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Sample records for flare electron spectra

  1. Characteristics of energetic solar flare electron spectra

    NASA Technical Reports Server (NTRS)

    Moses, Dan; Droege, Wolfgang; Meyer, Peter; Evenson, Paul

    1989-01-01

    A 55 event survey of energy spectra of 0.1-100 MeV interplanetary electrons originating from solar flares as measured by two spectrometers onboard the ISEE 3 (ICE) spacecraft for the years 1978-1982 has been completed. Spectra generated using the maximum flux of a given event in each energy channel were restricted to events with a well-defined flux rise time. Two broad groups of electron spectra are considered. In one group, the spectra are well represented by a single power law in rigidity with spectral index in the range 3-4.5. The spectra in the other group deviate from a power law in rigidity systematically in that they harden with increasing rigidity. Events with near power-law spectra are found to be correlated with long-duration soft X-ray events, whereas those with hardening spectra are correlated with short-duration events. The possible variation of acceleration and propagation processes with the properties of the flare site is discussed, using the duration of the soft X-ray flare emission as an indicator of the physical parameters of the flare site (flare volume, density, coronal height, and magnetic field geometry).

  2. The energy spectra of solar flare electrons

    NASA Technical Reports Server (NTRS)

    Evenson, P. A.; Hovestadt, D.; Meyer, P.; Moses, D.

    1985-01-01

    A survey of 50 electron energy spectra from .1 to 100 MeV originating from solar flares was made by the combination of data from two spectrometers onboard the International Sun Earth Explorer-3 spacecraft. The observed spectral shapes of flare events can be divided into two classes through the criteria of fit to an acceleration model. This standard two step acceleration model, which fits the spectral shape of the first class of flares, involves an impulsive step that accelerates particles up to 100 keV and a second step that further accelerates these particles up to 100 MeV by a single shock. This fit fails for the second class of flares that can be characterized as having excessively hard spectra above 1 MeV relative to the predictions of the model. Correlations with soft X-ray and meter radio observations imply that the acceleration of the high energy particles in the second class of flares is dominated by the impulsive phase of the flares.

  3. COLLISIONAL RELAXATION OF ELECTRONS IN A WARM PLASMA AND ACCELERATED NONTHERMAL ELECTRON SPECTRA IN SOLAR FLARES

    SciTech Connect

    Kontar, Eduard P.; Jeffrey, Natasha L. S.; Bian, N. H.; Emslie, A. Gordon

    2015-08-10

    Extending previous studies of nonthermal electron transport in solar flares, which include the effects of collisional energy diffusion and thermalization of fast electrons, we present an analytic method to infer more accurate estimates of the accelerated electron spectrum in solar flares from observations of the hard X-ray spectrum. Unlike for the standard cold-target model, the spatial characteristics of the flaring region, especially the necessity to consider a finite volume of hot plasma in the source, need to be taken into account in order to correctly obtain the injected electron spectrum from the source-integrated electron flux spectrum (a quantity straightforwardly obtained from hard X-ray observations). We show that the effect of electron thermalization can be significant enough to nullify the need to introduce an ad hoc low-energy cutoff to the injected electron spectrum in order to keep the injected power in non-thermal electrons at a reasonable value. Rather, the suppression of the inferred low-energy end of the injected spectrum compared to that deduced from a cold-target analysis allows the inference from hard X-ray observations of a more realistic energy in injected non-thermal electrons in solar flares.

  4. Electron acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Droge, Wolfgang; Meyer, Peter; Evenson, Paul; Moses, Dan

    1989-01-01

    For the period Spetember 1978 to December 1982, 55 solar flare particle events for which the instruments on board the ISEE-3 spacecraft detected electrons above 10 MeV. Combining data with those from the ULEWAT spectrometer electron spectra in the range from 0.1 to 100 MeV were obtained. The observed spectral shapes can be divided into two classes. The spectra of the one class can be fit by a single power law in rigidity over the entire observed range. The spectra of the other class deviate from a power law, instead exhibiting a steepening at low rigidities and a flattening at high rigidities. Events with power-law spectra are associated with impulsive (less than 1 hr duration) soft X-ray emission, whereas events with hardening spectra are associated with long-duration (more than 1 hr) soft X-ray emission. The characteristics of long-duration events are consistent with diffusive shock acceleration taking place high in the corona. Electron spectra of short-duration flares are well reproduced by the distribution functions derived from a model assuming simultaneous second-order Fermi acceleration and Coulomb losses operating in closed flare loops.

  5. The flares of August 1972. [solar flare characteristics and spectra

    NASA Technical Reports Server (NTRS)

    Zirin, H.; Tanaka, K.

    1973-01-01

    Observations of the August, 1972 flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms, and spectra, are analyzed. The region (McMath 11976) showed inverted polarity from its inception on July 11; the great activity was due to extremely high shear and gradients in the magnetic field, as well as a constant invasion of one polarity into the opposite; observations in lambda 3835 show remarkable fast flashes in the impulsive flare of 18:38 UT on Aug. 2 with lifetimes of 5 sec, which may be due to dumping of particles in the lower chromosphere. Flare loops show evolutionary increases of their tilts to the neutral line in the flares of Aug. 4 and 7. Spectroscopic observations show red asymmetry and red shift of the H alpha emission in the flash phase of the Aug. 7 flare, as well as substantial velocity shear in the photosphere during the flare, somewhat like earthquake movement along a fault. Finally the total H alpha emission of the Aug. 7 flare could be measured accurately as about 2.5 x 10 to the 30th power erg, considerably less than coarser previous estimates for great flares.

  6. EMITTING ELECTRONS SPECTRA AND ACCELERATION PROCESSES IN THE JET OF Mrk 421: FROM THE LOW STATE TO THE GIANT FLARE STATE

    SciTech Connect

    Yan Dahai; Zhang Li; Fan Zhonghui; Zeng Houdun; Yuan Qiang

    2013-03-10

    We investigate the electron energy distributions (EEDs) and the acceleration processes in the jet of Mrk 421 through fitting the spectral energy distributions (SEDs) in different active states in the frame of a one-zone synchrotron self-Compton model. After assuming two possible EEDs formed in different acceleration models: the shock-accelerated power law with exponential cut-off (PLC) EED and the stochastic-turbulence-accelerated log-parabolic (LP) EED, we fit the observed SEDs of Mrk 421 in both low and giant flare states using the Markov Chain Monte Carlo method which constrains the model parameters in a more efficient way. The results from our calculations indicate that (1) the PLC and LP models give comparably good fits for the SED in the low state, but the variations of model parameters from low state to flaring can be reasonably explained only in the case of the PLC in the low state; and (2) the LP model gives better fits compared to the PLC model for the SED in the flare state, and the intra-day/night variability observed at GeV-TeV bands can be accommodated only in the LP model. The giant flare may be attributed to the stochastic turbulence re-acceleration of the shock-accelerated electrons in the low state. Therefore, we may conclude that shock acceleration is dominant in the low state, while stochastic turbulence acceleration is dominant in the flare state. Moreover, our result shows that the extrapolated TeV spectra from the best-fit SEDs from optical through GeV with the two EEDs are different. It should be considered with caution when such extrapolated TeV spectra are used to constrain extragalactic background light models.

  7. Electron beams in solar flares

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Dennis, Brian R.; Benz, Arnold O.

    1994-01-01

    A list of publications resulting from this program includes 'The Timing of Electron Beam Signatures in Hard X-Ray and Radio: Solar Flare Observations by BATSE/Compton Gamma-Ray Observatory and PHOENIX'; 'Coherent-Phase or Random-Phase Acceleration of Electron Beams in Solar Flares'; 'Particle Acceleration in Flares'; 'Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares'; 'Sequences of Correlated Hard X-Ray and Type 3 Bursts During Solar Flares'; and 'Solar Electron Beams Detected in Hard X-Rays and Radiowaves.' Abstracts and reprints of each are attached to this report.

  8. An upper limit on the hardness of the nonthermal electron spectra produced during the flash phase of solar flares.

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1971-01-01

    The observations of impulsive solar-flare X-rays above 10 keV made with OGO-5 satellite have been analyzed in order to study the variation of the nonthermal electron spectrum from one flare to another. The X-ray spectrum at the maxima of 129 impulsive X-ray bursts is represented by KE to the minus-gamma power photons per sq cm per sec per keV, and the frequency of occurrence of bursts with different values of gamma is studied. It is found that for gamma less than 4.0 the frequency of bursts rapidly decreases with the decrease in the value of gamma. The probability of occurrence of a burst with gamma less than 2.3 is extremely small.

  9. Bayesian model comparison of solar flare spectra

    NASA Astrophysics Data System (ADS)

    Ireland, J.; Holman, G.

    2012-12-01

    The detailed understanding of solar flares requires an understanding of the physics of accelerated electrons, since electrons carry a large fraction of the total energy released in a flare. Hard X-ray energy flux spectral observations of solar flares can be fit with different parameterized models of the interaction of the flare-accelerated electrons with the solar plasma. Each model describes different possible physical effects that may occur in solar flares. Bayesian model comparison provides a technique for assessing which model best describes the data. The advantage of this technique over others is that it can fully account for the different number and type of parameters in each model. We demonstrate this using Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectral data from the GOES (Geostationary Operational Environmental Satellite) X4.8 flare of 23-July-2002. We suggest that the observed spectrum can be reproduced using two different parameterized models of the flare electron content. The first model assumes that the flare-accelerated electron spectrum consisting of a single power law with a fixed low energy cutoff assumed to be below the range of fitted X-ray energies, interacting with a non-uniformly ionized target. The second model assumes that the flare-accelerated electron spectrum has a broken power law and a low energy cutoff, which interacts with a fully ionized target plasma. The low energy cutoff in this model is a parameter used in fitting the data. We will introduce and use Bayesian model comparison techniques to decide which model best explains the observed data. This work is funded by the NASA Solar and Heliospheric Physics program.

  10. Solar flare soft-X-ray spectra from Very Low Frequency observations of ionospheric modulations: Possibility of uninterrupted observation of non-thermal electron-plasma interaction in solar atmosphere.

    NASA Astrophysics Data System (ADS)

    Palit, Sourav; Chakrabarti, Sandip Kumar; Ray, Suman

    2016-07-01

    The hard and soft X-ray regions of a solar flare spectrum are the manifestation of interaction, namely of bremsstrahlung radiation of the non-thermal electrons moving inward in the denser part of the solar atmosphere with the plasma heated by those energetic electrons. The continuous and uninterrupted knowledge of X-ray photon spectra of flares are of great importance to derive information on the electron acceleration and hence time-evolution of energy transport and physics during solar flares. Satellite observations of solar X-ray spectrum are often limited by the restricted windows in each duty cycle to avoid the interaction of detectors and instruments with harmful energetic charge particles. In this work we have tried to tackle the problem by examining the possibility of using Earth's ionosphere and atmosphere as the detector of such transient events. Earth's lower ionosphere and upper atmosphere are the places where the X-rays and gamma-rays from such astronomical sources are absorbed. The electron-ion production rates due to the ionization of such energetic photons at different heights depend on the intensity and wavelength of the injected spectra and hence vary from one source to another. Obviously the electron and ion density vs. altitude profile has the imprint of the incident photon spectrum. As a preliminary exercise we developed a novel deconvolution method to extract the soft X-ray part of spectra of some solar flares of different classes from the electron density profiles obtained from Very Low Frequency (VLF) observation of lower ionosphere during those events. The method presented here is useful to carry out a similar exercise to infer the higher energy part of solar flare spectra and spectra of more energetic events such as the GRBs, SGRs etc. with the possibilities of probing even lower parts of the atmosphere.

  11. Muon and Tau Neutrinos Spectra from Solar Flares

    NASA Astrophysics Data System (ADS)

    Fargion, Daniele; Moscato, Federica

    2003-12-01

    Most power-full solar flare as the ones occurred on 23th February 1956, September 29th 1989, 28th October and on 2nd-4th November 2003 are sources of cosmic rays, X, gamma and neutrino bursts. These flares took place both on front or in the edge and in the hidden solar disk. The 4th November event was the most powerful X event in the highest known rank category X28 just at horizons. The observed and estimated total flare energy (EFL ≃ 1031div 1033 erg) should be a source of a prompt secondary neutrino burst originated, by proton-proton-pion production on the sun itself; a more delayed and spread neutrino flux signal arise by the solar charged flare particles reaching the terrestrial atmosphere. These first earliest prompt solar neutrino burst might be observed, in a few neutrino clustered events, in present or future largest neutrino underground detectors as Super-Kamiokande one, in time correlation with the X-Radio flare. The onset in time correlation has great statistical significance. Our first estimate on the neutrino number events detection at the Super-Kamiokande II Laboratory for horizontal or hidden flare is found to be few events: NeV_bar{ν}_e≃ 0.63&etae ()/(35 MeV) ()/(1031 erg); and NeV_bar{ν}μ ≃ 3.58()/(200 MeV) ()/(1031erg) η,SUB>μ, where η≃ 1, Eνμ > 113 MeV. Our first estimates of neutrino signals in largest underground detectors hint for few events in correlation with X, gamma, radio onser. Our approximated spectra for muons and taus from these rare solar eruption are shown over the most common background. The muon and tau signature is very peculiar and characteristic over electron and anti-electron neutrino fluxes. The rise of muon neutrinos will be detectable above the minimal muon threshold Eν ≃ 113 MeV energy, or above the pion and Δ ° thresholds (Eν≃ 151 and 484 MeV). Any large neutrino flare event record might also verify the expected neutrino flavour mixing leading to a few as well as a comparable

  12. Observations of solar flare photon energy spectra from 20 keV to 7 MeV

    NASA Technical Reports Server (NTRS)

    Yoshimori, M.; Watanabe, H.; Nitta, N.

    1985-01-01

    Solar flare photon energy spectra in the 20 keV to 7 MeV range are derived from the Apr. 1, Apr. 4, apr. 27 and May 13, 1981 flares. The flares were observed with a hard X-ray and a gamma-ray spectrometers on board the Hinotori satellite. The results show that the spectral shape varies from flare to flare and the spectra harden in energies above about 400 keV. Effects of nuclear line emission on the continuum and of higher energy electron bremsstrahlung are considered to explain the spectral hardening.

  13. 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).

  14. Relativistic electron transport and bremsstrahlung production in solar flares

    NASA Astrophysics Data System (ADS)

    Miller, James A.; Ramaty, Reuven

    1989-09-01

    A Monte Carlo simulation of ultrarelativistic electron transport in solar flare magnetic loops has been developed. It includes Coulomb, synchrotron, and bremsstrahlung energy losses; pitch-angle scattering by Alfven and whistler turbulence in the coronal region of the loop; and magnetic mirroring in the converging magnetic flux tubes beneath the transition region. Depth distributions, time profiles, energy spectra, and angular distributions of the resulting bremsstrahlung emission are calculated. It is found that both the preferential detection of solar flares with greater than 10 MeV emission near the limb of the sun and the observation of ultrarelativistic electron bremsstrahlung from flares on the disk are consequences of the loop transport model. The declining portions of the observed time profiles of greater than 10 MeV emission from solar flares can also be accounted for, and it is proposed that these portions are determined by transport and not acceleration.

  15. Energetics of Accelerated Ions and Electrons in Flares

    NASA Astrophysics Data System (ADS)

    Share, G. H.; Mugler, A. J.; Murphy, R. J.; Schwartz, R. A.

    2001-12-01

    We have analyzed hard X-ray and gamma-ray emission from 176 solar flares observed from 1980 to 1989 by the Solar Maximum Mission HXRBS and GRS experiments. This joint analysis provides flare spectra from ~40 keV to 8.5 MeV. We compare the photon spectra integrated over the same time intervals by the two experiments. The agreement in most instances is good. We present the combined spectra for all of the flares. These combined spectra can be used to study the shape of the bremsstrahlung continuum and therefore the shape of the accelerated electron spectrum over a broad range in energy. We estimate the energy contained in accelerated electrons above cutoffs of 20 keV and 70 keV using the X-ray data obtained with the HXRBS experiment. These energies range from ~ 1028 to 1034 ergs for a cutoff of 20 keV and from ~ 1027 to 1032 ergs for a cutoff of 70 keV. The energy in accelerated ions can be estimated from the gamma-ray fluxes in nuclear lines. These lines are strong enough to individually determine the energy contained in ions for about 40 flares. We plan to sum gamma-ray spectra from the remaining flares, grouped by the energy contained in electrons, to reveal the weak nuclear lines and therefore to determine the average energy contained in ions in these groupings. This work expands on the study performed by Ramaty and Mandzhavize (2000) for 19 intense nuclear line flares where they concluded that energy is often equipartitioned between accelerated ions and electrons.

  16. IUE spectra of a flare in HR 5110: A flaring RS CVn or Algol system?

    NASA Technical Reports Server (NTRS)

    Simon, T.; Linsky, J. L.; Schiffer, F. H., III

    1981-01-01

    Ultraviolet spectra of the RS CVn type binary system HR 5110 were obtained with IUE on May 31, 1979 during a period of intense radio flaring of this star. High temperature transition region lines are present, but are not enhanced above observed quiescent strengths. The similarities of HR 5110 to the Algol system, As Eri, suggest that the 1979 May to June flare may involve mass exchange rather than annihilation of coronal magnetic fields.

  17. Implications of solar flare hard X-ray ``knee'' spectra observed by RHESSI

    NASA Astrophysics Data System (ADS)

    Conway, A. J.; Brown, J. C.; Eves, B. A. C.; Kontar, E.

    2003-08-01

    We analyse the RHESSI photon spectra of four flares that exhibit significant deviations from power laws - i.e. changes in the ``local'' Hard X-ray spectral index. These spectra are characterised by two regions of constant power law index connected by a region of changing spectral index - the ``knee''. We develop theoretical and numerical methods of describing such knees in terms of variable photon spectral indices and we study the results of their inversions for source mean thin target and collisional thick target injection electron spectra. We show that a particularly sharp knee can produce unphysical negative values in the electron spectra, and we derive inequalities that can be used to test for this without the need for an inversion to be performed. Such unphysical features would indicate that source model assumptions were being violated, particularly strongly for the collisional thick target model which assumes a specific form for electron energy loss. For all four flares considered here we find that the knees do not correspond to unphysical electron spectra. In the three flares that have downward knees we conclude that the knee can be explained in terms of transport effects through a region of non-uniform ionisation. In the other flare, which has an upward knee, we conclude that it is most likely a feature of the accelerated spectrum.

  18. Electron acceleration in impulsive solar flares

    SciTech Connect

    Kane, S.R.; Benz, A.O.; Treumann, R.A.

    1982-12-01

    Simultaneous observations of the hard X-ray, microwave, and type III and DCIM (decimetric)radio bursts associated with the 1978 December 4 solar flare have been used to study the physical parameters relevant to the acceleration and propagation of energetic electrons during the impulsive phase of a solar flare. The hard X-ray observations were made with the X-ray spectrometer aboard the ISEE 3 spacecraft. The radio spectra in metric and decimetric bands were recorded with the radiospectrograph located at Durnten, near Zurich, Switzerland. The microwave observations were made at the Sagamore Hill and Bern observatories. The three metric type III bursts coincided with the three most prominent hard X-ray peaks. This is the fist time a clear one-to-one association between single type III bursts and hard X-ray peaks has been established. The average delay of the type III bursts with respect to the X-ray peaks was 0.5 s. The harder the X-ray spectrum, the higher was the drift rate of the associated type III burst. The characteristic electron energies inferred from the drift rate are of the order of 70 keV. The observed increase in the high-frequency cutoff of the metric type III bursts during the impulsive phase has been examined in terms of the decreasing altitude of the electron acceleration/injection region, the increasing hardness of the electron spectrum, and the decreasing acceleration time. A pulsating decimetric continuum (DCIM) was also found to be present during and before the impulsive phase. The DCIM source seems to coincide spatially with the electron acceleration region and the (projected) origin of the associated type II shock.ction region.

  19. Modeling solar flare hard X-ray images and spectra observed with RHESSI

    NASA Astrophysics Data System (ADS)

    Sui, Linhui

    2004-12-01

    predictions of the standard flare models: the downward motion of flare loops in the early impulsive phase of each flare, and an initially stationary coronal source above the loops. These features are believed to be related to the formation and development of a current sheet. In particular, the downward loop motion seems to be a common phenomenon in flares, suggesting the necessity for modifications to the existing standard flare models. Finally, thanks to the broad energy coverage of the RHESSI spectra, a low- energy cutoff of 28(+/-2) keV in the nonthermal electron distribution was determined for the April 15, 2002, flare. As a result, the energy carried by the nonthermal electrons is found to be comparable to the thermal energy of the flare, but one order of magnitude larger than the kinetic energy of the associated coronal mass ejection. The method used to deduce the electron low- energy cutoff will be useful in the analyses of similar events.

  20. Energetic electrons in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Batchelor, D. A.

    1984-01-01

    A new analysis was made of a thermal flare model proposed by Brown, Melrose, and Spicer (1979) and Smith and Lilliequist (1979). They assumed the source of impulsive hard X-rays to be a plasma at a temperature of order 10 to the 8th power K, initially located at the apex of a coronal arch, and confined by ion-acoustic turbulence in a collisionless conduction front. Such a source would expand at approximately the ion-sound speed, C sub S = square root of (k T sub e/m sub i), until it filled the arch. Brown, Melrose, and Spicer and Smith and Brown (1980) argued that the source assumed in this model would not explain the simultaneous impulsive microwave emission. In contrast, the new results presented herein suggest that this model leads to the development of a quasi-Maxwellian distribution of electrons that explains both the hard X-ray and microwave emissions. This implies that the source sizes can be determined from observations of the optically-thick portions of microwave spectra and the temperatures obtained from associated hard X-ray observations. In this model, the burst emission would rise to a maximum in a time, t sub r, approximately equal to L/c sub s, where L is the half-length of the arch. New observations of these impulsive flare emissions were analyzed herein to test this prediction of the model. Observations made with the Solar Maximum Mission spacecraft and the Bern Radio Observatory are in good agreement with the model.

  1. Energetic electrons generated during solar flares

    NASA Astrophysics Data System (ADS)

    Mann, Gottfried

    2015-12-01

    > electrons are accelerated up to energies beyond 30 keV is one of the open questions in solar physics. A flare is considered as the manifestation of magnetic reconnection in the solar corona. Which mechanisms lead to the production of energetic electrons in the magnetic reconnection region is discussed in this paper. Two of them are described in more detail.

  2. Gamma-ray emission and electron acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Petrosian, Vahe; Mctiernan, James M.; Marschhauser, Holger

    1994-01-01

    Recent observations have extended the spectra of the impulsive phase of flares to the GeV range. Such high-energy photons can be produced either by electron bremsstrahlung or by decay of pions produced by accelerated protons. In this paper we investigate the effects of processes which become important at high energies. We examine the effects of synchrotron losses during the transport of electrons as they travel from the acceleration region in the corona to the gamma-ray emission sites deep in the chromosphere and photosphere, and the effects of scattering and absorption of gamma rays on their way from the photosphere to space instruments. These results are compared with the spectra from so-called electron-dominated flares, observed by GRS on the Solar Maximum Mission, which show negligible or no detectable contribution from accelerated protons. The spectra of these flares show a distinct steepening at energies below 100 keV and a rapid falloff at energies above 50 MeV. Following our earlier results based on lower energy gamma-ray flare emission we have modeled these spectra. We show that neither the radiative transfer effects, which are expected to become important at higher energies, nor the transport effects (Coulomb collisions, synchrotron losses, or magnetic field convergence) can explain such sharp spectral deviations from a simple power law. These spectral deviations from a power law are therefore attributed to the acceleration process. In a stochastic acceleration model the low-energy steepening can be attributed to Coulomb collision and the rapid high-energy steepening can result from synchrotron losses during the acceleration process.

  3. EGRET High Energy Capability and Multiwavelength Flare Studies and Solar Flare Proton Spectra

    NASA Technical Reports Server (NTRS)

    Chupp, Edward L.

    1998-01-01

    The accomplishments of the participation in the Compton Gamma Ray Observatory Guest investigator program is summarized in this report. The work involved the study of Energetic Gamma Ray Experiment Telescope (EGRET)/Total Absorption Shower Counter(TASC) flare data. The specific accomplishments were the use of the accelerator neutron measurements obtained at the University of New Hampshire to verify the TASC response function and to modify the TASC fitting program to include a high energy neutron contribution, and to determine a high energy neutron contribution to the emissions from the 1991 June 11, solar flare. The next step in the analysis of this event was doing fits to the TASC energy-loss spectra as a function of time. A significant hardening of the solar proton spectrum over time was found for the flare. Further data was obtained from the Yohkoh HXT time histories and images for the 1991 October 27 flare. The results to date demonstrate that the TASC spectral analysis contributes crucial information on the particle spectrum interacting at the Sun. The report includes a paper accepted for publication, a draft of a paper to be delivered at the 26th International Cosmic Ray Conference and an abstract of a paper to be presented at the Meeting of the American Physical Society.

  4. EGRET High Energy Capability and Multiwavelength Flare Studies and Solar Flare Proton Spectra

    NASA Technical Reports Server (NTRS)

    Chupp, Edward L.

    1997-01-01

    UNH was assigned the responsibility to use their accelerator neutron measurements to verify the TASC response function and to modify the TASC fitting program to include a high energy neutron contribution. Direct accelerator-based measurements by UNH of the energy-dependent efficiencies for detecting neutrons with energies from 36 to 720 MeV in NaI were compared with Monte Carlo TASC calculations. The calculated TASC efficiencies are somewhat lower (by about 20%) than the accelerator results in the energy range 70-300 MeV. The measured energy-loss spectrum for 207 MeV neutron interactions in NaI were compared with the Monte Carlo response for 200 MeV neutrons in the TASC indicating good agreement. Based on this agreement, the simulation was considered to be sufficiently accurate to generate a neutron response library to be used by UNH in modifying the TASC fitting program to include a neutron component in the flare spectrum modeling. TASC energy-loss data on the 1991 June 11 flare was transferred to UNH. Also included appendix: Gamma-rays and neutrons as a probe of flare proton spectra: the solar flare of 11 June 1991.

  5. Energetic electrons and photospheric electric currents during solar flares

    NASA Astrophysics Data System (ADS)

    Musset, S.; Vilmer, N.; Bommier, V.

    2015-12-01

    Solar flares are among the most energetic events in the solar system. Magnetic energy previously stored in the coronal magnetic field is transferred to particle acceleration, plasma motion and plasma heating. Magnetic energy release is likely to occur in coronal currents sheets associated with regions of strong gradient of magnetic connectivity. Coronal current sheets can be traced by their footprints at the surface on the Sun, in e.g. photospheric current ribbons. We aim to study the relationship between the current ribbons observed at the photospheric level which trace coronal current sheets, and the flare energetic electrons traced by their X-ray emissions. The photospheric magnetic field and vertical current density are calculated from SDO/HMI spectropolarimetric data using the UNNOFIT inversion and Metcalf disambiguation codes, while the X-ray images and spectra are reconstructed from RHESSI data. In a first case (the GOES X2.2 flare of February 15, 2011), a spatial correlation is observed between the photospheric current ribbons and the coronal X-ray emissions from energetic electrons (Musset et al., 2015). Moreover, a conjoint evolution of both the photospheric currents and the X-ray emission is observed during the course of the flare. Both results are interpreted as consequences of the magnetic reconnection in coronal current sheets. Propagation of the reconnection sites to new structures during the flare results in new X-ray emission sites and local increase of the photospheric currents We will examine in this contribution whether similar results are obtained for other X-class flares.

  6. Energetic electrons and photospheric electric currents during solar flares

    NASA Astrophysics Data System (ADS)

    Musset, Sophie; Vilmer, Nicole; Bommier, Veronique

    2016-07-01

    It is currently admitted that solar flares are powered by magnetic energy previously stored in the coronal magnetic field. During magnetic reconnection processes, this energy is transferred to particle acceleration, plasma motion and plasma heating. Magnetic energy release is likely to occur on coronal currents sheets along regions of strong gradient of magnetic connectivity. These coronal current sheets can be traced by their footprints at the surface on the Sun, i.e. by photospheric current ribbons. We aim to study the relation between these current ribbons observed at the photospheric level, tracing the coronal current sheets, and the flare energetic electrons traced by their X-ray emissions. The photospheric magnetic field and vertical current density have been calculated from SDO/HMI spectropolarimetric data with the UNNOFIT inversion and Metcalf disambiguation codes, while the X-ray images and spectra have been reconstructed from RHESSI data. In a first case, the GOES X2.2 flare of February 15, 2011, a spatial correlation is observed between the photospheric current ribbons and the coronal X-ray emissions from energetic electrons. Moreover, a conjoint evolution of both the photospheric currents and the X-ray emission is observed during the course of the flare. Both results are interpreted as consequences of the magnetic reconnection in coronal current sheets, and propagation of the reconnection sites to new structures during the flare, leading to new X-ray emission and local increase of the photospheric currents (Musset et al., 2015). We shall discuss here similar results obtained for other X-class flares.

  7. Energy spectra of ions from impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Reames, D. V.; Richardson, I. G.; Wenzel, K.-P.

    1992-01-01

    A study of the energy spectra of ions from impulsive solar flares in the 0.1-100 MeV region is reported. Most of the events studied are dominated by He and these He spectra show a persistent steepening or break above about 10 MeV resulting in an increase in the power-law spectral indices from about 2 to about 3.5 or more. Spectra of H, He-3, O, and Fe have spectral indices that are consistent with a value of about 3.5 above about 2 MeV/amu. One event, dominated by protons, shows a clear maximum in the spectrum near 1 MeV. If the rollover in the spectrum below 1 MeV is interpreted as a consequence of matter traversal in the solar atmosphere, then the source of the acceleration would lie only about 800 km above the photosphere, well below the corona. Alternative interpretations are that trapping in the acceleration region directly causes a peak in the resulting ion spectrum or that low-energy particles encounter significant additional scattering during transport from the flare.

  8. Implications of X-Ray Observations for Electron Acceleration and Propagation in Solar Flares

    NASA Technical Reports Server (NTRS)

    Holman, G. D.; Aschwanden, M. J.; Aurass, H.; Battaglia, M.; Grigis, P. C.; Kontar, E. P.; Liu, W.; Saint-Hilaire, P.; Zharkova, V. V.

    2011-01-01

    High-energy X-rays and gamma-rays from solar flares were discovered just over fifty years ago. Since that time, the standard for the interpretation of spatially integrated flare X-ray spectra at energies above several tens of keV has been the collisional thick-target model. After the launch of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in early 2002, X-ray spectra and images have been of sufficient quality to allow a greater focus on the energetic electrons responsible for the X-ray emission, including their origin and their interactions with the flare plasma and magnetic field. The result has been new insights into the flaring process, as well as more quantitative models for both electron acceleration and propagation, and for the flare environment with which the electrons interact. In this article we review our current understanding of electron acceleration, energy loss, and propagation in flares. Implications of these new results for the collisional thick-target model, for general flare models, and for future flare studies are discussed.

  9. Energy spectra of ions from impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Reames, D. V.; Richardson, I. G.; Wenzel, K.-P.

    1991-01-01

    A study of the energy spectra of ions from impulsive solar flares in the 0.1 to 100 MeV region is reported with data from the combined observations of experiments on the ISEE 3 and IMP 8 spacecraft. Most of the events studied are dominated by He, and these He spectra show a persistent steepening or break above about 10 MeV resulting in an increase in the power-law spectral indices from about 2 to about 3.5 or more. One event, dominated by protons, shows a clear maximum in the spectrum near 1 MeV. If the rollover in the spectrum below 1 MeV is interpreted as a consequence of matter traversal in the solar atmosphere, then the source of the acceleration would lie only about 800 km above the photosphere, well below the corona. An alternative interpretation is that trapping in the acceleration region directly causes a peak in the spectrum.

  10. Interstellar Electron Density Spectra

    NASA Astrophysics Data System (ADS)

    Lambert, Hendrick Clark

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

  11. Electron precipitation in solar flares - Collisionless effects

    NASA Technical Reports Server (NTRS)

    Vlahos, L.; Rowland, H. L.

    1984-01-01

    A large fraction of the electrons which are accelerated during the impulsive phase of solar flares stream towards the chromosphere and are unstable to the growth of plasma waves. The linear and nonlinear evolution of plasma waves as a function of time is analyzed with a set of rate equations that follows, in time, the nonlinearly coupled system of plasma waves-ion fluctuations. As an outcome of the fast transfer of wave energy from the beam to the ambient plasma, nonthermal electron tails are formed which can stabilize the anomalous Doppler resonance instability responsible for the pitch angle scattering of the beam electrons. The non-collisional losses of the precipitating electrons are estimated, and the observational implication of these results are discussed.

  12. Solar flare accelerated electron transport through the turbulent solar wind

    NASA Astrophysics Data System (ADS)

    Reid, Hamish; Kontar, Eduard

    Solar flare accelerated electron beams can become unstable during transport from the Sun to the Earth, producing plasma waves in the turbulent inner heliosphere. We simulate solar electron beam propagation to the Earth in the weak turbulent regime taking into account the self-consistent generation of plasma waves. Induced plasma waves interact with the density fluctuations from low frequency MHD turbulence present in the background plasma. These fluctuations act to suppress the generation of waves, most acutely when fluctuations have large amplitudes or small wavelengths. The reduction of plasma wave generation alters the wave distribution which changes electron beam transport. Assuming an observed 5/3 Kolmogorov-type power density spectra of fluctuations, we investigate the energy spectra of the electron beam near the Earth. We find the presence of turbulence in the background plasma alters the spectral index below the break energy of the double power-law formed at 1AU. From an initial single power-law electron distribution, we find a range of spectra below the break energy, with higher levels of turbulence corresponding to a higher spectral index.

  13. Solar flare composition and thermodynamics from RESIK X-ray spectra

    SciTech Connect

    Sylwester, B.; Sylwester, J.; Kępa, A.; Mrozek, T.; Phillips, K. J. H. E-mail: js@cbk.pan.wroc.pl E-mail: kennethjhphillips@yahoo.com

    2014-06-01

    Previous estimates of the solar flare abundances of Si, S, Cl, Ar, and K from the RESIK X-ray crystal spectrometer on board the CORONAS-F spacecraft were made on the assumption of isothermal X-ray emission. We investigate the effect on these estimates by relaxing this assumption and instead determining the differential emission measure (DEM) or thermal structure of the emitting plasma by re-analyzing RESIK data for a GOES class M1.0 flare on 2002 November 14 (SOL2002-11-14T22:26) for which there was good data coverage. The analysis method uses a maximum-likelihood (Withbroe-Sylwester) routine for evaluating the DEM. In a first step, called here AbuOpt, an optimized set of abundances of Si, S, Ar, and K is found that is consistent with the observed spectra. With these abundances, the DEM evolution during the flare is found. The abundance optimization leads to revised abundances of silicon and sulfur in the flare plasma: A(S) = 6.94 ± 0.06 and A(Si) = 7.56 ± 0.08 (on a logarithmic scale with A(H) = 12). Previously determined abundances of Ar, K, and Cl from an isothermal assumption are still the preferred values. During the flare's maximum phase, the X-ray-emitting plasma has a basically two-temperature structure, with the cooler plasma with approximately constant temperature (3-6 MK) and a hotter plasma with temperature 16-21 MK. Using imaging data from the RHESSI hard X-ray spacecraft, the emission volume of the hot plasma is deduced from which lower limits of the electron density N{sub e} and the thermal content of the plasma are given.

  14. X-RAY FLARES OF EV Lac: STATISTICS, SPECTRA, AND DIAGNOSTICS

    SciTech Connect

    Huenemoerder, David P.; Schulz, Norbert S.; Testa, Paola; Drake, Jeremy J.; Osten, Rachel A.; Reale, Fabio

    2010-11-10

    We study the spectral and temporal behavior of X-ray flares from the active M dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the amplitude, shape, and scale. The flares range from very short (<1 ks) to long ({approx}10{sup 4} s) duration events with a range of shapes and amplitudes for all durations. We extract spectra for composite flares to study their mean evolution and to compare flares of different lengths. Evolution of spectral features in the density-temperature plane shows probable sustained heating. The short flares are significantly hotter than the longer flares. We determined an upper limit to the Fe K fluorescent flux, the best-fit value being close to what is expected for compact loops.

  15. High-resolution X-ray spectra of solar flares. III - General spectral properties of X1-X5 type flares

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Feldman, U.; Kreplin, R. W.; Cohen, L.

    1980-01-01

    High-resolution X-ray spectra of six class X1-X5 solar flares are discussed. The spectra were recorded by spaceborne Bragg crystal spectrometers in the ranges 1.82-1.97, 2.98-3.07 and 3.14-3.24 A. Electron temperatures derived from dielectronic satellite line to resonance line ratios for Fe XXV and Ca XIX are found to remain fairly constant around 22,000,000 and 16,000,000 K respectively during the rise phase of the flares, then decrease by approximately 6,000,000 K during the decay phase. Nonthermal motions derived from line widths for the April 27, 1979 event are found to be greatest during the rise phase (approximately 130 km/sec) and decrease to about 60 km/sec during decay. Volume emission measures for Fe XXV, Ca XIX and Ca XX are derived from photon fluxes as a function of temperature, and examination of the intensity behavior of the Fe K alpha emission as a function of time indicates that it is a result of fluorescence. Differences between the present and previous observations of temperature variation are discussed, and it is concluded that the flare plasmas are close to ionization equilibrium for the flares investigated.

  16. Energetic Electrons in Solar Flares - As Viewed in X-Rays

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2004-01-01

    Hard X-ray observations provide the most direct diagnostic we have of the suprathermal electrons and the hottest thermal plasma present in solar flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is obtaining the most comprehensive observations of individual solar flares ever available in hard X-rays. For the first time, high-resolution spectra are available for a large number of flares that accurately display the spectral shape and its evolution and, in many cases, allow us to identify the transition from the bremsstrahlung X-rays produced by suprathermal electrons to the bremsstrahlung at lower energies emitted by thermal plasma. Also, for the first time, images can be produced in arbitrary energy bands above 3 keV, and spectra of distinct imaged components can be obtained. I will review what we have learned from RHESSI observations about flare suprathermal electron distributions and their evolution Next, I will present computations of the energy deposited by these suprathermal electrons in individual flares and compare this with the energy contained in the hot thermal plasma. I will point out unsolved problems in deducing both suprathermal electron distributions and the energy content of the thermal plasma, and discuss possible solutions. Finally, I will present evidence that electron acceleration is associated with magnetic reconnection in the corona.

  17. On the 'fast electron hypothesis' for stellar flares

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1990-01-01

    It is pointed out that Gurzadyan's (1988) fast-electron hypothesis for stellar flares encounters certain difficulties. The origin of the fast electrons is obscure. Negative flares and predicted ratios of X-ray to optical fluxes are not necessarily a proof of the fast-electron hypothesis. When the electrons thermalize, they will yield X-ray fluxes which are orders of magnitude too large to be consistent with observations.

  18. Acceleration of electrons during the flash phase of solar flares

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1974-01-01

    The characteristics of the electron acceleration process operating during the flash phase of solar flares are deduced from the high time resolution observations of impulsive solar X rays greater than or equal to 10 keV and other flash phase emissions from small solar flares, and the implications of these findings are discussed.

  19. Onset of electron acceleration in a flare loop

    SciTech Connect

    Sharykin, Ivan; Liu, Siming; Fletcher, Lyndsay

    2014-09-20

    We carried out a detailed analysis of X-ray and radio observations of a simple flare loop that occurred on 2002 August 12, with the impulsive hard X-ray (HXR) light curves dominated by a single pulse. The emission spectra of the early impulsive phase are consistent with an isothermal model in the coronal loop with a temperature reaching several keV. A power-law high-energy spectral tail is evident near the HXR peak time, in accordance with the appearance of footpoints at high energies, and is well correlated with the radio emission. The energy content of the thermal component keeps increasing gradually after the disappearance of this nonthermal component. These results suggest that electron acceleration only covers the central period of a longer and more gradual energy dissipation process and that the electron transport within the loop plays a crucial role in the formation of the inferred power-law electron distribution. The spectral index of power-law photons shows a very gradual evolution, indicating that the electron accelerator is in a quasi-steady state, which is confirmed by radio observations. These results are consistent with the theory of stochastic electron acceleration from a thermal background. Advanced modeling with coupled electron acceleration and spatial transport processes is needed to explain these observations more quantitatively, which may reveal the dependence of the electron acceleration on the spatial structure of the acceleration region.

  20. Thermalisation and hard X-ray bremsstrahlung efficiency of self-interacting solar flare fast electrons

    NASA Astrophysics Data System (ADS)

    Galloway, R. K.; Helander, P.; MacKinnon, A. L.; Brown, J. C.

    2010-09-01

    Context. Most theoretical descriptions of the production of solar flare bremsstrahlung radiation assume the collision of dilute accelerated particles with a cold, dense target plasma, neglecting interactions of the fast particles with each other. This is inadequate for situations where collisions with this background plasma are not completely dominant, as may be the case in, for example, low-density coronal sources. Aims: We aim to formulate a model of a self-interacting, entirely fast electron population in the absence of a dense background plasma, to investigate its implications for observed bremsstrahlung spectra and the flare energy budget. Methods: We derive approximate expressions for the time-dependent distribution function of the fast electrons using a Fokker-Planck approach. We use these expressions to generate synthetic bremsstrahlung X-ray spectra as would be seen from a corresponding coronal source. Results: We find that our model qualitatively reproduces the observed behaviour of some flares. As the flare progresses, the model's initial power-law spectrum is joined by a lower energy, thermal component. The power-law component diminishes, and the growing thermal component proceeds to dominate the total emission over timescales consistent with flare observations. The power-law exhibits progressive spectral hardening, as is seen in some flare coronal sources. We also find that our model requires a factor of 7-10 fewer accelerated electrons than the cold, thick target model to generate an equivalent hard X-ray flux. Conclusions: This model forms the basis of a treatment of self-interactions among flare fast electrons, a process which affords a more efficient means to produce bremsstrahlung photons and so may reduce the efficiency requirements placed on the particle acceleration mechanism. It also provides a useful description of the thermalisation of fast electrons in coronal sources.

  1. Uncertainty Estimation in Fitting Parameterized Models to Solar Flare Hard X-ray Spectra

    NASA Astrophysics Data System (ADS)

    Ireland, Jack; Tolbert, A. K.; Holman, G. D.; Dennis, B. R.; Schwartz, R. A.

    2012-05-01

    We compare four different methods of estimating the uncertainty in fit parameters when fitting models to Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectral data. Two flare spectra are studied: one from the GOES (Geostationary Operational Environmental Satellite) X1.3 class flare of 19-January-2005, and the other from the X4.8 flare of 23-July-2002. Three of our methods rely on assumptions about the shape of the hyper-surface formed by the weighted sum of the squares of the differences between the model fit and the data as a function of the fit parameters, evaluated around the minimum value of the hyper-surface, to generate uncertainty estimates. The fourth method is based on Bayesian data analysis techniques. The four methods give approximately equal uncertainty estimates for the 19-January-2005 model parameters, but give very different uncertainty estimates for the 23-July-2002 model parameters. This is because the assumptions required for the first three methods hold approximately for the 19-January-2005 analysis, but do not hold for the 23-July-2002 analysis. The Bayesian-based method does not require these assumptions, and so can give reliable uncertainty estimates regardless of the shape of the hyper-surface formed by the model fit to the data. We show that for the 23-July-2002 spectrum, there is a 95% probability that the low energy cutoff to the model distribution of emitting flare electrons lies below approximately 40keV, and a 68% probability that it lies in the estimated range 7-36 keV. The most probable flare electron energy flux is approximately 1028.1 erg-1sec-1 with a 68% credible interval estimated at 1028.1-29.1 erg-1sec-1, and a 95% credible interval estimated at 1028.0-30.3 erg-1sec-1. For the 19-January-2005 spectrum, these quantities are more tightly constrained to 105±4 keV and 1027.66±0.01 erg-1sec-1 (68% uncertainties). The reasons for these disparate results are discussed. This work is funded by the NASA Solar and Heliospheric

  2. Ultrarelativistic electrons and solar flare gamma-radiation

    NASA Technical Reports Server (NTRS)

    Semukhin, P. E.; Kovaltsov, G. A.

    1985-01-01

    Ten solar flares with gamma radiation in excess of 10 MeV were observed. Almost all took place within a heliolatitude greater than 60 deg, close to the solar limb, an indication of the essential anisotropy of high-energy gamma radiation. This high-energy solar flare gamma radiation can be explained by the specific features of the bremsstrahlung of ultrarelativistic electrons trapped within the magnetic arc of the solar atmosphere, even if the acceleration of the electrons is anisotropic.

  3. Narrowband Gyrosynchrotron Bursts: Probing Electron Acceleration in Solar Flares

    NASA Astrophysics Data System (ADS)

    Fleishman, Gregory D.; Nita, Gelu M.; Kontar, Eduard P.; Gary, Dale E.

    2016-07-01

    Recently, in a few case studies we demonstrated that gyrosynchrotron microwave emission can be detected directly from the acceleration region when the trapped electron component is insignificant. For the statistical study reported here, we have identified events with steep (narrowband) microwave spectra that do not show a significant trapped component and, at the same time, show evidence of source uniformity, which simplifies the data analysis greatly. Initially, we identified a subset of more than 20 radio bursts with such narrow spectra, having low- and high-frequency spectral indices larger than three in absolute value. A steep low-frequency spectrum implies that the emission is nonthermal (for optically thick thermal emission, the spectral index cannot be steeper than two), and the source is reasonably dense and uniform. A steep high-frequency spectrum implies that no significant electron trapping occurs, otherwise a progressive spectral flattening would be observed. Roughly half of these radio bursts have RHESSI data, which allow for detailed, joint diagnostics of the source parameters and evolution. Based on an analysis of radio-to-X-ray spatial relationships, timing, and spectral fits, we conclude that the microwave emission in these narrowband bursts originates directly from the acceleration regions, which have a relatively strong magnetic field, high density, and low temperature. In contrast, the thermal X-ray emission comes from a distinct loop with a smaller magnetic field, lower density, but higher temperature. Therefore, these flares likely occurred due to interaction between two (or more) magnetic loops.

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  5. Signatures of Accelerated Electrons in Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Benz, Arnold O.

    2015-08-01

    Flares energize electrons (and ions) to supra-thermal energies. In most cases the final distribution in momentum or energy space is non-Maxwellian. The non-thermal part of the energy can be the source for various emissions, including hard X-rays, synchrotron radiation and coherent radio emission. Such non-thermal emissions may contain information on the acceleration process. Several acceleration scenarios have been proposed: electric DC field, stochastic, and shock acceleration. There is observational evidence for all three scenarios. The new data come from SDO, X-ray (RHESSI), radio observations (Nobeyama, VLA and e-Callisto). Solar energetic particles are an additional channel of information.Tiny solar microflares and huge stellar flares in binary systems (RS CVns) and dMe dwarfs differ by more than 10 orders of magnitude in released energy. Yet the relation between peak luminosity in thermal (soft) X-ray and non-thermal synchrotron (radio) emission is surprisingly constant. This observational fact indicates that flare acceleration scales with energy release over a large range. Electron acceleration in flares seems to be a universal process. The constraint on simultaneous thermal X-rays and non-thermal (radio) synchrotron emission seems to select on particular kind of flare. In this subset, there seems to be only one type of acceleration.Yet, small deviations are noted: Small solar flares are softer in hard X-rays. Solar nanoflares are relatively weak in synchrotron emission. The recently noted case of radio-poor preflares will also be presented. The deviations suggest that the acceleration is less efficient in small flares and in the early phase of flares. Larger deviations are reported occasionally for solar flares and more often from stellar flares, where either thermal or non-thermal emission seems to be missing completely.The location of the acceleration in solar flares remains disputed. Observations suggesting acceleration in the soft X-ray top-tops, above

  6. Flare and CME onset: UV spectra show fast 3-D flow

    NASA Astrophysics Data System (ADS)

    Innes, D. E.

    We present observations taken in the corona above a flare that occurred on the west limb of the Sun. SUMER spectra show large red (400 km/s) and blue (700 km/s) Dopplershifts in Fe XX (107 K), Cr XVI (5×106 K), Si IX (106 K) and O III (105 K) emission lines. These shifts are associated with a fast moving (500 km/s) optical emission front detected in high cadence images, taken with the coronagraph MICA. Yohkoh images, taken 8 min after the hard X-ray peak, show fast soft X-ray ejecta that can be extrapolated back to the position of pre-flare coronal arcade structure seen in EIT 195 images. The observations are interpreted as evidence of a blast wave propagating through the active region coronal loop structure very early in the flare evolution.

  7. Evidence for beamed electrons in a limb X-ray flare observed by Hard X-Ray Imaging Spectrometer (HXIS)

    NASA Technical Reports Server (NTRS)

    Haug, Eberhard; Elwert, Gerhard

    1986-01-01

    The limb flare of November 18, 1980, 14:51 UT, was investigated on the basis of X-ray images taken by the Hard X-ray Imaging Spectrometer (HXIS) and of X-ray spectra from the Hard X-Ray Burst Spectrometer (HXRBS) aboard the Solar Maximum Mission (SMM). The impulsive burst was also recorded at microwave frequencies between 2 and 20 GHz whereas no optical flare and no radio event at frequencies below 1 GHz were reported. The flare occurred directly at the SW limb of the solar disk. Taking advantage of the spatial resolution of HXIS images, the time evolution of the X-radiation originating from relatively small source regions can be studied. Using Monte Carlo computations of the energy distribution of energetic electrons traversing the solar plasma, the bremsstrahlung spectra produced by the electrons were derived.

  8. Influence of Stellar Flares on the Chemical Composition of Exoplanets and Spectra

    NASA Astrophysics Data System (ADS)

    Venot, Olivia; Rocchetto, Marco; Carl, Shaun; Roshni Hashim, Aysha; Decin, Leen

    2016-10-01

    More than three thousand exoplanets have been detected so far, and more and more spectroscopic observations of exoplanets are performed. Future instruments (James Webb Space Telescope (JWST), E-ELT, PLATO, Ariel, etc.,) are eagerly awaited, as they will be able to provide spectroscopic data with greater accuracy and sensitivity than what is currently available. This will allow more accurate conclusions to be drawn regarding the chemistry and dynamics of exoplanetary atmospheres, provided that the observational data are carefully processed. One important aspect to consider is temporal stellar atmospheric disturbances that can influence the planetary composition, and hence spectra, and potentially can lead to incorrect assumptions about the steady-state atmospheric composition of the planet. In this paper, we focus on perturbations coming from the host star in the form of flare events that significantly increase photon flux impingement on the exoplanets atmosphere. In some cases, particularly for M stars, this sudden increase may last for several hours. We aim to discover to what extent a stellar flare is able to modify the chemical composition of the planetary atmosphere and, therefore, influence the resulting spectra. We use a one-dimensional thermo-photochemical model to study the neutral atmospheric composition of two hypothetical planets located around the star AD Leo. We place the two planets at different distances from the star, which results in effective atmospheric temperatures of 412 and 1303 K. AD Leo is an active star that has already been observed during a flare. Therefore, we use the spectroscopic data from this flare event to simulate the evolution of the chemical composition of the atmospheres of the two hypothetical planets. We compute synthetic spectra to evaluate the implications for observations. The increase in the incoming photon flux affects the chemical abundances of some important species (such as H and NH3), down to altitudes associated with

  9. Differences between electron energy distributions in both steady and flare states of Mrk 501

    NASA Astrophysics Data System (ADS)

    Peng, Yaping; Yan, Dahai; Zhang, Li

    2014-08-01

    Possible electron energy distributions (EEDs) for Mrk 501 are studied through fitting multiband energy spectra in both steady and flare states with a one-zone synchrotron self-Compton model. Two kinds of the EEDs formed in different acceleration and cooling processes are assumed: a power law with an exponential cut-off (PLC) EED and a log-parabolic (LP) EED. The Markov Chain Monte Carlo method is used to estimate the model parameters in our fits. The results show that the LP model fits the spectral energy distributions better in both steady and flare states than PLC model, and the changes of model parameters from steady state to flare state can be explained reasonably. Therefore, it is concluded that the EEDs and the acceleration mechanisms in both steady and flare states would be the same for Mrk 501. Compared to Mrk 421 having different EEDs in different states, our analysis indicates that both acceleration and cooling processes are different in the jets of these two sources.

  10. The energy spectra of solar flare hydrogen, helium, oxygen, and iron - Evidence for stochastic acceleration

    NASA Technical Reports Server (NTRS)

    Mazur, J. E.; Mason, G. M.; Klecker, B.; Mcguire, R. E.

    1992-01-01

    The time-integrated differential energy spectra of H, He, O, and Fe measured in 10 large flare events observed at 1 AU over the energy range of 0.3-80 MeV/nucleon showed consistent patterns in their spectral shapes: particles with larger mean mass-to-charge ratios were generally less abundant at higher energies. A steady state model of stochastic particle acceleration with rigidity-dependent diffusion coefficients fit the spectra best; spectra representative of diffusive shock acceleration also described the spectra of some events with the same number of free parameters, but often fell off faster in energy above 30 MeV per nucleon than the observations. The two model predictions differed most at energies near 0.1 MeV per nucleon, below the lowest energies observed in this study. The stochastic model quantitatively described the observed spectral ordering with less efficient acceleration of species with larger mean mass-to-charge ratios.

  11. QUASI-PERIODIC PULSATIONS IN SOLAR AND STELLAR FLARES: RE-EVALUATING THEIR NATURE IN THE CONTEXT OF POWER-LAW FLARE FOURIER SPECTRA

    SciTech Connect

    Inglis, A. R.; Ireland, J.; Dominique, M.

    2015-01-10

    The nature of quasi-periodic pulsations (QPPs) in solar and stellar flares remains debated. Recent work has shown that power-law-like Fourier power spectra are an intrinsic property of solar and stellar flare signals, a property that many previous studies of this phenomenon have not accounted for. Hence a re-evaluation of the existing interpretations and assumptions regarding QPPs is needed. We adopt a Bayesian method for investigating this phenomenon, fully considering the Fourier power-law properties of flare signals. Using data from the PROBA2/Large Yield Radiometer, Fermi/Gamma-ray Burst Monitor, Nobeyama Radioheliograph, and Yohkoh/HXT instruments, we study a selection of flares from the literature identified as QPP events. Additionally, we examine optical data from a recent stellar flare that appears to exhibit oscillatory properties. We find that, for all but one event tested, an explicit oscillation is not required to explain the observations. Instead, the flare signals are adequately described as a manifestation of a power law in the Fourier power spectrum. However, for the flare of 1998 May 8, strong evidence for an explicit oscillation with P ≈ 14-16 s is found in the 17 GHz radio data and the 13-23 keV Yohkoh/HXT data. We conclude that, most likely, many previously analyzed events in the literature may be similarly described by power laws in the flare Fourier power spectrum, without invoking a narrowband, oscillatory component. Hence the prevalence of oscillatory signatures in solar and stellar flares may be less than previously believed. The physical mechanism behind the appearance of the observed power laws is discussed.

  12. CORONAL ELECTRON DISTRIBUTION IN SOLAR FLARES: DRIFT-KINETIC MODEL

    SciTech Connect

    Minoshima, Takashi; Kusano, Kanya; Masuda, Satoshi; Miyoshi, Yoshizumi

    2011-05-10

    Using a model of particle acceleration and transport in solar flares, we investigate the height distribution of coronal electrons by focusing on the energy-dependent pitch-angle scattering. When pitch-angle scattering is not included, the peak heights of loop-top electrons are constant, regardless of their energy, owing to the continuous acceleration and compression of the electrons via shrinkage of magnetic loops. On the other hand, under pitch-angle scattering, the electron heights are energy-dependent: intermediate-energy electrons are at a higher altitude, whereas lower and higher energy electrons are at lower altitudes. This implies that the intermediate-energy electrons are inhibited from following the shrinking field lines to lower altitudes because pitch-angle scattering causes efficient precipitation of these electrons into the footpoint and their subsequent loss from the loop. This result is qualitatively consistent with the position of the above-the-loop-top hard X-ray (HXR) source that is located above coronal HXR loops emitted by lower energy electrons and microwaves emitted by higher energy electrons. Quantitative agreement with observations might be achieved by considering primary acceleration before the onset of loop shrinkage and additional pitch-angle scattering via wave-particle interactions.

  13. Magnetic structure and nonthermal electrons in the X6.9 flare on 2011 August 9

    SciTech Connect

    Hwangbo, Jung-Eun; Lee, Dae-Young; Lee, Jeongwoo; Park, Sung-Hong; Kim, Sujin; Bong, Su-Chan; Kim, Yeon-Han; Cho, Kyung-Suk; Park, Young-Deuk

    2014-12-01

    The 2011 August 9 flare is one of the largest X-ray flares of sunspot cycle 24, but spatial information is rather limited due to its position close to the western limb. This paper presents information about the location of high-energy electrons derived from hard X-ray and microwave spectra obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the Korean Solar Radio Burst Locator (KSRBL), respectively. The KSRBL microwave spectrum shows significant fluxes at low frequencies, implying that the high-energy electrons reside in a coronal volume highly concentrated at strong magnetic fields, and rapidly expanding with decreasing magnetic fields. After a simple modeling of the microwave spectrum, we found that the microwave source should be located above the inner pair of magnetic poles in a large quadrupolar configuration. The time-dependent evolution of the magnetic field distribution and total nonthermal energy derived from the microwave spectra is also consistent with the standard picture of multiple magnetic reconnections recurring at a magnetic null point that forms above the magnetic quadrupoles and moves up with time.

  14. Electronic spectra of semiconductor nanocrystals

    SciTech Connect

    Alivisatos, A.P.

    1993-12-31

    Semiconductor nanocrystals smaller than the bulk exciton show substantial quantum confinement effects. Recent experiments including Stark effect, resonance Raman, valence band photoemission, and near edge X-ray adsorption will be used to put together a picture of the nanocrystal electronic states.

  15. OPTIMAL ELECTRON ENERGIES FOR DRIVING CHROMOSPHERIC EVAPORATION IN SOLAR FLARES

    SciTech Connect

    Reep, J. W.; Bradshaw, S. J.; Alexander, D. E-mail: stephen.bradshaw@rice.edu

    2015-08-01

    In the standard model of solar flares, energy deposition by a beam of electrons drives strong chromospheric evaporation leading to a significantly denser corona and much brighter emission across the spectrum. Chromospheric evaporation was examined in great detail by Fisher et al., who described a distinction between two different regimes, termed explosive and gentle evaporation. In this work, we examine the importance of electron energy and stopping depths on the two regimes and on the atmospheric response. We find that with explosive evaporation, the atmospheric response does not depend strongly on electron energy. In the case of gentle evaporation, lower energy electrons are significantly more efficient at heating the atmosphere and driving up-flows sooner than higher energy electrons. We also find that the threshold between explosive and gentle evaporation is not fixed at a given beam energy flux, but also depends strongly on the electron energy and duration of heating. Further, at low electron energies, a much weaker beam flux is required to drive explosive evaporation.

  16. Modeling Flare Hard X-ray Emission from Electrons in Contracting Magnetic Islands

    NASA Astrophysics Data System (ADS)

    Guidoni, Silvina E.; Allred, Joel C.; Alaoui, Meriem; Holman, Gordon D.; DeVore, C. Richard; Karpen, Judith T.

    2016-05-01

    The mechanism that accelerates particles to the energies required to produce the observed impulsive hard X-ray emission in solar flares is not well understood. It is generally accepted that this emission is produced by a non-thermal beam of electrons that collides with the ambient ions as the beam propagates from the top of a flare loop to its footpoints. Most current models that investigate this transport assume an injected beam with an initial energy spectrum inferred from observed hard X-ray spectra, usually a power law with a low-energy cutoff. In our previous work (Guidoni et al. 2016), we proposed an analytical method to estimate particle energy gain in contracting, large-scale, 2.5-dimensional magnetic islands, based on a kinetic model by Drake et al. (2010). We applied this method to sunward-moving islands formed high in the corona during fast reconnection in a simulated eruptive flare. The overarching purpose of the present work is to test this proposed acceleration model by estimating the hard X-ray flux resulting from its predicted accelerated-particle distribution functions. To do so, we have coupled our model to a unified computational framework that simulates the propagation of an injected beam as it deposits energy and momentum along its way (Allred et al. 2015). This framework includes the effects of radiative transfer and return currents, necessary to estimate flare emission that can be compared directly to observations. We will present preliminary results of the coupling between these models.

  17. MULTITHERMAL REPRESENTATION OF THE KAPPA-DISTRIBUTION OF SOLAR FLARE ELECTRONS AND APPLICATION TO SIMULTANEOUS X-RAY AND EUV OBSERVATIONS

    SciTech Connect

    Battaglia, Marina; Motorina, Galina; Kontar, Eduard P. E-mail: eduard.kontar@glasgow.ac.uk

    2015-12-10

    Acceleration of particles and plasma heating is one of the fundamental problems in solar flare physics. An accurate determination of the spectrum of flare-energized electrons over a broad energy range is crucial for our understanding of aspects such as the acceleration mechanism and the total flare energy. Recent years have seen a growing interest in the kappa-distribution as a representation of the total spectrum of flare-accelerated electrons. In this work we present the kappa-distribution as a differential emission measure. This allows for inferring the electron distribution from X-ray observations and EUV observations by simultaneously fitting the proposed function to RHESSI and SDO/AIA data. This yields the spatially integrated electron spectra of a coronal source from less than 0.1 keV up to several tens of keV. The method is applied to a single-loop GOES C4.1 flare. The results show that the total energy can only be determined accurately by combining RHESSI and AIA observations. Simultaneously fitting the proposed representation of the kappa-distribution reduces the electron number density in the analyzed flare by a factor of ∼30 and the total flare energy by a factor of ∼5 compared with the commonly used fitting of RHESSI spectra. The spatially integrated electron spectrum of the investigated flare between 0.043 and 24 keV is consistent with the combination of a low-temperature (∼2 MK) component and a hot (∼11 MK) kappa-like component with spectral index 4, reminiscent of solar wind distributions.

  18. Relativistic Electrons Produced by Reconnecting Electric Fields in a Laser-driven Bench-top Solar Flare

    NASA Astrophysics Data System (ADS)

    Zhong, J. Y.; Lin, J.; Li, Y. T.; Wang, X.; Li, Y.; Zhang, K.; Yuan, D. W.; Ping, Y. L.; Wei, H. G.; Wang, J. Q.; Su, L. N.; Li, F.; Han, B.; Liao, G. Q.; Yin, C. L.; Fang, Y.; Yuan, X.; Wang, C.; Sun, J. R.; Liang, G. Y.; Wang, F. L.; Ding, Y. K.; He, X. T.; Zhu, J. Q.; Sheng, Z. M.; Li, G.; Zhao, G.; Zhang, J.

    2016-08-01

    Laboratory experiments have been carried out to model the magnetic reconnection process in a solar flare with powerful lasers. Relativistic electrons with energy up to megaelectronvolts are detected along the magnetic separatrices bounding the reconnection outflow, which exhibit a kappa-like distribution with an effective temperature of ˜109 K. The acceleration of non-thermal electrons is found to be more efficient in the case with a guide magnetic field (a component of a magnetic field along the reconnection-induced electric field) than in the case without a guide field. Hardening of the spectrum at energies ≥500 keV is observed in both cases, which remarkably resembles the hardening of hard X-ray and γ-ray spectra observed in many solar flares. This supports a recent proposal that the hardening in the hard X-ray and γ-ray emissions of solar flares is due to a hardening of the source-electron spectrum. We also performed numerical simulations that help examine behaviors of electrons in the reconnection process with the electromagnetic field configurations occurring in the experiments. The trajectories of non-thermal electrons observed in the experiments were well duplicated in the simulations. Our numerical simulations generally reproduce the electron energy spectrum as well, except for the hardening of the electron spectrum. This suggests that other mechanisms such as shock or turbulence may play an important role in the production of the observed energetic electrons.

  19. THE SOLAR FLARE CHLORINE ABUNDANCE FROM RESIK X-RAY SPECTRA

    SciTech Connect

    Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Kuznetsov, V. D. E-mail: js@cbk.pan.wroc.pl E-mail: kvd@izmiran.ru

    2011-09-01

    The abundance of chlorine is determined from X-ray spectra obtained with the RESIK instrument on CORONAS-F during solar flares between 2002 and 2003. Using weak lines of He-like Cl, Cl XVI, between 4.44 and 4.50 A, and with temperatures and emission measures from GOES on an isothermal assumption, we obtained A(Cl) = 5.75 {+-} 0.26 on a scale A(H) = 12. The uncertainty reflects an approximately a factor of two scatter in measured line fluxes. Nevertheless, our value represents what is probably the best solar determination yet obtained. It is higher by factors of 1.8 and 2.7 than Cl abundance estimates from an infrared sunspot spectrum and nearby H II regions. The constancy of the RESIK abundance values over a large range of flares (GOES class from below C1 to X1) argues for any fractionation that may be present in the low solar atmosphere to be independent of the degree of solar activity.

  20. Ion and relativistic electron acceleration by Alfven and whistler turbulence in solar flares

    NASA Technical Reports Server (NTRS)

    Miller, James A.; Ramaty, Reuven

    1987-01-01

    A model is proposed in which turbulent Alfven and whistler waves simultaneously produce the proton and electron spectra implied by the gamma-ray observations noted during the impulsive phase of the June 3, 1982 flare. The results demonstrate that protons can be accelerated to several GeV in less than about 10 sec by Alfven turbulence whose energy density is greater than a few erg/cu cm. It is also found that electrons may be accelerated to tens of MeV on similar time scales by whistler and Alfven turbulence. A lower limit on the energy density of the Alfven turbulence is obtained which is small compared to the total magnetic energy density.

  1. TIME-RESOLVED PROPERTIES AND GLOBAL TRENDS IN dMe FLARES FROM SIMULTANEOUS PHOTOMETRY AND SPECTRA

    SciTech Connect

    Kowalski, Adam F.; Hawley, Suzanne L.; Davenport, James R. A.; Wisniewski, John P.; Osten, Rachel A.; Hilton, Eric J.; Holtzman, Jon A.; Schmidt, Sarah J.

