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Sample records for studying excited structure

  1. Study of excited nucleons and their structure

    SciTech Connect

    Burkert, Volker D.

    2014-01-01

    Recent advances in the study of excited nucleons are discussed. Much of the progress has been achieved due to the availability of high precision meson production data in the photoproduction and electroproduction sectors, the development of multi-channel partial wave analysis techniques, and advances in Lattice QCD with predictions of the full excitation spectrum.

  2. Configuration interaction study of the ground and excited states of TiO2 ring structures

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Takashi; Whitten, Jerry L.

    2011-03-01

    Theoretical studies of the ground and lowest excited singlet and triplet states of a series of titanium dioxide ring structures, (TiO2)2n, n = 3-9, are reported. Calculations are based on many-electron configuration theory, where energies of states and geometrical structures are determined by variational energy minimization. The lowest energy excited states correspond to excitations from oxygen 2p levels to unoccupied 3d orbitals on titanium. For each ring system, two types of excited state solutions are investigated: those that maintain periodic symmetry for individual orbitals and solutions that allow the symmetry to be broken. The latter solutions which correspond to localized states or excitons are found to be significantly lower in energy than the symmetric solutions. We compare the vertical excitation energy of these well-defined geometrical structures with size effects reported in experimental studies.

  3. Excitation Methods for Bridge Structures

    SciTech Connect

    Farrar, C.R.; Duffy, T.A.; Cornwell, P.J.; Doebling, S.W.

    1999-02-08

    This paper summarizes the various methods that have been used to excited bridge structures during dynamic testing. The excitation methods fall into the general categories of ambient excitation methods and measured-input excitation methods. During ambient excitation the input to the bridge is not directly measured. In contrast, as the category label implies, measured-input excitations are usually applied at a single location where the force input to the structure can be monitored. Issues associated with using these various types of measurements are discussed along with a general description of the various excitation methods.

  4. X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

    DOE PAGES

    Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.; ...

    2016-07-06

    We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa) studied. We have also investigated the electronic and magneticmore » excitations in single-crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high-resolution Ir L-3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu2Ir2O7 (found to possess an actual stoichiometry of Eu2.18Ir1.82O7.06) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations« less

  5. X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

    SciTech Connect

    Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.; Tian, Di; Kim, J.; Upton, M. H.; Casa, D.; Gog, T.; Islam, Z.; Jeon, Byung -Gu; Kim, Kee Hoon; Desgreniers, S.; Kim, Yong Baek; Julian, S. J.; Kim, Young -June

    2016-07-06

    We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high-resolution Ir L-3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu2Ir2O7 (found to possess an actual stoichiometry of Eu2.18Ir1.82O7.06) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations

  6. X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

    SciTech Connect

    Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.; Tian, Di; Kim, J.; Upton, M. H.; Casa, D.; Gog, T.; Islam, Z.; Jeon, Byung -Gu; Kim, Kee Hoon; Desgreniers, S.; Kim, Yong Baek; Julian, S. J.; Kim, Young -June

    2016-07-06

    We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high-resolution Ir L-3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu2Ir2O7 (found to possess an actual stoichiometry of Eu2.18Ir1.82O7.06) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations

  7. Change in electronic structure upon optical excitation of 8-vinyladenosine: an experimental and theoretical study.

    PubMed

    Kodali, Goutham; Kistler, Kurt A; Narayanan, Madhavan; Matsika, Spiridoula; Stanley, Robert J

    2010-01-14

    8-Vinyladenosine (8VA) is an adenosine analog, like 2-aminopurine (2AP), that has a red-shifted absorption and high fluorescence quantum yield. When introduced into double-stranded DNA (dsDNA), its base-pairing and base-stacking properties are similar to those of adenine. Of particular interest, the fluorescence quantum yield of 8VA is sensitive to base stacking, making it a very useful real-time probe of DNA structure. The fundamental photophysics underlying this fluorescence quenching by base stacking is not well understood, and thus exploring the excited state electronic structure of the analog is warranted. In this study, we report on changes in the electronic structure of 8VA upon optical excitation. Stark spectroscopy was performed on 8VA monomer in frozen ethanol glass at 77 K to obtain the direction and degree of charge redistribution in the form of the difference dipole moment, Deltamu(01) = 4.7 +/- 0.3 D, and difference static polarizability, tr(Delta(alpha)01) = 21 +/- 11 A(3), for the S(0)-->S(1) transition. In addition, solvatochromism experiments were performed on 8VA in various solvents and analyzed using Bakhshiev's model. High level ab initio methods were employed to calculate transition energies, oscillator strengths, and dipole moments of the ground and excited states of 8VA. The direction of Deltamu(01) was assigned in the molecular frame for the lowest optically accessible state. Our study shows that the angle between ground and excited state dipole moment plays a critical role in understanding the change in electronic structure upon optical excitation. Compared to 2AP, 8VA has a larger difference dipole moment which, with twice the extinction coefficient, suggests that 8VA is superior as a two-photon probe for microscopy studies. To this end, we have measured the ratio of the two-photon fluorescence yields of the two analogs by excitation at the respective monomer absorption maxima. We show that 8VA is indeed a significantly brighter two

  8. Synthesis, crystal structure and DFT studies of a dual fluorescent ketamine: Structural changes in the ground and excited states

    NASA Astrophysics Data System (ADS)

    Latha, V.; Balakrishnan, C.; Neelakantan, M. A.

    2015-07-01

    A fluorescent probe 2Z,2‧Z-3,3‧-(4,4‧-methylenebis(4,1-phenylene) bis(azanediyl))bis (1,3-diphenylprop-2-en-1-one) (L) was synthesized and characterized by IR, 1H NMR, ESI-mass, UV-visible and fluorescence spectral techniques. The single crystal analysis illustrates the existence of L in ketamine form. The crystal structure is stabilized by intramolecular and intermolecular hydrogen bonding. The thermal stability of L was studied by TG analysis. The fluorescence spectrum of L shows dual emission, and is due to excited state intramolecular proton transfer (ESIPT) process. This is supported by the high Stokes shift value. Electronic structure calculations of L in the ground and excited state have been carried out using DFT and TD-DFT at B3LYP/6-31G (d,p) level, respectively. The vibrational spectrum was computed at this level and compared with experimental values. Major orbital contributions for the electronic transitions were assigned with the help of TD-DFT. The changes in the Mulliken charge, bond lengths and bond angles between the ground and excited states of the tautomers demonstrate that twisted intramolecular charge transfer (TICT) process occurs along with ESIPT in the excited state.

  9. Ab initio, DFT, and spectroscopic studies of excited-state structure and dynamics of 9-ethylfluorene

    NASA Astrophysics Data System (ADS)

    Boo, Bong Hyun; Lee, Jae Kwang; Lim, Edward C.

    2008-12-01

    Fluorescence excitation and resonant two-photon ionization spectra were measured for 9-ethylfluorene ( EFR) molecule cooled in pulsed supersonic expansion of He in the range of 286.5 ˜ 300 nm. The structures and energies of the global and local minima and the transition states separating them are evaluated with the B3LYP/6-31G(d) and MP2/cc-pVTZ methods. It is found that the vertical excitation energies of fluorene and the EFR conformers can be reliably predicted by the time-dependent DFT method within 8.72%. The vibrational bands above the electronic origin are assigned on the basis of the RCIS/6-31G(d) calculation. Ethyl (or ethene) elimination from the excited neutral and/or ionic molecule is presumed to occur as an activation process along the adiabatic potential energy surface.

  10. First-principle studies of electronic structure and magnetic excitations in FeSe monolayer

    NASA Astrophysics Data System (ADS)

    Bazhirov, Timur; Cohen, Marvin L.

    2013-03-01

    Recent experimental advances made it possible to study single-layered superconducting systems of iron-based compounds. The results show evidence of significant enhancement of superconducting properties compared to the bulk case. We use first-principle pseudopotential density functional theory techniques and the local spin-density approximation to study the electronic properties of an FeSe monolayer in different spin configurations. The results show that the experimental shape of the Fermi surface is best described by a checkerboard antiferromagnetic (AFM) spin arrangement. To explore the underlying pairing mechanism, we study the evolution of the non-magnetic to the AFM-ordered structures under constrained magnetization, and we estimate the electronic coupling to magnetic excitations involving transfer and increase of iron magnetic moments and compare it to the electron-phonon coupling. Finally, we simulate the substrate-induced interaction by using uniform charge doping and show that the latter can lead to an increase in the density of states at the Fermi level and possibly produce higher superconducting transition temperatures. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility

  11. Excited-state dynamics of oxazole: A combined electronic structure calculations and dynamic simulations study

    NASA Astrophysics Data System (ADS)

    Cao, Jun; Xie, Zhi-Zhong; Yu, Xiaodong

    2016-08-01

    In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S2 state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the Osbnd C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2sbnd 5 bond formation. The azirine and bicyclic intermediates in the S0 state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T1 state have been proposed for these phototranspositions.

  12. Reducing crosstalk in array structures by controlling the excitation voltage of individual elements: a feasibility study.

    PubMed

    Bybi, A; Grondel, S; Assaad, J; Hladky-Hennion, A-C; Granger, C; Rguiti, M

    2013-08-01

    This paper describes a procedure to minimize crosstalk between the individual elements of a piezoelectric transducer array. A two-dimensional finite elements model was developed and the excitation voltages predicted by the model were applied to the array prototypes made of PZT 27 ceramic. Symmetric and asymmetric linear phased arrays operating at approximately 450 kHz were tested in the feasibility study. The studies were carried out at low frequency to facilitate the fabrication of the transducer arrays and to check the feasibility in this case. The novelty of our approach is to offer active cancellation of crosstalk in transducer arrays generating continuous waves, even in the presence of fabrication defects. The experimental results showed the validity of the approach and demonstrated that crosstalk can be reduced by about 6-10 dB. In ultrasonic imaging systems, this method could be introduced by using a multichannel generator providing electrical signals containing both phased signals required to focalize and deflect the acoustic beam associated with the correction signals.

  13. Excited-State Structure of Oligothiophene Dendrimers: Computational and Experimental Study

    DTIC Science & Technology

    2010-01-01

    supramolecular calculations of the systems with strong covalent bonding and high geometrical disorder. Approximations to the excitation energies are often done...Badaeva et al. (73) Kobko, N.; Masunov, A.; Tretiak, S. Chem. Phys. Lett. 2004, 392, 444–451. (74) Bartholomew , G. P.; Rumi, M.; Pond, S. J. K.; Perry, J

  14. Excitation of a composite structure by collisions

    SciTech Connect

    Newby, N.D. Jr.

    1984-08-01

    A simple model is employed to study the excitation of a composite structure by collisions. The composite structure is a diatomic ''molecule'' composed of two equal point masses joined by a Hooke's law spring of constant, k/sub 1/. This structure, in an unexcited state, makes a one-dimensional head-on collision with a fixed wall. The interaction with the wall is mediated by a second Hooke's law spring of constant, k/sub 2/. After rebounding from the wall the diatom may be in an excited state. The excitation energy is calculated as a function of the hardness of the wall. An eigenvalue problem is solved which yields an infinite number of ..beta..'s (..beta.. = k/sub 1//k/sub 2/) which leave the diatom unexcited. The phenomenon of ''double hitting'' : when a soft structure strikes a hard wall: is discussed. The maximum energy transfer into the internal mode is 23%. An air-track experiment is suggested to check the theoretical predictions.

  15. Neutron Scattering Studies of Structural and Magnetic Excitations in Lamellar Copper Oxides — a Review

    NASA Astrophysics Data System (ADS)

    Birgeneau, Robert J.; Shirane, Gen

    The following sections are included: * INTRODUCTION * La2-xSrxCuO4 STRUCTURE AND LATTICE DYNAMICS * MAGNETIC ORDERING IN La2CuO4 * Stoichiometric Material * Lightly Doped La2CuO4 * 2D STATIC AND DYNAMIC SPIN CORRELATIONS IN La2CuO4 * SPIN CORRELATIONS IN INSULATING, METALLIC AND SUPERCONDUCTING La2-xSrxCuO4 * NEUTRON SCATTERING STUDIES OF La2NiO4 and La2CoO4 * ANTIFERROMAGNETISM IN YBa2Cu3O6+x * CONCLUSIONS * ACKNOWLEDGEMENTS * References

  16. X-ray absorption fine structure and X-ray excited optical luminescence studies of II-VI semiconducting nanostructures

    NASA Astrophysics Data System (ADS)

    Murphy, Michael Wayne

    2010-06-01

    Various II-VI semiconducting nanomaterials such as ZnO-ZnS nanoribbons (NRs), CdSxSe1-x nanostructures, ZnS:Mn NRs, ZnS:Mn,Eu nanoprsims (NPs), ZnO:Mn nanopowders, and ZnO:Co nanopowders were synthesized for study. These materials were characterized by techniques such as scanning electron microscopy, transmission electron microscopy, element dispersive X-ray spectroscopy, selected area electron diffraction, and X-ray diffraction. The electronic and optical properties of these nanomaterials were studied by X-ray absorption fine structure (XAFS) spectroscopy and X-ray excited optical luminescence (XEOL) techniques, using tuneable soft X-rays from a synchrotron light source. The complementary nature ofthe XAFS and XEOL techniques give site, element and chemical specific measurements which allow a better understanding of the interplay and role of each element in the system. Chemical vapour deposition (CVD) of ZnS powder in a limited oxygen environment resulted in side-by-side biaxial ZnO-ZnS NR heterostructures. The resulting NRs contained distinct wurtzite ZnS and wurtzite ZnO components with widths of 10--100 nm and 20 --500 nm, respectively and a uniform interface region of 5-15 nm. XAFS and XEOL measurements revealed the luminescence of ZnO-ZnS NRs is from the ZnO component. The luminescence of CdSxSe1-x nanostructures is shown to be dependent on the S to Se ratio, with the band-gap emission being tunable between that of pure CdS and CdSe. Excitation of the CdSxSe 1-x nanostructures by X-ray in XEOL has revealed new de-excitation channels which show a defect emission band not seen by laser excitation. CVD of Mn2+ doped ZnS results in nanostructures with luminescence dominated by the yellow Mn2+ emission due to energy transfer from the ZnS host to the Mn dopant sites. The addition of EuCl3 to the reactants in the CVD process results in a change in morphology from NR to NP. Zn1-xMnxO and Zn1-xCOxO nanopowders were prepared by sol-gel methods at dopant concentrations

  17. Hetero-ring-expansion design for purine analogs: A theoretical study on the structural, electronic, and excited-state properties

    NASA Astrophysics Data System (ADS)

    Zhang, Laibin; Zhou, Liuzhu; Tian, Jianxiang; Li, Xiaoming

    2014-03-01

    A series of hetero-ring-expanded purine analogs are designed and their structural, electronic and excited-state properties are investigated by DFT calculations. The results indicate that the designed analogs can form stable base pairs with natural counterparts. Compared with natural ones, these size-expanded analogs and corresponding base pairs have smaller ionization potentials and HOMO-LUMO gaps. Furthermore, the A-analogs have ionization potentials even lower than natural G. Finally, the electronic absorption spectra are calculated and the nature of the low-lying excited states is discussed. These observations imply their promising applications as molecular wires and new DNA motifs.

  18. Study of effects of design details on structural response to acoustic excitation

    NASA Technical Reports Server (NTRS)

    Rudder, F. F., Jr.

    1972-01-01

    The normal mode vibration characteristics of one-dimensional and two-dimensional panel arrays were investigated analytically and experimentally. The finite element displacement method was used to formulate the structural models. The structural models include a stiffness and consistent mass matrix for thin-walled open-section beams not previously reported, and a modification of a rectangular plate bending element to include a fundamental interior mode for the element as a generalized coordinate. Provision for adding lumped masses to represent accelerometers is also included. For the one-dimensional panel, the normal mode stress resultants are obtained by integrating the equilibrium equations directly. For the two-dimensional panel arrays, the solution for the stress resultants in the cover sheet was attempted by introducing stress functions dependent upon the displacement field of the plate element. This approach, although incomplete, is a natural extension of the one-dimensional analysis for plate elements. The exerimental program which was used to verify the analysis is described and experimental results are compared with the analysis.

  19. Structural dynamics of phenylisothiocyanate in the light-absorbing excited states: resonance Raman and complete active space self-consistent field calculation study.

    PubMed

    Ouyang, Bing; Xue, Jia-Dan; Zheng, Xuming; Fang, Wei-Hai

    2014-05-21

    The excited state structural dynamics of phenyl isothiocyanate (PITC) after excitation to the light absorbing S2(A'), S6(A'), and S7(A') excited states were studied by using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The UV absorption bands of PITC were assigned. The vibrational assignments were done on the basis of the Fourier transform (FT)-Raman and FT-infrared measurements, the density-functional theory computations, and the normal mode analysis. The A-, B-, and C-bands resonance Raman spectra in cyclohexane, acetonitrile, and methanol solvents were, respectively, obtained at 299.1, 282.4, 266.0, 252.7, 228.7, 217.8, and 208.8 nm excitation wavelengths to probe the corresponding structural dynamics of PITC. The results indicated that the structural dynamics in the S2(A'), S6(A'), and S7(A') excited states were very different. The conical intersection point CI(S2/S1) were predicted to play important role in the low-lying excited state decay dynamics. Two major decay channels were predicted for PITC upon excitation to the S2(A') state: the radiative S(2,min) → S0 transition and the nonradiative S2 → S1 internal conversion via CI(S2/S1). The differences in the decay dynamics between methyl isothiocyanate and PITC in the first light absorbing excited state were discussed. The role of the intersystem crossing point ISC(S1/T1) in the excited state decay dynamics of PITC is evaluated.

  20. Structural dynamics of phenylisothiocyanate in the light-absorbing excited states: Resonance Raman and complete active space self-consistent field calculation study

    SciTech Connect

    Ouyang, Bing Xue, Jia-Dan Zheng, Xuming E-mail: zxm@zstu.edu.cn; Fang, Wei-Hai E-mail: fangwh@dnu.edu.cn

    2014-05-21

    The excited state structural dynamics of phenyl isothiocyanate (PITC) after excitation to the light absorbing S{sub 2}(A′), S{sub 6}(A′), and S{sub 7}(A′) excited states were studied by using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The UV absorption bands of PITC were assigned. The vibrational assignments were done on the basis of the Fourier transform (FT)-Raman and FT-infrared measurements, the density-functional theory computations, and the normal mode analysis. The A-, B-, and C-bands resonance Raman spectra in cyclohexane, acetonitrile, and methanol solvents were, respectively, obtained at 299.1, 282.4, 266.0, 252.7, 228.7, 217.8, and 208.8 nm excitation wavelengths to probe the corresponding structural dynamics of PITC. The results indicated that the structural dynamics in the S{sub 2}(A′), S{sub 6}(A′), and S{sub 7}(A′) excited states were very different. The conical intersection point CI(S{sub 2}/S{sub 1}) were predicted to play important role in the low-lying excited state decay dynamics. Two major decay channels were predicted for PITC upon excitation to the S{sub 2}(A′) state: the radiative S{sub 2,min} → S{sub 0} transition and the nonradiative S{sub 2} → S{sub 1} internal conversion via CI(S{sub 2}/S{sub 1}). The differences in the decay dynamics between methyl isothiocyanate and PITC in the first light absorbing excited state were discussed. The role of the intersystem crossing point ISC(S{sub 1}/T{sub 1}) in the excited state decay dynamics of PITC is evaluated.

  1. Excited state structures and decay dynamics of 1,3-dimethyluracils in solutions: resonance Raman and quantum mechanical calculation study.

    PubMed

    Li, Ming-Juan; Liu, Ming-Xia; Zhao, Yan-Ying; Pei, Ke-Mei; Wang, Hui-Gang; Zheng, Xuming; Fang, Wei Hai

    2013-10-03

    The resonance Raman spectroscopic study of the excited state structural dynamics of 1,3-dimethyluracil (DMU), 5-bromo-1,3-dimethyluracil (5BrDMU), uracil, and thymine in water and acetonitrile were reported. Density functional theory calculations were carried out to help elucidate the ultraviolet electronic transitions associated with the A-, and B-band absorptions and the vibrational assignments of the resonance Raman spectra. The effect of the methylation at N1, N3 and C5 sites of pyrimidine ring on the structural dynamics of uracils in different solvents were explored on the basis of the resonance Raman intensity patterns. The relative resonance Raman intensities of DMU and 5BrDMU are computed at the B3LYP-TD level. Huge discrepancies between the experimental resonance Raman intensities and the B3LYP-TD predicted ones were observed. The underlying mechanism was briefly discussed. The decay channel through the S1((1)nπ*)/S2((1)ππ*) conical intersection and the S1((1)nπ*)/T1((3)ππ*) intersystem crossing were revealed by using the CASSCF(8,7)/6-31G(d) level of theory calculations.

  2. Excitation of a slow wave structure

    SciTech Connect

    Zhang Peng; Lau, Y. Y.; Hoff, Brad; French, D. M.; Luginsland, J. W.

    2012-12-15

    The Green's function on a slow wave structure is constructed. The Green's function includes all radial modes, and for each radial mode, all space harmonics. We compare the analytic solution of the frequency response on the slow wave structure with that obtained from a particle-in-cell code. Favorable comparison is obtained when the first few lower order modes are resonantly excited. This gives some confidence in the prediction of converting a pulse train into radiation using a slow wave structure.

  3. Theory of elementary excitations in quasiperiodic structures

    NASA Astrophysics Data System (ADS)

    Albuquerque, E. L.; Cottam, M. G.

    2003-03-01

    The aim of this work is to present a comprehensive and up-to-date review of the main physical properties (such as energy profiles, localization, scale laws, multifractal analysis, transmission spectra, transmission fingerprints, electronic structures, magnetization curves and thermodynamic properties) of the elementary excitations that can propagate in multilayered structures with constituents arranged in a quasiperiodic fashion. These excitations include plasmon-polaritons, spin waves, light waves and electrons, among others. A complex fractal or multifractal profile of the energy spectra is the common feature among these excitations. The quasiperiodic property is formed by the incommensurate arrangement of periodic unit cells and can be of the type referred to as deterministic (or controlled) disorder. The resulting excitations are characterized by the nature of their Fourier spectrum, which can be dense pure point (as for the Fibonacci sequence) or singular continuous (as for the Thue-Morse and double-period sequences). These sequences are described in terms of a series of generations that obey particular recursion relations, and they can be considered as intermediate systems between a periodic crystal and the random amorphous solids, thus defining a novel description of disorder. A discussion is also included of some spectroscopic techniques used to probe the excitations, emphasizing Raman and Brillouin light scattering.

  4. Structural and photophysical studies on gallium(III) 8-hydroxyquinoline-5-sulfonates. Does excited state decay involve ligand photolabilisation?

    PubMed

    Ramos, M Luísa; de Sousa, Andreia R E; Justino, Licínia L G; Fonseca, Sofia M; Geraldes, Carlos F G C; Burrows, Hugh D

    2013-03-14

    Multinuclear ((1)H, (13)C and (71)Ga) magnetic resonance spectroscopy (1D and 2D), DFT calculations and luminescence techniques have been used to study 8-hydroxyquinoline-5-sulfonate (8-HQS) and its complexes with Ga(III) in aqueous solutions. The study combines the high sensitivity of luminescence techniques and the selectivity of multinuclear NMR spectroscopy with the structural details accessible through DFT calculations, and aims to obtain a complete understanding of the complexation between the Ga(3+) ion and 8-HQS, and how this influences the luminescence behaviour. A full speciation study has been performed on this system and three complexes detected, with (metal : ligand) 1 : 1, 1 : 2 and 1 : 3 stoichiometries, the results being consistent with those previously found for the system Al(III)-8-HQS. Complexation in these systems is relevant to their potential biomedical, sensing and optoelectronic applications. On binding to Ga(III), a marked increase is seen in the intensity of the 8-HQS fluorescence band, which is accompanied by changes in the absorption spectra. These support the use of 8-HQS as a sensitive fluorescent sensor to detect Ga(3+) metal ions in surface waters, biological fluids, etc., and its metal complexes as an emitting or charge transport layer in light emitting devices. However, the fluorescence quantum yield of the Ga(III)-8-HQS 1 : 3 complex is about 35% of that of the corresponding system with Al(III). Although this may be due in part to a heavy atom effect favouring S(1)→ T(1) intersystem crossing with Ga(3+), this does not agree with transient absorption measurements on the triplet state yield, which is lower with the Ga(III) system than with Al(III). Instead, it is suggested that photolabilisation of ligand exchange plays a major role in nonradiative decay of the excited state and that this is more efficient with the Ga(3+) complex. Based on these results, suggestions are made of ways of enhancing fluorescence

  5. Study of Various Slanted Air-Gap Structures of Interior Permanent Magnet Synchronous Motor with Brushless Field Excitation

    SciTech Connect

    Tolbert, Leon M; Lee, Seong T

    2010-01-01

    This paper shows how to maximize the effect of the slanted air-gap structure of an interior permanent magnet synchronous motor with brushless field excitation (BFE) for application in a hybrid electric vehicle. The BFE structure offers high torque density at low speed and weakened flux at high speed. The unique slanted air-gap is intended to increase the output torque of the machine as well as to maximize the ratio of the back-emf of a machine that is controllable by BFE. This irregularly shaped air-gap makes a flux barrier along the d-axis flux path and decreases the d-axis inductance; as a result, the reluctance torque of the machine is much higher than a uniform air-gap machine, and so is the output torque. Also, the machine achieves a higher ratio of the magnitude of controllable back-emf. The determination of the slanted shape was performed by using magnetic equivalent circuit analysis and finite element analysis (FEA).

  6. Structure of Low-Lying Excited States of Guanine in DNA and Solution: Combined Molecular Mechanics and High-Level Coupled Cluster Studies

    DOE PAGES

    Kowalski, Karol; Valiev, Marat

    2007-01-01

    High-level ab-initio equation-of-motion coupled-cluster methods with singles, doubles, and noniterative triples are used, in conjunction with the combined quantum mechanical molecular mechanics approach, to investigate the structure of low-lying excited states of the guanine base in DNA and solvated environments. Our results indicate that while the excitation energy of the first excited state is barely changed compared to its gas-phase counterpart, the excitation energy of the second excited state is blue-shifted by 0.24 eV.

  7. Excitation of guided waves in layered structures with negative refraction.

    PubMed

    Shadrivov, Ilya; Ziolkowski, Richard; Zharov, Alexander; Kivshar, Yuri

    2005-01-24

    We study the electromagnetic beam reflection from layered structures that include the so-called double-negative metamaterials, also called left-handed metamaterials. We predict that such structures can demonstrate a giant lateral Goos-Hänchen shift of the scattered beam accompanied by a splitting of the reflected and transmitted beams due to the resonant excitation of surface waves at the interfaces between the conventional and double-negative materials as well as due to the excitation of leaky modes in the layered structures. The beam shift can be either positive or negative, depending on the type of the guided waves excited by the incoming beam. We also perform finite-difference time-domain simulations and confirm the major effects predicted analytically.

  8. Theoretical studies of electronically excited states

    SciTech Connect

    Besley, Nicholas A.

    2014-10-06

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

  9. Structural responses to arbitrarily coherent stationary random excitations

    NASA Astrophysics Data System (ADS)

    Lin, Jia-Hao; Zhang, Wen-Shou; Li, Jian-Jun

    1994-03-01

    The pseudo-excitation or fast CQC method for a single excitation problem is extended to deal with general MIMO (multi-input, multi-output) problems in which the excitations can be fully or partially coherent, i.e. the excitation PSD matrices are more general Hermitian matrices. This extension makes the analyses of structural responses to general stationary multipoint excitations computationally more efficient and convenient.

  10. Spectroscopic and Raman excitation profile studies of 3-benzoylpyridine

    NASA Astrophysics Data System (ADS)

    Sett, Pinaky; Datta, Shirsendu; Chowdhury, Joydeep; Ghosh, Manash; Mallick, Prabal Kumar

    2017-03-01

    In the present work IR, UV absorption and Raman spectra including Raman excitation profiles and structure of 3-benzoyl pyridine have been investigated. Detailed studies on the vibrational and electronic properties of the molecule have been carried out. All these studies are aided with valuable quantum chemical calculations. The structural changes encountered on excitation to the low lying excited states have been investigated. Theoretical profiles determined by the sum-over-states method based on pertinent Franck-Condon and Herzberg-Teller terms have satisfactorily simulated the experimentally measured relative Raman intensities and these are also in compliance with the structural changes and potential energy distributions.

  11. Structural characterization, thermoluminescence studies and kinetic parameters of SrSO4:Eu nanophosphors under X-ray and gamma excitations.

    PubMed

    Jayasudha, S; Madhukumar, K; Nair, C M K; Nair, Resmi G; Anandakumar, V M; Elias, Thayal Singh

    2016-02-15

    Nanostructured SrSO4:Eu phosphors with high thermoluminescence (TL) emission temperatures have been synthesized through a controlled chemical precipitation method. Structural analysis and TL studies under both γ-ray and X-ray excitations were done. The phosphors were characterized using Powder X-ray diffraction, X-ray photoelectron spectroscopy, SEM, TEM, thermogravimetry, UV-VIS and photoluminescence studies. The average crystallite size estimated using PXRD data is found to be around 40nm. XPS and PL studies reveal that Eu(2+) ions are the luminescence emission centres in the phosphor. The phosphor is found to be highly TL sensitive to both γ-rays and X-rays with very high emission temperature which is not reported so far. The emission behaviour is suitable for environmental radiation dosimetry applications. The TL glow curve shows well-defined isolated high temperature emission peak at 312°C under 2Gy γ-excitation and 284°C for low energy diagnostic X-ray irradiation and 271°C for high energy therapeutic X-rays. Chen's peak shape method is applied to obtain the kinetic parameters behind the TL emission. The TL mechanism is found to follow second order kinetics, suggesting the probability of re-trapping of charge carriers.

  12. Structural characterization, thermoluminescence studies and kinetic parameters of SrSO4:Eu nanophosphors under X-ray and gamma excitations

    NASA Astrophysics Data System (ADS)

    Jayasudha, S.; Madhukumar, K.; Nair, C. M. K.; Nair, Resmi G.; Anandakumar, V. M.; Elias, Thayal Singh

    2016-02-01

    Nanostructured SrSO4:Eu phosphors with high thermoluminescence (TL) emission temperatures have been synthesized through a controlled chemical precipitation method. Structural analysis and TL studies under both γ-ray and X-ray excitations were done. The phosphors were characterized using Powder X-ray diffraction, X-ray photoelectron spectroscopy, SEM, TEM, thermogravimetry, UV-VIS and photoluminescence studies. The average crystallite size estimated using PXRD data is found to be around 40 nm. XPS and PL studies reveal that Eu2 + ions are the luminescence emission centres in the phosphor. The phosphor is found to be highly TL sensitive to both γ-rays and X-rays with very high emission temperature which is not reported so far. The emission behaviour is suitable for environmental radiation dosimetry applications. The TL glow curve shows well-defined isolated high temperature emission peak at 312 °C under 2 Gy γ-excitation and 284 °C for low energy diagnostic X-ray irradiation and 271 °C for high energy therapeutic X-rays. Chen's peak shape method is applied to obtain the kinetic parameters behind the TL emission. The TL mechanism is found to follow second order kinetics, suggesting the probability of re-trapping of charge carriers.

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

    NASA Astrophysics Data System (ADS)

    Hübner, Olaf; Hornung, Julius; Himmel, Hans-Jörg

    2015-07-01

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

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

    SciTech Connect

    Hübner, Olaf; Hornung, Julius; Himmel, Hans-Jörg

    2015-07-14

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

  15. Structure, Excitation, and Evolution of Shocks: A Multi- Wavelength Study of Herbig-Haro 1/2

    NASA Astrophysics Data System (ADS)

    Reipurth, Bo

    2013-10-01

    More than 1000 Herbig-Haro {HH} objects are known today. Among these, HH 1 and HH 2 are taking a special place because they remain the brightest known HH objects in the sky. As such, they have been studied at all wavelengths, from X-rays to the radio continuum, and with all observing techniques. Adding to this their fine bipolar morphology displaying two major bow shocks and a finely collimated jet, it is no surprise that HH 1 and 2 constitute the reference frame against which data on all other HH objects are compared. We propose to observe HH 1/2 with the following narrowband filters {in order of wavelength} offered by WFC3: [Ne IV] 2425, Mg II 2795+2802, [O II] 3726+28, H-beta 4861, [O III] 5007, [O I] 6300, H-alpha 6563, [S II] 6717, and [S II] 6731. These lines probe different shock velocities and physical parameters, hence the analysis of the resulting images allow us to explore a number of scientific questions related to the physical conditions in the shocks, their structure and their kinematics. We have at our disposal the sophisticated adaptive grid code "yguazu'' in which the gasdynamic equations are integrated together with a many-species ionization network. This allows us to compute both 2D and full 3D models of HH flows from which we can directly obtain predictions of emission maps in all of the above transitions, aiding the interpretation of the line ratio maps. The resulting study will provide a major step forward in our understanding of the shock physics of outflows from young stars.Note: We have received permission to change the three quad filters {[Ne IV] 2425, [S II] 6717, [S II] 6731} and instead add 1 orbit to MgII and 1 orbit to [OII] to improve S/N.

  16. Excited states of a significantly ruffled porphyrin: computational study on structure-induced rapid decay mechanism via intersystem crossing.

    PubMed

    Bai, Fu-Quan; Nakatani, Naoki; Nakayama, Akira; Hasegawa, Jun-ya

    2014-06-12

    The compound meso-tetra-tert-butylporphyrin (H2T(t-Bu)P) is a significantly ruffled porphyrin and known as a good quencher. Compared with planar porphyrins, H2T(t-Bu)P showed bathochromic shift and rapid radiationless decay of the (1)(π, π*) excited state. Density functional theory, approximated coupled-cluster theory, and complete active space self-consistent field method level calculations were performed for the potential energy surface (PES) of the low-lying singlet and triplet states of H2T(t-Bu)P. The origin of the bathochromic shift in the absorption and fluorescence spectra was attributed to both steric distortions of the ring and electronic effects of the substituents. The nonradiative deactivation process of H2T(t-Bu)P via intersystem crossing (ISC) is proposed as (S1 → T2 → T1 → S0). Along a nonplanar distortion angle, the PESs of the S1 and T2 states are very close to each other, which suggests that many channels exist for ISC. For the T1 → S0 transition, minimum energy ISC points were located, and spin-orbit coupling (SOC) was evaluated. The present results indicate that the ISC can also occur at the T1/S0 intersection, in addition to the vibrational SOC promoted by specific normal modes.

  17. Elementary Excitations and Dynamic Structure of Quantum Fluids

    NASA Astrophysics Data System (ADS)

    Saarela, M.

    The equations of motion method for studying excitations and dynamic structure of quantum fluids is reviewed in this series of lectures. The method is based on the least action principle where one minimizes the action integral of the dynamic system. As a result one gets the continuity equations, which connect the density fluctuations and currents to an external driving force. The external force is assumed to infinitesimal and the response of the system to that is linear. The real poles of the linear response function determine the elementary excitation modes and the imaginary part of the self energy defines the continuum limit and gives the finite lifetime of the decaying modes. Our dynamic wave function contains time-dependent one- and two-particle correlation functions, which includes couplings between three modes. Thus one mode can split into two modes if energy and momentum are conserved. We begin with the Feenberg's β-derivative formulation of the optimized ground state and then derive general equations of motion for the dynamic system from the least action principle. We show how the simplest one-body approximation leads to the Feynman theory of excitations. By including the fluctuating two-body correlation function within the uniform limit one recovers the correlated basic function approximation. The fully consistent theory gives a good account of the elementary excitations and we show results on current patterns in the maxon-roton regions and on the precursor of the liquid-solid phase transition. Finally we apply the method to the excitations of the impurity and derive the hydrodynamic effective mass of the 3He impurity in 4He and the 3He dynamic structure function.

  18. Modal parameter extraction from large operating structures using ambient excitation

    SciTech Connect

    James, G.H. III; Carne, T.G.; Mayes, R.L.

    1995-12-31

    A technique called the Natural Excitation Technique or has been developed to response extract response parameters from large operational structure when subjected to random and unmeasured forces such as wind, road noise, aerodynamics, or waves. Six applications of NExT to ambient excitation testing and NExT analysis are surveyed in this paper with a minimum of technical detail. In the first application, NExT was applied to a controlled-yaw Horizontal-Axis Wind Turbine (HAWT). By controlling the yaw degree of freedom an important class of rotating coordinate system effects are reduced. A new shape extraction procedure was applied to this data set with good results. The second application was to a free-yaw HAWT. The complexity of the response has prompted further analytical studies and the development of a specialized visualization package. The third application of NExT was to a parked three-bladed Vertical-Axis Wind Turbine (VAWT) in which traditional modal testing could not excite all modes of interest. The shape extraction process used cross-correlation functions directly in a time-domain shape-fitting routine. The fourth application was to ground transportation systems. Ongoing work to improve driver and passenger comfort in tractor-trailer vehicles and to refine automobile body and tire models will use NExT. NExT has been used to process ambient vibration data for Finite Element Model correlation and is being used to study Structural Health Monitoring with ambient excitation. Shape fitting was performed using amplitude and phase information taken directly from the cross-spectra. The final application is to an offshore structure. This work is on-going, however initial studies have found a high-modal density, high noise content, and sparse data set.

  19. X-ray-excited optical luminescence and X-ray absorption fine-structures studies of CdWO4 scintillator.

    PubMed

    Novais, S M V; Valerio, M E G; Macedo, Z S

    2012-07-01

    X-ray-excited optical luminescence (XEOL) emission and excitation spectra as well as the EXAFS signal of CdWO(4) were measured in the energy region of the Cd and W absorption edges. From EXAFS refinement, structural parameters such as number of atoms, distance from the absorbing atom and width of coordination shells in the W neighborhood were determined. The role of W-O interactions on the intrinsic luminescence of CdWO(4) is discussed. The efficiencies of conversion, transfer and emission processes involved in the scintillation mechanism showed to be high when self-trapped excitons are formed locally by direct excitation of W ions. Annihilation of these excitons provides the characteristic scintillation of CdWO(4), a broad band emission with maximum at 500 nm. The presence of two energetically different O positions in the lattice gives rise to the composite structure of the luminescence band, and no influence of extrinsic defects was noticed. A mismatch between the X-ray absorption coefficient and the zero-order luminescence curves corroborates that the direct excitation of Cd ions induces secondary electronic excitations not very effective in transferring energy to the luminescent group, WO(6).

  20. Structure Determination and Excited State Proton Transfer Reaction of 1-NAPHTHOL-AMMONIA Clusters in the S_{1} State Studied by Uv-Ir Mid-Ir Spectroscopy

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Shunpei; Miyazaki, Mitsuhiko; Martin, Weiler; Ishikawa, Haruki; Fujii, Masaaki

    2013-06-01

    1-naphthol ammonia clusters have been studied long time as a benchmark system of the excited state proton transfer (ESPT) reactions. Understanding the ESPT reaction in this system has still not been fully established. To detect the cluster size dependence of the S_{1} state properties, many researcher extensively investigated such as emission spectra, lifetime, solvents (ammonia) evaporation pattern. Curiously, cluster structure that is fundamental to discuss the reaction has not been determined for the system. Thus we applied an IR spectroscopy to the S_{1} states of the system to determine the cluster structure and to discuss the minimum size inducing the ionic dissociation of the O-H bond in the S_{1} state. IR spectra were recorded not only the O-H and N-H stretching region (3 {μ}m) but also the skeletal vibrational region (5.5-10 {μ}m). Though O-H and N-H stretching vibrations do not provide useful structural information due to the broadness, the skeletal vibrations hold the sharpness even in the S_{1} states. Changes in the skeletal vibrations due to the ammonia solvation, e.g. C-O stretching and C-O-H bending, will be discussed based on a comparison with theoretical calculations. O. Cheshnovsky and S. Leutwylar, J. Chem. Phys. 1, 4127 (1988). S. K. Kim et al., Chem. Phys. lett. 228, 369 (1994). C. Dedonder-Lardeux et al., Phys. Chem, Chem, Phys. 3, 4316 (2001).

  1. Structure and excitation conditions of the southern part of the Orion B molecular cloud: a CO multiline study.

    NASA Astrophysics Data System (ADS)

    Kramer, C.; Stutzki, J.; Winnewisser, G.

    1996-03-01

    We present extended maps of ^12^CO and ^13^CO (J=2->1 and J=3->2) of the southern part of the Orion B region covering a ~40'x70' area (in [21), and encompassing the NGC 2024 HII region, the interface region between NGC 2024 and the optical nebula IC434, the reflection nebula NGC 2023, and the Horsehead Nebula B33. The physical conditions in these different regions vary significantly due to the influence of the OB association lying to the west and due to the embedded stars. The CO emission originates from many clumps, most apparent in individual velocity channel maps. The observed low-J CO and isotopic CO line ratios are inconsistent with the standard interpretation in terms of a single temperature gas component along the line of sight in LTE. They require an outward temperature gradient on the cloud surface, as is naturally expected to arise from external UV heating. A consistent interpretation for both absolute line brightnesses and the intensity ratios can be reached in terms of PDR models. These indicate densities within the bulk of Orion B of at least close to 10^5^ cm^-3^. In addition we analyse the structure by subdividing the [21 emission of Orion B into clumps using an automated procedure. The shape, orientation, LTE mass, virial mass, and stability of these clumps is examined. The mass spectrum of the clumps follows a power law, dN/dM{prop.to}M^-α^, with α=1.65+/-0.24. We find an average volume filling factor of the clumps of 0.3 and a contrast between local and clump densities of 60 or higher.

  2. Structure of excited states and properties of organic dyes

    NASA Astrophysics Data System (ADS)

    Klessinger, M.

    1992-03-01

    Optimized geometries and charge distributions for the ground state and the first allowed π,π* excited singlet state are reported for some polyenes, polyene aldehydes, merocyanines and cyanines, which may be considered as representatives of conjugated chain chromophores of organic dyes. The dependence of excited state properties on molecular structure is discussed in relation to spectroscopic properties of these systems.

  3. Excited baryon structure using exclusive reactions with CLAS12

    NASA Astrophysics Data System (ADS)

    Carman, Daniel S.

    2016-05-01

    Studying excited nucleon structure through exclusive electroproduction reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. Electrocouplings for N* states in the mass range below 1.8 GeV have been determined from analyses of CLAS πN, ηN, and ππN data. This work made it clear that consistency of independent analyses of exclusive channels with different couplings and non-resonant backgrounds but the same N* electro-excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying N* states preferentially decay through the ππN channel instead of πN. Data from the KY channels will therefore be critical to provide an independent analysis with which to compare the extracted electrocouplings for the high-lying N* states against those determined from the πN and ππN channels. A program to study excited N* decays to non-strange and strange exclusive final states using CLAS12 will measure differential cross sections to be used as input to extract the γvNN* transition form factors for the most prominent N* states in the range of invariant energy W up 3 GeV in the virtually unexplored domain of momentum transfers Q2 up to 12 GeV2.

  4. Excitation Energy Transfer Dynamics and Excited-State Structure in Chlorosomes of Chlorobium phaeobacteroides

    PubMed Central

    Pšenčík, Jakub; Ma, Ying-Zhong; Arellano, Juan B.; Hála, Jan; Gillbro, Tomas

    2003-01-01

    The excited-state relaxation within bacteriochlorophyll (BChl) e and a in chlorosomes of Chlorobium phaeobacteroides has been studied by femtosecond transient absorption spectroscopy at room temperature. Singlet-singlet annihilation was observed to strongly influence both the isotropic and anisotropic decays. Pump intensities in the order of 1011 photons × pulse−1 × cm−2 were required to obtain annihilation-free conditions. The most important consequence of applied very low excitation doses is an observation of a subpicosecond process within the BChl e manifold (∼200–500 fs), manifesting itself as a rise in the red part of the Qy absorption band of the BChl e aggregates. The subsequent decay of the kinetics measured in the BChl e region and the corresponding rise in the baseplate BChl a is not single-exponential, and at least two components are necessary to fit the data, corresponding to several BChl e→BChl a transfer steps. Under annihilation-free conditions, the anisotropic kinetics show a generally slow decay within the BChl e band (10–20 ps) whereas it decays more rapidly in the BChl a region (∼1 ps). Analysis of the experimental data gives a detailed picture of the overall time evolution of the energy relaxation and energy transfer processes within the chlorosome. The results are interpreted within an exciton model based on the proposed structure. PMID:12547796

  5. In-flight investigation of a rotating cylinder-based structural excitation system for flutter testing

    NASA Technical Reports Server (NTRS)

    Vernon, Lura

    1993-01-01

    A research excitation system was test flown at the NASA Dryden Flight Research Facility on the two-seat F-16XL aircraft. The excitation system is a wingtip-mounted vane with a rotating slotted cylinder at the trailing edge. As the cylinder rotates during flight, the flow is alternately deflected upward and downward through the slot, resulting in a periodic lift force at twice the cylinder's rotational frequency. Flight testing was conducted to determine the excitation system's effectiveness in the subsonic, transonic, and supersonic flight regimes. Primary research objectives were to determine the system's ability to develop adequate force levels to excite the aircraft's structure and to determine the frequency range over which the system could excite structural modes of the aircraft. In addition, studies were conducted to determine optimal excitation parameters, such as sweep duration, sweep type, and energy levels. The results from the exciter were compared with results from atmospheric turbulence excitation at the same flight conditions. The comparison indicated that the vane with a rotating slotted cylinder provides superior results. The results from the forced excitation were of higher quality and had less variation than the results from atmospheric turbulence. The forced excitation data also invariably yielded higher structural damping values than those from the atmospheric turbulence data.

  6. Excitation and Evolution of Structure in Galaxies

    NASA Technical Reports Server (NTRS)

    Weinberg, Martin D.

    1996-01-01

    Even casual examination shows that most disk galaxies are not truly symmetric but exhibit a variety of morphological peculiarities of which spiral arms and bars are the most pronounced. After decades of effort, we now know that these features may be driven by environmental disturbance acting directly on the disk, in addition to self-excitation of a local disturbance (e.g. by swing amplification). However, all disks are embedded within halos and therefore are not dynamically independent. Are halos susceptible to such disturbances as well? If so, can the affect disks and on what time scales? y Until recently, conventional wisdom was that halos acted to stabilize disks but otherwise remained relatively inert. The argument behind this assumption is as follows. Halos, spheroids and bulges are supported against their own gravity by the random motion of their stars, a so-called "hot" distribution. On all but the largest scales, they look like a nearly homogeneous thermal bath of stars. Because all self-sustaining patterns or waves in a homogeneous universe of stars with a Maxwellian velocity distribution are predicted to damp quickly (e.g. Ikeuchi et al. 1974), one expects that any pattern will be strongly damped in halos and spheroids as well. However, recent work suggests that halos do respond to tidal encounters by companions or cluster members and are susceptible to induction of long-lived modes.

  7. Physical structure of the excitable membrane of unmyelinated axons: X-ray scattering study and electrophysiological properties of pike olfactory nerve.

    PubMed

    Luzzati, V; Mateu, L; Vachette, P; Benoit, E; Charpentier, G; Kado, R

    2000-11-17

    The aim of this work was to elicit correlations between physical structure and physiological functions in excitable membranes. Freshly dissected pike olfactory nerves were studied by synchrotron radiation X-ray scattering experiments and their physiological properties were tested by electrophysiological techniques. The scattering spectra contained a sharply oriented equatorial component (i.e. normal to the nerve axis), and an isotropic background. After background subtraction, the equatorial component displayed a weak and fairly sharp spectrum of oriented microtubules, and a strong and diffuse band of almost the same shape and position as the band computed for an isolated myelin membrane. We ascribed this spectrum to the axonal membranes. Under the action of temperature and of two local anesthetics, the spectrum underwent a contraction (or expansion) in the s-direction, equivalent to the structure undergoing an expansion (or contraction) in the direction perpendicular to the plane of the membrane. The main observations were: (i) with increasing temperature, membrane thickness decreased with a thermal expansion coefficient equal to -0.97(+/-0.19) 10(-3) degrees C(-1). The polarity and amplitude of this coefficient are typical of lipid-containing systems with the hydrocarbon chains in a disordered conformation. The amplitude and propagation velocity of the compound action potentials were drastically and reversibly reduced by lowering the temperature from 20 degrees C to 5 degrees C. (ii) Exposing the nerve to two local anesthetics (tetracaine and dibucaine) had the effect of decreasing membrane thickness. Action potentials were fully inhibited by these anesthetics. (iii) Upon depolarization, induced by replacing NaCl with KCl in the outer medium, approximately 25 % of the membranes were found to associate by apposing their outer faces. Electrophysiological activity was reversibly impaired by the KCl treatment. (iv) No detectable structural effect was observed upon

  8. a Theoretical Study of Projectile Delta Excitations in

    NASA Astrophysics Data System (ADS)

    Jo, Yung

    1995-01-01

    An approach is proposed for the investigation of the projectile Delta excitations induced by charge exchange reactions in the intermediate energy region. The nuclear structure part of the formalism is based on the particle-hole model and the nuclear reaction part is treated within the plane-wave impulse approximation (PWIA). In the nuclear structure part, all important nuclear medium effects are included. We take into account the nucleon knock-out mode and the related nucleon particle -nucleon hole (NN^{-1}) correlations. In order to perform the calculations, we first set up coupled-channel (CC) equations for the excited nucleons. The Lanczos method is adopted to solve this CC equations. In this dissertation we study the contribution of the projectile delta excitation process to (p, n) reaction spectra from a nuclear target. The spin observables are also calculated and discussed.

  9. A novel sensitivity-based method for damage detection of structures under unknown periodic excitations

    NASA Astrophysics Data System (ADS)

    Naseralavi, S. S.; Salajegheh, E.; Fadaee, M. J.; Salajegheh, J.

    2014-06-01

    This paper presents a technique for damage detection in structures under unknown periodic excitations using the transient displacement response. The method is capable of identifying the damage parameters without finding the input excitations. We first define the concept of displacement space as a linear space in which each point represents displacements of structure under an excitation and initial condition. Roughly speaking, the method is based on the fact that structural displacements under free and forced vibrations are associated with two parallel subspaces in the displacement space. Considering this novel geometrical viewpoint, an equation called kernel parallelization equation (KPE) is derived for damage detection under unknown periodic excitations and a sensitivity-based algorithm for solving KPE is proposed accordingly. The method is evaluated via three case studies under periodic excitations, which confirm the efficiency of the proposed method.

  10. Molecular and vibrational structure of tetroxo d0 metal complexes in their excited states. a study based on time-dependent density functional calculations and Franck-Condon theory.

    PubMed

    Jose, Linta; Seth, Michael; Ziegler, Tom

    2012-02-23

    We have applied time dependent density functional theory to study excited state structures of the tetroxo d(0) transition metal complexes MnO(4)(-), TcO(4)(-), RuO(4), and OsO(4). The excited state geometry optimization was based on a newly implemented scheme [Seth et al. Theor. Chem. Acc. 2011, 129, 331]. The first excited state has a C(3v) geometry for all investigated complexes and is due to a "charge transfer" transition from the oxygen based HOMO to the metal based LUMO. The second excited state can uniformly be characterized by "charge transfer" from the oxygen HOMO-1 to the metal LUMO with a D(2d) geometry for TcO(4)(-), RuO(4), and OsO(4) and two C(2v) geometries for MnO(4)(-). It is finally found that the third excited state of MnO(4)(-) representing the HOMO to metal based LUMO+1 orbital transition has a D(2d) geometry. On the basis of the calculated excited state structures and vibrational modes, the Franck-Condon method was used to simulate the vibronic structure of the absorption spectra for the tetroxo d(0) transition metal complexes. The Franck-Condon scheme seems to reproduce the salient features of the experimental spectra as well as the simulated vibronic structure for MnO(4)(-) generated from an alternative scheme [Neugebauer J. J. Phys. Chem. A 2005, 109, 1168] that does not apply the Franck-Condon approximation.

  11. Optimal Filtering Methods to Structural Damage Estimation under Ground Excitation

    PubMed Central

    Hsieh, Chien-Shu; Liaw, Der-Cherng; Lin, Tzu-Hsuan

    2013-01-01

    This paper considers the problem of shear building damage estimation subject to earthquake ground excitation using the Kalman filtering approach. The structural damage is assumed to take the form of reduced elemental stiffness. Two damage estimation algorithms are proposed: one is the multiple model approach via the optimal two-stage Kalman estimator (OTSKE), and the other is the robust two-stage Kalman filter (RTSKF), an unbiased minimum-variance filtering approach to determine the locations and extents of the damage stiffness. A numerical example of a six-storey shear plane frame structure subject to base excitation is used to illustrate the usefulness of the proposed results. PMID:24453869

  12. Electronic structure and optical properties of 2,5,8,11-tetra-tert-butylperylene polyhedral crystals from x-ray absorption near-edge structure and x-ray excited optical luminescence studies

    NASA Astrophysics Data System (ADS)

    Lv, Jingyu; Ko, Peter J. Y.; Zhang, Ying; Liu, Lijia; Zhang, Xiujuan; Zhang, Xiaohong; Sun, Xuhui; Sham, T. K.

    2011-06-01

    X-ray absorption near-edge structure (XANES) and x-ray excited optical luminescence (XEOL) have been used to study the optical properties of 2,5,8,11-tetra-tert-butylperylene (TBPe) polyhedral crystals with morphology varies from cube to rhombic dodecahedron. Benefit from the high resolution of synchrotron radiation spectroscopy, C 1s to π∗ and σ∗ transitions from different carbon sites in TBPe can be clearly distinguished in the carbon K-edge XANES. XEOL studies reveal that different crystals exhibit multiple emission bands with different branching ratio. It is also found that all the polyhedral crystals exhibit a weak luminescence in the near infrared, which is absent in the powder sample.

  13. Coherent Structures in a Supersonic Jet Excited by Plasma Actuators

    NASA Astrophysics Data System (ADS)

    Gaitonde, Datta; Samimy, Mo

    2010-11-01

    Simulations are used in conjunction with experimental measurements to understand the coherent structures generated by excitation of a Mach 1.3 jet by eight localized arc filament plasma actuators uniformly distributed just upstream of the nozzle exit. Several modes are excited, including the axisymmetric (m=0), helical (m=1-3), and mixed modes (m=±1, ±2) modes. The Strouhal number for all cases is fixed at 0.3, which corresponds to the most amplified frequency. The simulations reproduce the distinct coherent structures measured in the experiment for each azimuthal mode. Detailed analysis of instantaneous, time- and phase-averaged quantities highlights a complex coherent structure generation, evolution and dissipation process. A key feature observed is the initiation of hairpin-like structures with tips/heads in the outer region of the jet shear layer and legs extending forward and slightly inclined in the direction of the jet axis, where the velocity is higher. The subsequent interactions of these structures yield different composite structures in the downstream region. For example, for m=0, adjacent hairpin structures merge to yield axisymmetric rings, with the legs connecting successive structures in the form of ribs in the braid region; and with m=1 and 2 mode excitation, distinct helical and double-helical structures are observed, respectively, with the hairpins forming substructures in the coils.

  14. Concept study of a novel energy harvesting-enabled tuned mass-damper-inerter (EH-TMDI) device for vibration control of harmonically-excited structures

    NASA Astrophysics Data System (ADS)

    Salvi, Jonathan; Giaralis, Agathoklis

    2016-09-01

    A novel dynamic vibration absorber (DVA) configuration is introduced for simultaneous vibration suppression and energy harvesting from oscillations typically exhibited by large-scale low-frequency engineering structures and structural components. The proposed configuration, termed energy harvesting-enabled tuned mass-damper-inerter (EH-TMDI) comprises a mass grounded via an in-series electromagnetic motor (energy harvester)-inerter layout, and attached to the primary structure through linear spring and damper in parallel connection. The governing equations of motion are derived and solved in the frequency domain, for the case of harmonically-excited primary structures, here modelled as damped single-degree- of-freedom (SDOF) systems. Comprehensive parametric analyses proved that by varying the mass amplification property of the grounded inerter, and by adjusting the stiffness and the damping coefficients using simple optimum tuning formulae, enhanced vibration suppression (in terms of primary structure peak displacement) and energy harvesting (in terms of relative velocity at the terminals of the energy harvester) may be achieved concurrently and at nearresonance frequencies, for a fixed attached mass. Hence, the proposed EH-TMDI allows for relaxing the trade-off between vibration control and energy harvesting purposes, and renders a dual-objective optimisation a practically-feasible, reliable task.

  15. Excitation of Terahertz Charge Transfer Plasmons in Metallic Fractal Structures

    NASA Astrophysics Data System (ADS)

    Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Vabbina, Phani Kiran; Karabiyik, Mustafa; Pala, Nezih

    2017-08-01

    There have been extensive researches on terahertz (THz) plasmonic structures supporting resonant modes to demonstrate nano and microscale devices with high efficiency and responsivity as well as frequency selectivity. Here, using antisymmetric plasmonic fractal Y-shaped (FYS) structures as building blocks, we introduce a highly tunable four-member fractal assembly to support charge transfer plasmons (CTPs) and classical dipolar resonant modes with significant absorption cross section in the THz domain. We first present that the unique geometrical nature of the FYS system and corresponding spectral response allow for supporting intensified dipolar plasmonic modes under polarised light exposure in a standalone structure. In addition to classical dipolar mode, for the very first time, we demonstrated CTPs in the THz domain due to the direct shuttling of the charges across the metallic fractal microantenna which led to sharp resonant absorption peaks. Using both numerical and experimental studies, we have investigated and confirmed the excitation of the CTP modes and highly tunable spectral response of the proposed plasmonic fractal structure. This understanding opens new and promising horizons for tightly integrated THz devices with high efficiency and functionality.

  16. Ground and Flight Test Structural Excitation Using Piezoelectric Actuators

    NASA Technical Reports Server (NTRS)

    Voracek, David F.; Reaves, Mercedes C.; Horta, Lucas G.; Potter, Starr; Richwine, David (Technical Monitor)

    2002-01-01

    A flight flutter experiment at the National Aeronautics and Space Administration (NASA) Dryden Flight Research Center, Edwards, California, used an 18-inch half-span composite model called the Aerostructures Test Wing (ATW). The ATW was mounted on a centerline flight test fixture on the NASA F-15B and used distributed piezoelectric strain actuators for in-flight structural excitation. The main focus of this paper is to investigate the performance of the piezoelectric actuators and test their ability to excite the first-bending and first-torsion modes of the ATW on the ground and in-flight. On the ground, wing response resulting from piezoelectric and impact excitation was recorded and compared. The comparison shows less than a 1-percent difference in modal frequency and a 3-percent increase in damping. A comparison of in-flight response resulting from piezoelectric excitation and atmospheric turbulence shows that the piezoelectric excitation consistently created an increased response in the wing throughout the flight envelope tested. The data also showed that to obtain a good correlation between the piezoelectric input and the wing accelerometer response, the input had to be nearly 3.5 times greater than the turbulence excitation on the wing.

  17. The structure of the hydrated electron. Part 2. A mixed quantum/classical molecular dynamics embedded cluster density functional theory: single-excitation configuration interaction study.

    PubMed

    Shkrob, Ilya A; Glover, William J; Larsen, Ross E; Schwartz, Benjamin J

    2007-06-21

    Adiabatic mixed quantum/classical (MQC) molecular dynamics (MD) simulations were used to generate snapshots of the hydrated electron in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the hydrated electron were extracted from the MQC MD simulations and embedded in a roughly 18 Ax18 Ax18 A matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory (DFT) with the Becke-Lee-Yang-Parr functional and single-excitation configuration interaction (CIS) methods were then applied to these embedded clusters. The salient feature of these hybrid DFT(CIS)/MQC MD calculations is significant transfer (approximately 18%) of the excess electron's charge density into the 2p orbitals of oxygen atoms in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the singly occupied and the lower unoccupied molecular orbitals, the density of states, the absorption spectra in the visible and ultraviolet, the hyperfine coupling (hfcc) tensors, and the infrared (IR) and Raman spectra of these embedded water cluster anions. The calculated hfcc tensors were used to compute electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectra for the hydrated electron that compared favorably to the experimental spectra of trapped electrons in alkaline ice. The calculated vibrational spectra of the hydrated electron are consistent with the red-shifted bending and stretching frequencies observed in resonance Raman experiments. In addition to reproducing the visible/near IR absorption spectrum, the hybrid DFT model also accounts for the hydrated electron's 190-nm absorption band in the ultraviolet. Thus, our study suggests that to explain several important experimentally observed properties of the hydrated electron, many-electron effects must be accounted for: one-electron models that do not allow for mixing of the excess

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    SciTech Connect

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

    2014-12-14

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

  20. Comprehensive Studies of Ultrafast Laser Excited Warm Dense Gold

    NASA Astrophysics Data System (ADS)

    Chen, Zhijiang; Mo, Mianzhen; Russell, Brandon; Tsui, Ying; Wang, Xijie; Ng, Andrew; Glenzer, Siegfried

    2016-10-01

    Isochoric excitation of solids by ultrafast laser pulses is an important approach to generate warm dense matter in laboratory. Electrical conductivity, structural dynamics and lattice stabilities are the most important properties in ultrafast laser excited warm dense matter. To investigate these properties, we have developed multiple advanced capabilities at SLAC recently, including the measurement of semi-DC electrical conductivity with ultrafast THz radiation, the study of solid and liquid structural dynamics by ultrafast electron diffraction (UED), and the investigation of lattice stability using frequency domain interferometry (FDI) on both front and rear surfaces. Due to the non-reversible nature in exciting solid to warm dense matter, all these diagnostics are implemented with single-shot approaches, reducing the uncertainties due to shot-to-shot fluctuations. In this talk, we will introduce these novel capabilities and present some highlighted studies in warm dense gold, which was uniformly excited by ultrafast laser pulses at 400nm. We appreciate the supports from DOE FES under FWP #100182.

  1. Ultrafast Structural Dynamics of Tertiary Amines upon Electronic Excitation

    NASA Astrophysics Data System (ADS)

    Cheng, Xinxin; Minitti, Michael P.; Deb, Sanghamitra; Zhang, Yao; Budarz, James; Weber, Peter M.

    2011-06-01

    The structural response of several tertiary amines to electronic excitation has been investigated using Rydberg Fingerprint Spectroscopy. The 3p Rydberg states are reached by excitation with a 5.93 eV photon while 3s states are populated by electronic relaxation from 3p state. We observe binding energy shifts on ultrafast time scales in all peaks that reflect the structural change of the molecular ion cores. The shifts are in the range of 15 meV to 30 meV, within time scales of less than 500 fs, depending on the specific molecular systems and the nature of the electronic state. In cases where the p states are spectrally separate, the trends of the energy shifts are different for the p_z and p_x_y Rydberg states whereas the p_z and s states are similar. This suggests that the response of the Rydberg states to structural displacements depends on the symmetry. Very fast binding energy shifts, observed on sub-picosecond time scales, are attributed to the structural adjustment from a pyramidal to a planar structure upon Rydberg excitation. The quantitative values of the binding energy shifts can also be affected by laser chirp, which we model using simulations.

  2. Antenna structure and excitation dynamics in photosystem I. I. Studies of detergent-isolated photosystem I preparations using time-resolved fluorescence analysis.

    PubMed Central

    Owens, T G; Webb, S P; Alberte, R S; Mets, L; Fleming, G R

    1988-01-01

    The temporal and spectral properties of fluorescence decay in isolated photosystem I (PS I) preparations from algae and higher plants were measured using time-correlated single photon counting. Excitations in the PS I core antenna decay with lifetimes of 15-40 ps and 5-6 ns. The fast decay results from efficient photochemical quenching by P700, whereas the slow decay is attributed to core antenna complexes lacking a trap. Samples containing core and peripheral antenna complexes exhibited an additional intermediate lifetime (150-350 ps) decay. The PS I core antenna is composed of several spectral forms of chlorophyll a that are not temporally resolved in the decays. Analysis of the temporal and spectral properties of the decays provides a description of the composition, structure, and dynamics of energy transfer and trapping reactions in PS I. The core antenna size dependence of the spectral properties and the contributions of the spectral forms to the time-resolved decays show that energy is not concentrated in the longest wavelength absorbing pigments but is nearly homogenized among the spectral forms. These data suggest that the "funnel" description of antenna structure and energy transfer (Seely, G. R. 1973. J. Theor. Biol. 40:189-199) may not be applicable to the PS I core antenna. PMID:3134059

  3. Excited state structural events of a dual-emission fluorescent protein biosensor for Ca²⁺ imaging studied by femtosecond stimulated Raman spectroscopy.

    PubMed

    Wang, Yanli; Tang, Longteng; Liu, Weimin; Zhao, Yongxin; Oscar, Breland G; Campbell, Robert E; Fang, Chong

    2015-02-12

    Fluorescent proteins (FPs) are luminescent biomolecules that emit characteristic hues upon irradiation. A group of calmodulin (CaM)-green FP (GFP) chimeras have been previously engineered to enable the optical detection of calcium ions (Ca(2+)). We investigate one of these genetically encoded Ca(2+) biosensors for optical imaging (GECOs), GEM-GECO1, which fluoresces green without Ca(2+) but blue with Ca(2+), using femtosecond stimulated Raman spectroscopy (FSRS). The time-resolved FSRS data (<800 cm(-1)) reveal that initial structural evolution following 400 nm photoexcitation involves small-scale coherent proton motions on both ends of the chromophore two-ring system with a <250 fs time constant. Upon Ca(2+) binding, the chromophore adopts a more twisted conformation in the protein pocket with increased hydrophobicity, which inhibits excited-state proton transfer (ESPT) by effectively trapping the protonated chromophore in S1. Both the chromophore photoacidity and local environment form the ultrafast structural dynamics basis for the dual-emission properties of GEM-GECO1. Its photochemical transformations along multidimensional reaction coordinates are evinced by distinct stages of FSRS spectral evolution, particularly related to the ∼460 and 504 cm(-1) modes. The direct observation of lower frequency modes provides crucial information about the nuclear motions preceding ESPT, which enriches our understanding of photochemistry and enables the rational design of new biosensors.

  4. A self-excited flapper from fluid-structure interaction

    NASA Astrophysics Data System (ADS)

    Curet, Oscar M.; Breuer, Kenneth S.

    2010-11-01

    The flexible nature of lifting and propulsive surfaces is a common characteristic of aquatic and aerial locomotion in animals. These surfaces may not only move actively, but also passively or with a combination of both. What is the nature of this passive movement? What is the role of this passive motion on force generation, efficiency and muscle control? Here, we present results using a simple wing model with two degrees of freedom designed to study passive flapping, and fluid-structure interaction. The wing is composed of a flat plate with a hinged trailing flap. The wing is cantilevered to the main body to enable a flapping motion with a well-defined natural frequency. We test the wing model in a wind tunnel. At low speed the wing is stationary. Above a critical velocity the trailing wing section starts to oscillate, generating an oscillating lift force on the wing. This oscillating lift force results on a self-excited flapping motion of the wing. We measure the kinematics and the forces generated by the wing as a function of flow velocity and stiffness of the cantilever. Comparisons with aeroelasticity theory will be presented as well as details of the fluid-structure interactions.

  5. Disentangling structural information from core-level excitation spectra

    NASA Astrophysics Data System (ADS)

    Niskanen, Johannes; Sahle, Christoph J.; Gilmore, Keith; Uhlig, Frank; Smiatek, Jens; Föhlisch, Alexander

    2017-07-01

    Core-level spectra of liquids can be difficult to interpret due to the presence of a range of local environments. We present computational methods for investigating core-level spectra based on the idea that both local structural parameters and the x-ray spectra behave as functions of the local atomic configuration around the absorbing site. We identify correlations between structural parameters and spectral intensities in defined regions of interest, using the oxygen K-edge excitation spectrum of liquid water as a test case. Our results show that this kind of analysis can find the main structure-spectral relationships of ice, liquid water, and supercritical water.

