Simulation of energy spectrum of GEM detector from an x-ray quantum

NASA Astrophysics Data System (ADS)

Malinowski, K.; Chernyshova, M.; Czarski, T.; Kowalska-Strzęciwilk, E.; Linczuk, P.; Wojeński, A.; Krawczyk, R.; Gąska, M.

2018-01-01

This paper presents the results of the energy resolution simulation for the triple GEM-based detector for x-ray quantum of 5.9 keV . Photons of this energy are emitted by 55Fe source, which is a standard calibration marker for this type of detectors. The calculations were made in Garfield++ in two stages. In the first stage, the distribution of the amount of primary electrons generated in the drift volume by the x-ray quantum was simulated using the Heed program. Secondly, the primary electrons of the resulting quantitative distribution were treated as a source of electron avalanches propagated through the whole volume of the triple GEM-based detector. The distribution of the obtained signals created a spectrum corresponding to the peak at 5.9 keV, which allowed us to determine the theoretical energy resolution of the detector. Its knowledge allows observing and improving the eventual experimental deterioration of the energy resolution, inevitably accompanying processes of registration and processing of the signals.

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

Andrés, Nahuel, E-mail: nandres@iafe.uba.ar; Gómez, Daniel; Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón I, 1428 Buenos Aires

We present a full two-fluid magnetohydrodynamic (MHD) description for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure, and electron inertia. According to this description, each plasma species introduces a new spatial scale: the ion inertial length λ{sub i} and the electron inertial length λ{sub e}, which are not present in the traditional MHD description. In the present paper, we seek for possible changes in the energy power spectrum in fully developed turbulent regimes, using numerical simulations of the two-fluid equations in two-and-a-half dimensions. We have been able to reproduce different scaling laws in differentmore » spectral ranges, as it has been observed in the solar wind for the magnetic energy spectrum. At the smallest wavenumbers where plain MHD is valid, we obtain an inertial range following a Kolmogorov k{sup −5∕3} law. For intermediate wavenumbers such that λ{sub i}{sup −1}≪k≪λ{sub e}{sup −1}, the spectrum is modified to a k{sup −7∕3} power-law, as has also been obtained for Hall-MHD neglecting electron inertia terms. When electron inertia is retained, a new spectral region given by k>λ{sub e}{sup −1} arises. The power spectrum for magnetic energy in this region is given by a k{sup −11∕3} power law. Finally, when the terms of electron inertia are retained, we study the self-consistent electric field. Our results are discussed and compared with those obtained in the solar wind observations and previous simulations.« less

Time-dependent Models for Blazar Emission with the Second-order Fermi Acceleration

NASA Astrophysics Data System (ADS)

Asano, Katsuaki; Takahara, Fumio; Kusunose, Masaaki; Toma, Kenji; Kakuwa, Jun

2014-01-01

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101-232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range of Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 1038 erg s-1, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

Polarization characteristics of radiation in both 'light' and conventional undulators

NASA Astrophysics Data System (ADS)

Potylitsyn, A. P.; Kolchuzhkin, A. M.; Strokov, S. A.

2017-07-01

As a rule, an intensity spectrum of undulator radiation (UR) is calculated by using the classical approach, even for electron energy higher than 10 GeV. Such a spectrum is determined by an electron trajectory in an undulator while neglecting radiation loss. Using Planck's law, the UR photon spectrum can be calculated from the obtained intensity spectrum, for both linear and nonlinear regimes. The electron radiation process in a field of strong electromagnetic waves is considered within the quantum electrodynamics framework, using the Compton scattering process or radiation in a 'light' undulator. A comparison was made of the results from using these two approaches, for UR spectra generated by 250-GeV electrons in an undulator with a 11.5-mm period; this comparison shows that they coincide with high accuracy. The characteristics of the collimated UR beam (i.e. spectrum and circular polarization) were simulated while taking into account the discrete process of photon emission along an electron trajectory in both undulator types. Both spectral photon distributions and polarization dependence on photon energy are 'smoothed', in comparison to that expected for a long undulator-the latter of which considers the ILC positron source (ILC Technical Design Report).

Injection and trapping of tunnel-ionized electrons into laser-produced wakes.

PubMed

Pak, A; Marsh, K A; Martins, S F; Lu, W; Mori, W B; Joshi, C

2010-01-15

A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.

PIC simulations of the trapped electron filamentation instability in finite-width electron plasma waves

NASA Astrophysics Data System (ADS)

Winjum, B. J.; Banks, J. W.; Berger, R. L.; Cohen, B. I.; Chapman, T.; Hittinger, J. A. F.; Rozmus, W.; Strozzi, D. J.; Brunner, S.

2012-10-01

We present results on the kinetic filamentation of finite-width nonlinear electron plasma waves (EPW). Using 2D simulations with the PIC code BEPS, we excite a traveling EPW with a Gaussian transverse profile and a wavenumber k0λDe= 1/3. The transverse wavenumber spectrum broadens during transverse EPW localization for small width (but sufficiently large amplitude) waves, while the spectrum narrows to a dominant k as the initial EPW width increases to the plane-wave limit. For large EPW widths, filaments can grow and destroy the wave coherence before transverse localization destroys the wave; the filaments in turn evolve individually as self-focusing EPWs. Additionally, a transverse electric field develops that affects trapped electrons, and a beam-like distribution of untrapped electrons develops between filaments and on the sides of a localizing EPW. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the Laboratory Research and Development Program at LLNL under project tracking code 12-ERD-061. Supported also under Grants DE-FG52-09NA29552 and NSF-Phy-0904039. Simulations were performed on UCLA's Hoffman2 and NERSC's Hopper.

Time-dependent models for blazar emission with the second-order Fermi acceleration

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

Asano, Katsuaki; Takahara, Fumio; Toma, Kenji

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101–232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range ofmore » Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 10{sup 38} erg s{sup –1}, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.« less

Nonlinear Electron and Ion Density Modulations Driven by Interfering High-Intensity Laser Pulses

NASA Astrophysics Data System (ADS)

Chen, S.; Zhang, P.; Saleh, N.; Sheng, Z. M.; Widjaja, C.; Umstadter, D.

2002-11-01

The optical spectrum from interaction of two crossed ultra short laser beams (400 fs) with underdense plasma is measured at various angles. Enhancement and broadening of the spectrum in the forward direction of one of the beams shows evidence of energy transfer between the two laser beams(G. Shvets, N. J. Fisch, A. Pukhov, and J. Meyer-ter-Vehn, Phys. Rev. E 60, 2218 (1999).), which is confirmed by a 2-D PIC simulation. The spectrum and scattered power indicate that a large amplitude electron density modulation is driven, which is attributed to the ponderomotive force of the interference, in agreement with simple analysis and simulation(δn/n_0>10). Stokes and anti-Stokes satellites reveals that the energy transfer is accompanied by a large amplitude nonlinear ion acoustic wave created by the laser interference in the strongly driven limit. The wavelength shift indicates that the ion acoustic wave's speed is 2.3×10^6m/s, corresponding to the electron temperature 119 keV, which is attributed to stochastic heating, also found in the simulation. Besides being of interest in basic plasma physics, this research is also relevant to fast igniter fusion or ion acceleration experiments, in which a laser pulse may potentially beat with a reflected weaker pulse, with intensities comparable to those used in the experiment(Y. Sentoku, et al., Appl. Phys. B 74, 207-215 (2002).).

Modeling the Effect of Surface Modification of Gold Nanoparticles Irradiated with 60Co on the Secondary Particles Emission Spectrum

NASA Astrophysics Data System (ADS)

Belousov, A. V.; Morozov, V. N.; Krusanov, G. A.; Kolyvanova, M. A.; Chernyaev, A. P.; Shtil, A. A.

2018-03-01

The Monte Carlo method (computer simulation) is used to construct a physical model of secondary particles emission induced by the simulated irradiation of a gold nanoparticle with 60Co. It is demonstrated that the modification of the nanoparticle surface with polyethylene glycol affects the spectrum of secondary electrons produced in a nanoparticle and leaving it and its shell. The model takes into account the size and the chemical composition of the shell and provides an opportunity to design antitumor radiosensitizers based on gold nanoparticles.

The Negative Ion Photoelectron Spectrum of meta -Benzoquinone Radical Anion (MBQ •– ): A Joint Experimental and Computational Study

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

Chen, Bo; Hrovat, David A.; Deng, S. H. M.

Negative ion photoelectron (NIPE) spectra of the radical anion of meta-benzoquinone (MBQ, m-OC6H4O) have been obtained at 20 K, using both 355 and 266 nm lasers for electron photodetachment. The spectra show well-resolved peaks and complex spectral patterns. The electron affinity of MBQ is determined from the first resolved peak to be 2.875 ±17 0.010 eV. Single-point, CASPT2/aug-cc-pVTZ//CASPT2/ aug-cc-pVDZ calculations predict accurately the positions of the 0-0 bands in the NIPE spectrum for formation of the four lowest electronic states of neutral MBQ from the 2A2 state of MBQ•-. In addition, the Franck-Condon factors that are computed from the CASPT2/aug-cc-pVDZmore » optimized geometries,vibrational frequencies, and normal mode vectors, successfully simulate the intensities and frequencies of the vibrational peaks in the NIPE spectrum that are associated with each of these electronic states. The successful simulation of the NIPE spectrum of MBQ•- allows the assignment of 3B2 as the ground state of MBQ, followed by the 1B2 and 1A1 electronic states, respectively 9.0 ± 0.2 and 16.6 ± 0.2 kcal/mol higher in energy than the triplet. These experimental energy differences are in good agreement with the calculated values of 9.7 and 15.7 kcal/mol. The relative energies of these two singlet states in MBQ confirm the previous prediction that their relative energies would be reversed from those in meta-benzoquinodimethane (MBQDM, m-CH2C6H4CH2).« less

Acceleration and Pickup Ring of Energetic Electrons Observed in Relativistic Magnetic Reconnection Simulations

NASA Astrophysics Data System (ADS)

Ping, Y. L.; Zhong, J. Y.; Wang, X. G.; Sheng, Z. M.; Zhao, G.

2017-11-01

Pickup ring of energetic electrons found in relativistic magnetic reconnection (MR) driven by two relativistic intense femtosecond laser pulses is investigated by particle simulation in 3D geometry. Magnetic reconnection processes and configurations are characterized by plasma current density distributions at different axial positions. Two helical structures associated with the circular polarization of laser pulses break down in the reconnection processes to form a current sheet between them, where energetic electrons are found to pile up and the outflow relativistic electron jets are observed. In the field line diffusion region, electrons are accelerated to multi-MeV with a flatter power-law spectrum due to MR. The development of the pickup ring of energetic electrons is strongly dependent upon laser peak intensities.

Understanding the inelastic electron-tunneling spectra of alkanedithiols on gold.

PubMed

Solomon, Gemma C; Gagliardi, Alessio; Pecchia, Alessandro; Frauenheim, Thomas; Di Carlo, Aldo; Reimers, Jeffrey R; Hush, Noel S

2006-03-07

We present results for a simulated inelastic electron-tunneling spectra (IETS) from calculations using the "gDFTB" code. The geometric and electronic structure is obtained from calculations using a local-basis density-functional scheme, and a nonequilibrium Green's function formalism is employed to deal with the transport aspects of the problem. The calculated spectrum of octanedithiol on gold(111) shows good agreement with experimental results and suggests further details in the assignment of such spectra. We show that some low-energy peaks, unassigned in the experimental spectrum, occur in a region where a number of molecular modes are predicted to be active, suggesting that these modes are the cause of the peaks rather than a matrix signal, as previously postulated. The simulations also reveal the qualitative nature of the processes dominating IETS. It is highly sensitive only to the vibrational motions that occur in the regions of the molecule where there is electron density in the low-voltage conduction channel. This result is illustrated with an examination of the predicted variation of IETS with binding site and alkane chain length.

Ultrafast X-ray Auger probing of photoexcited molecular dynamics

DOE PAGES

McFarland, B. K.; Farrell, J. P.; Miyabe, S.; ...

2014-06-23

Here, molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation—X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towardsmore » high kinetic energies, resulting from a particular C–O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.« less

A Monte Carlo Simulation for Understanding Energy Measurements of Beta Particles Detected by the UCNb Experiment

NASA Astrophysics Data System (ADS)

Feng, Chi; UCNb Collaboration

2011-10-01

It is theorized that contributions to the Fierz interference term from scalar interaction beyond the Standard Model could be detectable in the spectrum of neutron beta-decay. The UCNb experiment run at the Los Alamos Neutron Science Center aims to accurately measure the neutron beta-decay energy spectrum to detect a nonzero interference term. The instrument consists of a cubic ``integrating sphere'' calorimeter attached with up to 4 photomultiplier tubes. The inside of the calorimeter is coated with white paint and a thin UV scintillating layer made of deuterated polystyrene to contain the ultracold neutrons. A Monte Carlo simulation using the Geant4 toolkit is developed in order to provide an accurate method of energy reconstruction. Offline calibration with the Kellogg Radiation Laboratory 140 keV electron gun and conversion electron sources will be used to validate the Monte Carlo simulation to give confidence in the energy reconstruction methods and to better understand systematics in the experiment data.

Room scatter effects in Total Skin Electron Irradiation: Monte Carlo simulation study.

PubMed

Nevelsky, Alexander; Borzov, Egor; Daniel, Shahar; Bar-Deroma, Raquel

2017-01-01

Total Skin Electron Irradiation (TSEI) is a complex technique which usually involves the use of large electron fields and the dual-field approach. In this situation, many electrons scattered from the treatment room floor are produced. However, no investigations of the effect of scattered electrons in TSEI treatments have been reported. The purpose of this work was to study the contribution of floor scattered electrons to skin dose during TSEI treatment using Monte Carlo (MC) simulations. All MC simulations were performed with the EGSnrc code. Influence of beam energy, dual-field angle, and floor material on the contribution of floor scatter was investigated. Spectrum of the scattered electrons was calculated. Measurements of dose profile were performed in order to verify MC calculations. Floor scatter dependency on the floor material was observed (at 20 cm from the floor, scatter contribution was about 21%, 18%, 15%, and 12% for iron, concrete, PVC, and water, respectively). Although total dose profiles exhibited slight variation as functions of beam energy and dual-field angle, no dependence of the floor scatter contribution on the beam energy or dual-field angle was found. The spectrum of the scattered electrons was almost uniform between a few hundred KeV to 4 MeV, and then decreased linearly to 6 MeV. For the TSEI technique, dose contribution due to the electrons scattered from the room floor may be clinically significant and should be taken into account during design and commissioning phases. MC calculations can be used for this task. © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

Spectrum and Angular Distribution of γ-rays from Radiative Damping in Extremely Relativistic Laser-Plasma Interaction

NASA Astrophysics Data System (ADS)

Pandit, Rishi; Sentoku, Yasuhiko

2013-10-01

Effects of the radiative damping in the interaction of extremely intense laser (> 1022 W/cm2) with dense plasma is studied via a relativistic collisional particle-in-cell simulation, PICLS. When the laser intensity is getting close to 1024 W/cm2, the effect of quantum electrodynamics (QED) appears. We had calculated γ-rays from the radiative damping processes based on the classical model [1], but had taken into account the QED effect [2] in the spectrum calculation. In ultra-intense laser-plasma interaction, electrons are accelerated by the strong laser fields and emit γ-ray photons mainly via two processes, namely, Bremsstrahlung and radiative damping. Such relativistic γ-ray has wide range of frequencies and the angular distribution depends on the hot electron source. Comparing the details of γ-rays from the Bremsstrahlung and the radiative damping in simulations, we will discuss the laser parameters and the target conditions (geometry and material) to distinguish the photons from each process and also the QED effect in the γ-rays spectrum at the extremely relativistic intensity. Supported by US DOE DE-SC0008827.

X-rays diagnostics of the hot electron energy distribution in the intense laser interaction with metal targets

NASA Astrophysics Data System (ADS)

Kostenko, O. F.; Andreev, N. E.; Rosmej, O. N.

2018-03-01

A two-temperature hot electron energy distribution has been revealed by modeling of bremsstrahlung emission, measured by the radiation attenuation and half-shade methods, and Kα emission from a massive silver cylinder irradiated by a subpicosecond s-polarized laser pulse with a peak intensity of about 2 × 1019 W/cm2. To deduce parameters of the hot electron spectrum, we have developed semi-analytical models of generation and measurements of the x-rays. The models are based on analytical expressions and tabulated data on electron stopping power as well as cross-sections of generation and absorption of the x-rays. The Kα emission from thin silver foils deposited on low-Z substrates, both conducting and nonconducting, has been used to verify the developed models and obtained hot electron spectrum. The obtained temperatures of the colder and hotter electron components are in agreement with the values predicted by kinetic simulations of the cone-guided approach to fast ignition [Chrisman et al., Phys. Plasmas 15, 056309 (2008)]. The temperature of the low-energy component of the accelerated electron spectrum is well below the ponderomotive scaling and Beg's law. We have obtained relatively low conversion efficiency of laser energy into the energy of hot electrons propagating through the solid target of about 2%. It is demonstrated that the assumption about a single-temperature hot electron energy distribution with the slope temperature described by the ponderomotive scaling relationship, without detailed analysis of the hot electron spectrum, can lead to strong overestimation of the laser-to-electron energy-conversion efficiency, in particular, the conversion efficiency of laser energy into the high-temperature component of the hot electron distribution.

Gate-controlled current and inelastic electron tunneling spectrum of benzene: a self-consistent study.

PubMed

Liang, Y Y; Chen, H; Mizuseki, H; Kawazoe, Y

2011-04-14

We use density functional theory based nonequilibrium Green's function to self-consistently study the current through the 1,4-benzenedithiol (BDT). The elastic and inelastic tunneling properties through this Au-BDT-Au molecular junction are simulated, respectively. For the elastic tunneling case, it is found that the current through the tilted molecule can be modulated effectively by the external gate field, which is perpendicular to the phenyl ring. The gate voltage amplification comes from the modulation of the interaction between the electrodes and the molecules in the junctions. For the inelastic case, the electron tunneling scattered by the molecular vibrational modes is considered within the self-consistent Born approximation scheme, and the inelastic electron tunneling spectrum is calculated.

Contribution from individual nearby sources to the spectrum of high-energy cosmic-ray electrons

NASA Astrophysics Data System (ADS)

Sedrati, R.; Attallah, R.

2014-04-01

In the last few years, very important data on high-energy cosmic-ray electrons and positrons from high-precision space-born and ground-based experiments have attracted a great deal of interest. These particles represent a unique probe for studying local comic-ray accelerators because they lose energy very rapidly. These energy losses reduce the lifetime so drastically that high-energy cosmic-ray electrons can attain the Earth only from rather local astrophysical sources. This work aims at calculating, by means of Monte Carlo simulation, the contribution from some known nearby astrophysical sources to the cosmic-ray electron/positron spectra at high energy (≥ 10 GeV). The background to the electron energy spectrum from distant sources is determined with the help of the GALPROP code. The obtained numerical results are compared with a set of experimental data.

Effect of the electric field pattern on the generation of fast electrons in front of lower hybrid launchers

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

Valade, Laurent, E-mail: laurent.valade@cea.fr; Ekedahl, Annika; Colas, Laurent

2015-12-10

The effect of the detailed waveguide spectrum on the electron acceleration has been studied for the 3.7 GHz LHCD launchers in Tore Supra, i.e. the ITER-like passive-active multijunction (PAM) launcher and the fully-active-multijunction (FAM) launcher, using test electron modelling technique. The detailed launched antenna wave spectrum is used as input to the code that computes the dynamics of the electrons in the electric field. Comparison with the LHCD launchers in EAST, operating at 2.45 GHz and 4.6 GHz, has also been made. The simulations show that the PAM-design generates lower flux of fast electrons than FAM-launchers, this could be themore » consequence of the wider waveguide of PAM-launcher (14.65 mm for Tore-Supra) than FAM-launcher (8 mm for Tore-Supra)« less

Electron and optical properties of fullerene C70 within the conception of a strongly correlated state

NASA Astrophysics Data System (ADS)

Lobanov, B. V.; Murzashev, A. I.

2017-02-01

In the framework of the Hubbard model in the static fluctuation approximation, the energy spectrum of fullerene C70 with allowance for different lengths of the bonds between nonequivalent nodes is calculated. On the basis of the calculated energy spectrum, the optical absorption spectrum in the ultraviolet and visible region is simulated. A good qualitative agreement between the calculated and measured absorption spectra and between the measured and theoretical values of the gap width between the highest occupied and the lowest unoccupied molecular orbital is found.

Feasibility of producing a short, high energy s-band linear accelerator using a klystron power source.

PubMed

Baillie, Devin; St Aubin, J; Fallone, B G; Steciw, S

2013-04-01

To use a finite-element method (FEM) model to study the feasibility of producing a short s-band (2.9985 GHz) waveguide capable of producing x-rays energies up to 10 MV, for applications in a linac-MR, as well as conventional radiotherapy. An existing waveguide FEM model developed by the authors' group is used to simulate replacing the magnetron power source with a klystron. Peak fields within the waveguide are compared with a published experimental threshold for electric breakdown. The RF fields in the first accelerating cavity are scaled, approximating the effect of modifications to the first coupling cavity. Electron trajectories are calculated within the RF fields, and the energy spectrum, beam current, and focal spot of the electron beam are analyzed. One electron spectrum is selected for Monte Carlo simulations and the resulting PDD compared to measurement. When the first cavity fields are scaled by a factor of 0.475, the peak magnitude of the electric fields within the waveguide are calculated to be 223.1 MV∕m, 29% lower than the published threshold for breakdown at this operating frequency. Maximum electron energy increased from 6.2 to 10.4 MeV, and beam current increased from 134 to 170 mA. The focal spot FWHM is decreased slightly from 0.07 to 0.05 mm, and the width of the energy spectrum increased slightly from 0.44 to 0.70 MeV. Monte Carlo results show dmax is at 2.15 cm for a 10 × 10 cm(2) field, compared with 2.3 cm for a Varian 10 MV linac, while the penumbral widths are 4.8 and 5.6 mm, respectively. The authors' simulation results show that a short, high-energy, s-band accelerator is feasible and electric breakdown is not expected to interfere with operation at these field strengths. With minor modifications to the first coupling cavity, all electron beam parameters are improved.

Synchrotron Self-Compton Emission from the Crab and Other Pulsars

NASA Astrophysics Data System (ADS)

Harding, Alice K.; Kalapotharakos, Constantinos

2015-09-01

Results of a simulation of synchrotron self-Compton (SSC) emission from a rotation-powered pulsar are presented. The radiating particles are assumed to be both accelerated primary electrons and a spectrum of electron-positron pairs produced in cascades near the polar cap. They follow trajectories in a slot gap using 3D force-free magnetic field geometry, gaining pitch angles through resonant cyclotron absorption of radio photons, radiating and scattering synchrotron emission at high altitudes out to and beyond the light cylinder. Full angular dependence of the synchrotron photon density is simulated in the scattering and all processes are treated in the inertial observer frame. Spectra for the Crab and Vela pulsars as well as two energetic millisecond pulsars, B1821-24 and B1937+21, are simulated using this model. The simulation of the Crab pulsar radiation can reproduce both the flux level and the shape of the observed optical to hard X-ray emission assuming a pair multiplicity of {M}+=3× {10}5, as well as the very-high-energy emission above 50 GeV detected by MAGIC and VERITAS, with both the synchrotron and SSC components reflecting the shape of the pair spectrum. Simulations of Vela, B1821-24, and B1937+21, for {M}+ up to 105, do not produce pair SSC emission that is detectable by current telescopes, indicating that only Crab-like pulsars produce significant SSC components. The pair synchrotron emission matches the observed X-ray spectrum of the millisecond pulsars, and the predicted peak of this emission at 1-10 MeV would be detectable with planned Compton telescopes.

When will Low-Contrast Features be Visible in a STEM X-Ray Spectrum Image?

PubMed

Parish, Chad M

2015-06-01

When will a small or low-contrast feature, such as an embedded second-phase particle, be visible in a scanning transmission electron microscopy (STEM) X-ray map? This work illustrates a computationally inexpensive method to simulate X-ray maps and spectrum images (SIs), based upon the equations of X-ray generation and detection. To particularize the general procedure, an example of nanostructured ferritic alloy (NFA) containing nm-sized Y2Ti2O7 embedded precipitates in ferritic stainless steel matrix is chosen. The proposed model produces physically appearing simulated SI data sets, which can either be reduced to X-ray dot maps or analyzed via multivariate statistical analysis. Comparison to NFA X-ray maps acquired using three different STEM instruments match the generated simulations quite well, despite the large number of simplifying assumptions used. A figure of merit of electron dose multiplied by X-ray collection solid angle is proposed to compare feature detectability from one data set (simulated or experimental) to another. The proposed method can scope experiments that are feasible under specific analysis conditions on a given microscope. Future applications, such as spallation proton-neutron irradiations, core-shell nanoparticles, or dopants in polycrystalline photovoltaic solar cells, are proposed.

Electronic excitations and their effect on the interionic forces in simulations of radiation damage in metals.

PubMed

Race, C P; Mason, D R; Sutton, A P

2009-03-18

Using time-dependent tight-binding simulations of radiation damage cascades in a model metal we directly investigate the nature of the excitations of a system of quantum mechanical electrons in response to the motion of a set of classical ions. We furthermore investigate the effect of these excitations on the attractive electronic forces between the ions. We find that the electronic excitations are well described by a Fermi-Dirac distribution at some elevated temperature, even in the absence of the direct electron-electron interactions that would be required in order to thermalize a non-equilibrium distribution. We explain this result in terms of the spectrum of characteristic frequencies of the ionic motion. Decomposing the electronic force into four well-defined components within the basis of instantaneous electronic eigenstates, we find that the effect of accumulated excitations in weakening the interionic bonds is mostly (95%) accounted for by a thermal model for the electronic excitations. This result justifies the use of the simplifying assumption of a thermalized electron system in simulations of radiation damage with an electronic temperature dependence and in the development of temperature-dependent classical potentials.

A new energy transfer channel from carotenoids to chlorophylls in purple bacteria.

PubMed

Feng, Jin; Tseng, Chi-Wei; Chen, Tingwei; Leng, Xia; Yin, Huabing; Cheng, Yuan-Chung; Rohlfing, Michael; Ma, Yuchen

2017-07-10

It is unclear whether there is an intermediate dark state between the S 2 and S 1 states of carotenoids. Previous two-dimensional electronic spectroscopy measurements support its existence and its involvement in the energy transfer from carotenoids to chlorophylls, but there is still considerable debate on the origin of this dark state and how it regulates the energy transfer process. Here we use ab initio calculations on excited-state dynamics and simulated two-dimensional electronic spectrum of carotenoids from purple bacteria to provide evidence supporting that the dark state may be assigned to a new A g + state. Our calculations also indicate that groups on the conjugation backbone of carotenoids may substantially affect the excited-state levels and the energy transfer process. These results contribute to a better understanding of carotenoid excited states.Carotenoids harvest energy from light and transfer it to chlorophylls during photosynthesis. Here, Feng et al. perform ab initio calculations on excited-state dynamics and simulated 2D electronic spectrum of carotenoids, supporting the existence of a new excited state in carotenoids.

The composition of cosmic rays near the Bend (10 to the 15th power eV) from a study of muons in air showers at sea level

NASA Technical Reports Server (NTRS)

Goodman, J. A.; Gupta, S. C.; Freudenreich, H. T.; Sivaprasad, K.; Tonwar, S. C.; Yodh, G. B.; Ellsworth, R. W.; Goodman, M. C.; Bogert, M. C.; Burnstein, R.

1985-01-01

The distribution of muons near shower cores was studied at sea level at Fermilab using the E594 neutrino detector to sample the muon with E testing 3 GeV. These data are compared with detailed Monte Carlo simulations to derive conclusions about the composition of cosmic rays near the bend in the all particle spectrum. Monte Carlo simulations generating extensive air showers (EAS) with primary energy in excess of 50 TeV are described. Each shower record contains details of the electron lateral distribution and the muon and hadron lateral distributions as a function of energy, at the observation level of 100g/cm. The number of detected electrons and muons in each case was determined by a Poisson fluctuation of the number incident. The resultant predicted distribution of muons, electrons, the rate events are compared to those observed. Preliminary results on the rate favor a heavy primary dominated cosmic ray spectrum in energy range 50 to 1000 TeV.

Evaluation of the Effect of Source Geometry on the Output of Miniature X-ray Tube for Electronic Brachytherapy through Simulation

PubMed Central

Barati, B.; Zabihzadeh, M.; Tahmasebi Birgani, M.J.; Chegini, N.; Fatahiasl, J.; Mirr, I.

2018-01-01

Objective: The use of miniature X-ray source in electronic brachytherapy is on the rise so there is an urgent need to acquire more knowledge on X-ray spectrum production and distribution by a dose. The aim of this research was to investigate the influence of target thickness and geometry at the source of miniature X-ray tube on tube output. Method: Five sources were simulated based on problems each with a specific geometric structure and conditions using MCNPX code. Tallies proportional to the output were used to calculate the results for the influence of source geometry on output. Results: The results of this work include the size of the optimal thickness of 5 miniature sources, energy spectrum of the sources per 50 kev and also the axial and transverse dose of simulated sources were calculated based on these thicknesses. The miniature source geometric was affected on the output x-ray tube. Conclusion: The result of this study demonstrates that hemispherical-conical, hemispherical and truncated-conical miniature sources were determined as the most suitable tools. PMID:29732338

Simulation and Digitization of a Gas Electron Multiplier Detector Using Geant4 and an Object-Oriented Digitization Program

NASA Astrophysics Data System (ADS)

McMullen, Timothy; Liyanage, Nilanga; Xiong, Weizhi; Zhao, Zhiwen

2017-01-01

Our research has focused on simulating the response of a Gas Electron Multiplier (GEM) detector using computational methods. GEM detectors provide a cost effective solution for radiation detection in high rate environments. A detailed simulation of GEM detector response to radiation is essential for the successful adaption of these detectors to different applications. Using Geant4 Monte Carlo (GEMC), a wrapper around Geant4 which has been successfully used to simulate the Solenoidal Large Intensity Device (SoLID) at Jefferson Lab, we are developing a simulation of a GEM chamber similar to the detectors currently used in our lab. We are also refining an object-oriented digitization program, which translates energy deposition information from GEMC into electronic readout which resembles the readout from our physical detectors. We have run the simulation with beta particles produced by the simulated decay of a 90Sr source, as well as with a simulated bremsstrahlung spectrum. Comparing the simulation data with real GEM data taken under similar conditions is used to refine the simulation parameters. Comparisons between results from the simulations and results from detector tests will be presented.

POLARIMETRIC STUDIES OF MAGNETIC TURBULENCE WITH AN INTERFEROMETER

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

Lee, Hyeseung; Cho, Jungyeon; Lazarian, A.

2016-11-01

We study statistical properties of synchrotron polarization emitted from media with magnetohydrodynamic (MHD) turbulence. We use both synthetic and MHD turbulence simulation data for our studies. We obtain the spatial spectrum and its derivative with respect to the wavelength of synchrotron polarization arising from both synchrotron radiation and Faraday rotation fluctuations. In particular, we investigate how the spectrum changes with frequency. We find that our simulations agree with the theoretical predication in Lazarian and Pogosyan. We conclude that the spectrum of synchrotron polarization and its derivative can be very informative tools to obtain detailed information about the statistical properties ofmore » MHD turbulence from radio observations of diffuse synchrotron polarization. They are especially useful for recovering the statistics of a turbulent magnetic field as well as the turbulent density of electrons. We also simulate interferometric observations that incorporate the effects of noise and finite telescope beam size, and demonstrate how we recover statistics of underlying MHD turbulence.« less

Geant4 simulations of the absorption of photons in CsI and NaI produced by electrons with energies up to 4 MeV and their application to precision measurements of the β-energy spectrum with a calorimetric technique

NASA Astrophysics Data System (ADS)

Huyan, X.; Naviliat-Cuncic, O.; Voytas, P.; Chandavar, S.; Hughes, M.; Minamisono, K.; Paulauskas, S. V.

2018-01-01

The yield of photons produced by electrons slowing down in CsI and NaI was studied with four electromagnetic physics constructors included in the Geant4 toolkit. The subsequent absorption of photons in detector geometries used for measurements of the β spectrum shape was also studied with a focus on the determination of the absorption fraction. For electrons with energies in the range 0.5-4 MeV, the relative photon yields determined with the four Geant4 constructors differ at the level of 10-2 in amplitude and the relative absorption fractions differ at the level of 10-4 in amplitude. The differences among constructors enabled the estimation of the sensitivity to Geant4 simulations for the measurement of the β energy spectrum shape in 6He decay using a calorimetric technique with ions implanted in the active volume of detectors. The size of the effect associated with photons escaping the detectors was quantified in terms of a slope which, on average, is respectively - 5 . 4 %/MeV and - 4 . 8 %/MeV for the CsI and NaI geometries. The corresponding relative uncertainties as determined from the spread of results obtained with the four Geant4 constructors are 0.0067 and 0.0058.

Full Quantum Dynamics Simulation of a Realistic Molecular System Using the Adaptive Time-Dependent Density Matrix Renormalization Group Method.

PubMed

Yao, Yao; Sun, Ke-Wei; Luo, Zhen; Ma, Haibo

2018-01-18

The accurate theoretical interpretation of ultrafast time-resolved spectroscopy experiments relies on full quantum dynamics simulations for the investigated system, which is nevertheless computationally prohibitive for realistic molecular systems with a large number of electronic and/or vibrational degrees of freedom. In this work, we propose a unitary transformation approach for realistic vibronic Hamiltonians, which can be coped with using the adaptive time-dependent density matrix renormalization group (t-DMRG) method to efficiently evolve the nonadiabatic dynamics of a large molecular system. We demonstrate the accuracy and efficiency of this approach with an example of simulating the exciton dissociation process within an oligothiophene/fullerene heterojunction, indicating that t-DMRG can be a promising method for full quantum dynamics simulation in large chemical systems. Moreover, it is also shown that the proper vibronic features in the ultrafast electronic process can be obtained by simulating the two-dimensional (2D) electronic spectrum by virtue of the high computational efficiency of the t-DMRG method.

Spectroscopy of the simplest Criegee intermediate CH2OO: simulation of the first bands in its electronic and photoelectron spectra.

PubMed

Lee, Edmond P F; Mok, Daniel K W; Shallcross, Dudley E; Percival, Carl J; Osborn, David L; Taatjes, Craig A; Dyke, John M

2012-09-24

CH(2)OO, the simplest Criegee intermediate, and ozone are isoelectronic. They both play very important roles in atmospheric chemistry. Whilst extensive experimental studies have been made on ozone, there were no direct gas-phase studies on CH(2)OO until very recently when its photoionization spectrum was recorded and kinetics studies were made of some reactions of CH(2)OO with a number of molecules of atmospheric importance, using photoionization mass spectrometry to monitor CH(2)OO. In order to encourage more direct studies on CH(2)OO and other Criegee intermediates, the electronic and photoelectron spectra of CH(2)OO have been simulated using high level electronic structure calculations and Franck-Condon factor calculations, and the results are presented here. Adiabatic and vertical excitation energies of CH(2)OO were calculated with TDDFT, EOM-CCSD, and CASSCF methods. Also, DFT, QCISD and CASSCF calculations were performed on neutral and low-lying ionic states, with single energy calculations being carried out at higher levels to obtain more reliable ionization energies. The results show that the most intense band in the electronic spectrum of CH(2) OO corresponds to the B(1)A' ← X(1)A' absorption. It is a broad band in the region 250-450 nm showing extensive structure in vibrational modes involving O-O stretching and C-O-O bending. Evidence is presented to show that the electronic absorption spectrum of CH(2)OO has probably been recorded in earlier work, albeit at low resolution. We suggest that CH(2)OO was prepared in this earlier work from the reaction of CH(2)I with O(2) and that the assignment of the observed spectrum solely to CH(2)IOO is incorrect. The low ionization energy region of the photoelectron spectrum of CH(2)OO consists of two overlapping vibrationally structured bands corresponding to one-electron ionizations from the highest two occupied molecular orbitals of the neutral molecule. In each case, the adiabatic component is the most intense and the adiabatic ionization energies of these bands are expected to be very close, at 9.971 and 9.974 eV at the highest level of theory used. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Triphenylamine based organic dyes for dye sensitized solar cells: A theoretical approach

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

Mohankumar, V.; Pandian, Muthu Senthil; Ramasamy, P., E-mail: ramasamyp@ssn.edu.in

2016-05-23

The geometry, electronic structure and absorption spectra for newly designed triphenylamine based organic dyes were investigated by density functional theory (DFT) and time dependent density functional theory (TD-DFT) with the Becke 3-Parameter-Lee-Yang-parr(B3LYP) functional, where the 6-31G(d,p) basis set was employed. All calculations were performed using the Gaussian 09 software package. The calculated HOMO and LUMO energies show that charge transfer occurs in the molecule. Ultraviolet–visible (UV–vis) spectrum was simulated by TD-DFT in gas phase. The calculation shows that all of the dyes can potentially be good sensitizers for DSSC. The LUMOs are just above the conduction band of TiO{sub 2}more » and their HOMOs are under the reduction potential energy of the electrolytes (I{sup −}/I{sub 3}{sup −}) which can facilitate electron transfer from the excited dye to TiO{sub 2} and charge regeneration process after photo oxidation respectively. The simulated absorption spectrum of dyes match with solar spectrum. Frontier molecular orbital results show that among all the three dyes, the “dye 3” can be used as potential sensitizer for DSSC.« less

Simulation studies of plasma waves in the electron foreshock - The generation of downshifted oscillations

NASA Technical Reports Server (NTRS)

Dum, C. T.

1990-01-01

The generation of waves with frequencies downshifted from the plasma frequency, as observed in the electron foreshock, is analyzed by particle simulation. Wave excitation differs fundamentally from the familiar excitation of the plasma eigenmodes by a gentle bump-on-tail electron distribution. Beam modes are destabilized by resonant interaction with bulk electrons, provided the beam velocity spread is very small. These modes are stabilized, starting with the higher frequencies, as the beam is broadened and slowed down by the interaction with the wave spectrum. Initially a very cold beam is also capable of exciting frequencies considerably above the plasma frequency, but such oscillations are quickly stabilized. Low-frequency modes persist for a long time, until the bump in the electron distribution is completely 'ironed' out. This diffusion process also is quite different from the familiar case of well-separated beam and bulk electrons. A quantitative analysis of these processes is carried out.

Probing the structural and dynamical properties of liquid water with models including non-local electron correlation

NASA Astrophysics Data System (ADS)

Del Ben, Mauro; Hutter, Jürg; VandeVondele, Joost

2015-08-01

Water is a ubiquitous liquid that displays a wide range of anomalous properties and has a delicate structure that challenges experiment and simulation alike. The various intermolecular interactions that play an important role, such as repulsion, polarization, hydrogen bonding, and van der Waals interactions, are often difficult to reproduce faithfully in atomistic models. Here, electronic structure theories including all these interactions at equal footing, which requires the inclusion of non-local electron correlation, are used to describe structure and dynamics of bulk liquid water. Isobaric-isothermal (NpT) ensemble simulations based on the Random Phase Approximation (RPA) yield excellent density (0.994 g/ml) and fair radial distribution functions, while various other density functional approximations produce scattered results (0.8-1.2 g/ml). Molecular dynamics simulation in the microcanonical (NVE) ensemble based on Møller-Plesset perturbation theory (MP2) yields dynamical properties in the condensed phase, namely, the infrared spectrum and diffusion constant. At the MP2 and RPA levels of theory, ice is correctly predicted to float on water, resolving one of the anomalies as resulting from a delicate balance between van der Waals and hydrogen bonding interactions. For several properties, obtaining quantitative agreement with experiment requires correction for nuclear quantum effects (NQEs), highlighting their importance, for structure, dynamics, and electronic properties. A computed NQE shift of 0.6 eV for the band gap and absorption spectrum illustrates the latter. Giving access to both structure and dynamics of condensed phase systems, non-local electron correlation will increasingly be used to study systems where weak interactions are of paramount importance.

Synchrotron Self-Compton Emission from the Crab and Other Pulsars

NASA Technical Reports Server (NTRS)

Harding, Alice K.; Kalapotharakos, Konstantinos

2015-01-01

Results of a simulation of synchrotron-self Compton (SSC) emission from a rotation-powered pulsar are presented. The radiating particles are assumed to be both accelerated primary electrons and a spectrum of electron-positron pairs produced in cascades near the polar cap. They follow trajectories in a slot gap using 3D force-free magnetic field geometry, gaining pitch angles through resonant cyclotron absorption of radio photons, radiating and scattering synchrotron emission at high altitudes out to and beyond the light cylinder. Full angular dependence of the synchrotron photon density is simulated in the scattering and all processes are treated in the inertial observer frame. Spectra for the Crab and Vela pulsars as well as two energetic millisecond pulsars, B1821-24 and B1937+21 are simulated using this model. The simulation of the Crab pulsar radiation can reproduce both the flux level and the shape of the observed optical to hard X-ray emission assuming a pair multiplicity of M+ = 3x10(exp 5), as well as the very-high- energy emission above 50 GeV detected by MAGIC and VERITAS, with both the synchrotron and SSC components reflecting the shape of the pair spectrum. Simulations of Vela, B1821-24 and B1937+21, for M+ up to 10(exp 5), do not produce pair SSC emission that is detectable by current telescopes, indicating that only Crab-like pulsars produce significant SSC components. The pair synchrotron emission matches the observed X-ray spectrum of the millisecond pulsars and the predicted peak of this emission at 1-10 MeV would be detectable with planned Compton telescopes.

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

Minami, R., E-mail: minami@prc.tsukuba.ac.jp; Imai, T.; Kariya, T.

Temporally and spatially resolved soft x-ray and end-loss-electron analyses of the electron cyclotron heated plasmas are carried out by using a semiconductor detector array and an electrostatic energy analyzer in the GAMMA 10 tandem mirror. The flux and the energy spectrum of the end loss electrons are measured by a multi-grid energy analyzer. Recently, the electron cyclotron heating power modulation experiments have been started in order to generate and control the high heat flux and to make the edge localized mode-like intermittent heat load pattern for the divertor simulation studies by the use of these detectors for electron properties.

Post-reionization Kinetic Sunyaev-Zel'dovich Signal in the Illustris simulation

NASA Astrophysics Data System (ADS)

Park, Hyunbae; Alvarez, Marcelo A.; Bond, John Richard

2017-06-01

Using Illustris, a state-of-art cosmological simulation of gravity, hydrodynamics, and star-formation, we revisit the calculation the angular power spectrum of the kinetic Sunyaev-Zel'dovich effect from the post-reionization (z < 6) epoch by Shaw et al. (2012). We not only report the updated value given by the analytical model used in previous studies, but go over the simplifying assumptions made in the model. The assumptions include using gas density for free electron density and neglecting the connected term arising due to the fourth order nature of momentum power spectrum that sources the signal. With these assumptions, Illustris gives slightly (˜ 10%) larger signal than in their work. Then, the signal is reduced by ˜ 20% when using actual free electron density in the calculation instead of gas density. This is because larger neutral fraction in dense regions results in loss of total free electron and suppression of fluctuations in free electron density. We find that the connected term can take up to half of the momentum power spectrum at z < 2. Due to a strong suppression of low-z signal by baryonic physics, the extra contribution from the connected term to ˜ 10% level although it may have been underestimated due to the finite box-size of Illustris. With these corrections, our result is very close to the original result of Shaw et al. (2012), which is well described by a simple power-law, D_l = 1.38[l/3000]0.21 μK^2, at 3000 < l < 10000.

Characterization of the fast electrons distribution produced in a high intensity laser target interaction

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

Westover, B.; Lawrence Livermore National Laboratory, Livermore, California 94550; Chen, C. D.

2014-03-15

Experiments on the Titan laser (∼150 J, 0.7 ps, 2 × 10{sup 20} W cm{sup −2}) at the Lawrence Livermore National Laboratory were carried out in order to study the properties of fast electrons produced by high-intensity, short pulse laser interacting with matter under conditions relevant to Fast Ignition. Bremsstrahlung x-rays produced by these fast electrons were measured by a set of compact filter-stack based x-ray detectors placed at three angles with respect to the target. The measured bremsstrahlung signal allows a characterization of the fast electron beam spectrum, conversion efficiency of laser energy into fast electron kinetic energy and angular distribution. A Monte Carlo codemore » Integrated Tiger Series was used to model the bremsstrahlung signal and infer a laser to fast electron conversion efficiency of 30%, an electron slope temperature of about 2.2 MeV, and a mean divergence angle of 39°. Simulations were also performed with the hybrid transport code ZUMA which includes fields in the target. In this case, a conversion efficiency of laser energy to fast electron energy of 34% and a slope temperature between 1.5 MeV and 4 MeV depending on the angle between the target normal direction and the measuring spectrometer are found. The observed temperature of the bremsstrahlung spectrum, and therefore the inferred electron spectrum are found to be angle dependent.« less

Quantum Entanglement Molecular Absorption Spectrum Simulator

NASA Technical Reports Server (NTRS)

Nguyen, Quang-Viet; Kojima, Jun

2006-01-01

Quantum Entanglement Molecular Absorption Spectrum Simulator (QE-MASS) is a computer program for simulating two photon molecular-absorption spectroscopy using quantum-entangled photons. More specifically, QE-MASS simulates the molecular absorption of two quantum-entangled photons generated by the spontaneous parametric down-conversion (SPDC) of a fixed-frequency photon from a laser. The two-photon absorption process is modeled via a combination of rovibrational and electronic single-photon transitions, using a wave-function formalism. A two-photon absorption cross section as a function of the entanglement delay time between the two photons is computed, then subjected to a fast Fourier transform to produce an energy spectrum. The program then detects peaks in the Fourier spectrum and displays the energy levels of very short-lived intermediate quantum states (or virtual states) of the molecule. Such virtual states were only previously accessible using ultra-fast (femtosecond) laser systems. However, with the use of a single-frequency continuous wave laser to produce SPDC photons, and QEMASS program, these short-lived molecular states can now be studied using much simpler laser systems. QE-MASS can also show the dependence of the Fourier spectrum on the tuning range of the entanglement time of any externally introduced optical-path delay time. QE-MASS can be extended to any molecule for which an appropriate spectroscopic database is available. It is a means of performing an a priori parametric analysis of entangled photon spectroscopy for development and implementation of emerging quantum-spectroscopic sensing techniques. QE-MASS is currently implemented using the Mathcad software package.

Multi-dimensional PIC-simulations of parametric instabilities for shock-ignition conditions

NASA Astrophysics Data System (ADS)

Riconda, C.; Weber, S.; Klimo, O.; Héron, A.; Tikhonchuk, V. T.

2013-11-01

Laser-plasma interaction is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion using two-dimensional particle-in-cell (PIC) simulations of an intense laser beam propagating in a hot, large-scale, non-uniform plasma. The temporal evolution and interdependence of Raman- (SRS), and Brillouin- (SBS), side/backscattering as well as Two-Plasmon-Decay (TPD) are studied. TPD is developing in concomitance with SRS creating a broad spectrum of plasma waves near the quarter-critical density. They are rapidly saturated due to plasma cavitation within a few picoseconds. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below one hundred keV.

The Impact of Baryonic Physics on the Kinetic Sunyaev–Zel’dovich Effect

NASA Astrophysics Data System (ADS)

Park, Hyunbae; Alvarez, Marcelo A.; Bond, J. Richard

2018-02-01

Poorly understood “baryonic physics” impacts our ability to predict the power spectrum of the kinetic Sunyaev–Zel’dovich (kSZ) effect. We study this in a sample high-resolution simulation of galaxy formation and feedback, Illustris. The high resolution of Illustris allows us to probe the kSZ power spectrum on multipoles {\\ell }={10}3{--}3× {10}4. Strong AGN feedback in Illustris nearly wipes out gas fluctuations at k≳ 1 h {Mpc}}-1 and at late times, likely somewhat underpredicting the kSZ power generated at z≲ 1. The post-reionization kSZ power spectrum for Illustris is well-fit by {{ \\mathcal D }}{\\ell }z< 6=1.38{[{\\ell }/3000]}0.21 μ {{{K}}}2 over 3000≲ {\\ell } ≲ 10,000, somewhat lower than most other reported values but consistent with the analysis of Shaw et al. Our analysis of the bias of free electrons reveals subtle effects associated with the multi-phase gas physics and stellar fractions that affect even linear scales. In particular, there are fewer electrons in biased galaxies, due to gas-cooling and star formation, and this leads to an electron bias of less than one, even at low wavenumbers. The combination of bias and electron fraction that determines the overall suppression is relatively constant, {f}e2{b}e02∼ 0.7, but more simulations are needed to see if this is Illustris-specific. By separating the kSZ power into different terms, we find that at least 6% (10%) of the signal at ℓ = 3000 (10,000) comes from non-Gaussian connected four-point density and velocity correlations, {< δ vδ v> }c, even without correcting for the Illustris simulation box-size. A challenge going forward will be accurately modeling long-wave velocity modes simultaneously with Illustris-like high resolution to capture the complexities of galaxy formation and its correlations with large-scale flows.

Integration of Semiconducting Sulfides for Full-Spectrum Solar Energy Absorption and Efficient Charge Separation.

PubMed

Zhuang, Tao-Tao; Liu, Yan; Li, Yi; Zhao, Yuan; Wu, Liang; Jiang, Jun; Yu, Shu-Hong

2016-05-23

The full harvest of solar energy by semiconductors requires a material that simultaneously absorbs across the whole solar spectrum and collects photogenerated electrons and holes separately. The stepwise integration of three semiconducting sulfides, namely ZnS, CdS, and Cu2-x S, into a single nanocrystal, led to a unique ternary multi-node sheath ZnS-CdS-Cu2-x S heteronanorod for full-spectrum solar energy absorption. Localized surface plasmon resonance (LSPR) in the nonstoichiometric copper sulfide nanostructures enables effective NIR absorption. More significantly, the construction of pn heterojunctions between Cu2-x S and CdS leads to staggered gaps, as confirmed by first-principles simulations. This band alignment causes effective electron-hole separation in the ternary system and hence enables efficient solar energy conversion. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Franck-Condon simulation of the single-vibronic-level emission spectra of HPCl/DPCl and the chemiluminescence spectrum of HPCl, including anharmonicity.

PubMed

Chau, Foo-Tim; Mok, Daniel K W; Lee, Edmond P F; Dyke, John M

2004-07-22

Restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] potential energy functions (PEFs) were calculated for the X (2)A" and A (2)A' states of HPCl employing the augmented correlation-consistent polarized-valence-quadruple-zeta (aug-cc-pVQZ) basis set. Further geometry optimization calculations were carried out on both electronic states of HPCl at the RCCSD(T) level with all electron and quasirelativistic effective core potential basis sets of better than the aug-cc-pVQZ quality, and also including some core electrons, in order to obtain more reliable geometrical parameters and relative electronic energy of the two states. Anharmonic vibrational wave functions of the two states of HPCl and DPCl, and Franck-Condon (FC) factors of the A (2)A'-X (2)A" transition were computed employing the RCCSD(T)/aug-cc-pVQZ PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the single-vibronic-level (SVL) emission spectra of HPCl and DPCl reported by Brandon et al. [J. Chem. Phys. 119, 2037 (2003)] and the chemiluminescence spectrum reported by Bramwell et al. [Chem. Phys. Lett. 331, 483 (2000)]. Comparison between simulated and observed SVL emission spectra gives the experimentally derived equilibrium geometry of the A (2)A' state of HPCl of r(e)(PCl) = 2.0035 +/- 0.0015 A, theta(e) = 116.08 +/- 0.60 degrees, and r(e)(HP) = 1.4063+/-0.0015 A via the iterative Franck-Condon analysis procedure. Comparison between simulated and observed chemiluminescence spectra confirms that the vibrational population distribution of the A (2)A' state of HPCl is non-Boltzmann, as proposed by Baraille et al. [Chem. Phys. 289, 263 (2003)].

Simulation of the single-vibronic-level emission spectrum of HPS.

PubMed

Mok, Daniel K W; Lee, Edmond P F; Chau, Foo-tim; Dyke, John M

2014-05-21

We have computed the potential energy surfaces of the X¹A' and ùA" states of HPS using the explicitly correlated multi-reference configuration interaction (MRCI-F12) method, and Franck-Condon factors between the two states, which include anharmonicity and Duschinsky rotation, with the aim of testing the assignment of the recently reported single-vibronic-level (SVL) emission spectrum of HPS [R. Grimminger, D. J. Clouthier, R. Tarroni, Z. Wang, and T. J. Sears, J. Chem. Phys. 139, 174306 (2013)]. These are the highest level calculations on these states yet reported. It is concluded that our spectral simulation supports the assignments of the molecular carrier, the electronic states involved and the vibrational structure of the experimental laser induced fluorescence, and SVL emission spectra proposed by Grimminger et al. [J. Chem. Phys. 139, 174306 (2013)]. However, there remain questions unanswered regarding the relative electronic energies of the two states and the geometry of the excited state of HPS.

When will low-contrast features be visible in a STEM X-ray spectrum image?

DOE PAGES

Parish, Chad M.

2015-04-01

When will a small or low-contrast feature, such as an embedded second-phase particle, be visible in a scanning transmission electron microscopy (STEM) X-ray map? This work illustrates a computationally inexpensive method to simulate X-ray maps and spectrum images (SIs), based upon the equations of X-ray generation and detection. To particularize the general procedure, an example of nanostructured ferritic alloy (NFA) containing nm-sized Y 2Ti 2O 7 embedded precipitates in ferritic stainless steel matrix is chosen. The proposed model produces physically appearing simulated SI data sets, which can either be reduced to X-ray dot maps or analyzed via multivariate statistical analysis.more » Comparison to NFA X-ray maps acquired using three different STEM instruments match the generated simulations quite well, despite the large number of simplifying assumptions used. A figure of merit of electron dose multiplied by X-ray collection solid angle is proposed to compare feature detectability from one data set (simulated or experimental) to another. The proposed method can scope experiments that are feasible under specific analysis conditions on a given microscope. As a result, future applications, such as spallation proton–neutron irradiations, core-shell nanoparticles, or dopants in polycrystalline photovoltaic solar cells, are proposed.« less

Electron-excited energy dispersive x-ray spectrometry in the variable pressure scanning electron microscope (EDS/VPSEM): it's not microanalysis anymore!

NASA Astrophysics Data System (ADS)

Newbury, Dale E.; Ritchie, Nicholas W. M.

2015-10-01

X-ray spectra suffer significantly degraded spatial resolution when measured in the variable-pressure scanning electron microscope (VPSEM, chamber pressure 1 Pa to 2500 Pa) as compared to highvacuum SEM (operating pressure < 10 mPa). Depending on the gas path length, electrons that are scattered hundreds of micrometers outside the focused beam can contribute 90% or more of the measured spectrum. Monte Carlo electron trajectory simulation, available in NIST DTSA-II, models the gas scattering and simulates mixed composition targets, e.g., particle on substrate. The impact of gas scattering at the major (C > 0.1 mass fraction), minor (0.01 <= C <= 0.1), and trace (C < 0.01) constituent levels can be estimated. NIST DTSA-II for Java-platforms is available free at: http://www.cstl.nist.gov/div837/837.02/epq/dtsa2/index.html).

Dependence of synergy current driven by lower hybrid wave and electron cyclotron wave on the frequency and parallel refractive index of electron cyclotron wave for Tokamaks

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

Huang, J.; Chen, S. Y., E-mail: sychen531@163.com; Tang, C. J.

2014-01-15

The physical mechanism of the synergy current driven by lower hybrid wave (LHW) and electron cyclotron wave (ECW) in tokamaks is investigated using theoretical analysis and simulation methods in the present paper. Research shows that the synergy relationship between the two waves in velocity space strongly depends on the frequency ω and parallel refractive index N{sub //} of ECW. For a given spectrum of LHW, the parameter range of ECW, in which the synergy current exists, can be predicted by theoretical analysis, and these results are consistent with the simulation results. It is shown that the synergy effect is mainlymore » caused by the electrons accelerated by both ECW and LHW, and the acceleration of these electrons requires that there is overlap of the resonance regions of the two waves in velocity space.« less

Simulation of Electronic Circular Dichroism of Nucleic Acids: From the Structure to the Spectrum.

PubMed

Padula, Daniele; Jurinovich, Sandro; Di Bari, Lorenzo; Mennucci, Benedetta

2016-11-14

We present a quantum mechanical (QM) simulation of the electronic circular dichroism (ECD) of nucleic acids (NAs). The simulation combines classical molecular dynamics, to obtain the structure and its temperature-dependent fluctuations, with a QM excitonic model to determine the ECD. The excitonic model takes into account environmental effects through a polarizable embedding and uses a refined approach to calculate the electronic couplings in terms of full transition densities. Three NAs with either similar conformations but different base sequences or similar base sequences but different conformations have been investigated and the results were compared with experimental observations; a good agreement was seen in all cases. A detailed analysis of the nature of the ECD bands in terms of their excitonic composition was also carried out. Finally, a comparison between the QM and the DeVoe models clearly revealed the importance of including fluctuations of the excitonic parameters and of accurately determining the electronic couplings. This study demonstrates the feasibility of the ab initio simulation of the ECD spectra of NAs, that is, without the need of experimental structural or electronic data. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shape of intrinsic alpha pulse height spectra in lanthanide halide scintillators

NASA Astrophysics Data System (ADS)

Wolszczak, W.; Dorenbos, P.

2017-06-01

Internal contamination with actinium-227 and its daughters is a serious drawback in low-background applications of lanthanide-based scintillators. In this work we showed the important role of nuclear γ de-excitations on the shape of the internal alpha spectrum measured in scintillators. We calculated with Bateman equations the activities of contamination isotopes and the time evolution of actinium-227 and its progenies. Next, we measured the intrinsic background spectra of LaBr3(Ce), LaBr3(Ce,Sr) and CeBr3 with a digital spectroscopy technique, and we analyzed them with a pulse shape discrimination method (PSD) and a time-amplitude analysis. Finally, we simulated the α background spectrum with Geant4 tool-kit, consequently taking into account complex α-γ-electron events, the α / β ratio dependence on the α energy, and the electron/γ nonproportionality. We found that α-γ mixed events have higher light yield than expected for alpha particles alone, which leads to overestimation of the α / β ratio when it is measured with internal 227Th and 223Ra isotopes. The time-amplitude analysis showed that the α peaks of 219Rn and 215Po in LaBr3(Ce) and LaBr3(Ce,Sr) are not symmetric. We compared the simulation results with the measured data and provided further evidence of the important role of mixed α-γ-electron events for understanding the shape of the internal α spectrum in scintillators.

Monte Carlo simulation of HERD calorimeter

NASA Astrophysics Data System (ADS)

Xu, M.; Chen, G. M.; Dong, Y. W.; Lu, J. G.; Quan, Z.; Wang, L.; Wang, Z. G.; Wu, B. B.; Zhang, S. N.

2014-07-01

The High Energy cosmic-Radiation Detection (HERD) facility onboard China's Space Station is planned for operation starting around 2020 for about 10 years. It is designed as a next generation space facility focused on indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. The calorimeter plays an essential role in the main scientific objectives of HERD. A 3-D cubic calorimeter filled with high granularity crystals as active material is a very promising choice for the calorimeter. HERD is mainly composed of a 3-D calorimeter (CALO) surrounded by silicon trackers (TK) from all five sides except the bottom. CALO is made of 9261 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. Here the simulation results of the performance of CALO with GEANT4 and FLUKA are presented: 1) the total absorption CALO and its absorption depth for precise energy measurements (energy resolution: 1% for electrons and gammarays beyond 100 GeV, 20% for protons from 100 GeV to 1 PeV); 2) its granularity for particle identification (electron/proton separation power better than 10-5); 3) the homogenous geometry for detecting particles arriving from every unblocked direction for large effective geometrical factor (<3 m2sr for electron and diffuse gammarays, >2 m2sr for cosmic ray nuclei); 4) expected observational results such as gamma-ray line spectrum from dark matter annihilation and spectrum measurement of various cosmic ray chemical components.

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

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

Sung, C., E-mail: csung@physics.ucla.edu; White, A. E.; Greenwald, M.

2016-04-15

Long wavelength turbulent electron temperature fluctuations (k{sub y}ρ{sub s} < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local,more » electrostatic ion-scale simulations (k{sub y}ρ{sub s} ≲ 1.7) performed at r/a ∼ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].« less

Simulation of decay processes and radiation transport times in radioactivity measurements

NASA Astrophysics Data System (ADS)

García-Toraño, E.; Peyres, V.; Bé, M.-M.; Dulieu, C.; Lépy, M.-C.; Salvat, F.

2017-04-01

The Fortran subroutine package PENNUC, which simulates random decay pathways of radioactive nuclides, is described. The decay scheme of the active nuclide is obtained from the NUCLEIDE database, whose web application has been complemented with the option of exporting nuclear decay data (possible nuclear transitions, branching ratios, type and energy of emitted particles) in a format that is readable by the simulation subroutines. In the case of beta emitters, the initial energy of the electron or positron is sampled from the theoretical Fermi spectrum. De-excitation of the atomic electron cloud following electron capture and internal conversion is described using transition probabilities from the LLNL Evaluated Atomic Data Library and empirical or calculated energies of released X rays and Auger electrons. The time evolution of radiation showers is determined by considering the lifetimes of nuclear and atomic levels, as well as radiation propagation times. Although PENNUC is designed to operate independently, here it is used in conjunction with the electron-photon transport code PENELOPE, and both together allow the simulation of experiments with radioactive sources in complex material structures consisting of homogeneous bodies limited by quadric surfaces. The reliability of these simulation tools is demonstrated through comparisons of simulated and measured energy spectra from radionuclides with complex multi-gamma spectra, nuclides with metastable levels in their decay pathways, nuclides with two daughters, and beta plus emitters.

Properties of laser-produced GaAs plasmas measured from highly resolved X-ray line shapes and ratios

NASA Astrophysics Data System (ADS)

Seely, J. F.; Fein, J.; Manuel, M.; Keiter, P.; Drake, P.; Kuranz, C.; Belancourt, Patrick; Ralchenko, Yu.; Hudson, L.; Feldman, U.

2018-03-01

The properties of hot, dense plasmas generated by the irradiation of GaAs targets by the Titan laser at Lawrence Livermore National Laboratory were determined by the analysis of high resolution K shell spectra in the 9 keV to 11 keV range. The laser parameters, such as relatively long pulse duration and large focal spot, were chosen to produce a steady-state plasma with minimal edge gradients, and the time-integrated spectra were compared to non-LTE steady state spectrum simulations using the FLYCHK and NOMAD codes. The bulk plasma streaming velocity was measured from the energy shifts of the Ga He-like transitions and Li-like dielectronic satellites. The electron density and the electron energy distribution, both the thermal and the hot non-thermal components, were determined from the spectral line ratios. After accounting for the spectral line broadening contributions, the plasma turbulent motion was measured from the residual line widths. The ionization balance was determined from the ratios of the He-like through F-like spectral features. The detailed comparison of the experimental Ga spectrum and the spectrum simulated by the FLYCHK code indicates two significant discrepancies, the transition energy of a Li-like dielectronic satellite (designated t) and the calculated intensity of a He-like line (x), that should lead to improvements in the kinetics codes used to simulate the X-ray spectra from highly-charged ions.

Influence of electromechanical coupling on optical properties of InGaN quantum-dot based light-emitting diodes.

PubMed

Barettin, Daniele; Maur, Matthias Auf der; Carlo, Aldo di; Pecchia, Alessandro; Tsatsulnikov, Andrei F; Sakharov, Alexei V; Lundin, Wsevolod V; Nikolaev, Andrei E; Usov, Sergey O; Cherkashin, Nikolay; Hÿtch, Martin J; Karpov, Sergey Yu

2017-01-06

The impact of electromechanical coupling on optical properties of light-emitting diodes (LEDs) with InGaN/GaN quantum-dot (QD) active regions is studied by numerical simulations. The structure, i.e. the shape and the average In content of the QDs, has been directly derived from experimental data on out-of-plane strain distribution obtained from the geometric-phase analysis of a high-resolution transmission electron microscopy image of an LED structure grown by metalorganic vapor-phase epitaxy. Using continuum [Formula: see text] calculations, we have studied first the lateral and full electromechanical coupling between the QDs in the active region and its impact on the emission spectrum of a single QD located in the center of the region. Our simulations demonstrate the spectrum to be weakly affected by the coupling despite the strong common strain field induced in the QD active region. Then we analyzed the effect of vertical coupling between vertically stacked QDs as a function of the interdot distance. We have found that QCSE gives rise to a blue-shift of the overall emission spectrum when the interdot distance becomes small enough. Finally, we compared the theoretical spectrum obtained from simulation of the entire active region with an experimental electroluminescence (EL) spectrum. While the theoretical peak emission wavelength of the selected central QD corresponded well to that of the EL spectrum, the width of the latter one was determined by the scatter in the structures of various QDs located in the active region. Good agreement between the simulations and experiment achieved as a whole validates our model based on realistic structure of the QD active region and demonstrates advantages of the applied approach.

Investigation on the energy spectrums of electrons in atmospheric pressure argon plasma jets and their dependences on the applied voltage

NASA Astrophysics Data System (ADS)

Chen, Xinxian; Tan, Zhenyu; Liu, Yadi; Li, Xiaotong; Pan, Jie; Wang, Xiaolong

2017-08-01

This work presents a systematical investigation on the spatiotemporal evolution of the energy spectrum of electrons in atmospheric pressure argon plasma jets and its dependence on the applied voltage. The investigations are carried out by means of the numerical simulation based on a particle-in-cell Monte-Carlo collision model. The characteristics of the spatiotemporal evolution of the energy spectrum of electrons (ESE) in the discharge space have been presented, and especially the mechanisms of inducing these characteristics have also been revealed. The present work shows the following conclusions. In the evolution of ESE, there is a characteristic time under each applied voltage. Before the characteristic time, the peak value of ESE decreases, the peak position shifts toward high energy, and the distribution of ESE becomes wider and wider, but the reverse is true after the characteristic time. The formation of these characteristics can be mainly attributed to the transport of electrons toward a low electric field as well as a balance between the energy gained from the electric field including the effect of space charges and the energy loss due to inelastic collisions in the process of electron transport. The characteristic time decreases with the applied voltage. In addition, the average energy of electrons at the characteristic time can be increased by enhancing the applied voltage. The results presented in this work are of importance for regulating and controlling the energy of electrons in the plasma jets applied to plasma medicine.

