WorldWideScience

Sample records for cell excitation dynamics

  1. Dynamics of Elastic Excitable Media

    CERN Document Server

    Cartwright, J H E; Hernández-García, E; Piro, O; Cartwright, Julyan H. E.; Eguiluz, Victor M.; Hernandez-Garcia, Emilio; Piro, Oreste

    1999-01-01

    The Burridge-Knopoff model of earthquake faults with viscous friction is equivalent to a van der Pol-FitzHugh-Nagumo model for excitable media with elastic coupling. The lubricated creep-slip friction law we use in the Burridge-Knopoff model describes the frictional sliding dynamics of a range of real materials. Low-dimensional structures including synchronized oscillations and propagating fronts are dominant, in agreement with the results of laboratory friction experiments. Here we explore the dynamics of fronts in elastic excitable media.

  2. Ovarian Cancer Cell Adhesion/Migration Dynamics on Micro-Structured Laminin Gradients Fabricated by Multiphoton Excited Photochemistry

    Directory of Open Access Journals (Sweden)

    Ruei-Yu He

    2015-07-01

    Full Text Available Haptotaxis, i.e., cell migration in response to adhesive gradients, has been previously implicated in cancer metastasis. A better understanding of cell migration dynamics and their regulation could ultimately lead to new drug targets, especially for cancers with poor prognoses, such as ovarian cancer. Haptotaxis has not been well-studied due to the lack of biomimetic, biocompatible models, where, for example, microcontact printing and microfluidics approaches are primarily limited to 2D surfaces and cannot produce the 3D submicron features to which cells respond. Here we used multiphoton excited (MPE phototochemistry to fabricate nano/microstructured gradients of laminin (LN as 2.5D models of the ovarian basal lamina to study the haptotaxis dynamics of a series of ovarian cancer cells. Using these models, we found that increased LN concentration increased migration speed and also alignment of the overall cell morphology and their cytoskeleton along the linear axis of the gradients. Both these metrics were enhanced on LN compared to BSA gradients of the same design, demonstrating the importance of both topographic and ECM cues on the adhesion/migration dynamics. Using two different gradient designs, we addressed the question of the roles of local concentration and slope and found that the specific haptotactic response depends on the cell phenotype and not simply the gradient design. Moreover, small changes in concentration strongly affected the migration properties. This work is a necessary step in studying haptotaxis in more complete 3D models of the tumor microenvironment for ovarian and other cancers.

  3. The effect of noise and coupling on beta cell excitation dynamics

    DEFF Research Database (Denmark)

    Bursting electrical behavior is commonly observed in a variety of nerve and endocrine cells, including that in electrically coupled β-cells located in intact pancreatic islets. However, individual β-cells usually display either spiking or very fast bursting behavior, and the difference between is...

  4. Dynamics Analysis and Transition Mechanism of Bursting Calcium Oscillations in Non-Excitable Cells

    Institute of Scientific and Technical Information of China (English)

    ZHANG Feng; LU Qi-Shao; DUAN Li-Xia

    2007-01-01

    A one-pool model with Ca2+-activated inositol-trisphosphate-concentration degradation is considered.For complex bursting Ca2+ oscillation,point-cycle bursting of subHopf-subHopf type is found to be in the intermediate state from quasi-periodic bursting to Point-point bursting of subHopf-subHopf type.The fast-slow burster analysis is used to study the transition mechanisms among simple periodic oscillation,quasi-periodic bursting,point-point and point-cycle burstings.The dynamics analysis of different oscillations provides better insight into the generation and transition mechanisms of complex intra- and inter-cellular Ca2+signalling.

  5. Dynamic Testing: Toward a Multiple Exciter Test

    Science.gov (United States)

    2015-04-01

    55 Defense AT&L: March–April 2015 Dynamic Testing Toward a Multiple Exciter Test Michael T. Hale n William A. Barber Hale is an electronics...has taken decades of advancements in vibration control and exciter technology. Below are a short historical path of the evolution of the discipline...toward multiple exciter /multiple degree-of-freedom (MDOF) testing, an example of an MDOF vibration system and a discussion of benefits of the

  6. Dynamical Structure of Nuclear Excitation in Continuum

    Institute of Scientific and Technical Information of China (English)

    ZHANG Chun-Lei; ZHANG Huan-Qiao; ZHANG Xi-Zhen

    2005-01-01

    @@ Dynamical structures of collective excitation in continuum are studied by calculating the isoscalar and isovector strength as well as transition density of nuclei near the drip-line such as 28O and 34Ca. It is found that for some excited states in continuum the proton and neutron transition density calculated from isoscalar and isovector excitation at some given energies may be different, which will affect the calculation of the polarization for nuclei with N ≠ Z.

  7. Correlating excited state and charge carrier dynamics with photovoltaic parameters of perylene dye sensitized solar cells: influences of an alkylated carbazole ancillary electron-donor.

    Science.gov (United States)

    Li, Yang; Wang, Junting; Yuan, Yi; Zhang, Min; Dong, Xiandui; Wang, Peng

    2017-01-18

    Two perylene dyes characteristic of electron-donors phenanthrocarbazole (PC) and carbazyl functionalized PC are selected to study the complicated dynamics of excited states and charge carriers, which underlie the photovoltaic parameters of dye-sensitized solar cells (DSCs). We have combined femtosecond fluorescence up-conversion and time-resolved single-photon counting techniques to probe the wavelength-dependent photoluminescence dynamics of dye molecules not only dissolved in THF but also grafted on the surface of oxide nanoparticles. Excited state relaxation and electron injection both occur on a similar timescale, resulting in a very distributive kinetics of electron injection. It is also found that the carbazyl ancillary electron-donor causes a faster electron injection, which over-compensates the adverse impact of a slightly shorter lifetime of the equilibrium excited state. Nanosecond transient absorption and transient photovoltage decay measurements have shown that conjugating carbazyl to PC can effectively slow down the kinetics of charge recombination of electrons in titania with both photo-oxidized dye molecules and triiodide anions, improving the cell photovoltage.

  8. Dynamical analysis of highly excited molecular spectra

    Energy Technology Data Exchange (ETDEWEB)

    Kellman, M.E. [Univ. of Oregon, Eugene (United States)

    1993-12-01

    The goal of this program is new methods for analysis of spectra and dynamics of highly excited vibrational states of molecules. In these systems, strong mode coupling and anharmonicity give rise to complicated classical dynamics, and make the simple normal modes analysis unsatisfactory. New methods of spectral analysis, pattern recognition, and assignment are sought using techniques of nonlinear dynamics including bifurcation theory, phase space classification, and quantization of phase space structures. The emphasis is chaotic systems and systems with many degrees of freedom.

  9. Dynamics of excitable nodes on random graphs

    Indian Academy of Sciences (India)

    K Manchanda; T Umeshkanta Singh; R Ramaswamy

    2011-11-01

    We study the interplay of topology and dynamics of excitable nodes on random networks. Comparison is made between systems grown by purely random (Erd˝os–Rényi) rules and those grown by the Achlioptas process. For a given size, the growth mechanism affects both the thresholds for the emergence of different structural features as well as the level of dynamical activity supported on the network.

  10. Dynamics of excited m-dichlorobenzene

    Institute of Scientific and Technical Information of China (English)

    YUAN Liwei; WANG Yanqiu; WANG Li; BAI Jiling; HE Guozhong

    2004-01-01

    Dynamics of excited m-dichlorobenzene is investigated in real time by femtosecond pump-probe method, combined with time-of-flight mass spectrometric detection in a supersonic molecular beam. The yields of the parent ion and daughter ion C6H4Cl+ are examined as a function of the delay between the 270 and 810 nm femtosecond laser pulses, respectively. The lifetime of the first singlet excited state S1 of m-dichlorobenzene is measured. The origin of this daughter ion C6H4Cl+ is discussed. The ladder mechanism is proposed to form the fragment ion.In addition, our experimental results exhibit a rapid damped sinusoidal oscillation over intermediate time delays, which is due to quantum beat effects.

  11. Evolution of Excited Convective Cells in Plasmas

    DEFF Research Database (Denmark)

    Pécseli, Hans; Juul Rasmussen, Jens; Sugai, H.

    1984-01-01

    Convective cells are excited externally in a fully ionized magnetized plasma and their space-time evolution is investigated by two-dimensional potential measurements. A positive cell is excited externally by control of the end losses in the 'scrape off' layer of a plasma column produced by surface...

  12. Dynamic range of hypercubic stochastic excitable media

    CERN Document Server

    de Assis, Vladimir R V

    2007-01-01

    We study the response properties of d-dimensional hypercubic excitable networks to a stochastic stimulus. Each site, modelled either by a three-state stochastic susceptible-infected-recovered-susceptible (SIRS) system or by the probabilistic Greenberg-Hastings cellular automaton (GHCA), is continuously and independently stimulated by an external Poisson rate h. The response function (mean density of active sites rho versus h) is obtained via simulations (for d=1, 2, 3, 4) and mean field approximations at the single-site and pair levels (for all d). In any dimension, the dynamic range of the response function is maximized precisely at the nonequilibrium phase transition to self-sustained activity, in agreement with a reasoning recently proposed. Moreover, the maximum dynamic range attained at a given dimension d is a decreasing function of d.

  13. Excited State Dynamics in Carbon Nanotubes

    Science.gov (United States)

    Miyamoto, Yoshiyuki

    2004-03-01

    Carbon nanotube, one of the most promising materials for nano-technology, still suffers from its imperfection in crystalline structure that will make performance of nanotube behind theoretical limit. From the first-principles simulations, I propose efficient methods to overcome the imperfection. I show that photo-induced ion dynamics can (1) identify defects in nanotubes, (2) stabilize defected nanotubes, and (3) purify contaminated nanotubes. All of these methods can be alternative to conventional heat treatments and will be important techniques for realizing nanotube-devices. Ion dynamics under electronic excitation has been simulated with use of the computer code FPSEID (First-Principles Simulation tool for Electron Ion Dynamics) [1], which combines the time-dependent density functional method [2] to classical molecular dynamics. This very challenging approach is time-consuming but can automatically treat the level alternation of differently occupied states, and can observe initiation of non-adiabatic decay of excitation. The time-dependent Kohn-Sham equation has been solved by using the Suzuki-Trotter split operator method [3], which is a numerically stable method being suitable for plane wave basis, non-local pseudopotentials, and parallel computing. This work has been done in collaboration with Prof. Angel Rubio, Prof. David Tomanek, Dr. Savas Berber and Mina Yoon. Most of present calculations have been done by using the SX5 Vector-Parallel system in the NEC Fuchu-plant, and the Earth Simulator in Yokohama Japan. [1] O. Sugino and Y. Miyamoto, Phys. Rev. B59, 2579 (1999); ibid, B66 089901(E) (2001) [2] E. Runge and E. K. U. Gross, Phys. Rev. Lett. 52, 997 (1984). [3] M. Suzuki, J. Phys. Soc. Jpn. 61, L3015 (1992).

  14. Fission dynamics at low excitation energy. 2

    CERN Document Server

    Aritomo, Y; Ivanyuk, F A

    2014-01-01

    The mass asymmetry in the fission of U-236 at low excitation energy is clarified by the analysis of the trajectories obtained by solving the Langevin equations for the shape degrees of freedom. It is demonstrated that the position of the peaks in the mass distribution of fission fragments is determined mainly by the saddle point configuration originating from the shell correction energy. The width of the peaks, on the other hand, results from the shape fluctuations close to the scission point caused by the random force in the Langevin equation. We have found out that the fluctuations between elongated and compact shapes are essential for the fission process. According to our results the fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup, but is accompanied by the fluctuations between elongated and compact shapes. This picture presents a new viewpoint of fission dynamics and the splitting mechanism.

  15. Fission dynamics at low excitation energy

    CERN Document Server

    Aritomo, Y

    2013-01-01

    The origin of mass asymmetry in the fission of uranium at a low excitation energy is clarified by a trajectory analysis of the Langevin equation. The positions of the peaks in the mass distribution of fission fragments are mainly determined by fission saddle points originating from the shell correction energy. The widths of the peaks, on the other hand, result from a shape fluctuation around the scission point caused by the random force in the Langevin equation. We found that a random vibration in the oblate direction of fissioning fragments is essential for the fission process. According to this picture, fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup. This is expected to lead to a new viewpoint of fission dynamics and the splitting mechanism.

  16. The photodissociation and reaction dynamics of vibrationally excited molecules

    Energy Technology Data Exchange (ETDEWEB)

    Crim, F.F. [Univ. of Wisconsin, Madison (United States)

    1993-12-01

    This research determines the nature of highly vibrationally excited molecules, their unimolecular reactions, and their photodissociation dynamics. The goal is to characterize vibrationally excited molecules and to exploit that understanding to discover and control their chemical pathways. Most recently the author has used a combination of vibrational overtone excitation and laser induced fluorescence both to characterize vibrationally excited molecules and to study their photodissociation dynamics. The author has also begun laser induced grating spectroscopy experiments designed to obtain the electronic absorption spectra of highly vibrationally excited molecules.

  17. Optimal Dynamical Range of Excitable Networks at Criticality

    CERN Document Server

    Kinouchi, Osame

    2006-01-01

    A recurrent idea in the study of complex systems is that optimal information processing is to be found near bifurcation points or phase transitions. However, this heuristic hypothesis has few (if any) concrete realizations where a standard and biologically relevant quantity is optimized at criticality. Here we give a clear example of such a phenomenon: a network of excitable elements has its sensitivity and dynamic range maximized at the critical point of a non-equilibrium phase transition. Our results are compatible with the essential role of gap junctions in olfactory glomeruli and retinal ganglionar cell output. Synchronization and global oscillations also appear in the network dynamics. We propose that the main functional role of electrical coupling is to provide an enhancement of dynamic range, therefore allowing the coding of information spanning several orders of magnitude. The mechanism could provide a microscopic neural basis for psychophysical laws.

  18. Excited State Spectra and Dynamics of Phenyl-Substituted Butadienes

    DEFF Research Database (Denmark)

    Wallace-Williams, Stacie E.; Schwartz, Benjamin J.; Møller, Søren

    1994-01-01

    A combination of steady-state and dynamic spectral measurements are used to provide new insights into the nature of the excited-state processes of all-trans-1,4-diphenyl-1,3-butadiene and several analogs: 1,4-diphenyl- 1,3-cyclopentadiene, 1,1,4,4-tetraphenylbutadiene, 1,2,3,4-tetraphenyl-1,3-cyc...... indicate that phenyl torsional motion is not important to the excited-state dynamics and reveal alternative excited-state reaction pathways. The results demonstrate how molecular systems that are structually similar can exhibit different electronic properties and excited-state dynamics....

  19. Entropy Rate Maps of Complex Excitable Dynamics in Cardiac Monolayers

    Directory of Open Access Journals (Sweden)

    Alexander Schlemmer

    2015-02-01

    Full Text Available The characterization of spatiotemporal complexity remains a challenging task. This holds in particular for the analysis of data from fluorescence imaging (optical mapping, which allows for the measurement of membrane potential and intracellular calcium at high spatial and temporal resolutions and, therefore, allows for an investigation of cardiac dynamics. Dominant frequency maps and the analysis of phase singularities are frequently used for this type of excitable media. These methods address some important aspects of cardiac dynamics; however, they only consider very specific properties of excitable media. To extend the scope of the analysis, we present a measure based on entropy rates for determining spatiotemporal complexity patterns of excitable media. Simulated data generated by the Aliev–Panfilov model and the cubic Barkley model are used to validate this method. Then, we apply it to optical mapping data from monolayers of cardiac cells from chicken embryos and compare our findings with dominant frequency maps and the analysis of phase singularities. The studies indicate that entropy rate maps provide additional information about local complexity, the origins of wave breakup and the development of patterns governing unstable wave propagation.

  20. Dynamic response of nuclear fuel assembly excited by pressure pulsations

    Directory of Open Access Journals (Sweden)

    Zeman V.

    2012-12-01

    Full Text Available The paper deals with dynamic load calculation of the hexagonal type nuclear fuel assembly caused by spatial motion of the support plates in the reactor core. The support plate motion is excited by pressure pulsations generated by main circulation pumps in the coolant loops of the primary circuit of the nuclear power plant. Slightly different pumps revolutions generate the beat vibrations which causes an amplification of fuel assembly component dynamic deformations and fuel rods coating abrasion. The cyclic and central symmetry of the fuel assembly makes it possible the system decomposition into six identical revolved fuel rod segments which are linked with central tube and skeleton by several spacer grids in horizontal planes.The modal synthesis method with condensation of the fuel rod segments is used for calculation of the normal and friction forces transmitted between fuel rods and spacer grids cells.

  1. Lithium. Effects on excitable cell membranes

    NARCIS (Netherlands)

    Ploeger, Egbert Johan

    1974-01-01

    LITHIUM: Effects on excitable cell membranes. Lithium salts have been used in the treatment of manic-depressive psychosis for many years but their mechanism of action is not well understood. Many workers assume that the action of lithium on catecholamine metabolism and/or on electrolyte distribution

  2. Effects of cell cycle noise on excitable gene circuits

    CERN Document Server

    Veliz-Cuba, Alan; Bennett, Matthew R; Josić, Krešimir; Ott, William

    2016-01-01

    We assess the impact of cell cycle noise on gene circuit dynamics. For bistable genetic switches and excitable circuits, we find that transitions between metastable states most likely occur just after cell division and that this concentration effect intensifies in the presence of transcriptional delay. We explain this concentration effect with a 3-states stochastic model. For genetic oscillators, we quantify the temporal correlations between daughter cells induced by cell division. Temporal correlations must be captured properly in order to accurately quantify noise sources within gene networks.

  3. Dynamics of excited m-dichlorobenzene

    Institute of Scientific and Technical Information of China (English)

    YUAN; Liwei; WANG; Yanqiu; WANG; Li; BAI; Jiling; HE; Guozh

    2004-01-01

    . Phys.Chem. A, 2003, 107: 6580-6586.[12]Imura, K., Kishimoto, N., Ohno, K., Two-dimensional penning ionization electron spectroscopy of dichlorobenzenes: orbital reactivity and anisotropic interaction of dichlorobenzenes with He*(23S), J. Phys. Chem. A, 2001, 105: 9111-9122.[13]Olesik, S., Baer, T., Morrow, J. C., Dissociation rates of energy-selected dichloro- and dibromobenzene ions, J. Phys. Chem.,1986, 90: 3563-3568.[14]Yoshida, N., Hirakawa, Y., Imasaka, T., Development of tunable picosecond dye laser for multiphoton ionization of dioxin precursors in supersonic jet/time-of-flight mass spectrometry, Anal.Chem., 2001, 73: 4417-4421.[15]Deguchi, T., Takeyasu, N., Imasaka, T., Measurement of the first excited singlet state lifetime of chlorobenzenes by a pump probe method using a narrow band tunable picosecond laser, Appl.Spectrom., 2002, 56(9): 1241-1243.[16]Brown, P., Kinetic studies in mass spectrometry, Ⅳ.The[M-Cl]reaction in substituted chlorobenzenes and the question of molecular ion isomerization, Org. Mass Spectrom., 1970, 3:639-642.[17]Felker, P. M., Zewail, A. H., Direct observation of nonchaotic multilevel vibrational energy flow in isolated polyatomic molecules, Phy. Rev. Lett., 1984, 30: 501-504.[18]Felker, P. M., Zewail, A. H., Dynamics of intramolecular vibrational-energy redistribution(IVR), I. Coherence effects, J. Chem.Phys., 1985, 82: 2961-3010.[19]Felker, P. M., Zewail, A. H., Purely rotational coherence effect and time-resolved sub-Doppler spectroscopy of large molecules, I.Theoretical, J. Chem. Phys., 1987, 86: 2460-2499.[20]Rosker, M. J., Wise, F. W., Tang, C. L., Femtosecond relaxation dynamics of large molecules, Phys. Rev. Lett., 1986, 57: 321-324.[21]Scherer, N. F., Khundkar, L. R., Rose, T. S. et al., Sub-Doppler measurement of excited-state rotational constants and rotational coherence by picosecond multiphoton ionization mass spectrometry, J. Phys. Chem., 1987, 91: 6478-6483.

  4. Bifurcations in dynamical systems with parametric excitation

    NARCIS (Netherlands)

    Fatimah, Siti

    2002-01-01

    This thesis is a collection of studies on coupled nonconservative oscillator systems which contain an oscillator with parametric excitation. The emphasis this study will, on the one hand, be on the bifurcations of the simple solutions such as fixed points and periodic orbits, and on the other hand o

  5. Origin of ultrafast excited state dynamics of 1-nitropyrene.

    Science.gov (United States)

    Murudkar, Sushant; Mora, Aruna K; Singh, Prabhat K; Nath, Sukhendu

    2011-10-01

    Time-resolved emission measurements in subpicosecond time domain have been carried out for 1-nitropyrene in different solvents to understand the mechanism for the observed ultrafast decay of its first excited singlet state. Excited-state dynamics of 1-nitropyrene is found to be independent of the solvent viscosity. This result contradicts the proposition in the literature (J. Phys. Chem. A 2007, 111, 552) that the ultrafast decay in 1-nitropyrene is due to the large amplitude torsional motion of the nitro group around the pyrene moiety. Excited-state dynamics of 1-nitropyrene in solvents with different dielectric constants shows that excited-state lifetime suddenly increases after a certain value of the dielectric constant. Detailed quantum chemical calculations have been carried out to understand the process that is responsible for the observed effect of the dielectric constant on the excited-state dynamics of 1-nitropyrene. It is seen that the excited-state lifetime and the singlet-triplet energy gap follow similar variation with the dielectric constant of the medium. Such a correlation between the excited-state lifetime and the singlet-triplet energy gap supports the fact that the observed ultrafast decay for 1-nitropyrene is due to an efficient intersystem crossing rather than to the torsional motion of the nitro group as proposed in the literature.

  6. Dynamic analysis of parametrically excited system under uncertainties and multi-frequency excitations

    Science.gov (United States)

    Wei, Sha; Han, Qinkai; Peng, Zhike; Chu, Fulei

    2016-05-01

    Some system parameters in mechanical systems are always uncertain due to uncertainties in geometric and material properties, lubrication condition and wear. For a more reasonable estimation of dynamic analysis of the parametrically excited system, the effect of uncertain parameters should be taken into account. This paper presents a new non-probabilistic analysis method for solving the dynamic responses of parametrically excited systems under uncertainties and multi-frequency excitations. By using the multi-dimensional harmonic balance method (MHBM) and the Chebyshev inclusion function (CIF), an interval multi-dimensional harmonic balance method (IMHBM) is obtained. To illustrate the accuracy of the proposed method, a time-varying geared system of wind turbine with different kinds of uncertainties is demonstrated. By comparing with the results of the scanning method, it is shown that the presented method is valid and effective for the parametrically excited system with uncertainties and multi-frequency excitations. The effects of some uncertain system parameters including uncertain mesh stiffnesses and uncertain bearing stiffnesses on the frequency responses of the system are also discussed in detail. It is shown that the dynamic responses of the system are insensitive to the uncertain mesh stiffness and bearing stiffnesses of the planetary gear stage. The uncertain bearing stiffnesses of the intermediate and high-speed stages will lead to relatively large uncertainties in the dynamic responses around resonant regions. It will provide valuable guidance for the optimal design and condition monitoring of wind turbine gearboxes.

  7. Nonlinear dynamics of a flexible portal frame under support excitation

    Science.gov (United States)

    de Paula, Aline Souza; Balthazar, José Manoel; Felix, Jorge Luis Palacios

    2012-11-01

    This paper presents a nonlinear dynamic analysis of a flexible portal frame subjected to support excitation, which is provided by an electro-dynamical shaker. The problem is reduced to a mathematical model of four degrees of freedom and the equations of motion are derived via Lagrangian formulation. The main goal of this study is to investigate the dynamic interactions between a flexible portal frame and a non-ideal support excitation. The numerical analysis shows a complex behavior of the system, which can be observed by phase spaces, Poincaŕ sections and bifurcation diagrams..

  8. Steady-state solutions of cell volume in a cardiac myocyte model elaborated for membrane excitation, ion homeostasis and Ca2+ dynamics.

    Science.gov (United States)

    Cha, Chae Young; Noma, Akinori

    2012-08-21

    The cell volume continuously changes in response to varying physiological conditions, and mechanisms underlying volume regulation have been investigated in both experimental and theoretical studies. Here, general formulations concerning cell volume change are presented in the context of developing a comprehensive cell model which takes Ca(2+) dynamics into account. Explicit formulas for charge conservation and steady-state volumes of the cytosol and endoplasmic reticulum (ER) are derived in terms of membrane potential, amount of ions, Ca(2+)-bound buffer molecules, and initial cellular conditions. The formulations were applied to a ventricular myocyte model which has plasma-membrane Ca(2+) currents with dynamic gating mechanisms, Ca(2+)-buffering reactions with diffusive and non-diffusive buffer proteins, and Ca(2+) uptake into or release from the sarcoplasmic reticulum (SR) accompanied by compensatory cationic or anionic currents through the SR membrane. Time-dependent volume changes in cardiac myocytes induced by varying extracellular osmolarity or by action potential generation were successfully simulated by the novel formulations. Through application of bifurcation analysis, the existence and uniqueness of steady-state solutions of the cell volume were validated, and contributions of individual ion channels and transporters to the steady-state volume were systematically analyzed. The new formulas are consistent with previous fundamental theory derived from simple models of minimum compositions. The new formulations may be useful for examination of the relationship between cell function and volume change in other cell types.

  9. Highly excited and exotic meson spectrum from dynamical lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Jozef Dudek, Robert Edwards, David Richards, Christopher Thomas

    2009-12-01

    Using a new quark-field construction algorithm and a large variational basis of operators, we extract a highly excited isovector meson spectrum on dynamical anisotropic lattices. We show how carefully constructed operators can be used to identify the continuum spin of extracted states. This method allows us to extract, with confidence, excited states, states of high spin and states with exotic quantum numbers, including, for the first time, spin-four states.

  10. π-Conjugated Organometallic Isoindigo Oligomer and Polymer Chromophores: Singlet and Triplet Excited State Dynamics and Application in Polymer Solar Cells.

    Science.gov (United States)

    Goswami, Subhadip; Gish, Melissa K; Wang, Jiliang; Winkel, Russell W; Papanikolas, John M; Schanze, Kirk S

    2015-12-01

    An isoindigo based π-conjugated oligomer and polymer that contain cyclometalated platinum(II) "auxochrome" units were subjected to photophysical characterization, and application of the polymer in bulk heterojunction polymer solar cells with PCBM acceptor was examined. The objective of the study was to explore the effect of the heavy metal centers on the excited state properties, in particular, intersystem crossing to a triplet (exciton) state, and further how this would influence the performance of the organometallic polymer in solar cells. The materials were characterized by electrochemistry, ground state absorption, emission, and picosecond-nanosecond transient absorption spectroscopy. Electrochemical measurements indicate that the cyclometalated units have a significant impact on the HOMO energy level of the chromophores, but little effect on the LUMO, which is consistent with localization of the LUMO on the isoindigo acceptor unit. Picosecond-nanosecond transient absorption spectroscopy reveals a transient with ∼100 ns lifetime that is assigned to a triplet excited state that is produced by intersystem crossing from a singlet state on a time scale of ∼130 ps. This is the first time that a triplet state has been observed for isoindigo π-conjugated chromophores. The performance of the polymer in bulk heterojunction solar cells was explored with PC61BM as an acceptor. The performance of the cells was optimum at a relatively high PCBM loading (1:6, polymer:PCBM), but the overall efficiency was relatively low with power conversion efficiency (PCE) of 0.22%. Atomic force microscopy of blend films reveals that the length scale of the phase separation decreases with increasing PCBM content, suggesting a reason for the increase in PCE with acceptor loading. Energetic considerations show that the triplet state in the polymer is too low in energy to undergo charge separation with PCBM. Further, due to the relatively low LUMO energy of the polymer, charge transfer

  11. Nonlinear Dynamical Analysis for the Cable Excited with Parametric and Forced Excitation

    Directory of Open Access Journals (Sweden)

    C. Z. Qian

    2014-01-01

    Full Text Available Considering the deck vibration effect on the cable in cable-stayed bridge, using nonlinear structure dynamics theory, the nonlinear dynamical equation for the stayed cable excited with deck vibration is proposed. Research shows that the vertical vibration of the deck has a combined parametric and forced excitation effect on the cable when the angle of the cable is taken into consideration. Using multiscale method, the 1/2 principle parametric resonance is studied and the bifurcation equation is obtained. Despite the parameters analysis, the bifurcation characters of the dynamical system are studied. At last, by means of numerical method and software MATHMATIC, the effect rules of system parameters to the dynamical behavior of the system are studied, and some useful conclusions are obtained.

  12. Dynamic Coherence in Excitonic Molecular Complexes under Various Excitation Conditions

    CERN Document Server

    Chenu, Aurélia; Mancal, Tomáš

    2013-01-01

    In this paper, we investigate the relevance of dynamic electronic coherence under conditions natural to light-harvesting systems. We formulate the results of a quantum mechanical treatment of a weak light-matter interaction in terms of experimental observable, such as the incident light spectrum and the absorption spectrum of the material, and we derive the description of the incoherent F\\"orster type energy transfer fully from the wave function formalism. We demonstrate that excitation of a coherent superposition of electronic eigenstates of natural light-harvesting complexes by sunlight or by excitation transfer from a neighboring antenna is unlikely and that dynamical coherence therefore cannot play any significant role in natural photosynthesis, regardless of their life time. Dynamical coherence as a transient phenomenon must be strictly distinguished from the effect of excited state delocalization (also termed quantum coherence in the literature) which is established by interaction between the pigments a...

  13. Dynamics of Microbeams under Multi-Frequency Excitations

    Directory of Open Access Journals (Sweden)

    Alwathiqbellah Ibrahim

    2017-01-01

    Full Text Available This paper presents an investigation of the dynamics of microbeams under multiple harmonic electrostatic excitation frequencies. First, the response of a cantilever microbeam to two alternating current (AC source excitation is examined. We show by simulations the response of the microbeam at primary resonance (near the fundamental natural frequency and at secondary resonances (near half, superharmonic, and twice, subharmonic, the fundamental natural frequency. A multimode Galerkin method combined with the Euler-Bernoulli beam equation, accounting for the nonlinear electrostatic force, has been used to develop a reduced order model. The response of the cantilever microbeam to three AC source excitation is also investigated and shown as a promising technique to enhance the bandwidth of resonators. Finally, an experimental study of a clamped-clamped microbeam is conducted, demonstrating the multi-frequency excitation resonances using two, three, and four AC sources.

  14. Nonlinear dynamic response of stay cables under axial harmonic excitation

    Institute of Scientific and Technical Information of China (English)

    Xu XIE; He ZHAN; Zhi-cheng ZHANG

    2008-01-01

    This paper proposes a new numerical simulation method for analyzing the parametric vibration of stay cables based on the theory of nonlinear dynamic response of structures under the asynchronous support excitation.The effects of important parameters related to parametric vibration of cables,I.e., characteristics of structure,excitation frequency,excitation amplitude,damping effect of the air and the viscous damping coefficient of the cables,were investigated by using the proposed method for the cables with significant length difference as examples.The analysis results show that nonlinear finite element method is a powerful technique in analyzing the parametric vibration of cables,the behavior of parametric vibration of the two cables with different Irvine parameters has similar properties,the amplitudes of parametric vibration of cables are related to the frequency and amplitude of harmonic support excitations and the effect of distributed viscous damping on parametric vibration of the cables is very small.

  15. Dynamics of Microbeams under Multi-Frequency Excitations

    KAUST Repository

    Ibrahim, Alwathiqbellah

    2017-01-24

    This paper presents an investigation of the dynamics of microbeams under multiple harmonic electrostatic excitation frequencies. First, the response of a cantilever microbeam to two alternating current (AC) source excitation is examined. We show by simulations the response of the microbeam at primary resonance (near the fundamental natural frequency) and at secondary resonances (near half, superharmonic, and twice, subharmonic, the fundamental natural frequency). A multimode Galerkin method combined with the Euler-Bernoulli beam equation, accounting for the nonlinear electrostatic force, has been used to develop a reduced order model. The response of the cantilever microbeam to three AC source excitation is also investigated and shown as a promising technique to enhance the bandwidth of resonators. Finally, an experimental study of a clamped-clamped microbeam is conducted, demonstrating the multi-frequency excitation resonances using two, three, and four AC sources.

  16. Inhibition causes ceaseless dynamics in networks of excitable nodes

    Science.gov (United States)

    Larremore, Daniel B.; Shew, Woodrow L.; Ott, Edward; Sorrentino, Francesco; Restrepo, Juan G.

    2014-01-01

    The collective dynamics of a network of excitable nodes changes dramatically when inhibitory nodes are introduced. We consider inhibitory nodes which may be activated just like excitatory nodes but, upon activating, decrease the probability of activation of network neighbors. We show that, although the direct effect of inhibitory nodes is to decrease activity, the collective dynamics becomes self-sustaining. We explain this counterintuitive result by defining and analyzing a “branching function” which may be thought of as an activity-dependent branching ratio. The shape of the branching function implies that for a range of global coupling parameters dynamics are self-sustaining. Within the self-sustaining region of parameter space lies a critical line along which dynamics take the form of avalanches with universal scaling of size and duration, embedded in ceaseless timeseries of activity. Our analyses, confirmed by numerical simulation, suggest that inhibition may play a counterintuitive role in excitable networks. PMID:24745460

  17. Toward the excited meson spectrum of dynamical QCD

    Energy Technology Data Exchange (ETDEWEB)

    Dudek, Jozef J.; Edwards, Robert G.; Peardon, Michael J.; Richards, David G.; Thomas, Christopher E.

    2010-08-01

    We present a detailed description of the extraction of the highly excited isovector meson spectrum on dynamical anisotropic lattices using a new quark-field construction algorithm and a large variational basis of operators. With careful operator construction, the combination of these techniques is used to identify the continuum spin of extracted states reliably, overcoming the reduced rotational symmetry of the cubic lattice. Excited states, states with exotic quantum numbers (0+-, 1-+ and 2+-) and states of high spin are resolved, including, for the first time in a lattice QCD calculation, spin-four states. The determinations of the spectrum of isovector mesons and kaons are performed on dynamical lattices with two volumes and with pion masses down to ~ 400 MeV, with statistical precision typically at or below 1% even for highly excited states.

  18. Modelling hair follicle growth dynamics as an excitable medium.

    Directory of Open Access Journals (Sweden)

    Philip J Murray

    Full Text Available The hair follicle system represents a tractable model for the study of stem cell behaviour in regenerative adult epithelial tissue. However, although there are numerous spatial scales of observation (molecular, cellular, follicle and multi follicle, it is not yet clear what mechanisms underpin the follicle growth cycle. In this study we seek to address this problem by describing how the growth dynamics of a large population of follicles can be treated as a classical excitable medium. Defining caricature interactions at the molecular scale and treating a single follicle as a functional unit, a minimal model is proposed in which the follicle growth cycle is an emergent phenomenon. Expressions are derived, in terms of parameters representing molecular regulation, for the time spent in the different functional phases of the cycle, a formalism that allows the model to be directly compared with a previous cellular automaton model and experimental measurements made at the single follicle scale. A multi follicle model is constructed and numerical simulations are used to demonstrate excellent qualitative agreement with a range of experimental observations. Notably, the excitable medium equations exhibit a wider family of solutions than the previous work and we demonstrate how parameter changes representing altered molecular regulation can explain perturbed patterns in Wnt over-expression and BMP down-regulation mouse models. Further experimental scenarios that could be used to test the fundamental premise of the model are suggested. The key conclusion from our work is that positive and negative regulatory interactions between activators and inhibitors can give rise to a range of experimentally observed phenomena at the follicle and multi follicle spatial scales and, as such, could represent a core mechanism underlying hair follicle growth.

  19. Potassium accumulation as dynamic modulator of neurohypophysial excitability.

    Science.gov (United States)

    Foley, J; Nguyen, H; Bennett, C B; Muschol, M

    2010-08-11

    Activity-dependent modulation of excitable responses from neurohypophysial axons and their secretory swellings has long been recognized as an important regulator of arginine vasopressin and oxytocin release during patterned stimulation. Various activity-dependent mechanisms, including action potential broadening, potassium accumulation, and autocrine or paracrine feedback, have been proposed as underlying mechanisms. However, the relevance of any specific mechanism on net excitability in the intact preparation, during different levels of overall activation, and during realistic stimulation with trains of action potentials has remained largely undetermined. Using high-speed optical recordings and potentiometric dyes, we have quantified the dynamics of global excitability under physiologically more realistic conditions, that is in the intact neurohypophysis during trains of stimuli at varying frequencies and levels of overall activity. Net excitability facilitated during stimulation at low frequencies or at low activity. During persistent high-intensity or high-frequency stimulation, net excitability became severely depressed. Depression of excitable responses was strongly affected by manipulations of extracellular potassium levels, including changes to resting [K(+)](out), increases of interstitial spaces with hypertonic solutions and inhibition of Na(+)/K(+) ATPase activity. Application of the GABA(A) receptor blocker bicuculline or manipulations of Ca(2+) influx showed little effect. Numerical simulation of K(+) accumulation on action potentials of individual axons reproduced optically recorded population responses, including the overall depression of action potential (AP) amplitudes, modest AP broadening and the prominent loss of hyperpolarizing undershoots. Hence, extracellular potassium accumulation dominates activity-dependent depression of neurohypophysial excitability under elevated stimulation conditions. The intricate dependence on the short

  20. Experimental Study on Free Spanning Submarine Pipeline Under Dynamic Excitation

    Institute of Scientific and Technical Information of China (English)

    李昕; 刘亚坤; 周晶; 马恒春; 朱彤

    2002-01-01

    Seismic load has a significant effect on the response of a free spanning submarine pipeline when the pipeline is constructed in a seismically active region. The model experiment is performed on an underwater shaking table to simulate the response of submarine pipelines under dynamic input. In consideration of the effects of the terrestrial and submarine pipeline, water depth, support condition, distance from seabed, empty and full pipeline, and span on dynamic response, 120 groups of experiments are conducted. Affecting factors are analyzed and conclnsions are drawn for reference. For the control of dynamic response, the span of a submarine pipeline is by far more important than the other factors. Meanwhile, the rosponse difference between a submarine pipeline under sine excitation and that under random excitation exists in experiments.

  1. Femtosecond Excited State Dynamics of Size Selected Neutral Molecular Clusters.

    Science.gov (United States)

    Montero, Raúl; León, Iker; Fernández, José A; Longarte, Asier

    2016-07-21

    The work describes a novel experimental approach to track the relaxation dynamics of an electronically excited distribution of neutral molecular clusters formed in a supersonic expansion, by pump-probe femtosecond ionization. The introduced method overcomes fragmentation issues and makes possible to retrieve the dynamical signature of a particular cluster from each mass channel, by associating it to an IR transition of the targeted structure. We have applied the technique to study the nonadiabatic relaxation of pyrrole homoclusters. The results obtained exciting at 243 nm, near the origin of the bare pyrrole electronic absorption, allow us to identify the dynamical signature of the dimer (Py)2, which exhibits a distinctive lifetime of τ1 ∼ 270 fs, considerably longer than the decays recorded for the monomer and bigger size clusters (Py)n>2. A possible relationship between the measured lifetime and the clusters geometries is tentatively discussed.

  2. Stochastic differential equation model for cerebellar granule cell excitability.

    Science.gov (United States)

    Saarinen, Antti; Linne, Marja-Leena; Yli-Harja, Olli

    2008-02-29

    Neurons in the brain express intrinsic dynamic behavior which is known to be stochastic in nature. A crucial question in building models of neuronal excitability is how to be able to mimic the dynamic behavior of the biological counterpart accurately and how to perform simulations in the fastest possible way. The well-established Hodgkin-Huxley formalism has formed to a large extent the basis for building biophysically and anatomically detailed models of neurons. However, the deterministic Hodgkin-Huxley formalism does not take into account the stochastic behavior of voltage-dependent ion channels. Ion channel stochasticity is shown to be important in adjusting the transmembrane voltage dynamics at or close to the threshold of action potential firing, at the very least in small neurons. In order to achieve a better understanding of the dynamic behavior of a neuron, a new modeling and simulation approach based on stochastic differential equations and Brownian motion is developed. The basis of the work is a deterministic one-compartmental multi-conductance model of the cerebellar granule cell. This model includes six different types of voltage-dependent conductances described by Hodgkin-Huxley formalism and simple calcium dynamics. A new model for the granule cell is developed by incorporating stochasticity inherently present in the ion channel function into the gating variables of conductances. With the new stochastic model, the irregular electrophysiological activity of an in vitro granule cell is reproduced accurately, with the same parameter values for which the membrane potential of the original deterministic model exhibits regular behavior. The irregular electrophysiological activity includes experimentally observed random subthreshold oscillations, occasional spontaneous spikes, and clusters of action potentials. As a conclusion, the new stochastic differential equation model of the cerebellar granule cell excitability is found to expand the range of dynamics

  3. Excitation dynamics of interacting Rydberg atoms in small lattices

    Energy Technology Data Exchange (ETDEWEB)

    Wu, G., E-mail: gwu@physnet.uni-hamburg.de [Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany); Physikalisches Institut, Universität Heidelberg, Im Neuenheimer Feld 226, 69120 Heidelberg (Germany); Kurz, M.; Liebchen, B. [Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany); Schmelcher, P. [Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany); The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)

    2015-01-23

    We study the Rydberg excitation dynamics of laser-driven atoms confined in a one-dimensional three-site lattice with open boundary conditions. Different regular excitation patterns are obtained within various parameter regimes. In the case of a weak Rydberg–Rydberg interaction, the excitation probability possesses a nodal structure which is characterized by an envelope with a period inversely proportional to the interaction. For strong Rydberg interaction we observe dipole blockade and antiblockade effects and an appropriate detuning leads to an overall oscillatory behavior of the Rydberg probability density which is modulated only by small oscillations. Besides an exact diagonalization procedure we study the system by performing first and second order perturbation theory as well as a spectral analysis. - Highlights: • We study Rydberg excitation in small 1-d lattices. • For weak Rydberg interaction, the excitation probability possesses an envelope structure. • For strong Rydberg interaction, we observe dipole blockade and antiblockade effects. • A specific detuning leads to degeneracy and regular oscillatory behavior of the Rydberg density.

  4. Dynamic responses under the excitation of pulse sequences

    Institute of Scientific and Technical Information of China (English)

    Dai Junwu(戴君武); Mai Tong; George C. Lee; Qi Xiaozhai(齐霄斋); Bai Wenting(白文婷)

    2004-01-01

    This paper studies the dynamic responses of SDOF system under pulse-dominant excitations. The purpose of the study is to prepare for scrutiny of some near-field pulse-dominant ground motions and their potential to cause structural damage. Extending the single pulse dynamics, we consider the effect of pulse sequences. This kind of excitation was particularly obvious in some of previous earthquakes such as Northridge (1994) and Chi-Chi (1995). Based on the duration,peak and rise and decay era of the main pulse as well as its relationship with the predecessor and successor pulses, we propose a classification for the pulse sequences. Consequent studies have been carried out for acceleration, velocity and displacement response spectra of the main pulse with either a predecessor or a successor pulse. The analysis also includes general response behaviors in different fundamental period segments and special aspects of response at certain points (e.g., the corresponding peak points).

  5. Dynamics of a Parametrically Excited System with Two Forcing Terms

    Directory of Open Access Journals (Sweden)

    Anastasia Sofroniou

    2014-09-01

    Full Text Available Motivated by the dynamics of a trimaran, an investigation of the dynamic behaviour of a double forcing parametrically excited system is carried out. Initially, we provide an outline of the stability regions, both numerically and analytically, for the undamped linear, extended version of the Mathieu equation. This paper then examines the anticipated form of response of our proposed nonlinear damped double forcing system, where periodic and quasiperiodic routes to chaos are graphically demonstrated and compared with the case of the single vertically-driven pendulum.

  6. Ontogeny of electrically excitable cells in cultured olfactory epithelium.

    OpenAIRE

    Schubert, D; Stallcup, W.; LaCorbiere, M; Kidokoro, Y; Orgel, L

    1985-01-01

    A primary system has been developed in which it is possible to study the production of electrically excitable neuron-like cells from a precursor population of olfactory epithelial cells. Rat nasal epithelium was dissociated and placed in culture. The initial surviving cells are flat and ciliated and contain glial fibrillary acidic protein (GFAP). After 3-5 days electrically excitable cells appear that contain neuron-specific enolase but not GFAP. These round cells originate by means of the di...

  7. Dynamic patterns and their interactions in networks of excitable elements.

    Science.gov (United States)

    Gong, Pulin; Steel, Harrison; Robinson, Peter; Qi, Yang

    2013-10-01

    Formation of localized propagating patterns is a fascinating self-organizing phenomenon that happens in a wide range of spatially extended, excitable systems in which individual elements have resting, activated, and refractory states. Here we study a type of stochastic three-state excitable network model that has been recently developed; this model is able to generate a rich range of pattern dynamics, including localized wandering patterns and localized propagating patterns with crescent shapes and long-range propagation. The collective dynamics of these localized patterns have anomalous subdiffusive dynamics before symmetry breaking and anomalous superdiffusive dynamics after that, showing long-range spatiotemporal coherence in the system. In this study, the stability of the localized wandering patterns is analyzed by treating an individual localized pattern as a subpopulation to develop its average response function. This stability analysis indicates that when the average refractory period is greater than a certain value, there are too many elements in the refractory state after being activated to allow the subpopulation to support a self-sustained pattern; this is consistent with symmetry breaking identified by using an order parameter. Furthermore, in a broad parameter space, the simple network model is able to generate a range of interactions between different localized propagating patterns including repulsive collisions and partial and full annihilations, and interactions between localized propagating patterns and the refractory wake behind others; in this study, these interaction dynamics are systematically quantified based on their relative propagation directions and the resultant angles between them before and after their collisions. These results suggest that the model potentially provides a modeling framework to understand the formation of localized propagating patterns in a broad class of systems with excitable properties.

  8. What Gets a Cell Excited? Kinky Curves

    Science.gov (United States)

    Kay, Alan R.

    2014-01-01

    Hodgkin and Huxley's (5) revealing the origins of cellular excitability is one of the great triumphs of physiology. In an extraordinarily deft series of papers, they were able to measure the essential electrical characteristics of neurons and synthesize them into a quantitative model that accounts for the excitability of neurons and other…

  9. Evolution of Externally Excited Convective Cells in Plasmas

    DEFF Research Database (Denmark)

    Sugai, H.; Juul Rasmussen, Jens; Thomsen, Kenneth

    1983-01-01

    Convective cells are excited externally in a fully ionized magnetized plasma, and their space-time evolution is investigated by two-dimensional potential measurements. A positive cell is excited externally in the `scrape-off' layer of a plasma column produced by surface ionization. Its interaction...

  10. Bistable dynamics underlying excitability of ion homeostasis in neuron models.

    Directory of Open Access Journals (Sweden)

    Niklas Hübel

    2014-05-01

    Full Text Available When neurons fire action potentials, dissipation of free energy is usually not directly considered, because the change in free energy is often negligible compared to the immense reservoir stored in neural transmembrane ion gradients and the long-term energy requirements are met through chemical energy, i.e., metabolism. However, these gradients can temporarily nearly vanish in neurological diseases, such as migraine and stroke, and in traumatic brain injury from concussions to severe injuries. We study biophysical neuron models based on the Hodgkin-Huxley (HH formalism extended to include time-dependent ion concentrations inside and outside the cell and metabolic energy-driven pumps. We reveal the basic mechanism of a state of free energy-starvation (FES with bifurcation analyses showing that ion dynamics is for a large range of pump rates bistable without contact to an ion bath. This is interpreted as a threshold reduction of a new fundamental mechanism of ionic excitability that causes a long-lasting but transient FES as observed in pathological states. We can in particular conclude that a coupling of extracellular ion concentrations to a large glial-vascular bath can take a role as an inhibitory mechanism crucial in ion homeostasis, while the Na⁺/K⁺ pumps alone are insufficient to recover from FES. Our results provide the missing link between the HH formalism and activator-inhibitor models that have been successfully used for modeling migraine phenotypes, and therefore will allow us to validate the hypothesis that migraine symptoms are explained by disturbed function in ion channel subunits, Na⁺/K⁺ pumps, and other proteins that regulate ion homeostasis.

  11. Excitation and dynamics of liquid tin micrometer droplet generation

    Science.gov (United States)

    Rollinger, B.; Abhari, R. S.

    2016-07-01

    The dynamics of capillary breakup-based droplet generation are studied for an excitation system based on a tunable piezoelectrically actuated oscillating piston, which generates acoustic pressure waves at the dispenser nozzle. First, the non-ideal pressure boundary conditions of droplet breakup are measured using a fast response pressure probe. A structural analysis shows that the axial modes of the excitation system are the main reasons for the resonance peaks in the pressure response. Second, a correlation between the nozzle inlet pressure and the droplet timing jitter is established with the help of experiments and a droplet formation model. With decreasing wave number, the growth rate of the main excitation decreases, while noise contributions with wave numbers with higher growth rates lead to a non-deterministic structure of the droplet train. A highly coherent and monodisperse droplet stream is obtained when the excitation system is tuned to generate high acoustic pressures at the desired operation frequency and when the noise level on the jet is limited. The jet velocity, hence droplet spacing for a set frequency is then adjusted by varying the reservoir pressure, according to the trade-off between lowest wave number and acceptable timing jitter.

  12. Dynamics of two-electron excitations in helium

    Energy Technology Data Exchange (ETDEWEB)

    Caldwell, C.D.; Menzel, A.; Frigo, S.P. [Univ. of Central Florida, Orlando, FL (United States)] [and others

    1997-04-01

    Excitation of both electrons in helium offers a unique window for studying electron correlation at the most basic level in an atom in which these two electrons and the nucleus form a three-body system. The authors utilized the first light available at the U-8 undulator-SGM monochromator beamline to investigate the dynamic parameters, partial cross sections, differential cross sections, and photoelectron angular distribution parameters ({beta}), with a high resolving power for the photon beam and at the highly differential level afforded by the use of their electron spectrometer. In parallel, they carried out detailed calculations of the relevant properties by a theoretical approach that is based on the hyperspherical close-coupling method. Partial photoionization cross sections {sigma}{sub n}, and photoelectron angular distributions {beta}{sub n} were measured for all possible final ionic states He{sup +}(n) in the region of the double excitations N(K,T){sup A} up to the N=5 threshold. At a photon energy bandpass of 12 meV below the thresholds N=3, 4, and 5, this level of differentiation offers the most critical assessment of the dynamics of the two-electron excitations to date. The experimental data were seen to be very well described by the most advanced theoretical calculations.

  13. Excited state dynamics of the astaxanthin radical cation

    Science.gov (United States)

    Amarie, Sergiu; Förster, Ute; Gildenhoff, Nina; Dreuw, Andreas; Wachtveitl, Josef

    2010-07-01

    Femtosecond transient absorption spectroscopy in the visible and NIR and ultrafast fluorescence spectroscopy were used to examine the excited state dynamics of astaxanthin and its radical cation. For neutral astaxanthin, two kinetic components corresponding to time constants of 130 fs (decay of the S 2 excited state) and 5.2 ps (nonradiative decay of the S 1 excited state) were sufficient to describe the data. The dynamics of the radical cation proved to be more complex. The main absorption band was shifted to 880 nm (D 0 → D 3 transition), showing a weak additional band at 1320 nm (D 0 → D 1 transition). We found, that D 3 decays to the lower-lying D 2 within 100 fs, followed by a decay to D 1 with a time constant of 0.9 ps. The D 1 state itself exhibited a dual behavior, the majority of the population is transferred to the ground state in 4.9 ps, while a small population decays on a longer timescale of 40 ps. Both transitions from D 1 were found to be fluorescent.

  14. Quantification of Dynamic Excitation Potential of Pedestrian Population Crossing Footbridges

    Directory of Open Access Journals (Sweden)

    Stana Žcaronivanović

    2011-01-01

    Full Text Available Due to their slenderness, many modern footbridges may vibrate significantly under pedestrian traffic. Consequently, the vibration serviceability of these structures under human-induced dynamic loading is becoming their governing design criterion. Many current vibration serviceability design guidelines, concerned with prediction of the vibration in the vertical direction, estimate a single response level that corresponds to an "average" person crossing the bridge with the step frequency that matches a footbridge natural frequency. However, different pedestrians have different dynamic excitation potential, and therefore could generate significantly different vibration response of the bridge structure. This paper aims to quantify this potential by estimating the range of structural vibrations (in the vertical direction that could be induced by different individuals and the probability of occurrence of any particular vibration level. This is done by introducing the inter- and intra-subject variability in the walking force modelling. The former term refers to inability of a pedestrian to induce an exactly the same force with each step while the latter refers to different forces (in terms of their magnitude, frequency and crossing speed induced by different people. Both types of variability are modelled using the appropriate probability density functions. The probability distributions were then implemented into a framework procedure for vibration response prediction under a single person excitation. Instead of a single response value obtained using currently available design guidelines, this new framework yields a range of possible acceleration responses induced by different people and a distribution function for these responses. The acceleration ranges estimated are then compared with experimental data from two real-life footbridges. The substantial differences in the dynamic response induced by different people are obtained in both the numerical and

  15. Coherent and Incoherent Structural Dynamics in Laser-Excited Antimony

    CERN Document Server

    Waldecker, Lutz; Bertoni, Roman; Vasileiadis, Thomas; Garcia, Martin E; Zijlstra, Eeuwe S; Ernstorfer, Ralph

    2016-01-01

    We investigate the excitation of phonons in photoexcited antimony and demonstrate that the entire electron-lattice interactions, in particular coherent and incoherent electron-phonon coupling, can be probed simultaneously. Using femtosecond electron diffraction (FED) with high temporal resolution, we observe the coherent excitation of the fully symmetric \\Ag\\ optical phonon mode via the shift of the minimum of the atomic potential energy surface. Molecular dynamics simulations are performed to quantify the change in lattice potential and the associated real-space amplitude of the coherent atomic oscillations. In addition, our experimental configuration allows observing the energy transfer from electrons to phonons via incoherent electron-lattice scattering events. Applying a modified two-temperature model, the electron-phonon coupling is determined from the data as a function of electronic temperature.

  16. Adaptive Dynamic Surface Control for Generator Excitation Control System

    Directory of Open Access Journals (Sweden)

    Zhang Xiu-yu

    2014-01-01

    Full Text Available For the generator excitation control system which is equipped with static var compensator (SVC and unknown parameters, a novel adaptive dynamic surface control scheme is proposed based on neural network and tracking error transformed function with the following features: (1 the transformation of the excitation generator model to the linear systems is omitted; (2 the prespecified performance of the tracking error can be guaranteed by combining with the tracking error transformed function; (3 the computational burden is greatly reduced by estimating the norm of the weighted vector of neural network instead of the weighted vector itself; therefore, it is more suitable for the real time control; and (4 the explosion of complicity problem inherent in the backstepping control can be eliminated. It is proved that the new scheme can make the system semiglobally uniformly ultimately bounded. Simulation results show the effectiveness of this control scheme.

  17. Spiral-wave dynamics in excitable medium with excitability modulated by rectangle wave

    Institute of Scientific and Technical Information of China (English)

    Yuan Guo-Yong

    2011-01-01

    We numerically study the dynamics of spiral waves in the excitable system with the excitability modulated by a rectangle wave. The tip trajectories and their variations with the modulation period T are explained by the corresponding spectrum analysis. For a large T, the external modulation leads to the occurrence of more frequency peaks and these frequencies change with the modulation period according to their specific rules, respectively. Some of the frequencies and a primary frequency f1 determine the corresponding curvature periods, which are locked into rational multiplies of the modulation period. These frequency-locking behaviours and the limited life-span of the frequencies in their variations with the modulation period constitute many resonant entrainment bands in the T axis. In the main bands, which follow the relation T/T12=m/n,the size variable Rx of the tip trajectory is a monotonic increasing function of T. The rest of the frequencies are linear combinations of the two ones. Due to the complex dynamics, many unique tip trajectories appear at some certain T. We find also that spiral waves are eliminated when T is chosen from the end of the main resonant bands. This offers a useful method of controling the spiral wave.

  18. Electronic excited states and relaxation dynamics in polymer heterojunction systems

    Science.gov (United States)

    Ramon, John Glenn Santos

    The potential for using conducting polymers as the active material in optoelectronic devices has come to fruition in the past few years. Understanding the fundamental photophysics behind their operations points to the significant role played by the polymer interface in their performance. Current device architectures involve the use of bulk heterojunctions which intimately blend the donor and acceptor polymers to significantly increase not only their interfacial surface area but also the probability of exciton formation within the vicinity of the interface. In this dissertation, we detail the role played by the interface on the behavior and performance of bulk heterojunction systems. First, we explore the relation between the exciton binding energy to the band offset in determining device characteristics. As a general rule, when the exciton binding energy is greater than the band offset, the exciton remains the lowest energy excited state leading to efficient light-emitting properties. On the other hand, if the offset is greater than the binding energy, charge separation becomes favorable leading to better photovoltaic behavior. Here, we use a Wannier function, configuration interaction based approach to examine the essential excited states and predict the vibronic absorption and emission spectra of the PPV/BBL, TFB/F8BT and PFB/F8BT heterojunctions. Our results underscore the role of vibrational relaxation in the formation of charge-transfer states following photoexcitation. In addition, we look at the relaxation dynamics that occur upon photoexcitation. For this, we adopt the Marcus-Hush semiclassical method to account for lattice reorganization in the calculation of the interconversion rates in TFB/F8BT and PFB/F8BT. We find that, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, a regeneration pathway to the optically active lowest excitonic state in TFB/F8BT is possible via thermal repopulation from the exciplex. Finally

  19. Nonadiabatic Excited-State Molecular Dynamics Modeling of Photoinduced Dynamics in Conjugated Molecules

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, Tammie [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Center for Nonlinear Studies (CNLS) and Center for Integrated Nanotechnologies (CINT), Theoretical Division; Fernandez-Alberti, Sebastian [Univ. Nacional de Quilmes, Buenos Aires (Argentina); Chernyak, Vladimir [Wayne State Univ., Detroit, MI (United States). Dept. of Chemistry; Roitberg, Adrian E. [Univ. of Florida, Gainesville, FL (United States). Depts. of Physics and Chemistry. Quantum Theory Project; Tretiak, Sergei [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Center for Nonlinear Studies (CNLS) and Center for Integrated Nanotechnologies (CINT), Theoretical Division

    2011-01-10

    Nonadiabatic dynamics generally defines the entire evolution of electronic excitations in optically active molecular materials. It is commonly associated with a number of fundamental and complex processes such as intraband relaxation, energy transfer, and light harvesting influenced by the spatial evolution of excitations and transformation of photoexcitation energy into electrical energy via charge separation (e.g., charge injection at interfaces). To treat ultrafast excited-state dynamics and exciton/charge transport we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework incorporating quantum transitions. Our calculations rely on the use of the Collective Electronic Oscillator (CEO) package accounting for many-body effects and actual potential energy surfaces of the excited states combined with Tully’s fewest switches algorithm for surface hopping for probing nonadiabatic processes. This method is applied to model the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene, PPV). Our analysis shows intricate details of photoinduced vibronic relaxation and identifies specific slow and fast nuclear motions that are strongly coupled to the electronic degrees of freedom, namely, torsion and bond length alternation, respectively. Nonadiabatic relaxation of the highly excited mA{sub g} state is predicted to occur on a femtosecond time scale at room temperature and on a picosecond time scale at low temperature.

  20. Sub-50 fs excited state dynamics of 6-chloroguanine upon deep ultraviolet excitation.

    Science.gov (United States)

    Mondal, Sayan; Puranik, Mrinalini

    2016-05-18

    The photophysical properties of natural nucleobases and their respective nucleotides are ascribed to the sub-picosecond lifetime of their first singlet states in the UV-B region (260-350 nm). Electronic transitions of the ππ* type, which are stronger than those in the UV-B region, lie at the red edge of the UV-C range (100-260 nm) in all isolated nucleobases. The lowest energetic excited states in the UV-B region of nucleobases have been investigated using a plethora of experimental and theoretical methods in gas and solution phases. The sub-picosecond lifetime of these molecules is not a general attribute of all nucleobases but specific to the five primary nucleobases and a few xanthine and methylated derivatives. To determine the overall UV photostability, we aim to understand the effect of more energetic photons lying in the UV-C region on nucleobases. To determine the UV-C initiated photophysics of a nucleobase system, we chose a halogen substituted purine, 6-chloroguanine (6-ClG), that we had investigated previously using resonance Raman spectroscopy. We have performed quantitative measurements of the resonance Raman cross-section across the Bb absorption band (210-230 nm) and constructed the Raman excitation profiles. We modeled the excitation profiles using Lee and Heller's time-dependent theory of resonance Raman intensities to extract the initial excited state dynamics of 6-ClG within 30-50 fs after photoexcitation. We found that imidazole and pyrimidine rings of 6-ClG undergo expansion and contraction, respectively, following photoexcitation to the Bb state. The amount of distortions of the excited state structure from that of the ground state structure is reflected by the total internal reorganization energy that is determined at 112 cm(-1). The contribution of the inertial component of the solvent response towards the total reorganization energy was obtained at 1220 cm(-1). In addition, our simulation also yields an instantaneous response of the first

  1. Control of hair cell excitability by vestibular primary sensory neurons.

    OpenAIRE

    Brugeaud, Aurore; Travo, Cécile; Demêmes, Danielle; Lenoir, Marc; Llorens, Jordi; Puel, Jean-Luc; Chabbert, Christian

    2007-01-01

    International audience; In the rat utricle, synaptic contacts between hair cells and the nerve fibers arising from the vestibular primary neurons form during the first week after birth. During that period, the sodium-based excitability that characterizes neonate utricle sensory cells is switched off. To investigate whether the establishment of synaptic contacts was responsible for the modulation of the hair cell excitability, we used an organotypic culture of rat utricle in which the setting ...

  2. Dynamical correlations and collective excitations of Yukawa liquids

    CERN Document Server

    Donko, Zoltan; Hartmann, Peter

    2008-01-01

    In dusty (complex) plasmas, containing mesoscopic charged grains, the grain-grain interaction in many cases can be well described through a Yukawa potential. In this Review we summarize the basics of the computational and theoretical approaches capable of describing many-particle Yukawa systems in the liquid and solid phases and discuss the properties of the dynamical density and current correlation spectra of three- and two-dimensional strongly coupled Yukawa systems, generated by molecular dynamics simulations. We show details of the $\\omega(k)$ dispersion relations for the collective excitations in these systems, as obtained theoretically following the quasilocalized charge approximation, as well as from the fluctuation spectra created by simulations. The theoretical and simulation results are also compared with those obtained in complex plasma experiments.

  3. Stripes in cuprate superconductors: Excitations and dynamic dichotomy

    Energy Technology Data Exchange (ETDEWEB)

    Seibold, G., E-mail: goetz@physik.tu-cottbus.de [Institut fuer Physik, BTU Cottbus, P.O. Box 101344, 03013 Cottbus (Germany); Grilli, M.; Lorenzana, J. [SMC-INFM-CNR, Dipartimento di Fisica, Universita di Roma ' La Sapienza' , P.le Aldo Moro 5, I-00185 Roma (Italy)

    2012-11-01

    We present a short account of the present experimental situation of stripes in cuprates followed by a review of our present understanding of their ground state and excited state properties. Collective modes, the dynamical structure factor, and the optical conductivity of stripes are computed using the time-dependent Gutzwiller approximation applied to realistic one band and three band Hubbard models, and are found to be in excellent agreement with experiment. On the other hand, experiments like angle-resolved photoemission and scanning tunneling microscopy show the coexistence of stripes at high energies with Fermi liquid quasiparticles at low energies. We show that a phenomenological model going beyond mean-field can reconcile this dynamic dichotomy.

  4. Nonadiabatic excited-state molecular dynamics: On-the-fly limiting of essential excited states

    Science.gov (United States)

    Nelson, Tammie; Naumov, Artem; Fernandez-Alberti, Sebastian; Tretiak, Sergei

    2016-12-01

    The simulation of nonadiabatic dynamics in extended molecular systems involving hundreds of atoms and large densities of states is particularly challenging. Nonadiabatic coupling terms (NACTs) represent a significant numerical bottleneck in surface hopping approaches. Rather than using unreliable NACT cutting schemes, here we develop "on-the-fly" state limiting methods to eliminate states that are no longer essential for the non-radiative relaxation dynamics as a trajectory proceeds. We propose a state number criteria and an energy-based state limit. The latter is more physically relevant by requiring a user-imposed energy threshold. For this purpose, we introduce a local kinetic energy gauge by summing contributions from atoms within the spatial localization of the electronic wavefunction to define the energy available for upward hops. The proposed state limiting schemes are implemented within the nonadiabatic excited-state molecular dynamics framework to simulate photoinduced relaxation in poly-phenylene vinylene (PPV) and branched poly-phenylene ethynylene (PPE) oligomers for benchmark evaluation.