  6. TMS studies of preictal cortical excitability change.

    PubMed

    Richardson, Mark P; Lopes da Silva, Fernando H

    2011-12-01

    The transition between the interictal and ictal states may be characterised in terms of the dynamics of a complex system. Seizures may emerge because of a change in system parameters, but these parameters may be invisible to passive observation. Therefore, a number of investigators have developed methods to probe the system using stimulation; these probing stimuli may reveal important hidden parameters. Here we describe studies from two sets of investigators working independently, which have shown that motor responses to transcranial magnetic brain stimulation (TMS) differ between the interictal state remote from any seizure, and a period of hours immediately prior to a seizure. We place these studies in the context of the known physiology of motor responses to TMS and discuss how actively probing the state of brain excitability may open new windows on its dynamics. Copyright © 2011 Elsevier B.V. All rights reserved.

  7. Laser Excited Fluorescence Studies Of Black Liquor

    NASA Astrophysics Data System (ADS)

    Horvath, J. J.; Semerjian, H. G.

    1986-10-01

    Laser excited fluorescence of black liquor was investigated as a possible monitoring technique for pulping processes. A nitrogen pumped dye laser was used to examine the fluorescence spectrum of black liquor solutions. Various excitation wavelengths were used between 290 and 403 nm. Black liquor fluorescence spectra were found to vary with both excitation wavelength and black liquor concentration. Laser excited fluorescence was found to be a sensitive technique for measurement of black liquor with good detection limits and linear response over a large dynamic range.

  8. Sub-Doppler two-photon-excitation Rydberg spectroscopy of atomic xenon: mass-selective studies of isotopic and hyperfine structure

    NASA Astrophysics Data System (ADS)

    Kono, Mitsuhiko; He, Yabai; Baldwin, Kenneth G. H.; Orr, Brian J.

    2016-03-01

    Mass-selective sub-Doppler two-photon excitation (TPE) spectroscopy is employed to resolve isotopic contributions for transitions to high-energy Rydberg levels of xenon in an atomic beam, using narrowband pulses of coherent ultraviolet light at 205-213 nm generated by nonlinear-optical conversion processes. Previous research (Kono et al 2013 J. Phys. B: At. Mol. Opt. Phys. 46 35401), has determined isotope energy shifts and hyperfine structure for 33 high-energy Rydberg levels of gas-phase xenon and accessed Rydberg levels at TPE energies in the range of 94 100-97 300 cm-1 with unprecedented spectroscopic resolution. The new isotopic-mass-resolved results were obtained by adding a pulsed free-jet atomic-beam source and a mass-selective time-of-flight detector to the apparatus in order to discern individual xenon isotopes and extract previously unresolved spectroscopic information. Resulting isotope energy shifts and hyperfine-coupling parameters are examined with regard to trends in principal quantum number n and in atomic angular-momentum quantum numbers, together with empirical and theoretical precedents for such trends.

  9. Neutron star structure and collective excitations of finite nuclei

    NASA Astrophysics Data System (ADS)

    Paar, N.; Moustakidis, Ch. C.; Marketin, T.; Vretenar, D.; Lalazissis, G. A.

    2014-07-01

    A method is introduced that establishes relations between properties of collective excitations in finite nuclei and the phase transition density nt and pressure Pt at the inner edge separating the liquid core and the solid crust of a neutron star. A theoretical framework that includes the thermodynamic method, relativistic nuclear energy density functionals, and the quasiparticle random-phase approximation is employed in a self-consistent calculation of (nt,Pt) and collective excitations in nuclei. Covariance analysis shows that properties of charge-exchange dipole transitions, isovector giant dipole and quadrupole resonances, and pygmy dipole transitions are correlated with the core-crust transition density and pressure. A set of relativistic nuclear energy density functionals, characterized by systematic variation of the density dependence of the symmetry energy of nuclear matter, is used to constrain possible values for (nt,Pt). By comparing the calculated excitation energies of giant resonances, energy-weighted pygmy dipole strength, and dipole polarizability with available data, we obtain the weighted average values: nt=0.0955±0.0007 fm-3 and Pt=0.59±0.05 MeV fm-3. This approach crucially depends on experimental results for collective excitations in nuclei and, therefore, accurate measurements are necessary to further constrain the structure of the crust of neutron stars.

  10. Peak earthquake response of structures under multi-component excitations

    NASA Astrophysics Data System (ADS)

    Song, Jianwei; Liang, Zach; Chu, Yi-Lun; Lee, George C.

    2007-12-01

    Accurate estimation of the peak seismic responses of structures is important in earthquake resistant design. The internal force distributions and the seismic responses of structures are quite complex, since ground motions are multi-directional. One key issue is the uncertainty of the incident angle between the directions of ground motion and the reference axes of the structure. Different assumed seismic incidences can result in different peak values within the scope of design spectrum analysis for a given structure and earthquake ground motion record combination. Using time history analysis to determine the maximum structural responses excited by a given earthquake record requires repetitive calculations to determine the critical incident angle. This paper presents a transformation approach for relatively accurate and rapid determination of the maximum peak responses of a linear structure subjected to three-dimensional excitations within all possible seismic incident angles. The responses can be deformations, internal forces, strains and so on. An irregular building structure model is established using SAP2000 program. Several typical earthquake records and an artificial white noise are applied to the structure model to illustrate the variation of the maximum structural responses for different incident angles. Numerical results show that for many structural parameters, the variation can be greater than 100%. This method can be directly applied to time history analysis of structures using existing computer software to determine the peak responses without carrying out the analyses for all possible incident angles. It can also be used to verify and/or modify aseismic designs by using response spectrum analysis.

  11. First-principles study of optical excitations in alphaquartz

    SciTech Connect

    Chang, Eric K.; Rohlfing, Michael; Louie, Steven G.

    1999-06-15

    The properties of silicon dioxide have been studied extensively over the years. However, there still remain major unanswered questions regarding the nature of the optical spectrum and the role of excitonic effects in this technologically important material. In this work, we present an ab initio study of the optical absorption spectrum of alpha-quartz, using a newly developed first-principles method which includes self-energy and electron-hole interaction effects. The quasiparticle band structure is computed within the GW approximation to obtain a quantitative description of the single-particle excitations. The Bethe-Salpeter equation for the electron-hole excitations is solved to obtain the optical spectrum and to understand the spatial extent and physical properties of the excitons. The theoretical absorption spectrum is found to be in excellent agreement with the measured spectrum. We show that excitonic effects are crucial in the frequency range up to 5 eV above the absorption threshold.

  12. Synthesis, structural, and photophysical studies of π-fused acenaphtho[1,2-d]imidazole-based excited-state intramolecular proton transfer molecules

    NASA Astrophysics Data System (ADS)

    Somasundaram, Sivaraman; Kamaraj, Eswaran; Hwang, Su Jin; Jung, Sooyoung; Choi, Moon Gun; Park, Sanghyuk

    2017-06-01

    Orange-red fluorescent molecules are promising materials for use in a new generation of displays, light sources, and chemosensors because conventional red-emitters have lower fluorescence quantum efficiencies. In this work, a set of orange-emitting fused imidazole series 2-(7-(4-fluorophenyl)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol (AHPI-F), 2-(7-(4-chlorophenyl)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol (AHPI-Cl), and 2-(7-(4-bromophenyl)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol (AHPI-Br) have been synthesized via multicomponent reaction method with high yield. Synthesized molecules were fully characterized by 1H NMR, 13C NMR, GC-Mass, UV-vis. absorption, PL, and TGA-DSC. The compounds AHPI-F, AHPI-Cl, AHPI-Br showed large Stokes' shifted emission due to excited-state intramolecular proton transfer (ESIPT) process, and they effectively formed large single crystals. The crystal structure of each compound was identified by X-ray crystallographic analysis. To elucidate the photophysical properties of the molecule, theoretical calculation were performed by density functional theory (DFT) with B3LYP 6-31G(d,p) basis sets using the identified molecular conformations from X-ray analysis. Calculated electronic properties including HOMO-LUMO levels were compared with the experimental results. As a result of ESIPT process, extended conjugation length through acenaphto[1,2-d]imidazole, and charge transfer characteristics by the introduction of halogen atoms, all of the materials showed orange ESIPT emission with no spatial overlap between absorption (λmax,abs = 325 nm) and emission (λmax,ems = 578 nm).

  13. Simultaneous excitation system for efficient guided wave structural health monitoring

    NASA Astrophysics Data System (ADS)

    Hua, Jiadong; Michaels, Jennifer E.; Chen, Xin; Lin, Jing

    2017-10-01

    Many structural health monitoring systems utilize guided wave transducer arrays for defect detection and localization. Signals are usually acquired using the ;pitch-catch; method whereby each transducer is excited in turn and the response is received by the remaining transducers. When extensive signal averaging is performed, the data acquisition process can be quite time-consuming, especially for metallic components that require a low repetition rate to allow signals to die out. Such a long data acquisition time is particularly problematic if environmental and operational conditions are changing while data are being acquired. To reduce the total data acquisition time, proposed here is a methodology whereby multiple transmitters are simultaneously triggered, and each transmitter is driven with a unique excitation. The simultaneously transmitted waves are captured by one or more receivers, and their responses are processed by dispersion-compensated filtering to extract the response from each individual transmitter. The excitation sequences are constructed by concatenating a series of chirps whose start and stop frequencies are randomly selected from a specified range. The process is optimized using a Monte-Carlo approach to select sequences with impulse-like autocorrelations and relatively flat cross-correlations. The efficacy of the proposed methodology is evaluated by several metrics and is experimentally demonstrated with sparse array imaging of simulated damage.

  14. The structure of triply excited, negative-ion resonances in the autoionizing region of helium

    NASA Astrophysics Data System (ADS)

    Trantham, K. W.; Jacka, M.; Rau, A. R. P.; Buckman, S. J.

    1999-02-01

    The formation and decay of the two lowest-lying, triply excited 0953-4075/32/3/021/img7 resonances in the autoionizing region of the helium spectrum (57-60 eV) have been studied by measuring electron-impact excitation functions for the n = 2 singly excited states of helium as a function of electron scattering angle. These results offer unambiguous confirmation of the classification of these states as 0953-4075/32/3/021/img8 and 0953-4075/32/3/021/img9, respectively. Furthermore, the observation of the relative strengths of the decay of these features into the various final states enables some speculation as to the structure of the three excited electrons.

  15. Theoretical study on the excited-state intramolecular proton transfer in the aromatic schiff base salicylidene methylamine: an electronic structure and quantum dynamical approach.

    PubMed

    Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, José M

    2006-04-13

    The proton-transfer dynamics in the aromatic Schiff base salicylidene methylamine has been theoretically analyzed in the ground and first singlet (pi,pi) excited electronic states by density functional theory calculations and quantum wave-packet dynamics. The potential energies obtained through electronic calculations that use the time-dependent density functional theory formalism, which predict a barrierless excited-state intramolecular proton transfer, are fitted to a reduced three-dimensional potential energy surface. The time evolution in this surface is solved by means of the multiconfiguration time-dependent Hartree algorithm applied to solve the time-dependent Schrödinger equation. It is shown that the excited-state proton transfer occurs within 11 fs for hydrogen and 25 fs for deuterium, so that a large kinetic isotope effect is predicted. These results are compared to those of the only previous theoretical work published on this system [Zgierski, M. Z.; Grabowska, A. J. Chem. Phys. 2000, 113, 7845], reporting a configuration interaction singles barrier of 1.6 kcal mol(-1) and time reactions of 30 and 115 fs for the hydrogen and deuterium transfers, respectively, evaluated with the semiclassical instanton approach.

  16. Glycine in an electronically excited state: ab initio electronic structure and dynamical calculations.

    PubMed

    Muchová, Eva; Slavícek, Petr; Sobolewski, Andrzej L; Hobza, Pavel

    2007-06-21

    The goal of this study is to explore the photochemical processes following optical excitation of the glycine molecule into its two low-lying excited states. We employed electronic structure methods at various levels to map the PES of the ground state and the two low-lying excited states of glycine. It follows from our calculations that the photochemistry of glycine can be regarded as a combination of photochemical behavior of amines and carboxylic acid. The first channel (connected to the presence of amino group) results in ultrafast decay, while the channels characteristic for the carboxylic group occur on a longer time scale. Dynamical calculations provided the branching ratio for these channels. We also addressed the question whether conformationally dependent photochemistry can be observed for glycine. While electronic structure calculations favor this possibility, the ab initio multiple spawning (AIMS) calculations showed only minor relevance of the reaction path resulting in conformationally dependent dynamics.

  17. "Parallel factor analysis of multi-excitation ultraviolet resonance Raman spectra for protein secondary structure determination".

    PubMed

    Oshokoya, Olayinka O; JiJi, Renee D

    2015-09-10

    Protein secondary structural analysis is important for understanding the relationship between protein structure and function, or more importantly how changes in structure relate to loss of function. The structurally sensitive protein vibrational modes (amide I, II, III and S) in deep-ultraviolet resonance Raman (DUVRR) spectra resulting from the backbone C-O and N-H vibrations make DUVRR a potentially powerful tool for studying secondary structure changes. Experimental studies reveal that the position and intensity of the four amide modes in DUVRR spectra of proteins are largely correlated with the varying fractions of α-helix, β-sheet and disordered structural content of proteins. Employing multivariate calibration methods and DUVRR spectra of globular proteins with varying structural compositions, the secondary structure of a protein with unknown structure can be predicted. A disadvantage of multivariate calibration methods is the requirement of known concentration or spectral profiles. Second-order curve resolution methods, such as parallel factor analysis (PARAFAC), do not have such a requirement due to the "second-order advantage." An exceptional feature of DUVRR spectroscopy is that DUVRR spectra are linearly dependent on both excitation wavelength and secondary structure composition. Thus, higher order data can be created by combining protein DUVRR spectra of several proteins collected at multiple excitation wavelengths to give multi-excitation ultraviolet resonance Raman data (ME-UVRR). PARAFAC has been used to analyze ME-UVRR data of nine proteins to resolve the pure spectral, excitation and compositional profiles. A three factor model with non-negativity constraints produced three unique factors that were correlated with the relative abundance of helical, β-sheet and poly-proline II dihedral angles. This is the first empirical evidence that the typically resolved "disordered" spectrum represents the better defined poly-proline II type structure.

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

    PubMed Central

    Xiao, H. Y.; Weber, W. J.; Zhang, Y.; Zu, X. T.; Li, S.

    2015-01-01

    The response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser, electron and ion irradiations. PMID:25660219

  19. Ultrafast electron diffraction: Excited state structures and chemistries of aromatic carbonyls

    SciTech Connect

    Park, Sang Tae; Feenstra, Jonathan S.; Zewail, Ahmed H.

    2006-05-07

    The photophysics and photochemistry of molecules with complex electronic structures, such as aromatic carbonyls, involve dark structures of radiationless processes. With ultrafast electron diffraction (UED) of isolated molecular beams it is possible to determine these transient structures, and in this contribution we examine the nature of structural dynamics in two systems, benzaldehyde and acetophenone. Both molecules are seen to undergo a bifurcation upon excitation (S{sub 2}). Following femtosecond conversion to S{sub 1}, the bifurcation leads to the formation of molecular dissociation products, benzene and carbon monoxide for benzaldehyde, and benzoyl and methyl radicals for acetophenone, as well as intersystem crossing to the triplet state in both cases. The structure of the triplet state was determined to be 'quinoidlike' of {pi}{pi}* character with the excitation being localized in the phenyl ring. For the chemical channels, the product structures were also determined. The difference in photochemistry between the two species is discussed with respect to the change in large amplitude motion caused by the added methyl group in acetophenone. This discussion is also expanded to compare these results with the prototypical aliphatic carbonyl compounds, acetaldehyde and acetone. From these studies of structural dynamics, experimental and theoretical, we provide a landscape picture for, and the structures involved in, the radiationless pathways which determine the fate of molecules following excitation. For completeness, the UED methodology and the theoretical framework for structure determination are described in this full account of an earlier communication [J. S. Feenstra et al., J. Chem. Phys. 123, 221104 (2005)].

  20. EXCITATION OF STRUCTURAL RESONANCE DUE TO A BEARING FAILURE

    SciTech Connect

    Leishear, R; David Stefanko, D

    2007-04-30

    Vibration due to a bearing failure in a pump created significant vibrations in a fifteen foot by fifteen foot by eight feet tall mounting platform due to excitation of resonant frequencies. In this particular application, an 18,000 pound pump was mounted to a structural steel platform. When bearing damage commenced, the platform vibrated with sufficient magnitude that conversations could not be heard within forty feet of the pump. Vibration analysis determined that the frequency of the bearing was coincident to one of the natural frequencies of the pump, which was, in turn, coincident to one of the natural frequencies of the mounting platform. This coincidence of frequencies defines resonance. Resonance creates excessive vibrations when the natural frequency of a structure is coincident to an excitation frequency. In this well documented case, the excitation frequency was related to ball bearing failures. The pump is a forty foot long vertical pump used to mix nuclear waste in 1,300,000 gallon tanks. A 300 horsepower drive motor is mounted to a structural steel platform on top of the tank. The pump hangs down into the tank from above to mix the waste and is inaccessible after installation. Initial awareness of the problem was due to increased noise from the pump. Initial vibration analysis indicated that the vibration levels of the bearing were within the expected range for this type of bearing, and the resonant condition was not obvious. Further analysis consisted of disassembly of the motor to inspect the bearings and extensive vibration monitoring. Vibration data for the bearings was obtained from the manufacturer and compared to measured vibration plots for the pump and mounting platform. Vibration data measured along the length of the pump was available from full scale testing, and vibrations were also measured at the installed pump. One of the axial frequencies of the pump, the platform frequency in the vertical direction, and the ball spin frequency for the

  1. Quantifying uncertainties of a Soil-Foundation Structure-Interaction System under Seismic Excitation

    SciTech Connect

    Tong, C

    2008-04-07

    We applied a spectrum of uncertainty quantification (UQ) techniques to the study of a two-dimensional soil-foundation-structure-interaction (2DSFSI) system (obtained from Professor Conte at UCSD) subjected to earthquake excitation. In the process we varied 19 uncertain parameters describing material properties of the structure and the soil. We present in detail the results for the different stages of our UQ analyses.

  2. Magnetic structure and excitations in BaV10O15

    NASA Astrophysics Data System (ADS)

    Dissanayake, Sachith; Lee, Jooseop; Iida, Kazuki; Stone, Matthew; Matsuda, Masaaki; Kazita, Tomomasa; Katsufuji, Takuro; Lee, Seunghun

    2013-03-01

    Recently, new type of frustrated magnets, BaV10O15 and SrV10O15, were found to exhibit interesting physics due to the magnetic V2.8+ ions with mixed valence. Using elastic and inelastic neutron scattering measurements we have examined the magnetic structure and excitations of BaV10O15. Magnetic excitations show highly dispersive two modes along c axis. Furthermore, two excitations are dispersionless along the a-axis. And very interestingly, along the b-axis one excitation is dispersionless while the other is strongly dispersive. Magnetic ground state of BaV10O15 was studied using neutron powder diffraction data, which order below 45 K with magnetic wave vector Qm = (1/2 0 0). Here we present the possible magnetic structures of BaV10O15 using representation analysis, which can explain both the magnetic diffraction data and the basic features of the magnetic excitations observed in different directions. Linear spinwave calculations were also performed to shed light in understanding an effective spin hamiltonian for this system.

  3. A comparative study of porphyrin dye sensitizers YD2-o-C8, SM315 and SM371 for solar cells: the electronic structures and excitation-related properties

    NASA Astrophysics Data System (ADS)

    Li, Xing-Yu; Zhang, Cai-Rong; Yuan, Li-Hua; Zhang, Mei-Ling; Chen, Yu-Hong; Liu, Zi-Jiang

    2016-10-01

    Understanding the electronic structures and excitation properties of dye sensitizers has significant importance to improve the photon-energy conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). Here, based upon the results calculated using density functional theory, the electronic structures and excitation related properties of porphyrin dye sensitizers YD2-o-C8, SM315, and SM371 were analyzed. It was found that the similar electronic structures of YD2-o-C8 and SM371 result in similar absorption spectra, excitation, and free energy variation for electron injection (EI) and dye regeneration. However, since the electronic structure of the benzothiadiazole unit is well-coupled to that of the porphyrin ring, introducing benzothiadiazole into porphyrin dyes generates a decrease in the lowest unoccupied molecular orbital energy, red-shift and splitting of absorption bands. Meanwhile, remarkably it increases the transferred charges of excitation, which is responsible for the superior short-circuit current density of SM315 sensitized DSSCs. Furthermore, the transition configurations and molecular orbitals indicate the diarylamine group acts as an electronic donor, and the different EI modes with different timescales coexist in excited states due to the multi-configurations of transition. The results of structure-property relationships are favorable to develop novel dye sensitizers for DSSCs.

  4. Recent Theoretical Studies On Excitation and Recombination

    NASA Technical Reports Server (NTRS)

    Pradhan, Anil K.

    2000-01-01

    New advances in the theoretical treatment of atomic processes in plasmas are described. These enable not only an integrated, unified, and self-consistent treatment of important radiative and collisional processes, but also large-scale computation of atomic data with high accuracy. An extension of the R-matrix work, from excitation and photoionization to electron-ion recombination, includes a unified method that subsumes both the radiative and the di-electronic recombination processes in an ab initio manner. The extensive collisional calculations for iron and iron-peak elements under the Iron Project are also discussed.

  5. Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz

    SciTech Connect

    Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco Casula, Michele; Sorella, Sandro

    2015-06-07

    We study the ionization energy, electron affinity, and the π → π{sup ∗} ({sup 1}L{sub a}) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the {sup 1}L{sub a} excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral {sup 1}L{sub a} excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.

  6. Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz.

    PubMed

    Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco; Sorella, Sandro; Casula, Michele

    2015-06-07

    We study the ionization energy, electron affinity, and the π → π(∗) ((1)La) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the (1)La excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral (1)La excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.

  7. Fluorescent excitation transfer as a tool for the phase transition studies

    NASA Astrophysics Data System (ADS)

    Goun, Alexei

    2012-02-01

    The use of the fluorescent resonant excitation transfer technique (FRET) to study the phase transition kinetics is demonstrated. The laser temperature jump is applied to the water/2,6-lutidine mixture and causes the demixing. Coumarin 480 and hydroxypyrene laser dyes form excitation transfer that interrogates the spatial structure of the system. Due to the differential solubility of these dyes in the components of the mixture, the excitation transfer ceases once the phase separation occurs. The spatial resolution of the method is determined by the Forster distance of the excitation transfer pair, and in this case is equal to 3 nm. The phase separation is completed within 1 microsecond. The rising edge of the fluorescence is consistent with polynomial growth of the phase separated domains, and not with Cahn-Hilliard fixed length instability. The theoretical model for the excitation transfer in a variety of systems such as separation of binary mixture, phase reorganization of membranes, formation of lamellar structure is developed.

  8. Dynamic insight into protein structure utilizing red edge excitation shift.

    PubMed

    Chattopadhyay, Amitabha; Haldar, Sourav

    2014-01-21

    Proteins are considered the workhorses in the cellular machinery. They are often organized in a highly ordered conformation in the crowded cellular environment. These conformations display characteristic dynamics over a range of time scales. An emerging consensus is that protein function is critically dependent on its dynamics. The subtle interplay between structure and dynamics is a hallmark of protein organization and is essential for its function. Depending on the environmental context, proteins can adopt a range of conformations such as native, molten globule, unfolded (denatured), and misfolded states. Although protein crystallography is a well established technique, it is not always possible to characterize various protein conformations by X-ray crystallography due to transient nature of these states. Even in cases where structural characterization is possible, the information obtained lacks dynamic component, which is needed to understand protein function. In this overall scenario, approaches that reveal information on protein dynamics are much appreciated. Dynamics of confined water has interesting implications in protein folding. Interfacial hydration combines the motion of water molecules with the slow moving protein molecules. The red edge excitation shift (REES) approach becomes relevant in this context. REES is defined as the shift in the wavelength of maximum fluorescence emission toward higher wavelengths, caused by a shift in the excitation wavelength toward the red edge of absorption spectrum. REES arises due to slow rates (relative to fluorescence lifetime) of solvent relaxation (reorientation) around an excited state fluorophore in organized assemblies such as proteins. Consequently, REES depends on the environment-induced motional restriction imposed on the solvent molecules in the immediate vicinity of the fluorophore. In the case of a protein, the confined water in the protein creates a dipolar field that acts as the solvent for a fluorophore

  9. Experimental study of planar opposed jets with acoustic excitation

    NASA Astrophysics Data System (ADS)

    Li, Wei-Feng; Huang, Guo-Feng; Tu, Gong-Yi; Liu, Hai-Feng; Wang, Fu-Chen

    2013-01-01

    Oscillation behaviors of planar opposed jets with acoustic excitation were experimentally investigated. The flow regimes of planar opposed jets at various exit air velocities, nozzle separations, excitation frequencies, and excitation amplitudes have been identified by a flow visualization technique combining with a high-speed camera. Results show that planar opposed jets exhibit horizontal instability at L/H ≤ 4 (where L is the nozzle separation and H is the slit height of the planar nozzle) and deflecting oscillation at L/H ≥ 6. The deflecting oscillation is originally started by the antisymmetric structures in the planar jets and is self-sustained by the periodic changes of the velocity field and the pressure field. At L/H ≤ 4, the acoustic excitation results in the horizontal periodic oscillation, whose frequency is equal to the excitation frequency. The acoustic excitation of oscillation amplitude less than 10% has negligible influence on the deflecting oscillation; for synchronous or asynchronous excitation with higher amplitude, the transition from the deflecting oscillation to a steady state or horizontal oscillation occurs.

  10. Electron structure of excited configurations in Ca2V2O7 studied by electron-induced core-ionization loss spectroscopy, appearance-potential spectroscopy, and x-ray-photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Curelaru, I. M.; Strid, K.-G.; Suoninen, E.; Minni, E.; Rönnhult, T.

    1981-04-01

    We have measured the electron-induced core-ionization loss (CILS) spectra, the appearance-potential (APS) spectra, and the x-ray-photoelectron (XPS) spectra of Ca2V2O7, that is a prototype for a series of luminescent materials with general formula M2V2O7(M=Mg, Ca, Sr, Ba, Zn, Cd, Hg). From the analysis of the data provided by the edge spectroscopies (CILS and APS) and their comparison with the XPS binding energies, we deduced the electronic structure of the outer orbitals (occupied and empty) involved in these processes. Our data illustrate the strong many-body effects that occur in the excitation and decay of localized atomiclike configurations within the big ionic cluster V2O4-7. Excitation of core levels in calcium, outside the V2O4-7 ion, seems to involve more extended orbitals, since the screening is more efficient. Usefulness of complementary studies by x-ray emission and Auger electron spectroscopy is anticipated.

  11. Computing electronic structures: A new multiconfiguration approach for excited states

    NASA Astrophysics Data System (ADS)

    Cancès, Éric; Galicher, Hervé; Lewin, Mathieu

    2006-02-01

    We present a new method for the computation of electronic excited states of molecular systems. This method is based upon a recent theoretical definition of multiconfiguration excited states [due to one of us, see M. Lewin, Solutions of the multiconfiguration equations in quantum chemistry, Arch. Rat. Mech. Anal. 171 (2004) 83-114]. Our algorithm, dedicated to the computation of the first excited state, always converges to a stationary state of the multiconfiguration model, which can be interpreted as an approximate excited state of the molecule. The definition of this approximate excited state is variational. An interesting feature is that it satisfies a non-linear Hylleraas-Undheim-MacDonald type principle: the energy of the approximate excited state is an upper bound to the true excited state energy of the N-body Hamiltonian. To compute the first excited state, one has to deform paths on a manifold, like this is usually done in the search for transition states between reactants and products on potential energy surfaces. We propose here a general method for the deformation of paths which could also be useful in other settings. We also compare our method to other approaches used in Quantum Chemistry and give some explanation of the unsatisfactory behaviours which are sometimes observed when using the latters. Numerical results for the special case of two-electron systems are provided: we compute the first singlet excited state potential energy surface of the H2 molecule.

  12. Computing electronic structures: A new multiconfiguration approach for excited states

    SciTech Connect

    Cances, Eric . E-mail: cances@cermics.enpc.fr; Galicher, Herve . E-mail: galicher@cermics.enpc.fr; Lewin, Mathieu . E-mail: lewin@cermic.enpc.fr

    2006-02-10

    We present a new method for the computation of electronic excited states of molecular systems. This method is based upon a recent theoretical definition of multiconfiguration excited states [due to one of us, see M. Lewin, Solutions of the multiconfiguration equations in quantum chemistry, Arch. Rat. Mech. Anal. 171 (2004) 83-114]. Our algorithm, dedicated to the computation of the first excited state, always converges to a stationary state of the multiconfiguration model, which can be interpreted as an approximate excited state of the molecule. The definition of this approximate excited state is variational. An interesting feature is that it satisfies a non-linear Hylleraas-Undheim-MacDonald type principle: the energy of the approximate excited state is an upper bound to the true excited state energy of the N-body Hamiltonian. To compute the first excited state, one has to deform paths on a manifold, like this is usually done in the search for transition states between reactants and products on potential energy surfaces. We propose here a general method for the deformation of paths which could also be useful in other settings. We also compare our method to other approaches used in Quantum Chemistry and give some explanation of the unsatisfactory behaviours which are sometimes observed when using the latter. Numerical results for the special case of two-electron systems are provided: we compute the first singlet excited state potential energy surface of the H {sub 2} molecule.

  13. Modal shape identification of large structure exposed to wind excitation by operational modal analysis technique

    NASA Astrophysics Data System (ADS)

    De Vivo, A.; Brutti, C.; Leofanti, J. L.

    2013-08-01

    Research efforts during recent decades qualify Operational Modal Analysis (OMA) as an interesting tool that is able to identify the modal characteristic parameters of structures excited randomly by environmental loads, eliminating the problem of measuring the external exciting forces. In this paper, an existing OMA technique, the Natural Excitation Technique (NExT) was studied and implemented in order to achieve, from the wind force, the modal parameters of Vega Launcher, the new European launcher vehicle for small and medium satellites. Following a brief summary of the fundamental equations of the method, the modal parameters of Vega are calculated using the OMA technique; the results are then compared with those achieved using a traditional Experimental Modal Analysis under excitation induced by shakers. The comparison shows there is a very good agreement between the results obtained by the two different methods, OMA and the traditional experimental analysis, proving that OMA is a reliable tool to analyse the dynamic behaviour of large structures. Finally, this approach can be used for any type of large structure in civil and mechanical fields and the technique appears to be very promising for further applications.

  14. Repetitive impact response of a beam structure subjected to harmonic base excitation

    NASA Astrophysics Data System (ADS)

    Ervin, Elizabeth K.; Wickert, J. A.

    2007-10-01

    This paper investigates the forced response dynamics of a clamped-clamped beam to which a rigid body is attached, and in the presence of periodic or non-periodic impacts between the body and a comparatively compliant base structure. The assembly is subjected to base excitation at specified frequency and acceleration, and the potentially complex responses that occur are examined analytically. The two sets of natural frequencies and vibration modes of the beam-rigid body structure (in its in-contact state, and in its not-in-contact state), are used to treat the forced response problem through a series of algebraic mappings among those states. A modal analysis based on extended operators for the (continuous) beam and (discrete) rigid body establishes a piecewise linear state-to-state mapping for transition between the in-contact and not-in-contact conditions. The contact force, impulse, and displacement each exhibit complex response characteristics as a function of the excitation frequency. Periodic responses occurring at the excitation frequency, period-doubling bifurcations, grazing impacts, sub-harmonic regions, fractional harmonic resonances, and apparently chaotic responses each occur at various combinations of damping, excitation frequency, and contact stiffness. The results of parameter studies in structural asymmetry and the eccentricity of the contact point's location are discussed.

  15. Modeling of Sound Transmission through Shell Structures with Turbulent Boundary Layer Excitation

    NASA Technical Reports Server (NTRS)

    Tang, Yvette Y.; Silcox, Richard J.; Robinson, Jay H.

    1996-01-01

    The turbulent boundary layer (TBL) pressure field is an important source of cabin noise during cruise of high subsonic and supersonic commercial aircraft. The broadband character of this excitation field results in an interior noise spectrum that dominates the overall sound pressure level (SPL) and speech interference metrics in the forward and midcabins of many aircraft. In the authors' previous study, sound transmission through an aircraft fuselage, modeled by two concentric cylindrical sandwich shells and excited by a TBL statistical model was investigated analytically. An assessment of point and global structural vibration levels and resulting interior noise levels was obtained for different TBL models, flight conditions and fuselage structural designs. However, due to the complication of the shell structure, the important noise transmission mechanisms were difficult to discern. Previous experience has demonstrated that a fundamental understanding of the range of modes (or wavenumbers) generated by the TBL source both in the structure and the acoustic cavity is key to the development of both active and passive control technologies. In an initial effort to provide this insight, the objective of this paper is to develop an analytical model of sound transmission through a simple unstiffened cylindrical aluminum shell excited by a TBL pressure field. The description of the turbulent pressure field is based on the Corcos formulation for the cross-spectral density (CSD) of the pressure fluctuations. The coupled shell and interior and exterior acoustic equations are solved for the structural displacement and the interior acoustic response using a Galerkin approach to obtain analytical solutions. Specifically, this study compares the real part of the normalized CSD of the TBL excitation field, the structural displacement and the interior acoustic field. Further the modal compositions of the structural and cavity response are examined and some inference of the dominant

  16. Influence of ligand substitution on excited state structural dynamics in Cu(I) bisphenanthroline complexes.

    PubMed

    Lockard, Jenny V; Kabehie, Sanaz; Zink, Jeffrey I; Smolentsev, Grigory; Soldatov, Alexander; Chen, Lin X

    2010-11-18

    This study explores the influences of steric hindrance and excited state solvent ligation on the excited state dynamics of Cu(I) diimine complexes. Ultrafast excited state dynamics of Cu(I)bis(3,8-di(ethynyltrityl)-1,10-phenanthroline) [Cu(I)(detp)(2)](+) are measured using femtosecond transient absorption spectroscopy. The steady state electronic absorption spectra and measured lifetimes are compared to those of Cu(I)bis(1,10-phenanthroline), [Cu(I)(phen)(2)](+), and Cu(I)bis(2-9-dimethyl-1,10-phenanthroline), [Cu(I)(dmp)(2)](+), model complexes to determine the influence of different substitution patterns of the phenanthroline ligand on the structural dynamics associated with the metal to ligand charge transfer excited states. Similarities between the [Cu(I)(detp)(2)](+) and [Cu(I)(phen)(2)](+) excited state lifetimes were observed in both coordinating and noncoordinating solvents and attributed to the lack of steric hindrance from substitution at the 2- and 9-positions. The solution-phase X-ray absorption spectra of [Cu(I)(detp)(2)](+), [Cu(I)(phen)(2)](+), and [Cu(I)(dmp)(2)](+) are reported along with finite difference method calculations that are used to determine the degree of ground state dihedral angle distortion in solution and to account for the pre-edge features observed in the XANES region.

  17. Triplet excited states of cyclic disulfides and related compounds: electronic structures, geometries, energies, and decay.

    PubMed

    Ginagunta, Saroja; Bucher, Götz

    2011-02-03

    We have performed a computational study on the properties of a series of heterocycles bearing two adjacent heteroatoms, focusing on the structures and electronic properties of their first excited triplet states. If the heteroatoms are both heavy chalcogens (S, Se, or Te) or isoelectronic species, then the lowest excited triplet state usually has (π*, σ*) character. The triplet energies are fairly low (30-50 kcal mol(-1)). The (π*, σ*) triplet states are characterized by a significantly lengthened bond between the two heteroatoms. Thus, in 1,2-dithiolane (1b), the S-S bond length is calculated to be 2.088 Å in the singlet ground state and 2.568 Å in the first triplet excited state. The spin density is predicted to be localized almost exclusively on the sulfur atoms. Replacing one heavy chalcogen atom by an oxygen atom or an NR group results in a significant destabilization of the (π*, σ*) triplet excited state, which then no longer is lower in energy than an open-chain biradical. The size of the heterocyclic ring also contributes to the stability of the (π*, σ*) triplet state, with five-membered rings being more favorable than six-membered rings. Benzoannulation, finally, usually lowers the energy of the (π*, σ*) triplet excited states. If one of the heteroatoms is an oxygen or nitrogen atom, however, the corresponding lowest triplet states are better described as σ,π-biradicals.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  19. Radial structures and nonlinear excitation of Geodesic Acoustic Modes

    NASA Astrophysics Data System (ADS)

    Chen, Liu; Zonca, Fulvio

    2007-11-01

    In this paper, we show that GAMs constitute a continuous spectrum due to radial inhomogeneities. The existence of singular layer, thus, suggests linear mode conversion to short-wavelength kinetic GAM (KGAM) via finite ion Larmor radii. This result is demonstrated by derivations of the GAM mode structure and dispersion relation in the singular layer. At the lowest order in krρi, with kr the radial wave vector and ρi the ion Larmor radius, the well known kinetic dispersion relation of GAM is recovered. At the next relevant order, O(kr^2ρi^2), we show that KGAM propagates in the low-temperature and/or high safety-factor domain; i.e., typically, radially outward, and a corresponding damping rate is derived. In this work, we also show that, while KGAM is linearly stable due to ion Landau damping, it can be nonlinearly excited by finite-amplitude DW turbulence via 3-wave parametric interactions. The resultant 3-wave system exhibits the typical prey-predator self-regulatory dynamics.

  20. Role of vortex structures in excitation of condensed system self-oscillatory burning

    NASA Astrophysics Data System (ADS)

    Samsonov, V. P.; Murunov, E. Y.; Alexeev, M. V.

    2008-08-01

    The effect of free convection and vortex structures arising near the “singing” flame of a gasoline blow torch on excitation of thermal self-oscillations in a resonator tube is studied experimentally. A technique for measuring the oscillation amplitude of the gas column is suggested. It is found that the excitation of acoustic oscillations decreases the height of the singing flame and the mass velocity of burning but raises the gasoline combustion efficiency. The variation of the temperature field of the singing flame over an oscillation cycle is studied by digital photometry. Hysteretic dependences of the acoustic oscillation amplitude on the thermal power of the gasoline diffusion flame are obtained. A mechanism explaining the influence of vortex structures on the self-oscillatory mode of burning in condensed systems is discussed.

  1. Optical near-field excitations on plasmonic nanoparticle-based structures.

    PubMed

    Foteinopoulou, S; Vigneron, J P; Vandenbem, C

    2007-04-02

    We investigate optical excitations on single silver nanospheres and nanosphere composites with the Finite Difference Time Domain (FDTD) method. Our objective is to achieve polarization control of the enhanced local field, pertinent to SERS applications. We employ dimer and quadrumer structures, which can display broadband and highly confined near-field-intensity enhancement comparable to or exceeding the resonant value of smaller sized isolated spheres. Our results demonstrate that the polarization of the enhanced field can be controlled by the orientation of the multimers in respect to the illumination, rather than the illumination itself. In particular, we report cases where the enhanced field shares the same polarization with the exciting field, and cases where it is predominantly perpendicular to the source field. We call the later phenomenon depolarized enhancement. Furthermore, we study a realizable nanolens based on a tapered self-similar silver nanosphere array. The time evolution of the fields in such structures show conversion of a diffraction limited Gaussian beam to a focused spot, through sequential coupling of the nano-array spheres' Mie-plasmons. For a longitudinally excited nanolens design we observed the formation of an isolated focus with size about one tenth the vacuum wavelength. We believe such nanolens will aid scanning near-field optical microscopy (SNOM) detection and the excitation of surface plasmon based guiding devices.

  2. Semiempirical Modeling of Ag Nanoclusters: New Parameters for Optical Property Studies Enable Determination of Double Excitation Contributions to Plasmonic Excitation.

    PubMed

    Gieseking, Rebecca L; Ratner, Mark A; Schatz, George C

    2016-07-07

    Quantum mechanical studies of Ag nanoclusters have shown that plasmonic behavior can be modeled in terms of excited states where collectivity among single excitations leads to strong absorption. However, new computational approaches are needed to provide understanding of plasmonic excitations beyond the single-excitation level. We show that semiempirical INDO/CI approaches with appropriately selected parameters reproduce the TD-DFT optical spectra of various closed-shell Ag clusters. The plasmon-like states with strong optical absorption comprise linear combinations of many singly excited configurations that contribute additively to the transition dipole moment, whereas all other excited states show significant cancellation among the contributions to the transition dipole moment. The computational efficiency of this approach allows us to investigate the role of double excitations at the INDO/SDCI level. The Ag cluster ground states are stabilized by slight mixing with doubly excited configurations, but the plasmonic states generally retain largely singly excited character. The consideration of double excitations in all cases improves the agreement of the INDO/CI absorption spectra with TD-DFT, suggesting that the SDCI calculation effectively captures some of the ground-state correlation implicit in DFT. These results provide the first evidence to support the commonly used assumption that single excitations are in many cases sufficient to describe the optical spectra of plasmonic excitations quantum mechanically.

  3. Semiempirical modeling of Ag nanoclusters: New parameters for optical property studies enable determination of double excitation contributions to plasmonic excitation

    DOE PAGES

    Gieseking, Rebecca L.; Ratner, Mark A.; Schatz, George C.

    2016-06-03

    Quantum mechanical studies of Ag nanoclusters have shown that plasmonic behavior can be modeled in terms of excited states where collectivity among single excitations leads to strong absorption. However, new computational approaches are needed to provide understanding of plasmonic excitations beyond the single-excitation level. We show that semiempirical INDO/CI approaches with appropriately selected parameters reproduce the TD-DFT optical spectra of various closed-shell Ag clusters. The plasmon-like states with strong optical absorption comprise linear combinations of many singly excited configurations that contribute additively to the transition dipole moment, whereas all other excited states show significant cancellation among the contributions to themore » transition dipole moment. The computational efficiency of this approach allows us to investigate the role of double excitations at the INDO/SDCI level. The Ag cluster ground states are stabilized by slight mixing with doubly excited configurations, but the plasmonic states generally retain largely singly excited character. The consideration of double excitations in all cases improves the agreement of the INDO/CI absorption spectra with TD-DFT, suggesting that the SDCI calculation effectively captures some of the ground-state correlation implicit in DFT. Furthermore, these results provide the first evidence to support the commonly used assumption that single excitations are in many cases sufficient to describe the optical spectra of plasmonic excitations quantum mechanically.« less

  4. Excited states of Ne isoelectronic ions: SAC-CI study

    NASA Astrophysics Data System (ADS)

    Das, A. K.; Ehara, M.; Nakatsuji, H.

    2001-01-01

    Excited states of the s, p, and d symmetries up to principal quantum number n = 4 are studied for the first eight members of Ne isoelectronic sequence (Ne to Cl7+) by the SAC-CI (symmetry-adapted-cluster configuration-interaction) method. The valence STO basis sets of Clementi et al. and the optimized excited STO are used by the STO-6G expansion method. The calculated transition energies agree well with the experimental values wherever available.

  5. Simulation Analysis of a Strip Dipole Excited Electromagnetic Band-Gap (EBG) Structure

    DTIC Science & Technology

    2015-07-01

    ARL-TR-7337 ● JULY 2015 US Army Research Laboratory Simulation Analysis of a Strip Dipole Excited Electromagnetic Band-Gap (EBG...Simulation Analysis of a Strip Dipole Excited Electromagnetic Band-Gap (EBG) Structure by Seth A McCormick and William O Coburn Sensors and...4/2015 4. TITLE AND SUBTITLE Simulation Analysis of a Strip Dipole Excited Electromagnetic Band-Gap (EBG) Structure 5a. CONTRACT NUMBER 5b

  6. Lifetimes and Structure of Excited States of 73AS

    NASA Astrophysics Data System (ADS)

    Bucurescu, D.; Căta-Danil, I.; Ivaşcu, M.; Mărginean, N.; Stroe, L.; Ur, C. A.; Dinu, N.

    The lifetimes of twelve low spin excited states in 73As, below 2 MeV excitation, have been measured with the DSA method in the 73Ge(p,nγ) reaction. The existing data (energy levels, electromagnetic moments, transition probabilities and branching ratios, one-nucleon transfer spectroscopic factors) are discussed in the frame of multi-shell interacting boson-fermion model calculations. A good agreement is obtained for a large number of levels.

  7. Nonlinear structured-illumination enhanced temporal focusing multiphoton excitation microscopy with a digital micromirror device

    PubMed Central

    Cheng, Li-Chung; Lien, Chi-Hsiang; Da Sie, Yong; Hu, Yvonne Yuling; Lin, Chun-Yu; Chien, Fan-Ching; Xu, Chris; Dong, Chen Yuan; Chen, Shean-Jen

    2014-01-01

    In this study, the light diffraction of temporal focusing multiphoton excitation microscopy (TFMPEM) and the excitation patterning of nonlinear structured-illumination microscopy (NSIM) can be simultaneously and accurately implemented via a single high-resolution digital micromirror device. The lateral and axial spatial resolutions of the TFMPEM are remarkably improved through the second-order NSIM and projected structured light, respectively. The experimental results demonstrate that the lateral and axial resolutions are enhanced from 397 nm to 168 nm (2.4-fold) and from 2.33 μm to 1.22 μm (1.9-fold), respectively, in full width at the half maximum. Furthermore, a three-dimensionally rendered image of a cytoskeleton cell featuring ~25 nm microtubules is improved, with other microtubules at a distance near the lateral resolution of 168 nm also able to be distinguished. PMID:25136483

  8. Nonlinear structured-illumination enhanced temporal focusing multiphoton excitation microscopy with a digital micromirror device.

    PubMed

    Cheng, Li-Chung; Lien, Chi-Hsiang; Da Sie, Yong; Hu, Yvonne Yuling; Lin, Chun-Yu; Chien, Fan-Ching; Xu, Chris; Dong, Chen Yuan; Chen, Shean-Jen

    2014-08-01

    In this study, the light diffraction of temporal focusing multiphoton excitation microscopy (TFMPEM) and the excitation patterning of nonlinear structured-illumination microscopy (NSIM) can be simultaneously and accurately implemented via a single high-resolution digital micromirror device. The lateral and axial spatial resolutions of the TFMPEM are remarkably improved through the second-order NSIM and projected structured light, respectively. The experimental results demonstrate that the lateral and axial resolutions are enhanced from 397 nm to 168 nm (2.4-fold) and from 2.33 μm to 1.22 μm (1.9-fold), respectively, in full width at the half maximum. Furthermore, a three-dimensionally rendered image of a cytoskeleton cell featuring ~25 nm microtubules is improved, with other microtubules at a distance near the lateral resolution of 168 nm also able to be distinguished.

  9. Structural control and health monitoring of building structures with unknown ground excitations: Experimental investigation

    NASA Astrophysics Data System (ADS)

    He, Jia; Xu, You-Lin; Zhan, Sheng; Huang, Qin

    2017-03-01

    When health monitoring system and vibration control system both are required for a building structure, it will be beneficial and cost-effective to integrate these two systems together for creating a smart building structure. Recently, on the basis of extended Kalman filter (EKF), a time-domain integrated approach was proposed for the identification of structural parameters of the controlled buildings with unknown ground excitations. The identified physical parameters and structural state vectors were then utilized to determine the control force for vibration suppression. In this paper, the possibility of establishing such a smart building structure with the function of simultaneous damage detection and vibration suppression was explored experimentally. A five-story shear building structure equipped with three magneto-rheological (MR) dampers was built. Four additional columns were added to the building model, and several damage scenarios were then simulated by symmetrically cutting off these columns in certain stories. Two sets of earthquakes, i.e. Kobe earthquake and Northridge earthquake, were considered as seismic input and assumed to be unknown during the tests. The structural parameters and the unknown ground excitations were identified during the tests by using the proposed identification method with the measured control forces. Based on the identified structural parameters and system states, a switching control law was employed to adjust the current applied to the MR dampers for the purpose of vibration attenuation. The experimental results show that the presented approach is capable of satisfactorily identifying structural damages and unknown excitations on one hand and significantly mitigating the structural vibration on the other hand.

  10. Specific features of the mechanisms of excitation of erbium photoluminescence in epitaxial Si:Er/Si structures

    SciTech Connect

    Yablonskiy, A. N. Andreev, B. A.; Krasilnikova, L. V.; Kryzhkov, D. I.; Kuznetsov, V. P.; Krasilnik, Z. F.

    2010-11-15

    The excitation spectra and kinetics of erbium photoluminescence and silicon interband photoluminescence in Si:Er/Si structures under conditions of high-intensity pulse optical excitation are studied. It is shown that, in the interband photoluminescence spectra of the Si:Er/Si structures, both the luminescence of free excitons and the emission associated with the electron-hole plasma can be observed, depending on the excitation power and wavelength. It is found that the formation of a peak in the erbium photoluminescence excitation spectra at high pumping powers correlates with the Mott transition from the exciton gas to the electron-hole plasma. It is demonstrated that, in the Si:Er/Si structures, the characteristic rise times of erbium photoluminescence substantially depend on the concentration of charge carriers.

  11. Mode specific excited state dynamics study of bis(phenylethynyl)benzene from ultrafast Raman loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Roy, Khokan; Kayal, Surajit; Ariese, Freek; Beeby, Andrew; Umapathy, Siva

    2017-02-01

    Femtosecond transient absorption (fs-TA) and Ultrafast Raman Loss Spectroscopy (URLS) have been applied to reveal the excited state dynamics of bis(phenylethynyl)benzene (BPEB), a model system for one-dimensional molecular wires that have numerous applications in opto-electronics. It is known from the literature that in the ground state BPEB has a low torsional barrier, resulting in a mixed population of rotamers in solution at room temperature. For the excited state this torsional barrier had been calculated to be much higher. Our femtosecond TA measurements show a multi-exponential behaviour, related to the complex structural dynamics in the excited electronic state. Time-resolved, excited state URLS studies in different solvents reveal mode-dependent kinetics and picosecond vibrational relaxation dynamics of high frequency vibrations. After excitation, a gradual increase in intensity is observed for all Raman bands, which reflects the structural reorganization of Franck-Condon excited, non-planar rotamers to a planar conformation. It is argued that this excited state planarization is also responsible for its high fluorescence quantum yield. The time dependent peak positions of high frequency vibrations provide additional information: a rapid, sub-picosecond decrease in peak frequency, followed by a slower increase, indicates the extent of conjugation during different phases of excited state relaxation. The CC triple (-C≡C-) bond responds somewhat faster to structural reorganization than the CC double (>C=C<) bonds. This study deepens our understanding of the excited state of BPEB and analogous linear pi-conjugated systems and may thus contribute to the advancement of polymeric "molecular wires."

  12. Mode specific excited state dynamics study of bis(phenylethynyl)benzene from ultrafast Raman loss spectroscopy.

    PubMed

    Roy, Khokan; Kayal, Surajit; Ariese, Freek; Beeby, Andrew; Umapathy, Siva

    2017-02-14

    Femtosecond transient absorption (fs-TA) and Ultrafast Raman Loss Spectroscopy (URLS) have been applied to reveal the excited state dynamics of bis(phenylethynyl)benzene (BPEB), a model system for one-dimensional molecular wires that have numerous applications in opto-electronics. It is known from the literature that in the ground state BPEB has a low torsional barrier, resulting in a mixed population of rotamers in solution at room temperature. For the excited state this torsional barrier had been calculated to be much higher. Our femtosecond TA measurements show a multi-exponential behaviour, related to the complex structural dynamics in the excited electronic state. Time-resolved, excited state URLS studies in different solvents reveal mode-dependent kinetics and picosecond vibrational relaxation dynamics of high frequency vibrations. After excitation, a gradual increase in intensity is observed for all Raman bands, which reflects the structural reorganization of Franck-Condon excited, non-planar rotamers to a planar conformation. It is argued that this excited state planarization is also responsible for its high fluorescence quantum yield. The time dependent peak positions of high frequency vibrations provide additional information: a rapid, sub-picosecond decrease in peak frequency, followed by a slower increase, indicates the extent of conjugation during different phases of excited state relaxation. The CC triple (-C≡C-) bond responds somewhat faster to structural reorganization than the CC double (>C=C<) bonds. This study deepens our understanding of the excited state of BPEB and analogous linear pi-conjugated systems and may thus contribute to the advancement of polymeric "molecular wires."

  13. Theoretical study of K-shell excitations in formaldehyde

    NASA Astrophysics Data System (ADS)

    Trofimov, A. B.; Moskovskaya, T. E.; Gromov, E. V.; Köppel, H.; Schirmer, J.

    2001-08-01

    The C 1s and O 1s excitation of formaldehyde (H2CO) has been studied within an ab initio framework. The second-order algebraic-diagrammatic construction [ADC(2)] polarization propagator method has been used to calculate energies and oscillator strengths of the electronic transitions. For selected C 1s excited states also multireference configuration-interaction (MRCI) calculations were performed. The vibrational excitations accompanying the electronic transitions have been studied using a linear vibronic coupling model. The theoretical C 1s and O 1s spectra are in excellent qualitative agreement with high-resolution K-shell photoabsorption measurements. The present results support the previous assignments of the C 1s spectrum, while they revise the interpretation of the O 1s spectrum above 537 eV. In contrast to the C 1s case, the main photoabsorption intensity in the O 1s spectrum is due to nd rather than to np Rydberg excitations. For the two lowest singlet excited states, that is, the 1B1(C 1s-->π*) single excitation and the 1B2(C 1s,n-->π*2) double excitation, we find vibronic interaction with the 1A1(C 1s-->3s) and 1A2(C 1s-->3d) Rydberg states via the ν4 out-of-plane bending mode. In addition, the 1B2(C 1s,n-->π*2) and the 1A1(C 1s-->3s) states interact via the ν5 mode. The vibronic coupling leads to a complex spectral pattern in the low-energy part of the C 1s excitation spectrum, allowing one to interpret the finer details of the experiment.

  14. Ground-state and excited-state structures of tungsten-benzylidyne complexes.

    PubMed

    Lovaasen, Benjamin M; Lockard, Jenny V; Cohen, Brian W; Yang, Shujiang; Zhang, Xiaoyi; Simpson, Cheslan K; Chen, Lin X; Hopkins, Michael D

    2012-05-21

    The molecular structure of the tungsten-benzylidyne complex trans-W(≡CPh)(dppe)(2)Cl (1; dppe = 1,2-bis(diphenylphosphino)ethane) in the singlet (d(xy))(2) ground state and luminescent triplet (d(xy))(1)(π*(WCPh))(1) excited state (1*) has been studied using X-ray transient absorption spectroscopy, X-ray crystallography, and density functional theory (DFT) calculations. Molecular-orbital considerations suggest that the W-C and W-P bond lengths should increase in the excited state because of the reduction of the formal W-C bond order and decrease in W→P π-backbonding, respectively, between 1 and 1*. This latter conclusion is supported by comparisons among the W-P bond lengths obtained from the X-ray crystal structures of 1, (d(xy))(1)-configured 1(+), and (d(xy))(2) [W(CPh)(dppe)(2)(NCMe)](+) (2(+)). X-ray transient absorption spectroscopic measurements of the excited-state structure of 1* reveal that the W-C bond length is the same (within experimental error) as that determined by X-ray crystallography for the ground state 1, while the average W-P/W-Cl distance increases by 0.04 Å in the excited state. The small excited-state elongation of the W-C bond relative to the M-E distortions found for M(≡E)L(n) (E = O, N) compounds with analogous (d(xy))(1)(π*(ME))(1) excited states is due to the π conjugation within the WCPh unit, which lessens the local W-C π-antibonding character of the π*(WCPh) lowest unoccupied molecular orbital (LUMO). These conclusions are supported by DFT calculations on 1 and 1*. The similar core bond distances of 1, 1(+), and 1* indicates that the inner-sphere reorganization energy associated with ground- and excited-state electron-transfer reactions is small.

  15. Ground-state and excited-state structures of tungsten-benzylidyne complexes

    SciTech Connect

    Lovaasen, B. M.; Lockard, J. V.; Cohen, B. W.; Yang, S.; Zhang, X.; Simpson, C. K.; Chen, L. X.; Hopkins, M. D.

    2012-01-01

    The molecular structure of the tungsten-benzylidyne complex trans-W({triple_bond}CPh)(dppe){sub 2}Cl (1; dppe = 1,2-bis(diphenylphosphino)ethane) in the singlet (d{sub xy}){sup 2} ground state and luminescent triplet (d{sub xy}){sup 1}({pi}*(WCPh)){sup 1} excited state (1*) has been studied using X-ray transient absorption spectroscopy, X-ray crystallography, and density functional theory (DFT) calculations. Molecular-orbital considerations suggest that the W-C and W-P bond lengths should increase in the excited state because of the reduction of the formal W-C bond order and decrease in W {yields} P {pi}-backbonding, respectively, between 1 and 1*. This latter conclusion is supported by comparisons among the W-P bond lengths obtained from the X-ray crystal structures of 1, (d{sub xy}){sup 1}-configured 1{sup +}, and (d{sub xy}){sup 2} [W(CPh)(dppe){sub 2}(NCMe)]{sup +} (2{sup +}). X-ray transient absorption spectroscopic measurements of the excited-state structure of 1* reveal that the W-C bond length is the same (within experimental error) as that determined by X-ray crystallography for the ground state 1, while the average W-P/W-Cl distance increases by 0.04 {angstrom} in the excited state. The small excited-state elongation of the W-C bond relative to the M-E distortions found for M({triple_bond}E)L{sub n} (E = O, N) compounds with analogous (d{sub xy}){sup 1}({pi}*(ME)){sup 1} excited states is due to the {pi} conjugation within the WCPh unit, which lessens the local W-C {pi}-antibonding character of the {pi}*(WCPh) lowest unoccupied molecular orbital (LUMO). These conclusions are supported by DFT calculations on 1 and 1*. The similar core bond distances of 1, 1{sup +}, and 1* indicates that the inner-sphere reorganization energy associated with ground- and excited-state electron-transfer reactions is small.

  16. The Structure of the Nucleon and it's Excited States

    SciTech Connect

    1995-02-20

    The past year has been an exciting and productive one for particle physics research at Abilene Christian University. The thrust of our experimental investigations is the study of the nucleon and its excited states. Laboratories where these investigations are presently being conducted are the AGS at Brookhaven, Fermilab and LAMPF. Some analysis of the data for experiments at the Petersburg Nuclear Physics Institute (Gatchina, Russia) is still in progress. Scheduling of activities at different laboratories inevitably leads to occasional conflicts. This likelihood is increased by the present budget uncertainties at the laboratories that make long-term scheduling difficult. For the most part, the investigators have been able to avoid such conflicts. Only one experiment received beam time in 1994 (E890 at the AGS). The situation for 1995-1996 also appears manageable at this point. E890 and another AGS experiment (E909) will run through May, 1995. El 178 at LAMPF is presently scheduled for August/September 1995. E866 at Fermilab is scheduled to start in Spring/Summer 1996. Undergraduate student involvement has been a key element in this research contract since its inception. Summer students participated at all of the above laboratories in 1994 and the same is planned in 1995. A transition to greater involvement by graduate students will provide cohesiveness to ACU involvement at a given laboratory and full-time on-site involvement in the longer running experiments at FNAL and BNL. Funds to support a full-time graduate student are requested this year. Finally, collaboration by Russian, Croatian and Bosnian scientists has proven to be mutually beneficial to these experimental programs and to the overall programs at the institutions involved. Past support has been augmented by other grants from government agencies and from the Research Council at Abilene Christian University. Additional funds are requested in this renewal to enable more programmatic support for these

  17. Optimizing Excited-State Electronic-Structure Codes for Intel Knights Landing: A Case Study on the BerkeleyGW Software

    SciTech Connect

    Deslippe, Jack; da Jornada, Felipe H.; Vigil-Fowler, Derek; Barnes, Taylor; Wichmann, Nathan; Raman, Karthik; Sasanka, Ruchira; Louie, Steven G.

    2016-10-06

    We profile and optimize calculations performed with the BerkeleyGW code on the Xeon-Phi architecture. BerkeleyGW depends both on hand-tuned critical kernels as well as on BLAS and FFT libraries. We describe the optimization process and performance improvements achieved. We discuss a layered parallelization strategy to take advantage of vector, thread and node-level parallelism. We discuss locality changes (including the consequence of the lack of L3 cache) and effective use of the on-package high-bandwidth memory. We show preliminary results on Knights-Landing including a roofline study of code performance before and after a number of optimizations. We find that the GW method is particularly well-suited for many-core architectures due to the ability to exploit a large amount of parallelism over plane-wave components, band-pairs, and frequencies.

  18. Vibrationally Excited HCN around AFGL 2591: A Probe of Protostellar Structure

    NASA Astrophysics Data System (ADS)

    Veach, Todd J.; Groppi, Christopher E.; Hedden, Abigail

    2013-03-01

    Vibrationally excited molecules with submillimeter rotational transitions are potentially excellent probes of physical conditions near protostars. This study uses observations of the v = 1 and v = 2 ro-vibrational modes of HCN (4-3) to probe this environment. The presence or absence and relative strengths of these ro-vibrational lines probe the gas excitation mechanism and physical conditions in warm, dense material associated with protostellar disks. We present pilot observations from the Heinrich Hertz Submillimeter Telescope and follow-up observations from the Submillimeter Array. All vibrationally excited HCN (4-3) v = 0, v = 1, and v = 2 lines were observed. The existence of the three v = 2 lines at approximately equal intensity imply collisional excitation with a density of greater than (1010 cm-3) and a temperature of >1000 K for the emitting gas. This warm, high-density material should directly trace structures formed in the protostellar envelope and disk environment. Further, the line shapes of the v = 2 emission may suggest a Keplerian disk. This Letter demonstrates the utility of this technique which is of particular interest due to the recent inauguration of the Atacama Large Millimeter Array.

  19. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    SciTech Connect

    Van Tassle, Aaron Justin

    2006-01-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  20. Modulation of excitability as an early change leading to structural adaptation in the motor cortex.

    PubMed

    Manto, Mario; Oulad ben Taib, Nordeyn; Luft, Andreas R

    2006-02-01

    The excitability of the motor cortex is a function of single cell excitability, synaptic strength, and the balance between excitatory cells and inhibitory cells. Sustained periods of sensory stimulation enhance the excitability in the motor cortex. This adaptation, which represents an early change in cortical network function effective in motor learning and recovery from a motor deficit, is followed by longer-lasting changes, such as modifications in cortical somatotopy, and by structural plasticity. Interventions aiming at increasing excitability also positively affect learning processes. Recent studies highlight that the cerebellum, especially the interpositus nucleus, plays a key function in the adaptation of the motor cortex to repeated trains of peripheral stimulation. Interpositus neurons, which receive inputs from the sensorimotor cortex and the spinal cord, are involved in somesthetic reflex behaviors and assist the cerebral cortex in transforming sensory signals to motor-oriented commands by acting via the cerebello-thalamo-cortical projections. Moreover, climbing fibers originating in the inferior olivary complex and innervating the nucleus interpositus mediate highly integrated sensorimotor information derived from spinal modules. The intermediate cerebellum allows the motor cortex to tune the gain of polysynaptic responses originating from the spinal cord after repetitive trains of peripheral stimulation, allowing an online calibration of cutaneo-muscular responses. Copyright 2005 Wiley-Liss, Inc.

  1. Relativistic atomic structure calculations and electron impact excitations of Fe23+

    NASA Astrophysics Data System (ADS)

    El-Maaref, A. A.

    2016-02-01

    Relativistic calculations using the multiconfiguration Dirac-Fock method for energy levels, oscillator strengths, and electronic dipole transition probabilities of Li-like iron (Fe23+) are presented. A configuration state list with the quantum numbers nl, where n = 2 - 7 and l = s , p , d , f , g , h , i has been considered. Excitations up to three electrons and correlation contributions from higher orbitals up to 7 l have been included. Contributions from core levels have been taken into account, EOL (extended optimal level) type calculations have been applied, and doubly excited levels are considered. The calculations have been executed by using the fully relativistic atomic structure package GRASP2K. The present calculations have been compared with the available experimental and theoretical sources, the comparisons show a good agreement between the present results of energy levels and oscillator strengths with the literature. In the second part of the present study, the atomic data (energy levels, and radiative parameters) have been used to calculate the excitation and deexcitation rates of allowed transitions by electron impact, as well as the population densities of some excited levels at different electron temperatures.

  2. VIBRATIONALLY EXCITED HCN AROUND AFGL 2591: A PROBE OF PROTOSTELLAR STRUCTURE

    SciTech Connect

    Veach, Todd J.; Groppi, Christopher E.; Hedden, Abigail

    2013-03-10

    Vibrationally excited molecules with submillimeter rotational transitions are potentially excellent probes of physical conditions near protostars. This study uses observations of the v = 1 and v = 2 ro-vibrational modes of HCN (4-3) to probe this environment. The presence or absence and relative strengths of these ro-vibrational lines probe the gas excitation mechanism and physical conditions in warm, dense material associated with protostellar disks. We present pilot observations from the Heinrich Hertz Submillimeter Telescope and follow-up observations from the Submillimeter Array. All vibrationally excited HCN (4-3) v = 0, v = 1, and v = 2 lines were observed. The existence of the three v = 2 lines at approximately equal intensity imply collisional excitation with a density of greater than (10{sup 10} cm{sup -3}) and a temperature of >1000 K for the emitting gas. This warm, high-density material should directly trace structures formed in the protostellar envelope and disk environment. Further, the line shapes of the v = 2 emission may suggest a Keplerian disk. This Letter demonstrates the utility of this technique which is of particular interest due to the recent inauguration of the Atacama Large Millimeter Array.

  3. Nonlinear acoustics with low-profile piezoceramic excitation for crack detection in metallic structures

    NASA Astrophysics Data System (ADS)

    Parsons, Z.; Staszewski, W. J.

    2006-08-01

    Structural damage detection is one of the major maintenance activities in a wide range of industries. A variety of different methods have been developed for detection of fatigue cracks in metallic structures over the last few decades. This includes techniques based on stress/acoustic waves propagating in monitored structures. Classical ultrasonic techniques used in nondestructive testing and evaluation are based on linear amplitude and/or phase variations of reflected, transmitted or scattered waves. In recent years a range of different techniques utilizing nonlinear phenomena in vibration and acoustic signals have been developed. It appears that these techniques are more sensitive to damage alterations than other techniques used for damage detection based on linear behaviour. The paper explores the use of low-profile piezoceramic actuators with low-frequency excitation in nonlinear acoustics. The method is used to detect a fatigue crack in an aluminium plate. The results are compared with modal/vibration excitation performed with an electromagnetic shaker. The study shows that piezoelectric excitation with surface-bonded low-profile piezoceramic transducers is suitable for crack detection based on nonlinear acoustics.

  4. Can Excited State Electronic Coherence Be Tuned via Molecular Structural Modification? A First-Principles Quantum Electronic Dynamics Study of Pyrazolate-Bridged Pt(II) Dimers.

    PubMed

    Lingerfelt, David B; Lestrange, Patrick J; Radler, Joseph J; Brown-Xu, Samantha E; Kim, Pyosang; Castellano, Felix N; Chen, Lin X; Li, Xiaosong

    2017-03-09

    Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a binuclear platinum complex, where a persistent periodic beating in the transient absorption signal's anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of binuclear platinum complexes exhibiting a range of interplatinum distances. Results suggest that the long-lived coherence can only result when competitive electronic couplings are in balance. At longer Pt-Pt distances, the electronic couplings between the two halves of the binuclear system weaken, and exciton localization and recombination is favored on short time scales. For short Pt-Pt distances, electronic couplings between the states in the coherent superposition are stronger than the coupling with other excitonic states, leading to long-lived coherence.