Effect of electron transport properties on unipolar CdZnTe radiation detectors: LUND, SpectrumPlus, and Coplanar Grid

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

Ralph B. James

2000-01-07

Device simulations of (1) the laterally-contacted-unipolar-nuclear detector (LUND), (2) the SpectrumPlus, (3) and the coplanar grid made of Cd{sub 0.9}Zn{sub 0.1}Te (CZT) were performed for {sup 137}Cs irradiation by 662.15 keV gamma-rays. Realistic and controlled simulations of the gamma-ray interactions with the CZT material were done using the MCNP4B2 Monte Carlo program, and the detector responses were simulated using the Sandia three-dimensional multielectrode simulation program (SandTMSP). The simulations were done for the best and the worst expected carrier nobilities and lifetimes of currently commercially available CZT materials for radiation detector applications. For the simulated unipolar devices, the active device volumesmore » were relatively large and the energy resolutions were fairly good, but these performance characteristics were found to be very sensitive to the materials properties. The internal electric fields, the weighting potentials, and the charge induced efficiency maps were calculated to give insights into the operation of these devices.« less

Plasmon tsunamis on metallic nanoclusters.

PubMed

Lucas, A A; Sunjic, M

2012-03-14

A model is constructed to describe inelastic scattering events accompanying electron capture by a highly charged ion flying by a metallic nanosphere. The electronic energy liberated by an electron leaving the Fermi level of the metal and dropping into a deep Rydberg state of the ion is used to increase the ion kinetic energy and, simultaneously, to excite multiple surface plasmons around the positively charged hole left behind on the metal sphere. This tsunami-like phenomenon manifests itself as periodic oscillations in the kinetic energy gain spectrum of the ion. The theory developed here extends our previous treatment (Lucas et al 2011 New J. Phys. 13 013034) of the Ar(q+)/C(60) charge exchange system. We provide an analysis of how the individual multipolar surface plasmons of the metallic sphere contribute to the formation of the oscillatory gain spectrum. Gain spectra showing characteristic, tsunami-like oscillations are simulated for Ar(15+) ions capturing one electron in distant collisions with Al and Na nanoclusters.

The effects of Coulomb collisions on O+, H+, and He+ plasmas for topside incoherent scatter radar applications at Jicamarca

NASA Astrophysics Data System (ADS)

Milla, M. A.; Kudeki, E.; Chau, J. L.

2012-12-01

Coulomb collision effects on incoherent scatter radar signals become important when radar beams are pointed perpendicular to the Earth's magnetic field (B). To study these effects, Milla and Kudeki [2011] developed a procedure to estimate the spectrum of plasma density fluctuations (also known as incoherent scatter spectrum) based on simulations of collisional particle trajectories in single-ion component plasmas. In these simulations, collision effects on the particle motion are modeled using the standard Fokker-Planck model of Rosenbluth et al. [1957]. We have recently generalized the procedure of Milla and Kudeki to consider the case of multiple ion components in order to study the characteristics of the incoherent scatter spectrum in O+, H+, and He+ ionospheric plasmas, which is needed for the analysis of topside perpendicular-to-B observations at the Jicamarca Radio Observatory. In this presentation, we will report on the development of this new approach and on the characteristics of the spectrum models that were developed. The simulation results show that the ion collision process can be fairly well approximated as a Gaussian motion process, a model that has been previously studied in the literature by different authors. However, in the case of electron collisions, the process is not Gaussian having a complicated dependence on plasma parameters. As it will be discussed, electron collisions have a significant impact on the shape of the incoherent scatter spectrum. The ultimate application of the models that were developed is the simultaneous estimation of plasma drifts, densities, and temperatures of the topside equatorial ionosphere in perpendicular-to-B experiments at Jicamarca. This experimental evaluation will have a broader impact since the accuracy of the Fokker-Planck collision model will be tested. References: Milla, M. A., and E. Kudeki (2011), Incoherent scatter spectral theories-Part II: Modeling the spectrum for modes propagating perpendicular to B, IEEE Transactions on Geoscience and Remote Sensing, 49(1), 329-345, doi:10.1109/TGRS.2010.2057253. Rosenbluth, M. N., W. M. MacDonald, and D. L. Judd (1957), Fokker-Planck equation for an inverse-square force, Physical Review, 107(1), 1-6, doi:10.1103/PhysRev.107.1.

Footprints of electron correlation in strong-field double ionization of Kr close to the sequential-ionization regime

NASA Astrophysics Data System (ADS)

Li, Xiaokai; Wang, Chuncheng; Yuan, Zongqiang; Ye, Difa; Ma, Pan; Hu, Wenhui; Luo, Sizuo; Fu, Libin; Ding, Dajun

2017-09-01

By combining kinematically complete measurements and a semiclassical Monte Carlo simulation we study the correlated-electron dynamics in the strong-field double ionization of Kr. Interestingly, we find that, as we step into the sequential-ionization regime, there are still signatures of correlation in the two-electron joint momentum spectrum and, more intriguingly, the scaling law of the high-energy tail is completely different from early predictions on the low-Z atom (He). These experimental observations are well reproduced by our generalized semiclassical model adapting a Green-Sellin-Zachor potential. It is revealed that the competition between the screening effect of inner-shell electrons and the Coulomb focusing of nuclei leads to a non-inverse-square central force, which twists the returned electron trajectory at the vicinity of the parent core and thus significantly increases the probability of hard recollisions between two electrons. Our results might have promising applications ranging from accurately retrieving atomic structures to simulating celestial phenomena in the laboratory.

Multi-Orbital contributions in High Harmonic Generation

NASA Astrophysics Data System (ADS)

Guehr, Markus

2009-05-01

The high harmonic spectrum generated from atoms or molecules in a strong laser field contains information about the electronic structure of the generation medium. In the high harmonic generation (HHG) process, a free electron wave packet tunnel-ionizes from the molecular orbital in a strong laser field. After being accelerated by the laser electric field, the free electron wave packet coherently recombines to the orbital from which is was initially ionized, thereby emitting the harmonic spectrum. Interferences between the free electron wave packet and the molecular orbital will shape the spectrum in a characteristic way. These interferences have been used to tomographically image the highest occupied molecular orbital (HOMO) of N2 [1]. Molecular electronic states energetically below the HOMO should contribute to laser-driven high harmonic generation (HHG), but this behavior has not been observed previously. We have observed evidence of HHG from multiple orbitals in aligned N2 [2]. The tunneling ionization (and therefore the harmonic generation) is most efficient if the orbital has a large extension in the direction of the harmonic generation polarization. The HOMO with its σg symmetry therefore dominates the harmonic spectrum if the molecular axis is parallel to the harmonic generation polarization, the lower bound πu HOMO-1 dominates in the perpendicular case. The HOMO contributions appear as a regular plateau with a cutoff in the HHG spectrum. In contrast, the HOMO-1 signal is strongly peaked in the cutoff region. We explain this by semi-classical simulations of the recombination process that show constructive interferences between the HOMO-1 and the recombining wave packet in the cutoff region. The ability to monitor several orbitals opens the route to imaging coherent superpositions of electronic orbitals. [1] J. Itatani et al., Nature 432, 867 (2004)[2] B. K. McFarland, J. P. Farrell, P. H. Bucksbaum and M. Gühr, Science 322, 1232 (2008)

Radiation transport in kinetic simulations and the influence of photoemission on electron current in self-sustaining discharges

DOE PAGES

Fierro, Andrew S.; Moore, Christopher Hudson; Scheiner, Brett; ...

2017-01-12

A kinetic description for electronic excitation of helium for principal quantum number nmore » $$\\leqslant $$ 4 has been included into a particle-in-cell (PIC) simulation utilizing direct simulation Monte Carlo (DSMC) for electron-neutral interactions. The excited electronic levels radiate state-dependent photons with wavelengths from the extreme ultraviolet (EUV) to visible regimes. Photon wavelengths are chosen according to a Voigt distribution accounting for the natural, pressure, and Doppler broadened linewidths. This method allows for reconstruction of the emission spectrum for a non-thermalized electron energy distribution function (EEDF) and investigation of high energy photon effects on surfaces, specifically photoemission. A parallel plate discharge with a fixed field (i.e. space charge neglected) is used to investigate the effects of including photoemission for a Townsend discharge. When operating at a voltage near the self-sustaining discharge threshold, it is observed that the electron current into the anode is higher when including photoemission from the cathode than without even when accounting for self-absorption from ground state atoms. As a result, the photocurrent has been observed to account for as much as 20% of the total current from the cathode under steady-state conditions.« less

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

Nakanotani, Masaru; Matsukiyo, Shuichi; Hada, Tohru

A shock–shock interaction is investigated by using a one-dimensional full particle-in-cell simulation. The simulation reproduces the collision of two symmetrical high Mach number quasi-perpendicular shocks. The basic structure of the shocks and ion dynamics is similar to that obtained by previous hybrid simulations. The new aspects obtained here are as follows. Electrons are already strongly accelerated before the two shocks collide through multiple reflection. The reflected electrons self-generate waves upstream between the two shocks before they collide. The waves far upstream are generated through the right-hand resonant instability with the anomalous Doppler effect. The waves generated near the shock aremore » due to firehose instability and have much larger amplitudes than those due to the resonant instability. The high-energy electrons are efficiently scattered by the waves so that some of them gain large pitch angles. Those electrons can be easily reflected at the shock of the other side. The accelerated electrons form a power-law energy spectrum. Due to the accelerated electrons, the pressure of upstream electrons increases with time. This appears to cause the deceleration of the approaching shock speed. The accelerated electrons having sufficiently large Larmor radii are further accelerated through the similar mechanism working for ions when the two shocks are colliding.« less

Modeling quantum cascade lasers: Coupled electron and phonon transport far from equilibrium and across disparate spatial scales

DOE PAGES

Shi, Y. B.; Mei, S.; Jonasson, O.; ...

2016-12-28

Quantum cascade lasers (QCLs) are high-power coherent light sources in the midinfrared and terahertz parts of the electromagnetic spectrum. They are devices in which the electronic and lattice systems are far from equilibrium, strongly coupled to one another, and the problem bridges disparate spatial scales. Here, we present our ongoing work on the multiphysics and multiscale simulation of far-from-equilibrium transport of charge and heat in midinfrared QCLs.

Metallic hydrogen with a strong electron-phonon interaction at a pressure of 300-500 GPa

NASA Astrophysics Data System (ADS)

Degtyarenko, N. N.; Mazur, E. A.; Grishakov, K. S.

2017-08-01

Atomic metallic hydrogen with a lattice with FDDD symmetry is shown to have a stable phase under hydrostatic compression pressure in the range of 350-500 GPа. The resulting structure has a stable spectrum regarding the collapse of the phonons. Ab-unitio simulation method has been used to calculate the structural, electronic, phononic and other characteristics of the normal metallic phase of the hydrogen at a pressure of 350-500 GPA.

Gigavolt Bound free Transitions Driven by Extreme Light

DTIC Science & Technology

2016-05-12

negligible role in near term scenarios, but become interesting in the multi-exawatt regime. A significant advance in numerical particle tracking is... negligible , the total momentum distribution is f(p) = ∑ i |Srip| 2 (14) where i indexes each ion. By loading a large number of ions into any given simulation...spectrum of tunnel ionized electrons. RR is the force acting on an electron due to its own fields. This force is normally negligible , only becoming

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.

Toward 10 meV electron energy-loss spectroscopy resolution for plasmonics.

PubMed

Bellido, Edson P; Rossouw, David; Botton, Gianluigi A

2014-06-01

Energy resolution is one of the most important parameters in electron energy-loss spectroscopy. This is especially true for measurement of surface plasmon resonances, where high-energy resolution is crucial for resolving individual resonance peaks, in particular close to the zero-loss peak. In this work, we improve the energy resolution of electron energy-loss spectra of surface plasmon resonances, acquired with a monochromated beam in a scanning transmission electron microscope, by the use of the Richardson-Lucy deconvolution algorithm. We test the performance of the algorithm in a simulated spectrum and then apply it to experimental energy-loss spectra of a lithographically patterned silver nanorod. By reduction of the point spread function of the spectrum, we are able to identify low-energy surface plasmon peaks in spectra, more localized features, and higher contrast in surface plasmon energy-filtered maps. Thanks to the combination of a monochromated beam and the Richardson-Lucy algorithm, we improve the effective resolution down to 30 meV, and evidence of success up to 10 meV resolution for losses below 1 eV. We also propose, implement, and test two methods to limit the number of iterations in the algorithm. The first method is based on noise measurement and analysis, while in the second we monitor the change of slope in the deconvolved spectrum.

Quasi-linear analysis of the extraordinary electron wave destabilized by runaway electrons

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

Pokol, G. I.; Kómár, A.; Budai, A.

2014-10-15

Runaway electrons with strongly anisotropic distributions present in post-disruption tokamak plasmas can destabilize the extraordinary electron (EXEL) wave. The present work investigates the dynamics of the quasi-linear evolution of the EXEL instability for a range of different plasma parameters using a model runaway distribution function valid for highly relativistic runaway electron beams produced primarily by the avalanche process. Simulations show a rapid pitch-angle scattering of the runaway electrons in the high energy tail on the 100–1000 μs time scale. Due to the wave-particle interaction, a modification to the synchrotron radiation spectrum emitted by the runaway electron population is foreseen, exposing amore » possible experimental detection method for such an interaction.« less

Electron emission from condensed phase material induced by fast protons.

PubMed

Shinpaugh, J L; McLawhorn, R A; McLawhorn, S L; Carnes, K D; Dingfelder, M; Travia, A; Toburen, L H

2011-02-01

Monte Carlo track simulation has become an important tool in radiobiology. Monte Carlo transport codes commonly rely on elastic and inelastic electron scattering cross sections determined using theoretical methods supplemented with gas-phase data; experimental condensed phase data are often unavailable or infeasible. The largest uncertainties in the theoretical methods exist for low-energy electrons, which are important for simulating electron track ends. To test the reliability of these codes to deal with low-energy electron transport, yields of low-energy secondary electrons ejected from thin foils have been measured following passage of fast protons. Fast ions, where interaction cross sections are well known, provide the initial spectrum of low-energy electrons that subsequently undergo elastic and inelastic scattering in the material before exiting the foil surface and being detected. These data, measured as a function of the energy and angle of the emerging electrons, can provide tests of the physics of electron transport. Initial measurements from amorphous solid water frozen to a copper substrate indicated substantial disagreement with MC simulation, although questions remained because of target charging. More recent studies, using different freezing techniques, do not exhibit charging, but confirm the disagreement seen earlier between theory and experiment. One now has additional data on the absolute differential electron yields from copper, aluminum and gold, as well as for thin films of frozen hydrocarbons. Representative data are presented.

Electron emission from condensed phase material induced by fast protons†

PubMed Central

Shinpaugh, J. L.; McLawhorn, R. A.; McLawhorn, S. L.; Carnes, K. D.; Dingfelder, M.; Travia, A.; Toburen, L. H.

2011-01-01

Monte Carlo track simulation has become an important tool in radiobiology. Monte Carlo transport codes commonly rely on elastic and inelastic electron scattering cross sections determined using theoretical methods supplemented with gas-phase data; experimental condensed phase data are often unavailable or infeasible. The largest uncertainties in the theoretical methods exist for low-energy electrons, which are important for simulating electron track ends. To test the reliability of these codes to deal with low-energy electron transport, yields of low-energy secondary electrons ejected from thin foils have been measured following passage of fast protons. Fast ions, where interaction cross sections are well known, provide the initial spectrum of low-energy electrons that subsequently undergo elastic and inelastic scattering in the material before exiting the foil surface and being detected. These data, measured as a function of the energy and angle of the emerging electrons, can provide tests of the physics of electron transport. Initial measurements from amorphous solid water frozen to a copper substrate indicated substantial disagreement with MC simulation, although questions remained because of target charging. More recent studies, using different freezing techniques, do not exhibit charging, but confirm the disagreement seen earlier between theory and experiment. One now has additional data on the absolute differential electron yields from copper, aluminum and gold, as well as for thin films of frozen hydrocarbons. Representative data are presented. PMID:21183539

Boron doped simulated graphene field effect transistor model

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

Sharma, Preetika, E-mail: preetikamadhav@yahoo.co.in; Gupta, Shuchi, E-mail: sgupta@pu.ac.in; Kaur, Inderpreet, E-mail: inderpreety@yahoo.co.in

2016-05-06

Graphene based electronic devices due to its unique properties has transformed electronics. A Graphene Field Effect Transistor (GNRFET) model is simulated in Virtual Nano Lab (VNL) and the calculations are based on density functional theory (DFT). Simulations were performed on this pristine GNRFET model and the transmission spectrum was observed. The graph obtained showed a uniform energy gap of +1 to −1eV and the highest transmission peak at −1.75 eV. To this pristine model of GNRFET, doping was introduced and its effect was seen on the Fermi level obtained in the transmission spectrum. Boron as a dopant was used whichmore » showed variations in both the transmission peaks and the energy gap. In this model, first the single boron was substituted in place of carbon and Fermi level showed an energy gap of 1.5 to −0.5eV with the highest transmission peak at −1.3 eV. In another variation in the model, two carbon atoms were replaced by two boron atoms and Fermi level shifted from 2 to 0.25eV. In this observation, the highest transmission peak was observed at −1(approx.). The use of nanoelectronic devices have opened many areas of applications as GFET is an excellent building block for electronic circuits, and is being used in applications such as high-performance frequency doublers and mixers, digital modulators, phase detectors, optoelectronics and spintronics.« less

Solute-Solvent Charge-Transfer Excitations and Optical Absorption of Hydrated Hydroxide from Time-Dependent Density-Functional Theory.

PubMed

Opalka, Daniel; Sprik, Michiel

2014-06-10

The electronic structure of simple hydrated ions represents one of the most challenging problems in electronic-structure theory. Spectroscopic experiments identified the lowest excited state of the solvated hydroxide as a charge-transfer-to-solvent (CTTS) state. In the present work we report computations of the absorption spectrum of the solvated hydroxide ion, treating both solvent and solute strictly at the same level of theory. The average absorption spectrum up to 25 eV has been computed for samples taken from periodic ab initio molecular dynamics simulations. The experimentally observed CTTS state near the onset of the absorption threshold has been analyzed at the generalized-gradient approximation (GGA) and with a hybrid density-functional. Based on results for the lowest excitation energies computed with the HSE hybrid functional and a Davidson diagonalization scheme, the CTTS transition has been found 0.6 eV below the first absorption band of liquid water. The transfer of an electron to the solvent can be assigned to an excitation from the solute 2pπ orbitals, which are subject to a small energetic splitting due to the asymmetric solvent environment, to the significantly delocalized lowest unoccupied orbital of the solvent. The distribution of the centers of the excited state shows that CTTS along the OH(-) axis of the hydroxide ion is avoided. Furthermore, our simulations indicate that the systematic error arising in the calculated spectrum at the GGA originates from a poor description of the valence band energies in the solution.

Monte Carlo simulation of MOSFET dosimeter for electron backscatter using the GEANT4 code.

PubMed

Chow, James C L; Leung, Michael K K

2008-06-01

The aim of this study is to investigate the influence of the body of the metal-oxide-semiconductor field effect transistor (MOSFET) dosimeter in measuring the electron backscatter from lead. The electron backscatter factor (EBF), which is defined as the ratio of dose at the tissue-lead interface to the dose at the same point without the presence of backscatter, was calculated by the Monte Carlo simulation using the GEANT4 code. Electron beams with energies of 4, 6, 9, and 12 MeV were used in the simulation. It was found that in the presence of the MOSFET body, the EBFs were underestimated by about 2%-0.9% for electron beam energies of 4-12 MeV, respectively. The trend of the decrease of EBF with an increase of electron energy can be explained by the small MOSFET dosimeter, mainly made of epoxy and silicon, not only attenuated the electron fluence of the electron beam from upstream, but also the electron backscatter generated by the lead underneath the dosimeter. However, this variation of the EBF underestimation is within the same order of the statistical uncertainties as the Monte Carlo simulations, which ranged from 1.3% to 0.8% for the electron energies of 4-12 MeV, due to the small dosimetric volume. Such small EBF deviation is therefore insignificant when the uncertainty of the Monte Carlo simulation is taken into account. Corresponding measurements were carried out and uncertainties compared to Monte Carlo results were within +/- 2%. Spectra of energy deposited by the backscattered electrons in dosimetric volumes with and without the lead and MOSFET were determined by Monte Carlo simulations. It was found that in both cases, when the MOSFET body is either present or absent in the simulation, deviations of electron energy spectra with and without the lead decrease with an increase of the electron beam energy. Moreover, the softer spectrum of the backscattered electron when lead is present can result in a reduction of the MOSFET response due to stronger recombination in the SiO2 gate. It is concluded that the MOSFET dosimeter performed well for measuring the electron backscatter from lead using electron beams. The uncertainty of EBF determined by comparing the results of Monte Carlo simulations and measurements is well within the accuracy of the MOSFET dosimeter (< +/- 4.2%) provided by the manufacturer.

Theoretical comparison and experimental test of the secular and nonperturbative approaches on the ESR lineshapes of randomly oriented, anisotropic systems undergoing internal motion

NASA Astrophysics Data System (ADS)

Benetis, N. P.; Sjöqvist, L.; Lund, A.; Maruani, J.

The nuclear Zeeman and the electronic nonsecular parts of the spin Hamiltonian complicate the ESR lineshape of exchanging anisotropic spin systems by introducing, at high field, "forbidden" transitions and, at low field, additional shift and splitting. We compare the nonperturbative with the secular approach for such systems. The exchange is treated within the Kaplan-Alexander limit and both A and g tensors are included, resulting in spectrum asymmetry, in contrast to previous separate treatments. The two approaches are then used to simulate the powder spectrum of OCH 2COO - and compare the results to experimental spectra of an irradiated powder of ZnAc. The powder X-band spectra simulations using the secular approach appear to be accurate. For both the low-field (20 to 200 G) and the high-field (Q-band) regions, however, the nonsecular part of the electronic term and the nuclear Zeeman term, respectively, cannot be neglected. On the other hand, the approximate approach is much faster and consequently more appropriate for treating large, multisite exchanging systems.

A model of the saturation of coupled electron and ion scale gyrokinetic turbulence

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

Staebler, Gary M.; Howard, Nathan T.; Candy, Jeffrey M.

A new paradigm of zonal flow mixing as the mechanism by which zonal E × B fluctuations impact the saturation of gyrokinetic turbulence has recently been deduced from the nonlinear 2D spectrum of electric potential fluctuations in gyrokinetic simulations. These state of the art simulations span the physical scales of both ion and electron turbulence. It was found that the zonal flow mixing rate, rather than zonal flow shearing rate, competes with linear growth at both electron and ion scales. A model for saturation of the turbulence by the zonal flow mixing was developed and applied to the quasilinear trappedmore » gyro-Landau fluid transport model (TGLF). The first validation tests of the new saturation model are reported in this paper with data from L-mode and high-β p regime discharges from the DIII-D tokamak. Lastly, the shortfall in the predicted L-mode edge electron energy transport is improved with the new saturation model for these discharges but additional multiscale simulations are required in order to verify the safety factor and collisionality dependencies found in the modeling.« less

SOFT: a synthetic synchrotron diagnostic for runaway electrons

NASA Astrophysics Data System (ADS)

Hoppe, M.; Embréus, O.; Tinguely, R. A.; Granetz, R. S.; Stahl, A.; Fülöp, T.

2018-02-01

Improved understanding of the dynamics of runaway electrons can be obtained by measurement and interpretation of their synchrotron radiation emission. Models for synchrotron radiation emitted by relativistic electrons are well established, but the question of how various geometric effects—such as magnetic field inhomogeneity and camera placement—influence the synchrotron measurements and their interpretation remains open. In this paper we address this issue by simulating synchrotron images and spectra using the new synthetic synchrotron diagnostic tool SOFT (Synchrotron-detecting Orbit Following Toolkit). We identify the key parameters influencing the synchrotron radiation spot and present scans in those parameters. Using a runaway electron distribution function obtained by Fokker-Planck simulations for parameters from an Alcator C-Mod discharge, we demonstrate that the corresponding synchrotron image is well-reproduced by SOFT simulations, and we explain how it can be understood in terms of the parameter scans. Geometric effects are shown to significantly influence the synchrotron spectrum, and we show that inherent inconsistencies in a simple emission model (i.e. not modeling detection) can lead to incorrect interpretation of the images.

A model of the saturation of coupled electron and ion scale gyrokinetic turbulence

DOE PAGES

Staebler, Gary M.; Howard, Nathan T.; Candy, Jeffrey M.; ...

2017-05-09

A new paradigm of zonal flow mixing as the mechanism by which zonal E × B fluctuations impact the saturation of gyrokinetic turbulence has recently been deduced from the nonlinear 2D spectrum of electric potential fluctuations in gyrokinetic simulations. These state of the art simulations span the physical scales of both ion and electron turbulence. It was found that the zonal flow mixing rate, rather than zonal flow shearing rate, competes with linear growth at both electron and ion scales. A model for saturation of the turbulence by the zonal flow mixing was developed and applied to the quasilinear trappedmore » gyro-Landau fluid transport model (TGLF). The first validation tests of the new saturation model are reported in this paper with data from L-mode and high-β p regime discharges from the DIII-D tokamak. Lastly, the shortfall in the predicted L-mode edge electron energy transport is improved with the new saturation model for these discharges but additional multiscale simulations are required in order to verify the safety factor and collisionality dependencies found in the modeling.« less

An Application of the Direct Coulomb Electron Pair Production Process to the Energy Measurement of the "VH-Group" in the "Knee" Region of the "All-Particle" Energy Spectrum

NASA Technical Reports Server (NTRS)

Derrickson, J. H.; Wu, J.; Christl, M. J.; Fountain, W. F.; Parnell, T. A.

1999-01-01

The "all-particle" cosmic ray energy spectrum appears to be exhibiting a significant change in the spectral index just above approximately 3000 TeV. This could indicate (1) a change in the propagation of the cosmic rays in the galactic medium, and/or (2) the upper limit of the supernova shock wave acceleration mechanism, and/or (3) a new source of high-energy cosmic rays. Air shower and JACEE data indicate the spectral change is associated with a composition change to a heavier element mixture whereas DICE does not indicate this. A detector concept will be presented that utilizes the energy dependence of the production of direct Coulomb electron-positron pairs by energetic heavy ions. Monte Carlo simulations of a direct electron pair detector consisting of Pb target foils interleaved with planes of 1-mm square scintillating optical fibers will be discussed. The goal is to design a large area, non-saturating instrument to measure the energy spectrum of the individual cosmic ray elements in the "VH-group" for energies greater than 10 TeV/nucleon.

Anharmonic Vibrational Analyses of Pentapeptide Conformations Explored with Enhanced Sampling Simulations.

PubMed

Otaki, Hiroki; Yagi, Kiyoshi; Ishiuchi, Shun-Ichi; Fujii, Masaaki; Sugita, Yuji

2016-10-06

An accurate theoretical prediction of the vibrational spectrum of polypeptides remains to be a challenge due to (1) their conformational flexibility and (2) non-negligible anharmonic effects. The former makes the search for conformers that contribute to the spectrum difficult, and the latter requires an expensive, quantum mechanical calculation for both electrons and vibrations. Here, we propose a new theoretical approach, which implements an enhanced conformational sampling by the replica-exchange molecular dynamics method, a structural clustering to identify distinct conformations, and a vibrational structure calculation by the second-order vibrational quasi-degenerate perturbation theory (VQDPT2). A systematic mode-selection scheme is developed to reduce the cost of VQDPT2 and the generation of a potential energy surface by the electronic structure calculation. The proposed method is applied to a pentapeptide, SIVSF-NH 2 , for which the infrared spectrum has recently been measured in the gas phase with high resolution in the OH and NH stretching region. The theoretical spectrum of the lowest energy conformer is obtained with a mean absolute deviation of 11.2 cm -1 from the experimental spectrum. Furthermore, the NH stretching frequencies of the five lowest energy conformers are found to be consistent with the literature values measured for small peptides with a similar secondary structure. Therefore, the proposed method is a promising way to analyze the vibrational spectrum of polypeptides.

Experimental and theoretical study of the electronic spectrum of the BAr2 complex: Transition to the excited valence B(2s2p2 2D) state

NASA Astrophysics Data System (ADS)

Krumrine, Jennifer R.; Alexander, Millard H.; Yang, Xin; Dagdigian, Paul J.

2000-03-01

The 2s2p22D←2s22p 2P valence transition in the BAr2 cluster is investigated in a collaborative experimental and theoretical study. Laser fluorescence excitation spectra of a supersonic expansion of B atoms entrained in Ar at high source backing pressures display several features not assignable to the BAr complex. Resonance fluorescence is not observed, but instead emission from the lower 3s state. Size-selected fluorescence depletion spectra show that these features in the excitation spectrum are primarily due to the BAr2 complex. This electronic transition within BAr2 is modeled theoretically, similarly to our earlier study of the 3s←2p transition [M. H. Alexander et al., J. Chem. Phys. 106, 6320 (1997)]. The excited potential energy surfaces of the fivefold degenerate B(2s2p22D) state within the ternary complex are computed in a pairwise-additive model employing diatomic BAr potential energy curves which reproduce our previous experimental observations on the electronic states emanating from the B(2D)+Ar asymptote. The simulated absorption spectrum reproduces reasonably well the observed fluorescence depletion spectrum. The theoretical model lends insight into the energetics of the approach of B to multiple Ar atoms, and how the orientation of B p-orbitals governs the stability of the complex.

Study of Collective Beam Effects in Energy Recovery Linac Driven Free Electron Lasers

NASA Astrophysics Data System (ADS)

Hall, Christpher C.

Collective beam effects such as coherent synchrotron radiation (CSR) and longitudinal space charge (LSC) can degrade the quality of high-energy electron beams used for applications such as free-electron lasers (FELs). The advent of energy recovery linac (ERL)-based FELs brings exciting possibilities for very high-average current FELs that can operate with greater efficiency. However, due to the structure of ERLs, they may be even more susceptible to CSR. It is therefore necessary that these collective beam effects be well understood if future ERL-based designs are to be successful. The Jefferson Laboratory ERL driven IR FEL provides an ideal test-bed for looking at how CSR impacts the electron beam. Due to its novel design we can easily test how CSR's impact on the beam varies as a function of compression within the machine. In this work we will look at measurements of both average energy loss and energy spectrum fragmentation as a function of bunch compression. These results are compared to particle tracking simulations including a 1D CSR model and, in general, good agreement is seen between simulation and measurement. Of particular interest is fragmentation of the energy spectrum that is observed due to CSR and LSC. We will also show how this fragmentation develops and how it can be mitigated through use of the sextupoles in the JLab FEL. Finally, a more complete 2D model is used to simulate CSR-beam interaction. Due to the parameters of the experiment it is expected that a 2D CSR model would yield different results than the 1D CSR model. However, excellent agreement is seen between the two CSR model results.

Ab initio modeling of nonequilibrium electron-ion dynamics of iron in the warm dense matter regime

NASA Astrophysics Data System (ADS)

Ogitsu, T.; Fernandez-Pañella, A.; Hamel, S.; Correa, A. A.; Prendergast, D.; Pemmaraju, C. D.; Ping, Y.

2018-06-01

The spatiotemporal electron and ion relaxation dynamics of iron induced by femtosecond laser pulses was studied using a one-dimensional two-temperature model (1D-TTM) where electron and ion temperature-dependent thermophysical parameters such as specific heat (C ), electron-phonon coupling (G ), and thermal conductivity (K ) were calculated with ab initio density-functional-theory (DFT) simulations. Based on the simulated time evolutions of electron and ion temperature distributions [Te(x ,t ) and Ti(x ,t ) ], the time evolution of x-ray absorption near-edge spectroscopy (XANES) was calculated and compared with experimental results reported by Fernandez-Pañella et al., where the slope of XANES spectrum at the onset of absorption (s ) was used due to its excellent sensitivity to the electron temperature. Our results indicate that the ion temperature dependence on G and C , which is largely neglected in the past studies, is very important for studying the nonequilibrium electron-ion relaxation dynamics of iron in warm dense matter (WDM) conditions. It is also shown that the 1 /s behavior becomes very sensitive to the thermal gradient profile, in other words, to the values of K in a TTM simulation, for target thickness of about two to four times the mean free path of conduction electrons. Our approach based on 1D-TTM and XANES simulations can be used to determine the optimal combination of target geometry and laser fluence for a given target material, which will enable us to tightly constrain the thermophysical parameters under electron-ion nonequilibrium WDM conditions.

Simulating Terrestrial Gamma-ray Flashes using SWORD (Invited)

NASA Astrophysics Data System (ADS)

Gwon, C.; Grove, J.; Dwyer, J. R.; Mattson, K.; Polaski, D.; Jackson, L.

2013-12-01

We report on simulations of the relativistic feedback discharges involved with the production of terrestrial gamma-ray flashes (TGFs). The simulations were conducted using Geant4 using the SoftWare for the Optimization of Radiation Detectors (SWORD) framework. SWORD provides a graphical interface for setting up simulations in select high-energy radiation transport engines. Using Geant4, we determine avalanche length, the energy spectrum of the electrons and gamma-rays as they leave the field region, and the feedback factor describing the degree to which the production of energetic particles is self-sustaining. We validate our simulations against previous work in order to determine the reliability of our results. This work is funded by the Office of Naval Research.

Simulation of pyroshock environments using a tunable resonant fixture

DOEpatents

Davie, N.T.

1996-10-15

Disclosed are a method and apparatus for simulating pyrotechnic shock for the purpose of qualifying electronic components for use in weapons, satellite, and aerospace applications. According to the invention, a single resonant bar fixture has an adjustable resonant frequency in order to exhibit a desired shock response spectrum upon mechanical impact. The invention eliminates the need for availability of a large number of different fixtures, capable of exhibiting a range of shock response characteristics, in favor of a single tunable system. 32 figs.

Simulation of pyroshock environments using a tunable resonant fixture

DOEpatents

Davie, Neil T.

1996-01-01

Disclosed are a method and apparatus for simulating pyrotechnic shock for the purpose of qualifying electronic components for use in weapons, satellite, and aerospace applications. According to the invention, a single resonant bar fixture has an adjustable resonant frequency in order to exhibit a desired shock response spectrum upon mechanical impact. The invention eliminates the need for availability of a large number of different fixtures, capable of exhibiting a range of shock response characteristics, in favor of a single tunable system.

A first-principle calculation of the XANES spectrum of Cu2+ in water

NASA Astrophysics Data System (ADS)

La Penna, G.; Minicozzi, V.; Morante, S.; Rossi, G. C.; Stellato, F.

2015-09-01

The progress in high performance computing we are witnessing today offers the possibility of accurate electron density calculations of systems in realistic physico-chemical conditions. In this paper, we present a strategy aimed at performing a first-principle computation of the low energy part of the X-ray Absorption Spectroscopy (XAS) spectrum based on the density functional theory calculation of the electronic potential. To test its effectiveness, we apply the method to the computation of the X-ray absorption near edge structure part of the XAS spectrum in the paradigmatic, but simple case of Cu2+ in water. In order to keep into account the effect of the metal site structure fluctuations in determining the experimental signal, the theoretical spectrum is evaluated as the average over the computed spectra of a statistically significant number of simulated metal site configurations. The comparison of experimental data with theoretical calculations suggests that Cu2+ lives preferentially in a square-pyramidal geometry. The remarkable success of this approach in the interpretation of XAS data makes us optimistic about the possibility of extending the computational strategy we have outlined to the more interesting case of molecules of biological relevance bound to transition metal ions.

Computer simulation of the Farley-Buneman instability and anomalous electron heating in the auroral ionosphere

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

Machida, S.; Goertz, C.K.

1988-09-01

We study the nonlinear saturation of the Farley-Buneman instability in a collisional plasma by a 2 1/2 dimensional electrostatic particle simulation which includes inelastic and elastic collisions of electrons and elastic collision of ions with neutrals. In our simulation, a uniform convection electric field is applied externally so that the relative velocity between the electrons and ions is greater than the ion sound speed and destabilizes the instability. We find a nonlinear frequency shift from higher to lower frequencies and diffusion of the wave spectrum in two dimensional wave number space. We are especially interested in finding whether the saturatedmore » wave turbulence can account for the anomalous heating rates observed in the polar ionosphere by Schlegel and St.-Maurice (1981). We find that the dominant mechanism for electron heating is due to an enhanced effective electron collision frequency and hence enhanced resistive heating as suggested by Primdahl (1986) and Robinson (1986) and not due to the heating of electrons by the electric field of the waves parallel to the magnetic field. For the ionospheric conditions discussed by Schlegel and St.-Maurice (1981) we find an anomalous heating rate of about 4 x 10/sup -7/ W/m/sup 3/. copyright American Geophysical Union 1988« less

Singlet and doublet states UV-vis spectrum and electronic properties of 3-methylchrysene and 4-methylchrysene in glass matrix.

PubMed

Husain, Mudassir M; Tandon, H C; Varadwaj, Pradeep R

2008-03-01

The ultraviolet-visual spectrum of 3-methylchrysene, 4-methylchrysene and their radical cations formed by ultraviolet radiations, were measured in glass matrix at the room temperature. In the measured singlet state spectrum we were able to identify the alpha, p, beta, beta' (Clar's) or (1)L(b), (1)L(a)(1)B(b), (1)B(a) (Platt's notation) bands. The presence of alpha, beta or (1)L(b), (1)B(b) was confirmed by calculating their wavelength ratio lambda(alpha)/lambda(beta). Since matrix induces perturbation in the measured spectrum; it becomes necessary to take into account the perturbation while computing the spectrum. An effort has been made in this work to simulate the electronic spectrum in the same environment as is measured. This study presents the first calculated spectrum of these systems and their cations in glass matrix by semi empirical methods. To observe the magnitude of perturbation and hence to see the spectral shift in glass matrix, the spectrum was calculated in the free state as well. Spectral properties such as frontier orbitals gap, dipole moment, mean polarizabilities and its tensors were also computed both in glass matrix and free state using semiemperical method. The measured bands of 3-methylchrysene cation at wavelength 416.50 and 473.85 nm closely match with the available diffuse intersteallar bands (DIBs) at 417.55 and 472.64 nm, respectively. Also the observed 474.85 nm band of 4-methylchrysene cation matches the DIB at 476.00 nm.

Temporal characterization of ultrashort linearly chirped electron bunches generated from a laser wakefield accelerator

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

Zhang, C. J.; Hua, J. F.; Wan, Y.

A new method for diagnosing the temporal characteristics of ultrashort electron bunches with linear energy chirp generated from a laser wakefield accelerator is described. When the ionization-injected bunch interacts with the back of the drive laser, it is deflected and stretched along the direction of the electric field of the laser. Upon exiting the plasma, if the bunch goes through a narrow slit in front of the dipole magnet that disperses the electrons in the plane of the laser polarization, it can form a series of bunchlets that have different energies but are separated by half a laser wavelength. Sincemore » only the electrons that are undeflected by the laser go through the slit, the energy spectrum of the bunch is modulated. By analyzing the modulated energy spectrum, the shots where the bunch has a linear energy chirp can be recognized. Consequently, the energy chirp and beam current profile of those bunches can be reconstructed. Lastly, this method is demonstrated through particle-in-cell simulations and experiment.« less

Particle acceleration in laser-driven magnetic reconnection

DOE PAGES

Totorica, S. R.; Abel, T.; Fiuza, F.

2017-04-03

Particle acceleration induced by magnetic reconnection is thought to be a promising candidate for producing the nonthermal emissions associated with explosive phenomena such as solar flares, pulsar wind nebulae, and jets from active galactic nuclei. Laboratory experiments can play an important role in the study of the detailed microphysics of magnetic reconnection and the dominant particle acceleration mechanisms. We have used two- and three-dimensional particle-in-cell simulations to study particle acceleration in high Lundquist number reconnection regimes associated with laser-driven plasma experiments. For current experimental conditions, we show that nonthermal electrons can be accelerated to energies more than an order ofmore » magnitude larger than the initial thermal energy. The nonthermal electrons gain their energy mainly from the reconnection electric field near the X points, and particle injection into the reconnection layer and escape from the finite system establish a distribution of energies that resembles a power-law spectrum. Energetic electrons can also become trapped inside the plasmoids that form in the current layer and gain additional energy from the electric field arising from the motion of the plasmoid. We compare simulations for finite and infinite periodic systems to demonstrate the importance of particle escape on the shape of the spectrum. Based on our findings, we provide an analytical estimate of the maximum electron energy and threshold condition for observing suprathermal electron acceleration in terms of experimentally tunable parameters. We also discuss experimental signatures, including the angular distribution of the accelerated particles, and construct synthetic detector spectra. Finally, these results open the way for novel experimental studies of particle acceleration induced by reconnection.« less

Energy spectrum of argon ions emitted from Filippov type Sahand plasma focus.

PubMed

Mohammadnejad, M; Pestehe, S J; Mohammadi, M A

2013-07-01

The energy and flux of the argon ions produced in Sahand plasma focus have been measured by employing a well-designed Faraday cup. The secondary electron emission effects on the ion signals are simulated and the dimensions of Faraday cup are optimized to minimize these effects. The measured ion energy spectrum is corrected for the ion energy loss and charge exchange in the background gas. The effects of the capacitor bank voltage and working gas pressure on the ion energy spectrum are also investigated. It has been shown that the emitted ion number per energy increases as the capacitor bank voltage increases. Decreasing the working gas pressure leads to the increase in the number of emitted ion per energy.

The electronic characterization of biphenylene—Experimental and theoretical insights from core and valence level spectroscopy

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

Lüder, Johann; Sanyal, Biplab; Eriksson, Olle

In this paper, we provide detailed insights into the electronic structure of the gas phase biphenylene molecule through core and valence spectroscopy. By comparing results of X-ray Photoelectron Spectroscopy (XPS) measurements with ΔSCF core-hole calculations in the framework of Density Functional Theory (DFT), we could decompose the characteristic contributions to the total spectra and assign them to non-equivalent carbon atoms. As a difference with similar molecules like biphenyl and naphthalene, an influence of the localized orbitals on the relative XPS shifts was found. The valence spectrum probed by photoelectron spectroscopy at a photon energy of 50 eV in conjunction withmore » hybrid DFT calculations revealed the effects of the localization on the electronic states. Using the transition potential approach to simulate the X-ray absorption spectroscopy measurements, similar contributions from the non-equivalent carbon atoms were determined from the total spectrum, for which the slightly shifted individual components can explain the observed asymmetric features.« less

The effect of electronically steering a phased array ultrasound transducer on near-field tissue heating.

PubMed

Payne, Allison; Vyas, Urvi; Todd, Nick; de Bever, Joshua; Christensen, Douglas A; Parker, Dennis L

2011-09-01

This study presents the results obtained from both simulation and experimental techniques that show the effect of mechanically or electronically steering a phased array transducer on proximal tissue heating. The thermal response of a nine-position raster and a 16-mm diameter circle scanning trajectory executed through both electronic and mechanical scanning was evaluated in computer simulations and experimentally in a homogeneous tissue-mimicking phantom. Simulations were performed using power deposition maps obtained from the hybrid angular spectrum (HAS) method and applying a finite-difference approximation of the Pennes' bioheat transfer equation for the experimentally used transducer and also for a fully sampled transducer to demonstrate the effect of acoustic window, ultrasound beam overlap and grating lobe clutter on near-field heating. Both simulation and experimental results show that electronically steering the ultrasound beam for the two trajectories using the 256-element phased array significantly increases the thermal dose deposited in the near-field tissues when compared with the same treatment executed through mechanical steering only. In addition, the individual contributions of both beam overlap and grating lobe clutter to the near-field thermal effects were determined through comparing the simulated ultrasound beam patterns and resulting temperature fields from mechanically and electronically steered trajectories using the 256-randomized element phased array transducer to an electronically steered trajectory using a fully sampled transducer with 40 401 phase-adjusted sample points. Three distinctly different three distinctly different transducers were simulated to analyze the tradeoffs of selected transducer design parameters on near-field heating. Careful consideration of design tradeoffs and accurate patient treatment planning combined with thorough monitoring of the near-field tissue temperature will help to ensure patient safety during an MRgHIFU treatment.

Cascade model of gamma-ray bursts: Power-law and annihilation-line components

NASA Technical Reports Server (NTRS)

Harding, A. K.; Sturrock, P. A.; Daugherty, J. K.

1988-01-01

If, in a neutron star magnetosphere, an electron is accelerated to an energy of 10 to the 11th or 12th power eV by an electric field parallel to the magnetic field, motion of the electron along the curved field line leads to a cascade of gamma rays and electron-positron pairs. This process is believed to occur in radio pulsars and gamma ray burst sources. Results are presented from numerical simulations of the radiation and photon annihilation pair production processes, using a computer code previously developed for the study of radio pulsars. A range of values of initial energy of a primary electron was considered along with initial injection position, and magnetic dipole moment of the neutron star. The resulting spectra was found to exhibit complex forms that are typically power law over a substantial range of photon energy, and typically include a dip in the spectrum near the electron gyro-frequency at the injection point. The results of a number of models are compared with data for the 5 Mar., 1979 gamma ray burst. A good fit was found to the gamma ray part of the spectrum, including the equivalent width of the annihilation line.

Anion photoelectron imaging spectroscopy of glyoxal

NASA Astrophysics Data System (ADS)

Xue, Tian; Dixon, Andrew R.; Sanov, Andrei

2016-09-01

We report a photoelectron imaging study of the radical-anion of glyoxal. The 532 nm photoelectron spectrum provides the first direct spectroscopic determination of the adiabatic electron affinity of glyoxal, EA = 1.10 ± 0.02 eV. This assignment is supported by a Franck-Condon simulation of the experimental spectrum that successfully reproduces the observed spectral features. The vertical detachment energy of the radical-anion is determined as VDE = 1.30 ± 0.04 eV. The reported EA and VDE values are attributed to the most stable (C2h symmetry) isomers of the neutral and the anion.

Simulations of a molecular plasma in collisional-radiative nonequilibrium

NASA Technical Reports Server (NTRS)

Cambier, Jean-Luc; Moreau, Stephane

1993-01-01

A code for the simulation of nonequilibrium plasmas is being developed, with the capability to couple the plasma fluid-dynamics for a single fluid with a collisional-radiative model, where electronic states are treated as separate species. The model allows for non-Boltzmann distribution of the electronic states. Deviations from the Boltzmann distributions are expected to occur in the rapidly ionizing regime behind a strong shock or in the recombining regime during a fast expansion. This additional step in modeling complexity is expected to yield more accurate predictions of the nonequilibrium state and the radiation spectrum and intensity. An attempt at extending the code to molecular plasma flows is presented. The numerical techniques used, the thermochemical model, and the results of some numerical tests are described.

Using DTSA-II to simulate and interpret energy dispersive spectra from particles.

PubMed

Ritchie, Nicholas W M

2010-06-01

A high quality X-ray spectrum image of a 3.3 mum diameter sphere of K411 glass resting on a copper substrate was collected at 25 keV. The same sample configuration was modeled using the NISTMonte Monte Carlo simulation of electron and X-ray transport as is integrated into the quantitative X-ray microanalysis software package DTSA-II. The distribution of measured and simulated X-ray intensity compare favorably for all the major lines present in the spectra. The simulation is further examined to investigate the influence of angle-of-incidence, sample thickness, and sample diameter on the generated and measured X-ray intensity. The distribution of generated X-rays is seen to deviate significantly from a naive model which assumes that the distribution of generated X-rays is similar to bulk within the volume they share in common. It is demonstrated that the angle at which the electron beam strikes the sample has nonnegligible consequences. It is also demonstrated that within the volume that the bulk and particle share in common that electrons, which have exited and later reentered the particle volume, generate a significant fraction of the X-rays. Any general model of X-ray generation in particles must take into account the lateral spread of the scattered electron beam.

A combined molecular dynamics and Monte Carlo simulation of the spatial distribution of energy deposition by proton beams in liquid water.

PubMed

Garcia-Molina, Rafael; Abril, Isabel; Heredia-Avalos, Santiago; Kyriakou, Ioanna; Emfietzoglou, Dimitris

2011-10-07

We have evaluated the spatial distribution of energy deposition by proton beams in liquid water using the simulation code SEICS (Simulation of Energetic Ions and Clusters through Solids), which combines molecular dynamics and Monte Carlo techniques and includes the main interaction phenomena between the projectile and the target constituents: (i) the electronic stopping force due to energy loss to target electronic excitations, including fluctuations due to the energy-loss straggling, (ii) the elastic scattering with the target nuclei, with their corresponding energy loss and (iii) the dynamical changes in projectile charge state due to electronic capture and loss processes. An important feature of SEICS is the accurate account of the excitation spectrum of liquid water, based on a consistent solid-state description of its energy-loss-function over the whole energy and momentum space. We analyse how the above-mentioned interactions affect the depth distribution of the energy delivered in liquid water by proton beams with incident energies of the order of several MeV. Our simulations show that the position of the Bragg peak is determined mainly by the stopping power, whereas its width can be attributed to the energy-loss straggling. Multiple elastic scattering processes contribute slightly only at the distal part of the Bragg peak. The charge state of the projectiles only changes when approaching the end of their trajectories, i.e. near the Bragg peak. We have also simulated the proton-beam energy distribution at several depths in the liquid water target, and found that it is determined mainly by the fluctuation in the energy loss of the projectile, evaluated through the energy-loss straggling. We conclude that a proper description of the target excitation spectrum as well as the inclusion of the energy-loss straggling is essential in the calculation of the proton beam depth-dose distribution.

Communication: Relaxation-limited electronic currents in extended reservoir simulations

NASA Astrophysics Data System (ADS)

Gruss, Daniel; Smolyanitsky, Alex; Zwolak, Michael

2017-10-01

Open-system approaches are gaining traction in the simulation of charge transport in nanoscale and molecular electronic devices. In particular, "extended reservoir" simulations, where explicit reservoir degrees of freedom are present, allow for the computation of both real-time and steady-state properties but require relaxation of the extended reservoirs. The strength of this relaxation, γ, influences the conductance, giving rise to a "turnover" behavior analogous to Kramers turnover in chemical reaction rates. We derive explicit, general expressions for the weak and strong relaxation limits. For weak relaxation, the conductance increases linearly with γ and every electronic state of the total explicit system contributes to the electronic current according to its "reduced" weight in the two extended reservoir regions. Essentially, this represents two conductors in series—one at each interface with the implicit reservoirs that provide the relaxation. For strong relaxation, a "dual" expression-one with the same functional form-results, except now proportional to 1/γ and dependent on the system of interest's electronic states, reflecting that the strong relaxation is localizing electrons in the extended reservoirs. Higher order behavior (e.g., γ2 or 1/γ2) can occur when there is a gap in the frequency spectrum. Moreover, inhomogeneity in the frequency spacing can give rise to a pseudo-plateau regime. These findings yield a physically motivated approach to diagnosing numerical simulations and understanding the influence of relaxation, and we examine their occurrence in both simple models and a realistic, fluctuating graphene nanoribbon.

Evaluation of the hazard from exposure to electron irradiation simulating that in the synchronous orbit

NASA Technical Reports Server (NTRS)

Lippincott, S. W.; Foelsche, T.; Montour, J. L.; Bender, R.; Wilson, I. J.

1972-01-01

The electron spectrum predicted for the synchronous orbit was simulated to determine the effects that might occur to astroscientists exposed to such irradiation while on a prolonged space station mission in that region. Miniature pigs were exposed to monoenergetic and spectral-fractionated irradiations with 0.5 to 2.1 MeV electrons. Clinical and pathological alterations observed in biopsies were correlated with depth-dose pattern and length of post irradiation period up to one year. With monoenergetic electrons, the lowest dose causing a recognizable lesion was 1450 rad and with increasing dose lesions appeared earlier and were more severe. At the highest dose given, 2650 rad, ulceration extending into the dermis was present by twenty one days and required about four months for complete healing. Spectral-fractionated irradiations, in which the total dose range was essentially comparable to that of the monoenergetic series, resulted in very minimal outer dermis edema at 1790 rad and at no dose employed did necrosis of epidermis or ulceration into dermis occur.

Calculation on spectrum of direct DNA damage induced by low-energy electrons including dissociative electron attachment.

PubMed

Liu, Wei; Tan, Zhenyu; Zhang, Liming; Champion, Christophe

2017-03-01

In this work, direct DNA damage induced by low-energy electrons (sub-keV) is simulated using a Monte Carlo method. The characteristics of the present simulation are to consider the new mechanism of DNA damage due to dissociative electron attachment (DEA) and to allow determining damage to specific bases (i.e., adenine, thymine, guanine, or cytosine). The electron track structure in liquid water is generated, based on the dielectric response model for describing electron inelastic scattering and on a free-parameter theoretical model and the NIST database for calculating electron elastic scattering. Ionization cross sections of DNA bases are used to generate base radicals, and available DEA cross sections of DNA components are applied for determining DNA-strand breaks and base damage induced by sub-ionization electrons. The electron elastic scattering from DNA components is simulated using cross sections from different theoretical calculations. The resulting yields of various strand breaks and base damage in cellular environment are given. Especially, the contributions of sub-ionization electrons to various strand breaks and base damage are quantitatively presented, and the correlation between complex clustered DNA damage and the corresponding damaged bases is explored. This work shows that the contribution of sub-ionization electrons to strand breaks is substantial, up to about 40-70%, and this contribution is mainly focused on single-strand break. In addition, the base damage induced by sub-ionization electrons contributes to about 20-40% of the total base damage, and there is an evident correlation between single-strand break and damaged base pair A-T.

Measurement and simulation for a complementary imaging with the neutron and X-ray beams

NASA Astrophysics Data System (ADS)

Hara, Kaoru Y.; Sato, Hirotaka; Kamiyama, Takashi; Shinohara, Takenao

2017-09-01

By using a composite source system, we measured radiographs of the thermal neutron and keV X-ray in the 45-MeV electron linear accelerator facility at Hokkaido University. The source system provides the alternative beam of neutron and X-ray by switching the production target onto the electron beam axis. In the measurement to demonstrate a complementary imaging, the detector based on a vacuum-tube type neutron color image intensifier was applied to the both beams for dual-purpose. On the other hand, for reducing background in a neutron transmission spectrum, test measurements using a gadolinium-type neutron grid were performed with a cold neutron source at Hokkaido University. In addition, the simulations of the neutron and X-ray transmissions for various substances were performed using the PHITS code. A data analysis procedure for estimating the substance of sample was investigated through the simulations.

Simulation of Quiet-Sun Hard X-rays Related to Solar Wind Superhalo Electrons

NASA Astrophysics Data System (ADS)

Wang, W.; Wang, L.; Krucker, S.; Hannah, I. G.

2016-12-01

Abstract. In this paper, we propose that the accelerated electrons in the quiet-Sun could collide with the solar atmosphere to emit Hard X-rays (HXRs) via non-thermal bremsstrahlung, while some of these electrons would move upwards and escape into the interplanetary medium, to form a superhalo electron population measured in the solar wind. After considering the electron energy loss due to Coulomb collisions and the ambipolar electrostatic potential, we find that the sources of superhalo could only occur high in the corona (at a heliocentric altitude ≥ 1.9 Rs), to remain a power-law shape of electron spectrum as observed by STEREO at 1 AU near solar minimum (Wang et al, 2012).The modeled quiet-Sun HXRs related to the superhalo electrons fit well to a power-law spectrum, f(ɛ) ∝ ɛ-γ, with an index γ ≈ 2.0-2.3 (3.3-3.7) at 10-100 keV, for the warm/cold thick-target (thin-target) emissions produced by the downward-traveling (upward-traveling) accelerated electrons. These simulated quiet-Sun spectra are significantly harder than the observed spectra of most solar HXR flares. Assuming that the quiet-Sun sources cover 5% of the solar surface, the modeled thin-target HXRs are more than six orders of magnitude weaker than the RHESSI upper limits of quiet-Sun HXRs (Hannah et al., 2010). Using the thick-target model for the downward-traveling electrons, the RHESSI upper limits restrict the number of downward-traveling electrons to maximal ≈ 3 times the number of escaping electrons. This ratio is fundamentally different from what is observed during solar flares associated with escaping electrons where the fraction of downward-traveling electrons dominates by a factor of 100 to 1000 over the escaping population. References: 1. Hannah et al., APJ, 724, 487(2010) 2. Wang et al., APJ Letters,753,L23(2012) 3. Yang et al., RAA,Vol.15,No.3,348-362(2015) 4. Brown J.C., Solar Physics,Vol.18,Issue 3,489,502­­­(1971)

High Energy Cosmic Ray Electron Spectra measured from the ATIC Balloon Experiment

NASA Technical Reports Server (NTRS)

Chang, J.; Schmidt, W. K. H.; Adams, J. H.; Ahn, H. S.; Bashindzhagyan, G.; Batkov, K. E.; Christl, M.; Fazely, A. R.; Ganel, O.; Gunasingha, R. M.

2003-01-01

The Advanced Thin Ionization Calorimeter Balloon Experiment (ATIC) is specifically designed for high energy cosmic ray ion detection. From simulation and a CERN beam test exposure we find that the design consisting of a graphite target and an energy detection device, a totally active calorimeter of BGO scintillator, gives us sufficient information to distinguish electrons from protons up to the TeV energy range. Balloon observations were successfully carried out over Antarctica in both 2000/2001 and 2002/2003 for a total of more than 35 days. This paper presents preliminary results on the spectrum of high energy electrons observed in the first ATIC flight.

Ionization heating in rare-gas clusters under intense XUV laser pulses

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

Arbeiter, Mathias; Fennel, Thomas

The interaction of intense extreme ultraviolet (XUV) laser pulses ({lambda}=32 nm, I=10{sup 11}-10{sup 14} W/cm{sup 2}) with small rare-gas clusters (Ar{sub 147}) is studied by quasiclassical molecular dynamics simulations. Our analysis supports a very general picture of the charging and heating dynamics in finite samples under short-wavelength radiation that is of relevance for several applications of free-electron lasers. First, up to a certain photon flux, ionization proceeds as a series of direct photoemission events producing a jellium-like cluster potential and a characteristic plateau in the photoelectron spectrum as observed in Bostedt et al. [Phys. Rev. Lett. 100, 133401 (2008)]. Second,more » beyond the onset of photoelectron trapping, nanoplasma formation leads to evaporative electron emission with a characteristic thermal tail in the electron spectrum. A detailed analysis of this transition is presented. Third, in contrast to the behavior in the infrared or low vacuum ultraviolet range, the nanoplasma energy capture proceeds via ionization heating, i.e., inner photoionization of localized electrons, whereas collisional heating of conduction electrons is negligible up to high laser intensities. A direct consequence of the latter is a surprising evolution of the mean energy of emitted electrons as function of laser intensity.« less

Direct observation and theory of trajectory-dependent electronic energy losses in medium-energy ion scattering.

PubMed

Hentz, A; Parkinson, G S; Quinn, P D; Muñoz-Márquez, M A; Woodruff, D P; Grande, P L; Schiwietz, G; Bailey, P; Noakes, T C Q

2009-03-06

The energy spectrum associated with scattering of 100 keV H+ ions from the outermost few atomic layers of Cu(111) in different scattering geometries provides direct evidence of trajectory-dependent electronic energy loss. Theoretical simulations, combining standard Monte Carlo calculations of the elastic scattering trajectories with coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter, reproduce the effects well and provide a means for far more complete analysis of medium-energy ion scattering data.

OSA Proceedings of the Topical Meeting (5th) on Short-Wave Length Coherent Radiation: Generation and Applications Held in Monterey, California on 8-10 April 1991. Volume 11

DTIC Science & Technology

1992-05-22

PIC simulation code to study several of the constraints imposed by plasma phenomena on the propagation of ultrashort high intensity laser pulses in...and radiation spectrum of free electrons in the focus of an ultrashort high intensity laser pulse is solved. Motion and radiation of electrons in a...higher harmonics. These studies are intended as a prelude to experiments with high intensity ultrashort laser pulses . To investigate the motion of

Solvent effects on the absorption spectrum and first hyperpolarizability of keto-enol tautomeric forms of anil derivatives: A Monte Carlo/quantum mechanics study

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

Adriano Junior, L.; Fonseca, T. L.; Castro, M. A.

2016-06-21

Theoretical results for the absorption spectrum and electric properties of the enol and keto tautomeric forms of anil derivatives in the gas-phase and in solution are presented. The electronic properties in chloroform, acetonitrile, methanol, and water were determined by carrying out sequential Monte Carlo simulations and quantum mechanics calculations based on the time dependent density functional theory and on the second-order Møller–Plesset perturbation theory method. The results illustrate the role played by electrostatic interactions in the electronic properties of anil derivatives in a liquid environment. There is a significant increase of the dipole moment in solution (20%-100%) relative to themore » gas-phase value. Solvent effects are mild for the absorption spectrum and linear polarizability but they can be particularly important for first hyperpolarizability. A large first hyperpolarizability contrast between the enol and keto forms is observed when absorption spectra present intense lowest-energy absorption bands. Dynamic results for the first hyperpolarizability are in qualitative agreement with the available experimental results.« less

ENDOR-Induced EPR of Disordered Systems: Application to X-Irradiated Alanine.

PubMed

Kusakovskij, Jevgenij; Maes, Kwinten; Callens, Freddy; Vrielinck, Henk

2018-02-15

The electron paramagnetic resonance (EPR) spectra of radiation-induced radicals in organic solids are generally composed of multiple components that largely overlap due to their similar weak g anisotropy and a large number of hyperfine (HF) interactions. Such properties make these systems difficult to study using standard cw EPR spectroscopy even in single crystals. Electron-nuclear double-resonance (ENDOR) spectroscopy is a powerful and widely used complementary technique. In particular, ENDOR-induced EPR (EIE) experiments are useful for separating the overlapping contributions. In the present work, these techniques were employed to study the EPR spectrum of stable radicals in X-irradiated alanine, which is widely used in dosimetric applications. The principal values of all major proton HF interactions of the dominant radicals were determined by analyzing the magnetic field dependence of the ENDOR spectrum at 50 K, where the rotation of methyl groups is frozen. Accurate simulations of the EPR spectrum were performed after the major components were separated using an EIE analysis. As a result, new evidence in favor of the model of the second dominant radical was obtained.

In Quest of the Alanine R3 Radical: Multivariate EPR Spectral Analyses of X-Irradiated Alanine in the Solid State.

PubMed

Jåstad, Eirik O; Torheim, Turid; Villeneuve, Kathleen M; Kvaal, Knut; Hole, Eli O; Sagstuen, Einar; Malinen, Eirik; Futsaether, Cecilia M

2017-09-28

The amino acid l-α-alanine is the most commonly used material for solid-state electron paramagnetic resonance (EPR) dosimetry, due to the formation of highly stable radicals upon irradiation, with yields proportional to the radiation dose. Two major alanine radical components designated R1 and R2 have previously been uniquely characterized from EPR and electron-nuclear double resonance (ENDOR) studies as well as from quantum chemical calculations. There is also convincing experimental evidence of a third minor radical component R3, and a tentative radical structure has been suggested, even though no well-defined spectral signature has been observed experimentally. In the present study, temperature dependent EPR spectra of X-ray irradiated polycrystalline alanine were analyzed using five multivariate methods in further attempts to understand the composite nature of the alanine dosimeter EPR spectrum. Principal component analysis (PCA), maximum likelihood common factor analysis (MLCFA), independent component analysis (ICA), self-modeling mixture analysis (SMA), and multivariate curve resolution (MCR) were used to extract pure radical spectra and their fractional contributions from the experimental EPR spectra. All methods yielded spectral estimates resembling the established R1 spectrum. Furthermore, SMA and MCR consistently predicted both the established R2 spectrum and the shape of the R3 spectrum. The predicted shape of the R3 spectrum corresponded well with the proposed tentative spectrum derived from spectrum simulations. Thus, results from two independent multivariate data analysis techniques strongly support the previous evidence that three radicals are indeed present in irradiated alanine samples.

