4pt] [1] J. P. Briand et al., Phys.Rev.Lett. 65(1990)159.[0pt] [2] J.P. Briand, AIP Conference Proceedings 215 (1990) 513.

Advanced Modular "All in One" Battery System with Intelligent Autonomous Cell Balancing Management

NASA Astrophysics Data System (ADS)

Petitdidier, X.; Pasquier, E.; Defer, M.; Koch, M.; Knorr, W.

2008-09-01

A new generation of energy storage systems based on Li-ion technology emerged at the end of the last century.To perform the first tests in safe conditions, Saft designed a simple electronic.Today, all Li-ion batteries for autonomous applications such as drones, launchers, missiles, torpedoes and "human" applications such as cellular, laptop, hybrid vehicle and nearly sub-marines need a Battery Management System.The minimum in terms of functions is the overcharge and over-discharge protections.For a battery made of 2 cells connected in series or more, a balancing system is added to maintain the available energy during all the life of the battery. For stringent/demanding applications, the state of charge and state of health are calculated by one or more computers.It is now time to take benefit of the past 10 years of Saft's experience in the domain to re-evaluate the constraints of Li-ion batteries and provide customers with improved products by optimizing the battery management.Benefits of electronic for satellite applications:• Full control over battery.• Confidence whatever the possible change of conditions in environment.• The battery system can resist long exposure to gradient conditions with mitigated and stabilized impact on performances.• The balancing function allow to use all the energy of all the cells: optimize of installed energy (compact design, mass saving). It started out with the basic fact that electrochemists are not intended to be space rated electronic experts and vice versa, even if Saft has a good heritage in the electronic battery management system. Consequently, considering heritage and expertise in their respective core businesses, Saft and ASP teamed up.It became necessary to provide an "all in one" modular energy storage system with intelligent autonomous cell balancing management.

Technical note: optimization for improved tube-loading efficiency in the dual-energy computed tomography coupled with balanced filter method.

PubMed

Saito, Masatoshi

2010-08-01

This article describes the spectral optimization of dual-energy computed tomography using balanced filters (bf-DECT) to reduce the tube loadings and dose by dedicating to the acquisition of electron density information, which is essential for treatment planning in radiotherapy. For the spectral optimization of bf-DECT, the author calculated the beam-hardening error and air kerma required to achieve a desired noise level in an electron density image of a 50-cm-diameter cylindrical water phantom. The calculation enables the selection of beam parameters such as tube voltage, balanced filter material, and its thickness. The optimal combination of tube voltages was 80 kV/140 kV in conjunction with Tb/Hf and Bi/Mo filter pairs; this combination agrees with that obtained in a previous study [M. Saito, "Spectral optimization for measuring electron density by the dual-energy computed tomography coupled with balanced filter method," Med. Phys. 36, 3631-3642 (2009)], although the thicknesses of the filters that yielded a minimum tube output were slightly different from those obtained in the previous study. The resultant tube loading of a low-energy scan of the present bf-DECT significantly decreased from 57.5 to 4.5 times that of a high-energy scan for conventional DECT. Furthermore, the air kerma of bf-DECT could be reduced to less than that of conventional DECT, while obtaining the same figure of merit for the measurement of electron density and effective atomic number. The tube-loading and dose efficiencies of bf-DECT were considerably improved by sacrificing the quality of the noise level in the images of effective atomic number.

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

Smith, K.L.

This document has been developed to provide guidance in the interchange of electronic CAD data with Martin Marietta Energy Systems, Inc., Oak Ridge, Tennessee. It is not meant to be as comprehensive as the existing standards and specifications, but to provide a minimum set of practices that will enhance the success of the CAD data exchange. It is now a Department of Energy (DOE) Oak Ridge Field Office requirement that Architect-Engineering (A-E) firms prepare all new drawings using a Computer Aided Design (CAD) system that is compatible with the Facility Manager`s (FM) CAD system. For Oak Ridge facilities, the CADmore » system used for facility design by the FM, Martin Marietta Energy Systems, Inc., is Intregraph. The format for interchange of CAD data for Oak Ridge facilities will be the Intergraph MicroStation/IGDS format.« less

Small area silicon diffused junction X-ray detectors

NASA Technical Reports Server (NTRS)

Walton, J. T.; Pehl, R. H.; Larsh, A. E.

1982-01-01

The low-temperature performance of silicon diffused junction detectors in the measurement of low energy X-rays is reported. The detectors have an area of 0.04 sq cm and a thickness of 100 microns. The spectral resolutions of these detectors were found to be in close agreement with expected values, indicating that the defects introduced by the high-temperature processing required in the device fabrication were not deleteriously affecting the detection of low-energy X-rays. Device performance over a temperature range of 77 K to 150 K is given. These detectors were designed to detect low-energy X-rays in the presence of minimum ionizing electrons. The successful application of silicon-diffused junction technology to X-ray detector fabrication may facilitate the development of other novel silicon X-ray detector designs.

Multi-energy x-ray detector calibration for T e and impurity density (n Z) measurements of MCF plasmas

DOE PAGES

Maddox, J.; Pablant, N.; Efthimion, P.; ...

2016-09-07

Here, soft x-ray detection with the new "multi-energy" PILATUS3 detector systems holds promise as a magnetically confined fusion (MCF) plasma diagnostic for ITER and beyond. The measured x-ray brightness can be used to determine impurity concentrations, electron temperatures, n 2 eZ eff products, and to probe the electron energy distribution. However, in order to be effective, these detectors which are really large arrays of detectors with photon energy gating capabilities must be precisely calibrated for each pixel. The energy-dependence of the detector response of the multi-energy PILATUS3 system with 100 K pixels has been measured at Dectris Laboratory. X-rays emittedmore » from a tube under high voltage bombard various elements such that they emit x-ray lines from Zr-Lα to Ag-Kα between 1.8 and 22.16 keV. Each pixel on the PILATUS3 can be set to a minimum energy threshold in the range from 1.6 to 25 keV. This feature allows a single detector to be sensitive to a variety of x-ray energies, so that it is possible to sample the energy distribution of the x-ray continuum and line-emission. PILATUS3 can be configured for 1D or 2D imaging of MCF plasmas with typical spatial energy and temporal resolution of 1 cm, 0.6 keV, and 5 ms, respectively.« less

Low energy isomers of (H{sub 2}O){sub 25} from a hierarchical method based on Monte Carlo temperature basin paving and molecular tailoring approaches benchmarked by MP2 calculations

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

Sahu, Nityananda; Gadre, Shridhar R., E-mail: gadre@iitk.ac.in, E-mail: sotiris.xantheas@pnnl.gov; Rakshit, Avijit

2014-10-28

We report new global minimum candidate structures for the (H{sub 2}O){sub 25} cluster that are lower in energy than the ones reported previously and correspond to hydrogen bonded networks with 42 hydrogen bonds and an interior, fully coordinated water molecule. These were obtained as a result of a hierarchical approach based on initial Monte Carlo Temperature Basin Paving sampling of the cluster's Potential Energy Surface with the Effective Fragment Potential, subsequent geometry optimization using the Molecular Tailoring Approach with the fragments treated at the second order Møller-Plesset (MP2) perturbation (MTA-MP2) and final refinement of the entire cluster at the MP2more » level of theory. The MTA-MP2 optimized cluster geometries, constructed from the fragments, were found to be within <0.5 kcal/mol from the minimum geometries obtained from the MP2 optimization of the entire (H{sub 2}O){sub 25} cluster. In addition, the grafting of the MTA-MP2 energies yields electronic energies that are within <0.3 kcal/mol from the MP2 energies of the entire cluster while preserving their energy rank order. Finally, the MTA-MP2 approach was found to reproduce the MP2 harmonic vibrational frequencies, constructed from the fragments, quite accurately when compared to the MP2 ones of the entire cluster in both the HOH bending and the OH stretching regions of the spectra.« less

Increase of intrinsic emittance induced by multiphoton photoemission from copper cathodes illuminated by femtosecond laser pulses

NASA Astrophysics Data System (ADS)

An, Chenjie; Zhu, Rui; Xu, Jun; Liu, Yaqi; Hu, Xiaopeng; Zhang, Jiasen; Yu, Dapeng

2018-05-01

Electron sources driven by femtosecond laser have important applications in many aspects, and the research about the intrinsic emittance is becoming more and more crucial. The intrinsic emittance of polycrystalline copper cathode, which was illuminated by femtosecond pulses (FWHM of the pulse duration was about 100 fs) with photon energies above and below the work function, was measured with an extremely low bunch charge (single-electron pulses) based on free expansion method. A minimum emittance was obtained at the photon energy very close to the effective work function of the cathode. When the photon energy decreased below the effective work function, emittance increased rather than decreased or flattened out to a constant. By investigating the dependence of photocurrent density on the incident laser intensity, we found the emission excited by pulsed photons with sub-work-function energies contained two-photon photoemission. In addition, the portion of two-photon photoemission current increased with the reduction of photon energy. We attributed the increase of emittance to the effect of two-photon photoemission. This work shows that conventional method of reducing the photon energy of excited light source to approach the room temperature limit of the intrinsic emittance may be infeasible for femtosecond laser. There would be an optimized photon energy value near the work function to obtain the lowest emittance for pulsed laser pumped photocathode.

Electron attachment to the guanine-cytosine nucleic acid base pair and the effects of monohydration and proton transfer.

PubMed

Gupta, Ashutosh; Jaeger, Heather M; Compaan, Katherine R; Schaefer, Henry F

2012-05-17

The guanine-cytosine (GC) radical anion and its interaction with a single water molecule is studied using ab initio and density functional methods. Z-averaged second-order perturbation theory (ZAPT2) was applied to GC radical anion for the first time. Predicted spin densities show that the radical character is localized on cytosine. The Watson-Crick monohydrated GC anion is compared to neutral GC·H2O, as well as to the proton-transferred analogue on the basis of structural and energetic properties. In all three systems, local minima are identified that correspond to water positioned in the major and minor grooves of macromolecular DNA. On the anionic surface, two novel structures have water positioned above or below the GC plane. On the neutral and anionic surfaces, the global minimum can be described as water interacting with the minor groove. These structures are predicted to have hydration energies of 9.7 and 11.8 kcal mol(-1), respectively. Upon interbase proton-transfer (PT), the anionic global minimum has water positioned in the major groove, and the hydration energy increases to 13.4 kcal mol(-1). PT GC·H2O(•-) has distonic character; the radical character resides on cytosine, while the negative charge is localized on guanine. The effects of proton transfer are further investigated through the computed adiabatic electron affinities (AEA) of GC and monohydrated GC, and the vertical detachment energies (VDE) of the corresponding anions. Monohydration increases the AEAs and VDEs by only 0.1 eV, while proton-transfer increases the VDEs substantially (0.8 eV). The molecular charge distribution of monohydrated guanine-cytosine radical anion depends heavily on interbase proton transfer.

Effect of H2 binding on the nonadiabatic transition probability between singlet and triplet states of the [NiFe]-hydrogenase active site.

PubMed

Kaliakin, Danil S; Zaari, Ryan R; Varganov, Sergey A

2015-02-12

We investigate the effect of H2 binding on the spin-forbidden nonadiabatic transition probability between the lowest energy singlet and triplet electronic states of [NiFe]-hydrogenase active site model, using a velocity averaged Landau-Zener theory. Density functional and multireference perturbation theories were used to provide parameters for the Landau-Zener calculations. It was found that variation of the torsion angle between the terminal thiolate ligands around the Ni center induces an intersystem crossing between the lowest energy singlet and triplet electronic states in the bare active site and in the active site with bound H2. Potential energy curves between the singlet and triplet minima along the torsion angle and H2 binding energies to the two spin states were calculated. Upon H2 binding to the active site, there is a decrease in the torsion angle at the minimum energy crossing point between the singlet and triplet states. The probability of nonadiabatic transitions at temperatures between 270 and 370 K ranges from 35% to 32% for the active site with bound H2 and from 42% to 38% for the bare active site, thus indicating the importance of spin-forbidden nonadiabatic pathways for H2 binding on the [NiFe]-hydrogenase active site.

The magnetic local time distribution of energetic electrons in the radiation belt region

NASA Astrophysics Data System (ADS)

Allison, Hayley J.; Horne, Richard B.; Glauert, Sarah A.; Zanna, Giulio Del

2017-08-01

Using 14 years of electron flux data from the National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites, a statistical study of the magnetic local time (MLT) distribution of the electron population is performed across a range of activity levels, defined by AE, AE*, Kp, solar wind velocity (Vsw), and VswBz. Three electron energies (>30, >100, and >300 keV) are considered. Dawn-dusk flux asymmetries larger than order of magnitude were observed for >30 and >100 keV electrons. For >300 keV electrons, dawn-dusk asymmetries were primarily due to a decrease in the average duskside flux beyond L* ˜ 4.5 that arose with increasing activity. For the >30 keV population, substorm injections enhance the dawnside flux, which may not reach the duskside as the electrons can be on open drift paths and lost to the magnetopause. The asymmetries in the >300 keV population are attributed to the combination of magnetopause shadowing and >300 keV electron injections by large electric fields. We suggest that 3-D radiation belt models could set the minimum energy boundary (Emin) to 30 keV or above at L* ˜ 6 during periods of low activity. However, for more moderate conditions, Emin should be larger than 100 keV and, for very extreme activities, ˜300 keV. Our observations show the extent that in situ electron flux readings may vary during active periods due to the MLT of the satellite and highlight the importance of 4-D radiation belt models to fully understand radiation belt processes.

The Magnetic Local Time Distribution of Energetic Electrons in the Radiation Belt Region

NASA Astrophysics Data System (ADS)

Allison, H. J.

2017-12-01

Using fourteen years of electron flux data from the National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites (POES), a statistical study of the magnetic local time (MLT) distribution of the electron population is performed across a range of activity levels, defined by AE, AE*, Kp, solar wind velocity (Vsw), and VswBz. Three electron energies (>30, >100, and >300 keV) are considered. Dawn-dusk flux asymmetries larger than order of magnitude were observed for >30 and >100 keV electrons. For >300 keV electrons, dawn-dusk asymmetries were primarily due to a decrease in the average dusk-side flux beyond L* ˜ 4.5 that arose with increasing activity. For the >30 keV population, substorm injections enhance the dawn-side flux, which may not reach the dusk-side as the electrons can be on open drift paths and lost to the magnetopause. The asymmetries in the >300 keV population are attributed to the combination of magnetopause shadowing and >300 keV electron injections by large electric fields. We suggest that 3D radiation belt models could set the minimum energy boundary (Emin) to 30 keV or above at L* ˜6 during periods of low activity. However, for more moderate conditions, Emin should be larger than 100 keV and, for very extreme activities, ˜300 keV. Our observations show the extent that in-situ electron flux readings may vary during active periods due to the MLT of the satellite and highlight the importance of 4D radiation belt models to fully understand radiation belt processes.

Development of a 32-channel ASIC for an X-ray APD detector onboard the ISS

NASA Astrophysics Data System (ADS)

Arimoto, Makoto; Harita, Shohei; Sugita, Satoshi; Yatsu, Yoichi; Kawai, Nobuyuki; Ikeda, Hirokazu; Tomida, Hiroshi; Isobe, Naoki; Ueno, Shiro; Mihara, Tatehiro; Serino, Motoko; Kohmura, Takayoshi; Sakamoto, Takanori; Yoshida, Atsumasa; Tsunemi, Hiroshi; Hatori, Satoshi; Kume, Kyo; Hasegawa, Takashi

2018-02-01

We report on the design and performance of a mixed-signal application specific integrated circuit (ASIC) dedicated to avalanche photodiodes (APDs) in order to detect hard X-ray emissions in a wide energy band onboard the International Space Station. To realize wide-band detection from 20 keV to 1 MeV, we use Ce:GAGG scintillators, each coupled to an APD, with low-noise front-end electronics capable of achieving a minimum energy detection threshold of 20 keV. The developed ASIC has the ability to read out 32-channel APD signals using 0.35 μm CMOS technology, and an analog amplifier at the input stage is designed to suppress the capacitive noise primarily arising from the large detector capacitance of the APDs. The ASIC achieves a performance of 2099 e- + 1.5 e-/pF at root mean square (RMS) with a wide 300 fC dynamic range. Coupling a reverse-type APD with a Ce:GAGG scintillator, we obtain an energy resolution of 6.7% (FWHM) at 662 keV and a minimum detectable energy of 20 keV at room temperature (20 °C). Furthermore, we examine the radiation tolerance for space applications by using a 90 MeV proton beam, confirming that the ASIC is free of single-event effects and can operate properly without serious degradation in analog and digital processing.

Oxygen enhanced switching to combustion of lower rank fuels

DOEpatents

Kobayashi, Hisashi; Bool, III, Lawrence E.; Wu, Kuang Tsai

2004-03-02

A furnace that combusts fuel, such as coal, of a given minimum energy content to obtain a stated minimum amount of energy per unit of time is enabled to combust fuel having a lower energy content, while still obtaining at least the stated minimum energy generation rate, by replacing a small amount of the combustion air fed to the furnace by oxygen. The replacement of oxygen for combustion air also provides reduction in the generation of NOx.

Topology-energy relationships and lowest energy configurations for pentagonal dodecahedral (H2O)20X clusters, X=empty, H2O, NH3, H3O+: The importance of O-topology

NASA Astrophysics Data System (ADS)

Anick, David J.

2010-04-01

For (H2O)20X water clusters consisting of X enclosed by the 512 dodecahedral cage, X=empty, H2O, NH3, and H3O+, databases are made consisting of 55-82 isomers optimized via B3LYP/6-311++G∗∗. Correlations are explored between ground state electronic energy (Ee) or electronic energy plus zero point energy (Ee+ZPE) and the clusters' topology, defined as the set of directed H-bonds. Linear regression is done to identify topological features that correlate with cluster energy. For each X, variables are found that account for 99% of the variance in Ee and predict it with a rms error under 0.2 kcal/mol. The method of analysis emphasizes the importance of an intermediate level of structure, the "O-topology," consisting of O-types and a list of O pairs that are bonded but omitting H-bond directions, as a device to organize the databases and reduce the number of structures one needs to consider. Relevant variables include three parameters, which count the number of H-bonds having particular donor and acceptor types; |M|2, where M is the cluster's vector dipole moment; and the projection of M onto the symmetry axis of X. Scatter diagrams for Ee or Ee+ZPE versus |M| show that clusters fall naturally into "families" defined by the values of certain discrete parameters, the "major parameters," for each X. Combining "family" analysis and O-topologies, a small group of clusters is identified for each X that are candidates to be the global minimum, and the minimum is determined. For X=H3O+, one cluster with central hydronium lies just 2.08 kcal/mol above the lowest isomer with surface hydronium. Implications of the methodology for dodecahedral (H2O)20(NH4+) and (H2O)20(NH4+)(OH-) are discussed, and new lower energy isomers are found. For MP2/TZVP, the lowest-energy (H2O)20(NH4+) isomer features a trifurcated H-bond. The results suggest a much more efficient and comprehensive way of seeking low-energy water cluster geometries that may have wide applicability.

Topology-energy relationships and lowest energy configurations for pentagonal dodecahedral (H2O)20X clusters, X = empty, H2O, NH3, H3O+: the importance of O-topology.

PubMed

Anick, David J

2010-04-28

For (H(2)O)(20)X water clusters consisting of X enclosed by the 5(12) dodecahedral cage, X = empty, H(2)O, NH(3), and H(3)O(+), databases are made consisting of 55-82 isomers optimized via B3LYP/6-311++G(**). Correlations are explored between ground state electronic energy (Ee) or electronic energy plus zero point energy (Ee+ZPE) and the clusters' topology, defined as the set of directed H-bonds. Linear regression is done to identify topological features that correlate with cluster energy. For each X, variables are found that account for 99% of the variance in Ee and predict it with a rms error under 0.2 kcal/mol. The method of analysis emphasizes the importance of an intermediate level of structure, the "O-topology," consisting of O-types and a list of O pairs that are bonded but omitting H-bond directions, as a device to organize the databases and reduce the number of structures one needs to consider. Relevant variables include three parameters, which count the number of H-bonds having particular donor and acceptor types; absolute value(M)(2), where M is the cluster's vector dipole moment; and the projection of M onto the symmetry axis of X. Scatter diagrams for Ee or Ee+ZPE versus absolute value(M) show that clusters fall naturally into "families" defined by the values of certain discrete parameters, the "major parameters," for each X. Combining "family" analysis and O-topologies, a small group of clusters is identified for each X that are candidates to be the global minimum, and the minimum is determined. For X = H(3)O(+), one cluster with central hydronium lies just 2.08 kcal/mol above the lowest isomer with surface hydronium. Implications of the methodology for dodecahedral (H(2)O)(20)(NH(4)(+)) and (H(2)O)(20)(NH(4)(+))(OH(-)) are discussed, and new lower energy isomers are found. For MP2/TZVP, the lowest-energy (H(2)O)(20)(NH(4)(+)) isomer features a trifurcated H-bond. The results suggest a much more efficient and comprehensive way of seeking low-energy water cluster geometries that may have wide applicability.

A generalized force-modified potential energy surface (G-FMPES) for mechanochemical simulations

DOE PAGES

Subramanian, Gopinath; Mathew, Nithin; Leiding, Jeffery A.

2015-10-05

We describe the modifications that a spatially varying external load produces on a Born-Oppenheimer potential energy surface (PES) by calculating static quantities of interest. The effects of the external loads are exemplified using electronic structure calculations (at the HF/6-31G** level) of two different molecules: ethane and hexahydro-1,3,5-trinitro-s-triazine (RDX). The calculated transition states and The Hessian matrices of stationary points show that spatially varying external loads shift the stationary points and modify the curvature of the PES, thereby affecting the harmonic transition rates by altering both the energy barrier as well as the prefactor. The harmonic spectra of both molecules aremore » blue-shifted with increasing compressive “pressure.” Some stationary points on the RDX-PES disappear under application of the external load, indicating the merging of an energy minimum with a saddle point.« less

Direct dynamics simulation of dioxetane formation and decomposition via the singlet .O-O-CH2-CH2. biradical: Non-RRKM dynamics

NASA Astrophysics Data System (ADS)

Sun, Rui; Park, Kyoyeon; de Jong, Wibe A.; Lischka, Hans; Windus, Theresa L.; Hase, William L.

2012-07-01

Electronic structure calculations and direct chemical dynamics simulations are used to study the formation and decomposition of dioxetane on its ground state singlet potential energy surface. The stationary points for 1O2 + C2H4, the singlet .O-O-CH2-CH2. biradical, the transition state (TS) connecting this biradical with dioxetane, and the two transition states and gauche .O-CH2-CH2-O. biradical connecting dioxetane with the formaldehyde product molecules are investigated at different levels of electronic structure theory including UB3LYP, UMP2, MRMP2, and CASSCF and a range of basis sets. The UB3LYP/6-31G* method was found to give representative energies for the reactive system and was used as a model for the simulations. UB3LYP/6-31G* direct dynamics trajectories were initiated at the TS connecting the .O-O-CH2-CH2. biradical and dioxetane by sampling the TS's vibrational energy levels, and rotational and reaction coordinate energies, with Boltzmann distributions at 300, 1000, and 1500 K. This corresponds to the transition state theory model for trajectories that pass the TS. The trajectories were directed randomly towards both the biradical and dioxetane. A small fraction of the trajectories directed towards the biradical recrossed the TS and formed dioxetane. The remainder formed 1O2 + C2H4 and of these ˜ 40% went directly from the TS to 1O2 + C2H4 without getting trapped and forming an intermediate in the .O-O-CH2-CH2. biradical potential energy minimum, a non-statistical result. The dioxetane molecules which are formed dissociate to two formaldehyde molecules with a rate constant two orders of magnitude smaller than that predicted by Rice-Ramsperger-Kassel-Marcus theory. The reaction dynamics from dioxetane to the formaldehyde molecules do not follow the intrinsic reaction coordinate or involve trapping in the gauche .O-CH2-CH2-O. biradical potential energy minimum. Important non-statistical dynamics are exhibited for this reactive system.

Temporal change in the electromechanical properties of dielectric elastomer minimum energy structures

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

Buchberger, G., E-mail: erda.buchberger@jku.at; Hauser, B.; Jakoby, B.

Dielectric elastomer minimum energy structures (DEMES) are soft electronic transducers and energy harvesters with potential for consumer goods. The temporal change in their electromechanical properties is of major importance for engineering tasks. Therefore, we study acrylic DEMES by impedance spectroscopy and by optical methods for a total time period of approx. 4.5 months. We apply either compliant electrodes from carbon black particles only or fluid electrodes from a mixture of carbon black particles and silicone oil. From the measurement data, the equivalent series capacitances and resistances as well as the bending angles of the transducers are obtained. We find thatmore » the equivalent series capacitances change in average between −12 %/1000 h and −4.0 %/1000 h, while the bending angles decrease linearly with slopes ranging from −15 %/1000 h to −7 %/1000 h. Transducers with high initial bending angles and electrodes from carbon black particles show the smallest changes of the electromechanical characteristics. The capacitances decrease faster for DEMES with fluid electrodes. Some DEMES of this type reveal huge and unpredictable fluctuations of the resistances over time due to the ageing of the contacts. Design guidelines for DEMES follow directly from the observed transient changes of their electromechanical performance.« less

Intrinsic Conformational Preferences of Cα,α-Dibenzylglycine

PubMed Central

Casanovas, Jordi; Nussinov, Ruth; Alemán, Carlos

2009-01-01

The intrinsic conformational preferences of Cα,α-dibenzylglycine, a symmetric α,α-dialkylated amino acid bearing two benzyl substituents on the α-carbon atom, have been determined using quantum chemical calculations at the B3LYP/6-31+G(d,p) level. A total of 46 minimum energy conformations were found for the N-acetyl-N'-methylamide derivative, even though only 9 of them showed a relative energy lower than 5.0 kcal/mol. The latter involves C7, C5 and α' backbone conformations stabilized by intramolecular hydrogen bonds and/or N-H…π interactions. Calculation of the conformational free energies in different environments (gas-phase, carbon tetrachloride, chloroform, methanol and water solutions) indicates that four different minima (two C5 and two C7) are energetically accessible at room temperature in the gas-phase, while in methanol and aqueous solutions one such minimum (C5) becomes the only significant conformation. Comparison with results recently reported for Cα,α-diphenylglycine indicates that substitution of phenyl side groups by benzyl enhances the conformational flexibility leading to (i) a reduction of the strain of the peptide backbone; and (ii) alleviating the repulsive interactions between the π electron density of the phenyl groups and the lone pairs of the carbonyl oxygen atoms. PMID:18465898

Characterization of an F-center in an alkali halide cluster

NASA Astrophysics Data System (ADS)

Bader, R. F. W.; Platts, J. A.

1997-11-01

The removal of a fluorine atom from its central position in a cubiclike Li14F13+ cluster creates an F-center vacancy that may or may not be occupied by the remaining odd electron. The topology exhibited by the electron density in Li14F12+, the F-center cluster, enables one to make a clear distinction between the two possible forms that the odd electron can assume. If it possesses a separate identity, then a local maximum in the electron density will be found within the vacancy and the F-center will behave quantum mechanically as an open system, bounded by a surface of local zero flux in the gradient vector field of the electron density. If, however, the density of the odd electron is primarily delocalized onto the neighboring ions, then a cage critical point, a local minimum in the density, will be found at the center of the vacancy. Without an associated local maximum, the vacancy has no boundary and is undefined. Self-consistent field (SCF) calculations with geometry optimization of the Li14F13+ cluster and of the doublet state of Li14F12+ show that the creation of the central vacancy has only a minor effect upon the geometry of the cluster, the result of a local maximum in the electron density being formed within the vacancy. Thus the F-center is the physical manifestation of a non-nuclear attractor in the electron density. It is consequently a proper open system with a definable set of properties, the most characteristic being its low kinetic energy per electron. In addition to determining the properties of the F-center, the effect of its formation on the energies, volumes, populations, both electron and spin, and electron localizations of the ions in the cluster are determined.

Is HO3 minimum cis or trans? An analytic full-dimensional ab initio isomerization path.

PubMed

Varandas, A J C

2011-05-28

The minimum energy path for isomerization of HO(3) has been explored in detail using accurate high-level ab initio methods and techniques for extrapolation to the complete basis set limit. In agreement with other reports, the best estimates from both valence-only and all-electron single-reference methods here utilized predict the minimum of the cis-HO(3) isomer to be deeper than the trans-HO(3) one. They also show that the energy varies by less than 1 kcal mol(-1) or so over the full isomerization path. A similar result is found from valence-only multireference configuration interaction calculations with the size-extensive Davidson correction and a correlation consistent triple-zeta basis, which predict the energy difference between the two isomers to be of only Δ = -0.1 kcal mol(-1). However, single-point multireference calculations carried out at the optimum triple-zeta geometry with basis sets of the correlation consistent family but cardinal numbers up to X = 6 lead upon a dual-level extrapolation to the complete basis set limit of Δ = (0.12 ± 0.05) kcal mol(-1). In turn, extrapolations with the all-electron single-reference coupled-cluster method including the perturbative triples correction yield values of Δ = -0.19 and -0.03 kcal mol(-1) when done from triple-quadruple and quadruple-quintuple zeta pairs with two basis sets of increasing quality, namely cc-cpVXZ and aug-cc-pVXZ. Yet, if added a value of 0.25 kcal mol(-1) that accounts for the effect of triple and perturbative quadruple excitations with the VTZ basis set, one obtains a coupled cluster estimate of Δ = (0.14 ± 0.08) kcal mol(-1). It is then shown for the first time from systematic ab initio calculations that the trans-HO(3) isomer is more stable than the cis one, in agreement with the available experimental evidence. Inclusion of the best reported zero-point energy difference (0.382 kcal mol(-1)) from multireference configuration interaction calculations enhances further the relative stability to ΔE(ZPE) = (0.51 ± 0.08) kcal mol(-1). A scheme is also suggested to model the full-dimensional isomerization potential-energy surface using a quadratic expansion that is parametrically represented by a Fourier analysis in the torsion angle. The method illustrated at the raw and complete basis-set limit coupled-cluster levels can provide a valuable tool for a future analysis of the available (incomplete thus far) experimental rovibrational data. This journal is © the Owner Societies 2011

On the nature of bonding in binary Be2O2 and Si2O2 clusters: rhombic four-center four-electron π and σ bonds.

PubMed

Wang, Kang; Wang, Ying-Jin; Li, Da-Zhi; Ou, Ting; Zhao, Xiao-Yun; Zhai, Hua-Jin

2016-04-14

The structural and electronic properties and chemical bonding of binary Be2O2 and Si2O2 clusters have been studied using quantum chemical calculations at the B3LYP level. For the Be2O2 cluster, the potential energy surface is probed by unbiased structural searches and the global-minimum structure was established using the B3LYP calculations, complemented by PBE0 and single-point CCSD(T) calculations for top isomers. The perfectly planar D2h Be2O2 ((1)Ag) global minimum is well defined, being at least 3.64 eV lower in energy than alternative structures at the CCSD(T)//B3LYP/aug-cc-pVTZ level. Chemical bonding analyses show that D2h Be2O2 and Si2O2 clusters possess the rhombic four-center four-electron (4c-4e) π bond, that is, the o-bond, a conception derived from electron-deficient boron oxide clusters lately. Furthermore, the Be2O2 and Si2O2 clusters also exhibit rhombic 4c-4e σ bonds, both for the radial and tangential σ frameworks (σr and σt). The σt framework is classified as an o-bond only formally, due to the secondary contribution from the Be/Si s component. The three-fold (π, σr, and σt) o-bonds in Be2O2 and Si2O2 are considered to resemble the three-fold aromaticity in all-metal Al4(2-) dianions. A 4c-4e o-bond makes use of four O 2p electrons, which would otherwise be two lone-pairs, for a delocalized and completely bonding orbital, as well as a residual nonbonding orbital. Three-fold o-bonds thus greatly stabilize the binary Be2O2 and Si2O2 clusters. We anticipate that the bonding concept should be applicable to additional molecular systems, including those with larger heterocyclic rings.

25 CFR 547.15 - What are the minimum technical standards for electronic data communications between system...

Code of Federal Regulations, 2013 CFR

2013-04-01

... data communications between system components? 547.15 Section 547.15 Indians NATIONAL INDIAN GAMING... AND EQUIPMENT § 547.15 What are the minimum technical standards for electronic data communications between system components? (a) Sensitive data. Communication of sensitive data must be secure from...

25 CFR 547.15 - What are the minimum technical standards for electronic data communications between system...

Code of Federal Regulations, 2014 CFR

2014-04-01

... data communications between system components? 547.15 Section 547.15 Indians NATIONAL INDIAN GAMING... AND EQUIPMENT § 547.15 What are the minimum technical standards for electronic data communications between system components? (a) Sensitive data. Communication of sensitive data must be secure from...

A multi-purpose readout electronics for CdTe and CZT detectors for x-ray imaging applications

NASA Astrophysics Data System (ADS)

Yue, X. B.; Deng, Z.; Xing, Y. X.; Liu, Y. N.

2017-09-01

A multi-purpose readout electronics based on the DPLMS digital filter has been developed for CdTe and CZT detectors for X-ray imaging applications. Different filter coefficients can be synthesized optimized either for high energy resolution at relatively low counting rate or for high rate photon-counting with reduced energy resolution. The effects of signal width constraints, sampling rate and length were numerical studied by Mento Carlo simulation with simple CRRC shaper input signals. The signal width constraint had minor effect and the ENC was only increased by 6.5% when the signal width was shortened down to 2 τc. The sampling rate and length depended on the characteristic time constants of both input and output signals. For simple CR-RC input signals, the minimum number of the filter coefficients was 12 with 10% increase in ENC when the output time constant was close to the input shaping time. A prototype readout electronics was developed for demonstration, using a previously designed analog front ASIC and a commercial ADC card. Two different DPLMS filters were successfully synthesized and applied for high resolution and high counting rate applications respectively. The readout electronics was also tested with a linear array CdTe detector. The energy resolutions of Am-241 59.5 keV peak were measured to be 6.41% in FWHM for the high resolution filter and to be 13.58% in FWHM for the high counting rate filter with 160 ns signal width constraint.

X-Ray and TeV Gamma-Ray Emission from Parallel Electron-Positron or Electron-Proton Beams in BL Lacertae Objects

NASA Astrophysics Data System (ADS)

Krawczynski, H.

2007-04-01

In this paper we discuss models of the X-ray and TeV γ-ray emission from BL Lac objects based on parallel electron-positron or electron-proton beams that form close to the central black hole, due to the strong electric fields generated by the accretion disk and possibly also by the black hole itself. Fitting the energy spectrum of the BL Lac object Mrk 501, we obtain tight constraints on the beam properties. Launching a sufficiently energetic beam requires rather strong magnetic fields close to the black hole (~100-1000 G). However, the model fits imply that the magnetic field in the emission region is only ~0.02 G. Thus, the particles are accelerated close to the black hole and propagate a considerable distance before instabilities trigger the dissipation of energy through synchrotron and self-Compton emission. We discuss various approaches to generate enough power to drive the jet and, at the same time, to accelerate particles to ~20 TeV energies. Although the parallel beam model has its own problems, it explains some of the long-standing problems that plague models based on Fermi-type particle acceleration, such as the presence of a very high minimum Lorentz factor of accelerated particles. We conclude with a brief discussion of the implications of the model for the difference between the processes of jet formation in BL Lac-type objects and those in quasars.

