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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. 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.

  3. 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

  4. Structure of low-lying states in 140Sm studied by Coulomb excitation

    NASA Astrophysics Data System (ADS)

    Klintefjord, M.; Hadyńska-KlÈ©k, K.; Görgen, A.; Bauer, C.; Bello Garrote, F. L.; Bönig, S.; Bounthong, B.; Damyanova, A.; Delaroche, J.-P.; Fedosseev, V.; Fink, D. A.; Giacoppo, F.; Girod, M.; Hoff, P.; Imai, N.; Korten, W.; Larsen, A.-C.; Libert, J.; Lutter, R.; Marsh, B. A.; Molkanov, P. L.; Naïdja, H.; Napiorkowski, P.; Nowacki, F.; Pakarinen, J.; Rapisarda, E.; Reiter, P.; Renstrøm, T.; Rothe, S.; Seliverstov, M. D.; Siebeck, B.; Siem, S.; Srebrny, J.; Stora, T.; Thöle, P.; Tornyi, T. G.; Tveten, G. M.; Van Duppen, P.; Vermeulen, M. J.; Voulot, D.; Warr, N.; Wenander, F.; De Witte, H.; Zielińska, M.

    2016-05-01

    The electromagnetic structure of 140Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 21+ state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that 140Sm shows considerable γ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region.

  5. 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.

  6. Excited-state structure of oligothiophene dendrimers: computational and experimental study.

    PubMed

    Badaeva, Ekaterina; Harpham, Michael R; Guda, Ramakrishna; Süzer, Özgün; Ma, Chang-Qi; Bäuerle, Peter; Goodson, Theodore; Tretiak, Sergei

    2010-12-01

    The nature of one and two-photon absorption enhancement in a series of oligothiophene dendrimers, recently proposed for applications in entangled photon sensors and solar cells, has been analyzed using both theory (time dependent density functional theory calculations) and experiment (fluorescence upconversion measurements). The linear absorption spectra exhibit a red shift of the absorption maxima and broadening as a function of dendrimer generations. The two-photon absorption cross sections increase sharply with the number of thiophene units in the dendrimer. The cooperative enhancement in absorption two-photon cross sections is explained by (i) an increase in the excited-state density for larger molecules and (ii) delocalization of the low-lying excited states over extended thiophene chains. Fluorescence anisotropy measurements and examination of the calculated excited-state properties reveal that this delocalization is accompanied by a size-dependent decrease in excited-state symmetries. A substantial red shift of the emission maxima for larger dendrimers is explained through the vibronic planarization of the longest linear α-thiophene chain for the emitting excited state. For higher generations, the fluorescence quantum yield decreases due to increased nonradiative decay efficiency (e.g., intersystem crossing). The detailed information about the dendrimer 3D structure and excitations provides guidance for further optimizations of dendritic structures for nonlinear optical and opto-electronic applications. PMID:21077602

  7. A search for manifestation of two types of collective excitations in dynamic structure of a liquid metal: Ab initio study of collective excitations in liquid Na.

    PubMed

    Bryk, Taras; Wax, J-F

    2016-05-21

    Using a combination of ab initio molecular dynamics and several fit models for dynamic structure of liquid metals, we explore an issue of possible manifestation of non-acoustic collective excitations in longitudinal dynamics having liquid Na as a case study. A model with two damped harmonic oscillators (DHOs) in time domain is used for analysis of the density-density time correlation functions. Another similar model with two propagating contributions and three lowest exact sum rules is considered, as well as an extended hydrodynamic model known as thermo-viscoelastic one which permits two types of propagating modes outside the hydrodynamic region to be used for comparison with ab initio obtained time correlation functions and calculations of dispersions of collective excitations. Our results do not support recent suggestions that, even in simple liquid metals, non-hydrodynamics transverse excitations contribute to the longitudinal collective dynamics and can be detected as a DHO-like spectral shape at their transverse frequency. We found that the thermo-viscoelastic dynamic model permits perfect description of the density-density and current-current time correlation functions of the liquid Na in a wide range of wave numbers, which implies that the origin of the non-hydrodynamic collective excitations contributing to longitudinal dynamics can be short-wavelength heat waves. PMID:27208952

  8. Computational Studies on Structural, Excitation, and Charge-Transfer Properties of Ureidopeptidomimetics.

    PubMed

    Joy, Sherin; Sureshbabu, Vommina V; Periyasamy, Ganga

    2016-07-14

    Peptides with ureido group enclosing backbones are considered peptidomimetics and are known for their higher stabilities, biocompatibilities, antibiotic, inhibitor, and charge-transduction activities. These peptidomimetics have some unique applications, which are quite different from those of natural peptides. Hence, it is imperative to appreciate their properties at a microscopic level. In this regard, this work outlines, in detail, the charge transfer (CT) properties, hole-migration dynamics, and electronic structures of various experimentally comprehended ureidopeptidomimetic models using density functional theory (DFT). Time-dependent DFT and complete active space self-consistent field computations on basic models provide the necessary evidence for the viability of CT from the end enfolding the ureido group to the other end with a carboxylate entity. This donor-to-acceptor CT has been reflected in excitation studies, in which the higher intensity band corresponds to CT from the π orbital of the ureido group to the π* orbital of the carboxylate entity. Further, hole-migration studies have shown that charge can evolve from the ureido end, whereas the hole generated at the carboxylate end does not migrate. However, hole migration has been reported to occur from both ends (amino and carboxylate ends) in glycine oligopeptides, and our studies show that the ability to transfer and migrate charge can be tuned by modifying the donor and acceptor functional groups in both the neutral and cationic charge states. We have analyzed the possibility of hole migration following ionization using DFT-based wave-packet propagation and found its occurrence on a ∼2-5 fs time scale, which reflects the charge-transduction ability of peptidomimetics. PMID:27314639

  9. 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.

  10. Excited States and photodebromination of selected polybrominated diphenyl ethers: computational and quantitative structure--property relationship studies.

    PubMed

    Luo, Jin; Hu, Jiwei; Wei, Xionghui; Li, Lingyun; Huang, Xianfei

    2015-01-01

    This paper presents a density functional theory (DFT)/time-dependent DFT (TD-DFT) study on the lowest lying singlet and triplet excited states of 20 selected polybrominateddiphenyl ether (PBDE) congeners, with the solvation effect included in the calculations using the polarized continuum model (PCM). The results obtained showed that for most of the brominated diphenyl ether (BDE) congeners, the lowest singlet excited state was initiated by the electron transfer from HOMO to LUMO, involving a π-σ* excitation. In triplet excited states, structure of the BDE congeners differed notably from that of the BDE ground states with one of the specific C-Br bonds bending off the aromatic plane. In addition, the partial least squares regression (PLSR), principal component analysis-multiple linear regression analysis (PCA-MLR), and back propagation artificial neural network (BP-ANN) approaches were employed for a quantitative structure-property relationship (QSPR) study. Based on the previously reported kinetic data for the debromination by ultraviolet (UV) and sunlight, obtained QSPR models exhibited a reasonable evaluation of the photodebromination reactivity even when the BDE congeners had same degree of bromination, albeit different patterns of bromination. PMID:25569092

  11. Excited state structure of 4-(dimethylamino)benzonitrile studied by femtosecond mid-infrared spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Chudoba, C.; Kummrow, A.; Dreyer, J.; Stenger, J.; Nibbering, E. T. J.; Elsaesser, T.; Zachariasse, K. A.

    1999-08-01

    Combining femtosecond transient vibrational spectroscopy and high-level calculations is a powerful tool in the determination of excited-state structures. Striking differences in the experimental vibrational pattern of the locally excited states of 4-(dimethylamino)benzonitrile (DMABN) and 4-aminobenzonitrile (ABN) are explained on the basis of molecular structures obtained from ab initio complete-active-space self-consistent-field (CASSCF) calculations, giving evidence for a strong sensitivity of the molecular structure on modest changes in the substituents. The 4.0 ps charge-transfer time for DMABN in acetonitrile is resolved for the first time by tracking the downshifted CN stretching mode.

  12. Variational study on the vibrational level structure and vibrational level mixing of highly vibrationally excited S₀ D₂CO.

    PubMed

    Rashev, Svetoslav; Moule, David C; Rashev, Vladimir

    2012-11-01

    We perform converged high precision variational calculations to determine the frequencies of a large number of vibrational levels in S(0) D(2)CO, extending from low to very high excess vibrational energies. For the calculations we use our specific vibrational method (recently employed for studies on H(2)CO), consisting of a combination of a search/selection algorithm and a Lanczos iteration procedure. Using the same method we perform large scale converged calculations on the vibrational level spectral structure and fragmentation at selected highly excited overtone states, up to excess vibrational energies of ∼17,000 cm(-1), in order to study the characteristics of intramolecular vibrational redistribution (IVR), vibrational level density and mode selectivity. PMID:22750345

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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 S2,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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. Step-scan FTIR absorption difference time-resolved spectroscopy studies the excited state electronic structures and decay kinetics of d6 transition metal polypyridine complexes

    NASA Astrophysics Data System (ADS)

    Smith, G. D.; Paegel, B. M.; Palmer, R. A.; Chen, P.; Omberg, K. M.; Meyer, T. J.

    1998-06-01

    Step-scan FTIR absorption difference time-resolved spectroscopy (S2 FTIR ΔA TRS) has been used to study the photo-excited states of several low-spin d6 transition metal polypyridine complexes. Insight into the distribution of electron density in the excited states is obtained by comparing the ground and excited state vibrational frequencies of various bands sensitive to electronic structure. The multiplex, registration, and IR throughput advantages of this interferometric technique are significant in comparison with other methods currently used to probe photo-excited processes on the nanosecond time scale. The S2 FTIR ΔA TR spectra were obtained by use of a step-scan modified Bruker IFS 88 FTIR spectrometer equipped with an AC/DC-coupled photovoltaic Kolmar Technologies MCT detector with a 20 ns rise time and a 100/200 MHz PAD82a transient digitizer. The complexes were excited with frequency-tripled pulses from a Q-switched Quanta-Ray DCR1A Nd:YAG laser (355 nm, 10 ns, 10 Hz, 3 mJ/pulse). Data were collected with 10 ns time resolution.

  19. 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).

  20. 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.

  1. 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.

  2. Photo-excited terahertz switch based on composite metamaterial structure

    NASA Astrophysics Data System (ADS)

    Wang, Guocui; Zhang, Jianna; Zhang, Bo; He, Ting; He, Yanan; Shen, Jingling

    2016-09-01

    A photo-excited terahertz switch based on a composite metamaterial structure was designed by integration of photoconductive silicon into the gaps of split-ring resonators. The conductivity of the silicon that was used to fill the gaps in the split-ring resonators was tuned dynamically as a function of the incident pump power using laser excitation, leading to a change in the composite metamaterial structure's properties. We studied the transmission characteristics of the composite metamaterial structure for various silicon conductivities, and the results indicated that this type of composite metamaterial structure could be used as a resonance frequency tunable terahertz metamaterial switch. We also designed other structures by filling different gaps with silicon, and proved that these structures could be used as terahertz metamaterial switches can change the working mode from a single frequency to multiple frequencies.

  3. Ballistic effects and intersubband excitations in multiple quantum well structures

    NASA Astrophysics Data System (ADS)

    Schneider, H.; Schönbein, C.; Schwarz, K.; Walther, M.

    1998-07-01

    We have studied the transport properties of electrons in asymmetric quantum well structures upon far-infrared optical excitation of carriers from the lowest subband into the continuum. Here the photocurrent consists of a coherent component originating from ballistic transport upon excitation, and of an incoherent part associated with asymmetric diffusion and relaxation processes, which occur after the coherence has been lost. The signature of the coherent contribution is provided by a sign reversal of the photocurrent upon changing the excitation energy. This sign reversal arises from the energy-dependent interference between continuum states, which have a twofold degeneracy characterized by positive and negative momenta. The interference effect also allows us to estimate the coherent mean free path ( >20 nm at 77K). In specifically designed device structures, we use both the coherent and incoherent components in order to achieve a pronounced photovoltaic infrared response for detector applications.

  4. X-ray-Excited Optical Luminescence (XEOL) and X-ray Absorption Fine Structures (XAFS) Studies of Gold(I) Complexes with Diphosphine and Bipyridine Ligands

    SciTech Connect

    Kim, Pil-Sook G.; Hu, Yongfeng; Brandys, Marie-C.; Burchell, Tara J.; Puddephatt, Richard J.; Sham, Tsun K.

    2008-10-14

    Synchrotron techniques, X-ray-excited optical luminescence (XEOL) combined with X-ray absorption fine structures (XAFS), have been used to study the electronic structure and optical properties of a series of luminescent gold(I) complexes with diphosphine and bipyridine ligands using tunable X-rays (in the regions of the C and P K-edges and the Au L{sub 3}-edge) and UV from synchrotron light sources. The effects of gold-ligand and aurophilic interactions on the luminescence from these gold(I) complexes have been investigated. It is found that the luminescence from these complexes is phosphorescence, primarily due to the decay of the Au (5d) {yields} PR{sub 3} ({pi}*), metal to ligand charge transfer (MLCT) excitation as well as contributions from the conjugated {pi}-system in the bipyridine ligands via the gold-nitrogen bond. The large Au 5d spin-orbit coupling enhances the intersystem crossing. The elongation of the hydrocarbon chain of the diphosphine ligand does not greatly affect the spectral features of the luminescence from the gold(I) complexes. However, the intensity of the luminescence was reduced significantly when the bipyridine ligand was replaced with 1,2-bis(4-pyridylamido)benzene. The aurophilic interaction, as investigated by EXAFS at the Au L{sub 3}-edge, is shown to be only one of the factors that contribute to the luminescence of the complexes.

  5. 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.

  6. 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. PMID:26562181

  7. 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.

  8. 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.

  9. Variational study on the vibrational level structure and IVR behavior of highly vibrationally excited S0 formaldehyde.

    PubMed

    Rashev, Svetoslav; Moule, David C

    2012-02-15

    We perform large scale converged variational vibrational calculations on S(0) formaldehyde up to very high excess vibrational energies (E(v)), E(v)∼17,000cm(-1), using our vibrational method, consisting of a specific search/selection/Lanczos iteration procedure. Using the same method we investigate the vibrational level structure and intramolecular vibrational redistribution (IVR) characteristics for various vibrational levels in this energy range in order to assess the onset of IVR. PMID:22185953

  10. 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.

  11. Geometries and electronic structures of the ground and low-lying excited states of FeCO: An ab initio study

    NASA Astrophysics Data System (ADS)

    Hirano, Tsuneo; Okuda, Rei; Nagashima, Umpei; Jensen, Per

    2012-12-01

    FeCO is a molecule of astrophysical interest. We report here theoretical calculations of its geometrical parameters, electronic structures, and molecular constants (such as dipole moment and spin-orbit coupling constant) in the electronic ground state tilde{X}3Σ - and the low-lying triplet and quintet excited states. The calculations were made at the MR-SDCI+Q_DK3/[5ZP ANO-RCC (Fe, C, O)] and MR-AQCC_DK3/[5ZP ANO-RCC (Fe, C, O)] levels of theory. A multi-reference calculation was required to describe correctly the wavefunctions of all states studied. For all triplet states, the σ-donation through the 10σ molecular orbital (MO) as well as the π-back-donation through the 4π MO are observed, and the dipole moment vector points from O toward Fe as expected. However, in the excited quintet states 5Π, 5Φ, and 5Δ, the almost negligible contribution of Fe 4s to the 10σ MO makes the dipole moment vector point from Fe toward O, i.e., in the same direction as in CO. In the tilde{X}3Σ - state, the electron provided by the σ-donation through the 10σ MO is shared between the Fe atom and the C end of the CO residue to form a coordinate-covalent Fe-C bond. In the tilde{a}5Σ - state (the high-spin counterpart of tilde{X}3Σ -), the σ-donation through the 10σ MO is not significant and so the Fe-C bond is rather ionic. The π-back-donation through the 4π MO is found to be of comparable importance in the two electronic states; it has a slightly larger magnitude in the tilde{X}3Σ - state. The difference in the molecular properties of the low-spin tilde{X}3Σ - and the high-spin tilde{a}5Σ - states can be understood in terms of the dynamical electron correlation effects.

  12. 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.

  13. 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.

  14. 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.

  15. Active control of tensegrity structures under random excitation

    NASA Astrophysics Data System (ADS)

    Ganesh Raja, M.; Narayanan, S.

    2007-06-01

    In this paper we consider vibration control of tensegrity structures under stationary and nonstationary random excitations. These excitations may be representative of many physical loading conditions, such as earthquake, wind, aerodynamic and acoustic excitations. The optimal control theory based on H2 and \\mathrm {H}_{\\infty } controller with full state and limited state feedback is used for the control. The response of the tensegrity structure is represented by the zero lag covariance matrix and the same is obtained by solving the matrix Lyapunov equation. The force generated by the electro-mechanical coupling of the piezoelectric actuator is used in the formulation. A tensegrity structure of class-1 comprising of two modules, with 24 pretension cables and six struts with piezoelectric actuators, is considered.

  16. 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.

  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. 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.

  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. 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.

  1. Dissociative excitation study of iron pentacarbonyl molecule

    NASA Astrophysics Data System (ADS)

    Ribar, Anita; Danko, Marián; Országh, Juraj; Ferreira da Silva, Filipe; Utke, Ivo; Matejčík, Štefan

    2015-04-01

    The processes of dissociative excitation (DE) and dissociative ionisation with excitation (DIE) of iron pentacarbonyl, Fe(CO)5, have been studied using a crossed electron-molecule beam experimental apparatus (Electron Induced Fluorescence Apparatus, EIFA). Using EIFA we were able to record the emission spectrum of the molecule in the UV-VIS range, as well as the photon efficiency curves initiated by electron impact. The emission spectrum of Fe(CO)5 initiated by impact of 50 eV electrons was recorded in the spectral range between 200 nm and 470 nm. It shows a high density of emission lines and bands (mainly iron lines and carbonyl bands). Additionally, we have measured photon efficiency curves (PECs) as a function of the electron impact energy for several lines and bands. On the basis of the PECs we have discussed the reaction mechanism and the energetics of the reactions associated with the DE and DIE processes. Contribution to the Topical Issue "Elementary Processes with Atoms and Molecules in Isolated and Aggregated States", edited by Friedrich Aumayr, Bratislav Marinkovic, Štefan Matejčík, John Tanis and Kurt H. Becker.

  2. 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.

  3. Structures and Low-Energy Excitations of Amorphous Gas Hydrates

    NASA Astrophysics Data System (ADS)

    Kikuchi, Tatsuya; Inamura, Yasuhiro; Onoda-Yamamuro, Noriko; Yamamuro, Osamu

    2012-09-01

    We have prepared amorphous clathrate hydrates of Ar, CD4, Xe, and SF6 by depositing mixed vapors of water and guest molecules on a substrate at ca. 10 K. The structure and vibrational density of states were investigated by neutron diffraction and inelastic scattering techniques, respectively. The radial distribution functions of the amorphous hydrates are larger than that of pure amorphous ice in the region around 4 Å (the center-edge distance of the 12-hedral cage), indicating that a local cagelike structure is maintained even in the amorphous solids. The incorporation of the guest molecules decreases the intensity of the phonon excitation below 7 meV, which is known as a low-energy excitation characteristic of amorphous ice. This may be due to the effect that the disorder, defects and distortion producing the low-energy excitation are reduced by a hydrophobic hydration between the guest and water molecules and the resultant hydrogen-bond formation. A similar effect was also observed in the libration mode of water molecules at about 60 meV. The present work has revealed the relation among the local cage formation, hydrogen bonds, and low energy excitations in amorphous hydrates that is the simplest hydrophobic hydration system (H2O--gas mixture).

  4. Synthesis of vibration control and health monitoring of building structures under unknown excitation

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    The vibration control and health monitoring of building structures have been actively investigated in recent years but often treated separately according to the primary objective pursued. In this study, a time-domain integrated vibration control and health monitoring approach is proposed based on the extended Kalman filter (EKF) for identifying the physical parameters of the controlled building structures without the knowledge of the external excitation. The physical parameters and state vectors of the building structure are then estimated and used for the determination of the control force for the purpose of the vibration attenuation. The interaction between the health monitoring and vibration control is revealed and assessed. The feasibility and reliability of the proposed approach is numerically demonstrated via a five-story shear building structure equipped with magneto-rheological (MR) dampers. Two types of excitations are considered: (1) the EI-Centro ground excitation underneath of the building and (2) a swept-frequency excitation applied on the top floor of the building. Results show that the structural parameters as well as the unknown dynamic loadings could be identified accurately; and, at the same time, the structural vibration is significantly reduced in the building structure.

  5. Contribution of electronic excitation to the structural evolution of ultrafast laser-irradiated tungsten nanofilms

    NASA Astrophysics Data System (ADS)

    Murphy, Samuel T.; Giret, Yvelin; Daraszewicz, Szymon L.; Lim, Anthony C.; Shluger, Alexander L.; Tanimura, Katsumi; Duffy, Dorothy M.

    2016-03-01

    The redistribution of the electron density in a material during laser irradiation can have a significant impact on its structural dynamics. This electronic excitation can be incorporated into two temperature molecular dynamics (2T-MD) simulations through the use of electronic temperature dependent potentials. Here, we study the structural dynamics of laser irradiated tungsten nanofilms using 2T-MD simulations with an electronic temperature dependent potential and compare the results to equivalent simulations that employ a ground-state interatomic potential. Electronic excitation leads to an expansion of the crystal and a decrease in the melting point of tungsten. During laser irradiation these factors ensure that the threshold fluences to the different melting regimes are reduced. Furthermore, both heterogenous and homogeneous melting are predicted to occur more rapidly due to excitation and oscillations in the film thickness will be accentuated.

  6. 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.

  7. 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

  8. 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.

  9. Vertical and adiabatic electronic excitations in biphenylene: A theoretical study

    NASA Astrophysics Data System (ADS)

    Beck, M. E.; Rebentisch, R.; Hohlneicher, G.; Fülscher, M. P.; Serrano-Andrés, L.; Roos, B. O.

    1997-12-01

    The low-lying singlet states of biphenylene have been studied using ab initio methods. Vertical excitation energies were calculated by multiconfigurational perturbation theory (CASPT2), starting from a complete active space self-consistent field (CASSCF) reference. The geometries of the most important low-lying excited states were individually optimized at the CASSCF level to study the difference between vertical and adiabatic excitations. Extended atomic natural orbital (ANO)-type basis sets were used to calculate state energies. Geometry optimizations were done with smaller ANO-type basis sets. Excitations from the ground state to the 1 1B3g and 1 1B2u excited singlet states lead to pronounced geometry changes which alter the bond alternation pattern. The theoretical results provide a solid basis for the assignment and interpretation of experimental spectra.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    We study the ionization energy, electron affinity, and the π → π∗ (1La) 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 1La 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 1La 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.

  11. 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.

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. Study of nonlinear oscillations due to exciter control

    SciTech Connect

    Abed, E.; Tsolas, N.; Varaiya, P.

    1983-01-01

    The effect of excitation system parameters on power system stability is studied here. The classical swing equation for a power generator augmented with an exciter is shown to undergo a Hopf bifurcation to periodic solutions. Only unstable oscillations occur for realistic parameter values and characterize the attractor of the stable equilibrium point. Attention is focussed on the global behavior of the oscillations as the critical parameter is varied. The analysis is carried out for a single machine connected to an infinite bus case.

  19. 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

    2016-07-01

    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.

  20. Multi-stage identification scheme for detecting damage in structures under ambient excitations

    NASA Astrophysics Data System (ADS)

    Bao, Chunxiao; Hao, Hong; Li, Zhong-Xian

    2013-04-01

    Structural damage identification methods are critical to the successful application of structural health monitoring (SHM) systems to civil engineering structures. The dynamic response of civil engineering structures is usually characterized by high nonlinearity and non-stationarity. Accordingly, an improved Hilbert-Huang transform (HHT) method which is adaptive, output-only and applicable to system identification of in-service structures under ambient excitations is developed in this study. Based on this method, a multi-stage damage detection scheme including the detection of damage occurrence, damage existence, damage location and the estimation of damage severity is developed. In this scheme, the improved HHT method is used to analyse the structural acceleration response, the obtained instantaneous frequency detects the instant of damage occurrence, the instantaneous phase is sensitive to minor damage and provides reliable damage indication, and the damage indicator developed based on statistical analysis of the Hilbert marginal spectrum detects damage locations. Finally, the response sampled at the detected damage location is continuously analysed to estimate the damage severity. Numerical and experimental studies of frame structures under ambient excitations are performed. The results demonstrate that this scheme accomplishes the above damage detection functions within one flow. It is robust, time efficient, simply implemented and applicable to the real-time SHM of in-service structures.

  1. Supersolid structure and excitation spectrum of soft-core bosons in three dimensions

    NASA Astrophysics Data System (ADS)

    Ancilotto, Francesco; Rossi, Maurizio; Toigo, Flavio

    2013-09-01

    By means of a mean-field method, we have studied the zero-temperature structure and excitation spectrum of a three-dimensional soft-core bosonic system for a value of the interaction strength that favors a crystal structure made of atomic nanoclusters arranged with fcc ordering. In addition to the longitudinal and transverse phonon branches expected for a normal crystal, the excitation spectrum shows a soft mode related to the breaking of gauge symmetry, which signals a partial superfluid character of the solid. Additional evidence of supersolidity is provided by the calculation of the superfluid fraction, which shows a first-order drop, from 1 to 0.4, at the liquid-supersolid transition and a monotonic decrease as the interaction strength parameter is increased. The conditions for the coexistence of the supersolid with the homogeneous superfluid are discussed, and the surface tension of a representative solid-liquid interface is calculated.

  2. Insights into heme structure from Soret excitation Raman spectroscopy.

    PubMed

    Callahan, P M; Babcock, G T

    1981-02-17

    Laser lines in resonance with the Soret band optical transitions of several heme proteins and heme model compounds have been used to obtain Raman spectra of these species. Correlations between the observed frequency of a polarized mode in the 1560-1600-cm-1 region and the heme iron spin and coordination geometry have been developed. The position of this band is also a function of the pattern of porphyrin pyrrole ring beta-carbon substitution, and therefore structural information can be extracted from the Raman data only after this dependence has been taken into account. Quantitative correlations between the frequency of this band and the porphyrin core size are presented for three commonly occurring classes of heme compounds: (a) protoheme derivatives, (b) iron porphyrins in which all ring positions are saturated, and (c) heme alpha species. A polarized mode in the 1470-1510-cm-1 region is also consistently enhanced upon Soret excitation of these compounds, but is relatively insensitive to peripheral substituents, and can be used in conjunction with the polarized mode described above to assign heme geometries. In the frequency region above 1600 cm-1, a vibration is observed which also responds to changes in porphyrin geometry. However, this band is sometimes obscured by vibrations of unsaturated beta-carbon substituents, particularly in the case of protoheme derivatives. The normal coordinate analysis developed by Abe and co-workers [Abe, M., Kitagawa, T., & Kyogoku, Y. (1978) J Chem. Phys. 69, 4526-4534] is used to rationalize the dependence of the various modes on porphyrin geometry and peripheral substitution.

  3. 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

  4. 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.

  5. The response characteristics of long cylindrical marine structures under different excitations

    SciTech Connect

    Park, H.I.

    1994-12-31

    Long cylindrical marine structures such as risers, TLP tendons, ocean pipes are subjected to several kinds of excitations of forcing, parametric, combined, self-excited etc. In this work, the response characteristics of the slender marine structures is investigated for the first three excitations. The governing partial differential equation of lateral motion of a slender structure is reduced to a non-linear differential equation with an integrand. The non-linear equation is solved numerically. The time histories of response amplitudes of the three excitations are obtained for actual TLP tethers: Hutton, Jolliet and Snoore TLPs. The response of combined excitation is most dominant for all three tethers. The total displacement is largest in the case of the Jolliet tether which corresponds to the second instability region. The response curves of combined excitation are also obtained. When the strength of forcing excitation is increased, the response amplitude of combined excitation evenly increases. However, when the strength of parametric excitation is increased, the response amplitude of combined excitation increases strongly and slightly in the even and odd numbers of instability regions, respectively.

  6. 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.

  7. 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.

  8. 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.

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

    DOE PAGES

    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,more » electron and ion irradiations.« less

  10. Variation after Angular Momentum Projection for the Study of Excited States Based on Antisymmetrized Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Kanada-En'yo, Y.

    1998-12-01

    In order to study the structure of excited states we perform a variational calculation after spin parity projection (VAP) within the framework of antisymmetrized molecular dynamics (AMD). The framework is proven to be a new powerful approach for the study of the various structures of excited states because it is free from model assumptions such as inert cores, existence of clusters, and the axial symmetry. By using finite range interactions with a density dependent term we reproduce well all the energy levels below 15 MeV in 12C. This is the first theoretical model that reproduces many E2 transition rates and β decays to 12C successfully.

  11. Controlled agglomeration of Tb-doped Y{sub 2}O{sub 3} nanocrystals studied by x-ray absorption fine structure, x-ray excited luminescence, and photoluminescence

    SciTech Connect

    Soo, Y.L.; Huang, S.W.; Kao, Y.H.; Chhabra, V.; Kulkarni, B.; Veliadis, J.V.; Bhargava, R.N.

    1999-10-01

    Local environment surrounding Y atoms in Y{sub 2}O{sub 3}:Tb nanocrystals under various heat treatment conditions has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. X-ray excited luminescence (XEL) with the incident x-ray energy near Y {ital K} edge and Tb {ital L} edges has also been measured to investigate the mechanisms of x-ray-to-visible down conversion in these doped nanoparticles. The observed changes in EXAFS, XEL, and photoluminescent data can be explained on the basis of increased average size of the nanoparticles as confirmed by transmission electron microscopy studies. Our results thus demonstrate that the doped nanoparticles can agglomerate to a controllable degree by varying the heat treatment temperature. At higher temperatures, the local environment surrounding Y atoms in the nanoparticles is found to become similar to that in bulk Y{sub 2}O{sub 3} while the XEL output still shows the characteristics of nanocrystals. These results indicate that appropriate heat treatment can afford an effective means to control the intensity and signal-to-background ratio of green luminescence output of these doped nanocrystal phosphors, potentially useful for some device applications. {copyright} {ital 1999 American Institute of Physics.}

  12. An impact excitation system for repeatable, high-bandwidth modal testing of miniature structures

    NASA Astrophysics Data System (ADS)

    Bediz, Bekir; Korkmaz, Emrullah; Burak Ozdoganlar, O.

    2014-06-01

    Miniature components and devices are increasingly seen in a myriad of applications. In general, the dynamic behavior of miniature devices is critical to their functionality and performance. However, modal testing of miniature structures poses many challenges. This paper presents a design and evaluation of an impact excitation system (IES) for repeatable, high-bandwidth, controlled-force modal testing of miniature structures. Furthermore, a dynamic model of the system is derived and experimentally validated to enable the identification of the system parameters that yield single-hit impacts with desired bandwidth and force magnitude. The system includes a small instrumented impact tip attached to a custom designed flexure-based body, an automated electromagnetic release mechanism, and various precision positioners. The excitation bandwidth and the impact force magnitude can be controlled by selecting the system parameters. The dynamic model of the system includes the structural dynamics of the flexure-based body, the electromagnetic force and the associated eddy-current damping, and the impact event. A validation study showed an excellent match between the model simulations and experiments in terms of impact force and bandwidth. The model is then used to create process maps that relate the system parameters to the number of hits (single vs. multiple), the impact force magnitudes and the excitation bandwidths. These process maps can be used to select system parameters or predict system response for a given set of parameters. A set of experiments is conducted to compare the performances of the IES and a (manual) miniature impact hammer. It is concluded that the IES significantly improves repeatability in terms of the impact bandwidth, location, and force magnitude, while providing a high excitation-bandwidth and excellent coherence values. The application of the IES is demonstrated through modal testing of a miniature contact-probe system.

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

    PubMed

    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

  14. 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

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

    PubMed

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

    2016-07-15

    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.

  16. Super-spiral structures in an excitable medium

    NASA Astrophysics Data System (ADS)

    Perez-Muñuzuri, V.; Aliev, R.; Vasiev, B.; Perez-Villar, V.; Krinsky, V. I.

    1991-10-01

    ROTATING spiral waves have been observed in various excitable media, including heart muscle1, retinae2, cultures of the slime mould Dyctiostelium discoideum3,4 and chemical oscillators such as the Belousov-Zhabotinsky (BZ) reaction5-7. Under certain conditions the spiral wave does not exhibit simple periodic rotation, but quasiperiodic8 (or 'compound'9) rotation, in which the spiral's origin (the tip) meanders10. Recent calculations11 have shown that highly meandering tip motion can impose superstructures on spiral waves. Here we reproduce these patterns experimentally, using the BZ reaction as the excitable medium. We induce high tip meander by applying pulses of electrical current locally at the tip12. Image processing of the patterns reveals a spiral wave of larger wavelength superimposed on the original wave, an effect that can be described in terms of a Doppler shift in the original spiral.

  17. 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.

  18. 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.

  19. Magnetic structure and spin excitations in BaMn2Bi2

    DOE PAGES

    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 tomore » be unchanged by the 100 K structural phase transition.« less

  20. 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.

  1. Excitation of kink oscillations of coronal loops: statistical study

    NASA Astrophysics Data System (ADS)

    Zimovets, I. V.; Nakariakov, V. M.

    2015-05-01

    Context. Solar flares are often accompanied by kink (transverse) oscillations of coronal loops. Despite intensive study of these oscillations in recent years, the mechanisms that excite them are still not known. Aims: We aim to clarify the excitation mechanisms for these kink oscillations of coronal loops. Methods: We analysed 58 kink-oscillation events observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during its first four years (2010-2014) with the use of the JHelioviewer. Association of these oscillation events with flares, lower coronal (r ≲ 1.4 R⊙) eruptions and plasma ejections, coronal mass ejections (CMEs), and coronal Type-II radio bursts is studied. Results: We find that 44 of these 58 oscillation events (76%) were associated with CMEs observed in the white light emission. Moreover, 57 events (98%) were accompanied by lower coronal eruptions/ejections (LCEs) observed in the extreme-ultraviolet band in the parental active regions. In the remaining event an LCE was not clearly seen, but it was definitely associated with a CME too. The main observational finding is that the kink oscillations were excited by the deviation of loops from their equilibria by a nearby LCE in 55 events (95%). In three remaining events, it was difficult to reliably determine the cause of the oscillations because of limitations in the observational data. We also found that 53 events (91%) were associated with flares. In five remaining events, the parental active regions were behind the limb and we could not directly see flare sites. It indicates that there is a close relationship between these two kinds of solar activity. However, the estimated speeds of a hypothetical driver of kink oscillations by flares were found to be lower than 500 km s-1 in 80% of the cases. Such low speeds do not favour the association of the oscillation excitation with a shock wave, as usually assumed. That only 23 (40%) of the oscillation events were found

  2. 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.

  3. Experimental study of propagation of instability waves in a submerged jet under transverse acoustic excitation

    NASA Astrophysics Data System (ADS)

    Mironov, A. K.; Krasheninnikov, S. Yu.; Maslov, V. P.; Zakharov, D. E.

    2016-07-01

    An experimental study was conducted on the specific features of instability wave propagation in the mixing layer of a turbulent jet when the jet is excited by an external acoustic wave. We used the technique of conditional phase averaging of data obtained by particle image velocimetry using the reference signal of a microphone placed near the jet. The influence of the excitation frequency on the characteristics of large-scale structures in the mixing layer was investigated. It is shown that the propagation patterns of the instability waves agree well with previously obtained data on the localization of acoustic sources in turbulent jets.

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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.

  9. A Study of Power Systems Stability Enhancement Effects by Excitation Control of Superconducting Generator with High Response Excitation based on Detailed Excitation Circuit Model

    NASA Astrophysics Data System (ADS)

    Wu, Guohong; Shirato, Hideyuki

    SCG (Superconducting Generator) has a superconducting field winding, which leads to many advantages such as small size, high generation efficiency, low impedance, and so on, and be considered as one of the candidates to meet the needs of high stability and high efficiency in the future power system networks. SCG with high response excitation is especially expected to be able to enhance the transient stability of power system by its SMES (Superconducting Magnetic Energy System) effect. The SMES effect of SCG is recognized that its behaviors are dominated by the structures and controls of its excitation system. For this reason, in order to verify exactly how the SMES effect of SCG influences on the power system stability, the electrical circuits of SCG high response excitation are modeled in detail for conducting digital simulation, and its influence on excitation voltage and active power output of SCG are discussed as well. The simulation results with a typical one machine - infinite bus power system model shows that the SMES effect can be certainly obtained when its exciting power is supplied from SCG terminal bus and may considerably lead to an improvement of power system transient stability.

  10. 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.

  11. Spectroscopic study of excitations in pi-conjugated polymers

    NASA Astrophysics Data System (ADS)

    Yang, Cungeng

    This dissertation deals with spin-physics of photo excitations in pi-conjugated polymers. Optical and magneto-optical spectroscopies, including continuous wave and time-resolved photo-induced absorption, photoluminescence, electroluminescence, and their optically detected magnetic resonance, were used to study steady state and transient photogeneration, energy transfer, spin relaxation, and spin dependent recombination process in the time domain from tens of nanoseconds to tens of milliseconds in polymer materials including regio-random poly (3-hexyl-thiophene-2,5-diyl), regio-regular poly (3-hexyl-thiophene-2,5-diyl), poly (9,9-dioctyl-fluorenyl-2,7-diyl), poly (poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene) of various morphologies, and transition metal complex poly (Pt-quinoxene). Our studies provided the tools to clarify the physical pictures regarding two types of long-lived photoexcitations, namely polarons (both germinate polaron-pairs, and unpaired polarons) and triplet excitons, which are the major excitations in these exotic semiconductors in electrical and optical related applications. From measurements of transient fluorescence and transient fluorescence detected magnetic resonance we show that photogenerated geminate polaron pairs live up to hundreds of microseconds following laser pulsed excitation. This conclusion is in agreement with the delayed formation of triplet excitons that we measured by transient photoinduced absorption. It also agrees with the weak spin-lattice relaxation rate in polymers that we measured using the optically detected magnetic resonance dynamic in thin films and organic light emitting devices. Randomly captured nongeminate polaron pairs were shown to be the major source of optically detected magnetic resonance signal at steady, state. We found that the dynamics and magnitude of the signal depend on the spin-relaxation rate, generation rate and decay rate of the geminate pairs and nongeminate pairs. Importantly we

  12. Structural health monitoring by high-frequency vibration measurement with non-contact laser excitation

    NASA Astrophysics Data System (ADS)

    Kajiwara, I.; Miyamoto, D.; Hosoya, N.; Nishidome, C.

    2011-04-01

    This paper proposes a vibration testing and health monitoring system based on an impulse response excited by a laser ablation. High power YAG pulse laser is used for producing an ideal impulse force on structural surface. It is possible to measure high frequency vibration responses in this system. A health monitoring system is constructed by this vibration testing system and a damage detecting algorithm. A microscopic damage of structures can be extracted by detecting fluctuations of high frequency vibration response with the present health monitoring system. In this study, loosening of bolt tightening torques is defined as the damage of the system. The damage is detected and identified by statistical evaluations with Recognition-Taguchi method.

  13. Fluid-loaded vibration of thin structures due to turbulent excitation

    NASA Astrophysics Data System (ADS)

    Tomko, Jason Robert

    Flow-induced structural acoustics involves the study of the vibration of a structure induced by a fluid flow as well as the resulting sound generated and radiated by the motion of the system. The thesis examines several aspects of flow-induced structural vibration for fluid-loaded systems. A new method, termed Magnitude-Phase Identification, is derived to experimentally obtain a modal decomposition of the vibration of a structure using two-point measurements. MPI was used to measure the auto-spectral density of various modes for a non-fluid-loaded, rectangular, clamped plate excited by a spatially-homogeneous turbulent boundary layer. These results agreed well with theory. Using MPI, it was shown that when both fluid-loading and a spatially non-homogeneous wall pressure field is applied to a structure that the mode shapes become dependent on the forcing field, an effect which does not occur when either characteristic is applied individually. Furthermore, the resulting mode shapes are potentially highly asymmetric. It was shown through a discretized string model that these results can be attributed to the increased damping induced by fluid loading. Internal acoustic wall pressure fields due to a ducted rotor were measured, and it was shown that the acoustic effects of the rotor can be approximated by replacing the rotor with a continuous ring of dipoles located at the blade tip. The finite length of the duct was accounted for through use of a method of images. The theoretical results from this model match well with the measured values. Lastly, the vibration of a fluid-loaded duct excited by an internal rotor is measured through use of MPI. The resulting vibration field appears similar to the field examined earlier due to fluid loading, with a decrease in the coherent vibration magnitude for increasing spatial separation from the reference location.

  14. 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.

  15. 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. PMID:25234878

  16. 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

  17. 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.

  18. Structure, magnetic order and excitations in the 245 family of Fe-based superconductors.

    PubMed

    Bao, Wei

    2015-01-21

    Elastic neutron scattering simultaneously probes both the crystal structure and magnetic order in a material. Inelastic neutron scattering measures phonons and magnetic excitations. Here, we review the average composition, crystal structure and magnetic order in the 245 family of Fe-based superconductors and in related insulating compounds from neutron diffraction works. A three-dimensional phase-diagram summarizes various structural, magnetic and electronic properties as a function of the sample composition. A high pressure phase diagram for the superconductor is also provided. Magnetic excitations and the theoretic Heisenberg Hamiltonian are provided for the superconductor. Issues for future works are discussed. PMID:25427222

  19. 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.

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

    PubMed

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

    2012-08-01

    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.

  1. Relative fine-structure intensities in two-photon excitation

    NASA Technical Reports Server (NTRS)

    Crosley, D. R.; Bischel, W. K.

    1984-01-01

    A discrepancy is pointed out between experimental determinations of the relative intensities for different fine-structure components of the two-photon transitions 2p3P 3p3P in oxygen and 2p3 4S0 - 2p2 3p4D0 in nitrogen, which agreed well with calculations involving a single virtual intermediate level, and a two-photon selection rule dJ not equal to one, derived in a purely theoretical and erroneous treatment of these transitions. Five other experiments are also briefly examined, with the conclusion that relative fine-structure intensities in two-photon transitions are well understood as straightforward extensions of angular momentum coupling in single-photon cases, in accordance with allowed dJ = 0, + or -1, and + or -2 transitions.

  2. 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.

  3. 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.

  4. Scanning Laser Doppler Vibrometry Application to Artworks: New Acoustic and Mechanical Exciters for Structural Diagnostics

    NASA Astrophysics Data System (ADS)

    Agnani, A.; Esposito, E.

    After first attempts some years ago, the scanning laser Doppler vibrometer has become an effective way of diagnosing different types of artworks; successful applications regard frescoes, icons, mosaics, ceramic artefacts and wood inlays. Also application to historical bridges has been successfully developed and a recently approved European Commission project will see the employment of scanning laser Doppler Vibrometry (SLDV) for the dynamical characterization of ancient buildings. However, a critical issue consists in the adequate excitation of the structure under test. Moreover different types of defects and different kinds of artworks require different types of excitation, so this topic needs a deep consideration. In this work we will present two new types of exciters developed at our Department, namely an acoustic exciter and a mechanical one. Acoustic exciters allow remote non-invasive loading but are limited in the lower frequency range and in the amount of vibrational energy input into the structure. The proposed automatic tapping device based on a commercial impact hammer overcomes these problems. Also another acoustic exciter, a HyperSonic Sound (HSS) source has been evaluated, showing interesting features as regards sound radiation.

  5. 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].

  6. 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

    2016-01-01

    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

  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. Electronic excited States of polynucleotides: a study by electroabsorption spectroscopy.

    PubMed

    Krawczyk, Stanislaw; Luchowski, Rafal

    2007-02-01

    Electroabsorption spectra were obtained for single-stranded polynucleotides poly(U), poly(C), poly(A), and poly(G) in glycerol/water glass at low temperature, and the differences in permanent dipole moment (Deltamu) and polarizability (Deltaalpha) were estimated for several spectral ranges covering the lowest energy absorption band around 260 nm. In each spectral range, the electrooptical parameters associated with apparent features in the absorption spectrum exhibit distinct values representing either a dominant single transition or the resultant value for a group of a relatively narrow cluster of overlapping transitions. The estimated spacing in energy between electronic origins of these transitions is larger than the electronic coupling within the Coulombic interaction model which is usually adopted in computational studies. The electroabsorption data allow us to distinguish a weak electronic transition associated with a wing in polynucleotide absorption spectra, at an energy below the electronic origin in absorption spectra of monomeric nucleobases. In poly(C) and poly(G), these low-energy transitions are related to increased values of Deltamu and Deltaalpha, possibly indicating a weak involvement of charge resonance in the respective excited states. A model capable of explaining the origin of low-energy excited states, based on the interaction of pipi* and npi* transitions in neighboring bases, is introduced and briefly discussed on the grounds of point dipole interaction. PMID:17266277

  11. 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.

  12. 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.

  13. Nanometer-scale scanning magnetometry of spin structures and excitations using Nitrogen-vacancy centers

    NASA Astrophysics Data System (ADS)

    Dovzhenko, Yuliya

    The development of increasingly sensitive scanning techniques has led to new insights into the physics of interacting condensed matter systems. Recently, Nitrogen-Vacancy (NV) centers in diamond emerged as a promising scanning magnetic imaging platform capable of operating in a broad range of temperatures and magnetic fields, with sensitivity and resolution capable of imaging a single electron spin with sub-nanometer resolution under ambient conditions. In this talk we will review some of the recent developments in this new scanning platform. We will describe our recent progress in using a single NV center in a scanning diamond nano-pillar to study condensed matter magnetism at both room and low temperatures. In particular, we demonstrate the use of scanning NV magnetometry to image stray fields originating from static chiral spin structures, as well as to detect resonant and off-resonant low-energy spin excitations.

  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. On inertia nonlinearity in irregular-plan isolated structures under seismic excitations

    NASA Astrophysics Data System (ADS)

    Amin Afshar, Majid; Aghaei Pour, Sepehr

    2016-02-01

    The influence of nonlinear inertia as a function of acceleration, velocity, and displacement is investigated for an asymmetric isolated structure. Six degrees of freedom (6-DOFs) are defined to illustrate translational and rotational displacements of the superstructure and base isolation. Motion equations of such DOFs are derived using the Lagrangian formalism. Two coordinate systems of the reference are defined, one fixed on the building base (global coordinate) and the other at the torsional isolation level (local coordinate). The motion governing equations in the conventional approach is formulated on a linear form in the global coordinate system, whereas in the novel approach, the local coordinate system leads to a nonlinear form of dynamic equations. The difference between two linear and nonlinear models is appeared because of the existence of nonlinear inertia terms just in the nonlinear one. Afterwards, three particular types of isolated structures are employed with the peculiar ratio of torsional-lateral coupled frequency on symmetric frequency. Numerical analysis is applied to investigate the performance of two structural models by exerting harmonic excitations and earthquakes. The results are obtained while analyzing time history and frequency content and show that the coupling effects of nonlinear inertia lead to differences in the responses of linear and nonlinear models of such structures; also, some nonlinear phenomena such as energy transfer between modes, saturation, rigid displacement, and super-harmonic created due to geometrical (inertial) nonlinearities are studied.

  16. 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.