Ultra-High-Contrast Laser Acceleration of Relativistic Electrons in Solid Targets

NASA Astrophysics Data System (ADS)

Higginson, Drew Pitney

The cone-guided fast ignition approach to Inertial Confinement Fusion requires laser-accelerated relativistic electrons to deposit kilojoules of energy within an imploded fuel core to initiate fusion burn. One obstacle to coupling electron energy into the core is the ablation of material, known as preplasma, by laser energy proceeding nanoseconds prior to the main pulse. This causes the laser-absorption surface to be pushed back hundreds of microns from the initial target surface; thus increasing the distance that electrons must travel to reach the imploded core. Previous experiments have shown an order of magnitude decrease in coupling into surrogate targets when intentionally increasing the amount of preplasma. Additionally, for electrons to deposit energy within the core, they should have kinetic energies on the order of a few MeV, as less energetic electrons will be stopped prior to the core and more energetic electrons will pass through the core without depositing much energy. Thus a quantitative understanding of the electron energy spectrum and how it responds to varied laser parameters is paramount for fast ignition. For the first time, this dissertation quantitatively investigates the acceleration of electrons using an ultra-high-contrast laser. Ultra-high-contrast lasers reduce the laser energy that reaches the target prior to the main pulse; drastically reducing the amount of preplasma. Experiments were performed in a cone-wire geometry relevant to fast ignition. These experiments irradiated the inner-tip of a Au cone with the laser and observed electrons that passed through a Cu wire attached to the outer-tip of the cone. The total emission of Kalpha x-rays is used as a diagnostic to infer the electron energy coupled into the wire. Imaging the x-ray emission allowed an effective path-length of electrons within the wire to be determined, which constrained the electron energy spectrum. Experiments were carried out on the ultra-high-contrast Trident laser at Los Alamos National Laboratory and at the low-contrast Titan laser at Lawrence Livermore National Laboratory. The targets were irradiated using these 1.054 microm wavelength lasers at intensities from 1019 to 10 20 W/cm2. The coupling of energy into the Cu wire was found to be 2.7x higher when the preplasma was reduced using high-contrast. Additionally, higher laser intensity elongated the effective path-length of electrons within the wire, indicating that their kinetic energy was higher. To understand the physics behind laser-acceleration of electrons and to examine how this mechanism is affected by the presence of preplasma, simulations were performed to model the laser interaction. This simulations modeled the interaction using a 0.1 to 3 microm exponential preplasma scale length for the high-contrast cases and hydronamically simulated longer scale preplasma (˜25 microm) for the low-contrast case. The simulations show that absorption of laser light increases from only 20% with a 0.1 microm scale length to nearly 90% with a long low-contrast-type preplasma. However, as observed in experiments, a smaller fraction of this absorbed energy is transported to the diagnostic wire, which is due to an increased distance that the electrons must travel to reach the wire and increase angular divergence of the electrons. The simulations show that increasing the preplasma scale length from 0.1 to 3 microm increases the average energy by a factor of 2.5x. This is consistent with an increased interaction length over which the electrons can gain energy from the laser. The simulated electrons are compared with experimental data by injecting them into another simulation modeling the transport of electrons through the cone-wire target. This method quantitatively reproduced the experimentally measured the Kalpha x-ray emission profiles in the high-contrast cases, which gives confidence in the simulations and the generated electron distributions. By showing that the reduction of preplasma increases coupling into surrogate targets this work shows a significant advantage for the fast ignition scheme. Such work gives confidence to facilities that increasing the contrast of their laser systems will increase electron coupling. Additionally, detailed investigation of these high-contrast systems will aid researchers in understanding the effect that preplasma has on the acceleration of electrons.

Influence of the pulsating electric field on the ECR heating in a nonuniform magnetic field

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

Balmashnov, A. A., E-mail: abalmashnov@sci.pfu.edu.ru; Umnov, A. M.

2011-12-15

According to a computer simulation, the randomized pulsating electric field can strongly influence the ECR plasma heating in a nonuniform magnetic field. It has been found out that the electron energy spectrum is shifted to the high energy region. The obtained effect is intended to be used in the ECR sources for effective X-ray generation.

Transport Simulations for Fast Ignition on NIF

NASA Astrophysics Data System (ADS)

Strozzi, D. J.; Tabak, M.; Grote, D. P.; Town, R. P. J.; Kemp, A. J.

2009-11-01

Calculations of the transport and deposition of a relativistic electron beam into fast-ignition fuel configurations are presented. The hybrid PIC code LSP is used, run in implicit mode and with fluid background particles. The electron beam distribution is chosen based on explicit PIC simulations of the short-pulse LPI. These generally display two hot-electron temperatures, one close to the ponderomotive scaling and one that is much lower. Fast-electron collisions utilize the formulae of J. R. Davies [S. Atzeni et al., Plasma Phys. Controlled Fusion 51 (2009)], and are done with a conservative, relativistic grid-based method similar to Lemons et al., J. Comput. Phys. 228 (2009). We include energy loss off both bound and free electrons in partially-ionized media (such as a gold cone), and have started to use realistic ionization and non-ideal EOS models. We have found the fractional energy coupling into the dense fuel is higher for CD than DT targets, due to the enhanced resistivity and resulting magnetic fields. The coupling enhancement due to magnetic fields and beam characteristics (such as angular spectrum) will be quantified.

The Spatially Uniform Spectrum of the Fermi Bubbles: The Leptonic Active Galactic Nucleus Jet Scenario

NASA Astrophysics Data System (ADS)

Yang, H.-Y. K.; Ruszkowski, M.

2017-11-01

The Fermi bubbles are among the most important findings of the Fermi Gamma-ray Space Telescope; however, their origin is still elusive. One of the unique features of the bubbles is that their gamma-ray spectrum, including a high-energy cutoff at ˜110 GeV and the overall shape of the spectrum, is nearly spatially uniform. The high-energy spectral cutoff is suggestive of a leptonic origin due to synchrotron and inverse-Compton cooling of cosmic-ray (CR) electrons; however, even for a leptonic model, it is not obvious why the spectrum should be spatially uniform. In this work, we investigate the bubble formation in the leptonic active galactic nucleus (AGN) jet scenario using a new CRSPEC module in FLASH that allows us to track the evolution of a CR spectrum during the simulations. We show that the high-energy cutoff is caused by fast electron cooling near the Galactic center (GC) when the jets were launched. Afterwards, the dynamical timescale becomes the shortest among all relevant timescales, and therefore the spectrum is essentially advected with only mild cooling losses. This could explain why the bubble spectrum is nearly spatially uniform: the CRs from different parts of the bubbles as seen today all share the same origin near the GC at an early stage of the bubble expansion. We find that the predicted CR spatial and spectral distribution can simultaneously match the normalization, spectral shape, and high-energy cutoff of the observed gamma-ray spectrum and their spatial uniformity, suggesting that past AGN jet activity is a likely mechanism for the formation of the Fermi bubbles.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Mathematical simulation of the spectrum of a nonequilibrium laser plasma

NASA Astrophysics Data System (ADS)

Mazhukin, V. I.; Nikiforov, M. G.; Fievet, Christian

2006-02-01

A method is proposed for calculating the spectrum of a nonequilibrium plasma, which is based on a nonequilibrium collision—radiation model including all common line broadening mechanisms (natural, pressure, Doppler, and quadratic Stark effect broadening) and supplemented with the energy balance equations for electrons and ions. The nonequilibrium populations of the ground and excited states of neutral atoms and ions for an arbitrary instant of time are found by solving kinetic equations. The shape of each spectral line is determined by its central core calculated in the collision approximation up to the frequency boundary of its applicability, where the central core is 'joined' with the line wings calculated in the quasi-static approximation. The validity of this theoretical model is confirmed by simulations of a number of experimental studies of emission spectra under the conditions of a local thermodynamic equilibrium. It is shown that the calculated and experimental data obtained for the ground-state lines of the first carbon ion and neutral helium and argon atoms are in good agreement. The nonequilibrium spectrum of the optical breakdown in argon is calculated. Mathematical simulations showed that the intensities of nonequilibrium line spectra can be noticeably (by several times) lower than those of equilibrium spectra.

Spectroscopic measurements of hydrogen ion temperature during divertor recombination

NASA Astrophysics Data System (ADS)

Stotler, D. P.; Skinner, C. H.; Karney, C. F. F.

1999-01-01

We explore the possibility of using the neutral Hα spectral line profile to measure the ion temperature, Ti, in a recombining plasma. Since the Hα emissions due to recombination are larger than those due to other mechanisms, interference from nonrecombining regions contributing to the chord integrated data is insignificant. A Doppler and Stark broadened Hα spectrum is simulated by the DEGAS 2 neutral transport code using assumed plasma conditions. The application of a simple fitting procedure to this spectrum yields an electron density, ne, and Ti consistent with the assumed plasma parameters if the spectrum is dominated by recombination from a region of modest ne variation. General measurements of the ion temperature by Hα spectroscopy appear feasible within the context of a model for the entire divertor plasma.

Adaptive method for electron bunch profile prediction

DOE PAGES

Scheinker, Alexander; Gessner, Spencer

2015-10-15

We report on an experiment performed at the Facility for Advanced Accelerator Experimental Tests (FACET) at SLAC National Accelerator Laboratory, in which a new adaptive control algorithm, one with known, bounded update rates, despite operating on analytically unknown cost functions, was utilized in order to provide quasi-real-time bunch property estimates of the electron beam. Multiple parameters, such as arbitrary rf phase settings and other time-varying accelerator properties, were simultaneously tuned in order to match a simulated bunch energy spectrum with a measured energy spectrum. Thus, the simple adaptive scheme was digitally implemented using matlab and the experimental physics and industrialmore » control system. Finally, the main result is a nonintrusive, nondestructive, real-time diagnostic scheme for prediction of bunch profiles, as well as other beam parameters, the precise control of which are important for the plasma wakefield acceleration experiments being explored at FACET.« less

Adaptive method for electron bunch profile prediction

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

Scheinker, Alexander; Gessner, Spencer

2015-10-01

We report on an experiment performed at the Facility for Advanced Accelerator Experimental Tests (FACET) at SLAC National Accelerator Laboratory, in which a new adaptive control algorithm, one with known, bounded update rates, despite operating on analytically unknown cost functions, was utilized in order to provide quasi-real-time bunch property estimates of the electron beam. Multiple parameters, such as arbitrary rf phase settings and other time-varying accelerator properties, were simultaneously tuned in order to match a simulated bunch energy spectrum with a measured energy spectrum. The simple adaptive scheme was digitally implemented using matlab and the experimental physics and industrial controlmore » system. The main result is a nonintrusive, nondestructive, real-time diagnostic scheme for prediction of bunch profiles, as well as other beam parameters, the precise control of which are important for the plasma wakefield acceleration experiments being explored at FACET. © 2015 authors. Published by the American Physical Society.« less

Dynamical core-hole screening in the x-ray absorption spectra of hydrogenated carbon nanotubes and graphene

NASA Astrophysics Data System (ADS)

Wessely, O.; Katsnelson, M. I.; Nilsson, A.; Nikitin, A.; Ogasawara, H.; Odelius, M.; Sanyal, B.; Eriksson, O.

2007-10-01

We have calculated the electronic structure and the x-ray absorption (XA) spectrum of a hydrogenated single graphite plane, in order to simulate recent experimental results on hydrogenated single wall carbon nanotubes (SWCNT) as well as hydrogenated graphene. We find that the presence of H induces a substantial component of sp3 bonding and as a result the π and π* components to the electronic structure vanish. We have calculated a theoretical x-ray absorption spectrum using a multiband version of the Mahan-Nozières-De Dominicis theory. By making a fitting of the XA signal of C atoms that have H attached to them and C atoms without H in the vicinity we obtain a good representation of the experimental data and we can draw the conclusion that in the experiments [A. Nikitin , Phys. Rev. Lett. 95, 225507 (2005)] some 35-50 % H have been absorbed in the SWCNT.

Retrieving the Quantitative Chemical Information at Nanoscale from Scanning Electron Microscope Energy Dispersive X-ray Measurements by Machine Learning

NASA Astrophysics Data System (ADS)

Jany, B. R.; Janas, A.; Krok, F.

2017-11-01

The quantitative composition of metal alloy nanowires on InSb(001) semiconductor surface and gold nanostructures on germanium surface is determined by blind source separation (BSS) machine learning (ML) method using non negative matrix factorization (NMF) from energy dispersive X-ray spectroscopy (EDX) spectrum image maps measured in a scanning electron microscope (SEM). The BSS method blindly decomposes the collected EDX spectrum image into three source components, which correspond directly to the X-ray signals coming from the supported metal nanostructures, bulk semiconductor signal and carbon background. The recovered quantitative composition is validated by detailed Monte Carlo simulations and is confirmed by separate cross-sectional TEM EDX measurements of the nanostructures. This shows that SEM EDX measurements together with machine learning blind source separation processing could be successfully used for the nanostructures quantitative chemical composition determination.

A comparison of the relative biological effectiveness of low energy electronic brachytherapy sources in breast tissue: a Monte Carlo study.

PubMed

White, Shane A; Reniers, Brigitte; de Jong, Evelyn E C; Rusch, Thomas; Verhaegen, Frank

2016-01-07

Electronic brachytherapy sources use low energy photons to treat the tumor bed during or after breast-conserving surgery. The relative biological effectiveness of two electronic brachytherapy sources was explored to determine if spectral differences due to source design influenced radiation quality and if radiation quality decreased with distance in the breast. The RBE was calculated through the number of DNA double strand breaks (RBEDSB) using the Monte Carlo damage simulator (MCDS) in combination with other Monte Carlo electron/photon spectrum calculations. 50kVp photons from the Intrabeam (Carl Zeiss Surgical) and Axxent (Xoft) through 40-mm spherical applicators were simulated to account for applicator and tissue attenuation in a variety of breast tissue compositions. 40kVp Axxent photons were also simulated. Secondary electrons (known to be responsible for most DNA damage) spectra at different distance were inputted into MCDS to calculate the RBEDSB. All RBEDSB used a cobalt-60 reference. RBEDSB data was combined with corresponding average photon spectrum energy for the Axxent and applied to model-based average photon energy distributions to produce an RBEDSB map of an accelerated partial breast irradiation (APBI) patient. Both Axxent and Intrabeam 50kVp spectra were shown to have a comparable RBEDSB of between 1.4 and 1.6 at all distances in spite of progressive beam hardening. The Axxent 40kVp also demonstrated a similar RBEDSB at distances. Most RBEDSB variability was dependent on the tissue type as was seen in rib (RBEDSB  ≈  1.4), gland (≈1.55), adipose (≈1.59), skin (≈1.52) and lung (≈1.50). RBEDSB variability between both sources was within 2%. A correlation was shown between RBEDSB and average photon energy and used to produce an RBEDSB map of a dose distribution in an APBI patient dataset. Radiation quality is very similar between electronic brachytherapy sources studied. No significant reductions in RBEDSB were observed with increasing distance from the source.

Sci-Sat AM: Radiation Dosimetry and Practical Therapy Solutions - 11: Commissioning of a system for the measurement of electron stopping powers

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

McEwen, Malcolm; Roy, Timothy; Tessier, Frederic

Purpose: To develop the techniques required to experimentally determine electron stopping powers for application in primary standards and dosimetry protocols. Method and Materials: A large-volume HPGe detector system (>80% efficiency) was commissioned for the measurement of high energy (5–35 MeV) electron beams. As a proof of principle the system was used with a Y-90/Sr-90 radioactive source. Thin plates of absorbing material (< 0.1 gcm-2) were then placed between the source and detector and the emerging electron spectrum was acquired. The full experimental geometry was modelled using the EGSnrc package to validate the detector design, optimize the experimental setup and comparemore » measured and calculated spectra. Results: The biggest challenge using a beta source was to identify a robust spectral parameter to determine for each measurement. An end-point-fitting routine was used to determine the maximum energy, Emax, of the beta spectrum for each absorber thickness t. The parameter dEmax/dt is related to the electron stopping power and the same routine was applied to both measured and simulated spectra. Although the standard uncertainty in dEmax/dt was of the order of 5 %, by taking the ratio of measured and Monte Carlo values for dEmax/dt the uncertainty of the fitting routine was eliminated and the uncertainty was reduced to less than 2 %. The agreement between measurement and simulation was within this uncertainty estimate. Conclusion: The investigation confirmed the experimental approach and demonstrated that EGSnrc could accurately determine correction factors that will be required for the final measurement setup in a linac beam.« less

Effect of carbon nano tube working electrode thickness on charge transport kinetics and photo-electrochemical characteristics of dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Gacemi, Yahia; Cheknane, Ali; Hilal, Hikmat S.

2018-02-01

Physiochemical processes at the photo-electrode and the counter electrode of dye sensitized solar cells (DSSCs) involving having carbon nanotubes (CNTs) instead of the TiO2 layer, within the working electrode, are simulated in this work. Attention is paid to find the effect of CNT layer thickness on photo-electrochemical (PEC) characteristics of the CNT-DSSCs. Comparison with other conventional TiO2-DSSC systems, taking into account the working electrode film thickness, is also described here. To achieve these goals, a model is presented to explain charge transport and electron recombination which involve electron photo-excitation in dye molecules, injection of electrons from the excited dye to CNT working electrode conduction band, diffusion of electrons inside the CNT electrode, charge transfer between oxidized dye and (I-) and recombination of electrons. The simulation is based on solving non-linear equations using the Newton-Raphson numerical method. This concept is proposed for modelling numerical Faradaic impedance at the photo-electrode and the platinum counter electrode. It then simulates the cell impedance spectrum describing the locus of the three semicircles in the Nyquist diagram. The transient equivalent circuit model is also presented based on optimizing current-voltage curves of CNT-DSSCs so as to optimize the fill factor (FF) and conversion efficiency (η). The results show that the simulated characteristics of CNT-DSSCs, with different active CNT layer thicknesses, are superior to conventional TiO2-DSSCs.

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.

X-ray absorption spectroscopy to determine originating depth of electrons that form an inelastic background of Auger electron spectrum

NASA Astrophysics Data System (ADS)

Isomura, Noritake; Cui, Yi-Tao; Murai, Takaaki; Oji, Hiroshi; Kimoto, Yasuji

2017-07-01

In Auger electron spectroscopy (AES), the spectral background is mainly due to inelastic scattering of Auger electrons that lose their kinetic energy in a sample bulk. To investigate the spectral components within this background for SiO2(19.3 nm)/Si(100) with known layer thickness, X-ray absorption spectroscopy (XAS) was used in the partial-electron-yield (PEY) mode at several electron kinetic energies to probe the background of the Si KLL Auger peak. The Si K-edge PEY-XAS spectra constituted of both Si and SiO2 components at each kinetic energy, and their component fractions were approximately the same as those derived from the simulated AES background for the same sample structure. The contributions of Auger electrons originating from layers at different depths to the inelastic background could thus be identified experimentally.

Compton interaction of free electrons with intense low frequency radiation

NASA Technical Reports Server (NTRS)

Illarionov, A. F.; Kompaneyets, D. A.

1978-01-01

Electron behavior in an intense low frequency radiation field, with induced Compton scattering as the primary mechanism of interaction, is investigated. Evolution of the electron energy spectrum is studied, and the equilibrium spectrum of relativistic electrons in a radiation field with high brightness temperature is found. The induced radiation pressure and heating rate of an electron gas are calculated. The direction of the induced pressure depends on the radiation spectrum. The form of spectrum, under the induced force can accelerate electrons to superrelativistic energies is found.

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

PubMed

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

2007-01-01

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

Plugged in: Electronics use in youth and young adults with autism spectrum disorder.

PubMed

MacMullin, Jennifer A; Lunsky, Yona; Weiss, Jonathan A

2016-01-01

Although electronic technology currently plays an integral role for most youth, there are growing concerns of its excessive and compulsive use. This study documents patterns and impact of electronics use in individuals with autism spectrum disorder compared to typically developing peers. Participants included 172 parents of typically developing individuals and 139 parents of individuals with an autism spectrum disorder diagnosis, ranging in age from 6 to 21 years. Parents completed an online survey of demographics and the frequency, duration, and problematic patterns of electronics use in their youth and young adults. Individuals with autism spectrum disorder were reported to use certain electronics more often in the last month and on an average day, and had greater compulsive Internet and video game use than individuals without autism spectrum disorder. Across both samples, males used video games more often than females. Compared to parents of individuals without autism spectrum disorder, parents of individuals with autism spectrum disorder were significantly more likely to report that electronics use was currently having a negative impact. The implications of problematic electronics use for individuals with autism spectrum disorder are discussed. © The Author(s) 2015.

Bidirectional Energy Cascades and the Origin of Kinetic Alfvenic and Whistler Turbulence in the Solar Wind

NASA Technical Reports Server (NTRS)

Che, H.; Goldstein, M. L.; Vinas, A. F.

2014-01-01

The observed steep kinetic scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quiet time suggest them as a possible source of free energy to drive kinetic turbulence. Using particle-in-cell simulations, we explore how the free energy released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfvénic and whistler turbulence are excited that evolve through inverse and forward magnetic energy cascades.

Probing plasmonic breathing modes optically

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

Krug, Markus K., E-mail: markus.krug@uni-graz.at; Reisecker, Michael; Hohenau, Andreas

2014-10-27

The confinement of surface plasmon modes in flat nanoparticles gives rise to plasmonic breathing modes. With a vanishing net dipole moment, breathing modes do not radiate, i.e., they are optically dark. Having thus escaped optical detection, breathing modes were only recently revealed in silver nanodisks with electron energy loss spectroscopy in an electron microscope. We show that for disk diameters >200 nm, retardation induced by oblique optical illumination relaxes the optically dark character. This makes breathing modes and thus the full plasmonic mode spectrum accessible to optical spectroscopy. The experimental spectroscopy data are in excellent agreement with numerical simulations.

On the nature of solvatochromic effect: The riboflavin absorption spectrum as a case study

NASA Astrophysics Data System (ADS)

Daidone, Isabella; Amadei, Andrea; Aschi, Massimiliano; Zanetti-Polzi, Laura

2018-03-01

We present here the calculation of the absorption spectrum of riboflavin in acetonitrile and dimethyl sulfoxide using a hybrid quantum/classical approach, namely the perturbed matrix method, based on quantum mechanical calculations and molecular dynamics simulations. The calculated spectra are compared to the absorption spectrum of riboflavin previously calculated in water and to the experimental spectra obtained in all three solvents. The experimentally observed variations in the absorption spectra upon change of the solvent environment are well reproduced by the calculated spectra. In addition, the nature of the excited states of riboflavin interacting with different solvents is investigated, showing that environment effects determine a recombination of the gas-phase electronic states and that such a recombination is strongly affected by the polarity of the solvent inducing significant changes in the absorption spectra.

Simulating a Measurement of the 2nd Knee in the Cosmic Ray Spectrum with an Atmospheric Fluorescence Telescope Tower Array

PubMed Central

Liu, Jiali; Yang, Qunyu; Bai, Yunxiang; Cao, Zhen

2014-01-01

A fluorescence telescope tower array has been designed to measure cosmic rays in the energy range of 1017–1018 eV. A full Monte Carlo simulation, including air shower production, light generation and propagation, detector response, electronics, and trigger system, has been developed for that purpose. Using such a simulation tool, the detector configuration, which includes one main tower array and two side-trigger arrays, 24 telescopes in total, has been optimized. The aperture and the event rate have been estimated. Furthermore, the performance of the X max⁡ technique in measuring composition has also been studied. PMID:24737964

Two-dimensional Nonlinear Simulations of Temperature-anisotropy Instabilities with a Proton-alpha Drift

NASA Astrophysics Data System (ADS)

Markovskii, S. A.; Chandran, Benjamin D. G.; Vasquez, Bernard J.

2018-04-01

We present two-dimensional hybrid simulations of proton-cyclotron and mirror instabilities in a proton-alpha plasma with particle-in-cell ions and a neutralizing electron fluid. The instabilities are driven by the protons with temperature perpendicular to the background magnetic field larger than the parallel temperature. The alpha particles with initially isotropic temperature have a nonzero drift speed with respect to the protons. The minor ions are known to influence the relative effect of the proton-cyclotron and mirror instabilities. In this paper, we show that the mirror mode can dominate the power spectrum at the nonlinear stage even if its linear growth rate is significantly lower than that of the proton-cyclotron mode. The proton-cyclotron instability combined with the alpha-proton drift is a possible cause of the nonzero magnetic helicity observed in the solar wind for fluctuations propagating nearly parallel to the magnetic field. Our simulations generally confirm this concept but reveal a complex helicity spectrum that is not anticipated from the linear theory of the instability.

RAiSE II: resolved spectral evolution in radio AGN

NASA Astrophysics Data System (ADS)

Turner, Ross J.; Rogers, Jonathan G.; Shabala, Stanislav S.; Krause, Martin G. H.

2018-01-01

The active galactic nuclei (AGN) lobe radio luminosities modelled in hydrodynamical simulations and most analytical models do not address the redistribution of the electron energies due to adiabatic expansion, synchrotron radiation and inverse-Compton scattering of cosmic microwave background photons. We present a synchrotron emissivity model for resolved sources that includes a full treatment of the loss mechanisms spatially across the lobe, and apply it to a dynamical radio source model with known pressure and volume expansion rates. The bulk flow and dispersion of discrete electron packets is represented by tracer fields in hydrodynamical simulations; we show that the mixing of different aged electrons strongly affects the spectrum at each point of the radio map in high-powered Fanaroff & Riley type II (FR-II) sources. The inclusion of this mixing leads to a factor of a few discrepancy between the spectral age measured using impulsive injection models (e.g. JP model) and the dynamical age. The observable properties of radio sources are predicted to be strongly frequency dependent: FR-II lobes are expected to appear more elongated at higher frequencies, while jetted FR-I sources appear less extended. The emerging FR0 class of radio sources, comprising gigahertz peaked and compact steep spectrum sources, can potentially be explained by a population of low-powered FR-Is. The extended emission from such sources is shown to be undetectable for objects within a few orders of magnitude of the survey detection limit and to not contribute to the curvature of the radio spectral energy distribution.

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.

Observation of Betatron X-Ray Radiation in a Self-Modulated Laser Wakefield Accelerator Driven with Picosecond Laser Pulses

DOE PAGES

Albert, F.; Lemos, N.; Shaw, J. L.; ...

2017-03-31

We investigate a new regime for betatron x-ray emission that utilizes kilojoule-class picosecond lasers to drive wakes in plasmas. When such laser pulses with intensities of ~ 5 × 1 0 18 W / cm 2 are focused into plasmas with electron densities of ~ 1 × 1 0 19 cm - 3 , they undergo self-modulation and channeling, which accelerates electrons up to 200 MeV energies and causes those electrons to emit x rays. The measured x-ray spectra are fit with a synchrotron spectrum with a critical energy of 10–20 keV, and 2D particle-in-cell simulations were used to modelmore » the acceleration and radiation of the electrons in our experimental conditions« less

Simulating Excitons in MoS2 with Time-Dependent Density Functional Theory

NASA Astrophysics Data System (ADS)

Flamant, Cedric; Kolesov, Grigory; Kaxiras, Efthimios

Monolayer molybdenum disulfide, owing to its graphene-like two-dimensional geometry whilst still having a finite bandgap, is a material of great interest in condensed matter physics and for potential application in electronic devices. In particular, MoS2 exhibits significant excitonic effects, a desirable quality for fundamental many-body research. Time-dependent density functional theory (TD-DFT) allows us to simulate dynamical effects as well as temperature-based effects in a natural way given the direct treatment of the time evolution of the system. We present a TD-DFT study of monolayer MoS2 exciton dynamics, examining various qualitative and quantitative predictions in pure samples and in the presence of defects. In particular, we generate an absorption spectrum through simulated pulse excitation for comparison to experiment and also analyze the response of the exciton in an external electric field.In this work we also discuss the electronic structure of the exciton in MoS2 with and without vacancies.

Transient Spectra in TDDFT: Corrections and Correlations

NASA Astrophysics Data System (ADS)

Parkhill, John; Nguyen, Triet

We introduce an atomistic, all-electron, black-box electronic structure code to simulate transient absorption (TA) spectra and apply it to simulate pyrazole and a GFP chromophore derivative. The method is an application of OSCF2, our dissipative extension of time-dependent density functional theory. We compare our simulated spectra directly with recent ultra-fast spectroscopic experiments, showing that they are usefully predicted. We also relate bleaches in the TA signal to Fermi-blocking which would be missed in a simplified model. An important ingredient in the method is the stationary-TDDFT correction scheme recently put forwards by Fischer, Govind, and Cramer which allows us to overcome a limitation of adiabatic TDDFT. We demonstrate that OSCF2 is able to predict both the energies of bleaches and induced absorptions, as well as the decay of the transient spectrum, with only the molecular structure as input. With remaining time we will discuss corrections which resolve the non-resonant behavior of driven TDDFT, and correlated corrections to mean-field dynamics.

Stopping dynamics of ions passing through correlated honeycomb clusters

NASA Astrophysics Data System (ADS)

Balzer, Karsten; Schlünzen, Niclas; Bonitz, Michael

2016-12-01

A combined nonequilibrium Green functions-Ehrenfest dynamics approach is developed that allows for a time-dependent study of the energy loss of a charged particle penetrating a strongly correlated system at zero and finite temperatures. Numerical results are presented for finite inhomogeneous two-dimensional Fermi-Hubbard models, where the many-electron dynamics in the target are treated fully quantum mechanically and the motion of the projectile is treated classically. The simulations are based on the solution of the two-time Dyson (Keldysh-Kadanoff-Baym) equations using the second-order Born, third-order, and T -matrix approximations of the self-energy. As application, we consider protons and helium nuclei with a kinetic energy between 1 and 500 keV/u passing through planar fragments of the two-dimensional honeycomb lattice and, in particular, examine the influence of electron-electron correlations on the energy exchange between projectile and electron system. We investigate the time dependence of the projectile's kinetic energy (stopping power), the electron density, the double occupancy, and the photoemission spectrum. Finally, we show that, for a suitable choice of the Hubbard model parameters, the results for the stopping power are in fair agreement with ab initio simulations for particle irradiation of single-layer graphene.

Ab Initio Modeling of the Electronic Absorption Spectrum of Previtamin D in Solution

NASA Astrophysics Data System (ADS)

Zhu, Tianyang

To study the solvent effects of water on the previtamin D absorption spectrum, we use the quantum mechanics (QM)/molecular mechanics (MM) method combined with replica-exchange molecular dynamics (REMD). The QM method is applied for the previtamin D molecule and the MM method is used for the water molecules. To enhance conformational sampling of the flexible previtamin D molecule we apply REMD. Based on the REMD structures, we calculate the macroscopic ensemble of the absorption spectrum in solution by time-dependent density functional theory (TDDFT). Comparison between the calculated spectrum in the gas phase and in the solution reveals minor influences of the solvent on the absorption spectrum. In the conventional molecule dynamics simulation, the previtamin D molecule can be trapped by local minimum and cannot overcome energetics barriers when it is calculated at the room temperature. In addition, the higher temperature calculation for the molecule in REMD allows to overcome energetics barriers and to change the structure to other rotational isomers, then switch to the lower temperature and gives a more complete result in the configuration space for the lower temperature.

Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble

PubMed Central

Yan, Wenchao; Chen, Liming; Li, Dazhang; Zhang, Lu; Hafz, Nasr A. M.; Dunn, James; Ma, Yong; Huang, Kai; Su, Luning; Chen, Min; Sheng, Zhengming; Zhang, Jie

2014-01-01

Desktop laser plasma acceleration has proven to be able to generate gigaelectronvolt-level quasi-monoenergetic electron beams. Moreover, such electron beams can oscillate transversely (wiggling motion) in the laser-produced plasma bubble/channel and emit collimated ultrashort X-ray flashes known as betatron radiation with photon energy ranging from kiloelectronvolts to megaelectronvolts. This implies that usually one cannot obtain bright betatron X-rays and high-quality electron beams with low emittance and small energy spread simultaneously in the same accelerating wave bucket. Here, we report the first (to our knowledge) experimental observation of two distinct electron bunches in a single laser shot, one featured with quasi-monoenergetic spectrum and another with continuous spectrum along with large emittance. The latter is able to generate high-flux betatron X-rays. Such is observed only when the laser self-guiding is extended over 4 mm at a fixed plasma density (4 × 1018 cm−3). Numerical simulation reveals that two bunches of electrons are injected at different stages due to the bubble evolution. The first bunch is injected at the beginning to form a stable quasi-monoenergetic electron beam, whereas the second one is injected later due to the oscillation of the bubble size as a result of the change of the laser spot size during the propagation. Due to the inherent temporal synchronization, this unique electron–photon source can be ideal for pump–probe applications with femtosecond time resolution. PMID:24711405

DXRaySMCS: a user-friendly interface developed for prediction of diagnostic radiology X-ray spectra produced by Monte Carlo (MCNP-4C) simulation.

PubMed

Bahreyni Toossi, M T; Moradi, H; Zare, H

2008-01-01

In this work, the general purpose Monte Carlo N-particle radiation transport computer code (MCNP-4C) was used for the simulation of X-ray spectra in diagnostic radiology. The electron's path in the target was followed until its energy was reduced to 10 keV. A user-friendly interface named 'diagnostic X-ray spectra by Monte Carlo simulation (DXRaySMCS)' was developed to facilitate the application of MCNP-4C code for diagnostic radiology spectrum prediction. The program provides a user-friendly interface for: (i) modifying the MCNP input file, (ii) launching the MCNP program to simulate electron and photon transport and (iii) processing the MCNP output file to yield a summary of the results (relative photon number per energy bin). In this article, the development and characteristics of DXRaySMCS are outlined. As part of the validation process, output spectra for 46 diagnostic radiology system settings produced by DXRaySMCS were compared with the corresponding IPEM78. Generally, there is a good agreement between the two sets of spectra. No statistically significant differences have been observed between IPEM78 reported spectra and the simulated spectra generated in this study.

Three-dimensional kinetic simulations of whistler turbulence in solar wind on parallel supercomputers

NASA Astrophysics Data System (ADS)

Chang, Ouliang

The objective of this dissertation is to study the physics of whistler turbulence evolution and its role in energy transport and dissipation in the solar wind plasmas through computational and theoretical investigations. This dissertation presents the first fully three-dimensional (3D) particle-in-cell (PIC) simulations of whistler turbulence forward cascade in a homogeneous, collisionless plasma with a uniform background magnetic field B o, and the first 3D PIC simulation of whistler turbulence with both forward and inverse cascades. Such computationally demanding research is made possible through the use of massively parallel, high performance electromagnetic PIC simulations on state-of-the-art supercomputers. Simulations are carried out to study characteristic properties of whistler turbulence under variable solar wind fluctuation amplitude (epsilon e) and electron beta (betae), relative contributions to energy dissipation and electron heating in whistler turbulence from the quasilinear scenario and the intermittency scenario, and whistler turbulence preferential cascading direction and wavevector anisotropy. The 3D simulations of whistler turbulence exhibit a forward cascade of fluctuations into broadband, anisotropic, turbulent spectrum at shorter wavelengths with wavevectors preferentially quasi-perpendicular to B o. The overall electron heating yields T ∥ > T⊥ for all epsilone and betae values, indicating the primary linear wave-particle interaction is Landau damping. But linear wave-particle interactions play a minor role in shaping the wavevector spectrum, whereas nonlinear wave-wave interactions are overall stronger and faster processes, and ultimately determine the wavevector anisotropy. Simulated magnetic energy spectra as function of wavenumber show a spectral break to steeper slopes, which scales as k⊥lambda e ≃ 1 independent of betae values, where lambdae is electron inertial length, qualitatively similar to solar wind observations. Specific spectral indices from simulated wavevector energy spectra do not match the frequency spectral indices from observations due to the inapplicability of Taylor's hypothesis. In contrast, the direct comparison of simulated frequency energy spectra and solar wind observations shows a closer similarity. Electron density fluctuations power spectra also exhibit a close similarity to solar wind observations and MHD predications, both qualitatively and quantitatively. Linear damping represents an intermediate fraction of the total dissipation of whistler turbulence over a wide range of betae and epsilone. The relative importance of linear damping by comparison to nonlinear dissipation increases with increasing beta e but decreases with increasing epsilone. Correlation coefficient calculations imply that the nonlinear dissipation processes in our simulation are primarily associated with dissipation in regions of intermittent current sheet structures. The simulation results suggest that whistler fluctuations could be the substantial constituent of solar wind turbulence at higher frequencies and short wavelengths, and support the magnetosonic-whistler interpretation of the quasilinear scenario. An even larger scale 3D whistler turbulence simulation exhibits both a forward cascade to shorter wavelengths with wavevectors preferentially k⊥ > k∥, and an inverse cascade to longer wavelengths with wavevectors k ≳ k⊥. The inverse cascade process is primarily driven by the nonlinear wave-wave interaction. It is shown that the energy inverse cascade rate is similar to the energy forward cascade rate at early times although the overall energy in the two cascades is very different. The presence of inverse cascade process does not affect qualitative conclusions established from the whistler turbulence forward cascade simulations.

Dermatopathology effects of simulated solar particle event radiation exposure in the porcine model.

PubMed

Sanzari, Jenine K; Diffenderfer, Eric S; Hagan, Sarah; Billings, Paul C; Gridley, Daila S; Seykora, John T; Kennedy, Ann R; Cengel, Keith A

2015-07-01

The space environment exposes astronauts to risks of acute and chronic exposure to ionizing radiation. Of particular concern is possible exposure to ionizing radiation from a solar particle event (SPE). During an SPE, magnetic disturbances in specific regions of the Sun result in the release of intense bursts of ionizing radiation, primarily consisting of protons that have a highly variable energy spectrum. Thus, SPE events can lead to significant total body radiation exposures to astronauts in space vehicles and especially while performing extravehicular activities. Simulated energy profiles suggest that SPE radiation exposures are likely to be highest in the skin. In the current report, we have used our established miniature pig model system to evaluate the skin toxicity of simulated SPE radiation exposures that closely resemble the energy and fluence profile of the September, 1989 SPE using either conventional radiation (electrons) or proton simulated SPE radiation. Exposure of animals to electron or proton radiation led to dose-dependent increases in epidermal pigmentation, the presence of necrotic keratinocytes at the dermal-epidermal boundary and pigment incontinence, manifested by the presence of melanophages in the derm is upon histological examination. We also observed epidermal hyperplasia and a reduction in vascular density at 30 days following exposure to electron or proton simulated SPE radiation. These results suggest that the doses of electron or proton simulated SPE radiation results in significant skin toxicity that is quantitatively and qualitatively similar. Radiation-induced skin damage is often one of the first clinical signs of both acute and non-acute radiation injury where infection may occur, if not treated. In this report, histopathology analyses of acute radiation-induced skin injury are discussed. Copyright © 2015 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.

The effect of 111In radionuclide distance and auger electron energy on direct induction of DNA double-strand breaks: a Monte Carlo study using Geant4 toolkit.

PubMed

Piroozfar, Behnaz; Raisali, Gholamreza; Alirezapour, Behrouz; Mirzaii, Mohammad

2018-04-01

In this study, the effect of 111 In position and Auger electron energy on direct induction of DSBs was investigated. The Geant4-DNA simulation toolkit was applied using a simple B-DNA form extracted from PDBlib library. First, the simulation was performed for electrons with energies of 111 In and equal emission probabilities to find the most effective electron energies. Then, 111 In Auger electrons' actual spectrum was considered and their contribution in DSB induction analysed. The results showed that the most effective electron energy is 183 eV, but due to the higher emission probability of 350 eV electrons, most of the DSBs were induced by the latter electrons. Also, it was observed that most of the DSBs are induced by electrons emitted within 4 nm of the central axis of the DNA and were mainly due to breaks with <4 base pairs distance in opposing strands. Whilst, when 111 In atoms are very close to the DNA, 1.3 DSBs have been obtained per decay of 111 In atoms. The results show that the most effective Auger electrons are the 350 eV electrons from 111 In atoms with <4 nm distance from the central axis of the DNA which induce ∼1.3 DSBs per decay when bound to the DNA. This value seems reasonable when compared with the reported experimental data.

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.

Design of the Experimental Exposure Conditions to Simulate Ionizing Radiation Effects on Candidate Replacement Materials for the Hubble Space Telescope

NASA Technical Reports Server (NTRS)

Smith, L. Montgomery

1998-01-01

In this effort, experimental exposure times for monoenergetic electrons and protons were determined to simulate the space radiation environment effects on Teflon components of the Hubble Space Telescope. Although the energy range of the available laboratory particle accelerators was limited, optimal exposure times for 50 keV, 220 keV, 350 keV, and 500 KeV electrons were calculated that produced a dose-versus-depth profile that approximated the full spectrum profile, and were realizable with existing equipment. For the case of proton exposure, the limited energy range of the laboratory accelerator restricted simulation of the dose to a depth of .5 mil. Also, while optimal exposure times were found for 200 keV, 500 keV and 700 keV protons that simulated the full spectrum dose-versus-depth profile to this depth, they were of such short duration that the existing laboratory could not be controlled to within the required accuracy. In addition to the obvious experimental issues, other areas exist in which the analytical work could be advanced. Improved computer codes for the dose prediction- along with improved methodology for data input and output- would accelerate and make more accurate the calculational aspects. This is particularly true in the case of proton fluxes where a paucity of available predictive software appears to exist. The dated nature of many of the existing Monte Carlo particle/radiation transport codes raises the issue as to whether existing codes are sufficient for this type of analysis. Other areas that would result in greater fidelity of laboratory exposure effects to the space environment is the use of a larger number of monoenergetic particle fluxes and improved optimization algorithms to determine the weighting values.

Characterizing high energy spectra of NIF ignition Hohlraums using a differentially filtered high energy multipinhole x-ray imager.

PubMed

Park, Hye-Sook; Dewald, E D; Glenzer, S; Kalantar, D H; Kilkenny, J D; MacGowan, B J; Maddox, B R; Milovich, J L; Prasad, R R; Remington, B A; Robey, H F; Thomas, C A

2010-10-01

Understanding hot electron distributions generated inside Hohlraums is important to the national ignition campaign for controlling implosion symmetry and sources of preheat. While direct imaging of hot electrons is difficult, their spatial distribution and spectrum can be deduced by detecting high energy x-rays generated as they interact with target materials. We used an array of 18 pinholes with four independent filter combinations to image entire Hohlraums with a magnification of 0.87× during the Hohlraum energetics campaign on NIF. Comparing our results with Hohlraum simulations indicates that the characteristic 10-40 keV hot electrons are mainly generated from backscattered laser-plasma interactions rather than from Hohlraum hydrodynamics.

Engineering electronic states of periodic and quasiperiodic chains by buckling

NASA Astrophysics Data System (ADS)

Mukherjee, Amrita; Nandy, Atanu; Chakrabarti, Arunava

2017-07-01

The spectrum of spinless, non-interacting electrons on a linear chain that is buckled in a non-uniform, quasiperiodic manner is investigated within a tight binding formalism. We have addressed two specific cases, viz., a perfectly periodic chain wrinkled in a quasiperiodic Fibonacci pattern, and a quasiperiodic Fibonacci chain, where the buckling also takes place in a Fibonacci pattern. The buckling brings distant neighbors in the parent chain to close proximity, which is simulated by a tunnel hopping amplitude. It is seen that, in the perfectly ordered case, increasing the strength of the tunnel hopping (that is, bending the segments more) absolutely continuous density of states is retained towards the edges of the band, while the central portion becomes fragmented and host subbands of narrowing widths containing extended, current carrying states, and multiple isolated bound states formed as a result of the bending. A switching ;on; and ;off; of the electronic transmission can thus be engineered by buckling. On the other hand, in the second example of a quasiperiodic Fibonacci chain, imparting a quasiperiodic buckling is found to generate continuous subband(s) destroying the usual multifractality of the energy spectrum. We present exact results based on a real space renormalization group analysis, that is corroborated by explicit calculation of the two terminal electronic transport.

Experimental and Computational Investigations of the Threshold Photoelectron Spectrum of the HCCN Radical

NASA Astrophysics Data System (ADS)

Gans, B.; Falvo, Cyril; Coudert, L. H.; Garcia, Gustavo A.; Küger, J.; Loison, J.-C.

2017-06-01

The HCCN radical, already detected in the interstellar medium, is also important for nitrile chemistry in Titan's atmosphere. Quite recently the photoionization spectrum of the radical has been recorded using mass selected threshold photoelectron (TPE) spectroscopy and this provided us with the first spectroscopic information about the HCCN} cation. Modeling such a spectrum requires accounting for the non-rigidity of HCCN and for the Renner-Teller effect in HCCN+. In its ^3A'' electronic ground state, HCCN is a non-rigid molecule as the potential for the \\angle{HCC} bending angle is very shallow. Vibronic couplings with the same bending angle leads, in the ^2Π electronic ground state of HCCN+, to a strong Renner-Teller effect giving rise to a bent ^2A' and a quasi-linear ^2A'' state. In this paper the photoionization spectrum of the HCCN radical is simulated. The model developped treats the \\angle{HCC} bending angle as a large amplitude coordinate in both the radical and the cation and accounts for the overall rotation and the Renner-Teller couplings. Gaussian quadrature are used to calculate matrix elements of the three potential energy functions retrieved through ab initio calculations and rovibrational operators going to infinity for the linear configuration are treated rigorously. The HCCN TPE spectrum is computed with the above model calculating all rotational components and choosing the appropriate lineshape. This synthetic spectrum will be shown in the paper and compared with the experimental one.^b Guélin and Cernicharo, A&A 244 (1991) L21 Loison et al., Icarus 247 (2015) 218 Garcia, Krüger, Gans, Falvo, Coudert, and Loison, J. Chem. Phys. (2017) submitted Koput, J. Phys. Chem. A 106 (2002) 6183 Zhao, Zhang, and Sun, J. Phys. Chem. A 112 (2008) 12125

Vibrational-rotational temperature measurement of N2 in the lower thermosphere by the rocket experiment

NASA Astrophysics Data System (ADS)

Kurihara, J.; Oyama, K.; Suzuki, K.; Iwagami, N.

The vibrational temperature (Tv), the rotational temperature (Tr) and the density of atmospheric N2 between 100 - 150 km were measured in situ by a sounding rocket S310-30, over Kagoshima, Japan at 10:30 UT on February 6, 2002. The main purpose of this rocket experiment is to study the dynamics and the thermal energy budget in the lower thermosphere. N2 was ionized using an electron gun and the emission of the 1st negative bands of N2+ was measured by a sensitive spectrometer. Tv and Tr were determined by fitting the observed spectrum for the simulated spectrum, and the number density was deduced from the intensities of the spectrum. We will report preliminary results of our measurement and discuss the observed thermal structure that indicates the effect of tides and gravity waves.

[Research on the emission spectrum of NO molecule's γ-band system by corona discharge].

PubMed

Zhai, Xiao-dong; Ding, Yan-jun; Peng, Zhi-min; Luo, Rui

2012-05-01

The optical emission spectrum of the gamma-band system of NO molecule, A2 sigma+ --> X2 pi(r), has been analyzed and calculated based on the energy structure of NO molecule' doublet states. By employing the theory of diatomic molecular Spectra, some key parameters of equations for the radiative transition intensity were evaluated theoretically, including the potentials of the doublet states of NO molecule's upper and lower energy levels, the electronic transition moments calculated by using r-centroid approximation method, and the Einstein coefficient of different vibrational and rotational levels. The simulated spectrum of the gamma-band system was calculated as a function of different vibrational and rotational temperature. Compared to the theoretical spectroscopy, the measured results were achieved from corona discharge experiments of NO and N2. The vibrational and rotational temperatures were determined approximately by fitting the measured spectral intensities with the calculated ones.

Influence of the Proton Pressure Tensor on the Turbulent Velocity Spectrum at Ion Kinetic Scales

NASA Astrophysics Data System (ADS)

Vasquez, B. J.; Markovskii, S.

2011-12-01

Numerical hybrid simulations with particle protons and fluid electrons are presented for turbulent fluctuations with spatial variations in a plane perpendicular to the background magnetic field. The steepened portion of the proton bulk velocity spectrum is found at smaller wavenumbers for larger background proton temperature. The velocity spectrum is determined, in part, by the proton pressure tensor. The proton pressure tensor is shown to possess non-gyrotropic and finite off-diagonal components in the places where the turbulent fluctuations have developed strong gradients. Proton demagnetization at these places is a factor in the departure from a Maxwellian velocity distribution function. How demagnetization could connect with both reversible and effectively irreversible aspects of the pressure tensor is considered. The effectively irreversible aspect corresponds to the net heating of the protons and to the dissipation of the turbulent energy cascade.

Analytical response function for planar Ge detectors

NASA Astrophysics Data System (ADS)

García-Alvarez, Juan A.; Maidana, Nora L.; Vanin, Vito R.; Fernández-Varea, José M.

2016-04-01

We model the response function (RF) of planar HPGe x-ray spectrometers for photon energies between around 10 keV and 100 keV. The RF is based on the proposal of Seltzer [1981. Nucl. Instrum. Methods 188, 133-151] and takes into account the full-energy absorption in the Ge active volume, the escape of Ge Kα and Kβ x-rays and the escape of photons after one Compton interaction. The relativistic impulse approximation is employed instead of the Klein-Nishina formula to describe incoherent photon scattering in the Ge crystal. We also incorporate a simple model for the continuous component of the spectrum produced by the escape of photo-electrons from the active volume. In our calculations we include external interaction contributions to the RF: (i) the incoherent scattering effects caused by the detector's Be window and (ii) the spectrum produced by photo-electrons emitted in the Ge dead layer that reach the active volume. The analytical RF model is compared with pulse-height spectra simulated using the PENELOPE Monte Carlo code.

Dynamical Core-Hole Screening in the X-Ray Absorption Spectra of Hydrogenated Carbon Nanotubes And Graphene

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

Wessely, O.; /Uppsala U. /Imperial Coll., London; Katsnelson, M.I.

2009-04-30

We have calculated the electronic structure and the x-ray absorption (XA) spectrum of a hydrogenated single graphite plane, in order to simulate recent experimental results on hydrogenated single wall carbon nanotubes (SWCNT) as well as hydrogenated graphene. We find that the presence of H induces a substantial component of sp{sup 3} bonding and as a result the {pi} and {pi}* components to the electronic structure vanish. We have calculated a theoretical x-ray absorption spectrum using a multiband version of the Mahan-Nozieres-De Dominicis theory. By making a fitting of the XA signal of C atoms that have H attached to themmore » and C atoms without H in the vicinity we obtain a good representation of the experimental data and we can draw the conclusion that in the experiments [A. Nikitin et al., Phys. Rev. Lett. 95, 225507 (2005)] some 35-50 % H have been absorbed in the SWCNT.« less

Evolution of Xe spectrum and ion charge under sudden incoming radiation

NASA Astrophysics Data System (ADS)

Klapisch, Marcel; Busquet, Michel

2012-06-01

Experiments [1] and simulations of Xe at high temperature were recently reported, due to the possible scaling of astrophysical radiative shocks [2]. We used the newest version of HULLAC [3] to compute energy levels, radiative and collisional transition rates and level populations in a Coronal Radiative Model for the ions Xe9+ to Xe44+ (36263 configurations), at electron temperature of 100 eV and electron density of 10^19 -- 10^21 e/cm^3, in the presence of an external Planckian radiation field. Static and time dependent influence of the radiation on ion charge and spectrum is described. We show an effect of shell structure on relaxation of ion charge when the radiation field is suddenly turn on.[4pt] [1] Busquet, M., Thais, F., Gonzalez, M., et al., J. App. Phys. 107, 083302 (2010).[0pt] [2] Ryutov, D., Drake, R. P., Kane, J., et al., Astrophys. J. 518, 821 (1999).[0pt] [3] Klapisch, M. and Busquet, M., High Ener. Dens. Phys. 7, 98 (2011).

DichroCalc: Improvements in Computing Protein Circular Dichroism Spectroscopy in the Near-Ultraviolet.

PubMed

Jasim, Sarah B; Li, Zhuo; Guest, Ellen E; Hirst, Jonathan D

2017-12-16

A fully quantitative theory connecting protein conformation and optical spectroscopy would facilitate deeper insights into biophysical and simulation studies of protein dynamics and folding. The web server DichroCalc (http://comp.chem.nottingham.ac.uk/dichrocalc) allows one to compute from first principles the electronic circular dichroism spectrum of a (modeled or experimental) protein structure or ensemble of structures. The regular, repeating, chiral nature of secondary structure elements leads to intense bands in the far-ultraviolet (UV). The near-UV bands are much weaker and have been challenging to compute theoretically. We report some advances in the accuracy of calculations in the near-UV, realized through the consideration of the vibrational structure of the electronic transitions of aromatic side chains. The improvements have been assessed over a set of diverse proteins. We illustrate them using bovine pancreatic trypsin inhibitor and present a new, detailed analysis of the interactions which are most important in determining the near-UV circular dichroism spectrum. Copyright © 2018. Published by Elsevier Ltd.

Calibration of imaging plates to electrons between 40 and 180 MeV

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

Rabhi, N., E-mail: nesrine.rabhi@celia.u-bordeaux.fr; Batani, D.; Boutoux, G.

2016-05-15

This paper presents the response calibration of Imaging Plates (IPs) for electrons in the 40-180 MeV range using laser-accelerated electrons at Laboratoire d’Optique Appliquée (LOA), Palaiseau, France. In the calibration process, the energy spectrum and charge of electron beams are measured by an independent system composed of a magnetic spectrometer and a Lanex scintillator screen used as a calibrated reference detector. It is possible to insert IPs of different types or stacks of IPs in this spectrometer in order to detect dispersed electrons simultaneously. The response values are inferred from the signal on the IPs, due to an appropriate chargemore » calibration of the reference detector. The effect of thin layers of tungsten in front and/or behind IPs is studied in detail. GEANT4 simulations are used in order to analyze our measurements.« less

Design of sub-Angstrom compact free-electron laser source

NASA Astrophysics Data System (ADS)

Bonifacio, Rodolfo; Fares, Hesham; Ferrario, Massimo; McNeil, Brian W. J.; Robb, Gordon R. M.

2017-01-01

In this paper, we propose for first time practical parameters to construct a compact sub-Angstrom Free Electron Laser (FEL) based on Compton backscattering. Our recipe is based on using picocoulomb electron bunch, enabling very low emittance and ultracold electron beam. We assume the FEL is operating in a quantum regime of Self Amplified Spontaneous Emission (SASE). The fundamental quantum feature is a significantly narrower spectrum of the emitted radiation relative to classical SASE. The quantum regime of the SASE FEL is reached when the momentum spread of the electron beam is smaller than the photon recoil momentum. Following the formulae describing SASE FEL operation, realistic designs for quantum FEL experiments are proposed. We discuss the practical constraints that influence the experimental parameters. Numerical simulations of power spectra and intensities are presented and attractive radiation characteristics such as high flux, narrow linewidth, and short pulse structure are demonstrated.

Negative ion photoelectron spectroscopy of P 2N 3 –: Electron affinity and electronic structures of P 2N 3 ˙

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

Hou, Gao -Lei; Chen, Bo; Transue, Wesley J.

2016-04-19

The recent successful synthesis of P 2N 3 –, a planar all-inorganic aromatic molecule, represents a breakthrough in inorganic chemistry, because, like its isolobal counterparts C 5H 5– and cyclo-P 5 –, P 2N 3 – has potential to serve as a new ligand for transition metals and a building block in solid-state molecular architectures. In light of its importance, we report here a negative ion photoelectron spectroscopy (NIPES) and ab initio study of P 2N 3 –, to investigate the electronic structures of P 2N 3 – and its neutral P 2N 3• radical. The adiabatic detachment energy ofmore » P 2N 3 – (electron affinity of P 2N 3•) was determined to be 3.765 ± 0.010 eV, indicating high stability for the P 2N 3 – anion. Ab initio electronic structure calculations reveal five low-lying electronic states in the neutral P 2N 3• radical. Calculation of the Franck-Condon factors (FCFs) for each anion-to-neutral electronic transition and comparison of the resulting simulated NIPE spectrum with the vibrational structure in the observed spectrum allows the first four excited states of P 2N 3• to be determined to lie 6.2, 6.7, 11.5, and 22.8 kcal/mol -1 above the ground state of the radical, which is found to be a 6π-electron, 2A 1, σ state.« less

Temperature dependence of the hydrated electron's excited-state relaxation. II. Elucidating the relaxation mechanism through ultrafast transient absorption and stimulated emission spectroscopy

NASA Astrophysics Data System (ADS)

Farr, Erik P.; Zho, Chen-Chen; Challa, Jagannadha R.; Schwartz, Benjamin J.

2017-08-01

The structure of the hydrated electron, particularly whether it exists primarily within a cavity or encompasses interior water molecules, has been the subject of much recent debate. In Paper I [C.-C. Zho et al., J. Chem. Phys. 147, 074503 (2017)], we found that mixed quantum/classical simulations with cavity and non-cavity pseudopotentials gave different predictions for the temperature dependence of the rate of the photoexcited hydrated electron's relaxation back to the ground state. In this paper, we measure the ultrafast transient absorption spectroscopy of the photoexcited hydrated electron as a function of temperature to confront the predictions of our simulations. The ultrafast spectroscopy clearly shows faster relaxation dynamics at higher temperatures. In particular, the transient absorption data show a clear excess bleach beyond that of the equilibrium hydrated electron's ground-state absorption that can only be explained by stimulated emission. This stimulated emission component, which is consistent with the experimentally known fluorescence spectrum of the hydrated electron, decreases in both amplitude and lifetime as the temperature is increased. We use a kinetic model to globally fit the temperature-dependent transient absorption data at multiple temperatures ranging from 0 to 45 °C. We find the room-temperature lifetime of the excited-state hydrated electron to be 137 ±40 fs, in close agreement with recent time-resolved photoelectron spectroscopy (TRPES) experiments and in strong support of the "non-adiabatic" picture of the hydrated electron's excited-state relaxation. Moreover, we find that the excited-state lifetime is strongly temperature dependent, changing by slightly more than a factor of two over the 45 °C temperature range explored. This temperature dependence of the lifetime, along with a faster rate of ground-state cooling with increasing bulk temperature, should be directly observable by future TRPES experiments. Our data also suggest that the red side of the hydrated electron's fluorescence spectrum should significantly decrease with increasing temperature. Overall, our results are not consistent with the nearly complete lack of temperature dependence predicted by traditional cavity models of the hydrated electron but instead agree qualitatively and nearly quantitatively with the temperature-dependent structural changes predicted by the non-cavity hydrated electron model.

Intensity of primary cosmic-ray electrons of energy exceeding 8 GeV

NASA Technical Reports Server (NTRS)

Freier, P.; Gilman, C.; Waddington, C. J.

1977-01-01

Results are reported for measurement of the intensity and energy spectrum of primary cosmic-ray electrons with a spark-chamber-counter-emulsion detector flown at a mean altitude of 3 g/sq cm residual atmosphere. A least-squares fit to the flight data yields an electron spectrum from 8 to 80 GeV of approximately 93E to the -2.91 power electrons/sq m/sec per sr/GeV. The results are compared with those of previous experiments as well as with the spectrum obtained for galactic nonthermal radiation. It is concluded that a 'clumpy' magnetic field proportional to the square root of matter density is consistent with measurements of high-energy electrons and synchrotron radiation toward the center of the Galaxy, that a gradual steepening of the electron spectrum relative to the proton spectrum is consistent with an electron lifetime of 1 million years, and that the density of cosmic-ray nucleons and electrons should be essentially uniform throughout the Galaxy if the nucleons have the same lifetime as the electrons and if they traversed 4 to 5 g/sq cm in that lifetime.

[Measurement of rotational and vibrational temperatures in arc plasma based on the first negative system of N2+ (B(2) sigma --> X(2) sigma)].

PubMed

Tu, Xin; Yan, Jian-hua; Ma, Zeng-yi; Li, Xiao-dong; Pan, Xin-chao; Cen, Ke-fa; Cheron, Bruno

2006-12-01

The molecular emission spectra lines of the first negative system N2+ (B(2) sigma--> X(2) sigma ) are frequently observed in the plasma source containing nitrogen. (0-0) and (1--1) N2+ first negative system molecular bands around 391. 4 nm can be used to the measure the rotational and vibrational temperatures in a DC argon-nitrogen plasma at atmospheric pressure. The proposed method based on the comparison between this experimental emission spectrum and the computer simulated one is presented. The effect of the apparatus function, vibrational temperature and rotational temperatures on the line structure of numerical simulated spectrum is discussed. The results show that the electron temperature, rotational temperature, vibrational temperature and kinetic temperature of plasma arc are almost the same, which can be interpreted as that DC argon-nitrogen arc plasma at atmospheric pressure is in LTE under their experimental conditions.

Isolation, spectroscopic and density functional theory studies of 7-(4-methoxyphenyl)-9H-furo[2,3-f]chromen-9-one: a new flavonoid from the bark of Millettia ovalifolia.

PubMed

Taj Ur Rahman; Arfan, Mohammad; Mahmood, Tariq; Liaqat, Wajiha; Gilani, Mazhar Amjad; Uddin, Ghias; Ludwig, Ralf; Zaman, Khair; Choudhary, M Iqbal; Khattak, Khanzadi Fatima; Ayub, Khurshid

2015-07-05

The phytochemical examination of chloroform soluble fraction (FX2) of methanolic extract of bark of Millettia ovalifolia yielded a new flavonoid; 7-(4-methoxyphenyl)-9H-furo [2,3-f]chromen-9-one (1). Compound 1 is characterized by spectroscopic analytical techniques such as UV, IR, 1D, 2D NMR spectroscopy, and mass spectrometry. A theoretical model is also developed for obtaining geometric, electronic and spectroscopic properties of 1. The geometry optimization and harmonic vibration simulations have been carried out at B3LYP/6-31G(d,p). The vibrational spectrum of compound 1 shows nice correlation with the experimental IR spectrum, through a scaling factor of 0.9613. (1)H and (13)C NMR chemical shifts are simulated using Cramer's re-parameterized function WP04 at 6-31G(d,p) basis set, and correlate nicely with the experimental chemical shifts. Copyright © 2015 Elsevier B.V. All rights reserved.

Isolation, spectroscopic and density functional theory studies of 7-(4-methoxyphenyl)-9H-furo[2,3-f]chromen-9-one: A new flavonoid from the bark of Millettia ovalifolia

NASA Astrophysics Data System (ADS)

Rahman, Taj Ur; Arfan, Mohammad; Mahmood, Tariq; Liaqat, Wajiha; Gilani, Mazhar Amjad; Uddin, Ghias; Ludwig, Ralf; Zaman, Khair; Choudhary, M. Iqbal; Khattak, Khanzadi Fatima; Ayub, Khurshid

2015-07-01

The phytochemical examination of chloroform soluble fraction (FX2) of methanolic extract of bark of Millettia ovalifolia yielded a new flavonoid; 7-(4-methoxyphenyl)-9H-furo [2,3-f]chromen-9-one (1). Compound 1 is characterized by spectroscopic analytical techniques such as UV, IR, 1D, 2D NMR spectroscopy, and mass spectrometry. A theoretical model is also developed for obtaining geometric, electronic and spectroscopic properties of 1. The geometry optimization and harmonic vibration simulations have been carried out at B3LYP/6-31G(d,p). The vibrational spectrum of compound 1 shows nice correlation with the experimental IR spectrum, through a scaling factor of 0.9613. 1H and 13C NMR chemical shifts are simulated using Cramer's re-parameterized function WP04 at 6-31G(d,p) basis set, and correlate nicely with the experimental chemical shifts.

A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

NASA Astrophysics Data System (ADS)

Egidi, Franco; Segado, Mireia; Koch, Henrik; Cappelli, Chiara; Barone, Vincenzo

2014-12-01

In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π*, π-π*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

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

Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it

In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

General relativistic magnetohydrodynamical κ-jet models for Sagittarius A*

NASA Astrophysics Data System (ADS)

Davelaar, J.; Mościbrodzka, M.; Bronzwaer, T.; Falcke, H.

2018-04-01

Context. The observed spectral energy distribution of an accreting supermassive black hole typically forms a power-law spectrum in the near infrared (NIR) and optical wavelengths, that may be interpreted as a signature of accelerated electrons along the jet. However, the details of acceleration remain uncertain. Aim. In this paper, we study the radiative properties of jets produced in axisymmetric general relativistic magnetohydrodynamics (GRMHD) simulations of hot accretion flows onto underluminous supermassive black holes both numerically and semi-analytically, with the aim of investigating the differences between models with and without accelerated electrons inside the jet. Methods: We assume that electrons are accelerated in the jet regions of our GRMHD simulation. To model them, we modify the electrons' distribution function in the jet regions from a purely relativistic thermal distribution to a combination of a relativistic thermal distribution and the κ-distribution function (the κ-distribution function is itself a combination of a relativistic thermal and a non-thermal power-law distribution, and thus it describes accelerated electrons). Inside the disk, we assume a thermal distribution for the electrons. In order to resolve the particle acceleration regions in the GRMHD simulations, we use a coordinate grid that is optimized for modeling jets. We calculate jet spectra and synchrotron maps by using the ray tracing code RAPTOR, and compare the synthetic observations to observations of Sgr A*. Finally, we compare numerical models of jets to semi-analytical ones. Results: We find that in the κ-jet models, the radio-emitting region size, radio flux, and spectral index in NIR/optical bands increase for decreasing values of the κ parameter, which corresponds to a larger amount of accelerated electrons. This is in agreement with analytical predictions. In our models, the size of the emission region depends roughly linearly on the observed wavelength λ, independently of the assumed distribution function. The model with κ = 3.5, ηacc = 5-10% (the percentage of electrons that are accelerated), and observing angle i = 30° fits the observed Sgr A* emission in the flaring state from the radio to the NIR/optical regimes, while κ = 3.5, ηacc < 1%, and observing angle i = 30° fit the upper limits in quiescence. At this point, our models (including the purely thermal ones) cannot reproduce the observed source sizes accurately, which is probably due to the assumption of axisymmetry in our GRMHD simulations. The κ-jet models naturally recover the observed nearly-flat radio spectrum of Sgr A* without invoking the somewhat artificial isothermal jet model that was suggested earlier. Conclusions: From our model fits we conclude that between 5% and 10% of the electrons inside the jet of Sgr A* are accelerated into a κ distribution function when Sgr A* is flaring. In quiescence, we match the NIR upper limits when this percentage is <1%.

Hybrid classical/quantum simulation for infrared spectroscopy of water

NASA Astrophysics Data System (ADS)

Maekawa, Yuki; Sasaoka, Kenji; Ube, Takuji; Ishiguro, Takashi; Yamamoto, Takahiro

2018-05-01

We have developed a hybrid classical/quantum simulation method to calculate the infrared (IR) spectrum of water. The proposed method achieves much higher accuracy than conventional classical molecular dynamics (MD) simulations at a much lower computational cost than ab initio MD simulations. The IR spectrum of water is obtained as an ensemble average of the eigenvalues of the dynamical matrix constructed by ab initio calculations, using the positions of oxygen atoms that constitute water molecules obtained from the classical MD simulation. The calculated IR spectrum is in excellent agreement with the experimental IR spectrum.