X-ray and TeV Gamma-Ray Emission from Parallel Electron-Positron or Electron-Proton Beams in BL Lac Objects

NASA Astrophysics Data System (ADS)

Krawczynski, Henric

2007-04-01

In this contribution we discuss models of the X-rays and TeV gamma-ray emission from BL Lac objects based on parallel electron-positron or electron-proton beams that form close to the central black hole owing to the strong electric fields generated by the accretion disk and possibly also by the black hole itself. Fitting the energy spectrum of the BL Lac object Mrk 501, we obtain tight constrains on the beam properties. Launching a sufficiently energetic beam requires rather strong magnetic fields close to the black hole 100-1000 G. However, the model fits imply that the magnetic field in the emission region is only 0.02 G. Thus, the particles are accelerated close to the black hole and propagate a considerable distance before instabilities trigger the dissipation of energy through synchrotron and self-Compton emission. We discuss various approaches to generate enough power to drive the jet and, at the same time, to accelerate particles to 20 TeV energies. Although the parallel beam model has its own problems, it explains some of the long-standing problems that plague models based on Fermi type particle acceleration, like the presence of a very high minimum Lorentz factor of accelerated particles. We conclude with a brief discussion of the implications of the model for the difference between the processes of jet formation in BL Lac type objects and in quasars.

Improvements of low-level radioxenon detection sensitivity by a state-of-the art coincidence setup.

PubMed

Cagniant, A; Le Petit, G; Gross, P; Douysset, G; Richard-Bressand, H; Fontaine, J-P

2014-05-01

The ability to quantify isotopic ratios of 135, 133 m, 133 and 131 m radioxenon is essential for the verification of the Comprehensive Nuclear-Test Ban Treaty (CTBT). In order to improve detection limits, CEA has developed a new on-site setup using photon/electron coincidence (Le Petit et al., 2013. J. Radioanal. Nucl. Chem., DOI : 10.1007/s 10697-013-2525-8.). Alternatively, the electron detection cell equipped with large silicon chips (PIPS) can be used with HPGe detector for laboratory analysis purpose. This setup allows the measurement of β/γ coincidences for the detection of (133)Xe and (135)Xe; and K-shell Conversion Electrons (K-CE)/X-ray coincidences for the detection of (131m)Xe, (133m)Xe and (133)Xe as well. Good energy resolution of 11 keV at 130 keV and low energy threshold of 29 keV for the electron detection were obtained. This provides direct discrimination between K-CE from (133)Xe, (133m)Xe and (131m)Xe. Estimation of Minimum Detectable Activity (MDA) for (131m)Xe is in the order of 1mBq over a 4 day measurement. An analysis of an environmental radioxenon sample using this method is shown. © 2013 The Authors. Published by Elsevier Ltd All rights reserved.

First-principles study of structural, electronic, linear and nonlinear optical properties of Ga{2}PSb ternary chalcopyrite

NASA Astrophysics Data System (ADS)

Ouahrani, T.; Reshak, A. H.; de La Roza, A. Otero; Mebrouki, M.; Luaña, V.; Khenata, R.; Amrani, B.

2009-12-01

We report results from first-principles density functional calculations using the full-potential linear augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) and the Engel-Vosko-generalized gradient approximation (EV-GGA) were used for the exchange-correlation energy of the structural, electronic, linear and nonlinear optical properties of the chalcopyrite Ga2PSb compound. The valence band maximum (VBM) is located at the Γv point, and the conduction band minimum (CBM) is located at the Γc point, resulting in a direct band gap of about 0.365 eV for GGA and 0.83 eV for EV-GGA. In comparison with the experimental one (1.2 eV) we found that EV-GGA calculation gives energy gap in reasonable agreement with the experiment. The spin orbit coupling has marginal influence on the optical properties. The ground state quantities such as lattice parameters (a, c and u), bulk modules B and its pressure derivative B^primeare evaluated.

Advanced electric propulsion system concept for electric vehicles. Addendum 1: Voltage considerations

NASA Technical Reports Server (NTRS)

Raynard, A. E.; Forbes, F. E.

1980-01-01

The two electric vehicle propulsion systems that best met cost and performance goals were examined to assess the effect of battery pack voltage on system performance and cost. A voltage range of 54 to 540 V was considered for a typical battery pack capacity of 24 k W-hr. The highest battery specific energy (W-hr/kg) and the lowest cost ($/kW-hr) were obtained at the minimum voltage level. The flywheel system traction motor is a dc, mechanically commutated with shunt field control, and due to the flywheel the traction motor and the battery are not subject to extreme peaks of power demand. The basic system uses a permanent-magnet motor with electronic commutation supplied by an ac power control unit. In both systems battery cost were the major factor in system voltage selection, and a battery pack with the minimum voltage of 54 V produced the lowest life-cycle cost. The minimum life-cycle cost for the basic system with lead-acid batteries was $0.057/km and for the flywheel system was $0.037/km.

Refining the reaction mechanism of O2 towards its co-substrate in cofactor-free dioxygenases

PubMed Central

2016-01-01

Cofactor-less oxygenases perform challenging catalytic reactions between singlet co-substrates and triplet oxygen, in spite of apparently violating the spin-conservation rule. In 1-H-3-hydroxy-4-oxoquinaldine-2,4-dioxygenase, the active site has been suggested by quantum chemical computations to fine tune triplet oxygen reactivity, allowing it to interact rapidly with its singlet substrate without the need for spin inversion, and in urate oxidase the reaction is thought to proceed through electron transfer from the deprotonated substrate to an aminoacid sidechain, which then feeds the electron to the oxygen molecule. In this work, we perform additional quantum chemical computations on these two systems to elucidate several intriguing features unaddressed by previous workers. These computations establish that in both enzymes the reaction proceeds through direct electron transfer from co-substrate to O2 followed by radical recombination, instead of minimum-energy crossing points between singlet and triplet potential energy surfaces without formal electron transfer. The active site does not affect the reactivity of oxygen directly but is crucial for the generation of the deprotonated form of the co-substrates, which have redox potentials far below those of their protonated forms and therefore may transfer electrons to oxygen without sizeable thermodynamic barriers. This mechanism seems to be shared by most cofactor-less oxidases studied so far. PMID:28028471

Refining the reaction mechanism of O2 towards its co-substrate in cofactor-free dioxygenases.

PubMed

Silva, Pedro J

2016-01-01

Cofactor-less oxygenases perform challenging catalytic reactions between singlet co-substrates and triplet oxygen, in spite of apparently violating the spin-conservation rule. In 1- H -3-hydroxy-4-oxoquinaldine-2,4-dioxygenase, the active site has been suggested by quantum chemical computations to fine tune triplet oxygen reactivity, allowing it to interact rapidly with its singlet substrate without the need for spin inversion, and in urate oxidase the reaction is thought to proceed through electron transfer from the deprotonated substrate to an aminoacid sidechain, which then feeds the electron to the oxygen molecule. In this work, we perform additional quantum chemical computations on these two systems to elucidate several intriguing features unaddressed by previous workers. These computations establish that in both enzymes the reaction proceeds through direct electron transfer from co-substrate to O 2 followed by radical recombination, instead of minimum-energy crossing points between singlet and triplet potential energy surfaces without formal electron transfer. The active site does not affect the reactivity of oxygen directly but is crucial for the generation of the deprotonated form of the co-substrates, which have redox potentials far below those of their protonated forms and therefore may transfer electrons to oxygen without sizeable thermodynamic barriers. This mechanism seems to be shared by most cofactor-less oxidases studied so far.

Self-Assembly Strategies for Integrating Light Harvesting and Charge Separation in Artificial Photosynthetic Systems

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

Wasielewski, Michael R.

In natural photosynthesis, organisms optimize solar energy conversion through organized assemblies of photofunctional chromophores and catalysts within proteins that provide specifically tailored environments for chemical reactions. As with their natural counterparts, artificial photosynthetic systems for practical solar fuels production must collect light energy, separate charge, and transport charge to catalytic sites where multielectron redox processes will occur. While encouraging progress has been made on each aspect of this complex problem, researchers have not yet developed self-ordering and self-assembling components and the tailored environments necessary to realize a fully-functional artificial system. Previously researchers have used complex, covalent molecular systems comprised ofmore » chromophores, electron donors, and electron acceptors to mimic both the light-harvesting and the charge separation functions of photosynthetic proteins. These systems allow for study of the dependencies of electron transfer rate constants on donor?acceptor distance and orientation, electronic interaction, and the free energy of the reaction. The most useful and informative systems are those in which structural constraints control both the distance and the orientation between the electron donors and acceptors. Self-assembly provides a facile means for organizing large numbers of molecules into supramolecular structures that can bridge length scales from nanometers to macroscopic dimensions. The resulting structures must provide pathways for migration of light excitation energy among antenna chromophores, and from antennas to reaction centers. They also must incorporate charge conduits, that is, molecular 'wires' that can efficiently move electrons and holes between reaction centers and catalytic sites. The central scientific challenge is to develop small, functional building blocks with a minimum number of covalent linkages, which also have the appropriate molecular recognition properties to facilitate self-assembly of complete, functional artificial photosynthetic systems. In this Account, we explore how self-assembly strategies involving ?-stacking can be used to integrate light harvesting with charge separation and transport.« less

Recent Advances in Understanding Radiation Belt Dynamics in the Earth's Inner Zone and Slot Region

NASA Astrophysics Data System (ADS)

Li, X.

2015-12-01

Comprehensive measurements of the inner belt protons from the Relativistic Electron and Proton Telescope (REPT) onboard Van Allen Probes, in a geo-transfer-like orbit, revealed new features of inner belt protons in terms of their spectrum distribution, spatial distribution, pitch angle distribution, and their different source populations. Concurrent measurements from the Relativistic Electron and Proton Telescope integrated little experiment (REPTile) on board Colorado Student Space Weather Experiment (CSSWE) CubeSat, in a highly inclined low Earth orbit, and REPT demonstrated that there exist sub-MeV electrons in the inner belt and their flux level is orders of magnitude higher than the background associated with the inner belt protons, while higher energy electron (>1.6 MeV) measurements cannot be distinguished from the background. Analysis on sub-MeV electrons data in the inner belt and slot region from the Magnetic Electron Ion Spectrometer (MagEIS) on board Van Allen Probes revealed rather complicated pitch angle distribution of these energetic electrons, with the 90 deg-minimum (butterfly) pitch angle distribution dominating near the magnetic equator. Furthermore, it is clearly shown from MagEIS measurements that 10s - 100s keV electrons are commonly seen penetrating into the inner belt region during geomagnetic active times while protons of similar energies are hardly seen there. These are part of a summary of the most recent measurements and understanding of the dynamics of energetic particles in the inner zone and slot region to be exhibited and discussed in this presentation.

Kondo scattering in δ-doped LaTiO3/SrTiO3 interfaces: Renormalization by spin-orbit interactions

NASA Astrophysics Data System (ADS)

Das, Shubhankar; Rastogi, A.; Wu, Lijun; Zheng, Jin-Cheng; Hossain, Z.; Zhu, Yimei; Budhani, R. C.

2014-08-01

We present a study of δ doping at the LaTiO3/SrTiO3 interface with isostructural antiferromagnetic perovskite LaCrO3 that dramatically alters the properties of the two-dimensional electron gas at the interface. The effects include a reduction in sheet-carrier density, prominence of the low-temperature resistivity minimum, enhancement of weak antilocalization below 10 K, and observation of a strong anisotropic magnetoresistance (MR). The positive and negative MR for out-of-plane and in-plane fields, respectively, and the field and temperature dependencies of MR suggest Kondo scattering by localized Ti3+ moments renormalized by spin-orbit interaction at T < 10 K, with the increased δ-layer thickness. Electron-energy-loss spectroscopy and density functional calculations provide convincing evidence of blocking of electron transfer from LTO to STO by the δ layer.

Ion acoustic solitons in an electronegative plasma with electron trapping and nonextensivity effects

NASA Astrophysics Data System (ADS)

Ali Shan, S.

2018-03-01

The impact of electron trapping and nonextensivity on the low frequency ion acoustic solitary waves in an electronegative plasma is investigated. The energy integral equation with the Sagdeev truncated approach is derived, which is then solved with the help of suitable parameters and necessary conditions to get the solitary structures. The minimum Mach (M) number needed to calculate the solitary structures is found to be varying under the impact of trapping efficiency determining factor β and entropic index q. The results have been illustrated with the help of physically acceptable parameters and the amplitude of nonlinear solitary structures is found to be modified significantly because of electron trapping efficiency β and entropic index q. This study has been made with reference to Laboratory observation, which can also be helpful in Space and astrophysical plasmas where electronegative plasmas have been reported.

Ionic-to-Electronic Conductivity Crossover in CdTe-AgI-As2Te3 Glasses: An 110mAg Tracer Diffusion Study.

PubMed

Kassem, M; Alekseev, I; Bokova, M; Le Coq, D; Bychkov, E

2018-04-12

Conductivity isotherms of (CdTe) x (AgI) 0.5- x/2 (As 2 Te 3 ) 0.5- x/2 glasses (0.0 ≤ x ≤ 0.15) reveal a nonmonotonic behavior with increasing CdTe content reminiscent of mixed cation effect in oxide and chalcogenide glasses. Nevertheless, the apparent similarity appears to be partly incorrect. Using 110m Ag tracer diffusion measurements, we show that semiconducting CdTe additions produce a dual effect: (i) decreasing the Ag + ion transport by a factor of ≈200 with a simultaneous increase of the diffusion activation energy and (ii) increasing the electronic conductivity by 1.5 orders of magnitude. Consequently, the conductivity minimum at x = 0.05 reflects an ionic-to-electronic transport crossover; the silver-ion transport number decreases by 3 orders of magnitude with increasing x.

ECRH and its effects on neoclassical transport in a stellarator

NASA Astrophysics Data System (ADS)

Seol, Jaechun

The banana center orbit deviates significantly from the magnetic surface due to the symmetry-breaking term in the magnetic field configuration. Energetic electrons can escape the plasma without collision, since the drift speed is proportional to the perpendicular energy of electron and the collision frequency is reduced as the electron energy goes up. A direct loss flux can be generated from energetic electron population in a stellarator. Thus energetic electron populations can substantially modify the neoclassical transport properties in stellarators. A model accounting for this change in transport is developed assuming the presence of electron cyclotron resonance heating (ECRH). The quasilinear diffusion coefficient for second harmonic X-mode ECRH is developed for a bumpy stellarator. Care is taken in accounting for the pitch-angle dependence of the quasilinear diffusion coefficient since application to experiments with narrow resonance zones is of interest. Weakly relativistic effects are considered through the mass effect on the cyclotron frequency. For trapped particles in a three dimensional configuration, collisionless loss zones exist in velocity space. Radio-frequency (rf) waves accelerate trapped electrons into the direct loss zone in bumpy stellarators and produce a direct loss flux. An analytic expression for this loss flux is derived; it is proportional to the rf field strength and the value of the zeroth order distribution function at the minimum speed for collisionless loss. The direct loss flux of electrons is another source of a non-ambipolar particle flux in bumpy stellarators. This additional non-ambipolar flux modifies the ambipolarity equation which generally has multiple roots for the radial electric field. An electron root (large positive Er) is easily obtained if the electrons are in the 1/nu regime and the ions are in the nu regime.

Strain engineering on electronic structure and carrier mobility in monolayer GeP3

NASA Astrophysics Data System (ADS)

Zeng, Bowen; Long, Mengqiu; Zhang, Xiaojiao; Dong, Yulan; Li, Mingjun; Yi, Yougen; Duan, Haiming

2018-06-01

Using density functional theory coupled with the Boltzmann transport equation with relaxation time approximation, we have studied the strain effect on the electronic structure and carrier mobility of two-dimensional monolayer GeP3. We find that the energies of valence band maximum and conduction band minimum are nearly linearly shifted with a biaxial strain in the range of  ‑4% to 6%, and the band structure experiences a remarkable transition from semiconductor to metal with the appropriate compression (‑5% strain). Under biaxial strain, the mobility of the electron and hole in monolayer GeP3 reduces and increases by more than one order of magnitude, respectively. It is suggested that it is possible to perform successive transitions from an n-type semiconductor (‑4% strain) to a good performance p-semiconductor (+6% strain) by applying strain in monolayer GeP3, which is potentially useful for flexible electronics and nanosized mechanical sensors.

Electrons In The Low Density Solar Wind

NASA Technical Reports Server (NTRS)

Ogilvie, Keith W.; Desch, Michael; Fitzenreiter, Richard; Vondrak, Richard R. (Technical Monitor)

2000-01-01

The recent occurrence of an interval (May 9th to May 12th, 1999) of abnormally low density solar wind has drawn attention to such events. The SWE instrument on the Wind spacecraft observed nine similar events between launch (November 1994) and August 1999: one in 1997, three in 1998, and five in January-August 1999. No such events were observed in 1996, the year of solar minimum. This already suggests a strong dependence upon solar activity. In this paper we discuss observations of the electron strahl, a strong anisotropy in the solar wind electrons above 60 eV directed along the magnetic field and observed continuously during the periods of low density in 1998 and 1999. When the solar wind density was less than 2/cc, the angular width of the strahl was below 3.5 degrees and the temperature deduced from the slope of the electron strahl phase density (as a function of energy in the energy range 200 to 800 eV) was 100 to 150 eV, equivalent to a typical coronal electron temperature. Three examples of this phenomenon, observed on Feb. 20- 22, April 26-27 and May 9-12, 1999, are discussed to show their similarity to one another. These electron observations are interpreted to show that the strahl occurs as a result of the conservation of the first adiabatic invariant, combined with the lack of coulomb collisions as suggested by Fairfield and Scudder, 1985.

Track-average LET of secondary electrons generated in LiF:Mg,Ti and liquid water by 20-300 kV x-ray, 137Cs and 60Co beams.

PubMed

Cabrera-Santiago, A; Massillon-Jl, G

2016-11-21

Electrons generated in matter by photons could be a fundamental basis for an adequate analysis of radiation effects and damage. We have studied separately the 'primary electrons' generated directly by photons from the 'secondary electrons' (SE) produced by electron-electron interactions. In this work, track-average linear energy transfer, [Formula: see text], of SE in LiF:Mg,Ti and liquid water produced by twelve photon energy beams from 20 kV x-ray to 60 Co gamma rays have been investigated using the EGSnrc Monte Carlo Code. The exposure of LiF:Mg,Ti in different phantom materials has been considered. Depending on the photon energy, SE represent 40%-90% of the total electron fluence (TEF) between 1 keV and 10 keV, being higher when the photon energy increases. Independent of the medium, [Formula: see text] versus mean photon energy displays a local minimum at around 40 keV, followed by a local maximum at ~80 keV-100 keV. The [Formula: see text] of SE generated by the x-ray beams are of order of 11 keV µm -1 to 19 keV µm -1 in LiF:Mg,Ti and 5 keV µm -1 to 9 keV µm -1 in liquid water which represent 3-5 times those produced by 60 Co gamma rays in both media. These values were considerably greater than those of TEF, by factors of 3-8. Furthermore, [Formula: see text] of SE generated in liquid water by 20 kV-200 kV x-rays are similar to those of 76 MeV-120 MeV 3 He ions. Contrary to the TEF, where [Formula: see text] were independent of the phantom material, at low photon energies [Formula: see text] of SE was found to be sensitive to the surrounding medium showing higher values within the phantom than in air. This result, which agrees with published experimental results, implies the importance of the SE ionization density for an understanding of dosimeter response induced by photon beams.

On the timing performance of thin planar silicon sensors

NASA Astrophysics Data System (ADS)

Akchurin, N.; Ciriolo, V.; Currás, E.; Damgov, J.; Fernández, M.; Gallrapp, C.; Gray, L.; Junkes, A.; Mannelli, M.; Martin Kwok, K. H.; Meridiani, P.; Moll, M.; Nourbakhsh, S.; Pigazzini, S.; Scharf, C.; Silva, P.; Steinbrueck, G.; de Fatis, T. Tabarelli; Vila, I.

2017-07-01

We report on the signal timing capabilities of thin silicon sensors when traversed by multiple simultaneous minimum ionizing particles (MIP). Three different planar sensors, with depletion thicknesses 133, 211, and 285 μm, have been exposed to high energy muons and electrons at CERN. We describe signal shape and timing resolution measurements as well as the response of these devices as a function of the multiplicity of MIPs. We compare these measurements to simulations where possible. We achieve better than 20 ps timing resolution for signals larger than a few tens of MIPs.

Experimental investigations of the minimum ignition energy and the minimum ignition temperature of inert and combustible dust cloud mixtures.

PubMed

Addai, Emmanuel Kwasi; Gabel, Dieter; Krause, Ulrich

2016-04-15

The risks associated with dust explosions still exist in industries that either process or handle combustible dust. This explosion risk could be prevented or mitigated by applying the principle of inherent safety (moderation). This is achieved by adding an inert material to a highly combustible material in order to decrease the ignition sensitivity of the combustible dust. The presented paper deals with the experimental investigation of the influence of adding an inert dust on the minimum ignition energy and the minimum ignition temperature of the combustible/inert dust mixtures. The experimental investigation was done in two laboratory scale equipment: the Hartmann apparatus and the Godbert-Greenwald furnace for the minimum ignition energy and the minimum ignition temperature test respectively. This was achieved by mixing various amounts of three inert materials (magnesium oxide, ammonium sulphate and sand) and six combustible dusts (brown coal, lycopodium, toner, niacin, corn starch and high density polyethylene). Generally, increasing the inert materials concentration increases the minimum ignition energy as well as the minimum ignition temperatures until a threshold is reached where no ignition was obtained. The permissible range for the inert mixture to minimize the ignition risk lies between 60 to 80%. Copyright © 2016 Elsevier B.V. All rights reserved.

Evaluation of lens dose from anterior electron beams: comparison of Pinnacle and Gafchromic EBT3 film.

PubMed

Sonier, Marcus; Wronski, Matt; Yeboah, Collins

2015-03-08

Lens dose is a concern during the treatment of facial lesions with anterior electron beams. Lead shielding is routinely employed to reduce lens dose and minimize late complications. The purpose of this work is twofold: 1) to measure dose pro-files under large-area lead shielding at the lens depth for clinical electron energies via film dosimetry; and 2) to assess the accuracy of the Pinnacle treatment planning system in calculating doses under lead shields. First, to simulate the clinical geometry, EBT3 film and 4 cm wide lead shields were incorporated into a Solid Water phantom. With the lead shield inside the phantom, the film was positioned at a depth of 0.7 cm below the lead, while a variable thickness of solid water, simulating bolus, was placed on top. This geometry was reproduced in Pinnacle to calculate dose profiles using the pencil beam electron algorithm. The measured and calculated dose profiles were normalized to the central-axis dose maximum in a homogeneous phantom with no lead shielding. The resulting measured profiles, functions of bolus thickness and incident electron energy, can be used to estimate the lens dose under various clinical scenarios. These profiles showed a minimum lead margin of 0.5 cm beyond the lens boundary is required to shield the lens to ≤ 10% of the dose maximum. Comparisons with Pinnacle showed a consistent overestimation of dose under the lead shield with discrepancies of ~ 25% occur-ring near the shield edge. This discrepancy was found to increase with electron energy and bolus thickness and decrease with distance from the lead edge. Thus, the Pinnacle electron algorithm is not recommended for estimating lens dose in this situation. The film measurements, however, allow for a reasonable estimate of lens dose from electron beams and for clinicians to assess the lead margin required to reduce the lens dose to an acceptable level.

Pseudo paths towards minimum energy states in network dynamics

NASA Astrophysics Data System (ADS)

Hedayatifar, L.; Hassanibesheli, F.; Shirazi, A. H.; Vasheghani Farahani, S.; Jafari, G. R.

2017-10-01

The dynamics of networks forming on Heider balance theory moves towards lower tension states. The condition derived from this theory enforces agents to reevaluate and modify their interactions to achieve equilibrium. These possible changes in network's topology can be considered as various paths that guide systems to minimum energy states. Based on this theory the final destination of a system could reside on a local minimum energy, ;jammed state;, or the global minimum energy, balanced states. The question we would like to address is whether jammed states just appear by chance? Or there exist some pseudo paths that bound a system towards a jammed state. We introduce an indicator to suspect the location of a jammed state based on the Inverse Participation Ratio method (IPR). We provide a margin before a local minimum where the number of possible paths dramatically drastically decreases. This is a condition that proves adequate for ending up on a jammed states.

Minimum airflow reset of single-duct VAV terminal boxes

NASA Astrophysics Data System (ADS)

Cho, Young-Hum

Single duct Variable Air Volume (VAV) systems are currently the most widely used type of HVAC system in the United States. When installing such a system, it is critical to determine the minimum airflow set point of the terminal box, as an optimally selected set point will improve the level of thermal comfort and indoor air quality (IAQ) while at the same time lower overall energy costs. In principle, this minimum rate should be calculated according to the minimum ventilation requirement based on ASHRAE standard 62.1 and maximum heating load of the zone. Several factors must be carefully considered when calculating this minimum rate. Terminal boxes with conventional control sequences may result in occupant discomfort and energy waste. If the minimum rate of airflow is set too high, the AHUs will consume excess fan power, and the terminal boxes may cause significant simultaneous room heating and cooling. At the same time, a rate that is too low will result in poor air circulation and indoor air quality in the air-conditioned space. Currently, many scholars are investigating how to change the algorithm of the advanced VAV terminal box controller without retrofitting. Some of these controllers have been found to effectively improve thermal comfort, indoor air quality, and energy efficiency. However, minimum airflow set points have not yet been identified, nor has controller performance been verified in confirmed studies. In this study, control algorithms were developed that automatically identify and reset terminal box minimum airflow set points, thereby improving indoor air quality and thermal comfort levels, and reducing the overall rate of energy consumption. A theoretical analysis of the optimal minimum airflow and discharge air temperature was performed to identify the potential energy benefits of resetting the terminal box minimum airflow set points. Applicable control algorithms for calculating the ideal values for the minimum airflow reset were developed and applied to actual systems for performance validation. The results of the theoretical analysis, numeric simulations, and experiments show that the optimal control algorithms can automatically identify the minimum rate of heating airflow under actual working conditions. Improved control helps to stabilize room air temperatures. The vertical difference in the room air temperature was lower than the comfort value. Measurements of room CO2 levels indicate that when the minimum airflow set point was reduced it did not adversely affect the indoor air quality. According to the measured energy results, optimal control algorithms give a lower rate of reheating energy consumption than conventional controls.

Minimum time and fuel flight profiles for an F-15 airplane with a Highly Integrated Digital Electronic Control (HIDEC) system

NASA Technical Reports Server (NTRS)

Haering, E. A., Jr.; Burcham, F. W., Jr.

1984-01-01

A simulation study was conducted to optimize minimum time and fuel consumption paths for an F-15 airplane powered by two F100 Engine Model Derivative (EMD) engines. The benefits of using variable stall margin (uptrim) to increase performance were also determined. This study supports the NASA Highly Integrated Digital Electronic Control (HIDEC) program. The basis for this comparison was minimum time and fuel used to reach Mach 2 at 13,716 m (45,000 ft) from the initial conditions of Mach 0.15 at 1524 m (5000 ft). Results were also compared to a pilot's estimated minimum time and fuel trajectory determined from the F-15 flight manual and previous experience. The minimum time trajectory took 15 percent less time than the pilot's estimate for the standard EMD engines, while the minimum fuel trajectory used 1 percent less fuel than the pilot's estimate for the minimum fuel trajectory. The F-15 airplane with EMD engines and uptrim, was 23 percent faster than the pilot's estimate. The minimum fuel used was 5 percent less than the estimate.

Observation of atomic oxygen O(1S) green-line emission in the summer polar upper mesosphere associated with high-energy (≥30 keV) electron precipitation during high-speed solar wind streams

NASA Astrophysics Data System (ADS)

Lee, Young-Sook; Kwak, Young-Sil; Kim, Kyung-Chan; Solheim, Brian; Lee, Regina; Lee, Jaejin

2017-01-01

The auroral green-line emission at 557.7 nm wavelength as arising from the atomic oxygen O(1S → 1D) transition typically peaks at an altitude of 100 km specifically in the nightside oval, induced by auroral electrons within an energy range of 100 eV-30 keV. Intense aurora is known as being suppressed by sunlight in summer daytime but usually occurs in low electrical background conductivity. However, in the present study in summer (July) sunlit condition, enhancements of O(1S) emission rates observed by using the Wind Imaging Interferometer/UARS were frequently observed at low altitudes below 90 km, where ice particles are created initially as subvisible and detected as polar mesosphere summer echoes, emerging to be an optical phenomenon of polar mesospheric clouds. The intense O(1S) emission occurring in summer exceeds those occurring in the daytime in other seasons both in occurrence and in intensity, frequently accompanied by occurrences of supersonic neutral velocity (300-1500 m s-1). In the mesosphere, ion motion is controlled by electric field and the momentum is transferred to neutrals. The intense O(1S) emission is well associated with high-energy electron precipitation as observed during an event of high-speed solar wind streams. Meanwhile, since the minimum occurrences of O(1S) emission and supersonic velocity are maintained even in the low precipitation flux, the mechanism responsible is not only related to high-energy electron precipitation but also presumably to the local conditions, including the composition of meteoric-charged ice particles and charge separation expected in extremely low temperatures (<150 K).

Dirac dispersion generates unusually large Nernst effect in Weyl semimetals

NASA Astrophysics Data System (ADS)

Watzman, Sarah J.; McCormick, Timothy M.; Shekhar, Chandra; Wu, Shu-Chun; Sun, Yan; Prakash, Arati; Felser, Claudia; Trivedi, Nandini; Heremans, Joseph P.

2018-04-01

Weyl semimetals contain linearly dispersing electronic states, offering interesting features in transport yet to be thoroughly explored thermally. Here we show how the Nernst effect, combining entropy with charge transport, gives a unique signature for the presence of Dirac bands and offers a diagnostic to determine if trivial pockets play a role in this transport. The Nernst thermopower of NbP exceeds its conventional thermopower by a 100-fold, and the temperature dependence of the Nernst effect has a pronounced maximum. The charge-neutrality condition dictates that the Fermi level shifts with increasing temperature toward the energy that has the minimum density of states (DOS). In NbP, the agreement of the Nernst and Seebeck data with a model that assumes this minimum DOS resides at the Dirac points is taken as strong experimental evidence that the trivial (non-Dirac) bands play no role in high-temperature transport.

Strong far-infrared intersubband absorption under normal incidence in heavily n-type doped nonalloy GaSb-AlSb superlattices

NASA Technical Reports Server (NTRS)

Samoska, L. A.; Brar, Berinder; Kroemer, H.

1993-01-01

We report on long-wavelength intersubband absorption under normal incidence in heavily doped binary-binary GaSb-AlSb superlattices. Due to a small energy difference between the ellipsoidal L valleys in GaSb and the low-density-of-states Gamma minimum, electrons spill over from the first Gamma subband into the higher-energy L subband in GaSb wells, where they are allowed to make an intersubband transition under normally incident radiation. A peak fractional absorption per quantum well of 6.8 x 10 exp 3 (absorption coefficient alpha of about 8500/cm) is observed at about 15 microns wavelength for a sheet concentration of 1.6 x 10 exp 12 sq cm/well.

Research progress in radiation detectors, pattern recognition programs, and radiation damage determination in DNA

NASA Technical Reports Server (NTRS)

Baily, N. A.

1973-01-01

The radiological implications of statistical variations in energy deposition by ionizing radiation were investigated in the conduct of the following experiments: (1) study of the production of secondary particles generated by the passage of the primary radiation through bone and muscle; (2) the study of the ratio of nonreparable to reparable damage in DNA as a function of different energy deposition patterns generated by X rays versus heavy fast charged particles; (3) the use of electronic radiography systems for direct fluoroscopic tomography and for the synthesis of multiple planes and; (4) the determination of the characteristics of systems response to split fields having different contrast levels, and of minimum detectable contrast levels between the halves under realistic clinical situations.

Heat engine by exorcism of Maxwell Demon using spin angular momentum reservoir

NASA Astrophysics Data System (ADS)

Bedkihal, Salil; Wright, Jackson; Vaccaro, Joan; Gould, Tim

Landauer's erasure principle is a hallmark in thermodynamics and information theory. According to this principle, erasing one bit of information incurs a minimum energy cost. Recently, Vaccaro and Barnett (VB) have explored the role of multiple conserved quantities in memory erasure. They further illustrated that for the energy degenerate spin reservoirs, the cost of erasure can be solely in terms of spin angular momentum and no energy. Motivated by the VB erasure, in this work we propose a novel optical heat engine that operates under a single thermal reservoir and a spin angular momentum reservoir. The novel heat engine exploits ultrafast processes of phonon absorption to convert thermal phonon energy to coherent light. The entropy generated in this process then corresponds to a mixture of spin up and spin down populations of energy degenerate electronic ground states which acts as demon's memory. This information is then erased using a polarised spin reservoir that acts as an entropy sink. The proposed heat engines goes beyond the traditional Carnot engine.

Selective CO2 reduction conjugated with H2O oxidation utilizing semiconductor/metal-complex hybrid photocatalysts

NASA Astrophysics Data System (ADS)

Morikawa, T.; Sato, S.; Arai, T.; Uemura, K.; Yamanaka, K. I.; Suzuki, T. M.; Kajino, T.; Motohiro, T.

2013-12-01

We developed a new hybrid photocatalyst for CO2 reduction, which is composed of a semiconductor and a metal complex. In the hybrid photocatalyst, ΔG between the position of conduction band minimum (ECBM) of the semiconductor and the CO2 reduction potential of the complex is an essential factor for realizing fast electron transfer from the conduction band of semiconductor to metal complex leading to high photocatalytic activity. On the basis of this concept, the hybrid photocatalyst InP/Ru-complex, which functions in aqueous media, was developed. The photoreduction of CO2 to formate using water as an electron donor and a proton source was successfully achieved as a Z-scheme system by functionally conjugating the InP/Ru-complex photocatalyst for CO2 reduction with a TiO2 photocatalyst for water oxidation. The conversion efficiency from solar energy to chemical energy was ca. 0.04%, which approaches that for photosynthesis in a plant. Because this system can be applied to many other inorganic semiconductors and metal-complex catalysts, the efficiency and reaction selectivity can be enhanced by optimization of the electron transfer process including the energy-band configurations, conjugation conformations, and catalyst structures. This electrical-bias-free reaction is a huge leap forward for future practical applications of artificial photosynthesis under solar irradiation to produce organic species.

The multi-species Farley-Buneman instability in the solar chromosphere

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

Madsen, Chad A.; Dimant, Yakov S.; Oppenheim, Meers M.

2014-03-10

Empirical models of the solar chromosphere show intense electron heating immediately above its temperature minimum. Mechanisms such as resistive dissipation and shock waves appear insufficient to account for the persistence and uniformity of this heating as inferred from both UV lines and continuum measurements. This paper further develops the theory of the Farley-Buneman instability (FBI) which could contribute substantially to this heating. It expands upon the single-ion theory presented by Fontenla by developing a multiple-ion-species approach that better models the diverse, metal-dominated ion plasma of the solar chromosphere. This analysis generates a linear dispersion relationship that predicts the critical electronmore » drift velocity needed to trigger the instability. Using careful estimates of collision frequencies and a one-dimensional, semi-empirical model of the chromosphere, this new theory predicts that the instability may be triggered by velocities as low as 4 km s{sup -1}, well below the neutral acoustic speed. In the Earth's ionosphere, the FBI occurs frequently in situations where the instability trigger speed significantly exceeds the neutral acoustic speed. From this, we expect neutral flows rising from the photosphere to have enough energy to easily create electric fields and electron Hall drifts with sufficient amplitude to make the FBI common in the chromosphere. If so, this process will provide a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet Sun.« less

The Effects of Wave Escape on Fast Magnetosonic Wave Turbulence in Solar Flares

NASA Technical Reports Server (NTRS)

Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.; Karpen, Judith T.; DeVore, C. Richard

2012-01-01

One of the leading models for electron acceleration in solar flares is stochastic acceleration by weakly turbulent fast magnetosonic waves ("fast waves"). In this model, large-scale flows triggered by magnetic reconnection excite large-wavelength fast waves, and fast-wave energy then cascades from large wavelengths to small wavelengths. Electron acceleration by large-wavelength fast-waves is weak, and so the model relies on the small-wavelength waves produced by the turbulent cascade. In order for the model to work, the energy cascade time for large-wavelength fast waves must be shorter than the time required for the waves to propagate out of the solar-flare acceleration region. To investigate the effects of wave escape, we solve the wave kinetic equation for fast waves in weak turbulence theory, supplemented with a homogeneous wave-loss term.We find that the amplitude of large-wavelength fast waves must exceed a minimum threshold in order for a significant fraction of the wave energy to cascade to small wavelengths before the waves leave the acceleration region.We evaluate this threshold as a function of the dominant wavelength of the fast waves that are initially excited by reconnection outflows.