  5. Excitation and Ionisation dynamics in high-frequency plasmas

    Science.gov (United States)

    O'Connell, D.

    2008-07-01

    Non-thermal low temperature plasmas are widely used for technological applications. Increased demands on plasma technology have resulted in the development of various discharge concepts based on different power coupling mechanisms. Despite this, power dissipation mechanisms in these discharges are not yet fully understood. Of particular interest are low pressure radio-frequency (rf) discharges. The limited understanding of these discharges is predominantly due to the complexity of the underlying mechanisms and difficult diagnostic access to important parameters. Optical measurements are a powerful diagnostic tool offering high spatial and temporal resolution. Optical emission spectroscopy (OES) provides non-intrusive access, to the physics of the plasma, with comparatively simple experimental requirements. Improved advances in technology and modern diagnostics now allow deeper insight into fundamental mechanisms. In low pressure rf discharges insight into the electron dynamics within the rf cycle can yield vital information. This requires high temporal resolution on a nano-second time scale. The optical emission from rf discharges exhibits temporal variations within the rf cycle. These variations are particularly strong, in for example capacitively coupled plasmas (CCPs), but also easily observable in inductively coupled plasmas (ICPs), and can be exploited for insight into power dissipation. Interesting kinetic and non-linear coupling effects are revealed in capacitive systems. The electron dynamics exhibits a complex spatio-temporal structure. Excitation and ionisation, and, therefore, plasma sustainment is dominated through directed energetic electrons created through the dynamics of the plasma boundary sheath. In the relatively simple case of an asymmetric capacitively coupled rf plasma the complexity of the power dissipation is exposed and various mode transitions can be clearly observed and investigated. At higher pressure secondary electrons dominate the

  6. Response moments of dynamic systems under non-Gaussian random excitation by the equivalent non-Gaussian excitation method

    Science.gov (United States)

    Tsuchida, Takahiro; Kimura, Koji

    2016-09-01

    Equivalent non-Gaussian excitation method is proposed to obtain the response moments up to the 4th order of dynamic systems under non-Gaussian random excitation. The non-Gaussian excitation is prescribed by the probability density and the power spectrum, and is described by an Ito stochastic differential equation. Generally, moment equations for the response, which are derived from the governing equations for the excitation and the system, are not closed due to the nonlinearity of the diffusion coefficient in the equation for the excitation even though the system is linear. In the equivalent non-Gaussian excitation method, the diffusion coefficient is replaced with the equivalent diffusion coefficient approximately to obtain a closed set of the moment equations. The square of the equivalent diffusion coefficient is expressed by a quadratic polynomial. In numerical examples, a linear system subjected to nonGaussian excitations with bimodal and Rayleigh distributions is analyzed by using the present method. The results show that the method yields the variance, skewness and kurtosis of the response with high accuracy for non-Gaussian excitation with the widely different probability densities and bandwidth. The statistical moments of the equivalent non-Gaussian excitation are also investigated to describe the feature of the method.

  7. Dynamic Effects in Core Electron Impact Excitation of Lanthanum

    Science.gov (United States)

    Nuroh, Kofi

    2000-05-01

    Experimental data of inelastic electron scattering exciting inner3d-shell of metallic lanthanum show strong dependence on the projectile electron energy.^1 Calculations based on an atomic physics description of the triply ionized free atom are made. The large spin-orbit coupling constant of the 3d-hole leads to an approximate jK-coupling. The resulting excitation strength is formulated in terms of the Born approximation including resonant contributions. The intensity is folded with a Lorentzian broadening with full width at half maximum (FWHM) parameter Γ. This parameter is considered to be dependent on the projectile electron energy so that the dynamic effects found in experimental electron-energy-loss-spectra (EELS) may be addressed. The systematic variation of the relative intensities of the spin-orbit doublet structures with exciation energy found in experiment is generally accounted for as Γ is varied from the experimentally measured values of 0.7eV - 0.5eV and beyond^2 ^1J. Kanski and G. Wendin, Phys. Rev.B24, 1981 (4977). ^2K. Nuroh, Physica Scripta 61, 2000(in press).

  8. Excited-State Dynamics of Oxyluciferin in Firefly Luciferase

    KAUST Repository

    Snellenburg, Joris J.

    2016-11-23

    The color variations of light emitted by some natural and mutant luciferases are normally attributed to collective factors referred to as microenvironment effects; however, the exact nature of these interactions between the emitting molecule (oxyluciferin) and the active site remains elusive. Although model studies of noncomplexed oxyluciferin and its variants have greatly advanced the understanding of its photochemistry, extrapolation of the conclusions to the real system requires assumptions about the polarity and proticity of the active site. To decipher the intricate excited-state dynamics, global and target analysis is performed here for the first time on the steady-state and time-resolved spectra of firefly oxyluciferin complexed with luciferase from the Japanese firefly (Luciola cruciata). The experimental steady-state and time resolved luminescence spectra of the oxyluciferin/luciferase complex in solution are compared with the broadband time-resolved firefly bioluminescence recorded in vivo. The results demonstrate that de-excitation of the luminophore results in a complex cascade of photoinduced proton transfer processes and can be interpreted by the pH dependence of the emitted light. It is confirmed that proton transfer is the central event in the spectrochemistry of this system for which any assignment of the pH dependent emission to a single chemical species would be an oversimplification.

  9. A Dynamic Branch-Switching Method for Parametrically Excited Systems

    Directory of Open Access Journals (Sweden)

    A.Y.T. Leung

    1999-01-01

    Full Text Available The branch-switching algorithm in static is applied to steady state dynamic problems. The governing ordinary differential equations are transformed to nonlinear algebraic equations by means of harmonic balance method using multiple frequency components. The frequency components of the (irrational nonlinearity of oscillator are obtained by Fast Fourier Transform and Toeplitz Jacobian method (FFT/TJM. All singularities, folds, flips, period doubling and period bubbling, are computed accurately in an analytical manner. Coexisting solutions can be predicted without using initial condition search. The consistence of both stability criteria in time and frequency domains is discussed. A highly nonlinear parametrically excited system is given as example. All connected solution paths are predicted.

  10. Purkinje cell intrinsic excitability increases after synaptic long term depression.

    Science.gov (United States)

    Yang, Zhen; Santamaria, Fidel

    2016-09-01

    Coding in cerebellar Purkinje cells not only depends on synaptic plasticity but also on their intrinsic membrane excitability. We performed whole cell patch-clamp recordings of Purkinje cells in sagittal cerebellar slices in mice. We found that inducing long-term depression (LTD) in the parallel fiber to Purkinje cell synapses results in an increase in the gain of the firing rate response. This increase in excitability is accompanied by an increase in the input resistance and a decrease in the amplitude of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel-mediated voltage sag. Application of a HCN channel blocker prevents the increase in input resistance and excitability without blocking the expression of synaptic LTD. We conclude that the induction of parallel fiber-Purkinje cell LTD is accompanied by an increase in excitability of Purkinje cells through downregulation of the HCN-mediated h current. We suggest that HCN downregulation is linked to the biochemical pathway that sustains synaptic LTD. Given the diversity of information carried by the parallel fiber system, we suggest that changes in intrinsic excitability enhance the coding capacity of the Purkinje cell to specific input sources.

  11. Dynamic Model of a Structure Carrying Stationary Humans and Assessment of its Response to Walking Excitation

    OpenAIRE

    Pedersen, Lars

    2007-01-01

    A flooring-system, e.g. a floor in a building, is excited dynamically when a person walks across the floor, and resonant excitation might bring structural vibrations to unacceptable levels. Stationary (non-moving) crowds of people might be present on the same floor and they will sense the floor vibrations, but they will also interact dynamically with the floor in a passive sense, thus altering the dynamic system excited to vibration by the walking person. Consequently, the vibration level of ...

  12. Excited-State Dynamics in Colloidal Semiconductor Nanocrystals.

    Science.gov (United States)

    Rabouw, Freddy T; de Mello Donega, Celso

    2016-10-01

    Colloidal semiconductor nanocrystals have attracted continuous worldwide interest over the last three decades owing to their remarkable and unique size- and shape-, dependent properties. The colloidal nature of these nanomaterials allows one to take full advantage of nanoscale effects to tailor their optoelectronic and physical-chemical properties, yielding materials that combine size-, shape-, and composition-dependent properties with easy surface manipulation and solution processing. These features have turned the study of colloidal semiconductor nanocrystals into a dynamic and multidisciplinary research field, with fascinating fundamental challenges and dazzling application prospects. This review focuses on the excited-state dynamics in these intriguing nanomaterials, covering a range of different relaxation mechanisms that span over 15 orders of magnitude, from a few femtoseconds to a few seconds after photoexcitation. In addition to reviewing the state of the art and highlighting the essential concepts in the field, we also discuss the relevance of the different relaxation processes to a number of potential applications, such as photovoltaics and LEDs. The fundamental physical and chemical principles needed to control and understand the properties of colloidal semiconductor nanocrystals are also addressed.

  13. Oncotripsy: Targeting cancer cells selectively via resonant harmonic excitation

    CERN Document Server

    Heyden, Stefanie

    2015-01-01

    We investigate a method of selectively targeting cancer cells by means of ultrasound harmonic excitation at their resonance frequency, which we refer to as oncotripsy. The geometric model of the cells takes into account the cytoplasm, nucleus and nucleolus, as well as the plasma membrane and nuclear envelope. Material properties are varied within a pathophysiologically-relevant range. A first modal analysis reveals the existence of a spectral gap between the natural frequencies and, most importantly, resonant growth rates of healthy and cancerous cells. The results of the modal analysis are verified by simulating the fully-nonlinear transient response of healthy and cancerous cells at resonance. The fully nonlinear analysis confirms that cancerous cells can be selectively taken to lysis by the application of carefully tuned ultrasound harmonic excitation while simultaneously leaving healthy cells intact.

  14. Oncotripsy: Targeting cancer cells selectively via resonant harmonic excitation

    Science.gov (United States)

    Heyden, S.; Ortiz, M.

    2016-07-01

    We investigate a method of selectively targeting cancer cells by means of ultrasound harmonic excitation at their resonance frequency, which we refer to as oncotripsy. The geometric model of the cells takes into account the cytoplasm, nucleus and nucleolus, as well as the plasma membrane and nuclear envelope. Material properties are varied within a pathophysiologically-relevant range. A first modal analysis reveals the existence of a spectral gap between the natural frequencies and, most importantly, resonant growth rates of healthy and cancerous cells. The results of the modal analysis are verified by simulating the fully-nonlinear transient response of healthy and cancerous cells at resonance. The fully nonlinear analysis confirms that cancerous cells can be selectively taken to lysis by the application of carefully tuned ultrasound harmonic excitation while simultaneously leaving healthy cells intact.

  15. Effects of abnormal excitation on the dynamics of spiral waves

    Science.gov (United States)

    Min-Yi, Deng; Xue-Liang, Zhang; Jing-Yu, Dai

    2016-01-01

    The effect of physiological and pathological abnormal excitation of a myocyte on the spiral waves is investigated based on the cellular automaton model. When the excitability of the medium is high enough, the physiological abnormal excitation causes the spiral wave to meander irregularly and slowly. When the excitability of the medium is low enough, the physiological abnormal excitation leads to a new stable spiral wave. On the other hand, the pathological abnormal excitation destroys the spiral wave and results in the spatiotemporal chaos, which agrees with the clinical conclusion that the early after depolarization is the pro-arrhythmic mechanism of some anti-arrhythmic drugs. The mechanisms underlying these phenomena are analyzed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11365003 and 11165004).

  16. Dynamics of cell orientation

    Science.gov (United States)

    de, Rumi; Zemel, Assaf; Safran, Samuel A.

    2007-09-01

    Many physiological processes depend on the response of biological cells to mechanical forces generated by the contractile activity of the cell or by external stresses. Using a simple theoretical model that includes the forces due to both the mechanosensitivity of cells and the elasticity of the matrix, we predict the dynamics and orientation of cells in both the absence and presence of applied stresses. The model predicts many features observed in measurements of cellular forces and orientation including the increase with time of the cellular forces in the absence of applied stress and the consequent decrease of the force in the presence of quasi-static stresses. We also explain the puzzling observation of parallel alignment of cells for static and quasi-static stresses and of nearly perpendicular alignment for dynamically varying stresses. In addition, we predict the response of the cellular orientation to a sinusoidally varying applied stress as a function of frequency.

  17. Cable dynamics under non-ideal support excitations: Nonlinear dynamic interactions and asymptotic modelling

    Science.gov (United States)

    Guo, Tieding; Kang, Houjun; Wang, Lianhua; Zhao, Yueyu

    2016-12-01

    Cable dynamics under ideal longitudinal support motions/excitations assumes that the support's mass, stiffness and mechanical energy are infinite. However, for many long/slender support structures, their finite mass and stiffness should be taken into account and the cable-support dynamic interactions should be modelled and evaluated. These moving supports are non-ideal support excitations, deserving a proper coupling analysis. For systems with a large support/cable mass ratio, using the multiple scale method and asymptotic approximations, a cable-support coupled reduced model, with both cable's geometric nonlinearity and cable-support coupling nonlinearity included, is established asymptotically and validated numerically in this paper. Based upon the reduced model, cable's nonlinear responses under non-ideal support excitations(and also the coupled responses) are found, with stability and bifurcation characteristics determined. By finding the modifications caused by the support/cable mass ratio, boundary damping, and internal detuning, full investigations into coupling-induced dynamic effects on the cable are conducted. Finally, the approximate analytical results based on the reduced model are verified by numerical results from the original full model.

  18. Single cell dynamic phenotyping

    OpenAIRE

    Katherin Patsch; Chi-Li Chiu; Mark Engeln; Agus, David B.; Parag Mallick; Shannon M. Mumenthaler; Daniel Ruderman

    2016-01-01

    Live cell imaging has improved our ability to measure phenotypic heterogeneity. However, bottlenecks in imaging and image processing often make it difficult to differentiate interesting biological behavior from technical artifact. Thus there is a need for new methods that improve data quality without sacrificing throughput. Here we present a 3-step workflow to improve dynamic phenotype measurements of heterogeneous cell populations. We provide guidelines for image acquisition, phenotype track...

  19. Some Comments on the Nonlinear Dynamics of a Portal Frame under Base Excitation

    Directory of Open Access Journals (Sweden)

    Aline Souza de Paula

    2013-01-01

    Full Text Available This paper presents a nonlinear dynamic analysis of a flexible portal frame subjected to support excitation, which is provided by an electro-dynamical shaker. The main goal of this study is to investigate the dynamic interactions between a flexible portal frame and a nonlinear electrical support excitation. The numerical analysis shows a complex behavior of the system, which can be observed by phase spaces, Poincaré sections and bifurcation diagrams.

  20. Excitation-energy sorting in superfluid fission dynamics

    Directory of Open Access Journals (Sweden)

    Schmidt K.-H.

    2010-10-01

    Full Text Available It is now well established that at moderate excitation energies the nucleus temperature does not vary with increasing excitation energy. We show that, as a consequence, two nuclei with different temperatures brought into contact show a rather surprising energy-sorting mechanism where the hotter nucleus transfers all its excitation energy to the colder one. The scission configuration of the fission process offers a unique possibility to observe this phenomenon. The energy-sorting mechanism is clearly reflected by the mean number of prompt neutrons as a function of the fragment mass and by the dependence of the local even-odd effect with mass asymmetry.

  1. Propagation of excitation in long 1D chains: Transition from regular quantum dynamics to stochastic dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Benderskii, V. A., E-mail: bender@icp.ac.ru [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation); Kats, E. I., E-mail: efim.i.kats@gmail.com [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation)

    2013-01-15

    The quantum dynamics problem for a 1D chain consisting of 2N + 1 sites (N Much-Greater-Than 1) with the interaction of nearest neighbors and an impurity site at the middle differing in energy and in coupling constant from the sites of the remaining chain is solved analytically. The initial excitation of the impurity is accompanied by the propagation of excitation over the chain sites and with the emergence of Loschmidt echo (partial restoration of the impurity site population) in the recurrence cycles with a period proportional to N. The echo consists of the main (most intense) component modulated by damped oscillations. The intensity of oscillations increases with increasing cycle number and matrix element C of the interaction of the impurity site n = 0 with sites n = {+-}1 (0 < C {<=} 1; for the remaining neighboring sites, the matrix element is equal to unity). Mixing of the components of echo from neighboring cycles induces a transition from the regular to stochastic evolution. In the regular evolution region, the wave packet propagates over the chain at a nearly constant group velocity, embracing a number of sites varying periodically with time. In the stochastic regime, the excitation is distributed over a number of sites close to 2N, with the populations varying irregularly with time. The model explains qualitatively the experimental data on ballistic propagation of the vibrational energy in linear chains of CH{sub 2} fragments and predicts the possibility of a nondissipative energy transfer between reaction centers associated with such chains.

  2. An updating method for structural dynamics models with unknown excitations

    Energy Technology Data Exchange (ETDEWEB)

    Louf, F; Charbonnel, P E; Ladeveze, P [LMT-Cachan (ENS Cachan/CNRS/Paris 6 University) 61, avenue du Prsident Wilson, F-94235 Cachan Cedex (France); Gratien, C [Astrium (EADS space transportation) - Service TE 343 66, Route de Verneuil, 78133 Les Mureaux Cedex (France)], E-mail: charbonnel@lmt.ens-cachan.fr, E-mail: ladeveze@lmt.ens-cachan.fr, E-mail: louf@lmt.ens-cachan.fr, E-mail: christian.gratien@astrium.eads.net

    2008-11-01

    This paper presents an extension of the Constitutive Relation Error (CRE) updating method to complex industrial structures, such as space launchers, for which tests carried out in the functional context can provide significant amounts of information. Indeed, since several sources of excitation are involved simultaneously, a flight test can be viewed as a multiple test. However, there is a serious difficulty in that these sources of excitation are partially unknown. The CRE updating method enables one to obtain an estimate of these excitations. We present a first application of the method using a very simple finite element model of the Ariane V launcher along with measurements performed at the end of an atmospheric flight.

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

    Science.gov (United States)

    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. Death, dynamics and disorder: Terminating reentry in excitable media by dynamically-induced inhomogeneities

    Indian Academy of Sciences (India)

    Johannes Breur; Sitabhra Sinha

    2005-04-01

    Formation of feedback loops of excitation waves (reentrant circuit) around non-conducting ventricular scar tissue is a common cause of cardiac arrhythmias, such as ventricular tachycardia, often leading to death. This is typically treated by rapid stimulation from an implantable device (ICD). However, the mechanisms of reentry termination success and, more importantly, failure, are poorly understood. To study such mechanisms, we simulated pacing termination of reentry in a model of cardiac tissue having significant restitution and dispersion properties. Our results show that rapid pacing dynamically generates conduction inhomogeneities in the reentrant circuit, leading to successful pacing termination of tachycardia. The study suggests that more effective pacing algorithms can be designed by taking into account the role of such dynamical inhomogeneities.

  5. Nonlinear Dynamics of Self-excitation in Autoparametric Systems

    NARCIS (Netherlands)

    2003-01-01

    Various types of self-excited oscillators are implemented into an autoparametric system, and the study of the solutions, stabilities and bifurcations, shows very different results. First, we implement the Rayleigh type oscillator into a suitable autoparametric system. The bifurcation analysis of the

  6. Molecular Dynamics Simulation of Chain Folding for Polyethylene Subjected to Vibration Excitation

    Directory of Open Access Journals (Sweden)

    Junfeng Gu

    2014-01-01

    Full Text Available We propose a molecular dynamics method with vibration excitation, named as VEMD, to investigate the vibration effect on chain folding for polymer molecule. The VEMD method is based on the introduction of periodic force, the amplitude and frequency of which can be adjusted, and the method was applied to the folding simulation of a polyethylene chain. Simulation results show that the vibration excitation significantly affects the folding of the polyethylene, and frequency and amplitude of the vibration excitation play key roles in VEMD. Different frequencies and amplitudes will determine how and to what extent does the vibration excitation affect the folding process of the polyethylene structure.

  7. Simultaneous live cell imaging using dual FRET sensors with a single excitation light.

    Directory of Open Access Journals (Sweden)

    Yusuke Niino

    Full Text Available Fluorescence resonance energy transfer (FRET between fluorescent proteins is a powerful tool for visualization of signal transduction in living cells, and recently, some strategies for imaging of dual FRET pairs in a single cell have been reported. However, these necessitate alteration of excitation light between two different wavelengths to avoid the spectral overlap, resulting in sequential detection with a lag time. Thus, to follow fast signal dynamics or signal changes in highly motile cells, a single-excitation dual-FRET method should be required. Here we reported this by using four-color imaging with a single excitation light and subsequent linear unmixing to distinguish fluorescent proteins. We constructed new FRET sensors with Sapphire/RFP to combine with CFP/YFP, and accomplished simultaneous imaging of cAMP and cGMP in single cells. We confirmed that signal amplitude of our dual FRET measurement is comparable to of conventional single FRET measurement. Finally, we demonstrated to monitor both intracellular Ca(2+ and cAMP in highly motile cardiac myocytes. To cancel out artifacts caused by the movement of the cell, this method expands the applicability of the combined use of dual FRET sensors for cell samples with high motility.

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

    Science.gov (United States)

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

    2017-02-01

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

  9. Topological determinants of self-sustained activity in a simple model of excitable dynamics on graphs

    Science.gov (United States)

    Fretter, Christoph; Lesne, Annick; Hilgetag, Claus C.; Hütt, Marc-Thorsten

    2017-02-01

    Simple models of excitable dynamics on graphs are an efficient framework for studying the interplay between network topology and dynamics. This topic is of practical relevance to diverse fields, ranging from neuroscience to engineering. Here we analyze how a single excitation propagates through a random network as a function of the excitation threshold, that is, the relative amount of activity in the neighborhood required for the excitation of a node. We observe that two sharp transitions delineate a region of sustained activity. Using analytical considerations and numerical simulation, we show that these transitions originate from the presence of barriers to propagation and the excitation of topological cycles, respectively, and can be predicted from the network topology. Our findings are interpreted in the context of network reverberations and self-sustained activity in neural systems, which is a question of long-standing interest in computational neuroscience.

  10. Excited State Dynamics of Protonated Phenylalanine and Tyrosine: Photo-Induced Reactions Following Electronic Excitation.

    Science.gov (United States)

    Féraud, Géraldine; Broquier, Michel; Dedonder, Claude; Jouvet, Christophe; Grégoire, Gilles; Soorkia, Satchin

    2015-06-11

    The electronic spectroscopy and the electronic excited state properties of cold protonated phenylalanine and protonated tyrosine have been revisited on a large spectral domain and interpreted by comparison with ab initio calculations. The protonated species are stored in a cryogenically cooled Paul trap, maintained at ∼10 K, and the parent and all the photofragment ions are mass-analyzed in a time-of-flight mass spectrometer, which allows detecting the ionic species with an improved mass resolution compared to what is routinely achieved with a quadrupole mass spectrometer. These new results emphasize the competition around the band origin between two proton transfer reactions from the ammonium group toward either the aromatic chromophore or the carboxylic acid group. These reactions are initiated by the coupling of the locally excited ππ* state with higher charge transfer states, the positions and coupling of which depend on the conformation of the protonated molecules. Each of these reaction processes gives rise to specific fragmentation channels that supports the conformer selectivity observed in the photofragmentation spectra of protonated tyrosine and phenylalanine.

  11. Elastic Dynamic Stability of Big-Span Power Transmission Tower Subjected to Seismic Excitations

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hang; LI Li; FANG Qin-han; YE Kun

    2009-01-01

    By combining the time-history response analysis and the eigenvalue buckling analysis,this paper developed a computational procedure to study the elastic dynamic stability of a transmission tower by APDL language in ANSYS.The influences of different input directions of seismic excitations and damping ratio on the elastic dynamic stability of tower were discussed.The following conclusions were obtained:(1) Longitudinal direction of the transmission lines is the worst input direction of seismic excitation for the transmission tower.(2) Dead load has no significant effect on the critical load and the occurrence time of buckling.(3) Vertical input of seismic excitations has no great effect on the dynamic stability of the transmission tower.(4) Damping effect has an influence on the dynamic stability of the transmission tower; however,the inherent characteristics of dynamic buckling is not changed.

  12. ANALYSIS OF GLOBAL DYNAMICS IN A PAIAMETIICALLY EXCITED THIN PLATE

    Institute of Scientific and Technical Information of China (English)

    张伟

    2001-01-01

    The global bifurcations and chaos of a simply supported rectangular thin plate with parametric excitation are analyzed. The formulas of the thin plate are derived by yon Karman type equation and Galerkin's approach. The method of multiple scales is used to obtain the averaged equations. Based on the averaged equations, the theory of the normal form is used to give the explicit expressions of the normal form associated with a double zero and a pair of pure imaginary eigenvalues by Maple program. On the basis of the normal form, a global bifurcation analysis of the parametrically excited recta ngular thin plate is given by the global perturbation method developed by Kovacic and Wiggins. The chaotic motion of thin plate is also found by numerical simulation.

  13. Excited-State Dynamics of Carotenoids Studied by Femtosecond Transient Absorption Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Ingu; Pang, Yoonsoo [Department of Physics and Photon Science, Gwangju (Korea, Republic of); Lee, Sebok [Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of)

    2014-03-15

    Carotenoids, natural antenna pigments in photosynthesis share a symmetric backbone of conjugated polyenes. Contrary to the symmetric and almost planar geometries of carotenoids, excited state structure and dynamics of carotenoids are exceedingly complex. In this paper, recent infrared and visible transient absorption measurements and excitation dependent dynamics of 8'-apo-β-caroten-8'-al and 7',7'-dicyano-7'-apo-β-carotene will be reviewed. The recent visible transient absorption measurements of 8'-apo-β-caroten-8'-al in polar and nonpolar solvents will also be introduced to emphasize the complex excited-state dynamics and unsolved problems in the S{sub 2} and S{sub 1} excited states.

  14. Excited-state dynamics of hybrid multichromophoric systems: toward an excitation wavelength control of the charge separation pathways.

    Science.gov (United States)

    Banerji, Natalie; Duvanel, Guillaume; Perez-Velasco, Alejandro; Maity, Santanu; Sakai, Naomi; Matile, Stefan; Vauthey, Eric

    2009-07-23

    The photophysical properties of two hybrid multichromophoric systems consisting of an oligophenylethynyl (OPE) scaffold decorated by 10 red or blue naphthalene diimides (NDIs) have been investigated using femtosecond spectroscopy. Ultrafast charge separation was observed with both red and blue systems. However, the nature of the charge-separated state and its lifetime were found to differ substantially. For the red system, electron transfer occurs from the OPE scaffold to an NDI unit, independently of whether the OPE or an NDI is initially excited. However, charge separation upon OPE excitation is about 10 times faster, and takes place with a 100 fs time constant. The average lifetime of the ensuing charge-separated state amounts to about 650 ps. Charge separation in the blue system depends on which of the OPE scaffold or an NDI is excited. In the first case, an electron is transferred from the OPE to an NDI and the hole subsequently shifts to another NDI unit, whereas in the second case symmetry-breaking charge separation between two NDI units occurs. Although the charges are located on two NDIs in both cases, different recombination dynamics are observed. This is explained by the location of the ionic NDI moieties that depends on the charge separation pathway, hence on the excitation wavelength. The very different dynamics observed with red and blue systems can be accounted for by the oxidation potentials of the respective NDIs that are higher and lower than that of the OPE scaffold. Because of this, the relative energies of the two charge-separated states (hole on the OPE or an NDI) are inverted.

  15. Quantum dynamics and topological excitations in interacting dipolar particles

    Science.gov (United States)

    Rey, Ana

    2016-05-01

    Dipole-dipole interactions, long-range and anisotropic interactions that arise due to the virtual exchange of photons, are of fundamental importance in optical physics, and are enabling a range of new quantum technologies including quantum networks and optical lattice atomic clocks. In this talk I will first discuss how arrays of dipolar particles with a simple J = 0- J = 1 internal level structure can naturally host topological and chiral excitations including Weyl quasi-particles. Weyl fermions were first predicted to exist in the context of high energy physics but only recently have been observed in solid state systems. I will discuss a proposal of using Mott insulators of Sr atoms to observe and probe the Weyl excitation spectrum and its non-trivial chirality. Finally I will report on a recent experiment done at JILA which validates the underlying microscopic model that predicts the existence of these excitations. The experiment measured the collective emission from a coherently driven gas of ultracold 88 Sr atoms and observed a highly directional and anisotropic emission intensity and a substantial broadening of the atomic spectral lines. All of the measurements are well reproduced by the theoretical model. These investigations open the door for the exploration of novel quantum many-body systems involving strongly interacting atoms and photons, and are useful guides for further developments of optical atomic clocks and other applications involving dense atomic ensembles. AFOSR, MURI-AFOSR, ARO,NSF-PHY-1521080, JILA-NSF-PFC-1125844.

  16. Ultrafast thermal dynamics of nano-ripples formation via laser double pulses excitation

    Science.gov (United States)

    Du, Guangqing; Wu, Yanmin; Uddin, Noor; Yang, Qing; Chen, Feng; Lu, Yu; Bian, Hao; Hou, Xun

    2016-09-01

    The ultrafast thermal dynamics of nano-ripples formation on gold film via ultrafast laser double pulses excitation is theoretically investigated by numerical simulations. The non-equilibrium thermal modulations with respect to the electron and phonon energy transfers within gold film is proposed for predicting the nano-ripples formation. It is revealed that the nano-ripples contrast on gold film surface can be well controlled via tuning the pulse energy ratio, pulse separation and pulse exchange of ultrafast laser double-pulse. It is attributed to the tunable energy transfer routes between the electron thermal diffusion and the electron-phonon coupling via tuning double pulses parameters. The study provides theoretical basis for producing high-contrast ripples for a wide range application in the fields such as high-absorptive solar cells, surface friction devices and super-hydrophobic surface.

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

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Guorong [National Research Council Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023 (China); Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Neville, Simon P. [Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5 (Canada); Schalk, Oliver [National Research Council Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); Department of Physics, AlbaNova University Center, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm (Sweden); Sekikawa, Taro [Department of Applied Physics, Hokkaido University, Kita-13 Nishi-8, Kita-ku, Sapporo 060-8628 (Japan); Ashfold, Michael N. R. [School of Chemistry, University of Bristol, Bristol BS8 1TS (United Kingdom); Worth, Graham A. [School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Stolow, Albert, E-mail: astolow@uottawa.ca [National Research Council Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5 (Canada); Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5 (Canada)

    2016-01-07

    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 A{sub 2}(πσ{sup ∗}) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B{sub 1}(π3p{sub y}) Rydberg state, followed by prompt internal conversion to the A{sub 2}(πσ{sup ∗}) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A{sub 2}(πσ{sup ∗}) 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 A{sub 2}(πσ{sup ∗}) state, facilitating wavepacket motion around the potential barrier in the N–CH{sub 3} dissociation coordinate.

  18. Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Deyne, Andy Van Yperen-De; Pauwels, Ewald; Ghysels, An; Waroquier, Michel; Van Speybroeck, Veronique; Hemelsoet, Karen, E-mail: karen.hemelsoet@ugent.be [Center for Molecular Modeling (CMM), Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); De Meyer, Thierry [Center for Molecular Modeling (CMM), Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); Department of Textiles, Ghent University, Technologiepark 907, 9052 Zwijnaarde (Belgium); De Clerck, Karen [Department of Textiles, Ghent University, Technologiepark 907, 9052 Zwijnaarde (Belgium)

    2014-04-07

    A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed.

  19. Rapid developmental maturation of neocortical FS cell intrinsic excitability.

    Science.gov (United States)

    Goldberg, Ethan M; Jeong, Hyo-Young; Kruglikov, Ilya; Tremblay, Robin; Lazarenko, Roman M; Rudy, Bernardo

    2011-03-01

    Fast-spiking (FS) cells are a prominent subtype of neocortical γ-aminobutyric acidergic interneurons that mediate feed-forward inhibition and the temporal sculpting of information transfer in neural circuits, maintain excitation/inhibition balance, and contribute to network oscillations. FS cell dysfunction may be involved in the pathogenesis of disorders such as epilepsy, autism, and schizophrenia. Mature FS cells exhibit coordinated molecular and cellular specializations that facilitate rapid responsiveness, including brief spikes and sustained high-frequency discharge. We show that these features appear during the second and third postnatal weeks driven by upregulation of K(+) channel subunits of the Kv3 subfamily. The low membrane resistance and fast time constant characteristic of FS cells also appears during this time, driven by expression of a K(+) leak current mediated by K(ir)2 subfamily inward rectifier K(+) channels and TASK subfamily 2-pore K(+) channels. Blockade of this leak produces dramatic depolarization of FS cells suggesting the possibility for potent neuromodulation. Finally, the frequency of FS cell membrane potential oscillations increases during development and is markedly slower in TASK-1/3 knockout mice, suggesting that TASK channels regulate FS cell rhythmogenesis. Our findings imply that some of the effects of acidosis and/or anesthetics on brain function may be due to blockade of TASK channels in FS cells.

  20. Dynamics of optically excited tungsten and silicon for ripples formation

    Science.gov (United States)

    Zhang, Hao; Li, Chen; Colombier, Jean-Philippe; Cheng, Guanghua; Stoian, Razvan

    2015-03-01

    We measured the dielectric constant of optically excited silicon and tungsten using a dual-angle femtosecond reflectivity pump-probe technique. The energy deposition in the formation of laser-induced periodic surface structures (LIPSS) is then investigated by simulating the laser pulse interaction with an initially random distributed rough surface using 3D-Finite Difference Time Domain (FDTD) method, with the measured dielectric constant as a material input. We found in the FDTD simulation periodic energy deposition patterns both perpendicular and parallel to the laser polarization. The origin of them are discussed for originally plasmonic and non-plasmonic material.

  1. Molecular excitation dynamics and relaxation quantum theory and spectroscopy

    CERN Document Server

    Valkunas, Leonas; Mancal, Tomas

    2013-01-01

    Meeting the need for a work that brings together quantum theory and spectroscopy to convey excitation processes to advanced students and specialists wishing to conduct research and understand the entire field rather than just single aspects.Written by an experienced author and recognized authority in the field, this text covers numerous applications and offers examples taken from different disciplines. As a result, spectroscopists, molecular physicists, physical chemists, and biophysicists will all find this a must-have for their research. Also suitable as supplementary reading in graduate

  2. Tracking excited-state charge and spin dynamics in iron coordination complexes

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe

    2014-01-01

    to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)(3)](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate......Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons(1-4). But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited...... states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics(5) and the flux limitations of ultrafast X-ray sources(6,7). Such a situation exists for archetypal poly-pyridyl iron complexes, such as [Fe(2...

  3. Ultrafast Relaxation Dynamics of Photo-excited Dirac Fermion in Three Dimensional Dirac Semimetal Cadmium Arsenide

    CERN Document Server

    Lu, Wei; Liu, Xuefeng; Lu, Hong; Li, Caizhen; Lai, Jiawei; Zhao, Chuan; Tian, Ye; Liao, Zhimin; Jia, Shuang; Sun, Dong

    2016-01-01

    Three dimensional (3D) Dirac semimetal exhibiting ultrahigh mobility has recently attracted enormous research interests as 3D analogues of graphene. From the prospects of future application toward electronic/optoelectronic devices with extreme performance, it is crucial to understand the relaxation dynamics of photo-excited carriers and their coupling with lattice. In this work, we report ultrafast transient reflection measurements of photo-excited carrier dynamics in cadmium arsenide (Cd3As2), which is among the most stable Dirac semimetals that have been confirmed experimentally. With low energy probe photon of 0.3 eV, photo-excited Dirac Fermions dynamics closing to Dirac point are probed. Through transient reflection measurements on bulk and nanoplate samples that have different doping intensities, and systematic probe wavelength, pump power and lattice temperature dependent measurements, the dynamical evolution of carrier distributions can be retrieved qualitatively using a two-temperature model. The pho...

  4. Laser pulse trains for controlling excited state dynamics of adenine in water.

    Science.gov (United States)

    Petersen, Jens; Wohlgemuth, Matthias; Sellner, Bernhard; Bonačić-Koutecký, Vlasta; Lischka, Hans; Mitrić, Roland

    2012-04-14

    We investigate theoretically the control of the ultrafast excited state dynamics of adenine in water by laser pulse trains, with the aim to extend the excited state lifetime and to suppress nonradiative relaxation processes. For this purpose, we introduce the combination of our field-induced surface hopping method (FISH) with the quantum mechanical-molecular mechanical (QM/MM) technique for simulating the laser-driven dynamics in the condensed phase under explicit inclusion of the solvent environment. Moreover, we employ parametric pulse shaping in the frequency domain in order to design simplified laser pulse trains allowing to establish a direct link between the pulse parameters and the controlled dynamics. We construct pulse trains which achieve a high excitation efficiency and at the same time keep a high excited state population for a significantly extended time period compared to the uncontrolled dynamics. The control mechanism involves a sequential cycling of the population between the lowest and higher excited states, thereby utilizing the properties of the corresponding potential energy surfaces to avoid conical intersections and thus to suppress the nonradiative decay to the ground state. Our findings provide a means to increase the fluorescence yield of molecules with an intrinsically very short excited state lifetime, which can lead to novel applications of shaped laser fields in the context of biosensing.

  5. In vivo spectral imaging of different cell types in the small intestine by two-photon excited autofluorescence

    Science.gov (United States)

    Orzekowsky-Schroeder, Regina; Klinger, Antje; Martensen, Björn; Blessenohl, Maike; Gebert, Andreas; Vogel, Alfred; Hüttmann, Gereon

    2011-11-01

    Spectrally resolved two-photon excited autofluorescence imaging is used to distinguish different cell types and functional areas during dynamic processes in the living gut. Excitation and emission spectra of mucosal tissue and tissue components are correlated to spectra of endogenous chromophores. We show that selective excitation with only two different wavelengths within the tuning range of a Ti:sapphire femtosecond laser system yields excellent discrimination between enterocytes, antigen presenting cells and lysosomes based on the excitation and emission properties of their autofluorescence. The method is employed for time-lapse microscopy over up to 8 h. Changes of the spectral signature with the onset of photodamage are demonstrated, and their origin is discussed.

  6. Excitable human dynamics driven by extrinsic events in massive communities

    CERN Document Server

    Mathiesen, Joachim; Ahlgren, Peter T H; Jensen, Mogens H

    2013-01-01

    Using empirical data from a social media site (Twitter) and on trading volumes of financial securities, we analyze the correlated human activity in massive social organizations. The activity, typically excited by real-world events and measured by the occurrence rate of international brand names and trading volumes, is characterized by intermittent fluctuations with bursts of high activity separated by quiescent periods. These fluctuations are broadly distributed with an inverse cubic tail and have long-range temporal correlations with a $1/f$ power spectrum. We describe the activity by a stochastic point process and derive the distribution of activity levels from the corresponding stochastic differential equation. The distribution and the corresponding power spectrum are fully consistent with the empirical observations.

  7. Excitation Dynamics in Hetero-bichromophoric Calixarene Systems.

    Science.gov (United States)

    Tosi, Irene; Segado Centellas, Mireia; Campioli, Elisa; Iagatti, Alessandro; Lapini, Andrea; Sissa, Cristina; Baldini, Laura; Cappelli, Chiara; Di Donato, Mariangela; Sansone, Francesco; Santoro, Fabrizio; Terenziani, Francesca

    2016-06-03

    In this work, the dynamics of electronic energy transfer (EET) in bichromophoric donor-acceptor systems, obtained by functionalizing a calix[4]arene scaffold with two dyes, was experimentally and theoretically characterized. The investigated compounds are highly versatile, due to the possibility of linking the dye molecules to the cone or partial cone structure of the calix[4]arene, which directs the two active units to the same or opposite side of the scaffold, respectively. The dynamics and efficiency of the EET process between the donor and acceptor units was investigated and discussed through a combined experimental and theoretical approach, involving ultrafast pump-probe spectroscopy and density functional theory based characterization of the energetic and spectroscopic properties of the system. Our results suggest that the external medium strongly determines the particular conformation adopted by the bichromophores, with a direct effect on the extent of excitonic coupling between the dyes and hence on the dynamics of the EET process itself.

  8. Microbial Cell Dynamics Lab (MCDL)

    Data.gov (United States)

    Federal Laboratory Consortium — The Microbial Cell Dynamics Laboratory at PNNL enables scientists to study the molecular details of microbes under relevant environmental conditions. The MCDL seeks...

  9. Isovector and isoscalar dipole excitations in $^{9}$Be and $^{10}$Be studied with antisymmetrized molecular dynamics

    CERN Document Server

    Kanada-En'yo, Yoshik

    2015-01-01

    Isovector and isoscalar dipole excitations in $^9$Be and $^{10}$Be are investigated in the framework of antisymmetrized molecular dynamics, in which angular-momentum and parity projections are performed. In the present method, 1p-1h excitations on the ground state and large amplitude $\\alpha$-cluster mode are incorporated. The isovector giant dipole resonance (GDR) in $E>20$ MeV shows the two peak structure which is understood by the dipole excitation in the 2$\\alpha$ core part with the prolate deformation. Because of valence neutron modes against the $2\\alpha$ core, low-energy E1 resonances appear in $E20$ MeV.

  10. Different dynamics of ultraviolet upconversion in Tm3+:ZBLAN glass under blue laser excitation

    Science.gov (United States)

    Yang, Haigui; Gao, Jinsong

    2013-10-01

    Ultraviolet upconversion luminescence around 292 nm, 350 nm and 363 nm in Tm3+:ZBLAN glass was observed clearly by pulsed excitation at 464 nm. Upconversion dynamics was discussed in detail by an analysis of the measured intensity dependence, decay curves and excitation spectra of upconversion luminescence, from which it was clarified that upconversion luminescence around 292 nm and 350 nm from 1I6 level was attributed to excited state absorption, while that around 363 nm from 1D2 level was attributed to energy transfer process.

  11. Different dynamics of ultraviolet upconversion in Tm{sup 3+}:ZBLAN glass under blue laser excitation

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Haigui, E-mail: yanghg@ciomp.ac.cn [Key Laboratory of Optical System Advanced Manufacturing Technology, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun 130033 (China); State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun 130033 (China); Gao, Jinsong [Key Laboratory of Optical System Advanced Manufacturing Technology, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun 130033 (China)

    2013-10-01

    Ultraviolet upconversion luminescence around 292 nm, 350 nm and 363 nm in Tm{sup 3+}:ZBLAN glass was observed clearly by pulsed excitation at 464 nm. Upconversion dynamics was discussed in detail by an analysis of the measured intensity dependence, decay curves and excitation spectra of upconversion luminescence, from which it was clarified that upconversion luminescence around 292 nm and 350 nm from {sup 1}I{sub 6} level was attributed to excited state absorption, while that around 363 nm from {sup 1}D{sub 2} level was attributed to energy transfer process.

  12. Ultrafast electronic dynamics in laser-excited crystalline bismuth

    Directory of Open Access Journals (Sweden)

    Chekalin S.

    2013-03-01

    Full Text Available Femtosecond spectroscopy was applied to capture complex dynamics of non equilibrium electrons in bismuth. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along the Γ-T direction of the Brillouin zone

  13. Excited-state dynamics of bacteriorhodopsin probed by broadband femtosecond fluorescence spectroscopy.

    Science.gov (United States)

    Schmidt, B; Sobotta, C; Heinz, B; Laimgruber, S; Braun, M; Gilch, P

    2005-01-07

    The impact of varying excitation densities (approximately 0.3 to approximately 40 photons per molecule) on the ultrafast fluorescence dynamics of bacteriorhodopsin has been studied in a wide spectral range (630-900 nm). For low excitation densities, the fluorescence dynamics can be approximated biexponentially with time constants of <0.15 and approximately 0.45 ps. The spectrum associated with the fastest time constant peaks at 650 nm, while the 0.45 ps component is most prominent at 750 nm. Superimposed on these kinetics is a shift of the fluorescence maximum with time (dynamic Stokes shift). Higher excitation densities alter the time constants and their amplitudes. These changes are assigned to multi-photon absorptions.

  14. Structural Influence on Excited State Dynamics in Simple Amines

    DEFF Research Database (Denmark)

    Klein, Liv Bærenholdt

    is femtosecond time-resolved photoelectron velocity map imaging (VMI), which is a newtechnique in the Copenhagen lab. The design, building and implementation of the VMI spectrometer has been a very substantial part of the thesis work. This techniques oers enhanced information content in the form of ecient......Simple amines are basic model system of nitrogen-containing chromophores that appear widely in nature. They are also ideal systems for detailed investigation of nonadiabatic dynamical processes and ultrafast temporal evolution of electronic states of the Rydberg type. This investigation, combining...... experiments with calculations, provides new insight into the nature of the internal conversion processes that mediate the dynamical evolution between Rydberg states, and how structural variations in simple amine system have a large impact on the non-adiabatic processes. The experimental method of choice...

  15. Ultrafast dynamics in DNA base pairs following ultraviolet excitation.

    Science.gov (United States)

    Orr-Ewing, Andrew

    2015-03-01

    Photo-protective mechanisms in DNA are essential to maintain the integrity of the genetic code by preventing damage from absorption of solar ultraviolet (UV) radiation. We have used time-resolved infra-red (TRIR) spectroscopy to observe the dynamics of Watson-Crick nucleobase pairs following absorption of femtosecond UV laser pulses. The base pairs are prepared as nucleosides in solution, and photo-induced dynamics are probed in the carbonyl and N-H bond stretching regions using broadband IR pulses with picosecond time resolution. Results will be presented for the guanine-cytosine (G-C) base pair, contrasting the rapid recovery of ground-state products (the photo-protection pathway) with formation of other photoproducts which might represent photo-damage mechanisms. This work is a collaboration with the group of Prof F. Temps (Christian-Albrechts-Universitat zu Kiel). This research is supported by ERC Advanced Grant 290966 CAPRI.

  16. Maintenance and termination of neocortical oscillations by dynamic modulation of intrinsic and synaptic excitability

    Science.gov (United States)

    FRÖHLICH, FLAVIO; BAZHENOV, MAXIM; TIMOFEEV, IGOR; SEJNOWSKI, TERRENCE J.

    2010-01-01

    Mechanisms underlying seizure cessation remain elusive. The Lennox-Gastaut syndrome, a severe childhood epileptic disorder, is characterized by episodes of seizure with alternating epochs of spike-wave and fast run discharges. In a detailed computational model that incorporates extracellular potassium dynamics, we studied the dynamics of these state transitions between slow and fast oscillations. We show that dynamic modulation of synaptic transmission can cause termination of paroxysmal activity. An activity-dependent shift in the balance between synaptic excitation and inhibition towards more excitation caused seizure termination by favoring the slow oscillatory state, which permits recovery of baseline extracellular potassium concentration. We found that slow synaptic depression and change in chloride reversal potential can have similar effects on the seizure dynamics. Our results indicate a novel role for synaptic dynamics during epileptic neural activity patterns. PMID:20556224

  17. Dynamic Response Analysis for Embedded Large-Cylinder Breakwaters Under Wave Excitation

    Institute of Scientific and Technical Information of China (English)

    王元战; 祝振宇; 周枝荣

    2004-01-01

    A numerical model is developed for dynamic analysis of large-cylinder breakwaters embedded in soft soil. In the model, the large cylinder is taken as a rigid body divided into elements and the soft soil is replaced by discrete 3D nonlinear spring-dashpot systems. The numerical model is used to simulate the dynamic response of a large-cylinder breakwater to breaking wave excitation. The effects of the dynamic stress-strain relationship models of the soil, the radius and embedded depth of the cylinder, the nonlinear behaviors of the soil, and the limit strength condition of the soil on the dynamic responses of the large-cylinder structure are investigated with an example given. It is indicated that the above-mentioned factors have significant effects on the dynamic responses of an embedded large cylinder breakwater under breaking wave excitation.

  18. Ultrafast dynamics of ligand and substrate interaction in endothelial nitric oxide synthase under Soret excitation.

    Science.gov (United States)

    Hung, Chih-Chang; Yabushita, Atsushi; Kobayashi, Takayoshi; Chen, Pei-Feng; Liang, Keng S

    2016-01-01

    Ultrafast transient absorption spectroscopy of endothelial NOS oxygenase domain (eNOS-oxy) was performed to study dynamics of ligand or substrate interaction under Soret band excitation. Photo-excitation dissociates imidazole ligand in 4ps. The eNOS-oxy without additive is partially bound with water molecule, thus its photoexcited dynamics also shows ligand dissociation in <800fs. Then it followed by vibrational cooling coupled with charge transfer in 4.8ps, and recombination of ligand to distal side of heme in 12ps.

  19. Dynamic responses of a multilayer piezoelectric hollow cylinder under electric potential excitation

    Institute of Scientific and Technical Information of China (English)

    WANG Hui-ming; CHEN Yun-min; DING Hao-jiang

    2005-01-01

    The dynamic responses of a multilayer piezoelectric infinite hollow cylinder under electric potential excitation were obtained. The method of superposition was used to divide the solution into two parts, the part satisfying the mechanical boundary conditions and continuity conditions was first obtained by solving a system of linear equations;the other part was obtained by the separation of variables method. The present method is suitable for a multilayer piezoelectric infinite hollow cylinder consisting of arbitrary layers and subjected to arbitrary axisymmetric electric excitation. Dynamic responses of stress and electric potential are finally presented and analyzed.

  20. Quantum Dynamics of Entanglement and Single Excitation Transfer in LH1-RC-Type Trimer

    Institute of Scientific and Technical Information of China (English)

    潭庆收; 匡乐满

    2012-01-01

    In this paper, we study quantum dynamics of entanglement and single excitation transfer (SET) in an LH1-RC-type trimer which can describe a basic unit cell in the LH1-RC complex in the photosynthetic process. It is shown that there exists a sudden change of entanglement at the critic point of quantum phase transition (QPT) of the system at low temperatures, the entanglement sudden change caused by the QPT is suppressed at higher temperatures. We investigate the influence of environment on entanglement and SET. We show the generation of the dephasing-assisted entanglement between a donor and an acceptor and the existence of the steady-state entanglement, and demonstrate the entanglement transfer from donor-donor entanglement to donor-acceptor entanglement in the dynamic evolution. We reveal the close relation between the SET probability and donor-acceptor entanglement. Especially, we find that the SET probability is proportional to the amount of donor-acceptor entanglement under certain conditions.

  1. Nonlinear Dynamic Behavior of a Flexible Structure to Combined External Acoustic and Parametric Excitation

    Directory of Open Access Journals (Sweden)

    Paulo S. Varoto

    2006-01-01

    Full Text Available Flexible structures are frequently subjected to multiple inputs when in the field environment. The accurate determination of the system dynamic response to multiple inputs depends on how much information is available from the excitation sources that act on the system under study. Detailed information include, but are not restricted to appropriate characterization of the excitation sources in terms of their variation in time and in space for the case of distributed loads. Another important aspect related to the excitation sources is how inputs of different nature contribute to the measured dynamic response. A particular and important driving mechanism that can occur in practical situations is the parametric resonance. Another important input that occurs frequently in practice is related to acoustic pressure distributions that is a distributed type of loading. In this paper, detailed theoretical and experimental investigations on the dynamic response of a flexible cantilever beam carrying a tip mass to simultaneously applied external acoustic and parametric excitation signals have been performed. A mathematical model for transverse nonlinear vibration is obtained by employing Lagrange’s equations where important nonlinear effects such as the beam’s curvature and quadratic viscous damping are accounted for in the equation of motion. The beam is driven by two excitation sources, a sinusoidal motion applied to the beam’s fixed end and parallel to its longitudinal axis and a distributed sinusoidal acoustic load applied orthogonally to the beam’s longitudinal axis. The major goal here is to investigate theoretically as well as experimentally the dynamic behavior of the beam-lumped mass system under the action of these two excitation sources. Results from an extensive experimental work show how these two excitation sources interacts for various testing conditions. These experimental results are validated through numerically simulated results

  2. Manual for Dynamic Triaxial Cell

    DEFF Research Database (Denmark)

    Pedersen, Thomas Schmidt; Ibsen, Lars Bo

    This report is a test report that describes the test setup for a dynamic triaxial cell at the Laboratory for Geotechnique at Aalborg University.......This report is a test report that describes the test setup for a dynamic triaxial cell at the Laboratory for Geotechnique at Aalborg University....

  3. Obtaining maximum muscle excitation for normalizing shoulder electromyography in dynamic contractions.

    Science.gov (United States)

    Hodder, Joanne N; Keir, Peter J

    2013-10-01

    Muscle specific maximal voluntary isometric contractions (MVIC) are commonly used to elicit reference amplitudes to normalize electromyographic signals (EMG). It has been questioned whether this is appropriate for normalizing EMG from dynamic contractions. This study compares EMG amplitude when shoulder muscle activity from dynamic contractions is normalized to isometric and isokinetic maximal excitation as well as a hybrid approach currently used in our laboratory. Anterior, middle and posterior deltoid, upper and lower trapezius, pectoralis major, latissimus dorsi and infraspinatus were monitored during (1) manually resisted MVICs, and (2) maximum voluntary dynamic concentric contractions (MVDC) on an isokinetic dynamometer. Dynamic contractions were performed (a) at 30°/s about the longitudinal, frontal and sagittal axes of the shoulder, and (b) during manual bi-rotation of a tilted wheel at 120°/s. EMG from the wheel task was normalized to the maximum excitation from (i) the muscle specific MVIC, (ii) from any MVIC (MVICALL), (iii) for any MVDC, (iv) from any exertion (maximum experimental excitation, MEE). Mean EMG from the wheel task was up to 45% greater when normalized to muscle specific isometric contractions (method i) than when normalized to MEE (method iv). Seventy-five percent of MEE's occurred during MVDCs. This study presents an 20 useful and effective process for obtaining the greatest excitation from the shoulder muscles when normalizing dynamic efforts.

  4. Excitation-energy dependence of solvation dynamics in room-temperature ionic liquids

    Science.gov (United States)

    Kim, Daekeon; Park, Sang-Won; Shim, Youngseon; Kim, Hyung J.; Jung, YounJoon

    2016-07-01

    Influence of the excitation energy of a probe solute molecule on its solvation dynamics and emission spectrum in 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI+PF6-) is studied via molecular dynamics simulations using a coarse-grained model description. By exciting the probe at different energies, each with an extremely narrow distribution, ensuing solvent relaxation and its dynamic variance are monitored using the isoconfigurational ensemble method. Resulting Stokes shift function, S(t), indicates that long-time solvent relaxation becomes slower with the decreasing excitation energy and approaches the equilibrium correlation function, C(t), of solvent fluctuations. This suggests that the system excited at the red-edge of the spectrum observes linear response better than that at the blue-edge. A detailed analysis of nonequilibrium trajectories shows that the effect of initial configurations on variance of relaxation dynamics is mainly confined to short times; it reaches a maximum around 0.1 ≲ t ≲ 1 ps and diminishes as time further increases. The influence of the initial velocity distribution, on the other hand, tends to grow with time and dominates the long-time variations of dynamics. The emission spectrum shows the red-edge effect in accord with previous studies.

  5. Spectroscopic signatures of excited state dynamics in organic materials

    NARCIS (Netherlands)

    Tempelaar, Roel

    2015-01-01

    In our quest for a green energy supply, the sun is arguably the most promising option. In natural photosynthesis, solar light harvesting has been optimized through a long time of evolution. Understanding the physics of this phenomenon opens avenues to improve man-made solar cells in order to maximiz

  6. Nonlinear dynamics of a sliding beam on two supports under sinusoidal excitation

    Indian Academy of Sciences (India)

    R J Somnay; R A Ibrahim

    2006-08-01

    This study deals with the nonlinear dynamics associated with large deformation of a beam sliding on two-knife edge supports under external excitation. The beam is referred to as a Gospodnetic–Frisch-Fay beam, after the researchers who reported its static deformation in closed form. The freedom of the beam to slide on its supports imparts a nonlinear characteristic to the force-deflection response. The restoring elastic force of the beam possesses characteristics similar to those of the roll-restoring moment of ships. The Gospodnetic–Frisch-Fay exact solution is given in terms of elliptic functions. A curve fit of the exact solution up to eleventh-order is constructed to establish the governing equation of motion under external excitation. The dynamic stability of the unperturbed beam is examined for the damped and undamped cases. The undamped case reveals periodic orbits and one homoclinic orbit depending on the value of the initial conditions. The response to a sinusoidal excitation at a frequency below the linear natural frequency is numerically estimated for different excitation amplitude and different values of initial conditions covered by the area of the homoclinic orbit. The safe basins of attraction are plotted for different values of excitation amplitude. It is found that the safe region of operation is reduced as the excitation amplitude increases.

  7. Dynamized Preparations in Cell Culture

    Directory of Open Access Journals (Sweden)

    Ellanzhiyil Surendran Sunila

    2009-01-01

    Full Text Available Although reports on the efficacy of homeopathic medicines in animal models are limited, there are even fewer reports on the in vitro action of these dynamized preparations. We have evaluated the cytotoxic activity of 30C and 200C potencies of ten dynamized medicines against Dalton's Lymphoma Ascites, Ehrlich's Ascites Carcinoma, lung fibroblast (L929 and Chinese Hamster Ovary (CHO cell lines and compared activity with their mother tinctures during short-term and long-term cell culture. The effect of dynamized medicines to induce apoptosis was also evaluated and we studied how dynamized medicines affected genes expressed during apoptosis. Mother tinctures as well as some dynamized medicines showed significant cytotoxicity to cells during short and long-term incubation. Potentiated alcohol control did not produce any cytotoxicity at concentrations studied. The dynamized medicines were found to inhibit CHO cell colony formation and thymidine uptake in L929 cells and those of Thuja, Hydrastis and Carcinosinum were found to induce apoptosis in DLA cells. Moreover, dynamized Carcinosinum was found to induce the expression of p53 while dynamized Thuja produced characteristic laddering pattern in agarose gel electrophoresis of DNA. These results indicate that dynamized medicines possess cytotoxic as well as apoptosis-inducing properties.

  8. No question about exciting questions in cell biology.

    Directory of Open Access Journals (Sweden)

    Thomas D Pollard

    2013-12-01

    Full Text Available Although we have a good grasp of many important processes in cell biology, including knowledge of many molecules involved and how they interact with each other, we still do not understand most of the dynamical features that are the essence of living systems. Fortunately, we now have the ability to dissect biological systems in enough detail to understand their dynamics, including the use of mathematical models to account for past observations and predict future experiments. This deep level of mechanistic understanding should be our goal—not simply to satisfy our scientific curiosity, but also to understand the causes of disease well enough to predict risks, make early diagnoses, and treat effectively. Many big questions remain to be answered before we reach this goal of understanding cellular dynamics.

  9. No question about exciting questions in cell biology.

    Science.gov (United States)

    Pollard, Thomas D

    2013-12-01

    Although we have a good grasp of many important processes in cell biology, including knowledge of many molecules involved and how they interact with each other, we still do not understand most of the dynamical features that are the essence of living systems. Fortunately, we now have the ability to dissect biological systems in enough detail to understand their dynamics, including the use of mathematical models to account for past observations and predict future experiments. This deep level of mechanistic understanding should be our goal—not simply to satisfy our scientific curiosity, but also to understand the causes of disease well enough to predict risks, make early diagnoses, and treat effectively. Many big questions remain to be answered before we reach this goal of understanding cellular dynamics.

  10. The dynamics and excitation of torsional waves in geodynamo simulations

    CERN Document Server

    Teed, Robert J; Tobias, Steven M

    2013-01-01

    The predominant force balance in rapidly rotating planetary cores is between Coriolis, pressure, buoyancy and Lorentz forces. This magnetostrophic balance leads to a Taylor state where the spatially averaged azimuthal Lorentz force is compelled to vanish on cylinders aligned with the rotation axis. Any deviation from this state leads to a torsional oscillation, signatures of which have been observed in the Earth's secular variation and are thought to influence length of day variations via angular momentum conservation. In order to investigate the dynamics of torsional oscillations, we perform several three-dimensional dynamo simulations in a spherical shell. We find torsional oscillations, identified by their propagation at the correct Alfv\\'{e}n speed, in many of our simulations. We find that the frequency, location and direction of propagation of the waves are influenced by the choice of parameters. Torsional waves are observed within the tangent cylinder and also have the ability to pass through it. Severa...

  11. Dynamic Model of a Structure Carrying Stationary Humans and Assessment of its Response to Walking Excitation

    DEFF Research Database (Denmark)

    Pedersen, Lars

    2007-01-01

    A flooring-system, e.g. a floor in a building, is excited dynamically when a person walks across the floor, and resonant excitation might bring structural vibrations to unacceptable levels. Stationary (non-moving) crowds of people might be present on the same floor and they will sense the floor...... that different techniques (different parameters calculated from structural response time series) are proposed for assessing floor serviceability. The paper looks into the influence of the stationary crowd of people on the floor response to walking excitation and into the influence of the crowd on different...... parameters calculated from structural response time series for assessing the serviceability limit state. A numerical approach based on simulation of floor excitation is employed for the investigations, and the paper describes the study assumptions and the findings related to the influence of the presence...

  12. Dynamical potential approach to dissociation of H-C bond in HCO highly excited vibration

    Institute of Scientific and Technical Information of China (English)

    Fang Chao; Wu Guo-Zhen

    2009-01-01

    The highly excited vibrational levels of HCO in the electronic ground state, X1A', are employed to determine the coefficients of an algebraic Hamiltonian, by which the dynamical potential is derived and shown to be very useful for interpreting thc intramolecular vibrational relaxation (IVR) which operates via the HCO bending motion. The IVR inhibits the dissociation of H atom and enhances the stochastic degree of dynamical character. This approach is from a global viewpoint on a series of levels classified by the polyad number which is a constant of motion in a certain dynamical domain. In this way, the seemingly complicated level structure shows very regular picture, dynamically.

  13. Excited-state solvation and proton transfer dynamics of DAPI in biomimetics and genomic DNA.

    Science.gov (United States)

    Banerjee, Debapriya; Pal, Samir Kumar

    2008-08-14

    The fluorescent probe DAPI (4',6-diamidino-2-phenylindole) is an efficient DNA binder. Studies on the DAPI-DNA complexes show that the probe exhibits a wide variety of interactions of different strengths and specificities with DNA. Recently the probe has been used to report the environmental dynamics of a DNA minor groove. However, the use of the probe as a solvation reporter in restricted environments is not straightforward. This is due to the presence of two competing relaxation processes (intramolecular proton transfer and solvation stabilization) in the excited state, which can lead to erroneous interpretation of the observed excited-state dynamics. In this study, the possibility of using DAPI to unambiguously report the environmental dynamics in restricted environments including DNA is explored. The dynamics of the probe is studied in bulk solvents, biomimetics like micelles and reverse micelles, and genomic DNA using steady-state and picosecond-resolved fluorescence spectroscopies.

  14. SOME DYNAMICAL BEHAVIOR OF THE STUART-LANDAU EQUATION WITH A PERIODIC EXCITATION

    Institute of Scientific and Technical Information of China (English)

    陈芳启; 梁建术; 陈予恕

    2004-01-01

    The lock-in periodic solutions of the Stuart-Landau equation with a periodic excitation are studied. Using singularity theory, the bifurcation behavior of these solutions with respect to the excitation amplitude and frequency are investigated in detail,respectively. The results show that the universal unfolding with respect to the excitation amplitude possesses codimension 3. The transition sets in unfolding parameter plane and the bifurcation diagrams are plotted under some conditions. Additionally, it has also been proved that the bifurcation problem with respect to frequence possesses infinite codimension.Therefore the dynamical bifurcation behavior is very complex in this case. Some new dynamical phenomena are presented, which are the supplement of the results obtained by Sun Liang et al.

  15. Dynamics of the Chemistry of Electronically Excited Atoms in Defined Quantum States.

    Science.gov (United States)

    1978-05-01

    laser development . In essence, this research concerns itself with the elucidation of the role of electronic energy in affecting the chemistry or photochemistry of excited halogen atoms and molecules. While much is known about the dynamics of chemical and physical processes which are carried out on the lowest potential energy hypersurface correlating with reactants and products in their electronic ground state, relatively little is known about the dynamics of such phenomena as energy transfer and chemical reactivity on higher-lying potential

  16. Self-modulated dynamics of a relativistic charged particle beam in plasma wake field excitation

    Energy Technology Data Exchange (ETDEWEB)

    Akhter, T.; Fedele, R. [Dipartimento di Fisica ‘Ettore Pancini’, Università di Napoli Federico II and INFN Sezione di Napoli, Napoli (Italy); Nicola, S. De [CNR-SPIN and INFN Sezione di Napoli, Napoli (Italy); Tanjia, F. [Dipartimento di Fisica ‘Ettore Pancini’, Università di Napoli Federico II and INFN Sezione di Napoli, Napoli (Italy); Jovanović, D. [Institute of Physics, University of Belgrade, Belgrade (Serbia); Mannan, A. [Department of Physics, Jahangirnagar University, Savar, Dhaka (Bangladesh)

    2016-09-01

    The self-modulated dynamics of a relativistic charged particle beam is provided within the context of the theory of plasma wake field excitation. The self-consistent description of the beam dynamics is provided by coupling the Vlasov equation with a Poisson-type equation relating the plasma wake potential to the beam density. An analysis of the beam envelope self-modulation is then carried out and the criteria for the occurrence of the instability are discussed thereby.