The time-resolved photoelectron spectrum of toluene using a perturbation theory approach

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

Richings, Gareth W.; Worth, Graham A., E-mail: g.a.worth@bham.ac.uk

A theoretical study of the intra-molecular vibrational-energy redistribution of toluene using time-resolved photo-electron spectra calculated using nuclear quantum dynamics and a simple, two-mode model is presented. Calculations have been carried out using the multi-configuration time-dependent Hartree method, using three levels of approximation for the calculation of the spectra. The first is a full quantum dynamics simulation with a discretisation of the continuum wavefunction of the ejected electron, whilst the second uses first-order perturbation theory to calculate the wavefunction of the ion. Both methods rely on the explicit inclusion of both the pump and probe laser pulses. The third method includesmore » only the pump pulse and generates the photo-electron spectrum by projection of the pumped wavepacket onto the ion potential energy surface, followed by evaluation of the Fourier transform of the autocorrelation function of the subsequently propagated wavepacket. The calculations performed have been used to study the periodic population flow between the 6a and 10b16b modes in the S{sub 1} excited state, and compared to recent experimental data. We obtain results in excellent agreement with the experiment and note the efficiency of the perturbation method.« less

Density functional theory and phytochemical study of Pistagremic acid

NASA Astrophysics Data System (ADS)

Ullah, Habib; Rauf, Abdur; Ullah, Zakir; Fazl-i-Sattar; Anwar, Muhammad; Shah, Anwar-ul-Haq Ali; Uddin, Ghias; Ayub, Khurshid

2014-01-01

We report here for the first time a comparative theoretical and experimental study of Pistagremic acid (P.A). We have developed a theoretical model for obtaining the electronic and spectroscopic properties of P.A. The simulated data showed nice correlation with the experimental data. The geometric and electronic properties were simulated at B3LYP/6-31 G (d, p) level of density functional theory (DFT). The optimized geometric parameters of P.A were found consistent with those from X-ray crystal structure. Differences of about 0.01 and 0.15 Å in bond length and 0.19-1.30° degree in the angles, respectively; were observed between the experimental and theoretical data. The theoretical vibrational bands of P.A were found to correlate with the experimental IR spectrum after a common scaling factor of 0.963. The experimental and predicted UV-Vis spectra (at B3LYP/6-31+G (d, p)) have 36 nm differences. This difference from experimental results is because of the condensed phase nature of P.A. Electronic properties such as Ionization Potential (I.P), Electron Affinities (E.A), co-efficient of highest occupied molecular orbital (HOMO), co-efficient of lowest unoccupied molecular orbital (LUMO) of P.A were estimated for the first time however, no correlation can be made with experiment. Inter-molecular interaction and its effect on vibrational (IR), electronic and geometric parameters were simulated by using Formic acid as model for hydrogen bonding in P.A.

Optimal simulations of ultrasonic fields produced by large thermal therapy arrays using the angular spectrum approach

PubMed Central

Zeng, Xiaozheng; McGough, Robert J.

2009-01-01

The angular spectrum approach is evaluated for the simulation of focused ultrasound fields produced by large thermal therapy arrays. For an input pressure or normal particle velocity distribution in a plane, the angular spectrum approach rapidly computes the output pressure field in a three dimensional volume. To determine the optimal combination of simulation parameters for angular spectrum calculations, the effect of the size, location, and the numerical accuracy of the input plane on the computed output pressure is evaluated. Simulation results demonstrate that angular spectrum calculations performed with an input pressure plane are more accurate than calculations with an input velocity plane. Results also indicate that when the input pressure plane is slightly larger than the array aperture and is located approximately one wavelength from the array, angular spectrum simulations have very small numerical errors for two dimensional planar arrays. Furthermore, the root mean squared error from angular spectrum simulations asymptotically approaches a nonzero lower limit as the error in the input plane decreases. Overall, the angular spectrum approach is an accurate and robust method for thermal therapy simulations of large ultrasound phased arrays when the input pressure plane is computed with the fast nearfield method and an optimal combination of input parameters. PMID:19425640

Simulation of background from low-level tritium and radon emanation in the KATRIN spectrometers

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

Leiber, B.; Collaboration: KATRIN Collaboration

The KArlsruhe TRItium Neutrino (KATRIN) experiment is a large-scale experiment for the model independent determination of the mass of electron anti-neutrinos with a sensitivity of 200 meV/c{sup 2}. It investigates the kinematics of electrons from tritium beta decay close to the endpoint of the energy spectrum at 18.6 keV. To achieve a good signal to background ratio at the endpoint, a low background rate below 10{sup −2} counts per second is required. The KATRIN setup thus consists of a high luminosity windowless gaseous tritium source (WGTS), a magnetic electron transport system with differential and cryogenic pumping for tritium retention, andmore » electro-static retarding spectrometers (pre-spectrometer and main spectrometer) for energy analysis, followed by a segmented detector system for counting transmitted beta-electrons. A major source of background comes from magnetically trapped electrons in the main spectrometer (vacuum vessel: 1240 m{sup 3}, 10{sup −11} mbar) produced by nuclear decays in the magnetic flux tube of the spectrometer. Major contributions are expected from short-lived radon isotopes and tritium. Primary electrons, originating from these decays, can be trapped for hours, until having lost almost all their energy through inelastic scattering on residual gas particles. Depending on the initial energy of the primary electron, up to hundreds of low energetic secondary electrons can be produced. Leaving the spectrometer, these electrons will contribute to the background rate. This contribution describes results from simulations for the various background sources. Decays of {sup 219}Rn, emanating from the main vacuum pump, and tritium from the WGTS that reaches the spectrometers are expected to account for most of the background. As a result of the radon alpha decay, electrons are emitted through various processes, such as shake-off, internal conversion and the Auger deexcitations. The corresponding simulations were done using the KASSIOPEIA framework, which has been developed for the KATRIN experiment for low-energy electron tracking, field calculation and detector simulation. The results of the simulations have been used to optimize the design parameters of the vacuum system with regard to radon emanation and tritium pumping, in order to reach the stringent requirements of the neutrino mass measurement.« less

Perspective on the Cosmic-ray Electron Spectrum above TeV

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

Fang, Kun; Wang, Bing-Bing; Bi, Xiao-Jun

2017-02-20

The AMS-02 has measured the cosmic-ray electron (plus positron) spectrum up to ∼TeV with unprecedented precision. The spectrum can be well described by a power law without any obvious features above 10 GeV. The satellite instrument Dark Matter Particle Explorer (DAMPE), which was launched a year ago, will measure the electron spectrum up to 10 TeV with high-energy resolution. The cosmic electrons beyond TeV may be attributed to few local cosmic-ray sources, such as supernova remnants. Therefore, spectral features, such as cut-off and bumps, can be expected at high energies. In this work, we provide a careful study on themore » perspective of the electron spectrum beyond TeV. We first examine our astrophysical source models on the latest leptonic data of AMS-02 to give a self-consistent picture. Then we focus on the discussion about the candidate sources, which could be electron contributors above TeV. Depending on the properties of the local sources (especially on the nature of Vela), DAMPE may detect interesting features in the electron spectrum above TeV in the future.« less

Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

NASA Astrophysics Data System (ADS)

Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

2016-10-01

We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

Derivatization and diffusive motion of molecular fullerenes: Ab initio and atomistic simulations

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

Berdiyorov, G., E-mail: gberdiyorov@qf.org.qa; Tabet, N.; Harrabi, K.

2015-07-14

Using first principles density functional theory in combination with the nonequilibrium Green's function formalism, we study the effect of derivatization on the electronic and transport properties of C{sub 60} fullerene. As a typical example, we consider [6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PCBM), which forms one of the most efficient organic photovoltaic materials in combination with electron donating polymers. Extra peaks are observed in the density of states (DOS) due to the formation of new electronic states localized at/near the attached molecule. Despite such peculiar behavior in the DOS of an isolated molecule, derivatization does not have a pronounced effect onmore » the electronic transport properties of the fullerene molecular junctions. Both C{sub 60} and PCBM show the same response to finite voltage biasing with new features in the transmission spectrum due to voltage induced delocalization of some electronic states. We also study the diffusive motion of molecular fullerenes in ethanol solvent and inside poly(3-hexylthiophene) lamella using reactive molecular dynamics simulations. We found that the mobility of the fullerene reduces considerably due to derivatization; the diffusion coefficient of C{sub 60} is an order of magnitude larger than the one for PCBM.« less

Multi-scale virtual view on the precessing jet SS433

NASA Astrophysics Data System (ADS)

Monceau-Baroux, R.; Porth, O.; Meliani, Z.; Keppens, R.

2014-07-01

Observations of SS433 infer how an X-ray binary gives rise to a corkscrew patterned relativistic jet. XRB SS433 is well known on a large range of scales for wich we realize 3D simulation and radio mappings. For our study we use relativistic hydrodynamic in special relativity using a relativistic effective polytropic index. We use parameters extracted from observations to impose thermodynamical conditions of the ISM and jet. We follow the kinetic and thermal energy content, of the various ISM and jet regions. Our simulation follows simultaneously the evolution of the population of electrons which are accelerated by the jet. The evolving spectrum of these electrons, together with an assumed equipartition between dynamic and magnetic pressure, gives input for estimating the radio emission from our simulation. Ray tracing according to a direction of sight then realizes radio mappings of our data. Single snapshots are realised to compare with VLA observation as in Roberts et al. 2008. A radio movie is realised to compare with the 41 days movie made with the VLBA instrument. Finaly a larger scale simulation explore the discrepancy of opening angle between 10 and 20 degree between the large scale observation of SS433 and its close in observation.

The imprint of Gould's belt on the local cosmic ray electron spectrum

NASA Astrophysics Data System (ADS)

Pohl, M.; Perrot, C.; Grenier, I.

2001-08-01

In a recent paper Pohl and Esposito (1998) demonstrated that if the sources of cosmic-rays are discrete, as are Supernova Remnants (SNR), then the spectra of cosmic-ray electrons largely vary with location and time and the locally measured electron spectrum may not be representative of the electron spectra elsewhere in the Galaxy, which could be substantially harder than the local one. They have shown that the observed excess of γ-ray emission above 1 GeV can in fact be partially explained as a correspondingly hard inverse Compton component, provided the bulk of cosmic-ray electrons is produced in SNR. As part of a program to model the Galactic γ-ray foreground we have continued the earlier studies by investigating the impact of the star forming region Gould's Belt on the local electron spectrum. If the electron sources in Gould's Belt were continous, the local electron spectrum would be slightly hardened. If the electron sources are discrete, which is the more probable case, the variation in the local electron spectrum found by Pohl & Esposito persists. 1 The local cosmic-ray electron spectrum The recent detections of non-thermal X-ray synchrotron radiation from the supernova remnants SN1006 (Koyama et al., 1995), RX J1713.7-3946 (Koyama et al., 1997), IC443 (Keohane et al., 1997; Slane et al., 1999), Cas A (Allen et al., 1997), and RCW86 (Borkowski et al., 2001) and the subsequent detections of SN1006 (Tanimori et al., 1998), RX J1713.7-3946 (Muraishi et al., 2000), and Cas A (Aharonian et al., 2001) at TeV energies support the hypothesis that at least Galactic cosmic-ray electrons are accelerated predominantly in SNR. The Galactic distribution and spectrum of cosmic-ray electrons are intimately linked to the distribution and nature of their sources. Supernovae and hence their remnants are tran-

Few-cycle pulse generation in an x-ray free-electron laser.

PubMed

Dunning, D J; McNeil, B W J; Thompson, N R

2013-03-08

A method is proposed to generate trains of few-cycle x-ray pulses from a free-electron laser (FEL) amplifier via a compact "afterburner" extension consisting of several few-period undulator sections separated by electron chicane delays. Simulations show that in the hard x ray (wavelength ~0.1 nm; photon energy ~10 keV) and with peak powers approaching normal FEL saturation (GW) levels, root mean square pulse durations of 700 zs may be obtained. This is approximately two orders of magnitude shorter than that possible for normal FEL amplifier operation. The spectrum is discretely multichromatic with a bandwidth envelope increased by approximately 2 orders of magnitude over unseeded FEL amplifier operation. Such a source would significantly enhance research opportunity in atomic dynamics and push capability toward nuclear dynamics.

Investigation of ionization-induced electron injection in a wakefield driven by laser inside a gas cell

DOE PAGES

Audet, T. L.; Hansson, M.; Lee, P.; ...

2016-02-16

Ionization-induced electron injection was investigated experimentally by focusing a driving laser pulse with a maximum normalized potential of 1.2 at different positions along the plasma density profile inside a gas cell, filled with a gas mixture composed of 99%H 2+1%N 2. Changing the laser focus position relative to the gas cell entrance controls the accelerated electron bunch properties, such as the spectrum width, maximum energy, and accelerated charge. Simulations performed using the 3D particle-in-cell code WARP with a realistic density profile give results that are in good agreement with the experimental ones. Lastly, we discuss the interest of this regimemore » for optimizing the bunch charge in a selected energy window.« less

An ab-initio study of mechanical, dynamical and electronic properties of MgEu intermetallic

NASA Astrophysics Data System (ADS)

Kumar, S. Ramesh; Jaiganesh, G.; Jayalakshmi, V.

2018-04-01

The theoretical investigation on the mechanical, dynamical and electronic properties of MgEu in CsCl-type structure has been carried out through the ab-initio calculations within the framework of the density functional theory and the density functional perturbation theory. For the purpose, Vienna Ab initio Simulation Package and Phonopy packages were used. Our calculated ground-state properties of MgEu are in good agreement with other available results. Our computed elastic constants and phonon spectrum results suggest that MgEu is mechanically and dynamically stable up to 5 GPa. The thermodynamic quantities as a function of temperatures are also reported and discussed. The band structure, density of states and charge density also calculated to understand the electronic properties of MgEu.

Bremsstrahlung hard x-ray source driven by an electron beam from a self-modulated laser wakefield accelerator

NASA Astrophysics Data System (ADS)

Lemos, N.; Albert, F.; Shaw, J. L.; Papp, D.; Polanek, R.; King, P.; Milder, A. L.; Marsh, K. A.; Pak, A.; Pollock, B. B.; Hegelich, B. M.; Moody, J. D.; Park, J.; Tommasini, R.; Williams, G. J.; Chen, Hui; Joshi, C.

2018-05-01

An x-ray source generated by an electron beam produced using a Self-Modulated Laser Wakefield Accelerator (SM-LWFA) is explored for use in high energy density science facilities. By colliding the electron beam, with a maximum energy of 380 MeV, total charge of >10 nC and a divergence of 64 × 100 mrad, from a SM-LWFA driven by a 1 ps 120 J laser, into a high-Z foil, an x/gamma-ray source was generated. A broadband bremsstrahlung energy spectrum with temperatures ranging from 0.8 to 2 MeV was measured with an almost 2 orders of magnitude flux increase when compared with other schemes using LWFA. GEANT4 simulations were done to calculate the source size and divergence.

Background evaluation for the neutron sources in the Daya Bay experiment

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

Gu, W. Q.; Cao, G. F.; Chen, X. H.

2016-07-06

Here, we present an evaluation of the background induced by 241Am–13C neutron calibration sources in the Daya Bay reactor neutrino experiment. Furthermore, as a significant background for electron-antineutrino detection at 0.26 ± 0.12 detector per day on average, it has been estimated by a Monte Carlo simulation that was benchmarked by a special calibration data set. This dedicated data set also provides the energy spectrum of the background.

Quasi-monoenergetic laser-plasma acceleration of electrons to 2 GeV

PubMed Central

Wang, Xiaoming; Zgadzaj, Rafal; Fazel, Neil; Li, Zhengyan; Yi, S. A.; Zhang, Xi; Henderson, Watson; Chang, Y.-Y.; Korzekwa, R.; Tsai, H.-E.; Pai, C.-H.; Quevedo, H.; Dyer, G.; Gaul, E.; Martinez, M.; Bernstein, A. C.; Borger, T.; Spinks, M.; Donovan, M.; Khudik, V.; Shvets, G.; Ditmire, T.; Downer, M. C.

2013-01-01

Laser-plasma accelerators of only a centimetre’s length have produced nearly monoenergetic electron bunches with energy as high as 1 GeV. Scaling these compact accelerators to multi-gigaelectronvolt energy would open the prospect of building X-ray free-electron lasers and linear colliders hundreds of times smaller than conventional facilities, but the 1 GeV barrier has so far proven insurmountable. Here, by applying new petawatt laser technology, we produce electron bunches with a spectrum prominently peaked at 2 GeV with only a few per cent energy spread and unprecedented sub-milliradian divergence. Petawatt pulses inject ambient plasma electrons into the laser-driven accelerator at much lower density than was previously possible, thereby overcoming the principal physical barriers to multi-gigaelectronvolt acceleration: dephasing between laser-driven wake and accelerating electrons and laser pulse erosion. Simulations indicate that with improvements in the laser-pulse focus quality, acceleration to nearly 10 GeV should be possible with the available pulse energy. PMID:23756359

Deleterious effects of nonthermal electrons in shock ignition concept.

PubMed

Nicolaï, Ph; Feugeas, J-L; Touati, M; Ribeyre, X; Gus'kov, S; Tikhonchuk, V

2014-03-01

Shock ignition concept is a promising approach to inertial confinement fusion that may allow obtaining high fusion energy gains with the existing laser technology. However, the spike driving laser intensities in the range of 1-10 PW/cm2 produces the energetic electrons that may have a significant effect on the target performance. The hybrid numerical simulations including a radiation hydrodynamic code coupled to a rapid Fokker-Planck module are used to asses the role of hot electrons in the shock generation and the target preheat in the time scale of 100 ps and spatial scale of 100 μm. It is shown that depending on the electron energy distribution and the target density profile the hot electrons can either increase the shock amplitude or preheat the imploding shell. In particular, the exponential electron energy spectrum corresponding to the temperature of 30 keV in the present HiPER target design preheats the deuterium-tritium shell and jeopardizes its compression. Ways of improving the target performance are suggested.

Diffuse Galactic Continuum Gamma Rays. A Model Compatible with EGRET Data and Cosmic-ray Measurements

NASA Technical Reports Server (NTRS)

Strong, Andrew W.; Moskalenko, Igor V.; Reimer, Olaf

2004-01-01

We present a study of the compatibility of some current models of the diffuse Galactic continuum gamma-rays with EGRET data. A set of regions sampling the whole sky is chosen to provide a comprehensive range of tests. The range of EGRET data used is extended to 100 GeV. The models are computed with our GALPROP cosmic-ray propagation and gamma-ray production code. We confirm that the "conventional model" based on the locally observed electron and nucleon spectra is inadequate, for all sky regions. A conventional model plus hard sources in the inner Galaxy is also inadequate, since this cannot explain the GeV excess away from the Galactic plane. Models with a hard electron injection spectrum are inconsistent with the local spectrum even considering the expected fluctuations; they are also inconsistent with the EGRET data above 10 GeV. We present a new model which fits the spectrum in all sky regions adequately. Secondary antiproton data were used to fix the Galactic average proton spectrum, while the electron spectrum is adjusted using the spectrum of diffuse emission it- self. The derived electron and proton spectra are compatible with those measured locally considering fluctuations due to energy losses, propagation, or possibly de- tails of Galactic structure. This model requires a much less dramatic variation in the electron spectrum than models with a hard electron injection spectrum, and moreover it fits the y-ray spectrum better and to the highest EGRET energies. It gives a good representation of the latitude distribution of the y-ray emission from the plane to the poles, and of the longitude distribution. We show that secondary positrons and electrons make an essential contribution to Galactic diffuse y-ray emission.

Broad band simulation of Gamma Ray Bursts (GRB) prompt emission in presence of an external magnetic field

NASA Astrophysics Data System (ADS)

Ziaeepour, Houri; Gardner, Brian

2011-12-01

The origin of prompt emission in GRBs is not yet well understood. The simplest and most popular model is Synchrotron Self-Compton (SSC) emission produced by internal shocks inside an ultra-relativistic jet. However, recent observations of a delayed high energy component by the Fermi-LAT instrument have encouraged alternative models. Here we use a recently developed formulation of relativistic shocks for GRBs to simulate light curves and spectra of synchrotron and self-Compton emissions in the framework of internal shock model. This model takes into account the evolution of quantities such as densities of colliding shells, and fraction of kinetic energy transferred to electrons and to induced magnetic field. We also extend this formulation by considering the presence of a precessing external magnetic field. These simulations are very realistic and present significant improvement with respect to previous phenomenological GRB simulations. They reproduce light curves of separate peaks of real GRBs and variety of spectral slopes at E > Epeak observed by the Fermi-LAT instrument. The high energy emission can be explained by synchrotron emission and a subdominant contribution from inverse Compton. We also suggest an explanation for extended tail emission and relate it to the screening of the magnetic field and/or trapping of accelerated electrons in the electromagnetic energy structure of the plasma in the shock front. Spectral slopes of simulated bursts at E << Epeak are consistent with theoretical prediction and at E < Epeak can be flatter if the spectrum of electrons is roughly flat or has a shallow slope at low energies. The observed flat spectra at soft gamma-ray and hard x-ray bands is the evidence that there is a significant contribution at E < Epeak from lower Lorentz factor wing of electron distribution which have a roughly random acceleration rather than being thermal. This means that the state of matter in the jet at the time of ejection is most probably nonthermal. As for the effect of a precessing external magnetic field, we show that due to the fast variation of other quantities, its signature in the Power Distribution Spectrum (PDS) is significantly suppressed and only when the duration of the burst is few times longer than the oscillation period it can be detected, otherwise either it is confused with the Poisson noise or with intrinsic variations of the emission. Therefore, low significant oscillations observed in the PDS of GRB 090709a are most probably due to a precessing magnetic field.

Anomalous Electron Spectrum and Its Relation to Peak Structure of Electron Scattering Rate in Cuprate Superconductors

NASA Astrophysics Data System (ADS)

Gao, Deheng; Mou, Yingping; Feng, Shiping

2018-02-01

The recent discovery of a direct link between the sharp peak in the electron quasiparticle scattering rate of cuprate superconductors and the well-known peak-dip-hump structure in the electron quasiparticle excitation spectrum is calling for an explanation. Within the framework of the kinetic-energy-driven superconducting mechanism, the complicated line-shape in the electron quasiparticle excitation spectrum of cuprate superconductors is investigated. It is shown that the interaction between electrons by the exchange of spin excitations generates a notable peak structure in the electron quasiparticle scattering rate around the antinodal and nodal regions. However, this peak structure disappears at the hot spots, which leads to that the striking peak-dip-hump structure is developed around the antinodal and nodal regions, and vanishes at the hot spots. The theory also confirms that the sharp peak observed in the electron quasiparticle scattering rate is directly responsible for the remarkable peak-dip-hump structure in the electron quasiparticle excitation spectrum of cuprate superconductors.

Pseudorandom binary injection of levitons for electron quantum optics

NASA Astrophysics Data System (ADS)

Glattli, D. C.; Roulleau, P.

2018-03-01

The recent realization of single-electron sources lets us envision performing electron quantum optics experiments, where electrons can be viewed as flying qubits propagating in a ballistic conductor. To date, all electron sources operate in a periodic electron injection mode, leading to energy spectrum singularities in various physical observables which sometimes hide the bare nature of physical effects. To go beyond this, we propose a spread-spectrum approach where electron flying qubits are injected in a nonperiodic manner following a pseudorandom binary bit pattern. Extending the Floquet scattering theory approach from periodic to spread-spectrum drive, the shot noise of pseudorandom binary sequences of single-electron injection can be calculated for leviton and nonleviton sources. Our new approach allows us to disentangle the physics of the manipulated excitations from that of the injection protocol. In particular, the spread-spectrum approach is shown to provide better knowledge of electronic Hong-Ou-Mandel correlations and to clarify the nature of the pulse train coherence and the role of the dynamical orthogonality catastrophe for noninteger charge injection.

Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

DOE PAGES

Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; ...

2015-09-25

Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities ofmore » $${10}^{15}-{10}^{16}\\;$$ W cm–2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about $25$ and $$40\\;\\mathrm{eV}$$ for simulated delay times up to $$+70\\;\\mathrm{fs}$$ after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and $$30\\;$$eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. In conclusion, we resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.« less

Combined Space Environmental Exposure Tests of Multi-Junction GaAs/Ge Solar Array Coupons

NASA Technical Reports Server (NTRS)

Hoang, Bao; Wong, Frankie; Corey, Ron; Gardiner, George; Funderburk, Victor V.; Gahart, Richard; Wright, Kenneth H.; Schneider, Todd; Vaughn, Jason

2010-01-01

A set of multi-junction GaAs/Ge solar array test coupons were subjected to a sequence of 5-year increments of combined environmental exposure tests. The purpose of this test program is to understand the changes and degradation of the solar array panel components, including its ESD mitigation design features in their integrated form, after multiple years (up to 15) of simulated geosynchronous space environment. These tests consist of: UV radiation, electrostatic discharge (ESD), electron/proton particle radiation, thermal cycling, and ion thruster plume exposures. The solar radiation was produced using a Mercury-Xenon lamp with wavelengths in the UV spectrum ranging from 230 to 400 nm. The ESD test was performed in the inverted-gradient mode using a low-energy electron (2.6 - 6 keV) beam exposure. The ESD test also included a simulated panel coverglass flashover for the primary arc event. The electron/proton radiation exposure included both 1.0 MeV and 100 keV electron beams simultaneous with a 40 keV proton beam. The thermal cycling included simulated transient earth eclipse for satellites in geosynchronous orbit. With the increasing use of ion thruster engines on many satellites, the combined environmental test also included ion thruster exposure to determine whether solar array surface erosion had any impact on its performance. Before and after each increment of environmental exposures, the coupons underwent visual inspection under high power magnification and electrical tests that included characterization by LAPSS, Dark I-V, and electroluminescence. This paper discusses the test objective, test methodologies, and preliminary results after 5 years of simulated exposure.

Microdosimetry of low-energy electrons.

PubMed

Liamsuwan, Thiansin; Emfietzoglou, Dimitris; Uehara, Shuzo; Nikjoo, Hooshang

2012-12-01

To investigate differences in energy depositions and microdosimetric parameters of low-energy electrons in liquid and gaseous water using Monte Carlo track structure simulations. KURBUC-liq (Kyushu University and Radiobiology Unit Code for liquid water) was used for simulating electron tracks in liquid water. The inelastic scattering cross sections of liquid water were obtained from the dielectric response model of Emfietzoglou et al. (Radiation Research 2005;164:202-211). Frequencies of energy deposited in nanometre-size cylindrical targets per unit absorbed dose and associated lineal energies were calculated for 100-5000 eV monoenergetic electrons and the electron spectrum of carbon K edge X-rays. The results for liquid water were compared with those for water vapour. Regardless of electron energy, there is a limit how much energy electron tracks can deposit in a target. Phase effects on the frequencies of energy depositions are largely visible for the targets with diameters and heights smaller than 30 nm. For the target of 2.3 nm by 2.3 nm (similar to dimension of DNA segments), the calculated frequency- and dose-mean lineal energies for liquid water are up to 40% smaller than those for water vapour. The corresponding difference is less than 12% for the targets with diameters ≥ 30 nm. Condensed-phase effects are non-negligible for microdosimetry of low-energy electrons for targets with sizes smaller than a few tens of nanometres, similar to dimensions of DNA molecular structures and nucleosomes.

Electronic polarization effect on low-frequency infrared and Raman spectra of aprotic solvent: Molecular dynamics simulation study with charge response kernel by second order Møller-Plesset perturbation method

NASA Astrophysics Data System (ADS)

Isegawa, Miho; Kato, Shigeki

2007-12-01

Low-frequency infrared (IR) and depolarized Raman scattering (DRS) spectra of acetonitrile, methylene chloride, and acetone liquids are simulated via molecular dynamics calculations with the charge response kernel (CRK) model obtained at the second order Møller-Plesset perturbation (MP2) level. For this purpose, the analytical second derivative technique for the MP2 energy is employed to evaluate the CRK matrices. The calculated IR spectra reasonably agree with the experiments. In particular, the agreement is excellent for acetone because the present CRK model well reproduces the experimental polarizability in the gas phase. The importance of interaction induced dipole moments in characterizing the spectral shapes is stressed. The DRS spectrum of acetone is mainly discussed because the experimental spectrum is available only for this molecule. The calculated spectrum is close to the experiment. The comparison of the present results with those by the multiple random telegraph model is also made. By decomposing the polarizability anisotropy time correlation function to the contributions from the permanent, induced polarizability and their cross term, a discrepancy from the previous calculations is observed in the sign of permanent-induce cross term contribution. The origin of this discrepancy is discussed by analyzing the correlation functions for acetonitrile.

Effect of shape and thickness of asbestos bundles and fibres on EDS microanalysis: A Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Moro, D.; Valdre, G.

2016-02-01

Quantitative microanalysis of tiny asbestos mineral fibres by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDS) still represents a complex analytical issue. This complexity arises from the variable fibre shape and small thickness (< 5 μm) compared with the penetration of the incident electron beam. Here, we present the results of Monte Carlo simulations of chrysotile, crocidolite and amosite fibres (and bundles of fibres) of circular and square section and thicknesses from 0.1 μm to 10 μm, to investigate the effect of shape and thickness on SEM-EDS microanalysis. The influence of shape and thickness on the simulated spectrum was investigated for electron beam energies of 5, 15 and 25 keV, respectively. A strong influence of the asbestos bundles and fibres shape and thickness on the detected EDS X-ray intensity was observed. The X-ray intensity trends as a function of fibre thickness showed a non-linear dependence for all the elements and minerals. In general, the X-ray intensities showed a considerable reduction for thicknesses below about 5 μm at 5 keV, 2 μm at 15 keV, and 5 μm at 25 keV. Correction parameters, k-ratios, for the asbestos fibre thickness effect, are reported.

Electromagnetic interaction of spacecraft with ambient environment

NASA Astrophysics Data System (ADS)

Ku, Hwar-Ching; Silver, David M.

1993-01-01

A model of the midcourse space experiment (MSX) spacecraft and its electromagnetic environment has been developed using the potential of large spacecraft in the Auroral region (POLAR) code. The geometric model has a resolution of 0.341 meters and uses six materials to simulate the electrical surface properties of MSX. The vehicle model includes features such as the major instruments, electronic boxes, radiators, a dewar and open bay, a booster attachment ring, and three different orientations of the solar panels. The electron and ion composition and temperature environment are modeled as a function of the solar activity. Additional parameters include the ram-wake orientation, the hot electron spectrum, day-night-twilight variations, latitudinal variations, and solar panel voltage biasing. Nominal low spacecraft charging cases are described. Calculation with a high peak energetic electron flux produces a ground potential of -180 volts and differential charging as high as 66 volts.

Energy spectrum of cosmic-ray electrons at TeV energies.

PubMed

Aharonian, F; Akhperjanian, A G; Barres de Almeida, U; Bazer-Bachi, A R; Becherini, Y; Behera, B; Benbow, W; Bernlöhr, K; Boisson, C; Bochow, A; Borrel, V; Braun, I; Brion, E; Brucker, J; Brun, P; Brucker, R; Bulik, T; Büsching, I; Boutelier, T; Carrigan, S; Chadwick, P M; Charbonnier, A; Chaves, R C G; Cheesebrough, A; Chounet, L M; Clapson, A C; Coignet, G; Costamante, L; Dalton, M; Degrange, B; Deil, C; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubois, F; Dubus, G; Dyks, J; Dyrda, M; Egberts, K; Emmanoulopoulos, D; Espigat, P; Farnier, C; Feinstein, F; Fiasson, A; Fontaine, G; Füsling, M; Gabici, S; Gallant, Y A; Gérard, L; Giebels, B; Glicenstein, J F; Glück, B; Goret, P; Hadjichristidis, C; Hauser, D; Hauser, M; Heinz, S; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hoffmann, A; Hofmann, W; Holleran, M; Hoppe, S; Horns, D; Jacholkowska, A; de Jager, O C; Jung, I; Katarzyński, K; Kaufmann, S; Kendziorra, E; Kerschhaggl, M; Khangulyan, D; Khélifi, B; Keogh, D; Komin, Nu; Kosack, K; Lamanna, G; Lenain, J P; Lohse, T; Marandon, V; Martin, J M; Martineau-Huynh, O; Marcowith, A; Maurin, D; McComb, T J L; Medina, C; Moderski, R; Moulin, E; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Niemiec, J; Nolan, S J; Ohm, S; Olive, J F; de Oña Wilhelmi, E; Orford, K J; Osborne, J L; Ostrowski, M; Panter, M; Pedaletti, G; Pelletier, G; Petrucci, P O; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raubenheimer, B C; Raue, M; Rayner, S M; Renaud, M; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Ruppel, J; Sahakian, V; Santangelo, A; Schlickeiser, R; Schöck, F M; Schröder, R; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Skilton, J L; Sol, H; Spangler, D; Stawarz, Ł; Steenkamp, R; Stegmann, C; Superina, G; Tam, P H; Tavernet, J P; Terrier, R; Tibolla, O; van Eldik, C; Vasileiadis, G; Venter, C; Vialle, J P; Vincent, P; Vivier, M; Völk, H J; Volpe, F; Wagner, S J; Ward, M; Zdziarski, A A; Zech, A

2008-12-31

The very large collection area of ground-based gamma-ray telescopes gives them a substantial advantage over balloon or satellite based instruments in the detection of very-high-energy (>600 GeV) cosmic-ray electrons. Here we present the electron spectrum derived from data taken with the High Energy Stereoscopic System (H.E.S.S.) of imaging atmospheric Cherenkov telescopes. In this measurement, the first of this type, we are able to extend the measurement of the electron spectrum beyond the range accessible to direct measurements. We find evidence for a substantial steepening in the energy spectrum above 600 GeV compared to lower energies.

Radiation detector spectrum simulator

DOEpatents

Wolf, Michael A.; Crowell, John M.

1987-01-01

A small battery operated nuclear spectrum simulator having a noise source nerates pulses with a Gaussian distribution of amplitudes. A switched dc bias circuit cooperating therewith generates several nominal amplitudes of such pulses and a spectral distribution of pulses that closely simulates the spectrum produced by a radiation source such as Americium 241.

Radiation detector spectrum simulator

DOEpatents

Wolf, M.A.; Crowell, J.M.

1985-04-09

A small battery operated nuclear spectrum simulator having a noise source generates pulses with a Gaussian distribution of amplitudes. A switched dc bias circuit cooperating therewith to generate several nominal amplitudes of such pulses and a spectral distribution of pulses that closely simulates the spectrum produced by a radiation source such as Americium 241.

A terrain based simulation system to predict the interference caused by networks of spread spectrum systems

NASA Astrophysics Data System (ADS)

Hagen, William E.; Holtzman, Julian C.

The Army Terrain Integrated Interference Prediction System (ATIIPS), a CAD terrain based simulation tool for determining the degradation effects on a network on nonspread spectrum radios caused by a network of spread spectrum radios is presented. A brief overview of the program is given, with typical graphics displays shown. Typical results for both a link simulation of interference and for a network simulation, using a slow hopped FM/FSK spread spectrum interfering radio network on a narrow band FM/FSK fixed frequency digital radio are presented.

Electron-electron interaction and spin-orbit coupling in InAs/AlSb heterostructures with a two-dimensional electron gas

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

Gavrilenko, V. I.; Krishtopenko, S. S., E-mail: ds_a-teens@mail.ru; Goiran, M.

2011-01-15

The effect of electron-electron interaction on the spectrum of two-dimensional electron states in InAs/AlSb (001) heterostructures with a GaSb cap layer with one filled size-quantization subband. The energy spectrum of two-dimensional electrons is calculated in the Hartree and Hartree-Fock approximations. It is shown that the exchange interaction decreasing the electron energy in subbands increases the energy gap between subbands and the spin-orbit splitting of the spectrum in the entire region of electron concentrations, at which only the lower size-quantization band is filled. The nonlinear dependence of the Rashba splitting constant at the Fermi wave vector on the concentration of two-dimensionalmore » electrons is demonstrated.« less

[A Method to Reconstruct Surface Reflectance Spectrum from Multispectral Image Based on Canopy Radiation Transfer Model].

PubMed

Zhao, Yong-guang; Ma, Ling-ling; Li, Chuan-rong; Zhu, Xiao-hua; Tang, Ling-li

2015-07-01

Due to the lack of enough spectral bands for multi-spectral sensor, it is difficult to reconstruct surface retlectance spectrum from finite spectral information acquired by multi-spectral instrument. Here, taking into full account of the heterogeneity of pixel from remote sensing image, a method is proposed to simulate hyperspectral data from multispectral data based on canopy radiation transfer model. This method first assumes the mixed pixels contain two types of land cover, i.e., vegetation and soil. The sensitive parameters of Soil-Leaf-Canopy (SLC) model and a soil ratio factor were retrieved from multi-spectral data based on Look-Up Table (LUT) technology. Then, by combined with a soil ratio factor, all the parameters were input into the SLC model to simulate the surface reflectance spectrum from 400 to 2 400 nm. Taking Landsat Enhanced Thematic Mapper Plus (ETM+) image as reference image, the surface reflectance spectrum was simulated. The simulated reflectance spectrum revealed different feature information of different surface types. To test the performance of this method, the simulated reflectance spectrum was convolved with the Landsat ETM + spectral response curves and Moderate Resolution Imaging Spectrometer (MODIS) spectral response curves to obtain the simulated Landsat ETM+ and MODIS image. Finally, the simulated Landsat ETM+ and MODIS images were compared with the observed Landsat ETM+ and MODIS images. The results generally showed high correction coefficients (Landsat: 0.90-0.99, MODIS: 0.74-0.85) between most simulated bands and observed bands and indicated that the simulated reflectance spectrum was well simulated and reliable.

Spatially Mapping Energy Transfer from Single Plasmonic Particles to Semiconductor Substrates via STEM/EELS.

PubMed

Li, Guoliang; Cherqui, Charles; Bigelow, Nicholas W; Duscher, Gerd; Straney, Patrick J; Millstone, Jill E; Masiello, David J; Camden, Jon P

2015-05-13

Energy transfer from plasmonic nanoparticles to semiconductors can expand the available spectrum of solar energy-harvesting devices. Here, we spatially and spectrally resolve the interaction between single Ag nanocubes with insulating and semiconducting substrates using electron energy-loss spectroscopy, electrodynamics simulations, and extended plasmon hybridization theory. Our results illustrate a new way to characterize plasmon-semiconductor energy transfer at the nanoscale and bear impact upon the design of next-generation solar energy-harvesting devices.

Characterization of an 800 nm SASE FEL at Saturation

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

Nuhn, Heinz-Dieter

2002-11-13

VISA (Visible to Infrared SASE Amplifier) is an FEL (Free Electron Laser) designed to saturate at a radiation wavelength of 800 nm within a 4-m long, strong focusing undulator. Large gain is achieved by driving the FEL with the 72 MeV, high brightness beam of BNL's Accelerator Test Facility (ATF). We present measurements that demonstrate saturation in addition to the frequency spectrum of the FEL radiation. Energy, gain length and spectral characteristics are compared and shown to agree with simulation and theoretical predictions.

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

Theoretical studies on the structural and spectra properties of two C74 fullerenes and the chlorinated species C74Cl10

NASA Astrophysics Data System (ADS)

Zheng, Mei; Song, Xitong; Li, Xiaoqi; Qi, Jiayuan

2018-07-01

The geometrical/electronic structures, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy of two especially C74 fullerenes (D3h-C74 and C1-C74) and the chlorinated species C1-C74Cl10, which are newly isolated in the experiment, have been calculated by means of the density functional theory (DFT) method. Effective changes in the electronic structure and simulated X-ray spectra have been observed after chlorination. Strong isomer dependence has been found in both spectra, thus the 'fingerprints' in the spectra can be employed as a tool to identify the isomers. The ultraviolet-visible (UV-vis) absorption spectrum of C1-C74Cl10 has been performed by using the time-dependent DFT method. The generated UV-vis spectrum coincides with the previous experimental counterpart. The results of this work can provide useful information especially for isomer identification and further study on fullerenes by means of the aforementioned spectroscopy techniques.

Scaling laws for positron production in laser-electron beam collisions

NASA Astrophysics Data System (ADS)

Blackburn, Tom; Ilderton, Anton; Murphy, Christopher; Marklund, Mattias

2017-10-01

Showers of gamma rays and positrons are produced when a multi-GeV electron beam collides with a super-intense laser pulse. All-optical realisation of this geometry, where the electron beam is generated by laser-wakefield acceleration, is currently attracting much experimental interest as a probe of radiation reaction and QED effects. These interactions may be modelled theoretically in the framework of strong-field QED or numerically by large-scale PIC simulation. To complement these, we present analytical scaling laws for the electron beam energy loss, gamma ray spectrum, and the positron yield and energy that are valid in the radiation-reaction-dominated regime. These indicate that by employing the collision of a 2 GeV electron beam with a laser pulse of intensity 5 ×1021Wcm-2 , it is possible to produce 10,000 positrons in a single shot at currently available laser facilities. The authors acknowledge support from the Knut and Alice Wallenberg Foundation.

Diffraction based method to reconstruct the spectrum of the Thomson scattering x-ray source

NASA Astrophysics Data System (ADS)

Chi, Zhijun; Yan, Lixin; Zhang, Zhen; Zhou, Zheng; Zheng, Lianmin; Wang, Dong; Tian, Qili; Wang, Wei; Nie, Zan; Zhang, Jie; Du, Yingchao; Hua, Jianfei; Shi, Jiaru; Pai, Chihao; Lu, Wei; Huang, Wenhui; Chen, Huaibi; Tang, Chuanxiang

2017-04-01

As Thomson scattering x-ray sources based on the collision of intense laser and relativistic electrons have drawn much attention in various scientific fields, there is an increasing demand for the effective methods to reconstruct the spectrum information of the ultra-short and high-intensity x-ray pulses. In this paper, a precise spectrum measurement method for the Thomson scattering x-ray sources was proposed with the diffraction of a Highly Oriented Pyrolytic Graphite (HOPG) crystal and was demonstrated at the Tsinghua Thomson scattering X-ray source. The x-ray pulse is diffracted by a 15 mm (L) ×15 mm (H)× 1 mm (D) HOPG crystal with 1° mosaic spread. By analyzing the diffraction pattern, both x-ray peak energies and energy spectral bandwidths at different polar angles can be reconstructed, which agree well with the theoretical value and simulation. The higher integral reflectivity of the HOPG crystal makes this method possible for single-shot measurement.

Diffraction based method to reconstruct the spectrum of the Thomson scattering x-ray source.

PubMed

Chi, Zhijun; Yan, Lixin; Zhang, Zhen; Zhou, Zheng; Zheng, Lianmin; Wang, Dong; Tian, Qili; Wang, Wei; Nie, Zan; Zhang, Jie; Du, Yingchao; Hua, Jianfei; Shi, Jiaru; Pai, Chihao; Lu, Wei; Huang, Wenhui; Chen, Huaibi; Tang, Chuanxiang

2017-04-01

As Thomson scattering x-ray sources based on the collision of intense laser and relativistic electrons have drawn much attention in various scientific fields, there is an increasing demand for the effective methods to reconstruct the spectrum information of the ultra-short and high-intensity x-ray pulses. In this paper, a precise spectrum measurement method for the Thomson scattering x-ray sources was proposed with the diffraction of a Highly Oriented Pyrolytic Graphite (HOPG) crystal and was demonstrated at the Tsinghua Thomson scattering X-ray source. The x-ray pulse is diffracted by a 15 mm (L) ×15 mm (H)× 1 mm (D) HOPG crystal with 1° mosaic spread. By analyzing the diffraction pattern, both x-ray peak energies and energy spectral bandwidths at different polar angles can be reconstructed, which agree well with the theoretical value and simulation. The higher integral reflectivity of the HOPG crystal makes this method possible for single-shot measurement.

A Numerical Model for Two-Plasmon-Decay Hot-Electron Production and Mitigation in Direct-Drive Implosions

NASA Astrophysics Data System (ADS)

Myatt, J. F.; Shaw, J. G.; Solodov, A. A.; Maximov, A. V.; Short, R. W.; Seka, W.; Follett, R. K.; Edgell, D. H.; Froula, D. H.; Goncharov, V. N.

2015-11-01

Hot-electron preheat, caused by laser-plasma instabilities, can impair the performance of inertial confinement fusion implosions. It is therefore imperative to understand processes that can generate hot electrons and to design mitigation strategies should preheat be found to be excessive at the ignition scale (laser-plasma interactions do not follow hydrodynamic scaling). For this purpose, a new 3-D model [laser-plasma simulation environment (LPSE)] has been constructed that computes hot-electron generation in direct-drive plasmas based on the assumption that two-plasmon decay is the dominant, hot-electron-producing instability. It uses an established model of TPD-driven turbulence together with a new GPU based hybrid particle method of hot-electron production. The time-dependent hot-electron power, total energy, and energy spectrum are computed and compared with data from recent OMEGA implosion experiments that have sought to mitigate TPD by the use of multilayered (mid- Z) ablators. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Developing the Primordial Inflation Polarization Explorer (PIPER) Microwave Polarimeter for Constraining Inflation

NASA Astrophysics Data System (ADS)

Lazear, Justin Scott

The Inflationary Big Bang model of cosmology generically predicts the existence of a background of gravitational waves due to Inflation, which coupled into the B-mode power spectrum during the epochs of Recombination and Reionization. A measurement of the primordial B-mode spectrum would verify the reality of the Inflationary model and constrain the allowed models of Inflation. In Chapter 1 we describe the background physics of cosmology and Inflation, and the challenges involved with measuring the primordial B-mode spectrum. In Chapter 2 we describe the Primordial Inflation Polarization Explorer (PIPER), a high-altitude balloon-borne microwave polarimeter optimized to measure the B-mode spectrum on large angular scales. We examine the high level design of PIPER and how it addresses the challenges presented in Chapter 1. Following the high level design, we examine in detail the electronics developed for PIPER, both for in-flight operations and for laboratory development. In Chapter 3 we describe the Transition Edge Sensor (TES) bolometers that serve as PIPER's detectors, analyze the Superconducting Quantum Interference Device (SQUID) amplifiers and Mutli-channel Electronics (MCE) detector readout chain, and finally present the characterization of both detector parameters and noise of a single pixel device with a PIPER-like (Backshort Under Grid, BUG) architecture to validate the detector design. In Chapter 4 we present a description of the HKE electronics, used to measure all non-detector science timestreams in PIPER, as well as flight housekeeping and laboratory development. In addition to the operation of the HKE electronics, we develop a model to quantify the performance of the HKE thermometry reader (TRead). A simple simulation pipeline is developed and used to explore the consequences of imperfect foreground removal in Chapter 5. The details of estimating the instrument noise as projected onto a sky map is developed also developed. In particular, we address whether PIPER may be able to get significant science return with only a fraction of its planned flights by optimizing the order that the frequency bands are flown. Additionally, we look at how a spatially varying calibration gain error would affect measurements of the B-mode spectrum. Finally, a series of appendices presents the physics of SQUIDs, develops techniques for estimating noise of circuits and amplifiers, and introduces techniques from control systems. In addition, a few miscellaneous results used throughout the work are derived.

A reinterpretation of the electronic spectrum of pyrrole: A quantum dynamics study

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

Neville, S. P.; Worth, G. A., E-mail: g.a.worth@bham.ac.uk

The first band in the electronic spectrum of pyrrole is calculated from wavepacket propagations performed using the MCTDH method. To do so, two model Hamiltonians are constructed to describe seven low-lying excited electronic states of pyrrole. These Hamiltonians are based on the vibronic coupling model, and are parameterised via fitting to extensive CASPT2 and EOM-CCSD calculations. A detailed analysis of the structure of pyrrole's electronic spectrum in the range 5.5 to 6.5 eV is made. The role of intensity borrowing from transitions to ππ{sup *} states by lower-lying 3s and 3p Rydberg states is assessed, and reassignments of much ofmore » the spectrum are subsequently made which indicate that most of the states in the spectrum are predominantly Rydberg in character. The resulting conclusions drawn serve to highlight the limitations of assignments based on the matching of calculated vertical excitation energies and the positions of peak maxima observed in electronic spectra.« less

Coupling hydrodynamics and radiation calculations for star-jet interactions in active galactic nuclei

NASA Astrophysics Data System (ADS)

de la Cita, V. M.; Bosch-Ramon, V.; Paredes-Fortuny, X.; Khangulyan, D.; Perucho, M.

2016-06-01

Context. Stars and their winds can contribute to the non-thermal emission in extragalactic jets. Because of the complexity of jet-star interactions, the properties of the resulting emission are closely linked to those of the emitting flows. Aims: We simulate the interaction between a stellar wind and a relativistic extragalactic jet and use the hydrodynamic results to compute the non-thermal emission under different conditions. Methods: We performed relativistic axisymmetric hydrodynamical simulations of a relativistic jet interacting with a supersonic, non-relativistic stellar wind. We computed the corresponding streamlines out of the simulation results and calculated the injection, evolution, and emission of non-thermal particles accelerated in the jet shock, focusing on electrons or e±-pairs. Several cases were explored, considering different jet-star interaction locations, magnetic fields, and observer lines of sight. The jet luminosity and star properties were fixed, but the results are easily scalable when these parameters are changed. Results: Individual jet-star interactions produce synchrotron and inverse Compton emission that peaks from X-rays to MeV energies (depending on the magnetic field), and at ~100-1000 GeV (depending on the stellar type), respectively. The radiation spectrum is hard in the scenarios explored here as a result of non-radiative cooling dominance, as low-energy electrons are efficiently advected even under relatively high magnetic fields. Interactions of jets with cold stars lead to an even harder inverse Compton spectrum because of the Klein-Nishina effect in the cross section. Doppler boosting has a strong effect on the observer luminosity. Conclusions: The emission levels for individual interactions found here are in the line of previous, more approximate, estimates, strengthening the hypothesis that collective jet-star interactions could significantly contribute at high energies under efficient particle acceleration.

Ab initio calculations of supramolecular complexes of fullerene C60 with CdTe and CdS

NASA Astrophysics Data System (ADS)

Kvyatkovskii, O. E.; Zakharova, I. B.; Ziminov, V. M.

2014-06-01

This paper presents the results of ab initio quantum-chemical calculations of supramolecular complexes C60CdHal, [C60]4CdHal, and [C60]6CdHal (Hal = S, Te), which simulate the defects forming in fullerite during the absorption or adsorption of cadmium telluride (sulfide). Calculations of the electronic structure of complexes with inclusion of their relaxation to the equilibrium state have been performed in terms of the density functional theory with the B3LYP hybrid functional. The obtained enthalpies of formation of complexes show that their formation leads to the energy gain of the order of 0.5-1.5 eV depending on the complex type. It has been shown that the formation of tetrahedral complexes [C60]4CdTe with the intercalated CdTe molecule is possible only with a considerable distortion of the tetrahedral void. The energy spectrum of low-lying excited electron states for the linear and octahedral complexes has been calculated. It has been found that a decrease in symmetry with the formation of complexes leads to the appearance of excited states of allowed singlet transitions in the electron spectrum, which are forbidden in optical spectra of initial components.

Identification of pristine and defective graphene nanoribbons by phonon signatures in the electron transport characteristics

NASA Astrophysics Data System (ADS)

Christensen, Rasmus B.; Frederiksen, Thomas; Brandbyge, Mads

2015-02-01

Inspired by recent experiments where electron transport was measured across graphene nanoribbons (GNRs) suspended between a metal surface and the tip of a scanning tunneling microscope [Koch et al., Nat. Nanotechnol. 7, 713 (2012), 10.1038/nnano.2012.169], we present detailed first-principles simulations of inelastic electron tunneling spectroscopy (IETS) of long pristine and defective armchair and zigzag nanoribbons under a range of charge carrier conditions. For the armchair ribbons we find two robust IETS signals around 169 and 196 mV corresponding to the D and G modes of Raman spectroscopy as well as additional fingerprints due to various types of defects in the edge passivation. For the zigzag ribbons we show that the spin state strongly influences the spectrum and thus propose IETS as an indirect proof of spin polarization.

Electron path control of high-order harmonic generation by a spatially inhomogeneous field

NASA Astrophysics Data System (ADS)

Mohebbi, Masoud; Nazarpoor Malaei, Sakineh

2016-04-01

We theoretically investigate the control of high-order harmonics cut-off and as-pulse generation by a chirped laser field using a metallic bow tie-shaped nanostructure. The numerical results show that the trajectories of the electron wave packet are strongly modified, the short quantum path is enhanced, the long quantum path is suppressed and the low modulated spectrum of the harmonics can be remarkably extended. Our calculated results also show that, by confining electron motion, a broadband supercontinuum with the width of 1670 eV can be produced which directly generates an isolated 34 as-pulse without phase compensation. To explore the underlying mechanism responsible for the cut-off extension and the quantum path selection, we perform time-frequency analysis and a classical simulation based on the three-step model.

Communication: Microsecond dynamics of the protein and water affect electron transfer in a bacterial bc1 complex

NASA Astrophysics Data System (ADS)

Martin, Daniel R.; Matyushov, Dmitry V.

2015-04-01

Cross-membrane electron transport between cofactors localized in proteins of mitochondrial respiration and bacterial photosynthesis is the source of all biological energy. The statistics and dynamics of nuclear fluctuations in these protein/membrane/water heterogeneous systems are critical for their energetic efficiency. The results of 13 μs of atomistic molecular dynamics simulations of the membrane-bound bc1 bacterial complex are analyzed here. The reaction is affected by a broad spectrum of nuclear modes, with the slowest dynamics in the range of time-scales ˜0.1-1.6 μs contributing half of the reaction reorganization energy. Two reorganization energies are required to describe protein electron transfer due to dynamical arrest of protein conformations on the observation window. This mechanistic distinction allows significant lowering of activation barriers for reactions in proteins.

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

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

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

2015-09-28

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

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

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

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

2015-09-28

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

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

PubMed

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

2015-09-28

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

Comparing simulation of plasma turbulence with experiment

NASA Astrophysics Data System (ADS)

Ross, David W.; Bravenec, Ronald V.; Dorland, William; Beer, Michael A.; Hammett, G. W.; McKee, George R.; Fonck, Raymond J.; Murakami, Masanori; Burrell, Keith H.; Jackson, Gary L.; Staebler, Gary M.

2002-01-01

The direct quantitative correspondence between theoretical predictions and the measured plasma fluctuations and transport is tested by performing nonlinear gyro-Landau-fluid simulations with the GRYFFIN (or ITG) code [W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993); M. A. Beer and G. W. Hammett, Phys. Plasmas 3, 4046 (1996)]. In an L-mode reference discharge in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], which has relatively large fluctuations and transport, the turbulence is dominated by ion temperature gradient (ITG) modes. Trapped electron modes and impurity drift waves also play a role. Density fluctuations are measured by beam emission spectroscopy [R. J. Fonck, P. A. Duperrex, and S. F. Paul, Rev. Sci. Instrum. 61, 3487 (1990)]. Experimental fluxes and corresponding diffusivities are analyzed by the TRANSP code [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, edited by B. Coppi, G. G. Leotta, D. Pfirsch, R. Pozzoli, and E. Sindoni (Pergamon, Oxford, 1980), Vol. 1, p. 19]. The shape of the simulated wave number spectrum is close to the measured one. The simulated ion thermal transport, corrected for E×B low shear, exceeds the experimental value by a factor of 1.5 to 2.0. The simulation overestimates the density fluctuation level by an even larger factor. On the other hand, the simulation underestimates the electron thermal transport, which may be accounted for by modes that are not accessible to the simulation or to the BES measurement.

SU-E-T-782: Using Light Output From Doped Plastic Scintillators to Resolve the Linear Energy Transfer Spectrum of Clinical Electron Beams

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

Nusrat, H; Pang, G; Ahmad, S

2015-06-15

Purpose: This research seeks to develop a portable, clinically-suitable linear energy transfer (LET) detector. In radiotherapy, absorbed dose is commonly used to measure the amount of delivered radiation, though, it is not a good indicator of actual biological damage. LET is the energy absorbed per unit length by a medium along charged particle’s pathway; studies have shown that LET correlates well with relative biological effectiveness (RBE). Methods: According to Birks’ law, light output of plastic scintillators is stopping-power dependent. This dependency can be varied through doping by various high-Z elements. By measuring light output signals of differently doped plastic scintillatorsmore » (represented by column vector S, where each row corresponds to different scintillator material), the fluence of charged particles of a given LET (represented by column vector Φ, where each row corresponds to different LET bins) can be unfolded by S=R*Φ where R is system response matrix (each row represents a different scintillator, each column corresponds to different electron LET). Monte Carlo (MC) GEANT4.10.1 was used to evaluate ideal detector response of BC408 scintillating material doped with various concentrations of several high Z dopants. Measurements were performed to validate MC. Results: Signal for 1%-lead doped BC408 and the non-doped scintillator was measured experimentally by guiding light emitted by the scintillator (via in-house made taper, fiber system) to a PMT and then an electrometer. Simulations of 1%Pb-doped scintillator to non-doped scintillator revealed 9.3% reduction in light output for 6 MeV electrons which compared well (within uncertainty) with measurements showing 10% reduction (6MeV electrons). Conclusion: Measurements were used to validate MC simulation of light output from doped scintillators. The doping of scintillators is a viable technique to induce LET dependence. Our goal is to use this effect to resolve the LET spectrum of an incident beam.« less

Phonon anharmonicity and negative thermal expansion in SnSe

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

Bansal, Dipanshu; Hong, Jiawang; Li, Chen W.

In this paper, the anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy,more » in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. Finally, the origin of the anharmonic phonon thermodynamics is linked to the electronic structure.« less

MCNP modelling of the wall effects observed in tissue-equivalent proportional counters.

PubMed

Hoff, J L; Townsend, L W

2002-01-01

Tissue-equivalent proportional counters (TEPCs) utilise tissue-equivalent materials to depict homogeneous microscopic volumes of human tissue. Although both the walls and gas simulate the same medium, they respond to radiation differently. Density differences between the two materials cause distortions, or wall effects, in measurements, with the most dominant effect caused by delta rays. This study uses a Monte Carlo transport code, MCNP, to simulate the transport of secondary electrons within a TEPC. The Rudd model, a singly differential cross section with no dependence on electron direction, is used to describe the energy spectrum obtained by the impact of two iron beams on water. Based on the models used in this study, a wall-less TEPC had a higher lineal energy (keV.micron-1) as a function of impact parameter than a solid-wall TEPC for the iron beams under consideration. An important conclusion of this study is that MCNP has the ability to model the wall effects observed in TEPCs.

Phonon anharmonicity and negative thermal expansion in SnSe

DOE PAGES

Bansal, Dipanshu; Hong, Jiawang; Li, Chen W.; ...

2016-08-09

In this paper, the anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy,more » in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. Finally, the origin of the anharmonic phonon thermodynamics is linked to the electronic structure.« less

Photodissociation of HCN and HNC isomers in the 7-10 eV energy range

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

Chenel, Aurelie; Roncero, Octavio, E-mail: octavio.roncero@csic.es; Aguado, Alfredo

2016-04-14

The ultraviolet photoabsorption spectra of the HCN and HNC isomers have been simulated in the 7-10 eV photon energy range. For this purpose, the three-dimensional adiabatic potential energy surfaces of the 7 lowest electronic states, and the corresponding transition dipole moments, have been calculated, at multireference configuration interaction level. The spectra are calculated with a quantum wave packet method on these adiabatic potential energy surfaces. The spectra for the 3 lower excited states, the dissociative electronic states, correspond essentially to predissociation peaks, most of them through tunneling on the same adiabatic state. The 3 higher electronic states are bound, hereaftermore » electronic bound states, and their spectra consist of delta lines, in the adiabatic approximation. The radiative lifetime towards the ground electronic states of these bound states has been calculated, being longer than 10 ns in all cases, much longer that the characteristic predissociation lifetimes. The spectra of HCN is compared with the available experimental and previous theoretical simulations, while in the case of HNC there are no previous studies to our knowledge. The spectrum for HNC is considerably more intense than that of HCN in the 7-10 eV photon energy range, which points to a higher photodissociation rate for HNC, compared to HCN, in astrophysical environments illuminated by ultraviolet radiation.« less

Experimental studies of fundamental aspects of Auger emission process in Cu(100) and Ag(100)

NASA Astrophysics Data System (ADS)

Joglekar, Prasad Vivek

Auger spectra at the low energies are accompanied by large contributions unrelated to the Auger transition. The Auger unrelated contributions can obscure the Auger peak and affect the quantitative analysis of the materials under investigation. In this dissertation we present a methodology to measure experimentally the Auger unrelated contributions and eliminate it from the Auger spectrum for obtaining an Auger spectrum inherent to the Auger transition. We used Auger Photoelectron Coincidence Spectroscopy (APECS) to obtain the Auger spectrum. APECS measures the Auger spectrum in coincidence with the core energy level and thus discriminating the contributions arising from secondary electrons and electrons arising from the non-Auger transition. Although APECS removes most of the Auger unrelated contributions, it cannot distinguish the contribution which is measured in coincidence with the inelastically scattered valence band electrons emitted at the core energy. To measure this inelastically scattered valence band contribution we did a series of measurements on Ag(100) to study NVV Auger spectrum in coincidence with 4p energy level and Cu(100) to study MVV Auger spectrum in coincidence with 3p energy level. The coincidence detection of the core and Auger-valence electrons was achieved by the two cylindrical mirror analyzers (CMAs). One CMA was fixed over a range of energies in between VB and core energy level while other CMA scanned corresponding low energy electrons from 0 to70eV. The spectrums measured were fit to a parameterized function which was extrapolated to get an estimate of inelastically scattered valence band electrons. The estimated contribution was subtracted for the Ag and Cu APECS spectrum to obtain a spectrum solely due to Auger transition with inelastically scattered Auger electron and multi Auger decay contributions associated with the transition. In the latter part of this dissertation, we propose a theoretical model based on the spectral intensity contributions arising from elastically scattered electrons from the atomic layers and relate it with the data obtained from our experiments to estimate the Auger related contribution.

Spectrum of coherent transition radiation generated by a modulated electron beam

NASA Astrophysics Data System (ADS)

Naumenko, G. A.; Potylitsyn, A. P.; Karataev, P. V.; Shipulya, M. A.; Bleko, V. V.

2017-07-01

The spectrum of coherent transition radiation has been recorded with the use of a Martin-Puplett interferometer. It has been shown that the spectrum includes monochromatic lines that are caused by the modulation of an electron beam with the frequency of an accelerating radio-frequency field νRF and correspond to resonances at ν k = kνRF k ≤ 10. To determine the length of an electron bunch from the measurement of the spectrum from a single bunch, it is necessary to use a spectrometer with the resolution Δνsp > νRF.

Electromagnetic ion/ion cyclotron instability - Theory and simulations

NASA Technical Reports Server (NTRS)

Winske, D.; Omidi, N.

1992-01-01

Linear theory and 1D and 2D hybrid simulations are employed to study electromagnetic ion/ion cyclotron (EMIIC) instability driven by the relative streaming of two field-aligned ion beams. The characteristics of the instability are studied as a function of beam density, propagation angle, electron-ion temperature ratios, and ion beta. When the propagation angle is near 90 deg the EMIIC instability has the characteristics of an electrostatic instability, while at smaller angles electromagnetic effects play a significant role as does strong beam coupling. The 2D simulations point to a narrowing of the wave spectrum and accompanying coherent effects during the linear growth stage of development. The EMIIC instability is an important effect where ion beta is low such as in the plasma-sheet boundary layer and upstream of slow shocks in the magnetotail.

Non-inductive current generation in fusion plasmas with turbulence

NASA Astrophysics Data System (ADS)

Wang, Weixing; Ethier, S.; Startsev, E.; Chen, J.; Hahm, T. S.; Yoo, M. G.

2017-10-01

It is found that plasma turbulence may strongly influence non-inductive current generation. This may have radical impact on various aspects of tokamak physics. Our simulation study employs a global gyrokinetic model coupling self-consistent neoclassical and turbulent dynamics with focus on electron current. Distinct phases in electron current generation are illustrated in the initial value simulation. In the early phase before turbulence develops, the electron bootstrap current is established in a time scale of a few electron collision times, which closely agrees with the neoclassical prediction. The second phase follows when turbulence begins to saturate, during which turbulent fluctuations are found to strongly affect electron current. The profile structure, amplitude and phase space structure of electron current density are all significantly modified relative to the neoclassical bootstrap current by the presence of turbulence. Both electron parallel acceleration and parallel residual stress drive are shown to play important roles in turbulence-induced current generation. The current density profile is modified in a way that correlates with the fluctuation intensity gradient through its effect on k//-symmetry breaking in fluctuation spectrum. Turbulence is shown to deduct (enhance) plasma self-generated current in low (high) collisionality regime, and the reduction of total electron current relative to the neoclassical bootstrap current increases as collisionality decreases. The implication of this result to the fully non-inductive current operation in steady state burning plasma regime should be investigated. Finally, significant non-inductive current is observed in flat pressure region, which is a nonlocal effect and results from turbulence spreading induced current diffusion. Work supported by U.S. DOE Contract DE-AC02-09-CH11466.

The effect of plasma inhomogeneities on (i) radio emission generation by non-gyrotropic electron beams and (ii) particle acceleration by Langmuir waves

NASA Astrophysics Data System (ADS)

Tsiklauri, D.