25 CFR 547.14 - What are the minimum technical standards for electronic random number generation?

Code of Federal Regulations, 2011 CFR

2011-04-01

... CLASS II GAMES § 547.14 What are the minimum technical standards for electronic random number generation... rules of the game. For example, if a bingo game with 75 objects with numbers or other designations has a... serial correlation (outcomes shall be independent from the previous game); and (x) Test on subsequences...

25 CFR 547.14 - What are the minimum technical standards for electronic random number generation?

Code of Federal Regulations, 2012 CFR

2012-04-01

... CLASS II GAMES § 547.14 What are the minimum technical standards for electronic random number generation... rules of the game. For example, if a bingo game with 75 objects with numbers or other designations has a... serial correlation (outcomes shall be independent from the previous game); and (x) Test on subsequences...

25 CFR 547.14 - What are the minimum technical standards for electronic random number generation?

Code of Federal Regulations, 2010 CFR

2010-04-01

... CLASS II GAMES § 547.14 What are the minimum technical standards for electronic random number generation... rules of the game. For example, if a bingo game with 75 objects with numbers or other designations has a... serial correlation (outcomes shall be independent from the previous game); and (x) Test on subsequences...

Optical Analysis of Transparent Polymeric Material Exposed to Simulated Space Environment

NASA Technical Reports Server (NTRS)

Edwards, David L.; Finckenor, Miria M.

1999-01-01

Transparent polymeric materials are being designed and utilized as solar concentrating lenses for spacecraft power and propulsion systems. These polymeric lenses concentrate solar energy onto energy conversion devices such as solar cells and thermal energy systems. The conversion efficiency is directly related to the transmissivity of the polymeric lens. The Environmental Effects Group of the Marshall Space Flight Center's Materials, Processes, and Manufacturing Department exposed a variety of materials to a simulated space environment and evaluated them for an, change in optical transmission. These materials include Lexan(TM), polyethylene terephthalate (PET). several formulations of Tefzel(TM). and Teflon(TM), and silicone DC 93-500. Samples were exposed to a minimum of 1000 Equivalent Sun Hours (ESH) of near-UV radiation (250 - 400 nm wavelength). Data will be presented on materials exposed to charged particle radiation equivalent to a five-year dose in geosynchronous orbit. These exposures were performed in MSFC's Combined Environmental Effects Test Chamber, a unique facility with the capability to expose materials simultaneously or sequentially to protons, low-energy electrons, high-energy electrons, near UV radiation and vacuum UV radiation.Prolonged exposure to the space environment will decrease the polymer film's transmission and thus reduce the conversion efficiency. A method was developed to normalize the transmission loss and thus rank the materials according to their tolerance to space environmental exposure. Spectral results and the material ranking according to transmission loss are presented.

Electronic Nose Testing Procedure for the Definition of Minimum Performance Requirements for Environmental Odor Monitoring

PubMed Central

Eusebio, Lidia; Capelli, Laura; Sironi, Selena

2016-01-01

Despite initial enthusiasm towards electronic noses and their possible application in different fields, and quite a lot of promising results, several criticalities emerge from most published research studies, and, as a matter of fact, the diffusion of electronic noses in real-life applications is still very limited. In general, a first step towards large-scale-diffusion of an analysis method, is standardization. The aim of this paper is describing the experimental procedure adopted in order to evaluate electronic nose performances, with the final purpose of establishing minimum performance requirements, which is considered to be a first crucial step towards standardization of the specific case of electronic nose application for environmental odor monitoring at receptors. Based on the experimental results of the performance testing of a commercialized electronic nose type with respect to three criteria (i.e., response invariability to variable atmospheric conditions, instrumental detection limit, and odor classification accuracy), it was possible to hypothesize a logic that could be adopted for the definition of minimum performance requirements, according to the idea that these are technologically achievable. PMID:27657086

Electronic Nose Testing Procedure for the Definition of Minimum Performance Requirements for Environmental Odor Monitoring.

PubMed

Eusebio, Lidia; Capelli, Laura; Sironi, Selena

2016-09-21

Despite initial enthusiasm towards electronic noses and their possible application in different fields, and quite a lot of promising results, several criticalities emerge from most published research studies, and, as a matter of fact, the diffusion of electronic noses in real-life applications is still very limited. In general, a first step towards large-scale-diffusion of an analysis method, is standardization. The aim of this paper is describing the experimental procedure adopted in order to evaluate electronic nose performances, with the final purpose of establishing minimum performance requirements, which is considered to be a first crucial step towards standardization of the specific case of electronic nose application for environmental odor monitoring at receptors. Based on the experimental results of the performance testing of a commercialized electronic nose type with respect to three criteria (i.e., response invariability to variable atmospheric conditions, instrumental detection limit, and odor classification accuracy), it was possible to hypothesize a logic that could be adopted for the definition of minimum performance requirements, according to the idea that these are technologically achievable.

Helical coil buckling mechanism for a stiff nanowire on an elastomeric substrate

NASA Astrophysics Data System (ADS)

Chen, Youlong; Liu, Yilun; Yan, Yuan; Zhu, Yong; Chen, Xi

2016-10-01

When a stiff nanowire is deposited on a compliant soft substrate, it may buckle into a helical coil form when the system is compressed. Using theoretical and finite element method (FEM) analyses, the detailed three-dimensional coil buckling mechanism for a silicon nanowire (SiNW) on a polydimethylsiloxane (PDMS) substrate is studied. A continuum mechanics approach based on the minimization of the strain energy in the SiNW and elastomeric substrate is developed. Due to the helical buckling, the bending strain in SiNW is significantly reduced and the maximum local strain is almost uniformly distributed along SiNW. Based on the theoretical model, the energy landscape for different buckling modes of SiNW on PDMS substrate is given, which shows that both the in-plane and out-of-plane buckling modes have the local minimum potential energy, whereas the helical buckling model has the global minimum potential energy. Furthermore, the helical buckling spacing and amplitudes are deduced, taking into account the influences of the elastic properties and dimensions of SiNWs. These features are verified by systematic FEM simulations and parallel experiments. As the effective compressive strain in elastomeric substrate increases, the buckling profile evolves from a vertical ellipse to a lateral ellipse, and then approaches to a circle when the effective compressive strain is larger than 30%. The study may shed useful insights on the design and optimization of high-performance stretchable electronics and 3D complex nano-structures.

Electronic and optical properties of α-InX (X = S, Se and Te) monolayer: Under strain conditions

NASA Astrophysics Data System (ADS)

Jalilian, Jaafar; Safari, Mandana

2017-04-01

Using ab initio study, the structural, electronic and optical properties of α-InX (X = S, Se and Te) are investigated under tensile and compressive strain conditions. The results illustrate that exerting biaxial tensile and compressive strain conditions can lead to a tunable energy gap with a linear trend. The shape of valence band maximum (VBM) and conduction band minimum (CBM) is so sensitive to applying tensile and compressive strain. Besides, a shift in optical spectra toward shorter wavelength (blue shift) occurs under compression. The exerting tensile strain, on the other hand, gives rise to a red shift in optical spectra correspondingly. The results have been presented that InX monolayers can be good candidates for optoelectronic applications as well.

Electronic transport in Thue-Morse gapped graphene superlattice under applied bias

NASA Astrophysics Data System (ADS)

Wang, Mingjing; Zhang, Hongmei; Liu, De

2018-04-01

We investigate theoretically the electronic transport properties of Thue-Morse gapped graphene superlattice under an applied electric field. The results indicate that the combined effect of the band gap and the applied bias breaks the angular symmetry of the transmission coefficient. The zero-averaged wave-number gap can be greatly modulated by the band gap and the applied bias, but its position is robust against change of the band gap. Moreover, the conductance and the Fano factor are strongly dependent not only on the Fermi energy but also on the band gap and the applied bias. In the vicinity of the new Dirac point, the minimum value of the conductance obviously decreases and the Fano factor gradually forms a Poissonian value plateau with increasing of the band gap.

Modulation of the electronic property of phosphorene by wrinkle and vertical electric field

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

Li, Yan; Wei, Zhongming, E-mail: zmwei@semi.ac.cn; Li, Jingbo, E-mail: jbli@semi.ac.cn

2015-09-14

The electronic properties of wrinkled phosphorene and its response to charge injection and external vertical electric field have been studied using first-principles calculations. It is found that small-size wrinkle systems have lower energy than wrinkle-free monolayer, suggesting that free-standing phosphorene spontaneously forms small protrusion on its nanosheet. The ratio of wrinkle height to curvature radius increases with enlarging height, indicating a promotion of field enhancement factor. Furthermore, the injected charges mostly distribute at peak and valley. Direct-to-indirect band-gap transition has been found for zigzag wrinkle with height of 14.81 Å. The band gaps of wrinkled nanosheets decrease almost linearly with increasingmore » field, which is caused by charge separation of valence band maximum and conduction band minimum.« less

A mechanism for deep chromospheric heating during solar flares

NASA Technical Reports Server (NTRS)

Machado, M. E.; Emslie, A. G.; Mauas, P. J.

1986-01-01

The role of the negative hydrogen ion, H(-), in the energy balance of the deep solar chromosphere is reexamined and it is found, in contrast with earlier authors, that H(-) is a source of heating at these levels. The response of this region to an ionizing flux of flare-associated UV radiation (1500 to 1900 A) is then addressed: it is found that the excess ionization of Si to Si(+) increases the local electron number density considerably, since most species are largely neutral at deep chromospheric levels. This in turn increases the electron-hydrogen atom association rate, the H(-) abundance, and the rate of absorption of photospheric radiation by this ion. It is found that the excess absorption by this process may lead to a substantial temperature enhancement at temperature minimum levels during flares.

Impact of the wetting layer thickness on the emission wavelength of direct band gap GeSn/Ge quantum dots

NASA Astrophysics Data System (ADS)

Ilahi, Bouraoui; Al-Saigh, Reem; Salem, Bassem

2017-07-01

The effects of the wetting layer thickness (t WL) on the electronic properties of direct band gap type-I strained dome shaped Ge(1-x)Sn x quantum dot (QD) embedded in Ge matrix is numerically studied. The emission wavelength and the energy difference between S and P electron levels have been evaluated as a function of t WL for different QD size and composition with constant height to diameter ratio. The emission wavelength is found to be red shifted by increasing the wetting layer thickness, with smaller size QD being more sensitive to the variation of t WL. Furthermore, the minimum Sn composition required to fit the directness criteria is found to reduce by increasing the wetting layer thickness.

Experimental and theoretical investigation of three-dimensional nitrogen-doped aluminum clusters AI 8N - and AI 8N

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

Wang, Leiming; Huang, Wei; Wang, Lai S.

The structure and electronic properties of the Al 8N - and Al 8N clusters were investigated by combined photoelectron spectroscopy and ab initio studies. Congested photoelectron spectra were observed and experimental evidence was obtained for the presence of multiple isomers for Al 8N - Global minimum searches revealed several structures for Al 8N - with close energies. The calculated vertical detachment energies of the two lowest-lying isomers, which are of C 2v and C s symmetry, respectively, were shown to agree well with the experimental data. Unlike the three-dimensional structures of Al 6N - and Al 7N -, in whichmore » the dopant N atom has a high coordination number of 6,the dopant N atom in the two low-lying isomers of Al 8N - has a lower coordination number of 4 and 5, respectively. The competition between the Al–Al and Al–N interactions are shown to determine the global minimum structures of the doped aluminum clusters and results in the structural diversity for both Al 8N - and Al8N. © 2009 American Institute of Physics« less

Photodissociation Dynamics of Phenol: Multistate Trajectory Simulations including Tunneling

DOE PAGES

Xu, Xuefei; Zheng, Jingjing; Yang, Ke R.; ...

2014-10-27

We report multistate trajectory simulations, including coherence, decoherence, and multidimensional tunneling, of phenol photodissociation dynamics. The calculations are based on full-dimensional anchor-points reactive potential surfaces and state couplings fit to electronic structure calculations including dynamical correlation with an augmented correlation-consistent polarized valence double-ζ basis set. The calculations successfully reproduce the experimentally observed bimodal character of the total kinetic energy release spectra and confirm the interpretation of the most recent experiments that the photodissociation process is dominated by tunneling. Analysis of the trajectories uncovers an unexpected dissociation pathway for one quantum excitation of the O–H stretching mode of the S 1more » state, namely, tunneling in a coherent mixture of states starting in a smaller R OH (~0.9–1.0 Å) region than has previously been invoked. The simulations also show that most trajectories do not pass close to the S 1–S 2 conical intersection (they have a minimum gap greater than 0.6 eV), they provide statistics on the out-of-plane angles at the locations of the minimum energy adiabatic gap, and they reveal information about which vibrational modes are most highly activated in the products.« less

Wave function delocalization and large-amplitude vibrations of helium on corrugated aromatic microsurfaces: tetracene.He and pentacene.He van der Waals complexes.

PubMed

Xu, Minzhong; Bacić, Zlatko

2007-08-09

We report accurate quantum three-dimensional calculations of highly excited intermolecular vibrational states of the van der Waals (vdW) complexes tetracene.He and pentacene.He in the S1 excited electronic state. The aromatic molecules were taken to be rigid and the intermolecular potential energy surfaces (IPESs) were modeled as a sum of atom-atom Lennard-Jones pair potentials. The IPESs are corrugated in the direction of the long (x) axis of the aromatic molecules, due to the presence of the symmetrically equivalent global double minimum for tetracene.He, and a triple minimum (central global minimum and two equivalent local minima) for pentacene.He, on each side of the aromatic plane. Both IPESs have two additional minor equivalent local minima further away from the center of the molecule. The vdW vibrational states analyzed in this work cover about 80% of the well depths of the IPESs. The mode coupling is generally weak for those states whose out-of-plane (z) mode is unexcited. However, the z-mode fundamental is strongly coupled to the short-axis (y) in-plane mode, so that the pure z-mode excitation could not be identified. The He atom exhibits large in-plane spatial delocalizaton already in the ground vdW vibrational state, which increases rapidly upon the excitation of the in-plane x and y modes, with little hindrance by the corrugation of the aromatic microsurfaces. For the vdW vibrational energies considered, the He atom spatial delocalization reaches Deltax and Deltay values of approximately 5 and 4 A, respectively, and is limited only by the finite size of the aromatic substrates. Side-crossing delocalization of the wave functions on both sides of the molecular plane is found at excitation energies >30 cm(-1), giving rise to the energy splittings of the pairs of states symmetric/antisymmetric with respect to the aromatic plane; the splittings show strong vdW vibrational mode specificity.

Detailed study of the water trimer potential energy surface

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

Fowler, J.E.; Schaefer, H.F. III

The potential energy surface of the water trimer has been studied through the use of ab initio quantum mechanical methods. Five stationary points were located, including one minimum and two transition states. All geometries were optimized at levels up to the double-[Zeta] plus polarization plus diffuse (DZP + diff) single and double excitation coupled cluster (CCSD) level of theory. CCSD single energy points were obtained for the minimum, two transition states, and the water monomer using the triple-[Zeta] plus double polarization plus diffuse (TZ2P + diff) basis at the geometries predicted by the DZP + diff CCSD method. Reported aremore » the following: geometrical parameters, total and relative energies, harmonic vibrational frequencies and infrared intensities for the minimum, and zero point vibrational energies for the minimum, two transition states, and three separated water molecules. 27 refs., 5 figs., 10 tabs.« less

Elucidating the real-time Ag nanoparticle growth on α-Ag2WO4 during electron beam irradiation: experimental evidence and theoretical insights.

PubMed

Pereira, Wyllamanney da Silva; Andrés, Juan; Gracia, Lourdes; San-Miguel, Miguel A; da Silva, Edison Z; Longo, Elson; Longo, Valeria M

2015-02-21

Why and how Ag is formed when electron beam irradiation takes place on α-Ag2WO4 in a vacuum transmission electron microscopy chamber? To find an answer, the atomic-scale mechanisms underlying the formation and growth of Ag on α-Ag2WO4 have been investigated by detailed in situ transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) studies, density functional theory based calculations and ab initio molecular dynamics simulations. The growth process at different times, chemical composition, size distribution and element distribution were analyzed in depth at the nanoscale level using FE-SEM, operated at different voltages (5, 10, 15, and 20 kV), and TEM with energy dispersive spectroscopy (EDS) characterization. The size of Ag nanoparticles covers a wide range of values. Most of the Ag particles are in the 20-40 nm range. The nucleation and formation of Ag on α-Ag2WO4 is a result of structural and electronic changes in the AgOx (x = 2,4, 6, and 7) clusters used as constituent building blocks of this material, consistent with metallic Ag formation. First principle calculations point out that Ag-3 and Ag-4-fold coordinated centers, located in the sub-surface of the (100) surface, are the most energetically favorable to undergo the diffusion process to form metallic Ag. Ab initio molecular dynamics simulations and the nudged elastic band (NEB) method were used to investigate the minimum energy pathways of these Ag atoms from positions in the first slab layer to outward sites on the (100) surface of α-Ag2WO4. The results point out that the injection of electrons decreases the activation barrier for this diffusion step and this unusual behavior results from the presence of a lower energy barrier process.

Diffusion Region's Structure at the Subsolar Magnetopause with MMS Data

NASA Astrophysics Data System (ADS)

Cozzani, G.; Retino, A.; Califano, F.; Alexandrova, A.; Catapano, F.; Fu, H.; Le Contel, O.; Khotyaintsev, Y. V.; Vaivads, A.; Ahmadi, N.; Lindqvist, P. A.; Breuillard, H.; Mirioni, L.; Ergun, R.; Torbert, R. B.; Giles, B. L.; Russell, C. T.; Nakamura, R.; Moore, T. E.; Fuselier, S. A.; Mauk, B.; Burch, J.

2017-12-01

Magnetic reconnection occurs in the magnetosphere in thin current sheets, where a change in the magneticfield topology leads to rapid conversion of magnetic energy into ion and electron energy. To allow for magneticfield reconfiguration, both ions and electrons have to become demagnetized in the ion and electron diffusionregions, respectively. MMS spacecraft observations at inter-spacecraft separation ˜ 10 km (correspondingto ˜ 5 d_e at the magnetopause) allow, for the first time, to make multi-point studies of the structure of theelectron diffusion region (EDR). We present MMS observations on January,27th 2017 of one magnetopausecrossing close to the subsolar point showing several signatures consistent with an EDR encounter nearbya magnetic field minimum. The proximity to the reconnection site is further substantiated by the FirstOrder Taylor Expansion (FOTE) method applied to the magnetic field data. Observations suggest that allspacecraft passed through the EDR. Despite of the small inter-spacecraft separation (7 km), the observationsshow important differences among spacecraft. We focus on the comparison between MMS3 and MMS4 sincethey show the most striking differences. MMS3 measures a stronger parallel electron heating and highercurrent densities than MMS4. Both satellites observe crescent-shaped electron distribution functions on themagnetospheric side but MMS4 observes them over a longer time interval. These observations suggest thatMMS3 is passing closer to the reconnection site than MMS4. The differences between the observations by thetwo spacecraft indicate that the EDR is rather structured over scales of a few electron inertial lengths. Wealso evaluate the Generalized Ohm's law and find that the electric field is mainly balanced by the divergenceof the electron pressure tensor while the electron inertia term is negligible.

Tantalum-based semiconductors for solar water splitting.

PubMed

Zhang, Peng; Zhang, Jijie; Gong, Jinlong

2014-07-07

Solar energy utilization is one of the most promising solutions for the energy crises. Among all the possible means to make use of solar energy, solar water splitting is remarkable since it can accomplish the conversion of solar energy into chemical energy. The produced hydrogen is clean and sustainable which could be used in various areas. For the past decades, numerous efforts have been put into this research area with many important achievements. Improving the overall efficiency and stability of semiconductor photocatalysts are the research focuses for the solar water splitting. Tantalum-based semiconductors, including tantalum oxide, tantalate and tantalum (oxy)nitride, are among the most important photocatalysts. Tantalum oxide has the band gap energy that is suitable for the overall solar water splitting. The more negative conduction band minimum of tantalum oxide provides photogenerated electrons with higher potential for the hydrogen generation reaction. Tantalates, with tunable compositions, show high activities owning to their layered perovskite structure. (Oxy)nitrides, especially TaON and Ta3N5, have small band gaps to respond to visible-light, whereas they can still realize overall solar water splitting with the proper positions of conduction band minimum and valence band maximum. This review describes recent progress regarding the improvement of photocatalytic activities of tantalum-based semiconductors. Basic concepts and principles of solar water splitting will be discussed in the introduction section, followed by the three main categories regarding to the different types of tantalum-based semiconductors. In each category, synthetic methodologies, influencing factors on the photocatalytic activities, strategies to enhance the efficiencies of photocatalysts and morphology control of tantalum-based materials will be discussed in detail. Future directions to further explore the research area of tantalum-based semiconductors for solar water splitting are also discussed.

[Principles of energy sources of totally implantable hearing aids for inner ear hearing loss].

PubMed

Baumann, J W; Leysieffer, H

1998-02-01

A fully implantable hearing aid consists of a sound receptor (microphone), an electronic amplifier including active audio-signal processing, an electromechanical transducer (actuator) for stimulating the ear by vibration, and an energy source. The energy source may be either a primary cell or a rechargeable (secondary) cell. As the energy requirements of an implantable hearing aid are dependent on the operating principle of the actuator, the operating principles of electromagnetic and piezoelectric transducers were examined with respect to their relative power consumption. The analysis showed that the energy requirements of an implantable hearing aid are significantly increased when an electromagnetic transducer is used. The power consumption of a piezoelectric transducer was found to be less than that of the electronic components alone. The energy needed to run a fully implantable hearing aid under these conditions would be 38 mWH per day. Primary cells cannot provide the energy needed for a minimum operation time of 5 years (70 WH), and therefore rechargeable cells must be used. A theoretical appraisal was carried out on nickel-cadmium, nickel-metal hydride, and lithium-ion cells to determine their suitability as well as to assess the risks associated with their use in an implant. Safety measures were drawn up from the results. Ni-MH cells were found to be the most suitable for use as an energy source for implantable hearing-aids because they are more robust than Li ion cells and their storage capacity is double that of Ni-Cd cells of similar size.

Potential Energy Curves and Transport Properties for the Interaction of He with Other Ground-state Atoms

NASA Technical Reports Server (NTRS)

Partridge, Harry; Stallcop, James R.; Levin, Eugene; Arnold, Jim (Technical Monitor)

2001-01-01

The interactions of a He atom with a heavier atom are examined for 26 different elements, which are consecutive members selected from three rows (Li - Ne, Na - Ar, and K,Ca, Ga - Kr) and column 12 (Zn,Cd) of the periodic table. Interaction energies are determined wing high-quality ab initio calculations for the states of the molecule that would be formed from each pair of atoms in their ground states. Potential energies are tabulated for a broad range of Interatomic separation distances. The results show, for example, that the energy of an alkali interaction at small separations is nearly the same as that of a rare-gas interaction with the same electron configuration for the dosed shells. Furthermore, the repulsive-range parameter for this region is very short compared to its length for the repulsion dominated by the alkali-valence electron at large separations (beyond about 3-4 a(sub 0)). The potential energies in the region of the van der Waals minimum agree well with the most accurate results available. The ab initio energies are applied to calculate scattering cross sections and obtain the collision integrals that are needed to determine transport properties to second order. The theoretical values of Li-He total scattering cross sections and the rare-gas atom-He transport properties agree well (to within about 1%) with the corresponding measured data. Effective potential energies are constructed from the ab initio energies; the results have been shown to reproduce known transport data and can be readily applied to predict unknown transport properties for like-atom interactions.

SU-E-T-98: An Analysis of TG-51 Electron Beam Calibration Correction Factor Uncertainty

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

Lee, P; Alvarez, P; Taylor, P

Purpose: To analyze the uncertainty of the TG-51 electron beam calibration correction factors for farmer type ion chambers currently used by institutions visited by IROC Houston. Methods: TG-51 calibration data were collected from 181 institutions visited by IROC Houston physicists for 1174 and 197 distinct electron beams from modern Varian and Elekta accelerators, respectively. Data collected and analyzed included ion chamber make and model, nominal energy, N{sub D,w}, I{sub 50}, R{sub 50}, k’R{sub 50}, d{sub ref}, P{sub gr} and pdd(d{sub ref}). k’R{sub 50} data for parallel plate chambers were excluded from the analysis. Results: Unlike photon beams, electron nominal energymore » is a poor indicator of the actual energy as evidenced by the range of R{sub 50} values for each electron beam energy (6–22MeV). The large range in R{sub 50} values resulted k’R{sub 50} values with a small standard deviation but large range between maximum value used and minimum value (0.001–0.029) used for a specific Varian nominal energy. Varian data showed more variability in k’R{sub 50} values than the Elekta data (0.001–0.014). Using the observed range of R{sub 50} values, the maximum spread in k’R{sub 50} values was determined by IROC Houston and compared to the spread of k’R{sub 50} values used in the community. For Elekta linacs the spreads were equivalent, but for Varian energies of 6 to 16MeV, the community spread was 2 to 6 times larger. Community P{sub gr} values had a much larger range of values for 6 and 9 MeV values than predicted. The range in Varian pdd(d{sub ref} ) used by the community for low energies was large, (1.4–4.9 percent), when it should have been very close to unity. Exradin, PTW Roos and PTW farmer chambers N{sub D,w} values showed the largest spread, ≥11 percent. Conclusion: While the vast majority of electron beam calibration correction factors used are accurate, there is a surprising spread in some of the values used.« less

The streaming of 1.3 - 2.3 MeV cosmic-ray protons during periods between prompt solar particle events. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Marshall, F. E.

1977-01-01

The anisotropy of 1.3 to 2.3 MeV protons in interplanetary space was measured using the Caltech electron/isotope spectrometer aboard IMP-7 for 317 6 hour periods from 72/273 to 74/2. Periods dominated by prompt solar particle events are not included. The convective and diffusive anisotropies were determined from the observed anisotropy using concurrent solar wind speed measurements and observed energy spectra. The diffusive flow of particles was found to be typically toward the sun, indicating a positive radial gradient in the particle density. This anisotropy was inconsistent with previously proposed sources of low energy proton increases seen at 1 AU which involve continual solar acceleration. The typical properties of this new component of low-energy cosmic rays were determined for this period which is near solar minimum.

Efficient Steplike Carrier Multiplication in Percolative Networks of Epitaxially Connected PbSe Nanocrystals.

PubMed

Kulkarni, Aditya; Evers, Wiel H; Tomić, Stanko; Beard, Matthew C; Vanmaekelbergh, Daniel; Siebbeles, Laurens D A

2018-01-23

Carrier multiplication (CM) is a process in which a single photon excites two or more electrons. CM is of interest to enhance the efficiency of a solar cell. Until now, CM in thin films and solar cells of semiconductor nanocrystals (NCs) has been found at photon energies well above the minimum required energy of twice the band gap. The high threshold of CM strongly limits the benefits for solar cell applications. We show that CM is more efficient in a percolative network of directly connected PbSe NCs. The CM threshold is at twice the band gap and increases in a steplike fashion with photon energy. A lower CM efficiency is found for a solid of weaker coupled NCs. This demonstrates that the coupling between NCs strongly affects the CM efficiency. According to device simulations, the measured CM efficiency would significantly enhance the power conversion efficiency of a solar cell.

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas with linear density and temperature ramps

NASA Astrophysics Data System (ADS)

Hashemzadeh, M.

2018-01-01

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas are investigated in the presence of various laser intensities and linear density and temperature ramps. Considering the ponderomotive force and using the momentum transfer and energy equations, the nonlinear electron density is derived. Taking into account the paraxial approximation and nonlinear electron density, a nonlinear differential equation, governing the focusing and defocusing of the laser beam, is obtained. Results show that in the absence of ramps the laser beam is focused between a minimum and a maximum value of laser intensity. For a certain value of laser intensity and initial electron density, the self-focusing process occurs in a temperature range which reaches its maximum at turning point temperature. However, the laser beam is converged in a narrow range for various amounts of initial electron density. It is indicated that the σ2 parameter and its sign can affect the self-focusing process for different values of laser intensity, initial temperature, and initial density. Finally, it is found that although the electron density ramp-down diverges the laser beam, electron density ramp-up improves the self-focusing process.

High-Energy Electron Shell in ECR Ion Source:

NASA Astrophysics Data System (ADS)

Niimura, M. G.; Goto, A.; Yano, Y.

1997-05-01

As an injector of cyclotrons and RFQ linacs, ECR ion source (ECRIS) is expected to deliver highly charged ions (HCI) at high beam-current (HBC). Injections of light gases and supplementary electrons have been employed for enhancement of HCI and HBC, respectively. Further amelioration of the performance may be feasible by investigating the hot-electron ring inside an ECRIS. Its existence has been granted because of the MeV of Te observable via X-ray diagnostics. However, its location, acceleration mechanism, and effects on the performance are not well known.We found them by deriving the radially negative potential distribution for an ECRIS from measured endloss-current data. It was evidenced from a hole-burning on the parabolic potential profile (by uniformly distributed warm-electron space charges of 9.5x10^5cm-3) and from a local minimum of the electrostatically-trapped ion distribution. A high-energy electron shell (HEES) was located right on the ECR-radius of 6 cm with shell-halfwidth of 1 cm. Such a thin shell around core plasma can only be generated by the Sadeev-Shapiro or v_phxBz acceleration mechanism that can raise Te up to a relativistic value. Here, v_ph is the phase velocity of ES Bernstein waves propagating backwards against incident microwave and Bz the axial mirror magnetic field. The HEES carries diamagnetic current which reduces the core magnetic pressure, thereby stabilizing the ECR surface against driftwave instabilities similarly to gas-mixing.

Theoretical study of the structural and electronic properties of novel stanene-based buckled nanotubes and their adsorption behaviors

NASA Astrophysics Data System (ADS)

Abbasi, Amirali; Sardroodi, Jaber Jahanbin; Ebrahimzadeh, Alireza Rastkar; Yaghoobi, Mina

2018-03-01

Density functional theory calculations were performed to investigate the geometrical, electronic and adsorption properties of stanene based nanotubes in order to fully exploit the gas sensing capability of these nanotubes. The strain energy, structural parameters and electronic properties of stanene-based nanotubes with armchair and zigzag chirality with various diameters were examined in detail. The results show that, these nanotubes have a buckled structure, in which the tin atoms were arranged in chair-like honeycomb configuration. Calculated strain energy for considered nanotubes are relatively small compared to some other nanotubes pointed to flexibility of stanene mono layer. It was found that the strain energies for (4, 0), (5, 0) and (6, 0) nanotubes have negative values, indicating their stability with respect to stanene nanosheet. The band structure calculations reveal that the armchair nanotubes are semiconductors with two maximums with nearly same energies in valence band. However, the zigzag ones show both conductor and semiconductor behaviors by direct band gap in ᴦ point. Also the spatial distribution of molecular orbitals in valence band maximums and conduction band minimums were presented and discussed. Moreover, the adsorption behaviors of (6, 6) and (8, 8) nanotubes as chemical O3 detection device were investigated in detail. We found that O3 molecule dissociates into O2 over the considered nanotubes, being an effective strategy to help in the reduction of the concentration of these harmful pollutants in the environment. The results also suggest that O3 dissociation over the (6, 6) nanotube is more favorable in energy than that on the (8, 8) nanotube. The results present a great potential of stanene based nanotube for application as a highly sensitive ozone gas sensor.

Charge-transfer excitons at organic semiconductor surfaces and interfaces.

PubMed

Zhu, X-Y; Yang, Q; Muntwiler, M

2009-11-17

When a material of low dielectric constant is excited electronically from the absorption of a photon, the Coulomb attraction between the excited electron and the hole gives rise to an atomic H-like quasi-particle called an exciton. The bound electron-hole pair also forms across a material interface, such as the donor/acceptor interface in an organic heterojunction solar cell; the result is a charge-transfer (CT) exciton. On the basis of typical dielectric constants of organic semiconductors and the sizes of conjugated molecules, one can estimate that the binding energy of a CT exciton across a donor/acceptor interface is 1 order of magnitude greater than k(B)T at room temperature (k(B) is the Boltzmann constant and T is the temperature). How can the electron-hole pair escape this Coulomb trap in a successful photovoltaic device? To answer this question, we use a crystalline pentacene thin film as a model system and the ubiquitous image band on the surface as the electron acceptor. We observe, in time-resolved two-photon photoemission, a series of CT excitons with binding energies < or = 0.5 eV below the image band minimum. These CT excitons are essential solutions to the atomic H-like Schrodinger equation with cylindrical symmetry. They are characterized by principal and angular momentum quantum numbers. The binding energy of the lowest lying CT exciton with 1s character is more than 1 order of magnitude higher than k(B)T at room temperature. The CT(1s) exciton is essentially the so-called exciplex and has a very low probability of dissociation. We conclude that hot CT exciton states must be involved in charge separation in organic heterojunction solar cells because (1) in comparison to CT(1s), hot CT excitons are more weakly bound by the Coulomb potential and more easily dissociated, (2) density-of-states of these hot excitons increase with energy in the Coulomb potential, and (3) electronic coupling from a donor exciton to a hot CT exciton across the D/A interface can be higher than that to CT(1s) as expected from energy resonance arguments. We suggest a design principle in organic heterojunction solar cells: there must be strong electronic coupling between molecular excitons in the donor and hot CT excitons across the D/A interface.

Materials science in pre-plated leadframes for electronic packages

NASA Astrophysics Data System (ADS)

Liu, Lilin

Au/Pd/Ni pre-plated leadframes (PPF) are high performance frames for accommodating high-end electronic packages. Cost and reliability are major concerns in their wide application. The present work, from a materials science point view, deepens the understanding of PPFs, optimizes the conventional PPFs, develops a novel PPF architecture and models the residual stress relaxation in heteroepitaxial thin films. The wire pull test, the solderability test, and High-Resolution Transmission Electron Microscopy (HRTEM) were employed to characterize the PPFs in order to understand the relationship between performance and microstructure. We optimized the electroplating profiles and determined the minimum thickness of the Pd layer with the PPF performance satisfying the industry standards. Further increasing the Pd layer thickness beyond the critical thickness will not enhance the performance more, but increase the product cost. With the optimized electroplating profile, the electroplated Au layer is epitaxially deposited on the Pd layer, and so does the Pd layer on the Ni layer. Misfit dislocations and nanotwins are present at the interface between the Pd and Ni layers, which are generated to release the about 10.4% misfit strain between the Pd and Ni lattices. This work demonstrates that the electro-deposition technique can electroplate epitaxy-like Pd films on the highly (200) textured Ni films, which are grown on the Cu substrates. A novel technique for impeding Cu out-diffusion in Cu alloy based pre-plated leadframes was developed by electroplating a 3-4 nm thick Sn layer on a Cu alloy base prior to electroplating a Ni layer. A 10-14 nm thick epitaxy-like and dense (Cu,Ni)3Sn intermetallic compound (IMC) layer is automatically formed en route of diffuse reaction, which leads to a drastic reduction in Cu out-diffusion and hence improves significantly the protection of the leadframes against oxidation and corrosion attack. The oxidation behaviours were quantified by Electron Diffraction X-ray (EX) incorporated in Scanning Electron Microscopy (SEM) in the present work, which is a good complementary to the traditional weight gain test by a balance. A diffusion/oxidation model was developed to estimate the effective diffusion coefficient of Cu in the formed IMC nanolayers. The estimated Cu diffusion coefficient in the IMC interlayer is about 1.6x10 -22m2/s at 250°C, which is around 7~11 orders lower than the interdiffusion coefficients for eta- Cu6Sn5 and epsilon- Cu3Sn phases at corresponding temperatures. Based on the dislocation theory of twinning, analytical solutions by using the hybrid superposition and Fourier transformation approach were derived for the calculation of various energies involved in the misfit twinning process. For a given epilayer thickness and lattice mismatch strain, the twin formation energy should reach its minimum to determine the twin width and a zero minimum formation energy determines the critical thickness for misfit twinning. The effect of elastic mismatch between the epilayer and the substrate on the critical thickness was studied comprehensively, revealing that an elastically soft epilayer has a large critical thickness. Moreover, a misfit-twin-and-perfect-dislocation predominance chart is constructed to predict the predominant regions of misfit twinning and perfect dislocation in the mismatch strain and the specific twin boundary energy domain. Multiple misfit twins in epilayer/substrate systems were studied by summing up the stress and displacement fields of individual twins. In principle, the energy minimization approach can be applied to multiple misfit twins, although only periodic arrays of parallel and alternating twins were investigated here in detail. The equilibrium twin width and equilibrium twin spacing of a periodic array of twins represent the misfit twin morphology. The theoretical results indicate that the difference in elastic constants between an epilayer and its substrate has great effects on the morphology of equilibrium twins. The theoretical predictions agree with experimental observations.