    2013-07-15

    We present a homogeneous analysis of line and continuum emission from simultaneous high-cadence spectra and photometry covering near-ultraviolet and optical wavelengths for 20 M dwarf flares. These data were obtained to study the white-light continuum components at bluer and redder wavelengths than the Balmer jump. Our goals were to break the degeneracy between emission mechanisms that have been fit to broadband colors of flares and to provide constraints for radiative-hydrodynamic (RHD) flare models that seek to reproduce the white-light flare emission. The main results from the analysis are the following: (1) the detection of Balmer continuum (in emission) that is present during all flares and with a wide range of relative contributions to the continuum flux at bluer wavelengths than the Balmer jump; (2) a blue continuum at flare maximum that is linearly decreasing with wavelength from {lambda} = 4000-4800 A, indicative of hot, blackbody emission with typical temperatures of T{sub BB} {approx} 9000-14, 000 K; (3) a redder continuum apparent at wavelengths longer than H{beta} ({lambda} {approx}> 4900 A) which becomes relatively more important to the energy budget during the late gradual phase. The hot blackbody component and redder continuum component have been detected in previous studies of flares. However, we have found that although the hot blackbody emission component is relatively well-represented by a featureless, single-temperature Planck function, this component includes absorption features and has a continuum shape strikingly similar to the spectrum of an A-type star as directly observed in our flare spectra. New model constraints are presented for the time evolution among the hydrogen Balmer lines and between Ca II K and the blackbody continuum emission. We calculate Balmer jump flux ratios and compare to the solar-type flare heating predictions from RHD models. The model ratios are too large and the blue-optical ({lambda} = 4000-4800 A) slopes are too

  2. Flare plasma dynamics obseved with the YOHKOH Bragg crystal spectrometer. III. Spectral signatures of electron-beam-heated atmospheres.

    NASA Astrophysics Data System (ADS)

    Marriska, John. T.

    1995-05-01

    Using numerical simulations of an electon-beam-heated solar flare, we investigate the observational consequences of variations in the electron beam total energy flux and the low-energy cut off value for models with both low and high initial densities. To do this we use the evolution of the physical parameters of the simulated flares to synthesize the time evolution of the spectrum in the wavelength region surrounding tha Ca xix resonance line. These spectra are then summed over a 9 s time interval to simulate typical spectra from the Yohkoh Bragg crystal spectometer and the first three moments are computed for comparison with observational results. This comparison shows that no single low or high initial density model satisfies the observed average behavior of the Ca xix resonance line. Low initial density models produce too large a blue shift velocity, while high initial density model have lines that are too narrow. Comparison of these models with the Yohkok data suggests that the key problem for models of the impulsive phase ofa solar flare is producing significant amounts of stationary hot plasma early in the flare.

  3. Comparing Solar-Flare Acceleration of >-20 MeV Protons and Electrons Above Various Energies

    NASA Technical Reports Server (NTRS)

    Shih, Albert Y.

    2010-01-01

    A large fraction (up to tens of percent) of the energy released in solar flares goes into accelerated ions and electrons, and studies indicate that these two populations have comparable energy content. RHESSI observations have shown a striking close linear correlation between the 2.223 MeV neutron-capture gamma-ray line and electron bremsstrahlung emission >300 keV, indicating that the flare acceleration of >^20 MeV protons and >300 keV electrons is roughly proportional over >3 orders of magnitude in fluence. We show that the correlations of neutron-capture line fluence with GOES class or with bremsstrahlung emission at lower energies show deviations from proportionality, primarily for flares with lower fluences. From analyzing thirteen flares, we demonstrate that there appear to be two classes of flares with high-energy acceleration: flares that exhibit only proportional acceleration of ions and electrons down to 50 keV and flares that have an additional soft, low-energy bremsstrahlung component, suggesting two separate populations of accelerated electrons. We use RHESSI spectroscopy and imaging to investigate a number of these flares in detail.

  4. Extreme ultraviolet spectra of solar flares from the extreme ultraviolet spectroheliograph SPIRIT onboard the CORONAS-F satellite

    SciTech Connect

    Shestov, S.; Kuzin, S.; Reva, A.

    2014-01-01

    We present detailed extreme ultraviolet (EUV) spectra of four large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 Å and 280-330 Å. These spectra were obtained by the slitless spectroheliograph SPIRIT onboard the CORONAS-F satellite. To our knowledge, these are the first detailed EUV spectra of large flares obtained with a spectral resolution of ∼0.1 Å. We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based on the calculation of synthetic spectra (the CHIANTI database was used), with simultaneous calculations of the differential emission measure (DEM) and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of T = 0.5-16 MK; most of the lines belong to Fe, Ni, Ca, Mg, and Si ions. In all the considered flares, intense hot lines from Ca XVII, Ca XVIII, Fe XX, Fe XXII, and Fe XXIV are observed. The calculated DEMs have a peak at T ∼ 10 MK. The densities were determined using Fe XI-Fe XIII lines and averaged 6.5 × 10{sup 9} cm{sup –3}. We also discuss the identification, accuracy, and major discrepancies of the spectral line intensity prediction.

  5. A Test of Thick-Target Nonuniform Ionization as an Explanation for Breaks in Solar Flare Hard X-Ray Spectra

    NASA Technical Reports Server (NTRS)

    Holman, gordon; Dennis Brian R.; Tolbert, Anne K.; Schwartz, Richard

    2010-01-01

    Solar nonthermal hard X-ray (HXR) flare spectra often cannot be fitted by a single power law, but rather require a downward break in the photon spectrum. A possible explanation for this spectral break is nonuniform ionization in the emission region. We have developed a computer code to calculate the photon spectrum from electrons with a power-law distribution injected into a thick-target in which the ionization decreases linearly from 100% to zero. We use the bremsstrahlung cross-section from Haug (1997), which closely approximates the full relativistic Bethe-Heitler cross-section, and compare photon spectra computed from this model with those obtained by Kontar, Brown and McArthur (2002), who used a step-function ionization model and the Kramers approximation to the cross-section. We find that for HXR spectra from a target with nonuniform ionization, the difference (Delta-gamma) between the power-law indexes above and below the break has an upper limit between approx.0.2 and 0.7 that depends on the power-law index delta of the injected electron distribution. A broken power-law spectrum with a. higher value of Delta-gamma cannot result from nonuniform ionization alone. The model is applied to spectra obtained around the peak times of 20 flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI from 2002 to 2004 to determine whether thick-target nonuniform ionization can explain the measured spectral breaks. A Monte Carlo method is used to determine the uncertainties of the best-fit parameters, especially on Delta-gamma. We find that 15 of the 20 flare spectra require a downward spectral break and that at least 6 of these could not be explained by nonuniform ionization alone because they had values of Delta-gamma with less than a 2.5% probability of being consistent with the computed upper limits from the model. The remaining 9 flare spectra, based on this criterion, are consistent with the nonuniform ionization model.

  6. Electronic spectra of astrophysically interesting cations

    SciTech Connect

    Maier, John P. Rice, Corey A. Mazzotti, Fabio J. Johnson, Anatoly

    2015-01-22

    The electronic spectra of polyacetylene cations were recorded at 20K in the laboratory in an ion trap instrument. These can then be compared with diffuse interstellar band (DIB) absorptions. Examination of recently published data shows that the attribution of a weak DIB at ∼506.9 nm to diacetylene cation is not justified. Study of the higher excited electronic states of polyacetylene cations shows that their widths can still be sufficiently narrow for consideration as DIB carriers.

  7. Soft X-ray diagnostics of electron-heated solar flare atmospheres

    NASA Technical Reports Server (NTRS)

    Li, Peng; Emslie, A. Gordon; Mariska, John T.

    1989-01-01

    The dependence of the impulsive-phase Ca XIX w line profile on the form of the flare energy input (assumed to be due to the collisional degradation of a beam of high-energy electrons) is considered. The injected flux spectrum has the form of a power law with a low-energy 'knee', and the effects of varying the total energy flux, spectral index, and knee energy on the w line profile during the impulsive phase have been evaluated. Early in the burst, blueshifts of order 400 km/s are noted, and the peak intensity of the blueshifted component together with spatially unresolved hard X-ray burst spectra can be used to determine the beam filling factor.

  8. SOLAR WIND DENSITY TURBULENCE AND SOLAR FLARE ELECTRON TRANSPORT FROM THE SUN TO THE EARTH

    SciTech Connect

    Reid, Hamish A. S.; Kontar, Eduard P. E-mail: eduard@astro.gla.ac.u

    2010-09-20

    Solar flare accelerated electron beams propagating away from the Sun can interact with the turbulent interplanetary media, producing plasma waves and Type III radio emission. These electron beams are detected near the Earth with a double power-law energy spectrum. We simulate electron beam propagation from the Sun to the Earth in the weak turbulent regime taking into account the self-consistent generation of plasma waves and subsequent wave interaction with density fluctuations from low-frequency MHD turbulence. The rate at which plasma waves are induced by an unstable electron beam is reduced by background density fluctuations, most acutely when fluctuations have large amplitudes or small wavelengths. This suppression of plasma waves alters the wave distribution which changes the electron beam transport. Assuming a 5/3 Kolmogorov-type power-density spectrum of fluctuations often observed near the Earth, we investigate the corresponding energy spectrum of the electron beam after it has propagated 1 AU. We find a direct correlation between the spectrum of the double power-law below the break energy and the turbulent intensity of the background plasma. For an initial spectral index of 3.5, we find a range of spectra below the break energy between 1.6 and 2.1, with higher levels of turbulence corresponding to higher spectral indices.

  9. An investigation of solar flares and associated solar radio bursts on ionospheric total electron content

    NASA Astrophysics Data System (ADS)

    Uwamahoro, Jean

    2016-07-01

    Solar transients events such as Coronal Mass Ejections (CMEs) and solar flares represent are the cause of various aspects of space weather and can impact the modern man made technological system. Such solar transients are often associated with solar radio bursts (SRBs), particularly of type II and III that , at ground level can be detected by the CALLISTO (Compact Astronomical Low-frequency Low-cost Instrument for Spectroscopy and Transportable Observatories) solar spectrometer. The present study aims at investigating solar flares and associated SRBs impact on the ionospheric total electron content (TEC). SRBs data used are dynamic spectra covering the 2014-2015 period and detected by the CALLISTO instrument that is installed at the university of Rwanda, Kigali. To investigate ionospheric impact, we use TEC data from IGS stations located at almost the same universal time zone, and correlate the observed TEC changes to the corresponding observed solar bursts events. Preliminary observations resulting from this study indicate a slight enhancement in TEC during the burst event days. The observed TEC enhancement on the burst day can be associated to increased UV and X-rays radiations and particle acceleration that are associated with SRBs events. This work is a contribution to more understanding of the geo-space impact of solar transients phenomena for modeling and prediction.

  10. An investigation of solar flares and associated solar radio bursts impact on ionospheric total electron content

    NASA Astrophysics Data System (ADS)

    Tuyizere, Sarathiel

    2016-07-01

    Solar transients events such as Coronal Mass Ejections (CMEs) and solar flares represent the cause of various aspects of space weather and can impact the modern man made technological system. Such solar transients are often associated with solar radio bursts (SRBs), particularly of type II and III that , at ground level can be detected by the CALLISTO (Compact Astronomical Low-frequency Low-cost Instrument for Spectroscopy and Transportable Observatories) solar spectrometer. The present study aims at investigating solar flares and associated SRBs impact on the ionospheric total electron content (TEC). SRBs data used are dynamic spectra covering the 2014-2015 period and detected by the CALLISTO instrument that is installed at the university of Rwanda, Kigali. To investigate ionospheric impact, we use TEC data from IGS stations located at almost the same universal time zone, and correlate the observed TEC changes to the corresponding observed solar bursts events. Preliminary observations resulting from this study indicate a slight enhancement in TEC during the burst event days. The observed TEC enhancement on the burst day can be associated to increased UV and X-rays radiations and particle acceleration that are associated with SRBs events. This work is a contribution to more understanding of the geo-space impact of solar transients phenomena for modeling and prediction.

  11. HF Accelerated Electron Fluxes, Spectra, and Ionization

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert C.; Jensen, Joseph B.

    2015-10-01

    Wave particle interactions, an essential aspect of laboratory, terrestrial, and astrophysical plasmas, have been studied for decades by transmitting high power HF radio waves into Earth's weakly ionized space plasma, to use it as a laboratory without walls. Application to HF electron acceleration remains an active area of research (Gurevich in Usp Fizicheskikh Nauk 177(11):1145-1177, 2007) today. HF electron acceleration studies began when plasma line observations proved (Carlson et al. in J Atmos Terr Phys 44:1089-1100, 1982) that high power HF radio wave-excited processes accelerated electrons not to ~eV, but instead to -100 times thermal energy (10 s of eV), as a consequence of inelastic collision effects on electron transport. Gurevich et al (J Atmos Terr Phys 47:1057-1070, 1985) quantified the theory of this transport effect. Merging experiment with theory in plasma physics and aeronomy, enabled prediction (Carlson in Adv Space Res 13:1015-1024, 1993) of creating artificial ionospheres once ~GW HF effective radiated power could be achieved. Eventual confirmation of this prediction (Pedersen et al. in Geophys Res Lett 36:L18107, 2009; Pedersen et al. in Geophys Res Lett 37:L02106, 2010; Blagoveshchenskaya et al. in Ann Geophys 27:131-145, 2009) sparked renewed interest in optical inversion to estimate electron spectra in terrestrial (Hysell et al. in J Geophys Res Space Phys 119:2038-2045, 2014) and planetary (Simon et al. in Ann Geophys 29:187-195, 2011) atmospheres. Here we present our unpublished optical data, which combined with our modeling, lead to conclusions that should meaningfully improve future estimates of the spectrum of HF accelerated electron fluxes. Photometric imaging data can significantly improve detection of emissions near ionization threshold, and confirm depth of penetration of accelerated electrons many km below the excitation altitude. Comparing observed to modeled emission altitude shows future experiments need electron density profiles

  12. Inner-shell transitions in Fe XIX-XXII in the X-ray spectra of solar flares and Tokamaks

    NASA Technical Reports Server (NTRS)

    Phillips, K. J. H.; Lemen, J. R.; Cowan, R. D.; Doschek, G. A.; Leibacher, J. W.

    1983-01-01

    Calculated spectra of the ions Fe XIX-XXII for various densities and temperatures are presented, thereby extending the work begun by Doschek, Feldman, and Cowan (1981). The calculations are based on a code (the Cowan code) that computes both the level structure of an ion and intensity factors for the 1s-2p satellite lines. A comparison is made between the calculated spectra and those observed in solar flares by the P78-1 and SMM instruments. The observed intensities of Fe XX lines, which are the most sensitive to density, are found to agree well with those calculated in the low-density limit. The agreement for lines arising from other ions is also very good. It is also seen that the predicted density variations in Fe XX are confirmed by the higher density Princeton Large Torus plasmas. Thus a possible useful density diagnostic is indicated for tokamak and high-density astrophysical plasmas, perhaps including some solar flares.

  13. Non-thermal recombination - a neglected source of flare hard X-rays and fast electron diagnostics (Corrigendum)

    NASA Astrophysics Data System (ADS)

    Brown, J. C.; Mallik, P. C. V.; Badnell, N. R.

    2010-06-01

    Brown and Mallik (BM) recently claimed that non-thermal recombination (NTR) can be a dominant source of flare hard X-rays (HXRs) from hot coronal and chromospheric sources. However, major discrepancies between the thermal continua predicted by BM and by the Chianti database as well as RHESSI flare data, led us to discover substantial errors in the heuristic expression used by BM to extend the Kramers expressions beyond the hydrogenic case. Here we present the relevant corrected expressions and show the key modified results. We conclude that, in most cases, NTR emission was overestimated by a factor of 1-8 by BM but is typically still large enough (as much as 20-30% of the total emission) to be very important for electron spectral inference and detection of electron spectral features such as low energy cut-offs since the recombination spectra contain sharp edges. For extreme temperature regimes and/or if the Fe abundance were as high as some values claimed, NTR could even be the dominant source of flare HXRs, reducing the electron number and energy budget, problems such as in the extreme coronal HXR source cases reported by e.g. Krucker et al.

  14. Electron impact polarization expected in solar EUV lines from flaring chromospheres/transition regions

    NASA Technical Reports Server (NTRS)

    Fineschi, S.; Fontenla, Juan M.; Macneice, P.; Ljepojevic, N. N.

    1991-01-01

    We have evaluated lower bounds on the degree of impact Extreme Ultraviolet/Ultraviolet (EUV/UV) line polarization expected during solar flares. This polarization arises from collisional excitation by energetic electrons with non-Maxwellian velocity distributions. Linear polarization was observed in the S I 1437 A line by the Ultraviolet Spectrometer and Polarimeter/Solar Maximum Mission (UVSP/SMM) during a flare on 15 July 1980. An early interpretation suggested that impact excitation by electrons propagating through the steep temperature gradient of the flaring transition region/high chromosphere produced this polarization. Our calculations show that the observed polarization in this UV line cannot be due to this effect. We find instead that, in some flare models, the energetic electrons can produce an impact polarization of a few percent in EUV neutral helium lines (i.e., lambda lambda 522, 537, and 584 A).

  15. DETERMINATION OF LOW-ENERGY CUTOFFS AND TOTAL ENERGY OF NONTHERMAL ELECTRONS IN A SOLAR FLARE ON 2002 APRIL 15

    NASA Technical Reports Server (NTRS)

    Sui, Linhui; Holman, Gordon D.; Dennis, Brian R.

    2005-01-01

    The determination of the low-energy cutoff to the spectrum of accelerated electrons is decisive for the estimation of the total nonthermal energy in solar flares. Because thermal bremsstrahlung dominates the low-energy part of flare X-ray spectra, this cutoff energy is difficult to determine with spectral fitting alone. We have used anew method that combines spatial, spectral, and temporal analysis to determine the cutoff energy for the M1.2 flare observed with RHESSI on 2002 April 15. A low-energy cutoff of 24 +/- 2 keV is required to ensure that the assumed thermal emissions always dominate over nonthermal emissions at low energies (<20 keV) and that the spectral fitting results are consistent with the RHESSI light curves and images. With this cutoff energy, we obtain a total nonthermal energy in electrons of (1.6 +/- 1) x 10(exp 30) ergs that is comparable to the peak energy in the thermal plasma, estimated from RHESSI observations to be (6 +/- 0.6) x 10(exp 29) ergs assuming a filling factor of 1.

  16. Stochastic acceleration of electrons by fast magnetosonic waves in solar flares: the effects of anisotropy in velocity and wavenumber space

    SciTech Connect

    Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.

    2014-11-20

    We develop a model for stochastic acceleration of electrons in solar flares. As in several previous models, the electrons are accelerated by turbulent fast magnetosonic waves ({sup f}ast waves{sup )} via transit-time-damping (TTD) interactions. (In TTD interactions, fast waves act like moving magnetic mirrors that push the electrons parallel or anti-parallel to the magnetic field). We also include the effects of Coulomb collisions and the waves' parallel electric fields. Unlike previous models, our model is two-dimensional in both momentum space and wavenumber space and takes into account the anisotropy of the wave power spectrum F{sub k} and electron distribution function f {sub e}. We use weak turbulence theory and quasilinear theory to obtain a set of equations that describes the coupled evolution of F{sub k} and f {sub e}. We solve these equations numerically and find that the electron distribution function develops a power-law-like non-thermal tail within a restricted range of energies E in (E {sub nt}, E {sub max}). We obtain approximate analytic expressions for E {sub nt} and E {sub max}, which describe how these minimum and maximum energies depend upon parameters such as the electron number density and the rate at which fast-wave energy is injected into the acceleration region at large scales. We contrast our results with previous studies that assume that F{sub k} and f {sub e} are isotropic, and we compare one of our numerical calculations with the time-dependent hard-X-ray spectrum observed during the 1980 June 27 flare. In our numerical calculations, the electron energy spectra are softer (steeper) than in models with isotropic F{sub k} and f {sub e} and closer to the values inferred from observations of solar flares.

  17. OBSERVATION OF HEATING BY FLARE-ACCELERATED ELECTRONS IN A SOLAR CORONAL MASS EJECTION

    SciTech Connect

    Glesener, Lindsay; Bain, Hazel M.; Krucker, Säm; Lin, Robert P.

    2013-12-20

    We report a Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observation of flare-accelerated electrons in the core of a coronal mass ejection (CME) and examine their role in heating the CME. Previous CME observations have revealed remarkably high thermal energies that can far surpass the CME's kinetic energy. A joint observation by RHESSI and the Atmospheric Imaging Assembly of a partly occulted flare on 2010 November 3 allows us to test the hypothesis that this excess energy is collisionally deposited by flare-accelerated electrons. Extreme ultraviolet (EUV) images show an ejection forming the CME core and sheath, with isothermal multifilter analysis revealing temperatures of ∼11 MK in the core. RHESSI images reveal a large (∼100 × 50 arcsec{sup 2}) hard X-ray (HXR) source matching the location, shape, and evolution of the EUV plasma, indicating that the emerging CME is filled with flare-accelerated electrons. The time derivative of the EUV emission matches the HXR light curve (similar to the Neupert effect observed in soft and HXR time profiles), directly linking the CME temperature increase with the nonthermal electron energy loss, while HXR spectroscopy demonstrates that the nonthermal electrons contain enough energy to heat the CME. This is the most direct observation to date of flare-accelerated electrons heating a CME, emphasizing the close relationship of the two in solar eruptive events.

  18. Statistical analysis of the dynamics of secondary electrons in the flare of a high-voltage beam-type discharge

    SciTech Connect

    Demkin, V. P.; Mel'nichuk, S. V.

    2014-09-15

    In the present work, results of investigations into the dynamics of secondary electrons with helium atoms in the presence of the reverse electric field arising in the flare of a high-voltage pulsed beam-type discharge and leading to degradation of the primary electron beam are presented. The electric field in the discharge of this type at moderate pressures can reach several hundred V/cm and leads to considerable changes in the kinetics of secondary electrons created in the process of propagation of the electron beam generated in the accelerating gap with a grid anode. Moving in the accelerating electric field toward the anode, secondary electrons create the so-called compensating current to the anode. The character of electron motion and the compensating current itself are determined by the ratio of the field strength to the concentration of atoms (E/n). The energy and angular spectra of secondary electrons are calculated by the Monte Carlo method for different ratios E/n of the electric field strength to the helium atom concentration. The motion of secondary electrons with threshold energy is studied for inelastic collisions of helium atoms and differential analysis is carried out of the collisional processes causing energy losses of electrons in helium for different E/n values. The mechanism of creation and accumulation of slow electrons as a result of inelastic collisions of secondary electrons with helium atoms and selective population of metastable states of helium atoms is considered. It is demonstrated that in a wide range of E/n values the motion of secondary electrons in the beam-type discharge flare has the character of drift. At E/n values characteristic for the discharge of the given type, the drift velocity of these electrons is calculated and compared with the available experimental data.

  19. Statistical analysis of the dynamics of secondary electrons in the flare of a high-voltage beam-type discharge

    NASA Astrophysics Data System (ADS)

    Demkin, V. P.; Mel'nichuk, S. V.

    2014-09-01

    In the present work, results of investigations into the dynamics of secondary electrons with helium atoms in the presence of the reverse electric field arising in the flare of a high-voltage pulsed beam-type discharge and leading to degradation of the primary electron beam are presented. The electric field in the discharge of this type at moderate pressures can reach several hundred V/cm and leads to considerable changes in the kinetics of secondary electrons created in the process of propagation of the electron beam generated in the accelerating gap with a grid anode. Moving in the accelerating electric field toward the anode, secondary electrons create the so-called compensating current to the anode. The character of electron motion and the compensating current itself are determined by the ratio of the field strength to the concentration of atoms (Е/n). The energy and angular spectra of secondary electrons are calculated by the Monte Carlo method for different ratios E/n of the electric field strength to the helium atom concentration. The motion of secondary electrons with threshold energy is studied for inelastic collisions of helium atoms and differential analysis is carried out of the collisional processes causing energy losses of electrons in helium for different E/n values. The mechanism of creation and accumulation of slow electrons as a result of inelastic collisions of secondary electrons with helium atoms and selective population of metastable states of helium atoms is considered. It is demonstrated that in a wide range of E/n values the motion of secondary electrons in the beam-type discharge flare has the character of drift. At E/n values characteristic for the discharge of the given type, the drift velocity of these electrons is calculated and compared with the available experimental data.

  20. From electron maps to acceleration models in the physics of flare

    NASA Astrophysics Data System (ADS)

    Massone, Anna Maria

    Electron maps reconstructed from RHESSI visibilities represent a powerful source of information for constraining models of electron acceleration in solar plasma physics during flaring events. In this talk I will describe how and to which extent electron maps can be utilized to estimate local electron spectral indices, the evolution of centroid position at different energies in the electron space and the compatibility of RHESSI observations with different theoretical models for the acceleration mechanisms.

  1. A comparison of helium and heavy ion spectra in He/3/ rich solar flares with a model calculation

    NASA Technical Reports Server (NTRS)

    Mobius, E.; Hovestadt, D.; Klecker, B.; Scholer, M.; Gloeckler, G.

    1981-01-01

    He isotopes, O and Fe in He(3) rich solar flares are studied during the 1977 to 1979 period with the MPI/UoMd particle experiment on ISEE-1 and ISEE-3. The study revealed that the He(3) spectrum is generally harder than that of He(4), and the O spectrum is harder than that of Fe. The spectra are compared with a stationary model based on stochastic Fermi acceleration in Alfven turbulence including a rigidity dependent particle loss. Model calculations fit the He(3) and He(4) spectra between 0.4 and 4.0 MeV/nucleon, with discrepancies at lower and higher energies, and the O and Fe spectra cannot be fitted simultaneously.

  2. Electron acceleration at slow-mode shocks in the magnetic reconnection region in solar flares

    NASA Astrophysics Data System (ADS)

    Mann, Gottfried; Aurass, Henry; Önel, Hakan; Warmuth, Alexander

    2016-04-01

    A solar flare appears as an sudden enhancement of the emission of electromagnetic radiation of the Sun covering a broad range of the spectrum from the radio up to the gamma-ray range. That indicates the generation of energetic electrons during flares, which are considered as the manifestation of magnetic reconnection in the solar corona. Spacecraft observations in the Earth's magnetosphere, as for instance by NASA's MMS mission, have shown that electrons can efficiently accelerated at the slow-mode shocks occuring in the magnetic reconnection region. This mechanism is applied to solar flares. The electrons are accelerated by the cross-shock potential at slow-mode shocks resulting in magnetic field aligned beams of energetic electrons in the downstream region. The interaction of this electron beam with the plasma leads to the excitation of whistler waves and, subsequently, to a strong heating of the electrons in the downstream region. Considering this process under coronal circumstances, enough electrons with energies >30keV are generated in the magnetic reconnection region as required for the hard X-ray radiation during solar flares as observed by NASA's RHESSI mission.

  3. Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Benz, Arnold O.

    1996-01-01

    We compare electron densities measured at three different locations in solar flares: (1) in Soft X-Ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps (n(sub e, sup SXR) = (0.2-2.5) x 10(exp 11)/ cu cm); (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zuerich (n(sub e, sup upflow) = (0.3-11) x 10(exp 10)/cu cm; and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [n(sub e, sup acc) = (0.6-10) x 10(exp 9)/cu cm]. The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range n(sub e, sup upflow)/n(sub e, sup SXR) = 0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., n(sub e, sup acc)/n(sub e, sup SXR) = 0.005- 0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models).

  4. Pentacene Derivatives: Electronic Structure and Spectra

    NASA Astrophysics Data System (ADS)

    Netusil, Ross; Ilie, Carolina; Kane, Thorin; Damkaci, Fehmi

    2013-03-01

    The variation in composition and structure of the substituent groups of pentacene compounds promises a broad range of electronic structures and behaviors and provides a vast and alluring field of inquiry with avenues of exploration. These include the development of synthetic schema, the process of design for novel derivatives and, in order to identify those hypothesized compounds which demonstrate the desired behavior, the identification and refinement of computational tools that make accurate predictions about the electronic behavior of theoretical compounds. Two computational techniques and six pentacene derivatives are here examined. One technique was used to predict the vibrational spectra of the compounds, in order to both acquire data about the optical conductivity of the compounds and to establish a pool of theoretical data against which experimental data will be compared. The molecular orbital energy level diagram of the same six compounds was derived using a second approach, with the same goals of discerning between valid and invalid predictive schema by comparison with pending experimental data and between hypothesized compounds which show promise and those which present little potential for use in organic semiconductor technology.

  5. The smallest hard X-ray flare?

    NASA Astrophysics Data System (ADS)

    Glesener, Lindsay; Krucker, Sam; Hannah, Iain; Smith, David M.; Grefenstette, Brian; Marsh, Andrew; Hudson, Hugh S.; White, Stephen M.; Chen, Bin

    2016-05-01

    We report a NuSTAR observation of a small solar flare on 2015 September 1, estimated to be on the order of a GOES class A.05 flare in brightness. This flare is fainter than any hard X-ray (HXR) flares in the existing literature, and with a peak rate of only ˜5 counts s-1 detector-1 observed by RHESSI, is effectively the smallest that can just barely be detected by the current standard (indirectly imaging) solar HXR instrumentation, though we expect that smaller flares will continue to be discovered as instrumental and observational techniques progress. The flare occurred during a solar observation by the highly sensitive NuSTAR astrophysical HXR spacecraft, which used its direct focusing optics to produce detailed flare spectra and images. The flare exhibits properties commonly observed in larger flares, including a fast rise and more gradual decay, and similar spatial dimensions to the RHESSI microflares. We will discuss the presence of non-thermal (flare-accelerated) electrons during the impulsive phase. The flare is small in emission measure, temperature, and energy, though not in physical dimensions. Its presence is an indication that flares do indeed scale down to smaller energies and retain what we customarily think of as “flarelike” properties.

  6. Quantum synchrotron spectra from semirelativistic electrons in teragauss magnetic fields

    NASA Technical Reports Server (NTRS)

    Brainerd, J. J.

    1987-01-01

    Synchrotron spectra are calculated from quantum electrodynamic transition rates for thermal and power-law electron distributions. It is shown that quantum effects appear in thermal spectra when the photon energy is greater than the electron temperature, and in power-law spectra when the electron energy in units of the electron rest mass times the magnetic field strength in units of the critical field strength is of order unity. These spectra are compared with spectra calculated from the ultrarelativistic approximation for synchrotron emission. It is found that the approximation for the power-law spectra is good, and the approximation for thermal spectra produces the shape of the spectrum accurately but fails to give the correct normalization. Single photon pair creation masks the quantum effects for power-law distributions, so only modifications to thermal spectra are important for gamma-ray bursts.

  7. Using Models for How Energetic Electrons Heat the Atmosphere During Flares

    NASA Technical Reports Server (NTRS)

    Allred, Joel

    2011-01-01

    Using models for how energetic electrons heat the atmosphere during flares, we simulate the radiative-hydrodynamic response of the lower solar atmosphere to flare heating. The simulations account for much of the non-LTE, optically thick radiative transfer that occurs in the chromosphere. Our models predict an increase in white light continuum during the flare on the order of 20%, but this is highly sensitive to the electron beam flux used in the simulation. We find that a majority of the white light continuum originates in the chromosphere as a result of Balmer and Paschen recombinations, but a significant portion also forms in the photosphere which has been heated by radiative backwarming.

  8. Temperature and Electron Density Diagnostics of a Candle-flame-shaped Flare

    NASA Astrophysics Data System (ADS)

    Guidoni, S. E.; McKenzie, D. E.; Longcope, D. W.; Plowman, J. E.; Yoshimura, K.

    2015-02-01

    Candle-flame-shaped flares are archetypical structures that provide indirect evidence of magnetic reconnection. A flare resembling Tsuneta's famous 1992 candle-flame flare occurred on 2011 January 28; we present its temperature and electron density diagnostics. This flare was observed with Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Hinode/X-Ray Telescope (XRT), and Solar Terrestrial Relations Observatory Ahead (STEREO-A)/Extreme Ultraviolet Imager, resulting in high-resolution, broad temperature coverage, and stereoscopic views of this iconic structure. The high-temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the posteruption flare arcade, a feature that has been observed in other long-duration events. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this high-intensity elongated structure. Electron density maps reveal that reconnected loops that are successively connected at their tops to the tower develop a density asymmetry of about a factor of two between the two legs, giving the appearance of "half-loops." We calculate average temperatures with a new fast differential emission measure (DEM) method that uses SDO/AIA data and analyze the heating and cooling of salient features of the flare. Using STEREO observations, we show that the tower and the half-loop brightenings are not a line-of-sight projection effect of the type studied by Forbes & Acton. This conclusion opens the door for physics-based explanations of these puzzling, recurrent solar flare features, previously attributed to projection effects. We corroborate the results of our DEM analysis by comparing them with temperature analyses from Hinode/XRT.

  9. TEMPERATURE AND ELECTRON DENSITY DIAGNOSTICS OF A CANDLE-FLAME-SHAPED FLARE

    SciTech Connect

    Guidoni, S. E.; Plowman, J. E.

    2015-02-10

    Candle-flame-shaped flares are archetypical structures that provide indirect evidence of magnetic reconnection. A flare resembling Tsuneta's famous 1992 candle-flame flare occurred on 2011 January 28; we present its temperature and electron density diagnostics. This flare was observed with Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Hinode/X-Ray Telescope (XRT), and Solar Terrestrial Relations Observatory Ahead (STEREO-A)/Extreme Ultraviolet Imager, resulting in high-resolution, broad temperature coverage, and stereoscopic views of this iconic structure. The high-temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the posteruption flare arcade, a feature that has been observed in other long-duration events. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this high-intensity elongated structure. Electron density maps reveal that reconnected loops that are successively connected at their tops to the tower develop a density asymmetry of about a factor of two between the two legs, giving the appearance of ''half-loops''. We calculate average temperatures with a new fast differential emission measure (DEM) method that uses SDO/AIA data and analyze the heating and cooling of salient features of the flare. Using STEREO observations, we show that the tower and the half-loop brightenings are not a line-of-sight projection effect of the type studied by Forbes and Acton. This conclusion opens the door for physics-based explanations of these puzzling, recurrent solar flare features, previously attributed to projection effects. We corroborate the results of our DEM analysis by comparing them with temperature analyses from Hinode/XRT.

  10. X-ray line and continuum spectra of solar flares from 0.5 to 8.5 angstroms.

    PubMed

    Meekins, J F; Kreplin, R W; Chubb, T A; Friedman, H

    1968-11-22

    Two crystal spectrometers aboard the orbiting solar observatory OSO-4 cover the wavelength ranges 0.5 to 3.9 angstroms and 1.0 to 8.5 angstroms. Within this range, there appear emission lines from hydrogen-like and helium-like states of calcium, sulfur, silicon, magnesium, and aluminum. The Mg XII Lyman-alpha is present strongly in all x-ray flares. The most intense flares (such as class 3) produce strong Si XIV Lyman-alpha and often S XVI Lyman-alpha. Emission, in the form of Ka lines of highly ionized states of calcium, iron, aluminum, and silicon is usually present. The continuum from 1 to 10 angstroms always dominates the line emission by more than an order of magnitude. Electron temperatures derived from the slope of the continuum spectrum are in the range of 10(7) to 10(8) degrees K, considerably higher than theoretical ionization equilibrium temperatures.

  11. Diffusive transport of energetic electrons in the 2004, May 21 solar flare

    NASA Astrophysics Data System (ADS)

    Musset, Sophie; Kontar, Eduard; Vilmer, Nicole

    2016-07-01

    Solar flares are associated with efficient particle acceleration, in particular with the production of energetic electrons which are diagnosed through the X-ray and radio emissions that they produce when interacting with the solar atmosphere. Particle transport from the acceleration sites to the radiation sites remains of the challenging topic in the field of high energy solar physics and has an important impact on the interpretation of the particle emissions in the context of acceleration models. In order to address the transport of flare associated energetic electrons in the low corona, we use imaging spectroscopic observations from RHESSI of the 2004 May 21 solar flare which presents together with the usually observed HXR footpoints a well observed coronal non-thermal X-ray source. The number of X-ray emitting energetic electrons in the coronal source is compared to the number of electrons needed to produce the hard X-ray emission in the footpoints and is found twice as large. Such an excess of the number of electrons in the coronal source cannot be explained in the context of the standard model of X-ray emissions in which the dominant electron transport is collisional. In the present flare, an additional process is needed to explain how energetic electrons can be efficiently trapped in the corona. In the hypothesis of turbulent pitch-angle scattering of hard X-ray producing energetic electrons (Kontar et al, 2014), diffusive transport can indeed lead to a confinement of energetic electrons in the coronal source. Based on this assumption, we estimated for the present event the mean-free path of energetic electrons and found a value of 10^8 - 10^9 meters, much smaller than the size of the observed flaring loop itself. This implies that a diffusive transport of energetic electrons is dominant in this flare which is in good agreement with the results of a previous study based on the gyrosynchrotron emissions from the energetic electrons (Kuznetsov & Kontar, 2015).

  12. THE n-DISTRIBUTION OF ELECTRONS AND DOUBLE LAYERS IN THE ELECTRON-BEAM-RETURN-CURRENT SYSTEM OF SOLAR FLARES

    SciTech Connect

    Karlicky, Marian

    2012-05-01

    We investigate processes in the electron-beam-return-current system in the impulsive phase of solar flares to answer a question about the formation of the n-electron distribution detected in this phase of solar flares. An evolution of the electron-beam-return-current system with an initial local density depression is studied using a three-dimensional electromagnetic particle-in-cell model. In the system the strong double layer is formed. Its electric field potential increases with the electron beam flux. In this electric field potential, the electrons of background plasma are strongly accelerated and propagate in the return-current direction. The high-energy part of their distribution at the high-potential side of the strong double layer resembles that of the n-distribution. Thus, the detection of the n-distributions, where a form of the high-energy part of the distribution is the most important, can indicate the presence of strong double layers in solar flares. The similarity between processes in solar flare loops and those in the downward current region of the terrestrial aurora, where the double layers were observed by FAST satellite, supports this idea.

  13. OBSERVATIONAL EVIDENCE OF ELECTRON-DRIVEN EVAPORATION IN TWO SOLAR FLARES

    SciTech Connect

    Li, D.; Ning, Z. J.; Zhang, Q. M.

    2015-11-01

    We have explored the relationship between hard X-ray (HXR) emissions and Doppler velocities caused by the chromospheric evaporation in two X1.6 class solar flares on 2014 September 10 and October 22, respectively. Both events display double ribbons and the Interface Region Imaging Spectrograph slit is fixed on one of their ribbons from the flare onset. The explosive evaporations are detected in these two flares. The coronal line of Fe xxi 1354.09 Å shows blueshifts, but the chromospheric line of C i 1354.29 Å shows redshifts during the impulsive phase. The chromospheric evaporation tends to appear at the front of the flare ribbon. Both Fe xxi and C i display their Doppler velocities with an “increase-peak-decrease” pattern that is well related to the “rising-maximum-decay” phase of HXR emissions. Such anti-correlation between HXR emissions and Fe xxi Doppler shifts and correlation with C i Doppler shifts indicate the electron-driven evaporation in these two flares.

  14. Evidence of electron acceleration around the reconnection X-point in a solar flare

    SciTech Connect

    Narukage, Noriyuki; Shimojo, Masumi; Sakao, Taro

    2014-06-01

    Particle acceleration is one of the most significant features that are ubiquitous among space and cosmic plasmas. It is most prominent during flares in the case of the Sun, with which huge amounts of electromagnetic radiation and high-energy particles are expelled into the interplanetary space through acceleration of plasma particles in the corona. Though it has been well understood that energies of flares are supplied by the mechanism called magnetic reconnection based on the observations in X-rays and EUV with space telescopes, where and how in the flaring magnetic field plasmas are accelerated has remained unknown due to the low plasma density in the flaring corona. We here report the first observational identification of the energetic non-thermal electrons around the point of the ongoing magnetic reconnection (X-point), with the location of the X-point identified by soft X-ray imagery and the localized presence of non-thermal electrons identified from imaging-spectroscopic data at two microwave frequencies. Considering the existence of the reconnection outflows that carries both plasma particles and magnetic fields out from the X-point, our identified non-thermal microwave emissions around the X-point indicate that the electrons are accelerated around the reconnection X-point. Additionally, the plasma around the X-point was also thermally heated up to 10 MK. The estimated reconnection rate of this event is ∼0.017.

  15. Electron density diagnostics in the 10-100 A interval for a solar flare

    NASA Technical Reports Server (NTRS)

    Brown, W. A.; Bruner, M. E.; Acton, L. W.; Mason, H. E.

    1986-01-01

    Electron density measurements from spectral-line diagnostics are reported for a solar flare on July 13, 1982, 1627 UT. The spectrogram, covering the 10-95 A interval, contained usable lines of helium-like ions C V, N VI, O VII, and Ne IX which are formed over the temperature interval 0.7-3.5 x 10 to the 6th K. In addition, spectral-line ratios of Si IX, Fe XIV, and Ca XV were compared with new theoretical estimates of their electron density sensitivity to obtain additional electron density diagnostics. An electron density of 3 x 10 to the 10th/cu cm was obtained. The comparison of these results from helium-like and other ions gives confidence in the utility of these tools for solar coronal analysis and will lead to a fuller understanding of the phenomena observed in this flare.

  16. Accumulation of accelerated electrons in coronal loops and time delays of solar flare nonthermal emission

    NASA Astrophysics Data System (ADS)

    Tsap, Yu. T.; Stepanov, A. V.; Kopylova, Yu. G.

    2015-12-01

    The mechanisms by which accelerated electrons accumulate in flare loops with regard to the observed time delays between peaks of prolonged (≫1 s) hard X-ray pulses with different energies are considered. The focus is on an analysis of electron pitch-angle scattering by background plasma particles and/or turbulent pulsations in extreme cases of frequent and rare collisions. It was shown that it is difficult to explain the origination of time delays in the scope of a diffusion model when the electron free path length ( l) in the corona is smaller than the flare loop length ( L). The accumulation of energetic particles in loops at l > L is related to a trap-plus-precipitation model in which the regime of weak pitch angle diffusion of trapped electrons in the loss cone predominates.

  17. Properties of solar flare electrons, deduced from hard X-ray and spatially resolved microwave observations

    NASA Technical Reports Server (NTRS)

    Marsh, K. A.; Hurford, G. J.; Zirin, H.; Dulk, G. A.; Dennis, B. R.; Frost, K. J.; Orwig, L. E.

    1981-01-01

    An important question concerning an understanding of impulsive solar flares is related to the energetic electrons responsible for the microwave and the hard X-ray emission. A description is presented of an investigation in which spatially resolved microwave observations of an impulsive flare and hard X-ray data from the Solar Maximum Mission (SMM) are used to test the hypothesis that the two types of emission come from the same basic electron population. The considered observations are found to imply that the microwaves and hard X-rays were not produced by a common population of electrons with either a Maxwellian or single power-law energy distribution. It is suggested that the calculations should be repeated when observations of stronger events become available, for which a better determination of the X-ray spectrum is possible. The possibility is considered that microwaves and moderately hard X-rays come from spatially different regions.

  18. Energetic electrons from solar flares and associated type 3 radio bursts from metric to hectometric wave frequencies

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1972-01-01

    Distinct Kev electron events as observed by satellites near the earth are, in general, associated with solar flares which are accompained by the emission of both metric and hectometric type 3 radio bursts. The positions of these flares are mainly on the western hemisphere of the sun. These results show that Kev electrons propagate under the control of the magnetic field in the interplanetary space and that, while propagating through this space, these electrons excite type 3 radio bursts from metric to hectometric wave frequencies. Emission characteristics of hectometric type 3 bursts are briefly considered in relation to the positions of associated flares.

  19. Faint Coronal Hard X-rays From Accelerated Electrons in Solar Flares

    NASA Astrophysics Data System (ADS)

    Glesener, Lindsay Erin

    Solar flares are huge explosions on the Sun that release a tremendous amount of energy from the coronal magnetic field, up to 1033 ergs, in a short time (100--1000 seconds), with much of the energy going into accelerated electrons and ions. An efficient acceleration mechanism is needed, but the details of this mechanism remain relatively unknown. A fraction of this explosive energy reaches the Earth in the form of energetic particles, producing geomagnetic storms and posing dangers to spaceborne instruments, astronauts, and Earthbound power grids. There are thus practical reasons, as well as intellectual ones, for wishing to understand this extraordinary form of energy release. Through imaging spectroscopy of the hard X-ray (HXR) emission from solar flares, the behavior of flare-accelerated electrons can be studied. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI ) spacecraft launched in 2002 with the goal of better understanding flare particle acceleration. Using rotation modulation collimators, RHESSI is able to cover a wide energy range (3 keV--17 MeV) with fine angular and energy resolutions. RHESSI's success in the last 10 years in investigating the relationship between energetic electrons and ions, the nature of faint sources in the corona, the energy distribution of flares, and several other topics have significantly advanced the understanding of flares. But along with the wealth of information revealed by RHESSI come some clear observational challenges. Very few, if any, RHESSI observations have come close to imaging the electron acceleration region itself. This is undoubtedly due to a lack of both sensitivity (HXRs from electron beams in the tenuous corona are faint) and dynamic range (HXR sources at chromospheric flare footpoints are much brighter and tend to obscure faint coronal sources). Greater sensitivity is also required to investigate the role that small flares in the quiet Sun could play in heating the corona. The Focusing Optics

  20. Energetic electron propagation in the decay phase of non-thermal flare emission

    SciTech Connect

    Huang, Jing; Yan, Yihua; Tsap, Yuri T.

    2014-06-01

    On the basis of the trap-plus-precipitation model, the peculiarities of non-thermal emission in the decay phase of solar flares have been considered. The calculation formulas for the escape rate of trapped electrons into the loss cone in terms of time profiles of hard X-ray (HXR) and microwave (MW) emission have been obtained. It has been found that the evolution of the spectral indices of non-thermal emission depend on the regimes of the pitch angle diffusion of trapped particles into the loss cone. The properties of non-thermal electrons related to the HXR and MW emission of the solar flare on 2004 November 3 are studied with Nobeyama Radioheliograph, Nobeyama Radio Polarimeters, RHESSI, and Geostationary Operational Environmental Satellite observations. The spectral indices of non-thermal electrons related to MW and HXR emission remained constant or decreased, while the MW escape rate as distinguished from that of the HXRs increased. This may be associated with different diffusion regimes of trapped electrons into the loss cone. New arguments in favor of an important role of the superstrong diffusion for high-energy electrons in flare coronal loops have been obtained.

  1. Electron distribution functions in solar flares from combined X-ray and extreme-ultraviolet observations

    SciTech Connect

    Battaglia, M.; Kontar, E. P.

    2013-12-20

    Simultaneous solar flare observations with SDO and RHESSI provide spatially resolved information about hot plasma and energetic particles in flares. RHESSI allows the properties of both hot (≳8 MK) thermal plasma and non-thermal electron distributions to be inferred, while SDO/AIA is more sensitive to lower temperatures. We present and implement a new method to reconstruct electron distribution functions from SDO/AIA data. The combined analysis of RHESSI and AIA data allows the electron distribution function to be inferred over the broad energy range from 0.1 keV up to a few tens of keV. The analysis of two well-observed flares suggests that the distributions in general agree to within a factor of three when the RHESSI values are extrapolated into the intermediate range 1-3 keV, with AIA systematically predicting lower electron fluxes. Possible instrumental and numerical effects, as well as potential physical origins for this discrepancy, are discussed. The inferred electron distribution functions in general show one or two nearly Maxwellian components at energies below ∼15 keV and a non-thermal tail above.

  2. Radio Spectroscopic Imaging of Bi-directional Electron Beam Pairs in a Solar Flare

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Wang, Zhitao; Gary, Dale E.

    2016-05-01

    In solar flares, energetic electrons are believed to be accelerated at or near the magnetic reconnection site. They propagate outward along newly reconnected field lines usually in the form of electron beams. These beams can emit radio waves commonly known as type III radio bursts. An important feature of these bursts is that they are emitted near the local plasma frequency or its harmonic, which is only a function of the ambient plasma density. In particular, an electron beam propagating upward in the corona encounters plasma with lower and lower density, producing a radio burst with a “normal” frequency slope (whose frequency decreases in time). Similarly, a downward propagating beam produces a reverse-slope burst. Sometimes both the normal- and reverse-slope type III bursts are observed simultaneously. These type III burst with opposite slopes have been considered to be the signature of a pair of bi-directional electron beams emerging from a common acceleration site. However, previous studies had no imaging capability to locate these bursts and put them in the flare context. Here we report observations of decimetric type III burst pairs by the Karl G. Jansky Very Large Array (VLA) during the impulsive phase of a C5.6 flare. Using VLA’s unprecedented ultra-high-cadence spectroscopic imaging capability, we demonstrate that the type III burst pairs indeed correspond to high speed (~0.1c), bi-directional electron beams emerging from a common site in the corona where post-flare loops appeared later on. Implications of our results on magnetic reconnection and particle acceleration will be briefly discussed.

  3. Electron energy-loss spectra in molecular fluorine

    NASA Technical Reports Server (NTRS)

    Nishimura, H.; Cartwright, D. C.; Trajmar, S.

    1979-01-01

    Electron energy-loss spectra in molecular fluorine, for energy losses from 0 to 17.0 eV, have been taken at incident electron energies of 30, 50, and 90 eV and scattering angles from 5 to 140 deg. Features in the spectra above 11.5 eV energy loss agree well with the assignments recently made from optical spectroscopy. Excitations of many of the eleven repulsive valence excited electronic states are observed and their location correlates reasonably well with recent theoretical results. Several of these excitations have been observed for the first time and four features, for which there are no identifications, appear in the spectra.

  4. Energy transport by energetic electrons released during solar flares. II - Current filamentation and plasma heating

    NASA Technical Reports Server (NTRS)

    Winglee, R. M.; Dulk, G. A.; Pritchett, P. L.

    1988-01-01

    Two-dimensional electrostatic particle simulations are performed in order to investigate energy transport associated with the propagation of energetic electrons through a flaring flux tube. Results indicate that as the energetic electrons flow outward, a return current of ambient plasma electrons is drawn inward (to maintain quasi-neutrality) which can be spatially separate from the primary current carried by the energetic electrons. Return current electrons are shown to accumulate on either side of the acceleration region of the energetic electrons, and depletions of ambient plasma electrons develop in the return current regions. Plasma ions accelerate across the field lines to produce current closure or charge neutralization, achieving energies comparable to those of the energetic electrons.

  5. Neutrons and Gamma Rays from Solar Flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Murphy, R. J.

    1983-01-01

    The theory of neutron and gamma-ray production in flares is reviewed and comparisons of the calculations with data are made. The principal conclusions pertain to the accelerated proton and electron numbers and spectra in flares and to the interaction site of these particles in the solar atmosphere. For the June 21, 1980 flare, from which high-energy neutrons and high-energy ( MeV) photons were seen, the electron-to-proton ratio is energy dependent and much smaller than unity at energies greater than 1 MeV. The interaction site of these particles appears to be the solar chromosphere.

  6. Particle Acceleration in Solar Flares

    NASA Astrophysics Data System (ADS)

    Petrosian, V.

    Several new observations notably high spatial and spectral X-ray observations of impulsive phase of solar flares by YOHKOH and RHESSI, and Solar Energetic Particle (SEP) spectra by ACE have provided strong evidence in favor of stochastic acceleration of electrons, protons and other ions by plasma waves or turbulence. Theoretical arguments also favor such a model if the seed particles come from the background thermal plasma. I will describe these evidences and the theoretical framework for evaluation of the accelerated particle spectra, their transport and radiation. The predictions of the models will be compared with several features of the observations with specific emphasize on heating vs acceleration by turbulence, thermal vs nonthermal electron spectra, looptop vs footpoint emission fro flaring loops, electron vs proton acceleration rates and 3He vs 4He (and other ion) abundances in SEPs.

  7. Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

    NASA Astrophysics Data System (ADS)

    Parshin, A. S.; Igumenov, A. Yu.; Mikhlin, Yu. L.; Pchelyakov, O. P.; Zhigalov, V. S.

    2016-05-01

    The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.

  8. Electron acceleration in the turbulent reconnecting current sheets in solar flares

    NASA Astrophysics Data System (ADS)

    Wu, G. P.; Huang, G. L.

    2009-07-01

    Context: We investigate the nonlinear evolution of the electron distribution in the presence of the strong inductive electric field in the reconnecting current sheets (RCS) of solar flares. Aims: We aim to study the characteristics of nonthermal electron-beam plasma instability and its influence on electron acceleration in RCS. Methods: Including the external inductive field, the one-dimensional Vlasov simulation is performed with a realistic mass ratio for the first time. Results: Our principal findings are as follows: 1) the Buneman instability can be quickly excited on the timescale of 10-7 s for the typical parameters of solar flares. After saturation, the beam-plasma instabilities are excited due to the non-Maxwellian electron distribution; 2) the final velocity of the electrons trapped by these waves is of the same order as the phase speed of the waves, while the untrapped electrons continue to be accelerated; 3) the inferred anomalous resistance of the current sheet and the energy conversion rate are basically of the same order as those previously estimated, e.g., “the analysis of Martens”. Conclusions: The Buneman instability is excited on the timescale of 10-7 s and the wave-particle resonant interaction limits the low-energy electrons to be further accelerated in RCS.

  9. Microwave imaging of a solar limb flare - Comparison of spectra and spatial geometry with hard X-rays

    NASA Technical Reports Server (NTRS)

    Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.

    1985-01-01

    A solar limb flare was mapped using the Very Large Array (VLA) together with hard X-ray (HXR) spectral and spatial observations of the Solar Maximum Mission satellite. Microwave flux records from 2.8 to 19.6 GHz were instrumental in determining the burst spectrum, which has a maximum at 10 GHz. The flux spectrum and area of the burst sources were used to determine the number of electrons producing gyrosynchrotron emission, magnetic field strength, and the energy distribution of gyrosynchrotron-emitting electrons. Applying the thick target model to the HXR spectrum, the number of high energy electrons responsible for the X-ray bursts was found to be 10 to the 36th, and the electron energy distribution was approximately E exp -5, significantly different from the parameters derived from the microwave observations. The HXR imaging observations exhibit some similiarities in size and structure o the first two burst sources mapped with the VLA. However, during the initial burst, the HXR source was single and lower in the corona than the double 6 cm source. The observations are explained in terms of a single loop with an isotropic high-energy electron distribution which produced the microwaves, and a larger beamed component which produced the HXR at the feet of the loop.

  10. Copper(II) phthalocyanine: Electronic and vibrational tunneling spectra

    SciTech Connect

    Hipps, K.W. )

    1989-08-10

    Inelastic electron tunneling spectra (IETS) obtained from Al-AlO{sub x}-CuPc-M junctions (M = Pb or Tl) are presented and compared with previous reports. Improved experimental methods allow them to report the entire spectrum in the region below 16,000 cm{sup {minus}1} in both bias directions. In contrast to previous studies, they will show that (a) tunneling spectra are very dependent upon the AlO{sub x}/CuPc and CuPc/M imbedded interfaces, (b) spectra contain both temperature-dependent and temperature-independent features, and (c) certain electronic and the vibrational features depend on junction bias.

  11. Radio and hard X-ray signatures of flare accelerated electrons

    NASA Astrophysics Data System (ADS)

    Vilmer, N. R.

    2003-12-01

    While imaging and spectral radio observations in the decimetric-dekametric domain provide signatures of non-thermal electrons in the middle and upper corona, hard X-rays as well as microwaves trace flare accelerated electrons in the low corona and the chromosphere. Radio observations combined with hard X-ray observations thus allow to analyse the signature of energetic electrons in a whole range of coronal heights. We shall present here the results of multiwavelength studies primarily based on the analysis of HXR and decimetric/metric spatially resolved observations from RHESSI and the Nançay Radioheliograph. We shall outline how these combined observations provide information on the magnetic structures at different spatial scales in which energetic electrons are accelerated and injected as well as on the link between the production of energetic electrons interacting at the Sun and the injection of escaping electrons giving rise to the radio emissions at the lowest frequencies.

  12. The nature of relativistic electron intensity changes during solar flare quiet times between 1963 and 1969

    NASA Technical Reports Server (NTRS)

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

    1971-01-01

    Time variations of the 3-12 MeV interplanetary electron intensity, observed by the Explorer-18, -28, and -33 spacecrafts, have been studied in detail. Apart from solar flare effects, there are five distinct periods when the electron intensity has undergone a series of increases, and these are strongly correlated with solar rotation. The intensity increases are separate phenomena, and are strikingly anticorrelated with increases in the low energy solar proton intensity. The electron energy spectrum during those quiet-time increases is typically represented by dJ/dE = k E/2.0 + or - 0.25 similar to the galactic electron spectrum. There are, in addition, Forbush decreases in the electron intensity frequently coincident with those in the neutron monitor. It is concluded that these characteristics all support the hypothesis of a galactic origin for the electrons observed during quiet-time increases.

  13. Energetic electrons, type III radio bursts, and impulsive solar flare X-rays

    SciTech Connect

    Kane, S.R.

    1981-08-01

    Observations of impulsive hard X-ray and type III radio bursts made during the maximum of the last solar activity cycle have been analyzed for a statistical study of the relationship between these two solar flare phenomena. Spectral measurements of 10--68 keV X-rays, which covered 7068 hr of observation time and the range 10/sup -8/ to 10/sup -5/ ergs cm/sup -2/ s/sup -1/ of flux of X-rays > or approx. =20 keV, were made with the University of California (Berkeley) experiment aboard the OGO 5 satellite. The radio data consisted of copies of the original spectral records as well as tabulated data. The principle findings are: (1) about 20% of impulsive hard X-ray bursts are correlated with type III radio bursts; conversely, only approx.3% of the reported type III radio bursts are correlated with impulsive X-rays bursts; (2) the location of the associated H..cap alpha.. flare on the solar disk has little or no effect on the X-ray--type III burst correlation; (3) the magnitude of the X-ray--type III burst correlation increases systematically with the increase in the following quantities: intensity and starting frequency of the type III burst, peak energy flux and spectral hardness of the X-ray burst, and the peak nonthermal emission measure and spectral hardness of the ''instantaneous'' electron spectrum > or approx. =20 keV inside the x-ray source; (4) the observations are consistent with the electron populations responsible for both the X-ray and type III emissions being accelerated in a single acceleration process; (5) the observations suggest a flare model where the primary instability responsible for electron acceleration during the impulsive phase occurs in the corona. The exact location of this instability varies from one flare to another as well as during the impulsive phase of a single flare and determines the hardness of the accelerated electron spectrum and the characteristics of associated X-ray, EUV, optical, and radio emissions.

  14. Solar Flare Track Exposure Ages in Regolith Particles: A Calibration for Transmission Electron Microscope Measurements

    NASA Technical Reports Server (NTRS)

    Berger, Eve L.; Keller, Lindsay P.

    2015-01-01

    Mineral grains in lunar and asteroidal regolith samples provide a unique record of their interaction with the space environment. Space weathering effects result from multiple processes including: exposure to the solar wind, which results in ion damage and implantation effects that are preserved in the rims of grains (typically the outermost 100 nm); cosmic ray and solar flare activity, which result in track formation; and impact processes that result in the accumulation of vapor-deposited elements, impact melts and adhering grains on particle surfaces. Determining the rate at which these effects accumulate in the grains during their space exposure is critical to studies of the surface evolution of airless bodies. Solar flare energetic particles (mainly Fe-group nuclei) have a penetration depth of a few millimeters and leave a trail of ionization damage in insulating materials that is readily observable by transmission electron microscope (TEM) imaging. The density of solar flare particle tracks is used to infer the length of time an object was at or near the regolith surface (i.e., its exposure age). Track measurements by TEM methods are routine, yet track production rate calibrations have only been determined using chemical etching techniques [e.g., 1, and references therein]. We used focused ion beam-scanning electron microscope (FIB-SEM) sample preparation techniques combined with TEM imaging to determine the track density/exposure age relations for lunar rock 64455. The 64455 sample was used earlier by [2] to determine a track production rate by chemical etching of tracks in anorthite. Here, we show that combined FIB/TEM techniques provide a more accurate determination of a track production rate and also allow us to extend the calibration to solar flare tracks in olivine.

  15. Electron trapping and acceleration by kinetic Alfvén waves in solar flares

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Zimovets, I. V.; Rankin, R.

    2016-05-01

    Context. Theoretical models and spacecraft observations of solar flares highlight the role of wave-particle interaction for non-local electron acceleration. In one scenario, the acceleration of a large electron population up to high energies is due to the transport of electromagnetic energy from the loop-top region down to the footpoints, which is then followed by the energy being released in dense plasma in the lower atmosphere. Aims: We consider one particular mechanism of non-linear electron acceleration by kinetic Alfvén waves. Here, waves are generated by plasma flows in the energy release region near the loop top. We estimate the efficiency of this mechanism and the energies of accelerated electrons. Methods: We use analytical estimates and test-particle modelling to investigate the effects of electron trapping and acceleration by kinetic Alfvén waves in the inhomogeneous plasma of the solar corona. Results: We demonstrate that, for realistic wave amplitudes, electrons can be accelerated up to 10-1000 keV during their propagation along magnetic field lines. Here the electric field that is parallel to the direction of the background magnetic field is about 10 to 103 times the amplitude of the Dreicer electric field. The acceleration mechanism strongly depends on electron scattering which is due to collisions that only take place near the loop footpoints. Conclusions: The non-linear wave-particle interaction can play an important role in the generation of relativistic electrons within flare loops. Electron trapping and coherent acceleration by kinetic Alfvén waves represent the energy cascade from large-scale plasma flows that originate at the loop-top region down to the electron scale. The non-diffusive character of the non-linear electron acceleration may be responsible for the fast generation of high-energy particles.

  16. Behaviour of Electron Content in the Ionospheric D-Region During Solar X-Ray Flares

    NASA Astrophysics Data System (ADS)

    Todorović Drakul, M.; Čadež, V. M.; Bajčetić, J.; Popović, L. Č.; Blagojević, D.; Nina, A.

    2016-08-01

    One of the most important parameters in ionospheric plasma research, also having a wide practical application in wireless satellite telecommunications, is the total electron content (TEC) representing the columnal electron number density. The F-region with high electron density provides the biggest contribution to TEC while the relatively weakly ionized plasma of the D-region (60 km - 90 km above Earth's surface) is often considered as a negligible cause of satellite signal disturbances. However, sudden intensive ionization processes, like those induced by solar X-ray flares, can cause relative increases of electron density that are significantly larger in the D-region than in regions at higher altitudes. Therefore, one cannot exclude a priori the D-region from investigations of ionospheric influences on propagation of electromagnetic signals emitted by satellites. We discuss here this problem which has not been sufficiently treated in literature so far. The obtained results are based on data collected from the D-region monitoring by very low frequency radio waves and on vertical TEC calculations from the Global Navigation Satellite System (GNSS) signal analyses, and they show noticeable variations in the D-region's electron content (TEC_{D}) during activity of a solar X-ray flare (it rises by a factor of 136 in the considered case) when TEC_{D} contribution to TEC can reach several percent and which cannot be neglected in practical applications like global positioning procedures by satellites.

  17. TEMPORAL VARIATIONS OF X-RAY SOLAR FLARE LOOPS: LENGTH, CORPULENCE, POSITION, TEMPERATURE, PLASMA PRESSURE, AND SPECTRA

    SciTech Connect

    Jeffrey, Natasha L. S.; Kontar, Eduard P.

    2013-04-01

    The spatial and spectral properties of three solar flare coronal X-ray loops are studied before, during, and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density, and thermal pressure. We observe a decrease in the loop length, width, and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to increasing width. The volume variations are more pronounced than the position variations, often known as magnetic field line contraction. We believe this is the first dedicated study examining the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission, and thermal pressure, with the minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low {beta} plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density. This produces increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.

  18. Energetic electrons, Type III radio bursts, and impulsive solar flare X-rays

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1981-01-01

    Observations of impulsive hard X-ray and type III radio bursts made during the maximum of the last solar activity cycle are analyzed. Spectral measurements of 10-68 keV X-rays were made with the University of California (Berkeley) experiment aboard the OGO 5 satellite. About 20% of impulsive hard X-ray bursts are correlated with type III radio bursts, whereas only about 3% of the reported type III radio bursts are correlated with impulsive X-ray bursts. The location of the associated H gamma flare on the solar disk has little effect on the X-ray-type III burst correlation. The magnitude of the X-ray-type III burst correlation increases systematically with an increase in the intensity and starting frequency of the radio burst, the peak energy and hardness of the X-ray burst, and the peak nonthermal emission measure and spectral hardness of the electron spectrum not less than 20 keV inside the X-ray source. Observations are consistent with the electron populations responsible for both the X-ray and type III emissions accelerated in a single acceleration process; they also suggest a flare model where the primary instability causing electron acceleration during the impulsive phase occurs in the corona.

  19. Quasi-periodic Acceleration of Electrons in the Flare on 2012 July 19

    NASA Astrophysics Data System (ADS)

    Huang, Jing; Kontar, Eduard P.; Nakariakov, Valery M.; Gao, Guannan

    2016-11-01

    Quasi-periodic pulsations (QPPs) of nonthermal emission in an M7.7 class flare on 2012 July 19 are investigated with spatially resolved observations at microwave and HXR bands and with spectral observations at decimetric, metric waves. Microwave emission at 17 GHz of two footpoints, HXR emission at 20–50 keV of the north footpoint and loop top, and type III bursts at 0.7–3 GHz show prominent in-phase oscillations at 270 s. The microwave emission of the loop leg has less pulsation but stronger emission. Through the estimation of plasma density around the loop top from EUV observations, we find that the local plasma frequency would be 1.5 GHz or even higher. Thus, type III bursts at 700 MHz originate above the loop top. Quasi-periodic acceleration or injection of energetic electrons is proposed to dominate these in-phase QPPs of nonthermal emission from footpoints, loop top, and above. In the overlying region, drifting pulsations (DPS) at 200–600 MHz oscillate at a distinct period (200 s). Its global structure drifts toward lower frequency, which is closely related to upward plasmoids observed simultaneously from EUV emission. Hence, nonthermal emission from overlying plasmoids and underlying flaring loops show different oscillating periods. Two individual systems of quasi-periodic acceleration of electrons are proposed to coincide in the bi-direction outflows from the reconnection region.

  20. Peak-flux-density spectra of large radio bursts and proton emission from flares. Environmental research papers, July 1981-July 1985

    SciTech Connect

    Cliver, E.W.; McNamara, L.F.; Gentile, L.C.