  5. Coherent and incoherent structural dynamics in laser-excited antimony

    NASA Astrophysics Data System (ADS)

    Waldecker, Lutz; Vasileiadis, Thomas; Bertoni, Roman; Ernstorfer, Ralph; Zier, Tobias; Valencia, Felipe H.; Garcia, Martin E.; Zijlstra, Eeuwe S.

    2017-02-01

    We investigate the excitation of phonons in photoexcited antimony and demonstrate that the entire electron-lattice interactions, in particular coherent and incoherent electron-phonon coupling, can be probed simultaneously. Using femtosecond electron diffraction (FED) with high temporal resolution, we observe the coherent excitation of the fully symmetric A1 g optical phonon mode via the shift of the minimum of the atomic potential energy surface. Ab initio molecular dynamics simulations on laser excited potential energy surfaces are performed to quantify the change in lattice potential and the associated real-space amplitude of the coherent atomic oscillations. Good agreement is obtained between the parameter-free calculations and the experiment. In addition, our experimental configuration allows observing the energy transfer from electrons to phonons via incoherent electron-lattice scattering events. The electron-phonon coupling is determined as a function of electronic temperature from our DFT calculations and the data by applying different models for the energy transfer.

  6. Controlling multipolar surface plasmon excitation through the azimuthal phase structure of electron vortex beams

    NASA Astrophysics Data System (ADS)

    Ugarte, Daniel; Ducati, Caterina

    2016-05-01

    We have theoretically studied how the azimuthal phase structure of an electron vortex beam excites surface plasmons on metal particles of different geometries as observed in electron energy loss spectroscopy (EELS). We have developed a semiclassical approximation combining a ring-shaped beam and the dielectric formalism. Our results indicate that for the case of total orbital angular momentum transfer, we can manipulate surface plasmon multipole excitation and even attain an enhancement factor of several orders of magnitude. Since electron vortex beams interact with particles mostly through effects due to azimuthal symmetry, i.e., in the plane perpendicular to the electron beam, anisotropy information (longitudinal and transversal) of the sample may be derived in EELS studies by comparing nonvortex and vortex beam measurements.

  7. Non-stationary random vibration analysis of structures under multiple correlated normal random excitations

    NASA Astrophysics Data System (ADS)

    Li, Yanbin; Mulani, Sameer B.; Kapania, Rakesh K.; Fei, Qingguo; Wu, Shaoqing

    2017-07-01

    An algorithm that integrates Karhunen-Loeve expansion (KLE) and the finite element method (FEM) is proposed to perform non-stationary random vibration analysis of structures under excitations, represented by multiple random processes that are correlated in both time and spatial domains. In KLE, the auto-covariance functions of random excitations are discretized using orthogonal basis functions. The KLE for multiple correlated random excitations relies on expansions in terms of correlated sets of random variables reflecting the cross-covariance of the random processes. During the response calculations, the eigenfunctions of KLE used to represent excitations are applied as forcing functions to the structure. The proposed algorithm is applied to a 2DOF system, a 2D cantilever beam and a 3D aircraft wing under both stationary and non-stationary correlated random excitations. Two methods are adopted to obtain the structural responses: a) the modal method and b) the direct method. Both the methods provide the statistics of the dynamic response with sufficient accuracy. The structural responses under the same type of correlated random excitations are bounded by the response obtained by perfectly correlated and uncorrelated random excitations. The structural response increases with a decrease in the correlation length and with an increase in the correlation magnitude. The proposed methodology can be applied for the analysis of any complex structure under any type of random excitation.

  8. Coded excitation ultrasonic needle tracking: An in vivo study

    PubMed Central

    Xia, Wenfeng; Ginsberg, Yuval; West, Simeon J.; Nikitichev, Daniil I.; Ourselin, Sebastien; David, Anna L.; Desjardins, Adrien E.

    2016-01-01

    obtained with Barker coded excitation, and they were visually absent with Golay coded excitation. The spatial tracking accuracy was unaffected by coded excitation. Conclusions Coded excitation is a viable method for improving the SNR in ultrasonic tracking without compromising spatial accuracy. This method provided SNR increases that are consistent with theoretical expectations, even in the presence of physiological motion. With the ultrasonic tracking system in this study, the SNR increases will have direct clinical implications in a broad range of interventional procedures by improving visibility of medical devices at large depths. PMID:27370125

  9. Role of free carriers excited by ultrafast Bessel beams for submicron structuring applications

    NASA Astrophysics Data System (ADS)

    Velpula, Praveen Kumar; Bhuyan, Manoj Kumar; Mauclair, Cyril; Colombier, Jean-Philippe; Stoian, Razvan

    2014-07-01

    Ultrafast Bessel beams are ideal sources for high aspect ratio submicron structuring applications because of their nondiffracting nature and higher stability in nonlinear propagation. We report here on the interaction of ultrafast Bessel beams at various laser energies and pulse durations with transparent materials (fused silica) and define their impact on photoinscription regimes, i.e., formation of positive and negative refractive index structures. The laser pulse duration was observed to be key in deciding the type of the structures via excitation efficiency. To understand the relevant mechanisms for forming these different structures, the free carrier behavior as a function of laser pulse duration and energy was studied by capturing instantaneous excitation profiles using time-resolved microscopy. Time-resolved imaging and simulation studies reveal that low carrier densities are generated for ultrashort pulses, leading to soft positive index alterations via presumably nonthermally induced structural transitions involving defects. On the other hand, the high free carrier density generation in the case of longer pulse durations leads to hydrodynamic expansion, resulting in high aspect ratio submicron-size wide voids. Delayed ionization, carrier defocusing, and lower nonlinear effects are responsible for the confinement of energy, resulting in efficient energy deposition on-axis.

  10. Electron impact excitation studies of unstable atomic species

    NASA Astrophysics Data System (ADS)

    Abdellatif, Ady Kamel

    The polarization of Balmer-alpha radiation excited in collisions of electrons with atomic hydrogen is presented for an electron energy range from threshold to 1000 eV. Measurements are in good agreement with calculations carried out using either convergent-close-coupling or R-matrix with pseudo-states approaches. Cascade is demonstrated to have a significant effect. Balmer-alpha excitation function data are also presented. A previous measurement of the polarization of Balmer-alpha following dissociative excitation of H2 by electrons is confirmed and extended. The electron impact excitation spectrum of atomic and molecular nitrogen in the VUV range (800 A--1800 A) is presented. The excitation functions of the 1135 A and the 1200 A transitions are obtained. About 5% of nitrogen molecules are dissociated using a microwave discharge source and a mixture of 95% helium and 5% nitrogen gases. Other lines proved to have too small an emission cross section for the electron impact excitation process on atomic nitrogen. Thus the 1243 A, 1494 A, 1745 A N lines and the 1085 A N+ line could not be studied using the small dissociation fractions obtained in the present work. Electron impact excitation of fluorine and sulfur atoms is presented. The spectrum of Sulfur Hexafluoride (SF6) in the VUV range from 800 A--1700 A is recorded. A 70% dissociation fraction was obtained using the microwave discharge unit with SF6 and He targets. The absolute emission cross section for the 807 A fluorine transition is found to be 2.21 +/- 1.20 x 10-19 cm 2 at 200 eV electron energy. As for sulfur, the absolute emission cross section for the 1474 A transition is 2.46 +/- 1.38 x 10-19 cm2 at 95 eV and for the 1667 A transition is 1.87 +/- 1.31 x 10-19 cm 2 at 85 eV.

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

    DOE PAGES

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

    2015-02-09

    In this study, the response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser,more » electron and ion irradiations.« less

  12. Electronic excitation induced structural and optical modifications in InGaN/GaN quantum well structures grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Prabakaran, K.; Ramesh, R.; Jayasakthi, M.; Surender, S.; Pradeep, S.; Balaji, M.; Asokan, K.; Baskar, K.

    2017-03-01

    The present study focuses on the electronic excitation induced structural and optical properties of InGaN/GaN quantum well (QW) structures grown by metal organic chemical vapor deposition technique. These excitations were produced using Au7+ ion irradiation with 100 MeV energy. The X-ray rocking curves intensity and full width at half-maximum values corresponding to the planes of (0 0 0 2) and (1 0 -1 5) of the irradiated QW structures show the modifications in the screw and edge-type dislocation densities vary with the ion fluences. The structural characteristics using the reciprocal space mapping indicate the intermixing effects in InGaN/GaN QW structures. Atomic force microscopy images confirmed the presence of nanostructures and the surface modification due to heavy ion irradiation. The irradiated QW structures exhibited degraded photoluminescence intensity and a subsequent decrease in the yellow luminescence band intensity with the fluences of 1 × 1011 and 5 × 1012 ions/cm2 compared to the pristine QW structures.

  13. Raman spectroscopic study of the Chromobacterium violaceum pigment violacein using multiwavelength excitation and DFT calculations.

    PubMed

    Jehlička, Jan; Edwards, Howell G M; Němec, Ivan; Oren, Aharon

    2015-01-01

    Violacein is a bisindole pigment occurring as a biosynthetic product of Chromobacterium violaceum and Janthinobacterium lividum. It has some structural similarities to the cyanobacterial UV-protective pigment scytonemin, which has been the subject of comprehensive spectroscopic and structural studies. A detailed experimental Raman spectroscopic study with visible and near-infrared excitation of violacein produced by C. violaceum has been undertaken and supported using theoretical DFT calculations. Raman spectra with 514 and 785 nm excitation of cultivated cells as well as extracts and Gaussian (B3LYP/6-311++G(d,p)) calculations with proposed molecular vibrational assignments are reported here.

  14. In-flight investigation of a rotating cylinder-based structural excitation system for flutter testing

    NASA Technical Reports Server (NTRS)

    Vernon, Lura

    1993-01-01

    A research excitation system was test flown at the NASA Dryden Flight Research Facility on the two-seat F-16XL aircraft. The excitation system is a wingtip-mounted vane with a rotating slotted cylinder at the trailing edge. As the cylinder rotates during flight, the flow is alternately deflected upward and downward through the slot, resulting in a periodic lift force at twice the cylinder's rotational frequency. Flight testing was conducted to determine the excitation system's effectiveness in the subsonic and transonic flight regimes. Primary research objectives were to determine the system's ability to develop adequate force levels to excite the aircraft's structure and to determine the frequency range over which the system could excite structural modes of the aircraft. The results from the exciter were compared with results from atmospheric turbulence excitation at the same flight conditions. The results from the forced excitation were of higher quality and had less variation than the results from atmospheric turbulence. The forced excitation data also invariably yielded higher structural damping values than those from the atmospheric turbulence data.

  15. In-flight investigation of a rotating cylinder-based structural excitation system for flutter testing

    NASA Technical Reports Server (NTRS)

    Vernon, Lura

    1993-01-01

    A research excitation system was test flown at the NASA Dryden Flight Research Facility on the two-seat F-16XL aircraft. The excitation system is a wingtip-mounted vane with a rotating slotted cylinder at the trailing edge. As the cylinder rotates during flight, the flow is alternately deflected upward and downward through the slot, resulting in a periodic lift force at twice the cylinder's rotational frequency. Flight testing was conducted to determine the excitation system's effectiveness in the subsonic and transonic flight regimes. Primary research objectives were to determine the system's ability to develop adequate force levels to excite the aircraft's structure and to determine the frequency range over which the system could excite structural modes of the aircraft. The results from the exciter were compared with results from atmospheric turbulence excitation at the same flight conditions. The results from the forced excitation were of higher quality and had less variation than the results from atmospheric turbulence. The forced excitation data also invariably yielded higher structural damping values than those from the atmospheric turbulence data.

  16. Effect of structural modifications on the spectroscopic properties and dynamics of the excited states of peridinin

    PubMed Central

    Chatterjee, Nirmalya; Niedzwiedzki, Dariusz M.; Aoki, Kazuyoshi; Kajikawa, Takayuki; Katsumura, Shigeo; Hashimoto, Hideki; Frank, Harry A.

    2013-01-01

    The spectroscopic properties and dynamics of the lowest excited singlet states of peridinin and two derivatives have been studied by steady-state absorption and fast-transient optical spectroscopic techniques. One derivative denoted PerOlEs, possesses a double bond and a methyl ester group instead of the r-ylid-enebutenolide of peridinin. Another derivative denoted PerAcEs, is the biosynthetic precursor of peridinin and possesses a triple bond and a methyl ester group corresponding to the r-ylidenbutenolide function. Ultrafast time-resolved spectroscopic experiments in the visible and near-infrared regions were performed on the molecules and reveal the energies and regarding the structural features and interactions responsible for the unusual solvent-induced changes in the steady-state and transient absorption spectra and dynamics of dynamics of the excited electronic states. The data also provide information peridinin. PMID:19000898

  17. Photodissociation of FONO: an excited state nonadiabatic dynamics study.

    PubMed

    Hilal, Allaa R; Hilal, Rifaat

    2017-03-01

    The photo dissociation of nitrosyl fluorite, FONO, a potential source of atmospheric fluorine, underlies its active role in ozone depletion and other activities in the troposphere. In the present work, the electronic structure of FONO is revisited at high level of ab initio and density functional theory (DFT) theoretical levels. Several different post SCF methods were used to compute excited states, vertical excitation energies and intensities, namely configuration interaction with single excitations (CIS), equation of motion coupled cluster with single and double excitations (EOM-CCSD), and symmetry adopted cluster configuration interaction (SAC-CI) methods. The potential energy functions along two internal coordinates, namely the F-ONO bond and the FONO dihedral angle, have been computed on the ground state relaxed potential energy surface (PES) for the ground, 5A' and 5A″ excited states using the EOM-CCSD method. In the gas phase, the decay of the excited states of FONO was examined closely by calculating the UV photoabsorption cross-section spectrum and by nonadiabatic dynamics simulations. Nonadiabatic dynamics were simulated by sampling 300 trajectories in two spectral windows at 3.0 ± 0.25 and 4.5 ± 0.25 eV using the surface hopping method. Two different photodissociation reaction pathways with two main products, including multifragmentation (FO+NO) and atomic elimination (F) mechanisms were identified. For the cis-isomer, the main photochemical channel is F+NO2, representing 67% of all processes. For the trans-isomer, however, the main dissociation pathway is (FO+NO). Graphical Abstract Photodisscociation of nitrosyl fluorite (FONO) seems to underlie its active role in ozone depletion and other activities in the troposphere. The present research revisits the electronic structure of FONO at high level of ab initio and DFT theoretical levels. Cis-trans isomerization and dissociation in the ground and low lying excited states were examined

  18. Live-cell visualization of excitation energy dynamics in chloroplast thylakoid structures

    PubMed Central

    Iwai, Masakazu; Yokono, Makio; Kurokawa, Kazuo; Ichihara, Akira; Nakano, Akihiko

    2016-01-01

    The intricate molecular processes underlying photosynthesis have long been studied using various analytic approaches. However, the three-dimensional (3D) dynamics of such photosynthetic processes remain unexplored due to technological limitations related to investigating intraorganellar mechanisms in vivo. By developing a system for high-speed 3D laser scanning confocal microscopy combined with high-sensitivity multiple-channel detection, we visualized excitation energy dynamics in thylakoid structures within chloroplasts of live Physcomitrella patens cells. Two distinct thylakoid structures in the chloroplast, namely the grana and stroma lamellae, were visualized three-dimensionally in live cells. The simultaneous detection of the shorter (than ~670 nm) and longer (than ~680 nm) wavelength regions of chlorophyll (Chl) fluorescence reveals different spatial characteristics—irregular and vertical structures, respectively. Spectroscopic analyses showed that the shorter and longer wavelength regions of Chl fluorescence are affected more by free light-harvesting antenna proteins and photosystem II supercomplexes, respectively. The high-speed 3D time-lapse imaging of the shorter and longer wavelength regions also reveals different structural dynamics—rapid and slow movements within 1.5 seconds, respectively. Such structural dynamics of the two wavelength regions of Chl fluorescence would indicate excitation energy dynamics between light-harvesting antenna proteins and photosystems, reflecting the energetically active nature of photosynthetic proteins in thylakoid membranes. PMID:27416900

  19. Skirting terahertz waves in a photo-excited nanoslit structure

    SciTech Connect

    Shalaby, Mostafa E-mail: thomas.feurer@iap.unibe.ch; Fabiańska, Justyna; Feurer, Thomas E-mail: thomas.feurer@iap.unibe.ch; Peccianti, Marco; Ozturk, Yavuz; Vidal, Francois; Morandotti, Roberto; Sigg, Hans

    2014-04-28

    Terahertz fields can be dramatically enhanced as they propagate through nanometer-sized slits. The enhancement is mediated by a significant accumulation of the induced surface charges on the surrounding metal. This enhancement is shown here to be dynamically modulated while the nanoslits are gradually shunted using a copropagating optical beam. The terahertz fields are found to skirt the nanoscale photo-excited region underneath the slits, scattering to the far field and rigorously mapping the near field.

  20. Application of time-series-based damage detection algorithms to structures under ambient excitations

    NASA Astrophysics Data System (ADS)

    Loh, Chin-Hsiung; Chan, Chuan-Kai; Lee, Chung-Hsien

    2016-04-01

    Operational modal analysis (OMA) is to extract the dynamic characteristics of structures based on vibration responses of structures without considering the excitation measurement. In this study both modal-based and signal-based system identification and feature extraction techniques are used to study the nonlinear inelastic response of a test structure ( a 3- story steel frame subjected to a series of earthquake and white noise excitations back to back) using both input and output response data or output only measurement and identify the damage location. For the modal-based identification, the multi-variant autoregressive model (MV-AR model) is used to identify the dynamic characteristics of structure. The MV-AR model parameters are then used to develop the vectors of autoregressive model and Mahalanobis distance, and then to identify the damage features and locate the damage. From the signal-based feature identification two damage features will be discussed: (1) the enhancement of time-frequency analysis of acceleration responses, and (2) WPT based energy damage indices. Discussion on the correlation of the extract local damage features from measurements with the global damage indices, such as null-space and subspace damage indices, is also made.

  1. Electromagnetic response of buried cylindrical structures for line current excitation

    NASA Astrophysics Data System (ADS)

    Pajewski, Lara; Ponti, Cristina

    2013-04-01

    arbitrary arrangements of cylinders in the soil. As future work, the presented analysis, carried out in the spectral domain, will be extended to a time-domain solution following an approach analogous to the one developed in [6] for pulsed plane-wave excitation. [1] M. Di Vico, F. Frezza, L. Pajewski, and G. Schettini, "Scattering by a Finite Set of Perfectly Conducting Cylinders Buried in a Dielectric Half-Space: a Spectral-Domain Solution," IEEE Transactions Antennas and Propagation, vol. 53(2), 719-727, 2005. [2] M. Di Vico, F. Frezza, L. Pajewski, and G. Schettini, "Scattering by Buried Dielectric Cylindrical Structures," Radio Science, vol. 40(6), RS6S18, 2005. [3] F. Frezza, L. Pajewski, C. Ponti, and G. Schettini, "Scattering by Perfectly-Conducting Cylinders Buried in a Dielectric Slab through the Cylindrical Wave Approach," IEEE Transactions Antennas and Propagation, vol. 57(4), 1208-1217, 2009. [4] F. Frezza, L. Pajewski, C. Ponti, and G. Schettini, "Accurate Wire-Grid Modeling of Buried Conducting Cylindrical Scatterers," Nondestructive Testing and Evaluation (Special Issue on "Civil Engineering Applications of Ground Penetrating Radar"), vol. 27(3), pp. 199-207, 2012. [5] F. Frezza, L. Pajewski, C. Ponti, G. Schettini, and N. Tedeschi, "Electromagnetic Scattering by a Metallic Cylinder Buried in a Lossy Medium with the Cylindrical Wave Approach," IEEE Geoscience and Remote Sensing Letters, vol. 10(1), pp. 179-183, 2013. [6] F. Frezza, P. Martinelli, L. Pajewski, and G. Schettini, "Short-Pulse Electromagnetic Scattering from Buried Perfectly-Conducting Cylinders," IEEE Geoscience and Remote Sensing Letters, vol. 4(4), pp. 611-615, 2007.

  2. The Fundamental Structure and the Reproduction of Spiral Wave in a Two-Dimensional Excitable Lattice.

    PubMed

    Qian, Yu; Zhang, Zhaoyang

    2016-01-01

    In this paper we have systematically investigated the fundamental structure and the reproduction of spiral wave in a two-dimensional excitable lattice. A periodically rotating spiral wave is introduced as the model to reproduce spiral wave artificially. Interestingly, by using the dominant phase-advanced driving analysis method, the fundamental structure containing the loop structure and the wave propagation paths has been revealed, which can expose the periodically rotating orbit of spiral tip and the charity of spiral wave clearly. Furthermore, the fundamental structure is utilized as the core for artificial spiral wave. Additionally, the appropriate parameter region, in which the artificial spiral wave can be reproduced, is studied. Finally, we discuss the robustness of artificial spiral wave to defects.

  3. The Fundamental Structure and the Reproduction of Spiral Wave in a Two-Dimensional Excitable Lattice

    PubMed Central

    Qian, Yu; Zhang, Zhaoyang

    2016-01-01

    In this paper we have systematically investigated the fundamental structure and the reproduction of spiral wave in a two-dimensional excitable lattice. A periodically rotating spiral wave is introduced as the model to reproduce spiral wave artificially. Interestingly, by using the dominant phase-advanced driving analysis method, the fundamental structure containing the loop structure and the wave propagation paths has been revealed, which can expose the periodically rotating orbit of spiral tip and the charity of spiral wave clearly. Furthermore, the fundamental structure is utilized as the core for artificial spiral wave. Additionally, the appropriate parameter region, in which the artificial spiral wave can be reproduced, is studied. Finally, we discuss the robustness of artificial spiral wave to defects. PMID:26900841

  4. Structural damage detection based on covariance of covariance matrix with general white noise excitation

    NASA Astrophysics Data System (ADS)

    Hui, Yi; Law, Siu Seong; Ku, Chiu Jen

    2017-02-01

    Covariance of the auto/cross-covariance matrix based method is studied for the damage identification of a structure with illustrations on its advantages and limitations. The original method is extended for structures under direct white noise excitations. The auto/cross-covariance function of the measured acceleration and its corresponding derivatives are formulated analytically, and the method is modified in two new strategies to enable successful identification with much fewer sensors. Numerical examples are adopted to illustrate the improved method, and the effects of sampling frequency and sampling duration are discussed. Results show that the covariance of covariance calculated from responses of higher order modes of a structure play an important role to the accurate identification of local damage in a structure.

  5. Magnetic structure and spin excitations in BaMn2Bi2

    DOE PAGES

    Calder, Stuart A.; Saparov, Bayrammurad I; Cao, H. B.; ...

    2014-02-19

    We present a single crystal neutron scattering study of BaMn2Bi2, a recently synthesized material with the same ThCr2Si2type structure found in several Fe-based unconventional superconducting materials. We show long range magnetic order, in the form of a G-type antiferromagnetic structure, to exist up to 390 K with an indication of a structural transition at 100 K. Utilizing inelastic neutron scattering we observe a spin-gap of 16 meV, with spin-waves extending up to 55 meV. We find these magnetic excitations are well fit to a J1-J2-Jc Heisenberg model and present values for the exchange interactions. The spin wave spectrum appears tomore » be unchanged by the 100 K structural phase transition.« less

  6. Exclusive studies of the GDR in excited nuclei.

    SciTech Connect

    Nanal, V.

    1998-09-07

    The GDR in {sup 164}Er at 62 MeV excitation energy has been studied in coincidence with the evaporation residues, selected using the Argonne fragment mass analyzer (FMA). The {sup 164}Er* has a prolate shape with deformation statistical model fit to the data indicate that similar to the ground state.

  7. A vibration isolation system in low frequency excitation region using negative stiffness structure for vehicle seat

    NASA Astrophysics Data System (ADS)

    Le, Thanh Danh; Ahn, Kyoung Kwan

    2011-12-01

    This paper designs and fabricates a vibration isolation model for improving vibration isolation effectiveness of the vehicle seat under low excitation frequencies. The feature of the proposed system is to use two symmetric negative stiffness structures (NSS) in parallel to a positive stiffness structure. Here, theoretical analysis of the proposed system is clearly presented. Then, the design procedure is derived so that the resonance peak of frequency-response curve drifts to the left, the load support capacity of the system is maintained, the total size of the system is reduced for easy practical application and especially, the bending of the frequency-response curve is minimized. Next the dynamic equation of the proposed system is set up. Then, the harmonic balance (HB) method is employed to seek the characteristic of the motion transmissibility of the proposed system at the steady state for each of the excitation frequency. From this characteristic, the curves of the motion transmission are predicted according to the various values of the configurative parameters of the system. Then, the time responses to the sinusoidal, multi frequency and random excitations are also investigated by simulation and experiment. In addition, the isolation performance comparison between the system with NSS and system without NSS is realized. The simulation results reveal that the proposed system has larger frequency region of isolation than that of the system without NSS. The experimental results confirm also that with a random excitation mainly spreading from 0.1 to 10 Hz, the isolation performance of the system with NSS is greatly improved, where the RMS values of the mass displacement may be reduced to 67.2%, whereas the isolation performance of the system without NSS is bad. Besides, the stability of the steady-state response is also studied. Finally, some conclusions are given.

  8. Development of collective structures over noncollective excitations in 139Nd

    NASA Astrophysics Data System (ADS)

    Bhowal, S.; Gangopadhyay, G.; Petrache, C. M.; Ragnarsson, I.; Singh, A. K.; Bhattacharya, S.; Hübel, H.; Neußer-Neffgen, A.; Al-Khatib, A.; Bringel, P.; Bürger, A.; Nenoff, N.; Schönwaßer, G.; Hagemann, G. B.; Herskind, B.; Jensen, D. R.; Sletten, G.; Fallon, P.; Görgen, A.; Bednarczyk, P.; Curien, D.; Korichi, A.; Lopez-Martens, A.; Rao, B. V. T.; Reddy, T. S.; Singh, Nirmal

    2011-08-01

    High-spin states in 139Nd were investigated using the reaction 96Zr(48Ca,5n) at a beam energy of 195 MeV and γ-ray coincidences were acquired with the Euroball spectrometer. Apart from several dipole bands at medium excitation energy, three quadrupole bands have been observed at high spin. Linking transitions connecting two of the high-spin bands to low-energy states have been observed. Calculations based on the cranked-Nilsson-Strutinsky formalism have been used to assign configurations for the high-spin quadrupole bands.

  9. Lifetimes and structure of excited states of 115Sb

    NASA Astrophysics Data System (ADS)

    Lobach, Yu. N.; Bucurescu, D.

    1998-06-01

    Lifetimes of excited states of 115Sb were measured by the Doppler shift attenuation method in the (α,2nγ) reaction at Eα = 27.2 MeV. The experimental level scheme and the electromagnetic transition probabilities have been interpreted in terms of the interacting boson-fermion model. A reasonable agreement with the experiment was obtained for the positive-parity states. The experimental data also show the applicability of the cluster-vibrational model for the mixing of two 9/2+ states having different intrinsic configurations.

  10. Omnidirectional excitation of sidewall gap-plasmons in a hybrid gold-nanoparticle/aluminum-nanopore structure

    NASA Astrophysics Data System (ADS)

    Lumdee, Chatdanai; Kik, Pieter G.

    2016-06-01

    The gap-plasmon resonance of a gold nanoparticle inside a nanopore in an aluminum film is investigated in polarization dependent single particle microscopy and spectroscopy. Scattering and transmission measurements reveal that gap-plasmons of this structure can be excited and observed under normal incidence excitation and collection, in contrast to the more common particle-on-a-mirror structure. Correlation of numerical simulations with optical spectroscopy suggests that a local electric field enhancement factor in excess of 50 is achieved under normal incidence excitation, with a hot-spot located near the top surface of the structure. It is shown that the strong field enhancement from this sidewall gap-plasmon mode can be efficiently excited over a broad angular range. The presented plasmonic structure lends itself to implementation in low-cost, chemically stable, easily addressable biochemical sensor arrays providing large optical field enhancement factors.

  11. Strong steric hindrance effect on excited state structural dynamics of Cu(I) diimine complexes.

    PubMed

    Gothard, Nosheen A; Mara, Michael W; Huang, Jier; Szarko, Jodi M; Rolczynski, Brian; Lockard, Jenny V; Chen, Lin X

    2012-03-08

    The metal-to-ligand-charge-transfer (MLCT) excited state of Cu(I) diimine complexes is known to undergo structural reorganization, transforming from a pseudotetrahedral D(2d) symmetry in the ground state to a flattened D(2) symmetry in the MLCT state, which allows ligation with a solvent molecule, forming an exciplex intermediate. Therefore, the structural factors that influence the coordination geometry change and the solvent accessibility to the copper center in the MLCT state could be used to control the excited state properties. In this study, we investigated an extreme case of the steric hindrance caused by attaching bulky tert-butyl groups in bis(2,9-di-tert-butyl-1,10-phenanthroline)copper(I), [Cu(I)(dtbp)(2)](+). The two bulky tert-butyl groups on the dtbp ligand lock the MLCT state into the pseudotetrahedral coordination geometry and completely block the solvent access to the copper center in the MLCT state of [Cu(I)(dtbp)(2)](+). Using ultrafast transient absorption spectroscopy and time-resolved emission spectroscopy, we investigated the MLCT state property changes due to the steric hindrance and demonstrated that [Cu(I)(dtbp)(2)](+) exhibited a long-lived emission but no subpicosecond component that was previously assigned as the flattening of the pseudotetrahedral coordination geometry. This suggests the retention of its pseudotetrahedral D(2d) symmetry and the blockage of the solvent accessibility. We made a comparison between the excited state dynamics of [Cu(I)(dtbp)(2)](+) with its mono-tert-butyl counterpart, bis(2-tert-butyl-1,10-phenanthroline)copper(I) [Cu(I)(tbp)(2)](+). The subpicosecond component assigned to the flattening of the D(2d) coordination geometry in the MLCT excited state was again present in the latter because the absence of a tert-butyl on the phenanthroline allows flattening to the pseudotetrahedral coordination geometry. Unlike the [Cu(I)(dtbp)(2)](+), [Cu(I)(tbp)(2)](+) exhibited no detectable emission at room temperature in

  12. Spectrum and Structure of Excited Baryons with CLAS

    NASA Astrophysics Data System (ADS)

    Burkert, Volker D.

    2017-01-01

    In this contribution I discuss recent results in light quark baryon spectroscopy involving CLAS data and higher level analysis results from the partial wave analysis by the Bonn-Gatchina group. New baryon states were discovered largely based on the open strangeness production channels γp → K+Λ and γp → K+Σ0. The data illustrate the great potential of the kaon-hyperon channel in the discovery of higher mass baryon resonances in s-channel production. Other channels with discovery potential, such as γp → pω and γp → ϕp are also discussed. In the second part I will demonstrate on data the sensitivity of meson electroproduction to expose the active degrees of freedom underlying resonance transitions as a function of the probed distance scale. For several of the prominent excited states in the lower mass range the short distance behavior is described by a core of three dressed-quarks with running quark mass, and meson-baryon contributions make up significant parts of the excitation strength at large distances. Finally, I give an outlook of baryon resonance physics at the 12 GeV CEBAF electron accelerator. Talk presented at the CRC-16 Symposium, Bonn University, June 6-9, 2016.

  13. Analysis of structure optimal control under earthquake excitation using Pseudospectral Legendre method

    NASA Astrophysics Data System (ADS)

    Tsai, H. C.

    2015-12-01

    This research formulates a structure optimal control problem with earthquake excitation. In the paper, the Pseudospectral Legendre method is used to solve the optimal control problem. The method discretizes objective function and constrains by Legendre-Gauss-Lobatto points in the range. Then objective integral function and differential constrains are approximated by Legendre interpolating functions. The results present optimal control force to reduce the structural response under earthquake excitation

  14. Radial structures and nonlinear excitation of geodesic acoustic modes

    NASA Astrophysics Data System (ADS)

    Zonca, F.; Chen, L.

    2008-08-01

    Geodesic acoustic modes (GAM) are shown to constitute a continuous spectrum due to radial inhomogeneities. The importance and theoretical as well as experimental implications of this fact are discussed in this work. The existence of a singular layer causes GAM to mode convert to short-wavelength kinetic GAM (KGAM) via finite ion Larmor radii; analogous to kinetic Alfvén waves (KAW). Furthermore, it is shown that KGAM can be nonlinearly excited by drift-wave (DW) turbulence via 3-wave parametric interactions, and the resultant driven-dissipative nonlinear system exhibits typical prey-predator self-regulatory dynamics, consistent with recent experimental observations on HL-2A. The degeneracy of GAM/KGAM with beta-induced Alfvén eigenmodes (BAE) is demonstrated and discussed, with emphasis on its important role in the complex self-organized behaviors of burning plasmas.

  15. Ultrafast modulation of electronic structure by coherent phonon excitations

    NASA Astrophysics Data System (ADS)

    Weisshaupt, J.; Rouzée, A.; Woerner, M.; Vrakking, M. J. J.; Elsaesser, T.; Shirley, E. L.; Borgschulte, A.

    2017-02-01

    Femtosecond x-ray absorption spectroscopy with a laser-driven high-harmonic source is used to map ultrafast changes of x-ray absorption by femtometer-scale coherent phonon displacements. In LiBH4, displacements along an Ag phonon mode at 10 THz are induced by impulsive Raman excitation and give rise to oscillatory changes of x-ray absorption at the Li K edge. Electron density maps from femtosecond x-ray diffraction data show that the electric field of the pump pulse induces a charge transfer from the BH4- to neighboring Li+ ions, resulting in a differential Coulomb force that drives lattice vibrations in this virtual transition state.

  16. Coded excitation for diverging wave cardiac imaging: a feasibility study

    NASA Astrophysics Data System (ADS)

    Zhao, Feifei; Tong, Ling; He, Qiong; Luo, Jianwen

    2017-02-01

    Diverging wave (DW) based cardiac imaging has gained increasing interest in recent years given its capacity to achieve ultrahigh frame rate. However, the signal-to-noise ratio (SNR), contrast, and penetration depth of the resulting B-mode images are typically low as DWs spread energy over a large region. Coded excitation is known to be capable of increasing the SNR and penetration for ultrasound imaging. The aim of this study was therefore to test the feasibility of applying coded excitation in DW imaging to improve the corresponding SNR, contrast and penetration depth. To this end, two types of codes, i.e. a linear frequency modulated chirp code and a set of complementary Golay codes were tested in three different DW imaging schemes, i.e. 1 angle DW transmit without compounding, 3 and 5 angles DW transmits with coherent compounding. The performances (SNR, contrast ratio (CR), contrast-to-noise ratio (CNR), and penetration) of different imaging schemes were investigated by means of simulations and in vitro experiments. As for benchmark, corresponding DW imaging schemes with regular pulsed excitation as well as the conventional focused imaging scheme were also included. The results showed that the SNR was improved by about 10 dB using coded excitation while the penetration depth was increased by 2.5 cm and 1.8 cm using chirp code and Golay codes, respectively. The CNR and CR gains varied with the depth for different DW schemes using coded excitations. Specifically, for non-compounded DW imaging schemes, the gain in the CR was about 5 dB and 3 dB while the gain in the CNR was about 4.5 dB and 3.5 dB at larger depths using chirp code and Golay codes, respectively. For compounded imaging schemes, using coded excitation, the gain in the penetration and contrast were relatively smaller compared to non-compounded ones. Overall, these findings indicated the feasibility of coded excitation in improving the image quality of DW imaging. Preliminary in vivo cardiac images

  17. Damage detection and quantification in a structural model under seismic excitation using time-frequency analysis

    NASA Astrophysics Data System (ADS)

    Chan, Chun-Kai; Loh, Chin-Hsiung; Wu, Tzu-Hsiu

    2015-04-01

    In civil engineering, health monitoring and damage detection are typically carry out by using a large amount of sensors. Typically, most methods require global measurements to extract the properties of the structure. However, some sensors, like LVDT, cannot be used due to in situ limitation so that the global deformation remains unknown. An experiment is used to demonstrate the proposed algorithms: a one-story 2-bay reinforce concrete frame under weak and strong seismic excitation. In this paper signal processing techniques and nonlinear identification are used and applied to the response measurements of seismic response of reinforced concrete structures subject to different level of earthquake excitations. Both modal-based and signal-based system identification and feature extraction techniques are used to study the nonlinear inelastic response of RC frame using both input and output response data or output only measurement. From the signal-based damage identification method, which include the enhancement of time-frequency analysis of acceleration responses and the estimation of permanent deformation using directly from acceleration response data. Finally, local deformation measurement from dense optical tractor is also use to quantify the damage of the RC frame structure.

  18. The Impact of Structural Heterogeneity on Excitation-Inhibition Balance in Cortical Networks.

    PubMed

    Landau, Itamar D; Egger, Robert; Dercksen, Vincent J; Oberlaender, Marcel; Sompolinsky, Haim

    2016-12-07

    Models of cortical dynamics often assume a homogeneous connectivity structure. However, we show that heterogeneous input connectivity can prevent the dynamic balance between excitation and inhibition, a hallmark of cortical dynamics, and yield unrealistically sparse and temporally regular firing. Anatomically based estimates of the connectivity of layer 4 (L4) rat barrel cortex and numerical simulations of this circuit indicate that the local network possesses substantial heterogeneity in input connectivity, sufficient to disrupt excitation-inhibition balance. We show that homeostatic plasticity in inhibitory synapses can align the functional connectivity to compensate for structural heterogeneity. Alternatively, spike-frequency adaptation can give rise to a novel state in which local firing rates adjust dynamically so that adaptation currents and synaptic inputs are balanced. This theory is supported by simulations of L4 barrel cortex during spontaneous and stimulus-evoked conditions. Our study shows how synaptic and cellular mechanisms yield fluctuation-driven dynamics despite structural heterogeneity in cortical circuits. Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.

  19. Excitation energy-dependent nature of Raman scattering spectrum in GaInNAs/GaAs quantum well structures.

    PubMed

    Erol, Ayse; Akalin, Elif; Sarcan, Fahrettin; Donmez, Omer; Akyuz, Sevim; Arikan, Cetin M; Puustinen, Janne; Guina, Mircea

    2012-11-28

    The excitation energy-dependent nature of Raman scattering spectrum, vibration, electronic or both, has been studied using different excitation sources on as-grown and annealed n- and p-type modulation-doped Ga1 - xInxNyAs1 - y/GaAs quantum well structures. The samples were grown by molecular beam technique with different N concentrations (y = 0%, 0.9%, 1.2%, 1.7%) at the same In concentration of 32%. Micro-Raman measurements have been carried out using 532 and 758 nm lines of diode lasers, and the 1064 nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements. Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak. In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples. Line shapes of the Raman scattering spectrum with the 785 and 1064 nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements. On the other hand, Raman scattering spectrum with the 532 nm line has exhibited only vibrational modes. As a complementary tool of Raman scattering measurements with the excitation source of 532 nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out. The results exhibited that the nature of the Raman scattering spectrum is strongly excitation energy-dependent, and with suitable excitation energy, electronic and/or vibrational transitions can be investigated.

  20. Motor Cortex Excitability and BDNF Levels in Chronic Musculoskeletal Pain According to Structural Pathology.

    PubMed

    Caumo, Wolnei; Deitos, Alícia; Carvalho, Sandra; Leite, Jorge; Carvalho, Fabiana; Dussán-Sarria, Jairo Alberto; Lopes Tarragó, Maria da Graça; Souza, Andressa; Torres, Iraci Lucena da Silva; Fregni, Felipe

    2016-01-01

    The central sensitization syndrome (CSS) encompasses disorders with overlapping symptoms in a structural pathology spectrum ranging from persistent nociception [e.g., osteoarthritis (OA)] to an absence of tissue injuries such as the one presented in fibromyalgia (FM) and myofascial pain syndrome (MPS). First, we hypothesized that these syndromes present differences in their cortical excitability parameters assessed by transcranial magnetic stimulation (TMS), namely motor evoked potential (MEP), cortical silent period (CSP), short intracortical inhibition (SICI) and short intracortical facilitation (SICF). Second, considering that the presence of tissue injury could be detected by serum neurotrophins, we hypothesized that the spectrum of structural pathology (i.e., from persistent nociception like in OA, to the absence of tissue injury like in FM and MPS), could be detected by differential efficiency of their descending pain inhibitory system, as assessed by the conditioned pain modulation (CPM) paradigm. Third, we explored whether brain-derived neurotrophic factor (BDNF) had an influence on the relationship between motor cortex excitability and structural pathology. This cross-sectional study pooled baseline data from three randomized clinical trials. We included females (n = 114), aged 19-65 years old with disability by chronic pain syndromes (CPS): FM (n = 19), MPS (n = 54), OA (n = 27) and healthy subjects (n = 14). We assessed the serum BDNF, the motor cortex excitability by parameters the TMS measures and the change on numerical pain scale [NPS (0-10)] during CPM-task. The adjusted mean (SD) on the SICI observed in the absence of tissue injury was 56.36% lower than with persistent nociceptive input [0.31(0.18) vs. 0.55 (0.32)], respectively. The BDNF was inversely correlated with the SICI and with the change on NPS (0-10)during CPM-task. These findings suggest greater disinhibition in the motor cortex and the descending pain inhibitory system in FM and MPS

  1. Motor Cortex Excitability and BDNF Levels in Chronic Musculoskeletal Pain According to Structural Pathology

    PubMed Central

    Caumo, Wolnei; Deitos, Alícia; Carvalho, Sandra; Leite, Jorge; Carvalho, Fabiana; Dussán-Sarria, Jairo Alberto; Lopes Tarragó, Maria da Graça; Souza, Andressa; Torres, Iraci Lucena da Silva; Fregni, Felipe

    2016-01-01

    The central sensitization syndrome (CSS) encompasses disorders with overlapping symptoms in a structural pathology spectrum ranging from persistent nociception [e.g., osteoarthritis (OA)] to an absence of tissue injuries such as the one presented in fibromyalgia (FM) and myofascial pain syndrome (MPS). First, we hypothesized that these syndromes present differences in their cortical excitability parameters assessed by transcranial magnetic stimulation (TMS), namely motor evoked potential (MEP), cortical silent period (CSP), short intracortical inhibition (SICI) and short intracortical facilitation (SICF). Second, considering that the presence of tissue injury could be detected by serum neurotrophins, we hypothesized that the spectrum of structural pathology (i.e., from persistent nociception like in OA, to the absence of tissue injury like in FM and MPS), could be detected by differential efficiency of their descending pain inhibitory system, as assessed by the conditioned pain modulation (CPM) paradigm. Third, we explored whether brain-derived neurotrophic factor (BDNF) had an influence on the relationship between motor cortex excitability and structural pathology. This cross-sectional study pooled baseline data from three randomized clinical trials. We included females (n = 114), aged 19–65 years old with disability by chronic pain syndromes (CPS): FM (n = 19), MPS (n = 54), OA (n = 27) and healthy subjects (n = 14). We assessed the serum BDNF, the motor cortex excitability by parameters the TMS measures and the change on numerical pain scale [NPS (0–10)] during CPM-task. The adjusted mean (SD) on the SICI observed in the absence of tissue injury was 56.36% lower than with persistent nociceptive input [0.31(0.18) vs. 0.55 (0.32)], respectively. The BDNF was inversely correlated with the SICI and with the change on NPS (0–10)during CPM-task. These findings suggest greater disinhibition in the motor cortex and the descending pain inhibitory system in FM and

  2. Theoretical Studies of Excited State Dynamics in Semiconductor Materials

    NASA Astrophysics Data System (ADS)

    Liu, Jin

    The motivation of this research work is to investigate excited state dynamics of semiconductor systems using quantum computational techniques. The detailed ultrafast photoinduced processes, such as charge recombination, charge relaxation, energy/charge transfer, etc., sometimes cannot be fully addressed by spectroscopy experiments. The nonadiabatic molecular dynamics (NAMD), on the other hand, provides critical insights into the complex processes. In this thesis, we apply the NAMD simulation method to various semiconductor systems, ranging from bulk crystals, nanoparticles to clusters, to study the electronic and optical properties of semiconductors. The first chapter outlines important concepts in excited states dynamics and semiconductor disciplinary. The second chapter explains the theoretical methodology related to the research work, including approximations, computational methods and simulation details, etc. Starting from chapter three to chapter six, we present a comprehensive study focusing on silicon clusters, cadmium selenide quantum dots, cycloparaphenylenes and perovskites. Potential applications include solar harvesting, photoluminescence, energy transfer, etc.

  3. Fine structure zonal flow excitation by beta-induced Alfvén eigenmode

    NASA Astrophysics Data System (ADS)

    Qiu, Zhiyong; Chen, Liu; Zonca, Fulvio

    2016-10-01

    Nonlinear excitation of low frequency zonal structure (LFZS) by beta-induced Alfvén eigenmode (BAE) is investigated using nonlinear gyrokinetic theory. It is found that electrostatic zonal flow (ZF), rather than zonal current, is preferentially excited by finite amplitude BAE. In addition to the well-known meso-scale radial envelope structure, ZF is also found to exhibit fine radial structure due to the localization of BAE with respect to mode rational surfaces. Specifically, the zonal electric field has an even mode structure at the rational surface where radial envelope peaks.

  4. Structural-acoustic optimization of structures excited by turbulent boundary layer flow

    NASA Astrophysics Data System (ADS)

    Shepherd, Micah R.

    In order to reduce noise radiation of aircraft or marine panels, a general structural-acoustic optimization technique is presented. To compute the structural-acoustic response, a modal approach based on finite element / boundary element analysis is used which can easily incorporate fluid loading, added structures and static pre-loads. Simple deterministic or complex random forcing functions are included in the analysis by transforming their cross-spectral density matrices to modal space. Particular emphasis is placed in this dissertation on structures excited by the fluctuating pressures due to turbulent boundary layer (TBL) flow. An efficient frequency-spacing is also used to minimize evaluation time but ensure accuracy. The response from the structural-acoustic analysis is coupled to an evolutionary strategy with covariance matrix adaptation (CMA-ES) to find the best design for low noise and weight. CMA-ES, a stochastic optimizer with robust search properties, samples candidate solutions from a multi-variate normal distribution and adapts the covariance matrix to favor good solutions. The optimization procedure is validated by minimizing the sound radiated by a point-driven ribbed panel and comparing the optimization results to an exhaustive search of the design space. Structural-acoustic optimization is then performed on a curved marine panel with heavy fluid loading excited by slow TBL flow. A weighted combination of noise radiation and mass are minimized by changing the thickness of strips and patches of elements. An uncorrelated pressure approximation is used to estimate the modal force due to TBL flow thus reducing the evaluation time required to compute the objective function. The results show that the best noise reduction is achieved by minimizing the modal acceptance of energy by the panel. This is equivalent to pushing the structural modes away from the peak frequency range of the forcing function. Additionally, the Pareto trade-off curve between total

  5. Spatial-dependent resonance mode and frequency of rotationally periodic structures subjected to standing wave excitation

    NASA Astrophysics Data System (ADS)

    Zhang, Dongsheng; Wang, Shiyu

    2017-09-01

    This work examines the distinct resonance vibration of rotationally periodic structures. An analytical model of a sample stepped-plate structure subjected to standing wave excitation is developed by elasticity theory. Spatial-dependent resonance mode and resonance frequency are formulated by perturbation-superposition method. Different from the natural mode and natural frequency, a sinusoidal fluctuation of the resonance frequency is identified between the two split natural frequencies for single standing wave excitation. The resonance mode does not have preferred orientation because it is determined by excitation orientation. The resonance behaviors are different from those near the repeated natural frequencies. The response to a standing wave pair is also calculated and compared with that to the mathematically equivalent traveling wave, where significant difference is identified. The results indicate that purer traveling wave can be created by using a standing wave pair with pre-selected spatial phase and excitation frequency. Reverse traveling direction can be realized by altering excitation frequency. A test rig is designed and fabricated for verification purpose. The experiment validates that the response near the split natural frequencies is in phase with the external standing wave excitation. The resonance frequency varies with the excitation orientation for the split natural frequencies but it remains constant for the repeated natural frequencies. Potential applications of the spatial-dependent resonance mode and frequency are presented.

  6. Vertical excitation profile in diffusion injected multi-quantum well light emitting diode structure

    NASA Astrophysics Data System (ADS)

    Riuttanen, L.; Kivisaari, P.; Svensk, O.; Vasara, T.; Myllys, P.; Oksanen, J.; Suihkonen, S.

    2015-03-01

    Due to their potential to improve the performance of light-emitting diodes (LEDs), novel device structures based on nanowires, surface plasmons, and large-area high-power devices have received increasing amount of interest. These structures are almost exclusively based on the double hetero junction (DHJ) structure, that has remained essentially unchanged for decades. In this work we study a III-nitride diffusion injected light-emitting diode (DILED), in which the active region is located outside the pn-junction and the excitation of the active region is based on bipolar diffusion of charge carriers. This unorthodox approach removes the need of placing the active region in the conventional current path and thus enabling carrier injection in device structures, which would be challenging to realize with the conventional DHJ design. The structure studied in this work is has 3 indium gallium nitride / gallium nitride (InGaN/GaN) quantum wells (QWs) under a GaN pn-junction. The QWs are grown at diferent growth temperatures for obtaining distinctive luminescence peaks. This allows to obtain knowledge on the carrier diffusion in the structure. When the device is biased, all QWs emit light indicating a significant diffusion current into the QW stack.

  7. Perfect optical vortex enhanced surface plasmon excitation for plasmonic structured illumination microscopy imaging

    NASA Astrophysics Data System (ADS)

    Zhang, Chonglei; Min, Changjun; Du, Luping; Yuan, X.-C.

    2016-05-01

    We propose an all-optical technique for plasmonic structured illumination microscopy (PSIM) with perfect optical vortex (POV). POV can improve the efficiency of the excitation of surface plasma and reduce the background noise of the excited fluorescence. The plasmonic standing wave patterns are excited by POV with fractional topological charges for accurate phase shift of {-2π/3, 0, and 2π/3}. The imaging resolution of less than 200 nm was produced. This PSIM technique is expected to be used as a wide field, super resolution imaging technique in dynamic biological imaging.

  8. Theoretical investigation of the molecular structures and excitation spectra of triphenylamine and its derivatives

    NASA Astrophysics Data System (ADS)

    Sumimoto, Michinori; Yokogawa, Daisuke; Komeda, Masahiro; Yamamoto, Hidetoshi; Hori, Kenji; Fujimoto, Hitoshi

    2011-10-01

    The molecular geometries, electronic structures, and excitation energies of NPh 3, NPh 2Me, NPhMe 2, and NMe 3, were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region.

  9. Acoustic and vibration response of a structure with added noise control treatment under various excitations.

    PubMed

    Rhazi, Dilal; Atalla, Noureddine

    2014-02-01

    The evaluation of the acoustic performance of noise control treatments is of great importance in many engineering applications, e.g., aircraft, automotive, and building acoustics applications. Numerical methods such as finite- and boundary elements allow for the study of complex structures with added noise control treatment. However, these methods are computationally expensive when used for complex structures. At an early stage of the acoustic trim design process, many industries look for simple and easy to use tools that provide sufficient physical insight that can help to formulate design criteria. The paper presents a simple and tractable approach for the acoustic design of noise control treatments. It presents and compares two transfer matrix-based methods to investigate the vibroacoustic behavior of noise control treatments. The first is based on a modal approach, while the second is based on wave-number space decomposition. In addition to the classical rain-on-the-roof and diffuse acoustic field excitations, the paper also addresses turbulent boundary layer and point source (monopole) excitations. Various examples are presented and compared to a finite element calculation to validate the methodology and to confirm its relevance along with its limitations.

  10. Non-contact mode excitation of small structures in air using ultrasound radiation force

    NASA Astrophysics Data System (ADS)

    Huber, Thomas M.; Purdham, John C.; Fatemi, Mostafa; Kinnick, Randall R.; Greenleaf, James F.

    2005-04-01

    With the advent of MEMS, modal analysis of small structures is increasingly important. However, conventional excitation techniques normally require contact, which may not be feasible for small objects. We present a non-contact method that uses interference of ultrasound frequencies in air to produce low-frequency excitation of structures. Objects studied included hard-drive HGA suspensions and MEMS devices. The vibration induced by the ultrasound radiation force was varied in a wide range from 0 Hz to 50 kHz. Object motion was detected using a laser vibrometer; measured frequencies agreed with expected values. Also demonstrated was the unique capability to selectively enhance or suppress modes independently. For example, the ratio of the vibrational amplitudes of the 175 Hz first-bending and 1.33 kHz torsional modes of a small cantilever could be changed from in excess of 10:1 to less than 1:10 by shifting the ultrasound modulation phase 90 degrees. Similar changes were obtained for a 3 mm square MEMS mirror in the ratios of vibration amplitude around its two separate axes. Torsional modes of a hard-drive suspension could be selectively enhanced by over a factor of two by moving the ultrasound focus point from near the center to near the edge of the suspension.

  11. Theoretical investigation of the molecular structures and excitation spectra of triphenylamine and its derivatives.

    PubMed

    Sumimoto, Michinori; Yokogawa, Daisuke; Komeda, Masahiro; Yamamoto, Hidetoshi; Hori, Kenji; Fujimoto, Hitoshi

    2011-10-15

    The molecular geometries, electronic structures, and excitation energies of NPh(3), NPh(2)Me, NPhMe(2), and NMe(3), were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region. Copyright © 2011 Elsevier B.V. All rights reserved.

  12. Parametric and Non-Parametric Vibration-Based Structural Identification Under Earthquake Excitation

    NASA Astrophysics Data System (ADS)

    Pentaris, Fragkiskos P.; Fouskitakis, George N.

    2014-05-01

    The problem of modal identification in civil structures is of crucial importance, and thus has been receiving increasing attention in recent years. Vibration-based methods are quite promising as they are capable of identifying the structure's global characteristics, they are relatively easy to implement and they tend to be time effective and less expensive than most alternatives [1]. This paper focuses on the off-line structural/modal identification of civil (concrete) structures subjected to low-level earthquake excitations, under which, they remain within their linear operating regime. Earthquakes and their details are recorded and provided by the seismological network of Crete [2], which 'monitors' the broad region of south Hellenic arc, an active seismic region which functions as a natural laboratory for earthquake engineering of this kind. A sufficient number of seismic events are analyzed in order to reveal the modal characteristics of the structures under study, that consist of the two concrete buildings of the School of Applied Sciences, Technological Education Institute of Crete, located in Chania, Crete, Hellas. Both buildings are equipped with high-sensitivity and accuracy seismographs - providing acceleration measurements - established at the basement (structure's foundation) presently considered as the ground's acceleration (excitation) and at all levels (ground floor, 1st floor, 2nd floor and terrace). Further details regarding the instrumentation setup and data acquisition may be found in [3]. The present study invokes stochastic, both non-parametric (frequency-based) and parametric methods for structural/modal identification (natural frequencies and/or damping ratios). Non-parametric methods include Welch-based spectrum and Frequency response Function (FrF) estimation, while parametric methods, include AutoRegressive (AR), AutoRegressive with eXogeneous input (ARX) and Autoregressive Moving-Average with eXogeneous input (ARMAX) models[4, 5

  13. Assessment of excitation mechanisms and structural flexibility influence in excitation propagation in multi-megawatt wind turbine gearboxes: Experiments and flexible multibody model optimization

    NASA Astrophysics Data System (ADS)

    Helsen, Jan; Marrant, Ben; Vanhollebeke, Frederik; De Coninck, Filip; Berckmans, Dries; Vandepitte, Dirk; Desmet, Wim

    2013-10-01

    Reliable gearbox design calculations require sufficient insight in gearbox dynamics, which is determined by the interaction between the different excitation mechanisms and the gearbox modal behavior. Both external gearbox excitation originating from the wind turbine drive train and internal gearbox excitation are important. Moreover with regard to the modal behavior the different gearbox structural components: planet carrier, shafts and housing are of influence. The main objective of this article is the experimental investigation of the interaction between the different excitation mechanisms and the gearbox modal behavior. The insights gathered are used to prove the need for accurate gear mesh representation and structural flexibility within the corresponding flexible multibody gearbox simulation model. Experiments are conducted on a dynamic 13.2 MW test facility on which two multi-megawatt wind turbine gearboxes are placed back to back and subjected to a speed run-up. Measurement sensors consist of bearing displacement sensors, torque sensors, encoders and accelerometers distributed over the gearbox. Excitation order amplitudes on different locations in the gearbox are determined by means of a Time Varying Discrete Fourier Transform (TVDFT) order tracking on the measured sensor signals. Moreover the propagation of this excitation throughout the gearbox is assessed. Relating the orders to the corresponding excitation source allows the definition of order influence regions within the gearbox. The interaction between the gear mesh order excitation and structural flexibility is shown.

  14. Acoustic and flexural excitation of a floating structure by a single laser pulse.

    PubMed

    Philp, W R; Podlesak, M; Pierce, S G

    1996-12-20

    The acoustic and flexural vibrations of a small-scale floating structure following irradiation by a pulsed Nd:glass laser are compared with a radiated underwater sound field. A single subablative laser pulse of 600-μs duration was used both to bend and shock the floating structure at the irradiation site. The laser pulse caused the structure to flex at a frequency of approximately 1 kHz whereas relaxation oscillations in the laser output simultaneously excited ultrasonic Lamb waves within the material bulk. We present results to illustrate the broad bandwidth provided by this unusual form of excitation.

  15. THE STRUCTURE OF SPIRAL SHOCKS EXCITED BY PLANETARY-MASS COMPANIONS

    SciTech Connect

    Zhu, Zhaohuan; Stone, James M.; Rafikov, Roman R.; Dong, Ruobing E-mail: rdong2013@berkeley.edu

    2015-11-10

    Direct imaging observations have revealed spiral structures in protoplanetary disks. Previous studies have suggested that planet-induced spiral arms cannot explain some of these spiral patterns, due to the large pitch angle and high contrast of the spiral arms in observations. We have carried out three-dimensional (3D) hydrodynamical simulations to study spiral wakes/shocks excited by young planets. We find that, in contrast with linear theory, the pitch angle of spiral arms does depend on the planet mass, which can be explained by the nonlinear density wave theory. A secondary (or even a tertiary) spiral arm, especially for inner arms, is also excited by a massive planet. With a more massive planet in the disk, the excited spiral arms have larger pitch angle and the separation between the primary and secondary arms in the azimuthal direction is also larger. We also find that although the arms in the outer disk do not exhibit much vertical motion, the inner arms have significant vertical motion, which boosts the density perturbation at the disk atmosphere. Combining hydrodynamical models with Monte-Carlo radiative transfer calculations, we find that the inner spiral arms are considerably more prominent in synthetic near-IR images using full 3D hydrodynamical models than images based on two-dimensional models assuming vertical hydrostatic equilibrium, indicating the need to model observations with full 3D hydrodynamics. Overall, companion-induced spiral arms not only pinpoint the companion’s position but also provide three independent ways (pitch angle, separation between two arms, and contrast of arms) to constrain the companion’s mass.

  16. UVA-visible photo-excitation of guanine radical cations produces sugar radicals in DNA and model structures

    PubMed Central

    Adhikary, Amitava; Malkhasian, Aramice Y. S.; Collins, Sean; Koppen, Jessica; Becker, David; Sevilla, Michael D.

    2005-01-01

    This work presents evidence that photo-excitation of guanine radical cations results in high yields of deoxyribose sugar radicals in DNA, guanine deoxyribonucleosides and deoxyribonucleotides. In dsDNA at low temperatures, formation of C1′• is observed from photo-excitation of G•+ in the 310–480 nm range with no C1′• formation observed ≥520 nm. Illumination of guanine radical cations in 2′dG, 3′-dGMP and 5′-dGMP in aqueous LiCl glasses at 143 K is found to result in remarkably high yields (∼85–95%) of sugar radicals, namely C1′•, C3′• and C5′•. The amount of each of the sugar radicals formed varies dramatically with compound structure and temperature of illumination. Radical assignments were confirmed using selective deuteration at C5′ or C3′ in 2′-dG and at C8 in all the guanine nucleosides/tides. Studies of the effect of temperature, pH, and wavelength of excitation provide important information about the mechanism of formation of these sugar radicals. Time-dependent density functional theory calculations verify that specific excited states in G•+ show considerable hole delocalization into the sugar structure, in accord with our proposed mechanism of action, namely deprotonation from the sugar moiety of the excited molecular radical cation. PMID:16204456

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

    PubMed

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

    2016-10-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  19. Nuclear structure effects of the nuclei {sup 152,154,156}Dy at high excitation energy and large angular momentum

    SciTech Connect

    Martin, V.; Egido, J.L.

    1995-06-01

    Using the finite-temperature Hartree-Fock-Bogoliubov formalism we analyze the properties of the nuclei {sup 152,154,156}Dy at the quasicontinuum region from {ital I}=0{h_bar} to 70{h_bar} and excitation energy up to approximately 16 MeV. We discuss energy gaps, shapes, moments of inertia, and entropy among others. The role of shape fluctuations is studied in the frame of classical statistics and we find large effects on several observables. A very rich structure is found in terms of excitation energy and angular momentum.

  20. Comparative study of microlaser excitation thermography and microultrasonic excitation thermography on submillimeter porosity in carbon fiber reinforced polymer composites

    NASA Astrophysics Data System (ADS)

    Zhang, Hai; Fernandes, Henrique; Hassler, Ulf; Ibarra-Castanedo, Clemente; Genest, Marc; Robitaille, François; Joncas, Simon; Maldague, Xavier

    2017-04-01

    Stitching is used to reduce incomplete infusion of T-joint core (dry-core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Thermographic approaches including microvibrothermography, microlaser line thermography, and microlaser spot thermography on the basis of pulsed and lock-in techniques were proposed. These techniques are used to detect the submillimeter porosities in a stitched T-joint carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to validate the thermographic results. Finally an experimental comparison of microlaser excitation thermography and microultrasonic excitation thermography was conducted.

  1. Ground- and excited-state structural orientation of 2-(2`-hydroxyphenyl)benzazoles in cyclodextrins

    SciTech Connect

    Roberts, E.L.; Dey, J.; Warner, I.M.

    1996-12-12

    The effects of {alpha}-, {beta}-, {gamma}-, and 2,6-di-O-methyl-{beta}-cyclodextrins (CDs) on the ground- and excited-state properties of 2-(2`-hydroxyphenyl)benzoxazole, 2-(2`-hydroxyphenyl)benzothiazole, and 2-(2`-hydroxyphenyl)benzimidazole in aqueous media are investigated. Steady-state fluorescence measurements are used to characterize the interaction of CDs with these azoles. Absorbance measurements indicate increased solubility of the azoles in aqueous solutions of CDs. Measurements of acidity constants (pK{sub a}) and data from induced circular dichroism indicate increased ground- and excited-state acidities of the phenolic protons of the molecules in the presence of CDs and axial orientation of the molecules within the CD cavity, respectively. The data further suggest a planar structure for HBO and a twisted confirmation for both HBT and HBI. The association constants of the inclusion complexes have also been estimated. These studies are further supplemented by comparative spectroscopic studies of 2-(2`-methoxyphenyl)benzothiazole in aqueous solutions of CDs. On the basis of the spectral data acquired, it is believed that the HBA molecules exist as zwitterionic tautomers in the presence of CDs. 35 refs., 6 figs., 2 tabs.

  2. The effect of dimerization on the excited state behavior of methylated xanthine derivatives: a computational study.

    PubMed

    Nachtigallová, Dana; Aquino, Adelia J A; Horn, Shawn; Lischka, Hans

    2013-08-01

    The behavior of monomers and dimers of methylated xanthine derivatives in their excited states is investigated by means of the ADC(2), CASSCF, and CASPT2 methods. The results of the calculations of stationary points in the ground and excited states, minima on the S0/S1 crossing seams and the relaxation pathways are used to provide the interpretation of experimental observations of the monomer xanthine derivatives. The effect of dimerization on the excited state properties is studied for various relative orientations of the monomers in the dimer complexes in comparison with the relevant monomer species. A significant stabilization in the excited state minima of dimers is observed. These can act as trapping sites. Various types of conical intersections, with both localized and delocalized characters of wavefunctions, have been found, mainly energetically above the lowest bright excited state in the FC region. In addition, structures with the bonds formed between the two monomers were also found on the crossing seams. The possibility of ultrafast relaxation via these conical intersections is discussed.

  3. On the nature of excited states of photosynthetic reaction centers: An ultrafast infrared study

    SciTech Connect

    Haran, G.; Wynne, K.; Reid, G.D.

    1995-12-31

    Bacterial photosynthetic reaction centers (RC) contain eight chromophores forming a well-defined supramolecular structure within a protein framework. Theoretical studies suggest that the excited states of these chromophores are delocalized and contain important contributions from charge-transfer and resonance states. There is no clear-cut experimental evidence pertaining to the degree of localization of excited states. We have used ultrafast near and mid-infrared spectroscopic methods to investigate the character of some of the excited states. Exciting the 800 nm, absorption band, we followed the fate of the excitation energy using either the stimulated emission of the special pair at 920 nm or a transient absorption at 1.2 {mu}m. For a completely localized system, Forster theory-based calculations are expected to accurately predict the kinetics of energy transfer. It was found, however, that calculated rates arc much faster than measured rates. This corroborates a delocalized picture, with internal conversion rather than energy transfer between states. We have also measured the transient absorption spectrum of the RC in the infrared spectral region, detecting several new low-lying electronic states. Assignments for these states, and implications for the localization problem will be discussed.

  4. Plasmon excitations in sodium atomic planes: a time-dependent density functional theory study.

    PubMed

    Wang, Bao-Ji; Xu, Yuehua; Ke, San-Huang

    2012-08-07

    The collective electronic excitation in planar sodium clusters is studied by time-dependent density functional theory calculations. The formation and development of the resonances in photoabsorption spectra are investigated in terms of the shape and size of the two-dimensional (2D) systems. The nature of these resonances is revealed by the frequency-resolved induced charge densities present on a real-space grid. For long double chains, the excitation is similar to that in long single atomic chains, showing longitudinal modes, end and central transverse modes. However, for 2D planes consisting of (n × n) atoms with n being up to 16, new 2D characteristic modes emerge regardless of the symmetries considered. For in-plane excitations, besides the equivalent end mode, mixed modes with contrary polarity occur. The relation between the frequency of the primary modes and the system size is similar to the case of a 2D electron gas but with a correction due to the realistic atomic structure. For excitations perpendicular to the plane there are corner, side center, bulk center, and circuit modes. Our calculation reveals the importance of dimensionality for plasmon excitation and how it evolves from 1D to 2D.

  5. Fluorescence excitation enhancement by Bloch surface wave in all-polymer one-dimensional photonic structure

    SciTech Connect

    Fornasari, L.; Floris, F.; Patrini, M.; Guizzetti, G.; Marabelli, F.; Canazza, G.; Comoretto, D.

    2014-08-04

    We demonstrate photoluminescence excitation enhancement in an all-polymer flexible one-dimensional photonic crystal structure capped with a fluorescent organic ultrathin film. When optical matching conditions between the excitation beam and the Bloch Surface Wave mode supported by the photonic structure are achieved, a ten times enhancement of the photoluminescence is observed. We notice that in these systems luminescence signal reinforcement is achieved by increasing the pump efficiency with no need of spectral resonance to the emission of the chosen fluorophore. All these features make these systems suitable candidates for easy, flexible, and cheap fluorescent sensing.