Partial-wave analysis for positronium-xenon collisions in the ultralow-energy region

NASA Astrophysics Data System (ADS)

Shibuya, Kengo; Saito, Haruo

2018-05-01

We propose a method to convert measured positronium annihilation rates in gaseous xenon into total and differential cross sections of positronium-xenon collisions in an ultralow-energy region of less than 80 meV where their experimental determinations as functions of the positronium kinetic energy are extremely difficult. This method makes it possible to determine not only the s -wave collisional parameters but also the p -wave and d -wave parameters. We have found a small positive value of the scattering length, A0=2.06 ±0.10 a0 , which indicates that the positronium-xenon interaction in this energy region is repulsive and suggests that it is dominated by the scattering amplitude of the positron rather than that of the electron. An extrapolation of the analytical result into the experimentally inaccessible energy regions from 80 meV to 1.0 eV indicates that there should not be a Ramsauer-Townsend minimum but rather a peak in the total cross section at an energy of approximately 0.4 eV.

Regulating energy transfer of excited carriers and the case for excitation-induced hydrogen dissociation on hydrogenated graphene

PubMed Central

Bang, Junhyeok; Meng, Sheng; Sun, Yi-Yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, S. B.

2013-01-01

Understanding and controlling of excited carrier dynamics is of fundamental and practical importance, particularly in photochemistry and solar energy applications. However, theory of energy relaxation of excited carriers is still in its early stage. Here, using ab initio molecular dynamics (MD) coupled with time-dependent density functional theory, we show a coverage-dependent energy transfer of photoexcited carriers in hydrogenated graphene, giving rise to distinctively different ion dynamics. Graphene with sparsely populated H is difficult to dissociate due to inefficient transfer of the excitation energy into kinetic energy of the H. In contrast, H can easily desorb from fully hydrogenated graphane. The key is to bring down the H antibonding state to the conduction band minimum as the band gap increases. These results can be contrasted to those of standard ground-state MD that predict H in the sparse case should be much less stable than that in fully hydrogenated graphane. Our findings thus signify the importance of carrying out explicit electronic dynamics in excited-state simulations. PMID:23277576

Electronic structure and photochemistry of squaraine dyes: basic theoretical analysis and direct detection of the photoisomer of a symmetrical squarylium cyanine.

PubMed

Momicchioli, Fabio; Tatikolov, Aleksandr S; Vanossi, Davide; Ponterini, Glauco

2004-04-01

The photoisomerization kinetics of a squaraine dye has been the object both of experimental investigation and of interpretation in the framework of a qualitative theoretical model formulated by the aid of simple HMO calculations and orbital symmetry considerations. Such a model has first confirmed that the electronic structure and the spectroscopic properties of symmetrical squaraines are related to those of the parent cyanines, with ketocyanines as intermediate systems. Extension of the approach to structures twisted by 90[degree] about a polymethine bond has then provided insight into the electronic aspects and the mechanism of the photoisomerization of the squaraine under study. The reaction, previously indirectly investigated by fluorescence analysis, has been directly monitored by laser flash photolysis. These experiments indicate that, while photoisomerization is likely the main radiationless decay route from the spectroscopic minimum of the lowest excited singlet state (S(1)), the cis photoisomer is produced with only a 1% yield, likely because of an unfavourable cis/trans branching ratio from the perpendicular minimum of the S(1)-state potential energy surface. In contrast with what found for symmetrical cyanines, an increase in the solvent polarity was found to accelerate both the direct, excited-state reaction and, to a much larger extent, the ground-state back-isomerization. Such observations are consistent with predictions of the theoretical model and provide a clue for the identification of the isomerization coordinate.

Ascent trajectory optimization for stratospheric airship with thermal effects

NASA Astrophysics Data System (ADS)

Guo, Xiao; Zhu, Ming

2013-09-01

Ascent trajectory optimization with thermal effects is addressed for a stratospheric airship. Basic thermal characteristics of the stratospheric airship are introduced. Besides, the airship’s equations of motion are constructed by including the factors about aerodynamic force, added mass and wind profiles which are developed based on horizontal-wind model. For both minimum-time and minimum-energy flights during ascent, the trajectory optimization problem is described with the path and terminal constraints in different scenarios and then, is converted into a parameter optimization problem by a direct collocation method. Sparse Nonlinear OPTimizer(SNOPT) is employed as a nonlinear programming solver and two scenarios are adopted. The solutions obtained illustrate that the trajectories are greatly affected by the thermal behaviors which prolong the daytime minimum-time flights of about 20.8% compared with that of nighttime in scenario 1 and of about 10.5% in scenario 2. And there is the same trend for minimum-energy flights. For the energy consumption of minimum-time flights, 6% decrease is abstained in scenario 1 and 5% decrease in scenario 2. However, a few energy consumption reduction is achieved for minimum-energy flights. Solar radiation is the principal component and the natural wind also affects the thermal behaviors of stratospheric airship during ascent. The relationship between take-off time and performance of airship during ascent is discussed. it is found that the take-off time at dusk is best choice for stratospheric airship. And in addition, for saving energy, airship prefers to fly downwind.

Nonadiabatic effects in C-Br bond scission in the photodissociation of bromoacetyl chloride

NASA Astrophysics Data System (ADS)

Valero, Rosendo; Truhlar, Donald G.

2006-11-01

Bromoacetyl chloride photodissociation has been interpreted as a paradigmatic example of a process in which nonadiabatic effects play a major role. In molecular beam experiments by Butler and co-workers [J. Chem. Phys. 95, 3848 (1991); J. Chem. Phys. 97, 355 (1992)], BrCH2C(O )Cl was prepared in its ground electronic state (S0) and excited with a laser at 248nm to its first excited singlet state (S1). The two main ensuing photoreactions are the ruptures of the C-Cl bond and of the C-Br bond. A nonadiabatic model was proposed in which the C-Br scission is strongly suppressed due to nonadiabatic recrossing at the barrier formed by the avoided crossing between the S1 and S2 states. Recent reduced-dimensional dynamical studies lend support to this model. However, another interpretation that has been given for the experimental results is that the reduced probability of C-Br scission is a consequence of incomplete intramolecular energy redistribution. To provide further insight into this problem, we have studied the energetically lowest six singlet electronic states of bromoacetyl chloride by using an ab initio multiconfigurational perturbative electronic structure method. Stationary points (minima and saddle points) and minimum energy paths have been characterized on the S0 and S1 potential energy surfaces. The fourfold way diabatization method has been applied to transform five adiabatic excited electronic states to a diabatic representation. The diabatic potential energy matrix of the first five excited singlet states has been constructed along several cuts of the potential energy hypersurfaces. The thermochemistry of the photodissociation reactions and a comparison with experimental translational energy distributions strongly suggest that nonadiabatic effects dominate the C-Br scission, but that the reaction proceeds along the energetically allowed diabatic pathway to excited-state products instead of being nonadiabatically suppressed. This conclusion is also supported by the low values of the diabatic couplings on the C-Br scission reaction path. The methodology established in the present study will be used for the construction of global potential energy surfaces suitable for multidimensional dynamics simulations to test these preliminary interpretations.

Improved Potential Energy Surface of Ozone Constructed Using the Fitting by Permutationally Invariant Polynomial Function

DOE PAGES

Ayouz, Mehdi; Babikov, Dmitri

2012-01-01

New global potential energy surface for the ground electronic state of ozone is constructed at the complete basis set level of the multireference configuration interaction theory. A method of fitting the data points by analytical permutationally invariant polynomial function is adopted. A small set of 500 points is preoptimized using the old surface of ozone. In this procedure the positions of points in the configuration space are chosen such that the RMS deviation of the fit is minimized. New ab initio calculations are carried out at these points and are used to build new surface. Additional points are added tomore » the vicinity of the minimum energy path in order to improve accuracy of the fit, particularly in the region where the surface of ozone exhibits a shallow van der Waals well. New surface can be used to study formation of ozone at thermal energies and its spectroscopy near the dissociation threshold.« less

Structure and screening in molecular and metallic hydrogen at high pressure

NASA Technical Reports Server (NTRS)

Wood, D. M.; Ashcroft, N. W.

1981-01-01

A variational wavefunction is used to express the (spin restricted) Hartree-Fock energy as reciprocal lattice sums for static lattice FCC monatomic hydrogen and diatomic Pa3 molecular hydrogen. In the monatomic phase the hydrogenic orbital range closely parallels the inverse Thomas-Fermi wavevector; the corresponding energy E has a minimum of -0.929 Ryd/electron at r sub s = 1.67. For the diatomic phase E(r sub s) is similar, but the constituent energies, screening, and bond length reflect a qualitative change in the nature of the solid at r sub s = 2.8. This change is interpreted in terms of a transition from protons as structural units (at high density) to weakly interacting models (at low density). Insensitivity of the total energy to a rapid fall in the bond length suggests association with the rotational transition where the rapid molecular orientations characteristic of high pressures disappear and the molecules rotate freely at low pressure.

Effect of off-normal events on the reactor first wall

NASA Astrophysics Data System (ADS)

Igitkhanov, Yu; Bazylev, B.

2011-12-01

In this paper, we analyse the energy deposition and erosion of the W/EUROFER blanket module for the first wall (FW) of DEMO due to the runaway electrons (RE) and vertical displacements events (VDEs). The DEMO data for transients were extrapolated from ITER data by using the scaling arguments. The simulations were performed at an RE deposition energy in the range 30-100 MJ m-2 over 0.05-0.3 s. In the case of a 'hot' VDE, all stored plasma energy is deposited on the FW area for ~1 s. For a VDE following the thermal quench phase the remaining magnetic energy is deposited on the FW for ~0.3 s. It is shown that the minimum W thickness needed for preventing failure of the W/EUROFER bond (assumed to be the EUROFER creep point) is large enough, causing armour melting. Both RE and VDE in DEMO will pose a major life-time issue depending on their frequency.

Ab initio/DFT/GIAO-CCSD(T) calculational study of the t-butyl cation: comparison of experimental data with structures, energetics, IR vibrational frequencies, and 13C NMR chemical shifts indicating preferred C(s) conformation.

PubMed

Rasul, Golam; Chen, Jonathan L; Prakash, G K Surya; Olah, George A

2009-06-18

The C(s) conformation of the tert-butyl cation 3 was established to be the preferred global energy minimum using a combination of ab initio, DFT, and CCSD(T) methodology with correlation-consistent basis sets. The potential energy surface of methyl rotation involving the C(3v), C(s), and C(3h) forms, however, in accord with previous studies, is quite flat. The computed IR absorptions of 3 indicate that it has the greatest degree of electron donation from C-H bonds into the C(+)-C bonds. The experimental (13)C NMR chemical shifts also agree very well with the experimental data.

A theoretical study of bond selective photochemistry in CH2BrI

NASA Astrophysics Data System (ADS)

Liu, Kun; Zhao, Hongmei; Wang, Caixia; Zhang, Aihua; Ma, Siyu; Li, Zonghe

2005-01-01

Bromoiodomethane photodissociation in the low-lying excited states has been characterized using unrestricted Hartree-Fock, configuration-interaction-singles, and complete active space self-consistent field calculations with the SDB-aug-cc-pVTZ, aug-cc-pVTZ, and 3-21g** basis sets. According to the results of the vertical excited energies and oscillator strengths of these low-lying excited states, bond selectivity is predicted. Subsequently, the minimum energy paths of the first excited singlet state and the third excited state for the dissociation reactions were calculated using the complete active space self-consistent field method with 3-21g** basis set. Good agreement is found between the calculations and experimental data. The relationships of excitations, the electronic structures at Franck-Condon points, and bond selectivity are discussed.

Motor Controller

NASA Technical Reports Server (NTRS)

1988-01-01

M.H. Marks Enterprises' Power Factor Controller (PFC) matches voltage with motor's actual need. Plugged into a motor, PFC continuously determines motor load by sensing shifts between voltage and current flow. When it senses a light load, it cuts voltage to the minimum needed. It offers potential energy savings ranging from eight percent up to 65 percent depending on the application. Myles Marks started out with the notion of writing an article for Popular Electronics magazine at the same time offering to furnish kits to readers interested in assembling PFC's. Within two weeks from publication he had orders for 500 kits and orders are still coming three years later.

The C4H7+ cation. A theoretical investigation

NASA Technical Reports Server (NTRS)

Koch, W.; Liu, B.; DeFrees, D. J.

1988-01-01

The potential energy surface of the C4H7+ cation has been investigated with ab initio quantum chemical theory. Extended basis set calculations, including electronic correlation, show that cyclobutyl and cyclopropylcarbinyl cation are equally stable isomers. The saddle point connecting these isomers lies 0.6 kcal/mol above the minima. The global C4H7+ minimum corresponds to the 1-methylallyl cation, which is 9.0 kcal/mol more stable than the cyclobutyl and the cyclopropylcarbinyl cation and 9.5 kcal/mol below the 2-methylallyl cation. These results are in excellent agreement with experimental data.

Fast-timing Capabilities of Silicon Sensors for the CMS High-Granularity Calorimeter at the High-Luminosity LHC

NASA Astrophysics Data System (ADS)

Akchurin, Nural; CMS Collaboration

2017-11-01

We report on the signal timing capabilities of thin silicon sensors when traversed by multiple simultaneous minimum ionizing particles (MIP). Three different planar sensors, 133, 211, and 285 μm thick in depletion thickness, have been exposed to high energy muons and electrons at CERN. We describe signal shape and timing resolution measurements as well as the response of these devices as a function of the multiplicity of MIPs. We compare these measurements to simulations where possible. We achieve better than 20 ps timing resolution for signals larger than a few tens of MIPs.

Incident flux angle induced crystal texture transformation in nanostructured molybdenum films

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

Chen, L.; Lu, T.-M.; Wang, G.-C.

2012-07-15

Molybdenum films were observed to undergo a dramatic change in crystal texture orientation when the incident flux angle was varied in an oblique angle sputter deposition on amorphous substrates. Reflection high-energy electron diffraction pole figure and scanning electron microscopy were used to analyze in detail the texture orientation of the films. The normal incident deposition resulted in a fiber texture film with the minimum energy (110) crystal plane parallel to the substrate surface. A (110)[110] biaxial texture was observed for the samples grown with low incident angles of less than 45 Degree-Sign , with respect to the surface normal. Onmore » the other hand, for an oblique angle deposition of larger than 60 Degree-Sign , a (111)[112] biaxial texture was observed and appeared to be consistent with a zone T structure where the geometrically fastest growth [001] direction of a crystal plays a dominant role in defining the texture. We argue that a structural transition had occurred when the incident flux was varied from near normal incidence to a large angle.« less

DFT approach to (benzylthio)acetic acid: Conformational search, molecular (monomer and dimer) structure, vibrational spectroscopy and some electronic properties

NASA Astrophysics Data System (ADS)

Sienkiewicz-Gromiuk, Justyna

2018-01-01

The DFT studies were carried out with the B3LYP method utilizing the 6-31G and 6-311++G(d,p) basis sets depending on whether the aim of calculations was to gain the geometry at equilibrium, or to calculate the optimized molecular structure of (benzylthio)acetic acid (Hbta) in the forms of monomer and dimer. The minimum conformational energy search was followed by the potential energy surface (PES) scan of all rotary bonds existing in the acid molecule. The optimized geometrical monomeric and dimeric structures of the title compound were compared with the experimental structural data in the solid state. The detailed vibrational interpretation of experimental infrared and Raman bands was performed on the basis of theoretically simulated ESFF-scaled wavenumbers calculated for the monomer and dimer structures of Hbta. The electronic characteristics of Hbta is also presented in terms of Mulliken atomic charges, frontier molecular orbitals and global reactivity descriptors. Additionally, the MEP and ESP surfaces were computed to predict coordination sites for potential metal complex formation.

Position sensitivity by light splitting in scintillator arrays

NASA Astrophysics Data System (ADS)

Bisplinghoff, J.; Bollmann, R.; Cloth, P.; Dohrmann, F.; Dorner, G.; Drüke, V.; Ernst, J.; Eversheim, P. D.; Filges, D.; Gasthuber, M.; Gebel, R.; Groβ, A.; Groβ-Hardt, R.; Hinterberger, F.; Jahn, R.; Kühl, L.; Lahr, U.; Langkau, R.; Lippert, G.; Mayer-Kuckuk, T.; Maschuw, R.; Mertler, G.; Metsch, B.; Mosel, F.; Paetz gen. Schieck, H.; Petry, H. R.; Prasuhn, D.; Przewoski, B. v.; Rohdjeβ, H.; Rosendaal, D.; Rossen, P. v.; Scheid, H.; Schirm, N.; Schwandt, F.; Scobel, W.; Sprute, L.; Stein, H.; Theis, D.; Weber, J.; Wiedmann, W.; Woller, K.; Ziegler, R.; EDDA Collaboration

1993-05-01

A novel detector design of overlapping plastic scintillator elements in cylindrical geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles: each particle traversing the detector from the axis outwards will produce light in several elements. The relative amounts of energy deposited in those elements allow one to interpolate on the particle trajectory beyond the resolution given by the granularity. The detector covers the angular range 10° ≤ Θlab ≤ 72° and 0° ≤ ϕ ≤ 360° with an inner layer of scintillator bars of triangular cross section and an outer layer of rings. The material is BC408. Tests with minimum ionizing electron beams show that spatial resolutions of ΔΘlab ≈ 1.5° and Δϕ12 ≈ 1.5° (FWHM) can be obtained for electrons or proton pairs with energies in the GeV range. In the EDDA experiment the ultimate spatial resolution is then determined by the size of the interaction area rather than by the intrinsic pulse height resolution of the detector.

Influence of microstructure and surface topography on the electrical conductivity of Cu and Ag thin films obtained by magnetron sputtering

NASA Astrophysics Data System (ADS)

Polonyankin, D. A.; Blesman, A. I.; Postnikov, D. V.

2017-05-01

Conductive thin films formation by copper and silver magnetron sputtering is one of high technological areas for industrial production of solar energy converters, energy-saving coatings, flat panel displays and touch control panels because of their high electrical and optical properties. Surface roughness and porosity, average grain size, internal stresses, orientation and crystal lattice type, the crystallinity degree are the main physical properties of metal films affecting their electrical resistivity and conductivity. Depending on the film thickness, the dominant conduction mechanism can affect bulk conductivity due to the flow of electron gas, and grain boundary conductivity. The present investigation assesses the effect of microstructure and surface topography on the electrical conductivity of magnetron sputtered Cu and Ag thin films using X-ray diffraction analysis, scanning electron and laser interference microscopy. The highest specific conductivity (78.3 MS m-1 and 84.2 MS m-1, respectively, for copper and silver films at the thickness of 350 nm) were obtained with the minimum values of roughness and grain size as well as a high degree of lattice structuredness.

Light-induced defects in hybrid lead halide perovskite

NASA Astrophysics Data System (ADS)

Sharia, Onise; Schneider, William

One of the main challenges facing organohalide perovskites for solar application is stability. Solar cells must last decades to be economically viable alternatives to traditional energy sources. While some causes of instability can be avoided through engineering, light-induced defects can be fundamentally limiting factor for practical application of the material. Light creates large numbers of electron and hole pairs that can contribute to degradation processes. Using ab initio theoretical methods, we systematically explore first steps of light induced defect formation in methyl ammonium lead iodide, MAPbI3. In particular, we study charged and neutral Frenkel pair formation involving Pb and I atoms. We find that most of the defects, except negatively charged Pb Frenkel pairs, are reversible, and thus most do not lead to degradation. Negative Pb defects create a mid-gap state and localize the conduction band electron. A minimum energy path study shows that, once the first defect is created, Pb atoms migrate relatively fast. The defects have two detrimental effects on the material. First, they create charge traps below the conduction band. Second, they can lead to degradation of the material by forming Pb clusters.

Ferromagnetic core valve gives rapid action on minimum energy

NASA Technical Reports Server (NTRS)

Larson, A. V.; Tinkham, J. P.

1967-01-01

Miniature solenoid valve controls propellant flow during tests on a coaxial plasma accelerator. It uses an advanced ferromagnetic core design which meets all the rapid-acting requirements with a minimum of input energy.

Enhanced Compton Backscattering in a Periodic Mirror System for Polarized Positron Beam Generation

NASA Astrophysics Data System (ADS)

Miyahara, Yoshikazu

2002-05-01

By colliding a circularly polarized high power laser beam with a high-energy electron beam, intense circularly polarized γ-rays can be generated, which in turn can be used to produce a longitudinally polarized positron beam for a linear collider. In the present paper, an optical mirror system with periodic focal points is considered to generate intense polarized γ-rays. A CO2 laser beam propagates back and forth in a series of holed mirrors in a straight line. The diffraction loss through the holes is negligibly small, so that the laser beam can be used repeatedly for the collision. The beam size is reduced to 22 μm at a minimum and kept the same in 20 unit cells, ten of which are combined in series. A 5.8 GeV electron beam is focused to 30 μm at a minimum in a series of triplets of permanent quadrupole magnets to generate γ-rays of 60 MeV at a maximum. A γ-ray yield required for a positron beam in a linear collider can be obtained by 10 laser sources with a power of 3.1 kW each, which is considerably lower than the total power assumed in a previous proposal.

Note: measurement of extreme-short current pulse duration of runaway electron beam in atmospheric pressure air.

PubMed

Tarasenko, V F; Rybka, D V; Burachenko, A G; Lomaev, M I; Balzovsky, E V

2012-08-01

This note reports the time-amplitude characteristic of the supershort avalanche electron beam with up to 20 ps time resolution. For the first time it is shown that the electron beam downstream of small-diameter diaphragms in atmospheric pressure air has a complex structure which depends on the interelectrode gap width and cathode design. With a spherical cathode and collimator the minimum duration at half maximum of the supershort avalanche electron beam current pulse was shown to be ~25 ps. The minimum duration at half maximum of one peak in the pulses with two peaks can reach ~25 ps too.

Ab initio molecular dynamics simulations of AlN responding to low energy particle radiation

NASA Astrophysics Data System (ADS)

Xi, Jianqi; Liu, Bin; Zhang, Yanwen; Weber, William J.

2018-01-01

Ab initio molecular dynamics simulations of low energy recoil events in wurtzite AlN have been performed to determine threshold displacement energies, defect production and evolution mechanisms, role of partial charge transfer during the process, and the influence of irradiation-induced defects on the properties of AlN. The results show that the threshold displacement energies, Ed, along the direction parallel to the basal planes are smaller than those perpendicular to the basal planes. The minimum Ed values are determined to be 19 eV and 55 eV for N and Al atom, respectively, which occur along the [ 1 ¯ 1 ¯ 20 ] direction. In general, the threshold displacement energies for N are smaller than those for Al atom, indicating the N defects would be dominant under irradiation. The defect production mechanisms have been analyzed. It is found that charge transfer and redistribution for both the primary knock-on atom and the subsequent recoil atoms play a significant role in defect production and evolution. Similar to the trend in oxide materials, there is a nearly linear relationship between Ed and the total amount of charge transfer at the potential energy peak in AlN, which provides guidance on the development of charge-transfer interatomic potentials for classic molecular dynamics simulations. Finally, the response behavior of AlN to low energy irradiation is qualitatively investigated. The existence of irradiation-induced defects significantly modifies the electronic structure, and thus affects the magnetic, electronic and optical properties of AlN. These findings further enrich the understanding of defects in the wide bandgap semiconductor of AlN.

Quantification of the precipitation loss of radiation belt electrons observed by SAMPEX

NASA Astrophysics Data System (ADS)

Tu, Weichao; Selesnick, Richard; Li, Xinlin; Looper, Mark

2010-07-01

Based on SAMPEX/PET observations, the rates and the spatial and temporal variations of electron loss to the atmosphere in the Earth's radiation belt were quantified using a drift diffusion model that includes the effects of azimuthal drift and pitch angle diffusion. The measured electrons by SAMPEX can be distinguished as trapped, quasi-trapped (in the drift loss cone), and precipitating (in the bounce loss cone). The drift diffusion model simulates the low-altitude electron distribution from SAMPEX. After fitting the model results to the data, the magnitudes and variations of the electron lifetime can be quantitatively determined based on the optimum model parameter values. Three magnetic storms of different magnitudes were selected to estimate the various loss rates of ˜0.5-3 MeV electrons during different phases of the storms and at L shells ranging from L = 3.5 to L = 6.5 (L represents the radial distance in the equatorial plane under a dipole field approximation). The storms represent a small storm, a moderate storm from the current solar minimum, and an intense storm right after the previous solar maximum. Model results for the three individual events showed that fast precipitation losses of relativistic electrons, as short as hours, persistently occurred in the storm main phases and with more efficient loss at higher energies over wide range of L regions and over all the SAMPEX-covered local times. In addition to this newly discovered common feature of the main phase electron loss for all the storm events and at all L locations, some other properties of the electron loss rates, such as the local time and energy dependence that vary with time or locations, were also estimated and discussed. This method combining model with the low-altitude observations provides direct quantification of the electron loss rate, a prerequisite for any comprehensive modeling of the radiation belt electron dynamics.

The Cosmic-Ray Electron and Positron Spectra Measured at 1 AU during Solar Minimum Activity

NASA Astrophysics Data System (ADS)

Boezio, M.; Carlson, P.; Francke, T.; Weber, N.; Suffert, M.; Hof, M.; Menn, W.; Simon, M.; Stephens, S. A.; Bellotti, R.; Cafagna, F.; Castellano, M.; Circella, M.; De Marzo, C.; Finetti, N.; Papini, P.; Piccardi, S.; Spillantini, P.; Ricci, M.; Casolino, M.; De Pascale, M. P.; Morselli, A.; Picozza, P.; Sparvoli, R.; Barbiellini, G.; Bravar, U.; Schiavon, P.; Vacchi, A.; Zampa, N.; Grimani, C.; Mitchell, J. W.; Ormes, J. F.; Streitmatter, R. E.; Golden, R. L.; Stochaj, S. J.

2000-03-01

We report on a new measurement of the cosmic-ray electron and positron spectra. The data were collected by the balloon-borne experiment CAPRICE94, which was flown from Lynn Lake, Canada, on 1994 August 8-9 at an altitude corresponding to 3.9 g cm-2 of average residual atmosphere. The experiment used the NMSU-WIZARD/CAPRICE94 balloon-borne magnet spectrometer equipped with a solid radiator Ring Imaging Cerenkov (RICH) detector, a time-of-flight system, a tracking device consisting of drift chambers and multiwire proportional chambers, and a silicon-tungsten calorimeter. This was the first time a RICH detector was used together with an imaging calorimeter in a balloon-borne experiment. A total of 3211 electrons, with a rigidity at the spectrometer between 0.3 and 30 GV, and 734 positrons, between 0.3 and 10 GV, were identified with small backgrounds from other particles. The absolute energy spectra were determined in the energy region at the top of the atmosphere between 0.46 and 43.6 GeV for electrons and between 0.46 and 14.6 GeV for positrons. We found that the observed positron spectrum and the positron fraction are consistent with a pure secondary origin. A comparison of the theoretically predicted interstellar spectrum of electrons shows that the injection spectrum of primary electrons is steeper than that of the nucleonic components of cosmic rays. Furthermore, the observed electron and positron spectra can be reproduced from the interstellar spectra by a spherically symmetric model for solar modulation; hence, the modulation is independent of the sign of the particle charge.

Barriers and facilitators to the implementation of an evidence-based electronic minimum dataset for nursing team leader handover: A descriptive survey.

PubMed

Spooner, Amy J; Aitken, Leanne M; Chaboyer, Wendy

2017-11-15

There is widespread use of clinical information systems in intensive care units however, the evidence to support electronic handover is limited. The study aim was to assess the barriers and facilitators to use of an electronic minimum dataset for nursing team leader shift-to-shift handover in the intensive care unit prior to its implementation. The study was conducted in a 21-bed medical/surgical intensive care unit, specialising in cardiothoracic surgery at a tertiary referral hospital, in Queensland, Australia. An established tool was modified to the intensive care nursing handover context and a survey of all 63 nursing team leaders was undertaken. Survey statements were rated using a 6-point Likert scale with selections from 'strongly disagree' to 'strongly agree', and open-ended questions. Descriptive statistics were used to summarise results. A total of 39 team leaders responded to the survey (62%). Team leaders used general intensive care work unit guidelines to inform practice however they were less familiar with the intensive care handover work unit guideline. Barriers to minimum dataset uptake included: a tool that was not user friendly, time consuming and contained too much information. Facilitators to minimum dataset adoption included: a tool that was user friendly, saved time and contained relevant information. Identifying the complexities of a healthcare setting prior to the implementation of an intervention assists researchers and clinicians to integrate new knowledge into healthcare settings. Barriers and facilitators to knowledge use focused on usability, content and efficiency of the electronic minimum dataset and can be used to inform tailored strategies to optimise team leaders' adoption of a minimum dataset for handover. Copyright © 2017 Australian College of Critical Care Nurses Ltd. Published by Elsevier Ltd. All rights reserved.

Noncovalent interactions between cisplatin and graphene prototypes.

PubMed

Cuevas-Flores, Ma Del Refugio; Garcia-Revilla, Marco Antonio; Bartolomei, Massimiliano

2018-01-15

Cisplatin (CP) has been widely used as an anticancer drug for more than 30 years despite severe side effects due to its low bioavailability and poor specificity. For this reason, it is paramount to study and design novel nanomaterials to be used as vectors capable to effectively deliver the drug to the biological target. The CP square-planar geometry, together with its low water solubility, suggests that it could be possibly easily adsorbed on 2D graphene nanostructures through the interaction with the related highly conjugated π-electron system. In this work, pyrene has been first selected as the minimum approximation to the graphene plane, which allows to properly study the noncovalent interactions determining the CP adsorption. In particular, electronic structure calculations at the MP2C and DFT-SAPT levels of theory have allowed to obtain benchmark interaction energies for some limiting configurations of the CP-pyrene complex, as well as to assess the role of the different contributions to the total interaction: it has been found that the parallel configurations of the aggregate are mainly stabilized around the minimum region by dispersion, in a similar way as for complexes bonded through π-π interactions. Then, the benchmark interaction energies have been used to test corresponding estimations obtained within the less expensive DFT to validate an optimal exchange-correlation functional which includes corrections to take properly into account for the dispersion contribution. Reliable DFT interaction energies have been therefore obtained for CP adsorbed on graphene prototypes of increasing size, ranging from coronene, ovalene, and up to C 150 H 30 . Finally, DFT geometry optimizations and frequency calculations have also allowed a reliable estimation of the adsorption enthalpy of CP on graphene, which is found particularly favorable (about -20 kcal/mol at 298 K and 1 bar) being twice that estimated for the corresponding benzene adsorption. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Formation, optical properties, and electronic structure of thin Yb silicide films on Si(111)

NASA Astrophysics Data System (ADS)

Galkin, N. G.; Maslov, A. M.; Polyarnyi, V. O.

2005-06-01

Continuous very thin (2.5-3.0 nm) and thin (16-18 nm) ytterbium suicide films with some pinhole density (3×107- 1×108 cm-2) have been formed on Si(111) by solid phase epitaxy (SPE) and reactive deposition epitaxy (RDE) growth methods on templates. The stoichiometric ytterbium suicide (YbSi2) formation has shown in SPE grown films by AES and EELS data. Very thin Yb suicide films grown by RDE method had the silicon enrichment in YbSi2 suicide composition. The analysis of LEED data and AFM imaging has shown that ytterbium suicide films had non-oriented blocks with the polycrystalline structure. The analysis of scanning region length dependencies of the root mean square roughness deviation (σR(L)) for grown suicide films has shown that the formation of ytterbium suicide in SPE and RDE growth methods is determined by the surface diffusion of Yb atoms during the three-dimensional growth process. Optical functions (n, k, α, ɛ1, ɛ2, Im ɛ1-1, neff, ɛeff) of ytterbium silicide films grown on Si(1 1 1) have been calculated from transmittance and reflectance spectra in the energy range of 0.1-6.2 eV. Two nearly discrete absorption bands have been observed in the electronic structure of Yb silicide films with different composition, which connected with interband transitions on divalent and trivalent Yb states. It was established that the reflection coefficient minimum in R-spectra at energies higher 4.2 eV corresponds to the state density minimum in Yb suicide between divalent and trivalent Yb states. It was shown from optical data that Yb silicide films have the semi-metallic properties with low state densities at energies less 0.4 eV and high state densities at 0.5-2.5 eV.

Ab initio calculation of proton-coupled electron transfer rates using the external-potential representation: A ubiquinol complex in solution

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

Yamamoto, Takeshi; Kato, Shigeki

2007-06-14

In quantum-mechanical/molecular-mechanical (QM/MM) treatment of chemical reactions in condensed phases, one solves the electronic Schroedinger equation for the solute (or an active site) under the electrostatic field from the environment. This Schroedinger equation depends parametrically on the solute nuclear coordinates R and the external electrostatic potential V. This fact suggests that one may use R and V as natural collective coordinates for describing the entire system, where V plays the role of collective solvent variables. In this paper such an (R,V) representation of the QM/MM canonical ensemble is described, with particular focus on how to treat charge transfer processes inmore » this representation. As an example, the above method is applied to the proton-coupled electron transfer of a ubiquinol analog with phenoxyl radical in acetonitrile solvent. Ab initio free-energy surfaces are calculated as functions of R and V using the reference interaction site model self-consistent field method, the equilibrium points and the minimum free-energy crossing point are located in the (R,V) space, and then the kinetic isotope effects (KIEs) are evaluated approximately. The results suggest that a stiffer proton potential at the transition state may be responsible for unusual KIEs observed experimentally for related systems.« less

On a gas electron multiplier based synthetic diagnostic for soft x-ray tomography on WEST with focus on impurity transport studies

NASA Astrophysics Data System (ADS)

Jardin, A.; Mazon, D.; Malard, P.; O'Mullane, M.; Chernyshova, M.; Czarski, T.; Malinowski, K.; Kasprowicz, G.; Wojenski, A.; Pozniak, K.

2017-08-01

The tokamak WEST aims at testing ITER divertor high heat flux component technology in long pulse operation. Unfortunately, heavy impurities like tungsten (W) sputtered from the plasma facing components can pollute the plasma core by radiation cooling in the soft x-ray (SXR) range, which is detrimental for the energy confinement and plasma stability. SXR diagnostics give valuable information to monitor impurities and study their transport. The WEST SXR diagnostic is composed of two new cameras based on the Gas Electron Multiplier (GEM) technology. The WEST GEM cameras will be used for impurity transport studies by performing 2D tomographic reconstructions with spectral resolution in tunable energy bands. In this paper, we characterize the GEM spectral response and investigate W density reconstruction thanks to a synthetic diagnostic recently developed and coupled with a tomography algorithm based on the minimum Fisher information (MFI) inversion method. The synthetic diagnostic includes the SXR source from a given plasma scenario, the photoionization, electron cloud transport and avalanche in the detection volume using Magboltz, and tomographic reconstruction of the radiation from the GEM signal. Preliminary studies of the effect of transport on the W ionization equilibrium and on the reconstruction capabilities are also presented.