  17. 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.

  18. Structural relaxation dynamics of electronically excited XeArN clusters

    NASA Astrophysics Data System (ADS)

    Goldberg, Alexander; Jortner, Joshua

    1997-12-01

    In this article we explore the structural, dynamic, and spectroscopic implications of large local configurational changes in electronically excited Xe*ArN (N=12,54,146,199) heteroclusters, where the Xe* [≡Xe(3P1)] atom is excited to the lowest dipole-allowed extravalence Rydberg excitation. The ultrafast femtosecond and picosecond dynamics driven by the short-range repulsive interaction between the vertically excited Xe* Rydberg and the cluster Ar atoms was studied by molecular dynamics simulations. From the analysis of the time dependence of the structural parameters for site-specific Xe excitations in medium-sized (N=54) and large (N=146,199) clusters, two general configurational relaxation phenomena were established: a "bubble" formation (i.e., a large configurational dilation around Xe*) for Xe interior sites and a "spring" formation (i.e., the stretching of Xe* outside the cluster) for Xe surface sites. General Xe site-specific features of both bubble and spring formation involve ultrashort (Gaussian) energy transfer to the cluster (˜50-100 fs characteristic times τET) inducing configurational relaxation, which manifests a multimodal time solution. The initial (Gaussian) temporal mode (˜150-300 fs characteristic times τ0>τET) is followed by an exponential mode (ps lifetime τ1), with subsequent impact induced, damped vibrational coherence effects with frequencies (ω2,ω3), and exponential decay (ps lifetimes τ2,τ3). The bubble formation for the central site of Xe*Ar146 or Xe*Ar54 is induced by energy transfer of τET≅60 fs followed by subsequent multimodal dilation with τ0≅170 fs and τ1≅2 ps, and a subsequent expansion with coherent motion of vibrational wave packets with ω2,ω3≅20, 40 cm-1 and τ2,τ3≅2, 6 ps. The bubble reaches an equilibrium configuration after ˜10 ps with asymptotic spatial expansion of ΔRb*=0.7-0.8 Å. The spring formation for an exterior surface site of Xe*Ar146 is τET≅80 fs and τ0≅210 fs, which is followed

  19. Electronic Structure and Dynamics of Higher-Lying Excited States in Light Harvesting Complex 1 from Rhodobacter sphaeroides.

    PubMed

    Dahlberg, Peter D; Ting, Po-Chieh; Massey, Sara C; Martin, Elizabeth C; Hunter, C Neil; Engel, Gregory S

    2016-06-23

    Light harvesting in photosynthetic organisms involves efficient transfer of energy from peripheral antenna complexes to core antenna complexes, and ultimately to the reaction center where charge separation drives downstream photosynthetic processes. Antenna complexes contain many strongly coupled chromophores, which complicates analysis of their electronic structure. Two-dimensional electronic spectroscopy (2DES) provides information on energetic coupling and ultrafast energy transfer dynamics, making the technique well suited for the study of photosynthetic antennae. Here, we present 2DES results on excited state properties and dynamics of a core antenna complex, light harvesting complex 1 (LH1), embedded in the photosynthetic membrane of Rhodobacter sphaeroides. The experiment reveals weakly allowed higher-lying excited states in LH1 at 770 nm, which transfer energy to the strongly allowed states at 875 nm with a lifetime of 40 fs. The presence of higher-lying excited states is in agreement with effective Hamiltonians constructed using parameters from crystal structures and atomic force microscopy (AFM) studies. The energy transfer dynamics between the higher- and lower-lying excited states agree with Redfield theory calculations.

  20. 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.

  1. Study of excited nucleon states at EBAC: status and plans

    SciTech Connect

    Hiroyuki Kamano

    2009-12-01

    We present an overview of a research program for the excited nucleon states in Excited Baryon Analysis Center (EBAC) at Jefferson Lab. Current status of our analysis of the meson production reactions based on the unitary dynamical coupled-channels model is summarized, and the N* pole positions extracted from the constructed scattering amplitudes are presented. Our plans for future developments are also discussed.

  2. Vibrational modes in excited Rydberg states of acetone: A computational study

    NASA Astrophysics Data System (ADS)

    Shastri, Aparna; Singh, Param Jeet

    2016-04-01

    Computational studies of electronically excited states of the acetone molecule [(CH3)2CO] and its fully deuterated isotopologue [(CD3)2CO] are performed using the time dependent density functional (TDDFT) methodology. In addition to vertical excitation energies for singlet and triplet states, equilibrium geometries and vibrational frequencies of the n=3 Rydberg states (3s, 3p and 3d) are obtained. This is the first report of geometry optimization and frequency calculations for the 3px, 3pz, 3dyz, 3dxy, 3dxz, 3dx2-y2 and 3dz2 Rydberg states. Results of the geometry optimization indicate that the molecule retains approximate C2V geometry in most of these excited Rydberg states, with the most significant structural change seen in the CCO bond angle which is found to be reduced from the ground state value. Detailed comparison of the computationally predicted vibrational wavenumbers with experimental studies helps to confirm several of the earlier vibronic assignments while leading to revised/new assignments for some of the bands. The important role of hot bands in analysis of the room temperature photoabsorption spectra of acetone is corroborated by this study. While the vibrational frequencies in excited Rydberg states are overall found to be close to those of the ionic ground state, geometry optimization and vibrational frequency computation for each excited state proves to be very useful to arrive at a consistent set of vibronic assignments. Isotopic substitution helps in consolidating and confirming assignments. An offshoot of this study is the interpretation of the band at ~8.47 eV as the π-3s Rydberg transition converging to the second ionization potential.

  3. Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S{sub 1}(π,π{sup *}) electronic state

    SciTech Connect

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

    2014-01-21

    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 S{sub 1}(π,π{sup *}) 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 S{sub 0} and S{sub 1}(π,π{sup *}) 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 S{sub 0} and S{sub 1}(π,π{sup *}) 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 S{sub 1}(π,π{sup *}) excited state.

  4. Structural Heterogeneity in the Localized Excited States of Poly(3-hexylthiophene).

    PubMed

    Yu, Wenjian; Magnanelli, Timothy J; Zhou, Jiawang; Bragg, Arthur E

    2016-06-01

    Transient hole-burning and resonantly enhanced Raman spectroscopies are used to probe heterogeneities among localized singlet excitons of poly(3-hexylthiophene) in solution. Transient hole-burning spectroscopy facilitated by population dumping through wavelength-selective stimulated emission exposes inhomogeneous broadening of the exciton absorption band in the near-infrared, as reflected by correlations between stimulated emission and excited-state absorption transition energies. Dump-induced spectral diffusion of the exciton absorption band reflects structural fluctuations in the locally excited polymer. This diffusion is observed to occur slightly faster or slower than the nonequilibrium relaxation that follows direct excitation of the polymer (8-9 ps), with the time scale for diffusion varying with subpopulation: dumping across small vs large band gaps results in diffusion over 5 vs 35 ps, respectively. Furthermore, incomplete spectral relaxation of transient holes reflects that subsets of locally excited structural motifs prepared through photoexcitation cannot interchange through structural fluctuations that occur over the singlet-exciton lifetime. Raman spectra of the C═C/C-C stretching region collected in resonance at energies across the exciton absorption band exhibit frequency and intensity trends (Raman "dispersion") ascribed to variation in the local effective conjugation length. Together, results explicitly reveal heterogeneities among excitonic states associated with variations and fluctuations in local conformational order. PMID:27167593

  5. Single pulse laser excitation of structural vibration using power densities below the surface ablation threshold

    NASA Astrophysics Data System (ADS)

    Philp, W. R.; Booth, D. J.; Perry, N. D.

    1995-08-01

    This paper describes sub-ablation optical excitation of flexural vibration in cantilevers and a suspended truck-wheel rim by using a single 600μs, Nd:glass laser pulse with energies between 1J and 40J. The excitation is consistent with the photothermal production of a localized thermoelastic bending moment at the site of the laser irradiation. This method of excitation has been combined with fibre optic sensing and modal analysis of the resulting vibrations to provide a practical method of remotely measuring the structural properties upon which the frequencies of vibration depend. The modal frequencies of slot-damaged cantilevers are presented to demonstrate the possible application of this non-contact measurement technique for non-destructive testing.

  6. 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

  7. 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.

  8. 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.

  9. Generating functions and stability study of multivariate self-excited epidemic processes

    NASA Astrophysics Data System (ADS)

    Saichev, A. I.; Sornette, D.

    2011-09-01

    We present a stability study of the class of multivariate self-excited Hawkes point processes, that can model natural and social systems, including earthquakes, epileptic seizures and the dynamics of neuron assemblies, bursts of exchanges in social communities, interactions between Internet bloggers, bank network fragility and cascading of failures, national sovereign default contagion, and so on. We present the general theory of multivariate generating functions to derive the number of events over all generations of various types that are triggered by a mother event of a given type. We obtain the stability domains of various systems, as a function of the topological structure of the mutual excitations across different event types. We find that mutual triggering tends to provide a significant extension of the stability (or subcritical) domain compared with the case where event types are decoupled, that is, when an event of a given type can only trigger events of the same type.

  10. 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.

  11. 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.

  12. 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.

  13. Identification of the structure parameters using short-time non-stationary stochastic excitation

    NASA Astrophysics Data System (ADS)

    Jarczewska, Kamila; Koszela, Piotr; Śniady, PaweŁ; Korzec, Aleksandra

    2011-07-01

    In this paper, we propose an approach to the flexural stiffness or eigenvalue frequency identification of a linear structure using a non-stationary stochastic excitation process. The idea of the proposed approach lies within time domain input-output methods. The proposed method is based on transforming the dynamical problem into a static one by integrating the input and the output signals. The output signal is the structure reaction, i.e. structure displacements due to the short-time, irregular load of random type. The systems with single and multiple degrees of freedom, as well as continuous systems are considered.

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

    PubMed

    Shabelansky, Anastasia; Dowling-Guyer, Seana

    2016-01-01

    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

  15. Theoretical Studies on the Reaction Pathways of Electronically Excited Daaf

    NASA Astrophysics Data System (ADS)

    Quenneville, J.; Moore, D. S.

    2009-12-01

    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'-diamino-4, 4'-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.

  16. Ultrafast electronic processes in highly excited solids: subpicosecond optical studies

    NASA Astrophysics Data System (ADS)

    Petite, Guillaume

    1998-09-01

    Modern short pulse lasers are efficient tools for production of high levels of electronic excitation in solids under irradiation, a state which mimics that of the same materials after the passage of any particle which deposits its energy under the form of electronic excitation. Because they can also be used in a number of optical experiments of charge carriers and defect detection, they offer the unique opportunity of unraveling the ultrafast kinetic aspects of atomic processes induced by the electronic excitation, whose final state is the only aspect accessible in the case of other irradiations. After mentioning a few orders of magnitudes concerning the energy deposition, we will show some examples of recent experiments concerning the mechanisms of irradiation defect creation in insulators. The perspectives opened by recent developments of light sources in a wide range of wavelengths will be finally presented.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Modeling stresses in piezoelectric smart structures under combined thermal and mechanical excitations

    NASA Astrophysics Data System (ADS)

    Koko, Tamunoiyala S.; Smith, Malcolm J.; Orisamolu, Irewole R.

    1999-06-01

    In this paper, the integrated finite element methodology developed in our earlier work for designing active vibration control strategies in smart structures, is extended to compute the stresses and strains in the structure, due to combined thermal, mechanical and electrical excitations. A layered composite brick elements with linear strain-displacement and linear thermopiezoelectric constitutive relations is used to model the structure. The method, which has been encoded into a software called SMARTCOM provides a design and analysis capability that simultaneously accounts for the coupled thermopiezoelectric and control capabilities of the smart structural systems. Numerical examples are provided for structures with surface bonded piezoelectric sensors and actuators, under various types of mechanical, thermal and electrical load. Comparisons are made to other available solutions to verify the accuracy of the SMARTCOM simulations. The method provides accurate results and is seen as a valuable tool for the design and analysis of these smart structures.

  3. Theoretical study on the dehydrogenation reaction of dihydrogen bonded phenol-borane-trimethylamine in the excited state.

    PubMed

    Yang, Yonggang; Liu, Yufang; Yang, Dapeng; Li, Hui; Jiang, Kai; Sun, Jinfeng

    2015-12-28

    Time dependent density functional theory (TDDFT) and transition state theory (TST) have been performed to study the dehydrogenation process of dihydrogen bonded phenol-borane-trimethylamine (phenol-BTMA) in the excited state. The potential curve of phenol-BTMA in the ground state confirms that the dehydrogenation process does not occur in the ground state. The analysis of the geometric structure and infrared spectra demonstrate that the dihydrogen bond O-H···H1-B of phenol-BTMA is considerably strengthened with the cleavage of O-H when excited to the first excited state. Based on the geometric structure in the first excited state, a transition state is found with the only imaginary frequency pointing to the formation of the hydrogen molecule. This finding implies the occurrence of the dehydrogenation process of phenol-BTMA in the excited state. The dehydrogenation reaction is fully completed in the reaction product and the new formed hydrogen molecule moves away from the plane of the benzene ring. This work provides a theoretical model for the dehydrogenation process of phenol-BTMA in the excited state.

  4. X-ray excited optical luminescence from hexagonal boron nitride nanotubes: electronic structures and the role of oxygen impurities.

    PubMed

    Liu, Lijia; Sham, Tsun-Kong; Han, Weiqiang; Zhi, Chunyi; Bando, Yoshio

    2011-01-25

    We report a study on the optical luminescence properties and the electronic structures of boron nitride nanotubes (BNNTs). BNNTs with natural B (80% (11)B and 20% (10)B) and pure (10)B are investigated in comparison with hexagonal BN crystals using X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL). We find that the BNNT specimen synthesized with natural B contains more oxide impurities than that with pure (10)B, resulting in significantly different behavior in optical luminescence. All BN samples with hexagonal structures are found to emit strong luminescence, but the emission spectra are strongly morphology- and structure-dependent. XEOL and XANES measurements were carried out at the B K-edge, N K-edge, and O K-edge in order to reveal the origin of different luminescence channels and the corresponding electronic structures in these BN materials.

  5. Identification of structural systems with full characteristic matrices under single point excitation

    NASA Astrophysics Data System (ADS)

    Ghafory-Ashtiany, Mohsen; Adhami, Behnam; Khanlari, Karen

    2014-12-01

    The aim of "System Identification" is to determine modal and system properties of structural systems. This is while in "Damage Detection", the identification of system characteristic matrices is as important as or even more important than the identification of frequency characteristics. Because of various constraints - i.e. difficulties in force excitation of structures due to their large size, geometry, and location - in practice only single excitation and partial measurement, at selected degrees of freedom, is possible. In this paper, a single dynamic load was applied to identify a structural system only along one of the degrees of freedom of the structure. Further, responses corresponding to a few degrees of freedom were also measured. To identify a system with this sort of restricted information, a new approach was introduced enabling identification of the structure's parameters of mass, damping and stiffness. Taking into account the significant effect of noise reduction in improving system identification accuracy levels, a noise reduction technique was also proposed. The accuracy of the method was also assessed against noise level and location of single excitation. It was shown that as noise level increases, identification errors will also increase (less than 3.5 percent). It was further observed that applying single force at the first storey of the flexural structure would yield the lowest error levels in the identification results. Later, the method's efficiency and precision were examined through the application of a "closed loop solution" to a six-storey flexural structure, and a four-span Pratt truss. The obtained results showed that the proposed method could act as an effective model in identification of system properties.

  6. Cross-shell excitation in two-proton knockout: Structure of {sup 52}Ca

    SciTech Connect

    Gade, A.; Brown, B. A.; Campbell, C. M.; Cook, J. M.; Dinca, D.-C.; Glasmacher, T.; Hansen, P. G.; Terry, J. R.; Janssens, R. V. F.; Carpenter, M. P.; Zhu, S.; Bazin, D.; Mueller, W. F.; Broda, R.; Fornal, B.; Deacon, A. N.; Freeman, S. J.; Kay, B. P.; Mantica, P. F.; Tostevin, J. A.

    2006-08-15

    The two-proton knockout reaction {sup 9}Be({sup 54}Ti,{sup 52}Ca+{gamma}) has been studied at 72 MeV/nucleon. Besides the strong feeding of the {sup 52}Ca ground state, the only other sizeable cross section proceeds to a 3{sup -} level at 3.9 MeV. There is no measurable direct yield to the first excited 2{sup +} state at 2.6 MeV. The results illustrate the potential of such direct reactions for exploring cross-shell proton excitations in neutron-rich nuclei and confirms the doubly-magic nature of {sup 52}Ca.

  7. Multiple support excitations of open-plane frames by a filtered white noise and soil-structure interaction

    NASA Astrophysics Data System (ADS)

    Allam, Mehter M.

    2010-09-01

    Seismic structural design is essentially the estimation of structural response to a forced motion, which may be deterministic or stochastic, imposed on the ground. The assumption that the same ground motion acts at every point of the base of the structure (or at every support) is not always justifiable; particularly in case of very large structures when considerable spatial variability in ground motion can exist over significant distances—example long span bridges. This variability is partly due to the delay in arrival of the excitation at different supports (which is called the wave passage effect) and due to heterogeneity in the ground medium which results in incoherency and local effects. The current study examines the influence of the wave passage effect (in terms of delay in arrival of horizontal ground excitation at different supports and neglecting transmission through the structure) on the response of a few open-plane frame building structures with soil-structure interaction. The ground acceleration has been modeled by a suitably filtered white noise. As a special case, the ground excitation at different supports has also been treated as statistically independent to model the extreme case of incoherence due to local effects and due to modifications to the ground motion resulting from wave reflections and refractions in heterogeneous soil media. The results indicate that, even for relatively short spanned building frames, wave passage effect can be significant. In the absence of soil-structure interaction, it can significantly increase the root mean square (rms) value of the shear in extreme end columns for the stiffer frames but has negligible effect on the flexible frames when total displacements are considered. It is seen that pseudo-static displacements increasingly contribute to the rms value of column shear as the time delay increases both for the stiffer and for the more flexible frames. When soil-structure interaction is considered, wave passage

  8. COLLISIONAL EXCITATION OF THE [C II] FINE STRUCTURE TRANSITION IN INTERSTELLAR CLOUDS

    SciTech Connect

    Goldsmith, Paul F.; Langer, William D.; Pineda, Jorge L.; Velusamy, T.

    2012-11-15

    We analyze the collisional excitation of the 158 {mu}m (1900.5 GHz) fine structure transition of ionized carbon in terms of line intensities produced by simple cloud models. The single C{sup +} fine structure transition is a very important coolant of the atomic interstellar medium (ISM) and of photon-dominated regions in which carbon is partially or completely in ionized form. The [C II] line is widely used as a tracer of star formation in the Milky Way and other galaxies. Excitation of the [C II] fine structure transition can be via collisions with hydrogen molecules, atoms, and electrons. Analysis of [C II] observations is complicated by the fact that it is difficult to determine the optical depth of the line. We discuss the excitation of the [C II] line, deriving analytic results for several limiting cases and carry out numerical solutions using a large velocity gradient model for a more inclusive analysis. For antenna temperatures up to 1/3 of the brightness temperature of the gas kinetic temperature, the antenna temperature is linearly proportional to the column density of C{sup +} irrespective of the optical depth of the transition. This is appropriately referred to as the effectively optically thin approximation. We review the critical densities for excitation of the [C II] line by various collision partners, briefly analyze C{sup +} absorption, and conclude with a discussion of C{sup +} cooling and how the considerations for line intensities affect the behavior of this important coolant of the ISM.

  9. Vibrational and Rotational Structure and Excited-State Dynamics of Pyrene

    NASA Astrophysics Data System (ADS)

    Kowaka, Yasuyuki; Ashizawa, Nolitaka; Baba, Masaaki

    2010-06-01

    Pyrene is one of the prototypical compact polycyclic aromatic hydrocarbons (PAHs), and It is important to investigate its molecular structure precisely, because it does not conform to Hückel's 4n+2 rule. We analyzed high-resolution and ultrahigh-resolution spectra of jet-cooled pyrene and elucidated the vibrational and rotational structures in the S_0 ^1A_g and S_1 ^1B3u states. We conclude that the molecule is planar with D2h symmetry. The rotational constants and vibrational normal energies are very similar for the S_0 and S_1 states, indicating that its geometrical structure and potential energy curves are not changed much upon electronic excitation. This small change is common to large PAH molecules because the changes of bond orders by one electron excitation is diluted with a large number of π electrons. The rates of Radiationless transitions in the S_1 state are closely related with the molecular structure and the potential energy curves. Intersystem crossing (ISC) to the triplet state is expected to be very slow in planar PAHs. Internal conversion (IC) to the S_0 state does not occur, if the molecular structure and potential energy curves are identical for the S_0 and S_1 states. In perylene, the fluorescence lifetime is 1400 ns, and the fluorescence quantum yield is considerably high. These properties are attributed to its small changes in molecular structure and potential energy curves upon S_1 ← S_0 excitation. M. Baba, Y. Kowaka et al., J. Chem. Phys., 131, 224318 (2009)

  10. 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.

  11. Observation of Metastable Structural Excitations and Concerted Atomic Motions on a Crystal Surface

    NASA Astrophysics Data System (ADS)

    Hwang, Ing-Shouh; Golovchenko, Jene

    1992-11-01

    The addition of a small number of lead atoms to a germanium(111) surface reduces the energy barrier for activated processes, and with a tunneling microscope it is possible to observe concerted atomic motions and metastable structures on this surface near room temperature. The formation and annihilation of these metastable structural surface excitations is associated with the shift in position of large numbers of germanium surface atoms along a specific row direction like beads on an abacus. The effect provides a mechanism for understanding the transport of atoms on a semiconductor surface.

  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 of continuous one-dimensional structures under steady harmonic excitation

    NASA Technical Reports Server (NTRS)

    Johnson, E. H.; Segenreich, S. A.; Ashley, H.; Rizzi, P.

    1976-01-01

    The paper examines some questions relating to the optimal design of continuous one-dimensional structures driven by harmonically oscillating loads. Optimal-control methods are applied to a cantilever bar driven sinusoidally by an axial force at its tip to illustrate the minimum-weight design of one-dimensional structures under dynamic excitation. Realistic constraints are imposed during the optimizations, including a maximum allowable stress amplitude at any point along the bar and a minimum cross-sectional area. It is shown that in the absence of damping, the design space may contain many disjoint feasible regions, and multiple optima can exist. Detailed solutions are obtained for continuous bars with an excitation frequency less than, and then greater than, the fundamental free-vibration frequency. It is found that above a certain excitation frequency, two or more arcs with different constraints characterize the optimal designs. It is concluded that when more than two different constrained arcs characterize the optimal solution, the continuum approach may be impractical, and finite-element approximations may offer the only alternative.

  14. 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.

  15. 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

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

    PubMed

    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 ( 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. PMID:27649202

  17. Structural optimization for the avoidance of self-excited vibrations based on analytical models

    NASA Astrophysics Data System (ADS)

    Spelsberg-Korspeter, Gottfried

    2010-11-01

    Self-excited vibrations are a severe problem in many technical applications. In many cases they are caused by friction as for example in disk and drum brakes, clutches, saws and paper calenders. The goal to suppress self-excited vibrations can be reached by active and passive techniques, the latter ones being preferable due to the lower costs. Among design engineers it is known that breaking the symmetries of structures is sometimes helpful to avoid self-excited vibrations. This has been verified from an analytical point of view in a recent paper. The goal of the present paper is to use this analytical insight for a systematic structural optimization of rotors in frictional contact. The first system investigated is a simple discrete model of a rotor in frictional contact. As a continuous example a rotating beam in frictional contact is considered and optimized with respect to its bending stiffness. Finally a brake disk is optimized giving some attention to the feasibility of the modifications for the production process.

  18. 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.

  19. Nonlinear system identification of base-excited structures using an intelligent parameter varying (IPV) modeling approach

    NASA Astrophysics Data System (ADS)

    Saadat, Soheil; Buckner, Gregory D.; Furukawa, Tadatoshi; Noori, Mohammad N.

    2003-07-01

    Health monitoring and damage detection strategies for base-excited structures typically rely on accurate models of the system dynamics. Restoring forces in these structures can exhibit highly non-linear characteristics, thus accurate non-linear system identification is critical. Parametric system identification approaches are commonly used, but require a priori knowledge of restoring force characteristics. Non-parametric approaches do not require this a priori information, but they typically lack direct associations between the model and the system dynamics, providing limited utility for health monitoring and damage detection. In this paper a novel system identification approach, the Intelligent Parameter Varying (IPV) method, is used to identify constitutive non-linearities in structures subject to seismic excitations. IPV overcomes the limitations of traditional parametric and non-parametric approaches, while preserving the unique benefits of each. It uses embedded radial basis function networks to estimate the constitutive characteristics of inelastic and hysteretic restoring forces in a multi-degree-of-freedom structure. Simulation results are compared to those of a traditional parametric approach, the prediction error method. These results demonstrate the effectiveness of IPV in identifying highly nonlinear restoring forces, without a priori information, while preserving a direct association with the structural dynamics.

  20. Long-Lived Excited-State Dynamics of i-Motif Structures Probed by Time-Resolved Infrared Spectroscopy.

    PubMed

    Keane, Páraic M; Baptista, Frederico R; Gurung, Sarah P; Devereux, Stephen J; Sazanovich, Igor V; Towrie, Michael; Brazier, John A; Cardin, Christine J; Kelly, John M; Quinn, Susan J

    2016-05-01

    UV-generated excited states of cytosine (C) nucleobases are precursors to mutagenic photoproduct formation. The i-motif formed from C-rich sequences is known to exhibit high yields of long-lived excited states following UV absorption. Here the excited states of several i-motif structures have been characterized following 267 nm laser excitation using time-resolved infrared spectroscopy (TRIR). All structures possess a long-lived excited state of ∼300 ps and notably in some cases decays greater than 1 ns are observed. These unusually long-lived lifetimes are attributed to the interdigitated DNA structure which prevents direct base stacking overlap.

  1. 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.

  2. Excited-state proton coupled charge transfer modulated by molecular structure and media polarization.

    PubMed

    Demchenko, Alexander P; Tang, Kuo-Chun; Chou, Pi-Tai

    2013-02-01

    Charge and proton transfer reactions in the excited states of organic dyes can be coupled in many different ways. Despite the complementarity of charges, they can occur on different time scales and in different directions of the molecular framework. In certain cases, excited-state equilibrium can be established between the charge-transfer and proton-transfer species. The interplay of these reactions can be modulated and even reversed by variations in dye molecular structures and changes of the surrounding media. With knowledge of the mechanisms of these processes, desired rates and directions can be achieved, and thus the multiple emission spectral features can be harnessed. These features have found versatile applications in a number of cutting-edge technological areas, particularly in fluorescence sensing and imaging.

  3. 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.

  4. Neuron absorption study and mid-IR optical excitations

    NASA Astrophysics Data System (ADS)

    Guo, Dingkai; Chen, Xing; Vadala, Shilpa; Leach, Jennie; Kostov, Yordan; Bewley, William W.; Kim, Chul-Soo; Kim, Mijin; Canedy, Chadwick L.; Merritt, Charles D.; Vurgaftman, Igor; Meyer, Jerry R.; Choa, Fow-Sen

    2012-02-01

    Neuronal optical excitation can provide non-contacting tools to explore brain circuitry and a durable stimulation interface for cardiac pacing and visual as well as auditory sensory neuronal stimulation. To obtain accurate absorption spectra, we scan the transmission of neurons in cell culture medium, and normalize it by subtracting out the absorption spectrum of the medium alone. The resulting spectra show that the main neuronal absorption peaks are in the 3000- 6000nm band, although there is a smaller peak near 1450nm. By coupling the output of a 3μm interband cascade laser (ICL) into a mid-IR fluorozirconate fiber, we can effectively deliver more than 1J/cm2 photon intensity to the excitation site for neuronal stimulation.

  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. 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

  7. 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.

  8. 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.

  9. Resonant Raman scattering in Nd{sub 2}O{sub 3} and the electronic structure of Sr{sub 2}RuO{sub 4} studied by synchrotron radiation excitation.

    SciTech Connect

    Ederer, D. L.

    1998-12-03

    This paper is intended to illustrate two points. The first being the extensive growth of resonant Raman soft x-ray scattering due to the emergence of third-generation x-ray sources. With these sources, the ubiquitous presence of Raman scattering near the 3d and 4d ionization thresholds has been used to elucidate the excitation process in a number of rare earth and transition metal compounds. Such scattering can produce dramatic changes in the emission spectrum, as we show in our example of inelastic scattering at the 3d threshold of Nd{sub 2}O{sub 3}. Photon-in photon-out soft x-ray spectroscopy is adding a new dimension to soft x-ray spectroscopy by providing many opportunities for exciting research, especially at third-generation synchrotrons light sources. Second, it is very effective to use theory and experiment to characterize the electronic properties of materials. In particular we confirmed in-plane oxygen-ruthenium bonding in Sr{sub 2}RuO{sub 4}, this first copperless perovskite superconductor, by analyses using calculations, soft x-ray emission spectroscopy (SXE) and photoelectron spectroscopy (PES). Measurements of this type illustrate the importance of combining SXE and PES measurements with theoretical calculations.

  10. 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

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

    PubMed

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

    2016-05-19

    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.

  12. NDT testing by holographic interferometry applied to the structural diagnostic of artwork conservations by means of sound wave excitation

    NASA Astrophysics Data System (ADS)

    Vincitorio, Fabio; Ramil, Alberto; López, Ana J.; Saavedra, Emilio; Yáñez, Armando

    2008-06-01

    Techniques based on holographic interferometry have achieved a mature state of non destructive testing applications in industry and nowadays they are rising as interesting and promising tools in the field of conservation practices; giving information about the condition of structural integration of artworks. In the practice of these techniques it is necessary to generate a relative deformation in the object under study. Depending of the characteristics of the artwork, different methods may be used to achieve the desired displacement; being thermal excitation by means of filament lamps and wave sounds generated by speakers the most common. By applying these methods the deformation process usually involves a large area of the object, which limits the information obtained of a finite region. However, the use of a wave sound emitter of small dimensions, like a low power monotone buzzer, allows to decrease the affected area and to obtain information about the structural integrity of localized points of the surface. In the present study conventional double exposure double way holographic technique based on holographic films was used to obtain an out of plain deformation pattern caused by a sound emitter in an oil painting which has suffered heavy structural damage. Optimization of the excitation sound wave characteristics (frequency and amplitude) and the adjustment and calibration of the experimental set up, in order to obtain precise information about the physical and mechanical integrity of localized points of the painting are reported.

  13. A theoretical study of the isotope effects on the fluorescence excitation spectrum of 5-aminotropolone

    NASA Astrophysics Data System (ADS)

    Paz, Juan J.; Moreno, Miquel; Lluch, José M.

    1998-05-01

    A combined ab initio+nuclear dynamics study is performed to theoretically analyze the intramolecular H-atom transfer process in 5-aminotropolone in both the ground (S0) and first excited (S1) singlet electronic states. A complete active space self-consistent field (CASSCF) method is used to optimize the geometries. Energies are then corrected through the second order Møller-Plesset perturbation theory. These results are used to build up reduced bidimensional energy surfaces so that the nuclear wave functions for the nuclear motions in both electronic states are obtained. In particular we have analyzed the six isotopomers that result from deuteration of the amino and hydroxy groups of 5-aminotropolone. It is found that for symmetric structures (-OH/-NH2, -OH/-ND2, -OD/-NH2, and -OD/-ND2), the two lowest vibrational levels in both S0 and S1 appear as a quasidegenerated tunneling doublet. The tunneling splitting in S0 is much lower so that the doublet at the origin, seen in the fluorescence excitation spectra of 5-aminotropolone, can be entirely assigned to the S1 state. In agreement with the experimental findings, this splitting greatly diminishes when the transferring hydrogen is substituted by a deuterium, whereas deuteration of the amino group produces only a modest decrease of such a splitting. A quite different result is found for the nonsymmetric isotopically substituted structures (-OH/-NHD and -OD/-NHD), as the isotope induced asymmetry, combined with the high energy barrier in the S0 potential energy surface, leads to a complete localization of the two lowest vibrational wave functions in S0. On the other hand, for S1 the asymmetry and energy barriers are low enough so that an important degree of delocalization of the two lowest vibrational wave functions is found. These results are again in agreement with the presence of an isotope induced quartet in the fluorescence excitation spectra of these species.

  14. Excited Hadrons and the Analytical Structure of Bound-State Interaction Kernels

    NASA Astrophysics Data System (ADS)

    El-Bennich, Bruno; Krein, Gastão; Rojas, Eduardo; Serna, Fernando E.

    2016-10-01

    We highlight Hermiticity issues in bound-state equations whose kernels are subject to a highly asymmetric mass and momentum distribution and whose eigenvalue spectrum becomes complex for radially excited states. We trace back the presence of imaginary parts in the eigenvalues and wave functions to truncation artifacts and suggest how they can be eliminated in the case of charmed mesons. The solutions of the gap equation in the complex plane, which play a crucial role in the analytic structure of the Bethe-Salpeter kernel, are discussed for several interaction models and qualitatively and quantitatively compared to analytic continuations by means of complex-conjugate pole models fitted to real solutions.

  15. Structural tuning intra- versus inter-molecular proton transfer reaction in the excited state.

    PubMed

    Chung, Min-Wen; Liao, Jia-Ling; Tang, Kuo-Chun; Hsieh, Cheng-Chih; Lin, Tsung-Yi; Liu, Chun; Lee, Gene-Hsiang; Chi, Yun; Chou, Pi-Tai

    2012-07-01

    A series of 2-pyridyl-pyrazole derivatives 1-4 possessing five-membered ring hydrogen bonding configuration are synthesized, the structural flexibility of which is strategically tuned to be in the order of 1 > 2 > 3 > 4. This system then serves as an ideal chemical model to investigate the correlation between excited-state intramolecular proton transfer (ESIPT) reaction and molecular skeleton motion associated with hydrogen bonds. The resulting luminescence data reveal that the rate of ESIPT decreases upon increasing the structural constraint. At sufficiently low concentration where negligible dimerization is observed, ESIPT takes place in 1 and 2 but is prohibited in 3 and 4, for which high geometry constraint is imposed. The results imply that certain structural bending motions associated with hydrogen bonding angle/distance play a key role in ESIPT. This trend is also well supported by the DFT computational approach, in which the barrier associated with ESIPT is in the order of 1 < 2 < 3 < 4. Upon increasing the concentration in cyclohexane, except for 2, the rest of the title compounds undergo ground-state dimerization, from which the double proton transfer takes place in the excited state, resulting in a relatively blue shifted dimeric tautomer emission (cf. the monomer tautomer emission). The lack of dimerization in 2 is rationalized by substantial energy required to adjust the angle of hydrogen bond via twisting the propylene bridge prior to dimerization. PMID:22618273

  16. 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.

  17. 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

  18. 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.

  19. Study on rule-based adaptive fuzzy excitation control technology

    NASA Astrophysics Data System (ADS)

    Zhao, Hui; Wang, Hong-jun; Liu, Lu-yuan; Yue, You-jun

    2008-10-01

    Power system is a kind of typical non-linear system, it is hard to achieve excellent control performance with conventional PID controller under different operating conditions. Fuzzy parameter adaptive PID exciting controller is very efficient to overcome the influence of tiny disturbances, but the performance of the control system will be worsened when operating conditions of the system change greatly or larger disturbances occur. To solve this problem, this article presents a rule adaptive fuzzy control scheme for synchronous generator exciting system. In this scheme the control rule adaptation is implemented by regulating the value of parameter di under the given proportional divisors K1, K2 and K3 of fuzzy sets Ai and Bi. This rule adaptive mechanism is constituted by two groups of original rules about the self-generation and self-correction of the control rule. Using two groups of rules, the control rule activated by status 1 and 2 in figure 2 system can be regulated automatically and simultaneously at the time instant k. The results from both theoretical analysis and simulation show that the presented scheme is effective and feasible and possesses good performance.

  20. Hadronic interactions in large N_c QCD: Studies of excited baryon decays and scattering relations

    NASA Astrophysics Data System (ADS)

    Dakin, Daniel C.

    Decays and scattering events are two of the principal ways to learn about particle physics. Decays, in which a particle spontaneously disintegrates and we examine the debris, are quantified by a decay width. The decay of a resonance state provides information about the structure of the state and the interaction between its components. In particular, we can learn about the dynamics of quarks and gluons by studying the decay of hadrons. Scattering, in which particles are directed towards each other and interact, are quantified by partial-wave amplitudes. These amplitudes give us information about the interaction between the scattered particles. In principle, all of hadronic physics follows from quantum chromodynamics (QCD), which describes the interactions of quarks and gluons. However, the techniques of perturbation theory are not applicable to QCD at low energy because the strong coupling constant (the natural choice for the expansion parameter) is large at the energy scale of hadronic physics. A powerful model-independent method is the 1/Nc expansion in which the number of quark color degrees of freedom (Nc) is treated as a large number. This thesis presents the application of the 1/ Nc expansion to the calculation of physical observables for excited baryons, pion-nucleon scattering, and pion photoproduction. The framework of the contracted SU(4) group that emerges in large Nc QCD is applied to the study of excited baryon decays. The Nc power scaling of the excited baryon's decay width depends on the symmetry of its spin-flavor wavefunction. The scaling with Nc for different symmetries is discussed in the context of a quark-shell model that permits mixing of different symmetry types. The subtle issues concerning the legitimacy of applying the contracted SU(4) group theory to excited baryons are discussed. The contracted SU(4) spin-flavor symmetry severely restricts the angular momentum and isospin dependence of partial-wave amplitudes. The consequences of this

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

    DOE PAGES

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, II Woong; Walko, Donald A.; Dufresne, Eric M.; Jaewoo, Jeong; Samant, Mahesh G.; et al

    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

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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. PMID:26406047

  7. Spin-orbit excitations and electronic structure of the putative Kitaev magnet α -RuCl3

    NASA Astrophysics Data System (ADS)

    Sandilands, Luke J.; Tian, Yao; Reijnders, Anjan A.; Kim, Heung-Sik; Plumb, K. W.; Kim, Young-June; Kee, Hae-Young; Burch, Kenneth S.

    2016-02-01

    Mott insulators with strong spin-orbit coupling have been proposed to host unconventional magnetic states, including the Kitaev quantum spin liquid. The 4 d system α -RuCl3 has recently come into view as a candidate Kitaev system, with evidence for unusual spin excitations in magnetic scattering experiments. We apply a combination of optical spectroscopy and Raman scattering to study the electronic structure of this material. Our measurements reveal a series of orbital excitations involving localized total angular momentum states of the Ru ion, implying that strong spin-orbit coupling and electron-electron interactions coexist in this material. Analysis of these features allows us to estimate the spin-orbit coupling strength, as well as other parameters describing the local electronic structure, revealing a well-defined hierarchy of energy scales within the Ru d states. By comparing our experimental results with density functional theory calculations, we also clarify the overall features of the optical response. Our results demonstrate that α -RuCl3 is an ideal material system to study spin-orbit coupled magnetism on the honeycomb lattice.

  8. 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.

  9. 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.

  10. Shape Coexistence in the Neutron-Deficient Even-Even Hg182-188 Isotopes Studied via Coulomb Excitation

    NASA Astrophysics Data System (ADS)

    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-KleÂķ, 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.

    2014-04-01

    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.

  11. 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. PMID:24815644

  12. 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.

  13. 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.

  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. Excited States and Photodebromination of Selected Polybrominated Diphenyl Ethers: Computational and Quantitative Structure—Property Relationship Studies

    PubMed Central

    Luo, Jin; Hu, Jiwei; Wei, Xionghui; Li, Lingyun; Huang, Xianfei

    2015-01-01

    This paper presents a density functional theory (DFT)/time-dependent DFT (TD-DFT) study on the lowest lying singlet and triplet excited states of 20 selected polybrominateddiphenyl ether (PBDE) congeners, with the solvation effect included in the calculations using the polarized continuum model (PCM). The results obtained showed that for most of the brominated diphenyl ether (BDE) congeners, the lowest singlet excited state was initiated by the electron transfer from HOMO to LUMO, involving a π–σ* excitation. In triplet excited states, structure of the BDE congeners differed notably from that of the BDE ground states with one of the specific C–Br bonds bending off the aromatic plane. In addition, the partial least squares regression (PLSR), principal component analysis-multiple linear regression analysis (PCA-MLR), and back propagation artificial neural network (BP-ANN) approaches were employed for a quantitative structure-property relationship (QSPR) study. Based on the previously reported kinetic data for the debromination by ultraviolet (UV) and sunlight, obtained QSPR models exhibited a reasonable evaluation of the photodebromination reactivity even when the BDE congeners had same degree of bromination, albeit different patterns of bromination. PMID:25569092

  16. 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.

  17. Electronic Structure of the Ground and Excited States of the CuA Site by NMR Spectroscopy

    PubMed Central

    Abriata, Luciano A.; Ledesma, Gabriela N.; Pierattelli, Roberta; Vila, Alejandro J.

    2009-01-01

    The electronic properties of Thermus thermophilus CuA in the oxidized form were studied by 1H and 13C NMR spectroscopy. All the 1H and 13C resonances from cysteine and imidazole ligands were observed and assigned in a sequence-specific fashion. The detection of net electron spin density on a peptide moiety is attributed to the presence of a H-bond to a coordinating sulfur atom. This hydrogen-bond is conserved in all natural CuA variants, and is important to maintain the electronic structure of the metal site, rendering the two Cys ligands nonequivalent. The anomalous temperature dependence of the chemical shifts is explained by the presence of a low-lying excited state located about 600 cm-1 above the ground state. The room temperature shifts can be described as the thermal average of a σu* ground state and a πu excited state. These results provide a detailed description of the electronic structure of the CuA site at atomic resolution in solution at physiologically relevant temperature. PMID:19146411

  18. Electronic structure and polaronic excitation in FeVO{sub 4}

    SciTech Connect

    Dixit, A.; Lawes, G.; Chen, P.; Musfeldt, J. L.

    2011-10-03

    We investigated the electronic properties of FeVO{sub 4} films using optical, valence band x-ray photoelectron, and infrared spectroscopies. These studies show that FeVO{sub 4} is a direct bandgap system with a 2.7 eV gap with the Fermi level in the middle of the valence band maximum and conduction band minimum. A polaronic excitation is also observed in the middle infrared, indicating the importance of charge-lattice coupling in this multiferroic material. Fits to a model for the optical response of large polarons yield a binding energy of approximately 130 meV.

  19. Near-complete structural characterization of phosphatidylcholines using electron impact excitation of ions from organics.

    PubMed

    Campbell, J Larry; Baba, Takashi

    2015-06-01

    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.

  20. 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.

  1. Parents' and children's ratings of sleep behavior, excitement, and tiredness: a 10-week longitudinal study.

    PubMed

    Fisher, B E; Ross, K; Wilson, A

    1994-06-01

    In a 10-week longitudinal study, 29 parents and their children kept daily records of the children's sleep behaviors, excitement levels, and tiredness levels. Although the hypothesized increase in sleep behaviors such as sleepwalking and restlessness during the week of Christmas did not occur, children rated as more excitable by their parents and themselves exhibited a higher frequency of sleep behaviors. Positive associations were also found between averaged tiredness ratings and sleep scores. The results support previous findings of an association between arousal characteristics of children and their sleep behavior. Moderate validity coefficients were obtained for parents' and children's ratings of excitement, tiredness, and nocturnal waking.

  2. Harmonic plasma waves excitation and structure evolution of intense ion beams in background plasmas

    NASA Astrophysics Data System (ADS)

    Hu, Zhang-Hu; Wang, You-Nian

    2016-08-01

    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.

  3. Excited electronic structure of methylcyanoacetylene probed by VUV Fourier-transform absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Lamarre, N.; Gans, B.; Vieira Mendes, L. A.; Gronowski, M.; Guillemin, J.-C.; De Oliveira, N.; Douin, S.; Chevalier, M.; Crépin, C.; Kołos, R.; Boyé-Péronne, S.

    2016-10-01

    High resolution photoabsorption spectrum of gas-phase methylcyanoacetylene (CH3C3 N) has been recorded from 44 500 to 130 000 cm-1 at room temperature with a vacuum ultraviolet Fourier-transform spectrometer on the DESIRS synchrotron beamline (SOLEIL). The absolute photoabsorption cross section in this range is reported for the first time. Valence shell transitions and Rydberg series converging to the ground state X˜+2E of the cation as well as series converging to electronically excited states (A˜+A21 and C˜+) are observed and assigned. Time-dependent density-functional-theory calculations have been performed to support the assignment of the experimental spectrum in the low energy range. A tentative scaling of the previously measured CH3C3N+ ion yield by Lamarre et al. [17] is proposed, based on the comparison of the absorption data above the first ionization potential with the observed autoionization structures.

  4. 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.

  5. 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.

  6. Study of nonlinear oscillations due to exciter control using Hopf bifurcation

    SciTech Connect

    Abed, E.; Tsolas, N.; Varaiya, P.

    1983-01-01

    The effect of excitation system parameters on power system stability is studied here. The classical swing equation for a power generator augmented with an exciter is shown to undergo a Hopf bifurcation to periodic solutions. Only unstable oscillations occur for realistic parameter values and characterize the attractor of the stable equilibrium point. Attention is focussed on the global behavior of the oscillations as the critical parameter is varied. The analysis is carred out for a single machine connected to an infinite bus case.

  7. 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.

  8. Study of Microstructure and Transient, Instantaneous Current in Different Excitations During Silicon Micromachining

    NASA Astrophysics Data System (ADS)

    Kulkarni, A. V.; Jain, V. K.; Misra, K. A.

    2012-09-01

    Study of transient, instantaneous current during silicon micromachining using electrochemical spark process is carried out. Voltage excitation of three kinds namely, dc, Half wave rectified and ac are used to carve the micro channels. The transient and instantaneous process current is measured online and analyzed for each excitation. Micromachining and the surface topography results are presented. The transient current reveals the mechanism of the spark formation and explains the inherent process stages.

  9. 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.

  10. Theoretical investigation on properties of the ground and lowest excited states of a red emitter with donor-π-acceptor structure

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojun; Zhang, Xiao; Hou, Yanbing; Teng, Feng; Lou, Zhidong

    2011-03-01

    The ground and excited state properties of DCDPC, particularly designed as a red emitter for organic light emitting diodes applications have been studied by means of density functional theory (DFT) and time-dependent (TD)DFT. The electronic and geometrical structures of DCDPC in acetone, tetrahydrofuran and benzene solvents are reported for the first time. The experimental absorption and fluorescence spectra are reproduced by calculations. By comparison with experimental data, insight on the performance of 10 exchange correlation functionals is also given. M06 in the frame of DFT and TDDFT with a polarizable continuum model and a medium sized basis set emerges as the most effective strategy. Beside the good agreement between the calculational and experimental spectra proving the accuracy of the strategy, the calculations allow further insights into the electronic structure for the family of isophorone-based light emitting materials with D-π-A structure, especially the electronic and geometrical structures for the excited states.

  11. 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.

  12. Analysis and Control of Vibrational Power Transmission to Machinery Supporting Structures Subjected to a Multi-Excitation System, Part Iii: Vibrational Power Cancellation and Control Experiments

    NASA Astrophysics Data System (ADS)

    Koh, Y. K.; White, R. G.