  6. γvNN^* Transition Amplitudes and Excited Baryon Structure from CLAS

    NASA Astrophysics Data System (ADS)

    Mokeev, Victor

    2013-04-01

    Studying excited nucleon structure through exclusive-meson electroproduction reactions is key for understanding the nature of the strong interaction in the non-perturbative regime. With its nearly complete coverage of the final-state phase space, the CLAS detector at JLab has provided the lion's share of the world's meson-electroproduction data for differential cross sections and the asymmetries arising from single- and double-polarization observables. Electrocouplings for most of the excited nucleon states (N^*) in mass range of up to 1.8 GeV have been determined from several analyses of the CLAS data for photon virtualities (Q^2) up to 5.0 GeV^2 for the ^amp;+n, ^0p, and ηp channels [1,3] as well as for the ^amp;+^amp;-p reaction for Q^2 < 1.5 GeV^2 [2,3]. Physics analyses of these N^* electrocouplings [2,3] have revealed that the structure of excited nucleon is formed of an internal core of dressed quarks with an external meson-baryon cloud. Our N^*-electrocoupling results afford access to the non-perturbative strong interaction responsible for generating the different N^* states and will also provide testing ground for the inspired by QCD quark model predictions. A dedicated experiment will run after the 12 GeV upgrade to JLab on the extraction of the N^* electrocouplings in the yet unexplored region of high photon virtualities ranging from 5.0 to 12 GeV^2. The anticipated results are of particular importance in providing a understanding of the nature of confinement and dynamical chiral symmetry breaking in baryons based upon the QCD [3].[4pt] [1] I.G. Aznauryan and V.D. Burkert, Prog. Part. Nucl. Phys. 67, 1 (2012).[0pt] [2] V.I. Mokeev et al. (CLAS Collaboration), Phys. Rev. C86, 035203 (2012).[0pt] [3] I.G. Aznauryan et al., ``Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction,'' arXiv:1212.4891[nucl-th].

  7. Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas

    NASA Astrophysics Data System (ADS)

    Kobayashi, T.; Itoh, K.; Ido, T.; Kamiya, K.; Itoh, S.-I.; Miura, Y.; Nagashima, Y.; Fujisawa, A.; Inagaki, S.; Ida, K.; Hoshino, K.

    2016-08-01

    Self-regulation between structure and turbulence, which is a fundamental process in the complex system, has been widely regarded as one of the central issues in modern physics. A typical example of that in magnetically confined plasmas is the Low confinement mode to High confinement mode (L-H) transition, which is intensely studied for more than thirty years since it provides a confinement improvement necessary for the realization of the fusion reactor. An essential issue in the L-H transition physics is the mechanism of the abrupt “radial” electric field generation in toroidal plasmas. To date, several models for the L-H transition have been proposed but the systematic experimental validation is still challenging. Here we report the systematic and quantitative model validations of the radial electric field excitation mechanism for the first time, using a data set of the turbulence and the radial electric field having a high spatiotemporal resolution. Examining time derivative of Poisson’s equation, the sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally observed radial current that excites the radial electric field within a few factors of magnitude.

  8. Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas

    PubMed Central

    Kobayashi, T.; Itoh, K.; Ido, T.; Kamiya, K.; Itoh, S.-I.; Miura, Y.; Nagashima, Y.; Fujisawa, A.; Inagaki, S.; Ida, K.; Hoshino, K.

    2016-01-01

    Self-regulation between structure and turbulence, which is a fundamental process in the complex system, has been widely regarded as one of the central issues in modern physics. A typical example of that in magnetically confined plasmas is the Low confinement mode to High confinement mode (L-H) transition, which is intensely studied for more than thirty years since it provides a confinement improvement necessary for the realization of the fusion reactor. An essential issue in the L-H transition physics is the mechanism of the abrupt “radial” electric field generation in toroidal plasmas. To date, several models for the L-H transition have been proposed but the systematic experimental validation is still challenging. Here we report the systematic and quantitative model validations of the radial electric field excitation mechanism for the first time, using a data set of the turbulence and the radial electric field having a high spatiotemporal resolution. Examining time derivative of Poisson’s equation, the sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally observed radial current that excites the radial electric field within a few factors of magnitude. PMID:27489128

  9. Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas.

    PubMed

    Kobayashi, T; Itoh, K; Ido, T; Kamiya, K; Itoh, S-I; Miura, Y; Nagashima, Y; Fujisawa, A; Inagaki, S; Ida, K; Hoshino, K

    2016-08-04

    Self-regulation between structure and turbulence, which is a fundamental process in the complex system, has been widely regarded as one of the central issues in modern physics. A typical example of that in magnetically confined plasmas is the Low confinement mode to High confinement mode (L-H) transition, which is intensely studied for more than thirty years since it provides a confinement improvement necessary for the realization of the fusion reactor. An essential issue in the L-H transition physics is the mechanism of the abrupt "radial" electric field generation in toroidal plasmas. To date, several models for the L-H transition have been proposed but the systematic experimental validation is still challenging. Here we report the systematic and quantitative model validations of the radial electric field excitation mechanism for the first time, using a data set of the turbulence and the radial electric field having a high spatiotemporal resolution. Examining time derivative of Poisson's equation, the sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally observed radial current that excites the radial electric field within a few factors of magnitude.

  10. Mobility power flow analysis of an L-shaped plate structure subjected to acoustic excitation

    NASA Technical Reports Server (NTRS)

    Cuschieri, J. M.

    1989-01-01

    An analytical investigation based on the Mobility Power Flow method is presented for the determination of the vibrational response and power flow for two coupled flat plate structures in an L-shaped configuration, subjected to acoustical excitation. The principle of the mobility power flow method consists of dividing the global structure into a series of subsystems coupled together using mobility functions. Each separate subsystem is analyzed independently to determine the structural mobility functions for the junction and excitation locations. The mobility functions, together with the characteristics of the junction between the subsystems, are then used to determine the response of the global structure and the power flow. In the coupled plate structure considered here, mobility power flow expressions are derived for excitation by an incident acoustic plane wave. In this case, the forces (acoustic pressures) acting on the structure are dependent on the response of the structure because of the scattered pressure component. The interaction between the structure and the fluid leads to the derivation of a corrected mode shape for the plates' normal surface velocity and also for the structure mobility functions. The determination of the scattered pressure components in the expressions for the power flow represents an additional component in the power flow balance for the source plate and the receiver plate. This component represents the radiated acoustical power from the plate structure.

  11. Dynamic response analysis of linear stochastic truss structures under stationary random excitation

    NASA Astrophysics Data System (ADS)

    Gao, Wei; Chen, Jianjun; Cui, Mingtao; Cheng, Yi

    2005-03-01

    This paper presents a new method for the dynamic response analysis of linear stochastic truss structures under stationary random excitation. Considering the randomness of the structural physical parameters and geometric dimensions, the computational expressions of the mean value, variance and variation coefficient of the mean square value of the structural displacement and stress response under the stationary random excitation are developed by means of the random variable's functional moment method and the algebra synthesis method from the expressions of structural stationary random response of the frequency domain. The influences of the randomness of the structural physical parameters and geometric dimensions on the randomness of the mean square value of the structural displacement and stress response are inspected by the engineering examples.

  12. An experimental study of electron acceleration with detuning of the bunch repetition frequency from that of an excited wake field

    NASA Astrophysics Data System (ADS)

    Linnik, A. F.; Onishchenko, I. N.; Pristupa, V. I.

    2017-02-01

    We have experimentally studied the excitation of wake fields in a dielectric structure by a train of relativistic electron bunches and the acceleration of subsequent bunches of the same train due to detuning of the bunch repetition frequency relative to that of the wake field excited in the dielectric structure at the Cherenkov resonance. Electron bunches of the first (leading) part of the train excite the wake wave, and bunches of the second (trailing) part of this train are shifted to the accelerating phase of the wake wave so as to gain additional energy. The possibility of controlling the number (repetition frequency) of bunches exciting the wake field in the dielectric structure and the number of subsequently accelerated bunches has been investigated by changing the value of detuning.

  13. Optical properties in complex-structured nanometric quantum wells: Photoluminescence, photoluminescence excitation, and Stokes shift

    NASA Astrophysics Data System (ADS)

    Silva, A. A. P.; Vasconcellos, Áurea. R.; Luzzi, Roberto; Meneses, E. A.; Laureto, E.

    2009-10-01

    Systems in which one or more directions are in the nanometric space scale exhibit significantly some peculiar phenomena and processes. We consider here the case of nanometric quantum wells with complex structure, displaying fractal-like characteristics, which are part of semiconductor heterostructures. An extensive theoretical study of the optical properties of photoluminescence and excited photoluminescence, and then involving absorption and the question of emergence of the so-called Stokes shift that is observed in some cases are performed. The results are compared with some experimental data. This is of relevance for opening up the possibility to use optical measurements to perform a (nondestructive) quality control of samples grown under different methods and protocols.

  14. Effect of Particle Damping on an Acoustically Excited Curved Vehicle Panel Structure with varied Equipment Assemblies

    NASA Technical Reports Server (NTRS)

    Parsons, David; Smith, Andrew; Knight, Brent; Hunt, Ron; LaVerde, Bruce; Craigmyle, Ben

    2012-01-01

    Particle dampers provide a mechanism for diverting energy away from resonant structural vibrations. This experimental study provides data from trials to determine how effective use of these dampers might be for equipment mounted to a curved orthogrid vehicle panel. Trends for damping are examined for variations in damper fill level, component mass, and excitation energy. A significant response reduction at the component level would suggest that comparatively small, thoughtfully placed, particle dampers might be advantageously used in vehicle design. The results of this test will be compared with baseline acoustic response tests and other follow-on testing involving a range of isolation and damping methods. Instrumentation consisting of accelerometers, microphones, and still photography data will be collected to correlate with the analytical results.

  15. Performance evaluation of a novel rotational damper for structural reinforcement steel frames subjected to lateral excitations

    NASA Astrophysics Data System (ADS)

    Sanati, M.; Khadem, S. E.; Mirzabagheri, S.; Sanati, H.; Khosravieh, M. Y.

    2014-03-01

    In this study, a novel rotational damper called a Rotational Friction Viscoelastic Damper (RFVD) is introduced. Some viscoelastic pads are added to the Rotational Friction Damper (RFD) in addition to the friction discs used in this conventional device. Consequently, the amount of energy dissipated by the damper increases in low excitation frequencies. In fact, the input energy to the structure is simultaneously dissipated in the form of friction and heat by frictional discs and viscoelastic pads. In order to compare the performance of this novel damper with the earlier types, a set of experiments were carried out. According to the test results, the RFVD showed a better performance in dissipating input energy to the structure when compared to the RFD. The seismic behavior of steel frames equipped with these dampers was also numerically evaluated based on a nonlinear time history analysis. The numerical results verified the performance of the dampers in increasing the energy dissipation and decreasing the energy input to the structural elements. In order to achieve the maximum dissipated energy, the dampers need to be installed in certain places called critical points in the structure. An appropriate approach is presented to properly find these points. Finally, the performance of the RFVDs installed at these critical points was investigated in comparison to some other configurations and the validity of the suggested method in increasing the energy dissipation was confirmed.

  16. Hedgehog excitations in double-exchange magnetism: Energetics and electronic structure

    NASA Astrophysics Data System (ADS)

    Pekker, David; Goldbart, Paul; Salamon, Myron; Abanov, Alexander

    2004-03-01

    Topological hedgehog excitations of the magnetic state are believed to play an important role in the three-dimensional ferromagnet-to-paramagnet phase transition. This is true not only in Heisenberg magnets but also in double-exchange magnets, for which the transition is accompanied by a metal-insulator transition. The energetics and electronic structure of hedgehog excitations in double-exchange systems are investigated using a model in which the electrons move through a lattice of classical spins, to which they are coupled via Hund's Rule interactions. The core energy of hedgehog excitations is determined, as is the extent to which charge is expelled from the hedgehog cores. In settings involving pairs of hedgehogs, the manner in which the electronic energetics determines the magnetic structure is explored variationally, especially in the region between the hedgehogs.

  17. Effect of structure and size on the excited states dynamics of CaArn clusters

    NASA Astrophysics Data System (ADS)

    Plata, Jose J.; Heitz, Marie-Catherine; Spiegelman, Fernand

    2013-01-01

    The time-resolved photoelectron spectra, probing the non-adiabatic dynamics of CaAr n clusters excited by a pump pulse in the vicinity of the 4 s4 p 1P line of calcium, are simulated. The simulations involve Diatomics-In-Molecules modelling of the excited electronic structure, excited states dynamics with electronic transitions, and classical approximations to derive the time-resolved photoelectron spectra. The oscillations in the time-dependence of the spectra, associated with the relative motion of calcium with respect to the argon cluster, and the corresponding nonadiabatic relaxation processes are analysed according to cluster size ( n ≈ 55 and 147), structure (icosahedral versus cuboctahedral shape) and local environment (substitution versus surface deposition of calcium, surface type).

  18. Ultrafast internal conversion dynamics of highly excited pyrrole studied with VUV/UV pump probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Horton, Spencer L.; Liu, Yusong; Chakraborty, Pratip; Matsika, Spiridoula; Weinacht, Thomas

    2017-02-01

    We study the relaxation dynamics of pyrrole after excitation with an 8 eV pump pulse to a state just 0.2 eV below the ionization potential using vacuum ultraviolet/ultraviolet pump probe spectroscopy. Our measurements in conjunction with electronic structure calculations indicate that pyrrole undergoes rapid internal conversion to the ground state in less than 300 fs. We find that internal conversion to the ground state dominates over dissociation.

  19. On the glitches in the force transmitted by an electrodynamic exciter to a structure

    NASA Technical Reports Server (NTRS)

    Rao, Dantam K.

    1987-01-01

    Around resonance, the force transmitted by an exciter into a structure will be smaller or greater than a reference force generated by its coils due to electromechanical interaction. A simple analysis is presented which reveals how this phenomenon of force drop-off is controlled by three factors. The first factor, called Armature Mass Factor, describes a purely mechanical interaction between the structure and the exciter. The electromechanical energy conversion and its interaction with the structure yields two additional factors, called Electrical Resistance and Electrical Inductance Factors. They describe the effects of coil resistance, inductance and magnetic field strength relative to structural damping and stiffness. Present analysis indicates that, under proper circumstances, more than 90 percent of the force drop-off can be eliminated if armature-to-structure mass ratio is smaller or equal to half of modal loss factor.

  20. Plasmon-mediated synthesis of silver cubes with unusual twinning structures using short wavelength excitation.

    PubMed

    Personick, Michelle L; Langille, Mark R; Zhang, Jian; Wu, Jinsong; Li, Shuyou; Mirkin, Chad A

    2013-06-10

    The plasmon-mediated synthesis of silver nanoparticles is a versatile synthetic method which leverages the localized surface plasmon resonance (LSPR) of nanoscale silver to generate particles with non-spherical shapes and control over dimensions. Herein, a method is reported for controlling the twinning structure of silver nanoparticles, and consequently their shape, via the plasmon-mediated synthesis, solely by varying the excitation wavelength between 400, 450, and 500 nm, which modulates the rate of Ag⁺ reduction. Shorter, higher energy excitation wavelengths lead to faster rates of reaction, which in turn yield structures containing a greater number of twin boundaries. With this method, silver cubes can be synthesized using 450 nm excitation, which represents the first time this shape has been realized by a plasmon-mediated synthetic approach. In addition, these cubes contain an unusual twinning structure composed of two intersecting twin boundaries or multiple parallel twin boundaries. With respect to their twinning structure, these cubes fall between planar-twinned and multiply twinned nanoparticles, which are synthesized using 500 and 400 nm excitation, respectively.

  1. Computational Prediction of Structures and Optical Excitations for Nanoscale Ultrasmall ZnS and CdSe Clusters.

    PubMed

    Nguyen, Kiet A; Pachter, Ruth; Day, Paul N

    2013-08-13

    Small semiconductor nanoclusters are important for understanding the initial formation and growth of quantum dots and also for application, for example in the tunability provided by size. However, electronic structures and effects of capping ligands have not been systematically characterized. Thus, ground and excited state calculations using coupled-cluster methods were carried out to provide benchmarks for evaluating the applicability of density functional theory (DFT) and time-dependent DFT (TDDFT) with different functionals for the ground and excited states, respectively. Our computed data suggests that the popular B3LYP functional does not deliver optimal results for the ground and excited state. While the PBE0 functional was found to provide a good description for both the ground and excited states for small bare (ZnS)n and bare and ligated (CdSe)n clusters, the results for the hydrated (ZnS)n clusters were found to deteriorate significantly. However, the errors appear to decrease with increasing cluster size. Excitation energies obtained with the long-range hybrid CAM-B3LYP and CA-B3LYP were found to provide more consistent results for both anhydrous and hydrated (ZnS)n clusters. However, their performance in spectral predictions for larger clusters requires further study. Using PBE0, electronic structures of the ground and excited states for (ZnS)n and (CdSe)n up to n = 37 using DFT and TDDFT, respectively, were re-examined. With the exception of the cage-core (ZnS)13, (CdSe)13, and (CdSe)14, small (ZnS)n and (CdSe)n are predicted to be spheroids and tubular structures (6, 8-12, 15-19) with squares and hexagons, similar to the structures of carbon single-wall nanotubes. Wurtzite (n = 23-27, 36, 37) and cage-core (n = 29-35) structures are energetically more favorable for larger clusters. We find that water and amines increase the intensities and blue shift the excitations of bare clusters. One photon absorption spectra predicted by TDDFT with the PCM

  2. Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S1(π,π*) electronic state

    PubMed Central

    Shin, Hee Won; Ocola, Esther J.; Kim, Sunghwan; Laane, Jaan

    2014-01-01

    The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(π,π*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(π,π*) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(π,π*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(π,π*) excited state. PMID:25669377

  3. Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer, Photoisomerization and Fluorescence Probe Properties.

    PubMed

    Hota, Prasanta Kumar; Singh, Anil Kumar

    2014-07-27

    Numerous studies of donor-acceptor conjugated linear polyenes have been carried out with the goal to understand the exact nature of the excited state electronic structure and dynamics. In this article we discuss our endeavours with regard to the excited state intramolecular charge transfer, photoisomerization and fluorescence probe properties of various donor-acceptor substituted compounds of diphenylpolyene [Ar(CH = CH) n Ar] series and ethenylindoles.

  4. Optically excited structural transition in atomic wires on surfaces at the quantum limit

    NASA Astrophysics Data System (ADS)

    Frigge, T.; Hafke, B.; Witte, T.; Krenzer, B.; Streubühr, C.; Samad Syed, A.; Mikšić Trontl, V.; Avigo, I.; Zhou, P.; Ligges, M.; von der Linde, D.; Bovensiepen, U.; Horn-von Hoegen, M.; Wippermann, S.; Lücke, A.; Sanna, S.; Gerstmann, U.; Schmidt, W. G.

    2017-03-01

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  5. Optically excited structural transition in atomic wires on surfaces at the quantum limit.

    PubMed

    Frigge, T; Hafke, B; Witte, T; Krenzer, B; Streubühr, C; Samad Syed, A; Mikšić Trontl, V; Avigo, I; Zhou, P; Ligges, M; von der Linde, D; Bovensiepen, U; Horn-von Hoegen, M; Wippermann, S; Lücke, A; Sanna, S; Gerstmann, U; Schmidt, W G

    2017-03-29

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  6. Resonance excitation of the spin-wave current in hybrid structures

    NASA Astrophysics Data System (ADS)

    Lyapilin, I. I.; Okorokov, M. S.; Bebenin, N. G.

    2017-10-01

    Using the non-equilibrium statistical operator (NSO) method, we have investigated the spin transport through the interface in a semiconductor/ferromagnetic insulator hybrid structure. We have analyzed the effective parameters approximation, when each of the considered subsystems (conduction electrons, magnons, and phonons) is characterized by its effective temperature. We have constructed the macroscopic equations describing the spin-wave current caused by both the resonantly exciting spin subsystem of conduction electrons and an inhomogeneous temperature field in the ferromagnetic insulator. We have shown that the spin-wave current excitation under combined resonance conditions exhibits a resonant nature.

  7. Structure and conformational dynamics of molecules in the excited electronic states: theory and experiment

    NASA Astrophysics Data System (ADS)

    Godunov, I. A.; Bataev, V. A.; Maslov, D. V.; Yakovlev, N. N.

    2016-12-01

    The structure of conformational non-rigid molecules in the excited electronic states are investigated by joint theoretical and experimental methods. The theoretical part of work consist of two stages. In first stage the ab initio quantum-chemical calculations are carried out using high level methods. In second stage the vibrational problems of the various dimensions are solved by variational method for vibrations of large amplitude. In experimental part of work the vibronic spectra are investigated: gas-phase absorption and also, fluorescence excitation spectra of jet-cooled molecules. Some examples are considered.

  8. Controlling the coexistence of structural phases and the optical properties of gallium nanoparticles with optical excitation

    NASA Astrophysics Data System (ADS)

    MacDonald, K. F.; Fedotov, V. A.; Pochon, S.; Stevens, G.; Kusmartsev, F. V.; Emel'yanov, V. I.; Zheludev, N. I.

    2004-08-01

    We have observed reversible structural transformations, induced by optical excitation at 1.55 μm, between the β, γ and liquid phases of gallium in self-assembled gallium nanoparticles, with a narrow size distribution around 50 nm, on the tip of an optical fiber. Only a few tens of nanowatts of optical excitation per particle are required to control the transformations, which take the form of a dynamic phase coexistence and are accompanied by substantial changes in the optical properties of the nanoparticle film. The time needed to achieve phase equilibrium is in the microsecond range, and increases sharply near the transition temperatures.

  9. [Selective excitation spectra and energy level structure of Dy3+:ThO2 crystal].

    PubMed

    Yin, M; Krupa, J C

    2001-08-01

    Dy3+:ThO2 crystal was grown by the flux technique for the first time. The emission spectra, excitation spectra and fluorescence decay curves were measured and discussed. By using emission spectra obtained under selective dye laser excitation at 12 K, together with the crystal-field theory, the site symmetry of Dy3+ ions in ThO2 was determined as C3 nu and its energy level structure was tabulated. The lifetime of radiative level 4F9/2 was also determined as 0.40 ms.

  10. Structural dynamics verification facility study

    NASA Technical Reports Server (NTRS)

    Kiraly, L. J.; Hirchbein, M. S.; Mcaleese, J. M.; Fleming, D. P.

    1981-01-01

    The need for a structural dynamics verification facility to support structures programs was studied. Most of the industry operated facilities are used for highly focused research, component development, and problem solving, and are not used for the generic understanding of the coupled dynamic response of major engine subsystems. Capabilities for the proposed facility include: the ability to both excite and measure coupled structural dynamic response of elastic blades on elastic shafting, the mechanical simulation of various dynamical loadings representative of those seen in operating engines, and the measurement of engine dynamic deflections and interface forces caused by alternative engine mounting configurations and compliances.

  11. Electronic and structural properties of low-lying excited states of vitamin B12.

    PubMed

    Lodowski, Piotr; Jaworska, Maria; Kornobis, Karina; Andruniów, Tadeusz; Kozlowski, Pawel M

    2011-11-17

    Time-dependent density functional theory (TD-DFT) has been applied to explore electronically excited states of vitamin B(12) (cyanocobalamin or CNCbl). To explain why the Co-C bond in CNCbl does not undergo photodissociation under conditions of simple photon excitation, electronically excited states have been computed along the Co-C(CN) stretched coordinate. It was found that the repulsive (3)(σ(Co-C) → σ*(Co-C)) triplet state drops in energy as the Co-C(CN) bond lengthens, but it does not become dissociative. Low-lying excited states were also computed as function of two axial bond lengths. Two energy minima have been located on the S(1)/CNCbl, as well as T(1)/CNCbl, surfaces. The full geometry optimization was carried out for each minimum and electronic properties associated with each optimized structure were analyzed in details. One minimum was described as excitation having mixed ππ*/MLCT (metal-to-ligand charge transfer) character, while the second as ligand-to-metal charge transfer (LMCT) transition. Neither of them, however, can be viewed as pure MLCT or LMCT transitions since additional excitation to or from σ-bonds (SB) of N-Co-C unit have also noticeable contributions. Inclusion of solvent altered the character of one of the excitations from ππ*/MLCT/SBLCT to ππ*/LMCT/LSBCT-type, and therefore, both of them gained significant contribution from LMCT/LSBCT transition. Finally, the nature of S(1) electronic state has been comparatively analyzed in CNCbl and MeCbl cobalamins.

  12. Modeling an Excitable Biosynthetic Tissue with Inherent Variability for Paired Computational-Experimental Studies

    PubMed Central

    Kim, Jong M.; Kirkton, Robert D.; Bursac, Nenad; Henriquez, Craig S.

    2017-01-01

    To understand how excitable tissues give rise to arrhythmias, it is crucially necessary to understand the electrical dynamics of cells in the context of their environment. Multicellular monolayer cultures have proven useful for investigating arrhythmias and other conduction anomalies, and because of their relatively simple structure, these constructs lend themselves to paired computational studies that often help elucidate mechanisms of the observed behavior. However, tissue cultures of cardiomyocyte monolayers currently require the use of neonatal cells with ionic properties that change rapidly during development and have thus been poorly characterized and modeled to date. Recently, Kirkton and Bursac demonstrated the ability to create biosynthetic excitable tissues from genetically engineered and immortalized HEK293 cells with well-characterized electrical properties and the ability to propagate action potentials. In this study, we developed and validated a computational model of these excitable HEK293 cells (called “Ex293” cells) using existing electrophysiological data and a genetic search algorithm. In order to reproduce not only the mean but also the variability of experimental observations, we examined what sources of variation were required in the computational model. Random cell-to-cell and inter-monolayer variation in both ionic conductances and tissue conductivity was necessary to explain the experimentally observed variability in action potential shape and macroscopic conduction, and the spatial organization of cell-to-cell conductance variation was found to not impact macroscopic behavior; the resulting model accurately reproduces both normal and drug-modified conduction behavior. The development of a computational Ex293 cell and tissue model provides a novel framework to perform paired computational-experimental studies to study normal and abnormal conduction in multidimensional excitable tissue, and the methodology of modeling variation can be

  13. Theoretical Studies of Chemical Reactions following Electronic Excitation

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.

    2003-01-01

    The use of multi-configurational wave functions is demonstrated for several processes: tautomerization reactions in the ground and excited states of the DNA base adenine, dissociation of glycine molecule after electronic excitation, and decomposition/deformation of novel rare gas molecules HRgF. These processes involve bond brealung/formation and require multi-configurational approaches that include dynamic correlation.

  14. Flight and analytical investigations of a structural mode excitation system on the YF-12A airplane

    NASA Technical Reports Server (NTRS)

    Goforth, E. A.; Murphy, R. C.; Beranek, J. A.; Davis, R. A.

    1987-01-01

    A structural excitation system, using an oscillating canard vane to generate force, was mounted on the forebody of the YF-12A airplane. The canard vane was used to excite the airframe structural modes during flight in the subsonic, transonic, and supersonic regimes. Structural modal responses generated by the canard vane forces were measured at the flight test conditions by airframe-mounted accelerometers. Correlations of analytical and experimental aeroelastic results were made. Doublet lattice, steady state double lattice with uniform lag, Mach box, and piston theory all produced acceptable analytical aerodynamic results within the restrictions that apply to each. In general, the aerodynamic theory methods, carefully applied, were found to predict the dynamic behavior of the YF-12A aircraft adequately.

  15. Low temperature resistivity study of nanostructured polypyrrole films under electronic excitations

    NASA Astrophysics Data System (ADS)

    Chandra, Subhash; Annapoorni, S.; Singh, Fouran; Sonkawade, R. G.; Rana, J. M. S.; Ramola, R. C.

    2010-01-01

    The synthesis of nanostructured polypyrrole (Ppy) films by electrochemical process and their modifications by electronic excitations induced by swift heavy ion irradiations is reported in this paper. The electrical property of ion beam irradiated polypyrrole was investigated at low temperature by resistivity measurements. The structural and optical properties were also studied using X-ray diffraction (XRD), UV-vis spectroscopy and scanning electron microscopy (SEM). At low temperature, the polypyrrole films show the metallic behaviour after ion beam irradiation. UV-vis spectroscopy shows a red shift in the absorbance edge and thus reduction in band gap with increasing ion fluence. The structural studies show that the percentage crystallinity improves with increase in ion fluence. The SEM study corroborates the results of structural analysis and shows the formation of rod type structures along with the evolution of amorphous phase with increasing ion fluence.

  16. Vibrational structure of the S 2 (1B u) excited state of diphenyloctatetraene observed by femtosecond stimulated Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kukura, Philipp; McCamant, David W.; Davis, Paul H.; Mathies, Richard A.

    2003-11-01

    Femtosecond time-resolved stimulated Raman spectroscopy (FSRS) is used to study the vibrational structure and dynamics of the S 2 state of diphenyloctatetraene. Strong vibrational features at 1184, 1259 and 1578 cm -1 whose linewidths are determined by the S 2 electronic lifetime are observed at early times after photoexcitation at 397 nm. Kinetic analysis of the integrated Raman intensities as well as the transient absorption reveals an exponential decay of the S 2 state on the order of 100 fs. These results demonstrate the ability of FSRS to study the vibrational structure of excited state and chemical reaction dynamics on the femtosecond timescale.

  17. Magnetic structures and excitations in CePd2(Al,Ga)2 series: Development of the "vibron" states

    NASA Astrophysics Data System (ADS)

    Klicpera, M.; Boehm, M.; Doležal, P.; Mutka, H.; Koza, M. M.; Rols, S.; Adroja, D. T.; Puente Orench, I.; Rodríguez-Carvajal, J.; Javorský, P.

    2017-02-01

    CePd2Al2 -xGax compounds crystallizing in the tetragonal CaBe2Ge2 -type structure (space group P 4 /n m m ) and undergoing a structural phase transition to an orthorhombic structure (C m m e ) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd2Al2 is described by an incommensurate propagation vector k ⃗=(δx,1/2 +δy,0 ) with δx=0.06 and δy=0.04 . The magnetic moments order antiferromagnetically within the a b planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) μB/Ce3 +. CePd2Ga2 reveals a magnetic structure composed of two components: the first is described by the propagation vector k1⃗=(1/2 ,1/2 ,0 ) , and the second one propagates with k2⃗=(0 ,1/2 ,0 ) . The magnetic moments of both components are aligned along the same direction—the orthorhombic [100] direction—and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors k1⃗ and k2⃗ describe also the magnetic structure of substituted CePd2Al2 -xGax compounds, except the one with x =0.1 .CePd2Al1.9Ga0.1 with magnetic structure described by k ⃗ and k1⃗ stays on the border between pure CePd2Al2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd2Al2 , while only two crystal field (CF) excitations are expected from the splitting of ground state J =5/2 of the Ce3 + ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd2Al2 . A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional

  18. Theoretical Studies on Excitation Energy Fluctuations of Pigments in a Light-Harvesting Complex

    NASA Astrophysics Data System (ADS)

    Higashi, Masahiro; Saito, Shinji

    2014-03-01

    Excitation energy fluctuations of pigments in light-harvesting complexes play an important role in the excitation energy transfer dynamics. It is considered that protein environment controls the excitation energy fluctuation to maximize the efficiency of excitation energy transfer. However, the detailed mechanism is still unknown. The high computational cost of reliable electronic structure calculations for excited states prevents us from carrying out a large number of sampling needed to evaluate the excitation energy fluctuations. To overcome this difficulty, we develop a new method called molecular mechanics with Shepard interpolation corrections (MMSIC), which enable us to generate potential energy surfaces for pigments in light-harvesting complexes efficiently. We illustrate the new method by application to bacteriochlorophyll a pigments in the Fenna-Matthews-Olson complex. The MMSIC calculations are more than a million times faster than the direct electronic structure calculations, and the calculated results are in good agreement with the experimental results.

  19. Dynamics of Excited States for Fluorescent Emitters with Hybridized Local and Charge-Transfer Excited State in Solid Phase: A QM/MM Study.

    PubMed

    Fan, Jianzhong; Cai, Lei; Lin, Lili; Wang, Chuan-Kui

    2016-12-01

    The highly efficient organic light-emitting diodes (OLEDS) based on fluorescent emitters with hybridized local and charge-transfer (HLCT) excited state have attracted great attention recently. The excited-state dynamics of the fluorescent molecule with consideration of molecular interaction are studied using the hybrid quantum mechanics/molecular mechanics method. The results show that, in solid state, the internal conversion rate (KIC) between the first singlet excited state (S1) and the ground state (S0) is smaller than the fluorescent rate (Kr), while in gas phase KIC is much larger than Kr. By analyzing the Huang-Rhys (HR) factor and reorganization energy (λ), we find that these two parameters in solid state are much smaller than those in gas phase due to the suppression of the vibration modes in low-frequency regions (<200 cm(-1)) related with dihedral angles between donor and acceptor groups. This is further demonstrated by the geometrical analysis that variation of the dihedral angle between geometries of S1 and S0 is smaller in solid state than that in gas phase. Moreover, combining the dynamics of the excited states and the adiabatic energy structures calculated in solid state, we illustrate the suggested "hot-exciton" mechanism of the HLCT emitters in OLEDs. Our work presents a rational explanation for the experimental results and demonstrates the importance of molecular interaction for theoretical simulation of the working principle of OLEDs.

  20. Infrared/ultraviolet quadruple resonance spectroscopy to investigate structures of electronically excited states

    SciTech Connect

    Weiler, M.; Bartl, K.; Gerhards, M.

    2012-03-21

    Molecular beam investigations in combination with IR/UV spectroscopy offer the possibility to obtain structural information on isolated molecules and clusters. One of the demanding tasks is the discrimination of different isomers, e.g., by the use of isomer specific UV excitations. If this discrimination fails due to overlaying UV spectra of different isomers, IR/IR methods offer another possibility. Here, we present a new IR/UV/IR/UV quadruple resonance technique to distinguish between different isomers especially in the electronically excited state. Due to the IR spectra, structural changes and photochemical pathways in excited states can be assigned and identified. The method is applied to the dihydrated cluster of 3-hydroxyflavone which has been investigated as photochemically relevant system and proton wire model in the S{sub 1} state. By applying the new IR/UV/IR/UV technique, we are able to show experimentally that both in the electronic ground (S{sub 0}) and the electronically excited state (S{sub 1}) two isomers have to be assigned.

  1. Structure related modification of the shock induced excitation in Guinea pig papillary muscle.

    PubMed

    Windisch, Herbert; Platzer, Dieter

    2007-01-01

    Here, we present our recent findings from mapping experiments in field stimulated guinea pig papillary muscle. We monitored the developing local excitation during applied shocks (2.5-10 V/cm, 5 or 10 ms) with very high spatial and temporal resolution. Time maps, based on the occurrence of the maximal upstroke velocities, on exceeding 50% of the signal amplitudes, and on exceeding a presumed excitation threshold of -60 mV were constructed. The local, micro-structure related modulation of the excitation process was gained by subtracting a first-order fit (representing the general tendencies) of these time maps from the original ones. The resulting local time maps show the small, locally appearing temporal deviations related to local tissue discontinuities. In general, structure related modulations were found during the whole excitation phase, even during complex signal developments. In regions with positive shock induced polarizations, with increasing shock strength, the local temporal deviations were diminished; in negatively polarized regions, increased, respectively.

  2. Second harmonic excitation spectroscopy in studies of Fano-type coupling in plasmonic arrays (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Walsh, Gary F.; Trevino, Jacob T.; Pecora, Emanuele Francesco; Dal Negro, Luca

    2015-09-01

    Scattering by plasmon resonances of metallic nanoparticles can be tailored by particle material, size, shape, and local as well as long-range order. In this presentation we discuss a series of experiments in which long-range Fano-type coupling between grating resonances and localized surface palsmon (LSP) resonances were studied using second harmonic excitation (SH-E) spectroscopy. By tuning the excitation wavelength of a femtosecond laser and measuring the relative second harmonic (SH) signal we demonstrated that when long-range grating resonances spectrally overlap with those of the LSPs, electromagnetic field enhancement occurs on the surface of the nanoparticles leading to an increase in nonlinear scattering. This effect has been demonstrated for periodic arrays of monomers and dimers, bi-periodic antenna arrays for multi-spectral focusing to a single point, and chirped nanoparticle structures for broadband field enhancement. Results are supported by finite difference time domain simulations showing that electromagnetic fields are enhanced close on the surface of the nanoparticles when long-range structural resonances are excited. These studies have revealed design principles for engineering the interplay of photonic and plasmonic coupling for future linear and nonlinear plasmonic devices.

  3. Fine structure of a resonantly excited p -shell exciton in a CdTe quantum dot

    NASA Astrophysics Data System (ADS)

    Smoleński, T.; Kazimierczuk, T.; Goryca, M.; Wojnar, P.; Kossacki, P.

    2016-05-01

    We present a polarization-resolved photoluminescence excitation study of the absorption spectrum of a p -shell neutral exciton in a single CdTe/ZnTe quantum dot. We find that the fine structure of the p -shell exciton is completely analogous to the fine structure of the s -shell exciton, including the selection rules and the effects of a magnetic field applied in Faraday and Voigt configurations. The energy spectrum of the p -shell exciton is found to be well described by introducing respective isotropic and anisotropic constants of the exchange interaction between a p -shell electron and a p -shell hole. The typical values of these exchange constants averaged over several randomly selected quantum dots yield δ0p p=(0.92 ±0.16 ) meV and δ1p p=(0.58 ±0.25 ) meV. Additionally, we demonstrate that the nonresonant relaxation of the p -shell exciton conserves the exciton spin to a very high degree for both bright and dark exciton configurations.

  4. Band-structure-based collisional model for electronic excitations in ion-surface collisions

    SciTech Connect

    Faraggi, M.N.; Gravielle, M.S.; Alducin, M.; Silkin, V.M.; Juaristi, J.I.

    2005-07-15

    Energy loss per unit path in grazing collisions with metal surfaces is studied by using the collisional and dielectric formalisms. Within both theories we make use of the band-structure-based (BSB) model to represent the surface interaction. The BSB approach is based on a model potential and provides a precise description of the one-electron states and the surface-induced potential. The method is applied to evaluate the energy lost by 100 keV protons impinging on aluminum surfaces at glancing angles. We found that when the realistic BSB description of the surface is used, the energy loss obtained from the collisional formalism agrees with the dielectric one, which includes not only binary but also plasmon excitations. The distance-dependent stopping power derived from the BSB model is in good agreement with available experimental data. We have also investigated the influence of the surface band structure in collisions with the Al(100) surface. Surface-state contributions to the energy loss and electron emission probability are analyzed.

  5. The transverse velocity and excitation structure of the HH 110 jet

    NASA Astrophysics Data System (ADS)

    Riera, A.; López, R.; Raga, A. C.; Estalella, R.; Anglada, G.

    2003-03-01

    We present long-slit spectroscopic observations of the HH 110 jet obtained with the 4.2 m William Herschel Telescope. We have obtained for the first time, spectra for slit positions along and across the jet axis (at the position of knots B, C, I, J and P) to search for the observational signatures of entrainment and turbulence by studying the kinematics and the excitation structure. We find that the HH 110 flow accelerates from a velocity of 35 km s-1 in knot A up to 110 km s-1 in knot P. We find some systematic trends for the variation of the emission line ratios along the jet. No clear trends for the variation of the radial velocity are seen across the width of the jet beam. The cross sections of the jet show complex radial velocity and line emission structures which differ quite strongly from each other. Based on observations made with the 4.2 m William Herschel Telescope operated on La Palma by the Issac Newton Group of Telescopes at the Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

  6. Phase space interrogation of the empirical response modes for seismically excited structures

    NASA Astrophysics Data System (ADS)

    Paul, Bibhas; George, Riya C.; Mishra, Sudib K.

    2017-07-01

    Conventional Phase Space Interrogation (PSI) for structural damage assessment relies on exciting the structure with low dimensional chaotic waveform, thereby, significantly limiting their applicability to large structures. The PSI technique is presently extended for structure subjected to seismic excitations. The high dimensionality of the phase space for seismic response(s) are overcome by the Empirical Mode Decomposition (EMD), decomposing the responses to a number of intrinsic low dimensional oscillatory modes, referred as Intrinsic Mode Functions (IMFs). Along with their low dimensionality, a few IMFs, retain sufficient information of the system dynamics to reflect the damage induced changes. The mutually conflicting nature of low-dimensionality and the sufficiency of dynamic information are taken care by the optimal choice of the IMF(s), which is shown to be the third/fourth IMFs. The optimal IMF(s) are employed for the reconstruction of the Phase space attractor following Taken's embedding theorem. The widely referred Changes in Phase Space Topology (CPST) feature is then employed on these Phase portrait(s) to derive the damage sensitive feature, referred as the CPST of the IMFs (CPST-IMF). The legitimacy of the CPST-IMF is established as a damage sensitive feature by assessing its variation with a number of damage scenarios benchmarked in the IASC-ASCE building. The damage localization capability, remarkable tolerance to noise contamination and the robustness under different seismic excitations of the feature are demonstrated.

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

    SciTech Connect

    Xiao, Haiyan Y.; Weber, William J.; Zhang, Yanwen; Zu, X. T.; Li, Sean

    2015-02-09

    In this study, the response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser, electron and ion irradiations.

  8. Theoretical studies of excited state 1,3 dipolar cycloadditions

    NASA Astrophysics Data System (ADS)

    Belluccci, Michael A.

    The 1,3 dipolar photocycloaddition reaction between 3-hydroxy-4',5,7-trimethoxyflavone (3-HTMF) and methyl cinnamate is investigated in this work. Since its inception in 2004 [JACS, 124, 13260 (2004)], this reaction remains at the forefront in the synthetic design of the rocaglamide natural products. The reaction is multi-faceted in that it involves multiple excited states and is contingent upon excited state intramolecular proton transfer (ESIPT) in 3-HTMF. Given the complexity of the reaction, there remain many questions regarding the underlying mechanism. Consequently, throughout this work we investigate the mechanism of the reaction along with a number of other properties that directly influence it. To investigate the photocycloaddition reaction, we began by studying the effects of different solvent environments on the ESIPT reaction in 3-hydroxyflavone since this underlying reaction is sensitive to the solvent environment and directly influences the cycloaddition. To study the ESIPT reaction, we developed a parallel multi-level genetic program to fit accurate empirical valence bond (EVB) potentials to ab initio data. We found that simulations with our EVB potentials accurately reproduced experimentally determined reaction rates, fluorescence spectra, and vibrational frequency spectra in all solvents. Furthermore, we found that the ultrafast ESIPT process results from a combination of ballistic transfer and intramolecular vibrational redistribution. To investigate the cycloaddition reaction mechanism, we utilized the string method to obtain minimum energy paths on the ab initio potential. These calculations demonstrated that the reaction can proceed through formation of an exciplex in the S1 state, followed by a non-adiabatic transition to the ground state. In addition, we investigated the enantioselective catalysis of the reaction using alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolan-4,5-dimethanol alcohol (TADDOL). We found that TADDOL lowered the energy

  9. Possible spin excitation structure in monolayer FeSe grown on SrTiO3

    NASA Astrophysics Data System (ADS)

    Gao, Yi; Yu, Yan; Zhou, Tao; Huang, Huaixiang; Wang, Qiang-Hua

    2017-07-01

    Based on recent high-resolution angle-resolved photoemission spectroscopy measurement in monolayer FeSe grown on SrTiO3, we constructed a tight-binding model and proposed a superconducting (SC) pairing function which can well fit the observed band structure and SC gap anisotropy. Then we investigated the spin excitation spectra in order to determine the possible sign structure of the SC order parameter. We found that a resonancelike spin excitation may occur if the SC order parameter changes sign along the Fermi surfaces. However, this resonance is located at different locations in momentum space compared to other FeSe-based superconductors, suggesting that the Fermi surface shape and pairing symmetry in monolayer FeSe grown on SrTiO3 may be different from other FeSe-based superconductors.

  10. Low-ionization structures in planetary nebulae - I. Physical, kinematic and excitation properties

    NASA Astrophysics Data System (ADS)

    Akras, Stavros; Gonçalves, Denise R.

    2016-01-01

    Though the low-ionization small-scale structures (LISs) such as knots, filaments and jets of planetary nebulae (PNe) are known for ˜30 yr, some of their observational properties are not well established. In consequence, our ability to include them in the wider context of the formation and evolution of PNe is directly affected. Why most structures have lower densities than the PN shells hosting them? Is their intense emission in low-ionization lines the key to their main excitation mechanism? Therefore, if considered altogether, can LISs line ratios, chemical abundances and kinematics enlighten the interplay between the different excitation and formation processes? Here we present a spectroscopic analysis of five PNe that possess LISs confirming that all nebular components have comparable electron temperatures, whereas the electron density is systematically lower in LISs than in the surrounding nebula. Chemical abundances of LISs versus other PN components do not show significant differences as well. By using diagnostic diagrams from shock models, we demonstrate that LISs' main excitation is due to shocks, whereas the other components are mainly photoionized. We also propose new diagnostic diagrams involving a few emission lines ([N II], [O III], [S II]) and log(fshocks/f*), where fshocks and f* are the ionization photon fluxes due to the shocks and the central star ionizing continuum, respectively. A robust relation differentiating the structures is found, with the shock-excited clearly having log(fshocks/f*) > -1; while the photoionized structures have log(fshocks/f*) < -2. A transition zone, with -2 < log(fshocks/f*) < -1, where both mechanisms are equally important, is also defined.

  11. Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure

    PubMed Central

    Zhang, Yaxin; Zhou, Yucong; Gang, Yin; Jiang, Guili; Yang, Ziqiang

    2017-01-01

    Coherent terahertz radiation from multiple electron beams excitation within a plasmonic crystal-like structure (a three-dimensional holes array) which is composed of multiple stacked layers with 3 × 3 subwavelength holes array has been proposed in this paper. It has been found that in the structure the electromagnetic fields in each hole can be coupled with one another to construct a composite mode with strong field intensity. Therefore, the multiple electron beams injection can excite and efficiently interact with such mode. Meanwhile, the coupling among the electron beams is taken place during the interaction so that a very strong coherent terahertz radiation with high electron conversion efficiency can be generated. Furthermore, due to the coupling, the starting current density of this mechanism is much lower than that of traditional electron beam-driven terahertz sources. This multi-beam radiation system may provide a favorable way to combine photonics structure with electronics excitation to generate middle, high power terahertz radiation. PMID:28112234

  12. Structural damage detection using auto correlation functions of vibration response under sinusoidal excitation

    NASA Astrophysics Data System (ADS)

    Zhang, Muyu; Schmidt, Rüdiger; Markert, Bernd

    2015-07-01

    Structural damage detection using time domain vibration responses has attracted more and more researchers in recent years because of its simplicity in calculation and no requirement of a finite element model. This paper proposes a new approach to locate the damage using the auto correlation function of vibration response signals under sinusoidal excitation from different measurement points of the structure, based on which a vector named Auto Correlation Function at Maximum Point Value Vector (AMV) is formulated. A sensitivity analysis of the normalized AMV with respect to the local stiffness shows that under several specific frequency excitations, the normalized AMV has a sharp change around the local stiffness change location, which means that even when the damage is very small, the normalized AMV is a good indicator for the damage. In order to locate the damage, a damage index is defined as the relative change of the normalized AMV before and after damage. Several example cases in stiffness reduction detection of a frame structure valid the results of the sensitivity analysis, demonstrate the efficiency of the normalized AMV in damage localization and the effect of the excitation frequency on its detectability.

  13. Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure

    NASA Astrophysics Data System (ADS)

    Zhang, Yaxin; Zhou, Yucong; Gang, Yin; Jiang, Guili; Yang, Ziqiang

    2017-01-01

    Coherent terahertz radiation from multiple electron beams excitation within a plasmonic crystal-like structure (a three-dimensional holes array) which is composed of multiple stacked layers with 3 × 3 subwavelength holes array has been proposed in this paper. It has been found that in the structure the electromagnetic fields in each hole can be coupled with one another to construct a composite mode with strong field intensity. Therefore, the multiple electron beams injection can excite and efficiently interact with such mode. Meanwhile, the coupling among the electron beams is taken place during the interaction so that a very strong coherent terahertz radiation with high electron conversion efficiency can be generated. Furthermore, due to the coupling, the starting current density of this mechanism is much lower than that of traditional electron beam-driven terahertz sources. This multi-beam radiation system may provide a favorable way to combine photonics structure with electronics excitation to generate middle, high power terahertz radiation.

  14. Possible Itinerant Moment Contributions to the Magnetic Excitations in Gd, Studied by Neutron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Granroth, G. E.; Aczel, A. A.; Fernandez-Baca, J. A.; Nagler, S. E.

    2013-03-01

    Many experimental features in magnetic superconductors are also present when these complex materials are in the normal state. Therefore studies of simpler itinerant magnets may help provide understanding of these phenomena. We chose to study Gd as it is has an ~ 0 . 6μB itinerant moment in addition to a ~ 7 . 0μB localized moment. The SEQUOIA spectrometer, at the Spallation Neutron Source at Oak Ridge National Laboratory, was used in fine resolution mode with Ei=50 meV neutrons, to measure the magnetic excitations in a 12 gm 160Gd single crystal. The crystal was mounted with the h 0 l plane horizontal and rotated around the vertical axis to map out the excitations. The measured magnetic structure factor for the acoustic modes in the hh 0 direction has an intensity step at h ~ 0 . 3 . Electronic band structure calculations (W. M. Temmerman and P. A. Sterne, J. Phys: Condes. Matter,2, 5529 (1990)) show this Q position to be near several band crossings of the Fermi surface. A detailed analysis, including instrumental resolution, is presented to clarify any relationship between the magnetic structure factor and the electronic band structure. This work was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

  15. Magnetic Excitations in the Nearly Localized, Itinerant Magnet Gd, Studied by Neutron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Graroth, G. E.; Aczel, A. A.; Fernandez-Baca, J. A.; Nagler, S. E.

    2012-02-01

    Many of the current questions about magnetic superconductors are present when these complex materials are in the normal state. Therefore studies of simpler itinerant magnets may help provide understanding of these phenomena. We chose to study an Itinerant magnet near to the fully localized limit. The system of choice, Gd has a total moment size of ˜7.6 μB of which ˜0.6μB of that is itinerant. We used the SEQUOIA spectrometer, at the Spallation Neutron Source at Oak Ridge National Laboratory, to measure the magnetic excitations in a 12 gm ^160Gd single crystal. The fine resolution Fermi chopper was spun at 360 Hz and phased for Ei = 50 meV. The crystal was mounted with the h0l plane horizontal and then rotated around the vertical axis in 1^o steps. This method, and the large out of plane detector coverage of SEQUOIA, provided continuous coverage of a large region of reciprocal space allowing us to map the magnetic excitations. This map provides a measured structure factor for comparison to spin wave models with and without itinerancy effects. There measurements also more clearly resolve the excitations along the h00 direction than in previous studies (J. W. Cable, R. M. Nicklow and N. Wakabayashi Phys. Rev. B 32, 1710 (1985)).

  16. Identification of structural stiffness and excitation forces in time domain using noncontact vision-based displacement measurement

    NASA Astrophysics Data System (ADS)

    Feng, Dongming; Feng, Maria Q.

    2017-10-01

    The emerging noncontact vision-based displacement sensor system offers a promising alternative to the conventional sensors for quantitative structural integrity assessment. Significant advantages of the noncontact vision-based sensor include its low cost, ease of operation, and flexibility to extract structural displacement responses at multiple points. This study aims to link the measured displacement data to the quantification of the structural health condition, by validating the feasibility of simultaneous identification of structural stiffness and unknown excitation forces in time domain using output-only vision-based displacement measurement. Numerical analysis are first carried out to investigate the accuracy, convergence and robustness of identified results to different noise levels, sensor numbers, and initial estimates of structural parameters. Then, experiment on a laboratory scaled beam structure is conducted. Results show that the global stiffness of the beam specimen as well as external hammer excitation forces can be successfully and accurately identified from displacement measurement at two points using one camera. The proposed output-only time-domain identification procedure utilizing vision-based displacement measurement represents a low-cost method for either periodic or long-term bridge performance assessment.

  17. Characteristics of Excitable Dog Behavior Based on Owners' Report from a Self-Selected Study.

    PubMed

    Shabelansky, Anastasia; Dowling-Guyer, Seana

    2016-03-15

    Past research has found that excitable dog behavior is prevalent among sheltered and owned dogs and many times is a reason for canine relinquishment. In spite of its prevalence in the canine population, excitable behavior is relatively unstudied in the scientific literature. The intent of this research was to understand the experience of owners of excitable dogs through the analysis of self-administered online questionnaires completed by owners as part of another study. We found that certain daily scenarios tended to prompt excitable behavior, with excitability most common when the owner or other people came to the dog's home. All owners experienced some level of frustration with their dog's excitable behavior, with the majority being very frustrated. Many dogs in the sample had other behavior problems, with disobedient, destructive, chasing and barking behaviors being the most commonly reported. Other characteristics of excitable dogs also are discussed. Although the ability to generalize from these results is likely limited, due to targeted recruitment and selection of owners of more excitable dogs, this research provides valuable insights into the owner's experience of excitable behavior. We hope this study prompts more research into canine excitable behavior which would expand our understanding of this behavior and help behaviorists, veterinarians, and shelters develop tools for managing it, as well as provide better education to owners of excitable dogs.

  18. Characteristics of Excitable Dog Behavior Based on Owners’ Report from a Self-Selected Study

    PubMed Central

    Shabelansky, Anastasia; Dowling-Guyer, Seana

    2016-01-01

    Simple Summary This study provides information about owners’ experiences with their dogs’ excitable behavior. We found that certain daily scenarios tended to prompt excitable behavior. The majority of owners in this self-selected sample were very frustrated with their excitable dog. Many dogs in the sample had other behavior problems. Abstract Past research has found that excitable dog behavior is prevalent among sheltered and owned dogs and many times is a reason for canine relinquishment. In spite of its prevalence in the canine population, excitable behavior is relatively unstudied in the scientific literature. The intent of this research was to understand the experience of owners of excitable dogs through the analysis of self-administered online questionnaires completed by owners as part of another study. We found that certain daily scenarios tended to prompt excitable behavior, with excitability most common when the owner or other people came to the dog’s home. All owners experienced some level of frustration with their dog’s excitable behavior, with the majority being very frustrated. Many dogs in the sample had other behavior problems, with disobedient, destructive, chasing and barking behaviors being the most commonly reported. Other characteristics of excitable dogs also are discussed. Although the ability to generalize from these results is likely limited, due to targeted recruitment and selection of owners of more excitable dogs, this research provides valuable insights into the owner’s experience of excitable behavior. We hope this study prompts more research into canine excitable behavior which would expand our understanding of this behavior and help behaviorists, veterinarians, and shelters develop tools for managing it, as well as provide better education to owners of excitable dogs. PMID:26999222

  19. Dynamics of the higher lying excited states of cyanine dyes. An ultrafast fluorescence study.

    PubMed

    Guarin, Cesar A; Villabona-Monsalve, Juan P; López-Arteaga, Rafael; Peon, Jorge

    2013-06-20

    The electronic relaxation dynamics of the second singlet excited states of several cyanine dyes was studied through the femtosecond fluorescence up-conversion technique. Our interest in these molecules comes from the potential applications of systems with upper excited singlet states with a long lifetime, which can include electron and energy transfer from the higher lying singlets after one- or two-photon absorption. We studied three series of cyanines with 4-quinolyl, 2-quinolyl, or benzothiazolyl type end groups, each with varying sp(2) carbon conjugation lengths in the methinic bridge. The dynamics after electronic excitation to singlet states above the fluorescent state vary significantly as a function of cyanine structure and conjugation length. In particular, for the 4-quinolyl series the cyanine with an intermediate conjugation length (three methinic carbons) has the slowest S2 decays with lifetimes of 5.4 ps in ethanol and 6.6 ps in ethylene glycol. On the other hand, we observed that the 2-quinolyl family has S2 decay times in the subpicosecond range independent of the conjugation length between the end groups. The slowest internal conversion was observed for the benzothiazolyl type cyanine with five methinic carbons, with an S2 lifetime of 17.3 ps in ethanol. For the planar cyanines of this study we observed for the first time a clear systematic trend in the S2 decay times which closely follow the energy gap law. It was also demonstrated that a slow S2 decay is as well observed upon excitation through degenerate two-photon absorption with near-IR pulses. The present study isolates the most important variables for the design of cyanines with long S2 lifetimes.

  20. The impact of vertical human-structure interaction on the response of footbridges to pedestrian excitation

    NASA Astrophysics Data System (ADS)

    Van Nimmen, K.; Lombaert, G.; De Roeck, G.; Van den Broeck, P.

    2017-08-01

    In the present paper, a detailed crowd model is applied to investigate the impact of vertical human-structure interaction (HSI) on the dynamic response of footbridges to pedestrian excitation. Assuming that the walking behaviour of the pedestrian is not affected by the motion of the supporting structure, the contact force between the pedestrian and the supporting structure is decomposed into the force exerted by the pedestrian on a perfectly rigid floor and an interaction term determined by the mechanical interaction between the person and the structure. The model is also used to evaluate the impact of various simplifying assumptions and inter- and intra-person variabilities. The results show that for the low-frequency dynamic behaviour of footbridges (< 6 Hz) , HSI leads to an effective damping ratio which is (significantly) higher than the inherent damping ratio of the empty structure. In addition, it is demonstrated that the detailed moving crowd model can be well approximated by a time-invariant crowd-structure model. Furthermore, the influence of inter- and intra-person variability in step frequency is observed to decrease as the impact of HSI increases. Finally, it is shown that in many cases accounting for HSI leads to a significant reduction in the response of footbridges to pedestrian excitation which may be considered in practical design.

  1. Excitation study of the Lageos-derived Chandler wobble

    NASA Technical Reports Server (NTRS)

    Gross, R. S.; Chao, B. F.

    1985-01-01

    Euler (1765) has deduced that any nonspherical rigid body which is rotating about some axis that is not its principal moment of inertia axis will experience a wobble as it rotates. The earth's wobble predicted by Euler was actually detected by Chandler (1891). The present paper is concerned with this wobble which is now known as the Chandler wobble. The Chandler wobble has now been under observation for more than 80 years. During part of this time, the amplitude of the wobble has actually been seen to grow. It follows that there must be some mechanisms operating to maintain (or excite) the Chandler wobble preventing it from decaying. Possible excitation mechanisms considered include earthquakes and meteorological variations. In this paper, an analysis is conducted of Lageos polar motion data for the period 1977-1983 to find out what can be learned from these data about the excitation mechanisms.

  2. Initiation of re-entry in an excitable medium: Structural investigation of cardiac tissue using a genetic algorithm

    NASA Astrophysics Data System (ADS)

    Scarle, S.; Clayton, R. H.

    2006-09-01

    The detailed mechanisms by which re-entry and ventricular fibrillation are initiated in the heart remain poorly understood because they are difficult to investigate experimentally. We have used a simplified excitable media computational model of action potential propagation to systematically study how re-entry can be produced by diffuse regions of inexcitable tissue. Patterns of excitable and inexcitable tissue were generated using a genetic algorithm. The inexcitable tissue was modeled in two ways: (i) diffusive, electrically connected but inexcitable tissue, or (ii) zero-flux, areas of tissue electrically disconnected in the same way as zero-flux boundary conditions. We were able to evolve patterns of diffuse inexcitable tissue that favored re-entry, but no single structure or pattern emerged. Diffusive inexcitable regions were inherently less arrhythmogenic than zero-flux inexcitable ones.

  3. Resonance of Non-Linear Systems Subjected to Multi-Parametrically Excited Structures: (Comparison Between two Methods, Response and Stability)

    NASA Astrophysics Data System (ADS)

    El-Bassiouny, A. F.; Eissa, M.

    2004-01-01

    Most mechanical systems or structures are subject to parametric or self excitations. In the present work, simultaneous principal parametric resonance of two-degree-of-freedom systems with quadratic and cubic non-linearities subject to multi-frequency parametric excitations in the presence of two-to-one internal resonance is investigated. Two approximate methods are applied to construct a set of first order, non-linear ordinary differential equations governing the modulation of the amplitudes and phases of oscillations. The applied methods are; the method of multiple time scale perturbation and the generalized synchronization methods. Steady state solutions and their stability are studied for selected values of the different parameters. The obtained results from both methods are in excellent agreement.

  4. Influence of heat generated by a Raman excitation laser on the structural analysis of thin amorphous silicon film

    NASA Astrophysics Data System (ADS)

    Novák, P.; Očenášek, J.; Prušáková, L.; Vavruňková, V.; Savková, J.; Rezek, J.

    2016-02-01

    In the present work we investigate thin amorphous silicon film fabricated by plasma enhanced chemical vapor deposition. In particular, we analyze changes in the recorded Raman spectra caused by excitation laser irradiation. Solid phase crystallization, hydrogen diffusive outflow and Raman spectra peak shifts have been observed experimentally and analyzed numerically. The role of film thickness on all these features is pointed out. The study involves laser powers between 0.1 mW and 10 mW focused to a spot diameter of ∼1 μm and film thicknesses between 50 and ∼2000 nm. Additionally, the laser induced temperature fields were analyzed by means of numerical simulation and the Raman spectral shift trough Balkanski model. Results are correlated to structural analysis by Raman spectroscopy, optical microscopy, scanning electron microscopy and atomic force microscopy. It was found that the hydrogen content and solid phase fraction identified by Raman spectroscopy are highly sensitive to the applied excitation laser power.

  5. Statistical structuring theory in parametrically excitable dynamical systems with a Gaussian pump

    NASA Astrophysics Data System (ADS)

    Klyatskin, V. I.; Koshel, K. V.

    2016-03-01

    Based on the idea of the statistical topography, we analyze the problem of emergence of stochastic structure formation in linear and quasilinear problems described by first-order partial differential equations. The appearance of a parametric excitation on the background of a Gaussian pump is a specific feature of these problems. We obtain equations for the probability density of the solutions of these equations, whence it follows that the stochastic structure formation emerges with probability one, i.e., for almost every realization of the random parameters of the medium.

  6. Influence of ligand substitution on excited state structural dynamics in Cu(I) bis-phenanthroline complexes.

    SciTech Connect

    Lockard, J. V.; Kabehie, S.; Zink, J. I.; Smolentsev, G.; Soldatov, A.; Chen, L. X.

    2010-01-01

    This study explores the influences of steric hindrance and excited state solvent ligation on the excited state dynamics of Cu{sup I} diimine complexes. Ultrafast excited state dynamics of Cu(I)bis(3,8-di(ethynyltrityl)-1,10-phenanthroline) [Cu{sup I}(detp){sub 2}]{sup +} are measured using femtosecond transient absorption spectroscopy. The steady state electronic absorption spectra and measured lifetimes are compared to those of Cu(I)bis(1,10-phenanthroline), [Cu{sup I}(phen){sub 2}]{sup +}, and Cu(I)bis(2-9-dimethyl-1,10-phenanthroline), [Cu{sup I}(dmp){sub 2}]{sup +}, model complexes to determine the influence of different substitution patterns of the phenanthroline ligand on the structural dynamics associated with the metal to ligand charge transfer excited states. Similarities between the [Cu{sup I}(detp){sub 2}]{sup +} and [Cu{sup I}(phen){sub 2}]{sup +} excited state lifetimes were observed in both coordinating and noncoordinating solvents and attributed to the lack of steric hindrance from substitution at the 2- and 9-positions. The solution-phase X-ray absorption spectra of [Cu{sup I}(detp){sub 2}]{sup +}, [Cu{sup I}(phen){sub 2}]{sup +}, and [Cu{sup I}(dmp){sub 2}]{sup +} are reported along with finite difference method calculations that are used to determine the degree of ground state dihedral angle distortion in solution and to account for the pre-edge features observed in the XANES region.

  7. Cell Adhesion on Micro-Structured Fibronectin Gradients Fabricated by Multiphoton Excited Photochemistry

    PubMed Central

    Chen, Xiyi; Su, Yuan-Deng; Ajeti, Visar; Chen, Shean-Jen; Campagnola, Paul J.

    2013-01-01

    Concentration gradients of ECM proteins play active roles in many areas of cell biology including wound healing and metastasis. They may also form the basis of tissue engineering scaffolds, as these can direct cell adhesion and migration and promote new matrix synthesis. To better understand cell–matrix interactions on attractive gradients, we have used multiphoton excited (MPE) photochemistry to fabricate covalently linked micro-structured gradients from fibronectin (FN). The gradient design is comprised of a parallel series of individual linear gradients with overall dimensions of approximately 800 × 800 μm, where a linear dynamic range of nearly 10-fold in concentration was achieved. The adhesion dynamics of 3T3 fibroblasts were investigated, where the cell morphology and actin cytoskeleton became increasingly elongated and aligned with the direction of the gradient at increasing protein concentration. Moreover, the cell morphologies are distinct when adhered to regions of differing FN concentration but with similar topography. These results show that the fabrication approach allows investigating the roles of contact guidance and ECM cues on the cell–matrix interactions. We suggest this design overcomes some of the limitations with other fabrication methods, especially in terms of 3D patterning capabilities, and will serve as a new tool to study cell–matrix interactions. PMID:23710258

  8. Enzymatic activity of alkaline phosphatase inside protein and polymer structures fabricated via multiphoton excitation.

    PubMed

    Basu, Swarna; Campagnola, Paul J

    2004-01-01

    We demonstrate micron scale control of bioactivity through the use of multiphoton excited photochemistry, where this technique has been used to cross-link three-dimensional matrixes of alkaline phosphatase, bovine serum albumin, and polyacrylamide and combinations therein. Using a fluorescence-based assay (ELF-97), the enzymatic activity has been studied using a Michaelis-Menten analysis, and we have measured the specificity constants kcat/KM for alkaline phosphatase in both the protein and polymer matrixes to be on the order of 10(5)-10(6) M(-1) s(-1)and are comparable to known literature values in other environments. It is found that the enzyme is simply entrapped in the polymer matrix, whereas it is completely covalently bound in the protein structures. The relative reaction rate of alkaline phosphatase bound to BSA with the ELF substrate was measured as a function of cross-link density and was found to decrease in the more tightly formed matrixes, indicating a decrease in the diffusion in the matrix.

  9. Excitation rate and background measurements during LIF studies on krypton

    NASA Astrophysics Data System (ADS)

    Whitehead, C. A.; Cannon, B. D.; Wacker, J. F.

    1993-04-01

    The Krypton Isotope Laser Analysis (KILA) method is being developed at the Pacific Northwest Laboratory (PNL) to measure Kr-85 concentrations in small air samples. The technique uses high-resolution lasers to excite individual isotopes of krypton specifically to induce Kr-85 to fluorescence for detection by optical means. Production of krypton metastables via two-photon excitation to the 2p(sub 6) state has been shown to be 0.15% efficient in 0.13 mTorr of krypton--sufficiently high to demonstrate overall feasibility of the KILA method. Since this goal was met, focus has been directed toward development of a working vacuum ultraviolet (VUV) fluorescence detection system and toward understanding the VUV background. This report describes the progress made in these two areas. The second step of the KILA process is to optically pump all except the Kr-85 isotopes from the metastable state back to the ground state using laser-induced fluorescence (LIF). The rate of this process and the VUV background afterward will determine the sensitivity and selectivity of the KILA approach. De-excitation of the metastable population was accomplished via one-photon absorption of a continuous-wave (c-w) laser to the 2p(sub 8) energy level. Non-isotopically selective de-excitation rates as high as 5 x 10(exp 5)/sec have been measured, yielding a signal-to-background ratio of g reater than 10(exp 6). The lifetime of the metastables is 1.2 msec in 200 mTorr of neon--much longer than the time required to de-excite krypton metastables and to detect fluorescence produced by Kr-85. After attaining these high de-excitation rates, a gated VUV detection system was built with a dynamic range large enough to measure a small background following de-excitation of large metastable populations. Future experiments will focus on reducing the background level by another 2-3 orders of magnitude and perfecting the isotopically selective de-excitation technique with known samples.

  10. Excitation rate and background measurements during LIF studies on krypton

    SciTech Connect

    Whitehead, C.A.; Cannon, B.D.; Wacker, J.F.