Ab initio conformational analysis of N-formyl ?-alanine amide including electron correlation

NASA Astrophysics Data System (ADS)

Yu, Ching-Hsing; Norman, Mya A.; Schäfer, Lothar; Ramek, Michael; Peeters, Anik; van Alsenoy, Christian

2001-06-01

The conformational properties of N-formyl L-alanine amide (ALA) were investigated using RMP2/6-311G∗∗ ab initio gradient geometry optimization. One hundred forty four structures of ALA were optimized at 30° grid points in its φ(N-C(α)), ψ(C(α)-C‧) conformational space. Using cubic spline functions, the grid structures were then used to construct analytical representations of complete surfaces, in φ,ψ-space, of bond lengths, bond angles, torsional sensitivity and electrostatic atomic charges. Analyses show that, in agreement with previous studies, the right-handed helical conformation, αR, is not a local energy minimum of the potential energy surface of ALA. Comparisons with protein crystallographic data show that the characteristic differences between geometrical trends in dipeptides and proteins, previously found for ab initio dipeptide structures obtained without electron correlation, are also found in the electron-correlated geometries. In contrast to generally accepted features of force fields used in empirical molecular modeling, partial atomic charges obtained by the CHELPG method are found to be not constant, but to vary significantly throughout the φ,ψ-space. By comparing RHF and MP2 structures, the effects of dispersion forces on ALA were studied, revealing molecular contractions for those conformations, in which small adjustments of torsional angles entail large changes in non-bonded distances.

Molecular Functionalization of Graphene Oxide for Next-Generation Wearable Electronics.

PubMed

Zarrin, Hadis; Sy, Serubbabel; Fu, Jing; Jiang, Gaopeng; Kang, Keunwoo; Jun, Yun-Seok; Yu, Aiping; Fowler, Michael; Chen, Zhongwei

2016-09-28

Acquiring reliable and efficient wearable electronics requires the development of flexible electrolyte membranes (EMs) for energy storage systems with high performance and minimum dependency on the operating conditions. Herein, a freestanding graphene oxide (GO) EM is functionalized with 1-hexyl-3-methylimidazolium chloride (HMIM) molecules via both covalent and noncovalent bonds induced by esterification reactions and electrostatic πcation-π stacking, respectively. Compared to the commercial polymeric membrane, the thin HMIM/GO membrane demonstrates not only slightest performance sensitivity to the operating conditions but also a superior hydroxide conductivity of 0.064 ± 0.0021 S cm(-1) at 30% RH and room temperature, which was 3.8 times higher than that of the commercial membrane at the same conditions. To study the practical application of the HMIM/GO membranes in wearable electronics, a fully solid-state, thin, flexible zinc-air battery and supercapacitor are made exhibiting high battery performance and capacitance at low humidified and room temperature environment, respectively, favored by the bonded HMIM molecules on the surface of GO nanosheets. The results of this study disclose the strong potential of manipulating the chemical structure of GO to work as a lightweight membrane in wearable energy storage devices, possessing highly stable performance at different operating conditions, especially at low relative humidity and room temperature.

Characteristics of pitch angle distributions of hundreds of keV electrons in the slot region and inner radiation belt

NASA Astrophysics Data System (ADS)

Zhao, H.; Li, X.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.; Baker, D. N.; Jaynes, A. N.; Malaspina, D. M.

2014-12-01

The pitch angle distribution (PAD) of energetic electrons in the slot region and inner radiation belt received little attention in the past decades due to the lack of quality measurements. Using the state-of-the-art pitch angle-resolved data from the Magnetic Electron Ion Spectrometer instrument onboard the Van Allen Probes, a detailed analysis of hundreds of keV electron PADs below L = 4 is performed, in which the PADs are categorized into three types: normal (flux peaking at 90°), cap (exceedingly peaking narrowly around 90°), and 90° minimum (lower flux at 90°) PADs. By examining the characteristics of the PADs of ˜460 keV electrons for over a year, we find that the 90° minimum PADs are generally present in the inner belt (L<2), while normal PADs dominate at L˜3.5-4. In the region between, 90° minimum PADs dominate during injection times and normal PADs dominate during quiet times. Cap PADs appear mostly at the decay phase of storms in the slot region and are likely caused by the pitch angle scattering of hiss waves. Fitting the normal PADs into sinnα form, the parameter n is much higher below L = 3 than that in the outer belt and relatively constant in the inner belt but changes significantly in the slot region (2 < L < 3) during injection times. As for the 90° minimum PADs, by performing a detailed case study, we find in the slot region this type of PAD is likely caused by chorus wave heating, but this mechanism can hardly explain the formation of 90° minimum PADs at the center of inner belt.

5 CFR 532.267 - Special wage schedules for aircraft, electronic, and optical instrument overhaul and repair...

Code of Federal Regulations, 2010 CFR

2010-01-01

... a minimum, include the air transportation and electronics industries in the following North American... 11 Electronics Mechanic 11 Electronic Computer Mechanic 11 Television Station Mechanic 11 (d) The...

Design of an integrated sensor system for the detection of traces of different molecules in the air

NASA Astrophysics Data System (ADS)

Strle, D.; Muševič, I.

2015-04-01

This article presents the design of a miniature detection system and its associated signal processing electronics, which can detect and selectively recognize vapor traces of different materials in the air - including explosives. It is based on the array of surface-functionalized COMB capacitive sensors and extremely low noise, analog, integrated electronic circuit, hardwired digital signal processing hardware and additional software running on a PC. The instrument is sensitive and selective, consumes a minimum amount of energy, is very small (few mm3) and cheap to produce in large quantities, and is insensitive to mechanical influences. Using an electronic detection system built of low noise analog front-end and hard-wired digital signal processing, it is possible to detect less than 0.3ppt of TNT molecules in the atmosphere (3 TNT molecules in 1013 molecules of the air) at 25°C on a 1 Hz bandwidth using very small volume and approx. 10 mA current from a 5V supply voltage. The sensors are implemented in a modified MEMS process and analog electronics in 0.18 um CMOS technology.

Computational studies for a multiple-frequency electron cyclotron resonance ion source (abstract)

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

Alton, G.D.

1996-03-01

The number density of electrons, the energy (electron temperature), and energy distribution are three of the fundamental properties which govern the performance of electron cyclotron resonance (ECR) ion sources in terms of their capability to produce high charge state ions. The maximum electron energy is affected by several processes including the ability of the plasma to absorb power. In principle, the performances of an ECR ion source can be realized by increasing the physical size of the ECR zone in relation to the total plasma volume. The ECR zones can be increased either in the spatial or frequency domains inmore » any ECR ion source based on B-minimum plasma confinement principles. The former technique requires the design of a carefully tailored magnetic field geometry so that the central region of the plasma volume is a large, uniformly distributed plasma volume which surrounds the axis of symmetry, as proposed in Ref. . Present art forms of the ECR source utilize single frequency microwave power supplies to maintain the plasma discharge; because the magnetic field distribution continually changes in this source design, the ECR zones are relegated to thin {open_quote}{open_quote}surfaces{close_quote}{close_quote} which surround the axis of symmetry. As a consequence of the small ECR zone in relation to the total plasma volume, the probability for stochastic heating of the electrons is quite low, thereby compromising the source performance. This handicap can be overcome by use of broadband, multiple frequency microwave power as evidenced by the enhanced performances of the CAPRICE and AECR ion sources when two frequency microwave power was utilized. We have used particle-in-cell codes to simulate the magnetic field distributions in these sources and to demonstrate the advantages of using multiple, discrete frequencies over single frequencies to power conventional ECR ion sources. (Abstract Truncated)« less

Physics reach of the XENON1T dark matter experiment

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

Aprile, E.; Anthony, M.; Aalbers, J.

2016-04-01

The XENON1T experiment is currently in the commissioning phase at the Laboratori Nazionali del Gran Sasso, Italy. In this article we study the experiment's expected sensitivity to the spin-independent WIMP-nucleon interaction cross section, based on Monte Carlo predictions of the electronic and nuclear recoil backgrounds. The total electronic recoil background in 1 tonne fiducial volume and (1, 12) keV electronic recoil equivalent energy region, before applying any selection to discriminate between electronic and nuclear recoils, is (1.80 ± 0.15) · 10{sup −4} (kg·day·keV){sup −1}, mainly due to the decay of {sup 222}Rn daughters inside the xenon target. The nuclear recoil background in the correspondingmore » nuclear recoil equivalent energy region (4, 50) keV, is composed of (0.6 ± 0.1) (t·y){sup −1} from radiogenic neutrons, (1.8 ± 0.3) · 10{sup −2} (t·y){sup −1} from coherent scattering of neutrinos, and less than 0.01 (t·y){sup −1} from muon-induced neutrons. The sensitivity of XENON1T is calculated with the Profile Likelihood Ratio method, after converting the deposited energy of electronic and nuclear recoils into the scintillation and ionization signals seen in the detector. We take into account the systematic uncertainties on the photon and electron emission model, and on the estimation of the backgrounds, treated as nuisance parameters. The main contribution comes from the relative scintillation efficiency L{sub eff}, which affects both the signal from WIMPs and the nuclear recoil backgrounds. After a 2 y measurement in 1 t fiducial volume, the sensitivity reaches a minimum cross section of 1.6 · 10{sup −47} cm{sup 2} at m{sub χ} = 50 GeV/c{sup 2}.« less

Selective CO{sub 2} reduction conjugated with H{sub 2}O oxidation utilizing semiconductor/metal-complex hybrid photocatalysts

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

Morikawa, T., E-mail: morikawa@mosk.tytlabs.co.jp; Sato, S., E-mail: morikawa@mosk.tytlabs.co.jp; Arai, T., E-mail: morikawa@mosk.tytlabs.co.jp

2013-12-10

We developed a new hybrid photocatalyst for CO{sub 2} reduction, which is composed of a semiconductor and a metal complex. In the hybrid photocatalyst, ΔG between the position of conduction band minimum (E{sub CBM}) of the semiconductor and the CO{sub 2} reduction potential of the complex is an essential factor for realizing fast electron transfer from the conduction band of semiconductor to metal complex leading to high photocatalytic activity. On the basis of this concept, the hybrid photocatalyst InP/Ru-complex, which functions in aqueous media, was developed. The photoreduction of CO{sub 2} to formate using water as an electron donor andmore » a proton source was successfully achieved as a Z-scheme system by functionally conjugating the InP/Ru-complex photocatalyst for CO{sub 2} reduction with a TiO{sub 2} photocatalyst for water oxidation. The conversion efficiency from solar energy to chemical energy was ca. 0.04%, which approaches that for photosynthesis in a plant. Because this system can be applied to many other inorganic semiconductors and metal-complex catalysts, the efficiency and reaction selectivity can be enhanced by optimization of the electron transfer process including the energy-band configurations, conjugation conformations, and catalyst structures. This electrical-bias-free reaction is a huge leap forward for future practical applications of artificial photosynthesis under solar irradiation to produce organic species.« less

Collisionless absorption, hot electron generation, and energy scaling in intense laser-target interaction

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

Liseykina, T., E-mail: tatyana.tiseykina@uni-rostock.de; Institute of Computational Technologies SD RAS, Acad. Lavrentjev Ave. 6, 630090 Novosibirsk; Mulser, P.

2015-03-15

Among the various attempts to understand collisionless absorption of intense and superintense ultrashort laser pulses, a whole variety of models and hypotheses has been invented to describe the laser beam target interaction. In terms of basic physics, collisionless absorption is understood now as the interplay of the oscillating laser field with the space charge field produced by it in the plasma. A first approach to this idea is realized in Brunel's model the essence of which consists in the formation of an oscillating charge cloud in the vacuum in front of the target, therefore frequently addressed by the vague termmore » “vacuum heating.” The investigation of statistical ensembles of orbits shows that the absorption process is localized at the ion-vacuum interface and in the skin layer: Single electrons enter into resonance with the laser field thereby undergoing a phase shift which causes orbit crossing and braking of Brunel's laminar flow. This anharmonic resonance acts like an attractor for the electrons and leads to the formation of a Maxwellian tail in the electron energy spectrum. Most remarkable results of our investigations are the Brunel like spectral hot electron distribution at the relativistic threshold, the minimum of absorption at Iλ{sup 2}≅(0.3−1.2)×10{sup 21} Wcm{sup −2}μm{sup 2} in the plasma target with the electron density of n{sub e}λ{sup 2}∼10{sup 23}cm{sup −3}μm{sup 2}, the drastic reduction of the number of hot electrons in this domain and their reappearance in the highly relativistic domain, and strong coupling, beyond expectation, of the fast electron jets with the return current through Cherenkov emission of plasmons. The hot electron energy scaling shows a strong dependence on intensity in the moderately relativistic domain Iλ{sup 2}≅(10{sup 18}−10{sup 20}) Wcm{sup −2}μm{sup 2}, a scaling in vague accordance with current published estimates in the range Iλ{sup 2}≅(0.14−3.5)×10{sup 21} Wcm{sup −2}μm{sup 2}, and again a distinct power increase beyond I=3.5×10{sup 21} Wcm{sup −2}μm{sup 2}. The low energy electrons penetrate normally to the target surface, the energetic electrons propagate in laser beam direction.« less

Triple differential cross-sections of Ne (2s2) in coplanar to perpendicular plane geometry

NASA Astrophysics Data System (ADS)

Chen, L. Q.; Khajuria, Y.; Chen, X. J.; Xu, K. Z.

2003-10-01

The distorted wave Born approximation (DWBA) with the spin averaged static exchange potential has been used to calculate the triple differential cross-sections (TDCSs) for Ne (2s^2) ionization by electron impact in coplanar to perpendicular plane symmetric geometry at 110.5 eV incident electron energy. The present theoretical results at gun angles Psi = 0^circ (coplanar symmetric geometry) and Psi = 90^circ (perpendicular plane geometry) are in satisfactory agreement with the available experimental data. A deep interference minimum appears in the TDCS in the coplanar symmetric geometry and a strong peak at scattering angle xi = 90^circ caused by the single collision mechanism has been observed in the perpendicular plane geometry. The TDCSs at the gun angles Psi = 30^circ, and Psi = 60^circ are predicted.

Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

DOE PAGES

Teknowijoyo, S.; Cho, K.; Tanatar, M. A.; ...

2016-08-29

A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth Δλ measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced pointlike disorder, indicating the absence of symmetry-imposed nodes. Surprisingly, the superconducting transition temperature T c increases by 0.4 K from T c0 ≈ 8.8 K while the structural transition temperature T s decreases by 0.9 K from T s0 ≈ 91.2 K after electron irradiation. Finally, we discuss several explanations for the T c enhancement and propose that local strengthening ofmore » the pair interaction by irradiation-induced Frenkel defects most likely explains the phenomenon.« less

Rock climbing: A local-global algorithm to compute minimum energy and minimum free energy pathways.

PubMed

Templeton, Clark; Chen, Szu-Hua; Fathizadeh, Arman; Elber, Ron

2017-10-21

The calculation of minimum energy or minimum free energy paths is an important step in the quantitative and qualitative studies of chemical and physical processes. The computations of these coordinates present a significant challenge and have attracted considerable theoretical and computational interest. Here we present a new local-global approach to study reaction coordinates, based on a gradual optimization of an action. Like other global algorithms, it provides a path between known reactants and products, but it uses a local algorithm to extend the current path in small steps. The local-global approach does not require an initial guess to the path, a major challenge for global pathway finders. Finally, it provides an exact answer (the steepest descent path) at the end of the calculations. Numerical examples are provided for the Mueller potential and for a conformational transition in a solvated ring system.

Ultraviolet photodissociation action spectroscopy of the N-pyridinium cation

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

Hansen, Christopher S., E-mail: csh297@uowmail.edu.au; Trevitt, Adam J., E-mail: adamt@uow.edu.au; Blanksby, Stephen J.

2015-01-07

The S{sub 1}←S{sub 0} electronic transition of the N-pyridinium ion (C{sub 5}H{sub 5}NH{sup +}) is investigated using ultraviolet photodissociation (PD) spectroscopy of the bare ion and also the N{sub 2}-tagged complex. Gas-phase N-pyridinium ions photodissociate by the loss of molecular hydrogen (H{sub 2}) in the photon energy range 37 000–45 000 cm{sup −1} with structurally diagnostic ion-molecule reactions identifying the 2-pyridinylium ion as the exclusive co-product. The photodissociation action spectra reveal vibronic details that, with the aid of electronic structure calculations, support the proposal that dissociation occurs through an intramolecular rearrangement on the ground electronic state following internal conversion. Quantum chemical calculationsmore » are used to analyze the measured spectra. Most of the vibronic features are attributed to progressions of totally symmetric ring deformation modes and out-of-plane modes active in the isomerization of the planar excited state towards the non-planar excited state global minimum.« less

Dissociative Ionization of Benzene by Electron Impact

NASA Technical Reports Server (NTRS)

Huo, Winifred; Dateo, Christopher; Kwak, Dochan (Technical Monitor)

2002-01-01

We report a theoretical study of the dissociative ionization (DI) of benzene from the low-lying ionization channels. Our approach makes use of the fact that electron motion is much faster than nuclear motion and DI is treated as a two-step process. The first step is electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model. For the unimolecular dissociation step, we study the steepest descent reaction path to the minimum of the ion potential energy surface. The path is used to analyze the probability of unimolecular dissociation and to determine the product distributions. Our analysis of the dissociation products and the thresholds of the productions are compared with the result dissociative photoionization measurements of Feng et al. The partial oscillator strengths from Feng et al. are then used in the iBED cross section calculations.

Electronic structure, thermodynamic properties and hydrogenation of LaPtIn and CePtIn compounds by ab-initio methods

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

Jezierski, Andrzej, E-mail: andrzej.jezierski@ifmpan.poznan.pl; Szytuła, Andrzej

2016-02-15

The electronic structures and thermodynamic properties of LaPtIn and CePtIn are studied by means of ab-initio full-relativistic full-potential local orbital basis (FPLO) method within densities functional (DFT) methodologies. We have also examined the influence of hydrogen on the electronic structure and stability of CePtInH and LaPtInH systems. The positions of the hydrogen atoms have been found from the minimum of the total energy. Our calculations have shown that band structure and topology of the Fermi surfaces changed significantly during the hydrogenation. The thermodynamic properties (bulk modulus, Debye temperatures, constant pressure heat capacity) calculated in quasi-harmonic Debye-Grüneisen model are in amore » good agreement with the experimental data. We have applied different methods of the calculation of the equation of states (EOS) (Murnaghan, Birch-Murnaghan, Poirier–Tarantola, Vinet). The thermodynamic properties are presented for the pressure 0« less

Communication: A new ab initio potential energy surface for HCl-H2O, diffusion Monte Carlo calculations of D0 and a delocalized zero-point wavefunction.

PubMed

Mancini, John S; Bowman, Joel M

2013-03-28

We report a global, full-dimensional, ab initio potential energy surface describing the HCl-H2O dimer. The potential is constructed from a permutationally invariant fit, using Morse-like variables, to over 44,000 CCSD(T)-F12b∕aug-cc-pVTZ energies. The surface describes the complex and dissociated monomers with a total RMS fitting error of 24 cm(-1). The normal modes of the minima, low-energy saddle point and separated monomers, the double minimum isomerization pathway and electronic dissociation energy are accurately described by the surface. Rigorous quantum mechanical diffusion Monte Carlo (DMC) calculations are performed to determine the zero-point energy and wavefunction of the complex and the separated fragments. The calculated zero-point energies together with a De value calculated from CCSD(T) with a complete basis set extrapolation gives a D0 value of 1348 ± 3 cm(-1), in good agreement with the recent experimentally reported value of 1334 ± 10 cm(-1) [B. E. Casterline, A. K. Mollner, L. C. Ch'ng, and H. Reisler, J. Phys. Chem. A 114, 9774 (2010)]. Examination of the DMC wavefunction allows for confident characterization of the zero-point geometry to be dominant at the C(2v) double-well saddle point and not the C(s) global minimum. Additional support for the delocalized zero-point geometry is given by numerical solutions to the 1D Schrödinger equation along the imaginary-frequency out-of-plane bending mode, where the zero-point energy is calculated to be 52 cm(-1) above the isomerization barrier. The D0 of the fully deuterated isotopologue is calculated to be 1476 ± 3 cm(-1), which we hope will stand as a benchmark for future experimental work.

On the critical flame radius and minimum ignition energy for spherical flame initiation

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

Chen, Zheng; Burke, M. P.; Ju, Yiguang

2011-01-01

Spherical flame initiation from an ignition kernel is studied theoretically and numerically using different fuel/oxygen/helium/argon mixtures (fuel: hydrogen, methane, and propane). The emphasis is placed on investigating the critical flame radius controlling spherical flame initiation and its correlation with the minimum ignition energy. It is found that the critical flame radius is different from the flame thickness and the flame ball radius and that their relationship depends strongly on the Lewis number. Three different flame regimes in terms of the Lewis number are observed and a new criterion for the critical flame radius is introduced. For mixtures with Lewis numbermore » larger than a critical Lewis number above unity, the critical flame radius is smaller than the flame ball radius but larger than the flame thickness. As a result, the minimum ignition energy can be substantially over-predicted (under-predicted) based on the flame ball radius (the flame thickness). The results also show that the minimum ignition energy for successful spherical flame initiation is proportional to the cube of the critical flame radius. Furthermore, preferential diffusion of heat and mass (i.e. the Lewis number effect) is found to play an important role in both spherical flame initiation and flame kernel evolution after ignition. It is shown that the critical flame radius and the minimum ignition energy increase significantly with the Lewis number. Therefore, for transportation fuels with large Lewis numbers, blending of small molecule fuels or thermal and catalytic cracking will significantly reduce the minimum ignition energy.« less

Pseudo Jahn-Teller coupling in trioxides XO3(0,1,-1) with 22 and 23 valence electrons

NASA Astrophysics Data System (ADS)

Grein, Friedrich

2013-05-01

D3h and C2v geometries and energies, vertical excitation energies, as well as minimal energy paths as function of the O1(z)-X-O2 angle α were obtained for XO3(0,1,-1) (X = B, Al, Ga; C, Si, Ge; N, P, As; S, Se) molecules and ions with 22 and 23 valence electrons (VE), using density functional theory (DFT), coupled cluster with single and double substitutions with noniterative triple excitations (CCSD(T)), equation of motion (EOM)-CCSD, time-dependent DFT, and multi-reference configuration interaction methods. It is shown that pseudo Jahn-Teller (PJT) coupling increases as the central atom X becomes heavier, due to decreases in excitation energies. As is well known for CO3, the excited 1E' states of the 22 VE systems SiO3, GeO3; NO_3 ^ +, PO3+, AsO3+; BO3-, AlO3-, GaO3- have strong vibronic coupling with the 1A1' ground state via the e' vibrational modes, leading to a C2v minimum around α = 145°. For first and second row X atoms, there is an additional D3h minimum (α = 120°). Interacting excited states have minima around 135°. In the 23 VE systems CO3-, SiO3-; NO3, PO3; SO3+, coupling of the excited 2E' with the 2A2' ground state via the e' mode does not generate a C2v state. Minima of interacting excited states are close to 120°. However, due to very strong PJT coupling, a double-well potential is predicted for GeO3-, AsO3, and SeO3+, with a saddle point at D3h symmetry. Interaction of the b2 highest occupied molecular orbital with the b2 lowest unoccupied molecular orbital, both oxygen lone pair molecular orbitals, is seen as the reason for the C2v stabilization of 22 VE molecules.

Electron transfer and reaction mechanism of laccases.

PubMed

Jones, Stephen M; Solomon, Edward I

2015-03-01

Laccases are part of the family of multicopper oxidases (MCOs), which couple the oxidation of substrates to the four electron reduction of O2 to H2O. MCOs contain a minimum of four Cu's divided into Type 1 (T1), Type 2 (T2), and binuclear Type 3 (T3) Cu sites that are distinguished based on unique spectroscopic features. Substrate oxidation occurs near the T1, and electrons are transferred approximately 13 Å through the protein via the Cys-His pathway to the T2/T3 trinuclear copper cluster (TNC), where dioxygen reduction occurs. This review outlines the electron transfer (ET) process in laccases, and the mechanism of O2 reduction as elucidated through spectroscopic, kinetic, and computational data. Marcus theory is used to describe the relevant factors which impact ET rates including the driving force, reorganization energy, and electronic coupling matrix element. Then, the mechanism of O2 reaction is detailed with particular focus on the intermediates formed during the two 2e(-) reduction steps. The first 2e(-) step forms the peroxide intermediate, followed by the second 2e(-) step to form the native intermediate, which has been shown to be the catalytically relevant fully oxidized form of the enzyme.

Electronic tunneling through a potential barrier on the surface of a topological insulator

NASA Astrophysics Data System (ADS)

Zhou, Benliang; Zhou, Benhu; Zhou, Guanghui

2016-12-01

We investigate the tunneling transport for electrons on the surface of a topological insulator (TI) through an electrostatic potential barrier. By using the Dirac equation with the continuity conditions for all segments of wave functions at the interfaces between regions inside and outside the barrier, we calculate analytically the transmission probability and conductance for the system. It is demonstrated that, the Klein paradox can also been observed in the system same as in graphene system. Interestingly, the conductance reaches the minimum value when the incident electron energy is equal to the barrier strength. Moreover, with increasing barrier width, the conductance turns up some tunneling oscillation peaks, and larger barrier strength can cause lower conductance, shorter period but larger oscillation amplitude. The oscillation amplitude decreases as the barrier width increases, which is similar as that of the system consisting of the compressive uniaxial strain applied on a TI, but somewhat different from that of graphene system where the oscillation amplitude is a constant. The findings here imply that an electrostatic barrier can greatly influence the electron tunneling transport of the system, and may provide a new way to realize directional filtering of electrons.

Optimization of vibratory energy harvesters with stochastic parametric uncertainty: a new perspective

NASA Astrophysics Data System (ADS)

Haji Hosseinloo, Ashkan; Turitsyn, Konstantin

2016-04-01

Vibration energy harvesting has been shown as a promising power source for many small-scale applications mainly because of the considerable reduction in the energy consumption of the electronics and scalability issues of the conventional batteries. However, energy harvesters may not be as robust as the conventional batteries and their performance could drastically deteriorate in the presence of uncertainty in their parameters. Hence, study of uncertainty propagation and optimization under uncertainty is essential for proper and robust performance of harvesters in practice. While all studies have focused on expectation optimization, we propose a new and more practical optimization perspective; optimization for the worst-case (minimum) power. We formulate the problem in a generic fashion and as a simple example apply it to a linear piezoelectric energy harvester. We study the effect of parametric uncertainty in its natural frequency, load resistance, and electromechanical coupling coefficient on its worst-case power and then optimize for it under different confidence levels. The results show that there is a significant improvement in the worst-case power of thus designed harvester compared to that of a naively-optimized (deterministically-optimized) harvester.

Adhesion of a bimetallic interface. Ph.D. Thesis - Case Western Reserve Univ.; [for Al, Mg, and Zn

NASA Technical Reports Server (NTRS)

Ferrante, J.

1978-01-01

The Hohenberg-Kohn and Kohn-Sham formalisms are used to examine binding (binding energy as a function of separation) for combinations of the simple metals Al(111), Zn(0001), Mg(0001), and Na(110) in contact. Similar metal contacts between Al, Zn, Mg, and Na are examined self-consistently in an ab initio calculation using the Kohn-Sham formalism. Crystallinity is included using the Aschroft pseudopotential via first order perturbation theory for the electron-ion interaction; and the ion-ion interaction is included exactly via a lattice sum. Binding energy was determined both in the local-density approximation and including gradient corrections to the exchange and correlation energy. Binding was found in all cases. In dissimilar metal contacts, interfacial bonding was greater than that in the weaker material predicting the possibility of metallic transfer. The nonzero position of the energy minimum in like metal contacts is explained in terms of consistency between the Ashcroft pseudopotential and the bulk charge density. Good agreement with experimental surface energies is obtained in the self-consistent calculation when nonlocal terms are included.

Evaluation of lens dose from anterior electron beams: comparison of Pinnacle and Gafchromic EBT3 film

PubMed Central

Wronski, Matt; Yeboah, Collins

2015-01-01

Lens dose is a concern during the treatment of facial lesions with anterior electron beams. Lead shielding is routinely employed to reduce lens dose and minimize late complications. The purpose of this work is twofold: 1) to measure dose profiles under large‐area lead shielding at the lens depth for clinical electron energies via film dosimetry; and 2) to assess the accuracy of the Pinnacle treatment planning system in calculating doses under lead shields. First, to simulate the clinical geometry, EBT3 film and 4 cm wide lead shields were incorporated into a Solid Water phantom. With the lead shield inside the phantom, the film was positioned at a depth of 0.7 cm below the lead, while a variable thickness of solid water, simulating bolus, was placed on top. This geometry was reproduced in Pinnacle to calculate dose profiles using the pencil beam electron algorithm. The measured and calculated dose profiles were normalized to the central‐axis dose maximum in a homogeneous phantom with no lead shielding. The resulting measured profiles, functions of bolus thickness and incident electron energy, can be used to estimate the lens dose under various clinical scenarios. These profiles showed a minimum lead margin of 0.5 cm beyond the lens boundary is required to shield the lens to ≤10% of the dose maximum. Comparisons with Pinnacle showed a consistent overestimation of dose under the lead shield with discrepancies of ∼25% occurring near the shield edge. This discrepancy was found to increase with electron energy and bolus thickness and decrease with distance from the lead edge. Thus, the Pinnacle electron algorithm is not recommended for estimating lens dose in this situation. The film measurements, however, allow for a reasonable estimate of lens dose from electron beams and for clinicians to assess the lead margin required to reduce the lens dose to an acceptable level. PACS number(s): 87.53.Bn, 87.53.Kn, 87.55.‐x, 87.55.D‐ PMID:27074448

Ratio of shear viscosity to entropy density in multifragmentation of Au + Au

NASA Astrophysics Data System (ADS)

Zhou, C. L.; Ma, Y. G.; Fang, D. Q.; Li, S. X.; Zhang, G. Q.

2012-06-01

The ratio of the shear viscosity (η) to entropy density (s) for the intermediate energy heavy-ion collisions has been calculated by using the Green-Kubo method in the framework of the quantum molecular dynamics model. The theoretical curve of η/s as a function of the incident energy for the head-on Au + Au collisions displays that a minimum region of η/s has been approached at higher incident energies, where the minimum η/s value is about 7 times Kovtun-Son-Starinets (KSS) bound (1/4π). We argue that the onset of minimum η/s region at higher incident energies corresponds to the nuclear liquid gas phase transition in nuclear multifragmentation.

New model of inverting substation for DC traction with regenerative braking system

NASA Astrophysics Data System (ADS)

Omar, Abdul Malek Saidina; Samat, Ahmad Asri Abd; Isa, Siti Sarah Mat; Shamsuddin, Sarah Addyani; Jamaludin, Nur Fadhilah; Khyasudeen, Muhammad Farris

2017-08-01

This paper presents a power electronic devices application focus on modeling, analysis, and control of switching power converter in the inverting DC substation with regenerative braking system which is used to recycle the surplus regenerative power by feed it back to the main AC grid. The main objective of this research is to improve the switching power electronic converter of the railway inverting substation and optimize the maximum kinetic energy recovery together with minimum power losses from the railway braking system. Assess performance including efficiency and robustness will be evaluated in order to get the best solution for the design configuration. Research methodology included mathematical calculation, simulation, and detail analysis on modeling of switching power converter on inverting substation. The design stage separates to four main areas include rectification mode, regenerative mode, control inverter mode and filtering mode. The simulation result has shown that the regenerative inverter has a capability to accept a maximum recovery power on the regeneration mode. Total energy recovery has increase and power losses have decreases because inverter abilities to transfer the surplus energy back to the main AC supply. An Inverter controller with PWM Generator and PI Voltage Regulator has been designed to control voltage magnitude and frequency of the DC traction system.

Maruhn-Greiner Maximum of Uranium Fission for Confirmation of Low Energy Nuclear Reactions LENR via a Compound Nucleus with Double Magic Numbers

NASA Astrophysics Data System (ADS)

Hora, H.; Miley, G. H.

2007-12-01

One of the most convincing facts about LENR due to deuterons of very high concentration in host metals as palladium is the measurement of the large scale minimum of the reaction probability depending on the nucleon number A of generated elements at A = 153 where a local maximum was measured. This is similar to the fission of uranium at A = 119 where the local maximum follows from the Maruhn-Greiner theory if the splitting nuclei are excited to about MeV energy. The LENR generated elements can be documented any time after the reaction by SIMS or K-shell X-ray excitation to show the very unique distribution with the local maximum. An explanation is based on the strong Debye screening of the Maxwellian deuterons within the degenerate rigid electron background especially within the swimming electron layer at the metal surface or at interfaces. The deuterons behave like neutrals at distances of about 2 picometers. They may form clusters due to soft attraction in the range above thermal energy. Clusters of 10 pm diameter may react over long time probabilities (megaseconds) with Pd nuclei leading to a double magic number compound nucleus which splits like in fission to the A = 153 element distribution.

Measurement Of Gas Electron Multiplier (GEM) Detector Characteristics

NASA Astrophysics Data System (ADS)

Park, Seongtae; Baldelomar, Edwin; Park, Kwangjune; Sosebee, Mark; White, Andy; Yu, Jaehoon

2011-06-01

The High Energy Physics group of the University of Texas at Arlington has been developing gas electron multiplier detectors to use them as sensitive gap detectors in digital hadron calorimeters for the International Linear Collider, a future high energy particle accelerator. For this purpose, we constructed numerous GEM detectors that employ double GEM layers. In this study, two kinds of prototype GEM detectors were tested; one with 28×28 cm2 active area double GEM structure with a 3 mm drift gap, a 1 mm transfer gap and a 1 mm induction gap and the other with two 3×3 cm2 GEM foils in the amplifier stage with a 5 mm drift gap, a 2 mm transfer gap and a 1 mm induction gap. The detectors' characteristics from exposure to high-energy charged particles and other radiations were measured using cosmic rays and 55Fe radioactive source. From the 55Fe tests, we observed two well separated characteristic X-ray emission peaks and confirmed the detectors' functionality. We also measured chamber gains to be over 6000 at a high voltage of 395 V across each GEM electrode. The responses to cosmic rays show the spectra that fit well to Landau distributions as expected from minimum ionizing particles.

Probing the structural evolution of ruthenium doped germanium clusters: Photoelectron spectroscopy and density functional theory calculations

PubMed Central

Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun

2016-01-01

We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen− (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen− clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen−/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters. PMID:27439955

Rank restriction for the variational calculation of two-electron reduced density matrices of many-electron atoms and molecules

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

Naftchi-Ardebili, Kasra; Hau, Nathania W.; Mazziotti, David A.

2011-11-15

Variational minimization of the ground-state energy as a function of the two-electron reduced density matrix (2-RDM), constrained by necessary N-representability conditions, provides a polynomial-scaling approach to studying strongly correlated molecules without computing the many-electron wave function. Here we introduce a route to enhancing necessary conditions for N representability through rank restriction of the 2-RDM. Rather than adding computationally more expensive N-representability conditions, we directly enhance the accuracy of two-particle (2-positivity) conditions through rank restriction, which removes degrees of freedom in the 2-RDM that are not sufficiently constrained. We select the rank of the particle-hole 2-RDM by deriving the ranks associatedmore » with model wave functions, including both mean-field and antisymmetrized geminal power (AGP) wave functions. Because the 2-positivity conditions are exact for quantum systems with AGP ground states, the rank of the particle-hole 2-RDM from the AGP ansatz provides a minimum for its value in variational 2-RDM calculations of general quantum systems. To implement the rank-restricted conditions, we extend a first-order algorithm for large-scale semidefinite programming. The rank-restricted conditions significantly improve the accuracy of the energies; for example, the percentages of correlation energies recovered for HF, CO, and N{sub 2} improve from 115.2%, 121.7%, and 121.5% without rank restriction to 97.8%, 101.1%, and 100.0% with rank restriction. Similar results are found at both equilibrium and nonequilibrium geometries. While more accurate, the rank-restricted N-representability conditions are less expensive computationally than the full-rank conditions.« less

DETERMINING MINIMUM IGNITION ENERGIES AND QUENCHING DISTANCES OF DIFFICULT-TO-IGNITE COMPOUNDS

EPA Science Inventory

Minimum spark energies and corresponding flat-plate electrode quenching distances required to initiate propagation of a combustion wave have been experimentally measured for four flammable hydrofluorocarbon (HFC) refrigerants and propane using ASTM (American Society for Testing a...