    1996-10-01

    The study of time-averaged vibrational power input to flexible beams and rectangular plates subjected to co-located simultaneously sinusoidal force and moment excitations has resulted in various potential vibration control schemes, both active and passive approaches, based on minimization of the resultant vibrational power input to the structures. The theory and analytical results have been presented in the two companion papers. In this paper the experimental arrangements for verification of the theoretical predictions are described. The optimal moment arm concept for the vibration levels by using combined force and moment excitations is validated on beams and rectangular plates experimentally. It is also demonstrated that by using a set of force and moment seating devices with predetermined moment arms, the vibrational response around the fundamental resonance frequency of a supporting rectangular plate caused by unbalance motor excitations can be reduced.

  13. Excited and enhanced twinborn acoustic-induced mutual forces in oblique grating structures

    NASA Astrophysics Data System (ADS)

    Lu, Shuifang; Zhang, Xin; Wu, Fugen; Yao, Yuanwei; Chen, Zongwang

    2016-07-01

    We propose a water-immersed geometrically oblique grating structure patterned with a 1D periodic array of oblique rhombuses. Twin acoustic-induced mutual forces (both repulsive and attractive) between coupled steel plates were realized in this system when the external plane wave normally impacted the plates. Calculations showed that the emerging forces are more than an order of magnitude larger than the corresponding induced force of a conventional grating structure. We also found that the strong acoustic-induced mutual forces stem from the resonant excitation of nonleaky flexural Lamb modes in the coupled plates, and that these forces couple more strongly with the external incident acoustic waves. Furthermore, the amplitudes and resonant wavelengths of these forces can be coarsely controlled by changing the symmetry of the system and finely adjusted by varying the slant angle and the edge-length of the oblique rhombus. The proposed acoustic system could potentially be applied in sensors and in the ultrasonic detection of weak signals in water.

  14. Low energy excitations in iridates studied with Resonant Inelastic X-ray Scattering

    NASA Astrophysics Data System (ADS)

    Liu, Xuerong

    2013-03-01

    In the iridium oxides, the strong spin-orbit coupling (SOC) of the 5d iridium electrons entangles the orbital and spin degrees of freedom, providing opportunities for exotic magnetic states with highly anisotropic exchange interactions. At the same time, the spatially extended 5d electrons are expected to have much stronger hybridization with the oxygen 2p orbitals, comparing with that in 3d transition element compounds. Both factors make crystal symmetry and local environment crucial in determining the electronic and magnetic properties of the iridates. We present here our resonant inelastic X-ray scattering (RIXS) studies of a number of octahedrally coordinated iridates with special structures, exploring these effects. In particular, for the 1-D spin 1/2 chain compound, Sr3CuIrO6, the wavefunction of the hole in the t2g manifold was reconstructed based on the RIXS spectra. Our results show that it is significantly modified from the isotropic shape expected for Jeff = 1 / 2 states in the strong SOC limit, due to the distortion of the oxygen octahedral cage. This distortion is comparable to, or smaller than, that present in most iridates and thus this work emphasizes the importance of local symmetry for the iridate families. Further, the magnetic excitations of this material were also measured. A large gap of ~30 meV, was found, comparable to the magnetic dispersion bandwidth. This is in contrast to the gapless dispersion expected for linear chain with isotropic Heisenberg exchange interaction. We also studied Na4Ir3O8 which has a hyperkagome lattice, and is a candidate quantum spin liquid. Here, a low energy continuum is observed below the d-d excitations. Optical conductivity measurements performed on the same sample and polarization dependence of the RIXS signal suggest that these excitations are magnetic in origin, agreeing with the spin-liquid state prediction. The work at Brookhaven was supported by the U.S. Department of Energy, Division of Materials Science

  15. 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.

  16. 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.

  17. Special features of the excitation spectra and kinetics of photoluminescence of the Si{sub 1-x}Ge{sub x}:Er/Si structures with relaxed heterolayers

    SciTech Connect

    Krasilnikova, L. V. Yablonskiy, A. N.; Stepikhova, M. V.; Drozdov, Yu. N.; Shengurov, V. G.; Krasilnik, Z. F.

    2010-11-15

    Luminescent properties of heteroepitaxial Si{sub 1-x}Ge{sub x}:Er/Si structures with relaxed heterolayers are studied. The results of combined studies of the excitation spectra and kinetics of photoluminescence (PL) are used to single out the components providing the largest contribution to the PL signal of the Si{sub 1-x}Ge{sub x}:Er/Si structures in the wavelength region of 1.54 {mu}m. It is shown that relaxation of elastic stresses in the Si{sub 1-x}Ge{sub x}:Er heterolayer affects only slightly the kinetic characteristics of erbium luminescence and manifests itself in insignificant contribution of the defects and defect-impurity complexes to the luminescent response of the Si{sub 1-x}Ge{sub x}:Er/Si structures. In the excitation spectra of the erbium PL, special features related to the possibility of the rare-earth impurity excitation at energies lower than the band gap of the Si{sub 1} {sub -x}Ge{sub x} solid solution are revealed. It is shown that a peak the width of which depends on the band gap of the solid solution and the extent of its relaxation is observed in the excitation spectra of the erbium-related PL in the Si{sub 1-x}Ge{sub x}:Er/Si structures in the wavelength region of 1040-1050 nm. The observed specific features are accounted for by involvement of intermediate levels in the band gap of the Si{sub 1-x}Ge{sub x}:Er solid solution in the process of excitation of an Er{sup 3+} ion.

  18. 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

  19. Measurements and analyses of principal dynamic parameters of building structures as a function of type of vibration excitation

    NASA Astrophysics Data System (ADS)

    Bartmański, Cezary; Bochenek, Wojciech; Passia, Henryk; Szade, Adam

    2006-06-01

    The methods of direct measurement and analysis of the dynamic response of a building structure through real-time recording of the amplitude of low-frequency vibration (tilt) have been presented. Subject to analyses was the reaction induced either by kinematic excitation (road traffic and mining-induced vibration) or controlled action of solid-fuel rocket micro-engines installed on the building. The forces were analysed by means of a set of transducers installed both in the ground and on the structure. After the action of excitation forces has been stopped, the system (structure) makes damped vibration around the static equilibrium position. It has been shown that the type of excitation affects the accuracy of evaluation of principal dynamic parameters of the structure. In the authors opinion these are the decrement of damping and natural vibration frequency. Positive results of tests with the use of excitation by means of short-action (0.6 second) rocket micro-engines give a chance to develop a reliable method for periodical assessment of acceptable loss of usability characteristics of building structures heavily influenced by environmental effects.

  20. Cyclometalated gold(III) trioxadiborrin complexes: studies of the bonding and excited states.

    PubMed

    Ayoub, Nicholas A; Browne, Amberle R; Anderson, Bryce L; Gray, Thomas G

    2016-03-01

    Trioxadiborrins are chelating ligands that assemble in dehydration reactions of boronic acids. They are structurally related to β-diketonate ligands, but have a 2-charge. Little is known of the bonding properties of trioxadiborrin ligands. Presented here are density-functional theory (DFT) studies of cyclometalated gold(III) trioxadiborrins. Substituent effects are evaluated, and comparison is made to the cyclometalating 2-(4-tolyl)pyridine (tpy) ligand on gold. The tpy ligand binds more strongly than any trioxadiborrin ligand considered here, and the two ligands bind competitively to gold. The 1,3-diphenyl trioxadiborrin ligand of 1 has a larger absolute binding enthalpy to gold than its β-diketonate analogue. Conjugation between boron and aryl substituents delocalizes charge and attenuates the trioxadiborrin's binding capacity. Steric effects that disrupt conjugation between boron and aryl substituents cause the trioxadiborrin to chelate more tightly. Fragment bond orders are divided into in-plane and out-of-plane contributions for square planar 1. In-plane bonding accounts for 88% of bond order between (tpy)Au2+ and the trioxadiborrin ligand. Cyclometalated gold(III) trioxadiborrin complexes were previously shown to be phosphorescent. Spin-unrestricted triplet-state geometry optimizations find that the ten largest excited-state distortions all occur on the tpy ligand. A plot of spin density in triplet 1 shows spin to reside predominantly on tpy. The 77 K luminescence spectrum of 1 is reported here. Time-dependent DFT and configuration interaction singles calculations (corrected for doubles excitations) overestimate the emission energy by ∼ 0.12 eV. PMID:26821088

  1. Cyclometalated gold(III) trioxadiborrin complexes: studies of the bonding and excited states.

    PubMed

    Ayoub, Nicholas A; Browne, Amberle R; Anderson, Bryce L; Gray, Thomas G

    2016-03-01

    Trioxadiborrins are chelating ligands that assemble in dehydration reactions of boronic acids. They are structurally related to β-diketonate ligands, but have a 2-charge. Little is known of the bonding properties of trioxadiborrin ligands. Presented here are density-functional theory (DFT) studies of cyclometalated gold(III) trioxadiborrins. Substituent effects are evaluated, and comparison is made to the cyclometalating 2-(4-tolyl)pyridine (tpy) ligand on gold. The tpy ligand binds more strongly than any trioxadiborrin ligand considered here, and the two ligands bind competitively to gold. The 1,3-diphenyl trioxadiborrin ligand of 1 has a larger absolute binding enthalpy to gold than its β-diketonate analogue. Conjugation between boron and aryl substituents delocalizes charge and attenuates the trioxadiborrin's binding capacity. Steric effects that disrupt conjugation between boron and aryl substituents cause the trioxadiborrin to chelate more tightly. Fragment bond orders are divided into in-plane and out-of-plane contributions for square planar 1. In-plane bonding accounts for 88% of bond order between (tpy)Au2+ and the trioxadiborrin ligand. Cyclometalated gold(III) trioxadiborrin complexes were previously shown to be phosphorescent. Spin-unrestricted triplet-state geometry optimizations find that the ten largest excited-state distortions all occur on the tpy ligand. A plot of spin density in triplet 1 shows spin to reside predominantly on tpy. The 77 K luminescence spectrum of 1 is reported here. Time-dependent DFT and configuration interaction singles calculations (corrected for doubles excitations) overestimate the emission energy by ∼ 0.12 eV.

  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. PMID:20164647

  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. 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)

  5. 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

  6. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: Key role of the excited-state hydrogen-bond strengthening

    NASA Astrophysics Data System (ADS)

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-01

    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.

  7. 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.

  8. 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.

  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. 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

  11. 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.

  12. 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.

  13. High-frequency collective excitations in molten and glassy Te studied by inelastic neutron scattering

    SciTech Connect

    Ruiz-Martin, M. D.; Jimenez-Ruiz, M.; Bermejo, F. J.

    2006-03-01

    The spectra of collective excitations of liquid and glassy tellurium have been studied by means of inelastic neutron scattering. Here we report on the dynamics of liquid Te as measured at two different temperatures, just above melting (T{sub m}=723 K) and at {approx}1000 K as well as the glass that is studied at room temperature. Estimates for the velocity of propagating excitations for both temperatures have been obtained from the experimental data, and a contrasting behavior is found with respect to anomalies shown by the adiabatic sound velocity measured by ultrasound methods. The origin of such differences is finally discussed.

  14. 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.

  15. 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.

  16. 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.

  17. Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy.

    PubMed

    Wilkinson, Iain; Boguslavskiy, Andrey E; Mikosch, Jochen; Bertrand, Julien B; Wörner, Hans Jakob; Villeneuve, David M; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert

    2014-05-28

    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 (B̃)(1)B1/(Ã)(1)A2, 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 (B̃)(1)B1 diabatic state is presented. Signatures of the oscillatory motion on the (B̃)(1)B1/(Ã)(1)A2 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 (c̃)(3)B2 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.

  18. 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.

  19. 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

  20. 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.

  1. 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)

  2. 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.

  3. Cross-shell excitations near the island of inversion : structure of {sup 30}Mg.

    SciTech Connect

    Deacon, A. N.; Smith, J. F.; Freeman, S. J.; Janssens, R. V. F.; Carpenter, M. P.; Hadinia, B.; Hoffman, C. R.; Kay, B. P.; Lauritsen, T.; Lister, C. J.; O'Donnell, D.; Ollier, J.; Otsuka, T.; Seweryniak, D.; Spohr, K.-M.; Steppenbeck, D.; Tabor, S. L.; Tripathi, V.; Utsuno, Y.; Wady, P. T.; Zhu, S.

    2010-09-07

    Excited states in {sup 30}Mg have been populated to {approx}6{h_bar} and 5 MeV excitation energy with the {sup 14}C({sup 18}O,2p) reaction. Firm spin assignments for states with J>2{h_bar} have been made in this nucleus. The level scheme is compared to shell-model calculations using the Universal sd effective interaction and the Monte Carlo shell model method. Calculations employing a full sd model space fail to reproduce the observed levels. The results indicate that excitations across the N=20 gap are required at relatively low excitation energy to achieve a description of the data. The incorporation of the f{sub 7/2} and p{sub 3/2} orbitals into the model space gives improved results but indicate the need for further refinement of the models to reproduce the observed spectra.

  4. 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)

  5. 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. PMID:27028374

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. Extensions of Fixed-Node Diffusion Monte Carlo to the Study of the Rotationally Excited States of H_2D^+

    NASA Astrophysics Data System (ADS)

    Wellen, Bethany A.; Petit, Andrew S.; McCoy, Anne B.

    2012-06-01

    Diffusion Monte Carlo (DMC) has been shown to be a highly successful technique for treating quantum zero-point effects of very floppy molecules and clusters. Our group has developed a fixed-node DMC methodology that allows us to expand the application of the approach to studies of rotationally excited states of such systems. We recently applied this approach to the study of H_3^+. We chose this system because of the availability of a global potential energy surface of spectroscopic accuracy, and the results of converged variational calculations have been reported that can be used to assess the accuracy of the DMC calculations. As a symmetric top molecule, the nodal structures of the rotationally excited states of H_3^+ are well known and can be used in fixed-node DMC calculations. We have recently extended this methodology to asymmetric top molecules, using H_2D^+ as a test system for these types of molecules as it has a κ value near zero. Here, we describe these extensions and present the results of DMC calculations of representative rotationally excited states of H_2D^+. A. S. Petit, B. A. Wellen, and A. B. McCoy, J. Chem. Phys. 136, 074101 (2012).

  13. 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.

  14. Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited ( S 1) electronic state

    NASA Astrophysics Data System (ADS)

    Koroleva, L. A.; Tyulin, V. I.; Matveev, V. K.; Pentin, Yu. A.

    2012-04-01

    The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited ( S 1) electronic state. The ν00 trans = 25861 cm-1 values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state ( S 1) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v') transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ν00 trans trans origin allowed the table to be extended to high quantum numbers v'. The torsional vibration frequencies up to v' = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited ( S 1) electronic state.

  15. 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

  16. 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.

  17. a Study of Quasi-One Systems: Excitation of the Active Electron to its First Excited State

    NASA Astrophysics Data System (ADS)

    Redd, Emmett Richter

    Experimental angular differential cross sections (ADCS) of four Quasi-One-Electron (QOE) scattering systems (Li('+), Na('+) + H and Be('+), Mg('+) + He) are reported. These ADCS are determined for exciting the 'active' electron to its first excited state. The angular range of the ADCS is from 0 to (TURN)3 mrad(,lab) with an angular resolution of (TURN)120 (mu)rad(,lab). The energy range is from 19.4 to 150 keV with an energy-loss resolution of (TURN)1 eV. The ADCS are compared to the available theories. The agreement between experiment and theory ranges from very poor to fair. No experiments exist which allow direct comparison to the present results. Integration of the present ADCS gives results which are compared to the experimental and theoretical total He targets cross section results. The agreement changes from energy to energy. Theoretical total cross section results exist in the cases involving H targets and are in very poor to fair agreement with the present results. No experimental total cross sections exist in the H target case for comparison with the present results. The most striking feature occurs in the Na('+) + H ADCS. Here the value of the ADCS at zero angle changes by 2 1/2 orders of magnitude from (3.96 (+OR-) 2.00) x 10('-15) cm('2)/sr at 35.9 keV (v = 1/4 a.u.) to (1.03 (+OR-) 0.25) x 10('-12) cm('2)/sr at 143.8 keV (v = 1/2 a.u.). This steep rise in the ADCS at zero angle is interpreted as showing the onset of a direct excitation mechanism (mechanism ii in the QOE literature). Qualitative agreement between previous QOE results (at lower energy using He targets) and the present Na('+) + H results is shown. Massey parameter scaling is shown to supply relatively little information on the ADCS. Finally, the results are probed to show the similarities of the underlying scattering mechanisms. For systems with the same target, the ADCS show quantitatively comparable results implying considerable similarities. Although all the systems are shown to be

  18. A relativistic time-dependent density functional study of the excited states of the mercury dimer.

    PubMed

    Kullie, Ossama

    2014-01-14

    In previous works on Zn2 and Cd2 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(2) + 6s6p), (6s(2) + 6s7s), and (6s(2) + 6s7p) atomic asymptotes for the mercury dimer Hg2. 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 Hg2 including a comparative analysis with the lighter dimers of the group 12, Cd2, and Zn2, 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 Hg2.

  19. A relativistic time-dependent density functional study of the excited states of the mercury dimer

    NASA Astrophysics Data System (ADS)

    Kullie, Ossama

    2014-01-01

    In previous works on Zn2 and Cd2 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 (6s2 + 6s6p), (6s2 + 6s7s), and (6s2 + 6s7p) atomic asymptotes for the mercury dimer Hg2. 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 Hg2 including a comparative analysis with the lighter dimers of the group 12, Cd2, and Zn2, 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 Hg2.

  20. Study of orbitally excited B mesons and evidence for a new Bπ resonance

    NASA Astrophysics Data System (ADS)

    Aaltonen, T.; Amerio, S.; Amidei, D.; Anastassov, A.; Annovi, A.; Antos, J.; Apollinari, G.; Appel, J. A.; Arisawa, T.; Artikov, A.; Asaadi, J.; Ashmanskas, W.; Auerbach, B.; Aurisano, A.; Azfar, F.; Badgett, W.; Bae, T.; Barbaro-Galtieri, A.; Barnes, V. E.; Barnett, B. A.; Barria, P.; Bartos, P.; Bauce, M.; Bedeschi, F.; Behari, S.; Bellettini, G.; Bellinger, J.; Benjamin, D.; Beretvas, A.; Bhatti, A.; Bland, K. R.; Blumenfeld, B.; Bocci, A.; Bodek, A.; Bortoletto, D.; Boudreau, J.; Boveia, A.; Brigliadori, L.; Bromberg, C.; Brucken, E.; Budagov, J.; Budd, H. S.; Burkett, K.; Busetto, G.; Bussey, P.; Butti, P.; Buzatu, A.; Calamba, A.; Camarda, S.; Campanelli, M.; Canelli, F.; Carls, B.; Carlsmith, D.; Carosi, R.; Carrillo, S.; Casal, B.; Casarsa, M.; Castro, A.; Catastini, P.; Cauz, D.; Cavaliere, V.; Cavalli-Sforza, M.; Cerri, A.; Cerrito, L.; Chen, Y. C.; Chertok, M.; Chiarelli, G.; Chlachidze, G.; Cho, K.; Chokheli, D.; Clark, A.; Clarke, C.; Convery, M. E.; Conway, J.; Corbo, M.; Cordelli, M.; Cox, C. A.; Cox, D. J.; Cremonesi, M.; Cruz, D.; Cuevas, J.; Culbertson, R.; d'Ascenzo, N.; Datta, M.; de Barbaro, P.; Demortier, L.; Deninno, M.; Devoto, F.; D'Errico, M.; Di Canto, A.; Di Ruzza, B.; Dittmann, J. R.; D'Onofrio, M.; Donati, S.; Dorigo, M.; Driutti, A.; Ebina, K.; Edgar, R.; Elagin, A.; Erbacher, R.; Errede, S.; Esham, B.; Farrington, S.; Feindt, M.; Fernández Ramos, J. P.; Field, R.; Flanagan, G.; Forrest, R.; Franklin, M.; Freeman, J. C.; Frisch, H.; Funakoshi, Y.; Galloni, C.; Garfinkel, A. F.; Garosi, P.; Gerberich, H.; Gerchtein, E.; Giagu, S.; Giakoumopoulou, V.; Gibson, K.; Ginsburg, C. M.; Giokaris, N.; Giromini, P.; Giurgiu, G.; Glagolev, V.; Glenzinski, D.; Gold, M.; Goldin, D.; Golossanov, A.; Gomez, G.; Gomez-Ceballos, G.; Goncharov, M.; González López, O.; Gorelov, I.; Goshaw, A. T.; Goulianos, K.; Gramellini, E.; Grinstein, S.; Grosso-Pilcher, C.; Group, R. C.; Guimaraes da Costa, J.; Hahn, S. R.; Han, J. Y.; Happacher, F.; Hara, K.; Hare, M.; Harr, R. F.; Harrington-Taber, T.; Hatakeyama, K.; Hays, C.; Heck, M.; Heinrich, J.; Herndon, M.; Hocker, A.; Hong, Z.; Hopkins, W.; Hou, S.; Hughes, R. E.; Husemann, U.; Hussein, M.; Huston, J.; Introzzi, G.; Iori, M.; Ivanov, A.; James, E.; Jang, D.; Jayatilaka, B.; Jeon, E. J.; Jindariani, S.; Jones, M.; Joo, K. K.; Jun, S. Y.; Junk, T. R.; Kambeitz, M.; Kamon, T.; Karchin, P. E.; Kasmi, A.; Kato, Y.; Ketchum, W.; Keung, J.; Kilminster, B.; Kim, D. H.; Kim, H. S.; Kim, J. E.; Kim, M. J.; Kim, S. B.; Kim, S. H.; Kim, Y. K.; Kim, Y. J.; Kimura, N.; Kirby, M.; Knoepfel, K.; Kondo, K.; Kong, D. J.; Konigsberg, J.; Kotwal, A. V.; Kreps, M.; Kroll, J.; Kruse, M.; Kuhr, T.; Kurata, M.; Laasanen, A. T.; Lammel, S.; Lancaster, M.; Lannon, K.; Latino, G.; Lee, H. S.; Lee, J. S.; Leo, S.; Leone, S.; Lewis, J. D.; Limosani, A.; Lipeles, E.; Lister, A.; Liu, H.; Liu, Q.; Liu, T.; Lockwitz, S.; Loginov, A.; Lucà, A.; Lucchesi, D.; Lueck, J.; Lujan, P.; Lukens, P.; Lungu, G.; Lys, J.; Lysak, R.; Madrak, R.; Maestro, P.; Malik, S.; Manca, G.; Manousakis-Katsikakis, A.; Marchese, L.; Margaroli, F.; Marino, P.; Martínez, M.; Matera, K.; Mattson, M. E.; Mazzacane, A.; Mazzanti, P.; McNulty, R.; Mehta, A.; Mehtala, P.; Mesropian, C.; Miao, T.; Mietlicki, D.; Mitra, A.; Miyake, H.; Moed, S.; Moggi, N.; Moon, C. S.; Moore, R.; Morello, M. J.; Mukherjee, A.; Muller, Th.; Murat, P.; Mussini, M.; Nachtman, J.; Nagai, Y.; Naganoma, J.; Nakano, I.; Napier, A.; Nett, J.; Neu, C.; Nigmanov, T.; Nodulman, L.; Noh, S. Y.; Norniella, O.; Oakes, L.; Oh, S. H.; Oh, Y. D.; Oksuzian, I.; Okusawa, T.; Orava, R.; Ortolan, L.; Pagliarone, C.; Palencia, E.; Palni, P.; Papadimitriou, V.; Parker, W.; Pauletta, G.; Paulini, M.; Paus, C.; Phillips, T. J.; Piacentino, G.; Pianori, E.; Pilot, J.; Pitts, K.; Plager, C.; Pondrom, L.; Poprocki, S.; Potamianos, K.; Prokoshin, F.; Pranko, A.; Ptohos, F.; Punzi, G.; Ranjan, N.; Redondo Fernández, I.; Renton, P.; Rescigno, M.; Rimondi, F.; Ristori, L.; Robson, A.; Rodriguez, T.; Rolli, S.; Ronzani, M.; Roser, R.; Rosner, J. L.; Ruffini, F.; Ruiz, A.; Russ, J.; Rusu, V.; Sakumoto, W. K.; Sakurai, Y.; Santi, L.; Sato, K.; Saveliev, V.; Savoy-Navarro, A.; Schlabach, P.; Schmidt, E. E.; Schwarz, T.; Scodellaro, L.; Scuri, F.; Seidel, S.; Seiya, Y.; Semenov, A.; Sforza, F.; Shalhout, S. Z.; Shears, T.; Shepard, P. F.; Shimojima, M.; Shochet, M.; Shreyber-Tecker, I.; Simonenko, A.; Sliwa, K.; Smith, J. R.; Snider, F. D.; Sorin, V.; Song, H.; Stancari, M.; St. Denis, R.; Stentz, D.; Strologas, J.; Sudo, Y.; Sukhanov, A.; Suslov, I.; Takemasa, K.; Takeuchi, Y.; Tang, J.; Tecchio, M.; Teng, P. K.; Thom, J.; Thomson, E.; Thukral, V.; Toback, D.; Tokar, S.; Tollefson, K.; Tomura, T.; Tonelli, D.; Torre, S.; Torretta, D.; Totaro, P.; Trovato, M.; Ukegawa, F.; Uozumi, S.; Vázquez, F.; Velev, G.; Vellidis, C.; Vernieri, C.; Vidal, M.; Vilar, R.; Vizán, J.; Vogel, M.; Volpi, G.; Wagner, P.; Wallny, R.; Wang, S. M.; Waters, D.; Wester, W. C.; Whiteson, D.; Wicklund, A. B.; Wilbur, S.; Williams, H. H.; Wilson, J. S.; Wilson, P.; Winer, B. L.; Wittich, P.; Wolbers, S.; Wolfe, H.; Wright, T.; Wu, X.; Wu, Z.; Yamamoto, K.; Yamato, D.; Yang, T.; Yang, U. K.; Yang, Y. C.; Yao, W.-M.; Yeh, G. P.; Yi, K.; Yoh, J.; Yorita, K.; Yoshida, T.; Yu, G. B.; Yu, I.; Zanetti, A. M.; Zeng, Y.; Zhou, C.; Zucchelli, S.; CDF Collaboration

    2014-07-01

    Using the full CDF Run II data sample, we report evidence for a new resonance, which we refer to as B(5970), found simultaneously in the B0π+ and B+π- mass distributions with a significance of 4.4 standard deviations. We further report the first study of resonances consistent with orbitally excited B+ mesons and an updated measurement of the properties of orbitally excited B0 and Bs0 mesons. We measure the masses and widths of all states, as well as the relative production rates of the B1, B2*, and B(5970) states and the branching fraction of the Bs2*0 state to either B*+K- and B+K-. Furthermore, we measure the production rates of the orbitally excited B0,+ states relative to the B0,+ ground state. The masses of the new B(5970) resonances are 5978±5(stat)±12(syst) MeV/c2 for the neutral state and 5961±5(stat)±12(syst) MeV /c2 for the charged state, assuming that the resonance decays into Bπ final states. The properties of the orbitally excited and the new B(59700,+) states are compatible with isospin symmetry.

  1. 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.

  2. 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.

  3. 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

  4. Photostability via sloped conical intersections: a computational study of the excited states of the naphthalene radical cation.

    PubMed

    Hall, Katherine F; Boggio-Pasqua, Martial; Bearpark, Michael J; Robb, Michael A

    2006-12-21

    On the basis of an extensive ab initio electronic structure study of the ground and excited-state potential energy surfaces of the naphthalene radical cation (N*+), we propose a mechanism for its ultrafast nonradiative relaxation from the second excited state (D2) down to the ground state (D0), which could explain the experimentally observed photostability [Zhao, L.; Lian, R.; Shkrob I. A.; Crowell, R. A.; Pommeret, S.; Chronister, E. L.; Liu, A. D.; Trifunac, A. D. J. Phys. Chem. A., 2004, 108, 25]. The proposed photophysical relaxation pathway involves internal conversion from the D2 state down to the D0 state via two consecutive, accessible, sloped conical intersections (CIs). The two crossings, D0/D1 and D1/D2, are characterized at the complete active space self-consistent field (CASSCF) level. At this level of theory, the D0/D1 crossing is energetically readily accessible, while the D1/D2 CI appears too high in energy to be involved in internal conversion. However, the inclusion of dynamic correlation effects, via single point CASPT2 calculations including excitations out of the valence pi- and sigma-orbitals, lowers the D0 and D2 state energies with respect to D1. Extrapolations at the CASPT2 level predict that the D1/D2 crossing is then significantly lower in energy than with CASSCF indicating that with a higher-level treatment of dynamic correlation it may be energetically accessible following vertical excitation to D2. N*+ is proposed as one of the species contributing to a series of diffuse infrared absorption bands originating from interstellar clouds. Understanding the mechanism for photostability in the gas phase, therefore, has important consequences for astrophysics.

  5. 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.

  6. 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.

  7. Local excitation and interference of surface phonon polaritons studied by near-field infrared microscopy.

    PubMed

    Huber, A J; Ocelic, N; Hillenbrand, R

    2008-03-01

    We demonstrate that mid-infrared surface phonon polariton excitation, propagation and interference can be studied by scattering-type near-field optical microscopy (s-SNOM). In our experiments we image surface phonon polaritons (SPPs) propagating on flat SiC crystals. They are excited by weakly focused illumination of single or closely spaced metal disks we fabricated on the SiC surface by conventional photolithography. SPP imaging is performed by pseudo-heterodyne interferometric detection of infrared light scattered by the metal tip of our s-SNOM. The pseudo-heterodyne technique simultaneously yields optical amplitude and phase images which allows us to measure the SPP wave vector--including its sign--and the propagation length and further to study SPP interference. High resolution imaging of SPPs could be applied to investigate for example SPP focusing or heat transfer by SPPs in low dimensional nanostructures.

  8. Excited state dynamics of single metal and semiconductor nanowires studied by transient absorption microscopy

    NASA Astrophysics Data System (ADS)

    Lo, Shun S.; Shi, Hong Y.; Major, Todd A.; Petchsang, Nattasamon; Huang, Libai; Kuno, Masaru K.; Hartland, Gregory V.

    2013-03-01

    Transient absorption microscopy (TAM) is a relatively new technique that allows the study of single nanostructures with sub-picosecond time resolution. Here, we present results for CdTe and Au Nanowires (NW). For the first material, we find an interesting power dependence of the excited dynamics, suggesting that a trap-filling mechanism is responsible for the observed behaviour. Additionally, acoustic phonons were observed, which were well described using continuum elastic models.[2] Carrier diffusion along these NWs are also reported. In the case of Au NWs, the propagation of surface plasmon polaritons was investigated. The results are in agreement with previous studies performed with fluorescence based techniques.[3,4] Unlike fluorescence techniques, multiple measurements on the same nanostructures are possible with TAM allowing one-to-one comparisons under different excitation polarizations and environments. NSF Award CHE-1110560 and CHE-0946447, Univ. of Notre Dame Strategic Research Initiative. L. Huang, DOE (DE-FC02-04ER15533)

  9. Ultrafast structural flattening motion in photoinduced excited state dynamics of a bis(diimine) copper(I) complex.

    PubMed

    Du, Likai; Lan, Zhenggang

    2016-03-21

    The ultrafast photoinduced structural change dynamics of a prototypical Cu(I) complex, namely, [Cu(dmp)2](+) (dmp = 2,9-dimethyl-1,10-phenanthroline), is investigated based on the theoretical analysis of static and dynamical calculations at the all-atomic level. This work mainly focuses on the intriguing structural flattening features of [Cu(dmp)2](+) occurring in the metal-to-ligand charge transfer singlet excited state ((1)MLCT) on the sub-picosecond timescale. Our estimated time constant (∼ 675 fs) of this "flattening" motion is in good agreement with recent experimental values. The full-dimensional excited-state nonadiabatic dynamic simulation provides a direct view of the ultrafast photoinduced events of [Cu(dmp)2](+), especially, the structural flattening mechanism on the S1 state. Several molecular motions (such as Cu-N stretching, the motion of the substituted groups etc.) with distinguishable time scales are involved in the flattening dynamics. The Fourier transformation of the time-dependent oscillation of the Cu-N bond and the N-Cu-N bond angle provides consistent conclusions with the experimental spectrum analysis. These dynamics details imply that various nuclear motions are strongly coupled in the high-dimensional excited-state potential energy surface responsible for the geometrical evolution of [Cu(dmp)2](+). This work provides us a unique fundamental understanding of the ultrafast photoinduced excited-state nonadiabatic process of Cu(I) complexes and their derivatives, which should have potential impacts on various research fields, such as photo-catalysts, dye-sensitized solar cells (DSSCs), and organic light emitting diodes (OLEDs). PMID:26758674

  10. Ultrafast structural flattening motion in photoinduced excited state dynamics of a bis(diimine) copper(I) complex.

    PubMed

    Du, Likai; Lan, Zhenggang

    2016-03-21

    The ultrafast photoinduced structural change dynamics of a prototypical Cu(I) complex, namely, [Cu(dmp)2](+) (dmp = 2,9-dimethyl-1,10-phenanthroline), is investigated based on the theoretical analysis of static and dynamical calculations at the all-atomic level. This work mainly focuses on the intriguing structural flattening features of [Cu(dmp)2](+) occurring in the metal-to-ligand charge transfer singlet excited state ((1)MLCT) on the sub-picosecond timescale. Our estimated time constant (∼ 675 fs) of this "flattening" motion is in good agreement with recent experimental values. The full-dimensional excited-state nonadiabatic dynamic simulation provides a direct view of the ultrafast photoinduced events of [Cu(dmp)2](+), especially, the structural flattening mechanism on the S1 state. Several molecular motions (such as Cu-N stretching, the motion of the substituted groups etc.) with distinguishable time scales are involved in the flattening dynamics. The Fourier transformation of the time-dependent oscillation of the Cu-N bond and the N-Cu-N bond angle provides consistent conclusions with the experimental spectrum analysis. These dynamics details imply that various nuclear motions are strongly coupled in the high-dimensional excited-state potential energy surface responsible for the geometrical evolution of [Cu(dmp)2](+). This work provides us a unique fundamental understanding of the ultrafast photoinduced excited-state nonadiabatic process of Cu(I) complexes and their derivatives, which should have potential impacts on various research fields, such as photo-catalysts, dye-sensitized solar cells (DSSCs), and organic light emitting diodes (OLEDs).

  11. Structural and optical properties of ZnO and ZnO:Fe nanoparticles under dense electronic excitations

    SciTech Connect

    Kumar, Shiv; Singh, Ranjan Kr.; Ghosh, Anup K.; Asokan, K.; Kanjilal, D.; Chatterjee, S.

    2013-10-28

    We report on the changes in structural, morphological, and optical properties of sol-gel derived ZnO and ZnO:Fe nanoparticles due to dense electronic excitations produced by heavy ion irradiations using 200 MeV Ag{sup +15} ion beams. X-ray diffraction studies with Rietveld refinement show that the samples are single phase and tensile strain has been developed in the ion-irradiated samples. The Raman spectroscopy measurements show that ion-irradiation results in microscopic structural disorders and breaking of translational symmetry giving rise to local distortions in the lattice. Atomic force microscopy studies show that roughness of the pellets increases strongly for pure ZnO as compared with Fe-doped ZnO due to ion-irradiation. Fourier transform infrared analysis confirms tetrahedral coordination of O ions surrounding the Zn-ions and surface modification of the nanoparticles. The UV-Vis spectroscopy measurements show that the band gap increases on Fe doping which may be due to 4s–3d and 2p–3d interactions and the Burstein-Moss band filling effect. The band gap decreases after irradiation which can be interpreted on the basis of creation of some new localized energy states above the valence band. Photoluminescence (PL) intensity is enhanced and two new emission bands viz. a blue band at ∼480 nm (related to surface defects) and a green band at ∼525 nm (related to O vacancies) are observed in ion-irradiated nanoparticles. The enhancement of PL-intensity in irradiated samples is attributed to the increase of different defect states and Zn−O bonds on the surfaces of the irradiated nanoparticles arising from surface modification.

  12. Effect of elastic excitations on the surface structure of hadfield steel under friction

    NASA Astrophysics Data System (ADS)

    Kolubaev, A. V.; Ivanov, Yu. F.; Sizova, O. V.; Kolubaev, E. A.; Aleshina, E. A.; Gromov, V. E.

    2008-02-01

    The structure of the Hadfield steel (H13) surface layer forming under dry friction is examined. The deformation of the material under the friction surface is studied at a low slip velocity and a low pressure (much smaller than the yields stress of H13 steel). The phase composition and defect substructure on the friction surface are studied using scanning, optical, and diffraction electron microscopy methods. It is shown that a thin highly deformed nanocrystalline layer arises near the friction surface that transforms into a polycrystalline layer containing deformation twins and dislocations. The nanocrystalline structure and the presence of oxides in the surface layer and friction zone indicate a high temperature and high plastic strains responsible for the formation of the layer. It is suggested that the deformation of the material observed far from the surface is due to elastic wave generation at friction.

  13. Spread of excitation in 3-D models of the anisotropic cardiac tissue. III. Effects of ventricular geometry and fiber structure on the potential distribution.

    PubMed

    Colli Franzone, P; Guerri, L; Pennacchio, M; Taccardi, B

    1998-07-01

    In a previous paper we studied the spread of excitation in a simplified model of the left ventricle, affected by fiber structure and obliqueness, curvature of the wall and Purkinje network. In the present paper we investigate the extracellular potential distribution u in the same ventricular model. Given the transmembrane potential v, associated with the spreading excitation, the extracellular potential u is obtained as solution of a linear elliptic equation with the source term related to v. The potential distributions were computed for point stimulations at different intramural depths. The results of the simulations enabled us to identify a number of common features which appears in all the potential patterns irrespective of pacing site. In addition, by splitting the sources into an axial and conormal component, we were able to evaluate the contribution of the classical uniform dipole layer to the total potential field and the role of the superimposed axial component.

  14. Theoretical Study of the Damping of Collective Excitations in a Bose-Einstein Condensate

    SciTech Connect

    Vincent Liu, W.

    1997-11-01

    We study the damping of low-lying collective excitations of condensates in a weakly interacting Bose gas model within the framework of an imaginary time path integral. A general expression of the damping rate has been obtained for both the very low temperature regime and the higher temperature regime. For the latter, the result is new and applicable to recent experiments. Theoretical predictions for the damping rate are compared with the experimental values. {copyright} {ital 1997} {ital The American Physical Society}

  15. Study of laser emission losses in rhodamine 6G solutions under quasilongitudinal laser excitation

    SciTech Connect

    Aristov, A.V.; Eremenko, A.S.; Nikolaev, A.B.

    1986-08-01

    As a result of studies of the reciprocal of the quantum yield of stimulated laser emission as a function of the reciprocal of the useful loss factor, a quantitative dependence of induced losses in the pumping and lasing channels on the volume density of absorbed exciting radiation has been established. It is concluded from quantitative evidence that the margin of an appreciable increase in lasing efficiency for rhodamine 6G solutions consists in a decrease of the pumping-induced light scattering.

  16. 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.

  17. 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).

  18. [Numerical Simulation of Propagation of Electric Excitation in the Heart Wall Taking into Account Its Fibrous-Laminar Structure].

    PubMed

    Vasserman, I N; Matveenko, V P; Shardakov, I N; Shestakov, A P

    2015-01-01

    The propagation of excitation wave in the inhomogeneous anisotropic finite element model of cardiac muscle is investigated. In this model, the inhomogeneity stands for the rotation of anisotropy axes through the wall thickness and results from a fibrous-laminar structure of the cardiac muscle tissue. Conductivity of the cardiac muscle is described using a monodomain model and the Aliev-Panfilov equations are used as the relationships between the transmembrane current and transmembrane potential. Numerical simulation is performed by applying the splitting algorithm, in which the partial differential solution to the nonlinear boundary value problem is reduced to a sequence of simple ordinary differential equations and linear partial differential equations. The simulation is carried out for a rectangular block of the cardiac tissue, the minimal size of which is considered to be the thickness of the heart wall. Two types of distribution of the fiber orientation angle are discussed. The first case corresponds 'to the left ventricle of a dog. The endocardium and epicardium fibers are generally oriented in the meridional direction. The angle of fiber orientation varies smoothly through the wall thickness making a half-turn. A circular layer, in which the fibers are oriented in the circumferential direction locates deep in the cardiac wall. The results of calculations show that for this case the wave form strongly depends on a place of initial excitation. For the endocardial and epicardial initial excitation one can see the earlier wave front propagation in the endocardium and epicardium, respectively. At the intramural initial excitation the simultaneous wave front propagation in the endocardium and epicardium occurs, but there is a wave front lag in the middle of the wall. The second case refers to the right ventricle of a swine, in which the endocardium and epicardium fibers are typically oriented in the circumferential direction, whereas the subepicardium fibers

  19. Excited-State Structure Modifications Due to Molecular Substituents and Exciton Scattering in Conjugated Molecules.

    PubMed

    Li, Hao; Catanzaro, Michael J; Tretiak, Sergei; Chernyak, Vladimir Y

    2014-02-20

    Attachment of chemical substituents (such as polar moieties) constitutes an efficient and convenient way to modify physical and chemical properties of conjugated polymers and oligomers. Associated modifications in the molecular electronic states can be comprehensively described by examining scattering of excitons in the polymer's backbone at the scattering center representing the chemical substituent. Here, we implement effective tight-binding models as a tool to examine the analytical properties of the exciton scattering matrices in semi-infinite polymer chains with substitutions. We demonstrate that chemical interactions between the substitution and attached polymer are adequately described by the analytical properties of the scattering matrices. In particular, resonant and bound electronic excitations are expressed via the positions of zeros and poles of the scattering amplitude, analytically continued to complex values of exciton quasi-momenta. We exemplify the formulated concepts by analyzing excited states in conjugated phenylacetylenes substituted by perylene. PMID:26270830

  20. 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.

  1. Structural deformation of a ring-shaped Re(I) diimine dinuclear complex in the excited state

    NASA Astrophysics Data System (ADS)

    Tanaka, Sei'ichi; Matsubara, Yoshitaka; Asatani, Tsuyoshi; Morimoto, Tatsuki; Ishitani, Osamu; Onda, Ken

    2016-10-01

    We investigated the excited state of a ring-shaped dinuclear Re(I) diimine bis-carbonyl complex that shows promise with regard to efficient photosensitized reactions and multi-electron storage, using time-resolved infrared (TR-IR) vibrational spectroscopy and quantum chemical calculations. Anomalous peaks in the CO stretching region of the TR-IR spectrum were well reproduced by the calculations. It was found that metal-to-ligand charge transfer occurs only in one of the Re complex units, and that the excited state geometry is deformed relative to the ground state in order to relax the associated steric tension. This structural deformation generates the unique photophysical properties of the complex.

  2. Onset of collectivity in 96,98Sr studied via Coulomb excitation

    NASA Astrophysics Data System (ADS)

    Clément, E.; Görgen, A.; Dijon, A.; de France, G.; Bastin, B.; Blazhev, A.; Bree, N.; Butler, P.; Delahaye, P.; Ekstrom, A.; Georgiev, G.; Hasan, N.; Iwanicki, J.; Jenkins, D.; Korten, W.; Larsen, A. C.; Ljungvall, J.; Moschner, K.; Napiorkowski, P.; Pakarinen, J.; Petts, A.; Renstrom, T.; Seidlitz, M.; Siem, S.; Sotty, C.; Srebrny, J.; Stefanescu, I.; Tveten, G. M.; Van de Walle, J.; Warr, N.; Wrzosek-Lipska, K.; Zielińska, M.; Bauer, C.; Bruyneel, B.; Butterworth, J.; Fitzpatrick, C.; Fransen, C.; Gernhäuser, R.; Hess, H.; Lutter, R.; Marley, P.; Reiter, P.; Siebeck, B.; Vermeulen, M.; Wiens, A.; De Witte, H.

    2014-03-01

    A rapid onset of quadrupole deformation is known to occur around the neutron number 60 in the neutron-rich Zr and Sr isotopes. This shape change has made the neutron-rich A = 100 region an active area of experimental and theoretical studies for many decades now. We report in this contribution new experimental results in the neutron rich 96,98Sr investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross section supporting the scenario of shape coexistence/change at N=60. Future perspectives are presented including the recent experimental campaign performed at ILL-Grenoble.

  3. Vulnerability in an excitable medium: analytical and numerical studies of initiating unidirectional propagation.

    PubMed Central

    Starmer, C F; Biktashev, V N; Romashko, D N; Stepanov, M R; Makarova, O N; Krinsky, V I

    1993-01-01

    Cardiac tissue can display unusual responses to certain stimulation protocols. In the wake of a conditioning wave of excitation, spiral waves can be initiated by applying stimuli timed to occur during a period of vulnerability (VP). Although vulnerability is well known in cardiac and chemical media, the determinants of the VP and its boundaries have received little theoretical and analytical study. From numerical and analytical studies of reaction-diffusion equations, we have found that 1) vulnerability is an inherent property of Beeler-Reuter and FitzHugh-Nagumo models of excitable media; 2) the duration of the vulnerable window (VW) the one-dimensional analog of the VP, is sensitive to the medium properties and the size of the stimulus field; and 3) the amplitudes of the excitatory and recovery processes modulate the duration of the VW. The analytical results reveal macroscopic behavior (vulnerability) derived from the diffusion of excitation that is not observable at the level of isolated cells or single reaction units. PMID:8298011

  4. 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

  5. RF-excited unstable-resonator planar CO{sub 2} laser on all-metal electrode-waveguide structure

    SciTech Connect

    Mineev, A P; Nefedov, S M; Pashinin, Pavel P E-mail: nefedov@kapella.gpi.r

    2006-07-31

    The radiation characteristics of a planar CO{sub 2} laser excited by a diffusion-cooled rf discharge at a frequency of 40 MHz are studied. A single-mode cw lasing power of {approx}50 W is achieved with an efficiency of {approx}10% for a nearly diffraction-limited radiation divergence of 4-7 mrad. The spatial structure, output power, stability and laser radiation quality are studied as functions of longitudinal and angular alignments of the resonator mirror for two types of hybrid unstable-waveguide resonators of the laser. It is shown that for the resonator corresponding to the negative branch of the stability diagram, a misalignment of 0.02 rad of the mirrors leads to a 50% decrease in the output laser power, while its value for the positive branch resonator is about 100 times smaller. It is found that for the resonator corresponding to the negative branch, the sensitivity to the violation of confocal arrangement of the mirrors upon an increase in the resonator length is an order of magnitude higher. The dependence of the density of input rf power on the working gas pressure is studied experimentally in the interval 50-110 Torr. Power density values of 1-4 W cm{sup -2} are obtained for normal discharge current density. These values are important for optimisation and scaling of the lasing characteristics of high-power planar CO{sub 2} lasers. (special issue devoted to the 90th anniversary of a.m. prokhorov)

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. Shear-layer acoustic radiation in an excited subsonic jet: experimental study

    NASA Astrophysics Data System (ADS)

    Fleury, Vincent; Bailly, Christophe; Juvé, Daniel

    2005-10-01

    The subharmonic acoustic radiation of a tone excited subsonic jet shear-layer has been investigated experimentally. Two jet velocities U=20 mṡs and U=40 mṡs were studied. For U=20 mṡs, the natural boundary-layer at the nozzle exit is laminar. When the perturbation is applied, the fluctuations of the first and the second subharmonics of the excitation frequency are detected in the shear-layer. In addition, the first subharmonic near pressure field along the spreading jet is constituted of two strong maxima of sinusoidal shape. The far-field directivity pattern displays two lobes separated by an extinction angle θ at around 85° from the jet axis. These observations follow the results of Bridges about the vortex pairing noise. On the other hand, for U=40 mṡs, the initial boundary-layer is transitional and only the first subharmonic is observed in the presence of the excitation. The near pressure field is of Gaussian shape in the jet periphery and the acoustic far-field is superdirective as observed by Laufer and Yen. The state of the initial shear-layer seems to be the key feature to distinguish these two different radiation patterns. To cite this article: V. Fleury et al., C. R. Mecanique 333 (2005).