    1993-04-01

    The Krypton Isotope Laser Analysis (KILA) method is being developed at the Pacific Northwest Laboratory (PNL) to measure [sup 85]Kr concentrations in small air samples. The technique uses high-resolution lasers to excite individual isotopes of krypton specifically to induce [sup 85]Kr to fluorescence for detection by optical means. Production of krypton metastables via two-photon excitation to the 2p[sub 6] state has been shown to be 0.15% efficient in 0.13 mTorr of krypton--sufficiently high to demonstrate overall feasibility of the KILA method. Since this goal was met, focus has been directed toward development of a working vacuum ultraviolet (VUV) fluorescence detection system and toward understanding the VUV background. This report describes the progress made in these two areas. The second step of the KILA process is to optically pump all except the [sup 85]Kr isotopes from the metastable state back to the ground state using laser-induced fluorescence (LIF). The rate of this process and the VUV background afterward will determine the sensitivity and selectivity of the KILA approach. De-excitation of the metastable population was accomplished via one-photon absorption of a continuous-wave (c-w) laser to the 2p[sub 8] energy level. Non-isotopically selective de-excitation rates as high as 5 [times] 10[sup 5] sec[sup [minus]1] have been measured, yielding a signal-to-background ratio of >10[sup 6]. The lifetime of the metastables is 1.2 msec in 200 mTorr of neon--much longer than the time required to de-excite krypton metastables and to detect fluorescence produced by [sup 85]Kr. After attaining these high de-excitation rates, a gated VUV detection system was built with a dynamic range large enough to measure a small background following de-excitation of large metastable populations. Future experiments will focus on reducing the background level by another 2--3 orders of magnitude and perfecting the isotopically selective de-excitation technique with known samples.

  11. Excitation rate and background measurements during LIF studies on krypton

    SciTech Connect

    Whitehead, C.A.; Cannon, B.D.; Wacker, J.F.

    1993-04-01

    The Krypton Isotope Laser Analysis (KILA) method is being developed at the Pacific Northwest Laboratory (PNL) to measure {sup 85}Kr concentrations in small air samples. The technique uses high-resolution lasers to excite individual isotopes of krypton specifically to induce {sup 85}Kr to fluorescence for detection by optical means. Production of krypton metastables via two-photon excitation to the 2p{sub 6} state has been shown to be 0.15% efficient in 0.13 mTorr of krypton--sufficiently high to demonstrate overall feasibility of the KILA method. Since this goal was met, focus has been directed toward development of a working vacuum ultraviolet (VUV) fluorescence detection system and toward understanding the VUV background. This report describes the progress made in these two areas. The second step of the KILA process is to optically pump all except the {sup 85}Kr isotopes from the metastable state back to the ground state using laser-induced fluorescence (LIF). The rate of this process and the VUV background afterward will determine the sensitivity and selectivity of the KILA approach. De-excitation of the metastable population was accomplished via one-photon absorption of a continuous-wave (c-w) laser to the 2p{sub 8} energy level. Non-isotopically selective de-excitation rates as high as 5 {times} 10{sup 5} sec{sup {minus}1} have been measured, yielding a signal-to-background ratio of >10{sup 6}. The lifetime of the metastables is 1.2 msec in 200 mTorr of neon--much longer than the time required to de-excite krypton metastables and to detect fluorescence produced by {sup 85}Kr. After attaining these high de-excitation rates, a gated VUV detection system was built with a dynamic range large enough to measure a small background following de-excitation of large metastable populations. Future experiments will focus on reducing the background level by another 2--3 orders of magnitude and perfecting the isotopically selective de-excitation technique with known samples.

  12. Short-range ordered photonic structures of lamellae-forming diblock copolymers for excitation-regulated fluorescence enhancement

    NASA Astrophysics Data System (ADS)

    Kim, Se Hee; Kim, Ki-Se; Char, Kookheon; Yoo, Seong Il; Sohn, Byeong-Hyeok

    2016-05-01

    Photonic crystals can be represented by periodic nanostructures with alternating refractive indices, which create artificial stop bands with the appearance of colors. In this regard, nanodomains of block copolymers and the corresponding structural colors have been intensively studied in the past. However, the practical application of photonic crystals of block copolymers has been limited to a large degree because of the presence of large defects and grain boundaries in the nanodomains of block copolymers. The present study focuses on the alternative opportunity of short-range ordered nanodomains of block copolymers for fluorescence enhancement, which also has a direct relevance to the development of fluorescence sensors or detectors. The enhancement mechanism was found to be interconnected with the excitation process rather than the alternation of the decay kinetics. In particular, we demonstrate that randomly oriented, but regular grains of lamellae of polystyrene-block-polyisoprene, PS-b-PI, diblock copolymers and their blend with PS homopolymers can behave as Bragg mirrors to induce multiple reflections of the excitation source inside the photonic structures. This process in turn significantly increases the effective absorption of the given fluorophores inside the polymeric photonic structures to amplify the fluorescence signal.Photonic crystals can be represented by periodic nanostructures with alternating refractive indices, which create artificial stop bands with the appearance of colors. In this regard, nanodomains of block copolymers and the corresponding structural colors have been intensively studied in the past. However, the practical application of photonic crystals of block copolymers has been limited to a large degree because of the presence of large defects and grain boundaries in the nanodomains of block copolymers. The present study focuses on the alternative opportunity of short-range ordered nanodomains of block copolymers for fluorescence

  13. Optimization and Validation of Rotating Current Excitation with GMR Array Sensors for Riveted Structures Inspection.

    PubMed

    Ye, Chaofeng; Udpa, Lalita; Udpa, Satish

    2016-09-16

    In eddy current non-destructive testing of a multi-layered riveted structure, rotating current excitation, generated by orthogonal coils, is advantageous in providing sensitivity to defects of all orientations. However, when used with linear array sensors, the exciting magnetic flux density ( B x ) of the orthogonal coils is not uniform over the sensor region, resulting in an output signal magnitude that depends on the relative location of the defect to the sensor array. In this paper, the rotating excitation coil is optimized to achieve a uniform B x field in the sensor array area and minimize the probe size. The current density distribution of the coil is optimized using the polynomial approximation method. A non-uniform coil design is derived from the optimized current density distribution. Simulation results, using both an optimized coil and a conventional coil, are generated using the finite element method (FEM) model. The signal magnitude for an optimized coil is seen to be more robust with respect to offset of defects from the coil center. A novel multilayer coil structure, fabricated on a multi-layer printed circuit board, is used to build the optimized coil. A prototype probe with the optimized coil and 32 giant magnetoresistive (GMR) sensors is built and tested on a two-layer riveted aluminum sample. Experimental results show that the optimized probe has better defect detection capability compared with a conventional non-optimized coil.

  14. Optimization and Validation of Rotating Current Excitation with GMR Array Sensors for Riveted Structures Inspection

    PubMed Central

    Ye, Chaofeng; Udpa, Lalita; Udpa, Satish

    2016-01-01

    In eddy current non-destructive testing of a multi-layered riveted structure, rotating current excitation, generated by orthogonal coils, is advantageous in providing sensitivity to defects of all orientations. However, when used with linear array sensors, the exciting magnetic flux density (Bx) of the orthogonal coils is not uniform over the sensor region, resulting in an output signal magnitude that depends on the relative location of the defect to the sensor array. In this paper, the rotating excitation coil is optimized to achieve a uniform Bx field in the sensor array area and minimize the probe size. The current density distribution of the coil is optimized using the polynomial approximation method. A non-uniform coil design is derived from the optimized current density distribution. Simulation results, using both an optimized coil and a conventional coil, are generated using the finite element method (FEM) model. The signal magnitude for an optimized coil is seen to be more robust with respect to offset of defects from the coil center. A novel multilayer coil structure, fabricated on a multi-layer printed circuit board, is used to build the optimized coil. A prototype probe with the optimized coil and 32 giant magnetoresistive (GMR) sensors is built and tested on a two-layer riveted aluminum sample. Experimental results show that the optimized probe has better defect detection capability compared with a conventional non-optimized coil. PMID:27649202

  15. Excitation energies of a water-bridged twisted retinal structure in the bacteriorhodopsin proton pump: a theoretical investigation.

    PubMed

    Wolter, Tino; Welke, Kai; Phatak, Prasad; Bondar, Ana-Nicoleta; Elstner, Marcus

    2013-08-14

    The first proton transfer in the bacteriorhodopsin photocycle takes place during the L → M transition. Structural details of the pre proton transfer L intermediate have been investigated using experiments and computations. Here, we assess L-state structural models by performing hybrid quantum mechanical/molecular mechanical molecular dynamics and excitation energy calculations. The computations suggest that a water-bridged twisted retinal structure gives the closest agreement with the experimental L/bR shift in the excitation energy.

  16. Optimization of a hybrid vibration absorber for vibration control of structures under random force excitation

    NASA Astrophysics Data System (ADS)

    Cheung, Y. L.; Wong, W. O.; Cheng, L.

    2013-02-01

    A recently reported design of a hybrid vibration absorber (HVA) which is optimized to suppress resonant vibration of a single degree-of-freedom (SDOF) system is re-optimized for suppressing wide frequency band vibration of the SDOF system under stationary random force excitation. The proposed HVA makes use of the feedback signals from the displacement and velocity of the absorber mass for minimizing the vibration response of the dynamic structure based on the H2 optimization criterion. The objective of the optimal design is to minimize the mean square vibration amplitude of a dynamic structure under a wideband excitation, i.e., the total area under the vibration response spectrum is minimized in this criterion. One of the inherent limitations of the traditional passive vibration absorber is that its vibration suppression is low if the mass ratio between the absorber mass and the mass of the primary structure is low. The active element of the proposed HVA helps further reduce the vibration of the controlled structure and it can provide significant vibration absorption performance even at a low mass ratio. Both the passive and active elements are optimized together for the minimization of the mean square vibration amplitude of the primary system. The proposed HVA are tested on a SDOF system and continuous vibrating structures with comparisons to the traditional passive vibration absorber.

  17. Magnetic excitations in (SiO 2)Co nano-composite films: Brillouin light scattering study

    NASA Astrophysics Data System (ADS)

    Stashkevich, A. A.; Roussigné, Y.; Stognij, A. I.; Novitskii, N. I.; Wurtz, G.; Zayats, A. V.; Viau, G.; Chaboussant, G.; Ott, F.; Lutsev, L. V.; Djemia, P.; Kostylev, M. P.; Belotelov, V.

    2009-04-01

    Behaviour of magnetic excitations in the Damon-Eshbach (DE) and backward volume (BV) geometries in nano-composite (SiO 2) 100-xCo x (50% at< x<80% at) films has been studied by Brillouin light scattering (BLS). It has been shown that it is the structure of Stokes/anti-Stokes BLS lines in the DE geometry that allows reliable identification of dipole-exchange spin waves (SW) and numerical estimation of the value of the effective exchange constant A eff of a super-ferromagnetic nano-granular sample ( x=80% at).

  18. Effect of structural distortion and polarization in localization of electronic excitations in organic semiconductor materials

    NASA Astrophysics Data System (ADS)

    Nayyar, Iffat; Batista, Enrique; Tretiak, Sergei; Saxena, Avadh; Smith, Darryl; Martin, Richard

    2012-02-01

    Organic polymers find varied applications in optoelectronic devices such as solar cells, light emitting diodes and lasers. Detailed understanding of charge carrier transport by polarons and excitonic energy transfer producing singlet and triplet excitations is critical to improve their efficiency. We benchmarked the ability of current functional models to describe the spatial extent of self-trapped neutral and charged excitations for MEH-PPV owing to its superior luminescence and experimental evidence. Now we are interested in distinguishing between two distinct origins leading to localization; spatial localization of the wavefunction by itself on the undistorted geometry and localization of the wavefunction assured by distortion of the structure during its relaxation. We suggest localization is produced by electronic rearrangements and character of the functional. We also observe that different functionals place the highest occupied and lowest virtual orbitals at different positions in the energy band diagram based on their ability to predict the extent of localization of these states.

  19. Vibronic structure and coupling of higher excited electronic states in carotenoids

    NASA Astrophysics Data System (ADS)

    Krawczyk, Stanisław; Luchowski, Rafał

    2013-03-01

    Absorption spectra of all-trans carotenoids (lycopene, violaxanthin, ζ-carotene) at low temperature exhibit peculiar features in the UV range. The transition to the 11Ag+ state ('cis-band') weakens on cooling, indicating that it is induced by thermal deformations of the conjugated chain. The higher energy band has unique vibrational structure indicating the vibronic coupling of nBu with another electronic state. The electroabsorption spectra point to the electric field-induced mixing of the nBu state with the vibrational continuum of a lower-lying excited state (Fano effect). These observations widen the basis for elucidation of the vibronic coupling effects in the lower excited states.

  20. Electronic excitation transport in photosynthesis and crystal and molecular structures of porphyrin compounds

    SciTech Connect

    Yang, Shumei.

    1991-04-22

    The excitation energy transfer in three photosynthetic organism samples, Bacteriochlorophyll a-protein from Prosthecochloris aestuarii, and enriched photosystem I particles from spinach chloroplasts, have been investigated by pump-probe ultrafast spectroscopy. The isotropic photobleaching profiles were best described by two exponential decay components in one Bchl a-protein complex, and three exponential decay components in another. The experimental results from the three samples show that nonrandom chromophore orientations exist and Sauer's pebble mosaic'' model is an appropriate one for excitation transfer in these samples. The polarized pump-probe transients have been analyzed in terms of an exciton hopping model that incorporates the known geometry of the Bchl a-protein. The crystal and molecular structures of four metalloporphyrins have been determined by X-ray diffraction and molecular mechanics. 207 refs., 44 figs., 15 tabs.

  1. Re and Br X-ray absorption near-edge structure study of the ground and excited states of [ReBr(CO)3(bpy)] interpreted by DFT and TD-DFT calculations.

    PubMed

    Záliš, Stanislav; Milne, Chris J; El Nahhas, Amal; Blanco-Rodríguez, Ana María; van der Veen, Renske M; Vlček, Antonín

    2013-05-20

    X-ray absorption spectra of fac-[ReBr(CO)3(bpy)] near the Re L3- and Br K-edges were measured in a steady-state mode as well as time-resolved at 630 ps after 355 nm laser pulse excitation. Relativistic spin-orbit time-dependent density functional theory (TD-DFT) calculations account well for the shape of the near-edge absorption (the ″white line″) of the ground-state Re spectrum, assigning the lowest-lying transitions as core-to-ligand metal-to-ligand charge transfer from Re 2p(3/2) into predominantly π*(bpy) molecular orbitals (MOs) containing small 5d contributions, followed in energy by transitions into π* Re(CO)3 and delocalized σ*/π* MOs. Transitions gain their intensities from Re 5d and 6s participation in the target orbitals. The 5d character is distributed over many unoccupied MOs; the 5d contribution to any single empty MO does not exceed 29%. The Br K-edge spectrum is dominated by the ionization edge and multiple scattering features, the pre-edge electronic transitions being very weak. Time-resolved spectra measured upon formation of the lowest electronic excited state show changes characteristic of simultaneous Re and Br electronic depopulation: shifts of the Re and Br edges and the Re white line to higher energies and emergence of new intense pre-edge features that are attributed by TD-DFT to transitions from Re 2p(3/2) and Br 1s orbitals into a vacancy in the HOMO-1 created by electronic excitation. Experimental spectra together with quantum chemical calculations provide a direct evidence for a ReBr(CO)3 → bpy delocalized charge transfer character of the lowest excited state. Steady-state as well as time-resolved Re L3 spectra of [ReCl(CO)3(bpy)] and [Re(Etpy)(CO)3(bpy)](+) are very similar to those of the Br complex, in agreement with similar (TD) DFT calculated transition energies as well as delocalized excited-state spin densities and charge changes upon excitation.

  2. Semiempirical studies of atomic structure

    NASA Astrophysics Data System (ADS)

    Curtis, L. J.

    The energy level structure, transition probabilities, and general spectroscopic properties of highly-ionized many-electron systems are studied through the combined use of sensitive semiempirical data systematizations, selected precision experimental measurements, and specialized theoretical computations. Measurements are made primarily through the use of fast ion beam excitation methods, which are combined with available data from laser- and tokamak-produced plasmas, astrophysical sources, and conventional light sources. The experimental studies are strengthened through large scale ab initio calculations. Large blocks of data are predictively systematized and parameterized along isoelectric, homologous, isoionic, Rydberg, and yrast series, to provide a comprehensive and reliable data base.

  3. Theoretical studies on the reaction pathways of electronically excited DAAF

    SciTech Connect

    Quenneville, Jason M; Moore, David S

    2009-01-01

    The use of temporally and spectrally shaped ultrafast laser pulses to initiate, as well as detect, high explosives is being explored at Los Alamos. High level ab initio calculations, presented here, are employed to help guide and interpret the experiments. The ground and first excited electronic states of 3,3{prime}-diamino-4,4{prime}-azoxyfurazan (DAAF) are investigated using complete active space self-consistent field (CASSCF) and time-dependent density functional theory (TD-DFT). The geometrical and energetic character of the excited state minima, conical intersections and reaction pathways of DAAF are described. Two radiative and two non-radiative excited state population quenching mechanisms are outlined, and possible pathways for photochemical and spectroscopic control are discussed. The use of laser light to control chemical reactions has many applications. The initiation and the detection of explosives are two such applications currently under development at Los Alamos. Though inherently experimental, the project can be aided by theory through both prediction and interpretation. When the laser light is in the UV/visible region of the electromagnetic spectrum, the absorbing molecule is excited electronically and excitation decay may occur either radiatively (fluorescence or phosphorescence) or non-radiatively (through internal conversion). In many cases decay of the excitation occurs through a mixture of processes, and maximizing the desired result requires sophisticated laser pulses whose amplitude has been optimally modulated in time and/or frequency space. Control of cis-stilbene photochemistry was recently demonstrated in our group, and we aim to extend this work to high explosive compounds. Maximizing radiative decay leads to increased fluorescence quantum yields and enhances the possibility of spectral detection of the absorbing molecule. Maximizing non-radiative decay can lead to chemistry, heating of the sample and possibly detonation initiation in

  4. Comparative study on atomic and molecular Rydberg-state excitation in strong infrared laser fields

    NASA Astrophysics Data System (ADS)

    Lv, Hang; Zuo, Wanlong; Zhao, Lei; Xu, Haifeng; Jin, Mingxing; Ding, Dajun; Hu, Shilin; Chen, Jing

    2016-03-01

    Rydberg-state excitation of atoms in strong infrared laser fields provides a new complementary aspect of the perspective of atom-strong field interactions. In this article, we perform an experimental and theoretical study on the corresponding process of diatomic molecules, N2 and O2. We show that neutral molecules can also survive strong 800-nm laser fields in high Rydberg states, while their behavior is remarkably different in comparison with their companion atoms, Ar and Xe. The Rydberg excitation of N2 generally behaves similarly to Ar, while that of O2 is more significantly suppressed than the ionization compared to Xe in a high intensity region, which can be understood in the frame of a semiclassical picture, together with their different structures of molecular orbitals. However, distinct quantum features in the Rydberg excitation processes that are apparently beyond the semiclassical picture have been identified, i.e., the less suppressed probability of O2 at low intensity and the oscillation behavior of the ratio between N2 and Ar, indicating that our understanding of the relevant physics is still far from complete.

  5. Magnetic structure and spin excitations in BaMn2Bi2

    SciTech Connect

    Calder, Stuart A.; Saparov, Bayrammurad I; Cao, H. B.; Niedziela, Jennifer L.; Lumsden, Mark D.; Sefat, Athena Safa; Christianson, Andrew D.

    2014-02-19

    We present a single crystal neutron scattering study of BaMn2Bi2, a recently synthesized material with the same ThCr2Si2type structure found in several Fe-based unconventional superconducting materials. We show long range magnetic order, in the form of a G-type antiferromagnetic structure, to exist up to 390 K with an indication of a structural transition at 100 K. Utilizing inelastic neutron scattering we observe a spin-gap of 16 meV, with spin-waves extending up to 55 meV. We find these magnetic excitations are well fit to a J1-J2-Jc Heisenberg model and present values for the exchange interactions. The spin wave spectrum appears to be unchanged by the 100 K structural phase transition.

  6. Low-energy d-d excitations in MnO studied by resonant x-ray fluorescence spectroscopy

    SciTech Connect

    Butorin, S.M.; Guo, J.; Magnuson, M.

    1997-04-01

    Resonant soft X-ray emission spectroscopy has been demonstrated to possess interesting abilities for studies of electronic structure in various systems, such as symmetry probing, alignment and polarization dependence, sensitivity to channel interference, etc. In the present abstract the authors focus on the feasibility of resonant soft X-ray emission to probe low energy excitations by means of resonant electronic X-ray Raman scattering. Resonant X-ray emission can be regarded as an inelastic scattering process where a system in the ground state is transferred to a low excited state via a virtual core excitation. The energy closeness to a core excitation of the exciting radiation enhances the (generally) low probability for inelastic scattering at these wavelengths. Therefore soft X-ray emission spectroscopy (in resonant electronic Raman mode) can be used to study low energy d-d excitations in transition metal systems. The involvement of the intermediate core state allows one to use the selection rules of X-ray emission, and the appearance of the elastically scattered line in the spectra provides the reference to the ground state.

  7. EEMD-MUSIC-Based Analysis for Natural Frequencies Identification of Structures Using Artificial and Natural Excitations

    PubMed Central

    Amezquita-Sanchez, Juan P.; Romero-Troncoso, Rene J.; Osornio-Rios, Roque A.; Garcia-Perez, Arturo

    2014-01-01

    This paper presents a new EEMD-MUSIC- (ensemble empirical mode decomposition-multiple signal classification-) based methodology to identify modal frequencies in structures ranging from free and ambient vibration signals produced by artificial and natural excitations and also considering several factors as nonstationary effects, close modal frequencies, and noisy environments, which are common situations where several techniques reported in literature fail. The EEMD and MUSIC methods are used to decompose the vibration signal into a set of IMFs (intrinsic mode functions) and to identify the natural frequencies of a structure, respectively. The effectiveness of the proposed methodology has been validated and tested with synthetic signals and under real operating conditions. The experiments are focused on extracting the natural frequencies of a truss-type scaled structure and of a bridge used for both highway traffic and pedestrians. Results show the proposed methodology as a suitable solution for natural frequencies identification of structures from free and ambient vibration signals. PMID:24683346

  8. EEMD-MUSIC-based analysis for natural frequencies identification of structures using artificial and natural excitations.

    PubMed

    Camarena-Martinez, David; Amezquita-Sanchez, Juan P; Valtierra-Rodriguez, Martin; Romero-Troncoso, Rene J; Osornio-Rios, Roque A; Garcia-Perez, Arturo

    2014-01-01

    This paper presents a new EEMD-MUSIC- (ensemble empirical mode decomposition-multiple signal classification-) based methodology to identify modal frequencies in structures ranging from free and ambient vibration signals produced by artificial and natural excitations and also considering several factors as nonstationary effects, close modal frequencies, and noisy environments, which are common situations where several techniques reported in literature fail. The EEMD and MUSIC methods are used to decompose the vibration signal into a set of IMFs (intrinsic mode functions) and to identify the natural frequencies of a structure, respectively. The effectiveness of the proposed methodology has been validated and tested with synthetic signals and under real operating conditions. The experiments are focused on extracting the natural frequencies of a truss-type scaled structure and of a bridge used for both highway traffic and pedestrians. Results show the proposed methodology as a suitable solution for natural frequencies identification of structures from free and ambient vibration signals.

  9. Excitation Dependent Phosphorous Property and New Model of the Structured Green Luminescence in ZnO

    PubMed Central

    Ye, Honggang; Su, Zhicheng; Tang, Fei; Wang, Mingzheng; Chen, Guangde; Wang, Jian; Xu, Shijie

    2017-01-01

    The copper induced green luminescence (GL) with two sets of fine structures in ZnO crystal has been found for several decades (i.e., R. Dingle, Phys. Rev. Lett. 23, 579 (1969)), but the physical origin of the doublet still remains as an open question up to now. In this paper, we provide new insight into the mechanism of the structured GL band in terms of new experimental findings and theoretical calculations. It is found, for the first time, that the GL signal exhibits persistent afterglow for tens of minutes after the switch-off of below-band-gap excitation light but it cannot occur under above-band-gap excitation. Such a phosphorous property may be interpreted as de-trapping and feeding of electrons from a shallow trapping level via the conduction band to the Cu-related luminescence centers where the Cu3+ ion is proposed to work as the final state of the GL emission. From first-principles calculation, such a Cu3+ ion in wurtzite ZnO prefers a high spin 3d8 state with two non-degenerated half-filled orbitals due to the Jahn-Teller effect, probably leading to the double structures in photoluminescence spectrum. Therefore, this model gives a comprehensively new understanding on the mechanism of the structured GL band in ZnO. PMID:28150699

  10. Excitation Dependent Phosphorous Property and New Model of the Structured Green Luminescence in ZnO

    NASA Astrophysics Data System (ADS)

    Ye, Honggang; Su, Zhicheng; Tang, Fei; Wang, Mingzheng; Chen, Guangde; Wang, Jian; Xu, Shijie

    2017-02-01

    The copper induced green luminescence (GL) with two sets of fine structures in ZnO crystal has been found for several decades (i.e., R. Dingle, Phys. Rev. Lett. 23, 579 (1969)), but the physical origin of the doublet still remains as an open question up to now. In this paper, we provide new insight into the mechanism of the structured GL band in terms of new experimental findings and theoretical calculations. It is found, for the first time, that the GL signal exhibits persistent afterglow for tens of minutes after the switch-off of below-band-gap excitation light but it cannot occur under above-band-gap excitation. Such a phosphorous property may be interpreted as de-trapping and feeding of electrons from a shallow trapping level via the conduction band to the Cu-related luminescence centers where the Cu3+ ion is proposed to work as the final state of the GL emission. From first-principles calculation, such a Cu3+ ion in wurtzite ZnO prefers a high spin 3d8 state with two non-degenerated half-filled orbitals due to the Jahn-Teller effect, probably leading to the double structures in photoluminescence spectrum. Therefore, this model gives a comprehensively new understanding on the mechanism of the structured GL band in ZnO.

  11. Excitation Dependent Phosphorous Property and New Model of the Structured Green Luminescence in ZnO.

    PubMed

    Ye, Honggang; Su, Zhicheng; Tang, Fei; Wang, Mingzheng; Chen, Guangde; Wang, Jian; Xu, Shijie

    2017-02-02

    The copper induced green luminescence (GL) with two sets of fine structures in ZnO crystal has been found for several decades (i.e., R. Dingle, Phys. Rev. Lett. 23, 579 (1969)), but the physical origin of the doublet still remains as an open question up to now. In this paper, we provide new insight into the mechanism of the structured GL band in terms of new experimental findings and theoretical calculations. It is found, for the first time, that the GL signal exhibits persistent afterglow for tens of minutes after the switch-off of below-band-gap excitation light but it cannot occur under above-band-gap excitation. Such a phosphorous property may be interpreted as de-trapping and feeding of electrons from a shallow trapping level via the conduction band to the Cu-related luminescence centers where the Cu(3+) ion is proposed to work as the final state of the GL emission. From first-principles calculation, such a Cu(3+) ion in wurtzite ZnO prefers a high spin 3d(8) state with two non-degenerated half-filled orbitals due to the Jahn-Teller effect, probably leading to the double structures in photoluminescence spectrum. Therefore, this model gives a comprehensively new understanding on the mechanism of the structured GL band in ZnO.

  12. Causal feedforward control of a stochastically excited fuselage structure with active sidewall panel.

    PubMed

    Misol, Malte; Haase, Thomas; Monner, Hans Peter; Sinapius, Michael

    2014-10-01

    This paper provides experimental results of an aircraft-relevant double panel structure mounted in a sound transmission loss facility. The primary structure of the double panel system is excited either by a stochastic point force or by a diffuse sound field synthesized in the reverberation room of the transmission loss facility. The secondary structure, which is connected to the frames of the primary structure, is augmented by actuators and sensors implementing an active feedforward control system. Special emphasis is placed on the causality of the active feedforward control system and its implications on the disturbance rejection at the error sensors. The coherence of the sensor signals is analyzed for the two different disturbance excitations. Experimental results are presented regarding the causality, coherence, and disturbance rejection of the active feedforward control system. Furthermore, the sound transmission loss of the double panel system is evaluated for different configurations of the active system. A principal result of this work is the evidence that it is possible to strongly influence the transmission of stochastic disturbance sources through double panel configurations by means of an active feedforward control system.

  13. Structural relaxation in the singlet excited state of star-shaped oligofluorenes having a truxene or isotruxene as a core.

    PubMed

    Fujitsuka, Mamoru; Cho, Dae Won; Huang, Hsin-Hau; Yang, Jye-Shane; Majima, Tetsuro

    2011-11-24

    Oligofluorenes attract wide attention due to their excellent fluorescent properties. For the detailed understanding of the excited state properties, ultrafast processes have to be clarified. Here, we have investigated the structural relaxation in the singlet excited state of star-shaped oligofluorenes with a truxene or isotruxene core, to which oligofluorenes (n = 1-4) were attached. The transient absorption peak showed red-shift with time upon excitation. The fluorescence decay profiles in the picosecond domain showed the fast component in addition to the component corresponding to the singlet excited state lifetime. These ultrafast phenomena can be attributed to the structural relaxation, i.e., planarization, in the singlet excited state. The planarization process was supported by the theoretical calculation based on the time-dependent density functional theory. Furthermore, dependence of two-photon absorption cross section on the core of the star-shaped oligofluorene has been elucidated. © 2011 American Chemical Society

  14. Vertical flows and structures excited by magnetic activity in the Galactic center region

    NASA Astrophysics Data System (ADS)

    Kakiuchi, Kensuke; Suzuki, Takeru K.; Fukui, Yasuo; Torii, Kazufumi; Machida, Mami; Matsumoto, Ryoji

    2017-01-01

    Various observations show peculiar features in the Galactic Center region, such as loops and filamentary structure. It is still unclear how such characteristic features are formed. Magnetic field is believed to play very important roles in the dynamics of gas in the Galaxy Center. Suzuki et al. (2015) performed a global magneto-hydrodynamical simulation focusing on the Galactic Center with an axisymmetric gravitational potential and claimed that non-radial motion is excited by magnetic activity. We further analyzed their simulation data and found that vertical motion is also excited by magnetic activity. In particular, fast down flows with speed of ~100 km/s are triggered near the footpoint of magnetic loops that are buoyantly risen by Parker instability. These downward flows are accelerated by the vertical component of the gravity, falling along inclined field lines. As a result, the azimuthal and radial components of the velocity are also excited, which are observed as high velocity features in a simulated position-velocity diagram. Depending on the viewing angle, these fast flows will show a huge variety of characteristic features in the position-velocity diagram.

  15. Electronic structures and population dynamics of excited states of xanthione and its derivatives

    NASA Astrophysics Data System (ADS)

    Fedunov, Roman G.; Rogozina, Marina V.; Khokhlova, Svetlana S.; Ivanov, Anatoly I.; Tikhomirov, Sergei A.; Bondarev, Stanislav L.; Raichenok, Tamara F.; Buganov, Oleg V.; Olkhovik, Vyacheslav K.; Vasilevskii, Dmitrii A.

    2017-09-01

    A new compound, 1,3-dimethoxy xanthione (DXT), has been synthesized and its absorption (stationary and transient) and luminescence spectra have been measured in n-hexane and compared with xanthione (XT) spectra. The pronounced broadening of xanthione vibronic absorption band related to the electronic transition to the second singlet excited state has been observed. Distinctions between the spectra of xanthione and its methoxy derivatives are discussed. Quantum chemical calculations of these compounds in the ground and excited electronic states have been accomplished to clarify the nature of electronic spectra changes due to modification of xanthione by methoxy groups. Appearance of a new absorption band of DXT caused by symmetry changes has been discussed. Calculations of the second excited state structure of xanthione and its methoxy derivatives confirm noticeable charge transfer (about 0.1 of the charge of an electron) from the methoxy group to thiocarbonyl group. Fitting of the transient spectra of XT and DXT has been fulfilled and the time constants of internal conversion S2 →S1 and intersystem crossing S1 →T1 have been determined. A considerable difference between the time constants of internal conversion S2 →S1 in XT and DXT is uncovered.

  16. Enhanced water removal in a fuel cell stack by droplet atomization using structural and acoustic excitation

    NASA Astrophysics Data System (ADS)

    Palan, Vikrant; Shepard, W. Steve

    This work examines new methods for enhancing product water removal in fuel cell stacks. Vibration and acoustic based methods are proposed to atomize condensed water droplets in the channels of a bipolar plate or on a membrane electrode assembly (MEA). The vibration levels required to atomize water droplets of different sizes are first examined using two different approaches: (1) exciting the droplet at the same energy level required to form that droplet; and (2) by using a method called 'vibration induced droplet atomization', or VIDA. It is shown analytically that a 2 mm radius droplet resting on a bipolar-like plate can be atomized by inducing acceleration levels as low as 250 g at a certain frequency. By modeling the direct structural excitation of a simplified bipolar plate using a realistic source, the response levels that can be achieved are then compared with those required levels. Furthermore, a two-cell fuel cell finite element model and a boundary element model of the MEA were developed to demonstrate that the acceleration levels required for droplet atomization may be achieved in both the bipolar plate as well as the MEA through proper choice of excitation frequency and source strength.

  17. A closer look at the apparent correlation of structural and functional connectivity in excitable neural networks

    NASA Astrophysics Data System (ADS)

    Messé, Arnaud; Hütt, Marc-Thorsten; König, Peter; Hilgetag, Claus C.

    2015-01-01

    The relationship between the structural connectivity (SC) and functional connectivity (FC) of neural systems is a central focus in brain network science. It is an open question, however, how strongly the SC-FC relationship depends on specific topological features of brain networks or the models used for describing excitable dynamics. Using a basic model of discrete excitable units that follow a susceptible - excited - refractory dynamic cycle (SER model), we here analyze how functional connectivity is shaped by the topological features of a neural network, in particular its modularity. We compared the results obtained by the SER model with corresponding simulations by another well established dynamic mechanism, the Fitzhugh-Nagumo model, in order to explore general features of the SC-FC relationship. We showed that apparent discrepancies between the results produced by the two models can be resolved by adjusting the time window of integration of co-activations from which the FC is derived, providing a clearer distinction between co-activations and sequential activations. Thus, network modularity appears as an important factor shaping the FC-SC relationship across different dynamic models.

  18. Hysteretic Performance Identification for a Frame Structure with MR Damper under Limited Excitations

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Zhou, Ren; He, Jia; Masri, Sami F.

    2010-05-01

    Nonlinearity exists widely in engineering structures and may arise in damaged structures, but the identification theory for nonlinear dynamic systems is far less established than that for linear systems. Most of the currently available vibration-based identification approaches for structural damage detection are based on eigenvalues and mode shapes extraction which are suitable for linear systems. For the purpose of early warning and damage prognosis, it is crucial to develop efficient and reliable identification methods for nonlinear hysteretic performance because the restoring force is the direct indicator of damage initiation and development. In this paper, a general time series data-based approach was employed to identify the nonlinear behavior of a multi-degree-of-freedom frame structure equipped with a MR damper only using the excitation force applied on limited locations and the corresponding structural response measurement. The performance of the proposed methodology was validated for a 4-story frame model structure with and without a MR damper. The system matrices of the linear frame model structure were identified firstly with a least-squares techniques and the equivalent system of the frame structure with MR damper were identified. Then the location and the hysteretic performance of the MR damper were identified and compared with the test measurements. Results show that the proposed data-based approach is efficient for nonlinear behavior identification of engineering structures.

  19. Directional excitability of the utricle: a study by thermoconvective stimulation.

    PubMed

    Suzuki, M; Aoki, M; Kadir, A

    1994-01-01

    The frog utricular macula was stimulated by thermoconvective flow in four different directions. The evoked utricular nerve action potentials were recorded via a glass suction electrode. The maximum spikes and the time constants of the potentials were counted. The spike counts and the time constants were not significantly different among stimuli. This suggests that the utricle has the same physiological excitability to any directional stimulus.

  20. Decomposing the Excited State Dynamics of Carotenoids in Light Harvesting Complexes and Dissecting Pulse Structures from Optimal Control Experiments

    NASA Astrophysics Data System (ADS)

    Papagiannakis, Emmanouil; van Stokkum, Ivo H. M.; van Grondelle, Rienk; Vengris, Mikas; Valkunas, Leonas; Cogdell, Richard J.; Larsen, Delmar S.

    Dispersed transient absorption and multi-pump spectroscopies were used to illustrate how the interplay between excited-state dynamics, saturation, and annihilation phenomena in the LH2 protein from Rhodopseudomonas acidophila generates structured pulses in optimal control experiments.

  1. Electronic and structural elements that regulate the excited-state dynamics in purine nucleobase derivatives.

    PubMed

    Crespo-Hernández, Carlos E; Martínez-Fernández, Lara; Rauer, Clemens; Reichardt, Christian; Mai, Sebastian; Pollum, Marvin; Marquetand, Philipp; González, Leticia; Corral, Inés

    2015-04-08

    The excited-state dynamics of the purine free base and 9-methylpurine are investigated using experimental and theoretical methods. Femtosecond broadband transient absorption experiments reveal that excitation of these purine derivatives in aqueous solution at 266 nm results primarily in ultrafast conversion of the S2(ππ*) state to the vibrationally excited (1)nπ* state. Following vibrational and conformational relaxation, the (1)nπ* state acts as a doorway state in the efficient population of the triplet manifold with an intersystem crossing lifetime of hundreds of picoseconds. Experiments show an almost 2-fold increase in the intersystem crossing rate on going from polar aprotic to nonpolar solvents, suggesting that a solvent-dependent energy barrier must be surmounted to access the singlet-to-triplet crossing region. Ab initio static and surface-hopping dynamics simulations lend strong support to the proposed relaxation mechanism. Collectively, the experimental and computational results demonstrate that the accessibility of the nπ* states and the topology of the potential energy surfaces in the vicinity of conical intersections are key elements in controlling the excited-state dynamics of the purine derivatives. From a structural perspective, it is shown that the purine chromophore is not responsible for the ultrafast internal conversion in the adenine and guanine monomers. Instead, C6 functionalization plays an important role in regulating the rates of radiative and nonradiative relaxation. C6 functionalization inhibits access to the (1)nπ* state while simultaneously facilitating access to the (1)ππ*(La)/S0 conical intersection, such that population of the (1)nπ* state cannot compete with the relaxation pathways to the ground state involving ring puckering at the C2 position.

  2. Electronic and Structural Elements That Regulate the Excited-State Dynamics in Purine Nucleobase Derivatives

    PubMed Central

    2015-01-01

    The excited-state dynamics of the purine free base and 9-methylpurine are investigated using experimental and theoretical methods. Femtosecond broadband transient absorption experiments reveal that excitation of these purine derivatives in aqueous solution at 266 nm results primarily in ultrafast conversion of the S2(ππ*) state to the vibrationally excited 1nπ* state. Following vibrational and conformational relaxation, the 1nπ* state acts as a doorway state in the efficient population of the triplet manifold with an intersystem crossing lifetime of hundreds of picoseconds. Experiments show an almost 2-fold increase in the intersystem crossing rate on going from polar aprotic to nonpolar solvents, suggesting that a solvent-dependent energy barrier must be surmounted to access the singlet-to-triplet crossing region. Ab initio static and surface-hopping dynamics simulations lend strong support to the proposed relaxation mechanism. Collectively, the experimental and computational results demonstrate that the accessibility of the nπ* states and the topology of the potential energy surfaces in the vicinity of conical intersections are key elements in controlling the excited-state dynamics of the purine derivatives. From a structural perspective, it is shown that the purine chromophore is not responsible for the ultrafast internal conversion in the adenine and guanine monomers. Instead, C6 functionalization plays an important role in regulating the rates of radiative and nonradiative relaxation. C6 functionalization inhibits access to the 1nπ* state while simultaneously facilitating access to the 1ππ*(La)/S0 conical intersection, such that population of the 1nπ* state cannot compete with the relaxation pathways to the ground state involving ring puckering at the C2 position. PMID:25763596

  3. Nonlinear excitation of finite-radial-scale zonal structures by toroidal Alfvén eigenmode

    NASA Astrophysics Data System (ADS)

    Qiu, Zhiyong; Chen, Liu; Zonca, Fulvio

    2017-05-01

    The set of equations describing nonlinear evolution of a single toroidal Alfvén eigenmode are derived, including both zero frequency zonal structure (ZFZS) generation and wave-particle phase space nonlinearities. The simplified case of neglecting wave-particle phase space nonlinearity is then investigated to focus on different roles of energetic particles and bulk plasmas on ZFZS generation. It is shown that energetic particles and bulk plasma play dominant roles in ZFZS generation in different nonlinear stages, and the corresponding processes are qualitatively different. Several properties of ZFZS generation, e.g. fine- versus meso-scale, forced driven versus spontaneous excitation, are clarified by the present analysis.

  4. Two-photon excitation improves multifocal structured illumination microscopy in thick scattering tissue

    PubMed Central

    Ingaramo, Maria; York, Andrew G.; Wawrzusin, Peter; Milberg, Oleg; Hong, Amy; Weigert, Roberto; Shroff, Hari; Patterson, George H.

    2014-01-01

    Multifocal structured illumination microscopy (MSIM) provides a twofold resolution enhancement beyond the diffraction limit at sample depths up to 50 µm, but scattered and out-of-focus light in thick samples degrades MSIM performance. Here we implement MSIM with a microlens array to enable efficient two-photon excitation. Two-photon MSIM gives resolution-doubled images with better sectioning and contrast in thick scattering samples such as Caenorhabditis elegans embryos, Drosophila melanogaster larval salivary glands, and mouse liver tissue. PMID:24706872

  5. Strength failure of spatial reticulated structures under multi-support excitation

    NASA Astrophysics Data System (ADS)

    Ye, Jihong; Zhang, Zhiqiang; Chu, Ye

    2011-03-01

    Under strong earthquakes, long-span spatial latticed structures may collapse due to dynamic instability or strength failure. The elasto-plastic dynamic behaviors of three spatial latticed structures, including two double-layer cylindrical shells and one spherical shell constructed for the 2008 Olympic Games in Beijing, were quantitatively examined under multi-support excitation (MSE) and uniform support excitation (USE). In the numerical analyses, several important parameters were investigated such as the peak acceleration and displacement responses at key joints, the number and distribution of plastic members, and the deformation of the shell at the moment of collapse. Analysis results reveal the features and the failure mechanism of the spatial latticed structures under MSE and USE. In both scenarios, the double-layer reticulated shell collapses in the "overflow" mode, and the collapse is governed by the number of invalid plastic members rather than the total number of plastic members, beginning with damage to some of the local regions near the supports. By comparing the numbers and distributions of the plastic members under MSE to those under USE, it was observed that the plastic members spread more sufficiently and the internal forces are more uniform under MSE, especially in cases of lower apparent velocities in soils. Due to the effects of pseudo-static displacement, the stresses in the members near the supports under MSE are higher than those under USE.

  6. Non-iridescent transmissive structural color filter featuring highly efficient transmission and high excitation purity.

    PubMed

    Shrestha, Vivek Raj; Lee, Sang-Shin; Kim, Eun-Soo; Choi, Duk-Yong

    2014-05-12

    Nanostructure based color filtering has been considered an attractive replacement for current colorant pigmentation in the display technologies, in view of its increased efficiencies, ease of fabrication and eco-friendliness. For such structural filtering, iridescence relevant to its angular dependency, which poses a detrimental barrier to the practical development of high performance display and sensing devices, should be mitigated. We report on a non-iridescent transmissive structural color filter, fabricated in a large area of 76.2 × 25.4 mm(2), taking advantage of a stack of three etalon resonators in dielectric films based on a high-index cavity in amorphous silicon. The proposed filter features a high transmission above 80%, a high excitation purity of 0.93 and non-iridescence over a range of 160°, exhibiting no significant change in the center wavelength, dominant wavelength and excitation purity, which implies no change in hue and saturation of the output color. The proposed structure may find its potential applications to large-scale display and imaging sensor systems.

  7. Excited-state symmetry breaking of linear quadrupolar chromophores: A transient absorption study

    NASA Astrophysics Data System (ADS)

    Dozova, Nadia; Ventelon, Lionel; Clermont, Guillaume; Blanchard-Desce, Mireille; Plaza, Pascal

    2016-11-01

    The photophysical properties of two highly symmetrical quadrupolar chromophores were studied by both steady-state and transient absorption spectroscopy. Their excited-state behavior is dominated by the solvent-induced Stokes shift of the stimulated-emission band. The origin of this shift is attributed to symmetry breaking that confers a non-vanishing dipole moment to the excited state of both compounds. This dipole moment is large and constant in DMSO, whereas symmetry breaking appears significantly slower and leading to smaller excited-state dipole in toluene. Time-dependant increase of the excited-state dipole moment induced by weak solvation is proposed to explain the results in toluene.

  8. Redistribution of Kv1 and Kv7 enhances neuronal excitability during structural axon initial segment plasticity

    PubMed Central

    Kuba, Hiroshi; Yamada, Rei; Ishiguro, Go; Adachi, Ryota

    2015-01-01

    Structural plasticity of the axon initial segment (AIS), the trigger zone of neurons, is a powerful means for regulating neuronal activity. Here, we show that AIS plasticity is not limited to structural changes; it also occurs as changes in ion-channel expression, which substantially augments the efficacy of regulation. In the avian cochlear nucleus, depriving afferent inputs by removing cochlea elongated the AIS, and simultaneously switched the dominant Kv channels at the AIS from Kv1.1 to Kv7.2. Due to the slow activation kinetics of Kv7.2, the redistribution of the Kv channels reduced the shunting conductance at the elongated AIS during the initiation of action potentials and effectively enhanced the excitability of the deprived neurons. The results indicate that the functional plasticity of the AIS works cooperatively with the structural plasticity and compensates for the loss of afferent inputs to maintain the homeostasis of auditory circuits after hearing loss by cochlea removal. PMID:26581625

  9. Redistribution of Kv1 and Kv7 enhances neuronal excitability during structural axon initial segment plasticity.

    PubMed

    Kuba, Hiroshi; Yamada, Rei; Ishiguro, Go; Adachi, Ryota

    2015-11-19

    Structural plasticity of the axon initial segment (AIS), the trigger zone of neurons, is a powerful means for regulating neuronal activity. Here, we show that AIS plasticity is not limited to structural changes; it also occurs as changes in ion-channel expression, which substantially augments the efficacy of regulation. In the avian cochlear nucleus, depriving afferent inputs by removing cochlea elongated the AIS, and simultaneously switched the dominant Kv channels at the AIS from Kv1.1 to Kv7.2. Due to the slow activation kinetics of Kv7.2, the redistribution of the Kv channels reduced the shunting conductance at the elongated AIS during the initiation of action potentials and effectively enhanced the excitability of the deprived neurons. The results indicate that the functional plasticity of the AIS works cooperatively with the structural plasticity and compensates for the loss of afferent inputs to maintain the homeostasis of auditory circuits after hearing loss by cochlea removal.

  10. Excited-state energies and fine structure of highly charged lithiumlike ions

    NASA Astrophysics Data System (ADS)

    Li, Jin-ying; Ding, Da-jun; Wang, Zhi-wen

    2013-10-01

    The full-core-plus-correlation method (FCPC) is extended to calculate the energies and fine structures of 1s2nd and 1s2nf (n≤5) states for the lithiumlike systems with high nuclear charge from Z = 41 to 50. In calculating energy, the higher-order relativistic contribution is estimated under a hydrogenic approximation. The nonrelativistic energies and wave functions are calculated by the Rayleigh-Ritz method. The mass polarization and the relativistic corrections including the kinetic energy correction, the Darwin term, the electron-electron contact term, and the orbit-orbit interaction are calculated perturbatively as the first-order correction. The quantum-electrodynamics contributions to the energy and to the fine-structure splitting are estimated by using the effective nuclear charge formula. The excited energies, the fine structures, and other relevant term energies are given and compared with the data available in the literature.

  11. Excitation, response, and fatigue life estimation methods for the structural design of externally blown flaps

    NASA Technical Reports Server (NTRS)

    Ungar, E. E.; Chandiramani, K. L.; Barger, J. E.

    1972-01-01

    Means for predicting the fluctuating pressures acting on externally blown flap surfaces are developed on the basis of generalizations derived from non-dimensionalized empirical data. Approaches for estimation of the fatigue lives of skin-stringer and honeycomb-core sandwich flap structures are derived from vibration response analyses and panel fatigue data. Approximate expressions for fluctuating pressures, structural response, and fatigue life are combined to reveal the important parametric dependences. The two-dimensional equations of motion of multi-element flap systems are derived in general form, so that they can be specialized readily for any particular system. An introduction is presented of an approach to characterizing the excitation pressures and structural responses which makes use of space-time spectral concepts and promises to provide useful insights, as well as experimental and analytical savings.

  12. Electronic structure and charge transfer excitation energies of three endohedral fullerene- ZnTPP/ZnPc dyads

    NASA Astrophysics Data System (ADS)

    Amerikheirabadi, Fatemeh; Basurto, Luis; Zope, Rajendra; Baruah, Tunna

    2015-03-01

    Organic donor-acceptor (D-A) moieties make up the main component of organic photovoltaics (OPVs). It has been proved that the open circuit voltage of these devices which is a parameter in efficiency determination, is directly related to the charge transfer excited states of the D-A pairs. Fullerenes having lots of interesting acceptor properties and porphyrins as well as phthalocyanines possessing intriguing donor characteristics, are shown to be promising nominees. In this work, we computationally analyze three donor-acceptor dyads of Zn-tetraphenyl porphyrin and Zn-phthalocyanine with novel endohedral fullerenes: Sc3N@C80_ZnTPP, Y3N@C80_ZnTPPandSc3N@C80_ZnPc.TheSc3N@C80_and Y3N@C80 belong to a particular class of fullerenes called trimetallic nitride endohedral fullerenes where the trimellatic nitrides form the endohedral units. Density functional theory, as implemented in NRLMOL code, is used to study the electronic structure and the related properties of these D-A complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group. We find that the CT excitation energies are larger for endohedral fullerene based dyads compared to similar C60 based dyads.

  13. Damage detection of metro tunnel structure through transmissibility function and cross correlation analysis using local excitation and measurement

    NASA Astrophysics Data System (ADS)

    Feng, Lei; Yi, Xiaohua; Zhu, Dapeng; Xie, Xiongyao; Wang, Yang

    2015-08-01

    In a modern metropolis, metro rail systems have become a dominant mode for mass transportation. The structural health of a metro tunnel is closely related to public safety. Many vibration-based techniques for detecting and locating structural damage have been developed in the past several decades. However, most damage detection techniques and validation tests are focused on bridge and building structures; very few studies have been reported on tunnel structures. Among these techniques, transmissibility function and cross correlation analysis are two well-known diagnostic approaches. The former operates in frequency domain and the latter in time domain. Both approaches can be applied to detect and locate damage through acceleration data obtained from sensor arrays. Furthermore, the two approaches can directly utilize structural response data without requiring excitation measurement, which offers advantages in field testing on a large structure. In this research, a numerical finite element model of a metro tunnel is built and different types of structural defects are introduced at multiple locations of the tunnel. Transmissibility function and cross correlation analysis are applied to perform structural damage detection and localization, based on simulated structural vibration data. Numerical results demonstrate that the introduced defects can be successfully identified and located. The sensitivity and feasibility of the two approaches have been verified when sufficient distribution of measurement locations is available. Damage detection results of the two different approaches are compared and discussed.

  14. Theoretical study of the vertical excited states of benzene, pyrimidine, and pyrazine by the symmetry adapted cluster--configuration interaction method.

    PubMed

    Li, Yongjian; Wan, Jian; Xu, Xin

    2007-07-30

    The ground state and the excited states of benzene, pyrimidine, and pyrazine have been examined by using the symmetry adapted cluster-configuration interaction (SAC-CI) method. Detailed characterizations and the structures of the absorption peaks in the vacuum ultraviolet (VUV), low energy electron impact (LEEI), and electron energy loss (EEL) spectra were theoretically clarified by calculating the excitation energy and the oscillator strength for each excited state. We show that SAC-CI has the power to well reproduce the electronic excitation spectra (VUV, LEEI, and EEL) simultaneously to an accuracy for both the singlet and the triplet excited states originated from the low-lying pi --> pi*, n --> pi*, pi --> sigma* and n --> sigma* excited states of the titled compounds. The present results are compared with those of the previous theoretical studies by methods, such as EOM-CCSD(T), STEOM-CCSD, CASPT2 and TD-B3LYP, etc. (c) 2007 Wiley Periodicals, Inc.

  15. A Study of the Nearfield of an Excited Spherical Shell.

    DTIC Science & Technology

    1980-03-17

    1969). 19. Lazan , B . J ., Damping of Material and Members in Structural Mechanics, Pergamon Press, New York, 1968. 20. Morse, P. M. and Feshback, H...a> j - J -d W Cw ~-Q U 0 CC-3 130 10311G A086A 006 PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESE-ETC F/ B 90/1 A STUDY OF THE NEARFIELD OF AN...University Press, University Park, PA, 1968. 13. Levy, B . R. and Keller, J . B ., "Diffraction by a Smooth Object," Comm. on Pure and Appl. Math. XII

  16. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    DOE PAGES

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; ...

    2016-02-26

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiatedmore » at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.« less

  17. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    PubMed Central

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

    2016-01-01

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems. PMID:26915398

  18. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy.

    PubMed

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J; Jung, Il Woong; Walko, Donald A; Dufresne, Eric M; Jeong, Jaewoo; Samant, Mahesh G; Parkin, Stuart S P; Freeland, John W; Evans, Paul G; Wen, Haidan

    2016-02-26

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

  19. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

    2016-02-01

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

  20. Excitation energy transfer: Study with non-Markovian dynamics

    SciTech Connect

    Liang Xianting

    2010-11-15

    In this paper, we investigate the non-Markovian dynamics of a model to mimic the excitation energy transfer (EET) between chromophores in photosynthesis systems. The numerical path integral method is used. This method includes the non-Markovian effects of the environmental affects, and it does not need the perturbation approximation in solving the dynamics of systems of interest. It implies that the coherence helps the EET between chromophores through lasting the transfer time rather than enhancing the transfer rate of the EET. In particular, the non-Markovian environment greatly increases the efficiency of the EET in the photosynthesis systems.

  1. Theoretical study on the excited states of HCN

    NASA Astrophysics Data System (ADS)

    Nayak, Malaya K.; Chaudhuri, Rajat K.; Krishnamachari, S. N. L. G.

    2005-05-01

    In the flash-photolysis of oxazole, iso-oxazole, and thiozole a transient band system was observed in the region 2500-3050 Å. This band system was attributed to a meta-stable form of HCN, i.e., either HNC or triplet HCN. Theoretical investigations have been carried out on the ground and excited states of HCN to characterize this and other experimentally observed transitions. The predicted geometries are compared with the experiment and earlier theoretical calculations. The present calculations show that the band system in the region 2500-3050 Å corresponds to the transition 43-A'←13-A' of HCN.

  2. Feasibility study: Monodisperse polymer particles containing laser-excitable dyes

    NASA Technical Reports Server (NTRS)

    Vanderhoff, John W.; Chen, Jing-Hong

    1993-01-01

    The objective was to determine the feasibility of the preparation of monodisperse spherical poly(methyl methacrylate) and polystyrene particles that contain laser-excitable dyes in the size range 0.1 microns to 1 cm. Poly(methyl methacrylate) and polystyrene were chosen because of their excellent optical properties. The sphericity was required for uniformity of spectral output of re-irradiated light from the dye-containing particles. The monodispersity was required to give each particle the same optical properties when exposed to laser light.

  3. Feasibility study: Monodisperse polymer particles containing laser-excitable dyes

    NASA Technical Reports Server (NTRS)

    Vanderhoff, John W.; Chen, Jing-Hong

    1993-01-01

    The objective was to determine the feasibility of the preparation of monodisperse spherical poly(methyl methacrylate) and polystyrene particles that contain laser-excitable dyes in the size range 0.1 microns to 1 cm. Poly(methyl methacrylate) and polystyrene were chosen because of their excellent optical properties. The sphericity was required for uniformity of spectral output of re-irradiated light from the dye-containing particles. The monodispersity was required to give each particle the same optical properties when exposed to laser light.

  4. Minority Achievement Gaps in STEM: Findings of a Longitudinal Study of Project Excite

    ERIC Educational Resources Information Center

    Olszewski-Kubilius, Paula; Steenbergen-Hu, Saiying; Thomson, Dana; Rosen, Rhoda

    2017-01-01

    This longitudinal study examined the outcomes of Project Excite on reducing minority students' achievement gaps in STEM over 14 years. Project Excite was designed to provide intensive supplemental enrichment and accelerated programming for high-potential, underrepresented minority students from third through eighth grades to better prepare them…

  5. Minority Achievement Gaps in STEM: Findings of a Longitudinal Study of Project Excite

    ERIC Educational Resources Information Center

    Olszewski-Kubilius, Paula; Steenbergen-Hu, Saiying; Thomson, Dana; Rosen, Rhoda

    2017-01-01

    This longitudinal study examined the outcomes of Project Excite on reducing minority students' achievement gaps in STEM over 14 years. Project Excite was designed to provide intensive supplemental enrichment and accelerated programming for high-potential, underrepresented minority students from third through eighth grades to better prepare them…

  6. EPICARDIAL AND INTRAMURAL EXCITATION DURING VENTRICULAR PACING: EFFECT OF MYOCARDIAL STRUCTURE

    PubMed Central

    Taccardi, Bruno; Punske, Bonnie B.; Macchi, Emilio; MacLeod, Robert S.; Ershler, Philip R.

    2009-01-01

    Published studies show that ventricular pacing in canine hearts produces three distinct patterns of epicardial excitation: elliptical isochrones near an epicardial pacing site, with asymmetrical bulges; areas with high propagation velocity, up to 2 or 3 m/s and numerous breakthrough sites; lower velocity areas (< 1 m/s) where excitation moves across the epicardial projection of the septum. With increasing pacing depth the magnitude of epicardial potential maxima becomes asymmetrical. The electrophysiological mechanisms that generate the distinct patterns have not been fully elucidated. In this study we investigated those mechanisms experimentally. Under pentobarbital anesthesia epicardial and intramural excitation isochrone and potential maps have been recorded from 22 exposed or isolated dog hearts, by means of epicardial electrode arrays and transmural plunge electrodes. In 5 experiments, a ventricular cavity was perfused with diluted Lugol solution. Results The epicardial bulges result from electrotonic attraction from the helically shaped subepicardial portions of the wave front. The high velocity patterns and the associated multiple breakthroughs are due to involvement of the Purkinje network. The low velocity at the septum crossing is due to the missing Purkinje involvement in that area. The asymmetric magnitude of the epicardial potential maxima and the shift of the breakthrough sites provoked by deep stimulation are a consequence of the epi-endocardial obliqueness of the intramural fibers. These results improve our understanding of intramural and epicardial propagation during PVCs and paced beats. This can be useful for interpreting epicardial maps recorded at surgery or inversely computed from body surface ECGs. PMID:18263708

  7. Effects of citalopram on the excitability of the human motor cortex: a paired magnetic stimulation study.

    PubMed

    Robol, Elisa; Fiaschi, Antonio; Manganotti, Paolo

    2004-06-15

    Several recent reports suggest the possibility of monitoring pharmacological effects on brain excitability through transcranial magnetic stimulation (TMS). Different drugs have been studied using paired magnetic stimulation in normal subjects and patients. In particular, it has been suggested that antidepressant drugs may have an appreciable effect on motor excitability. The aim of the present study was to investigate motor area excitability in normal subjects after oral administration of a single dose of citalopram, a selective serotonin reuptake inhibitor (SSRI) antidepressant. Motor cortex excitability was studied by single and paired transcranial magnetic stimulation before and 2.5 and 36 (t1/2=36 h) h after oral administration of 30 mg of citalopram. Cortical excitability was measured using different transcranial magnetic stimulation parameters: motor threshold (MT), motor-evoked potential (MEP) amplitude and latency, motor recruitment, duration of cortical silent period (CSP), intracortical inhibition and intracortical facilitation. Spinal excitability and peripheral nerve conduction were measured by F response and M wave. Temporary but significant increases in motor threshold, motor-evoked potentials, silent period and intracortical inhibition were observed 2.5 h after drug administration, without any significant changes in motor-evoked potential amplitude and latency and spinal excitability parameters. Our findings suggest that a single oral dose of citalopram can induce significant but transitory suppression of motor cortex excitability in normal subjects.

  8. Structural identification of triacylglycerol isomers using electron impact excitation of ions from organics (EIEIO).

    PubMed

    Baba, Takashi; Campbell, J Larry; Le Blanc, J C Yves; Baker, Paul R S

    2016-11-01

    Electron-induced dissociation or electron impact excitation of ions from organics (EIEIO) was applied to triacylglycerols (TAGs) for in-depth molecular structure analysis using MS. In EIEIO, energetic electrons (∼10 eV) fragmented TAG ions to allow for regioisomeric assignment of identified acyl groups at the sn-2 or sn-1/3 positions of the glycerol backbone. In addition, carbon-carbon double bond locations within the acyl chains could also be assigned by EIEIO. Beyond the analysis of lipid standards, this technique was applied to edible oils and natural lipid extracts to demonstrate the power of this method to provide in-depth structural elucidation of TAG molecular species. Copyright © 2016 by the American Society for Biochemistry and Molecular Biology, Inc.

  9. Interaction between spin-wave excitations and pure spin currents in magnetic structures

    NASA Astrophysics Data System (ADS)

    Azevedo, Antonio

    2012-02-01

    The generation of pure spin current (PSC) in magnetic structures has attracted much attention not only for its fundamental importance in spintronics, but also because it opens up potential applications. One of the most exciting aspects of this area is the interplay between spin-waves (SW) and PSC. Here we report experimental results in which the PSC, generated by both spin pumping (SPE) [1] and spin Seebeck (SSE) [2] effects, can exert a spin-transfer torque sufficient to compensate the SW relaxation in yttrium iron garnet (YIG)/non-magnetic structures. By measuring the propagation of SW packets in single-crystal YIG films we were able to observe the amplification of volume and magnetostatic modes (MSW) by both SSE and SHE [3,4]. The excitation and detection of the SW packets is carried out by using a MSW delay line device. In both cases the amplification is attributed to the spin-transfer torque due to PSC generated by SSE as well as SHE. It will also be presented new results in which PSC are simultaneously excited by SSE and SPE effects in YIG films. While the spin current generated by SPE is obtained by exciting the ferromagnetic resonance (FMR) of the YIG film, the spin current due to SSE is created by applying a temperature gradient along the film plane. The effect of the superposition of both spin currents is characterized by measuring the spin Hall voltage (VH) along thin strips of Pt deposited on top of the YIG films. Whereas VH corresponding to the uniform FMR is amplified due the SSE the voltages corresponding to the other magnetostatic spin-wave modes are attenuated [5]. [4pt] [1] Y. Tserkovnyak, et al., Rev. Mod. Phys. 77, 1375 (2005).[0pt] [2] K. Uchida, et al., Nature 455, 778 (2008).[0pt] [3] E. Padr'on-Hern'andez, A. Azevedo, and S. M. Rezende, Phys. Rev. Letts., 107, 197203 (2011).[0pt] [4] E. Padr'on-Hern'andez, A. Azevedo, and S. M. Rezende, Appl. Phys. Letts., 99 (2011) in press.[0pt] [5] G.L. da Silva, L.H. Vilela-Leão, S. M. Rezende and A

  10. Luminescent copper(I) halide and pseudohalide phenanthroline complexes revisited: simple structures, complicated excited state behavior.

    PubMed

    Nitsch, Jörn; Kleeberg, Christian; Fröhlich, Roland; Steffen, Andreas

    2015-04-21

    We have synthesized a series of luminescent trigonal [CuX(dtbphen)] (X = I (), Br (), Cl (), CN (), dtbphen = 2,9-di-tert-butylphenanthroline) and tetrahedral [Cu2(μ-I)2(L)2] (L = phenanthroline (), 2,9-dimethylphenanthroline ()) copper diimine complexes. Bearing in mind the chemical simplicity of this class of long-known Cu(i) phenanthroline compounds, it is surprising that they exhibit non-trivial photophysical properties, which have not been fully recognized. They display broad XMLCT absorption between ca. 450-600 nm, and the broad emission between ca. 550-850 nm in the solid state occurring with lifetimes on the μs timescale indicates phosphorescence, although the energetic overlap between excitation and emission suggests thermally activated delayed fluorescence (TADF) from S1. In line with the latter assumption, low temperature measurements of in the solid state show an energetic separation of emission and excitation. However, a counter-intuitive decrease of emission intensity and simultaneous increase of the emission lifetime at low temperatures are observed for , which indicates two triplet states also being involved. Our DFT and TD-DFT calculations show that emission from the lowest excited triplet state T1 is of (3)LMXCT nature, separated by only ca. 0.16 eV from S1. Low temperature photophysical measurements at 77 K in a glassy matrix of in 2-Me-THF and of in the solid state are in agreement with the theoretical results, revealing in addition that π-interactions in the solid state also greatly influence the photophysical properties, making a clear conclusion towards TADF ambiguous. This study suggests that other related simple and long-known Cu(i) systems may exhibit a similar, more complex excited state behavior than previously appreciated, involving several emitting states and important intermolecular interactions.

  11. Intramolecular excited-state proton-transfer studies on flavones in different environments

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjay; Jain, Sapan K.; Sharma, Neera; Rastogi, Ramesh C.

    2001-02-01

    The absorption and fluorescence spectra of some biologically active flavones have been studied as a function of the acidity (pH/H 0) of the solution. Dissociation constants have been determined for the ground and first excited singlet states. The results are compared with those obtained from Forster-Weller calculations. The acidity constants obtained by fluorimetric titration method are in complete agreement (in most of the systems) with ground state data indicating a excited state deactivation prior to prototropic equilibration. Compared to umbelliferones, flavones are only weakly fluorescent in alkaline solution. This behaviour is explained by the small energy difference between the singlet excited state and triplet excited state giving rise to more efficient intersystem crossing. Most of the flavones studied here undergo adiabatic photodissociation in the singlet excited state indicating the formation of an exciplex or a phototautomer.

  12. Theoretical study on the excited states of HCN

    SciTech Connect

    Nayak, Malaya K.; Chaudhuri, Rajat K.; Krishnamachari, S.N.L.G.

    2005-05-08

    In the flash-photolysis of oxazole, iso-oxazole, and thiozole a transient band system was observed in the region 2500-3050 A. This band system was attributed to a meta-stable form of HCN, i.e., either HNC or triplet HCN. Theoretical investigations have been carried out on the ground and excited states of HCN to characterize this and other experimentally observed transitions. The predicted geometries are compared with the experiment and earlier theoretical calculations. The present calculations show that the band system in the region 2500-3050 A corresponds to the transition 4 {sup 3}-A{sup '}<{sup -}1 {sup 3}-A{sup '} of HCN.

  13. Mobility power flow analysis of coupled plate structure subjected to mechanical and acoustic excitation

    NASA Technical Reports Server (NTRS)

    Cuschieri, J. M.

    1992-01-01

    The mobility power flow approach that was previously applied in the derivation of expressions for the vibrational power flow between coupled plate substructures forming an L configuration and subjected to mechanical loading is generalized. Using the generalized expressions, both point and distributed mechanical loads on one or both of the plates can be considered. The generalized approach is extended to deal with acoustic excitation of one of the plate substructures. In this case, the forces (acoustic pressures) acting on the structure are dependent on the response of the structure because of the scattered pressure component. The interaction between the plate structure and the acoustic fluid leads to the derivation of a corrected mode shape for the plates' normal surface velocity and also for the structure mobility functions. The determination of the scattered pressure components in the expressions for the power flow represents an additional component in the power flow balance for the source plate and the receiver plate. This component represents the radiated acoustical power from the plate structure. For a number of coupled plate substrates, the acoustic pressure generated by one substructure will interact with the motion of another substructure. That is, in the case of the L-shaped plate, acoustic interaction exists between the two plate substructures due to the generation of the acoustic waves by each of the substructures. An approach to deal with this phenomena is described.