    1985-08-19

    From this study of the peak-flux-density spectra of nearly 200 large (sp > or = 2 GHz) > or = 800 solar flux units) microwave bursts and their associated proton and sweep-frequency emissions, the authors found the following: (1) There appear to be two basic peak-flux-density spectral types: (a) U-shaped, with two maxima > or = 800 sfu in the range of 200 MHz to > or = 19 GHz (59% of all events) and (b) cutoff, with a spectral maximum > or = 800 sfu at f > or = 2 GHz and Sp(200 MHz) < 100 sfu (18%). (2) If the current NOAA proton-prediction threshold of J (> 10 MeV) > or = 10 protons/sq cm/sec/sr had been in effect during the period covered by the data base (1965-1979), the U-burst yes or no proton event forecast tool would have had a false alarm rate of approx. 50% and would have failed to provide a warning for approx. 50% of the significant prompt proton flares attributable to disk flares during this period. (3) The associations of flare-bursts of different peak flux density spectral type with Type II and/or Type IV bursts and with > 10-MeV proton events of any peak intensity are given. (4) In 74% of the microwave bursts with u-shaped spectra, the 200 MHz emission peak occurred during a Type III event. For 49% of the U-bursts, a Type II was in progress during, or began < or = 0.5 min after, the peak 200-MHz emission. (5) Several (8 of 46) of the proton events with J (> 10 MeV) > or = 10 protons/sq cm/sec/sr (1965-1979) originated in visible hemisphere flares with relatively weak (Sp < or = 300 sfu) and associated 200-MHz emission.

  1. The Formation of Kappa-Distribution Accelerated Electron Populations in Solar Flares

    NASA Astrophysics Data System (ADS)

    Bian, N. H.; Kontar, E.; Emslie, G.

    2015-12-01

    Driven by recent RHESSI observations of confined loop-top hard X-ray sources in solar flares, we consider stochastic acceleration of electrons in the presence of Coulomb collisions. If electron escape from the acceleration region can be neglected, the electron distribution function is determined by a balance between diffusive acceleration and collisions. Such a scenario admits a stationary solution for the electron distribution function that takes the form of a kappa distribution. We show that the evolution toward this kappa distribution involves a "wave front" propagating forwards in velocity space, so that electrons of higher energy are accelerated later; the acceleration time scales as the power three-half of the energy. At sufficiently high energies escape from the finite-length acceleration region will eventually dominate. For such energies, the electron velocity distribution function is obtained by solving a time-dependent Fokker-Planck equation in the "leaky-box" approximation. Solutions are obtained in the limit of a small escape rate from an acceleration region that can effectively be considered a thick target.

  2. The formation of kappa-distribution accelerated electron populations in solar flares

    SciTech Connect

    Bian, Nicolas H.; Stackhouse, Duncan J.; Kontar, Eduard P.; Emslie, A. Gordon E-mail: d.stackhouse.1@research.gla.ac.uk E-mail: emslieg@wku.edu

    2014-12-01

    Driven by recent RHESSI observations of confined loop-top hard X-ray sources in solar flares, we consider stochastic acceleration of electrons in the presence of Coulomb collisions. If electron escape from the acceleration region can be neglected, the electron distribution function is determined by a balance between diffusive acceleration and collisions. Such a scenario admits a stationary solution for the electron distribution function that takes the form of a kappa distribution. We show that the evolution toward this kappa distribution involves a 'wave front' propagating forward in velocity space, so that electrons of higher energy are accelerated later; the acceleration timescales with energy according to τ{sub acc} ∼ E {sup 3/2}. At sufficiently high energies escape from the finite-length acceleration region will eventually dominate. For such energies, the electron velocity distribution function is obtained by solving a time-dependent Fokker-Planck equation in the 'leaky-box' approximation. Solutions are obtained in the limit of a small escape rate from an acceleration region that can effectively be considered a thick target.

  3. Multispectral elastic scanning lidar for industrial flare research: characterizing the electronic subsystem and application.

    PubMed

    Guerrero-Rascado, Juan Luis; Facundes da Costa, Renata; Bedoya, Andrés Esteban; Guardani, Roberto; Alados-Arboledas, Lucas; Bastidas, Álvaro Efrain; Landulfo, Eduardo

    2014-12-15

    This work deals with the analysis of the electronic subsystem of a multiwavelength elastic scanning lidar. Several calibration tests are applied to the Cubatão scanning lidar placed at the industrial area of Cubatão in the State of São Paulo (Brazil), in order to improve the knowledge of its performing itself and to design protocols for correcting lidar signal for undesirable instrumental effects. In particular, the trigger delay is assessed by means of zero-bin and bin-shift tests for analog (AN) and photo-counting (PC) signals, respectively. Dark current test is also performed to detect potential range-dependency that could affect lidar products. All tests were performed at different spatial resolutions. These instrumental corrections were applied to a case study of data acquired for characterizing the optical and microphysical properties of particles in an industrial flare. To that aim, a graphical method based on the space defined by the extinction-related Angström exponent versus its spectral curvature is used to derive the contribution of fine aerosol to extinction and the size of the fine aerosols in the industrial flare, therefore revealing features of the processes occurring inside the flame. Our study demonstrates the potential of this new technique for the study and measurement of industrial emissions. PMID:25607056

  4. Multispectral elastic scanning lidar for industrial flare research: characterizing the electronic subsystem and application.

    PubMed

    Guerrero-Rascado, Juan Luis; Facundes da Costa, Renata; Bedoya, Andrés Esteban; Guardani, Roberto; Alados-Arboledas, Lucas; Bastidas, Álvaro Efrain; Landulfo, Eduardo

    2014-12-15

    This work deals with the analysis of the electronic subsystem of a multiwavelength elastic scanning lidar. Several calibration tests are applied to the Cubatão scanning lidar placed at the industrial area of Cubatão in the State of São Paulo (Brazil), in order to improve the knowledge of its performing itself and to design protocols for correcting lidar signal for undesirable instrumental effects. In particular, the trigger delay is assessed by means of zero-bin and bin-shift tests for analog (AN) and photo-counting (PC) signals, respectively. Dark current test is also performed to detect potential range-dependency that could affect lidar products. All tests were performed at different spatial resolutions. These instrumental corrections were applied to a case study of data acquired for characterizing the optical and microphysical properties of particles in an industrial flare. To that aim, a graphical method based on the space defined by the extinction-related Angström exponent versus its spectral curvature is used to derive the contribution of fine aerosol to extinction and the size of the fine aerosols in the industrial flare, therefore revealing features of the processes occurring inside the flame. Our study demonstrates the potential of this new technique for the study and measurement of industrial emissions.

  5. Multiple-wavelength analysis of energy release during a solar flare - Thermal and nonthermal electron populations

    NASA Technical Reports Server (NTRS)

    Willson, Robert F.; Lang, Kenneth R.; Klein, Karl-Ludwig; Kerdraon, Alain; Trottet, Gerard

    1990-01-01

    Collaborative solar investigations by Tufts University and the Observatoire de Paris have resulted in simultaneous radio observations with the Very Large Array (VLA) and the Nancay Radioheliograph (NR), comparisons of this radio data with X-ray observations, and theoretical interpretations of the dominant radiation mechanisms during a weak impulsive solar flare observed on May 28, 1988. The VLA has mapped the flaring structures at time intervals of 3.3 s, showing that the preflash and flash-phase components of the impulsive emission originate in spatially separated sources. The 20.7 cm preflash source is ascribed to thermal gyroresonance emission from coronal loops with typical magnetic field strengths of up to 270 G; this emission is associated with heating and exhibits no detectable hard X-ray radiation above 30 keV. The flash-phase 20.7 cm source and the hard X-ray emission are attributed to nonthermal electrons in the coronal and chromospheric portions of a magnetic loop. The combination of imaging observations at 20.7 and 91.6 cm excludes emission from a confined hot plasma during the flash phase.

  6. Using Supra-Arcade Downflows as Probes of Electron Acceleration During Solar Flares

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina L.

    2011-01-01

    Extracting information from coronal features above flares has become more reliable with the availability of increasingly higher spatial and temporal-resolution data in recent decades. We are now able to sufficiently probe the region high above long-duration flaring active regions where reconnection is expected to be continually occurring. Flows in the supra-arcade region, first observed with Yohkoh/SXT, have been theorized to be associated with newly-reconnected outflowing loops. High resolution data appears to confirm these assertions. Assuming that these flows are indeed reconnection outflows, then the detection of those directed toward the solar surface (i.e. downflowing) should be associated with particle acceleration between the current sheet and the loop footpoints rooted in the chromosphere. RHESSI observations of highly energetic particles with respect to downflow detections could potentially constrain electron acceleration models. I will discuss measurements of these supra-arcade downflows (SADs) in relation to reconnection model parameters and present preliminary findings comparing the downflow timings with high-energy RHESSI lightcurves.

  7. The electronic spectra of mu-peroxodicobalt(III) complexes

    NASA Technical Reports Server (NTRS)

    Miskowski, Vincent M.

    1987-01-01

    Problems found in the determination of the electronic spectra of mu-peroxodicobalt(III) complexes are considered, and the common formation of different mu-peroxocomplexes upon oxygenation of Co(II)-ligand solutions is discussed. Three classes of spectra have been identified: (1) planar single bridged complexes; (2) nonplanar single-bridged complexes with a dihedral angle near 145 deg; and (3) dibridged mu-OH(-),O2(2-) complexes with a dihedral angle near 60 deg. All of the peroxide ligand-to-metal charge-transfer spectra are found to be consistent with a simple model that assumes a sinusoidal dependence of pi-asterisk O2(2-) energies and sigma-overlaps upon the dihedral angle.

  8. Electronic spectra and structures of some biologically important xanthines

    NASA Astrophysics Data System (ADS)

    Shukla, M. K.; Mishra, P. C.

    1994-08-01

    Electronic absorption and fluorescence spectra of aqueous solutions of xanthine, caffeine, theophylline and theobromine have been studied at different pH. The observed spectra have been interpreted in terms of neutral and ionic forms of the molecules with the help of molecular orbital calculations. At neutral and acidic pH, the spectra can be assigned to the corresponding most stable neutral forms, with the exception that the fluorescence of xanthine at acidic pH appears to originate from the lowest singlet excited state of a cation of the molecule. At alkaline pH, xanthine and theophylline exist mainly as their monoanions. In xanthine and theophylline at alkaline pH, fluorescence originates from the lowest singlet excited state of the corresponding anion. However, in caffeine and theobromine, even at alkaline pH, fluorescence belongs to the neutral species. On the whole, the properties of xanthine are quite different from those of the methyl xanthines.

  9. Electronic spectra from TDDFT and machine learning in chemical space

    SciTech Connect

    Ramakrishnan, Raghunathan; Hartmann, Mia; Tapavicza, Enrico; Lilienfeld, O. Anatole von

    2015-08-28

    Due to its favorable computational efficiency, time-dependent (TD) density functional theory (DFT) enables the prediction of electronic spectra in a high-throughput manner across chemical space. Its predictions, however, can be quite inaccurate. We resolve this issue with machine learning models trained on deviations of reference second-order approximate coupled-cluster (CC2) singles and doubles spectra from TDDFT counterparts, or even from DFT gap. We applied this approach to low-lying singlet-singlet vertical electronic spectra of over 20 000 synthetically feasible small organic molecules with up to eight CONF atoms. The prediction errors decay monotonously as a function of training set size. For a training set of 10 000 molecules, CC2 excitation energies can be reproduced to within ±0.1 eV for the remaining molecules. Analysis of our spectral database via chromophore counting suggests that even higher accuracies can be achieved. Based on the evidence collected, we discuss open challenges associated with data-driven modeling of high-lying spectra and transition intensities.

  10. Acceleration of electrons and ions by strong lower-hybrid turbulence in solar flares

    NASA Technical Reports Server (NTRS)

    Spicer, D. S.; Bingham, R.; Su, J. J.; Shapiro, V. D.; Shevchenko, V.; Ma, S.; Dawson, J. M.; Mcclements, K. G.

    1994-01-01

    One of the outstanding problems in solar flare theory is how to explain the 10-20 keV and greater hard x-ray emissions by a thick target bremsstrahlung model. The model requires the acceleration mechanism to accelerate approximately 10(exp 35) electrons sec(exp -l) with comparable energies, without producing a large return current which persists for long time scales after the beam ceases to exist due to Lenz's law, thereby, producing a self-magnetic field of order a few mega-Gauss. In this paper, we investigate particle acceleration resulting from the relaxation of unstable ion ring distributions, producing strong wave activity at the lower hybrid frequency. It is shown that strong lower hybrid wave turbulence collapses in configuration space producing density cavities containing intense electrostatic lower hybrid wave activity. The collapse of these intense nonlinear wave packets saturate by particle acceleration producing energetic electron and ion tails. There are several mechanisms whereby unstable ion distributions could be formed in the solar atmosphere, including reflection at perpendicular shocks, tearing modes, and loss cone depletion. Numerical simulations of ion ring relaxation processes, obtained using a 2 1/2-D fully electromagnetic, relativistic particle in cell code are discussed. We apply the results to the problem of explaining energetic particle production in solar flares. The results show the simultaneous acceleration of both electrons and ions to very high energies: electrons are accelerated to energies in the range 10-500 keV, while ions are accelerated to energies of the order of MeVs, giving rise to x-ray emission and gamma-ray emission respectively. Our simulations also show wave generation at the electron cyclotron frequency. We suggest that these waves are the solar millisecond radio spikes. The strong turbulence collapse process leads to a highly filamented plasma producing many localized regions for particle acceleration and resulting in

  11. The electron impact mass spectra of di- and trinitrofluoranthenes.

    PubMed

    Ramdahl, T; Zielinska, B; Arey, J; Kondrat, R W

    1988-07-01

    The fragmentation pathways of a series of 18 dinitrofluoranthenes (DNF) and four trinitrofluoranthenes have been studied under electron impact conditions. In general, multiple losses of NO2, NO and CO from the molecular ion were observed. Quinonoid ions were observed in the spectra of DNF containing conjugated nitro groups. In addition, some unique fragmentation pathways were detected in the ortho-substituted 1,2- and 2,3-DNF and in the peri-substituted 3,4-DNF.

  12. On the Solution of the Continuity Equation for Precipitating Electrons in Solar Flares

    NASA Technical Reports Server (NTRS)

    Emslie, A. Gordon; Holman, Gordon D.; Litvinenko, Yuri E.

    2014-01-01

    Electrons accelerated in solar flares are injected into the surrounding plasma, where they are subjected to the influence of collisional (Coulomb) energy losses. Their evolution is modeled by a partial differential equation describing continuity of electron number. In a recent paper, Dobranskis & Zharkova claim to have found an "updated exact analytical solution" to this continuity equation. Their solution contains an additional term that drives an exponential decrease in electron density with depth, leading them to assert that the well-known solution derived by Brown, Syrovatskii & Shmeleva, and many others is invalid. We show that the solution of Dobranskis & Zharkova results from a fundamental error in the application of the method of characteristics and is hence incorrect. Further, their comparison of the "new" analytical solution with numerical solutions of the Fokker-Planck equation fails to lend support to their result.We conclude that Dobranskis & Zharkova's solution of the universally accepted and well-established continuity equation is incorrect, and that their criticism of the correct solution is unfounded. We also demonstrate the formal equivalence of the approaches of Syrovatskii & Shmeleva and Brown, with particular reference to the evolution of the electron flux and number density (both differential in energy) in a collisional thick target. We strongly urge use of these long-established, correct solutions in future works.

  13. On the solution of the continuity equation for precipitating electrons in solar flares

    SciTech Connect

    Emslie, A. Gordon; Holman, Gordon D.; Litvinenko, Yuri E. E-mail: gordon.d.holman@nasa.gov

    2014-09-01

    Electrons accelerated in solar flares are injected into the surrounding plasma, where they are subjected to the influence of collisional (Coulomb) energy losses. Their evolution is modeled by a partial differential equation describing continuity of electron number. In a recent paper, Dobranskis and Zharkova claim to have found an 'updated exact analytical solution' to this continuity equation. Their solution contains an additional term that drives an exponential decrease in electron density with depth, leading them to assert that the well-known solution derived by Brown, Syrovatskii and Shmeleva, and many others is invalid. We show that the solution of Dobranskis and Zharkova results from a fundamental error in the application of the method of characteristics and is hence incorrect. Further, their comparison of the 'new' analytical solution with numerical solutions of the Fokker-Planck equation fails to lend support to their result. We conclude that Dobranskis and Zharkova's solution of the universally accepted and well-established continuity equation is incorrect, and that their criticism of the correct solution is unfounded. We also demonstrate the formal equivalence of the approaches of Syrovatskii and Shmeleva and Brown, with particular reference to the evolution of the electron flux and number density (both differential in energy) in a collisional thick target. We strongly urge use of these long-established, correct solutions in future works.

  14. Impulsive phase of solar flares. 1: Characteristics of high energy electrons

    NASA Technical Reports Server (NTRS)

    Leach, J.; Petrosian, V.

    1981-01-01

    The variation along a magnetic field line of the energy and pitch angle distribution of high energy electrons injected into a cold hydrogen plasma containing either an open or closed magnetic field structure was investigated. The problem is formulated as a time independent Fokker-Planck Equation for the electron number distribution as a function of the electron energy, electron pitch angle, and the structure of the global magnetic field. Simple analytic solution valid in the small pitch angle regime and for slowly varying magnetic field is presented. For the more general situation a numerical code for solving the Fokker-Planck Equation was used and it was found that the analytic expression agrees well with the numerical results to values of the pitch angle much larger than expected. For most practical applications, one many confidently use the analytic expression instead of having to resort to lengthy numerical computations. These results are useful in the study of the nonthermal models of the impulsive phase of solar flares.

  15. Gamma-ray lines and neutrons from solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Murphy, R. J.; Kozlovsky, B.; Lingenfelter, R. E.

    1983-01-01

    The energy spectrum of accelerated protons and nuclei at the site of a limb flare was derived by a technique, using observations of the time dependent flux of high energy neutrons at the earth. This energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra was previously derived using observations of 4 to 7 MeV to 2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep to produce any significant amount of radiation from pi meson decay. It is suggested that the observed 10 MeV gamma rays from the flare are bremsstrahlung of relativistic electrons. Previously announced in STAR as N83-19695

  16. Gamma-ray lines and neutrons from solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Murphy, R. J.; Kozlovsky, B.; Lingenfelter, R. E.

    1983-01-01

    The energy spectrum of accelerated protons and nuclei at the site of a limb flare was derived by a technique, using observations of the time dependent flux of high energy neutrons at the Earth. This energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra was previously derived using observations of 4 to 7 MeV to 2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep to produce any significant amount of radiation from pi meson decay. It is suggested that the observed 10 MeV gamma rays from the flare are bremsstrahlung of relativistic electrons.

  17. Electron inertia modifications to X-point reconnection in solar flares

    NASA Astrophysics Data System (ADS)

    McClements, K. G.; Thyagaraja, A.; Ben Ayed, N.; Fletcher, L.

    The evolution of perturbations to a current-free magnetic X-point is studied as a paradigm for short timescale energy release in solar flares, taking into account electron inertia as well as resistivity. Electron inertia is found to have a negligible effect whenever the collisionless skin depth is less than the resistive scale length. Non-potential magnetic field energy in this resistive MHD limit initially reaches equipartition with flow energy, in accordance with ideal MHD, and is then dissipated extremely rapidly, on an Alfvénic timescale that is essentially independent of Lundquist number. In agreement with resistive MHD results obtained by previous authors [1], the magnetic field energy and kinetic energy are then observed to decay on a longer timescale and exhibit oscillatory behavior, reflecting the existence of discrete normal modes with finite real frequency. When the collisionless skin depth exceeds the resistive scale length, the field energy again decays on an Alfvénic timescale, while the kinetic energy (which is equally partitioned between ions and electrons in this case) decays on the electron collision timescale. In this regime filaments appear in the field and velocity profiles, suggesting the possibility of particle acceleration in oppositely-directed current channels and symmetrical precipitation out of the acceleration region. Both the rapid decay in field energy and the filamentation process arise from phase mixing associated with a continuous eigenmode spectrum that replaces the discrete resistive MHD spectrum [2]. Because of the Alfvénic timescale of the field decay, very modest perturbation amplitudes are sufficient for the corresponding inductive electric fields to produce hard X-ray emitting electrons on sub-second timescales. The model thus provides a framework for interpreting observations of short timescale energy release and particle acceleration in the impulsive phase of flares. This work was supported by the United Kingdom

  18. Comparison of optical and electron spectra in an infra-red free electron laser

    SciTech Connect

    MacLeod, A.M.; Gillespie, W.A.; Martin, P.F.

    1995-12-31

    Time-resolved electron and optical spectra recently acquired at the FELIX facility are presented, showing the evolution of the respective macropulses. A comparison is made between the optical power output during the macropulse and the measured power extracted from the electron beam using a simple model of the cavity losses. Data are available for a wide range of operating conditions: the wavelength range is from 9 {mu}m to 28 {mu}m and detuning are between 1/4{lambda} and 2{lambda}. The effect of rapid electron beam energy changes on the optical and electron spectra will also be discussed.

  19. Gas dynamics in the impulsive phase of solar flares. I. Thick-target heating by nonthermal electrons

    SciTech Connect

    Nagai, F.; Emslie, A.G.

    1984-04-15

    In this paper we investigate numerically the gas dynamical response of the solar atmosphere to a flare energy input in the form of precipitating nonthermal electrons. The origin of these electrons is not addressed: the spectral and temporal characteristics of the injected flux are instead inferred through a thick-target model of hard X-ray bremsstrahlung production. The electrons are assumed to spiral about preexisting magnetic field lines, enabling a one-dimensional spatial treatment to be preformed. All electron energy losses are assumed to be due to Coulomb collisions with ambient particles; i.e., we neglect return-current ohmic effects and collective plasma processes. One of the main aims of the study is to contrast our results with earlier work on conductive heating of the flare atmosphere; detailed consideration of this issue will bepresented in later papers.

  20. Toward the Accurate Simulation of Two-Dimensional Electronic Spectra

    NASA Astrophysics Data System (ADS)

    Giussani, Angelo; Nenov, Artur; Segarra-Martí, Javier; Jaiswal, Vishal K.; Rivalta, Ivan; Dumont, Elise; Mukamel, Shaul; Garavelli, Marco

    2015-06-01

    Two-dimensional pump-probe electronic spectroscopy is a powerful technique able to provide both high spectral and temporal resolution, allowing the analysis of ultrafast complex reactions occurring via complementary pathways by the identification of decay-specific fingerprints. [1-2] The understanding of the origin of the experimentally recorded signals in a two-dimensional electronic spectrum requires the characterization of the electronic states involved in the electronic transitions photoinduced by the pump/probe pulses in the experiment. Such a goal constitutes a considerable computational challenge, since up to 100 states need to be described, for which state-of-the-art methods as RASSCF and RASPT2 have to be wisely employed. [3] With the present contribution, the main features and potentialities of two-dimensional electronic spectroscopy are presented, together with the machinery in continuous development in our groups in order to compute two-dimensional electronic spectra. The results obtained using different level of theory and simulations are shown, bringing as examples the computed two-dimensional electronic spectra for some specific cases studied. [2-4] [1] Rivalta I, Nenov A, Cerullo G, Mukamel S, Garavelli M, Int. J. Quantum Chem., 2014, 114, 85 [2] Nenov A, Segarra-Martí J, Giussani A, Conti I, Rivalta I, Dumont E, Jaiswal V K, Altavilla S, Mukamel S, Garavelli M, Faraday Discuss. 2015, DOI: 10.1039/C4FD00175C [3] Nenov A, Giussani A, Segarra-Martí J, Jaiswal V K, Rivalta I, Cerullo G, Mukamel S, Garavelli M, J. Chem. Phys. submitted [4] Nenov A, Giussani A, Fingerhut B P, Rivalta I, Dumont E, Mukamel S, Garavelli M, Phys. Chem. Chem. Phys. Submitted [5] Krebs N, Pugliesi I, Hauer J, Riedle E, New J. Phys., 2013,15, 08501

  1. Radio and X-ray Diagnostics of Electron Beams in Solar Flares

    NASA Astrophysics Data System (ADS)

    Vilmer, Nicole; Kontar, Eduard; Hamish; Reid, A. S.; Maksimovic, Milan

    Solar flares are associated with efficient production of energetic particles at all energies. While energetic electrons and ions interacting with the solar atmosphere produce high energy X-rays and gamma-rays, the energetic electrons escaping to the corona and interplanetary medium produce coherent radio emissions (in particular type III bursts) and may be directly detected by experiments aboard spacecraft. We shall present the results of two statistical studies combining X-ray observations from RHESSI and of type III bursts observed in the decimeter/meter range and imaged by the Nançay Radioheliograph We shall show how the combination of X-ray and radio observations allows for some events to deduce the characteristics of the electron beam acceleration sites (height and size). We shall also present the results of a recent study on the percentage of decimetric/metric type III bursts observed with Nançay which have a counterpart at lower frequencies (namely in the range 14 to 1 MHz ) observed with Wind/Waves. This study is based on a list of events for which X-ray emission (by RHESSI) is also observed in connection with the type III bursts. We shall discuss the different reasons which could explain the extent or not of the metric type III burst to the hectometric range.

  2. Electronic and vibrational spectra of some rare earth trifluoromethanesulfonates crystals

    NASA Astrophysics Data System (ADS)

    Paul, P.; Ghosh, M.; Neogy, D.; Mallick, P. K.

    2011-01-01

    The Raman and infrared spectra of some rare earth (dysprosium and terbium) trifluoromethanesulfonates crystals have been analyzed. Different vibrational frequencies of trifluoromethanesulfonate ions (CF 3SO 3-) are identified and assigned to different vibrations of the SO 3 and CF 3 groups. Electronic transitions of R 3+ ions (R = Dy, Tb) in these salts have been assigned to transitions from the ground to different energy levels of the ground multiplet. The electronic energy levels of the rare earth ions are also determined theoretically with the help of single electron crystal field theory. They are found to yield results not only in good agreement with the observed spectral data but also in good conformity with those obtained previously from magnetic measurements.

  3. Electronic and vibrational spectra of some rare earth trifluoromethanesulfonates crystals.

    PubMed

    Paul, P; Ghosh, M; Neogy, D; Mallick, P K

    2011-01-01

    The Raman and infrared spectra of some rare earth (dysprosium and terbium) trifluoromethanesulfonates crystals have been analyzed. Different vibrational frequencies of trifluoromethanesulfonate ions (CF3SO3-) are identified and assigned to different vibrations of the SO3 and CF3 groups. Electronic transitions of R3+ ions (R=Dy, Tb) in these salts have been assigned to transitions from the ground to different energy levels of the ground multiplet. The electronic energy levels of the rare earth ions are also determined theoretically with the help of single electron crystal field theory. They are found to yield results not only in good agreement with the observed spectral data but also in good conformity with those obtained previously from magnetic measurements.

  4. EPR and electronic absorption spectra of copper bearing turquoise mineral

    NASA Astrophysics Data System (ADS)

    Sharma, K. B. N.; Moorthy, L. R.; Reddy, B. J.; Vedanand, S.

    1988-10-01

    Electron paramagnetic resonance and optical absorption spectra of turquoise have been studied both at room and low temperatures. It is concluded from the EPR spectra that the ground state of Cu 2+ ion in turquoise is 2A g(d x2- y2) and it is sited in an elongated rhombic octahedron (D 2π). The observed absorption bands at 14970 and 18354 cm -1 are assigned at 2A g→ 2B 1 g( dx2- y2→ xy) and 2A g→[ su2B 3g(d x 2-y 2→d yz) respectively assuming D 2π symmetry which are inconsistent with EPR studies. The three bands in the NIR region are attributed to combinations of fundamental modes of the H 2O molecule present in the sample.

  5. THE SPECIFIC ACCELERATION RATE IN LOOP-STRUCTURED SOLAR FLARES-IMPLICATIONS FOR ELECTRON ACCELERATION MODELS

    SciTech Connect

    Guo, Jingnan; Emslie, A. Gordon; Piana, Michele E-mail: piana@dima.unige.it

    2013-03-20

    We analyze electron flux maps based on RHESSI hard X-ray imaging spectroscopy data for a number of extended coronal-loop flare events. For each event, we determine the variation of the characteristic loop length L with electron energy E, and we fit this observed behavior with models that incorporate an extended acceleration region and an exterior 'propagation' region, and which may include collisional modification of the accelerated electron spectrum inside the acceleration region. The models are characterized by two parameters: the plasma density n in, and the longitudinal extent L{sub 0} of, the acceleration region. Determination of the best-fit values of these parameters permits inference of the volume that encompasses the acceleration region and of the total number of particles within it. It is then straightforward to compute values for the emission filling factor and for the specific acceleration rate (electrons s{sup -1} per ambient electron above a chosen reference energy). For the 24 events studied, the range of inferred filling factors is consistent with a value of unity. The inferred mean value of the specific acceleration rate above E{sub 0} = 20 keV is {approx}10{sup -2} s{sup -1}, with a 1{sigma} spread of about a half-order-of-magnitude above and below this value. We compare these values with the predictions of several models, including acceleration by large-scale, weak (sub-Dreicer) fields, by strong (super-Dreicer) electric fields in a reconnecting current sheet, and by stochastic acceleration processes.

  6. Electron Emission Sites on Carbon Nanotubes and the Energy Spectra

    NASA Astrophysics Data System (ADS)

    Oshima, Chuhei; Matsuda, Kohei; Kona, Takayuki; Mogami, Yuhta; Komaki, Masashi; Murata, Yoshitaka; Yamashita, Tetsutane; Saito, Yahachi; Hata, Koichi; Takakura, Akihiro

    2001-11-01

    Two kinds of electron emission sites on carbon nanotubes have been clarified; one is a nanoprotrusion exhibiting deformed honeycomb structures composed of carbon hexagons,pentagons and possibly heptagons. The other is either an edged species or adsorbates. The emission spectra show two characteristic features; a broad main peak as compared with theoretical curves based on Fowler-Nordheim theory, and an additional shoulder at about 0.5 eV from EF, of which the features are observed independent of the emission direction. The broad main peak may indicate that energy band bending occurs near the emission sites.

  7. Ionisation Equilibrium for the Non-Maxwellian Electron n-Distributions in Solar Flares: Updated Calculations

    NASA Astrophysics Data System (ADS)

    Dzifčáková, Elena; Dudík, Jaroslav

    2015-12-01

    We use the latest available atomic data to calculate the ionisation and recombination rates for the non-Maxwellian n-distributions, which were shown previously to provide a good fit to the enhanced intensities of dielectronic satellite lines during solar flares. The ionisation and recombination coefficients are subsequently used to derive the ionisation equilibrium. To do so, we consider odd values of n ranging from 1 to 19, i.e., from Maxwellian to strongly non-Maxwellian cases. These calculations involve all elements with proton number up to 30, i.e., H to Zn. The n-distributions modify both the ionisation and the recombination rates. The ionisation rates decrease more steeply at lower pseudo-temperatures, while the radiative recombination rate is reduced due to a lower number of low-energy electrons. The peaks of the dielectronic recombination rates become narrower. These changes are reflected in the ionisation equilibrium. Ion abundance peaks become narrower and can also be shifted, mostly towards higher temperatures. The He-like ions are an important exception, as they are formed in a larger temperature range than that for the Maxwellian distribution. The ions Si xiii - xiv used previously for the diagnostics of the n-distributions are affected only weakly, confirming the determination of n. The ionisation equilibria are available as the electronic supplementary material in a format compatible with the CHIANTI database.

  8. Bulk Energization of Electrons in Solar Flares by Alfvén Waves

    NASA Astrophysics Data System (ADS)

    Melrose, D. B.; Wheatland, M. S.

    2014-03-01

    Bulk energization of electrons to 10 - 20 keV in solar flares is attributed to dissipation of Alfvén waves that transport energy and potential downward to an acceleration region near the chromosphere. The acceleration involves the parallel electric field that develops in the limit of inertial Alfvén waves (IAWs). A two-potential model for IAWs is used to relate the parallel potential to the cross-field potential transported by the waves. We identify a maximum parallel potential in terms of a maximum current density that corresponds to the threshold for the onset of anomalous resistivity. This maximum is of order 10 kV when the threshold is that for the Buneman instability. We argue that this restricts the cross-field potential in an Alfvén wave to about 10 kV. Effective dissipation requires a large number of up- and down-current paths associated with multiple Alfvén waves. The electron acceleration occurs in localized, transient, anomalously conducting regions (LTACRs) and is associated with the parallel electric field determined by Ohm's law with an anomalous resistivity. We introduce an idealized model in which the LTACRs are (upward-)current sheets, a few skin depths in thickness, separated by much larger regions of weaker return current. We show that this model can account semi-quantitatively for bulk energization.

  9. Evolution of the Coronal Magnetic Structures traced by X-ray and Radio Emitting Electrons during the Flare of 3 November 2003

    NASA Astrophysics Data System (ADS)

    Vilmer, N. R.; Dauphin, C.; Krucker, S.

    2004-05-01

    During their transit on the solar disk AR 0488 and AR0486 produced 12 X-class flares. Two of these flares (28 October 2003 and 3 November 2003) were observed at both X-ray/gamma-ray wavelengths by the RHESSI experiment and by the Nancay Radioheliograph. We shall present here results for the 3 November 2003 event which was observed and imaged up to several 100 keV by RHESSI and which produced at radio wavelengths a type II burst with an unusually high starting frequency and a long duration continuum extending from the low corona to the interplanetary medium. The combined analysis of RHESSI sources at energies above a few hundred keV and of metric/decimetric sources observed by the NRH shows a spatial extension of both X-ray and radio sources traced by energetic electrons between the impulsive part of the event and the late energetic X-ray phase associated with the radio continuum. This spatial extension will be discussed in the context of the shock-associated type II burst and of the CME onset. Analysis of radio and X-ray spectra will be tentatively done to investigate the nature of the radio continuum.

  10. Electronic spectra of C4H3Cl+ isomers

    NASA Astrophysics Data System (ADS)

    Chakrabarty, S.; Rudnev, V.; Fulara, J.; Dietsche, R.; Nagy, A.; Garkusha, I.; Mazzotti, F. J.; Rice, C. A.; Maier, J. P.

    2012-12-01

    Two experimental methods were applied to identify the structure and electronic transitions of C4H3Cl+ isomers. The first is a direct absorption technique where mass-selected ions are embedded in 6 K neon matrices using a mass-selected ion beam and absorption spectra of different C4H3Cl+ isomers were thus observed. The second is a gas phase method on ions which have been collisional cooled with cryogenic helium inside of a 22-pole ion trap. The c-type (1)2 A‧ ← X 2 A″ electronic transition of a C4H3Cl+ isomer could then be measured by a one-colour, two-photon technique at 20 and 50 K in the gas phase. The two sets of data, complemented by calculated excitation energies, allowed the assignment of particular isomers. Rotational structure in the gas phase spectra was resolved for C4H3 35Cl+ and C4H3 37Cl+ isomers of cis-1-chlorobutenynylium. The analysis leads to the spectroscopic constants: T 00 = 19 184.680(5), ? , ? , ? , ? , ? and ? (all in cm-1).

  11. Electronic spectra of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation and radical

    DOE PAGES

    Peter R. Craig; Miller, John R.; Havlas, Zdenek; Trujillo, Marianela; Rempala, Pawel; Kirby, James P.; Noll, Bruce C.; Michl, Josef

    2016-05-02

    In this study, properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF–4 anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical,more » whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ~0.1 V upon going from 1 to 1a« less

  12. Very Local Interstellar Spectra for Galactic Electrons, Protons and Helium

    NASA Astrophysics Data System (ADS)

    Potgieter, Marius

    2014-10-01

    The local interstellar spectra (LIS) for cosmic rays at energies below ˜30 GeV/nuc are increasingly obscured from view at Earth by solar modulation, the lower the energy becomes. These charged particles encounter significant changes in the heliosphere, over an 11-year cycle, which include processes such as convection, diffusion, adiabatic energy losses and gradient, curvature and current sheet drifts. Particle drifts cause charge-sign-dependent modulation and a 22-year cycle, adding complexity to determining the respective very LIS from observations only at Earth. However, with measurements now made by the Voyager 1 spacecraft in the vicinity of the heliopause, it is possible to determine a very LIS for galactic electrons between ˜5 and ˜120 MeV. At these low energies, also galactic protons observed in the outer heliosphere had been completely obscured by the so-called anomalous component which is accelerated inside the heliosheath. Since August 2012, these anomalous cosmic rays are substantially depleted at Voyager 1 so that for cosmic ray ions, it is now possible to obtain a lower limit to their very LIS. Combining numerical modelling of solar modulation with the accurate measurements by the PAMELA mission and with Voyager observations, the lower limit of the very LIS for electrons, protons and helium and other ions can be determined from ˜5 MeV and above. These spectra are called heliopause spectra which is considered to be the lowest possible very LIS. Also, from an astrophysics point of view, the determination of what can be called a very LIS, not just an averaged galactic spectrum, is encouraging. The mentioned aspects are discussed, focusing on a comparison of recent heliospheric observations and corresponding solar modulation modelling.

  13. Proportionality law between the flare SXR intensity and the number of released solar near-relativistic electrons

    NASA Astrophysics Data System (ADS)

    Agueda, N.; Klein, K.-L.; SEPServer Consortium

    2015-05-01

    We study a set of solar near-relativistic (NR; >50 keV) electron events observed by the Wind and the ACE spacecraft near the Earth orbit. Interplanetary transport simulations are used to take into account the propagation effects from the source to the spacecraft. Inversion methods developed within the EU/FP7 SEPServer project are then used to extract, from directional intensities observed near the Earth orbit, the electron release history in the low solar corona. We compare the release time histories with context electromagnetic observations of solar eruptions, in soft X-rays, radio, hard X-rays and white light. The distribution of release profiles is bimodal. NR electrons are released during either short (<30 min) or long (>2 h) periods. Short release episodes appear to originate in solar flares, in coincidence with the timing of type III radio bursts reaching the local plasma line measured at 1 AU. The origin of long release episodes seems to be more intricate. They are associated with signatures of long acceleration processes in the low corona (long decay of the soft X-ray emission, type IV radio bursts, and time-extended microwave emission). We present a proportionality empirical law between the intensity of the SXR flare and the number of electrons released during flare-accelerated events.

  14. Measurement of the Multi-T{bold e}V Gamma-Ray Flare Spectra of Markarian 421 and Markarian 501

    SciTech Connect

    Krennrich, F.; Biller, S.D.; Bond, I.H.; Boyle, P.J.; Bradbury, S.M.; Breslin, A.C.; Buckley, J.H.; Burdett, A.M.; Gordo, J.B.; Carter-Lewis, D.A.; Catanese, M.; Cawley, M.F.; Fegan, D.J.; Finley, J.P.; Gaidos, J.A.; Hall, T.; Hillas, A.M.; Lamb, R.C.; Lessard, R.W.; Masterson, C.; McEnery, J.E.; Mohanty, G.; Moriarty, P. and others.

    1999-01-01

    The energy spectrum of Markarian 421 in flaring states has been measured from 0.3 to 10 TeV using both small and large zenith angle observations with the Whipple Observatory 10 m imaging telescope. The large zenith angle technique is useful for extending spectra to high energies, and the extraction of spectra with this technique is discussed. The resulting spectrum of Markarian 421 is fitted reasonably well by a simple power law: J(E)=E{sup {minus}2.54{plus_minus}0.03{plus_minus}0.10} photons m{sup {minus}1} s{sup {minus}1} TeV{sup {minus}1}, where the first set of errors is statistical and the second set is systematic. This is in contrast to our recently reported spectrum of Markarian 501, which over a similar energy range has substantial curvature. The differences in TeV energy spectra of gamma-ray blazars reflect both the physics of the gamma-ray production mechanism and possibly differential absorption effects at the source or in the intergalactic medium. Since Markarian 421 and Markarian 501 have almost the same redshift (0.031 and 0.033, respectively), the difference in their energy spectra must be intrinsic to the sources and not due to intergalactic absorption, assuming the intergalactic infrared background is uniform. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}

  15. Turbulent Pitch-angle Scattering and Diffusive Transport of Hard X-Ray-producing Electrons in Flaring Coronal Loops

    NASA Astrophysics Data System (ADS)

    Kontar, Eduard P.; Bian, Nicolas H.; Emslie, A. Gordon; Vilmer, Nicole

    2014-01-01

    Recent observations from RHESSI have revealed that the number of non-thermal electrons in the coronal part of a flaring loop can exceed the number of electrons required to explain the hard X-ray-emitting footpoints of the same flaring loop. Such sources cannot, therefore, be interpreted on the basis of the standard collisional transport model, in which electrons stream along the loop while losing their energy through collisions with the ambient plasma; additional physical processes, to either trap or scatter the energetic electrons, are required. Motivated by this and other observations that suggest that high-energy electrons are confined to the coronal region of the source, we consider turbulent pitch-angle scattering of fast electrons off low-frequency magnetic fluctuations as a confinement mechanism, modeled as a spatial diffusion parallel to the mean magnetic field. In general, turbulent scattering leads to a reduction of the collisional stopping distance of non-thermal electrons along the loop, and hence to an enhancement of the coronal hard X-ray source relative to the footpoints. The variation of source size L with electron energy E becomes weaker than the quadratic behavior pertinent to collisional transport, with the slope of L(E) depending directly on the mean free path λ associated with the non-collisional scattering mechanism. Comparing the predictions of the model with observations, we find that λ ~ (108-109) cm for ~30 keV, less than the length of a typical flaring loop and smaller than, or comparable to, the size of the electron acceleration region.

  16. Turbulent pitch-angle scattering and diffusive transport of hard X-ray-producing electrons in flaring coronal loops

    SciTech Connect

    Kontar, Eduard P.; Bian, Nicolas H.; Emslie, A. Gordon; Vilmer, Nicole E-mail: emslieg@wku.edu

    2014-01-10

    Recent observations from RHESSI have revealed that the number of non-thermal electrons in the coronal part of a flaring loop can exceed the number of electrons required to explain the hard X-ray-emitting footpoints of the same flaring loop. Such sources cannot, therefore, be interpreted on the basis of the standard collisional transport model, in which electrons stream along the loop while losing their energy through collisions with the ambient plasma; additional physical processes, to either trap or scatter the energetic electrons, are required. Motivated by this and other observations that suggest that high-energy electrons are confined to the coronal region of the source, we consider turbulent pitch-angle scattering of fast electrons off low-frequency magnetic fluctuations as a confinement mechanism, modeled as a spatial diffusion parallel to the mean magnetic field. In general, turbulent scattering leads to a reduction of the collisional stopping distance of non-thermal electrons along the loop, and hence to an enhancement of the coronal hard X-ray source relative to the footpoints. The variation of source size L with electron energy E becomes weaker than the quadratic behavior pertinent to collisional transport, with the slope of L(E) depending directly on the mean free path λ associated with the non-collisional scattering mechanism. Comparing the predictions of the model with observations, we find that λ ∼ (10{sup 8}-10{sup 9}) cm for ∼30 keV, less than the length of a typical flaring loop and smaller than, or comparable to, the size of the electron acceleration region.

  17. Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

    National Institute of Standards and Technology Data Gateway

    SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

  18. Impulsive H-alpha diagnostics of electron-beam-heated solar flare model chromospheres

    NASA Technical Reports Server (NTRS)

    Canfield, Richard C.; Gayley, Kenneth G.

    1987-01-01

    Time-dependent H-alpha profiles were computed for the dynamic model atmospheres of Fisher, Canfield, and McClymont (1985) simulating the effects of an intense impulsively initiated power-law beam of electrons incident on the chromosphere. The temporal response of H-alpha arises from three separate physical mechanisms, whose relative importance varies over the line profile. The fastest variations (typically less than 0.1 s for the explosive heating discussed here) arise from energy imbalance; these are apparent on chromospheric heating and cooling time scales and have their greatest amplitude at line center. Slower variations arise from ionization imbalance and are most apparent in the blue wing. The slowest variations arise from hydrodynamic effects and are related to the formation of a chromospheric condensation; these are most apparent in the red wing. These results provide a basis for the design and analysis of observations of H-alpha, in coordination with hard X-rays or microwaves, to test mechanisms of energy transport in solar flares.

  19. A FAST FLARE AND DIRECT REDSHIFT CONSTRAINT IN FAR-ULTRAVIOLET SPECTRA OF THE BLAZAR S5 0716+714

    SciTech Connect

    Danforth, Charles W.; Nalewajko, Krzysztof; France, Kevin; Keeney, Brian A.

    2013-02-10

    The BL Lacertae object S5 0716+714 is one of the most studied blazars on the sky due to its active variability and brightness in many bands, including very-high-energy gamma rays. We present here two serendipitous results from recent far-ultraviolet spectroscopic observations by the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (HST). First, during the course of our 7.3 hr HST observations, the blazar increased in flux rapidly by {approx}40% (-0.45 mag hr{sup -1}) followed by a slower decline (+0.36 mag hr{sup -1}) to previous FUV flux levels. We model this flare using asymmetric flare templates and constrain the physical size and energetics of the emitting region. Furthermore, the spectral index of the object softens considerably during the course of the flare from {alpha}{sub {nu}} Almost-Equal-To -1.0 to {alpha}{sub {nu}} Almost-Equal-To -1.4. Second, we constrain the source redshift directly using the {approx}30 intervening absorption systems. A system at z = 0.2315 is detected in Ly{alpha}, Ly{beta}, O VI, and N V and defines the lower bound on the source redshift. No absorbers are seen in the remaining spectral coverage (0.2315 < z {sub Ly{alpha}} {approx}< 0.47) and we set a statistical upper bound of z < 0.322 (95% confidence) on the blazar. This is the first direct redshift limit for this object and is consistent with literature estimates of z = 0.31 {+-} 0.08 based on the detection of a host galaxy.

  20. On the sensitivity of the goes flare classification to properties of the electron beam in the thick-target model

    SciTech Connect

    Reep, J. W.; Bradshaw, S. J.; McAteer, R. T. J. E-mail: stephen.bradshaw@rice.edu

    2013-11-20

    The collisional thick-target model, wherein a large number of electrons are accelerated down a flaring loop, can be used to explain many observed properties of solar flares. In this study, we focus on the sensitivity of (GOES) flare classification to the properties of the thick-target model. Using a hydrodynamic model with RHESSI-derived electron beam parameters, we explore the effects of the beam energy flux (or total non-thermal energy), the cut-off energy, and the spectral index of the electron distribution on the soft X-rays observed by GOES. We conclude that (1) the GOES class is proportional to the non-thermal energy E {sup α} for α ≈ 1.7 in the low-energy passband (1-8 Å) and ≈1.6 in the high-energy passband (0.5-4 Å); (2) the GOES class is only weakly dependent on the spectral index in both passbands; (3) increases in the cut-off will increase the flux in the 0.5-4 Å passband but decrease the flux in the 1-8 Å passband, while decreases in the cut-off will cause a decrease in the 0.5-4 Å passband and a slight increase in the 1-8 Å passband.

  1. Fine structure of inelastic electron scattering cross-section spectra for MN

    NASA Astrophysics Data System (ADS)

    Parshin, A. S.; Igumenov, A. Yu; Mikhlin, Yu L.; Pchelyakov, O. P.; Zhigalov, V. S.

    2016-04-01

    The comparative analysis of the reflection electron energy loss spectra and the inelastic electron scattering cross-section spectra for Mn was carried out. It is shown that inelastic electron scattering cross-section spectra have certain advantages in the study of the interaction of electrons with the substance as compared to the electron energy loss spectra. The inelastic electron scattering cross section spectra fine structure was analysed by fitting the experimental spectra using the 3 parameters Lorentzian-type formula of Tougaard. This method was used for the quantitative analysis of the contributions of various loss processes in the inelastic electron scattering cross section spectra, determination of the loss peaks energies and origin.

  2. Reconstruction of images from radiofrequency electron paramagnetic resonance spectra.

    PubMed

    Smith, C M; Stevens, A D

    1994-12-01

    This paper discusses methods for obtaining image reconstructions from electron paramagnetic resonance (EPR) spectra which constitute object projections. An automatic baselining technique is described which treats each spectrum consistently; rotating the non-horizontal baselines which are caused by stray magnetic effects onto the horizontal axis. The convolved backprojection method is described for both two- and three-dimensional reconstruction and the effect of cut-off frequency on the reconstruction is illustrated. A slower, indirect, iterative method, which does a non-linear fit to the projection data, is shown to give a far smoother reconstructed image when the method of maximum entropy is used to determine the value of the final residual sum of squares. Although this requires more computing time than the convolved backprojection method, it is more flexible and overcomes the problem of numerical instability encountered in deconvolution. Images from phantom samples in vitro are discussed. The spectral data for these have been accumulated quickly and have a low signal-to-noise ratio. The results show that as few as 16 spectra can still be processed to give an image. Artifacts in the image due to a small number of projections using the convolved backprojection reconstruction method can be removed by applying a threshold, i.e. only plotting contours higher than a given value. These artifacts are not present in an image which has been reconstructed by the maximum entropy technique. At present these techniques are being applied directly to in vivo studies.

  3. Electron energy spectra in helium observed in a microplasma collisional electron spectroscopy detector

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, A. A.; Mustafaev, A. S.; Tsyganov, A. B.; Chirtsov, A. S.; Yakovleva, V. I.

    2012-10-01

    The energy spectra of fast electrons resulting from pair collisions between metastable atoms and from collisions of the second kind with electrons are observed in the afterglow of a helium-filled microplasma collisional electron spectroscopy (CES) detector at a pressure of 5-40 Torr. It is demonstrated that impurities present in the main inert gas can be detected and their composition can be determined using a planar double-electrode detector in which the cathode simultaneously serves as an analyzer of electrons in the afterglow.

  4. Electron-impact mass spectra of carbomethoxyl derivatives of cyclopropylthiophenes

    SciTech Connect

    Kadentsev, V.I.; Kolotyrkina, N.G.; Chizhov, O.S.; Shostakovskii, V.M.; Vasil'vitskii, A.A.; Zlatkina, V.L.

    1987-01-10

    In the mass spectra of carbomethoxyl derivatives of cyclopropylthiophene, intense ion peaks are observed, corresponding to successive elimination of MeO and COOMe radicals and the neutral fragments MeOH, HCOOMe, and CO from M/sup +./, so that the number of carbomethoxyl substituents in CPR can be determined. Mono- and gem-dicarbomethoxyl derivatives of cyclopropylthiophenes are characterized by rearrangements of M/sup +./ with migration of the MeO groups to the carbon atom adjacent to the thiophene ring. The presence of a methyl substituent at this carbon atom hinders this rearrangement. For the monocarbomethoxyl derivatives of cyclopropylthiophenes under electron impact, a splitting off of the methyl substituent of the ester groups is observed.

  5. Millimeter emission of solar flares

    NASA Astrophysics Data System (ADS)

    Nagnibeda, V. G.; Smirnova, V. V.; Ryzhov, V. S.; Zhiltsov, A. V.

    2013-06-01

    We analyzed two unique radio observations of millimeter solar flares at 93 and 140 GHz with the THz component in these spectra. Data were obtained from ground-based radio-telescope RT-7.5 operated by Bauman Moscow State Technical University (BMSTU) with the spacial resolution of 2.5 and 1.5 arc-minutes. We analyzed temporal structure of observed radio-bursts and their dynamics in comparison with soft and hard X-ray light-curves obtained from GOES and RHESSI space-based observations. It was found the 140 GHz emission enhancement at the spectra that is new independent confirmation of the THz component existance. Also, we analyzed data of microwave solar flares with the emission enhanced at 35 GHz obtained from Nobeyama radioheliograph (NoRH) and radiopolarimeter (NoRP). It was found that the maximum of the flux density spectra was shifted toward high frequencies that didn't agree with the model spectrum obtained from microwave observations. We assumed, that such kind of spectra are associated with the gyro-synchrotron radiation of the significant number of high-energetic electrons emission with energies of about 500 keV. The emission mechanism at millimeter waves is the gyro-synchrotron radiation. However, if the energetic electrons are not enough the thermal emission mechanism could be dominant factor at millimeter radiation that could also explain the spectral maximum shift to high frequencies.

  6. Particle kinematics in solar flares: observations and theory

    NASA Astrophysics Data System (ADS)

    Battaglia, Marina

    2008-12-01

    This thesis is devoted to the study of particle acceleration and propagation processes in solar flares. Solar flares are amongst the most powerful and energetic activity phenomena our Sun exhibits. They release energy of the order of 10(32) erg in seconds to minutes. In the process, electrons and protons are accelerated to relativistic energies, making flares very efficient particle accelerators. The most compelling observational signatures of flares can be found in X-rays and extreme ultra-violet wavelengths. Due to atmospheric absorption, those wavelengths can only be studied from space. Since the beginning of the space age, countless flares have been observed by satellites. The present work is largely based on observations by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), an X-ray satellite which has been observing the Sun since February 2002. It is a NASA mission with substantial Swiss hardware and software contribution. Using RHESSI observations of flares of different intensity, a deeper understanding of the particle transport and energy transport processes in flare loops, as well as the acceleration site and acceleration mechanism is sought. The time evolution of images and spectra is studied along with the quantitative relations between X-ray sources observed in the corona (coronal sources) and from the chromosphere (footpoints). The spectral relations found between coronal sources and footpoints are compared to the so-called ``intermediate thin-thick target model'', which was based on observations by the satellite Yohkoh. We show that the spectral relations between coronal sources and footpoints observed with RHESSI cannot be explained by the intermediate thin-thick target model. In a next step, return currents in the flare loop were considered. With this extension to the existing model, the spectra of the coronal source and the footpoints, as well as the relations between them can be explained, indicating the importance of return currents in

  7. On the analysis of photo-electron spectra

    SciTech Connect

    Gao, C.-Z.; Dinh, P.M.; Reinhard, P.-G.; Suraud, E.

    2015-09-15

    We analyze Photo-Electron Spectra (PES) for a variety of excitation mechanisms from a simple mono-frequency laser pulse to involved combination of pulses as used, e.g., in attosecond experiments. In the case of simple pulses, the peaks in PES reflect the occupied single-particle levels in combination with the given laser frequency. This usual, simple rule may badly fail in the case of excitation pulses with mixed frequencies and if resonant modes of the system are significantly excited. We thus develop an extension of the usual rule to cover all possible excitation scenarios, including mixed frequencies in the attosecond regime. We find that the spectral distributions of dipole, monopole and quadrupole power for the given excitation taken together and properly shifted by the single-particle energies provide a pertinent picture of the PES in all situations. This leads to the derivation of a generalized relation allowing to understand photo-electron yields even in complex experimental setups.

  8. Protein Influence on Electronic Spectra Modeled by Multipoles and Polarizabilities.

    PubMed

    Söderhjelm, Pär; Husberg, Charlotte; Strambi, Angela; Olivucci, Massimo; Ryde, Ulf

    2009-03-10

    We have developed automatic methods to calculate multipoles and anisotropic polarizabilities for all atoms and bond centers in a protein and to include such a model in the calculation of electronic properties at any level of quantum mechanical theory. This approach is applied for the calculation of the electronic spectra of retinal in rhodopsin at the CASPT2//CASSCF level (second-order multiconfigurational perturbation theory) for the wild-type protein, as well as two mutants and isorhodopsin in QM/MM structures based on two crystal structures. We also perform a detailed investigation of the importance and distance dependence of the multipoles and the polarizabilities for both the absolute and the relative absorption energies. It is shown that the model of the surrounding protein strongly influences the spectrum and that different models give widely different results. For example, the Amber 1994 and 2003 force fields give excitation energies that differ by up to 16 kJ/mol. For accurate excitation energies, multipoles up to quadrupoles and anisotropic polarizabilities are needed. However, interactions with residues more than 10 Å from the chromophore can be treated with a standard polarizable force field without any dipoles or quadrupoles.

  9. Two-dimensional electronic-vibrational spectra: modeling correlated electronic and nuclear motion.

    PubMed

    Terenziani, F; Painelli, A

    2015-05-21

    We calculate 2D electronic-vibrational (2D-EV) spectra of solvated organic dyes modeled in terms of a reduced set of electronic diabatic states (the essential states) non-adiabatically coupled to molecular vibrations. An effective overdamped coordinate, whose dynamics is described by the Smoluchowski diffusion equation, accounts for polar solvation. Results are discussed for two dyes with distinctively different spectroscopic behavior: 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) and 8-(N,N-dibutylamino)-2-azachrysene (AAC). Linear absorption and fluorescence spectra of DCM are well reproduced based on a minimal two-state model. The same model leads to 2D-EV spectra in good agreement with the recent experimental data reported by Oliver and coworkers for DCM in DMSO. In contrast, linear spectra of AAC show a subtle interplay between a locally-excited (LE) and a charge-transfer (CT) excitation, calling for a three-state model. Calculated 2D-EV spectra for AAC show a qualitatively different behavior, demonstrating that the experimental data for DCM do not support a LE/CT interplay. This resolves the long-lasting discussion about the nature of low-lying excitations of DCM in favor of the simplest picture. PMID:25912698

  10. CONSTRAINING SOLAR FLARE DIFFERENTIAL EMISSION MEASURES WITH EVE AND RHESSI

    SciTech Connect

    Caspi, Amir; McTiernan, James M.; Warren, Harry P.

    2014-06-20

    Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from ≲2 to ≳50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly observed solar flares. EVE is sensitive to ∼2-25 MK thermal plasma emission, and RHESSI to ≳10 MK; together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from the EVE data also constrain the low energy cutoff of the non-thermal electrons, a crucial parameter for flare energetics. The DEM analysis can also be used to predict the soft X-ray flux in the poorly observed ∼0.4-5 nm range, with important applications for geospace science.

  11. A thermal/nonthermal approach to solar flares

    NASA Technical Reports Server (NTRS)

    Benka, Stephen G.

    1991-01-01

    An approach for modeling solar flare high-energy emissions is developed in which both thermal and nonthermal particles coexist and contribute to the radiation. The thermal/nonthermal distribution function is interpreted physically by postulating the existence of DC sheets in the flare region. The currents then provide both primary plasma heating through Joule dissipation, and runaway electron acceleration. The physics of runaway acceleration is discussed. Several methods are presented for obtaining approximations to the thermal/nonthermal distribution function, both within the current sheets and outside of them. Theoretical hard x ray spectra are calculated, allowing for thermal bremsstrahlung from the heated plasma electrons impinging on the chromosphere. A simple model for hard x ray images of two-ribbon flares is presented. Theoretical microwave gyrosynchrotron spectra are calculated and analyzed, uncovering important new effects caused by the interplay of thermal and nonthermal particles. The theoretical spectra are compared with observed high resolution spectra of solar flares, and excellent agreement is found, in both hard x rays and microwaves. The future detailed application of this approach to solar flares is discussed, as are possible refinements to this theory.

  12. Electron acceleration in a flare plasma via coronal circuits. (German Title: Elektronenbeschleunigung im Flareplasma modelliert mit koronalen Schaltkreisen)

    NASA Astrophysics Data System (ADS)

    Önel, Hakan

    2008-08-01

    The Sun is a star, which due to its proximity has a tremendous influence on Earth. Since its very first days mankind tried to "understand the Sun", and especially in the 20th century science has uncovered many of the Sun's secrets by using high resolution observations and describing the Sun by means of models. As an active star the Sun's activity, as expressed in its magnetic cycle, is closely related to the sunspot numbers. Flares play a special role, because they release large energies on very short time scales. They are correlated with enhanced electromagnetic emissions all over the spectrum. Furthermore, flares are sources of energetic particles. Hard X-ray observations (e.g., by NASA's RHESSI spacecraft) reveal that a large fraction of the energy released during a flare is transferred into the kinetic energy of electrons. However the mechanism that accelerates a large number of electrons to high energies (beyond 20 keV) within fractions of a second is not understood yet. The thesis at hand presents a model for the generation of energetic electrons during flares that explains the electron acceleration based on real parameters obtained by real ground and space based observations. According to this model photospheric plasma flows build up electric potentials in the active regions in the photosphere. Usually these electric potentials are associated with electric currents closed within the photosphere. However as a result of magnetic reconnection, a magnetic connection between the regions of different magnetic polarity on the photosphere can establish through the corona. Due to the significantly higher electric conductivity in the corona, the photospheric electric power supply can be closed via the corona. Subsequently a high electric current is formed, which leads to the generation of hard X-ray radiation in the dense chromosphere. The previously described idea is modelled and investigated by means of electric circuits. For this the microscopic plasma parameters

  13. Electronic states and spectra of BiTe

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Laufs, S.; Fink, E. H.

    2010-09-01

    NIR/VIS emission spectra of the bismuth telluride radical, BiTe, were measured in the 3600-20 000 cm -1 region with a Fourier-transform spectrometer. BiTe was produced by reaction of bismuth and tellurium vapors and excited by energy transfer from metastable oxygen O 2( a1Δ g) in a fast-flow system. The spectrum of BiTe was found to be markedly different from those of the previously studied BiO, BiS and BiSe radicals. The A24Π 1/2 → X12Π 1/2 transition which forms the most prominent and extended band system in these molecules was not observed for BiTe, and the X22Π 3/2 → X12Π 1/2 fine structure transition shows up with a different structure and at much lower wavenumbers than in the spectra of the lighter bismuth chalcogenides. The only common feature is the C14Σ -1/2 → X12Π 1/2 system which is found in the range 16 500-19 000 cm -1 similar to the three other molecules. Besides the X2 → X1 and C1 → X1 systems, seven other transitions show up by short Δ ν = 0 sequences only. With help of the data derived from the analyses of the X2 → X1 and C1 → X1 systems and theoretical predictions of electronic and vibrational energies and transition probabilities of the strongest transitions of BiTe by Lingott et al. [7] the spectra were assigned to the transitions C14Σ -1/2 → X22Π 3/2, C14Σ -1/2 → A24Π 1/2, A44Π 1/2 → A24Π 1/2, A44Π 1/2 → X22Π 3/2, B12Π 1/2 → A24Π 1/2, B12Π 1/2 → A14Π 3/2, and B22Π 3/2 → X22Π 3/2.

  14. Transport inhibition of coronal energetic electrons by multiple double layers: application to solar flares and expansion of the corona

    NASA Astrophysics Data System (ADS)

    Li, T.; Drake, J. F.; Swisdak, M. M.

    2012-12-01

    The transport of electrons from a coronal acceleration site to the chromosphere and out to the solar wind is a key issue in understanding the dynamics of solar flares and the expansion of the hot corona. The physics of how these energetic electrons transport from the corona remains poorly understood. Using a particle-in-cell code, we recently simulated an initial system of very hot electrons in contact with cold electrons along the local magnetic field, and found that transport inhibition begins when the hot electrons start to propagate from the source region [1]. This is due to the formation of a large-amplitude, localized electrostatic electric field, in the form of a double layer (DL), which is driven by an ion/return-current-electron streaming instability. The DL provides a potential barrier that suppresses the hot electron transport into the cold electron region, and significantly reduces electron heat flux. The result can help explain the observed prolonged duration of looptop hard X-ray emission. As a continued effort, simulations of increasing sizes are performed. Larger simulations allow the system to evolve for longer time and give rise to more complex dynamics. Instead of a single DL observed in smaller simulations [1], multiple DLs are generated. A succession of many weak DLs, occurring from the corona to the Earth, was considered to make up the interplanetary potential difference in exospheric solar wind models [2]. The observation of multiple DLs in the larger simulations favors this scenario. The dynamics of multiple DLs and the associated transport regulation are being investigated, and the application to solar flares and coronal expansion will be discussed. [1] T.C. Li, J.F. Drake and M. Swisdak, ApJ, in press, 2012 [2] C. Lacombe, et. al., Ann. Geophysicae, 20, 609, 2002

  15. Non-thermal electron acceleration in low Mach number collisionless shocks. I. Particle energy spectra and acceleration mechanism

    SciTech Connect

    Guo, Xinyi; Narayan, Ramesh; Sironi, Lorenzo

    2014-10-20

    Electron acceleration to non-thermal energies in low Mach number (M{sub s} ≲ 5) shocks is revealed by radio and X-ray observations of galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with M{sub s} = 3 and a quasi-perpendicular pre-shock magnetic field. We find that about 15% of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p ≅ 2.4. Initially, thermal electrons are energized at the shock front via shock drift acceleration (SDA). The accelerated electrons are then reflected back upstream where their interaction with the incoming flow generates magnetic waves. In turn, the waves scatter the electrons propagating upstream back toward the shock for further energization via SDA. In summary, the self-generated waves allow for repeated cycles of SDA, similarly to a sustained Fermi-like process. This mechanism offers a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.

  16. Near-infrared electronic spectra of BiSe

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Breidohr, R.; Meinecke, F.; Fink, E. H.

    2009-11-01

    NIR/VIS emission spectra of BiSe were measured in the 5800-20,000 cm -1 region with a Fourier-transform spectrometer. BiSe was produced by reaction of bismuth and selenium vapors and excited by energy transfer from metastable oxygen O 2( a1Δ g) in a fast-flow system. The spectrum of BiSe was found to be closely related to those of the previously studied BiO and BiS radicals. Four band systems were unambiguously assigned to the transitions X22Π 3/2 → X12Π 1/2, A24Π 1/2 → X12Π 1/2, C14Σ -1/2 → X12Π 1/2 and C14Σ -1/2 → A24Π 1/2 and the electronic energies and vibrational constants of the states X12Π 1/2, X22Π 3/2, A24Π 1/2 and C14Σ -1/2 were derived.

  17. VLF Remote -Sensing of the Lower Ionosphere with AWESOME Receivers: Solar Flares, Lightning-induced Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares

    NASA Astrophysics Data System (ADS)

    Inan, U. S.; Cohen, M.; Scherrer, P.; Scherrer, D.

    2006-11-01

    Stanford University Very Low Frequency (VLF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas of a couple of meters in size, the sensitivity of these instruments allows the measurement of magnetic fields as low as several tens of femtoTesla per root Hz, in the frequency range of ~300 Hz to 50 kHz. This sensitivity well exceeds that required to detect any event above the ambient atmospheric noise floor, determined by the totality of lightning activity on this planet. In recent years, as cost of production, timing accuracy (due to low cost GPS cards), and data handling flexibility of the systems has improved, it has become possible to distribute many of these instruments in the form of arrays, to perform interferometric and holographic imaging of the lower ionosphere. These goals can be achieved using the newest version of the Stanford VLF receiver, known as AWESOME: Atmospheric Weather Educational System for Observation and Modeling of Electromagnetics. In the context of the IHY/UNBSS program for 2007, the AWESOME receivers can be used extensively as part of the United Nations initiative to place scientific instruments in developing countries. Drawing on the Stanford experiences from setting up arrays of VLF receivers, including an interferometer in Alaska, the Holographic Array for Ionospheric and Lightning research (HAIL) consisting of instruments at 13 different high schools in mid-western United States, a broader set of ELF/VLF receivers in Alaska, and various receivers abroad, including in France, Japan, Greece, Turkey, and India, a global network of ELF/VLF receivers offer possibilities for a wide range of scientific topics

  18. AD Leonis: Flares observed by XMM-Newton and Chandra

    NASA Astrophysics Data System (ADS)

    van den Besselaar, E. J. M.; Raassen, A. J. J.; Mewe, R.; van der Meer, R. L. J.; Güdel, M.; Audard, M.