  11. 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}.

  12. 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.

  13. Studying σ 54-dependent transcription at the single-molecule level using alternating-laser excitation (ALEX) spectroscopy

    NASA Astrophysics Data System (ADS)

    Heilemann, M.; Lymperopoulos, K.; Wigneshweraraj, S. R.; Buck, M.; Kapanidis, A. N.

    2007-07-01

    We present single-molecule fluorescence studies of σ 54-dependent gene-transcription complexes using singlemolecule fluorescence resonance energy transfer (smFRET) and alternating-laser excitation (ALEX) spectroscopy. The ability to study one biomolecule at the time allowed us to resolve and analyze sample heterogeneities and extract structural information on subpopulations and transient intermediates of transcription; such information is hidden in bulk experiments. Using site-specifically labeled σ 54 derivatives and site-specifically labeled promoter-DNA fragments, we demonstrate that we can observe single diffusing σ 54-DNA and transcription-initiation RNA polymerase-σ 54- DNA complexes, and that we can measure distances within such complexes; the identity of the complexes has been confirmed using electrophoretic-mobility-shift assays. Our studies pave the way for understanding the mechanism of abortive initiation and promoter escape in σ 54-dependent transcription.

  14. 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.

  15. Magneto-optic far-infrared study of Sr14Cu24O41 : Triplet excitations in chains

    NASA Astrophysics Data System (ADS)

    Hüvonen, D.; Nagel, U.; Rõõm, T.; Haas, P.; Dressel, M.; Hwang, J.; Timusk, T.; Wang, Y.-J.; Akimitsu, J.

    2007-10-01

    Using far-infrared spectroscopy, we have studied the magnetic field and temperature dependence of the spin gap modes in the chains of Sr14Cu24O41 . Two triplet modes T1 and T2 were found in the center of the Brillouin zone at Δ1=9.65meV and Δ2=10.86meV in zero magnetic field. The T1 mode was excited when the electric field vector E of the light was polarized along the b axis (perpendicular to the planes of chains and ladders) and T2 was excited for E‖a (perpendicular to the chains and along the rungs). Up to the maximum magnetic field of 18T , applied along the chains, the electron g factors of these two modes were similar, g1c=2.049 and g2c=2.044 . Full linewidth at half maximum for both modes was 1cm-1 (0.12meV) at 4K and increased with T . The temperature dependence of mode energies and line intensities was in agreement with the inelastic neutron scattering results from two groups [M. Matsuda , Phys. Rev. B 59, 1060 (1999); L. P. Regnault , ibid 59, 1055 (1999)]. The T1 mode has not been observed by inelastic neutron scattering in the points of the k space equivalent to the center of the Brillouin zone. Our study indicates that the zone structure model of magnetic excitations of Sr14Cu24O41 must be modified to include a triplet mode at 9.65meV in the center of the magnetic Brillouin zone.

  16. A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II

    SciTech Connect

    Bane, Karl

    2015-09-23

    The Linac Coherent Light Source (LCLS) at SLAC, the world’s first hard X-ray FEL, is being upgraded to the LCLS-II. The major new feature will be the installation of 35 cryomodules (CMs) of TESLA-type, superconducting accelerating structures, to allow for high rep-rate operation. It is envisioned that eventually the LCLS-II will be able to deliver 300 pC, 1 kA pulses of beam at a rate of 1 MHz. At a cavity temperature of 2 K, any heat generated (even on the level of a few watts) is expensive to remove. In the last linac of LCLS-II, L3—where the peak current is highest—the power radiated by the bunches in the CMs is estimated at 13.8 W (charge 300 pC option, rep rate 1 MHz). But this calculation ignores resonances that can be excited between the bunch frequency and higher order mode (HOM) frequencies in the CMs, which in principle can greatly increase this number. In the present work we calculate the multi-bunch wakefields excited in a CM of LCLS-II, in order to estimate the probability of the beam losing a given amount of power. Along theway, we find some interesting properties of the resonant interaction. In detail, we begin this report by finding the wakes experienced by bunches far back in the bunch train. Then we present a complementary approach that calculates the field amplitude excited in steady-state by a train of bunches, and show that the two approaches agree. Next we obtain the properties of the 450 longitudinal HOMs that cover the range 3–5 GHz in the CMs of LCLS-II, where we include the effects of the inter-CM ceramic dampers. At the end we apply our method using these modes.

  17. Cluster structures of 18O and 20O up to 20 MeV excitation energy from the (7Li, p)-reaction

    NASA Astrophysics Data System (ADS)

    Dorsch, T.; Bohlen, H. G.; von Oertzen, W.; Krücken, R.; Faestermann, T.; Mahgoub, M.; Kokalova, T.; Wheldon, C.; Milin, M.; Wirth, H.; Hertenberger, R.

    2008-05-01

    We studied the band structure of 18O and 20O using the (7Li, p)-reaction at an incident energy of 44 MeV on 12C and 14C targets. Spectra have been measured from the ground state up to 20 MeV excitation energy. We found 27 and 38 new states for 18O and 20O, respectively. The even-parity bands have been analysed up to now, i.e., some bands were extended by further members. The 0+ band head of the molecular band in 18O at 7.796(5) MeV was identified for the first time.

  18. 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

  19. Morphology-dependent luminescence from ZnO nanostructures - An X-ray excited optical luminescence study at the Zn K-edge

    SciTech Connect

    Lobacheva, Olga; Murphy, Michael W; Ko, Jun Young Peter; Sham, Tsun-Kong

    2009-08-28

    ZnO nanostructures have been synthesized by thermal evaporation on Si substrates. It is found that the morphologies of the nanostructures are governed by growth conditions such as temperature, carrier-gas flow rate, and the nature of the substrate (with and without a catalyst). We report X-ray excited optical luminescence from ZnO nanostructures of distinctly different morphologies in the energy and time domain using excitation photon energies across the Zn K-edge. X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) study has clearly shown the morphology dependence of the ZnO optical properties. A correlation of luminescence with morphology, size, and crystallinity emerges.

  20. Different patterns of cortical excitability in major depression and vascular depression: a transcranial magnetic stimulation study

    PubMed Central

    2013-01-01

    Background Clinical and functional studies consider major depression (MD) and vascular depression (VD) as different neurobiological processes. Hypoexcitability of the left frontal cortex to transcranial magnetic stimulation (TMS) is frequently reported in MD, whereas little is known about the effects of TMS in VD. Thus, we aimed to assess and compare motor cortex excitability in patients with VD and MD. Methods Eleven VD patients, 11 recurrent drug-resistant MD patients, and 11 healthy controls underwent clinical, neuropsychological and neuroimaging evaluations in addition to bilateral resting motor threshold, cortical silent period, and paired-pulse TMS curves of intracortical excitability. All patients continued on psychotropic drugs, which were unchanged throughout the study. Results Scores on one of the tests evaluating frontal lobe abilities (Stroop Color-Word interference test) were worse in patients compared with controls. The resting motor threshold in patients with MD was significantly higher in the left hemisphere compared with the right (p < 0.05), and compared with the VD patients and controls. The cortical silent period was bilaterally prolonged in MD patients compared with VD patients and controls, with a statistically significant difference in the left hemisphere (p < 0.01). No differences were observed in the paired-pulse curves between patients and controls. Conclusions This study showed distinctive patterns of motor cortex excitability between late-onset depression with subcortical vascular disease and early-onset recurrent drug resistant MD. The data provide a TMS model of the different processes underlying VD and MD. Additionally, our results support the “Vascular depression hypothesis” at the neurophysiological level, and confirm the inter-hemispheric asymmetry to TMS in patients with MD. We were unable to support previous findings of impaired intracortical inhibitory mechanisms to TMS in patients with MD, although a drug

  1. 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.

  2. Age-related structural abnormalities in the human retina-choroid complex revealed by two-photon excited autofluorescence imaging.

    PubMed

    Han, Meng; Giese, Guenter; Schmitz-Valckenberg, Steffen; Bindewald-Wittich, Almut; Holz, Frank G; Yu, Jiayi; Bille, Josef F; Niemz, Markolf H

    2007-01-01

    The intensive metabolism of photoreceptors is delicately maintained by the retinal pigment epithelium (RPE) and the choroid. Dysfunction of either the RPE or choroid may lead to severe damage to the retina. Two-photon excited autofluorescence (TPEF) from endogenous fluorophores in the human retina provides a novel opportunity to reveal age-related structural abnormalities in the retina-choroid complex prior to apparent pathological manifestations of age-related retinal diseases. In the photoreceptor layer, the regularity of the macular photoreceptor mosaic is preserved during aging. In the RPE, enlarged lipofuscin granules demonstrate significantly blue-shifted autofluorescence, which coincides with the depletion of melanin pigments. Prominent fibrillar structures in elderly Bruch's membrane and choriocapillaries represent choroidal structure and permeability alterations. Requiring neither slicing nor labeling, TPEF imaging is an elegant and highly efficient tool to delineate the thick, fragile, and opaque retina-choroid complex, and may provide clues to the trigger events of age-related macular degeneration.

  3. Single Molecule Spectroscopy and Scanning Probe Microscopy to Investigate Excited State Energy Transport in Quantum Dot Higher Order Structures

    NASA Astrophysics Data System (ADS)

    van Orden, Alan; Gelfand, Martin; Ryan, Duncan; Whitcomb, Kevin

    2014-03-01

    Single molecule fluorescence spectroscopy and scanning probe microscopy have been used to investigate small isolated clusters of CdSe/ZnS nanocrystalline quantum dots dispersed on insulating, conducting, and semiconducting surfaces. The aggregated quantum dots exhibit excited state energy transfer and charge transport which affects the time dependent autocorrelation of the photoluminescence (PL) emission intensity, photon counting statistics, blinking statistics, and PL lifetime, as observed by single molecule fluorescence spectroscopy. The structural arrangement of the nanocrystals and the electron transfer between the quantum dots and substrate can be investigated using atomic force microscopy, transmission electron microscopy, and scanning tunneling microscopy. These combined experiments provide novel perspectives on energy and electron transport in quantum dot higher order structures and the effects of structural arrangements, substrates, and attached ligands. These insights will enhance the development of technological applications of quantum dots, including bioimaging, display technology, and alternative energy technology. Research supported by NSF Grant 1059089.

  4. The electronic structure and charge transfer excited states of the endohedral trimetallic nitride C80 (I(h)) fullerenes-Zn-tetraphenyl porphyrin dyads.

    PubMed

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

    2015-02-28

    Endohedral fullerenes offer the possibility of tuning their properties through a choice of the endohedral unit. The Sc3N@C80 fullerene is the most abundant fullerene after C60 and C70. Recently, Sc3N@C80 has been tested for light harvesting properties with encouraging results. In this work, we study the electronic structure of three endohedral fullerene-Zn tetraphenyl porphyrin complexes using density functional theory. The binding between the components in these complexes arises due to van der Waals interaction. A fragment orbital analysis is carried out to examine the interaction between the two components which shows that a small charge transfer occurs in the ground state from the ZnTPP to the fullerenes and that the orientation of the Sc3N plane affects the ground state charge transfer. The charge transfer excited state energies are calculated using our perturbative delta-SCF method. A comparison with earlier calculations shows that the charge transfer excitation energy increases as C60-ZnTPP < C70-ZnTPP < Sc3N@C80-ZnTPP < Y3N@C80-ZnTPP. The orientation of the endohedral unit does not influence the excitation energy in the donor-acceptor complexes.

  5. Time-resolved study of excited states of N2 near its first ionization threshold

    NASA Astrophysics Data System (ADS)

    Moise, Angelica; Prince, Kevin C.; Richter, Robert

    2011-03-01

    Two-photon, two-color double-resonance ionization spectroscopy combining synchrotron vacuum ultraviolet radiation with a tunable near-infrared (NIR) laser has been used to investigate gerade symmetry states of the nitrogen molecule. The rotationally resolved spectrum of an autoionizing 1Σg- state has been excited via the intermediate c4 (v = 0) 1Πu Rydberg state. We present the analysis of the band located at Tv = 10 800.7 ± 2 cm-1 with respect to the intermediate state, 126 366 ± 11 cm-1 with respect to the ground state, approximately 700 cm-1 above the first ionization threshold. From the analysis a rotational constant of Bv = 1.700 ± 0.005 cm-1 has been determined for this band. Making use of the pulsed structure of the two radiation beams, lifetimes of several rotational levels of the intermediate state have been measured. We also report rotationally-averaged fluorescence lifetimes (300 K) of several excited electronic states accessible from the ground state by absorption of one photon in the range of 13.85-14.9 eV. The averaged lifetimes of the c4 (0) and c5 (0) states are 5.6 and 4.4 ns, respectively, while the b' (12), c'4 (4, 5, 6), and c'5 (0) states all have lifetimes in the range of hundreds of picoseconds.

  6. Solar Coronal Structure Study

    NASA Technical Reports Server (NTRS)

    Nitta, Nariaki; Bruner, Marilyn E.; Saba, Julia; Strong, Keith; Harvey, Karen

    2000-01-01

    The subject of this investigation is to 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 ground-based data. Each rocket flight produced both spectral and imaging data. These joint datasets are useful for understanding the physical state of various features in the solar atmosphere at different heights ranging from the photosphere to the corona at the time of the, rocket flights, which took place during the declining phase of a solar cycle, 2-4 years before the minimum. The investigation is narrowly focused on comparing the physics of small- and medium-scale strong-field structures with that of large-scale, weak fields. As we close th is investigation, we have to recall that our present position in the understanding of basic solar physics problems (such as coronal heating) is much different from that in 1995 (when we proposed this investigation), due largely to the great success of SOHO and TRACE. In other words, several topics and techniques we proposed can now be better realized with data from these missions. For this reason, at some point of our work, we started concentrating on the 1992 data, which are more unique and have more supporting data. As a result, we discontinued the investigation on small-scale structures, i.e., bright points, since high-resolution TRACE images have addressed more important physics than SPDE EUV images could do. In the final year, we still spent long time calibrating the 1992 data. The work was complicated because of the old-fashioned film, which had problems not encountered with more modern CCD detectors. After our considerable effort on calibration, we were able to focus on several scientific topics, relying heavily on the SPDE UV images. They include the relation between filaments and filament channels, the identification of hot

  7. Quantum Scattering Study of Ro-Vibrational Excitations in N+N(sub 2) Collisions under Re-entry Conditions

    NASA Technical Reports Server (NTRS)

    Wang, Dunyou; Stallcop, James R.; Dateo, Christopher E.; Schwenke, David W.; Huo, Winifred M.

    2004-01-01

    A three-dimensional time-dependent quantum dynamics approach using a recently developed ab initio potential energy surface is applied to study ro-vibrational excitation in N+N2 exchange scattering for collision energies in the range 2.1- 3.2 eV. State-to-state integral exchange cross sections are examined to determine the distribution of excited rotational states of N(sub 2). The results demonstrate that highly-excited rotational states are produced by exchange scattering and furthermore, that the maximum value of (Delta)j increases rapidly with increasing collision energies. Integral exchange cross sections and exchange rate constants for excitation to the lower (upsilon = 0-3) vibrational energy levels are presented as a function of the collision energy. Excited-vibrational-state distributions for temperatures at 2,000 K and 10,000 K are included.

  8. Theoretical studies for excited-state tautomerization in the 7-azaindole-(CH3OH)n (n = 1 and 2) complexes in the gas phase.

    PubMed

    Fang, Hua; Kim, Yongho

    2011-12-01

    The excited-state tautomerization of 7-azaindole (7AI) complexes bonded with either one or two methanol molecule(s) was studied by systematic quantum mechanical calculations in the gas phases. Electronic structures and energies for the reactant, transition state (TS), and product were computed at the complete active space self-consistent field (CASSCF) levels with the second-order multireference perturbation theory (MRPT2) to consider the dynamic electron correlation. The time-dependent density functional theory (TDDFT) was also used for comparison. The excited-state double proton transfer (ESDPT) in 7AI-CH(3)OH occurs in a concerted but asynchronous mechanism. Similarly, such paths are also found in the two transition states during the excited-state triple proton transfer (ESTPT) of the 7AI-(CH(3)OH)(2) complex. In the first TS, the pyrrole ring proton first migrated to methanol, while in the second the methanol proton moved first to the pyridine ring. The CASSCF level with the MRPT2 correction showed that the former path was much preferable to the latter, and the ESDPT is much slower than the ESTPT. Additionally, the vibrational-mode enhanced tautomerization in the 7AI-(CH(3)OH)(2) complex was also studied. We found that the excitation of the low-frequency mode shortens the reaction path to increase the tautomerization rate. Overall, most TDDFT methods used in this study predicted different TS structures and barriers from the CASSCF methods with MRPT2 corrections.

  9. Ab initio study on electronically excited states of lithium isocyanide, LiNC

    NASA Astrophysics Data System (ADS)

    Yasumatsu, Hisato; Jeung, Gwang-Hi

    2014-01-01

    The electronically excited states of the lithium isocyanide molecule, LiNC, were studied by means of ab initio calculations. The bonding nature of LiNC up to ˜10 eV is discussed on the basis of the potential energy surfaces according to the interaction between the ion-pair and covalent states. The ion-pair states are described by Coulomb attractive interaction in the long distance range, while the covalent ones are almost repulsive or bound with a very shallow potential dent. These two states interact each other to form adiabatic potential energy surfaces with non-monotonic change in the potential energy with the internuclear distance.

  10. Study of the effect of excited state concentration on photodegradation of the p3ht polymer.

    PubMed

    Peters, V N; Alexander, Rohan; Peters, D'Angelo A; Noginov, M A

    2016-01-01

    We have studied photoinduced reduction of absorption and emission in p3ht, a semiconducting polymer, and found that the rate of photodegradation (destruction of the constituent thiophene rings) does not correlate with the luminescence intensity and, correspondingly, does not depend on the excited state concentration. This conclusion rules out Purcell enhancement of radiative decay rate as a possible explanation of the recently discovered reduction of the p3ht photodegradation rate in the vicinity of metallic substrates and lamellar metal-dielectric metamaterials. PMID:27629230

  11. Study of the effect of excited state concentration on photodegradation of the p3ht polymer

    NASA Astrophysics Data System (ADS)

    Peters, V. N.; Alexander, Rohan; Peters, D.’Angelo A.; Noginov, M. A.

    2016-09-01

    We have studied photoinduced reduction of absorption and emission in p3ht, a semiconducting polymer, and found that the rate of photodegradation (destruction of the constituent thiophene rings) does not correlate with the luminescence intensity and, correspondingly, does not depend on the excited state concentration. This conclusion rules out Purcell enhancement of radiative decay rate as a possible explanation of the recently discovered reduction of the p3ht photodegradation rate in the vicinity of metallic substrates and lamellar metal-dielectric metamaterials.

  12. Study of the effect of excited state concentration on photodegradation of the p3ht polymer

    PubMed Central

    Peters, V. N.; Alexander, Rohan; Peters, D’Angelo A.; Noginov, M. A.

    2016-01-01

    We have studied photoinduced reduction of absorption and emission in p3ht, a semiconducting polymer, and found that the rate of photodegradation (destruction of the constituent thiophene rings) does not correlate with the luminescence intensity and, correspondingly, does not depend on the excited state concentration. This conclusion rules out Purcell enhancement of radiative decay rate as a possible explanation of the recently discovered reduction of the p3ht photodegradation rate in the vicinity of metallic substrates and lamellar metal-dielectric metamaterials. PMID:27629230

  13. Topographic mapping of subsurface fluorescent structures in tissue using multiwavelength excitation

    PubMed Central

    Kim, Anthony; Roy, Mathieu; Dadani, Farhan N.; Wilson, Brian C.

    2010-01-01

    Different colors of visible light penetrate to varying depths in tissue due to the wavelength dependence of tissue optical absorption and elastic scattering. We exploit this to map the contour of the closest surface of a buried fluorescent object. This uses a novel algorithm based on the diffusion theory description of light propagation in tissue at each excitation wavelength to derive metrics that define the depth of the top surface of the object. The algorithm was validated using a tissue-simulating phantom. It was then demonstrated in vivo by subsurface brain tumor topography in a rodent model, using the fluorescence signal from protoporphyrin IX that is preferentially synthesized within malignant cells following systemic application of aminolevulinic acid. Comparisons to histomorphometry in the brain post mortem show the spatial accuracy of the technique. This method has potential for fluorescence image-guided tumor surgery, as well as other biomedical and nonbiological applications in subsurface sensing. PMID:21198200

  14. Recoil excitation of vibrational structure in the carbon 1s photoelectron spectrum of CF4.

    PubMed

    Thomas, T Darrah; Kukk, Edwin; Sankari, Rami; Fukuzawa, Hironobu; Prümper, Georg; Ueda, Kiyoshi; Püttner, Ralph; Harries, James; Tamenori, Yusuke; Tanaka, Takahiro; Hoshino, Masamitsu; Tanaka, Hiroshi

    2008-04-14

    The carbon 1s photoelectron spectrum of CF4 measured at photon energies from 330 to 1500 eV shows significant contributions from nonsymmetric vibrational modes. These increase linearly as the photon energy increases. The excitation of these modes, which is not predicted in the usual Franck-Condon point of view, arises from the recoil momentum imparted to the carbon atom in the ionization process. A theory is presented for quantitative prediction of the recoil effect; the predictions of this theory are in agreement to the measurements. The experiments also yield the vibrational frequencies of the symmetric and asymmetric stretching modes in core-ionized CF4, the change in CF bond length upon ionization, -0.61 pm, and the Lorentzian linewidth of the carbon 1s hole, 67 meV.

  15. Electron impact excitation of the Ne II and Ne III fine structure levels

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Loch, S. D.; Pindzola, M. S.; Cumbee, R.; Stancil, P. C.; Ballance, C. P.; McLaughlin, B. M.

    2016-05-01

    Electron impact excitation cross sections and rate coefficients of the low lying levels of the Ne II and Ne III ions are of great interest in cool molecular environments including young stellar objects, photodissociation regions, active galactic nuclei, and X-ray dominated regions. We have carried out details computations for cross sections and rate coefficients using the Dirac R-matrix codes (DARC), the Breit-Pauli R-matrix codes (BP) and the Intermediate Coupling Frame Transformation (ICFT) codes, for both Ne II and Ne III. We also compare our results with previous calculations. We are primarily interested in rate coefficients in the temperature range below 1000 K, and the focus is on obtaining the most accurate rate coefficients for those temperatures. We present both a recommended set of effective collision strengths and an indication of the uncertainties on these values. Work at Auburn University and UGA partly supported by NASA Grant NNX15AE47G.

  16. Spiroconjugated intramolecular charge-transfer emission in non-typical spiroconjugated molecules: the effect of molecular structure upon the excited-state configuration.

    PubMed

    Zhu, Linna; Zhong, Cheng; Liu, Cui; Liu, Zhongyin; Qin, Jingui; Yang, Chuluo

    2013-04-01

    A set of terfluorenes and terfluorene-like molecules with different pendant substitutions or side groups were designed and synthesized, their photophysical properties and the excited-state geometries were studied. Dual fluorescence emissions were observed in compounds with rigid pendant groups bearing electron-donating N atoms. According to our earlier studies, in this set of terfluorenes, the blue emission is from the local π-π* transition, while the long-wavelength emission is attributed to a spiroconjugation-like through-space charge-transfer process. Herein, we probe further into how the molecular structures (referring to the side groups, the type of linkage between central fluorene and the 2,2'-azanediyldiethanol units, and-most importantly-the amount of pendant groups), as well as the excited-state geometries, affect the charge-transfer process of these terfluorenes or terfluorene-like compounds. 9-(9,9,9'',9''-tetrahexyl-9H,9'H,9''H-[2,2':7',2''-terfluoren]-9'-yl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolone (TFPJH), with only one julolidine pendant group, was particularly synthesized, which exhibits complete "perpendicular" conformation between julolidine and the central fluorene unit in the excited state, thus typical spiroconjugation could be achieved. Notably, its photophysical behaviors resemble those of TFPJ with two pendant julolidines. This study proves that spiroconjugation does happen in these terfluorene derivatives, although their structures are not in line with the typical orthogonal π fragments. The spiroconjugation charge-transfer emission closely relates to the electron-donating N atoms on the pendant groups, and to the rigid connection between the central fluorene and the N atoms, whereas the amount of pendant groups and the nature of the side chromophores have little effect. These findings may shed light on the understanding of the through-space charge-transfer properties and the emission color tuning of fluorene derivatives.

  17. Theoretical investigation of rotational rainbow structures in X-Na2 collisions using CI potential surfaces. II. Combined rotational-vibrational excitation for X = He scattering

    NASA Astrophysics Data System (ADS)

    Müller, Wolfgang; Schinke, Reinhard

    1981-08-01

    Combined rotational-vibrational excitaton cross sections for He-Na2 scattering are reported for collision energies of 0.05?E?0.15 eV. The infinite-order-sudden (IOS) approximation is used to decouple the rotational and the orbital angular momenta, whereas the vibrational degree of freedom is treated exactly by solving vibrationally coupled radial equations. An analytical potential energy surface obtained from 160 ab initio CI energies is used in these scattering calculations. The cross sections for vibrational excitation or de-excitation are extremely small compared to the vibrationally elastic cross sections but increase rapidly with the collision energy. The influence of the target vibration on pure rotational excitation processes is negligibly small for energies considered in this study, such that the rigid-rotor approximation applied previously for the same system is confirmed to be reasonable. Furthermore, the rotational rainbow structures which are characteristic for the He-Na2 system depend only very slightly on whether the molecule is initially in the ground n = 0 or the first vibrationally excited state n = 1. This was in contradiction to the experimental finding of Bergmann et al. [J. Chem. Phys. 72, 4777 (1980)], who reported a dramatic enhancement of the rotational energy transfer for scattering within the n = 1 vibrational state. The rotational rainbow maxima occur at almost equal positions independent of whether the transition is vibrationally elastic or inelastic. A small shift to wider scattering angles in the case of Δn = 1 is observed at lower energies.

  18. [Density functional theory study of surface-enhanced raman spectra and excited state of 1,4-benzenedithiol].

    PubMed

    Shao, Yang-Fan; Li, Chong-Yang; Feng, Yuan-Ming; Lin, Wang

    2014-02-01

    Raman scattering spectra and optimized geometries of the 1,4-benzenedithiol molecule and complexes have been calculated using density functional theory (DFT) with B3LYP functional at the level of 6-311G+(d) basis set for C, H, S atoms and LanL2DZ for Ag, Au atoms, respectively. The optimized 1,4-benzenedithiol molecule was non-planar structure and the angle between benzene ring plane and S-H is 20.20. By means of the simulation of molecule adsorbed on gold and silver cluster, we concluded that gold clusters are nearly parallel to the benzenedithiol molecule and silver clusters are almost perpendicular to the molecular surface. The authors studied the interaction between Raman intensity and molecular properties, such as static polarizablity and charge distribution. The Raman intensity of 1,4-BDT-Au2, 1,4-BDT-Ag2 and Ag2-1,4-BDT-Au2 were in good agreement with static polarizability. The excited states of Ag2-1,4-BDT-Au2 complex were calculated using time-dependent density functional theory (TDDFT). And the simulated absorption spectra and several allowed singlet excited states were analyzed to investigate the surface-enhanced Raman chemical enhancement mechanism. PMID:24822413

  19. First-principles study of Ce3 +-doped lanthanum silicate nitride phosphors: Neutral excitation, Stokes shift, and luminescent center identification

    NASA Astrophysics Data System (ADS)

    Jia, Yongchao; Miglio, Anna; Poncé, Samuel; Gonze, Xavier; Mikami, Masayoshi

    2016-04-01

    We study from first principles two lanthanum silicate nitride compounds, LaSi3N5 and La3Si6N11 , pristine as well as doped with Ce3 + ion, in view of explaining their different emission color, and characterizing the luminescent center. The electronic structures of the two undoped hosts are similar, and do not give a hint to quantitatively describe such difference. The 4 f →5 d neutral excitation of the Ce3 + ions is simulated through a constrained density functional theory method coupled with a Δ SCF analysis of total energies, yielding absorption energies. Afterwards, atomic positions in the excited state are relaxed, yielding the emission energies and Stokes shifts. Based on these results, the luminescent centers in LaSi3N5 :Ce and La3Si6N11 :Ce are identified. The agreement with the experimental data for the computed quantities is quite reasonable and explains the different color of the emitted light. Also, the Stokes shifts are obtained within 20% difference relative to experimental data.

  20. Study of nonlinear optical absorption properties of Sb2Se3 nanoparticles in the nanosecond and femtosecond excitation regime

    NASA Astrophysics Data System (ADS)

    Molli, Muralikrishna; Pradhan, Prabin; Dutta, Devarun; Jayaraman, Aditya; Bhat Kademane, Abhijit; Muthukumar, V. Sai; Kamisetti, Venkataramaniah; Philip, Reji

    2016-05-01

    In this work, we report for the first time, the nonlinear optical absorption properties of antimony selenide (Sb2Se3) nanoparticles synthesized through solvothermal route. X-ray diffraction results revealed the crystalline nature of the nanoparticles. Electron microscopy studies revealed that the nanoparticles are in the range of 10-40 nm. Elemental analysis was performed using EDAX. The nanosecond optical limiting effect was characterized by using fluence-dependent transmittance measurements with 15-ns laser pulses at 532 and 1064 nm excitation wavelengths. Mechanistically, effective two-photon (2PA) absorption and nonlinear scattering processes were the dominant nonlinear processes at both the wavelengths. At 800 nm excitation in the femtosecond regime (100 fs), the nonlinear optical absorption was found to be a three-photon (3PA) process. Both 2PA and 3PA processes were explained using the band structure and density of states of Sb2Se3 obtained using density functional theory. These nanoparticles exhibit strong intensity-dependent nonlinear optical absorption and hence could be considered to have optical power-limiting applications in the visible range.

  1. Local excitation of the 5-bromouracil chromophore in DNA. Computational and UV spectroscopic studies.

    PubMed

    Storoniak, Piotr; Rak, Janusz; Polska, Katarzyna; Blancafort, Lluís

    2011-04-21

    The UV electronic transition energies and their oscillator strengths for two stacked dimers having B-DNA geometries and consisting of 5-bromouracil ((Br)U) and a purine base were studied at the MS-CASPT2/6-311G(d) level with an active space of 12 orbitals and 12 electrons. The calculated energy of the first vertical (π,π*) transitions for the studied dimers remain in fair agreement with the maxima in the difference spectra measured for duplexes with the 5'-A(Br)U-3' or 5'-G(Br)U-3' sequences. Our MS-CASPT2 results show that the charge transfer (CT) states in which an electron is transferred from A/G to (Br)U are located at much higher energies than the first (π,π*) transitions, which involve local excitation (LE) of (Br)U. Moreover, CT transitions are characterized by small oscillator strengths, which implies that they could not be excited directly. The results of the current studies suggest that the formation of the reactive uracil-5-yl radical in DNA is preceded by the formation of the highly oxidative LE state of (Br)U, which is followed by electron transfer, presumably from guanine.

  2. Excited state enol-keto tautomerization in salicylic acid: A supersonic free jet study

    NASA Astrophysics Data System (ADS)

    Bisht, Prem B.; Petek, Hrvoje; Yoshihara, Keitaro; Nagashima, Umpei

    1995-10-01

    Excited state enol-keto isomerization in salicylic acid (SA) monomer and dimer has been studied in a supersonic free jet expansion. Two carboxylic group rotamers of SA with significantly different photophysical properties are found in the expansion. Rotamer I, the major form of SA in the expansion, has an intramolecular hydrogen bond and can undergo excited state tautomerization reaction. Its S1 origin is at 335.34 nm. Single vibronic level emission spectra are dominated by progressions in OH stretching (3230 cm-1), and in-plane bending of the carboxylic group (240 cm-1). The spectra appear to consist of two components, normal (UV) and tautomer (BLUE) emissions, even at the origin. The intensity of the BLUE relative to the UV emission depends on the vibronic state, rather than the excess vibrational energy between the origin and 1100 cm-1. The fluorescence decay time profiles for both the emission components of rotamer I are identical within ˜1 ns experimental time resolution. A nonradiative decay process with an activation energy of ˜1100 cm-1 is deduced from an abrupt decrease in fluorescence lifetimes above this energy. The rotamer II cannot undergo excited state tautomerization. Its electronic origin is at 311.52 nm and emits only UV fluorescence. Upon increasing the concentration of the SA sample, a new spectrum is observed. Due to a nonlinear concentration dependence of the intensity and the propensity of SA to form dimers in solution, it is assigned to the SA dimer. This spectrum shows possible evidence of double proton transfer in the S1 state.

  3. Switching of the triplet excited state of rhodamine/naphthaleneimide dyads: an experimental and theoretical study.

    PubMed

    Cui, Xiaoneng; Zhao, Jianzhang; Lou, Zhangrong; Li, Shujing; Wu, Huijian; Han, Ke-Li

    2015-01-01

    Rhodamine-bromonaphthaleneimide (RB-NI) and rhodamine-bromonaphthalenediimide (RB-NDI) dyads were prepared for switching of the triplet excited states. Bromo-NI or bromo-NDI parts in the dyads are the spin converters, i.e., the triplet state producing modules, whereas the RB unit is the acid-activatable electron donor/energy acceptor. NI and NDI absorb at 359 and 541 nm, and the T1 state energy levels are 2.25 and 1.64 eV, respectively. RB undertakes the reversible spirolactam (RB-c) ↔ opened amide (RB-o) transformation. RB-c shows no visible light absorption, and the triplet-state energy level is ET1 = 3.36 eV. Conversely RB-o shows strong absorption at 557 nm, and ET1 is 1.73 eV. Thus, the acid-activated fluorescence-resonance-energy-transfer (FRET) competes with the ISC of NI or NDI. No triplet state was observed for the dyads with nanosecond time-resolved transient absorption spectroscopy. Upon addition of acid, strong fluorescence and long-living triplet excited states were observed. Thus, the producing of triplet state is acid-activatable. The triplet state of RB-NI is localized on RB-o part, whereas in RB-NDI the triplet state is delocalized on both the NDI and RB-o units. The ISC of spin converter was not outcompeted by RET. These studies are useful for switching of triplet excited state. PMID:25436874

  4. Excited state non-adiabatic dynamics of N-methylpyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study

    NASA Astrophysics Data System (ADS)

    Wu, Guorong; Neville, Simon P.; Schalk, Oliver; Sekikawa, Taro; Ashfold, Michael N. R.; Worth, Graham A.; Stolow, Albert

    2016-01-01

    The dynamics of N-methylpyrrole following excitation at wavelengths in the range 241.5-217.0 nm were studied using a combination of time-resolved photoelectron spectroscopy (TRPES), ab initio quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree method, as well as high-level photoionization cross section calculations. Excitation at 241.5 and 236.2 nm results in population of the A2(πσ∗) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B1(π3py) Rydberg state, followed by prompt internal conversion to the A2(πσ∗) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A2(πσ∗) state was found to vary with excitation wavelength, decreasing by one order of magnitude upon tuning from 241.5 nm to 236.2 nm and by more than three orders of magnitude when excited at 217.0 nm. The order of magnitude difference in lifetimes measured at the longer excitation wavelengths is attributed to vibrational excitation in the A2(πσ∗) state, facilitating wavepacket motion around the potential barrier in the N-CH3 dissociation coordinate.

  5. Excited-state dynamics of furan studied by sub-20-fs time-resolved photoelectron imaging using 159-nm pulses

    NASA Astrophysics Data System (ADS)

    Spesyvtsev, R.; Horio, T.; Suzuki, Y.-I.; Suzuki, T.

    2015-07-01

    The excited-state dynamics of furan were studied by time-resolved photoelectron imaging using a sub-20-fs deep UV (198 nm) and vacuum UV (159 nm) light source. The 198- and 159-nm pulses produce photoionization signals in both pump-probe and probe-pump pulse sequences. When the 198-nm pulse precedes the 159-nm pulse, it creates the 1A2(3s) Rydberg and 1B2(ππ∗) valence states, and the former decays exponentially with a time constant of about 20 fs whereas the latter exhibits more complex wave-packet dynamics. When the 159-nm pulse precedes the 198-nm pulse, a wave packet is created on the 1A1(ππ∗) valence state, which rapidly disappears from the observation window owing to structural deformation. The 159-nm photoexcitation also creates the 3s and 3px,y Rydberg states non-adiabatically.

  6. Kinetics studies following state-selective laser excitation. Final progress report, March 15, 1984--July 15, 1993

    SciTech Connect

    Keto, J.W.

    1994-04-01

    The objective of this contract was the study of state-to-state, electronic energy transfer reactions relevant to the excited state chemistry observed in discharges. We studied deactivation reactions and excitation transfer in collisions of excited states of xenon and krypton atoms with Ar, Kr, Xe and chlorine. The reactant states were excited selectively in two-photon transitions using tunable u.v. and v.u.v. lasers. Excited states produced by the collision were observed by their fluorescence. Reaction rates were measured by observing the time dependent decay of signals from reactant and product channels. In addition we measured interaction potentials of the reactants by laser spectroscopy where the laser induced fluorescence or ionization is measured as a function of laser wavelength (excitation spectra) or by measuring fluorescence spectra at fixed laser frequencies with monochromators. The spectra were obtained in the form of either lineshapes or individual lines from rovibrational transitions of bound states. Our research then required several categories of experiments in order to fully understand a reaction process: 1. High resolution laser spectroscopy of bound molecules or lineshapes of colliding pairs is used to determine potential curves for reactants. 2. Direct measurements of state-to-state reaction rates were measured by studying the time dependent loss of excited reactants and the time dependent formation of products. 3. The energy selectivity of a laser can be used to excite reactants on an excited surface with controlled internuclear configurations. For free states of reactants (as exist in a gas cell) this has been termed laser assisted reactions, while for initially bound states (as chemically bound reactants or dimers formed in supersonic beams) the experiments have been termed photo-fragmentation spectroscopy.

  7. Theoretical studies of collisional relaxation of highly excited SO{sub 2} in an Ar bath

    SciTech Connect

    Lendvay, G.; Schatz, G.C.; Harding, L.B.

    1995-12-31

    This paper describes molecular dynamics studies of collisional relaxation of highly excited SO{sub 2} in an Ar bath. Most of the calculations use a newly developed global ab initio potential surface for SO{sub 2} that correctly describes the superoxide (SOO) and ring isomers of SO{sub 2} that occur as secondary minima on the ground state potential surface at high energies (about 75% of the dissociation energy) above the C{sub 2v} minimum. Rate constants for the S + O{sub 2} and O + SO reactions are calculated to test this surface, and to examine the importance of electronically excited states in the O + SO recombination. The Ar + SO{sub 2} collisions are described by summing the ab initio potential with empirical intermolecular potentials. The resulting average vibrational energy transfer <{Delta}E> per collision is in good agreement with direct measurements (done at energies where the secondary minima are not populated) at 1000K, but the agreement is poorer at 300K. The agreement is significantly better than was obtained in a previous theoretical study, and our results indicate that the use of improved intramolecular and intermolecular potentials is crucial to obtaining the better results. The energy dependence of <{Delta}E> is found to be much stronger at energies where the secondary minima on the potential surface are accessible, however much of this effect is reproduced using a potential that has the same dissociation energy but not the secondary minima.

  8. Cell Structure Study.

    ERIC Educational Resources Information Center

    Ekstrom, James V.

    2000-01-01

    Presents an activity in which students use microscopes and digital images to examine Elodea, a fresh water plant, before and after the process of plasmolysis, identify plant cellular structures before and after plasmolysis, and calculate the size of the plant's vacuole. (ASK)

  9. Internal intensity standards for heme protein UV resonance Raman studies: excitation profiles of cacodylic acid and sodium selenate.

    PubMed

    Song, S H; Asher, S A

    1991-02-01

    We examine the utility of SO4(2-), ClO4-, cacodylic acid, and SeO4(2-) as internal intensity standards for Raman spectral measurements of protein structure. We find that 0.1 M SO4(2-) and ClO4- perturb the protein tertiary structure of aquomethemoglobin (met-Hb) and its fluoride (met-HbF) and azide (met-HbN3) complexes. Changes occur for the tryptophan near-UV absorption bands, the iron spin state is altered, and the fluoride ligand affinity decreases. Concentrations of ClO4- and SO4(2-) as low as 0.1 M suppress the met-HbF quaternary R----T transition induced by the allosteric effector inositol hexaphosphate (IHP). In contrast, similar concentrations of cacodylic acid and SeO4(2-) show little effect on the hemoglobin tertiary or quaternary protein structures or upon the R----T transition induced by IHP. We measure the Raman cross sections of cacodylic acid and SeO4(2-) between 218 and 514.5 nm and find that for UV excitation they are ca. 5-fold larger than ClO4- or SO4(2-). Thus, cacodylic acid and selenate can be used at lower concentrations. Cacodylic acid and SeO4(2-) are superior Raman internal intensity standards for protein structural studies.

  10. Ab initio molecular orbital study on the excited states of [2.2]-, [3.3]-, and siloxane-bridged paracyclophanes.

    PubMed

    Shirai, Soichi; Iwata, Suehiro; Maegawa, Yoshifumi; Tani, Takao; Inagaki, Shinji

    2012-10-18

    Paracyclophanes are simple idealized model molecules for the study of interacting π-stacking systems. In this study, the excited states of [2.2]paracyclophane ([2.2]PCP), [3.3]paracyclophane ([3.3]PCP), and siloxane-bridged paracyclophane (SiPCP) are systematically investigated using the multiconfiguration quasi-degenerated perturbation theory (MCQDPT) method. The excited states of the alkyl- and silyl-substituted benzene monomers and benzene dimer, which can be regarded as the building blocks of paracyclophanes, are also examined at the same level of theory for more detailed understanding. The accuracy of the time-dependent density functional theory (TD-DFT) method required for excited state geometry optimization of the paracyclophanes is confirmed from calculations of the benzene dimer. The equilibrium distances between the benzene rings of the paracyclophanes in the first excited states are shorter than those in the ground state, and the benzene rings at the excited state optimized geometries are in an almost eclipsed parallel configuration, which indicates excimer formation. The calculated transition energies and oscillator strengths are generally in good agreement with the corresponding experimental results. A clear correlation between the excited state properties and the molecular structures is systematically demonstrated based on the calculation results for the substituted benzene monomers and benzene dimer. The transition energies of SiPCP are close to the corresponding absorption and fluorescence energies of the experimentally studied phenylene-silica hybrids, which indicates that the electronic properties of organic-silica hybrids, which is a new class of material with potential in photofunctional applications, can be approximated by simple siloxane-bridged cyclophane derivatives.

  11. Repetitive Transcranial Direct Current Stimulation Induced Excitability Changes of Primary Visual Cortex and Visual Learning Effects—A Pilot Study

    PubMed Central

    Sczesny-Kaiser, Matthias; Beckhaus, Katharina; Dinse, Hubert R.; Schwenkreis, Peter; Tegenthoff, Martin; Höffken, Oliver

    2016-01-01

    Studies on noninvasive motor cortex stimulation and motor learning demonstrated cortical excitability as a marker for a learning effect. Transcranial direct current stimulation (tDCS) is a non-invasive tool to modulate cortical excitability. It is as yet unknown how tDCS-induced excitability changes and perceptual learning in visual cortex correlate. Our study aimed to examine the influence of tDCS on visual perceptual learning in healthy humans. Additionally, we measured excitability in primary visual cortex (V1). We hypothesized that anodal tDCS would improve and cathodal tDCS would have minor or no effects on visual learning. Anodal, cathodal or sham tDCS were applied over V1 in a randomized, double-blinded design over four consecutive days (n = 30). During 20 min of tDCS, subjects had to learn a visual orientation-discrimination task (ODT). Excitability parameters were measured by analyzing paired-stimulation behavior of visual-evoked potentials (ps-VEP) and by measuring phosphene thresholds (PTs) before and after the stimulation period of 4 days. Compared with sham-tDCS, anodal tDCS led to an improvement of visual discrimination learning (p < 0.003). We found reduced PTs and increased ps-VEP ratios indicating increased cortical excitability after anodal tDCS (PT: p = 0.002, ps-VEP: p = 0.003). Correlation analysis within the anodal tDCS group revealed no significant correlation between PTs and learning effect. For cathodal tDCS, no significant effects on learning or on excitability could be seen. Our results showed that anodal tDCS over V1 resulted in improved visual perceptual learning and increased cortical excitability. tDCS is a promising tool to alter V1 excitability and, hence, perceptual visual learning. PMID:27375452

  12. Regge spectra of excited mesons, harmonic confinement, and QCD vacuum structure

    NASA Astrophysics Data System (ADS)

    Nedelko, Sergei N.; Voronin, Vladimir E.

    2016-05-01

    An approach to QCD vacuum as a medium describable in terms of a statistical ensemble of almost everywhere homogeneous Abelian (anti-)self-dual gluon fields is briefly reviewed. These fields play the role of the confining medium for color charged fields as well as underline the mechanism of realization of chiral S UL(Nf)×S UR(Nf) and UA(1 ) symmetries. Hadronization formalism based on this ensemble leads to manifestly defined quantum effective meson action. Strong, electromagnetic, and weak interactions of mesons are represented in the action in terms of nonlocal n -point interaction vertices given by the quark-gluon loops averaged over the background ensemble. New systematic results for the mass spectrum and decay constants of radially excited light, heavy-light mesons, and heavy quarkonia are presented. The interrelation between the present approach, models based on ideas of soft-wall anti-de Sitter/QCD, light-front holographic QCD, and the picture of harmonic confinement is outlined.

  13. Solvent effects on excited-state electron-transfer rate of pyrene-labeled deoxyuridine: A theoretical study

    NASA Astrophysics Data System (ADS)

    Maekawa, Shintaro; Sato, Ryuma; Hirao, Kimihiko; Shigeta, Yasuteru

    2016-01-01

    Solvent effects on the quenching process from the first excited state of 5-(1-pyrenyl)-2‧-deoxyuridine (Py-dU) were theoretically examined. Our results suggest that the excited-state electron transfer occurs without the so-called proton-coupled electron transfer process, which supports experimental results. Although there are no remarkable differences observed in the structure and the corresponding S1 excitation energy between the solutions of MeOH and MeCN within a polarizable continuum model, we report here that hydrogen bonds between the explicit MeOH molecule with the dU moiety, whose structure was frequently found in molecular dynamics simulations, result in an enhancement of the electron-transfer rate constant.

  14. Laboratory studies of 3.3 micron emission from naphthalene induced by 193 and 248 nanometer excitation

    NASA Technical Reports Server (NTRS)

    Williams, Richard M.; Leone, Stephen R.