2014-12-01

Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [1]. Here recent progress in an alternative to the plasma emission model using Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts will be presented. In particular, (i) Fourier space drift (refraction) of non-gyrotropic electron beam-generated wave packets, caused by the density gradient [1,2], (ii) parameter space investigation of numerical runs [3], (iii) concurrent generation of whistler waves [4] and a separate problem of (iv) electron acceleration by Langmuir waves in a background magnetised plasma with an increasing density profile [5] will be discussed. In all considered cases the density inhomogeneity-induced wave refraction plays a crucial role. In the case of non-gyrotropic electron beam, the wave refaction transforms the generated wave packets from standing into freely escaping EM radiation. In the case of electron acceleration by Langmuir waves, a positive density gradient in the direction of wave propagation causes a decrease in the wavenumber, and hence a higher phase velocity vph=ω/k. The k-shifted wave is then subject to absorption by a faster electron by wave-particle interaction. The overall effect is an increased number of high energy electrons in the energy spectrum. [1] D. Tsiklauri, Phys. Plasmas 18, 052903 (2011) [2] H. Schmitz, D. Tsiklauri, Phys. Plasmas 20, 062903 (2013) [3] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 19, 112903 (2012) [4] M. Skender, D. Tsiklauri, Phys. Plasmas 21, 042904 (2014) [5] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 21, 012903 (2014)

Modeling the effect of 1 MeV electron irradiation on the performance of n+-p-p+ silicon space solar cells

NASA Astrophysics Data System (ADS)

Hamache, Abdelghani; Sengouga, Nouredine; Meftah, Afak; Henini, Mohamed

2016-06-01

Energetic particles such as electrons and protons induce severe degradation on the performance of solar cells used to power satellites and space vehicles. This degradation is usually attributed to lattice damage in the active region of the solar cell. One of the phenomena observed in silicon solar cells exposed to 1 MeV electron irradiation is the anomalous degradation of the short circuit current. It initially decreases followed by a recovery before falling again with increasing electron fluence. This behavior is usually attributed to type conversion of the solar cell active region. The other figures of merit, on the other hand, decrease monotonically. In this work numerical simulator SCAPS (Solar Cell Capacitance Simulator) is used to elucidate this phenomenon. The current-voltage characteristics of a Si n+-p-p+ structure are calculated under air mass zero spectrum with the fluence of 1 MeV electrons as a variable parameter. The effect of irradiation on the solar cell is simulated by a set of defects of which the energy levels lie deep in energy gap of silicon (much larger than the characteristic thermal energy kT far from either the conduction or valence band). Although several types of deep levels are induced by irradiation including deep donors (exchange electrons mainly with the conduction band), deep acceptors (exchange electrons mainly with the valence band) and/or generation-recombination centers (exchange electrons with both the conduction and valence bands), it was found that, only one of them (the shallowest donor) is responsible for the anomalous degradation of the short circuit current. It will be also shown, by calculating the free charge carrier profile in the active region, that this behavior is not related to type conversion but to a lateral widening of the space charge region.

First-principles calculation of the optical properties of an amphiphilic cyanine dye aggregate.

PubMed

Haverkort, Frank; Stradomska, Anna; de Vries, Alex H; Knoester, Jasper

2014-02-13

Using a first-principles approach, we calculate electronic and optical properties of molecular aggregates of the dye amphi-pseudoisocyanine, whose structures we obtained from molecular dynamics (MD) simulations of the self-aggregation process. Using quantum chemistry methods, we translate the structural information into an effective time-dependent Frenkel exciton Hamiltonian for the dominant optical transitions in the aggregate. This Hamiltonian is used to calculate the absorption spectrum. Detailed analysis of the dynamic fluctuations in the molecular transition energies and intermolecular excitation transfer interactions in this Hamiltonian allows us to elucidate the origin of the relevant time scales; short time scales, on the order of up to a few hundreds of femtoseconds, result from internal motions of the dye molecules, while the longer (a few picosecond) time scales we ascribe to environmental motions. The absorption spectra of the aggregate structures obtained from MD feature a blue-shifted peak compared to that of the monomer; thus, our aggregates can be classified as H-aggregates, although considerable oscillator strength is carried by states along the entire exciton band. Comparison to the experimental absorption spectrum of amphi-PIC aggregates shows that the simulated line shape is too wide, pointing to too much disorder in the internal structure of the simulated aggregates.

Evidence of conformational exchange averaging in the thermal rotational spectrum of ethyl cyanoformate.

PubMed

True, Nancy S

2006-06-15

The Stark modulated low resolution microwave spectrum of ethyl cyanoformate between 21.5 and 24.0 GHz at 210, 300, and 358 K, which shows the J + 1 <-- J = 8 <-- 7 bands of three species, is compared to simulations based on electronic structure calculations at the MP2/6-311++G theory level. Calculations at this theory level reproduce the relative energies of the syn-anti and syn-gauche conformers, obtained in a previous study, and indicate that the barrier to conformer exchange is approximately 360 cm(-1) higher in energy than the syn-anti minimum. Simulated spectra of the eigenstates of the calculated O-ethyl torsional potential function reproduce the relative intensities and shapes of the lower and higher frequency bands which correspond to transitions of the syn-anti and syn-gauche conformers, respectively, but fail to reproduce the intense center band in the experimental spectra. A model incorporating exchange averaging reproduces the intensity of the center band and its temperature dependence. These simulations indicate that a large fraction of the thermal population at all three temperatures undergoes conformational exchange with an average energy specific rate constant, , of approximately 25 GHz. This model can explain anomalies present in rotational spectra of many other compounds composed of mixtures of conformers.

An analytic formula for the relativistic incoherent Thomson backscattering spectrum for a drifting bi-Maxwellian plasma

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

Naito, O.

2015-08-15

An analytic formula has been derived for the relativistic incoherent Thomson backscattering spectrum for a drifting anisotropic plasma when the scattering vector is parallel to the drifting direction. The shape of the scattering spectrum is insensitive to the electron temperature perpendicular to the scattering vector, but its amplitude may be modulated. As a result, while the measured temperature correctly represents the electron distribution parallel to the scattering vector, the electron density may be underestimated when the perpendicular temperature is higher than the parallel temperature. Since the scattering spectrum in shorter wavelengths is greatly enhanced by the existence of drift, themore » diagnostics might be used to measure local electron current density in fusion plasmas.« less

Black Box Real-Time Transient Absorption Spectroscopy and Electron Correlation

NASA Astrophysics Data System (ADS)

Parkhill, John

2017-06-01

We introduce an atomistic, all-electron, black-box electronic structure code to simulate transient absorption (TA) spectra and apply it to simulate pyrazole and a GFP- chromophore derivative1. The method is an application of OSCF2, our dissipative exten- sion of time-dependent density-functional theory. We compare our simulated spectra directly with recent ultra-fast spectroscopic experiments. We identify features in the TA spectra to Pauli-blocking which may be missed without a first-principles model. An important ingredient in this method is the stationary-TDDFT correction scheme recently put forwards by Fischer, Govind, and Cramer which allows us to overcome a limitation of adiabatic TDDFT. We demonstrate that OSCF2 is able to reproduce the energies of bleaches and induced absorptions, as well as the decay of the transient spectrum, with only the molecular structure as input. We show that the treatment of electron correlation is the biggest hurdle for TA simulations, which motivates the second half of the talk a new method for realtime electron correlation. We continue to derive and propagate self-consistent electronic dynamics. Extending our derivation of OSCF2 to include electron correlation we obtain a non-linear correlated one-body equation of motion which corrects TDHF. Similar equations are known in quantum kinetic theory, but rare in electronic structure. We introduce approximations that stabilize the theory and reduce its computational cost. We compare the resulting dynamics with well-known exact and approximate theories showing improvements over TDHF. When propagated EE2 changes occupation numbers like exact theory, an important feature missing from TDHF or TDDFT. We introduce a rotating wave approximation to reduce the scaling of the model to O(N^4), and enable propagation on realistically large systems. The equation-of-motion does not rely on a pure-state model for the electronic state, and could be used to study the relationship between electron correlation and relaxation/dephasing or as a non-adiabatic kernel for TDDFT. We show that a quasi-thermal Fermi-Dirac population of one-particle states is a stationary state of the method reached as the endpoint of propagation in some limits. We discuss this 'thermalization' of an isolated quantum many-body system in the context of the eigenstate thermalization hypothesis.

Optical diagnosis and theoretical simulation of laser induced lead plasma spectrum

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

Hong Bofu; Chuan Songchen; Bao Yuanman

2012-01-15

Plasmas generated during incipient laser ablation of lead in air were studied using emission spectroscopy and fast photography by an intensified charge coupled device (ICCD) camera. An improved plasma emission model was introduced, invoking one-dimensional radiative transfer, to describe the observed emission spectra, while taking into account Gaussian intensity distribution of the laser used to form plasma. The effects of different parameters to the fitting results are discussed. The plasma temperature got by Saha-Boltzmann plot method and the electron number density got by line broadening method were compared with the fitting results. We also found that the distribution of plasmamore » temperature is more uniform than that of the electron number density in the radial direction.« less

Sensitivity of echo enabled harmonic generation to sinusoidal electron beam energy structure

DOE PAGES

Hemsing, E.; Garcia, B.; Huang, Z.; ...

2017-06-19

Here, we analytically examine the bunching factor spectrum of a relativistic electron beam with sinusoidal energy structure that then undergoes an echo-enabled harmonic generation (EEHG) transformation to produce high harmonics. The performance is found to be described primarily by a simple scaling parameter. The dependence of the bunching amplitude on fluctuations of critical parameters is derived analytically, and compared with simulations. Where applicable, EEHG is also compared with high gain harmonic generation (HGHG) and we find that EEHG is generally less sensitive to several types of energy structure. In the presence of intermediate frequency modulations like those produced by themore » microbunching instability, EEHG has a substantially narrower intrinsic bunching pedestal.« less

Effect of the diffusion parameters on the observed γ-ray spectrum of sources and their contribution to the local all-electron spectrum: The EDGE code

NASA Astrophysics Data System (ADS)

López-Coto, R.; Hahn, J.; BenZvi, S.; Dingus, B.; Hinton, J.; Nisa, M. U.; Parsons, R. D.; Greus, F. Salesa; Zhang, H.; Zhou, H.

2018-11-01

The positron excess measured by PAMELA and AMS can only be explained if there is one or several sources injecting them. Moreover, at the highest energies, it requires the presence of nearby ( ∼ hundreds of parsecs) and middle age (maximum of ∼ hundreds of kyr) sources. Pulsars, as factories of electrons and positrons, are one of the proposed candidates to explain the origin of this excess. To calculate the contribution of these sources to the electron and positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma rays to the Earth), a code to treat the propagation of electrons and compute their diffusion from a central source with a flexible injection spectrum. Using this code, we can derive the source's gamma-ray spectrum, spatial extension, the all-electron density in space, the electron and positron flux reaching the Earth and the positron fraction measured at the Earth. We present in this paper the foundations of the code and study how different parameters affect the gamma-ray spectrum of a source and the electron flux measured at the Earth. We also studied the effect of several approximations usually performed in these studies. This code has been used to derive the results of the positron flux measured at the Earth in [1].

Fermi LAT Results and Perspectives in Measurements of High Energy Galactic Cosmic Rays

NASA Technical Reports Server (NTRS)

Moiseev, Alexander

2010-01-01

Real breakthrough during last 1-1.5 years in cosmic ray electrons: ATIC, HESS, Pamela, and finally Fermi-LAT. New quality data have made it possible to start quantitative modeling. With the new data more puzzles than before on CR electrons origin. Need "multi-messenger" campaign: electrons, positrons, gammas, X-ray, radio, neutrino... It is viable that we are dealing with at least two distinct mechanisms of "primary" electron (both signs) production: a softer spectrum of negative electrons, and a harder spectrum of both e(+)+e(-). Exotic (e.g. DM) origin is not ruled out. Upper limits on CR electrons anisotropy are set. Good perspectives to have the Fermi LAT results on proton spectrum and positron fraction.

Track Structure Model for Radial Distributions of Electron Spectra and Event Spectra from High-Energy Ions

NASA Technical Reports Server (NTRS)

Cucinotta, F. A.; Katz, R.; Wilson, J. W.

1998-01-01

An analytic method is described for evaluating the average radial electron spectrum and the radial and total frequency-event spectrum for high-energy ions. For high-energy ions, indirect events make important contributions to frequency-event spectra. The method used for evaluating indirect events is to fold the radial electron spectrum with measured frequency-event spectrum for photons or electrons. The contribution from direct events is treated using a spatially restricted linear energy transfer (LET). We find that high-energy heavy ions have a significantly reduced frequency-averaged final energy (yF) compared to LET, while relativistic protons have a significantly increased yF and dose-averaged lineal energy (yD) for typical site sizes used in tissue equivalent proportional counters. Such differences represent important factors in evaluating event spectra with laboratory beams, in space- flight, or in atmospheric radiation studies and in validation of radiation transport codes. The inadequacy of LET as descriptor because of deviations in values of physical quantities, such as track width, secondary electron spectrum, and yD for ions of identical LET is also discussed.

Methodology and application of high performance electrostatic field simulation in the KATRIN experiment

NASA Astrophysics Data System (ADS)

Corona, Thomas

The Karlsruhe Tritium Neutrino (KATRIN) experiment is a tritium beta decay experiment designed to make a direct, model independent measurement of the electron neutrino mass. The experimental apparatus employs strong ( O[T]) magnetostatic and (O[10 5 V/m]) electrostatic fields in regions of ultra high (O[10-11 mbar]) vacuum in order to obtain precise measurements of the electron energy spectrum near the endpoint of tritium beta-decay. The electrostatic fields in KATRIN are formed by multiscale electrode geometries, necessitating the development of high performance field simulation software. To this end, we present a Boundary Element Method (BEM) with analytic boundary integral terms in conjunction with the Robin Hood linear algebraic solver, a nonstationary successive subspace correction (SSC) method. We describe an implementation of these techniques for high performance computing environments in the software KEMField, along with the geometry modeling and discretization software KGeoBag. We detail the application of KEMField and KGeoBag to KATRIN's spectrometer and detector sections, and demonstrate its use in furthering several of KATRIN's scientific goals. Finally, we present the results of a measurement designed to probe the electrostatic profile of KATRIN's main spectrometer in comparison to simulated results.

Spec2Harv: Converting Spectrum output to HARVEST input

Treesearch

Eric J. Gustafson; Luke V. Rasmussen; Larry A. Leefers

2003-01-01

Spec2Harv was developed to automate the conversion of harvest schedules generated by the Spectrum model into script files that can be used by the HARVEST simulation model to simulate the implementation of the Spectrum schedules in a spatially explicit way.

Beam energy considerations for gold nano-particle enhanced radiation treatment.

PubMed

Van den Heuvel, F; Locquet, Jean-Pierre; Nuyts, S

2010-08-21

A novel approach using nano-technology enhanced radiation modalities is investigated. The proposed methodology uses antibodies labeled with organically inert metals with a high atomic number. Irradiation using photons with energies in the kilo-electron volt (keV) range shows an increase in dose due to a combination of an increase in photo-electric interactions and a pronounced generation of Auger and/or Coster-Krönig (A-CK) electrons. The dependence of the dose deposition on various factors is investigated using Monte Carlo simulation models. The factors investigated include agent concentration, spectral dependence looking at mono-energetic sources as well as classical bremsstrahlung sources. The optimization of the energy spectrum is performed in terms of physical dose enhancement as well as the dose deposited by Auger and/or Coster-Krönig electrons and their biological effectiveness. A quasi-linear dependence on concentration and an exponential decrease within the target medium is observed. The maximal dose enhancement is dependent on the position of the target in the beam. Apart from irradiation with low-photon energies (10-20 keV) there is no added benefit from the increase in generation of Auger electrons. Interestingly, a regular 110 kVp bremsstrahlung spectrum shows a comparable enhancement in comparison with the optimized mono-energetic sources. In conclusion we find that the use of enhanced nano-particles shows promise to be implemented quite easily in regular clinics on a physical level due to the advantageous properties in classical beams.

Beam energy considerations for gold nano-particle enhanced radiation treatment

NASA Astrophysics Data System (ADS)

Van den Heuvel, F.; Locquet, Jean-Pierre; Nuyts, S.

2010-08-01

A novel approach using nano-technology enhanced radiation modalities is investigated. The proposed methodology uses antibodies labeled with organically inert metals with a high atomic number. Irradiation using photons with energies in the kilo-electron volt (keV) range shows an increase in dose due to a combination of an increase in photo-electric interactions and a pronounced generation of Auger and/or Coster-Krönig (A-CK) electrons. The dependence of the dose deposition on various factors is investigated using Monte Carlo simulation models. The factors investigated include agent concentration, spectral dependence looking at mono-energetic sources as well as classical bremsstrahlung sources. The optimization of the energy spectrum is performed in terms of physical dose enhancement as well as the dose deposited by Auger and/or Coster-Krönig electrons and their biological effectiveness. A quasi-linear dependence on concentration and an exponential decrease within the target medium is observed. The maximal dose enhancement is dependent on the position of the target in the beam. Apart from irradiation with low-photon energies (10-20 keV) there is no added benefit from the increase in generation of Auger electrons. Interestingly, a regular 110 kVp bremsstrahlung spectrum shows a comparable enhancement in comparison with the optimized mono-energetic sources. In conclusion we find that the use of enhanced nano-particles shows promise to be implemented quite easily in regular clinics on a physical level due to the advantageous properties in classical beams.

Nonadiabatic Dynamics May Be Probed through Electronic Coherence in Time-Resolved Photoelectron Spectroscopy.

PubMed

Bennett, Kochise; Kowalewski, Markus; Mukamel, Shaul

2016-02-09

We present a hierarchy of Fermi golden rules (FGRs) that incorporate strongly coupled electronic/nuclear dynamics in time-resolved photoelectron spectroscopy (TRPES) signals at different levels of theory. Expansion in the joint electronic and nuclear eigenbasis yields the numerically most challenging exact FGR (eFGR). The quasistatic Fermi Golden Rule (qsFGR) neglects nuclear motion during the photoionization process but takes into account electronic coherences as well as populations initially present in the pumped matter as well as those generated internally by coupling between electronic surfaces. The standard semiclassical Fermi Golden Rule (scFGR) neglects the electronic coherences and the nuclear kinetic energy during the ionizing pulse altogether, yielding the classical Condon approximation. The coherence contributions depend on the phase-profile of the ionizing field, allowing coherent control of TRPES signals. The photoelectron spectrum from model systems is simulated using these three levels of theory. The eFGR and the qsFGR show temporal oscillations originating from the electronic or vibrational coherences generated as the nuclear wave packet traverses a conical intersection. These oscillations, which are missed by the scFGR, directly reveal the time-evolving splitting between electronic states of the neutral molecule in the curve-crossing regime.

Stochastic acceleration of electrons. I - Effects of collisions in solar flares

NASA Technical Reports Server (NTRS)

Hamilton, Russell J.; Petrosian, Vahe

1992-01-01

Stochastic acceleration of thermal electrons to nonrelativistic energies is studied under solar flare conditions. We show that, in turbulent regions, electron-whistler wave interactions can result in the acceleration of electrons in times comparable to or shorter than the Coulomb collision time. The kinetic equation describing the evolution of the electron energy distribution including stochastic acceleration by whistlers and energy loss via Coulomb interactions is solved for an initial thermal electron energy spectrum. In general, the shape of the resulting electron distributions are characterized by the energy E(c) where systematic energy gain by turbulence equals energy loss due to Coulomb collisions. For energies less than E(c), the spectra are steep (quasi-thermal) whereas above E(c), the spectra are power laws. We find that hard X-ray spectra computed using the electron distributions obtained from our numerical simulations are able to explain the complex spectral shapes and variations observed in impulsive hard X-ray bursts. In particular, we show that the gradual steepening observed by Lin et al. (1981) could be due to a systematic increase in the density of the plasma (due to evaporation) and the increasing importance of collisions instead of the appearance of a superhot thermal component.

Interpretation of cw-ESR spectra of p-methyl-thio-phenyl-nitronyl nitroxide in a nematic liquid crystalline phase.

PubMed

Collauto, Alberto; Zerbetto, Mirco; Brustolon, Marina; Polimeno, Antonino; Caneschi, Andrea; Gatteschi, Dante

2012-03-07

In this paper we report on the characterization by continuous wave electron spin resonance spectroscopy (cw-ESR) of a nitronyl nitroxide radical in a nematic phase. A detailed analysis is performed by exploiting an innovative modeling strategy alternative to the usual spectral simulation approach: most of the molecular parameters needed to calculate the spectrum are evaluated a priori and the ESR spectrum is obtained by direct application of the stochastic Liouville equation. Allowing a limited set of fitting parameters it is possible to reproduce satisfactorily ESR spectra in the temperature range 260 K-340 K including the nematic-to-isotropic phase transition (325.1 K). Our results open the way to a more quantitative understanding of the ordering and mobility of nitronyl nitroxide radicals in nanostructured environments.

IceTop tank response to muons

NASA Astrophysics Data System (ADS)

Demirörs, L.; Beimforde, M.; Eisch, J.; Madsen, J.; Niessen, P.; Spiczak, G.M.; Stoyanov, S.; Tilav, S

The calibration of the surface air shower array of IceCube - IceTop is based on identifying and understanding the muon response of each IceTop tank. Special calibration runs are carried out throughout the year and are supplemented with austral season measurements with tagging telescope for vertical muons. The vertical equivalent muon (VEM) charge value of each tank is determined and monitored by keeping track of its variation with time and temperature. We also study muons that stop and decay in the tank. The energy spectrum of the electrons from muon decay (Michel spectrum) is well known with maximum energy of 53 MeV. This energy is usually deposited inside the tank and can also be used as a calibration tool. We use both these spectra and compare them to a Monte Carlo simulation to gain a better understanding of the tank properties.

The EPR study of Mn(2+) ion doped DADT single crystal produced under high pressure and temperature.

PubMed

Ceylan, Ümit; Tapramaz, Recep

2016-01-05

An EPR study on Cu(2+) and VO(2+) doped di ammonium d-tartrate single crystals has been reported in previous papers, but the same host did not accept Mn(2+) ion at the same reaction conditions in previous trials. In this study EPR study of Mn(2+) ion doped di ammonium d tartrate single crystal, (DADT) [(NH4)2C4H4O6], produced in a reactor under high pressure and high temperature. The electronic transitions were determined by the optical absorption spectrum. Hyperfine splitting and g values of the Mn(2+) ion forming a complex in the lattice were measured from experimental spectra and spin-spin dipolar splitting parameters D and E were found by the spectrum simulation techniques. Copyright © 2015 Elsevier B.V. All rights reserved.

DAMPE squib? Significance of the 1.4 TeV DAMPE excess

NASA Astrophysics Data System (ADS)

Fowlie, Andrew

2018-05-01

We present a Bayesian and frequentist analysis of the DAMPE charged cosmic ray spectrum. The spectrum, by eye, contained a spectral break at about 1TeV and a monochromatic excess at about 1.4TeV. The break was supported by a Bayes factor of about 1010 and we argue that the statistical significance was resounding. We investigated whether we should attribute the excess to dark matter annihilation into electrons in a nearby subhalo. We found a local significance of about 3.6σ and a global significance of about 2.3σ, including a two-dimensional look-elsewhere effect by simulating 1000 pseudo-experiments. The Bayes factor was sensitive to our choices of priors, but favoured the excess by about 2 for our choices. Thus, whilst intriguing, the evidence for a signal is not currently compelling.

A stretch/compress scheme for a high temporal resolution detector for the magnetic recoil spectrometer time (MRSt)

DOE PAGES

Hilsabeck, T. J.; Frenje, J. A.; Hares, J. D.; ...

2016-08-02

Here we present a time-resolved detector concept for the magnetic recoil spectrometer for time-resolved measurements of the NIF neutron spectrum. The measurement is challenging due to the time spreading of the recoil protons (or deuterons) as they transit an energy dispersing magnet system. Ions arrive at the focal plane of the magnetic spectrometer over an interval of tens of nanoseconds. We seek to measure the time-resolved neutron spectrum with 20 ps precision by manipulating an electron signal derived from the ions. A stretch-compress scheme is employed to remove transit time skewing while simultaneously reducing the bandwidth requirements for signal recording.more » Simulation results are presented along with design concepts for structures capable of establishing the required electromagnetic fields.« less

A stretch/compress scheme for a high temporal resolution detector for the magnetic recoil spectrometer time (MRSt)

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

Hilsabeck, T. J.; Frenje, J. A.; Hares, J. D.

Here we present a time-resolved detector concept for the magnetic recoil spectrometer for time-resolved measurements of the NIF neutron spectrum. The measurement is challenging due to the time spreading of the recoil protons (or deuterons) as they transit an energy dispersing magnet system. Ions arrive at the focal plane of the magnetic spectrometer over an interval of tens of nanoseconds. We seek to measure the time-resolved neutron spectrum with 20 ps precision by manipulating an electron signal derived from the ions. A stretch-compress scheme is employed to remove transit time skewing while simultaneously reducing the bandwidth requirements for signal recording.more » Simulation results are presented along with design concepts for structures capable of establishing the required electromagnetic fields.« less

Electron heating and acceleration during magnetic reconnection

NASA Astrophysics Data System (ADS)

Dahlin, Joel

2017-10-01

Magnetic reconnection is thought to be an important driver of energetic particles in a variety of astrophysical phenomena such as solar flares and magnetospheric storms. However, the observed fraction of energy imparted to a nonthermal component can vary widely in different regimes. We use kinetic particle-in-cell (PIC) simulations to demonstrate the important role of the non-reversing (guide) field in controlling the efficiency of electron acceleration in collisionless reconnection. In reconnection where the guide field is smaller than the reconnecting component, the dominant electron accelerator is a Fermi-type mechanism that preferentially energizes the most energetic particles. In strong guide field reconnection, the field-line contraction that drives the Fermi mechanism becomes weak. Instead, parallel electric fields are primarily responsible for driving electron heating but are ineffective in driving the energetic component of the spectrum. Three-dimensional simulations reveal that the stochastic magnetic field that develops during 3D guide field reconnection plays a vital role in particle acceleration and transport. The reconnection outflows that drive Fermi acceleration also expel accelerating particles from energization regions. In 2D reconnection, electrons are trapped in island cores and acceleration ceases, whereas in 3D the stochastic magnetic field enables energetic electrons to leak out of islands and freely sample regions of energy release. A finite guide field is required to break initial 2D symmetry and facilitate escape from island structures. We show that reconnection with a guide field comparable to the reconnecting field generates the greatest number of energetic electrons, a regime where both (a) the Fermi mechanism is an efficient driver and (b) energetic electrons may freely access acceleration sites. These results have important implications for electron acceleration in solar flares and reconnection-driven dissipation in turbulence.

Electron Surfing Acceleration in High Mach Number Shocks

NASA Astrophysics Data System (ADS)

Hoshino, M.; Amano, T.; Matsumoto, Y.

2016-12-01

Many energetic events associated with shock waves have been argued in this context of the diffusive shock acceleration (DSA), and the origin of high-energy particles observed in astrophysical shocks are believed to be attributed to DSA. However, electron nonthermal acceleration still remains an unresolved issue of considerable interest. While cosmic rays of supernova remnant shocks with power-law spectra are believed to be produced by DSA, energetic electrons with a power-law energy spectrum are rarely ever observed at interplanetary shocks and at planetary bow shocks (e.g., Lario et al. 2003), and the diffusive-type acceleration seems to be necessarily malfunctioning in the heliosphere. The malfunctioning reason is thought to be a lack of pre-acceleration mechanism of supra-thermal electrons.In this presentation, we propose that the supra-thermal electrons can be generated by the mechanism of shock surfing acceleration (SSA) in a high Mach number magnetosonic shock. In the surfing mechanism, a series of large-amplitude electrostatic waves are excited by Buneman instability in the foot region under the interaction between the reflected ions and the incoming electrons, and it is argued that the electrons trapped in the electrostatic waves can be accelerated up to a relativistic energy (Hoshino and Shimada, 2002). Since the electron SSA has been studied based on one- or two-dimensional PIC simulations so far, SSA in three-dimensional system is questionable and remains an open question. We discuss based on our theoretical model and three-dimensional PIC simulation with a high-performance computing that the efficiency of SSA in three-dimensional system remains amazingly strong and plays an important role on the electron pre-acceleration/injection problem.

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

Effect of Molecular Rotation on Charge Transport Phenomena

NASA Astrophysics Data System (ADS)

Garg, O. P.; Lamba, Vijay Kr; Kaushik, D. K.

2015-12-01

The study of electron transport properties of molecular systems could be explained on the basis of the Landauer formalism. Unfortunately, due to the complexity of the experimental setup, most of these measurements have no control over the details of the electrode geometry, rotation of molecules, variation in angle of contacts, effect of fano resonances associated with side groups attached to rigid backbones, which results in a spectrum of IV-characteristics. Theoretical models can therefore help to understand and helps to develop new applications such as molecular sensors, etc. Thus we used simulation methods that generate the required structural ensemble, which is then analyzed with Green’s function methods to characterize the electronic transport properties. In present work we had discussed applications of this approach to understand the conductance in molecular system in the direction of controlling electron transport through molecules and studied the effect of rotation of sandwiched molecule.

Determination of the Goos-Hanchen shift in dielectric waveguides via photo emission electron microscopy in the visible spectrum

DOE PAGES

Stenmark, Theodore; Word, R. C.; Konenkamp, R.

2016-02-16

Photoemission Electron Microscopy (PEEM) is a versatile tool that relies on the photoelectric effect to produce high-resolution images. Pulse lasers allow for multi-photon PEEM where multiple photons are required excite a single electron. This non-linear process can directly image the near field region of electromagnetic fields in materials. We use this ability here to analyze wave propagation in a linear dielectric waveguide with wavelengths of 410nm and 780nm. The propagation constant of the waveguide can be extracted from the interference pattern created by the coupled and incident light and shows distinct polarization dependence. Furthermore, the electromagnetic field interaction at themore » boundaries can then be deduced which is essential to understand power flow in wave guiding structures. These results match well with simulations using finite element techniques.« less

Intense γ ray generated by refocusing laser pulse on wakefield accelerated electrons

NASA Astrophysics Data System (ADS)

Feng, Jie; Wang, Jinguang; Li, Yifei; Zhu, Changqing; Li, Minghua; He, Yuhang; Li, Dazhang; Wang, Weimin; Chen, Liming

2017-09-01

Ultrafast x/γ ray emission from the combination of laser wake-field acceleration and plasma mirror has been investigated as a promising Thomson scattering source. However, the photon energy and yield of radiation are limited to the intensity of reflected laser pulses. We use the 2D particle in cell simulation to demonstrate that a 75TW driven laser pulse can be refocused on the accelerated electron bunches through a hemispherical plasma mirror with a small f number of 0.25. The energetic electrons with the maximum energy about 350 MeV collide with the reflected laser pulse of a0 = 3.82 at the focal spot, producing high order multi-photon Thomson scattering, and resulting in the scattering spectrum which extends up to 21.2 MeV. Such a high energy γ ray source could be applied to photonuclear reaction and materials science.

A pulsed, mono-energetic and angular-selective UV photo-electron source for the commissioning of the KATRIN experiment

NASA Astrophysics Data System (ADS)

Behrens, J.; Ranitzsch, P. C.-O.; Beck, M.; Beglarian, A.; Erhard, M.; Groh, S.; Hannen, V.; Kraus, M.; Ortjohann, H.-W.; Rest, O.; Schlösser, K.; Thümmler, T.; Valerius, K.; Wierman, K.; Wilkerson, J. F.; Winzen, D.; Zacher, M.; Weinheimer, C.

2017-06-01

The KATRIN experiment aims to determine the neutrino mass scale with a sensitivity of 200 {meV/c^2} (90% C. L.) by a precision measurement of the shape of the tritium β -spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. To determine the transmission properties of the KATRIN main spectrometer, a mono-energetic and angular-selective electron source has been developed. In preparation for the second commissioning phase of the main spectrometer, a measurement phase was carried out at the KATRIN monitor spectrometer where the device was operated in a MAC-E filter setup for testing. The results of these measurements are compared with simulations using the particle-tracking software "Kassiopeia", which was developed in the KATRIN collaboration over recent years.

Electromagnetic cascades in pulsars

NASA Technical Reports Server (NTRS)

Daugherty, J. K.; Harding, A. K.

1981-01-01

The development of pair photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters and follows the curvature radiation emitted by the primary, the conversion of this radiation e(+) - e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma ray spectrum above 25 MeV, and that the final gamma ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.

Calculating the electron temperature in the lightning channel by continuous spectrum

NASA Astrophysics Data System (ADS)

Xiangcheng, DONG; Jianhong, CHEN; Xiufang, WEI; Ping, YUAN

2017-12-01

Based on the theory of plasma continuous radiation, the relationship between the emission intensity of bremsstrahlung and recombination radiation and the plasma electron temperature is obtained. During the development process of a return stroke of ground flash, the intensity of continuous radiation spectrum is separated on the basis of the spectrums with obviously different luminous intensity at two moments. The electron temperature of the lightning discharge channel is obtained through the curve fitting of the continuous spectrum intensity. It is found that electron temperature increases with the increase of wavelength and begins to reduce after the peak. The peak temperature of the two spectra is close to 25 000 K. To be compared with the result of discrete spectrum, the electron temperature is fitted by the O I line and N II line of the spectrum respectively. The comparison shows that the high temperature value is in good agreement with the temperature of the lightning core current channel obtained from the ion line information, and the low temperature at the high band closes to the calculation result of the atomic line, at a low band is lower than the calculation of the atomic line, which reflects the temperature of the luminous channel of the outer corona.

Naval electronic warfare simulation for effectiveness assessment and softkill programmability facility

NASA Astrophysics Data System (ADS)

Lançon, F.

2011-06-01

The Anti-ship Missile (ASM) threat to be faced by ships will become more diverse and difficult. Intelligence, rules of engagement constraints, fast reaction-time for effective softkill solution require specific tools to design Electronic Warfare (EW) systems and to integrate it onboard ship. SAGEM Company provides decoy launcher system [1] and its associated Naval Electronic Warfare Simulation tool (NEWS) to permit softkill effectiveness analysis for anti-ship missile defence. NEWS tool generates virtual environment for missile-ship engagement and counter-measure simulator over a wide spectrum: RF, IR, EO. It integrates EW Command & Control (EWC2) process which is implemented in decoy launcher system and performs Monte-Carlo batch processing to evaluate softkill effectiveness in different engagement situations. NEWS is designed to allow immediate EWC2 process integration from simulation to real decoy launcher system. By design, it allows the final operator to be able to program, test and integrate its own EWC2 module and EW library onboard, so intelligence of each user is protected and evolution of threat can be taken into account through EW library update. The objectives of NEWS tool are also to define a methodology for trial definition and trial data reduction. Growth potential would permit to design new concept for EWC2 programmability and real time effectiveness estimation in EW system. This tool can also be used for operator training purpose. This paper presents the architecture design, the softkill programmability facility concept and the flexibility for onboard integration on ship. The concept of this operationally focused simulation, which is to use only one tool for design, development, trial validation and operational use, will be demonstrated.

A correlation electron cyclotron emission diagnostic and the importance of multifield fluctuation measurements for testing nonlinear gyrokinetic turbulence simulations.

PubMed

White, A E; Schmitz, L; Peebles, W A; Carter, T A; Rhodes, T L; Doyle, E J; Gourdain, P A; Hillesheim, J C; Wang, G; Holland, C; Tynan, G R; Austin, M E; McKee, G R; Shafer, M W; Burrell, K H; Candy, J; DeBoo, J C; Prater, R; Staebler, G M; Waltz, R E; Makowski, M A

2008-10-01

A correlation electron cyclotron emission (CECE) diagnostic has been used to measure local, turbulent fluctuations of the electron temperature in the core of DIII-D plasmas. This paper describes the hardware and testing of the CECE diagnostic and highlights the importance of measurements of multifield fluctuation profiles for the testing and validation of nonlinear gyrokinetic codes. The process of testing and validating such codes is critical for extrapolation to next-step fusion devices. For the first time, the radial profiles of electron temperature and density fluctuations are compared to nonlinear gyrokinetic simulations. The CECE diagnostic at DIII-D uses correlation radiometry to measure the rms amplitude and spectrum of the electron temperature fluctuations. Gaussian optics are used to produce a poloidal spot size with w(o) approximately 1.75 cm in the plasma. The intermediate frequency filters and the natural linewidth of the EC emission determine the radial resolution of the CECE diagnostic, which can be less than 1 cm. Wavenumbers resolved by the CECE diagnostic are k(theta) < or = 1.8 cm(-1) and k(r) < or = 4 cm(-1), relevant for studies of long-wavelength turbulence associated with the trapped electron mode and the ion temperature gradient mode. In neutral beam heated L-mode plasmas, core electron temperature fluctuations in the region 0.5 < r/a < 0.9, increase with radius from approximately 0.5% to approximately 2%, similar to density fluctuations that are measured simultaneously with beam emission spectroscopy. After incorporating "synthetic diagnostics" to effectively filter the code output, the simulations reproduce the characteristics of the turbulence and transport at one radial location r/a = 0.5, but not at a second location, r/a = 0.75. These results illustrate that measurements of the profiles of multiple fluctuating fields can provide a significant constraint on the turbulence models employed by the code.

X-ray High-resolution Spectroscopy for Laser-produced Plasma

NASA Astrophysics Data System (ADS)

Barbato, F.; Scarpellini, D.; Malizia, A.; Gaudio, P.; Richetta, M.; Antonelli, L.

The study of the emission spectrum gives information about the material generating the spectrum itself and the condition in which this is generated. The wavelength spectra lines are linked to the specific element and plasma conditions (electron temperature, density), while their shape is influenced by several physical effects like Stark and Doppler ones. In this work we study the X-ray emission spectra of a copper laser-produced plasma by using a spherical bent crystal spectrometer to measure the electron temperature. The facility used is the laser TVLPS, at the Tor Vergata University in Rome. It consists of a Nd:Glass source (in first harmonic - 1064 nm) whose pulse parameters are: 8 J in energy, time duration of 15 ns and a focal spot diameter of 200 μm. The adopted spectrometer is based on a spherical bent crystal of muscovite. The device combines the focusing property of a spherical mirror with the Bragg's law. This allows to obtain a great power resolution but a limited range of analysis. In our case the resolution is on average 80 eV. As it is well-known, the position of the detector on the Rowland's circle is linked to the specific spectral range which has been studied. To select the area to be investigated, we acquired spectra by means of a flat spectrometer. The selected area is centered on 8.88 Å. To calibrate the spectrum we wrote a ray-tracing MATLAB code, which calculates the detector alignment parameters and calibration curve. We used the method of line ratio to measure the electron temperature. This is possible because we assumed the plasma to be in LTE condition. The temperature value was obtained comparing the experimental one, given by the line ratio, with the theoretical one, preceded by FLYCHK simulations.

Microbunching-instability-induced sidebands in a seeded free-electron laser

DOE PAGES

Zhang, Zhen; Lindberg, Ryan; Fawley, William M.; ...

2016-05-02

Measurements of the multishot-averaged, soft x-ray, self-seeding spectrum at the LCLS free-electron laser often have a pedestal-like distribution around the seeded wavelength, which limits the spectral purity and can negatively affect some user applications not employing a post-undulator monochromator. In this paper, we study the origins of such pedestals, focusing on longitudinal phase space modulations produced by the microbunching instability upstream of the free-electron laser (FEL) undulator. Furthermore, we show from theory and numerical simulation that both energy and density modulations can induce sidebands in a high-gain, seeded FEL whose fractional strength typically grows as the square of the undulatormore » length. The results place a tight constraint on the longitudinal phase space uniformity of the electron beam for a seeded FEL, possibly requiring the amplitude of long-wavelength modulations to be much smaller than the typical incoherent energy spread if the output sideband power is to remain only a couple percent or less of the amplified seed power.« less

An analytical model for calculating microdosimetric distributions from heavy ions in nanometer site targets.

PubMed

Czopyk, L; Olko, P

2006-01-01

The analytical model of Xapsos used for calculating microdosimetric spectra is based on the observation that straggling of energy loss can be approximated by a log-normal distribution of energy deposition. The model was applied to calculate microdosimetric spectra in spherical targets of nanometer dimensions from heavy ions at energies between 0.3 and 500 MeV amu(-1). We recalculated the originally assumed 1/E(2) initial delta electrons spectrum by applying the Continuous Slowing Down Approximation for secondary electrons. We also modified the energy deposition from electrons of energy below 100 keV, taking into account the effective path length of the scattered electrons. Results of our model calculations agree favourably with results of Monte Carlo track structure simulations using MOCA-14 for light ions (Z = 1-8) of energy ranging from E = 0.3 to 10.0 MeV amu(-1) as well as with results of Nikjoo for a wall-less proportional counter (Z = 18).

Measurement and analysis of electron-neutral collision frequency in the calibrated cutoff probe

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

You, K. H.; Seo, B. H.; Kim, J. H.

2016-03-15

As collisions between electrons and neutral particles constitute one of the most representative physical phenomena in weakly ionized plasma, the electron-neutral (e-n) collision frequency is a very important plasma parameter as regards understanding the physics of this material. In this paper, we measured the e-n collision frequency in the plasma using a calibrated cutoff-probe. A highly accurate reactance spectrum of the plasma/cutoff-probe system, which is expected based on previous cutoff-probe circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], is obtained using the calibrated cutoff-probe method, and the e-n collision frequency is calculated based on the cutoff-probe circuitmore » model together with the high-frequency conductance model. The measured e-n collision frequency (by the calibrated cutoff-probe method) is compared and analyzed with that obtained using a Langmuir probe, with the latter being calculated from the measured electron-energy distribution functions, in wide range of gas pressure.« less

Femtosecond dynamics and laser control of charge transport in trans-polyacetylene.

PubMed

Franco, Ignacio; Shapiro, Moshe; Brumer, Paul

2008-06-28

The induction of dc electronic transport in rigid and flexible trans-polyacetylene oligomers according to the omega versus 2omega coherent control scenario is investigated using a quantum-classical mean field approximation. The approach involves running a large ensemble of mixed quantum-classical trajectories under the influence of omega+2omega laser fields and choosing the initial conditions by sampling the ground-state Wigner distribution function for the nuclei. The vibronic couplings are shown to change the mean single-particle spectrum, introduce ultrafast decoherence, and enhance intramolecular vibrational and electronic relaxation. Nevertheless, even in the presence of significant couplings, limited coherent control of the electronic dynamics is still viable, the most promising route involving the use of femtosecond pulses with a duration that is comparable to the electronic dephasing time. The simulations offer a realistic description of the behavior of a simple coherent control scenario in a complex system and provide a detailed account of the femtosecond photoinduced vibronic dynamics of a conjugated polymer.

Sn nanothreads in GaAs: experiment and simulation

NASA Astrophysics Data System (ADS)

Semenikhin, I.; Vyurkov, V.; Bugaev, A.; Khabibullin, R.; Ponomarev, D.; Yachmenev, A.; Maltsev, P.; Ryzhii, M.; Otsuji, T.; Ryzhii, V.

2016-12-01

The gated GaAs structures like the field-effect transistor with the array of the Sn nanothreads was fabricated via delta-doping of vicinal GaAs surface by Sn atoms with a subsequent regrowth. That results in the formation of the chains of Sn atoms at the terrace edges. Two device models were developed. The quantum model accounts for the quantization of the electron energy spectrum in the self-consistent two-dimensional electric potential, herewith the electron density distribution in nanothread arrays for different gate voltages is calculated. The classical model ignores the quantization and electrons are distributed in space according to 3D density of states and Fermi-Dirac statistics. It turned out that qualitatively both models demonstrate similar behavior, nevertheless, the classical one is in better quantitative agreement with experimental data. Plausibly, the quantization could be ignored because Sn atoms are randomly placed along the thread axis. The terahertz hot-electron bolometers (HEBs) could be based on the structure under consideration.

Balloon measurements of the energy spectrum of cosmic electrons between 1 and 25 GeV.

NASA Technical Reports Server (NTRS)

Earl, J. A.; Neely, D. E.; Rygg, T. A.

1972-01-01

During three balloon flights made in 1966 and 1967, cosmic electrons were investigated with the aid of a hodoscope detector that provided extensive and detailed information on each cosmic-ray event triggering the apparatus. Similar information obtained during calibration exposures to protons and pions as well as to electrons was used to provide identification of cosmic electrons and to determine their energies. Differential primary electron intensities measured in the range from 1 to 25 GeV were substantially larger than some earlier measurements. In conjunction with existing measurements at energies above 100 GeV, this finding indicates that the energy spectrum of cosmic electrons is steeper than that of cosmic-ray nuclei and consequently suggests that Compton/synchrotron energy loss plays a significant role in shaping the electron spectrum.

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

Carr, Roger

The VISA (Visible to Infrared SASE Amplifier) FEL is designed to obtain high gain at a radiation wavelength of 800nm. The FEL uses the high brightness electron beam of the Accelerator Test Facility (ATF), with energy of 72MeV. VISA uses a novel, 4 m long, strong focusing undulator with a gap of 6mm and a period of 1.8cm. To obtain large gain the beam and undulator axis have to be aligned to better than 50{micro}m. Results from initial measurements on the alignment, gain, and spectrum will be presented and compared to theoretical calculations and simulations.

International Collaboration for Galactic Cosmic Ray Simulation at the NASA Space Radiation Laboratory

NASA Technical Reports Server (NTRS)

Norbury, John W.; Slaba, Tony C.; Rusek, Adam; Durante, Marco; Reitz, Guenther

2015-01-01

An international collaboration on Galactic Cosmic Ray (GCR) simulation is being formed to make recommendations on how to best simulate the GCR spectrum at ground based accelerators. The external GCR spectrum is significantly modified when it passes through spacecraft shielding and astronauts. One approach for simulating the GCR space radiation environment at ground based accelerators would use the modified spectrum, rather than the external spectrum, in the accelerator beams impinging on biological targets. Two recent workshops have studied such GCR simulation. The first workshop was held at NASA Langley Research Center in October 2014. The second workshop was held at the NASA Space Radiation Investigators' workshop in Galveston, Texas in January 2015. The anticipated outcome of these and other studies may be a report or journal article, written by an international collaboration, making accelerator beam recommendations for GCR simulation. This poster describes the status of GCR simulation at the NASA Space Radiation Laboratory and encourages others to join the collaboration.

Observations and modeling of wave-induced microburst electron precipitation

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

Rosenberg, T.J.; Wei, R.; Detrick, D.L.

1990-05-01

Energy-time features of X ray microbursts are examined and compared with the predictions of a test particle simulation model of wave-induced electron precipitation resulting from gyroresonant wave-particle interactions in the magnetosphere. An algorithm designed to search the E > 25 keV counting rate data for single isolated microbursts identified 651 events in a 3-hr interval. The distribution of burst durations ranged from 0.2 to 1.2 s. Approximately two-thirds of the distribution were narrow bursts (0.2 - 0.6 s), the rest wide (0.6 - 1.2 s), with the average burst durations equal to {minus}0.4 s and {minus}0.7 s, respectively, for themore » two classes. The precipitation was characterized by exponential electron spectra with e-folding energies Eo of 25-50 keV. Individual and superposed microburst profiles show that the X ray energy spectrum is softest near the peak of the energy influx. Computer simulations of the flux- and energy-time profiles of direct and mirrored electron precipitation induced by a whistler-mode wave pulse of 0.2-s duration and linear frequency increase from 2 to 4 kHz were performed for plasma, energetic particle and wave parameters appropriate for the location and geophysical conditions of the observations. In general, the results provide further support for the guroresonant test particle simulation model, and for the belief that the observed type of microbursts originates in the vicinity of the magnetic equator in a gyroresonant process involving discrete chorus emissions.« less

Electronic Warfare

DTIC Science & Technology

2012-02-08

EMOE is the background electromagnetic environment and the friendly, neutral, and adversarial electronic order of battle within the...X-RayELF VLF MF VHF SHFLF HF Radio Spectrum Visible Spectrum UHF EHF Gamma Ray Cosmic Ray The top bar shows how the electromagnetic spectrum is...effects of sunspots, lightning, and precipitation static. Essentially, the EME is the global EM background . Figure I-2. Electromagnetic Environment

Bulk Comptonization by Turbulence in Black Hole Accretion Discs

NASA Astrophysics Data System (ADS)

Kaufman, Jason

Radiation pressure dominated accretion discs may have turbulent velocities that exceed the electron thermal velocities. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. We discuss how to self-consistently resolve and interpret this effect in calculations of spectra of radiation MHD simulations. In particular, we show that this effect is dominated by radiation viscous dissipation and can be treated as thermal Comptonization with an equivalent temperature. We investigate whether bulk Comptonization may provide a physical basis for warm Comptonization models of the soft X-ray excess in AGN. We characterize our results with temperatures and optical depths to make contact with other models of this component. We show that bulk Comptonization shifts the Wien tail to higher energy and lowers the gas temperature, broadening the spectrum. More generally, we model the dependence of this effect on a wide range of fundamental accretion disc parameters, such as mass, luminosity, radius, spin, inner boundary condition, and the alpha parameter. Because our model connects bulk Comptonization to one dimensional vertical structure temperature profiles in a physically intuitive way, it will be useful for understanding this effect in future simulations run in new regimes. We also develop a global Monte Carlo code to study this effect in global radiation MHD simulations. This code can be used more broadly to compare global simulations with observed systems, and in particular to investigate whether magnetically dominated discs can explain why observed high Eddington accretion discs appear to be thermally stable.

Auroral and photoelectron fluxes in cometary ionospheres

NASA Astrophysics Data System (ADS)

Bhardwaj, A.; Haider, S. A.; Spinghal, R. P.

1990-05-01

The analytical yield spectrum method has been used to ascertain photoelectron and auroral electron fluxes in cometary ionospheres, with a view to determining the effects of cometocentric distances, solar zenith angle, and solar minimum and maximum conditions. Auroral electron fluxes are thus calculated for monoenergetic and observed primary electron spectra; auroral electrons are found to make a larger contribution to the observed electron spectrum than EUV-generated photoelectrons. Good agreement is established with extant theoretical works.

Quantum simulation of ultrafast dynamics using trapped ultracold atoms.

PubMed

Senaratne, Ruwan; Rajagopal, Shankari V; Shimasaki, Toshihiko; Dotti, Peter E; Fujiwara, Kurt M; Singh, Kevin; Geiger, Zachary A; Weld, David M

2018-05-25

Ultrafast electronic dynamics are typically studied using pulsed lasers. Here we demonstrate a complementary experimental approach: quantum simulation of ultrafast dynamics using trapped ultracold atoms. Counter-intuitively, this technique emulates some of the fastest processes in atomic physics with some of the slowest, leading to a temporal magnification factor of up to 12 orders of magnitude. In these experiments, time-varying forces on neutral atoms in the ground state of a tunable optical trap emulate the electric fields of a pulsed laser acting on bound charged particles. We demonstrate the correspondence with ultrafast science by a sequence of experiments: nonlinear spectroscopy of a many-body bound state, control of the excitation spectrum by potential shaping, observation of sub-cycle unbinding dynamics during strong few-cycle pulses, and direct measurement of carrier-envelope phase dependence of the response to an ultrafast-equivalent pulse. These results establish cold-atom quantum simulation as a complementary tool for studying ultrafast dynamics.

SOLAR WIND TURBULENCE FROM MHD TO SUB-ION SCALES: HIGH-RESOLUTION HYBRID SIMULATIONS

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

Franci, Luca; Verdini, Andrea; Landi, Simone

2015-05-10

We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wavenumbers. The simulation results simultaneously exhibit several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magnetohydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and themore » parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind, large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm’s law.« less

Solar Wind Turbulence from MHD to Sub-ion Scales: High-resolution Hybrid Simulations

NASA Astrophysics Data System (ADS)

Franci, Luca; Verdini, Andrea; Matteini, Lorenzo; Landi, Simone; Hellinger, Petr

2015-05-01

We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wavenumbers. The simulation results simultaneously exhibit several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magnetohydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind, large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm’s law.

Simulating Valence-to-Core X-ray Emission Spectroscopy of Transition Metal Complexes with Time-Dependent Density Functional Theory.

PubMed

Zhang, Yu; Mukamel, Shaul; Khalil, Munira; Govind, Niranjan

2015-12-08

Valence-to-core (VtC) X-ray emission spectroscopy (XES) has emerged as a powerful technique for the structural characterization of complex organometallic compounds in realistic environments. Since the spectrum represents electronic transitions from the ligand molecular orbitals to the core holes of the metal centers, the approach is more chemically sensitive to the metal-ligand bonding character compared with conventional X-ray absorption techniques. In this paper we study how linear-response time-dependent density functional theory (LR-TDDFT) can be harnessed to simulate K-edge VtC X-ray emission spectra reliably. LR-TDDFT allows one to go beyond the single-particle picture that has been extensively used to simulate VtC-XES. We consider seven low- and high-spin model complexes involving chromium, manganese, and iron transition metal centers. Our results are in good agreement with experiment.

The Synchrotron Spectrum of Fast Cooling Electrons Revisited.

PubMed

Granot; Piran; Sari

2000-05-10

We discuss the spectrum arising from synchrotron emission by fast cooling (FC) electrons, when fresh electrons are continually accelerated by a strong blast wave, into a power-law distribution of energies. The FC spectrum has so far been described by four power-law segments divided by three break frequencies nusa

Ab initio calculation of the electronic absorption spectrum of liquid water

NASA Astrophysics Data System (ADS)

Martiniano, Hugo F. M. C.; Galamba, Nuno; Cabral, Benedito J. Costa

2014-04-01

The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O-H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.

Studies on solar hard X-Rays and gamma-rays: Compton backscatter, anisotropy, polarization and evidence for two phases of acceleration. Ph.D. Thesis - Maryland Univ.

NASA Technical Reports Server (NTRS)

Bai, T.

1977-01-01

Observations of solar X-rays and gamma-rays from large flares show that the hard X-ray spectrum extends into the gamma ray region, where a flattening in the spectrum of the continuum emission is observed above about 1 MeV. This emission is believed to be due to bremsstrahlung. In addition to electron-proton collisions, at energies greater than approximately 500 keV, bremsstrahlung due to electron-electron collisions becomes significant. Bremsstrahlung production was calculated for a variety of electron spectra extending from the nonrelativistic region to relativistic energies and electron-electron bremsstrahlung is taken into account. By comparing these calculations with data, it is shown that the flattening in the spectrum of the continuum emission can be best explained by an electron spectrum consisting of two distinctive components. This evidence, together with information on the X-ray and gamma ray time profiles, implied the existence of two phases of acceleration. The first phase accelerates electrons mainly up to about several hundred keV; the second phase accelerates a small fraction of the electrons accelerated in the first phase to relativistic energies and accelerates protons to tens and hundreds of MeV.

Comparison of RF spectrum prediction methods for dynamic spectrum access

NASA Astrophysics Data System (ADS)

Kovarskiy, Jacob A.; Martone, Anthony F.; Gallagher, Kyle A.; Sherbondy, Kelly D.; Narayanan, Ram M.

2017-05-01

Dynamic spectrum access (DSA) refers to the adaptive utilization of today's busy electromagnetic spectrum. Cognitive radio/radar technologies require DSA to intelligently transmit and receive information in changing environments. Predicting radio frequency (RF) activity reduces sensing time and energy consumption for identifying usable spectrum. Typical spectrum prediction methods involve modeling spectral statistics with Hidden Markov Models (HMM) or various neural network structures. HMMs describe the time-varying state probabilities of Markov processes as a dynamic Bayesian network. Neural Networks model biological brain neuron connections to perform a wide range of complex and often non-linear computations. This work compares HMM, Multilayer Perceptron (MLP), and Recurrent Neural Network (RNN) algorithms and their ability to perform RF channel state prediction. Monte Carlo simulations on both measured and simulated spectrum data evaluate the performance of these algorithms. Generalizing spectrum occupancy as an alternating renewal process allows Poisson random variables to generate simulated data while energy detection determines the occupancy state of measured RF spectrum data for testing. The results suggest that neural networks achieve better prediction accuracy and prove more adaptable to changing spectral statistics than HMMs given sufficient training data.

A design of calibration single star simulator with adjustable magnitude and optical spectrum output system

NASA Astrophysics Data System (ADS)

Hu, Guansheng; Zhang, Tao; Zhang, Xuan; Shi, Gentai; Bai, Haojie

2018-03-01

In order to achieve multi-color temperature and multi-magnitude output, magnitude and temperature can real-time adjust, a new type of calibration single star simulator was designed with adjustable magnitude and optical spectrum output in this article. xenon lamp and halogen tungsten lamp were used as light source. The control of spectrum band and temperature of star was realized with different multi-beam narrow band spectrum with light of varying intensity. When light source with different spectral characteristics and color temperature go into the magnitude regulator, the light energy attenuation were under control by adjusting the light luminosity. This method can completely satisfy the requirements of calibration single star simulator with adjustable magnitude and optical spectrum output in order to achieve the adjustable purpose of magnitude and spectrum.

Investigation of the Electromagnetic Radiation Emitted by Sub-GeV Electrons in a Bent Crystal.

PubMed

Bandiera, L; Bagli, E; Germogli, G; Guidi, V; Mazzolari, A; Backe, H; Lauth, W; Berra, A; Lietti, D; Prest, M; De Salvador, D; Vallazza, E; Tikhomirov, V

2015-07-10

The radiation emitted by 855 MeV electrons via planar channeling and volume reflection in a 30.5-μm-thick bent Si crystal has been investigated at the MAMI (Mainzer Mikrotron) accelerator. The spectral intensity was much more intense than for an equivalent amorphous material, and peaked in the MeV range in the case of channeling radiation. Differently from a straight crystal, also for an incidence angle larger than the Lindhard angle, the spectral intensity remains nearly as high as for channeling. This is due to volume reflection, for which the intensity remains high at a large incidence angle over the whole angular acceptance, which is equal to the bending angle of the crystal. Monte Carlo simulations demonstrated that incoherent scattering significantly influences both the radiation spectrum and intensity, either for channeling or volume reflection. In the latter case, it has been shown that incoherent scattering increases the radiation intensity due to the contribution of volume-captured particles. As a consequence, the experimental spectrum becomes a mixture of channeling and pure volume reflection radiations. These results allow a better understanding of the radiation emitted by electrons subjected to coherent interactions in bent crystals within a still-unexplored energy range, which is relevant for possible applications for innovative and compact x-ray or γ-ray sources.

Electronic structure and rovibrational properties of ZnOH in the X̃²A' electronic state: a computational molecular spectroscopy study.

PubMed

Hirano, Tsuneo; Andaloussi, Mounir Ben Dahman; Nagashima, Umpei; Jensen, Per

2014-09-07

The three-dimensional ground-state potential energy surface of ZnOH has been calculated ab initio at the MR-SDCI+Q_DK3/[QZP ANO-RCC (Zn, O, H)] level of theory and used as basis for a study of the rovibrational properties carried out by means of the program MORBID (Morse Oscillator Rigid Bender Internal Dynamics). The electronic ground state is  (2)A' (correlating with (2)Σ(+) at the linear configuration). The equilibrium structure has r(e)(Zn-O) = 1.8028 Å, r(e)(O-H) = 0.9606 Å, and ∠e(Zn-O-H) = 114.9°. The Zn-O bond is essentially ionic, with appreciable covalency. The bonding character is compared with those of FeOH (quasi-linear) and CsOH (linear). The rovibrationally averaged structural parameters, determined as expectation values over MORBID wavefunctions, are ⟨r(Zn-O)⟩0 = 1.8078 Å, ⟨r(O-H)⟩0 = 0.9778 Å, and ⟨∠(Zn-O-H)⟩0 = 117°. The Yamada-Winnewisser quasi-linearity parameter is found to be γ0 = 0.84, which is close to 1.0 as expected for a bent molecule. Since no experimental rovibrational spectrum has been reported thus far, this spectrum has been simulated from the ab initio potential energy and dipole moment surfaces. The amphoteric character of ZnOH is also discussed.

Plugged In: Electronics Use in Youth and Young Adults with Autism Spectrum Disorder

ERIC Educational Resources Information Center

MacMullin, Jennifer A.; Lunsky, Yona; Weiss, Jonathan A.

2016-01-01

Although electronic technology currently plays an integral role for most youth, there are growing concerns of its excessive and compulsive use. This study documents patterns and impact of electronics use in individuals with autism spectrum disorder compared to typically developing peers. Participants included 172 parents of typically developing…

[Diagnosis of electron energy and comparative effects of OH, O or O3 on NO oxidation in pulsed corona discharge].

PubMed

Xuan, Jian-yong; Luo, Zhong-yang; Zhao, Lei; Jiang, Jian-ping; Gao, Xiang

2012-05-01

The spectrum of excited N2 molecules and ions was measured by optical emission spectroscopy in pulsed corona discharge with a wire-to-plate reactor. The ratio of emission intensities emitted by the excited molecules and ions of N2 was compared with numerical simulation to determine average electron energies and electric field distributions. Within 2 cm distance from wire electrode in horizontal and vertical directions, electric field and average electron energies appear to be in the ranges of 11.05 19.6 MV x m(-1) and 10.10-13.92 eV respectively; as the distance increases, average electron energies and electric field show a similar trend: first decrease and then increase. Chemically active species, such as OH, O and O3, can be generated through the energetic electron collisions with H2O and O2 directly or indirectly. For the NO oxidation, there is no coexistence of NO and O3, whereas there is a coexistence of NO and OH. NO is oxidized by O3 or O more efficiently than by OH radical.

Symmetry Breaking by Parallel Flow Shear

NASA Astrophysics Data System (ADS)

Li, Jiacong; Diamond, Patrick

2015-11-01

Plasma rotation is important in reducing turbulent transport, suppressing MHD instabilities, and is beneficial to confinement. Intrinsic rotation without an external momentum input is of interest for its plausible application on ITER. k∥ spectrum asymmetry is required for residual Reynolds stress that drives the intrinsic rotation. Parallel flows are reported in linear devices without magnetic shear. In CSDX, parallel flows are mostly peaked in the core [Thakur et al., 2014]; more robust flows and reversed profiles are seen in PANTA [Oldenburger, et al. 2012]. A novel mechanism for symmetry breaking in momentum transport is proposed. Magnetic shear or mean flow profile are not required. A seed parallel flow shear (PFS) sets the sign of residual stress by selecting certain modes to grow faster. The resulted spectrum imbalance leads to a nonzero residual stress, which further drives a parallel flow with ∇n as the free energy source, adding to the shear until saturated by diffusion. Balanced flow gradient is set by Π∥Res /χϕ . Residual stress is calculated for ITG turbulence and collisional drift wave turbulence where electron-ion and electron-neutral collisions are discussed and compared. Numerical simulation is proposed for testing the effect of PFS.

Middle UV to near-IR spectrum of electron-excited SO2

USGS Publications Warehouse

Ajello, J.M.; Aguilar, A.; Mangina, R.S.; James, G.K.; Geissler, P.; Trafton, L.

2008-01-01

We investigated the electron impact–induced fluorescence spectrum of SO2 to provide excitation cross sections for modeling Io's emission spectrum and analyzing Cassini Imaging Science Subsystem observations. The electron-excited middle-ultraviolet visible optical near-infrared (VOIR) emission spectrum of SO2 gas was generated in the laboratory and studied from 2000 to 11,000 Å at a resolution of Δλ ∼ 2.5 Å full width at half maximum (FWHM). The VOIR laboratory spectrum longward of 6000 Å consists entirely of S I, II and O I, II multiplets for electron impact energies above ∼15 eV. Between 2000 and 6000 Å, we find previously identified molecular bands from both SO and SO2. This work represents a significant improvement in spectral resolution over our earlier work done at 18 Å FWHM. From a measurement of the medium-resolution spectrum, we provide detailed 25- and 100-eV emission cross sections for spectral features from 2000 to 11,000 Å. On the basis of these data, we suggest future ground-based and satellite telescopic observations in the VOIR that are of promise for understanding Io's atmosphere.

Middle UV to Near-IR Spectrum of Electron-Excited SO2

NASA Technical Reports Server (NTRS)

Ajello, Joseph M.; Aguilar, Alejandro; Mangina, Rao S.; James, Geoffrey K.; Geissler, Paul; Trafton, Laurence

2008-01-01

We investigated the electron impact-induced fluorescence spectrum of SO2 to provide excitation cross sections for modeling Io's mission spectrum and analyzing Cassini Imaging Science Subsystem observations. The electron-excited middle-ultraviolet visible optical near-infrared (VOIR) emission spectrum of SO2 gas was generated in the laboratory and studied from 2000 to 11,000 A at a resolution of (Delta)(lamda) approximately 2.5 A full width at half maximum (FWHM). The VOIR laboratory spectrum longward of 6000 A consists entirely of S I, II and O I, II multiplets for electron impact energies above approximately 15 eV. Between 2000 and 6000 A, we find previously identified molecular bands from both SO and SO2. This work represents a significant improvement in spectral resolution over our earlier work done at 18 A FWHM. From a measurement of the medium-resolution spectrum, we provide detailed 25- and 100-eV emission cross sections for spectral features from 2000 to 11,000 A . On the basis of these data, we suggest future ground-based and satellite telescopic observations in the VOIR that are of promise for understanding Io's atmosphere.

Validation of radiative transfer computation with Monte Carlo method for ultra-relativistic background flow

NASA Astrophysics Data System (ADS)

Ishii, Ayako; Ohnishi, Naofumi; Nagakura, Hiroki; Ito, Hirotaka; Yamada, Shoichi

2017-11-01

We developed a three-dimensional radiative transfer code for an ultra-relativistic background flow-field by using the Monte Carlo (MC) method in the context of gamma-ray burst (GRB) emission. For obtaining reliable simulation results in the coupled computation of MC radiation transport with relativistic hydrodynamics which can reproduce GRB emission, we validated radiative transfer computation in the ultra-relativistic regime and assessed the appropriate simulation conditions. The radiative transfer code was validated through two test calculations: (1) computing in different inertial frames and (2) computing in flow-fields with discontinuous and smeared shock fronts. The simulation results of the angular distribution and spectrum were compared among three different inertial frames and in good agreement with each other. If the time duration for updating the flow-field was sufficiently small to resolve a mean free path of a photon into ten steps, the results were thoroughly converged. The spectrum computed in the flow-field with a discontinuous shock front obeyed a power-law in frequency whose index was positive in the range from 1 to 10 MeV. The number of photons in the high-energy side decreased with the smeared shock front because the photons were less scattered immediately behind the shock wave due to the small electron number density. The large optical depth near the shock front was needed for obtaining high-energy photons through bulk Compton scattering. Even one-dimensional structure of the shock wave could affect the results of radiation transport computation. Although we examined the effect of the shock structure on the emitted spectrum with a large number of cells, it is hard to employ so many computational cells per dimension in multi-dimensional simulations. Therefore, a further investigation with a smaller number of cells is required for obtaining realistic high-energy photons with multi-dimensional computations.