  14. Damage detection in membrane structures using non-contact laser excitation and wavelet transformation

    NASA Astrophysics Data System (ADS)

    Huda, Feblil; Kajiwara, Itsuro; Hosoya, Naoki

    2014-08-01

    In this paper, a vibration testing and health monitoring system based on an impulse response excited by laser is proposed to detect damage in membrane structures. A high power Nd: YAG pulse laser is used to supply an ideal impulse to a membrane structure by generating shock waves via laser-induced breakdown in air. A health monitoring apparatus is developed with this vibration testing system and a damage detecting algorithm which only requires the vibration mode shape of the damaged membrane. Artificial damage is induced in membrane structure by cutting and tearing the membrane. The vibration mode shapes of the membrane structure extracted from vibration testing by using the laser-induced breakdown and laser Doppler vibrometer are then analyzed by 2-D continuous wavelet transformation. The location of damage is determined by the dominant peak of the wavelet coefficient which can be seen clearly by applying a boundary treatment and the concept of an iso-surface to the 2-D wavelet coefficient. The applicability of the present approach is verified by finite element analysis and experimental results, demonstrating the ability of the method to detect and identify the positions of damage induced on the membrane structure.

  15. Analysis on pseudo excitation of random vibration for structure of time flight counter

    NASA Astrophysics Data System (ADS)

    Wu, Qiong; Li, Dapeng

    2015-03-01

    Traditional computing method is inefficient for getting key dynamical parameters of complicated structure. Pseudo Excitation Method(PEM) is an effective method for calculation of random vibration. Due to complicated and coupling random vibration in rocket or shuttle launching, the new staging white noise mathematical model is deduced according to the practical launch environment. This deduced model is applied for PEM to calculate the specific structure of Time of Flight Counter(ToFC). The responses of power spectral density and the relevant dynamic characteristic parameters of ToFC are obtained in terms of the flight acceptance test level. Considering stiffness of fixture structure, the random vibration experiments are conducted in three directions to compare with the revised PEM. The experimental results show the structure can bear the random vibration caused by launch without any damage and key dynamical parameters of ToFC are obtained. The revised PEM is similar with random vibration experiment in dynamical parameters and responses are proved by comparative results. The maximum error is within 9%. The reasons of errors are analyzed to improve reliability of calculation. This research provides an effective method for solutions of computing dynamical characteristic parameters of complicated structure in the process of rocket or shuttle launching.

  16. Role of structural relaxations and vibrational excitations in the high-frequency dynamics of liquids and glasses

    NASA Astrophysics Data System (ADS)

    Chong, Song-Ho

    2006-09-01

    We present theoretical investigation on the high-frequency collective dynamics in liquids and glasses at microscopic length scales and in the terahertz frequency region based on the mode-coupling theory for ideal liquid-glass transition. We focus on recently investigated issues from inelastic-x-ray-scattering and computer-simulation studies for dynamic structure factors and longitudinal and transversal current spectra: the anomalous dispersion of the high-frequency sound velocity and the nature of the low-frequency excitation called the boson peak. It will be discussed how the sound mode interferes with other low-lying modes present in the system. Thereby, we provide a systematic explanation of the anomalous sound-velocity dispersion in systems—ranging from high temperature liquid down to deep inside the glass state—in terms of the contributions from the structural-relaxation processes and from vibrational excitations called the anomalous-oscillation peak (AOP). A possibility of observing negative dispersion—the decrease of the sound velocity upon increase of the wave number—is argued when the sound-velocity dispersion is dominated by the contribution from the vibrational dynamics. We also show that the low-frequency excitation, observable in both of the glass-state longitudinal and transversal current spectra at the same resonance frequency, is the manifestation of the AOP. As a consequence of the presence of the AOP in the transversal current spectra, it is predicted that the transversal sound velocity also exhibits the anomalous dispersion. These results of the theory are demonstrated for a model of the Lennard-Jones system.

  17. Study on loss mechanism of SMA tracheal stent subjected to cough excitation.

    PubMed

    Zhu, Zhiwen; Li, Xinmiao; Xu, Jia

    2015-01-01

    A kind of Ti-Ni shape memory alloy (SMA) hysteretic nonlinear model is developed, and the loss mechanism of a SMA tracheal stent subjected to cough excitation is studied in this paper. Nonlinear differential items are introduced to express the hysteretic phenomena of Ti-Ni SMA, and the fitting effect of the SMA constitutive model on the experimental data is proved by the partial least-square regression method. The nonlinear dynamic model of a Ti-Ni SMA tracheal stent subjected to cough excitation is developed, and the system's dynamic response is obtained. The numerical results show that the system's vibration is little in weak excitation, becomes large with the increase of the stochastic excitation, and finally becomes little again with the further increase of the stochastic excitation; the stochastic resonance phenomenon occurs in the process, which may cause stent fracture or loss.

  18. Structural basis for dual excitation and photoisomerization of the Aequorea victoria green fluorescent protein.

    PubMed

    Brejc, K; Sixma, T K; Kitts, P A; Kain, S R; Tsien, R Y; Ormö, M; Remington, S J

    1997-03-18

    The 2.1-A resolution crystal structure of wild-type green fluorescent protein and comparison of it with the recently determined structure of the Ser-65 --> Thr (S65T) mutant explains the dual wavelength absorption and photoisomerization properties of the wild-type protein. The two absorption maxima are caused by a change in the ionization state of the chromophore. The equilibrium between these states appears to be governed by a hydrogen bond network that permits proton transfer between the chromophore and neighboring side chains. The predominant neutral form of the fluorophore maximally absorbs at 395 nm. It is maintained by the carboxylate of Glu-222 through electrostatic repulsion and hydrogen bonding via a bound water molecule and Ser-205. The ionized form of the fluorophore, absorbing at 475 nm, is present in a minor fraction of the native protein. Glu-222 donates its charge to the fluorophore by proton abstraction through a hydrogen bond network, involving Ser-205 and bound water. Further stabilization of the ionized state of the fluorophore occurs through a rearrangement of the side chains of Thr-203 and His-148. UV irradiation shifts the ratio of the two absorption maxima by pumping a proton relay from the neutral chromophore's excited state to Glu-222. Loss of the Ser-205-Glu-222 hydrogen bond and isomerization of neutral Glu-222 explains the slow return to the equilibrium dark-adapted state of the chromophore. In the S65T structure, steric hindrance by the extra methyl group stabilizes a hydrogen bonding network, which prevents ionization of Glu-222. Therefore the fluorophore is permanently ionized, causing only a 489-nm excitation peak. This new understanding of proton redistribution in green fluorescent protein should enable engineering of environmentally sensitive fluorescent indicators and UV-triggered fluorescent markers of protein diffusion and trafficking in living cells.

  19. Structural Basis for Dual Excitation and Photoisomerization of the Aequorea victoria Green Fluorescent Protein

    NASA Astrophysics Data System (ADS)

    Brejc, Katjusa; Sixma, Titia K.; Kitts, Paul A.; Kain, Steven R.; Tsien, Roger Y.; Ormo, Mats; Remington, S. James

    1997-03-01

    The 2.1- angstrom resolution crystal structure of wild-type green fluorescent protein and comparison of it with the recently determined structure of the Ser-65 --> Thr (S65T) mutant explains the dual wavelength absorption and photoisomerization properties of the wild-type protein. The two absorption maxima are caused by a change in the ionization state of the chromophore. The equilibrium between these states appears to be governed by a hydrogen bond network that permits proton transfer between the chromophore and neighboring side chains. The predominant neutral form of the fluorophore maximally absorbs at 395 nm. It is maintained by the carboxylate of Glu-222 through electrostatic repulsion and hydrogen bonding via a bound water molecule and Ser-205. The ionized form of the fluorophore, absorbing at 475 nm, is present in a minor fraction of the native protein. Glu-222 donates its charge to the fluorophore by proton abstraction through a hydrogen bond network, involving Ser-205 and bound water. Further stabilization of the ionized state of the fluorophore occurs through a rearrangement of the side chains of Thr-203 and His-148. UV irradiation shifts the ratio of the two absorption maxima by pumping a proton relay from the neutral chromophore's excited state to Glu-222. Loss of the Ser-205-Glu-222 hydrogen bond and isomerization of neutral Glu-222 explains the slow return to the equilibrium dark-adapted state of the chromophore. In the S65T structure, steric hindrance by the extra methyl group stabilizes a hydrogen bonding network, which prevents ionization of Glu-222. Therefore the fluorophore is permanently ionized, causing only a 489-nm excitation peak. This new understanding of proton redistribution in green fluorescent protein should enable engineering of environmentally sensitive fluorescent indicators and UV-triggered fluorescent markers of protein diffusion and trafficking in living cells.

  20. Damage detection in composite structures using vibration response under stochastic excitation

    NASA Astrophysics Data System (ADS)

    Yang, Zhichun; Wang, Le; Wang, Hui; Ding, Yan; Dang, Xiaojuan

    2009-09-01

    The investigations in damage detection methods based on vibration response are reviewed according to two categories, i.e. model-based damage detection method (MBDDM) and non-model-based damage detection method (NMBDDM). Then a new concept of inner product vector (IPV) is introduced using the cross correlation function of the measured vibration responses of the structure, and the corresponding damage detection method is proposed based on this vector. It is theoretically proved that the elements in IPV of a structure is the inner product of the time domain vibration responses of corresponding measurement points, and this vector can be directly calculated using the measured time domain vibration responses. Under white noise excitation the IPV of a structure is a weighted summation of mode shapes of the structure, and the weighted factors of the summation only depend on modal parameters of the structure. The effect of measurement noise on IPV is also considered, and the effect can be eliminated by the definition of IPV and an interpolation technique. The difference of IPVs between the intact and damaged structure is adopted as the damage index, and damage location is determined by the abrupt change in the difference of IPV. In order to distinguish the abrupt change caused by structural damage and measurement noise, two thresholds are proposed to classify the damaged and intact structures. Numerical simulation results of damage detection of single-location and multi-location delamination in a composite laminate beam demonstrate the effectiveness and veracity of the proposed method, even though measurement noise is considered in the vibration responses.

  1. Electron transfer, excitation, and ionization in {alpha}-H collisions studied with a Sturmian basis

    SciTech Connect

    Winter, Thomas G.

    2007-12-15

    Cross sections have been determined for electron transfer, direct excitation, and ionization in collisions between {alpha} particles and H(1s) atoms at {alpha} energies 3 keV-38.4 MeV, extending earlier work [Phys. Rev. A 25, 697 (1982)] restricted to total transfer at 20-200 keV. Transfer as well as excitation cross sections into individual states up to 3d have been determined with several coupled-Sturmian pseudostate bases, and tests of basis sensitivity have been carried out. These and ionization cross sections have been compared with existing experimental and other coupled-state results. Structure is observed in the lower-energy excitation cross sections, which is believed not to be an artifact of the bases used. Ionization and excitation cross sections have also been compared with corresponding Born results at higher energies.

  2. Optical reflection spectra of the structures with surface plasmons excited at the metal-amplifying heterogeneous medium boundary

    NASA Astrophysics Data System (ADS)

    Andreev, A.; Nazvanov, V.

    2017-04-01

    In this paper the results of computer simulations of the optical reflection spectra of the structures with surface plasmons excited at the interface between metal and dielectric with optical amplification are presented. To calculate the reflectance the method of scattering matrices was used. It is shown that the enhanced reflectance from an amplifying heterogeneous metal-dielectric medium with simultaneous surface plasmon excitation is possible.

  3. Ab initio molecular dynamics study on the excitation dynamics of psoralen compounds

    NASA Astrophysics Data System (ADS)

    Nakai, H.; Yamauchi, Y.; Nakata, A.; Baba, T.; Takahashi, H.

    2003-08-01

    Ab initio molecular dynamics (AIMD) simulations are performed for studying the S0→T1 excitation dynamics of psoralen compounds; namely, nonsubstituted psoralen, 5-methoxypsoralen (5-MOP), and 8-methoxypsoralen (8-MOP). The density functional theory calculations at the B3LYP/D95V level are used for evaluating the atomic forces in every AIMD step. The specific behavior of 8-MOP in the T1 state, which has been reported by the experimental study, is found to be due to a unique open-ring structure, which leads to a different spin distribution in comparison with the cases of psoralen and 5-MOP and further to a crossing between the S0 and T1 states.

  4. Complex Impedance Studies of Optically Excited Strontium Barium Niobate

    DTIC Science & Technology

    2007-11-02

    has a tetragonal tungsten - bronze structure. The unit cell for this structure, illustrated below in Fig. 2.1, consists of ten oxygen octahedra joined...4 Kittel, pp. 373-374. 5 P. B. Jamieson, et al, “Ferroelectric Tungsten Bronze -Type Crystal Structures. I. Barium Strontium Niobate...Oxford, 1987). 2. C. Kittel, Introduction to Solid State Physics, (Wiley, New York, 1986). 3. P. B. Jamieson, et al, “Ferroelectric Tungsten

  5. Understanding Ultrafast Dynamics of Conformation Specific Photo-Excitation: A Femtosecond Transient Absorption and Ultrafast Raman Loss Study.

    PubMed

    Roy, Khokan; Kayal, Surajit; Ravi Kumar, Venkatraman; Beeby, Andrew; Ariese, Freek; Umapathy, Siva

    2017-09-07

    Excited state ultrafast conformational reorganization is recognized as an important phenomenon that facilitates light-induced functions of many molecular systems. This report describes the femtosecond and picosecond conformational relaxation dynamics of middle-ring and terminal ring twisted conformers of the acetylene π-conjugated system bis(phenylethynyl)benzene, a model system for molecular wires. Through excitation wavelength dependent, femtosecond-transient absorption measurements, we found that the middle-ring and terminal ring twisted conformers relax at femtosecond (400-600 fs) and picosecond (20-24 ps) time scales, respectively. Actinic pumping into the red flank of the absorption spectrum leads to excitation of primarily planar conformers, and results in very different excited state dynamics. In addition, ultrafast Raman loss spectroscopic studies revealed the vibrational mode dependent relaxation dynamics for different excitation wavelengths. To corroborate our experimental findings, DFT and time-dependent DFT calculations were carried out. The Franck-Condon simulation indicated that the vibronic structure observed in the electronic absorption and the fluorescence spectra are due to progressions and combinations of several vibrational modes corresponding to the phenyl ring and the acetylenic groups. Furthermore, the middle ring torsional rotation matches the room-temperature electronic absorption, in stark contrast to the terminal ring torsional rotation. Finally, we show that the middle-ring twisted conformer undergoes femtosecond torsional planarization dynamic, whereas the terminal rings relax on a few tens of picosecond time scale.

  6. Shape coexistence in the neutron-deficient even-even (182-188)Hg isotopes studied via coulomb excitation.

    PubMed

    Bree, N; Wrzosek-Lipska, K; Petts, A; Andreyev, A; Bastin, B; Bender, M; Blazhev, A; Bruyneel, B; Butler, P A; Butterworth, J; Carpenter, M P; Cederkäll, J; Clément, E; Cocolios, T E; Deacon, A; Diriken, J; Ekström, A; Fitzpatrick, C; Fraile, L M; Fransen, Ch; Freeman, S J; Gaffney, L P; García-Ramos, J E; Geibel, K; Gernhäuser, R; Grahn, T; Guttormsen, M; Hadinia, B; Hadyńska-Kle K, K; Hass, M; Heenen, P-H; Herzberg, R-D; Hess, H; Heyde, K; Huyse, M; Ivanov, O; Jenkins, D G; Julin, R; Kesteloot, N; Kröll, Th; Krücken, R; Larsen, A C; Lutter, R; Marley, P; Napiorkowski, P J; Orlandi, R; Page, R D; Pakarinen, J; Patronis, N; Peura, P J; Piselli, E; Rahkila, P; Rapisarda, E; Reiter, P; Robinson, A P; Scheck, M; Siem, S; Singh Chakkal, K; Smith, J F; Srebrny, J; Stefanescu, I; Tveten, G M; Van Duppen, P; Van de Walle, J; Voulot, D; Warr, N; Wenander, F; Wiens, A; Wood, J L; Zielińska, M

    2014-04-25

    Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85  MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in Hg182-188 were extracted. Information on the deformation of the ground and the first excited 0+ states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0+ state was noted in Hg182,184. The results are compared to beyond mean field and interacting-boson based models and interpreted within a two-state mixing model. Partial agreement with the model calculations was obtained. The presence of two different structures in the light even-mass mercury isotopes that coexist at low excitation energy is firmly established.

  7. Experimental Study of Nucleon Structure and QCD

    SciTech Connect

    Jian-Ping Chen

    2012-03-01

    Overview of Experimental Study of Nucleon Structure and QCD, with focus on the spin structure. Nucleon (spin) Structure provides valuable information on QCD dynamics. A decade of experiments from JLab yields these exciting results: (1) valence spin structure, duality; (2) spin sum rules and polarizabilities; (3) precision measurements of g{sub 2} - high-twist; and (4) first neutron transverse spin results - Collins/Sivers/A{sub LT}. There is a bright future as the 12 GeV Upgrade will greatly enhance our capability: (1) Precision determination of the valence quark spin structure flavor separation; and (2) Precision extraction of transversity/tensor charge/TMDs.

  8. Experimental studies of excitations in a BEC in light-induced gauge fields

    NASA Astrophysics Data System (ADS)

    Li, Chuan-Hsun; Blasing, David; Olson, Abraham; Niffenegger, Robert; Chen, Yong P.

    2014-05-01

    We present our experimental studies of various excitation processes in a 87Rb Bose-Einstein condensate (BEC) in the presence of Raman light-induced gauge fields. We have systematically studied controllable inter-band excitations by modulating the strength of the Raman coupling, and probed the resultant decay from the upper dressed bands and heating of the BEC. We also present preliminary results probing the effects of synthetic spin-orbit coupling and gauge fields on collective excitations as well as photoassociation processes in the BEC.

  9. Signal processing and damage detection in a frame structure excited by chaotic input force

    NASA Astrophysics Data System (ADS)

    Salvino, Liming W.; Pines, Darryll J.; Todd, Michael D.; Nichols, Jonathan

    2003-07-01

    This paper discusses the development of a general time-frequency data analysis method, the Empirical Mode Decomposition (EMD) and Hilbert Spectrum, and its application to structural health monitoring. The focus of this work is on feature extraction from structural response time series data. This is done by tracking unique characteristics of the adaptive decomposition components and developing a damage index based on previously introduced fundamental relationships connecting the instantaneous phase of a measured time series to the structural mass and stiffness parameters. Damage detection applications are investigated for a laboratory experiment of a simple frame (a model of a multi-story building) where damage is incurred by removing bolts at various locations. The frame is excited by a low dimensional deterministic chaos input as well as by broadband random signal. The time series output of the frame response is then analyzed with the EMD method. The time-frequency features and instantaneous phase relationships are extracted and examined for changes which may occur due to damage. These results are compared to results from other newly developed detection algorithms based on geometric properties of a chaotic attractor. Our results illustrate that the EMD and instantaneous phase detection approach, based on time-frequency analysis along with simple physics-based models, can be used to determine the presence and location of structural damage and permits the development of a reliable damage detection methodology.

  10. Near-complete structural characterization of phosphatidylcholines using electron impact excitation of ions from organics.

    PubMed

    Campbell, J Larry; Baba, Takashi

    2015-06-02

    Although lipids are critical components of many cellular assemblies and biological pathways, accurate descriptions of their molecular structures remain difficult to obtain. Many benchtop characterization methods require arduous and time-consuming procedures, and multiple assays are required whenever a new structural feature is probed. Here, we describe a new mass-spectrometry-based workflow for enhanced structural lipidomics that, in a single experiment, can yield almost complete structural information for a given glycerophospholipid (GPL) species. This includes the lipid's sum (Brutto) composition from the accurate mass measured for the intact lipid ion and the characteristic headgroup fragment, the regioisomer composition from fragment ions unique to the sn-1 and sn-2 positions, and the positions of carbon-carbon double bonds in the lipid acyl chains. Here, lipid ions are fragmented using electron impact excitation of ions from organics (EIEIO)--a technique where the singly charged lipid ions are irradiated by an electron beam, producing diagnostic product ions. We have evaluated this methodology on various lipid standards, as well as on a biological extract, to demonstrate this new method's utility.

  11. Structural Optimization by Quantum Monte Carlo: Investigating the Low-Lying Excited States of Ethylene.

    PubMed

    Barborini, Matteo; Sorella, Sandro; Guidoni, Leonardo

    2012-04-10

    We present full structural optimizations of the ground state and of the low lying triplet state of the ethylene molecule by means of Quantum Monte Carlo methods. Using the efficient structural optimization method based on renormalization techniques and on adjoint differentiation algorithms recently proposed [Sorella, S.; Capriotti, L. J. Chem. Phys.2010, 133, 234111], we present the variational convergence of both wave function parameters and atomic positions. All of the calculations were done using an accurate and compact wave function based on Pauling's resonating valence bond representation: the Jastrow Antisymmetrized Geminal Power (JAGP). All structural and wave function parameters are optimized, including coefficients and exponents of the Gaussian primitives of the AGP and the Jastrow atomic orbitals. Bond lengths and bond angles are calculated with a statistical error of about 0.1% and are in good agreement with the available experimental data. The Variational and Diffusion Monte Carlo calculations estimate vertical and adiabatic excitation energies in the ranges 4.623(10)-4.688(5) eV and 3.001(5)-3.091(5) eV, respectively. The adiabatic gap, which is in line with other correlated quantum chemistry methods, is slightly higher than the value estimated by recent photodissociation experiments. Our results demonstrate how Quantum Monte Carlo calculations have become a promising and computationally affordable tool for the structural optimization of correlated molecular systems.

  12. Ab initio study of collective excitations in a disparate mass molten salt.

    PubMed

    Bryk, Taras; Klevets, Ivan

    2012-12-14

    Ab initio molecular dynamics simulations and the approach of generalized collective modes are applied for calculations of spectra of longitudinal and transverse collective excitations in molten LiBr. Dispersion and damping of low- and high-frequency branches of collective excitations as well as wave-number dependent relaxing modes were calculated. The main mode contributions to partial, total, and concentration dynamic structure factors were estimated in a wide region of wave numbers. A role of polarization effects is discussed from comparison of mode contributions to concentration dynamic structure factors calculated for molten LiBr from ab initio and classical rigid ion simulations.

  13. Collective excitations in supercritical fluids: analytical and molecular dynamics study of "positive" and "negative" dispersion.

    PubMed

    Bryk, Taras; Mryglod, Ihor; Scopigno, Tullio; Ruocco, Giancarlo; Gorelli, Federico; Santoro, Mario

    2010-07-14

    The approach of generalized collective modes is applied to the study of dispersion curves of collective excitations along isothermal lines of supercritical pure Lennard-Jones fluid. An effect of structural relaxation and other nonhydrodynamic relaxation processes on the dispersion law is discussed. A simple analytical expression for the dispersion law in the long-wavelength region of acoustic excitations is obtained within a three-variable viscoelastic model of generalized hydrodynamics. It is shown that the deviation from the linear dependence in the long-wavelength region can be either "positive" or "negative" depending on the ratio between the high-frequency (elastic) and isothermal speed of sound. An effect of thermal fluctuations on positive and negative dispersion is estimated from the analytical solution of a five-variable thermoviscoelastic model that generalizes the results of the viscoelastic treatment. Numerical results are reported for a Lennard-Jones supercritical fluid along two isothermal lines T(*)=1.71,4.78 with different densities and discussed along the theoretical expressions derived.

  14. Investigation of excited states in 47Ca through a high-statistics beta-decay study

    NASA Astrophysics Data System (ADS)

    Smith, Jenna; Griffin Collaboration

    2015-10-01

    Recent developments in nuclear many-body calculation methods have extended the application of ab initio interactions to the calcium isotopes (e.g. Refs.). Detailed nuclear data for these isotopes are necessary to evaluate the many-body calculation methods and to test the predictive power of the interactions. Transfer reactions from 48Ca have identified many excited states of 47Ca, but only four states have been identified in previous beta-decay experiments. High-statistics beta-decay studies using modern detection systems can provide detailed information on level energies, branching ratios, and spin/parity assignments, while comparison to other population methods can yield information about the structure of these states. A recent experiment at TRIUMF-ISAC used the GRIFFIN spectrometer to investigate the levels populated by beta decay in more detail. The decay scheme has been considerably extended and angular correlations between cascading gamma-ray transitions allow spin and parity assignments to be made for some of the observed excited states. An overview of the experimental apparatus as well as a discussion of the results from preliminary analysis will be presented.

  15. How Parallel Are Excited State Potential Energy Surfaces from Time-Independent and Time-Dependent DFT? A BODIPY Dye Case Study.

    PubMed

    Komoto, Keenan T; Kowalczyk, Tim

    2016-10-06

    To support the development and characterization of chromophores with targeted photophysical properties, excited-state electronic structure calculations should rapidly and accurately predict how derivatization of a chromophore will affect its excitation and emission energies. This paper examines whether a time-independent excited-state density functional theory (DFT) approach meets this need through a case study of BODIPY chromophore photophysics. A restricted open-shell Kohn-Sham (ROKS) treatment of the S1 excited state of BODIPY dyes is contrasted with linear-response time-dependent density functional theory (TDDFT). Vertical excitation energies predicted by the two approaches are remarkably different due to overestimation by TDDFT and underestimation by ROKS relative to experiment. Overall, ROKS with a standard hybrid functional provides the more accurate description of the S1 excited state of BODIPY dyes, but excitation energies computed by the two methods are strongly correlated. The two approaches also make similar predictions of shifts in the excitation energy upon functionalization of the chromophore. TDDFT and ROKS models of the S1 potential energy surface are then examined in detail for a representative BODIPY dye through molecular dynamics sampling on both model surfaces. We identify the most significant differences in the sampled surfaces and analyze these differences along selected normal modes. Differences between ROKS and TDDFT descriptions of the S1 potential energy surface for this BODIPY derivative highlight the continuing need for validation of widely used approximations in excited state DFT through experimental benchmarking and comparison to ab initio reference data.

  16. Three-dimensional structure of self-excited dust density waves under microgravity conditions

    SciTech Connect

    Arp, Oliver; Menzel, Kristoffer; Piel, Alexander

    2008-09-07

    Self-excited dust density waves in a dusty plasma, containing micrometer-sized particles, have been observed under microgravity conditions at low gas pressures and high dust densities. The waves emerge spontaneously and propagate from the void edge radially outwards to the plasma boundary. We found that the wave propagates obliquely to the local ion flow in regions with high electric fields close to the sheath, whereas it propagates parallel in the plasma bulk. So far the observation was limited to a fixed two-dimensional section through the discharge volume. Recent experiments were performed on parabolic flights in a parallel plate rf discharge, which used the technique of scanning video microscopy. This technique utilizes the high temporal coherence of the waves to reconstruct their full three-dimensional structure. The analysis yields a surprising global spatial coherence of the wave phenomenon.

  17. Harmonic plasma waves excitation and structure evolution of intense ion beams in background plasmas

    SciTech Connect

    Hu, Zhang-Hu Wang, You-Nian

    2016-08-15

    The long-term dynamic evolutions of intense ion beams in plasmas have been investigated with two-dimensional electromagnetic particle simulations, taking into account the effect of the two-stream instability between beam ions and plasma electrons. Depending on the initial beam radial density profile and velocity distribution, ring structures may be formed in the beam edge regions. At the later stage of beam-plasma interactions, the ion beams are strongly modulated by the two-stream instability and multiple density spikes are formed in the longitudinal direction. The formation of these density spikes is shown to result from the excitation of harmonic plasma waves when the instability gets saturated. Comparisons between the beam cases with initial flat-top and Gaussian radial density profiles are made, and a higher instability growth rate is observed for the flat-top profile case.

  18. Study of EMIC wave excitation using direct ion measurements

    NASA Astrophysics Data System (ADS)

    Min, Kyungguk; Liu, Kaijun; Bonnell, John W.; Breneman, Aaron W.; Denton, Richard E.; Funsten, Herbert O.; Jahn, Jöerg-Micha; Kletzing, Craig A.; Kurth, William S.; Larsen, Brian A.; Reeves, Geoffrey D.; Spence, Harlan E.; Wygant, John R.

    2015-04-01

    With data from Van Allen Probes, we investigate electromagnetic ion cyclotron (EMIC) wave excitation using simultaneously observed ion distributions. Strong He band waves occurred while the spacecraft was moving through an enhanced density region. We extract from helium, oxygen, proton, and electron mass spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sinm-type distribution functions, we find that the observed ions make up about 15% of the total ions, but about 85% of them are still missing. By making legitimate estimates of the unseen cold (below ˜2 eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of linear instability analyses and hybrid simulations are carried out. The simulated waves generally vary as predicted by linear theory. They are more sensitive to the cold O+ concentration than the cold He+ concentration. Increasing the cold O+ concentration weakens the He band waves but enhances the O band waves. Finally, the exact cold ion composition is suggested to be in a range when the simulated wave spectrum best matches the observed one.

  19. Study of {sup 179}Hf{sup m2} excitation

    SciTech Connect

    Vishnevsky, I. N.; Zheltonozhsky, V. A. Savrasov, A. N.; Mazur, V. M.

    2016-12-15

    Isomeric ratios of {sup 179}Hf{sup m2,g} yields in the (γ, n) reaction and the cross section for the {sup 179}Hf{sup m2} population in the (α, p) reaction are measured for the first time at the end-point energies of 15.1 and 17.5 MeV for bremsstrahlung photons and 26 MeV for alpha particles. The results are σ = (1.1 ± 0.11) × 10{sup −27} cm{sup 2} for the {sup 176}Lu(α, p){sup 179}Hf{sup m2} reaction and Y{sub m2}/Y{sub g} = (6.1 ± 0.3) × 10{sup −6} and (3.7 ± 0.2) × 10{sup −6} for the {sup 180}Hf(γ, n){sup 179}Hf{sup m22} reaction at E{sub ep} =15.1 and 17.5 MeV, respectively. The experimental data on the relative {sup 179}Hf{sup m2} yield indicate a single-humped shape of the excitation function for the {sup 180}Hf(γ, n){sup 179}Hf{sup m2} reaction. Simulation is performed using the TALYS-1.4 and EMPIRE-3.2 codes.

  20. Towards computational modeling of excitation-contraction coupling in cardiac myocytes: reconstruction of structures and proteins from confocal imaging.

    PubMed

    Sachse, Frank B; Savio-Galimberti, Eleonora; Goldhaber, Joshua I; Bridge, John H B

    2009-01-01

    Computational models of excitation-contraction (EC) coupling in myocytes are valuable tools for studying the signaling cascade that transduces transmembrane voltage into mechanical responses. A key component of these models is the appropriate description of structures involved in EC coupling, such as the sarcolemma and ion channels. This study aims at developing an approach for spatial reconstruction of these structures. We exemplified our approach by reconstructing clusters of ryanodine receptors (RyRs) together with the sarcolemma of rabbit ventricular myocytes. The reconstructions were based on dual labeling and three-dimensional (3D) confocal imaging of segments of fixed and permeabilized myocytes lying flat or on end. The imaging led to 3D stacks of cross-sections through myocytes. Methods of digital image processing were applied to deconvolve, filter and segment these stacks. Finally, we created point meshes representing RyR distributions together with volume and surface meshes of the sarcolemma. We suggest that these meshes are suitable for computational studies of structure-function relationships in EC coupling. We propose that this approach can be extended to reconstruct other structures and proteins involved in EC coupling.

  1. Ultrafast transient absorption microscopy: Study of excited state dynamics in PtOEP crystals

    NASA Astrophysics Data System (ADS)

    Davydova, Dar'ya; de la Cadena, Alejandro; Demmler, Stefan; Rothhardt, Jan; Limpert, Jens; Pascher, Torbjörn; Akimov, Denis; Dietzek, Benjamin

    2016-01-01

    We report a novel transient absorption microscope based on a tailor-made femtosecond fiber laser system operating at 250 kHz. The setup is applied to study PtOEP crystals embedded in a PBMA polymer matrix by analyzing the excited state dynamics in specific points of the sample as well as by spatially resolved excited state dynamics of the crystals. The results reveal the impact of the distortions of the crystal lattice, such as microcracks or amorphous regions caused by non-thermal melting on a lifetime of the excited triplet states of PtOEP crystals. Although transient absorption studies without any spatial resolution of PtOEP in solution and thin films were reported before, the study of spatially resolved excited state dynamics of micrometer-sized PtOEP crystals is performed for the first time to the best of our knowledge.

  2. Angular dependent study on ferromagnetic resonance and spin excitations by spin rectification

    SciTech Connect

    Zhang, Yichao; Fan, Xiaolong Zhao, Xiaobing; Rao, Jinwei; Zhou, Hengan; Guo, Dangwei; Xue, Desheng; Gui, Y. S.; Hu, C.-M.

    2015-01-14

    We report angular dependent spin rectification spectra which are applied to studying spin excitations in single permalloy stripe. Based on planar Hall effect, those spin excitations generate special resonant dc Hall voltages, which have been characterized as functions of the amplitude and direction of applied magnetic field. Through high angular resolution 2D mappings, the evolutions of different spin excitation can be directly presented, and the dynamic magnetic parameters such as the gyromagnetic ratio, effective exchange field, as well as the quantized numbers of standing spin waves can be accurately determined through fitting the angular evolution of each resonance.

  3. Optimization of structures undergoing harmonic or stochastic excitation. Ph.D. Thesis; [atmospheric turbulence and white noise

    NASA Technical Reports Server (NTRS)

    Johnson, E. H.

    1975-01-01

    The optimal design was investigated of simple structures subjected to dynamic loads, with constraints on the structures' responses. Optimal designs were examined for one dimensional structures excited by harmonically oscillating loads, similar structures excited by white noise, and a wing in the presence of continuous atmospheric turbulence. The first has constraints on the maximum allowable stress while the last two place bounds on the probability of failure of the structure. Approximations were made to replace the time parameter with a frequency parameter. For the first problem, this involved the steady state response, and in the remaining cases, power spectral techniques were employed to find the root mean square values of the responses. Optimal solutions were found by using computer algorithms which combined finite elements methods with optimization techniques based on mathematical programming. It was found that the inertial loads for these dynamic problems result in optimal structures that are radically different from those obtained for structures loaded statically by forces of comparable magnitude.

  4. Narrow structure in the excitation function of η photoproduction off the neutron.

    PubMed

    Werthmüller, D; Witthauer, L; Keshelashvili, I; Aguar-Bartolomé, P; Ahrens, J; Annand, J R M; Arends, H J; Bantawa, K; Beck, R; Bekrenev, V; Braghieri, A; Branford, D; Briscoe, W J; Brudvik, J; Cherepnya, S; Demissie, B; Dieterle, M; Downie, E J; Drexler, P; Fil'kov, L V; Fix, A; Glazier, D I; Hamilton, D; Heid, E; Hornidge, D; Howdle, D; Huber, G M; Jaegle, I; Jahn, O; Jude, T C; Käser, A; Kashevarov, V L; Kondratiev, R; Korolija, M; Kruglov, S P; Krusche, B; Kulbardis, A; Lisin, V; Livingston, K; MacGregor, I J D; Maghrbi, Y; Mancell, J; Manley, D M; Marinides, Z; Martinez, M; McGeorge, J C; McNicoll, E F; Metag, V; Middleton, D G; Mushkarenkov, A; Nefkens, B M K; Nikolaev, A; Novotny, R; Oberle, M; Ostrick, M; Oussena, B; Pedroni, P; Pheron, F; Polonski, A; Prakhov, S N; Robinson, J; Rosner, G; Rostomyan, T; Schumann, S; Sikora, M H; Sober, D; Starostin, A; Supek, I; Thiel, M; Thomas, A; Unverzagt, M; Watts, D P

    2013-12-06

    The photoproduction of η mesons off nucleons bound in 2H and 3He has been measured in coincidence with recoil protons and recoil neutrons for incident photon energies from threshold up to 1.4 GeV. The experiments were performed at the Mainz MAMI accelerator, using the Glasgow tagged photon facility. Decay photons from the η→2γ and η→3π0 decays and the recoil nucleons were detected with an almost 4π electromagnetic calorimeter combining the Crystal Ball and TAPS detectors. The data from both targets are of excellent statistical quality and show a narrow structure in the excitation function of γn→nη. The results from the two measurements are consistent, taking into account the expected effects from nuclear Fermi motion. The best estimates for position and intrinsic width of the structure are W=(1670±5)  MeV and Γ=(30±15)  MeV. For the first time precise results for the angular dependence of this structure have been extracted.

  5. Response measurements for two building structures excited by noise from a large horizontal axis wind turbine generator

    NASA Astrophysics Data System (ADS)

    Hubbard, H. H.; Shepherd, K. P.

    1984-11-01

    Window and wall acceleration measurements and interior noise measurements ere made for two different building structures during excitation by noise from the WTS-4 horizontal axis wind turbine generator operating in a normal power generation mode. With turbine noise input pulses resulted in acceleration pulses for the wall and window elements of the two tests buildings. Response spectra suggest that natural vibration modes of the structures are excited. Responses of a house trailer were substantially greater than those for a building of sturdier construction. Peak acceleration values correlate well with similar data for houses excited by flyover noise from commercial and military airplanes and helicopters, and sonic booms from supersonic aircraft. Interior noise spectra have peaks at frequencies corresponding to structural vibration modes and room standing waves; and the levels for particular frequencies and locations can be higher than the outside levels.

  6. Response measurements for two building structures excited by noise from a large horizontal axis wind turbine generator

    NASA Technical Reports Server (NTRS)

    Hubbard, H. H.; Shepherd, K. P.

    1984-01-01

    Window and wall acceleration measurements and interior noise measurements ere made for two different building structures during excitation by noise from the WTS-4 horizontal axis wind turbine generator operating in a normal power generation mode. With turbine noise input pulses resulted in acceleration pulses for the wall and window elements of the two tests buildings. Response spectra suggest that natural vibration modes of the structures are excited. Responses of a house trailer were substantially greater than those for a building of sturdier construction. Peak acceleration values correlate well with similar data for houses excited by flyover noise from commercial and military airplanes and helicopters, and sonic booms from supersonic aircraft. Interior noise spectra have peaks at frequencies corresponding to structural vibration modes and room standing waves; and the levels for particular frequencies and locations can be higher than the outside levels.

  7. Photoionization study of doubly-excited helium at ultra-high resolution

    SciTech Connect

    Kaindl, G.; Schulz, K.; Domke, M.

    1997-04-01

    Ever since the pioneering work of Madden & Codling and Cooper, Fano & Prats on doubly-excited helium in the early sixties, this system may be considered as prototypical for the study of electron-electron correlations. More detailed insight into these states could be reached only much later, when improved theoretical calculations of the optically-excited {sup 1}P{sup 0} double-excitation states became available and sufficiently high energy resolution ({delta}E=4.0 meV) was achieved. This allowed a systematic investigation of the double-excitation resonances of He up to excitation energies close to the double-ionization threshold, I{sub infinity}=79.003 eV, which stimulated renewed theoretical interest into these correlated electron states. The authors report here on striking progress in energy resolution in this grazing-incidence photon-energy range of grating monochromators and its application to hitherto unobservable states of doubly-excited He. By monitoring an extremely narrow double-excitation resonance of He, with a theoretical lifetime width of less than or equal to 5 {mu}eV, a resolution of {delta}E=1.0 meV (FWHM) at 64.1 eV could be achieved. This ultra-high spectral resolution, combined with high photon flux, allowed the investigation of new Rydberg resonances below the N=3 ionization threshold, I{sub 3}, as well as a detailed comparison with ab-initio calculations.

  8. Structure of the photochemical reaction path populated via promotion of CF(2)I(2) into its first excited state.

    PubMed

    El-Khoury, Patrick Z; Tarnovsky, Alexander N; Schapiro, Igor; Ryazantsev, Mikhail N; Olivucci, Massimo

    2009-10-08

    The photochemical reaction path following the promotion of CF(2)I(2) into its lowest-lying excited electronic singlet state has been modeled using ab initio multiconfigurational quantum chemical calculations. It is found that a conical intersection drives the electronically excited CF(2)I(2)* species either to the CF(2)I + I radical pair or back to the starting CF(2)I(2) structure. The structures of the computed relaxation pathways explain the photoproduct selectivity previously observed in the gas phase. Furthermore, the results provide the basis for explaining the condensed-phase photochemistry of CF(2)I(2).

  9. Spatial structure of the electromagnetic field inside the ionospheric Alfvén resonator excited by atmospheric lightning activity

    NASA Astrophysics Data System (ADS)

    Plyasov, A. A.; Surkov, V. V.; Pilipenko, V. A.; Fedorov, E. N.; Ignatov, V. N.

    2012-09-01

    We have theoretically estimated ULF spectra on the ground and at ionospheric altitudes in the frequency range of the ionospheric Alfvén resonator (IAR). The IAR has been considered to be excited either by a separate lightning stroke or stochastic global thunderstorm activity. The spectra of both horizontal magnetic and electric components are shown to reveal the spectral resonant structure in the upper ionosphere. The IAR excitation for different ionospheric conditions has been compared. The IAR eigenfrequencies latitudinal inhomogeneity results in the smoothing and shift of the spectral resonance structure. The feasibility of the IAR signature detection by low-orbiting satellites with magnetic or electric sensors is discussed.

  10. Lasing studies of new coumarin derivatives under laser and lamp excitation

    SciTech Connect

    Aristov, A. V.; Veselova, T. V.; Kozlovskii, D. A.; Komlev, I. V.; Levin, M. B.; Reznichenko, A. V.; Tavrizova, M. A.; Cherkasov, A. S.

    1988-09-01

    The luminescence characteristics and results of a study of the comparative laser efficiency of ethanol solutions of a series of coumarin derivatives and rhodamine 6G are presented. It is shown that under laser excitation (neodymium laser third harmonic) and lamp excitation, the solutions of certain coumarins match rhodamine 6G in lasing efficiency values. A comparatively low photostability of the investigated coumarin solutions and its weak dependence on the spectral composition of the pumping radiation have been observed.

  11. Spectroscopic studies of the internal modes of aminoaromatics by fluorescence excitation and dispersed emission in supersonic jet

    SciTech Connect

    Yan, S.

    1992-01-01

    A systematic study for the NH[sub 2] inversional mode in aniline and para substituted anilines has been performed using the techniques of fluorescence excitation and dispersed emission in supersonic jet. The transitions of the nitrogen inversion mode in aniline and para substituted anilines have been assigned in both the fluorescence excitation and dispersed emission spectra, which are strongly supported by the evidence of a large deuterium shift, the presence of a strong hot band, and the intense second overtone transition of the amino inversion in the excitation spectra of all the aniline molecules. The potential surface of each aniline has been fit using the observed inversional levels in both the ground and excited states. The molecular structure of each aniline has been investigated based on the experimental results. The NH[sub 2] torsional transition is assigned in the excitation spectrum of each aniline molecule for the first time. The absence of a torsional hot band and no observable tunneling splitting in the NH[sub 2] torsional mode indicates that the NH[sub 2] torsion mode in the anilines must have a very high first quanta in the ground state. The mechanism of I[sup 2][sub 0] and T[sup 2][sub 0] splittings in the excitation spectrum of p-toluidine has been explained by using molecular symmetry. The splittings are caused by the torsion-torsion coupling between the NH[sub 2] and CH[sub 3] groups. The structure of p-amino-p[prime]-methyl-trans-stilbene (PPTS) has been studied by spectroscopic methods and X-ray diffraction. The nearly planar geometry of the proton donor in the PPTS crystal dimer provides important evidence that the structure of gas phase PPTS is planar in the ground state. The absence of the hot band and I[sup 2][sub 0] in the excitation spectrum of PPTS indicates that the potential surface of PPTS must be a single well in both states, which is consistent with the X-ray result.

  12. Picosecond excitation energy transfer of allophycocyanin studied in solution and in crystals.

    PubMed

    Ranjbar Choubeh, Reza; Sonani, Ravi R; Madamwar, Datta; Struik, Paul C; Bader, Arjen N; Robert, Bruno; van Amerongen, Herbert

    2017-07-28

    Cyanobacteria perform photosynthesis with the use of large light-harvesting antennae called phycobilisomes (PBSs). These hemispherical PBSs contain hundreds of open-chain tetrapyrrole chromophores bound to different peptides, providing an arrangement in which excitation energy is funnelled towards the PBS core from where it can be transferred to photosystem I and/or photosystem II. In the PBS core, many allophycocyanin (APC) trimers are present, red-light-absorbing phycobiliproteins that covalently bind phycocyanobilin (PCB) chromophores. APC trimers were amongst the first light-harvesting complexes to be crystallized. APC trimers have two spectrally different PCBs per monomer, a high- and a low-energy pigment. The crystal structure of the APC trimer reveals the close distance (~21 Å) between those two chromophores (the distance within one monomer is ~51 Å) and this explains the ultrafast (~1 ps) excitation energy transfer (EET) between them. Both chromophores adopt a somewhat different structure, which is held responsible for their spectral difference. Here we used spectrally resolved picosecond fluorescence to study EET in these APC trimers both in crystallized and in solubilized form. We found that not all closely spaced pigment couples consist of a low- and a high-energy pigment. In ~10% of the cases, a couple consists of two high-energy pigments. EET to a low-energy pigment, which can spectrally be resolved, occurs on a time scale of tens of picoseconds. This transfer turns out to be three times faster in the crystal than in the solution. The spectral characteristics and the time scale of this transfer component are similar to what have been observed in the whole cells of Synechocystis sp. PCC 6803, for which it was ascribed to EET from C-phycocyanin to APC. The present results thus demonstrate that part of this transfer should probably also be ascribed to EET within APC trimers.

  13. Rotationally resolved IR-diode laser studies of ground-state CO2 excited by collisions with vibrationally excited pyridine.

    PubMed

    Johnson, Jeremy A; Kim, Kilyoung; Mayhew, Maurine; Mitchell, Deborah G; Sevy, Eric T

    2008-03-27

    Relaxation of highly vibrationally excited pyridine (C5NH5) by collisions with carbon dioxide has been investigated using diode laser transient absorption spectroscopy. Vibrationally hot pyridine (E' = 40,660 cm(-1)) was prepared by 248 nm excimer laser excitation followed by rapid radiationless relaxation to the ground electronic state. Pyridine then collides with CO2, populating the high rotational CO2 states with large amounts of translational energy. The CO2 nascent rotational population distribution of the high-J (J = 58-80) tail of the 00(0)0 state was probed at short times following the excimer laser pulse to measure rate constants and probabilities for collisions populating these CO2 rotational states. Doppler spectroscopy was used to measure the CO2 recoil velocity distribution for J = 58-80 of the 00(0)0 state. The energy-transfer distribution function, P(E,E'), from E' - E approximately 1300-7000 cm(-1) was obtained by re-sorting the state-indexed energy-transfer probabilities as a function of DeltaE. P(E,E') is fit to an exponential or biexponential function to determine the average energy transferred in a single collision between pyridine and CO2. Also obtained are fit parameters that can be compared to previously studied systems (pyrazine, C6F6, methylpyrazine, and pyrimidine/CO2). Although the rotational and translational temperatures that describe pyridine/CO2 energy transfer are similar to previous systems, the energy-transfer probabilities are much smaller. P(E,E') fit parameters for pyridine/CO2 and the four previously studied systems are compared to various donor molecular properties. Finally, P(E,E') is analyzed in the context of two models, one indicating that P(E,E') shape is primarily determined by the low-frequency out-of-plane donor vibrational modes, and the other that indicates that P(E,E') shape can be determined from how the donor molecule final density of states changes with DeltaE.

  14. Structures and properties of electronically excited chromophores in solution from the polarizable continuum model coupled to the time-dependent density functional theory.

    PubMed

    Mennucci, Benedetta; Cappelli, Chiara; Guido, Ciro Achille; Cammi, Roberto; Tomasi, Jacopo

    2009-04-02

    This paper provides an overview of recent research activities concerning the quantum-mechanical description of structures and properties of electronically excited chromophores in solution. The focus of the paper is on a specific approach to include solvent effects, namely the polarizable continuum model (PCM). Such a method represents an efficient strategy if coupled to proper quantum-mechanical descriptions such as the time-dependent density functional theory (TDDFT). As a result, the description of molecules in the condensed phase can be extended to excited states still maintaining the computational efficiency and the physical reliability of the ground-state calculations. The most important theoretical and computational aspects of the coupling between PCM and TDDFT are presented and discussed together with an example of application to the study of the low-lying electronic excited states of push-pull chromophores in different solvents.

  15. Electron beam excitation of coherent sub-terahertz radiation in periodic structures manufactured by 3D printing

    NASA Astrophysics Data System (ADS)

    Phipps, A. R.; MacLachlan, A. J.; Robertson, C. W.; Zhang, L.; Konoplev, I. V.; Cross, A. W.; Phelps, A. D. R.

    2017-07-01

    For the creation of novel coherent sub-THz sources excited by electron beams there is a requirement to manufacture intricate periodic structures to produce and radiate electromagnetic fields. The specification and the measured performance is reported of a periodic structure constructed by additive manufacturing and used successfully in an electron beam driven sub-THz radiation source. Additive manufacturing, or ;3D printing;, is promising to be quick and cost-effective for prototyping these periodic structures.

  16. Electronic structure and excitations in oxygen deficient CeO2-δ from DFT calculations

    NASA Astrophysics Data System (ADS)

    Jarlborg, T.; Barbiellini, B.; Lane, C.; Wang, Yung Jui; Markiewicz, R. S.; Liu, Zhi; Hussain, Zahid; Bansil, A.

    2014-04-01

    The electronic structures of supercells of CeO2-δ have been calculated within the density functional theory (DFT). The equilibrium properties such as lattice constants, bulk moduli, and magnetic moments are well reproduced by the generalized gradient approximation (GGA). Electronic excitations are simulated by robust total-energy calculations for constrained states with atomic core holes or valence holes. Pristine ceria CeO2 is found to be a nonmagnetic insulator with magnetism setting in as soon as oxygens are removed from the structure. In the ground state of defective ceria, the Ce-f majority band resides near the Fermi level but appears at about 2 eV below the Fermi level in photoemission spectroscopy experiments due to final-state effects. We also tested our computational method by calculating threshold energies in Ce-M5 and O-K x-ray absorption spectroscopy and comparing theoretical predictions with the corresponding measurements. Our result that f electrons reside near the Fermi level in the ground state of oxygen-deficient ceria is crucial for understanding the catalytic properties of CeO2 and related materials.

  17. The spectroscopy of singlets and triplets excites electronic states, spatial and electronic structure of hydrocarbons and quantum classifications in chemmotology

    NASA Astrophysics Data System (ADS)

    Obukhov, A. E.

    2016-12-01

    In this work we demonstrate the physical foundations of the spectroscopy of the grounds states: E- and X-ray, (RR) Raman scattering the NMR 1H and 13C and IR-, EPR- absorption and the singlets and triplets electronic excited states in the multinuclear hydrocarbons in chemmotology. The parameters of UV-absorption, RR-Raman scattering of light, the fluorescence and the phosphorescence and day-lasers at the pumping laser and lamp, OLEDs and OTETs- are measurements. The spectral-energy properties are briefly studied. The quantum-chemical LCAO-MO SCF expanded-CI PPP/S and INDO/S methods in the electronic and spatial structure hidrocarbons are considered.

  18. Characteristic length scale of the magnon accumulation in Fe3O4/Pt bilayer structures by incoherent thermal excitation

    NASA Astrophysics Data System (ADS)

    Anadón, A.; Ramos, R.; Lucas, I.; Algarabel, P. A.; Morellón, L.; Ibarra, M. R.; Aguirre, M. H.

    2016-07-01

    The dependence of Spin Seebeck effect (SSE) with the thickness of the magnetic materials is studied by means of incoherent thermal excitation. The SSE voltage signal in Fe3O4/Pt bilayer structure increases with the magnetic material thickness up to 100 nm, approximately, showing signs of saturation for larger thickness. This dependence is well described in terms of a spin current pumped in the platinum film by the magnon accumulation in the magnetic material. The spin current is generated by a gradient of temperature in the system and detected by the Pt top contact by means of inverse spin Hall effect. Calculations in the frame of the linear response theory adjust with a high degree of accuracy the experimental data, giving a thermal length scale of the magnon accumulation (Λ) of 17 ± 3 nm at 300 K and Λ = 40 ± 10 nm at 70 K.

  19. LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Two-photon-excited luminescence of biologically active solid-state structures

    NASA Astrophysics Data System (ADS)

    Gorelik, V. S.; Kozulin, E. A.

    1994-05-01

    A study was made of the characteristics of two-photon-excited luminescence of a number of pharmaceutical and biologically active solid-state materials: aspirin, sulfadimethoxine, Streptocid (sulfanilamide), pig insulin, and lysozyme. This luminescence was excited by pulse-periodic laser radiation. The characteristics of the luminescence spectra were compared with the familiar spectra of two-photon-excited luminescence of L-tryptophan. The results were used to determine the characteristics of molecular excitons in the investigated organic crystals and to estimate the concentration of tryptophan in solid-state proteins.

  20. Model Studies of CBES (Chemically Bound Excited States) Decomposition.

    DTIC Science & Technology

    1988-02-01

    J BENARD ET RL. FES 68 SC5467 BSR UNCLSSIFIED AFA -TR-87--S71 F94611-B6-C-0072 F/6l 7/2 ML mhmmommhhhum F fLlflllfsfff.. EEsonhEEE IN12 .... 1 %L...concentrations below 10 torr, using only glass, teflon or stainless steel for construction, and avoiding condensation except of microscopically thin...electric deep fat fryer by a stainless steel support structure. The pot was filled with cooking oil whose temperature (TI) was measured by a metal band

  1. Reflection of a TE-polarised Gaussian beam from a layered structure under conditions of resonance excitation of waveguide modes

    SciTech Connect

    Sokolov, V I; Marusin, N V; Molchanova, S I; Savelyev, A G; Khaydukov, E V; Panchenko, V Ya

    2014-11-30

    The problem of reflection of a TE-polarised Gaussian light beam from a layered structure under conditions of resonance excitation of waveguide modes using a total internal reflection prism is considered. Using the spectral approach we have derived the analytic expressions for the mode propagation lengths, widths and depths of m-lines (sharp and narrow dips in the angular dependence of the specular reflection coefficient), depending on the structure parameters. It is shown that in the case of weak coupling, when the propagation lengths l{sub m} of the waveguide modes are mainly determined by the extinction coefficient in the film, the depth of m-lines grows with the mode number m. In the case of strong coupling, when l{sub m} is determined mainly by the radiation of modes into the prism, the depth of m-lines decreases with increasing m. The change in the TE-polarised Gaussian beam shape after its reflection from the layered structure is studied, which is determined by the energy transfer from the incident beam into waveguide modes that propagate along the structure by the distance l{sub m}, are radiated in the direction of specular reflection and interfere with a part of the beam reflected from the working face of the prism. It is shown that this interference can lead to the field intensity oscillations near m-lines. The analysis of different methods for determining the parameters of thin-film structures is presented, including the measurement of mode angles θ{sub m} and the reflected beam shape. The methods are based on simultaneous excitation of a few waveguide modes in the film with a strongly focused monochromatic Gaussian beam, the waist width of which is much smaller than the propagation length of the modes. As an example of using these methods, the refractive index and the thickness of silicon monoxide film on silica substrate at the wavelength 633 nm are determined. (fibre and integrated-optical structures)

  2. Excited-state molecular structures captured by X-ray transient absorption spectroscopy: a decade and beyond.

    PubMed

    Chen, Lin X; Zhang, Xiaoyi; Lockard, Jenny V; Stickrath, Andrew B; Attenkofer, Klaus; Jennings, Guy; Liu, Di-Jia

    2010-03-01

    Transient molecular structures along chemical reaction pathways are important for predicting molecular reactivity, understanding reaction mechanisms, as well as controlling reaction pathways. During the past decade, X-ray transient absorption spectroscopy (XTA, or LITR-XAS, laser-initiated X-ray absorption spectroscopy), analogous to the commonly used optical transient absorption spectroscopy, has been developed. XTA uses a laser pulse to trigger a fundamental chemical process, and an X-ray pulse(s) to probe transient structures as a function of the time delay between the pump and probe pulses. Using X-ray pulses with high photon flux from synchrotron sources, transient electronic and molecular structures of metal complexes have been studied in disordered media from homogeneous solutions to heterogeneous solution-solid interfaces. Several examples from the studies at the Advanced Photon Source in Argonne National Laboratory are summarized, including excited-state metalloporphyrins, metal-to-ligand charge transfer (MLCT) states of transition metal complexes, and charge transfer states of metal complexes at the interface with semiconductor nanoparticles. Recent developments of the method are briefly described followed by a future prospective of XTA. It is envisioned that concurrent developments in X-ray free-electron lasers and synchrotron X-ray facilities as well as other table-top laser-driven femtosecond X-ray sources will make many breakthroughs and realise dreams of visualizing molecular movies and snapshots, which ultimately enable chemical reaction pathways to be controlled.

  3. Excited-state molecular structures captured by x-ray transient absorption spectroscopy : a decade and beyond.

    SciTech Connect

    Chen, L. X.; Zhang, X.; Lockard, J. V.; Stickrath, A. B.; Attenkofer, K.; Jennings, G.; Liu, D.-J.; Northwestern Univ.

    2010-03-02

    Transient molecular structures along chemical reaction pathways are important for predicting molecular reactivity, understanding reaction mechanisms, as well as controlling reaction pathways. During the past decade, X-ray transient absorption spectroscopy (XTA, or LITR-XAS, laser-initiated X-ray absorption spectroscopy), analogous to the commonly used optical transient absorption spectroscopy, has been developed. XTA uses a laser pulse to trigger a fundamental chemical process, and an X-ray pulse(s) to probe transient structures as a function of the time delay between the pump and probe pulses. Using X-ray pulses with high photon flux from synchrotron sources, transient electronic and molecular structures of metal complexes have been studied in disordered media from homogeneous solutions to heterogeneous solution-solid interfaces. Several examples from the studies at the Advanced Photon Source in Argonne National Laboratory are summarized, including excited-state metalloporphyrins, metal-to-ligand charge transfer (MLCT) states of transition metal complexes, and charge transfer states of metal complexes at the interface with semiconductor nanoparticles. Recent developments of the method are briefly described followed by a future prospective of XTA. It is envisioned that concurrent developments in X-ray free-electron lasers and synchrotron X-ray facilities as well as other table-top laser-driven femtosecond X-ray sources will make many breakthroughs and realise dreams of visualizing molecular movies and snapshots, which ultimately enable chemical reaction pathways to be controlled.

  4. Ab initio study on an excited-state intramolecular proton-transfer reaction in ionic liquid.

    PubMed

    Hayaki, Seigo; Kimura, Yoshifumi; Sato, Hirofumi

    2013-06-06

    An excited-state intramolecular proton transfer (ESIPT) reaction of 4'-N,N-dimethylamino-3-hydroxyflavone in room temperature ionic liquid is theoretically investigated using RISM-SCF-SEDD, which is a hybrid method of molecular liquid theory and ab initio molecular orbital theory. The photo-excitation and proton-transfer processes are computed by considering the solvent fluctuation. The calculated absorption and emission energy are in good agreement with the experiments. The changes in the dipole moment indicate that the drastic solvation relaxation is accompanied by the excitation and an ESIPT process, which is consistent with the remarkable dynamic Stokes shift observed in the experiments. We calculated the nonequilibrium free-energy contour as a function of the proton coordinate and the solvation coordinate. We conclude that although immediately after the excitation the barrier height of the ESIPT process is relatively small, the barrier becomes larger as the solvation relaxation to the excited normal state proceeds. The solvation relaxation process is also investigated on the basis of microscopic solvation structure obtained by RISM calculations.

  5. Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps

    NASA Astrophysics Data System (ADS)

    Dang, Qiankun; Xu, Fuxing; Wang, Liang; Huang, Xiaohua; Dai, Xinhua; Fang, Xiang; Wang, Rizhi; Ding, Chuan-Fan

    2016-04-01

    The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.

  6. Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps.

    PubMed

    Dang, Qiankun; Xu, Fuxing; Wang, Liang; Huang, Xiaohua; Dai, Xinhua; Fang, Xiang; Wang, Rizhi; Ding, Chuan-Fan

    2016-04-01

    The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.

  7. Hyperspectral imaging fluorescence excitation scanning for detecting colorectal cancer: pilot study

    NASA Astrophysics Data System (ADS)

    Leavesley, Silas J.; Wheeler, Mikayla; Lopez, Carmen; Baker, Thomas; Favreau, Peter F.; Rich, Thomas C.; Rider, Paul F.; Boudreaux, Carole W.

    2016-03-01

    Optical spectroscopy and hyperspectral imaging have shown the theoretical potential to discriminate between cancerous and non-cancerous tissue with high sensitivity and specificity. To date, these techniques have not been able to be effectively translated to endoscope platforms. Hyperspectral imaging of the fluorescence excitation spectrum represents a new technology that may be well-suited for endoscopic implementation. However, the feasibility of detecting differences between normal and cancerous mucosa using fluorescence excitation-scanning hyperspectral imaging has not been evaluated. The objective of this pilot study was to evaluate the changes in the fluorescence excitation spectrum of resected specimen pairs of colorectal adenocarcinoma and normal colorectal mucosa. Patients being treated for colorectal adenocarcinoma were enrolled. Representative adenocarcinoma and normal colonic mucosa specimens were collected from each case. Specimens were flash frozen in liquid nitrogen. Adenocarcinoma was confirmed by histologic evaluation of H&E permanent sections. Hyperspectral image data of the fluorescence excitation of adenocarcinoma and surrounding normal tissue were acquired using a custom microscope configuration previously developed in our lab. Results demonstrated consistent spectral differences between normal and cancerous tissues over the fluorescence excitation spectral range of 390-450 nm. We conclude that fluorescence excitation-scanning hyperspectral imaging may offer an alternative approach for differentiating adenocarcinoma and surrounding normal mucosa of the colon. Future work will focus on expanding the number of specimen pairs analyzed and will utilize fresh tissues where possible, as flash freezing and reconstituting tissues may have altered the autofluorescence properties.

  8. Numerical and experimental study of a compressive-mode energy harvester under random excitations

    NASA Astrophysics Data System (ADS)

    Li, H. T.; Yang, Z.; Zu, J.; Qin, W. Y.

    2017-03-01

    Piezoelectric energy harvester working in compressive mode has shown outstanding performance under harmonic excitation. However, it is still not clear if the compressive-mode energy harvester can sustain its superiority under random excitations. This paper presents a theoretical and experimental study on a nonlinear compressive-mode piezoelectric energy harvester under random excitations. First, a comprehensive distributed parameter electro-elastic model is developed using the extended Hamilton’s principle and the Euler–Bernoulli beam theory. The embedded force amplification effect of the flexural motion is analytically predicted. Then, the model is numerically solved under random excitations. Strong nonlinear responses was observed in both mechanical and electrical responses. Furthermore, a prototype was fabricated and tested. The experimental data show a good agreement with the model estimations under different level excitations and resistances. The results under random excitation demonstrate that the compressive-mode energy harvester significantly outperforms the state-of-the-art systems in terms of output voltage and normalized power density. If the optimal resistance is chosen in the harvesting circuit, the root mean square power of the prototype will reach three times higher than that of the counterparts.

  9. Energy, fine structure, hyperfine structure, and radiative transition rates of the high-lying multi-excited states for B-like neon

    NASA Astrophysics Data System (ADS)

    Zhang, Chun Mei; Chen, Chao; Sun, Yan; Gou, Bing Cong; Shao, Bin

    2015-04-01

    The Rayleigh-Ritz variational method with multiconfiguration interaction wave functions is used to obtain the energies of high-lying multi-excited quartet states 1 s 22 s2 pnl and 1 s 22 p 2 nl 4Pe,o ( n ≥ 2) in B-like neon, including the mass polarization and relativistic corrections. The fine structure and hyperfine structure of the excited quartet states for this system are investigated. Configuration structures of the high-lying multi-excited series are further identified by relativistic corrections and fine structure splittings. The transition rates and wavelengths are also calculated. Calculated wavelengths include the quantum electrodynamic effects. The results are compared with other theoretical and experimental data in the literature.

  10. Excitation spectra of photoluminescence and its kinetics in structures with self-assembled Ge:Si nanoislands

    SciTech Connect

    Yablonskiy, A. N. Baidakova, N. A. Novikov, A. V.; Lobanov, D. N.; Shaleev, M. V.

    2015-11-15

    The spectral and time characteristics of photoluminescence associated with the radiative recombination of charge carriers in SiGe/Si(001) multilayer structures with self-assembled Ge:Si islands are investigated. The time dependences of the photoluminescence of Ge:Si islands in a wide range of delay times after the pump pulse are considered at various optical-excitation levels. The photoluminescence-excitation spectra from Ge(Si) islands in the SiGe/Si(001) structures are investigated in the region of band-to-band and subband optical pumping corresponding to various time components in the photoluminescence-relaxation kinetics. A significant difference in the shape of the excitation spectra is revealed for fast (0–100 μs) and slow (100 μs–50 ms) components of the photoluminescence signal from the islands. The significant dependence of the photoluminescence-excitation spectra of Ge(Si)/Si(001) islands on the optical-pump power is shown to be associated with the prolonged diffusion of nonequilibrium charge carriers from bulk-silicon layers to Ge:Si islands at high excitation levels.

  11. Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution

    SciTech Connect

    Shaw, G B; Grant, C D; Shirota, H; Castner Jr., E W; Meyer, G J; Chen, L X

    2006-10-05

    Ultrafast excited state structural dynamics of [Cu{sup I}(dmp){sub 2}]{sup +} (dmp = 2,9-dimethyl-1,10-phenanthroline) have been studied to identify structural origins of transient spectroscopic changes during the photoinduced metal-to-ligand-charge-transfer (MLCT) transition that induces an electronic configuration change from Cu(I) (3d{sup 10}) to Cu(II) (3d{sup 9}). This study has important connections with the flattening of the Franck-Condon state tetrahedral geometry and the ligation of Cu(II)* with the solvent observed in the thermally equilibrated MLCT state by our previous laser-initiated time-resolved x-ray absorption spectroscopy (LITR-XAS) results. To better understand the structural photodynamics of Cu(I) complexes, we have studied both [Cu{sup I}(dmp){sub 2}]{sup +} and [Cu{sup I}(dpp){sub 2}]{sup +} (dpp = 2,9-diphenyl-1,10-phenanthroline) in solvents with different dielectric constants, viscosities and thermal diffusivities by transient absorption spectroscopy. The observed spectral dynamics suggest that a solvent-independent inner-sphere relaxation process is occurring despite the large amplitude motions due to the flattening of the tetrahedral coordinated geometry. The singlet fluorescence dynamics of photoexcited [Cu{sup I}(dmp){sub 2}]{sup +} were measured in the coordinating solvent acetonitrile, using the fluorescence upconversion method at different emission wavelengths. At the bluest emission wavelengths, a prompt fluorescence lifetime of 66 fs is attributed to the excited state deactivation processes due to the internal conversion and intersystem crossing at the Franck-Condon state geometry. The differentiation between the prompt fluorescence lifetime with the tetrahedral Franck-Condon geometry and that with the flattened tetrahedral geometry uncovers an unexpected ultrafast flattening process in the MLCT state of [Cu{sup I}(dmp){sub 2}]{sup +}. These results provide guidance for future x-ray structural studies on ultrafast time scale, as

  12. The flow of excitation energy in LHCII monomers: implications for the structural model of the major plant antenna.

    PubMed Central

    Gradinaru, C C; Ozdemir, S; Gülen, D; van Stokkum, I H; van Grondelle, R; van Amerongen, H

    1998-01-01

    Spectral and kinetic information on energy transfer within the light-harvesting complex II (LHCII) monomer was obtained from this subpicosecond transient absorption study, by using selective excitation (663, 669, 672, 678, and 682 nm) of various Chl a absorption bands and detecting the induced changes over the entire Qy region (650-700 nm). It is shown that transfer from the pigment(s) absorbing around 663 nm to the low energy ones occurs in 5 +/- 1 ps, whereas the 670-nm excitation is delivered to the same "destination" in two phases (0.30 +/- 0.05 ps, and 12 +/- 2 ps), and a fast equilibration (lifetime 0.45 +/- 0.05 ps) takes place within the main absorption band (675-680 nm). From comparison with results from similar time-resolved measurements on trimeric samples, it can be concluded that the intramonomeric energy transfer completely determines the spectral equilibration observed in native LHCII complexes. To correlate the measured lifetimes and their associated spectra with the pigment organization within the available structural model of LHCII (. Nature. 367:614-621), extensive but straightforward theoretical modeling was used. Thus it is demonstrated that the pigment assignment (Chl a or Chl b) given by Kuhlbrandt and co-workers cannot simultaneously describe the dichroic spectra and the transient absorption results for the rather homologous LHCII and CP29 proteins. A more recent assignment for CP29, in which a Chl b molecule ("Chl b5") is identified as a Chl a (Dr. R. Bassi, personal communication), leads to a much better description of both CP29 and LHCII. Furthermore, the orientations of the transition dipole moments, which have not been obtained in the crystal structure, are now assigned for most of the Chl's. PMID:9826626

  13. Heat release and flame structure measurements of self-excited acoustically-driven premixed methane flames

    SciTech Connect

    Kopp-Vaughan, Kristin M.; Tuttle, Steven G.; Renfro, Michael W.; King, Galen B.