  17. Spreading and atomization dynamics of ultrasonically excited droplets

    Science.gov (United States)

    Kumar, Ranganathan; Deepu, P.; Basu, Saptarshi

    2013-11-01

    The dynamics of a sessile droplet under the combined influence of standing pressure wave and a constant substrate acceleration is investigated experimentally. The asymmetric acoustic force field results in radial spreading of the droplet. The spreading rate varies inversely with viscosity which is explained using an analytical model. In low viscosity droplets, towards the end of droplet spreading capillary waves grow to form ligaments of varying length and time scales, ultimately leading to droplet disintegration. Proper Orthogonal Decomposition of high speed images from the droplet spreading phase predicts the likelihood of atomization. The different regimes in the life of surface ligaments are identified. Viscous dissipation plays a crucial role in determining the initial ligament momentum and thus the frequency of ligament breakup. However in the current experimental conditions the growth of a typical ligament is governed by inertial and capillary forces and the influence of viscosity in the ligament growth phase is rather negligible. By including the effect of acoustic pressure, a characteristic timescale is deduced which collapses the ligament growth profiles for different fluids on a straight line.

  18. Influence of second sideband excitation on the dynamics of trapped ions in a cavity

    Institute of Scientific and Technical Information of China (English)

    刘翔; 方卯发

    2003-01-01

    We study the dynamics of a trapped ion placed at an antinode of the standing wave inside a high finesse cavity with consideration of the second sideband excitation between the ionic internal levels and the light field. We investigate the entanglement of the three subsystems embodying the ionic internal levels, the vibrational mode of the ion and the cavity field.

  19. Influence of second sideband excitation on the dynamics of trapped ions in a cavity

    Institute of Scientific and Technical Information of China (English)

    刘翔; 方卯发

    2003-01-01

    We study the dynamics of a trapped ion placed at an antinode of the standing wave inside a high finesse cavitywith consideration of the second sideband excitation between the ionic internal levels and the light field. We investigatethe entanglement of the three subsystems embodying the ionic internal levels, the vibrational mode of the ion and thecavity field.

  20. Excited-State Dynamics of Melamine and Its Lysine Derivative Investigated by Femtosecond Transient Absorption Spectroscopy

    Directory of Open Access Journals (Sweden)

    Yuyuan Zhang

    2016-11-01

    Full Text Available Melamine may have been an important prebiotic information carrier, but its excited-state dynamics, which determine its stability under UV radiation, have never been characterized. The ability of melamine to withstand the strong UV radiation present on the surface of the early Earth is likely to have affected its abundance in the primordial soup. Here, we studied the excited-state dynamics of melamine (a proto-nucleobase and its lysine derivative (a proto-nucleoside using the transient absorption technique with a UV pump, and UV and infrared probe pulses. For melamine, the excited-state population decays by internal conversion with a lifetime of 13 ps without coupling significantly to any photochemical channels. The excited-state lifetime of the lysine derivative is slightly longer (18 ps, but the dominant deactivation pathway is otherwise the same as for melamine. In both cases, the vast majority of excited molecules return to the electronic ground state on the aforementioned time scales, but a minor population is trapped in a long-lived triplet state.

  1. Excited-State Dynamics of Melamine and Its Lysine Derivative Investigated by Femtosecond Transient Absorption Spectroscopy.

    Science.gov (United States)

    Zhang, Yuyuan; Beckstead, Ashley A; Hu, Yuesong; Piao, Xijun; Bong, Dennis; Kohler, Bern

    2016-11-30

    Melamine may have been an important prebiotic information carrier, but its excited-state dynamics, which determine its stability under UV radiation, have never been characterized. The ability of melamine to withstand the strong UV radiation present on the surface of the early Earth is likely to have affected its abundance in the primordial soup. Here, we studied the excited-state dynamics of melamine (a proto-nucleobase) and its lysine derivative (a proto-nucleoside) using the transient absorption technique with a UV pump, and UV and infrared probe pulses. For melamine, the excited-state population decays by internal conversion with a lifetime of 13 ps without coupling significantly to any photochemical channels. The excited-state lifetime of the lysine derivative is slightly longer (18 ps), but the dominant deactivation pathway is otherwise the same as for melamine. In both cases, the vast majority of excited molecules return to the electronic ground state on the aforementioned time scales, but a minor population is trapped in a long-lived triplet state.

  2. Separating annihilation and excitation energy transfer dynamics in light harvesting systems.

    Science.gov (United States)

    Vengris, Mikas; Larsen, Delmar S; Valkunas, Leonas; Kodis, Gerdenis; Herrero, Christian; Gust, Devens; Moore, Thomas; Moore, Ana; van Grondelle, Rienk

    2013-09-26

    The dependence of excitation energy transfer kinetics on the electronic state of the acceptor (ground vs excited) has been resolved with a novel multipulse prePump-Pump-Probe spectroscopy. The primary energy transfer and annihilation dynamics in two model light-harvesting systems were explored: an artificially synthesized carotenoid-zinc-phthalocyanine dyad and a naturally occurring light-harvesting peridinin-chlorophyll protein complex from Amphidinium carterae. Both systems use carotenoid as the primary excitation energy donor with porphyrin chromophores as the acceptor molecules. The prePump-Pump-Probe transient signals were analyzed with Monte Carlo modeling to explicitly address the underlying step-by-step kinetics involved in both excitation migration and annihilation processes. Both energy transfer and annihilation dynamics were demonstrated to occur with approximately the same rate in both systems, regardless of the excitation status of the acceptor pigments. The possible reasons for these observations are discussed in the framework of the Förster energy transfer model.

  3. Fully Suspended, Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig With Forced Excitation

    Science.gov (United States)

    Morrison, Carlos R.; Provenza, Andrew; Kurkov, Anatole; Montague, Gerald; Duffy, Kirsten; Mehmed, Oral; Johnson, Dexter; Jansen, Ralph

    2004-01-01

    The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig, a significant advancement in the Dynamic Spin Rig (DSR), is used to perform vibration tests of turbomachinery blades and components under rotating and nonrotating conditions in a vacuum. The rig has as its critical components three magnetic bearings: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feed-forward control feature, which will enable the excitation of various natural blade modes in bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and nonrotating, unbladed rotor and a fully levitated, rotating and nonrotating, bladed rotor in which a pair of blades was arranged 180 degrees apart from each other. These tests include the bounce mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For nonrotating blades, a blade-tip excitation amplitude of approximately 100 g/A was achieved at the first-bending critical (approximately 144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 70 mils was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 908 relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.

  4. Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics

    Science.gov (United States)

    Franklin-Mergarejo, R.; Alvarez, D. Ondarse; Tretiak, S.; Fernandez-Alberti, S.

    2016-08-01

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications.

  5. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    Energy Technology Data Exchange (ETDEWEB)

    Van Tassle, Aaron Justin [Univ. of California, Berkeley, CA (United States)

    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.

  6. Synchronization enhancement via an oscillatory bath in a network of self-excited cells

    Indian Academy of Sciences (India)

    B R Nana Nbendjo; H G Enjieu Kadji; Hilda A Cerdeira

    2015-02-01

    The possibility of using a dynamic environment to achieve and optimize phase synchronization in a network of self-excited cells with free-end boundary conditions is addressed in this paper. The dynamic environment is an oscillatory bath coupled linearly to a network of four cells. The boundaries of the stable solutions of the dynamical states as well as the ranges of coupling parameters leading to stability and instability of synchronization are determined. Numerical simulations are used to check the accuracy and to complement the result obtained from analytical treatment. The robustness of synchronization strategy is tested using a local and global injection of Gaussian white noise in the network. The control gain parameter of the bath coupling can modulate the occurrence of synchronization in the network without prior requirement of direct coupling among all the cells. The process of synchronization obtained through local injection is independent of the node at which noise is injected into the system. As compared to local injection, the global injection scheme increases the range of noise amplitude for which synchronization occurs in the network.

  7. On the phase-correlation and phase-fluctuation dynamics of a strongly excited Bose gas

    Energy Technology Data Exchange (ETDEWEB)

    Sakhel, Roger R., E-mail: rogersakhel@yahoo.com [Department of Basic Sciences, Faculty of Information Technology, Isra University, Amman 11622 (Jordan); The Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, Trieste 34151 (Italy); Sakhel, Asaad R. [Department of Applied Sciences, Faculty of Engineering Technology, Balqa Applied University, Amman 11134 (Jordan); The Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, Trieste 34151 (Italy); Ghassib, Humam B. [Department of Physics, The University of Jordan, Amman 11942 (Jordan)

    2015-12-01

    The dynamics of a Bose–Einstein condensate (BEC) is explored in the wake of a violent excitation caused by a strong time-dependent deformation of a trapping potential under the action of an intense stirring laser. The system is a two-dimensional BEC confined to a power-law trap with hard-wall boundaries. The stirring agent is a moving red-detuned laser potential. The time-dependent Gross–Pitaevskii equation is solved numerically by the split-step Crank–Nicolson method in real time. The phase correlations and phase fluctuations are examined as functions of time to demonstrate the evolving properties of a strongly-excited BEC. Of special significance is the occurrence of spatial fluctuations while the condensate is being excited. These oscillations arise from stirrer-induced density fluctuations. While the stirrer is inside the trap, a reduction in phase coherence occurs, which is attributed to phase fluctuations.

  8. Striking dynamics of II-VI microcavity polaritons after linearly polarized excitation

    Energy Technology Data Exchange (ETDEWEB)

    Martin, M.D.; Ballarini, D.; Amo, A.; Klopotowsi, L.; Vina, L. [Grupo de Semiconductores (SEMICUAM), Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, C/ Francisco Tomas y Valiente 7, 28049 Cantoblanco, Madrid (Spain); Kavokin, A.V. [Laboratoire des Sciences et Materiaux pour l' Electronique, et d' Automatique, Universite Blaise Pascal - Clermont-Ferrand II, 63177 Aubiere Cedex (France); Andre, R. [Laboratoire de Spectrometrie Physique (CNRS UMR5588), Universite Joseph Fourier, 38042 Grenoble (France)

    2005-11-01

    We present a detailed study of the polariton spin dynamics in a II-VI microcavity after linearly polarized excitation. We have found that the vertically polarized (i.e. TE) emission is systematically larger than the horizontally polarized one (i.e. TM) for both, vertically and horizontally polarized excitation. Furthermore, a persistent difference between the two components of the emission is observed, leading to a net and constant (within the duration of the emission) linear polarization degree. Additionally, we have observed marked oscillations of the linear polarization degree once the excitation power is raised above the polariton-polariton stimulated scattering threshold. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Elucidation of the Relationships between H-Bonding Patterns and Excited State Dynamics in Cyclovalone

    Directory of Open Access Journals (Sweden)

    Marco Lamperti

    2014-08-01

    Full Text Available Cyclovalone is a synthetic curcumin derivative in which the keto-enolic system is replaced by a cyclohexanone ring. This modification of the chemical structure might in principle result in an excited state that is more stable than that of curcumin, which in turn should produce an enhanced phototoxicity. Indeed, although curcumin exhibits photosensitized antibacterial activity, this compound is characterized by very fast excited-state dynamics which limit its efficacy as a photosensitizer. In previous works we showed that the main non-radiative decay pathway of keto-enolic curcuminoids is through excited-state transfer of the enolic proton to the keto-oxygen. Another effective deactivation pathway involves an intermolecular charge transfer mechanism occurring at the phenyl rings, made possible by intramolecular H-bonding between the methoxy and the hydroxyl substituent. In this paper we present UV-Vis and IR absorption spectra data with the aim of elucidating the intramolecular charge distribution of this compound and its solvation patterns in different environments, with particular focus on solute-solvent H-bonding features. Moreover, we discuss steady state and time-resolved fluorescence data that aim at characterizing the excited-state dynamics of cyclovalone, and we compare its decay photophysics to that of curcumin. Finally, because during the characterization procedures we found evidence of very fast photodegradation of cyclovalone, its photostability in four organic solvents was studied by HPLC and the corresponding relative degradation rates were calculated.

  10. First-Principles Investigation of Electronic Excitation Dynamics in Water under Proton Irradiation

    Science.gov (United States)

    Reeves, Kyle; Kanai, Yosuke

    2015-03-01

    A predictive and quantitative understanding of electronic excitation dynamics in water under proton irradiation is of great importance in many technological areas ranging from utilizing proton beam therapy to preventing nuclear reactor damages. Despite its importance, an atomistic description of the excitation mechanism has yet to be fully understood. Identifying how a high-energy proton dissipates its kinetic energy into the electronic excitation is crucial for predicting atomistic damages, later resulting in the formation of different chemical species. In this work, we use our new, large-scale first-principles Ehrenfest dynamics method based on real-time time-dependent density functional theory to simulate the electronic response of bulk water to a fast-moving proton. In particular, we will discuss the topological nature of the electronic excitation as a function of the proton velocity. We will employ maximally-localized functions to bridge our quantitative findings from first-principles simulations to a conceptual understanding in the field of water radiolysis.

  11. Multifrequency Excitation Method for Rapid and Accurate Dynamic Test of Micromachined Gyroscope Chips

    Directory of Open Access Journals (Sweden)

    Yan Deng

    2014-10-01

    Full Text Available A novel multifrequency excitation (MFE method is proposed to realize rapid and accurate dynamic testing of micromachined gyroscope chips. Compared with the traditional sweep-frequency excitation (SFE method, the computational time for testing one chip under four modes at a 1-Hz frequency resolution and 600-Hz bandwidth was dramatically reduced from 10 min to 6 s. A multifrequency signal with an equal amplitude and initial linear-phase-difference distribution was generated to ensure test repeatability and accuracy. The current test system based on LabVIEW using the SFE method was modified to use the MFE method without any hardware changes. The experimental results verified that the MFE method can be an ideal solution for large-scale dynamic testing of gyroscope chips and gyroscopes.

  12. Multifrequency excitation method for rapid and accurate dynamic test of micromachined gyroscope chips.

    Science.gov (United States)

    Deng, Yan; Zhou, Bin; Xing, Chao; Zhang, Rong

    2014-10-17

    A novel multifrequency excitation (MFE) method is proposed to realize rapid and accurate dynamic testing of micromachined gyroscope chips. Compared with the traditional sweep-frequency excitation (SFE) method, the computational time for testing one chip under four modes at a 1-Hz frequency resolution and 600-Hz bandwidth was dramatically reduced from 10 min to 6 s. A multifrequency signal with an equal amplitude and initial linear-phase-difference distribution was generated to ensure test repeatability and accuracy. The current test system based on LabVIEW using the SFE method was modified to use the MFE method without any hardware changes. The experimental results verified that the MFE method can be an ideal solution for large-scale dynamic testing of gyroscope chips and gyroscopes.

  13. The transfer function method for gear system dynamics applied to conventional and minimum excitation gearing designs

    Science.gov (United States)

    Mark, W. D.

    1982-01-01

    A transfer function method for predicting the dynamic responses of gear systems with more than one gear mesh is developed and applied to the NASA Lewis four-square gear fatigue test apparatus. Methods for computing bearing-support force spectra and temporal histories of the total force transmitted by a gear mesh, the force transmitted by a single pair of teeth, and the maximum root stress in a single tooth are developed. Dynamic effects arising from other gear meshes in the system are included. A profile modification design method to minimize the vibration excitation arising from a pair of meshing gears is reviewed and extended. Families of tooth loading functions required for such designs are developed and examined for potential excitation of individual tooth vibrations. The profile modification design method is applied to a pair of test gears.

  14. Benchmarking the stochastic time-dependent variational approach for excitation dynamics in molecular aggregates

    Science.gov (United States)

    Chorošajev, Vladimir; Gelzinis, Andrius; Valkunas, Leonas; Abramavicius, Darius

    2016-12-01

    Time dependent variational approach is a convenient method to characterize the excitation dynamics in molecular aggregates for different strengths of system-bath interaction a, which does not require any additional perturbative schemes. Until recently, however, this method was only applicable in zero temperature case. It has become possible to extend this method for finite temperatures with the introduction of stochastic time dependent variational approach. Here we present a comparison between this approach and the exact hierarchical equations of motion approach for describing excitation dynamics in a broad range of temperatures. We calculate electronic population evolution, absorption and auxiliary time resolved fluorescence spectra in different regimes and find that the stochastic approach shows excellent agreement with the exact approach when the system-bath coupling is sufficiently large and temperatures are high. The differences between the two methods are larger, when temperatures are lower or the system-bath coupling is small.

  15. Trans-cis photoisomerization of azobenzene by n→π* excitation:A semiclassical dynamics study

    Institute of Scientific and Technical Information of China (English)

    Shuai Yuan; Wei Feng Wu; Yusheng Dou; Jian She Zhao

    2008-01-01

    A realistic dynamics simulation study is reported for the trans-cis photoisomerization of azobenzene triggered by the n→π*excitation and the results show that the formation of cis isomer follows the rotational motion around the N=N bond.The simulation find that the CNN bond angle bending vibrations also play a significant role in the vibronic coupling between the HOMO and LUMO,which essentially leads a nonadiabatic transition of the molecule to the electronic ground state.

  16. Magnetic correlation, excitation and slow dynamics in concentrated spin-glass alloys

    Indian Academy of Sciences (India)

    Kiyoichiro Motoya

    2004-07-01

    Three kinds of neutron scattering experiments have been performed to clarify the role of magnetic clusters on the various properties of re-entrant spin-glasses. The presence of two kinds of spin-wave excitations, the limitations of magnetic phase diagrams and the mechanism of slow dynamics have been discussed based on the results of in-elastic scattering, diffuse scattering and time-resolved small-angle scattering experiments, respectively.

  17. Study on Dynamics of Polygonal Wear of Automotive Tire Caused by Self-Excited Vibration

    Directory of Open Access Journals (Sweden)

    Shuguang Zuo

    2014-01-01

    Full Text Available Considering the underlying reason of tire polygonal wear, a unified mechanical tire model is developed to analyze the different vibration properties between the driving wheel and follower wheel. And the LuGre dynamic friction model is applied to determine the frictional forces between the wheel with a slip angel and the road. Through the stability analysis with Lyapunov theory, it is found that tread self-excited vibration is periodic oscillation caused by Hopf bifurcation. The analysis of the lateral vibration of driving wheel shows that the tread vibration system loses its stability and self-excited vibration occurs when the wheel is rolling at a high speed, is over-loaded, is having a large toe-in angle, or is under a low tire pressure. On this basis, the dynamic behaviors of the driving and follower wheels are distinguished with different slip rates by the numerical simulation. Compared with the dynamic behaviors of the follower wheel under the same condition, the self-excited vibration occurs on the driving wheel with more limited parameter scope, lower oscillation energy, and lower occurrence, which explains why the polygonal wear is less likely to occur on the driving wheel.

  18. Dichotomous Role of Exciting the Donor or the Acceptor on Charge Generation in Organic Solar Cells.

    Science.gov (United States)

    Hendriks, Koen H; Wijpkema, Alexandra S G; van Franeker, Jacobus J; Wienk, Martijn M; Janssen, René A J

    2016-08-10

    In organic solar cells, photoexcitation of the donor or acceptor phase can result in different efficiencies for charge generation. We investigate this difference for four different 2-pyridyl diketopyrrolopyrrole (DPP) polymer-fullerene solar cells. By comparing the external quantum efficiency spectra of the polymer solar cells fabricated with either [60]PCBM or [70]PCBM fullerene derivatives as acceptor, the efficiency of charge generation via donor excitation and acceptor excitation can both be quantified. Surprisingly, we find that to make charge transfer efficient, the offset in energy between the HOMO levels of donor and acceptor that govern charge transfer after excitation of the acceptor must be larger by ∼0.3 eV than the offset between the corresponding two LUMO levels when the donor is excited. As a consequence, the driving force required for efficient charge generation is significantly higher for excitation of the acceptor than for excitation of the donor. By comparing charge generation for a total of 16 different DPP polymers, we confirm that the minimal driving force, expressed as the photon energy loss, differs by about 0.3 eV for exciting the donor and exciting the acceptor. Marcus theory may explain the dichotomous role of exciting the donor or the acceptor on charge generation in these solar cells.

  19. Wavelet transforms to probe long- and short-range forces by thermally excited dynamic force spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Malegori, Giovanna; Ferrini, Gabriele, E-mail: gabriele@dmf.unicatt.it [Dipartimento di Matematica e Fisica, Universita Cattolica, I-25121 Brescia (Italy)

    2011-05-13

    The use of wavelet transforms in thermally excited dynamic force spectroscopy allows us to gain insight into the fundamental thermodynamical properties of a cantilever's Brownian motion as well as giving a meaningful and intuitive representation of the cantilever dynamics in time and frequency caused by the interaction with long- and short-range forces. The possibility of carrying out measurements across the jump-to-contact transition without interruption, providing information on both van der Waals forces and short-range adhesion surface forces, is remarkable.

  20. Interplay between topology and dynamics in excitation patterns on hierarchical graphs

    Directory of Open Access Journals (Sweden)

    Marc Hütt

    2009-09-01

    Full Text Available In a recent publication [Müller-Linow et al. (2008 PLoS Computational Biology 4, 1000190] two types of correlations between network topology and dynamics have been observed: waves propagating from central nodes and module-based synchronization. Remarkably, the dynamic behavior of hierarchical modular networks can switch from one of these modes to the other as the level of spontaneous network activation changes. Here we attempt to capture the origin of this switching behavior in a mean-field model as well in a formalism, where excitation waves are regarded as avalanches on the graph.

  1. Photoexcited breathers in conjugated polyenes: an excited-state molecular dynamics study.

    Science.gov (United States)

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

    2003-03-04

    pi-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.

  2. Detection of Damage in a Lattice Mast Excited by Wind by Dynamic Measurements

    DEFF Research Database (Denmark)

    Pedersen, Lars

    2007-01-01

    The paper illustrates the effectiveness of monitoring the dynamic response of a system for detection of damage herein using an output-only assessment scheme. The system is a 20 m height steel lattice mass excited by wind and the mast is instrumented with accelerometers picking up dynamic responses...... under ambient loading conditions. The paper presents the instrumentation and considerations regarding layout of instrumentation and strategies for acquisition and processing of data. Damage in the mast is provoked using a hacksaw and the cross sectional area of one the diagonals of the mast (one located...... close to the foundation) is gradually reduced by sawing deeper and deeper into the diagonal. During the process of introducing damage to the mast, its dynamic responses are recorded. By postprocessing these recordings, the changes in dynamic characteristics of the mast with the size of damage...

  3. Topological Influence of Lyotropic Liquid Crystalline Systems on Excited-State Proton Transfer Dynamics.

    Science.gov (United States)

    Roy, Bibhisan; Satpathi, Sagar; Hazra, Partha

    2016-03-29

    In the present work, we have investigated the excited-state proton transfer (ESPT) dynamics inside lipid-based reverse hexagonal (HII), gyroid Ia3d, and diamond Pn3m LLC phases. Polarized light microscopy (PLM) and small-angle X-ray scattering (SAXS) techniques have been employed for the characterization of LLC systems. Time-resolved fluorescence results reveal the retarded ESPT dynamics inside liquid crystalline systems compared to bulk water, and it follows the order HII water and it follows the order H2O constant and different channel diameters of these LLC systems. However, the dissociation dynamics is found to be slower than bulk water and it follows the order HII dissociation dynamics in these liquid crystalline systems.

  4. Quantum dynamics of electronic excitations in biomolecular chromophores: role of the protein environment and solvent

    CERN Document Server

    Gilmore, J; Gilmore, Joel; Kenzie, Ross H. Mc

    2006-01-01

    We consider continuum dielectric models as minimal models to understand the effect of the surrounding protein and solvent on the quantum dynamics of electronic excitations in a biological chromophore. For these models we describe expressions for the frequency dependent spectral density which describes the coupling of the electronic levels in the chromophore to its environment. We find the contributions to the spectral density from each component of the chromophore environment: the bulk solvent, protein, and water bound to the protein. The relative importance of each component is determined by the time scale on which one is considering the quantum dynamics of the chromophore. Our results provide a natural explanation and model for the different time scales observed in the spectral density extracted from the solvation dynamics probed by ultra-fast laser spectroscopy techniques such as the dynamic Stokes shift and three pulse photon echo spectroscopy. Our results can be used to define under what conditions the d...

  5. Transcription Dynamics in Living Cells.

    Science.gov (United States)

    Lenstra, Tineke L; Rodriguez, Joseph; Chen, Huimin; Larson, Daniel R

    2016-07-01

    The transcription cycle can be roughly divided into three stages: initiation, elongation, and termination. Understanding the molecular events that regulate all these stages requires a dynamic view of the underlying processes. The development of techniques to visualize and quantify transcription in single living cells has been essential in revealing the transcription kinetics. They have revealed that (a) transcription is heterogeneous between cells and (b) transcription can be discontinuous within a cell. In this review, we discuss the progress in our quantitative understanding of transcription dynamics in living cells, focusing on all parts of the transcription cycle. We present the techniques allowing for single-cell transcription measurements, review evidence from different organisms, and discuss how these experiments have broadened our mechanistic understanding of transcription regulation.

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

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Guorong [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Neville, Simon P.; Worth, Graham A., E-mail: g.a.worth@bham.ac.uk [School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Schalk, Oliver [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); Department of Physics, AlbaNova University Center, Stockholm University, Roslagstullsbacken 21, 109 61 Stockholm (Sweden); Sekikawa, Taro [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); Department of Applied Physics, Hokkaido University, Kita-13 Nishi-8, Kita-ku, Sapporo 060-8628 (Japan); Ashfold, Michael N. R. [School of Chemistry, University of Bristol, Bristol BS8 1TS (United Kingdom); Stolow, Albert, E-mail: astolow@uottawa.ca [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); Departments of Chemistry and Physics, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5 (Canada)

    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.

  7. Versatile single-molecule multi-color excitation and detection fluorescence setup for studying biomolecular dynamics

    KAUST Repository

    Sobhy, M. A.

    2011-11-07

    Single-molecule fluorescence imaging is at the forefront of tools applied to study biomolecular dynamics both in vitro and in vivo. The ability of the single-molecule fluorescence microscope to conduct simultaneous multi-color excitation and detection is a key experimental feature that is under continuous development. In this paper, we describe in detail the design and the construction of a sophisticated and versatile multi-color excitation and emission fluorescence instrument for studying biomolecular dynamics at the single-molecule level. The setup is novel, economical and compact, where two inverted microscopes share a laser combiner module with six individual laser sources that extend from 400 to 640 nm. Nonetheless, each microscope can independently and in a flexible manner select the combinations, sequences, and intensities of the excitation wavelengths. This high flexibility is achieved by the replacement of conventional mechanical shutters with acousto-optic tunable filter (AOTF). The use of AOTF provides major advancement by controlling the intensities, duration, and selection of up to eight different wavelengths with microsecond alternation time in a transparent and easy manner for the end user. To our knowledge this is the first time AOTF is applied to wide-field total internal reflection fluorescence (TIRF) microscopy even though it has been commonly used in multi-wavelength confocal microscopy. The laser outputs from the combiner module are coupled to the microscopes by two sets of four single-mode optic fibers in order to allow for the optimization of the TIRF angle for each wavelength independently. The emission is split into two or four spectral channels to allow for the simultaneous detection of up to four different fluorophores of wide selection and using many possible excitation and photoactivation schemes. We demonstrate the performance of this new setup by conducting two-color alternating excitation single-molecule fluorescence resonance energy

  8. Ultrafast excited state dynamics of the green fluorescent protein chromophore and its kindling fluorescent protein analogue.

    Science.gov (United States)

    Addison, Kiri; Heisler, Ismael A; Conyard, Jamie; Dixon, Tara; Page, Philip C Bulman; Meech, Stephen R

    2013-01-01

    Fluorescent proteins exhibit a very diverse range of photochemical behaviour, from efficient fluorescence through photochromism to photochemical reactivity. Remarkably this diverse behaviour arises from chromophores which have very similar structures. Here we describe measurements and modelling of the excited state dynamics in the chromophores of GFP (HBDI) and the kindling fluorescent protein, KFP (FHBMI). The methods are ultrafast fluorescence spectroscopy with sub 50 fs time resolution and the modelling is based on the Smoluchowski equation. The excited state decays of both chromophores are very fast, longer for their anions than for the neutral form and independent of wavelength. Detailed studies show the mean fluorescence wavelength to be independent of time. The excited state decay times are also observed to be a very weak function of solvent polarity and viscosity. These results are modelled utilising recently calculated potential energy surfaces for the ground and excited states as a function of the twist coordinates about the two bridging bonds of the chromophore. For FHBMI and the scarce data on the neutral HBDI the calculations are not successful suggesting the need for refinement of these potential energy surfaces. For HBDI in methanol the simulation is successful provided a strong dependence of the radiationless decay rate on the coordinate is assumed. Such dependence should be included in future calculations of excited state dynamics. When the simulations are extended to more viscous solvents they fail to reproduce the observed weak viscosity dependence. The implications of these results for the nature of the coordinate leading to radiationless decay in the chromophore and for the photodynamics of fluorescent proteins are discussed.

  9. Variation of Excited-State Dynamics in Trifluoromethyl Functionalized C60 Fullerenes

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jaehong; Ramirez, Jessica J.; Clikeman, Tyler T.; Larson, Bryon W.; Boltalina, Olga V.; Strauss, Steven H.; Rumbles, Garry

    2016-09-07

    We report on electronically excited-state dynamics of three different trifluoromethyl C60 fullerenes (TMFs, C60(CF3)n: C60/4-1, C60/6-2, and C60/10-1, featuring four, six, and ten trifluoromethyl groups, respectively) using steady-state and time-resolved optical spectroscopy as well as ultrafast pump/probe transient absorption spectroscopy. C60/4-1 and C60/6-2 dissolved in toluene solvent show near-unity S1--T1 intersystem crossing quantum yield (..phi..ISC), ca. 1 ns S1-state lifetimes, and microsecond-timescale T1-state lifetimes, which are typical of the fullerene class. On the other hand, C60/10-1 exhibits a dominant sub-nanosecond nonradiative S1--S0 relaxation mechanism and negligible ..phi..ISC, therefore decreasing the average excited-state lifetime (..tau..avg) by about 5 orders of magnitude compared to that of C60/4-1 and C60/6-2 (..tau..avg approx. 17 us and 54 us for C60/4-1 and C60/6-2, respectively, whereas ..tau..avg approx. 100 ps for C60/10-1). These excited-state characteristics of C60/4-1 and C60/6-2 are preserved in polymer matrix, suggesting that fullerene/polymer interactions do not modulate intrinsic photophysics of trifluoromethyl-substituted fullerenes. The contrasting excited- state study results of C60/4-1 and C60/6-2 to that of C60/10-1 infer that intrinsic optical properties and excited-state dynamics can be affected by the substitution on the fullerene.

  10. Dynamics of sessile and pendant drop excited by surface acoustic waves: gravity effects and correlation between oscillatory and translational motions

    CERN Document Server

    Bussonière, Adrien; Brunet, Philippe; Matar, Olivier Bou

    2016-01-01

    When sessile droplets are excited by ultrasonic traveling surface acoustic waves (SAWs), they undergo complex dynamics with both oscillations and translational motion. While the nature of the Rayleigh-Lamb quadrupolar drop oscillations has been identified, their origin and their influence on the drop mobility remains unexplained. Indeed the physics behind this peculiar dynamics is complex with nonlinearities involved both at the excitation level (acoustic streaming and radiation pressure) and in the droplet response (nonlinear oscillations and contact line dynamics). In this paper, we investigate the dynamics of sessile and pendant drops excited by SAWs. For pendant drops, so-far unreported dynamics are observed close to the drop detachment threshold with the suppression of the translational motion. Away from this threshold, the comparison between pendant and sessile drop dynamics allows us to identify the role played by gravity or more generally by an initial or dynamically induced stretching of the drop. In...

  11. Steady-state responses of a belt-drive dynamical system under dual excitations

    Science.gov (United States)

    Ding, Hu

    2016-02-01

    The stable steady-state periodic responses of a belt-drive system with a one-way clutch are studied. For the first time, the dynamical system is investigated under dual excitations. The system is simultaneously excited by the firing pulsations of the engine and the harmonic motion of the foundation. Nonlinear discrete-continuous equations are derived for coupling the transverse vibration of the belt spans and the rotations of the driving and driven pulleys and the accessory pulley. The nonlinear dynamics is studied under equal and multiple relations between the frequency of the firing pulsations and the frequency of the foundation motion. Furthermore, translating belt spans are modeled as axially moving strings. A set of nonlinear piecewise ordinary differential equations is achieved by using the Galerkin truncation. Under various relations between the excitation frequencies, the time histories of the dynamical system are numerically simulated based on the time discretization method. Furthermore, the stable steady-state periodic response curves are calculated based on the frequency sweep. Moreover, the convergence of the Galerkin truncation is examined. Numerical results demonstrate that the one-way clutch reduces the resonance amplitude of the rotations of the driven pulley and the accessory pulley. On the other hand, numerical examples prove that the resonance areas of the belt spans are decreased by eliminating the torque-transmitting in the opposite direction. With the increasing amplitude of the foundation excitation, the damping effect of the one-way clutch will be reduced. Furthermore, as the amplitude of the firing pulsations of the engine increases, the jumping phenomena in steady-state response curves of the belt-drive system with or without a one-way clutch both occur.

  12. Non-adiabatic Excited State Molecule Dynamics Modeling of Photochemistry and Photophysics of Materials

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, Tammie Renee [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tretiak, Sergei [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-01-06

    Understanding and controlling excited state dynamics lies at the heart of all our efforts to design photoactive materials with desired functionality. This tailor-design approach has become the standard for many technological applications (e.g., solar energy harvesting) including the design of organic conjugated electronic materials with applications in photovoltaic and light-emitting devices. Over the years, our team has developed efficient LANL-based codes to model the relevant photophysical processes following photoexcitation (spatial energy transfer, excitation localization/delocalization, and/or charge separation). The developed approach allows the non-radiative relaxation to be followed on up to ~10 ps timescales for large realistic molecules (hundreds of atoms in size) in the realistic solvent dielectric environment. The Collective Electronic Oscillator (CEO) code is used to compute electronic excited states, and the Non-adiabatic Excited State Molecular Dynamics (NA-ESMD) code is used to follow the non-adiabatic dynamics on multiple coupled Born-Oppenheimer potential energy surfaces. Our preliminary NA-ESMD simulations have revealed key photoinduced mechanisms controlling competing interactions and relaxation pathways in complex materials, including organic conjugated polymer materials, and have provided a detailed understanding of photochemical products and intermediates and the internal conversion process during the initiation of energetic materials. This project will be using LANL-based CEO and NA-ESMD codes to model nonradiative relaxation in organic and energetic materials. The NA-ESMD and CEO codes belong to a class of electronic structure/quantum chemistry codes that require large memory, “long-queue-few-core” distribution of resources in order to make useful progress. The NA-ESMD simulations are trivially parallelizable requiring ~300 processors for up to one week runtime to reach a meaningful restart point.

  13. Small Amplitude Dynamics of Nonhomogeneous Magnetization Distributions: The Excitation Spectrum of Stripe Domains

    Science.gov (United States)

    Ebels, Ursula; Buda, Liliana D.; Ounadjela, Kamel; Wigen, Phillip E.

    The general purpose of this review is to introduce to the dynamics of small amplitude excitations of nonhomogeneous magnetization distributions. This is in contrast to the dynamics of the magnetization reversal process, which corresponds to large amplitude perturbations, discussed in other contributions of this book. Small amplitude oscillations can be studied by ferromagnetic resonance or Brillouin light scattering. The latter technique isused to investigate the excitation spectrum in laterally constrained structures.This review introduces ferromagnetic resonance and focuses on the role of the pumping field orientation. Upon varying the pumping field orientation, fundamental modes can be selectively excited, giving, in particular, access to regions of varying magnetic orientation. This is demonstrated for the excitation spectrum of magnetic domains and domain walls of the stripe domain structure in metallic thin films. These stripe domains can be considered laterally constrained magnetic units 40-100 nm wide, separated by domain walls.Such experiments provide information on the domain and domain wall structure and in principle yield the internal fields and the coupling fields of the domains, as well as the wall mass and the stabilizing forces of the domain walls. The wall mass itself is a dynamic parameter which intervenes upon wall acceleration but is of less importance when considering steady-state wall propagation in the magnetization reversal process. However, the wall mass depends sensitively on the spin configuration inside the wall, and therefore resonance experiments can provide insight into the structure of the domain wall. The wall structure, on the other hand, plays an important role in spin-polarized transport experiments, investigating the contribution of a domain wall to the resistance [1] or the transfer of momentum from the conduction electrons to the wall [2,3].

  14. Excited states in electron-transfer reaction products : ultrafast relaxation dynamics of an isolated acceptor radical anion.

    OpenAIRE

    D. A. Horke; Roberts, G.M.; Verlet, J. R. R.

    2011-01-01

    The spectroscopy and ultrafast relaxation dynamics of excited states of the radical anion of a representative charge-transfer acceptor molecule, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, have been studied in the gas phase using time-resolved photoelectron spectroscopy. The photoelectron spectra reveal that at least two anion excited states are bound. Time-resolved studies show that both excited states are very short-lived and internally convert to the anion ground state, with the ...

  15. Developing Dynamic Digital Image Correlation Technique to Monitor Structural Damage of Old Buildings under External Excitation

    Directory of Open Access Journals (Sweden)

    Ming-Hsiang Shih

    2014-01-01

    Full Text Available The capacity of buildings to resist external excitation is an important factor to consider for the structural design of buildings. When subject to external excitation, a building may suffer a certain degree of damages, and its residual capacity to resist external excitation cannot be evaluated. In this research, dynamic digital image correlation method combined with parameter evaluation available in system identification is used to evaluate the structural capacity to resist external excitation. The results reveal possible building latent safety problems so that timely structural reinforcement or dismantling of the building can be initiated to alleviate further damages. The results of experiments using the proposed method conform to the results obtained using the conventional method, but this method is more convenient and rapid than the latter in the subsequent procedure of data processing. If only the frequency change is used, the damages suffered by the building can be detected, but the damage location is not revealed. The interstory drift mode shape (IDMS based on the characteristic of story drift has higher sensitivity than the approximate story damage index (ADSI method based on modal frequency and vibration type; however, both indices can be used to determine the degree and location of building damages.

  16. Dynamics of Below-Band-Gap Carrier in Highly Excited GaN

    Institute of Scientific and Technical Information of China (English)

    郭冰; 黄锦圣; 叶志镇; 江红星; 林景瑜

    2003-01-01

    Femtosecond time-resolved reflectivity was used to investigate below-band-gap (3.1 eV) carrier dynamics in a nominally undoped GaN epilayer under high excitation. A 2.5-ps rising process can be observed in the transient trace. This shot rising time results from the hot phonon effects which can cause a delayed energy relaxation of the initial photocarriers toward the band edge. From the density dependence of the carrier dynamics, the Mott density was estimated to be 1.51-1.56 × 1019 cm-3. Below the Mott density, the initial probed carrier dynamics was explained to the effect of acoustic phonon-assisted tunnelling for localized states, where a significant excitation density dependence of the tunnelling probability was observed due to the optically induced bandtail extension to lower energies. Above the Mott density, the measured carrier dynamics reflected the relaxation of an electron-hole plasma, in which a distinct fast decay component of 2.3 ps was observed due to the onset of nonlinear relaxation processes such Auger recombination.

  17. The mechanism of the NH4 ion oscillatory transport across the excitable cell membrane

    Directory of Open Access Journals (Sweden)

    Radenović Čedomir N.

    2005-01-01

    Full Text Available This paper presents results on typical oscillations of the membrane potential induced by the excitation of the cell membrane by different concentrations of the NH4Cl solution. The existence of four classes of oscillations of the membrane potential and several different single and local impulses rhythmically occurring were determined. It is known that the oscillatory processes of the membrane potential are in direct dependence on oscillatory transport processes of NH4 and Cl ions across the excitable cell membrane. A hypothesis on a possible mechanism of oscillatory transport processes of NH4 and Cl ions across the excitable cell membrane is also presented.

  18. Inscribing Optical Excitability to Non-Excitable Cardiac Cells: Viral Delivery of Optogenetic Tools in Primary Cardiac Fibroblasts

    Science.gov (United States)

    Yu, Jinzhu; Entcheva, Emilia

    2016-01-01

    We describe in detail a method to introduce optogenetic actuation tools, a mutant version of channelrhodopsin- 2, ChR2(H134R), and archaerhodopsin (ArchT), into primary cardiac fibroblasts (cFB) in vitro by adenoviral infection to yield quick, robust, and consistent expression. Instructions on adjusting infection parameters such as the multiplicity of infection and virus incubation duration are provided to generalize the method for different lab settings or cell types. Specific conditions are discussed to create hybrid co-cultures of the optogenetically modified cFB and non-transformed cardiomyocytes to obtain light- sensitive excitable cardiac syncytium, including stencil-patterned cell growth. We also describe an all-optical framework for the functional testing of responsiveness of these opsins in cFB. The presented methodology provides cell-specific tools for the mechanistic investigation of the functional bioelectric contribution of different non-excitable cells in the heart and their electrical coupling to cardiomyocytes under different conditions. PMID:26965132

  19. Dynamical theory of spectroscopy with femtosecond pulse excitation(Ⅲ)——Transient rate equation in Liouville space

    Institute of Scientific and Technical Information of China (English)

    陆靖; 范康年

    1999-01-01

    A dynamical theory of spectroscopy with femtosecond pulse excitation is developed in Liouville space. By using density matrix formalism, the transient rate equation that can be reduced to the classical KHD expression in CW case is obtained. This theory is applied to the Raman excitation profile of IBr and the results are in agreement with the experiments.

  20. Photoactivated excited states of DNA repair photolyase: Dynamical and semiempircal identification

    Science.gov (United States)

    Zheng, Xuehe; Ly, Ngan M.; Stuchebrukhov, Alexei A.

    DNA damage caused by UV light radiation is often naturally repaired in a process initiated by excited state electron transfer from the photoactivated photolyase enzyme to the DNA cyclobutane pyrimidine dimer lesion. The active cofactor in the excited state electron transfer in the photolyase is the two-electron fully reduced form of the flavin adenine dinucleotide (FADH-). To calculate electron tunneling matrix element and model the DNA binding with photolyase, the LUMO of the FADH- calculated using extended Huckel method was previously chosen from the SCF wavefunctions. Recently, the DNA-photolyase complex was crystallized in its bound form, in good agreement with our previous model in even minute details at the active site. Here we carry out molecular dynamics simulation of the entire complex using the new experimental structure of Anacystis nidulans and identify the low-lying photoactivated states of the enzyme for the dynamical confirmations. Our results from ZINDO/S CIS calculations are compared with experimental UV spectra, and their implications for excited state electron transfer and energy transfer are discussed.0

  1. Data-driven modelling of vertical dynamic excitation of bridges induced by people running

    Science.gov (United States)

    Racic, Vitomir; Morin, Jean Benoit

    2014-02-01

    With increasingly popular marathon events in urban environments, structural designers face a great deal of uncertainty when assessing dynamic performance of bridges occupied and dynamically excited by people running. While the dynamic loads induced by pedestrians walking have been intensively studied since the infamous lateral sway of the London Millennium Bridge in 2000, reliable and practical descriptions of running excitation are still very rare and limited. This interdisciplinary study has addressed the issue by bringing together a database of individual running force signals recorded by two state-of-the-art instrumented treadmills and two attempts to mathematically describe the measurements. The first modelling strategy is adopted from the available design guidelines for human walking excitation of structures, featuring perfectly periodic and deterministic characterisation of pedestrian forces presentable via Fourier series. This modelling approach proved to be inadequate for running loads due to the inherent near-periodic nature of the measured signals, a great inter-personal randomness of the dominant Fourier amplitudes and the lack of strong correlation between the amplitudes and running footfall rate. Hence, utilising the database established and motivated by the existing models of wind and earthquake loading, speech recognition techniques and a method of replicating electrocardiogram signals, this paper finally presents a numerical generator of random near-periodic running force signals which can reliably simulate the measurements. Such a model is an essential prerequisite for future quality models of dynamic loading induced by individuals, groups and crowds running under a wide range of conditions, such as perceptibly vibrating bridges and different combinations of visual, auditory and tactile cues.

  2. Excited state dynamics of thiophene and bithiophene: new insights into theoretically challenging systems.

    Science.gov (United States)

    Prlj, Antonio; Curchod, Basile F E; Corminboeuf, Clémence

    2015-06-14

    The computational elucidation and proper description of the ultrafast deactivation mechanisms of simple organic electronic units, such as thiophene and its oligomers, is as challenging as it is contentious. A comprehensive excited state dynamics analysis of these systems utilizing reliable electronic structure approaches is currently lacking, with earlier pictures of the photochemistry of these systems being conceived based upon high-level static computations or lower level dynamic trajectories. Here a detailed surface hopping molecular dynamics of thiophene and bithiophene using the algebraic diagrammatic construction to second order (ADC(2)) method is presented. Our findings illustrate that ring puckering plays an important role in thiophene photochemistry and that the photostability increases when going upon dimerization into bithiophene.

  3. Dynamical resonance in F+H2 chemical reaction and rotational excitation effect

    Institute of Scientific and Technical Information of China (English)

    YANG XueMing; XIE DaiQian; ZHANG DongHui

    2007-01-01

    Reaction resonance is a frontier topic in chemical dynamics research, and it is also essential to the understanding of mechanisms of elementary chemical reactions. This short article describes an important development in the frontier of research. Experimental evidence of reaction resonance has been detected in a full quantum state resolved reactive scattering study of the F+H2 reaction. Highly accurate full quantum scattering theoretical modeling shows that the reaction resonance is caused by two Feshbach resonance states. Further studies show that quantum interference is present between the two resonance states for the forward scattering product. This study is a significant step forward in our understanding of chemical reaction resonance in the benchmark F+H2 system. Further experimental studies on the effect of H2 rotational excitation on dynamical resonance have been carried out. Dynamical resonance in the F+H2 (j = 1) reaction has also been observed.

  4. Chaotic motion of the dynamical system under both additive and multiplicative noise excitations

    Institute of Scientific and Technical Information of China (English)

    Li Xiu-Chun; Xu Wei; Li Rui-Hong

    2008-01-01

    With both additive and multiplicative noise excitations,the effect on the chaotic behaviour of the dynamical system is investigated in this paper.The random Melnikov theorem with the mean-square criterion that applies to a type of dynamical systems is analysed in order to obtain the conditions for the possible occurrence of chaos.As an example,for the Duffing system,we deduce its concrete expression for the threshold of multiplicative noise amplitude for the rising of chaos,and by combining figures,we discuss the influences of the amplitude,intensity and frequency of both bounded noises on the dynamical behaviour of the Duffing system separately.Finally,numerical simulations are.

  5. Coupling dynamic analysis of a liquid-filled spherical container subject to arbitrary excitation

    Institute of Scientific and Technical Information of China (English)

    Jing Lü; Shimin Wang; Tianshu Wang

    2012-01-01

    Using spherical coordinates,the coupling nonlinear dynamic system of a liquid-filled spherical tank,which can be excited discretionarily,is deduced by the H-O variational principle,and the viscous damping is introduced via the liquid dissipation function.The kinetic equations of the coupling system are deduced by the relationship between the velocity of liquid particles and the disturbed liquid surface equation.Normal differential equations are obtained through the Galerkin method.An equivalent mechanical model is developed for liquid sloshing in a spherical tank subject to arbitrary excitation.The fixed and slosh masses,as well as the spring and damping constants,are determined in such a way as to satisfy the principle of equivalence.Numerical simula tions illustrate the theoretical results in this paper as well.

  6. Excitation dynamics of a low bandgap silicon-bridged dithiophene copolymer and its composites with fullerenes

    Science.gov (United States)

    Othonos, Andreas; Itskos, Grigorios; Neophytou, Marios; Choulis, Stelios A.

    2012-04-01

    We report on excitation dynamics in pristine and bulk heterojunction films of the low bandgap silicon-bridged dithiophene copolymer poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2', 3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5'-diyl] with methanofullerene derivatives. The combination of ultrafast transient transmission and photoluminescence allows us to probe the relaxation of both exciton and polaron states in a relatively wide spectral and temporal range. Measurements reveal that the majority of excitations undergo ultrashort non-radiative relaxation while a small fraction of the photoexcited species decays slowly within hundreds of ps. In the blend films, significantly longer decays are observed suggesting the presence of long lived holes and/or charged-transfer type of excitons.

  7. On the dynamics of excited atoms in time dependent electromagnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Foerre, Morten

    2004-06-01

    This thesis is composed of seven scientific publications written in the period 2001-2004. The focus has been set on Rydberg atoms of hydrogen and lithium in relatively weak electromagnetic fields. Such atoms have been studied extensively during many years, both experimentally and theoretically, They are relatively easy to handle in the laboratory. Their willingness to react to conventional field sources and their long lifetimes, are two reasons for this. Much new insight into fundamental quantum mechanics has been extracted from such studies. By exciting a non-hydrogenic ground state atom or molecule into a highly excited state, many properties of atomic hydrogen are adopted. In many cases the dynamics of such systems can be accurately described by the hydrogenic theory, or alternatively by some slightly modified version like quantum defect theory. In such theories the Rydberg electron(s) of the non-hydrogenic Rydberg system is treated like it is confined in a modified Coulomb potential, which arises from the non-hydrogenic core. defined by the non-excited electrons and the nucleus. The more heavily bound core electrons are less influenced from external perturbations than the excited electrons, giving rise to the so-called frozen-core approximation. where the total effect of the core electrons is put into a modified Coulomb potential. A major part of this thesis has been allocated to the study of core effects in highly excited states of lithium. In collaboration with time experimental group of Erik Horsdal-Pedersen at Aarhus University, we have considered several hydrogenic and non-hydrogenic aspects of such states, when exposed to weak slowly varying electromagnetic fields. The dynamics was restricted to one principal shell (intrashell). Two general features were observed, either the hydrogenic theory applied or alternatively, in case of massive deviation, the dynamics was accurately described by quantum defect theory, clearly demonstrating the usefulness of such

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

    Science.gov (United States)

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

    2013-06-20

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

  9. History-Dependent Excitability as a Single-Cell Substrate of Transient Memory for Information Discrimination

    Science.gov (United States)

    Baroni, Fabiano; Torres, Joaquín J.; Varona, Pablo

    2010-01-01

    Neurons react differently to incoming stimuli depending upon their previous history of stimulation. This property can be considered as a single-cell substrate for transient memory, or context-dependent information processing: depending upon the current context that the neuron “sees” through the subset of the network impinging on it in the immediate past, the same synaptic event can evoke a postsynaptic spike or just a subthreshold depolarization. We propose a formal definition of History-Dependent Excitability (HDE) as a measure of the propensity to firing in any moment in time, linking the subthreshold history-dependent dynamics with spike generation. This definition allows the quantitative assessment of the intrinsic memory for different single-neuron dynamics and input statistics. We illustrate the concept of HDE by considering two general dynamical mechanisms: the passive behavior of an Integrate and Fire (IF) neuron, and the inductive behavior of a Generalized Integrate and Fire (GIF) neuron with subthreshold damped oscillations. This framework allows us to characterize the sensitivity of different model neurons to the detailed temporal structure of incoming stimuli. While a neuron with intrinsic oscillations discriminates equally well between input trains with the same or different frequency, a passive neuron discriminates better between inputs with different frequencies. This suggests that passive neurons are better suited to rate-based computation, while neurons with subthreshold oscillations are advantageous in a temporal coding scheme. We also address the influence of intrinsic properties in single-cell processing as a function of input statistics, and show that intrinsic oscillations enhance discrimination sensitivity at high input rates. Finally, we discuss how the recognition of these cell-specific discrimination properties might further our understanding of neuronal network computations and their relationships to the distribution and functional

  10. History-dependent excitability as a single-cell substrate of transient memory for information discrimination.

    Directory of Open Access Journals (Sweden)

    Fabiano Baroni

    Full Text Available Neurons react differently to incoming stimuli depending upon their previous history of stimulation. This property can be considered as a single-cell substrate for transient memory, or context-dependent information processing: depending upon the current context that the neuron "sees" through the subset of the network impinging on it in the immediate past, the same synaptic event can evoke a postsynaptic spike or just a subthreshold depolarization. We propose a formal definition of History-Dependent Excitability (HDE as a measure of the propensity to firing in any moment in time, linking the subthreshold history-dependent dynamics with spike generation. This definition allows the quantitative assessment of the intrinsic memory for different single-neuron dynamics and input statistics. We illustrate the concept of HDE by considering two general dynamical mechanisms: the passive behavior of an Integrate and Fire (IF neuron, and the inductive behavior of a Generalized Integrate and Fire (GIF neuron with subthreshold damped oscillations. This framework allows us to characterize the sensitivity of different model neurons to the detailed temporal structure of incoming stimuli. While a neuron with intrinsic oscillations discriminates equally well between input trains with the same or different frequency, a passive neuron discriminates better between inputs with different frequencies. This suggests that passive neurons are better suited to rate-based computation, while neurons with subthreshold oscillations are advantageous in a temporal coding scheme. We also address the influence of intrinsic properties in single-cell processing as a function of input statistics, and show that intrinsic oscillations enhance discrimination sensitivity at high input rates. Finally, we discuss how the recognition of these cell-specific discrimination properties might further our understanding of neuronal network computations and their relationships to the distribution and

  11. Ultrafast excited-state dynamics at interfaces: fluorescent DNA probes at the dodecane/water interface

    Science.gov (United States)

    Licari, Giuseppe; Vauthey, Eric

    2015-08-01

    Although the interfaces between two isotropic media are of primary importance in many areas of science and technology, their properties are only partially understood. Our strategy to obtain an insight into these properties is to investigate the ultrafast excited-state dynamics of environment-sensitive molecular probes at liquid interfaces using time-resolved surface second harmonic generation, and to compare it with the dynamics of the same molecules in bulk solutions. Additionally, this approach gives rich information on how the chemical reactivity may change when going from the bulk phase to the interface. This is illustrated by an investigation performed with a series of fluorescent DNA probes at the dodecane/water interface without and with the presence of DNA in the aqueous phase. Substantial differences in the conformation of these cyanine dyes (aggregated or not) and in the excited-state dynamics are observed when going from bulk solutions to the interface. Moreover, the presence of double-stranded DNA in the aqueous phase induces some chirality at the interface.

  12. Biophysical Neural Spiking, Bursting, and Excitability Dynamics in Reconfigurable Analog VLSI.

    Science.gov (United States)

    Yu, T; Sejnowski, T J; Cauwenberghs, G

    2011-10-01

    We study a range of neural dynamics under variations in biophysical parameters underlying extended Morris-Lecar and Hodgkin-Huxley models in three gating variables. The extended models are implemented in NeuroDyn, a four neuron, twelve synapse continuous-time analog VLSI programmable neural emulation platform with generalized channel kinetics and biophysical membrane dynamics. The dynamics exhibit a wide range of time scales extending beyond 100 ms neglected in typical silicon models of tonic spiking neurons. Circuit simulations and measurements show transition from tonic spiking to tonic bursting dynamics through variation of a single conductance parameter governing calcium recovery. We similarly demonstrate transition from graded to all-or-none neural excitability in the onset of spiking dynamics through the variation of channel kinetic parameters governing the speed of potassium activation. Other combinations of variations in conductance and channel kinetic parameters give rise to phasic spiking and spike frequency adaptation dynamics. The NeuroDyn chip consumes 1.29 mW and occupies 3 mm × 3 mm in 0.5 μm CMOS, supporting emerging developments in neuromorphic silicon-neuron interfaces.

  13. Optimal placement of excitations and sensors for verification of large dynamical systems

    Science.gov (United States)

    Salama, M.; Rose, T.; Garba, J.

    1987-01-01

    The computationally difficult problem of the optimal placement of excitations and sensors to maximize the observed measurements is studied within the framework of combinatorial optimization, and is solved numerically using a variation of the simulated annealing heuristic algorithm. Results of numerical experiments including a square plate and a 960 degrees-of-freedom Control of Flexible Structure (COFS) truss structure, are presented. Though the algorithm produces suboptimal solutions, its generality and simplicity allow the treatment of complex dynamical systems which would otherwise be difficult to handle.

  14. Excited states in electron-transfer reaction products: ultrafast relaxation dynamics of an isolated acceptor radical anion.

    Science.gov (United States)

    Horke, Daniel A; Roberts, Gareth M; Verlet, Jan R R

    2011-08-04

    The spectroscopy and ultrafast relaxation dynamics of excited states of the radical anion of a representative charge-transfer acceptor molecule, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, have been studied in the gas phase using time-resolved photoelectron spectroscopy. The photoelectron spectra reveal that at least two anion excited states are bound. Time-resolved studies show that both excited states are very short-lived and internally convert to the anion ground state, with the lower energy state relaxing within 200 fs and a near-threshold valence-excited state relaxing on a 60 fs time scale. These excited states, and in particular the valence-excited state, present efficient pathways for electron-transfer reactions in the highly exergonic inverted region which commonly displays rates exceeding predictions from electron-transfer theory.

  15. A METHOD FOR CALCULATING THE LYAPUNOV EXPONENT SPECTRUM OF A PERIODICALLY EXCITED ON-AUTONOMOUS DYNAMICAL SYSTEM

    Institute of Scientific and Technical Information of China (English)

    Cheng Changjun; Fan Xiaojun

    2000-01-01

    The relation between the Lyapunov exponent spectrun of a periodically excited non-autono mous dynamical system and the Lyapunov exponent spectrum of the corresponding autonomous system is given and the validity of the relation is verified theoretically and computationally. A direct method for calculating the Lyapunov exponent spectrum of non-autonomous dynamical systems is suggested in this paper, which makes it more convenient to calculate the Lyapunov exponent spectrum of the dynamical system periodically excited. Following the defi nition of the Lyapunov dimension D(LA) of the autonomous system, the definition of the Lyapunov dimension Dl of the non-autonomous dynamical system is also given, and the difference be- tween them is the integer 1, namely, D(A)L - DL = 1. For a quasi-poriodically excited dynamical system, similar conclusions are formed.

  16. Insights into the isomerization of photochromic oxazines from the excitation dynamics of BODIPY-oxazine dyads.

    Science.gov (United States)

    Deniz, Erhan; Battal, Mutlu; Cusido, Janet; Sortino, Salvatore; Raymo, Françisco M

    2012-08-07

    We synthesized five BODIPY-oxazine dyads in one to four synthetic steps from known precursors. They differ in the nature of the unsaturated spacer linking the oxazine photochrome to either the conjugated framework or the boron center of the BODIPY fluorophore. Despite the π-character of the linkers, the two functional components are electronically isolated in the ground state and the BODIPY fluorophore maintains its absorption and, with one exception, emission properties unaltered. Instead, the photochemical response of the photochromic component is completely suppressed within all dyads. Rather than the expected opening of the oxazine ring, the laser excitation of these molecular assemblies results in the effective population of the BODIPY triplet in four of the five dyads. Control experiments with appropriate model compounds indicate that the local excitation of the oxazine component results first in intersystem crossing and then energy transfer to the BODIPY component. In fact, the transfer of energy from the triplet state of the former to the triplet state of the latter competes successfully with the opening of the oxazine ring and prevents the isomerization of the photochromic component. These observations demonstrate, for the very first time, that the photoinduced opening of these photochromic oxazines occurs along the potential energy surface of their triplet state. Such valuable mechanistic insights into their excitation dynamics can guide the design of novel members of this family of photochromic compounds with improved photochemical properties.

  17. Complex dynamics of an archetypal self-excited SD oscillator driven by moving belt friction

    Science.gov (United States)

    Zhi-Xin, Li; Qing-Jie, Cao; Léger, Alain

    2016-01-01

    We propose an archetypal self-excited system driven by moving belt friction, which is constructed with the smooth and discontinuous (SD) oscillator proposed by the Cao et al. and the classical moving belt. The moving belt friction is modeled as the Coulomb friction to formulate the mathematical model of the proposed self-excited SD oscillator. The equilibrium states of the unperturbed system are obtained to show the complex equilibrium bifurcations. Phase portraits are depicted to present the hyperbolic structure transition, the multiple stick regions, and the friction-induced asymmetry phenomena. The numerical simulations are carried out to demonstrate the friction-induced vibration of multiple stick-slip phenomena and the stick-slip chaos in the perturbed self-excited system. The results presented here provide an opportunity for us to get insight into the mechanism of the complex friction-induced nonlinear dynamics in mechanical engineering and geography. Project supported by the National Natural Science Foundation of China (Grant Nos. 11372082 and 11572096) and the National Basic Research Program of China (Grant No. 2015CB057405).

  18. Fast and slow dynamics in a nonlinear elastic bar excited by longitudinal vibrations

    CERN Document Server

    Favrie, Nicolas; Payan, Cédric

    2014-01-01

    Heterogeneous materials, such as rocks and concrete, have a complex dynamics including hysteresis, nonlinear elasticity and viscoelasticity. It is very sensitive to microstructural changes and damage. The goal of this paper is to propose a physical model describing the longitudinal vibrations of this class of material, and to develop a numerical strategy for solving the evolution equations. The theory relies on the coupling between two processes with radically-different time scales: a fast process at the frequency of the excitation, governed by nonlinear elasticity and viscoelasticity; a slow process, governed by the evolution of defects. The evolution equations are written as a nonlinear hyperbolic system with relaxation. A time-domain numerical scheme is developed, based on a splitting strategy. The numerical simulations show qualitative agreement with the features observed experimentally by Dynamic Acousto-Elastic Testing.

  19. Total dynamic response of a PSS vehicle negotiating asymmetric road excitations

    Science.gov (United States)

    Zhu, Jian Jun; Khajepour, Amir; Esmailzadeh, Ebrahim

    2012-12-01

    A planar suspension system (PSS) is a novel automobile suspension system in which an individual spring-damper strut is implemented in both the vertical and longitudinal directions, respectively. The wheels in a vehicle with such a suspension system can move back and forth relative to the chassis. When a PSS vehicle experiences asymmetric road excitations, the relative longitudinal motion of wheels with respect to the chassis in two sides of the same axle are not identical, and thus the two wheels at one axle will not be aligned in the same axis. The total dynamic responses, including those of the bounce, pitch and the roll of the PSS vehicle, to the asymmetric road excitation may exhibit different characteristics from those of a conventional vehicle. This paper presents an investigation into the comprehensive dynamic behaviour of a vehicle with the PSS, in such a road condition, on both the straight and curved roads. The study was carried out using an 18 DOF full-car model incorporating a radial-spring tyre-ground contact model and a 2D tyre-ground dynamic friction model. Results demonstrate that the total dynamic behaviour of a PSS vehicle is generally comparable with that of the conventional vehicle, while PSS exhibits significant improvement in absorbing the impact forces along the longitudinal direction when compared to the conventional suspension system. The PSS vehicle is found to be more stable than the conventional vehicle in terms of the directional performance against the disturbance of the road potholes on a straight line manoeuvre, while exhibiting a very similar handling performance on a curved line.

  20. Multi-degree-of-freedom coupling dynamic characteristic of TBM disc cutter under shock excitation

    Institute of Scientific and Technical Information of China (English)

    霍军周; 孙晓龙; 李广庆; 李涛; 孙伟

    2015-01-01

    When the tunneling boring machine (TBM) cutterhead tunnels, the excessive vibration and damage are a severe engineering problem, thereby the anti-vibration design is a key technology in the disc cutter system. The structure of disc cutter contains many joint interfaces among cutter ring, cutter body, bearings and cutter shaft. On account of the coupling for dynamic contact and the transfer path among joint interface, mechanical behavior of disc cutter becomes extremely complex under the impact of heavy-duty, which puts forward higher requirements for disc cutter design. A multi-degree-of-freedom coupling dynamic model, which contains a cutter ring, a cutter body, two bearings and cutter shaft, is established, considering the external stochastic excitations, bearing nonlinear contact force, multidirectional mutual coupling vibration, etc. Based on the parameters of an actual project and the strong impact external excitations, the modal properties and dynamic responses are analyzed, as well as the cutter shaft and bearings’ loads and load transmission law are obtained. Numerical results indicate the maximum radial and axial cutter ring amplitudes of dynamic responses are 0.568 mm and 0.112 mm;the maximum radial and axial vibration velocities are 41.1 mm/s and 38.9 mm/s;the maximum radial and axial vibration accelerations are 94.7 m/s2 and 58.6 m/s2;the maximum swing angle and angular velocity of cutter ring are 0.007° and 0.0074 rad/s, respectively. Finally, the maximum load of bearing roller is 40.3 kN. The proposed research lays a foundation for structure optimization design of disc cutter and cutter base, as well as model selection, modification and fatigue life of the cutter bearing.