    2003-12-01

    The M-dwarf AD Leonis has been observed with the Reflection Grating Spectrometers and the European Photon Imaging Camera aboard XMM-Newton and also with the Low Energy Transmission Grating Spectrometer aboard the Chandra X-ray Observatory. In the observation taken with XMM-Newton five large flares produced by AD Leo were identified and only one in the observation taken with Chandra. A quiescent level to the lightcurves is difficult to define, since several smaller flares mutually overlap each other. However, we defined a quasi-steady state outside of obvious flares or flare decays. The spectra from the flare state and the quasi-steady state are analysed separately. From these spectra the temperature structure was derived with a multi-temperature model and with a differential emission measure model. The multi-temperature model was also used to determine the relative abundances of \\element{C}, \\element{N}, \\element{O}, \\element{Ne}, \\element{Mg}, \\element{Si}, \\element{S}, and \\element{Fe}. \\element{He}-like ions, such as O Vii and Ne Ix, produce line triplets which are used to determine or constrain the electron temperature and electron density of the corresponding ion. During the flare state a higher emission measure at the hottest temperature is found for both XMM-Newton and Chandra observations. The derived abundances suggest the presence of an inverse First Ionization Potential effect in the corona of AD Leo.

  19. Implications of RHESSI Observations for Solar Flare Models and Energetics

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2006-01-01

    Observations of solar flares in X-rays and gamma-rays provide the most direct information about the hottest plasma and energetic electrons and ions accelerated in flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed over 18000 solar flares in X-rays and gamma-rays since its launch in February of 2002. RHESSI observes the full Sun at photon energies from as low as 3 keV to as high as 17 MeV with a spectral resolution on the order of 1 keV. It also provides images in arbitrary bands within this energy range with spatial resolution as good as 3 seconds of arc. Full images are typically produced every 4 seconds, although higher time resolution is possible. This unprecedented combination of spatial, spectral, and temporal resolution, spectral range and flexibility has led to fundamental advances in our understanding of flares. I will show RHESSI and coordinated observations that confirm coronal magnetic reconnection models for eruptive flares and coronal mass ejections, but also present new puzzles for these models. I will demonstrate how the analysis of RHESSI spectra has led to a better determination of the energy flux and total energy in accelerated electrons, and of the energy in the hot, thermal flare plasma. I will discuss how these energies compare with each other and with the energy contained in other flare-related phenomena such as interplanetary particles and coronal mass ejections.

  20. Flare Hybrids

    NASA Astrophysics Data System (ADS)

    Tomczak, M.; Dubieniecki, P.

    2015-12-01

    On the basis of the Solar Maximum Mission observations, Švestka ( Solar Phys. 121, 399, 1989) introduced a new class of flares, the so-called flare hybrids. When they start, they look like typical compact flares (phase 1), but later on, they look like flares with arcades of magnetic loops (phase 2). We summarize the characteristic features of flare hybrids in soft and hard X-rays as well as in the extreme ultraviolet; these features allow us to distinguish flare hybrids from other flares. In this article, additional energy release or long plasma cooling timescales are suggested as possible causes of phase 2. We estimate the frequency of flare hybrids, and study the magnetic configurations favorable for flare hybrid occurrence. Flare hybrids appear to be quite frequent, and the difference between the lengths of magnetic loops in the two interacting loop systems seem to be a crucial parameter for determining their characteristics.

  1. Energy of microwave-emitting electrons and hard x-ray/microwave source model in solar flares

    NASA Technical Reports Server (NTRS)

    Nitta, N.; Kosugi, T.

    1986-01-01

    Based on the rate of increse of the microwave flux relative to the hard X-ray flux at various energies from the onset to the peak of a flare, the mean energy of microwave-emitting electrons is estimated for 22 flares observed simultaneously in hard X-rays and microwaves. The energy of electrons varying in proportion to the 17 GHz emission is found to concentrate below 100 keV, and the mean energy or eletrons emitting 70 keV x-rays is less than about 130 keV for thin-target and less than about 180 keV for thick-target emission models, suggesting that the 17 GHz emission derives from electrons with energy of less than a few hundred keV. The magnetic field strength in the microwave source is found to be 500-1000 G for the thick-target and 1000-2000 G for the thin-target case, and 16 of the 22 events examined can be successfully explained by the thick-target model. Of the six events which cannot be explained by the thick-target model, two events give L of less than about 300 km.

  2. Nonthermal X-ray Spectral Flattening toward Low Energies in Early Impulsive Flares

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2007-01-01

    The determination of the low-energy cutoff to nonthermal electron distributions is critical to the calculation of the nonthermal energy in solar flares. The most direct evidence for low-energy cutoffs is flattening of the power-law, nontherma1 X-ray spectra at low energies. However, because of the plasma preheating often seen in flares, the thermal emissions at low energies may hide such spectral flattening of the nonthermal component. We select a category of flares, which we call "early impulsive flares", in which the > 25 keV hard X-ray (HXR) flux increase is delayed by less than 30 s after the flux increase at lower energies. Thus, the plasma preheating in these flares is minimal, so the nonthermal spectrum can be determined to lower energies than in flares with significant preheating. Out of a sample of 33 early impulsive flares observed by the Ramaty High Energy Solar Spectroscopy Imager (RHESSI), 9 showed spectral flattening toward low energies. In these events, the break energy of the double power-law fit to the HXR spectra lies in the range of 10-50 keV, significantly lower than the value we have seen for other flares that do not show such early impulsive emissions. In particular, it correlates with the HXR flux. After correcting the spatially-integrated spectra for albedo from isotropically emitted X-rays and using RHESSI imaging spectroscopy to exclude the extended albedo halo, we find that albedo associated with isotropic or nearly isotropic electrons can only account for the spectral flattening in 3 flares near Sun center. The spectral flattening in the remaining 6 flares is found to be consistent with the existence of a low-energy cutoff in the electron spectrum, falling in the range of 15-50 keV, which also correlates with the HXR flux.

  3. Detecting Solar Neutrino Flares and Flavors

    NASA Astrophysics Data System (ADS)

    Fargion, D.

    2004-06-01

    Most power-full solar flare as the ones occurred on 23th February 1956, September 29th 1989 and recent ones occurred on 28th October, on 2nd-4th and 13th November 2003 have been respectively recorded by Radio-X- and Cosmic Rays detectors. These flares took place most in the open or in the edge and in the hidden solar disk (as for the September 29th, 1989 beyond 105Wo and for last November 2003 flare events). The 4th November event was the most powerful X event in the highest known rank category X28. The observed and estimated total flare energy E = 1031-1033 erg should be a source also of a prompt secondary neutrino burst originated, by proton-proton-pion production on the sun itself; a more delayed and spread neutrino flux signal arise later on the terrestrial atmosphere. These first earliest prompt solar neutrino burst might be already recorde, in a few neutrino clustered events, in largest neutrino underground detectors as Super-Kamiokande one, in time correlation with the sharp X-Radio flare onset. Our first estimate at the Super-Kamiokande II Laboratory is found to be a few (1-5) events. Their discover (or absence) should constrains the solar flare acceleration, energetic and its inner environment. Any large neutrino flare event might even verify the expected neutrino flavour mixing leading to comparable electron- muon event as well as a comparable energy fluence and spectra. Rare Tau appearence by neutrino muon into tau conversion might also arise.

  4. Late variability of flux and spectra of the tTidal disruption flare Sw J1644+57 from XMM-Newton data

    NASA Astrophysics Data System (ADS)

    González-Rodríguez, A.; Castro-Tirado, A. J.; Guerrero, M. A.; Castellón, A.

    2014-12-01

    We describe the late spectral variability and flux evolution of TDF Sw J1644+57, a Tidal Disruption Flare which left the typical potential trend proportional to t(-5/3) in 2012, maintaining a quiescent flux until nowadays. Sixteen X-ray observations of ESA satellite XMM-Newton have been used in this study, including the one performed on 17th July, 2013. A search for optical emission in BOOTES/CASANDRA database has been performed too. Late X-ray fluxes show that the source flux decline does not follow the expected TDF trend at the time of the last XMM-Newton observation. Moreover, the spectra fitting parameters, in particular the neutral hydrogen column density, N_{H}, and the power-law index, Γ, indicate that the source darkening has diminished and that the spectral shape has flattened with time. The disruption of the star could have come to an end. Nevertheless, a quiescent X-ray flux continues. Evidence for a quiescent X-ray flux is presented.

  5. VLF Remote Sensing of the Lower Ionosphere: Solar Flares, Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares

    NASA Astrophysics Data System (ADS)

    Tan, J. H.; Cohen, M.; Inan, U. S.; Scherrer, P. H.; Scherrer, D.

    2005-12-01

    Stanford University Very Low Frequency (VLF) and Extremely Low Frequency (ELF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via ELF/VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas of a couple of meters in size, the sensitivity of these instruments allows the measurement of magnetic fields as low as several tens of femtoTesla per root-Hz, in the frequency range of ~30 Hz to 50 kHz. This sensitivity well exceeds that required to detect any event above the ambient atmospheric noise floor, determined by the totality of lightning activity on the planet. In recent years, as cost of production, timing accuracy (due to low cost GPS clocks), and data handling flexibility of the systems has improved, it has become possible to distribute many of these instruments in the form of arrays, to perform interferometric and holographic imaging of the lower ionosphere. In the context of the IHY in 2007, the ELF/VLF receiver can used extensively as part of the United Nations initiative to place scientific instruments in developing countries. Stanford University's past experiences setting up arrays of ELF/VLF receivers include an interferometer in Alaska, the Holographic Array for Ionospheric and Lightning research (HAIL) consisting of instruments at 13 different high schools in mid-western United States, a broader set of ELF/VLF receivers in Alaska, and various receivers abroad, including in France, Japan, Greece, Turkey, Ireland, and India. A global network of ELF/VLF receivers offer possibilities for a wide range of scientific topics, as well as serving as a means for educational outreach. These goals will be achieved using the newest version of the Stanford VLF receiver, known as AWESOME

  6. Electron transport estimated from electron spectra using electron spectrometer in LFEX laser target experiments

    NASA Astrophysics Data System (ADS)

    Ozaki, T.; Hata, M.; Matsuo, K.; Kojima, S.; Arikawa, Y.; Fujioka, S.; Sakagami, H.; Sunahara, A.; Nagatomo, H.; Johzaki, T.; Yogo, A.; Morace, A.; Zhang, Z.; Shiraga, H.; Sakata, S.; Nagai, T.; Abe, Y.; Lee, S.; Nakai, M.; Nishimura, H.; Azechi, H.; FIREX Group; GXII-LFEX Group

    2016-05-01

    Hot electrons which are generated from targets irradiated by a high-intense laser are measured by two electron spectrometers (ESMs). However, total electron energy observed by the ESM is only less than 1%. Hot electrons are confined by self-fields due to the huge current. When an external magnetic field of several hundred Tesla is applied during the laser irradiation on targets, the ESM signals always increase. In the simulation, the same result can be obtained. The reason is that the Alfvén limit can be mitigated due to the external longitudinal magnetic field.

  7. TIME-DEPENDENT MODELS OF FLARES FROM SAGITTARIUS A*

    SciTech Connect

    Dodds-Eden, Katie; Genzel, Reinhard; Gillessen, Stefan; Eisenhauer, Frank; Sharma, Prateek; Quataert, Eliot; Porquet, Delphine

    2010-12-10

    The emission from Sgr A*, the supermassive black hole in the Galactic Center, shows order of magnitude variability ('flares') a few times a day that is particularly prominent in the near-infrared (NIR) and X-rays. We present a time-dependent model for these flares motivated by the hypothesis that dissipation of magnetic energy powers the flares. We show that episodic magnetic reconnection can occur near the last stable circular orbit in time-dependent magnetohydrodynamic simulations of black hole accretion-the timescales and energetics of these events are broadly consistent with the flares from Sgr A*. Motivated by these results, we present a spatially one-zone time-dependent model for the electron distribution function in flares, including energy loss due to synchrotron cooling and adiabatic expansion. Synchrotron emission from transiently accelerated particles can explain the NIR/X-ray light curves and spectra of a luminous flare observed on 2007 April 4. A significant decrease in the magnetic field strength during the flare (coincident with the electron acceleration) is required to explain the simultaneity and symmetry of the simultaneous light curves. Our models predict that the NIR and X-ray spectral indices are related by {Delta}{alpha} {approx_equal} 0.5 (where {nu}F{sub {nu}} {proportional_to} {nu}{sup {alpha}}) and that there is only modest variation in the spectral index during flares. We also explore implications of this model for longer wavelength (radio-submillimeter) emission seemingly associated with X-ray and NIR flares; we argue that a few hour decrease in the submillimeter emission is a more generic consequence of large-scale magnetic reconnection than delayed radio emission from adiabatic expansion.

  8. Solar flares

    NASA Technical Reports Server (NTRS)

    Zirin, H.

    1974-01-01

    A review of the knowledge about solar flares which has been obtained through observations from the earth and from space by various methods. High-resolution cinematography is best carried out at H-alpha wavelengths to reveal the structure, time history, and location of flares. The classification flares in H alpha according to either physical or morphological criteria is discussed. The study of flare morphology, which shows where, when, and how flares occur, is important for evaluating theories of flares. Consideration is given to studies of flares by optical spectroscopy, radio emissions, and at X-ray and XUV wavelengths. Research has shown where and possibly why flares occur, but the physics of the instability involved, of the particle acceleration, and of the heating are still not understood.

  9. Combined Particle Acceleration in Solar Flares and Associated CME Shocks

    NASA Astrophysics Data System (ADS)

    Petrosian, Vahe

    2016-07-01

    I will review some observations of the characteristics of accelerated electrons seen near Earth (as SEPs) and those producing flare radiation in the low corona and chromosphere. The similarities and differences between the numbers, spectral distribution, etc. of the two population can shed light on the mechanism and sites of the acceleration. I will show that in some events the origin of both population appears to be the flare site while in others, with harder SEP spectra, in addition to acceleration at the flare site, there appears to be a need for a second stage re-acceleration in the associated fast Coronal Mass Ejection (CME) environment. This scenario can also describe a similar dichotomy that exists between the so called impulsive, highly enriched (3He and heavy ions) and softer SEP ion events, and stronger more gradual SEP events with near normal ionic abundances and harder spectra. I will also describe under what conditions such hardening can be achieved.

  10. Cumulant approach for electronic excitations in x-ray and electron spectra

    NASA Astrophysics Data System (ADS)

    Rehr, J. J.

    A quantitative treatment of electronic excitations and other many-body effects in x-ray and electron spectra has long been challenging. Physically, electronic correlations and atomic vibrations lead to inelastic losses and damping effects that are ignored in ground state methods or approximations such as TDDFT. Quasi-particle (QP) approaches such as the GW approximation yield significant improvements, as demonstrated in real-space Green's function and GW/Bethe-Salpeter equation calculations, but still ignore multi-electron excitations. Recently such excitations have been treated with considerable success using cumulant expansion techniques and the quasi-boson approximation. In this beyond QP approach, excitations such as plasmons and electron-hole excitations appear as satellites in the spectral function. The method naturally accounts for multiple-satellites and can be extended to include extrinsic losses and interference effects. Extensions for effects of vibrations and strong correlations including charge-transfer satellites may also be possible. These advances are illustrated with a number of applications. Supported by DOE Grant DE-FG02-97ER45623.

  11. Formation of the 0.511.-MeV line in solar flares. [statistical mechanics of line spectra for gamma rays

    NASA Technical Reports Server (NTRS)

    Crannell, C. J.; Joyce, G.; Ramaty, R.; Werntz, C.

    1976-01-01

    The gamma-ray line produced at 0.51-MeV was studied and is shown to be the result of either of free annihilation of positrons with electrons or of the decay of positronium by 2-photon emission. Positron annihilation from the bound state of positronium may also proceed by 3-photon emission, resulting in a continuum with energies up to 0.51-MeV. Accurate calculations of the rates of free annihilation and positronium formation in a solar-flare plasma are presented. Estimates of the positronium-formulation rates by charge exchange and the rates of dissociation and quenching are also considered. The temperature and density dependence of the ratio of 3-photon to 2-photon emission was obtained. It is shown that when the ratio of free electrons to neutral atoms in the plasma is approximately unity or greater, the Doppler width of the 0.51-MeV line is a function of the temperature of the annihilation region. For the small ion densities characteristics of the photosphere, the width is predominantly a function of the density.

  12. Electronic Spectra of the Jet-Cooled Acetaminophen

    NASA Astrophysics Data System (ADS)

    Lee, Seung Jun; Min, Ahreum; Kim, Yusic; Choi, Myong Yong; Chang, Jinyoung; Lee, Sang Hak; Kim, Seong Keun

    2010-06-01

    Resonant two-photon ionization (R2PI), laser induced fluorescence (LIF) and UV-UV double resonance spectra of the jet-cooled acetaminophen, widely used as a pain reliever and fever reducer, were obtained in the gas phase. Conformational characterizations for acetaminophen will be presented with an aid of spectroscopic techniques and DFT B3LYP calculations.

  13. The Energetics of White-light Flares Observed by SDO/HMI and RHESSI

    NASA Astrophysics Data System (ADS)

    Huang, Neng-Yi; Xu, Yan; Wang, Haimin

    2016-11-01

    White-light (WL) flares have been observed and studied for more than a century since their first discovery. However, some fundamental physics behind the brilliant emission remains highly controversial. One of the important facts in addressing the flare energetics is the spatio-temporal correlation between the WL emission and the hard X-ray (HXR) radiation, presumably suggesting that energetic electrons are the energy sources. In this study, we present a statistical analysis of 25 strong flares (≥M5) observed simultaneously by the Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics Observatory (SDO), and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Among these events, WL emission was detected by SDO/HMI in 13 flares, associated with HXR emission. To quantitatively describe the strength of WL emission, equivalent area (EA) is defined as the integrated contrast enhancement over the entire flaring area. Our results show that the EA is inversely proportional to the HXR power-law index, indicating that stronger WL emission tends to be associated with a larger population of high energy electrons. However, no obvious correlation is found between WL emission and flux of non-thermal electrons at 50 keV. For the other group of 13 flares without detectable WL emission, the HXR spectra are softer (larger power-law index) than those flares with WL emission, especially for the X-class flares in this group.

  14. Observations of the scatter-free solar-flare electrons in the energy range 20-1000 keV

    NASA Technical Reports Server (NTRS)

    Wang, J. R.; Fisk, L. A.; Lin, R. P.

    1971-01-01

    Observations of the scatter-free electron events from solar active region McMath No. 8905 are presented. The measurements were made on Explorer 33 satellite. The data show that more than 80% of the electrons from these events undergo no or little scattering and that these electrons travel only approximately 1.5 a.u. between the sun and the earth. The duration of these events cannot be accounted fully by velocity dispersion alone. It is suggested that these electrons could be continuously injected into interplanetary medium for a time interval of approximately 2 to 3 minutes. Energy spectra of these electrons are discussed.

  15. MEASUREMENTS OF ABSOLUTE ABUNDANCES IN SOLAR FLARES

    SciTech Connect

    Warren, Harry P.

    2014-05-01

    We present measurements of elemental abundances in solar flares with the EUV Variability Experiment (EVE) on the Solar Dynamics Observatory. EVE observes both high temperature Fe emission lines (Fe XV-Fe XXIV) and continuum emission from thermal bremsstrahlung that is proportional to the abundance of H. By comparing the relative intensities of line and continuum emission it is possible to determine the enrichment of the flare plasma relative to the composition of the photosphere. This is the first ionization potential or FIP bias (f). Since thermal bremsstrahlung at EUV wavelengths is relatively insensitive to the electron temperature, it is important to account for the distribution of electron temperatures in the emitting plasma. We accomplish this by using the observed spectra to infer the differential emission measure distribution and FIP bias simultaneously. In each of the 21 flares that we analyze we find that the observed composition is close to photospheric. The mean FIP bias in our sample is f = 1.17 ± 0.22. This analysis suggests that the bulk of the plasma evaporated during a flare comes from deep in the chromosphere, below the region where elemental fractionation occurs.

  16. Analytic and numerical calculations of quantum synchrotron spectra from relativistic electron distributions

    NASA Technical Reports Server (NTRS)

    Brainerd, J. J.; Petrosian, V.

    1987-01-01

    Calculations are performed numerically and analytically of synchrotron spectra for thermal and power-law electron distributions using the single-particle synchrotron power spectrum derived from quantum electrodynamics. It is found that the photon energy at which quantum effects appear is proportional to temperature and independent of field strength for thermal spectra; quantum effects introduce an exponential roll-off away from the classical spectra. For power law spectra, the photon energy at which quantum effects appear is inversely proportional to the magnetic field strength; quantum effects produce a steeper power law than is found classically. The results are compared with spectra derived from the classical power spectrum with an energy cutoff ensuring conservation of energy. It is found that an energy cutoff is generally an inadequate approximation of quantum effects for low photon energies and for thermal spectra, but gives reasonable results for high-energy emission from power-law electron distributions.

  17. Coincidence studies of diffraction structures in binary encounter electron spectra

    SciTech Connect

    Liao, C.; Hagmann, S.; Richard, P.

    1994-12-31

    The authors have measured binary encounter electron (BEe) production in collisions of 0.3 MeV/u Cu{sup q+} (q=4,12) projectiles on H{sub 2} targets from 0 to 70 degrees with respect to the beam direction. Prominent features are the appearance of the BEe peak splitting and a very strong forward peaked angular distribution which are attributed to the diffractive scattering of the quasifree target electrons in the short range potential of the projectile. Using electron-projectile final charge state coincidence techniques, different collision reaction channels can be separated. Measurements of this type are being pursued.

  18. Electronic structure and photoelectron spectra of osmium and ruthenium tetraoxides

    SciTech Connect

    Topol', I.A.; Vovna, V.I.; Kazachek, M.V.

    1988-01-01

    The X/sub ..cap alpha../-SW method has been used in the nonrelativistic and quasirelativistic approximations to calculate the electronic structures of OsO/sub 4/, RuO/sub 4/, and FeO/sub 4/. When the 5d element is replaced by a 4d or 3d one, the electron-density redistribution is due mainly to the d electrons. All the d electrons in FeO/sub 4/ are localized on the iron atom, which markedly reduced the ionic and covalent bonding on the transition from RuO/sub 4/ to FeO/sub 4/, which explains the instability of FeO/sub 4/. The calculated spin-orbit splittings agree well with the structure of the PES bands, which enables one to establish the sequence of MO ionization energies unambiguously.

  19. HARD X-RAY AND MICROWAVE EMISSIONS FROM SOLAR FLARES WITH HARD SPECTRAL INDICES

    SciTech Connect

    Kawate, T.; Nishizuka, N.; Oi, A.; Ohyama, M.; Nakajima, H.

    2012-03-10

    We analyze 10 flare events that radiate intense hard X-ray (HXR) emission with significant photons over 300 keV to verify that the electrons that have a common origin of acceleration mechanism and energy power-law distribution with solar flares emit HXRs and microwaves. Most of these events have the following characteristics. HXRs emanate from the footpoints of flare loops, while microwaves emanate from the tops of flare loops. The time profiles of the microwave emission show delays of peak with respect to those of the corresponding HXR emission. The spectral indices of microwave emissions show gradual hardening in all events, while the spectral indices of the corresponding HXR emissions are roughly constant in most of the events, though rather rapid hardening is simultaneously observed in some for both indices during the onset time and the peak time. These characteristics suggest that the microwave emission emanates from the trapped electrons. Then, taking into account the role of the trapping of electrons for the microwave emission, we compare the observed microwave spectra with the model spectra calculated by a gyrosynchrotron code. As a result, we successfully reproduce the eight microwave spectra. From this result, we conclude that the electrons that have a common acceleration and a common energy distribution with solar flares emit both HXR and microwave emissions in the eight events, though microwave emission is contributed to by electrons with much higher energy than HXR emission.

  20. Dynamics of quantal heating in electron systems with discrete spectra

    NASA Astrophysics Data System (ADS)

    Dietrich, Scott; Mayer, William; Vitkalov, Sergey; Bykov, A. A.

    2015-05-01

    The temporal evolution of quantal Joule heating of two-dimensional (2D) electrons in a GaAs quantum well placed in quantizing magnetic fields is studied using a difference-frequency method. The method is based on measurements of the electron conductivity oscillating at the beat frequency f =f1-f2 between two microwaves applied to the 2D system at frequencies f1 and f2. The method provides direct access to the dynamical characteristics of the heating and yields the inelastic-scattering time τi n of 2D electrons. The obtained τi n is strongly temperature dependent, varying from 0.13 ns at 5.5 K to 1 ns at 2.4 K in magnetic field B =0.333 T . When the temperature T exceeds the Landau-level separation, the relaxation rate 1 /τi n is proportional to T2, indicating electron-electron interaction as the dominant mechanism limiting the quantal heating. At lower temperatures, the rate tends to be proportional to T3, indicating considerable contribution from electron-phonon scattering.

  1. Dynamics of Quantal Heating in Electron Systems with Discrete Spectra

    NASA Astrophysics Data System (ADS)

    Mayer, William; Dietrich, Scott; Vitkalov, Sergey; Bykov, Alexey

    2015-03-01

    The temporal evolution of quantal Joule heating of 2D electrons in GaAs quantum well placed in quantizing magnetic fields is studied using a difference frequency method. The method is based on measurements of the electron conductivity oscillating at the beat frequency f =f1 -f2 between two microwaves applied to 2D system at frequencies f1 and f2. The method provides direct access to the dynamical characteristics of the heating and yields the inelastic scattering time τin of 2D electrons. The obtained τin is strongly temperature dependent, varying from 0.13 ns at 5.5K to 1 ns at 2.4K in magnetic field B=0.333T. When temperature T exceeds the Landau level separation the relaxation rate 1 /τin is proportional to T2, indicating the electron-electron interaction as the dominant mechanism limiting the quantal heating. At lower temperatures the rate tends to be proportional to T3, indicating considerable contribution from electron-phonon scattering. This work was supported by the National Science Foundation (DMR 1104503), the Russian Foundation for Basic Research (project no.14-02-01158) and the Ministry of Education and Science of the Russian Federation.

  2. Stochastic particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Droege, W.; Schlickeiser, R.

    1985-01-01

    It is proposed that particles during the second phase of solar flares are accelerated by stochastic resonant scattering off hydromagnetic waves and first order Fermi acceleration in shock waves generated in the impulsive phase of the flare. Solutions allow arbitrary power law momentum dependences of the momentum diffusion coefficient as well as the momentum diffusion coefficient as well as the momentum loss time. The acceleration time scale to a characteristic energy approximately 100 keV for protons can be as short as 5s. The resulting electron spectra show a characteristic double power law with a transition around 200 keV and are correlated to the proton spectra evaluated under equal boundary conditions, indicating that electrons and protons are accelerated by the same mechanism. The correlation between the different spectral indices in the electron double power law and between electron and proton spectra are governed by the ratio of first to second order acceleration and therefore allow a determination of the Alfven Mach number of the shock wave.

  3. 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.

  4. Particle Acceleration in Solar Flares and Associated CME Shocks

    NASA Astrophysics Data System (ADS)

    Petrosian, Vahé

    2016-10-01

    Observations relating the characteristics of electrons seen near Earth (solar energetic particles [SEPs]) and those producing flare radiation show that in certain (prompt) events the origin of both populations appears to be the flare site, which shows strong correlation between the number and spectral index of SEP and hard X-ray radiating electrons, but in others (delayed), which are associated with fast coronal mass ejections (CMEs), this relation is complex and SEPs tend to be harder. Prompt event spectral relation disagrees with that expected in thick or thin target models. We show that using a more accurate treatment of the transport of the accelerated electrons to the footpoints and to Earth can account for this discrepancy. Our results are consistent with those found by Chen & Petrosian for two flares using nonparametric inversion methods, according to which we have weak diffusion conditions, and trapping mediated by magnetic field convergence. The weaker correlations and harder spectra of delayed events can come about by reacceleration of electrons in the CME shock environment. We describe under what conditions such a hardening can be achieved. Using this (acceleration at the flare and reacceleration in the CME) scenario, we show that we can describe the similar dichotomy that exists between the so-called impulsive, highly enriched (3He and heavy ions), and softer SEP events and stronger, more gradual SEP events with near-normal ionic abundances and harder spectra. These methods can be used to distinguish the acceleration mechanisms and to constrain their characteristics.

  5. Energy spectra of Penning electrons in non-local plasma at middle and high pressures

    NASA Astrophysics Data System (ADS)

    Stefanova, M.; Pramatarov, P.; Kudryavtsev, A.; Peyeva, R.

    2014-05-01

    A recently-developed collisional electron spectroscopy (CES) method enabled us to measure the energy spectra of groups of fast non-local electrons in a collisional mode at high pressures, where no collisional energy relaxation of electrons in the different groups takes place in the volume, and the different groups of electrons behave independently of each other. We recorded the energy spectra of groups of fast electrons created via Penning ionization of Ar and N2 impurities by metastable He atoms at He pressures of 30 and 200 Torr. The experiments were conducted in the non-local negative glow plasma of a short dc microdischarge. The Penning electrons' energy spectra were recorded by means of an additional electrode - a sensor located at the boundary of the discharge volume, in contrast with the classical Langmuir probe. The spectra are characterized by the appearance of maxima at characteristic energies corresponding to the energy of the electrons released via Penning reactions. Using the Penning electrons' energy spectra, one can detect and identify the presence of different atomic and molecular admixtures in He at high pressures.

  6. Electronic states and spectra of BiS

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Meinecke, F.; Fink, E. H.

    2009-11-01

    NIR/VIS emission spectra of BiS were measured in the 5800-25 000 cm -1 region with a Fourier-transform spectrometer. BiS was produced by reaction of bismuth and sulfur vapor and excited by energy transfer from metastable oxygen O 2( a1Δ g) in a fast-flow system. The spectrum of BiS was found to be closely related to that of the previously studied BiO radical [O. Shestakov et al., J. Mol. Spectrosc. 190 (1998) 28-77]. Five transitions connecting the Ω-components of the first three excited states, A4Π( A13/2, A21/2), B2Π( B11/2), and C4Σ -( C11/2, C23/2), with the components of the strongly split ground state, X2Π( X11/2, X23/2, have been observed and analyzed.

  7. Substorm effects in auroral spectra. [electron spectrum hardening

    NASA Technical Reports Server (NTRS)

    Eather, R. H.; Mende, S. B.

    1973-01-01

    A substorm time parameter is defined and used to order a large body of photometric data obtained on aircraft expeditions at high latitudes. The statistical analysis demonstrates hardening of the electron spectrum at the time of substorm, and it is consistent with the accepted picture of poleward expansion of aurora at the time of substorm and curvature drift of substorm-injected electrons. These features are not evident from a similar analysis in terms of magnetic time. We conclude that the substorm time concept is a useful ordering parameter for auroral data.

  8. Analysis of flares in the chromosphere and corona of main- and pre-main-sequence M-type stars

    NASA Astrophysics Data System (ADS)

    Crespo-Chacón, I.

    2015-11-01

    having an accretion disk) we carry out a detailed analysis of an extremely long rise phase and of a shorter, weaker flare (allowing us to compare the results with those reported for young stars but surrounded by disks). Assuming multitemperature models to describe the coronal flaring plasma, we have calculated the metal abundance, the electron temperatures and the respective emission measures by fitting the spectra with the Astrophysical Plasma Emission Code included in the XSPEC software, which calculates spectral models for hot, optically thin plasmas. Moreover, we are able to estimate the size of the flaring loops by using theoretical models. These sizes give us an idea about the extent of the corona. For those flares in which heating does not entirely drive the flare evolution we use the models reported by Reale (2007) and Reale et al. (1997) for the rise and decay phases, respectively, including the effect of sustained heating during the decay. Instead, the stellar version of the Kopp & Poletto (1984)'s solar two-ribbon flare model (Poletto et al. 1988) is used when the residual heating completely drives the flare over the plasma cooling. Later, we apply the so-called RTV scaling laws (Rosner et al. 1978) and other fundamental laws of physics to determine additional characteristics of the plasma contained in the flaring loops (electron density and pressure), as well as the volume of the flaring region, the heating rate per unit volume, and the strength of the magnetic field required to confine this plasma. Making some assumptions we are also able to estimate the number of loops involved in the observed flares and the kind of magnetic structures present in the atmosphere of these types of stars. Finally, we discuss and interpret the results in the context of solar and stellar flares reported so far.

  9. Electron Spin Resonance Spectra of Photogenerated Polarons in Poly(Paraphenylene Vinylene)

    NASA Astrophysics Data System (ADS)

    Murata, Kazuhiro; Kuroda, Shin-ichi; Shimoi, Yukihiro; Abe, Shuji; Noguchi, Takanobu; Ohnishi, Toshihiro

    1996-12-01

    Light-induced ESR (LESR) measurements have been performed on undoped poly(parapheny- lene vinylene) (PPV) down to 4 K. The ESR signal increases significantly for the excitation energy above 3.1 3.2 eV, as in the case of the excitation spectra of photocarriers reported in PPV derivatives. The anisotropic light-induced ESR spectra in oriented samples are well reproduced by the spectra calculated using a theoretical polaron spin distribution in the case of finite electron-electron interaction. These spectral features indicate that the observed spins are photogenerated polarons.

  10. Pulsed HF radiowave absorption measurements at 2.1 MHZ. over Delhi under quiet and solar flare conditions and related electron density height profiles

    NASA Astrophysics Data System (ADS)

    Balachandra Swamy, A. C.

    EXTENDED ABSTRACT Pulsed HF radiowave absorption measurements at 2.1 MHZ. over Delhi under quiet and solar flare conditions and related electron density height profiles A.C.Balachandra swmay & Late C.S.G.K. Setty Absorption of radio waves in the ionosphere is of great practical importance for radio communication and navigation systems. The first attempt to measure the absolute magnitude of the radiowave absorption were made by appletion and Ratcliffe (1930) using the frequency change method for medium frequency waves reflected from the E-region. They concluded from their experiment that the main part of the attenuation occurred below the reflection level and named the absorption region, D-region of the ionosphere. One of the basic properties of the ionosphere is the absorption of high Frequency Radiowaves. HF radiowave absorption results mainly from collisions between electrons (which are set into forced oscillations by the electric field of the wave) and neutral air particles, the RF energy abstracted from the wave being converted into thermal energy. The radiowave absorption in the ionosphere depends on electron density and collision frequency. The most important absorbing regions are the D-region and the lower E-region (50-100 Km.) The regular diurnal variation of the electron density in this height range is caused mainly by the changes in the depth of penetration of solar XUV radiations with solar zenith angle under quiet solar conditions. In 1937 Dellinger J.H.identified fade outs in high frequency radio circuits as due to abnormal ionospheric absorption associated with solar flares. The onset of the fade out was usually rapid and the duration was typically tens of minutes like that of the visible flare, because of the sudden onset, the immediate effects of solar flares are known collectively as sudden Ionospheric Disturbances (STD). The phenomenon discovered by Dellinger is usually called a short Wave Fadeout(SWF). Since the SWF is due to abnormal absorption

  11. Flare evolution and magnetic configuration study

    NASA Astrophysics Data System (ADS)

    Berlicki, A.; Schmieder, B.; Aulanier, G.; Vilmer, N.; Yan, Y. H.

    We will present the analysis of M1.0 confined flare emission and evolution in the context of the topology of the coronal magnetic field. This flare was observed in NOAA 0162 on 22 October 2002. The multiwavelength data were taken during a coordinated observational campaign between ground based instruments and space observatories. The photospheric line-of-sight magnetic field observations were obtained with THEMIS and SOHO/MDI. We used these data to perform linear force-free field extrapolation of magnetic field into the corona. Our extrapolation provides an explanation of the appearance of H-alpha flare ribbons. An elongated shape of X-ray emission observed by Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) also follow the predicted shape of extrapolated field lines. Moreover, the X-ray emission observed by RHESSI permit to see thermal emission of coronal loops heated probably by non-thermal electrons, accelerated during the reconnection processes. The presence of non-thermal particles can be deduced from RHESSI X-ray spectra reconstructed during the gradual phase of the flare. On Huairou vector magnetograms of the AR we see that there was strong shear between one of main negative spot and the north small positive spot. The extrapolation with non-constant alpha force-free field model did not obtain any loop to connect these two spots.

  12. Electronic Spectra of Bare and Solvated Ruthenium Polypyridine Complexes

    NASA Astrophysics Data System (ADS)

    Xu, Shuang; Smith, James E. T.; Weber, J. Mathias

    2016-06-01

    We present work on a prototypical water oxidation catalyst, namely the aqua-complex [(bpy)(tpy)Ru-OH_2]2+ (2,2'-bpy = bipyridine, tpy = 2,2':6',2"-terpyridine), and its hydrated clusters [(bpy)(tpy)Ru-OH_2]2+ ·(H2O)_n, with n = 1 - 4. This complex is the starting species in a catalytic cycle for water oxidation. We couple electrospray ionization mass spectrometry with laser spectroscopy to circumvent challenges that arise in reactive solutions from speciation. Here, we report the electronic spectrum of [(bpy)(tpy)Ru-OH_2]2+ by photodissociation spectroscopy of mass selected, cryogenically prepared ions, and we examine effects of its microhydration environment on its electronic structure. In particular, we investigate the solvatochromic shift of the spectral envelope upon sequential addition of water molecules up to the tetrahydrate.

  13. Electron spectra and structure of atomic and molecular clusters

    SciTech Connect

    Dehmer, Patricia M.

    1980-01-01

    Changes in electronic structure that occur during the stepwise transition from gas phase monomers to large clusters which resemble the condensed phase were studied. This basic information on weakly bound clusters is critical to the understanding of such phenomena as nucleation, aerosol formation, catalysis, and gas-to-particle conversion, yet there exist almost no experimental data on neutral particle energy levels or binding energies as a function of cluster size. (GHT)

  14. Theory of microwave and X-ray emission. [application to behavior of nonthermal electrons created at impulsive phase of solar flares

    NASA Technical Reports Server (NTRS)

    Takakura, T.

    1973-01-01

    The behaviour of the nonthermal electrons created at the impulsive phase of flares has been deduced from the microwave impulsive bursts and hard X-ray burst by many researchers. There is almost no doubt of the emission mechanisms that radio emissions are due to gyrosynchrotron emission and hard X-rays are collisional bremsstrahlung. However, there remain three controversial problems. One is whether the emission sources of the microwave impulsive burst and hard X-ray burst are common or not. Another is whether the injection of the nonthermal electrons into the source is impulsive or continuous. The other is the relation among the nonthermal electrons, soft X-rays, EUV flash, H-alpha kernels, and white light flares. These three problems are not independent of each other.

  15. X-ray spectra from the Cornell Electron-Beam Ion Source (CEBIS I)

    SciTech Connect

    Johnson, B.M.; Jones, K.W.; Kostroun, V.O.; Ghanbari, E.; Janson, S.W.

    1985-01-01

    Radiation emitted from the Cornell electron beam ion source (CEBIS I) has been surveyed with a Si(Li) x-ray detector. These spectra can be used to estimate backgrounds from electron bremsstrahlung and to evaluate the feasibility of atomic physics experiments using the CEBIS I source in this configuration. 1 ref., 2 figs.

  16. Disentangling electronic and vibronic coherences in two-dimensional echo spectra.

    PubMed

    Kreisbeck, Christoph; Kramer, Tobias; Aspuru-Guzik, Alán

    2013-08-15

    The prevalence of long-lasting oscillatory signals in two-dimensional (2D) echo spectroscopy of light-harvesting complexes has led to a search for possible mechanisms. We investigate how two causes of oscillatory signals are intertwined: (i) electronic coherences supporting delocalized wavelike motion and (ii) narrow bands in the vibronic spectral density. To disentangle the vibronic and electronic contributions, we introduce a time-windowed Fourier transform of the signal amplitude. We find that 2D spectra can be dominated by excitations of pathways which are absent in excitonic energy transport. This leads to an underestimation of the lifetime of electronic coherences by 2D spectra.

  17. Reliable modeling of the electronic spectra of realistic uranium complexes

    NASA Astrophysics Data System (ADS)

    Tecmer, Paweł; Govind, Niranjan; Kowalski, Karol; de Jong, Wibe A.; Visscher, Lucas

    2013-07-01

    We present an EOMCCSD (equation of motion coupled cluster with singles and doubles) study of excited states of the small [UO2]2+ and [UO2]+ model systems as well as the larger UVIO2(saldien) complex. In addition, the triples contribution within the EOMCCSDT and CR-EOMCCSD(T) (completely renormalized EOMCCSD with non-iterative triples) approaches for the [UO2]2+ and [UO2]+ systems as well as the active-space variant of the CR-EOMCCSD(T) method—CR-EOMCCSd(t)—for the UVIO2(saldien) molecule are investigated. The coupled cluster data were employed as benchmark to choose the "best" appropriate exchange-correlation functional for subsequent time-dependent density functional (TD-DFT) studies on the transition energies for closed-shell species. Furthermore, the influence of the saldien ligands on the electronic structure and excitation energies of the [UO2]+ molecule is discussed. The electronic excitations as well as their oscillator dipole strengths modeled with TD-DFT approach using the CAM-B3LYP exchange-correlation functional for the [UVO2(saldien)]- with explicit inclusion of two dimethyl sulfoxide molecules are in good agreement with the experimental data of Takao et al. [Inorg. Chem. 49, 2349 (2010), 10.1021/ic902225f].

  18. Reliable Modeling of the Electronic Spectra of Realistic Uranium Complexes

    SciTech Connect

    Tecmer, Pawel; Govind, Niranjan; Kowalski, Karol; De Jong, Wibe A.; Visscher, Lucas

    2013-07-21

    We present an EOMCCSD (equation of motion coupled cluster with singles and doubles) study of excited states of the small [UO2]2+ and [UO2]+ model systems as well as the larger UV IO2(saldien) complex. In addition, the triples contribution within the EOMCCSDT and CR-EOMCCSD(T) (completely renormalized EOMCCSD with non-iterative triples) approaches for the [UO2]2+ and [UO2]+ systems as well as the active-space variant of the CR-EOMCCSD(T) method | CREOMCCSd(t) | for the UV IO2(saldien) molecule are investigated. The coupled cluster data was employed as benchmark to chose the "best" appropriate exchange--correlation functional for subsequent time-dependent density functional (TD-DFT) studies on the transition energies for closed-shell species. Furthermore, the influence of the saldien ligands on the electronic structure and excitation energies of the [UO2]+ molecule is discussed. The electronic excitations as well as their oscillator dipole strengths modeled with TD-DFT approach using the CAM-B3LYP exchange{correlation functional for the [UV O2(saldien)]- with explicit inclusion of two DMSOs are in good agreement with the experimental data of Takao et al. [Inorg. Chem. 49, 2349-2359, (2010)].

  19. Electronic States and Spectra of BiO

    NASA Astrophysics Data System (ADS)

    Shestakov, O.; Breidohr, R.; Demes, H.; Setzer, K. D.; Fink, E. H.

    1998-07-01

    The electronic spectrum of the BiO radical has been studied by Fourier transform emission spectroscopy, laser-induced fluorescence, and excimer laser photolysis techniques. Six new electronic states,A1(Ω = 3/2) (Te= 11 528.8 cm-1, ωe= 530.4 cm-1, ωexe= 2.42 cm-1),G(Ω = 3/2) (Te= 20 273 cm-1, ωe= 499 cm-1, ωexe= 2.6 cm-1),H(Ω = 1/2) (Te= 20 469.76(6) cm-1, ωe= 471.63(18) cm-1, ωexe= 2.153(35) cm-1),I(Ω = 1/2) (Te= 21 982.50(2) cm-1, ωe= 506.50(11) cm-1, ωexe= 3.263(34) cm-1),J(Ω = 3/2) (Te= 25 598.95(42) cm-1, ωe= 489.95(16) cm-1, ωexe= 2.309(45) cm-1), andK(Ω = 1/2) (Te= 26 744.7(2) cm-1, ωe= 420.6(4) cm-1, ωexe= 5.25(5) cm-1), and 14 new electronic transitions (A1← X1,G → X2,H ↔ X1,H → A2(A),I ↔ X1,I → A2,J ↔ X1,J ↔ X2,K ↔ X1,K ↔ X2,K → A2,B ↔ X2,B → A2,C ↔ X2) have been detected. Time-resolved measurements of the fluorescence decays have yielded the radiative lifetimes of thev= 0 levels of most states up to <30 500 cm-1energy (τX2= 480 ± 100 μs, τA2= 9.3 ± 1.5 μs, τH= 15 ± 3 μs, τI= 16 ± 3 μs, τJ= 4.9 ± 0.9 μs, τK= 2.6 ± 0.3 μs, τB= 0.55 ± 0.08 μs, τC= 0.84 ± 0.15 μs) and rate constants for quenching of the states by some rare gas atoms and simple molecules. The new electronic statesA1,G,H,I,J, andKand the previously known levelsX1,X2,A2(A),B,C, andDare assigned to spin-orbit states arising from low-energy valence configurations of BiO with the help of detailed theoretical data calculated by Alekseyevet al.(J. Chem. Phys.100,8956-8968 (1994)).

  20. Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory

    NASA Astrophysics Data System (ADS)

    Tait, E. W.; Ratcliff, L. E.; Payne, M. C.; Haynes, P. D.; Hine, N. D. M.

    2016-05-01

    Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable.

  1. Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory.

    PubMed

    Tait, E W; Ratcliff, L E; Payne, M C; Haynes, P D; Hine, N D M

    2016-05-18

    Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable. PMID:27094207

  2. Solar Flares

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina

    2013-01-01

    Because the Earth resides in the atmosphere of our nearest stellar neighbor, events occurring on the Sun's surface directly affect us by interfering with satellite operations and communications, astronaut safety, and, in extreme circumstances, power grid stability. Solar flares, the most energetic events in our solar system, are a substantial source of hazardous space weather affecting our increasingly technology-dependent society. While flares have been observed using ground-based telescopes for over 150 years, modern space-bourne observatories have provided nearly continuous multi-wavelength flare coverage that cannot be obtained from the ground. We can now probe the origins and evolution of flares by tracking particle acceleration, changes in ionized plasma, and the reorganization of magnetic fields. I will walk through our current understanding of why flares occur and how they affect the Earth and also show several examples of these fantastic explosions.

  3. Flare Plasma Iron Abundance

    NASA Technical Reports Server (NTRS)

    Dennis, Brian R.; Dan, Chau; Jain, Rajmal; Schwartz, Richard A.; Tolbert, Anne K.

    2008-01-01

    The equivalent width of the iron-line complex at 6.7 keV seen in flare X-ray spectra suggests that the iron abundance of the hottest plasma at temperatures >approx.10 MK may sometimes be significantly lower than the nominal coronal abundance of four times the photospheric value that is commonly assumed. This conclusion is based on X-ray spectral observations of several flares seen in common with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Solar X-ray Spectrometer (SOXS) on the second Indian geostationary satellite, GSAT-2. The implications of this will be discussed as it relates to the origin of the hot flare plasma - either plasma already in the corona that is directly heated during the flare energy release process or chromospheric plasma that is heated by flare-accelerated particles and driven up into the corona. Other possible explanations of lower-than-expected equivalent widths of the iron-line complex will also be discussed.

  4. Flare-antenna unit for system in which flare is remotely activated by radio

    NASA Astrophysics Data System (ADS)

    Hiltz, Frederick F.; Wilson, Charles E.

    1995-06-01

    A flare-antenna assembly has flare material enclosed in a cylindrical antenna and forms part of a marker beacon. The flare aids in the search for the marker beacon by providing means for both visual and infrared detection. The flare is actuated in response to a specific remote radio signal being received by the antenna. The received signal is decoded by the electronic system within the marker beacon. If the received signal meets the necessary criteria the electronic system generates an electrical signal that detonates a squib embedded in the flare material. The detonation of the squib activates the flare.

  5. X-ray Photoemission Spectra and Electronic Structure of Coumarin and its Derivatives.

    PubMed

    Wickrama Arachchilage, Anoja P; Wang, Feng; Feyer, Vitaliy; Plekan, Oksana; Acres, Robert G; Prince, Kevin C

    2016-09-15

    The electronic structures of coumarin and three of its derivatives (7-amino-4-methylcoumarin, 7-amino-4-(trifluoro)methylcoumarin, and 4-hydroxycoumarin) have been studied by theoretical calculations, and compared with experimental valence and core photoelectron spectra to benchmark the predicted spectra. The outer valence band spectra of the first three compounds showed good agreement with theoretical calculations for a single isomer, whereas the spectrum of 4-hydroxycoumarin indicated the presence of more than one tautomer, consistent with published results. Calculations of core level spectra of carbon, nitrogen, oxygen, and fluorine of the first three compounds are also in satisfactory agreement with our measurements. The carbon and oxygen 1s spectra of 4-hydroxycoumarin allow us to identify and quantify the populations of the principle tautomers present. The 4-hydroxy enol form is the most stable isomer at 348 K, followed by the diketo form, with 1.3 kJ·mol(-1) lower energy. PMID:27545582

  6. Electronic absorption spectra of cryogenic systems with hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Meister, T. G.; Zelikina, G. Ya.; Artamonova, O. M.

    1989-05-01

    The thermodynamic equilibrium ? has been studied by recording the 1Lb band of benzene and toluene (YR 2) dissolved in liquid Kr and CF 4 (toluene was also dissolved in liquid Ar), with addition of CHF 3(R 1XH) in a broad temperature range for each of the systems. The narrowness of the vibronic components (VC) of the 1Lb band in cryogenic solvents, i.e. liquified gases, made it possible to work with the separate vibronic components 6 10( A00) for benzene and 0-0 for toluene. The values of the equilibrium constant K were obtained by measuring the integrated intensities of the VCs of the 1Lb band of the complex and of the monomer. The enthalpy Wg  |Δ Hg| of the unexcited complex R 1XH⋯YR 2 formation was obtained from the temperature dependence of the K values; the enthalpy change Δ W due to the electronic excitation in YR 2 was obtained from the spectral shift due to the H-bond formation; therefore the enthalpy We  |Δ He| of formation of the excited complex R 1XH⋯(YE) 2* was calculated: We = Wg - Δ W. For both complexes in all the solvents used the following enthalpy values were obtained: Wg = 2.4±0.4 kcal mol -1; We = 1.6±0.5 kcal mol -1.

  7. Lunar surface cosmic ray experiment. [including solar flare studies

    NASA Technical Reports Server (NTRS)

    Price, P. B.

    1974-01-01

    The galactic cosmic ray and solar flare experiment on Apollo 16 is reported. The published papers presented describe the experiment, equipment, data processing techniques, and operational history. The principle findings include: (1) The composition of heavy ions in interplanetary space at energies between approximately 30 and 130 MeV/nucleon is the same, within experimental errors. (2) The ability of a Lexan stack to determine simultaneously the energy spectra of major elements from He up to Fe in the energy interval 0.2 to 30 MeV/nucleon revealed systematic changes in the composition of solar flare particles as a function of energy. (3) Heavy ions emitted in a solar flare appear to be completely stripped of electrons, and are not in charge equilibrium at the time of acceleration and releases from the sun.

  8. Effect of electron beam pulse width on time-of-flight spectra

    NASA Technical Reports Server (NTRS)

    Misakian, M.; Mumma, M. J.

    1974-01-01

    A simple but useful formula describing the effect of electron gun pulse width on the time of flight (TOF) spectra measured in translational spectroscopy experiments is developed. An approximately monoenergetic pulsed electrostatically focused electron beam traverses a scattering cell filled with a Maxwellian gas. Inelastic electron collisions with the gas produce metastable particles, ions, scattered electrons, and photons which then pass through a collimating slit system at right angles to the electron beam. TOF techniques are used to separate the photon signal from the metastable particle signal and to measure the TOF distribution of the metastable species.

  9. Mirroring of fast solar flare electrons on a downstream corotating interaction region

    NASA Technical Reports Server (NTRS)

    Anderson, K. A.; Sommers, J.; Lin, R. P.; Pick, M.; Chaizy, P.; Murphy, N.; Smith, E. J.; Phillips, J. L.

    1995-01-01

    We discuss an example of confinement of fast solar electrons by a discrete solar wind-interplanetary magnetic field structure on February 22, 1991. The structure is about 190,000 km in width and is clearly defined by changes in the direction of the magnetic field at the Ulysses spacecraft. This structure carries electrons moving toward the Sun as well as away from the Sun. A loss cone in the angular distribution of the fast electrons shows that mirroring, presumably magnetic, takes place downstream from the spacecraft. Following passage of this narrow structure, the return flux vanishes for 21 min after which time the mirroring resumes and persists for several hours. We identify the enhanced magnetic field region lying downstream from the Ulysses spacecraft that is responsible for the mirroring to be a corotating stream interaction region. Backstreaming suprathermal electron measurements by the Los Alamos National Laboratory plasma experiment on the Ulysses spacecraft support this interpretation.

  10. Mirroring of fast solar flare electrons on a downstream corotating interaction region

    SciTech Connect

    Anderson, K.A.; Sommers, J.; Lin, R.P.; Pick, M.; Chaizy, P.; Murphy, N.; Smith, E.J.; Phillips, J.L.

    1995-01-01

    The authors discuss an example of confinement of fast solar electrons by a discrete solar wind-interplanetary magnetic field structure on February 22, 1991. The structure is about 190,000 km in width and is clearly defined by changes in the direction of the magnetic field at the Ulysses spacecraft. This structure carries electrons moving toward the Sun as well as away from the Sun. A loss cone in the angular distribution of the fast electrons shows that mirroring, presumably magnetic, takes place downstream from the spacecraft. Following passage of this narrow structure, the return flux vanishes for 21 min after which time the mirroring resumes and persists for several hours. The authors identify the enhanced magnetic field region lying downstream from the Ulysses spacecraft that is responsible for the mirroring to be a corotating stream interaction region. Backstreaming suprathermal electron measurements by the Los Alamos National Laboratory plasma experiment on the Ulysses spacecraft support this interpretation. 12 refs., 9 figs.

  11. Complex time dependent wave packet technique for thermal equilibrium systems - Electronic spectra

    NASA Technical Reports Server (NTRS)

    Reimers, J. R.; Wilson, K. R.; Heller, E. J.

    1983-01-01

    A time dependent wave packet method is presented for the rapid calculation of the properties of systems in thermal equilibrium and is applied, as an illustration, to electronic spectra. The thawed Gaussian approximation to quantum wave packet dynamics combined with evaluation of the density matrix operator by imaginary time propagation is shown to give exact electronic spectra for harmonic potentials and excellent results for both a Morse potential and for the band contours of the three transitions of the visible electronic absorption spectrum of the iodine molecule. The method, in principle, can be extended to many atoms (e.g., condensed phases) and to other properties (e.g., infrared and Raman spectra and thermodynamic variables).

  12. Particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Forman, M. A.

    1987-01-01

    The most direct signatures of particle acceleration in flares are energetic particles detected in interplanetary space and in the Earth atmosphere, and gamma rays, neutrons, hard X-rays, and radio emissions produced by the energetic particles in the solar atmosphere. The stochastic and shock acceleration theories in flares are reviewed and the implications of observations on particle energy spectra, particle confinement and escape, multiple acceleration phases, particle anistropies, and solar atmospheric abundances are discussed.

  13. FLARING PATTERNS IN BLAZARS

    SciTech Connect

    Paggi, A.; Cavaliere, A.; Tavani, M.; Vittorini, V.; D'Ammando, F.

    2011-08-01

    Blazars radiate from relativistic jets launched by a supermassive black hole along our line of sight; the subclass of flat spectrum radio quasars exhibits broad emission lines, a telltale sign of a gas-rich environment and high accretion rate, contrary to the other subclass of the BL Lacertae objects. We show that this dichotomy of the sources in physical properties is enhanced in their flaring activity. The BL Lac flares yielded spectral evidence of being driven by further acceleration of highly relativistic electrons in the jet. Here, we discuss spectral fits of multi-{lambda} data concerning strong flares of the two flat spectrum radio quasars 3C 454.3 and 3C 279 recently detected in {gamma}-rays by the AGILE and Fermi satellites. We find that optimal spectral fits are provided by external Compton radiation enhanced by increasing production of thermal seed photons by growing accretion. We find such flares to trace patterns on the jet-power-electron-energy plane that diverge from those followed by flaring BL Lac objects and discuss why these occur.

  14. Unfolding linac photon spectra and incident electron energies from experimental transmission data, with direct independent validation

    SciTech Connect

    Ali, E. S. M.; McEwen, M. R.; Rogers, D. W. O.

    2012-11-15

    Purpose: In a recent computational study, an improved physics-based approach was proposed for unfolding linac photon spectra and incident electron energies from transmission data. In this approach, energy differentiation is improved by simultaneously using transmission data for multiple attenuators and detectors, and the unfolding robustness is improved by using a four-parameter functional form to describe the photon spectrum. The purpose of the current study is to validate this approach experimentally, and to demonstrate its application on a typical clinical linac. Methods: The validation makes use of the recent transmission measurements performed on the Vickers research linac of National Research Council Canada. For this linac, the photon spectra were previously measured using a NaI detector, and the incident electron parameters are independently known. The transmission data are for eight beams in the range 10-30 MV using thick Be, Al and Pb bremsstrahlung targets. To demonstrate the approach on a typical clinical linac, new measurements are performed on an Elekta Precise linac for 6, 10 and 25 MV beams. The different experimental setups are modeled using EGSnrc, with the newly added photonuclear attenuation included. Results: For the validation on the research linac, the 95% confidence bounds of the unfolded spectra fall within the noise of the NaI data. The unfolded spectra agree with the EGSnrc spectra (calculated using independently known electron parameters) with RMS energy fluence deviations of 4.5%. The accuracy of unfolding the incident electron energy is shown to be {approx}3%. A transmission cutoff of only 10% is suitable for accurate unfolding, provided that the other components of the proposed approach are implemented. For the demonstration on a clinical linac, the unfolded incident electron energies and their 68% confidence bounds for the 6, 10 and 25 MV beams are 6.1 {+-} 0.1, 9.3 {+-} 0.1, and 19.3 {+-} 0.2 MeV, respectively. The unfolded spectra

  15. Theoretical electronic absorption and natural circular dichroism spectra of (-)-trans-cyclooctene

    NASA Astrophysics Data System (ADS)

    Pedersen, Thomas Bondo; Koch, Henrik

    2000-02-01

    Using the random phase approximation and coupled cluster singles and doubles linear response theory in conjunction with two basis sets of augmented double-zeta quality and two nuclear geometries, we have calculated electronic absorption and natural circular dichroism spectra of (-)-trans-cyclooctene. We present a density functional theory optimized nuclear geometry whose ground state electric dipole moment and harmonic vibrational spectrum compare well with experimental data. The coupled cluster results obtained with this nuclear geometry are in good agreement with experimental electronic spectra, although the original interpretation of the most intense low-lying band as a π→π* transition is contradicted.

  16. The gamma-ray spectra of halocarbons in positron-electron annihilation process

    NASA Astrophysics Data System (ADS)

    Ma, X. G.; Zhu, Y. H.; Liu, Y.

    2015-10-01

    The gamma-ray spectra of the positron annihilation process in methane CH4 and its fully substituent halocarbons CF4, CCl4, and CBr4 have been studied. The theoretical predictions of the inner valence electrons agree well with the experimental measurements for all these molecules. That the outermost s electrons in carbon or halogen atoms dominate the gamma-ray spectra has been confirmed for the first time. The positrophilic site has also been found in these molecules and understanding of annihilation processes in molecules has been enhanced.

  17. Microplume model of spatial-yield spectra. [applying to electron gas degradation in molecular nitrogen gas

    NASA Technical Reports Server (NTRS)

    Green, A. E. S.; Singhal, R. P.

    1979-01-01

    An analytic representation for the spatial (radial and longitudinal) yield spectra is developed in terms of a model containing three simple 'microplumes'. The model is applied to electron energy degradation in molecular nitrogen gas for 0.1 to 5 keV incident electrons. From the nature of the cross section input to this model it is expected that the scaled spatial yield spectra for other gases will be quite similar. The model indicates that each excitation, ionization, etc. plume should have its individual spatial and energy dependence. Extensions and aeronomical and radiological applications of the model are discussed.

  18. Photoelectron spectra and electronic structure of nitrogen analogues of boron β-diketonates

    NASA Astrophysics Data System (ADS)

    Tikhonov, Sergey A.; Vovna, Vitaliy I.; Borisenko, Aleksandr V.

    2016-07-01

    The electronic structure of the valence levels of seven nitrogen-containing boron complexes was investigated using methods of ultraviolet photoelectron spectroscopy and density functional theory. The ionization energies of π- and σ-levels were obtained from photoelectron spectra. The electronic structure of nitrogen-containing compounds was compared with the electronic structure of β-diketonates. It was shown the influence of various substituents on carbon and nitrogen atoms of six-membered ring on the electronic structure of complexes. The changes in the electronic structure after the substitution of atoms in condensed cycles have been identified. In order to compare the experimental vertical ionization energies IEi with Kohn-Sham orbital energies εi we used the analogue of Koopmans theorem and average amendment to the orbital energy of the electrons (δbari). For 26 electronic levels of seven studied complexes, the calculated values are in good accordance with experimental energy intervals between electron levels.

  19. Electronic structure of some adenosine receptor antagonists. III. Quantitative investigation of the electronic absorption spectra of alkyl xanthines

    NASA Astrophysics Data System (ADS)

    Moustafa, H.; Shalaby, Samia H.; El-sawy, K. M.; Hilal, Rifaat

    2002-07-01

    Quantitative and comparative investigation of the electronic absorption spectra of theophylline, caffeine and their derivatives is reported. The spectra of theophylline, caffeine and theobromine were compared to establish the predominant tautomeric species in solution. This comparison, analysis of solvent effects and assignments of the observed transitions via MO computations indicate the exits of only one tautomeric species in solution that is the N7 form. A low-lying triplet state was identified which corresponds to a HOMO-LUMO transition. This relatively long-lived T 1 state is always less polar than the ground state and may very well underlie the photochemical reactivity of alkyl xanthines. Substituents of different electron donating or withdrawing strengths and solvent effects are investigated and analyzed. The present analysis is facilitated via computer deconvolution of the observed spectra and MO computation.

  20. Quantitative analysis of flare accelerated electrons through their hard X-ray and microwave radiation

    NASA Technical Reports Server (NTRS)

    Klein, K. L.; Trottet, G.

    1985-01-01

    Hard X-ray and microwave modelling that takes into account the temporal evolution of the electron spectrum as well as the inhomogeneity of the magnetic field and the ambient medium in the radio source is presented. This method is illustrated for the June 29 1980 10:41 UT event. The implication on the process of acceleration/injection is discussed.

  1. The First Very Local Interstellar Spectra for Galactic Protons, Helium and Electrons

    NASA Astrophysics Data System (ADS)

    Potgieter, M. S.; Vos, E. E.; Nndanganeni, R. R.

    2014-06-01

    Low-energy galactic electrons (1-300 MeV) are significantly modulated, almost extraordinary, in the heliosheath in contrast to the rest of the heliosphere, indicating that modulation conditions in the heliosheath are quite different for these particles. Low-energy protons and helium (1-100 MeV/nuc), on the other hand, are dominated by the anomalous component which originates inside the inner heliosheath so that the very local interstellar spectra for these particles had been properly concealed until recently. Basic mechanisms responsible for these effects are been studied with comprehensive numerical models for the transport of these particles, from the modulation boundary, through the heliosheath, across the solar wind termination shock, up to Earth. Together with measurements made by the two Voyager spacecraft, now with Voyager 1 beyond the heliopause, possibly entering the very local interstellar medium, it is possible to determine heliopause spectra at these low energies for the first time. Together with PAMELA spectra observed at Earth, these heliopause spectra can be determined accurately up to 50 GeV. Such spectra should be considered as the lowest possible very local interstellar spectra for galactic electrons, protons and helium, and of great relevance to solar modulation and galactic propagation studies.

  2. Gamma-ray spectra of hexane (C6H14) in positron-electron annihilation process

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoguang; Wang, Feng

    2013-08-01

    Theoretical gamma-ray spectra of molecule hexane have been calculated and compared with the experimental results in both gas (Iwata et al., 1997a) and liquid (Kerr et al., 1965) phases. The present study reveals that in gas phase not all valence electrons of hexane contribute the same degree in the electron-positron annihilation of hexane. The electrons which dominate the positron-electron annihilation of molecules are called positrophilic electrons. The positrophilic electrons are predominately found to involve the electrons on the lowest occupied valence orbital (LOVO) of a free molecule in gas phase. When hexane is confined in liquid phase, however, the intermolecular interactions ultimately eliminate the free molecular orientation and selectivity for the positrophilic electrons in the gas phase. As a result, the gamma-ray spectra of hexane become an "averaged" contribution from all valence electrons, which is again in agreement with liquid phase measurement. The roles of valence electrons in annihilation process for gas and liquid phases of hexane have been recognized for the first time in the present study.

  3. Plasma scale-length effects on electron energy spectra in high-irradiance laser plasmas.

    PubMed

    Culfa, O; Tallents, G J; Rossall, A K; Wagenaars, E; Ridgers, C P; Murphy, C D; Dance, R J; Gray, R J; McKenna, P; Brown, C D R; James, S F; Hoarty, D J; Booth, N; Robinson, A P L; Lancaster, K L; Pikuz, S A; Faenov, A Ya; Kampfer, T; Schulze, K S; Uschmann, I; Woolsey, N C

    2016-04-01

    An analysis of an electron spectrometer used to characterize fast electrons generated by ultraintense (10^{20}Wcm^{-2}) laser interaction with a preformed plasma of scale length measured by shadowgraphy is presented. The effects of fringing magnetic fields on the electron spectral measurements and the accuracy of density scale-length measurements are evaluated. 2D EPOCH PIC code simulations are found to be in agreement with measurements of the electron energy spectra showing that laser filamentation in plasma preformed by a prepulse is important with longer plasma scale lengths (>8 μm). PMID:27176413

  4. Solar flare model atmospheres

    NASA Technical Reports Server (NTRS)

    Hawley, Suzanne L.; Fisher, George H.

    1993-01-01

    Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

  5. Simulation of femtosecond two-dimensional electronic spectra of conical intersections

    SciTech Connect

    Krčmář, Jindřich; Gelin, Maxim F.; Domcke, Wolfgang

    2015-08-21

    We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed.