    2009-10-15

    An open-open organ pipe burner (Rijke tube) with a bluff-body ring was used to create a self-excited, acoustically-driven, premixed methane-air conical flame, with equivalence ratios ranging from 0.85 to 1.05. The feed tube velocities corresponded to Re = 1780-4450. Coupled oscillations in pressure, velocity, and heat release from the flame are naturally encouraged at resonant frequencies in the Rijke tube combustor. This coupling creates sustainable self-excited oscillations in flame front area and shape. The period of the oscillations occur at the resonant frequency of the combustion chamber when the flame is placed {proportional_to}1/4 of the distance from the bottom of the tube. In this investigation, the shape of these acoustically-driven flames is measured by employing both OH planar laser-induced fluorescence (PLIF) and chemiluminescence imaging and the images are correlated to simultaneously measured pressure in the combustor. Past research on acoustically perturbed flames has focused on qualitative flame area and heat release relationships under imposed velocity perturbations at imposed frequencies. This study reports quantitative empirical fits with respect to pressure or phase angle in a self-generated pressure oscillation. The OH-PLIF images were single temporal shots and the chemiluminescence images were phase averaged on chip, such that 15 exposures were used to create one image. Thus, both measurements were time resolved during the flame oscillation. Phase-resolved area and heat release variations throughout the pressure oscillation were computed. A relation between flame area and the phase angle before the pressure maximum was derived for all flames in order to quantitatively show that the Rayleigh criterion was satisfied in the combustor. Qualitative trends in oscillating flame area were found with respect to feed tube flow rates. A logarithmic relation was found between the RMS pressure and both the normalized average area and heat release rate

  14. The excitation of long period seismic waves by a source spanning a structural discontinuity

    NASA Astrophysics Data System (ADS)

    Woodhouse, J. H.

    Simple theoretical results are obtained for the excitation of seismic waves by an indigenous seismic source in the case that the source volume is intersected by a structural discontinuity. In the long wavelength approximation the seismic radiation is identical to that of a point source placed on one side of the discontinuity or of a different point source placed on the other side. The moment tensors of these two equivalent sources are related by a specific linear transformation and may differ appreciably both in magnitude and geometry. Either of these sources could be obtained by linear inversion of seismic data but the physical interpretation is more complicated than in the usual case. A source which involved no volume change would, for example, yield an isotropic component if, during inversion, it were assumed to lie on the wrong side of the discontinuity. The problem of determining the true moment tensor of the source is indeterminate unless further assumptions are made about the stress glut distribution; one way to resolve this indeterminancy is to assume proportionality between the integrated stress glut on each side of the discontinuity.

  15. High resolution study of the rotational structure of doubly excited vibrational states of 32S16O18O: The first analysis of the 2ν1, ν1 +ν3 , and 2ν3 bands

    NASA Astrophysics Data System (ADS)

    Ulenikov, O. N.; Bekhtereva, E. S.; Gromova, O. V.; Zamotaeva, V. A.; Kuznetsov, S. I.; Sydow, C.; Bauerecker, S.

    2017-03-01

    The high resolution infrared spectra of the 32S16O18O molecule were recorded with a Bruker IFS 120 HR Fourier transform interferometer for the first time in the region of 1800-2800 cm-1 where the bands 2ν1, ν1 +ν3 , and 2ν3 are located. About 3970, 2960 and 3450 transitions were assigned in the experimental spectra with the maximum values of quantum numbers Jmax. /Kamax. equal to 59/20, 68/25, and 43/18 to the bands 2ν1, ν1 +ν3 , and 2ν3, respectively. The subsequent weighted fit of experimentally assigned transitions was made with the Hamiltonian model which takes into account the resonance interactions between the studied vibrational states. As the result, a set of 39 fitted parameters was obtained which reproduces the initial 3213 ro-vibrational energy values obtained from the assigned transitions with the drms = 2.4 ×10-4cm-1 .

  16. Thermographic inspection of a wind turbine rotor blade segment utilizing natural conditions as excitation source, Part I: Solar excitation for detecting deep structures in GFRP

    NASA Astrophysics Data System (ADS)

    Worzewski, Tamara; Krankenhagen, Rainer; Doroshtnasir, Manoucher; Röllig, Mathias; Maierhofer, Christiane; Steinfurth, Henrik

    2016-05-01

    This study evaluates whether subsurface features in rotor blades, mainly made of Glass Fibre Reinforced Plastics (GFRP), can generally be detected with "solar thermography". First, the suitability of the sun is tested for acting as a heat source for applying active thermography on a 30 mm thick GFRP test specimen. Second, a defective rotor blade segment is inspected outdoors under ideal natural conditions using the sun as excitation source. Additionally, numerical FEM-simulations are performed and the comparability between experiment and simulation is evaluated for outdoor measurements.

  17. Development of a microwave probe for the optical study of microwave-excited spin physics

    NASA Astrophysics Data System (ADS)

    Ou, Yu-Sheng; Chiu, Yi-Hsin; Adur, Rohan; Odenthal, Patrick; Kawakami, Roland; Hammel, P. Chris; Johnston-Halperin, Ezekiel

    2014-03-01

    We have developed an experimental probe that allows simultaneous broadband microwave excitation and optical excitation/detection at variable temperature and magnetic field. Specifically, we have designed a unique sample probe with a microwave stripline based sample mount that allows for direct optical access to the sample under study within a magneto- optical cryostat. This powerful combination enables optical studies of spintronic systems under microwave excitation using both CW (e.g. photo- and electro-luminescence) and time resolved (e.g. time resolved absorption/transmission and time resolved Kerr rotation, TRKR) techniques. To benchmark the capabilities of this probe we present data demonstrating simultaneous ferromagnetic resonance (FMR) and TRKR in a Fe/MgO/GaAs heterostructure. Such studies have potential applications in the study of FMR driven spin pumping and interaction of free carrier spins with native and engineered defects. MRSEC (DMR-0820414).

  18. A TDDFT study on the excited-state intramolecular proton transfer (ESIPT): excited-state equilibrium induced by electron density swing.

    PubMed

    Zhang, Mingzhen; Yang, Dapeng; Ren, Baiping; Wang, Dandan

    2013-07-01

    One important issue of current interest is the excited-state equilibrium for some ESITP dyes. However, so far, the information about the driving forces for excited-state equilibrium is very limited. In this work, the time-dependent density functional theory (TDDFT) method was employed to investigate the nature of the excited-state intramolecular proton transfer (ESIPT). The geometric structures, vibrational frequencies, frontier molecular orbitals (MOs) and the potential-energy curves for 1-hydroxy-11H-benzo[b]fluoren-11-one (HHBF) in the ground and the first singlet excited state were calculated. Analysis of the results shows that the intramolecular hydrogen bond of HHBF is strengthened from E to E*. Moreover, it is found that electron density swing between the proton acceptor and donor provides the driving forces for the forward and backward ESIPT, enabling the excited-state equilibrium to be established. Furthermore, we proposed that the photoexcitation and the interchange of position for electron-donating and electron-withdrawing groups are the main reasons for the electron density swing. The potential-energy curves suggest that the forward ESIPT and backward ESIPT may happen on the similar timescale, which is faster than the fluorescence decay of both E* and K* forms.

  19. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: key role of the excited-state hydrogen-bond strengthening.

    PubMed

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-15

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  20. Feasibility study: Monodisperse polymer particles containing laser-excitable dyes

    NASA Technical Reports Server (NTRS)

    Venkateswarlu, Putcha; He, K. X.; Sharma, A.

    1993-01-01

    The optical properties associated with small particles, which include aerosols, hydrosols and solid microspheres have an impact on several areas of science and engineering. Since the advent of high-speed computers and lasers, the interaction of light with matter in the form of small particles with a discontinuous optical boundary relative to the surroundings has been much better understood. Various nonlinear optical effects have been observed involving interaction of a laser beam with both solid microspheres and liquid microdroplets. These include observation of second and third harmonic generation, four wave mixing, optical visibility, two photon absorption, observation of stimulated emission and lasing, and Stimulated Raman Scattering. Many of these effects are observed with laser intensities which are orders of magnitude less than that required by threshold condition for interactions in macroscopic bulk medium. The primary reason for this is twofold. The front surface of the microsphere acts as a thick lens to enhance the internal intensity of the input laser radiation, and the spherical shape of the droplet acts as an optical cavity to provide feedback at specific wavelengths corresponding to the whispering gallery modes or the morphology dependent resonances (MDR's). The most interesting and significant recent finding in this field is undoubtedly the existence of resonance peaks in linear and nonlinear optical spectra. Such resonance peaks are only dependent on the particle morphology, which means the size, shape and refractive index of the particle. Because of the simultaneous presence of these resonances, they have been referred to by many names, including structural resonances, whispering modes or whispering gallery modes, creeping waves, circumferential waves, surfaces modes, and virtual modes. All of these names refer to the same phenomena, i.e. morphology dependent resonances (MDR's) which has already been described and predicted precisely by

  1. Close-coupling calculations of fine-structure excitation of Ne II due to H and electron collisions

    NASA Astrophysics Data System (ADS)

    Stancil, Phillip C.; Cumbee, Renata; Wang, Qianxia; Loch, Stuart; Pindzola, Michael; Schultz, David R.; Buenker, Robert; McLaughlin, Brendan; Ballance, Connor

    2016-06-01

    Fine-structure transitions within the ground term of ions and neutral atoms dominate the cooling in a variety of molecular regions and also provide important density and temperature diagnostics. While fine-structure rates due to electron collisions have been studied for many systems, data are generally sparse for elements larger than oxygen, at low temperatures, and for collisions due to heavy particles. We provide rate coefficients for H collisions for the first time. The calculations were performed using the quantum molecular-orbital close-coupling approach and the elastic approximation. The heavy-particle collisions use new potential energies for the lowest-lying NeH+ states computed with the MRDCI method. The focus of the electron-impact calculations is to provide fine-structure excitation rate coefficients down to 10 K. We compare with previous calculations at higher temperatures (Griffin et al. 2001), and use a range of calculations to provide an estimate of the uncertainty on our recommended rate coefficients. A brief discussion of astrophysical applications is also provided.Griffin, D.C., et al., 2001, J. Phys. B, 34, 4401This work partially supported by NASA grant No. NNX15AE47G.

  2. Beyond Time-Dependent Density Functional Theory Using Only Single Excitations: Methods for Computational Studies of Excited States in Complex Systems.

    PubMed

    Herbert, John M; Zhang, Xing; Morrison, Adrian F; Liu, Jie

    2016-05-17

    Single-excitation methods, namely, configuration interaction singles and time-dependent density functional theory (TDDFT), along with semiempirical versions thereof, represent the most computationally affordable electronic structure methods for describing electronically excited states, scaling as [Formula: see text] absent further approximations. This relatively low cost, combined with a treatment of electron correlation, has made TDDFT the most widely used excited-state quantum chemistry method over the past 20+ years. Nevertheless, certain inherent problems (beyond just the accuracy of this or that exchange-correlation functional) limit the utility of traditional TDDFT. For one, it affords potential energy surfaces whose topology is incorrect in the vicinity of any conical intersection (CI) that involves the ground state. Since CIs are the conduits for transitions between electronic states, the TDDFT description of photochemistry (internal conversion and intersystem crossing) is therefore suspect. Second, the [Formula: see text] cost can become prohibitive in large systems, especially those that involve multiple electronically coupled chromophores, for example, the antennae structures of light-harvesting complexes or the conjugated polymers used in organic photovoltaics. In such cases, the smallest realistic mimics might already be quite large from the standpoint of ab initio quantum chemistry. This Account describes several new computational methods that address these problems. Topology around a CI can be rigorously corrected using a "spin-flip" version of TDDFT, which involves an α → β spin-flipping transition in addition to occupied → virtual excitation of one electron. Within this formalism, singlet states are generated via excitation from a high-spin triplet reference state, doublets from a quartet, etc. This provides a more balanced treatment of electron correlation between ground and excited states. Spin contamination is problematic away from the

  3. Excitation spectra of Ag3-DNA bases complexes: A benchmark study

    NASA Astrophysics Data System (ADS)

    Maksimov, D. A.; Pomogaev, V. A.; Kononov, A. I.

    2017-04-01

    Assessment of different ab initio and TDDFT methods was studied for calculation of the excitation energies of the complexes of pyrimidine bases with positively charged Ag3+ clusters. Performance of CIS, CIS(D), CC2, ADC(2), MP2, and TDDFT techniques with the use of different hybrid-GGA and meta-hybrid-GGA functionals and basis sets is studied. We found that M06-2X functional shows good accuracy in comparison with the ADC(2) ab initio method and that the geometry optimization approach can strongly affect the excitation spectra of the complexes. Our results may have important implications for further studies of ligand-stabilized silver nanoclusters.

  4. Studies of Phonons and Electronic Excitations in Semiconductor Heterostructures

    DTIC Science & Technology

    1992-03-31

    studies are primarily experimental fo- cusing on the technique of Raman scattering. 92-11243 9 2 4 2 7 /1 3 9 f 1118I II 14. SUBJECT TERMS 15.N4BROPAE...drop across the quantum well in units of e/2;k and Q is the external f charge in units of XA/4neL; L and A V a- are the width and the area of the MAX...the domains with F = E,2/ed and F = E13 /ed coexist leading to voltage oscillations associated with the motion of the domain boundary. There is also a

  5. Excited-state properties and environmental effects for protonated schiff bases: a theoretical study.

    PubMed

    Aquino, Adélia J A; Barbatti, Mario; Lischka, Hans

    2006-10-13

    Complete active space self-consistent field (CASSCF), multireference configuration interaction (MRCI), density functional theory (DFT), time dependent DFT (TDDFT) and the singles and doubles coupled-cluster (CC2) methodologies have been used to study the ground state and excited states of protonated and neutral Schiff bases (PSB and SB) as models for the retinal chromophore. Systems with two to four conjugated double bonds are investigated. Geometry relaxation effects are studied in the excited pipi* state using the aforementioned methods. Taking the MRCI results as reference we find that CASSCF results are quite reliable even though overshooting of geometry changes is observed. TDDFT does not reproduce bond alternation well in the pipi* state. CC2 takes an intermediate position. Environmental effects due to solvent or protein surroundings have been studied in the excited states of the PSBs and SBs using a water molecule and solvated formate as model cases. Particular emphasis is given to the proton transfer process from the PSB to its solvent partner in the excited state. It is found that its feasibility is significantly enhanced in the excited state as compared to the ground state, which means that a proton transfer could be initiated already at an early step in the photodynamics of PSBs.

  6. Electrophorus electricus as a model system for the study of membrane excitability.

    PubMed

    Gotter, A L; Kaetzel, M A; Dedman, J R

    1998-01-01

    The stunning sensations produced by electric fish, particularly the electric eel, Electrophorus electricus, have fascinated scientists for centuries. Within the last 50 years, however, electric cells of Electrophorus have provided a unique model system that is both specialized and appropriate for the study of excitable cell membrane electrophysiology and biochemistry. Electric tissue generates whole animal electrical discharges by means of membrane potentials that are remarkably similar to those of mammalian neurons, myocytes and secretory cells. Electrocytes express ion channels, ATPases and signal transduction proteins common to these other excitable cells. Action potentials of electrocytes represent the specialized end function of electric tissue whereas other excitable cells use membrane potential changes to trigger sophisticated cellular processes, such as myofilament cross-bridging for contraction, or exocytosis for secretion. Because electric tissue lacks these functions and the proteins associated with them, it provides a highly specialized membrane model system. This review examines the basic mechanisms involved in the generation of the electrical discharge of the electric eel and the membrane proteins involved. The valuable contributions that electric tissue continues to make toward the understanding of excitable cell physiology and biochemistry are summarized, particularly those studies using electrocytes as a model system for the study of the regulation of membrane excitability by second messengers and signal transduction pathways.

  7. On the influence of frequency-dependent elastic properties in vibro-acoustic modelling of porous materials under structural excitation

    NASA Astrophysics Data System (ADS)

    Van der Kelen, C.; Göransson, P.; Pluymers, B.; Desmet, W.

    2014-12-01

    The aspects related to modelling the frequency dependence of the elastic properties of air-saturated porous materials have been largely neglected in the past for several reasons. For acoustic excitation of porous materials, the material behaviour can be quite well represented by models where the properties of the solid frame have little influence. Only recently has the importance of the dynamic moduli of the frame come into focus. This is related to a growing interest in the material behaviour due to structural excitation. Two aspects stand out in connection with the elastic-dynamic behaviour. The first is related to methods for the characterisation of the dynamic moduli of porous materials. The second is a perceived lack of numerical methods able to model the complex material behaviour under structural excitation, in particular at higher frequencies. In the current paper, experimental data from a panel under structural excitation, coated with a porous material, are presented. In an attempt to correlate the experimental data to numerical predictions, it is found that the measured quasi-static material parameters do not suffice for an accurate prediction of the measured results. The elastic material parameters are then estimated by correlating the numerical prediction to the experimental data, following the physical behaviour predicted by the augmented Hooke's law. The change in material behaviour due to the frequency-dependent properties is illustrated in terms of the propagation of the slow wave and the shear wave in the porous material.

  8. Calculations of Excitation Functions of Some Structural Fusion Materials for ( n, t) Reactions up to 50 MeV Energy

    NASA Astrophysics Data System (ADS)

    Tel, E.; Durgu, C.; Aktı, N. N.; Okuducu, Ş.

    2010-06-01

    Fusion serves an inexhaustible energy for humankind. Although there have been significant research and development studies on the inertial and magnetic fusion reactor technology, there is still a long way to go to penetrate commercial fusion reactors to the energy market. Tritium self-sufficiency must be maintained for a commercial power plant. For self-sustaining (D-T) fusion driver tritium breeding ratio should be greater than 1.05. So, the working out the systematics of ( n, t) reaction cross sections is of great importance for the definition of the excitation function character for the given reaction taking place on various nuclei at different energies. In this study, ( n, t) reactions for some structural fusion materials such as 27Al, 51V, 52Cr, 55Mn, and 56Fe have been investigated. The new calculations on the excitation functions of 27Al( n, t)25Mg, 51V( n, t)49Ti, 52Cr( n, t)50V, 55Mn( n, t)53Cr and 56Fe( n, t)54Mn reactions have been carried out up to 50 MeV incident neutron energy. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. The pre-equilibrium calculations involve the new evaluated the geometry dependent hybrid model, hybrid model and the cascade exciton model. Equilibrium effects are calculated according to the Weisskopf-Ewing model. Also in the present work, we have calculated ( n, t) reaction cross-sections by using new evaluated semi-empirical formulas developed by Tel et al. at 14-15 MeV energy. The calculated results are discussed and compared with the experimental data taken from the literature.

  9. Study of radially excited Ds(21 S 0) and Ds(3P)

    NASA Astrophysics Data System (ADS)

    Tian, Yu; Zhao, Ze; Zhang, Ai-Lin

    2017-08-01

    The unobserved JP = 0- radial excitation Ds(21 S 0) is anticipated to have mass 2650 MeV (denoted as Ds(2650)). Study of hadronic production is an important way to identify highly excited states. We study hadronic production of Ds(2650) from higher excited resonances in a 3 P 0 model. Relevant hadronic partial decay widths are found to be very small, which implies it is difficult to observe Ds(2650) in hadronic decays of higher excited resonances. Hadronic decay widths of radially excited Ds(3P) have also been estimated. The total decay widths of four Ds(3P) are large, but the branching ratios in the Ds(2650)η channel are very small, which implies that it seems impossible to observe Ds(2650) in hadronic decays of Ds(3P). The dominant decay channels of the four Ds(3P) have been pointed out, and D1(2420), D1(2430), , D(2550), D(2600), (11D2)D(2750) and are possible to observe in hadronic production from Ds(3P). Supported by National Natural Science Foundation of China (11475111)

  10. Excited baryons

    SciTech Connect

    Mukhopadhyay, N.C.

    1986-01-01

    The status of the theory of the low-energy approach to hadron structure is reviewed briefly by surveying a few relevant models. A few examples of tests needed to sort out the predictions of different models pertaining to the quark-gluon structure of hadrons are discussed, and given the resulting physics objectives, a few experimental options for excited baryon research at CFBAF are suggested. (LEW)

  11. Comparison endpoint study of process plasma and secondary electron beam exciter optical emission spectroscopy

    SciTech Connect

    Stephan Thamban, P. L.; Yun, Stuart; Padron-Wells, Gabriel; Hosch, Jimmy W.; Goeckner, Matthew J.

    2012-11-15

    Traditionally process plasmas are often studied and monitored by optical emission spectroscopy. Here, the authors compare experimental measurements from a secondary electron beam excitation and direct process plasma excitation to discuss and illustrate its distinctiveness in the study of process plasmas. They present results that show excitations of etch process effluents in a SF{sub 6} discharge and endpoint detection capabilities in dark plasma process conditions. In SF{sub 6} discharges, a band around 300 nm, not visible in process emission, is observed and it can serve as a good indicator of etch product emission during polysilicon etches. Based on prior work reported in literature the authors believe this band is due to SiF{sub 4} gas phase species.

  12. Study of the vortex-induced pressure excitation source in a Francis turbine draft tube by particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Favrel, A.; Müller, A.; Landry, C.; Yamamoto, K.; Avellan, F.

    2015-12-01

    Francis turbines operating at part-load experience the development of a precessing cavitation vortex rope at the runner outlet, which acts as an excitation source for the hydraulic system. In case of resonance, the resulting pressure pulsations seriously compromise the stability of the machine and of the electrical grid to which it is connected. As such off-design conditions are increasingly required for the integration of unsteady renewable energy sources into the existing power system, an accurate assessment of the hydropower plant stability is crucial. However, the physical mechanisms driving this excitation source remain largely unclear. It is for instance essential to establish the link between the draft tube flow characteristics and the intensity of the excitation source. In this study, a two-component particle image velocimetry system is used to investigate the flow field at the runner outlet of a reduced-scale physical model of a Francis turbine. The discharge value is varied from 55 to 81 % of the value at the best efficiency point. A particular set-up is designed to guarantee a proper optical access across the complex geometry of the draft tube elbow. Based on phase-averaged velocity fields, the evolution of the vortex parameters with the discharge, such as the trajectory and the circulation, is determined for the first time. It is shown that the rise in the excitation source intensity is induced by an enlargement of the vortex trajectory and a simultaneous increase in the precession frequency, as well as the vortex circulation. Below a certain value of discharge, the structure of the vortex abruptly changes and loses its coherence, leading to a drastic reduction in the intensity of the induced excitation source.

  13. Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy

    NASA Astrophysics Data System (ADS)

    Wilkinson, Iain; Boguslavskiy, Andrey E.; Mikosch, Jochen; Bertrand, Julien B.; Wörner, Hans Jakob; Villeneuve, David M.; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert

    2014-05-01

    The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed ({tildeB})1B1/(Ã)1A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright ({tildeB})1B1 diabatic state is presented. Signatures of the oscillatory motion on the ({tildeB})1B1/(Ã)1A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the ({tildec})3B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented.

  14. X-ray excited optical luminescence studies or ZnS and ZnO nanostructures.

    SciTech Connect

    Rosenberg, R. A.; Shenoy, G. K.; Heigl, F.; Lee, S.-T.; Tien, L. -C.; Norton, D.; Pearton, S.; Kim, P.-S. G.; Zhou, X. T.; Sham, T. K.; Experimental Facilities Division; Canadian Synchrotron Radiation Facility; City Univ. of Hong Kong; Univ. of Florida; Univ. of Western Ontario

    2006-01-01

    Due to their potential as optoelectronic devices, luminescing nanostructures have been among the most studied in the recent past. Room-temperature UV lasing has been demonstrated in ZnO nanowires. For highly asymmetric wurtzite structures, the orientation of the emitting luminescent dipole with respect to the excited state polarization can play a role in the luminescence yield. ZnS is an important, wide bandgap (E{sub g} = 3.54 eV for the thermodynamically stable zinc blende form at room temperature) II-VI semiconductor. It has been developed for a number of applications including UV light-emitting diodes, injection lasers and phosphors. In this presentation we will discuss results of a study on ZnS nanostructurees using synchrotron-radiation-based, x-ray-excited optical luminescence (XEOL). Results on ZnO will be presented elsewhere. The experimental approach has been described previously. All measurements were performed on beamline 4-ID-C at the Advanced Photon Source. Samples were prepared by a high-temperature growth technique described previously. Briefly, ZnS powder was placed in the center of a horizontal alumina tube upstream of a Si wafer, which was covered with 2 nm thiol-capped gold nanoparticles (used to catalyze the growth). The tube was heated to 1000 C while an Ar/H{sub 2} gas mixture flowed through the tube. This process resulted in the formation of nanoribbons of lengths in the range 10-100 {micro}m and widths less than 100 nm. The samples were characterized by high-resolution TEM images, which showed large areas of hexagonal wurtzite structure interspersed by nanosized regions with cubic sphalerite structure. Using XEOL, we have determined the local phase of the luminescing sites in ZnS nanowires. The inset of the accompanying figure shows the temperature-dependent optical spectrum obtained when exciting the nanowires with 1100 eV x-rays. There are three main peaks: a band-edge, exiton state at 338 nm, a defect-related emission at 430 nm, and a Au

  15. Significantly increased surface plasmon polariton mode excitation using a multilayer insulation structure in a metal-insulator-metal plasmonic waveguide.

    PubMed

    Yang, Hongyan; Li, Jianqing; Xiao, Gongli

    2014-06-10

    In this paper, we propose a novel multilayer insulation structure in a metal-insulator-metal (MIM) plasmonic waveguide to explore the possibility of increasing surface plasmon polariton (SPP) mode excitation. Numerical investigations show that the effective refractive index of the multilayer insulation structure affects symmetric SPP mode excitation. The significant enhancement of electric field intensity in horizontal and vertical profiles with a dipole in SiO2 compared with in Al2O3 is observed in the proposed MIM plasmonic waveguides due to a combination of the improved optical density and dipole radiation intensities under a low refractive index. The Au/SiO2/Al2O3/SiO2/Au geometry shows the best enhancement performances, which can serve as an excellent guideline for designing and optimizing a high-performance SPP source using a multilayer insulation structure.

  16. Spontaneously Fluctuating Motor Cortex Excitability in Alternating Hemiplegia of Childhood: A Transcranial Magnetic Stimulation Study

    PubMed Central

    Stern, William M.; Desikan, Mahalekshmi; Hoad, Damon; Jaffer, Fatima; Strigaro, Gionata; Sander, Josemir W.; Rothwell, John C.; Sisodiya, Sanjay M.

    2016-01-01

    Background Alternating hemiplegia of childhood is a very rare and serious neurodevelopmental syndrome; its genetic basis has recently been established. Its characteristic features include typically-unprovoked episodes of hemiplegia and other transient or more persistent neurological abnormalities. Methods We used transcranial magnetic stimulation to assess the effect of the condition on motor cortex neurophysiology both during and between attacks of hemiplegia. Nine people with alternating hemiplegia of childhood were recruited; eight were successfully tested using transcranial magnetic stimulation to study motor cortex excitability, using single and paired pulse paradigms. For comparison, data from ten people with epilepsy but not alternating hemiplegia, and ten healthy controls, were used. Results One person with alternating hemiplegia tested during the onset of a hemiplegic attack showed progressively diminishing motor cortex excitability until no response could be evoked; a second person tested during a prolonged bilateral hemiplegic attack showed unusually low excitability. Three people tested between attacks showed asymptomatic variation in cortical excitability, not seen in controls. Paired pulse paradigms, which probe intracortical inhibitory and excitatory circuits, gave results similar to controls. Conclusions We report symptomatic and asymptomatic fluctuations in motor cortex excitability in people with alternating hemiplegia of childhood, not seen in controls. We propose that such fluctuations underlie hemiplegic attacks, and speculate that the asymptomatic fluctuation we detected may be useful as a biomarker for disease activity. PMID:26999520

  17. Spontaneously Fluctuating Motor Cortex Excitability in Alternating Hemiplegia of Childhood: A Transcranial Magnetic Stimulation Study.

    PubMed

    Stern, William M; Desikan, Mahalekshmi; Hoad, Damon; Jaffer, Fatima; Strigaro, Gionata; Sander, Josemir W; Rothwell, John C; Sisodiya, Sanjay M

    2016-01-01

    Alternating hemiplegia of childhood is a very rare and serious neurodevelopmental syndrome; its genetic basis has recently been established. Its characteristic features include typically-unprovoked episodes of hemiplegia and other transient or more persistent neurological abnormalities. We used transcranial magnetic stimulation to assess the effect of the condition on motor cortex neurophysiology both during and between attacks of hemiplegia. Nine people with alternating hemiplegia of childhood were recruited; eight were successfully tested using transcranial magnetic stimulation to study motor cortex excitability, using single and paired pulse paradigms. For comparison, data from ten people with epilepsy but not alternating hemiplegia, and ten healthy controls, were used. One person with alternating hemiplegia tested during the onset of a hemiplegic attack showed progressively diminishing motor cortex excitability until no response could be evoked; a second person tested during a prolonged bilateral hemiplegic attack showed unusually low excitability. Three people tested between attacks showed asymptomatic variation in cortical excitability, not seen in controls. Paired pulse paradigms, which probe intracortical inhibitory and excitatory circuits, gave results similar to controls. We report symptomatic and asymptomatic fluctuations in motor cortex excitability in people with alternating hemiplegia of childhood, not seen in controls. We propose that such fluctuations underlie hemiplegic attacks, and speculate that the asymptomatic fluctuation we detected may be useful as a biomarker for disease activity.

  18. Ultrafast excited-state dynamics of tetraphenylethylene studied by semiclassical simulation

    SciTech Connect

    Zhao Guangjiu; Han Keli; Lei Yibo; Dou Yusheng

    2007-09-07

    Detailed simulation study is reported for the excited-state dynamics of photoisomerization of cis-tetraphenylethylene (TPE) following excitation by a femtosecond laser pulse. The technique for this investigation is semiclassical dynamics simulation, which is described briefly in the paper. Upon photoexcitation by a femtosecond laser pulse, the stretching motion of the ethylenic bond of TPE is initially excited, leading to a significant lengthening of ethylenic bond in 300 fs. Twisting motion about the ethylenic bond is activated by the energy released from the relaxation of the stretching mode. The 90 deg. twisting about the ethylenic bond from an approximately planar geometry to nearly a perpendicular conformation in the electronically excited state is completed in 600 fs. The torsional dynamics of phenyl rings which is temporally lagging behind occurs at about 5 ps. Finally, the twisted TPE reverts to the initial conformation along the twisting coordinate through nonadiabatic transitions. The simulation results provide a basis for understanding several spectroscopic observations at molecular levels, including ultrafast dynamic Stokes shift, multicomponent fluorescence, viscosity dependence of the fluorescence lifetime, and radiationless decay from electronically excited state to the ground state along the isomerization coordinate.

  19. Vertical Singlet Excitations on Adenine Dimer: A Time Dependent Density Functional Study

    NASA Astrophysics Data System (ADS)

    Crespo-Hernández, Carlos E.; Marai, Christopher N. J.

    2007-12-01

    The condense phase, excited state dynamics of the adenylyl(3'→5')adenine (ApA) dinucleotide has been previously studied using transient absorption spectroscopy with femtosecond time resolution (Crespo-Hernández et al. Chem. Rev. 104, 1977-2019 (2004)). An ultrafast and a long-lived component were observed with time constants of <1 ps and 60±16 ps, respectively. Comparison of the time constants measured for the dinucleotide with that for the adenine nucleotide suggested that the fast component observed in ApA could be assigned to monomer dynamics. The long-lived component observed in ApA was assigned to an excimer state that originates from a fraction of base stacked conformations present at the time of excitation. In this contribution, supermolecule calculations using the time dependent implementation of density functional theory is used to provide more insights on the origin of the initial Franck-Condon excitations. Monomer-like, localized excitations are observed for conformations having negligible base stacking interactions, whereas delocalized excitations are predicted for conformations with significant vertical base-base overlap.

  20. Comparative study of excitation patterns in the masseter muscle before and after orthognathic surgery.

    PubMed

    Eckardt, L; Harzer, W; Schneevoigt, R

    1997-12-01

    This study was designed to inquire into changes occurring in the electromyographic activity throughout the masseter muscle after orthognathic surgical treatment of various bite anomalies. A total of 32 adult patients showing distinct class II (n = 15) or class III malocclusions (n = 17) were entered into the investigation. All patients had monopolar surface electromyograms of the masseter muscle taken prior to presurgical orthodontic treatment and after removal of their orthodontic appliances after surgery. Twenty eugnathic adult patients served as controls. Unlike bipolar lead readings, simultaneous sampling from 16 electrodes permits the registration of the overall excitation pattern in the entire muscle. Recordings were taken during clenching, chewing and protrusion of the lower jaw against a defined force. Comparison with preoperative EMGs proved postsurgical distribution of excitation in class 11 patients to approximate the excitation pattern of eugnathic patients. By contrast, correction in class III malocclusions produced a shift in excitation maxima in the sense of a cranial advance. Harmonization, as evident in class II patients, did not occur. The postoperative discords in masseter excitation patterns, as observed after correction of class III anomalies, are indicative of the risk of relapse and the prolonged phase of retention associated with these conditions.

  1. The red edge excitation shift phenomenon can be used to unmask protein structural ensembles: implications for NEMO-ubiquitin interactions.

    PubMed

    Catici, Dragana A M; Amos, Hope E; Yang, Yi; van den Elsen, Jean M H; Pudney, Christopher R

    2016-06-01

    To understand complex molecular interactions, it is necessary to account for molecular flexibility and the available equilibrium of conformational states. Only a small number of experimental approaches can access such information. Potentially steady-state red edge excitation shift (REES) spectroscopy can act as a qualitative metric of changes to the protein free energy landscape (FEL) and the equilibrium of conformational states. First, we validate this hypothesis using a single Trp-containing protein, NF-κB essential modulator (NEMO). We provide detailed evidence from chemical denaturation studies, macromolecular crowding studies, and the first report of the pressure dependence of the REES effect. Combination of these data demonstrate that the REES effect can report on the 'ruggedness' of the FEL and we present a phenomenological model, based on realistic physical interpretations, for fitting steady-state REES data to allow quantification of this aspect of the REES effect. We test the conceptual framework we have developed by correlating findings from NEMO ligand-binding studies with the REES data in a range of NEMO-ligand binary complexes. Our findings shed light on the nature of the interaction between NEMO and poly-ubiquitin, suggesting that NEMO is differentially regulated by poly-ubiquitin chain length and that this regulation occurs via a modulation of the available equilibrium of conformational states, rather than gross structural change. This study therefore demonstrates the potential of REES as a powerful tool for tackling contemporary issues in structural biology and biophysics and elucidates novel information on the structure-function relationship of NEMO and key interaction partners. © 2016 Federation of European Biochemical Societies.

  2. Early time excited-state structural evolution of pyranine in methanol revealed by femtosecond stimulated Raman spectroscopy.

    PubMed

    Wang, Yanli; Liu, Weimin; Tang, Longteng; Oscar, Breland; Han, Fangyuan; Fang, Chong

    2013-07-25

    To understand chemical reactivity of molecules in condensed phase in real time, a structural dynamics technique capable of monitoring molecular conformational motions on their intrinsic time scales, typically on femtoseconds to picoseconds, is needed. We have studied a strong photoacid pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, HPTS, pK(a)* ≈ 0) in pure methanol and observed that excited-state proton transfer (ESPT) is absent, in sharp contrast with our previous work on HPTS in aqueous solutions wherein ESPT prevails following photoexcitation. Two transient vibrational marker bands at ~1477 (1454) and 1532 (1528) cm(-1) appear in CH3OH (CD3OD), respectively, rising within the instrument response time of ~140 fs and decaying with 390-470 (490-1400) fs and ~200 ps time constants in CH3OH (CD3OD). We attribute the mode onset to small-scale coherent proton motion along the pre-existing H-bonding chain between HPTS and methanol, and the two decay stages to the low-frequency skeletal motion-modulated Franck-Condon relaxation within ~1 ps and subsequent rotational diffusion of H-bonding partners in solution before fluorescence. The early time kinetic isotope effect (KIE) of ~3 upon methanol deuteration argues active proton motions particularly within the first few picoseconds when coherent skeletal motions are underdamped. Pronounced quantum beats are observed for high-frequency modes consisting of strong phenolic COH rocking (1532 cm(-1)) or H-out-of-plane wagging motions (952 cm(-1)) due to anharmonic coupling to coherent low-frequency modes impulsively excited at ca. 96, 120, and 168 cm(-1). The vivid illustration of atomic motions of HPTS in varying H-bonding geometry with neighboring methanol molecules unravels the multidimensional energy relaxation pathways immediately following photoexcitation, and provides compelling evidence that, in lieu of ESPT, the photoacidity of HPTS promptly activates characteristic low-frequency skeletal motions to search phase

  3. Simulation and Theoretical Study of Spontaneous Excitation of Convective Cells by Kinetic Alfven Waves

    NASA Astrophysics Data System (ADS)

    Lin, Yu; Zonca, Fulvio; Chen, Liu

    2015-11-01

    It has been recently demonstrated that, generally, electrostatic (ES) and magnetostatic (MS) convective cells (CCs), or zonal flows, can be excited simultaneously by kinetic Alfven waves (KAWs). In this paper, spontaneous excitations of electrostatic as well as magnetostatic convective cells by KAWs are investigated through hybrid simulations, and the results are compared with the analytical theory based on the nonlinear gyrokinetic equations. In the hybrid simulation, ions are treated as fully kinetic particles, and electrons are treated as a massless fluid. It is found that finite ion-Larmor-radius (FILR) effects play a crucial. Furthermore, ES and MS convective cells are intrinsically coupled and must be treated on an equal footing. Excellent agreement is obtained for mode structure and generation rate of convective cells by KAW, demonstrating that ESCC and MSCC are indeed coupled, and that spontaneous CC excitation is suppressed at long wavelength, showing the crucial destabilizing role of FILR effects in the excitation via modulational instabilities. This work is supported by US DoE, NSF, ITER-CN, and NSFC grants.

  4. Structure and Excitation Transfer Pathways in the Chlorophyll-Carotenoid Aggregate of the Photosynthetic Unit of Purple Bacteria

    NASA Astrophysics Data System (ADS)

    Schulten, Klaus

    1998-03-01

    The absorption of light by light harvesting complexes and transfer of electronic excitation to the photosynthetic reaction center (RC) has been investigated on the basis of an atomic level model of the so-called photosynthetic unit of the photosynthetic bacterium Rb. sphaeroides. The photosynthetic unit combines in the intracytoplasmic membrane a nanometric (20-100 nm) assembly of three protein complexes: (i) the photosynthetic reaction center, (ii) a ring-shaped light harvesting complex LH-I, and (iii) multiple copies of a similar complex, LH-II. The unit has been modeled using the known structure of LH-II of Rs. molischianum. The lecture describes in detail the organization of chromophores involved in primary light absorption and excitation transfer: a hierarchy of ring-shaped chlorophyl aggregates with attached carotenoids. A quantum-mechanical description of the entire light harvesting process is developed employing electron structure calculations of individual and aggregated chlorophylls and carotenoids and associated effective Hamiltonian descriptions. The transfer times calculated, ranging between 100 fs and 100 ps for various processes, are found in close agreement with measured transfer rates. The results suggest that excitons are the key carriers of the excitation transfered. The photoprotection of chlorophylls by chlorophylls through triplet excitation transfer is also described.

  5. Effect of weight-related labels on corticospinal excitability during observation of grasping: a TMS study.

    PubMed

    Senot, Patrice; D'Ausilio, Alessandro; Franca, Michele; Caselli, Luana; Craighero, Laila; Fadiga, Luciano

    2011-05-01

    Recent studies of corticospinal excitability during observation of grasping and lifting of objects of different weight have highlighted the role of agent's kinematics in modulating observer's motor excitability. Here, we investigate whether explicit weight-related information, provided by written labels on the objects, modulate the excitability of the observer's motor system and how this modulation is affected when there is a conflict between label and object's weight. We measured TMS-evoked motor potentials (MEPs) from right hand intrinsic muscles, while subjects were observing an actor lifting objects of different weights, in some trials labeled (heavy/light) in congruent or incongruent way. Results confirmed a weight-related modulation of MEPs based on kinematic cues. Interestingly, any conflict between the labels and the actual weight (i.e., explicit versus implicit information), although never consciously noticed by the observer, deeply affected the mirroring of others' actions. Our findings stress the automatic involvement of the mirror-neuron system.

  6. R-matrix study of electron impact excitation and dissociation of CH+ ions

    NASA Astrophysics Data System (ADS)

    Chakrabarti, K.; Dora, A.; Ghosh, R.; Choudhury, B. S.; Tennyson, Jonathan

    2017-09-01

    Electron impact excitation and electron impact dissociation of CH+ ions are studied in the framework of the R-matrix method using the diatomic version of the UK molecular R-matrix codes. A configuration interaction calculation is first performed to yield the potential energy curves of the lowest eight singlet and triplet states of CH+. Scattering calculations are then performed to yield vibrationally-resolved electronic excitations to the lowest three bound states, namely the a {}3{{\\Pi }}, A {}1{{\\Pi }} and the b {}3{{{Σ }}}-. Electron impact dissociation cross sections are obtained from the assumption that all electronic excitations above the dissociation threshold result in dissociation. Bound states of CH and resonance positions and widths of Feshbach resonances in the e-CH+ system are also calculated at the CH+ equilibrium bond length 2.137 a0.

  7. A study of quasi-mode parametric excitations in lower-hybrid heating of tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Villalon, E.; Bers, A.

    1980-03-01

    A detailed linear and non-linear analysis of quasi-mode parametric excitations, relevant to experiments in supplementary heating of tokamak plasmas, is presented. The linear analysis includes the full ion-cyclotron harmonic quasi-mode spectrum, while the nonlinear one, considering depletion of the pump electric field, is applied to the recent Alcator A heating experiment. The quasi-mode excitations are studied independently for the plasma edge and the main bulk of the plasma, and for the two typical regimes in overall density. It is concluded that the excited spectrum has a frequency close to the initial pump frequency, while the wave-number spectrum may be different from the initial linear spectrum.

  8. Vibronic excitation of single molecules: a new technique for studying low-temperature dynamics.

    PubMed

    Kiraz, Alper; Ehrl, Moritz; Hellriegel, Christian; Bräuchle, Christoph; Zumbusch, Andreas

    2005-05-01

    Herein, we present vibronic excitation and detection of purely electronic zero-phonon lines (ZPL) of single molecules as a new tool for investigating dynamics at cryogenic temperatures. Applications of this technique to study crystalline and amorphous matrix materials are presented. In the crystalline environment, spectrally stable ZPLs are observed at moderate excitation powers. By contrast, investigations at higher excitation intensities reveal the opening of local degrees of freedom and spectral jumps, which we interpret as the observation of elementary steps in the melting of a crystal. We compare these results to spectral single-molecule trajectories recorded in a polymer. The way in which much more complicated spectral features can be analysed is shown. Surprisingly, pronounced spectral shifts on a previously not accessible large energy scale are observed, which are hard to reconcile with the standard two-level model system used to describe low-temperature dynamics in disordered systems.

  9. Study of the beam-foil excitation mechanism using Cl projectiles, 2 10 MeV

    NASA Astrophysics Data System (ADS)

    Jupén, C.; Denne, B.; Ekberg, J. O.; Engström, L.; Litzén, U.; Martinson, I.; Tai-Meng, W.; Trigueiros, A.; Veje, E.

    1982-11-01

    We have studied beam-foil excitation of chlorine projectiles by means of optical spectrometry, in the projectile energy range 2-10 MeV. This is a preliminary report, concentrating on the 3p and 3d level excitations in Cl VII (sodium-like chlorine) and in Cl VIII (neon-like chlorine). A discussion of the results is given, and it is concluded that the 3p and 3d levels in Cl VII and Cl VIII are populated by the same mechanism, namely molecular-orbital electron promotions.

  10. Study of intermediates from transition metal excited-state electron-transfer reactions

    SciTech Connect

    Hoffman, M.Z.

    1992-07-31

    Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

  11. Study of fragmentation at low excitation energies within a dynamical microscopic theory

    SciTech Connect

    Dhawan, Jatinder K.; Puri, Rajeev K.

    2007-05-15

    We present the theoretical study of fragmentation at low excitation energies within dynamical microscopic theory namely, simulated annealing clusterization algorithm (SACA) and quantum molecular dynamics (QMD) model. For low excitation energy reactions, we choose the balance energies for a large number of reactions throughout the periodic table. We see that SACA gives multiplicities in terms of power law. For light fragments, it is close to 1/3, whereas, for heavier fragments it is nearly mass independent suggesting their origin in terms of participant-spectator picture.

  12. Hydrodynamic study of edge spin-vortex excitations of fractional quantum Hall fluid

    NASA Astrophysics Data System (ADS)

    Rabiu, M.; Mensah, S. Y.; Seini, I. Y.; Abukari, S. S.

    2016-07-01

    We undertake a theoretical study of edge spin-vortex excitations in fractional quantum Hall fluid. This is done in view of quantised Euler hydrodynamics theory. The dispersions of true excitations for fractions within 0 ≤ ν ≤ 1 are simulated which exhibit universal similarities and differences in behaviour. The differences arise from different edge smoothness and spin (pseudo-spin) polarisations, in addition to spin-charge competition. In particular, tuning the spin-charge factor causes coherent spin flipping associated with partial and total polarisations of edge spin-vortices. This observation is tipped as an ideal mechanism for realisation of functional spintronic devices.

  13. Multiple hydrogen bonding in excited states of aminopyrazine in methanol solution: time-dependent density functional theory study.

    PubMed

    Chai, Shuo; Yu, Jie; Han, Yong-Chang; Cong, Shu-Lin

    2013-11-01

    Aminopyrazine (AP) and AP-methanol complexes have been theoretically studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The excited-state hydrogen bonds are discussed in detail. In the ground state the intermolecular multiple hydrogen bonds can be formed between AP molecule and protic solvents. The AP monomer and hydrogen-bonded complex of AP with one methanol are photoexcited initially to the S2 state, and then transferred to the S1 state via internal conversion. However the complex of AP with two methanol molecules is directly excited to the S1 state. From the calculated electronic excited energies and simulated absorption spectra, we find that the intermolecular hydrogen bonds are strengthened in the electronic excited states. The strengthening is confirmed by the optimized excited-state geometries. The photochemical processes in the electronic excited states are significantly influenced by the excited-state hydrogen bond strengthening.

  14. Efficient Excitation of High-Frequency Exchange-Dominated Spin Waves in Periodic Ferromagnetic Structures

    NASA Astrophysics Data System (ADS)

    Navabi, Aryan; Chen, Cai; Barra, Anthony; Yazdani, Mohsen; Yu, Guoqiang; Montazeri, Mohammad; Aldosary, Mohammed; Li, Junxue; Wong, Kin; Hu, Qi; Shi, Jing; Carman, Gregory P.; Sepulveda, Abdon E.; Khalili Amiri, Pedram; Wang, Kang L.

    2017-03-01

    Spin waves are of great interest as an emerging solution for computing beyond the limitations of scaled transistor technology. In such applications, the frequency of the spin waves is important as it affects the overall frequency performance of the resulting devices. In conventional ferromagnetic thin films, the magnetization dynamics in ferromagnetic resonance and spin waves are limited by the saturation magnetization of the ferromagnetic (FM) material and the external bias field. High-frequency applications would require high external magnetic fields which limit the practicality in a realistic device. One solution is to couple microwave excitations to perpendicular standing spin waves (PSSWs) which can enable higher oscillation frequencies. However, efficient coupling to these modes remains a challenge since it requires an excitation that is nonuniform across the FM material thickness and current methods have proven to be inefficient, resulting in weak excitations. Here, we show that by creating periodic undulations in a 100-nm-thick Co40Fe40B20 layer, high-frequency PSSWs (>20 GHz ) can be efficiently excited using micrometer-sized transducers at bias fields below 100 Oe which absorb nearly 10% of the input rf power. Efficient excitation of such spin waves at low fields may enable high-frequency spintronic applications using exchange-dominated magnetic oscillations using very low external magnetic fields and, with design optimizations, can bring about alternative possibilities in the field.

  15. Electron spectroscopy studies of argon K-shell excitation and vacancy cascades

    SciTech Connect

    Southworth, S.H.; MacDonald, M.A.; LeBrun, T.; Azuma, Y.; Cooper, J.W.

    1995-02-01

    Electron spectroscopy combined with tunable synchrotron radiation has been used for studies of Ar K-shell excitation and vacancy decay processes. In addition, electrons and fluorescent X-rays have been recorded in coincidence to select subsets of the ejected electron spectra. Examples are presented for Ar 1s photoelectrons and KLL and LMM Auger spectra.

  16. Molecular Level Understanding of Interfaces and Excited State Electronic Structure in Organic Solar Cells Using Soft X-ray Techniques

    NASA Astrophysics Data System (ADS)

    Gliboff, Matthew

    Transparent conductive oxides like indium tin oxide (ITO) are common substrates for optoelectronic devices, including organic light emitting diodes and organic solar cells. Tailoring the interface between the oxide and the active layer by adjusting the work function or wettability of the oxide can improve the performance of these devices in both emissive and photovoltaic applications. Molecular design of self-assembled monolayers (SAMs) allows for a range of surface properties using the same oxide material. The molecular ordering and conformation adopted by the SAMs determine properties such as work function and wettability at these critical interfaces. I use angle-dependent near edge x-ray absorption fine structure (NEXAFS) spectroscopy, to determine the molecular orientations of a variety of dipolar phosphonic acid surface modifiers. For a model system, phenylphosphonic acid on indium zinc oxide, the SAMs prove to be surprisingly well-oriented, with the phenyl ring adopting a well-defined tilt angle of 12-16° from the surface normal. The NEXAFS results agree with polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) results and orientations calculated from density functional theory (DFT). These results not only provide a detailed picture of the molecular structure of a technologically important class of SAMs, but they also resolve a long-standing ambiguity regarding the vibrational-mode assignments for phosphonic acids on oxide surfaces, thus improving the utility of PM-IRRAS for future studies. The effect of fluorination on the orientation of these phosponic-acid SAMs is non-trivial, due to the combined effects of the fluorination on binding mode and steric packing. The latter effects are found to be more dominant in aliphatic SAMs, leading to a more upright orientation in the fluorinated SAM. In the aromatic case, the fluorinated SAM adopted a less upright orientation which I attribute to changes in binding mode. The relationship

  17. Numerical Study of an AC MHD Generation with Double-side Exciting Winding

    NASA Astrophysics Data System (ADS)

    Intani, Pattana; Buttapeng, Chainarong; Sasaki, Toru; Kikuchi, Takashi; Harada, Nobuhiro

    This paper studies physical phenomena, performance and optimal operating point of an AC MHD generator under the slip value by using a numerical simulation. The double-side exciting winding of the generator is considered. Its structure consists of a channel, an insulator and stators. Channel type is a flat rectangular and the liquid flows along the channel as a conductor. Channel wall acted as an insulator separates metal fluid and stator coils. The top and bottom stator winding of the generator is connected to polyphase system. Under this condition, it can produce a magnetic field by means of time harmonic function in the same direction of the metal fluid. An interaction between traveling wave and metal fluid is explained by finite element method under Maxwell's equation and Ohm law. The distribution of magnetic vector potential and magnetic flux density throughout channel is evidently shown in xy-plane. Power flow in AC MHD generator is evaluated by slip value. The optimal operating point of an AC MHD generator performance is reported by active power 0.99kW, reactive power 50kVAR, mechanical power 1.58kW, power dissipation 0.59kW and electrical efficiency 62.5%.

  18. Sound transmission in the chest under surface excitation - An experimental and computational study with diagnostic applications

    PubMed Central

    Peng, Ying; Dai, Zoujun; Mansy, Hansen A.; Sandler, Richard H.; Balk, Robert A; Royston, Thomas. J

    2014-01-01

    Chest physical examination often includes performing chest percussion, which involves introducing sound stimulus to the chest wall and detecting an audible change. This approach relies on observations that underlying acoustic transmission, coupling, and resonance patterns can be altered by chest structure changes due to pathologies. More accurate detection and quantification of these acoustic alterations may provide further useful diagnostic information. To elucidate the physical processes involved, a realistic computer model of sound transmission in the chest is helpful. In the present study, a computational model was developed and validated by comparing its predictions with results from animal and human experiments which involved applying acoustic excitation to the anterior chest while detecting skin vibrations at the posterior chest. To investigate the effect of pathology on sound transmission, the computational model was used to simulate the effects of pneumothorax on sounds introduced at the anterior chest and detected at the posterior. Model predictions and experimental results showed similar trends. The model also predicted wave patterns inside the chest, which may be used to assess results of elastography measurements. Future animal and human tests may expand the predictive power of the model to include acoustic behavior for a wider range of pulmonary conditions. PMID:25001497

  19. Sound transmission in the chest under surface excitation: an experimental and computational study with diagnostic applications.

    PubMed

    Peng, Ying; Dai, Zoujun; Mansy, Hansen A; Sandler, Richard H; Balk, Robert A; Royston, Thomas J

    2014-08-01

    Chest physical examination often includes performing chest percussion, which involves introducing sound stimulus to the chest wall and detecting an audible change. This approach relies on observations that underlying acoustic transmission, coupling, and resonance patterns can be altered by chest structure changes due to pathologies. More accurate detection and quantification of these acoustic alterations may provide further useful diagnostic information. To elucidate the physical processes involved, a realistic computer model of sound transmission in the chest is helpful. In the present study, a computational model was developed and validated by comparing its predictions with results from animal and human experiments which involved applying acoustic excitation to the anterior chest, while detecting skin vibrations at the posterior chest. To investigate the effect of pathology on sound transmission, the computational model was used to simulate the effects of pneumothorax on sounds introduced at the anterior chest and detected at the posterior. Model predictions and experimental results showed similar trends. The model also predicted wave patterns inside the chest, which may be used to assess results of elastography measurements. Future animal and human tests may expand the predictive power of the model to include acoustic behavior for a wider range of pulmonary conditions.

  20. Design study and performance analysis of 12S-14P field excitation flux switching motor for hybrid electric vehicle

    NASA Astrophysics Data System (ADS)

    Husin, Zhafir Aizat; Sulaiman, Erwan; Khan, Faisal; Mazlan, Mohamed Mubin Aizat; Othman, Syed Muhammad Naufal Syed

    2015-05-01

    This paper presents a new structure of 12slot-14pole field excitation flux switching motor (FEFSM) as an alternative candidate of non-Permanent Magnet (PM) machine for HEV drives. Design study, performance analysis and optimization of field excitation flux switching machine with non-rare-earth magnet for hybrid electric vehicle drive applications is done. The stator of projected machine consists of iron core made of electromagnetic steels, armature coils and field excitation coils as the only field mmf source. The rotor is consisted of only stack of iron and hence, it is reliable and appropriate for high speed operation. The design target is a machine with the maximum torque, power and power density, more than 210Nm, 123kW and 3.5kW/kg, respectively, which competes with interior permanent magnet synchronous machine used in existing hybrid electric vehicle. Some design feasibility studies on FEFSM based on 2D-FEA and deterministic optimization method will be applied to design the proposed machine.

  1. Effect of hydration on the lowest singlet PiPi* excited-state geometry of guanine: a theoretical study.

    PubMed

    Shukla, M K; Leszczynski, Jerzy

    2005-09-15

    An ab-initio computational study was performed to investigate the effect of explicit hydration on the ground and lowest singlet PiPi* excited-state geometry and on the selected stretching vibrational frequencies corresponding to the different NH sites of the guanine acting as hydrogen-bond donors. The studied systems consisted of guanine interacting with one, three, five, six, and seven water molecules. Ground-state geometries were optimized at the HF level, while excited-state geometries were optimized at the CIS level. The 6-311G(d,p) basis set was used in all calculations. The nature of potential energy surfaces was ascertained via the harmonic vibrational frequency analysis; all structures were found minima at the respective potential energy surfaces. The changes in the geometry and the stretching vibrational frequencies of hydrogen-bond-donating sites of the guanine in the ground and excited state consequent to the hydration are discussed. It was found that the first solvation shell of the guanine can accommodate up to six water molecules. The addition of the another water molecule distorts the hydrogen-bonding network by displacing other neighboring water molecules away from the guanine plane.

  2. Excitation of plasmons in Ag/Fe/W structure by spin-polarized electrons

    SciTech Connect

    Samarin, Sergey N.; Kostylev, Mikhail; Williams, J. F.; Artamonov, Oleg M.; Baraban, Alexander P.; Guagliardo, Paul

    2015-09-07

    Using Spin-polarized Electron-Energy Loss Spectroscopy (SPEELS), the plasmon excitations were probed in a few atomic layers thick Ag film deposited on an Fe layer or on a single crystal of W(110). The measurements were performed at two specular geometries with either a 25° or 72° angle of incidence. On a clean Fe layer (10 atomic layers thick), Stoner excitation asymmetry was observed, as expected. Deposition of a silver film on top of the Fe layer dramatically changed the asymmetry of the SPEELS spectra. The spin-effect depends on the kinematics of the scattering: angles of incidence and detection. The spin-dependence of the plasmon excitations in the silver film on the W(110) surface and on the ferromagnetic Fe film is suggested to arise from the spin-active Ag/W or Ag/Fe interfaces.

  3. Electronic structure and excited state properties of iron carbene photosensitizers - A combined X-ray absorption and quantum chemical investigation

    NASA Astrophysics Data System (ADS)

    Ericson, Fredric; Honarfar, Alireza; Prakash, Om; Tatsuno, Hideyuki; Fredin, Lisa A.; Handrup, Karsten; Chabera, Pavel; Gordivska, Olga; Kjær, Kasper S.; Liu, Yizhu; Schnadt, Joachim; Wärnmark, Kenneth; Sundström, Villy; Persson, Petter; Uhlig, Jens

    2017-09-01

    The electronic structure and excited state properties of a series of iron carbene photosensitizers are elucidated through a combination of X-ray absorption measurements and density functional theory calculations. The X-ray absorption spectra are discussed with regard to the unusual bonding environment in these carbene complexes, highlighting the difference between ferrous and ferric carbene complexes. The valence electronic structure of the core excited FeIII - 3d5 complex is predicted by calculating the properties of a CoIII - 3d6 carbene complex using the Z+1 approximation. Insight is gained into the potential of sigma-donating ligands as strategy to tune properties for light harvesting applications.

  4. Photoelectron Spectroscopic Study on Decay Processes of Core-Excited States of NaNO2

    NASA Astrophysics Data System (ADS)

    Kamada, Masao; Azuma, Junpei; Ueda, Yuki; Yamamoto, Isamu; Imamura, Masaki; Takahashi, Kazutoshi

    2015-05-01

    The absorption and resonant photoelectron spectra of NaNO2 films have been measured at Na-L, N-K, and O-K core levels. The complete understanding of the electronic structures of NaNO2 in a wide energy region is proposed in a band scheme. Resonant photoelectron spectra indicate that the lowest excited states of N-K and O-K excitations (NK-LES and OK-LES) decay predominantly through participator and spectator Auger processes, whereas the normal Auger decay process is negligibly small. The decay probabilities of the NK-LES and OK-LES through the participator Auger process are estimated to be about 47 and 54%, respectively. The delocalization lifetimes of the NK-LES and OK-LES are also estimated to be more than 40 and 28 fs, respectively.

  5. Theoretical study of time-resolved luminescence in semiconductors. II. Pulsed excitation

    NASA Astrophysics Data System (ADS)

    Maiberg, Matthias; Scheer, Roland

    2014-09-01

    In the second part of this series, we studied TRL decay on semiconductor layers and thin film homostructures after a pulsed excitation by simulation with Synopsys TCAD® and by mathematical approximation. Again, our working example is Cu(In,Ga)Se2. We investigate the influence of the excitation pulse length, axial diffusion, bulk-defects, and defects at the contacts, as well as space charge on the TRL-decay separately by quasi one-dimensional simulations of semiconductor layers and semiconductor homostructures. Material parameters like defect density, carrier mobility, and surface recombination velocity are varied in a wide range, such that the calculations are applicable to other semiconductors. We further study the influence of multi-pulse excitation. We show how material parameters such as carrier lifetime and carrier mobility can be extracted from the TRL transients and how the samples can be characterized by excitation dependent measurements in the open circuit case. We can explain some effects found in luminescence experiments, like an increased decay in semiconductor junctions due to the electric field in the space charge region. However, we also discuss the effect of charge storage which may lead to decreased decay. It is revealed that under high injection conditions single layers within a semiconductor stack can be characterized in terms of carrier lifetime.

  6. Etude numerique et experimentale de la reponse vibro-acoustique des structures raidies a des excitations aeriennes et solidiennes

    NASA Astrophysics Data System (ADS)

    Mejdi, Abderrazak

    Les fuselages des avions sont generalement en aluminium ou en composite renforces par des raidisseurs longitudinaux (lisses) et transversaux (cadres). Les raidisseurs peuvent etre metalliques ou en composite. Durant leurs differentes phases de vol, les structures d'avions sont soumises a des excitations aeriennes (couche limite turbulente : TBL, champs diffus : DAF) sur la peau exterieure dont l'energie acoustique produite se transmet a l'interieur de la cabine. Les moteurs, montes sur la structure, produisent une excitation solidienne significative. Ce projet a pour objectifs de developper et de mettre en place des strategies de modelisations des fuselages d'avions soumises a des excitations aeriennes et solidiennes. Tous d'abord, une mise a jour des modeles existants de la TBL apparait dans le deuxieme chapitre afin de mieux les classer. Les proprietes de la reponse vibro-acoustique des structures planes finies et infinies sont analysees. Dans le troisieme chapitre, les hypotheses sur lesquelles sont bases les modeles existants concernant les structures metalliques orthogonalement raidies soumises a des excitations mecaniques, DAF et TBL sont reexamines en premier lieu. Ensuite, une modelisation fine et fiable de ces structures est developpee. Le modele est valide numeriquement a l'aide des methodes des elements finis (FEM) et de frontiere (BEM). Des tests de validations experimentales sont realises sur des panneaux d'avions fournis par des societes aeronautiques. Au quatrieme chapitre, une extension vers les structures composites renforcees par des raidisseurs aussi en composites et de formes complexes est etablie. Un modele analytique simple est egalement implemente et valide numeriquement. Au cinquieme chapitre, la modelisation des structures raidies periodiques en composites est beaucoup plus raffinee par la prise en compte des effets de couplage des deplacements planes et transversaux. L'effet de taille des structures finies periodiques est egalement pris en

  7. Mode shape reconstruction of an impulse excited structure using continuous scanning laser Doppler vibrometer and empirical mode decomposition.

    PubMed

    Kyong, Yongsoo; Kim, Daesung; Dayou, Jedol; Park, Kyihwan; Wang, Semyung

    2008-07-01

    For vibration testing, discrete types of scanning laser Doppler vibrometer (SLDV) have been developed and have proven to be very useful. For complex structures, however, SLDV takes considerable time to scan the surface of structures and require large amounts of data storage. To overcome these problems, a continuous scan was introduced as an alternative. In this continuous method, the Chebyshev demodulation (or polynomial) technique and the Hilbert transform approach have been used for mode shape reconstruction with harmonic excitation. As an alternative, in this paper, the Hilbert-Huang transform approach is applied to impact excitation cases in terms of a numerical approach, where the vibration of the tested structure is modeled using impulse response functions. In order to verify this technique, a clamped-clamped beam was chosen as the test rig in the numerical simulation and real experiment. This paper shows that with additional innovative steps of using ideal bandpass filters and nodal point determination in the postprocessing, the Hilbert-Huang transformation can be used to create a better mode shape reconstruction even in the impact excitation case.

  8. N=50 core excited states studied in the 4696Pd50 nucleus

    NASA Astrophysics Data System (ADS)

    Palacz, M.; Nyberg, J.; Grawe, H.; Sieja, K.; de Angelis, G.; Bednarczyk, P.; Blazhev, A.; Curien, D.; Dombradi, Z.; Dorvaux, O.; Ekman, J.; Gałkowski, J.; Górska, M.; Iwanicki, J.; Jaworski, G.; Kownacki, J.; Ljungvall, J.; Moszyński, M.; Nowacki, F.; Rudolph, D.; Sohler, D.; Wolski, D.; Ziębliński, M.

    2012-07-01

    The four-proton hole 96Pd neighbor of the doubly-magic 100Sn nucleus was studied in-beam, using a fusion-evaporation reaction of a 58Ni beam on a 45Sc target. States of 96Pd were established up to an excitation energy of 9707 keV. A core-excited odd-parity isomer with T1/2=37.7(1.1) ns was identified. Shell model calculations were performed in four different model spaces. Even-parity states of 96Pd are very well reproduced in large-scale shell model (LSSM) calculations in which excitations are allowed of up to five g9/2 protons and neutrons across the N=Z=50 gap, to the g7/2, d5/2, d3/2, and s1/2 orbitals. The odd-parity isomer can be only qualitatively interpreted though, employing calculation in the full fpg shell model space, with just one particle-hole core excitation.

  9. Experimental and computational studies on the electronic excited states of nitrobenzene

    NASA Astrophysics Data System (ADS)

    Krishnakumar, Sunanda; Das, Asim Kumar; Singh, Param Jeet; Shastri, Aparna; Rajasekhar, B. N.