  1. Protein dynamics tunes excited state positions in light-harvesting complex II.

    Science.gov (United States)

    Vrandecic, Kamarniso; Rätsep, Margus; Wilk, Laura; Rusevich, Leonid; Golub, Maksym; Reppert, Mike; Irrgang, Klaus-Dieter; Kühlbrandt, Werner; Pieper, Jörg

    2015-03-12

    Light harvesting and excitation energy transfer in photosynthesis are relatively well understood at cryogenic temperatures up to ∼100 K, where crystal structures of several photosynthetic complexes including the major antenna complex of green plants (LHC II) are available at nearly atomic resolution. The situation is much more complex at higher or even physiological temperatures, because the spectroscopic properties of antenna complexes typically undergo drastic changes above ∼100 K. We have addressed this problem using a combination of quasielastic neutron scattering (QENS) and optical spectroscopy on native LHC II and mutant samples lacking the Chl 2/Chl a 612 pigment molecule. Absorption difference spectra of the Chl 2/Chl a 612 mutant of LHC II reveal pronounced changes of spectral position and their widths above temperatures as low as ∼80 K. The complementary QENS data indicate an onset of conformational protein motions at about the same temperature. This finding suggests that excited state positions in LHC II are affected by protein dynamics on the picosecond time scale. In more detail, this means that at cryogenic temperatures the antenna complex is trapped in certain protein conformations. At higher temperature, however, a variety of conformational substates with different spectral position may be thermally accessible. At the same time, an analysis of the widths of the absorption difference spectra of Chl 2/Chl a 612 reveals three different reorganization energies or Huang-Rhys factors in different temperature ranges, respectively. These findings imply that (dynamic) pigment-protein interactions fine-tune electronic energy levels and electron-phonon coupling of LHC II for efficient excitation energy transfer at physiological temperatures.

  2. Relaxation dynamics in the excited states of a ketocyanine dye probed by femtosecond transient absorption spectroscopy

    Indian Academy of Sciences (India)

    Jahur A Mondal; Sandeep Verma; Hirendra N Ghosh; Dipak K Palit

    2008-01-01

    Relaxation dynamics of the excited singlet states of 2,5-bis-(N-methyl-N-1,3-propdienylaniline)-cyclopentanone (MPAC), a ketocyanine dye, have been investigated using steady-state absorption and emission as well as femtosecond time-resolved absorption spectroscopic techniques. Following photoexcitation using 400 nm light, the molecule is excited to the S2 state, which is fluorescent in rigid matrices at 77 K. S2 state is nearly non-fluorescent in solution and has a very short lifetime (0.5 ± 0.2 ps). In polar aprotic solvents, the S1 state follows a complex multi-exponential relaxation dynamics consisting of torsional motion of the donor groups, solvent re-organization as well as photoisomerization processes. However, in alcoholic solvents, solvent re-organization via intermolecular hydrogen-bonding interaction is the only relaxation process observed in the S1 state. In trifluoroethanol, a strong hydrogen bonding solvent, conversion of the non-hydrogen-bonded form, which is formed following photoexcitation, to the hydrogen-bonded complex has been clearly evident in the relaxation process of the S1 state.

  3. Excited-state dynamics of size-dependent colloidal TiO2-Au nanocomposites

    Science.gov (United States)

    Karam, Tony E.; Khoury, Rami A.; Haber, Louis H.

    2016-03-01

    The ultrafast excited-state dynamics of size-dependent TiO2-Au nanocomposites synthesized by reducing gold nanoclusters to the surface of colloidal TiO2 nanoparticles are studied using pump-probe transient absorption spectroscopy with 400 nm excitation pulses. The results show that the relaxation processes of the plasmon depletion band, which are described by electron-phonon and phonon-phonon scattering lifetimes, are independent of the gold nanocluster shell size surrounding the TiO2 nanoparticle core. The dynamics corresponding to interfacial electron transfer between the gold nanoclusters and the TiO2 bandgap are observed to spectrally overlap with the gold interband transition signal, and the electron transfer lifetimes are shown to significantly decrease as the nanocluster shell size increases. Additionally, size-dependent periodic oscillations are observed and are attributed to acoustic phonons of a porous shell composed of aggregated gold nanoclusters around the TiO2 core, with frequencies that decrease and damping times that remain constant as the nanocluster shell size increases. These results are important for the development of improved catalytic nanomaterial applications.

  4. Simulating Excited State Dynamics in Systems with Multiple Avoided Crossings Using Mapping Variable Ring Polymer Molecular Dynamics.

    Science.gov (United States)

    Duke, Jessica R; Ananth, Nandini

    2015-11-05

    Mapping variable ring polymer molecular dynamics (MV-RPMD) is an approximate quantum dynamics method based on imaginary-time path integrals for simulating electronically nonadiabatic photochemical processes. By employing a mapping protocol to transform from a discrete electronic state basis to continuous Cartesian phase-space variables, the method captures electronic state transitions coupled to nuclear motion using only classical MD trajectories. In this work, we extend the applicability of MV-RPMD to simulations of photoinduced excited electronic state dynamics in nonadiabatic systems with multiple avoided crossings. We achieve this by deriving a new electronic state population estimator in the phase space of electronic variables that is exact at equilibrium and numerically accurate in real time. Further, we introduce an efficient constraint protocol to initialize an MV-RPMD simulation to a particular electronic state. We numerically demonstrate the accuracy of this estimator and constraint technique in describing electronic state dynamics from an initial nonequilibrium state in six model systems, three of which describe photodissociation.

  5. Global Dynamic Characteristic of Nonlinear Torsional Vibration System under Harmonically Excitation

    Institute of Scientific and Technical Information of China (English)

    SHI Peiming; LIU Bin; HOU Dongxiao

    2009-01-01

    Torsional vibration generally causes serious instability and damage problems in many rotating machinery parts. The global dynamic characteristic of nonlinear torsional vibration system with nonlinear rigidity and nonlinear friction force is investigated. On the basis of the generalized dissipation Lagrange's equation, the dynamics equation of nonlinear torsional vibration system is deduced. The bifurcation and chaotic motion in the system subjected to an external harmonic excitation is studied by theoretical analysis and numerical simulation. The stability of unperturbed system is analyzed by using the stability theory of equilibrium positions of Hamiltonian systems. The criterion of existence of chaos phenomena under a periodic perturbation is given by means of Melnikov's method. It is shown that the existence of homoclinic and heteroclinic orbits in the unperturbed system implies chaos arising from breaking of homoclinic or heteroclinic orbits under perturbation. The validity of the result is checked numerically. Periodic doubling bifurcation route to chaos, quasi-periodic route to chaos, intermittency route to chaos are found to occur due to the amplitude varying in some range. The evolution of system dynamic responses is demonstrated in detail by Poincare maps and bifurcation diagrams when the system undergoes a sequence of periodic doubling or quasi-periodic bifurcations to chaos. The conclusion can provide reference for deeply researching the dynamic behavior of mechanical drive systems.

  6. Excited electronic state decomposition mechanisms and dynamics of nitramine energetic materials and model systems

    Science.gov (United States)

    Greenfield, Margo

    Energetic materials play an important role in aeronautics, the weapon industry, and the propellant industry due to their broad applications as explosives and fuels. RDX (1,3,5-trinitrohexahydro-s-triazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) are compounds which contain high energy density. Although RDX and HMX have been studied extensively over the past several decades a complete understanding of their decomposition mechanisms and dynamics is unknown. Time of flight mass spectroscopy (TOFMS) UV photodissociation (ns) experiments of gas phase RDX, HMX, and CL-20 generate the NO molecule as the initial decomposition product. Four different vibronic transitions of the initial decomposition product, the NO molecule, are observed: A2Sigma(upsilon'=0)←X 2pi(upsilon"=0,1,2,3). Simulations of the rovibronic intensities for the A←X transitions demonstrate that NO dissociated from RDX, HMX, and CL-20 is rotationally cold (˜20 K) and vibrationally hot (˜1800 K). Conversely, experiments on the five model systems (nitromethane, dimethylnitramine (DMNA), nitropyrrolidine, nitropiperidine and dinitropiperazine) produce rotationally hot and vibrationally cold spectra. Laser induced fluorescence (LIF) experiments are performed to rule out the possible decomposition product OH, generated along with NO, perhaps from the suggested HONO elimination mechanism. The OH radical is not observed in the fluorescence experiments, indicating the HONO decomposition intermediate is not an important pathway for the excited electronic state decomposition of cyclic nitramines. The NO molecule is also employed to measure the dynamics of the excited state decomposition. A 226 nm, 180 fs light pulse is utilized to photodissociate the gas phase systems. Stable ion states of DMNA and nitropyrrolidine are observed while the energetic materials and remaining model systems present the NO molecule as the only

  7. High-Speed Rotor Analytical Dynamics on Flexible Foundation Subjected to Internal and External Excitation

    Science.gov (United States)

    Jivkov, Venelin S.; Zahariev, Evtim V.

    2016-12-01

    The paper presents a geometrical approach to dynamics simulation of a rigid and flexible system, compiled of high speed rotating machine with eccentricity and considerable inertia and mass. The machine is mounted on a vertical flexible pillar with considerable height. The stiffness and damping of the column, as well as, of the rotor bearings and the shaft are taken into account. Non-stationary vibrations and transitional processes are analyzed. The major frequency and modal mode of the flexible column are used for analytical reduction of its mass, stiffness and damping properties. The rotor and the foundation are modelled as rigid bodies, while the flexibility of the bearings is estimated by experiments and the requirements of the manufacturer. The transition effects as a result of limited power are analyzed by asymptotic methods of averaging. Analytical expressions for the amplitudes and unstable vibrations throughout resonance are derived by quasi-static approach increasing and decreasing of the exciting frequency. Analytical functions give the possibility to analyze the influence of the design parameter of many structure applications as wind power generators, gas turbines, turbo-generators, and etc. A numerical procedure is applied to verify the effectiveness and precision of the simulation process. Nonlinear and transitional effects are analyzed and compared to the analytical results. External excitations, as wave propagation and earthquakes, are discussed. Finite elements in relative and absolute coordinates are applied to model the flexible column and the high speed rotating machine. Generalized Newton - Euler dynamics equations are used to derive the precise dynamics equations. Examples of simulation of the system vibrations and nonstationary behaviour are presented.

  8. Excitation dynamics in a lattice Bose gas within the time-dependent Gutzwiller mean-field approach

    Energy Technology Data Exchange (ETDEWEB)

    Krutitsky, Konstantin V. [Fakultaet fuer Physik der Universitaet Duisburg-Essen, Campus Duisburg, Lotharstrasse 1, D-47048 Duisburg (Germany); Navez, Patrick [Fakultaet fuer Physik der Universitaet Duisburg-Essen, Campus Duisburg, Lotharstrasse 1, D-47048 Duisburg (Germany); Institut fuer Theoretische Physik, TU Dresden, D-01062 Dresden (Germany)

    2011-09-15

    The dynamics of the collective excitations of a lattice Bose gas at zero temperature is systematically investigated using the time-dependent Gutzwiller mean-field approach. The excitation modes are determined within the framework of the linear-response theory as solutions of the generalized Bogoliubov-de Gennes equations valid in the superfluid and Mott-insulator phases at arbitrary values of parameters. The expression for the sound velocity derived in this approach coincides with the hydrodynamic relation. We calculate the transition amplitudes for the excitations in the Bragg scattering process and show that the higher excitation modes make significant contributions. We simulate the dynamics of the density perturbations and show that their propagation velocity in the limit of week perturbation is satisfactorily described by the predictions of the linear-response analysis.

  9. The dynamic modeling and design improvement of a piezoelectric exciter of a touch screen device for efficient tactile feedback

    Science.gov (United States)

    Park, Young-Min; Kim, Kwang-Joon

    2011-05-01

    Piezoelectric exciters have been receiving greater attention recently as a vibration source for tactile feedback in devices with touch screens, such as a mobile phones, in place of DC motors due to lower energy consumption and smaller volume. Their insufficient excitation level, however, still remains a problem. In this paper, dynamic modeling and design improvement of a piezoelectric exciter are presented. The excitation performance is defined as the acceleration response at the center of a touch screen per electric power and to be maximized around 250 Hz where the index finger is most sensitive. The piezoelectric exciter consists of a z-shaped metal beam, a piezoelectric layer on the long horizontal segment and an adhesive layer between the short horizontal segment and the touch screen. Assuming that the piezoelectric exciter is attached onto a rigid ground due to its low mechanical impedance compared with that of the touch screen, the piezoelectric exciter is dynamically modeled by applying Hamilton's principle, where the adhesive layer is treated as a distributed stiffness. The touch screen is modeled approximately as a simply supported beam such that it may have the same fundamental natural frequency and bending stiffness as the screen based on measurements. The performance improvement is focused on the change of five geometric parameters of the piezoelectric exciter: length of the long horizontal segment, thickness of the piezoelectric layer, thickness of the elastic metal layer, width of the beams and tip mass. The procedure to improve the performance of the piezoelectric exciter via dynamic modeling is presented together with experimental results on a prototype. Effectiveness of the design modification and limitations in practice are further discussed as well.

  10. Regulation of granule cell excitability by a low-threshold calcium spike in turtle olfactory bulb

    DEFF Research Database (Denmark)

    Pinato, Giulietta; Midtgaard, Jens

    2003-01-01

    Granule cells excitability in the turtle olfactory bulb was analyzed using whole cell recordings in current- and voltage-clamp mode. Low-threshold spikes (LTSs) were evoked at potentials that are subthreshold for Na spikes in normal medium. The LTSs were evoked from rest, but hyperpolarization...

  11. IMPROVEMENT OF EXPRESSION FOR EXCITATION BY AN ELECTRIC DIPOLE IN GTEM CELL

    Institute of Scientific and Technical Information of China (English)

    Ren Liehui; Chen Zhiyu

    2002-01-01

    On the basis of Wilson's work in which the vertical electric dipole is centrally located in GHz Transverse ElectroMagnetic (GTEM) cell, we deduce the expression for the field distribution excited by an electric dipole in the case that the dipole is not centrally located. It will be useful for EMC measurements using GTEM cell.

  12. IMPROVEMENT OF EXPRESSION FOR EXCITATION BY AN ELECTRIC DIPOLE IN GTEM CELL

    Institute of Scientific and Technical Information of China (English)

    RenLiehui; ChenZhiyu

    2002-01-01

    On the basis of Wilson's work in which the vertical electric dipole is centrally located in GHz Transverse ElectroMagntic(GTEM) cell, we deduce the expression for the field distribution excited by an electric dipole in the case that the dipole is not centrally located.It will be useful for EMCmeasurements using GTEM cell.

  13. Progress in dynamic study on the triplet excited states and radical ions of DNA and its components

    Institute of Scientific and Technical Information of China (English)

    宋钦华; 林念芸; 姚思德; 张加山

    2000-01-01

    Progress in dynamic study on the triplet excited states and radical ions of DNA and its components is reviewed. It has been found that acetone is the only effective sensitizer for the study of the triplet excited states of DNA components. The transient absorption spectrum of guanyl radical cation resulting from the interaction of triplet acetone and DNA was observed directly, and the original evidence for selective damage of DNA by excited photosensitizer was obtained for the first time, which offered a new pathway for obtaining the main transient species of selective damage of DNA by photonucleases and illustrating initial oxidation mechanism of DNA via electron transfer.

  14. Isovector and isoscalar dipole excitations in 9Be and 10Be studied with antisymmetrized molecular dynamics

    Science.gov (United States)

    Kanada-En'yo, Yoshiko

    2016-02-01

    Isovector and isoscalar dipole excitations in 9Be and 10Be are investigated in the framework of antisymmetrized molecular dynamics, in which angular-momentum and parity projections are performed. In the present method, 1p-1h excitation modes built on the ground state and a large amplitude α -cluster mode are taken into account. The isovector giant dipole resonance (GDR) in E >20 MeV shows the two-peak structure, which is understood from the dipole excitation in the 2 α core part with the prolate deformation. Because of valence neutron modes against the 2 α core, low-energy E 1 resonances appear in E Thomas-Reiche-Kuhn sum rule and 10 % of the calculated energy-weighted sum. The dipole resonance at E ˜15 MeV in 10Be can be interpreted as the parity partner of the ground state having a 6He+α structure and has remarkable E 1 strength because of the coherent contribution of two valence neutrons. The isoscalar dipole strength for some low-energy resonances is significantly enhanced by the coupling with the α -cluster mode. For the E 1 strength of 9Be, the calculation overestimates the energy-weighted sum (EWS) in the low-energy (E <20 MeV) and GDR (20

  15. Dynamics and quantumness of excitation energy transfer through a complex quantum network

    CERN Document Server

    Qin, M; Zhao, X L; Yi, X X

    2015-01-01

    Understanding the mechanisms of efficient and robust energy transfer in organic systems provides us with new insights for the optimal design of artificial systems. In this paper, we explore the dynamics of excitation energy transfer (EET) through a complex quantum network by a toy model consisting of three sites coupled to environments. We study how the coherent evolution and the noise-induced decoherence work together to reach efficient EET and illustrate the role of the phase factor attached to the coupling constant in the EET. By comparing the differences between the Markovian and non-Markovian dynamics, we discuss the effect of environment and the spatial structure of system on the dynamics and the efficiency of EET. A intuitive picture is given to show how the exciton is transferred through the system. Employing the simple model, we show the robustness of EET efficiency under the influence of the environment and elucidate the important role of quantum coherence in EET. We go further to study the quantum ...

  16. Dynamic Balance of Excitation and Inhibition in Human and Monkey Neocortex

    Science.gov (United States)

    Dehghani, Nima; Peyrache, Adrien; Telenczuk, Bartosz; Le van Quyen, Michel; Halgren, Eric; Cash, Sydney S.; Hatsopoulos, Nicholas G.; Destexhe, Alain

    2016-03-01

    Balance of excitation and inhibition is a fundamental feature of in vivo network activity and is important for its computations. However, its presence in the neocortex of higher mammals is not well established. We investigated the dynamics of excitation and inhibition using dense multielectrode recordings in humans and monkeys. We found that in all states of the wake-sleep cycle, excitatory and inhibitory ensembles are well balanced, and co-fluctuate with slight instantaneous deviations from perfect balance, mostly in slow-wave sleep. Remarkably, these correlated fluctuations are seen for many different temporal scales. The similarity of these computational features with a network model of self-generated balanced states suggests that such balanced activity is essentially generated by recurrent activity in the local network and is not due to external inputs. Finally, we find that this balance breaks down during seizures, where the temporal correlation of excitatory and inhibitory populations is disrupted. These results show that balanced activity is a feature of normal brain activity, and break down of the balance could be an important factor to define pathological states.

  17. Pygmy and Giant Dipole Resonances by Coulomb Excitation using a Quantum Molecular Dynamics model

    CERN Document Server

    Tao, C; Zhang, G Q; Cao, X G; Wang, D Q Fang H W

    2012-01-01

    Pygmy and Giant Dipole Resonance (PDR and GDR) in Ni isotopes have been investigated by Coulomb excitation in the framework of the Isospin-dependent Quantum Molecular Dynamics model (IQMD). The spectra of $\\gamma$ rays are calculated and the peak energy, the strength and Full Width at Half Maximum (FWHM) of GDR and PDR have been extracted. Their sensitivities to nuclear equation of state, especially to its symmetry energy term are also explored. By a comparison with the other mean-field calculations, we obtain the reasonable values for symmetry energy and its slope parameter at saturation, which gives an important constrain for IQMD model. In addition, we also studied the neutron excess dependence of GDR and PDR parameters for Ni isotopes and found that the energy-weighted sum rule (EWSR) $PDR_{m_1}/GDR_{m_1}%$ increases linearly with the neutron excess.

  18. Dynamic responses of base isolated NPPs under seismic excitations and aircraft crashes

    Energy Technology Data Exchange (ETDEWEB)

    Noh, Sang Hoon; Kim, Hyun Uk; Joo, Kwang Ho [KHNP, Daejeon (Korea, Republic of)

    2012-10-15

    Seismic isolation (SI) is a type of seismic design that is based on the concept of reducing the seismic demand rather than increasing the resistance capacity of the structure and related systems. Applying this technology leads to improved performance of structures that will remain essentially elastic during a design basis earthquake. In the application of the system to a nuclear power plant (NPP) structure to gain seismic resistance advantages, other safety issues should also be considered. One of those issues is the safety of an NPP against an aircraft crash (ACC). In this study, responses of a seismically isolated structure, such as acceleration and displacement, were obtained from a time domain non linear analysis to check the performance of SI system under seismic excitation. In addition, the dynamic responses of NPP structures with or without SI against an ACC were compared and other considerations are discussed.

  19. Pulsed excitation dynamics of an optomechanical crystal resonator near its quantum ground-state of motion

    CERN Document Server

    Meenehan, Sean M; MacCabe, Gregory S; Marsili, Francesco; Shaw, Matthew D; Painter, Oskar

    2015-01-01

    Using pulsed optical excitation and read-out along with single phonon counting techniques, we measure the transient back-action, heating, and damping dynamics of a nanoscale silicon optomechanical crystal cavity mounted in a dilution refrigerator at a base temperature of 11mK. In addition to observing a slow (~740ns) turn-on time for the optical-absorption-induced hot phonon bath, we measure for the 5.6GHz `breathing' acoustic mode of the cavity an initial phonon occupancy as low as 0.021 +- 0.007 (mode temperature = 70mK) and an intrinsic mechanical decay rate of 328 +- 14 Hz (mechanical Q-factor = 1.7x10^7). These measurements demonstrate the feasibility of using short pulsed measurements for a variety of quantum optomechanical applications despite the presence of steady-state optical heating.

  20. Origin of long-lived coherence and excitation dynamics in pigment-protein complexes

    CERN Document Server

    Zhang, Zhedong

    2015-01-01

    We uncover the mechanism of long-lived coherence that the discrete vibrational modes effectively weaken the exciton-environment interaction. This subsequently demonstrates the role of vibrational coherence which greatly contributes to long-lived feature of the excitonic coherence that has been observed in femtosecond experiments. To test the validity of our effective theory, we study the pigment-protein complex in details by exploring the energy transfer and coherence dynamics. The ground-state coherence generated by incoherent radiations is demonstrated to be significant to promote the excitation energy transfer. This on the other hand, seems to be natural from the point of view of nonequilibriumness, which funnels the downhill immigration of excitons. Moreover we also confirm that the considerable improvement of energy transfer is always accompanied by the long-lived oscillation of coherence.

  1. Origin of long-lived quantum coherence and excitation dynamics in pigment-protein complexes

    Science.gov (United States)

    Zhang, Zhedong; Wang, Jin

    2016-11-01

    We explore the mechanism for the long-lived quantum coherence by considering the discrete phonon modes: these vibrational modes effectively weaken the exciton-environment interaction, due to the new composite (polaron) formed by excitons and vibrons. This subsequently demonstrates the role of vibrational coherence which greatly contributes to long-lived feature of the excitonic coherence that has been observed in femtosecond experiments. The estimation of the timescale of coherence elongated by vibrational modes is given in an analytical manner. To test the validity of our theory, we study the pigment-protein complex in detail by exploring the energy transfer and coherence dynamics. The ground-state vibrational coherence generated by incoherent radiations is shown to be long-survived and is demonstrated to be significant in promoting the excitation energy transfer. This is attributed to the nonequilibriumness of the system caused by the detailed-balance-breaking, which funnels the downhill migration of excitons.

  2. PATH INTEGRAL SOLUTION OF NONLINEAR DYNAMIC BEHAVIOR OF STRUCTURE UNDER WIND EXCITATION

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    A numerical scheme for the nonlinear behavior of structure under wind excitation is investigated. With the white noise filter of turbulent-wind fluctuations, the nonlinear motion equation of structures subjected to wind load was modeled as the Ito' s stochastic differential equation. The state vector associated with such a model is a diffusion process. A continuous linearization strategy in the time-domain was adopted.Based on the solution series of its stochastic linearization equations, the formal probabilistic density of the structure response was developed by the path integral technique. It is shown by the numerical example of a guyed mast that compared with the frequency-domain method and the time-domain nonlinear analysis, the proposed approach is highlighted by high accuracy and effectiveness. The influence of the structure non-linearity on the dynamic reliability assessment is also analyzed in the example.

  3. Dynamics of multiple bubbles, excited by femtosecond filament in water: Role of aberrations

    CERN Document Server

    Potemkin, F V

    2014-01-01

    Using shadow photography, we observed microsecond time scale evolution of multiple cavitation bubbles, excited by tighty focused femtosecond laser pulse in water under supercritical power regime (~100 Pcr). In these extreme conditions high energy delivery into the microvolume of liquid sample leads to creation of single filament which becomes a source of cavitation region formation. When aberrations were added to the optical scheme the hot spots along the filament axis are formed. At high energies (more than 40uJ) filaments in these hot spots are fired and, as a result, complex pattern of cavitation bubbles is created. The bubbles can be isolated from each other or build exotic drop-shaped cavitation region, which evolution at the end of its life, before the final collapse, contains the jet emission. The dynamics of the cavitation pattern was investigated from pulse energy and focusing. We found that greater numerical aperture of the focusing optics leads to greater cavitation area length. The strong interact...

  4. Nonlinear Dynamic Characteristics and Optimal Control of SMA Composite Wings Subjected to Stochastic Excitation

    Directory of Open Access Journals (Sweden)

    Zhi-Wen Zhu

    2015-01-01

    Full Text Available A kind of high-aspect-ratio shape memory alloy (SMA composite wing is proposed to reduce the wing’s fluttering. The nonlinear dynamic characteristics and optimal control of the SMA composite wings subjected to in-plane stochastic excitation are investigated where the great bending under the flight loads is considered. The stochastic stability of the system is analyzed, and the system’s response is obtained. The conditions of stochastic Hopf bifurcation are determined, and the probability density of the first-passage time is obtained. Finally, the optimal control strategy is proposed. Numerical simulation shows that the stability of the system varies with bifurcation parameters, and stochastic Hopf bifurcation appears in the process; the reliability of the system is improved through optimal control, and the first-passage time is delayed. Finally, the effects of the control strategy are proved by experiments. The results of this paper are helpful for engineering applications of SMA.

  5. Enhanced energy transfer in respiratory-deficient endothelial cells probed by microscopic fluorescence excitation spectroscopy

    Science.gov (United States)

    Schneckenburger, Herbert; Gschwend, Michael H.; Bauer, Manfred; Strauss, Wolfgang S. L.; Steiner, Rudolf W.

    1996-12-01

    Mitochondrial malfunction may be concomitant with changes of the redox states of the coenzymes nicotinamide adenine dinucleotide (NAD+/NADH), as well as flavin.mononucleotide or dinucleotide. The intrinsic fluorescence of these coenzymes was therefore proposed to be a measure of malfunction. Since mitochondrial fluorescence is strongly superposed by autofluorescence from various cytoplasmatic fluorophores, cultivated endothelial cells were incubated with the mitochondrial marker rhodamine 123 (R123), and after excitation of flavin molecules, energy transfer to R123 was investigated. Due to spectral overlap of flavin and R123 fluorescence, energy transfer flavin yields R123 could not be detected from their emission spectra. Therefore, the method of microscopic fluorescence excitation spectroscopy was established. When detecting R123 fluorescence, excitation maxima at 370 - 390 nm and 420-460 nm were assigned to flavins, whereas a pronounced excitation band at 465 - 490 nm was attributed to R123. Therefore, excitation at 475 nm reflected the intracellular concentration of R123, whereas excitation at 385 nm reflected flavin excitation with a subsequent energy transfer to R123 molecules. An enhanced energy transfer after inhibition of specific enzyme complexes of the respiratory chain is discussed in the present article.

  6. Nonlinear Dynamic Analysis of Coupled Gear-Rotor-Bearing System with the Effect of Internal and External Excitations

    Institute of Scientific and Technical Information of China (English)

    ZHOU Shihua; SONG Guiqiu; REN Zhaohui; WEN Bangchun

    2016-01-01

    Extensive studies on nonlinear dynamics of gear systems with internal excitation or external excitation respectively have been carried out. However, the nonlinear characteristics of gear systems under combined internal and external excitations are scarcely investigated. An eight-degree-of-freedom(8-DOF) nonlinear spur gear-rotor-bearing model, which contains backlash, transmission error, eccentricity, gravity and input/output torque, is established, and the coupled lateral-torsional vibration characteristics are studied. Based on the equations of motion, the coupled spur gear-rotor-bearing system(SGRBS) is investigated using the Runge-Kutta numerical method, and the effects of rotational speed, error fluctuation and load fluctuation on the dynamic responses are explored. The results show that a diverse range of nonlinear dynamic characteristics such as periodic motion, quasi-periodic motion, chaotic behaviors and impacts exhibited in the system are strongly attributed to the interaction between internal and external excitations. Significantly, the changing rotational speed could effectively control the vibration of the system. Vibration level increases with the increasing error fluctuation. Whereas the load fluctuation has an influence on the nonlinear dynamic characteristics and the increasing excitation force amplitude makes the vibration amplitude increase, the chaotic motion may be restricted. The proposed model and numerical results can be used for diagnosis of faults and vibration control of practical SGRBS.

  7. Nonlinear dynamic analysis of coupled gear-rotor-bearing system with the effect of internal and external excitations

    Science.gov (United States)

    Zhou, Shihua; Song, Guiqiu; Ren, Zhaohui; Wen, Bangchun

    2016-03-01

    Extensive studies on nonlinear dynamics of gear systems with internal excitation or external excitation respectively have been carried out. However, the nonlinear characteristics of gear systems under combined internal and external excitations are scarcely investigated. An eight-degree-of-freedom(8-DOF) nonlinear spur gear-rotor-bearing model, which contains backlash, transmission error, eccentricity, gravity and input/output torque, is established, and the coupled lateral-torsional vibration characteristics are studied. Based on the equations of motion, the coupled spur gear-rotor-bearing system(SGRBS) is investigated using the Runge-Kutta numerical method, and the effects of rotational speed, error fluctuation and load fluctuation on the dynamic responses are explored. The results show that a diverse range of nonlinear dynamic characteristics such as periodic motion, quasi-periodic motion, chaotic behaviors and impacts exhibited in the system are strongly attributed to the interaction between internal and external excitations. Significantly, the changing rotational speed could effectively control the vibration of the system. Vibration level increases with the increasing error fluctuation. Whereas the load fluctuation has an influence on the nonlinear dynamic characteristics and the increasing excitation force amplitude makes the vibration amplitude increase, the chaotic motion may be restricted. The proposed model and numerical results can be used for diagnosis of faults and vibration control of practical SGRBS.

  8. Excited-state intramolecular proton transfer to carbon atoms: nonadiabatic surface-hopping dynamics simulations.

    Science.gov (United States)

    Xia, Shu-Hua; Xie, Bin-Bin; Fang, Qiu; Cui, Ganglong; Thiel, Walter

    2015-04-21

    Excited-state intramolecular proton transfer (ESIPT) between two highly electronegative atoms, for example, oxygen and nitrogen, has been intensely studied experimentally and computationally, whereas there has been much less theoretical work on ESIPT to other atoms such as carbon. We have employed CASSCF, MS-CASPT2, RI-ADC(2), OM2/MRCI, DFT, and TDDFT methods to study the mechanistic photochemistry of 2-phenylphenol, for which such an ESIPT has been observed experimentally. According to static electronic structure calculations, irradiation of 2-phenylphenol populates the bright S1 state, which has a rather flat potential in the Franck-Condon region (with a shallow enol minimum at the CASSCF level) and may undergo an essentially barrierless ESIPT to the more stable S1 keto species. There are two S1/S0 conical intersections that mediate relaxation to the ground state, one in the enol region and one in the keto region, with the latter one substantially lower in energy. After S1 → S0 internal conversion, the transient keto species can return back to the S0 enol structure via reverse ground-state hydrogen transfer in a facile tautomerization. This mechanistic scenario is verified by OM2/MRCI-based fewest-switches surface-hopping simulations that provide detailed dynamic information. In these trajectories, ESIPT is complete within 118 fs; the corresponding S1 excited-state lifetime is computed to be 373 fs in vacuum. Most of the trajectories decay to the ground state via the S1/S0 conical intersection in the keto region (67%), and the remaining ones via the enol region (33%). The combination of static electronic structure computations and nonadiabatic dynamics simulations is expected to be generally useful for understanding the mechanistic photophysics and photochemistry of molecules with intramolecular hydrogen bonds.

  9. Shape dynamics of growing cell walls

    CERN Document Server

    Banerjee, Shiladitya; Dinner, Aaron R

    2015-01-01

    We introduce a general theoretical framework to study the shape dynamics of actively growing and remodeling surfaces. Using this framework we develop a physical model for growing bacterial cell walls and study the interplay of cell shape with the dynamics of growth and constriction. The model allows us to derive constraints on cell wall mechanical energy based on the observed dynamics of cell shape. We predict that exponential growth in cell size requires a constant amount of cell wall energy to be dissipated per unit volume. We use the model to understand and contrast growth in bacteria with different shapes such as spherical, ellipsoidal, cylindrical and toroidal morphologies. Coupling growth to cell wall constriction, we predict a discontinuous shape transformation, from partial constriction to cell division, as a function of the chemical potential driving cell-wall synthesis. Our model for cell wall energy and shape dynamics relates growth kinetics with cell geometry, and provides a unified framework to d...

  10. Optogenetics-enabled assessment of viral gene and cell therapy for restoration of cardiac excitability.

    Science.gov (United States)

    Ambrosi, Christina M; Boyle, Patrick M; Chen, Kay; Trayanova, Natalia A; Entcheva, Emilia

    2015-12-01

    Multiple cardiac pathologies are accompanied by loss of tissue excitability, which leads to a range of heart rhythm disorders (arrhythmias). In addition to electronic device therapy (i.e. implantable pacemakers and cardioverter/defibrillators), biological approaches have recently been explored to restore pacemaking ability and to correct conduction slowing in the heart by delivering excitatory ion channels or ion channel agonists. Using optogenetics as a tool to selectively interrogate only cells transduced to produce an exogenous excitatory ion current, we experimentally and computationally quantify the efficiency of such biological approaches in rescuing cardiac excitability as a function of the mode of application (viral gene delivery or cell delivery) and the geometry of the transduced region (focal or spatially-distributed). We demonstrate that for each configuration (delivery mode and spatial pattern), the optical energy needed to excite can be used to predict therapeutic efficiency of excitability restoration. Taken directly, these results can help guide optogenetic interventions for light-based control of cardiac excitation. More generally, our findings can help optimize gene therapy for restoration of cardiac excitability.

  11. Side population analysis using a violet-excited cell-permeable DNA binding dye.

    Science.gov (United States)

    Telford, William G; Bradford, Jolene; Godfrey, William; Robey, Robert W; Bates, Susan E

    2007-04-01

    Hoechst 33342 side population (SP) analysis is a common method for identifying stem cells in mammalian hematopoietic and nonhematopoietic tissues. Although widely employed for stem cell analysis, this method requires an ultraviolet (UV) laser to excite Hoechst 33342. Flow cytometers equipped with UV sources are not common because of the cost of both the laser and optics that can transmit light UV light. Violet laser sources are inexpensive and are now common fixtures on flow cytometers, but have been previously shown to provide insufficient Hoechst dye excitation for consistent resolution of SP cells. One solution to this problem is to identify additional fluorescent substrates with the same pump specificity as Hoechst 33342, but with better violet excitation characteristics. DyeCycle Violet reagent has emission characteristics similar to those of Hoechst 33342, but with a longer wavelength excitation maxima (369 nm). When this dye is loaded into hematopoietic cells, a sharply resolved side population was also observed, similar in appearance to that seen with Hoechst 33342. Unlike Hoechst SP, DCV SP was similar in appearance with both violet and UV excitation. DCV SP could be inhibited fumitremorgin C, and showed the same membrane pump specificity as Hoechst 33342. Simultaneous immunophenotyping with stem cell markers in mouse bone marrow demonstrated that DCV SP was restricted to the stem cell lineage(-) Sca-1(+) c-kit(+) cells population, as is Hoechst SP. Pending confirmation by functional analysis of DCV SP cells, these results suggest that DCV efflux identified approximately the same stem cell population as did Hoechst 33342 efflux. Substituting DCV for Hoechst 33342 in the SP technique may, therefore, allow side population analysis on flow cytometers with violet lasers.

  12. Dynamics of sessile and pendant drops excited by surface acoustic waves: Gravity effects and correlation between oscillatory and translational motions

    Science.gov (United States)

    Bussonnière, A.; Baudoin, M.; Brunet, P.; Matar, O. Bou

    2016-05-01

    When sessile droplets are excited by ultrasonic traveling surface acoustic waves (SAWs), they undergo complex dynamics with both oscillations and translational motion. While the nature of the Rayleigh-Lamb quadrupolar drop oscillations has been identified, their origin and their influence on the drop mobility remains unexplained. Indeed, the physics behind this peculiar dynamics is complex with nonlinearities involved both at the excitation level (acoustic streaming and radiation pressure) and in the droplet response (nonlinear oscillations and contact line dynamics). In this paper, we investigate the dynamics of sessile and pendant drops excited by SAWs. For pendant drops, so-far unreported dynamics are observed close to the drop detachment threshold with the suppression of the translational motion. Away from this threshold, the comparison between pendant and sessile drop dynamics allows us to identify the role played by gravity or, more generally, by an initial or dynamically induced stretching of the drop. In turn, we elucidate the origin of the resonance frequency shift, as well as the origin of the strong correlation between oscillatory and translational motion. We show that for sessile drops, the velocity is mainly determined by the amplitude of oscillation and that the saturation observed is due to the nonlinear dependence of the drop response frequency on the dynamically induced stretching.

  13. Molecular-dynamics study of the dynamical excitations in commensurate monolayer films of nitrogen molecules on graphite: A test of the corrugation in the nitrogen-graphite potential

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Bruch, Ludwig Walter

    1995-01-01

    The dynamical excitations in a commensurate monolayer solid of N2 molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well as coherent intermediate scattering functions and dynamical structure factors have been ca...... demonstrated from the time dependence of the mean-square displacement of the molecules and the two-dimensional diffusion coefficient is estimated to be 2–3×10-5 cm2/s at 75–80 K.......The dynamical excitations in a commensurate monolayer solid of N2 molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well as coherent intermediate scattering functions and dynamical structure factors have been...

  14. Photoluminescence Excitation Spectroscopy Characterization of Cadmium Telluride Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Moore, James E.; Wang, Xufeng; Grubbs, Elizabeth K.; Drayton, Jennifer; Johnston, Steve; Levi, Dean; Lundstrom, Mark S.; Bermel, Peter

    2016-11-21

    The use of steady-state photoluminescence spectroscopy as a contactless characterization tool, suitable for inline optical characterization, has been previously demonstrated for high efficiency solar cells such as GaAs. In this paper, we demonstrate the use of PLE characterization on a thin film CdS/CdTe np heterojunction solar cell, and compare the results to measured EQE and I-V data. In contrast to previous work on high-quality GaAs, the PLE and EQE spectra do not match closely here. We still find, however, that reliable material parameters can be extracted from the PLE measurements. We also provide a physical explanation of the limits defining the cases when the PLE and EQE spectra may be expected to match.

  15. Excitation of the dynamical dipole in the charge asymmetric reaction {sup 16}O + {sup 116}Sn

    Energy Technology Data Exchange (ETDEWEB)

    Corsi, A. [Dipartimento di Fisica, Universita di Milano, Milano (Italy); INFN Sezione di Milano, Milano (Italy); Wieland, O. [INFN Sezione di Milano, Milano (Italy); Kravchuk, V.L. [Laboratori Nazionali INFN di Legnaro, Legnaro (Italy); Bracco, A. [Dipartimento di Fisica, Universita di Milano, Milano (Italy); INFN Sezione di Milano, Milano (Italy); Camera, F. [Dipartimento di Fisica, Universita di Milano, Milano (Italy); INFN Sezione di Milano, Milano (Italy)], E-mail: franco.camera@mi.infn.it; Benzoni, G.; Blasi, N.; Brambilla, S. [INFN Sezione di Milano, Milano (Italy); Crespi, F.C.L.; Giussani, A.; Leoni, S. [Dipartimento di Fisica, Universita di Milano, Milano (Italy); INFN Sezione di Milano, Milano (Italy); Million, B. [INFN Sezione di Milano, Milano (Italy); Montanari, D.; Moroni, A. [Dipartimento di Fisica, Universita di Milano, Milano (Italy); INFN Sezione di Milano, Milano (Italy); Gramegna, F.; Lanchais, A.; Mastinu, P. [Laboratori Nazionali INFN di Legnaro, Legnaro (Italy); Brekiesz, M.; Kmiecik, M.; Maj, A. [Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Krakow (Poland)] (and others)

    2009-08-24

    The {gamma}-ray emission from the dynamical dipole formed in heavy-ion collisions during the process leading to fusion was measured for the N/Z asymmetric reaction {sup 16}O + {sup 116}Sn at beam energies of 8.1 and 15.6 MeV/nucleon. High-energy {gamma}-rays and charged particles were measured in coincidence with the heavy recoiling residual nuclei. The data are compared with those from the N/Z symmetric reaction {sup 64}Ni + {sup 68}Zn at bombarding energies of 4.7 and 7.8 MeV/nucleon, leading to the same CN with the same excitation energies as calculated from kinematics. The measured yield of the high-energy {gamma}-rays from the {sup 16}O-induced reaction is found to exceed that of the thermalized CN and the excess yield increases with bombarding energy. The data are in rather good agreement with the predictions for the dynamical dipole emission based on the Boltzmann-Nordheim-Vlasov model. In addition, a comparison with existing data in the same mass region is performed to extract information on the dipole moment dependence.

  16. Ultrafast excited state dynamics of S2 and S1 states of triphenylmethane dyes.

    Science.gov (United States)

    Singhal, Pallavi; Ghosh, Hirendra N

    2014-08-21

    Excited state dynamics of S2 and S1 states for a series of TPM dyes, pyrogallol red (PGR), bromopyrogallol red (Br-PGR) and aurin tricarboxylic acid (ATC), have been monitored by using ultrafast transient absorption and fluorescence up-conversion techniques. Optical absorption studies indicate that all the TPM dyes exist as keto-enol tautomers depending upon the pH of the solution. Interestingly, all the TPM dyes give S2 emission (major emitting state) in addition to weak S1 emission. S2 emission lifetimes as fast as ∼150-300 fs and S1 emission lifetimes of 2-5 ns were observed depending upon the molecular structure of the dyes. Femtosecond transient absorption studies suggest the presence of an ultrafast non-radiative decay channel from the S2 state in addition to S2 luminescence. The vibrational relaxation time from hot S1 state is found to be 2-6 ps. The heavy atom effect has been observed in ultrafast relaxation dynamics of Br-PGR.

  17. Excitation of the dynamical dipole in the charge asymmetric reaction 16O + 116Sn

    Science.gov (United States)

    Corsi, A.; Wieland, O.; Kravchuk, V. L.; Bracco, A.; Camera, F.; Benzoni, G.; Blasi, N.; Brambilla, S.; Crespi, F. C. L.; Giussani, A.; Leoni, S.; Million, B.; Montanari, D.; Moroni, A.; Gramegna, F.; Lanchais, A.; Mastinu, P.; Brekiesz, M.; Kmiecik, M.; Maj, A.; Bruno, M.; D'Agostino, M.; Geraci, E.; Vannini, G.; Barlini, S.; Casini, G.; Chiari, M.; Nannini, A.; Ordine, A.; Di Toro, M.; Rizzo, C.; Colonna, M.; Baran, V.

    2009-08-01

    The γ-ray emission from the dynamical dipole formed in heavy-ion collisions during the process leading to fusion was measured for the N/Z asymmetric reaction 16O + 116Sn at beam energies of 8.1 and 15.6 MeV/nucleon. High-energy γ-rays and charged particles were measured in coincidence with the heavy recoiling residual nuclei. The data are compared with those from the N/Z symmetric reaction 64Ni + 68Zn at bombarding energies of 4.7 and 7.8 MeV/nucleon, leading to the same CN with the same excitation energies as calculated from kinematics. The measured yield of the high-energy γ-rays from the 16O-induced reaction is found to exceed that of the thermalized CN and the excess yield increases with bombarding energy. The data are in rather good agreement with the predictions for the dynamical dipole emission based on the Boltzmann-Nordheim-Vlasov model. In addition, a comparison with existing data in the same mass region is performed to extract information on the dipole moment dependence.

  18. Electronic excitation dynamics in multichromophoric systems described via a polaron-representation master equation.

    Science.gov (United States)

    Kolli, Avinash; Nazir, Ahsan; Olaya-Castro, Alexandra

    2011-10-21

    We derive a many-site version of the non-Markovian time-convolutionless polaron master equation [Jang et al., J. Chem Phys. 129, 101104 (2008)] to describe electronic excitation dynamics in multichromophoric systems. By treating electronic and vibrational degrees of freedom in a combined frame (polaron frame), this theory is capable of interpolating between weak and strong exciton-phonon coupling and is able to account for initial non-equilibrium bath states and spatially correlated environments. Besides outlining a general expression for the expected value of any electronic system observable in the original frame, we also discuss implications of the Markovian and Secular approximations highlighting that they need not hold in the untransformed frame despite being strictly satisfied in the polaron frame. The key features of the theory are illustrated using as an example a four-site subsystem of the Fenna-Mathews-Olson light-harvesting complex. For a spectral density including a localised mode, we show that oscillations of site populations may only be observed when non-equilibrium bath effects are taken into account. Furthermore, we illustrate how this formalism allows us to identify the electronic and vibrational components of the oscillatory dynamics.

  19. Capillary effect on the sloshing of a fluid in a rectangular tank submitted to sinusoidal vertical dynamical excitation

    Institute of Scientific and Technical Information of China (English)

    MEZIANI Bachir; OURRAD Ouerdia

    2014-01-01

    Surface tension effects on fluid sloshing in a tank subjected to external excitation has been less studied. This work aims at understanding this phenomenon in order to derive practical solutions to problems faced in several engineering. A tank containing a fluid with a free surface is submitted to gravity and capillary forces and subject to external dynamic excitation. Introduction of vertical sinusoidal dynamical excitation leads to a problem of paramtric oscillations governed by the Mathieu equation. Analysis of the Mathieu equation shows the existence of stable and unstable regions in the stability diagram. Some results induced by harmonic excitations on the fluid sloshing are presented. When the external dynamical excitation amplitude e is small, periodic solutions appear in stable regions and when e increases, the fluid behavior is not perfectly periodic and the amplitudes are not regular. Nonlinear effects make the behavior of the fluid complicated and render it almost unpredictable. In stable regions, the solution remains bounded at any time. When changing the perturbation parameter e, the phase difference increases and also with the increase of the surface tension.

  20. a Study on Excited State Dynamics of Simple Molecules: Time Dependent Wavepacket Approach

    Science.gov (United States)

    Ryu, Jae-Seok

    1995-01-01

    Potential energy surfaces for the excited states of ethylene and dihalomethanes are determined by utilizing all available information from absorption and resonance Raman experiments and ab initio calculations. The theoretical treatment of absorption and resonance Raman excitation profiles utilize the well developed wavepacket methodology. The electronic spectrum of ethylene in the 50,000 -66,000cm^{-1} region has been assigned to overlapping valence pipi ^* ("N --> V") and pi3s Rydberg ("N --> R") transitions. In this thesis the hypothesis is made and tested that all of the observed structure is due to one pipi^* excited state. For the pipi^* electronic N --> V transition of ethylene, the V-state potential is constructed by considering a dynamical torsional barrier height which changes with the C-C distance. The spectrum that results from this single surface does not provide adequate agreement with experiment. The standard overlapping N --> V plus pi3s description is then considered quantitatively. In order to fit the observed spectra it is necessary to use a very large value for the N --> R (3s) oscillator strength and a very small value for the N --> V transition strength. Both of these values disagree with the results of ab initio calculation. Use of a large C = C displacement for N --> V transition can increase the oscillator strength for this state but this results in the expectation of strong overtone intensity in the resonance Raman spectrum in disagreement with experiment. Hence, the traditional assignment is also rejected and an alternative is sought. The most likely explanation for the strong structured absorption beginning at 57,500cm^{-1} is that it results from transitions to two coupled surfaces due to the N --> V state with B_{1u} symmetry and another Rydberg state of pi3p _{y} origin with B_{1g} symmetry. This new assignment of the ethylene spectrum predicts a constant depolarization. The traditional assignment predicts strong dispersion which is

  1. Nanophotonics and nanochemistry: controlling the excitation dynamics for frequency up- and down-conversion in lanthanide-doped nanoparticles.

    Science.gov (United States)

    Chen, Guanying; Yang, Chunhui; Prasad, Paras N

    2013-07-16

    Nanophotonics is an emerging science dealing with the interaction of light and matter on a nanometer scale and holds promise to produce new generation nanophosphors with highly efficient frequency conversion of infrared (IR) light. Scientists can control the excitation dynamics by using nanochemistry to produce hierarchically built nanostructures and tailor their interfaces. These nanophosphors can either perform frequency up-conversion from IR to visible or ultraviolet (UV) or down-conversion, which results in the IR light being further red shifted. Nanophotonics and nanochemistry open up numerous opportunities for these photon converters, including in high contrast bioimaging, photodynamic therapy, drug release and gene delivery, nanothermometry, and solar cells. Applications of these nanophosphors in these directions derive from three main stimuli. Light excitation and emission within the near-infrared (NIR) "optical transparency window" of tissues is ideal for high contrast in vitro and in vivo imaging. This is due to low natural florescence, reduced scattering background, and deep penetration in tissues. Secondly, the naked eye is highly sensitive in the visible range, but it has no response to IR light. Therefore, many scientists have interest in the frequency up-conversion of IR wavelengths for security and display applications. Lastly, frequency up-conversion can convert IR photons to higher energy photons, which can then readily be absorbed by solar materials. Current solar devices do not use abundant IR light that comprises almost half of solar energy. In this Account, we present our recent work on nanophotonic control of frequency up- and down-conversion in fluoride nanophosphors, and their biophotonic and nanophotonic applications. Through nanoscopic control of phonon dynamics, electronic energy transfer, local crystal field, and surface-induced non-radiative processes, we were able to produce new generation nanophosphors with highly efficient frequency

  2. Evidence of dynamical dipole excitation in the fusion-evaporation of the 40Ca+152Sm heavy system

    Science.gov (United States)

    Parascandolo, C.; Pierroutsakou, D.; Alba, R.; Del Zoppo, A.; Maiolino, C.; Santonocito, D.; Agodi, C.; Baran, V.; Boiano, A.; Colonna, M.; Coniglione, R.; De Filippo, E.; Di Toro, M.; Emanuele, U.; Farinon, F.; Guglielmetti, A.; Inglima, G.; La Commara, M.; Martin, B.; Mazzocchi, C.; Mazzocco, M.; Rizzo, C.; Romoli, M.; Sandoli, M.; Signorini, C.; Silvestri, R.; Soramel, F.; Strano, E.; Torresi, D.; Trifirò, A.; Trimarchi, M.

    2016-04-01

    The excitation of the dynamical dipole mode along the fusion path was investigated for the first time in the formation of a heavy compound nucleus in the A ˜190 mass region. The compound nucleus was formed at identical conditions of excitation energy and spin from two entrance channels: the charge-asymmetric 40Ca+152Sm and the nearly charge-symmetric 48Ca+144Sm at Elab=11 and 10.1 MeV/nucleon, respectively. High-energy γ rays and light charged particles were measured in coincidence with evaporation residues by means of the MEDEA multidetector array (Laboratori Nazionali del Sud, Italy) coupled to four parallel plate avalanche counters. The charged particle multiplicity spectra and angular distributions were used to pin down the average excitation energy, the average mass, and the average charge of the compound nucleus. The γ -ray multiplicity spectrum and angular distribution related to the nearly charge-symmetric channel were employed to obtain new data on the giant dipole resonance in the compound nucleus. The dynamical dipole mode excitation in the charge-asymmetric channel was evidenced, in a model-independent way, by comparing the γ -ray multiplicity spectra and angular distributions of the two entrance channels with each other. Calculations of the dynamical dipole mode in the 40Ca+152Sm channel, based on a collective bremsstrahlung analysis of the reaction dynamics, are presented. Possible interesting implications in the superheavy-element quest are discussed.

  3. Ultrafast dynamics of laser-pulse excited semiconductors: non-Markovian quantum kinetic equations with nonequilibrium correlations

    Directory of Open Access Journals (Sweden)

    V.V.Ignatyuk

    2004-01-01

    Full Text Available Non-Markovian kinetic equations in the second Born approximation are derived for a two-zone semiconductor excited by a short laser pulse. Both collision dynamics and running nonequilibrium correlations are taken into consideration. The energy balance and relaxation of the system to equilibrium are discussed. Results of numerical solution of the kinetic equations for carriers and phonons are presented.

  4. Epigenetic dynamics across the cell cycle

    DEFF Research Database (Denmark)

    Kheir, Tony Bou; Lund, Anders H.

    2010-01-01

    Progression of the mammalian cell cycle depends on correct timing and co-ordination of a series of events, which are managed by the cellular transcriptional machinery and epigenetic mechanisms governing genome accessibility. Epigenetic chromatin modifications are dynamic across the cell cycle...... a correct inheritance of epigenetic chromatin modifications to daughter cells. In this chapter, we summarize the current knowledge on the dynamics of epigenetic chromatin modifications during progression of the cell cycle....

  5. Excitation Method of Linear-Motor-Type Rail Brake without Using Power Sources by Dynamic Braking with Zero Electrical Output

    Science.gov (United States)

    Sakamoto, Yasuaki; Kashiwagi, Takayuki; Hasegawa, Hitoshi; Sasakawa, Takashi; Fujii, Nobuo

    The eddy current rail brake is a type of braking system used in railway vehicles. Because of problems such as rail heating and problems associated with ensuring that power is supplied when the feeder malfunctions, this braking system has not been used for practical applications in Japan. Therefore, we proposed the use of linear induction motor (LIM) technology in eddy current rail brake systems. The LIM rail brake driven by dynamic braking can reduce rail heating and generate the energy required for self-excitation. In this paper, we present an excitation system and control method for the LIM rail brake driven by “dynamic braking with zero electrical output”. The proposed system is based on the concept that the LIM rail brake can be energized without using excitation power sources such as a feeder circuit and that high reliability can be realized by providing an independent excitation system. We have studied this system and conducted verification tests using a prototype LIM rail brake on a roller rig. The results show that the system performance is adequate for commercializing the proposed system, in which the LIM rail brake is driven without using any excitation power source.

  6. Hilbert spectrum and intrinsic oscillation mode of dynamic response of a bilinear SDOF system: influence of harmonic excitation amplitude

    Institute of Scientific and Technical Information of China (English)

    Zhang Yushan; Liang Jianwen; Hu Yuxian

    2005-01-01

    Under harmonic wave excitation, the dynamic response of a bilinear SDOF system can be expressed by the Hilbert spectrum. The Hilbert spectrum can be formulated by (1) the inter-wave combination mechanism between the steady response and the transient response when the system behaves linearly, or (2) the intra-wave modulation mechanism embedded in one intrinsic mode function (IMF) component when the system behaves nonlinearly. The temporal variation of the instantaneous frequency of the IMF component is consistent with the system nonlinear behavior of yielding and unloading. As a thorough study of this fundamental structural dynamics problem, this article investigates the influence of the amplitude of the harmonic wave excitation on the Hilbert spectrum and the intrinsic oscillatory mode of the dynamic response of a bilinear SDOF system.

  7. Plant Cell Imaging Based on Nanodiamonds with Excitation-Dependent Fluorescence.

    Science.gov (United States)

    Su, Li-Xia; Lou, Qing; Jiao, Zhen; Shan, Chong-Xin

    2016-12-01

    Despite extensive work on fluorescence behavior stemming from color centers of diamond, reports on the excitation-dependent fluorescence of nanodiamonds (NDs) with a large-scale redshift from 400 to 620 nm under different excitation wavelengths are so far much fewer, especially in biological applications. The fluorescence can be attributed to the combined effects of the fraction of sp(2)-hybridized carbon atoms among the surface of the fine diamond nanoparticles and the defect energy trapping states on the surface of the diamond. The excitation-dependent fluorescent NDs have been applied in plant cell imaging for the first time. The results reported in this paper may provide a promising route to multiple-color bioimaging using NDs.

  8. Plant Cell Imaging Based on Nanodiamonds with Excitation-Dependent Fluorescence

    Science.gov (United States)

    Su, Li-Xia; Lou, Qing; Jiao, Zhen; Shan, Chong-Xin

    2016-09-01

    Despite extensive work on fluorescence behavior stemming from color centers of diamond, reports on the excitation-dependent fluorescence of nanodiamonds (NDs) with a large-scale redshift from 400 to 620 nm under different excitation wavelengths are so far much fewer, especially in biological applications. The fluorescence can be attributed to the combined effects of the fraction of sp2-hybridized carbon atoms among the surface of the fine diamond nanoparticles and the defect energy trapping states on the surface of the diamond. The excitation-dependent fluorescent NDs have been applied in plant cell imaging for the first time. The results reported in this paper may provide a promising route to multiple-color bioimaging using NDs.

  9. Plasmonic Nanoparticle-based Hybrid Photosensitizers with Broadened Excitation Profile for Photodynamic Therapy of Cancer Cells

    Science.gov (United States)

    Wang, Peng; Tang, Hong; Zhang, Peng

    2016-10-01

    Photodynamic therapy combining nanotechnology has shown great potential with improved therapeutic efficacy and fewer side effects. Ideal photosensitizers for cancer treatment should both have good singlet oxygen production capability and be excitable by light illuminations with deep tissue penetration. Here we report a type of hybrid photosensitizers consisting of plasmonic silver nanoparticles and photosensitizing molecules, where strong resonance coupling between the two leads to a broadened excitation profile and exceptionally high singlet oxygen production under both visible light and infrared light excitations. Our results indicate that the hybrid photosensitizers display low cytotoxicity without light illumination yet highly enhanced photodynamic inhibition efficacy against Hela cells under a broad spectrum of light illuminations including the near-infrared light, which has great implication in photodynamic therapy of deep-tissue cancers.

  10. Isoscalar giant monopole resonance in Sn isotopes by Coulomb excitations using a quantum molecular dynamics model

    CERN Document Server

    Tao, C; Zhang, G Q; Cao, X G; Fang, D Q; Wang, H W; Xu, J

    2013-01-01

    The isoscalar giant monopole resonance (ISGMR) in Sn isotopes and other nuclei has been investigated by Coulomb excitations in the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. The spectrum of GMR has been calculated by taking the root-mean-square (RMS) radius of a nucleus as its monopole moment. The peak energy, the full width at half maximum (FWHM), and the strength of GMR extracted by a Gaussian fit to the spectrum have been studied. The GMR peak energies for Sn isotopes from the calculations using a mass-number dependent Gaussian wave-packet width $\\sigma_r$ for nucleons are found to be overestimated and show a weak dependence on the mass number compared with the experimental data. However, it has been found that experimental data of the GMR peak energies for $^{40}$Ca, $^{56}$Ni, $^{90}$Zr and $^{208}$Pb as well as Sn isotopes can be nicely reproduced after taking into account the isospin dependence in isotope chains in addition to the mass number dependence of $\\sigma_r$ fo...

  11. Dynamic response of mechanical systems to impulse process stochastic excitations: Markov approach

    Science.gov (United States)

    Iwankiewicz, R.

    2016-05-01

    Methods for determination of the response of mechanical dynamic systems to Poisson and non-Poisson impulse process stochastic excitations are presented. Stochastic differential and integro-differential equations of motion are introduced. For systems driven by Poisson impulse process the tools of the theory of non-diffusive Markov processes are used. These are: the generalized Itô’s differential rule which allows to derive the differential equations for response moments and the forward integro-differential Chapman-Kolmogorov equation from which the equation governing the probability density of the response is obtained. The relation of Poisson impulse process problems to the theory of diffusive Markov processes is given. For systems driven by a class of non-Poisson (Erlang renewal) impulse processes an exact conversion of the original non-Markov problem into a Markov one is based on the appended Markov chain corresponding to the introduced auxiliary pure jump stochastic process. The derivation of the set of integro-differential equations for response probability density and also a moment equations technique are based on the forward integro-differential Chapman-Kolmogorov equation. An illustrating numerical example is also included.

  12. Dynamic magnetization switching and spin wave excitations by voltage-induced torque

    Science.gov (United States)

    Shiota, Yoichi

    2013-03-01

    The effect of electric fields on ultrathin ferromagnetic metal layer is one of the promising approaches for manipulating the spin direction with low-energy consumption, localization, and coherent behavior. Several experimental approaches to realize it have been investigated using ferromagnetic semiconductors, magnetostriction together with piezo-electric materials, multiferroic materials, and ultrathin ferromagnetic layer. In this talk, we will present a dynamic control of spins by voltage-induced torque. We used the magnetic tunnel junctions with ultrathin ferromagnetic layer, which shows voltage-induced perpendicular magnetic anisotropy change. By applying the voltage to the junction, the magnetic easy-axis in the ultrathin ferromagnetic layer changes from in-plane to out-of-plane, which causes a precession of the spins. This precession resulted in a two-way toggle switching by determining an appropriate pulse length. On the other hand, an application of rf-voltage causes an excitation of a uniform spin-wave. Since the precession of spin associates with an oscillation in the resistance of the junction, the applied rf-signal is rectified and produces a dc-voltage. From the spectrum of the dc-voltage as a function of frequency, we could estimate the voltage-induced torque. This research was supported by CREST-JST, G-COE program, and JSPS for the fellowship. Collaborators include T. Nozaki, S. Miwa, F. Bonell, N. Mizuochi, T. Shinjo, and Y. Suzuki.

  13. High-Speed Rotor Analytical Dynamics on Flexible Foundation Subjected to Internal and External Excitation

    Directory of Open Access Journals (Sweden)

    Jivkov Venelin S.

    2016-12-01

    Full Text Available The paper presents a geometrical approach to dynamics simulation of a rigid and flexible system, compiled of high speed rotating machine with eccentricity and considerable inertia and mass. The machine is mounted on a vertical flexible pillar with considerable height. The stiffness and damping of the column, as well as, of the rotor bearings and the shaft are taken into account. Non-stationary vibrations and transitional processes are analyzed. The major frequency and modal mode of the flexible column are used for analytical reduction of its mass, stiffness and damping properties. The rotor and the foundation are modelled as rigid bodies, while the flexibility of the bearings is estimated by experiments and the requirements of the manufacturer. The transition effects as a result of limited power are analyzed by asymptotic methods of averaging. Analytical expressions for the amplitudes and unstable vibrations throughout resonance are derived by quasi-static approach increasing and decreasing of the exciting frequency. Analytical functions give the possibility to analyze the influence of the design parameter of many structure applications as wind power generators, gas turbines, turbo-generators, and etc. A numerical procedure is applied to verify the effectiveness and precision of the simulation process.

  14. On the nature of nuclear dissipation, as a hallmark for collective dynamics at finite excitation

    CERN Document Server

    Hofmann, H; Yamaji, S; Hofmann, Helmut; Ivanyuk, Fedor A; Yamaji, Shuhei

    1995-01-01

    We study slow collective motion of isoscalar type at finite excitation. The collective variable is parameterized as a shape degree of freedom and the mean field is approximated by a deformed shell model potential. We concentrate on situations of slow motion, as guaranteed, for instance, by the presence of a strong friction force, which allows us to apply linear response theory. The prediction for nuclear dissipation of some models of internal motion are contrasted. They encompass such opposing cases as that of pure independent particle motion and the one of "collisional dominance". For the former the wall formula appears as the macroscopic limit, which is here simulated through Strutinsky smoothing procedures. It is argued that this limit hardly applies to the actual nuclear situation. The reason is found in large collisional damping present for nucleonic dynamics at finite temperature T. The level structure of the mean field as well as the T-dependence of collisional damping determine the T-dependence of fri...

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

    Science.gov (United States)

    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.

  16. The mechanism of abrupt transition between theta and hyper-excitable spiking activity in medial entorhinal cortex layer II stellate cells.