Growth of calcium phosphates on magnesium substrates for corrosion control in biomedical applications via immersion techniques.

PubMed

Shadanbaz, Shaylin; Walker, Jemimah; Staiger, Mark P; Dias, George J; Pietak, Alexis

2013-01-01

Magnesium (Mg) has been suggested as a revolutionary biodegradable replacement for current permanent metals used in orthopedic applications. Current investigations concentrate on the control of the corrosion rate to match bone healing. Calcium phosphate coatings have been a recent focus of these investigations through various coating protocols. Within this investigation, an in situ crystallization technique was utilized as an inexpensive and relatively simple method to produce a brushite and monetite coating on pure Mg. Coatings were characterized using energy dispersive spectroscopy, glancing angle X-ray diffraction and field emission scanning electron microscopy. Corrosion protection properties of the coatings were assessed in physiological buffers, Earles balanced salt solution, minimum essential media, and minimum essential media containing serum albumin, over a 4-week period. Using this novel coating protocol, our findings indicate brushite and monetite coated Mg to have significant corrosive protective effects when compared with its uncoated counterpart whilst maintaining high coating substrate adhesion, homogeneity, and reproducibility. Copyright © 2012 Wiley Periodicals, Inc.

Glass Forming Ability in Systems with Competing Orderings

NASA Astrophysics Data System (ADS)

Russo, John; Romano, Flavio; Tanaka, Hajime

2018-04-01

Some liquids, if cooled rapidly enough to avoid crystallization, can be frozen into a nonergodic glassy state. The tendency for a material to form a glass when quenched is called "glass-forming ability," and it is of key significance both fundamentally and for materials science applications. Here, we consider liquids with competing orderings, where an increase in the glass-forming ability is signaled by a depression of the melting temperature towards its minimum at triple or eutectic points. With simulations of two model systems where glass-forming ability can be tuned by an external parameter, we are able to interpolate between crystal-forming and glass-forming behavior. We find that the enhancement of the glass-forming ability is caused by an increase in the structural difference between liquid and crystal: stronger competition in orderings towards the melting point minimum makes a liquid structure more disordered (more complex). This increase in the liquid-crystal structure difference can be described by a single adimensional parameter, i.e., the interface energy cost scaled by the thermal energy, which we call the "thermodynamic interface penalty." Our finding may provide a general physical principle for not only controlling the glass-forming ability but also the emergence of glassy behavior of various systems with competing orderings, including orderings of structural, magnetic, electronic, charge, and dipolar origin.

Non-Adiabatic Effects on Excited States of Vinylidene Observed with Slow Photoelectron Velocity-Map Imaging.

PubMed

DeVine, Jessalyn A; Weichman, Marissa L; Zhou, Xueyao; Ma, Jianyi; Jiang, Bin; Guo, Hua; Neumark, Daniel M

2016-12-21

High-resolution slow photoelectron velocity-map imaging spectra of cryogenically cooled X̃ 2 B 2 H 2 CC - and D 2 CC - in the region of the vinylidene triplet excited states are reported. Three electronic bands are observed and, with the assistance of electronic structure calculations and quantum dynamics on ab initio-based near-equilibrium potential energy surfaces, are assigned as detachment to the [Formula: see text] 3 B 2 (T 1 ), b̃ 3 A 2 (T 2 ), and à 1 A 2 (S 1 ) excited states of neutral vinylidene. This work provides the first experimental observation of the à singlet excited state of H 2 CC. While regular vibrational structure is observed for the ã and à electronic bands, a number of irregular features are resolved in the vicinity of the b̃ band vibrational origin. High-level ab initio calculations suggest that this anomalous structure arises from a conical intersection between the ã and b̃ triplet states near the b̃ state minimum, which strongly perturbs the vibrational levels in the two electronic states through nonadiabatic coupling. Using the adiabatic electron affinity of H 2 CC previously measured to be 0.490(6) eV by Ervin and co-workers [J. Chem. Phys. 1989, 91, 5974], term energies for the excited neutral states of H 2 CC are found to be T 0 (ã 3 B 2 ) = 2.064(6), T 0 (b̃ 3 A 2 ) = 2.738(6), and T 0 (à 1 A 2 ) = 2.991(6) eV.

Magnetic fields in Supernova Remnants and Pulsar-Wind Nebulae: Deductions from X-ray Observations

NASA Astrophysics Data System (ADS)

Reynolds, S. P.

2016-06-01

Magnetic field strengths B in synchrotron sources are notoriously difficult to measure. Simple arguments such as equipartition of energy can give values for which the total energy is a minimum, but there is no guarantee that Nature obeys it, or even if so, what particle population (just electrons? electrons plus ions?) should have an energy density comparable to that in magnetic field. However, the operation of synchrotron losses can provide additional information, if those losses are manifested in the synchrotron spectra as steepenings of the spectral-energy distribution above some characteristic frequency often called a "break" (though it is more typically a gradual curvature). A source of known age, if it has been accelerating particles continuously, will have such a break above the energy at which particle radiative lifetimes equal the source age, and this can give B. However, in spatially resolved sources such as supernova remnants (SNRs) and pulsar-wind nebulae (PWNe), systematic advection of particles, if at a known rate, gives a second measure of particle age to compare with radiative lifetimes. In most young SNRs, synchrotron X-rays make a contribution to the X-ray spectrum, and are usually found in thin rims at the remnant edges. If the rims are thin in the radial direction due to electron energy losses, a magnetic-field strength can be estimated. I present recent modeling of this process, along with models in which rims are thin due to decay of magnetic turbulence, and apply them to the remnants of SN 1006 and Tycho. In PWNe, outflows of relativistic plasma behind the pulsar wind termination shock are likely quite inhomogeneous, so magnetic-field estimates based on source lifetimes and assuming spatial uniformity can give misleading values for B. I shall discuss inhomogeneous PWN models and the effects they can have on B estimates.

Poster — Thur Eve — 26: Evaluation of lens dose from anterior electron beams: comparison of Pinnacle and Gafchromic EBT3 film

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

Sanier, M; Wronski, M; Yeboah, C

The purpose of this work is twofold: 1) to measure dose profiles under lead shielding at the level of the lens for a range of clinical electron energies via film dosimetry; and, 2) to assess the validity of the Pinnacle treatment planning system (TPS) in calculating the penumbral doses under lead shielding with the heterogeneous electron algorithm. First, a film calibration curve that spanned the electron energies of interest, 6–18MeV, was created. Next, EBT3 film and lead shielding were incorporated into a solid water phantom with the film positioned 7mm below the lead and a variable thickness of bolus onmore » top. This geometry was reproduced in the Pinnacle TPS and used to calculate dose profiles using the heterogeneous electron algorithm. The measured vs. calculated dose profiles were normalized to d{sub max} in a homogeneous phantom with no lead shielding and compared. Pinnacle consistently overestimated the dose distal to the lead shielding with significant discrepancies occurring near the edge of the lead shield reaching 25% at the edge and 35% in the open field region. The film measurements showed that a minimum lead margin of 5mm extending beyond the diameter of the lens is required to adequately shield the lens to ≤10% of the dose at d{sub max}. These measurements allow for a reasonable estimate of the dose to the lens from anterior electron beams. They also allow for clinicians to assess the extent of the lead margin required to reduce the lens dose to an acceptable amount prior to radiotherapy treatment.« less

A statistical study of the inner edge of the electron plasma sheet and the net convection potential as a function of geomagnetic activity

NASA Astrophysics Data System (ADS)

Jiang, F.; Kivelson, M. G.; Walker, R. J.; Khurana, K. K.; Angelopoulos, V.; Hsu, T.

2011-06-01

A widely accepted explanation of the location of the inner edge of the electron plasma sheet and its dependence on electron energy is based on drift motions of individual particles. The boundary is identified as the separatrix between drift trajectories linking the tail to the dayside magnetopause (open paths) and trajectories closed around the Earth. A statistical study of the inner edge of the electron plasma sheet using THEMIS Electrostatic Analyzer plasma data from November 2007 to April 2009 enabled us to examine this model. Using a dipole magnetic field and a Volland-Stern electric field with shielding, we find that a steady state drift boundary model represents the average location of the electron plasma sheet boundary and reflects its variation with the solar wind electric field in the local time region between 21:00 and 06:00, except at high activity levels. However, the model does not reproduce the observed energy dispersion of the boundaries. We have also used the location of the inner edge of the electron plasma sheet to parameterize the potential drop of the tail convection electric field as a function of solar wind electric field (Esw) and geomagnetic activity. The range of Esw examined is small because the data were acquired near solar minimum. For the range of values tested (meaningful statistics only for Esw < 2 mV/m), reasonably good agreement is found between the potential drop of the tail convection electric field inferred from the location of the inner edge and the polar cap potential drop calculated from the model of Boyle et al. (1997).

Fragment charge difference method for estimating donor-acceptor electronic coupling: Application to DNA π-stacks

NASA Astrophysics Data System (ADS)

Voityuk, Alexander A.; Rösch, Notker

2002-09-01

The purpose of this communication is two-fold. We introduce the fragment charge difference (FCD) method to estimate the electron transfer matrix element HDA between a donor D and an acceptor A, and we apply this method to several aspects of hole transfer electronic couplings in π-stacks of DNA, including systems with several donor-acceptor sites. Within the two-state model, our scheme can be simplified to recover a convenient estimate of the electron transfer matrix element HDA=(1-Δq2)1/2(E2-E1)/2 based on the vertical excitation energy E2-E1 and the charge difference Δq between donor and acceptor. For systems with strong charge separation, Δq≳0.95, one should resort to the FCD method. As favorable feature, we demonstrate the stability of the FCD approach for systems which require an approach beyond the two-state model. On the basis of ab initio calculations of various DNA related systems, we compared three approaches for estimating the electronic coupling: the minimum splitting method, the generalized Mulliken-Hush (GMH) scheme, and the FCD approach. We studied the sensitivity of FCD and GMH couplings to the donor-acceptor energy gap and found both schemes to be quite robust; they are applicable also in cases where donor and acceptor states are off resonance. In the application to π-stacks of DNA, we demonstrated for the Watson-Crick pair dimer [(GC),(GC)] how structural changes considerably affect the coupling strength of electron hole transfer. For models of three Watson-Crick pairs, we showed that the two-state model significantly overestimates the hole transfer coupling whereas simultaneous treatment of several states leads to satisfactory results.

Energy-efficient algorithm for broadcasting in ad hoc wireless sensor networks.

PubMed

Xiong, Naixue; Huang, Xingbo; Cheng, Hongju; Wan, Zheng

2013-04-12

Broadcasting is a common and basic operation used to support various network protocols in wireless networks. To achieve energy-efficient broadcasting is especially important for ad hoc wireless sensor networks because sensors are generally powered by batteries with limited lifetimes. Energy consumption for broadcast operations can be reduced by minimizing the number of relay nodes based on the observation that data transmission processes consume more energy than data reception processes in the sensor nodes, and how to improve the network lifetime is always an interesting issue in sensor network research. The minimum-energy broadcast problem is then equivalent to the problem of finding the minimum Connected Dominating Set (CDS) for a connected graph that is proved NP-complete. In this paper, we introduce an Efficient Minimum CDS algorithm (EMCDS) with help of a proposed ordered sequence list. EMCDS does not concern itself with node energy and broadcast operations might fail if relay nodes are out of energy. Next we have proposed a Minimum Energy-consumption Broadcast Scheme (MEBS) with a modified version of EMCDS, and aimed at providing an efficient scheduling scheme with maximized network lifetime. The simulation results show that the proposed EMCDS algorithm can find smaller CDS compared with related works, and the MEBS can help to increase the network lifetime by efficiently balancing energy among nodes in the networks.

Minimum energy control for in vitro neurons.

PubMed

Nabi, Ali; Stigen, Tyler; Moehlis, Jeff; Netoff, Theoden

2013-06-01

To demonstrate the applicability of optimal control theory for designing minimum energy charge-balanced input waveforms for single periodically-firing in vitro neurons from brain slices of Long-Evans rats. The method of control uses the phase model of a neuron and does not require prior knowledge of the neuron's biological details. The phase model of a neuron is a one-dimensional model that is characterized by the neuron's phase response curve (PRC), a sensitivity measure of the neuron to a stimulus applied at different points in its firing cycle. The PRC for each neuron is experimentally obtained by measuring the shift in phase due to a short-duration pulse injected into the periodically-firing neuron at various phase values. Based on the measured PRC, continuous-time, charge-balanced, minimum energy control waveforms have been designed to regulate the next firing time of the neuron upon application at the onset of an action potential. The designed waveforms can achieve the inter-spike-interval regulation for in vitro neurons with energy levels that are lower than those of conventional monophasic pulsatile inputs of past studies by at least an order of magnitude. They also provide the advantage of being charge-balanced. The energy efficiency of these waveforms is also shown by performing several supporting simulations that compare the performance of the designed waveforms against that of phase shuffled surrogate inputs, variants of the minimum energy waveforms obtained from suboptimal PRCs, as well as pulsatile stimuli that are applied at the point of maximum PRC. It was found that the minimum energy waveforms perform better than all other stimuli both in terms of control and in the amount of energy used. Specifically, it was seen that these charge-balanced waveforms use at least an order of magnitude less energy than conventional monophasic pulsatile stimuli. The significance of this work is that it uses concepts from the theory of optimal control and introduces a novel approach in designing minimum energy charge-balanced input waveforms for neurons that are robust to noise and implementable in electrophysiological experiments.

Minimum energy control for in vitro neurons

NASA Astrophysics Data System (ADS)

Nabi, Ali; Stigen, Tyler; Moehlis, Jeff; Netoff, Theoden

2013-06-01

Objective. To demonstrate the applicability of optimal control theory for designing minimum energy charge-balanced input waveforms for single periodically-firing in vitro neurons from brain slices of Long-Evans rats. Approach. The method of control uses the phase model of a neuron and does not require prior knowledge of the neuron’s biological details. The phase model of a neuron is a one-dimensional model that is characterized by the neuron’s phase response curve (PRC), a sensitivity measure of the neuron to a stimulus applied at different points in its firing cycle. The PRC for each neuron is experimentally obtained by measuring the shift in phase due to a short-duration pulse injected into the periodically-firing neuron at various phase values. Based on the measured PRC, continuous-time, charge-balanced, minimum energy control waveforms have been designed to regulate the next firing time of the neuron upon application at the onset of an action potential. Main result. The designed waveforms can achieve the inter-spike-interval regulation for in vitro neurons with energy levels that are lower than those of conventional monophasic pulsatile inputs of past studies by at least an order of magnitude. They also provide the advantage of being charge-balanced. The energy efficiency of these waveforms is also shown by performing several supporting simulations that compare the performance of the designed waveforms against that of phase shuffled surrogate inputs, variants of the minimum energy waveforms obtained from suboptimal PRCs, as well as pulsatile stimuli that are applied at the point of maximum PRC. It was found that the minimum energy waveforms perform better than all other stimuli both in terms of control and in the amount of energy used. Specifically, it was seen that these charge-balanced waveforms use at least an order of magnitude less energy than conventional monophasic pulsatile stimuli. Significance. The significance of this work is that it uses concepts from the theory of optimal control and introduces a novel approach in designing minimum energy charge-balanced input waveforms for neurons that are robust to noise and implementable in electrophysiological experiments.

Energetic constraints on life in deep marine sediments

NASA Astrophysics Data System (ADS)

Amend, J.; LaRowe, D.

2013-12-01

Microorganisms are abundant in deep-sea sediments, but what percentage of cells is active, how fast do they grow, and what factors control their diversity and population size? Geochemical modelling of redox reaction energetics can help in answering these questions. Calculations of Gibbs energies reveal which reactions are thermodynamically possible, but they also highlight which geochemical variables (e.g., temperature, pressure, pH, composition) may control microbial activity and how the amount and type of biomass are affected by energy limitations. We will discuss recent results from sediment cores collected at the Peru Margin (active continental shelf with high primary productivity and significant organic matter accumulation), the South Pacific Gyre (ultra-slow sedimentation rate and low organic carbon content), and the Juan de Fuca Ridge flank (high rate of sedimentation influenced by hydrothermal circulation). However, this approach to evaluating bioenergetic potential and predicting microbial activity can be applied to any environment where the geochemistry is well characterized, even if microbiology data have not been collected. When Gibbs energies are calculated on a basis of per mole of electrons transferred (as is commonly done), aerobic oxidation of hydrogen and organic matter in South Pacific Gyre sediments is the most exergonic. Based on this, one might posit that the fastest catabolic rates and the largest biomass would be found there. However, cell counts at Juan de Fuca and the Peru Margin are several orders of magnitude higher. When recast as energy densities (in J per cm3 of sediment), we observe far more energy available in sediments at Juan de Fuca and the Peru Margin than at those in the South Pacific Gyre. We also note that the identity of the most exergonic reaction changes with depth, suggesting corresponding changes in the microbial community structure. The thermodynamic approach used here for energy supply can also be used for energy demand, including the often-considered minimum or threshold energy, also referred to as the biological energy quantum. Based on this energetic minimum theory, many reactions cannot support microbial communities because their energy yield is apparently too low. However, we show that when evaluated as energy densities, some energetically ';impossible' catabolisms become ';possible' and vice versa.

Conformationally controlled ultrafast intersystem crossing in bithiophene systems.

PubMed

Skov, Anders B; Larsen, Martin A B; Liisberg, Mikkel B; Hansen, Thorsten; Sølling, Theis I

2018-05-16

Bithiophenes serve as model systems for larger polythiophenes used in solar cell applications and molecular electronics. We report a study of ultrafast dynamics of two bithiophene systems measured with femtosecond time-resolved photoelectron spectroscopy, and show that their intersystem crossing takes place within the first few picoseconds after excitation, in line with previous studies. We show that the intersystem crossing rate can be explained in terms of arguments based on symmetry of the S1 minimum energy geometry, which depends on the specific conformation of bithiophene. Furthermore, this work shows that the minor cis-conformer contributes to an even higher intersystem crossing rate than the major trans conformer. The work presented here can provide guiding principles towards the design of solar cell components with even faster formation of long-lived excited states for solar energy harvesting.

First-principles study on electron transport properties of carbon-silicon mixed chains

NASA Astrophysics Data System (ADS)

Hu, Wei; Zhou, Qinghua; Liang, Yan; Liu, Wenhua; Wang, Tao; Wan, Haiqing

2018-03-01

In this paper, the transport properties of carbon-silicon mixed chains are studied by using the first-principles. We studied five atomic chain models. In these studies, we found that the equilibrium conductances of atomic chains appear to oscillate, the maximum conductance and the minimum conductance are more than twice the difference. Their I-V curves are linear and show the behavior of metal resistance, M5 system and M2 system current ratio is the largest in 0.9 V, which is 3.3, showing a good molecular switch behavior. In the case of bias, while the bias voltage increases, the transmission peaks move from the Fermi level. The resonance transmission peak height is reduced near the Fermi level. In the higher energy range, a large resonance transmission peak reappears, there is still no energy cut-off range.

Simulation of demand-response power management in smart city

NASA Astrophysics Data System (ADS)

Kadam, Kshitija

Smart Grids manage energy efficiently through intelligent monitoring and control of all the components connected to the electrical grid. Advanced digital technology, combined with sensors and power electronics, can greatly improve transmission line efficiency. This thesis proposed a model of a deregulated grid which supplied power to diverse set of consumers and allowed them to participate in decision making process through two-way communication. The deregulated market encourages competition at the generation and distribution levels through communication with the central system operator. A software platform was developed and executed to manage the communication, as well for energy management of the overall system. It also demonstrated self-healing property of the system in case a fault occurs, resulting in an outage. The system not only recovered from the fault but managed to do so in a short time with no/minimum human involvement.

Field-orientation dependence of low-energy quasiparticle excitations in the heavy-electron superconductor UBe(13).

PubMed

Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Haga, Yoshinori; Yamamoto, Etsuji; Amitsuka, Hiroshi; Tsutsumi, Yasumasa; Machida, Kazushige

2015-04-10

Low-energy quasiparticle excitations in the superconducting (SC) state of UBe_{13} were studied by means of specific-heat (C) measurements in a rotating field. Quite unexpectedly, the magnetic-field dependence of C(H) is linear in H with no angular dependence at low fields in the SC state, implying that the gap is fully open over the Fermi surfaces, in stark contrast to previous expectations. In addition, a characteristic cubic anisotropy of C(H) was observed above 2 T with a maximum (minimum) for H∥[001] ([111]) within the (11[over ¯]0) plane, in the normal as well as in the SC states. This oscillation possibly originates from the anisotropic response of the heavy quasiparticle bands, and might be a key to understand the unusual properties of UBe_{13}.

Ni doping effect on the electronic and sensing properties of 2D SnO2

NASA Astrophysics Data System (ADS)

Patel, Anjali; Roondhe, Basant; Jha, Prafulla K.

2018-05-01

In the present work using state of art first principles calculations under the frame work of density functional theory the effect of Nickel (Ni) doping on electronic as well as sensing properties of most stable two dimensional (2D) T-SnO2 phase towards ethanol (C2H5OH) has been observed. It has been found that Ni atom when dope on T-SnO2 causes prominent decrement in the band gap from 2.26 eV to 1.48 eV and improves the sensing phenomena of pristine T-SnO2 towards C2H5OH by increasing the binding energy from -0.18eV to -0.93eV. The comparative analysis of binding energy shows that Ni improves the binding of C2H5OH by 5.16 times the values for pristine T-SnO2. The doping of Ni into 2D T-SnO2 reduces the band gap through lowering of the conduction band minimum, thereby increasing the electron affinity which increases the sensing performance of T-SnO2. The variation in the electronic properties after and before the exposure of ethanol reinforced to use Ni:SnO2 nano structure for sensing applications. The results indicate that the Ni doped T-SnO2 can be utilized in improved optoelectronic as well as sensor devices in the future.

Energy Minimization of Discrete Protein Titration State Models Using Graph Theory.

PubMed

Purvine, Emilie; Monson, Kyle; Jurrus, Elizabeth; Star, Keith; Baker, Nathan A

2016-08-25

There are several applications in computational biophysics that require the optimization of discrete interacting states, for example, amino acid titration states, ligand oxidation states, or discrete rotamer angles. Such optimization can be very time-consuming as it scales exponentially in the number of sites to be optimized. In this paper, we describe a new polynomial time algorithm for optimization of discrete states in macromolecular systems. This algorithm was adapted from image processing and uses techniques from discrete mathematics and graph theory to restate the optimization problem in terms of "maximum flow-minimum cut" graph analysis. The interaction energy graph, a graph in which vertices (amino acids) and edges (interactions) are weighted with their respective energies, is transformed into a flow network in which the value of the minimum cut in the network equals the minimum free energy of the protein and the cut itself encodes the state that achieves the minimum free energy. Because of its deterministic nature and polynomial time performance, this algorithm has the potential to allow for the ionization state of larger proteins to be discovered.

Energy Minimization of Discrete Protein Titration State Models Using Graph Theory

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

Purvine, Emilie AH; Monson, Kyle E.; Jurrus, Elizabeth R.

There are several applications in computational biophysics which require the optimization of discrete interacting states; e.g., amino acid titration states, ligand oxidation states, or discrete rotamer angles. Such optimization can be very time-consuming as it scales exponentially in the number of sites to be optimized. In this paper, we describe a new polynomial-time algorithm for optimization of discrete states in macromolecular systems. This algorithm was adapted from image processing and uses techniques from discrete mathematics and graph theory to restate the optimization problem in terms of maximum flow-minimum cut graph analysis. The interaction energy graph, a graph in which verticesmore » (amino acids) and edges (interactions) are weighted with their respective energies, is transformed into a flow network in which the value of the minimum cut in the network equals the minimum free energy of the protein, and the cut itself encodes the state that achieves the minimum free energy. Because of its deterministic nature and polynomial-time performance, this algorithm has the potential to allow for the ionization state of larger proteins to be discovered.« less

Energy Minimization of Discrete Protein Titration State Models Using Graph Theory

PubMed Central

Purvine, Emilie; Monson, Kyle; Jurrus, Elizabeth; Star, Keith; Baker, Nathan A.

2016-01-01

There are several applications in computational biophysics which require the optimization of discrete interacting states; e.g., amino acid titration states, ligand oxidation states, or discrete rotamer angles. Such optimization can be very time-consuming as it scales exponentially in the number of sites to be optimized. In this paper, we describe a new polynomial-time algorithm for optimization of discrete states in macromolecular systems. This algorithm was adapted from image processing and uses techniques from discrete mathematics and graph theory to restate the optimization problem in terms of “maximum flow-minimum cut” graph analysis. The interaction energy graph, a graph in which vertices (amino acids) and edges (interactions) are weighted with their respective energies, is transformed into a flow network in which the value of the minimum cut in the network equals the minimum free energy of the protein, and the cut itself encodes the state that achieves the minimum free energy. Because of its deterministic nature and polynomial-time performance, this algorithm has the potential to allow for the ionization state of larger proteins to be discovered. PMID:27089174

Equilibrium Droplets on Deformable Substrates: Equilibrium Conditions.

PubMed

Koursari, Nektaria; Ahmed, Gulraiz; Starov, Victor M

2018-05-15

Equilibrium conditions of droplets on deformable substrates are investigated, and it is proven using Jacobi's sufficient condition that the obtained solutions really provide equilibrium profiles of both the droplet and the deformed support. At the equilibrium, the excess free energy of the system should have a minimum value, which means that both necessary and sufficient conditions of the minimum should be fulfilled. Only in this case, the obtained profiles provide the minimum of the excess free energy. The necessary condition of the equilibrium means that the first variation of the excess free energy should vanish, and the second variation should be positive. Unfortunately, the mentioned two conditions are not the proof that the obtained profiles correspond to the minimum of the excess free energy and they could not be. It is necessary to check whether the sufficient condition of the equilibrium (Jacobi's condition) is satisfied. To the best of our knowledge Jacobi's condition has never been verified for any already published equilibrium profiles of both the droplet and the deformable substrate. A simple model of the equilibrium droplet on the deformable substrate is considered, and it is shown that the deduced profiles of the equilibrium droplet and deformable substrate satisfy the Jacobi's condition, that is, really provide the minimum to the excess free energy of the system. To simplify calculations, a simplified linear disjoining/conjoining pressure isotherm is adopted for the calculations. It is shown that both necessary and sufficient conditions for equilibrium are satisfied. For the first time, validity of the Jacobi's condition is verified. The latter proves that the developed model really provides (i) the minimum of the excess free energy of the system droplet/deformable substrate and (ii) equilibrium profiles of both the droplet and the deformable substrate.

Neutral and charged gallium clusters: structures, physical properties and implications for the melting features

NASA Astrophysics Data System (ADS)

Núñez, Sara; López, José M.; Aguado, Andrés

2012-09-01

We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims.We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims. Electronic supplementary information (ESI) available: Atomic coordinates (in xyz format and Å units) and point group symmetries for the global minimum structures reported in this paper. See DOI: 10.1039/c2nr31222k

Minimum energy dissipation required for a logically irreversible operation

NASA Astrophysics Data System (ADS)

Takeuchi, Naoki; Yoshikawa, Nobuyuki

2018-01-01

According to Landauer's principle, the minimum heat emission required for computing is linked to logical entropy, or logical reversibility. The validity of Landauer's principle has been investigated for several decades and was finally demonstrated in recent experiments by showing that the minimum heat emission is associated with the reduction in logical entropy during a logically irreversible operation. Although the relationship between minimum heat emission and logical reversibility is being revealed, it is not clear how much free energy is required to be dissipated for a logically irreversible operation. In the present study, in order to reveal the connection between logical reversibility and free energy dissipation, we numerically demonstrated logically irreversible protocols using adiabatic superconductor logic. The calculation results of work during the protocol showed that, while the minimum heat emission conforms to Landauer's principle, the free energy dissipation can be arbitrarily reduced by performing the protocol quasistatically. The above results show that logical reversibility is not associated with thermodynamic reversibility, and that heat is not only emitted from logic devices but also absorbed by logic devices. We also formulated the heat emission from adiabatic superconductor logic during a logically irreversible operation at a finite operation speed.

Concentrated energy addition for active drag reduction in hypersonic flow regime

NASA Astrophysics Data System (ADS)

Ashwin Ganesh, M.; John, Bibin

2018-01-01

Numerical optimization of hypersonic drag reduction technique based on concentrated energy addition is presented in this study. A reduction in wave drag is realized through concentrated energy addition in the hypersonic flowfield upstream of the blunt body. For the exhaustive optimization presented in this study, an in-house high precision inviscid flow solver has been developed. Studies focused on the identification of "optimum energy addition location" have revealed the existence of multiple minimum drag points. The wave drag coefficient is observed to drop from 0.85 to 0.45 when 50 Watts of energy is added to an energy bubble of 1 mm radius located at 74.7 mm upstream of the stagnation point. A direct proportionality has been identified between energy bubble size and wave drag coefficient. Dependence of drag coefficient on the upstream added energy magnitude is also revealed. Of the observed multiple minimum drag points, the energy deposition point (EDP) that offers minimum wave drag just after a sharp drop in drag is proposed as the most optimum energy addition location.

Energy deposition by heavy ions: Additivity of kinetic and potential energy contributions in hillock formation on CaF2

PubMed Central

Wang, Y. Y.; Grygiel, C.; Dufour, C.; Sun, J. R.; Wang, Z. G.; Zhao, Y. T.; Xiao, G. Q.; Cheng, R.; Zhou, X. M.; Ren, J. R.; Liu, S. D.; Lei, Y.; Sun, Y. B.; Ritter, R.; Gruber, E.; Cassimi, A.; Monnet, I.; Bouffard, S.; Aumayr, F.; Toulemonde, M.

2014-01-01

Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5 MeV) highly charged ions (Xe22+ to Xe30+) as well as swift (kinetic energies between 12 and 58 MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface. PMID:25034006

Energy deposition by heavy ions: additivity of kinetic and potential energy contributions in hillock formation on CaF2.

PubMed

Wang, Y Y; Grygiel, C; Dufour, C; Sun, J R; Wang, Z G; Zhao, Y T; Xiao, G Q; Cheng, R; Zhou, X M; Ren, J R; Liu, S D; Lei, Y; Sun, Y B; Ritter, R; Gruber, E; Cassimi, A; Monnet, I; Bouffard, S; Aumayr, F; Toulemonde, M

2014-07-18

Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5 MeV) highly charged ions (Xe(22+) to Xe(30+)) as well as swift (kinetic energies between 12 and 58 MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface.

Conformational analysis and circular dichroism of bilirubin, the yellow pigment of jaundice

NASA Astrophysics Data System (ADS)

Lightner, David A.; Person, Richard; Peterson, Blake; Puzicha, Gisbert; Pu, Yu-Ming; Bojadziev, Stefan

1991-06-01

Conformational analysis of (4Z, 15Z)-bilirubin-IX(alpha) by molecular mechanics computations reveals a global energy minimum folded conformation. Powerful added stabilization is achieved through intramolecular hydrogen bonding. Theoretical treatment of bilirubin as a molecular exciton predicts an intense bisignate circular dichroism spectrum for the folded conformation: (Delta) (epsilon) is congruent to 270 L (DOT) mole-1 (DOT) cm-1 for the $OM450 nm electronic transition(s). Synthesis of bilirubin analogs with propionic acid groups methylated at the (alpha) or (beta) position introduces an allosteric effect that allows for an optical resolution of the pigments, with enantiomers exhibiting the theoretically predicted circular dichroism.

Inorganic resist materials based on zirconium phosphonate for atomic force microscope lithography

NASA Astrophysics Data System (ADS)

Kang, Mankyu; Kim, Seonae; Jung, JinHyuck; Kim, Heebom; Shin, Inkyun; Jeon, Chanuk; Lee, Haiwon

2014-03-01

New inorganic resist materials based on metal complexes were investigated for atomic force microscope (AFM) lithography. Phosphoric acids are good for self-assembly because of their strong binding energy. In this work, zirconium phosphonate system are newly synthesized for spin-coatable materials in aqueous solutions and leads to negative tone pattern for improving line edge roughness. Low electron exposure by AFM lithography could generate a pattern by electrochemical reaction and cross-linking of metal-oxo complexes. It has been reported that the minimum pattern results are affected by lithographic speed, and the applied voltage between a tip and a substrate.

Electrocontact material based on silver dispersion-strengthened by nickel, titanium, and zinc oxides

NASA Astrophysics Data System (ADS)

Zeer, G. M.; Zelenkova, E. G.; Belousov, O. V.; Beletskii, V. V.; Nikolaev, S. V.; Ledyaeva, O. N.

2017-09-01

Samples of a composite electrocontact material based on silver strengthened by the dispersed phases of zinc and titanium oxides have been investigated by the electron microscopy and energy dispersive X-ray spectroscopy. A uniform distribution of the oxide phases containing 2 wt % zinc oxide in the initial charge has been revealed. The increase in the amount of zinc oxide leads to an increase of the size of the oxide phases. It has been shown that at the zinc oxide content of 2 wt %, the minimum wear is observed in the process of electroerosion tests; at 3 wt %, an overheating and welding of the contacts are observed.

Angular distribution measurement of fragment ions from a molecule using a new beamline consisting of a Grasshopper monochromator

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

Saito, N.; Suzuki, I. H.; Onuki, H.

1989-07-01

Optical characteristics of a new beamline consisting of a premirror, a Grasshopper monochromator, and a refocusing mirror have been investigated. The intensity of the monochromatic soft x-ray was estimated to be about 10/sup 8/ photons/(s 100 mA) at 500 eV with the storage electron energy of 600 MeV and the minimum slit width. This slit width provides a resolution of about 500. Angular distributions of fragment ions from an inner-shell excited nitrogen molecule have been measured with a rotatable time-of-flight mass spectrometer by using this beamline.

Ni-Mn-Ga shape memory nanoactuation

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

Kohl, M., E-mail: manfred.kohl@kit.edu; Schmitt, M.; Krevet, B.

2014-01-27

To probe finite size effects in ferromagnetic shape memory nanoactuators, double-beam structures with minimum dimensions down to 100 nm are designed, fabricated, and characterized in-situ in a scanning electron microscope with respect to their coupled thermo-elastic and electro-thermal properties. Electrical resistance and mechanical beam bending tests demonstrate a reversible thermal shape memory effect down to 100 nm. Electro-thermal actuation involves large temperature gradients along the nanobeam in the order of 100 K/μm. We discuss the influence of surface and twin boundary energies and explain why free-standing nanoactuators behave differently compared to constrained geometries like films and nanocrystalline shape memory alloys.

Ni-Mn-Ga shape memory nanoactuation

NASA Astrophysics Data System (ADS)

Kohl, M.; Schmitt, M.; Backen, A.; Schultz, L.; Krevet, B.; Fähler, S.

2014-01-01

To probe finite size effects in ferromagnetic shape memory nanoactuators, double-beam structures with minimum dimensions down to 100 nm are designed, fabricated, and characterized in-situ in a scanning electron microscope with respect to their coupled thermo-elastic and electro-thermal properties. Electrical resistance and mechanical beam bending tests demonstrate a reversible thermal shape memory effect down to 100 nm. Electro-thermal actuation involves large temperature gradients along the nanobeam in the order of 100 K/μm. We discuss the influence of surface and twin boundary energies and explain why free-standing nanoactuators behave differently compared to constrained geometries like films and nanocrystalline shape memory alloys.

Ab initio molecular dynamics simulations of AlN responding to low energy particle radiation

DOE PAGES

Xi, Jianqi; Liu, Bin; Zhang, Yanwen; ...