    1995-01-01

    Laboratory studies of infrared emission from gas-phase naphthalene in the 3.3 micrometer region following ultraviolet laser excitation are used to interpret the unidentified infrared bands observed in many astronomical objects. A time-resolved Fourier transform infrared emission technique acquires the time and spectrally resolved data. Two excitation wavelengths are employed: 193 nm and 248 nm. The infrared emission features are strongly dependent on the initial excitation energy. Wavelength-resolved spectra recorded 6.8 microseconds after the laser pulse show a 45/cm redshift from the gas-phase absorption spectra for 193 nm excitation and 25/cm for 248 nm excitation. We hypothesize that a series of sequence bands originating from the highly vibrationally excited ensemble of molecules is responsible for the observed shift. As collisional and radiative deactivation removes energy from the highly vibrationally excited molecules, the maximum in the emission profile gradually approaches the customary absorption maximum. This indicates that the amount of redshift is strongly dependent on the amount of internal vibrational energy in the molecule at the time of the vibrational transition.

  15. Observation of structural relaxation during exciton self-trapping via excited-state resonant impulsive stimulated Raman spectroscopy

    SciTech Connect

    Mance, J. G.; Felver, J. J.; Dexheimer, S. L.

    2015-02-28

    We detect the change in vibrational frequency associated with the transition from a delocalized to a localized electronic state using femtosecond vibrational wavepacket techniques. The experiments are carried out in the mixed-valence linear chain material [Pt(en){sub 2}][Pt(en){sub 2}Cl{sub 2}]⋅(ClO{sub 4}){sub 4} (en = ethylenediamine, C{sub 2}H{sub 8}N{sub 2}), a quasi-one-dimensional system with strong electron-phonon coupling. Vibrational spectroscopy of the equilibrated self-trapped exciton is carried out using a multiple pulse excitation technique: an initial pump pulse creates a population of delocalized excitons that self-trap and equilibrate, and a time-delayed second pump pulse tuned to the red-shifted absorption band of the self-trapped exciton impulsively excites vibrational wavepacket oscillations at the characteristic vibrational frequencies of the equilibrated self-trapped exciton state by the resonant impulsive stimulated Raman mechanism, acting on the excited state. The measurements yield oscillations at a frequency of 160 cm{sup −1} corresponding to a Raman-active mode of the equilibrated self-trapped exciton with Pt-Cl stretching character. The 160 cm{sup −1} frequency is shifted from the previously observed wavepacket frequency of 185 cm{sup −1} associated with the initially generated exciton and from the 312 cm{sup −1} Raman-active symmetric stretching mode of the ground electronic state. We relate the frequency shifts to the changes in charge distribution and local structure that create the potential that stabilizes the self-trapped state.

  16. Photoexcited breathers in conjugated polyenes: An excited-state molecular dynamics study

    PubMed Central

    Tretiak, S.; Saxena, A.; Martin, R. L.; Bishop, A. R.

    2003-01-01

    π-conjugated polymers have become an important class of materials for electronic devices. Design of these devices requires understanding such processes as photochemical reactions, spatial dynamics of photoexcitations, and energy and charge transport, which in turn involve complex coupled electron-vibrational dynamics. Here we study nonlinear photoexcitation dynamics in the polyene oligomers by using a quantum-chemical method suitable for the simulation of excited-state molecular dynamics in extended molecular systems with sizes up to hundreds of atoms. The method is based on the adiabatic propagation of the ground-state and transition single-electron density matrices along the trajectory. The simulations reveal formation of a self-localized vibronic excitation (“breather” or multiquanta bound state) with a typical period of 34 fs and allows us to identify specific slow and fast nuclear motions strongly coupled to the electronic degrees of freedom. The effect of chain imperfections and chemical defects on the dynamics is also investigated. A complementary two-dimensional analysis of corresponding transition density matrices provides an efficient way to monitor time-dependent real-space localization of the photoexcitation by identifying the underlying changes in charge densities and bond orders. Possible correlated electronic and vibrational spectroscopic signatures of photoexcited breathers are predicted, and generalizations to energy localization in complex macromolecules are discussed. PMID:12594339

  17. Autoionization study of the Argon 2p satellites excited near the argon 2s threshold

    SciTech Connect

    Wang, H.; Glans, P.; Hemmers, O.

    1997-04-01

    The dynamics of near-threshold photoionization is a complex phenomenon in which the many-electron character of the wavefunctions plays an important role. According to generalized time-independent resonant scattering theory, the transition matrix element from an initial state to a final state is the summation of the amplitudes of direct photoionization and an indirect term in which intermediate states are involved and the resonant behavior is embedded. Studies of the interference effects of intermediate states have been explored in the cases where the direct term is negligible. In the present work, electron time-of-flight spectra of the Ar 2p satellites were measured at two angles (magic and 0{degrees}) in the dipole plane with the exciting photon energy tuned in the vicinity of the Ar 2s threshold. For excitation far below or above the 2s threshold, the 2p satellites spectrum is dominated by 3p to np shakeup contributions upon the ionization of a 2p electron.

  18. A study of vibrationally excited N2(+) ions in the daytime thermosphere

    SciTech Connect

    Hsu, L.

    1992-01-01

    The role of vibrationally excited N2(+) ions in the daytime thermosphere is studied. Ionization rates of the neutrals N2(+), O2(+), and O by solar extreme ultraviolet radiations with wavelengths below lambda 1050A and by impact of photoelectrons with energies between 10 to 500 eV are calculated. A photochemical model with ambipolar diffusion of ions included is used to obtain the altitude profiles of N2(+), O2(+), O(+), O(+)(P-2), O(+)(D-2), O2(+)(a(sup 4)pi(sub u)), NO(+), and N(+) ion densities. Vibrational level densities and vibrational distribution of the X(sup 2)((sigma(sub g)))(sup +), A(sup 2)pi(sub u), and B(sup 2)((sigma(sub u)))(sup +) electronic states of N2(+) ions are then calculated by taking into consideration the direct ionization-excitation of N2(+) ions by solar extreme ultraviolet radiations and photoelectron impacts, fluorescent scattering of sunlight, chemical reactions, collision with neutrals, and radiative emissions. Column emission rates for the (0,0) band at lambda 3914A, (0,1) band at lambda 4277A, (1,2) band at lambda 4236A, and (2,3) band at lambda 4199A of the N2(+) first negative band system are then computed and compared with rocket flight data.

  19. Low-lying excited states in armchair polyacene within Pariser-Parr-Pople model: A density matrix renormalization group study

    SciTech Connect

    Das, Mousumi

    2014-03-28

    We studied the nature of the ground state and low-lying excited states of armchair polyacene oligomers (Polyphenanthrene) within long-range Pariser-Parr-Pople model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. The ground state of all armchair polyacenes studied is found to be singlet. The results show that lowest singlet dipole allowed excited state has higher energy for armchair polyacenes as compared to linear fused polyacenes. Moreover, unlike linear fused polyacenes, the lowest singlet excited state of these oligomers is always found to lie below the lowest dipole forbidden two-photon state indicating that these armchair polyacene oligomers strongly fluoresce. The calculations of low-lying excitations on singly and triply electron doped armchair polyacene oligomers show a low energy band with strong transition dipole moment that coupled to charge conductivity. This implies armchair polyacene posses novel field-effect transistor properties.

  20. Vibro-acoustic analysis of the acoustic-structure interaction of flexible structure due to acoustic excitation

    NASA Astrophysics Data System (ADS)

    Djojodihardjo, Harijono

    2015-03-01

    The application of BE-FE acoustic-structure interaction on a structure subject to acoustic load is elaborated using the boundary element-finite element acoustic structural coupling and the utilization of the computational scheme developed earlier. The plausibility of the numerical treatment is investigated and validated through application to generic cases. The analysis carried out in the work is intended to serve as a baseline in the analysis of acoustic structure interaction for lightweight structures. Results obtained thus far exhibit the robustness of the method developed.

  1. Excited-State Tautomerization of 7-Azaindole in Nonpolar Solution: A Theoretical Study Based on Liquid-Phase Potential Surfaces of Mean Force.

    PubMed

    Fang, Hua; Kim, Yongho

    2013-08-13

    Excited state tautomerization of a 7-azaindole (7AI) complex with one methanol molecule in heptane was studied using variational transition state theory including multidimensional tunneling (VTST/MT) with the dielectric continuum model for the solvent effect. Electronic structures and energies for reactants and transition state (TS) in solution were computed at the complete active space self-consistent field (CASSCF) level with second-order multireference perturbation theory (MRPT2) to take into consideration of dynamic electron correlation. The polarizable continuum model using the integral equation formalism (IEFPCM) and the SMD model were used for the excited-state solvent effect. Excited-state surfaces of potential of the mean force in solution were generated for the first time at the MRPT2//SMD/CASSCF(10,9)/6-31G(d,p) level. The position of TS on the reaction coordinate substantially depended on the dynamic electron correlation. The two protons in the excited-state tautomerization were transferred in a concerted but asynchronous process. Calculated HH/DD kinetic isotope effect (KIE) and the ratio of Arrhenius pre-exponential factors, A(HH)/A(DD), agreed very well with the corresponding experimental values. The shape of the adiabatic energy surfaces in the excited-state strongly depended on the position of isotopes due to the asynchronicity of the reaction path, and the tunneling effect was essential for reproducing experimental KIEs. The pyrrolic proton moved a twice longer distance by tunneling than the hydroxyl proton in the most probable tunneling path at 292 K. This study strongly suggests that the mechanism of the excited-state double proton transfer in heptane is triggered by proton transfer from the pyrrolic nitrogen of 7AI to alcohol (protolytic pathway), rather than by proton transfer from alcohol to the pyridine nitrogen of 7AI (solvolytic pathway).

  2. The Circumstellar Structure and Excitation Effects around the Massive Protostar Cepheus A HW 2

    NASA Astrophysics Data System (ADS)

    Torrelles, J. M.; Patel, N. A.; Curiel, S.; Ho, P. T. P.; Garay, G.; Rodríguez, L. F.

    2007-09-01

    We report SMA 335 GHz continuum observations with angular resolution of ~0.3", together with VLA ammonia observations with ~1" resolution toward Cep A HW 2. We find that the flattened disk structure of the dust emission observed by Patel et al. is preserved at the 0.3" scale, showing an elongated structure of ~0.6" size (450 AU) peaking on HW 2. In addition, two ammonia cores are observed, one associated with a hot core previously reported and an elongated core with a double peak separated by ~1.3", with signs of heating at the inner edges of the gas facing HW 2. The double-peaked ammonia structure, as well as the double-peaked CH3CN structure reported previously (and proposed to be two independent hot cores), surround both the dust emission as well as the double-peaked SO2 disk structure found by Jiménez-Serra et al. All these results argue against the interpretation of the elongated dust-gas structure as due to a chance superposition of different cores; instead, they imply that it is physically related to the central massive object within a ``disk-protostar-jet '' system.

  3. Excited-state structure, vibrations, and nonradiative relaxation of jet-cooled 5-fluorocytosine.

    PubMed

    Lobsiger, Simon; Trachsel, Maria A; Den, Takuya; Leutwyler, Samuel

    2014-03-20

    The S0 → S1 vibronic spectrum and S1 state nonradiative relaxation of jet-cooled keto-amino 5-fluorocytosine (5FCyt) are investigated by two-color resonant two-photon ionization spectroscopy at 0.3 and 0.05 cm(–1) resolution. The 0(0)(0) rotational band contour is polarized in-plane, implying that the electronic transition is (1)ππ*. The electronic transition dipole moment orientation and the changes of rotational constants agree closely with the SCS-CC2 calculated values for the (1)ππ* (S1) transition of 5FCyt. The spectral region from 0 to 300 cm(–1) is dominated by overtone and combination bands of the out-of-plane ν1′ (boat), ν2′ (butterfly), and ν3′ (HN–C6H twist) vibrations, implying that the pyrimidinone frame is distorted out-of-plane by the (1)ππ* excitation, in agreement with SCS-CC2 calculations. The number of vibronic bands rises strongly around +350 cm(–1); this is attributed to the (1)ππ* state barrier to planarity that corresponds to the central maximum of the double-minimum out-of-plane vibrational potentials along the ν1′, ν2′, and ν3′ coordinates, which gives rise to a high density of vibronic excitations. At +1200 cm(–1), rapid nonradiative relaxation (k(nr) ≥ 10(12) s(–1)) sets in, which we interpret as the height of the (1)ππ* state barrier in front of the lowest S1/S0 conical intersection. This barrier in 5FCyt is 3 times higher than that in cytosine. The lifetimes of the ν′ = 0, 2ν1′, 2ν2′, 2ν1′ + 2ν2′, 4ν2′, and 2ν1′ + 4ν2′ levels are determined from Lorentzian widths fitted to the rotational band contours and are τ ≥ 75 ps for ν′ = 0, decreasing to τ ≥ 55 ps at the 2ν1′ + 4ν2′ level at +234 cm(–1). These gas-phase lifetimes are twice those of S1 state cytosine and 10–100 times those of the other canonical nucleobases in the gas phase. On the other hand, the 5FCyt gas-phase lifetime is close to the 73 ps lifetime in room-temperature solvents. This lack of

  4. Experimental studies of collective excitations of a BEC in light-induced gauge fields

    NASA Astrophysics Data System (ADS)

    Li, Chuan-Hsun; Niffenegger, Robert; Blasing, David; Olson, Abraham; Chen, Yong P.

    2015-05-01

    We present our experimental studies of collective modes including spin dipole mode and scissors mode of a 87Rb Bose-Einstein condensate (BEC) in the presence of Raman light-induced gauge fields and synthetic spin-orbit coupling (SOC). By Raman dressing the mf spin states within the F =1 manifold, we engineer atoms' energy-momentum dispersion to create synthetic SOC, and spin dependent synthetic electric and magnetic fields. We have used spin dependent synthetic electric fields to make two BECs with different spins oscillate and collide in the optical trap. We have studied the effects of SOC on both the momentum damping and thermalization behaviors of the BECs when undergoing such spin dipole oscillations. We have also used spatially dependent synthetic electric fields to excite the scissors mode, which has been used as a probe for superfluidity. We have investigated the effects of the synthetic gauge fields and SOC on the measured scissors mode.

  5. Mechanistic Study on Electronic Excitation Dissociation of the Cellobiose-Na+ Complex

    NASA Astrophysics Data System (ADS)

    Huang, Yiqun; Pu, Yi; Yu, Xiang; Costello, Catherine E.; Lin, Cheng

    2016-02-01

    The recent development of electron activated dissociation (ExD) techniques has opened the door for high-throughput, detailed glycan structural elucidation. Among them, ExD methods employing higher-energy electrons offer several advantages over low-energy electron capture dissociation (ECD), owing to their applicability towards chromophore-labeled glycans and singly charged ions, and ability to provide more extensive structural information. However, a lack of understanding of these processes has hindered rational optimization of the experimental conditions for more efficient fragmentation as well as the development of informatics tools for interpretation of the complex glycan ExD spectra. Here, cellobiose-Na+ was used as the model system to investigate the fragmentation behavior of metal-adducted glycans under irradiation of electrons with energy exceeding their ionization potential, and served as the basis on which a novel electronic excitation dissociation (EED) mechanism was proposed. It was found that ionization of the glycan produces a mixture of radical cations and ring-opened distonic ions. These distonic ions then capture a low-energy electron to produce diradicals with trivial singlet-triplet splitting, and subsequently undergo radical-induced dissociation to produce a variety of fragment ions, the abundances of which are influenced by the stability of the distonic ions from which they originate.

  6. Cryogenic exciter

    SciTech Connect

    Bray, James William; Garces, Luis Jose

    2012-03-13

    The disclosed technology is a cryogenic static exciter. The cryogenic static exciter is connected to a synchronous electric machine that has a field winding. The synchronous electric machine is cooled via a refrigerator or cryogen like liquid nitrogen. The static exciter is in communication with the field winding and is operating at ambient temperature. The static exciter receives cooling from a refrigerator or cryogen source, which may also service the synchronous machine, to selected areas of the static exciter and the cooling selectively reduces the operating temperature of the selected areas of the static exciter.

  7. Semiactive Control Using MR Dampers of a Frame Structure under Seismic Excitation

    SciTech Connect

    Gattulli, Vincenzo; Lepidi, Marco; Potenza, Francesco; Carneiro, Rubia

    2008-07-08

    The paper approaches the multifaceted task of semiactively controlling the seismic response of a prototypal building model, through interstorey bracings embedding magnetorheological dampers. The control strategy is based on a synthetic discrete model, purposely formulated in a reduced space of significant dynamic variables, and consistently updated to match the modal properties identified from the experimental response of the modeled physical structure. The occurrence of a known eccentricity in the mass distribution, breaking the structural symmetry, is also considered. The dissipative action of two magnetorheological dampers is governed by a clipped-optimal control strategy. The dampers are positioned in order to deliver two eccentric and independent forces, acting on the first-storey displacements. This set-up allows the mitigation of the three-dimensional motion arising when monodirectional ground motion is imposed on the non-symmetric structure. Numerical investigations on the model response to natural accelerograms are presented. The effectiveness of the control strategy is discussed through synthetic performance indexes.

  8. Proteopedia: Exciting Advances in the 3D Encyclopedia of Biomolecular Structure

    NASA Astrophysics Data System (ADS)

    Prilusky, Jaime; Hodis, Eran; Sussman, Joel L.

    Proteopedia is a collaborative, 3D web-encyclopedia of protein, nucleic acid and other structures. Proteopedia ( http://www.proteopedia.org ) presents 3D biomolecule structures in a broadly accessible manner to a diverse scientific audience through easy-to-use molecular visualization tools integrated into a wiki environment that anyone with a user account can edit. We describe recent advances in the web resource in the areas of content and software. In terms of content, we describe a large growth in user-added content as well as improvements in automatically-generated content for all PDB entry pages in the resource. In terms of software, we describe new features ranging from the capability to create pages hidden from public view to the capability to export pages for offline viewing. New software features also include an improved file-handling system and availability of biological assemblies of protein structures alongside their asymmetric units.

  9. Active control synthesis for flexible space structures excited by persistent disturbances

    NASA Technical Reports Server (NTRS)

    Wie, Bong; Gonzalez, Marcelo

    1990-01-01

    Both classical and state-space synthesis methods for active control of flexible space structures in the presence of persistent disturbances are presented. The methods exploit the so-called internal model principle for asymptotic disturbance rejection. A generic example of flexible space structures is used to illustrate the simplicity of the proposed design methodologies. The concept of a disturbance rejection filter dipole is introduced from a classical control viewpoint. It is shown that the proposed design methods will invariably make use of non-minimum-phase compensation for a class of noncolocated control problems. The need for tradeoffs between performance and parameter robustness is discussed.

  10. Biochemical studies of the excitable membrane of paramecium tetraurelia. IX. Antibodies against ciliary membrane proteins

    PubMed Central

    1983-01-01

    The excitable ciliary membrane of Paramecium regulates the direction of the ciliary beat, and thereby the swimming behavior of this organism. One approach to the problem of identifying the molecular components of the excitable membrane is to use antibodies as probes of function. We produced rabbit antisera against isolated ciliary membranes and against partially purified immobilization antigens derived from three serotypes (A, B, and H), and used these antisera as reagents to explore the role of specific membrane proteins in the immobilization reaction and in behavior. The immobilization characteristics and serotype cross- reactivities of the antisera were examined. We identified the antigens recognized by these sera using immunodiffusion and immunoprecipitation with 35S-labeled ciliary membranes. The major antigen recognized in homologous combinations of antigen-antiserum is the immobilization antigen (i-antigen), approximately 250,000 mol wt. Several secondary antigens, including a family of polypeptides of 42,000-45,000 mol wt, are common to the membranes of serotypes A, B, and H, and antibodies against these secondary antigens can apparently immobilize cells. This characterization of antiserum specificity has provided the basis for our studies on the effects of the antibodies on electrophysiological properties of cells and electron microscopic localization studies, which are reported in the accompanying paper. We have also used these antibodies to study the mechanism of cell immobilization by antibodies against the i-antigen. Monovalent fragments (Fab) against purified i- antigens bound to, but did not immobilize, living cells. Subsequent addition of goat anti-Fab antibodies caused immediate immobilization, presumably by cross-linking Fab fragments already bound to the surface. We conclude that antigen-antibody interaction per se is not sufficient for immobilization, and that antibody bivalency, which allows antigen cross-linking, is essential. PMID:6415066

  11. Three-dimensional structure and multistable optical switching of triple-twisted particle-like excitations in anisotropic fluids

    NASA Astrophysics Data System (ADS)

    Smalyukh, Ivan I.; Lansac, Yves; Clark, Noel A.; Trivedi, Rahul P.

    2010-02-01

    Control of structures in soft materials with long-range order forms the basis for applications such as displays, liquid-crystal biosensors, tunable lenses, distributed feedback lasers, muscle-like actuators and beam-steering devices. Bistable, tristable and multistable switching of well-defined structures of molecular alignment is of special interest for all of these applications. Here we describe the facile optical creation and multistable switching of localized configurations in the molecular orientation field of a chiral nematic anisotropic fluid. These localized chiro-elastic particle-like excitations-dubbed `triple-twist torons'-are generated by vortex laser beams and embed the localized three-dimensional (3D) twist into a uniform background. Confocal polarizing microscopy and computer simulations reveal their equilibrium internal structures, manifesting both skyrmion-like and Hopf fibration features. Robust generation of torons at predetermined locations combined with both optical and electrical reversible switching can lead to new ways of multistable structuring of complex photonic architectures in soft materials.

  12. Damage detection on framed structures: modal curvature evaluation using Stockwell Transform under seismic excitation

    NASA Astrophysics Data System (ADS)

    Ditommaso, Rocco; Ponzo, F. C.; Auletta, G.

    2015-06-01

    The key parameters for damage detection and localization are eigenfrequencies, related equivalent viscous damping factors and mode shapes. The classical approach is based on the evaluation of these structural parameters before and after a seismic event, but by using a modern approach based on time-frequency transformations it is possible to quantify these parameters throughout the ground shaking phase. In particular with the use of the S-Transform, it is possible to follow the temporal evolution of the structural dynamics parameters before, during and after an earthquake. In this paper, a methodology for damage localization on framed structures subjected to strong motion earthquakes is proposed based on monitoring the modal curvature variation in the natural frequency of a structure. Two examples of application are described to illustrate the technique: Computer simulation of the nonlinear response of a model, and several laboratory (shaking table) tests performed at the University of Basilicata (Italy). Damage detected using the proposed approach and damage revealed via visual inspections in the tests are compared.

  13. Theoretical Study on Vibronic Interactions and Photophysics of Low-Lying Excited Electronic States of Polycyclic Aromatic Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Samala, Nagaprasad Reddy; Mahapatra, S.

    2014-06-01

    Polycyclic aromatic hydrocarbons (PAHs), in particular, their radical cation (PAH^+), have long been postulated to be the important molecular species in connection with the spectroscopic observations in the interstellar medium. Motivated by numerous important observations by stellar as well as laboratory spectroscopists, we undertook detailed quantum mechanical studies of the structure and dynamics of electronically excited PAH^+ in an attempt to establish possible synergism with the recorded data In this study, we focus on the quantum chemistry and dynamics of the doublet ground (X) and low-lying excited (A, B and C) electronic states of the radical cation of tetracene (Tn), pentacene (Pn), and hexacene (Hn) molecule. This study is aimed to unravel photostability, spectroscopy, and time-dependent dynamics of their excited electronic states. In order to proceed with the theoretical investigations, we construct suitable multistate and multimode Hamiltonian for these systems with the aid of extensive ab initio calculations of their electronic energy surfaces. The diabatic coupling surfaces are derived from the calculated adiabatic electronic energies. First principles nuclear dynamics calculations are then carried out employing the constructed Hamiltonians and with the aid of time-independent and time-dependent quantum mechanical methods. We compared our theoretical results with available photoelectron spectroscopy, zero kinetic energy photoelectron (ZEKE) spectroscopy and matrix isolation spectroscopy (MIS) results. A peak at 8650 Å in the B state spectrum of Tn^+ is in good agreement with the DIB at 8648 Å observed by Salama et al. Similarly in Pn^+, a peak at 8350 Å can be correlated to the DIB at 8321 Å observed by Salama et al. J. Zhang et al., J. Chem. Phys., 128,104301 (2008).; F. Salama, Origins of Life Evol. Biosphere, 28, 349 (1998).; F. Salama et al., Planet. Space Sci., 43, 1165 (1995).; F. Salama et al., Astrophys. J., 526, 265 (1999).; J

  14. Study on antilock brake system with elastic membrane vibration generated by controlled solenoid excitation

    NASA Astrophysics Data System (ADS)

    Wibowo, Zakaria, Lambang, Lullus; Triyono, Muhayat, Nurul

    2016-03-01

    The most effective chassis control system for improving vehicle safety during severe braking is anti-lock braking system (ABS). Antilock effect can be gained by vibrate the pad brake at 7 to 20 cycle per second. The aim of this study is to design a new method of antilock braking system with membrane elastic vibrated by solenoid. The influence of the pressure fluctuations of brake fluid is investigated. Vibration data is collected using a small portable accelerometer-slam stick. The experiment results that the vibration of brake pad caused by controlled solenoid excitation at 10 Hz is obtained by our new method. The result of measurements can be altered by varying brake fluid pressure.

  15. Human Ecstasy Use is Associated with Increased Cortical Excitability: An fMRI Study

    PubMed Central

    Bauernfeind, Amy L; Dietrich, Mary S; Blackford, Jennifer U; Charboneau, Evonne J; Lillevig, James G; Cannistraci, Christopher J; Woodward, Neil D; Cao, Aize; Watkins, Tristan; Di Iorio, Christina R; Cascio, Carissa; Salomon, Ronald M; Cowan, Ronald L

    2011-01-01

    The serotonergic neurotoxin, 3,4-methylenedioxymethamphetamine (MDMA/Ecstasy), is a highly popular recreational drug. Human recreational MDMA users have neurocognitive and neuropsychiatric impairments, and human neuroimaging data are consistent with animal reports of serotonin neurotoxicity. However, functional neuroimaging studies have not found consistent effects of MDMA on brain neurophysiology in human users. Several lines of evidence suggest that studying MDMA effects in visual system might reveal the general cortical and subcortical neurophysiological consequences of MDMA use. We used 3 T functional magnetic resonance imaging during visual stimulation to compare visual system lateral geniculate nucleus (LGN) and Brodmann Area (BA) 17 and BA 18 activation in 20 long abstinent (479.95±580.65 days) MDMA users and 20 non-MDMA user controls. Lifetime quantity of MDMA use was strongly positively correlated with blood oxygenation level-dependent (BOLD) signal intensity in bilateral LGN (rs=0.59; p=0.007), BA 17 (rs=0.50; p=0.027), and BA 18 (rs=0.48; p=0.031), and with the spatial extent of activation in BA 17 (rs=0.059; p=0.007) and BA 18 (rs=0.55; p=0.013). There were no between-group differences in brain activation in any region, but the heaviest MDMA users showed a significantly greater spatial extent of activation than controls in BA 17 (p=0.031) and BA 18 (p=0.049). These results suggest that human recreational MDMA use may be associated with a long-lasting increase in cortical excitability, possibly through loss of serotonin input to cortical and subcortical regions. When considered in the context of previous results, cortical hyper-excitability may be a biomarker for MDMA-induced serotonin neurotoxicity. PMID:21326196

  16. Excited state structural dynamics in higher lying electronic states: S2 state of malachite green

    NASA Astrophysics Data System (ADS)

    Laptenok, Sergey P.; Addison, Kiri; Heisler, Ismael A.; Meech, Stephen R.

    2014-06-01

    The S2 fluorescence of malachite green is measured with sub 100 fs time resolution. Ultrafast spectral dynamics in the S2 state preceding S2 decay are resolved. Measurements in different solvents show that these sub 100 fs dynamics are insensitive to medium polarity and viscosity. They are thus assigned to ultrafast structural evolution between the S2 Franck-Condon and equilibrium configurations.

  17. THE PHOTOTOXOICITY OF POLYCYCLIC AROMATIC HYDROCARBONS: A THEORETICAL STUDY OF EXCITED STATES AND CORRELATION TO EXPERIMENT

    EPA Science Inventory



    Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHS) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calcu...

  18. Studies of magnetopause structure

    NASA Technical Reports Server (NTRS)

    Speiser, Theodore W.

    1991-01-01

    From the International Sun-Earth Explorers (ISEE) 1 magnetopause crossings on November 10, 1977, three-dimensional distribution functions for energetic ions were studied in the magnetosphere, through the magnetopause, and in the magnetosheath (Speiser and Williams, 1982). The particle distributions were particularly examined at and near the times that Russell and Elphic (1978) identified as flux transfer events (FTE). Using a simple, one-dimensional, quasi-static model, particle orbits were followed numerically, from the magnetosphere into the sheath. The inner, trapped, distribution initializes the distribution function. Liouville's theorem allows the inner distribution to be mapped into the sheath following the orbits. This mapping is shown for four mangetosheath ion flows (MIF's) corresponding to four flux transfer events. Results from the studies are discussed. A brief discussion of current sheet particle motion is presented.

  19. Experimental and Quantum-Chemical Study of Electronically Excited States of Protolytic Isovanillin Species

    NASA Astrophysics Data System (ADS)

    Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Yu.

    2014-05-01

    Methods of electronic spectroscopy and quantum chemistry are used to compare protolytic vanillin and isovanillin species. Three protolytic species: anion, cation, and neutral are distinguished in the ground state of the examined molecules. Vanillin and isovanillin in the ground state in water possess identical spectral characteristics: line positions and intensities in the absorption spectra coincide. Minima of the electrostatic potential demonstrate that the deepest isomer minimum is observed on the carbonyl oxygen atom. However, investigations of the fluorescence spectra show that the radiative properties of isomers differ. An analysis of results of quantum-chemical calculations demonstrate that the long-wavelength ππ* transition in the vanillin absorption spectra is formed due to electron charge transfer from the phenol part of the molecule to oxygen atoms of the methoxy and carbonyl groups, and in the isovanillin absorption spectra, it is formed only on the oxygen atom of the methoxy group. The presence of hydroxyl and carbonyl groups in the structure of the examined molecules leads to the fact that isovanillin in the ground S0 state, the same as vanillin, possesses acidic properties, whereas in the excited S1 state, they possess basic properties. A comparison of the рKа values of aqueous solutions demonstrates that vanillin possesses stronger acidic and basic properties in comparison with isovanillin.

  20. Study on discrimination of oral cancer from normal using blood plasma based on fluorescence steady and excited state at excitation wavelength 280 nm

    NASA Astrophysics Data System (ADS)

    Rekha, Pachaiappan; Aruna, Prakasa Rao; Ganesan, Singaravelu

    2016-03-01

    Many research works based on fluorescence spectroscopy have proven its potential in the diagnosis of various diseases using the spectral signatures of the native key fluorophores such as tryptophan, tyrosine, collagen, NADH, FAD and porphyrin. These fluorophores distribution, concentration and their conformation may be changed depending upon the pathological and metabolic conditions of cells and tissues. In this study, we have made an attempt to characterize the blood plasma of normal subject and oral cancer patients by native fluorescence spectroscopy at 280 nm excitation. Further, the fluorescence data were analyzed by employing the multivariate statistical method - linear discriminant analyses (LDA) using leaves one out cross validation method. The results illustrate the potential of fluorescence spectroscopy technique in the diagnosis of oral cancer using blood plasma.

  1. Time-dependent density functional theory study on the electronic excited-state hydrogen bonding of the chromophore coumarin 153 in a room-temperature ionic liquid.

    PubMed

    Wang, Dandan; Hao, Ce; Wang, Se; Dong, Hong; Qiu, Jieshan

    2012-03-01

    In the present work, in order to investigate the electronic excited-state intermolecular hydrogen bonding between the chromophore coumarin 153 (C153) and the room-temperature ionic liquid N,N-dimethylethanolammonium formate (DAF), both the geometric structures and the infrared spectra of the hydrogen-bonded complex C153-DAF(+) in the excited state were studied by a time-dependent density functional theory (TDDFT) method. We theoretically demonstrated that the intermolecular hydrogen bond C(1) = O(1)···H(1)-O(3) in the hydrogen-bonded C153-DAF(+) complex is significantly strengthened in the S(1) state by monitoring the spectral shifts of the C=O group and O-H group involved in the hydrogen bond C(1) = O(1)···H(1)-O(3). Moreover, the length of the hydrogen bond C(1) = O(1)···H(1)-O(3) between the oxygen atom and hydrogen atom decreased from 1.693 Å to 1.633 Å upon photoexcitation. This was also confirmed by the increase in the hydrogen-bond binding energy from 69.92 kJ mol(-1) in the ground state to 90.17 kJ mol(-1) in the excited state. Thus, the excited-state hydrogen-bond strengthening of the coumarin chromophore in an ionic liquid has been demonstrated theoretically for the first time.

  2. Estimating the probability distribution of von Mises stress for structures undergoing random excitation. Part 1: Derivation

    SciTech Connect

    Segalman, D.; Reese, G.

    1998-09-01

    The von Mises stress is often used as the metric for evaluating design margins, particularly for structures made of ductile materials. For deterministic loads, both static and dynamic, the calculation of von Mises stress is straightforward, as is the resulting calculation of reliability. For loads modeled as random processes, the task is different; the response to such loads is itself a random process and its properties must be determined in terms of those of both the loads and the system. This has been done in the past by Monte Carlo sampling of numerical realizations that reproduce the second order statistics of the problem. Here, the authors present a method that provides analytic expressions for the probability distributions of von Mises stress which can be evaluated efficiently and with good precision numerically. Further, this new approach has the important advantage of providing the asymptotic properties of the probability distribution.

  3. Proof of shock-excited H2 in low-ionization structure of PNe

    NASA Astrophysics Data System (ADS)

    Akras, Stavros; Gonçalves, Denise R.; Ramos-Larios, Gerardo

    2016-07-01

    We report the detection of near-IR H2 line emission from the low-ionization structures (LISs) in planetary nebulae. The deepest, high-angular resolution H2 1-0 S(1) at 2.122 μm, and H2 2-1 S(1) at 2.248 μm images of K 4-47 and NGC 7662, obtained using NIRI@Gemini-North, are presented here. K 4-47 reveals a remarkable high-collimated bipolar structure, with the H2 emission emanating from the walls of the outflows and a pair of knots at the tips of these outflows. The H2 1-0 S(1)/2-1 S(1) line ratio is ∼⃒7-8 which indicates shock interaction due to both the lateral expansion of the gas and the high-velocity knots. The strongest line, H2 v=1-0 S(1), is also detected in several LISs located at the periphery of the outer shell of the elliptical PN NGC 7662, whereas only four knots are detected in the H2 v = 2-1 S(1) line. These knots have H2 v = 1-0 S(1)/v = 2-1 S(1) values between 3 and 5. These data confirm the presence of molecular gas in both highly (K 4-47) and slowly moving LISs (NGC 7662). The H2 emission in K 4-47 is powered by shocks, whereas in NGC 7662 is due to photo-ionization by the central star. Moreover, a likely correlation is found between the H2 v = 1-0 S(1)/H2 v = 2-1 S(1) and [N II]/Hα line ratios.

  4. Structure of electron tracks in water. 2. Distribution of primary ionizations and excitations in water radiolysis. [accelerated electrons

    SciTech Connect

    Pimblott, S.M.; Mozumder, A. )

    1991-09-19

    A procedure for the calculation of entity-specific ionization and excitation probabilities for water radiolysis at low linear energy transfer (LET) has been developed. The technique pays due attention to the effects of the ionization threshold and the energy dependence of the ionization efficiency. The numbers of primary ionizations and excitations are not directly proportional to the spur energy. At a given spur energy, ionization follows a binomial distribution subject to an energetically possible maximum. The excitation distribution for a spur of given energy and with a given number of ionizations is given by a geometric series. The occurrence probabilities depend upon the cross sections of ionization, excitation, and other inferior processes. Following the low-LET radiolysis of liquid water the most probable spurs contain one ionization, two ionizations, or one ionization and one excitation, while in water vapor they contain either one ionization or one excitation. In liquid water the most probable outcomes for spurs corresponding to the most probable energy loss (22 eV) and to the mean energy loss (38 eV) are one ionization and one excitation, and two ionizations and one excitation, respectively. In the vapor, the most probable energy loss is 14 eV which results in one ionization or one excitation and the mean energy loss is 34 eV for which the spur of maximum probability contains one ionization and two excitations. The total calculated primary yields for low-LET radiolysis are in approximate agreement with experiment in both phases.

  5. Ultrafast spectroscopy of electron transfer dynamics in liquids; excitation transfer studies of phase transitions

    NASA Astrophysics Data System (ADS)

    Goun, Alexei A.

    tetradecyltrimethylammonium bromide (TTAB). It was found that the effective coupling is reduced compared to donor/acceptor pairs dissolved in simple liquids. In the 2nd half of thesis we have addressed the question of the dynamics of phase transitions. We have demonstrated the ability to use the fluorescent excitation-transfer technique to study the demixing of liquids specifically, kinetics of demixing water and 2,6-dimethylpyridine. These two liquids possess a low critical temperature point, which allowed us to use a temperature jump from a laser pulse to initiate the process of phase separation. It was found that Coumarin480 laser dye and HPTS (8-Hydroxypyrene-1,3,6-trisulfonic acid) fluorescent dye have significantly different solubilities in the components of the mixture. These dyes undergo excitation transfer from Coumarin480 to HPTS in the uniform state, but not in the phase-separated state. A system with a temperature jump pump and an excitation transfer probe measured the time scale of the initial step of the phase separation.

  6. The discrepant kinematics of recombination and collisionally excited lines in NGC 7009 as a function of ionization structure

    NASA Astrophysics Data System (ADS)

    Torres-Peimbert, S.; Richer, M. R.; Georgiev, L.; Arrieta, A.

    2014-10-01

    We have analyzed the kinematics of emission of the planetary nebula NGC 7009 from long slit spectroscopy from the UVES spectrograph at the VLT of ESO. In particular we are interested in comparing lines excited by recombination and collisions with electrons to determine whether similarities or differences could be useful in elucidating the well-known abundance discrepancy derived from them. We construct position-velocity maps for recombination, fluorescence, charge transfer, and collisionally excited lines.We find a plasma component emitting in the C II, N II, O II, and Ne II recombination lines whose kinematics are discrepant: they are incompatible with the ionization structure derived from all other evidence and the kinematics derived from all of these lines are unexpectedly very similar. We found direct evidence for a recombination contribution to [N II] λ5755. Once taken into account, the electron temperatures from [N II], [O III], and [Ne III] agree at a given position and velocity. The electron densities derived from [O II] and [Ar IV] are consistent with direct imaging and the distribution of hydrogen emission. The kinematics of the C II, N II, O II, and Ne II lines does not coincide with the kinematics of the [O III] and [Ne III] forbidden emission, indicating that there is an additional plasma component to the recombination emission that arises from a different volume from that giving rise to the forbidden emission from the parent ions within NGC 7009. Thus, the chemical abundances derived from either type of line are correct only for the plasma component from which they arise. Apart from [N II] λ5755, we find no anomaly with the forbidden lines usually used to determine chemical abundances in ionized nebulae, so the abundances derived from them should be reliable for the medium from which they arise.

  7. Studies of Photo-Excited and Trapped Electrons in Cubic BISMUTH(12) Silicon OXYGEN(20)

    NASA Astrophysics Data System (ADS)

    Nouchi, Pascale

    We present experimental and theoretical studies of charge transport processes in cubic n-type Bi _{12}SiO_{20 } (n-BSO). We first study the room-temperature photocurrent response to short-pulse illumination in two n-BSO samples called CT1 and SU1 in previous publications. These experiments suggest that drifting electrons spend much time in shallow traps. They allow us to estimate the corresponding trap-limited mobility and to measure the electron lifetime in the conduction band and the dwell time in shallow traps. In sample CT1, we also study the transient photocurrent behavior below room temperature: we find that the charge transport is limited by two sets of shallow traps with energy depths equal to 410 +/- 50 meV and 650 +/- 80 meV. In sample SU1, we directly measure the trap-limited mobility and find it is equal to 0.24 +/- 0.07 cm^2V ^{-1}s^ {-1} at room temperature. We then describe what we believe to be the first measurement of the pure conduction band mobility in n-BSO which we find to be 4.4 +/- 1.3 cm^2V ^{-1}s^ {-1} in SU1. We describe the novel holographic "time-of-flight" technique we developed for this measurement in which we observe the average time for a photoexcited charge carrier to drift in the dark (because of a strong applied electric field) over the period of a grating of charged traps created in the crystal by two interfering short laser pulses. We also use this technique to study the temperature dependence of the mobility. These results suggest the existence of shallow traps of energy depth equal to 320 +/- 40 meV. We also derive an analytical solution to the standard material equations which describes the build-up of the photorefractive grating in the dark after an initial low-energy, spatially -sinusoidal, short-pulse excitation. It is the first short -pulse solution to be developed in a band transport model containing both deep photoexcitable traps and shallow thermally excitable traps. The build-up of the space-charge field includes two

  8. Note: Excited State Studies of Ozone using State-Specific Multireference Coupled Cluster Methods

    SciTech Connect

    Bhaskaran-Nair, Kiran; Kowalski, Karol

    2012-12-07

    Vertical excitation energies obtained with state-specific multi-reference coupled cluster (MRCC) methods are reported for the ozone molecule. Using state-specific MRCC non-iterative methods with singles, doubles, and non-iterative triples (MRCCSD(T)) we obtain 4.40 eV for the challenging doubly excited 21A1 state when using a reliable model space. This estimate is in good agreement with experiment (4.5 eV). We also compare our MRCC results with the excitation energies obtained with high-order equation-of-motion coupled cluster methods

  9. Hyperfine structure in 229gTh3+ as a probe of the 229gTh→ 229mTh nuclear excitation energy.

    PubMed

    Beloy, K

    2014-02-14

    We identify a potential means to extract the 229gTh→ 229mTh nuclear excitation energy from precision microwave spectroscopy of the 5F(5/2,7/2) hyperfine manifolds in the ion 229gTh3+. The hyperfine interaction mixes this ground fine structure doublet with states of the nuclear isomer, introducing small but observable shifts to the hyperfine sublevels. We demonstrate how accurate atomic structure calculations may be combined with the measurement of the hyperfine intervals to quantify the effects of this mixing. Further knowledge of the magnetic dipole decay rate of the isomer, as recently reported, allows an indirect determination of the nuclear excitation energy.

  10. Multiconfiguration Dirac-Hartree-Fock calculations of excitation energies, oscillator strengths, and hyperfine structure constants for low-lying levels of Sm I

    NASA Astrophysics Data System (ADS)

    Zhou, Fuyang; Qu, Yizhi; Li, Jiguang; Wang, Jianguo

    2015-11-01

    The multiconfiguration Dirac-Hartree-Fock method was employed to calculate the total and excitation energies, oscillator strengths, and hyperfine structure constants for low-lying levels of Sm i. In the first-order perturbation approximation, we systematically analyzed correlation effects from individual electrons and electron pairs. It was found that the core correlations are of importance for the physical quantities concerned. Based on the analysis, the important configuration state wave functions were selected to constitute atomic state wave functions. By using this computational model, our excitation energies, oscillator strengths, and hyperfine structure constants are in better agreement with experimental values than earlier theoretical works.

  11. Excited state structural evolution during charge-transfer reactions in betaine-30.

    PubMed

    Ruchira Silva, W; Frontiera, Renee R

    2016-07-27

    Ultrafast photo-induced charge-transfer reactions are fundamental to a number of photovoltaic and photocatalytic devices, yet the multidimensional nature of the reaction coordinate makes these processes difficult to model theoretically. Here we use femtosecond stimulated Raman spectroscopy to probe experimentally the structural changes occurring following photoexcitation in betaine-30, a canonical intramolecular charge-transfer complex. We observe changes in vibrational mode frequencies and amplitudes on the femtosecond timescale, which for some modes results in frequency shifts of over 20 cm(-1) during the first 200 fs following photoexcitation. These rapid mode-specific frequency changes track the planarization of the molecule on the 400 ± 100 fs timescale. Oscillatory amplitude modulations of the observed high frequency Raman modes indicate coupling between specific high frequency and low frequency vibrational motions, which we quantify for 6 low frequency modes and 4 high frequency modes. Analysis of the mode-specific kinetics is suggestive of the existence of a newly discovered electronic state involved in a relaxation pathway, which may be a low-lying triplet state. These results directly track the multiple nuclear coordinates involved in betaine-30's reactive pathway, and should be of use in rationally designing molecular systems with rapid electron transfer processes. PMID:26725657

  12. Sound Transmission through Cylindrical Shell Structures Excited by Boundary Layer Pressure Fluctuations

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    This paper examines sound transmission into two concentric cylindrical sandwich shells subject to turbulent flow on the exterior surface of the outer shell. The interior of the shells is filled with fluid medium and there is an airgap between the shells in the annular space. The description of the pressure field is based on the cross-spectral density formulation of Corcos, Maestrello, and Efimtsov models of the turbulent boundary layer. The classical thin shell theory and the first-order shear deformation theory are applied for the inner and outer shells, respectively. Modal expansion and the Galerkin approach are used to obtain closed-form solutions for the shell displacements and the radiation and transmission pressures in the cavities including both the annular space and the interior. The average spectral density of the structural responses and the transmitted interior pressures are expressed explicitly in terms of the summation of the cross-spectral density of generalized force induced by the boundary layer turbulence. The effects of acoustic and hydrodynamic coincidences on the spectral density are observed. Numerical examples are presented to illustrate the method for both subsonic and supersonic flows.