    Directory of Open Access Journals (Sweden)

    Tilman Kispersky

    Full Text Available Recent studies have shown that stellate cells (SCs of the medial entorhinal cortex become hyper-excitable in animal models of temporal lobe epilepsy. These studies have also demonstrated the existence of recurrent connections among SCs, reduced levels of recurrent inhibition in epileptic networks as compared to control ones, and comparable levels of recurrent excitation among SCs in both network types. In this work, we investigate the biophysical and dynamic mechanism of generation of the fast time scale corresponding to hyper-excitable firing and the transition between theta and fast firing frequency activity in SCs. We show that recurrently connected minimal networks of SCs exhibit abrupt, threshold-like transition between theta and hyper-excitable firing frequencies as the result of small changes in the maximal synaptic (AMPAergic conductance. The threshold required for this transition is modulated by synaptic inhibition. Similar abrupt transition between firing frequency regimes can be observed in single, self-coupled SCs, which represent a network of recurrently coupled neurons synchronized in phase, but not in synaptically isolated SCs as the result of changes in the levels of the tonic drive. Using dynamical systems tools (phase-space analysis, we explain the dynamic mechanism underlying the genesis of the fast time scale and the abrupt transition between firing frequency regimes, their dependence on the intrinsic SC's currents and synaptic excitation. This abrupt transition is mechanistically different from others observed in similar networks with different cell types. Most notably, there is no bistability involved. 'In vitro' experiments using single SCs self-coupled with dynamic clamp show the abrupt transition between firing frequency regimes, and demonstrate that our theoretical predictions are not an artifact of the model. In addition, these experiments show that high-frequency firing is burst-like with a duration modulated by an M-current.

  17. Influence of environment induced correlated fluctuations in electronic coupling on coherent excitation energy transfer dynamics in model photosynthetic systems.

    Science.gov (United States)

    Huo, Pengfei; Coker, David F

    2012-03-21

    Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light

  18. Excited-state structural dynamics of a dual-emission calmodulin-green fluorescent protein sensor for calcium ion imaging

    Science.gov (United States)

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

    2014-01-01

    Fluorescent proteins (FPs) have played a pivotal role in bioimaging and advancing biomedicine. The versatile fluorescence from engineered, genetically encodable FP variants greatly enhances cellular imaging capabilities, which are dictated by excited-state structural dynamics of the embedded chromophore inside the protein pocket. Visualization of the molecular choreography of the photoexcited chromophore requires a spectroscopic technique capable of resolving atomic motions on the intrinsic timescale of femtosecond to picosecond. We use femtosecond stimulated Raman spectroscopy to study the excited-state conformational dynamics of a recently developed FP-calmodulin biosensor, GEM-GECO1, for calcium ion (Ca2+) sensing. This study reveals that, in the absence of Ca2+, the dominant skeletal motion is a ∼170 cm−1 phenol-ring in-plane rocking that facilitates excited-state proton transfer (ESPT) with a time constant of ∼30 ps (6 times slower than wild-type GFP) to reach the green fluorescent state. The functional relevance of the motion is corroborated by molecular dynamics simulations. Upon Ca2+ binding, this in-plane rocking motion diminishes, and blue emission from a trapped photoexcited neutral chromophore dominates because ESPT is inhibited. Fluorescence properties of site-specific protein mutants lend further support to functional roles of key residues including proline 377 in modulating the H-bonding network and fluorescence outcome. These crucial structural dynamics insights will aid rational design in bioengineering to generate versatile, robust, and more sensitive optical sensors to detect Ca2+ in physiologically relevant environments. PMID:24987121

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

    Science.gov (United States)

    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 ).

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

    Energy Technology Data Exchange (ETDEWEB)

    Lockard, J. V.; Kabehie, S.; Zink, J. I.; Smolentsev, G.; Soldatov, A.; Chen, L. X. (Chemical Sciences and Engineering Division); (Northwestern Univ.); (Univ. of California at Los Angeles); (Southern Federal Univ.); (Lund Univ.)

    2010-01-01

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

  1. Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

    Science.gov (United States)

    Sturm, F. P.; Tong, X. M.; Palacios, A.; Wright, T. W.; Zalyubovskaya, I.; Ray, D.; Shivaram, N.; Martín, F.; Belkacem, A.; Ranitovic, P.; Weber, Th.

    2017-01-01

    We used ultrashort femtosecond vacuum ultraviolet (VUV) and infrared (IR) pulses in a pump-probe scheme to map the dynamics and nonequilibrium dissociation channels of excited neutral H2 molecules. A nuclear wave packet is created in the B Σ+1u state of the neutral H2 molecule by absorption of the ninth harmonic of the driving infrared laser field. Due to the large stretching amplitude of the molecule excited in the B Σ+1u electronic state, the effective H2+ ionization potential changes significantly as the nuclear wave packet vibrates in the bound, highly electronically and vibrationally excited B potential-energy curve. We probed such dynamics by ionizing the excited neutral molecule using time-delayed VUV-or-IR radiation. We identified the nonequilibrium dissociation channels by utilizing three-dimensional momentum imaging of the ion fragments. We found that different dissociation channels can be controlled, to some extent, by changing the IR laser intensity and by choosing the wavelength of the probe laser light. Furthermore, we concluded that even in a benchmark molecular system such as H2*, the interpretation of the nonequilibrium multiphoton and multicolor ionization processes is still a challenging task, requiring intricate theoretical analysis.

  2. Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics

    Science.gov (United States)

    Kunnus, Kristjan; Josefsson, Ida; Rajkovic, Ivan; Schreck, Simon; Quevedo, Wilson; Beye, Martin; Grübel, Sebastian; Scholz, Mirko; Nordlund, Dennis; Zhang, Wenkai; Hartsock, Robert W.; Gaffney, Kelly J.; Schlotter, William F.; Turner, Joshua J.; Kennedy, Brian; Hennies, Franz; Techert, Simone; Wernet, Philippe; Odelius, Michael; Föhlisch, Alexander

    2016-10-01

    Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited state moieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)5 in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS-RXRS with transform-limited x-ray pulses is given—which will be covered experimentally by upcoming transform-limited x-ray sources.

  3. Direct QM/MM excited-state dynamics of retinal protonated Schiff base in isolation and methanol solution.

    Science.gov (United States)

    Punwong, Chutintorn; Owens, Jane; Martínez, Todd J

    2015-01-22

    We use the full multiple spawning (FMS) dynamics approach with a hybrid quantum mechanics/molecular mechanics (QM/MM) reparameterized semiempirical method to investigate the excited-state dynamics of retinal protonated Schiff base (RPSB) in isolation, in neat methanol solution, and in methanol solution with a Cl(-) counterion. The excited-state lifetime is dramatically affected by MeOH solvent, which slows down the photoisomerization by an order of magnitude. We show that this is due to charge migration in the RPSB chromophore and the concomitant solvent friction in polar media. Simulation results are compared to experiments where available, with good agreement for excited-state lifetimes, bond selectivity of isomerization, and the time/energy-resolved fluorescence spectrum. We find that the inclusion of a Cl(-) counterion in the simulations has little effect on lifetimes, mechanism, or bond selectivity. In contrast to previous studies limited to RPSB and a surrounding counterion, we find that the placement of the counterion has little effect on bond selectivity. This suggests that dielectric screening can spoil the effect of a counterion in directing excited-state reactivity.

  4. Multicolor excitation two-photon microscopy: in vivo imaging of cells and tissues

    Science.gov (United States)

    Li, Dong; Zheng, Wei; Qu, Jianan Y.

    2010-02-01

    Two-photon microscopy based on endogenous fluorescence provides non-invasive imaging of living biological system. Reduced nicotinamide adenine dinucleotide (NADH), flavin adenine dinucleotide (FAD), keratin, collagen and elastin are the endogenous fluorophores widely used as the contrast agents for imaging metabolism and morphology of living cells and tissue. The fluorescence of tryptophan, a kind of essential amino acid, conveys the information on cellular protein content, structure and microenvironment. However, it can't be effectively excited by the commonly used Ti:sapphire femtosecond laser. Because each endogenous fluorophore provides limited information, it is desirable to simultaneously excite fluorescence from as many fluorophores as possible to obtain accurate biochemical and morphological information on biomedical samples. In this study, we demonstrate that the supercontinuum generation from a photonic crystal fiber (PCF) excited by an ultrafast source can be used to excite multiple endogenous nonlinear optical signals simultaneously. By employing the spectral lifetime detection capability, this technology provides a unique approach to sense the fine structure, protein distribution and cellular metabolism of cells and tissues in vivo. In particular, with application of acetic acid, a safe contrast agent used for detection cervical cancer for many years, the tryptophan signals reveal cellular morphology and even cell-cell junctions clearly. Moreover, it was found that the pH value dependent lifetime of tryptophan fluorescence could provide the qualitative information on the gradient of pH value in epithelial tissue. Finally, we will demonstrate the potential of our multi-color TPEF microscopy to investigate the early development of cancer in epithelial tissue.

  5. Molecular Dynamics Simulation of Strong Shock Waves Propagating in Dense Deuterium With the Effect of Excited Electrons

    CERN Document Server

    Liu, Hao; Kang, Wei; Zhang, Ping; Duan, Huiling; He, X T

    2016-01-01

    We present a molecular dynamics simulation of shock waves propagating in dense deuterium with the electron force field method [J. T. Su and W. A. Goddard, Phys. Rev. Lett. 99, 185003 (2007)], which explicitly takes the excitation of electrons into consideration. Non-equilibrium features associated with the excitation of electrons are systematically investigated. We show that chemical bonds in D$_2$ molecules lead to a more complicated shock wave structure near the shock front, compared with the results of classical molecular dynamics simulation. Charge separation can bring about accumulation of net charges on the large scale, instead of the formation of a localized dipole layer, which might cause extra energy for the shock wave to propagate. In addition, the simulations also display that molecular dissociation at the shock front is the major factor corresponding to the "bump" structure in the principal Hugoniot. These results could help to build a more realistic picture of shock wave propagation in fuel mater...

  6. Local Control Theory in Trajectory Surface Hopping Dynamics Applied to the Excited-State Proton Transfer of 4-Hydroxyacridine.

    Science.gov (United States)

    Curchod, Basile F E; Penfold, Thomas J; Rothlisberger, Ursula; Tavernelli, Ivano

    2015-07-20

    The application of local control theory combined with nonadiabatic ab initio molecular dynamics to study the photoinduced intramolecular proton transfer reaction in 4-hydroxyacridine was investigated. All calculations were performed within the framework of linear-response time-dependent density functional theory. The computed pulses revealed important information about the underlying excited-state nuclear dynamics highlighting the involvement of collective vibrational modes that would normally be neglected in a study performed on model systems constrained to a subset of the full configuration space. This study emphasizes the strengths of local control theory for the design of pulses that can trigger chemical reactions associated with the population of a given molecular excited state. In addition, analysis of the generated pulses can help to shed new light on the photophysics and photochemistry of complex molecular systems.

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

    Science.gov (United States)

    Palan, Vikrant; Shepard, W. Steve

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Palan, Vikrant; Shepard, W. Steve [Department of Mechanical Engineering, The University of Alabama, 290 Hardaway Hall, Box 870276, Tuscaloosa, AL 35487 (United States)

    2006-09-22

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

  9. Size-Dependent Transition to High-Dimensional Chaotic Dynamics in a Two-Dimensional Excitable Medium

    CERN Document Server

    Strain, M C; Strain, Matthew C.; Greenside, Henry S.

    1997-01-01

    The spatiotemporal dynamics of an excitable medium with multiple spiral defects is shown to vary smoothly with system size from short-lived transients for small systems to extensive chaos for large systems. A comparison of the Lyapunov dimension density with the average spiral defect density suggests an average dimension per spiral defect varying between three and seven. We discuss some implications of these results for experimental studies of ventricular fibrillation.

  10. Ab initio interaction potentials for X and B excited states of He-I{sub 2} for studying dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Prosmiti, Rita; Garcia-Gutierrez, Leonor; Delgado-Tellez, Laura; Valdes, Alvaro; Villarreal, Pablo; Delgado-Barrio, Gerardo, E-mail: rita@imaff.cfmac.csic.e [Instituto de Fisica Fundamental (CSIC), Serrano 123, 28006 Madrid (Spain)

    2009-11-01

    Ab initio CCSD(T) and MRCI approaches were employed to construct potential energy surfaces of the ground and the B electronic excited states of He-I{sub 2} complex, while full quantum mechanical methods were applied to study its spectroscopy and dynamics. A description of the approach adopted, together with the results obtained and their comparison with recent experimental data, as well as further improvements are presented.

  11. Cell Division, Differentiation and Dynamic Clustering

    CERN Document Server

    Kaneko, K; Kaneko, Kunihiko; Yomo, Tetsuya

    1993-01-01

    A novel mechanism for cell differentiation is proposed, based on the dynamic clustering in a globally coupled chaotic system. A simple model with metabolic reaction, active transport of chemicals from media, and cell division is found to show three successive stages with the growth of the number of cells; coherent growth, dynamic clustering, and fixed cell differentiation. At the last stage, disparity in activities, germ line segregation, somatic cell differentiation, and homeochaotic stability against external perturbation are found. Our results, in consistency with the experiments of the preceding paper, imply that cell differentiation can occur without a spatial pattern. From dynamical systems viewpoint, the new concept of ``open chaos" is proposed, as a novel and general scenario for systems with growing numbers of elements, also seen in economics and sociology.A

  12. ARTICLES: A Surface Femtosecond Two-Photon Photoemission Spectrometer for Excited Electron Dynamics and Time-Dependent Photochemical Kinetics

    Science.gov (United States)

    Ren, Ze-feng; Zhou, Chuan-yao; Ma, Zhi-bo; Xiao, Chun-lei; Mao, Xin-chun; Dai, Dong-xu; LaRue, Jerry; Cooper, Russell; Wodtke, Alec M.; Yang, Xue-ming

    2010-06-01

    A surface femtosecond two-photon photoemission (2PPE) spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferometer was built for the time-resolved 2PPE (TR-2PPE) measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu(111) surface. A scheme for measuring time-dependent 2PPE (TD-2PPE) spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2(110). We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.

  13. The dynamic excitation of a granular chain for biomedical ultrasound applications: contact mechanics finite element analysis and validation

    Science.gov (United States)

    Gélat, P.; Yang, J.; Thomas, P. J.; Hutchins, D. A.; Akanji, O.; Davis, L. A. J.; Freear, S.; Harput, S.; Saffari, N.

    2016-01-01

    There has been recent interest in the transmission of acoustic signals along granular chains of spherical beads to produce waveforms of relevance to biomedical ultrasound applications. Hertzian contact between adjacent beads can introduce different harmonic content into the signal as it propagates. This transduction mechanism has the potential to be of use in both diagnostic and therapeutic ultrasound applications, and is the object of the study presented here. Although discrete dynamics models of this behaviour exist, a more comprehensive solution must be sought if changes in shape and deformation of individual beads are to be considered. Thus, the finite element method was used to investigate the dynamics of a granular chain of six, 1 mm diameter chrome steel spherical beads excited at one end using a sinusoidal displacement signal at 73 kHz. Output from this model was compared with the solution provided by the discrete dynamics model, and good overall agreement obtained. In addition, it was able to resolve the complex dynamics of the granular chain, including the multiple collisions which occur. It was demonstrated that under dynamic excitation conditions, the inability of discrete mechanics models to account for elastic deformation of the beads when these lose contact, could lead to discrepancies with experimental observations.

  14. The dynamic regulation of cortical excitability is altered in episodic ataxia type 2

    DEFF Research Database (Denmark)

    Helmich, Rick C; Siebner, Hartwig R; Giffin, Nicola

    2010-01-01

    Episodic ataxia type 2 and familial hemiplegic migraine are two rare hereditary disorders that are linked to dysfunctional ion channels and are characterized clinically by paroxysmal neurological symptoms. Impaired regulation of cerebral excitability is thought to play a role in the occurrence......-pulse transcranial magnetic stimulation at an interstimulus interval of 2 and 10 ms to assess intracortical inhibition and facilitation, respectively. The time course of burst-induced excitability changes differed between groups. Healthy controls showed a short-lived increase in excitability that was only present 50...... ms after the burst. In contrast, patients with episodic ataxia type 2 showed an abnormally prolonged increase in corticospinal excitability that was still present 250 ms after the transcranial magnetic stimulation burst. Furthermore, while controls showed a decrease in intracortical facilitation...

  15. An Experimental Investigation of the Dynamic Behavior of an In-Plane MEMS Shallow Arch Under Electrostatic Excitation

    KAUST Repository

    Ramini, Abdallah

    2016-01-20

    We present experimental investigation of the nonlinear dynamics of a clamped-clamped in-plane MEMS shallow arch when excited by an electrostatic force. We explore the dynamic behaviors of the in-plane motion of the shallow arches via frequency sweeps in the neighborhood of the first resonance frequency. The shallow arch response is video microscopy recorded and analyzed by means of digital imaging. The experimental data show local softening behavior for small DC and AC loads. For high voltages, the experimental investigation reveals interesting dynamics, where the arch exhibits a dynamic snap-Through behavior. These attractive experimental results verify the previously reported complex behavior of in-plane MEMS arches and show promising results to implement these structures for variety of sensing and actuation applications. © Copyright 2015 by ASME.

  16. Excited state intramolecular proton transfer and charge transfer dynamics of a 2-(2'-hydroxyphenyl)benzoxazole derivative in solution.

    Science.gov (United States)

    Kim, Chul Hoon; Park, Jaehun; Seo, Jangwon; Park, Soo Young; Joo, Taiha

    2010-05-13

    Excited state intramolecular proton transfer (ESIPT) and subsequent intramolecular charge transfer (ICT) dynamics of a 2-(2'-hydroxyphenyl)benzoxazole derivative conjugated with an electron withdrawing group (HBOCE) in solutions and a polymer film has been investigated by femtosecond time-resolved fluorescence (TRF) and TRF spectra measurements without the conventional spectral reconstruction method. TRF with high enough resolution (benzoxazole groups is invoked to account for the dispersive ESIPT dynamics in liquids. From the TRF spectra of both the enol and keto isomers, we have identified the ICT reaction of the keto isomer occurring subsequent to the ESIPT. The ICT proceeds also by two time constants of near instantaneous and 2.7 ps. Since the ICT dynamics of HBOCE is rather close to the polar solvation dynamics, we argue that the ICT is barrierless and determined mostly by the solvent fluctuation.

  17. Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

    Energy Technology Data Exchange (ETDEWEB)

    Laursen, S.L.

    1990-01-01

    Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly.

  18. The dynamic regulation of cortical excitability is altered in episodic ataxia type 2.

    Science.gov (United States)

    Helmich, Rick C; Siebner, Hartwig R; Giffin, Nicola; Bestmann, Sven; Rothwell, John C; Bloem, Bastiaan R

    2010-12-01

    Episodic ataxia type 2 and familial hemiplegic migraine are two rare hereditary disorders that are linked to dysfunctional ion channels and are characterized clinically by paroxysmal neurological symptoms. Impaired regulation of cerebral excitability is thought to play a role in the occurrence of these paroxysms, but the underlying mechanisms are poorly understood. Normal ion channels are crucial for coordinating neuronal firing in response to facilitatory input. Thus, we hypothesized that channel dysfunction in episodic ataxia type 2 and familial hemiplegic migraine may impair the ability to adjust cerebral excitability after facilitatory events. We tested this hypothesis in patients with episodic ataxia type 2 (n = 6), patients with familial hemiplegic migraine (n = 7) and healthy controls (n = 13). All subjects received a high-frequency burst (10 pulses at 20 Hz) of transcranial magnetic stimulation to transiently increase the excitability of the motor cortex. Acute burst-induced excitability changes were probed at 50, 250, 500 and 1000 ms after the end of the burst. This was done using single-pulse transcranial magnetic stimulation to assess corticospinal excitability, and paired-pulse transcranial magnetic stimulation at an interstimulus interval of 2 and 10 ms to assess intracortical inhibition and facilitation, respectively. The time course of burst-induced excitability changes differed between groups. Healthy controls showed a short-lived increase in excitability that was only present 50 ms after the burst. In contrast, patients with episodic ataxia type 2 showed an abnormally prolonged increase in corticospinal excitability that was still present 250 ms after the transcranial magnetic stimulation burst. Furthermore, while controls showed a decrease in intracortical facilitation during the 1 s period following the transcranial magnetic stimulation burst, patients with episodic ataxia type 2 had increased intracortical facilitation 1000 ms after the burst

  19. Dynamic culture improves cell reprogramming efficiency.

    Science.gov (United States)

    Sia, Junren; Sun, Raymond; Chu, Julia; Li, Song

    2016-06-01

    Cell reprogramming to pluripotency is an inefficient process and various approaches have been devised to improve the yield of induced pluripotent stem cells. However, the effect of biophysical factors on cell reprogramming is not well understood. Here we showed that, for the first time, dynamic culture with orbital shaking significantly improved the reprogramming efficiency in adherent cells. Manipulating the viscosity of the culture medium suggested that the improved efficiency is mainly attributed to convective mixing rather than hydrodynamic shear stress. Temporal studies demonstrated that the enhancement of reprogramming efficiency required the dynamic culture in the middle but not early phase. In the early phase, fibroblasts had a high proliferation rate, but as the culture became over-confluent in the middle phase, expression of p57 was upregulated to inhibit cell proliferation and consequently, cell reprogramming. Subjecting the over confluent culture to orbital shaking prevented the upregulation of p57, thus improving reprogramming efficiency. Seeding cells at low densities to avoid over-confluency resulted in a lower efficiency, and optimal reprogramming efficiency was attained at a high seeding density with dynamic culture. Our findings provide insight into the underlying mechanisms of how dynamic culture condition regulate cell reprogramming, and will have broad impact on cell engineering for regenerative medicine and disease modeling.

  20. Excited-state dynamics of dGMP measured by steady-state and femtosecond fluorescence spectroscopy.

    Science.gov (United States)

    Miannay, Francois-Alexandre; Gustavsson, Thomas; Banyasz, Akos; Markovitsi, Dimitra

    2010-03-11

    The room-temperature fluorescence of 2'-deoxyguanosine 5'-monophosphate (dGMP) in aqueous solution is studied by steady-state and time-resolved fluorescence spectroscopy. The steady-state fluorescence spectrum of dGMP shows one band centered at 334 nm but has an extraordinary long red tail, extending beyond 700 nm. Both the fluorescence quantum yield and the relative weight of the 334 nm peak increase with the excitation wavelength. The initial fluorescence anisotropy after excitation at 267 nm is lower than 0.2 for all emission wavelengths, indicating an ultrafast S(2) --> S(1) internal conversion. The fluorescence decays depend strongly on the emission wavelength, getting longer with the wavelength. A rise time of 100-150 fs was observed for wavelengths longer than 450 nm, in accordance with a gradual red shift of the time-resolved spectra. The results are discussed in terms of a relaxation occurring mainly on the lowest excited (1)pi pi*-state surface toward a conical intersection with the ground state, in line with recent theoretical predictions. Our results show that the excited-state population undergoes a substantial "spreading out" before reaching the CI, explaining the complex dynamics observed.

  1. The dynamics and spectral characteristics of the GPS TEC wave packets excited by the solar terminator

    Science.gov (United States)

    Afraimovich, E. L.; Edemsky, I. K.; Voeykov, S. V.; Yasukevich, Y. V.; Zhivetiev, I. V.

    2009-04-01

    The great variety of solar terminator (ST) -linked phenomena in the atmosphere gave rise to a num¬ber of studies on the analysis of ionosphere parameter variations obtained by different ionosphere sounding methods. Main part of experimental data was obtained using methods for analyzing the spectrum of ionosphere parameter variations in separate local points. To identify ST-generated wave disturbances it is necessary to measure the dynamic and spectral characteristics of the wave disturbances and to compare it with spatial-temporal characteristics of ST. Using TEC measurements from the dense network of GPS sites GEONET (Japan), we have obtained the first GPS-TEC image of the space structure of medium-scale traveling wave packets (MS TWP) excited by the solar terminator. We use two known forms of the 2D GPS-TEC image for our presentation of the space structure of ST-generated MS TWP: 1) - the diagram "distance-time"; 2) - the 2D-space distribution of the values of filtered TEC series dI (λ, φ, t) on the latitude φ and longitude λ for each 30-sec TEC counts. We found that the time period and wave-length of ST-generated wave packets are about 10-20 min and 200-300 km, respectively. Dynamic images analysis of dI (λ, φ, t) gives precise estimation of velocity and azimuth of TWP wave front propagation. We use the method of determining velocity of traveling ionosphere disturbances (SADM-GPS), which take into account the relative moving of subionosphere points. We found that the velocity of the TWP phase front, traveling along GEONET sites, varies in accordance with the velocity of the ST line displacement. The space image of MS TWP manifests itself in pronounced anisotropy and high coherence over a long distance of about 2000 km. The TWP wave front extends along the ST line with the angular shift of about 20°. The hypothesis on the connection between the TWP generation and the solar terminator can be tested in the terminator local time (TLT) system: d

  2. Application of liposome-encapsulated ceramic phoshpors for cancer cell imaging under near infrared excitation

    Energy Technology Data Exchange (ETDEWEB)

    Akiyama, Hirotada; Otsuka, Hiroko; Tashiro, Fumio [Department of Biological Science and Technology, Tokyo University of Science (Japan); Tokuzen, Kimikazu; Soga, Kohei, E-mail: hakiyama@rs.noda.tus.ac.j [Polyscale Technology Research Center, Tokyo University of Science (Japan)

    2010-06-01

    Bioimaging with fluorescent probes is used as an invaluable tool in a biomedical field both in vivo and in vitro. However, organic dyes have some problems such as photo-breaching and cytotoxicity due to short wavelength with high quantum energy. Recently, a new approach using rare-earth-doped ceramic nanophosphors (RED-CNP) shows that fluorescence from RED-CNP in both visible (upconversion) and near infrared (NIR) wavelength region under NIR excitation is available for bioimaging. In order to efficiently introduce the RED-CNP into cancer cells, in this study we have developed a lipid nano-particles of liposome-encapsulated erbium (Er) ion-doped Y{sub 2}O{sub 3} (lipo-Y{sub 2}O{sub 3}). Cationic lipo-Y{sub 2}O{sub 3} could clearly visualize the intracellular region of human hepatocellular carcinoma Huh-7 cells by a fluorescence microscope measurements equipped with near-infrared excitation source scanning. The results imply that the lipo-Y{sub 2}O{sub 3} would potentially be useful material for imaging of cancer cells. The embedded Y{sub 2}O{sub 3} in the liposome having cancer-specific ligands and/or antibodies on its surface should have a great potential for cancer cell imaging in general in living subjects.

  3. Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

    Energy Technology Data Exchange (ETDEWEB)

    Chu, P.M.Y.

    1991-10-01

    The vibrational to translational (V{yields}T) energy transfer in collisions between large highly vibrationally excited polyatomics and rare gases was investigated by time-of-flight techniques. Two different methods, UV excitation followed by intemal conversion and infrared multiphoton excitation (IRMPE), were used to form vibrationally excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively. The product translational energy was found to be independent of the vibrational excitation. These results indicate that the probability distribution function for V{yields}T energy transfer is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases most likely occurs through a rotationally mediated process. Photodissociation of nitrobenzene in a molecular beam was studied at 266 nm. Two primary dissociation channels were identified including simple bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy radical. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Secondary dissociation of the phenoxy radicals to carbon monoxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. A supersonic methyl radical beam source is developed. The beam source configuration and conditions were optimized for CH{sub 3} production from the thermal decomposition of azomethane. Elastic scattering of methyl radical and neon was used to differentiate between the methyl radicals and the residual azomethane in the molecular beam.

  4. Pressure-induced emergence of unusually high-frequency transverse excitations in a liquid alkali metal: Evidence of two types of collective excitations contributing to the transverse dynamics at high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Bryk, Taras [Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Street, UA-79011 Lviv (Ukraine); Lviv Polytechnic National University, 12 S. Bandera Street, UA-79013 Lviv (Ukraine); Ruocco, G. [Dipartimento di Fisica, Universita di Roma La Sapienza, 5 Piazzale Aldo Moro, I-00185 Roma (Italy); Center for Life Nano Science @Sapienza, Istituto Italiano di Tecnologia, 295 Viale Regina Elena, I-00161 Roma (Italy); Scopigno, T. [Dipartimento di Fisica, Universita di Roma La Sapienza, 5 Piazzale Aldo Moro, I-00185 Roma (Italy); IPCF-CNR, c/o Universita di Roma La Sapienza, 5 Piazzale Aldo Moro, I-00185 Roma (Italy); Seitsonen, Ari P. [Département de Chimie, Université de Zurich, Winterthurerstrasse 190, CH-8057 Zürich (Switzerland); Département de Chimie, École Normale Supérieure, 24 rue Lhomond, F-75005 Paris (France)

    2015-09-14

    Unlike phonons in crystals, the collective excitations in liquids cannot be treated as propagation of harmonic displacements of atoms around stable local energy minima. The viscoelasticity of liquids, reflected in transition from the adiabatic to elastic high-frequency speed of sound and in absence of the long-wavelength transverse excitations, results in dispersions of longitudinal (L) and transverse (T) collective excitations essentially different from the typical phonon ones. Practically, nothing is known about the effect of high pressure on the dispersion of collective excitations in liquids, which causes strong changes in liquid structure. Here dispersions of L and T collective excitations in liquid Li in the range of pressures up to 186 GPa were studied by ab initio simulations. Two methodologies for dispersion calculations were used: direct estimation from the peak positions of the L/T current spectral functions and simulation-based calculations of wavenumber-dependent collective eigenmodes. It is found that at ambient pressure, the longitudinal and transverse dynamics are well separated, while at high pressures, the transverse current spectral functions, density of vibrational states, and dispersions of collective excitations yield evidence of two types of propagating modes that contribute strongly to transverse dynamics. Emergence of the unusually high-frequency transverse modes gives evidence of the breakdown of a regular viscoelastic theory of transverse dynamics, which is based on coupling of a single transverse propagating mode with shear relaxation. The explanation of the observed high-frequency shift above the viscoelastic value is given by the presence of another branch of collective excitations. With the pressure increasing, coupling between the two types of collective excitations is rationalized within a proposed extended viscoelastic model of transverse dynamics.

  5. Dynamical Adaptation in Terrorist Cells/Networks

    DEFF Research Database (Denmark)

    Hussain, Dil Muhammad Akbar; Ahmed, Zaki

    2010-01-01

    Typical terrorist cells/networks have dynamical structure as they evolve or adapt to changes which may occur due to capturing or killing of a member of the cell/network. Analytical measures in graph theory like degree centrality, betweenness and closeness centralities are very common and have long...

  6. Sorting cells by their dynamical properties

    Science.gov (United States)

    Henry, Ewan; Holm, Stefan H.; Zhang, Zunmin; Beech, Jason P.; Tegenfeldt, Jonas O.; Fedosov, Dmitry A.; Gompper, Gerhard

    2016-10-01

    Recent advances in cell sorting aim at the development of novel methods that are sensitive to various mechanical properties of cells. Microfluidic technologies have a great potential for cell sorting; however, the design of many micro-devices is based on theories developed for rigid spherical particles with size as a separation parameter. Clearly, most bioparticles are non-spherical and deformable and therefore exhibit a much more intricate behavior in fluid flow than rigid spheres. Here, we demonstrate the use of cells’ mechanical and dynamical properties as biomarkers for separation by employing a combination of mesoscale hydrodynamic simulations and microfluidic experiments. The dynamic behavior of red blood cells (RBCs) within deterministic lateral displacement (DLD) devices is investigated for different device geometries and viscosity contrasts between the intra-cellular fluid and suspending medium. We find that the viscosity contrast and associated cell dynamics clearly determine the RBC trajectory through a DLD device. Simulation results compare well to experiments and provide new insights into the physical mechanisms which govern the sorting of non-spherical and deformable cells in DLD devices. Finally, we discuss the implications of cell dynamics for sorting schemes based on properties other than cell size, such as mechanics and morphology.

  7. Nonlinear dynamics and bifurcation characteristics of shape memory alloy thin films subjected to in-plane stochastic excitation

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Zhi-Wen [Department of Mechanics, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072 (China); Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control 92 Weijin Road, Nankai District, Tianjin 300072 (China); Zhang, Qing-Xin [Department of Mechanics, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072 (China); Xu, Jia, E-mail: xujia_ld@163.com [Department of Mechanics, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072 (China)

    2014-11-03

    A kind of shape memory alloy (SMA) hysteretic nonlinear model was developed, and the nonlinear dynamics and bifurcation characteristics of the SMA thin film subjected to in-plane stochastic excitation were investigated. Van der Pol difference item was introduced to describe the hysteretic phenomena of the SMA strain–stress curves, and the nonlinear dynamic model of the SMA thin film subjected to in-plane stochastic excitation was developed. The conditions of global stochastic stability of the system were determined in singular boundary theory, and the probability density function of the system response was obtained. Finally, the conditions of stochastic Hopf bifurcation were analyzed. The results of theoretical analysis and numerical simulation indicate that self-excited vibration is induced by the hysteretic nonlinear characteristics of SMA, and stochastic Hopf bifurcation appears when the bifurcation parameter was changed; there are two limit cycles in the stationary probability density of the dynamic response of the system in some cases, which means that there are two vibration amplitudes whose probabilities are both very high, and jumping phenomena between the two vibration amplitudes appear with the change in conditions. The results obtained in this current paper are helpful for the application of the SMA thin film in stochastic vibration fields. - Highlights: • Hysteretic nonlinear model of shape memory alloy was developed. • Van der Pol item was introduced to interpret hysteretic strain–stress curves. • Nonlinear dynamic characteristics of the shape memory alloy film were analyzed. • Jumping phenomena were observed in the change of the parameters.

  8. Dynamical quorum sensing and synchronization in collections of excitable and oscillatory catalytic particles

    Science.gov (United States)

    Tinsley, M. R.; Taylor, A. F.; Huang, Z.; Wang, F.; Showalter, K.

    2010-06-01

    We present experimental studies of interacting excitable and oscillatory catalytic particles in well-stirred and spatially distributed systems. A number of distinct paths to synchronized oscillatory behavior are described. We present an example of a Kuramoto type transition in a well-stirred system with a collective rhythm emerging on increasing the number density of oscillatory particles. Groups of spatially distributed oscillatory particles become entrained to a common frequency by organizing centers. Quorum sensing type transitions are found in populations of globally and locally coupled excitable particles, with a sharp transition from steady state to fully synchronized behavior at a critical density or group size.

  9. Probing excited states dynamics in CO cations using few-cycle IR and EUV laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Alnaser, A S [Department of Physics, American University in Sharjah, Sharjah (United Arab Emirates); Bocharova, I; Singh, K P; Wei, C; Cocke, C L; Litvinyuk, I V [J. R. Macdonald Laboratory, Physics Department, Kansas State University (United States); Kling, M, E-mail: aalnaser@aus.ed [Max-Planck Institute for Quantum Optics, Garching (Germany)

    2009-11-01

    We have used few-cycle IR and EUV laser pulses in pump-probe arrangement to trace out the dissociation pathways in CO when exploded by strong laser fields. We present two preliminary sets of data of different pump pulses. In these sets, different excited state of CO cations are populated using (< 10 fs) IR, and EUV pulses respectively. We followed the time evolution of these states using the time-resolved Coulomb explosion imaging technique. We compare the time evolution of IR- and EUV-induced excited states by measuring the KER of the fragment ions as a function of the time delay between the pump and the IR probe pulse.

  10. High-energy magnetic excitations from dynamic stripes in LBCO (x=1/8)

    OpenAIRE

    Xu, Guangyong; Tranquada, J. M.; Perring, T. G.; Gu, G. D.; Fujita, M.; Yamada, K.

    2007-01-01

    We use inelastic neutron scattering to study the temperature dependence of magnetic excitations (for energies up to 100 meV) in the cuprate La$_{1.875}$Ba$_{0.125}$CuO$_4$. This compound exhibits stripe order below a temperature of ~50 K; previous measurements have shown that the magnetic excitations of the stripe-ordered phase have an hour-glass-like dispersion, with a saddle point at ~50 meV. Here we compare measurements in the disordered phase taken at 65 and 300 K. At energies on the scal...

  11. Excited state dynamics of Kr N clusters probed with time- and energy-resolved photoluminescence methods

    Science.gov (United States)

    Karnbach, R.; Castex, M. C.; Keto, J. W.; Joppien, M.; Wörmer, J.; Zimmerer, G.; Möller, T.

    1993-02-01

    Excitation and decay processes in Kr N clusters ( N=2-10 4) were investigated via time- and energy-resolved fluorescence methods with synchrotron radiation excitation. In small clusters ( N<50) in addition to the well-known emission bands of condensed Kr another broad continuous emission is observed. It is assigned to a radiative decay of Kr excimers desorbing from the cluster surface. There are indications that the cluster size where the desorption rate becomes slow is related to a change in sign of the electron affinity of the cluster. Changes of spectral distribution of the fluorescence light with cluster size are interpreted as variations of the vibrational energy flow.

  12. Ultrafast excited state dynamics of Pt(II) chromophores bearing multiple infrared absorbers.

    Science.gov (United States)

    Glik, Elena A; Kinayyigit, Solen; Ronayne, Kate L; Towrie, Michael; Sazanovich, Igor V; Weinstein, Julia A; Castellano, Felix N

    2008-08-04

    The paper reports the synthesis, structural characterization, electrochemistry, ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopy associated with two independent d (8) square planar Pt(II) diimine chromophores, Pt(dnpebpy)Cl 2 ( 1) and Pt(dnpebpy)(C[triple bond]Cnaph) 2 ( 2), where dnpebpy = 4,4'-(CO 2CH 2- (t) Bu) 2-2,2'-bipyridine and CCnaph = naphthylacetylide. The neopentyl ester substitutions provided markedly improved complex solubility relative to the corresponding ethyl ester which facilitates synthetic elaboration as well as spectroscopic investigations. Following 400 nm pulsed laser excitation in CH 2Cl 2, the 23 cm (-1) red shift in the nu C=O vibrations in 1 are representative of a complex displaying a lowest charge-transfer-to-diimine (CT) excited state. The decay kinetics in 1 are composed of two time constants assigned to vibrational cooling of the (3)CT excited-state concomitant with its decay to the ground state (tau = 2.2 +/- 0.4 ps), and to cooling of the formed vibrationally hot ground electronic state (tau = 15.5 +/- 4.0 ps); we note that an assignment of the latter to a ligand field state cannot be excluded. Ultrafast TA data quantitatively support these assignments yielding an excited-state lifetime of 2.7 +/- 0.4 ps for the (3)CT excited-state of 1 and could not detect any longer-lived species. The primary intention of this study was to develop a Pt (II) complex ( 2) bearing dual infrared spectroscopic tags (C[triple bond]C attached to the metal and CO (ester) attached to the diimine ligand) to independently track the movement of charge density in different segments of the molecule following pulsed light excitation. Femtosecond laser excitation of 2 in CH 2Cl 2 at 400 nm simultaneously induces a red-shift in both the nu C=O (-30 cm (-1)) and the nu C[triple bond]C (-61 cm (-1)) vibrations. The TRIR data in 2 are consistent with a charge transfer assignment, and the significant decrease of the energy of the nu

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

    Science.gov (United States)

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

    2016-12-01

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

  14. Evidence that the cortical motor command for the initiation of dynamic plantarflexion consists of excitation followed by inhibition

    DEFF Research Database (Denmark)

    Taube, Wolfgang; Lundbye-Jensen, Jesper; Schubert, Martin;

    2011-01-01

    At the onset of dynamic movements excitation of the motor cortex (M1) is spatially restricted to areas representing the involved muscles whereas adjacent areas are inhibited. The current study elucidates whether the cortical motor command for dynamic contractions is also restricted to a certain...... population of cortical neurons responsible for the fast corticospinal projections. Therefore, corticospinal transmission was assessed with high temporal resolution during dynamic contractions after both, magnetic stimulation over M1 and the brainstem. The high temporal resolution could be obtained...... by conditioning the soleus H-reflex with different interstimulus intervals by cervicomedullary stimulation (CMS-conditioning) and transcranial magnetic stimulation (TMS) of M1 (M1-conditioning). This technique provides a precise time course of facilitation and inhibition. CMS- and M1-conditioning produced...

  15. Neural Network Identification and Control of a Parametrically Excited Structural Dynamic Model of an F-15 Tail Section

    Directory of Open Access Journals (Sweden)

    Ayman A. El-Badawy

    2000-01-01

    Full Text Available We investigated the design of a neural-network-based adaptive control system for a smart structural dynamic model of the twin tails of an F-15 tail section. A neural network controller was developed and tested in computer simulation for active vibration suppression of the model subjected to parametric excitation. First, an emulator neural network was trained to represent the structure to be controlled and thus used in predicting the future responses of the model. Second, a neurocontroller to determine the necessary control action on the structure was developed. The control was implemented through the application of a smart material actuator. A strain gauge sensor was assumed to be on each tail. Results from computer-simulation studies have shown great promise for control of the vibration of the twin tails under parametric excitation using artificial neural networks.

  16. Excited-state quantum phase transitions in many-body systems with infinite-range interaction: Localization, dynamics, and bifurcation

    Science.gov (United States)

    Santos, Lea F.; Távora, Marco; Pérez-Bernal, Francisco

    2016-07-01

    Excited-state quantum phase transitions (ESQPTs) are generalizations of quantum phase transitions to excited levels. They are associated with local divergences in the density of states. Here, we investigate how the presence of an ESQPT can be detected from the analysis of the structure of the Hamiltonian matrix, the level of localization of the eigenstates, the onset of bifurcation, and the speed of the system evolution. Our findings are illustrated for a Hamiltonian with infinite-range Ising interaction in a transverse field. This is a version of the Lipkin-Meshkov-Glick (LMG) model and the limiting case of the one-dimensional spin-1/2 system with tunable interactions realized with ion traps. From our studies for the dynamics, we uncover similarities between the LMG and the noninteracting XX models.

  17. Sensitivity Analysis of Centralized Dynamic Cell Selection

    DEFF Research Database (Denmark)

    Lopez, Victor Fernandez; Alvarez, Beatriz Soret; Pedersen, Klaus I.;

    2016-01-01

    mechanism and solutions involving cell switching in general. Simulation results show that such solutions can greatly benefit from the use of receivers with interference suppression capabilities and a larger number of antennas, with a maximum data rate gain of 120%. High performance gains are observed...... with two different traffic models, and it is not necessary to be able to connect to a large number of cells in order to reap most of the benefits of the centralized dynamic cell selection....

  18. Structure and dynamics of metalloproteins in live cells.

    Science.gov (United States)

    Cook, Jeremy D; Penner-Hahn, James E; Stemmler, Timothy L

    2008-01-01

    X-ray absorption spectroscopy (XAS) has emerged as one of the premier tools for investigating the structure and dynamic properties of metals in cells and in metal containing biomolecules. Utilizing the high flux and broad energy range of X-rays supplied by synchrotron light sources, one can selectively excite core electronic transitions in each metal. Spectroscopic signals from these electronic transitions can be used to dissect the chemical architecture of metals in cells, in cellular components, and in biomolecules at varying degrees of structural resolution. With the development of ever-brighter X-ray sources, X-ray methods have grown into applications that can be utilized to provide both a cellular image of the relative distribution of metals throughout the cell as well as a high-resolution picture of the structure of the metal. As these techniques continue to grow in their capabilities and ease of use, so too does the demand for their application by chemists and biochemists interested in studying the structure and dynamics of metals in cells, in cellular organelles, and in metalloproteins.

  19. Fuel Cell Manufacturing Diagnostic Techniques: IR Thermography with Reactive Flow through Excitation

    Energy Technology Data Exchange (ETDEWEB)

    Manak, A. J.; Ulsh, M.; Bender, G.

    2012-01-01

    While design and material considerations for PEMFCs have a large impact on cost, it is also necessary to consider a transition to high volume production of fuel cell systems, including MEA components, to enable economies of scale and reduce per unit cost. One of the critical manufacturing tasks is developing and deploying techniques to provide in‐process measurement of fuel cell components for quality control. This effort requires a subsidiary task: The study of the effect of manufacturing defects on performance and durability with the objective to establish validated manufacturing tolerances for fuel cell components. This work focuses on the development of a potential quality control method for gas diffusion electrodes (GDEs). The method consists of infrared (IR) thermography combined with reactive flow through (RFT) excitation. Detection of catalyst loading reduction defects in GDE catalyst layers will be presented.

  20. Excitation-contraction coupling of human induced pluripotent stem cell-derived cardiomyocytes

    Directory of Open Access Journals (Sweden)

    Christopher eKane

    2015-09-01

    Full Text Available Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs hold enormous potential in many fields of cardiovascular research. Overcoming many of the limitations of their embryonic counterparts, the application of iPSC-CMs ranges from facilitating investigation of familial cardiac disease and pharmacological toxicity screening to personalized medicine and autologous cardiac cell therapies. The main factor preventing the full realization of this potential is the limited maturity of iPSC-CMs, which display a number of substantial differences in comparison to adult cardiomyocytes. Excitation-contraction coupling, a fundamental property of cardiomyocytes, is often described in iPSC-CMs as being more analogous to neonatal than adult cardiomyocytes. With calcium handling linked, directly or indirectly, to almost all other properties of cardiomyocytes, a solid understanding of this process will be crucial to fully realizing the potential of this technology.Here we discuss the implications of differences in excitation-contraction coupling when considering the potential applications of iPSC-CMs in a number of areas as well as detailing the current understanding of this fundamental process in these cells.

  1. The dynamic regulation of cortical excitability is altered in episodic ataxia type 2.

    NARCIS (Netherlands)

    Helmich, R.C.G.; Siebner, H.R.; Giffin, N.; Bestmann, S.; Rothwell, J.C.; Bloem, B.R.

    2010-01-01

    Episodic ataxia type 2 and familial hemiplegic migraine are two rare hereditary disorders that are linked to dysfunctional ion channels and are characterized clinically by paroxysmal neurological symptoms. Impaired regulation of cerebral excitability is thought to play a role in the occurrence of th

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

    Energy Technology Data Exchange (ETDEWEB)

    Ouyang, Bing, E-mail: ouyangbing.zj@foxmail.com; Xue, Jia-Dan, E-mail: jenniexue@126.com; Zheng, Xuming, E-mail: zhengxuming126@126.com, E-mail: zxm@zstu.edu.cn, E-mail: fangwh@dnu.edu.cn [Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018 (China); Fang, Wei-Hai, E-mail: zxm@zstu.edu.cn, E-mail: fangwh@dnu.edu.cn, E-mail: fangwh@dnu.edu.cn [Department of Chemistry, Beijing Normal University, Beijing 100875 (China)

    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.

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

    Science.gov (United States)

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

    2014-05-21

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

  4. Standing-wave-excited multiplanar fluorescence in a laser scanning microscope reveals 3D information on red blood cells

    CERN Document Server

    Amor, Rumelo; Amos, William Bradshaw; McConnell, Gail

    2014-01-01

    Standing-wave excitation of fluorescence is highly desirable in optical microscopy because it improves the axial resolution. We demonstrate here that multiplanar excitation of fluorescence by a standing wave can be produced in a single-spot laser scanning microscope by placing a plane reflector close to the specimen. We report that the relative intensities in each plane of excitation depend on the Stokes shift of the fluorochrome. We show by the use of dyes specific for the cell membrane how standing-wave excitation can be exploited to generate precise contour maps of the surface membrane of red blood cells, with an axial resolution of ~90 nm. The method, which requires only the addition of a plane mirror to an existing confocal laser scanning microscope, may well prove useful in studying diseases which involve the red cell membrane, such as malaria.

  5. The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

    Science.gov (United States)

    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

  6. Non-linear dynamic characteristics and optimal control of giant magnetostrictive film subjected to in-plane stochastic excitation

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Z. W., E-mail: zhuzhiwen@tju.edu.cn [Department of Mechanics, Tianjin University, 300072, Tianjin (China); Tianjin Key Laboratory of Non-linear Dynamics and Chaos Control, 300072, Tianjin (China); Zhang, W. D., E-mail: zhangwenditju@126.com; Xu, J., E-mail: xujia-ld@163.com [Department of Mechanics, Tianjin University, 300072, Tianjin (China)

    2014-03-15

    The non-linear dynamic characteristics and optimal control of a giant magnetostrictive film (GMF) subjected to in-plane stochastic excitation were studied. Non-linear differential items were introduced to interpret the hysteretic phenomena of the GMF, and the non-linear dynamic model of the GMF subjected to in-plane stochastic excitation was developed. The stochastic stability was analysed, and the probability density function was obtained. The condition of stochastic Hopf bifurcation and noise-induced chaotic response were determined, and the fractal boundary of the system's safe basin was provided. The reliability function was solved from the backward Kolmogorov equation, and an optimal control strategy was proposed in the stochastic dynamic programming method. Numerical simulation shows that the system stability varies with the parameters, and stochastic Hopf bifurcation and chaos appear in the process; the area of the safe basin decreases when the noise intensifies, and the boundary of the safe basin becomes fractal; the system reliability improved through stochastic optimal control. Finally, the theoretical and numerical results were proved by experiments. The results are helpful in the engineering applications of GMF.

  7. Non-Geometric Conditional Phase Gate by Quantum Zeno Dynamics in Laser-Excited Nitrogen-Vacancy Centers

    Institute of Scientific and Technical Information of China (English)

    SU Wan-Jun; SHEN Li-Tuo; WU Huai-Zhi; LIN Xiu

    2013-01-01

    Based on the quantum Zeno dynamics,we propose a two-qubit non-geometric conditional phase gate between two nitrogen-vacancy centers coupled to a whispering-gallery mode cavity.The varying phases design of periodic laser can be used for realizing non-geometric conditional phase gate,and the cavity mode is virtually excited during the gate operation.Thus,the fidelity of the gate operation is insensitive to cavity decay and the fluctuation of the preset laser intensity.The numerical simulation with a realistic set of experimental parameters shows that the gate fidelity 0.987 can be within reached in the near future.

  8. Feedback Control and Dynamic Behaviour of Z-Source Converter Fed Separately Excited DC Motor and Centrifugal Pump Set

    Directory of Open Access Journals (Sweden)

    Saswati Swapna Dash

    2014-07-01

    Full Text Available This paper presents an overall study of Feedback Control of Z-Source Converter Fed Separately excited DC motor with centrifugal Pump Set. Z-source converter can be used for both voltage buck and boost mode using LC impedance network. In this paper the dynamic modeling of Z-source with motor load and centrifugal pump set is carried out with new findings. The compensators for speed feedback loop are designed by taking average state space analysis and small signal model of the system. The feedback loop is designed by classical control methods. The experiment is done in MATLAB work environment and the result is verified by Simulation.

  9. A photosynthetic-plasmonic-voltaic cell: Excitation of photosynthetic bacteria and current collection through a plasmonic substrate

    Science.gov (United States)

    Samsonoff, Nathan; Ooms, Matthew D.; Sinton, David

    2014-01-01

    Excitation of photosynthetic biofilms using surface-confined evanescent light fields enables energy dense photobioreactors, while electrode-adhered biofilms can provide electricity directly. Here, we demonstrate concurrent light delivery and electron transport through a plasmonically excited metal film. Biofilms of cyanobacterium Synechococcus bacillaris on 50-nm gold films are excited via the Kretschmann configuration at λ = 670 nm. Cells show light/dark response to plasmonic excitation and grow denser biofilms, closer to the electrode surface, as compared to the direct irradiated case. Directly irradiated biofilms produced average electrical powers of 5.7 μW/m2 and plasmonically excited biofilms produced average electrical powers of 5.8 μW/m2, with individual biofilms producing as much as 12 μW/m2.

  10. A photosynthetic-plasmonic-voltaic cell: Excitation of photosynthetic bacteria and current collection through a plasmonic substrate

    Energy Technology Data Exchange (ETDEWEB)

    Samsonoff, Nathan; Ooms, Matthew D.; Sinton, David [Department of Mechanical and Industrial Engineering, and Institute for Sustainable Energy, University of Toronto, Toronto M5S 3G8 (Canada)

    2014-01-27

    Excitation of photosynthetic biofilms using surface-confined evanescent light fields enables energy dense photobioreactors, while electrode-adhered biofilms can provide electricity directly. Here, we demonstrate concurrent light delivery and electron transport through a plasmonically excited metal film. Biofilms of cyanobacterium Synechococcus bacillaris on 50-nm gold films are excited via the Kretschmann configuration at λ = 670 nm. Cells show light/dark response to plasmonic excitation and grow denser biofilms, closer to the electrode surface, as compared to the direct irradiated case. Directly irradiated biofilms produced average electrical powers of 5.7 μW/m{sup 2} and plasmonically excited biofilms produced average electrical powers of 5.8 μW/m{sup 2}, with individual biofilms producing as much as 12 μW/m{sup 2}.

  11. The fundamental role of localised vibrations in excitation dynamics in photosynthetic light-harvesting systems

    CERN Document Server

    Kolli, Avinash; Scholes, Gregory D; Olaya-Castro, Alexandra

    2012-01-01

    The importance of fast vibrations in enhancing and controlling energy transfer and conversion in biomolecules is an issue of current debate. In this article we show that coupling between localised high-frequency vibrations and electronic degrees of freedom is fundamental for efficient excitation transport in photosynthetic light-harvesting systems with high degree of disorder. We consider the cryptophyte antennae protein phycoerythrin 545 and discuss how the balance between electronic interactions and coupling to fast vibronic modes supports the biological function of these antennae by generating a non-cascaded transport that leads to a rapid, directed and wider spatial distribution of excitation energy across the complex. Furthermore, we illustrate signatures of vibronic influence in the beating of excitonic coherences and show that mechanisms supporting coherent evolution of excitons also assist coupling to selected modes that enhance energy transfer to preferential sites in the complex. We therefore argue ...

  12. Communication: Excited states, dynamic correlation functions and spectral properties from full configuration interaction quantum Monte Carlo.

    Science.gov (United States)

    Booth, George H; Chan, Garnet Kin-Lic

    2012-11-21

    In this communication, we propose a method for obtaining isolated excited states within the full configuration interaction quantum Monte Carlo framework. This method allows for stable sampling with respect to collapse to lower energy states and requires no uncontrolled approximations. In contrast with most previous methods to extract excited state information from quantum Monte Carlo methods, this results from a modification to the underlying propagator, and does not require explicit orthogonalization, analytic continuation, transient estimators, or restriction of the Hilbert space via a trial wavefunction. Furthermore, we show that the propagator can directly yield frequency-domain correlation functions and spectral functions such as the density of states which are difficult to obtain within a traditional quantum Monte Carlo framework. We demonstrate this approach with pilot applications to the neon atom and beryllium dimer.

  13. Development and Implementation of an Ultrafast Vacuum-UV (8eV) Light Source for use in UV-VUV Pump Probe Experiments of Neutral Excited State Dynamics

    Science.gov (United States)

    Liu, Yusong; Horton, Spencer; Matsika, Spiridoula; Weinacht, Thomas

    2016-05-01

    Probing neutral excited state dynamics in polyatomic molecules with ultrafast laser systems enables us to study phenomena such as internal conversion, isomerization, intersystem crossing, and dissociation. Using the third harmonic (260 nm) and the fifth harmonic (156 nm) of our laser system we have developed an apparatus to perform pump-probe experiments for the study neutral excited state dynamics in various polyatomic molecules. The fifth harmonic of our laser system is generated through the four-wave-mixing process of k5 ω = 2k3 ω -kω performed with a non-collinear geometry in an argon gas cell. In several polyatomic molecular systems of interest a photon with 8 eV of energy gives us the unique ability to ionize from essentially anywhere along the excited state potential, but does not produce any ionization yield from the ground state. This enables us to measure excited state lifetimes without the photon energy becoming too low to ionize while the nuclear wave-packet is traveling on the excited state potential. We also have the advantage of working in the perturbative weak-field ionization regime. These experiments can also be directly compare to strong-field ionization experiments conducted with a UV-pump and an IR-probe conducted on the same molecules.

  14. Nonlinear dynamic analysis of atomic force microscopy under deterministic and random excitation

    Energy Technology Data Exchange (ETDEWEB)

    Pishkenari, Hossein Nejat [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Behzad, Mehdi [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)], E-mail: m_behzad@sharif.edu; Meghdari, Ali [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

    2008-08-15

    The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for some of exciting parameters under deterministic vibration. The basin of attraction of two stable solutions is different and dependent on the exciting frequency. From this analysis the range of the frequency which will result in a unique periodic response can be obtained and used in practical experiments. Furthermore the analytical responses determined by perturbation techniques can be used to detect the parameter region where the chaotic motion is avoided. On the other hand for FM-AFM, the relation between frequency shift and the system parameters can be extracted and used for investigation of the system nonlinear behavior. The nonlinear behavior of the oscillating tip can easily explain the observed shift of frequency as a function of tip sample distance. Also in this paper we have investigated the AM-AFM system response under a random excitation. Using two different methods we have obtained the statistical properties of the tip motion. The results show that we can use the mean square value of tip motion to image the sample when the excitation signal is random.

  15. An electromagnetic compressive force by cell exciter stimulates chondrogenic differentiation of bone marrow-derived mesenchymal stem cells.

    Science.gov (United States)

    Park, Sang-Hyug; Sim, Woo Young; Park, Sin Wook; Yang, Sang Sik; Choi, Byung Hyune; Park, So Ra; Park, Kwideok; Min, Byoung-Hyun

    2006-11-01

    In this study, we present a biological micro-electromechanical system and its application to the chondrogenic differentiation of rabbit bone marrow-derived mesenchymal stem cells (MSCs). Actuated by an electromagnetic force, the micro cell exciter was designed to deliver a cyclic compressive load (CCL) with various magnitudes. Two major parts in the system are an actuator and a cartridge-type chamber. The former has a permanent magnet and coil, and the latter is equipped with 7 sample dishes and 7 metal caps. Mixed with a 2.4% alginate solution, the alginate/MSC layers were positioned in the sample dishes; the caps contained chondrogenic defined medium without transforming growth factor-beta (TGF-beta). Once powered, the actuator coil-derived electromagnetic force pulled the metal caps down, compressing the samples. The cyclic load was given at 1-Hz frequency for 10 min twice a day. Samples in the dishes without a cap served as a control. The samples were analyzed at 3, 5, and 7 days after stimulation for cell viability, biochemical assays, histologic features, immunohistochemistry, and gene expression of the chondrogenic markers. Applied to the alginate/MSC layer, the CCL system enhanced the synthesis of cartilage-specific matrix proteins and the chondrogenic markers, such as aggrecan, type II collagen, and Sox9. We found that the micromechanically exerted CCL by the cell exciter was very effective in enhancing the chondrogenic differentiation of MSCs, even without using exogenous TGF-beta.

  16. Electronic Structure and Excited-State Dynamics of an Arduengo-Type Carbene and its Imidazolone Oxidation Product.

    Science.gov (United States)

    Schmitt, Hans-Christian; Flock, Marco; Welz, Eileen; Engels, Bernd; Schneider, Heidi; Radius, Udo; Fischer, Ingo

    2017-03-02

    We describe an investigation of the excited-state dynamics of isolated 1,3-di-tert-butyl-imidazoline-2-ylidene (tBu2 Im, C11 H20 N2 , m/z=180), an Arduengo-type carbene, by time- and frequency-resolved photoionization using a picosecond laser system. The energies of several singlet and triplet excited states were calculated by time-dependent density functional theory (TD-DFT). The S1 state of the carbene deactivates on a 100 ps time scale possibly by intersystem crossing. In the experiments we observed an additional signal at m/z=196, that was assigned to the oxidation product 1,3-di-tert-butyl-imidazolone, tBu2 ImO. It shows a well-resolved resonance-enhanced multiphoton ionization (REMPI) spectrum with an origin located at 36951 cm(-1) . Several low-lying vibrational bands could be assigned, with a lifetime that depends strongly on the excitation energy. At the origin the lifetime is longer than 3 ns, but drops to 49 ps at higher excess energies. To confirm formation of the imidazolone we also performed experiments on benzimidazolone (BzImO) for comparison. Apart from a redshift for BzImO the spectra of the two compounds are very similar. The TD-DFT values display a very good agreement with the experimental data.

  17. High Excitation Transfer Efficiency from Energy Relay Dyes in Dye-Sensitized Solar Cells

    KAUST Repository

    Hardin, Brian E.

    2010-08-11

    The energy relay dye, 4-(Dicyanomethylene)-2-methyl-6-(4- dimethylaminostyryl)-4H-pyran (DCM), was used with a near-infrared sensitizing dye, TT1, to increase the overall power conversion efficiency of a dye-sensitized solar cell (DSC) from 3.5% to 4.5%. The unattached DCM dyes exhibit an average excitation transfer efficiency (EÌ?TE) of 96% inside TT1-covered, mesostructured TiO2 films. Further performance increases were limited by the solubility of DCM in an acetonitrile based electrolyte. This demonstration shows that energy relay dyes can be efficiently implemented in optimized dye-sensitized solar cells, but also highlights the need to design highly soluble energy relay dyes with high molar extinction coefficients. © 2010 American Chemical Society.

  18. Dynamical parametric instability of carbon nanotubes under axial harmonic excitation by nonlocal continuum theory

    Science.gov (United States)

    Wang, Yi-Ze; Li, Feng-Ming

    2016-08-01

    Structures under parametric load can be induced to the parametric instability in which the excitation frequency is located the instability region. In the present work, the parametric instability of double-walled carbon nanotubes is studied. The axial harmonic excitation is considered and the nonlocal continuum theory is applied. The critical equation is derived as the Mathieu form by the Galerkin's theory and the instability condition is presented with the Bolotin's method. Numerical calculations are performed and it can be seen that the van der Waals interaction can enhance the stability of double-walled nanotubes under the parametric excitation. The parametric instability becomes more obvious with the matrix stiffness decreasing and small scale coefficient increasing. The parametric instability is going to be more significant for higher mode numbers. For the nanosystem with the soft matrix and higher mode number, the small scale coefficient and the ratio of the length to the diameter have obvious influences on the starting point of the instability region.

  19. Charge state dynamics of the nitrogen vacancy center in diamond under near-infrared excitation

    Science.gov (United States)

    Ji, Peng; Dutt, M. V. Gurudev

    2016-05-01

    The negatively charged NV defect center (NV-) in diamond has become prominent for applications in quantum information, nanoscale magnetic and electric field sensing, and fluorescent biological markers. Switching between NV- and neutral charge states (NV0) have been extensively studied and modeled using exciting laser wavelengths that are shorter than the NV- zero-phonon line (ZPL), and typically result in decreased fluorescence from the NV- state. In this work, we report on the experimental observation that NV0 converts to NV- under excitation with near-infrared (1064 nm) light, resulting in increased fluorescence from the NV- state. We have observed this effect in both ensembles of NVs in bulk diamond, and in diamond nanocrystals, and find that it is robust both at room and low temperature. We carried out microwave and two-color excitation combined with spectral and time-resolved experimental studies. We used rate-equation modeling and find evidence for competition between one-photon and two-photon processes for hole and electron ionization. This finding may help elucidate the study of the NV energy level structure, and impact recently emerging research in single-shot measurement of the NV- spin state via spin-to-charge conversion.

  20. Ultrafast Excited State Dynamics in Molecular Motors: Coupling of Motor Length to Medium Viscosity.

    Science.gov (United States)

    Conyard, Jamie; Stacko, Peter; Chen, Jiawen; McDonagh, Sophie; Hall, Christopher R; Laptenok, Sergey P; Browne, Wesley R; Feringa, Ben L; Meech, Stephen R

    2017-03-07

    Photochemically driven molecular motors convert the energy of incident radiation to intramolecular rotational motion. The motor molecules considered here execute four step unidirectional rotational motion. This comprises a pair of successive light induced isomerizations to a metastable state followed by thermal helix inversions. The internal rotation of a large molecular unit required in these steps is expected to be sensitive to both the viscosity of the medium and the volume of the rotating unit. In this work, we describe a study of motor motion in both ground and excited states as a function of the size of the rotating units. The excited state decay is ultrafast, highly non-single exponential, and is best described by a sum of three exponential relaxation components. The average excited state decay time observed for a series of motors with substituents of increasing volume was determined. While substitution does affect the lifetime, the size of the substituent has only a minor effect. The solvent polarity dependence is also slight, but there is a significant solvent viscosity effect. Increasing the viscosity has no effect on the fastest of the three decay components, but it does lengthen the two slower decay times, consistent with them being associated with motion along an intramolecular coordinate displacing a large solvent volume. However, these slower relaxation times are again not a function of the size of the substituent. We conclude that excited state decay arises from motion along a coordinate which does not necessarily require complete rotation of the substituents through the solvent, but is instead more localized in the core structure of the motor. The decay of the metastable state to the ground state through a helix inversion occurs 14 orders of magnitude more slowly than the excited state decay, and was measured as a function of substituent size, solvent viscosity and temperature. In this case neither substituent size nor solvent viscosity influences

  1. Nonlinear dynamics of cell orientation

    Science.gov (United States)

    Safran, S. A.; de, Rumi

    2009-12-01

    The nonlinear dependence of cellular orientation on an external, time-varying stress field determines the distribution of orientations in the presence of noise and the characteristic time, τc , for the cell to reach its steady-state orientation. The short, local cytoskeletal relaxation time distinguishes between high-frequency (nearly perpendicular) and low-frequency (random or parallel) orientations. However, τc is determined by the much longer, orientational relaxation time. This behavior is related to experiments for which we predict the angle and characteristic time as a function of frequency.