2018-01-30

Ab initio molecular dynamics simulations of low energy recoil events in wurtzite AlN have been performed to determine threshold displacement energies, defect production and evolution mechanisms, role of partial charge transfer during the process, and the influence of irradiation-induced defects on the properties of AlN. Here, the results show that the threshold displacement energies, E d, along the direction parallel to the basal planes are smaller than those perpendicular to the basal planes. The minimum E d values are determined to be 19 eV and 55 eV for N and Al atom, respectively, which occur along the [more » $$\\overline{11}20$$] direction. In general, the threshold displacement energies for N are smaller than those for Al atom, indicating the N defects would be dominant under irradiation. The defect production mechanisms have been analyzed. It is found that charge transfer and redistribution for both the primary knock-on atom and the subsequent recoil atoms play a significant role in defect production and evolution. Similar to the trend in oxide materials, there is a nearly linear relationship between E d and the total amount of charge transfer at the potential energy peak in AlN, which provides guidance on the development of charge-transfer interatomic potentials for classic molecular dynamics simulations. Finally, the response behavior of AlN to low energy irradiation is qualitatively investigated. The existence of irradiation-induced defects significantly modifies the electronic structure, and thus affects the magnetic, electronic and optical properties of AlN. In conclusion, these findings further enrich the understanding of defects in the wide bandgap semiconductor of AlN.« less

Ab initio molecular dynamics simulations of AlN responding to low energy particle radiation

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

Xi, Jianqi; Liu, Bin; Zhang, Yanwen

Ab initio molecular dynamics simulations of low energy recoil events in wurtzite AlN have been performed to determine threshold displacement energies, defect production and evolution mechanisms, role of partial charge transfer during the process, and the influence of irradiation-induced defects on the properties of AlN. Here, the results show that the threshold displacement energies, E d, along the direction parallel to the basal planes are smaller than those perpendicular to the basal planes. The minimum E d values are determined to be 19 eV and 55 eV for N and Al atom, respectively, which occur along the [more » $$\\overline{11}20$$] direction. In general, the threshold displacement energies for N are smaller than those for Al atom, indicating the N defects would be dominant under irradiation. The defect production mechanisms have been analyzed. It is found that charge transfer and redistribution for both the primary knock-on atom and the subsequent recoil atoms play a significant role in defect production and evolution. Similar to the trend in oxide materials, there is a nearly linear relationship between E d and the total amount of charge transfer at the potential energy peak in AlN, which provides guidance on the development of charge-transfer interatomic potentials for classic molecular dynamics simulations. Finally, the response behavior of AlN to low energy irradiation is qualitatively investigated. The existence of irradiation-induced defects significantly modifies the electronic structure, and thus affects the magnetic, electronic and optical properties of AlN. In conclusion, these findings further enrich the understanding of defects in the wide bandgap semiconductor of AlN.« less

Influence of cathode geometry on electron dynamics in an ultrafast electron microscope.

PubMed

Ji, Shaozheng; Piazza, Luca; Cao, Gaolong; Park, Sang Tae; Reed, Bryan W; Masiel, Daniel J; Weissenrieder, Jonas

2017-09-01

Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover.

Influence of cathode geometry on electron dynamics in an ultrafast electron microscope

PubMed Central

Ji, Shaozheng; Piazza, Luca; Cao, Gaolong; Park, Sang Tae; Reed, Bryan W.; Masiel, Daniel J.; Weissenrieder, Jonas

2017-01-01

Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover. PMID:28781982

Potential energy surface and quantum dynamics study of rovibrational states for HO(3) (X (2)A'').

PubMed

Braams, Bastiaan J; Yu, Hua-Gen

2008-06-07

An analytic potential energy surface has been constructed by fitting to about 28 thousand energy points for the electronic ground-state (X (2)A'') of HO(3). The energy points are calculated using a hybrid density functional HCTH and a large basis set aug-cc-pVTZ, i.e., a HCTH/aug-cc-pVTZ density functional theory (DFT) method. The DFT calculations show that the trans-HO(3) isomer is the global minimum with a potential well depth of 9.94 kcal mol(-1) with respect to the OH + O(2) asymptote. The equilibrium geometry of the cis-HO(3) conformer is located 1.08 kcal mol(-1) above that of the trans-HO(3) one with an isomerization barrier of 2.41 kcal mol(-1) from trans- to cis-HO(3). By using this surface, a rigorous quantum dynamics (QD) study has been carried out for computing the rovibrational energy levels of HO(3). The calculated results determine a dissociation energy of 6.15 kcal mol(-1), which is in excellent agreement with the experimental value of Lester et al. [J. Phys. Chem. A, 2007, 111, 4727.].

Effect of ageing on precipitation and impact energy of 2101 economical duplex stainless steel

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

Zhang Wei; College of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200240; Jiang Laizhu

2009-01-15

The impact energy and microstructure of a thermally aged 2101 duplex stainless steel with composition of Fe-21.4Cr-1.2Ni-5.7Mn-0.23 N-0.31Mo were studied. The results showed that the room temperature impact energy of specimens decreased gradually with ageing temperature up to 700 deg. C and then increased with aging over 700 deg. C. The minimum value of impact energy was 37 J after 700 deg. C aging, which was only 34% of that for as-annealed specimens. For specimens aged at 700 deg. C, the room temperature impact energy decreased significantly after 3 min and was halved after 10 min. Fractographs showed that, withmore » increasing aging time, the fracture morphology changed from fibrous fracture to transgranular and intragranular fracture. Scanning electron micrographs revealed that many precipitates were distributed along {alpha}/{gamma} and {alpha}/{alpha} interfaces. The precipitates were extracted and confirmed by X-ray diffraction to be Cr{sub 2}N. Therefore, it can be concluded that precipitation of Cr{sub 2}N is the main reason for the decrease of impact energy in aged 2101 duplex stainless steel.« less

Possible explanation of the solar-neutrino puzzle

NASA Technical Reports Server (NTRS)

Bethe, H. A.

1986-01-01

A new derivation of the Mikheyev and Smirnov (1985) mechanism for the conversion of electron neutrinos into mu neutrinos when traversing the sun is presented, and various hypotheses set forth. It is assumed that this process is responsible for the detection of fewer solar neutrinos than expected, with neutrinos below a minimum energy, E(m), being undetectable. E(m) is found to be about 6 MeV, and the difference of the squares of the respective neutrino masses is calculated to be 6 X 10 to the - 5th sq eV. A restriction on the neutrino mixing angle is assumed such that the change of density near the crossing point is adiabatic. It is predicted that no resonance conversion of neutrinos will occur in the dense core of supernovae, but conversion of electron neutrinos to mu neutrinos will occur as they escape outward through a density region around 100.

Plasmon-induced artificial photosynthesis

PubMed Central

Ueno, Kosei; Oshikiri, Tomoya; Shi, Xu; Zhong, Yuqing; Misawa, Hiroaki

2015-01-01

We have successfully developed a plasmon-induced artificial photosynthesis system that uses a gold nanoparticle-loaded oxide semiconductor electrode to produce useful chemical energy as hydrogen and ammonia. The most important feature of this system is that both sides of a strontium titanate single-crystal substrate are used without an electrochemical apparatus. Plasmon-induced water splitting occurred even with a minimum chemical bias of 0.23 V owing to the plasmonic effects based on the efficient oxidation of water and the use of platinum as a co-catalyst for reduction. Photocurrent measurements were performed to determine the electron transfer between the gold nanoparticles and the oxide semiconductor. The efficiency of water oxidation was determined through spectroelectrochemical experiments aimed at elucidating the electron density in the gold nanoparticles. A set-up similar to the water-splitting system was used to synthesize ammonia via nitrogen fixation using ruthenium instead of platinum as a co-catalyst. PMID:26052419

First-principles simulation on thermoelectric propertiesof transition metal dichalcogenide monolayers

NASA Astrophysics Data System (ADS)

Nakamura, Koichi

2018-06-01

Thermoelectric properties of transition metal dichalcogenide (TMDC) monolayer models, such as Seebeck coefficient and lattice heat capacity, were simulated on the basis of first-principles calculations. The calculated Seebeck coefficients are appropriate for the thermoelectric element of all the TMDC monolayer models introduced in this study. In the MoX2/WX2 (X = S, Se, and Te) heterojunction structure, carrier electrons and holes are respectively distributed in the MoX2 and WX2 regions by adopting a common Fermi energy for both electronic structures. In particular, in the X = Te case, the practical carrier concentration with a large Seebeck coefficient can be evaluated without doping. The lattice heat capacities and their temperature dependence tendencies can be classified on the basis of the minimum frequencies of the optical modes. The quotient of the lattice thermal conductivity over the phonon relaxation time gives the temperature-independent specific values according to the kind of TMDC monolayer.

Angle-resolved photoemission observation of Mn-pnictide hybridization and negligible band structure renormalization in BaMn 2 As 2 and BaMn 2 Sb 2

DOE PAGES

Zhang, W. -L.; Richard, P.; van Roekeghem, A.; ...

2016-10-31

We performed an angle-resolved photoemission spectroscopy study of BaMn 2As 2 and BaMn 2Sb 2, which are isostructural to the parent compound BaFe 2As 2 of the 122 family of ferropnictide superconductors. We show the existence of a strongly k z-dependent band gap with a minimum at the Brillouin zone center, in agreement with their semiconducting properties. Despite the half filling of the electronic 3d shell, we show that the band structure in these materials is almost not renormalized from the Kohn-Sham bands of density functional theory. Finally, our photon-energy-dependent study provides evidence for Mn-pnictide hybridization, which may play amore » role in tuning the electronic correlations in these compounds.« less

Three-dimensional graphdiyne as a topological nodal-line semimetal

NASA Astrophysics Data System (ADS)

Nomura, Takafumi; Habe, Tetsuro; Sakamoto, Ryota; Koshino, Mikito

2018-05-01

We study the electronic band structure of three-dimensional ABC-stacked (rhombohedral) graphdiyne, which is a new planar carbon allotrope recently fabricated. Using first-principles calculation, we show that the system is a nodal-line semimetal, in which the conduction band and valence band cross at a closed ring in the momentum space. We derive the minimum tight-binding model and the low-energy effective Hamiltonian in a 4 ×4 matrix form. The nodal line is protected by a nontrivial winding number, and it ensures the existence of the topological surface state in a finite-thickness slab. The Fermi surface of the doped system exhibits a peculiar, self-intersecting hourglass structure, which is quite different from the torus or pipe shape in the previously proposed nodal semimetals. Despite its simple configuration, three-dimensional graphdiyne offers unique electronic properties distinct from any other carbon allotropes.

Information dynamics in living systems: prokaryotes, eukaryotes, and cancer.

PubMed

Frieden, B Roy; Gatenby, Robert A

2011-01-01

Living systems use information and energy to maintain stable entropy while far from thermodynamic equilibrium. The underlying first principles have not been established. We propose that stable entropy in living systems, in the absence of thermodynamic equilibrium, requires an information extremum (maximum or minimum), which is invariant to first order perturbations. Proliferation and death represent key feedback mechanisms that promote stability even in a non-equilibrium state. A system moves to low or high information depending on its energy status, as the benefit of information in maintaining and increasing order is balanced against its energy cost. Prokaryotes, which lack specialized energy-producing organelles (mitochondria), are energy-limited and constrained to an information minimum. Acquisition of mitochondria is viewed as a critical evolutionary step that, by allowing eukaryotes to achieve a sufficiently high energy state, permitted a phase transition to an information maximum. This state, in contrast to the prokaryote minima, allowed evolution of complex, multicellular organisms. A special case is a malignant cell, which is modeled as a phase transition from a maximum to minimum information state. The minimum leads to a predicted power-law governing the in situ growth that is confirmed by studies measuring growth of small breast cancers. We find living systems achieve a stable entropic state by maintaining an extreme level of information. The evolutionary divergence of prokaryotes and eukaryotes resulted from acquisition of specialized energy organelles that allowed transition from information minima to maxima, respectively. Carcinogenesis represents a reverse transition: of an information maximum to minimum. The progressive information loss is evident in accumulating mutations, disordered morphology, and functional decline characteristics of human cancers. The findings suggest energy restriction is a critical first step that triggers the genetic mutations that drive somatic evolution of the malignant phenotype.

Growth and analysis of gallium arsenide-gallium antimonide single and two-phase nanoparticles

NASA Astrophysics Data System (ADS)

Schamp, Crispin T.

When evaluating the path of phase transformations in systems with nanoscopic dimensions one often relies on bulk phase diagrams for guidance because of the lack of phase diagrams that show the effect of particle size. The GaAs-GaSb pseudo-binary alloy is chosen for study to gain insight into the size dependence of solid-solubility in a two-phase system. To this end, a study is performed using independent laser ablation of high purity targets of GaAs and GaSb. The resultant samples are analyzed by transmission electron microscopy. Experimental results indicate that GaAs-GaSb nanoparticles have been formed with compositions that lie within the miscibility gap of bulk GaAs-GaSb. An unusual nanoparticle morpohology resembling the appearance of ice cream cones has been observed in single component experiments. These particles are composed of a spherical cap of Ga in contact with a crystalline cone of either GaAs or GaSb. The cones take the projected 2-D shape of a triangle or a faceted gem. The liquid Ga is found to consistently be of spherical shape and wets to the widest corners of the cone, suggesting an energy minimum exists at that wetting condition. To explore this observation a liquid sphere is modeled as being penetrated by a solid gem. The surface energies of the solid and liquid, and interfacial energy are summed as a function of penetration depth, with the sum showing a cusped minimum at the penetration depth corresponding to the waist of the gem. The angle of contact of the liquid wetting the cone is also calculated, and Young's contact angle is found to occur when the derivative of the total energy with respect to penetration depth is zero, which can be a maximum or a minimum depending on the geometrical details. The spill-over of the meniscus across the gem corners is found to be energetically favorable when the contact angle achieves the value of the equilibrium angle; otherwise the meniscus is pinned at the corners.

Spectroscopic, Homo-Lumo and NLO studies of tetra fluoro phthalate doped Coumarin crystals using DFT method

NASA Astrophysics Data System (ADS)

Latha, B.; Kumaresan, P.; Nithiyanantham, S.; Sampathkumar, K.

2017-08-01

In the present examination, a methodical study has been done on the development of unadulterated and Coumarin doped Tetrafluoro Phthalate precious stones. Powder X-beam diffraction studies were done and the cross section parameters were computed by minimum square technique in pure and doped crystals. FT-IR, UV-Vis, Thermal, Micro-hardness and Dielectric studies were additionally done for the pure and doped crystals. The tentatively watched FT-IR and FT-Raman groups were allotted to various ordinary methods of the atom. The steadiness and charge delocalization of the particle were likewise concentrations were done by characteristic security orbital (NBO) examination. The HOMO-LUMO energies depict the charge exchange happens inside the particle. Atomic electrostatic potential has been broken down the electronic properties such as excitation energies, oscillator quality, wavelengths and HOMO-LUMO energies were acquired by time-subordinate DFT (TD-DFT) approach. The SHG of pure and doped TFP stones were examined through Nd:YAG Q-exchanged laser.

Efficient Steplike Carrier Multiplication in Percolative Networks of Epitaxially Connected PbSe Nanocrystals

DOE PAGES

Kulkarni, Aditya; Evers, Wiel H.; Tomic, Stanko; ...

2017-12-14

Here, carrier multiplication (CM) is a process in which a single photon excites two or more electrons. CM is of interest to enhance the efficiency of a solar cell. Until now, CM in thin films and solar cells of semiconductor nanocrystals (NCs) has been found at photon energies well above the minimum required energy of twice the band gap. The high threshold of CM strongly limits the benefits for solar cell applications. We show that CM is more efficient in a percolative network of directly connected PbSe NCs. The CM threshold is at twice the band gap and increases inmore » a steplike fashion with photon energy. A lower CM efficiency is found for a solid of weaker coupled NCs. This demonstrates that the coupling between NCs strongly affects the CM efficiency. According to device simulations, the measured CM efficiency would significantly enhance the power conversion efficiency of a solar cell.« less

Dissociative Ionization of Aromatic and Heterocyclic Molecules

NASA Technical Reports Server (NTRS)

Huo, Winifred M.

2003-01-01

Space radiation poses a major health hazard to humans in space flight. The high-energy charged particles in space radiation ranging from protons to high atomic number, high-energy (HZE) particles, and the secondary species they produce, attack DNA, cells, and tissues. Of the potential hazards, long-term health effects such as carcinogenesis are likely linked to the DNA lesions caused by secondary electrons in the 1 - 30 eV range. Dissociative ionization (DI) is one of the electron collision processes that can damage the DNA, either directly by causing a DNA lesion, or indirectly by producing radicals and cations that attack the DNA. To understand this process, we have developed a theoretical model for DI. Our model makes use of the fact that electron motion is much faster than nuclear motion and assumes DI proceeds through a two-step process. The first step is electron-impact ionization resulting in a particular state of the molecular ion in the geometry of the neutral molecule. In the second step the ion undergoes unimolecular dissociation. Thus the DI cross section sigma(sup DI)(sub a) for channel a is given by sigma(sup DI)(sub a) = sigma(sup I)(sub a) P(sub D) with sigma(sup I)(sub a) the ionization cross section of channel a and P(sub D) the dissociation probability. This model has been applied to study the DI of H2O, NH3, and CH4, with results in good agreement with experiment. The ionization cross section sigma(sup I)(sub a) was calculated using the improved binary encounter-dipole model and the unimolecular dissociation probability P(sub D) obtained by following the minimum energy path determined by the gradients and Hessians of the electronic energy with respect to the nuclear coordinates of the ion. This model is used to study the DI from the low-lying channels of benzene and pyridine to understand the different product formation in aromatic and heterocyclic molecules. DI study of the DNA base thymine is underway. Solvent effects will also be discussed.

Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation

NASA Astrophysics Data System (ADS)

Ahmadi, N.; Wilder, F. D.; Usanova, M.; Ergun, R.; Argall, M. R.; Goodrich, K.; Eriksson, S.; Germaschewski, K.; Torbert, R. B.; Lindqvist, P. A.; Le Contel, O.; Khotyaintsev, Y. V.; Strangeway, R. J.; Schwartz, S. J.; Giles, B. L.; Burch, J.

2017-12-01

The Magnetospheric Multiscale (MMS) mission observed electron whistler waves at the center and at the gradients of magnetic holes on the dayside magnetosheath. The magnetic holes are nonlinear mirror structures which are anti-correlated with particle density. We used expanding box Particle-in-cell simulations and produced the mirror instability magnetic holes. We show that the electron whistler waves can be generated at the gradients and the center of magnetic holes in our simulations which is in agreement with MMS observations. At the nonlinear regime of mirror instability, the proton and electron temperature anisotropy are anti-correlated with the magnetic hole. The plasma is unstable to electron whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are dominant, electron temperature anisotropy develops at the edges of the magnetic holes and electrons become isotropic at the magnetic field minimum. We investigate the possible mechanism for enhancing the electron temperature anisotropy and analyze the electron pitch angle distributions and electron distribution functions in our simulations and compare it with MMS observations.

Production, Thermalization and Transport of Photoelectrons in the Mars Environment

NASA Astrophysics Data System (ADS)

Mitchell, D. L.; Xu, S.; Mazelle, C. X.; Steckiewicz, M.; Luhmann, J. G.; Connerney, J. E. P.; Andersson, L.

2016-12-01

The Solar Wind Electron Analyzer (SWEA) on the MAVEN spacecraft provides a detailed look at the production, thermalization, and transport of photoelectrons in the Mars environment. The MAVEN orbit routinely samples altitudes down to 150 km over wide ranges of solar zenith angle, local time, longitude, latitude and altitude. The altitude range extends into the region of photochemical equilibrium. SWEA's nominal energy resolution of 17% (ΔE/E, FWHM) is insufficient to resolve the photoelectron peaks at 23 and 27 eV, which result from photoionization of CO2 and O by the intense He II line in the solar EUV spectrum. However, during some orbits the spacecraft charged to -18 V near periapsis, which shifted the He II photoelectron features to lower energies, thus allowing them to be resolved. During several week-long deep dip campaigns, the periapsis altitude was lowered to 120 km. Thermalization of primary photoelectrons is very rapid at this altitude, resulting in a residual population at 7 eV, where the cross section to interaction with CO2 has a minimum. At altitudes above the 200 km, collisions become negligible (mean free path > 100 km), and the motion of suprathermal electrons is controlled by the magnetic field. Electron energy-pitch angle distributions reveal transport of photoelectrons from the day to the night hemisphere on both closed crustal magnetic loops and on open lines that extend into the tail. Mapping of such open field lines reveals the regions of the tail with access to the day-side ionosphere, which provide a conduit for ion outflow and loss.

Characteristics of Pitch Angle Distributions of 100s Kev Electrons in the Slot Region and Inner Radiation Belt­­­­­­­­

NASA Astrophysics Data System (ADS)

Zhao, H.; Li, X.; Blake, J. B.; Fennell, J.; Claudepierre, S. G.; Baker, D. N.; Jaynes, A. N.; Malaspina, D.

2014-12-01

The pitch angle distribution (PAD) of energetic electrons in the slot region and inner radiation belt received little attention in the past decades due to the lack of quality measurements. Using the state-of-art pitch-angle-resolved data from the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard the Van Allen Probes, a detailed analysis of 100s keV electron PADs below L =4 is performed, in which the PADs is categorized into three types: normal (flux peaking at 90°), cap (exceedingly peaking narrowly around 90°) and 90°-minimum (lower flux at 90°) PADs. By examining the characteristics of the PADs of 460 keV electrons for over a year, we find that the 90°-minimum PADs are generally present in the inner belt (L<2), while normal PADs dominate at L~3.5-4. In the region between, 90°-minimum PADs dominate during injection times and normal PADs dominate during quiet times. Cap PADs appear mostly at the decay phase of storms in the slot region and are likely caused by the pitch angle scattering of hiss waves. Fitting the normal PADs into sinnα form, the parameter n is much higher below L=3 than that in the outer belt and relatively constant in the inner belt but changes significantly in the slot region (2

What have we learned about the energetic particle dynamics in the inner belt and slot region from Van Allen Probes and CSSWE missions?

NASA Astrophysics Data System (ADS)

Li, Xinlin; Baker, Daniel N.; Kanekal, Shrikanth; Fennell, Joseph; Selesnick, Richard; Claudepierre, Seth; Blake, Bernard; Zhao, Hong; Jaynes, Allison

2016-07-01

Comprehensive measurements of energetic protons (10s of MeV) in the inner belt (L<2) and slot region (21.6 MeV) measurements cannot be distinguished from the background. Analysis on sub-MeV electrons data in the inner belt and slot region from the Magnetic Electron Ion Spectrometer (MagEIS) on board Van Allen Probes revealed rather complicated pitch angle distribution of these energetic electrons, with the 90 deg-minimum (butterfly) pitch angle distribution dominating near the magnetic equator. These are part of a summary of the most recent measurements and understanding of the dynamics of energetic particles in the inner zone and slot region to be exhibited and discussed in this presentation.

Communication: An accurate global potential energy surface for the ground electronic state of ozone

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

Dawes, Richard, E-mail: dawesr@mst.edu, E-mail: hguo@unm.edu; Lolur, Phalgun; Li, Anyang

We report a new full-dimensional and global potential energy surface (PES) for the O + O{sub 2} → O{sub 3} ozone forming reaction based on explicitly correlated multireference configuration interaction (MRCI-F12) data. It extends our previous [R. Dawes, P. Lolur, J. Ma, and H. Guo, J. Chem. Phys. 135, 081102 (2011)] dynamically weighted multistate MRCI calculations of the asymptotic region which showed the widely found submerged reef along the minimum energy path to be the spurious result of an avoided crossing with an excited state. A spin-orbit correction was added and the PES tends asymptotically to the recently developed long-rangemore » electrostatic model of Lepers et al. [J. Chem. Phys. 137, 234305 (2012)]. This PES features: (1) excellent equilibrium structural parameters, (2) good agreement with experimental vibrational levels, (3) accurate dissociation energy, and (4) most-notably, a transition region without a spurious reef. The new PES is expected to allow insight into the still unresolved issues surrounding the kinetics, dynamics, and isotope signature of ozone.« less

Perspectives: Black Holes

NASA Technical Reports Server (NTRS)

Dolan, Joseph F.; Fisher, Richard R. (Technical Monitor)

2001-01-01

When asked to discuss Cyg XR-1, E. E. Salpeter once concluded, 'A black hole in Cyg X(R)-1 is the most conservative hypothesis.' Recent observations now make it likely that a black hole in Cyg XR-1 is the only hypothesis tenable. Chandrasekhar first showed that compact stars - those with the inward force of gravity on their outer layers balanced by the pressure generated by the Pauli exclusion principle acting on its electrons (in white dwarfs) or nucleons (in neutron stars) - have a maximum mass. Equilibrium is achieved at a minimum of the total energy of the star, which is the sum of the positive Fermi energy and the negative gravitational energy. The maximum mass attainable in equilibrium is found by setting E = 0: M(max) = 1.5 M(Sun). If the mass of the star is larger than this, then E can be decreased without bound by decreasing the star's radius and increasing its (negative) gravitational energy. No equilibrium value of the radius exist, and general relativity predicts that gravitational collapse to a point occurs. This point singularity is a black hole.

Development of a Multicenter Density Functional Tight Binding Model for Plutonium Surface Hydriding.

PubMed

Goldman, Nir; Aradi, Bálint; Lindsey, Rebecca K; Fried, Laurence E

2018-05-08

We detail the creation of a multicenter density functional tight binding (DFTB) model for hydrogen on δ-plutonium, using a framework of new Slater-Koster interaction parameters and a repulsive energy based on the Chebyshev Interaction Model for Efficient Simulation (ChIMES), where two- and three-center atomic interactions are represented by linear combinations of Chebyshev polynomials. We find that our DFTB/ChIMES model yields a total electron density of states for bulk δ-Pu that compares well to that from Density Functional Theory, as well as to a grid of energy calculations representing approximate H 2 dissociation paths on the δ-Pu (100) surface. We then perform molecular dynamics simulations and minimum energy pathway calculations to determine the energetics of surface dissociation and subsurface diffusion on the (100) and (111) surfaces. Our approach allows for the efficient creation of multicenter repulsive energies with a relatively small investment in initial DFT calculations. Our efforts are particularly pertinent to studies that rely on quantum calculations for interpretation and validation, such as experimental determination of chemical reactivity both on surfaces and in condensed phases.

The electron affinity of Al13H cluster: high level ab initio study

NASA Astrophysics Data System (ADS)

Moc, Jerzy

2014-11-01

Al13H clusters have been considered candidates for cluster assembled materials. Here we have carried out benchmark calculations for the Al13H cluster, both neutral and anionic, with the aim of verifying the nature of stationary points on the potential energy surface, studying dynamics of H atom and determining an adiabatic electron affinity. A range of correlated methods applied include second-order perturbation theory (MP2), spin-component-scaled MP2, coupled electron pair (CEPA) and coupled cluster singles and doubles with perturbative triple corrections (CCSD(T)). These methods are used in combination with the correlation consistent basis sets through aug-cc-pVTZ including extrapolation to the complete basis set (CBS) limit. Performance of several different flavours of density functional theory (DFT) such as generalised gradient approximation (GGA), hybrid GGA, meta-GGA and hybrid-meta-GGA is assessed with respect to the ab initio correlated reference data. The harmonic force constant analysis is systematically performed with the MP2 and DFT methods. The MP2 results show that for neutral Al13H only the hollow structure is a potential energy minimum, with the bridged structure being a transition state for the H shift from the hollow site to the adjacent hollow site. The CCSD(T)/aug-cc-pVTZ (CCSD(T)/CBS) estimate of the energy barrier to this H shift is 2.6 (2.9) kcal/mol, implying that the H atom movement over the Al13H cluster surface is facile. By contrast, the DFT force constant analysis results suggest additional terminal and bridged minima structures. For the anion Al13H-, exhibiting 'stiffer' potential energy surface compared to the neutral, the existence of the hollow and terminal isomers is consistent with the earlier photoelectron spectroscopy assignment. The adiabatic electron affinity of Al13H is determined to be 2.00 and 1.95 eV (the latter including the ΔZPE correction) based on the CCSD(T) energies extrapolated to the CBS limit, whereas the respective CCSD(T)/CBS thermodynamic EA values are 2.79 and 2.80 eV.

Design of BAs-AlN monolayered honeycomb heterojunction structures: A first-principles study

NASA Astrophysics Data System (ADS)

Camacho-Mojica, Dulce C.; López-Urías, Florentino

2016-04-01

BAs and AlN are semiconductor materials with an indirect and direct gap respectively in the bulk phase. Recently, electronic calculations have demonstrated that a single-layer or few layers of BAs and AlN exhibit a graphite-like structure with interesting electronic properties. In this work, infinite sheets single-layer heterojunction structures based on alternated strips with honeycomb BAs and AlN layers are investigated using first-principles density functional theory calculations. Optimized geometries, density of states, band-gaps, formation energies, and wave functions are studied for different strip widths joined along zigzag and armchair edges. Results in optimized heterojunction geometries revealed that BAs narrow strips exhibit a corrugation effect due to a lattice mismatch. It was found that zigzag heterojunctions are more energetically favored than armchair heterojunctions. Furthermore, the formation energy presents a maximum at the point where the heterojunction becomes a planar structure. Electronic charge density results yielded a more ionic behavior in Alsbnd N bonds than the Bsbnd As bonds in accordance with monolayer results. It was observed that the conduction band minimum for both heterojunctions exhibit confined states located mainly at the entire AlN strips whereas the valence band maximum exhibits confined states located mainly at BAs strips. We expect that the present investigation will motivate more experimental and theoretical studies on new layered materials made of III-V semiconductors.

Electronic properties of functionalized (5,5) beryllium oxide nanotubes.

PubMed

Chigo Anota, Ernesto; Cocoletzi, Gregorio Hernández

2013-05-01

Using the density functional theory (DFT) we study the structural and electronic properties of functionalized (5,5) chirality single wall beryllium oxide nanotubes (SW-BeONTs), i.e. armchair nanotubes. The nanotube surface and ends are functionalized by the hydroxyl (OH) functional group. Our calculations consider the Hamprecht-Cohen-Tozer-Handy functional in the generalized gradient approximation (HCTH-GGA) to deal with the exchange-correlation energies, and the base function with double polarization (DNP). The geometry optimization of both defects free and with point defects nanotubes is done applying the criterion of minimum energy. Six configurations are considered: The OH oriented toward the Be (on the surface and at the end), toward the O (on the surface and at the end) and placed at the nanotube ends. Simulation results show that the nanotube functionalization takes place at the nanotube ends with the BeO bond displaying hydrogen-like bridge bonds. Moreover the nanotube semiconductor behavior remains unchanged. The polarity is high (it shows a transition from covalent to ionic) favoring solvatation. On the other hand, the work function low value suggests this to be a good candidate for the device fabrication. When the nanotube contains surface point defects the work function is reduced which provides excellent possibilities for the use of this material in the electronic industry. Copyright © 2013 Elsevier Inc. All rights reserved.

Wireless sensors powered by microbial fuel cells.

PubMed

Shantaram, Avinash; Beyenal, Haluk; Raajan, Raaja; Veluchamy, Angathevar; Lewandowski, Zbigniew

2005-07-01

Monitoring parameters characterizing water quality, such as temperature, pH, and concentrations of heavy metals in natural waters, is often followed by transmitting the data to remote receivers using telemetry systems. Such systems are commonly powered by batteries, which can be inconvenient at times because batteries have a limited lifetime and must be recharged or replaced periodically to ensure that sufficient energy is available to power the electronics. To avoid these inconveniences, a microbial fuel cell was designed to power electrochemical sensors and small telemetry systems to transmit the data acquired by the sensors to remote receivers. The microbial fuel cell was combined with low-power, high-efficiency electronic circuitry providing a stable power source for wireless data transmission. To generate enough power for the telemetry system, energy produced by the microbial fuel cell was stored in a capacitor and used in short bursts when needed. Since commercial electronic circuits require a minimum 3.3 V input and our cell was able to deliver a maximum of 2.1 V, a DC-DC converter was used to boost the potential. The DC-DC converter powered a transmitter, which gathered the data from the sensor and transmitted it wirelessly to a remote receiver. To demonstrate the utility of the system, temporal variations in temperature were measured, and the data were wirelessly transmitted to a remote receiver.

An Investigation of Low Earth Orbit Internal Charging

NASA Technical Reports Server (NTRS)

NeergaardParker, Linda; Minow, Joseph I.; Willis, Emily M.

2014-01-01

Low Earth orbit is usually considered a relatively benign environment for internal charging threats due to the low flux of penetrating electrons with energies of a few MeV that are encountered over an orbit. There are configurations, however, where insulators and ungrounded conductors used on the outside of a spacecraft hull may charge when exposed to much lower energy electrons of some 100's keV in a process that is better characterized as internal charging than surface charging. For example, the minimal radiation shielding afforded by thin thermal control materials such as metalized polymer sheets (e.g., aluminized Kapton or Mylar) and multilayer insulation may allow electrons of 100's of keV to charge underlying materials. Yet these same thermal control materials protect the underlying insulators and ungrounded conductors from surface charging currents due to electrons and ions at energies less than a few keV as well as suppress the photoemission, secondary electron, and backscattered electron processes associated with surface charging. We investigate the conditions required for this low Earth orbit "internal charging" to occur and evaluate the environments for which the process may be a threat to spacecraft. First, we describe a simple one-dimensional internal charging model that is used to compute the charge accumulation on materials under thin shielding. Only the electron flux that penetrates exposed surface shielding material is considered and we treat the charge balance in underlying insulation as a parallel plate capacitor accumulating charge from the penetrating electron flux and losing charge due to conduction to a ground plane. Charge dissipation due to conduction can be neglected to consider the effects of charging an ungrounded conductor. In both cases, the potential and electric field is computed as a function of time. An additional charge loss process is introduced due to an electrostatic discharge current when the electric field reaches a prescribed breakdown strength. For simplicity, the amount of charge lost in the discharge is treated as a random percentage of the total charge between a set maximum and minimum amount so a user can consider partial discharges of insulating materials (small loss of charge) or arcing from a conductor (large loss of charge). We apply the model to electron flux measurements from the NOAA-19 spacecraft to demonstrate that charging can reach levels where electrostatic discharges occur and estimate the magnitude of the discharge.

Improved kinetic neoclassical transport calculation for a low-collisionality QH-mode pedestal

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

Battaglia, D. J.; Burrell, K. H.; Chang, C. S.

The role of neoclassical, anomalous and neutral transport to the overall H-mode pedestal and scrape-off layer (SOL) structure in an ELM-free QH-mode discharge on DIII-D is explored using XGC0, a 5D full-f multi-species particle-in-cell drift-kinetic solver with self-consistent neutral recycling and sheath potentials. The work in this paper builds on previous work aimed at achieving quantitative agreement between the flux-driven simulation and the experimental electron density, impurity density and orthogonal measurements of impurity temperature and flow profiles. Improved quantitative agreement is achieved by performing the calculations with a more realistic electron mass, larger neutral density and including finite-Larmor-radius corrections self-consistentlymore » in the drift-kinetic motion of the particles. Consequently, the simulations provide stronger evidence that the radial electric field (E r) in the pedestal is primarily established by the required balance between the loss of high-energy tail main ions against a pinch of colder main ions and impurities. The kinetic loss of a small population of ions carrying a large proportion of energy and momentum leads to a separation of the particle and energy transport rates and introduces a source of intrinsic edge torque. Ion orbit loss and finite orbit width effects drive the energy distributions away from Maxwellian, and describe the anisotropy, poloidal asymmetry and local minimum near the separatrix observed in the T i profile.« less

Improved kinetic neoclassical transport calculation for a low-collisionality QH-mode pedestal

DOE PAGES

Battaglia, D. J.; Burrell, K. H.; Chang, C. S.; ...