  6. High-cadence and High-resolution Hα Imaging Spectroscopy of a Circular Flare's Remote Ribbon with IBIS

    NASA Astrophysics Data System (ADS)

    Deng, Na; Tritschler, Alexandra; Jing, Ju; Chen, Xin; Liu, Chang; Reardon, Kevin; Denker, Carsten; Xu, Yan; Wang, Haimin

    2013-06-01

    We present an unprecedented high-resolution Hα imaging spectroscopic observation of a C4.1 flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76 cm Dunn Solar Telescope on 2011 October 22 in the active region NOAA 11324. Such a two-dimensional spectroscopic observation covering the entire evolution of a flare ribbon with high spatial (0.''1 pixel-1 image scale), cadence (4.8 s), and spectral (0.1 Å step size) resolution is rarely reported. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in three-dimensional fan-spine reconnection but so far has been rarely studied. During the flare impulsive phase, we define "core" and "halo" structures in the observed ribbon based on IBIS narrowband images in the Hα line wing and line center. Examining the Hα emission spectra averaged in the flare core and halo areas, we find that only those from the flare cores show typical nonthermal electron beam heating characteristics that have been revealed by previous theoretical simulations and observations of flaring Hα line profiles. These characteristics include broad and centrally reversed emission spectra, excess emission in the red wing with regard to the blue wing (i.e., red asymmetry), and redshifted bisectors of the emission spectra. We also observe rather quick timescales for the heating (~30 s) and cooling (~14-33 s) in the flare core locations. Therefore, we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution. The flare cores show two-stage motion (a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon) during the two impulsive phases of the flare. Some cores jump quickly (30 km s-1) between discrete

  7. High-cadence and high-resolution Hα imaging spectroscopy of a circular flare's remote ribbon with IBIS

    SciTech Connect

    Deng, Na; Jing, Ju; Chen, Xin; Liu, Chang; Xu, Yan; Wang, Haimin; Tritschler, Alexandra; Reardon, Kevin; Denker, Carsten

    2013-06-01

    We present an unprecedented high-resolution Hα imaging spectroscopic observation of a C4.1 flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76 cm Dunn Solar Telescope on 2011 October 22 in the active region NOAA 11324. Such a two-dimensional spectroscopic observation covering the entire evolution of a flare ribbon with high spatial (0.''1 pixel{sup –1} image scale), cadence (4.8 s), and spectral (0.1 Å step size) resolution is rarely reported. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in three-dimensional fan-spine reconnection but so far has been rarely studied. During the flare impulsive phase, we define 'core' and 'halo' structures in the observed ribbon based on IBIS narrowband images in the Hα line wing and line center. Examining the Hα emission spectra averaged in the flare core and halo areas, we find that only those from the flare cores show typical nonthermal electron beam heating characteristics that have been revealed by previous theoretical simulations and observations of flaring Hα line profiles. These characteristics include broad and centrally reversed emission spectra, excess emission in the red wing with regard to the blue wing (i.e., red asymmetry), and redshifted bisectors of the emission spectra. We also observe rather quick timescales for the heating (∼30 s) and cooling (∼14-33 s) in the flare core locations. Therefore, we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution. The flare cores show two-stage motion (a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon) during the two impulsive phases of the flare. Some cores jump quickly (30 km s{sup –1

  8. Spectral Analysis on Solar Flares with an Emission > 300 keV

    NASA Astrophysics Data System (ADS)

    Vargas, R.; Connaughton, V.

    2013-12-01

    The continuum gamma-ray emission from solar flares is caused when a population of electrons is accelerated to relativistic speeds and interacts with the solar plasma. However, it has been theorized that the gamma-ray emission from some brighter flares comes from two populations of electrons. Using the Gamma-Ray Burst Monitor (GBM), we studied the gamma-ray emission spectra of solar flares and paid special attention to the solar flares that showed emission above 300 keV. We found that the emission above 300 keV was better fit with a broken power-law than a single power-law, evidence that the gamma-ray emission from certain solar flares involved two populations of electrons. Specifically, our best model involved a broken power law that had a steeper slope before the break in energy than after. We studied the spectral parameters as a function of time during the period of the high-energy emission. We also found that solar flares with emission above 300 keV form a small subset (~4%) of flares that trigger GBM above 20 keV. One of the flares with an emission greater than 300 keV was fitted with a Broken Power Law model. Only data from the BGO detector was used in making the plots. Various parameters of the fit have been plotted vs. time with the top two graphs representing the light curves of the flare from different detectors (BGO-0 and NaI-4). A spectral fit for bn100612038 for the time interval of [45s-50s] using only the BGO (0) detector file. Data from this fit was used in creating the other plots.

  9. Propagation anisotropies of solar flare protons and electrons at low energies in interplanetary space.

    NASA Technical Reports Server (NTRS)

    Pyle, K. R.

    1973-01-01

    Flux anisotropies in interplanetary space were investigated for protons with E greater than 0.66 MeV and electrons with E greater than 400 keV. Data were taken from the University of Chicago charged-particle telescope aboard the deep-space probe Pioneer 7 and from the Goddard Space Flight Center magnetometer aboard the same spacecraft. Flux anisotropies lying to the east of the average interplanetary magnetic field direction were first reported by McCracken et al. (1971), late in a solar particle event, for proton energies greater than 7.5 MeV. This work extends this investigation to much lower proton energies, studies the proton and electron anisotropies during both early and late phases of a particle event, and makes use of detailed magnetic field data. The investigation consists of two parts, a study of many periods taken at random during solar events, for both protons and electrons, and a detailed analysis of one period, early in an event, during which the magnetic field was near the solar direction.

  10. Comparison between Monte Carlo and experimental aluminum and silicon electron energy loss spectra

    NASA Astrophysics Data System (ADS)

    Dapor, Maurizio; Calliari, Lucia; Scarduelli, Giorgina

    2011-07-01

    A Monte Carlo (MC) simulation is described and used to calculate the energy distribution spectra of backscattered electrons from Al and Si. For the simulations, elastic scattering cross sections are calculated by numerically solving the Dirac equation in a central field. Inelastic scattering cross sections are computed within the dielectric response theory developed by Ritchie, and by Tung et al. Extension from the optical case to non-zero momentum transfer is done according to Ritchie and Howie. To evaluate surface and bulk contributions to the spectra, the Monte Carlo model treats the surface excitations according to the Werner differential surface and volume excitation probability theory. The Monte Carlo calculations are compared with the experimental reflection electron energy loss (REEL) spectra acquired in our laboratory.

  11. Calculation of Electronic Absorption Spectra with Account of Thermal Geometry Fluctuations

    NASA Astrophysics Data System (ADS)

    Guzha, Maris V.; Svitenkov, Andrew I.

    2016-08-01

    An influence of thermal fluctuations of molecule's geometry on calculated electronic-absorption Vis/Uv spectra is considered. Paper presents the quantum chemical modeling of the electronic-absorption spectra for the collection of graphene samples (44, 56, 60, 68 atoms). The calculations were performed by time dependent density functional theory (TDDFT) method in combination with molecular dynamics (MD) simulation at T=300 K. The noticeable changing of spectra relative to single point TDDFT calculation was discovered for two of four structures. We associate achieved results with perturbation of hydrogen and carbon atoms on the edges of the structures. We believe that suggested methodology will be useful in application engineering researches of novel molecules and molecular complexes.

  12. Electron spectra line shape analysis of highly oriented pyrolytic graphite and nanocrystalline diamond.

    PubMed

    Lesiak, Beata; Zemek, Josef; Houdkova, Jana; Kromka, Alexander; Józwik, Adam

    2010-01-01

    The X-ray excited Auger electron spectroscopy (XAES), X-ray photoelectron spectroscopy (XPS) and elastic peak electron spectroscopy (EPES) methods were applied in investigating samples of nanocrystalline diamond and highly oriented pyrolytic graphite of various C sp(2)/sp(3) ratios, crystallinity conditions and grain sizes. The composition at the surface was estimated from the XPS. The C sp(2)/sp(3) ratio was evaluated from the width of the XAES first derivative C KLL spectra and from fitting of XPS C 1s spectra into components. The pattern recognition (PR) method applied for analyzing the spectra line shapes exhibited high accuracy in distinguishing different carbon materials. The PR method was found to be a potentially useful approach for identification, especially important for technological applications in fields of materials engineering and for controlling the chemical reaction products during synthesis.

  13. Analysis of electron spin resonance spectra of irradiated gingers: Organic radical components derived from carbohydrates

    NASA Astrophysics Data System (ADS)

    Yamaoki, Rumi; Kimura, Shojiro; Ohta, Masatoshi

    2010-04-01

    Electron spin resonance (ESR) spectral characterizations of gingers irradiated with electron beam were studied. Complex asymmetrical spectra (near g=2.005) with major spectral components (line width=2.4 mT) and minor signals (at 6 mT apart) were observed in irradiated gingers. The spectral intensity decreased considerably 30 days after irradiation, and continued to decrease steadily thereafter. The spectra simulated on the basis of characteristics of free radical components derived from carbohydrates in gingers are in good agreement with the observed spectra. Analysis showed that shortly after irradiation the major radical components of gingers were composed of radical species derived from amylose and cellulose, and the amylose radicals subsequently decreased considerably. At 30 days after irradiation, the major radical components of gingers were composed of radical species derived from cellulose, glucose, fructose or sucrose.

  14. First principles calculation of electron ionization mass spectra for selected organic drug molecules.

    PubMed

    Bauer, Christoph Alexander; Grimme, Stefan

    2014-11-21

    This study presents a showcase for the novel Quantum Chemistry Electron Ionization Mass Spectrometry (QCEIMS) method on five FDA-approved drugs. The method allows a first-principles electronic structure-based prediction of EI mass spectra in principle for any molecule. The systems in this case study are organic substances of nominal masses between 404 and 853 atomic mass units and cover a wide range of functional groups and organic molecular structure motifs. The results demonstrate the widespread applicability of the QCEIMS method for the unbiased computation of EI mass spectra even for larger molecules. Its strengths compared to standard (static) or database driven approaches in such cases are highlighted. Weak points regarding the required computation times or the approximate character of the employed QC methods are also discussed. We propose QCEIMS as a viable and robust way of predicting EI mass spectra for sizeable organic molecules relevant to medicinal and pharmaceutical chemistry.

  15. BATSE Solar Flare Spectroscopy

    NASA Technical Reports Server (NTRS)

    Schwartz, R. A.

    1998-01-01

    This final report describes the progress originally proposed: (1) the continued improvement of a software and database environment capable of supporting all users of BATSE solar data as well as providing scientific expertise and effort to the BATSE solar community; (2) the continued participation with the PI team and other guest investigators in the detailed analysis of the BATSE detectors' response at low energies; (3) using spectroscopic techniques to fully exploit the potential of electron time-of-flight studies; and, (4) a full search for flare gamma-ray line emission at 2.2 MeV from all GOES X-class flares observed with BATSE.

  16. Spectral study of suggested Apollo sites. [proposals for financial support and the electronic spectra of pyroxenes

    NASA Technical Reports Server (NTRS)

    Mccord, T. B.

    1973-01-01

    The spectrophotometry (0.3 to 1.1 microns) of visited and proposed Apollo landing sites is presented along with proposals for financial support of the spectral study. The electronic spectra of pyroxenes is investigated along with an interpretation of telescopic spectral reflectivity curves of the moon. Reprints of published articles related to these studies are included.

  17. Effects of Electronic-State-Dependent Solute Polarizability: Application to Solute-Pump/Solvent-Probe Spectra.

    PubMed

    Sun, Xiang; Ladanyi, Branka M; Stratt, Richard M

    2015-07-23

    Experimental studies of solvation dynamics in liquids invariably ask how changing a solute from its electronic ground state to an electronically excited state affects a solution's dynamics. With traditional time-dependent-fluorescence experiments, that means looking for the dynamical consequences of the concomitant change in solute-solvent potential energy. But if one follows the shift in the dynamics through its effects on the macroscopic polarizability, as recent solute-pump/solvent-probe spectra do, there is another effect of the electronic excitation that should be considered: the jump in the solute's own polarizability. We examine the spectroscopic consequences of this solute polarizability change in the classic example of the solvation dye coumarin 153 dissolved in acetonitrile. After demonstrating that standard quantum chemical methods can be used to construct accurate multisite models for the polarizabilities of ground- and excited-state solvation dyes, we show via simulation that this polarizability change acts as a contrast agent, significantly enhancing the observable differences in optical-Kerr spectra between ground- and excited-state solutions. A comparison of our results with experimental solute-pump/solvent-probe spectra supports our interpretation and modeling of this spectroscopy. We predict, in particular, that solute-pump/solvent-probe spectra should be sensitive to changes in both the solvent dynamics near the solute and the electronic-state-dependence of the solute's own rotational dynamics. PMID:25299940

  18. Two-dimensional spectra of electron collisions with acrylonitrile and methacrylonitrile reveal nuclear dynamics

    SciTech Connect

    Regeta, K. Allan, M.

    2015-05-14

    Detailed experimental information on the motion of a nuclear packet on a complex (resonant) anion potential surface is obtained by measuring 2-dimensional (2D) electron energy loss spectra. The cross section is plotted as a function of incident electron energy, which determines which resonant anion state is populated, i.e., along which normal coordinate the wave packet is launched, and of the electron energy loss, which reveals into which final states each specific resonant state decays. The 2D spectra are presented for acrylonitrile and methacrylonitrile, at the incident energy range 0.095-1.0 eV, where the incoming electron is temporarily captured in the lowest π{sup ∗} orbital. The 2D spectra reveal selectivity patterns with respect to which vibrations are excited in the attachment and de-excited in the detachment. Further insight is gained by recording 1D spectra measured along horizontal, vertical, and diagonal cuts of the 2D spectrum. The methyl group in methacrylonitrile increases the resonance width 7 times. This converts the sharp resonances of acrylonitrile into boomerang structures but preserves the essence of the selectivity patterns. Selectivity of vibrational excitation by higher-lying shape resonances up to 8 eV is also reported.

  19. Double power-law spectra of energetic electrons in the Earth magnetotail

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Hoshino, M.; Lutsenko, V. N.; Petrukovich, A. A.; Imada, S.; Zelenyi, L. M.

    2013-01-01

    In this paper, we consider electron acceleration in the vicinity of X-line and corresponding formation of energy spectra. We develop an analytical model including the effect of the electron trapping by electrostatic fields and surfing acceleration. Speiser, Fermi and betatron mechanisms of acceleration are also taken into account. Analytical estimates are verified by the numerical integration of electron trajectories. The surfing mechanism and adiabatic heating are responsible for the formation of the double power-law spectrum in agreement with the previous studies. The energy of the spectrum knee is about ~150 keV for typical conditions of the Earth magnetotail. We compare theoretical results with the spacecraft observations of electron double power-law spectra in the magnetotail and demonstrate that the theory is able to describe typical energy of the spectra knee. We also estimate the role of relativistic effects and magnetic field fluctuations on the electron acceleration: the acceleration is more stable for relativistic electrons, while fluctuations of the magnetic field cannot significantly decrease the gained energy for typical magnetospheric conditions.

  20. Evolution and magnetic topology of the M 1.0 flare of October 22, 2002

    NASA Astrophysics Data System (ADS)

    Berlicki, A.; Schmieder, B.; Vilmer, N.; Aulanier, G.; Del Zanna, G.

    2004-09-01

    In this paper we analyse an M 1.0 confined flare observed mainly during its gradual phase. We use the data taken during a coordinated observational campaign between ground based instruments (THEMIS and VTT) and space observatories (SoHO/CDS and MDI, TRACE and RHESSI). We use these multi-wavelength observations to study the morphology and evolution of the flare, to analyse its gradual phase and to understand the role of various heating mechanisms. During the flare, RHESSI observed emission only within the 3-25 keV spectral range. The RHESSI spectra indicate that the emission of the flare was mainly of thermal origin with a small non-thermal component observed between 10 and 20 keV. Nevertheless, the energy contained in the non-thermal electrons is negligible compared to the thermal energy of the flaring plasma. The temperature of plasma obtained from the fitting of the RHESSI X-ray spectra was between 8.5 and 14 MK. The lower temperature limit is typical for a plasma contained in post flare loops observed in X-rays. Higher temperatures were observed during a secondary peak of emission corresponding to a small impulsive event. The SoHO/CDS observations performed in EUV Fe XIX line also confirm the presence of a hot plasma at temperatures similar to those obtained from RHESSI spectra. The EUV structures were located at the same place as RHESSI X-ray emission. The magnetic topology analysis of the AR coming from a linear force-free field extrapolation explains the observed features of the gradual phase of the flare i.e. the asymmetry of the ribbons and their fast propagation. The combination of the multi-wavelength observations with the magnetic model further suggests that the onset of the flare would be due to the reconnection of an emerging flux in a sheared magnetic configuration.

  1. COMPARISON OF PHOTOMETRIC VARIABILITY BEFORE AND AFTER STELLAR FLARES

    SciTech Connect

    Karoff, C.

    2014-01-20

    The energy in the solar acoustic spectrum is known to be correlated with flares, but it is not known if the same is true for stellar flares. In order to answer this question, we have analyzed 73 flares in 39 solar-like stars. These flares were identified in the 854 solar-like stars observed by the Kepler spacecraft that have stellar parameters measured with asteroseismology. Though we were not able to identify a statistically significant enhancement of the energy in the high-frequency part of the post-flare acoustic spectra compared to the pre-flare spectra of these stars, we did identify a larger variability between the energy in the high-frequency part of the post- and pre-flare acoustic spectra compared to spectra taken at random times.

  2. On the fine structure of spectra of the inelastic-electron-scattering cross section and the Si surface parameter

    SciTech Connect

    Parshin, A. S. Igumenov, A. Yu.; Mikhlin, Yu. L.; Pchelyakov, O. P.; Nikiforov, A. I.; Timofeev, V. A.

    2015-04-15

    Reflection electron-energy loss spectra are obtained for a series of Si samples with different crystallographic orientations, prepared under different technological conditions. Using the experimental spectra, the electron energy loss dependences of the product of the mean inelastic free path and differential inelastic electron scattering cross section are calculated. A new technique is suggested for analyzing the spectra of inelastic electron scattering cross section by simulating experimental spectra with the use of the three-parameter Tougaard universal cross section functions. The results of the simulation are used to determine the nature of loss peaks and to calculate the surface parameter.

  3. Vibrationally high-resolved electronic spectra of MCl2 (M = C, Si, Ge, Sn, Pb) and photoelectron spectra of MCl2-

    NASA Astrophysics Data System (ADS)

    Ran, Yibin; Pang, Min; Shen, Wei; Li, Ming; He, Rongxing

    2016-10-01

    We systematically studied the vibrational-resolved electronic spectra of group IV dichlorides using the Franck-Condon approximation combined with the Duschinsky and Herzberg-Teller effects in harmonic and anharmonic frameworks (only the simulation of absorption spectra includes the anharmonicity). Calculated results showed that the band shapes of simulated spectra are in accordance with those of the corresponding experimental or theoretical ones. We found that the symmetric bend mode in progression of absorption is the most active one, whereas the main contributor in photoelectron spectra is the symmetric stretching mode. Moreover, the Duschinsky and anharmonic effects exert weak influence on the absorption spectra, except for PbCl2 molecule. The theoretical insights presented in this work are significant in understanding the photophysical properties of MCl2 (M = C, Si, Ge, Sn, Pb) and studying the Herzberg-Teller and the anharmonic effects on the absorption spectra of new dichlorides of this main group.

  4. SUB-THz RADIATION MECHANISMS IN SOLAR FLARES

    SciTech Connect

    Fleishman, Gregory D.; Kontar, Eduard P.

    2010-02-01

    Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well known and new in this context, and calculates a representative set of their spectra produced by (1) free-free emission, (2) GS emission, (3) synchrotron emission from relativistic positrons/electrons, (4) diffusive radiation, and (5) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.

  5. Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets

    SciTech Connect

    Pentlehner, D.; Slenczka, A.

    2015-01-07

    Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm{sup −1}) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.

  6. Pressure dependence of Hexanitrostilbene Raman/ electronic absorption spectra to validate DFT EOS

    NASA Astrophysics Data System (ADS)

    Farrow, Darcie; Alam, Kathleen; Martin, Laura; Fan, Hongyou; Kay, Jeffrey; Wixom, Ryan

    2015-06-01

    Due to its thermal stability and low vapor pressure, Hexanitrostilbene (HNS) is often used in high-temperature or vacuum applications as a detonator explosive or in mild detonating fuse. Toward improving the accuracy of the equation of state used in hydrodynamic simulations of the performance of HNS, we have measured the Raman and electronic absorption spectra of this material under static pressure in a diamond anvil cell. Density functional theory calculations were used to simulate the pressure dependence of the Raman/Electronic spectra along the Hugoniot and 300K isotherm for comparison and to aid in interpreting the data. We will discuss changes in the electronic structure of HNS under pressure, validation of a DFT predicted equation of state (EOS), and using this data as a basis for understanding future pulsed Raman measurements on dynamically compressed HNS samples.

  7. Simulation of High Resolution Vibrational and Electronic Spectra with a Multifrequency Virtual Spectrometer

    NASA Astrophysics Data System (ADS)

    Biczysko, Malgorzata; Bloino, Julien; Barone, Vincenzo

    2013-06-01

    Moving from the common practice of extracting numerical data from experiment to be compared with quantum mechanical (QM) results toward a direct vis-à-vis} comparison of experimental and simulated spectra would strongly reduce any arbitrariness in analysis of complex experimental outcomes and allow a proper account of the information connected to both position and shape of spectral bands. The development of such ``virtual ab initio spectrometers'' for a wide range of wavelengths has been one of our major research goals in the last years [1,2]. Recent methodological advances from our group allow simulation of optical (IR, Raman, UV-vis, etc.) spectra line-shapes for medium-to-large closed- and open-shell molecular systems. Vibrational spectra are computed including anharmonicities through perturbative corrections while electronic spectra line-shapes are simulated accounting for the vibrational structure. Well resolved and accurate theoretical spectra provide data as close as possible to the results directly available from experiment allowing to avoid ambiguities in analysis of the latter. Several examples illustrating interpretation, assignment or revision of experimental spectra for prototypes of bio-molecular systems (phenyl radical, glycine, thymine, pyrimidine, anisole dimer) will be presented. 1. V. Barone, A. Baiardi, M. Biczysko, J. Bloino, C. Cappelli, F. Lipparini Phys. Chem. Chem. Phys, 14, 12404, 2012 2. M. Biczysko, J. Bloino, G. Brancato, et al. Theor. Chem. Acc. 113, 1201, 2012

  8. A sodium atom in a large water cluster: Electron delocalization and infrared spectra

    NASA Astrophysics Data System (ADS)

    Cwiklik, Lukasz; Buck, Udo; Kulig, Waldemar; Kubisiak, Piotr; Jungwirth, Pavel

    2008-04-01

    Ab initio molecular dynamics simulations modeling low-energy collisions of a sodium atom with a cluster with more than 30 water molecules are presented. We follow the dynamics of the atom-cluster interaction and the delocalization of the valence electron of sodium together with the changes in the electron binding energy. This electron tends to be shared by the nascent sodium cation and the water cluster. IR spectra of the sodium-water cluster are both computationally and experimentally obtained, with a good agreement between the two approaches.

  9. Theoretical Study of the Electronic Spectra of a Polycyclic Aromatic Hydrocarbon, Naphthalene, and its Derivatives

    NASA Technical Reports Server (NTRS)

    Du, Ping; Salama, Farid; Loew, Gilda H.

    1993-01-01

    In order to preselect possible candidates for the origin of diffuse interstellar bands observed, semiempirical quantum mechanical method INDO/S was applied to the optical spectra of neutral, cationic, and anionic states of naphthalene and its hydrogen abstraction and addition derivatives. Comparison with experiment shows that the spectra of naphthalene and its ions were reliably predicted. The configuration interaction calculations with single-electron excitations provided reasonable excited state wavefunctions compared to ab initio calculations that included higher excitations. The degree of similarity of the predicted spectra of the hydrogen abstraction and derivatives to those of naphthalene and ions depends largely on the similarity of the it electron configurations. For the hydrogen addition derivatives, very little resemblance of the predicted spectra to naphthalene was found because of the disruption of the aromatic conjugation system. The relevance of these calculations to astrophysical issues is discussed within the context of these polycyclic aromatic hydrocarbon models. Comparing the calculated electronic energies to the Diffuse Interstellar Bands (DIBs), a list of possible candidates of naphthalene derivatives is established which provides selected candidates for a definitive test through laboratory studies.

  10. Infrared reflection spectra in contactless nondestructive measurements of the electron density and mobility in indium phosphide

    SciTech Connect

    Il'in, M.A.; Karasev, P.Yu.; Denisova, N.A.; Rezvov, A.V.; Tyurina, S.V.

    1988-07-01

    On the basis of numerical calculations and experimental studies we analyze the possibilities of measuring the electrophysical parameters of indium phosphide by means of infrared reflection spectra at wavelengths ranging from 5 to 200 /mu/m. We demonstrate that contactless nondestructive measurements of the electron density in the range 10/sup 16/-10/sup 20/ cm/sup /minus/3/ can be made with a relative error not exceeding 15%, and of mobility with a relative error not exceeding 25%. A nomogram method is presented for rapid conversion of data form infrared reflection spectra into the parameters being measured.

  11. FUV Continuum in Flare Kernels Observed by IRIS

    NASA Astrophysics Data System (ADS)

    Daw, Adrian N.; Kowalski, Adam; Allred, Joel C.; Cauzzi, Gianna

    2016-05-01

    Fits to Interface Region Imaging Spectrograph (IRIS) spectra observed from bright kernels during the impulsive phase of solar flares are providing long-sought constraints on the UV/white-light continuum emission. Results of fits of continua plus numerous atomic and molecular emission lines to IRIS far ultraviolet (FUV) spectra of bright kernels are presented. Constraints on beam energy and cross sectional area are provided by cotemporaneous RHESSI, FERMI, ROSA/DST, IRIS slit-jaw and SDO/AIA observations, allowing for comparison of the observed IRIS continuum to calculations of non-thermal electron beam heating using the RADYN radiative-hydrodynamic loop model.

  12. Correlation of electronic structures of three cyclic dipeptides with their photoemission spectra

    NASA Astrophysics Data System (ADS)

    Arachchilage, Anoja P. Wickrama; Wang, Feng; Feyer, Vitaliy; Plekan, Oksana; Prince, Kevin C.

    2010-11-01

    We have investigated the electronic structure of three cyclic dipeptides: cyclo(Glycyl-Glycyl) (cGG), cyclo(Leucyl-Prolyl) (cLP), and cyclo(Phenylalanyl-Prolyl) (cPP). These compounds are biologically active and cLP and cPP are derived from cGG (also known as diketopiperazine), by the addition of the respective functional groups of the amino acids, namely, phenyl, alkyl or a fused pyrrolidine ring (proline). Experimental valence and core level spectra have been interpreted in the light of theoretical calculations to identify the basic chemical properties associated with the central ring, and with the additional functional groups in cLP and cPP. The theoretically simulated spectra of all three cyclic dipeptides in both valence and core spaces agreed reasonably well with the experimental spectra. The three molecules displayed similarities in their core spectra, suggesting that the diketopiperazine structure plays an important role in determining the inner shell spectrum. The experimental C 1s spectra of cLP and cPP are analogous but differ from cGG due to the side chains attached to the diketopiperazine structure. Single spectral peaks in the N 1s (and O 1s) spectra of the dipeptides indicate that the chemical environment of the nitrogen atoms (and oxygen atoms) are very similar, although they show a small splitting in the simulated spectra of cPL and cPP, due to the reduction of their point group symmetry. Valence band spectra of the three dipeptides in the frontier orbital region of 9-11 eV exhibit similarities; however theoretical analysis shows that significant changes occur due to the involvement of the side chain in the frontier orbitals of cPP, while lesser changes are found for cLP.

  13. Energy-dependent timing of thermal emission in solar flares

    NASA Astrophysics Data System (ADS)

    Jain, Rajmal; Rajpurohit, Arvind; Awasthi, Arun; Aschwanden, Markus

    A study of thermal emission in solar flares using high-resolution X-ray spectra observed by the Si detector onboard "Solar X-ray Spectrometer" (SOXS) has been conducted. The SOXS onboard GSAT-2 Indian spacecraft was launched by GSLV-D2 rocket on 08 May 2003. With this we investigate the energy dependent timing of thermal emission in solar flares. Firstly we model the spectral-temporal evolution of the X-ray flux F(e,t) assuming multi-temperature plasma governed by thermal conduction cooling. This model is found in agreement with the temperature and emission measure derived from the fitting of the spectra observed by the Si detector. We investigate 10 M-class flares and found that the emission in the energy range e=6 -20 keV is dominated by temperatures T=15 -50 MK while the power-law index (gamma) of the thermal spectrum varies over 2.7 -4.3. The temperature-dependent cooling time varies between 22 and 310 s. The electron density (ne) obtained for the flares under investigation ranges between 0.03 and 5X1011 cm-3 suggests that conduction cooling of thermal X-ray plasma dominates over radiative cooling in the initial phase of the flare. The current study also provides an alternative method for separating thermal from non-thermal spectra, which enables us to measure the break-energy point to be varying between 17 and 220.7 keV.

  14. THE SOLAR FLARE IRON ABUNDANCE

    SciTech Connect

    Phillips, K. J. H.; Dennis, B. R. E-mail: Brian.R.Dennis@nasa.gov

    2012-03-20

    The abundance of iron is measured from emission line complexes at 6.65 keV (Fe line) and 8 keV (Fe/Ni line) in RHESSI X-ray spectra during solar flares. Spectra during long-duration flares with steady declines were selected, with an isothermal assumption and improved data analysis methods over previous work. Two spectral fitting models give comparable results, viz., an iron abundance that is lower than previous coronal values but higher than photospheric values. In the preferred method, the estimated Fe abundance is A(Fe) = 7.91 {+-} 0.10 (on a logarithmic scale, with A(H) = 12) or 2.6 {+-} 0.6 times the photospheric Fe abundance. Our estimate is based on a detailed analysis of 1898 spectra taken during 20 flares. No variation from flare to flare is indicated. This argues for a fractionation mechanism similar to quiet-Sun plasma. The new value of A(Fe) has important implications for radiation loss curves, which are estimated.

  15. Photon-deficient Compton scattering by nonthermal electrons - Comparison with gamma-ray burst spectra

    NASA Technical Reports Server (NTRS)

    Zdziarski, Andrzej A.; Lamb, Don Q.

    1986-01-01

    The model of gamma-ray-burst spectra proposed by Zdziarski and Lamb (1986, 1987) is reviewed and compared with observed spectra. In the model, the spectrum arises from multiple Compton scatterings in a nonthermal source with a deficit of soft photons. The steady-state electron distribution in such a source is a nonthermal power law that joins at low energies onto a thermal distribution that may be either optically thick or thin. Both cases lead naturally to a two-component spectrum with a photon-energy index in the X-ray spectrum which is much less than one and a photon-energy index in the gamma-ray spectrum which is larger than the X-ray photon-energy index. Fits to the observed gamma-ray-burst spectra (where data exist for both X-ray and gamma-ray energies) show good agreement with the model.

  16. Theoretical Study of FH2– Electron Photodetachment Spectra on New Ab Initio Potential Energy Surfaces.

    PubMed

    Yu, Dequan; Chen, Jun; Cong, Shulin; Sun, Zhigang

    2015-12-17

    The FH2– anion has a stable structure that resembles a configuration in the vicinity of the transition state for neutral reaction F + H2 → HF + H. Electron photodetachment spectra of the FH2– anion reveal the neutral reaction dynamics in the critical transition-state region. Accurate quantum dynamics simulations of the photodetachment spectra using highly accurate new ab initio potential energy surfaces for both anionic and neutral FH2 are performed and compared with all available experimental results. The results provide reliable interpretations for the experimental observations of FH2– photoelectron detachment and reveal a detailed picture of the molecular dynamics around the transition state of the F + H2 reaction. The latest high-resolution photoelectron detachment spectra [Kim et al. Science, 2015, 349, 510-513] confirm the high accuracy of our new potential energy surface for describing the resonance-enhanced reactivity of the neutral F + H2 reaction.

  17. The Properties and Origins of Resonant Patterns in the Energy Spectra of the Inner Electron Belt

    NASA Astrophysics Data System (ADS)

    Ukhorskiy, A. Y.; Sitnov, M. I.; Mitchell, D. G.; Takahashi, K.; Lanzerotti, L. J.

    2013-12-01

    The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on the Van Allen Probes mission provides electron and ion measurements from ~20 keV to ~10 MeV. High temporal and energy resolution electron measurements at RBSPICE show that energy spectra of the inner belt electrons exhibit regular resonance patterns which are more pronounced during intervals of increased geomagnetic activity. While these modulations were previously inferred from electron precipitation measurements on the low orbiting spacecraft, RBSPICE provides important insights into their properties at the equator where these patterns are formed. The modulations are observed over the entire inner belt and approximately follow 1/L energy dependence. This suggests that the modulation patterns are produced in the process of drift-resonant interaction of radiation belt electrons with large-scale fluctuations in the geomagnetic field. In this paper we describe properties of the resonant patterns and discuss their generation mechanisms.

  18. Molecular dynamics and semiclassical electronic spectra of naphthalene . Arn clusters (n <= 4)

    NASA Astrophysics Data System (ADS)

    Troxler, Thomas; Leutwyler, Samuel

    1993-09-01

    Molecular dynamics simulations were performed for van der Waals clusters naphthaleneṡArn, n=1 to 4. For all isomers and conformers of these clusters, dynamical quantities such as velocity autocorrelation functions, vibrational power spectra, and semiclassical electronic absorption spectra were calculated over a wide energy range, and averaged over a canonical distribution at temperatures in the range T=5 to 30 K. Electronic absorption spectra were calculated for the origin bands according to the semiclassical method [L. E. Fried and S. Mukamel, J. Chem. Phys. 96, 116 (1992)] and are compared with the corresponding experimental naphthaleneṡArn R2PI spectra [T. Troxler and S. Leutwyler, J. Chem. Phys. 95, 4010 (1991)]. The appearance of distinct absorption bands due to specific isomers for a given cluster size, as observed experimentally, is well reproduced by the simulations. Comparison of calculated electronic shifts for different isomers allows clear assignments in the experimental spectra. Increasing the simulation temperature to T=15-25 K is accompanied by band broadening and the appearance of sidebands towards the blue. Especially strong sidebands appear for naphṡAr2 and all clusters containing the Ar2 subunit, due to large-amplitude surface rotation/translation of the argon dimer on the naphthalene surface, in agreement with experiment. For clusters containing the n=3 and n=4 subunits the spectral broadening is smaller. For the n=4 (4+0)-isomer, the calculated band shape increases less than for the other n=4 isomers, mainly due to the motional narrowing effect of cluster fluxionality. Above 25 K, isomerization between different possible topological structures also occurs by side-crossing motion of one or several argon atoms.

  19. Retrieval of Electronic Spectra of Charge Carriers in Organic Field-Effect Transistors from Charge Modulation Reflectance Spectra Distorted by Optical Interference

    NASA Astrophysics Data System (ADS)

    Miyata, Kiyoshi; Ishino, Yuta; Watanabe, Kazuya; Miwa, Kazumoto; Uemura, Takafumi; Takeya, Jun; Matsumoto, Yoshiyasu

    2013-06-01

    Charge modulation (CM) spectroscopy is useful for detecting and characterizing the electronic structure of charge carriers accumulated in organic field-effect transistors (OFETs). However, CM spectra are distorted by optical interference due to multiple reflections in OFETs particularly when reflection configurations are used. In this study, we demonstrated a method for retrieving the spectra of complex refractive indices of carriers from the distorted CM spectra by using a 4×4 matrix algorithm with general transition matrices. We tested this method by applying it to the CM spectra of a rubrene single-crystal FET measured at several incident angles of light. In spite of the strong distortion of the CM spectra, we could retrieve the spectrum of the imaginary part of refractive indices, which is similar to that observed in the transmission configuration. This method extends the applicability of CM spectroscopy to OFETs with opaque electrodes, where transmission configurations cannot possibly be applied.

  20. Electronic and vibrational spectra of matrix isolated anthracene radical cations - Experimental and theoretical aspects

    NASA Technical Reports Server (NTRS)

    Szczepanski, Jan; Vala, Martin; Talbi, Dahbia; Parisel, Olivier; Ellinger, Yves

    1993-01-01

    The IR vibrational and visible/UV electronic absorption spectra of the anthracene cation, An(+), were studied experimentally, in argon matrices at 12 K, as well as theoretically, using ab initio calculations for the vibrational modes and enhanced semiempirical methods with configuration interaction for the electronic spectra. It was found that both approaches predicted well the observed photoelectron spectrum. The theoretical IR intensities showed some remarkable differences between neutral and ionized species (for example, the CH in-plane bending modes and CC in-plane stretching vibrations were predicted to increase by several orders of magnitude upon ionization). Likewise, estimated experimental IR intensities showed a significant increase in the cation band intensities over the neutrals. The implication of these findings for the hypothesis that polycyclic aromatic hydrocarbon cations are responsible for the unidentified IR emission bands from interstellar space is discussed.

  1. Vibronic and Vibrational Coherences in Two-Dimensional Electronic Spectra of Supramolecular J-Aggregates

    PubMed Central

    2013-01-01

    In J-aggregates of cyanine dyes, closely packed molecules form mesoscopic tubes with nanometer-diameter and micrometer-length. Their efficient energy transfer pathways make them suitable candidates for artificial light harvesting systems. This great potential calls for an in-depth spectroscopic analysis of the underlying energy deactivation network and coherence dynamics. We use two-dimensional electronic spectroscopy with sub-10 fs laser pulses in combination with two-dimensional decay-associated spectra analysis to describe the population flow within the aggregate. Based on the analysis of Fourier-transform amplitude maps, we distinguish between vibrational or vibronic coherence dynamics as the origin of pronounced oscillations in our two-dimensional electronic spectra. PMID:23461650

  2. F region electron density irregularity spectra near auroral acceleration and shear regions

    NASA Technical Reports Server (NTRS)

    Basu, S.; Basu, S.; Mackenzie, E.; Coley, W. R.; Hanson, W. B.; Lin, C. S.

    1984-01-01

    Two orbits of the Atmosphere Explorer D yielded data on F region electron irregularities in the high latitude ionosphere. Data were taken with a retarding potential analyzer, an ion drift meter, a low energy electron experiment and a photoelectron spectrometer. Auroral forms were simultaneously visually sighted by DMSP spacecraft. The irregularities were associated with auroral excitation and large structured flow regions. Steep spectra with one-dimensional spectral index values for wavelengths over 1 km were observed in the acceleration region. Large amplitude irregularities appeared in large structured flow regions and displayed shallow spectra, indicating the presence of large power spectral densities at scale lengths of about 100 m. It is suspected that large velocities or shears in the velocities in adjacent precipitation regions cause the F region density perturbations.

  3. DFT computation and experimental analysis of vibrational and electronic spectra of phenoxy acetic acid herbicides

    NASA Astrophysics Data System (ADS)

    Arul Dhas, D.; Hubert Joe, I.; Roy, S. D. D.; Balachandran, S.

    2013-05-01

    An absolute vibrational analysis has been attempted on the basis of experimental FTIR and NIR-FT Raman spectra with calculated vibrational wavenumbers and intensities of phenoxy acetic acids. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers have been calculated with the help of B3LYP method with Dunning correlation consistent basis set aug-cc-pVTZ. The electronic structures of molecular fragments were described in terms of natural bond orbital analysis, which shows intermolecular Osbnd H⋯O and intramolecular Csbnd H⋯O hydrogen bonds. The electronic absorption spectra with different solvents have been investigated in combination with time-dependent density functional theory calculation. The pKa values of phenoxy acetic acids were compared.

  4. Sensitivity Analysis of X-ray Spectra from Scanning Electron Microscopes

    SciTech Connect

    Miller, Thomas Martin; Patton, Bruce W.; Weber, Charles F.; Bekar, Kursat B.

    2014-10-01

    The primary goal of this project is to evaluate x-ray spectra generated within a scanning electron microscope (SEM) to determine elemental composition of small samples. This will be accomplished by performing Monte Carlo simulations of the electron and photon interactions in the sample and in the x-ray detector. The elemental inventories will be determined by an inverse process that progressively reduces the difference between the measured and simulated x-ray spectra by iteratively adjusting composition and geometric variables in the computational model. The intended benefit of this work will be to develop a method to perform quantitative analysis on substandard samples (heterogeneous phases, rough surfaces, small sizes, etc.) without involving standard elemental samples or empirical matrix corrections (i.e., true standardless quantitative analysis).

  5. Theoretical analysis of electronic absorption spectra of vitamin B12 models

    NASA Astrophysics Data System (ADS)

    Andruniow, Tadeusz; Kozlowski, Pawel M.; Zgierski, Marek Z.

    2001-10-01

    Time-dependent density-functional theory (TD-DFT) is applied to analyze the electronic absorption spectra of vitamin B12. To accomplish this two model systems were considered: CN-[CoIII-corrin]-CN (dicyanocobinamide, DCC) and imidazole-[CoIII-corrin]-CN (cyanocobalamin, ImCC). For both models 30 lowest excited states were calculated together with transition dipole moments. When the results of TD-DFT calculations were directly compared with experiment it was found that the theoretical values systematically overestimate experimental data by approximately 0.5 eV. The uniform adjustment of the calculated transition energies allowed detailed analysis of electronic absorption spectra of vitamin B12 models. All absorption bands in spectral range 2.0-5.0 eV were readily assigned. In particular, TD-DFT calculations were able to explain the origin of the shift of the lowest absorption band caused by replacement of the-CN axial ligand by imidazole.

  6. The sun's spots and flares

    NASA Technical Reports Server (NTRS)

    Rust, David M.

    1987-01-01

    The Solar Maximum Mission (SMM), designed to study the solar activity, was launched on February 14, 1980, just before the 1980 peak of sunspot and flare activity. The seven instruments aboard the SMM, information received by each of the instruments, and the performance of these instruments are described, together with the repair mission carried out to replace the attitude control module and the defective electronics in the satellite's observatory. The highlights of the scientific results obtained by the SMM mission and the new discoveries made are discussed, with special attention given to the flare loops, flare loop interactions, and the mass ejection events recorded.

  7. Electronic Transition Spectra of Thiophenoxy and Phenoxy Radicals in Hollow Cathode Discharges

    NASA Astrophysics Data System (ADS)

    Araki, Mitsunori; Wako, Hiromichi; Niwayama, Kei; Tsukiyama, Koichi

    2014-06-01

    Diffuse interstellar bands (DIBs) still remain the longest standing unsolved problem in spectroscopy and astrochemistry, although several hundreds of DIBs have been already detected. It is expected that identifications of DIBs can give us crucial information for extraterrestrial organic molecule. One of the best approaches to identify carrier molecules of DIBs is a measurement of DIB candidate molecule produced in the laboratory to compare their absorption spectra with astronomically observed DIB spectra. Radical in a gas phase is a potential DIB candidate molecule. The electronic transitions of polyaromatic hydrocarbon radicals result in optical absorption. However, because radicals are unstable, their electronic transitions are difficult to observe using a laboratory spectrometer system. To solve this difficulty, we have developed a glow-discharge cell using a hollow cathode in which radicals can be effectively produced as a high-density plasma. The radicals produced were measured by using the cavity ringdown (CRD) spectrometer and the discharge emission spectrometer. The CRD spectrometer, which consists of a tunable pulse laser system, an optical cavity and a discharge device, is an apparatus to observe an high-resolution optical absorption spectrum. The electronic transition of the thiophenoxy radical C6H5OS was observed in the discharge emission of thiophenol C6H5OH. The electronic transition frequency of the thiophenoxy radical was measured. A optical discharge emission was examined by using a HORIBA Jobin Yvon iHR320 monochromator. We detected the phenoxy radical C6H5O in the discharge of phenol C6H5OH. The band observed at 6107 Å in the discharge was assigned to the electronic transition of the phenoxy radical on the basis of the sample gas dependences and the reported low resolution spectrum. The electronic transition frequency of the phenoxy radical was measured. Comparison studies of the thiophenoxy and phenoxy radicals were made with known DIB spectra

  8. Characteristics of gamma-ray line flares

    NASA Technical Reports Server (NTRS)

    Bai, T.; Dennis, B.

    1983-01-01

    Observations of solar gamma rays by the Solar Maximum Mission (SMM) demonstrate that energetic protons and ions are rapidly accelerated during the impulsive phase. To understand the acceleration mechanisms for these particles, the characteristics of the gamma ray line flares observed by SMM were studied. Some very intense hard X-ray flares without detectable gamma ray lines were also investigated. Gamma ray line flares are distinguished from other flares by: (1) intense hard X-ray and microwave emissions; (2) delay of high energy hard X-rays; (3) emission of type 2 and/or type 4 radio bursts; and (4) flat hard X-ray spectra (average power law index: 3.1). The majority of the gamma ray line flares shared all these characteristics, and the remainder shared at least three of them. Positive correlations were found between durations of spike bursts and spatial sizes of flare loops as well as between delay times and durations of spike bursts.

  9. Kinetic energies to analyze the experimental auger electron spectra by density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Endo, Kazunaka

    2016-02-01

    In the Auger electron spectra (AES) simulations, we define theoretical modified kinetic energies of AES in the density functional theory (DFT) calculations. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. This method is applied to simulate Auger electron spectra (AES) of 2nd periodic atom (Li, Be, B, C, N, O, F)-involving substances (LiF, beryllium, boron, graphite, GaN, SiO2, PTFE) by deMon DFT calculations using the model molecules of the unit cell. Experimental KVV (valence band electrons can fill K-shell core holes or be emitted during KVV-type transitions) AES of the (Li, O) atoms in the substances agree considerably well with simulation of AES obtained with the maximum kinetic energies of the atoms, while, for AES of LiF, and PTFE substance, the experimental F KVV AES is almost in accordance with the spectra from the transitionstate kinetic energy calculations.

  10. N2 positive and N2/+/ band systems and the energy spectra of auroral electrons.

    NASA Technical Reports Server (NTRS)

    Shemansky, D. E.; Donahue, T. M.; Zipf, E. C., Jr.

    1972-01-01

    Use of the relative emission rates of the auroral N2 positive and N2(+) band systems to limit the permissible range of differential electron fluxes in auroras, due to remarkable differences in electron excitation functions for the two kinds of systems. Use of recently measured electron cross sections and many observational data from ground based and rocket studies shows that the results are consistent with spectra equivalent to a power law E to the minus 1.4 power for primaries and secondaries combined. The unified primary spectra of Rees (1969) and secondary spectra of Rees et al. (1969) fail seriously to predict the optical ratios. It is shown that Rees' primary spectrum is deficient in slow primaries, owing to the use of defective Monte Carlo results of Maeda (1965). Doubt is thereby cast on the validity of experimental results for the differential spectrum below 50 eV reported by Feldman et al. (1971) because of the rapid decrease in flux with energy shown by those measurements.

  11. t-SURFF: fully differential two-electron photo-emission spectra

    NASA Astrophysics Data System (ADS)

    Scrinzi, Armin

    2012-08-01

    The time-dependent surface flux (t-SURFF) method is extended to single and double ionization of two-electron systems. Fully differential double emission spectra by strong pulses at extreme UV and infrared wavelengths are calculated using simulation volumes that only accommodate the effective range of the atomic binding potential and the quiver radius of free electrons in the external field. For a model system, we found a pronounced dependence of shake-up and non-sequential double ionization on the phase and duration of the laser pulse. The extension to fully three-dimensional calculations is discussed.

  12. Signatures of current loop coalescence in solar flares

    NASA Technical Reports Server (NTRS)

    Sakai, J.; Nakajima, H.; Zaidman, E.; Tajima, T.; Kosugi, T.; Brunel, F.

    1986-01-01

    The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory. Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions; (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra; (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities; and (4) the double peak (or triple peak) structure in these profiles, participate in the coalescence process, yielding varieties of phenomena.

  13. Electronic absorption spectra of linear and cyclic Cn+ n=7-9 in a neon matrix

    NASA Astrophysics Data System (ADS)

    Fulara, Jan; Shnitko, Ivan; Batalov, Anton; Maier, John P.

    2005-07-01

    The Cn+n=7-9 cations were produced by electron-impact ionization of perchloronaphthalene, mass selected, and their electronic absorption spectra in 6K neon matrices recorded. The linear and cyclic isomers of C7+ and C8+ are detected. Three systems of linear C7+ are observed with origin bands near 770, 332, and 309nm. The cyclic C7+ shows two transitions near 676 and 448nm. One system of linear C9+ is observed commencing at 371nm. Linear C8+ shows five dipole-allowed electronic transitions from the X˜Πg2 ground state, and the strongest ones have the origin bands at 890.8 and 308.1nm. Five electronic transitions of cyclic C8+ are also discernible.

  14. Optical Spectral Observations of a Flickering White-light Kernel in a C1 Solar Flare

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay

    2015-01-01

    We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, <=0.''5 (1015 cm2) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a "blue continuum bump" in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

  15. OPTICAL SPECTRAL OBSERVATIONS OF A FLICKERING WHITE-LIGHT KERNEL IN A C1 SOLAR FLARE

    SciTech Connect

    Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay

    2015-01-10

    We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, ≤0.''5 (10{sup 15} cm{sup 2}) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a ''blue continuum bump'' in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

  16. Theoretical investigation on the vibrational and electronic spectra of three isomeric forms of dicobalt octacarbonyl

    NASA Astrophysics Data System (ADS)

    Karakaş, Duran; Kariper, Sultan Erkan

    2014-03-01

    Three isomeric forms of dicobalt octacarbonyl, [Co2(CO)8], with C2v, D3d and D2d point group were optimized by using density functional theory (DFT/B3LYP) method with LANL2DZ basis set for the cobalt atoms and 6-31G(d) basis set for the other atoms in the gas phase. Electronic structures, carbonyl stretching frequencies and Mulliken population analysis were determined from the optimized structures. Electronic structures indicate that each of the dicobalt octacarbonyl isomers have been constituted from two trigonal bipyramidal geometry. While the isomer C2v has two bridged carbonyl groups, in the isomers D3d and D2d all carbonyl groups are coordinating as terminal. The calculated C-O stretching frequencies are in a good agreement with experimental frequencies. Experimental C-O stretching frequencies were assigned to isomers according to the calculated frequencies. Mulliken population analysis show that free carbonyl ligands transfer their electron to the cobalt atoms during formation of the complexes. The electronic spectra of isomers were obtained by using time dependent density functional theory (TD-DFT/B3LYP) method with LANL2DZ basis set for the cobalt atoms and 6-31G(d) basis set for the other atoms in the gas phase. The theoretical electronic spectra of isomers are in a good agreement with experimental spectra. The calculated bands at 277.9, 278.1 and 284.1 nm for isomers C2v, D2d and D3d were assigned to metal-ligand charge transfer transitions and the shoulder at 344.6 nm was assigned to pure metal center transitions for isomer D3d.

  17. Flare models: Chapter 9 of solar flares

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A. (Editor)

    1979-01-01

    By reviewing the properties of solar flares analyzed by each of the seven teams of the Skylab workshop, a set of primary and secondary requirements of flare models are derived. A number of flare models are described briefly and their properties compared with the primary requirements. It appears that, at this time, each flare model has some strong points and some weak points. It has not yet been demonstrated that any one flare model meets all the proposed requirements.

  18. Reconstruction of the energy spectrum of electrons accelerated in the April 15, 2002 solar flare based on IRIS X-ray spectrometer measurements

    NASA Astrophysics Data System (ADS)

    Motorina, G. G.; Kudryavtsev, I. V.; Lazutkov, V. P.; Savchenko, M. I.; Skorodumov, D. V.; Charikov, Yu. E.

    2016-04-01

    We reconstruct the energy distribution of electrons accelerated in the April 15, 2002 solar flare on the basis of the data from the IRIS X-ray spectrometer onboard the CORONAS-F satellite. We obtain the solution to the integral equations describing the transformation of the spectrum of X-ray photons during the recording and reconstruction of the spectrum of accelerated electrons in the bremsstrahlung source using the random search method and the Tikhonov regularization method. In this event, we detected a singularity in the electron spectrum associated with the existence of a local minimum in the energy range 40-60 keV, which cannot be detected by a direct method.

  19. SCATTERING POLARIZATION IN SOLAR FLARES

    SciTech Connect

    Štěpán, Jiří; Heinzel, Petr

    2013-11-20

    There is ongoing debate about the origin and even the very existence of a high degree of linear polarization of some chromospheric spectral lines observed in solar flares. The standard explanation of these measurements is in terms of the impact polarization caused by non-thermal proton and/or electron beams. In this work, we study the possible role of resonance line polarization due to radiation anisotropy in the inhomogeneous medium of the flare ribbons. We consider a simple two-dimensional model of the flaring chromosphere and we self-consistently solve the non-LTE problem taking into account the role of resonant scattering polarization and of the Hanle effect. Our calculations show that the horizontal plasma inhomogeneities at the boundary of the flare ribbons can lead to a significant radiation anisotropy in the line formation region and, consequently, to a fractional linear polarization of the emergent radiation of the order of several percent. Neglecting the effects of impact polarization, our model can provide a clue for resolving some of the common observational findings, namely: (1) why a high degree of polarization appears mainly at the edges of the flare ribbons; (2) why polarization can also be observed during the gradual phase of a flare; and (3) why polarization is mostly radial or tangential. We conclude that radiation transfer in realistic multi-dimensional models of solar flares needs to be considered as an essential ingredient for understanding the observed spectral line polarization.

  20. Self-Consistent Synchrotron Spectra from Trans-Relativistic Electron Acceleration

    NASA Astrophysics Data System (ADS)

    Becker, Peter A.

    2015-01-01

    Most existing analytical models describing the second-order Fermi acceleration of relativistic electrons due to collisions with MHD waves assume that the injected seed particles are already highly relativistic, despite the fact that the most prevalent source of particles is usually the non-relativistic thermal background gas. This presents a problem because the momentum dependence of the momentum diffusion coefficient describing the interaction between the electrons and the MHD waves is qualitatively different in the non-relativistic and highly relativistic limits. The lack of an analytical model has forced workers to rely on numerical simulations to obtain particle spectra describing the trans-relativistic case. In this work, we present the first analytical solution to the global, trans-relativistic problem of electron acceleration, obtained by using a hybrid form for the momentum diffusion coefficient, given by the sum of the two asymptotic forms. We refer to this process as "quasi hard-sphere scattering." The model also incorporates the appropriate momentum dependence for the particle escape timescale, and the effect of synchrotron and inverse-Compton losses, which are critical for establishing the location of the high-energy cutoff in the particle spectrum. Since synchrotron and inverse-Compton losses are included in the transport equation, the resulting radiation spectra are computed self-consistently. The results can be used to model the acceleration of radiating electrons in AGN and solar environments, applications of both types are discussed.

  1. Electronic spectra and DFT calculations of some pyrimido[1,2-a]benzimidazole derivatives

    NASA Astrophysics Data System (ADS)

    Elshakre, Mohamed E.; Moustafa, H.; Hassaneen, Huwaida. M. E.; Moussa, Abdelrahim. Z.

    2015-06-01

    Ground state properties of 2,4-diphenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine, compound 1, and its derivatives are investigated experimentally and theoretically in Dioxane and DMF. The calculations show that all the studied compounds (1-7) are non-planar, resulting in a significant impact on the electronic and structural properties. The ground state properties of compounds 1-7 at B3LYP/6-311G (d, p) show that compound 5 has the lowest EHOMO, ELUMO, and ΔE indicating highest reactivity. Compound 7 is found to have the highest polarity. The observed UV spectra in Dioxane and DMF of compounds 1-4 show 2 bands, while compounds 5-7 show 4 bands in both solvents. Band maxima (λmax) and intensities of the spectra are found to have solvent dependence reflected as blue and red shifts. The theoretical spectra computed at TD-B3LYP/6-311G (d, p) in gas phase, Dioxane and DMF indicate a good agreement with the observed spectra.

  2. Limiting Superluminal Electron and Neutrino Velocities Using the 2010 Crab Nebula Flare and the IceCube PeV Neutrino Events

    NASA Technical Reports Server (NTRS)

    Stecker, Floyd W.

    2014-01-01

    The observation of two PetaelectronVolt (PeV)-scale neutrino events reported by Ice Cube allows one to place constraints on Lorentz invariance violation (LIV) in the neutrino sector. After first arguing that at least one of the PetaelectronVolt IceCube events was of extragalactic origin, I derive an upper limit for the difference between putative superluminal neutrino and electron velocities of less than or equal to approximately 5.6 x 10(exp -19) in units where c = 1, confirming that the observed PetaelectronVolt neutrinos could have reached Earth from extragalactic sources. I further derive a new constraint on the superluminal electron velocity, obtained from the observation of synchrotron radiation from the Crab Nebula flare of September, 2010. The inference that the greater than 1 GigaelectronVolt gamma-rays from synchrotron emission in the flare were produced by electrons of energy up to approx. 5.1 PetaelectronVolt indicates the nonoccurrence of vacuum Cerenkov radiation by these electrons. This implies a new, strong constraint on superluminal electron velocities delta(sub e) less than or equal to approximately 5 x 10(exp -21). It immediately follows that one then obtains an upper limit on the superluminal neutrino velocity alone of delta(sub v) less than or equal to approximately 5.6 x 10(exp -19), many orders of magnitude better than the time-of-flight constraint from the SN1987A neutrino burst. However, if the electrons are subluminal the constraint on the absolute value of delta(sub e) less than or equal to approximately 8 x 10(exp -17), obtained from the Crab Nebula gamma-ray spectrum, places a weaker constraint on superluminal neutrino velocity of delta(sub v) less than or equal to approximately 8 x 10(exp -17).

  3. Updated calculations of the ionization equilibrium for the non-Maxwellian electron n-distributions in solar flares

    NASA Astrophysics Data System (ADS)

    Dzifcakova, Elena; Dudík, Jaroslav

    2015-08-01

    Observed flare high intensities of the Si XIId satellite lines in comparison with the Si XIII allowed lines cannot be interpreted under the assumption of a Maxwellian distribution. This behavior of the relative line intensities can be explained by the presence of n-distribution with a higher and narrower shape than the Maxwellian one. This distribution can be formed in flaring plasma in the electric double layers and its presence is associated with type III radio bursts.The latest atomic data to calculate the ionization equilibrium for the non-thermal n-distributions with n ranging from 1 to 19 were used. These calculations involve each of elements with atomic number up to 30. The n-distributions influence both the ionization and recombination rates and make the ion abundance peaks narrower. They can also shift the maxima of the ion abundance peaks in comparison with the Maxwellian distribution and can influence the temperature diagnostics.

  4. Where Is the Electronic Oscillator Strength? Mapping Oscillator Strength across Molecular Absorption Spectra.

    PubMed

    Zheng, Lianjun; Polizzi, Nicholas F; Dave, Adarsh R; Migliore, Agostino; Beratan, David N

    2016-03-24

    The effectiveness of solar energy capture and conversion materials derives from their ability to absorb light and to transform the excitation energy into energy stored in free carriers or chemical bonds. The Thomas-Reiche-Kuhn (TRK) sum rule mandates that the integrated (electronic) oscillator strength of an absorber equals the total number of electrons in the structure. Typical molecular chromophores place only about 1% of their oscillator strength in the UV-vis window, so individual chromophores operate at about 1% of their theoretical limit. We explore the distribution of oscillator strength as a function of excitation energy to understand this circumstance. To this aim, we use familiar independent-electron model Hamiltonians as well as first-principles electronic structure methods. While model Hamiltonians capture the qualitative electronic spectra associated with π electron chromophores, these Hamiltonians mistakenly focus the oscillator strength in the fewest low-energy transitions. Advanced electronic structure methods, in contrast, spread the oscillator strength over a very wide excitation energy range, including transitions to Rydberg and continuum states, consistent with experiment. Our analysis rationalizes the low oscillator strength in the UV-vis spectral region in molecules, a step toward the goal of oscillator strength manipulation and focusing.

  5. A STATISTICAL STUDY OF THE SPECTRAL HARDENING OF CONTINUUM EMISSION IN SOLAR FLARES

    SciTech Connect

    Kong, X.; Chen, Y.; Li, G. E-mail: gang.li@uah.edu

    2013-09-10

    The observed hard X-ray and {gamma}-ray continuum in solar flares is interpreted as Bremsstrahlung emission of accelerated non-thermal electrons. It has been noted for a long time that in many flares the energy spectra show hardening at energies around or above 300 keV. In this paper, we first conduct a survey of spectral hardening events that were previously studied in the literature. We then perform a systematic examination of 185 flares from the Solar Maximum Mission. We identify 23 electron-dominated events whose energy spectra show clear double power laws. A statistical study of these events shows that the spectral index below the break ({gamma}{sub 1}) anti-correlates with the break energy ({epsilon}{sub b}). Furthermore, {gamma}{sub 1} also anti-correlates with Fr, the fraction of photons above the break compared to the total photons. A hardening spectrum, as well as the correlations between ({gamma}{sub 1}, {epsilon}{sub b}) and ({gamma}{sub 1}, Fr), provide stringent constraints on the underlying electron acceleration mechanism. Our results support a recent proposal that electrons are being accelerated diffusively at a flare termination shock with a width of the order of an ion inertial length scale.

  6. Ab Initio Infrared Spectra and Electronic Response Calculations for the Insulating Phases of VO2

    NASA Astrophysics Data System (ADS)

    Hendriks, Christopher; Huffman, Tyler; Walter, Eric; Qazilbash, Mumtaz; Krakauer, Henry

    Previous studies have shown that, under doping or tensile strain and upon heating, the well-known vanadium dioxide (VO2) transition from an insulating monoclinic (M1) to a metallic rutile (R) phase progresses through a triclinic symmetry (T) phase and a magnetic monoclinic phase (M2), both of which are insulating. Structurally, this progression from M1 to R through T and M2 can be characterized by the progressive breaking of the V dimers. Investigation of the effect of these structural changes on the insulating phases of VO2 may help resolve questions surrounding the long-debated issue of the respective roles of electronic correlation and Peierls mechanisms in driving the MIT. We investigated electronic and vibrational properties of the insulating phases of VO2 in the framework of DFT+U. We will present ab initio calculations of infrared spectra and optical electronic responses for the insulating phases and compare these to available experimental measurements. Supported by ONR.

  7. Experimental and DFT studies on the vibrational and electronic spectra of 9-anthracenemethanol

    NASA Astrophysics Data System (ADS)

    Kou, Shanshan; Zhou, Hu; Tang, Guodong; Li, Rongqing; Zhang, Yu; Zhao, Jianying; Wei, Changmei

    2012-10-01

    Vibrational spectral measurements were made for 9-anthracenemethanol. Optimized geometrical structure and harmonic vibration frequencies were computed based on ab initio and density functional theory B3LYP methods using 6-311G∗∗ and LANL2DZ basis sets. The equilibrium geometries got from all of the methods and basis were compared with X-ray diffraction results. The IR and UV-vis spectra of the title compound were computed using all of the methods and choose the most appropriate way to discuss. And the absorption spectra were calculated both in gas phase and in CH3CH2OH and CH3CN solution. The calculated results matched well with the experimental values. On the basis, the first excited state electronic transition energy has been calculated using time-dependent density functional theory.

  8. Simulating electron spin resonance spectra of nitroxide spin labels from molecular dynamics and stochastic trajectories

    PubMed Central

    Sezer, Deniz; Freed, Jack H.; Roux, Benoît

    2008-01-01

    Simulating electron spin resonance spectra of nitroxide spin labels from motional models is necessary for the quantitative analysis of experimental spectra. We present a framework for modeling the spin label dynamics by using trajectories such as those from molecular dynamics (MD) simulations combined with stochastic treatment of the global protein tumbling. This is achieved in the time domain after two efficient numerical integrators are developed: One for the quantal dynamics of the spins and the other for the classical rotational diffusion. For the quantal dynamics, we propagate the relevant part of the spin density matrix in Hilbert space. For the diffusional tumbling, we work with quaternions, which enables the treatment of anisotropic diffusion in a potential expanded as a sum of spherical harmonics. Time-averaging arguments are invoked to bridge the gap between the smaller time step of the MD trajectories and the larger time steps appropriate for the rotational diffusion and∕or quantal spin dynamics. PMID:18447510

  9. Electron-positron pairs, Compton reflection, and the X-ray spectra of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Zdziarski, Andrzej A.; Ghisellini, Gabriele; George, Ian M.; Fabian, A. C.; Svensson, Roland; Done, Chris

    1990-01-01

    It is shown here that reprocessing of radiation fron nonthermal pair cascades by cold material in the central parts of active galactic nuclei (AGN) gives rise to X-ray and gamma-ray spectra that satisfy current observational constraints. An average 1-30 keV X-ray spectral index alpha(x) of about 0.7 in the compact range 30-300 is obtained for a wide range of Lorentz factors of the injected electrons. The gamma-ray spectra are steep, with alpha(gamma) about two, and satisfy the observational constraints. Radiation from pair cascades exhibits steep power law decreases in soft X-rays similar to those observed in AGN. The overall picture is consistent with AGN having an accretion disk which intercepts and reprocesses a substantial fraction of the nonthermal continuum incident upon it from above and below.

  10. Temperature dependence of Q-band electron paramagnetic resonance spectra of nitrosyl heme proteins.

    PubMed Central

    Flores, M; Wajnberg, E; Bemski, G

    1997-01-01

    The Q-band (35 GHz) electron paramagnetic resonance (EPR) spectra of nitrosyl hemoglobin (HbNO) and nitrosyl myoglobin (MbNO) were studied as a function of temperature between 19 K and 200 K. The spectra of both heme proteins show two classes of variations as a function of temperature. The first one has previously been associated with the existence of two paramagnetic species, one with rhombic and the other with axial symmetry. The second one manifests itself in changes in the g-factors and linewidths of each species. These changes are correlated with the conformational substates model and associate the variations of g-values with changes in the angle of the N(his)-Fe-N(NO) bond in the rhombic species and with changes in the distance between Fe and N of the proximal (F8) histidine in the axial species. PMID:9414233

  11. Magnetic phases in lunar material and their electron magnetic resonance spectra - Apollo 14.

    NASA Technical Reports Server (NTRS)

    Weeks, R. A.

    1972-01-01

    Electron magnetic resonance spectra of soil samples 14163,68, 14148,31, 14149,47, 14156,31, and 14003,60, and of fragmental rocks 14301,66, 14303,42, 14310,68, 14311,36, 14318,36, and 14321,166 have been recorded at 9 and 35 GHz at 300 K and at 9 GHz at 130 K. One spectral component, the characteristic ferromagnetic resonance, of all the soil samples is 50 to 1000 times more intense than any other component in the soils or in the spectra of the rocks. The intensity of this component in Apollo 11, Apollo 12, and Apollo 14 soils varies only within one order of magnitude. It varies with depth below lunar surface but is not correlated with depth. The intensity does not have any correlation with the fraction of glassy particles nor with the fraction of anorthositic particles.

  12. Flare energetics: analysis of a large flare on YZ Canis Minoris observed simultaneously in the ultraviolet, optical and radio.