  2. Dynamic nuclear spin polarization in the resonant laser excitation of an InGaAs quantum dot.

    Science.gov (United States)

    Högele, A; Kroner, M; Latta, C; Claassen, M; Carusotto, I; Bulutay, C; Imamoglu, A

    2012-05-11

    Resonant optical excitation of lowest-energy excitonic transitions in self-assembled quantum dots leads to nuclear spin polarization that is qualitatively different from the well-known optical orientation phenomena. By carrying out a comprehensive set of experiments, we demonstrate that nuclear spin polarization manifests itself in quantum dots subjected to finite external magnetic field as locking of the higher energy Zeeman transition to the driving laser field, as well as the avoidance of the resonance condition for the lower energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear spin polarization originating from noncollinear hyperfine interaction and find excellent agreement between experiment and theory. Our results provide evidence for the significance of noncollinear hyperfine processes not only for nuclear spin diffusion and decay, but also for buildup dynamics of nuclear spin polarization in a coupled electron-nuclear spin system.

  3. Identification of the nonlinear excitation force acting on a bowed string using the dynamical responses at remote locations

    Energy Technology Data Exchange (ETDEWEB)

    Debut, V.; Antunes, J. [ITN, ADL, P-2686 Sacavem Codex (Portugal); Delaune, X. [CEA Saclay, DEN, DM2S, SEMT, Lab Etud Dynam, F-01101 Gif Sur Yvette (France)

    2010-07-01

    For achieving realistic numerical simulations of bowed string instruments, based on physical modeling, a good understanding of the actual friction interaction phenomena is of great importance. Most work published in the field including our own has assumed that bow/string frictional forces behave according to the classical Coulomb stick-slip model, with an empirical velocity-dependent sliding friction coefficient. Indeed, the basic self-excited string motions (such as the Helmholtz regime) are well captured using such friction model. However, recent work has shown that the tribological behavior of the bow/string rosin interface is rather complex, therefore the basic velocity-dependent Coulomb model may be an over-simplistic representation of the friction force. More specifically, it was suggested that a more accurate model of the interaction force can be achieved by coupling the system dynamical equations with a thermal model which encapsulates the complex interface phenomena. In spite of the interesting work performed by Askenfelt, a direct measurement of the actual dynamical friction forces without disturbing the string motion is quite difficult. Therefore, in this work we develop a modal-based identification technique making use of inverse methods and optimization techniques, which enables the identification of the interface force, as well as the string self-excited motion, from the dynamical reactions measured at the string end supports. The method gives convincing results using simulated data originated from nonlinear computations of a bowed string. Furthermore, in cases where the force identifications are very sensitive to errors in the transfer function modal parameters, we suggest a method to improve the modal frequencies used for the identifications. Preliminary experimental results obtained using a basic bowing device, by which the string is excited with the stick of the bow, are then presented. Our identifications, from the two dynamical string reactions

  4. Molecular-dynamics simulations of the dynamical excitations in commensurate submonolayer films of nitrogen molecules on graphite

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Bruch, Ludwig Walter; Taub, H.

    1996-01-01

    The dynamics of commensurate submonolayer solids of N-2 molecules adsorbed on the basal planes of graphite have been studied using molecular-dynamics simulations. The calculations yielded the temperature dependence of the Brillouin-zone-center gap in the acoustic-phonon branches, for comparison...

  5. Nonlinear excitation kinetics of biased quantum wells. Coherent dynamical screening effect

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Jepsen, Peter Uhd

    2006-01-01

    In this paper we describe a strongly nonlinear process of ultrafast photoexcitation of a biased quantum well. This process is governed by coherent dynamical screening, where the instantaneously polarized photoexcited carriers screen initial bias field. This results in a dynamic modification...

  6. Effect of CH stretching excitation on the reaction dynamics of F + CHD{sub 3} → DF + CHD{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jiayue; Zhang, Dong; Chen, Zhen; Jiang, Bo [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, 457 Zhongshan Road, Dalian, Liaoning 116023 (China); Blauert, Florian [Dynamics at Surfaces, Faculty of Chemistry, Georg-August-Universität Göttingen, 37077 Göttingen (Germany); Dai, Dongxu; Wu, Guorong, E-mail: wugr@dicp.ac.cn, E-mail: xmyang@dicp.ac.cn; Zhang, Donghui; Yang, Xueming, E-mail: wugr@dicp.ac.cn, E-mail: xmyang@dicp.ac.cn [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, 457 Zhongshan Road, Dalian, Liaoning 116023 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2015-07-28

    The vibrationally excited reaction of F + CHD{sub 3}(ν{sub 1} = 1) → DF + CHD{sub 2} at a collision energy of 9.0 kcal/mol is investigated using the crossed-beams and time-sliced velocity map imaging techniques. Detailed and quantitative information of the CH stretching excitation effects on the reactivity and dynamics of the title reaction is extracted with the help of an accurate determination of the fraction of the excited CHD{sub 3} reagent in the crossed-beam region. It is found that all vibrational states of the CHD{sub 2} products observed in the ground-state reaction, which mainly involve the excitation of the umbrella mode of the CHD{sub 2} products, are severely suppressed by the CH stretching excitation. However, there are four additional vibrational states of the CHD{sub 2} products appearing in the excited-state reaction which are not presented in the ground-state reaction. These vibrational states either have the CH stretching excitation retained or involve one quantum excitation in the CH stretching and the excitation of the umbrella mode. Including all observed vibrational states, the overall cross section of the excited-state reaction is estimated to be 66.6% of that of the ground-state one. Experimental results also show that when the energy of CH stretching excitation is released during the reaction, it is deposited almost exclusively as the rovibrational energy of the DF products, with little portion in the translational degree of freedom. For vibrational states of the CHD{sub 2} products observed in both ground- and excited-state reactions, the CH stretching excitation greatly suppresses the forward scattered products, causing a noticeable change in the product angular distributions.

  7. Numerical simulation of magnetospheric ULF waves excited by positive and negative impulses of solar wind dynamic pressure

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The sources of ultra low frequency (ULF) waves in the magnetosphere are generally believed to be either the external solar wind perturbations or the internal plasma instabilities. When a sudden impulse of the solar wind dynamic pressure impinges on the magnetopause, ULF waves might be excited and thus the solar wind energy is transported into the earth’s magnetosphere. In this paper, we study the ULF waves excited by different kinds of sudden solar wind pressure impulses through an MHD simulation. We primarily focus on the responses of the earth’s magnetosphere to positive/negative impulses of solar wind dynamic pressure, and positive-negative impulse pairs. The simulation results show that the ULF waves excited by positive and negative impulse have the same amplitude and frequency, with 180° difference in phase, if the amplitude and durations of the input impulses are the same. In addition, it is found that field line resonances (FLRs) occur at certain L-shell regions of the earth’s magneto-sphere after the impact of different positive-negative impulse pairs, which appear to be related to the duration of the impulses and the time interval between the sequential impulses. Another result is that the energy from the solar wind could be transported deeper into the inner magnetosphere by an impulse pair than by a single pulse impact. The results presented in this paper could help us to better understand how energy is transported from solar wind to the earth’s magnetosphere via ULF waves. Also, these results provide some new clues to understanding of how energetic particles in the inner magnetosphere response to different kinds of solar wind pressure impulse impacts including inter-planetary shocks.

  8. Laser-induced dissociation dynamics of triatomic molecule in electronic excited states: A full-dimensional quantum mechanics study.

    Science.gov (United States)

    Sun, Zhaopeng; Yang, Chuanlu; Zheng, Yujun

    2015-12-14

    We present a detailed theoretical approach to investigate the laser-induced dissociation dynamics of a triatomic molecule on its electronic excited state in full dimensional case. In this method, the time evolution of the time-dependent system is propagated via combined the split operator method and the expansion of Chebyshev polynomials (or short-time Chebyshev propagation) and the system wave functions are expanded in terms of molecular rotational bases. As an example of the application of this formalism, the dissociation dynamics of H3(+)→H2(+)+H induced by ultrashort UV laser pulses are investigated on new Born-Oppenheimer potential energy surfaces. Our numerical results show that the signals of dissociation products will be easier to observe as the increasing of field strength. Driving by a 266 nm laser beam, the calculated central value of kinetic-energy-release is 2.04 eV which shows excellent agreement with the experimental estimation of 2.1 eV. When the H3(+) ion is rotationally excited, the spatial distribution of product fragments will become well converged.

  9. Dynamic Spin Rig Upgraded With a Five- Axis-Controlled Three-Magnetic-Bearing Support System With Forward Excitation

    Science.gov (United States)

    Morrison, Carlos R.; Mehmed, Oral

    2003-01-01

    The NASA Glenn Research Center Dynamic Spin Rig is used for experimental evaluation of vibration analysis methods and dynamic characteristics for rotating systems. Measurements are made while rotors are spun and vibrated in a vacuum chamber. The rig has been upgraded with a new active magnetic bearing rotor support and excitation system. This design is expected to provide operational improvements over the existing rig. The rig will be able to be operated in either the old or new configuration. In the old configuration, two ball bearings support the vertical shaft of the rig, with the test article located between the bearings. Because the bearings operate in a vacuum, lubrication is limited to grease. This limits bearing life and speed. In addition, the old configuration employs two voice-coil electromagnetic shakers to apply oscillatory axial forces or transverse moments to the rotor shaft through a thrust bearing. The excitation amplitudes that can be imparted to the test article with this system are not adequate for components that are highly damped. It is expected that the new design will overcome these limitations.

  10. Chemical Reactivity Dynamics and Quantum Chaos in Highly Excited Hydrogen Atoms in an External Field: A Quantum Potential Approach

    Directory of Open Access Journals (Sweden)

    B. Maiti

    2002-04-01

    Full Text Available Abstract: Dynamical behavior of chemical reactivity indices like electronegativity, hardness, polarizability, electrophilicity and nucleophilicity indices is studied within a quantum fluid density functional framework for the interactions of a hydrogen atom in its ground electronic state (n = 1 and an excited electronic state (n = 20 with monochromatic and bichromatic laser pulses. Time dependent analogues of various electronic structure principles like the principles of electronegativity equalization, maximum hardness, minimum polarizability and maximum entropy have been found to be operative. Insights into the variation of intensities of the generated higher order harmonics on the color of the external laser field are obtained. The quantum signature of chaos in hydrogen atom has been studied using a quantum theory of motion and quantum fluid dynamics. A hydrogen atom in the electronic ground state (n = 1 and in an excited electronic state ( n = 20 behaves differently when placed in external oscillating monochromatic and bichromatic electric fields. Temporal evolutions of Shannon entropy, quantum Lyapunov exponent and Kolmogorov – Sinai entropy defined in terms of the distance between two initially close Bohmian trajectories for these two cases show marked differences. It appears that a larger uncertainty product and a smaller hardness value signal a chaotic behavior.

  11. Dynamic analysis and modal test of long-span cable-stayed bridge based on ambient excitation

    Institute of Scientific and Technical Information of China (English)

    CHEN Chang-song; YAN Dong-huang

    2007-01-01

    To study the stifilless distilbution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs.Based on the simplified model four stiffness formulae were deduced according to Hamilton principle.These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively.An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation.The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge.The results show that the errors of frequencies between theoretical analysis and test results are less than 10%mostly,and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stifiness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.

  12. Molecular dynamics simulation of strong shock waves propagating in dense deuterium, taking into consideration effects of excited electrons

    Science.gov (United States)

    Liu, Hao; Zhang, Yin; Kang, Wei; Zhang, Ping; Duan, Huiling; He, X. T.

    2017-02-01

    We present a molecular dynamics simulation of shock waves propagating in dense deuterium with the electron force field method [J. T. Su and W. A. Goddard, Phys. Rev. Lett. 99, 185003 (2007), 10.1103/PhysRevLett.99.185003], which explicitly takes the excitation of electrons into consideration. Nonequilibrium features associated with the excitation of electrons are systematically investigated. We show that chemical bonds in D2 molecules lead to a more complicated shock wave structure near the shock front, compared with the results of classical molecular dynamics simulation. Charge separation can bring about accumulation of net charges on large scales, instead of the formation of a localized dipole layer, which might cause extra energy for the shock wave to propagate. In addition, the simulations also display that molecular dissociation at the shock front is the major factor that accounts for the "bump" structure in the principal Hugoniot. These results could help to build a more realistic picture of shock wave propagation in fuel materials commonly used in the inertial confinement fusion.

  13. High-frequency vibration energy harvesting from impulsive excitation utilizing intentional dynamic instability caused by strong nonlinearity

    Science.gov (United States)

    Remick, Kevin; Dane Quinn, D.; Michael McFarland, D.; Bergman, Lawrence; Vakakis, Alexander

    2016-05-01

    The authors investigate a vibration-based energy harvesting system utilizing essential (nonlinearizable) nonlinearities and electromagnetic coupling elements. The system consists of a grounded, weakly damped linear oscillator (primary system) subjected to a single impulsive load. This primary system is coupled to a lightweight, damped oscillating attachment (denoted as nonlinear energy sink, NES) via a neodymium magnet and an inductance coil, and a piano wire, which generates an essential geometric cubic stiffness nonlinearity. Under impulsive input, the transient damped dynamics of this system exhibit transient resonance captures (TRCs) causing intentional large-amplitude and high-frequency instabilities in the response of the NES. These TRCs result in strong energy transfer from the directly excited primary system to the light-weight attachment. The energy is harvested by the electromagnetic elements in the coupling and, in the present case, dissipated in a resistive element in the electrical circuit. The primary goal of this work is to numerically, analytically, and experimentally demonstrate the efficacy of employing this type of intentional high-frequency dynamic instability to achieve enhanced vibration energy harvesting under impulsive excitation.

  14. A dynamic analysis of the radiation excitation from the activation of a current collecting system in space

    Science.gov (United States)

    Wang, J.; Hastings, D. E.

    1991-01-01

    Current collecting systems moving in the ionosphere will induce electromagnetic wave radiation. The commonly used static analysis is incapable of studying the situation when such systems undergo transient processes. A dynamic analysis has been developed, and the radiation excitation processes are studied. This dynamic analysis is applied to study the temporal wave radiation from the activation of current collecting systems in space. The global scale electrodynamic interactions between a space-station-like structure and the ionospheric plasma are studied. The temporal evolution and spatial propagation of the electric wave field after the activation are described. The wave excitations by tethered systems are also studied. The dependencies of the temporal Alfven wave and lower hybrid wave radiation on the activation time and the space system structure are discussed. It is shown that the characteristics of wave radiation are determined by the matching of two sets of characteristic frequencies, and a rapid change in the current collection can give rise to substantial transient radiation interference. The limitations of the static and linear analysis are examined, and the condition under which the static assumption is valid is obtained.

  15. Molecular dynamics simulation of strong shock waves propagating in dense deuterium, taking into consideration effects of excited electrons.

    Science.gov (United States)

    Liu, Hao; Zhang, Yin; Kang, Wei; Zhang, Ping; Duan, Huiling; He, X T

    2017-02-01

    We present a molecular dynamics simulation of shock waves propagating in dense deuterium with the electron force field method [J. T. Su and W. A. Goddard, Phys. Rev. Lett. 99, 185003 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.185003], which explicitly takes the excitation of electrons into consideration. Nonequilibrium features associated with the excitation of electrons are systematically investigated. We show that chemical bonds in D_{2} molecules lead to a more complicated shock wave structure near the shock front, compared with the results of classical molecular dynamics simulation. Charge separation can bring about accumulation of net charges on large scales, instead of the formation of a localized dipole layer, which might cause extra energy for the shock wave to propagate. In addition, the simulations also display that molecular dissociation at the shock front is the major factor that accounts for the "bump" structure in the principal Hugoniot. These results could help to build a more realistic picture of shock wave propagation in fuel materials commonly used in the inertial confinement fusion.

  16. Collective dynamics of cell migration and cell rearrangements

    Science.gov (United States)

    Kabla, Alexandre

    Understanding multicellular processes such as embryo development or cancer metastasis requires to decipher the contributions of local cell autonomous behaviours and long range interactions with the tissue environment. A key question in this context concerns the emergence of large scale coordination in cell behaviours, a requirement for collective cell migration or convergent extension. I will present a few examples where physical and mechanical aspects play a significant role in driving tissue scale dynamics. Geometrical confinement is one of the key external factors influencing large scale coordination during collective migration. Using a combination of in vitro experiments and numerical simulations, we show that the velocity correlation length, measured in unconfined conditions, provides a convenient length scale to predict the dynamic response under confinement. The same length scale can also be used to quantify the influence range of directional cues within the cell population. Heterogeneity within motile cell populations is frequently associated with an increase in their invasive capability and appears to play an important role during cancer metastasis. Using in silico experiments, we studied the way cell invasion is influenced by both the degree of cell coordination and the amount of variability in the motile force of the invading cells. Results suggest that mechanical heterogeneity dramatically enhances the invasion rate through an emerging cooperative process between the stronger and weaker cells, accounting for a number of observed invasion phenotypes. Effective convergent extension requires on a consistent orientation of cell intercalation at the tissue scale, most often in relation with planar cell polarity mechanisms to define the primary axes of deformation. Using a novel modelling approach for cells mechanical interactions, we studied the dynamics of substrate free motile cell populations. Ongoing work shows in particular that nematic order emerges

  17. Light-induced damage and its diagnosis in two-photon excited autofluorescence imaging of retinal pigment epithelium cells

    Science.gov (United States)

    Chen, Danni; Qu, Junle; Xu, Gaixia; Zhao, Lingling; Niu, Hanben

    2007-05-01

    In this paper, a novel method for the differentiation of the retinal pigment epithelium (RPE) cells after light-induced damage by two-photon excitation is presented. Fresh samples of RPE cells of pig eyes are obtained from local slaughterhouse. Light-induced damage is produced by the output from Ti: sapphire laser which is focused onto the RPE layer. We study the change of the autofluorescence properties of RPE after two-photon excitation with the same wavelength. Preliminary results show that after two-photon excitation, there are two clear changes in the emission spectrum. The first change is the blue-shift of the emission peak. The emission peak of the intact RPE is located at 592nm, and after excitation, it shifts to 540nm. It is supposed that the excitation has led to the increased autofluorescence of flavin whose emission peak is located at 540nm. The second change is the increased intensity of the emission peak, which might be caused by the accelerated aging because the autofluorescence of RPE would increase during aging process. Experimental results indicate that two-photon excitation could not only lead to the damage of the RPE cells in multiphoton RPE imaging, but also provide an evaluation of the light-induced damage.

  18. Electronic Excited State and Vibrational Dynamics of Water Solution of Cytosine Observed by Time-resolved Transient Absorption Spectroscopy with Sub-10fs Deep Ultraviolet Laser Pules

    Directory of Open Access Journals (Sweden)

    Kobayashi Takayoshi.

    2013-03-01

    Full Text Available Time-resolved transient absorption spectroscopy for water solution of cytosine with sub-10fs deep ultraviolet laser pulse is reported. Ultrafast electronic excited state dynamics and coherent molecular vibrational dynamics are simultaneously observed and their relaxation mechanisms are discussed.

  19. The influence of the excitation pulse length on ultrafast magnetization dynamics in nickel

    Directory of Open Access Journals (Sweden)

    A. Fognini

    2015-03-01

    Full Text Available The laser-induced demagnetization of a ferromagnet is caused by the temperature of the electron gas as well as the lattice temperature. For long excitation pulses, the two reservoirs are in thermal equilibrium. In contrast to a picosecond laser pulse, a femtosecond pulse causes a non-equilibrium between the electron gas and the lattice. By pump pulse length dependent optical measurements, we find that the magnetodynamics in Ni caused by a picosecond laser pulse can be reconstructed from the response to a femtosecond pulse. The mechanism responsible for demagnetization on the picosecond time scale is therefore contained in the femtosecond demagnetization experiment.

  20. Dynamics of excited-state intramolecular proton transfer reactions in piroxicam. Role of triplet states

    Science.gov (United States)

    Cho, Dae Won; Kim, Yong Hee; Yoon, Minjoong; Jeoung, Sae Chae; Kim, Dongho

    1994-08-01

    The picosecond time-resolved fluorescence and transient absorption behavior of piroxicam at room temperature are reported. The keto tautomer in the excited singlet state ( 1K*) formed via the fast intramolecular proton transfer (≈ 20 ps) is observed. The short-lived (7.5 ns) triplet state of keto tauomer ( 3K*) is generated from 1K * in toluene whereas it is hardly observed in ethanol. Consequently, rapid reverse proton transfer takes place from 3K * to the enol triplet state ( 3E *.

  1. Dynamically Excited Outer Solar System Objects in the Hubble Space Telescope Archive

    CERN Document Server

    Fuentes, Cesar I; Holman, Matthew J

    2011-01-01

    We present the faintest mid ecliptic latitude survey in the second part of HST archival search for outer Solar System bodies. We report the discovery of 28 new trans-Neptunian objects and 1 small centaur (R ~ 2km) in the band 5{\\circ} - 20{\\circ} off the ecliptic. The inclination distribution of these excited ob jects is consistent with the distribution derived from brighter ecliptic surveys. We suggest that the size and inclination distribution should be estimated consistently using suitable surveys with calibrated search algorithms and reliable orbital information.

  2. Dynamical Lie algebra method for highly excited vibrational state of asymmetric linear tetratomic molecules

    Institute of Scientific and Technical Information of China (English)

    FENG; Dongtai(冯东太); DING; Shiliang(丁世良); WANG; Meishan(王美山)

    2003-01-01

    The highly excited vibrational states of asymmetric linear tetratomic molecules are studied in the framework of Lie algebra. By using symmetric group U1(4) U2(4) U3(4), we construct the Hamiltonian that includes not only Casimir operators but also Majorana operators M12,M13 and M23, which are useful for getting potential energy surface and force constants in Lie algebra method. By Lie algebra treatment, we obtain the eigenvalues of the Hamiltonian, and make the concrete calculation for molecule C2HF.

  3. Dynamic Excitation of Monopiles by Steep and Breaking Waves: Experimental and Numerical Study

    DEFF Research Database (Denmark)

    Bredmose, Henrik; Slabiak, Peter; Sahlberg-Nielsen, Lasse;

    2013-01-01

    . The measured data for structural acceleration is analysed with respect to individual wave parameters. It is found that the largest accelerations occur for breaking waves. The measured wave field and structural response are reproduced numerically with a fully nonlinear potential flow solver for the undisturbed...... wave kinematics, combined with a finite element model with Morison-based forcing. A good overall reproduction of the wave field and structural response is achieved for two selected episodes. For some of the waves, however, the numerical response magnitude does not match the observed excitations...

  4. Dynamics of B cells in germinal centres.

    Science.gov (United States)

    De Silva, Nilushi S; Klein, Ulf

    2015-03-01

    Humoral immunity depends on the germinal centre (GC) reaction during which somatically mutated high-affinity memory B cells and plasma cells are generated. Recent studies have uncovered crucial cues that are required for the formation and the maintenance of GCs and for the selection of high-affinity antibody mutants. In addition, it is now clear that these events are promoted by the dynamic movements of cells within and between GCs. These findings have resolved the complexities of the GC reaction in greater detail than ever before. This Review focuses on these recent advances and discusses their implications for the establishment of humoral immunity.

  5. Factors affecting the dynamic response of pre-stressed anchors after transient excitation

    Institute of Scientific and Technical Information of China (English)

    Xu Huijun; Li Qingfeng

    2011-01-01

    The wide application of pre-stressed bolting technology in coal mine tunnels has made the nondestructive stress wave reflection method of determining bolting quality an important one.The effect of the support plate on the dynamic response of the pre-stressed anchor is of particular interest.A theoreticalanalysis and numerical simulations are used to identify the factors affecting the contact stress between the support plate and the rock wall.A formula allowing the calculation of contact stress is presented.Stress wave propagation through the nut,support plate,and rock wall are predicted.The dynamic response signals were measured in the field using prestressed anchors pre-tightened to different torques.The effects from the support plate on the dynamic response were recorded and the results compared to the predictions of pre-stressed anchor.This work provides a theoretical reference for the signal processing of dynamic reflected wave signals in anchor bolts.

  6. The dynamics of "stretched molecules": Experimental studies of highly vibrationally excited molecules with stimulated emission pumping

    NARCIS (Netherlands)

    Silva, M.; Jongma, R.; Field, R. W.; Wodtke, A. M.

    2001-01-01

    We review stimulated emission pumping as used to study molecular dynamics. The review presents unimolecular as well as scattering studies. Topics include intramolecular vibrational redistribution, unimolecular isomerization and dissociation, van der Waals clusters, rotational energy transfer, vibrat

  7. Parallel Dynamic Analysis of a Large-Scale Water Conveyance Tunnel under Seismic Excitation Using ALE Finite-Element Method

    Directory of Open Access Journals (Sweden)

    Xiaoqing Wang

    2016-01-01

    Full Text Available Parallel analyses about the dynamic responses of a large-scale water conveyance tunnel under seismic excitation are presented in this paper. A full three-dimensional numerical model considering the water-tunnel-soil coupling is established and adopted to investigate the tunnel’s dynamic responses. The movement and sloshing of the internal water are simulated using the multi-material Arbitrary Lagrangian Eulerian (ALE method. Nonlinear fluid–structure interaction (FSI between tunnel and inner water is treated by using the penalty method. Nonlinear soil-structure interaction (SSI between soil and tunnel is dealt with by using the surface to surface contact algorithm. To overcome computing power limitations and to deal with such a large-scale calculation, a parallel algorithm based on the modified recursive coordinate bisection (MRCB considering the balance of SSI and FSI loads is proposed and used. The whole simulation is accomplished on Dawning 5000 A using the proposed MRCB based parallel algorithm optimized to run on supercomputers. The simulation model and the proposed approaches are validated by comparison with the added mass method. Dynamic responses of the tunnel are analyzed and the parallelism is discussed. Besides, factors affecting the dynamic responses are investigated. Better speedup and parallel efficiency show the scalability of the parallel method and the analysis results can be used to aid in the design of water conveyance tunnels.

  8. Dynamical Tide in Action: Tidally Excited Oscillations in Kepler Heartbeat Stars

    Science.gov (United States)

    Guo, Zhao; Gies, Douglas R.; Shporer, Avi; Fuller, Jim; Isaacson, Howard T.; Kepler Eclipsing Binary Working Group

    2017-01-01

    We perform a global variability study of heartbeat stars, a class of eccentric binaries whose light curves resemble a cardiogram. The equilibrium tide is modeled by the light curve synthesis code ELC, taking advantage of the information of many possible stellar pairings from a MESA isochrone.We examine the power spectra of light curve residuals closely, searching for signatures of rotation and oscillations. Special attention is given to systems that show tidally excited oscillations/pulsations. Pulsation phases (w.r.t periastron passage) are extracted to identify the azimuthal number m, the degree of detuning (i.e., the difference between the driving frequency and the intrinsic eigenfrequency of stars), and the possibility of resonance-locking. To study non-linear mode coupling, we also search for tidally excited non-orbital-harmonic frequencies.For four particular double-lined systems with Keck HIRES spectra, we derive the orbital and fundamental parameters which can lead to further detailed asteroseismic modeling.

  9. Quantum molecular dynamics simulations of hydrogen production and solar cells

    Science.gov (United States)

    Mou, Weiwei

    The global energy crisis presents two major challenges for scientists around the world: Producing cleaner energy which is sustainable for the environment; And improving the efficiency of energy production as well as consumption. It is crucial and yet elusive to understand the atomistic mechanisms and electronic properties, which are needed in order to tackle those challenges. Quantum molecular dynamics simulations and nonadiabatic quantum molecular dynamics are two of the dominant methods used to address the atomistic and electronic properties in various energy studies. This dissertation is an ensemble of three studies in energy research: (1) Hydrogen production from the reaction of aluminum clusters with water to provide a renewable energy cycle; (2) The photo-excited charge transfer and recombination at a quaterthiophene/zinc oxide interface to improve the power conversion efficiency of hybrid poly(3-hexylthiophene) (P3HT) /ZnO solar cells; and (3) the charge transfer at a rubrene/C60 interface to understand why phenyl groups in rubrene improve the performance of rubrene/C60 solar cells.

  10. Imaging Cellular Dynamics with Spectral Relaxation Imaging Microscopy: Distinct Spectral Dynamics in Golgi Membranes of Living Cells

    Science.gov (United States)

    Lajevardipour, Alireza; Chon, James W. M.; Chattopadhyay, Amitabha; Clayton, Andrew H. A.

    2016-11-01

    Spectral relaxation from fluorescent probes is a useful technique for determining the dynamics of condensed phases. To this end, we have developed a method based on wide-field spectral fluorescence lifetime imaging microscopy to extract spectral relaxation correlation times of fluorescent probes in living cells. We show that measurement of the phase and modulation of fluorescence from two wavelengths permit the identification and determination of excited state lifetimes and spectral relaxation correlation times at a single modulation frequency. For NBD fluorescence in glycerol/water mixtures, the spectral relaxation correlation time determined by our approach exhibited good agreement with published dielectric relaxation measurements. We applied this method to determine the spectral relaxation dynamics in membranes of living cells. Measurements of the Golgi-specific C6-NBD-ceramide probe in living HeLa cells revealed sub-nanosecond spectral dynamics in the intracellular Golgi membrane and slower nanosecond spectral dynamics in the extracellular plasma membrane. We interpret the distinct spectral dynamics as a result of structural plasticity of the Golgi membrane relative to more rigid plasma membranes. To the best of our knowledge, these results constitute one of the first measurements of Golgi rotational dynamics.

  11. Abnormal cell-intrinsic and network excitability in the neocortex of serotonin-deficient Pet-1 knockout mice.

    Science.gov (United States)

    Puzerey, Pavel A; Kodama, Nathan X; Galán, Roberto F

    2016-02-01

    Neurons originating from the raphe nuclei of the brain stem are the exclusive source of serotonin (5-HT) to the cortex. Their serotonergic phenotype is specified by the transcriptional regulator Pet-1, which is also necessary for maintaining their neurotransmitter identity across development. Transgenic mice in which Pet-1 is genetically ablated (Pet-1(-/-)) show a dramatic reduction (∼80%) in forebrain 5-HT levels, yet no investigations have been carried out to assess the impact of such severe 5-HT depletion on the function of target cortical neurons. Using whole cell patch-clamp methods, two-dimensional (2D) multielectrode arrays (MEAs), 3D morphological neuronal reconstructions, and animal behavior, we investigated the impact of 5-HT depletion on cortical cell-intrinsic and network excitability. We found significant changes in several parameters of cell-intrinsic excitability in cortical pyramidal cells (PCs) as well as an increase in spontaneous synaptic excitation through 5-HT3 receptors. These changes are associated with increased local network excitability and oscillatory activity in a 5-HT2 receptor-dependent manner, consistent with previously reported hypersensitivity of cortical 5-HT2 receptors. PC morphology was also altered, with a significant reduction in dendritic complexity that may possibly act as a compensatory mechanism for increased excitability. Consistent with this interpretation, when we carried out experiments with convulsant-induced seizures to asses cortical excitability in vivo, we observed no significant differences in seizure parameters between wild-type and Pet-1(-/-) mice. Moreover, MEA recordings of propagating field potentials showed diminished propagation of activity across the cortical sheath. Together these findings reveal novel functional changes in neuronal and cortical excitability in mice lacking Pet-1.

  12. Ultrafast excited state dynamics of tris-(2,2'-bipyridine) Ruthenium (II)

    Energy Technology Data Exchange (ETDEWEB)

    Yeh, Alvin T.W. [Univ. of California, Berkeley, CA (United States)

    2000-03-01

    Time resolved anisotropy measurements and time dependent transient absorption measurements are used to study the evolution of the photoexcited Franck-Condon state to the formation of the long-lived triplet metal-to-ligand charge-transfer (3MLCT) state in tris-(2,2’-bipyridine) ruthenium. [Ru(bpy)3]2+ represents a large class of inorganic compounds with interesting and potentially applicable photophysical properties. These compounds have generated much interest in the inorganic chemistry community because their photophysical properties are easily manipulated by synthetic chemistry methods. However, little remains known about the processes which govern the evolution horn initial photoexcitation to the formation of the long-lived excited state.

  13. Dynamics of excited instantons in the system of forced Gursey nonlinear differential equations

    Energy Technology Data Exchange (ETDEWEB)

    Aydogmus, F., E-mail: fatma.aydogmus@gmail.com [Istanbul University, Department of Physics, Faculty of Science (Turkey)

    2015-02-15

    The Gursey model is a 4D conformally invariant pure fermionic model with a nonlinear spinor self-coupled term. Gursey proposed his model as a possible basis for a unitary description of elementary particles following the “Heisenberg dream.” In this paper, we consider the system of Gursey nonlinear differential equations (GNDEs) formed by using the Heisenberg ansatz. We use it to understand how the behavior of spinor-type Gursey instantons can be affected by excitations. For this, the regular and chaotic numerical solutions of forced GNDEs are investigated by constructing their Poincaré sections in phase space. A hierarchical cluster analysis method for investigating the forced GNDEs is also presented.

  14. Structural and dynamical aspects of skin studied by multiphoton excitation fluorescence microscopy-based methods

    DEFF Research Database (Denmark)

    Bloksgaard, Maria; Brewer, Jonathan R.; Bagatolli, Luis

    2013-01-01

    This mini-review reports on applications of particular multiphoton excitation microscopy-based methodologies employed in our laboratory to study skin. These approaches allow in-depth optical sectioning of the tissue, providing spatially resolved information on specific fluorescence probes...... excised skin, including applications of fluctuation correlation spectroscopy on transdermal penetration of liposomes are presented and discussed. The data from the different studies reported reveal the intrinsic heterogeneity of skin and also prove these strategies to be powerful noninvasive tools......-carboxyethyl)-5-(and-6)-carboxyfluorescein) and diffusion coefficients of distinct fluorescence probes (raster imaging correlation spectroscopy) can be obtained from different regions of the tissue. Comparative studies of different tissue strata, but also between equivalent regions of normal and abnormal...

  15. Dynamic Analyses of Isolated Structures under Bi-Directional Excitations of Near-Field Ground Motions

    Directory of Open Access Journals (Sweden)

    Gokhan Ozdemir

    2012-01-01

    Full Text Available Nonlinear response history analyses (NRHA of a 3-story isolated reinforced concrete (RC building are carried out under both uni- and bi-directional earthquake excitations of near-field records. NRHA are conducted for a wide range of yield strength (Q/W of lead rubber bearings (LRB, and isolation period (T. Selected near-field records are used to investigate both the contribution of orthogonal components on maximum isolator displacements and accuracy of equivalent lateral force (ELF procedure on estimation of maximum isolator displacements. Analyses results show that both the contribution of orthogonal components and accuracy of ELF procedure depend on the soil condition where isolation system is implemented.

  16. Electron Elevator: Excitations across the Band Gap via a Dynamical Gap State.

    Science.gov (United States)

    Lim, A; Foulkes, W M C; Horsfield, A P; Mason, D R; Schleife, A; Draeger, E W; Correa, A A

    2016-01-29

    We use time-dependent density functional theory to study self-irradiated Si. We calculate the electronic stopping power of Si in Si by evaluating the energy transferred to the electrons per unit path length by an ion of kinetic energy from 1 eV to 100 keV moving through the host. Electronic stopping is found to be significant below the threshold velocity normally identified with transitions across the band gap. A structured crossover at low velocity exists in place of a hard threshold. An analysis of the time dependence of the transition rates using coupled linear rate equations enables one of the excitation mechanisms to be clearly identified: a defect state induced in the gap by the moving ion acts like an elevator and carries electrons across the band gap.

  17. Green's functions for analysis of dynamic response of wheel/rail to vertical excitation

    Science.gov (United States)

    Mazilu, Traian

    2007-09-01

    An analytical model to simulate wheel/rail interaction using the Green's functions method is proposed in this paper. The model consists of a moving wheel on a discretely supported rail. Particularly for this model of rail, the bending and the longitudinal displacement are coupled due to the rail pad and a complex model of the rail pad is adopted. An efficient method for solving a time-domain analysis for wheel/rail interaction is presented. The method is based on the properties of the rail's Green functions and starting to these functions, a track's Green matrix is assembled for the numerical simulations of wheel/rail response due to three kinds of vertical excitations: the steady-state interaction, the rail corrugation and the wheel flat. The study points to influence of the worn rail—rigid contact—on variation in the wheel/rail contact force. The concept of pinned-pinned inhibitive rail pad is also presented.

  18. Electron-ion coincidence spectrometer for studies on decay dynamics of core-excited molecules

    Energy Technology Data Exchange (ETDEWEB)

    Kaneyasu, T. [UVSOR Facility, Institute for Molecular Science, Nishigonaka 38, Myodaiji, Okazaki 444-8585 (Japan)], E-mail: kaneyasu@ims.ac.jp; Hikosaka, Y.; Shigemasa, E. [UVSOR Facility, Institute for Molecular Science, Nishigonaka 38, Myodaiji, Okazaki 444-8585 (Japan)

    2007-05-15

    We have developed an Auger electron-ion coincidence spectrometer to measure energy- and angular-correlations among the particles ejected on decay of core-excited/ionized molecules. The apparatus consists of a double toroidal electron analyzer and a three-dimensional ion momentum spectrometer, both of which are terminated by time- and position-sensitive detectors. For extracting the ions into the ion momentum spectrometer, a pulsed electric field is applied to the interaction region, according to each Auger electron observation. To evaluate the performance of the ion momentum spectrometer, momentum vectors of fragment ions produced through the dissociation from the selected molecular ion states following N{sub 2} core photoionization have been observed. The momentum, energy and angular resolutions achieved by the spectrometer have been estimated from the events associated with the formation of N{sub 2}{sup 2+} and with the pair formation of N{sup +}+{sup N+}.

  19. Excited-state dynamics and nonlinear optical response of Ge nanocrystals embedded in silica matrix

    Science.gov (United States)

    Razzari, Luca; Gnoli, Andrea; Righini, Marcofabio; Dâna, Aykutlu; Aydinli, Atilla

    2006-05-01

    We use a dedicated Z-scan setup, arranged to account for cumulative effects, to study the nonlinear optical response of Ge nanocrystals embedded in silica matrix. Samples are prepared with plasma-enchanced chemical-vapor deposition and post-thermal annealing. We measure a third-order nonlinear refraction coefficient of γ =1×10-16m2/W. The nonlinear absorption shows an intensity-independent coefficient of β =4×10-10m/W related to fast processes. In addition, we measure a second β component around 10-9m /W with a relaxation time of 300μs that rises linearly with the laser intensity. We associate its origin to the absorption of excited carriers from a surface-defect state with a long depopulation time.

  20. Coherence and population dynamics of chlorophyll excitations in FCP complex: Two-dimensional spectroscopy study

    CERN Document Server

    Butkus, Vytautas; Augulis, Ramūnas; Gall, Andrew; Büchel, Claudia; Robert, Bruno; Zigmantas, Donatas; Valkunas, Leonas; Abramavicius, Darius

    2015-01-01

    The energy transfer processes and coherent phenomena in the fucoxanthin-chlorophyll protein complex, which is responsible for the light harvesting function in marine algae diatoms, were investigated at 77 K by using two-dimensional electronic spectroscopy. Experiments performed on the femtosecond and picosecond timescales led to separation of spectral dynamics, witnessing evolutions of coherence and population states of the system in the spectral region of ${\\rm Q}_{y}$ transitions of chlorophylls $a$ and $c$. Analysis of the coherence dynamics allowed us to identify chlorophyll (Chl) $a$ and fucoxanthin intramolecular vibrations dominating over the first few picoseconds. Closer inspection of the spectral region of the ${\\rm Q}_{y}$ transition of Chl $c$ revealed previously not identified mutually non-interacting chlorophyll $c$ states participating in femtosecond or picosecond energy transfer to the Chl $a$ molecules. Consideration of separated coherent and incoherent dynamics allowed us to hypothesize the v...

  1. Coherence and population dynamics of chlorophyll excitations in FCP complex: Two-dimensional spectroscopy study.

    Science.gov (United States)

    Butkus, Vytautas; Gelzinis, Andrius; Augulis, Ramūnas; Gall, Andrew; Büchel, Claudia; Robert, Bruno; Zigmantas, Donatas; Valkunas, Leonas; Abramavicius, Darius

    2015-06-07

    Energy transfer processes and coherent phenomena in the fucoxanthin-chlorophyll protein complex, which is responsible for the light harvesting function in marine algae diatoms, were investigated at 77 K by using two-dimensional electronic spectroscopy. Experiments performed on femtosecond and picosecond timescales led to separation of spectral dynamics, witnessing evolutions of coherence and population states of the system in the spectral region of Qy transitions of chlorophylls a and c. Analysis of the coherence dynamics allowed us to identify chlorophyll (Chl) a and fucoxanthin intramolecular vibrations dominating over the first few picoseconds. Closer inspection of the spectral region of the Qy transition of Chl c revealed previously not identified, mutually non-interacting chlorophyll c states participating in femtosecond or picosecond energy transfer to the Chl a molecules. Consideration of separated coherent and incoherent dynamics allowed us to hypothesize the vibrations-assisted coherent energy transfer between Chl c and Chl a and the overall spatial arrangement of chlorophyll molecules.

  2. On the importance of excited state dynamic response electron correlation in polarizable embedding methods

    DEFF Research Database (Denmark)

    Eriksen, Janus J.; Sauer, Stephan P. A.; Mikkelsen, Kurt Valentin

    2012-01-01

    We investigate the effect of including a dynamic reaction field at the lowest possible ab inito wave function level of theory, namely the Hartree-Fock (HF) Self-Consistent Field (SCF) level within the Polarizable Embedding (PE) formalism. We formulate HF based PE within the linear response theory...... picture leading to the PE-Random-Phase Approximation (PE-RPA) and bridge the expressions to a Second-Order Polarization Propagator Approximation (SOPPA) frame such that dynamic reaction field contributions are included at the RPA level in addition to the static response described at the SOPPA level...... but with HF induced dipole moments. We conduct calculations on para-nitro-aniline and para-nitro-phenolate using said model in addition to dynamic PE-RPA and PE-CAM-B3LYP. We compare the results to recently published PE-CCSD data and demonstrate how the cost effective SOPPA based model successfully recovers...

  3. An organic transistor-based system for reference-less electrophysiological monitoring of excitable cells.

    Science.gov (United States)

    Spanu, A; Lai, S; Cosseddu, P; Tedesco, M; Martinoia, S; Bonfiglio, A

    2015-03-06

    In the last four decades, substantial advances have been done in the understanding of the electrical behavior of excitable cells. From the introduction in the early 70's of the Ion Sensitive Field Effect Transistor (ISFET), a lot of effort has been put in the development of more and more performing transistor-based devices to reliably interface electrogenic cells such as, for example, cardiac myocytes and neurons. However, depending on the type of application, the electronic devices used to this aim face several problems like the intrinsic rigidity of the materials (associated with foreign body rejection reactions), lack of transparency and the presence of a reference electrode. Here, an innovative system based on a novel kind of organic thin film transistor (OTFT), called organic charge modulated FET (OCMFET), is proposed as a flexible, transparent, reference-less transducer of the electrical activity of electrogenic cells. The exploitation of organic electronics in interfacing the living matters will open up new perspectives in the electrophysiological field allowing us to head toward a modern era of flexible, reference-less, and low cost probes with high-spatial and high-temporal resolution for a new generation of in-vitro and in-vivo monitoring platforms.

  4. Somatosensory stimulation suppresses the excitability of pyramidal cells in the hippocampal CA1 region in rats

    Institute of Scientific and Technical Information of China (English)

    Yang Wang; Zhouyan Feng; Jing Wang; Xiaojing Zheng

    2014-01-01

    The hippocampal region of the brain is important for encoding environment inputs and memory formation. However, the underlying mechanisms are unclear. To investigate the behavior of indi-vidual neurons in response to somatosensory inputs in the hippocampal CA1 region, we recorded and analyzed changes in local ifeld potentials and the ifring rates of individual pyramidal cells and interneurons during tail clamping in urethane-anesthetized rats. We also explored the mechanisms underlying the neuronal responses. Somatosensory stimulation, in the form of tail clamping, chan-ged local ifeld potentials into theta rhythm-dominated waveforms, decreased the spike ifring of py-ramidal cells, and increased interneuron ifring. In addition, somatosensory stimulation attenuated orthodromic-evoked population spikes. These results suggest that somatosensory stimulation sup-presses the excitability of pyramidal cells in the hippocampal CA1 region. Increased inhibition by local interneurons might underlie this effect. These ifndings provide insight into the mechanisms of signal processing in the hippocampus and suggest that sensory stimulation might have thera-peutic potential for brain disorders associated with neuronal hyperexcitability.

  5. Influence of orientation degree of freedom on fission dynamics of higly excited nuclei

    Directory of Open Access Journals (Sweden)

    Nadtochy P.N.

    2013-12-01

    Full Text Available Four-dimensional dynamical model was developed and employed for study fission characteristics in a wide range of fissility parameter. The three collective shape coordinates plus the K coordinate, which is the spin of the nucleus with respect to the symmetry (fission axis, were considered dynamically from the ground state deformation till the scission into fission fragments. A modified one-body mechanism for nuclear dissipation with a reduction coefficient ks of the contribution from a “wall” formula have been used in the study. The four-dimensional calculations for heavy nuclei could describe the fission fragment mass-energy distribution (MED parameters and prescission neutron multiplicity with almost single ks value, in contrast with 3D dynamical calculations, where a consistent description of all observables with the same ks is not possible for heavy nuclei. The estimation of a dissipation coefficient for the orientation degree of freedom γK = 0.077(MeV zs−1/2 is good for heavy nuclei and lower value of γK = 0.05(MeV zs−1/2 is needed for nuclei with mass A ≃ 200. The results of 4D and 3D Langevin dynamical calculations for light nuclei near the Businaro-Gallone point predict close results for the fission fragment MED parameters and prescission particles multiplicities.

  6. Dynamical structure factors and excitation modes of the bilayer Heisenberg model

    Science.gov (United States)

    Lohöfer, M.; Coletta, T.; Joshi, D. G.; Assaad, F. F.; Vojta, M.; Wessel, S.; Mila, F.

    2015-12-01

    Using quantum Monte Carlo simulations along with higher-order spin-wave theory, bond-operator and strong-coupling expansions, we analyze the dynamical spin structure factor of the spin-half Heisenberg model on the square-lattice bilayer. We identify distinct contributions from the low-energy Goldstone modes in the magnetically ordered phase and the gapped triplon modes in the quantum disordered phase. In the antisymmetric (with respect to layer inversion) channel, the dynamical spin structure factor exhibits a continuous evolution of spectral features across the quantum phase transition, connecting the two types of modes. Instead, in the symmetric channel, we find a depletion of the spectral weight when moving from the ordered to the disordered phase. While the dynamical spin structure factor does not exhibit a well-defined distinct contribution from the amplitude (or Higgs) mode in the ordered phase, we identify an only marginally damped amplitude mode in the dynamical singlet structure factor, obtained from interlayer bond correlations, in the vicinity of the quantum critical point. These findings provide quantitative information in direct relation to possible neutron or light scattering experiments in a fundamental two-dimensional quantum-critical spin system.

  7. Temporal dynamics of motor cortex excitability during perception of natural emotional scenes

    NARCIS (Netherlands)

    Borgomaneri, Sara; Gazzola, Valeria; Avenanti, Alessio

    2014-01-01

    Although it is widely assumed that emotions prime the body for action, the effects of visual perception of natural emotional scenes on the temporal dynamics of the human motor system have scarcely been investigated. Here, we used single-pulse transcranial magnetic stimulation (TMS) to assess motor e

  8. Excited-state dynamics in diketopyrrolopyrrole-based copolymer for organic photovoltaics investigated by transient optical spectroscopy

    Science.gov (United States)

    Matsuzaki, Hiroyuki; Furube, Akihiro; Katoh, Ryuzi; Pratap Singh, Samarendra; Sonar, Prashant; Williams, Evan Laurence; Vijila, Chellappan; Sandhya Subramanian, Gomathy; Gorelik, Sergey; Hobley, Jonathan

    2014-01-01

    We investigate the photoexcited state dynamics in a donor-acceptor copolymer, poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene} (pDPP-TNT), by picosecond fluorescence and femtosecond transient absorption spectroscopies. Time-resolved fluorescence lifetime measurements of pDPP-TNT thin films reveal that the lifetime of the singlet excited state is 185 ± 5 ps and that singlet-singlet annihilation occurs at excitation photon densities above 6 × 1017 photons/cm3. From the results of singlet-singlet annihilation analysis, we estimate that the single-singlet annihilation rate constant is (6.0 ± 0.2) × 10-9 cm3 s-1 and the singlet diffusion length is ~7 nm. From the comparison of femtosecond transient absorption measurements and picosecond fluorescence measurements, it is found that the time profile of the photobleaching signal in the charge-transfer (CT) absorption band coincides with that of the fluorescence intensity and there is no indication of long-lived species, which clearly suggests that charged species, such as polaron pairs and triplet excitons, are not effectively photogenerated in the neat pDPP-TNT polymer.

  9. Excitation power dynamics of photoluminescence in InGaN /GaN quantum wells with enhanced carrier localization

    Science.gov (United States)

    Kazlauskas, K.; Tamulaitis, G.; Mickevičius, J.; Kuokštis, E.; Žukauskas, A.; Cheng, Yung-Chen; Wang, Hsiang-Cheng; Huang, Chi-Feng; Yang, C. C.

    2005-01-01

    Excitation-power dynamics of near-band-edge photoluminescence (PL) peak position in InxGa1-xN/GaN multiple quantum wells (x˜0.15) was analyzed as a function of well width. The analysis was based on energy reference provided by photoreflectance (PR) spectra. The difference in spectral position of the PR feature and low-excitation PL band (the Stokes Shift) revealed carrier localization energy, which exhibited a remarkable sensitivity to the well width, increasing from 75meV in 2nm wells to about 250meV in 4nm wells. Meanwhile collating of the PR data with the flat-band model for the optical transition energy in quantum wells rendered a relatively weak (0.5MV/cm) built-in piezoelectric field. The blueshift of the PL peak position with increasing photoexcitation power density was shown to be in qualitative agreement with the model of filling of the band-tail states with some contribution from screening of built-in field in the thickest (4nm) wells. Increased incident photon energy resulted in an additional blueshift of the PL peak, which was explained by a nonthermalized distribution of localized carriers and/or carrier localization in the interface region. Our results are consistent with a concept of emission from partially relaxed large In-rich regions with internal band potential fluctuations, which are enhanced with increasing the growth time.

  10. Ultrafast Excited-State Dynamics of Diketopyrrolopyrrole (DPP)-Based Materials: Static versus Diffusion-Controlled Electron Transfer Process

    KAUST Repository

    Alsulami, Qana

    2015-06-25

    Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

  11. Excitation relaxation dynamics and energy transfer in pigment-protein complexes of a dinoflagellate, revealed by ultrafast fluorescence spectroscopy.

    Science.gov (United States)

    Tanaka, Kazunori; Iida, Satoko; Takaichi, Shinichi; Mimuro, Mamoru; Murakami, Akio; Akimoto, Seiji

    2016-12-01

    Photosynthetic light-harvesting complexes, found in aquatic photosynthetic organisms, contain a variety of carotenoids and chlorophylls. Most of the photosynthetic dinoflagellates possess two types of light-harvesting antenna complexes: peridinin (Peri)-chlorophyll (Chl) a/c-protein, as an intrinsic thylakoid membrane complex protein (iPCP), and water-soluble Peri-Chl a-protein, as an extrinsic membrane protein (sPCP) on the inner surface of the thylakoid. Peri is a unique carotenoid that has eight C=C bonds and one C=O bond, which results in a characteristic absorption band in the green wavelength region. In the present study, excitation relaxation dynamics of Peri in solution and excitation energy transfer processes of sPCP and the thylakoid membranes, prepared from the photosynthetic dinoflagellate, Symbiodinium sp., are investigated by ultrafast time-resolved fluorescence spectroscopy. We found that Peri-to-Chl a energy transfer occurs via the Peri S1 state with a time constant of 1.5 ps or 400 fs in sPCP or iPCP, respectively, and that Chl c-to-Chl a energy transfer occurs in the time regions of 350-400 fs and 1.8-2.6 ps.

  12. Modulation of voltage-gated conductances of retinal horizontal cells by UV-excited TiO2 nanoparticles.

    Science.gov (United States)

    Meshik, Xenia; Choi, Min; Baker, Adam; Malchow, R Paul; Covnot, Leigha; Doan, Samuel; Mukherjee, Souvik; Farid, Sidra; Dutta, Mitra; Stroscio, Michael A

    2016-11-22

    This study examines the ability of optically-excited titanium dioxide nanoparticles to influence voltage-gated ion channels in retinal horizontal cells. Voltage clamp recordings were obtained in the presence and absence of TiO2 and ultraviolet laser excitation. Significant current changes were observed in response to UV light, particularly in the -40 mV to +40 mV region where voltage-gated Na(+) and K(+) channels have the highest conductance. Cells in proximity to UV-excited TiO2 exhibited a left-shift in the current-voltage relation of around 10 mV in the activation of Na(+) currents. These trends were not observed in control experiments where cells were excited with UV light without being exposed to TiO2. Electrostatic force microscopy confirmed that electric fields can be induced in TiO2 with UV light. Simulations using the Hodgkin-Huxley model yielded results which agreed with the experimental data and showed the I-V characteristics of individual ion channels in the presence of UV-excited TiO2.

  13. Modeling cell dynamics under mobile phone radiation.

    Science.gov (United States)

    Minelli, Tullio Antonio; Balduzzo, Maurizio; Milone, Francesco Ferro; Nofrate, Valentina

    2007-04-01

    Perturbations by pulse-modulated microwave radiation from GSM mobile phones on neuron cell membrane gating and calcium oscillations have been suggested as a possible mechanism underlying activation of brain states and electroencephalographic epiphenomena. As the employ of UMTS phones seems to reveal other symptoms, a unified phenomenological framework is needed. In order to explain possible effects of mobile phone radiation on cell oscillations, GSM and UMTS low-frequency envelopes have been detected, recorded and used as input in cell models. Dynamical systems endowed with contiguous regular and chaotic regimes suitable to produce stochastic resonance can both account for the perturbation of the neuro-electrical activity and even for the low intensity of the signal perceived by high sensitive subjects. Neuron models of this kind can be employed as a reductionist hint for the mentioned phenomenology. The Hindmarsh-Rose model exhibits frequency enhancement and regularization phenomena induced by weak GSM and UMTS. More realistic simulations of cell membrane gating and calcium oscillations have been performed with the help of an adaptation of the Chay-Keizer dynamical system. This scheme can explain the suspected subjective sensitivity to mobile phone signals under the thermal threshold, in terms of cell calcium regularity mechanisms. Concerning the two kinds of emission, the stronger occupation of the ELF band of last generation UMTS phones is compensated by lower power emitted.

  14. STUDY OF STATIC AND DYNAMIC STABILITY OF THIN-WALLED BARS EXCITED BY PERIODICAL AXIAL EXTERNAL FORCES.

    Directory of Open Access Journals (Sweden)

    Minodora Maria PASĂRE

    2010-10-01

    Full Text Available In these paper, starting from the relations for the displacements and spinning the transversal section of a bar with thin walls of sections opened expressed by the corresponding influence functions and introducing the components of the exterior forces distributed and the moments of the exterior forces distributed due to the inertia forces, the exciting axial forces together with the following effect of these and of the reaction forces of the elastic environment for leaning it may reach to the system of the equations of parametric vibrations under the form of three integral equation These equations may serve for the study of vibrations of the bars, to study the static stability and to study the dynamic stability

  15. Partial Dynamical SU(3) Symmetry and the Nature of the Lowest K=0 Collective Excitation in Deformed Nuclei

    CERN Document Server

    Leviatan, A

    1999-01-01

    We discuss the implications of partial dynamical SU(3) symmetry (PDS) for thestructure of the lowest K=0^{+} (K=0_2) collective excitation in deformednuclei. We consider an interacting boson model Hamiltonian whose ground andgamma bands have good SU(3) symmetry while the K=0_2 band is mixed. It is shownthat the double-phonon components in the K=0_2 wave function arise from SU(3)admixtures which, in turn, can be determined from absolute E2 rates connectingthe K=0_2 and ground bands. An explicit expression is derived for theseadmixtures in terms of the ratio of K=0_2 and gamma bandhead energies. TheSU(3) PDS predictions are compared with existing data and with broken-SU(3)calculations for ^{168}Er.

  16. Plasmon switching: observation of dynamic surface plasmon steering by selective mode excitation in a sub-wavelength slit.

    Science.gov (United States)

    Raghunathan, S B; Gan, C H; van Dijk, T; Ea Kim, B; Schouten, H F; Ubachs, W; Lalanne, P; Visser, T D

    2012-07-02

    We report a plasmon steering method that enables us to dynamically control the direction of surface plasmons generated by a two-mode slit in a thin metal film. By varying the phase between different coherent beams that are incident on the slit, individual waveguide modes are excited. Different linear combinations of the two modes lead to different diffracted fields at the exit of the slit. As a result, the direction in which surface plasmons are launched can be controlled. Experiments confirm that it is possible to distribute an approximately constant surface plasmon intensity in any desired proportion over the two launching directions. We also find that the anti-symmetric mode generates surface plasmons more efficiently than the fundamental symmetric mode.

  17. Collective excitations in liquid DMSO : FIR spectrum, Low frequency vibrational density of states and ultrafast dipolar solvation dynamics

    CERN Document Server

    Hazra, Milan

    2016-01-01

    Valuable dynamical and structural information about neat liquid DMSO at ambient conditions can be obtained through study of low frequency vibrations in the far infrared (FIR), that is, terahertz regime. For DMSO, collective excitations as well as single molecule stretches and bends have been measured by different kinds of experiments such as OHD-RIKES and terahertz spectroscopy. In the present work we investigate the intermolecular vibrational spectrum of DMSO through three different computational techniques namely (i) the far-infra red spectrum obtained through Fourier transform of total dipole moment auto time correlation function, (ii) from Fourier transform of the translational and angular velocity time autocorrelation functions and a (iii) quenched normal mode analysis of the parent liquid at 300K. The three spectrum, although exhibit differences among each other, reveal similar features which are in good, semi-quantitative, agreement with experimental results. Study of participation ratio of the density...

  18. Enhanced multi-spectral imaging of live breast cancer cells using immunotargeted gold nanoshells and two-photon excitation microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Bickford, Lissett; Sun Jiantang; Fu, Kun; Lewinski, Nastassja; Nammalvar, Vengadesan; Chang, Joseph; Drezek, Rebekah [Department of Bioengineering, Rice University, Houston, TX 77005 (United States)], E-mail: drezek@rice.edu

    2008-08-06

    We demonstrate the capability of using immunotargeted gold nanoshells as contrast agents for in vitro two-photon microscopy. The two-photon luminescence properties of different-sized gold nanoshells are first validated using near-infrared excitation at 780 nm. The utility of two-photon microscopy as a tool for imaging live HER2-overexpressing breast cancer cells labeled with anti-HER2-conjugated nanoshells is then explored and imaging results are compared to normal breast cells. Five different imaging channels are simultaneously examined within the emission wavelength range of 451-644 nm. Our results indicate that under near-infrared excitation, superior contrast of SK-BR-3 cancer cells labeled with immunotargeted nanoshells occurs at an emission wavelength ranging from 590 to 644 nm. Luminescence from labeled normal breast cells and autofluorescence from unlabeled cancer and normal cells remain imperceptible under the same conditions.

  19. Enhanced multi-spectral imaging of live breast cancer cells using immunotargeted gold nanoshells and two-photon excitation microscopy

    Science.gov (United States)

    Bickford, Lissett; Sun, Jiantang; Fu, Kun; Lewinski, Nastassja; Nammalvar, Vengadesan; Chang, Joseph; Drezek, Rebekah

    2008-08-01

    We demonstrate the capability of using immunotargeted gold nanoshells as contrast agents for in vitro two-photon microscopy. The two-photon luminescence properties of different-sized gold nanoshells are first validated using near-infrared excitation at 780 nm. The utility of two-photon microscopy as a tool for imaging live HER2-overexpressing breast cancer cells labeled with anti-HER2-conjugated nanoshells is then explored and imaging results are compared to normal breast cells. Five different imaging channels are simultaneously examined within the emission wavelength range of 451-644 nm. Our results indicate that under near-infrared excitation, superior contrast of SK-BR-3 cancer cells labeled with immunotargeted nanoshells occurs at an emission wavelength ranging from 590 to 644 nm. Luminescence from labeled normal breast cells and autofluorescence from unlabeled cancer and normal cells remain imperceptible under the same conditions.

  20. NONLINEAR DYNAMIC INSTABILITY OF DOUBLE-WALLED CARBON NANOTUBES UNDER PERIODIC EXCITATION

    Institute of Scientific and Technical Information of China (English)

    Yiming Fu; Rengui Bi; Pu Zhang

    2009-01-01

    A multiple-elastic beam model based on Euler-Bernoulli-beam theory is presented to investigate the nonlinear dynamic instability of double-walled nanotubes. Taking the geometric nonlinearity of structure deformation, the effects of van der Waais forces as well as the non-coaxial curvature of each nested tube into account, the nonlinear parametric vibration governing equations are derived. Numerical results indicate that the double-walled nanotube (DWNT) can be considered as a single column when the van der Waals forces are sufficiently strong. The stiffness of medium could substantially reduce the area of the nonlinear dynamic instability region, in particular, the geometric nonlinearity can be out of account when the stiffness is large enough. The area of the principal nonlinear instability region and its shifting distance aroused by the nonlinearity both decrease with the increment of the aspect ratio of the nanotubes.

  1. Recent excitements in protein NMR: Large proteins and biologically relevant dynamics

    Indian Academy of Sciences (India)

    SAI CHAITANYA CHILIVERI; MANDAR V DESHMUKH

    2016-12-01

    The advent of Transverse Relaxation Optimized SpectroscopY (TROSY) and perdeuteration allowed biomolecularNMR spectroscopists to overcome the size limitation barrier (~20 kDa) in de novo structure determination of proteins.The utility of these techniques was immediately demonstrated on large proteins and protein complexes (e.g. GroELGroES,ClpP protease, Hsp90-p53, 20S proteasome, etc.). Further, recent methodological developments such asResidual Dipolar Couplings and Paramagnetic Relaxation Enhancement allowed accurate measurement of long-rangestructural restraints. Additionally, Carr-Purcell-Meiboom-Gill (CPMG), rotating frame relaxation experiments (R1ρ)and saturation transfer experiments (CEST and DEST) created never-before accessibility to the μs–ms timescaledynamic parameters that led to the deeper understanding of biological processes. Meanwhile, the excitement in thefield continued with a series of developments in the fast data acquisition methods allowing rapid structural studies onless stable proteins. This review aims to discuss important developments in the field of biomolecular NMRspectroscopy in the recent past, i.e., in the post TROSY era. These developments not only gave access to the structuralstudies of large protein assemblies, but also revolutionized tools in the arsenal of today’s biomolecular NMR and pointto a bright future of biomolecular NMR spectroscopy.

  2. On the dynamic behavior of composite panels under turbulent boundary layer excitations

    Science.gov (United States)

    Ciappi, E.; De Rosa, S.; Franco, F.; Vitiello, P.; Miozzi, M.

    2016-03-01

    In this work high Mach number aerodynamic and structural measurements acquired in the CIRA (Italian Aerospace Research Center) transonic wind tunnel and the models used to analyze the response of composite panels to turbulent boundary layer excitation are presented. The two investigated panels are CFRP (Carbon Fiber-Reinforced Polymer) composite plates and their lay-up is similar to configurations used in aeronautical structures. They differ only for the presence of an embedded viscoelastic layer. The experimental set-up has been designed to reproduce a pressure fluctuations field beneath a turbulent boundary layer as close as possible to those in flight. A tripping system, specifically conceived to this aim for this facility, has been used to generate thick turbulent boundary layers at Mach number values ranging between 0.4 and 0.8. It is shown that the designed setup provides a realistic representation of full scale size pressure spectra in the frequency range of interest for the noise component inside the fuselage, generated by turbulent boundary layer. The significant role of the viscoelastic layer at reducing panel's response is detailed and discussed. Finally, it is demonstrated that at high Mach number the aeroelastic effect cannot be neglected when analyzing the panel response, especially when composite materials are considered.

  3. Controlling Spiral Dynamics in Excitable Media by a Weakly Localized Pacing

    Institute of Scientific and Technical Information of China (English)

    LI Bing-Wei; SUN Li-Li; CHEN Bin; YING He-Ping

    2007-01-01

    @@ Spiral dynamics controlled by a weakly localized pacing around the spiral tip is investigated. Numerical simulations show two distinct characteristics when the pacing is applied with the weak amplitude for suitable frequencies:for a rigidly rotating spiral, a transition from rigid rotation to meandering motion is observed, and for unstable spiral waves, spiral breakup can be prevented. Successfully preventing spiral breakup is relevant to the modulation of the tip trajectory induced by a localized pacing.