    2016-11-01

    The gas phase electronic absorption spectrum of nitrobenzene (C6H5NO2) in the 4.5-11.2 eV region is recorded using synchrotron radiation with a view to comprehend the nature of the excited states. Electronic excited states of nitrobenzene are mainly classified as local excitations within the benzene ring or nitro group and charge transfer excitations between the benzene and nitro group, with some transitions showing percentage from both. The nature of molecular orbitals, their orderings and energies are obtained from density functional theory calculations which help in assigning partially assigned/unassigned features in earlier photoelectron spectroscopy studies. Optimized geometry of ionic nitrobenzene predicts redistribution of charge density in the benzene ring rather than the nitro group resulting in stabilization of the benzene ring π orbitals in comparison to the neutral molecule. Time dependent density functional theory computations are found to describe the experimental spectra well with respect to energies, relative intensities and nature of the observed transitions in terms of valence, Rydberg or charge transfer type. New insights into the interpretation of 1B2u←1A1g and 1B1u←1A1g shifted benzene transitions in light of the present computational calculations are presented. The first few members of the ns, np and nd type Rydberg series in nitrobenzene, converging to the first six ionization potentials, identified in the spectra as weak but sharp peaks are reported for the first time. In general, transitions to the lowest three unoccupied molecular orbitals 4b1, 3a2 and 5b1 are valence or charge transfer in nature, while excitations to higher orbitals are predominantly Rydberg in nature. This work presents a consolidated experimental study and theoretical interpretation of the electronic absorption spectrum of nitrobenzene.

  10. SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium

    NASA Astrophysics Data System (ADS)

    Schuller, F.; Csengeri, T.; Urquhart, J. S.; Duarte-Cabral, A.; Barnes, P. J.; Giannetti, A.; Hernandez, A. K.; Leurini, S.; Mattern, M.; Medina, S.-N. X.; Agurto, C.; Azagra, F.; Anderson, L. D.; Beltrán, M. T.; Beuther, H.; Bontemps, S.; Bronfman, L.; Dobbs, C. L.; Dumke, M.; Finger, R.; Ginsburg, A.; Gonzalez, E.; Henning, T.; Kauffmann, J.; Mac-Auliffe, F.; Menten, K. M.; Montenegro-Montes, F. M.; Moore, T. J. T.; Muller, E.; Parra, R.; Perez-Beaupuits, J.-P.; Pettitt, A.; Russeil, D.; Sánchez-Monge, Á.; Schilke, P.; Schisano, E.; Suri, S.; Testi, L.; Torstensson, K.; Venegas, P.; Wang, K.; Wienen, M.; Wyrowski, F.; Zavagno, A.

    2017-05-01

    Context. The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. Many large-scale surveys of the Galactic plane have been conducted recently, allowing for rapid progress in this field. Nevertheless, a sub-arcminute resolution global view of the large-scale distribution of molecular gas, from the diffuse medium to dense clouds and clumps, and of their relationshipto the spiral structure, is still missing. Aims: We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. Methods: The SEDIGISM survey covers 78 deg2 of the inner Galaxy (-60°≤ℓ≤ 18°, |b|≤ 0.5°) in the J = 2-1 rotational transition of 13CO. This isotopologue of CO is less abundant than 12CO by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the 13CO(2-1) and C18O(2-1) lines, plus several transitions from other molecules. Results: The observations have been completed. Data reduction is in progress, and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. To illustrate the scientific potential of this survey, preliminary results based on a science demonstration field covering -20°≤ℓ ≤ -18.5° are presented. Analysis of the 13CO(2-1) data in this field reveals compact clumps, diffuse clouds, and filamentary structures at a range of heliocentric distances. By combining our data with

  11. Red and blue shift of liquid water's excited states: A many body perturbation study

    NASA Astrophysics Data System (ADS)

    Ziaei, Vafa; Bredow, Thomas

    2016-08-01

    In the present paper, accurate optical absorption spectrum of liquid H2O is calculated in the energy range of 5-20 eV to probe the nature of water's excited states by means of many body perturbation approach. Main features of recent inelastic X-ray measurements are well reproduced, such as a bound excitonic peak at 7.9 eV with a shoulder at 9.4 eV as well as the absorption maximum at 13.9 eV, followed by a broad shoulder at 18.4 eV. The spectrum is dominated by excitonic effects impacting the structures of the spectrum at low and higher energy regimes mixed by single particle effects at high energies. The exciton distribution of the low-energy states, in particular of S1, is highly anisotropic and localized mostly on one water molecule. The S1 state is essentially a HOCO-LUCO (highest occupied crystal orbital - lowest unoccupied crystal orbital) transition and of intra-molecular type, showing a localized valence character. Once the excitation energy is increased, a significant change in the character of the electronically excited states occurs, characterized through emergence of multiple quasi-particle peaks at 7.9 eV in the quasi-particle (QP) transition profile and in the occurring delocalized exciton density distribution, spread over many more water molecules. The exciton delocalization following a change of the character of excited states at around 7.9 eV causes the blue shift of the first absorption band with respect to water monomer S1. However, due to reduction of the electronic band gap from gas to liquid phase, following enhanced screening upon condensation, the localized S1 state of liquid water is red-shifted with respect to S1 state of water monomer. For higher excitations, near vertical ionization energy (11 eV), quasi-free electrons emerge, in agreement with the conduction band electron picture. Furthermore, the occurring red and blue shift of the excited states are independent of the coupling of resonant and anti-resonant contributions to the

  12. The structure of the high-energy spin excitations in YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Hayden, Stephen

    2005-03-01

    The most obvious feature in the magnetic excitations of high-Tc superconductors is the so-called `resonance-mode'. This mode is strongly coupled to the superconductivity, however, it has not been found in the La2-x(Ba,Sr)xCuO4 family and is not universally present in Bi2Sr2CaCu2O8+δ. Here we use inelastic neutron scattering to characterize other excitations at higher energies which may be relevant to the superconductive pairing in YBa2Cu3O6.6. We observe a square-shaped continuum of excitations in reciprocal space [1]. These excitations have energies greater than the superconducting pairing energy, are present at Tc, and have spectral weight far exceeding that of the `resonance'. The discovery of similar excitations in La2-xBaxCuO4 [2] suggests that they are a general property of the copper oxides, and a candidate for mediating the electron pairing. Our data show that the high-energy magnetic excitations in the high-temperature superconductor YBa2Cu3O6.6 consists of a continuum of scattering bounded by a square and peaked at wavevector positions Qɛ =(1/2±ɛ,1/2±ɛ) and (1/2±ɛ,1/2ɛ). A similar structure is observed in the high-energy magnetic excitations of the magnetically ordered but weakly superconducting compound La1.85Ba0.125CuO4 [2]. This suggests there is universality, both in the low-energy and the high-energy spin dynamics between two very different classes of high-Tc superconductor. [1] S.M. Hayden, H.A. Mook, P.C. Dai, T.G. Perring, and F. Dogan, Nature 429, 531-534 (2004) [2] J.M. Tranquada, H. Woo, T.G. Perring, H. Goka, G.D. Gu , G. Xu, M. Fujita, K.Yamada K, Nature 429, 534-538 (2004).

  13. Nonradiative Relaxation Mechanisms of UV Excited Phenylalanine Residues: A Comparative Computational Study.

    PubMed

    Mališ, Momir; Došlić, Nađa

    2017-03-21

    The present work is directed toward understanding the mechanisms of excited state deactivation in three neutral model peptides containing the phenylalanine residue. The excited state dynamics of theγL(g+)folded form of N-acetylphenylalaninylamide (NAPA B) and its amide-N-methylated derivative (NAPMA B) is reviewed and compared to the dynamics of the monohydrated structure of NAPA (NAPAH). The goal is to unravel how the environment, and in particular solvation, impacts the photodynamics of peptides. The systems are investigated using reaction path calculations and surface hopping nonadiabatic dynamics based on the coupled cluster doubles (CC2) method and time-dependent density functional theory. The work emphasizes the role that excitation transfer from the phenylππ*to amidenπ*state plays in the deactivation of the three systems and shows how the ease of out-of-plane distortions of the amide group determines the rate of population transfer between the two electronic states. The subsequent dynamics on thenπ*state is barrierless along several pathways and leads to fast deactivation to the ground electronic state.

  14. Structure, initial excited-state relaxation, and energy storage of rhodopsin resolved at the multiconfigurational perturbation theory level.

    PubMed

    Andruniów, Tadeusz; Ferré, Nicolas; Olivucci, Massimo

    2004-12-28

    We demonstrate that a "brute force" quantum chemical calculation based on an ab initio multiconfigurational second order perturbation theory approach implemented in a quantum mechanics/molecular mechanics strategy can be applied to the investigation of the excited state of the visual pigment rhodopsin (Rh) with a computational error <5 kcal.mol(-1). As a consequence, the simulation of the absorption and fluorescence of Rh and its retinal chromophore in solution allows for a nearly quantitative analysis of the factors determining the properties of the protein environment. More specifically, we demonstrate that the Rh environment is more similar to the "gas phase" than to the solution environment and that the so-called "opsin shift" originates from the inability of the solvent to effectively "shield" the chromophore from its counterion. The same strategy is used to investigate three transient structures involved in the photoisomerization of Rh under the assumption that the protein cavity does not change shape during the reaction. Accordingly, the analysis of the initially relaxed excited-state structure, the conical intersection driving the excited-state decay, and the primary isolable bathorhodopsin intermediate supports a mechanism where the photoisomerization coordinate involves a "motion" reminiscent of the so-called bicycle-pedal reaction coordinate. Most importantly, it is shown that the mechanism of the approximately 30 kcal.mol(-1) photon energy storage observed for Rh is not consistent with a model based exclusively on the change of the electrostatic interaction of the chromophore with the protein/counterion environment.

  15. Study of the plasma and runaway electrons during inductionless current excitation in the V-20 torsatron

    SciTech Connect

    Bocharov, V.K.; Volkov, Y.F.; Dyatlov, V.G.; Kornienko, V.P.; Mitina, N.I.

    1982-05-01

    Inductionless current excitation has been studied in the V-20 torsatron with the plasma parameters n = 10/sup 12/--10/sup 13/ cm/sup -3/ and T/sub e/ = 40--60 eV. Since the plasma current was excited only in the initial stage of the discharge, it was possible to study the events in the plasma both with and without current flow. The plasma conductivity determined from measurements of the current and the voltage is an order of magnitude below the classical value calculated from the measured electron temperature. The discharge conditions under which a large number (Nroughly-equal(2--3)x10/sup 11/) of runaway electrons appear were studied. It is shown that the runaway occurs continuously throughout the discharge. When a certain limiting energy is reached (this energy depends on the confining properties of the confinement system), the runaway electrons escape from the confinement volume.

  16. Experimental and theoretical study on characteristics of pulse excitation in T-burners

    NASA Astrophysics Data System (ADS)

    Yan, Mi; Wang, Ningfei; Li, Junwei; Song, Anchen; Ma, Yu

    2017-05-01

    Pulse excitation is the key to measure the pressure-coupling response function of composite propellant. It is also a key trigger factor for nonlinear combustion instability. This paper aims at understanding characteristics of pulse excitation in T-burners. Pulse excitation is provided by black powder (BP). D2 law is used to calculate BP burning properties. Firstly, the experimental pressure history of a pulse excitation is analyzed. Pressure pulse and mean pressure increment are introduced to describe pulse excitation. Secondly, the modified zero-dimension model and one-dimension model of pressure pulse are established based on energy conservation and modification. The results of models indicate that the modified zero-dimensional model can accurately predict the pressure pulse. The modified zero-dimension model demonstrates that the pressure pulse is determined by pulse build-up time threshold, volume coefficient, effective weight fraction of BP, weight of BP et. al. When burning time of BP is larger than the threshold, volume coefficient is equal to 2, and effective weight fraction of BP is less than 1. The pressure pulse is approximately linear correlation with weight and effective weight fraction of BP. Otherwise, volume coefficient is larger than 2, and effective weight fraction of BP is equal to 1. The pressure pulse is approximately linear correlation with volume coefficient and BP weight. Thirdly, a zero-dimensional prediction model of mean pressure is established based on conservations of energy and mass. The prediction models of pressure pulse and mean pressure are validated by T-burner experiments. Finally, effects of BP burning properties on pressure pulse and mean pressure increment are studied. The results show that both pressure pulse and mean pressure increment increase with increasing BP weight, linearly. The pressure pulse is more sensitivity to the variations of burning time of BP. As burning time of BP decreases, the mean pressure increment

  17. Photochemical Kinetics of Excited States of Ozone and Oxygen: Laboratory Studies and Atmospheric Implications

    NASA Astrophysics Data System (ADS)

    Shi, Jichun

    The photochemistry of O_3 has matured through the extensive research efforts of the last two decades, but its completeness has been questioned by several laboratory and atmospheric observations, including the unusually complex kinetics for the ozone three-body recombination reaction at high pressures, the unexplained heavy ozone isotope enhancement in the stratosphere, and the deficiencies of current chemical models at 90-120 km. The model deficiencies may be related to several of the excited states of O_3 and O_2 . In this dissertation, the photochemical kinetics of these excited species have been studied in a series of laboratory measurements, which are divided into two groups: (1) the study of the excited intermediates formed in the ozone recombination reaction, and (2) the investigation of the unusual odd oxygen formation in O_2 under laser irradiation at 248 nm. The ozone recombination reaction has been investigated at room temperature by monitoring the time-resolved infrared chemiluminescence of ozone at 9.6 mum, 4.7 mum, and 3.4 mu m. These studies have indicated that the recombination reaction (O+O_2+M) apparently proceeds through an intermediate complex OM, and, for M=O _2, the recombination also involves the participation of a metastable electronic state, O_3(E). The three infrared emissions have also been used to analyze the deactivation of vibrationally excited O_3 (v). The unusual odd oxygen formation in O _2 at 248 nm has been studied in both pure O_2 and O_2+N _2 and O_2+Ar mixtures at pressures between 200 and 1600 torr and at temperatures between 298 and 370^circ K. The results have indicated that this odd oxygen formation is initiated by O_2 absorption in the Herzberg continuum, and it is autocatalytically accelerated by the photodissociation of vibrationally excited O_2(v) at 248 nm. These kinetics results have been used to study the possible roles of excited O_3 and O_2 species in the sources and sinks of odd oxygen at 90-120 km, and in the

  18. Studies of long range order and excitations in the iron arsenide superconductors

    NASA Astrophysics Data System (ADS)

    Pratt, Daniel K.

    The study of iron based superconductors began in 2006 when the compound LaOFeP was found to have a superconducting transition at a modest temperature Tc of 3.2 K. Because elemental iron is a strong ferromagnet, this discovery was a great surprise due to the fact that magnetic moments are generally associated with magnetic pair breaking. Soon after this discovery, variations of these superconductors were made through chemical substitutions and the Tc rose to 55 K two years later. The explosion of research that has followed these discoveries has led to the synthesis of several families of iron based superconductors whose high values of Tc are second only to the cuprates and which bringing them into the field of high temperature superconductivity (SC). This thesis focuses on how pressure and electron doping effect the crystallographic and magnetic properties of the iron based superconductors (Ca,Ba)Fe2 As2 which are part of a group of compounds known as 122s. Upon cooling, these compounds undergo a dual structural-magnetic transition from a tetragonal paramagnetic state to an orthorhombic and antiferromagnetic state. By tuning the pressure or dopant concentration knob, we have been able to show clearly that this has the effect of suppressing the magnetism and associated structural transition observed in un-doped or ambient pressure compounds. Neutron scattering measurements on CaFe2 As2 under pressure have demonstrated that the onset of superconductivity is observed after the stabilization of the room-temperature tetragonal phase at low temperatures under non-hydrostatic pressure. For the case of electron doping BaFe 2 As2, it is clear that a sufficient suppression of structural and magnetic ordering transitions is necessary for the appearance and optimization of superconductivity. These studies have provided key information about the static magnetic ordering and the associated magnetic excitations, and have allowed for the attempt to address questions about the

  19. Induced structural defects in Ti-doped ZnO and its two-photon-excitation

    NASA Astrophysics Data System (ADS)

    Martínez Julca, Milton A.; Rivera, Ivonnemary; Santillan Mercado, Jaime; Sierra, Heidy; Perales-Pérez, Oscar

    2016-03-01

    ZnO is a well-known luminescent material that reacts with light to generate free radicals enabling its use in cancer treatment by Photodynamic Therapy (PDT). Unfortunately, up to know, the photo-excitation of ZnO-based materials' requires excitation with ultraviolet light, which limits their biomedical applications. In this regard, this work investigates the effect of Ti species incorporation into the lattice of ZnO nanoparticles (NPs) with the aim of improving the corresponding optical properties and enabling the two-photoexcitation with 690nm-light (near infrared light). A modified polyol-based route was used to synthesize pure and Ti-doped (9% at.) ZnO NPs. X-ray diffraction confirmed the formation of ZnO-wurtzite whereas Scanning Electron Microscopy confirmed the formation of monodispersed 100-nm NPs. Raman Spectroscopy measurements evidenced the presence of zinc interstitials (Zni) and oxygen vacancies (VO) in the host oxide strcuture. Asynthesized NPs were excited using the technique of two-photon fluorescence microscopy (TPFM). The photoluminescence (PL) spectra generated from the analysis of TPFM images revealed a high emission peak presence in the green region (555 nm) that was assigned to VO. Also, a weak but noticeable band at 420 nm was detected, which is attributed to electron transition from the shallow donor level of Zni to the valence band. These PL transitions will favor triplet states formation necessary to yield cytotoxic reactive oxygen species. Furthermore, the presence of the PL peaks confirmed the Ti-ZnO NPs capacity to be excited by 690-nm light, thus, opening new possibilities for this NPs to be used in lightinduced bio-medical applications.

  20. Electronic Structure, Elementary Excitations, Optical and Transport Properties of Semiconductor Superlattices.

    DTIC Science & Technology

    1987-12-01

    Spectroscopy due to Collective Charge Density Excitations * (e) Plasmon in Quasi Periodic Layered Electron Gas Systems (2) Impurity Levels, Excitons ...34, (with G. Giuliani and G. Qin) Surface Sci. 142, 433 (1984). "Surface and Bulk Plasmon - Polariton Bands in Periodic Metallic Heterostructures", (with G... Plasmon Polaritons in Truncated Superlattices", R. Szenics, R. F. Wallis, G. Giuliani and J. J. Quinn, Surface Science (1986). "Ma.netic Polaron Effects in

  1. Study of two-photon excitation spectra of organic compounds absorbing in the UV region

    SciTech Connect

    Babenko, V A; Sychev, Andrei A

    2004-12-31

    A method is proposed for recording two-photon excitation (TPE) spectra of organic compounds with the help of picosecond pulses from a dye laser tunable in the range from 550 to 640 nm. The TPE spectra are obtained for organic scintillators and drugs: paraterphenyl in liquid and solid phases, stilbene single crystal and Streptocid powder, having a one-photon absorption band in the region from 270 to 350 nm. It is shown that the vibronic structure in the TPE spectra of these compounds is independent of their aggregate state and is an individual characteristic of each of the compounds. (active media)

  2. Electronic spectra of azaindole and its excited state mixing: A symmetry-adapted cluster configuration interaction study

    SciTech Connect

    Arulmozhiraja, Sundaram Coote, Michelle L.; Hasegawa, Jun-ya

    2015-11-28

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning’s cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n–π{sup ∗} state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of π-π{sup ∗} and n-π{sup ∗} states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition when compared to that of the zero-point level of the S{sub 1} state. The present study, however, shows that all the four lowest lying excited states, {sup 1}L{sub b} π-π{sup ∗}, {sup 1}L{sub a} π-π{sup ∗}, n-π{sup ∗}, and π-σ{sup ∗}, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S{sub 1} excited vibrational level. This multistate mixing, and especially the involvement of π-σ{sup ∗} state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

  3. Electronic spectra of azaindole and its excited state mixing: A symmetry-adapted cluster configuration interaction study

    NASA Astrophysics Data System (ADS)

    Arulmozhiraja, Sundaram; Coote, Michelle L.; Hasegawa, Jun-ya

    2015-11-01

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning's cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n-π∗ state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of π-π∗ and n-π∗ states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm-1 band in the S1←S0 transition when compared to that of the zero-point level of the S1 state. The present study, however, shows that all the four lowest lying excited states, 1Lb π-π∗, 1La π-π∗, n-π∗, and π-σ∗, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm-1 band in the S1←S0 transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S1 excited vibrational level. This multistate mixing, and especially the involvement of π-σ∗ state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

  4. Improving the sensitivity of high-frequency subharmonic imaging with coded excitation: A feasibility study

    PubMed Central

    Shekhar, Himanshu; Doyley, Marvin M.

    2012-01-01

    Purpose: Subharmonic intravascular ultrasound imaging (S-IVUS) could visualize the adventitial vasa vasorum, but the high pressure threshold required to incite subharmonic behavior in an ultrasound contrast agent will compromise sensitivity—a trait that has hampered the clinical use of S-IVUS. The purpose of this study was to assess the feasibility of using coded-chirp excitations to improve the sensitivity and axial resolution of S-IVUS. Methods: The subharmonic response of Targestar-pTM, a commercial microbubble ultrasound contrast agent (UCA), to coded-chirp (5%–20% fractional bandwidth) pulses and narrowband sine-burst (4% fractional bandwidth) pulses was assessed, first using computer simulations and then experimentally. Rectangular windowed excitation pulses with pulse durations ranging from 0.25 to 3 μs were used in all studies. All experimental studies were performed with a pair of transducers (20 MHz/10 MHz), both with diameter of 6.35 mm and focal length of 50 mm. The size distribution of the UCA was measured with a CasyTM Cell counter. Results: The simulation predicted a pressure threshold that was an order of magnitude higher than that determined experimentally. However, all other predictions were consistent with the experimental observations. It was predicted that: (1) exciting the agent with chirps would produce stronger subharmonic response relative to those produced by sine-bursts; (2) increasing the fractional bandwidth of coded-chirp excitation would increase the sensitivity of subharmonic imaging; and (3) coded-chirp would increase axial resolution. The experimental results revealed that subharmonic-to-fundamental ratios obtained with chirps were 5.7 dB higher than those produced with sine-bursts of similar duration. The axial resolution achieved with 20% fractional bandwidth chirps was approximately twice that achieved with 4% fractional bandwidth sine-bursts. Conclusions: The coded-chirp method is a suitable excitation strategy for

  5. Microfabrication of extracellular matrix structures using multipohoton-excited photochemistry: Application to modeling ovarian tissue in vitro

    NASA Astrophysics Data System (ADS)

    Ajeti, Visar

    The extracellular matrix plays a crucial role in tissue development, differentiation and homeostasis by providing the necessary biophysical and biochemical cues for the cells. In tumors, the composition and the structure of the microenvironment is thought to be manipulated by the cancers cells to support proliferative growth and enhanced migration as means of facilitated metastasis. Current in vitro tools to address these mechanistic events in tumor progression are lacking in part due to the difficulty in recapitulating the complexity of the composition and nanoarchitecture of the tumor microenvironment. In this thesis, we explore the feasibility of multiphoton-excited photochemistry as a fabrication tool for generating in vitro scaffolds that are highly repeatable, biologically relevant and relatively affordable in a research setting. The power of this technique lays in the capabilities of crosslinking whole extracellular matrix proteins in three dimensions (3D) to recreate key topographical features of the tissue with sub-micron resolution and high fidelity. The technological developments we present here enable direct translation of matrix topographies by using the high resolution image data of the tissue samples as a fabrication template. To this effect, we have applied the fabrication technique to generate gradients of crosslinked proteins as means of studying the role of haptotaxis in ovarian and breast cancers. Our findings show that cancer cells modulate their migration velocity and persistence in response to the changes in the composition of the extracellular matrix. In addition, we have examined structural features of the stroma in relation to cancer migration dynamics. We find that by recreating highly aligned nanoarchitectural features prevalent in cancer stroma, we see permissive and enhanced cell migration with cell morphologies similar to in vivo. We believe multiphoton fabrication to be an enabling tool in the next generation of tissue scaffolding

  6. Electron-impact Excitation of Ni II: Effective Collision Strengths for Optically Allowed Fine-structure Transitions

    NASA Astrophysics Data System (ADS)

    Cassidy, C. M.; Ramsbottom, C. A.; Scott, M. P.

    2011-09-01

    In this paper, we present collision strengths and Maxwellian averaged effective collision strengths for the electron-impact excitation of Ni II. Attention is expressly concentrated on the optically allowed fine-structure transitions between the 3d 9, 3d 84s, and 3d 74s 2 even parity levels and the 3d 84p and 3d 74s 4p odd parity levels. The parallel RMATRXII R-matrix package has been recently extended to allow for the inclusion of relativistic fine-structure effects. This suite of codes has been utilized in conjunction with the parallel PSTGF and PSTGICF programs in order to compute converged total collision strengths for the allowed transitions with which this study is concerned. All 113 LS terms identified with the 3d 9, 3d 84s, 3d 74s 2, 3d 84p, and 3d 74s 4p basis configurations were included in the target wavefunction representation, giving rise to a sophisticated 295 jj-level, 1930 coupled channel scattering complex. Maxwellian averaged effective collision strengths have been computed at 30 individual electron temperatures ranging from 30 to 1,000,000 K. This range comfortably encompasses all temperatures significant to astrophysical and plasma applications. The convergence of the collision strengths is exhaustively investigated and comparisons are made with previous theoretical works, where significant discrepancies exist for the majority of transitions. We conclude that intrinsic in achieving converged collision strengths and thus effective collision strengths for the allowed transitions is the combined inclusion of contributions from the (N + 1) partial waves extending to a total angular momentum value of L = 50 and further contributions from even higher partial waves accomplished by employing a "top-up" procedure.

  7. Electronic structure, excitation properties, and chemical transformations of extreme ultra-violet resist materials

    NASA Astrophysics Data System (ADS)

    Rangan, Sylvie; Bartynski, Robert A.; Narasimhan, Amrit; Brainard, Robert L.

    2017-07-01

    The electronic structure of extreme ultra violet resist materials and of their individual components, two polymers and two photoacid generators (PAGs), is studied using a combination of x-ray and UV photoemission spectroscopies, electron energy loss spectroscopy, and ab-initio techniques. It is shown that simple molecular models can be used to understand the electronic structure of each sample and describe the experimental data. Additionally, effects directly relevant to the photochemical processes are observed: low energy loss processes are observed for the phenolic polymer containing samples that should favor thermalization of electrons; PAG segregation is measured at the surface of the resist films that could lead to surface inhomogeneities; both PAGs are found to be stable upon irradiation in the absence of the polymer, contrasting with a high reactivity that can be followed upon x-ray irradiation of the full resist.

  8. Study of protein-surfactant interaction using excited state proton transfer

    NASA Astrophysics Data System (ADS)

    Sahu, Kalyanasis; Roy, Durba; Mondal, Sudip Kumar; Karmakar, Rana; Bhattacharyya, Kankan

    2005-03-01

    Excited state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulfonate) is studied in a lysozyme-cetyltrimethylammonium bromide (CTAB) complex using picosecond emission spectroscopy. The critical association concentration (CAC) of CTAB is found to be ˜0.4 mM. Using a kinetic analysis it is shown that deprotonation, recombination and dissociation of the geminate ion pair in the lysozyme-CTAB aggregate are faster than that in a CTAB micelle.

  9. Studies of Plasma Instability Processes Excited by Ground Based High Power HF ("Heating") Facilities

    DTIC Science & Technology

    2001-04-01

    by ground based high power HF (’ heating ’) facilities 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Dr. Alexander...Prescribed by ANSI Std. Z39-18 Grant SPC 00-4010 Final Report STUDIES OF PLASMA INSTABILITY PROCESSES EXCITED BY GROUND BASED HIGH POWER HF (" HEATING ...growing field of ionospheric HF heating . The main new results can be summarized as following: 1. Two sets of observations of suprathermal electrons

  10. Solar Coronal Structure Study

    NASA Technical Reports Server (NTRS)

    Bruner, Marilyn E.; Saba, Julia; Strong, Keith; Nitta, Nariaki; Harvey, Karen

    1997-01-01

    The subject of this investigation is the study the physics of the solar corona through the analysis of the EUV and UV data produced by two flights (12 May 1992 and 25 April 1994) of the Lockheed Solar Plasma Diagnostics Experiment (SPDE) sounding rocket payload, in combination with Yohkoh and groundbased data. These joint datasets are useful for understanding the physical state of the solar atmosphere from the photosphere to the corona at the time of the rocket flights. Each rocket flight produced both spectral and imaging data. Highlights of this initial year of the contract included compilation, scaling and co-alignment of image sets, substantial progress on the Bright Point study, initial work on the Active Region and Large Scale Structure studies, DRSC slit-aspect determination work and calibration activities. One paper was presented at the 1997 Annual Meeting of the AAS/SPD in Bozeman, Montana. An initial set of calibrated spectra were placed into the public domain via the World Wide Web. Three Quarterly Progress Reports have been submitted; progress for the fourth quarter of the contract is summarized in this Final Contract Report. The intent of the investigation is to compare the physics of small- and medium-scale structure with that of large-scale structures with weak fields. A study has been identified in each size domain. The calibration of the rocket data forms an important element of the work. Of equal importance is the slit-aspect solution, which determines the correspondence between locations along the spectrograph slit and points on the solar disk.

  11. Fibroblast proliferation alters cardiac excitation conduction and contraction: a computational study*

    PubMed Central

    Zhan, He-qing; Xia, Ling; Shou, Guo-fa; Zang, Yun-liang; Liu, Feng; Crozier, Stuart

    2014-01-01

    In this study, the effects of cardiac fibroblast proliferation on cardiac electric excitation conduction and mechanical contraction were investigated using a proposed integrated myocardial-fibroblastic electromechanical model. At the cellular level, models of the human ventricular myocyte and fibroblast were modified to incorporate a model of cardiac mechanical contraction and cooperativity mechanisms. Cellular electromechanical coupling was realized with a calcium buffer. At the tissue level, electrical excitation conduction was coupled to an elastic mechanics model in which the finite difference method (FDM) was used to solve electrical excitation equations, and the finite element method (FEM) was used to solve mechanics equations. The electromechanical properties of the proposed integrated model were investigated in one or two dimensions under normal and ischemic pathological conditions. Fibroblast proliferation slowed wave propagation, induced a conduction block, decreased strains in the fibroblast proliferous tissue, and increased dispersions in depolarization, repolarization, and action potential duration (APD). It also distorted the wave-front, leading to the initiation and maintenance of re-entry, and resulted in a sustained contraction in the proliferous areas. This study demonstrated the important role that fibroblast proliferation plays in modulating cardiac electromechanical behaviour and which should be considered in planning future heart-modeling studies. PMID:24599687

  12. Fibroblast proliferation alters cardiac excitation conduction and contraction: a computational study.

    PubMed

    Zhan, He-qing; Xia, Ling; Shou, Guo-fa; Zang, Yun-liang; Liu, Feng; Crozier, Stuart

    2014-03-01

    In this study, the effects of cardiac fibroblast proliferation on cardiac electric excitation conduction and mechanical contraction were investigated using a proposed integrated myocardial-fibroblastic electromechanical model. At the cellular level, models of the human ventricular myocyte and fibroblast were modified to incorporate a model of cardiac mechanical contraction and cooperativity mechanisms. Cellular electromechanical coupling was realized with a calcium buffer. At the tissue level, electrical excitation conduction was coupled to an elastic mechanics model in which the finite difference method (FDM) was used to solve electrical excitation equations, and the finite element method (FEM) was used to solve mechanics equations. The electromechanical properties of the proposed integrated model were investigated in one or two dimensions under normal and ischemic pathological conditions. Fibroblast proliferation slowed wave propagation, induced a conduction block, decreased strains in the fibroblast proliferous tissue, and increased dispersions in depolarization, repolarization, and action potential duration (APD). It also distorted the wave-front, leading to the initiation and maintenance of re-entry, and resulted in a sustained contraction in the proliferous areas. This study demonstrated the important role that fibroblast proliferation plays in modulating cardiac electromechanical behaviour and which should be considered in planning future heart-modeling studies.

  13. A comparative theoretical study on core-hole excitation spectra of azafullerene and its derivatives

    SciTech Connect

    Deng, Yunfeng; Gao, Bin; Deng, Mingsen; Luo, Yi

    2014-03-28

    The core-hole excitation spectra—near-edge x-ray absorption spectroscopy (NEXAFS), x-ray emission spectroscopy (XES), and x-ray photoelectron spectroscopy (XPS) shake-up satellites have been simulated at the level of density functional theory for the azafullerene C{sub 59}N and its derivatives (C{sub 59}N){sup +}, C{sub 59}HN, (C{sub 59}N){sub 2}, and C{sub 59}N–C{sub 60}, in which the XPS shake-up satellites were simulated using our developed equivalent core hole Kohn-Sham (ECH-KS) density functional theory approach [B. Gao, Z. Wu, and Y. Luo, J. Chem. Phys. 128, 234704 (2008)] which aims for the study of XPS shake-up satellites of large-scale molecules. Our calculated spectra are generally in good agreement with available experimental results that validates the use of the ECH-KS method in the present work. The nitrogen K-edge NEXAFS, XES, and XPS shake-up satellites spectra in general can be used as fingerprints to distinguish the azafullerene C{sub 59}N and its different derivatives. Meanwhile, different carbon K-edge spectra could also provide detailed information of (local) electronic structures of different molecules. In particular, a peak (at around 284.5 eV) in the carbon K-edge NEXAFS spectrum of the heterodimer C{sub 59}N–C{sub 60} is confirmed to be related to the electron transfer from the C{sub 59}N part to the C{sub 60} part in this charge-transfer complex.

  14. Isovector and isoscalar dipole excitations in 9Be and 10Be studied with antisymmetrized molecular dynamics

    NASA Astrophysics Data System (ADS)

    Kanada-En'yo, Yoshiko

    2016-02-01

    Isovector and isoscalar dipole excitations in 9Be and 10Be are investigated in the framework of antisymmetrized molecular dynamics, in which angular-momentum and parity projections are performed. In the present method, 1p-1h excitation modes built on the ground state and a large amplitude α -cluster mode are taken into account. The isovector giant dipole resonance (GDR) in E >20 MeV shows the two-peak structure, which is understood from the dipole excitation in the 2 α core part with the prolate deformation. Because of valence neutron modes against the 2 α core, low-energy E 1 resonances appear in E <20 MeV, exhausting about 20 % of the Thomas-Reiche-Kuhn sum rule and 10 % of the calculated energy-weighted sum. The dipole resonance at E ˜15 MeV in 10Be can be interpreted as the parity partner of the ground state having a 6He+α structure and has remarkable E 1 strength because of the coherent contribution of two valence neutrons. The isoscalar dipole strength for some low-energy resonances is significantly enhanced by the coupling with the α -cluster mode. For the E 1 strength of 9Be, the calculation overestimates the energy-weighted sum (EWS) in the low-energy (E <20 MeV) and GDR (20

  15. Study of Boundary Structures.

    DTIC Science & Technology

    1982-09-01

    THEORY OF ABC-CBA STACKING BOUNDARY IN fcc STRUCTURE .......... 11 - 4 TRANSITIONS AND PHASE EQUILIBRIA AMONG GRAIN BOUNDARY STRUCTURES...19 B THEORY OF ABC-CBA STACKING BOUNDARY IN fcc STRUCTURE .......... 37 C TRANSITIONS AND PHASE EQUILIBRIA AMONG GRAIN BOUNDARY...layer structure. 10 SECTION 3 THEORY OF ABC-CBA STACKING BOUNDARY IN fcc STRUCTURE The (111) planes of the fcc structure is stacked as ABCABC... as

  16. Spin-wave excitations induced by spin current in spin-valve structures

    NASA Astrophysics Data System (ADS)

    Liu, Haoliang; Sun, Dali; Zhang, Chuang; Groesbeck, Matthew; Vardeny, Zeev Valy; Department of Physics; Astronomy, University of Utah, Salt Lake City, Utah 84112, USA Team

    2016-03-01

    We have investigated the magnetization dynamics of NiFe/Pt/Co spin-valve structures with different Pt layer thickness, using a broadband ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) at ambient temperature. We found that the Gilbert damping factor, α of the two ferromagnetic (FM) layer films in the spin-valve structure are significantly larger than α of each individual FM layer. We interpret the increase in α in the spin-valve configuration as due to an interaction between the FM layers mediated by the induced spin current through the Pt interlayer when FMR conditions are met for one of the FM. This was verified by BLS of the spin-valve structure, in which the magnons density in the adjacent FM layer is enhanced upon FMR of the other FM layer. We have studied this spin-current-mediated interaction as a function of the Pt interlayer. Work supported by the MURI-AFOSR Grant FA9550-14-1-0037, and the UofU facility center supported by NSF-MRSEC Grant DMR-1121252.

  17. Density functional investigation of the electronic structure and charge transfer excited states of a multichromophoric antenna

    NASA Astrophysics Data System (ADS)

    Basurto, Luis; Zope, Rajendra R.; Baruah, Tunna

    2016-05-01

    We report an electronic structure study of a multichromophoric molecular complex containing two of each borondipyrromethane dye, Zn-tetraphenyl-porphyrin, bisphenyl anthracene and a fullerene. The snowflake shaped molecule behaves like an antenna capturing photon at different frequencies and transferring the photon energy to the porphyrin where electron transfer occurs from the porphyrin to the fullerene. The study is performed within density functional formalism using large polarized Guassian basis sets (12,478 basis functions in total). The energies of the HOMO and LUMO states in the complex, as adjudged by the ionization potential and the electron affinity values, show significant differences with respect to their values in participating subunits in isolation. These differences are also larger than the variations of the ionization potential and electron affinity values observed in non-bonded C60-ZnTPP complexes in co-facial arrangement or end-on orientations. An understanding of the origin of these differences is obtained by a systematic study of the effect of structural strain, the presence of ligands, the effect of orbital delocalization on the ionization energy and the electron affinity. Finally, a few lowest charge transfer energies involving electronic transitions from the porphyrin component to the fullerene subunit of the complex are predicted.

  18. The Study Of Excited States In 12N With Radioactive Ion Beams From BEARS

    NASA Astrophysics Data System (ADS)

    Galindo-Uribarri, A.; Gomez Del Campo, J.; Larochelle, Y.; Liang, F.; Shapira, D.; Varner, R.; Wiescher, M. C.; Powell, J.; Cerny, J.; McMahan, M. A.; O'Neil, J. P.

    2003-03-01

    Radioactive ion beams of 55 MeV 11C from the BEARS project at LBNL and a thick-target technique were used to study resonant states in 12N. With a reaction in inverse kinematics an excitation function of elastic scattering cross section was measured in a single exposure covering the center of mass energy range between 300 keV to 1100 keV. The elastic scattering reaction 11C(p,p)11C is related to the reaction 11C(p,γ)12N, an important branch point in the hot pp chains and a determinant of the evolution of supermassive stars. The data was analyzed using the R-matrix code MULTI. Preliminary results suggests that the first excited state in 12N (0.96 MeV) might play a more important role in determining the 11C(p,γ)12N reaction rate than previously believed.

  19. Vacuum ultraviolet resonance Raman studies of the excited electronic states of ethylene

    NASA Astrophysics Data System (ADS)

    Sension, Roseanne J.; Hudson, Bruce S.

    1989-02-01

    A resonance Raman study of ethylene has been performed with the use of excitation wavelengths ranging from 200 to 141 nm. Excitation resonant with the V(pi pi -asterisk) state results in Raman spectra exhibiting intensity in the C = C stretching vibration, the CH2 symmetric scissors vibration, the CH2 torsional vibration and the CH2 out-of-plane wagging vibrations. These spectra confirm that the V state is strongly twisted about the C-C bond. They also indicate that the C = CH2 groups are no longer planar in the V state. The spectrum obtained in resonance with the (pi 3d) Rydberg transitions once again exhibits activity in the CH2 symmetric scissors mode.

  20. Ab initio study of phonon-induced dephasing of plasmon excitations in silver quantum dots

    NASA Astrophysics Data System (ADS)

    Guo, Zhenyu; Habenicht, Bradley F.; Liang, Wan-Zhen; Prezhdo, Oleg V.

    2010-03-01

    Phonon-induced pure dephasing of electronic excitations in silver quantum dots (QDs) is investigated with ab initio molecular dynamics at ambient and low temperatures. Three types of electronic states are studied corresponding to bulk, surface, and plasmon excitations. The electron-phonon coupling is strongest for bulk states and decreases for surface and plasmon states. The plasmon states dephase within 30-40 fs, which is consistent with the recent experiments [M. Z. Liu, M. Pelton, and P. Guyot-Sionnest, Phys. Rev. B 79, 035418 (2009)]. The dephasing time shows weak dependence on the QD size but changes significantly with temperature. The bulk, surface, and plasmon states couple primarily to low-frequency acoustic phonons.

  1. Study of isospin violating phi excitation in e+e- → ωπ0

    NASA Astrophysics Data System (ADS)

    Li, Gang; Zhang, Yuan-Jiang; Zhao, Qiang

    2009-08-01

    We study the reaction e+e- → ωπ0 in the vicinity of the phi mass region. The isospin-violating phi excitation is accounted for by two major mechanisms. One is electromagnetic transition and the other is strong isospin violations. For the latter, we consider contributions from the intermediate hadronic meson loops and phi-ρ0 mixing as the major mechanisms via the t- and s-channel transitions, respectively. By fitting the recent KLOE data, we succeed in constraining the model parameters and extracting the phi → ωπ0 branching ratio. It shows that the branching ratio is sensitive to the phi excitation line shape and background contributions. Some crucial insights into the correlation between isospin violation and Okubo-Zweig-Iizuka rule evading transitions are also learned.

  2. Study of the12C excited states above the Hoyle State.

    NASA Astrophysics Data System (ADS)

    López-Saavedra, E.; Acosta, L.; Araujo, V.; Favela, F.; Huerta, A.; Aspiazu, J.; Murillo, G.; Policroniades, R.; Santa Rita, P.; Varela, A.; Chávez, E.

    2017-07-01

    In this work we study the low-lying excited states of12C, especially above the Hoyle state (0+, 7,654 MeV) through the use of the14N(d,α)12C reaction. The EN-Tandem at ININ delivered deuteron beams between 2.5 and 7.5 MeV. Typical beam intensities were 20-50 nA. Two different compounds were used to produce thin films: Si3N4 (150 nm) and of C5H5N5 (10 μm). Angular distributions of emitted α-particles were measured at each energy. The first results of the analysis are presented including quantum number assignments (energy, spin and parity) of the excited states populated.

  3. Adducing crystalline features from Raman scattering studies of cubic SiC using different excitation wavelengths

    NASA Astrophysics Data System (ADS)

    Chen, Shuai; Wan, Lingyu; Xie, Deng; Qiu, Zhi Ren; Jiang, Xiaodong; Tin, Chin-Che; Feng, Zhe Chuan

    2017-03-01

    A series of cubic 3C–SiC/Si samples with different thicknesses grown by chemical vapor deposition (CVD) was studied by Raman spectroscopy using laser excitation with different wavelengths plus spectral line shape analysis via two theoretical methods. Through comparative UV and visible excitation Raman measurements and theoretical analysis, the TO intensity was mainly affected by laser penetration depth and crystalline quality. The difference spectra were utilized to remove the second-order Raman signal from Si substrate. Using theoretical Raman simulation on LO-phonon and plasmon-coupling (LOPC) mode, the top layer near to the surface has big difference in electrical and optical properties compared to the deeper layer.

  4. TD-DFT and DFT/MRCI study of electronic excitations in Violaxanthin and Zeaxanthin

    NASA Astrophysics Data System (ADS)

    Götze, Jan Philipp; Thiel, Walter

    2013-03-01

    We report vibrationally broadened Franck-Condon (FC) spectra of Violaxanthin (Vx) and Zeaxanthin (Zx) for the lowest-energy 1Ag → 1Bu band that arises from the bright HOMO → LUMO single-electron excitation. Geometries were optimized using standard (1Ag) and time-dependent (1Bu) density functional theory (DFT) at the (TD-)CAM-B3LYP/6-31G(d) level, both in the gas phase and in acetone using a polarizable continuum model (PCM). DFT/MRCI multireference calculations were performed at the optimized (TD)-CAM-B3LYP structures to evaluate the energies of doubly excited states that are not accessible to linear response TD-DFT theory. The FC spectra were calculated using the time-independent (TI) scheme. The calculated spectra of Vx and Zx are very similar, with a red shift of about 0.1 eV for Zx relative to Vx, which is in agreement with the experimental data. The predicted spectral peaks of Vx and Zx deviate from experiment by less than 0.1 eV when performing the calculations in the gas phase. In the presence of acetone (PCM model), there are larger deviations so that a state specific correction scheme needs to be applied, which accounts for non-equilibrium solvent relaxation. The 1Ag → 1Bu vertical absorption energies and the corresponding vertical fluorescence energies from TD-CAM-B3LYP and DFT/MRCI agree reasonably well. The DFT/MRCI absorption and fluorescence energies for the doubly excited 2Ag and 2Bu states are found to be rather sensitive to the underlying geometry, in particular to the bond length alternation in the polyene chain. In acetone (PCM), Vx and Zx show little bond alternation, and thus the doubly excited Bu state becomes the lowest excited Bu state. (TD)-CAM-B3LYP appears to be suitable for generating realistic geometries for higher-level calculations in such molecules.

  5. Structural redundancy of dual and steel moment frame systems under seismic excitation

    NASA Astrophysics Data System (ADS)

    Song, Seung-Han

    The extensive investigation of structural failure after Northridge earthquake showed poor structural performance due to brittle member behavior and improper design. For example, the brittle steel connection fractures were totally unexpected of the highly regarded "ductile" systems. The lack of system ductile capacity and redundancy could lead to system instability and collapse. Since then, the design for redundancy has become a serious concern of both researchers and practitioners. Most reliability and redundancy studies in the past, however, have been limited to ideal simple systems. Structural redundancy under stochastic loads such as earthquakes has not been thoroughly investigated and hence not well understood or clearly defined, which could lead to misunderstandings and confusions among structural engineers. In this study, the redundancy of five-story and ten-story one-way and two-way dual systems of RC shear walls and three-story and nine-story special moment resisting frames (SMRF) is investigated in terms of system reliability. Major factors affecting redundancy considered include structural configuration (number of bays in lateral load resistance system, number and layout of shear walls, and so on), ductility capacity, uncertainty and correlation of shear wall strength. The redundancy of truly ductile SMRF systems of different configurations is also examined. A 4 x 4 bay and a 6 x 6 bay buildings of the same floor area but different numbers and sizes of beams and columns are designed and analyzed. In addition, three SMRF, 1 x 1, 2 x 2, and 3 x 3 bay systems, with torsion are investigated to examine the effect of ductile and brittle beam-column connection behaviors. The proposed uniform-risk redundancy factor is then compared with the reliability and redundancy factor (rho) in the 1996 SEAOC Blue Book, NEHRP 97, and UBC 97, which depends on the system configuration only. The results show the inadequacies of the latter approach in describing the redundancy

  6. Non-typical fluorescence studies of excited and ground state proton and hydrogen transfer

    NASA Astrophysics Data System (ADS)

    Gil, Michał; Kijak, Michał; Piwoński, Hubert; Herbich, Jerzy; Waluk, Jacek

    2017-03-01

    Fluorescence studies of tautomerization have been carried out for various systems that exhibit single and double proton or hydrogen translocation in various environments, such as liquid and solid condensed phases, ultracold supersonic jets, and finally, polymer matrices with single emitters. We focus on less explored areas of application of fluorescence for tautomerization studies, using porphycene, a porphyrin isomer, as an example. Fluorescence anisotropy techniques allow investigations of self-exchange reactions, where the reactant and product are formally identical. Excitation with polarized light makes it possible to monitor tautomerization in single molecules and to detect their three-dimensional orientation. Analysis of fluorescence from single vibronic levels of jet-isolated porphycene not only demonstrates coherent tunneling of two internal protons, but also indicates that the process is vibrational mode-specific. Next, we present bifunctional proton donor-acceptor systems, molecules that are able, depending on the environment, to undergo excited state single intramolecular or double intermolecular proton transfer. For molecules that have donor and acceptor groups located in separate moieties linked by a single bond, excited state tautomerization can be coupled to mutual twisting of the two subunits.

  7. New Zealand rugby health study: motor cortex excitability in retired elite and community level rugby players.

    PubMed

    Lewis, Gwyn N; Hume, Patria A; Stavric, Verna; Brown, Scott R; Taylor, Denise

    2017-01-13

    Rugby union is a high contact sport in which players frequently experience brain injuries. Acute brain injury is associated with altered corticomotor function. However, it is uncertain if long-term exposure to rugby is associated with any alterations in corticomotor function. The aim of the study was to assess measures of corticomotor excitability and inhibition in retired rugby players in comparison to retired non-contact sport players. The design was a cross-sectional study with three groups of retired athletes: elite rugby (n=23), community level rugby (n=28) and non-contact sport control (n=22). Assessments of corticomotor excitability were made using transcranial magnetic stimulation. Resting motor threshold was significantly higher and long-interval intracortical inhibition was greater in the elite rugby group compared to the control group. Participants in the two rugby groups had sustained significantly more concussions than the control group. We provide some evidence of altered corticomotor excitation and inhibition in retired elite rugby players in comparison to retired non-contact sport players. Given the absence of findings in the community rugby group, who had experienced a similar number of concussions, the association with previous brain injury is unclear.

  8. Ultrafast-electron-diffraction studies of predamaged tungsten excited by femtosecond optical pulses

    NASA Astrophysics Data System (ADS)

    Mo, M.; Chen, Z.; Li, R.; Wang, Y.; Shen, X.; Dunning, M.; Weathersby, S.; Makasyuk, I.; Coffee, R.; Zhen, Q.; Kim, J.; Reid, A.; Jobe, K.; Hast, C.; Tsui, Y.; Wang, X.; Glenzer, S.

    2016-10-01

    Tungsten is considered as the main candidate material for use in the divertor of magnetic confinement fusion reactors. However, radiation damage is expected to occur because of its direct exposure to the high flux of hot plasma and energetic neutrons in fusion environment. Hence, understanding the material behaviors of W under these adverse conditions is central to the design of magnetic fusion reactors. To do that, we have recently developed an MeV ultrafast electron diffraction probe to resolve the structural evolution of optically excited tungsten. To simulate the radiation damage effect, the tungsten samples were bombarded with 500 keV Cu ions. The pre-damaged and pristine W's were excited by 130fs, 400nm laser pulses, and the subsequent heated system was probed with 3.2MeV electrons. The pump probe measurement shows that the ion bombardment to the W leads to larger decay in Bragg peak intensities as compared to pristine W, which may be due to a phonon softening effect. The measurement also shows that pre-damaged W transitions into complete liquid phase for conditions where pristine W stays solid. Our new capability is able to test the theories of structural dynamics of W under conditions relevant to fusion reactor environment. The research was funded by DOE Fusion Energy Science under FWP #100182.

  9. Time-resolved x-ray excited optical luminescence studies of II-VI semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Rosenberg, R. A.; Lee, S.-T.; Kim, P.-S. G.

    2005-03-01

    Due to quantum confinement effects nanostructures often exhibit unique and intriguing fluorescence behavior. X-ray excited optical luminescence (XEOL) provides the capability to chemically map the sites responsible for producing low energy (1-6 eV) fluorescence. By taking advantage of the time structure of the x-ray pulses at the Advanced Photon Source, it also possible to determine the dynamic behavior of the states involved in the luminescence. In this presentation we show how this technique can be utilized to understand the XEOL from ZnS, ZnTe, and ZnO nanowires. Time-gated optical spectra show that the high-energy, band-edge states have a short lifetime while the lower-energy, deep-levels have a relatively long lifetime. X-ray excitation curves are obtained using the relevant optical photons as signals and compared to the corresponding x-ray absorption spectra. We will show how these results enable us to determine the local structure of the luminescent site(s).

  10. Development of collective structures over noncollective excitations in {sup 139}Nd

    SciTech Connect

    Bhowal, S.; Gangopadhyay, G.; Petrache, C. M.; Ragnarsson, I.; Singh, A. K.; Bhattacharya, S.; Huebel, H.; Neusser-Neffgen, A.; Al-Khatib, A.; Bringel, P.; Buerger, A.; Nenoff, N.; Schoenwasser, G.; Hagemann, G. B.; Herskind, B.; Jensen, D. R.; Sletten, G.; Fallon, P.; Goergen, A.; Bednarczyk, P.

    2011-08-15

    High-spin states in {sup 139}Nd were investigated using the reaction {sup 96}Zr({sup 48}Ca,5n) at a beam energy of 195 MeV and {gamma}-ray coincidences were acquired with the Euroball spectrometer. Apart from several dipole bands at medium excitation energy, three quadrupole bands have been observed at high spin. Linking transitions connecting two of the high-spin bands to low-energy states have been observed. Calculations based on the cranked-Nilsson-Strutinsky formalism have been used to assign configurations for the high-spin quadrupole bands.

  11. Structure and spectroscopy of ground and excited states of LiYb.

    PubMed

    Zhang, P; Sadeghpour, H R; Dalgarno, A

    2010-07-28

    Multireference configuration interaction and coupled cluster calculations have been carried out to determine the potential energy curves for the ground and low-lying excited states of the LiYb molecule. The scalar relativistic effects have been included by means of the Douglas-Kroll Hamiltonian and effective core potential and the spin-orbit couplings have been evaluated by the full microscopic Breit-Pauli operator. The LiYb permanent dipole moment, static dipole polarizability, and Franck-Condon factors have been determined. Perturbations of the vibrational spectrum due to nonadiabatic interactions are discussed.

  12. The excitability of the trigeminal motor system in sleep bruxism: a transcranial magnetic stimulation and brainstem reflex study.

    PubMed

    Gastaldo, Ernesto; Quatrale, Rocco; Graziani, Alessandro; Eleopra, Roberto; Tugnoli, Valeria; Tola, Maria Rosaria; Granieri, Enrico

    2006-01-01

    Since sleep bruxism (SB) is characterized by grinding and clenching of the teeth during sleep and could be an exaggerated manifestation of normal spontaneous rhythmic masticatory muscle activity, the aim of this study was to obtain a neurophysiological assessment of the excitability of the central jaw motor pathways in patients with signs and symptoms suggestive of SB. A total of 30 subjects diagnosed with SB on the basis of self-report of tooth grinding were studied using the "recovery cycle" of the masseter inhibitory reflex (MIR) elicited by electric and magnetic stimulation of the mental nerves and by recording the motor potentials evoked in masseter muscles by transcranial magnetic stimulation. Tests were done during daytime, when the subjects were awake. The data obtained were compared with data from a population of normal subjects. In the putative SB patients and in normal subjects, the MIRs evoked by single electric and magnetic stimuli were similar. With paired stimuli, the degree of suppression of the late silent period was significantly lower (P < .01) in the patients compared to normal subjects, particularly for magnetic stimuli, at various interstimulus intervals. No significant differences were found between the 2 groups of subjects in the masseter motor potentials evoked by transcranial magnetic stimulation. Although the data were only obtained during wakefulness in patients self-reporting signs and symptoms suggestive of SB, the findings suggest that an abnormal excitability of the central jaw motor pathways may be present in SB subjects. This increased excitability could derive from an impaired modulation of brainstem inhibitory circuits and not from altered cortical mechanisms. These results support the view that bruxism is mainly centrally mediated and that it involves subcortical structures. The study also indicates that use of the MIR elicited by the double-shock technique could be valuable in the evaluation of bruxism.

  13. The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

    NASA Astrophysics Data System (ADS)

    Trachsel, Maria A.; Wiedmer, Timo; Blaser, Susan; Frey, Hans-Martin; Li, Quansong; Ruiz-Barragan, Sergi; Blancafort, Lluís; Leutwyler, Samuel

    2016-10-01

    We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm-1 about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion and ν1 ' (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ˜ 500 cm-1, indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm-1. The S1⇝S0 internal conversion rate constant increases from kIC = 2 ṡ 109 s-1 near the S1(v = 0) level to 1 ṡ 1011 s-1 at Eexc = 516 cm-1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm-1. The ISC rate constant is 10-100 times lower than kIC; it increases from kISC = 2 ṡ 108 s-1 near S1(v = 0) to kISC = 2 ṡ 109 s-1 at Eexc = 516 cm-1. The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm-1. The T2 (3nπ∗) state lies >1500 cm-1 above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm-1. An upper limit to the adiabatic ionization energy of 1MCyt is determined as 8.41 ± 0.02 e

  14. The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine.

    PubMed

    Trachsel, Maria A; Wiedmer, Timo; Blaser, Susan; Frey, Hans-Martin; Li, Quansong; Ruiz-Barragan, Sergi; Blancafort, Lluís; Leutwyler, Samuel

    2016-10-07

    We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm(-1) about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon (1)ππ(∗) excitation predicted by the calculations. The methyl torsion and ν1(') (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ∼ 500 cm(-1), indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm(-1). The S1⇝S0 internal conversion rate constant increases from kIC = 2 ⋅ 10(9) s(-1) near the S1(v = 0) level to 1 ⋅ 10(11) s(-1) at Eexc = 516 cm(-1). The (1)ππ(∗) state of 1MCyt also relaxes into the lower-lying triplet T1 ((3)ππ(∗)) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm(-1). The ISC rate constant is 10-100 times lower than kIC; it increases from kISC = 2 ⋅ 10(8) s(-1) near S1(v = 0) to kISC = 2 ⋅ 10(9) s(-1) at Eexc = 516 cm(-1). The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm(-1). The T2 ((3)nπ(∗)) state lies >1500 cm(-1) above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm(-1). An upper limit to the adiabatic

  15. Study of mixed-symmetry excitations in 96Ru via inelastic proton-scattering

    NASA Astrophysics Data System (ADS)

    Hennig, A.; Spieker, M.; Werner, V.; Ahn, T.; Anagnostatou, V.; Cooper, N.; Derya, V.; Elvers, M.; Endres, J.; Goddard, P.; Heinz, A.; Hughes, R. O.; Ilie, G.; Mineva, M. N.; Pickstone, S. G.; Petkov, P.; Radeck, D.; Ross, T.; Savran, D.; Zilges, A.

    2015-02-01

    Mixed-symmetry states of octupole (L = 3) and hexadecapole (L = 4) character have been recently proposed in the N = 52 isotones 92 Zr and 94Mo, based on strong M1 transitions to the lowest-lying 3- and 4+ states, respectively. In order to investigate similar excitations in the heaviest stable N = 52 isotone 96Ru, two inelastic proton-scattering experiments have been performed at the Wright Nuclear Structure Laboratory (WNSL), Yale University, USA and the Institute for Nuclear Physics, University of Cologne, Germany. From the combined data of both experiments, absolute E1, M1, and E2 transition strengths were extracted, allowing for the identification of candidates for MS octupole and hexadecapole states. The structure of the low-lying 4+ states is investigated by means of sdg-IBM-2 calculations.

  16. The influence of heat excitations, vacancies and impurities on the energy electronic band-structure of metallic lithium

    SciTech Connect

    Popov, V.A.

    1999-07-01

    The Korringa-Kohn-Rostoker method with Green's function averaged over the atomic configurations in a complex Ising lattice and a muffin-tin potential was used to calculate the electronic-band structure in lithium containing vacancies and s, p, and d impurities. It is shown that substantial changes in the profile of the Fermi surface do not lead to necking, as was postulated previously, but cause splitting of the electronic states at the face of the Brillouin zone. This is attributed to the reduced symmetry of the crystal lattice with impurity excitation of the electronic-subsystem.

  17. Classification of the nonlinear dynamics and bifurcation structure of ultrasound contrast agents excited at higher multiples of their resonance frequency

    NASA Astrophysics Data System (ADS)

    Sojahrood, Amin Jafari; Kolios, Michael C.

    2012-07-01

    Through numerical simulation of the Hoff model we show that when ultrasound contrast agents (UCAs) are excited at frequencies which are close to integer (m>2) multiples of their natural resonance frequency, the bifurcation structure of the UCA oscillations as a function of pressure may be characterized by 3 general distinct regions. The UCA behavior starts with initial period one oscillations which undergoes a saddle node bifurcation to m coexisting attractors for an acoustic pressure above a threshold, P. Further increasing the pressure above a second threshold P, is followed by a sudden transition to period 1 oscillations.

  18. In situ studies of nanoscale electromechanical behavior of nacre under flexural stresses using band excitation PFM.

    PubMed

    Li, Tao; Chen, Lei; Zeng, Kaiyang

    2013-04-01

    In this paper, we have studied the electromechanical coupling behaviors of nacre under non-destructive flexural stresses. Band excitation piezoresponse force microscopy is used as the primary tool to characterize the piezoelectric properties of nacre. This method can differentiate various constituents in nacre at the nanoscale and track their in situ responses under tensile and compressive stresses. The local ferroelectric hysteresis behaviors of nacre are also studied. Based on the hysteresis loops observed under different stress states, various phenomena, including the stress-induced internal field and energy loss, are revealed in this study.

  19. Magnetic field control and wavelength tunability of SPP excitations using Al2O3/SiO2/Fe structures

    NASA Astrophysics Data System (ADS)

    Kaihara, Terunori; Shimizu, Hiromasa; Cebollada, Alfonso; Armelles, Gaspar

    2016-09-01

    Here, we show the high wavelength tunability and magnetic field modulation of surface plasmon polaritons (SPPs) of a waveguide mode that Double-layer Dielectrics and Ferromagnetic Metal, Al2O3/SiO2/Fe, trilayer structures exhibit when excited in the Otto configuration of attenuated total reflection setup. First by modeling, and then experimentally, we demonstrate that it is possible to tune the wavelength at which the angular dependent reflectance of these structures reaches its absolute minimum by simply adjusting the SiO2 intermediate dielectric layer thickness. This precise wavelength corresponds to the cut-off condition of SPPs' waveguide mode supported by the proposed structure, and it can be then switched between two values upon magnetization reversal of the Fe layer. In this specific situation, a large enhancement of the transverse magneto-optical effect is also obtained.

  20. Effects of electronic and nuclear interactions on the excited-state properties and structural dynamics of copper(I) diimine complexes.

    PubMed

    Mara, Michael W; Jackson, Nicholas E; Huang, Jier; Stickrath, Andrew B; Zhang, Xiaoyi; Gothard, Nosheen A; Ratner, Mark A; Chen, Lin X

    2013-02-14

    The effects of structural constraints on the metal-to-ligand charge transfer (MLCT) excited state structural dynamics of cuprous bis-2,9-diphenyl-phenanthroline ([Cu(I)(dpp)(2)](+)) in both coordinating acetonitrile and noncoordinating toluene were studied using X-ray transient absorption (XTA) spectroscopy and density functional theory (DFT) calculations. The phenyl groups attached to the phenanthroline ligands not only effectively shield the Cu(I) center from solvent molecules, but also force a flattened tetrahedral coordination geometry of the Cu(I) center. Consequently, the MLCT state lifetime in [Cu(I)(dpp)(2)](+) is solvent-independent, unlike the previously studied 2,9-methyl substituted bis-phenanthroline Cu(I) complex. The MLCT state of [Cu(I)(dpp)(2)](+) still undergoes a "pseudo Jahn-Teller distortion," with the angle between the two phenanthroline ligand planes decreased further by 7°. The XTA results indicate that, in the MLCT excited state of [Cu(I)(dpp)(2)](+), the phenyls at the 2, 9 positions of the phenanthroline rotate, breaking the π-π interaction with the phenanthroline ligands without ever rotating in-plane with the phenanthroline ligands. Hence, the transferred electron density from the Cu(I) center is localized on the phenanthroline moiety with no charge density present on the phenyl rings. The insight about the effect of the structural constraints on the MLCT state properties will guide the design of Cu(I) diimine complexes with suitable excited-state properties to function as earth-abundant dye sensitizers for solar electricity generation.

  1. Ultrafast Excited-State Dynamics of 6-Azauracil Studied by Femtosecond Transient Absorption Spectroscopy.

    PubMed

    Hua, XinZhong; Hua, LinQiang; Liu, XiaoJun

    2015-12-31

    The excited-state dynamics of 6-azauracil in different solvents have been studied using femtosecond transient absorption spectroscopy. The molecule is populated to the S2 state with a pump pulse at 264 nm. Broad-band white light continuum which covers from 320 to 600 nm is used as the probe. With a global fitting analysis of the measured transient spectra, three decay time constants, i.e., <0.3, 5.2 ± 0.1, and >1000 ps, are directly obtained in the solvent of acetonitrile. These newly observed lifetime constants are important in clarifying its decay dynamics as well as in providing a criterion for the ultrafast dynamics simulations in 6-azauracil using quantum chemical theories. In combination with previous theoretical works, the main decay channel is proposed: the initially populated S2 decays to S1 through internal conversion in <0.3 ps, followed by an intersystem crossing from S1 to T1 in 5.2 ± 0.1 ps. The >1000 ps component is due to the decay of the T1 state. A comparison of the excited-state dynamics in different solvents reveals that the decay from S1 to T1 shows a clear dependence on the polarity of the solvents. With higher polarity, the S1 excited state decays faster. This observation is in line with the prediction by Etinski et al. [ Phys. Chem. Chem. Phys. 2010 , 12 , 15665 - 15671 ], where a blue-shift of the T1 state potential energy surface leading to an increase of the intersystem crossing rate was proposed. With the new information obtained in the present measurement, a clearer picture of the decay dynamics of 6-azauracil on the S2 excited state is provided.

  2. A relativistic time-dependent density functional study of the excited states of the mercury dimer

    SciTech Connect

    Kullie, Ossama E-mail: ossama.kullie@unistra.fr

    2014-01-14

    In previous works on Zn{sub 2} and Cd{sub 2} dimers we found that the long-range corrected CAMB3LYP gives better results than other density functional approximations for the excited states, especially in the asymptotic region. In this paper, we use it to present a time-dependent density functional (TDDFT) study for the ground-state as well as the excited states corresponding to the (6s{sup 2} + 6s6p), (6s{sup 2} + 6s7s), and (6s{sup 2} + 6s7p) atomic asymptotes for the mercury dimer Hg{sub 2}. We analyze its spectrum obtained from all-electron calculations performed with the relativistic Dirac-Coulomb and relativistic spinfree Hamiltonian as implemented in DIRAC-PACKAGE. A comparison with the literature is given as far as available. Our result is excellent for the most of the lower excited states and very encouraging for the higher excited states, it shows generally good agreements with experimental results and outperforms other theoretical results. This enables us to give a detailed analysis of the spectrum of the Hg{sub 2} including a comparative analysis with the lighter dimers of the group 12, Cd{sub 2}, and Zn{sub 2}, especially for the relativistic effects, the spin-orbit interaction, and the performance of CAMB3LYP and is enlightened for similar systems. The result shows, as expected, that spinfree Hamiltonian is less efficient than Dirac-Coulomb Hamiltonian for systems containing heavy elements such as Hg{sub 2}.

  3. X-ray luminescence computed tomography via selective excitation: a feasibility study.

    PubMed

    Pratx, Guillem; Carpenter, Colin M; Sun, Conroy; Xing, Lei

    2010-12-01

    X-ray luminescence computed tomography (XLCT) is proposed as a new molecular imaging modality based on the selective excitation and optical detection of X-ray-excitable phosphor nanoparticles. These nano-sized particles can be fabricated to emit near-infrared (NIR) light when excited with X-rays, and, because because both X-rays and NIR photons propagate long distances in tissue, they are particularly well suited for in vivo biomedical imaging. In XLCT, tomographic images are generated by irradiating the subject using a sequence of programmed X-ray beams, while sensitive photo-detectors measure the light diffusing out of the subject. By restricting the X-ray excitation to a single, narrow beam of radiation, the origin of the optical photons can be inferred regardless of where these photons were detected, and how many times they scattered in tissue. This study presents computer simulations exploring the feasibility of imaging small objects with XLCT, such as research animals. The accumulation of 50 nm phosphor nanoparticles in a 2-mm-diameter target can be detected and quantified with subpicomolar sensitivity using less than 1 cGy of radiation dose. Provided sufficient signal-to-noise ratio, the spatial resolution of the system can be made as high as needed by narrowing the beam aperture. In particular, 1 mm spatial resolution was achieved for a 1-mm-wide X-ray beam. By including an X-ray detector in the system, anatomical imaging is performed simultaneously with molecular imaging via standard X-ray computed tomography (CT). The molecular and anatomical images are spatially and temporally co-registered, and, if a single-pixel X-ray detector is used, t