    NASA Astrophysics Data System (ADS)

    van den Oord, G. H. J.; Doyle, J. G.; Rodono, M.; Gary, D. E.; Henry, G. W.; Byrne, P. B.; Linsky, J. L.; Haisch, B. M.; Pagano, I.; Leto, G.

    1996-06-01

    The results of coordinated observations of the dMe star YZ CMi at optical, UV and radio wavelengths during 3-7 February 1983 are presented. YZ CMi showed repeated optical flaring with the largest flare having a magnitude of 3.8 in the U-band. This flare coincided with an IUE exposure which permits a comparison of the emission measure curves of YZ CMi in its flaring and quiescent state. During the flare a downward shift of the transition zone is observed while the radiative losses in the range 10^4^-10^7^K strongly increase. The optical flare is accompanied with a radio flare at 6cm, while at 20cm no emission is detected. The flare is interpreted in terms of optically thick synchrotron emission. We present a combined interpretation of the optical/radio flare and show that the flare can be interpreted within the context of solar two-ribbon/white-light flares. Special attention is paid to the bombardment of dMe atmospheres by particle beams. We show that the characteristic temperature of the heated atmosphere is almost independent of the beam flux and lies within the range of solar white-light flare temperatures. We also show that it is unlikely that stellar flares emit black-body spectra. The fraction of accelerated particles, as follows from our combined optical/radio interpretation is in good agreement with the fraction determined by two-ribbon flare reconnection models.

  13. Detection of nanoscale electron spin resonance spectra demonstrated using nitrogen-vacancy centre probes in diamond

    PubMed Central

    Hall, L. T.; Kehayias, P.; Simpson, D. A.; Jarmola, A.; Stacey, A.; Budker, D.; Hollenberg, L. C. L.

    2016-01-01

    Electron spin resonance (ESR) describes a suite of techniques for characterizing electronic systems with applications in physics, chemistry, and biology. However, the requirement for large electron spin ensembles in conventional ESR techniques limits their spatial resolution. Here we present a method for measuring ESR spectra of nanoscale electronic environments by measuring the longitudinal relaxation time of a single-spin probe as it is systematically tuned into resonance with the target electronic system. As a proof of concept, we extracted the spectral distribution for the P1 electronic spin bath in diamond by using an ensemble of nitrogen-vacancy centres, and demonstrated excellent agreement with theoretical expectations. As the response of each nitrogen-vacancy spin in this experiment is dominated by a single P1 spin at a mean distance of 2.7 nm, the application of this technique to the single nitrogen-vacancy case will enable nanoscale ESR spectroscopy of atomic and molecular spin systems. PMID:26728001

  14. Twin-peaks absorption spectra of excess electron in ionic liquids

    NASA Astrophysics Data System (ADS)

    Musat, Raluca M.; Kondoh, Takafumi; Yoshida, Yoichi; Takahashi, Kenji

    2014-07-01

    The solvated electron in room temperature ionic liquids (RTILs) has been the subject of several investigations and several reports exist on its nature and absorption spectrum. These studies concluded that the solvated electron exhibits an absorption spectrum peaking in the 1000-1400 nm region; a second absorption band peaking in the UV region has been assigned to the hole or dication radicals simultaneously formed in the system. Here we report on the fate of the excess electron in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, P14+/NTf2- using nanosecond pulse radiolysis. Scavenging experiments allowed us to record and disentangle the complex spectrum measured in P14+/NTf2-. We identified a bi-component absorption spectrum, due to the solvated electron, the absorption maxima located at 1080 nm and around 300 nm, as predicted by previous ab-initio molecular dynamics simulations for the dry excess electron. We also measured the spectra using different ionic liquids and confirmed the same feature of two absorption peaks. The present results have important implications for the characterization of solvated electrons in ionic liquids and better understanding of their structure and reactivity.

  15. 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

    2006-03-01

    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.

  16. General properties of the radiation spectra from relativistic electrons moving in Langmuir turbulence

    SciTech Connect

    Teraki, Yuto; Takahara, Fumio

    2014-05-20

    Using a numerical method, we examine the radiation spectra from relativistic electrons moving in Langmuir turbulence, which are expected to exist in high energy astrophysical objects. The spectral shape is characterized by the spatial scale λ, field strength σ, and frequency of the Langmuir waves, and in terms of frequency they are represented by ω{sub 0} = 2πc/λ, ω{sub st} = eσ/mc, and ω{sub p}, respectively. We normalize ω{sub st} and ω {sub p} by ω{sub 0} as a ≡ ω{sub st}/ω{sub 0} and b ≡ ω{sub p}/ω{sub 0}, and examine the spectral shape in the a–b plane. An earlier study based on the diffusive radiation in Langmuir turbulence (DRL) theory by Fleishman and Toptygin showed that the typical frequency is γ{sup 2}ω{sub p} and that the low frequency spectrum behaves as F {sub ω}∝ω{sup 1} for b > 1 irrespective of a. Here, we adopt the first principle numerical approach to obtain the radiation spectra in more detail. We generate Langmuir turbulence by superposing Fourier modes, injecting monoenergetic electrons, solving the equation of motion, and calculating the radiation spectra using a Lienard-Wiechert potential. We find different features from the DRL theory for a > b > 1. The peak frequency turns out to be γ{sup 2}ω{sub st}, which is higher than the γ{sup 2}ω{sub p} predicted by the DRL theory, and the spectral index of the low frequency region is not 1 but 1/3. This is because the typical deflection angle of electrons is larger than the angle of the beaming cone ∼1/γ. We call the radiation for this case 'wiggler radiation in Langmuir turbulence'.

  17. The beta-SiC(100) surface studied by low energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectra

    NASA Technical Reports Server (NTRS)

    Dayan, M.

    1986-01-01

    The beta-SiC(100) surface has been studied by low energy electron diffraction, Auger electron spectroscopy, high resolution electron energy loss spectra (HREELS), and core level excitation EELS. Two new Si-terminated phases have been discovered, one with (3 x 2) symmetry, and the other with (2 x 1) symmetry. Models are presented to describe these phases. New results, for the C-rich surface, are presented and discussed. In addition, core level excitation EELS results are given and compared with theory.

  18. Data-driven Radiative Hydrodynamic Modeling of the 2014 March 29 X1.0 Solar Flare

    NASA Astrophysics Data System (ADS)

    Rubio da Costa, Fatima; Kleint, Lucia; Petrosian, Vahé; Liu, Wei; Allred, Joel C.

    2016-08-01

    Spectroscopic observations of solar flares provide critical diagnostics of the physical conditions in the flaring atmosphere. Some key features in observed spectra have not yet been accounted for in existing flare models. Here we report a data-driven simulation of the well-observed X1.0 flare on 2014 March 29 that can reconcile some well-known spectral discrepancies. We analyzed spectra of the flaring region from the Interface Region Imaging Spectrograph (IRIS) in Mg ii h&k, the Interferometric BIdimensional Spectropolarimeter at the Dunn Solar Telescope (DST/IBIS) in Hα 6563 Å and Ca ii 8542 Å, and the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) in hard X-rays. We constructed a multithreaded flare loop model and used the electron flux inferred from RHESSI data as the input to the radiative hydrodynamic code RADYN to simulate the atmospheric response. We then synthesized various chromospheric emission lines and compared them with the IRIS and IBIS observations. In general, the synthetic intensities agree with the observed ones, especially near the northern footpoint of the flare. The simulated Mg ii line profile has narrower wings than the observed one. This discrepancy can be reduced by using a higher microturbulent velocity (27 km s-1) in a narrow chromospheric layer. In addition, we found that an increase of electron density in the upper chromosphere within a narrow height range of ≈800 km below the transition region can turn the simulated Mg ii line core into emission and thus reproduce the single peaked profile, which is a common feature in all IRIS flares.

  19. Densities of Stellar Flares from Spectral Lines

    NASA Astrophysics Data System (ADS)

    Mitra-Kraev, U.

    2006-08-01

    We present detailed analyses of spectral changes during X-ray flares. During flares the plasma is known to become hotter, but also changes in density are anticipated, as flares will rather be compact and dense than large and tenuous. We search for indications of changes in density in the spectra of Chandra High Energy Transmission Grating Spectrometer (HETGS) data. However, as flares usually last for at most up to one hour, only very bright flares will produce enough photons for a sufficiently well exposed spectrum. We chose long Chandra observations of flare stars which covered periods of time with flare activity that can be combined to compile one quiescent-only spectrum to be compared with a spectrum that is affected by flare activity. We show that with careful data analysis it is possible with the presently available instruments to detect spectral line changes between quiescent and flaring states, notably in the density- and temperature-sensitive lines of the He-like OVII triplet (21.6/21.8/22.1 A). Using cumulative distribution functions, we are also able to give solid statistical confidence limits. We also briefly discuss the diagnostic capabilities of other He-like line triplets and of observations carried out with the XMM-Newton Reflection Grating Spectrometer (RGS).

  20. Electronic Spectra of TRIS(2,2'-BIPYRIDINE)-METAL Complex Ions in Gas Phase

    NASA Astrophysics Data System (ADS)

    Xu, Shuang; Smith, James E. T.; Weber, J. Mathias

    2016-06-01

    Tris(bpy)-metal complexes (bpy = 2,2'-bipyridine) and their derivatives are important systems in metal-organic chemistry. While tris(bpy)-ruthenium, Ru(bpy)32+, has been extensively studied, less attention has been paid to analogous complexes involving first row transition metals. Here we report the electronic spectra of a series of dicationic tris(bpy) chelates with different transition metals, measured by photodisscociation spectroscopy of cryogenically prepared ions. We focus our attention on the π-π* transitions in the UV region of the spectrum.

  1. Electronic excitation spectra from time-dependent density functional response theory using plane-wave methods

    NASA Astrophysics Data System (ADS)

    Doltsinis, Nikos L.; Sprik, Michiel

    2000-11-01

    The time-dependent density functional response theory method for the computation of electronic excitation spectra has been implemented in a plane-wave basis set/pseudo-potential formalism. We compare our test results for N2 and H2CO to literature atomic basis set calculations and find good agreement. We also discuss some of the technical complications specific to the use of plane-wave basis sets. As an application, the thermally broadened photoabsorption spectrum of formamide at room temperature is computed by averaging over a number of vibrational configurations sampled from an ab initio molecular dynamics run and compared to experiment.

  2. Improved methods of measurement and analysis of conversion electron and beta-particle spectra

    PubMed

    Dragoun; Spalek; Rysavy; Kovalik; Yakushev; Brabec; Frana; Venos

    2000-03-01

    A general statistical test of the stability of measurement conditions was demonstrated on the beta-spectra of 241Pu cumulated during four years. The alpha- and gamma-ray spectroscopy indicated stability of the 241Pu source. Monte Carlo modelling of individual collision events clarified the role of electron scattering and energy losses within a radioactive source down to energies of several hundreds of eV. The impact ionization by beta-particles of carbon and oxygen atoms in a surface contamination layer on the 241Pu and 63Ni sources was observed. PMID:10724379

  3. X-ray and radio observations of energetic electrons produced in the 3 November 2003 solar flare at ~09:5000 UT

    NASA Astrophysics Data System (ADS)

    Dauphin, C.; Vilmer, N.; Lüthi, T.; Magun, A.; Krucker, S.; Schwartz, R.; Trottet, G.

    Hard X-ray and radio observations provide complementary observations of energetic electrons produced in solar flares. The GOES X4 flare on 03 November 2003 at ˜ 09:50 UT was observed and imaged up to several 100 keV by the RHESSI experiment. It was simultaneously observed at metric/decimetric wavelengths by the Nançay Radioheliograph (NRH) and at centimetric/millimetric wavelengths by radio instruments operated by the Institute of Applied Physics (University of Bern). We present in this contribution an analysis of these radio and X-ray data. The time profiles of the X-ray emission above 50 keV and of the centimetric/millimetric emissions show two main parts (impulsive emission lasting about three minutes) and a long duration emission (partially observed by RHESSI) separated in time by four minutes. At metric/decimetric wavelengths a type II burst with an unusually high frequency is observed between the impulsive emissions and the long duration radio continuum. Combined analysis of RHESSI sources at energies above a few hundred keV and of metric/decimetric sources observed by the NRH shows the extension in space of both X-ray and radio sources traced by energetic electrons between the impulsive part of the event and the late energetic X-ray phase associated with the strong radio continuum. Spectral analysis of the high energy X-ray continuum and of the centimetric/millimetric will be performed to infer the characteristics of energetic electrons in both parts of the events and to further investigate in this event the relationship between centimetric-millimetric emitting electrons and HXR/GR bremsstrahlung emitting ones.

  4. PROBING DYNAMICS OF ELECTRON ACCELERATION WITH RADIO AND X-RAY SPECTROSCOPY, IMAGING, AND TIMING IN THE 2002 APRIL 11 SOLAR FLARE

    SciTech Connect

    Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.; Kontar, Eduard P.

    2013-05-10

    Based on detailed analysis of radio and X-ray observations of a flare on 2002 April 11 augmented by realistic three-dimensional modeling, we have identified a radio emission component produced directly at the flare acceleration region. This acceleration region radio component has distinctly different (1) spectrum, (2) light curves, (3) spatial location, and, thus, (4) physical parameters from those of the separately identified trapped or precipitating electron components. To derive evolution of physical parameters of the radio sources we apply forward fitting of the radio spectrum time sequence with the gyrosynchrotron source function with five to six free parameters. At the stage when the contribution from the acceleration region dominates the radio spectrum, the X-ray- and radio-derived electron energy spectral indices agree well with each other. During this time the maximum energy of the accelerated electron spectrum displays a monotonic increase with time from {approx}300 keV to {approx}2 MeV over roughly one minute duration indicative of an acceleration process in the form of growth of the power-law tail; the fast electron residence time in the acceleration region is about 2-4 s, which is much longer than the time of flight and so requires a strong diffusion mode there to inhibit free-streaming propagation. The acceleration region has a relatively strong magnetic field, B {approx} 120 G, and a low thermal density, n{sub e} {approx}< 2 Multiplication-Sign 10{sup 9} cm{sup -3}. These acceleration region properties are consistent with a stochastic acceleration mechanism.

  5. Electronic and vibrational spectra and thermodynamic functions of 3- and 4-methoxy benzonitriles

    NASA Astrophysics Data System (ADS)

    Goel, R. K.; Agarwal, M. L.

    The i.r. absorption spectra of 3- and 4- methoxy benzonitriles have been recorded on a Perkin—Elmer 521 spectrophotometer, while the Raman spectrum of 4-methoxybenzonitrile was recorded on CODERG Raman spectrometer T800 triple monochromator. The near ultraviolet absorption spectra of both the molecules in vapour phase have been recorded on Medium Quartz Hilger spectrograph and that of 4-methoxybenzonitrile on DK-2A ratio recording spectrophotometer also. The assignment of fundamental frequencies to various modes of vibration have been proposed and on the basis of free internal rotation and assigned vibrational frequencies, the thermodynamic functions of the molecules have been computed on a VAX-11/780 computer. The analysis of the electronic spectra has been given in terms of fundamentals, their combinations and overtones. 4-Methoxy benzonitrile has exhibited two band systems corresponding to 1A1 g- 1B2 u(2600 Å) and 1A1 g- 1B1 u(2100 Å) system of benzene, while 3-methoxybenzonitrile exhibited only the former system. The red shift of 0,0 bands has been discussed.

  6. Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ferrara, E. C.; Harding, A. K.; McEnery, J. E.; Moiseev, A. A.; Ackemann, M.

    2012-01-01

    We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which, is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 Ge V. We confirm that the fraction rises with energy in the 20-100 Ge V range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.

  7. Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Brogland, A. W.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Ferrara, E. C.; Harding, A. K.; McEnery, J. E.

    2011-01-01

    We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting the Earth's shadow, which is offset in opposite directions for opposite charges due to the Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 GeV and 200 GeV, We confirm that the fraction rises with energy in the 20-100 GeV range and determine for the first time that it continues to rise between 100 and 200 GeV,

  8. Composition and spectra of primary cosmic-ray electrons and nuclei above 10 GeV

    NASA Technical Reports Server (NTRS)

    Meyer, P.

    1975-01-01

    Recent experiments have extended the knowledge of the flux and energy spectra of individual cosmic-ray components to much higher energies than had previously been accessible. Both electron and nuclear components show a behavior at high energy which is unexpected, and which carries information regarding the sources and the propagation of particles between sources and observer. Electromagnetic interactions which are suffered by the electrons in interstellar space should steepen their spectrum, a steepening that would reveal the average lifetime a cosmic-ray particle spends in the galaxy. Measurements up to 1000 GeV show no such steepening. It was discovered that the composition of the nuclear species which is now measured up to 100 GeV/nucleon changes with energy. This change indicates traversal of less interstellar matter by the high energy particles than by those of lower energy.-

  9. Measurement of separate cosmic-ray electron and positron spectra with the fermi large area telescope.

    PubMed

    Ackermann, M; Ajello, M; Allafort, A; Atwood, W B; Baldini, L; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bouvier, A; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cecchi, C; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cutini, S; de Angelis, A; de Palma, F; Dermer, C D; Digel, S W; do Couto E Silva, E; Drell, P S; Drlica-Wagner, A; Favuzzi, C; Fegan, S J; Ferrara, E C; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Germani, S; Giglietto, N; Giommi, P; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guiriec, S; Gustafsson, M; Hadasch, D; Harding, A K; Hayashida, M; Hughes, R E; Jóhannesson, G; Johnson, A S; Kamae, T; Katagiri, H; Kataoka, J; Knödlseder, J; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Llena Garde, M; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Madejski, G M; Mazziotta, M N; McEnery, J E; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nakamori, T; Nolan, P L; Norris, J P; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Omodei, N; Orlando, E; Ormes, J F; Ozaki, M; Paneque, D; Parent, D; Pesce-Rollins, M; Pierbattista, M; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Romani, R W; Roth, M; Sadrozinski, H F-W; Sbarra, C; Schalk, T L; Sgrò, C; Siskind, E J; Spandre, G; Spinelli, P; Strong, A W; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J G; Thayer, J B; Tibaldo, L; Tinivella, M; Torres, D F; Tosti, G; Troja, E; Uchiyama, Y; Usher, T L; Vandenbroucke, J; Vasileiou, V; Vianello, G; Vitale, V; Waite, A P; Winer, B L; Wood, K S; Wood, M; Yang, Z; Zimmer, S

    2012-01-01

    We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 GeV. We confirm that the fraction rises with energy in the 20-100 GeV range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.

  10. Dipole approximation in the L2,3 electron excited spectra in 3d transition metals

    NASA Astrophysics Data System (ADS)

    Nuroh, K.

    2008-12-01

    A theoretical model based on the autoionization and characteristic decay processes following electron impact ionization of a core electron in solids that has previously been used in calculating electron-energy-loss spectra of transition metals near the 3p -excitation edge has been extended to the 2p -excitation edge for S21c through N27i as well. In the first set of calculations, magnetic effects were ignored and the relative scattering intensity was formulated in terms of the electrostatic interaction U(p,d) between the 3p and 3d electrons of the intermediate resonant configuration state p5dn+1 , using many-body perturbation theory that led to a generalized Fano-type formula for the intensity profiles. In the second set of calculations in which magnetic effects were included as well, an analysis based on the Bethe-Born formalism of inelastic scattering of electrons on atoms was used. The nature of the relative magnitudes of U(p,d) and the spin-orbit parameters ς3p and ς3d and the localized nature of the 3p state necessitated the diagonalization of the intermediate configuration state p5dn+1 to determine the multiplet splitting and their corresponding intensities in the LS -coupling limit using fractional parentage scheme. The nonrelativistic multiconfiguration Hartree-Fock (MCHF) code was used in determining the ground and continuum state wave functions, and the itinerant 3d states in the solid were approximated with an atomic MCHF-wave function. The outline above is applied to the 2p -excitation edge, except that because of the relative magnitudes of U(p,d) , ς2p , and ς3d , it is found that LK coupling is suitable for Sc, Ti, and V, while jK coupling is appropriate for Cr to Ni when it comes to the diagonalization of the configuration p5dn+1 to determine the multiplet splitting and their associated scattering intensities. In the dipole approximation, the scattering intensities separate into two distinct manifolds that arise from the p3/2 and p1/2 states. The

  11. Theoretical calculations on the electron absorption spectra of selected Polycyclic Aromatic Hydrocarbons (PAH) and derivatives

    NASA Technical Reports Server (NTRS)

    Du, Ping

    1993-01-01

    As a theoretical component of the joint effort with the laboratory of Dr. Lou Allamandola to search for potential candidates for interstellar organic carbon compound that are responsible for the visible diffuse interstellar absorption bands (DIB's), quantum mechanical calculations were performed on the electron absorption spectra of selected polycyclic aromatic hydrocarbons (PAH) and derivatives. In the completed project, 15 different species of naphthalene, its hydrogen abstraction and addition derivatives, and corresponding cations and anions were studied. Using semiempirical quantum mechanical method INDO/S, the ground electronic state of each species was evaluated with restricted Hartree-Fock scheme and limited configuration interaction. The lowest energy spin state for each species was used for electron absorption calculations. Results indicate that these calculations are accurate enough to reproduce the spectra of naphthalene cation and anion observed in neon matrix. The spectral pattern of the hydrogen abstraction and addition derivatives predicted based on these results indicate that the electron configuration of the pi orbitals of these species is the dominant determinant. A combined list of 19 absorptions calculated from 4500 A to 10,400 A were compiled and suggested as potential candidates that are relevant for the DIB's absorptions. Continued studies on pyrene and derivatives revealed the ground state symmetries and multiplicities of its neutral, anionic, and cationic species. Spectral calculations show that the cation (B(sub 3g)-2) and the anion (A(sub u)-2) are more likely to have low energy absorptions in the regions between 10 kK and 20 kK, similar to naphthalene. These absorptions, together with those to be determined from the hydrogen abstraction and addition derivatives of pyrene, can be used to provide additional candidates and suggest experimental work in the search for interstellar compounds that are responsible for DIB's.

  12. The effect of implanting boron on the optical absorption and electron paramagnetic resonance spectra of silica

    NASA Astrophysics Data System (ADS)

    Magruder, R. H.; Stesmans, A.; Weeks, R. A.; Weller, R. A.

    2008-09-01

    Silica samples (type III, Corning 7940) were implanted with B using multiple energies to produce a layer ˜600 nm thick in which the concentration of B ranged from 0.034 to 2.04 at. %. Optical absorption spectra were measured from 1.8 to 6.5 eV. Electron paramagnetic resonance (EPR) measurements were generally made at ˜20.3 and 33 GHz for sample temperatures ranging from 77 to 100 K. Based on the EPR spectra three types of defects, namely, Eγ', the E'-type 73 G split doublet (E73'), and the peroxyradical (POR) were identified. No oxygen-associated hole centers (OHCs) nor specific B-associated paramagnetic defects were detected, not even at the largest B concentration of 2.04 at. %. Unlike previous assignments, there was no correlation between the 4.83 eV optical absorption band and the observed PORs. From these results, we infer that in addition to POR, there is at least one additional Si-related state absorbing in the 4.8-4.9 eV range that is likely diamagnetic. The 5.85 eV optical absorption band is found to be due to the Eγ' and E73' centers, with, in average, quite similar oscillator strengths inferred as before. Both the optical absorption and the electron spin resonance data can be satisfactorily explained without the need for specific B-associated defect site (s). As no OHCs are detected by ESR, these do not seem to make a detectable contribution to the optical spectra.

  13. Spatially and momentum resolved energy electron loss spectra from an ultra-thin PrNiO{sub 3} layer

    SciTech Connect

    Kinyanjui, M. K. Kaiser, U.; Benner, G.; Pavia, G.; Boucher, F.; Habermeier, H.-U.; Keimer, B.

    2015-05-18

    We present an experimental approach which allows for the acquisition of spectra from ultra-thin films at high spatial, momentum, and energy resolutions. Spatially and momentum (q) resolved electron energy loss spectra have been obtained from a 12 nm ultra-thin PrNiO{sub 3} layer using a nano-beam electron diffraction based approach which enabled the acquisition of momentum resolved spectra from individual, differently oriented nano-domains and at different positions of the PrNiO{sub 3} thin layer. The spatial and wavelength dependence of the spectral excitations are obtained and characterized after the analysis of the experimental spectra using calculated dielectric and energy loss functions. The presented approach makes a contribution towards obtaining momentum-resolved spectra from nanostructures, thin film, heterostructures, surfaces, and interfaces.

  14. Probe measurements of penning electron spectra in the afterglow of nonlocal helium microplasma

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, Anatoly; Belskiy, Denis; Gutsev, Sergey; Kosykh, Nikolay; Kryukov, Anton

    2012-10-01

    Method PLES [Blagoev A.B., Kolokolov, N.B., Kudryavtsev. Physica Scripta, 1994, v.50, p.371] is based on identification of atoms and molecules of impurities M by selective registration of groups of fast electrons e(f) created in Penning ionization: He(m) + M -> He +M+ + e(f). The electron energy spectrum e(f) contains discrete peaks corresponding to the difference between the energy 19.8 eV of metastable helium atoms He(m) and the ionization energies Ei of impurities M. Since the ionization potential Ei of each type of atom or molecule is a well-known, it is possible to identify the atoms or molecules M of the unknown impurity by their ionization potential Ei. Probe registration of the energy spectra of penning electrons is carried out in the nonlocal afterglow plasma of pulsed microdischarge in helium and its mixtures with argon, krypton and air. In helium, the non-local plasma condition corresponds to p xL < 5 Torr x cm, where p is the gas pressure and L is the plasma volume size. It is demonstrated that the obtained maxima appear at the characteristic energies corresponding exactly to the expected maxima for penning electrons of the known gas impurities used.

  15. Understanding the formation of the Mg II h&k lines during solar flares

    NASA Astrophysics Data System (ADS)

    Rubio Da Costa, Fatima; Kleint, Lucia; Petrosian, Vahe'; Liu, Wei; Allred, Joel C.

    2016-05-01

    The Mg II h&k lines are useful diagnostics for physical processes in the solar chromosphere. Understanding the line formation is crucial for the correct interpretation of spectral observations and characteristics such as line asymmetries or how their central reversals in the line cores disappear and turn into emission during flares are manifestations of various physical processes.Focusing on the well-observed X1.0 flare on 2014 March 29, we carried out a joint observational and modeling study to analyze the Mg II h&k spectra observed by IRIS. We constructed a multi-threaded flare loop model and used the time-dependent electron flux inferred from the RHESSI hard X-ray data as the input to the radiative hydrodynamic code RADYN to simulate the atmospheric response. Using the RH code we conducted a detailed modeling on line shape and evolution to derive how different atmospheric parameters may affect the MgII line emission.We successfully simulated the single-peaked Mg II h&k line profiles by increasing electron density in the upper chromosphere within a narrow height range of ≈ 800 km below the transition region. To our knowledge, this is the first successful attempt in reproducing such line-profile shapes under flaring conditions. We will discuss the implications of this result for diagnosing atmospheric dynamics and energy transport in solar flares.

  16. Spectral investigations of 2,5-difluoroaniline by using mass, electronic absorption, NMR, and vibrational spectra

    NASA Astrophysics Data System (ADS)

    Kose, Etem; Karabacak, Mehmet; Bardak, Fehmi; Atac, Ahmet

    2016-11-01

    One of the most significant aromatic amines is aniline, a primary aromatic amine replacing one hydrogen atom of a benzene molecule with an amino group (NH2). This study reports experimental and theoretical investigation of 2,5-difluoroaniline molecule (2,5-DFA) by using mass, ultraviolet-visible (UV-vis), 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared and Raman (FT-IR and FT-Raman) spectra, and supported with theoretical calculations. Mass spectrum (MS) of 2,5-DFA is presented with their stabilities. The UV-vis spectra of the molecule are recorded in the range of 190-400 nm in water and ethanol solvents. The 1H and 13C NMR chemical shifts are recorded in CDCl3 solution. The vibrational spectra are recorded in the region 4000-400 cm-1 (FT-IR) and 4000-10 cm-1 (FT-Raman), respectively. Theoretical studies are underpinned the experimental results as described below; 2,5-DFA molecule is optimized by using B3LYP/6-311++G(d,p) basis set. The mass spectrum is evaluated and possible fragmentations are proposed based on the stable structure. The electronic properties, such as excitation energies, oscillator strengths, wavelengths, frontier molecular orbitals (FMO), HOMO and LUMO energies, are determined by time-dependent density functional theory (TD-DFT). The electrostatic potential surface (ESPs), density of state (DOS) diagrams are also prepared and evaluated. In addition to these, reduced density gradient (RDG) analysis is performed, and thermodynamic features are carried out theoretically. The NMR spectra (1H and 13C) are calculated by using the gauge-invariant atomic orbital (GIAO) method. The vibrational spectra of 2,5-DFA molecule are obtained by using DFT/B3LYP method with 6-311++G(d,p) basis set. Fundamental vibrations are assigned based on the potential energy distribution (PED) of the vibrational modes. The nonlinear optical properties (NLO) are also investigated. The theoretical and experimental results give a detailed description of

  17. M Dwarf Flare Continuum Variations on One-second Timescales: Calibrating and Modeling of ULTRACAM Flare Color Indices

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam F.; Mathioudakis, Mihalis; Hawley, Suzanne L.; Wisniewski, John P.; Dhillon, Vik S.; Marsh, Tom R.; Hilton, Eric J.; Brown, Benjamin P.

    2016-04-01

    We present a large data set of high-cadence dMe flare light curves obtained with custom continuum filters on the triple-beam, high-speed camera system ULTRACAM. The measurements provide constraints for models of the near-ultraviolet (NUV) and optical continuum spectral evolution on timescales of ≈1 s. We provide a robust interpretation of the flare emission in the ULTRACAM filters using simultaneously obtained low-resolution spectra during two moderate-sized flares in the dM4.5e star YZ CMi. By avoiding the spectral complexity within the broadband Johnson filters, the ULTRACAM filters are shown to characterize bona fide continuum emission in the NUV, blue, and red wavelength regimes. The NUV/blue flux ratio in flares is equivalent to a Balmer jump ratio, and the blue/red flux ratio provides an estimate for the color temperature of the optical continuum emission. We present a new “color-color” relationship for these continuum flux ratios at the peaks of the flares. Using the RADYN and RH codes, we interpret the ULTRACAM filter emission using the dominant emission processes from a radiative-hydrodynamic flare model with a high nonthermal electron beam flux, which explains a hot, T ≈ 104 K, color temperature at blue-to-red optical wavelengths and a small Balmer jump ratio as observed in moderate-sized and large flares alike. We also discuss the high time resolution, high signal-to-noise continuum color variations observed in YZ CMi during a giant flare, which increased the NUV flux from this star by over a factor of 100. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium, based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofsica de Canarias, and observations, and based on observations made with the ESO Telescopes

  18. Measurements of Continuum Flux in Solar Flares

    NASA Astrophysics Data System (ADS)

    Kotrč, P.; Heinzel, P.; Procházka, O.

    2016-04-01

    A broad-band diagnostics of chromospheric flare plasma needs to analyze spectra covering many spectral lines and various continuum features. The flare spectra are well detected on the background of the solar disk, but the detection of flare line emission from the Sun-as-a-star in optical is much more difficult due to a strong background radiation. When the flare/background radiation contrast is strong enough to be detected, we need a device for measuring the flux from a selected part of the flaring region. Here we present technical demands for such an instrument and its brief description. This device denoted as Image Selector is a post-focus instrument installed at the horizontal solar telescope HSFA2 of the Ondřejov observatory, described by Kotrč (2009). Its core consists of a system of diaphragms, imaging Hα telescope and a fast spectrometer with dispersion of 3 px per Å but with cadency reaching up to 50 frames per second. The first solar flares observed recently by this novel technique provide quite interesting results. Our analysis of the data proves that the described device is sufficiently sensitive to detect variations in the Balmer continuum during solar flares.

  19. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    SciTech Connect

    Fujihashi, Yuta; Ishizaki, Akihito; Fleming, Graham R.

    2015-06-07

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  20. QED Approach to Modeling Spectra of the Multicharged Ions in a Plasma: Oscillator and Electron-ion Collision Strengths

    SciTech Connect

    Glushkov, A. V.; Khetselius, O. Yu.; Loboda, A. V.; Ignatenko, A.; Svinarenko, A.; Korchevsky, D.; Lovett, L.

    2008-10-22

    The uniform energy approach, formally based on the QED theory with using gauge invariant scheme of generation of the optimal one-electron representation, is used for the description of spectra of the multicharged ions in a laser plasma, calculation of electron-ion collision strengths, cross-sections in Ne-like and Ar-like ions.

  1. Study of polymorphism in imatinib mesylate: A quantum chemical approach using electronic and vibrational spectra

    NASA Astrophysics Data System (ADS)

    Srivastava, Anubha; Joshi, B. D.; Tandon, Poonam; Ayala, A. P.; Bansal, A. K.; Grillo, Damián

    2013-02-01

    Imatinib mesylate, 4-(4-methyl-piperazin-1-ylmethyl)-N-u[4-methyl-3-(4-pyridin-3-yl)pyrimidine-2-ylamino)phenyl]benzamide methanesulfonate is a therapeutic drug that is approved for the treatment of chronic myelogeneous leukemia (CML) and gastrointestinal stromal tumors (GIST). It is known that imatinib mesylate exists in two polymorphic forms α and β. However, β-form is more stable than the α-form. In this work, we present a detailed vibrational spectroscopic investigation of β-form by using FT-IR and FT-Raman spectra. These data are supported by quantum mechanical calculations using DFT employing 6-311G(d,p) basis set, which allow us to characterize completely the vibrational spectra of this compound. The FT-IR spectrum of α-form has also been discussed. The importance of hydrogen-bond formation in the molecular packing arrangements of both forms has been examined with the vibrational shifts observed due to polymorphic changes. The red shift of the NH stretching bands in the infrared spectrum from the computed wavenumber indicates the weakening of the NH bond. The UV-vis spectroscopic studies along with the HOMO-LUMO analysis of both polymorphs (α and β) were performed and their chemical activity has been discussed. The TD-DFT method was used to calculate the electronic absorption spectra in the gas phase as well as in the solvent environment using IEF-PCM model and 6-31G basis set. Finally, the results obtained complements to the experimental findings.

  2. Properties of electron flux spectra around the plasmapause in the chorus and hiss regions using POES.

    NASA Astrophysics Data System (ADS)

    Whittaker, Ian; Rodger, Craig; Clilverd, Mark

    2014-05-01

    The European FP7 PLASMON project aims to provide observations of plasmaspheric densities, and link the plasmaspheric variations to relativistic electron precipitation from the radiation belts. This is intended to assist in the estimation and prevent damage of space assets from space weather events as well as to improve forecasting (http://plasmon.elte.hu). As part of the PLASMON project, electron fluxes from the POES series of satellites are being used to determine the link between energetic electron precipitation energy spectra and magnitude to the position of the plasmapause. The MEPED instrument onboard POES measures electron flux from 90° (trapped particles) and 0° (losscone) telescopes, in 3 integral energy channels (>30, >100 and >300 keV). These fluxes have been compared to the DEMETER/IDP instrument to confirm that published geometric factor corrections (Yando et al. 2011) can be accurately applied to the POES data to produce as accurate as possible fluxes. These global fluxes have then been separated into regions in which Chorus (23:00-11:00 MLT) and Hiss (11:00-16:00 MLT) whistler mode waves are expected to occur, in 0.2 L-shell bins with a 20 minute temporal resolution. The plasmapause locations have been determined from the O'Brien and Moldwin (2003) models based on Kp, Ae and Dst peaks. We are currently comparing the POES spectral gradient and flux magnitude with plasmapause location and geomagnetic activity for the locations in which chorus and hiss are known to occur. This presentation will focus on the electron flux spectral gradient behaviour either side of the plasmapause, a value that is difficult to measure from ground based techniques.

  3. A comparison between spectra of runaway electron beams in SF{sub 6} and air

    SciTech Connect

    Zhang, Cheng; Wang, Ruexue; Yan, Ping; Shao, Tao; Tarasenko, Victor; Gu, Jianwei; Baksht, Evgenii

    2015-12-15

    Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF{sub 6} and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ∼1.6 ns and a full width at half maximum of 3–5 ns is used to produce RAE beams. The SAEBs in SF{sub 6} and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF{sub 6} and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF{sub 6} was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF{sub 6} in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF{sub 6} decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF{sub 6} decreased when the rise time of the voltage pulse increased.

  4. A comparison between spectra of runaway electron beams in SF6 and air

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Tarasenko, Victor; Gu, Jianwei; Baksht, Evgenii; Wang, Ruexue; Yan, Ping; Shao, Tao

    2015-12-01

    Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF6 and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ˜1.6 ns and a full width at half maximum of 3-5 ns is used to produce RAE beams. The SAEBs in SF6 and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF6 and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF6 was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF6 in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF6 decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF6 decreased when the rise time of the voltage pulse increased.

  5. ULTRAVIOLET AND INFRARED SPECTRA OF ELECTRON-BOMBARDED SOLID NITROGEN AND METHANE DILUTED IN SOLID NITROGEN

    SciTech Connect

    Wu, Yu-Jong; Chuang, Shiang-Jiun; Huang, Tzu-Ping; Chen, Hui-Fen

    2013-05-01

    The infrared (IR) and ultraviolet (UV) absorption spectra of pure solid N{sub 2} and CH{sub 4} diluted in solid N{sub 2} (1/100) irradiated with energetic electrons at 10 K were obtained. The IR absorption measurements of the electron-bombarded pure N{sub 2} solid reveal the formation of N{sub 3} and N{sub 3} {sup +}, which was confirmed by the observed electronic transitions A {sup 2}{Sigma}{sub u} {sup +}<- X {sup 2}{Pi}{sub g} of N{sub 3} and A {sup 3}{Pi}{sub u} <- X {sup 3}{Sigma}{sub g} {sup -} of N{sub 3} {sup +}. In the case of N{sub 2} ice containing a small proportion of CH{sub 4}, we have identified the products of irradiated CH{sub 4}/N{sub 2} ice, including N{sub 3}, C{sub n} N (n = 1-3), CN{sub 2}, (CN){sub 2}, CH{sub 3}N, HCN{sub 2}, HC{sub 2}N, C(NH){sub 2}, HNC, HCN, CH{sub 3}, C{sub 2}H, C{sub 2}H{sub 2}, CN{sup -}, NH{sub 3} {sup +}, and HC{sub 3}N{sup +}. UV absorption measurement of the ice sample was carried out and the possible carriers associated with the observed absorption bands were assigned and discussed.

  6. Two-dimensional terahertz correlation spectra of electronic excitations in semiconductor quantum wells.

    PubMed

    Kuehn, W; Reimann, K; Woerner, M; Elsaesser, T; Hey, R

    2011-05-12

    We discuss a novel approach for nonlinear two-dimensional (2D) spectroscopy in the terahertz (THz) frequency range which is based on a collinear interaction geometry of a sequence of THz pulses with the sample. The nonlinear polarization is determined by a phase-resolved measurement of the electric field transmitted through the sample as a function of the delay τ between two phase-locked pulses and the "real" time t. The information provided by a single 2D scan along the τ and t axes is equivalent to that from a noncollinear photon-echo setup equipped with four local oscillators, each interacting with a different diffracted order. We address basic concepts of collinear 2D THz spectroscopy, in particular data analysis and phasing issues. Different rephasing and nonrephasing contributions to the third-order response are separated and 2D correlation spectra derived. As a prototype application, 2D correlation spectra of intersubband excitations of electrons in semiconductor quantum wells are presented.

  7. Theoretical study of the structure and electronic spectra of fully protonated emeraldine oligomers

    NASA Astrophysics Data System (ADS)

    Zhekova, H.; Tadjer, A.; Ivanova, A.; Petrova, J.; Gospodinova, N.

    Polyaniline (PANI) is one of the most studied conducting polymers. Obtained in its conducting form (known as ?emeraldine salt?) by chemical or electrochemical oxidation of aniline in aqueous acidic medium, this polymer manifests an array of attractive properties. Nevertheless, these properties still need to be described at the molecular level. Intense theoretical investigations during the past few years aim at explaining the chain organization, conductivity mechanism, and other structural and spectral characteristics. Most studies adopt simplified models in which hydration effect is underestimated, since all simulations are performed either in vacuum or in the presence of a limited number of water molecules. The present computational study sheds light on the molecular organization of a number of model PANI hydrated clusters with different alignment and multiplicity, which can explain the experimentally recorded UV/VIS spectra. The influence of hydration and interaction with adjacent oligomers is estimated. Short-chain doubly protonated emeraldine oligomers are used as model systems. The calculations are performed at the semi-empirical (AM1) and/or molecular mechanics (AMBER96) level. Proper configurations of the clusters are selected using Monte Carlo simulations. Electron correlation (CIS) is accounted for upon evaluation of the absorption spectra of the clusters. The relative strength of the interchain coupling is estimated by simulation of PANI clusters consisting of two PANI tetramers in water. Comparison to experimental results is made.

  8. Simulation of Nitroxide Electron Paramagnetic Resonance Spectra from Brownian Trajectories and Molecular Dynamics Simulations

    PubMed Central

    DeSensi, Susan C.; Rangel, David P.; Beth, Albert H.; Lybrand, Terry P.; Hustedt, Eric J.

    2008-01-01

    A simulated continuous wave electron paramagnetic resonance spectrum of a nitroxide spin label can be obtained from the Fourier transform of a free induction decay. It has been previously shown that the free induction decay can be calculated by solving the time-dependent stochastic Liouville equation for a set of Brownian trajectories defining the rotational dynamics of the label. In this work, a quaternion-based Monte Carlo algorithm has been developed to generate Brownian trajectories describing the global rotational diffusion of a spin-labeled protein. Also, molecular dynamics simulations of two spin-labeled mutants of T4 lysozyme, T4L F153R1, and T4L K65R1 have been used to generate trajectories describing the internal dynamics of the protein and the local dynamics of the spin-label side chain. Trajectories from the molecular dynamics simulations combined with trajectories describing the global rotational diffusion of the protein are used to account for all of the dynamics of a spin-labeled protein. Spectra calculated from these combined trajectories correspond well to the experimental spectra for the buried site T4L F153R1 and the helix surface site T4L K65R1. This work provides a framework to further explore the modeling of the dynamics of the spin-label side chain in the wide variety of labeling environments encountered in site-directed spin labeling studies. PMID:18234808

  9. Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid.

    PubMed

    Prabhaharan, M; Prabakaran, A R; Srinivasan, S; Gunasekaran, S

    2015-03-01

    The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000cm(-1)) and FT-Raman spectra (400-4000cm(-1)) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (βtotal) of this molecular system and related properties (β, μ and Δα) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000K.

  10. Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid

    NASA Astrophysics Data System (ADS)

    Prabhaharan, M.; Prabakaran, A. R.; Srinivasan, S.; Gunasekaran, S.

    2015-03-01

    The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000 cm-1) and FT-Raman spectra (400-4000 cm-1) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (βtotal) of this molecular system and related properties (β, μ and Δα) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000 K.

  11. Electronic absorption spectra of charge-transfer complexes based on ferrocene and polyhalohydrocarbons

    SciTech Connect

    Germanova, L.F.; Balabanova, L.V.; Kochetkova, N.S.; Nelyubin, B.V.; Shuekhgeimer, M.G.; Vasil'eva, T.T.

    1986-01-10

    Polyhalomethanes, being as a rule strong electron acceptors, can play the role of photosensitizers of various classes of compounds including organometallic donors such as ferrocene, benchrotrene, etc. The authors found that polyhalohydrocarbons containing CHHal/sub 2/ and CHal/sub 3/ groups from with ferrocene charge-transfer complexes (CTC). Polyhalomethanes and polyhalo-2-pentenes show the highest activity in the reaction of complex formation with ferrocene. The compounds with the CBr/sub 3/ group in CTC have the highest extinction. An elongation of the alkyl chain in the molecule of polyhalogen derivatives and the presence of an additional halogen atom in the gamma position with respect to the CHal/sub 3/ group do not exert any significant influence on their CTC spectra with ferrocene.

  12. Nightmare from which you will never awake: Electronic to vibrational spectra!

    SciTech Connect

    De Silva, Nuwon

    2013-01-01

    The theoretical background of ab initio methods and density functional theory is provided. The anharmonicity associated with weakly bound metal cation dihydrogen complexes is examined using the vibrational self-consistent field (VSCF) method and the interaction between a hydrogen molecule and a metal cation is characterized. A study of molecular hydrogen clustering around the lithium cation and their accompanied vibrational anharmonicity employing VSCF is illustrated. A qualitative interpretation is provided of solvent-induced shifts of amides and simulated electronic absorption spectra using the combined time-dependent density functional theory/effective fragment potential method (TDDFT/EFP). An excited-state solvent assisted quadruple hydrogen atom transfer reaction of a coumarin derivative is elucidated using micro solvated quantum mechanical (QM) water and macro solvated EFP water. A dispersion correction to the QM-EFP1 interaction energy is presented.

  13. K-line spectra from tungsten heated by an intense pulsed electron beam.

    PubMed

    Pereira, N R; Weber, B V; Apruzese, J P; Mosher, D; Schumer, J W; Seely, J F; Szabo, C I; Boyer, C N; Stephanakis, S J; Hudson, L T

    2010-10-01

    The plasma-filled rod-pinch diode (PFRP) is an intense source of x-rays ideal for radiography of dense objects. In the PRFP megavoltage electrons from a pulsed discharge concentrate at the pointed end of a 1 mm diameter tapered tungsten rod. Ionization of this plasma might increase the energy of tungsten's Kα(1) fluorescence line, at 59.3182 keV, enough for the difference to be observed by a high-resolution Cauchois transmission crystal spectrograph. When the PFRP's intense hard bremsstrahlung is suppressed by the proper shielding, such an instrument gives excellent fluorescence spectra, albeit with as yet insufficient resolution to see any effect of tungsten's ionization. Higher resolution is possible with various straightforward upgrades that are feasible thanks to the radiation's high intensity.

  14. K-line spectra from tungsten heated by an intense pulsed electron beam

    SciTech Connect

    Pereira, N. R.; Weber, B. V.; Apruzese, J. P.; Mosher, D.; Schumer, J. W.; Seely, J. F.; Szabo, C. I.; Boyer, C. N.; Stephanakis, S. J.; Hudson, L. T.

    2010-10-15

    The plasma-filled rod-pinch diode (PFRP) is an intense source of x-rays ideal for radiography of dense objects. In the PRFP megavoltage electrons from a pulsed discharge concentrate at the pointed end of a 1 mm diameter tapered tungsten rod. Ionization of this plasma might increase the energy of tungsten's K{alpha}{sub 1} fluorescence line, at 59.3182 keV, enough for the difference to be observed by a high-resolution Cauchois transmission crystal spectrograph. When the PFRP's intense hard bremsstrahlung is suppressed by the proper shielding, such an instrument gives excellent fluorescence spectra, albeit with as yet insufficient resolution to see any effect of tungsten's ionization. Higher resolution is possible with various straightforward upgrades that are feasible thanks to the radiation's high intensity.

  15. Solvatochromic behavior of the electronic absorption spectra of gallic acid and some of its azo derivatives

    NASA Astrophysics Data System (ADS)

    Masoud, Mamdouh S.; Hagagg, Sawsan S.; Ali, Alaa E.; Nasr, Nessma M.

    The electronic absorption spectra of gallic acid and its azo derivatives have been studied in various solvents of different polarities. Multiple regression techniques were applied to calculate the regression and correlation coefficients based on an equation that relates the wavenumbers of the absorption band maxima (υmax-) to the solvent parameters; refractive index (n), dielectric constant (D), empirical Kamlet-Taft solvent parameters, π*(dipolarity/polarizability), α (solvent hydrogen-bond donor acidity) and β (solvent hydrogen-bond acceptor basicity). The fitting coefficient obtained from this analysis allows estimating the contribution of each type of interactions relative to total spectral shifts in solution. The dependence of υmax- on the solvent parameters indicates that the obtained bands are affected by specific and non-specific solute-solvent interactions.

  16. Solvatochromic behavior of the electronic absorption spectra of gallic acid and some of its azo derivatives.

    PubMed

    Masoud, Mamdouh S; Hagagg, Sawsan S; Ali, Alaa E; Nasr, Nessma M

    2012-08-01

    The electronic absorption spectra of gallic acid and its azo derivatives have been studied in various solvents of different polarities. Multiple regression techniques were applied to calculate the regression and correlation coefficients based on an equation that relates the wavenumbers of the absorption band maxima (υ(max)(-)) to the solvent parameters; refractive index (n), dielectric constant (D), empirical Kamlet-Taft solvent parameters, π*(dipolarity/polarizability), α (solvent hydrogen-bond donor acidity) and β (solvent hydrogen-bond acceptor basicity). The fitting coefficient obtained from this analysis allows estimating the contribution of each type of interactions relative to total spectral shifts in solution. The dependence of υ(max)(-) on the solvent parameters indicates that the obtained bands are affected by specific and non-specific solute-solvent interactions.

  17. GAS-PHASE ELECTRONIC SPECTRA OF POLYACETYLENE CATIONS: RELEVANCE OF HIGHER EXCITED STATES

    SciTech Connect

    Rice, C. A.; Rudnev, V.; Dietsche, R.; Maier, J. P.

    2010-07-15

    Transitions to higher electronic states of polyacetylene cations (HC{sub 2n}H{sup +}, n = 4, 5, 6) have been measured in the gas phase at {approx}20 K. The absorption spectra were obtained using a resonant two-color, two-photon fragmentation technique in an ion trap, allowing a direct comparison between laboratory and astrophysical data. The purpose was to investigate the relevance of such transitions to astronomical observations because the general expectation is that the bands could be too broad due to fast intramolecular processes. It is shown that the origin bands are still narrow enough (1-10 cm{sup -1}) to be considered, especially as the higher-lying transitions often possess large oscillator strengths.

  18. Combined treatment of relaxation and fluctuation dynamics in the calculation of two-dimensional electronic spectra

    SciTech Connect

    Seibt, Joachim; Pullerits, Tõnu

    2014-09-21

    While the theoretical description of population transfer subsequent to electronic excitation in combination with a line shape function description of vibrational dynamics in the context of 2D-spectroscopy is well-developed under the assumption of different timescales of population transfer and fluctuation dynamics, the treatment of the interplay between both kinds of processes lacks a comprehensive description. To bridge this gap, we use the cumulant expansion approach to derive response functions, which account for fluctuation dynamics and population transfer simultaneously. We compare 2D-spectra of a model system under different assumptions about correlations between fluctuations and point out under which conditions a simplified treatment is justified. Our study shows that population transfer and dissipative fluctuation dynamics cannot be described independent of each other in general. Advantages and limitations of the proposed calculation method and its compatibility with the modified Redfield description are discussed.

  19. Kinetic energy spectra in thermionic emission from small tungsten cluster anions: evidence for nonclassical electron capture.

    PubMed

    Concina, Bruno; Baguenard, Bruno; Calvo, Florent; Bordas, Christian

    2010-03-14

    The delayed electron emission from small mass-selected anionic tungsten clusters W(n)(-) has been studied for sizes in the range 9 < or = n < or = 21. Kinetic energy spectra have been measured for delays of about 100 ns after laser excitation by a velocity-map imaging spectrometer. They are analyzed in the framework of microreversible statistical theories. The low-energy behavior shows some significant deviations with respect to the classical Langevin capture model, which we interpret as possibly due to the influence of quantum dynamical effects such as tunneling through the centrifugal barrier, rather than shape effects. The cluster temperature has been extracted from both the experimental kinetic energy spectrum and the absolute decay rate. Discrepancies between the two approaches suggest that the sticking probability can be as low as a few percent for the smallest clusters.

  20. Ferromagnetic phases of lunar fines and breccias - Electron magnetic resonance spectra of Apollo 16 samples

    NASA Technical Reports Server (NTRS)

    Weeks, R. A.

    1973-01-01

    Electron magnetic resonance measurements have been made at 9 GHz and at temperatures from 1.2 to 400 K and 35 GHz (300 K) on samples of fines and breccias from Apollo 11-16. Unsorted Apollo 16 fines (less than 1 mm) have Delta H (average) = 580 G and specific intensities that have the same range as fines from the other Apollo collections. The magnetic properties of the 'characteristic' resonance are not in accord with those of iron particles. On the bases of the properties of the 'characteristic' resonance as a function of temperature and Apollo site, laboratory heat treatments on synthetic materials and lunar crystalline rocks and a comparison with the 'characteristic' resonance of the resonance spectra of breccia specimens for which iron particle sizes have been determined from other measurements, it is suggested that some fraction (about 20%) of the 'characteristic' resonance is due to sub-micron particles of ferric oxide phases.

  1. Quiescent and Flaring Structure in RS Canum Venaticorum Stars

    NASA Astrophysics Data System (ADS)

    Sanz-Forcada, J.; Brickhouse, N. S.; Dupree, A. K.

    2002-05-01

    Four of the most active RS CVn stars (V711 Tau, II Peg, σ Gem, and UX Ari) have been observed for a total of 3 Ms with the Extreme Ultraviolet Explorer satellite (EUVE) between 1992 and 2000 January. Flaring and quiescent states of extreme ultraviolet spectra (λλ70-740) and light curves (λλ75-175) have been analyzed to provide emission measure distributions (EMD) for these systems in the range logTe(K)~5.6-7.4, based principally on iron lines. Flux measurements obtained with IUE and the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (ORFEUS) complete the EMD in the lower temperature range [logTe(K)~4.0-5.6]. Frequent flaring activity has been found in the systems, including an increase during the rise phase by a factor of ~9 in the flux of σ Gem, the largest flare enhancement observed with EUVE. Analyses of the EUVE emission in the active single star AB Dor and the low-rotation giant star β Cet are also included. The EMDs are remarkably similar among all the stars, showing a narrow enhancement or ``bump'' around logTe(K)~6.9. These narrow bumps are apparently unrelated to rotation rate, spectral type, binarity, or evolutionary stage. Significant material is found at logTe(K)>~7.0 for the most active stars. Modulation of the EUV flux outside of flaring occurs in four of the stars (σ Gem, V711 Tau, UX Ari, AB Dor). The electron density ranges between Ne~1012 and ~1013 cm-3, measured at logTe(K)~7.0, and may reach higher values during flares. These densities and EMD values imply small scale sizes for emitting regions.

  2. Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

    SciTech Connect

    Vos, M.; Marmitt, G. G.; Finkelstein, Y.; Moreh, R.

    2015-09-14

    Reflection electron energy loss spectra from some insulating materials (CaCO{sub 3}, Li{sub 2}CO{sub 3}, and SiO{sub 2}) taken at relatively high incoming electron energies (5–40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO{sub 2}, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E − E{sub gap}){sup 1.5}. For CaCO{sub 3}, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li{sub 2}CO{sub 3} (7.5 eV) is the first experimental estimate.

  3. Electronic spectra of oxocomplexes of Re(V) with thiolato ligands

    NASA Astrophysics Data System (ADS)

    Gancheff, Jorge S.; Denis, Pablo A.; Hahn, F. Ekkehardt

    2010-08-01

    The electronic spectra of monooxo complexes of rhenium(V) with 1,2-benzenedithiolato (bdt 2-), 3,4-toluenenedithiolato (tdt 2-), maleonitriledithiolato (mnt 2-), and 1,2-dithiooxalato (dto 2-) ligands were investigated at the TD-DFT level employing several functionals and basis sets. The most important transitions are due to ligand-to-metal charge transfer (LMCT) with some minor contribution of ligand-to-metal-ligand charge transfer (LMLCT). However, for [ReO(dto) 2] - this statement does not hold because the transitions are due to metal-ligand-to-metal-ligand charge transfer (MLMLCT). This observation arises from the presence of the oxalate groups. These substituents increase the flexibility of this complex with respect to the complexes containing bdt 2-, mnt 2- and tdt 2-. In these complexes, the C-C backbone imposes a rigid geometry, which leads to the occupied rhenium-orbitals lying energetically below the sulfur-based orbitals. For the complexes [ReO(bdt) 2] -, [ReO(mnt) 2] - and [ReO(tdt) 2] -, the HOMO is a sulfur-based out-of-plane molecular orbital. However, the HOMO of [ReO(dto) 2] - shows a high contribution of the rhenium dx2- y2 and in-plane sulfur-centered orbitals. The comparison of the results obtained with several functionals clearly point to the PBE1PBE/LANL2DZ method as the best TD-DFT method to investigate the electronic spectra of monooxo complexes of Re(V) with thiolato ligands. The results obtained with larger basis sets suggest that the agreement between experiment and theory was due to an error cancellation between basis set incompleteness and deficiencies in the DFT methods.

  4. Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra.

    PubMed

    Vos, M; Marmitt, G G; Finkelstein, Y; Moreh, R

    2015-09-14

    Reflection electron energy loss spectra from some insulating materials (CaCO3, Li2CO3, and SiO2) taken at relatively high incoming electron energies (5-40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO2, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E - Egap)(1.5). For CaCO3, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li2CO3 (7.5 eV) is the first experimental estimate.

  5. Analysis of Gamma-Ray Data from Solar Flares in Cycles 21 and 22

    NASA Technical Reports Server (NTRS)

    Vestrand, W. Thomas

    1998-01-01

    One of our primary accomplishments under grant NAGW-35381 was the systematic derivation and compilation, for the first time, of physical parameters for all gamma-ray flares detected by the SMM GRS during its ten year lifetime. The flare parameters derived from the gamma-ray spectra include: bremsstrahlung fluence and best-fit power-law parameters, narrow nuclear line fluence, positron annihilation line fluence, neutron capture line fluence, and an indication of whether or not greater than 10 MeV emissions were present. We combined this compilation of flare parameters with our plots of counting rate time histories and flare spectra to construct an atlas of gamma-ray flare characteristics. The atlas time histories display four energy bands: 56-199 kev, 298526 keV, 4-8 MeV, and 10-25 MeV. These energy bands respectively measure nonrelativistic bremsstrahlung, trans-relativistic bremsstrahlung, nuclear de-excitation, and ultra-relativistic bremsstrahlung. The atlas spectra show the integrated high-energy spectra measured for all GRS flares and dissects them into electron bremsstrahlung, positron annihilation and nuclear emission components. The atlas has been accepted for publication in the Astrophysical Journal Supplements and is currently in press. The atlas materials were also supplied to the Solar Data Analysis Center at Goddard Space Flight Center and were made available through a web site at the University of New Hampshire. Since a uniform methodology was adopted for deriving the flare parameters, this atlas will be very useful for future statistical and correlative studies of solar flares-three independent groups are presently using it to correlate interplanetary energetic particle measurements with our gamma-ray measurements. A better model for the response of the GRS instrument to high energy radiation was also developed. A refined response model was needed because the old model was not adequate for predicting the first and second escape peaks associated with

  6. Spectral analysis and modeling of solar flares chromospheric condensation

    NASA Astrophysics Data System (ADS)

    Cauzzi, Gianna; Graham, David; Kowalski, Adam; Zangrilli, Luca; Simoes, Paulo; Allred, Joel C.

    2016-05-01

    We follow up on our recent analysis of the X1.1 flare SOL2014-09-10T17:45, where we studied the impulsive phase dynamics of tens of individual flaring "kernels", in both coronal (Fe XXI) and chromospheric (MgII) lines observed at high cadence with IRIS.We concentrate here on the chromospheric aspect of the phenomenon, extending the analysis to multiple spectral lines of Mg II, Fe II, Si I, C II. We show that many flaring kernels display high velocity downflows in the spectra of all these chromospheric lines, exhibiting distinct, transient and strongly redshifted spectral components.From modeling using RADYN with the thick-target interpretation, the presence of two spectral components appears to be consistent with a high flux beam of accelerated electrons, characterized by a hard spectrum. In particular the highest energy electrons heat the denser, lower layers of the atmosphere, while the bulk of the beam energy, deposited higher in the atmosphere, is sufficient to produce chromospheric evaporation with a corresponding condensation.

  7. KEPLER FLARES. I. ACTIVE AND INACTIVE M DWARFS

    SciTech Connect

    Hawley, Suzanne L.; Davenport, James R. A.; Kowalski, Adam F.; Wisniewski, John P.; Deitrick, Russell; Hilton, Eric J.; Hebb, Leslie

    2014-12-20

    We analyzed Kepler short-cadence M dwarf observations. Spectra from the Astrophysical Research Consortium 3.5 m telescope identify magnetically active (Hα in emission) stars. The active stars are of mid-M spectral type, have numerous flares, and have well-defined rotational modulation due to starspots. The inactive stars are of early M type, exhibit less starspot signature, and have fewer flares. A Kepler to U-band energy scaling allows comparison of the Kepler flare frequency distributions with previous ground-based data. M dwarfs span a large range of flare frequency and energy, blurring the distinction between active and inactive stars designated solely by the presence of Hα. We analyzed classical and complex (multiple peak) flares on GJ 1243, finding strong correlations between flare energy, amplitude, duration, and decay time, with only a weak dependence on rise time. Complex flares last longer and have higher energy at the same amplitude, and higher energy flares are more likely to be complex. A power law fits the energy distribution for flares with log E{sub K{sub p}}> 31 erg, but the predicted number of low-energy flares far exceeds the number observed, at energies where flares are still easily detectable, indicating that the power-law distribution may flatten at low energy. There is no correlation of flare occurrence or energy with starspot phase, the flare waiting time distribution is consistent with flares occurring randomly in time, and the energies of consecutive flares are uncorrelated. These observations support a scenario where many independent active regions on the stellar surface are contributing to the observed flare rate.

  8. Electronic structure, bonding, spectra, and linear and nonlinear electric properties of Ti@C28.

    PubMed

    Skwara, Bartłomiej; Góra, Robert W; Zaleśny, Robert; Lipkowski, Paweł; Bartkowiak, Wojciech; Reis, Heribert; Papadopoulos, Manthos G; Luis, Josep M; Kirtman, Bernard

    2011-09-22

    The potential energy surface (PES) of Ti@C(28) has been revisited, and the stationary points have been carefully characterized. In particular, the C(2v) symmetry structure considered previously turns out to be a transition state lying 2.3 kcal/mol above the ground state of C(3v) symmetry at the MP2/6-31G(d) level. A large binding energy of 181.3 kcal/mol is found at the ROMP2/6-31G(d) level. Topological analysis of the generalized Ti@C(28) density reveals four bond paths between Ti and carbon atoms of the host. The character of all four contacts corresponds to a partially covalent closed shell interaction. UV-vis, IR, and Raman spectra are calculated and compared with C(28)H(4). The dipole moment and the static electronic and double harmonic vibrational (hyper)polarizabilities have been obtained. Distortion of the fullerene cage due to encapsulation leads to nonzero diagonal components of the electronic first hyperpolarizability β, and to an increase in the diagonal components of the electronic polarizability α and second hyperpolarizability γ. However, introduction of the Ti atom causes a comparable or larger reduction in most cases due to localized bonding interactions. At the double harmonic level, the average vibrational β is much larger than its electronic counterpart, but the opposite is true for α and for the contribution to γ that has been calculated. There is also a very large anharmonic (nuclear relaxation) contribution to β which results from a shallow PES with four minima separated by very low barriers. Thus, the vibrational γ (and α) may, likewise, become much larger when anharmonicity is taken into account.

  9. Investigation of the electronic absorption spectra and the circular dichroism spectra of binuclear tetra-. mu. -mandelato complexes of Mo/sub 2//sup 4 +/

    SciTech Connect

    Golovaneva, I.F.; Akhmedov, E.L.; Kotel'nikova, A.S.

    1987-05-01

    The IR, electronic absorption, and circular dichroism spectra of the binuclear tetra-..mu..-mandelates of molybdenum(II) (Mo/sub 2//D-(-)-OOCCH(OH)C/sub 6/H/sub 5///sub 4/) and (Mo/sub 2//L-(+)-OOCCH(OH)C/sub 6/H/sub 5///sub 4/) have been studied. It has been established that Cotton effects are induced in all the electronic transitions of the symmetric (Mo/sub 2/O/sub 8/)chromophore under the influence of the asymmetric atom of the optically active mandelato ligand. The observed electronic transitions have been assigned on the basis of an analysis of the spectroscopic data obtained.

  10. Electronic spectra of oxygen containing polycyclic hydrocarbon cations and the protonated analogues

    NASA Astrophysics Data System (ADS)

    Chakraborty, Arghya; Fulara, Jan; Maier, John P.

    2015-08-01

    The electronic transitions of 9-fluorenone FL+ and 2,3,6,7-dibenzotropone DBT+ cations were detected in 6 K neon matrices following a mass-selective deposition. The absorptions at 649.2 and 472.2 nm are assigned to the 2 2 B 1 ← X ˜ 2 A 2 FL + and 2 2 A ' ← X ˜ 2 A ' DBT + transitions. Absorption spectra of protonated 9-fluorenone H+-FL and 2,3,6,7-dibenzotropone H+-DBT have also been measured. Protonation of the oxygenated polycyclic aromatic hydrocarbons is carried out in a hot cathode source via in situ produced protonated ethanol. Vibrationally resolved absorptions commencing at 423.3 nm of H-FL+ and two band systems of H-DBT+ with origins at 502.4 and 371.5 nm are assigned to the 2 1 A ' ← X ˜ 1 A ' electronic transition of 9-hydroxy-fluorenyl cation and 1 1 A ← X ˜ 1 A , 2 1 A ← X ˜ 1 A of 2,3,6,7-dibenzocycloheptenol cation. The assignments are based on vertical excitation energy calculations with time dependent density functional theory, symmetry adapted cluster configuration interaction, and MS-CASPT2 methods.

  11. Electronic spectra of oxygen containing polycyclic hydrocarbon cations and the protonated analogues.

    PubMed

    Chakraborty, Arghya; Fulara, Jan; Maier, John P

    2015-08-28

    The electronic transitions of 9-fluorenone FL(+) and 2,3,6,7-dibenzotropone DBT(+) cations were detected in 6 K neon matrices following a mass-selective deposition. The absorptions at 649.2 and 472.2 nm are assigned to the 2 (2)B1←X̃(2)A2 FL(+) and 2(2)A(')←X̃(2)A(') DBT(+) transitions. Absorption spectra of protonated 9-fluorenone H(+)-FL and 2,3,6,7-dibenzotropone H(+)-DBT have also been measured. Protonation of the oxygenated polycyclic aromatic hydrocarbons is carried out in a hot cathode source via in situ produced protonated ethanol. Vibrationally resolved absorptions commencing at 423.3 nm of H-FL(+) and two band systems of H-DBT(+) with origins at 502.4 and 371.5 nm are assigned to the 2(1)A(')←X̃(1)A(') electronic transition of 9-hydroxy-fluorenyl cation and 1 (1)A←X̃(1)A, 2 (1)A←X̃(1)A of 2,3,6,7-dibenzocycloheptenol cation. The assignments are based on vertical excitation energy calculations with time dependent density functional theory, symmetry adapted cluster configuration interaction, and MS-CASPT2 methods. PMID:26328848

  12. Structure and Electronic Spectra of Purine-Methyl Viologen Charge Transfer Complexes

    PubMed Central

    Jalilov, Almaz S.; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A.; Schatz, George C.; Lewis, Frederick D.