  13. Excitation energy transfer in natural photosynthetic complexes and chlorophyll trefoils: hole-burning and single complex/trefoil spectroscopic studies

    SciTech Connect

    Ryszard Jankowiak, Kansas State University, Department of Chemistry, CBC Bldg., Manhattan KS, 66505; Phone: 532-6785

    2012-09-12

    In this project we studied both natural photosynthetic antenna complexes and various artificial systems (e.g. chlorophyll (Chl) trefoils) using high resolution hole-burning (HB) spectroscopy and excitonic calculations. Results obtained provided more insight into the electronic (excitonic) structure, inhomogeneity, electron-phonon coupling strength, vibrational frequencies, and excitation energy (or electron) transfer (EET) processes in several antennas and reaction centers. For example, our recent work provided important constraints and parameters for more advanced excitonic calculations of CP43, CP47, and PSII core complexes. Improved theoretical description of HB spectra for various model systems offers new insight into the excitonic structure and composition of low-energy absorption traps in very several antenna protein complexes and reaction centers. We anticipate that better understanding of HB spectra obtained for various photosynthetic complexes and their simultaneous fits with other optical spectra (i.e. absorption, emission, and circular dichroism spectra) provides more insight into the underlying electronic structures of these important biological systems. Our recent progress provides a necessary framework for probing the electronic structure of these systems via Hole Burning Spectroscopy. For example, we have shown that the theoretical description of non-resonant holes is more restrictive (in terms of possible site energies) than those of absorption and emission spectra. We have demonstrated that simultaneous description of linear optical spectra along with HB spectra provides more realistic site energies. We have also developed new algorithms to describe both nonresonant and resonant hole-burn spectra using more advanced Redfield theory. Simultaneous description of various optical spectra for complex biological system, e.g. artificial antenna systems, FMO protein complexes, water soluble protein complexes, and various mutants of reaction centers

  14. Sexual excitement.

    PubMed

    Stoller, R J

    1976-08-01

    Sexual excitement depends on a scenario the person to be aroused has been writing since childhood. The story is an adventure, an autobiography disguised as fiction, in which the hero/heroine hides crucial intrapsychic conflicts, mysteries, screen memories of actual traumatic events and the resolution of these elements into a happy ending, best celebrated by orgasm. The function of the fantasy is to take these painful experiences and convert them to pleasure-triumph. In order to sharpen excitement-the vibration between the fear of original traumas repeating and the hope of a pleasurable conclusion this time-one introduces into the story elements of risk (approximations of the trauma) meant to prevent boredom and safety factors (sub-limnal signals to the storyteller that the risk are not truly dangerous). Sexual fantasy can be studied by means of a person's daydreams (including those chosen in magazines, books, plays, television, movies, and outright pornography), masturbatory behavior, object choice, foreplay, techniques of intercourse, or postcoital behavior. PMID:949223

  15. Sexual excitement.

    PubMed

    Stoller, R J

    1976-08-01

    Sexual excitement depends on a scenario the person to be aroused has been writing since childhood. The story is an adventure, an autobiography disguised as fiction, in which the hero/heroine hides crucial intrapsychic conflicts, mysteries, screen memories of actual traumatic events and the resolution of these elements into a happy ending, best celebrated by orgasm. The function of the fantasy is to take these painful experiences and convert them to pleasure-triumph. In order to sharpen excitement-the vibration between the fear of original traumas repeating and the hope of a pleasurable conclusion this time-one introduces into the story elements of risk (approximations of the trauma) meant to prevent boredom and safety factors (sub-limnal signals to the storyteller that the risk are not truly dangerous). Sexual fantasy can be studied by means of a person's daydreams (including those chosen in magazines, books, plays, television, movies, and outright pornography), masturbatory behavior, object choice, foreplay, techniques of intercourse, or postcoital behavior.

  16. First-Principles Studies of the Excited States of Chromophore Monomers and Dimers

    NASA Astrophysics Data System (ADS)

    Hamed, Samia; Sharifzadeh, Sahar; Neaton, Jeffrey

    2015-03-01

    Elucidation of the energy transfer mechanism in natural photosynthetic systems remains an exciting challenge. Through the careful analysis of excited states on individual chromophores and dimers - and the predictive first-principles methods used to compute them - we are building towards an understanding of the nature of excitation transfer among arrays of chromophores embedded in protein environments. Excitation energies, transition dipoles, and natural transition orbitals for the important low-lying singlet and triplet states of experimentally-relevant chromophores are obtained from first-principles time-dependent density functional theory (TDDFT) and many body perturbation theory. The effect of the Tamm-Dancoff approximation and the performance of several exchange-correlation functionals, including an optimally-tuned range-separated hybrid, are evaluated with TDDFT, and compared to MBPT calculations and experiments. This work has been supported by the DOE; computational resources have been provided by NERSC.

  17. Study of ultra-high gradient wakefield excitation by intense ultrashort laser pulses in plasma

    NASA Astrophysics Data System (ADS)

    Kotaki, Hideyuki; Kando, Masaki; Oketa, Takatsugu; Masuda, Shinichi; Koga, James K.; Kondo, Shuji; Kanazawa, Shuhei; Yokoyama, Takashi; Matoba, Toru; Nakajima, Kazuhisa

    2002-10-01

    We investigate a laser wakefield excited by intense laser pulses, and the possibility of generating an intense bright electron source by an intense laser pulse. The coherent wakefield excited by 2 TW, 50 fs laser pulses in a gas-jet plasma around 1018 cm-3 is measured with a time-resolved frequency domain interferometer (FDI). The results show an accelerating wakefield excitation of 20 GeV/m with good coherency. This is the first time-resolved measurement of laser wakefield excitation in a gas-jet plasma. The experimental results agree with the simulation results and linear theory. The pump-probe interferometer system of FDI will be modified to the optical injection system as a relativistic electron beam injector. In 1D particle in cell simulation we obtain results of high quality intense electron beam generation.

  18. The phototoxicity of polycyclic aromatic hydrocarbons: a theoretical study of excited states and correlation to experiment.

    PubMed

    Betowski, Leon D; Enlow, Mark; Riddick, Lee

    2002-06-01

    Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHs) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calculated for ten PAHs by several ab initio methods. The main method used for these calculations was the Configuration Interaction approach, modeling excited states as combinations of single substitutions out of the Hartree-Fock ground state. These calculations correlate well with both experimentally measured singlet and triplet state energies and also previous HOMO-LUMO gap energies that approximate the singlet state energies. The excited state calculations then correlate well with general models of photo-induced toxicity based for the PAHs.

  19. Spectroscopic manifestations of local crystal distortions in excited 4f states in crystals of huntite structure

    SciTech Connect

    Malakhovskii, A. V.; Gnatchenko, S. L.; Kachur, I. S.; Piryatinskaya, V. G.; Sukhachev, A. L.; Sokolov, A. E.; Strokova, A. Ya.; Kartashev, A. V.; Temerov, V. L.

    2013-01-15

    Optical absorption spectra of YbAl{sub 3}(BO{sub 3}){sub 4}, TmAl{sub 3}(BO{sub 3}){sub 4} and TbFe{sub 3}(BO{sub 3}){sub 4} trigonal crystals have been studied in temperature range 2-300 K. Temperature behavior of absorption lines parameters has shown, that during some f-f transitions the local environment of rare earth ions undergo distortions, which are absent in the ground state.

  20. Low-lying dipole excitations in vibrational nuclei: The Cd isotopic chain studied in photon scattering experiments

    NASA Astrophysics Data System (ADS)

    Kohstall, C.; Belic, D.; von Brentano, P.; Fransen, C.; Gade, A.; Herzberg, R.-D.; Jolie, J.; Kneissl, U.; Linnemann, A.; Nord, A.; Pietralla, N.; Pitz, H. H.; Scheck, M.; Stedile, F.; Werner, V.; Yates, S. W.

    2005-09-01

    High-resolution nuclear resonance fluorescence experiments (NRF) were performed on 110,111,112,114,116Cd at the bremsstrahlung facility of the 4.3-MV Dynamitron accelerator in Stuttgart to study the low-lying dipole strength distributions in these vibrational nuclei. Numerous excited states, most of them previously unknown, were observed in the excitation energy range up to 4 MeV. Detailed spectroscopic information has been obtained on excitation energies, spins, decay widths, decay branchings, and transition probabilities. For states in the even-even isotopes 110,112,114,116Cd, parities could be assigned from linear polarization measurements. Together with our previous results for 108,112,113,114Cd from NRF studies without polarization measurements, systematics was established for the dipole strength distributions of the stable nuclei within the Cd isotopic chain. The results are discussed with respect to the systematics of E1 two-phonon excitations and mixed-symmetry states in even-even nuclei near the Z=50 shell closure and the fragmentation of these excitation modes in the odd-mass Cd isotopes.

  1. Study on Thrust Improvement and Ripple Suppression of HTS Linear Switched Reluctance Motor with Coreless HTS Excitation Windings

    NASA Astrophysics Data System (ADS)

    Oto, Satoshi; Hirayama, Tadashi; Kawabata, Shuma

    This paper describes a linear switched reluctance motor (LSRM) in which HTS tapes are used for coreless excitation windings in order to reduce the thrust ripple and normal force. This LSRM consists of a mover with saliency structure, coreless HTS coils and a stator back yoke. In this paper, we first describe the operating principle of the HTS-LSRM. Next, we calculate performances of the HTS-LSRM using 3-D FEM analysis. The effects of the motor structure on the thrust characteristic and normal force characteristics are clarified from the numerical results. Furthermore, we investigate the motor structure for thrust improvement, thrust ripple and normal force reduction.

  2. Experimental study of jittering chimeras in a ring of excitable units

    NASA Astrophysics Data System (ADS)

    Klinshov, Vladimir; Shchapin, Dmitry; Lücken, Leonhard; Yanchuk, Serhiy; Nekorkin, Vladimir

    2016-06-01

    A new type of chimera-like regime is reported that we call "jittering chimera". The regime is observed in a ring of excitable units in which the excitation is invoked by an oscillator included into the ring. The jittering chimera is characterized by the presence of two domains, one with regular spiking and the other with irregular. A method to set and control desired chimera states in a physically implemented electronic circuit is developed.

  3. Study of excitation transfer in laser dye mixtures by direct measurement of fluorescence lifetime

    NASA Technical Reports Server (NTRS)

    Lin, C.; Dienes, A.

    1973-01-01

    By directly measuring the donor fluorescence lifetime as a function of acceptor concentration in the laser dye mixture Rhodamine 6G-Cresyl violet, we found that the Stern-Volmer relation is obeyed, from which the rate of excitation transfer is determined. The experimental results indicate that the dominant mechanism responsible for the efficient excitation transfer is that of resonance transfer due to long range dipole-dipole interaction.

  4. Excited states of154Nd studied through the decay of154Pr

    NASA Astrophysics Data System (ADS)

    Toh, Y.; Okano, K.; Taniguchi, A.; Yamada, S.; Kawase, Y.

    1996-12-01

    The neutron-rich isotope154Pr, the heaviest isotope of praseodymium, has been investigated by γ-ray multispectrum scaling and γ-γ-(t), X-γ-(t) coincidence experiments. The isotope154Pr was separated from235U fission products with the on-line isotope separator KUR-ISOL. The decay scheme of154Pr has been constructed consisting of 9 excited states and 12 transitions in154Nd, including 7 excited states newly found in the present experiment.

  5. 3D-FEM analysis of SPP excitation through nanoholes in asymmetric metal-insulator-metal structure at tip of circular truncated conical fiber

    NASA Astrophysics Data System (ADS)

    Oshikane, Y.; Murai, K.; Nakano, M.

    2014-09-01

    3D-electromagnetic (EM) analysis of surface plasmon polaritons (SPPs) excited by a single-mode (SM) propagation of visible lightwave in an optical fiber has been studied with a 3D-FEM package based on a finite element method. End of the fiber is formed to be a circular cone by wet etching process, and is FIBed to make a circular truncated conical shape with a flat circular surface a few micrometers in diameter. The flat end is covered with three layers of asymmetric metalinsulator- metal structure, thin metallic layer (M1), thick insulator layer (I), and thick metallic layer (M2), respectively. The outermost M2 layer has FIBed nanoholes to convert light waves at the extremity of the fiber into SPPs efficiently, and a bright tiny point light source will be generated on the surface of the M2 layer. In this study, the 3D-FEM models consists of both the MIM structure and the shrinking optical fiber tip coated with a metallic thin film has been designed and analyzed numerically. By applying perfect electric conductor and perfect magnetic conductor to planes containing the axis of rotation, the FEM model has a quarter of the circular truncated conical shape. The FEM analysis is formed in two steps. At the first step, a FEM mode analysis is performed to obtain a solution corresponding to the SM propagation in the fiber. The second level of action is the FEM analysis of EM field in the whole of model to find a stationary solution with the solution of mode analysis. Characteristic of wavelength-dependent excitation, propagation, and focusing of the SPPs will be presented with several experimental results of trial products of the fiber tip.

  6. Dissociation of chloromethanes upon resonant σ{sup *} excitation studied by x-ray scattering

    SciTech Connect

    Bohinc, R.; Bučar, K.; Kavčič, M.; Žitnik, M.; Journel, L.; Guillemin, R.; Marchenko, T.; Simon, M.; Cao, W.

    2013-10-07

    The dissociation process following the Cl K-shell excitation to σ{sup *} resonances is studied by high resolution spectroscopy of resonant elastic and inelastic x-ray scattering on CH{sub 3}Cl, CH{sub 2}Cl{sub 2}, CHCl{sub 3}, and CCl{sub 4} molecules. Calculations employing the transition potential and Delta-Kohn-Sham DFT approach are in good agreement with the measured total fluorescence yield and show the presence of a second quasidegenerate group of states with σ{sup *} character above the lowest σ{sup *} unoccupied molecular orbital for molecules with more than one Cl atom. A bandwidth narrowing and a nonlinear dispersion behavior is extracted from the Kα spectral maps for both σ{sup *} resonances. The fitted data indicate that the widths of the Franck-Condon distributions for the first and second σ{sup *} resonances are comparable for all the molecules under study. In addition, an asymmetric broadening of the emission peaks is observed for resonant elastic x-ray scattering with zero detuning on both σ{sup *} resonances. This is attributed to the fast dissociation, transferring about 0.15 of the scattering probability into higher vibrational modes.

  7. Excitation of ultrasonic Lamb waves using a phased array system with two array probes: phantom and in vitro bone studies.

    PubMed

    Nguyen, Kim-Cuong T; Le, Lawrence H; Tran, Tho N H T; Sacchi, Mauricio D; Lou, Edmond H M

    2014-07-01

    Long bones are good waveguides to support the propagation of ultrasonic guided waves. The low-order guided waves have been consistently observed in quantitative ultrasound bone studies. Selective excitation of these low-order guided modes requires oblique incidence of the ultrasound beam using a transducer-wedge system. It is generally assumed that an angle of incidence, θi, generates a specific phase velocity of interest, co, via Snell's law, θi=sin(-1)(vw/co) where vw is the velocity of the coupling medium. In this study, we investigated the excitation of guided waves within a 6.3-mm thick brass plate and a 6.5-mm thick bovine bone plate using an ultrasound phased array system with two 0.75-mm-pitch array probes. Arranging five elements as a group, the first group of a 16-element probe was used as a transmitter and a 64-element probe was a receiver array. The beam was steered for six angles (0°, 20°, 30°, 40°, 50°, and 60°) with a 1.6-MHz source signal. An adjoint Radon transform algorithm mapped the time-offset matrix into the frequency-phase velocity dispersion panels. The imaged Lamb plate modes were identified by the theoretical dispersion curves. The results show that the 0° excitation generated many modes with no modal discrimination and the oblique beam excited a spectrum of phase velocities spread asymmetrically about co. The width of the excitation region decreased as the steering angle increased, rendering modal selectivity at large angles. The phenomena were well predicted by the excitation function of the source influence theory. The low-order modes were better imaged at steering angle ⩾30° for both plates. The study has also demonstrated the feasibility of using the two-probe phased array system for future in vivo study.

  8. Ultrafast Excited-State Dynamics in the Green Fluorescent Protein Variant S65T/H148D 1. Mutagenesis and Structural Studies†

    PubMed Central

    Shu, Xiaokun; Kallio, Karen; Shi, Xinghua; Abbyad, Paul; Kanchanawong, Pakorn; Childs, William; Boxer, Steven G.; Remington, S. James

    2008-01-01

    Wild type green fluorescent protein (wt-GFP) and the variant S65T/H148D each exhibit two absorption bands, A and B, which are associated with the protonated and deprotonated chromophores respectively. Excitation of either band leads to green emission. In wt-GFP, excitation of band A (~390 nm) leads to green emission with a rise time of 10–15 picoseconds, due to excited state proton transfer (ESPT) from the chromophore hydroxyl group to an acceptor. This process produces an anionic excited state intermediate I* that subsequently emits a green photon. In the variant S65T/H148D, the A band absorbance maximum is red-shifted to ~415 nm and as detailed in the accompanying papers (1, 2), when the A band is excited, green fluorescence appears with rise time shorter than the instrument time resolution (~170 fs). Based on steady state spectroscopy and high resolution crystal structures of several variants described herein, we propose that in S65T/H148D, the red shift of absorption band A and the ultrafast appearance of green fluorescence upon excitation of band A is due to a very short (≤ 2.4 Å), and possibly low barrier, hydrogen bond between the chromophore hydroxyl and introduced Asp148. PMID:17918959

  9. Unexpected death related to restraint for excited delirium: a retrospective study of deaths in police custody and in the community

    PubMed Central

    Pollanen, M S; Chiasson, D A; Cairns, J T; Young, J G

    1998-01-01

    BACKGROUND: Some people in states of excited delirium die while in police custody. Emerging evidence suggests that physical restraint in certain positions may contribute to such deaths. In this study the authors determined the frequency of physical restraint among people in a state of excited delirium who died unexpectedly. METHODS: The authors reviewed the records of 21 cases of unexpected death in people with excited delirium, which were investigated by the Office of the Chief Coroner for Ontario between 1988 and 1995. Eyewitness testimony, findings during postmortem examinations, clinical history, toxicological data and other official documents describing the events surrounding the deaths were analyzed. Specific reference was made to documented eyewitness testimony of restraint method, body position and use of capsicum oleoresin (pepper) spray. Because cocaine was detected in the blood of some of these people during the postmortem examination, the role of cocaine in excited delirium was examined by comparing the cocaine levels in these cases with levels in 2 control groups: 19 people who died from acute cocaine intoxication and 21 people who had used cocaine shortly before they died but who had died from other causes. RESULTS: In all 21 cases of unexpected death associated with excited delirium, the deaths were associated with restraint (for violent agitation and hyperactivity), with the person either in a prone position (18 people [86%]) or subjected to pressure on the neck (3 [14%]). All of those who died had suddenly lapsed into tranquillity shortly after being restrained. The excited delirium was caused by a psychiatric disorder in 12 people (57%) and by cocaine-induced psychosis in 8 (38%). Eighteen people (86%) were in police custody when they died. Four (19%) had been sprayed with capsicum oleoresin, and heart disease was found in another 4 at autopsy. The blood level of cocaine in those whose excited delirium was cocaine induced was similar to levels

  10. Structural study of ammonium metatungstate

    SciTech Connect

    Christian, Joel B. Whittingham, M. Stanley

    2008-08-15

    Several techniques have been used to study the structure of the Keggin-type polyoxometalate salt ammonium metatungstate (AMT)-(NH{sub 4}){sub 6}[H{sub 2}W{sub 12}O{sub 40}]*nH{sub 2}O, a potential fuel cell catalyst. The dehydrated salt is comprised of a mixture of crystallites of different unit cells in a centered eutactic cubic configuration, with an average unit cell of a{approx_equal}12.295. Varied orientations of the Keggin ions in the cubic arrangement create the differences, and orientational variation within each unit cell size represents an energy well. Progressive hydration of each crystallite leads to expansion of the lattice, with the degree of expansion depending on the locations of the water added in relation to the Keggin ion, which is influenced by cation location and hydrogen bonding. The structural hypothesis is supported by electron diffraction of single and multicrystal samples, by powder density measurements, X-ray powder diffraction studies, synchrotron powder X-ray diffraction, and a priori structural modeling studies. Based on the structure, projected active site densities are compared with nanostructured platinum catalysts for fuel cell application. - Graphical abstract: The structure of ammonium metatungstate powders are highly dependent on hydration and POM molecule rotation, with cation and hydrogen bonding forces directing a mixture of structures that have been studied with bulk and single-crystal methods. The illustration shows Monte Carlo simulated anion structural disorder for the fully dehydrated form of the title compound.

  11. Influence of surface properties on the structure of granular silver films and excitation of localized plasmons

    NASA Astrophysics Data System (ADS)

    Shcherbinin, D. P.; Konshina, E. A.; Polischuk, V. A.

    2016-04-01

    Granular silver films deposited on a thin insulating film of amorphous hydrogenated carbon ( a-C:H) and transparent conducting electrode (polycrystalline indium tin oxide (ITO) layer) have been investigated by spectroscopy and microscopy methods. The extinction spectra of silver films on the surface of these materials are found to be significantly different. An annealing of silver films causes a blue shift of the peak of plasmon resonance band in the spectrum of silver nanoparticles: by 16 nm on the a-C:H surface and by 94 nm on the ITO surface. Silver films on the surface of a-C:H films are characterized by a narrower band in the extinction spectrum, which is peaked at 446 nm. The changes observed in the optical density of Ag films are related to the change in size and area of nanoparticles. The results of spectral studies of Ag films are in agreement with the data on the nanostructure obtained by scanning electron microscopy and statistical image processing. The spectra of granular silver films are shown to correlate well with the nanoparticle distribution function over the film area.

  12. Inelastic neutron scattering study and magnetic excitations on the low-dimensional antiferromagnet α - Cu2V2O7

    NASA Astrophysics Data System (ADS)

    Gitgeatpong, Ganatee; Zhao, Yang; Qiu, Yiming; Matan, Kittiwit

    Magnetic excitations of the low-dimensional antiferromagnet α - Cu2V2O7 have been investigated using inelastic neutron scattering. The study reveals unusual commensurate splitting of magnetic excitation branches centered at a wave vector (0, +/- δ , 0) with δ = 0.25 away from a magnetic zone center, where a magnetic Bragg peak is observed. The energy gap of 0.75 meV at (0, +/- δ , 0) was found to decrease as a function of temperature and the magnetic excitations become diffusive and disappear above 35 K coincident with TN = 33.4 K. A recent experiment at the Multi Axis Crystal Spectrometer, MACS, to map the excitations over a large momentum space clearly shows the splitting of the dispersion at most of the allowed magnetic reflections. This commensurate splitting of the spin-wave-type excitations without the magnetic Bragg reflections at the same commensurate wave vectors has not yet been previously observed and remains unexplained. In the presentation, the experimental data will be shown and the possible explanation will also be discussed.

  13. Sensorimotor cortex excitability and connectivity in Alzheimer's disease: A TMS-EEG Co-registration study.

    PubMed

    Ferreri, Florinda; Vecchio, Fabrizio; Vollero, Luca; Guerra, Andrea; Petrichella, Sara; Ponzo, David; Määtta, Sara; Mervaala, Esa; Könönen, Mervi; Ursini, Francesca; Pasqualetti, Patrizio; Iannello, Giulio; Rossini, Paolo Maria; Di Lazzaro, Vincenzo

    2016-06-01

    Several studies have shown that, in spite of the fact that motor symptoms manifest late in the course of Alzheimer's disease (AD), neuropathological progression in the motor cortex parallels that in other brain areas generally considered more specific targets of the neurodegenerative process. It has been suggested that motor cortex excitability is enhanced in AD from the early stages, and that this is related to disease's severity and progression. To investigate the neurophysiological hallmarks of motor cortex functionality in early AD we combined transcranial magnetic stimulation (TMS) with electroencephalography (EEG). We demonstrated that in mild AD the sensorimotor system is hyperexcitable, despite the lack of clinically evident motor manifestations. This phenomenon causes a stronger response to stimulation in a specific time window, possibly due to locally acting reinforcing circuits, while network activity and connectivity is reduced. These changes could be interpreted as a compensatory mechanism allowing for the preservation of sensorimotor programming and execution over a long period of time, regardless of the disease's progression. Hum Brain Mapp 37:2083-2096, 2016. © 2016 Wiley Periodicals, Inc. PMID:26945686

  14. Propagation of Electrical Excitation in a Ring of Cardiac Cells: A Computer Simulation Study

    NASA Technical Reports Server (NTRS)

    Kogan, B. Y.; Karplus, W. J.; Karpoukhin, M. G.; Roizen, I. M.; Chudin, E.; Qu, Z.

    1996-01-01

    The propagation of electrical excitation in a ring of cells described by the Noble, Beeler-Reuter (BR), Luo-Rudy I (LR I), and third-order simplified (TOS) mathematical models is studied using computer simulation. For each of the models it is shown that after transition from steady-state circulation to quasi-periodicity achieved by shortening the ring length (RL), the action potential duration (APD) restitution curve becomes a double-valued function and is located below the original ( that of an isolated cell) APD restitution curve. The distributions of APD and diastolic interval (DI) along a ring for the entire range of RL corresponding to quasi-periodic oscillations remain periodic with the period slightly different from two RLs. The 'S' shape of the original APD restitution curve determines the appearance of the second steady-state circulation region for short RLs. For all the models and the wide variety of their original APD restitution curves, no transition from quasi-periodicity to chaos was observed.

  15. A Study on the Excitation and Resonant Absorption of Coronal Loop Kink Oscillations

    NASA Astrophysics Data System (ADS)

    Yu, Dae Jung; Van Doorsselaere, Tom

    2016-11-01

    We study theoretically the issue of externally driven excitations of standing kink waves and their resonant absorption into torsionally polarized m = 1 waves in the coronal loops in pressureless plasmas. We use the ideal MHD equations, for which we develop an invariant imbedding method available in cylindrical geometry. We assume a sinusoidal density profile at the loop boundary where the density inside the loop is lower than the outside and vice versa. We present field distributions for these two cases and find that they have similar behaviors. We compare the results for the overdense loops, which describe the usual coronal loops, with the analytical solutions of Soler et al. obtained using the Frobenius method. Our results show some similarity for thin nonuniform layers but deviate a lot for thick nonuniform layers. For the first case, which describes the wave train propagation in funnels, we find that resonant absorption depends crucially on the thickness of the nonuniform boundary, loop length, and density contrast. The resonant absorption of the kink mode is dominant when the loop length is sufficiently larger compared with its radius (thin loop). The behavior of the far-field pattern of the scattered wave by the coronal loop is closely related to that of the resonant absorption. For the mode conversion phenomena in inhomogeneous plasmas, a certain universal behavior of the resonant absorption is found for the first time. We expect that the main feature may also apply to the overdense loops and discuss its relation to the damping rate.

  16. Electron excitation and autoionisation cross sections for elements of chemically peculiar stars: Study of bismuth

    NASA Astrophysics Data System (ADS)

    Predojević, B.; Pejčev, V.; Šević, D.; Marinković, B. P.

    2014-12-01

    Electron impact excitation from the ground state of bismuth atoms has been studied. A beam of electrons was scattered from a beam of atoms and the intensity of scattered electrons was measured for scattering angles up to 150° and incident electron energies of 40 and 60 eV. Obtained intensities were used for the calculation of relative differential cross sections (DCS). In addition, we recorded the energy loss-spectra at different incident electron energies and scattering angles. These spectra were analysed in order to identify the energy levels of bismuth atom below and above (autoionisation) the first ionization limit in electron spectroscopy. The presence of bismuth was confirmed in spectra of the chemically peculiar (CP) magnetic Ap 73 Dra and HR 465 and nonmagnetic Hg-Mn HR 7775 and χ Lupi stars. The obtained results for relative DCS and identified autoionised energy levels of bismuth were analysed and compared with previous experimental and theoretical data. The connection between our investigations of bismuth and astrophysical measurements are discussed.

  17. Observation of interactive behavior increases corticospinal excitability in humans: A transcranial magnetic stimulation study.

    PubMed

    Aihara, Tsuyoshi; Yamamoto, Shinji; Mori, Hirotaka; Kushiro, Keisuke; Uehara, Shintaro

    2015-11-01

    In humans, observation of others' behaviors increases corticospinal excitability (CSE), which is interpreted in the contexts of motor resonance and the "mirror neuron system" (MNS). It has been suggested that observation of another individual's behavior manifests an embodied simulation of his/her mental state through the MNS. Thus, the MNS may involve understanding others' intentions of behaviors, thoughts, and emotions (i.e., social cognition), and may therefore exhibit a greater response when observing human-interactive behaviors that require a more varied and complex understanding of others. In the present study, transcranial magnetic stimulation was applied to the primary motor cortex of participants observing human-interactive behaviors between two individuals (c.f. one person reaching toward an object in another person's hand) and non-interactive individual behavior (c.f. one person reaching toward an object on a dish). We carefully controlled the kinematics of behaviors in these two conditions to exclude potential effects of MNS activity changes associated with kinematic differences between visual stimuli. Notably, motor evoked potentials, that reflect CSE, from the first dorsal interosseous muscle exhibited greater amplitude when the participants observed interactive behaviors than when they observed non-interactive behavior. These results provide neurophysiological evidence that the MNS is activated to a greater degree during observation of human-interactive behaviors that contain additional information about the individuals' mental states, supporting the view that the MNS plays a critical role in social cognition in humans. PMID:26432377

  18. Picosecond laser studies of V-T processes in gases and electronic excitation transport in disordered systems

    SciTech Connect

    Hedstrom, J.F.

    1987-06-01

    SVL fluorescence spectroscopy was used to study intramolecular energy transfer from the 0/sup 0/ level of aniline induced by collisions with CO/sub 2/. Time-correlated photon counting was used to measure concentration dependent fluorescence depolarization for rhodamine 6G in glycerol. Fluorescence decays from these viscous solutions provide data for analyzing the three-dimensional, three-body excitation transport theory developed by Gochanour, Andersen and Fayer for disordered systems. The two-dimensional, two-body excitation theory developed by Loring and Fayer was also examined using time-resolved fluorescence depolarization techniques. The samples, made up of submonolayers of rhodamine 3B adsorbed onto optically flat fused silica yield fluorescence profiles which agree well with profiles developed from the theory for reduced surface coverages up to approx.0.4. At higher coverages, excitation trapping by rhodamine 3B aggregates truncates the depolarization process, yielding apparent reduced coverages which are appreciably lower than the true coverages.

  19. The origin of radiationless conversion of the excited state in the kindling fluorescent protein (KFP): femtosecond studies and quantum modeling

    NASA Astrophysics Data System (ADS)

    Shelaev, I.; Mironov, V.; Rusanov, A.; Gostev, F.; Bochenkova, A.; Sarkisov, O.; Nemukhin, A.; Savitsky, A.

    2011-06-01

    The Ala143Gly variant of the chromoprotein asCP from the sea anemony Anemonia sulcata, called the kindling fluorescent protein (KFP), is a promising candidate for the development of novel subdiffraction method of fluorescent microscopy. The pump-probe method with the delay times between the pump and probe pulses up to 5 ps was applied to study dynamics of the primary processes upon excitation of KFP. The differential absorption spectra at 80 fs delay showed the absorption peak in the range 450-510 nm with the maximum wavelength at 490 nm, which diminished almost twice by intensity by 400 fs and practically disappeared by 1.5 ps. The quantum calculations showed that upon photo-excitation of KFP to the first excited state S1, the fast radiationless relaxation occurred to the ground state S0 due to rotation of the phenolic fragment of the chromophore.

  20. Study of the dissociation of nitrous oxide following resonant excitation of the nitrogen and oxygen K-shells

    SciTech Connect

    Ceolin, D.; Travnikova, O.; Bao, Z.; Piancastelli, M. N.; Tanaka, T.; Hoshino, M.; Kato, H.; Tanaka, H.; Harries, J. R.; Tamenori, Y.; Pruemper, C.; Lischke, T.; Liu, X.-J.; Ueda, K.

    2008-01-14

    A photochemistry study on nitrous oxide making use of site-selective excitation of terminal nitrogen, central nitrogen, and oxygen 1s{yields}3{pi} excitations is presented. The resonant Auger decay which takes place following excitation can lead to dissociation of the N{sub 2}O{sup +} ion. To elucidate the nuclear dynamics, energy-resolved Auger electrons were detected in coincidence with the ionic dissociation products, and a strong dependence of the fragmentation pathways on the core-hole site was observed in the binding energy region of the first satellite states. A description based on the molecular orbitals as well as the correlation between the thermodynamical thresholds of ion formation and the first electronic states of N{sub 2}O{sup +} has been used to qualitatively explain the observed fragmentation patterns.

  1. Resonance Raman Intensities Demonstrate that C5 Substituents Affect the Initial Excited-State Structural Dynamics of Uracil More than C6 Substituents.

    PubMed

    Teimoory, Faranak; Loppnow, Glen R

    2016-05-01

    Resonance Raman derived initial excited-state structural dynamics provide insight into the photochemical mechanisms of pyrimidine nucleobases, in which the photochemistry appears to be dictated by the C5 and C6 substituents. The absorption and resonance Raman spectra and excitation profiles of 5,6-dideuterouracil were measured to further test this photochemical dependence on the C5 and C6 substituents. The resulting set of excited-state reorganization energies of the observed internal coordinates were calculated and compared to those of other 5- and 6-substituted uracils. The results show that the initial excited-state dynamics along the C5C6 stretch responds to changes in mass at C5 and C6 in the same manner but that the in-plane bends at C5 and C6 are more sensitive to substituents at the C5 position than at the C6 position. In addition, the presence of two deuterium substituents at C5 and C6 decreases the initial excited-state structural dynamics along these in-plane bends, in contrast to what is observed in the presence of two CH3 groups on C5 and C6. The results are discussed in the context of DNA nucleobase photochemistry.

  2. Electron-impact excitation of Ni II. Collision strengths and effective collision strengths for low-lying fine-structure forbidden transitions

    NASA Astrophysics Data System (ADS)

    Cassidy, C. M.; Ramsbottom, C. A.; Scott, M. P.; Burke, P. G.

    2010-04-01

    Context. Considerable demand exists for electron excitation data for ion{Ni}{ii}, since lines from this abundant ion are observed in a wide variety of laboratory and astrophysical spectra. The accurate theoretical determination of these data can present a significant challenge however, due to complications arising from the presence of an open 3d-shell in the description of the target ion. Aims: In this work we present collision strengths and Maxwellian averaged effective collision strengths for the electron-impact excitation of ion{Ni}{ii}. Attention is concentrated on the 153 forbidden fine-structure transitions between the energetically lowest 18 levels of ion{Ni}{ii}. Effective collision strengths have been evaluated at 27 individual electron temperatures ranging from 30-100 000 K. To our knowledge this is the most extensive theoretical collisional study carried out on this ion to date. Methods: The parallel R-matrix package RMATRX II has recently been extended to allow for the inclusion of relativistic effects. This suite of codes has been utilised in the present work in conjunction with PSTGF to evaluate collision strengths and effective collision strengths for all of the low-lying forbidden fine-structure transitions. The following basis configurations were included in the target model - 3d9, 3d84s, 3d84p, 3d74s2 and 3d74s4p - giving rise to a sophisticated 295 jj-level, 1930 coupled channel scattering problem. Results: Comprehensive comparisons are made between the present collisional data and those obtained from earlier theoretical evaluations. While the effective collision strengths agree well for some transitions, significant discrepancies exist for others. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/513/A55

  3. The Study of Dynamic Potentials of Highly Excited Vibrational States of DCP: From Case Analysis to Comparative Study with HCP.

    PubMed

    Wang, Aixing; Fang, Chao; Liu, Yibao

    2016-08-22

    The dynamic potentials of highly excited vibrational states of deuterated phosphaethyne (DCP) in the D-C and C-P stretching coordinates with anharmonicity and Fermi coupling are studied in this article and the results show that the D-C-P bending vibration mode has weak effects on D-C and C-P stretching modes under different Polyad numbers (P number). Furthermore, the dynamic potentials and the corresponding phase space trajectories of DCP are given, as an example, in the case of P = 30. In the end, a comparative study between deuterated phosphaethyne (DCP) and phosphaethyne (HCP) with dynamic potential is done, and it is elucidated that the uncoupled mode makes the original horizontal reversed symmetry breaking between the dynamic potential of HCP ( q 3 ) and DCP ( q 1 ), but has little effect on the vertical reversed symmetry, between the dynamic potential of HCP ( q 2 ) and DCP ( q 3 ).

  4. The Study of Dynamic Potentials of Highly Excited Vibrational States of DCP: From Case Analysis to Comparative Study with HCP

    PubMed Central

    Wang, Aixing; Fang, Chao; Liu, Yibao

    2016-01-01

    The dynamic potentials of highly excited vibrational states of deuterated phosphaethyne (DCP) in the D–C and C–P stretching coordinates with anharmonicity and Fermi coupling are studied in this article and the results show that the D-C-P bending vibration mode has weak effects on D–C and C–P stretching modes under different Polyad numbers (P number). Furthermore, the dynamic potentials and the corresponding phase space trajectories of DCP are given, as an example, in the case of P = 30. In the end, a comparative study between deuterated phosphaethyne (DCP) and phosphaethyne (HCP) with dynamic potential is done, and it is elucidated that the uncoupled mode makes the original horizontal reversed symmetry breaking between the dynamic potential of HCP (q3) and DCP (q1), but has little effect on the vertical reversed symmetry, between the dynamic potential of HCP (q2) and DCP (q3). PMID:27556452

  5. The Study of Dynamic Potentials of Highly Excited Vibrational States of DCP: From Case Analysis to Comparative Study with HCP.

    PubMed

    Wang, Aixing; Fang, Chao; Liu, Yibao

    2016-01-01

    The dynamic potentials of highly excited vibrational states of deuterated phosphaethyne (DCP) in the D-C and C-P stretching coordinates with anharmonicity and Fermi coupling are studied in this article and the results show that the D-C-P bending vibration mode has weak effects on D-C and C-P stretching modes under different Polyad numbers (P number). Furthermore, the dynamic potentials and the corresponding phase space trajectories of DCP are given, as an example, in the case of P = 30. In the end, a comparative study between deuterated phosphaethyne (DCP) and phosphaethyne (HCP) with dynamic potential is done, and it is elucidated that the uncoupled mode makes the original horizontal reversed symmetry breaking between the dynamic potential of HCP ( q 3 ) and DCP ( q 1 ), but has little effect on the vertical reversed symmetry, between the dynamic potential of HCP ( q 2 ) and DCP ( q 3 ). PMID:27556452

  6. Spin-orbit-driven magnetic structure and excitation in the 5d pyrochlore Cd2Os2O7.

    PubMed

    Calder, S; Vale, J G; Bogdanov, N A; Liu, X; Donnerer, C; Upton, M H; Casa, D; Said, A H; Lumsden, M D; Zhao, Z; Yan, J-Q; Mandrus, D; Nishimoto, S; van den Brink, J; Hill, J P; McMorrow, D F; Christianson, A D

    2016-01-01

    Much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, particularly on the formation of novel electronic states and manifested metal-insulator transitions (MITs). SOC plays a dominant role in 5d(5) iridates (Ir(4+)), undergoing MITs both concurrent (pyrochlores) and separated (perovskites) from the onset of magnetic order. However, the role of SOC for other 5d configurations is less clear. For example, 5d(3) (Os(5+)) systems are expected to have an orbital singlet with reduced effective SOC. The pyrochlore Cd2Os2O7 nonetheless exhibits a MIT entwined with magnetic order phenomenologically similar to pyrochlore iridates. Here, we resolve the magnetic structure in Cd2Os2O7 with neutron diffraction and then via resonant inelastic X-ray scattering determine the salient electronic and magnetic energy scales controlling the MIT. In particular, SOC plays a subtle role in creating the electronic ground state but drives the magnetic order and emergence of a multiple spin-flip magnetic excitation. PMID:27273216

  7. Spin-orbit-driven magnetic structure and excitation in the 5d pyrochlore Cd2Os2O7

    PubMed Central

    Calder, S.; Vale, J. G.; Bogdanov, N. A.; Liu, X.; Donnerer, C.; Upton, M. H.; Casa, D.; Said, A. H.; Lumsden, M. D.; Zhao, Z.; Yan, J. -Q.; Mandrus, D.; Nishimoto, S.; van den Brink, J.; Hill, J. P.; McMorrow, D. F.; Christianson, A. D.

    2016-01-01

    Much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, particularly on the formation of novel electronic states and manifested metal-insulator transitions (MITs). SOC plays a dominant role in 5d5 iridates (Ir4+), undergoing MITs both concurrent (pyrochlores) and separated (perovskites) from the onset of magnetic order. However, the role of SOC for other 5d configurations is less clear. For example, 5d3 (Os5+) systems are expected to have an orbital singlet with reduced effective SOC. The pyrochlore Cd2Os2O7 nonetheless exhibits a MIT entwined with magnetic order phenomenologically similar to pyrochlore iridates. Here, we resolve the magnetic structure in Cd2Os2O7 with neutron diffraction and then via resonant inelastic X-ray scattering determine the salient electronic and magnetic energy scales controlling the MIT. In particular, SOC plays a subtle role in creating the electronic ground state but drives the magnetic order and emergence of a multiple spin-flip magnetic excitation. PMID:27273216

  8. Spin-orbit-driven magnetic structure and excitation in the 5d pyrochlore Cd2Os2O7

    NASA Astrophysics Data System (ADS)

    Calder, S.; Vale, J. G.; Bogdanov, N. A.; Liu, X.; Donnerer, C.; Upton, M. H.; Casa, D.; Said, A. H.; Lumsden, M. D.; Zhao, Z.; Yan, J.-Q.; Mandrus, D.; Nishimoto, S.; van den Brink, J.; Hill, J. P.; McMorrow, D. F.; Christianson, A. D.

    2016-06-01

    Much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, particularly on the formation of novel electronic states and manifested metal-insulator transitions (MITs). SOC plays a dominant role in 5d5 iridates (Ir4+), undergoing MITs both concurrent (pyrochlores) and separated (perovskites) from the onset of magnetic order. However, the role of SOC for other 5d configurations is less clear. For example, 5d3 (Os5+) systems are expected to have an orbital singlet with reduced effective SOC. The pyrochlore Cd2Os2O7 nonetheless exhibits a MIT entwined with magnetic order phenomenologically similar to pyrochlore iridates. Here, we resolve the magnetic structure in Cd2Os2O7 with neutron diffraction and then via resonant inelastic X-ray scattering determine the salient electronic and magnetic energy scales controlling the MIT. In particular, SOC plays a subtle role in creating the electronic ground state but drives the magnetic order and emergence of a multiple spin-flip magnetic excitation.

  9. A Preliminary Transcranial Magnetic Stimulation Study of Cortical Inhibition and Excitability in High-Functioning Autism and Asperger Disorder

    ERIC Educational Resources Information Center

    Enticott, Peter G.; Rinehart, Nicole J.; Tonge, Bruce J.; Bradshaw, John L.; Fitzgerald, Paul B.

    2010-01-01

    Aim: Controversy surrounds the distinction between high-functioning autism (HFA) and Asperger disorder, but motor abnormalities are associated features of both conditions. This study examined motor cortical inhibition and excitability in HFA and Asperger disorder using transcranial magnetic stimulation (TMS). Method: Participants were diagnosed by…

  10. Experimental facility for reactor experiments on study of spectral-luminescent characteristics of nuclear-excited plasma

    NASA Astrophysics Data System (ADS)

    Gordienko, Yu N.; Batyrbekov, E. G.; Skakov, M. K.; Ponkratov, Yu V.; Khasenov, M. U.; Zaurbekova, Zh A.; Barsukov, N. I.; Kulsartov, T. V.; Tulubayev, Ye Yu

    2016-09-01

    The description of experimental facility and reactor ampoule device for carrying out the experiments on study of spectral-luminescent characteristics of nuclear-excited plasma formed by products of 6Li(n,α)T nuclear reaction under conditions of neutron irradiation is given in paper.

  11. Studies on linear, nonlinear optical and excited state dynamics of silicon nanoparticles prepared by picosecond laser ablation

    SciTech Connect

    Hamad, Syed; Nageswara Rao, S. V. S.; Pathak, A. P.; Krishna Podagatlapalli, G.; Mounika, R.; Venugopal Rao, S. E-mail: soma-venu@uohyd.ac.in

    2015-12-15

    We report results from our studies on the fabrication and characterization of silicon (Si) nanoparticles (NPs) and nanostructures (NSs) achieved through the ablation of Si target in four different liquids using ∼2 picosecond (ps) pulses. The consequence of using different liquid media on the ablation of Si target was investigated by studying the surface morphology along with material composition of Si based NPs. The recorded mean sizes of these NPs were ∼9.5 nm, ∼37 nm, ∼45 nm and ∼42 nm obtained in acetone, water, dichloromethane (DCM) and chloroform, respectively. The generated NPs were characterized by selected area electron diffraction (SAED), high resolution transmission microscopy (HRTEM), Raman spectroscopic techniques and Photoluminescence (PL) studies. SAED, HRTEM and Raman spectroscopy data confirmed that the material composition was Si NPs in acetone, Si/SiO{sub 2} NPs in water, Si-C NPs in DCM and Si-C NPs in chloroform and all of them were confirmed to be polycrystalline in nature. Surface morphological information of the fabricated Si substrates was obtained using the field emission scanning electron microscopic (FESEM) technique. FESEM data revealed the formation of laser induced periodic surface structures (LIPSS) for the case of ablation in acetone and water while random NSs were observed for the case of ablation in DCM and chloroform. Femtosecond (fs) nonlinear optical properties and excited state dynamics of these colloidal Si NPs were investigated using the Z-scan and pump-probe techniques with ∼150 fs (100 MHz) and ∼70 fs (1 kHz) laser pulses, respectively. The fs pump-probe data obtained at 600 nm consisted of single and double exponential decays which were tentatively assigned to electron-electron collisional relaxation (<1 ps) and non-radiative transitions (>1 ps). Large third order optical nonlinearities (∼10{sup −14} e.s.u.) for these colloids have been estimated from Z-scan data at an excitation wavelength of 680 nm

  12. Studies on linear, nonlinear optical and excited state dynamics of silicon nanoparticles prepared by picosecond laser ablation

    NASA Astrophysics Data System (ADS)

    Hamad, Syed; Krishna Podagatlapalli, G.; Mounika, R.; Nageswara Rao, S. V. S.; Pathak, A. P.; Venugopal Rao, S.

    2015-12-01

    We report results from our studies on the fabrication and characterization of silicon (Si) nanoparticles (NPs) and nanostructures (NSs) achieved through the ablation of Si target in four different liquids using ˜2 picosecond (ps) pulses. The consequence of using different liquid media on the ablation of Si target was investigated by studying the surface morphology along with material composition of Si based NPs. The recorded mean sizes of these NPs were ˜9.5 nm, ˜37 nm, ˜45 nm and ˜42 nm obtained in acetone, water, dichloromethane (DCM) and chloroform, respectively. The generated NPs were characterized by selected area electron diffraction (SAED), high resolution transmission microscopy (HRTEM), Raman spectroscopic techniques and Photoluminescence (PL) studies. SAED, HRTEM and Raman spectroscopy data confirmed that the material composition was Si NPs in acetone, Si/SiO2 NPs in water, Si-C NPs in DCM and Si-C NPs in chloroform and all of them were confirmed to be polycrystalline in nature. Surface morphological information of the fabricated Si substrates was obtained using the field emission scanning electron microscopic (FESEM) technique. FESEM data revealed the formation of laser induced periodic surface structures (LIPSS) for the case of ablation in acetone and water while random NSs were observed for the case of ablation in DCM and chloroform. Femtosecond (fs) nonlinear optical properties and excited state dynamics of these colloidal Si NPs were investigated using the Z-scan and pump-probe techniques with ˜150 fs (100 MHz) and ˜70 fs (1 kHz) laser pulses, respectively. The fs pump-probe data obtained at 600 nm consisted of single and double exponential decays which were tentatively assigned to electron-electron collisional relaxation (<1 ps) and non-radiative transitions (>1 ps). Large third order optical nonlinearities (˜10-14 e.s.u.) for these colloids have been estimated from Z-scan data at an excitation wavelength of 680 nm suggesting that the

  13. Electronic structure and optical properties of CdS{sub x}Se{sub 1−x} solid solution nanostructures from X-ray absorption near edge structure, X-ray excited optical luminescence, and density functional theory investigations

    SciTech Connect

    Murphy, M. W.; Yiu, Y. M. Sham, T. K.; Ward, M. J.; Liu, L.; Hu, Y.; Zapien, J. A.; Liu, Yingkai

    2014-11-21

    The electronic structure and optical properties of a series of iso-electronic and iso-structural CdS{sub x}Se{sub 1−x} solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

  14. Raman study of magnetic excitations and magnetoelastic coupling in α -SrCr2O4

    NASA Astrophysics Data System (ADS)

    Valentine, Michael E.; Koohpayeh, Seyed; Mourigal, Martin; McQueen, Tyrel M.; Broholm, Collin; Drichko, Natalia; Dutton, Siân E.; Cava, Robert J.; Birol, Turan; Das, Hena; Fennie, Craig J.