Systematic research on Ag2X (X = O, S, Se, Te) as visible and near-infrared light driven photocatalysts and effects of their electronic structures

NASA Astrophysics Data System (ADS)

Jiang, Wei; Wu, Zhaomei; Zhu, Yingming; Tian, Wen; Liang, Bin

2018-01-01

Four silver chalcogen compounds, Ag2O, Ag2S, Ag2Se and Ag2Te, can be utilized as visible-light-driven photocatalysts. In this research, the electronic structures of these compounds were analyzed by simulation and experiments to systematically reveal the relationship between photocatalytic performance and energetic structure. All four chalcogenides exhibited interesting photocatalytic activities under ultraviolet, visible and near-infrared light. However, their photocatalytic performances and stability significantly depended on the band gap width, and the valence band and conduct band position, which was determined by their composition. Increasing the X atomic number from O to Te resulted in the upward movement of the valence band top and the conduct band bottom, which resulted in narrower band gaps, a wider absorption spectrum, a weaker photo-oxidization capacity, a higher recombination probability of hole and electron pairs, lower quantum efficiency, and worse stability. Among them, Ag2O has the highest photocatalytic performance and stability due to its widest band gap and lowest position of VB and CB. The combined action of photogenerated holes and different radicals, depending on the different electronic structures, including anion ozone radical, hydroxide radical, and superoxide radical, was observed and understood. The results of experimental observations and simulations of the four silver chalcogen compounds suggested that a proper electronic structure is necessary to obtain a balance between photocatalytic performance and absorbable light region in the development of new photocatalysts.

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

Spectroscopic Measurements of Hydrogen Ion Temperature During Divertor Recombination

NASA Astrophysics Data System (ADS)

Stotler, D. P.; Skinner, C. H.; Karney, C. F. F.

1998-11-01

We explore the possibility of using the neutral H_α spectral line profile to measure the ion temperature Ti in a recombining plasma. Since the H_α emissions due to recombination are larger than those due to other mechanisms, interference from non-recombining regions contributing to the chord integrated data is insignificant. A chord integrated, Doppler and Stark broadened H_α spectrum is simulated by the DEGAS 2 Monte Carlo neutral transport code(D. Stotler and C. Karney, Contrib. Plasma Phys.) 34, 392 (1994). using assumed plasma conditions. The application of a simple fitting procedure to this spectrum yields an average electron density ne and Ti consistent with the assumed plasma parameters if the spectrum is dominated by recombination from a region of modest ne variation. The interpretation of experimental data is complicated by Zeeman splitting and light reflection off surfaces. Ion temperature measurements by H_α spectroscopy appear feasible within the context of a model for the entire divertor plasma that takes these effects into account.

Modeling of a Compact Terahertz Source based on the Two-Stream Instability

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

Svimonishvili, Tengiz

2016-05-17

THz radiation straddles the microwave and infrared bands of the electromagnetic spectrum, thus combining the penetrating power of lower-frequency waves and imaging capabilities of higher-energy infrared radiation. THz radiation is employed in various elds such as cancer research, biology, agriculture, homeland security, and environmental monitoring. Conventional vacuum electronic sources of THz radiation (e.g., fast- and slow-wave devices) either require very small structures or are bulky and expensive to operate. Optical sources necessitate cryogenic cooling and are presently capable of producing milliwatt levels of power at THz frequencies. We propose a millimeter and sub-millimeter wave source based on a well-known phenomenonmore » called the two-stream instability. The two-beam source relies on lowenergy and low-current electron beams for operation. Also, it is compact, simple in design, and does not contain expensive parts that require complex machining and precise alignment. In this dissertation, we perform 2-D particle-in-cell (PIC) simulations of the interaction region of the two-beam source. The interaction region consists of a beam pipe of radius ra and two electron beams of radius rb co-propagating and interacting inside the pipe. The simulations involve the interaction of unmodulated (no initial energy modulation) and modulated (energy-modulated, seeded at a given frequency) electron beams. In addition, both cold (monoenergetic) and warm (Gaussian) beams are treated.« less

Reflectance spectrum of plasmon waveguide interband cascade lasers and observation of the Berreman effect

NASA Astrophysics Data System (ADS)

Hinkey, Robert T.; Tian, Zhaobing; Yang, Rui Q.; Mishima, Tetsuya D.; Santos, Michael B.

2011-08-01

Noninvasive infrared reflectance measurements have been explored as a method for studying the optical properties of Si-doped cladding layers of plasmon waveguide interband cascade lasers. Measurements and theoretical simulations of the reflectance spectra were carried out on both the laser structures themselves, as well as highly doped InAs films grown on GaAs substrates. We have found that there is a sharp drop in the signal of the reflectance spectrum for p-polarized light oscillating near the plasma frequency. This is a manifestation of the so-called Berreman effect, which occurs at frequencies where the dielectric function approaches zero. This is distinct from the plasma edge feature seen in the reflectance spectrum of thick samples. The plasma frequencies of the highly doped layers were obtained by identifying the Berreman feature in the measured spectrum and fitting the spectrum to a modeled curve. Using a model for the effective mass, we were able to obtain measurements of the conduction electron concentration (in a range from 1018 to 1019 cm-3) in the waveguide cladding layers with values that were in good agreement with those found using Hall effect and SIMS measurements. The reflectance data was effectively used to achieve better calibration of the Si-doping during the growth of the n++-type InAs layers in the plasmon waveguide laser structures.

Energy Calibration of a Silicon-Strip Detector for Photon-Counting Spectral CT by Direct Usage of the X-ray Tube Spectrum

NASA Astrophysics Data System (ADS)

Liu, Xuejin; Chen, Han; Bornefalk, Hans; Danielsson, Mats; Karlsson, Staffan; Persson, Mats; Xu, Cheng; Huber, Ben

2015-02-01

The variation among energy thresholds in a multibin detector for photon-counting spectral CT can lead to ring artefacts in the reconstructed images. Calibration of the energy thresholds can be used to achieve homogeneous threshold settings or to develop compensation methods to reduce the artefacts. We have developed an energy-calibration method for the different comparator thresholds employed in a photon-counting silicon-strip detector. In our case, this corresponds to specifying the linear relation between the threshold positions in units of mV and the actual deposited photon energies in units of keV. This relation is determined by gain and offset values that differ for different detector channels due to variations in the manufacturing process. Typically, the calibration is accomplished by correlating the peak positions of obtained pulse-height spectra to known photon energies, e.g. with the aid of mono-energetic x rays from synchrotron radiation, radioactive isotopes or fluorescence materials. Instead of mono-energetic x rays, the calibration method presented in this paper makes use of a broad x-ray spectrum provided by commercial x-ray tubes. Gain and offset as the calibration parameters are obtained by a regression analysis that adjusts a simulated spectrum of deposited energies to a measured pulse-height spectrum. Besides the basic photon interactions such as Rayleigh scattering, Compton scattering and photo-electric absorption, the simulation takes into account the effect of pulse pileup, charge sharing and the electronic noise of the detector channels. We verify the method for different detector channels with the aid of a table-top setup, where we find the uncertainty of the keV-value of a calibrated threshold to be between 0.1 and 0.2 keV.

Simulation study on the effects of chemical structure and molecular size on the acceptor strength in poly(3-hexylthiophene)-based copolymer with alternating donor and acceptor for photovoltaic applications

NASA Astrophysics Data System (ADS)

Rassamesard, Areefen; Pengpan, Teparksorn

2017-02-01

This research assessed the effects of various chemical structures and molecular sizes on the simulated geometric parameters, electron structures, and spectroscopic properties of single-chain complex alternating donor-acceptor (D-A) monomers and copolymers that are intended for use as photoactive layer in a polymer solar cell by using Kohn-Sham density functional theory with B3LYP exchange-correlation functional. The 3-hexylthiophene (3HT) was selected for electron donor, while eight chemicals, namely thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), benzothiadiazole (BT), thiadiazolothieno-pyrazine (TPD), oxadiazole (OXD) and 5-diphenyl-1,2,4-triazole (TAZ), were employed as electron acceptor functional groups. The torsional angle, bridge bond length, intramolecular charge transfer, energy levels, and molecular orbitals were analyzed. The simulation results reveal that the geometry and electron structure of donor-acceptor monomer and copolymer are significantly impacted by heterocyclic rings, heteroatoms, fused rings, degree of steric hindrance and coplanarity of the acceptor molecular structure. Planar conformation was obtained from the D copolymer, and a pseudo-planar structure with the TD copolymer. The TAZ acceptor exhibited strong steric hindrance due to its bulky structure and non-planarity of its structure. An analysis of the electron structures indicated that the degree of intramolecular electron-withdrawing capability had the rank order TAZ  <  Z  <  D  <  TPD  <  OXD  <  TP  <  BT  <  TD. The TD is indicated as the most effective acceptor among those that were simulated. However, the small energy gaps of TD as well as TPD copolymer indicate that these two copolymers can be used in transparent conducting materials. The copolymer based on BT acceptor exhibited good intramolecular charge transfer and absorbed at 656 nm wavelength which is close to the maximum flux of solar spectrum. Hence, the BT acceptor functional group provides a compromise in the characteristics of a donor-acceptor copolymer, useful in a polymeric candidate material for the photoactive layer in a polymer solar cell.

Broad-spectrum non-toxic antiviral nanoparticles with a virucidal inhibition mechanism

NASA Astrophysics Data System (ADS)

Cagno, Valeria; Andreozzi, Patrizia; D'Alicarnasso, Marco; Jacob Silva, Paulo; Mueller, Marie; Galloux, Marie; Le Goffic, Ronan; Jones, Samuel T.; Vallino, Marta; Hodek, Jan; Weber, Jan; Sen, Soumyo; Janeček, Emma-Rose; Bekdemir, Ahmet; Sanavio, Barbara; Martinelli, Chiara; Donalisio, Manuela; Rameix Welti, Marie-Anne; Eleouet, Jean-Francois; Han, Yanxiao; Kaiser, Laurent; Vukovic, Lela; Tapparel, Caroline; Král, Petr; Krol, Silke; Lembo, David; Stellacci, Francesco

2018-02-01

Viral infections kill millions yearly. Available antiviral drugs are virus-specific and active against a limited panel of human pathogens. There are broad-spectrum substances that prevent the first step of virus-cell interaction by mimicking heparan sulfate proteoglycans (HSPG), the highly conserved target of viral attachment ligands (VALs). The reversible binding mechanism prevents their use as a drug, because, upon dilution, the inhibition is lost. Known VALs are made of closely packed repeating units, but the aforementioned substances are able to bind only a few of them. We designed antiviral nanoparticles with long and flexible linkers mimicking HSPG, allowing for effective viral association with a binding that we simulate to be strong and multivalent to the VAL repeating units, generating forces (~190 pN) that eventually lead to irreversible viral deformation. Virucidal assays, electron microscopy images, and molecular dynamics simulations support the proposed mechanism. These particles show no cytotoxicity, and in vitro nanomolar irreversible activity against herpes simplex virus (HSV), human papilloma virus, respiratory syncytial virus (RSV), dengue and lenti virus. They are active ex vivo in human cervicovaginal histocultures infected by HSV-2 and in vivo in mice infected with RSV.

New method for characterizing electron mediators in microbial systems using a thin-layer twin-working electrode cell.

PubMed

Hassan, Md Mahamudul; Cheng, Ka Yu; Ho, Goen; Cord-Ruwisch, Ralf

2017-01-15

Microbial biofilms are significant ecosystems where the existence of redox gradients drive electron transfer often via soluble electron mediators. This study describes the use of two interfacing working electrodes (WEs) to simulate redox gradients within close proximity (250µm) for the detection and quantification of electron mediators. By using a common counter and reference electrode, the potentials of the two WEs were independently controlled to maintain a suitable "voltage window", which enabled simultaneous oxidation and reduction of electron mediators as evidenced by the concurrent anodic and cathodic currents, respectively. To validate the method, the electrochemical properties of different mediators (hexacyanoferrate, HCF, riboflavin, RF) were characterized by stepwise shifting the "voltage window" (ranging between 25 and 200mV) within a range of potentials after steady equilibrium current of both WEs was established. The resulting differences in electrical currents between the two WEs were recorded across a defined potential spectrum (between -1V and +0.5V vs. Ag/AgCl). Results indicated that the technique enabled identification (by the distinct peak locations at the potential scale) and quantification (by the peak of current) of the mediators for individual species as well as in an aqueous mixture. It enabled a precise determination of mid-potentials of the externally added mediators (HCF, RF) and mediators produced by pyocyanin-producing Pseudomonas aeruginosa (WACC 91) culture. The twin working electrode described is particularly suitable for studying mediator-dependent microbial electron transfer processes or simulating redox gradients as they exist in microbial biofilms. Copyright © 2016 Elsevier B.V. All rights reserved.

Fast simulation of yttrium-90 bremsstrahlung photons with GATE.

PubMed

Rault, Erwann; Staelens, Steven; Van Holen, Roel; De Beenhouwer, Jan; Vandenberghe, Stefaan

2010-06-01

Multiple investigators have recently reported the use of yttrium-90 (90Y) bremsstrahlung single photon emission computed tomography (SPECT) imaging for the dosimetry of targeted radionuclide therapies. Because Monte Carlo (MC) simulations are useful for studying SPECT imaging, this study investigates the MC simulation of 90Y bremsstrahlung photons in SPECT. To overcome the computationally expensive simulation of electrons, the authors propose a fast way to simulate the emission of 90Y bremsstrahlung photons based on prerecorded bremsstrahlung photon probability density functions (PDFs). The accuracy of bremsstrahlung photon simulation is evaluated in two steps. First, the validity of the fast bremsstrahlung photon generator is checked. To that end, fast and analog simulations of photons emitted from a 90Y point source in a water phantom are compared. The same setup is then used to verify the accuracy of the bremsstrahlung photon simulations, comparing the results obtained with PDFs generated from both simulated and measured data to measurements. In both cases, the energy spectra and point spread functions of the photons detected in a scintillation camera are used. Results show that the fast simulation method is responsible for a 5% overestimation of the low-energy fluence (below 75 keV) of the bremsstrahlung photons detected using a scintillation camera. The spatial distribution of the detected photons is, however, accurately reproduced with the fast method and a computational acceleration of approximately 17-fold is achieved. When measured PDFs are used in the simulations, the simulated energy spectrum of photons emitted from a point source of 90Y in a water phantom and detected in a scintillation camera closely approximates the measured spectrum. The PSF of the photons imaged in the 50-300 keV energy window is also accurately estimated with a 12.4% underestimation of the full width at half maximum and 4.5% underestimation of the full width at tenth maximum. Despite its limited accuracy, the fast bremsstrahlung photon generator is well suited for the simulation of bremsstrahlung photons emitted in large homogeneous organs, such as the liver, and detected in a scintillation camera. The computational acceleration makes it very useful for future investigations of 90Y bremsstrahlung SPECT imaging.

Ionospheric response to infrasonic-acoustic waves generated by natural hazard events

NASA Astrophysics Data System (ADS)

Zettergren, M. D.; Snively, J. B.

2015-09-01

Recent measurements of GPS-derived total electron content (TEC) reveal acoustic wave periods of ˜1-4 min in the F region ionosphere following natural hazard events, such as earthquakes, severe weather, and volcanoes. Here we simulate the ionospheric responses to infrasonic-acoustic waves, generated by vertical accelerations at the Earth's surface or within the lower atmosphere, using a compressible atmospheric dynamics model to perturb a multifluid ionospheric model. Response dependencies on wave source geometry and spectrum are investigated at middle, low, and equatorial latitudes. Results suggest constraints on wave amplitudes that are consistent with observations and that provide insight on the geographical variability of TEC signatures and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field. Asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side, due to alignments of acoustic wave velocities parallel and perpendicular to field lines, respectively. Acoustic-wave-driven TEC perturbations are shown to have periods of ˜3-4 min, which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere. Furthermore, thermospheric acoustic waves couple with ion sound waves throughout the F region and topside ionosphere, driving plasma disturbances with similar periods and faster phase speeds. The associated magnetic perturbations of the simulated waves are calculated to be observable and may provide new observational insight in addition to that provided by GPS TEC measurements.

Time-dependent quantum transport: An efficient method based on Liouville-von-Neumann equation for single-electron density matrix

NASA Astrophysics Data System (ADS)

Xie, Hang; Jiang, Feng; Tian, Heng; Zheng, Xiao; Kwok, Yanho; Chen, Shuguang; Yam, ChiYung; Yan, YiJing; Chen, Guanhua

2012-07-01

Basing on our hierarchical equations of motion for time-dependent quantum transport [X. Zheng, G. H. Chen, Y. Mo, S. K. Koo, H. Tian, C. Y. Yam, and Y. J. Yan, J. Chem. Phys. 133, 114101 (2010), 10.1063/1.3475566], we develop an efficient and accurate numerical algorithm to solve the Liouville-von-Neumann equation. We solve the real-time evolution of the reduced single-electron density matrix at the tight-binding level. Calculations are carried out to simulate the transient current through a linear chain of atoms, with each represented by a single orbital. The self-energy matrix is expanded in terms of multiple Lorentzian functions, and the Fermi distribution function is evaluated via the Padè spectrum decomposition. This Lorentzian-Padè decomposition scheme is employed to simulate the transient current. With sufficient Lorentzian functions used to fit the self-energy matrices, we show that the lead spectral function and the dynamics response can be treated accurately. Compared to the conventional master equation approaches, our method is much more efficient as the computational time scales cubically with the system size and linearly with the simulation time. As a result, the simulations of the transient currents through systems containing up to one hundred of atoms have been carried out. As density functional theory is also an effective one-particle theory, the Lorentzian-Padè decomposition scheme developed here can be generalized for first-principles simulation of realistic systems.

High frequency RF waves

NASA Astrophysics Data System (ADS)

Horton, William; Brookman, M.; Goniche, M.; Peysson, Y.; Ekedahl, A.

2017-10-01

ECH and LHCD- are scattered by the density and magnetic field turbulence from drift waves as measured in and Tore Supra-WEST, EAST and DIII-D. Ray equations give the spreading from plasma refraction from the antenna through the core plasma until and change the parallel phase velocity evolves to where RF waves are absorbed by the electrons. Extensive LH ray tracing and absorption has been reported using the coupled CP3O ray tracing and LUKE electron phase space density code with collisionless electron-wave resonant absorption. In theory and simulations are shown for the ray propagation with the resulting electron distributions along with the predicted X ray distribution that compared to the measured X-ray spectrum. Lower-hybrid is essential for steady-state operation in tokamaks with control of the high-energy electrons intrinsic to tokamaks confinement and heating. The record steady tokamak plasma is Tore Supra a steady 6 minute steady state plasma with 1 Gigajoule energy passing through the plasma. WEST is repeating the experiments with ITER shaped separatrix and divertor chamber and EAST achieved comparable long-pulse plasmas. Results are presented from an IFS-3D spectral code with a pair of inside-outside LHCD antennas and a figure-8 magnetic separatrix are presented. Scattering of the slow wave into the fast wave wave is explored showing the RF scattering from drift wave dne and dB increases the core penetration may account the measured broad X-ray spectrum. Work supported by the DoE through Grants to the Institute for Fusion Studies [DE-FG02-04ER54742], ARLUT and General Atomics, San Diego, California, USA and the IRFM at Cadarache by the Comissariat Energie Atomique, France.

Optical Properties of Vibronically Coupled Cy3 Dimers on DNA Scaffolds.

PubMed

Cunningham, Paul D; Kim, Young C; Díaz, Sebastián A; Buckhout-White, Susan; Mathur, Divita; Medintz, Igor L; Melinger, Joseph S

2018-05-17

We examine the effect of electronic coupling on the optical properties of Cy3 dimers attached to DNA duplexes as a function of base pair (bp) separation using steady-state and time-resolved spectroscopy. For close Cy3-Cy3 separations, 0 and 1 bp between dyes, intermediate to strong electronic coupling is revealed by modulation of the absorption and fluorescence properties including spectral band shape, peak wavelength, and excited-state lifetime. Using a vibronic exciton model, we estimate coupling strengths of 150 and 266 cm -1 for the 1 and 0 bp separations, respectively, which are comparable to those found in natural light-harvesting complexes. For the strongest electronic coupling (0 bp separation), we observe that the absorption band shape is strongly affected by the base pairs that surround the dyes, where more strongly hydrogen-bonded G-C pairs produce a red-shifted absorption spectrum consistent with a J-type dimer. This effect is studied theoretically using molecular dynamics simulation, which predicts an in-line dye configuration that is consistent with the experimental J-type spectrum. When the Cy3 dimers are in a standard aqueous buffer, the presence of relatively strong electronic coupling is accompanied by decreased fluorescence lifetime, suggesting that it promotes nonradiative relaxation in cyanine dyes. However, we show that the use of a viscous solvent can suppress this nonradiative recombination and thereby restore the dimer fluorescent emission. Ultrafast transient absorption measurements of Cy3 dimers in both standard aqueous buffer and viscous glycerol buffer suggest that sufficiently strong electronic coupling increases the probability of excited-state relaxation through a dark state that is related to Cy3 torsional motion.

Degradation of poly(2-hydroxyethyl methacrylate) by gamma irradiation

NASA Astrophysics Data System (ADS)

Hill, David J. T.; O'Donnell, James H.; Pomery, Peter J.; Saadat, Giti

1996-11-01

Electron Spin Resinance (ESR) spectroscopy has been utilised to examine the effect of high energy radiation on poly(2-hydroxyethyl methacrylate) PHEMA. Radiation chemical yields ( G-values) for radicals were 1.7 and 1.2 for γ-irradiation at 77 K and ambient temperature, respectively. The ESR spectra at 77 and 300 K were simulated. The ESR spectrum at 77 K is a combination of six types of radicals ·CH 3, ·CH 2CH 2OH, COOCHCH 2OH, ·COO-, -CH- and ·CHO. However, after room temperature irradiation, the spectrum is a combination of methacrylate main chain scission radical and -CH-. The high stability of this radical at room temperature indicates the system is very rigid as a result of hydrogen bonding from the inherent side chain structure and radiation induced crosslinking due to labile hydrogen atoms in the side chain.

Lattice dynamics of Cs2NaYbF6 and Cs2NaYF6 elpasolites: Ab initio calculation

NASA Astrophysics Data System (ADS)

Chernyshev, V. A.; Petrov, V. P.; Nikiforov, A. E.; Zakir'yanov, D. O.

2015-06-01

The ab initio calculations of the crystal structure and the phonon spectrum of Cs2NaYbF6 and Cs2NaYF6 crystals with the elpasolite structure have been performed. The frequencies and types of fundamental vibrations have been determined. The calculations have been performed in the framework of the density functional theory using the molecular orbital method with hybrid functionals in the CRYSTAL09 program developed for the simulation of periodic structures. The outer 5 s and 5 p shells of the rare-earth ion have been described in Gaussian-type basis sets. The influence of inner shells, including 4 f electron shells, on the outer shells has been described using the pseudopotential. It has been shown that this approach allows the description of the phonon spectrum with the inclusion of the splitting of the longitudinal and transverse optical modes.

RefleX: X-ray absorption and reflection in active galactic nuclei for arbitrary geometries

NASA Astrophysics Data System (ADS)

Paltani, S.; Ricci, C.

2017-11-01

Reprocessed X-ray radiation carries important information about the structure and physical characteristics of the material surrounding the supermassive black hole (SMBH) in active galactic nuclei (AGN). We report here on a newly developed simulation platform, RefleX, which allows to reproduce absorption and reflection by quasi-arbitrary geometries. We show here the reliability of our approach by comparing the results of our simulations with existing spectral models such as pexrav, MYTorus and BNTorus. RefleX implements both Compton scattering on free electrons and Rayleigh scattering and Compton scattering on bound electrons. We show the effect of bound-electron corrections on a torus geometry simulated like in MYTorus. We release with this paper the RefleX executable, as well as RXTorus, a model that assumes absorption and reflection from a torus with a varying ratio of the minor to major axis of the torus. To allow major flexibility RXTorus is also distributed in three components: absorbed primary emission, scattered radiation and fluorescent lines. RXTorus is provided for different values of the abundance, and with (atomic configuration) or without (free-electron configuration) taking into account Rayleigh scattering and bound electrons. We apply the RXTorus model in both configurations on the XMM-Newton and NuSTAR spectrum of the Compton-thick AGN NGC 424 and find that the models are able to reproduce very well the observations, but that the assumption on the bound or free state of the electrons has significant consequences on the fit parameters. RefleX executable, user manual and example models are available at http://www.astro.unige.ch/reflex. A copy of the RefleX executable is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A31

Measurement of the cosmic ray e+ +e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope.

PubMed

Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Battelino, M; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bogaert, G; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Caliandro, G A; Cameron, R A; Caraveo, P A; Carlson, P; Casandjian, J M; Cecchi, C; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Cominsky, L R; Conrad, J; Cutini, S; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; Di Bernardo, G; do Couto E Silva, E; Drell, P S; Dubois, R; Dumora, D; Edmonds, Y; Farnier, C; Favuzzi, C; Focke, W B; Frailis, M; Fukazawa, Y; Funk, S; Fusco, P; Gaggero, D; Gargano, F; Gasparrini, D; Gehrels, N; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Glanzman, T; Godfrey, G; Grasso, D; Grenier, I A; Grondin, M-H; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hartman, R C; Hayashida, M; Hays, E; Hughes, R E; Jóhannesson, G; Johnson, A S; Johnson, R P; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocevski, D; Kuehn, F; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Massai, M M; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Moretti, E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Ozaki, M; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Pohl, M; Porter, T A; Profumo, S; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Schalk, T L; Sellerholm, A; Sgrò, C; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stephens, T E; Strickman, M S; Strong, A W; Suson, D J; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Tibolla, O; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Van Etten, A; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wallace, E; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M

2009-05-08

Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m;{2} sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.

The primary cosmic ray electron spectrum from 10 GeV to about 200 GeV

NASA Technical Reports Server (NTRS)

Silverberg, R. F.; Ormes, J. F.; Balasubrahmanyan, V. K.; Ryan, M. J.

1971-01-01

An ionization spectrometer consisting of 10.8 radiation lengths of tungsten and 35 radiation lengths of iron has been used to determine the energy spectrum of cosmic ray electrons above 10 GeV. The spectrometer was calibrated with electrons from 5.4 to 18 GeV and then flown at an altitude of 6 gm-cm/2 for 16 hours. Separation of electron initiated events from proton events was achieved by utilizing starting point distributions, the shower development in tungsten, and the energy deposited in the large thickness of iron absorber. The exponent of the differential energy spectrum of the electrons is -3.1 + or - 0.2 while the exponent of the background is consistent with the proton exponent of -2.7 + or -0.2.

Electronic and thermal properties of germanene and stanene by first-principles calculations

NASA Astrophysics Data System (ADS)

Jomehpour Zaveh, S.; Roknabadi, M. R.; Morshedloo, T.; Modarresi, M.

2016-03-01

The electronic, vibrational and thermal properties of germanene and stanene have been investigated based on density functional theory (DFT) and density functional perturbation theory (DFPT). The electronic band structure, total and partial density of states and phonon dispersion spectrum and states are analyzed. The phonon spectrum is positive for all modes in the first Brillouin zone and there is a phonon energy band gap between acoustic and optical modes which is around 50 cm-1 for both structure. The constant-volume specific heats of two structures are calculated by using phonon spectrum and density of states. The spin-orbit coupling (SOC) opens a direct energy band gap at the Dirac point, softens phonon spectrum and decreases phonon group velocity of ZA mode.

Simulation of external and internal electrostatic discharges at the spacecraft system test level

NASA Technical Reports Server (NTRS)

Whittlesey, A.; Leung, P.

1984-01-01

Environmental test activities concerned with space plasma-caused charging and discharing phenomena are discussed. It is pointed out that the origin of such an electrostatic discharge (ESD) is charging of spacecraft dielectrics by an energetic plasma in geosynchronous orbit, Jupiter's magnetosphere, or other similar space environments. In dealing with environmental testing problems, it is necessary to define the location and magnitude of any ESD's in preparation for a subsequent simulation of the given conditions. Questions of external and internal charging are discussed separately. The environmental hazard from an external discharge can be assessed by viewing the dielectric surface as one side of a parallel plate capacitor. In the case of internal charging, the level of environmental concern depends on the higher energy spectrum of the ambient electrons.

Ab initio calculation of the electronic absorption spectrum of liquid water

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

Martiniano, Hugo F. M. C.; Galamba, Nuno; Cabral, Benedito J. Costa, E-mail: ben@cii.fc.ul.pt

2014-04-28

The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are inmore » good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O–H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.« less

Galactic Cosmic Ray Simulator at the NASA Space Radiation Laboratory

NASA Technical Reports Server (NTRS)

Norbury, John W.; Slaba, Tony C.; Rusek, Adam

2015-01-01

The external Galactic Cosmic Ray (GCR) spectrum is significantly modified when it passes through spacecraft shielding and astronauts. One approach for simulating the GCR space radiation environment is to attempt to reproduce the unmodified, external GCR spectrum at a ground based accelerator. A possibly better approach would use the modified, shielded tissue spectrum, to select accelerator beams impinging on biological targets. NASA plans for implementation of a GCR simulator at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory will be discussed.

A NOVEL EMISSION SPECTRUM FROM A RELATIVISTIC ELECTRON MOVING IN A RANDOM MAGNETIC FIELD

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

Teraki, Yuto; Takahara, Fumio, E-mail: teraki@vega.ess.sci.osaka-u.ac.jp

2011-07-10

We numerically calculate the radiation spectrum from relativistic electrons moving in small-scale turbulent magnetic fields expected in high-energy astrophysical sources. Such a radiation spectrum is characterized by the strength parameter a = {lambda}{sub B} e|B|/mc {sup 2}, where {lambda}{sub B} is the length scale of the turbulent field. When a is much larger than the Lorentz factor of a radiating electron {gamma}, synchrotron radiation is realized, while a << 1 corresponds to the so-called jitter radiation regime. Because for 1 < a < {gamma} we cannot use either approximations, we should have recourse to the Lienard-Wiechert potential to evaluate themore » radiation spectrum, which is performed in this Letter. We generate random magnetic fields assuming Kolmogorov turbulence, inject monoenergetic electrons, solve the equation of motion, and calculate the radiation spectrum. We perform numerical calculations for several values of a with {gamma} = 10. We obtain various types of spectra ranging between jitter radiation and synchrotron radiation. For a {approx} 7, the spectrum takes a novel shape which had not been noticed up to now. It is like a synchrotron spectrum in the middle energy region, but in the low frequency region it is a broken power law and in the high frequency region an extra power-law component appears beyond the synchrotron cutoff. We give a physical explanation of these features.« less

Internal dosimetry through GATE simulations of preclinical radiotherapy using a melanin-targeting ligand

NASA Astrophysics Data System (ADS)

Perrot, Y.; Degoul, F.; Auzeloux, P.; Bonnet, M.; Cachin, F.; Chezal, J. M.; Donnarieix, D.; Labarre, P.; Moins, N.; Papon, J.; Rbah-Vidal, L.; Vidal, A.; Miot-Noirault, E.; Maigne, L.

2014-05-01

The GATE Monte Carlo simulation platform based on the Geant4 toolkit is under constant improvement for dosimetric calculations. In this study, we explore its use for the dosimetry of the preclinical targeted radiotherapy of melanoma using a new specific melanin-targeting radiotracer labeled with iodine 131. Calculated absorbed fractions and S values for spheres and murine models (digital and CT-scan-based mouse phantoms) are compared between GATE and EGSnrc Monte Carlo codes considering monoenergetic electrons and the detailed energy spectrum of iodine 131. The behavior of Geant4 standard and low energy models is also tested. Following the different authors’ guidelines concerning the parameterization of electron physics models, this study demonstrates an agreement of 1.2% and 1.5% with EGSnrc, respectively, for the calculation of S values for small spheres and mouse phantoms. S values calculated with GATE are then used to compute the dose distribution in organs of interest using the activity distribution in mouse phantoms. This study gives the dosimetric data required for the translation of the new treatment to the clinic.

Combined Modeling of Acceleration, Transport, and Hydrodynamic Response in Solar Flares. 1; The Numerical Model

NASA Technical Reports Server (NTRS)

Liu, Wei; Petrosian, Vahe; Mariska, John T.

2009-01-01

Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated the simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a -10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a non thermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.

Electron Spectrum of Nonlinear Cold Emission from a Metal under the Action of a Laser Shot

NASA Astrophysics Data System (ADS)

Golovinskii, P. A.; Mikhin, E. A.

2017-12-01

The nonlinear emission of electrons from a metal under the action of a femtosecond moderate-intensity laser pulse (laser shot) has been studied. A theoretical model of the process has been constructed based on the 1D nonstationary Schrödinger equation in the vacuum half-space with given boundary conditions for the electron wavefunction. This equation has been solved using the Laplace transformation. It has been assumed that the states of free electrons in a metal, which are described by the Sommerfeld theory of metals, are insignificantly influenced by the laser field. The energy spectrum of emitted electrons has been obtained, and its dependence on the parameters of the lased shot has been found. The calculated spectrum of nonlinear electron emission from a tungsten nanotip under the action of a 6.5-fs-long laser shot generating a field of 9.26 V/nm agrees with the experimental data.

Development of a radiographic method for measuring the discrete spectrum of the electron beam from a plasma focus device

NASA Astrophysics Data System (ADS)

Shamsian, Neda; Bidabadi, Babak Shirani; Pirjamadi, Hosein

2017-07-01

An indirect method is proposed for measuring the relative energy spectrum of the pulsed electron beam of a plasma focus device. The Bremsstrahlung x-ray, generated by the collision of electrons against the anode surface, was measured behind lead filters with various thicknesses using a radiographic film system. A matrix equation was considered in order to explain the relation between the x-ray dose and the spectral amplitudes of the electron beam. The electron spectrum of the device was measured at 0.6 mbar argon and 22 kV charging voltage, in four discrete energy intervals extending up to 500 keV. The results of the experiments show that most of the electrons are emitted in the 125-375 keV energy range and the spectral amplitude becomes negligible beyond 375 keV.

Fatigue failure of dental implants in simulated intraoral media.

PubMed

Shemtov-Yona, K; Rittel, D

2016-09-01

Metallic dental implants are exposed to various intraoral environments and repetitive loads during service. Relatively few studies have systematically addressed the potential influence of the environment on the mechanical integrity of the implants, which is therefore the subject of this study. Four media (groups) were selected for room temperature testing, namely dry air, saliva substitute, same with 250ppm of fluoride, and saline solution (0.9%). Monolithic Ti-6Al-4V implants were loaded until fracture, using random spectrum loading. The study reveals that the only aggressive medium of all is the saline solution, as it shortens significantly the spectrum fatigue life of the implants. The quantitative scanning electron fractographic analysis indicates that all the tested implants grew fatigue cracks of similar lengths prior to catastrophic fracture. However, the average crack growth rate in the saline medium was found to largely exceed that in other media, suggesting a decreased fracture toughness. The notion of a characteristic timescale for environmental degradation was proposed to explain the results of our spectrum tests that blend randomly low and high cycle fatigue. Random spectrum fatigue testing is powerful technique to assess and compare the mechanical performance of dental implants for various designs and/or environments. Copyright © 2016 Elsevier Ltd. All rights reserved.

Collisional Ion and Electron Scale Gyrokinetic Simulations in the Tokamak Pedestal

NASA Astrophysics Data System (ADS)

Belli, E. A.; Candy, J.; Snyder, P. B.

2016-10-01

A new gyrokinetic solver, CGYRO, has been developed for precise studies of high collisionality regimes, such as the H-mode pedestal and L-mode edge. Building on GYRO and NEO, CGYRO uses the same velocity-space coordinates as NEO to optimize the accuracy of the collision dynamics and allow for advanced operators beyond the standard Lorentz pitch-angle scattering model. These advanced operators include energy diffusion and finite-FLR collisional effects. The code is optimized for multiscale (coupled electron and ion turbulence scales) simulations, employing a new spatial discretization and array distribution scheme that targets scalability on next-generation (exascale) HPC systems. In this work, CGYRO is used to study the complex spectrum of modes in the pedestal region. The onset of the linear KBM with full collisional effects is assessed to develop an improved KBM/RBM model for EPED. The analysis is extended to high k to explore the role of electron-scale (ETG-range) physics. Comparisons with new analytic collisional theories are made. Inclusion of sonic toroidal rotation (including full centrifugal effects) for studies including heavy wall impurities is also reported. Work supported in part by the US DOE under DE-FC02-06ER54873 and DE-FC02-08ER54963.

The effect of plasma inhomogeneities on (i) radio emission generation by non-gyrotropic electron beams and (ii) particle acceleration by Langmuir waves

NASA Astrophysics Data System (ADS)

Tsiklauri, David

2015-04-01

Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [1]. Here recent progress in an alternative to the plasma emission model using Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts will be presented. In particular, (i) Fourier space drift (refraction) of non-gyrotropic electron beam-generated wave packets, caused by the density gradient [1,2], (ii) parameter space investigation of numerical runs [3], (iii) concurrent generation of whistler waves [4] and a separate problem of (iv) electron acceleration by Langmuir waves in a background magnetised plasma with an increasing density profile [5] will be discussed. In all considered cases the density inhomogeneity-induced wave refraction plays a crucial role. In the case of non-gyrotropic electron beam, the wave refraction transforms the generated wave packets from standing into freely escaping EM radiation. In the case of electron acceleration by Langmuir waves, a positive density gradient in the direction of wave propagation causes a decrease in the wavenumber, and hence a higher phase velocity vph = ω/k. The k-shifted wave is then subject to absorption by a faster electron by wave-particle interaction. The overall effect is an increased number of high energy electrons in the energy spectrum. [1] D. Tsiklauri, Phys. Plasmas 18, 052903 (2011); http://dx.doi.org/10.1063/1.3590928 [2] H. Schmitz, D. Tsiklauri, Phys. Plasmas 20, 062903 (2013); http://dx.doi.org/10.1063/1.4812453 [3] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 19, 112903 (2012); http://dx.doi.org/10.1063/1.4768429 [4] M. Skender, D. Tsiklauri, Phys. Plasmas 21, 042904 (2014); http://dx.doi.org/10.1063/1.4871723 [5] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 21, 012903 (2014); http://dx.doi.org/10.1063/1.4863494 This research is funded by the Leverhulme Trust Research Project Grant RPG-311

Comparative modelling of lower hybrid current drive with two launcher designs in the Tore Supra tokamak

NASA Astrophysics Data System (ADS)

Nilsson, E.; Decker, J.; Peysson, Y.; Artaud, J.-F.; Ekedahl, A.; Hillairet, J.; Aniel, T.; Basiuk, V.; Goniche, M.; Imbeaux, F.; Mazon, D.; Sharma, P.

2013-08-01

Fully non-inductive operation with lower hybrid current drive (LHCD) in the Tore Supra tokamak is achieved using either a fully active multijunction (FAM) launcher or a more recent ITER-relevant passive active multijunction (PAM) launcher, or both launchers simultaneously. While both antennas show comparable experimental efficiencies, the analysis of stability properties in long discharges suggest different current profiles. We present comparative modelling of LHCD with the two different launchers to characterize the effect of the respective antenna spectra on the driven current profile. The interpretative modelling of LHCD is carried out using a chain of codes calculating, respectively, the global discharge evolution (tokamak simulator METIS), the spectrum at the antenna mouth (LH coupling code ALOHA), the LH wave propagation (ray-tracing code C3PO), and the distribution function (3D Fokker-Planck code LUKE). Essential aspects of the fast electron dynamics in time, space and energy are obtained from hard x-ray measurements of fast electron bremsstrahlung emission using a dedicated tomographic system. LHCD simulations are validated by systematic comparisons between these experimental measurements and the reconstructed signal calculated by the code R5X2 from the LUKE electron distribution. An excellent agreement is obtained in the presence of strong Landau damping (found under low density and high-power conditions in Tore Supra) for which the ray-tracing model is valid for modelling the LH wave propagation. Two aspects of the antenna spectra are found to have a significant effect on LHCD. First, the driven current is found to be proportional to the directivity, which depends upon the respective weight of the main positive and main negative lobes and is particularly sensitive to the density in front of the antenna. Second, the position of the main negative lobe in the spectrum is different for the two launchers. As this lobe drives a counter-current, the resulting driven current profile is also different for the FAM and PAM launchers.

Explanation of the Knee-like Feature in the DAMPE Cosmic {e}^{-}+{e}^{+} Energy Spectrum

NASA Astrophysics Data System (ADS)

Fang, Kun; Bi, Xiao-Jun; Yin, Peng-Fei

2018-02-01

The DArk Matter Particle Explorer, a space-based high precision cosmic-ray detector, has just reported the new measurement of the total electron plus positron energy spectrum up to 4.6 TeV. A notable feature in the spectrum is the spectral break at ∼0.9 TeV, with the spectral index softening from ‑3.1 to ‑3.9. Such a feature is very similar to the knee at the cosmic nuclei energy spectrum. In this work, we propose that the knee-like feature can be explained naturally by assuming that the electrons are accelerated at the supernova remnants (SNRs) and released when the SNRs die out with lifetimes around 105 years. The cut-off energy of those electrons have already decreased to several TeV due to radiative cooling, which may induce the observed TeV spectral break. Another possibility is that the break is induced by a single nearby old SNR. Such a scenario may bring a large electron flux anisotropy that may be observable by the future detectors. We also show that a minor part of electrons escaping during the acceleration in young and nearby SNRs is able to contribute to a several TeV or higher energy region of the spectrum.

Formation and trapping of free radicals in irradiated purines: EPR and ENDOR of hypoxanthine derivatives studied as single crystals

NASA Astrophysics Data System (ADS)

Tokdemir, Sibel

Four different derivatives of hypoxanthine (hypoxanthine-HCl·H 2O, Na+·Inosine-·2.5H 2O, sodium inosine monophosphate, and calcium inosine monophosphate) were irradiated in the form of single crystals with the objective of identifying the radical products. To do so, magnetic resonance methods (EPR, ENDOR experiments and EPR spectrum simulations) were used to study radical products in crystals following x-irradiation at ˜10 K without warming, and under conditions of controlled warming. Also, computational chemistry methods were used in combination with the experimental methods to assist in identifying the radical products. Immediately following irradiation at 10 K, at least three different radicals were observed for hypoxanthine·HCl·H2O. R5.1 was identified at the product of electron addition followed by protonation of the parent at N3. R5.2 was identified as the product of electron loss followed by deprotonation at N7, and R5.3 was tentatively identified as the product of electron gain followed by protonation at 06. On warming to room temperature, three new radicals were observed: R6.1 and R6.3 were the products of net H addition to C8 and C2 respectively, while R6.2 was the product of OH addition to C8. At least four different radical products of Na+·Inosine - were detected immediately after irradiation at 10 K. R7.1 was identified as the electron-loss product of the parent hypoxanthine base, and R7.2 was identified as the product of net H-abstraction from C5 ' of the sugar. R7.3 and R7.4 were tentatively identified as the products of net H-addition to 06 (probably via electron addition followed by protonation), and the (doubly-negative) product of electron-gain, respectively. R7.5, the C8-H addition radical, was the only product detected on warming sodium inosine crystals to room temperature. Because the ENDOR spectra from sodium IMP irradiated at 10K were complex, it was possible to identify only two radicals. R8.1 was identified as the purine base electron-abstraction product, and R8.2 was identified as the 06 hydrogen-addition product. ENDOR spectra could be obtained from calcium IMP only at a few orientations. Thus, all radical identifications in this system are based on EPR spectrum simulations using likely radical structures based on results from other hypoxanthine-based systems.

Simulations of bremsstrahlung emission in ultra-intense laser interactions with foil targets

NASA Astrophysics Data System (ADS)

Vyskočil, Jiří; Klimo, Ondřej; Weber, Stefan

2018-05-01

Bremsstrahlung emission from interactions of short ultra-intense laser pulses with solid foils is studied using particle-in-cell (PIC) simulations. A module for simulating bremsstrahlung has been implemented in the PIC loop to self-consistently account for the dynamics of the laser–plasma interaction, plasma expansion, and the emission of gamma ray photons. This module made it possible to study emission from thin targets, where refluxing of hot electrons plays an important role. It is shown that the angular distribution of the emitted photons exhibits a four-directional structure with the angle of emission decreasing with the increase of the width of the target. Additionally, a collimated forward flash consisting of high energy photons has been identified in thin targets. The conversion efficiency of the energy of the laser pulse to the energy of the gamma rays rises with both the driving pulse intensity, and the thickness of the target. The amount of gamma rays also increases with the atomic number of the target material, despite a lower absorption of the driving laser pulse. The angular spectrum of the emitted gamma rays is directly related to the increase of hot electron divergence during their refluxing and its measurement can be used in experiments to study this process.

Measurements of the energy spectrum of electrons emanating from solid materials irradiated by a picosecond laser

DOE PAGES

Di Stefano, C. A.; Kuranz, C. C.; Seely, J. F.; ...

2015-04-01

Here, we present the results of experiments observing the properties of the electron stream generated laterally when a laser irradiates a metal. We also found that the directionality of the electrons is dependent upon their energies, with the higher-energy tail of the spectrum ( 1MeV and higher) being more narrowly focused. This behavior is likely due to the coupling of the electrons to the electric field of the laser. We performed these experiments by using the Titan laser to irradiate a metal wire, creating the electron stream of interest. These electrons propagate to nearby spectator wires of differing metals, causingmore » them to fluoresce at their characteristic K-shell energies. This fluorescence is recorded by a crystal spectrometer. By varying the distances between the wires, we are able to probe the divergence of the electron stream, while by varying the medium through which the electrons propagate (and hence the energy-dependence of electron attenuation), we are able to probe the energy spectrum of the stream.« less

Energy of atomic shakeoff electrons from positron decay of 37K

NASA Astrophysics Data System (ADS)

Behr, John; Fenker, Benjamin; Gorelov, Alexandre; Anholm, Melissa; Behling, Spencer; Mehlman, Michael; Melconian, Dan; Ashery, Danny; Gwinner, Gerald

2015-10-01

We have measured the low-energy atomic shakeoff electron spectrum from the β+ decay of 37K. We collect atomic electrons emitted from laser-cooled 37K using a nearly uniform electric field at low magnetic field into a position-sensitive microchannel plate. A coincidence with energetic β+s removes background. The differential position information translates to a differential electron energy spectrum. The energy spectrum from 1-100 eV is reproduced well by an analytic calculation for hydrogenic wavefunctions [Levinger PR 90 11 (1953)] using potassium quantum defects. Less than one percent of the electrons have energies higher than the 25 eV threshold for double DNA strand breaks, so relative biological effectiveness would not be altered by including these electrons. The average energy carried off by these electrons (a few eV) is smaller than expected from simple Thomas-Fermi estimates (65eV). Supported by NSERC, NRC through TRIUMF, U.S. D.O.E., State of Texas, Israel Science Foundation

Dual-mode MOS SOI nanoscale transistor serving as a building block for optical communication between blocks

NASA Astrophysics Data System (ADS)

Bendayan, Michael; Sabo, Roi; Zolberg, Roee; Mandelbaum, Yaakov; Chelly, Avraham; Karsenty, Avi

2017-02-01

We developed a new type of silicon MOSFET Quantum Well transistor, coupling both electronic and optical properties which should overcome the indirect silicon bandgap constraint, and serve as a future light emitting device in the range 0.8-2μm, as part of a new building block in integrated circuits allowing ultra-high speed processors. Such Quantum Well structure enables discrete energy levels for light recombination. Model and simulations of both optical and electric properties are presented pointing out the influence of the channel thickness and the drain voltage on the optical emission spectrum.

Monopole HOMs Dumping in the LCLS-II 1.3 GHz Structure

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

Lunin, Andrei; Khabiboulline, Timergali; Solyak, Nikolay

2017-05-01

Developing an upgrade of Linac Coherent Light Source (LCLS-II) is currently underway. The central part of LCLS-II is a continuous wave superconducting RF (CW SRF) electron linac. High order modes (HOMs) excited in SRF structures by passing beam may deteriorate beam quality and affect beam stability. In this paper we report the simulation results of monopole High Order Modes (HOM) spectrum in the 1.3 GHz accelerating structure. Optimum parameters of the HOM feedthrough are suggested for minimizing RF losses on the HOM antenna tip and for preserving an efficiency of monopole HOMs damping simultaneously.

Stellar and laboratory XUV/EUV line ratios in Fe XVIII and Fe XIX

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

Traebert, E.; Beiersdorfer, P.; Clementson, J.

2012-05-25

A so-called XUV excess has been suspected with the relative fluxes of Fe XVIII and Fe XIX lines observed in the XUV and EUV ranges of the spectrum of the star Capella as observed by the Chandra spacecraft, even after correction for interstellar absorption. This excess becomes apparent in the comparison of the observations with simulations of stellar spectra obtained using collisional-radiative models that employ, for example, the Atomic Plasma Emission Code (APEC) or the Flexible Atomic Code (FAC). We have addressed this problem by laboratory studies using the Livermore electron beam ion trap (EBIT).

Dissociative Excitation of Acetylene Induced by Electron Impact: Excitation-emission Cross-sections

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

Országh, Juraj; Danko, Marián; Čechvala, Peter

The optical emission spectrum of acetylene excited by monoenergetic electrons was studied in the range of 190–660 nm. The dissociative excitation and dissociative ionization associated with excitation of the ions initiated by electron impact were dominant processes contributing to the spectrum. The spectrum was dominated by the atomic lines (hydrogen Balmer series, carbon) and molecular bands (CH(A–X), CH(B–X), CH{sup +}(B–A), and C{sub 2}). Besides the discrete transitions, we have detected the continuum emission radiation of ethynyl radical C{sub 2}H(A–X). For most important lines and bands of the spectrum we have measured absolute excitation-emission cross sections and determined the energy thresholdsmore » of the particular dissociative channels.« less

Measurement of the Cosmic Ray e+ plus e- Spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope

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

Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.

Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m{sup 2}sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply-falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E{sup -3.0} and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.

Comparative characteristics of electron energy spectrum in PIG and arc type discharge plasmas

NASA Technical Reports Server (NTRS)

Romanyuk, L. I.; Suavilnyy, N. Y.

1978-01-01

The electron distribution functions relative to the velocity component directed along the magnetic field are compared for PIG and arc type discharges. The identity of these functions for the plasma region pierced by the primary electron beam and their difference in the peripheral part of the discharge are shown. It is concluded that the electron distribution function in the PIG type discharge is formed during one transit of the primary electron through the discharge gap. The mechanisms of electron energy spectrum formation in both the axis region and the peripheral region of the discharge are discussed.

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

Popovich, P.; Carter, T. A.; Friedman, B.

Numerical simulation of plasma turbulence in the Large Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991)] is presented. The model, implemented in the BOUndary Turbulence code [M. Umansky, X. Xu, B. Dudson et al., Contrib. Plasma Phys. 180, 887 (2009)], includes three-dimensional (3D) collisional fluid equations for plasma density, electron parallel momentum, and current continuity, and also includes the effects of ion-neutral collisions. In nonlinear simulations using measured LAPD density profiles but assuming constant temperature profile for simplicity, self-consistent evolution of instabilities and nonlinearly generated zonal flows results in a saturatedmore » turbulent state. Comparisons of these simulations with measurements in LAPD plasmas reveal good qualitative and reasonable quantitative agreement, in particular in frequency spectrum, spatial correlation, and amplitude probability distribution function of density fluctuations. For comparison with LAPD measurements, the plasma density profile in simulations is maintained either by direct azimuthal averaging on each time step, or by adding particle source/sink function. The inferred source/sink values are consistent with the estimated ionization source and parallel losses in LAPD. These simulations lay the groundwork for more a comprehensive effort to test fluid turbulence simulation against LAPD data.« less

The spectrum of the TiCl molecule in the 4200 A region

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

Phillips, J.G.; Davis, S.P.

1989-09-01

A detailed study of the TiCl spectrum between 4095 and 4200 A was made, and the presence of at least four electronic systems is reported. The wavelengths, wavenumbers, intensities, degradations, and characteristics of the observed band heads in the TiCl spectrum are listed. The J values and the intensities and wavelengths are given for the P and R branches of the four electronic systems. 5 refs.

The Effects of Low- and High-Energy Cutoffs on Solar Flare Microwave and Hard X-Ray Spectra

NASA Technical Reports Server (NTRS)

Holman, G. D.; Oegerle, William (Technical Monitor)

2002-01-01

Microwave and hard x-ray spectra provide crucial information about energetic electrons and their environment in solar flares. These spectra are becoming better determined with the Owens Valley Solar Array (OVSA) and the recent launch of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The proposed Frequency Agile Solar Radiotelescope (FASR) promises even greater advances in radio observations of solar flares. Both microwave and hard x-ray spectra are sensitive to cutoffs in the electron distribution function. The determination of the high-energy cutoff from these spectra establishes the highest electron energies produced by the acceleration mechanism, while determination of the low-energy cutoff is crucial to establishing the total energy in accelerated electrons. This paper will show computations of the effects of both high- and low-energy cutoffs on microwave and hard x-ray spectra. The optically thick portion of a microwave spectrum is enhanced and smoothed by a low-energy cutoff, while a hard x-ray spectrum is flattened below the cutoff energy. A high-energy cutoff steepens the microwave spectrum and increases the wavelength at which the spectrum peaks, while the hard x-ray spectrum begins to steepen at photon energies roughly an order of magnitude below the electron cutoff energy. This work discusses how flare microwave and hard x-ray spectra can be analyzed together to determine these electron cutoff energies. This work is supported in part by the NASA Sun-Earth Connection Program.

The Aircraft Infrared Measurements Guide

DTIC Science & Technology

1983-03-01

the infrared portion of the electromagnetic spectrum, but should include measure- ments across that portion of the spectrum using optical /electro... optical tech- nology. Comments should be addressed to: Commander/Director Office of Missile Electronic Warfare US Army Electronic Warfare Laboratory ATTN...58 Spatial Radiometer ................................................ 58 Seekers ( Nonimaging

[Calculating the stark broadening of welding arc spectra by Fourier transform method].

PubMed

Pan, Cheng-Gang; Hua, Xue-Ming; Zhang, Wang; Li, Fang; Xiao, Xiao

2012-07-01

It's the most effective and accurate method to calculate the electronic density of plasma by using the Stark width of the plasma spectrum. However, it's difficult to separate Stark width from the composite spectrum linear produced by several mechanisms. In the present paper, Fourier transform was used to separate the Lorentz linear from the spectrum observed, thus to get the accurate Stark width. And we calculated the distribution of the TIG welding arc plasma. This method does not need to measure arc temperature accurately, to measure the width of the plasma spectrum broadened by instrument, and has the function to reject the noise data. The results show that, on the axis, the electron density of TIG welding arc decreases with the distance from tungsten increasing, and changes from 1.21 X 10(17) cm(-3) to 1.58 x 10(17) cm(-3); in the radial, the electron density decreases with the distance from axis increasing, and near the tungsten zone the biggest electronic density is off axis.

Temperature dependence of the hydrated electron's excited-state relaxation. I. Simulation predictions of resonance Raman and pump-probe transient absorption spectra of cavity and non-cavity models

NASA Astrophysics Data System (ADS)

Zho, Chen-Chen; Farr, Erik P.; Glover, William J.; Schwartz, Benjamin J.

2017-08-01

We use one-electron non-adiabatic mixed quantum/classical simulations to explore the temperature dependence of both the ground-state structure and the excited-state relaxation dynamics of the hydrated electron. We compare the results for both the traditional cavity picture and a more recent non-cavity model of the hydrated electron and make definite predictions for distinguishing between the different possible structural models in future experiments. We find that the traditional cavity model shows no temperature-dependent change in structure at constant density, leading to a predicted resonance Raman spectrum that is essentially temperature-independent. In contrast, the non-cavity model predicts a blue-shift in the hydrated electron's resonance Raman O-H stretch with increasing temperature. The lack of a temperature-dependent ground-state structural change of the cavity model also leads to a prediction of little change with temperature of both the excited-state lifetime and hot ground-state cooling time of the hydrated electron following photoexcitation. This is in sharp contrast to the predictions of the non-cavity model, where both the excited-state lifetime and hot ground-state cooling time are expected to decrease significantly with increasing temperature. These simulation-based predictions should be directly testable by the results of future time-resolved photoelectron spectroscopy experiments. Finally, the temperature-dependent differences in predicted excited-state lifetime and hot ground-state cooling time of the two models also lead to different predicted pump-probe transient absorption spectroscopy of the hydrated electron as a function of temperature. We perform such experiments and describe them in Paper II [E. P. Farr et al., J. Chem. Phys. 147, 074504 (2017)], and find changes in the excited-state lifetime and hot ground-state cooling time with temperature that match well with the predictions of the non-cavity model. In particular, the experiments reveal stimulated emission from the excited state with an amplitude and lifetime that decreases with increasing temperature, a result in contrast to the lack of stimulated emission predicted by the cavity model but in good agreement with the non-cavity model. Overall, until ab initio calculations describing the non-adiabatic excited-state dynamics of an excess electron with hundreds of water molecules at a variety of temperatures become computationally feasible, the simulations presented here provide a definitive route for connecting the predictions of cavity and non-cavity models of the hydrated electron with future experiments.

Quantized impedance dealing with the damping behavior of the one-dimensional oscillator

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

Zhu, Jinghao; Zhang, Jing; Li, Yuan

2015-11-15

A quantized impedance is proposed to theoretically establish the relationship between the atomic eigenfrequency and the intrinsic frequency of the one-dimensional oscillator in this paper. The classical oscillator is modified by the idea that the electron transition is treated as a charge-discharge process of a suggested capacitor with the capacitive energy equal to the energy level difference of the jumping electron. The quantized capacitance of the impedance interacting with the jumping electron can lead the resonant frequency of the oscillator to the same as the atomic eigenfrequency. The quantized resistance reflects that the damping coefficient of the oscillator is themore » mean collision frequency of the transition electron. In addition, the first and third order electric susceptibilities based on the oscillator are accordingly quantized. Our simulation of the hydrogen atom emission spectrum based on the proposed method agrees well with the experimental one. Our results exhibits that the one-dimensional oscillator with the quantized impedance may become useful in the estimations of the refractive index and one- or multi-photon absorption coefficients of some nonmagnetic media composed of hydrogen-like atoms.« less

Quantized impedance dealing with the damping behavior of the one-dimensional oscillator

NASA Astrophysics Data System (ADS)

Zhu, Jinghao; Zhang, Jing; Li, Yuan; Zhang, Yong; Fang, Zhengji; Zhao, Peide; Li, Erping

2015-11-01

A quantized impedance is proposed to theoretically establish the relationship between the atomic eigenfrequency and the intrinsic frequency of the one-dimensional oscillator in this paper. The classical oscillator is modified by the idea that the electron transition is treated as a charge-discharge process of a suggested capacitor with the capacitive energy equal to the energy level difference of the jumping electron. The quantized capacitance of the impedance interacting with the jumping electron can lead the resonant frequency of the oscillator to the same as the atomic eigenfrequency. The quantized resistance reflects that the damping coefficient of the oscillator is the mean collision frequency of the transition electron. In addition, the first and third order electric susceptibilities based on the oscillator are accordingly quantized. Our simulation of the hydrogen atom emission spectrum based on the proposed method agrees well with the experimental one. Our results exhibits that the one-dimensional oscillator with the quantized impedance may become useful in the estimations of the refractive index and one- or multi-photon absorption coefficients of some nonmagnetic media composed of hydrogen-like atoms.

Turbulent FEL theory and experiment on ELSA at Bruyeres-le-Chatel

NASA Astrophysics Data System (ADS)

Chaix, P.; Guimbal, P.

1995-04-01

We consider the asymptotic behaviour of long pulse high current Compton free electron laser oscillators. It is known that if the current is high enough and the cavity losses low enough, sideband instabilities and non-linear mode couplings eventually lead to a strong broadening of the radiated spectrum, and to a strong efficiency enhancement. In this “post-sideband” regime, the electron dynamics along the wiggler is intrinsically stochastic, and the efficiency is due to chaotic diffusion of the electrons toward lower energies, rather than to standard synchrotron oscillations. This results in new scaling laws for saturation properties. We have obtained simple analytical estimates for the extracted efficiency and for the spectral width, in very good agreement with numerical simulations. The infrared ELSA free electron laser at Bruyères-le-Châtel has been used to obtain experimental evidence for these new scaling laws. In particular it has been verified that in the post-sideband regime, the ratio of the extracted efficiency to the relative spectral width is independent of the operating parameters, and close to 3/3 as predicted by theory.

Numerical modeling of laser-driven ion acceleration from near-critical gas targets

NASA Astrophysics Data System (ADS)

Tatomirescu, Dragos; Vizman, Daniel; d’Humières, Emmanuel

2018-06-01

In the past two decades, laser-accelerated ion sources and their applications have been intensely researched. Recently, it has been shown through experiments that proton beams with characteristics comparable to those obtained with solid targets can be obtained from gaseous targets. By means of particle-in-cell simulations, this paper studies in detail the effects of a near-critical density gradient on ion and electron acceleration after the interaction with ultra high intensity lasers. We can observe that the peak density of the gas jet has a significant influence on the spectrum features. As the gas jet density increases, so does the peak energy of the central quasi-monoenergetic ion bunch due to the increase in laser absorption while at the same time having a broadening effect on the electron angular distribution.

Hot electron induced NIR detection in CdS films.

PubMed

Sharma, Alka; Kumar, Rahul; Bhattacharyya, Biplab; Husale, Sudhir

2016-03-11

We report the use of random Au nanoislands to enhance the absorption of CdS photodetectors at wavelengths beyond its intrinsic absorption properties from visible to NIR spectrum enabling a high performance visible-NIR photodetector. The temperature dependent annealing method was employed to form random sized Au nanoparticles on CdS films. The hot electron induced NIR photo-detection shows high responsivity of ~780 mA/W for an area of ~57 μm(2). The simulated optical response (absorption and responsivity) of Au nanoislands integrated in CdS films confirms the strong dependence of NIR sensitivity on the size and shape of Au nanoislands. The demonstration of plasmon enhanced IR sensitivity along with the cost-effective device fabrication method using CdS film enables the possibility of economical light harvesting applications which can be implemented in future technological applications.

The Existence of a Designer Al=Al Double Bond in the LiAl2 H4- Cluster Formed by Electronic Transmutation.

PubMed

Lundell, Katie A; Zhang, Xinxing; Boldyrev, Alexander I; Bowen, Kit H

2017-12-22

The Al=Al double bond is elusive in chemistry. Herein we report the results obtained via combined photoelectron spectroscopy and ab initio studies of the LiAl 2 H 4 - cluster that confirm the formation of a conventional Al=Al double bond. Comprehensive searches for the most stable structures of the LiAl 2 H 4 - cluster have shown that the global minimum isomer I possesses a geometric structure which resembles that of Si 2 H 4 , demonstrating a successful example of the transmutation of Al atoms into Si atoms by electron donation. Theoretical simulations of the photoelectron spectrum discovered the coexistence of two isomers in the ion beam, including the one with the Al=Al double bond. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Higher harmonics generation in relativistic electron beam with virtual cathode

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

Kurkin, S. A., E-mail: KurkinSA@gmail.com; Badarin, A. A.; Koronovskii, A. A.

2014-09-15

The study of the microwave generation regimes with intense higher harmonics taking place in a high-power vircator consisting of a relativistic electron beam with a virtual cathode has been made. The characteristics of these regimes, in particular, the typical spectra and their variations with the change of the system parameters (beam current, the induction of external magnetic field) as well as physical processes occurring in the system have been analyzed by means of 3D electromagnetic simulation. It has been shown that the system under study demonstrates the tendency to the sufficient growth of the amplitudes of higher harmonics in themore » spectrum of current oscillations in the VC region with the increase of beam current. The obtained results allow us to consider virtual cathode oscillators as promising high power mmw-to-THz sources.« less

A Micropulse eye-safe all-fiber molecular backscatter coherent temperature lidar

NASA Astrophysics Data System (ADS)

Abari, Cyrus F.; Chu, Xinzhao; Mann, Jakob; Spuler, Scott

2016-06-01

In this paper, we analyze the performance of an all-fiber, micropulse, 1.5 μm coherent lidar for remote sensing of atmospheric temperature. The proposed system benefits from the recent advances in optics/electronics technology, especially an all-fiber image-reject homodyne receiver, where a high resolution spectrum in the baseband can be acquired. Due to the presence of a structured spectra resulting from the spontaneous Rayleigh-Brillouine scattering, associated with the relevant operating regimes, an accurate estimation of the temperature can be carried out. One of the main advantages of this system is the removal of the contaminating Mie backscatter signal by electronic filters at the baseband (before signal conditioning and amplification). The paper presents the basic concepts as well as a Monte-Carlo system simulation as the proof of concept.

Nanodosimetry of (125)I Auger electrons.

PubMed

Bantsar, Aliaksandr; Pszona, Stanislaw

2012-12-01

The nanodosimetric description of the radiation action of Auger electrons on nitrogen targets of nanometric size is presented. Experimental microdosimetry at nanometer scale for Auger electrons has been accomplished with the set-up called Jet Counter. This consists of a pulse-operated valve which injects an expanding nitrogen jet into an interaction chamber where a gaseous sensitive volume of cylindrical shape is created. The ionization cluster size distributions (ICSD) created by Auger electrons emitted by (125)I while crossing a nanometer-sized volume have been measured. The ICSD for the sensitive volumes corresponding to 3 and 12 nm in diameter (in unit density 1 g/cm(3)) irradiated by electrons emitted by a (125)I source were collected and compared with the corresponding Monte Carlo (MC) simulation. The preliminary results of the experiments with Auger electrons of (125)I interacting with a nitrogen jet having nanometric size comparable to a deoxyribonucleic acid (DNA) and nucleosome, showing the discrete spectrum of ICSD with extended cluster size, are described. The presented paper describes for the first time the nanodosimetric experiments with Auger electrons emitted by (125)I. A set of the new descriptors of the radiation quality describing the radiation effect at nanometer level is proposed. The ICSD were determined for the first time for an Auger emitter of (125)I.