  4. Spiking Excitable Semiconductor Laser as Optical Neurons: Dynamics, Clustering and Global Emerging Behaviors

    Science.gov (United States)

    2014-06-28

    feedback. Presented by C. Masoller 12. Congreso de Fisica Estadistica (FISES), Ourense, Spain, April, 2014. Characterizing the complex dynamics of a...rogue waves in semiconductor lasers. To be presented by J. Zamora Munt 5.3. Poster presentations 1. Congreso de Fisica Estadistica (FISES), Palma de...injection. Presented by M. S. Torre 5. Congreso de Fisica Estadistica (FISES), Ourense, Spain, April, 2014. Unveiling the complex organization of

  5. Coherence and population dynamics of chlorophyll excitations in FCP complex: Two-dimensional spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Butkus, Vytautas; Gelzinis, Andrius; Valkunas, Leonas [Department of Theoretical Physics, Faculty of Physics, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania); Center for Physical Sciences and Technology, Savanoriu Ave. 231, 02300 Vilnius (Lithuania); Augulis, Ramūnas [Center for Physical Sciences and Technology, Savanoriu Ave. 231, 02300 Vilnius (Lithuania); Gall, Andrew; Robert, Bruno [Institut de Biologie et Technologies de Saclay, Bât 532, Commissariat à l’Energie Atomique Saclay, 91191 Gif sur Yvette (France); Büchel, Claudia [Institut für Molekulare Biowissenschaften, Universität Frankfurt, Max-von-Laue-Straße 9, Frankfurt (Germany); Zigmantas, Donatas [Department of Chemical Physics, Lund University, P.O. Box 124, 22100 Lund (Sweden); Abramavicius, Darius, E-mail: darius.abramavicius@ff.vu.lt [Department of Theoretical Physics, Faculty of Physics, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania)

    2015-06-07

    Energy transfer processes and coherent phenomena in the fucoxanthin–chlorophyll protein complex, which is responsible for the light harvesting function in marine algae diatoms, were investigated at 77 K by using two-dimensional electronic spectroscopy. Experiments performed on femtosecond and picosecond timescales led to separation of spectral dynamics, witnessing evolutions of coherence and population states of the system in the spectral region of Q{sub y} transitions of chlorophylls a and c. Analysis of the coherence dynamics allowed us to identify chlorophyll (Chl) a and fucoxanthin intramolecular vibrations dominating over the first few picoseconds. Closer inspection of the spectral region of the Q{sub y} transition of Chl c revealed previously not identified, mutually non-interacting chlorophyll c states participating in femtosecond or picosecond energy transfer to the Chl a molecules. Consideration of separated coherent and incoherent dynamics allowed us to hypothesize the vibrations-assisted coherent energy transfer between Chl c and Chl a and the overall spatial arrangement of chlorophyll molecules.

  6. A novel order reduction method for nonlinear dynamical system under external periodic excitations

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The concept of approximate inertial manifold (AIM) is extended to develop a kind of nonlinear order reduction technique for non-autonomous nonlinear systems in second-order form in this paper.Using the modal transformation,a large nonlinear dynamical system is split into a ’master’ subsystem,a ’slave’ subsystem,and a ’negligible’ subsystem.Accordingly,a novel order reduction method (Method I) is developed to construct a low order subsystem by neglecting the ’negligible’ subsystem and slaving the ’slave’ subsystem into the ’master’ subsystem using the extended AIM.As a comparison,Method II accounting for the effects of both ’slave’ subsystem and the ’negligible’ subsystem is also applied to obtain the reduced order subsystem.Then,a typical 5-degree-of-freedom nonlinear dynamical system is given to compare the accuracy and efficiency of the traditional Galerkin truncation (ignoring the contributions of the slave and negligible subsystems),Method I and Method II.It is shown that Method I gives a considerable increase in accuracy for little computational cost in comparison with the standard Galerkin method,and produces almost the same accuracy as Method II.Finally,a 3-degree-of-freedom nonlinear dynamical system is analyzed by using the analytic method for showing predominance and convenience of Method I to obtain the analytically reduced order system.

  7. Explaining pathological changes in axonal excitability through dynamical analysis of conductance-based models

    Science.gov (United States)

    Coggan, Jay S.; Ocker, Gabriel K.; Sejnowski, Terrence J.; Prescott, Steven A.

    2011-10-01

    Neurons rely on action potentials, or spikes, to relay information. Pathological changes in spike generation likely contribute to certain enigmatic features of neurological disease, like paroxysmal attacks of pain and muscle spasm. Paroxysmal symptoms are characterized by abrupt onset and short duration, and are associated with abnormal spiking although the exact pathophysiology remains unclear. To help decipher the biophysical basis for 'paroxysmal' spiking, we replicated afterdischarge (i.e. continued spiking after a brief stimulus) in a minimal conductance-based axon model. We then applied nonlinear dynamical analysis to explain the dynamical basis for initiation and termination of afterdischarge. A perturbation could abruptly switch the system between two (quasi-)stable attractor states: rest and repetitive spiking. This bistability was a consequence of slow positive feedback mediated by persistent inward current. Initiation of afterdischarge was explained by activation of the persistent inward current forcing the system to cross a saddle point that separates the basins of attraction associated with each attractor. Termination of afterdischarge was explained by the attractor associated with repetitive spiking being destroyed. This occurred when ultra-slow negative feedback, such as intracellular sodium accumulation, caused the saddle point and stable limit cycle to collide; in that regard, the active attractor is not truly stable when the slowest dynamics are taken into account. The model also explains other features of paroxysmal symptoms, including temporal summation and refractoriness.

  8. Reciprocal modulation of IK1-INa extends excitability in cardiac ventricular cells

    Directory of Open Access Journals (Sweden)

    Anthony Varghese

    2016-11-01

    Full Text Available The inwardly rectifying potassium current (IK1 and the fast inward sodium current (INa are reciprocally modulated in mammalian ventricular myocytes. An increase in the expression of channels responsible for one of these two currents results in a corresponding increase in expression of the other. These currents are critical in the propagation of action potentials (AP during the normal functioning of the heart. This study identifies a physiological role for IK1-INa reciprocal modulation in ventricular fiber activation thresholds and conduction. Simulations of action potentials in single cells and propagating APs in cardiac fibers were carried out using an existing model of electrical activity in cardiac ventricular myocytes. The conductances, GK1, of the inwardly rectifying potassium current, and GNa, of the fast inward sodium current were modified independently and in tandem to simulate reciprocal modulation. In single cells, independent modulation of GK1 alone resulted in changes in activation thresholds that were qualitatively similar to those for reciprocal GK1-GNa modulation and unlike those due to independent modulation of GNa alone, indicating that GK1 determines the cellular activation threshold. On the other hand, the variations in conduction velocity in cardiac cell fibers were similar for independent GNa modulation and for tandem changes in GK1-GNa, suggesting that GNa is primarily responsible for setting tissue AP conduction velocity. Conduction velocity dependence on GK1-GNa is significantly affected by the intercellular gap junction conductance. While the effects on the passive fiber space constant due to changes in both GK1 and the intercellular gap junction conductance, Ggj, were in line with linear cable theory predictions, both conductances had surprisingly large effects on fiber activation thresholds. Independent modulation of GK1 rendered cardiac fibers inexcitable at higher levels of GK1 whereas tandem GK1-GNa changes allowed

  9. Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying πσ{sup ∗} states

    Energy Technology Data Exchange (ETDEWEB)

    Karmakar, Shreetama; Mukhopadhyay, Deb Pratim; Chakraborty, Tapas, E-mail: pctc@iacs.res.in [Physical Chemistry Department, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

    2015-05-14

    Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S{sub 1}←S{sub 0} absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S{sub 1} origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of πσ{sup ∗} character in the vicinity of the lowest valence ππ{sup ∗} state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ππ{sup ∗} and a nearby dissociative πσ{sup ∗} state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H{sub 2}O){sub n} clusters (n = 1-11), intensities of a number of πσ{sup ∗} states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the

  10. Diagnosis of basal cell carcinoma by two photon excited fluorescence combined with lifetime imaging

    Science.gov (United States)

    Fan, Shunping; Peng, Xiao; Liu, Lixin; Liu, Shaoxiong; Lu, Yuan; Qu, Junle

    2014-02-01

    Basal cell carcinoma (BCC) is the most common type of human skin cancer. The traditional diagnostic procedure of BCC is histological examination with haematoxylin and eosin staining of the tissue biopsy. In order to reduce complexity of the diagnosis procedure, a number of noninvasive optical methods have been applied in skin examination, for example, multiphoton tomography (MPT) and fluorescence lifetime imaging microscopy (FLIM). In this study, we explored two-photon optical tomography of human skin specimens using two-photon excited autofluorescence imaging and FLIM. There are a number of naturally endogenous fluorophores in skin sample, such as keratin, melanin, collagen, elastin, flavin and porphyrin. Confocal microscopy was used to obtain structures of the sample. Properties of epidermic and cancer cells were characterized by fluorescence emission spectra, as well as fluorescence lifetime imaging. Our results show that two-photon autofluorescence lifetime imaging can provide accurate optical biopsies with subcellular resolution and is potentially a quantitative optical diagnostic method in skin cancer diagnosis.

  11. A DYNAMIC MODEL FOR A DISC EXCITED BY VERTICALLY MISALIGNED, ROTATING, FRICTIONAL SLIDERS

    Institute of Scientific and Technical Information of China (English)

    OUYANG Huajiang; GU Yuanxian; YANG Haitian

    2004-01-01

    This paper presents a dynamic model for a disc subjected to two sliders rotating in the circumferential direction over the top and bottom surfaces of the disc. The two sliders are vertically misaligned and each is a mass-spring-damper system with friction between the slider and the disc.The moving loads produced by misaligned sliders can destabilise the whole system. Stability analysis is carried out in a simulated example. This model is meant to explain the friction mechanism for generating unstable vibration in many applications involving rotating discs.

  12. Dynamic Reliability Evaluation of Double-Layer Cylindrical Latticed Shell under Multi-Support Excitations

    Institute of Scientific and Technical Information of China (English)

    柳春光; 李会军

    2010-01-01

    To overcome the excessive computational cost and/or bad accuracy of traditional approaches,the probabilistic density evolution method(PDEM) is introduced.The dynamic reliability of a double-layer cylindrical latticed shell is evaluated by applying PDEM and Monte Carlo Method(MCM) respectively,and four apparent wave velocities(100 m/s,500 m/s,800 m/s and 1 200 m/s) and five thresholds(0.1 m,0.2 m,0.3 m,0.4 m and 0.5 m) are taken into consideration.Only the difference between threshold and maximal deformation...

  13. Dynamic tunneling ionization of excited hydrogen atoms: A precise experiment versus theories

    Science.gov (United States)

    Sauer, B. E.; Yoakum, S.; Moorman, L.; Koch, P. M.; Richards, D.; Dando, P. A.

    1992-01-01

    New data for n0=24,...,32 H atoms ionized by a linearly polarized, 9.908-GHz electric field are compared with calculations. Being more precise than laser multiphoton ionization experiments with tightly bound atoms, our experiments distinguish between tunneling through and classical escape over a slowly oscillating barrier and between one- and many-state dynamical processes. Formulas used to interpret low-frequency laser multiphoton ionization data poorly describe our results. Our data delineate ranges of validity of other partly successful models and are best reproduced by a new 3D semiclassical model.

  14. Dynamic tunneling ionization of excited hydrogen atoms: A precise experiment versus theories

    Energy Technology Data Exchange (ETDEWEB)

    Sauer, B.E.; Yoakum, S.; Moorman, L.; Koch, P.M. (Department of Physics, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States)); Richards, D.; Dando, P.A. (Mathematics Faculty, Open University, Milton Keynes MK7 6AA (United Kingdom))

    1992-01-27

    New data for {ital n}{sub 0}=24,...,32 H atoms ionized by a linearly polarized, 9.908-GHz electric field are compared with calculations. Being more precise than laser multiphoton ionization experiments with tightly bound atoms, our experiments distinguish between tunneling {ital through} and classical escape {ital over} a slowly oscillating barrier and between one- and many-state dynamical processes. Formulas used to interpret low-frequency laser multiphoton ionization data poorly describe our results. Our data delineate ranges of validity of other partly successful models and are best reproduced by a new 3D semiclassical model.

  15. Single photon emission dynamics of InP-InGaP quantum dots under p-shell excitation

    Science.gov (United States)

    Nowak, A. K.; Martín, M. D.; van der Meulen, H. P.; Ripalda, J. M.; González, L.; González, Y.; Viña, L.; Calleja, J. M.

    2014-10-01

    Single photon emitters based on InP/GaInP quantum dots have been studied under p-shell excitation by time-resolved photoluminescence and photon correlation spectroscopy. By tuning the excitation energy in resonance with quantum dot excited states, we observe a marked decrease of the antibunching time as a result of the increased excitation rate for decreasing energy detuning. A similar behavior is observed by increasing the pump power. The spectral dependence of the antibunching rate follows the energy profile of the excited state, as measured by photoluminescence excitation.

  16. Dynamic Solvent Effect on Ultrafast Charge Recombination Kinetics in Excited Donor-Acceptor Complexes.

    Science.gov (United States)

    Mikhailova, Tatyana V; Mikhailova, Valentina A; Ivanov, Anatoly I

    2016-11-23

    Manifestation of the dynamic solvent effect (DSE) on the charge recombination (CR) kinetics of photoexcited donor-acceptor complexes in polar solvents has been investigated within the framework of the multichannel stochastic model. The model takes into account the reorganization of both the solvent and a number of intramolecular high-frequency vibration modes as well as their relaxation. The non-Markovian solvent dynamics is described in terms of two relaxation modes. The similarities and differences inherent to ultrafast charge transfer reactions occurring in the nonequilibrium and thermal regimes have been identified. The most important differences are as follows: (1) the DSE is strong in the area of weak exergonicity and is weak in the area of strong exergonicity for thermal reactions, whereas for the nonequilibrium reactions, the regions of strong and weak DSEs are reversed; (2) an increase in the electronic coupling value results in a decrease in the magnitude of DSE for nonequilibrium electron transfer and in its increase for the thermal reactions; and (3) the two-staged regime most clearly manifests if the reorganization energy of the relaxation modes noticeably exceeds the CR free-energy gap. With an increase in electronic coupling, the kinetics approaches the exponential regime because in the limit of strong electronic coupling, the reaction includes only single, nonequilibrium, stage.

  17. Mean field dynamics of networks of delay-coupled noisy excitable units

    Science.gov (United States)

    Franović, Igor; Todorović, Kristina; Vasović, Nebojša; Burić, Nikola

    2016-06-01

    We use the mean-field approach to analyze the collective dynamics in macroscopic networks of stochastic Fitzhugh-Nagumo units with delayed couplings. The conditions for validity of the two main approximations behind the model, called the Gaussian approximation and the Quasi-independence approximation, are examined. It is shown that the dynamics of the mean-field model may indicate in a self-consistent fashion the parameter domains where the Quasi-independence approximation fails. Apart from a network of globally coupled units, we also consider the paradigmatic setup of two interacting assemblies to demonstrate how our framework may be extended to hierarchical and modular networks. In both cases, the mean-field model can be used to qualitatively analyze the stability of the system, as well as the scenarios for the onset and the suppression of the collective mode. In quantitative terms, the mean-field model is capable of predicting the average oscillation frequency corresponding to the global variables of the exact system.

  18. Analysis of Dynamic Response of Explosive Disposal Robot to Rough Road Excitation

    Institute of Scientific and Technical Information of China (English)

    MO Haijun; HUANG Ping; HU Qingchun; DUAN Fuhai

    2006-01-01

    When the explosive disposal robot traveling over a rough road, it will shake up and down, and generates dynamic loads. Furthermore, the jolt of the explosive disposal robot will result in oscillation and large inertia forces of the explosive, and will effect the stability of the grasped explosive, even cause the explosive slipping from the claw and falling to the ground, which seriously threats the safety of the robot and around environment. A tracked explosive disposal robot has been developed at South China University of Technology. This paper takes the explosive disposal robot and the grasped explosive as study object. Especially focuses on the response analysis of the grasped explosive when the robot traveling over a rough road. Analyzing the vibration characteristic of the explosive and the effects of the robot moving speeds on the stability of the explosive. The dynamic response of the explosive is obtained by simulation, the results show that the velocity of the robot is a sensitivity influence factor on the oscillation of grasped explosive.

  19. Molecular aspects of electrical excitation in lipid bilayers and cell membranes.

    Science.gov (United States)

    Mueller, P

    1976-01-01

    Several compounds of fungal or bacterial origin (EIM, alamethicin, monazomycin, DJ400B) can be incorporated into planar lipid bilayers where they form molecular channels and generate voltage-dependent ion conductances. When studied by voltage clamp, the kinetic and steady-state characteristics of these conductance changes are in every respect identical to those found in excitable cell membranes, and their major aspects can be quantitatively described by the Hodgkin-Huxley equations. Thus, the steady-state conductance is an expotential function of the membrane potential, the conductance rises with a sigmoid time course and decays exponentially, and the time constants of the conductance changes go through a maximum as a function of the potential. The conductances also show inactivation as seen in the sodium channels of nerve and the potassium channels of muscle. In addition, there appear for particular pulsing sequences certain kinetic transients that cannot be accounted for by the Hodgkin-Huxley equations but are also seen in identical form in nerve. Because the kinetics are identical in all excitable cell membranes and in these bilayers, it is likely that, in spite of the diverse chemical nature of the channel-forming molecules in the bilayers and the widely differing ion selectivities in the cellular systems, the mechanism by which the membrane opens and closes for the flow of ions is essentially the same in all cases. The kinetic data imply that a cooperative process is involved in the gating action. In principle, two different concepts could account for the kinetics--one involving an intramolecular configurational change within a complex permanent channel, the other, the assembly of a channel through the voltage-dependent aggregation of monomeric channel precursors. In the bilayers the high-order dependence of the steady-state conductance and of the gating time constants on the concentration of the channel formers suggests an aggregation mechanism in which the

  20. Ab initio nonadiabatic molecular dynamics of the ultrafast excitation energy transfer in small semiconducting carbon nanotube aggregates

    Science.gov (United States)

    Postupna, Olena; Long, Run; Prezhdo, Oleg

    2012-02-01

    Outstanding physical properties of carbon nanotubes (CNTs), such as well-defined optical resonance and ultrafast nonlinear response, result in CNTs gaining popularity in academic and industrial endeavors as potential effective energy generating devices. Following recent experiments on ultrafast excitation energy transfer in small semiconducting carbon nanotube aggregates [1], we report results of ab initio nonadiabatic molecular dynamics simulation of the energy transfer taking place in two carbon nanotube systems. We investigate the energy transfer between (8,4) and (10,0) CNTs, as well as (8,4) and (13,0) CNTs. In both cases, the CNTs are orthogonal to each other. Luer et al. in [1] elucidate the second excitonic transitions followed by fast intratube relaxation and energy transfer from the (8,4) CNT toward other acceptor tubes. Our project aims to provide a better understanding of the energy transfer mechanism in the given systems, which should foster development of a theory for the electronic structure and dynamics of CNT networks, hence enhancing their tailoring and application in the future. References 1.Larry Luer, Jared Crochet, Tobias Hertel, Giulio Cerullo, Gugliermo Lanzani. ACSNano. Vol.4, No. 7, 4265-4273

  1. Thermal Adaptability of the Light-Harvesting Complex 2 from Thermochromatium tepidum: Temperature-Dependent Excitation Transfer Dynamics.

    Science.gov (United States)

    Shi, Ying; Zhao, Ning-Jiu; Wang, Peng; Fu, Li-Min; Yu, Long-Jiang; Zhang, Jian-Ping; Wang-Otomo, Zheng-Yu

    2015-11-25

    The photosynthetic purple bacterium Thermochromatium (Tch.) tepidum is a thermophile that grows at an optimal temperature of ∼50 °C. We have investigated, by means of steady-state and time-resolved optical spectroscopies, the effects of temperature on the near-infrared light absorption and the excitation energy transfer (EET) dynamics of its light-harvesting complex 2 (LH2), for which the mesophilic counterpart of Rhodobacter (Rba.) sphaeroides 2.4.1 (∼30 °C) was examined in comparison. In a limited range around the physiological temperature (10-55 °C), the B800-to-B850 EET process of the Tch. tepidum LH2, but not the Rba. sphaeroides LH2, was found to be characteristically temperature-dependent, mainly because of a temperature-tunable spectral overlap. At 55 °C, the LH2 complex from Tch. tepidum maintained efficient near-infrared light harvesting and B800-to-B850 EET dynamics, whereas this EET process was disrupted in the case of Rba. sphaeroides 2.4.1 owing to the structural distortion of the LH2 complex. Our results reveal a remarkable thermal adaptability of the light-harvesting function of Tch. tepidum, which could enhance our understanding of the survival strategy of this thermophile in response to environmental challenges.

  2. The effect of solvent additives on morphology and excited-state dynamics in PCPDTBT:PCBM photovoltaic blends.

    Science.gov (United States)

    Etzold, Fabian; Howard, Ian A; Forler, Nina; Cho, Don M; Meister, Michael; Mangold, Hannah; Shu, Jie; Hansen, Michael Ryan; Müllen, Klaus; Laquai, Frédéric

    2012-06-27

    The dependence of the thin film morphology and excited-state dynamics for the low-bandgap donor-acceptor copolymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) in pristine films and in blends (1:2) with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) on the use of the solvent additive 1,8-octanedithiol (ODT) is studied by solid-state nuclear magnetic resonance (NMR) spectroscopy and broadband visible and near-infrared pump-probe transient absorption spectroscopy (TAS) covering a spectral range from 500-2000 nm. The latter allows monitoring of the dynamics of excitons, bound interfacial charge-transfer (CT) states, and free charge carriers over a time range from femto- to microseconds. The broadband pump-probe experiments reveal that excitons are not only generated in the polymer but also in PCBM-rich domains. Depending on the morphology controlled by the use of solvent additives, polymer excitons undergo mainly ultrafast dissociation (photovoltaic devices.

  3. Dynamics of plasma formation and permanent structural transformation in ZBLAN excited by tightly focused femtosecond laser pulses

    Science.gov (United States)

    Cho, Sung-Hak; Chang, Won-Seok; Kim, Kwang-Ryul; Hong, Jong Wook

    2009-01-01

    Time-resolved dynamics of plasma formation and bulk refractive-index modification in fluoride glass (ZBLAN) excited by a tightly focused femtosecond (130 fs) Ti:sapphire laser ( λp=790 nm) was observed in situ. The femtosecond time-resolved pump-probe measurement with perpendicularly linear polarized beams was used to study the dynamics of both plasma formation and induced permanent structural transformation with refractive-index change. In the refractive-index domain, the lifetime of induced plasma formation is ˜35 ps and structural transition time for forming the refractive-index change is ˜80 ps. In the optical damage domain, however, the lifetime of induced plasma formation is ˜40 ps and structural transition time for forming the optical damage is ˜140 ps. We found that the process of refractive-index bulk modification is significantly different from that of optical cracks. From the diffraction efficiency of Kogelnik's coupled mode theory, the maximum value of refractive-index change (Δ n) was estimated to be 1.3×10 -2. By the scanning of fluoride glass on the optical X-Y-Z stages, the fabrication of internal grating with refractive-index modification was demonstrated in fluoride glass using tightly focused femtosecond laser.

  4. Atomistic modeling of two-dimensional electronic spectra and excited-state dynamics for a Light Harvesting 2 complex.

    Science.gov (United States)

    van der Vegte, C P; Prajapati, J D; Kleinekathöfer, U; Knoester, J; Jansen, T L C

    2015-01-29

    The Light Harvesting 2 (LH2) complex is a vital part of the photosystem of purple bacteria. It is responsible for the absorption of light and transport of the resulting excitations to the reaction center in a highly efficient manner. A general description of the chromophores and the interaction with their local environment is crucial to understand this highly efficient energy transport. Here we include this interaction in an atomistic way using mixed quantum-classical (molecular dynamics) simulations of spectra. In particular, we present the first atomistic simulation of nonlinear optical spectra for LH2 and use it to study the energy transport within the complex. We show that the frequency distributions of the pigments strongly depend on their positions with respect to the protein scaffold and dynamics of their local environment. Furthermore, we show that although the pigments are closely packed the transition frequencies of neighboring pigments are essentially uncorrelated. We present the simulated linear absorption spectra for the LH2 complex and provide a detailed explanation of the states responsible for the observed two-band structure. Finally, we discuss the energy transfer within the complex by analyzing population transfer calculations and 2D spectra for different waiting times. We conclude that the energy transfer from the B800 ring to the B850 ring is mediated by intermediate states that are delocalized over both rings, allowing for a stepwise downhill energy transport.

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

    Science.gov (United States)

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

    2013-10-03

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

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

    Science.gov (United States)

    Teimoory, Faranak; Loppnow, Glen R

    2016-05-04

    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.

  7. Stochastic dynamical model of a growing network based on self-exciting point process

    CERN Document Server

    Golosovsky, Michael; 10.1103/PhysRevLett.109.098701

    2012-01-01

    We perform experimental verification of the preferential attachment model that is commonly accepted as a generating mechanism of the scale-free complex networks. To this end we chose citation network of Physics papers and traced citation history of 40,195 papers published in one year. Contrary to common belief, we found that citation dynamics of the individual papers follows the \\emph{superlinear} preferential attachment, with the exponent $\\alpha= 1.25-1.3$. Moreover, we showed that the citation process cannot be described as a memoryless Markov chain since there is substantial correlation between the present and recent citation rates of a paper. Basing on our findings we constructed a stochastic growth model of the citation network, performed numerical simulations based on this model and achieved an excellent agreement with the measured citation distributions.

  8. Detection, Evaluation, and Optimization of Optical Signals Generated by Fiber Optic Bragg Gratings Under Dynamic Excitations

    Science.gov (United States)

    Adamovsky, Grigory; Lekki, John; Lock, James A.

    2002-01-01

    The dynamic response of a fiber optic Bragg grating to mechanical vibrations is examined both theoretically and experimentally. The theoretical expressions describing the consequences of changes in the grating's reflection spectrum are derived for partially coherent beams in an interferometer. The analysis is given in terms of the dominant wavelength, optical bandwidth, and optical path difference of the interfering signals. Changes in the reflection spectrum caused by a periodic stretching and compression of the grating were experimentally measured using an unbalanced Michelson interferometer, a Michelson interferometer with a non-zero optical path difference. The interferometer's sensitivity to changes in dominant wavelength of the interfering beams was measured as a function of interferometer unbalance and was compared to theoretical predictions. The theoretical analysis enables the user to determine the optimum performance for an unbalanced interferometer.

  9. Critical appraisal of excited state nonadiabatic dynamics simulations of 9H-adeninea)

    Science.gov (United States)

    Barbatti, Mario; Lan, Zhenggang; Crespo-Otero, Rachel; Szymczak, Jaroslaw J.; Lischka, Hans; Thiel, Walter

    2012-12-01

    In spite of the importance of nonadiabatic dynamics simulations for the understanding of ultrafast photo-induced phenomena, simulations based on different methodologies have often led to contradictory results. In this work, we proceed through a comprehensive investigation of on-the-fly surface-hopping simulations of 9H-adenine in the gas phase using different electronic structure theories (ab initio, semi-empirical, and density functional methods). Simulations that employ ab initio and semi-empirical multireference configuration interaction methods predict the experimentally observed ultrafast deactivation of 9H-adenine with similar time scales, however, through different internal conversion channels. Simulations based on time-dependent density functional theory with six different hybrid and range-corrected functionals fail to predict the ultrafast deactivation. The origin of these differences is analyzed by systematic calculations of the relevant reaction pathways, which show that these discrepancies can always be traced back to topographical features of the underlying potential energy surfaces.

  10. Principal cell spiking, postsynaptic excitation, and oxygen consumption in the rat cerebellar cortex

    DEFF Research Database (Denmark)

    Thomsen, Kirsten; Hansen, Henning Piilgaard; Gjedde, Albert

    2009-01-01

    ) of postsynaptic excitation and PC spiking during evoked and ongoing neuronal activity in the rat. By inhibiting excitatory synaptic input using ionotropic glutamate receptor blockers, we found that the increase in CMRO2 evoked by parallel fiber (PF) stimulation depended entirely on postsynaptic excitation...

  11. Local administration of resveratrol inhibits excitability of nociceptive wide-dynamic range neurons in rat trigeminal spinal nucleus caudalis.

    Science.gov (United States)

    Shimazu, Yoshihito; Shibuya, Eri; Takehana, Shiori; Sekiguchi, Kenta; Oshima, Katsuo; Kamata, Hiroaki; Karibe, Hiroyuki; Takeda, Mamoru

    2016-06-01

    Although we recently reported that intravenous administration of resveratrol suppresses trigeminal nociception, the precise peripheral effect of resveratrol on nociceptive and non-nociceptive mechanical stimulation-induced trigeminal neuron activity in vivo remains to be determined. The aim of the present study was to investigate whether local subcutaneous administration of resveratrol attenuates mechanical stimulation-induced excitability of trigeminal spinal nucleus caudalis (SpVc) neuron activity in rats, in vivo. Extracellular single-unit recordings were made of SpVc wide-dynamic range (WDR) neuron activity in response to orofacial mechanical stimulation in pentobarbital-anesthetized rats. Neurons responded to non-noxious and noxious mechanical stimulation applied to the orofacial skin. Local subcutaneous administration of resveratrol (1-10mM) into the orofacial skin dose dependently and significantly reduced the mean number of SpVc WDR neurons firing in response to both non-noxious and noxious mechanical stimuli, with the maximal inhibition of discharge frequency in response to both stimuli being seen within 5min. These inhibitory effects were no longer evident after approximately 20min. The mean magnitude of inhibition by resveratrol (10mM) of SpVc neuron discharge frequency was almost equal to that of the local anesthetic 1% lidocaine (37mM). These results suggest that local injection of resveratrol into the peripheral receptive field suppresses the excitability of SpVc neurons, possibly via inhibition of Na(+) channels in the nociceptive nerve terminals of trigeminal ganglion neurons. Therefore, local subcutaneous administration of resveratrol may provide relief of trigeminal nociceptive pain, without side effects, thus contributing to the suite of complementary and alternative medicines used as local anesthetic agents.

  12. When do we need to account for the geometric phase in excited state dynamics ?

    CERN Document Server

    Ryabinkin, Ilya G; Izmaylov, Artur F

    2014-01-01

    We investigate a role of the geometric phase (GP) in an internal conversion process when the system changes its electronic state by passing through a conical intersection (CI). Local analysis of a two-dimensional linear vibronic coupling (LVC) model Hamiltonian in a vicinity of the CI shows that a role of the GP is twofold: First, it compensates for a repulsion created by the so-called diagonal Born-Oppenheimer correction (DBOC). Second, the GP enhances non-adiabatic transition probability for a wave-packet part that experiences a central collision with the CI. To assess significance of both GP contributions we propose two indicators that can be computed from parameters of electronic surfaces and initial conditions. To generalize our analysis to N-dimensional systems we introduce a reduction of a general N-dimensional LVC model to an effective 2D LVC model using a mode transformation that preserves short-time dynamics of the original N-dimensional model. Using examples of the bis(methylene) adamantyl cation, ...

  13. Theoretical Analysis of Time-Dependent Wave-Packet Dynamics:Proton Impact Excitation (2s- 2p) with Li Atom

    Institute of Scientific and Technical Information of China (English)

    CHEN Shao-Hao; WANG Feng; LI Jia-Ming

    2004-01-01

    Introducing a theoretical method to treat time-dependent wave-packet dynamics for atom collisions, we calculate the cross sections of proton impact excitation (2s - 2p) with a Li atom by directly numerically integrating the time-dependent Schrodinger equation on a three-dimensional Cartesian mesh. Our calculated results are in good agreement with the available experimental measurements.

  14. CALCULATION OF THE PROTON-TRANSFER RATE USING DENSITY-MATRIX EVOLUTION AND MOLECULAR-DYNAMICS SIMULATIONS - INCLUSION OF THE PROTON EXCITED-STATES

    NARCIS (Netherlands)

    MAVRI, J; BERENDSEN, HJC

    1995-01-01

    The methodology for treatment of proton transfer processes by density matrix evolution (DME) with inclusion of many excited states is presented. The DME method (Berendsen, H. J. C.; Mavri, J. J. Phys. Chem. 1993, 97, 13464) that simulates the dynamics of quantum systems embedded in a classical envir

  15. Optical control of cardiac cell excitability based on two-photon infrared absorption of AzoTAB

    CERN Document Server

    Shcherbakov, D; Erofeev, I; Astafiev, A

    2014-01-01

    Recent studies of AzoTAB activity in excitable cell cultures have shown that this substance is able to control excitability depending on isomer, cis or trans, predominating in the cellular membrane. Control of isomerization can be performed noninvasively by UV-visual radiation. At the same time it is well-known that azobenezenes can be effectively transformed from one isomer into another by two-photon absorption. Current work is devoted to the study of trans-AzoTAB two-photon transformation in aqueous solution and inside primal neonatal contractive rat cardiomyocytes. In accordance with results obtained Azo-TAB can be used as a probe for two-photon optical control of cardiac excitability.

  16. Sperm Cell Dynamics in Shallow Chambers

    Science.gov (United States)

    Condat, Carlos; Marconi, Veronica; Guidobaldi, Alejandro; Giojalas, Laura; Silhanek, Alejandro; Jeyaram, Yogesh; Moshchalkov, Victor

    2015-03-01

    Self-propelled microorganisms are attracted to surfaces. This makes their dynamic behavior in restricted geometries very different from that observed in the bulk. Here we analyze the motion of spermatozoids confined to shallow chambers, investigating the nature of the cell trajectories and their accumulation near the side boundaries. Observed cell trajectories are composed of a succession of quasi-circular and quasi-linear segments. This suggests that the cells follow a path of intermittent trappings near the top and down surfaces separated by stretches of quasi-free motion near the center of the gap. Use of microstructured petal-shaped edges limits accumulation near the borders and contributes to increase the concentration in the chamber interior. System stabilization occurs over times of the order of minutes, which agrees well with a theoretical estimate that assumes that the cell mean-square displacement is largely due to the quasi-linear segments. Pure quasi-circular trajectories would require several hours to stabilize. Our estimates also indicate that stabilization proceeds 2.5 times faster in the rosette geometries than in the smooth-edged chambers, which is another practical reason to prefer the former.

  17. Mechanosensing Dynamics of Red blood Cells

    Science.gov (United States)

    Wan, Jiandi

    2015-11-01

    Mechanical stress-induced deformation of human red blood cells (RBCs) plays important physiopathological roles in oxygen delivery, blood rheology, transfusion, and malaria. Recent studies demonstrate that, in response to mechanical deformation, RBCs release adenosine-5'-triphosphate (ATP), suggesting the existence of mechanotransductive pathways in RBCs. Most importantly, the released ATP from RBCs regulates vascular tone and impaired release of ATP from RBCs has been linked to diseases such as type II diabetes and cystic fibrosis. To date, however, the mechanisms of mechanotransductive release of ATP from RBCs remain unclear. Given that RBCs experience shear stresses continuously during the circulation cycle and the released ATP plays a central role in vascular physiopathology, understanding the mechanotransductive release of ATP from RBCs will provide not only fundamental insights to the role of RBCs in vascular homeostasis but also novel therapeutic strategies for red cell dysfunction and vascular disease. This talk describes the main research in my group on integrating microfluidic-based approaches to study the mechanosensing dynamics of RBCs. Specifically, I will introduce a micro?uidic approach that can probe the dynamics of shear-induced ATP release from RBCs with millisecond resolution and provide quantitative understandings of the mechanosensitive ATP release processes in RBCs. Furthermore, I will also describe our recent findings about the roles of the Piezo1 channel, a newly discovered mechanosensitive cation channel in the mechanotransductive ATP release in RBCs. Last, possible functions of RBCs in the regulation of cerebral blood flow will be discussed.

  18. Defect States in Copper Indium Gallium Selenide Solar Cells from Two-Wavelength Excitation Photoluminescence Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, Soren A.; Dippo, Patricia; Mansfield, Lorelle M.; Glynn, Stephen; Kuciauskas, Darius

    2016-11-21

    We use two-wavelength excitation photoluminescence spectroscopy to probe defect states in CIGS thin films. Above-Eg excitation is combined with a tunable IR bias light that modulates the population of the defect states. We find that IR illumination in the range of 1400-2000 nm (0.62-0.89 eV) causes a reduction of the PL intensity, the magnitude of which scales linearly with IR power. Further, KF post deposition treatment has only a modest influence on the effect of the IR excitation. Initial data suggest that we have developed an optical characterization tool for band-gap defect states.

  19. Exciton Dynamics in Alternative Solar Cell Materials: Polymers, Nanocrystals, and Small Molecules

    Science.gov (United States)

    Pundsack, Thomas J.

    To keep fossil fuel usage in 2040 even with 2010 usage, 50% of global energy will need to come from alternative sources such as solar cells. While the photovoltaic market is currently dominated by crystalline silicon, there are many low-cost solar cell materials such as conjugated polymers, semiconductor nanocrystals, and organic small molecules which could compete with fossil fuels. To create cost-competitive devices, understanding the excited state dynamics of these materials is necessary. The first section of this thesis looks at aggregation in poly(3-hexylthiophene) (P3HT) which is commonly used in organic photovoltaics. The amount of aggregation in P3HT thin films was controlled by using a mixture of regioregular and regiorandom P3HT. Even with few aggregates present, excited states were found to transfer from amorphous to aggregate domains in fits and the most reasonable fitting parameters.

  20. Tracking of mercury ions in living cells with a fluorescent chemodosimeter under single- or two-photon excitation

    Energy Technology Data Exchange (ETDEWEB)

    Lu Zhoujun [State Key Lab for Advanced Photonic Materials and Devices, Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China); Wang Peinan [State Key Lab for Advanced Photonic Materials and Devices, Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China)], E-mail: pnwang@fudan.edu.cn; Zhang Yu [State Key Lab for Advanced Photonic Materials and Devices, Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China); Chen Jiyao; Zhen Shen [Department of Physics, Fudan University, Shanghai 200433 (China); Leng Bing; Tian He [Labs for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237 (China)

    2007-08-10

    Tracking of Hg{sup 2+} in solutions as well as in living cells was conducted with a fluorescent chemodosimeter by measuring the spectral shift of its fluorescence under single- or two-photon excitation. The spectral hypsochromic shifts of this chemodosimeter when reacting with Hg{sup 2+} were found to be about 50 nm in acetonitrile/water solutions and 32 nm in Euglena gracilis 277 living cells. This chemodosimeter shows high sensitivity and selectivity, and is not influenced by the pH values. It can signal Hg{sup 2+} in solutions down to the ppb range under either single-photon excitation (SPE) at 405 nm or two-photon excitation (TPE) at 800 nm. However, with low cellular chemodosimeter concentrations, the SPE spectra were disturbed by the auto-fluorescence from the native fluorophore in the cell, while the TPE spectra were still of high quality since the two-photon absorption cross section of this chemodosimeter is much larger than that of the native fluorophores in the cell.

  1. Chaotic dynamic and control for micro-electro-mechanical systems of massive storage with harmonic base excitation

    Energy Technology Data Exchange (ETDEWEB)

    Perez Polo, Manuel F. [Departamento de Fisica, Ingenieria de Sistemas y Teoria de la Senal, Universidad de Alicante, Escuela Politecnica Superior, Campus de San Vicente, 03071 Alicante (Spain)], E-mail: manolo@dfists.ua.es; Perez Molina, Manuel [Facultad de Ciencias Matematicas, Universidad Nacional de Educacion a Distancia. UNED, C/Boyero 12-1A, Alicante 03007 (Spain)], E-mail: ma_perez_m@hotmail.com; Gil Chica, Javier [Departamento de Fisica, Ingenieria de Sistemas y Teoria de la Senal, Universidad de Alicante, Escuela Politecnica Superior, Campus de San Vicente, 03071 Alicante (Spain)], E-mail: gil@dfists.ua.es

    2009-02-15

    This paper explores chaotic behaviour and control of micro-electro-mechanical systems (MEMS), which consist of thousands of small read/write probe tips that access gigabytes of data stored in a non-volatile magnetic surface. The model of the system is formed by two masses connected by a nonlinear spring and a viscous damping. The paper shows that, by means of an adequate feedback law, the masses can behave as two coupled Duffing's oscillators, which may reach chaotic behaviour when harmonic forces are applied. The chaotic motion is destroyed by applying the following control strategies: (i) static output feedback control law with constant forces and (ii) geometric nonlinear control. The aim is to drive the masses to a set point even with harmonic base excitation, by using chaotic dynamics and nonlinear control. The paper shows that it is possible to obtain a positioning time around a few ms with sub-nanometre accuracy, velocities, accelerations and forces, as it appears in the design of present MEMS devices. Numerical simulations are used to verify the mathematical discussions.

  2. Center for Fluorescence Spectroscopy: advanced studies of fluorescence dynamics, lifetime imaging, clinical sensing, two-photon excitation, and light quenching

    Science.gov (United States)

    Lakowicz, Joseph R.; Malak, Henryk M.; Gryczynski, Ignacy; Szmacinski, Henryk; Kusba, Jozef; Akkaya, Engin; Terpetschnig, Ewald A.; Johnson, Michael L.

    1994-08-01

    The Center for Fluorescence Spectroscopy (CFS) is a multi-user facility providing state of the art time-resolved fluorescence instrumentation and software for scientists, whose research can be enhanced by such experimental data. The CFS is a national center, supported by the National Center for Research Resources Division of the National Institutes of Health, and in part by the National Science Foundation. Both time-domain (TD) and frequency- domain (FD) measurements (10 MHz to 10 Ghz) are available, with a wide range of excitation and emission wavelengths (UV to NIR). The data can be used to recover distances and site-to-site diffusion in protein, interactions between macromolecules, accessibility of fluorophores to quenchers, and the dynamic properties of proteins, membranes and nucleic acids. Current software provides for analysis of multi-exponential intensity and anisotropy decays, lifetime distribution, distance distributions for independent observation of fluorescence donors and acceptors, transient effects in collisional quenching, phase-modulation spectra and time-resolved emission spectra. Most programs provide for global analysis of multiple data sets obtained under similar experimental conditions. Data can be analyzed on-site by connection with the CFS computers through the internet. During six years of operation we have established scientific collaborations with over 30 academic and industrial groups in the United States. These collaborations have resulted in 63 scientific papers.

  3. Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals

    Science.gov (United States)

    Tang, Jau

    2008-04-01

    In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (<70nm for aluminum and <200nm for gold), but becomes less dependent if further thickness increases. Coherent phonon excitation and propagation from the stressed bulk atoms due to impulsive forces as well as the linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.

  4. Small amplitude Dynamic AFM: quantifying interactions with different tip detection and excitation schemes in presence of additional resonances

    CERN Document Server

    Costa, Luca

    2014-01-01

    Quantifying the tip-sample interaction at the nanoscale in Amplitude Modulation mode AFM is challenging, especially when measuring in liquids. Here, we derive formulas for the tip-sample conservative and dissipative interactions and investigate the effect that spurious resonances have on the measured interaction. Both direct and acoustic excitation are considered. We also highlight the differences between measuring directly the tip position or the cantilever deflection. We show that, when probing the tip-sample forces, the acoustically excited cantilever behavior is insensitive to spurious resonances as long as the measured signal corresponds to the tip position, or if the excitation force is correctly taken into account. Since the effective excitation force may depend on the presence of such spurious resonances, we consider the cases where the frequency is kept constant during the measurement so that the proportionality between excitation signal and actual excitation force is kept constant. With the present ...

  5. Dynamic cell culture system (7-IML-1)

    Science.gov (United States)

    Cogoli, Augusto

    1992-01-01

    This experiment is one of the Biorack experiments being flown on the International Microgravity Laboratory 1 (MIL-1) mission as part of an investigation studying cell proliferation and performance in space. One of the objectives of this investigation is to assess the potential benefits of bioprocessing in space with the ultimate goal of developing a bioreactor for continuous cell cultures in space. This experiment will test the operation of an automated culture chamber that was designed for use in a Bioreactor in space. The device to be tested is called the Dynamic Cell Culture System (DCCS). It is a simple device in which media are renewed or chemicals are injected automatically, by means of osmotic pumps. This experiment uses four Type I/O experiment containers. One DCCS unit, which contains a culture chamber with renewal of medium and a second chamber without a medium supply fits in each container. Two DCCS units are maintained under zero gravity conditions during the on-orbit period. The other two units are maintained under 1 gh conditions in a 1 g centrifuge. The schedule for incubator transfer is given.

  6. Experimental characterization of active acoustic metamaterial cell with controllable dynamic density

    Science.gov (United States)

    Akl, Wael; Baz, Amr

    2012-10-01

    Controlling wave propagation pattern within acoustic fluid domains has been the motivation for the acoustic metamaterials developments to target applications ranging from acoustic cloaking to passive noise control techniques. Currently, various numerical and analytical approaches exist to predict the fluid domain material properties necessary for specific propagation pattern. Physical attempts to realize such material properties have revealed engineered material constructions that are focused on predefined wave propagation patterns. In the current paper, coupled fluid-structure one-dimensional metamaterial cell, in which piezoelectric active ingredient has been introduced, is manufactured to achieve controllable dynamic density. The density-controllable cell has been manufactured by coupling a water-filled cavity with piezoelectric elements in a cell of 4.5 cm length and 4.1 cm diameter subject to impulse excitation. A finite element model of the cell has been developed and its predictions are validated against the experimental results. The validated model is utilized to predict the changes in the pressure gradient inside the developed cell which is a direct measure of the changes introduced to the dynamic density of the acoustic metamaterial domain. With such predictions, it is demonstrated that densities as high as 3.2 gm/cm3 and as low as 0.72 gm/cm3 can be achieved experimentally for excitation frequencies ranging between 100 Hz and 500 Hz.

  7. Theoretical study of different features of the fission process of excited nuclei in the framework of the modified statistical model and four-dimensional dynamical model

    Science.gov (United States)

    Eslamizadeh, H.

    2017-02-01

    Evaporation residue cross section, fission probability, anisotropy of fission fragment angular distribution, mass and energy distributions of fission fragments and the pre-scission neutron multiplicity for the excited compound nuclei {}168{{Y}}{{b}}, {}172{{Y}}{{b}}, {}178{{W}} and {}227{{P}}{{a}} produced in fusion reactions have been calculated in the framework of the modified statistical model and multidimensional dynamical model. In the dynamical calculations, the dynamics of fission of excited nuclei has been studied by solving three- and four-dimensional Langevin equations with dissipation generated through the chaos-weighted wall and window friction formula. Three collective shape coordinates plus the projection of total spin of the compound nucleus to the symmetry axis, K, were considered in the four-dimensional dynamical model. A non-constant dissipation coefficient of K, {γ }k, was applied in the four-dimensional dynamical calculations. A comparison of the results of the three- and four-dimensional dynamical models with the experimental data showed that the results of the four-dimensional dynamical model for the evaporation residue cross section, fission probability, anisotropy of fission fragment angular distribution, mass and energy distributions of fission fragments and the pre-scission neutron multiplicity are in better agreement with the experimental data. It was also shown that the modified statistical model can reproduce the above-mentioned experimental data by choosing appropriate values of the temperature coefficient of the effective potential, λ , and the scaling factor of the fission-barrier height, {r}s.

  8. Beta cell dynamics: beta cell replenishment, beta cell compensation and diabetes.

    Science.gov (United States)

    Cerf, Marlon E

    2013-10-01

    Type 2 diabetes, characterized by persistent hyperglycemia, arises mostly from beta cell dysfunction and insulin resistance and remains a highly complex metabolic disease due to various stages in its pathogenesis. Glucose homeostasis is primarily regulated by insulin secretion from the beta cells in response to prevailing glycemia. Beta cell populations are dynamic as they respond to fluctuating insulin demand. Beta cell replenishment and death primarily regulate beta cell populations. Beta cells, pancreatic cells, and extra-pancreatic cells represent the three tiers for replenishing beta cells. In rodents, beta cell self-replenishment appears to be the dominant source for new beta cells supported by pancreatic cells (non-beta islet cells, acinar cells, and duct cells) and extra-pancreatic cells (liver, neural, and stem/progenitor cells). In humans, beta cell neogenesis from non-beta cells appears to be the dominant source of beta cell replenishment as limited beta cell self-replenishment occurs particularly in adulthood. Metabolic states of increased insulin demand trigger increased insulin synthesis and secretion from beta cells. Beta cells, therefore, adapt to support their physiology. Maintaining physiological beta cell populations is a strategy for targeting metabolic states of persistently increased insulin demand as in diabetes.

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

    Directory of Open Access Journals (Sweden)

    Syed Hamad

    2015-12-01

    Full Text Available 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. 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 colloidal Si NPs find

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

    Energy Technology Data Exchange (ETDEWEB)

    Hamad, Syed; Nageswara Rao, S. V. S.; Pathak, A. P. [School of Physics, University of Hyderabad, Hyderabad 500046, Telangana (India); Krishna Podagatlapalli, G.; Mounika, R.; Venugopal Rao, S., E-mail: soma-venu@yahoo.com, E-mail: soma-venu@uohyd.ac.in [Advanced Center of Research in High Energy Materials (ACRHEM), University of Hyderabad, Hyderabad 500046, Telangana (India)

    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

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

    Science.gov (United States)

    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). 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 colloidal Si NPs find potential applications

  12. Dynamic imaging of cell-free and cell-associated viral capture in mature dendritic cells.

    Science.gov (United States)

    Izquierdo-Useros, Nuria; Esteban, Olga; Rodriguez-Plata, Maria T; Erkizia, Itziar; Prado, Julia G; Blanco, Julià; García-Parajo, Maria F; Martinez-Picado, Javier

    2011-12-01

    Dendritic cells (DCs) capture human immunodeficiency virus (HIV) through a non-fusogenic mechanism that enables viral transmission to CD4(+) T cells, contributing to in vivo viral dissemination. Although previous studies have provided important clues to cell-free viral capture by mature DCs (mDCs), dynamic and kinetic insight on this process is still missing. Here, we used three-dimensional video microscopy and single-particle tracking approaches to dynamically dissect both cell-free and cell-associated viral capture by living mDCs. We show that cell-free virus capture by mDCs operates through three sequential phases: virus binding through specific determinants expressed in the viral particle, polarized or directional movements toward concrete regions of the cell membrane and virus accumulation in a sac-like structure where trapped viral particles display a hindered diffusive behavior. Moreover, real-time imaging of cell-associated viral transfer to mDCs showed a similar dynamics to that exhibited by cell-free virus endocytosis leading to viral accumulation in compartments. However, cell-associated HIV type 1 transfer to mDCs was the most effective pathway, boosted throughout enhanced cellular contacts with infected CD4(+) T cells. Our results suggest that in lymphoid tissues, mDC viral uptake could occur either by encountering cell-free or cell-associated virus produced by infected cells generating the perfect scenario to promote HIV pathogenesis and impact disease progression.

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

    Science.gov (United States)

    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.

  14. Mitochondrial dynamics and the cell cycle

    Directory of Open Access Journals (Sweden)

    Penny M.A. Kianian

    2014-05-01

    Full Text Available Nuclear-mitochondrial (NM communication impacts many aspects of plant development including vigor, sterility and viability. Dynamic changes in mitochondrial number, shape, size, and cellular location takes place during the cell cycle possibly impacting the process itself and leading to distribution of this organelle into daughter cells. The genes that underlie these changes are beginning to be identified in model plants such as Arabidopsis. In animals disruption of the drp1 gene, a homolog to the plant drp3A and drp3B, delays mitochondrial division. This mutation results in increased aneuploidy due to chromosome mis-segregation. It remains to be discovered if a similar outcome is observed in plants. Alloplasmic lines provide an opportunity to understand the communication between the cytoplasmic organelles and the nucleus. Examples of studies in these lines, especially from the extensive collection in wheat, point to the role of mitochondria in chromosome movement, pollen fertility and other aspects of development. Genes involved in NM interaction also are believed to play a critical role in evolution of species and interspecific cross incompatibilities.

  15. Input dependent cell assembly dynamics in a model of the striatal medium spiny neuron network.

    Science.gov (United States)

    Ponzi, Adam; Wickens, Jeff

    2012-01-01

    The striatal medium spiny neuron (MSN) network is sparsely connected with fairly weak GABAergic collaterals receiving an excitatory glutamatergic cortical projection. Peri-stimulus time histograms (PSTH) of MSN population response investigated in various experimental studies display strong firing rate modulations distributed throughout behavioral task epochs. In previous work we have shown by numerical simulation that sparse random networks of inhibitory spiking neurons with characteristics appropriate for UP state MSNs form cell assemblies which fire together coherently in sequences on long behaviorally relevant timescales when the network receives a fixed pattern of constant input excitation. Here we first extend that model to the case where cortical excitation is composed of many independent noisy Poisson processes and demonstrate that cell assembly dynamics is still observed when the input is sufficiently weak. However if cortical excitation strength is increased more regularly firing and completely quiescent cells are found, which depend on the cortical stimulation. Subsequently we further extend previous work to consider what happens when the excitatory input varies as it would when the animal is engaged in behavior. We investigate how sudden switches in excitation interact with network generated patterned activity. We show that sequences of cell assembly activations can be locked to the excitatory input sequence and outline the range of parameters where this behavior is shown. Model cell population PSTH display both stimulus and temporal specificity, with large population firing rate modulations locked to elapsed time from task events. Thus the random network can generate a large diversity of temporally evolving stimulus dependent responses even though the input is fixed between switches. We suggest the MSN network is well suited to the generation of such slow coherent task dependent response which could be utilized by the animal in behavior.

  16. Input dependent cell assembly dynamics in a model of the striatal medium spiny neuron network

    Directory of Open Access Journals (Sweden)

    Adam ePonzi

    2012-03-01

    Full Text Available The striatal medium spiny neuron (MSNs network is sparsely connected with fairly weak GABAergic collaterals receiving an excitatory glutamatergic cortical projection. Peri stimulus time histograms (PSTH of MSN population response investigated in various experimental studies display strong firing rate modulations distributed throughout behavioural task epochs. In previous work we have shown by numerical simulation that sparse random networks of inhibitory spiking neurons with characteristics appropriate for UP state MSNs form cell assemblies which fire together coherently in sequences on long behaviourally relevant timescales when the network receives a fixed pattern of constant input excitation. Here we first extend that model to the case where cortical excitation is composed of many independent noisy Poisson processes and demonstrate that cell assembly dynamics is still observed when the input is sufficiently weak. However if cortical excitation strength is increased more regularly firing and completely quiescent cells are found, which depend on the cortical stimulation. Subsequently we further extend previous work to consider what happens when the excitatory input varies as it would in when the animal is engaged in behavior. We investigate how sudden switches in excitation interact with network generated patterned activity. We show that sequences of cell assembly activations can be locked to the excitatory input sequence and delineate the range of parameters where this behaviour is shown. Model cell population PSTH display both stimulus and temporal specificity, with large population firing rate modulations locked to elapsed time from task events. Thus the random network can generate a large diversity of temporally evolving stimulus dependent responses even though the input is fixed between switches. We suggest the MSN network is well suited to the generation of such slow coherent task dependent response

  17. Hyperinsulinism and diabetes: genetic dissection of beta cell metabolism-excitation coupling in mice.

    Science.gov (United States)

    Remedi, Maria Sara; Nichols, Colin G

    2009-12-01

    The role of metabolism-excitation coupling in insulin secretion has long been apparent, but in recent years, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism, and excitability in mice has brought the central importance of this pathway into sharp relief. We focus on these animal studies and how they provide important insights into not only metabolic and electrical regulation of insulin secretion, but also downstream consequences of alterations in this pathway and the etiology and treatment of insulin-secretion diseases in humans.

  18. Hyperinsulinism and Diabetes: Genetic dissection of β-cell metabolism-excitation coupling in mice

    Science.gov (United States)

    Remedi, Maria Sara; Nichols, Colin G.

    2011-01-01

    The role of metabolism-excitation coupling in insulin secretion has long been apparent but, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism and excitability in mice has brought the central importance of this pathway into sharp relief in recent years. We focus on these animal studies, and how they not only provide important insights to metabolic and electrical regulation of insulin secretion, but also to downstream consequences of alterations in this pathway, and to the etiology and treatment of insulin-secretion diseases in humans. PMID:19945402

  19. The excitation and characteristic frequency of the long-period volcanic event: An approach based on an inhomogeneous autoregressive model of a linear dynamic system

    Science.gov (United States)

    Nakano, M.; Kumagai, H.; Kumazawa, M.; Yamaoka, K.; Chouet, B.A.

    1998-01-01

    We present a method to quantify the source excitation function and characteristic frequencies of long-period volcanic events. The method is based on an inhomogeneous autoregressive (AR) model of a linear dynamic system, in which the excitation is assumed to be a time-localized function applied at the beginning of the event. The tail of an exponentially decaying harmonic waveform is used to determine the characteristic complex frequencies of the event by the Sompi method. The excitation function is then derived by operating an AR filter constructed from the characteristic frequencies to the entire seismogram of the event, including the inhomogeneous part of the signal. We apply this method to three long-period events at Kusatsu-Shirane Volcano, central Japan, whose waveforms display simple decaying monochromatic oscillations except for the beginning of the events. We recover time-localized excitation functions lasting roughly 1 s at the start of each event and find that the estimated functions are very similar to each other at all the stations of the seismic network for each event. The phases of the characteristic oscillations referred to the estimated excitation function fall within a narrow range for almost all the stations. These results strongly suggest that the excitation and mode of oscillation are both dominated by volumetric change components. Each excitation function starts with a pronounced dilatation consistent with a sudden deflation of the volumetric source which may be interpreted in terms of a choked-flow transport mechanism. The frequency and Q of the characteristic oscillation both display a temporal evolution from event to event. Assuming a crack filled with bubbly water as seismic source for these events, we apply the Van Wijngaarden-Papanicolaou model to estimate the acoustic properties of the bubbly liquid and find that the observed changes in the frequencies and Q are consistently explained by a temporal change in the radii of the bubbles

  20. Exploring the role of decoherence in condensed-phase nonadiabatic dynamics: a comparison of different mixed quantum/classical simulation algorithms for the excited hydrated electron.

    Science.gov (United States)

    Larsen, Ross E; Bedard-Hearn, Michael J; Schwartz, Benjamin J

    2006-10-12

    Mixed quantum/classical (MQC) molecular dynamics simulation has become the method of choice for simulating the dynamics of quantum mechanical objects that interact with condensed-phase systems. There are many MQC algorithms available, however, and in cases where nonadiabatic coupling is important, different algorithms may lead to different results. Thus, it has been difficult to reach definitive conclusions about relaxation dynamics using nonadiabatic MQC methods because one is never certain whether any given algorithm includes enough of the necessary physics. In this paper, we explore the physics underlying different nonadiabatic MQC algorithms by comparing and contrasting the excited-state relaxation dynamics of the prototypical condensed-phase MQC system, the hydrated electron, calculated using different algorithms, including: fewest-switches surface hopping, stationary-phase surface hopping, and mean-field dynamics with surface hopping. We also describe in detail how a new nonadiabatic algorithm, mean-field dynamics with stochastic decoherence (MF-SD), is to be implemented for condensed-phase problems, and we apply MF-SD to the excited-state relaxation of the hydrated electron. Our discussion emphasizes the different ways quantum decoherence is treated in each algorithm and the resulting implications for hydrated-electron relaxation dynamics. We find that for three MQC methods that use Tully's fewest-switches criterion to determine surface hopping probabilities, the excited-state lifetime of the electron is the same. Moreover, the nonequilibrium solvent response function of the excited hydrated electron is the same with all of the nonadiabatic MQC algorithms discussed here, so that all of the algorithms would produce similar agreement with experiment. Despite the identical solvent response predicted by each MQC algorithm, we find that MF-SD allows much more mixing of multiple basis states into the quantum wave function than do other methods. This leads to an

  1. The theorem about the transformer excitation current waveform mapping into the dynamic hysteresis loop branch for the sinusoidal magnetic flux case

    Directory of Open Access Journals (Sweden)

    Petrović Nenad

    2015-01-01

    Full Text Available This paper analyses aspects of the approximation theory application on the certain subsets of the measured samples of the transformer excitation current and the sinusoidal magnetic flux. The presented analysis is performed for single-phase transformer case, Epstein frame case and toroidal core case. In the paper the theorem of direct mapping the transformer excitation current in the stationary regime is proposed. The excitation current is mapped to the dynamic hysteresis loop branch (in further text DHLB by an appropriate cosine transformation. This theorem provides the necessary and satisfactory conditions for above described mapping. The theorem highlights that the transformer excitation current under the sinusoidal magnetic flux has qualitatively equivalent information about magnetic core properties as the DHLB. Furthermore, the theorem establishes direct relationship between the number of the transformer excitation current harmonics and their coefficients with the degree of the DHLB interpolation polynomial and its coefficients. The DHLB interpolation polynomial is calculated over the measured subsets of samples representing Chebyshev nodes of the first and the second kind. These nonequidistant Chebyshev nodes provides uniform convergence of the interpolation polynomial to the experimentally obtained DHLB with an excellent approximation accuracy and are applicable on the approximation of the static hysteresis loops and the DC magnetization curves as well.

  2. High-energy magnetic excitations from dynamic stripes in La1.875Ba0.125CuO4

    Science.gov (United States)

    Xu, Guangyong; Tranquada, J. M.; Perring, T. G.; Gu, G. D.; Fujita, M.; Yamada, K.

    2007-07-01

    We use inelastic neutron scattering to study the temperature dependence of magnetic excitations (for energies up to 100meV ) in the cuprate La1.875Ba0.125CuO4 . This compound exhibits stripe order below a temperature of ˜50K ; previous measurements have shown that the magnetic excitations of the stripe-ordered phase have an hour-glass-like dispersion, with a saddle point at ˜50meV . Here, we compare measurements in the disordered phase taken at 65 and 300K . At energies on the scale of kBT , there is substantial momentum broadening of the signal, and the low-energy incommensurate features can no longer be resolved at 300K . In contrast, there is remarkably little change in the scattered signal for energies greater than kBT . In fact, the momentum-integrated dynamic susceptibility is almost constant with temperature. The continuity of the magnetic excitations at E>50meV indicates that the character of the local antiferromagnetic spin correlations is independent of stripe ordering. Based on the smooth evolution of the lower-energy excitations into the spin waves of the stripe-ordered phase, we infer the existence of dynamic stripe correlations in the disordered phase. We reconsider the nature of the magnetic dispersion, and we discuss the correspondences between the thermal evolution of magnetic stripe correlations with other electronic properties of the cuprates.

  3. Excited state proton transfer dynamics of thioacetamide in S2(ππ*) state: resonance Raman spectroscopic and quantum mechanical calculations study.

    Science.gov (United States)

    Chen, Xiao; Zhao, Yanying; Zhang, Haibo; Xue, Jiadan; Zheng, Xuming

    2015-02-05

    The photophysics and photochemistry of thioacetamide (CH3CSNH2) after excitation to the S2 electronic state were investigated by using resonance Raman spectroscopy in conjunction with the complete active space self-consistent field (CASSCF) method and density functional theory (DFT) calculations. The A-band resonance Raman spectra in acetonitrile, methanol, and water were obtained at 299.1, 282.4, 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of thioacetamide in the S2 state. CASSCF calculations were done to determine the transition energies and structures of the lower-lying excited states, the conical intersection points CI(S2/S1) and CI(S1/S0), and intersystem crossing points. The structural dynamics of thioacetamide in the S2 state was revealed to be along eight Franck-Condon active vibrational modes ν15, ν11, ν14, ν10, ν8, ν12, ν18, and ν19, mostly in the CC/CS/CN stretches and the CNH8,9/CCH5,6,7/CCN/CCS in-plane bends as indicated by the corresponding normal mode descriptions. The S2 → S1 decay process via the S2/S1 conical intersection point as the major channel were excluded. The thione-thiol photoisomerization reaction mechanism of thioacetamide via the S2,FC → S'1,min excited state proton transfer (ESPT) reaction channel was proposed.