    2015-04-01

    Using Raman spectroscopy, we investigate the lattice phonons, magnetic excitations, and magnetoelastic coupling in the distorted triangular-lattice Heisenberg antiferromagnet α -SrCr2O4 , which develops helical magnetic order below 43 K. Temperature-dependent phonon spectra are compared to predictions from density functional theory calculations which allows us to assign the observed modes and identify weak effects arising from coupled lattice and magnetic degrees of freedom. Raman scattering associated with two-magnon excitations is observed at 20 and 40 meV. These energies are in general agreement with our ab initio calculations of exchange interactions and earlier theoretical predictions of the two-magnon Raman response of triangular-lattice antiferromagnets. The temperature dependence of the two-magnon excitations indicates that spin correlations persist well above the Néel temperature.

  15. Excited-state dynamics of furan studied by sub-20-fs time-resolved photoelectron imaging using 159-nm pulses

    SciTech Connect

    Spesyvtsev, R.; Horio, T.; Suzuki, Y.-I.; Suzuki, T.

    2015-07-07

    The excited-state dynamics of furan were studied by time-resolved photoelectron imaging using a sub-20-fs deep UV (198 nm) and vacuum UV (159 nm) light source. The 198- and 159-nm pulses produce photoionization signals in both pump-probe and probe-pump pulse sequences. When the 198-nm pulse precedes the 159-nm pulse, it creates the {sup 1}A{sub 2}(3s) Rydberg and {sup 1}B{sub 2}(ππ{sup ∗}) valence states, and the former decays exponentially with a time constant of about 20 fs whereas the latter exhibits more complex wave-packet dynamics. When the 159-nm pulse precedes the 198-nm pulse, a wave packet is created on the {sup 1}A{sub 1}(ππ{sup ∗}) valence state, which rapidly disappears from the observation window owing to structural deformation. The 159-nm photoexcitation also creates the 3s and 3p{sub x,y} Rydberg states non-adiabatically.

  16. Ultrafast FRET in a room temperature ionic liquid microemulsion: a femtosecond excitation wavelength dependence study.

    PubMed

    Adhikari, Aniruddha; Das, Dibyendu Kumar; Sasmal, Dibyendu Kumar; Bhattacharyya, Kankan

    2009-04-23

    Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to rhodamine 6G (R6G) is studied in a room temperature ionic liquid (RTIL) microemulsion by picosecond and femtosecond emission spectroscopy. The microemulsion is comprised of the RTIL 1-pentyl-3-methylimidazolium tetraflouroborate, [pmim][BF4], in TX-100/ benzene. We have studied the microemulsion with and without water. The time constants of FRET were obtained from the risetime of the acceptor (R6G) emission. In the RTIL microemulsion, FRET occurs on multiple time scales: 1, 250, and 3900 ps. In water containing RTIL microemulsion, the rise components are 1.5, 250, and 3900 ps. The 1 and 1.5 ps components are assigned to FRET at a close contact of donor and acceptor (RDA approximately 12 A). This occurs within the highly polar (RTIL/water) pool of the microemulsion. With increase in the excitation wavelength (lambdaex) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET (1 ps) increases from 4% to 100% in the RTIL microemulsion and 12% to 100% in the water containing RTIL microemulsion. It is suggested that at lambdaex = 435 nm, mainly the highly polar RTIL pool is probed where FRET is very fast due to the close proximity of the donor and the acceptor. The very long 3900 ps (RDA approximately 45 A) component may arise from FRET from a donor in the outer periphery of the microemulsion to an acceptor in the polar RTIL pool. The 250 ps component (RDA approximately 29 A) is assigned to FRET from a donor inside the surfactant chains. PMID:19127996

  17. SSME/side loads analysis for flight configuration, revision A. [structural analysis of space shuttle main engine under side load excitation

    NASA Technical Reports Server (NTRS)

    Holland, W.

    1974-01-01

    This document describes the dynamic loads analysis accomplished for the Space Shuttle Main Engine (SSME) considering the side load excitation associated with transient flow separation on the engine bell during ground ignition. The results contained herein pertain only to the flight configuration. A Monte Carlo procedure was employed to select the input variables describing the side load excitation and the loads were statistically combined. This revision includes an active thrust vector control system representation and updated orbiter thrust structure stiffness characteristics. No future revisions are planned but may be necessary as system definition and input parameters change.

  18. Coulomb Excitation and One-Neutron Transfer Studies of Stable and Radioactive Nuclei at HRIBF-ORNL

    SciTech Connect

    Allmond, James M

    2015-01-01

    Several stable and radioactive nuclei ranging from $A=58$ to 208 were recently studied in inverse kinematics by Coulomb excitation and heavy-ion induced one-neutron transfer at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory. These studies used a CsI-HPGe detector array to detect scattered charged particles and emitted $\\gamma$ rays from the in-beam reactions. A Bragg-curve detector was used to measure the energy loss of the various beams through the targets and to measure the radioactive beam compositions. Stable nickel, strontium, zirconium, molybdenum, tin, tellurium, and lead isotopes and neutron-rich radioactive tin and tellurium isotopes were among the nuclei recently studied. Coulomb excitation was used to measure the electromagnetic moments of the first excited states and heavy-ion induced one-neutron transfer was used to measure the absolute cross sections and lifetimes of the excited single-particle states. A sample of these results are presented here with an emphasis on the tin isotopes. In particular, a survey of the Bragg-curve measurements, Doppler corrections, and inconclusive $i_{13/2}$ candidate in $^{133}$\\textrm{Sn} are presented.

  19. [Study on the characters of phytoplankton chlorophyll fluorescence excitation spectra based on fourth-derivative].

    PubMed

    Lu, Lu; Su, Rong-Guo; Wang, Xiu-Lin; Zhu, Chen-Jian

    2007-11-01

    Chlorophyll fluorescence excitation spectra of six phytoplankton species, belonging to Bacillariophyta and Dinophyta, were dealt by fourth-derivative analysis with the Matlab program. The results show that between 350 nm and 550 nm six fluorescence peaks were found in the fourth-derivative spectra, which are representatives of non-pigments, chlorophylls and carotenoides respectively. The method makes Bacillariophyta and Dinophyta more distinguishable when the fourth-derivative spectra are compared with the chlorophyll fluorescence excitation spectra. It can be used not only to discriminate the two groups of algaes, but also to reduce the effect of noise. The fluorescence peaks in the fourth-derivative spectra are proved to be stable.

  20. Quantum-chemical study of electronically excited states of protolytic forms of vanillic acid

    NASA Astrophysics Data System (ADS)

    Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Y.

    2015-12-01

    The paper describes an analysis of possible ways of deactivation of electronically excited states of 4-hydroxy- 3-methoxy-benzoic acid (vanillic acid) and its protolytic forms with the use of quantum-chemical methods INDO/S (intermediate neglect of differential overlap with a spectroscopic parameterization) and MEP (molecular electrostatic potential). The ratio of radiative and non-radiative deactivation channels of the electronic excitation energy is established. The rate constants of photophysical processes (internal and intercombination conversions) occurring after the absorption of light in these forms are evaluated.

  1. Reactivity of a sodium atom in vibrationally excited water clusters: An ab initio molecular dynamics study

    NASA Astrophysics Data System (ADS)

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

    2008-07-01

    We investigated the reaction between a sodium atom and water molecules in both small and medium-size vibrationally excited water clusters using ab initio molecular dynamics simulations. Formation of NaOH was observed in small ( n = 4, 5) clusters, while water dissociation and subsequent geminate recombination accompanied by a transient formation of a Na +-OH - pair occurred in a 34 water cluster. Our results show that the initial step of the vibrationally excited reaction between a single sodium atom and water does not shut off in larger clusters and that it can also occur in the bulk water, however, more sodium atoms are likely required to stabilize the product.

  2. Lattice study of the leptonic decay constant of the pion and its excitations

    SciTech Connect

    Mastropas, Ekaterina; Richard, David

    2014-11-01

    We present a calculation of the decay constant of the pion, and its lowest-lying three excitations, at three values of the pion mass between around 400 and 700 MeV, using anisotropic clover lattices. We use the variational method to determine an optimal interpolating operator for each of the states. We find that the decay constant of the first excitation, and more notably of the second, is suppressed with respect to that of the ground-state pion, but that the suppression shows little dependence on the quark mass.

  3. High excitation power photoluminescence studies of ultra-low density GaAs quantum dots

    SciTech Connect

    Sonnenberg, D.; Graf, A.; Paulava, V.; Heyn, Ch.; Hansen, W.

    2013-12-04

    We fabricate GaAs epitaxial quantum dots (QDs) by filling of self-organized nanoholes in AlGaAs. The QDs are fabricated under optimized process conditions and have ultra-low density in the 10{sup 6} cm{sup −2} regime. At low excitation power the optical emission of single QDs exhibit sharp excitonic lines, which are attributed to the recombination of excitonic and biexcitonic states. High excitation power measurements reveal surprisingly broad emission lines from at least six QD shell states.

  4. Excited state intramolecular proton transfer (ESIPT) in 2-(2'-hydroxyphenyl)benzoxazole and its naphthalene-fused analogs: a TD-DFT quantum chemical study.

    PubMed

    Roohi, Hossein; Hejazi, Fahimeh; Mohtamedifar, Nafiseh; Jahantab, Mahjobeh

    2014-01-24

    The intramolecular proton transfer reactions in 2-(2'-hydroxyphenyl)benzoxazole (HBO) and its naphthalene-fused analogs, (HNB1-3) in both S0 and S1 states at the PBE1PBE/6-311++G(2d,2p) level of theory in the gas phase and water have been investigated to find the effects of extension of aromaticity on the intramolecular proton transfer and photophysical properties. The results show that the ground state intramolecular proton transfer (GSIPT) in the studied species is impossible. Excited states potential energy surface calculations support the existence of ESIPT process. Structural parameters, relative energy of isomers, H-bonding energy, adsorption and emission bands, vertical excitation and emission energies, oscillator strength, fluorescence rate constant, dipole moment, atomic charges and electron density at critical points were calculated. Orbital analysis shows that vertical S0→S1 transition in the studied molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π(*)). The potential of HNB2 molecule as an emissive and electron transport material in designing improved organic white light emitting diodes is predicted in this work. Our calculations are also supported by the experimental observations.

  5. Ne+, Ne2+, Ar+, and Ar2+ fine-structure electron-impact excitation data for applications in ultra low temperature plasmas

    NASA Astrophysics Data System (ADS)

    LI, YE; Wang, Qianxia; Pearce, Jonathan; Pindzola, Michael; Loch, Stuart; Stancil, Phillip C.; Cumbee, Renata; Ballance, Connor

    2016-01-01

    Fine-structure electron-impact excitation of ions plays an important role in cooling most interstellar environments and is important for far infrared (IR) and submillimeter (submm) observations. New atomic structure and collisonal data are presented using both semi-relativistic and fully-relativistic R-matrix methods for Ne+, Ne2+, Ar+, and Ar2+. Some illustrative modeling results using the data are also given.

  6. The Distribution of Interstellar Thermal Pressures in the Milky Way: New Data on the Fine-structure Excitation of C I from STIS Spectra in the HST Archive

    NASA Astrophysics Data System (ADS)

    Jenkins, Edward B.; Tripp, T. M.

    2006-06-01

    We have used the method of Jenkins & Tripp (2001: ApJS, 137, 297) to extract velocity profiles of the absorption by interstellar neutral carbon atoms in the 3 different fine-structure levels of the ground electronic state. The populations of these levels are governed by the balance between collisional excitations (and de-excitations) against radiative decay. By studying these populations, we can determine the different combinations of local temperatures and densities of the C I-bearing gas. We have analyzed virtually all of the stellar spectra in HST Archive that show clearly the multiplets of C I recorded with the E140H echelle grating of STIS. We have now expanded our coverage from the 21 stars in our original survey to a new total of 102 stars. This new study increases the coverage in Galactic longitudes well beyond that of the earlier observing program, which was mostly restricted to the intersections of the two HST continuous viewing zones and the plane of the Galaxy. We propose that substantial deviations of thermal pressures above and below a mean value are caused by interstellar turbulence, and we correlate these deviations with the kinematic properties of the gas. We derive an overall C I-weighted distribution function for the thermal pressures, and this distribution can be converted to one that applies to all of the neutral gas after we correct for changes in the ionization equilibrium between the neutral and ionized forms of carbon.This research was supported by grant HST-AR-09534.01 from the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  7. Selective studies of the excited rotational bands in the superdeformed nucleus {sup 151}Tb

    SciTech Connect

    Benzoni, G.; Bracco, A.; Crespi, F. C. L.; Conto, A. De; Leoni, S.; Million, B.; Montanari, D.; Robin, J.; Duchene, G.; Curien, D.; Byrski, Th.; Beck, F. A.; Bednarczyk, P.; Courtin, S.; Dorvaux, O.; Gall, B. J. P.; Joshi, P.; Nourreddine, A.; Piqueras, I.; Vivien, J. P.

    2007-04-15

    The experimental study of the unresolved rotational bands, forming ridge structures in {gamma}-{gamma} spectra, has been performed on the superdeformed nucleus {sup 151}Tb. {gamma} transitions from the reaction {sup 27}Al, at 155 MeV, on {sup 130}Te were measured with EUROBALL IV in high fold coincidence. The analysis of the intensities and count fluctuations of the ridge structures shows the existence of {approx_equal}30 discrete rotational bands of superdeformed nature, half of which is in direct coincidence with the superdeformed yrast band. A comparison with band mixing model predictions and with a previous work on the superdeformed nucleus {sup 143}Eu is presented.

  8. Spectroscopic and theoretical studies on the excited state in diimine dithiolate complexes of platinum(II)

    SciTech Connect

    Zuleta, J.A.; Bevilacqua, J.M.; Eisenberg, R. ); Proserpio, D.M. ); Harvey, P.D. )

    1992-06-10

    The photophysical properties of a series of Pt(N-N)(S-S) complexes have been studied where (N-N) is either an [alpha],[alpha][prime]-diimine or saturated diamine chelating ligand and (S-S) is either a dithiolate chelating ligand or two monothiolate ligands in order to determine the orbital composition of the excited state. The solvent dependence of the absorption spectra of these complexes and the temperature dependence of their emission intensities and lifetimes have been examined while the ligands have been systematically varied. The electronic spectra are found to be dependent on whether or not the nitrogen chelating ligand is unsaturated (contains a vacant [pi]* orbital). On the basis of the spectroscopic data, the lowest energy absorption band in the diimine complexes is assigned as a metal-dithiolate to [pi]*(diimine) transition, whereas in the diamine complexes it is assigned as a metal-to-dithiolate MLCT transition. The only room-temperature emissive complexes are those that contain an [alpha],[alpha][prime]-diimine chelating ligand. The nature of the emission in these complexes at all temperatures depends on the dithiolate ligand, and the temperature dependence of the emission spectra has been examined. The nature of the HOMO and LUMO has been examined experimentally using cyclic voltammetry. On the basis of the electrochemical and spectroscopic data, the emission from all of the Pt(diimine)(S-S) complexes except those of 1,2-dithiolate maleonitriledithiolate (mnt) is assigned as a [sup 3](d(Pt)/p(S)-[pi]*(diimine)) transition, while, for the mnt complexes, it corresponds to a [sup 3](d(Pt)/p(S)-[pi]*(mnt)) transition. These assignments are supported by extended Hueckel molecular orbital calculations.

  9. USANS study of wood structure

    NASA Astrophysics Data System (ADS)

    Garvey, Christopher J.; Knott, Robert B.; Searson, Matthew; Conroy, Jann P.

    2006-11-01

    Wood performs a vascular and structural function in trees. In this study we used the double-crystal diffractometer BT5 at the NIST Center for Neutron Scattering (Gaithersburg, USA) to study the pore structure inside wood sections. The slit-smeared intensity of scattered neutrons was measured from wood sections in directions parallel, orthogonal and transverse to the tree's trunk axis over a scattering vector range 0.00004-0.002 Å -1. The interpretation of the data in terms of a reductionist model consisting of infinitely long cylinders (cell lumens) is discussed.

  10. Development of methods to predict both the dynamic and the pseudo-static response of secondary structures subjected to seismic excitations

    SciTech Connect

    Subudhi, M.; Bezler, P.

    1984-01-01

    Multiple independent support excitation time history formulations have been used to investigate simplified methods to predict the inertial (or dynamic) component of response as well as the pseudo-static (or static) component of response of secondary structures subjected to seismic excitations. For the dynamic component the independent response spectrum method is used with current industry practice for the modal and direction of excitation combinations being adopted and various procedures for the group combination and sequence being investigated. SRSS combination between support groups is found to yield satisfactory results. For the static component, support grouping by elevation for preliminary design followed by support grouping by attachment point for final design assure overall safety in the design.

  11. Atomic resolution mapping of the excited-state electronic structure of Cu2O with time-resolved x-ray absorption spectroscopy

    SciTech Connect

    Hillyard, P. W.; Kuchibhatla, S. V. N. T.; Glover, T. E.; Hertlein, M. P.; Huse, Nils; Nachimuthu, P.; Saraf, L. V.; Thevuthasan, S.; Gaffney, K. J.

    2010-05-02

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that the conduction-band and valence-band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  12. Atomic Resolution Mapping of the Excited-State Electronic Structure of Cu2O with Time-Resolved X-Ray Absorption Spectroscopy

    SciTech Connect

    Hillyard, Patrick B.; Kuchibhatla, Satyanarayana V N T; Glover, T. E.; Hertlein, M. P.; Huse, N.; Nachimuthu, Ponnusamy; Saraf, Laxmikant V.; Thevuthasan, Suntharampillai; Gaffney, Kelly J.

    2009-09-29

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that that the conduction band and valence band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  13. Excitation-dependent variation in local symmetry in Ba2Mg(BO3)2 evidenced by Eu3+ luminescent structural probe

    NASA Astrophysics Data System (ADS)

    Jayakiruba, S.; Kumar, Gautam; Lakshminarasimhan, N.

    2016-05-01

    Eu3+ luminescence was studied in Ba2Mg(BO3)2 by selectively substituting at Mg site. The parent host Ba2Mg(BO3)2 and Ba2Mg0.9Eu0.05Li0.05(BO3)2 were synthesized by conventional solid state reaction method. Their isostructural nature was confirmed using powder X-ray diffraction technique. The photoluminescence excitation spectrum of Eu3+ exhibited a broad Eu3+sbnd O2- charge transfer band with a maximum at 253 nm along with other excitation transitions. The emission characteristics of Eu3+ were found to be excitation wavelength-dependent. The equally intense magnetic and electric dipole transitions for excitation under longer wavelengths showed the presence of Eu3+ at a site with non-inversion symmetry. Excitation using 253 nm resulted in the predominant magnetic dipole transition revealing Eu3+ at a site with inversion symmetry. The difference in the relative intensities of magnetic and electric dipole transitions originates from the change in symmetry around Eu3+ in Ba2Mg(BO3)2 under different excitations.

  14. Excitation-dependent variation in local symmetry in Ba2Mg(BO3)2 evidenced by Eu3+ luminescent structural probe

    NASA Astrophysics Data System (ADS)

    Jayakiruba, S.; Kumar, Gautam; Lakshminarasimhan, N.

    2016-05-01

    Eu3+ luminescence was studied in Ba2Mg(BO3)2 by selectively substituting at Mg site. The parent host Ba2Mg(BO3)2 and Ba2Mg0.9Eu0.05Li0.05(BO3)2 were synthesized by conventional solid state reaction method. Their isostructural nature was confirmed using powder X-ray diffraction technique. The photoluminescence excitation spectrum of Eu3+ exhibited a broad Eu3+sbnd O2- charge transfer band with a maximum at 253 nm along with other excitation transitions. The emission characteristics of Eu3+ were found to be excitation wavelength-dependent. The equally intense magnetic and electric dipole transitions for excitation under longer wavelengths showed the presence of Eu3+ at a site with non-inversion symmetry. Excitation using 253 nm resulted in the predominant magnetic dipole transition revealing Eu3+ at a site with inversion symmetry. The difference in the relative intensities of magnetic and electric dipole transitions originates from the change in symmetry around Eu3+ in Ba2Mg(BO3)2 under different excitations.

  15. Excited electronic states of limonene: A circular dichroism and photoelectron spectroscopy study of d-limonene

    NASA Astrophysics Data System (ADS)

    Brint, P.; Meshulam, Edna; Gedanken, Aharon

    1984-08-01

    The excited states of limonene are discussed in the light of vacuum-UV absorption, VUVCD and photoelectron spectroscopy measurements. Only one π → π* transition arising from the double bond of the ring is observed. The CD sign of the π → π* transition does not obey the octant rule formulated for chiral olefins.

  16. Generating Excitement: Build Your Own Generator to Study the Transfer of Energy

    ERIC Educational Resources Information Center

    Fletcher, Kurt; Rommel-Esham, Katie; Farthing, Dori; Sheldon, Amy

    2011-01-01

    The transfer of energy from one form to another can be difficult to understand. The electrical energy that turns on a lamp may come from the burning of coal, water falling at a hydroelectric plant, nuclear reactions, or gusts of wind caused by the uneven heating of the Earth. The authors have developed and tested an exciting hands-on activity to…

  17. Characterization of the excited states of DNA building blocks: a coupled cluster computational study.

    PubMed

    Benda, Zsuzsanna; Szalay, Péter G

    2016-09-14

    DNA building blocks consisting of up to four nucleobases are investigated using the EOM-CCSD and CC2-LR methods in two B-DNA-like arrangements of a poly-adenine:poly-thymine (poly-A:poly-T) system. Excitation energies and oscillator strengths are presented and the characteristics of the excited states are discussed. Excited states of single-stranded poly-A systems are highly delocalized, especially the spectroscopically bright states, where delocalization over up to four fragments can be observed. In the case of poly-T systems, the states are somewhat less delocalized, extending to maximally about three fragments. A single A:T Watson-Crick pair has highly localized states, while delocalization over base pairs can be observed for some excited states of the (A)2:(T)2 system, but intrastrand delocalization is more pronounced in this case, as well. As for the characteristics of the simulated UV absorption spectra, a significant decrease of intensity can be observed in the case of single strands with increasing chain length; this is due to the stacking interactions and is in accordance with previous results. On the other hand, the breaking of H-bonds between the two strands does not alter the spectral intensity considerably, it only causes a redshift of the absorption band, thus it is unable to explain the experimentally observed DNA hyperchromism on its own, and stacking interactions need to be considered for the description of this effect as well. PMID:27506397

  18. The study of excited oxygen molecule gas species production and quenching on thermal protection system materials

    NASA Technical Reports Server (NTRS)

    Nordine, Paul C.; Fujimoto, Gordon T.; Greene, Frank T.

    1987-01-01

    The detection of excited oxygen and ozone molecules formed by surface catalyzed oxygen atom recombination and reaction was investigated by laser induced fluorescence (LIF), molecular beam mass spectrometric (MBMS), and field ionization (FI) techniques. The experiment used partially dissociated oxygen flows from a microwave discharge at pressures in the range from 60 to 400 Pa or from an inductively coupled RF discharge at atmospheric pressure. The catalyst materials investigated were nickel and the reaction cured glass coating used for Space Shuttle reusable surface insulation tiles. Nonradiative loss processes for the laser excited states makes LIF detection of O2 difficult such that formation of excited oxygen molecules could not be detected in the flow from the microwave discharge or in the gaseous products of atom loss on nickel. MBMS experiments showed that ozone was a product of heterogeneous O atom loss on nickel and tile surfaces at low temperatures and that ozone is lost on these materials at elevated temperatures. FI was separately investigated as a method by which excited oxygen molecules may be conveniently detected. Partial O2 dissociation decreases the current produced by FI of the gas.

  19. Structural studies of ciliary components.

    PubMed

    Mizuno, Naoko; Taschner, Michael; Engel, Benjamin D; Lorentzen, Esben

    2012-09-14

    Cilia are organelles found on most eukaryotic cells, where they serve important functions in motility, sensory reception, and signaling. Recent advances in electron tomography have facilitated a number of ultrastructural studies of ciliary components that have significantly improved our knowledge of cilium architecture. These studies have produced nanometer-resolution structures of axonemal dynein complexes, microtubule doublets and triplets, basal bodies, radial spokes, and nexin complexes. In addition to these electron tomography studies, several recently published crystal structures provide insights into the architecture and mechanism of dynein as well as the centriolar protein SAS-6, important for establishing the 9-fold symmetry of centrioles. Ciliary assembly requires intraflagellar transport (IFT), a process that moves macromolecules between the tip of the cilium and the cell body. IFT relies on a large 20-subunit protein complex that is thought to mediate the contacts between ciliary motor and cargo proteins. Structural investigations of IFT complexes are starting to emerge, including the first three-dimensional models of IFT material in situ, revealing how IFT particles organize into larger train-like arrays, and the high-resolution structure of the IFT25/27 subcomplex. In this review, we cover recent advances in the structural and mechanistic understanding of ciliary components and IFT complexes. PMID:22683354

  20. Structural Studies of Ciliary Components

    PubMed Central

    Mizuno, Naoko; Taschner, Michael; Engel, Benjamin D.; Lorentzen, Esben

    2012-01-01

    Cilia are organelles found on most eukaryotic cells, where they serve important functions in motility, sensory reception, and signaling. Recent advances in electron tomography have facilitated a number of ultrastructural studies of ciliary components that have significantly improved our knowledge of cilium architecture. These studies have produced nanometer‐resolution structures of axonemal dynein complexes, microtubule doublets and triplets, basal bodies, radial spokes, and nexin complexes. In addition to these electron tomography studies, several recently published crystal structures provide insights into the architecture and mechanism of dynein as well as the centriolar protein SAS-6, important for establishing the 9-fold symmetry of centrioles. Ciliary assembly requires intraflagellar transport (IFT), a process that moves macromolecules between the tip of the cilium and the cell body. IFT relies on a large 20-subunit protein complex that is thought to mediate the contacts between ciliary motor and cargo proteins. Structural investigations of IFT complexes are starting to emerge, including the first three‐dimensional models of IFT material in situ, revealing how IFT particles organize into larger train-like arrays, and the high-resolution structure of the IFT25/27 subcomplex. In this review, we cover recent advances in the structural and mechanistic understanding of ciliary components and IFT complexes. PMID:22683354

  1. Electronic structure dynamics in a low bandgap polymer studied by time-resolved photoelectron spectroscopy.

    PubMed

    Cappel, Ute B; Plogmaker, Stefan; Terschlüsen, Joachim A; Leitner, Torsten; Johansson, Erik M J; Edvinsson, Tomas; Sandell, Anders; Karis, Olof; Siegbahn, Hans; Svensson, Svante; Mårtensson, Nils; Rensmo, Håkan; Söderström, Johan

    2016-08-01

    Means to measure the temporal evolution following a photo-excitation in conjugated polymers are a key for the understanding and optimization of their function in applications such as organic solar cells. In this paper we study the electronic structure dynamics by direct pump-probe measurements of the excited electrons in such materials. Specifically, we carried out a time-resolved photoelectron spectroscopy (TRPES) study of the polymer PCPDTBT by combining an extreme ultraviolet (XUV) high harmonic generation source with a time-of-flight spectrometer. After excitation to either the 1st excited state or to a higher excited state, we follow how the electronic structure develops and relaxes on the electron binding energy scale. Specifically, we follow a less than 50 fs relaxation of the higher exited state and a 10 times slower relaxation of the 1st excited state. We corroborate the results using DFT calculations. Our study demonstrates the power of TRPES for studying photo-excited electron energetics and dynamics of solar cell materials. PMID:27440450

  2. Ab initio calculations and supersonic jet studies on the geometry of 4-dimethylaminobenzonitrile (DMABN) and related compounds in the ground and excited state

    NASA Astrophysics Data System (ADS)

    Lommatzsch, Uwe; Brutschy, Bernhard

    1998-08-01

    Ab initio calculations at different levels of theory were performed to elucidate the geometry of 4-dimethylaminobenzonitrile (DMABN), 4-aminobenzonitrile (ABN) and 1-ethyl-2,3-dihydro-indole-5-carbonitrile (EIN) in the ground and first excited singlet state. The quantum chemical results are compared with experimental vibrational frequencies observed in the resonant two-photon ionization and dispersed emission spectra of the jet-cooled molecules and by simulating rotational band contours of vibronic transitions. The theoretical and experimental results are in good overall agreement. ABN is planar in the first electronically excited state, while the dimethylamino group of DMABN is twisted by 22° out of the phenyl ring plane. In the ground state the phenyl ring of EIN is distorted due to the five-membered ring. In the excited singlet state a further increase of this distortion of the molecular geometry takes place. The different geometries and the accompanying different electronic structures of these molecules may reflect the different photophysical behaviour in solution, which has been studied over the past three decades.

  3. A Study in Structured Discussion.

    ERIC Educational Resources Information Center

    Gutzmer, Willard Ernest

    This study tested the hypothesis that group interaction skill and useful learning occur in a discussion group which is academically structured. A class procedure involving a cognitive map, member skills and roles, and group etiquette was incorporated into a class ("Education and the Contemporary Scene," Fall Quarter, 1968) at the University of…

  4. The discrepant kinematics of recombination and collisionally-excited in NGC7009 as a function of ionization structure

    NASA Astrophysics Data System (ADS)

    Arrieta, A.; Richer, M.; Georgiev, L. N.; Torres-Peimbert, S.

    2014-04-01

    We present spatially- and velocity-resolved echelle spectroscopy for NGC 7009 obtained with the UVES spectrograph at the ESO VLT. We construct position-velocity maps for recombination, fluorescence, charge transfer, and collisionally excited lines. We find a plasma component emitting in the C II, N II, O II, and Ne II recombination lines whose kinematics are discrepant: They are incompatible with the ionization structure derived from all other evidence and the kinematics derived from all of these lines are unexpectedly very similar. We find direct evidence for a recombination contribution to [N II] 5755. Once taken into account, the electron temperatures from [N II], [O III], and [Ne III] agree at a given position and velocity, even though both the [N II] and [O III] temperatures clearly vary. The electron densities derived from [O II] and [Ar IV] are consistent with direct imaging and the distribution of hydrogen emission. The kinematics of the C II, N II, O II, and Ne II lines does not coincide with the kinematics of the [O III] and [Ne III] forbidden emission, indicating that there is an additional plasma component to the recombination emission that arises from a different volume from that giving rise to the forbidden emission from the parent ions within NGC 7009. Thus, the chemical abundances derived from either type of line are correct only for the plasma component from which they arise. Apart from [N II] 5755, we find no anomaly with the forbidden lines usually used to determine chemical abundances in ionized nebulae, so the abundances derived from them should be reliable for the medium from which they arise.

  5. Rotational and vibrational dynamics in the excited electronic state of deprotonated and protonated fluorescein studied by time-resolved photofragmentation in an ion trap

    PubMed Central

    Imanbaew, Dimitri; Gelin, Maxim F.; Riehn, Christoph

    2016-01-01

    Excited state dynamics of deprotonated and protonated fluorescein were investigated by polarization dependent femtosecond time-resolved pump-probe photofragmentation in a 3D ion trap. Transients of deprotonated fluorescein exhibit vibrational wavepacket dynamics with weak polarization dependence. Transients of protonated fluorescein show only effects of molecular alignment and rotational dephasing. The time resolved rotational anisotropy of protonated fluorescein is simulated by the calculated orientational correlation function. The observed differences between deprotonated and protonated fluorescein are ascribed to their different higher lying electronically excited states and corresponding structures. This is partially supported by time-dependent density functional theory calculations of the excited state structures. PMID:27376104

  6. Rotational and vibrational dynamics in the excited electronic state of deprotonated and protonated fluorescein studied by time-resolved photofragmentation in an ion trap.

    PubMed

    Imanbaew, Dimitri; Gelin, Maxim F; Riehn, Christoph

    2016-07-01

    Excited state dynamics of deprotonated and protonated fluorescein were investigated by polarization dependent femtosecond time-resolved pump-probe photofragmentation in a 3D ion trap. Transients of deprotonated fluorescein exhibit vibrational wavepacket dynamics with weak polarization dependence. Transients of protonated fluorescein show only effects of molecular alignment and rotational dephasing. The time resolved rotational anisotropy of protonated fluorescein is simulated by the calculated orientational correlation function. The observed differences between deprotonated and protonated fluorescein are ascribed to their different higher lying electronically excited states and corresponding structures. This is partially supported by time-dependent density functional theory calculations of the excited state structures. PMID:27376104

  7. Excited state non-adiabatic dynamics of pyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study

    SciTech Connect

    Wu, Guorong; Neville, Simon P.; Worth, Graham A.; Schalk, Oliver; Sekikawa, Taro; Ashfold, Michael N. R.; Stolow, Albert

    2015-02-21

    The dynamics of pyrrole excited at wavelengths in the range 242-217 nm are studied using a combination of time-resolved photoelectron spectroscopy and wavepacket propagations performed using the multi-configurational time-dependent Hartree method. Excitation close to the origin of pyrrole’s electronic spectrum, at 242 and 236 nm, is found to result in an ultrafast decay of the system from the ionization window on a single timescale of less than 20 fs. This behaviour is explained fully by assuming the system to be excited to the A{sub 2}(πσ{sup ∗}) state, in accord with previous experimental and theoretical studies. Excitation at shorter wavelengths has previously been assumed to result predominantly in population of the bright A{sub 1}(ππ{sup ∗}) and B{sub 2}(ππ{sup ∗}) states. We here present time-resolved photoelectron spectra at a pump wavelength of 217 nm alongside detailed quantum dynamics calculations that, together with a recent reinterpretation of pyrrole’s electronic spectrum [S. P. Neville and G. A. Worth, J. Chem. Phys. 140, 034317 (2014)], suggest that population of the B{sub 1}(πσ{sup ∗}) state (hitherto assumed to be optically dark) may occur directly when pyrrole is excited at energies in the near UV part of its electronic spectrum. The B{sub 1}(πσ{sup ∗}) state is found to decay on a timescale of less than 20 fs by both N-H dissociation and internal conversion to the A{sub 2}(πσ{sup ∗}) state.

  8. Studies of N* Structure from the CLAS Meson Electroproduction Data

    SciTech Connect

    Mokeev, Viktor I.; Aznauryan, Inna G.

    2014-01-01

    The transition {gamma}{sub v}pN amplitudes (electrocouplings) for prominent excited nucleon states obtained in a wide area of photon virtualities offer valuable information for the exploration of the N structure at different distances and allow us to access the complex dynamics of non-perturbative strong interaction. The current status in the studies of {gamma}{sub v}pN electrocouplings from the data on exclusive meson electroproduction off protons measured with the CLAS detector at Jefferson Lab is presented. The impact of these results on exploration of the N structure is discussed.

  9. (ggr, 2ggr) studies on doubly excited states of molecular hydrogen

    NASA Astrophysics Data System (ADS)

    Odagiri, Takeshi; Murata, Makoto; Kato, Masahiro; Kouchi, Noriyuki

    2004-10-01

    The doubly differential cross sections for the emission of two Lyman-agr photons in photoexcitation of H2 have been measured as a function of incident photon energy in the range of 30-44 eV with a photon-photon coincidence technique. A cross section curve that is free from ionization and thus is attributed entirely to the doubly excited states of H2 has been obtained for the first time. A simple theoretical calculation based on the reflection approximation and semiclassical treatment of the decay dynamics in the Q21Pgru(1) state of H2 has reproduced well the experimental cross section curve. It has been shown that this method, the (ggr, 2ggr) method, is an excellent tool for investigating spectroscopy and dynamics of doubly or multiply excited molecules.

  10. Two-Photon Excitation Microscopy for the Study of Living Cells and Tissues

    PubMed Central

    Benninger, Richard K.P.; Piston, David W.

    2013-01-01

    Two-photon excitation microscopy is an alternative to confocal microscopy that provides advantages for three-dimensional and deep tissue imaging. This unit will describe the basic physical principles behind two-photon excitation and discuss the advantages and limitations of its use in laser-scanning microscopy. The principal advantages of two-photon microscopy are reduced phototoxicity, increased imaging depth, and the ability to initiate highly localized photochemistry in thick samples. Practical considerations for the application of two-photon microscopy will then be discussed, including recent technological advances. This unit will conclude with some recent applications of two-photon microscopy that highlight the key advantages over confocal microscopy and the types of experiments which would benefit most from its application. PMID:23728746

  11. Study of intermediates from transition metal excited-state electron-transfer reactions

    SciTech Connect

    Hoffman, M.Z.

    1991-12-31

    During this period, conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used for the characterization of the intermediates that are involved in transition metal excited-state electron-transfer reactions. The intermediates of interest were the excited states of Ru(II) and Cr(III) photosensitizers, their reduced forms, and the species formed in the reactions of redox quenchers and electron-transfer agents. Of particular concern has been 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.

  12. Quantum dynamics study of fulvene double bond photoisomerization: The role of intramolecular vibrational energy redistribution and excitation energy

    SciTech Connect

    Blancafort, Lluis; Gatti, Fabien; Meyer, Hans-Dieter

    2011-10-07

    The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies.

  13. Microwave excitation for thermographic NDE: An experimental study and some theoretical evaluations

    SciTech Connect

    d`Ambrosio, G.; Massa, R.; Migliore, M.D.; Cavaccini, G.; Ciliberto, A.; Sabatino, C.

    1995-04-01

    The theme of microwave heating for thermographic nondestructive evaluation has been addressed experimentally. Slabs and sandwiches, made of Kevlar or fiberglass, containing artificial defects were heated by means of cavity applicators fed by 2.45 GHz high microwave power (600--1,700 W). The results, compared with the obtained using X-ray, ultrasound, and infrared excited thermography, showed the effectiveness of this technique. Some simple theoretical modeling has been also developed.

  14. Experimental study of the quasifission, fusion-fission, and de-excitation of Cf compound nuclei

    NASA Astrophysics Data System (ADS)

    Khuyagbaatar, J.; Hinde, D. J.; Carter, I. P.; Dasgupta, M.; Düllmann, Ch. E.; Evers, M.; Luong, D. H.; du Rietz, R.; Wakhle, A.; Williams, E.; Yakushev, A.

    2015-05-01

    Background: The fusion-evaporation reaction at energies around the Coulomb barrier is presently the only way to produce the heaviest elements. However, formation of evaporation residues is strongly hindered due to the competing fusion-fission and quasifission processes. Presently, a full understanding of these processes and their relationships has not been reached. Purpose: This work aims to use new fission measurements and existing evaporation residue and fission excitation function data for reactions forming Cf isotopes to investigate the dependence of the quasifission probability and characteristics on the identities of the two colliding nuclei in heavy element formation reactions. Method: Using the Australian National University's 14UD electrostatic accelerator and CUBE detector array, fission fragments from the 12C +235U , 34S +208Pb , 36S +206Pb , 36S +208Pb , and 44Ca +198Pt reactions were measured. Mass and angle distributions of fission fragments were extracted and compared to investigate the presence and characteristics of quasifission. Results: Mass-angle-correlated fission fragments were observed for the 44Ca +198Pt reaction; no correlation was observed in the other reactions measured. Flat-topped fission-fragment mass distributions were observed for 12C +235U at compound-nucleus excitation energies from 28 to 52 MeV. Less pronounced flat-topped distributions were observed, with very similar shapes, for all three sulfur-induced reactions at excitation energies lower than 45 MeV. Conclusions: A high probability of long-time-scale quasifission seems necessary to explain both the fission and evaporation residue data for the 34S +208Pb and 36S +206Pb reactions. Flat-topped mass distributions observed for 12C - and 34 ,36S -induced reactions are suggested to originate both from late-chance fusion-fission at low excitation energies and the persistence of shell effects at the higher energies associated with quasifission.

  15. Case study of piezoelectric flexible thin films in pulse excited electromechanical transducers

    NASA Astrophysics Data System (ADS)

    Salamon, Natalia; Gozdur, Roman; Turczyński, Marcin; Lisik, Zbigniew; Soupremanien, Ulrich; Ollier, Emmanuel; Monfray, Stéphane; Skotnicki, Thomas

    2014-08-01

    The paper presents the examination of modern flexible piezoelectric thin films made of PVDF (polyvinylidene difluoride) in terms of their application in electromechanical transducers, a brief overview of available piezoelectric materials and energy harvesting devices based on piezoelectric. In order to assess the usefulness of these films from the perspective of described devices, the energy efficiency coefficient determined under the pulse excitation conditions was taken into account. Normalized volumetric efficiency ratio allows to evaluate the commercially available flexible piezoelectric films.

  16. Acoustically excited heated jets. 1: Internal excitation

    NASA Technical Reports Server (NTRS)

    Lepicovsky, J.; Ahuja, K. K.; Brown, W. H.; Salikuddin, M.; Morris, P. J.

    1988-01-01

    The effects of relatively strong upstream acoustic excitation on the mixing of heated jets with the surrounding air are investigated. To determine the extent of the available information on experiments and theories dealing with acoustically excited heated jets, an extensive literature survey was carried out. The experimental program consisted of flow visualization and flowfield velocity and temperature measurements for a broad range of jet operating and flow excitation conditions. A 50.8-mm-diam nozzle was used for this purpose. Parallel to the experimental study, an existing theoretical model of excited jets was refined to include the region downstream of the jet potential core. Excellent agreement was found between theory and experiment in moderately heated jets. However, the theory has not yet been confirmed for highly heated jets. It was found that the sensitivity of heated jets to upstream acoustic excitation varies strongly with the jet operating conditions and that the threshold excitation level increases with increasing jet temperature. Furthermore, the preferential Strouhal number is found not to change significantly with a change of the jet operating conditions. Finally, the effects of the nozzle exit boundary layer thickness appear to be similar for both heated and unheated jets at low Mach numbers.

  17. Motor cortical excitability in peritoneal dialysis: a single-pulse TMS study.

    PubMed

    Matsumoto, Hideyuki; Saito, Katsunori; Konoma, Yuko; Okabe, Shingo; Ugawa, Yoshikazu; Ishibashi, Yoshitaka

    2015-01-01

    The aim of this paper is to investigate cortical excitability in patients with end-stage renal disease receiving peritoneal dialysis (PD) without any symptoms suggestive of uremic encephalopathy. We performed transcranial magnetic stimulation for 52 PD patients and 28 normal subjects. We compared the active motor threshold (AMT), resting motor threshold (RMT), root latency, central motor conduction time (CMCT), and cortical silent period (CSP) in PD patients to those in normal subjects. AMT, RMT, CMCT, and CSP were not significantly different between PD patients and normal subjects. However, root latency was significantly prolonged in PD patients compared to normal subjects. The root latency correlated linearly with HbA1c or duration of PD in the patients. The results suggest that the corticospinal tract and the cortical and spinal excitabilities are preserved but the peripheral nerves are disturbed in PD patients. The severity of peripheral neuropathy corresponds to the severity of DM and the duration of PD. We uncovered no evidence suggestive of any subclinical abnormality of the motor cortical excitability in PD patients. PMID:25376928

  18. Spectroscopic Study and Astronomical Detection of Vibrationally Excited n-PROPYL Cyanide

    NASA Astrophysics Data System (ADS)

    Müller, Holger S. P.; Wehres, Nadine; Wilkins, Olivia H.; Lewen, Frank; Schlemmer, Stephan; Walters, Adam; Vicente, Rémi; Liu, Delong; Garrod, Robin T.; Belloche, Arnaud; Menten, Karl M.

    2016-06-01

    We have obtained ALMA data of Sagittarius (Sgr for short) B2(N) between 84.0 and 114.4 GHz in its Early Science Cycles 0 and 1. We have focused our analyses on the northern, secondary hot molecular core Sgr B2(N2) because of the smaller line widths. The survey led to the first detection of a branched alkyl compound, iso-propyl cyanide, i-C_3H_7CN, in space besides the ˜2.5 times more abundant straight chain isomer n-propyl cyanide, a molecule which we had detected in our IRAM 30 m survey. We suspected to be able to detect n-propyl cyanide in vibrationally excited states in our ALMA data. We have recorded laboratory rotational spectra of this molecule in three large frequency regions and identified several excited vibrational states. The analyses of these spectra have focused on the 36 to 70 GHz and 89 to 127 GHz regions and on the four lowest excited vibrational states of both the lower lying gauche- and the slightly higher lying anti-conformer for which rotational constants had been published. We will present results of our laboratory spectroscopic investigations and will report on the detection of these states toward Sgr B2(N2). A. Belloche et al., Science 345 (2014) 1584. A. Belloche et al., A&A 499 (2009) 215. E. Hirota, J. Chem. Phys. 37 (1962) 2918.

  19. Corticospinal excitability is specifically modulated by motor imagery: a magnetic stimulation study.

    PubMed

    Fadiga, L; Buccino, G; Craighero, L; Fogassi, L; Gallese, V; Pavesi, G

    1999-02-01

    Transcranial magnetic stimulation (TMS) was used to investigate whether the excitability of the corticospinal system is selectively affected by motor imagery. To this purpose, we performed two experiments. In the first one we recorded motor evoked potentials from right hand and arm muscles during mental simulation of flexion/extension movements of both distal and proximal joints. In the second experiment we applied magnetic stimulation to the right and the left motor cortex of subjects while they were imagining opening or closing their right or their left hand. Motor evoked potentials (MEPs) were recorded from a hand muscle contralateral to the stimulated cortex. The results demonstrated that the excitability pattern during motor imagery dynamically mimics that occurring during movement execution. In addition, while magnetic stimulation of the left motor cortex revealed increased corticospinal excitability when subjects imagined ipsilateral as well as contralateral hand movements, the stimulation of the right motor cortex revealed a facilitatory effect induced by imagery of contralateral hand movements only. In conclusion, motor imagery is a high level process, which, however, manifests itself in the activation of those same cortical circuits that are normally involved in movement execution.

  20. Folding of 8-17 deoxyribozyme studied by three-color alternating-laser excitation of single molecules.

    PubMed

    Lee, Nam Ki; Koh, Hye Ran; Han, Kyu Young; Kim, Seong Keun

    2007-12-19

    The folding of 8-17 deoxyribozyme was investigated by three-color alternating-laser excitation (3c-ALEX), a new single-molecule fluorescence resonance energy transfer (FRET) method we recently developed. Since 3c-ALEX has the capability of simultaneously sorting fluorescent molecules based on their labeling status and monitoring three interprobe distances of a biomolecule by employing three-color FRET, it is an ideal tool to study folding of multibranched molecules. The 8-17 deoxyribozyme, a DNA enzyme that cleaves a specific RNA substrate, is a good model system for a multibranched molecule, since it has the structure of a three-way DNA junction with a bulge. Labeling all three branches of the 8-17 with different fluorescent probes, we studied its [Mg2+]-dependent folding in a Na+ buffer solution. With the stoichiometric sorting capability of 3c-ALEX, we first selected only the triply labeled 8-17 in a solution of all heterogeneous mixtures and then simultaneously measured all three interprobe distances of the selected species. Our results show that the 8-17 folds into a pyramidal form upon increasing [Mg2+], in a similar way with [Zn2+] as found in an earlier study conducted at the ensemble level. The apparent dissociation constant of Mg2+ was more than 100 times larger than that of Zn2+ and showed considerable variance with buffer concentration. No clear sign of two-step folding was observed for Mg2+, in contrast to the case of Zn2+. Compared with the hammerhead ribozyme, the 8-17 was found to require 10 times higher [Mg2+] to undergo folding. By comparison with the folding of several inactive 8-17 analogues, we found that the two conserved sequences (A and G) of the triad loop of the shortest branch are critical elements for folding, especially for the folding at low [Mg2+]. Our results suggest that the role of the stem loop is to provide a scaffold for the two bases to be properly positioned for the necessary interaction and that the two bases are directly

  1. Nucleon Resonance Structure Studies via Exclusive KY Electroproduction

    NASA Astrophysics Data System (ADS)

    Carman, Daniel S.