Electron impact excitation of coronene

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

Khakoo, M.A.; Ratliff, J.M.; Trajmar, S.

1990-12-15

A preliminary study of the electron-impact excitation of thermally evaporated coronene at 550{degree} C was carried out using electron-energy-loss spectroscopy. Measurements of the energy-loss spectra of coronene at high (100 eV) and low (5--20 eV) impact energies are presented. One of the high-energy spectra was converted to an apparent generalized oscillator strength spectrum and compared to the photoabsorption spectrum of coronene. Observations concerning vibrational excitation of coronene by electron impact are also presented and discussed.

Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species

DOE PAGES

Norell, Jesper; Jay, Raphael M.; Hantschmann, Markus; ...

2018-02-20

Here, we describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L 3-edge RIXS in the ferricyanide complex Fe(CN) 6 3-, we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject themore » presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.« less

Directed Field Ionization: A Genetic Algorithm for Evolving Electric Field Pulses

NASA Astrophysics Data System (ADS)

Kang, Xinyue; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

2017-04-01

When an ionizing electric field pulse is applied to a Rydberg atom, the electron's amplitude traverses many avoided crossings among the Stark levels as the field increases. The resulting superposition determines the shape of the time resolved field ionization spectrum at a detector. An engineered electric field pulse that sweeps back and forth through avoided crossings can control the phase evolution so as to determine the electron's path through the Stark map. In the region of n = 35 in rubidium there are hundreds of potential avoided crossings; this yields a large space of possible pulses. We use a genetic algorithm to search this space and evolve electric field pulses to direct the ionization of the Rydberg electron in rubidium. We present the algorithm along with a comparison of simulated and experimental results. This work was supported by the National Science Foundation under Grants No. 1607335 and No. 1607377 and used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant Number OCI-1053575.

Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species

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

Norell, Jesper; Jay, Raphael M.; Hantschmann, Markus

Here, we describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L 3-edge RIXS in the ferricyanide complex Fe(CN) 6 3-, we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject themore » presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.« less

Electronically controlled rejections of spoof surface plasmons polaritons

NASA Astrophysics Data System (ADS)

Zhou, Yong Jin; Xiao, Qian Xun

2017-03-01

We have proposed and experimentally demonstrated a band-notched surface plasmonic filter, which is composed of an ultra-wide passband plasmonic filter with a simple C-shaped ring on the back of the substrate. Enhanced narrowband or broadband rejections of spoof surface plasmon polaritons (SPPs) can be achieved with double C-shaped rings in the propagation or transverse direction. By mounting active components across the slit cut in the C-shaped ring, dynamic control of rejection of spoof SPPs can be accomplished. Both the rejection of spoof SPPs and the rejection bandwidth can be controlled when the Schottky barrier diode is forward-biased or reverse-biased. The frequency spectrum of the rejection band can be electronically adjusted by tuning the applied bias voltage across the varactor diode. Both simulated and measured results agree well and demonstrate dynamic control of propagation of spoof SPPs at the microwave frequencies. Such electronically controllable devices could find more applications in advanced plasmonic integrated functional circuits in microwave and terahertz frequencies.

Theory of terahertz emission from femtosecond-laser-induced microplasmas

NASA Astrophysics Data System (ADS)

Thiele, I.; Nuter, R.; Bousquet, B.; Tikhonchuk, V.; Skupin, S.; Davoine, X.; Gremillet, L.; Bergé, L.

2016-12-01

We present a theoretical investigation of terahertz (THz) generation in laser-induced gas plasmas. The work is strongly motivated by recent experimental results on microplasmas, but our general findings are not limited to such a configuration. The electrons and ions are created by tunnel ionization of neutral atoms, and the resulting plasma is heated by collisions. Electrons are driven by electromagnetic, convective, and diffusive sources and produce a macroscopic current which is responsible for THz emission. The model naturally includes both ionization current and transition-Cherenkov mechanisms for THz emission, which are usually investigated separately in the literature. The latter mechanism is shown to dominate for single-color multicycle laser pulses, where the observed THz radiation originates from longitudinal electron currents. However, we find that the often discussed oscillations at the plasma frequency do not contribute to the THz emission spectrum. In order to predict the scaling of the conversion efficiency with pulse energy and focusing conditions, we propose a simplified description that is in excellent agreement with rigorous particle-in-cell simulations.

Development of lithium doped radiation resistent solar cells

NASA Technical Reports Server (NTRS)

Berman, P. A.

1972-01-01

Lithium-doped solar cells have been fabricated with initial lot efficiencies averaging 11.9 percent in an air mass zero (AMO) solar simulator and a maximum observed efficiency of 12.8 percent. The best lithium-doped solar cells are approximately 15 percent higher in maximum power than state-of-the-art n-p cells after moderate to high fluences of 1-MeV electrons and after 6-7 months exposure to low flux irradiation by a Sr-90 beta source, which approximates the electron spectrum and flux associated with near Earth space. Furthermore, lithium-doped cells were found to degrade at a rate only one tenth that of state-of-the-art n-p cells under 28-MeV electron irradiation. Excellent progress has been made in quantitative predictions of post-irradiation current-voltage characteristics as a function of cell design by means of capacitance-voltage measurements, and this information has been used to achieve further improvements in lithium-doped cell design.

Microscopic Perspective on Photovoltaic Reciprocity in Ultrathin Solar Cells

NASA Astrophysics Data System (ADS)

Aeberhard, Urs; Rau, Uwe

2017-06-01

The photovoltaic reciprocity theory relates the electroluminescence spectrum of a solar cell under applied bias to the external photovoltaic quantum efficiency of the device as measured at short circuit conditions. Its derivation is based on detailed balance relations between local absorption and emission rates in optically isotropic media with nondegenerate quasiequilibrium carrier distributions. In many cases, the dependence of density and spatial variation of electronic and optical device states on the point of operation is modest and the reciprocity relation holds. In nanostructure-based photovoltaic devices exploiting confined modes, however, the underlying assumptions are no longer justifiable. In the case of ultrathin absorber solar cells, the modification of the electronic structure with applied bias is significant due to the large variation of the built-in field. Straightforward use of the external quantum efficiency as measured at short circuit conditions in the photovoltaic reciprocity theory thus fails to reproduce the electroluminescence spectrum at large forward bias voltage. This failure is demonstrated here by numerical simulation of both spectral quantities at normal incidence and emission for an ultrathin GaAs p -i -n solar cell using an advanced quantum kinetic formalism based on nonequilibrium Green's functions of coupled photons and charge carriers. While coinciding with the semiclassical relations under the conditions of their validity, the theory provides a consistent microscopic relationship between absorption, emission, and charge carrier transport in photovoltaic devices at arbitrary operating conditions and for any shape of optical and electronic density of states.

Microscopic Perspective on Photovoltaic Reciprocity in Ultrathin Solar Cells.

PubMed

Aeberhard, Urs; Rau, Uwe

2017-06-16

The photovoltaic reciprocity theory relates the electroluminescence spectrum of a solar cell under applied bias to the external photovoltaic quantum efficiency of the device as measured at short circuit conditions. Its derivation is based on detailed balance relations between local absorption and emission rates in optically isotropic media with nondegenerate quasiequilibrium carrier distributions. In many cases, the dependence of density and spatial variation of electronic and optical device states on the point of operation is modest and the reciprocity relation holds. In nanostructure-based photovoltaic devices exploiting confined modes, however, the underlying assumptions are no longer justifiable. In the case of ultrathin absorber solar cells, the modification of the electronic structure with applied bias is significant due to the large variation of the built-in field. Straightforward use of the external quantum efficiency as measured at short circuit conditions in the photovoltaic reciprocity theory thus fails to reproduce the electroluminescence spectrum at large forward bias voltage. This failure is demonstrated here by numerical simulation of both spectral quantities at normal incidence and emission for an ultrathin GaAs p-i-n solar cell using an advanced quantum kinetic formalism based on nonequilibrium Green's functions of coupled photons and charge carriers. While coinciding with the semiclassical relations under the conditions of their validity, the theory provides a consistent microscopic relationship between absorption, emission, and charge carrier transport in photovoltaic devices at arbitrary operating conditions and for any shape of optical and electronic density of states.

Spectral mismatch and solar simulator quality factor in advanced LED solar simulators

NASA Astrophysics Data System (ADS)

Scherff, Maximilian L. D.; Nutter, Jason; Fuss-Kailuweit, Peter; Suthues, Jörn; Brammer, Torsten

2017-08-01

Solar cell simulators based on light emitting diodes (LED) have the potential to achieve a large potential market share in the next years. As advantages they can provide a short and long time stable spectrum, which fits very well to the global AM1.5g reference spectrum. This guarantees correct measurements during the flashes and throughout the light engines’ life span, respectively. Furthermore, a calibration with a solar cell type of different spectral response (SR) as well as the production of solar cells with varying SR in between two calibrations does not affect the correctness of the measurement result. A high quality 21 channel LED solar cell spectrum is compared to former study comprising a standard modified xenon spectrum light source. It is shown, that the spectrum of the 21-channel-LED light source performs best for all examined cases.

Numerical analysis of the Anderson localization

NASA Astrophysics Data System (ADS)

Markoš, P.

2006-10-01

The aim of this paper is to demonstrate, by simple numerical simulations, the main transport properties of disordered electron systems. These systems undergo the metal insulator transition when either Fermi energy crosses the mobility edge or the strength of the disorder increases over critical value. We study how disorder affects the energy spectrum and spatial distribution of electronic eigenstates in the diffusive and insulating regime, as well as in the critical region of the metal-insulator transition. Then, we introduce the transfer matrix and conductance, and we discuss how the quantum character of the electron propagation influences the transport properties of disordered samples. In the weakly disordered systems, the weak localization and anti-localization as well as the universal conductance fluctuation are numerically simulated and discussed. The localization in the one dimensional system is described and interpreted as a purely quantum effect. Statistical properties of the conductance in the critical and localized regimes are demonstrated. Special attention is given to the numerical study of the transport properties of the critical regime and to the numerical verification of the single parameter scaling theory of localization. Numerical data for the critical exponent in the orthogonal models in dimension 2 < d, ≤ 5 are compared with theoretical predictions. We argue that the discrepancy between the theory and numerical data is due to the absence of the self-averaging of transmission quantities. This complicates the analytical analysis of the disordered systems. Finally, theoretical methods of description of weakly disordered systems are explained and their possible generalization to the localized regime is discussed. Since we concentrate on the one-electron propagation at zero temperature, no effects of electron-electron interaction and incoherent scattering are discussed in the paper.

Tuning the electrical and optical anisotropy of a monolayer black phosphorus magnetic superlattice

NASA Astrophysics Data System (ADS)

Li, X. J.; Yu, J. H.; Luo, K.; Wu, Z. H.; Yang, W.

2018-04-01

We investigate theoretically the effects of modulated periodic perpendicular magnetic fields on the electronic states and optical absorption spectrum in monolayer black phosphorus (phosphorene). We demonstrate that different phosphorene magnetic superlattice (PMS) orientations can give rise to distinct energy spectra, i.e. tuning the intrinsic electronic anisotropy. Rashba spin-orbit coupling (RSOC) develops a spin-splitting energy dispersion in this phosphorene magnetic superlattice. Anisotropic momentum-dependent carrier distributions along/perpendicular to the magnetic strips are demonstrated. The manipulations of these exotic electronic properties by tuning superlattice geometry, magnetic field and the RSOC term are addressed systematically. Accordingly, we find bright-to-dark transitions in the ground-state electron-hole pair transition rate spectrum and the PMS orientation-dependent anisotropic optical absorption spectrum. This feature offers us a practical way of modulating the electronic anisotropy in phosphorene by magnetic superlattice configurations and detecting this modulation capability by using an optical technique.

Theory of Parabolic Arcs in Interstellar Scintillation Spectra

NASA Astrophysics Data System (ADS)

Cordes, James M.; Rickett, Barney J.; Stinebring, Daniel R.; Coles, William A.

2006-01-01

Interstellar scintillation (ISS), observed as time variation in the intensity of a compact radio source, is caused by small-scale structure in the electron density of the interstellar plasma. Dynamic spectra of ISS show modulation in radio frequency and time. Here we relate the (two-dimensional) power spectrum of the dynamic spectrum-the secondary spectrum-to the scattered image of the source. Recent work has identified remarkable parabolic arcs in secondary spectra. Each point in a secondary spectrum corresponds to interference between points in the scattered image with a certain Doppler shift and a certain delay. The parabolic arc corresponds to the quadratic relation between differential Doppler shift and delay through their common dependence on scattering angle. We show that arcs will occur in all media that scatter significant power at angles larger than the rms angle. Thus, effects such as source diameter, steep spectra, and dissipation scales, which truncate high angle scattering, also truncate arcs. Arcs are equally visible in simulations of nondispersive scattering. They are enhanced by anisotropic scattering when the spatial structure is elongated perpendicular to the velocity. In weak scattering the secondary spectrum is directly mapped from the scattered image, and this mapping can be inverted. We discuss additional observed phenomena including multiple arcs and reverse arclets oriented oppositely to the main arc. These phenomena persist for many refractive scattering times, suggesting that they are due to large-scale density structures, rather than low-frequency components of Kolmogorov turbulence.

Simulation, Theory, and Observations of the Spectrum of the Rayleigh-Taylor Instability due to Laser Imprint of Planar Targets

NASA Astrophysics Data System (ADS)

Keskinen, M. J.; Karasik, Max; Bates, J. W.; Schmitt, A. J.

2006-10-01

A limitation on the efficiency of high gain direct drive inertial confinement fusion is the extent of pellet disruption caused by the Rayleigh-Taylor (RT) instability. The RT instability can be seeded by pellet surface irregularities and/or laser imprint nonuniformities. It is important to characterize the evolution of the RT instability, e.g., the k-spectrum of areal mass. In this paper we study the time-dependent evolution of the spectrum of the Rayleigh-Taylor instability due to laser imprint in planar targets. This is achieved using the NRL FAST hydrodynamic simulation code together with analytical models. It is found that the optically smoothed laser imprint-driven RT spectrum develops into an inverse power law in k-space after several linear growth times. FAST simulation code results are compared with recent NRL Nike KrF laser experimental data. An analytical model, which is a function of Froude and Atwood numbers, is derived for the RT spectrum and favorably compared with both FAST simulation and Nike observations.

Hydrogen Balmer Line Broadening in Solar and Stellar Flares

NASA Technical Reports Server (NTRS)

Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han; Tremblay, Pier-Emmanuel; Brown, Stephen; Carlsson, Mats; Osten, Rachel A.; Wisniewski, John P.; Hawley, Suzanne L.

2017-01-01

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigt profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a 'multithread' model improves the agreement with the observations. We revisit the three component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a 'hot spot' atmosphere heated by an ultra relativistic electron beam with reasonable filling factors: approximately 0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.

The electromagnetic ram action of the plasma focus as a paradigm for the generation of cosmic rays and the gigantic jets in active galaxies

NASA Technical Reports Server (NTRS)

Bostick, W. H.; Nardi, V.

1985-01-01

Recent measurements of the energy spectrum of the plasma-focus-generated deuteron beam yield as spectrum of the form N(E)=(approx.) E to the -2.7 for 1MeV E 13 MeV. Other measurements show that the beta 1 electron beam which is generated simultaneously with the deuteron beam is interrupted into segments of spacing 25ps and duration approximately 4ps. A stuttering-electro-magnetic-ram (ser) model of the plasma focus in proposed which is similar to Raudorf's electronic ram which produces a similar spectrum for an electron beam for 1Mev E 10MeV. It is proposed that the cosmic ray spectrum and the giganic galactic jets are both generated by ser action near the centers of active galaxies.

The electromagnetic Ram action of the plasma focus as a paradigm for the generation of cosmic rays and the gigantic jets in active galaxies

NASA Astrophysics Data System (ADS)

Bostick, W. H.; Nardi, V.

1985-08-01

Recent measurements of the energy spectrum of the plasma-focus-generated deuteron beam yield as spectrum of the form N(E)=(approx.) E to the -2.7 for 1MeV E 13 MeV. Other measurements show that the beta 1 electron beam which is generated simultaneously with the deuteron beam is interrupted into segments of spacing 25ps and duration approximately 4ps. A stuttering-electro-magnetic-ram (ser) model of the plasma focus in proposed which is similar to Raudorf's electronic ram which produces a similar spectrum for an electron beam for 1Mev E 10MeV. It is proposed that the cosmic ray spectrum and the giganic galactic jets are both generated by ser action near the centers of active galaxies.

Variability of the Magnetic Field Power Spectrum in the Solar Wind at Electron Scales

NASA Astrophysics Data System (ADS)

Roberts, Owen Wyn; Alexandrova, O.; Kajdič, P.; Turc, L.; Perrone, D.; Escoubet, C. P.; Walsh, A.

2017-12-01

At electron scales, the power spectrum of solar-wind magnetic fluctuations can be highly variable and the dissipation mechanisms of the magnetic energy into the various particle species is under debate. In this paper, we investigate data from the Cluster mission’s STAFF Search Coil magnetometer when the level of turbulence is sufficiently high that the morphology of the power spectrum at electron scales can be investigated. The Cluster spacecraft sample a disturbed interval of plasma where two streams of solar wind interact. Meanwhile, several discontinuities (coherent structures) are seen in the large-scale magnetic field, while at small scales several intermittent bursts of wave activity (whistler waves) are present. Several different morphologies of the power spectrum can be identified: (1) two power laws separated by a break, (2) an exponential cutoff near the Taylor shifted electron scales, and (3) strong spectral knees at the Taylor shifted electron scales. These different morphologies are investigated by using wavelet coherence, showing that, in this interval, a clear break and strong spectral knees are features that are associated with sporadic quasi parallel propagating whistler waves, even for short times. On the other hand, when no signatures of whistler waves at ∼ 0.1{--}0.2{f}{ce} are present, a clear break is difficult to find and the spectrum is often more characteristic of a power law with an exponential cutoff.

Measurement of the Cosmic Ray e + + e - Spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope

DOE PAGES

Abdo, A. A.

2009-05-04

Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m 2 sr at 300 GeV. Building on the gamma-ray analysis, we have developed in this paper an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E -3.0 and does not exhibit prominent spectral features. Finally, interpretations in terms of a conventional diffusive model as well as a potential local extra componentmore » are briefly discussed.« less

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

Xue, Haizhou; Zhang, Yanwen; Zhu, Zihua

Single crystalline 6H-SiC samples were irradiated at 150 K using 2MeV Pt ions. Local volume swelling is determined by electron energy loss spectroscopy (EELS), a nearly sigmoidal dependence with irradiation dose is observed. The disorder profiles and ion distribution are determined by Rutherford backscattering spectrometry (RBS), transmission electron microscopy and secondary ion mass spectrum. Since the volume swelling reaches 12% over the damage region under high ion fluence, lattice expansion is considered and corrected during the data analysis of RBS spectra to obtain depth profiles. Projectile and damage profiles are estimated by SRIM (Stopping and Range of Ions in Matter).more » Comparing with the measured profiles, SRIM code significantly overestimates the electronic stopping power for the slow heavy Pt ions, and large derivations are observed in the predicted ion distribution and the damage profiles. Utilizing the reciprocity method that is based on the invariance of the inelastic excitation in ion atom collisions against interchange of projectile and target, much lower electronic stopping is deduced. A simple approach based on reducing the density of SiC target in SRIM simulation is proposed to compensate the overestimated SRIM electronic stopping power values. Better damage profile and ion range are predicted.« less

OBSERVATIONS OF HIGH-ENERGY COSMIC-RAY ELECTRONS FROM 30 GeV TO 3 TeV WITH EMULSION CHAMBERS

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

Kobayashi, T.; Komori, Y.; Yoshida, K.

2012-12-01

We have performed a series of cosmic-ray electron observations using balloon-borne emulsion chambers since 1968. While we previously reported the results from subsets of the exposures, the final results of the total exposures up to 2001 are presented here. Our successive experiments have yielded a total exposure of 8.19 m{sup 2} sr day at altitudes of 4.0-9.4 g cm{sup -2}. The performance of the emulsion chambers was examined by accelerator beam tests and Monte Carlo simulations, and the on-board calibrations were carried out by using the flight data. In this work, we present the cosmic-ray electron spectrum in the energymore » range from 30 GeV to 3 TeV at the top of the atmosphere, which is well represented by a power-law function with an index of -3.28 {+-} 0.10. The observed data can also be interpreted in terms of diffusive propagation models. The evidence of cosmic-ray electrons up to 3 TeV suggests the existence of cosmic-ray electron sources at distances within {approx}1 kpc and times within {approx}1 Multiplication-Sign 10{sup 5} yr ago.« less

Spectroscopic and density functional theory studies of 5,7,3',5'-tetrahydroxyflavanone from the leaves of Olea ferruginea.

PubMed

Hashmi, Muhammad Ali; Khan, Afsar; Ayub, Khurshid; Farooq, Umar

2014-07-15

5,7,3',5'-Tetrahydroxyflavanone (1) was isolated from the leaves of Olea ferruginea and a theoretical model was developed for obtaining the electronic and spectroscopic properties of 1. The geometric and electronic properties were calculated at B3LYP/6-311 G (d, p) level of Density Functional Theory (DFT). The theoretical data was in good agreement with the experimental one. The optimized geometric parameters of compound 1 were calculated for the first time. The theoretical vibrational frequencies of 1 were found to correlate with the experimental IR spectrum after a scaling factor of 0.9811. The UV and NMR spectral data computed theoretically were in good agreement with the experimental data. Electronic properties of the compound i.e., ionization potential (IP), electron affinity (EA), coefficients of HOMO and LUMO were estimated computationally for the first time which can be used to explain its antioxidant as well as other related activities and more active sites on it. The intermolecular interactions and their effects on IR frequencies, electronic and geometric parameters were simulated using water molecule as a model for hydrogen bonding with flavonoid hydroxyl groups. Copyright © 2014 Elsevier B.V. All rights reserved.

Spectroscopic and density functional theory studies of 5,7,3‧,5‧-tetrahydroxyflavanone from the leaves of Olea ferruginea

NASA Astrophysics Data System (ADS)

Hashmi, Muhammad Ali; Khan, Afsar; Ayub, Khurshid; Farooq, Umar

2014-07-01

5,7,3‧,5‧-Tetrahydroxyflavanone (1) was isolated from the leaves of Olea ferruginea and a theoretical model was developed for obtaining the electronic and spectroscopic properties of 1. The geometric and electronic properties were calculated at B3LYP/6-311 G (d, p) level of Density Functional Theory (DFT). The theoretical data was in good agreement with the experimental one. The optimized geometric parameters of compound 1 were calculated for the first time. The theoretical vibrational frequencies of 1 were found to correlate with the experimental IR spectrum after a scaling factor of 0.9811. The UV and NMR spectral data computed theoretically were in good agreement with the experimental data. Electronic properties of the compound i.e., ionization potential (IP), electron affinity (EA), coefficients of HOMO and LUMO were estimated computationally for the first time which can be used to explain its antioxidant as well as other related activities and more active sites on it. The intermolecular interactions and their effects on IR frequencies, electronic and geometric parameters were simulated using water molecule as a model for hydrogen bonding with flavonoid hydroxyl groups.

High-energy electrons from the muon decay in orbit: Radiative corrections

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

Szafron, Robert; Czarnecki, Andrzej

2015-12-07

We determine the Ο(α) correction to the energy spectrum of electrons produced in the decay of muons bound in atoms. We focus on the high-energy end of the spectrum that constitutes a background for the muon-electron conversion and will be precisely measured by the upcoming experiments Mu2e and COMET. As a result, the correction suppresses the background by about 20%.

A Diffusion Cloud Chamber Study of Very Slow Mesons. II. Beta Decay of the Muon

DOE R&D Accomplishments Database

Lederman, L. M.; Sargent, C. P.; Rinehart, M.; Rogers, K.

1955-03-01

The spectrum of electrons arising from the decay of the negative mu meson has been determined. The muons are arrested in the gas of a high pressure hydrogen filled diffusion cloud chamber. The momenta of the decay electrons are determined from their curvature in a magnetic field of 7750 gauss. The spectrum of 415 electrons has been analyzed according to the theory of Michel.

A photoelectrochemical immunosensor for detection of α-fetoprotein based on Au-ZnO flower-rod heterostructures

NASA Astrophysics Data System (ADS)

Han, Zhizhong; Luo, Min; Chen, Li; Chen, Jinghua; Li, Chunyan

2017-04-01

In this work, a novel label free photoelectrochemical (PEC) immunosensor has been developed for the detection of α-fetoprotein (AFP). The immunosensor was based on Au-ZnO flower-rods (FRs) heterostructure, where Au nanoparticles (NPs) were firstly electrodeposited by cyclic voltammetry methods. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Mott-Schottky plot (MS), UV-vis diffuse reflectance spectrum and fluorescence emission spectrum were used for the characterizations of Au-ZnO FRs. The results demonstrated that Au NPs not only obviously enhanced the visible light absorption of ZnO FRs due to surface plasmon resonance (SPR) but also improved the separation of photo-generated electron-hole pairs. Therefore, the photocurrent of Au-ZnO FRs was increased under simulated sunlight. The photocurrent was reduced after the specific antibody-antigen immune reaction. And the photocurrent decrement was linear with the logarithm of AFP antigen concentration in the range from 0.005 ng mL-1 to 50 ng mL-1 with a low detection limit of 0.56 pg mL-1 (S/N = 3). The PEC immunosensor also exhibited high anti-interference property and acceptable stability. This work would provide a promising photoelectrochemical strategy for the detection of other proteins in clinical diagnosis.

Quantification by SEM-EDS in uncoated non-conducting samples

NASA Astrophysics Data System (ADS)

Galván Josa, V.; Castellano, G.; Bertolino, S. R.

2013-07-01

An approach to perform elemental quantitative analysis in a conventional scanning electron microscope with an energy dispersive spectrometer has been developed for non-conductive samples in which the conductive coating should be avoided. Charge accumulation effects, which basically decrease the energy of the primary beam, were taken into account by means of the Duane-Hunt limit. This value represents the maximum energy of the continuum X-ray spectrum, and is related to the effective energy of the incident electron beam. To validate the results obtained by this procedure, a non-conductive sample of known composition was quantified without conductive coating. Complementarily, changes in the X-ray spectrum due to charge accumulation effects were studied by Monte Carlo simulations, comparing relative characteristic intensities as a function of the incident energy. This methodology is exemplified here to obtain the chemical composition of white and reddish archaeological pigments belonging to the Ambato style of "Aguada" culture (Catamarca, Argentina 500-1100 AD). The results obtained in this work show that the quantification procedure taking into account the Duane-Hunt limit is suitable for this kind of samples. This approach may be recommended for the quantification of samples for which coating is not desirable, such as ancient artwork, forensic or archaeological samples, or when the coating element is also present in the sample.

Self-modulated laser wakefield accelerators as x-ray sources

DOE PAGES

Lemos, N.; Martins, J. L.; Tsung, F. S.; ...

2016-02-17

The development of a directional, small-divergence, and short-duration picosecond x-ray probe beam with an energy greater than 50 keV is desirable for high energy density science experiments. We therefore explore through particle-in-cell (PIC) computer simulations the possibility of using x-rays radiated by betatron-like motion of electrons from a self-modulated laser wakefield accelerator as a possible candidate to meet this need. Two OSIRIS 2D PIC simulations with mobile ions are presented, one with a normalized vector potential a 0 = 1.5 and the other with an a 0 = 3. We find that in both cases direct laser acceleration (DLA) ismore » an important additional acceleration mechanism in addition to the longitudinal electric field of the plasma wave. Together these mechanisms produce electrons with a continuous energy spectrum with a maximum energy of 300 MeV for a 0 = 3 case and 180 MeV in the a 0 = 1.5 case. Forward-directed x-ray radiation with a photon energy up to 100 keV was calculated for the a 0 = 3 case and up to 12 keV for the a 0 = 1.5 case. The x-ray spectrum can be fitted with a sum of two synchrotron spectra with critical photon energies of 13 and 45 keV for the a 0 of 3 and critical photon energies of 0.3 and 1.4 keV for a 0 of 1.5 in the plane of polarization of the laser. As a result, the full width at half maximum divergence angle of the x-rays was 62 × 1.9 mrad for a 0 = 3 and 77 × 3.8 mrad for a 0 = 1.5.« less

Vlasov Simulations of Ionospheric Heating Near Upper Hybrid Resonance

NASA Astrophysics Data System (ADS)

Najmi, A. C.; Eliasson, B. E.; Shao, X.; Milikh, G. M.; Papadopoulos, K.

2014-12-01

It is well-known that high-frequency (HF) heating of the ionosphere can excite field- aligned density striations (FAS) in the ionospheric plasma. Furthermore, in the neighborhood of various resonances, the pump wave can undergo parametric instabilities to produce a variety of electrostatic and electromagnetic waves. We have used a Vlasov simulation with 1-spatial dimension, 2-velocity dimensions, and 2-components of fields, to study the effects of ionospheric heating when the pump frequency is in the vicinity of the upper hybrid resonance, employing parameters currently available at ionospheric heaters such as HAARP. We have found that by seeding theplasma with a FAS of width ~20% of the simulation domain, ~10% depletion, and by applying a spatially uniform HF dipole pump electric field, the pump wave gives rise to a broad spectrum of density fluctuations as well as to upper hybrid and lower hybrid oscillating electric fields. We also observe collisionless bulk-heating of the electrons that varies non-linearly with the amplitude of the pump field.

A Monte Carlo Simulation of Prompt Gamma Emission from Fission Fragments

NASA Astrophysics Data System (ADS)

Regnier, D.; Litaize, O.; Serot, O.

2013-03-01

The prompt fission gamma spectra and multiplicities are investigated through the Monte Carlo code FIFRELIN which is developed at the Cadarache CEA research center. Knowing the fully accelerated fragment properties, their de-excitation is simulated through a cascade of neutron, gamma and/or electron emissions. This paper presents the recent developments in the FIFRELIN code and the results obtained on the spontaneous fission of 252Cf. Concerning the decay cascades simulation, a fully Hauser-Feshbach model is compared with a previous one using a Weisskopf spectrum for neutron emission. A particular attention is paid to the treatment of the neutron/gamma competition. Calculations lead using different level density and gamma strength function models show significant discrepancies of the slope of the gamma spectra at high energy. The underestimation of the prompt gamma spectra obtained regardless our de-excitation cascade modeling choice is discussed. This discrepancy is probably linked to an underestimation of the post-neutron fragments spin in our calculation.

Influence of the confinement potential on the size-dependent optical response of metallic nanometric particles

NASA Astrophysics Data System (ADS)

Zapata-Herrera, Mario; Camacho, Ángela S.; Ramírez, Hanz Y.

2018-06-01

In this paper, different confinement potential approaches are considered in the simulation of size effects on the optical response of silver spheres with radii at the few nanometer scale. By numerically obtaining dielectric functions from different sets of eigenenergies and eigenstates, we simulate the absorption spectrum and the field enhancement factor for nanoparticles of various sizes, within a quantum framework for both infinite and finite potentials. The simulations show significant dependence on the sphere radius of the dipolar surface plasmon resonance, as a direct consequence of energy discretization associated to the strong confinement experienced by conduction electrons in small nanospheres. Considerable reliance of the calculated optical features on the chosen wave functions and transition energies is evidenced, so that discrepancies in the plasmon resonance frequencies obtained with the three studied models reach up to above 30%. Our results are in agreement with reported measurements and shade light on the puzzling shift of the plasmon resonance in metallic nanospheres.

Multifractal analysis of electronic cardiogram taken from healthy and unhealthy adult subjects

NASA Astrophysics Data System (ADS)

Wang, Jun; Ning, Xinbao; Chen, Ying

2003-05-01

Electronic Cardiogram (ECG) data taken from healthy adult subjects are found to characterize multifractality. In order to quantitatively analyze multifractal spectrum, the area of the spectrum is computed. We have a comparison between the spectrum of the young subjects and that of the old ones. We find that the area of young adult subject's multifractal spectrum is far larger than the older one's and the logarithm of the area of the spectrum is inversely proportion to age. It shows that when time is running on human heartbeat energy is exponentially decreasing until heart failure. And distinct difference between the area of the multifractal spectrum of healthy subjects and that of having coronary disease is not found. We analyze the ECG data taken from patients with brain injury. The area of their ECG multifractal spectrum is distinctly descending. It shows that a person's multifractal spectrum is controlled mainly by his neurosystem. With advancing age, the neuroautonomic control of people's body on the ECG decreases and tends from multifractality to monofractality.

The TESS camera: modeling and measurements with deep depletion devices

NASA Astrophysics Data System (ADS)

Woods, Deborah F.; Vanderspek, Roland; MacDonald, Robert; Morgan, Edward; Villasenor, Joel; Thayer, Carolyn; Burke, Barry; Chesbrough, Christian; Chrisp, Michael; Clark, Kristin; Furesz, Gabor; Gonzales, Alexandria; Nguyen, Tam; Prigozhin, Gregory; Primeau, Brian; Ricker, George; Sauerwein, Timothy; Suntharalingam, Vyshnavi

2016-07-01

The Transiting Exoplanet Survey Satellite, a NASA Explorer-class mission in development, will discover planets around nearby stars, most notably Earth-like planets with potential for follow up characterization. The all-sky survey requires a suite of four wide field-of-view cameras with sensitivity across a broad spectrum. Deep depletion CCDs with a silicon layer of 100 μm thickness serve as the camera detectors, providing enhanced performance in the red wavelengths for sensitivity to cooler stars. The performance of the camera is critical for the mission objectives, with both the optical system and the CCD detectors contributing to the realized image quality. Expectations for image quality are studied using a combination of optical ray tracing in Zemax and simulations in Matlab to account for the interaction of the incoming photons with the 100 μm silicon layer. The simulations include a probabilistic model to determine the depth of travel in the silicon before the photons are converted to photo-electrons, and a Monte Carlo approach to charge diffusion. The charge diffusion model varies with the remaining depth for the photo-electron to traverse and the strength of the intermediate electric field. The simulations are compared with laboratory measurements acquired by an engineering unit camera with the TESS optical design and deep depletion CCDs. In this paper we describe the performance simulations and the corresponding measurements taken with the engineering unit camera, and discuss where the models agree well in predicted trends and where there are differences compared to observations.

MOLECULAR DISTORTION AND ELECTRONIC SPECTRUM OF AROMATIC COMPOUNDS. I. CHLORINATED DERIVATIVES OF ALKYL BENZENES.

DTIC Science & Technology

The absortion electronic spectrum of pentachlorobenzene, perchlorobenzene, 2,3,4,5,6-pentachlorotoluene, 2,3,4,5,6-pentachloro- 1 -chloromethylbenzene...2,3,4,5,6-pentachloro- 1 -dichloromethylbenzene, 2,3,4,5-tetrachloro- 1 -trichloromethylbenzene, 2,3,5,6-tetrachloro- 1 -trichloromethylbenzene

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

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

DOE PAGES

Acciarri, R.

2017-09-14

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

THE INFRARED SPECTRUM OF PROTONATED OVALENE IN SOLID PARA-HYDROGEN AND ITS POSSIBLE CONTRIBUTION TO INTERSTELLAR UNIDENTIFIED INFRARED EMISSION

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

Tsuge, Masashi; Bahou, Mohammed; Lee, Yuan-Pern

The mid-infrared emission from galactic objects, including reflection nebulae, planetary nebulae, proto-planetary nebulae, molecular clouds, etc, as well as external galaxies, is dominated by the unidentified infrared (UIR) emission bands. Large protonated polycyclic aromatic hydrocarbons (H{sup +}PAHs) were proposed as possible carriers, but no spectrum of an H{sup +}PAH has been shown to exactly match the UIR bands. Here, we report the IR spectrum of protonated ovalene (7-C{sub 32}H{sub 15} {sup +}) measured in a para -hydrogen ( p -H{sub 2}) matrix at 3.2 K, generated by bombarding a mixture of ovalene and p -H{sub 2} with electrons during matrixmore » deposition. Spectral assignments were made based on the expected chemistry and on the spectra simulated with the wavenumbers and infrared intensities predicted with the B3PW91/6-311++G(2d,2p) method. The close resemblance of the observed spectral pattern to that of the UIR bands suggests that protonated ovalene may contribute to the UIR emission, particularly from objects that emit Class A spectra, such as the IRIS reflection nebula, NGC 7023.« less

Photoinduced electron transfer process on emission spectrum of N,N‧-bis(salicylidene)-1,2-phenylenediamine as a Mg2+ cation chemosensor: A first principle DFT and TDDFT study

NASA Astrophysics Data System (ADS)

Taherpour, Avat (Arman); Jamshidi, Morteza; Rezaei, Omid; Belverdi, Ali Rezaei

2018-06-01

The electronic and optical properties of N,N‧-bis(salicylidene)-1,2-phenylenediamine (SPDA) ligand were studied as a chemical sensor of Mg2+ cation in two solvents (water and DMSO) using the ab initio theory through Density Functional Theory (DFT) and Time Dependent Density Functional theory (TDDFT) methods. The results show that the SPDA ligand has a high ability for chemical sensing of Mg2+. The results has also represented that HOMO-LUMO energy gap decreases 0.941 eV after the complex formation between SPDA and Mg2+. In addition, obvious changes are found in the UV-Vis absorption spectrum, optical analyses SPDA ligand and [SPDA.Mg]2+ complex, which it has the capability of detecting Mg2+ via the adsorptive UV-Vis and colorimetric methods. Emission spectrum calculations and photoinduced electron transfer (PET) process in water solution shows different wavelength emission spectrum in amount of 4.6 nm. An analysis of NBO (natural bond orbital) data indicates tangible changes in the electron transfers data from the electron pairs of ligand to the conjugated system, both prior and subsequent to Mg2+addition.

Galactic Cosmic Ray Simulation at the NASA Space Radiation Laboratory

NASA Technical Reports Server (NTRS)

Norbury, John W.; Slaba, Tony C.; Rusek, Adam

2015-01-01

The external Galactic Cosmic Ray (GCR) spectrum is significantly modified when it passes through spacecraft shielding and astronauts. One approach for simulating the GCR space radiation environment at ground based accelerators would use the modified spectrum, rather than the external spectrum, in the accelerator beams impinging on biological targets. Two recent workshops have studied such GCR simulation. The first workshop was held at NASA Langley Research Center in October 2014. The second workshop was held at the NASA Space Radiation Investigators' workshop in Galveston, Texas in January 2015. The results of these workshops will be discussed in this paper.

Structure and energetics of vinoxide and the X({sup 2}A{double{underscore}prime}) and A({sup 2}A{prime}) vinoxy radicals

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

Alconcel, L.S.; Deyerl, H.J.; Zengin, V.

1999-11-18

Enolate anions are intermediates in many organic reactions that involve carbon-carbon or carbon-oxygen food formation. They also play a key role in the development of stereoselective and stereocontrolled syntheses of complex compounds. Enolate radicals are important intermediates in combustion and photochemical smog cycles. In particular, the vinoxy radical, C{sub 2}H{sub 3}O{sup {sm{underscore}bullet}} is a major product of the reaction of odd oxygen and ethylene. The photoelectron spectrum of binoxide, C{sub 2}H{sub 3}O{sup {minus}}, at 355 nm is reported, showing photodetachment to both the X({sup 2}A{double{underscore}prime}) ground and first excited A({sup 2}A{prime}) states of the vinoxy radical. Both direct interpretations andmore » Franck-Condon simulations of the photoelectron spectrum of this simple enolate anion have been used to obtain insights into the energetics and structures of the anion and the ground and first excited state of the neutral radical. Franck-Condon simulations were generated from ab initio geometry and frequency calculations using the CASSCF method and showed good agreement with the vibrational structure visible in the experimental spectrum. The electron affinity (E.A.{sub exp} = 1.795 {+-} 0.015 eV; E.A.{sub calc} = 1.82 eV) and separation energy of the ground and first excited states (T{sub 0,exp} = 1.015 {+-} 0.015 eV; T{sub 0,calc} = 0.92 eV) obtained from the ab initio calculations are in good accord with the experimental values.« less

Nucleation and characterization of hydroxyapatite on thioglycolic acid-capped reduced graphene oxide/silver nanoparticles in simplified simulated body fluid

NASA Astrophysics Data System (ADS)

Zhao, Jun; Zhang, Zhaochun; Yu, Zhenwei; He, Zhenni; Yang, Shanshan; Jiang, Huiyi

2014-01-01

Herein hydroxyapatite (HA) has been synthesized by the nucleation on the surfaces of reduced graphene oxide/silver nanoparticles (rGO/AgNPs) chemisorbed with thioglycolic acid (TGA). The self-assembled monolayer of TGA formed on rGO/AgNPs was immersed in simplified simulated body fluid under gentle growth conditions, forming rGO/AgNPs/TGA/HA biocomposite. The phase structures and functional groups of biocomposite were analyzed by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. Enhanced Raman spectrum of TGA on prepared rGO/AgNPs was obtained with excitation at 633 nm, showing that TGA was chemisorbed on AgNPs through S atom and TGA molecular plane exhibited a tilted orientation with respect to AgNPs. The morphologies of biocomposite were investigated by means of atomic force microscope and transmission electron microscope coupled with energy dispersive spectrum. Analysis shows that the AgNPs uniformly distributed on the rGO nanosheets with the size of about 15-20 nm and HA formation initiated through Ca2+-adsorption upon complexation with sbnd COO- groups of TGA on AgNPs. The results obtained indicated that the rGO/AgNPs/TGA/HA biocomposite may have immense potential application in bone tissue engineering fields for its outstanding and stable activities.

An analytical method for computing voxel S values for electrons and photons.

PubMed

Amato, Ernesto; Minutoli, Fabio; Pacilio, Massimiliano; Campenni, Alfredo; Baldari, Sergio

2012-11-01

The use of voxel S values (VSVs) is perhaps the most common approach to radiation dosimetry for nonuniform distributions of activity within organs or tumors. However, VSVs are currently available only for a limited number of voxel sizes and radionuclides. The objective of this study was to develop a general method to evaluate them for any spectrum of electrons and photons in any cubic voxel dimension of practical interest for clinical dosimetry in targeted radionuclide therapy. The authors developed a Monte Carlo simulation in Geant4 in order to evaluate the energy deposited per disintegration (E(dep)) in a voxelized region of soft tissue from monoenergetic electrons (10-2000 keV) or photons (10-1000 keV) homogeneously distributed in the central voxel, considering voxel dimensions ranging from 3 mm to 10 mm. E(dep) was represented as a function of a dimensionless quantity termed the "normalized radius," R(n) = R∕l, where l is the voxel size and R is the distance from the origin. The authors introduced two parametric functions in order to fit the electron and photon results, and they interpolated the parameters to derive VSVs for any energy and voxel side within the ranges mentioned above. In order to validate the results, the authors determined VSV for two radionuclides ((131)I and (89)Sr) and two voxel dimensions and they compared them with reference data. A validation study in a simple sphere model, accounting for tissue inhomogeneities, is presented. The E(dep)(R(n)) for both monoenergetic electrons and photons exhibit a smooth variation with energy and voxel size, implying that VSVs for monoenergetic electrons or photons may be derived by interpolation over the range of energies and dimensions considered. By integration, S values for continuous emission spectra from β(-) decay may be derived as well. The approach allows the determination of VSVs for monoenergetic (Auger or conversion) electrons and (x-ray or gamma-ray) photons by means of two functions whose parameters can be interpolated from tabular data provided. Through integration, it is possible to generalize the method to any continuous (beta) spectrum, allowing to calculate VSVs for any electron and photon emitter in a voxelized structure.

Modelling space-based integral-field spectrographs and their application to Type Ia supernova cosmology

NASA Astrophysics Data System (ADS)

Shukla, Hemant; Bonissent, Alain

2017-04-01

We present the parameterized simulation of an integral-field unit (IFU) slicer spectrograph and its applications in spectroscopic studies, namely, for probing dark energy with type Ia supernovae. The simulation suite is called the fast-slicer IFU simulator (FISim). The data flow of FISim realistically models the optics of the IFU along with the propagation effects, including cosmological, zodiacal, instrumentation and detector effects. FISim simulates the spectrum extraction by computing the error matrix on the extracted spectrum. The applications for Type Ia supernova spectroscopy are used to establish the efficacy of the simulator in exploring the wider parametric space, in order to optimize the science and mission requirements. The input spectral models utilize the observables such as the optical depth and velocity of the Si II absorption feature in the supernova spectrum as the measured parameters for various studies. Using FISim, we introduce a mechanism for preserving the complete state of a system, called the partial p/partial f matrix, which allows for compression, reconstruction and spectrum extraction, we introduce a novel and efficient method for spectrum extraction, called super-optimal spectrum extraction, and we conduct various studies such as the optimal point spread function, optimal resolution, parameter estimation, etc. We demonstrate that for space-based telescopes, the optimal resolution lies in the region near R ˜ 117 for read noise of 1 e- and 7 e- using a 400 km s-1 error threshold on the Si II velocity.

Decorrelation dynamics and spectra in drift-Alfven turbulence

NASA Astrophysics Data System (ADS)

Fernandez Garcia, Eduardo

Motivated by the inability of one-fluid magnetohydrodynamics (MHD) to explain key turbulence characteristics in systems ranging from the solar wind and interstellar medium to fusion devices like the reversed field pinch, this thesis studies magnetic turbulence using a drift-Alfven model that extends MHD by including electron density dynamics. Electron effects play a significant role in the dynamics by changing the structure of turbulent decorrelation in the Alfvenic regime (where fast Alfvenic propagation provides the fastest decorrelation of the system): besides the familiar counter-propagating Alfvenic branches of MHD, an additional branch tied to the diamagnetic and eddy-turn- over rates enters in the turbulent response. This kinematic branch gives hydrodynamic features to turbulence that is otherwise strongly magnetic. Magnetic features are observed in the RMS frequency, energy partitions, cross-field energy transfer and in the turbulent response, whereas hydrodynamic features appear in the average frequency, self-field transfer, turbulent response and finally the wavenumber spectrum. These features are studied via renormalized closure theory and numerical simulation. The closure calculation naturally incorporates the eigenmode structure of the turbulent response in specifying spectral energy balance equations for the magnetic, kinetic and internal (density) energies. Alfvenic terms proportional to cross correlations and involved in cross field transfer compete with eddy-turn-over, self transfer, auto-correlation terms. In the steady state, the kinematic terms dominate the energy balances and yield a 5/3 Kolmogorov spectrum (as observed in the interstellar medium) for the three field energies in the strong turbulence, long wavelength limit. Alfvenic terms establish equipartition of kinetic and magnetic energies. In the limit where wavelengths are short compared to the gyroradius, the Alfvenic terms equipartition the internal and magnetic energies resulting in a steep (-2) spectrum fall-off for those energies while the largely uncoupled kinetic modes still obey a 5/3 law. From the numerical simulations, the response function of drift-Alfven turbulence is measured. Here, a statistical ensemble is constructed from small perturbations of the turbulent amplitudes at fixed wavenumber. The decorrelation structure born out of the eigenmode calculation is verified in the numerical measurement.

Theoretical Interpretation of Pass 8 Fermi -LAT e + + e - Data

DOE PAGES

Di Mauro, M.; Manconi, S.; Vittino, A.; ...

2017-08-17

The flux of positrons and electrons (e + + e -) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. Here, we discuss a number of interpretations of Pass 8 Fermi-LAT e + + e - spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We also found that the Fermi-LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positrons from cataloged PWNe, and amore » secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e + + e - Fermi-LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green's catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e + + e - Fermi-LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e + + e -spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

Theoretical Interpretation of Pass 8 Fermi -LAT e + + e - Data

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

Di Mauro, M.; Manconi, S.; Vittino, A.

The flux of positrons and electrons (e + + e -) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. Here, we discuss a number of interpretations of Pass 8 Fermi-LAT e + + e - spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We also found that the Fermi-LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positrons from cataloged PWNe, and amore » secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e + + e - Fermi-LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green's catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e + + e - Fermi-LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e + + e -spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

Particle acceleration model for the broad-band baseline spectrum of the Crab nebula

NASA Astrophysics Data System (ADS)

Fraschetti, F.; Pohl, M.

2017-11-01

We develop a simple one-zone model of the steady-state Crab nebula spectrum encompassing both the radio/soft X-ray and the GeV/multi-TeV observations. By solving the transport equation for GeV-TeV electrons injected at the wind termination shock as a log-parabola momentum distribution and evolved via energy losses, we determine analytically the resulting differential energy spectrum of photons. We find an impressive agreement with the observed spectrum of synchrotron emission, and the synchrotron self-Compton component reproduces the previously unexplained broad 200-GeV peak that matches the Fermi/Large Area Telescope (LAT) data beyond 1 GeV with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) data. We determine the parameters of the single log-parabola electron injection distribution, in contrast with multiple broken power-law electron spectra proposed in the literature. The resulting photon differential spectrum provides a natural interpretation of the deviation from power law customarily fitted with empirical multiple broken power laws. Our model can be applied to the radio-to-multi-TeV spectrum of a variety of astrophysical outflows, including pulsar wind nebulae and supernova remnants, as well as to interplanetary shocks.

Electron calibration of a high energy cosmic ray detector

NASA Technical Reports Server (NTRS)

Simnett, G. M.; Silverberg, R. F.; Crannell, C. J.; Gearhart, R. A.; Hagen, F. A.; Jones, W. V.; Kurz, R. J.; Ormes, J. F.; Price, R. D.

1972-01-01

The spectrum of cosmic ray electrons above 10 GeV was studied extensively. The spectrum is predicted to steepen at an energy which is related to the lifetime of electrons in the interstellar medium against losses due to inverse Compton collisions with photons and to synchrotron radiation in galactic magnetic fields. The experimental results diverge widely; the lack of agreement between the various measurements is due to a variety of experimental problems.

High energy primary electron spectrum observed by the emulsion chamber

NASA Technical Reports Server (NTRS)

Nishimura, J.; Fujii, M.; Aizu, H.; Hiraiwa, N.; Taira, T.; Kobayashi, T.; Niu, K.; Koss, T. A.; Lord, J. J.; Golden, R. L.

1978-01-01

A detector of the emulsion chamber type is used to measure the energy spectrum of cosmic-ray electrons. Two large emulsion chambers, each having an area of 40 by 50 sq cm, are exposed for about 25.5 hr at an average pressure altitude of 3.9 mbar. About 500 high-energy cascades (no less than about 600 GeV) are detected by searching for dark spots on the X-ray films. A power-law energy dependence formula is derived for the spectrum of primary cosmic-ray electrons in the energy region over 100 GeV. The results are in good agreement with the transition curves obtained previously by theoretical and Monte Carlo calculations.

The energy spectrum of Jovian electrons in interplanetary space

NASA Technical Reports Server (NTRS)

Christon, S. P.; Cummings, A. C.; Stone, E. C.; Webber, W. R.

1985-01-01

The energy spectrum of electrons with energies approximately 10 to approximately 180 MeV measured with the electron telescope on the Voyager 1 and 2 spacecraft in interplanetary space from 1978 to 1983 is reported. The kinetic energy of electrons is determined by double dE/dx measurements from the first two detectors (D1,D2) of a stack of eight solid state detectors and by the range of particle penetration into the remaining six detectors (D3 to D8) which are interleaved with tungsten absorbers.

Two-dimensional angular energy spectrum of electrons accelerated by the ultra-short relativistic laser pulse

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

Borovskiy, A. V.; Galkin, A. L.; Department of Physics of MBF, Pirogov Russian National Research Medical University, 1 Ostrovitianov Street, Moscow 117997

The new method of calculating energy spectra of accelerated electrons, based on the parameterization by their initial coordinates, is proposed. The energy spectra of electrons accelerated by Gaussian ultra-short relativistic laser pulse at a selected angle to the axis of the optical system focusing the laser pulse in a low density gas are theoretically calculated. The two-peak structure of the electron energy spectrum is obtained. Discussed are the reasons for its appearance as well as an applicability of other models of the laser field.

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.

Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00880e

PubMed Central

Prasad, Saumya; Mandal, Imon; Singh, Shubham; Paul, Ashim; Mandal, Bhubaneswar

2017-01-01

Electronic absorption spectra of proteins are primarily characterized over the ultraviolet region (185–320 nm) of the electromagnetic spectrum. While recent studies on peptide aggregates have revealed absorption beyond 350 nm, monomeric proteins lacking aromatic amino acids, disulphide bonds, and active site prosthetic groups are expected to remain optically silent beyond 250 nm. Here, in a joint theoretical and experimental investigation, we report the distinctive UV-Vis absorption spectrum between 250 nm [ε = 7338 M–1 cm–1] and 800 nm [ε = 501 M–1 cm–1] in a synthetic 67 residue protein (α3C), in monomeric form, devoid of aromatic amino acids. Systematic control studies with high concentration non-aromatic amino acid solutions revealed significant absorption beyond 250 nm for charged amino acids which constitute over 50% of the sequence composition in α3C. Classical atomistic molecular dynamics (MD) simulations of α3C reveal dynamic interactions between multiple charged sidechains of Lys and Glu residues present in α3C. Time-dependent density functional theory calculations on charged amino acid residues sampled from the MD trajectories of α3C reveal that the distinctive absorption features of α3C may arise from two different types of charge transfer (CT) transitions involving spatially proximal Lys/Glu amino acids. Specifically, we show that the charged amino (NH3+)/carboxylate (COO–) groups of Lys/Glu sidechains act as electronic charge acceptors/donors for photoinduced electron transfer either from/to the polypeptide backbone or to each other. Further, the sensitivity of the CT spectra to close/far/intermediate range of encounters between sidechains of Lys/Glu owing to the three dimensional protein fold can create the long tail in the α3C absorption profile between 300 and 800 nm. Finally, we experimentally demonstrate the sensitivity of α3C absorption spectrum to temperature and pH-induced changes in protein structure. Taken together, our investigation significantly expands the pool of spectroscopically active biomolecular chromophores and adds an optical 250–800 nm spectral window, which we term ProCharTS (Protein Charge Transfer Spectra), for label free probes of biomolecular structure and dynamics. PMID:28970921

Enhanced relativistic harmonics by electron nanobunching

NASA Astrophysics Data System (ADS)

an der Brügge, D.; Pukhov, A.

2010-03-01

It is shown that when a few-cycle, relativistically intense, p-polarized laser pulse is obliquely incident on overdense plasma, the surface electrons may form ultrathin, highly compressed layers with a width of a few nanometers. These electron "nanobunches" emit synchrotron radiation coherently. We calculate the one-dimensional synchrotron spectrum analytically and obtain a slowly decaying power law with an exponent of 4/3 or 6/5. This is much flatter than the 8/3 power of the Baeva-Gordienko-Pukhov spectrum, produced by a relativistically oscillating bulk skin layer. The synchrotron spectrum cutoff frequency is defined either by the electron relativistic γ-factor or by the thickness of the emitting layer. In the numerically demonstrated, locally optimal case, the radiation is emitted in the form of a single attosecond pulse, which contains almost the entire energy of the full optical cycle.

FEM design and simulation of a short, 10 MV, S-band Linac with Monte Carlo dose simulations.

PubMed

Baillie, Devin; St Aubin, J; Fallone, B G; Steciw, S

2015-04-01

Current commercial 10 MV Linac waveguides are 1.5 m. The authors' current 6 MV linear accelerator-magnetic resonance imager (Linac-MR) system fits in typical radiotherapy vaults. To allow 10 MV treatments with the Linac-MR and still fit within typical vaults, the authors design a 10 MV Linac with an accelerator waveguide of the same length (27.5 cm) as current 6 MV Linacs. The first design stage is to design a cavity such that a specific experimental measurement for breakdown is applicable to the cavity. This is accomplished through the use of finite element method (FEM) simulations to match published shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength from an electric breakdown study. A full waveguide is then designed and tuned in FEM simulations based on this cavity design. Electron trajectories are computed through the resulting radio frequency fields, and the waveguide geometry is modified by shifting the first coupling cavity in order to optimize the electron beam properties until the energy spread and mean energy closely match values published for an emulated 10 MV Linac. Finally, Monte Carlo dose simulations are used to compare the resulting photon beam depth dose profile and penumbra with that produced by the emulated 10 MV Linac. The shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength are all matched to within 0.1%. A first coupling cavity shift of 1.45 mm produces an energy spectrum width of 0.347 MeV, very close to the published value for the emulated 10 MV of 0.315 MeV, and a mean energy of 10.53 MeV, nearly identical to the published 10.5 MeV for the emulated 10 MV Linac. The depth dose profile produced by their new Linac is within 1% of that produced by the emulated 10 MV spectrum for all depths greater than 1.5 cm. The penumbra produced is 11% narrower, as measured from 80% to 20% of the central axis dose. The authors have successfully designed and simulated an S-band waveguide of length of 27.5 cm capable of producing a 10 MV photon beam. This waveguide operates well within the breakdown threshold determined for the cavity geometry used. The designed Linac produces depth dose profiles similar to those of the emulated 10 MV Linac (waveguide-length of 1.5 m) but yields a narrower penumbra.

FEM design and simulation of a short, 10 MV, S-band Linac with Monte Carlo dose simulations

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

Baillie, Devin; Aubin, J. St.; Steciw, S., E-mail: ssteciw@ualberta.ca

2015-04-15

Purpose: Current commercial 10 MV Linac waveguides are 1.5 m. The authors’ current 6 MV linear accelerator–magnetic resonance imager (Linac–MR) system fits in typical radiotherapy vaults. To allow 10 MV treatments with the Linac–MR and still fit within typical vaults, the authors design a 10 MV Linac with an accelerator waveguide of the same length (27.5 cm) as current 6 MV Linacs. Methods: The first design stage is to design a cavity such that a specific experimental measurement for breakdown is applicable to the cavity. This is accomplished through the use of finite element method (FEM) simulations to match publishedmore » shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength from an electric breakdown study. A full waveguide is then designed and tuned in FEM simulations based on this cavity design. Electron trajectories are computed through the resulting radio frequency fields, and the waveguide geometry is modified by shifting the first coupling cavity in order to optimize the electron beam properties until the energy spread and mean energy closely match values published for an emulated 10 MV Linac. Finally, Monte Carlo dose simulations are used to compare the resulting photon beam depth dose profile and penumbra with that produced by the emulated 10 MV Linac. Results: The shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength are all matched to within 0.1%. A first coupling cavity shift of 1.45 mm produces an energy spectrum width of 0.347 MeV, very close to the published value for the emulated 10 MV of 0.315 MeV, and a mean energy of 10.53 MeV, nearly identical to the published 10.5 MeV for the emulated 10 MV Linac. The depth dose profile produced by their new Linac is within 1% of that produced by the emulated 10 MV spectrum for all depths greater than 1.5 cm. The penumbra produced is 11% narrower, as measured from 80% to 20% of the central axis dose. Conclusions: The authors have successfully designed and simulated an S-band waveguide of length of 27.5 cm capable of producing a 10 MV photon beam. This waveguide operates well within the breakdown threshold determined for the cavity geometry used. The designed Linac produces depth dose profiles similar to those of the emulated 10 MV Linac (waveguide-length of 1.5 m) but yields a narrower penumbra.« less

Vibrational structure in the photo-electron spectrum of O2+2Sigma(g)-(sigmag2s)

NASA Technical Reports Server (NTRS)

Gardner, J. L.; Samson, J. A. R.

1974-01-01

Discrete vibrational structure has been observed in the photo-electron spectrum of oxygen at an ionization potential of 40.33 eV. Two levels, attributed to the 02(+) 2 sigma g- final state, have been detected with a vibrational spacing of 0.071 eV.

Indoor Fast Neutron Generator for Biophysical and Electronic Applications

NASA Astrophysics Data System (ADS)

Cannuli, A.; Caccamo, M. T.; Marchese, N.; Tomarchio, E. A.; Pace, C.; Magazù, S.

2018-05-01

This study focuses the attention on an indoor fast neutron generator for biophysical and electronic applications. More specifically, the findings obtained by several simulations with the MCNP Monte Carlo code, necessary for the realization of a shield for indoor measurements, are presented. Furthermore, an evaluation of the neutron spectrum modification caused by the shielding is reported. Fast neutron generators are a valid and interesting available source of neutrons, increasingly employed in a wide range of research fields, such as science and engineering. The employed portable pulsed neutron source is a MP320 Thermo Scientific neutron generator, able to generate 2.5 MeV neutrons with a neutron yield of 2.0 x 106 n/s, a pulse rate of 250 Hz to 20 KHz and a duty factor varying from 5% to 100%. The neutron generator, based on Deuterium-Deuterium nuclear fusion reactions, is employed in conjunction with a solid-state photon detector, made of n-type high-purity germanium (PINS-GMX by ORTEC) and it is mainly addressed to biophysical and electronic studies. The present study showed a proposal for the realization of a shield necessary for indoor applications for MP320 neutron generator, with a particular analysis of the transport of neutrons simulated with Monte Carlo code and described the two main lines of research in which the source will be used.

A full-dimensional multilayer multiconfiguration time-dependent Hartree study on the ultraviolet absorption spectrum of formaldehyde oxide

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

Meng, Qingyong, E-mail: mengqingyong@dicp.ac.cn; Meyer, Hans-Dieter, E-mail: hans-dieter.meyer@pci.uni-heidelberg.de

2014-09-28

Employing the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method in conjunction with the multistate multimode vibronic coupling Hamiltonian (MMVCH) model, we perform a full dimensional (9D) quantum dynamical study on the simplest Criegee intermediate, formaldehyde oxide, in five lower-lying singlet electronic states. The ultraviolet (UV) spectrum is then simulated by a Fourier transform of the auto-correlation function. The MMVCH model is built based on extensive MRCI(8e,8o)/aug-cc-pVTZ calculations. To ensure a fast convergence of the final calculations, a large number of ML-MCTDH test calculations is performed to find an appropriate multilayer separations (ML-trees) of the ML-MCTDH nuclear wave functions, and the dynamicalmore » calculations are carefully checked to ensure that the calculations are well converged. To compare the computational efficiency, standard MCTDH simulations using the same Hamiltonian are also performed. A comparison of the MCTDH and ML-MCTDH calculations shows that even for the present not-too-large system (9D here) the ML-MCTDH calculations can save a considerable amount of computational resources while producing identical spectra as the MCTDH calculations. Furthermore, the present theoretical B{sup ~} {sup 1}A{sup ′}←X{sup ~} {sup 1}A{sup ′} UV spectral band and the corresponding experimental measurements [J. M. Beames, F. Liu, L. Lu, and M. I. Lester, J. Am. Chem. Soc. 134, 20045–20048 (2012); L. Sheps, J. Phys. Chem. Lett. 4, 4201–4205 (2013); W.-L. Ting, Y.-H. Chen, W. Chao, M. C. Smith, and J. J.-M. Lin, Phys. Chem. Chem. Phys. 16, 10438–10443 (2014)] are discussed. To the best of our knowledge, this is the first theoretical UV spectrum simulated for this molecule including nuclear motion beyond an adiabatic harmonic approximation.« less

To acquire more detailed radiation drive by use of ``quasi-steady'' approximation in atomic kinetics

NASA Astrophysics Data System (ADS)

Ren, Guoli; Pei, Wenbing; Lan, Ke; Gu, Peijun; Li, Xin

2012-10-01

In current routine 2D simulation of hohlraum physics, we adopt the principal-quantum- number(n-level) average atom model(AAM) in NLTE plasma description. However, the detailed experimental frequency-dependant radiative drive differs from our n-level simulated drive, which reminds us the need of a more detailed atomic kinetics description. The orbital-quantum- number(nl-level) average atom model is a natural consideration, however the nl-level in-line calculation needs much more computational resource. By distinguishing the rapid bound-bound atomic processes from the relative slow bound-free atomic processes, we found a method to build up a more detailed bound electron distribution(nl-level even nlm-level) using in-line n-level calculated plasma conditions(temperature, density, and average ionization degree). We name this method ``quasi-steady approximation'' in atomic kinetics. Using this method, we re-build the nl-level bound electron distribution (Pnl), and acquire a new hohlraum radiative drive by post-processing. Comparison with the n-level post-processed hohlraum drive shows that we get an almost identical radiation flux but with more fine frequency-denpending spectrum structure which appears only in nl-level transition with same n number(n=0) .

Spectral and angular distribution of photons via radiative damping in extreme ultra-intense laser-plasma interaction

NASA Astrophysics Data System (ADS)

Pandit, Rishi; Sentoku, Yasuhiko

2012-10-01

Spectral and angular distribution of photons produced in the interaction of extremely intense laser (> 10^22,/cm^2) with dense plasma are studied with a help of a collisional particle-in-cell simulation, PICLS. In ultra-intense laser-plasma interaction, electrons are accelerated by the strong laser fields and emit γ-ray photons mainly via two processes, namely, Bremsstrahlung and radiative damping. We had developed numerical models of these processes in PICLS and study the spectrum and the angular distribution of γ-rays produced in the relativistic laser regime. Such relativistic γ-rays have wide range of frequencies and the angular distribution depends on the hot electron source. From the power loss calculation in PICLS we found that the Bremsstrahlung will get saturated at I > 10^22,/cm^2 while the radiative damping will continuously increase. Comparing the details of γ-rays from the Bremsstrahlung and the radiative damping in simulations, we will discuss the laser parameters and the target conditions (geometry and material) to distinguish the photons from each process and how to catch the signature of the radiative damping in future experiments.

Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets and Supernova Remnants

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Hartmann, D. H.; Hardee, P.; Hededal, C.; Mizunno, Y.; Fishman, G. J.