2016-07-15

The role of neoclassical, anomalous and neutral transport to the overall H-mode pedestal and scrape-off layer (SOL) structure in an ELM-free QH-mode discharge on DIII-D is explored using XGC0, a 5D full-f multi-species particle-in-cell drift-kinetic solver with self-consistent neutral recycling and sheath potentials. The work in this paper builds on previous work aimed at achieving quantitative agreement between the flux-driven simulation and the experimental electron density, impurity density and orthogonal measurements of impurity temperature and flow profiles. Improved quantitative agreement is achieved by performing the calculations with a more realistic electron mass, larger neutral density and including finite-Larmor-radius corrections self-consistentlymore » in the drift-kinetic motion of the particles. Consequently, the simulations provide stronger evidence that the radial electric field (E r) in the pedestal is primarily established by the required balance between the loss of high-energy tail main ions against a pinch of colder main ions and impurities. The kinetic loss of a small population of ions carrying a large proportion of energy and momentum leads to a separation of the particle and energy transport rates and introduces a source of intrinsic edge torque. Ion orbit loss and finite orbit width effects drive the energy distributions away from Maxwellian, and describe the anisotropy, poloidal asymmetry and local minimum near the separatrix observed in the T i profile.« less

The wet solidus of silica: predictions from the scaled particle theory and polarized continuum model.

PubMed

Ottonello, G; Richet, P; Vetuschi Zuccolini, M

2015-02-07

We present an application of the Scaling Particle Theory (SPT) coupled with an ab initio assessment of the electronic, dispersive, and repulsive energy terms based on the Polarized Continuum Model (PCM) aimed at reproducing the observed solubility behavior of OH2 over the entire compositional range from pure molten silica to pure water and wide pressure and temperature regimes. It is shown that the solution energy is dominated by cavitation terms, mainly entropic in nature, which cause a large negative solution entropy and a consequent marked increase of gas phase fugacity with increasing temperatures. Besides, the solution enthalpy is negative and dominated by electrostatic terms which depict a pseudopotential well whose minimum occurs at a low water fraction (XH2O) of about 6 mol. %. The fine tuning of the solute-solvent interaction is achieved through very limited adjustments of the electrostatic scaling factor γel which, in pure water, is slightly higher than the nominal value (i.e., γel  =  1.224 against 1.2), it attains its minimum at low H2O content (γel = 0.9958) and then rises again at infinite dilution (γel   =  1.0945). The complex solution behavior is interpreted as due to the formation of energetically efficient hydrogen bonding when OH functionals are in appropriate amount and relative positioning with respect to the discrete OH2 molecules, reinforcing in this way the nominal solute-solvent inductive interaction. The interaction energy derived from the SPT-PCM calculations is then recast in terms of a sub-regular Redlich-Kister expansion of appropriate order whereas the thermodynamic properties of the H2O component at its standard state (1-molal solution referred to infinite dilution) are calculated from partial differentiation of the solution energy over the intensive variables.

Defects responsible for abnormal n-type conductivity in Ag-excess doped PbTe thermoelectrics

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

Ryu, Byungki, E-mail: byungkiryu@keri.re.kr; Lee, Jae Ki; Lee, Ji Eun

Density functional calculations have been performed to investigate the role of Ag defects in PbTe thermoelectric materials. Ag-defects can be either donor, acceptor, or isovalent neutral defect. When Ag is heavily doped in PbTe, the neutral (Ag-Ag) dimer defect at Pb-site is formed and the environment changes to the Pb-rich/Te-poor condition. Under Pb-rich condition, the ionized Ag-interstitial defect (Ag{sub I}{sup +}) becomes the major donor. The formation energy of Ag{sub I}{sup +} is smaller than other native and Ag-related defects. Also it is found that Ag{sub I}{sup +} is an effective dopant. There is no additional impurity state near themore » band gap and the conduction band minimum. The charge state of Ag{sub I}{sup +} defect is maintained even when the Fermi level is located above the conduction band minimum. The diffusion constant of Ag{sub I}{sup +} is calculated based on the temperature dependent Fermi level, formation energy, and migration energy. When T > 550 K, the diffusion length of Ag within a few minutes is comparable to the grain size of the polycrystalline PbTe, implying that Ag is dissolved into PbTe and this donor defect is distributed over the whole lattice in Ag-excess doped polycrystalline PbTe. The predicted solubility of Ag{sub I}{sup +} well explains the increased electron carrier concentration and electrical conductivity reported in Ag-excess doped polycrystalline PbTe at T = 450–750 K [Pei et al., Adv. Energy Mater. 1, 291 (2011)]. In addition, we suggest that this abnormal doping behavior is also found for Au-doped PbTe.« less

Experimental evidence on microwave induced electron losses from ECRIS plasma

NASA Astrophysics Data System (ADS)

Sakildien, M.; Tarvainen, O.; Kronholm, R.; Izotov, I.; Skalyga, V.; Kalvas, T.; Jones, P.; Koivisto, H.

2018-06-01

The balance between warm and hot (>1 keV) electron density and their losses from the magnetic confinement system of an Electron Cyclotron Resonance Ion Source (ECRIS) plasma is considered to be one of the main factors determining the rate of the high charge state ion production. One of the key loss channels for heated electrons is thought to be induced by the injected microwaves. While this loss mechanism, referred to as rf-induced pitch angle scattering, has been studied theoretically and with computational tools, direct experimental evidence of its significance in minimum-B ECRIS plasmas remains limited. In this work, experimental evidence of microwave induced electron losses in the axial direction is presented in both continuous wave (CW) and pulsed operation of a 14 GHz ECRIS. In the CW mode, the experiment was carried out by comparing the characteristic X-ray emission from the plasma volume and from the surface of the biased disc located in the flux of the escaping electron at the axial magnetic mirror. Parametric sweeps of magnetic field, neutral gas pressure, and microwave power were conducted to determine their effect on electron losses. In the pulsed mode, the experiment was conducted by measuring the flux of escaping electrons through aluminum foils of different thicknesses providing some energy resolution. Both diagnostics support the view that rf-induced losses account for up to 70% of total hot electron losses and their importance depends on the source parameters, especially power and neutral gas pressure.

Fabrication of nanostructured transmissive optical devices on ITO-glass with UV1116 photoresist using high-energy electron beam lithography.

PubMed

Williams, Calum; Bartholomew, Richard; Rughoobur, Girish; Gordon, George S D; Flewitt, Andrew J; Wilkinson, Timothy D

2016-12-02

High-energy electron beam lithography for patterning nanostructures on insulating substrates can be challenging. For high resolution, conventional resists require large exposure doses and for reasonable throughput, using typical beam currents leads to charge dissipation problems. Here, we use UV1116 photoresist (Dow Chemical Company), designed for photolithographic technologies, with a relatively low area dose at a standard operating current (80 kV, 40-50 μC cm -2 , 1 nAs -1 ) to pattern over large areas on commercially coated ITO-glass cover slips. The minimum linewidth fabricated was ∼33 nm with 80 nm spacing; for isolated structures, ∼45 nm structural width with 50 nm separation. Due to the low beam dose, and nA current, throughput is high. This work highlights the use of UV1116 photoresist as an alternative to conventional e-beam resists on insulating substrates. To evaluate suitability, we fabricate a range of transmissive optical devices, that could find application for customized wire-grid polarisers and spectral filters for imaging, which operate based on the excitation of surface plasmon polaritons in nanosized geometries, with arrays encompassing areas ∼0.25 cm 2 .

B-spline algebraic diagrammatic construction: Application to photoionization cross-sections and high-order harmonic generation

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

Ruberti, M.; Averbukh, V.; Decleva, P.

2014-10-28

We present the first implementation of the ab initio many-body Green's function method, algebraic diagrammatic construction (ADC), in the B-spline single-electron basis. B-spline versions of the first order [ADC(1)] and second order [ADC(2)] schemes for the polarization propagator are developed and applied to the ab initio calculation of static (photoionization cross-sections) and dynamic (high-order harmonic generation spectra) quantities. We show that the cross-section features that pose a challenge for the Gaussian basis calculations, such as Cooper minima and high-energy tails, are found to be reproduced by the B-spline ADC in a very good agreement with the experiment. We also presentmore » the first dynamic B-spline ADC results, showing that the effect of the Cooper minimum on the high-order harmonic generation spectrum of Ar is correctly predicted by the time-dependent ADC calculation in the B-spline basis. The present development paves the way for the application of the B-spline ADC to both energy- and time-resolved theoretical studies of many-electron phenomena in atoms, molecules, and clusters.« less

Conceptual design of the gamma-to-electron magnetic spectrometer for the National Ignition Facility

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

Kim, Y., E-mail: yhkim@lanl.gov; Herrmann, H. W.; Jorgenson, H. J.

2014-11-15

The Gamma-to-Electron Magnetic Spectrometer (GEMS) diagnostic is designed to measure the prompt γ-ray energy spectrum during high yield deuterium-tritium (DT) implosions at the National Ignition Facility (NIF). The prompt γ-ray spectrum will provide “burn-averaged” observables, including total DT fusion yield, total areal density (ρR), ablator ρR, and fuel ρR. These burn-averaged observables are unique because they are essentially averaged over 4π, providing a global reference for the line-of-sight-specific measurements typical of x-ray and neutron diagnostics. The GEMS conceptual design meets the physics-based requirements: ΔE/E = 3%–5% can be achieved in the range of 2–25 MeV γ-ray energy. Minimum DT neutronmore » yields required for 15% measurement uncertainty at low-resolution mode are: 5 × 10{sup 14} DT-n for ablator ρR (at 0.2 g/cm{sup 2}); 2 × 10{sup 15} DT-n for total DT yield (at 4.2 × 10{sup −5} γ/n); and 1 × 10{sup 16} DT-n for fuel ρR (at 1 g/cm{sup 2})« less

Maruhn-Greiner Maximum for Confirmation of Low Energy Nuclear Reactions (LENR) via a Compound Nucleus with Double Magic Numbers

NASA Astrophysics Data System (ADS)

Hora, Heinrich; Miley, George

2007-03-01

One of the most convincing facts about LENR due to deuterons (ds) or protons of very high concentration in host metals of palladium is the measurement of the large scale minimum in the reaction probability with product elements centered around the nucleon number A = 153. The local maximum was measured in this region is similar to fission of uranium at A = 119 where the local maximum follows the Maruhn-Greiner mechanism^1. We suggest this phenomenon can be explained by the strong screening of the Maxwellian ds on the degenerate rigid electron background within the swimming electrons at the metal surface or thin filem interfaces. The deuterons behave like neutrals at distances of above 2 picometers (pm) and form clusters due to soft attraction in the range of thermal energy; 10 pm diameter clusters can react over long time scales (10^6 s) with Pd leading to double magic number compound nuclei 306x126 decaying via fission to an A=153 element distribution. J. Maruhn et al, Phys. Rev. Letters 32, 548 (1974) H. Hora, G.H. Miley, CzechJ. Phys. 48, 1111 (1998)

Fabrication of nanostructured transmissive optical devices on ITO-glass with UV1116 photoresist using high-energy electron beam lithography

NASA Astrophysics Data System (ADS)

Williams, Calum; Bartholomew, Richard; Rughoobur, Girish; Gordon, George S. D.; Flewitt, Andrew J.; Wilkinson, Timothy D.

2016-12-01

High-energy electron beam lithography for patterning nanostructures on insulating substrates can be challenging. For high resolution, conventional resists require large exposure doses and for reasonable throughput, using typical beam currents leads to charge dissipation problems. Here, we use UV1116 photoresist (Dow Chemical Company), designed for photolithographic technologies, with a relatively low area dose at a standard operating current (80 kV, 40-50 μC cm-2, 1 nAs-1) to pattern over large areas on commercially coated ITO-glass cover slips. The minimum linewidth fabricated was ˜33 nm with 80 nm spacing; for isolated structures, ˜45 nm structural width with 50 nm separation. Due to the low beam dose, and nA current, throughput is high. This work highlights the use of UV1116 photoresist as an alternative to conventional e-beam resists on insulating substrates. To evaluate suitability, we fabricate a range of transmissive optical devices, that could find application for customized wire-grid polarisers and spectral filters for imaging, which operate based on the excitation of surface plasmon polaritons in nanosized geometries, with arrays encompassing areas ˜0.25 cm2.

Temperature-driven evolution of critical points, interlayer coupling, and layer polarization in bilayer Mo S2

NASA Astrophysics Data System (ADS)

Du, Luojun; Zhang, Tingting; Liao, Mengzhou; Liu, Guibin; Wang, Shuopei; He, Rui; Ye, Zhipeng; Yu, Hua; Yang, Rong; Shi, Dongxia; Yao, Yugui; Zhang, Guangyu

2018-04-01

The recently emerging two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have been a fertile ground for exploring abundant exotic physical properties. Critical points, the extrema or saddle points of electronic bands, are the cornerstone of condensed-matter physics and fundamentally determine the optical and transport phenomena of the TMDCs. However, for bilayer Mo S2 , a typical TMDC and the unprecedented electrically tunable venue for valleytronics, there has been a considerable controversy on its intrinsic electronic structure, especially for the conduction band-edge locations. Moreover, interlayer hopping and layer polarization in bilayer Mo S2 which play vital roles in valley-spintronic applications have remained experimentally elusive. Here, we report the experimental observation of intrinsic critical points locations, interlayer hopping, layer-spin polarization, and their evolution with temperature in bilayer Mo S2 by performing temperature-dependent photoluminescence. Our measurements confirm that the conduction-band minimum locates at the Kc instead of Qc, and the energy splitting between Qc and Kc redshifts with a descent of temperature. Furthermore, the interlayer hopping energy for holes and temperature-dependent layer polarization are quantitatively determined. Our observations are in good harmony with density-functional theory calculations.

Conceptual design of the gamma-to-electron magnetic spectrometer for the National Ignition Facility

DOE PAGES

Kim, Y.; Herrmann, H. W.; Jorgenson, H. J.; ...

2014-08-01

The Gamma-to-Electron Magnetic Spectrometer (GEMS) diagnostic is designed to measure the prompt γ-ray energy spectrum during high yield deuterium-tritium (DT) implosions at the National Ignition Facility (NIF). The prompt γ-ray spectrum will provide ‘burn-averaged’ observables, including total DT fusion yield, total areal density (ρR), ablator ρR, and fuel ρR. These burn-averaged observables are unique because they are essentially averaged over 4π, providing a global reference for the line-of-sight-specific measurements typical of x-ray and neutron diagnostics. The GEMS conceptual design meets the physics-based requirements: ΔE/E = 3 - 5% can be achieved in the range of 2 - 25 MeV γ-raymore » energy. Minimum DT neutron yields required for 15% measurement uncertainty at low-resolution mode are: 5×10 14 DT-n for ablator ρR (at 0.2 g/cm 2); 2×10 15 DT-n for total DT yield (at 4.2×10 -5γ /n); and 1×10 16 DT-n for fuel ρR (at 1 g/cm 2).« less

Principle of Minimum Energy in Magnetic Reconnection in a Self-organized Critical Model for Solar Flares

NASA Astrophysics Data System (ADS)

Farhang, Nastaran; Safari, Hossein; Wheatland, Michael S.

2018-05-01

Solar flares are an abrupt release of magnetic energy in the Sun’s atmosphere due to reconnection of the coronal magnetic field. This occurs in response to turbulent flows at the photosphere that twist the coronal field. Similar to earthquakes, solar flares represent the behavior of a complex system, and expectedly their energy distribution follows a power law. We present a statistical model based on the principle of minimum energy in a coronal loop undergoing magnetic reconnection, which is described as an avalanche process. We show that the distribution of peaks for the flaring events in this self-organized critical system is scale-free. The obtained power-law index of 1.84 ± 0.02 for the peaks is in good agreement with satellite observations of soft X-ray flares. The principle of minimum energy can be applied for general avalanche models to describe many other phenomena.

HIGH VOLTAGE ION SOURCE

DOEpatents

Luce, J.S.

1960-04-19

A device is described for providing a source of molecular ions having a large output current and with an accelerated energy of the order of 600 kv. Ions are produced in an ion source which is provided with a water-cooled source grid of metal to effect maximum recombination of atomic ions to molecular ions. A very high accelerating voltage is applied to withdraw and accelerate the molecular ions from the source, and means are provided for dumping the excess electrons at the lowest possible potentials. An accelerating grid is placed adjacent to the source grid and a slotted, grounded accelerating electrode is placed adjacent to the accelerating grid. A potential of about 35 kv is maintained between the source grid and accelerating grid, and a potential of about 600 kv is maintained between the accelerating grid and accelerating electrode. In order to keep at a minimum the large number of oscillating electrons which are created when such high voltages are employed in the vicinity of a strong magnetic field, a plurality of high voltage cascaded shields are employed with a conventional electron dumping system being employed between each shield so as to dump the electrons at the lowest possible potential rather than at 600 kv.

Electronic structures and enhanced optical properties of blue phosphorene/transition metal dichalcogenides van der Waals heterostructures.

PubMed

Peng, Qiong; Wang, Zhenyu; Sa, Baisheng; Wu, Bo; Sun, Zhimei

2016-08-24

As a fast emerging topic, van der Waals (vdW) heterostructures have been proposed to modify two-dimensional layered materials with desired properties, thus greatly extending the applications of these materials. In this work, the stacking characteristics, electronic structures, band edge alignments, charge density distributions and optical properties of blue phosphorene/transition metal dichalcogenides (BlueP/TMDs) vdW heterostructures were systematically studied based on vdW corrected density functional theory. Interestingly, the valence band maximum and conduction band minimum are located in different parts of BlueP/MoSe2, BlueP/WS2 and BlueP/WSe2 heterostructures. The MoSe2, WS2 or WSe2 layer can be used as the electron donor and the BlueP layer can be used as the electron acceptor. We further found that the optical properties under visible-light irradiation of BlueP/TMDs vdW heterostructures are significantly improved. In particular, the predicted upper limit energy conversion efficiencies of BlueP/MoS2 and BlueP/MoSe2 heterostructures reach as large as 1.16% and 0.98%, respectively, suggesting their potential applications in efficient thin-film solar cells and optoelectronic devices.

Recombination-related properties of a-screw dislocations in GaN: A combined CL, EBIC, TEM study

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

Medvedev, O. S., E-mail: o.s.medvedev@spbu.ru; Mikhailovskii, V. Yu.; IRC for Nanotechnology, Research Park, St.-Petersburg State University

2016-06-17

Cathodoluminescence (CL), electron beam current (EBIC) and transmission electron microscopy (TEM) techniques have been applied to investigate recombination properties and structure of freshly introduced dislocations in low-ohmic GaN crystals. It was confirmed that the only a-screw dislocations exhibited an intense characteristic dislocation-related luminescence (DRL) which persisted up to room temperature and was red-shifted by about 0.3 eV with respect to the band gap energy not only in HVPE but also in MOCVD grown samples. EBIC contrast of the dislocations was found to be temperature independent indicating that the dislocation-related recombination level is situated below 200 meV with respect of conductionmore » band minimum. With the increasing of the magnification of the dislocation TEM cross-sectional images they were found to disappear, probably, due to the recombination enhanced dislocation glide (REDG) under electron beam exposure which was immediately observed in CL investigations on a large scale. The stacking fault ribbon in the core of dissociated a-screw dislocation which form a quantum well for electrons was proposed to play an important role both in DRL spectrum formation and in REDG.« less

Relaxation of exciton and photoinduced dimerization in crystalline C60

NASA Astrophysics Data System (ADS)

Suzuki, Masato; Iida, Takeshi; Nasu, Keiichiro

2000-01-01

We numerically investigate the lattice relaxation of photogenerated exciton in crystalline C60 so as to clarify the mechanism of the photoinduced dimerization processes in this material. In our theory, we deal with the π electrons together with the interatomic effective potentials. Calculations are mainly based on the mean-field theory for interelectron interactions but are also reinforced by taking the electron-hole correlation into account, so that we can obtain the exciton effect. Using a cluster model, we calculate the adiabatic potential energy surfaces of the excitons relevant to the photoinduced dimerization processes occurring in a face-centered-cubic crystal of C60. The potential surfaces of the Frenkel excitons turned out to be quite uneven with several energy minimum points during the structural changes from the Franck-Condon state to the dimerized state. This leads to the conclusion that various structural defects exist at low temperatures even in the single crystal, as an intrinsic property of this molecular crystal with a complicated intermolecular interaction. From the analysis of the potential surfaces of the charge-transfer (CT) excitons, it is confirmed that the CT exciton relaxes down to its self-trapped state, wherein the adjacent two molecules get close together. This implies that the CT between adjacent two molecules is one of mechanisms that triggers the photodimerization or the photopolymerization. The oscillator strength distributions are also calculated for various intermediate structures along the lattice relaxation path. As the dimerization reaction proceeds, the oscillator strength grows in the energy region below the fundamental absorption edge, and the lowest-energy peak, originally at about 1.9 eV, finally shifts down to about 1.7 eV in the final dimerized structure. These results clarify the electronic origins of the luminescence observed in the C60 single crystal. Moreover, the origins of the photoinduced absorption spectra observed by Bazhenov, Gorbunov, and Volkodav are elucidated by characteristics of the adiabatic potential energy surfaces obtained here.

The Bess Investigation of the Origin of Cosmic-ray Antiprotons and Search for Cosmological Antimatter

NASA Technical Reports Server (NTRS)

Mitchell, John; Yamamoto, Akira; Yoshimura, Koji; Makida, Yasuhiro; Matsuda, Shinya; Hasegawa, Masaya; Horikoshi, Atsushi; Tanaka,Ken-ichi; Suzuki, Junichi; Nishimura, Jun;

Exploring load, velocity, and surface disorder dependence of friction with one-dimensional and two-dimensional models.

PubMed

Dagdeviren, Omur E

2018-08-03

The effect of surface disorder, load, and velocity on friction between a single asperity contact and a model surface is explored with one-dimensional and two-dimensional Prandtl-Tomlinson (PT) models. We show that there are fundamental physical differences between the predictions of one-dimensional and two-dimensional models. The one-dimensional model estimates a monotonic increase in friction and energy dissipation with load, velocity, and surface disorder. However, a two-dimensional PT model, which is expected to approximate a tip-sample system more realistically, reveals a non-monotonic trend, i.e. friction is inert to surface disorder and roughness in wearless friction regime. The two-dimensional model discloses that the surface disorder starts to dominate the friction and energy dissipation when the tip and the sample interact predominantly deep into the repulsive regime. Our numerical calculations address that tracking the minimum energy path and the slip-stick motion are two competing effects that determine the load, velocity, and surface disorder dependence of friction. In the two-dimensional model, the single asperity can follow the minimum energy path in wearless regime; however, with increasing load and sliding velocity, the slip-stick movement dominates the dynamic motion and results in an increase in friction by impeding tracing the minimum energy path. Contrary to the two-dimensional model, when the one-dimensional PT model is employed, the single asperity cannot escape to the minimum energy minimum due to constraint motion and reveals only a trivial dependence of friction on load, velocity, and surface disorder. Our computational analyses clarify the physical differences between the predictions of the one-dimensional and two-dimensional models and open new avenues for disordered surfaces for low energy dissipation applications in wearless friction regime.

Predictions of thermal buckling strengths of hypersonic aircraft sandwich panels using minimum potential energy and finite element methods

NASA Technical Reports Server (NTRS)

Ko, William L.

1995-01-01

Thermal buckling characteristics of hypersonic aircraft sandwich panels of various aspect ratios were investigated. The panel is fastened at its four edges to the substructures under four different edge conditions and is subjected to uniform temperature loading. Minimum potential energy theory and finite element methods were used to calculate the panel buckling temperatures. The two methods gave fairly close buckling temperatures. However, the finite element method gave slightly lower buckling temperatures than those given by the minimum potential energy theory. The reasons for this slight discrepancy in eigensolutions are discussed in detail. In addition, the effect of eigenshifting on the eigenvalue convergence rate is discussed.

Effects of Energy Dissipation in the Sphere-Restricted Full Three-Body Problem

NASA Astrophysics Data System (ADS)

Gabriel, T. S. J.

Recently, the classical N-Body Problem has been adjusted to account for celestial bodies made of constituents of finite density. By imposing a minima on the achievable distance between particles, minimum energy resting states are allowed by the problem. The Full N-Body Problem allows for the dissipation of mechanical energy through surface-surface interactions via impacts or by way of tidal deformation. Barring exogeneous forces and allowing for the dissipation of energy, these systems have discrete, and sometimes multiple, minimum energy states for a given angular momentum. Building the dynamical framework of such finite density systems is a necessary process in outlining the evolution of rubble pile asteroids and other gravitational-granular systems such as protoplanetary discs, and potentially planetary rings, from a theoretical point of view. In all cases, resting states are expected to occur as a necessary step in the ongoing processes of solar system formation and evolution. Previous studies of this problem have been performed in the N=3 case where the bodies are indistinguishable spheres, with all possible relative equilibria and their stability having been identified as a function of the angular momentum of the system. These studies uncovered that at certain levels of angular momentum there exists two minimum energy states, a global and local minimum. Thus a question of interest is in which of these states a dissipative system would preferentially settle and the sensitivity of results to changes in dissipation parameters. Assuming equal-sized, perfectly-rigid bodies, this study investigates the dynamical evolution of three spheres under the influence of mutual gravity and impact mechanics as a function of dissipation parameters. A purpose-written, C-based, Hard Sphere Discrete Element Method code has been developed to integrate trajectories and resolve contact mechanics as grains evolve into minimum energy configurations. By testing many randomized initial conditions, statistics are measured regarding minimum energy states for a given angular momentum range. A trend in the Sphere-Restricted Full Three-Body Problem producing an end state of one configuration over another is found as a function of angular momentum and restitution.

Rapid localized deactivation of self-assembled monolayers by propagation-controlled laser-induced plasma and its application to self-patterning of electronics and biosensors

NASA Astrophysics Data System (ADS)

Kim, Jongsu; Kwon, Seung-Gab; Back, Seunghyun; Kang, Bongchul

2018-03-01

We present a novel laser-induced surface treatment process to rapidly control the spatial wettabilities of various functional solutions with submicron to micron resolutions. Ultrathin hydrophobic self-assembled monolayers (SAMs) that little absorb typical laser lights due to short penetration depth were selectively deactivated by instantaneous interaction with laser-induced metallic plasmas. The spatial region of the deactivated SAM, which corresponds to process resolution, is adjustable by controlling the spatial propagation of the plasma. This method leads to the parallel formation of hydrophilic functional solutions on glass substrates with a minimum resolution on the submicron scale. To show its feasibility in device engineering fields, this method was applied to the cost-effective fabrication of electronics and biosensors. Rapid self-patterning of electronic and biological functional solutions (silver nanoparticle solution and streptavidin protein solution) was successfully realized by selective deactivation of two different SAMs (tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) for electronics and the hetero-hybrid SAM (octadecyltrichlorosilane (OTS)/2-[methoxy(polyethyleneoxy)propyl] trichlorosilane (PEG)) for biosensors). As a result, this method can be exploited for the rapid and low-cost fabrication of various thin film devices such as electronics, biosensors, energy, displays, and photonics.

Simulation of irradiation exposure of electronic devices due to heavy ion therapy with Monte Carlo Code MCNP6

NASA Astrophysics Data System (ADS)

Lapins, Janis; Guilliard, Nicole; Bernnat, Wolfgang; Buck, Arnulf

2017-09-01

During heavy ion irradiation therapy the patient has to be located exactly at the right position to make sure that the Bragg peak occurs in the tumour. The patient has to be moved in the range of millimetres to scan the ill tissue. For that reason a special table was developed which allows exact positioning. The electronic control can be located outside the surgery. But that has some disadvantage for the construction. To keep the system compact it would be much more comfortable to put the electronic control inside the surgery. As a lot of high energetic secondary particles are produced during the therapy causing a high dose in the room it is important to find positions with low dose rates. Therefore, investigations are needed where the electronic devices should be located to obtain a minimum of radiation, help to prevent the failure of sensitive devices. The dose rate was calculated for carbon ions with different initial energy and protons over the entire therapy room with Monte Carlo particle tracking using MCNP6. The types of secondary particles were identified and the dose rate for a thin silicon layer and an electronic mixture material was determined. In addition, the shielding effect of several selected material layers was calculated using MCNP6.

Stability conditions for exact-exchange Kohn-Sham methods and their relation to correlation energies from the adiabatic-connection fluctuation-dissipation theorem.

PubMed

Bleiziffer, Patrick; Schmidtel, Daniel; Görling, Andreas

2014-11-28

The occurrence of instabilities, in particular singlet-triplet and singlet-singlet instabilities, in the exact-exchange (EXX) Kohn-Sham method is investigated. Hessian matrices of the EXX electronic energy with respect to the expansion coefficients of the EXX effective Kohn-Sham potential in an auxiliary basis set are derived. The eigenvalues of these Hessian matrices determine whether or not instabilities are present. Similar as in the corresponding Hartree-Fock case instabilities in the EXX method are related to symmetry breaking of the Hamiltonian operator for the EXX orbitals. In the EXX methods symmetry breaking can easily be visualized by displaying the local multiplicative exchange potential. Examples (N2, O2, and the polyyne C10H2) for instabilities and symmetry breaking are discussed. The relation of the stability conditions for EXX methods to approaches calculating the Kohn-Sham correlation energy via the adiabatic-connection fluctuation-dissipation (ACFD) theorem is discussed. The existence or nonexistence of singlet-singlet instabilities in an EXX calculation is shown to indicate whether or not the frequency-integration in the evaluation of the correlation energy is singular in the EXX-ACFD method. This method calculates the Kohn-Sham correlation energy through the ACFD theorem theorem employing besides the Coulomb kernel also the full frequency-dependent exchange kernel and yields highly accurate electronic energies. For the case of singular frequency-integrands in the EXX-ACFD method a regularization is suggested. Finally, we present examples of molecular systems for which the self-consistent field procedure of the EXX as well as the Hartree-Fock method can converge to more than one local minimum depending on the initial conditions.

Planar CoB18- Cluster: a New Motif for - and Metallo-Borophenes

NASA Astrophysics Data System (ADS)

Chen, Teng-Teng; Jian, Tian; Lopez, Gary; Li, Wan-Lu; Chen, Xin; Li, Jun; Wang, Lai-Sheng

2016-06-01

Combined Photoelectron Spectroscopy (PES) and theoretical calculations have found that anion boron clusters (Bn-) are planar and quasi-planar up to B25-. Recent works show that anion pure boron clusters continued to be planar at B27-,B30-,B35- and B36-. B35- and B36- provide the first experimental evidence for the viability of the two-dimensional (2D) boron sheets (Borophene). The 2D to three-dimensional (3D) transitions are shown to happen at B40-,B39- and B28-, which possess cage-like structures. These fullerene-like boron cage clusters are named as Borospherene. Recently, borophenes or similar structures are claimed to be synthesized by several groups. Following an electronic design principle, a series of transition-metal-doped boron clusters (M©Bn-, n=8-10) are found to possess the monocyclic wheel structures. Meanwhile, CoB12- and RhB12- are revealed to adopt half-sandwich-type structures with the quasi-planar B12 moiety similar to the B12- cluster. Very lately, we show that the CoB16- cluster possesses a highly symmetric Cobalt-centered drum-like structure, with a new record of coordination number at 16. Here we report the CoB18- cluster to possess a unique planar structure, in which the Co atom is doped into the network of a planar boron cluster. PES reveals that the CoB18- cluster is a highly stable electronic system with the first adiabatic detachment energy (ADE) at 4.0 eV. Global minimum searches along with high-level quantum calculations show the global minimum for CoB18- is perfectly planar and closed shell (1A1) with C2v symmetry. The Co atom is bonded with 7 boron atoms in the closest coordination shell and the other 11 boron atoms in the outer coordination shell. The calculated vertical detachment energy (VDE) values match quite well with our experimental results. Chemical bonding analysis by the Adaptive Natural Density Partitioning (AdNDP) method shows the CoB18- cluster is π-aromatic with four 4-centered-2-electron (4c-2e) π bonds and one 19-centered-2-electron (19c-2e) π bond, 10 π electrons in total. This perfectly planar structure reveals the viability of creating a new class of hetero-borophenes and metallo-borophenes by doping metal atoms into the plane of monolayer boron atoms. This gives a new approach to design perspective hetero-borophenes and metallo-borophenes materials with tunable chemical, magnetic and optical properties.

JET disruption studies in support of ITER

NASA Astrophysics Data System (ADS)

Riccardo, V.; Arnoux, G.; Cahyna, P.; Hender, T. C.; Huber, A.; Jachmich, S.; Kiptily, V.; Koslowski, R.; Krlin, L.; Lehnen, M.; Loarte, A.; Nardon, E.; Paprok, R.; Tskhakaya (Sr, D.; contributors, JET-EFDA

2010-12-01

Plasma disruptions affect plasma-facing and structural components of tokamaks due to electromechanical forces, thermal loads and generation of high energy runaway electrons (REs). Asymmetries in poloidal halo and toroidal plasma current can now be routinely measured in four positions 90° apart. Their assessment is used to validate the design of the ITER vessel support system and its in-vessel components. The challenge of disruption thermal loads comes from both the short duration over which a large energy has to be lost and the potential for asymmetries. The focus of this paper will be on localized heat loads. Resonant magnetic perturbations failed to reduce the generation of REs in JET. An explanation of the limitations applying to these attempts is offered together with a minimum guideline. The REs generated by a moderate, but fast, Ar injection in limiter plasmas show evidence of milder and more efficient losses due to the high Ar background density.

Poster - Thurs Eve-03: Dose verification using a 2D diode array (Mapcheck) for electron beam modeling, QA and patient customized cutouts.

PubMed

Ghasroddashti, E; Sawchuk, S

2008-07-01

To assess a diode detector array (MapCheck) for commissioning, quality assurance (QA); and patient specific QA for electrons. 2D dose information was captured for various depths at several square fields ranging from 2×2 to 25×25cm 2 , and 9 patient customized cutouts using both Mapcheck and a scanning water phantom. Beam energies of 6, 9, 12, 16 and 20 MeV produced by Varian linacs were used. The water tank, beam energies and fields were also modeled on the Pinnacle planning system obtaining dose information. Mapcheck, water phantom and Pinnacle results were compared. Relative output factors (ROF) acquired with Mapcheck were compared to an in-house algorithm (JeffIrreg). Inter- and intra-observer variability was also investigated Results: Profiles and %DD data for Mapcheck, water tank, and Pinnacle agree well. High-dose, low-dose-gradient comparisons agree to within 1% between Mapcheck and water phantom. Field size comparisons showed mostly sub-millimeter agreement. ROFs for Mapcheck and JeffIrreg agreed within 2.0% (mean=0.9%±0.6%). The current standard for electron commissioning and QA is the scanning water tank which may be inefficient. Our results demonstrate that MapCheck can potentially be an alternative. Also the dose distributions for patient specific electron treatment require verification. This procedure is particularly challenging when the minimum dimension across the central axis of the cutout is smaller than the range of the electrons in question. Mapcheck offers an easy and efficient way of determining patient dose distributions especially compared to using the alternatives, namely, ion chamber and film. © 2008 American Association of Physicists in Medicine.

Phonon-assisted optical absorption in BaSnO 3 from first principles

NASA Astrophysics Data System (ADS)

Monserrat, Bartomeu; Dreyer, Cyrus E.; Rabe, Karin M.

2018-03-01

The perovskite BaSnO3 provides a promising platform for the realization of an earth-abundant n -type transparent conductor. Its optical properties are dominated by a dispersive conduction band of Sn 5 s states and by a flatter valence band of O 2 p states, with an overall indirect gap of about 2.9 eV . Using first-principles methods, we study the optical properties of BaSnO3 and show that both electron-phonon interactions and exact exchange, included using a hybrid functional, are necessary to obtain a qualitatively correct description of optical absorption in this material. In particular, the electron-phonon interaction drives phonon-assisted optical absorption across the minimum indirect gap and therefore determines the absorption onset, and it also leads to the temperature dependence of the absorption spectrum. Electronic correlations beyond semilocal density functional theory are key to determine the dynamical stability of the cubic perovskite structure, as well as the correct energies of the conduction bands that dominate absorption. Our work demonstrates that phonon-mediated absorption processes should be included in the design of novel transparent conductor materials.