    2014-01-01

    The structure and properties of the electron donor-acceptor complexes formed between methyl viologen (MV) and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and 1H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well described by time-dependent (TD) DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2′-deoxyguanosine 3′-monophosphate GMP (DAD′DAD′ type) and 7-deazaguanosine zG (DAD′ADAD′ type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors. PMID:24294996

  13. Structure and electronic spectra of purine-methyl viologen charge transfer complexes.

    PubMed

    Jalilov, Almaz S; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A; Schatz, George C; Lewis, Frederick D

    2014-01-01

    The structure and properties of the electron donor-acceptor complexes formed between methyl viologen and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and (1)H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well-described by time-dependent DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2'-deoxyguanosine 3'-monophosphate (DAD'DAD' type) and 7-deazaguanosine (DAD'ADAD' type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors.

  14. The effect of electron measurements both inside and outside the heliosphere on the modelling of local interstellar spectra

    NASA Astrophysics Data System (ADS)

    Bisschoff, Driaan; Potgieter, Marius

    2016-07-01

    A local interstellar spectrum (LIS) for electrons can be calculated with Galactic propagation models to benefit both Galactic and heliospheric propagation studies by considering the improved measurements for cosmic rays (CRs) made over the last few years, such as by Voyager 1 and PAMELA. Cosmic ray measurements made by Voyager 1 outside the dominant influence of solar modulation uniquely allows the direct comparison of modelled Galactic spectra to experimental data. Recent improved analysis of the PAMELA electron spectra gives measurements for the exceptional solar minimum of 2009 which clearly depict ideal minimum modulation conditions for CRs in the heliosphere. Utilizing the GALPROP code, a LIS for electrons is computed to directly reproduce the electron spectra observed by Voyager 1. Using this LIS as input to a comprehensive solar modulation model enables the comparison with the PAMELA electron spectra. To accomplish reproducing the electron measurements of both CR experiments, we established a LIS with by varying the source spectrum and diffusion parameters in the GALPROP code. Inclusion of reacceleration in Galactic space improves the LIS to also match the lower energy PAMELA values after been modulated through a full 3D solar modulation model.

  15. Calculation of electron paramagnetic resonance spectra from Brownian dynamics trajectories: application to nitroxide side chains in proteins.

    PubMed Central

    Steinhoff, H J; Hubbell, W L

    1996-01-01

    We present a method to simulate electron paramagnetic resonance spectra of spin-labeled proteins that explicitly includes the protein structure in the vicinity of the attached spin label. The method is applied to a spin-labeled polyleucine alpha-helix trimer. From short (6 ns) stochastic dynamics simulations of this trimer, an effective potential energy function is calculated. Interaction with secondary and tertiary structures determine the reorientational motion of the spin label side chains. After reduction to a single particle problem, long stochastic dynamic trajectories (700 ns) of the spin label side-chain reorientation are calculated from which the Lamor frequency trajectory and subsequently the electron paramagnetic resonance spectrum is determined. The simulated spectra agree well with experimental electron paramagnetic resonance spectra of bacteriorhodopsin mutants with spin labels in similar secondary and tertiary environments as in the polyleucine. Images FIGURE 1 PMID:8889196

  16. Electron spectra of xenon clusters irradiated with a laser-driven plasma soft-x-ray laser pulse

    SciTech Connect

    Namba, S.; Takiyama, K.; Hasegawa, N.; Kishimoto, M.; Nishikino, M.; Kawachi, T.

    2011-11-15

    Xenon clusters were irradiated with plasma soft-x-ray laser pulses (having a wavelength of 13.9 nm, time duration of 7 ps, and intensities of up to 10 GW/cm{sup 2}). The laser photon energy was high enough to photoionize 4d core electrons. The cross section is large due to a giant resonance. The interaction was investigated by measuring the electron energy spectra. The photoelectron spectra for small clusters indicate that the spectral width due to the 4d hole significantly broadens with increasing cluster size. For larger clusters, the electron energy spectra evolve into a Maxwell-Boltzmann distribution, as a strongly coupled cluster nanoplasma is generated.

  17. The first very local interstellar spectra for galactic protons, helium, carbon and electrons below 50 GeV

    NASA Astrophysics Data System (ADS)

    Potgieter, Marius; Ngobeni, Mabedle Donald; Sibusiso Nkosi, Godfrey; Nndanganeni, Rendani; Vos, Etienne

    Low-energy galactic electrons (1-300 MeV) are significantly modulated, almost extraordinary, in the heliosheath in contrast to the rest of the heliosphere, indicating that modulation conditions in the heliosheath are quite different for these particles. In addition, Jovian electrons completely dominate galactic electrons at Earth below about 50 MeV. Low-energy protons and helium (1-100 MeV/nuc), on the other hand, are dominated by the anomalous component which originates inside the inner heliosheath so that the very local interstellar spectra for these particles had been properly concealed until recently. However, this is not the case for cosmic ray carbon. Basic mechanisms responsible for these effects are been studied with comprehensive numerical models for the transport of these particles, from the modulation boundary, through the inner heliosheath, across the solar wind termination shock, up to Earth. Together with measurements made by the two Voyager spacecraft, now with Voyager 1 beyond the heliopause and entering the very local interstellar medium, it is possible to determine heliopause spectra (HPS) at these low energies for the first time. Together with PAMELA spectra observed at Earth, these HPS can be determined accurately up to at least 50 GeV. Such spectra should be considered as the lowest possible very local interstellar spectra for galactic electrons, protons, helium and carbon, and are of great relevance to solar modulation and galactic propagation studies.

  18. Electron densities inferred from plasma wave spectra obtained by the Waves instrument on Van Allen Probes

    PubMed Central

    Kurth, W S; De Pascuale, S; Faden, J B; Kletzing, C A; Hospodarsky, G B; Thaller, S; Wygant, J R

    2015-01-01

    The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum. PMID:26167442

  19. Diagrammatic expansion for positive density-response spectra: Application to the electron gas

    NASA Astrophysics Data System (ADS)

    Uimonen, A.-M.; Stefanucci, G.; Pavlyukh, Y.; van Leeuwen, R.

    2015-03-01

    In a recent paper [Phys. Rev. B 90, 115134 (2014), 10.1103/PhysRevB.90.115134] we put forward a diagrammatic expansion for the self-energy which guarantees the positivity of the spectral function. In this work we extend the theory to the density-response function. We write the generic diagram for the density-response spectrum as the sum of "partitions." In a partition the original diagram is evaluated using time-ordered Green's functions on the left half of the diagram, antitime-ordered Green's functions on the right half of the diagram, and lesser or greater Green's function gluing the two halves. As there exists more than one way to cut a diagram in two halves, to every diagram corresponds more than one partition. We recognize that the most convenient diagrammatic objects for constructing a theory of positive spectra are the half-diagrams. Diagrammatic approximations obtained by summing the squares of half-diagrams do indeed correspond to a combination of partitions which, by construction, yield a positive spectrum. We develop the theory using bare Green's functions and subsequently extend it to dressed Green's functions. We further prove a connection between the positivity of the spectral function and the analytic properties of the polarizability. The general theory is illustrated with several examples and then applied to solve the long-standing problem of including vertex corrections without altering the positivity of the spectrum. In fact already the first-order vertex diagram, relevant to the study of gradient expansion, Friedel oscillations, etc., leads to spectra which are negative in certain frequency domain. We find that the simplest approximation to cure this deficiency is given by the sum of the zeroth-order bubble diagram, the first-order vertex diagram, and a partition of the second-order ladder diagram. We evaluate this approximation in the three-dimensional homogeneous electron gas and show the positivity of the spectrum for all frequencies and

  20. Temperature dependence on the electron paramagnetic resonance spectra of natural jasper from Taroko Gorge (Taiwan)

    NASA Astrophysics Data System (ADS)

    Hemantha Kumar, G. N.; Parthasarathy, G.; Chakradhar, R. P. S.; Rao, J. Lakshmana; Ratnakaram, Y. C.

    2010-04-01

    Structural properties of natural jasper from Taroko Gorge (Taiwan) have been investigated by means of powder X-ray diffraction, electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopic techniques. The EPR spectrum at room temperature exhibits a sharp resonance signal at g = 2.007 and two more resonance signals centered at g ≈ 4.3 and 14.0. The resonance signal at g = 2.007 has been attributed to the E' center and is related to a natural radiation-induced paramagnetic defect. Two more resonance signals centered at g ≈ 4.3 and 14.0 are characteristic of Fe3+ ions. The EPR spectra recorded at room temperature of jasper samples, heat-treated at temperatures ranging from 473 to 1,473 K exhibit marked temperature dependence. The resonance signal corresponding to E' center disappears at elevated temperatures. A broad, intense resonance signal centered at g ≈ 2.0 appears at elevated temperatures. This resonance signal is a characteristic of Fe3+ ions, which are present as hematite in the jasper sample. The intensity of the resonance signal becomes dominant at elevated temperatures at ≥873 K, masking g ≈ 4.3 and g ≈ 14.0 resonance signals. The EPR spectra of jasper heat-treated at 673 K have been recorded at temperatures between 123 and 296 K. The population of spin levels ( N) has been calculated for the broad g ≈ 2.0 resonance signal. It is found that N decreases with decreasing temperature. The linewidth (ΔH) of g ≈ 2.0 resonance signal of the heat-treated jasper is found to increase with decreasing temperature. This has been attributed to spin-spin interaction of the Fe3+ ions present in the form of hematite in the studied jasper sample.

  1. Solar flare ionization in the mesosphere observed by coherent-scatter radar

    NASA Technical Reports Server (NTRS)

    Parker, J. W.; Bowhill, S. A.

    1986-01-01

    The coherent-scatter technique, as used with the Urbana radar, is able to measure relative changes in electron density at one altitude during the progress of a solar flare when that altitude contains a statistically steady turbulent layer. This work describes the analysis of Urbana coherent-scatter data from the times of 13 solar flares in the period from 1978 to 1983. Previous methods of measuring electron density changes in the D-region are summarized. Models of X-ray spectra, photoionization rates, and ion-recombination reaction schemes are reviewed. The coherent-scatter technique is briefly described, and a model is developed which relates changes in scattered power to changes in electron density. An analysis technique is developed using X-ray flux data from geostationary satellites and coherent scatter data from the Urbana radar which empirically distinguishes between proposed D-region ion-chemical schemes, and estimates the nonflare ion-pair production rate.

  2. Vibronic Coupling Explains the Different Shape of Electronic Circular Dichroism and of Circularly Polarized Luminescence Spectra of Hexahelicenes.

    PubMed

    Liu, Yanli; Cerezo, Javier; Mazzeo, Giuseppe; Lin, Na; Zhao, Xian; Longhi, Giovanna; Abbate, Sergio; Santoro, Fabrizio

    2016-06-14

    We present the simulation of the absorption (ABS), electronic circular dichroism (ECD), emission (EMI), and circularly polarized luminescence (CPL) spectra for the weak electronic transition between the ground (S0) and the lowest excited state (S1) of hexahelicene, 2-methylhexahelicene, 2-bromohexahelicene, and 5-azahexahelicene. Vibronic contributions have been computed at zero Kelvin and at room temperature in harmonic approximation including Duschinsky effects and accounting for both Franck-Condon and Herzberg-Teller contributions. Our results nicely capture the effects of the different substituents on the experimental spectra. They also show that HT effects dominate the shape of ECD and CPL spectra where they even induce changes of signs; HT effects are also relevant in ABS and EMI, tuning the relative intensities of the different vibronic bands. HT effects are the main reason for the differences in the line shapes of ABS and ECD and of EMI and CPL spectra and for the mirror-symmetry breaking between ABS and EMI and between ECD and CPL spectra. In order to check the robustness of our results, given also that few examples of calculations of vibronic CPL spectra exist, we adopted both adiabatic and vertical approaches to define the model potential energy surfaces of the (S0) and the (S1) states; moreover we expanded the electric and magnetic dipole transition moments around both the S0 and S1 equilibrium geometries. PMID:27120334

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

    SciTech Connect

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

    2012-07-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  5. Analysis of Electron and Antineutrino Energy Spectra from Fissile Samples under Irradiation based on Gross Theory of Beta-decay

    NASA Astrophysics Data System (ADS)

    Yoshida, T.; Tachibana, T.; Chiba, S.

    2016-06-01

    We applied the gross theory of β-decay to calculate the reactor electron and antineutrino ({{{bar ν }}{e}}) spectra emitted from 235,238U and 239,241Pu by summing up all the contributions from a large number of decaying fission-products (FPs). We make it clear what kinds of transition types and FP nuclides are important to shape the lepton spectra. After taking the ambiguity in the current data for fission yields and Qβ-values into account, we suggested a possibility that the high-energy part of the widely referred electron-spectra by Schreckenbach et al., almost only one experimental data set available now, might possibly be too low. Arguments on a special role of the odd(Z)-odd(N) nuclides and on the consistency between U-238 and other fissiles in the experimental data lead to the importance of a new and independent measurement of electron energy spectra which could be converted into the reactor {{{bar ν }}{e}} spectra.

  6. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces.

    PubMed

    Mishchuk, Oleg A

    2016-12-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events.

  7. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces

    NASA Astrophysics Data System (ADS)

    Mishchuk, Oleg A.

    2016-04-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events.

  8. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces.

    PubMed

    Mishchuk, Oleg A

    2016-12-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events. PMID:27083583

  9. He-like argon, chlorine and sulfur spectra measurement from an Electron Cyclotron Resonance Ion Trap

    NASA Astrophysics Data System (ADS)

    Trassinelli, M.; Boucard, S.; Covita, D. S.; Gotta, D.; Hirtl, A.; Indelicato, P.; LeBigot, É.-O.; dos Santos, J. M. F.; Simons, L. M.; Stingelin, L.; Veloso, J. F. C. A.; Wasser, A.; Zmeskal, J.

    2007-03-01

    We present a new measurement on X-ray spectroscopy of multicharged argon, chlorine and sulfur obtained with the Electron Cyclotron Resonance Ion Trap installed at the Paul Scherrer Institut (Villigen, Switzerland). For this purpose, we used a crystal spectrometer with a spherically bent crystal having an energy resolution of about 0.4 eV. High intensity Kα X-ray spectra were obtained from ions with one 1s hole ranging from almost neutral to heliumlike charge states. In particular we observed the 1s2s 3S1 → 1s2 1S0 M1 and 1s2p 3P2 → 1s2 1S0 M2 transitions in He-like argon, chlorine and sulfur with unprecedented statistics and resolution. The preliminary analysis presented here describes a new technique to measure precisely energy differences between transitions using a Johann-type Bragg spectrometer. A recent characterization of the spectrometer will allow for a drastic reduction of the systematic errors.

  10. Vibrational and electronic spectra of 2-nitrobenzanthrone: An experimental and computational study.

    PubMed

    Onchoke, Kefa K; Chaudhry, Saad N; Ojeda, Jorge J

    2016-01-15

    The environmental pollutant 2-nitrobenzanthrone (2-NBA) poses human health hazards, and is formed by atmospheric reactions of NOX gases with atmospheric particulates. Though its mutagenic effects have been studied in biological systems, its comprehensive spectroscopic experimental data are scarce. Thus, vibrational and optical spectroscopic analysis (UV-Vis, and fluorescence) of 2-NBA was studied using both experimental and density functional theory employing B3LYP method with 6-311+G(d,p) basis set. The scaled theoretical vibrational frequencies show good agreement to experiment to within ~5 cm(-1) and <20 cm(-1) for frequencies <1800 cm(-1) and 2700-3200 cm(-1), respectively. In addition, predictions of the DFT frequencies below 1800 cm(-1) yield an overall root mean square (RMS) of ±20.1 and ±20.6 cm(-1) for benzanthrone and 2-NBA, respectively. On the basis of normal coordinate analysis complete assignments of harmonic experimental infrared and Raman bands are made. The influence of the nitro group substitution upon the benzanthrone structure and symmetric CH vibrations, and electronic spectra is noted. This study is useful for the development of spectroscopy-mutagenicity relationships in nitrated polycyclic aromatic hydrocarbons.

  11. Vibrational and electronic spectra of 2-nitrobenzanthrone: An experimental and computational study

    NASA Astrophysics Data System (ADS)

    Onchoke, Kefa K.; Chaudhry, Saad N.; Ojeda, Jorge J.

    2016-01-01

    The environmental pollutant 2-nitrobenzanthrone (2-NBA) poses human health hazards, and is formed by atmospheric reactions of NOX gases with atmospheric particulates. Though its mutagenic effects have been studied in biological systems, its comprehensive spectroscopic experimental data are scarce. Thus, vibrational and optical spectroscopic analysis (UV-Vis, and fluorescence) of 2-NBA was studied using both experimental and density functional theory employing B3LYP method with 6-311 + G(d,p) basis set. The scaled theoretical vibrational frequencies show good agreement to experiment to within ~ 5 cm- 1 and < 20 cm- 1 for frequencies < 1800 cm- 1 and 2700-3200 cm- 1, respectively. In addition, predictions of the DFT frequencies below 1800 cm- 1 yield an overall root mean square (RMS) of ± 20.1 and ± 20.6 cm- 1 for benzanthrone and 2-NBA, respectively. On the basis of normal coordinate analysis complete assignments of harmonic experimental infrared and Raman bands are made. The influence of the nitro group substitution upon the benzanthrone structure and symmetric CH vibrations, and electronic spectra is noted. This study is useful for the development of spectroscopy-mutagenicity relationships in nitrated polycyclic aromatic hydrocarbons.

  12. Understanding Solar Flare Statistics

    NASA Astrophysics Data System (ADS)

    Wheatland, M. S.

    2005-12-01

    A review is presented of work aimed at understanding solar flare statistics, with emphasis on the well known flare power-law size distribution. Although avalanche models are perhaps the favoured model to describe flare statistics, their physical basis is unclear, and they are divorced from developing ideas in large-scale reconnection theory. An alternative model, aimed at reconciling large-scale reconnection models with solar flare statistics, is revisited. The solar flare waiting-time distribution has also attracted recent attention. Observed waiting-time distributions are described, together with what they might tell us about the flare phenomenon. Finally, a practical application of flare statistics to flare prediction is described in detail, including the results of a year of automated (web-based) predictions from the method.

  13. Solar Flare Impulsive Phase Observations from SDO and Other Observatories

    NASA Technical Reports Server (NTRS)

    Chamberlin, Phillip C.; Woods, Thomas N.; Schrijver, Karel; Warren, Harry; Milligan, Ryan; Christe, Steven; Brosius, Jeffrey W.

    2010-01-01

    With the start of normal operations of the Solar Dynamics Observatory in May 2010, the Extreme ultraviolet Variability Experiment (EVE) and the Atmospheric Imaging Assembly (AIA) have been returning the most accurate solar XUV and EUV measurements every 10 and 12 seconds, respectively, at almost 100% duty cycle. The focus of the presentation will be the solar flare impulsive phase observations provided by EVE and AIA and what these observations can tell us about the evolution of the initial phase of solar flares. Also emphasized throughout is how simultaneous observations with other instruments, such as RHESSI, SOHO-CDS, and HINODE-EIS, will help provide a more complete characterization of the solar flares and the evolution and energetics during the impulsive phase. These co-temporal observations from the other solar instruments can provide information such as extending the high temperature range spectra and images beyond that provided by the EUV and XUV wavelengths, provide electron density input into the lower atmosphere at the footpoints, and provide plasma flows of chromospheric evaporation, among other characteristics.

  14. Nuclear processes and neutrino production in solar flares

    NASA Technical Reports Server (NTRS)

    Lingenfelter, R. E.; Ramaty, R.; Murphy, R. J.; Kozlovsky, S.

    1985-01-01

    The determination of flare neutrino flux is approached from the standpoint of recent observations and theoretical results on the nuclear processes in solar flares. Attention is given to the energy spectra and total numbers of accelerated particles in flares, as well as their resulting production of beta(+)-emitting radionuclei and pions; these should be the primary sources of neutrinos. The observed 0.511 MeV line flux for the June 21, 1980 flare is compared with the expected from the number and spectrum of accelerated particles.

  15. Electronic and oscillation absorption spectra of blood plamsa at surgical diseases of thyroid gland

    NASA Astrophysics Data System (ADS)

    Guminetskiy, S. G.; Motrich, A. V.; Poliansky, I. Y.; Hyrla, Ya. V.

    2011-09-01

    The results of investigating the absorption spectra of blood plasma in the visible and infrared parts of spectra obtained using the techniques of spherical photometer and spectrophotometric complex "Specord IR75" are presented. The possibility of using these spectra for diagnoses the cases of diffuse toxic goiter and nodular goiter and control of treatment process in postsurgical period in the cases of thyroid gland surgery is estimated.

  16. Electronic and oscillation absorption spectra of blood plamsa at surgical diseases of thyroid gland

    NASA Astrophysics Data System (ADS)

    Guminetskiy, S. G.; Motrich, A. V.; Poliansky, I. Y.; Hyrla, Ya. V.

    2012-01-01

    The results of investigating the absorption spectra of blood plasma in the visible and infrared parts of spectra obtained using the techniques of spherical photometer and spectrophotometric complex "Specord IR75" are presented. The possibility of using these spectra for diagnoses the cases of diffuse toxic goiter and nodular goiter and control of treatment process in postsurgical period in the cases of thyroid gland surgery is estimated.

  17. KINETIC ALFVEN TURBULENCE AND PARALLEL ELECTRIC FIELDS IN FLARE LOOPS

    SciTech Connect

    Zhao, J. S.; Wu, D. J.; Lu, J. Y.

    2013-04-20

    This study investigates the spectral structure of the kinetic Alfven turbulence in the low-beta plasmas. We consider a strong turbulence resulting from collisions between counterpropagating wavepackets with equal energy. Our results show that (1) the spectra of the magnetic and electric field fluctuations display a transition at the electron inertial length scale, (2) the turbulence cascades mainly toward the magnetic field direction as the cascade scale is smaller than the electron inertial length, and (3) the parallel electric field increases as the turbulent scale decreases. We also show that the parallel electric field in the solar flare loops can be 10{sup 2}-10{sup 4} times the Dreicer field as the turbulence reaches the electron inertial length scale.

  18. Further observations of protons resulting from the decay of neutrons ejected by solar flares

    NASA Technical Reports Server (NTRS)

    Evenson, P. A.; Kroeger, R.; Meyer, P.

    1985-01-01

    The solar flare of 1984 April 24 produced a large gamma ray fluence with energy 2MeV. The time profile of the interplanetary flux from this flare indicates the presence of decaying solar neutrons. This makes a total of three neutron flares so far observed by this method. The three flares are used to place constraints on the fluence and spectra of neutrons emitted by the Sun.

  19. Electronic spectra of Fe3+ oxides and oxide hydroxides in the near IR to near UV.

    USGS Publications Warehouse

    Sherman, David M.; Waite, T.D.

    1985-01-01

    Optical absorption and diffuse reflectance spectra of several Fe2O3 and FeOOH polymorphs (hematite, maghemite, goethite, lepidocrocite) in the near-IR to near-UV spectral regions (2000-200 nm) are presented. The spectra consist primarily of Fe3+ ligand field and ligand-to-metal charge-transfer transitions.-J.A.Z.

  20. Independent-electron analysis of the x-ray spectra from single-electron capture in Ne10 + collisions with He, Ne, and Ar atoms

    NASA Astrophysics Data System (ADS)

    Leung, Anthony C. K.; Kirchner, Tom

    2015-09-01

    We present a theoretical study on the x-ray spectra from single-electron capture in 4.54 keV/amu Ne10 +-He, -Ne, and -Ar collisions. Single-particle capture probabilities were calculated using the two-center basis generator method within the independent electron model. In this framework we investigated the effects of a time-dependent screening potential that models target response on capture cross sections and x-ray spectra. Excellent agreement is shown with the previously measured relative cross sections and x-ray spectra and calculations based on the classical trajectory Monte Carlo method using the no-response single-particle electron capture probabilities in a multinomial single-electron capture analysis. Our results demonstrate the importance of using this consistent statistical analysis of single-electron capture within the independent electron model; a requirement that a previous calculation for the same collision problem using the two-center atomic-orbital close-coupling method may not have considered.

  1. Dynamics of intramolecular electron transfer reaction of FAD studied by magnetic field effects on transient absorption spectra.

    PubMed

    Murakami, Masaaki; Maeda, Kiminori; Arai, Tatsuo

    2005-07-01

    The kinetics of intermediates generated from intramolecular electron-transfer reaction by photo irradiation of the flavin adenine dinucleotide (FAD) molecule was studied by a magnetic field effect (MFE) on transient absorption (TA) spectra. Existence time of MFE and MFE action spectra have a strong dependence on the pH of solutions. The MFE action spectra have indicated the existence of interconversion between the radical pair and the cation form of the triplet excited state of flavin part. All rate constants of the triplet and the radical pair were determined by analysis of the MFE action spectra and decay kinetics of TA. The obtained values for the interconversion indicate that the formation of cation radical promotes the back electron-transfer reaction to the triplet excited state. Further, rate constants of spin relaxation and recombination have been studied by the time profiles of MFE at various pH. The drastic change of those two factors has been obtained and can be explained by SOC (spin-orbit coupling) induced back electron-transfer promoted by the formation of a stacking conformation at pH > 2.5.

  2. Non-equilibrium ionization by a periodic electron beam. I. Synthetic coronal spectra and implications for interpretation of observations

    NASA Astrophysics Data System (ADS)

    Dzifčáková, E.; Dudík, J.; Mackovjak, Š.

    2016-05-01

    Context. Coronal heating is currently thought to proceed via the mechanism of nanoflares, small-scale and possibly recurring heating events that release magnetic energy. Aims: We investigate the effects of a periodic high-energy electron beam on the synthetic spectra of coronal Fe ions. Methods: Initially, the coronal plasma is assumed to be Maxwellian with a temperature of 1 MK. The high-energy beam, described by a κ-distribution, is then switched on every period P for the duration of P/ 2. The periods are on the order of several tens of seconds, similar to exposure times or cadences of space-borne spectrometers. Ionization, recombination, and excitation rates for the respective distributions are used to calculate the resulting non-equilibrium ionization state of Fe and the instantaneous and period-averaged synthetic spectra. Results: Under the presence of the periodic electron beam, the plasma is out of ionization equilibrium at all times. The resulting spectra averaged over one period are almost always multithermal if interpreted in terms of ionization equilibrium for either a Maxwellian or a κ-distribution. Exceptions occur, however; the EM-loci curves appear to have a nearly isothermal crossing-point for some values of κs. The instantaneous spectra show fast changes in intensities of some lines, especially those formed outside of the peak of the respective EM(T) distributions if the ionization equilibrium is assumed. Movies 1-5 are available in electronic form at http://www.aanda.org

  3. Electronic structure and intersubband magnetoabsorption spectra of CdSe/CdS core-shell nanowires

    NASA Astrophysics Data System (ADS)

    Xiong, Wen

    2016-10-01

    The electronic structures of CdSe/CdS core-shell nanowires are calculated based on the effective-mass theory, and it is found that the hole states in CdSe/CdS core-shell nanowires are strongly mixed, which are very different from the hole states in CdSe or CdS nanowires. In addition, we find the three highest hole states at the Γ point are almost localized in the CdSe core and the energies of the hole states in CdSe/CdS core-shell nanowires can be enhanced greatly when the core radius Rc increases and the total radius R is fixed. The degenerate hole states are split by the magnetic field, and the split energies will increase when |Jh | increases from 1/2 to 7/2, while they are almost not influenced by the change of the core radius Rc. The absorption spectra of CdSe/CdS core-shell nanowires at the Γ point are also studied in the magnetic field when the temperature T is considered, and we find there are only two peaks will arise if the core radius Rc and the temperature T increase. The intensity of each optical absorption can be considerably enhanced by increasing the core radius Rc when the temperature T is fixed, it is due to the increase of their optical transition matrix element. Meanwhile, the intensity of each optical absorption can be decreased when the temperature T increases and the core radius Rc is fixed, and this is because the Fermi-Dirac distribution function of the corresponding hole states will increase as the increase of the temperature T.

  4. DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid

    NASA Astrophysics Data System (ADS)

    Renuga Devi, T. S.; Sharmi kumar, J.; Ramkumaar, G. R.

    2015-02-01

    The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm-1 and 4000-50 cm-1 respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee-Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. 1H and 13C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule.

  5. DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid.

    PubMed

    Renuga Devi, T S; Sharmi kumar, J; Ramkumaar, G R

    2015-02-25

    The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm(-1) and 4000-50 cm(-1) respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee-Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. (1)H and (13)C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule.

  6. DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid.

    PubMed

    Renuga Devi, T S; Sharmi kumar, J; Ramkumaar, G R

    2015-02-25

    The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm(-1) and 4000-50 cm(-1) respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee-Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. (1)H and (13)C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule. PMID:25262144

  7. First-principles calculation of electronic spectra of light-harvesting complex II.

    PubMed

    König, Carolin; Neugebauer, Johannes

    2011-06-14

    We report on a fully quantum chemical investigation of important structural and environmental effects on the site energies of chlorophyll pigments in green-plant light-harvesting complex II (LHC II). Among the tested factors are technical and structural aspects as well as effects of neighboring residues and exciton couplings in the chlorophyll network. By employing a subsystem time-dependent density functional theory (TDDFT) approach based on the frozen density embedding (FDE) method we are able to determine site energies and electronic couplings separately in a systematic way. This approach allows us to treat much larger systems in a quantum chemical way than would be feasible with a conventional density functional theory. Based on this method, we have simulated a series of mutagenesis experiments to investigate the effect of a lack of one pigment in the chlorophyll network on the excitation properties of the other pigments. From these calculations, we can conclude that conformational changes within the chlorophyll molecules, direct interactions with neighboring residues, and interactions with other chlorophyll pigments can lead to non-negligible changes in excitation energies. All of these factors are important when site energies shall be calculated with high accuracy. Moreover, the redistribution of the oscillator strengths due to exciton coupling has a large impact on the calculated absorption spectra. This indicates that modeling mutagenesis experiments requires us to consider the entire set of chlorophyll molecules in the wild type and in the mutant, rather than just considering the missing chlorophyll pigment. An analysis of the mixing of particular excitations and the coupling elements in the FDEc calculation indicates that some pigments in the chlorophyll network act as bridges which mediate the interaction between other pigments. These bridges are also supported by the calculations on the "mutants" lacking the bridging pigment.

  8. Charge Prediction Machine: A tool for inferring precursor charge states of Electron Transfer Dissociation tandem mass spectra

    PubMed Central

    Carvalho, Paulo C; Cociorva, Daniel; Wong, Catherine; Carvalho, Maria da Gloria da C; Barbosa, Valmir C; Yates, John R

    2010-01-01

    Electron Transfer Dissociation (ETD) can dissociate highly charged ions. Efficient analysis of ions dissociated with ETD requires accurate determination of charge states for calculation of molecular weight. We created an algorithm to assign the charge state of ions often used for ETD. The program, Charge Prediction Machine (CPM), uses Bayesian decision theory to account for different charge reduction processes encountered in ETD, and can also handle multiplex spectra. CPM correctly assigned charge states to 98% of the 13,097 MS2 spectra from a combined dataset of four experiments. In a comparison between CPM and a competing program, Charger (ThermoFisher), CPM produced half the mistakes. PMID:19203245

  9. A dynamic flare with anomalously dense flare loops

    NASA Technical Reports Server (NTRS)

    Svestka, Z.; Fontenla, J. M.; Machado, M. E.; Martin, S. F.; Neidig, D. F.

    1986-01-01

    The dynamic flare of November 6, 1980 developed a rich system of growing loops which could be followed in H-alpha for 1.5 hours. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of b-values for a hydrogen atom reveal that this requires electron densities in the loops to be close to 10 to the 12th per cu cm. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10 to the 12th per cu cm if no nonthermal motions were present. It is now general knowledge that flare loops are initially observed in X-rays and become visible in H-alpha only after cooling. For such a high density a loop would cool through radiation from 10 to the 7th K to 10 to the 4th K within a few minutes so that the dense H-alpha loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in H-alpha. Therefore, the density must have been significantly smaller when the loops were formed and the flare loops were apparently both shrinking and becoming denser while cooling.

  10. Biggest Solar Flare on Record

    NASA Technical Reports Server (NTRS)

    2002-01-01

    View an animation from the Extreme ultraviolet Imaging Telescope (EIT). At 4:51 p.m. EDT, on Monday, April 2, 2001, the sun unleashed the biggest solar flare ever recorded, as observed by the Solar and Heliospheric Observatory (SOHO) satellite. The flare was definitely more powerful than the famous solar flare on March 6, 1989, which was related to the disruption of power grids in Canada. This recent explosion from the active region near the sun's northwest limb hurled a coronal mass ejection into space at a whopping speed of roughly 7.2 million kilometers per hour. Luckily, the flare was not aimed directly towards Earth. Solar flares, among the solar system's mightiest eruptions, are tremendous explosions in the atmosphere of the Sun capable of releasing as much energy as a billion megatons of TNT. Caused by the sudden release of magnetic energy, in just a few seconds flares can accelerate solar particles to very high velocities, almost to the speed of light, and heat solar material to tens of millions of degrees. Solar ejections are often associated with flares and sometimes occur shortly after the flare explosion. Coronal mass ejections are clouds of electrified, magnetic gas weighing billions of tons ejected from the Sun and hurled into space with speeds ranging from 12 to 1,250 miles per second. Depending on the orientation of the magnetic fields carried by the ejection cloud, Earth-directed coronal mass ejections cause magnetic storms by interacting with the Earth's magnetic field, distorting its shape, and accelerating electrically charged particles (electrons and atomic nuclei) trapped within. Severe solar weather is often heralded by dramatic auroral displays, northern and southern lights, and magnetic storms that occasionally affect satellites, radio communications and power systems. The flare and solar ejection has also generated a storm of high-velocity particles, and the number of particles with ten million electron-volts of energy in the space near

  11. The flare kernel in the impulsive phase

    NASA Technical Reports Server (NTRS)

    Dejager, C.

    1986-01-01

    The impulsive phase of a flare is characterized by impulsive bursts of X-ray and microwave radiation, related to impulsive footpoint heating up to 50 or 60 MK, by upward gas velocities (150 to 400 km/sec) and by a gradual increase of the flare's thermal energy content. These phenomena, as well as non-thermal effects, are all related to the impulsive energy injection into the flare. The available observations are also quantitatively consistent with a model in which energy is injected into the flare by beams of energetic electrons, causing ablation of chromospheric gas, followed by convective rise of gas. Thus, a hole is burned into the chromosphere; at the end of impulsive phase of an average flare the lower part of that hole is situated about 1800 km above the photosphere. H alpha and other optical and UV line emission is radiated by a thin layer (approx. 20 km) at the bottom of the flare kernel. The upward rising and outward streaming gas cools down by conduction in about 45 s. The non-thermal effects in the initial phase are due to curtailing of the energy distribution function by escape of energetic electrons. The single flux tube model of a flare does not fit with these observations; instead we propose the spaghetti-bundle model. Microwave and gamma-ray observations suggest the occurrence of dense flare knots of approx. 800 km diameter, and of high temperature. Future observations should concentrate on locating the microwave/gamma-ray sources, and on determining the kernel's fine structure and the related multi-loop structure of the flaring area.

  12. Origin of the Universal Correlation between the Flare Temperature and the Emission Measure for Solar and Stellar Flares.

    PubMed

    Shibata; Yokoyama

    1999-11-20

    We present a theory to explain the observed universal correlation between flare temperature T and emission measure EM=n2V for solar and stellar flares (including solar microflares observed by Yohkoh as well as protostellar flares observed by ASCA), where n is the electron density and V is the volume. The theory is based on a magnetic reconnection model with heat conduction and chromospheric evaporation, assuming that the gas pressure of a flare loop is comparable to the magnetic pressure. This theory predicts the relation EM~B-5T17/2, which explains well the observed correlation between EM and T in the range of 6x106 K < T<108 K and 1044flares, if the magnetic field strength B of a flare loop is nearly constant for solar and stellar flares.

  13. Recent research directions in Fribourg: nuclear dynamics in resonances revealed by 2-dimensional EEL spectra, electron collisions with ionic liquids and electronic excitation of pyrimidine

    NASA Astrophysics Data System (ADS)

    Allan, Michael; Regeta, Khrystyna; Gorfinkiel, Jimena D.; Mašín, Zdeněk; Grimme, Stefan; Bannwarth, Christoph

    2016-05-01

    The article briefly reviews three subjects recently investigated in Fribourg: (i) electron collisions with surfaces of ionic liquids, (ii) two-dimensional (2D) electron energy loss spectra and (iii) resonances in absolute cross sections for electronic excitation of unsaturated compounds. Electron energy loss spectra of four ionic liquids revealed a number of excited states, including triplet states. A solution of a dye in an ionic liquid showed an energy-loss band of the solute, but not in all ionic liquids. 2D spectra reveal state-to-state information (given resonance to given final state) and are shown to be an interesting means to gain insight into dynamics of nuclear motion in resonances. Absolute cross sections for pyrimidine are reported as a function of scattering angle and as a function of electron energy. They reveal resonant structure which was reproduced very nicely by R-matrix calculations. The calculation provided an assignment of the resonances which reveals common patterns in compounds containing double bonds.

  14. Calculation of vibrational and electronic excited state absorption spectra of arsenic-water complexes using density functional theory

    NASA Astrophysics Data System (ADS)

    Huang, L.; Lambrakos, S. G.; Shabaev, A.; Massa, L.

    2016-05-01

    Calculations are presented of vibrational and electronic excited-state absorption spectra for As-H2O complexes using density function theory (DFT) and time-dependent density functional theory (TD-DFT). DFT and TD-DFT can provide interpretation of absorption spectra with respect to molecular structure for excitation by electromagnetic waves at frequencies within the IR and UV-visible ranges. The absorption spectrum corresponding to excitation states of As-H2O complexes consisting of relatively small numbers of water molecules should be associated with response features that are intermediate between that of isolated molecules and that of a bulk system. DFT and TD-DFT calculated absorption spectra represent quantitative estimates that can be correlated with additional information obtained from laboratory measurements and other types of theory based calculations. The DFT software GAUSSIAN was used for the calculations of excitation states presented here.

  15. Soft-X-ray spectra of highly charged Os, Bi, Th, and U ions in an electron beam ion trap

    SciTech Connect

    Trabert, E; Beiersdorfer, P; Fournier, K B; Chen, M H

    2004-12-03

    Systematic variation of the electron-beam energy in an electron-beam ion trap has been employed to produce soft-X-ray spectra of Os, Bi, Th, and U with highest charge states ranging up to Ni-like ions. Guided by relativistic atomic structure calculations, the strongest lines have been identified with {Delta}n = 0 (n = 4 to n' = 4) transitions in Rb- to Cu-like ions. The rather weak 4p-4d transitions are much less affected by QED contributions than the dominant 4s-4p transitions. Our wavelength measurements consequently provide benchmarks with and (almost) without QED. Because the radiative corrections are not very sensitive to the number of electrons in the valence shell, our data, moreover, provide benchmarks for the evaluation of electron-electron interactions.

  16. The EVE Doppler Sensitivity and Flare Observations

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.; Woods, T. N.; Chamberlin, P. C.; Didkovsky, L.; Del Zanna, G.

    2011-01-01

    The Extreme-ultraviolet Variability Experiment (EVE) obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity of the EVE data. We find that the 30.4 nm line of He II has a random Doppler error below 0.001 nm (1 pm, better than 10 km/s as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE's optical layout, which (as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we find the line centroid to have a redshift of 16.8 +/- 5.9 km/s relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as Fe XXIV 19.2 nm, have well-determined Doppler components for major flares, with decreasing apparent blueshifts as expected from chromospheric evaporation flows.

  17. High-energy particle production in solar flares (SEP, gamma-ray and neutron emissions). [solar energetic particles

    NASA Technical Reports Server (NTRS)

    Chupp, E. L.

    1987-01-01

    Electrons and ions, over a wide range of energies, are produced in association with solar flares. Solar energetic particles (SEPs), observed in space and near earth, consist of electrons and ions that range in energy from 10 keV to about 100 MeV and from 1 MeV to 20 GeV, respectively. SEPs are directly recorded by charged particle detectors, while X-ray, gamma-ray, and neutron detectors indicate the properties of the accelerated particles (electrons and ions) which have interacted in the solar atmosphere. A major problem of solar physics is to understand the relationship between these two groups of charged particles; in particular whether they are accelerated by the same mechanism. The paper reviews the physics of gamma-rays and neutron production in the solar atmosphere and the method by which properties of the primary charged particles produced in the solar flare can be deduced. Recent observations of energetic photons and neutrons in space and at the earth are used to present a current picture of the properties of impulsively flare accelerated electrons and ions. Some important properties discussed are time scale of production, composition, energy spectra, accelerator geometry. Particular attention is given to energetic particle production in the large flare on June 3, 1982.

  18. iSpectra: An Open Source Toolbox For The Analysis of Spectral Images Recorded on Scanning Electron Microscopes.

    PubMed

    Liebske, Christian

    2015-08-01

    iSpectra is an open source and system-independent toolbox for the analysis of spectral images (SIs) recorded on energy-dispersive spectroscopy (EDS) systems attached to scanning electron microscopes (SEMs). The aim of iSpectra is to assign pixels with similar spectral content to phases, accompanied by cumulative phase spectra with superior counting statistics for quantification. Pixel-to-phase assignment starts with a threshold-based pre-sorting of spectra to create groups of pixels with identical elemental budgets, similar to a method described by van Hoek (2014). Subsequent merging of groups and re-assignments of pixels using elemental or principle component histogram plots enables the user to generate chemically and texturally plausible phase maps. A variety of standard image processing algorithms can be applied to groups of pixels to optimize pixel-to-phase assignments, such as morphology operations to account for overlapping excitation volumes over pixels located at phase boundaries. iSpectra supports batch processing and allows pixel-to-phase assignments to be applied to an unlimited amount of SIs, thus enabling phase mapping of large area samples like petrographic thin sections. PMID:26165853

  19. iSpectra: An Open Source Toolbox For The Analysis of Spectral Images Recorded on Scanning Electron Microscopes.

    PubMed

    Liebske, Christian

    2015-08-01

    iSpectra is an open source and system-independent toolbox for the analysis of spectral images (SIs) recorded on energy-dispersive spectroscopy (EDS) systems attached to scanning electron microscopes (SEMs). The aim of iSpectra is to assign pixels with similar spectral content to phases, accompanied by cumulative phase spectra with superior counting statistics for quantification. Pixel-to-phase assignment starts with a threshold-based pre-sorting of spectra to create groups of pixels with identical elemental budgets, similar to a method described by van Hoek (2014). Subsequent merging of groups and re-assignments of pixels using elemental or principle component histogram plots enables the user to generate chemically and texturally plausible phase maps. A variety of standard image processing algorithms can be applied to groups of pixels to optimize pixel-to-phase assignments, such as morphology operations to account for overlapping excitation volumes over pixels located at phase boundaries. iSpectra supports batch processing and allows pixel-to-phase assignments to be applied to an unlimited amount of SIs, thus enabling phase mapping of large area samples like petrographic thin sections.

  20. All-electron first-principles GW+Bethe-Salpeter calculation for optical absorption spectra of sodium clusters

    SciTech Connect

    Noguchi, Yoshifumi; Ohno, Kaoru

    2010-04-15

    The optical absorption spectra of sodium clusters (Na{sub 2n}, n{<=} 4) are calculated by using an all-electron first-principles GW+Bethe-Salpeter method with the mixed-basis approach within the Tamm-Dancoff approximation. In these small systems, the excitonic effect strongly affects the optical properties due to the confinement of exciton in the small system size. The present state-of-the-art method treats the electron-hole two-particle Green's function by incorporating the ladder diagrams up to the infinite order and therefore takes into account the excitonic effect in a good approximation. We check the accuracy of the present method by comparing the resulting spectra with experiments. In addition, the effect of delocalization in particular in the lowest unoccupied molecular orbital in the GW quasiparticle wave function is also discussed by rediagonalizing the Dyson equation.

  1. Quantum Chemical Study of the Reaction of C+ with Interstellar Ice: Predictions of Vibrational and Electronic Spectra of Reaction Products

    NASA Astrophysics Data System (ADS)

    Woon, David E.

    2015-06-01

    The C+ cation (CII) is the dominant form of carbon in diffuse clouds and an important tracer for star formation in molecular clouds. We studied the low energy deposition of C+ on ice using density functional theory calculations on water clusters as large as 18 H2O. Barrierless reactions occur with water to form two dominant sets of products: HOC + H3O+ and CO- + 2H3O+. In order to provide testable predictions, we have computed both vibrational and electronic spectra for pure ice and processed ice clusters. While vibrational spectroscopy is expected to be able to discern that C+ has reacted with ice by the addition of H3O+ features not present in pure ice, it does not provided characteristic bands that would discern between HOC and CO-. On the other hand, predictions of electronic spectra suggest that low energy absorptions may occur for CO- and not HOC, making it possible to distinguish one product from the other.

  2. Theoretical study of the electronic spectra of neutral and cationic NpO and NpO2

    NASA Astrophysics Data System (ADS)

    Kovács, Attila; Infante, Ivan

    2015-08-01

    The electronic spectra of neutral NpO and NpO2 as well as of their mono- (NpO+, NpO2+) and dications (NpO2+, NpO22+) were studied using multiconfigurational relativistic quantum chemical calculations at the complete active space self-consistent field/CASPT2 level of theory taking into account spin-orbit coupling. The active space included 16 orbitals: all the 7s, 6d, and 5f orbitals of neptunium together with selected orbitals of oxygen. The vertical excitation energies on the ground state geometries have been computed up to ca. 35 000 cm-1. The gas-phase electronic spectra were evaluated on the basis of the computed Einstein coefficients at 298 K and 3000 K. The computed vertical transition energies show good agreement with previous condensed-phase results on NpO2+ and NpO22+.

  3. Sub-Doppler electronic spectra of the benzene-(He)n complexes

    NASA Astrophysics Data System (ADS)

    Hayashi, Masato; Ohshima, Yasuhiro

    2013-06-01

    Excitation spectra of the benzene-(He)n (n = 1 and 2) van der Waals complexes in the vicinity of the S1 ← S0601 vibronic transition of the monomer were recorded by utilizing mass-selectivetwo-color resonance-enhanced two-photon ionization. Pulsed expansion with the stagnation pressure of 80 bar was incorporated for efficient formation of the most weakly bound aromatic complexes and extensive adiabatic cooling with the rotational temperature of <0.5 K. Sub-Doppler resolution yielding the line width of 250 MHz was realized in the collimated molecular beam by employing near Fourier-transform-limited ultraviolet pulses for the S1 ← S0 excitation. The observed transition frequencies were fitted to the conventional symmetric-top Hamiltonian with a standard deviation of <30 MHz, to derive the molecular constants with accuracy improved by a factor of 50 than those reported previously. The determined rotational constants set the distance of the He atom from the benzene ring to be: 3.602 ± 0.009 Å in the S0 state of the complex with n = 1. The distance is even larger than those of the analogous systems, i.e., benzene-Ne and -Ar, and this apparent anomaly is discussed with the recent theoretical results based on high-level quantum mechanical calculation coupled with the numerical solution of the 3D eigenvalue problem. The electronic excitation induces the increase by 0.063 ± 0.012 Å, as opposed to the contraction of other benzene-rare gas complexes. The distance and the change for n = 2 are almost the same (3.596 ± 0.006 Å and 0.067 ± 0.009 Å) as those for n = 1. We also recorded the excitation spectrum of the n = 1 complex with the mono 13C-substituted benzene molecule. The asymmetric substitution lifts the degeneracy of the S1 61 state in the benzene molecule, and two vibronic bands located nearby to each other were observed for the complex.

  4. pH-Induced changes in electronic absorption and fluorescence spectra of phenazine derivatives

    NASA Astrophysics Data System (ADS)

    Ryazanova, O. A.; Voloshin, I. M.; Makitruk, V. L.; Zozulya, V. N.; Karachevtsev, V. A.

    2007-04-01

    The visible electronic absorption and fluorescence spectra as well as fluorescence polarization degrees of imidazo-[4,5-d]-phenazine (F1), 2-methylimidazo-[4,5-d]-phenazine (F2), 2-trifluoridemethylimidazo-[4,5-d]-phenazine (F3), 1,2,3-triazole-[4,5-d]-phenazine (F4) and their glycosides, imidazo-[4,5-d]-phenazine-N1-β- D-ribofuranoside (F1rib), 1,2,3-triazole-[4,5-d]-phenazine-N1-β- D-glucopyranoside (F4gl), were investigated in aqueous buffered solutions over the pH range of 0-12, where the spectral transformations were found to be reversible. The effects of protonation and deprotonation on spectral properties of these dyes were studied. We have determined the ranges of pH, where individual ionic species are predominant. In aqueous buffered solutions the fluorescence was found only for neutral species of F1, F1rib, F2, and F4gl dyes, whereas for the ionic forms of these dyes, as well as for F3 and F4 ones, the fluorescence has not been detected. The concentrational deprotonation p Ka values were evaluated from experimental data. It was shown that donor-acceptor properties of the substituent group in the second position of the pentagonal ring substantially affect the values of the deprotonation constants and the character of protonation for chromophore. The substitution of a hydrogen atom in the NH-group by the sugar residue blocks the formation of the anionic species, and results in enhancement of the dye emission intensity. The steep emission dependence for F1 and F1rib over pH range of 0-7 with intensities ratio of IpH 7/ IpH 1 = 60 allows us to propose them as possible indicator dyes in luminescence based pH sensors for investigation of processes accompanied by acidification, e.g. as gastric pH-sensors. A comparative analysis of the studied dyes has shown that F4gl is the most promising compound to be used as a fluorescent probe for investigation of molecular hybridization of nucleic acids.

  5. VERITAS Observations of Day-scale Flaring of M 87 in 2010 April

    NASA Astrophysics Data System (ADS)

    Aliu, E.; Arlen, T.; Aune, T.; Beilicke, M.; Benbow, W.; Bouvier, A.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Byrum, K.; Cannon, A.; Cesarini, A.; Ciupik, L.; Collins-Hughes, E.; Connolly, M. P.; Cui, W.; Dickherber, R.; Duke, C.; Errando, M.; Falcone, A.; Finley, J. P.; Finnegan, G.; Fortson, L.; Furniss, A.; Galante, N.; Gall, D.; Godambe, S.; Griffin, S.; Grube, J.; Guenette, R.; Gyuk, G.; Hanna, D.; Holder, J.; Huan, H.; Hughes, G.; Hui, C. M.; Humensky, T. B.; Imran, A.; Kaaret, P.; Karlsson, N.; Kertzman, M.; Kieda, D.; Krawczynski, H.; Krennrich, F.; Lang, M. J.; LeBohec, S.; Madhavan, A. S.; Maier, G.; Majumdar, P.; McArthur, S.; McCann, A.; Moriarty, P.; Mukherjee, R.; Nuñez, P. D.; Ong, R. A.; Orr, M.; Otte, A. N.; Park, N.; Perkins, J. S.; Pichel, A.; Pohl, M.; Prokoph, H.; Quinn, J.; Ragan, K.; Reyes, L. C.; Reynolds, P. T.; Roache, E.; Rose, H. J.; Ruppel, J.; Saxon, D. B.; Schroedter, M.; Sembroski, G. H.; Şentürk, G. D.; Skole, C.; Staszak, D.; Tešić, G.; Theiling, M.; Thibadeau, S.; Tsurusaki, K.; Tyler, J.; Varlotta, A.; Vassiliev, V. V.; Vincent, S.; Vivier, M.; Wakely, S. P.; Ward, J. E.; Weekes, T. C.; Weinstein, A.; Weisgarber, T.; Williams, D. A.; Zitzer, B.

    2012-02-01

    VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M 87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 ± 0.16) × 10-11 cm-2 s-1 at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 ± 0.68) × 10-11 cm-2 s-1 for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0.90+0.22 -0.15 days. The shortest detected exponential rise time is three times as long, at 2.87+1.65 -0.99 days. The quality of the data sample is such that spectral analysis can be performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 ± 0.07. There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.

  6. VERITAS Observations of Day-scale Flaring of M 87 in 2010 April

    NASA Technical Reports Server (NTRS)

    Perkins, J. S>

    2012-01-01

    VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M 87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 +/- 0.16) x 10(exp -11)/sq cm/s at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 +/- 0.68) x 10(exp -11)/sq cm/s for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0,90 +0.22/-0.15 days, The shortest detected exponential rise time is three times as long, at 2.87 +1.65/-0.99 days. The quality of the data sample is such that spectral analysis can he performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 +/- 0.07, There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.

  7. VERITAS OBSERVATIONS OF DAY-SCALE FLARING OF M 87 IN 2010 APRIL

    SciTech Connect

    Aliu, E.; Errando, M.; Arlen, T.; Aune, T.; Bouvier, A.; Beilicke, M.; Buckley, J. H.; Bugaev, V.; Dickherber, R.; Benbow, W.; Bradbury, S. M.; Byrum, K.; Cannon, A.; Collins-Hughes, E.; Cesarini, A.; Connolly, M. P.; Ciupik, L.; Cui, W.; Duke, C.; Falcone, A.; and others

    2012-02-20

    VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M 87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 {+-} 0.16) Multiplication-Sign 10{sup -11} cm{sup -2} s{sup -1} at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 {+-} 0.68) Multiplication-Sign 10{sup -11} cm{sup -2} s{sup -1} for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0.90{sup +0.22}{sub -0.15} days. The shortest detected exponential rise time is three times as long, at 2.87{sup +1.65}{sub -0.99} days. The quality of the data sample is such that spectral analysis can be performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 {+-} 0.07. There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.

  8. M DWARFS IN SLOAN DIGITAL SKY SURVEY STRIPE 82: PHOTOMETRIC LIGHT CURVES AND FLARE RATE ANALYSIS

    SciTech Connect

    Kowalski, Adam F.; Hawley, Suzanne L.; Hilton, Eric J.; Becker, Andrew C.; Sesar, Branimir; West, Andrew A.; Bochanski, John J.

    2009-08-15

    We present a flare rate analysis of 50,130 M dwarf light curves in Sloan Digital Sky Survey Stripe 82. We identified 271 flares using a customized variability index to search {approx}2.5 million photometric observations for flux increases in the u and g bands. Every image of a flaring observation was examined by eye and with a point-spread function-matching and image subtraction tool to guard against false positives. Flaring is found to be strongly correlated with the appearance of H{alpha} in emission in the quiet spectrum. Of the 99 flare stars that have spectra, we classify eight as relatively inactive. The flaring fraction is found to increase strongly in stars with redder colors during quiescence, which can be attributed to the increasing flare visibility and increasing active fraction for redder stars. The flaring fraction is strongly correlated with |Z| distance such that most stars that flare are within 300 pc of the Galactic plane. We derive flare u-band luminosities and find that the most luminous flares occur on the earlier-type m dwarfs. Our best estimate of the lower limit on the flaring rate (averaged over Stripe 82) for flares with {delta}u {>=} 0.7 mag on stars with u < 22 is 1.3 flares hr{sup -1} deg{sup -2} but can vary significantly with the line of sight.

  9. M Dwarfs in Sloan Digital Sky Survey Stripe 82: Photometric Light Curves and Flare Rate Analysis

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam F.; Hawley, Suzanne L.; Hilton, Eric J.; Becker, Andrew C.; West, Andrew A.; Bochanski, John J.; Sesar, Branimir

    2009-08-01

    We present a flare rate analysis of 50,130 M dwarf light curves in Sloan Digital Sky Survey Stripe 82. We identified 271 flares using a customized variability index to search ~2.5 million photometric observations for flux increases in the u and g bands. Every image of a flaring observation was examined by eye and with a point-spread function-matching and image subtraction tool to guard against false positives. Flaring is found to be strongly correlated with the appearance of Hα in emission in the quiet spectrum. Of the 99 flare stars that have spectra, we classify eight as relatively inactive. The flaring fraction is found to increase strongly in stars with redder colors during quiescence, which can be attributed to the increasing flare visibility and increasing active fraction for redder stars. The flaring fraction is strongly correlated with |Z| distance such that most stars that flare are within 300 pc of the Galactic plane. We derive flare u-band luminosities and find that the most luminous flares occur on the earlier-type m dwarfs. Our best estimate of the lower limit on the flaring rate (averaged over Stripe 82) for flares with Δu >= 0.7 mag on stars with u < 22 is 1.3 flares hr-1 deg-2 but can vary significantly with the line of sight. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.

  10. Solar flares and energetic particles.

    PubMed

    Vilmer, Nicole

    2012-07-13

    Solar flares are now observed at all wavelengths from γ-rays to decametre radio waves. They are commonly associated with efficient production of energetic particles at all energies. These particles play a major role in the active Sun because they contain a large amount of the energy released during flares. Energetic electrons and ions interact with the solar atmosphere and produce high-energy X-rays and γ-rays. Energetic particles can also escape to the corona and interplanetary medium, produce radio emissions (electrons) and may eventually reach the Earth's orbit. I shall review here the available information on energetic particles provided by X-ray/γ-ray observations, with particular emphasis on the results obtained recently by the mission Reuven Ramaty High-Energy Solar Spectroscopic Imager. I shall also illustrate how radio observations contribute to our understanding of the electron acceleration sites and to our knowledge on the origin and propagation of energetic particles in the interplanetary medium. I shall finally briefly review some recent progress in the theories of particle acceleration in solar flares and comment on the still challenging issue of connecting particle acceleration processes to the topology of the complex magnetic structures present in the corona.

  11. A simplified Tamm-Dancoff density functional approach for the electronic excitation spectra of very large molecules

    NASA Astrophysics Data System (ADS)

    Grimme, Stefan

    2013-06-01

    Two approximations in the Tamm-Dancoff density functional theory approach (TDA-DFT) to electronically excited states are proposed which allow routine computations for electronic ultraviolet (UV)- or circular dichroism (CD) spectra of molecules with 500-1000 atoms. Speed-ups compared to conventional time-dependent DFT (TD-DFT) treatments of about two to three orders of magnitude in the excited state part at only minor loss of accuracy are obtained. The method termed sTDA ("s" for simplified) employs atom-centered Löwdin-monopole based two-electron repulsion integrals with the asymptotically correct 1/R behavior and perturbative single excitation configuration selection. It is formulated generally for any standard global hybrid density functional with given Fock-exchange mixing parameter ax. The method performs well for two standard benchmark sets of vertical singlet-singlet excitations for values of ax in the range 0.2-0.6. The mean absolute deviations from reference data are only 0.2-0.3 eV and similar to those from standard TD-DFT. In three cases (two dyes and one polypeptide), good mutual agreement between the electronic spectra (up to 10-11 eV excitation energy) from the sTDA method and those from TD(A)-DFT is obtained. The computed UV- and CD-spectra of a few typical systems (e.g., C60, two transition metal complexes, [7]helicene, polyalanine, a supramolecular aggregate with 483 atoms and about 7000 basis functions) compare well with corresponding experimental data. The method is proposed together with medium-sized double- or triple-zeta type atomic-orbital basis sets as a quantum chemical tool to investigate the spectra of huge molecular systems at a reliable DFT level.

  12. Research Investigation Directed Toward Extending the Useful Range of the Electromagnetic Spectrum. [atomic spectra and electronic structure of alkali metals

    NASA Technical Reports Server (NTRS)

    Hartmann, S. R.; Happer, W.

    1974-01-01

    The report discusses completed and proposed research in atomic and molecular physics conducted at the Columbia Radiation Laboratory from July 1972 to June 1973. Central topics described include the atomic spectra and electronic structure of alkali metals and helium, molecular microwave spectroscopy, the resonance physics of photon echoes in some solid state systems (including Raman echoes, superradiance, and two photon absorption), and liquid helium superfluidity.

  13. Measurement of the high energy component of the x-ray spectra in the VENUS electron cyclotron resonance ion source.

    PubMed

    Leitner, D; Benitez, J Y; Lyneis, C M; Todd, D S; Ropponen, T; Ropponen, J; Koivisto, H; Gammino, S

    2008-03-01

    High performance electron cyclotron resonance (ECR) ion sources, such as VENUS (Versatile ECR for NUclear Science), produce large amounts of x-rays. By studying their energy spectra, conclusions can be drawn about the electron heating process and the electron confinement. In addition, the bremsstrahlung from the plasma chamber is partly absorbed by the cold mass of the superconducting magnet, adding an extra heat load to the cryostat. Germanium or NaI detectors are generally used for x-ray measurements. Due to the high x-ray flux from the source, the experimental setup to measure bremsstrahlung spectra from ECR ion sources is somewhat different from that for the traditional nuclear physics measurements these detectors are generally used for. In particular, the collimation and background shielding can be problematic. In this paper, we will discuss the experimental setup for such a measurement, the energy calibration and background reduction, the shielding of the detector, and collimation of the x-ray flux. We will present x-ray energy spectra and cryostat heating rates depending on various ion source parameters, such as confinement fields, minimum B-field, rf power, and heating frequency. PMID:18377002

  14. Microsolvation in superfluid helium droplets studied by the electronic spectra of six porphyrin derivatives and one chlorine compound.

    PubMed

    Riechers, R; Pentlehner, D; Slenczka, A

    2013-06-28

    After almost two decades of high resolution molecular spectroscopy in superfluid helium droplets, the understanding of microsolvation is still the subject of intense experimental and theoretical research. According to the published spectroscopic work including microwave, infrared, and electronic spectroscopy, the latter appears to be particularly promising to study microsolvation because of the appearance of pure molecular transitions and spectrally separated phonon wings. Instead of studying the very details of the influence of the helium environment for one particular dopant molecule as previously done for phthalocyanine, the present study compares electronic spectra of a series of non-polar porphyrin derivatives when doped into helium droplets consisting of 10(4)-10(5) helium atoms. Thereby, we focus on the helium-induced fine structure, as revealed most clearly at the corresponding electronic origin. The interpretation and the assignment of particular features obtained in the fluorescence excitation spectra are based on additional investigations of dispersed emission spectra and of the saturation behavior. Besides many dopant-specific results, the experimental study provides strong evidence for a particular triple peak feature representing the characteristic signature of helium solvation for all seven related dopant species.

  15. Study of electron transition energies between anions and cations in spinel ferrites using differential UV-vis absorption spectra

    NASA Astrophysics Data System (ADS)

    Xue, L. C.; Wu, L. Q.; Li, S. Q.; Li, Z. Z.; Tang, G. D.; Qi, W. H.; Ge, X. S.; Ding, L. L.

    2016-07-01

    It is very important to determine electron transition energies (Etr) between anions and different cations in order to understand the electrical transport and magnetic properties of a material. Many authors have analyzed UV-vis absorption spectra using the curve (αhν)2 vs E, where α is the absorption coefficient and E(=hν) is the photon energy. Such an approach can give only two band gap energies for spinel ferrites. In this paper, using differential UV-vis absorption spectra, dα/dE vs E, we have obtained electron transition energies (Etr) between the anions and cations, Fe2+ and Fe3+ at the (A) and [B] sites and Ni2+ at the [B] sites for the (A)[B]2O4 spinel ferrite samples CoxNi0.7-xFe2.3O4 (0.0≤x≤0.3), CrxNi0.7Fe2.3-xO4 (0.0≤x≤0.3) and Fe3O4. We suggest that the differential UV-vis absorption spectra should be accepted as a general analysis method for determining electron transition energies between anions and cations.

  16. Measurement of the high energy component of the x-ray spectra in the VENUS electron cyclotron resonance ion source

    SciTech Connect

    Leitner, D.; Benitez, J. Y.; Lyneis, C. M.; Todd, D. S.; Ropponen, T.; Ropponen, J.; Koivisto, H.; Gammino, S.

    2008-03-15

    High performance electron cyclotron resonance (ECR) ion sources, such as VENUS (Versatile ECR for NUclear Science), produce large amounts of x-rays. By studying their energy spectra, conclusions can be drawn about the electron heating process and the electron confinement. In addition, the bremsstrahlung from the plasma chamber is partly absorbed by the cold mass of the superconducting magnet, adding an extra heat load to the cryostat. Germanium or NaI detectors are generally used for x-ray measurements. Due to the high x-ray flux from the source, the experimental setup to measure bremsstrahlung spectra from ECR ion sources is somewhat different from that for the traditional nuclear physics measurements these detectors are generally used for. In particular, the collimation and background shielding can be problematic. In this paper, we will discuss the experimental setup for such a measurement, the energy calibration and background reduction, the shielding of the detector, and collimation of the x-ray flux. We will present x-ray energy spectra and cryostat heating rates depending on various ion source parameters, such as confinement fields, minimum B-field, rf power, and heating frequency.

  17. Double photoexcitation involving 2p and 4f electrons in L3 -edge x-ray absorption spectra of protactinium

    NASA Astrophysics Data System (ADS)

    Hennig, Christoph; Le Naour, Claire; Auwer, Christophe Den

    2008-06-01

    The L3 -edge x-ray absorption spectrum of Pa(V) fluoride in aqueous solution show clear evidence for the double photoexcitation involving 2p and 4f electrons. A comparison with the [2p4f] double-electron excitations observed in the L3 -edge x-ray absorption spectra of other actinides (thorium, uranium, neptunium, plutonium, and americium) indicates a monotonic increase in the excitation energy. The sharp edgelike structure of the multielectron excitation reveals the origin of a shake-up channel.

  18. Effects of Incident Electron Fluence and Energy on the Election Yield Curves and Emission Spectra of Dielectrics

    NASA Technical Reports Server (NTRS)

    Sim, Alec; Dennison, J. R.; Thomson, Clint

    2005-01-01

    We present an experimental study of evolution of electron emission yields and spectra as a result of internal charge build up due to electron dose. Reliable total, backscattered and secondary yield curves and electron emission spectra for un-charged insulators using a low fluence, pulsed electron beam (= or < 5 microsec at = or < 3 nA/sq mm or = or < 10(exp 5) e/sq mm per pulse) with low energy electron and UV flooding to neutralize the charging between pulses. Quantifiable changes in yield curves are observed due to < 100 fC/sq mm fluences for several excellent dielectric thin film materials. We find good agreement with a phenomenological argument based on insulator charging predicted by the yield curve; this includes an approximately linear decrease in the magnitude of the yield as incident energies approach the crossover energies and an exponential decrease in yield as accumulated internal charge reduces the landing energy to asymptotically approach a steady state surface charge and unity yield. We also find that the exponential decay of yield curves with fluence exhibit an energy dependent decay constant, alpha(E), over a broad range of incident energies below, between and above the crossover energies. Finally, we present some preliminary physics-based models for this energy dependence and attempt to relate our charging measurements to knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and transport, and how the profile of trapped charge affects the transport and emission of charges from insulators.