  4. The stereo-dynamics of collisional autoionization of ammonia by helium and neon metastable excited atoms through molecular beam experiments

    Energy Technology Data Exchange (ETDEWEB)

    Falcinelli, Stefano, E-mail: stefano.falcinelli@unipg.it; Vecchiocattivi, Franco [Department of Civil and Environmental Engineering, University of Perugia, Via G. Duranti 93, 06125 Perugia (Italy); Bartocci, Alessio; Cavalli, Simonetta; Pirani, Fernando [Department of Chemistry, Biology, and Biotechnology, University of Perugia, Via Elce di sotto 8, 06123 Perugia (Italy)

    2015-10-28

    A combined analysis of both new (energy spectra of emitted electrons) and previously published (ionization cross sections) experimental data, measured under the same conditions and concerning electronically excited lighter noble gas –NH{sub 3} collisional autoionization processes, is carried out. Such an analysis, performed by exploiting a formulation of the full potential energy surface both in the real and imaginary parts, provides direct information on energetics, structure, and lifetime of the intermediate collision complex over all the configuration space. The marked anisotropy in the attraction of the real part, driving the approach of reagents, and the selective role of the imaginary component, associated to the charge transfer coupling between entrance and exit channels, suggests that reactive events occur almost exclusively in the molecular hemisphere containing the nitrogen lone pair. Crucial details on the stereo-dynamics of elementary collisional autoionization processes are then obtained, in which the open shell nature of the disclosed ionic core of metastable atom plays a crucial role. The same analysis also suggests that the strength of the attraction and the anisotropy of the interaction increases regularly along the series Ne{sup *}({sup 3}P), He{sup *}({sup 3}S), He{sup *}({sup 1}S)–NH{sub 3}. These findings can be ascribed to the strong rise of the metastable atom electronic polarizability (deformability) along the series. The obtained results can stimulate state of the art ab initio calculations focused on specific features of the transition state (energetics, structure, lifetime, etc.) which can be crucial for a further improvement of the adopted treatment and to better understand the nature of the leading interaction components which are the same responsible for the formation of the intermolecular halogen and hydrogen bond.

  5. The stereo-dynamics of collisional autoionization of ammonia by helium and neon metastable excited atoms through molecular beam experiments.

    Science.gov (United States)

    Falcinelli, Stefano; Bartocci, Alessio; Cavalli, Simonetta; Pirani, Fernando; Vecchiocattivi, Franco

    2015-10-28

    A combined analysis of both new (energy spectra of emitted electrons) and previously published (ionization cross sections) experimental data, measured under the same conditions and concerning electronically excited lighter noble gas -NH3 collisional autoionization processes, is carried out. Such an analysis, performed by exploiting a formulation of the full potential energy surface both in the real and imaginary parts, provides direct information on energetics, structure, and lifetime of the intermediate collision complex over all the configuration space. The marked anisotropy in the attraction of the real part, driving the approach of reagents, and the selective role of the imaginary component, associated to the charge transfer coupling between entrance and exit channels, suggests that reactive events occur almost exclusively in the molecular hemisphere containing the nitrogen lone pair. Crucial details on the stereo-dynamics of elementary collisional autoionization processes are then obtained, in which the open shell nature of the disclosed ionic core of metastable atom plays a crucial role. The same analysis also suggests that the strength of the attraction and the anisotropy of the interaction increases regularly along the series Ne*((3)P), He*((3)S), He*((1)S)-NH3. These findings can be ascribed to the strong rise of the metastable atom electronic polarizability (deformability) along the series. The obtained results can stimulate state of the art ab initio calculations focused on specific features of the transition state (energetics, structure, lifetime, etc.) which can be crucial for a further improvement of the adopted treatment and to better understand the nature of the leading interaction components which are the same responsible for the formation of the intermolecular halogen and hydrogen bond.

  6. Excitation Methods for Bridge Structures

    Energy Technology Data Exchange (ETDEWEB)

    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.

  7. Excited state dynamics of 9,9'-bianthryl in room temperature ionic liquids as revealed by picosecond time-resolved fluorescence study

    Indian Academy of Sciences (India)

    Dinesh Chandra Khara; Aniruddha Paul; Kotni Santhosh; Anunay Samanta

    2009-05-01

    Picosecond time-resolved fluorescence measurements have been carried out on 9,9'-bianthryl in three imidazolium ionic liquids to probe the excited state dynamics. In the early time-scale, the fluorescence spectra of bianthryl have been found to consist of emission from both locally excited (LE) and charge transfer (CT) states. The LE → CT relaxation time, as estimated from the decay of the fluorescence intensity of the LE emission, is found to vary between 230 and 390 ps, while the average solvent relaxation time, as estimated from the analysis of time-dependent fluorescence Stokes shift, is found to vary between 620 ps and 1840 ps, depending on the viscosity of the ionic liquids. The results confirm that while in conventional less viscous solvents the CT formation kinetics of bianthryl occurs simultaneously with the solvation dynamics, in ionic liquids the two processes mostly occur in different time scales.

  8. Ground and excited state properties of high performance anthocyanidin dyes-sensitized solar cells in the basic solutions

    Energy Technology Data Exchange (ETDEWEB)

    Prima, Eka Cahya [Advanced Functional Material Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia); Computational Material Design and Quantum Engineering Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia); International Program on Science Education, Universitas Pendidikan Indonesia (Indonesia); Yuliarto, Brian; Suyatman, E-mail: yatman@tf.itb.ac.id [Advanced Functional Material Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia); Dipojono, Hermawan Kresno [Computational Material Design and Quantum Engineering Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia)

    2015-09-30

    The aglycones of anthocyanidin dyes were previously reported to form carbinol pseudobase, cis-chalcone, and trans-chalcone due to the basic levels. The further investigations of ground and excited state properties of the dyes were characterized using density functional theory with PCM(UFF)/B3LYP/6-31+G(d,p) level in the basic solutions. However, to the best of our knowledge, the theoretical investigation of their potential photosensitizers has never been reported before. In this paper, the theoretical photovoltaic properties sensitized by dyes have been successfully investigated including the electron injections, the ground and excited state oxidation potentials, the estimated open circuit voltages, and the light harvesting efficiencies. The results prove that the electronic properties represented by dyes’ LUMO-HOMO levels will affect to the photovoltaic performances. Cis-chalcone dye is the best anthocyanidin aglycone dye with the electron injection spontaneity of −1.208 eV, the theoretical open circuit voltage of 1.781 V, and light harvesting efficiency of 56.55% due to the best HOMO-LUMO levels. Moreover, the ethanol solvent slightly contributes to the better cell performance than the water solvent dye because of the better oxidation potential stabilization in the ground state as well as in the excited state. These results are in good agreement with the known experimental report that the aglycones of anthocyanidin dyes in basic solvent are the high potential photosensitizers for dye-sensitized solar cell.

  9. Dynamic properties of excitation and two-tone inhibition in the cochlear nucleus studied using amplitude-modulated tones.

    Science.gov (United States)

    Moller, A R

    1976-06-18

    The dynamic properties of excitation and two-tone inhibition in the cochlear nucleus were studied from extracellularly recorded unit responses to two simultaneously presented tones. One tone was presented at the unit's characteristic frequency, CF, the other at the unit's best inhibitory frequency, BIF. One or both of the tones were amplitude-modulated with pseudorandom noise. The system under study is in general nonlinear, but can be considered to function as a linear system for small changes in sound intensity around a certain operating point. The dynamic properties are likely to be different at different operating points. A suitable method for the study of dynamic properties of such a system employs tones that are amplitude-modulated with pseudorandom noise. In the present study, the dynamic properties were assessed by cross-correlating the unit discharge rate with the modulation. This was accomplished by computing the cross-covariance function between a period of noise and a period histogram of the discharges, the histogram being locked to the periodicity of the pseudorandom noise. In this way, it has been shown in previous works (Moller, 1973, 1974b), that the cross-covariance function is a valid approximation of the system's impulse response function at a certain sound intensity, provided the modulation is kept at a low value. In the present study the computed cross-covariance function is thus an approximation of the change in discharge rate of the cochlear nucleus units in response to a brief increase in stimulus intensity. As the response of the system under the given circumstances is approximately that of a linear system, the integrated cross-covariance is an approximation of the system's step response function, i.e the change in discharge rate that resulte from a hypothetical step increase in stimulus intensity. The results of the present study can be summarized as follows: 1. The impulse and step response functions computed from the responses to the

  10. Structural Response Prediction: Full-field, Dynamic Pressure and Displacement Measurements of a Panel Excited by Shock Boundary-layer Interaction

    Science.gov (United States)

    2015-02-01

    interaction (SBLI) on the local response of outer mold line (OML) vehicle panel -structure. Vehicle bow -shocks and shocks emanating from vehicle corners...line (OML) vehicle panel -structure. Vehicle bow -shocks and shocks emanating from vehicle corners, protuberances, compression ramps and control...AFRL-RQ-WP-TP-2015-0046 STRUCTURAL RESPONSE PREDICTION: FULL-FIELD, DYNAMIC PRESSURE AND DISPLACEMENT MEASUREMENTS OF A PANEL EXCITED BY

  11. Analysis of the excited argon atoms in the GEC RF reference cell by means of one-dimensional PIC simulations

    Energy Technology Data Exchange (ETDEWEB)

    Lauro-Taroni, L [The Open University, Oxford Research Unit, Oxford, OX1 5HR (United Kingdom); Turner, M M [Plasma Research Laboratory, School of Physical Sciences and National Centre for Plasma Science and Technology, Dublin City University, Dublin (Ireland); Braithwaite, N StJ [Open University, Oxford Research Unit, Oxford, OX1 5HR (United Kingdom)

    2004-08-21

    We examine the question of whether the excited states in argon contribute significantly to ionization in a capacitively coupled plasma through metastable pooling and step-ionization processes. We look at this issue by means of a one-dimensional particle-in-cell (PIC) code, with collisions treated by a Monte Carlo collision package. In the range explored, 50-1000 mTorr, the main source of ionization, in the absence of secondary emission, is direct ionization from the ground state with a contribution from excited states that is negligible at lower pressures, but increases in importance at higher pressures. When secondary electrons are included, their interaction with ground state neutrals dominates the ionization. At higher pressures the metastable profiles can reveal useful information on the non-uniform mean electron energy across the discharge, even though these states do not necessarily play a significant role in ionization.

  12. Fluid dynamics and noise in bacterial cell-cell and cell-surface scattering

    CERN Document Server

    Drescher, Knut; Cisneros, Luis H; Ganguly, Sujoy; Goldstein, Raymond E; 10.1073/pnas.1019079108

    2011-01-01

    Bacterial processes ranging from gene expression to motility and biofilm formation are constantly challenged by internal and external noise. While the importance of stochastic fluctuations has been appreciated for chemotaxis, it is currently believed that deterministic long-range fluid dynamical effects govern cell-cell and cell-surface scattering - the elementary events that lead to swarming and collective swimming in active suspensions and to the formation of biofilms. Here, we report the first direct measurements of the bacterial flow field generated by individual swimming Escherichia coli both far from and near to a solid surface. These experiments allowed us to examine the relative importance of fluid dynamics and rotational diffusion for bacteria. For cell-cell interactions it is shown that thermal and intrinsic stochasticity drown the effects of long-range fluid dynamics, implying that physical interactions between bacteria are determined by steric collisions and near-field lubrication forces. This dom...

  13. Discharging dynamics in an electrolytic cell

    Science.gov (United States)

    Feicht, Sarah E.; Frankel, Alexandra E.; Khair, Aditya S.

    2016-07-01

    We analyze the dynamics of a discharging electrolytic cell comprised of a binary symmetric electrolyte between two planar, parallel blocking electrodes. When a voltage is initially applied, ions in the electrolyte migrate towards the electrodes, forming electrical double layers. After the system reaches steady state and the external current decays to zero, the applied voltage is switched off and the cell discharges, with the ions eventually returning to a uniform spatial concentration. At voltages on the order of the thermal voltage VT=kBT /q ≃25 mV, where kB is Boltzmann's constant, T is temperature, and q is the charge of a proton, experiments on surfactant-doped nonpolar fluids observe that the temporal evolution of the external current during charging and discharging is not symmetric [V. Novotny and M. A. Hopper, J. Electrochem. Soc. 126, 925 (1979), 10.1149/1.2129195; P. Kornilovitch and Y. Jeon, J. Appl. Phys. 109, 064509 (2011), 10.1063/1.3554445]. In fact, at sufficiently large voltages (several VT), the current during discharging is no longer monotonic: it displays a "reverse peak" before decaying in magnitude to zero. We analyze the dynamics of discharging by solving the Poisson-Nernst-Planck equations governing ion transport via asymptotic and numerical techniques in three regimes. First, in the "linear regime" when the applied voltage V is formally much less than VT, the charging and discharging currents are antisymmetric in time; however, the potential and charge density profiles during charging and discharging are asymmetric. The current evolution is on the R C timescale of the cell, λDL /D , where L is the width of the cell, D is the diffusivity of ions, and λD is the Debye length. Second, in the (experimentally relevant) thin-double-layer limit ɛ =λD/L ≪1 , there is a "weakly nonlinear" regime defined by VT≲V ≲VTln(1 /ɛ ) , where the bulk salt concentration is uniform; thus the R C timescale of the evolution of the current magnitude

  14. Morphological alterations in newly born dentate gyrus granule cells that emerge after status epilepticus contribute to make them less excitable.

    Directory of Open Access Journals (Sweden)

    Julián Tejada

    Full Text Available Computer simulations of external current stimulations of dentate gyrus granule cells of rats with Status Epilepticus induced by pilocarpine and control rats were used to evaluate whether morphological differences alone between these cells have an impact on their electrophysiological behavior. The cell models were constructed using morphological information from tridimensional reconstructions with Neurolucida software. To evaluate the effect of morphology differences alone, ion channel conductances, densities and distributions over the dendritic trees of dentate gyrus granule cells were the same for all models. External simulated currents were injected in randomly chosen dendrites belonging to one of three different areas of dentate gyrus granule cell molecular layer: inner molecular layer, medial molecular layer and outer molecular layer. Somatic membrane potentials were recorded to determine firing frequencies and inter-spike intervals. The results show that morphologically altered granule cells from pilocarpine-induced epileptic rats are less excitable than control cells, especially when they are stimulated in the inner molecular layer, which is the target area for mossy fibers that sprout after pilocarpine-induced cell degeneration. This suggests that morphological alterations may act as a protective mechanism to allow dentate gyrus granule cells to cope with the increase of stimulation caused by mossy fiber sprouting.

  15. Dynamic behaviour of human neuroepithelial cells in the developing forebrain

    Science.gov (United States)

    Subramanian, Lakshmi; Bershteyn, Marina; Paredes, Mercedes F.; Kriegstein, Arnold R.

    2017-01-01

    To understand how diverse progenitor cells contribute to human neocortex development, we examined forebrain progenitor behaviour using timelapse imaging. Here we find that cell cycle dynamics of human neuroepithelial (NE) cells differ from radial glial (RG) cells in both primary tissue and in stem cell-derived organoids. NE cells undergoing proliferative, symmetric divisions retract their basal processes, and both daughter cells regrow a new process following cytokinesis. The mitotic retraction of the basal process is recapitulated by NE cells in cerebral organoids generated from human-induced pluripotent stem cells. In contrast, RG cells undergoing vertical cleavage retain their basal fibres throughout mitosis, both in primary tissue and in older organoids. Our findings highlight developmentally regulated changes in mitotic behaviour that may relate to the role of RG cells to provide a stable scaffold for neuronal migration, and suggest that the transition in mitotic dynamics can be studied in organoid models. PMID:28139695

  16. Excited state dynamics of the Ho3+ ions in holmium singly doped and holmium, praseodymium-codoped fluoride glasses

    Science.gov (United States)

    Librantz, André Felipe Henriques; Jackson, Stuart D.; Jagosich, Fabio Henrique; Gomes, Laércio; Poirier, Gaël; Ribeiro, Sidney José Lima; Messaddeq, Younes

    2007-06-01

    The deactivation of the two lowest excited states of Ho3+ was investigated in Ho3+ singly doped and Ho3+, Pr3+-codoped fluoride (ZBLAN) glasses. We establish that 0.1-0.3mol% Pr3+ can efficiently deactivate the first excited (I75) state of Ho3+ while causing a small reduction of ˜40% of the initial population of the second excited (I65) state. The net effect introduced by the Pr3+ ion deactivation of the Ho3+ ion is the fast recovery of the ground state of Ho3+. The Burshstein model parameters relevant to the Ho3+→Pr3+ energy transfer processes were determined using a least squares fit to the measured luminescence decay. The energy transfer upconversion and cross relaxation parameters for 1948, 1151, and 532nm excitations of singly Ho3+-doped ZBLAN were determined. Using the energy transfer rate parameters we determine from the measured luminescence, a rate equation model for 650nm excitation of Ho3+-doped and Ho3+, Pr3+-doped ZBLAN glasses was developed. The rate equations were solved numerically and the population inversion between the I65 and the I75 excited states of Ho3+ was calculated to examine the beneficial effects on the gain associated with Pr3+ codoping.

  17. Cholinergic modulation differs between basal and apical dendritic excitation of hippocampal CA1 pyramidal cells.

    Science.gov (United States)

    Leung, L Stan; Péloquin, Pascal

    2010-08-01

    We hypothesize that endogenous cholinergic modulation of dendritic processing of hippocampal CA1 is layer specific, and it specifically enhances spike output resulting from basal as compared with the apical dendritic excitation. Laminar profiles of evoked field potentials were recorded in the CA1 area of urethane-anesthetized rats using multichannel silicon probes and analyzed as current source density. High-frequency stimulation of the pontis oralis (PnO) attenuated the midapical more than the basal or distal apical dendritic excitatory sink. Population spike (PS) and excitatory sink-PS potentiation resulting from basal dendritic excitation were facilitated, while the PS evoked by apical dendritic stimulation was attenuated by PnO stimulation. Perfusion of cholinergic agonist carbachol onto hippocampal slices in vitro also attenuated the apical more than the basal dendritic excitatory postsynaptic potentials. Excitatory sink attenuation and PS changes after PnO stimulation were blocked by systemic or local scopolamine and by intracerebroventricular (icv) M1 receptor antagonist pirenzepine but not by icv M2 receptor antagonist AFDX-116 or nicotinic antagonists. However, a hippocampal theta rhythm activated by PnO stimulation was blocked by systemic but not by local scopolamine. We conclude that endogenous acetylcholine mediates a stronger presynaptic inhibition of the midapical than basal and distal apical excitation mainly through M1 receptors.

  18. Excitable Scale Free Networks

    CERN Document Server

    Copelli, Mauro

    2007-01-01

    When a simple excitable system is continuously stimulated by a Poissonian external source, the response function (mean activity versus stimulus rate) generally shows a linear saturating shape. This is experimentally verified in some classes of sensory neurons, which accordingly present a small dynamic range (defined as the interval of stimulus intensity which can be appropriately coded by the mean activity of the excitable element), usually about one or two decades only. The brain, on the other hand, can handle a significantly broader range of stimulus intensity, and a collective phenomenon involving the interaction among excitable neurons has been suggested to account for the enhancement of the dynamic range. Since the role of the pattern of such interactions is still unclear, here we investigate the performance of a scale-free (SF) network topology in this dynamic range problem. Specifically, we study the transfer function of disordered SF networks of excitable Greenberg-Hastings cellular automata. We obser...

  19. Brain cell apoptosis and enhancement of nervous excitability in pregnant rats with high plasma levels of homocysteine.

    Science.gov (United States)

    Wang, Jun; Ge, Jing; Yang, Liu; Zhang, Haiyan; Li, Xuli; Xue, Dan

    2012-10-05

    Hyperhomocysteinemia is an important risk factor for preeclampsia-eclampsia. This study established a pregnant rat model of hyperhomocysteinemia, in which blood plasma homocysteine concentrations were twice or three times greater than that of normal pregnant rats. TUNEL revealed an increase in the number of apoptotic cells in the frontal cortex of pregnant rats with hyperhomocysteinemia. In addition, immunohistochemical staining detected activated nuclear factor-κB-positve cells in the frontal cortex. Reverse transcription-PCR detected that mRNA expression of the anti-apoptotic gene bcl-2 diminished in the frontal cortex. In situ hybridization and western blotting revealed that N-methyl-D-aspartate receptor 1 mRNA and protein expression was upregulated in the frontal cortex and hippocampus. These results indicate that hyperhomocysteinemia can induce brain cell apoptosis, increase nerve excitability, and promote the occurrence of preeclampsia in pregnant rats.

  20. Brain cell apoptosis and enhancement of nervous excitability in pregnant rats with high plasma levels of homocysteine

    Institute of Scientific and Technical Information of China (English)

    Jun Wang; Jing Ge; Liu Yang; Haiyan Zhang; Xuli Li; Dan Xue

    2012-01-01

    Hyperhomocysteinemia is an important risk factor for preeclampsia-eclampsia.This study established a pregnant rat model of hyperhomocysteinemia,in which blood plasma homocysteine concentrations were twice or three times greater than that of normal pregnant rats.TUNEL revealed an increase in the number of apoptotic cells in the frontal cortex of pregnant rats with hyperhomocysteinemia.In addition,immunohistochemical staining detected activated nuclear factor-κB-positve cells in the frontal cortex.Reverse transcription-PCR detected that mRNA expression of the anti-apoptotic gene bcl-2diminished in the frontal cortex.In situ hybridization and western blotting revealed that N-methyl-D-aspartate receptor 1 mRNA and protein expression was upregulated in the frontal cortex and hippocampus.These results indicate that hyperhomocysteinemia can induce brain cell apoptosis,increase nerve excitability,and promote the occurrence of preeclampsia in pregnant rats.

  1. Brain cell apoptosis and enhancement of nervous excitability in pregnant rats with high plasma levels of homocysteine☆

    Science.gov (United States)

    Wang, Jun; Ge, Jing; Yang, Liu; Zhang, Haiyan; Li, Xuli; Xue, Dan

    2012-01-01

    Hyperhomocysteinemia is an important risk factor for preeclampsia-eclampsia. This study established a pregnant rat model of hyperhomocysteinemia, in which blood plasma homocysteine concentrations were twice or three times greater than that of normal pregnant rats. TUNEL revealed an increase in the number of apoptotic cells in the frontal cortex of pregnant rats with hyperhomocysteinemia. In addition, immunohistochemical staining detected activated nuclear factor-κB-positve cells in the frontal cortex. Reverse transcription-PCR detected that mRNA expression of the anti-apoptotic gene bcl-2 diminished in the frontal cortex. In situ hybridization and western blotting revealed that N-methyl-D-aspartate receptor 1 mRNA and protein expression was upregulated in the frontal cortex and hippocampus. These results indicate that hyperhomocysteinemia can induce brain cell apoptosis, increase nerve excitability, and promote the occurrence of preeclampsia in pregnant rats. PMID:25538740

  2. Cryogenic exciter

    Science.gov (United States)

    Bray, James William [Niskayuna, NY; Garces, Luis Jose [Niskayuna, NY

    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.

  3. Multiplexing PKA and ERK1&2 kinases FRET biosensors in living cells using single excitation wavelength dual colour FLIM

    Science.gov (United States)

    Demeautis, Claire; Sipieter, François; Roul, Julien; Chapuis, Catherine; Padilla-Parra, Sergi; Riquet, Franck B.; Tramier, Marc

    2017-01-01

    Monitoring of different signalling enzymes in a single assay using multiplex biosensing provides a multidimensional workspace to elucidate biological processes, signalling pathway crosstalk, and determine precise sequence of events at the single living cell level. In this study, we interrogate the complexity in cAMP/PKA-MAPK/ERK1&2 crosstalk by using multi-parameter biosensing experiments to correlate biochemical activities simultaneously in time and space. Using a single excitation wavelength dual colour FLIM method we are able to detect fluorescence lifetime images of two donors to simultaneously measure PKA and ERK1&2 kinase activities in the same cellular localization by using FRET biosensors. To this end, we excite two FRET donors mTFP1 and LSSmOrange with a 440 nm wavelength and we alleviate spectral bleed-through associated limitations with the very dim-fluorescent acceptor ShadowG for mTFP1 and the red-shifted mKate2 for LSSmOrange. The simultaneous recording of PKA and ERK1&2 kinase activities reveals concomitant EGF-mediated activations of both kinases in HeLa cells. Under these conditions the subsequent Forskolin-induced cAMP release reverses the transient increase of EGF-mediated ERK1&2 kinase activity while reinforcing PKA activation. Here we propose a validated methodology for multiparametric kinase biosensing in living cells using FRET-FLIM. PMID:28106114

  4. Implementing dynamic clamp with synaptic and artificial conductances in mouse retinal ganglion cells.

    Science.gov (United States)

    Huang, Jin Y; Stiefel, Klaus M; Protti, Dario A

    2013-05-16

    Ganglion cells are the output neurons of the retina and their activity reflects the integration of multiple synaptic inputs arising from specific neural circuits. Patch clamp techniques, in voltage clamp and current clamp configurations, are commonly used to study the physiological properties of neurons and to characterize their synaptic inputs. Although the application of these techniques is highly informative, they pose various limitations. For example, it is difficult to quantify how the precise interactions of excitatory and inhibitory inputs determine response output. To address this issue, we used a modified current clamp technique, dynamic clamp, also called conductance clamp (1, 2, 3) and examined the impact of excitatory and inhibitory synaptic inputs on neuronal excitability. This technique requires the injection of current into the cell and is dependent on the real-time feedback of its membrane potential at that time. The injected current is calculated from predetermined excitatory and inhibitory synaptic conductances, their reversal potentials and the cell's instantaneous membrane potential. Details on the experimental procedures, patch clamping cells to achieve a whole-cell configuration and employment of the dynamic clamp technique are illustrated in this video article. Here, we show the responses of mouse retinal ganglion cells to various conductance waveforms obtained from physiological experiments in control conditions or in the presence of drugs. Furthermore, we show the use of artificial excitatory and inhibitory conductances generated using alpha functions to investigate the responses of the cells.

  5. Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance

    Energy Technology Data Exchange (ETDEWEB)

    Eles, P.T

    2005-07-01

    In the first part of the dissertation, spider dragline silk is studied by solid state NMR techniques. The dependence of NMR frequency on molecular orientation is exploited using the DECODER experiment to determine the orientation of the protein backbone within the silk fibre. Practical experimental considerations require that the silk fibres be wound about a cylindrical axis perpendicular to the external magnetic field, complicating the reconstruction of the underlying orientation distribution and necessitating the development of numerical techniques for this purpose. A two-component model of silk incorporating static b-sheets and polyglycine II helices adequately fits the NMR data and suggests that the b-sheets are well aligned along the silk axis (20 FWHM) while the helices are poorly aligned (68 FWHM). The effects of fibre strain, draw rate and hydration on orientation are measured. Measurements of the time-scale for peptide backbone motion indicate that when wet, a strain-dependent fraction of the poorly aligned component becomes mobile. This suggests a mechanism for the supercontraction of silk involving latent entropic springs that undergo a local strain-dependent phase transition, driving supercontraction. In the second part of this dissertation a novel method is developed for exciting NMR and nuclear quadrupole resonance (NQR) by rf irradiation at multiple frequencies that sum to (or differ by) the resonance frequency. This is fundamentally different than traditional NMR experiments where irradiation is applied on-resonance. With excitation outside the detection bandwidth, two-photon excitation allows for detection of free induction signals during excitation, completely eliminating receiver dead-time. A theoretical approach to describing two-photon excitation is developed based on average Hamiltonian theory. An intuition for two-photon excitation is gained by analogy to the coherent absorption of multiple photons requiring conservation of total energy and

  6. Impact of Dynamic Orbital Correlations on Magnetic Excitations in the Normal State of Iron-Based Superconductors

    Science.gov (United States)

    Lee, Wei-Cheng; Lv, Weicheng; Tranquada, John; Phillips, Philip

    2013-03-01

    We show here that orbital degrees of freedom produce a distinct signature in the magnetic excitation spectrum of iron-based superconductors above the magnetic ordering temperature. Because dxz and dyz orbitals are strongly connected with Fermi surface topology, the nature of magnetic excitations can be modified significantly due to the presence of either static or fluctuating orbital correlations. Within a five-orbital itinerant model, we show that static orbital order generally leads to an enhancement of commensurate magnetic excitations even when the original Fermi surface lacks nesting at commensurate wavevectors. When long-range orbital order is absent, Gaussian fluctuations beyond the standard random-phase approximation capture the effects of fluctuating orbital correlations on the magnetic excitations. We find that commensurate magnetic excitations can also be enhanced if the orbital correlations are strong. We propose that this unusual incommensurate-to-commensurate transformation is an important signature to distinguish orbital from spin physics in the normal state of iron-based superconductors. This work is supported by the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center, Grant No. DE-AC0298CH1088.

  7. Diverse mechanisms for photoprotection in photosynthesis. Dynamic regulation of photosystem II excitation in response to rapid environmental change.

    Science.gov (United States)

    Derks, Allen; Schaven, Kristin; Bruce, Doug

    2015-01-01

    Photosystem II (PSII) of photosynthesis catalyzes one of the most challenging reactions in nature, the light driven oxidation of water and release of molecular oxygen. PSII couples the sequential four step oxidation of water and two step reduction of plastoquinone to single photon photochemistry with charge accumulation centers on both its electron donor and acceptor sides. Photon capture, excitation energy transfer, and trapping occur on a much faster time scale than the subsequent electron transfer and charge accumulation steps. A balance between excitation of PSII and the use of the absorbed energy to drive electron transport is essential. If the absorption of light energy increases and/or the sink capacity for photosynthetically derived electrons decreases, potentially deleterious side reactions may occur, including the production of reactive oxygen species. In response, a myriad of fast (second to minutes timescale) and reversible photoprotective mechanisms are observed to regulate PSII excitation when the environment changes more quickly than can be acclimated to by gene expression. This review compares the diverse photoprotective mechanisms that are used to dissipate (quench) PSII excitation within the antenna systems of higher land plants, green algae, diatoms, and cyanobacteria. The molecular bases of how PSII excitation pressure is sensed by the antenna system and how the antenna then reconfigures itself from a light harvesting to an energy dissipative mode are discussed.

  8. Nonequilibrium population dynamics of phenotype conversion of cancer cells.

    Directory of Open Access Journals (Sweden)

    Joseph Xu Zhou

    Full Text Available Tumorigenesis is a dynamic biological process that involves distinct cancer cell subpopulations proliferating at different rates and interconverting between them. In this paper we proposed a mathematical framework of population dynamics that considers both distinctive growth rates and intercellular transitions between cancer cell populations. Our mathematical framework showed that both growth and transition influence the ratio of cancer cell subpopulations but the latter is more significant. We derived the condition that different cancer cell types can maintain distinctive subpopulations and we also explain why there always exists a stable fixed ratio after cell sorting based on putative surface markers. The cell fraction ratio can be shifted by changing either the growth rates of the subpopulations (Darwinism selection or by environment-instructed transitions (Lamarckism induction. This insight can help us to understand the dynamics of the heterogeneity of cancer cells and lead us to new strategies to overcome cancer drug resistance.

  9. OPTICAL BAND GAP EXCITATION AND PHOTOELECTRON GENERATION IN TITANIUM DIOXIDE-BASED SOLID STATE SOLAR CELLS

    OpenAIRE

    M. Rusop; T. SHIRATA; Soga, T.; Jimbo, T.

    2005-01-01

    The properties and optical band gap excitation of nanoporous titanium dioxide (TiO2) and transparent semiconducting copper iodide (CuI) films prepared by a XeCl excimer laser were investigated. The CuI films exhibited optical transmittance over 80% in the wavelength range from 400 to 900 nm with minimum resistivity of about 2 KΩcm. The optical absorption of these films showed a remarkable blue shift compared to that of polycrystalline of CuI, which can be explained from the formation of ultra...

  10. Desmosome dynamics in migrating epithelial cells requires the actin cytoskeleton

    Science.gov (United States)

    Roberts, Brett J.; Pashaj, Anjeza; Johnson, Keith R.; Wahl, James K.

    2011-01-01

    Re-modeling of epithelial tissues requires that the cells in the tissue rearrange their adhesive contacts in order to allow cells to migrate relative to neighboring cells. Desmosomes are prominent adhesive structures found in a variety of epithelial tissues that are believed to inhibit cell migration and invasion. Mechanisms regulating desmosome assembly and stability in migrating cells are largely unknown. In this study we established a cell culture model to examine the fate of desmosomal components during scratch wound migration. Desmosomes are rapidly assembled between epithelial cells at the lateral edges of migrating cells and structures are transported in a retrograde fashion while the structures become larger and mature. Desmosome assembly and dynamics in this system are dependent on the actin cytoskeleton prior to being associated with the keratin intermediate filament cytoskeleton. These studies extend our understanding of desmosome assembly and provide a system to examine desmosome assembly and dynamics during epithelial cell migration. PMID:21945137

  11. Multispectral fingerprinting for improved in vivo cell dynamics analysis

    Directory of Open Access Journals (Sweden)

    Cooper Cameron HJ

    2010-09-01

    Full Text Available Abstract Background Tracing cell dynamics in the embryo becomes tremendously difficult when cell trajectories cross in space and time and tissue density obscure individual cell borders. Here, we used the chick neural crest (NC as a model to test multicolor cell labeling and multispectral confocal imaging strategies to overcome these roadblocks. Results We found that multicolor nuclear cell labeling and multispectral imaging led to improved resolution of in vivo NC cell identification by providing a unique spectral identity for each cell. NC cell spectral identity allowed for more accurate cell tracking and was consistent during short term time-lapse imaging sessions. Computer model simulations predicted significantly better object counting for increasing cell densities in 3-color compared to 1-color nuclear cell labeling. To better resolve cell contacts, we show that a combination of 2-color membrane and 1-color nuclear cell labeling dramatically improved the semi-automated analysis of NC cell interactions, yet preserved the ability to track cell movements. We also found channel versus lambda scanning of multicolor labeled embryos significantly reduced the time and effort of image acquisition and analysis of large 3D volume data sets. Conclusions Our results reveal that multicolor cell labeling and multispectral imaging provide a cellular fingerprint that may uniquely determine a cell's position within the embryo. Together, these methods offer a spectral toolbox to resolve in vivo cell dynamics in unprecedented detail.

  12. Ultraviolet and visible upconversion dynamics in Er3+:YAlO3 under 2H11/2 excitation

    Institute of Scientific and Technical Information of China (English)

    Yang Hai-Gui; Dai Zhen-Wen; Sun Zhi-Wei

    2006-01-01

    The luminescence of Er3+:YAlO3 in ultraviolet, visible and infrared ranges under the 518 nm excitation of the multiples 2H11/2 have been investigated. Ultraviolet (275 nm and 318 nm), violet (405 nm and 413 nm) and blue (474 nm)upconversion and infrared downconversion luminescence has been observed. By means of measuring the fluorescence decay curves and using the theory of rate equations, the luminescence kinetics was studied in detail and the processes of energy transfer upconversion (ETU) and excitation state absorption (ESA) were proposed to explain the upconversion phenomena.

  13. Development and dynamics of cell polarity at a glance.

    Science.gov (United States)

    Campanale, Joseph P; Sun, Thomas Y; Montell, Denise J

    2017-04-01

    Cells exhibit morphological and molecular asymmetries that are broadly categorized as cell polarity. The cell polarity established in early embryos prefigures the macroscopic anatomical asymmetries characteristic of adult animals. For example, eggs and early embryos have polarized distributions of RNAs and proteins that generate global anterior/posterior and dorsal/ventral axes. The molecular programs that polarize embryos are subsequently reused in multiple contexts. Epithelial cells require apical/basal polarity to establish their barrier function. Migrating cells polarize in the direction of movement, creating distinct leading and trailing structures. Asymmetrically dividing stem cells partition different molecules between themselves and their daughter cells. Cell polarity can develop de novo, be maintained through rounds of cell division and be dynamically remodeled. In this Cell Science at a Glance review and poster, we describe molecular asymmetries that underlie cell polarity in several cellular contexts. We highlight multiple developmental systems that first establish cell/developmental polarity, and then maintain it. Our poster showcases repeated use of the Par, Scribble and Crumbs polarity complexes, which drive the development of cell polarity in many cell types and organisms. We then briefly discuss the diverse and dynamic changes in cell polarity that occur during cell migration, asymmetric cell division and in planar polarized tissues.

  14. Role of dynamical screening in excitation kinetics of biased quantum wells: Nonlinear absorption and ultrabroadband terahertz emission

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Monozon, B. S.; Jepsen, Peter Uhd

    2006-01-01

    calculations, in particular, predict the strongly nonlinear dependency of the effective optical absorption coefficient on the excitation pulse fluence, and ultrabroadband terahertz emission. Our theoretical model is free of fitting parameters. Calculations performed for internally biased InFaN/GaN quantum...

  15. Control of HOD photodissociation dynamics via bond-selective infrared multiphoton excitation and a femtosecond ultraviolet laser pulse

    DEFF Research Database (Denmark)

    Amstrup, Bjarne; Henriksen, Niels Engholm

    1992-01-01

    A scheme for controlling the outcome of a photodissociation process is studied. It involves two lasers—one intense laser in the infrared region which is supposed to excite a particular bond in the electronic ground state, and a second short laser pulse in the ultraviolet region which, at the righ...

  16. Non-contact electromagnetic exciter design with linear control method

    Science.gov (United States)

    Wang, Lin; Xiong, Xianzhi; Xu, Hua

    2017-01-01

    A non-contact type force actuator is necessary for studying the dynamic performance of a high-speed spindle system owing to its high-speed operating conditions. A non-contact electromagnetic exciter is designed for identifying the dynamic coefficients of journal bearings in high-speed grinding spindles. A linear force control method is developed based on PID controller. The influence of amplitude and frequency of current, misalignment and rotational speed on magnetic field and excitation force is investigated based on two-dimensional finite element analysis. The electromagnetic excitation force is measured with the auxiliary coils and calibrated by load cells. The design is validated by the experimental results. Theoretical and experimental investigations show that the proposed design can accurately generate linear excitation force with sufficiently large amplitude and higher signal to noise ratio. Moreover, the fluctuations in force amplitude are reduced to a greater extent with the designed linear control method even when the air gap changes due to the rotor vibration at high-speed conditions. Besides, it is possible to apply various types of excitations: constant, synchronous, and non-synchronous excitation forces based on the proposed linear control method. This exciter can be used as linear-force exciting and controlling system for dynamic performance study of different high-speed rotor-bearing systems.

  17. Exploring Neural Cell Dynamics with Digital Holographic Microscopy

    KAUST Repository

    Marquet, Pierre

    2013-04-21

    In this talk, I will present how digital holographic microscopy, as a powerful quantitative phase technique, can non-invasively measure cell dynamics and especially resolve local neuronal network activity through simultaneous multiple site optical recording.

  18. Ultrafast dynamics of a near-solid-density layer in an intense femtosecond laser-excited plasma

    Energy Technology Data Exchange (ETDEWEB)

    Adak, Amitava; Chatterjee, Gourab; Kumar Singh, Prashant; Lad, Amit D.; Brijesh, P.; Kumar, G. Ravindra, E-mail: grk@tifr.res.in [Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai 400005 (India); Blackman, David R. [York Plasma Institute, University of York, Heslington, York YO10 5DQ (United Kingdom); Robinson, A. P. L. [Central Laser Facility, Rutherford-Appleton Laboratory, Chilton, Didcot OX10 0QX (United Kingdom); Pasley, John [York Plasma Institute, University of York, Heslington, York YO10 5DQ (United Kingdom); Central Laser Facility, Rutherford-Appleton Laboratory, Chilton, Didcot OX10 0QX (United Kingdom)

    2014-06-15

    We report on the picosecond dynamics of a near-solid-density plasma generated by an intense, infrared (λ = 800 nm) femtosecond laser using time-resolved pump-probe Doppler spectrometry. An initial red-shift is observed in the reflected third harmonic (λ = 266 nm) probe pulse, which gets blue-shifted at longer probe-delays. A combination of particle-in-cell and radiation-hydrodynamics modelling is performed to model the pump laser interaction with the solid target. The results are post-processed to predict the Doppler shift. An excellent agreement is found between the results of such modelling and the experiment. The modelling suggests that the initial inward motion of the critical surface observed in the experiment is due to the passage of a shock-wave-like disturbance, launched by the pump interaction, propagating into the target. Furthermore, in order to achieve the best possible fit to the experimental data, it was necessary to incorporate the effects of bulk ion-acceleration resulting from the electrostatic field set up by the expulsion of electrons from the laser envelope. We also present results of time-resolved pump-probe reflectometry, which are corroborated with the spectrometry results using a 1-D reflectivity model.

  19. Dynamic Model and Vibration Power Flow of a Rigid-Flexible Coupling and Harmonic-Disturbance Exciting System for Flexible Robotic Manipulator with Elastic Joints

    Directory of Open Access Journals (Sweden)

    Yufei Liu

    2015-01-01

    Full Text Available This paper investigates the dynamic of a flexible robotic manipulator (FRM which consists of rigid driving base, flexible links, and flexible joints. With considering the motion fluctuations caused by the coupling effect, such as the motor parameters and mechanism inertias, as harmonic disturbances, the system investigated in this paper remains a parametrically excited system. An elastic restraint model of the FRM with elastic joints (FRMEJ is proposed, which considers the elastic properties of the connecting joints between the flexible arm and the driving base, as well as the harmonic disturbances aroused by the electromechanical coupling effect. As a consequence, the FRMEJ accordingly remains a flexible multibody system which conveys the effects of rigid-flexible couple and electromechanical couple. The Lagrangian function and Hamilton’s principle are used to establish the dynamic model of the FRMEJ. Based on the dynamic model proposed, the vibration power flow is introduced to show the vibration energy distribution. Numerical simulations are conducted to investigate the effect of the joint elasticities and the disturbance excitations, and the influences of the structure parameters and motion parameters on the vibration power flow are studied. The results obtained in this paper contribute to the structure design, motion optimization, and vibration control of FRMs.

  20. Protein dynamics in individual human cells: experiment and theory.

    Directory of Open Access Journals (Sweden)

    Ariel Aharon Cohen

    Full Text Available A current challenge in biology is to understand the dynamics of protein circuits in living human cells. Can one define and test equations for the dynamics and variability of a protein over time? Here, we address this experimentally and theoretically, by means of accurate time-resolved measurements of endogenously tagged proteins in individual human cells. As a model system, we choose three stable proteins displaying cell-cycle-dependant dynamics. We find that protein accumulation with time per cell is quadratic for proteins with long mRNA life times and approximately linear for a protein with short mRNA lifetime. Both behaviors correspond to a classical model of transcription and translation. A stochastic model, in which genes slowly switch between ON and OFF states, captures measured cell-cell variability. The data suggests, in accordance with the model, that switching to the gene ON state is exponentially distributed and that the cell-cell distribution of protein levels can be approximated by a Gamma distribution throughout the cell cycle. These results suggest that relatively simple models may describe protein dynamics in individual human cells.

  1. Dynamics of cell degradation. [nickel cadmium batteries

    Science.gov (United States)

    Mcdermott, P. P.

    1978-01-01

    The use of chemical and physical data as a supplement to linear regression models in the prediction of cell failure is discussed. Principal factors to be considered are the positive thickness and weight, and the negative thickness. A model for cell degradation and failure in accelerated life test cells is presented and predictions based on a teardown analysis are included.

  2. Extracting full-field dynamic strain on a wind turbine rotor subjected to arbitrary excitations using 3D point tracking and a modal expansion technique

    Science.gov (United States)

    Baqersad, Javad; Niezrecki, Christopher; Avitabile, Peter

    2015-09-01

    Health monitoring of rotating structures such as wind turbines and helicopter rotors is generally performed using conventional sensors that provide a limited set of data at discrete locations near or on the hub. These sensors usually provide no data on the blades or inside them where failures might occur. Within this paper, an approach was used to extract the full-field dynamic strain on a wind turbine assembly subject to arbitrary loading conditions. A three-bladed wind turbine having 2.3-m long blades was placed in a semi-built-in boundary condition using a hub, a machining chuck, and a steel block. For three different test cases, the turbine was excited using (1) pluck testing, (2) random impacts on blades with three impact hammers, and (3) random excitation by a mechanical shaker. The response of the structure to the excitations was measured using three-dimensional point tracking. A pair of high-speed cameras was used to measure displacement of optical targets on the structure when the blades were vibrating. The measured displacements at discrete locations were expanded and applied to the finite element model of the structure to extract the full-field dynamic strain. The results of the paper show an excellent correlation between the strain predicted using the proposed approach and the strain measured with strain-gages for each of the three loading conditions. The approach used in this paper to predict the strain showed higher accuracy than the digital image correlation technique. The new expansion approach is able to extract dynamic strain all over the entire structure, even inside the structure beyond the line of sight of the measurement system. Because the method is based on a non-contacting measurement approach, it can be readily applied to a variety of structures having different boundary and operating conditions, including rotating blades.

  3. 基于Excite-Timing Drive的正时同步带系统动力学分析%Dynamic analysis of a synchronous belt drive based on EXCITE-TD

    Institute of Scientific and Technical Information of China (English)

    卢小锐; 高文志; 张良良; 马俊达

    2013-01-01

    Here,a dynamic simulation of a synchronous belt drive of a kind of engines was performed using AVL-EXCITE TD software.The dynamic characteristics of the belt versus rotating speed were analyzed.The influence factors on the dynamic characteristics of the synchronous belt drive were also analyzed and optimized.The results showed that the reduction of the crankshaft speed fluctuations can improve the dynamic performance of the synchronous belt drive effectively.The results provided a basis for design of a valve system,and essential boundary conditions for analysis of a valve system,a timing system and overall NVH performance.%应用发动机分析软件AVL-ETD,对某四缸汽油机正时同步带传动系统进行动力学仿真计算.分析各转速下皮带动力学特性,对正时同步带系统动力学特性影响因素进行分析优化,获得降低曲轴的转速波动能有效提高正时同步带系统动力学性能.不仅为配气阀系及正时系统构件的改进设计提供依据,且为配气阀系、正时系统及整机NVH性能等分析提供必须的边界条件.

  4. Nonlinear optical effect and excited electron dynamics of semiconductor nanocrystals; Handotai nano kessh no hisenkei kogaku koka to reiki denshi dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Goto, T. [Tohoku University, Sendai (Japan)

    1996-08-20

    Investigations were given on nanocrystals of CuCl and CdTe with regard to their nonlinear optical mechanism. The experiment used a femto-second pump probe spectroscope. The experiment on CuCl nanocrystals revealed the following facts: in the case where one photon is absorbed into one nanocrystal, cascade mitigation occurs to the pair of electrons and holes, and exciters; and in the case where two photons are absorbed into one nanocrystal, exciter molecules are made via the pair of electrons and holes and the exciters. Thus, it was found that the optical nonlinearity occurs when more than two photons are absorbed into one nanocrystal, and inter-exciter interactions and formation of the exciter molecules are the physical causes thereof. The experiment on CdTe nanocrystals indicated that electrons and holes produced by laser beam are distributed instantaneously between the size-quantized discrete levels, and that temperature in the electron system drops with lapse of time. 9 refs., 6 figs.

  5. Mitochondrial dynamics and morphology in beta-cells.

    Science.gov (United States)

    Stiles, Linsey; Shirihai, Orian S

    2012-12-01

    Mitochondrial dynamics contribute to the regulation of mitochondrial shape as well as various mitochondrial functions and quality control. This is of particular interest in the beta-cell because of the key role mitochondria play in the regulation of beta-cell insulin secretion function. Moreover, mitochondrial dysfunction has been suggested to contribute to the development of Type 2 Diabetes. Genetic tools that shift the balance of mitochondrial fusion and fission result in alterations to beta-cell function and viability. Additionally, conditions that induce beta-cell dysfunction, such as exposure to a high nutrient environment, disrupt mitochondrial morphology and dynamics. While it has been shown that mitochondria display a fragmented morphology in islets of diabetic patients and animal models, the mechanism behind this is currently unknown. Here, we review the current literature on mitochondrial morphology and dynamics in the beta-cell as well as some of the unanswered question in this field.

  6. Cell shape dynamics: from waves to migration.

    Directory of Open Access Journals (Sweden)

    Meghan K Driscoll

    Full Text Available We observe and quantify wave-like characteristics of amoeboid migration. Using the amoeba Dictyostelium discoideum, a model system for the study of chemotaxis, we demonstrate that cell shape changes in a wave-like manner. Cells have regions of high boundary curvature that propagate from the leading edge toward the back, usually along alternating sides of the cell. Curvature waves are easily seen in cells that do not adhere to a surface, such as cells that are electrostatically repelled from surfaces or cells that extend over the edge of micro-fabricated cliffs. Without surface contact, curvature waves travel from the leading edge to the back of a cell at -35 µm/min. Non-adherent myosin II null cells do not exhibit these curvature waves. At the leading edge of adherent cells, curvature waves are associated with protrusive activity. Like regions of high curvature, protrusive activity travels along the boundary in a wave-like manner. Upon contact with a surface, the protrusions stop moving relative to the surface, and the boundary shape thus reflects the history of protrusive motion. The wave-like character of protrusions provides a plausible mechanism for the zig-zagging of pseudopods and for the ability of cells both to swim in viscous fluids and to navigate complex three dimensional topography.

  7. Characterization of altered intrinsic excitability in hippocampal CA1 pyramidal cells of the Aβ-overproducing PDAPP mouse☆

    Science.gov (United States)

    Kerrigan, T.L.; Brown, J.T.; Randall, A.D.

    2014-01-01

    Transgenic mice that accumulate Aβ peptides in the CNS are commonly used to interrogate functional consequences of Alzheimer's disease-associated amyloidopathy. In addition to changes to synaptic function, there is also growing evidence that changes to intrinsic excitability of neurones can arise in these models of amyloidopathy. Furthermore, some of these alterations to intrinsic properties may occur relatively early within the age-related progression of experimental amyloidopathy. Here we report a detailed comparison between the intrinsic excitability properties of hippocampal CA1 pyramidal neurones in wild-type (WT) and PDAPP mice. The latter is a well-established model of Aβ accumulation which expresses human APP harbouring the Indiana (V717F) mutation. At the age employed in this study (9–10 months) CNS Abeta was elevated in PDAPP mice but significant plaque pathology was absent. PDAPP mice exhibited no differences in subthreshold intrinsic properties including resting potential, input resistance, membrane time constant and sag. When CA1 cells of PDAPP mice were given depolarizing stimuli of various amplitudes they initially fired at a higher frequency than WT cells. Commensurate with this, PDAPP cells exhibited a larger fast afterdepolarizing potential. PDAPP mice had narrower spikes but action potential threshold, rate of rise and peak were not different. Thus not all changes seen in our previous studies of amyloidopathy models were present in PDAPP mice; however, narrower spikes, larger ADPs and the propensity to fire at higher frequencies were consistent with our prior work and thus may represent robust, cross-model, indices of amyloidopathy. This article is part of a Special Issue entitled ‘Neurodevelopment Disorder’. PMID:24055500

  8. Albumin nanoshell encapsulation of near-infrared-excitable rare-Earth nanoparticles enhances biocompatibility and enables targeted cell imaging.

    Science.gov (United States)

    Naczynski, Dominik J; Andelman, Tamar; Pal, David; Chen, Suzie; Riman, Richard E; Roth, Charles M; Moghe, Prabhas V

    2010-08-02

    The use of traditional fluorophores for in vivo imaging applications is limited by poor quantum yield, poor tissue penetration of the excitation light, and excessive tissue autofluorescence, while the use of inorganic fluorescent particles that offer a high quantum yield is frequently limited due to particle toxicity. Rare-earth-doped nanoparticles that utilize near-infrared upconversion overcome the optical limitations of traditional fluorophores, but are not typically suitable for biological application due to their insolubility in aqueous solution, lack of functional surface groups for conjugation of biomolecules, and potential cytotoxicity. A new approach to establish highly biocompatible and biologically targetable nanoshell complexes of luminescent rare-earth-doped NaYF(4) nanoparticles (REs) excitable with 920-980 nm near-infrared light for biomedical imaging applications is reported. The approach involves the encapsulation of NaYF(4) nanoparticles doped with Yb and Er within human serum albumin nanoshells to create water-dispersible, biologically functionalizable composite particles. These particles exhibit narrow size distributions around 200 nm and are stable in aqueous solution for over 4 weeks. The albumin shell confers cytoprotection and significantly enhances the biocompatibility of REs even at concentrations above 200 microg REs mL(-1). Composite particles conjugated with cyclic arginine-glycine-aspartic acid (cRGD) specifically target both human glioblastoma cell lines and melanoma cells expressing alpha(v)beta(3) integrin receptors. These findings highlight the promise of albumin-encapsulated rare-earth nanoparticles for imaging cancer cells in vitro and the potential for targeted imaging of disease sites in vivo.

  9. Direct measurement of excitation transfer dynamics between two trimers in C-phycocyanin hexamer from cyanobacterium Anabaena variabilis

    Science.gov (United States)

    Zhang, Jingmin; Zhao, Fuli; Zheng, Xiguang; Wang, Hezhou

    1999-05-01

    We provide the first experimental evidence for the excitation transfers between two trimers of an isolated C-phycocyanin hexamer (αβ) 6PCL RC27, at the end of the rod proximal to the core of PBS in cyanobacterium of Anabaena variabilis, with picosecond time-resolved fluorescence spectroscopy. Our results strongly suggest that the observed fluorescence decay constants around 20 and 10 ps time scales, shown in anisotropy decay, not in isotropic decay experiments arose from the excitation transfers between two trimers via two types of transfer pathways such as 1β 155↔6β 155 (2β 155↔5β 155 and 3β 155↔4β 155) and 2α 84↔5α 84 (3α 84↔6α 84 and 1α 84↔4α 84) channels and these could be described by Föster dipole-dipole resonance mechanism.

  10. Anomalous excited-state dynamics of lucifer yellow CH in solvents of high polarity: evidence for an intramolecular proton transfer.

    Science.gov (United States)

    Panda, Debashis; Mishra, Padmaja P; Khatua, Saumyakanti; Koner, Apurba L; Sunoj, Raghavan B; Datta, Anindya

    2006-05-04

    The photophysics of the fluorescent probe Lucifer yellow CH has been investigated using fluorescence spectroscopic and computational techniques. The nonradiative rate is found to pass through a minimum in solvents of intermediate empirical polarity. This apparently anomalous behavior is rationalized by considering the possibility of predominance of different kinds of nonradiative processes, viz. intersystem crossing (ISC) and excited-state proton transfer (ESPT), in solvents of low and high empirical polarity, respectively. The feasibility of the proton transfer is examined by the structure determined by the density functional theory (DFT) calculations. The predicted energy levels based on the time-dependent density functional theory (TD-DFT) method in the gas phase identifies the energy gap between the S(1) and nearest triplet state to be close enough to facilitate ISC. Photophysical investigation in solvent mixtures and in deuterated solvents clearly indicates the predominance of the solvent-mediated intramolecular proton transfer in the excited state of the fluorophore in protic solvents.

  11. Semi classical description of isotropic Non-Heisenberg magnets for spin S=3/2 and linear quadrupole excitation dynamics

    Directory of Open Access Journals (Sweden)

    Y Yousefi

    2012-09-01

    Full Text Available  In this paper, a system with spin S=3/2 with general isotropic nearest neighbor exchange within a mean field approximation possess is discnssed. We derive equations describing non-Heisenberg isotropic model using coherent states of SU(4 group in real parameters and then obtain dispersion equations of spin wave of dipole and quadrupole branches for a small linear excitation from the ground state.

  12. Theoretical Studies of the Role of Vibrational Excitation on the Dynamics of the Hydrogen-Transfer Reaction of F(^2P) + HCl → FH + Cl({^2}P)

    Science.gov (United States)

    Ray, Sara E.; Vissers, Gé W. M.; McCoy, Anne B.

    2009-06-01

    Hydrogen-transfer reactions are probed through vibrational excitation of the HCl bond in the pre-reactive F\\cdotsHCl complex. Such open-shell species provide a challenge for quantum dynamical calculations due to the need to take into account multiple potential energy surfaces to accurately describe the system.A three-dimensional, fully-coupled potential energy surface has been constructed based on electronic energies calculated at the multireference configuration interaction+Davidson correction (MRCI+Q) level of theory with an aug-cc-pVnZ (n=2,3,4) basis. Spin orbit calculations have also been included. Here we present the results of time-dependent quantum wave packet calculations on the asymmetric hydrogen-transfer reaction of F(^2P) + HCl. In these calculations, the reaction is initiated by vibrationally exciting the HCl stretching motion in the pre-reactive F\\cdotsHCl complex. The wave packet is propagated on the coupled potential energy surfaces. Product state distributions were calculated for reactions initiated in the first three vibrationally excited states of HCl, v=1-3. M. P. Deskevich, M. Y. Hayes, K. Takahashi, R. T. Skodje, and D. J. Nesbitt J. Chem. Phys. 124 (22) 224303 (2006) M. P. Deskevich and D. J. Nesbitt private communication(2007)

  13. Measurement and analysis of excitation functions and observation of mass-asymmetry effect on incomplete fusion dynamics

    Directory of Open Access Journals (Sweden)

    Rashid M.H.

    2011-10-01

    Full Text Available Excitation functions for sixteen evaporation residues produced in the interaction of 20Ne with 165Ho have been measured in the projectile energy range ≈88-164 MeV, using catcher foil activation technique followed by gamma-ray spectrometry. It has been found in general that the excitation functions of evaporation residues produced via xn/pxn channels satisfactorily reproduced with the statistical model code PACE-2 after subtraction of precursor decay contribution. The significant enhancement in the measured excitation functions for the residues produced in alpha emission channels over the PACE-2 predictions has been observed. These alpha emission channels are attributed to incomplete fusion reaction process. The results indicate the occurrence of incomplete fusion involving break-up of projectile 20Ne into 4He + 16O and /or 8Be + 12C followed by fusion of one of the fragments with target nucleus 165Ho. The analysis of the present data suggest that probability of incomplete fusion increases with projectile energy. The ICF fraction FICF also increases with increasing mass-asymmetry of the entrance channel.

  14. Kv3.3 channels harbouring a mutation of spinocerebellar ataxia type 13 alter excitability and induce cell death in cultured cerebellar Purkinje cells.

    Science.gov (United States)

    Irie, Tomohiko; Matsuzaki, Yasunori; Sekino, Yuko; Hirai, Hirokazu

    2014-01-01

    The cerebellum plays crucial roles in controlling sensorimotor functions. The neural output from the cerebellar cortex is transmitted solely by Purkinje cells (PCs), whose impairment causes cerebellar ataxia. Spinocerebellar ataxia type 13 (SCA13) is an autosomal dominant disease, and SCA13 patients exhibit cerebellar atrophy and cerebellar symptoms. Recent studies have shown that missense mutations in the voltage-gated K(+) channel Kv3.3 are responsible for SCA13. In the rodent brain, Kv3.3 mRNAs are expressed most strongly in PCs, suggesting that the mutations severely affect PCs in SCA13 patients. Nevertheless, how these mutations affect the function of Kv3.3 in PCs and, consequently, the morphology and neuronal excitability of PCs remains unclear. To address these questions, we used lentiviral vectors to express mutant mouse Kv3.3 (mKv3.3) channels harbouring an R424H missense mutation, which corresponds to the R423H mutation in the Kv3.3 channels of SCA13 patients, in mouse cerebellar cultures. The R424H mutant-expressing PCs showed decreased outward current density, broadened action potentials and elevated basal [Ca(2+)]i compared with PCs expressing wild-type mKv3.3 subunits or those expressing green fluorescent protein alone. Moreover, expression of R424H mutant subunits induced impaired dendrite development and cell death selectively in PCs, both of which were rescued by blocking P/Q-type Ca(2+) channels in the culture conditions. We therefore concluded that expression of R424H mutant subunits in PCs markedly affects the function of endogenous Kv3 channels, neuronal excitability and, eventually, basal [Ca(2+)]i, leading to cell death. These results suggest that PCs in SCA13 patients also exhibit similar defects in PC excitability and induced cell death, which may explain the pathology of SCA13.

  15. Solar excitation of CdS/Cu2S photovoltaic cells

    Science.gov (United States)

    Boer, K. W.

    1976-01-01

    Solar radiation of five typical clear weather days and under a variety of conditions is used to determine the spectral distribution of the photonflux at different planes of a CdS/Cu2S solar cell. The fractions of reflected and absorbed flux are determined at each of the relevant interfaces and active volume elements of the solar cell. The density of absorbed photons is given in respect to spectral and spatial distribution. The variance of the obtained distribution, with changes in insolation and absorption spectra of the active solar cell layers, is indicated. A catalog of typical examples is given in the appendix.

  16. Local Nucleosome Dynamics Facilitate Chromatin Accessibility in Living Mammalian Cells

    Directory of Open Access Journals (Sweden)

    Saera Hihara

    2012-12-01

    Full Text Available Genome information, which is three-dimensionally organized within cells as chromatin, is searched and read by various proteins for diverse cell functions. Although how the protein factors find their targets remains unclear, the dynamic and flexible nature of chromatin is likely crucial. Using a combined approach of fluorescence correlation spectroscopy, single-nucleosome imaging, and Monte Carlo computer simulations, we demonstrate local chromatin dynamics in living mammalian cells. We show that similar to interphase chromatin, dense mitotic chromosomes also have considerable chromatin accessibility. For both interphase and mitotic chromatin, we observed local fluctuation of individual nucleosomes (∼50 nm movement/30 ms, which is caused by confined Brownian motion. Inhibition of these local dynamics by crosslinking impaired accessibility in the dense chromatin regions. Our findings show that local nucleosome dynamics drive chromatin accessibility. We propose that this local nucleosome fluctuation is the basis for scanning genome information.

  17. Fluids as Dynamic Templates for Cytoskeletal Proteins in Plant Cells

    CERN Document Server

    Lofthouse, J T

    2008-01-01

    The Dynamic Template model of biological cell membranes and the cytoplasm as spatially organised fluid layers is extended to plant cells, and is shown to offer a feasible shear driven mechanism for the co-alignment of internal and external fibres observed during growth and tropic responses

  18. Exciter switch

    Science.gov (United States)

    Mcpeak, W. L.

    1975-01-01

    A new exciter switch assembly has been installed at the three DSN 64-m deep space stations. This assembly provides for switching Block III and Block IV exciters to either the high-power or 20-kW transmitters in either dual-carrier or single-carrier mode. In the dual-carrier mode, it provides for balancing the two drive signals from a single control panel located in the transmitter local control and remote control consoles. In addition to the improved switching capabilities, extensive monitoring of both the exciter switch assembly and Transmitter Subsystem is provided by the exciter switch monitor and display assemblies.

  19. Human mast cell mediator cocktail excites neurons in human and guinea-pig enteric nervous system.

    Science.gov (United States)

    Schemann, M; Michel, K; Ceregrzyn, M; Zeller, F; Seidl, S; Bischoff, S C

    2005-04-01

    Neuroimmune interactions are an integral part of gut physiology and involved in the pathogenesis of inflammatory and functional bowel disorders. Mast cells and their mediators are important conveyors in the communication from the innate enteric immune system to the enteric nervous system (ENS). However, it is not known whether a mediator cocktail released from activated human mast cells affects neural activity in the ENS. We used the Multi-Site Optical Recording Technique to image single cell activity in guinea-pig and human ENS after application of a mast cell mediator cocktail (MCMC) that was released from isolated human intestinal mucosa mast cells stimulated by IgE-receptor cross-linking. Local application of MCMC onto individual ganglia evoked an excitatory response consisting of action potential discharge. This excitatory response occurred in 31%, 38% or 11% neurons of guinea-pig submucous plexus, human submucous plexus, or guinea-pig myenteric plexus, respectively. Compound action potentials from nerve fibres or fast excitatory synaptic inputs were not affected by MCMC. This study demonstrates immunoneural signalling in the human gut and revealed for the first time that an MCMC released from stimulated human intestinal mast cells induces excitatory actions in the human and guinea-pig ENS.

  20. Relation Between the Cell Volume and the Cell Cycle Dynamics in Mammalian cell

    Science.gov (United States)

    Magno, A. C. G.; Oliveira, I. L.; Hauck, J. V. S.

    2016-08-01

    The main goal of this work is to add and analyze an equation that represents the volume in a dynamical model of the mammalian cell cycle proposed by Gérard and Goldbeter (2011) [1]. The cell division occurs when the cyclinB/Cdkl complex is totally degraded (Tyson and Novak, 2011)[2] and it reaches a minimum value. At this point, the cell is divided into two newborn daughter cells and each one will contain the half of the cytoplasmic content of the mother cell. The equations of our base model are only valid if the cell volume, where the reactions occur, is constant. Whether the cell volume is not constant, that is, the rate of change of its volume with respect to time is explicitly taken into account in the mathematical model, then the equations of the original model are no longer valid. Therefore, every equations were modified from the mass conservation principle for considering a volume that changes with time. Through this approach, the cell volume affects all model variables. Two different dynamic simulation methods were accomplished: deterministic and stochastic. In the stochastic simulation, the volume affects every model's parameters which have molar unit, whereas in the deterministic one, it is incorporated into the differential equations. In deterministic simulation, the biochemical species may be in concentration units, while in stochastic simulation such species must be converted to number of molecules which are directly proportional to the cell volume. In an effort to understand the influence of the new equation a stability analysis was performed. This elucidates how the growth factor impacts the stability of the model's limit cycles. In conclusion, a more precise model, in comparison to the base model, was created for the cell cycle as it now takes into consideration the cell volume variation