2006-01-01

We performed numerical simulations of particle acceleration, magnetic field generation, and emission from shocks in order to understand the observed emission from relativistic jets and supernova remnants. The investigation involves the study of collisionless shocks, where the Weibel instability is responsible for particle acceleration as well as magnetic field generation. A 3-D relativistic particle-in-cell (RPIC) code has been used to investigate the shock processes in electron-positron plasmas. The evolution of theWeibe1 instability and its associated magnetic field generation and particle acceleration are studied with two different jet velocities (0 = 2,5 - slow, fast) corresponding to either outflows in supernova remnants or relativistic jets, such as those found in AGNs and microquasars. Slow jets have intrinsically different structures in both the generated magnetic fields and the accelerated particle spectrum. In particular, the jet head has a very weak magnetic field and the ambient electrons are strongly accelerated and dragged by the jet particles. The simulation results exhibit jitter radiation from inhomogeneous magnetic fields, generated by the Weibel instability, which has different spectral properties than standard synchrotron emission in a homogeneous magnetic field.

A method for converting dose-to-medium to dose-to-tissue in Monte Carlo studies of gold nanoparticle-enhanced radiotherapy

NASA Astrophysics Data System (ADS)

Koger, B.; Kirkby, C.

2016-03-01

Gold nanoparticles (GNPs) have shown potential in recent years as a means of therapeutic dose enhancement in radiation therapy. However, a major challenge in moving towards clinical implementation is the exact characterisation of the dose enhancement they provide. Monte Carlo studies attempt to explore this property, but they often face computational limitations when examining macroscopic scenarios. In this study, a method of converting dose from macroscopic simulations, where the medium is defined as a mixture containing both gold and tissue components, to a mean dose-to-tissue on a microscopic scale was established. Monte Carlo simulations were run for both explicitly-modeled GNPs in tissue and a homogeneous mixture of tissue and gold. A dose ratio was obtained for the conversion of dose scored in a mixture medium to dose-to-tissue in each case. Dose ratios varied from 0.69 to 1.04 for photon sources and 0.97 to 1.03 for electron sources. The dose ratio is highly dependent on the source energy as well as GNP diameter and concentration, though this effect is less pronounced for electron sources. By appropriately weighting the monoenergetic dose ratios obtained, the dose ratio for any arbitrary spectrum can be determined. This allows complex scenarios to be modeled accurately without explicitly simulating each individual GNP.

High-power klystrons

NASA Astrophysics Data System (ADS)

Siambis, John G.; True, Richard B.; Symons, R. S.

1994-05-01

Novel emerging applications in advanced linear collider accelerators, ionospheric and atmospheric sensing and modification and a wide spectrum of industrial processing applications, have resulted in microwave tube requirements that call for further development of high power klystrons in the range from S-band to X-band. In the present paper we review recent progress in high power klystron development and discuss some of the issues and scaling laws for successful design. We also discuss recent progress in electron guns with potential grading electrodes for high voltage with short and long pulse operation via computer simulations obtained from the code DEMEOS, as well as preliminary experimental results. We present designs for high power beam collectors.

INITIAL GAIN MEASUREMENTS OF A 800 NM SASE FEL, VISA.

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

FRIGOLA,P.; MUROKH,A.; ET AL

2000-08-13

The VISA (Visible to Infrared SASE Amplifier) FEL is designed to obtain high gain at a radiation wavelength of 800nm. The FEL uses the high brightness electron beam of the Accelerator Test Facility (ATF), with energy of 72MeV. VISA uses a novel, 4 m long, strong focusing undulator with a gap of 6mm and a period of 1.8cm. To obtain large gain the beam and undulator axis have to be aligned to better than 50{micro}m. Results from initial measurements on the alignment, gain, and spectrum will be presented and compared to theoretical calculations and simulations.

Electronic structures at the interface between CuPc and black phosphorus

NASA Astrophysics Data System (ADS)

Wang, Can; Niu, Dongmei; Xie, Haipeng; Liu, Baoxing; Wang, Shitan; Zhu, Menglong; Gao, Yongli

2017-08-01

The electronic structure at the organic-inorganic semiconductor interface of π -conjugated copper phthalocyanine (CuPc) on a black phosphorus (BP) crystal surface is studied with photoemission spectroscopy and density functional theory calculations. From the photoemission spectra, we observe a shift of about 0.7 eV for the highest occupied molecular orbital, which originates from the transition of phase in the organic molecular thin film (from the interface phase to the bulk phase). On the other hand, we find 0.2 eV band bending at the CuPc/BP interface while the formation of an interface dipole is very small. According to our photoemission spectrum and theoretical simulation, we also define that the interaction between CuPc and BP is physisorption via van der Waals forces, rather than chemisorption. Our results provide a fundamental understanding of CuPc/BP interfacial interactions that could be important for future two-dimensional organic/inorganic heterostructure devices.

Temperature effect on the structural stabilities and electronic properties of X22H28 (X=C, Si and Ge) nanocrystals: A first-principles study

NASA Astrophysics Data System (ADS)

Deng, Xiao-Lin; Zhao, Yu-Jun; Wang, Ya-Ting; Liao, Ji-Hai; Yang, Xiao-Bao

2016-12-01

Based on ab initio molecular dynamic simulations, we have theoretically investigated the structural stabilities and electronic properties of X22H28 (X=C, Si, and Ge) nanocrystals, as a function of temperature with consideration of vibrational entropy effects. To compare the relative stabilities of X22H28 isomers, the vibration free energies are obtained according to the calculated phonon spectrum, where the typical modes are shown to be dominant to the structural stabilities. In addition, there is a significant gap reduction as the temperature increases from 0 K to 300 K, where the decrements are 0.2 /0.5 /0.6eV for C/Si/Ge nanocrystals, respectively. The dependence of energy gap on the variance of bond length is also analyzed according to the corresponding atomic attributions to the HOMO and LUMO levels.

Efficient proton acceleration and focusing by an ultraintense laser interacting with a parabolic double concave target with an extended rear

NASA Astrophysics Data System (ADS)

Bake, Muhammad Ali; Xie, Bai-Song; Aimidula, Aimierding; Wang, Hong-Yu

2013-07-01

A new scheme for acceleration and focusing of protons via an improved parabolic double concave target irradiated by an ultraintense laser pulse is proposed. When an intense laser pulse illuminates a concave target, the hot electrons are concentrated on the focal region of the rear cavity and they form a strong space-charge-separation field, which accelerates the protons. For a simple concave target, the proton energy spectrum becomes very broad outside the rear cavity because of transverse divergence of the electromagnetic fields. However, particle-in-cell simulations show that, when the concave target has an extended rear, the hot electrons along the wall surface induce a transverse focusing sheath field, resulting in a clear enhancement of proton focusing, which makes the lower proton energy spread, while, leads to a little reduction of the proton bunch peak energy.

A novel graphene oxide-polyimide as optical waveguide material: Synthesis and thermo-optic switch properties

NASA Astrophysics Data System (ADS)

Cao, Tianlin; Zhao, Fanyu; Da, Zulin; Qiu, Fengxian; Yang, Dongya; Guan, Yijun; Cao, Guorong; Zhao, Zerun; Li, Jiaxin; Guo, Xiaotong

2016-10-01

In this work, a novel graphene oxide-polyimide (GOPI) as optical waveguide material was prepared. The structure, mechanical, thermal property and morphology of the GOPI was characterized by using fourier transform infrared, UV-visible spectroscopy, near-infrared spectrum, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscope and transmission electron microscopy. The thermo-optic coefficients (dn/dT) are -9.16 × 10-4 (532 nm), -7.56 × 10-4 (650 nm) and -4.82 × 10-4 (850 nm) °C-1, respectively. Based on the thermo-optic effect of prepared GOPI as waveguide material, a Y-branch with branching angle of 0.143° and Mach-Zehnder thermo-optic switches were designed. Using finite difference beam propagation method (FD-BPM) method, the simulation results such as power consumptions and response times of two different thermo-optic switches were obtained.

Ab initio approach to the ion stopping power at the plasma-solid interface

NASA Astrophysics Data System (ADS)

Bonitz, Michael; Schlünzen, Niclas; Wulff, Lasse; Joost, Jan-Philip; Balzer, Karsten

2016-10-01

The energy loss of ions in solids is of key relevance for many applications of plasmas, ranging from plasma technology to fusion. Standard approaches are based on density functional theory or SRIM simulations, however, the applicability range and accuracy of these results are difficult to assess, in particular, for low energies. Here we present an independent approach that is based on ab initio nonequilibrium Green functions theory, e.g. that allows to incorporate electronic correlations effects of the solid. We present the first application of this method to low-temperature plasmas, concentrating on proton and alpha-particle stopping in a graphene layer. In addition to the stopping power we present time-dependent results for the local electron density, the spectral function and the photoemission spectrum that is directly accessible in optical, UV or x-ray diagnostics. http://www.itap.uni-kiel.de/theo-physik/bonitz/.

Electronic structure of CdSe-ZnS 2D nanoplatelets

NASA Astrophysics Data System (ADS)

Cruguel, Hervé; Livache, Clément; Martinez, Bertille; Pedetti, Silvia; Pierucci, Debora; Izquierdo, Eva; Dufour, Marion; Ithurria, Sandrine; Aubin, Hervé; Ouerghi, Abdelkarim; Lacaze, Emmanuelle; Silly, Mathieu G.; Dubertret, Benoit; Lhuillier, Emmanuel

2017-04-01

Among colloidal nanocrystals, 2D nanoplatelets (NPLs) made of cadmium chalcogenides have led to especially well controlled optical features. However, the growth of core shell heterostructures has so far been mostly focused on CdS shells, while more confined materials will be more promising to decouple the emitting quantum states of the core from their external environment. Using k.p simulation, we demonstrate that a ZnS shell reduces by a factor 10 the leakage of the wavefunction into the surrounding medium. Using X-ray photoemission (XPS), we confirm that the CdSe active layer is indeed unoxidized. Finally, we build an effective electronic spectrum for these CdSe/ZnS NPLs on an absolute energy scale which is a critical set of parameters for the future integration of this material into optoelectronic devices. We determine the work function (WF) to be 4.47 eV while the material is behaving as an n-type semiconductor.

A Nonmetal Plasmonic Z-Scheme Photocatalyst with UV- to NIR-Driven Photocatalytic Protons Reduction.

PubMed

Zhang, Zhenyi; Huang, Jindou; Fang, Yurui; Zhang, Mingyi; Liu, Kuichao; Dong, Bin

2017-05-01

Ultrabroad-spectrum absorption and highly efficient generation of available charge carriers are two essential requirements for promising semiconductor-based photocatalysts, towards achieving the ultimate goal of solar-to-fuel conversion. Here, a fascinating nonmetal plasmonic Z-scheme photocatalyst with the W 18 O 49 /g-C 3 N 4 heterostructure is reported, which can effectively harvest photon energies spanning from the UV to the nearinfrared region and simultaneously possesses improved charge-carrier dynamics to boost the generation of long-lived active electrons for the photocatalytic reduction of protons into H 2 . By combining with theoretical simulations, a unique synergistic photocatalysis effect between the semiconductive Z-scheme charge-carrier separation and metal-like localized-surface-plasmon-resonance-induced "hot electrons" injection process is demonstrated within this binary heterostructure. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theory and simulation of photogeneration and transport in Si-SiOx superlattice absorbers

PubMed Central

2011-01-01

Si-SiOx superlattices are among the candidates that have been proposed as high band gap absorber material in all-Si tandem solar cell devices. Owing to the large potential barriers for photoexited charge carriers, transport in these devices is restricted to quantum-confined superlattice states. As a consequence of the finite number of wells and large built-in fields, the electronic spectrum can deviate considerably from the minibands of a regular superlattice. In this article, a quantum-kinetic theory based on the non-equilibrium Green's function formalism for an effective mass Hamiltonian is used for investigating photogeneration and transport in such devices for arbitrary geometry and operating conditions. By including the coupling of electrons to both photons and phonons, the theory is able to provide a microscopic picture of indirect generation, carrier relaxation, and inter-well transport mechanisms beyond the ballistic regime. PMID:21711827

Trapped electron mode turbulence driven intrinsic rotation in Tokamak plasmas.

PubMed

Wang, W X; Hahm, T S; Ethier, S; Zakharov, L E; Diamond, P H

2011-02-25

Progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported. The turbulence-driven intrinsic torque associated with nonlinear residual stress generation due to zonal flow shear induced asymmetry in the parallel wave number spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing experimental empirical scalings of intrinsic rotation. The origin of current scaling is found to be enhanced k(∥) symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The intrinsic torque is proportional to the pressure gradient because both turbulence intensity and zonal flow shear, which are two key ingredients for driving residual stress, increase with turbulence drive, which is R/L(T(e)) and R/L(n(e)) for the trapped electron mode. © 2011 American Physical Society

The physics of the knee in the cosmic ray spectrum

NASA Astrophysics Data System (ADS)

Kampert, K.-H.; Antoni, T.; Apel, W. D.; Badea, F.; Bekk, K.; Bercuci, A.; Blümer, H.; Bollmann, E.; Bozdog, H.

Recent results from the KASCADE extensive air shower experiment are presented. After briefly reviewing the status of the experiment we report on tests of hadronic interaction models and emphasize the progress being made in understanding the properties and origin of the knee at Eknee ˜= 4 · 1015 eV. Analysing the muonand hadron trigger rates in the KASCADE calorimeter as well as the global properties of high energy hadrons in the shower core leads us to conclude that QGSJET still provides the best overall description of EAS data, being superior to DPMJET II-5 and NEXUS 2, for example. Performing high statistics CORSIKA simulations and applying sophisticated unfolding techniques to the electron and muon shower size distributions, we are able to successfully deconvolute the all-particle energy spectrum into energy spectra of 4 individual primary mass groups (p, He, C, Fe). Each of these preliminary energy distributions exhibits a knee like structure with a change of their knee positions suggesting a constant rigidity of R ˜= 2-3 PV.

The Planck's character and temperature of visible radiation of a pulse-periodic discharge in cesium vapor

NASA Astrophysics Data System (ADS)

Baksht, F. G.; Lapshin, V. F.

2016-02-01

The radiation spectrum of pulse-periodic discharge in cesium vapor has been simulated in the framework of a two-temperature multifluid radiative gasdynamic model. It is established that, at a broad range of vapor pressures, the discharge spectrum exhibits a Planck character in a significant part of the visible spectral interval, which accounts for the high quality of color rendering in the discharge radiation. The relation between color temperature T c and electron temperature T 0 on the discharge axis is determined by radial optical thickness τ R of the plasma column: T c ≈ T 0 at τ R ≈ 1, T c < T 0 at τ R < 1, and T c > T 0 at τ R > 1. As the vapor pressure increases from 83 to 1087 Torr, color rendering index Ra of the discharge radiation changes from 95 to 98 and the color temperature grows from 3600 to 5200 K.

Interacting Electrons and Holes in Quasi-2D Quantum Dots in Strong Magnetic Fields

NASA Astrophysics Data System (ADS)

Hawrylak, P.; Sheng, W.; Cheng, S.-J.

2004-09-01

Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and of excitonic quantum Hall droplets at a filling factorν=2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons.

Development of a Simple Positron Age-Momentum Setup

NASA Astrophysics Data System (ADS)

Sheffield, Thomas; Quarles, C. A.

2009-04-01

A positron age-momentum setup that uses NIM Bin electronic modules and a conventional multichannel analyzer (MCA) is described. The essential idea is to accumulate a Doppler broadened spectrum (sensitive to the annihilation electron momentum) using a high purity Germanium detector in coincidence with a BaF2 scintillation counter, which also serves as the stop signal in a conventional positron lifetime setup. The MCA that collects the Doppler spectrum is gated by a selected region of the lifetime spectrum. Thus we can obtain Doppler broadening spectra as a function of positron lifetime: an age-momentum spectrum. The apparatus has been used so far to investigate a ZnO sample where the size of different vacancy trapping sites may affect the positron lifetime and the Doppler broadening spectrum. We are also looking at polymer and rubber carbon-black composite samples where differences in the Doppler spectrum may arise from positron trapping or positronium formation in the samples. Correction for background and contribution from the positron source itself to the Doppler spectrum will be discussed.

Charcoal Regeneration. Part 1. Mechanism of TNT Adsorption

DTIC Science & Technology

1977-11-01

cycle and particle size 29 6 Electron spectra of virgin FS300 as received 30 ii=_ 7 Electron spectrum of TNT standard 31 8 Electron spectrum of TNT in...ground in a mortar and pestle and passed through a series of US standard sieves. The ground charcoal passing through a 325 sieve (average particle...every case were crushed manually in a mortar and pestle and dis- persed ultrasonically in order to obtain a dispersion suitable for measurement. Mass

Electron-positron pair production by ultrarelativistic electrons in a soft photon field

NASA Technical Reports Server (NTRS)

Mastichiadis, A.; Marscher, A. P.; Brecher, K.

1986-01-01

The fully differential cross section for photon-electron pair production is integrated numerically over phase space. Results are obtained for the astrophysically interesting case in which the interaction between an ultrarelativistic electron and a soft photon results in electron-positron pair production. The positron spectrum is a function of the energies of both the photon and the electron, as well as the angle of interaction. It is found that the energy at which the positron distribution peaks is inversely proportional to the photon energy and independent of the electron energy. The positron spectrum is integrated once more over initial electron energies for a power-law energy distribution of primary electrons. The same procedure is repeated for the recoil particle; it is shown that the peak of the recoil energy distribution depends linearly on the energy of the primary electron. Finally, semianalytical expressions are obtained for the energy losses of the primary electrons.

Electron impact contribution to infrared NO emissions in auroral conditions

NASA Astrophysics Data System (ADS)

Campbell, L.; Brunger, M. J.

2007-11-01

Infrared emissions from nitric oxide, other than nightglow, are observed in aurora, principally due to a chemiluminescent reaction between excited nitrogen atoms and oxygen molecules that produces vibrationally excited NO. The rates for this chemiluminescent reaction have recently been revised. Based on new measurements of electron impact vibrational excitation of NO, it has been suggested that electron impact may also be significant in producing auroral NO emissions. We show results of a detailed calculation which predicts the infrared spectrum observed in rocket measurements, using the revised chemiluminescent rates and including electron impact excitation. For emissions from the second vibrational level and above, the shape of the spectrum can be reproduced within the statistical errors of the analysis of the measurements, although there is an unexplained discrepancy in the absolute value of the emissions. The inclusion of electron impact improves the agreement of the shape of the predicted spectrum with the measurements by accounting for part of the previously unexplained peak in emissions from the first vibrational level.

Interpretation of the photoelectron spectra of FeS(2)(-) by a multiconfiguration computational approach.

PubMed

Clima, Sergiu; Hendrickx, Marc F A

2007-11-01

The ground states of FeS(2) and FeS(2)(-), and several low-lying excited electronic states of FeS(2) that are responsible for the FeS(2)(-) photoelectron spectrum, are calculated. At the B3LYP level an open, quasi-linear [SFeS](-) conformation is found as the most stable structure, which is confirmed at the ab initio CASPT2 computational level. Both the neutral and the anionic unsaturated complexes possess high-spin electronic ground states. For the first time a complete assignment of the photoelectron spectrum of FeS(2)(-) is proposed. The lowest energy band in this spectrum is ascribed to an electron detachment from the two highest-lying 3dpi antibonding orbitals (with respect to the iron-sulfur bonding) of iron. The next-lowest experimental band corresponds to an electron removal from nonbonding, nearly pure sulfur orbitals. The two highest bands in the spectra are assigned as electron detachments from pi and sigma bonding mainly sulfur orbitals.

Fermi LAT observations of cosmic-ray electrons from 7 GeV to 1 TeV

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

Ackermann, M.

We present the results of our analysis of cosmic-ray electrons using about 8 × 10 6 electron candidates detected in the first 12 months on-orbit by the Fermi Large Area Telescope. This work extends our previously published cosmic-ray electron spectrum down to 7 GeV, giving a spectral range of approximately 2.5 decades up to 1 TeV. We describe in detail the analysis and its validation using beam-test and on-orbit data. In addition, we describe the spectrum measured via a subset of events selected for the best energy resolution as a cross-check on the measurement using the full event sample. Ourmore » electron spectrum can be described with a power law ∝ E - 3.08 ± 0.05 with no prominent spectral features within systematic uncertainties. Within the limits of our uncertainties, we can accommodate a slight spectral hardening at around 100 GeV and a slight softening above 500 GeV.« less

Fermi LAT observations of cosmic-ray electrons from 7 GeV to 1 TeV

DOE PAGES

Ackermann, M.

2010-11-01

We present the results of our analysis of cosmic-ray electrons using about 8 × 10 6 electron candidates detected in the first 12 months on-orbit by the Fermi Large Area Telescope. This work extends our previously published cosmic-ray electron spectrum down to 7 GeV, giving a spectral range of approximately 2.5 decades up to 1 TeV. We describe in detail the analysis and its validation using beam-test and on-orbit data. In addition, we describe the spectrum measured via a subset of events selected for the best energy resolution as a cross-check on the measurement using the full event sample. Ourmore » electron spectrum can be described with a power law ∝ E - 3.08 ± 0.05 with no prominent spectral features within systematic uncertainties. Within the limits of our uncertainties, we can accommodate a slight spectral hardening at around 100 GeV and a slight softening above 500 GeV.« less

Systematic effects of foreground removal in 21-cm surveys of reionization

NASA Astrophysics Data System (ADS)

Petrovic, Nada; Oh, S. Peng

2011-05-01

21-cm observations have the potential to revolutionize our understanding of the high-redshift Universe. Whilst extremely bright radio continuum foregrounds exist at these frequencies, their spectral smoothness can be exploited to allow efficient foreground subtraction. It is well known that - regardless of other instrumental effects - this removes power on scales comparable to the survey bandwidth. We investigate associated systematic biases. We show that removing line-of-sight fluctuations on large scales aliases into suppression of the 3D power spectrum across a broad range of scales. This bias can be dealt with by correctly marginalizing over small wavenumbers in the 1D power spectrum; however, the unbiased estimator will have unavoidably larger variance. We also show that Gaussian realizations of the power spectrum permit accurate and extremely rapid Monte Carlo simulations for error analysis; repeated realizations of the fully non-Gaussian field are unnecessary. We perform Monte Carlo maximum likelihood simulations of foreground removal which yield unbiased, minimum variance estimates of the power spectrum in agreement with Fisher matrix estimates. Foreground removal also distorts the 21-cm probability distribution function (PDF), reducing the contrast between neutral and ionized regions, with potentially serious consequences for efforts to extract information from the PDF. We show that it is the subtraction of large-scale modes which is responsible for this distortion, and that it is less severe in the earlier stages of reionization. It can be reduced by using larger bandwidths. In the late stages of reionization, identification of the largest ionized regions (which consist of foreground emission only) provides calibration points which potentially allow recovery of large-scale modes. Finally, we also show that (i) the broad frequency response of synchrotron and free-free emission will smear out any features in the electron momentum distribution and ensure spectrally smooth foregrounds and (ii) extragalactic radio recombination lines should be negligible foregrounds.

Computer program to simulate Raman scattering

NASA Technical Reports Server (NTRS)

Zilles, B.; Carter, R.

1977-01-01

A computer program is described for simulating the vibration-rotation and pure rotational spectrum of a combustion system consisting of various diatomic molecules and CO2 as a function of temperature and number density. Two kinds of spectra are generated: a pure rotational spectrum for any mixture of diatomic and linear triatomic molecules, and a vibrational spectrum for diatomic molecules. The program is designed to accept independent rotational and vibrational temperatures for each molecule, as well as number densities.

Analysis and application of Fourier transform spectroscopy in atmospheric remote sensing

NASA Technical Reports Server (NTRS)

Park, J. H.

1984-01-01

An analysis method for Fourier transform spectroscopy is summarized with applications to various types of distortion in atmospheric absorption spectra. This analysis method includes the fast Fourier transform method for simulating the interferometric spectrum and the nonlinear least-squares method for retrieving the information from a measured spectrum. It is shown that spectral distortions can be simulated quite well and that the correct information can be retrieved from a distorted spectrum by this analysis technique.

Theoretical Interpretation of Pass 8 Fermi -LAT e {sup +} + e {sup −} Data

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

Di Mauro, M.; Manconi, S.; Donato, F.

The flux of positrons and electrons ( e {sup +} + e {sup −}) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. We discuss a number of interpretations of Pass 8 Fermi -LAT e {sup +} + e {sup −} spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We find that the Fermi -LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positronsmore » from cataloged PWNe, and a secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e {sup +} + e {sup −} Fermi -LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green’s catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e {sup +} + e {sup −} Fermi -LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e {sup +} + e {sup −} spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

The role of plasma density scale length on the laser pulse propagation and scattering in relativistic regime

NASA Astrophysics Data System (ADS)

Pishdast, Masoud; Ghasemi, Seyed Abolfazl; Yazdanpanah, Jamal Aldin

2017-10-01

The role of plasma density scale length on two short and long laser pulse propagation and scattering in under dense plasma have been investigated in relativistic regime using 1 D PIC simulation. In our simulation, different density scale lengths and also two short and long pulse lengths with temporal pulse duration τL = 60 fs and τL = 300 fs , respectively have been used. It is found that laser pulse length and density scale length have considerable effects on the energetic electron generation. The analysis of total radiation spectrum reveals that, for short laser pulses and with reducing density scale length, more unstable electromagnetic modes grow and strong longitudinal electric field generates which leads to the generation of more energetic plasma particles. Meanwhile, the dominant scattering mechanism is Raman scattering and tends to Thomson scattering for longer laser pulse.

Orszag Tang vortex - Kinetic study of a turbulent plasma

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

Parashar, T. N.; Servidio, S.; Shay, M. A.

Kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations based on particle in cell ions and fluid electrons. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. An earlier study estimated the dissipation in the system. A comparison of MHD and hybrid simulations showed similar behavior at large scales but substantial differences at small scales. The hybrid magnetic energy spectrum shows a break at the scale where Hall term in the Ohm's law becomes important. The protons heat perpendicularly and most of the energy is dissipated through magnetic interactions. Here, the space time structure of themore » system is studied using frequency-wavenumber (k-omega) decomposition. No clear resonances appear, ruling out the cyclotron resonances as a likely candidate for the perpendicular heating. The only distinguishable wave modes present, which constitute a small percentage of total energy, are magnetosonic modes.« less

Measurements of ionization states in warm dense aluminum with betatron radiation

NASA Astrophysics Data System (ADS)

Mo, M. Z.; Chen, Z.; Fourmaux, S.; Saraf, A.; Kerr, S.; Otani, K.; Masoud, R.; Kieffer, J.-C.; Tsui, Y.; Ng, A.; Fedosejevs, R.

2017-05-01

Time-resolved measurements of the ionization states of warm dense aluminum via K-shell absorption spectroscopy are demonstrated using betatron radiation generated from laser wakefield acceleration as a probe. The warm dense aluminum is generated by irradiating a free-standing nanofoil with a femtosecond optical laser pulse and was heated to an electron temperature of ˜20 -25 eV at a close-to-solid mass density. Absorption dips in the transmitted x-ray spectrum due to the Al4 + and Al5 + ions are clearly seen during the experiments. The measured absorption spectra are compared to simulations with various ionization potential depression models, including the commonly used Stewart-Pyatt model and an alternative modified Ecker-Kröll model. The observed absorption spectra are in approximate agreement with these models, though indicating a slightly higher state of ionization and closer agreement for simulations with the modified Ecker-Kröll model.

Theoretical investigation on the soft X-ray spectrum of the highly-charged W54+ ions

NASA Astrophysics Data System (ADS)

Ding, Xiaobin; Yang, Jiaoxia; Koike, Fumihiro; Murakami, Izumi; Kato, Daiji; Sakaue, Hiroyuki A.; Nakamura, Nobuyuki; Dong, Chenzhong

2018-01-01

A detailed level collisional-radiative model of the E1 transition spectrum of Ca-like W54+ ion has been constructed. All the necessary atomic data has been calculated by relativistic configuration interaction (RCI) method with the implementation of Flexible Atomic Code (FAC). The results are in reasonable agreement with the available experimental and previous theoretical data. The synthetic spectrum has explained the EBIT spectrum in 29.5-32.5 Å , while several new strong transitions has been predicted to be observed in 18.5-19.6 Å for the future EBIT experiment with electron density ne = 1012 cm-3 and electron beam energy Ee = 18.2 keV.

Impulsive solar X-ray bursts. III - Polarization, directivity, and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

NASA Technical Reports Server (NTRS)

Langer, S. H.; Petrosian, V.

1977-01-01

The paper presents the spectrum, directivity, and state of polarization of the bremsstrahlung radiation expected from a beam of high-energy electrons spiraling along radial magnetic field lines toward the photosphere. A Monte Carlo method is then described for evaluation of the spectrum, directivity, and polarization of X-rays diffusely reflected from stellar photospheres. The accuracy of the technique is evaluated through comparison with analytic results. The calculated characteristics of the incident X-rays are used to evaluate the spectrum, directivity, and polarization of the reflected and total X-ray fluxes. The results are compared with observations.

Cosmic-ray electron-positron spectrum from 7 GeV to 2 TeV with the Fermi Large Area Telescope

DOE PAGES

Abdollahi, S.; Ackermann, M.; Ajello, M.; ...

2017-04-15

Here, we present a measurement of the cosmic-ray electron+positron spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of 3.07 ± 0.02(stat + syst) ± 0.04(energy measurement). An exponential cutoff lower than 1.8 TeV is excluded at 95% CL.

Cosmic-ray electron-positron spectrum from 7 GeV to 2 TeV with the Fermi Large Area Telescope

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

Abdollahi, S.; Ackermann, M.; Ajello, M.

Here, we present a measurement of the cosmic-ray electron+positron spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of 3.07 ± 0.02(stat + syst) ± 0.04(energy measurement). An exponential cutoff lower than 1.8 TeV is excluded at 95% CL.

An Electromagnetic Spectrum for Millennial Students: Teaching Light, Color, Energy, and Frequency Using the Electronic Devices of Our Time

ERIC Educational Resources Information Center

Murphy, Maureen Kendrick

2010-01-01

In this article, a comparison of student learning outcomes is made in sophomore-level physical science classes using a "traditional" pedagogical approach versus a "modern" approach. Specifically, when students were taught the electromagnetic spectrum using diagrams and examples that incorporate technological advances and electronic devices of our…

Review of Twenty-First Century Portable Electronic Devices for Persons with Moderate Intellectual Disabilities and Autism Spectrum Disorders

ERIC Educational Resources Information Center

Mechling, Linda C.

2011-01-01

Use of portable electronic devices by persons with moderate intellectual disabilities and autism spectrum disorders is gaining increased research attention. The purpose of this review was to synthesize twenty-first century literature (2000-2010) focusing on these technologies. Twenty-one studies were identified which evaluated use of: (a) handheld…

Validation of Autism Spectrum Disorder Diagnoses in Large Healthcare Systems with Electronic Medical Records

ERIC Educational Resources Information Center

Coleman, Karen J.; Lutsky, Marta A.; Yau, Vincent; Qian, Yinge; Pomichowski, Magdalena E.; Crawford, Phillip M.; Lynch, Frances L.; Madden, Jeanne M.; Owen-Smith, Ashli; Pearson, John A.; Pearson, Kathryn A.; Rusinak, Donna; Quinn, Virginia P.; Croen, Lisa A.

2015-01-01

To identify factors associated with valid Autism Spectrum Disorder (ASD) diagnoses from electronic sources in large healthcare systems. We examined 1,272 charts from ASD diagnosed youth <18 years old. Expert reviewers classified diagnoses as confirmed, probable, possible, ruled out, or not enough information. A total of 845 were classified with…

Energy Spectrum of Cosmic-Ray Electron and Positron from 10 GeV to 3 TeV Observed with the Calorimetric Electron Telescope on the International Space Station.

PubMed

Adriani, O; Akaike, Y; Asano, K; Asaoka, Y; Bagliesi, M G; Bigongiari, G; Binns, W R; Bonechi, S; Bongi, M; Brogi, P; Buckley, J H; Cannady, N; Castellini, G; Checchia, C; Cherry, M L; Collazuol, G; Di Felice, V; Ebisawa, K; Fuke, H; Guzik, T G; Hams, T; Hareyama, M; Hasebe, N; Hibino, K; Ichimura, M; Ioka, K; Ishizaki, W; Israel, M H; Javaid, A; Kasahara, K; Kataoka, J; Kataoka, R; Katayose, Y; Kato, C; Kawanaka, N; Kawakubo, Y; Krawczynski, H S; Krizmanic, J F; Kuramata, S; Lomtadze, T; Maestro, P; Marrocchesi, P S; Messineo, A M; Mitchell, J W; Miyake, S; Mizutani, K; Moiseev, A A; Mori, K; Mori, M; Mori, N; Motz, H M; Munakata, K; Murakami, H; Nakahira, S; Nishimura, J; de Nolfo, G A; Okuno, S; Ormes, J F; Ozawa, S; Pacini, L; Palma, F; Papini, P; Penacchioni, A V; Rauch, B F; Ricciarini, S B; Sakai, K; Sakamoto, T; Sasaki, M; Shimizu, Y; Shiomi, A; Sparvoli, R; Spillantini, P; Stolzi, F; Takahashi, I; Takayanagi, M; Takita, M; Tamura, T; Tateyama, N; Terasawa, T; Tomida, H; Torii, S; Tsunesada, Y; Uchihori, Y; Ueno, S; Vannuccini, E; Wefel, J P; Yamaoka, K; Yanagita, S; Yoshida, A; Yoshida, K; Yuda, T

2017-11-03

First results of a cosmic-ray electron and positron spectrum from 10 GeV to 3 TeV is presented based upon observations with the CALET instrument on the International Space Station starting in October, 2015. Nearly a half million electron and positron events are included in the analysis. CALET is an all-calorimetric instrument with total vertical thickness of 30 X_{0} and a fine imaging capability designed to achieve a large proton rejection and excellent energy resolution well into the TeV energy region. The observed energy spectrum over 30 GeV can be fit with a single power law with a spectral index of -3.152±0.016 (stat+syst). Possible structure observed above 100 GeV requires further investigation with increased statistics and refined data analysis.

Transport electron through a quantum wire by side-attached asymmetric quantum-dot rings

NASA Astrophysics Data System (ADS)

Rostami, A.; Zabihi, S.; Rasooli S., H.; Seyyedi, S. K.

2011-12-01

The electronic conductance at zero temperature through a quantum wire with side-attached asymmetric quantum ring (as a scatter system) is theoretically studied using the non-interacting Anderson tunneling Hamiltonian method. We show that the asymmetric configuration of QD- scatter system strongly impresses the amplitude and spectrum of quantum wire nanostructure transmission characteristics. It is shown that whenever the balanced number of quantum dots in two rings is substituted by unbalanced scheme, the number of forbidden mini-bands in quantum wire conductance increases and QW-nanostructure electronic conductance contains rich spectral properties due to appearance of the new anti-resonance and resonance points in spectrum. Considering the suitable gap between nano-rings can strengthen the amplitude of new resonant peaks in the QW conductance spectrum. The proposed asymmetric quantum ring scatter system idea in this paper opens a new insight on designing quantum wire nano structure for given electronic conductance.

Measurement of the total spectrum of electrons and positrons in the energy range of 300–1500 GeV in the PAMELA experiment with the aid of a sampling calorimeter and a neutron detector

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

Karelin, A. V., E-mail: karelin@hotbox.ru; Voronov, S. A.; Galper, A. M.

2015-03-15

A method based on the use of a sampling calorimeter was developed for measuring the total energy spectrum of electrons and positrons from high-energy cosmic rays in the PAMELA satellite-borne experiment. This made it possible to extend the range of energies accessible to measurements by the magnetic system of the PAMELA spectrometer. Themethod involves a procedure for selecting electrons on the basis of features of a secondary-particle shower in the calorimeter. The results obtained by measuring the total spectrum of cosmic-ray electrons and positrons in the energy range of 300–1500 GeV by the method in question are presented on themore » basis of data accumulated over a period spanning 2006 and 2013.« less

Electron localization and optical absorption of polygonal quantum rings

NASA Astrophysics Data System (ADS)

Sitek, Anna; Serra, Llorenç; Gudmundsson, Vidar; Manolescu, Andrei

2015-06-01

We investigate theoretically polygonal quantum rings and focus mostly on the triangular geometry where the corner effects are maximal. Such rings can be seen as short core-shell nanowires, a generation of semiconductor heterostructures with multiple applications. We show how the geometry of the sample determines the electronic energy spectrum, and also the localization of electrons, with effects on the optical absorption. In particular, we show that irrespective of the ring shape low-energy electrons are always attracted by corners and are localized in their vicinity. The absorption spectrum in the presence of a magnetic field shows only two peaks within the corner-localized state domain, each associated with different circular polarization. This picture may be changed by an external electric field which allows previously forbidden transitions, and thus enables the number of corners to be determined. We show that polygonal quantum rings allow absorption of waves from distant ranges of the electromagnetic spectrum within one sample.

Energy Spectrum of Cosmic-Ray Electron and Positron from 10 GeV to 3 TeV Observed with the Calorimetric Electron Telescope on the International Space Station

NASA Astrophysics Data System (ADS)

Adriani, O.; Akaike, Y.; Asano, K.; Asaoka, Y.; Bagliesi, M. G.; Bigongiari, G.; Binns, W. R.; Bonechi, S.; Bongi, M.; Brogi, P.; Buckley, J. H.; Cannady, N.; Castellini, G.; Checchia, C.; Cherry, M. L.; Collazuol, G.; di Felice, V.; Ebisawa, K.; Fuke, H.; Guzik, T. G.; Hams, T.; Hareyama, M.; Hasebe, N.; Hibino, K.; Ichimura, M.; Ioka, K.; Ishizaki, W.; Israel, M. H.; Javaid, A.; Kasahara, K.; Kataoka, J.; Kataoka, R.; Katayose, Y.; Kato, C.; Kawanaka, N.; Kawakubo, Y.; Krawczynski, H. S.; Krizmanic, J. F.; Kuramata, S.; Lomtadze, T.; Maestro, P.; Marrocchesi, P. S.; Messineo, A. M.; Mitchell, J. W.; Miyake, S.; Mizutani, K.; Moiseev, A. A.; Mori, K.; Mori, M.; Mori, N.; Motz, H. M.; Munakata, K.; Murakami, H.; Nakahira, S.; Nishimura, J.; de Nolfo, G. A.; Okuno, S.; Ormes, J. F.; Ozawa, S.; Pacini, L.; Palma, F.; Papini, P.; Penacchioni, A. V.; Rauch, B. F.; Ricciarini, S. B.; Sakai, K.; Sakamoto, T.; Sasaki, M.; Shimizu, Y.; Shiomi, A.; Sparvoli, R.; Spillantini, P.; Stolzi, F.; Takahashi, I.; Takayanagi, M.; Takita, M.; Tamura, T.; Tateyama, N.; Terasawa, T.; Tomida, H.; Torii, S.; Tsunesada, Y.; Uchihori, Y.; Ueno, S.; Vannuccini, E.; Wefel, J. P.; Yamaoka, K.; Yanagita, S.; Yoshida, A.; Yoshida, K.; Yuda, T.; Calet Collaboration

2017-11-01

First results of a cosmic-ray electron and positron spectrum from 10 GeV to 3 TeV is presented based upon observations with the CALET instrument on the International Space Station starting in October, 2015. Nearly a half million electron and positron events are included in the analysis. CALET is an all-calorimetric instrument with total vertical thickness of 30 X0 and a fine imaging capability designed to achieve a large proton rejection and excellent energy resolution well into the TeV energy region. The observed energy spectrum over 30 GeV can be fit with a single power law with a spectral index of -3.152 ±0.016 (stat+syst ). Possible structure observed above 100 GeV requires further investigation with increased statistics and refined data analysis.

AC-driven bilayer graphene: quasienergy spectrum of electrons and generation of soliton-like electromagnetic pulse

NASA Astrophysics Data System (ADS)

Kukhar, Egor I.

2018-01-01

Quasienergy spectrum of electrons in biased bigraphene subjected to the linear polarized high-frequency electromagnetic radiation has been derived. Quasienergy bands of ac-driven bigraphene have been investigated. Dynamical appearing of the saddle points in band structure of biased bigraphene and energy gap modification have been predicted. Electromagnetic field equation has been written using obtained quasienergy spectrum. The solution corresponding to the soliton-like electromagnetic wave has been obtained. The conditions of soliton-like wave generation in ac-driven bigraphene have been discussed.

Electron residual energy due to stochastic heating in field-ionized plasma

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

Khalilzadeh, Elnaz; The Plasma Physics and Fusion Research School, Tehran; Yazdanpanah, Jam, E-mail: jamal.yazdan@gmail.com

2015-11-15

The electron residual energy originated from the stochastic heating in under-dense field-ionized plasma is investigated here. Initially, the optical response of plasma is modeled by using two counter-propagating electromagnetic waves. In this case, the solution of motion equation of a single electron indicates that by including the ionization, the electron with higher residual energy compared with that without ionization could be obtained. In agreement with chaotic nature of the motion, it is found that the electron residual energy will be significantly changed by applying a minor change in the initial conditions. Extensive kinetic 1D-3V particle-in-cell simulations have been performed inmore » order to resolve full plasma reactions. In this way, two different regimes of plasma behavior are observed by varying the pulse length. The results indicate that the amplitude of scattered fields in a proper long pulse length is high enough to act as a second counter-propagating wave and trigger the stochastic electron motion. On the contrary, the analyses of intensity spectrum reveal the fact that the dominant scattering mechanism tends to Thomson rather than Raman scattering by increasing the pulse length. A covariant formalism is used to describe the plasma heating so that it enables us to measure electron temperature inside and outside of the pulse region.« less

Planar Two-Plasmon-Decay Experiments at Polar-Direct-Drive Ignition-Relevant Scale Lengths at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Rosenberg, M. J.; Solodov, A. A.; Seka, W.; Myatt, J. F.; Regan, S. P.; Hohenberger, M.; Epstein, R.; Collins, T. J. B.; Turnbull, D. P.; Ralph, J. E.; Barrios, M. A.; Moody, J. D.

2015-11-01

Results from the first experiments at the National Ignition Facility (NIF) to probe two-plasmon -decay (TPD) hot-electron production at scale lengths relevant to polar-direct-drive (PDD) ignition are reported. The irradiation on one side of a planar CH foil generated a plasma at the quarter-critical surface with a predicted density gradient scale length of Ln ~ 600 μm , a measured electron temperature of Te ~ 3 . 5 to 4.0 keV, an overlapped laser intensity of I ~ 6 ×1014 W/cm2, and a predicted TPD threshold parameter of η ~ 4 . The hard x-ray spectrum and the Kα emission from a buried Mo layer were measured to infer the hot-electron temperature and the fraction of total laser energy converted to TPD hot electrons. Optical emission at ω/2 correlated with the time-dependent hard x-ray signal confirms that TPD is responsible for the hot-electron generation. The effect of laser beam angle of incidence on TPD hot-electron generation was assessed, and the data show that the beam angle of incidence did not have a strong effect. These results will be used to benchmark simulations of TPD hot-electron production at conditions relevant to PDD ignition-scale implosions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Likelihood reconstruction method of real-space density and velocity power spectra from a redshift galaxy survey

NASA Astrophysics Data System (ADS)

Tang, Jiayu; Kayo, Issha; Takada, Masahiro

2011-09-01

We develop a maximum likelihood based method of reconstructing the band powers of the density and velocity power spectra at each wavenumber bin from the measured clustering features of galaxies in redshift space, including marginalization over uncertainties inherent in the small-scale, non-linear redshift distortion, the Fingers-of-God (FoG) effect. The reconstruction can be done assuming that the density and velocity power spectra depend on the redshift-space power spectrum having different angular modulations of μ with μ2n (n= 0, 1, 2) and that the model FoG effect is given as a multiplicative function in the redshift-space spectrum. By using N-body simulations and the halo catalogues, we test our method by comparing the reconstructed power spectra with the spectra directly measured from the simulations. For the spectrum of μ0 or equivalently the density power spectrum Pδδ(k), our method recovers the amplitudes to an accuracy of a few per cent up to k≃ 0.3 h Mpc-1 for both dark matter and haloes. For the power spectrum of μ2, which is equivalent to the density-velocity power spectrum Pδθ(k) in the linear regime, our method can recover, within the statistical errors, the input power spectrum for dark matter up to k≃ 0.2 h Mpc-1 and at both redshifts z= 0 and 1, if the adequate FoG model being marginalized over is employed. However, for the halo spectrum that is least affected by the FoG effect, the reconstructed spectrum shows greater amplitudes than the spectrum Pδθ(k) inferred from the simulations over a range of wavenumbers 0.05 ≤k≤ 0.3 h Mpc-1. We argue that the disagreement may be ascribed to a non-linearity effect that arises from the cross-bispectra of density and velocity perturbations. Using the perturbation theory and assuming Einstein gravity as in simulations, we derive the non-linear correction term to the redshift-space spectrum, and find that the leading-order correction term is proportional to μ2 and increases the μ2-power spectrum amplitudes more significantly at larger k, at lower redshifts and for more massive haloes. We find that adding the non-linearity correction term to the simulation Pδθ(k) can fairly well reproduce the reconstructed Pδθ(k) for haloes up to k≃ 0.2 h Mpc-1.

Moments of the electron energy spectrum and partial branching fraction of B{yields}X{sub c}e{nu} decays at the Belle detector

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

Urquijo, P.; Barberio, E.; Dalseno, J.

2007-02-01

We report a measurement of the inclusive electron energy spectrum for charmed semileptonic decays of B mesons in a 140 fb{sup -1} data sample collected at the {upsilon}(4S) resonance with the Belle detector at the KEKB asymmetric energy e{sup +}e{sup -} collider. We determine the first four moments of the electron energy spectrum for threshold values of the electron energy between 0.4 and 2.0 GeV. In addition, we provide values of the partial branching fraction (zeroth moment) for the same electron threshold energies, and independent measurements of the B{sup +} and B{sup 0} partial branching fractions at 0.4 GeV andmore » 0.6 GeV electron threshold energies. We measure the independent B{sup +} and B{sup 0} partial branching fractions with electron threshold energies of 0.4 GeV to be {delta}B(B{sup +}{yields}X{sub c}e{nu})=(10.79{+-}0.25(stat.){+-}0.27(sys.))% and {delta}B(B{sup 0}{yields}X{sub c}e{nu})=(10.08{+-}0.30(stat.){+-}0.22(sys.))%. Full correlations between all measurements are evaluated.« less

Theory of Raman scattering in coupled electron-phonon systems

NASA Astrophysics Data System (ADS)

Itai, K.

1992-01-01

The Raman spectrum is calculated for a coupled conduction-electron-phonon system in the zero-momentum-transfer limit. The Raman scattering is due to electron-hole excitations and phonons as well. The phonons of those branches that contribute to the electron self-energy and the correction of the electron-phonon vertex are assumed to have flat energy dispersion (the Einstein phonons). The effect of electron-impurity scattering is also incorporated. Both the electron-phonon interaction and the electron-impurity interaction cause the fluctuation of the electron distribution between different parts of the Fermi surface, which results in overdamped zero-sound modes of various symmetries. The scattering cross section is obtained by solving the Bethe-Salpeter equation. The spectrum shows a lower threshold at the smallest Einstein phonon energy when only the electron-phonon interaction is taken into consideration. When impurities are also taken into consideration, the threshold disappears.

ATCA 16 cm observation of CIZA J1358.9-4750: Implication of merger stage and constraint on non-thermal properties

NASA Astrophysics Data System (ADS)

Akahori, Takuya; Kato, Yuichi; Nakazawa, Kazuhiro; Ozawa, Takeaki; Gu, Liyi; Takizawa, Motokazu; Fujita, Yutaka; Nakanishi, Hiroyuki; Okabe, Nobuhiro; Makishima, Kazuo

2018-06-01

We report the Australia Telescope Compact Array 16 cm observation of CIZA J1358.9-4750. Recent X-ray studies imply that this galaxy cluster is composed of merging, binary clusters. Using the EW367 configuration, we found no significant diffuse radio emission in and around the cluster. An upper limit of the total radio power at 1.4 GHz is ˜1.1 × 1022 W Hz-1 in 30 square arcminutes, which is a typical size for radio relics. It is known that an empirical relation holds between the total radio power and X-ray luminosity of the host cluster. The upper limit is about one order of magnitude lower than the power expected from the relation. Very young (˜70 Myr) shocks with low Mach numbers (˜1.3), which are often seen at an early stage of merger simulations, are suggested by the previous X-ray observation. The shocks may generate cosmic-ray electrons with a steep energy spectrum, which is consistent with non-detection of bright (>1023 W Hz-1) relic in this 16 cm band observation. Based on the assumption of energy equipartition, the upper limit gives a magnetic field strength of below 0.68f(Dlos/1 Mpc)-1(γmin/200)-1 μG, where f is the cosmic-ray total energy density over the cosmic-ray electron energy density, Dlos is the depth of the shock wave along the sightline, and γmin is the lower cutoff Lorentz factor of the cosmic-ray electron energy spectrum.

Electronic structures of WAlO(y) and WAlO(y)(-) (y = 2-4) determined by anion photoelectron spectroscopy and density functional theory calculations.

PubMed

Mann, Jennifer E; Waller, Sarah E; Jarrold, Caroline Chick

2012-07-28

The anion photoelectron spectra of WAlO(y)(-) (y = 2-4) are presented and assigned based on results of density functional theory calculations. The WAlO(2)(-) and WAlO(3)(-) spectra are both broad, with partially resolved vibrational structure. In contrast, the WAlO(4)(-) spectrum features well-resolved vibrational structure with contributions from three modes. There is reasonable agreement between experiment and theory for all oxides, and calculations are in particular validated by the near perfect agreement between the WAlO(4)(-) photoelectron spectrum and a Franck-Condon simulation based on computationally determined spectroscopic parameters. The structures determined from this study suggest strong preferential W-O bond formation, and ionic bonding between Al(+) and WO(y)(-2) for all anions. Neutral species are similarly ionic, with WAlO(2) and WAlO(3) having electronic structure that suggests Al(+) ionically bound to WO(y)(-) and WAlO(4) being described as Al(+2) ionically bound to WO(4)(-2). The doubly-occupied 3sp hybrid orbital localized on the Al center is energetically situated between the bonding O-local molecular orbitals and the anti- or non-bonding W-local molecular orbitals. The structures determined in this study are very similar to structures recently determined for the analogous MoAlO(y)(-)/MoAlO(y) cluster series, with subtle differences found in the electronic structures [S. E. Waller, J. E. Mann, E. Hossain, M. Troyer, and C. C. Jarrold, J. Chem. Phys. 137, 024302 (2012)].

Surface plasmon-enhanced photovoltaic device

DOEpatents

Kostecki, Robert; Mao, Samuel

2014-10-07

Photovoltaic devices are driven by intense photoemission of "hot" electrons from a suitable nanostructured metal. The metal should be an electron source with surface plasmon resonance within the visible and near-visible spectrum range (near IR to near UV (about 300 to 1000 nm)). Suitable metals include silver, gold, copper and alloys of silver, gold and copper with each other. Silver is particularly preferred for its advantageous opto-electronic properties in the near UV and visible spectrum range, relatively low cost, and simplicity of processing.

Comparison of Tropical and Extratropical Gust Factors Using Observed and Simulated Data

NASA Astrophysics Data System (ADS)

Edwards, R. P.; Schroeder, J. L.

2011-12-01

Questions of whether differences exist between tropical cyclone (TC) and extratropical (ET) wind have been the subject of considerable debate. This study will focus on the behavior of the gust factor (GF), the ratio of a peak wind speed of a certain duration and a mean wind speed of a certain duration, for three types of data: TC, ET, and simulated. For this project, the Universal Spectrum, a normalized, averaged spectrum for wind, was un-normalized and used to create simulated wind speed time series at a variety of wind speeds. Additional time series were created after modifying the spectrum to simulate the additional low-frequency energy observed in the TC wind spectrum as well as the reduction of high-frequency energy caused by a mechanical anemometer. The T and ET data used for this study were collected by Texas Tech University's mobile towers as part of various field efforts since 1998. Before comparisons were made, the database was divided into four roughness regimes based on the roughness length to ensure that differences observed in the turbulence statistics are not caused by differences in upstream terrain. The mean GF for the TC data set (open roughness regime), 1.49, was slightly higher than the ET value of 1.44 (Table 1). The distributions of GFs from each data type show similarities in shape between the base-simulated and ET data sets and between the TC and modified-simulated data set (Figure 1). These similarities are expected given the spectral similarities between the TC and modified-simulated data sets, namely additional low-frequency energy relative to the ET and base-simulated data. These findings suggest that the higher amount of low-frequency energy present in the tropical wind spectrum is partially responsible for the resulting higher GF for the tropical cyclone data. However, the modest increase in GF from the base to the modified simulated data suggest that there are more factors at work.

COMBINED MODELING OF ACCELERATION, TRANSPORT, AND HYDRODYNAMIC RESPONSE IN SOLAR FLARES. I. THE NUMERICAL MODEL

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

Liu Wei; Petrosian, Vahe; Mariska, John T.

2009-09-10

Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self-consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated themore » simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a {approx}10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a nonthermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.« less

Electron-Beam Diagnostic Methods for Hypersonic Flow Diagnostics

NASA Technical Reports Server (NTRS)

1994-01-01

The purpose of this work was the evaluation of the use of electron-bean fluorescence for flow measurements during hypersonic flight. Both analytical and numerical models were developed in this investigation to evaluate quantitatively flow field imaging concepts based upon the electron beam fluorescence technique for use in flight research and wind tunnel applications. Specific models were developed for: (1) fluorescence excitation/emission for nitrogen, (2) rotational fluorescence spectrum for nitrogen, (3) single and multiple scattering of electrons in a variable density medium, (4) spatial and spectral distribution of fluorescence, (5) measurement of rotational temperature and density, (6) optical filter design for fluorescence imaging, and (7) temperature accuracy and signal acquisition time requirements. Application of these models to a typical hypersonic wind tunnel flow is presented. In particular, the capability of simulating the fluorescence resulting from electron impact ionization in a variable density nitrogen or air flow provides the capability to evaluate the design of imaging instruments for flow field mapping. The result of this analysis is a recommendation that quantitative measurements of hypersonic flow fields using electron-bean fluorescence is a tractable method with electron beam energies of 100 keV. With lower electron energies, electron scattering increases with significant beam divergence which makes quantitative imaging difficult. The potential application of the analytical and numerical models developed in this work is in the design of a flow field imaging instrument for use in hypersonic wind tunnels or onboard a flight research vehicle.

Hydrogen Balmer Line Broadening in Solar and Stellar Flares

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

Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han

2017-03-10

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigtmore » profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a “multithread” model improves the agreement with the observations. We revisit the three-component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a “hot spot” atmosphere heated by an ultrarelativistic electron beam with reasonable filling factors: ∼0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.« less

Hydrogen Balmer Line Broadening in Solar and Stellar Flares

NASA Astrophysics Data System (ADS)

Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han; Tremblay, Pier-Emmanuel; Brown, Stephen; Carlsson, Mats; Osten, Rachel A.; Wisniewski, John P.; Hawley, Suzanne L.

2017-03-01

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigt profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a “multithread” model improves the agreement with the observations. We revisit the three-component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a “hot spot” atmosphere heated by an ultrarelativistic electron beam with reasonable filling factors: ˜0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.

The vibronic level structure of the cyclopentadienyl radical

NASA Astrophysics Data System (ADS)

Ichino, Takatoshi; Wren, Scott W.; Vogelhuber, Kristen M.; Gianola, Adam J.; Lineberger, W. Carl; Stanton, John F.

2008-08-01

The 351.1 nm photoelectron spectrum of the cyclopentadienide ion has been measured, which reveals the vibronic structure of the X~ 2E1'' state of the cyclopentadienyl radical. Equation-of-motion ionization potential coupled-cluster (EOMIP-CCSD) calculations have been performed to construct a diabatic model potential of the X~ 2E1'' state, which takes into account linear Jahn-Teller effects along the e2' normal coordinates as well as bilinear Jahn-Teller effects along the e2' and ring-breathing a1' coordinates. A simulation based on this ab initio model potential reproduces the spectrum very well, identifying the vibronic levels with linear Jahn-Teller angular momentum quantum numbers of +/-1/2. The angular distributions of the photoelectrons for these vibronic levels are highly anisotropic with the photon energies used in the measurements. A few additional weak photoelectron peaks are observed when photoelectrons ejected parallel to the laser polarization are examined. These peaks correspond to the vibronic levels for out-of-plane modes in the ground X~ 2E1'' state, which arise due to several pseudo-Jahn-Teller interactions with excited states of the radical and quadratic Jahn-Teller interaction in the X~ 2E1'' state. A variant of the first derivative of the energy for the EOMIP-CCSD method has been utilized to evaluate the strength of these nonadiabatic couplings, which have subsequently been employed to construct the model potential of the X~ 2E1'' state with respect to the out-of-plane normal coordinates. Simulations based on the model potential successfully reproduce the weak features that become conspicuous in the 0° spectrum. The present study of the photoelectron spectrum complements a previous dispersed fluorescence spectroscopic study Miller and co-workers [J. Chem. Phys. 114, 4855 (2001); 4869 (2001) Miller and co-workers [J. Chem. Phys.114, 4869 (2001)] to provide a detailed account of the vibronic structure of X~ 2E1'' cyclopentadienyl. The electron affinity of the cyclopentadienyl radical is determined to be 1.808+/-0.006 eV. This electron affinity and the gas-phase acidity of cyclopentadiene have been combined in a negative ion thermochemical cycle to determine the C-H bond dissociation energy of cyclopentadiene; D0(C5H6,C-H)=81.5+/-1.3 kcal mol-1. The standard enthalpy of formation of the cyclopentadienyl radical has been determined to be ΔfH298(C5H5)=63.2+/-1.4 kcal mol-1.

Bias effects on the electronic spectrum of a molecular bridge

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

Phillips, Heidi; Prociuk, Alexander; Dunietz, Barry D

2011-01-01

In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectralanalysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of themore » electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level.« less

Model Order Reduction Algorithm for Estimating the Absorption Spectrum

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

Van Beeumen, Roel; Williams-Young, David B.; Kasper, Joseph M.

The ab initio description of the spectral interior of the absorption spectrum poses both a theoretical and computational challenge for modern electronic structure theory. Due to the often spectrally dense character of this domain in the quantum propagator’s eigenspectrum for medium-to-large sized systems, traditional approaches based on the partial diagonalization of the propagator often encounter oscillatory and stagnating convergence. Electronic structure methods which solve the molecular response problem through the solution of spectrally shifted linear systems, such as the complex polarization propagator, offer an alternative approach which is agnostic to the underlying spectral density or domain location. This generality comesmore » at a seemingly high computational cost associated with solving a large linear system for each spectral shift in some discretization of the spectral domain of interest. In this work, we present a novel, adaptive solution to this high computational overhead based on model order reduction techniques via interpolation. Model order reduction reduces the computational complexity of mathematical models and is ubiquitous in the simulation of dynamical systems and control theory. The efficiency and effectiveness of the proposed algorithm in the ab initio prediction of X-ray absorption spectra is demonstrated using a test set of challenging water clusters which are spectrally dense in the neighborhood of the oxygen K-edge. On the basis of a single, user defined tolerance we automatically determine the order of the reduced models and approximate the absorption spectrum up to the given tolerance. We also illustrate that, for the systems studied, the automatically determined model order increases logarithmically with the problem dimension, compared to a linear increase of the number of eigenvalues within the energy window. Furthermore, we observed that the computational cost of the proposed algorithm only scales quadratically with respect to the problem dimension.« less

Electronic structure and linear optical properties of ZnSe and ZnSe:Mn.

PubMed

Su, Kang; Wang, Yuhua

2010-03-01

As an important wide band-gap II-VI semiconductor, ZnSe has attracted much attention for its various applications in photo-electronic devices such as blue light-emitting diodes and blue-green diode lasers. Mn-doped ZnSe is an excellent quantum dot material. The electronic structures of the sphalerite ZnSe and ZnSe:Mn were calculated using the Vienna ab initio Simulation Package with ultra-soft pseudo potentials and Material Studio. The calculated equilibrium lattice constants agree well with the experimental values. Using the optimized equilibrium lattice constants, the densities of states and energy band structures were further calculated. By analyzing the partial densities of states, the contributions of different electron states in different atoms were estimated. The p states of Zn mostly contribute to the top of the valence band, and the s states of Zn and the s states of Se have major effects on the bottom of the conduction band. The calculated results of ZnSe:Mn show the band gap was changed from 2.48 to 1.1 eV. The calculated linear optical properties, such as refractive index and absorption spectrum, are in good agreement with experimental values.

Statistical properties of radiation from VUV and X-ray free electron laser

NASA Astrophysics Data System (ADS)

Saldin, E. L.; Schneidmiller, E. A.; Yurkov, M. V.

1998-03-01

The paper presents a comprehensive analysis of the statistical properties of the radiation from a self-amplified spontaneous emission (SASE) free electron laser operating in linear and nonlinear mode. The investigation has been performed in a one-dimensional approximation assuming the electron pulse length to be much larger than a coherence length of the radiation. The following statistical properties of the SASE FEL radiation have been studied in detail: time and spectral field correlations, distribution of the fluctuations of the instantaneous radiation power, distribution of the energy in the electron bunch, distribution of the radiation energy after the monochromator installed at the FEL amplifier exit and radiation spectrum. The linear high gain limit is studied analytically. It is shown that the radiation from a SASE FEL operating in the linear regime possesses all the features corresponding to completely chaotic polarized radiation. A detailed study of statistical properties of the radiation from a SASE FEL operating in linear and nonlinear regime has been performed by means of time-dependent simulation codes. All numerical results presented in the paper have been calculated for the 70 nm SASE FEL at the TESLA Test Facility being under construction at DESY.

Two types of electron events in solar flares

NASA Technical Reports Server (NTRS)

Daibog, E. I.; Kurt, V. G.; Logachev, Y. I.; Stolpovsky, V. G.

1985-01-01

The fluxes and spectra of the flare electrons measured on board Venera-I3 and I4 space probes are compared with the parameters of the hard (E sub x approximately 55 keV) and thermal X-ray bursts. The electron flux amplitude has been found to correlate with flare importance in the thermal X-ray range (r approximately 0.8). The following two types of flare events have been found in the electron component of SCR. The electron flux increase is accompanied by a hard X-ray burst and the electron spectrum index in the approximately 25 to 200 keV energy range is gamma approximately 2 to 3. The electron flux increase is not accompanied by a hard X-ray burst and the electron spectrum is softer (Delta gamma approximately 0.7 to 1.0).

Electron-Electron and Electron-Phonon interactions effects on the tunnel electronic spectrum of PbS quantum dots

NASA Astrophysics Data System (ADS)

Wang, Hongyue; Lhuillier, Emmanuel; Yu, Qian; Mottaghizadeh, Alireza; Ulysse, Christian; Zimmers, Alexandre; Dubertret, Benoit; Aubin, Herve

2015-03-01

We present a tunnel spectroscopy study of the electronic spectrum of single PbS Quantum Dots (QDs) trapped between nanometer-spaced electrodes, measured at low temperature T=5 K. The carrier filling of the QD can be controlled either by the drain voltage in the shell filling regime or by a gate voltage. In the empty QD, the tunnel spectrum presents the expected signature of the 8x degenerated excited levels. In the drain controlled shell filling regime, the levels degeneracies are lifted by the global electrostatic Coulomb energy of the QD; in the gate controlled shell filling regime, the levels degeneracies are lifted by the intra-Coulomb interactions. In the charged quantum dot, electron-phonons interactions lead to the apparition of Franck-Condon side bands on the single excited levels and possibly Franck Condon blockade at low energy. The sharpening of excited levels at higher gate voltage suggests that the magnitude of electron-phonon interactions is decreased upon increasing the electron filling in the quantum dot. This work was supported by the French ANR Grants 10-BLAN-0409-01, 09-BLAN-0388-01, by the Region Ile-de-France in the framework of DIM Nano-K and by China Scholarship Council.

A multifrequency virtual spectrometer for complex bio-organic systems: vibronic and environmental effects on the UV/Vis spectrum of chlorophyll a.

PubMed

Barone, Vincenzo; Biczysko, Malgorzata; Borkowska-Panek, Monika; Bloino, Julien

2014-10-20

The subtle interplay of several different effects means that the interpretation and analysis of experimental spectra in terms of structural and dynamic characteristics is a challenging task. In this context, theoretical studies can be helpful, and as such, computational spectroscopy is rapidly evolving from a highly specialized research field toward a versatile and widespread tool. However, in the case of electronic spectra (e.g. UV/Vis, circular dichroism, photoelectron, and X-ray spectra), the most commonly used methods still rely on the computation of vertical excitation energies, which are further convoluted to simulate line shapes. Such treatment completely neglects the influence of nuclear motions, despite the well-recognized notion that a proper account of vibronic effects is often mandatory to correctly interpret experimental findings. Development and validation of improved models rooted into density functional theory (DFT) and its time-dependent extension (TD-DFT) is of course instrumental for the optimal balance between reliability and favorable scaling with the number of electrons. However, the implementation of easy-to-use and effective procedures to simulate vibrationally resolved electronic spectra, and their availability to a wide community of users, is at least equally important for reliable simulations of spectral line shapes for compounds of biological and technological interest. Here, such an approach has been applied to the study of the UV/Vis spectra of chlorophyll a. The results show that properly tailored approaches are feasible for state-of-the-art computational spectroscopy studies, and allow, with affordable computational resources, vibrational and environmental effects on the spectral line shapes to be taken into account for large systems. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

47 CFR 101.521 - Spectrum utilization.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 5 2012-10-01 2012-10-01 false Spectrum utilization. 101.521 Section 101.521 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES FIXED MICROWAVE SERVICES 24 GHz Service and Digital Electronic Message Service § 101.521 Spectrum utilization. All...