  19. Chromospheric-coronal coupling during solar flares: Current systems and particle acceleration

    NASA Technical Reports Server (NTRS)

    Winglee, Robert M.; Mckean, M. E.; Dulk, G. A.

    1989-01-01

    Two-dimensional (three velocity) electrostatic particle simulations are used to investigate the particle heating and acceleration associated with the impulsive phase of a solar flare. A crossfield current in the high corona (which is presumably driven by reconnection processes) is used to initiate the flare. Due to the differential motion of the electrons and ions, currents, and associated quasi-static electric fields are generated with the primary current and balancing return current being on adjacent field lines. These currents extend from the corona down into the chromosphere. Electrons can be accelerated to energies exceeding 100 keV on short time scales via the quasi-static fields and wave-particle interactions. The spectra of these electrons has a broken power-law distribution which hardens in time. The spatially separate primary and return currents are closed by the cross-field acceleration of the ambient ions into the primary current regions. These ions are then accelerated upwards into the corona by the same quasi-static electric field accelerating the electrons downwards. This acceleration can account for the broadened stationary and weak blue shifted component seen in soft x ray line emissions and enhancements in heavy ion abundances seen in the solar wind in associations with solar flares.

  20. Neutral pion production in solar flares

    NASA Technical Reports Server (NTRS)

    Forrest, D. J.; Vestrand, W. T.; Chupp, E. L.; Rieger, E.; Cooper, J. F.; Share, G. H.

    1985-01-01

    The Gamma-Ray Spectrometer (GRS) on SMM has detected more than 130 flares with emission approx 300 keV. More than 10 of these flares were detected at photon energies 10 MeV. Although the majority of the emission at 10 MeV must be from electron bremsstrahlung, at least two of the flares have spectral properties 40 MeV that require gamma rays from the decay of neutral pions. It is found that pion production can occur early in the impulsive phase as defined by hard X-rays near 100 keV. It is also found in one of these flares that a significant portion of this high-energy emission is produced well after the impulsive phase. This extended production phase, most clearly observed at high energies, may be a signature of the acceleration process which produces solar energetic particles (SEP's) in space.

  1. Influence of weak vibrational-electronic couplings on 2D electronic spectra and inter-site coherence in weakly coupled photosynthetic complexes

    SciTech Connect

    Monahan, Daniele M.; Whaley-Mayda, Lukas; Fleming, Graham R.; Ishizaki, Akihito

    2015-08-14

    Coherence oscillations measured in two-dimensional (2D) electronic spectra of pigment-protein complexes may have electronic, vibrational, or mixed-character vibronic origins, which depend on the degree of electronic-vibrational mixing. Oscillations from intrapigment vibrations can obscure the inter-site coherence lifetime of interest in elucidating the mechanisms of energy transfer in photosynthetic light-harvesting. Huang-Rhys factors (S) for low-frequency vibrations in Chlorophyll and Bacteriochlorophyll are quite small (S ≤ 0.05), so it is often assumed that these vibrations influence neither 2D spectra nor inter-site coherence dynamics. In this work, we explore the influence of S within this range on the oscillatory signatures in simulated 2D spectra of a pigment heterodimer. To visualize the inter-site coherence dynamics underlying the 2D spectra, we introduce a formalism which we call the “site-probe response.” By comparing the calculated 2D spectra with the site-probe response, we show that an on-resonance vibration with Huang-Rhys factor as small as S = 0.005 and the most strongly coupled off-resonance vibrations (S = 0.05) give rise to long-lived, purely vibrational coherences at 77 K. We moreover calculate the correlation between optical pump interactions and subsequent entanglement between sites, as measured by the concurrence. At 77 K, greater long-lived inter-site coherence and entanglement appear with increasing S. This dependence all but vanishes at physiological temperature, as environmentally induced fluctuations destroy the vibronic mixing.

  2. Solar Flares: Magnetohydrodynamic Processes

    NASA Astrophysics Data System (ADS)

    Shibata, Kazunari; Magara, Tetsuya

    2011-12-01

    This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one of the most explosive phenomena in the atmosphere of the Sun, releasing a huge amount of energy up to about 10^32 erg on the timescale of hours. Flares involve the heating of plasma, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes for producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), local enhancement of electric current in the corona (formation of a current sheet), and rapid dissipation of electric current (magnetic reconnection) that causes shock heating, mass ejection, and particle acceleration. The evolution toward the onset of a flare is rather quasi-static when free energy is accumulated in the form of coronal electric current (field-aligned current, more precisely), while the dissipation of coronal current proceeds rapidly, producing various dynamic events that affect lower atmospheres such as the chromosphere and photosphere. Flares manifest such rapid dissipation of coronal current, and their theoretical modeling has been developed in accordance with observations, in which numerical simulations proved to be a strong tool reproducing the time-dependent, nonlinear evolution of a flare. We review the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes mentioned above. We start with basic properties of flares, then go into the details of energy build-up, release and transport in flares where magnetic reconnection works as the central engine to produce a flare.

  3. Emergency flare tip repair

    SciTech Connect

    Harrison, G.A.

    1982-07-01

    Two damaged propane storage tank flares serving a large LPG storage facility near the Arabian Gulf were given emergency service. A diagram of over-all layout and spatial relationships between tanks and piping, and tables with general information relevant to selecting an acceptable radiant heat load factor and flare line flow characteristics were presented. The general equation for predicting radiant heat flux from a point source was used. The ignition of the temporary flare was discussed.

  4. Particle acceleration in flares

    NASA Technical Reports Server (NTRS)

    Benz, Arnold O.; Kosugi, Takeo; Aschwanden, Markus J.; Benka, Steve G.; Chupp, Edward L.; Enome, Shinzo; Garcia, Howard; Holman, Gordon D.; Kurt, Victoria G.; Sakao, Taro

    1994-01-01

    Particle acceleration is intrinsic to the primary energy release in the impulsive phase of solar flares, and we cannot understand flares without understanding acceleration. New observations in soft and hard X-rays, gamma-rays and coherent radio emissions are presented, suggesting flare fragmentation in time and space. X-ray and radio measurements exhibit at least five different time scales in flares. In addition, some new observations of delayed acceleration signatures are also presented. The theory of acceleration by parallel electric fields is used to model the spectral shape and evolution of hard X-rays. The possibility of the appearance of double layers is further investigated.

  5. Solar flares. [plasma physics

    NASA Technical Reports Server (NTRS)

    Rust, D. M.

    1979-01-01

    The present paper deals with explosions in a magnetized solar plasma, known as flares, whose effects are seen throughout the electromagnetic spectrum, from gamma-rays through the visible and to the radio band. The diverse phenomena associated with flares are discussed, along with the physical mechanisms that have been advanced to explain them. The impact of solar flare research on the development of plasma physics and magnetohydrodynamics is noted. The rapid development of solar flare research during the past 20 years, owing to the availability of high-resolution images, detailed magnetic field measurements, and improved spectral data, is illustrated.

  6. Flared tube attachment fitting

    NASA Technical Reports Server (NTRS)

    Alkire, I. D.; King, J. P., Jr.

    1980-01-01

    Tubes can be flared first, then attached to valves and other flow line components, with new fitting that can be disassembled and reused. Installed fitting can be disassembled so parts can be inspected. It can be salvaged and reused without damaging flared tube; tube can be coated, tempered, or otherwise treated after it has been flared, rather than before, as was previously required. Fitting consists of threaded male portion with conical seating surface, hexagonal nut with hole larger than other diameter of flared end of tube, and split ferrule.

  7. Prediction soft-X-ray spectrum of solar flares from Very Low Frequency observations: an inverse problem in ionospheric science

    NASA Astrophysics Data System (ADS)

    Palit, Sourav; Chakrabarti, Sandip Kumar; Ray, Suman

    2016-07-01

    Earth's lower ionosphere and upper atmosphere absorb X-rays and gamma-rays from astronomical sources such as solar flares, Short Gamma ray Repeaters (SGRs) or Gamma Ray Bursts (GRBs). The electron-ion production rates due to the ionization of such energetic photons at different heights depend on the intensity and wavelength of the injected spectrum and hence vary from one source to another. Obviously the ion density vs. altitude profile has the imprint of the incident photon spectrum. In this paper, we examine the possibility of inverting the electron density-height profiles uniquely by deconvolution of the VLF amplitude signal to obtain information on the injected spectrum. We have been able to reproduce the soft-X-ray part of the injected spectra from two different classes of solar flares with satisfactory accuracy. With the possibilities of probing even lower parts of the atmosphere, the method presented here is useful to carry out a similar exercise to infer the higher energy part of solar flare spectra and spectra of more energetic events such as the GRBs, SGRs etc. We show that to a certain accuracy, the Earth's atmosphere may be used as a gigantic detector of relatively strong ionizing extra-terrestrial events.

  8. Simulation of Vacuum UV Absorption and Electronic Circular Dichroism Spectra of Methyl Oxirane: The Role of Vibrational Effects.

    PubMed

    Hodecker, Manuel; Biczysko, Malgorzata; Dreuw, Andreas; Barone, Vincenzo

    2016-06-14

    Vibrationally resolved one-photon absorption and electronic circular dichroism spectra of (R)-methyl oxirane were calculated with different electronic and vibronic models selecting, through an analysis of the convergence of the results, the best compromise between reliability and computational cost. Linear-response TD-DFT/CAM-B3LYP/SNST electronic computations in conjunction with the simple vertical gradient vibronic model were chosen and employed for systematic comparison with the available experimental data. Remarkable agreement between simulated and experimental spectra was achieved for both one-photon absorption and circular dichroism concerning peak positions, relative intensities, and general spectral shapes considering the computational efficiency of the chosen theoretical approach. The significant improvement of the results with respect to smearing of vertical electronic transitions by phenomenological Gaussian functions and the possible inclusion of solvent effects by polarizable continuum models at a negligible additional cost paves the route toward the simulation and analysis of spectral shapes of complex molecular systems in their natural environment. PMID:27159495

  9. Analysis of the electronic, IR, and 1H NMR spectra of conjugated oligomers based on 4,4'-triphenylamine vinylene

    NASA Astrophysics Data System (ADS)

    Baryshnikov, G. V.; Minaeva, V. A.; Minaev, B. F.; Sun, V.-H.; Grigoras, M.

    2016-09-01

    Two types of conjugated oligomers based on 4,4'-triphenylamine vinylene have been synthesized and characterized by the methods of IR, UV-visible, and 1H NMR spectroscopy. The corresponding spectra have also been simulated theoretically at the density functional theory level with application of the B3LYP and BMK hybrid exchange-correlation functionals. A comparative analysis of the experimental and theoretical spectra of polymers and oligomers has revealed regularities of the manifestation of spectral signals depending on the conjugation chain length and the presence of a substituent in the triphenylamine core. It has been established, in particular, that the absolute intensity of IR bands satisfies a linear dependence with increase in the degree of polymerization; however, no frequency shift is observed at the same time. The position of the main peak in electron absorption spectra demonstrates the bathochromic shift with an increase in the oligomeric chain length due to the narrowing of the energy gap between the boundary molecular orbitals. Based on the theoretical estimation of the hydrogen atoms chemical shifts, the signals of various protons types in the strongly broadened experimental 1H NMR spectra of the bis-(4-iodine phenyl)-phenylamine and N,N-bis-(4-iodine phenyl)-4'-(phenylethynyl)-phenylamine polymerization products have also been identified.

  10. Electronic Absorption Spectra of Tetrapyrrole-Based Pigments via TD-DFT: A Reduced Orbital Space Study.

    PubMed

    Shrestha, Kushal; Virgil, Kyle A; Jakubikova, Elena

    2016-07-28

    Tetrapyrrole-based pigments play a crucial role in photosynthesis as principal light absorbers in light-harvesting chemical systems. As such, accurate theoretical descriptions of the electronic absorption spectra of these pigments will aid in the proper description and understanding of the overall photophysics of photosynthesis. In this work, time-dependent density functional theory (TD-DFT) at the CAM-B3LYP/6-31G* level of theory is employed to produce the theoretical absorption spectra of several tetrapyrrole-based pigments. However, the application of TD-DFT to large systems with several hundreds of atoms can become computationally prohibitive. Therefore, in this study, TD-DFT calculations with reduced orbital spaces (ROSs) that exclude portions of occupied and virtual orbitals are pursued as a viable, computationally cost-effective alternative to conventional TD-DFT calculations. The effects of reducing orbital space size on theoretical spectra are qualitatively and quantitatively described, and both conventional and ROS results are benchmarked against experimental absorption spectra of various tetrapyrrole-based pigments. The orbital reduction approach is also applied to a large natural pigment assembly that comprises the principal light-absorbing component of the reaction center in purple bacteria. Overall, we find that TD-DFT calculations with proper and judicious orbital space reductions can adequately reproduce conventional, full orbital space, TD-DFT results of all pigments studied in this work.

  11. Interferences in photo-detached electron spectra from a non-collinear tri-atomic anion

    NASA Astrophysics Data System (ADS)

    Afaq, A.; Farooq, K.; A. Khan, M.; Yi, Xue-Xi

    2014-10-01

    The electron flux oscillations in photo-detachment of a non-collinear tri-atomic anion have been studied by taking each atom of the system as a coherent source of detached-electron wave. These electron waves traversing along three different trajectories result in a quantum interference. An analytical expression of detached-electron flux is evaluated for various detached-electron energies and for different geometrical shapes of the system. The results show that the electron flux distributions exhibit molecular shape-induced oscillatory structures. These oscillations are explained using the semi-classical closed-orbit theory; the outgoing electron waves produced from one center are propagated in the vicinity of the sources at other centers. It is also observed that in a particular case our non-collinear tri-atomic system reduces to the collinear tri-atomic system recently published.

  12. The effect of drift on the evolution of the electron/positron spectra in an axisymmetric pulsar wind nebula

    SciTech Connect

    Vorster, Michael J.; Moraal, Harm

    2014-06-20

    Charged particles propagating through a structured magnetic field are subject to drift motion. The primary aim of the present paper is therefore to investigate the effects of gradient, curvature, and neutral sheet drift on the evolution of the electron and positron spectra in a pulsar wind nebula, where the drift motion is a direct result of the magnetic field having an Archimedean spiral structure. In order to investigate the evolution of the spectra, the steady-state, axisymmetric Fokker-Planck transport equation is solved numerically using a finite-difference scheme. Apart from drift motion, the transport processes of convection and diffusion, along with the energy loss processes of adiabatic cooling and synchrotron radiation, are also included in the model. It is found that drift, particularly neutral sheet drift, can lead to a quantitative difference in the evolution of the electron and positron spectra. This difference may be of importance when interpreting the positron excess observed by PAMELA and AMS-02 near Earth.

  13. Observations of particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.

    1979-01-01

    Solar flares provide several examples of nonthermal particle acceleration. The paper reviews the information gained about these processes via X-ray and gamma-ray astronomy, which can presently distinguish among three separate particle-acceleration processes at the sun: an impulsive accelerator of more than 20 keV electrons, a gradual accelerator of more than 20 keV electrons, and a gradual accelerator of more than 10 MeV ions. The acceleration energy efficiency (total particle energy divided by total flare energy) of any of these mechanisms cannot be less than about 0.1%, although the gradual acceleration does not occur in every flare. The observational material suggests that both the impulsive and gradual accelerations take place preferentially in closed magnetic-field structures, but that the electrons decay in these traps before they can escape. The ions escape very efficiently.

  14. Thick target bremsstrahlung spectra for 1.00-, 1.25-, and 1.40-Mev electrons

    USGS Publications Warehouse

    Miller, W.; Motz, J.W.; Cialella, C.

    1954-01-01

    The spectrum of radiation produced by 1.0-, 1.25-, and 1.40-Mev electrons incident on a thick tungsten target was measured at 0A????and 90A????with the incident beam by a method involving the magnetic analysis of Compton electrons. The effects of electron scattering and energy loss in the target preclude any simple interpretation of this data to yield a differential bremsstrahlung cross section. However, an estimate of the spectra to be expected at 0A????and 90A????was obtained by combining the Sauter expression for the bremsstrahlung cross section with the available information on electron scatter and energy loss in the target and backscatter from the target. The reliability of the estimate is limited because the Sauter formula was calculated by using the Born approximation, the electron scattering calculations are applicable to an infinite medium only, and the backscatter was estimated empirically from Bothe's experimental data which were obtained with lower energy electrons (370 kev). Furthermore electron energy straggling was neglected. Nevertheless, the predicted spectral shapes at 0A????and 90A????and the relative intensities at these two angles are in qualitative agreement with the measured values. The absolute magnitudes of the measured intensities at both angles are about a factor of two greater than the predicted values. ?? 1954 The American Physical Society.

  15. Determination of the pulse duration of an x-ray free electron laser using highly resolved single-shot spectra.

    PubMed

    Inubushi, Yuichi; Tono, Kensuke; Togashi, Tadashi; Sato, Takahiro; Hatsui, Takaki; Kameshima, Takashi; Togawa, Kazuaki; Hara, Toru; Tanaka, Takashi; Tanaka, Hitoshi; Ishikawa, Tetsuya; Yabashi, Makina

    2012-10-01

    We determined the pulse duration of x-ray free electron laser light at 10 keV using highly resolved single-shot spectra, combined with an x-ray free electron laser simulation. Spectral profiles, which were measured with a spectrometer composed of an ultraprecisely figured elliptical mirror and an analyzer flat crystal of silicon (555), changed markedly when we varied the compression strength of the electron bunch. The analysis showed that the pulse durations were reduced from 31 to 4.5 fs for the strongest compression condition. The method, which is readily applicable to evaluate shorter pulse durations, provides a firm basis for the development of femtosecond to attosecond sciences in the x-ray region.

  16. Experimental observation of the strong influence of crystal orientation on Electron Rutherford Backscattering Spectra

    NASA Astrophysics Data System (ADS)

    Vos, Maarten; Aizel, Koceila; Winkelmann, Aimo

    2010-06-01

    In Electron Rutherford Backscattering Spectroscopy (ERBS) energetic electrons (in our case up to 40 keV) impinge on a target and one measures the energy of elastically scattered electrons. This energy depends on the mass of the scattering atom, due to the recoil effect. This technique thus provides information about the sample composition. For single crystals the interaction of the projectile electron with the crystal potential modifies the angular intensity distribution of the scattered electrons. This leads, for example, to the well-known Kikuchi patterns. Here we investigate if such modified angular distribution has any influence on the intensity ratio of the observed elastic peaks in ERBS. Dramatic effects are found. Implications of these observations for quantitative surface analysis using energetic electrons are discussed.

  17. CORONAS-F observation of HXR and gamma-ray emissions from the solar flare X10 on 29 October 2003 as a probe of accelerated proton spectrum

    NASA Astrophysics Data System (ADS)

    Kurt, V. G.; Yushkov, B. Yu.; Kudela, K.; Galkin, V. I.; Kashapova, L. K.

    2015-04-01

    HXR and gamma-ray emissions in the 0.04—150 MeV energy range associated with the solar flare on 29 October 2003 (X10/3B) were observed at 20:38—20:58 UT by the SONG instrument aboard the CORONAS-F mission. We restored consecutive flare gamma-emission spectra from SONG and RHESSI data and found a good agreement of these spectra in the 0.1—10 MeV energy range. Two phases were identified which showed major changes in the spectral shape of flare emission: 20:38:00-20:44:20 UT and 20:44:20-20:58:00 UT. During the second phase an efficiency of proton acceleration increased considerably relatively to the efficiency of acceleration of high energy electrons. The pion-decay component of the flare gamma-emission was elicited statistically significant only during the second phase since 20:47:40 UT. A power law spectrum index of accelerated protons was estimated from the ratio between intensities of the pion-decay and gamma-line components. The hardest spectrum (power law index S=3.7) was at 20:48—20:51 UT when the intensity of the pion-decay emission was maximal. Our subdivision of the flare into two phases is consistent with sharp changes in the structure of the flare found by Ji et al. (2008) and Liu et al. (2009). This flare was accompanied by GLE 66. The time profile of the pion-decay gamma-emission was compared with the GLE onset time. It was shown that both protons interacting at the Sun and the particles responsible for the GLE onset could belong to the same population of accelerated particles.

  18. Pure absorption electron spin echo envelope modulation spectra by using the filter-diagonalization method for harmonic inversion.

    PubMed

    Jeschke, G; Mandelshtam, V A; Shaka, A J

    1999-03-01

    Harmonic inversion of electron spin echo envelope (ESEEM) time-domain signals by filter diagonalization is investigated as an alternative to Fourier transformation. It is demonstrated that this method features enhanced resolution compared to Fourier-transform magnitude spectra, since it can eliminate dispersive contributions to the line shape, even if no linear phase correction is possible. Furthermore, instrumental artifacts can be easily removed from the spectra if they are narrow either in time or frequency domain. This applies to echo crossings that are only incompletely eliminated by phase cycling and to spurious spectrometer frequencies, respectively. The method is computationally efficient and numerically stable and does not require extensive parameter adjustments or advance knowledge of the number of spectral lines. Experiments on gamma-irradiated methyl-alpha-d-glucopyranoside show that more information can be obtained from typical ESEEM time-domain signals by filter-diagonalization than by Fourier transformation.

  19. A QM/MM-MD study on protein electronic properties: Circular dichroism spectra of oxytocin and insulin

    NASA Astrophysics Data System (ADS)

    Kitagawa, Yuya; Akinaga, Yoshinobu; Kawashima, Yukio; Jung, Jaewoon; Ten-no, Seiichiro

    2012-06-01

    A QM/MM (quantum-mechanical/molecular-mechanical) molecular-dynamics approach based on the generalized hybrid-orbital (GHO) method, in conjunction with the second-order perturbation (MP2) theory and the second-order approximate coupled-cluster (CC2) model, is employed to calculate electronic property accounting for a protein environment. Circular dichroism (CD) spectra originating from chiral disulfide bridges of oxytocin and insulin at room temperature are computed. It is shown that the sampling of thermal fluctuation of molecular geometries facilitated by the GHO-MD method plays an important role in the obtained spectra. It is demonstrated that, while the protein environments in an oxytocin molecule have significant electrostatic influence on its chiral center, it is compensated by solvent induced charges. This gives a reasonable explanation to experimental observations. GHO-MD simulations starting from different experimental structures of insulin indicate that existence of the disulfide bridges with negative dihedral angles is crucial.

  20. Improving the accuracy and efficiency of time-resolved electronic spectra calculations: Cellular dephasing representation with a prefactor

    SciTech Connect

    Zambrano, Eduardo; Šulc, Miroslav; Vaníček, Jiří

    2013-08-07

    Time-resolved electronic spectra can be obtained as the Fourier transform of a special type of time correlation function known as fidelity amplitude, which, in turn, can be evaluated approximately and efficiently with the dephasing representation. Here we improve both the accuracy of this approximation—with an amplitude correction derived from the phase-space propagator—and its efficiency—with an improved cellular scheme employing inverse Weierstrass transform and optimal scaling of the cell size. We demonstrate the advantages of the new methodology by computing dispersed time-resolved stimulated emission spectra in the harmonic potential, pyrazine, and the NCO molecule. In contrast, we show that in strongly chaotic systems such as the quartic oscillator the original dephasing representation is more appropriate than either the cellular or prefactor-corrected methods.

  1. In situ laser Raman spectra of iron phthalocyanine adsorbed on copper and gold electrodes. [Electronic structure

    SciTech Connect

    Melendres, C.A.; Rios, C.B.; Feng, X.; McMasters, R.

    1983-01-01

    Raman spectra of iron phthalocyanine (FePc) and its tetrasulfonated derivative (FeTSPc) adsorbed on copper and gold electrodes have been observed in situ in 0.05 M H/sub 2/SO/sub 4/ solution. Results confirm the authors previous finding on the coordination of FePc to water molecules to solution. Evidence suggests that the iron phthalocyanines are probably oriented with their planes parallel to the electrode surface even in immersed electrodes. A decrease in intensity and broadening of some vibrational bands are observed on increasing cathodic polarization; these are attributed to a lifting of the degeneracy of the vibrational modes due to a change in symmetry of the adsorbed molecules brought about by polarization induced by the double-layer field. The effect of carbon on the Raman spectra is discussed. The iron phthalocyanines appear to be stable at potentials close to hydrogen evolution in the absence of oxygen. 18 references, 8 figures.

  2. Ultrafast optical nonlinearity, electronic absorption, vibrational spectra and solvent effect studies of ninhydrin

    NASA Astrophysics Data System (ADS)

    Sajan, D.; Devi, T. Uma; Safakath, K.; Philip, Reji; Němec, Ivan; Karabacak, M.

    2013-05-01

    FT-IR, FT-Raman and UV-Vis spectra of the nonlinear optical molecule ninhydrin have been recorded and analyzed. The equilibrium geometry, bonding features, and harmonic vibrational wavenumbers have been investigated with the help of B3LYP density functional theory method. A detailed interpretation of the vibrational spectra is carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. Solvent effects have been calculated using time-dependent density functional theory in combination with the polarized continuum model. Natural bond orbital analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule. Employing the open-aperture z-scan technique, nonlinear optical absorption of the sample has been studied in the ultrafast and short-pulse excitation regimes, using 100 fs and 5 ns laser pulses respectively. It is found that ninhydrin exhibits optical limiting for both excitations, indicating potential photonic applications.

  3. Electron-ion interaction effects in attosecond time-resolved photoelectron spectra

    SciTech Connect

    Zhang, C.-H.; Thumm, U.

    2010-10-15

    Photoionization by attosecond extreme ultraviolet (xuv) pulses into the laser-dressed continuum of the ionized atom is commonly described in strong-field approximation, neglecting the Coulomb interaction between the emitted photoelectron (PE) and the residual ion. By solving the time-dependent Schroedinger equation, we identify a temporal shift {delta}{tau} in streaked PE spectra, which becomes significant at low PE energies. Within an eikonal approximation, we trace this shift to the combined action of Coulomb and laser forces on the released PE, suggesting the experimental and theoretical scrutiny of their coupling in streaked PE spectra. Further, we examined the effect of initial state polarization by the laser pulse on the xuv streaked spectrum.

  4. Electronic energy loss spectra from mono-layer to few layers of phosphorene

    NASA Astrophysics Data System (ADS)

    Mohan, Brij; Thakur, Rajesh; Ahluwalia, P. K.

    2016-05-01

    Using first principles calculations, electronic and optical properties of few-layers phosphorene has been investigated. Electronic band structure show a moderate band gap of 0.9 eV in monolayer phosphorene which decreases with increasing number of layers. Optical properties of few-layers of phosphorene in infrared and visible region shows tunability with number of layers. Electron energy loss function has been plotted and huge red shift in plasmonic behaviours is found. These tunable electronic and optical properties of few-layers of phosphorene can be useful for the applications of optoelectronic devices.

  5. Influence of the physical structure of irradiated starches on their electron spin resonance spectra kinetics

    SciTech Connect

    Raffi, J.J.; Agnel, J.P.L.

    1983-06-23

    This study deals with the shape and kinetic changes of the ESR spectra of eight irradiated starchs, from several hours to several months after ..gamma..-irradiation. Whatever the origin and water content of the starches two major radicals or groups of radicals are observed. The kinetic law depends on the water content; two main zones are pointed out which are relative to the amorphous and crystalline parts of starches.

  6. A COLD, TENUOUS SOLAR FLARE: ACCELERATION WITHOUT HEATING

    SciTech Connect

    Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.; Kontar, Eduard P.

    2011-04-10

    We report the observation of an unusual cold, tenuous solar flare, which reveals itself via numerous and prominent non-thermal manifestations, while lacking any noticeable thermal emission signature. RHESSI hard X-rays and 0.1-18 GHz radio data from OVSA and Phoenix-2 show copious electron acceleration (10{sup 35} electrons s{sup -1} above 10 keV) typical for GOES M-class flares with electrons energies up to 100 keV, but GOES temperatures not exceeding 6.1 MK. The imaging, temporal, and spectral characteristics of the flare have led us to a firm conclusion that the bulk of the microwave continuum emission from this flare was produced directly in the acceleration region. The implications of this finding for the flaring energy release and particle acceleration are discussed.

  7. Induced changes in the electron paramagnetic resonance spectra of mammalian catalases.

    PubMed

    Williams-Smith, D L; Patel, K

    1975-10-20

    The EPR spectra of bovine liver catalase, rat liver catalase and human erythrocyte catalase have been measured at 9.0 degrees K. In N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic acid (HEPES) and Tris buffers at pH 7.0, the liver catalases show EPR spectra typical of rhombically distorted high spin ferric heme with major lines at g = 6.50, 5.35, 1.98. A number of extra lines are also seen; these are weak or absent in human erythrocyte catalase. The effect of the addition of formate, nitrite, acetate, fluoride, azide, hypophosphite and of inactivation with 3-amino-1,2,4-triazole on the degree of rhombic distortion has been studied. There is a good correlation between the low temperature EPR and room temperature optical changes for the binding of formic acid in HEPES and Tris. There is no evidence from EPR spectra for the presence of heme-heme interactions in the binding of formic acid to human erythrocyte catalase. The properties of catalase are altered in phosphate and in distilled water. This is a consequence of the low temperature of measurement. PMID:170980

  8. SOLAR FLARE CHROMOSPHERIC LINE EMISSION: COMPARISON BETWEEN IBIS HIGH-RESOLUTION OBSERVATIONS AND RADIATIVE HYDRODYNAMIC SIMULATIONS

    SciTech Connect

    Costa, Fatima Rubio da; Petrosian, Vahé; Kleint, Lucia; Dalda, Alberto Sainz; Liu, Wei

    2015-05-01

    Solar flares involve impulsive energy release, which results in enhanced radiation over a broad spectral range and a wide range of heights. In particular, line emission from the chromosphere can provide critical diagnostics of plasma heating processes. Thus, a direct comparison between high-resolution spectroscopic observations and advanced numerical modeling results could be extremely valuable, but has not yet been attempted. In this paper, we present such a self-consistent investigation of an M3.0 flare observed by the Dunn Solar Telescope’s Interferometric Bi-dimensional Spectrometer (IBIS) on 2011 September 24 which we have modeled using the radiative hydrodynamic code RADYN. We obtained images and spectra of the flaring region with IBIS in Hα 6563 Å and Ca ii 8542 Å, and with RHESSI in X-rays. The latter observations were used to infer the non-thermal electron population, which was passed to RADYN to simulate the atmospheric response to electron collisional heating. We then synthesized spectral lines and compared their shapes and intensities to those observed by IBIS and found a general agreement. In particular, the synthetic Ca ii 8542 Å profile fits well to the observed profile, while the synthetic Hα profile is fainter in the core than for the observation. This indicates that Hα emission is more responsive to the non-thermal electron flux than the Ca ii 8542 Å emission. We suggest that it is necessary to refine the energy input and other processes to resolve this discrepancy.

  9. Solar Flare Chromospheric Line Emission: Comparison Between IBIS High-resolution Observations and Radiative Hydrodynamic Simulations

    NASA Astrophysics Data System (ADS)

    Rubio da Costa, Fatima; Kleint, Lucia; Petrosian, Vahé; Sainz Dalda, Alberto; Liu, Wei

    2015-05-01

    Solar flares involve impulsive energy release, which results in enhanced radiation over a broad spectral range and a wide range of heights. In particular, line emission from the chromosphere can provide critical diagnostics of plasma heating processes. Thus, a direct comparison between high-resolution spectroscopic observations and advanced numerical modeling results could be extremely valuable, but has not yet been attempted. In this paper, we present such a self-consistent investigation of an M3.0 flare observed by the Dunn Solar Telescope’s Interferometric Bi-dimensional Spectrometer (IBIS) on 2011 September 24 which we have modeled using the radiative hydrodynamic code RADYN. We obtained images and spectra of the flaring region with IBIS in Hα 6563 Å and Ca ii 8542 Å, and with RHESSI in X-rays. The latter observations were used to infer the non-thermal electron population, which was passed to RADYN to simulate the atmospheric response to electron collisional heating. We then synthesized spectral lines and compared their shapes and intensities to those observed by IBIS and found a general agreement. In particular, the synthetic Ca ii 8542 Å profile fits well to the observed profile, while the synthetic Hα profile is fainter in the core than for the observation. This indicates that Hα emission is more responsive to the non-thermal electron flux than the Ca ii 8542 Å emission. We suggest that it is necessary to refine the energy input and other processes to resolve this discrepancy.

  10. Oxygen-induced changes in electron-energy-loss spectra for Al, Be and Ni. [Al; Be; Ni

    SciTech Connect

    Madden, H.H.; Landers, R.; Kleiman, G.G. , 13081-970 Campinas, Sao Paulo, Brasil); Zehner, D.M. )

    1999-09-01

    Electron-energy-loss spectroscopy (EELS) data are presented to illustrate line shape changes that occur as a result of oxygen interaction with metal surfaces. The metals were aluminum, beryllium and nickel. Core-level EELS data were taken for excitations from Al(2p), Be(1s), Ni(3p/3s) and O(1s) levels to the conduction band (CB) density of states (DOS) of the materials. The primary beam energies for the spectra were 300, 450, 300, and 1135 eV, respectively. The data are presented in both the (as measured) first-derivative and the integral forms. The integral spectra were corrected for coherent background losses and analyzed for CB DOS information. These spectra were found to be in qualitative agreement with published experimental and theoretical studies of these materials. One peak in the spectra for Al oxide is analyzed for its correlation with excitonic screening of the Al(2p) core hole. Similar evidence for exciton formation is found in the Ni(3p) spectra for Ni oxide. Data are also presented showing oxygen-induced changes in the lower-loss-energy EELS curves that, in the pure metal, are dominated by plasmon-loss and interband-transition signals. Single-scattering loss profiles in the integral form of the data were calculated using a procedure of Tougaard and Chorkendorff [S. Tougaard and I. Chorkendorff, Phys. Rev. B. [bold 35], 6570 (1987)]. For all three oxides these profiles are dominated by a feature with a loss energy of around 20[endash]25 eV. Although this feature has been ascribed by other researchers as due to bulk plasmon losses in the oxide, an alternative explanation is that the feature is simply due to O(2s)-to-CB-level excitations. An even stronger feature is found at 7 eV loss energy for Ni oxide. Speculation is given as to its source. The line shapes in both the core-level and noncore-level spectra can also be used simply as [open quotes]fingerprints[close quotes] of the surface chemistry of the materials. Our data were taken using commercially

  11. MODELING OF GYROSYNCHROTRON RADIO EMISSION PULSATIONS PRODUCED BY MAGNETOHYDRODYNAMIC LOOP OSCILLATIONS IN SOLAR FLARES

    SciTech Connect

    Mossessian, George; Fleishman, Gregory D.

    2012-04-01

    A quantitative study of the observable radio signatures of the sausage, kink, and torsional magnetohydrodynamic (MHD) oscillation modes in flaring coronal loops is performed. Considering first non-zero order effect of these various MHD oscillation modes on the radio source parameters such as magnetic field, line of sight, plasma density and temperature, electron distribution function, and the source dimensions, we compute time-dependent radio emission (spectra and light curves). The radio light curves (of both flux density and degree of polarization) at all considered radio frequencies are then quantified in both time domain (via computation of the full modulation amplitude as a function of frequency) and in Fourier domain (oscillation spectra, phases, and partial modulation amplitude) to form the signatures specific to a particular oscillation mode and/or source parameter regime. We found that the parameter regime and the involved MHD mode can indeed be distinguished using the quantitative measures derived in the modeling. We apply the developed approach to analyze radio burst recorded by Owens Valley Solar Array and report possible detection of the sausage mode oscillation in one (partly occulted) flare and kink or torsional oscillations in another flare.

  12. Local electron spectrum above 100 MeV derived from gamma-ray emissivity spectra

    NASA Technical Reports Server (NTRS)

    Strong, A. W.

    1985-01-01

    Two new determinations of the local gamma-ray emmissivity spectrum are in good accord and were used to derive constraints on the local electron spectrum. The requirement for an electron intensity above 1 GeV larger than previously believed is confirmed and no low energy upturn is then needed.

  13. Resonance Raman and temperature-dependent electronic absorption spectra of cavity and noncavity models of the hydrated electron

    PubMed Central

    Casey, Jennifer R.; Larsen, Ross E.; Schwartz, Benjamin J.

    2013-01-01

    Most of what is known about the structure of the hydrated electron comes from mixed quantum/classical simulations, which depend on the pseudopotential that couples the quantum electron to the classical water molecules. These potentials usually are highly repulsive, producing cavity-bound hydrated electrons that break the local water H-bonding structure. However, we recently developed a more attractive potential, which produces a hydrated electron that encompasses a region of enhanced water density. Both our noncavity and the various cavity models predict similar experimental observables. In this paper, we work to distinguish between these models by studying both the temperature dependence of the optical absorption spectrum, which provides insight into the balance of the attractive and repulsive terms in the potential, and the resonance Raman spectrum, which provides a direct measure of the local H-bonding environment near the electron. We find that only our noncavity model can capture the experimental red shift of the hydrated electron’s absorption spectrum with increasing temperature at constant density. Cavity models of the hydrated electron predict a solvation structure similar to that of the larger aqueous halides, leading to a Raman O–H stretching band that is blue-shifted and narrower than that of bulk water. In contrast, experiments show the hydrated electron has a broader and red-shifted O–H stretching band compared with bulk water, a feature recovered by our noncavity model. We conclude that although our noncavity model does not provide perfect quantitative agreement with experiment, the hydrated electron must have a significant degree of noncavity character. PMID:23382233

  14. Flares in childhood eczema.

    PubMed

    Langan, S M

    2009-01-01

    Eczema is a major public health problem affecting children worldwide. Few studies have directly assessed triggers for disease flares. This paper presents evidence from a published systematic review and a prospective cohort study looking at flare factors in eczema. This systematic review suggested that foodstuffs in selected groups, dust exposure, unfamiliar pets, seasonal variation, stress, and irritants may be important in eczema flares. We performed a prospective cohort study that focused on environmental factors and identified associations between exposure to nylon clothing, dust, unfamiliar pets, sweating, shampoo, and eczema flares. Results from this study also demonstrated some new key findings. First, the effect of shampoo was found to increase in cold weather, and second, combinations of environmental factors were associated with disease exacerbation, supporting a multiple component disease model. This information is likely to be useful to families and may lead to the ability to reduce disease flares in the future. PMID:20054505

  15. Effects of central metal on electronic structure, magnetic properties, infrared and Raman spectra of double-decker phthalocyanine

    NASA Astrophysics Data System (ADS)

    Suzuki, Atsushi; Oku, Takeo

    2016-09-01

    The effects of the central metal in double-decker metal phthalocyanine on the electronic structure, magnetic properties, and infrared and Raman spectra of the complex were investigated. Electron density distributions were delocalized on the phthalocyanine rings. The narrow energy gap and infrared peaks observed in the ultra-violet-visible-near infrared spectra of the systems were attributed to phthalocyanine ring-ring interactions the between overlapping π-orbitals on each ring. The chemical shift behavior of the phthalocyanine rings was separated by the deformation of their structure owing to nuclear magnetic interaction of the nuclear quadrupole interaction as determined by the electronic field gradient and asymmetric parameters. The magnetic parameters of principle g-tensors were dependent on the perturbation of the crystal field by the hybridization of the d-spin in the central metal conjugated with nitrogen ligands. In the case of the vanadyl system, the IR vibration modes were shifted by the soft vibration mode for resolving the symmetrical structure. Inactive Raman vibration modes arose from no-polarization on the phthalocyanine rings. Double-decker metal phthalocyanines have great advantages for the control of the magnetic mechanism for quantum spin entanglement in the relaxation process.

  16. Coronal vs chromospheric heating through co-spatial return currents during the 19 and 20 Jan 2005 solar flare

    NASA Astrophysics Data System (ADS)

    Alaoui, Meriem; Holman, Gordon D.

    2016-05-01

    The high electron flux required to explain the bremsstrahlung X-ray emission observed from solar flares is expected to be accompanied by a neutralizing co-spatial return current. In addition to resupplying the acceleration region with electrons, this return current will both heat the coronal plasma and flatten the electron distribution at lower energies. This flattening in the electron distribution in turn flattens the X-ray spectrum. We have found that return-current collisional thick-target model (RCCTTM) of Holman (2012) provides an acceptable fit to X-ray spectra with strong breaks for 18 flares observed with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). This is a 1D model similar to the collisional thick-target model (CTTM) with two additional assumptions: (1) electrons lose some of their energy through return current losses along their path to the thick target, where they lose all their remaining energy through Coulomb collisions; (2) the non-thermal beam is streaming in a warm target, which means that electrons will be thermalized at a non-zero energy. We assume this energy to be equal to the analytical value derived by Kontar et al. 2015. We show that return-current heating in the corona is about an order of magnitude higher than the heating at the footpoints at times during the flare.

  17. Formation of very hard electron and gamma-ray spectra of flat-spectrum radio quasars in the fast-cooling regime

    NASA Astrophysics Data System (ADS)

    Yan, Dahai; Zhang, Li; Zhang, Shuang-Nan

    2016-07-01

    In the external Compton scenario, we investigate the formation of a very hard electron spectrum in the fast-cooling regime, using a time-dependent emission model. It is shown that a very hard electron distribution, N^' }_e({γ ^' })∝ {γ ^' }^{-p}, with spectral index p ˜ 1.3 is formed below the minimum energy of injection electrons when inverse Compton scattering takes place in the Klein-Nishina regime, i.e. inverse Compton scattering of relativistic electrons on broad-line region radiation in flat-spectrum radio quasars. This produces a very hard gamma-ray spectrum and can explain in reasonable fashion the very hard Fermi-Large Area Telescope (LAT) spectrum of the flat-spectrum radio quasar 3C 279 during the extreme gamma-ray flare in 2013 December.

  18. Frequency distributions and correlations of solar X-ray flare parameters

    NASA Technical Reports Server (NTRS)

    Crosby, Norma B.; Aschwanden, Markus J.; Dennis, Brian R.

    1993-01-01

    Frequency distributions of flare parameters are determined from over 12,000 solar flares. The flare duration, the peak counting rate, the peak hard X-ray flux, the total energy in electrons, and the peak energy flux in electrons are among the parameters studied. Linear regression fits, as well as the slopes of the frequency distributions, are used to determine the correlations between these parameters. The relationship between the variations of the frequency distributions and the solar activity cycle is also investigated. Theoretical models for the frequency distribution of flare parameters are dependent on the probability of flaring and the temporal evolution of the flare energy build-up. The results of this study are consistent with stochastic flaring and exponential energy build-up. The average build-up time constant is found to be 0.5 times the mean time between flares.

  19. Synthesis of nanoparticles in helium droplets—A characterization comparing mass-spectra and electron microscopy data

    SciTech Connect

    Thaler, Philipp; Volk, Alexander; Lackner, Florian; Steurer, Johannes; Schnedlitz, Martin; Ernst, Wolfgang E.; Knez, Daniel; Haberfehlner, Georg

    2015-10-07

    Micrometer sized helium droplets provide an extraordinary environment for the growth of nanoparticles. The method promises great potential for the preparation of core-shell particles as well as one-dimensional nanostructures, which agglomerate along quantum vortices, without involving solvents, ligands, or additives. Using a new apparatus, which enables us to record mass spectra of heavy dopant clusters (>10{sup 4} amu) and to produce samples for transmission electron microscopy simultaneously, we synthesize bare and bimetallic nanoparticles consisting of various materials (Au, Ni, Cr, and Ag). We present a systematical study of the growth process of clusters and nanoparticles inside the helium droplets, which can be described with a simple theoretical model.

  20. Direct observation of Higgs mode oscillations in the pump-probe photoemission spectra of electron-phonon mediated superconductors

    NASA Astrophysics Data System (ADS)

    Kemper, A. F.; Sentef, M. A.; Moritz, B.; Freericks, J. K.; Devereaux, T. P.

    2015-12-01

    Using the nonequilibrium Keldysh formalism, we solve the equations of motion for electron-phonon superconductivity, including an ultrafast pump field. We present results for time-dependent photoemission spectra out of equilibrium which probe the dynamics of the superconducting gap edge. The partial melting of the order by the pump field leads to oscillations at twice the melted gap frequency, a hallmark of the Higgs or amplitude mode. Thus the Higgs mode can be directly excited through the nonlinear effects of an electromagnetic field and detected without requiring any additional symmetry breaking.

  1. Extreme ultraviolet ionization of pure He nanodroplets: mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra.

    PubMed

    Buchta, D; Krishnan, S R; Brauer, N B; Drabbels, M; O'Keeffe, P; Devetta, M; Di Fraia, M; Callegari, C; Richter, R; Coreno, M; Prince, K C; Stienkemeier, F; Ullrich, J; Moshammer, R; Mudrich, M

    2013-08-28

    The ionization dynamics of pure He nanodroplets irradiated by Extreme ultraviolet radiation is studied using Velocity-Map Imaging PhotoElectron-PhotoIon COincidence spectroscopy. We present photoelectron energy spectra and angular distributions measured in coincidence with the most abundant ions He(+), He2(+), and He3(+). Surprisingly, below the autoionization threshold of He droplets, we find indications for multiple excitation and subsequent ionization of the droplets by a Penning-like process. At high photon energies we observe inelastic collisions of photoelectrons with the surrounding He atoms in the droplets.

  2. Electronic spectra of iron monohydride in the infrared near 1.35 and 1.58 microm.

    PubMed

    Balfour, Walter J; Brown, John M; Wallace, Lloyd

    2004-10-22

    The complex, many-line spectrum of FeH, lying in the infrared region between 5500 and 7500 cm(-1), has been shown to consist of two separate electronic transitions: E (4)Pi-X (4)Delta and E (4)Pi-A (4)Pi. High resolution Fourier transform spectra from thermal emission have been rotationally analyzed in detail. Lambda doubling in both the E (4)Pi and A (4)Pi states is considerable. The experimentally determined energies and bond lengths of the newly characterized states are in good agreement with theoretical predictions.

  3. Electronic properties and absorption spectra of ZnSnP2 using mBJ potential

    NASA Astrophysics Data System (ADS)

    Joshi, Ritu; Ahuja, B. L.

    2015-06-01

    We present the energy bands and density of states of ZnSnP2 using full potential linearized augmented plane wave method with modified Becke Johnson potential. It is found that this compound has a direct band gap of about 2.01 eV at Γ point, which originates from the energy difference between P-3p and Sn-5s states. In addition, we have also calculated absorption spectra in the solar energy range and compared it with that of bulk Si to explore the applicability of ZnSnP2 in photovoltaic and optoelectronic devices.

  4. Measurements of Electron Spectra in the Forward Direction in Slow-Antiproton Carbon-Foil Collisions

    NASA Astrophysics Data System (ADS)

    Yamazaki, Yasunori; Kuroki, Kenro; Komaki, Ken-Ichiro; Andersen, Lars H.; Horsdal-Pedersen, Erik; Hvelplund, Preben; Knudsen, Helge; M{ø}ller, S{ø}ren P.; Uggerh{ø}j, Erik; Elsener, Konrad

    1990-08-01

    The spectrta of electrons emitted in the forward direction from antiproton and proton bombardments on carbon foils have been studied for projectile energies from 500 to 750 keV. Our main observation is that at the electron energy where the well-known convoy peak is observed for proton impact, the spectrum for equivelocity antiprotons is smooth, showing no indication of a deep anticusp. However, around 50 eV below the electron energy where the cusp is observed for proton impact, we have observed a small peak for antiproton impact. The energy and the relative intensity of the bump are found to be consistent with those predicted for electrons released from a wake-riding state.

  5. Angle-resolved Auger electron spectra induced by neon ion impact on aluminum

    NASA Technical Reports Server (NTRS)

    Pepper, S. V.; Aron, P. R.

    1986-01-01

    Auger electron emission from aluminum bombarded with 1 to 5 keV neon ions was studied by angle-resolved electron spectroscopy. The position and shape of the spectral features depended on the incident ion energy, angle of ion incidence, and electron take-off angle with respect to the aluminum surface. These spectral dependencies were interpreted in terms of the Doppler shift given to the Auger electron velocity by the excited atom ejected into the vacuum. For oblique ion incidence it is concluded that a flux of high energy atoms are ejected in a direction close to the projection of the ion beam on the target surface. In addition, a new spectral feature was found and identified as due to Auger emission from excited neon in the aluminum matrix.

  6. Relation of exact Gaussian basis methods to the dephasing representation: Theory and application to time-resolved electronic spectra

    NASA Astrophysics Data System (ADS)

    Šulc, Miroslav; Hernández, Henar; Martínez, Todd J.; Vaníček, Jiří

    2013-07-01

    We recently showed that the dephasing representation (DR) provides an efficient tool for computing ultrafast electronic spectra and that further acceleration is possible with cellularization [M. Šulc and J. Vaníček, Mol. Phys. 110, 945 (2012)], 10.1080/00268976.2012.668971. Here, we focus on increasing the accuracy of this approximation by first implementing an exact Gaussian basis method, which benefits from the accuracy of quantum dynamics and efficiency of classical dynamics. Starting from this exact method, the DR is derived together with ten other methods for computing time-resolved spectra with intermediate accuracy and efficiency. These methods include the Gaussian DR, an exact generalization of the DR, in which trajectories are replaced by communicating frozen Gaussian basis functions evolving classically with an average Hamiltonian. The newly obtained methods are tested numerically on time correlation functions and time-resolved stimulated emission spectra in the harmonic potential, pyrazine S0/S1 model, and quartic oscillator. Numerical results confirm that both the Gaussian basis method and the Gaussian DR increase the accuracy of the DR. Surprisingly, in chaotic systems the Gaussian DR can outperform the presumably more accurate Gaussian basis method, in which the two bases are evolved separately.

  7. Low energy X-ray spectra measured with a mercuric iodide energy dispersive spectrometer in a scanning electron microscope

    NASA Technical Reports Server (NTRS)

    Iwanczyk, J. S.; Dabrowski, A. J.; Huth, G. C.; Bradley, J. G.; Conley, J. M.

    1986-01-01

    A mercuric iodide energy dispersive X-ray spectrometer, with Peltier cooling provided for the detector and input field effect transistor, has been developed and tested in a scanning electron microscope. X-ray spectra were obtained with the 15 keV electron beam. An energy resolution of 225 eV (FWHM) for Mn-K(alpha) at 5.9 keV and 195 eV (FWHM) for the Mg-K line at 1.25 keV has been measured. Overall system noise level was 175 eV (FWHM). The detector system characterization with a carbon target demonstrated good energy sensitivity at low energies and lack of significant spectral artifacts at higher energies.

  8. Electronic absorption spectra of rare earth (III) species in NaCl-2CsCl eutectic based melts

    NASA Astrophysics Data System (ADS)

    Volkovich, V. A.; Ivanov, A. B.; Yakimov, S. M.; Tsarevskii, D. V.; Golovanova, O. A.; Sukhikh, V. V.; Griffiths, T. R.

    2016-09-01

    Electronic absorption spectra of ions of trivalent rare earth elements were measured in the melts based on NaCl-2CsCl eutectic in the wavelength ranges of 190-1350 and 1450-1700 nm. The measurements were performed at 550-850 °C. The EAS of Y, La, Ce and Lu containing melts have no absorption bands in the studied regions. For the remaining REEs (Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) the absorption bands in the EAS were assigned to the corresponding f-f electron transitions. The Stark effect was observed for Yb(III) F5/2 excited state. Increasing temperature leads to decreasing intensity of the absorption bands, except for the bands resulting from hypersensitive transitions. Beer's law was confirmed up to 0.4 M solutions of REE.

  9. Phase-modulated electronic wave packet interferometry reveals high resolution spectra of free Rb atoms and Rb*He molecules.

    PubMed

    Bruder, Lukas; Mudrich, Marcel; Stienkemeier, Frank

    2015-10-01

    Phase-modulated wave packet interferometry is combined with mass-resolved photoion detection to investigate rubidium atoms attached to helium nanodroplets in a molecular beam experiment. The spectra of atomic Rb electronic states show a vastly enhanced sensitivity and spectral resolution when compared to conventional pump-probe wave packet interferometry. Furthermore, the formation of Rb*He exciplex molecules is probed and for the first time a fully resolved vibrational spectrum for transitions between the lowest excited 5Π3/2 and the high-lying electronic states 2(2)Π, 4(2)Δ, 6(2)Σ is obtained and compared to theory. The feasibility of applying coherent multidimensional spectroscopy to dilute cold gas phase samples is demonstrated in these experiments.

  10. COMPTEL solar flare observations

    NASA Technical Reports Server (NTRS)

    Ryan, J. M.; Aarts, H.; Bennett, K.; Debrunner, H.; Devries, C.; Denherder, J. W.; Eymann, G.; Forrest, D. J.; Diehl, R.; Hermsen, W.

    1992-01-01

    COMPTEL as part of a solar target of opportunity campaign observed the sun during the period of high solar activity from 7-15 Jun. 1991. Major flares were observed on 9 and 11 Jun. Although both flares were large GOES events (greater than or = X10), they were not extraordinary in terms of gamma-ray emission. Only the decay phase of the 15 Jun. flare was observed by COMPTEL. We report the preliminary analysis of data from these flares, including the first spectroscopic measurement of solar flare neutrons. The deuterium formation line at 2.223 MeV was present in both events and for at least the 9 Jun. event, was comparable to the flux in the nuclear line region of 4-8 MeV, consistent with Solar-Maximum Mission (SSM) Observations. A clear neutron signal was present in the flare of 9 Jun. with the spectrum extending up to 80 MeV and consistent in time with the emission of gamma-rays, confirming the utility of COMPTEL in measuring the solar neutron flux at low energies. The neutron flux below 100 MeV appears to be lower than that of the 3 Jun. 1982 flare by more than an order of magnitude. The neutron signal of the 11 Jun. event is under study. Severe dead time effects resulting from the intense thermal x-rays require significant corrections to the measured flux which increase the magnitude of the associated systematic uncertainties.

  11. EVE-RHESSI Observations of Thermal and Nonthermal Solar Flare Emission

    NASA Astrophysics Data System (ADS)

    McTiernan, James; Caspi, A.; Warren, H.

    2013-07-01

    Solar flares accelerate electrons up to hundreds of MeV and heat plasma to tens of MK. In large (GOES M- and X-class) flares, in addition to the 10-25 MK plasma thought to be the result of chromospheric evaporation, even hotter plasma (up to 50 MK) may be directly heated in the corona. While observations of hard X-ray bremmstrahlung directly probe the nonthermal electron population, for large flares the spectra below 20-30 keV are typically dominated by thermal emission. The low energy extent of the nonthermal spectrum can be only loosely quantified by hard X-ray spectrometers, resulting in significant implications for calculating flare energy budgets and for constraining possible acceleration mechanisms. A precise characterization of the thermal emission is imperative. Extreme ultraviolet observations from the EUV Variability Experiment (EVE) on-board the Solar Dynamics Observatory (SDO), combined with X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI), currently offer the most comprehensive view of the flare temperature distribution. EVE observes EUV emission lines with peak formation temperatures of 2-20 MK, while RHESSI observes the X-ray bremsstrahlung of hot, 10-50 MK plasma; combined, the two instruments cover the full range of flare plasma temperatures. In this work, we handle the EVE-RHESSI data for a few large flares in three steps; first we calculate differential emission measures (DEMs) using EVE and RHESSI independently for purposes of cross-calibration. Second, we create combined EVE-RHESSI DEMs, fixing the nonthermal spectral parameters to those found using a RHESSI-only spectral fit. The final step is to unconstrain the nonthermal parameters (in particular, the low-energy cutoff of the spectrum) and let them be fit in the same process as the EVE-RHESSI DEM, to obtain a fully self-consistent thermal plus nonthermal model. This research is supported by NASA Heliophysics Guest Investigator Grant NNX12AH48G.

  12. THERMAL FRONTS IN SOLAR FLARES

    SciTech Connect

    Karlický, Marian

    2015-12-01

    We studied the formation of a thermal front during the expansion of hot plasma into colder plasma. We used a three-dimensional electromagnetic particle-in-cell model that includes inductive effects. In early phases, in the area of the expanding hot plasma, we found several thermal fronts, which are defined as a sudden decrease of the local electron kinetic energy. The fronts formed a cascade. Thermal fronts with higher temperature contrast were located near plasma density depressions, generated during the hot plasma expansion. The formation of the main thermal front was associated with the return-current process induced by hot electron expansion and electrons backscattered at the front. A part of the hot plasma was trapped by the thermal front while another part, mainly with the most energetic electrons, escaped and generated Langmuir and electromagnetic waves in front of the thermal front, as shown by the dispersion diagrams. Considering all of these processes and those described in the literature, we show that anomalous electric resistivity is produced at the location of the thermal front. Thus, the thermal front can contribute to energy dissipation in the current-carrying loops of solar flares. We estimated the values of such anomalous resistivity in the solar atmosphere together with collisional resistivity and electric fields. We propose that the slowly drifting reverse drift bursts, observed at the beginning of some solar flares, could be signatures of the thermal front.

  13. Thermal Fronts in Solar Flares

    NASA Astrophysics Data System (ADS)

    Karlický, Marian

    2015-12-01

    We studied the formation of a thermal front during the expansion of hot plasma into colder plasma. We used a three-dimensional electromagnetic particle-in-cell model that includes inductive effects. In early phases, in the area of the expanding hot plasma, we found several thermal fronts, which are defined as a sudden decrease of the local electron kinetic energy. The fronts formed a cascade. Thermal fronts with higher temperature contrast were located near plasma density depressions, generated during the hot plasma expansion. The formation of the main thermal front was associated with the return-current process induced by hot electron expansion and electrons backscattered at the front. A part of the hot plasma was trapped by the thermal front while another part, mainly with the most energetic electrons, escaped and generated Langmuir and electromagnetic waves in front of the thermal front, as shown by the dispersion diagrams. Considering all of these processes and those described in the literature, we show that anomalous electric resistivity is produced at the location of the thermal front. Thus, the thermal front can contribute to energy dissipation in the current-carrying loops of solar flares. We estimated the values of such anomalous resistivity in the solar atmosphere together with collisional resistivity and electric fields. We propose that the slowly drifting reverse drift bursts, observed at the beginning of some solar flares, could be signatures of the thermal front.

  14. Predicted CALET measurements of electron and positron spectra from 3 to 20 GeV using the geomagnetic field

    NASA Astrophysics Data System (ADS)

    Rauch, B. F.

    2014-05-01

    The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 for a planned 5 year mission. CALET consists of a charge detection module (CHD) with two segmented planes of 1 cm thick plastic scintillator, an imaging calorimeter (IMC) with a total of 3 radiation lengths (X∘) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 X∘ of lead tungstate (PWO) logs. The primary objectives of the experiment are to measure the electron e+e energy spectra from 1 GeV to 20 TeV, to detect gamma-rays above 10 GeV, and to measure the energy spectra of nuclei from protons through iron up to 1000 TeV. In this paper we describe how the geomagnetic field at the 51.6° inclination orbit of the ISS can be used to allow CALET to measure the distinct electron and positron fluxes. The positron fraction has been seen to rise above ˜10 GeV by previous experiments (HEAT, AMS-01), and more recently to continue to increase to higher energies (˜80 GeV for PAMELA, ˜200 GeV for Fermi and ˜350 GeV with the best statistics for AMS-02). Utilizing the geomagnetic cutoff, CALET will be able to distinguish electrons and positrons in the ˜3-20 GeV energy range where the positron fraction turns upward to complement existing high statistics measurements.

  15. Structure Prediction of Self-Assembled Dye Aggregates from Cryogenic Transmission Electron Microscopy, Molecular Mechanics, and Theory of Optical Spectra

    PubMed Central

    2016-01-01

    Cryogenic transmission electron microscopy (cryo-TEM) studies suggest that TTBC molecules self-assemble in aqueous solution to form single-walled tubes with a diameter of about 35 Å. In order to reveal the arrangement and mutual orientations of the individual molecules in the tube, we combine information from crystal structure data of this dye with a calculation of linear absorbance and linear dichroism spectra and molecular dynamics simulations. We start with wrapping crystal planes in different directions to obtain tubes of suitable diameter. This set of tube models is evaluated by comparing the resulting optical spectra with experimental data. The tubes that can explain the spectra are investigated further by molecular dynamics simulations, including explicit solvent molecules. From the trajectories of the most stable tube models, the short-range ordering of the dye molecules is extracted and the optimization of the structure is iteratively completed. The final structural model is a tube of rings with 6-fold rotational symmetry, where neighboring rings are rotated by 30° and the transition dipole moments of the chromophores form an angle of 74° with respect to the symmetry axis of the tube. This model is in agreement with cryo-TEM images and can explain the optical spectra, consisting of a sharp red-shifted J-band that is polarized parallel to to the symmetry axis of the tube and a broad blue-shifted H-band polarized perpendicular to this axis. The general structure of the homogeneous spectrum of this hybrid HJ-aggregate is described by an analytical model that explains the difference in redistribution of oscillator strength inside the vibrational manifolds of the J- and H-bands and the relative intensities and excitation energies of those bands. In addition to the particular system investigated here, the present methodology can be expected to aid the structure prediction for a wide range of self-assembled dye aggregates.

  16. Structure Prediction of Self-Assembled Dye Aggregates from Cryogenic Transmission Electron Microscopy, Molecular Mechanics, and Theory of Optical Spectra

    PubMed Central

    2016-01-01

    Cryogenic transmission electron microscopy (cryo-TEM) studies suggest that TTBC molecules self-assemble in aqueous solution to form single-walled tubes with a diameter of about 35 Å. In order to reveal the arrangement and mutual orientations of the individual molecules in the tube, we combine information from crystal structure data of this dye with a calculation of linear absorbance and linear dichroism spectra and molecular dynamics simulations. We start with wrapping crystal planes in different directions to obtain tubes of suitable diameter. This set of tube models is evaluated by comparing the resulting optical spectra with experimental data. The tubes that can explain the spectra are investigated further by molecular dynamics simulations, including explicit solvent molecules. From the trajectories of the most stable tube models, the short-range ordering of the dye molecules is extracted and the optimization of the structure is iteratively completed. The final structural model is a tube of rings with 6-fold rotational symmetry, where neighboring rings are rotated by 30° and the transition dipole moments of the chromophores form an angle of 74° with respect to the symmetry axis of the tube. This model is in agreement with cryo-TEM images and can explain the optical spectra, consisting of a sharp red-shifted J-band that is polarized parallel to to the symmetry axis of the tube and a broad blue-shifted H-band polarized perpendicular to this axis. The general structure of the homogeneous spectrum of this hybrid HJ-aggregate is described by an analytical model that explains the difference in redistribution of oscillator strength inside the vibrational manifolds of the J- and H-bands and the relative intensities and excitation energies of those bands. In addition to the particular system investigated here, the present methodology can be expected to aid the structure prediction for a wide range of self-assembled dye aggregates. PMID:27642380

  17. Electronic structures and optical spectra of BaO from first principles

    SciTech Connect

    Wu, Chang-Wei; Pan, Bo; Wang, Neng-Ping

    2015-08-21

    We present the results of first-principles study for the electronic structure and optical absorption spectrum of the alkaline-earth metal oxide BaO. The quasiparticle band structure is evaluated within the Hedin's GW approximation [Phys. Rev. 139, A796 (1965)]. Thereafter, the electron-hole interaction is taken into consideration and the Bethe-Salpeter equation for the electron-hole two-particle Green function is solved. The calculated quasiparticle band gap of BaO is 4.1 eV, which is in good agreement with the experimental result. The calculated optical absorption spectrum of BaO is also in agreement with the experimental data. In particular, the calculated excitation energy for the lowest exciton peak in the optical absorption spectrum of BaO reproduces very well the corresponding experimental result.

  18. Theoretical study of the electronic spectra of neutral and cationic NpO and NpO{sub 2}

    SciTech Connect

    Kovács, Attila; Infante, Ivan

    2015-08-21

    The electronic spectra of neutral NpO and NpO{sub 2} as well as of their mono- (NpO{sup +}, NpO{sub 2}{sup +}) and dications (NpO{sup 2+}, NpO{sub 2}{sup 2+}) were studied using multiconfigurational relativistic quantum chemical calculations at the complete active space self-consistent field/CASPT2 level of theory taking into account spin-orbit coupling. The active space included 16 orbitals: all the 7s, 6d, and 5f orbitals of neptunium together with selected orbitals of oxygen. The vertical excitation energies on the ground state geometries have been computed up to ca. 35 000 cm{sup −1}. The gas-phase electronic spectra were evaluated on the basis of the computed Einstein coefficients at 298 K and 3000 K. The computed vertical transition energies show good agreement with previous condensed-phase results on NpO{sub 2}{sup +} and NpO{sub 2}{sup 2+}.

  19. Structure, Vibrational and Electronic Spectra of Heterofullerene C48(BN)6

    SciTech Connect

    Manaa, M R; Xie, R; Smith, Jr., V H

    2004-01-15

    We report the geometrical structure, vibrational, and excitation spectra of novel, fullerene - analog C{sub 48}(BN){sub 6} using density functional calculations. The lowest energy structure is one in which B-N bonding is present as boron and nitrogen occupy each of the twelve pentagons of the fullerene cage. The cluster is polar with a net dipole moment of 0.55 Debye, which indicates an enhanced tendency toward reactivity with other media. The excitation spectrum shows that the lowest transition of 1.75 eV is dipole-allowed. The optical gap of C{sub 48}(BN){sub 6} is redshifted by 1.17 eV relative to that of C{sub 60}, suggesting possible use as single-molecule fluorescent probes for various applications.

  20. Age of the Harrison Street Beast: Electron paramagnetic resonance spectra from tooth enamel

    SciTech Connect

    Weeks, R.A.; Elam, J.M.; Davenport, C.; Bogard, J.S.

    1998-04-01

    Workers doing road reconstruction in 1993 in Fort Wayne, Indiana, uncovered remains of a large skeleton and contacted archaeologists for assessment prior to continuing work. The archaeologists excavated the remains which were located in a 19-cm thick layer of blue glay, a pedological deposit which forms from wet, anaerobic environments associated with bogs. This glay layer was located some 2 meters below the current ground level (Davenport 1996). In this paper, the authors present the results of an EPR analysis of tooth enamel (biogenic hydroxyapatite) from the Harrison Street Beast. The objectives of this study are: (1) determine an age for the specimen through EPR analysis of molar tooth enamel; (2) resolve and identify the radiation sensitive EPR spectral components; and (3) develop a provisional model for the creation of radiation-sensitive components in the EPR spectra.