    2016-10-01

    Studying the structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of N^* states in the mass range below 1.8 GeV have been determined from analyses of CLAS π N, η N, and π π N data. This work has made it clear that consistent results from independent analyses of several 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 π π N channel instead of π N. Data from the KY channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying N^* states against those determined from the π N and π π {N} channels. A program to study excited N^* state structure in both non-strange and strange exclusive electroproduction channels using CLAS12 will measure differential cross sections and polarization observables to be used as input to extract the γ _v{it{NN}}^* electrocoupling amplitudes for the most prominent N^* states in the range of invariant energy W up 3 GeV in the virtually unexplored domain of momentum transfers Q^2 up to 12 GeV^2.

  2. Nucleon resonance structure studies via exclusive KY electroproduction

    DOE PAGES

    Carman, Daniel S.

    2016-06-16

    Studying the structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings ofmore » $N^*$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $$\\pi N$$, $$\\eta N$$, and $$\\pi \\pi N$$ data. This work has made it clear that consistent results from independent analyses of several 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 $$\\pi \\pi N$$ channel instead of $$\\pi N$$. Data from the $KY$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^*$ states against those determined from the $$\\pi N$$ and $$\\pi \\pi N$$ channels. Lastly, a program to study excited $N^*$ state structure in both non-strange and strange exclusive electroproduction channels using CLAS12 will measure differential cross sections and polarization observables to be used as input to extract the $$\\gamma_vNN^*$$ electrocoupling amplitudes for the most prominent $N^*$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^2$ up to 12~GeV$^2$.« less

  3. Nucleon Resonance Structure Studies via Exclusive KY Electroproduction

    NASA Astrophysics Data System (ADS)

    Carman, Daniel S.

    2016-06-01

    Studying the structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of N^* states in the mass range below 1.8 GeV have been determined from analyses of CLAS π N , η N , and π π N data. This work has made it clear that consistent results from independent analyses of several 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 π π N channel instead of π N . Data from the KY channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying N^* states against those determined from the π N and π π {N} channels. A program to study excited N^* state structure in both non-strange and strange exclusive electroproduction channels using CLAS12 will measure differential cross sections and polarization observables to be used as input to extract the γ _v{{NN}}^* electrocoupling amplitudes for the most prominent N^* states in the range of invariant energy W up 3 GeV in the virtually unexplored domain of momentum transfers Q^2 up to 12 GeV^2.

  4. Label-free cellular structure imaging with 82 nm lateral resolution using an electron-beam excitation-assisted optical microscope.

    PubMed

    Fukuta, Masahiro; Masuda, Yuriko; Inami, Wataru; Kawata, Yoshimasa

    2016-07-25

    We present label-free and high spatial-resolution imaging for specific cellular structures using an electron-beam excitation-assisted optical microscope (EXA microscope). Images of the actin filament and mitochondria of stained HeLa cells, obtained by fluorescence and EXA microscopy, were compared to identify cellular structures. Based on these results, we demonstrated the feasibility of identifying label-free cellular structures at a spatial resolution of 82 nm. Using numerical analysis, we calculated the imaging depth region and determined the spot size of a cathodoluminescent (CL) light source to be 83 nm at the membrane surface.

  5. A structural study of gallstones.

    PubMed Central

    Bills, P M; Lewis, D

    1975-01-01

    A number of gallstones have been studied using methods which have not previously been applied to gallstones. In particular, the use of scanning electron microscopy and micro-x-radiography have allowed detailed observations to be made on the structure of the stones and the distribution of the various components within the stones. Large differences in structure have been shown to exist between stones having similar overall chemical compositions. In cholesterol gallstones containing calcium carbonate the crystalline nature, distribution and method of deposition of the calcium carbonate was studied and was found to vary from stone to stone. Evidence was found for the presence of fibrous material in the centre of many stones and it is possible that this material acted as a nucleus for the deposition of the other stone components. Images Fig 1 Fig 2 Fig 3 Fig 4 Fig 5 PMID:1183859

  6. Case study of small harbor excitation under storm and tsunami conditions

    NASA Astrophysics Data System (ADS)

    Synolakis, Costas; Maravelakis, Nikos; Kalligeris, Nikos; Skanavis, Vassilios; Kanoglu, Utku; Yalciner, Ahmet; Lynett, Pat

    2016-04-01

    Simultaneous nearshore and interior-to-ports wave and current measurements for small ports are not common, and few, if any, benchmarking cases at sufficient resolution exist to help validate numerical model of intermediate waves, or even long waves. The wave conditions inside the old Venetian harbor of Chania, Greece and offshore were measured and studied from 2012 to 2015. The construction of this harbor began in the 14th century, and since then, its layout has been modified to adapt to different social and to economic conditions. It is divided into a western and an eastern basin. The eastern basin is used by recreational vessels and fishing boats throughout the year. The western basin has an exposed entrance to the north, and it is essentially functional half of the year, because of the severe overtopping and flooding that occur during the northern winter storms. Our work is motivated by the necessity to protect the monument from severe winter storm conditions and allow safe mooring and all other recreational activities that take place in the exposed western basin. Two earlier studies had proposed the construction of a low crested breakwater near the harbor entrance. The first design has been partially constructed, while the second never materialized. The main disadvantage of both studies was the lack of any wave field measurements. At the same time, second order or complimentary phenomena such as harbor resonance had not been considered. To address the lack of field data, the offshore wave climate has been monitored since October 2012 using an AWAC 600kHz instrument, deployed at 23m depth. The response of the western and eastern basins of the harbor was measured with a TWR-2050 (deployed at 5.5m depth) and an RBRDuet T.D./wave (deployed at 2m depth) pressure gauges respectively. Significant wave heights ranging up to 5.8 m with significant periods of up to 10 sec were measured. The harbor pressure gauges are now being re-deployed in other locations to collect

  7. Aromatic Lateral Substituents Influence the Excitation Energies of Hexaaza Lanthanide Macrocyclic Complexes: A Wave Function Theory and Density Functional Study.

    PubMed

    Rabanal-León, Walter A; Murillo-López, Juliana A; Páez-Hernández, Dayán; Arratia-Pérez, Ramiro

    2015-09-24

    The high interest in lanthanide chemistry, and particularly in their luminescence, has been encouraged by the need of understanding the lanthanide chemical coordination and how the design of new luminescent materials can be affected by this. This work is focused on the understanding of the electronic structure, bonding nature, and optical properties of a set of lanthanide hexaaza macrocyclic complexes, which can lead to potential optical applications. Here we found that the DFT ground state of the open-shell complexes are mainly characterized by the manifold of low lying f states, having small HOMO-LUMO energy gaps. The results obtained from the wave function theory calculations (SO-RASSI) put on evidence the multiconfigurational character of their ground state and it is observed that the large spin-orbit coupling and the weak crystal field produce a strong mix of the ground and the excited states. The electron localization function (ELF) and the energy decomposition analysis (EDA) support the idea of a dative interaction between the macrocyclic ligand and the lanthanide center for all the studied systems; noting that, this interaction has a covalent character, where the d-orbital participation is evidenced from NBO analysis, leaving the f shell completely noninteracting in the chemical bonding. From the optical part we observed in all cases the characteristic intraligand (IL) (π-π*) and ligand to metal charge-transfer (LMCT) bands that are present in the ultraviolet and visible regions, and for the open-shell complexes we found the inherent f-f electronic transitions on the visible and near-infrared region. PMID:26325624

  8. Deuterium isotope effect on femtosecond solvation dynamics in an ionic liquid microemulsion: an excitation wavelength dependence study.

    PubMed

    Sasmal, Dibyendu Kumar; Mojumdar, Supratik Sen; Adhikari, Aniruddha; Bhattacharyya, Kankan

    2010-04-01

    The deuterium isotope effect on the solvation dynamics and the anisotropy decay of coumarin 480 (C480) in a room temperature ionic liquid (RTIL) microemulsion is studied by femtosecond up-conversion. The microemulsion consists of the RTIL 1-pentyl-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF(4)]) in triton X-100 (TX-100)/benzene. Replacement of H(2)O by D(2)O in the microemulsion causes retardation of solvation dynamics. The average solvation time of C480 (tau(s)) in RTIL microemulsion with 5 wt % D(2)O is approximately 1.5-1.7 times slower compared to that in the H(2)O containing RTIL microemulsion. This suggests that the main species in the microemulsion responsible for solvation is the water molecules. In both D(2)O and H(2)O containing RTIL microemulsion, the solvation dynamics exhibits marked dependence on the excitation wavelength (lambda(ex)) and becomes about 15 times faster as lambda(ex) increases from 375 to 435 nm. This is ascribed to the structural heterogeneity in the RTIL microemulsion. For lambda(ex) = 375 nm, the region near the TX-100 surfactant is probed where bound water molecules cause slow solvation dynamics. At 435 nm, the RTIL pool is selected where the water molecules are more mobile and hence gives rise to faster solvation. The average time constant of anisotropy decay shows opposite dependence on lambda(ex) and increases about 2.5-fold from 180 ps at lambda(ex) = 375 nm to 500 ps at lambda(ex) = 435 nm for D(2)O containing RTIL microemulsion. The slower anisotropy decay at lambda(ex) = 435 nm is ascribed to the higher viscosity of RTIL which causes greater friction at the core. PMID:20235504

  9. Excitation of the fundamental mode of the coaxial plasma slow-wave structure in a high-current REB Cherenkov plasma amplifier

    SciTech Connect

    Selivanov, I.A.; Shkvarunets, A.G.

    1992-07-01

    An experimental study has been carried out of the dispersion properties of a circular waveguide containing a hollow magnetized plasma. Such a plasma configuration can be used as a slow-wave structure in a Cherenkov microwave amplifier driven by a high-current relativistic electron beam. The radius of the external metal container was 1.8 cm, the mean radius of the plasma tube was 0.9 cm, and the thickness of the tube was 0.08 cm. The plasma density varied from 2{center_dot}10{sup 11} to 10{sup 14} cm{sup {minus}3}. The propagation of a monochromatic microwave signal with wavelength {lambda}{sub 0} = 2.42 cm and low power (12 W) through the coaxial plasma-filled waveguide was studied over a wide range of external magnetic field strengths. The threshold values of the magnetic field and plasma density above which the effective excitation and propagation of the basic plasma mode (the slow TM{sub 01} mode) have been found. These values are 0.6 T and 2{center_dot}10{sup 13} cm{sup {minus}3}, respectively. High-power microwave radiation (150 kW) has been transported through a plasma coax of length 30 cm in the regime in which the plasma density and external field strength exceed the threshold values. The experimental results are compared with analytical expressions and a numerical calculation performed for a magnetized plasma-filled waveguide. 11 refs., 6 figs.

  10. Acoustics of Excited Jets: A Historical Perspective

    NASA Technical Reports Server (NTRS)

    Brown, Cliffard A.

    2005-01-01

    The idea that a jet may be excited by external forcing is not new. The first published demonstration of a jet responding to external pressure waves occurred in the mid-1800's. It was not, however, until the 1950's, with the advent of commercial jet aircraft, that interest in the subject greatly increased. Researchers first used excited jets to study the structure of the jet and attempt to determine the nature of the noise sources. The jet actuators of the time limited the range (Reynolds and Mach numbers) of jets that could be excited. As the actuators improved, more realistic jets could be studied. This has led to a better understanding of how jet excitation may be used not only as a research tool to understand the flow properties and noise generation process, but also as a method to control jet noise.

  11. Electrical phosphenes: on the influence of conductivity inhomogeneities and small-scale structures of the orbita on the current density threshold of excitation.

    PubMed

    Lindenblatt, G; Silny, J

    2002-05-01

    Electrical and magnetic phosphenes, perceptions of light as a result of non-adequate stimulation of the eye by electrical current or magnetic induction, respectively, are one of the cornerstones to justify limit values for extreme low-frequency fields specified by statutory regulations. However, the mechanism and place of action, as well as the excitation threshold, remain unknown until now. We suggest that the origin of phosphene excitation is the synaptic layer of the eye. The current density threshold value for electrical phosphene excitation was numerically quantified for this area on the basis of a detailed geometrical model in original submillimetre resolution and specifically measured conductivities in the LF range. The threshold values found were 1.8 A m-2 at 60 Hz and 0.3 A m-2 at 25 Hz. These values are comparable with values of other excitable tissues. It has been shown that the current density threshold for phosphene generation depends on small-scale structures not taken into account by previous models. PMID:12195984

  12. Characterizing the Structures, Spectra, and Energy Landscapes Involved in the Excited-State Proton Transfer Process of Red Fluorescent Protein LSSmKate1.

    PubMed

    Chen, Fasheng; Zeng, Qiao; Zhuang, Wei; Liang, WanZhen

    2016-09-22

    By applying molecular dynamics (MD) simulations and quantum chemical calculations, we have characterized the states and processes involved in the excited-state proton transfer (ESPT) of LSSmKate1. MD simulations identify two stable structures in the electronic ground state of LSSmKate1, one with a protonated chromophore and the other with a deprotonated chromophore, thus leading to two separate low-energy absorption maxima with a large energy spacing, as observed in the calculated and experimentally measured absorption spectra. Proton transfer is induced by electronic excitation. When LSSmKate1 is excited, the electrons in the chromophore are transferred from the phenol ring to the N-acylimine moiety; the acidity of a phenolic hydroxyl group is thus enhanced. The calculated potential energy curves (PECs) exhibit energetic feasibility in the generation of the fluorescent species in LSSmKate1, and the exact agreement between the calculated and experimentally measured values of the large Stokes shift further provides solid theoretical evidence for the ESPT process taking place in photoexcited LSSmKate1. The molecular environments play a significant role in the geometries and absorption/emission energies of the chromophores. Overall, TD-ωB97X-D/molecular mechanics (MM) provides a better description of the optical properties of LSSmKate1 than TD-B3LYP/MM, although it always overestimates the excitation energies. PMID:27581731

  13. Characterizing the Structures, Spectra, and Energy Landscapes Involved in the Excited-State Proton Transfer Process of Red Fluorescent Protein LSSmKate1.

    PubMed

    Chen, Fasheng; Zeng, Qiao; Zhuang, Wei; Liang, WanZhen

    2016-09-22

    By applying molecular dynamics (MD) simulations and quantum chemical calculations, we have characterized the states and processes involved in the excited-state proton transfer (ESPT) of LSSmKate1. MD simulations identify two stable structures in the electronic ground state of LSSmKate1, one with a protonated chromophore and the other with a deprotonated chromophore, thus leading to two separate low-energy absorption maxima with a large energy spacing, as observed in the calculated and experimentally measured absorption spectra. Proton transfer is induced by electronic excitation. When LSSmKate1 is excited, the electrons in the chromophore are transferred from the phenol ring to the N-acylimine moiety; the acidity of a phenolic hydroxyl group is thus enhanced. The calculated potential energy curves (PECs) exhibit energetic feasibility in the generation of the fluorescent species in LSSmKate1, and the exact agreement between the calculated and experimentally measured values of the large Stokes shift further provides solid theoretical evidence for the ESPT process taking place in photoexcited LSSmKate1. The molecular environments play a significant role in the geometries and absorption/emission energies of the chromophores. Overall, TD-ωB97X-D/molecular mechanics (MM) provides a better description of the optical properties of LSSmKate1 than TD-B3LYP/MM, although it always overestimates the excitation energies.

  14. Resonant inelastic x-ray scattering study of charge excitations in La(2)CuO(4).

    PubMed

    Kim, Y J; Hill, J P; Burns, C A; Wakimoto, S; Birgeneau, R J; Casa, D; Gog, T; Venkataraman, C T

    2002-10-21

    We report a resonant inelastic x-ray scattering study of the dispersion relations of charge-transfer excitations in insulating La(2)CuO(4).. These data reveal two peaks, both of which show two-dimensional characteristics. The lowest energy excitation has a gap energy of approximately 2.2 eV at the zone enter, and a dispersion of approximately 1 eV. The spectral weight of this mode becomes dramatically smaller around (pi, pi). The second peak shows a smaller dispersion ( approximately 0.5 eV) with a zone-center energy of approximately 3.9 eV. We argue that these are both highly dispersive exciton modes damped by the presence of the electron-hole continuum.

  15. A theoretical study of the excited states of AmO2n +, n =1,2,3

    NASA Astrophysics Data System (ADS)

    Notter, François-Paul; Dubillard, Sébastien; Bolvin, Hélène

    2008-04-01

    The ground and excited states of the AmO2+, AmO22+, and AmO23+ ions have been studied using the four-component configuration interaction singles doubles, spin-orbit complete active space self-consistent field, and spin-orbit complete active space-order perturbation theory methods. The roles of scalar relativistic effects and spin-orbit coupling are analyzed; results with different methods are carefully compared by a precise analysis of the wave functions. A molecular spinor diagram is used in relation to the four-component calculations while a ligand field model is used for the two-step method. States with the same number of electrons in the four nonbonding orbitals are in very good agreement with the two methods while ligand field and charge transfer states do not have the same excitation energies.

  16. Study of 12C excited states decaying into three α particles using the thick target inverse kinematic technique

    NASA Astrophysics Data System (ADS)

    Barbui, M.; Hagel, K.; Gauthier, J.; Wuenschel, S.; de Souza, R. T.; Hudan, S.; Fang, D.; Goldberg, V. Z.; Zheng, H.; Giuliani, G.; Rapisarda, G.; Kim, E.-J.; Liu, X.; Natowitz, J. B.

    2016-05-01

    We will show that the Thick Target Inverse Kinematics (TTIK) technique can be used to investigate the breakup of excited selfconjugate nuclei into many alpha particles. Two test runs were performed at Cyclotron Institute of Texas A&M University to study the reaction 20Ne+α at maximum beam energies of 10 and 12 AMeV. Due to the limited statistics, only events with alpha multiplicity up to three were analyzed. The analysis of the three α-particle emission data allowed the identification of the Hoyle state and other 12C excited states decaying into three alpha particles. The results will be shown and compared with other data available in the literature.

  17. Excitation induced spectroscopic study and quenching effect in cerium samarium codoped lithium aluminoborate glasses

    NASA Astrophysics Data System (ADS)

    Kaur, Parvinder; Kaur, Simranpreet; Singh, Gurinder Pal; Arora, Deepawali; Kumar, Sunil; Singh, D. P.

    2016-08-01

    Lithium aluminium borate host has been codoped with cerium and samarium to prepare glass by conventional melt quench technique. Their structural and spectroscopic investigation has been carried out using XRD, FTIR and density measurements. The UV-Vis absorption spectra and fluorescence spectra (λexc.=380 nm and 400 nm) have been studied for spectroscopic analysis. The amorphous nature of the prepared samples is shown by XRD. The density is increasing with addition of cerium at the expense of aluminium, keeping other components constant. FTIR study also shows the presence of compact and stable tetrahedral BO4 units thus supporting the density results. The UV- Vis absorption spectra show a shift of optical absorption edge towards longer wavelength along with an increase in intensity of peaks with rising samarium concentration. The fluorescence spectra show a blue shift and subsequent suppression of cerium peaks with addition of samarium.

  18. Laboratory spectroscopic study and astronomical detection of vibrationally excited n-propyl cyanide

    NASA Astrophysics Data System (ADS)

    Müller, Holger S. P.; Walters, Adam; Wehres, Nadine; Belloche, Arnaud; Wilkins, Olivia H.; Liu, Delong; Vicente, Rémi; Garrod, Robin T.; Menten, Karl M.; Lewen, Frank; Schlemmer, Stephan

    2016-11-01

    Context. We performed a spectral line survey called Exploring Molecular Complexity with ALMA (EMoCA) toward Sagittarius B2(N) between 84.1 and 114.4 GHz with the Atacama Large Millimeter/submillimeter Array (ALMA) in its Cycles 0 and 1. We determined line intensities of n-propyl cyanide in the ground vibrational states of its gauche and anti conformers toward the hot molecular core Sagittarius B2(N2) which suggest that we should also be able to detect transitions pertaining to excited vibrational states. Aims: We wanted to determine spectroscopic parameters of low-lying vibrational states of both conformers of n-propyl cyanide to search for them in our ALMA data. Methods: We recorded laboratory rotational spectra of n-propyl cyanide in two spectral windows between 36 and 127 GHz. We searched for emission lines produced by these states in the ALMA spectrum of Sagittarius B2(N2). We modeled their emission and the emission of the ground vibrational states assuming local thermodynamic equilibrium (LTE). Results: We have made extensive assignments of a- and b-type transitions of the four lowest vibrational states of the gauche conformer which reach J and Ka quantum numbers of 65 and 20, respectively. We assigned mostly a-type transitions for the anti conformer with J and Ka quantum numbers up to 48 and 24, respectively. Rotational and Fermi perturbations between two anti states allowed us to determine their energy difference. The resulting spectroscopic parameters enabled us to identify transitions of all four vibrational states of each conformer in our ALMA data. The emission features of all states, including the ground vibrational state, are well-reproduced with the same LTE modeling parameters, which gives us confidence in the reliability of the identifications, even for the states with only one clearly detected line. Conclusions: Emission features pertaining to the highest excited vibrational states of n-propyl cyanide reported in this work have been identified just

  19. UV absorption study of collisional energy transfer in vibrationally highly excited SO/sub 2/ molecules

    SciTech Connect

    Heymann, M.; Hippler, H.; Nahr, D.; Plach, H.J.; Troe, J.

    1988-09-22

    Transient UV absorption spectra after UV laser excitation of SO/sub 2/ were recorded and analyzed with respect to collisional energy transfer. Byuse of previously determined calibration curves, the absorption-time signals were converted into average energy-number of collision profiles. Energy-dependent average energies transferred per collision (..delta..E) were derived for 22 different collision partners. The temperature dependence of (..delta..E) was determined over the range 300-1500 K by experiments in a CO/sub 2/ CW laser-heated reactor and in shock waves.

  20. Quantum mechanical study of the coupling of plasmon excitations to atomic-scale electron transport

    SciTech Connect

    Song Peng; Nordlander, Peter; Gao Shiwu

    2011-02-21

    The coupling of optical excitation and electron transport through a sodium atom in a plasmonic dimer junction is investigated using time-dependent density functional theory. The optical absorption and dynamic conductance is determined as a function of gap size. Surface plasmons are found to couple to atomic-scale transport through several different channels including dipolar, multipolar, and charge transfer plasmon modes. These findings provide insight into subnanoscale couplings of plasmons and atoms, a subject of general interest in plasmonics and molecular electronics.

  1. n,. pi. /sup */ state of jet-cooled benzophenone as studied by sensitized phosphorescence excitation spectroscopy

    SciTech Connect

    Kamei, S.; Sato, T.; Mikami, N.; Ito, M.

    1986-10-23

    The sensitized phosphorescence excitation spectrum of jet-cooled benzophenone due to the S/sub 1/(n,..pi../sup */) produced from S/sub 0/ transition has been measured. It was found that the spectrum consists exclusively of several long progressions of 60 cm/sup -1/ which is the in-phase torsional mode of the phenyl rings. The vibrational analysis and the potential calculation shows that the in the S/sub 1/(n,..pi../sup */) state great geometry changes occur in the dihedral angle between the phenyl rings, the C=O bond distance, and the C-C bonds adjacent to the C=O bond.

  2. Computational Studies of Flame Structures

    NASA Astrophysics Data System (ADS)

    Amin, Vaishali

    This thesis is concerned with computational studies of laminar flame structures using detailed and skeletal chemical kinetic mechanisms. Elementary reactions in these mechanisms control the observable combustion properties such as flame speed, autoignition temperature, ignition delay time, and extinction characteristics in nonpremixed and premixed flame phenomena. First part of thesis deals with computational investigations of influence of carbon monoxide and hydrogen addition on methane flames stabilized in counterflow configuration. Computations were performed employing detailed chemical kinetic mechanism---the San Diego mechanism. In case of nonpremixed flames, effect of carbon xvi monoxide addition on structure and critical condition of extinction were examined. Differences between addition on fuel and oxidizer sides were investigated and plausible explanation given for the differences. For premixed flames, effect of addition of hydrogen and carbon monoxide to reactant mixture was studied. Critical conditions of extinction were predicted using computations for various compositions. Rates of production and consumption of various species were calculated and flame structure was analyzed for nonpremixed and premixed flames. It was found that moderate amount of carbon monoxide addition to methane enhances flame reactivity. However, with large amount of carbon monoxide addition, additive chemistry dominates. Addition of increasing amounts of hydrogen in premixed reactant stream enhances methane flame reactivity. In second part of thesis, kinetic modeling was performed to elucidate the structure and mechanism of extinction and autoignition of nonpremixed toluene flames in counterflow configuration. Computations were performed using detailed chemistry to determine flame structure and to obtain values for critical conditions of extinction and autoignition. Sensitivity analysis of rate parameters, reaction pathway analysis, and spatial reaction rate profiles were used to

  3. Study of the Application of Separation Control by Unsteady Excitation to Civil Transport Aircraft

    NASA Technical Reports Server (NTRS)

    McLean, J. D.; Crouch, J. D.; Stoner, R. C.; Sakurai, S.; Seidel, G. E.; Feifel, W. M.; Rush, H. M.

    1999-01-01

    This study provides a preliminary assessment of the potential benefits of applying unsteady separation control to transport aircraft. Estimates are given for some of the costs associated with a specific application to high-lift systems. High-leverage areas for future research were identified during the course of the study. The study was conducted in three phases. Phase 1 consisted of a coarse screening of potential applications within the aerodynamics discipline. Potential benefits were identified and in some cases quantified in a preliminary way. Phase 2 concentrated on the application to the wing high-lift system, deemed to have the greatest potential benefit for commercial transports. A team of experts, including other disciplines (i.e. hydraulic, mechanical, and electrical systems, structures, configurations, manufacturing, and finance), assessed the feasibility, benefits, and costs to arrive at estimates of net benefits. In both phases of the study, areas of concern and areas for future research were identified. In phase 3 of this study, the high-leverage areas for future research were prioritized as a guide for future efforts aimed at the application of active flow control to commercial transport aircraft.

  4. Variational Monte Carlo study of soliton excitations in hard-sphere Bose gases

    NASA Astrophysics Data System (ADS)

    Rota, R.; Giorgini, S.

    2015-10-01

    By using a full many-body approach, we calculate the excitation energy, the effective mass, and the density profile of soliton states in a three-dimensional Bose gas of hard spheres at zero temperature. The many-body wave function used to describe the soliton contains a one-body term, derived from the solution of the Gross-Pitaevskii equation, and a two-body Jastrow term, which accounts for the repulsive correlations between atoms. We optimize the parameters in the many-body wave function via a variational Monte Carlo procedure, calculating the grand-canonical energy and the canonical momentum of the system in a moving reference frame where the soliton is stationary. As the density of the gas is increased, significant deviations from the mean-field predictions are found for the excitation energy and the density profile of both dark and gray solitons. In particular, the soliton effective mass m* and the mass m Δ N of missing particles in the region of the density depression are smaller than the result from the Gross-Pitaevskii equation, their ratio, however, being well reproduced by this theory up to large values of the gas parameter. We also calculate the profile of the condensate density around the soliton notch, finding good agreement with the prediction of the local-density approximation.

  5. Trajectory study of supercollision relaxation in highly vibrationally excited pyrazine and CO2.

    PubMed

    Li, Ziman; Sansom, Rebecca; Bonella, Sara; Coker, David F; Mullin, Amy S

    2005-09-01

    Classical trajectory calculations were performed to simulate state-resolved energy transfer experiments of highly vibrationally excited pyrazine (E(vib) = 37,900 cm(-1)) and CO(2), which were conducted using a high-resolution transient infrared absorption spectrometer. The goal here is to use classical trajectories to simulate the supercollision energy transfer pathway wherein large amounts of energy are transferred in single collisions in order to compare with experimental results. In the trajectory calculations, Newton's laws of motion are used for the molecular motion, isolated molecules are treated as collections of harmonic oscillators, and intermolecular potentials are formed by pairwise Lennard-Jones potentials. The calculations qualitatively reproduce the observed energy partitioning in the scattered CO(2) molecules and show that the relative partitioning between bath rotation and translation is dependent on the moment of inertia of the bath molecule. The simulations show that the low-frequency modes of the vibrationally excited pyrazine contribute most to the strong collisions. The majority of collisions lead to small DeltaE values and primarily involve single encounters between the energy donor and acceptor. The large DeltaE exchanges result from both single impulsive encounters and chattering collisions that involve multiple encounters.

  6. KEWPIE2: A cascade code for the study of dynamical decay of excited nuclei

    NASA Astrophysics Data System (ADS)

    Lü, Hongliang; Marchix, Anthony; Abe, Yasuhisa; Boilley, David

    2016-03-01

    KEWPIE-a cascade code devoted to investigating the dynamical decay of excited nuclei, specially designed for treating very low probability events related to the synthesis of super-heavy nuclei formed in fusion-evaporation reactions-has been improved and rewritten in C++ programming language to become KEWPIE2. The current version of the code comprises various nuclear models concerning the light-particle emission, fission process and statistical properties of excited nuclei. General features of the code, such as the numerical scheme and the main physical ingredients, are described in detail. Some typical calculations having been performed in the present paper clearly show that theoretical predictions are generally in accordance with experimental data. Furthermore, since the values of some input parameters cannot be determined neither theoretically nor experimentally, a sensibility analysis is presented. To this end, we systematically investigate the effects of using different parameter values and reaction models on the final results. As expected, in the case of heavy nuclei, the fission process has the most crucial role to play in theoretical predictions. This work would be essential for numerical modeling of fusion-evaporation reactions.

  7. Excited state electron transfer from aminopyrene to graphene: a combined experimental and theoretical study.

    PubMed

    Chakraborti, Himadri; Bramhaiah, Kommula; John, Neena Susan; Pal, Suman Kalyan

    2013-12-01

    The quenching of the fluorescence of 1-aminopyrene (1-Ap) by reduced graphene oxide (rGO) has been investigated using spectroscopic techniques. In spite of the upward curvature in the Stern-Volmer plot, the unchanged spectral signature of the absorption of 1-Ap in the presence of rGO and the decrease in fluorescence lifetime with increasing rGO concentration point toward the dynamic nature of the quenching. Detailed analysis of steady state and time-resolved spectroscopic data has shown that the quenching arises due to the photoinduced electron transfer from 1-Ap to rGO. This is again supported by estimating the Gibb's free energy change for the ground as well as excited state electron transfer. Ab initio calculations under the density functional theory (DFT) formalism reveal that the possibility of π-π stacking is very slim in the 1-Ap-rGO system and the electron density resides completely on 1-Ap in the highest occupied molecular orbital (HOMO) and on graphene in the lowest unoccupied molecular orbital (LUMO), supporting the experimental findings of the intermolecular electron transfer between 1-Ap and rGO in the excited state.

  8. Flapping current sheet motions in magnetotail excited by non-adiabatic ions: case study

    NASA Astrophysics Data System (ADS)

    Wei, X., Jr.

    2015-12-01

    The current sheet is a crucial region of the magnetotail, where energy reserve and release take place. The origin of the up-down motions of the current sheet, referred to as flapping motions, is among the most fundamental issues of magnetotail dynamics. Observational evidences suggest that the flapping motion is a kind of internal excited kink-like waves, but its particular propagating features such as the low phase speeds and the propagating direction from the tail center toward flanks do not match any local generation mechanisms previously established so far. Here we report observations of the current sheet flapping motions induced by non-adiabatic ions in the magnetic field configurations with a finite guiding component, whose population present periodic hemispherical asymmetries. Three type of current sheet flapping event in this paper will be discussed. This current sheet flapping phenomenon implies that the excitation mechanism of the current sheet flapping motions is a self-circulation process between the non-adiabatic ion population and the current sheet equilibrium itself.

  9. Effects of vibrational excitation on multidimensional tunneling: General study and proton tunneling in tropolone

    NASA Astrophysics Data System (ADS)

    Takada, Shoji; Nakamura, Hiroki

    1995-03-01

    Tunneling energy splittings of vibrationally excited states are calculated quantum mechanically using several models of two-dimensional symmetric double well potentials. Various effects of vibrational excitation on tunneling are found to appear, depending on the topography of potential energy surface; the symmetry of the mode coupling plays an essential role. Especially, oscillation of tunneling splitting with respect to vibrational quantum number can occur and is interpreted by a clear physical picture based on the semiclassical theory formulated recently [Takada and Nakamura, J. Chem. Phys. 100, 98 (1994)]. The mixed tunneling in the C region found there allows the wave functions to have nodal lines in classically inaccessible region and can cause the suppression of the tunneling. The above analysis is followed by the interpretation of recent experiments of proton tunneling in tropolone. Ab initio molecular orbital calculations are carried out for the electronically ground state. A simple three-dimensional model potential is constructed and employed to analyze the proton tunneling dynamics. Some of the experimentally observed intriguing features can be explained by the typical mechanisms discussed above.

  10. Studies of excited-state properties of multibranched triarylamine end-capped triazines.

    PubMed

    Liu, Chun; Tang, Kuo-Chun; Zhang, Hao; Pan, Hsiao-An; Hua, Jianli; Li, Bo; Chou, Pi-Tai

    2012-12-20

    Electron donor-acceptor types of multibranched triarylamine end-capped triazines have been systematically investigated by steady-state electronic spectroscopy, electrochemistry, femtosecond fluorescence anisotropy and solvent relaxation dynamics. The results, together with computational approach, have gained in-depth insight into their excited-state properties, especially the interactions between branches. Among different branched triarylamines of one, two and three arms, the interbranch interaction between each arm is weak, as evidenced by their nearly identical absorption spectral profile and frontier orbitals analyses. Upon S(0) → S(1) excitation, the electronic delocalization in the three-branched triarylamine end-capped triazine is resolved to be 680 ± 130 fs, followed by a slow (28 ± 3 ps) electronic localization into one branch and consequently a rotational depolarization of 2.0 ± 0.1 ns. Similar delocalization dynamics was resolved for the two-branched triarylamine end-capped triazine (electronic delocalization, 500 ± 90 fs; twisting localization, 21 ± 5 ps; rotational depolarization, 700 ± 30 ps). The comparable electron delocalization and solvent relaxation time scale may set up a new paradigm to investigate their specific correlation in the early time domain. PMID:23198687

  11. Efficient excitation of photoluminescence in a two-dimensional waveguide consisting of a quantum dot-polymer sandwich-type structure.

    PubMed

    Suárez, I; Larrue, A; Rodríguez-Cantó, P J; Almuneau, G; Abargues, R; Chirvony, V S; Martínez-Pastor, J P

    2014-08-15

    In this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10-50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is developed to pattern the PMMA into ridge structures by UV lithography in order to provide additional light confinement. The sandwich-type waveguide is analyzed in comparison to a similar one formed by a PMMA film homogeneously doped by the same QDs. A 100-fold enhancement in the waveguided PL is found for the sandwich-type case due to the higher concentration of QDs inside the waveguide.

  12. Structural studies of bee melittin

    SciTech Connect

    Eisenberg, D.; Terwilliger, T.C.; Tsui, F.

    1980-10-01

    The question of how proteins refold in passing from an aqueous phase to an amphipathic environment such as a membrane is beig addressed by a structural study of bee melittin. Melittin is the toxic, main protein of bee venom, and has been shown by others to integrate into natural and synthetic membranes and to lyse a variety of cells. This function is presumably related to its unusual sequence. Except for charges at the N-terminus and at lysine 7, the first 20 residues are largely apolar. In contrast, the last six residues contain four charges and two polar residues.

  13. Excited-state ring-opening mechanism of cyclic ketones: a MS-CASPT2//CASSCF study.

    PubMed

    Xia, Shu-Hua; Liu, Xiang-Yang; Fang, Qiu; Cui, Ganglong

    2015-04-16

    We have employed complete active space self-consistent field (CASSCF) and its second-order perturbation (MS-CASPT2) methods to study the S1 and T1 excited-state ring-opening mechanisms and S1 excited-state deactivation channels of cyclopropanone, cyclobutanone, cyclopentanone, and cyclohexanone. On the basis of optimized minima, transition states, conical intersections, refined energies, and relaxed two-dimensional S1 and T1 potential energy surfaces, we find that, with the ring-strain decrease from cyclopropanone to cyclohexanone, (1) the ring-opening S1 and T1 barrier increases from 0.0 and 0.0 to 19.7 and 10.4 kcal/mol, respectively; (2) the electronic state responsible for the dominant ring-opening reaction varies from the S1 state of cyclopropanone to the T1 state of cyclopentanone and cyclohexanone; and (3) the S1 ring opening gradually becomes inefficient even blocked in cyclopentanone and cyclohexanone. This work shows that these dissimilar excited-state dynamics could originate from different ring strain of small cyclic ketones.

  14. Scattering of electrically excited surface plasmon polaritons by gold nanoparticles studied by optical interferometry with a scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Rogez, Benoît.; Comtet, Geneviève; Le Moal, Eric; Abidi, Wafa; Remita, Hynd; Dujardin, Gérald; Boer-Duchemin, Elizabeth

    2015-07-01

    We study the scattering of electrically excited surface plasmon polaritons (SPP) from individual nanostructures. The tunneling electrons from a scanning tunneling microscope (STM) are used to excite an out-going, circular SPP wave on a thin (50-nm) gold film on which isolated gold nanoparticles (NPs) have been deposited. Interaction of the excited SPPs with the NPs leads to both in-plane (SPP-to-SPP) and out-of-plane (SPP-to-photon) scattering. We use SPP leakage radiation microscopy to monitor the interference between the incident and in-plane scattered SPP waves in the image plane. By changing the location of the STM tip, the distance of the pointlike SPP source to the scatterers can be varied at will, which constitutes a key advantage over other existing techniques. As well, the out-of-plane scattered radiation interferes with the direct light emission from the STM tip in the back focal plane (Fourier plane). This confirms the mutual coherence of the light and SPP emission resulting from the inelastic tunneling of an electron in the STM junction. We use this effect to demonstrate that SPP-to-photon scattering at NPs is highly directional.

  15. A 4.2 GS/sec. Synchronized Vertical Excitation System for SPS Studies - Steps Toward Wideband Feedback

    SciTech Connect

    Fox, John

    2012-07-10

    A 4.2 GS/sec. beam excitation system with accelerator synchronization and power stages is described. The system is capable of playing unique samples (32 samples/bunch) for 15,000 turns on selected bunch(es) in the SPS in syn- chronism with the injection and acceleration cycle. The purpose of the system is to excite internal modes of single-bunch vertical motion, and study the bunch dynamics in the presence of developing Electron cloud or TMCI effects. The system includes a synchronized master oscillator, SPS timing functions, an FPGA based arbitrary waveform generator, 4.2 GS/sec. D/A system and four 80W 20-1000 MHz amplifiers driving a tapered stripline pickup/kicker. A software GUI allows specification of various modulation signals, selection of bunches and turns to excite, while a remote control interface allows simple control/monitoring of the RF power stages located in the tunnel. The successful use of this system for SPS MD measurements in 2011 is a vital proof-of-principle for wideband feedback using similar functions to correct the beam motion.

  16. Trajectory and Model Studies of Collisions of Highly Excited Methane with Water Using an ab Initio Potential.

    PubMed

    Conte, Riccardo; Houston, Paul L; Bowman, Joel M

    2015-12-17

    Quasi-classical trajectory studies have been performed for the collision of internally excited methane with water using an accurate methane-water potential based on a full-dimensional, permutationally invariant analytical representation of energies calculated at a high level of theory. The results suggest that most energy transfer takes place at impact parameters smaller than about 8 Bohr; collisions at higher impact parameters are mostly elastic. Overall, energy transfer is fairly facile, with values for ⟨ΔEdown⟩ and ⟨ΔEup⟩ approaching almost 2% of the total excitation energy. A classical model previously developed for the collision of internally excited molecules with atoms (Houston, P. L.; Conte, R.; Bowman, J. M. J. Phys. Chem. A 2015, 119, 4695-4710) has been extended to cover collisions of internally excited molecules with other molecules. For high initial rotational levels, the agreement with the trajectory results is quite good (R(2) ≈ 0.9), whereas for low initial rotational levels it is only fair (R(2) ≈ 0.7). Both the model and the trajectories can be characterized by a four-dimensional joint probability distribution, P(J1,f,ΔE1,J2,f,ΔE2), where J1,f and J2,f are the final rotational levels of molecules 1 and 2 and ΔE1 and ΔE2 are the respective changes in internal energy. A strong anticorrelation between ΔE1 and ΔE2 is observed in both the model and trajectory results and can be explained by the model. There is evidence in the trajectory results for a small amount of V ↔ V energy transfer from the water, which has low internal energy, to the methane, which has substantial internal energy. This observation suggests that V ↔ V energy transfer in the other direction also occurs. PMID:26299678

  17. Trajectory and Model Studies of Collisions of Highly Excited Methane with Water Using an ab Initio Potential.

    PubMed

    Conte, Riccardo; Houston, Paul L; Bowman, Joel M

    2015-12-17

    Quasi-classical trajectory studies have been performed for the collision of internally excited methane with water using an accurate methane-water potential based on a full-dimensional, permutationally invariant analytical representation of energies calculated at a high level of theory. The results suggest that most energy transfer takes place at impact parameters smaller than about 8 Bohr; collisions at higher impact parameters are mostly elastic. Overall, energy transfer is fairly facile, with values for ⟨ΔEdown⟩ and ⟨ΔEup⟩ approaching almost 2% of the total excitation energy. A classical model previously developed for the collision of internally excited molecules with atoms (Houston, P. L.; Conte, R.; Bowman, J. M. J. Phys. Chem. A 2015, 119, 4695-4710) has been extended to cover collisions of internally excited molecules with other molecules. For high initial rotational levels, the agreement with the trajectory results is quite good (R(2) ≈ 0.9), whereas for low initial rotational levels it is only fair (R(2) ≈ 0.7). Both the model and the trajectories can be characterized by a four-dimensional joint probability distribution, P(J1,f,ΔE1,J2,f,ΔE2), where J1,f and J2,f are the final rotational levels of molecules 1 and 2 and ΔE1 and ΔE2 are the respective changes in internal energy. A strong anticorrelation between ΔE1 and ΔE2 is observed in both the model and trajectory results and can be explained by the model. There is evidence in the trajectory results for a small amount of V ↔ V energy transfer from the water, which has low internal energy, to the methane, which has substantial internal energy. This observation suggests that V ↔ V energy transfer in the other direction also occurs.

  18. Right hemisphere dominance directly predicts both baseline V1 cortical excitability and the degree of top-down modulation exerted over low-level brain structures.

    PubMed

    Arshad, Q; Siddiqui, S; Ramachandran, S; Goga, U; Bonsu, A; Patel, M; Roberts, R E; Nigmatullina, Y; Malhotra, P; Bronstein, A M

    2015-12-17

    Right hemisphere dominance for visuo-spatial attention is characteristically observed in most right-handed individuals. This dominance has been attributed to both an anatomically larger right fronto-parietal network and the existence of asymmetric parietal interhemispheric connections. Previously it has been demonstrated that interhemispheric conflict, which induces left hemisphere inhibition, results in the modulation of both (i) the excitability of the early visual cortex (V1) and (ii) the brainstem-mediated vestibular-ocular reflex (VOR) via top-down control mechanisms. However to date, it remains unknown whether the degree of an individual's right hemisphere dominance for visuospatial function can influence, (i) the baseline excitability of the visual cortex and (ii) the extent to which the right hemisphere can exert top-down modulation. We directly tested this by correlating line bisection error (or pseudoneglect), taken as a measure of right hemisphere dominance, with both (i) visual cortical excitability measured using phosphene perception elicited via single-pulse occipital trans-cranial magnetic stimulation (TMS) and (ii) the degree of trans-cranial direct current stimulation (tDCS)-mediated VOR suppression, following left hemisphere inhibition. We found that those individuals with greater right hemisphere dominance had a less excitable early visual cortex at baseline and demonstrated a greater degree of vestibular nystagmus suppression following left hemisphere cathodal tDCS. To conclude, our results provide the first demonstration that individual differences in right hemisphere dominance can directly predict both the baseline excitability of low-level brain structures and the degree of top-down modulation exerted over them. PMID:26518461

  19. Right hemisphere dominance directly predicts both baseline V1 cortical excitability and the degree of top-down modulation exerted over low-level brain structures.

    PubMed

    Arshad, Q; Siddiqui, S; Ramachandran, S; Goga, U; Bonsu, A; Patel, M; Roberts, R E; Nigmatullina, Y; Malhotra, P; Bronstein, A M

    2015-12-17

    Right hemisphere dominance for visuo-spatial attention is characteristically observed in most right-handed individuals. This dominance has been attributed to both an anatomically larger right fronto-parietal network and the existence of asymmetric parietal interhemispheric connections. Previously it has been demonstrated that interhemispheric conflict, which induces left hemisphere inhibition, results in the modulation of both (i) the excitability of the early visual cortex (V1) and (ii) the brainstem-mediated vestibular-ocular reflex (VOR) via top-down control mechanisms. However to date, it remains unknown whether the degree of an individual's right hemisphere dominance for visuospatial function can influence, (i) the baseline excitability of the visual cortex and (ii) the extent to which the right hemisphere can exert top-down modulation. We directly tested this by correlating line bisection error (or pseudoneglect), taken as a measure of right hemisphere dominance, with both (i) visual cortical excitability measured using phosphene perception elicited via single-pulse occipital trans-cranial magnetic stimulation (TMS) and (ii) the degree of trans-cranial direct current stimulation (tDCS)-mediated VOR suppression, following left hemisphere inhibition. We found that those individuals with greater right hemisphere dominance had a less excitable early visual cortex at baseline and demonstrated a greater degree of vestibular nystagmus suppression following left hemisphere cathodal tDCS. To conclude, our results provide the first demonstration that individual differences in right hemisphere dominance can directly predict both the baseline excitability of low-level brain structures and the degree of top-down modulation exerted over them.

  20. Theoretical studies of 2-quinolinol: Geometries, vibrational frequencies, isomerization, tautomerism, and excited states

    NASA Astrophysics Data System (ADS)

    Pan, Yi; Lau, Kai-Chung; Al-Mogren, Muneerah Mogren; Mahjoub, Ahmed; Hochlaf, Majdi

    2014-10-01

    We treat theoretically 2-quinolinol(lactam), an analog of carbostyril and DNA bases. We characterized the ground state structure of 2-quinolinol and its isomer(lactim) using density functional theory(DFT). The reaction profile and energetics for lactam-lactim tautomerization and cis-lactim to trans-lactim isomerization predicted with explicitly correlated methods. We explored the pattern of the lowest singlet and triplet manifolds of states and electronic S1 ← S0 transitions using multiconfigurational methodologies. The theoretical results are compared with available experimental data and used to interpret the on-going photoelectron study of 2-quinolinol. Our analysis should help to understand the effect of tautomerism and aromaticity on the DNA bases.